Method for controlling binder crystallation during drying process in electrode manufacturing

Abstract

The present disclosure provides a method of controlling binder crystallization during a drying process in electrode fabrication. A method of producing an electrode for battery fabrication includes: drying an electrode material in a compaction phase; applying an electric field to the electrode material during the compaction phase; and adjusting the frequency and magnitude of the electric field to control crystallization of the binder material. The electrode material includes a binder material. The crystallization rate of the binder material is increased or decreased.

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 a slurry of electrode materials, coating the electrode materials onto the surface of a current collector, drying the electrode materials, and calendering (compressing) the dried electrode materials. 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 battery electrodes, which includes multiple drying stages. Before drying, in the pre-drying stage (a), a slurry containing electrode particles 110 of electrode material 100, a binder material 120 having binder particles, and a solvent 130 is applied to a current collector 140. At the beginning of drying, in the 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. As the solvent 130 moves, some of the particles of the binder material 120 are transported along with the solvent 130. Due to the removal of the solvent 130, the electrode material 100 shrinks and begins to consolidate.

[0005] After the shrinkage stage (b), the thickness of the electrode material 100 remains constant, where the solvent 130 and the binder material 120 are retained in the network of the porous microstructure during the capillary action stage (c) and the compaction stage (d). In the 'capillary action stage', the binder material 120 and the electrode particles 110 begin to connect to form a pore network. The net convection of the solvent 130 still moves upward by capillary action, thus bringing more binder particles 120 towards the top surface of the electrode material 100. However, the slower effect allows diffusion to migrate some of the binder material 120 into a more balanced distribution.

[0006] In 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 material 120 begins to crystallize and loses its fluidity. In some cases, the solvent 130 may be trapped in the isolated pores by the crystallized binder material 120, thus requiring a longer drying process.

[0007] Finally, in the dried electrode (e), the solvent 130 has completely evaporated, and the electrode particles 110 are bonded together by the binder material 120 to form a porous nanostructure.

[0008] The present disclosure addresses these challenges related to controlling the crystallization of the binder in electrode materials for battery manufacturing. SUMMARY OF THE INVENTION

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

[0010] In one form, the present disclosure provides a method of producing an electrode for battery manufacturing. The method includes: drying an electrode material during a compaction stage; applying an electric field to the electrode material during the compaction stage; and adjusting the frequency and magnitude of the electric field to control the crystallization of a binder material. The electrode material includes a binder material.

[0011] In variations of the method that can be implemented individually or in any combination: the binder material is polyvinylidene fluoride; the crystalline binder material forms a nanoporous structure; the drying process is performed at a temperature in the range of 70°C to 120°C; the frequency is in the range of 0.01 Hz to 10 kHz; the magnitude is in the range of 0.1 kV / cm to 200 kV / cm; and the electric field is applied throughout the drying and compaction stage.

[0012] The present disclosure also provides a method of producing an electrode for battery manufacturing. The method includes: drying an electrode material during a compaction stage; applying an electric field to the electrode material during the compaction stage; and adjusting the frequency and magnitude of the electric field to reduce the crystallization rate of a binder material. The electrode material includes a binder material.

[0013] In variations of the method that can be implemented individually or in any combination: the binder material is polyvinylidene fluoride; the drying process is performed at a temperature in the range of 70°C to 120°C; the frequency is in the range of 0.01 Hz to 10 kHz; the magnitude is in the range of 0.1 kV / cm to 200 kV / cm; and the crystalline binder material forms a nanoporous structure.

[0014] In another form, the present disclosure provides another method of producing an electrode for battery manufacturing. The method includes: drying an electrode material during a compaction stage; applying an electric field to the electrode material during the compaction stage; and adjusting the frequency and magnitude of the electric field to increase the crystallization rate of a binder material. The electrode material includes a binder material.

[0015] In variations of the method that can be implemented individually or in any combination: the binder material is polyvinylidene fluoride; the crystalline binder material forms a nanoporous structure; the drying process is carried out at a temperature in the range of 70 °C to 120 °C; the frequency is in the range of 0.01 Hz to 10 kHz; the magnitude is in the range of 0.1 kV / cm to 200 kV / cm; and an electric field is applied throughout the drying and compaction stage.

[0016] Based on the description provided herein, additional applicable fields will become apparent. It should be understood that the description and specific examples are only for illustrative purposes 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 the drying process of a battery electrode according to the prior art;

[0019] Figure 2 is a graph showing isothermal crystallization in the presence of an electric field with different frequencies according to the teachings of the present disclosure;

[0020] Figure 3 is a graph showing isothermal crystallization in the presence of an electric field with different magnitudes according to the teachings of the present disclosure; and

[0021] Figure 4 is a flow chart showing a novel method for producing a battery electrode according to the teachings of the present disclosure.

[0022] The drawings described herein are only for illustrative purposes and are not intended to limit the scope of the present disclosure in any way. DETAILED DESCRIPTION

[0023] The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. It should be understood that throughout the drawings, corresponding reference numerals indicate the same or corresponding parts and features.

[0024] The present disclosure provides a novel method for controlling the distribution of a binder material during the drying process of a battery electrode, generally by applying an electric field to the electrode material during the compaction stage and adjusting the frequency and magnitude of the electric field to control the crystallization of the binder material. To control the distribution of the binder material and the nanoporous structure formed as the electrode material dries and the binder material crystallizes, an electric field is applied to the electrode material during the drying and compaction stage (see Figure 1)。The crystallization rate of the binder material and the resulting crystalline phase are controlled by adjusting the frequency and magnitude of the electric field, as elaborated in more detail below.

[0025] Reference Figure 2 , shows the crystallization of a typical binder material (e.g., ethylene carbonate) over time at a voltage magnitude of 80 kV / cm and a temperature of 198 Kelvin for several frequencies. The effect of the frequency of an AC (alternating current) electric field with a magnitude of 80 kV / cm on the crystallization rate is depicted as the ratio of the crystalline volume of the binder to the total volume of the binder (V 结晶 / V 总 ) versus a log t curve in seconds. At frequencies of 100 Hz or higher, no significant crystallization was observed over a time period of up to 50,000 seconds (about 14 hours). However, at a lower frequency of 18 Hz, crystallization was substantially complete after 10,000 seconds, and at 56 Hz, the crystallization rate increased by another factor of 10. Thus, the crystallization rate can be increased by increasing the frequency of the electric field. In one form of the present disclosure, the electric field has a frequency between 0.01 Hz and 10 kHz. However, it should be understood that other frequencies and frequency ranges may be employed depending on the specific electrode material. Additionally, it should be understood that frequencies between the ranges set forth herein are within the scope of the present disclosure. For example, within the frequency range of 0.01 Hz and 10 kHz, frequencies such as 100 Hz, 120 Hz, 200 Hz, etc. are within the teachings herein.

[0026] Reference Figure 3 , shows the crystallization of ethylene vinyl carbonate over time at a fixed frequency of 56.2 Hz, for different voltage magnitudes and a temperature of 198 Kelvin. Thus, the crystallization rate can be additionally or alternatively increased by increasing the magnitude of the electric field. Preliminary tests have shown that the crystallization rate at a fixed frequency of 56 Hz can be increased by increasing the electric field magnitude. In one form, the electric field has a magnitude between 0.1 kV / cm and 200 kV / cm. However, it should be understood that other frequencies and frequency ranges may be employed depending on the specific electrode material. Additionally, it should be understood that frequencies between the ranges set forth herein are within the scope of the present disclosure. For example, within the magnitude range of 0.1 kV / cm to 200 kV / cm, magnitudes such as 10 kV / cm, 50 kV / cm, 100 kV / cm, 120 kV / cm, 150 kV / cm, etc. are within the teachings herein.

[0027] By adjusting the frequency and / or magnitude of the electric field to change the crystallization rate, the point at which the binder material becomes immobile can be reduced or increased. In the case of delayed crystallization, the binder material can continue to diffuse through the electrode material. On the other hand, the crystallization rate can be increased to prevent the binder material 120 from further moving into the isolated pores. Additionally, the exact phase of the crystals formed can be optimized.

[0028] Reference Figure 4 , shows a method of producing a battery electrode. First, a slurry of the electrode material is applied to the surface of a current collector. The electrode material is in the form of a uniform slurry and is applied as a single integral layer. The electrode material generally includes electrode particles, a binder material, and a solvent, but is not necessarily limited thereto.

[0029] The electrode particles include active particles and may optionally include conductive additive particles. The active particles form the bulk 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, and graphene, etc. The conductive additive particles contribute to the conductivity of the electrode and the movement of ions to 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 can be implemented while remaining within the scope of the present disclosure.

[0030] The binder material can be any of a variety of polymeric materials used to hold the electrode particles together. For example, the binder material can be a fluorinated acrylic polymer, polytetrafluoroethylene (PTFE), polyvinylidene fluoride, polyacrylate, aliphatic polymer, aromatic polymer, oligosaccharide, polysaccharide, alginate, pectin, amylose, starch, gum, lignin, and protein, etc. It should be understood that other materials for binding the electrode particles can be utilized while remaining within the scope of the present disclosure.

[0031] The solvent is generally used to suspend or disperse the electrode particles and the binder particles 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.

[0032] After being applied to the current collector, the electrode material is dried to remove the solvent, leaving the binder material and the electrode particles, which form a porous nanostructure. The drying process is discussed in more detail above. In one form, the electrode material is dried at a temperature of 70 °C to 120 °C.

[0033] As discussed above, an electric field is applied to the electrode material 100 during the compaction stage of the drying process. Adjusting the frequency and magnitude of the electric field controls the crystallization rate of the binder material. In one form, the electric field has a frequency between 0.01 Hz and 10 kHz. In one form, the electric field has a magnitude between 0.1 kV / cm and 200 kV / cm. In one form, the electric field is applied throughout the compaction stage.

[0034] It should be understood that the magnitude and frequency of the electric field will vary depending on: the electrode material (especially the binder material), the volume of the electrode material, the drying stage at which the electric field is applied, temperature, solvent selection, and the material properties of the active material and conductive additive.

[0035] 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. This modification is desirable for various reasons, including: industrial practice; material, manufacturing, and assembly tolerances; and test capabilities.

[0036] 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".

[0037] 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.

[0038] According to the present invention, a method of producing an electrode for battery manufacturing includes: drying an electrode material including a binder material during a compaction stage; applying an electric field to the electrode material during the compaction stage; and adjusting the frequency and magnitude of the electric field to reduce the crystallization rate of the binder material.

[0039] In one aspect of the present invention, the binder material is polyvinylidene fluoride.

[0040] In one aspect of the present invention, the drying is performed at a temperature between 70 °C and 120 °C.

[0041] In one aspect of the present invention, the frequency is in the range of 0.01 Hz to 10 kHz.

[0042] In one aspect of the present invention, the magnitude is in the range of 0.1 kV / cm to 200 kV / cm.

[0043] In one aspect of the present invention, the crystalline binder material forms a nanoporous structure.

[0044] According to the present invention, a method of producing an electrode for battery manufacturing includes: drying an electrode material during a compaction drying stage, the electrode material including a binder material; applying an electric field to the electrode material during the compaction stage; and adjusting the frequency and magnitude of the electric field to increase the crystallization rate of the binder material.

[0045] In one aspect of the present invention, the binder material is polyvinylidene fluoride.

[0046] In one aspect of the present invention, the crystalline binder material forms a nanoporous structure.

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

[0048] In one aspect of the present invention, the frequency is in the range of 0.01 Hz to 10 kHz.

[0049] In one aspect of the present invention, the magnitude is in the range of 0.1 kV / cm to 200 kV / cm.

[0050] In one aspect of the present invention, the electric field is applied throughout the compaction drying stage.

Claims

1. A method of producing an electrode for battery manufacturing, the method comprising: drying an electrode material during a compaction stage, the electrode material comprising a binder material; applying an electric field to the electrode material during the compaction stage; and adjusting a frequency and magnitude of the electric field to control crystallization of the binder material.

2. The method of claim 1, wherein the binder material is polyvinylidene fluoride.

3. The method of claim 1, wherein the crystalline binder material forms a nanoporous structure.

4. The method of claim 1, wherein the drying is performed at a temperature of 70 °C to 120 °C.

5. The method of claim 1, wherein the frequency is in the range of 0.01 Hz to 10 kHz.

6. The method of claim 1, wherein the magnitude is in the range of 0.1 kV / cm to 200 kV / cm.

7. The method of claim 1, wherein the electric field is applied throughout the compaction drying stage.

8. The method of claim 1, wherein adjusting the frequency and magnitude of the electric field to control crystallization of the binder material comprises reducing a crystallization rate of the binder material.

9. The method of claim 1, wherein adjusting the frequency and magnitude of the electric field to control crystallization of the binder material comprises increasing a crystallization rate of the binder material.

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