WET COATING METHOD FOR PRODUCING SOLID BATTERY CELLS WITH A THERMOPLASTIC ELASTOMER BINDER

Abstract

A battery cell comprises A anode electrodes, each consisting of a layer of active anode material and an anode current collector; C cathode electrodes, each consisting of a layer of active cathode material and a cathode current collector; and S separators, where A, C, and S are integers greater than one. At least one of the active anode material layers of the A anode electrodes, the active cathode material layer of the C cathode electrodes, and the S separators comprise a thermoplastic binder.

Description

INTRODUCTION

[0001] The information provided in this section is intended to provide a general context for the disclosure. Work by the inventors identified herein, to the extent described in this section, as well as aspects of the description that may not be prior art at the time of filing, are neither expressly nor impliedly acknowledged as prior art over the present disclosure.

[0002] The present disclosure relates to solid-state battery cells and, more particularly, to a wet coating process for making solid-state battery cells with a thermoplastic elastomer binder.

[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, modules, and / or packs. A power control system is used to control the charging and / or discharging of the battery system during charging and / or driving. SUMMARY

[0004] A battery cell comprises A anode electrodes, each comprising a layer of active anode material and an anode current collector, C cathode electrodes, each comprising a layer of active cathode material and a cathode current collector, and S separators, where A, C, and S are integers greater than one. At least one of the layers of active anode material of the A anode electrodes, the layer of active cathode material of the C cathode electrodes, and the S separators comprise a thermoplastic binder.

[0005] In other features, the active cathode material layer of the C cathode electrodes comprises the active cathode material comprising 50 to 98 wt.% of the active cathode material layer and the thermoplastic binder comprising 1 to 20 wt.% of the active cathode material layer.

[0006] In other features, the active cathode material layer of the C cathode electrodes comprises at least a solid electrolyte and a conductive additive. The solid electrolyte comprises 1 to 50 wt.% of the active cathode material layer. The conductive additive comprises 0.1 to 8 wt.% of the active cathode material layer. The thermoplastic binder comprises 1 wt.% to 20 wt.% of the active cathode material layer.

[0007] In other features, the active cathode material is selected from a group consisting of rock salt layered oxides, spinel, polyanion, lithium transition metal oxides, surface-coated and / or doped cathode materials, and combinations thereof. The thermoplastic binder comprises polystyrene, including block copolymers, with a polystyrene content in the range of 10% to 70%. The thermoplastic binder is selected from the group consisting of styrene-ethylene-propylene (SEP), styrene-butadiene-styrene (SBS), styrene-ethylene / propylene-styrene (SEPS), ethylene-branched SEPS, ethylene-branched styrene-isoprene-styrene (SIS), styrene-[ethylene-(ethylene-propylene)]-styrene (SEEPS), styrene-ethylene-butylene-styrene (SEBS), ethylene-branched SEEPS and SEEPS with hydroxyl groups (SEEPS-OH).

[0008] In other features, the active anode material layer of the A-anode electrodes comprises the active anode material comprising 50 to 98 wt.% of the active anode material layer and the thermoplastic binder comprising 1 wt.% to 20 wt.% of the active anode material layer.

[0009] In other features, the active anode material layer of the A-anode electrodes comprises at least a solid electrolyte and a conductive additive. The solid electrolyte comprises 1 wt.% to 50 wt.% of the active anode material layer. The conductive additive comprises 0.1 wt.% to 8 wt.% of the active anode material layer. The thermoplastic binder comprises 1 wt.% to 20 wt.% of the active anode material layer. The active anode material is selected from a group consisting of a silicon-based material, a carbonaceous material, and a metal oxide, and combinations thereof.

[0010] In other features, 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.

[0011] Other features include S-separators comprising a solid electrolyte and a thermoplastic binder.

[0012] A method of manufacturing an electrode for an all-solid-state battery comprises mixing a thermoplastic binder, a solvent, and an active material to form a slurry; and applying the slurry to a current collector and drying the slurry to form an active material layer of an electrode.

[0013] In other features, the solvent has a polarity number in the range of 0.1 to 6.5. The active material comprises 50 to 98 wt.% of the active material layer, and the thermoplastic binder comprises 1 wt.% to 20 wt.% of the active material layer. The method includes adding a solid electrolyte and / or a conductive additive to the slurry prior to coating.

[0014] In further features, the thermoplastic binder is selected from the group consisting of styrene-ethylene-propylene (SEP), styrene-butadiene-styrene (SBS), styrene-ethylene-propylene-styrene (SEPS), ethylene-branched SEPS, ethylene-branched styrene-isoprene-styrene (SIS), styrene-[ethylene-(ethylene-propylene)]-styrene (SEEPS), styrene-ethylene-butylene-styrene (SEBS), ethylene-branched SEEPS and SEEPS with hydroxyl groups (SEEPS-OH).

[0015] A method for forming an electrolyte layer on a substrate comprises mixing a thermoplastic binder and a solvent to form a solution, and creating a slurry by adding a solid electrolyte to the solution. 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 method comprises applying the slurry to a film or layer of active material of an electrode and drying the slurry.

[0016] In other features, the solvent has a polarity number in the range of 0.1 to 6.5. The thermoplastic binder comprises 1 to 20 wt.% of the electrolyte layer. The solid electrolyte comprises 80 wt.% to 99 wt.% of the electrolyte layer.

[0017] In further features, the thermoplastic binder is selected from the group consisting of styrene-ethylene-propylene (SEP), styrene-butadiene-styrene (SBS), styrene-ethylene-propylene-styrene (SEPS), ethylene-branched SEPS, ethylene-branched styrene-isoprene-styrene (SIS), styrene-[ethylene-(ethylene-propylene)]-styrene (SEEPS), styrene-ethylene-butylene-styrene (SEBS), ethylene-branched SEEPS and SEEPS with hydroxyl groups (SEEPS-OH).

[0018] 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 provided for illustrative purposes only and are not intended to limit the scope of the disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The present disclosure will become more fully understood from the detailed description and the accompanying drawings, in which: Fig. 1 is a side cross-sectional view of an example of a solid-state battery cell having cathode electrodes, anode electrodes, and separators disposed within a battery cell casing according to the present disclosure; Fig. 2 is a more detailed side cross-sectional view of an example of the solid-state battery cell with cathode electrodes, anode electrodes, and separators disposed in a battery cell casing according to the present disclosure; Fig. 3 is a flow diagram of a method of making an electrode for a solid-state battery cell comprising a thermoplastic elastomer binder according to the present disclosure; Fig. 4 is a flow diagram of a method for making an electrolyte film for a solid-state battery cell comprising a thermoplastic elastomer binder according to the present disclosure; Fig. 5 is a flow diagram of a method for making a composite electrode for a solid-state battery cell comprising a thermoplastic elastomer binder according to the present disclosure; and Fig. 6 is a graph illustrating an example of discharge maintenance as a function of cycles for a solid-state battery cell employing a thermoplastic elastomer binder in accordance with the present disclosure.

[0020] Reference symbols may be reused in the drawings to identify similar and / or identical elements. DETAILED DESCRIPTION

[0021] Although the solid-state battery cells according to the present disclosure are shown in the context of electric vehicles, the solid-state battery cells may be used in stationary applications and / or other applications.

[0022] There are different ways to manufacture electrodes and / or separators for battery cells. For example, some battery cells can be manufactured by dry-pressing a powder mixture with a solid electrolyte (SE) (e.g., a sulfide-based SE (S-SE)) onto other layers such as an electrode or foil. Other examples use a dry fibrillation process, which pressed / cut a dry powder mixture and used a binder such as PTFE. Other examples use a wet coating process, which mixes an active material, a solid electrolyte, a binder, a conductive filler, and / or a solvent to form a slurry, and the slurry is applied to a current collector.

[0023] The wet coating process is likely the most promising method for scaling the production of battery cells with solid sulfide-based electrodes (S-SEs). When using S-SEs, according to the present disclosure, a low-polarity solvent compatible with the S-SEs is used. However, current binders (e.g., polyvinylidene difluoride (PVDF) and styrene-butadiene rubber (SBR)) are not soluble in low-polarity solvents.

[0024] The present disclosure relates to a method for manufacturing SSB using a wet coating process and a thermoplastic elastomer binder. The thermoplastic binder creates a strong bond between the active material particles and the surface of the current collector. For example, an NCM-Si battery cell manufactured using the method described below exhibits high capacity retention after cycling (e.g., -76.12% capacity retention after 500 cycles at 0.5°C and room temperature).

[0025] With reference now to Fig. 1, a solid-state 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 within a housing 50, where C, S, and A are integers greater than zero. The C cathode electrodes 20-1, 20-2, ..., and 20-C comprise layers of active cathode material 24 disposed on one or both sides of the cathode current collectors 26. The A anode electrodes 40-1, 40-2, ..., and 40-A comprise layers of active anode material 42 disposed on one or both sides of the anode current collectors 46.

[0026] In some examples, the layers of active anode material 42 and / or the layers of active cathode material 24 are freestanding electrodes disposed adjacent to (or attached to) the cathode current collectors 26 and / or the anode current collectors 46. In some examples, the layers of active anode material 42 and / or the layers of active cathode material 24 include coatings with one or more active materials, one or more conductive fillers / additives, and / or one or more binders applied to the current collectors.

[0027] In some examples, the cathode current collectors 26 and / or the anode current collectors 46 are formed from metal foil, metal mesh, or expanded metal. In some examples, the cathode current collectors 26 and / or the anode current collectors 46 are formed from one or more materials selected from a group consisting of copper, stainless steel, brass, bronze, zinc, aluminum, and / or their alloys. The outer tabs 28 and 48 connected to the current collectors of the cathode and anode electrodes, respectively, can be arranged on the same or opposite sides of the battery stack 12. The outer tabs 28 and 48 are connected to the terminals of the battery cells.

[0028] With reference now to the Fig. 2 shows an example of the solid-state battery cell. At least one of the anode electrode, the cathode electrode, and the separator is made with a thermoplastic binder. The active cathode material layer 24 includes active cathode material 110, a thermoplastic binder 114 (optional), and a solid electrolyte 112 (optional). The S-separators 32 include a solid electrolyte 120 and a thermoplastic binder 124 (optional). The active anode material layer 42 includes an active anode material 130, a solid electrolyte 132 (optional), and a thermoplastic binder 134 (optional). While the cathode electrodes 20, the anode electrodes 40 and the separators 32 are shown with the thermoplastic binder, one or more of the cathode electrodes 20, the anode electrodes 40 and / or the separators 32 comprise the thermoplastic binder (in any combination).

[0029] With reference now to Fig. 3 shows a method 300 for manufacturing a cathode electrode. At 310, a binder and a solvent are mixed to form solution A. At 314, a solid electrolyte and / or a conductive additive are optionally added to solution A to form suspension B. At 322, an active material is added to suspension B to form a slurry. At 326, the slurry is applied to the surface of the current collector and dried to form an active material layer of the electrode.

[0030] The electrode layer comprises, for example, electrode active material, a solid electrolyte, a conductive additive, and a thermoplastic binder. In some examples, the electrode active material comprises 50 wt. % to 98 wt. % of the active material layer. In some examples, the electrode active material comprises 70 wt. % to 98 wt. % of the active material layer. In some examples, the solid electrolyte comprises 1 wt. % to 50 wt. % of the active material layer. In some examples, the solid electrolyte comprises 1 wt. % to 30 wt. % of the active material layer. In some examples, the conductive additive comprises 0.1 wt. % to 8 wt. % of the active material layer. In some examples, the thermoplastic binder comprises 1 wt. % to 20 wt. %. In some examples, the thermoplastic binder comprises 1 wt. % to 10 wt. % of the active material layer. In some examples, the thermoplastic binder comprises 2 wt. % to 5 wt.-% of the active material layer.

[0031] In some examples, the slurry comprises a low-polarity solvent, the solid electrolyte, and the active electrode material (in the same proportions as the electrode layer). In some examples, the solids content of the slurry ranges between 20% and 75%. In some examples, the solids content of the slurry ranges between 30% and 50%.

[0032] In some examples, the low-polarity solvent has a polarity number ranging from 0.1 to 6.5. The polarity of a solvent is determined by its dielectric constant, which is a measure of its ability to separate positive and negative charges. Solvents with a dielectric constant greater than 5 are considered "polar," while those with a dielectric constant less than 5 are called "nonpolar." Polar solvents generally dissolve other polar substances because they carry a positive and a negative charge that attract the opposite charges of the polar substance. When a solid molecule is placed in a polar solvent, it can dissolve if it has its own polarity. In some examples, the low-polarity solvents include at least one of anisole, para-xylene, tetrahydrofuran (THF), heptane, ethyl propionate, methyl propionate, etc.

[0033] For cathode electrodes, the active cathode material is selected from a group consisting of rock-salt layered oxides, spinel, polyanion, lithium transition metal oxides, surface-coated and / or doped cathode materials, and / or low-voltage materials. Examples of rock-salt layered oxides include LiCoO2, LiNi x Mn y Co 1-x-y O2, LiNi x MnyAl 1-x-y O2, LiNi x Mn 1-x O2,Li 1+x MO2. Examples of spinel include LiMn2O4, LiNi 0,5 Mn 1,5 O4. Examples of polyanion cathodes include (LiV2(PO 4)3 ).

[0034] Examples of surface-coated and / or doped cathode materials include LiNbO3-coated LiMn2O4,Li2ZrO 3- or Li3PO4-coated LiNi x Mn y Co 1-x-y O2 and Al-doped LiMn2O4. Examples of low-voltage materials include lithiated metal oxide / sulfide (e.g., LiTiS2), Li2S, and sulfur.

[0035] For anode electrodes, the active anode material is selected from a group consisting of a silicon-based material, a carbonaceous material, and a metal oxide. Examples of silicon-based materials include Si, SiO x ,LiSiO x , Si / C,SiO x / C and LiSiO x / C. Examples of carbonaceous materials include graphite, hard carbon, soft carbon, etc. Examples of metal oxides include tin oxide (SnO2), iron oxide (Fe3O4), etc.

[0036] In some examples, the thermoplastic binder comprises polystyrene-containing block copolymers, wherein the polystyrene content ranges from 10% to 70% of the thermoplastic binder. In some examples, the thermoplastic binder comprises polystyrene-containing block copolymers, wherein the polystyrene content ranges from 30% to 45% of the thermoplastic binder.

[0037] Examples of thermoplastic binders include block copolymers and random block copolymers. Examples of block copolymers include styrene-ethylene-propylene (SEP), styrene-butadiene-styrene (SBS), styrene-ethylene-propylene-styrene (SEPS), ethylene-branched SEPS, and ethylene-branched styrene-isoprene-styrene (SIS). Examples of random block copolymers include styrene-[ethylene-(ethylene-propylene)]-styrene (SEEPS), styrene-ethylene-butylene-styrene (SEBS), ethylene-branched SEEPS, and SEEPS with hydroxyl groups (SEEPS-OH).

[0038] In some examples, the solid electrolyte comprises a sulfide-based solid electrolyte, a halide-based solid electrolyte, a hydride-based solid electrolyte, or another low grain boundary resistance solid electrolyte.

[0039] In some examples, the solid electrolyte is selected from a group consisting of pseudobinary sulfide, pseudoternary sulfide, and pseudoquaternary sulfide. Examples of pseudobinary sulfides include the Li2S-P2S5 system (Li3PS4, Li7P3S 11 and Li 9.6 P3S 12 ), Li2S-SnS2 system (Li4SnS4), the Li2S-SiS2 system, Li2S-GeS2 system, Li2S-B2S3 system, Li2S-Ga2S3 system, Li2S-P2S3 system and the Li2S-Al2S3 system.

[0040] Examples of pseudoternary sulfides include the Li2O-Li2S-P2S5 system, the Li2S-P2S S -P2O5 system, the Li2S-P2S5-GeS2 system (Li 3.25 Ge 0.25 P 0.75 S4 and Li 10 GeP2S 12 ),Li2S-P2S5-LiX(X = F,Cl,Br,I) system (Li6PS5Br,Li6PS5Cl,L7P2S8I and Li4PS4I),Li2S-As2S5-SnS2 system (Li 3.833 Sn 0.833 Ace 0.166 S4),Li2S-P2S5-Al2S3 system,Li2S-LiX-SiS2 (X = F, Cl, Br, I) system, 0.4LiI- 0.6 Li4SnS4 and Li 11 Si2PS 12Examples of pseudoquaternary sulfides include Li2O-Li2S-P2S5-P2O5, Li 9.54 Si 1.74 P 1.44 S 11 .7Cl 0.3 ,Li7P 2.9 Mn 0.1 S 10 .7I 0.3 and Li 10.35 [Sn 0.27 Si 1.08 ]P 1.65 S 12 .

[0041] Examples of halide-based solid electrolytes include Li3YCl6, Li3InCl6, Li3YBr6, LiI1, Li2CdCl4, Li2MgCl4, Li2CdI4, Li2ZnI4, and Li3OCl. Examples of hydride-based solid electrolytes include LiBH4, LiBH4-LiX (X = Cl, Br, or I), LiNH2, Li2NH, LiBH4-LiNH2, and Li3AlH6.

[0042] With reference now to Fig. 4 shows a method 400 for manufacturing an electrolyte foil. At 410, a thermoplastic binder and a solvent are combined to form a solution C. At 414, a solid electrolyte is added to the solution C to form a suspension D (corresponding to a slurry). At 418, the slurry is applied to the surface of the foil to form an electrolyte foil.

[0043] With reference now to Fig. 5 shows a method 500 for manufacturing an electrolyte foil. At 510, a thermoplastic binder and a solvent are combined to form a solution E. At 514, a solid electrolyte is added to the solution E to form a suspension F (corresponding to a slurry). At 418, the slurry is applied to the surface of the current collector to form a composite electrode.

[0044] The solid electrolyte layer comprises the solid electrolyte and the thermoplastic binder. The solid electrolyte comprises 80 wt% to 100 wt%. In some examples, the solid electrolyte comprises 90 wt% to 100 wt%. In some examples, the thermoplastic binder comprises 1 wt% to 20 wt%, if used. In some examples, the thermoplastic binder comprises 1 wt% to 10 wt%. In some examples, the thermoplastic binder comprises 2 wt% to 8 wt%.

[0045] In some examples, the electrolyte layer has a thickness in a range of 10 µm to 300 µm. In some examples, the electrolyte layer has a thickness in a range of 10 µm to 50 µm. In some examples, the electrolyte layer has a porosity in a range of 3% to 50% before condensation. In some examples, the electrolyte layer has a porosity in a range of 3% to 20% before condensation. In some examples, the slurry has a solids content in a range of 20% to 70% (e.g., and a solvent in a range of 30% to 75%). In some examples, the slurry has a solids content in a range of 30% to 50% (e.g., and a solvent in a range of 50% to 70%).

[0046] With reference now to Fig.Figure 6 shows capacity retention as a function of cycling. A battery cell comprises a silicon anode with a solid lithium phosphorus sulfide chloride (LPSCI) electrolyte and a thermoplastic binder. The cathode electrodes comprise a solid NMC, LPSCI electrolyte, and a conductive filler (Super P). The solid electrolyte layer comprises LPSCI pellets. The N / P ratio of the battery cell is approximately 2.5 (referring to the capacity ratio between the negative and positive electrodes). The thermoplastic binder, solid electrolyte, and Si powder were added sequentially to a solvent, with sufficient mixing and stirring between each step to obtain a mixed slurry. The slurry was applied to an anode current collector.The thermoplastic binder provides strong bonding between the Si nanoparticles and between the Si nanoparticles and the copper foil, contributing to the consistent cycling of the NCM-Si battery cells. As can be seen, the capacity retention is relatively high over a large number of cycles (e.g., -76.12% capacity retention after 500 cycles at 0.5 °C, room temperature).

[0047] The foregoing description is merely illustrative and is in no way intended to limit the disclosure, its application, or uses. The broad teachings of the disclosure may be embodied in a variety of forms. Although this disclosure contains specific examples, the true scope of the disclosure should not be so limited since other modifications will become apparent upon a study of the drawings, the specification, and the following claims. It is to be understood that one or more steps within a method may be performed in a different order (or simultaneously) without changing the principles of the present disclosure.Although each of the embodiments described above includes certain features, one or more of those features described with respect to any embodiment of the disclosure may be implemented in any other embodiment and / or combined with features of any other embodiment, even if that combination is not explicitly described. In other words, the described embodiments are not mutually exclusive, and combinations of one or more embodiments remain within the scope of this disclosure.

[0048] 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," "adjacent," "over," "above," "below," and "disposed." When a relationship between a first and a second element is not explicitly described as "direct" in the above disclosure, that relationship may be a direct relationship, where no other intervening elements are present between the first and second elements, or it may be an indirect relationship, where one or more intervening elements (either spatial or functional) are present between the first and second elements.As used herein, the phrase "at least one of A, B, and C" should be understood as logical (A OR B OR C) using a non-exclusive logical OR, and not as "at least one of A, at least one of B, and at least one of C."

[0049] In figures, the direction of an arrow, as indicated by the arrowhead, generally indicates the flow of information (e.g., data or instructions) of interest to the figure. 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 figure, 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. For information sent from element A to element B, element B may further send requests for the information to element A or acknowledge receipt of it.

Claims

[1] Battery cell, comprising: A anode electrodes, each comprising a layer of active anode material and an anode current collector; C cathode electrodes comprising a layer of active cathode material and a cathode current collector; and S separators, where A, C and S are integers greater than one, wherein at least one of the layers of active anode material of the A anode electrodes, the layer of active cathode material of the C cathode electrodes and the S separators comprises a thermoplastic binder. [2] The battery cell of claim 1, wherein the layer of active cathode material of the C cathode electrodes comprises: the active cathode material comprises 50 to 98 wt.% of the active cathode material layer, and wherein the thermoplastic binder comprises 1 wt% to 20 wt% of the layer of active cathode material. [3] The battery cell of claim 1, wherein the active cathode material layer of the C cathode electrodes comprises at least one solid electrolyte and one conductive additive. [4] Battery cell according to claim 3, wherein: the solid electrolyte comprises 1 to 50 wt.% of the layer of active cathode material, the conductive additive comprises 0.1 wt% to 8 wt% of the layer of active cathode material, and the thermoplastic binder comprises 1 wt% to 20 wt% of the layer of active cathode material. [5] The battery cell of claim 1, wherein the active cathode material is selected from a group consisting of rock salt layered oxides, spinel, polyanion, lithium transition metal oxides, surface coated and / or doped cathode materials, and combinations thereof. [6] Battery cell according to claim 1, wherein the thermoplastic binder comprises polystyrene including block copolymers and has a polystyrene ratio in the range of 10% to 70%. [7] Battery cell according to claim 6, wherein the thermoplastic binder is selected from the group consisting of styrene-ethylene-propylene (SEP), styrene-butadiene-styrene (SBS), styrene-ethylene / propylene-styrene (SEPS), ethylene-branched SEPS, ethylene-branched styrene-isoprene-styrene (SIS), styrene-[ethylene-(ethylene-propylene)]-styrene (SEEPS), styrene-ethylene-butylene-styrene (SEBS), ethylene-branched SEEPS and SEEPS with hydroxyl groups (SEEPS-OH). [8] A battery cell according to claim 1, wherein the layer of active anode material of the A anode electrodes comprises: wherein the active anode material comprises 50 to 98 wt.% of the layer of active anode material, and wherein the thermoplastic binder comprises 1 wt% to 20 wt% of the layer of active anode material. [9] A battery cell according to claim 8, wherein the layer of active anode material of the A anode electrodes comprises at least one solid electrolyte or a conductive additive. [10] Battery cell according to claim 9, wherein: the solid electrolyte comprises 1 wt% to 50 wt% of the layer of active anode material, the conductive additive comprises 0.1 wt% to 8 wt% of the layer of active anode material, and the thermoplastic binder comprises 1 wt% to 20 wt% of the layer of active anode material.

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