Patent Application
20200303741
Electric vehicles (EVs) are increasingly being utilized to replace traditional gas engine vehicles. EVs have several advantages over traditional gas engine vehicles, such as, but not limited to, not requiring as much maintenance, being environmentally friendly, and increased performance. However, unlike traditional gas engine vehicles that rely on gas for power, EVs rely on a plurality of battery cells for power. A current disadvantage of utilizing battery cells as a power source is the time it takes to charge the battery cells in comparison to the time it takes to refill a tank of gas. Thus, there is a need to improve charging rates in battery cells within EVs.
Embodiments described herein generally relate to improving conductive pathways within a battery cell. By improving conductive pathways within a battery cell, various advantages may be recognized such as fast charging of the battery cell. A solution to improving conductive pathways may include a battery cell comprising of an anode. The anode may further comprise of a current collector and an anode slurry in contact with the current collector. The anode slurry may comprise a first set of bonding materials. The battery cell may further include a plurality of materials from a first functional group. In one embodiment, the materials in the first functional group are configured to bond to the first set of bonding materials to orient particles within the anode into a vertical direction. The battery cell may further comprise a cathode and a separator placed between the cathode and anode.
In one embodiment, the first functional group may bond to a perimeter of the current collector in part due to the material make-up of the current collection. In such an embodiment, one or more materials within the current collector may have a strong bonding affinity the first functional group. In one embodiment, the first functional group is part of a self-assembled monolayer. In such an embodiment, the bonding materials may also be part of the self-assembled monolayer, such that the strong bonding affinity between the bonding materials and the first functional group may cause one or more particles within the anode to self-assemble in a particular direction. In one embodiment, the self-assembled monolayer may include alkanethiols. In such an embodiment, the first functional group may comprise alkanethiols. In one embodiment, the self-assembled monolayer may comprise one or more thiols comprising of sulfur. In such an embodiment, the first functional group may comprise one or more thiols comprising of sulfur. In one embodiment, the bonding materials may include gold (Au) particles.
In one embodiment, the anode may comprise one or more carbon particles. The one or more carbon particles may be oriented in the vertical direction between the separator and the current collector at least due to the self-assembled monolayer that may be formed between the carbon particles and between the carbon particles and the current collector. In one embodiment, due in part to the particles within the anode being oriented in the vertical direction, lithium ions may flow from the cathode to the anode in between one or more carbon particles that are oriented in the vertical direction in a vertical conduction pathway. The vertical conduction pathway may result in little to no tortuosity within the battery cell.
Features, embodiments, and advantages of the present disclosure are better understood when the following Detailed Description is read with reference to the accompanying drawings.
The embodiments described herein generally relate to improving conductive pathways within a battery cell. By improving conductive pathways within a battery cell, various advantages may be recognized such as fast charging of the battery cell. A battery cell within an EV may contain graphite-based anodes. However, there are certain limitations with graphite-based anodes. For example, graphite-based anodes may contain relatively high tortuosity because “flake” or “platelet-like” graphite particles are utilized in the anode. Tortuosity may be a measure of a deviation of an ionic pathway from a straight line. Stated another way, when ions travel from a cathode of a battery cell to an anode of the battery cell, during a charging process, the ionic pathway taken by one or more of the ions may include many curves and turns. This tortuosity may result in a longer charge time for the battery cell, as it takes the ions longer to reach the current collector within the anode of the battery cell.
Another technical problem with graphite-based anodes is that, by nature, graphite has effective ion diffusivity in the in-plane direction with respect to its crystal structure. As a result, it may be extremely thermodynamically unfavorable for ions to diffuse in the through-plane direction through graphite particles. Instead of diffusing in the through-plane direction, diffusion takes place in the in-plane direction. Such a diffusion requires ions to travel around the graphite particles to find an edge site to begin a redox reaction and subsequent diffusion. Traveling along the perimeter of graphite particles may increase tortuosity within a battery cell due to the path the ion must take.
To remedy the technical issues with graphite-based anodes, embodiments described herein describe a solution that orients the graphite particles of an anode (i.e., negative electrode) so that the two dimension (2D) planes within the graphite particles are oriented vertically. In one embodiment, oriented vertically may mean vertical with respect to a current collector (of an anode) and a separator. By orienting the graphite particles in a vertical direction, ions may have a direct pathway to access edge sites of the graphite crystal planes, which results in the ions having a shorter diffusion pathway. The vertical orientation may also lead to reduction in tortuosity within a battery cell because now an ionic pathway for an ion may be vertical or relatively vertical with little to no turns or curves. Short diffusion pathways and a reduction in tortuosity may increase the performance of a battery cell. For example, faster charging may be achieved with a short diffusion pathway and a reduction in tortuosity because ions may travel to the negative electrode faster than in a battery cell without the short diffusion pathway and the reduction in tortuosity.
In one embodiment, graphite particles within an anode may be vertically oriented by utilizing organic linkers which may self-assemble on the surface of the graphite particles and/or on the current collector. The organic linkers may be self-assembling monolayers, or any other type of organic polymer that may self-assemble. The organic linkers may bind selectively to the edge-sites of the graphite particles. In one embodiments, the organic linkers may bind to the edge-sites of the graphite particles, because the edge-sites may have a reduced energy barrier which may attract the organic linkers to the edge-sites. Once, the organic linkers are attached to the edge-site of a plurality of graphite particles it may cause the graphite particles to automatically orient in a vertical direction. As a result, the organic linkers may self-assemble the graphite particles in a vertical orientation such that organic linkers at the edge-sites of the graphite particles are connected to each other. In one embodiment, the organic linkers may be connected to one or more bonding particles within or attached to the graphite particles. Adding the organic linkers and/or the bonding particles to the graphite particles or the current collector may be referred to as functionalizing the graphite particles or functionalizing the current collector, respectively. In one embodiment, functionalizing the current collector may not include introducing bonding particles to the current collect because the current collector may already be comprised of elements or particles that may bond to the organic linkers. For example, the current collector may be comprised of copper and copper may naturally bind to one or more organic linkers utilized.
Electrode 102 may be a positive electrode (e.g., a cathode) comprised of different material types. For example, electrode 102 may be comprised of lithium-cobalt oxide (LiCoO2), lithium iron phosphate (LiFePO4), and/or another metal based alloy. Electrode 102 may, prior to the initiation of a charging process, contain a plurality of lithium ions. During the charging process, the lithium ions (e.g., positively charged lithium ions) within electrode 102 may flow, via electrolyte 112, through separator 106 to electrode 108. During a discharging process the opposite may take place and the lithium ions within electrode 108 may flow, via electrolyte 112, though separator 106 and back to electrode 102. Although electrolyte 112 is shown as a separate component within battery cell 100, in many instances, electrodes 102 and 108 may be soaked in electrolyte 112 such that lithium ions may flow between electrode 102 and electrode 108 via separator 106.
Terminal 104 may be a current collector attached to electrode 102. Terminal 104 may be a positive current collector. Terminal 104 may be comprised of various materials including, but not limited to, copper, nickel, and/or compounds including copper and/or nickel. During a charging process, lithium ions within electrode 102 may flow from electrode 102 and electrons may be released. These electrons may flow from electrode 102 to terminal 104 and then from terminal 104, via electron path 114, to terminal 110. Because current flows in the opposite direction of electrons, terminal 104 may collect current during the charging process. Separator 106 may separate electrode 102 and electrode 108 while allowing lithium ions to flow between electrode 102 and electrode 108. Separator 106 may be a microporous isolator with little to no electrical conductivity. Separator 106 may also prevent the flow of electrons within electrolyte 112. By preventing electrons from flowing within electrolyte 112, separator 106 may force electrons to flow via electron path 114. Separator 106 may be comprised of various microporous materials, including, but not limited to, polyolefin, polyethylene, polypropylene, and similar compounds.
Electrode 108 may be a negative electrode (e.g., an anode) comprised of different material types. For example, electrode 108 may be comprised of carbon (e.g., graphite), cobalt, nickel, manganese, aluminum, and/or compounds including carbon, cobalt, nickel, manganese, and/or aluminum. Electrode 108 may, prior to the initiation of a charging process, contain none of or a small amount of lithium ions. During the charging process, the lithium ions (e.g., positively charged lithium ions) within electrode 102 may flow, via electrolyte 112, through separator 106 and to electrode 108. During a discharging process, the opposite may take place and the lithium ions within electrode 108 may flow, via electrolyte 112, though separator 106 and to electrode 102.
Terminal 110 may be a current collector attached to electrode 108. Terminal 110 may be a negative current collector. Terminal 110 may be comprised of various materials including, but not limited to, aluminum and/or aluminum based compounds. During a charging process, electrons may flow to or from electrode 102 to terminal 104 and then from terminal 104, via electron path 114, to terminal 110. Because current flows in the opposite direction of electrons, terminal 110 may collect current during a discharging process (e.g., when lithium ions flow from electrode 108 to electrode 102).
Electrolyte 112 may be a solution of solvents, salts, and/or additivities that act as a transport medium for lithium ions. Lithium ions may flow between electrodes 102 and 108 via electrolyte 112. In one embodiment, when an external voltage is applied to one of or both of electrodes 102 and 108, the ions in electrolyte 112 are attracted to an electrode with the opposite charge. For example, when external voltage is applied to cell 100, the lithium ions may flow from electrode 102 to electrode 108. The flow of ions within electrolyte 112 is due to the fact that electrolyte 112 has a high ionic conductivity due to the material make up of electrolyte 112. Electrolyte 112 may be comprised of various materials such as ethylene carbonate (EC), dimethyl carbonate (DMC), and/or lithium salts (e.g., LiClO4, LiPF6, and the like). In a solid state version of cell 100, electrolyte 112 may be a solid and may act as the separator. In such an embodiment the solid electrolyte may act as the separator between the electrode 102 and electrode 108, replacing separator 106.
Electron path 114 may be a path through which electrons flow between electrode 102 and electrode 108. Separator 106 may allow the flow of lithium ions between electrode 102 and electrode 108 via electrolyte 112, but separator 106 may also prevent the flow of electrons between electrode 102 and electrode 108 via electrolyte 112. Because the electrons cannot flow via electrolyte 112, they instead flow between electrode 102 and electrode 108 via electron path 114. In one embodiment, device 116 may be attached to electron path 114 and during a discharging process the electrons flowing through electron path 114 (from electrode 108 to electrode 102) may power device 116. In one embodiment, device 116 may only be attached to electron path 114 during a discharge process. In such an embodiment, during a charging process when an external voltage is applied to cell 100, device 116 may be directly powered or partially powered by the external voltage source.
Device 116 may be a parasitic load attached to cell 100. Device 116 may operate based at least in part off of current produced by cell 100. Device 116 may be various devices such as an electronic motor, a laptop, a computing device, a processor, and/or one or more electronic devices. Device 116 may not be a part of cell 100, but instead relies on cell 100 for electrical power. For example, device 116 may be an electronic motor that receives electric energy from cell 100 via electron path 114 and device 116 may convert the electric energy into mechanical energy to perform one or more functions such as acceleration in an EV. During a charging process, when an external power source is connected to cell 100, device 116 may be powered by the external power source (e.g., external to cell 100). During a discharging process, when an external power source is not connected to cell 100, device 116 may be powered by cell 100.
In one embodiment, anode 200 of
To remedy the issues with graphite-based anodes according to prior systems, a new anode structure may be manufactured that comprises graphite (or other particle types) particles that are aligned in a vertical orientation instead of in a brick-and-mortar like structure.
At 310, the anode powder is functionalized, via one or more materials in a functional group, the anode slurry. Functionalizing may be defined as engineering an object (e.g., graphite particles, surface of a current collector, and the like) to interact with other objects. Functionalizing may be achieved by the inclusion of materials in functional groups. Functional groups may be specific moieties within molecules that are responsible for the characteristic chemical reactions of those molecules. Thus by using materials from a function group a predictable chemical reaction may be realized. In one embodiment, the anode power may be functionalized by the inclusion of one or more organic linkers such as self-assembling monolayers to the anode powder. In on embodiment, a self-assembly monolayer may include alkanethiols, copper, gold, and/or thiols comprising carbon-sulfur-hydrogen. In one embodiment, the anode powder may decorated with gold particles (or another suitable element). These gold particles may have a strong affinity and bond strength with thiols (carbon-sulfur-hydrogen). Thus, when the thiols are introduced either at 310 or a later point (e.g., 320, 325) they may bond to the gold particles that are decorated within the graphite particles within the anode powder creating a self-assembling monolayer. In one embodiment, the organic linkers may not have magnetic properties, as compounds with magnetic properties may noticeably increase the weight of the anode slurry, which may ultimately increase the weight to the resultant battery cell.
At 315, a first current collector foil is functionalized via one or more materials in a functional group. The first current foil may be a foil that is specific to the anode slurry. For example, the first current collector foil may be a copper foil, nickel foil, or the like. The surface of the first current collector foil may be functionalized by one or more materials from a function group. The function group may be the same as the functional group that functionalizes the anode slurry or it may be a function group that reacts with the function group that functionalizes the anode slurry. In either instance, the functionalized surface of the first current collector and the functionalized anode slurry may contain organic linkers that interact with each other such that the carbon particles within the anode slurry self-assemble, at some later point, in a vertical orientation. The self-assembly may occur after the coating process (320) or the drying process (325). In one embodiment, the first current collector foil may be functionalized via the inclusion of copper. In such an embodiment, thiols comprising carbon-sulfur-hydrogen may be capable of bonding to copper. Due in part to its ability to bond with copper and other elements such as gold, these thiols may be utilized to self-assemble graphite particles within an anode slurry to the first current collector foil in a vertical orientation.
At 320, the anode slurry is coated onto the first current collector foil and the cathode slurry is coated onto a second current collector foil. The first current collector foil may be a foil that is specific to the anode slurry. For example, the first current collector foil may be a copper foil, nickel foil, or the like. The second current collector foil may be a foil that is specific to a cathode slurry. For example, the second current collector foil may be an aluminum foil and the like. Each current collector foil may be delivered by large reels and may be fed into separate coating machines. While in separate coating machines, each current collector foil has a corresponding slurry that is spread on its surface. For example, the first current collector foil may be fed, by a large reel, into an anode coating machine. While in the anode coating machine, the anode slurry produced at 310 may be spread on the surface of the first current collector foil as the first current collector foil passes through the anode coating machine. During the coating process, the thickness of a coated current collector foil may be modified such that the coated current collector foil has a desired thickness. In one embodiment, the thickness of the coated current collector foil may alter the energy storage per unit area of an electrode that is formed from that coated current collector foil.
At 325, the coated first current collector foil and the coated second current collector foil are dried. The coated current collector foils may be dried by feeding the coated current collector foils into a drying oven. Inside the drying oven, the respective electrode material (e.g., cathode or anode slurry) may be baked onto the coated current collector foil. Once the electrode material is baked onto a coated current collector foil, the coated current collector foil may be cut (e.g., width wise) into a size desired for a particular application. At the end of 325, an anode sheet may be formed from the processing applied to the first current collector foil and a cathode sheet may be formed from the processing applied to the second current collector foil. In one embodiment, during 325, the organic linkers utilized to functionalize the anode slurry and the first current collector foil may self-assemble carbon particles within the anode slurry in a vertical orientation.
At 330, a separator is disposed between the cathode sheet and the anode sheet forming an electrode structure. The separator may be a microporous insulator. In one embodiment, a separator may be disposed between the cathode sheet and anode sheet in a prismatic cell structure. In a prismatic cell structure, the cathode and anode sheets are cut into individual electrode plates and the separator is placed in the middle of the electrode plates. In one embodiment, the separator may be applied as a single long strip in a zig zag fashion. In such an embodiment, the separator would be woven in between alternate electrodes in the stack. For example, a first layer in the prismatic cell may be a first cathode sheet, the second layer may be a separator, the third layer may be a first anode sheet, the fourth layer may be the separator, the fifth layer may be a second cathode sheet, the sixth layer may be the separator, the seventh layer may be a second anode sheet, and so forth. This stacked configuration may be used for high capacity battery applications to optimize space.
In one embodiment, a separator may be disposed between the cathode sheet and anode sheet in a cylindrical cell structure. In a cylindrical cell structure, the cathode sheet, the separator, and the anode sheet are wound onto a cylindrical mandrel in such a way that the cathode sheet and anode sheet are separated by the separator. The result of this winding process is a jelly roll. An advantage of the cylindrical cell structure is that it requires only two electrode strips which simplifies the construction process over other structures (e.g., prismatic cell). A first tab may be included on the cathode sheet and a second tab may be included on the anode sheet. Each respective tab may be a connection point to the respective electrode (e.g., to connect to an external device).
At 335, the electrode structure is placed in a holding container. The holding container may depend upon the cell structure of the electrode structure. For example, a holding container may be a can-shaped container for a cylindrical cell structure. At 340, once the electrode structure is inside the holding container the holding container is filled with an electrolyte and sealed. The filling of the holding container with the electrolyte may be referred to as an electrolyte wetting process. After the holding container is sealed the battery cell is formed. Once the battery cell is formed the battery cell may be charged and discharged once to activate the materials (e.g., cathode, anode, lithium ions, etc.) inside the battery cell to make the battery cell active.
Organic linker group 404C may be a set of organic linkers that are attached to the surface of current collector 408. Organic linker group 404C may functionalize the surface (e.g., one or more parts of the perimeter) of current collector 408 because the energy barrier on the surface may be less than the energy barrier of internal portions of current collector 408. Similar to organic linker group 404B, organic linker group 404C may self-assemble in a vertical orientation which may cause carbon particle 402B to orient in a vertical direction. Thus, organic linker group 404C and organic linker group 404B may be responsible for carbon particle 402B's vertical orientation. Carbon particle 402B's vertical orientation may serve as a base for carbon particle 402A's vertical orientation, because carbon particle 402B is closest to current collector 408. Organic linker group 404A may be attached to carbon particle 402A and another carbon particle that is not shown. Carbon particles may be vertically oriented from current collector 408 up until a separator.
Bonding particles 410 may be particles made of elements such as gold that have a strong bonding affinity to materials within current collector 408 and/or carbon particles 402A and 402B. In one embodiment, bonding particles 410 may be added to carbon particles 402A and 402B during the manufacturing process of vertically aligned carbon particle structure 400. The bonding particles may assimilate around the edges of carbon particles 402A and 402B. The inclusion of bonding particles 410 may allow organic linkers within organic linker groups 404A, 404B, and 404C to connect with carbon particles 402A and 402B as well as current collector 408. For example, organic linkers within organic linker groups 404A, 404B, and 404C may comprise thiols comprising carbon-sulfur-hydrogen. These thiols may have a strong bonding affinity to, for example, copper within current collector 408, and to bonding particles 410 that are located on or within carbon particles 402A and 402B. This strong bonding affinity may create a self-assembling monolayer comprising the thiols that self-assemble carbon particles 402A and 402B in a vertical orientation as illustrated in
The vertical orientation of carbon particles from current collector 408 to a separator may create ion pathway 406. During, for example, a charging process lithium ions may flow from the cathode through the separator and to the anode comprising carbon particle structure 400. Ion pathway 406 may be a conduction or diffusion pathway for one or more lithium ions. Lithium ions may follow ion pathway 406 in order to intercalate between layers of graphite within the anode. As can be seen from
Numerous specific details are set forth herein to provide a thorough understanding of the claimed subject matter. However, those skilled in the art will understand that the claimed subject matter may be practiced without these specific details. In other instances, methods, apparatuses, or systems that would be known by one of ordinary skill have not been described in detail so as not to obscure claimed subject matter.
While the present subject matter has been described in detail with respect to specific embodiments thereof, it will be appreciated that those skilled in the art, upon attaining an understanding of the foregoing may readily produce alterations to, variations of, and equivalents to such embodiments. Accordingly, it should be understood that the present disclosure has been presented for purposes of example rather than limitation, and does not preclude inclusion of such modifications, variations, and/or additions to the present subject matter as would be readily apparent to one of ordinary skill in the art. Indeed, the methods and systems described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the methods and systems described herein may be made without departing from the spirit of the present disclosure. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the present disclosure.
Conditional language used herein, such as, among others, “can,” “could,” “might,” “may,” “e.g.,” and the like, unless specifically stated otherwise, or otherwise understood within the context as used, is generally intended to convey that certain examples include, while other examples do not include, certain features, elements, and/or steps. Thus, such conditional language is not generally intended to imply that features, elements and/or steps are in any way required for one or more examples or that one or more examples necessarily include logic for deciding, with or without author input or prompting, whether these features, elements and/or steps are included or are to be performed in any particular example.
The terms “comprising,” “including,” “having,” and the like are synonymous and are used inclusively, in an open-ended fashion, and do not exclude additional elements, features, acts, operations, and so forth. Also, the term “or” is used in its inclusive sense (and not in its exclusive sense) so that when used, for example, to connect a list of elements, the term “or” means one, some, or all of the elements in the list. The use of “adapted to” or “configured to” herein is meant as open and inclusive language that does not foreclose devices adapted to or configured to perform additional tasks or steps. Additionally, the use of “based on” is meant to be open and inclusive, in that a process, step, calculation, or other action “based on” one or more recited conditions or values may, in practice, be based on additional conditions or values beyond those recited. Similarly, the use of “based at least in part on” is meant to be open and inclusive, in that a process, step, calculation, or other action “based at least in part on” one or more recited conditions or values may, in practice, be based on additional conditions or values beyond those recited. Headings, lists, and numbering included herein are for ease of explanation only and are not meant to be limiting.
The various features and processes described above may be used independently of one another, or may be combined in various ways. All possible combinations and sub-combinations are intended to fall within the scope of the present disclosure. In addition, certain method or process blocks may be omitted in some embodiments. The methods and processes described herein are also not limited to any particular sequence, and the blocks or states relating thereto can be performed in other sequences that are appropriate. For example, described blocks or states may be performed in any order other than that specifically disclosed, or multiple blocks or states may be combined in a single block or state. The example blocks or states may be performed in serial, in parallel, or in some other manner. Blocks or states may be added to or removed from the disclosed examples. Similarly, the example systems and components described herein may be configured differently than described. For example, elements may be added to, removed from, or rearranged compared to the disclosed examples.
