Method and system for lithium ion battery cell cathode

Abstract

A system and method for a lithium ion battery cell is disclosed. In one embodiment, a method for forming a cathode for a lithium ion battery cell includes forming a prelithiated cathode with a prelithiated reagent and positioning the prelithiated cathode in contact with an electrolyte. An electrolyte additive is infused into the electrolyte to form a passivation layer in the prelithiated cathode, the passivation layer inhibiting continued decomposition of the prelithiated reagent in the prelithiated cathode after completion of a lithium ion battery cell formation cycle.

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to U.S. Provisional Application No. 63 / 267,078, filed January 24, 2022, entitled "METHODS AND SYSTEMS FOR A LITHIUM-ION BATTERY CELL CATHODE," the entire contents of which are incorporated herein by reference for all purposes.

[0002] This description generally relates to cathodes for lithium-ion battery cells. [Background technology]

[0003] Lithium-ion (Li-ion) battery cells present a lightweight, compact, high-performance alternative to traditional battery cells, such as those used in lead-acid batteries. The high performance of Li-ion batteries, formed from Li-ion battery cells, includes desirable attributes such as increased charge cycles, high energy density, low self-discharge rates, and less heavy metal incorporation, as compared to, for example, nickel-cadmium and nickel-metal hydride battery cells. Thus, the use of Li-ion batteries in electric and hybrid electric vehicles is increasingly desirable. Particularly for fully electric vehicles, Li-ion batteries allow for longer durations between charging events. However, the energy density of Li-ion batteries remains lower than that of gasoline, and therefore strategies to improve their performance are desirable.

[0004] For example, the energy density and cycling capacity of a battery cell can be affected by the composition and elemental distribution of the Li-ion battery cell cathode. For example, by fabricating a cathode with a high Li content, which exceeds the transition metal content of the cathode, the cathode can have increased energy density and cycling capability compared to a cathode without excess Li. The excess Li can be introduced during the fabrication process of the cathode by adding a prelithiation reagent. The incorporation of Li into the cathode using a prelithiation reagent provides advantages from both a safety and scalability standpoint: in terms of safety, cathode prelithiation does not involve handling volatile Li metal, and in terms of scalability, cathode prelithiation can be relatively easily integrated into existing cathode manufacturing processes. Furthermore, cathode prelithiation eliminates the reliance on additional manufacturing equipment, thereby avoiding increased costs.

[0005] However, the inclusion of the cathode prelithiation reagent directly in the cathode active material layer slurry may suffer from other problems. As an example, in an ideal scenario, the prelithiation reagent may completely decompose after completing the formation cycle of the battery cell. When decomposition occurs, gas may be produced that can be removed after the formation cycle by performing a degassing procedure. However, in practice, at least a portion of the prelithiation reagent may remain intact on the cathode surface and proceed to decomposition during subsequent battery cell cycles.

[0006] Decomposition of the prelithiation reagent during operation of the battery cell may result in undesirable gas release from the battery cell. In some embodiments, a catalyst (e.g., a prelithiation catalyst) may be added to facilitate the decomposition of the prelithiation reagent. The catalyst may remain in the battery cell after the prelithiation reagent is decomposed and may cause gas generation during operation of the battery cell due to the increase in cathode surface area caused by the presence of the catalyst. In addition, the catalyst may promote electrolyte oxidation. Therefore, a strategy for deactivating any amount of the prelithiation reagent that remains undecomposed after performing the formation cycle of the battery cell may allow at least maintaining the electrochemical performance of the battery cell. In particular, a strategy that provides a beneficial ability to improve cycle performance while not adversely affecting the amount of additional capacity provided by the prelithiation reagent or the cycle performance of the cathode is desirable. Summary of the Invention

[0007] The inventors have identified the above problems and determined a solution to at least partially solve them. In one embodiment, a method for forming a cathode for a lithium-ion battery cell includes forming a prelithiated cathode with a prelithiated reagent, positioning the prelithiated cathode in contact with an electrolyte, and injecting an electrolyte additive into the electrolyte to form a passivation layer in the prelithiated cathode. The passivation layer can inhibit continued decomposition of the prelithiated reagent in the prelithiated cathode after completion of the lithium-ion battery cell formation cycle. In this way, undesirable reactions between the prelithiated reagent and the electrolyte can be avoided.

[0008] As an example, an electrolyte additive can be added to the electrolyte and oxidized during the charging cycle of the lithium-ion battery cell. A passivation layer is formed when the electrolyte additive is oxidized, which forms a barrier between the prelithiation reagent (e.g., non-decomposed prelithiation reagent) and the electrolyte, thereby mitigating gas generation by the prelithiation reagent during operation of the lithium-ion battery cell. Furthermore, the passivation layer can suppress impedance growth, thus improving the electrochemical performance of the lithium-ion battery cell.

[0009] It should be understood that the foregoing Summary is provided to introduce in a simplified form a selection of concepts that are further described in the Detailed Description. It is not intended to identify key or essential features of the claimed subject matter, the scope of which is uniquely defined by the claims that follow the Detailed Description. Moreover, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure. [Brief description of the drawings]

[0010] [Figure 1] 1 illustrates an embodiment of a process for forming a passivation layer on a prelithiated electrode component for a Li-ion battery cell. [Figure 2A] 1 shows a first embodiment of a coated prelithiated electrode for a Li-ion battery cell. [Figure 2B] 1 shows a second embodiment of a coated prelithiated electrode for a Li-ion battery cell. [Figure 3A] 2B illustrates an embodiment of the electrode of FIG. 2A having a passivation layer formed from at least one electrolyte additive. [Figure 3B] FIG. 2C illustrates an embodiment of the electrode of FIG. 2B having a passivation layer formed from at least one electrolyte additive. [Figure 4] FIG. 3B shows a detailed view of the particles of the electrode of FIG. 3A. [Diagram 5]An embodiment of a method for forming a passivated prelithiated cathode is provided. [Figure 6] 1 shows a first embodiment of a process for forming a passivation layer of a passivated prelithiated cathode. [Figure 7] 1 shows a second embodiment of a process for forming a passivation layer of a passivated prelithiated cathode. [Figure 8] 1 shows a first graph plotting the voltage profile of a Li-ion battery formed from cells without a passivation layer. [Figure 9] 13 shows a second graph plotting the voltage profile of a Li-ion battery formed from a cell having a passivation layer. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] The following description relates to a system and method for a lithium-ion battery cell. As illustrated in FIG. 1, a passivation layer can be formed on the chemical components of a pre-lithiated cathode of a lithium-ion battery cell by adding one of many electrolyte additives to the lithium-ion battery cell before an initial charge-discharge cycle is performed. An example of a structure of a pre-lithiated cathode before the formation of the passivation layer, e.g., before passivation, is shown in the schematic diagrams of FIG. 2A and FIG. 2B, and a corresponding example of a pre-lithiated cathode structure after passivation is depicted in FIG. 3A and FIG. 3B. Passivation can occur at the electrode level, thereby coating the surface of the pre-lithiated cathode, as well as at the particle level, thereby coating the surface of the pre-lithiated cathode component particles, as shown in FIG. 4. The passivation layer can be formed from one or more electrolyte additives that can be added to the battery cell electrolyte and oxidized during the initial charge cycle to coat the components of the pre-lithiated cathode that tend to facilitate parasitic reactions. An example of a method for forming a passivated, prelithiated cathode structure is depicted in Figure 5. Two different strategies for forming a passivation layer are shown in Figures 6 and 7. The effectiveness of one or more electrolyte additives in deactivating non-decomposed (e.g., intact and / or residual) prelithiation reagents is illustrated in a comparison of the voltage profile of a lithium-ion battery cell without a passivation layer, as shown in Figure 8, and the voltage profile of a lithium-ion battery cell with a passivation layer, as shown in Figure 9.

[0012] One or more electrolyte additives may be added to the electrolyte of a lithium (Li)-ion battery cell to passivate residual cathode components that do not decompose after a formation cycle of the lithium (Li)-ion battery cell, e.g., a charge / discharge activation cycle. The components of the cathode may include various species, described in more detail below, represented as particles in FIG. 1, which illustrates a process 10 for forming a passivation layer. It will be understood that the process 10 is a simplified illustrative depiction of the process 10 showing where the passivation layer is formed. For example, the cathode may be formed from multiple components, with each type of component being incorporated within the crystal structure or lattice of the cathode. Thus, the various types of components are represented as a single particle 12, which may be any of the multiple components of the cathode. Furthermore, the cathode includes multiple particles of each component type, which may be arranged or positioned relative to each other according to the crystal structure of the cathode.

[0013] The various species as represented by the particles 12 may include one or more of a prelithiation reagent, a conductive additive, a catalyst, and an active material of the cathode. Specific examples of the prelithiation reagent, the catalyst, and the active material are provided herein. The conductive filler or additive may be a carbon-based material that is included in the mixture forming the cathode, e.g., mixed with the active material, and / or included in the mixture forming the prelithiation reagent, and the electrolyte additive 16 may be injected into the electrolyte of the lithium-ion battery cell, as shown by arrow 14, thereby dispersing in the electrolyte and surrounding the particles 12.

[0014] The electrolyte additive 16 may remain mixed in the electrolyte until a lithium ion battery cell formation cycle is performed, as indicated by arrow 18. The electrolyte additive 16 may also remain mixed in the electrolyte during a lithium ion battery cell formation cycle. The formation cycle may be an initial charge / discharge cycle of the battery cell performed before the lithium ion battery cell is commercially available. Charging the battery cell during the formation cycle promotes oxidation of the electrolyte additive 16, which leads to the formation of a passivation layer on the surface of the particles 12, which is formed from the electrolyte additive 16, and the particles 12 become passivated particles.

[0015] The passivation layer of the passivated particles 12 may vary in coverage and thickness. For example, the first exemplary passivation layer 20a may completely coat the surface of the particles 12, forming a continuous and relatively uniform layer. As another example, the second exemplary passivation layer 20b may have a thickness greater than the first exemplary passivation layer 20a. The third exemplary passivation layer 20c may have a variable thickness and may coat a portion of the surface of the particles 12, for example, the third exemplary passivation layer 20c is not continuous but partially coats the particles 12. As illustrated in FIG. 1, the passivation layers may be formed with different physical attributes, such as thickness, uniformity, and surface area coverage, but may have the same effect of passivating the cathode component particles regardless of the variation in physical attributes.

[0016] The thickness and coverage of the passivation layer may vary depending on parameters such as the concentration of electrolyte additive in the electrolyte, the duration / rate of the charging cycle, and the interaction of the electrolyte additive with the cathode components according to the chemical nature of the components. For example, the thickness of the passivation layer may be in the range of 0.1 nm to 20 nm. When the electrolyte additive is selected to provide optimal capacity for passivating the target components such as prelithiation reagents, conductive additives, catalysts, and active materials, the passivation layer may have a reduced thickness of less than 10 nm while still providing effective passivation. In some examples, the thickness of the passivation layer may be maintained at less than 5 nm.

[0017] Additionally, the thickness of the passivation layer may vary depending on the component. For example, the thickness may be greater or less in the catalyst compared to the prelithiation reagent. Furthermore, the passivation layer may cover less than the total surface area of ​​the component particles (and the cathode surface), as shown by the third exemplary passivation layer 20c in FIG. 1. For example, the passivation layer may cover more than 50% but less than 100% of the surface area of ​​the component particles, e.g., the particles are partially coated. In other words, the passivation layer forms a partial coating. In another embodiment, the passivation layer may form a continuous coating covering the entire surface area of ​​each of the component particles, as shown by the first and second exemplary passivation layers 20a, 20b in FIG. 2, e.g., the particles are completely (100%) coated. In other words, the passivation is a complete coating. In yet another embodiment, some of the component particles may be partially coated and some of the component particles may be completely coated. The passivation layer may have a mass of 0.01% to 5% of the mass of the Li-ion battery cell chemistry (eg, excluding the outer housing and hardware / structural components).

[0018] When a passivation layer is formed on the surface of the prelithiation reagent particles from the electrolyte additive, the passivation layer can inhibit further decomposition of the prelithiation reagent particles remaining after the formation cycle. Further decomposition can be inhibited by forming an electrochemical and physical barrier between the prelithiation reagent particles and the electrolyte. Inhibiting further decomposition of the prelithiation reagent particles can alleviate gasification problems, such as the formation of gas due to decomposition. Similarly, forming a passivation layer on the surface of the catalyst particles remaining after the formation cycle, as well as on the surfaces of the conductive additive particles and the active material particles, can avoid further oxidation of the electrolyte at the surface, and can also alleviate the gassing problem. In addition, the passivation layer can suppress the increase in battery cell impedance due to excessive electrolyte oxidation. At the active material particle surface, the passivation layer can further alleviate the surface reconstruction of the active material particles and reduce the corresponding impedance growth.

[0019] The composition of the passivation layer may also depend on the type of electrolyte additive used and the type of particles on which the passivation layer is formed. The type of electrolyte additive may be selected, for example, based on the elements present in the electrolyte. As an example, the electrolyte may incorporate one or more of Li, C, O, F, B, among others, and the electrolyte additive species may be selected to be compatible with the elements of the electrolyte, for example, the electrolyte additive may be selected so that the resulting passivation layer does not react with the electrolyte. Since certain elements contained in the electrolyte additive may be incorporated into the passivation layer, the electrolyte additive with the target element may be selected to correspond to the element present in the electrolyte. For example, if lithium difluorobis(oxalo)phosphate (LiDFOP) is selected as the electrolyte additive, the passivation layer may include F and / or P.

[0020] Various techniques are available for incorporating additional Li into the cathode to form a prelithiated cathode, including incorporation via direct slurry mixing, where a prelithiation reagent is mixed into the cathode slurry, electrode-level prelithiation, where a prelithiation coating is formed on the surface of the cathode, and particle-level prelithiation, where particles of cathode active material are coated with a prelithiation coating. Regardless of the prelithiation technique, passivation of the cathode components can be made possible via a common passivation process. The passivation process can be activated by performing a first formation cycle of the battery cell, which causes oxidation of the electrolyte additive and bonding of the electrolyte additive to the surface of the cathode components as a passivation layer, as described above. Thus, a passivation layer can be formed on all surfaces and component particles of the cathode, as shown below with reference to Figures 3A-4.

[0021] Examples of cathode structures of lithium ion battery cells and passivation layers formed in the cathode structures are shown in Figures 2A-3B at the electrode level, e.g., electrode scale. For example, the passivation layers are shown in Figures 3A and 3B as coatings on the surface of the cathode structures, which are depicted in Figures 2A and 2B prior to completion of a formation cycle. The electrode level passivation layers may be formed as described above with reference to Figure 1 after a formation cycle has been performed. A detailed view of the composition of the passivated cathode structure of Figure 3A, which may similarly represent the composition of the passivated cathode structure of Figure 3B, is shown in Figure 4, illustrating the formation of passivation levels at the particle level, e.g., at the scale of particles of the cathode structure material.

[0022] 2A, there is shown a first schematic cross-section 100 illustrating a first exemplary coated cathode structure 101 for use in a lithium ion battery cell. Upon formation, the coated cathode structure 101 may be positioned within a lithium ion battery cell such that the coated cathode structure 101 may provide power to the lithium ion battery cell. In some examples, the lithium ion battery cell may be one of a plurality of lithium ion battery cells in a lithium ion battery cell pack, each of the plurality of lithium ion battery cells may have a substantially similar configuration to one another.

[0023] The coated cathode structure 101 may include a cathode current collector 102 having a first side 103a and a second side 103b, where the sides 103a, 103b may be opposite each other relative to an axis 114 parallel to a smallest dimension of the cathode current collector 102. The cathode current collector 102 may have a cathode active material layer 104 disposed or coated on one of the sides 103a, 103b, where the cathode active material layer 104 is in flush contact with the cathode current collector 102. Additionally, the cathode prelithiated layer 106 may be disposed or coated on the cathode active material layer 104 on the opposite side of the cathode current collector 102 relative to the axis 114 (e.g., opposite the side 103a or 103b of the cathode current collector 102 on which the cathode active material layer 104 is coated, such that the cathode active material layer 104 is sandwiched between the cathode current collector 102 and the cathode prelithiated layer 106). For example, the cathode active material layer 104 may be coated on the first side 103a of the cathode current collector 102, such that the coated cathode structure 101 may include, in order along the axis 114, the cathode current collector 102, the cathode active material layer 104, and the cathode prelithiated layer 106. Each of the sides 103a, 103b of the cathode current collector 102 can include a cathode active material layer 104 respectively disposed thereon, and one or both of the cathode active material layers 104 can include a cathode prelithiated layer(s) 106 respectively disposed thereon on the opposite side of the cathode current collector 102 (e.g., the coated cathode structure 101 can include, in order along the axis 114, a cathode prelithiated layer 106, a cathode active material layer 104, a cathode current collector 102, another cathode active material layer 104, and another cathode prelithiated layer 106).

[0024] The cathode current collector 102 may be a metal sheet or foil, such as Cu foil, Ni foil, Al foil, or any other configuration capable of conducting electricity and allowing electrical current therethrough. In one example, the thickness of the cathode current collector 102 may be 1-20 μm (e.g., about 10 μm). However, it will be understood that the thickness of the cathode current collector 102 may vary widely, for example, up to 50 μm. As used herein, "about" when referring to a numerical value may encompass a deviation of 5% or less.

[0025] The cathode active material layer 104 can be a slurry-based layer composed of at least a cathode active material, a first conductive additive, and a first binder. In some examples, the cathode active material can be a lithium intercalation / deintercalation material. For example, the lithium intercalation / deintercalation material can include one or more of lithium nickel manganese cobalt oxide (NMC), lithium iron phosphate (LFP), lithium manganese iron phosphate (LMFP), lithium nickel cobalt aluminum oxide (NCA), lithium cobalt oxide (LCO), lithium cobalt phosphate (LCP), lithium nickel phosphate (LNP), and lithium manganese phosphate (LMP), and / or any number of other lithium intercalation / deintercalation materials known to those skilled in the art. In additional or alternative examples, the cathode active material can be a lithium mixed metal oxide layered structure material. In some examples, the first conductive additive can be carbonaceous. For example, the first conductive additive can include carbon black, graphene, graphene oxide, and / or CNTs. In some examples, the first binder may include one or more polymers. For example, the first binder may include one or more of PVDF, polyvinylpyrrolidone, poly(ethylene) oxide (PEO) or crosslinked PEO, PTFE, PMMA, PAA, poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), one or more conductive polymers such as poly(3,4-ethylenedioxythiophene) (PEDOT), PEDOT polystyrene sulfonate (PEDOT:PSS), cellulose derivatives, and linear, semi-aromatic, or aromatic polyimides (PI).

[0026] As another example, the cathode prelithiation layer 106 can be a slurry-based layer comprised of at least a cathode prelithiation reagent. In some examples, the cathode prelithiation reagent is a layer of Li +For example, the cathodic prelithiation reagent may include one or more of Li3N, Li2O, Li2O2, Li2S, Li5FeO4, Li2S / M nanocomposite, LiF / M nanocomposite, and Li2O / M nanocomposite, where M is one or more metals.

[0027] The cathode prelithiation reagent may be formed as particles of a core material having a surface impurity layer formed thereon. For example, the core material may include one or more of Li2O2, Li2O, and Li2S, and the surface impurity layer may include one or more of LiOH and Li2CO3. In some examples, the surface impurity layer may be formed during preparation of a slurry for forming the cathode prelithiation layer 106 (e.g., may be actively or intentionally formed rather than formed as an undesired by-product) via exposure of the core material to a moisture and / or CO2-containing atmosphere. In additional or alternative examples, the surface impurity layer may be formed during preparation of a slurry for forming the cathode prelithiation layer 106 via exposure of the core material to a moisture and / or CO2-containing atmosphere (e.g., may be actively or intentionally formed rather than formed as an undesired by-product). In additional or alternative examples, the surface impurity layer may be formed during prelithiation of an anode of a lithium-ion battery cell by the deposition of Li + It may function as an additional (e.g., secondary) cathodic prelithiation reagent that may decompose to release ions. In such an embodiment, the surface impurity layer may be decomposed within the voltage window, optionally using a catalyst such as the cathodic catalyst discussed below.

[0028] In addition, as shown in FIG. 4, the cathode prelithiation layer 106 may further include a cathode catalyst. In some embodiments, the cathode catalyst may catalyze the decomposition of the cathode prelithiation reagent during the prelithiation of the anode of the lithium-ion battery cell. For example, the cathode catalyst may include an inactive cathode catalyst composed of one or more non-lithiated metal oxides or non-lithiated metal phosphates, and / or an active cathode catalyst composed of one or more lithium metal oxides or lithium metal phosphates. Another example of the cathode catalyst includes NMC. In other examples, the cathode prelithiation reagent may decompose during a practical battery cell operating voltage window that does not include the cathode catalyst.

[0029] In some examples, the cathode prelithiation layer 106 may further include a second binder. In some examples, the second binder may bind particles of the cathode prelithiation reagent to each other, to other particles of the cathode prelithiation layer 106, and / or to the surface of the cathode active material layer 104. For example, the second binder may include one or more of polyacrylonitrile (PAN), polyethylene glycol (PEG), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyhexafluoropropylene (PHFP), poly(methyl methacrylate) (PMMA), polyacrylic acid (PAA), poly(4-vinylpyridine), polyvinylpyrrolidone, carboxymethyl cellulose (CMC) derivatives, or copolymers thereof. In other examples, the cathode prelithiation layer 106 may be sufficiently adhered to the cathode active material layer 104 without the second binder.

[0030] In some examples, the cathode prelithiated layer 106 can further include a second conductive additive. In some examples, the second conductive additive can include a carbonaceous material that increases the electronic conductivity of the lithium ion battery cell. For example, the second conductive additive can include one or more of carbon black, carbon fiber, carbon nanoparticles, CNTs, graphene oxide, and graphene. In some examples, the amount of the first conductive additive in the cathode active material layer 104 can be reduced or eliminated due to the presence of the second conductive additive in the cathode prelithiated layer 106, which can serve a similar purpose in the lithium ion battery cell.

[0031] In some examples, the first and second binders may have the same composition (depending on the affinity of the first binder with the cathode active material and the affinity of the second binder with the cathode prelithiation reagent). In other examples, the first and second binders may have different compositions (again, depending on the affinity of the first binder with the cathode active material and the affinity of the second binder with the cathode prelithiation reagent). Similarly, in some examples, the first and second conductive additives may have the same composition, while in other examples, the first and second conductive additives may have different compositions.

[0032] In some examples, the cathode prelithiated layer 106 can include a non-negligible amount of a secondary cathode active material (e.g., NMC), which can be the same as or different from the cathode active material of the cathode active material layer 104. In one example, the secondary cathode active material can be included in the cathode prelithiated layer 106 as an (active) cathode catalyst.

[0033] The respective slurries forming the cathode active material layer 104 and the cathode prelithiated layer 106 may be prepared separately and cast in sequence. Specifically, the cathode active material layer 104 may be formed from a first slurry cast onto the cathode current collector 102, and the cathode prelithiated layer 106 may be formed from a second slurry cast onto the cathode active material layer 104, the second slurry being separate and independent from the first slurry and having a different composition. In this manner, the cathode active material layer 104 and the cathode prelithiated layer 106 may be formed as separate slurry-based coatings.

[0034] In some examples, the cathode active material layer 104 may include a plurality of pores. The plurality of pores may conform to a number of shapes and sizes. By way of example, the plurality of pores may have a defined shape, such as circular (e.g., spherical), elliptical (e.g., spheroidal), or irregular, independently, in any combination thereof among the plurality of pores. Thus, when a slurry having a sufficiently low viscosity and particles of a sufficiently small scale are coated onto the cathode active material layer 104, the slurry may soak or infiltrate those pores that are closest to the coating interface of the slurry with the cathode active material layer 104 (e.g., where the slurry first contacts the cathode active material layer 104), thereby improving the interlayer adhesion of the cathode active material layer 104 and the (eventually formed) cathode prelithiated layer 106, as compared to a slurry of relatively high viscosity and / or a cathode active material layer of relatively low porosity. During subsequent drying and calendaring of the slurry, the slurry may reach a maximum penetration depth and stop penetrating into the pores of cathode active material layer 104.

[0035] Specifically, as shown, a portion of the cathode prelithiated layer 106 may penetrate into the pores of the cathode active material layer 104 to a maximum penetration depth 111. Thus, the pores may include a plurality of filled pores 105a and a plurality of voids 105b, and the plurality of filled pores 105a is filled with the infiltrated portion of the cathode prelithiated layer 106. Accordingly, the remaining portion of the cathode prelithiated layer 106 that does not penetrate into the pores of the cathode active material layer 104 may extend away from the cathode active material layer 104 along the axis 114 to a maximum extent 110. Furthermore, the remaining portion of the cathode active material layer 104 that is not penetrated by the cathode prelithiated layer 106 (e.g., including a plurality of voids 105b) may extend away from the cathode prelithiated layer 106 along the axis 114 to a maximum extent 113. In some examples, maximum range 113 may be greater than maximum range 110 .

[0036] In some embodiments, the cathode prelithiated layer 106 may penetrate each of the pores sandwiched between the bulk and the lower region 108 of the cathode prelithiated layer 106 and may therefore be evenly distributed throughout the pores to the maximum penetration depth 111. However, in other embodiments, as shown, at least some of the pores 105b may remain between the bulk and the lower region 108 of the cathode prelithiated layer 106. Thus, in such embodiments, the cathode prelithiated layer 106 may not be evenly distributed among the pores sandwiched between the bulk and the lower region 108 of the cathode prelithiated layer 106.

[0037] 2B, a schematic cross-section 160 is shown illustrating another exemplary coated cathode structure 161 for use in a lithium ion battery. The coated cathode structure 161 may incorporate materials and components as described above with reference to FIG. 2A. Upon formation, the coated cathode structure 161 may be positioned within a lithium ion battery such that the coated cathode structure 161 may provide power to the lithium ion battery. In some examples, the lithium ion battery may be one of multiple lithium ion battery cells in a lithium ion battery pack, each of the multiple lithium ion battery cells may have a substantially similar configuration to one another.

[0038] The structural features of the coated cathode structure 161 may be considered to be substantially similar or the same as the coated cathode structure 101 of FIG. 2A, except as discussed below. Specifically, the coated cathode structure 161 may include a cathode current collector 162 having a first side 163a opposite a second side 163b with respect to an axis 174 parallel to the smallest dimension of the cathode current collector 162. The coated cathode structure 161 may further include a cathode active material layer 164 and a cathode prelithiated layer 166. The cathode active material layer 164 and the cathode prelithiated layer 166 may be formed as separate slurry-based coatings, the cathode active material layer 164 including a plurality of pores, the plurality of pores including a plurality of filled pores 165a (permeated by the cathode prelithiated layer 166) and a plurality of voids 165b. Thus, as should be readily apparent, the components of the coated cathode structure 161 may be numbered similarly to the components of the coated cathode structure 101 of FIG. 2A (e.g., the cathode current collector 162, the cathode active material layer 164, the cathode prelithiated layer 166, etc. may be substantially similar or the same as the cathode current collector 102, the cathode active material layer 104, the cathode prelithiated layer 106, etc., respectively, except as discussed below).

[0039] 2A , in the coated cathode structure 161, the cathode current collector 162 can have a cathode prelithiated layer 166 disposed or coated on one of the sides 163a, 163b, where the cathode prelithiated layer 166 is in surface-to-surface contact with the cathode current collector 162. Thus, the cathode active material layer 164 can be disposed or coated on the cathode prelithiated layer 166 on the opposite side of the cathode current collector 162 relative to the axis 174 (e.g., opposite the side 163a and / or 163b of the cathode current collector 162 on which the cathode prelithiated layer 166 is coated, such that the cathode prelithiated layer 166 is sandwiched between the cathode current collector 162 and the cathode active material layer 164). For example, the cathode prelithiated layer 166 can be coated on the first side 163a of the cathode current collector 162 such that the coated cathode structure 161 can include, in order along the axis 174, the cathode current collector 162, the cathode prelithiated layer 166, and the cathode active material layer 164. In other examples, each of the sides 163 a, 163 b of the cathode current collector 162 can include a cathode prelithiated layer 166 respectively disposed thereon, with one or both of the cathode prelithiated layers 166 including a cathode active material layer(s) 164 respectively disposed thereon on opposite sides of the cathode current collector 162 (e.g., the coated cathode structure 161 can include, in order along the axis 174, a cathode active material layer 164, a cathode prelithiated layer 166, a cathode current collector 162, another cathode prelithiated layer 166, and another cathode active material layer 164).

[0040] The permeated portion of the cathode prelithiated layer 166 may penetrate into the cathode active material layer 164 to a maximum penetration depth 171 (e.g., from a lower surface or area 167a of the cathode active material layer 164 to an upper surface or area 168b of the cathode prelithiated layer 166), and the remaining portion of the cathode prelithiated layer 166 may extend away from the cathode active material layer 164 along an axis 174 to a maximum extent 170 (e.g., from a lower surface or area 167a of the cathode active material layer 164 to a lower surface or area 168a of the cathode prelithiated layer 166). Additionally, the portion of the cathode active material layer 164 that is not permeated by the cathode prelithiated layer 166 may extend along an axis 174 away from the cathode prelithiated layer 166 to a maximum extent 173 (e.g., from an upper surface or area 168b of the cathode prelithiated layer 166 to an upper surface or area 167b of the cathode active material layer 164).

[0041] It will be understood that the aspects of the coated cathode structures 101 and 161 described in detail above with reference to Figures 2A and 2B are not mutually exclusive, and such aspects may be added, removed, substituted, or combined according to a given application. Furthermore, the depicted coated cathode structures are non-limiting examples of how the coated cathode structures may be configured. For example, the coated cathode structure may include a cathode current collector coated on both sides thereof with different coating configurations (e.g., the maximum penetration depth, maximum extent, total thickness, and / or relative layer order of the cathode active material and cathode prelithiation layers may differ between the coated sides of the cathode current collector). Furthermore, other methods for incorporating prelithiation reagents into the cathode are possible. For example, the prelithiation of the cathode may be achieved by electrochemical prelithiation or three-electrode anodic in situ prelithiation. Regardless of the prelithiation technique, the electrochemical performance of the battery cell may be improved by applying an electrolyte additive to inactivate the non-decomposed prelithiation reagents.

[0042] As mentioned above, the prelithiation layer is a layer that adds excess Li to the cathode active material. +can be formed on the cathode from a prelithiation reagent (the prelithiation reagent includes one or more species) to provide Li + may be provided to the cathode prior to or during the initial charge / discharge (e.g., formation cycle) of the Li-ion battery cell, and the prelithiation reagent may decompose into products during the formation cycle that do not interfere with the electrochemical performance of the cathode. In some examples, one or more catalysts may be included in the cathode to promote the decomposition of the prelithiation reagent.

[0043] In some embodiments, the prelithiation reagent may not completely decompose after the formation cycle, especially when the size of the Li-ion battery cell is expanded. Thus, residual undecomposed portions may remain in the cathode, which may continue to decompose during subsequent battery cell operation, resulting in the generation of undesirable gases, such as oxygen (O2) and / or nitrogen (N2). If one or more catalysts are added to catalyze the decomposition of the prelithiation reagent, the presence of the catalyst in the battery cell during cycling may also result in gas generation, as well as electrolyte oxidation side reactions.

[0044] Thus, by deactivating both the remaining prelithiation reagent and the corresponding catalyst, the release of gas from the cathode can be suppressed and the adverse effects on the stability of the battery cell can be mitigated. The deactivation of the prelithiation reagent and the catalyst can be achieved by incorporating an electrolyte additive configured to form a deactivation layer on the cathode, more specifically on the prelithiation reagent and the catalyst, as well as other cathode components, as shown in FIG. 1. The electrolyte additive can be one or more of borates, sultones, fluorinates, anhydrides, phosphorus-based compounds, cyano compounds, unsaturated alkyl compounds, and blends thereof. Furthermore, in some examples, the electrolyte additive can be a lithium salt of one of the aforementioned groups. For example, the electrolyte additive can be one or more of lithium bis(oxolato)borate (LiBOB), lithium 4-pyridyltrimethylborate (LPTB), lithium tetrafluoroborate (LiBF4), lithium oxalyldifluoroborate (LiDFOB), diisopropylfluorophosphate (DFP), LiDFOP, lithium tetrafluorooxalatophosphate (LiTFOP), lithium 4,5-dicyano-2-(trifluoromethyl)imidazole (LiTDI), lithium hexafluorophosphate (LiPF6), lithium di(trifluoromethanesulfonyl)imide (LiTFSI), lithium di(fluorosulfonyl)imide lithium (LiFSI), and any blends thereof.

[0045] In one example, electrolyte additives may traditionally be used to reduce corrosion on aluminum current collectors in Li-ion battery cells, stabilize the electrolyte of the battery cell, and / or form a coating on the anode of the battery cell to support the anode structure. However, as described herein, electrolyte additives may instead be used to coat prelithiation reagents, catalysts, and various other materials on the cathode that may facilitate gas formation within the battery cell.

[0046] For example, the schematic cross-section 300 of Figure 3A illustrates an exemplary passivated cathode structure 301 for use in a lithium-ion battery cell. The passivated cathode structure 301 of Figure 3A includes some of the components of the coated cathode structure 101 of Figure 2A. However, at least a portion of the prelithiated layer 106 shown in Figure 2A decomposes during the formation cycle, and the remaining portion of the prelithiated layer is shown as filled pores 105a proximate the top surface of the passivated cathode structure 301 (e.g., distal to the cathode current collector 162 along axis 114). The passivated cathode structure 301 further includes a passivation layer 302 formed with an electrolyte additive, such as the electrolyte additives described above. Although the passivation layer 302 is shown as a continuous layer that completely coats the top surface of the passivated cathode structure 301, in other embodiments, the passivation layer 302 may not be a continuous layer, but instead coat only a portion or portions of the top surface of the passivated cathode structure 301.

[0047] Similarly, the schematic cross section 360 of FIG. 3B shows another passivated cathode structure 361 after performing a formation cycle including the components of the coated cathode structure 161 of FIG. 2B. At least a portion of the prelithiation layer 166 shown in FIG. 2B decomposes, but some of the prelithiation reagents of the prelithiation layer remain, depicted as a plurality of filled pores 165a proximate the bottom of the passivated cathode structure 361 (e.g., proximate the cathode current collector 162 along the axis 174). The passivated cathode structure 361 also includes a passivation layer 302 formed with an electrolyte additive, the passivation layer 302 being located on the top surface of the passivated cathode structure 361. The electrolyte additive may be added to the electrolyte of the battery cell and may be oxidized during the formation cycle to form the passivation layer 302. The addition of the electrolyte additive may occur before or after the formation cycle of the battery cell, as further described below with reference to FIGS. 6 and 7.

[0048] Particle level passivation is also possible by the process 10 shown in Figure 1. At the particle level, the component particles forming the cathode structure, such as the passivated cathode structures 301, 361 of Figures 3A and 3B, can be passivated with a passivation layer formed from an electrolyte additive. For example, as shown in Figure 4, a particle level view 400 of the passivated cathode structure of Figure 3A is shown as indicated by the box in Figure 3A.

[0049] The particle level view 400 depicts cathode active material particles 402 that may form the cathode active material layer 104 of FIG. 3A, each of the cathode active material particles 402 being surrounded by a passivation layer 404. The passivated cathode structure includes conductive additive particles 406, which may be a carbon-based material as described above. The conductive additive particles 406 may also include a passivation layer 404 coating each of the conductive additive particles 406.

[0050] The prelithiation reagent particles 408 may remain in the passivated cathode structure after the formation cycle and may be coated with a passivation layer 404 that also coats the catalyst particles 410 incorporated to aid in the decomposition of the prelithiation reagent particles 408. As discussed above with respect to FIG. 3A, the passivation layer 404 shown in FIG. 4 is depicted as a continuous complete layer circumferentially surrounding each of the particles, although in other examples, the passivation layer 404 may provide partial coverage of the surface area of ​​each of the particles, e.g., less than 100% of the surface area. Additionally, the passivation layer 404 depicted in FIG. 4 is a non-limiting example, and the relative thickness of the passivation layer, as well as the relative size, shape, and positioning of different particle types, may vary from the illustrative example of FIG. 4.

[0051] Furthermore, the electrode-level and particle-level passivation shown in Figures 3A-4 may occur for different prelithiation processes and modes. For example, as illustrated in Figures 2A and 2B, the formation of a passivation layer on the component particles of the cathode structure as well as on the surface of the cathode structure may be observed for prelithiation processes other than the manufacture of a coated cathode composed of a permeated prelithiation layer. For example, prelithiation of the cathode at the particle level, such as the formation of a prelithiation layer on the active cathode material particles, as well as direct slurry incorporation of the prelithiation reagent, may also result in passivation of the cathode structure similar to that shown in Figures 3A-4.

[0052] The passivation layer may be a uniform layer on the surface of the cathode that remains stable during cycling of the battery cell and provides electronic insulation. In addition, the passivation layer may coat each particle of the cathode component, including particles of the prelithiation reagent remaining after the formation cycle, as illustrated in FIG. 4. The type (or types) of electrolyte additive that forms the passivation layer, as well as the amount of electrolyte additive(s), may be selected to produce a passivation layer without modifying the properties of the bulk electrolyte and without adversely affecting the additional charge capacity resulting from prelithiation of the cathode or reducing the cycling performance of the battery cell. For example, the chemical and / or physical properties of the electrolyte additive may enhance the cycling performance of the battery cell by suppressing parasitic reactions. It should be noted that hereinafter, reference to an electrolyte additive includes the simultaneous use of one or more electrolyte additives, where the electrolyte additive includes one or more lithium salts, as well as other additives, such as conductive carbon-based additives.

[0053] For example, electrolyte additives can inhibit impedance growth and gassing in battery cells. Impedance can increase due to electrolyte loss due to solid electrolyte interface (SEI) formation, high voltage operation, high temperature, moisture contamination, etc. By forming a passivation layer, electrolyte-related reactions at the cathode can be inhibited and impedance can be kept low, or at least uniform.

[0054] Gas generation due to prelithiation reagents and catalysts at the cathode may be mitigated by a barrier imposed by a passivation layer between the cathode surface and the electrolyte. The electrolyte additive may oxidize on the surface of the prelithiation additive / catalyst / carbon additive to form a layer via electrochemical or electrocatalytic reactions. Such a layer may be dense and / or insulating, adding a physical and / or electrochemical barrier to the decomposition of the prelithiation additive, and therefore preventing gas generation. For example, the passivation layer formed from the electrolyte additive may be a layer between the cathode and the electrolyte that forms 0.01%-5% of the total mass of the battery cell (excluding external components such as the housing).

[0055] The type and amount of electrolyte additive may be selected such that the decomposition potential of the prelithiation reagent is not increased to an unrealistic potential for the Li-ion battery, which may compromise the additional capacity enabled by cathode prelithiation. Similarly, the selection of electrolyte additive may affect the interfacial impedance between the electrolyte and the cathode active material. For example, an inappropriate electrolyte additive or amount of electrolyte additive may cause an increase in the interfacial impedance, reducing cell cycling performance, power performance, and worsening cell gassing. Therefore, the type of electrolyte additive may be selected to provide optimal results based on the type of electrolyte used in the battery cell to ensure chemical compatibility between the electrolyte additive, the resulting passivation layer, and the electrolyte, as an example. For example, elements present in the electrolyte may be considered when selecting the electrolyte additive.

[0056] To this end, electrolyte additives including, for example, LiBOB, LPTB, LiBF4, LiFOB, LiTFOP, LiPF6, LiTFSI, LiDFOB, LiFSI, and any blends thereof, may provide the desired effects described above. Moreover, the electrolyte additives may do so without compromising the additional capacity released by the prelithiation reagent or the cycling performance of the cathode. The electrolyte additives may provide the additional benefit of improving the cycling performance of the cathode.

[0057] The content of the electrolyte additives, including the combination of electrolyte additives, in the Li-ion battery cell may be in the range of 0.01% to 10% of the mass of the bulk electrolyte. In another embodiment, the electrolyte additives may be in the range of 0.01% to 5%, or in the range of 0.01% to 3% of the bulk electrolyte amount. The thickness of the passivation layer formed by the electrolyte additives may vary depending on the mass fraction of the electrolyte additives, and in one embodiment, may be in the range of 0.1 nm to 100 nm. In another embodiment, as described above, the thickness of the passivation layer may be in the range of 0.1 nm to 20 nm. In other embodiments, the thickness of the passivation layer may be in the range of 0.1 nm to 50 nm, or in the range of 0.1 nm to 10 nm.

[0058] The electrolyte additive may be added to the bulk electrolyte at a lithium salt concentration of 0.5M to 2.0M. As another example, the electrolyte additive may have a lithium salt concentration of 0.8M to 2.0M, or 0.8M to 1.5M. The bulk electrolyte may include a solvent that may include one or more of ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), fluoroethylene carbonate (FEC), 2,5-furan dimethyl carboxylate (FDMC), fluorinated diethyl carbonate (FDEC), carboxyl ester, fluorinated carboxyl ester, propyl propanoate (PP), ethyl propanoate (EP), propyl acetate (PA), and ethyl acetate (EA). In one example, the mass percentage of the electrolyte components may be 10% to 40% for EC, 20% to 40% for DMC, 20% to 40% for DEC, and 30% to 50% for EMC.

[0059] Referring now to FIG. 5, an embodiment of a method 500 for passivating a prelithiated cathode of a Li-ion battery cell, providing an electrochemical barrier that inhibits further decomposition of a prelithiation reagent used to provide an additional lithium source to the anode, as well as deactivating a catalyst used to aid in the decomposition of the prelithiation reagent is depicted. Specifically, at least a portion of the prelithiation reagent may decompose as the battery cell is cycled through a formation cycle. However, a remaining portion of the prelithiation reagent may remain intact, e.g., undecomposed, after the formation cycle. A passivation layer formed from at least one electrolyte additive may coat the remaining prelithiation reagent when the electrolyte additive is oxidized during the formation cycle, thereby inactivating the prelithiation reagent and inhibiting continued decomposition of the prelithiation reagent during subsequent battery cell cycles. It will be understood that the method 500 may be described in conjunction with the components described in detail above with reference to FIGS. 2A-4. For example, the prelithiated cathode may have the coated cathode structures 101 and 161 of Figures 2A and 2B. Additionally, while the embodiments described herein are directed to the formation of prelithiated cathodes, it will be understood that at least some of the embodiments described herein may be adapted to anodes of Li-ion battery cells. For example, the method 500 may be readily adapted or modified to a slurry for making a prelithiated anode with a passivation layer.

[0060] At 502, the method 500 includes forming a prelithiated cathode. As an example, forming the prelithiated cathode can include forming a homogenous mixture including a cathode prelithiation reagent that can be uniformly dispersed in a non-aqueous solvent. In some examples, the cathode prelithiation reagent can be selected from Li3N, Li2O, Li2O2, Li2S, Li5FeO4, Li2S / M nanocomposite, LiF / M nanocomposite, Li2O / M nanocomposite, or any combination of the above compounds, where M is one or more metals, and the non-aqueous solvent can be selected from DMF, NMP, DMAc, DMSO, MeCN, THF, toluene, or any combination of the above compounds. The one or more additives may be uniformly dispersed in the non-aqueous solvent, and the one or more additives may include one or more of a cathode catalyst (e.g., for catalyzing the decomposition of a cathode prelithiation reagent), a binder (e.g., for binding various components of the homogeneous mixture together), and a conductive carbon additive (e.g., for improving electronic conductivity in a lithium ion battery). In some examples, the cathode catalyst may be selected from an inactive cathode catalyst composed of one or more non-lithiated metal oxides or non-lithiated metal phosphates, and / or an active cathode catalyst composed of one or more lithium metal oxides or lithium metal phosphates.

[0061] Forming the prelithiated cathode may, in some embodiments, further include forming a slurry of the prelithiated cathode components, and casting the slurry onto the cathode substrate to form a slurry-coated cathode substrate. However, other techniques for incorporating the components into the cathode structure are possible. In one embodiment, the cathode substrate may include a porous cathode active material layer disposed on a cathode current collector. In one embodiment, the porous cathode active material layer may be formed by casting an additional separate slurry onto the cathode current collector prior to casting the slurry onto the cathode substrate. The prelithiated cathode may then be dried and calendered.

[0062] At 504, the method 500 includes adding an electrolyte to the container. For example, the electrolyte may be injected into a housing of a Li-ion battery cell. The electrolyte may be a mixture including one or more of the solvents, such as EC, DMC, DEC, and EMC, described above. The pre-lithiated cathode may be placed in the electrolyte at 506 such that the electrolyte contacts the pre-lithiated cathode. For example, the pre-lithiated cathode may be positioned in a Li-ion battery cell. At least a portion of the total surface area of ​​the pre-lithiated cathode may be in contact with the electrolyte. In one embodiment, the pre-lithiated cathode may be completely immersed in the electrolyte.

[0063] At 508, the method 500 includes forming a passivation layer on the surface of the prelithiated cathode and on the particles of the prelithiated cathode components, for example, the component particles including the particles of the prelithiated reagent that remain undecomposed after performing the formation cycle of the battery cell. For example, the anode can be electrically coupled to the cathode, which can be further coupled to a voltage source. To form the passivation layer, the electrolyte additive can be one or more of borates, sultones, fluorinates, anhydrides, phosphorus-based compounds, cyano compounds, unsaturated alkyl compounds, and blends thereof, and can also be one or more of LiBOB LPTB, LiBF4, LiFOB, LiTFOP, LiPF6, LiTFSI, LiFSI, and blends thereof, and can be added to the electrolyte via two possible strategies. More specifically, the electrolyte additive can be added to the electrolyte at different points during the formation process of the passivation layer.

[0064] A first strategy involves injecting the electrolyte additive before the formation cycle is performed, at 510. In some embodiments, the electrolyte additive may be added to the electrolyte earlier in method 500, such as at 504. Details of the first strategy are described in more detail below with reference to FIG. 6. A second strategy for forming the passivation layer, at 512, involves injecting the electrolyte additive after the formation cycle is performed. Details of the second strategy are described further below with reference to FIG. 7.

[0065] Turning now to Figure 6, method 600 illustrates a first formation process for passivation of a Li-ion battery cell cathode, for example, both electrode level passivation and particle level passivation. At 602, the battery cell may be assembled (if assembly has not already been completed during execution of method 500). For example, a pre-lithiated cathode may be formed as described in method 500 of Figure 5, or another method for making a pre-lithiated cathode, and added to the battery cell along with an anode, electrolyte, and any other battery cell components. The battery cell components, including the cathode and anode, may be positioned within the battery cell and appropriately bonded and / or secured in place with the electrolyte in contact with the cathode and anode.

[0066] At least one electrolyte additive, which may be any of the electrolyte additive species described above, is injected into the electrolyte, e.g., bulk electrolyte, at 604 to disperse the electrolyte additive within the electrolyte of the battery cell, and a formation cycle is performed at 606 to activate the battery cell. However, in other embodiments, the electrolyte additive may be added to the electrolyte during assembly of the battery cell, e.g., at 602. The electrolyte additive may be selected to have an oxidation potential higher than the decomposition oxidation potential of the cathode prelithiation reagent (wherein the prelithiation reagent is formed from one or more species). Thus, during the fill cycle of the formation cycle, oxidation of the prelithiation reagent may occur prior to oxidation of the electrolyte additive, and at least a portion of the prelithiation reagent (e.g., forming a prelithiation layer on the cathode) may decompose. Any remaining amount of the prelithiation reagent may subsequently be coated by an electrolyte additive layer or coating formed as a result of the electrolyte additive oxidation. The electrolyte additive coating is also formed on the catalyst, thereby passivating both the prelithiation reagent and the catalyst. The method ends.

[0067] 7, method 700 illustrates a second formation process of a passivation layer of a Li-ion battery cell cathode, such as electrode level passivation and particle level passivation. At 702, the battery cell may be assembled. As described above in 602 of method 600, the battery cell may be assembled by adding a prelithiated cathode, anode, electrolyte, and other battery cell components to the battery cell (if not already completed).

[0068] A formation cycle, e.g., an initial charge / discharge, of the battery cell is performed at 704 to operate the battery cell. During the charge cycle of the formation cycle, at least a portion of the prelithiation reagent forming the prelithiation layer at the cathode may decompose. However, a portion of the prelithiation reagent may not decompose.

[0069] At least one electrolyte additive, which may be any of the electrolyte additive species described above, is injected into the bulk electrolyte at 706 after the formation cycle. In some examples, the electrolyte additive may have an oxidation potential lower than the decomposition oxidation potential of the prelithiation reagent, and thus the electrolyte additive is added after the formation cycle to allow decomposition of the prelithiation reagent to occur that would otherwise be inhibited by oxidation of the electrolyte additive. However, in other examples, the electrolyte additive may have an oxidation potential equal to or lower than the decomposition oxidation potential of the prelithiation reagent. Any remaining portion of the prelithiation reagent may be coated with an electrolyte additive layer or coating formed as a result of the electrolyte additive oxidation. The electrolyte additive coating is also formed on the catalyst, thereby passivating both the prelithiation reagent and the catalyst. The method ends.

[0070] In some examples, especially during large-scale production of Li-ion batteries, method 700 may be preferred over method 600 because it is applicable to electrolyte additives with a wide range of oxidation potentials compared to the decomposition oxidation potential of the prelithiation reagent. Adding the electrolyte additive after the formation cycle avoids the decomposition destructive potential of the prelithiation reagent. Furthermore, in some examples, the electrolyte additive may be added during the formation cycle. For example, a charge cycle may be performed and the charge capacity of the battery cell may be evaluated. If the charge capacity does not meet the targeted expected capacity, the electrolyte additive may be injected before the start of the discharge cycle. In some examples, the electrolyte additive may be added to the battery cell upon determining that the performance of the battery cell does not meet the desired performance level. However, in other examples, the addition of the electrolyte additive may be included in the manufacturing process and may be added preemptively to counter possible anticipated effects of the prelithiation reagent.

[0071] Incorporating an electrolyte additive into a Li-ion battery cell may affect the cycle charge capacity of the battery cell during the formation cycle of the battery cell. For example, a comparison of the first charge capacity (FCC), first discharge capacity (FDC), and first cycle efficiency (FCE) of each of a first Li-ion battery cell without a passivation layer, a passivation layer formed with an electrolyte additive, and a second Li-ion battery cell with a passivation layer is shown in Table 1, where the electrolyte additive is LiDFOP. The first battery cell and the second battery cell may include similarly prelithiated cathodes. [Table 1]

[0072] The results summarized in Table 1 show that the capacity of the first battery cell is higher than that of the second battery cell during the first charging cycle. The higher FCC of the first battery cell is due to the additional capacity contribution from the decomposition of the prelithiation reagent disposed on the cathode of the first battery cell. The FDC of the second battery cell is higher than that of the first battery cell, and the FCE is also higher for the second battery cell than the first battery cell. The capacity comparison provided by Table 1 shows that the electrolyte additive effectively passivates the prelithiation reagent (and prelithiation catalyst) of the cathode while increasing the cycle capacity and efficiency of the battery cell.

[0073] The benefit provided by the electrolyte additive is further supported by a comparison of first cycle voltage profiles with and without a passivation layer formed from the electrolyte additive. For example, FIG. 8 depicts a first graph 800 plotting a first voltage profile for each cell of a first battery, where the cells of the first battery resemble the first battery cell of Table 1. FIG. 9 depicts a second graph 900 plotting a first voltage profile for each cell of a second battery, where the cells of the second battery resemble the second battery cell of Table 2. The electrolyte additive is LiDFOP.

[0074] In the first graph 800 of FIG. 8, a set of charge cycle voltage profiles 802 and a set of discharge cycle voltage profiles 804 are shown. The set of charge cycle voltage profiles 802 includes a region where the voltage plateaus, as indicated by the dashed region 806, due to the decomposition of the cathode prelithiation reagent. The second graph 900 of FIG. 9 similarly shows a set of charge cycle voltage profiles 902 and a set of discharge cycle voltage profiles 904. No plateau is observed in the region indicated by the dashed region 906. A comparison of the first graph 800 and the second graph 900 indicates that decomposition of the prelithiation reagent does not occur in the second battery cell due to the formation of a passivation layer, as demonstrated by the lack of a plateau in the second graph 900.

[0075] In this manner, the performance of the battery cell may be improved. An electrolyte additive may be added to the battery cell to create a passivation layer on the undecomposed prelithiation reagent of the cathode of the battery cell. The passivation layer may also coat the prelithiation catalyst used to promote the decomposition of the prelithiation reagent during the formation cycle of the battery cell, as well as other materials forming the cathode, such as the cathode active material and one or more conductive additives or fillers. The passivation layer may be formed with one or more electrolyte additives and may reduce both gassing and impedance growth in the battery cell caused by the decomposition of the prelithiation reagent during operation of the battery cell. Using electrolyte additives to passivate the prelithiation reagent may be a low-cost and effective strategy to increase the electrochemical performance of the battery cell and may be easily scaled up to larger cell formats.

[0076] The inventors have identified the problem of gas generation in lithium-ion battery cells during cycling when a prelithiated cathode using a prelithiated reagent or a prelithiated reagent containing a catalyst is used, and have addressed this problem by injecting an electrode additive into the electrolyte to form a passivation layer in the prelithiated cathode. The passivation layer is generated during the first charging phase, and is formed at both the electrode level and the particle level, which can inhibit the continued decomposition of the prelithiated reagent after the completion of the formation cycle of the lithium-ion battery cell. In this way, undesirable reactions between the prelithiated reagent and the electrolyte can be avoided.

[0077] Additionally, embodiments show (1) the formation of a passivation layer over prelithiated electrode components (as shown in FIG. 1 ), (2) coating the prelithiated electrode (as shown in FIGS. 2A and 2B ), (3) the formation of a passivation layer of electrolyte additive (as shown in FIGS. 3A and 3B ), (4) a detailed view of the particles of the electrode after forming the passivation layer (as shown in FIG. 4 ), (5) a method for passivating the prelithiated cathode (as shown in FIGS. 5-7 ), and (6) a first electrical performance demonstration of charging and discharging with a non-passivated layer and a passivated layer, respectively (as shown in FIGS. 8-9 ).

[0078] The present disclosure also provides support for a method for forming a cathode for a lithium-ion battery cell, which includes forming a prelithiated cathode with a prelithiated reagent, positioning the prelithiated cathode in contact with an electrolyte, and injecting an electrolyte additive into the electrolyte to form a passivation layer in the prelithiated cathode, the passivation layer inhibiting continued decomposition of the prelithiated reagent in the prelithiated cathode after completion of the lithium-ion battery cell formation cycle. In a first embodiment of the method, injecting the electrolyte additive to form a passivation layer further includes inhibiting the activity of a catalyst, the catalyst being used to promote the decomposition of the prelithiated reagent. In a second embodiment of the method, optionally including the first embodiment, injecting the electrolyte additive includes injecting one or more of borates, sultones, fluorinates, anhydrides, phosphorus-based compounds, cyano compounds, unsaturated alkyl compounds, lithium bis(oxolato)borate (LiBOB), lithium 4-pyridyltrimethylborate (LPTB), lithium tetrafluoroborate (LiBF4), lithium oxalyldifluoroborate (LiDFOB), lithium tetrafluorooxalatophosphate (LiTFOP), lithium hexafluorophosphate (LiPF6), lithium di(trifluoromethanesulfonyl)imide (LiTFSI), lithium di(fluorosulfonyl)imide (LiFSI), diisopropylfluorophosphate (DFP), lithium difluorobis(oxalato)phosphate (LiDFOP), and blends thereof. In a third embodiment of the method, optionally including one or both of the first and second embodiments, injecting the electrolyte additive includes adding an amount of the electrolyte additive in the range of 0.01% to 10% of the mass of the electrolyte, and adding a lithium salt having a concentration in the range of 0.5M to 2.0M in the electrolyte.In a fourth embodiment of the method, optionally including one or more of the first to third embodiments, injecting the electrolyte to form a passivation layer includes forming a layer having a content in the range of 0.01% to 5% of the mass of the chemical components of the lithium ion battery cell, the chemical components including the electrolyte, the prelithiated cathode, and the anode. In a fifth embodiment of the method, optionally including one or more of the first to fourth embodiments, injecting the electrolyte additive to form a passivation layer includes forming a passivation layer on a surface of the prelithiated cathode and on particles forming the prelithiated cathode, the particles forming the prelithiated cathode including particles of a prelithiated reagent that do not decompose after a formation cycle, particles of a cathode active material, particles of a catalyst, and particles of a conductive additive. In a sixth embodiment of the method, optionally including one or more or each of the first through fifth embodiments, injecting the electrolyte additive to form a passivation layer includes forming a barrier between the prelithiated cathode and the electrolyte to inhibit continued decomposition of the prelithiated reagent during cycling of the lithium ion battery cell after the formation cycle.

[0079] The present disclosure also provides a support for a lithium ion battery cell including an electrolyte, a cathode in contact with the electrolyte and coated with a prelithiation reagent, and an electrolyte additive added to the electrolyte, the electrolyte additive forming a passivation layer on the prelithiation reagent after an initial charge of the lithium ion battery cell. In a first embodiment of the system, the prelithiation reagent is one or more of Li3N, Li2O, Li2O2, Li2S, Li5FeO4, Li2S / M nanocomposite, LiF / M nanocomposite, and Li2O / metal nanocomposite. In a second embodiment of the system, optionally including the first embodiment, the electrolyte is formed of 10%-40% ethylene carbonate, 20%-40% dimethyl carbonate, 20%-40% diethyl carbonate, and 30%-50% ethyl methyl carbonate. A third embodiment of the system optionally includes one or both of the first and second embodiments, where the passivation layer forms at least one of a partial coating on the surface of the cathode and the particles forming the cathode, and a complete coating on the surface of the cathode and the particles forming the cathode. A fourth embodiment of the system optionally includes one or more or each of the first to third embodiments, where the cathode includes one or more catalysts configured to promote decomposition of the prelithiation reagent, and the passivation layer is a barrier between the one or more catalysts and the electrolyte. A fifth embodiment of the system optionally includes one or more or each of the first to fourth embodiments, where the passivation layer is formed when the electrolyte additive oxidizes during initial charging of the lithium ion battery cell. A sixth embodiment of the system optionally includes one or more or each of the first to fifth embodiments, where the passivation layer inhibits gas generation due to the prelithiation reagent and impedance growth of the lithium ion battery cell, where the impedance growth is due to surface reconstruction at the active material of the cathode. A seventh embodiment of the system optionally includes one or more or each of the first to sixth embodiments, wherein the passivation layer has a thickness in the range of 0.1 nm to 20 nm, and the thickness of the passivation layer varies according to the type of particle coated by the passivation layer.In an eighth embodiment of the system, optionally including one or more or each of the first to seventh embodiments, the passivation layer has a thickness of less than 10 nm.

[0080] The present disclosure also provides support for a method for forming a lithium ion battery cell, which includes assembling components of a lithium ion battery cell, the components including a prelithiated cathode having a prelithiated layer formed from a prelithiated reagent, adding an electrolyte to the lithium ion battery cell, the electrolyte contacting the prelithiated cathode, and injecting an electrolyte additive into the electrolyte to form a passivation layer on the prelithiated reagent of the prelithiated cathode, the passivation layer inhibiting gas formation by the prelithiated reagent. In a first embodiment of the method, injecting the electrolyte additive into the electrolyte includes injecting the electrolyte additive before performing a cycle of forming a lithium ion battery cell, and the passivation layer is also formed on the prelithiated catalyst, the cathode active material, and the conductive filler of the prelithiated cathode. In a second embodiment of the method, optionally including the first embodiment, injecting the electrolyte additive into the electrolyte includes injecting the electrolyte additive after performing a lithium ion battery cell formation cycle, and a passivation layer is also formed on the prelithiated catalyst, the cathode active material, and the conductive filler of the prelithiated cathode. In a third embodiment of the method, optionally including one or both of the first and second embodiments, injecting the electrolyte additive into the electrolyte to form a passivation layer includes inhibiting electrolyte oxidation in the prelithiated cathode material, and the prelithiated cathode material includes one or more of the prelithiated reagent, the catalyst, the cathode active material, and the conductive additive.

[0081] The following claims particularly point out certain combinations and subcombinations that are deemed novel and non-obvious. These claims may refer to "an" element or "first" element or equivalents thereof. Such claims should be understood to include the incorporation of one or more such elements, and do not require or exclude two or more such elements. Other combinations and subcombinations of the disclosed features, functions, elements, and / or properties may be claimed through amendment of the claims or through the presentation of new claims in this or a related application. Such claims, whether broader, narrower, equal, or different in scope to the original claims, are also considered to be included within the subject matter of this disclosure.

Claims

1. 1. A method for forming a cathode of a lithium ion battery cell, comprising: forming a prelithiated cathode using a prelithiating reagent; positioning the prelithiated cathode in contact with an electrolyte; injecting an electrolyte additive into the electrolyte to form a passivation layer in the prelithiated cathode, the passivation layer inhibiting continued decomposition of the prelithiation reagent in the prelithiated cathode after completion of a formation cycle of the lithium ion battery cell.

2. 2. The method of claim 1, wherein injecting the electrolyte additive to form the passivation layer further comprises inhibiting the activity of a catalyst, the catalyst being used to promote decomposition of the prelithiation reagent.

3. The electrolyte additive may be selected from the group consisting of borates, sultones, fluorinates, anhydrides, phosphorus compounds, cyano compounds, unsaturated alkyl compounds, lithium bis(oxolato)borate (LiBOB), lithium 4-pyridyltrimethylborate (LPTB), lithium tetrafluoroborate (LiBF ４ ), lithium oxalyl difluoroborate (LiDFOB), lithium tetrafluorooxalatophosphate (LiTFOP), lithium hexafluorophosphate (LiPF ６ 2. The method of claim 1, comprising injecting one or more of lithium di(trifluoromethanesulfonyl)imide (LiTFSI), lithium di(fluorosulfonyl)imide (LiFSI), diisopropylfluorophosphate (DFP), lithium difluorobis(oxalato)phosphate (LiDFOP), and blends thereof.

4. 2. The method of claim 1, wherein injecting the electrolyte additive comprises adding the electrolyte additive in an amount ranging from 0.01% to 10% of the mass of the electrolyte, and adding a lithium salt having a concentration in the electrolyte ranging from 0.5M to 2.0M.

5. 2. The method of claim 1, wherein injecting the electrolyte to form the passivation layer comprises forming a layer having a content in a range of 0.01% to 5% of a mass of chemical components of the lithium ion battery cell, the chemical components including the electrolyte, the prelithiated cathode, and an anode.

6. 2. The method of claim 1, wherein injecting the electrolyte additive to form the passivation layer comprises forming the passivation layer on a surface of the prelithiated cathode and on particles forming the prelithiated cathode, the particles forming the prelithiated cathode comprising particles of the prelithiation reagent, particles of a cathode active material, particles of a catalyst, and particles of a conductive additive that do not decompose after the formation cycle.

7. 2. The method of claim 1, wherein injecting the electrolyte additive to form the passivation layer comprises forming a barrier between the prelithiated cathode and the electrolyte to inhibit the continued decomposition of the prelithiated reagent during cycling of a lithium ion battery cell after the formation cycle.

8. 1. A lithium ion battery cell, comprising: An electrolyte; a cathode in contact with the electrolyte and coated with a prelithiation reagent; an electrolyte additive added to the electrolyte, the electrolyte additive forming a passivation layer on the prelithiation reagent after an initial charge of the lithium ion battery cell.

9. The prelithiation reagent is Li ３ N., Li ２ O., Li ２ O ２ , Li ２ S., Li. ５ FeO ４ , Li ２ S / M nanocomposites, LiF / M nanocomposites, and Li ２ 9. The lithium ion battery cell of claim 8, wherein the electrolyte is one or more of: 10% to 40% ethylene carbonate, 20% to 40% dimethyl carbonate, 20% to 40% diethyl carbonate, and 30% to 50% ethyl methyl carbonate.

10. 9. The lithium ion battery cell of claim 8, wherein the passivation layer forms at least one of a partial coating on the surface of the cathode and the particles forming the cathode, and a complete coating on the surface of the cathode and the particles forming the cathode.

11. 9. The lithium ion battery cell of claim 8, wherein the cathode includes one or more catalysts configured to promote decomposition of the prelithiation reagent, and the passivation layer is a barrier between the one or more catalysts and the electrolyte.

12. 9. The lithium ion battery cell of claim 8, wherein the passivation layer is formed when the electrolyte additive oxidizes during the initial charging of the lithium ion battery cell.

13. 9. The lithium ion battery cell of claim 8, wherein the passivation layer inhibits gas generation due to the prelithiation reagent and impedance growth of the lithium ion battery cell, the impedance growth resulting from surface reconstruction on the active material of the cathode.

14. 9. The lithium ion battery cell of claim 8, wherein the passivation layer has a thickness in the range of 0.1 nm to 20 nm, and the thickness of the passivation layer varies according to the type of particles coated by the passivation layer.

15. 9. The lithium ion battery cell of claim 8, wherein the passivation layer has a thickness of less than 10 nm.

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