Silicon anode electrode with active material particles coated with a solid electrolyte for solid-state battery cells

Abstract

Anode electrode for a battery cell, comprising: an anode active material layer comprising: an anode active material, an outer coating layer covering at least a portion of an outer surface of the particles of the anode active material layer, wherein the outer coating layer comprises a solid electrolyte, and a fibrillating binder, wherein the anode active material comprises a silicon alloy with a lithium alloy metal, and wherein the lithium alloy metal is selected from a group of aluminum (Al), tin (Sn) and magnesium (Mg).

Description

INTRODUCTION

[0001] The information contained in this section is intended to provide a general context for the disclosure. Work by the presently named inventors, to the extent described in this section, as well as aspects of the description that may not otherwise be considered prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against this disclosure.

[0002] The present disclosure relates to battery cells and, more particularly, to silicon anode electrodes having active material particles coated with a solid electrolyte for solid-state battery cells.

[0003] Electric vehicles (EVs), such as battery electric vehicles (BEVs), hybrid vehicles, and / or fuel cell vehicles, comprise one or more electric machines and a battery system with one or more battery cells, battery modules, and / or battery packs. A power control system is used to control the charging and / or discharging of the battery system during charging and / or driving.

[0004] Battery cells comprise cathode electrodes, anode electrodes, and separators. The cathode electrodes comprise a cathode active material layer disposed on a cathode current collector. The anode electrodes comprise an anode active material layer disposed on an anode current collector.

[0005] Various anode electrodes for battery cells as well as the battery cells themselves are known, for example, from DE 10 2023 108 210 B3 (state of the art according to Section 3(2) PatG), US 2023 / 0 231 182 A1 and US 2023 / 0 106 377 A1. SUMMARY

[0006] According to the invention, an anode electrode for a battery cell comprises an anode active material layer. The anode active material layer comprises an anode active material and an outer coating layer covering at least part of the outer surface of particles of the anode active material layer. The anode active material comprises a silicon alloy with a lithium alloy metal, and the lithium alloy metal is selected from a group consisting of aluminum (Al), tin (Sn), and magnesium (Mg). The outer coating layer comprises a solid electrolyte and a fibrillating binder.

[0007] In other features, the anode active material layer is arranged on an anode current collector. The fibrillating binder comprises polytetrafluoroethylene (PTFE). The softening point of the fibrillating binder ranges from 270°C to 380°C. The molecular weight of the fibrillating binder ranges from 105 g / mol to 109 g / mol.

[0008] For other features, the load on the anode active material layer is in the range of 4 mAh / cm 2 up to 30 mAh / cm 2The thickness of the anode active material layer ranges from 10 µm to 200 µm. The solid electrolyte is selected from a group consisting of a sulfide-based solid electrolyte, a halide-based solid electrolyte, and a hydride-based solid electrolyte. The solid electrolyte comprises a sulfidic solid electrolyte. The sulfidic solid electrolyte is selected from a group consisting of pseudobinary sulfide, pseudoternary sulfide, and pseudoquaternary sulfide. The anode active material layer comprises 70 wt% to 98 wt% of the anode active material layer, the solid electrolyte comprises 2 wt% to 30 wt% of the anode active material layer, and the fibrillating binder comprises 0.1 wt% to 5 wt% of the anode active material layer.

[0009] Also not described in accordance with the invention is an anode electrode for a battery cell comprising an anode current collector and an anode active material layer disposed on the anode current collector. The anode active material layer comprises an anode active material selected from a group consisting of silicon, a silicon alloy, and silicon / silicon oxide. An outer coating layer covers at least a portion of an outer surface of the particles of the anode active material layer. The outer coating layer comprises a solid electrolyte selected from a group consisting of a sulfide-based solid electrolyte, a halide-based solid electrolyte, and a hydride-based solid electrolyte. A fibrillating binder comprises polytetrafluoroethylene (PTFE).

[0010] For other features, the load on the anode active material layer is in the range of 4 mAh / cm2 up to 30 mAh / cm 2 The thickness of the anode active material layer ranges from 10 µm to 200 µm. The solid electrolyte comprises a sulfidic solid electrolyte. The sulfidic solid electrolyte is selected from a group consisting of pseudobinary sulfide, pseudoternary sulfide, and pseudoquaternary sulfide. The anode active material layer comprises 70 wt% to 98 wt% of the anode active material layer, the solid electrolyte comprises 2 wt% to 30 wt% of the anode active material layer, and the fibrillating binder comprises 0.1 wt% to 5 wt% of the anode active material layer.

[0011] Also not described in the invention is a method for producing an anode electrode for a battery cell, which comprises mixing and grinding a premixture comprising particles of an anode active material selected from a group consisting of silicon, a silicon alloy, and silicon / silicon oxide, and particles of a solid electrolyte selected from a group consisting of a sulfide-based solid electrolyte, a halide-based solid electrolyte, and a hydride-based solid electrolyte. The particles of the solid electrolyte at least partially coat the particles of the anode active material.The method comprises adding a fibrillating binder to the premix, mixing and shearing the premix to produce fibrils of the fibrillating binder and a mixture for an anode active material layer, and pressing the mixture to produce a free-standing anode active material layer or pouring the mixture onto an anode current collector to form the anode active material layer of the anode electrode.

[0012] In other features, the solid electrolyte consists of a sulfidic solid electrolyte. The sulfidic solid electrolyte is selected from a group consisting of pseudobinary sulfide, pseudoternary sulfide, and pseudoquaternary sulfide. The anode active material layer comprises 70 wt% to 98 wt% of the anode active material layer, the solid electrolyte comprises 2 wt% to 30 wt% of the anode active material layer, and the fibrillating binder comprises 0.1 wt% to 5 wt% of the anode active material layer.

[0013] Further areas of applicability of the present disclosure will become apparent from the detailed description, claims, and drawings. The detailed description and specific examples are for illustrative purposes only and are not intended to limit the scope of the disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The present disclosure will be more fully understood from the detailed description and the accompanying drawings, in which: Fig. 1 shows an example of a solid-state battery cell with anode electrodes, cathode electrodes and separators according to the present disclosure in a cross-sectional side view, Fig. 2 shows an example of a cathode electrode according to the present disclosure in a cross-sectional side view, Fig. 3A shows an example of an anode electrode according to the present disclosure before forming in a cross-sectional side view, Fig. 3B the anode electrode of Fig. 3A according to the present disclosure after forming in a cross-sectional side view, Fig. 3C and Fig. 3D show various examples of the morphology of particles of the anode active material according to the present disclosure, each in a cross-sectional side view, Fig. 4 shows a flowchart of an example of a method for manufacturing a cathode electrode according to the present disclosure, Fig. 5 shows a scanning electron micrograph of an example of an anode electrode with silicon active material and a fibrillating binder, Fig. 6 shows a scanning electron micrograph of an example of an anode electrode with silicon active material coated with a sulfidic solid electrolyte and a fibrillating binder according to the present disclosure, Fig. 7 shows a graph illustrating the voltage versus specific capacitance for a conventional anode electrode and an anode electrode with silicon active material coated with a solid electrolyte and a fibrillating binder according to the present disclosure, and Fig. 8 shows a graph illustrating capacity versus cycles for a conventional anode electrode and an anode electrode with silicon active material coated with a solid electrolyte and a fibrillating binder according to the present disclosure.

[0015] Reference symbols may be reused in the drawings to identify similar and / or identical elements. DETAILED DESCRIPTION

[0016] Although battery cells according to the present disclosure are shown in the context of electric vehicles, the battery cells may also be used in stationary applications and / or other applications.

[0017] A dry manufacturing process can be used to manufacture anode electrodes. Unlike wet processes, dry processes do not use solvents, and neither production equipment nor floor space for a drying phase are required. Silicon anode electrodes manufactured using the dry process, for example, comprise a layer of anode active material disposed on an anode current collector. The anode active material comprises silicon particles that are mixed / sheared with a fibrillating binder such as PTFE, cast onto an anode current collector, and calendered (or fabricated as a free-standing film on a removable substrate and laminated onto an anode current collector). However, the use of the PTFE binder reduces the performance of the anode electrode due to side reactions. The side reactions between the Li xSi compounds and the PTFE binder resulted in a high reversible capacity and a low initial coulombic efficiency (e.g., 15% to 20% reduction compared to silicon powder without a binder). The side reaction is as follows: 2nLixSi+x[−CF2−]n(PTFE)→2nx LiF+2nSi+nx C(amorphous) In particular, the side reaction between the Li x Si compounds and the PTFE binder consume active lithium in the anode electrode, which reduces the performance of the battery cell. The side reaction occurs not only at the contact points between the Li x Si compounds and the PTFE binder. The PTFE binder is completely reduced in the solid-state battery due to the expansion of the electrodes. It should be noted that the side reactions should be significantly reduced or prevented to enable dry-film silicon anodes.

[0018] An anode electrode according to the present disclosure is prepared by coating particles of anode active material (e.g., silicon) with a solid electrolyte (e.g., a sulfide solid electrolyte). For example, the particles of the anode active material and the solid electrolyte are premixed and ground to coat the active material with the solid electrolyte. The coated anode active material is then mixed / sheared with a fibrillating binder (e.g., PTFE) to create fibrils. The mixture is pressed and calendered to form the anode active material layer as a flexible, continuous dry film (or cast directly onto the anode current collector). When cast as a free-standing film, the anode active material layer is laminated to an anode current collector.

[0019] The solid electrolyte coating inhibits Li xSi / PTFE side reactions and increases the favorable transport of lithium ions in the anode electrode. As a result, the anode electrodes deliver high initial coulombic efficiency and high initial discharge capacity with stable cell cycling.

[0020] With reference now to Fig. 1, a battery cell 10 comprises C cathode electrodes 20, A anode electrodes 40, and S separators 32 arranged in a predetermined order in a battery cell stack 12, where C, S, and A are integers greater than zero. The battery cell stack 12 is arranged in a housing 50. The C cathode electrodes 20-1, 20-2, ..., and 20-C include cathode active material layers 24 arranged on one or both sides of a cathode current collector 26.

[0021] The A-anode electrodes 40-1, 40-2, ..., and 40-A comprise anode active material layers 42 arranged on one or both sides of the anode current collectors 46. During charging / discharging, the A-anode electrodes 40 and the C-cathode electrodes 20 exchange lithium ions.

[0022] In some examples, the cathode current collector 26 and / or the anode current collector 46 comprise metal foil, metal mesh, perforated metal, three-dimensional metal foam (3D metal foam), and / or expanded metal. In some examples, the current collectors are made from one or more materials selected from the group consisting of copper, stainless steel, brass, bronze, zinc, aluminum, and / or alloys thereof. The outer tabs 28 and 48 are connected to the current collectors of the cathode electrodes and anode electrodes, respectively, and can be disposed on the same or different sides of the battery cell stack 12. The outer tabs 28 and 48 are connected to the terminals of the battery cells.

[0023] With reference now to Fig. 2, one of the C cathode electrodes 20 is shown in more detail prior to formation. The cathode active material layer 24 of the C cathode electrodes 20 comprises a mixture of cathode active material 52 and a sulfide solid electrolyte 54. In some examples, the cathode material layer 24 further comprises a fibrillating binder and / or a conductive filler (neither shown).

[0024] With reference now to Fig. 3A shows one of the anode electrodes 40 prior to formation (lithiation of the silicon) in more detail. The anode active material layer 42 of the anode electrode 40 comprises the anode active material 62. The anode active material 62 is selected from a group consisting of silicon, a silicon alloy (e.g., a lithium alloy metal such as aluminum (Al), tin (Sn), magnesium (Mg), etc.), and silicon / silicon oxide (Si / SiO x). According to the invention, the anode active material comprises a silicon alloy with a lithium alloy metal, wherein the lithium alloy metal is selected from a group consisting of aluminum (Al), tin (Sn), and magnesium (Mg). Particles of the anode active material 62 are mixed with the solid electrolyte and ground to partially or completely coat an outer surface of the anode active material particles with a solid electrolyte 64 (e.g., sulfide). The coated anode active material is mixed / sheared with a fibrillating binder 66 prior to calendering.

[0025] In some examples, the fibrillating binder comprises polytetrafluoroethylene (PTFE). In some examples, the fibrillating binder has a particle size in a range of 100 µm to 800 µm. In some examples, the fibrillating binder has a particle size in a range of 300 µm to 700 µm. In some examples, the weight ratio between the fibrillating binder and the anode active material layer is in a range of 0.01:100 to 20:100 (e.g., 0.05:100). In some examples, the softening point of the fibrillating binder is in a range of 270 to 380°C. In some examples, the molecular weight of the fibrillating binder is in a range of 105 g / mol to 109 g / mol. In some examples, water is completely removed before use.

[0026] In Fig. 3B shows one of the A anode electrodes 40 in more detail after formation. After formation, the A anode electrodes 40 comprise lithiated anode active material (e.g., Li x Si), which fuses together under pressure, as shown at 68. The fibrils of the fibrillating binder 66 are largely encapsulated in the solid electrolyte 64.

[0027] In Fig. 3C, the solid electrolyte 64 may have a continuous morphology on an outer surface of the particles of the anode active material 62. In Fig. 3D, the solid electrolyte 64 may exhibit a discontinuous morphology on an outer surface of the particles of the anode active material 62. It should be noted that, due to the fact that the fibrillating binder tends to adhere to the solid electrolyte 64, the coating does not need to completely cover the anode active material to significantly reduce side reactions.

[0028] The dry film process described herein eliminates the use of organic solvents and simplifies the electrode fabrication process by eliminating the conventional drying step. The solvent-free dry film process circumvents the influence of the solvent on Li-ion conduction in the solid-state electrolyte and enables good electrochemical performance for a high-energy anode electrode.

[0029] In some examples, the anode active material layer 42 comprises the anode active material, the sulfidic solid electrolyte (coating the anode active material), and the fibrillating binder. In some examples, the anode active material comprises 70 wt.% to 98 wt.% of the anode active material layer, the solid electrolyte comprises 2 wt.% to 30 wt.% of the anode active material layer, and the fibrillating binder comprises 0.1 wt.% to 5 wt.% of the anode active material layer (e.g., with a weight percent ratio of 70:29:1). In some examples, the loading of the anode active material layer is in a range of 4 mAh / cm 2 up to 30 mAh / cm 2 In some examples, the thickness of the anode active material layer ranges from 10 µm to 200 µm.

[0030] In some examples, the solid electrolyte has low electronic conductivity and high Li-ion conductivity to prevent side reactions. The solid electrolyte provides a rough / deformable surface that promotes fibrillation of the binder. The solid electrolyte coating blocks side reactions between Li x Si and PTFE by encapsulating the PTFE in the solid electrolyte. The solid electrolyte creates a favorable transport of lithium ions in the lithiated silicon (Li x Si). The particles of the anode active material provide high capacitance and expand to form a compact anode electrode. The fibrils of the binder adhere the particles together like a "spider web" and form the dry film.

[0031] With reference now to Fig. 4 shows a flowchart for an example of a method for manufacturing a cathode electrode. At 110, particles of the anode active material (e.g., silicon) and particles of the solid electrolyte (e.g., a sulfide solid electrolyte) are premixed and ground to coat the active material particles. At 114, a fibrillating binder such as PTFE is added to the mixture. At 118, the mixture is mixed and sheared to fibrillate the fibrillating binder and create fibrils. At 122, the mixture forming the anode active material layer is pressed and / or heated to form a dry film. At 126, the anode active material layer is laminated to an anode current collector. Alternatively, the active material layer can be cast directly onto an anode current collector, and steps 122 and 126 can be omitted.

[0032] With reference now to Fig. 5 and Fig. 6 shows scanning electron micrographs of a conventional anode electrode (at 310) and an anode electrode according to the present disclosure (at 314). Fig. 5, the conventional anode electrode comprises 99 wt.% silicon active material (which is not coated with the sulfide solid electrolyte) and 1 wt.% fibrillating binder. Since the outer surface of the silicon particles is relatively smooth and hard, there is less fibrillation of the binder compared to Fig. 6.

[0033] In Fig. 6, an anode electrode comprising silicon active material (e.g., 70 wt%) is coated with a sulfidic solid electrolyte (e.g., 29 wt%) and mixed / sheared with a fibrillating binder (e.g., 1 wt%). The silicon particles are partially or completely coated with a solid electrolyte (e.g., a sulfidic solid electrolyte). As in Fig. As can be seen in Figure 6, the sulfide solid electrolyte with the deformable surface provides more adhesion sites for the formation of more fibrils in the dry film electrode. The PTFE fibrils bond between the solid electrolyte and form the dry film.

[0034] With reference now to Fig. 7 and Fig. 8, the performance of the anode electrode with the silicon active material coated with a sulfide solid electrolyte and the fibrillating binder exceeds the conventional anode electrode. Fig. 7, the performance of the coated anode electrode (at 314) in the first cycle (e.g., at 0.1C and room temperature) is compared with the conventional anode (at 310). Fig. Figure 8 shows the capacity as a function of cycles.

[0035] In some examples, the solid electrolyte is selected from a group consisting of a sulfide-based solid electrolyte, a halide-based solid electrolyte, a hydride-based solid electrolyte, and other solid electrolytes that exhibit low grain boundary resistance. In some examples, the sulfidic solid electrolyte is selected from a group consisting of pseudobinary sulfide, pseudoternary sulfide, and pseudoquaternary sulfide. Examples of a halide-based solid electrolyte include Li3YCl6, Li3InCl6, Li3YBr6, LiI1, Li2CdCl4, Li2MgCl4, Li2CdI4, Li2ZnI4, Li3OCl, and combinations thereof. Examples of a hydride-based solid electrolyte include LiBH4, LiBH4-LiX (where X = chlorine (Cl), bromine (Br) or iodine (I)), LiNH2, Li2NH, LiBH4-LiNH2, Li3AlH6 and combinations thereof.

[0036] Examples of pseudobinary sulfides include the Li2S-P2S5 system (Li3PS4, Li7P3S 11 and Li9,6 P3S 12 ), the Li2S-SnS2 system (Li4SnS4), the Li2S-SiS2 system, the Li2S-GeS2 system, the Li2S-B2S3 system, the Li2S-Ga2S3 system, the Li2S-P2S3 system, and the Li2S-Al2S3 system. Examples of pseudoternary sulfides include the Li2O-Li2S-P2S5 system, the Li2S-P2S5-P2O5 system, the Li2S-P2S5-GeS2 system (Li 3,25 Ge 0,25 P 0,75 S4 and Li 10 GeP2S 12 ), the Li2S-P2S5-LiX system (X = F, Cl, Br, I) (Li6PS5Br, Li6PS5Cl, L7P2S8I and Li4PS4I), the Li2S-As2S5-SnS2 system (Li 3,833 Sn 0,833 Ace 0,166 S4), the Li2S-P2S5-Al2S3 system, the Li2S-LiX-SiS2 system (X = F, Cl, Br, I), 0.4Lil·0.6Li4SnS4, the Li 11 Si2PS 12 and combinations thereof.

[0037] Examples of pseudoquaternary sulfides include the Li2O-Li2S-P2S5-P2O5 system, Li 9,54 Si 1,74 P 1,44 S 11,7 Cl 0,3 , Li7P 2,9 Mn 0,1 S 10,7 I 0,3 and Li 10,35 [Sn0,27 Si 1,08 ]P 1,65 S 12 Examples of a halide-based solid electrolyte include Li3YCl6, Li3InCl6, Li3YBr6, LiIl, Li2CdCl4, Li2MgCl4, Li2CdI4, Li2ZnI4, Li3OCl, and combinations thereof.

[0038] Spatial and functional relationships between elements (e.g., between modules, circuit elements, semiconductor layers, etc.) are described using various terms, including "connected," "engaging," "coupled," "adjacent," "beside," "on top of," "over," "below," and "disposed." If a relationship between first and second elements is not explicitly described as "direct" in the above disclosure, that relationship may be a direct relationship, with no other intervening elements between the first and second elements, or an indirect relationship, with one or more intervening elements (either spatial or functional) between the first and second elements.As used herein, the term “A, B and / or C” should be construed as logical (A ORed with B ORed with C) using a non-exclusive logical OR and should not be understood as “at least one of A, at least one of B and at least one of C”.

[0039] In the figures, the direction of an arrow, as indicated by the arrowhead, generally illustrates the flow of information (e.g., data or instructions) of interest to the illustration. For example, if element A and element B exchange a lot of information, but the information passed from element A to element B is relevant to the illustration, the arrow may point from element A to element B. This unidirectional arrow does not imply that no other information is passed from element B to element A. Furthermore, for information being sent from element A to element B, element B may send requests for or acknowledgments of receipt of the information to element A.

Claims

[1] Anode electrode for a battery cell, comprising: an anode active material layer, comprising: an anode active material, an outer coating layer that covers at least part of an outer surface of the particles of the anode active material layer, wherein the outer coating layer comprises a solid electrolyte, and a fibrillating binder, wherein the anode active material comprises a silicon alloy with a lithium alloy metal, and wherein the lithium alloy metal is selected from a group consisting of aluminium (Al), tin (Sn) and magnesium (Mg). [2] Anode electrode according to claim 1, wherein the anode active material layer is arranged on an anode current collector. [3] Anode electrode according to claim 1, wherein the fibrillating binder comprises polytetrafluoroethylene (PTFE). [4] Anode electrode according to claim 1, wherein the softening point of the fibrillating binder is in a range of 270 °C to 380 °C. [5] Anode electrode according to claim 1, wherein the molecular weight of the fibrillating binder is in the range of 105 g / mol to 109 g / mol. [6] Anode electrode according to claim 1, wherein the load on the anode active material layer is in the range of 4 mAh / cm² 2 up to 30 mAh / cm 2 lies. [7] Anode electrode according to claim 1, wherein the thickness of the anode active material layer is in a range of 10 µm to 200 µm. [8] Anode electrode according to claim 1, wherein the solid electrolyte is selected from a group consisting of a sulfide-based solid electrolyte, a halide-based solid electrolyte and a hydride-based solid electrolyte. [9] Anode electrode according to claim 1, wherein the solid electrolyte comprises a sulfide solid electrolyte.

Images