Controlling binder flowability during shrinkage phase of drying process in electrode manufacturing

Abstract

The present disclosure provides for "controlling binder flowability during the contraction phase of the drying process in electrode manufacturing". A method of producing a battery electrode includes applying an electrode material onto a surface of a current collector, the electrode material including a binder material having binder particles; initiating a drying process to dry the electrode material; and applying a non-uniform electric field to the electrode material during the drying process. The non-uniform electric field defines a magnitude gradient to generate a dielectrophoretic force on the binder particles, thereby moving the binder particles.

Description

Technical Field

[0001] The present disclosure relates to battery manufacturing, and more particularly, to drying electrodes for such batteries. Background Art

[0002] The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.

[0003] A typical process for manufacturing battery electrodes consists of mixing electrode materials, coating the electrode materials onto the surface of a current collector, drying the electrode materials, and calendaring (compressing) the dried electrodes. Each step of the electrode manufacturing process affects subsequent manufacturing steps and the overall performance of the battery.

[0004] Reference Figure 1 , shows a typical drying process for manufacturing an electrode battery, which includes multiple drying stages. Generally, during each stage, the mechanism by which solvent and binder particles move is different and may affect the performance of the battery, as elaborated in more detail below.

[0005] Prior to drying, in a pre-drying stage (a), a slurry containing electrode particles 110 of electrode material 100, particles of binder material 120, and solvent 130 is applied to a current collector 140. At the start of drying, in a shrinkage stage (b), the evaporation rate of the solvent 130 is high and the drying process is faster. In this stage, the solvent 130 easily moves to the top surface of the electrode material 100 where evaporation occurs. Small particles (such as binder particles 120) can be carried towards the surface with the solvent 130 and retained. Thus, without intervention, the concentration of small binder particles 120 can increase towards the top surface of the electrode material 100 and decrease towards the current collector 140. Due to the removal of the solvent 130, the electrode material 100 shrinks and begins to consolidate.

[0006] After the shrinkage stage (b), the thickness of the electrode material 100 remains constant, where the solvent 130 and the binder particles 120 are retained in the network of the porous microstructure during the capillary action stage (c) and the compaction stage (d). During the 'capillary action stage', the binder particles 120 and the electrode particles 110 start to connect to form a pore network. The solvent 130 and the binder particles 120 move through the pore network between the electrode particles 110 under capillary forces. The net convection of the solvent 130 still acts upward through capillary action, thereby bringing more binder particles 120 towards the top surface of the electrode material 100. However, the slower effect allows diffusion to migrate some binder particles 120 into a more balanced distribution. During the compaction stage (d), the porous microstructure of the electrode material 100 dries and solidifies, and isolated regions of the solvent 130 are formed. In the local evaporation regions, the binder particles 120 start to crystallize and lose their fluidity. Finally, in the dry electrode (e), the solvent 130 has completely evaporated, and the electrode particles 110 are bonded together by the binder particles 130 to form a porous structure.

[0007] During each stage, the mobility of the binder particles 120 towards the surface of the electrode material 100 depends on the binder material, the size of the particles, the thickness of the electrode material, and the temperature and air flow of the drying and the drying mechanism. Generally, a higher drying rate results in a higher binder concentration towards the top surface by initiating a stronger upward transport force for the binder and not leaving enough time for the binder to diffuse and balance. However, due to its shorter drying time, a higher drying rate is desirable for high-volume production. Therefore, it is desirable to control and mitigate binder migration while still maintaining a high drying rate.

[0008] This disclosure addresses these problems related to controlling the binder distribution in electrode materials for battery manufacturing. Summary of the Invention

[0009] This section provides a general overview of the disclosure and is not a full disclosure of its entire scope or all of its features.

[0010] In one form, the disclosure provides a method of producing a battery electrode. The method includes: applying an electrode material to a surface of a current collector, the electrode material including a binder material having binder particles; initiating a drying process to dry the electrode material; and applying a non-uniform electric field to the electrode material during the drying process. The non-uniform electric field defines a magnitude gradient to generate a dielectrophoretic force on the binder particles to move the binder particles.

[0011] In variants of the method that can be implemented individually or in any combination: the drying process is carried out in the temperature range of 70 °C to 120 °C; the electrode material is monolithic; the electric field is an AC electric field with a frequency between 0.01 Hz and 10 kHz; the electric field has a magnitude distribution ranging from 0.1 kV cm- 1 to 200 kV cm- 1 between; the electrode is a cathode, the binder material is polyvinylidene fluoride (PVDF), and the solvent is N-methyl-2-pyrrolidone (NMP); and the electrode is an anode, the binder material particles are water-soluble, and the solvent is water.

[0012] The present disclosure also provides another method for producing a battery electrode. The method includes: applying an electrode material to the surface of a current collector; applying a non-uniform electric field to the electrode material; and drying the electrode material during a drying process. The electrode material includes a binder material having binder particles. The non-uniform electric field defines a magnitude gradient to generate a dielectrophoretic force on the binder particles such that the particles of the binder material concentrate towards the current collector.

[0013] In variants of the method that can be implemented individually or in any combination: the electrode is a cathode, the binder material is polyvinylidene fluoride (PVDF), and the solvent is N-methyl-2-pyrrolidone (NMP); the electrode is an anode, the binder material particles are water-soluble, and the solvent is water; the drying process is carried out in the temperature range of 70 °C to 120 °C; the electric field has a magnitude distribution ranging from 0.1 kV cm- 1 to 200 kV cm- 1 between; and the electrode material is monolithic.

[0014] In another form, the present disclosure provides a method for producing a battery electrode. The method includes: applying an electrode material to a surface; applying a non-uniform electric field to the electrode material; and drying the electrode material during a drying process. The electrode material includes a binder material. The non-uniform electric field has a higher magnitude during a first time period and a lower magnitude during a second time period. The non-uniform electric field generates a dielectrophoretic force on the binder particles to move the binder particles.

[0015] In variants of the method that can be implemented individually or in any combination: the higher magnitude ranges from 0.1 kVcm -1 to 200 kV cm -1 between; the lower magnitude ranges from 0.1 kV cm -1 to 200 kV cm -1between; said first time period occurs before the start of the drying process; the electrode is a cathode, the binder material is polyvinylidene fluoride (PVDF), and the solvent is N-methyl-2-pyrrolidone (NMP); the drying process is carried out in a temperature range of 70 °C to 120 °C; and the electrode material is monolithic.

[0016] Based on the description provided herein, additional applicable fields will become apparent. It should be understood that the description and specific examples are for illustrative purposes only and are not intended to limit the scope of the present disclosure. Brief Description of the Drawings

[0017] For a better understanding of the present disclosure, various forms of the present disclosure will now be described by way of example with reference to the accompanying drawings, in which:

[0018] Figure 1 is a schematic diagram showing the stages of a battery electrode drying process according to the prior art;

[0019] Figure 2 is a schematic diagram showing particles in a non-uniform electric field according to the teachings of the present disclosure; and

[0020] Figure 3 is a flowchart showing a novel method of producing a battery electrode according to the teachings of the present disclosure.

[0021] The drawings described herein are for illustrative purposes only and are not intended to limit the scope of the present disclosure in any way. Detailed Description of the Embodiments

[0022] The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or use. It should be understood that throughout the drawings, corresponding reference numerals indicate the same or corresponding parts and features.

[0023] To counteract the non-uniform mobility of the binder particles as described above, the inventors have found that applying a non-uniform electric field to the electrode material can control the movement of the binder particles within the electrode material and thus control the final distribution of the binder particles. The non-uniform electric field has a voltage magnitude gradient to generate a dielectrophoretic force that acts on the binder particles 120, which is described in more detail below.

[0024] Now refer to Figure 2, showing a general use of dielectrophoretic force, in which a non-uniform electric field 210 is applied to particles 220 (such as particles of binder material 120). The non-uniform electric field 210 polarizes the particles 220, thereby inducing a force on the poles 230 along the field lines 240. The orientation of the resulting dipole (separation of opposite charges) depends on the relative polarizability of the particles 220 and the surrounding medium (such as a solvent). Since the electric field 210 is non-uniform, the pole 230 experiencing the maximum electric field will dominate the other pole, and the particle 220 will move. The corresponding magnitude gradients on the poles 230 and the particle 220 are oriented to move the particle 220 towards the current collector. In the negative dielectrophoresis arrangement shown in (a), the non-uniform electric field 210 has a greater magnitude in the direction of the current collector 140, and the particles are attracted towards the current collector 140. Alternatively, in the positive dielectrophoresis arrangement shown in (b), the magnitude gradient is configured to repel the particles 220 away from the top surface of the electrode material towards the current collector 140.

[0025] Reference Figure 3 , showing a novel method of using the above dielectrophoretic force to produce a battery electrode according to the teachings of the present disclosure. First, the electrode material 100 is applied to the surface of the current collector 140. The electrode material 100 is in the form of a homogeneous slurry and is applied as a single integral layer. The slurry components generally include electrode particles 110, binder material 120, and solvent 130, but are not necessarily limited thereto. In the single integral layer, the binder material is uniformly distributed upon the first application. No additional layers of different compositions are required.

[0026] The electrode particles 110 include active particles and may optionally include conductive additive particles. The active particles form the main body of the electrode and interact with ions in the battery fluid (such as lithium ions in a lithium battery). In one form of the present disclosure, the active particles are carbon materials such as graphite. In other forms, the active particles are lithium titanate (Li4Ti5O12), lithium nickel manganese cobalt oxide, graphene, and the like. The conductive additive particles contribute to the conductivity of the electrode and the movement of ions towards the active particles. In one form, the conductive additive particles include carbon black. It should be understood that other materials having the properties and functions described herein for the electrode particles 110 may be implemented while remaining within the scope of the present disclosure.

[0027] The binder material 120 has binder particles and can be any of a variety of polymeric materials used to hold the electrode particles 110 together. For example, the binder material 120 can be a fluorinated acrylic polymer, polytetrafluoroethylene (PTFE), polyvinylidene fluoride, polyacrylate, aliphatic polymer, aromatic polymer, oligosaccharide and polysaccharide, chitosan, alginate, pectin, amylose, starch, gum, lignin, and protein, etc. It should be understood that other materials for binding the electrode particles 110 can be utilized while remaining within the scope of the present disclosure.

[0028] The solvent 130 is typically used to suspend or disperse the electrode particles 110 and the binder particles 120 and can be any of a variety of materials, including for example H2O (water), N-methyl-2-pyrrolidone (NMP), dimethylformamide (DMF), dimethylacetamide (DMAC), and dimethyl sulfoxide (DMSO), etc. It should be understood that other solvents can be implemented while remaining within the scope of the present disclosure.

[0029] After being applied to the current collector, the electrode material 100 is dried to remove the solvent 130, leaving the binder material 120 and the electrode particles 110, and the binder material and the electrode particles form a porous nanostructure. In one form, the electrode material 100 is dried at a temperature of 70 °C to 120 °C.

[0030] During the drying process, a non-uniform electric field is applied to the electrode material 100. In one form, the electric field is an AC (alternating current) field with a frequency between 0.01 Hz and 10 kHz. In one form, the electric field has a magnitude of 0.1 kV cm- 1 to 200 kV cm- 1 of the order.

[0031] In various forms, the non-uniform electric field 210 can be applied during the pre-drying stage (a), during the shrinkage stage (b) of the drying process, during the capillary action stage (c), during the compaction stage (d) of the drying process, or any combination thereof. In one form, the dielectrophoretic force 210 causes the binder particles 220 to move into a predetermined distribution. For example, the predetermined distribution can cause the binder particles 120 to concentrate towards the surface of the current collector 140. If the non-uniform field 210 is applied in the pre-drying stage (a) before the start of the drying process, or if the dielectrophoretic force 210 is stronger than the force provided by the movement of the solvent 130, the particles 220 move to the predetermined distribution. In another form, the dielectrophoretic force 210 balances the movement of the solvent 130 during the drying process, thereby holding the binder particles 120 in place. In this form, the approximate distribution of the binder particles 120 is maintained as the original uniform distribution or the predetermined distribution of the pre-drying stage (a).

[0032] One method of moving the binder particles 120 to a predetermined distribution is to apply different voltage magnitude gradients at different stages of the drying process. In one form, the non-uniform electric field 210 has a higher magnitude during a first time period and a lower magnitude during a second time period. For example, a higher magnitude force can be applied before drying (a) to concentrate the binder particles 120 towards the surface of the current collector 140, and a lower magnitude force can be applied during the shrinkage stage (b). Alternatively, a higher magnitude force can be applied during the shrinkage stage (b), and a lower magnitude force can be applied during the compaction stage (d).

[0033] Unless otherwise expressly indicated herein, all numerical values indicating mechanical / thermal properties, percentage compositions, dimensions, and / or tolerances or other characteristics should be understood to be modified by the word "about" or "approximately" when describing the scope of the present disclosure. Such modification is desirable for various reasons, including: industrial practices; material, manufacturing, and assembly tolerances; and test capabilities.

[0034] As used herein, the phrase "at least one of A, B, and C" should be construed to represent the logic (A or B or C) using non-exclusive logic "or", and should not be construed to mean "at least one of A, at least one of B, and at least one of C".

[0035] The description of the present disclosure is merely exemplary in nature, and thus, variations that do not depart from the essence of the present disclosure are intended to be within the scope of the present disclosure. Such variations should not be regarded as departing from the spirit and scope of the present disclosure.

[0036] According to the present invention, a method of producing a battery electrode includes: applying an electrode material to the surface of a current collector, the electrode material including a binder material having binder particles; applying a non-uniform electric field to the electrode material, wherein the non-uniform electric field defines a magnitude gradient to generate a dielectrophoretic force on the binder particles such that the particles of the binder material concentrate towards the current collector; and drying the electrode material during a drying process.

[0037] In one aspect of the present invention, the electrode is a cathode, the binder material is polyvinylidene fluoride (PVDF), and the solvent is N-methyl-2-pyrrolidone (NMP).

[0038] In one aspect of the present invention, the electrode is an anode, the binder particles are water-soluble, and the solvent is water.

[0039] In one aspect of the present invention, the drying process is performed in a temperature range of 70 °C to 120 °C.

[0040] In one aspect of the present invention, the electric field has a range of 0.1 kV cm-1 to 200 kV cm- 1 in the magnitude distribution range.

[0041] In one aspect of the present invention, the electrode material is monolithic.

[0042] According to the present invention, a method for producing a battery electrode includes: applying an electrode material to a surface, the electrode material including a binder material having binder particles; applying a non-uniform electric field to the electrode material, the non-uniform electric field having a higher magnitude during a first time period and a lower magnitude during a second time period, wherein the non-uniform electric field generates a dielectrophoretic force on the binder particles, thereby moving the binder particles; and drying the electrode material during a drying process.

[0043] In one aspect of the present invention, the higher magnitude ranges from 0.1 kV cm- 1 to 200 kV cm- 1 therebetween.

[0044] In one aspect of the present invention, the lower magnitude ranges from 0.1 kV cm- 1 to 200 kV cm- 1 therebetween.

[0045] In one aspect of the present invention, the first time period occurs before the start of the drying process.

[0046] In one aspect of the present invention, the electrode is a cathode, the binder material is polyvinylidene fluoride (PVDF), and the solvent is N-methyl-2-pyrrolidone (NMP).

[0047] In one aspect of the present invention, the drying process is performed in a temperature range of 70 °C to 120 °C.

[0048] In one aspect of the present invention, the electrode material is monolithic.

Claims

1. A method of producing a battery electrode, the method comprising: Applying an electrode material to a surface of a current collector, the electrode material comprising a binder material having binder particles; Initiating a drying process to dry the electrode material; And Applying a non-uniform electric field to the electrode material during the drying process, Wherein the non-uniform electric field defines a magnitude gradient to generate a dielectrophoretic force on the binder particles, thereby moving the binder particles.

2. The method according to claim 1, wherein the drying process is performed in a temperature range of 70 °C to 120 °C.

3. The method according to claim 1, wherein the electrode material is monolithic.

4. The method according to claim 1, wherein the electric field is an AC electric field with a frequency between 0.01 Hz and 10 kHz.

5. The method according to claim 1, wherein the electric field has a magnitude distribution ranging from 0.1 kV / cm -1 to 200 kV / cm -1 with a distribution therebetween.

6. The method according to claim 1, wherein the electrode is a cathode, the binder material is polyvinylidene fluoride (PVDF), and the solvent is N-methyl-2-pyrrolidone (NMP).

7. The method according to claim 1, wherein the electrode is an anode, the binder particles are water-soluble, and the solvent is water.

8. The method according to claim 1, wherein the non-uniform electric field defines the magnitude gradient to generate a dielectrophoretic force on the binder particles such that the particles of the binder material are concentrated towards the current collector.

9. The method according to claim 1, wherein the non-uniform electric field has a higher magnitude during a first time period and a lower magnitude during a second time period.

10. The method according to claim 9, wherein the range of the higher magnitude is from 0.1 kV / cm -1 to 200 kV / cm -1 therebetween.

11. The method according to claim 9, wherein the range of the lower magnitude is from 0.1 kV / cm -1 to 200 kV / cm -1 therebetween.

12. The method according to claim 9, wherein the first time period occurs before the start of the drying process.

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