Patent Application
20240358635
The present disclosure relates to improvements in the structural components and physical characteristics of lithium battery articles. Standard lithium-ion batteries, for example, are prone to certain phenomena related to short circuiting and have experienced high temperature occurrences and ultimate firing as a result. Structural concerns with battery components have been found to contribute to such problems. Improvements provided herein include the utilization of thin metallized current collectors (aluminum and/or copper, as examples), high shrinkage rate materials, materials that become nonconductive upon exposure to high temperatures, and combinations thereof. Such improvements accord the ability to withstand certain imperfections (dendrites, unexpected electrical surges, etc.) within the target lithium battery through provision of ostensibly an internal fuse within the subject lithium batteries themselves that prevents undesirable high temperature results from short circuits. Battery articles and methods of use thereof including such improvements are also encompassed within this disclosure.
Also disclosed and encompassed herein is a constrained, wound lithium-ion battery cell with an internal fuse component and that exhibits significant improvements in terms of life-cycle times is provided. Disclosed herein are lithium-ion battery structures and configurations utilizing at least one thin metallized film current collector that provides safety features with low thermal runaway potential, low internal resistance, with a simplified manner of providing external electrical conductivity simultaneously. The provision of a highly constrained and wound structure thereof unexpectedly allows for extended charge/discharge cycle life that is significantly improved in comparison with previous wound lithium-ion battery devices. A range of shear and compression forces accords such results, with such forces permissible through various pathways, including winding curvatures, number of windings within the cell housing, hardness of housing, and structural geometries therein. Encompassed herein is also a method of providing long cycle life results for such specific devices.
Additionally, the internal fuse developments disclosed herein, exhibiting extremely thin current collector structures, further allow for the potential for repetitive folds and/or windings thereof within a single cell. Such a fold and/or winding possibility provides the capability of connecting two sides of a current collector which might otherwise be electrically insulated by a polymer layer situated between the two conducting layers, without the need for excessive internal weight and/or battery volume requirements. Ostensibly, the folded and/or wound current collector retains the internal fuse characteristics while simultaneously permitting for such high current capability, potentially allowing for very high power within any number of sized batteries without the need for the aforementioned excessive weight and volume requirements, creating new battery articles for different purposes with targeted high-power levels and as high safety benefits as possible. Additionally, such folded and/or wound batteries also exhibit constrained configurations that have been found to impart unexpectedly improved cycle life benefits heretofore unknown within this industry.
Lithium batteries remain prevalent around the world as an electricity source within a myriad of products. From rechargeable power tools, to electronic cars, to the ubiquitous cellular telephone (and like tablets, hand-held computers, etc.), lithium batteries (of different ion types) are utilized as the primary power source due to reliability, above-noted rechargeability, and longevity of usage. With such widely utilized power sources, however, comes certain problems, some of which have proven increasingly serious. Notably, safety issues have come to light wherein certain imperfections within such lithium batteries, whether due to initial manufacturing issues or time-related degradation problems, cause susceptibility to firing potentials during short circuit events. Basically, internal defects with conductive materials have been found to create undesirable high heat and, ultimately, fire, within such battery structures. As a result, certain products utilizing lithium batteries, from hand-held computerized devices (the Samsung Galaxy Note 7, as one infamous situation) to entire airplanes (the Boeing 787) have been banned from sales and/or usage until solutions to compromised lithium batteries used therein and therewith have been provided (and even to the extent that the Samsung Galaxy Note 7 has been banned from any airplanes in certain regions). Even the Tesla line of electric cars have exhibited notable problems with lithium battery components, leading to headline-grabbing stories of such expensive vehicles exploding as fireballs due to battery issues. Widespread recalls or outright bans thus remain today in relation to such lithium battery issues, leading to a significant need to overcome such problems.
These problems primarily exist due to manufacturing issues, whether in terms of individual battery components as made or as such components are constructed as individual batteries themselves. Looked at more closely, lithium batteries are currently made from six primary components, a cathode material, a cathode current collector (such as aluminum foil) on which the cathode material is coated, an anode material, an anode current collector (such as copper foil) on which the anode material is coated, a separator situated between each anode and cathode layer and typically made from a plastic material, and an electrolyte as a conductive organic solvent that saturates the other materials thereby providing a mechanism for the ions to conduct between the anode and cathode. These materials are typically wound together into a can, as shown in Prior Art
The generation of excessive heat internally may further create shrinkage of the plastic separator, causing it to move away from, detach, or otherwise increase the area of a short within the battery. In such a situation, the greater exposed short area within the battery may lead to continued current and increased heating therein, leading to the high temperature event which causes significant damage to the cell, including bursting, venting, and even flames and fire. Such damage is particularly problematic as the potential for firing and worse comes quickly and may cause the battery and potentially the underlying device to suffer an explosion as a result, putting a user in significant danger as well.
Lithium batteries (of many varied types) are particularly susceptible to problems in relation to short circuiting. Typical batteries have a propensity to exhibit increased discharge rates with high temperature exposures, leading to uncontrolled (runaway) flaring and firing on occasion, as noted above. Because of these possibilities, certain regulations have been put into effect to govern the actual utilization, storage, even transport of such battery articles. The ability to effectuate a proper protocol to prevent such runaway events related to short circuiting is of enormous importance, certainly. The problem has remained, however, as to how to actually corral such issues, particularly when component production is provided from myriad suppliers and from many different locations around the world.
Some have honed in on trying to provide proper and/or improved separators as a means to help alleviate potential for such lithium battery fires. Low melting point and/or shrinkage rate plastic membranes appear to create higher potentials for such battery firing occurrences. The general thought has then been to include certain coatings on such separator materials without reducing the electrolyte separation capabilities thereof during actual utilization. Thus, ceramic particles, for instance, have been utilized as polypropylene and/or polyethylene film coatings as a means to increase the dimensional stability of such films (increase melting point, for example). Binder polymers have been included, as well, as a constituent to improve cohesion between ceramic particles and adhesion to the plastic membrane (film). In actuality, though, the thermal increase imparted to the overall film structure with ceramic particle coatings has been found to be relatively low, thus rendering the dominant factor for such a separator issue to be the actual separator material(s) itself.
As a result, there have been designed and implemented, at least to a certain degree, separator materials that are far more thermally stable than the polyethylene and polypropylene porous films that make up the base layer of such typical ceramic-coated separators. These low shrinkage, dimensionally stable separators exhibit shrinkage less than 5% when exposed to temperatures of at least 200° C. (up to temperatures of 250, 300, and even higher), far better than the high shrinkage rates experienced by bare polymer films (roughly 5% shrinkage at 150° C.), and of ceramic-coated films (roughly at 180° C.) (such shrinkage measurement comparisons are provided in Prior Art
In Prior Art
This possible solution, however, is limited to simply replacing the separator alone with higher shrinkage rate characteristics. Although such a simple resolution would appear to be of great value, there still remains other manufacturing procedures and specified components (such as ceramic-coated separator types) that are widely utilized and may be difficult to supplant from accepted battery products. Thus, despite the obvious benefits of the utilization and inclusion of thermally stable separators, undesirable battery fires may still occur, particularly when ceramic coated separator products are considered safe for such purposes. Thus, it has been determined that there is at least another, solely internal battery cell structural mechanism that may remedy or at least reduce the chance for heat generation due to an internal short in addition to the utilization of such highly thermal stable separator materials. In such a situation, the occurrence of a short within such a battery cell would not result in deleterious high temperature damage due to the cessation of a completed internal circuit through a de facto internal fuse creation. Until now, however, nothing has been presented within the lithium battery art that easily resolves these problems. The present disclosure provides such a highly desirable cure making lithium battery cells extremely safe and reliable within multiple markets.
Even with such safety provisions within the lithium-ion battery industry, there is still the importance of overall usefulness and economic benefits for the user/customer. Thus, of further and particular interest is the necessity for such lithium-ion batteries to impart effective and long-term (repeated) charge and discharge cycles over the life thereof. Even with improvements in thermal runaway protections and other potential safety benefits, long-term performance levels are needed, particularly in terms of cost-effectiveness for users. In other words, even with safety levels potentially unmatched, the utilization of a lithium-ion battery with a limited cycle life would be inadequate as the user would expect much more. Charge and discharge capabilities are thus necessary over a significant time period, or least in terms of actual numbers of such charge/discharge cycles, to generate a marketable lithium-ion battery device. The ability to provide both a safe (at least in terms of thermal runaway issues) simultaneously with an appropriately long cycle life battery would be highly prized. To date, investigations into such possible increased cycle life concerns with lithium-ion batteries having certain safety benefits have been nonexistent. The present disclosure, however, provides results heretofore unexplored and/or understood within the pertinent industry.
As shown herein, metallized films for current collector utilization have been shown to increase safety in lithium battery cells. Other types of metallized films have been proposed (by CATL, for instance), but such disclosures have deemed that high internal resistance levels are required with such metallized film components, thereby providing a safety feature, but with a sacrifice of battery effectiveness and efficiency. As it is, nothing within the pertinent prior art discusses the capability of metallized film current collector components coupled with certain wound battery configurations for both increased safety aspects and long cycle life benefits. The present disclosure provides new developments in this specific area.
A distinct advantage of this disclosure is the ability through structural components to provide a mechanism to break the conductive pathway when an internal short occurs, stopping or greatly reducing the flow of current that may generate heat within the target battery cell. Another advantage is the ability to provide such a protective structural format within a lithium battery cell that also provides beneficial weight and cost improvements for the overall cell manufacture, transport and utilization. Thus, another advantage is the generation and retention of an internal fuse structure within a target battery cell until the need for activation thereof is necessitated.
A further distinct advantage of this disclosure is the simultaneous benefit of increased thermal runaway safety levels, reduced overall weight, and unexpectedly high cycle life rates for wound lithium-ion batteries. Another distinct advantage is the ability to compress such wound battery components to pressures necessary to impart such high cycle life rates through different pathways, including numbers of windings, certain geometries within the subject housing, the hardness of the actual housing itself, and even the actual curvature(s) of the wound battery components therein such a housing. Thus, another distinct advantage of the disclosure is the versatility of imparting such cycle life improvements in relation to the utilization of at least one metallized thin film current collector therein and therewith with a wound configuration of the battery components thereof within such a housing.
Accordingly, this disclosure encompasses an energy storage device comprising an anode, a cathode, at least one polymeric or fabric separator present between said anode and said cathode, and at least one current collector in contact with at least one of said anode and said cathode with the said anode or said cathode interposed between at least a portion of the said current collector and the said separator, said current collector comprising a conductive material coated on a polymeric material substrate, wherein said current collector stops conducting at the point of contact when exposed to a short circuit at the operating voltage of said energy storage device, said voltage being at least 2.0 volts. One example would be a current density at the point of contact of 0.1 amperes/square millimeter with a tip size of 1 square millimeter or less. Of course, for larger cells, the required threshold current density might be higher, and the cell might only stop conducting at a current density of at least 0.3 amperes/square millimeter, such as at least 0.6 amperes/square millimeter, or even at least 1.0 amperes/square millimeter. Methods of utilizing such a beneficial current collector component within an energy storage device (whether a battery, such as a lithium-ion battery, a capacitor, and the like) are also encompassed within this disclosure.
Such a novel current collector component is actually counterintuitive to those typically utilized and found within lithium (and other types) of batteries and energy storage devices today. Standard current collectors are provided are conductive metal structures, such as aluminum and/or copper panels of thicknesses that are thought to provide some type of protection to the overall battery, etc., structure. These typical current collector structures are designed to provide the maximum possible electrical conductivity within weight and space constraints. It appears, however, that such a belief has actually been misunderstood, particularly since the thick panels prevalent in today's energy storage devices will actually not only arc when a short occurs, but contribute greatly to runaway temperatures if and when such a situation occurs. Such a short may be caused, for example, by a dendritic formation within the separator. Such a malformation (whether caused at or during manufacture or as a result of long-term usage and thus potential degradation) may allow for voltage to pass unexpectedly from the anode to the cathode, thereby creating an increase in current and consequently in temperature at the location such occurs. Indeed, one potential source of short circuit causing defect are burrs that form on the edges of these thick typical current collectors when they are slit or cut with worn blades during repetitive manufacturing processes of multiple products (as is common nowadays). It has been repeatedly analyzed and understood, however, that the standard current collector materials merely exhibit a propensity to spark and allow for temperature increase, and further permitting the current present during such an occurrence to continue through the device, thus allowing for unfettered generation and movement, leaving no means to curtail the current and thus temperature level from increasing. This problem leads directly to runaway high temperature results; without any internal means to stop such a situation, the potential for fire generation and ultimately device immolation and destruction is typically imminent. Additionally, the current pathway (charge direction) of a standard current collector remains fairly static both before and during a short circuit event, basically exhibiting the same potential movement of electric charge as expected with movement from cathode to anode and then horizontally along the current collector in a specific direction. With a short circuit, however, this current pathway fails to prevent or at least curtail or delay such charge movement, allowing, in other words, for rapid discharge in runaway fashion throughout the battery itself. Coupled with the high temperature associated with such rapid discharge leads to the catastrophic issues (fires, explosions, etc.) noted above. To the contrary, and, again, highly unexpected and counterintuitive to the typical structures and configurations of lithium batteries, at least, the utilization of a current collector of the instant disclosure results in an extremely high current density measurement (due to the reduced thickness of the conductive element) and prevention of charge movement (e.g., no charge direction) in the event of a short circuit. In other words, with the particular structural limitations accorded the disclosed current collector component herein, the current density increases to such a degree that the resistance level imparts an extremely high, but contained, high temperature occurrence in relation to a short circuit. This resistance level thus causes the conductive material (e.g., as merely examples, aluminum and/or copper) to receive the short circuit charge but, due to the structural formation provided herein, the conductive material reacts immediately in relation to such a high temperature, localized charge. Combined with the other structural considerations of such a current collector component, namely the actual lack of a dimensionally stable polymeric material in contact with such a conductive material layer, the conductive material oxidizes instantly at the charge point thereon, leaving, for example, aluminum or cupric oxide, both nonconductive materials. With such instantaneous nonconductive material generation, the short circuit charge appears to dissipate as there is no direction available for movement thereof. Thus, with the current collector as now described, an internal short circuit occurrence results in an immediate cessation of current, effectively utilizing the immediate high temperature result from such a short to generate a barrier to further charge movement. As such, the lack of further current throughout the body of the energy storage device (in relation to the short circuit, of course) mutes such an undesirable event to such a degree that the short is completely contained, no runaway current or high temperature result occurs thereafter, and, perhaps most importantly, the current collector remains viable for its initial and protective purposes as the localized nonconductive material then present does not cause any appreciable reduction in current flow when the energy storage device (battery, etc.) operates as intended. Furthermore, the relatively small area of nonconductive material generation leaves significant surface area, etc., on the current collector, for further utilization without any need for repair, replacement, or other remedial action. The need to ensure such a situation, which, of course, does not always occur, but without certain precautions and corrections, as now disclosed, the potential for such a high temperature compromise and destruction event actually remains far higher than is generally acceptable. Thus, the entire current collector, due to its instability under the conditions of a short circuit, becomes a two-dimensional electrical fuse, preventing the potentially disastrous high currents associated with short circuits by using the instantaneous effect of that high current to destroy the ability of the current collector to conduct current at the point of the short circuit.
Such advantages are permitted in relation to such a novel resultant current collector that may be provided, with similar end results, through a number of different alternatives. In any of these alternative configurations, such a current collector as described herein functions ostensibly as an internal fuse within a target energy storage device (e.g., lithium battery, capacitor, etc.). In each instance (alternative), however, there is a current collector including a polymeric layer that is metallized on one or both sides thereof with at least one metallized side in contact with the anode or cathode of the target energy storage device. One alternative then is where the total thickness of the entire metallized (coated) polymeric substrate of the current collector is less than 20 microns with a resistance measurement of less than 1 ohm/square. Typical current collectors may exhibit these features but do so at far higher weight than those made with reinforcing polymeric substrates and without the inherent safety advantages of this invention disclosure. In this alternative structure, however, the very thin component allows for a short to react with the metal coat and in relation to the overall resistance levels to generate, with an excessively high temperature due to a current spike during such a short, a localized region of metal oxide that immediately prevents any further current movement therefrom.
Another possible alternative for such a novel current collector is the provision of a temperature dependent metal (or metallized) material that either shrinks from a heat source during a short or easily degrades at the specific material location into a nonconductive material (such as aluminum oxide from the aluminum current collector, as one example) (as alluded to above in a different manner). In this way, the current collector becomes thermally weak, in stark contrast to the aluminum and copper current collectors that are used today, which are quite thermally stable to high temperatures. As a result, an alloy of a metal with a lower inherent melting temperature may degrade under lower shorting current densities, improving the safety advantages of the lithium-based energy device disclosed herein. Another alternative is to manufacture the current collector by coating a layer of conductive material, for example copper or aluminum, on fibers or films that exhibit relatively high shrinkage rates at relatively low temperatures. Another possible manner of accomplishing such a result is to manufacture a current collector by coating a layer of conductive material, for example copper or aluminum, as above, on fibers or films that can swell or dissolve in electrolyte when the materials are heated to relatively high temperatures compared to the operating temperatures of the cells, but low compared to the temperatures that might cause thermal runaway. Examples of such polymers that can swell in lithium-ion electrolytes include polyvinylidiene fluoride and poly acrylonitrile, but there are others known to those with knowledge of the art. Yet another way to accomplish such an alternative internal electrical fuse generating process is to coat onto a substrate a metal, for example aluminum, that can oxidize under heat, at a total metal thickness that is much lower than usually used for lithium batteries. For example, a very thin aluminum current collector as used today may be 20 microns thick. A coating thickness of a total of less than 5 microns would break the circuit faster, and one less than 2 microns, or even less than 1 micron would break the circuit even faster. Even still, another way to accomplish the break in conductive pathway is to provide a current collector with limited conductivity that will degrade in the high current densities that surround a short, similar to the degradation found today in commercial fuses. This could be accomplished by providing a current collector with a resistivity of greater than 10 mOhm/square, or potentially preferably greater than 20 mOhm/square, or a potentially more preferred level of greater than 50 mOhm/square. The use of current collectors of different resistivities may further be selected differently for batteries that are designed for high power, which might use a relatively low resistance compared to cells designed for lower power and higher energy, and/or which might use a relatively high resistance. Still another way to accomplish the break in conductive pathway is to provide a current collector that will oxidize into a non-conductive material at temperatures that are far lower than aluminum, thus allowing the current collector to become inert in the area of the short before the separator degrades. Certain alloys of aluminum will oxidize faster than aluminum itself, and these alloys would cause the conductive pathway to deteriorate faster or at a lower temperature.
Thus, such alternative configurations garnering ostensibly the same current collector results and physical properties include a) wherein the total thickness of the coated polymeric substrate is less than 20 microns with resistance less than 1 ohm/square, b) the collector comprising a conductive material coated on a substrate comprising polymeric material, wherein the polymeric material exhibits heat shrinkage at 225° C. of at least 5%, c) wherein the collector metallized polymeric material swells in the electrolyte of the battery, such swelling increasing as the polymeric material is heated, d) wherein the collector conductive material total thickness is less than 5 microns when applied to a polymeric substrate, e) wherein the conductivity of the current collector is between 10 mOhm/square and 1 ohm/square, and f) wherein the metallized polymeric substrate of the collector exhibits at most 60% porosity. The utilization of any of these alternative configurations within an energy storage device with a separator exhibiting a heat shrinkage of less than 5% after 1 hour at 225° C. would also be within the purview of this disclosure. The overall utilization (method of use) of this type of energy storage device (battery, capacitor, etc.) is also encompassed herein.
This disclosure further encompasses an energy storage cell comprising battery components within a case (housing), said battery components comprising:
Thus, the comparative examples (Comp. 1-4) in Table 1 represent standard metal current collectors (Comp. 1-2) and polymer films alone (Comp. 3-4). Clearly, there are stark differences with the disclosed Examples 1-4 related to metallized film current collectors.
In order to be useful for coating and processing, the metallized film current collector should have an extensional force that is more than the minimum required for such processing. Thus, the extensional force for the metallized film should be more than 1 N/mm, preferably more than 5 N/mm, and more preferably more than 10 N/mm. To optimize the ability of the metallized film to breathe with the cell as the electrode materials expand and contract, the extensional force should be less than the metal foils themselves. Thus, the metallized film current collector should have an extensional force that is less than 600 N/mm, preferably less than 400 N/mm, and more preferably less than 300 N/mm.
As well, encompassed herein is such an energy storage cell as defined above wherein said stack is constrained within said case (housing).
Furthermore, this disclosure encompasses the energy storage cell noted above wherein said at least one metallized film substrate provides expansion and contraction room for the cell as it charges/discharges by compression and decompression in response to the pressure exerted on its coated face in the normal operation of said cell. Such a cell is preferably cylindrical in shape to allow for such a wound configuration, although other shapes are possible, as well. More than one of said anode or cathode may be coated on a metallized thin film current collector, as well.
Additionally, such a disclosure encompasses the same structure as noted above wherein said at least one metallized film provides thermal separation for the cell formed on each coated face. Again, more than one of said anode or cathode may be coated on a metallized thin film current collector in such a situation.
Furthermore, said at least one metallized film as present on either or both of said anode or cathode may impart a level of reduction (if not entire prevention) of cracking or compression of the coatings in response to charge/discharge volume changes in the cell, as well.
As it concerns the cathode materials and structures that may be utilized within the disclosed energy storage device, it has been realized that lithium-ion types are not the sole possibilities. Additionally, as one of ordinary skill in the art should understand, materials including sodium ion, lithium sulfur, LMNO, and the like, and potentially even NiMH and NiCad, may be present for such a purpose. The ability to further utilize recycled lithium materials (from prior lithium batteries) may be employed as well in this situation. The utilization of a proper metallized current collector with such cathode materials is the primary issue, in other words, and such other cathode types should work well for battery safety, effectiveness, and long cycle life benefits as described herein.
Generally, the cycle life of batteries is the number of charge and discharge cycles that a battery can complete before losing performance. The cycle life of a lithium-ion battery (as well other possible energy storage devices as discussed herein below) is affected significantly by the depth of discharge, which is the amount of a battery's storage capacity that is utilized. For example, a battery that is discharged only by 20% of its full energy capacity has a much greater cycle life than a battery that is discharged more deeply by 80% of its capacity so that only 20% of its full energy charge remains. Thus, a higher life cycle would impart far longer usage life of such a battery over time due to the ability to retain a better full energy charge in such a respect. The wound battery cells of this disclosure have been found to increase such life cycle levels significantly as compared with wound batteries without any metallized thin film current collectors present.
In a battery, the movement of lithium from anode to cathode during the charge-discharge causes expansion and contraction of the anode and cathode, known in the art as breathing of the battery. In a cell with metal foil current collectors of high modulus that exhibit a radius of curvature, this breathing causes the wound portions not only to move vertically to each other, but also laterally as the metal foil current collectors act as concentric springs winding and unwinding. This repetitive lateral movement of the current collectors causes the electrodes to undergo shear stress with each cycle, and such repetitive shear stress slowly dismantles the electrodes, separating particles, cracking particles and otherwise reducing the conductive pathways that are required for the electrode to function properly. Over time after repetitive shear stress cycling, the cell stops functioning correctly. This can happen after 250, 300, 500 or 700 cycles, where a cycle is defined as a full charge and discharge cycle from 0% to 100% state of charge (with the understanding that, in actual practice, a user may actually initiate a charging process when the device exhibits more than 0% discharge and charges to a level that is less than 100% charge) where the full charge or discharge occurs within one hour, known in the art as 1 C rate. Each combination of anode and cathode material in a battery design will have voltages associated with their fully charged and fully discharged state. Thus, for cathodes made from lithium (nickel-manganese-cobalt) oxide, the voltage range is usually 2.5 V-4.2 V, which is similar for all ratios of Ni, Mn, and Co, such as found in NMC111, NMC 523, NMC 622 or NMC 811 or other representative ratios. Similarly, lithium iron phosphate may have a voltage range of only 2.5 V-3.6 V for a full charge-discharge cycle. These voltage ranges are well known in the literature and are usually specified for a specific battery design. Thus, a charge from 0% to 100% state of charge will be through the full voltage range of the battery design.
This repetitive wear can result in a decay in the capacity of the battery, which is measured by charging the battery to full voltage at 1 C rate, holding it at a constant voltage until the charge current drops to C/10, resting for 30 minutes, and then discharging at 1 C rate to the minimum specified voltage for the battery design. The capacity of the battery in standard batteries may drop below 80% of the initial capacity in 250, 300, 500 or 700 cycles. The capacity of the inventive battery may remain above 80% of the initial capacity after 250 cycles, preferably 300 cycles, more preferably 500 cycles and most preferably 700 cycles.
However, if the current collector could be made in such a way that it allowed the cell to breath without imparting shear stress, the cell could be enabled to function for many more cycles without losing the conductive pathways that cause the cell to degrade.
One way to accomplish this is if the cell is configured in a way such that there is not a radius of curvature of the metal foil current collectors, this mode of cell degradation is also alleviated. Stacked pouch cells are one example that exhibits this geometry and does not undergo this mechanism of degradation. As shown in the examples below, even under constraint, the stacked pouch cells do not undergo this mechanism of degradation and can be cycled for thousands of cycles.
Another way, as particularly disclosed herein, is for the current collector to have an elastic modulus that is so low that it stretches and recovers with each cycle, substantially and effectively eliminating the rotational motion that would otherwise be caused by a rigid current collector with a radius of curvature.
Such specific battery component configurations not only impart the desired safety levels (thermal runaway) but generate heretofore unrealized, let alone investigated, levels of cycle life improvements. Without being bound to any specific scientific theory or theories, it is believed that such highly wound structures, particularly comprising at least one metallized thin film current collector (potentially preferably two for both the anode and the cathode) allows for the aforementioned capability of expansion and contraction of the battery cell components during charging and discharging as compared with typical and traditional foil current collectors (of significantly greater thickness and reduced capacity to expand/contract). When present within the confines of the case (housing) at a high compression level, the “flexible” nature accorded the cell components through the presence of such a metallized thin film current collector (or two), particularly in a wound state, allows for expansion/contraction effect thereof, thereby creating this phenomenon of increased cycle life over time.
As alluded to above, lithium battery cells typically come in two basic configurations overall, namely a rolled or stacked format. Rolled structures are commonly known and provided either in a cylindrical or jelly-roll configuration or an extended rolled (prismatic) format (similar to a stacked formation but with a continuous structure) (and in either a hard or soft case structure). Stacked structures are known as described with the different components (anode, collector, separator, cathode) in a stacked series within the confines of the battery housing. As noted above, such typical battery configurations utilize standard monolithic, or at least relatively thick, current collectors that add weight to the overall battery, of course, and which also contribute to the drawbacks described above (high internal resistance, runaway charge potentials with shorts, etc.). Such standard configurations further utilize tabs to provide conductivity from the internal portions externally for power transfer purposes. Rolled cells generally have a tab welded directly to the current collector that is accessible from outside the cell. Stacked cells generally have a tab welded to a stack of current collectors, and the tab either is welded to an electrode that is accessible from outside the cell, or the tab itself is sealed into the case in a way that it is accessible from outside the cell. In both cases, there are direct welding connections that reach from the current collector to the outside of the cell.
As it concerns such rolled cells, it should be well understood by the ordinarily skilled artisan that there are certain end uses for which these configurations are particularly important, including, without limitation, transportation, energy storage, consumer electronics and industrial applications. Stacked formations have certain beneficial end uses, as well, and the presence of metallized thin film current collectors have been found to be particularly valuable for both safety and overall weight considerations (at least). In terms of cycle life considerations, such stacked formations (again with at least one metallized thin film current collector present) appear to already exhibit similar measures and rates to typical (i.e., standard current collector) stacked cell structures. The safety and weight benefits thus already accord significant improvements with such a coupled life cycle value result.
The rolled (wound) battery configurations, as now determined and presented within this disclosure, exhibit both such safety and weight benefits, certainly, and, again, unexpectedly, with the relaxation of the shear forces that are normally present through the use of low-spring constant current collectors, also exhibit the cycle life improvements imparted as noted above. Such cycle life improvement in this manner is, again, unique and heretofore unknown within the lithium (and other type) rechargeable energy storage device industry.
Thus, this disclosure is directed to such wound energy storage devices (such as, without limitation, battery structures) in relation to the inclusion of at least one metallized thin film current collector for the aforementioned valuable and unexpected long cycle life benefits accorded thereby.
Furthermore, such a unique wound energy storage device (again, without limitation, a battery) may include a configuration wherein each side of the metallized film of either anode or cathode (or both) current collectors makes direct contact with either of the poles of the housing. As well, such metallized films may exhibit metallization on both sides of the subject current collector(s).
For any of these metallized substrates, it is desirable to have a low thickness to facilitate increase of the energy density of the cell. Any means can be used to obtain such thickness, including calendering, compressing, hot pressing, or even ablating material from the surface in a way that reduces total thickness. These thickness-reducing processes could be done before or after metallization. Thus, it is desirable to have a total thickness of the metallized substrate of less than 25 microns, preferably less than 20 microns, more preferably less than 16 microns, and potentially most preferably less than 14 microns. Commercial polyester films have been realized with thicknesses of at most 3 microns, and even lower at 1.2 microns. These types could serve as suitable substrates and allow the total thickness of the current collector to be less than 10 microns, preferably less than 6 microns, and more preferably less than 4 microns. Such ultra-thin current collectors (with proper conductivity as described above and throughout) may allow much higher energy density with improved safety performance, a result that has heretofore gone unexplored.
It is also desirable to have low weight for these metallized substrates. This could be achieved through the utilization of low-density polymer materials such as polyolefins or other low-density polymers including polyethylene, polypropylene, and polymethylpentene, as merely examples. It could also be achieved by having an open pore structure in the substrate or even through utilization of low basis weight substrates. Thus, the density of the polymer used in the substrate material could be less than 1.4 g/cm3, preferably less than 1.2 g/cm3, and potentially more preferably less than 1.0 g/cm3. Also, the areal density of the substrate material could be less than 20 g/m2, preferably less than 16 g/m2, and potentially most preferably less than 14 g/m2. Additionally, the areal density of the metal coated polymer substrate material could be less than 40 g/m2, preferably less than 30 g/m2, more preferably less than 25 g/m2, and potentially most preferably less than 20 g/m2.
Low weight can also be achieved with a porous polymer substrate. However, the porosity must not be too high for these materials, as such would result in low strength and high thickness, effectively defeating the purpose of the goals involved. Thus, such base materials would exhibit a porosity lower than about 60%, preferably lower than 50%, and potentially more preferably lower than 40%. Since solid materials can be used for this type of metal coated current collector, there is no lower limit to the porosity.
High strength is required to enable the materials to be processed at high speeds into batteries. This can be achieved by the use of elongated polymers, either from drawn fibers or from uniaxially or biaxially drawn films.
As presented below in the accompanying drawings the descriptions thereof, an energy storage device, such as a battery, as again a non-limiting example, is manufactured and thus provided in accordance with the disclosure wherein at least one current collector that exhibits the properties associated with no appreciable current movement after a short is in contact with one of a cathode or an anode, or two separate current collectors are in contact with both a cathode and an anode. Additionally, at least one separator and electrolytes (of any type, preferably liquid and flammable in nature) are also present with such at least one current collector, cathode, and anode, and sealed within a standard (suitable) energy storage device container. Such a general method of providing the disclosed wound battery device is to provide a lengthy rectangular structure of all of the layers of components (cathode current collector, cathode, separator, anode, anode current collector, with at least one of the current collectors involved, preferably both, being a metallized thin film current collector as described and in contact with either or both of the cathode and/or anode, as noted above) then rolling the entirety of the rectangular into a “jelly roll” structure around a rod or dowel (or like straight structure) to form a cylindrically shaped configuration thereof for placement within the subject case (housing). In such a manner, the dowel or rod (or, again, like structure) is then removed after introduction with a case leaving a centrally disposed opening into which liquid electrolytes may then be introduced themselves for dissipation throughout the case and battery components. The end result is the application of the wound battery components such that expansion and contraction of such components within the sealed case (housing) results in lower shear forces during the breathing of the cell as the cell undergoes charge-discharge cycling. The winding numbers that may impart such a compression level may range from 3 to 300, dependent certainly upon the initial thickness of the unwound structure prior to case (housing) introduction. The presence of this utilization of such metallized thin film current collector(s) allows for a thin structure initially and thus the ability to generate a significant increase in windings for such a rolled battery structure greater than present within standard current collector-based batteries. The case (housing) may range from a standard material (soft, potentially, when a tightly wound battery components structure is utilized and introduced therein) to a significantly hardness (and thus less flexible) material to ensure the wound battery structure introduced therein retains a coiled configuration. The radius of curvature measurement(s) of the wound battery structures introduced within a case (housing) (which is then sealed, of course, as would be for all such devices disclosed herein) may be applied and thus measured. Such a radius of curvature of the battery components, as noted above, may be at most 20 cm with a lower measure of about 500 microns.
Thus, this disclosure is directed to such wound battery structures in relation to the inclusion of at least one metallized thin film current collector for the aforementioned invaluable benefits accorded thereby within the lithium-ion battery art.
The cathode, anode, container, electrolytes, and in some situations, the separator, components are all standard, for the most part, and any material common in the industry may be used. The current collector utilized herewith and herein, however, is, as disclosed, not only a recent introduction within this battery art, but counterintuitive as an actual energy storage device component. As it concerns the separator component(s), however, one or more thereof may be provided as a low-shrink rate, and thus high temperature resistant non-woven types to impart further protection from any potential high temperature scenarios, ostensibly preventing thermal runaway by retaining separation between cathode and anode components.
While the primary advantage of this disclosure is enhanced safety for the cell, there are other advantages, as alluded to above, including reduced weight of the overall energy storage device through a reduced amount of metal weight in relation to such current collector components. Again, it is completely counterintuitive to utilize thin metallized coated polymeric layers, particularly of low dimensionally stable characteristics, for current collectors within such battery articles. The present mindset within this industry remains the thought that greater amounts of actual metal and/or insulator components are needed to effectuate the desired protective results (particularly from potential short circuit events). It has now been unexpectedly realized that not only is such a paradigm incorrect, but the effective remedy to short circuiting problems within lithium batteries, etc., is to reduce the amount of metal rather than increase, and couple the same with thermally unstable base layers. Thus, it has been not only realized, again, highly unexpectedly, that thin metal layers with such unstable base layers provide the ability to combat and effectively stop discharge events during short circuits, the overall effect is not only this far safer and more reliable result, but a significantly lower overall weight and volume of such component parts. Thus, the unexpected benefits of improved properties with lowered weight and volume requirements within energy storage products (batteries, etc.), accords far more to the industry than initially understood.
As a further explanation, aluminum, at a density of 2.7 g/cm3, at 20 microns thick would weigh 54 g/m2. However, the same metal coated at 1 micron on a 10-micron thick polypropylene film (density 0.9 g/cm3) would weigh 11.7 g/m2. This current collector reduction in weight can reduce the weight of the entire target energy storage device (e.g., battery), increasing mobility, increasing fuel mileage or electric range, and in general enhance the value of mobile electric applications.
Additionally, because of the high strength of films, the above example can also be made thinner, a total thickness of 11 microns compared to 20 microns, for example, again reducing the volume of the cell, thereby effectively increasing the energy density. In this way, a current collector of less than 15 microns, preferably less than 12, more preferably less than 10, and most preferably less than 8 microns total thickness, can be made and utilized for such a purpose and function.
With the bulk resistivity of aluminum at 2.7×10−8 ohm-m and of copper at 1.68×10−8 ohm-m, a thin coating can be made with less than 1 ohm/square, or less than 0.5 ohms/square, or even less than 0.1 ohms/square, or less than 0.05 ohms/square. The thickness of these conductive coatings could be less than 5 microns, preferably than 3 microns, more preferably less than 2 microns, potentially most preferably even less than 1 micron. It is extremely counterintuitive, when standard materials of general use in the market contain 10 microns or more of metal, that suitable performance could be obtained using much less metal. Indeed, most of the metal present in typical storage devices is included to give suitable mechanical properties for high speed and automated processing. It is one of the advantages of this invention to use a much lower density polymer material to provide the mechanical properties, allowing the metal thickness to be reduced to a level at which the safety of the cell is improved because of the inability of the current collector to support dangerously high current densities that result from internal electrical shorts and result in thermal runaway, smoke and fire.
Additionally, these conductive layers can be made by multiple layers. For example, a layer of aluminum may be a base layer, coated by a thin layer of copper. In this way, the bulk conductivity can be provided by the aluminum, which is light, in expensive and can easily be deposited by vapor phase deposition techniques. The copper can provide additional conductivity and passivation to the anode, while not adding significant additional cost and weight. This example is given merely to illustrate and experts in the art could provide many other multilayer conductive structures, any of which are excellent examples of this invention.
These thin metal coatings will in general result in higher resistance than in an aluminum or copper current collector of normal practice, providing a distinguishing feature of this invention in comparison. Such novel suitable current collectors can be made at greater than 10 mohm/square, preferably greater than 20 mohm/square, more preferably greater than 50 mohm/square, and potentially most preferably even greater than 100 mohm/square.
Additionally, cells made with the thermally weak current collectors described above could be made even more safe if the separator has a high thermal stability, such as potentially exhibiting low shrinkage at high temperatures, including less than 5% shrinkage after exposure to a temperature of 200° C. for 1 hour, preferably after an exposure of 250° C. for one hour, and potentially more preferably after an exposure to a temperature of 300° C. for one hour.
One way that this current collector will exhibit its usefulness is in the following test. A current source with both voltage and current limits can be set to a voltage limit similar to the operating voltage of the energy storage device in question. The current can then be adjusted, and the current collector tested under two configurations. In the first, a short strip of the current collector of known width is contacted through two metal connectors that contact the entire width of the sample. The current limit of the current source can be raised to see if there is a limit to the ability of the material to carry current, which can be measured as the total current divided by the width, achieving a result in A/cm, herein designated as the horizontal current density. The second configuration would be to contact the ground of the current source to one of the full width metal contacts, and then touch the tip of the probe, approximately 0.25 mm2, to a place along the strip of the current collector. If the current is too high, it will burn out the local area, and no current will flow. If the current is not too high for the current collector, then the full current up to the limit of the current source will flow. The result is a limit of current in A/mm2, herein designated as the vertical current density. In this way, a current collector which can reach a high current under both configurations would be similar to the prior art, and a current collector which could support the horizontal current when contacted under full width, but would not support a similar vertical current under point contact would be an example of the invention herein described.
For example, it may be desirable for a current collector to be able to support horizontal current density 0.1 A/cm, or 0.5 A/cm, or 1 A/cm or 2 A/cm or even 5 A/cm. And for a current collector that could support a horizontal current density as above, it would be desirable not to support a vertical current density of 0.1 A/mm2, or 0.5 A/mm2, or 1 A/mm2 or 2 A/mm2 or even 5 A/mm2.
As noted above, in order to reduce the chances, if not totally prevent, thermal runaway within a battery cell (particularly a lithium-ion rechargeable type, but others are possible as well, of course), there is needed a means to specifically cause any short circuit therein to basically exist within a short period of time, with reduced residence time within or on the subject current collector, and ultimately exhibit a resultant energy level of de minimis joule levels (i.e., less than 10, preferably less than 1, and most preferably less than 0.01). In such a situation, then, and as alluded to earlier, the electrical pathway from anode to cathode, and through the separator, with the thin conductive current collector in place, and organic flammable electrolyte present, it has been observed that the low-weight, thin current collector allows for such a desirable result, particularly in terms of dissipation of rogue charges at the collector surface and no appreciable temperature increase such that ignition of the electrolyte component would be imminent. Surprisingly, and without being bound to any specific scientific explanation or theory, it is believed that the conductive nature of the thin current collector material allows for short circuit electrical charges to merely reach the thin conductive current collector and immediately create a short duration high-energy event that reacts between the metal at the current collector surface with the electrical charge itself, thereby forming a metal oxide at that specific point on the current collector surface. The metal oxide provides insulation of further electrical activity and any current applied dissipates instantaneously, leaving a potential deformation within the collector itself, but with the aforementioned metal oxide present to protect from any further electrical charge activity at that specific location. Thus, the remaining current collector is intact and can provide the same capability as before, thus further providing such protections to any more potential short circuits or like phenomena. In the case of thermal runaway in prior art battery products, the anode, cathode, current collectors and separator comprise the electrical pathway which generates heat and provide the spark to ignite the cell in reaction to a short circuit, as an example. The further presence of ion transporting flammable electrolytes thus allows for the effective dangers with high temperature results associated with such unexpected electrical charges. In essence, the heat generated at the prior art current collector causes the initial electrochemical reactions within the electrolyte materials, leading, ultimately to the uncontrolled ignition of the electrolyte materials themselves. Thus, the disclosed current collector herein is, again, particularly valuable when utilized within battery cells including such flammable electrolytes. As examples, then, such electrolytes generally include organic solvents, such as carbonates, including propylene carbonate, ethylene carbonate, ethyl methyl carbonate, di ethyl carbonate, and di methyl carbonate, and others. These electrolytes are usually present as mixtures of the above materials, and perhaps with other solvent materials including additives of various types. These electrolytes also have a lithium salt component, an example of which is lithium hexafluorophosphate, LiPF6. Such electrolytes are preferred within the battery industry, but, as noted, do potentially contribute to dangerous situations. Again, the disclosed current collector in association with other battery components remedies these concerns significantly and surprisingly.
The metallized substrate may be any substrate as described within this disclosure. The ion storage material may be a cathode or anode material for lithium-ion (or other type of aforementioned rechargeable) batteries, as are well known in the art. Cathode materials may include lithium cobalt oxide LiCoO2, lithium iron phosphate LiFePO4, lithium manganese oxide LiMn2O4, lithium nickel manganese cobalt oxide LiNixMnyCozO2, lithium nickel cobalt aluminum oxide LiNixCoyAlzO2, or mixtures of the above or others as are known in the art (as noted above, such cathodes may also include, without limitation, sodium ion, sodium ion, lithium sulfur, LMNO, etc. and potentially even NiMH and NiCad).
Anode materials may include graphite, lithium titanate Li4Ti5O12, hard carbon, tin, silicon or mixtures thereof or others as are known in the art, including lithium metal. In addition, anodes which expand and contract to a higher degree may achieve a much longer cycle life. These anodes include, without limitation, silicon, silicon-oxides, tin, tin oxides, lithium metal, lithium metal alloys and other high-capacity anodes for lithium-ion batteries. Some of these, such as silicon, silicon-oxide, tin and others, exhibit very high growth on cell charge and shrinkage on cell discharge. The lower modulus current collectors in this invention will be particularly suited to accommodate the dimensional changes in the anode materials, and any others that undergo such severe dimensional change on charge and discharge of the cell. Additionally, for the anode, also included is the concept of an “anode-less” battery, in which the anode is formed by charging the battery, creating a layer of lithium metal on the anode current collector which serves as the anode. In addition, the ion storage material could include those used in other energy storage devices, such as supercapacitors. In such supercapacitors, the ion storage materials will include activated carbon, activated carbon fibers, carbide-derived carbon, carbon aerogel, graphite, graphene, and carbon nanotubes. The coating process can be any coating process that is generally known in the art. Knife over-roll and slot die are commonly used coating processes for lithium-ion batteries, but others may be used as well, including electroless plating. In the coating process, the ion storage material is in general mixed with other materials, including binders such as polyvinylidene fluoride or carboxymethyl cellulose, or other film-forming polymers. Other additives to the mixture include carbon black and other conducting additives.
Other cathode and anode structures may include sodium ion battery types, including, without limitation, sodium phosphate cathode systems, sodium metal, hard carbon, Prussian blue analogues, and layered transition metal oxides.
Counterelectrodes include other electrode materials that have different electrochemical potentials from the ion storage materials. In general, if the ion storage material is a lithium-ion anode material, then the counterelectrode would be made from a lithium-ion cathode material; with a sodium ion anode material, the counterelectrode would be manufactured from a suitable sodium ion counterpart, as well. In the case where the ion storage material is a lithium-ion cathode material, then the counterelectrode might be a lithium-ion anode material. In the case where the ion storage material is a supercapacitor material, the counterelectrode can be made from either a supercapacitor material, or in some cases from a lithium-ion anode or lithium-ion cathode material. In each case, the counterelectrode would include an ion storage material coated on a current collector material, which could be a metal foil, or a metallized film such as in this disclosure.
In the layering process, the disclosed electrode is layered with the counterelectrode with the electrode materials facing each other and a porous separator between them. As is commonly known in the art, the electrodes may be coated on both sides, and a stack of electrodes formed with the inventive electrode and counterelectrodes alternating with a separator between each layer. Alternatively, as is also known in the art, strips of electrode materials may be stacked as above, and then wound into a cylinder.
Packaging materials may include hard packages such as cans for cylindrical cells, flattened hard cases or polymer pouches which may be made from plastic, aluminum, steel, laminated materials or others without restrictions from the known art. In each case, there must be two means of making electrical contact through the case that can be held at different voltages and can conduct current. In some instances, a portion of the case itself forms one means, while a different portion of the case that is electrically isolated from the first portion forms another means. In other instances, the case may be nonconducting, but allows two metal conductors to protrude through the case, often referred to as tabs.
The liquid electrolyte is typically a combination/mixture of a polar solvent and a lithium salt. Commonly used polar solvents include, as noted above, propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, but other polar solvents, including ionic liquids or even water may be used. Lithium salts commonly utilized within this industry include, without limitation, LiPF6, LiPF4, LiBF4, LiClO4 and others. The electrolyte may also contain additives as are known in the art. In many cases, the electrolytes can be flammable, in which the safety features of the inventive metallized substrate current collectors can be advantageous preventing dangerous thermal runaway events which result in fire and damage both to the cell and external to the cell. It is interesting to note also that the extension of the cycle life of the battery can also be useful with solid electrolytes, as are commonly used in solid state lithium-ion batteries, such as ceramic, garnet, or polymer electrolytes, or composites thereof.
The following descriptions and examples are merely representations of potential embodiments of the present disclosure. The scope of such a disclosure and the breadth thereof in terms of claims following below would be well understood by the ordinarily skilled artisan within this area.
As noted above, the present disclosure is a major shift and is counterintuitive from all prior understandings and remedies undertaken within the lithium battery (and other energy storage device) industry. To the contrary, the novel devices described herein provide a number of beneficial results and properties that have heretofore been unexplored, not to mention unexpected, within this area. Initially, though, as comparisons, it is important to note the stark differences involved between prior devices and those currently disclosed and broadly covered herein.
A cathode for a lithium iron phosphate battery was obtained from GB Systems in China. The aluminum tab was removed as an example of a commercial current collector, and the thickness, areal density and resistance were measured, which are shown in Table 2, below. The aluminum foil was then touched with a hot soldering iron for 5 seconds, which was measured using an infrared thermometer to have a temperature of between 50° and 525° C. There was no effect of touching the soldering iron to the current collector. The thickness, areal density and resistance were measured. The material was placed in an oven at 175° C. for 30 minutes and the shrinkage measured. A photograph was taken and included in
An anode for a lithium iron phosphate battery was obtained from GB Systems in China. The copper tab was removed as an example of a commercial current collector, and the thickness, areal density and resistance were measured, which are shown in Table 2, below. The copper foil was then touched with a hot soldering iron in the same way as Example 1. There was no effect of touching the soldering iron to the current collector. The thickness, areal density and resistance were measured. The material was placed in an oven at 175° C. for 30 minutes and the shrinkage measured. A photograph was taken and included in
Polypropylene lithium battery separator material was obtained from MTI Corporation. The material was manufactured by Celgard with the product number 2500. The thickness, areal density and resistance were measured, which are shown in Table 2, below. The separator was then touched with a hot soldering iron in the same way as Example 1. Touching the thermometer to the current collector created a small hole. The diameter was measured and included in Table 1. The thickness, areal density and resistance were measured. The material was placed in an oven at 175° C. for 30 minutes and the shrinkage measured. A photograph was taken and included in
Ceramic coated polyethylene lithium battery separator material was obtained from MTI Corporation. The thickness, areal density and resistance were measured, which are shown in Table 2, below. The separator was then touched with a hot soldering iron in the same way as Example 1. Touching the soldering iron to the current collector created a small hole. The diameter was measured and included in Table 2. The thickness, areal density and resistance were measured. The material was placed in an oven at 175° C. for 30 minutes and the shrinkage measured. A photograph was taken and included in
Ceramic coated polypropylene lithium battery separator material was obtained from MTI Corporation. The thickness, areal density and resistance were measured, which are shown in Table 2, below. The separator was then touched with a hot soldering iron in the same way as Example 1. Touching the soldering iron to the current collector created a small hole. The diameter was measured and included in Table 2. The thickness, areal density and resistance were measured. The material was placed in an oven at 175° C. for 30 minutes and the shrinkage measured. A photograph was taken and included in
Aluminized biaxially oriented polyester film was obtained from All Foils Inc., which is designed to be used for helium filled party balloons. The aluminum coating holds the helium longer, giving longer lasting loft for the party balloons. The thickness, areal density and resistance were measured, which are shown in Table 2, below. The film was then touched with a hot soldering iron in the same way as Example 1. Touching the soldering iron to the current collector created a small hole. The diameter was measured and included in Table 2. The thickness, areal density and resistance were measured. The material was placed in an oven at 175° C. for 30 minutes and the shrinkage measured. A photograph was taken and included in
Dreamweaver Silver 25, a commercial lithium-ion battery separator was obtained. It is made from a blend of cellulose and polyacrylonitrile nanofibers and polyester microfibers in a papermaking process, and calendered to low thickness. The separator was then touched with a hot soldering iron in the same way as Example 1. Touching the thermometer to the current collector did not create a hole. The thickness, areal density and resistance were measured. The material was placed in an oven at 175° C. for 30 minutes and the shrinkage measured. Compared to the prior art, comparative examples #3-5, these materials have the advantage that they do not melt or shrink in the presence of heat, and so in a lithium-ion battery with an internal short, will not retreat to create an even bigger internal short. Such is seen in
Dreamweaver Gold 20, a commercially available prototype lithium-ion battery separator was obtained. It is made from a blend of cellulose and para-aramid nanofibers and polyester microfibers in a papermaking process, and calendered to low thickness. The separator was then touched with a hot soldering iron in the same way as Example 1. Touching the thermometer to the current collector did not create a hole. The thickness, areal density and resistance were measured. The material was placed in an oven at 175° C. for 30 minutes and the shrinkage measured. The advantages of this separator compared to the prior art separators are the same as for Example 2.
Comparative Examples 1-2 are existing current collector materials, showing very low resistance, high areal density and no response at exposure to either a hot solder tip or any shrinkage at 175° C.
Examples 1-3 are materials that have infinite resistance, have low areal density and melt on exposure to either 175° C. or a hot solder tip. They are excellent substrates for metallization according to this invention.
Examples 4 and 7 are examples of an aluminized polymer film which shows moderate resistance, low areal density and shrinks when exposed to 175° C. or a hot solder tip. It is an example of a potential cathode current collector composite film according to this invention. In practice, and as shown in further examples, it may be desirable to impart a higher level of metal coating for higher power batteries.
Examples 5-6 are materials that have infinite resistance, have low areal density, but have very low shrinkage when exposed to 175° C. or a hot solder tip. They are examples of the polymer substrate under this invention when the thickness of the metallized coating is thin enough such that the metallized coating will deteriorate under the high current conditions associated with a short. Additionally, the cellulose nanofibers and polyester microfibers will oxidize, shrink and ablate at temperatures far lower than the melting temperatures of the metal current collectors currently in practice.
Example 5 additionally is made from a fiber, polyacrylonitrile, that swells on exposure to traditional lithium-ion carbonate electrolytes, which is also an example of a polymer substrate under this invention such that the swelling will increase under heat and create cracks in the metalized coating which will break the conductive path, improving the safety of the cell by eliminating or greatly reducing the uniform conductive path of the current collector on the exposure to heat within the battery.
The material utilized in Example 5 was placed in the deposition position of a MBraun Vacuum Deposition System, using an intermetallic crucible and aluminum pellets. The chamber was evacuated to 3×10−5 mbar. The power was increased until the aluminum was melted, and then the power set so the deposition rate was 3 Angstroms/s. The deposition was run for 1 hour, with four samples rotating on the deposition plate. The process was repeated three times, so the total deposition time was 4 hours. The samples were measured for weight, thickness and resistance (DC and 1 kHz, 1 inch strip measured between electrodes 1 inch apart), which are shown in Table 2 below. Point resistance was also measured using a Hioki 3555 Battery HiTester at 1 KHz with the probe tips 1″ apart. The weight of added aluminum was calculated by the weight added during the process divided by the sample area. This is divided by the density of the material to give the average thickness of the coating.
A nonwoven polymer substrate was made by taking a polyethylene terephthalate microfiber with a flat cross section and making hand sheets at 20 g/m2 using the process of Tappi T206. These hand sheets were then calendered at 10 m/min, 2000 lbs/inch pressure using hardened steel rolls at 250° C. This material was metalized according to the process of Example 7, and the same measurements taken and reported in Table 3.
Material according to Example 5 was deposited according to the process of Example 7, except that the coating was done at a setting of 5 Angstroms/second for 60 minutes. The samples were turned over and coated on the back side under the same procedure. These materials were imaged under a scanning electron microscope (SEM), both on the surface and in cross section, and the images are presented in
Materials were prepared according to the procedure of Example 9, except the deposition on each side was for only 20 minutes.
The polymer substrate of Example 9 was prepared, except that the sheets were not calendered. The deposition of aluminum is at 5 Angstroms/second for 20 minutes on each side. Because the materials were not calendered, the porosity is very high, giving very high resistance values with a thin coat weight. Comparing Example 12 to Example 9 shows the benefits of calendering, which are unexpectedly high.
The aluminum coated polymer substrate from Example 10 was coated with a mixture of 97% NCM cathode material (NCM523, obtained from BASF), 1% carbon black and 2% PVDF binder in a solution of N-Methyl-2-pyrrolidone. The coat weight was 12.7 mg/cm2, at a thickness of 71 microns. This material was cut to fit a 2032 coin-cell and paired with graphite anode coated on copper foil current collector (6 mg/cm2, 96.75% graphite (BTR), 0.75% carbon black, 1.5% SBR and 1% CMC). A single layer coin cell was made by placing the anode, separator (Celgard 2320) and the NCM coated material into the cell, flooding with electrolyte (60 μL, 1.0M LiPF6 in EC:DEC:DMC=4:4:2 vol+2 w. % VC) and sealing the cell by crimping the shell. To obtain adequate conductivity, a portion of the aluminum coated polymer substrate from Example 9 was left uncoated with cathode material and folded over to contact the shell of the coin cell, completing the conductive pathway. The cell was formed by charging at a constant current of 0.18 mA to 4.2 V, then at constant voltage (4.2 V) until the current dropped to 0.04 mA. The cell was cycled three times between 4.2 V and 3.0 V at 0.37 mA and gave an average discharge capacity of 1.2 mAh.
A cell was made according to the procedure and using the materials from Example 13, except the separator used was Dreamweaver Silver 20. The cell was formed by charging at a constant current of 0.18 mA to 4.2 V, then at constant voltage (4.2 V) until the current dropped to 0.04 mA. The cell was cycled three times between 4.2 V and 3.0 V at 0.37 mA and gave an average discharge capacity of 0.8 mAh. Thus, in this and the previous example, working rechargeable lithium-ion cells were made with an aluminum thickness of less than 1 micron.
The aluminum tab of Comparative Example 1, approximately 2 cm×4 cm was connected to the ground of a current source through a metal connector contacting the entire width of the sample. The voltage limit was set to 4.0 V, and the current limit to 1.0 A. A probe connected to the high voltage of the current source was touched first to a metal connector contacting the entire width of the sample, and then multiple times to the aluminum tab, generating a short circuit at 1.0 A. The tip of the probe was approximately 0.25 mm2 area. When contacted across the entire width, the current flowed normally. On initial touch with the probe to the tab, sparks were generated, indicating very high initial current density. The resultant defects in the current collector only sometimes resulted in holes, and in other times there was ablation but the current collector remained intact. In all cases the circuit remained shorted with 1.0 A flowing. A micrograph was taken of an ablated defect, with no hole, and is shown in
The copper tab of Comparative Example 2 of similar dimensions was tested in the same way as Comparative Example 3. When contacted across the entire width, the current flowed normally. On initial touch with the probe to the tab, sparks were generated, indicating very high initial current density. The resultant defects in the current collector only sometimes resulted in holes, and in other times there was ablation but the current collector remained intact. In all cases the circuit remained shorted with 0.8 A flowing. A micrograph was taken of an ablated defect, with no hole, and is shown in
The inventive aluminum coated polymer substrate material of Example 8 of similar dimensions was tested using the same method as Comparative Examples 3-4. When contacted across the entire width, the current flowed normally. In each case of the touch of the probe to the inventive current collector directly, the sparks generated were far less, and the current ceased to flow after the initial sparks, leaving an open circuit. In all cases, the resultant defect was a hole. Micrographs of several examples of the holes are shown in
The key invention shown is that, when exposed to a short circuit as in Comparative Examples 3-4 and in Example 15, with the prior art the result is an ongoing short circuit, while with the inventive material the result is an open circuit, with no ongoing current flowing (i.e., no appreciable current movement). Thus, the prior art short circuit can and does generate heat which can melt the separator, dissolve the SEI layer and result in thermal runaway of the cell. The open circuit of the inventive current collector will not generate heat and thus provides for a cell which can support internal short circuits without allowing thermal runaway and the resultant smoke, heat and flames.
Of further interest herein are the unexpected benefits now discovered related to the utilization of such thin metallized film current collectors within constrained and wound battery devices and articles. Of particular benefit, and, again, unexpected in this manner, is the increase in life cycle for such constrained and wound batteries in relation specifically to the thin metallized film current collectors present therein. Such a phenomenon is described in greater detail below.
As shown in
The anode/current collector was produced through the initial mixing of anode powders (graphite, for instance) with binders to form a slurry that was then coated onto the surface of a copper foil dried, and then compressed. The cathode/current collector was likewise formed in a similar fashion with cathode powders (NMC523, a nickel, manganese, and cobalt cathode combination) mixed with binders into a slurry which was then coated onto the surface of an aluminum metallized film (provided by ChangYu and disclosed above as Example 7 dried, and then compressed. The anode/current collector was then slit into the appropriate size (308 in
A second wound cell of this disclosure was also manufactured in the same basic procedure as for Wound Cell Example 1. Thus, the same manner of slurry formation and coating on metallized films was undertaken with the following parameters and specifics:
Thus, with the same separators as above, similar “jelly-roll” cells were formed.
As it concerns the aluminized current collector components utilized within the wound cell examples of this disclosure, such films, as exhibited in Example 7, were manufactured by Chang Yu, composed of, as one example, a 6-micron thick polyethylene terephthalate (PET) film with 1 micron of aluminum coated via vacuum vapor deposition therein. Overall, such aluminized film current collectors exhibited the following characteristics and properties:
Additionally, conductivity measurements were taken on such metallized (aluminized films with a four-point probe and utilizing VanDer Pauw measurement calculations. The results were shown to be 40.9 mΩ/□, thus providing excellent low resistance.
In this manner, the wound batteries disclosed herein that exhibit improved and unexpectedly good cycle life characteristics will be provided in relation to, in one embodiment, the range of radius of curvature measurements corresponding to this formula.
Such manufactured wound cells (Wound Cell Examples and Comparatives) were then subjected to initial charge formations (life cycled) with the following parameters:
Such cells were either in accordance with this disclosure, and thus utilizing metallized film current collectors (with anode or cathode components) or comparative cells with conventional copper and/or aluminum foil current collector components.
The cycle life results were measured and presented in graphical representations in
An additional comparative experiment was undertaken to determine the effect of metallized film current collectors within stacked, unwound, battery structures. For this test, pouch cells (produced by SVolt) were provided in constrained formation between two plates with stacked electrodes alone (but, again, with metallized film current collectors present). Such a configuration thus included stacked anode, cathode, and current collector(s) components, but a separator (or separators) was provided either stacked (as the other components) or folded between each stack layer. In such formations, then, the metallized film current collector (which may be electrode-coated) was inserted individually between any separator folds. Without a wound structure for the metallized film current collector(s), the pouch cells were constrained between two plates and then cycled. The results showed the metallized film does not provide any noticeable benefit through mechanical compliance in the through-plane direction of the cell. As shown above, such metallized film current collectors that impart beneficial cycle times for cells that contain regions with extreme metallized film current collector curvature (through the hypothesis of metallized film stretching upon the swelling that occurs in a charging and discharging cell). With such a nearly identical result of cycle time performance for stacked, rather than wound, electrodes (e.g., the performance of constrained volume stacked pouched cells), it is evident that the utilization of constrained wound metallized film current collectors is critical for unexpectedly improved cycle time results. Batteries including metallized film current collectors as disclosed herein provide much better cycle time performance within constrained wound structures in comparison to constrained wound structures including standard metal current collector types. Thus, the criticality of wound structures, whether in terms of curvature measurements or applied constrained forces is shown herein as the unexpectedly high cycle time measurements generated in association with such metallized film current collectors have heretofore been unknown and unexplored within this art.
Thus, it has been shown that the wound examples with the disclosed thin metallized film current collectors therein (provided and described above) not only exhibit the desirable thickness, metal coating, and conductivity results needed to prevent thermal runaway within an electrolyte-containing battery, thereby providing not only a much safer and more reliable type, but one that requires far less internal weight components than ever before, without sacrificing safety, but, in fact, improving thereupon; additionally, such measured results indicate long life cycle lithium-ion wound (rolled) battery cells that have heretofore been unavailable within the industry. With such unique and heretofore unexplored battery cells including thin film current collectors within wound sealed structures, a reliable, safer, and more thorough electrically conducting device is provided. Any type of electrolyte may likewise be present as long as the metallized thin film current collector(s) is/are present, including, flammable liquid organic electrolytes, gelling electrolytes, and possible solid electrolytes (though no equivalency between such electrolytes is intended with such a disclosure; liquid flammable electrolytes are potentially preferred). There is thus provided a novel approach to utilizing thin metallized film current collectors within lithium-ion (and like) batteries, capacitors, power cells, etc., for effective power transfer and reduced thermal runaway potential.
Having described the invention in detail it is obvious that one skilled in the art will be able to make variations and modifications thereto without departing from the scope of the present disclosure. Accordingly, the scope of the present invention should be determined only by the claims appended hereto.
This application is a continuation-in-part of pending U.S. Non-Provisional patent application Ser. No. 17/107,889, filed on Nov. 30, 2020, which is a divisional of patented U.S. Non-Provisional patent application Ser. No. 15/770,007, filed on Sep. 9, 2017, now U.S. Pat. No. 10,854,868, issued on Dec. 1, 2020, the entirety of both applications herein being incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 15770007 | Oct 2018 | US |
| Child | 17107889 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 17107889 | Nov 2020 | US |
| Child | 17744864 | US |
