Patent Application
20220123279
Lithium ion batteries describe a class of rechargeable batteries in which lithium ions move between a negative electrode (i.e., anode) and a positive electrode (i.e., cathode). Liquid, solid, and polymer electrolytes can facilitate the movement of lithium ions between the anode and cathode. Lithium-ion batteries are growing in popularity for defense, automotive, and aerospace applications due to their high energy density and ability to undergo successive charge and discharge cycles.
Provided are methods for pre-lithiating a battery cell. The methods can include providing a battery cell which includes a cathode electrically connected to an anode by an interruptible external circuit. The anode includes a current collector, a host material applied to the current collector and comprising graphite, silicon particles, and/or SiOx particles, wherein x is less than or equal to 2, and lithium foil in contact with the current collector. The method further includes charging the battery cell and discharging the battery cell to deplete the lithium foil by causing lithium ions to migrate from the lithium foil to the cathode and/or the anode. The methods can further include subsequently iteratively charging and discharging the battery while the depleted lithium foil remains within the battery cell. The lithium foil can be pure elemental lithium metal. The lithium foil can be a lithium-magnesium alloy or a lithium-zinc alloy. The lithium foil can include 10 wt. % to 99 wt. % lithium and 1 wt. % to 90 wt. % magnesium. The anode can include two anode current collectors each having an inner face and an outer face, and the lithium foil can be disposed contiguous with the inner face of each anode current collector and the host material is applied to the outer face of each anode current collector. The host material can be applied to the anode current collector such that one or more regions of the anode current collector remain uncoated, and the lithium foil can be positioned contiguous with the one or more uncoated regions of the anode current collector. The anode current collector can include perforations.
Also provided are self-lithiating battery cells, which can include a cathode electrically connected to an anode by an interruptible external circuit. The anode can include a current collector, a host material applied to the current collector and comprising graphite, silicon particles, and/or SiOx particles, wherein x is less than or equal to 2, and lithium foil in contact with the current collector. The self-lithiating battery cells, upon iterative charging and discharging, can include a depleted lithium foil within the battery cell. The lithium foil can be pure elemental lithium metal. The lithium foil can be a lithium-magnesium alloy or a lithium-zinc alloy. The lithium foil can include 10 wt. % to 99 wt. % lithium and 1 wt. % to 90 wt. % magnesium. The anode can include two anode current collectors each having an inner face and an outer face, and the lithium foil can be disposed contiguous with the inner face of each anode current collector and the host material is applied to the outer face of each anode current collector. The host material can be applied to the anode current collector such that one or more regions of the anode current collector remain uncoated, and the lithium foil can be positioned contiguous with the one or more uncoated regions of the anode current collector. The anode current collector can include perforations.
Other objects, advantages and novel features of the exemplary embodiments will become more apparent from the following detailed description of exemplary embodiments and the accompanying drawings.
Embodiments of the present disclosure are described herein. It is to be understood, however, that the disclosed embodiments are merely examples and other embodiments can take various and alternative forms. The figures are not necessarily to scale; some features could be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention. As those of ordinary skill in the art will understand, various features illustrated and described with reference to any one of the figures can be combined with features illustrated in one or more other figures to produce embodiments that are not explicitly illustrated or described. The combinations of features illustrated provide representative embodiments for typical applications. Various combinations and modifications of the features consistent with the teachings of this disclosure, however, could be desired for particular applications or implementations.
Provided herein are self-lithiating battery cells methods for lithiating the same. The battery cells disclosed herein use lithium-based foils in contact with anode current collectors in a conventional lithium ion battery which obviate the need for a third electrode per battery cell and/or costly and burdensome pre-lithiation methods. The battery cells and methods provided herein minimize or eliminate low initial coulombic efficiency, inferior long-term cycling performance, and low energy density of battery cells.
Battery cell 10 can be used in any number of applications. For example,
Battery cell 10 generally operates by reversibly passing lithium ions between Anode 11 and cathode 14. Lithium ions move from cathode 14 to Anode 11 while charging, and move from Anode 11 to cathode 14 while discharging. At the beginning of a discharge, Anode 11 contains a high concentration of intercalated/alloyed lithium ions while cathode 14 is relatively depleted, and establishing a closed external circuit between Anode 11 and cathode 14 under such circumstances causes intercalated/alloyed lithium ions to be extracted from Anode 11. The extracted lithium atoms are split into lithium ions and electrons as they leave an intercalation/alloying host at an electrode-electrolyte interface. The lithium ions are carried through the micropores of separator 18 from Anode 11 to cathode 14 by the ionically conductive electrolyte 17 while, at the same time, the electrons are transmitted through the external circuit from Anode 11 to cathode 14 to balance the overall electrochemical cell. This flow of electrons through the external circuit can be harnessed and fed to a load device until the level of intercalated/alloyed lithium in the negative electrode falls below a workable level or the need for power ceases.
Battery cell 10 may be recharged after a partial or full discharge of its available capacity. To charge or re-power the lithium ion battery cell, an external power source (not shown) is connected to the positive and the negative electrodes to drive the reverse of battery discharge electrochemical reactions. That is, during charging, the external power source extracts the lithium ions present in cathode 14 to produce lithium ions and electrons. The lithium ions are carried back through the separator by the electrolyte solution, and the electrons are driven back through the external circuit, both towards Anode 11. The lithium ions and electrons are ultimately reunited at the negative electrode, thus replenishing it with intercalated/alloyed lithium for future battery cell discharge.
Lithium ion battery cell 10, or a battery module or pack comprising a plurality of battery cells 10 connected in series and/or in parallel, can be utilized to reversibly supply power and energy to an associated load device. Lithium ion batteries may also be used in various consumer electronic devices (e.g., laptop computers, cameras, and cellular/smart phones), military electronics (e.g., radios, mine detectors, and thermal weapons), aircrafts, and satellites, among others. Lithium ion batteries, modules, and packs may be incorporated in a vehicle such as a hybrid electric vehicle (HEV), a battery electric vehicle (BEV), a plug-in HEV, or an extended-range electric vehicle (EREV) to generate enough power and energy to operate one or more systems of the vehicle. For instance, the battery cells, modules, and packs may be used in combination with a gasoline or diesel internal combustion engine to propel the vehicle (such as in hybrid electric vehicles), or may be used alone to propel the vehicle (such as in battery powered vehicles).
Returning to
The microporous polymer separator 18 can comprise, in one embodiment, a polyolefin. The polyolefin can be a homopolymer (derived from a single monomer constituent) or a heteropolymer (derived from more than one monomer constituent), either linear or branched. If a heteropolymer derived from two monomer constituents is employed, the polyolefin can assume any copolymer chain arrangement including those of a block copolymer or a random copolymer. The same holds true if the polyolefin is a heteropolymer derived from more than two monomer constituents. In one embodiment, the polyolefin can be polyethylene (PE), polypropylene (PP), or a blend of PE and PP. The microporous polymer separator 18 may also comprise other polymers in addition to the polyolefin such as, but not limited to, polyethylene terephthalate (PET), polyvinylidene fluoride (PVdF), and or a polyamide (Nylon). Separator 18 can optionally be ceramic-coated with materials including one or more of ceramic type aluminum oxide (e.g., Al2O3), and lithiated zeolite-type oxides, among others. Lithiated zeolite-type oxides can enhance the safety and cycle life performance of lithium ion batteries, such as battery cell 10. Skilled artisans will undoubtedly know and understand the many available polymers and commercial products from which the microporous polymer separator 18 may be fabricated, as well as the many manufacturing methods that may be employed to produce the microporous polymer separator 18.
Active material 16 can include any lithium-based active material that can sufficiently undergo lithium intercalation and deintercalation while functioning as the positive terminal of battery cell 10. Active material 16 can also include a polymer binder material to structurally hold the lithium-based active material together. The active material 16 can comprise lithium transition metal oxides (e.g., layered lithium transitional metal oxides). Cathode current collector 15 can include aluminum or any other appropriate electrically conductive material known to skilled artisans, and can be formed in a foil or grid shape. Cathode current collector 15 can be treated (e.g., coated) with highly electrically conductive materials, including one or more of conductive carbon black, graphite, carbon nanotubes, carbon nanofiber, graphene, and vapor growth carbon fiber (VGCF), among others. The same highly electrically conductive materials can additionally or alternatively be dispersed within the host material 13.
Lithium transition metal oxides suitable for use as active material 16 can comprise one or more of spinel lithium manganese oxide (LiMn2O4), lithium cobalt oxide (LiCoO2), a nickel-manganese oxide spinel (Li(Ni0.5Mn1.5)O2), a layered nickel-manganese-cobalt oxide (having a general formula of xLi2MnO3.(1-x)LiMO2, where M is composed of any ratio of Ni, Mn and/or Co). A specific example of the layered nickel-manganese oxide spinel is xLi2MnO3.(1−x)Li(Ni1/3Mn1/3Co1/3)O2. Other suitable lithium-based active materials include Li(Ni1/3Mn1/3Co1/3)O2), LiNiO2, Lix+yMn2-yO4 (LMO, 0<x<1 and 0<y<0.1), or a lithium iron polyanion oxide, such as lithium iron phosphate (LiFePO4) or lithium iron fluorophosphate (Li2FePO4F). Other lithium-based active materials may also be utilized, such as LiNixM1-xO2 (M is composed of any ratio of Al, Co, and/or Mg), LiNi1-xCo1-yMnx+yO2 or LiMn1.5-xNi0.5-yMx+yO4 (M is composed of any ratio of Al, Ti, Cr, and/or Mg), stabilized lithium manganese oxide spinel (LixMn2-yMyO4, where M is composed of any ratio of Al, Ti, Cr, and/or Mg), lithium nickel cobalt aluminum oxide (e.g., LiNi0.8Co0.15Al0.05O2 or NCA), aluminum stabilized lithium manganese oxide spinel (LixMn2-xAlyO4), lithium vanadium oxide (LiV2O5), Li2MSiO4 (M is composed of any ratio of Co, Fe, and/or Mn), and any other high efficiency nickel-manganese-cobalt material (HE-NMC, NMC or LiNiMnCoO2). By “any ratio” it is meant that any element may be present in any amount. So, for example, M could be Al, with or without Co and/or Mg, or any other combination of the listed elements. In another example, anion substitutions may be made in the lattice of any example of the lithium transition metal based active material to stabilize the crystal structure. For example, any 0 atom may be substituted with an F atom.
The anode current collector 12 can include copper, aluminum, stainless steel, or any other appropriate electrically conductive material known to skilled artisans. Anode current collector 12 can be treated (e.g., coated) with highly electrically conductive materials, including one or more of conductive carbon black, graphite, carbon nanotubes, carbon nanofiber, graphene, and vapor growth carbon fiber (VGCF), among others. The host material 13 applied to the anode current collector 12 can include any lithium host material that can sufficiently undergo lithium ion intercalation, deintercalation, and alloying, while functioning as the negative terminal of the lithium ion battery 10. Host material 13 can optionally further include a polymer binder material to structurally hold the lithium host material together. For example, in one embodiment, host material 13 can include a carbonaceous material (e.g., graphite) and/or one or more of binders (e.g., polyvinyldiene fluoride (PVdF), an ethylene propylene diene monomer (EPDM) rubber, carboxymethoxyl cellulose (CMC), and styrene, 1,3-butadiene polymer (SBR)), among others known in the art.
Silicon has the highest known theoretical charge capacity for lithium, making it one of the most promising anode host materials 13 for rechargeable lithium-ion batteries. In two general embodiments, a silicon host material 13 can comprise Si particles and/or SiOx particles. SiOx particles, wherein generally x≤2, can vary in composition. In some embodiments, for some SiOx particles, x≈1. For example, x can be about 0.9 to about 1.1, or about 0.99 to about 1.01. Within a body of SiOx particles, SiO2 and/or Si domains may further exist. Silicon host material 13 comprising Si particles or SiOx particles can comprise average particle diameters of about 20 nm to about 20 μm, among other possible sizes.
During the first cycling of a “fresh” anode, silicon-based anodes typically exhibit inferior initial coulombic efficiency due to the generally irreversible capture of lithium during the first cycle. For example, in a silicon electrode, a solid electrolyte interface (SEI) layer can form on the host material 13 and capture lithium. In another example, in a SiOx electrode, lithium can become irreversibly captured through the formation of Li4SiO4 and/or Li2O within the host material 13. In either instance, the poor initial coulombic efficiency resulting from the inability of lithium to transport back to the cathode 14 can require excessive lithium loading of cathode active material 16 to compensate for the lithium consumed by the anode 11 during the first cycle, which detrimentally reduces the energy density of the battery cell 10.
Accordingly, provided herein are self-lithiating battery cells and methods for lithiating the same. The battery cells and methods provide anodes and battery cells which exhibit high initial coulombic efficiency and generally increase the performance of battery cells. The methods will be described in relation to the battery cell 10 of
During initial cycling of lithium ion batteries with silicon-based anodes the latter are lithiated by the cathode during charging, but not all lithium is returned to the cathode during subsequent discharge cycles. In the present disclosure, the lithium lost by the cathode 14 during initial charging is compensated during discharge by the lithium present in the lithium foil, which serves as a lithium reservoir. Pre-lithiation as conducted during charging 301 and discharging 302 can be conducted in iterative charge/discharge cycles by controlling the voltage window to avoid lithium plating and to ensure depletion of lithium from the lithium foil 311. Accordingly, the amount of lithium foil 311 can be tailored to the amount of lithium needed to resupply the cathode 14.
In some embodiments the lithium foil 311 comprises pure (e.g., >95% pure) elemental lithium, or a lithium alloy, among other bulk sources of lithium. The lithium foil 311 can take the form of a plate, thin foil, or other suitable configuration. In particular, the lithium foil 311 can comprise a lithium-magnesium alloy or a lithium-zinc alloy. A lithium-magnesium alloy can comprise lithium, magnesium, and optionally impurities. For example, a lithium-magnesium alloy can comprise 10 wt. % to 99 wt. % lithium and 1 wt. % to 99 wt. % magnesium, 50 wt. % to 99 wt. % lithium and 1 wt. % to 50 wt. % magnesium, or 65 wt. % to 99 wt. % lithium and 1 wt. % to 35 wt. % magnesium. All such alloys can optionally further include less than 2 wt. %, less than 0.5 wt. %, or less than 0.1 wt. % impurities. In such embodiments, the depleted lithium foil 312 comprises a magnesium skeleton which persists throughout the life of the battery. The weight added to the cell by the magnesium skeleton can be considered negligible relative to the pre-lithiation benefits of the lithium foil 311, and further lithium-magnesium alloys are advantageously highly stable in most manufacturing environments.
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While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms encompassed by the claims. The words used in the specification are words of description rather than limitation, and it is understood that various changes can be made without departing from the spirit and scope of the disclosure. As previously described, the features of various embodiments can be combined to form further embodiments of the invention that may not be explicitly described or illustrated. While various embodiments could have been described as providing advantages or being preferred over other embodiments or prior art implementations with respect to one or more desired characteristics, those of ordinary skill in the art recognize that one or more features or characteristics can be compromised to achieve desired overall system attributes, which depend on the specific application and implementation. These attributes can include, but are not limited to cost, strength, durability, life cycle cost, marketability, appearance, packaging, size, serviceability, weight, manufacturability, ease of assembly, etc. As such, embodiments described as less desirable than other embodiments or prior art implementations with respect to one or more characteristics are not outside the scope of the disclosure and can be desirable for particular applications.
