Aqueous graphite negative electrode amplification formulations and methods

Abstract

A negative electrode is provided. The negative electrode comprises a negative current collector and a negative active material layer arranged on the negative current collector. The anode active material layer includes an electrochemically active material, a dispersant polymer binder, an adhesive polymer binder, and a conductive filler. The electrochemically active material includes graphite. The dispersant polymer binder has amphiphilic properties, including a hydrophobic domain and a hydrophilic domain that stabilizes hydrophobic carbon in water. The adhesive polymer binder has a glass transition temperature and can provide flexibility, durability, and cohesive strength between carbon particles. The conductive filler includes a conductive carbon that reduces pore channels and charge transfer resistance at the binder active material interface.

Description

Technical Field

[0001] This disclosure relates to battery cells, and more specifically, to negative electrode electrodes formed using an aqueous negative electrode slurry. Background Technology

[0002] Electric vehicles (EVs), such as battery electric vehicles (BEVs), hybrid vehicles, and / or fuel cell vehicles, include one or more electric motors and a battery system comprising one or more battery cells, battery modules, and / or battery packs. A battery control module is used to control the charging and / or discharging of the battery system during charging and / or driving. EV manufacturers are pursuing higher power density to increase the driving range of EVs.

[0003] A battery cell includes a negative electrode, a positive electrode, and a separator arranged in a predetermined order within a casing. The negative electrode includes a negative current collector and a layer of negative active material disposed on one or both sides of the negative current collector. The negative active material layer is typically applied to the negative current collector as a slurry. However, sometimes the negative active layer material cannot be mixed well, and the slurry may not adhere satisfactorily to the negative current collector.

[0004] While existing methods and systems attempt to provide negative electrode electrodes with satisfactory electrochemical performance and achieve their specific purposes, a new and improved negative electrode is still needed. Therefore, a more efficient and higher-quality negative electrode is required. Summary of the Invention

[0005] According to several aspects of this disclosure, a negative electrode is provided. The negative electrode includes a negative current collector and a negative active material layer disposed on the negative current collector. The negative active material layer comprises an electrochemically active material, a dispersant polymer binder, an adhesive polymer binder, and a conductive filler. The electrochemically active material includes graphite. The dispersant polymer binder is amphiphilic, including hydrophobic and hydrophilic domains, the hydrophilic domains stabilizing hydrophobic carbon in water. The adhesive polymer binder has a glass transition temperature and provides flexibility, durability, and cohesive strength between carbon particles. The conductive filler includes conductive carbon, which reduces porosity and charge transfer resistance at the interface between the binder and the active material.

[0006] According to another aspect of this disclosure, the negative electrode has graphite, including at least one of natural graphite or artificial graphite.

[0007] According to another aspect of this disclosure, the negative electrode has an electrochemically active material comprising less than 10% by weight of at least one of the following: silicon (Si), silicon oxide (SiO), lithium silicon oxide (LiSiO), silicon oxide composite (SiO-c), nanostructured silicon (nano-Si), or nanocage silicon.

[0008] According to another aspect of this disclosure, the negative electrode has an electrochemically active material, which accounts for 94% to 97% by weight of the negative electrode.

[0009] According to another aspect of this disclosure, the negative electrode has a dispersant polymer binder comprising at least one of sodium carboxymethyl cellulose (CMC) or lithium carboxymethyl cellulose (CMC).

[0010] According to another aspect of this disclosure, sodium carboxymethyl cellulose (CMC) or lithium carboxymethyl cellulose (CMC) has a degree of substitution (DS) of less than 0.8.

[0011] According to another aspect of this disclosure, sodium carboxymethyl cellulose (CMC) or lithium carboxymethyl cellulose (CMC) has a molecular weight greater than 300 kilodaltons (kDa).

[0012] According to another aspect of this disclosure, sodium carboxymethyl cellulose (CMC) or lithium carboxymethyl cellulose (CMC) comprises a blend of a first CMC having a degree of substitution (DS) of at least 0.7 and a second CMC having a DS of 1.2.

[0013] According to another aspect of this disclosure, the dispersant polymer binder includes sodium polyacrylate or lithium polyacrylate.

[0014] According to another aspect of this disclosure, sodium carboxymethyl cellulose (CMC) or lithium carboxymethyl cellulose (CMC) accounts for 0.6% to 2.5% by weight of the negative electrode.

[0015] According to another aspect of this disclosure, the negative electrode has an adhesive polymer binder comprising at least one of styrene-butadiene rubber (SBR), styrene-acrylic rubber, nitrile rubber, or copolymers thereof.

[0016] According to another aspect of this disclosure, the negative electrode includes an adhesive polymer binder having a glass transition temperature of less than 20°C.

[0017] According to another aspect of this disclosure, the negative electrode includes an adhesive polymer binder, which accounts for 1.5% to 3.0% by weight of the negative electrode.

[0018] According to another aspect of this disclosure, the negative electrode has a conductive filler comprising at least one of carbon black, acetylene black, Ketjen black, carbon nanofibers, graphene, graphene nanosheets, carbon nanotubes, or combinations thereof.

[0019] According to another aspect of this disclosure, the negative electrode has a conductive filler comprising 0.3% to 1.2% by weight of the negative electrode.

[0020] According to several aspects of this disclosure, a negative electrode is provided. The negative electrode includes a negative current collector and a negative active material layer. The negative active material layer includes an electrochemically active material, a dispersant polymer binder, an adhesive polymer binder, and a conductive filler, wherein the electrochemically active material includes graphite. The dispersant polymer binder is amphiphilic, including hydrophobic and hydrophilic domains, the hydrophilic domains stabilizing hydrophobic carbon in water. The dispersant polymer includes a first carboxymethyl cellulose (CMC) with a degree of substitution (DS) of 0.7 and a second CMC with a DS of 1.2. The adhesive polymer binder has a glass transition temperature and provides flexibility, durability, and cohesive strength between carbon particles. The conductive filler includes conductive carbon, which reduces porosity and charge transfer resistance at the interface of the binder and active material. The conductive filler comprises 0.3% to 1.2% by weight of the negative electrode.

[0021] According to another aspect of this disclosure, the negative electrode has an electrochemically active material, which includes at least one of natural graphite or artificial graphite.

[0022] According to another aspect of this disclosure, the negative electrode has an adhesive polymer binder comprising at least one of styrene-butadiene rubber (SBR), styrene-acrylic rubber, nitrile rubber, or copolymers thereof.

[0023] According to another aspect of this disclosure, the negative electrode comprises 94% to 96% by weight of an electrochemically active material, 1.4% to 2.0% by weight of a dispersant polymer binder, 2.2% to 3.0% by weight of an adhesive polymer binder, and 0.4% to 1.0% by weight of a conductive filler.

[0024] According to several aspects of this disclosure, a method for forming an aqueous graphite anode is provided. The method includes preparing a slurry for coating a negative electrode current collector with a layer of anode active material, and coating the negative electrode current collector with the slurry to form a layer of anode active material disposed on an aqueous graphite anode. The anode active material layer includes an electrochemically active material, a dispersant polymer binder, an adhesive polymer binder, and a conductive filler, wherein the electrochemically active material includes graphite. The dispersant polymer binder is amphiphilic, including hydrophobic and hydrophilic domains, the hydrophilic domains stabilizing hydrophobic carbon in water. The dispersant polymer includes a first carboxymethyl cellulose (CMC) with a degree of substitution (DS) of 0.7 and a second CMC with a DS of 1.2. The adhesive polymer binder has a glass transition temperature and provides flexibility, durability, and cohesive strength between carbon particles. The conductive filler includes conductive carbon, which reduces porosity and charge transfer resistance at the interface between the binder and the active material. The conductive filler comprises 0.3% to 1.2% by weight of the anode active material layer.

[0025] When considered in conjunction with the accompanying drawings, the above-described features and advantages, as well as other features and advantages, of the currently disclosed systems and methods will become apparent from the specific embodiments and examples, including those described in the claims. Attached Figure Description

[0026] This disclosure will be more fully understood through detailed description and accompanying drawings, in which:

[0027] Figure 1 This is a perspective view illustrating an embodiment of a vehicle including a battery pack having multiple battery cells according to this disclosure.

[0028] Figure 2 This illustrates that, according to this disclosure, a setting is provided as follows: Figure 1 The diagram shows a perspective view of a battery cell within a battery pack, wherein the battery cell includes at least one electrode stack having a negative electrode layer using the negative electrode active material disclosed herein.

[0029] Figure 3 This is a diagram illustrating model carbon dispersions of different dispersant polymer binders used in the negative electrode active materials disclosed herein, according to the present disclosure.

[0030] Figure 4 This is a diagram illustrating the slurry processing properties of polymer binders with different dispersants having a degree of substitution of 0.7 in the negative electrode active materials disclosed herein, according to this disclosure.

[0031] Figure 5 This is a diagram illustrating the peel strength of different adhesive polymer concentrations used in the negative electrode active materials disclosed herein, according to this disclosure.

[0032] Figure 6This is a diagram illustrating the ion resistance and tortuosity of the negative electrode active material disclosed herein using different concentrations of conductive filler.

[0033] Figure 7 This is a diagram illustrating the ionic resistance and tortuosity of different conductive filler surface areas used in the negative electrode active materials disclosed herein, according to this disclosure.

[0034] Figure 8 This illustrates, according to the present disclosure, the method for forming such Figure 2 The flowchart shows the method for producing a water-based graphite anode. Detailed Implementation

[0035] Reference will now be made in detail to several embodiments of the present disclosure illustrated in the accompanying drawings. Wherever possible, the same or similar reference numerals are used in the drawings and description to refer to the same or similar parts or steps. The following description is merely exemplary in nature and is not intended to limit the present disclosure, its application, or its uses.

[0036] Reference Figure 1 This illustration shows a perspective view of a vehicle 10 having a battery pack 12 according to the present disclosure. The battery pack 12 is shown together with the exemplary vehicle 10. The vehicle 10 is an electric vehicle or a hybrid vehicle having wheels 11 driven by an electric motor / inverter 13. The electric motor / inverter 13 receives power from the battery pack 12. Although the vehicle 10 is shown as a passenger road vehicle, it should be understood that the battery pack 12 can be used with a variety of other types of vehicles. For example, the battery pack 12 can be used in marine vehicles such as boats or air vehicles such as drones or passenger planes. Furthermore, the battery pack 12 can be used as a stationary power source separate from and independent of the vehicle. The battery pack 12 includes a housing 14 for supporting a plurality of battery cells 18. In embodiments, the battery pack 12 may have fifty or more battery cells 18.

[0037] Now refer to Figure 2 The perspective view shows a setting according to one aspect of this disclosure, such as Figure 1The battery pack 12 shown contains battery cells 18. Each battery cell 18 has a housing 22 or casing and at least one electrode stack 24, which includes a positive electrode 26, a negative electrode 28, an electrolyte 30, and a separator 31. In some cases, the electrolyte 30 may include a solid electrolyte instead of a liquid electrolyte and a separator. Each battery cell 18 may have tens or hundreds of electrode stacks 24. Each electrode stack 24 is connected to current collectors 32, 34. The electrode stacks are placed in the housing 22 and the housing 22 is filled with suitable electrolyte 30. The current collectors 32, 34 are, for example, thin metal plates or foils disposed on either side of the electrode stacks 24 and / or the housing 22, and typically have a thickness of 0.4 mm to 1 mm. The current collectors 32, 34 may be made of copper or aluminum. The current collectors 32, 34 are attached to the electrode stacks 24 to transmit current to an external circuit (not shown).

[0038] Still refer to Figure 2 The negative electrode 36 includes a negative current collector 32 and a negative active material layer 38. The negative active material layer 38 includes a combination of active material, binder and conductive filler, which can optimize the processability and mechanical and electrochemical properties of the negative electrode.

[0039] Negative electrode active materials include electrochemically active materials, such as graphite. Graphite can include various geometries, such as flakes, spherical or spherical shapes, and combinations thereof. Additionally, negative electrode active materials may contain less than 10% by weight of silicon (Si) or lithium silicon oxide (LiSiO2). x ), silicon oxide (SiO) x The anode active material may include lithium silicon oxide and graphite, silicon oxide and graphite, silicon oxide composites (SiO-c), nanostructured silicon (nano-Si), nanocage silicon, and / or combinations thereof. The anode active material may include graphite, which may also include natural graphite and / or artificial graphite. Furthermore, the electrochemical anode active material may comprise approximately 94% to 97% by weight (e.g., 94% to 96% by weight) of the anode electrode. In this document, the term "approximately" is known to those skilled in the art. Alternatively, the term "approximately" may be understood to mean plus or minus 0.1% by weight.

[0040] The negative electrode active material includes a dispersant polymer binder. The dispersant polymer binder is amphiphilic, comprising hydrophobic domains and hydrophilic domains that stabilize hydrophobic carbon in water. The dispersant polymer binder may include at least one of sodium carboxymethyl cellulose (CMC) (NaCMC) or lithium carboxymethyl cellulose (CMC) (CMC-Li). The dispersant polymer binder may have a low degree of substitution (DS). Figure 3 As shown in the model carbon dispersion, polymers with lower DS improve the dispersibility of graphite in water and enhance electrochemical performance. For example, Figure 3The NaCMC shown has a DS of 0.7, which exhibits improved dispersibility and slurry quality due to its low Pascal-second (Pa·s) viscosity at higher shear rates (1 / s). In the examples, the dispersant polymer binder has a degree of substitution of less than 0.8, and more preferably 0.6 to 0.8.

[0041] The negative electrode active material contains a dispersant polymer binder to provide sufficient adsorption coverage, which imparts tert-functional stability to the resulting negative electrode slurry. A smooth, uniform slurry results in a fourfold increase in peel strength and increased flexibility of the negative electrode active material on the negative electrode current collector 32. Generally, depending on the specific graphite used, the dispersant polymer binder comprises 0.6% to 2.5% by weight of the negative electrode active material. Figure 4 As illustrated in the diagram, using NaCMC with a DS of 0.7 and approximately 2.0 wt% provided a more stable negative electrode active material in slurry form. Figure 4 The S-shaped curve shown indicates agglomeration or the presence of clumps, which is not a desirable outcome. For example, when using artificial graphite or flake graphite, the dispersant polymer binder can comprise about 1.5% to 2.5% by weight of the negative electrode active material. When using natural graphite or spherical graphite, the dispersant polymer binder can comprise about 0.6% to 1.4% by weight of the negative electrode active material. In the embodiments, the negative electrode active material comprises a dispersant polymer binder of 2.0% by weight of NaCMC with a substitution degree of 0.7. Throughout this document, the term "about" is known to those skilled in the art. Alternatively, the term "about" can be understood to mean plus or minus 0.1% by weight.

[0042] Furthermore, dispersant polymer binders can have high molecular weights to improve the cohesive strength between particles. For example, dispersant polymer binders can have molecular weights greater than 300 kilodaltons (kDa).

[0043] Dispersant polymer binders may comprise blends of multiple polymers, each with different properties to delay or prevent gelation of the dispersant polymer binder during the drying process. For example, a dispersant polymer binder may comprise a first polymer with a degree of substitution of 0.7 and a second polymer with a degree of substitution of 1.2. In another embodiment, the dispersant polymer binder may comprise a first polymer with a molecular weight of about 300 kDa and a second polymer with a molecular weight of about 400 kDa. Throughout this document, the term "about" is known to those skilled in the art. Alternatively, the term "about" may be understood to mean adding or subtracting 10 kDa.

[0044] Dispersant polymer binders may include ionically conductive polyacrylic acid. For example, polyacrylic acid may include mildly neutralized lithium polyacrylate or sodium polyacrylate.

[0045] The negative electrode active material includes an adhesive polymer binder with a low glass transition temperature to provide flexibility, durability, cohesive strength, and adhesion strength to the current collector between particles. The adhesive polymer binder is typically used as a partially crosslinked particle stabilized by a surfactant in water. In embodiments, the adhesive polymer binder includes styrene-butadiene rubber (SBR), styrene-acrylic rubber, nitrile rubber, or combinations thereof. The adhesive polymer binder has a low glass transition temperature, for example, less than 20°C. The adhesive polymer binder may contain about 1.5 wt% to 3.0 wt% (e.g., 2.2 wt% to 3.0 wt%) of the negative electrode active material. Figure 5 As illustrated in the figure, increasing the SBR content to a range of 2.0% to 2.8% by weight improved the durability of the negative electrode active material coating on the negative electrode current collector 32, as indicated by the increased peel strength (in Newtons per meter (N / m)). In this document, the term "about" is known to those skilled in the art. Alternatively, the term "about" can be understood to mean adding or subtracting 0.1% by weight.

[0046] The negative electrode active material includes conductive fillers or conductive carbon additives combined with the negative electrode active material, dispersant polymer, and adhesive polymer. The conductive fillers or conductive carbon reduce porosity and charge transfer resistance at the interface between the binder and active material. Figure 6 The decrease in ionic resistance (in ohms square centimeters) due to the increase in carbon black fraction (wt%) is shown. 2 (in units of ) Figure 7 This shows a comparison with a smaller surface area (45m²). 2 Carbon per g, increasing carbon content (e.g., 65m). 2 / g and 140m 2 The negative electrode active material formulation ( / g) exhibits improved ionic resistance. The conductive filler may include one or more of carbon black (CB), acetylene black, Ketjen black, carbon nanofibers, graphene, graphene nanosheets, carbon nanotubes, multi-walled carbon nanotubes, single-walled nanotubes, and / or combinations thereof. In embodiments, the conductive filler may comprise about 0.3 wt% to about 1.2 wt% (e.g., 0.4 wt% to 1.0 wt%) of the negative electrode. In another embodiment, the conductive filler may comprise about 0.5 wt% to about 1.0 wt% of the negative electrode. Throughout this document, the term "about" is known to those skilled in the art. Alternatively, the term "about" may be understood to mean plus or minus 0.1 wt%.

[0047] Reference Figure 8 The diagram illustrates a method 100 for forming a negative electrode according to the present disclosure. The method begins at block 102.

[0048] Box 102 describes the preparation of a slurry for coating a negative electrode current collector with a layer of negative electrode active material. The negative electrode active material layer comprises an electrochemically active material containing graphite, a dispersant polymer binder, an adhesive polymer binder, and a conductive filler. The dispersant polymer binder is amphiphilic, comprising hydrophobic domains and hydrophilic domains that stabilize hydrophobic carbon in water. The dispersant polymer binder comprises a first carboxymethyl cellulose (CMC) with a degree of substitution (DS) of 0.7 and a second CMC with a DS of 1.2. The conductive filler comprises conductive carbon that reduces porosity and charge transfer resistance at the interface between the binder and the active material. The conductive filler comprises 0.3% to 1.2% by weight of the negative electrode. The preparation of the slurry may include, for example, mixing the negative electrode active material, the dispersant polymer binder, the adhesive binder, and the conductive filler with water in a tank equipped with a mixer (e.g., a spiral mixer). Carbon and carbon-coated particles, such as graphite as a negative electrode active material, are typically hydrophobic and tend to aggregate in aqueous solutions rather than remain discrete particles, exhibiting poor cohesive strength that can lead to cracking and spalling when applied to a negative electrode current collector. However, due to the combination of negative electrode active material components disclosed herein, the resulting slurry maximizes the processability, slurry quality, dispersion quality, and mechanical integrity of the negative electrode, thereby providing satisfactory electrochemical performance. The method is then moved to box 104.

[0049] Box 104 depicts coating a negative electrode current collector with a slurry to form a layer of negative electrode active material disposed on an aqueous graphite negative electrode. Coating the negative electrode current collector may include, for example, spreading or casting the slurry onto the surface of the negative electrode current collector using a doctor blade, a stencil coater, or other suitable deposition techniques.

[0050] The negative electrode and method disclosed herein are advantageous and beneficial compared to existing technologies. The negative electrode active material used in the disclosed negative electrode provides an aqueous formulation for robust, high-quality graphite-based electrodes. The combination of materials can improve the quality of the slurry and electrode, mechanical durability, reduce electrode internal resistance, and exhibit high electrochemical performance. The formulation described herein provides stability of the negative electrode active material slurry, where no agglomeration or clumping and no peeling or cracking occur when the negative electrode active material slurry is coated onto a current collector. The dispersant polymer binder used in the formulation has low separation, improving the dispersibility of graphite in water and enhancing electrochemical performance. The concentration of the dispersant polymer binder used provides sufficient adsorption coverage, which imparts terticular stability to the resulting negative electrode active material slurry. Furthermore, the resulting smooth and uniform slurry leads to increased peel strength and flexibility of the negative electrode active material layer. Additionally, the adhesive polymer binder provides coating durability, and the conductive filler improves pore tortuosity and reduces ionic resistance.

[0051] This description is merely illustrative in nature and is in no way intended to limit this disclosure, its application, or its use. The broad teachings of this disclosure can be implemented in many forms. Therefore, while this disclosure includes specific embodiments, its true scope should not be so limited, as other modifications will become apparent upon examination of the drawings, description, and appended claims.

Claims

1. A negative electrode, comprising: Negative electrode current collector; and A negative electrode active material layer disposed on the negative electrode current collector, the negative electrode active material layer comprising: Electrochemically active materials, including graphite; A dispersant polymer binder having amphiphilic properties, comprising hydrophobic and hydrophilic domains, wherein the hydrophilic domains stabilize hydrophobic carbon in water; Adhesive polymer adhesive, adhesive, the adhesive polymer adhesive having a glass transition temperature, the adhesive polymer adhesive providing flexibility, durability and cohesive strength between carbon particles; as well as A conductive filler, comprising conductive carbon, which reduces porosity and charge transfer resistance at the interface of the adhesive active material.

2. The negative electrode according to claim 1, wherein, The graphite includes at least one of natural graphite or artificial graphite.

3. The negative electrode according to claim 1, wherein, The electrochemically active material includes at least one of the following in less than 10% by weight: silicon (Si), silicon oxide (SiO), lithium silicon oxide (LiSiO), silicon oxide composite (SiO-c), nanostructured silicon (nano-Si), or nanocage silicon.

4. The negative electrode according to claim 1, wherein, The electrochemically active material accounts for 94% to 97% by weight of the negative electrode.

5. The negative electrode according to claim 1, wherein, The dispersant polymer binder includes at least one of sodium carboxymethyl cellulose (CMC) or lithium carboxymethyl cellulose (CMC).

6. The negative electrode according to claim 5, wherein, The sodium carboxymethyl cellulose (CMC) or lithium carboxymethyl cellulose (CMC) has a degree of substitution (DS) of less than 0.

8.

7. The negative electrode according to claim 5, wherein, The sodium carboxymethyl cellulose (CMC) or lithium carboxymethyl cellulose (CMC) has a molecular weight greater than 300 kilodaltons (kDa).

8. The negative electrode according to claim 5, wherein, The sodium carboxymethyl cellulose (CMC) or lithium carboxymethyl cellulose (CMC) comprises a blend of a first CMC with a degree of substitution (DS) of at least 0.7 and a second CMC with a DS of 1.

2.

9. The negative electrode according to claim 5, wherein, The dispersant polymer binder includes sodium polyacrylate or lithium polyacrylate.

10. The negative electrode according to claim 5, wherein, The sodium carboxymethyl cellulose (CMC) or lithium carboxymethyl cellulose (CMC) comprises 0.6% to 2.5% by weight of the negative electrode.

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