Silicon negative electrode sheet and preparation method thereof

Abstract

This invention provides a silicon anode sheet and its preparation method. The silicon anode sheet includes: an active material layer containing silicon material, a conductive agent, and a fibrous binder; and a current collector disposed on the upper and lower surfaces of the active material layer, wherein the current collector is made of carbon felt material. According to the silicon anode sheet of this invention, on the one hand, the use of a fibrous binder in the active material layer can form a cross-linked bonding network, thereby effectively improving the flexibility of the electrode sheet and overcoming the deformation and stress problems caused by the volume expansion of the active material; on the other hand, the use of carbon felt material to make the current collector on the silicon anode sheet allows its rigidity to suppress electrode expansion, improve battery life, and its chemical properties to prevent electrolyte corrosion of the current collector, thereby effectively improving the battery's cycle performance.

Description

Technical Field

[0001] This invention relates to the field of battery technology, specifically to a silicon anode sheet and its preparation method. Background Technology

[0002] With the continuous development of the electric vehicle market and the increasing demands for electric vehicle performance, there is an urgent need to develop power batteries with high energy density, high safety, long cycle life, and low cost. To improve the energy density of power batteries, developing silicon-based anode systems with high specific capacity has become a key focus for the industry and the market. Currently, the main problems facing silicon-based anodes are: the significant volume changes in silicon-based materials lead to a series of issues, such as material particle breakage, electrode detachment, increased electrode polarization, rapid battery performance degradation, and poor battery cycle performance. Summary of the Invention

[0003] In view of this, the present invention provides a silicon negative electrode sheet and its preparation method, which can effectively improve the cycle performance of the battery.

[0004] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0005] According to a first aspect of the present invention, a silicon negative electrode sheet comprises:

[0006] An active material layer, wherein the active material layer contains silicon material, a conductive agent, and a fibrous binder;

[0007] A current collector is disposed on the upper and lower surfaces of the active material layer, wherein the current collector is made of carbon felt material.

[0008] Furthermore, the areal capacity of the active material layer is 3–6 mAh / cm³. 2 ,

[0009] The silicon material includes one or more of pure silicon, silicon suboxide, silicon oxide, pre-lithiated silicon, and silicon-carbon composite materials.

[0010] The conductive agent includes one or more of conductive graphite, carbon black, carbon fiber, carbon nanotubes, and graphene.

[0011] The fibrous binder includes polytetrafluoroethylene (PTFE), copolymers of other monomers and tetrafluoroethylene, or mixtures thereof, wherein the other monomers include ethylene or hexafluoropropylene.

[0012] Furthermore, the current collector has multiple through holes, the gap ratio of which is 20% to 50%, and the hole diameter is less than 30 μm.

[0013] Furthermore, the carbon felt material includes one or more of carbon fibers, carbon nanotubes, and carbon foam, wherein the carbon nanotubes include single-walled carbon nanotubes, multi-walled carbon nanotubes, or mixtures thereof.

[0014] The method for preparing a silicon negative electrode sheet according to a second aspect embodiment of the present invention includes the following steps:

[0015] S1, providing a current collector, the current collector being made of carbon felt material;

[0016] S2, providing an active material layer, the active material layer containing silicon material, conductive agent and fibrous binder;

[0017] S3, the current collector is attached to the upper and lower surfaces of the active material layer and hot-pressed to obtain a silicon negative electrode sheet.

[0018] Further, step S1 specifically includes:

[0019] A carbon felt material is provided, the carbon felt material comprising one or more of carbon fibers, carbon nanotubes and carbon foam, the carbon nanotubes comprising single-walled carbon nanotubes, multi-walled carbon nanotubes, or mixtures thereof;

[0020] The carbon felt material is perforated to obtain the current collector, with a perforation rate of 20% to 50% and a pore diameter of less than 30 μm.

[0021] Further, step S2 includes:

[0022] The silicon material, conductive agent, and fibrous binder are dry-mixed to obtain a mixture.

[0023] The mixture is hot-rolled to obtain the active material layer, wherein the mass ratio of the silicon material, conductive agent and binder is (0.1-90):(0.1-10):(0.2-20).

[0024] Furthermore, in step S2, the dry mixing is carried out in a drying chamber with a dew point temperature ≤ -30℃.

[0025] The silicon material includes one or more of pure silicon, silicon suboxide, silicon oxide, pre-lithiated silicon, and silicon-carbon composite materials.

[0026] The conductive agent includes one or more of conductive graphite, carbon black, carbon fiber, carbon nanotubes, and graphene.

[0027] The fibrous binder comprises polytetrafluoroethylene (PTFE), copolymers of other monomers and tetrafluoroethylene, or mixtures thereof, wherein the other monomers include ethylene or hexafluoropropylene, and in step 2, the areal capacity of the active material layer is 3–6 mAh / cm³.2 .

[0028] Furthermore, in step S3, the hot pressing composite is performed by one or more hot rolling processes.

[0029] Furthermore, in steps 2 and 3, the temperature of the hot rolling is 1°C to 20°C higher than the glass transition temperature of the fibrous binder, and the rolling pressure is 1 to 5 MPa.

[0030] The above-described technical solution of the present invention has at least one of the following beneficial effects:

[0031] According to an embodiment of the present invention, a silicon anode electrode includes an active material layer and a current collector. The active material layer contains silicon material, a conductive agent, and a fibrous binder. The current collector is made of carbon felt material and is disposed on the upper and lower surfaces of the active material layer. On the one hand, the use of a fibrous binder in the active material layer can form a cross-linked bonding network, thereby effectively improving the flexibility of the electrode and overcoming the deformation and stress problems caused by the volume expansion of the active material, thus improving the cycle stability of the battery. On the other hand, the current collector on the silicon anode electrode is made of carbon felt material, whose rigidity can suppress electrode expansion, improve battery life, and whose chemical properties can prevent electrolyte corrosion of the current collector, thereby improving the cycle performance of the battery. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the structure of a silicon negative electrode sheet according to a first aspect embodiment of the present invention.

[0033] Figure reference numerals: 100. Silicon anode sheet; 110. Active material layer; 120. Current collector. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the described embodiments of the present invention are within the scope of protection of the present invention.

[0035] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning understood by one of ordinary skill in the art to which this invention pertains. The terms "first," "second," and similar terms used in this invention do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Terms such as "connected" or "linked" are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. Terms such as "upper," "lower," "left," and "right" are used only to indicate relative positional relationships; when the absolute position of the described object changes, the relative positional relationship also changes accordingly.

[0036] The silicon anode electrode according to an embodiment of the present invention will now be described in detail with reference to the accompanying drawings.

[0037] According to the first aspect of the present invention, the silicon negative electrode 100, such as Figure 1 As shown, it includes: an active material layer 110 and a current collector 120.

[0038] The active material layer 110 contains silicon material, conductive agent and fibrous binder.

[0039] The current collector 120 is disposed on the upper and lower surfaces of the active material layer 110, wherein the current collector 120 is made of carbon felt material.

[0040] According to the silicon anode electrode 100 of the present invention, on the one hand, the active material layer 110 uses a fibrous binder to form a cross-linked bonding network, thereby effectively improving the flexibility of the electrode and overcoming the deformation and stress problems caused by the volume expansion of the active material, thereby improving the cycle stability of the battery; on the other hand, the current collector 120 on the silicon anode electrode 100 is made of carbon felt material, the rigidity of which can suppress the expansion of the electrode and improve the battery life, and its chemical properties can prevent the electrolyte from corroding the current collector, thereby improving the cycle performance of the battery.

[0041] In addition, carbon felt materials have advantages such as good flexibility, conductivity, electrochemical stability, easy processing, low resistivity, no environmental harm, and low price.

[0042] Preferably, the areal capacity of the active material layer 110 is 3–6 mAh / cm³. 2 .

[0043] Silicon materials may include one or more of pure silicon, silicon suboxide, silicon oxide, pre-lithiated silicon, and silicon-carbon composite materials.

[0044] Conductive agents may include one or more of conductive graphite, carbon black, carbon fiber, carbon nanotubes, and graphene.

[0045] Fiberized binders may include copolymers of polytetrafluoroethylene (PTFE), other monomers and tetrafluoroethylene, or mixtures thereof, wherein the other monomers include ethylene or hexafluoropropylene. These fiberized binders are preferred due to their high fiberization performance and low cost.

[0046] In some embodiments, the current collector 120 has a plurality of through holes (not shown), the clearance ratio of the through holes is 20% to 50%, and the hole diameter is less than 30 μm.

[0047] Therefore, by opening multiple through holes in the current collector 120, the steric hindrance of liquid entering the active material layer can be reduced during liquid injection, which can improve the liquid retention of the silicon negative electrode 100 and improve the battery cycle capability.

[0048] Preferably, the carbon felt material may include one or more of carbon fibers, carbon nanotubes, and carbon foam, and the carbon nanotubes may include single-walled carbon nanotubes, multi-walled carbon nanotubes, or mixtures thereof.

[0049] Among them, the current collector 120 made of carbon nanotubes is lighter and more compact than metal current collectors, which can significantly improve the energy density of the battery.

[0050] The method for preparing a silicon negative electrode sheet according to a second aspect embodiment of the present invention includes the following steps:

[0051] S1 provides a current collector, which is made of carbon felt material;

[0052] S2 provides an active material layer containing silicon material, conductive agent, and fibrous binder;

[0053] S3. Current collectors are attached to the upper and lower surfaces of the active material layer and then hot-pressed to obtain a silicon anode sheet.

[0054] According to the method for preparing silicon anode sheets according to embodiments of the present invention, the silicon anode sheets are prepared by dry electrode hot pressing, which avoids the problem of uneven dispersion caused by the migration of binder with solvent diffusion in traditional electrode preparation methods containing solvents. The binder can obtain better cohesion and prevent the silicon anode sheets from pulverizing.

[0055] Furthermore, step S1 may specifically include:

[0056] A carbon felt material is provided, the carbon felt material comprising one or more of carbon fibers, carbon nanotubes and carbon foam, the carbon nanotubes comprising single-walled carbon nanotubes, multi-walled carbon nanotubes, or mixtures thereof.

[0057] Carbon felt material is perforated to obtain a current collector, with a perforation rate of 20% to 50% and a pore diameter of less than 30 μm.

[0058] Further, step S2 may include:

[0059] Silicon material, conductive agent and fibrous binder are dry-mixed to obtain a mixture.

[0060] The mixture is hot-rolled to obtain an active material layer, wherein the mass ratio of silicon material, conductive agent and binder is (0.1~90):(0.1~10):(0.2~20).

[0061] In addition, in step S2, during dry mixing, graphite is added, including any one or more combinations of artificial graphite, natural graphite, or mesophase carbon microspheres.

[0062] Preferably, the mass ratio of graphite to silicon is (60-90):(10-40).

[0063] Specifically, adding graphite to the dry mixing process can improve the conductivity of the active material layer. On the other hand, graphite has a lower specific capacity than silicon, which can effectively reduce the volume expansion effect of the silicon anode sheet, thereby improving the cycle performance of the battery.

[0064] Furthermore, in step S2, the dry mixing is carried out in a drying chamber with a dew point temperature ≤ -30°C.

[0065] Silicon materials may include one or more of pure silicon, silicon suboxide, silicon oxide, pre-lithiated silicon, and silicon-carbon composite materials.

[0066] Conductive agents may include one or more of conductive graphite, carbon black, carbon fiber, carbon nanotubes, and graphene.

[0067] The fibrous binder may include polytetrafluoroethylene (PTFE), copolymers of other monomers and tetrafluoroethylene, or mixtures thereof, wherein the other monomers include ethylene or hexafluoropropylene, and in step 2, the areal capacity of the active material layer is 3–6 mAh / cm³. 2 .

[0068] Furthermore, in step S3, hot pressing is performed by one or more hot rolling processes.

[0069] Furthermore, in steps 2 and 3, the temperature of the hot roller pressing is 1℃-20℃ higher than the glass transition temperature of the fiberized binder, and the roller pressing pressure is 1~5MPa.

[0070] An embodiment of the method for preparing the silicon negative electrode sheet according to the present invention is as follows:

[0071] Under a dry environment with a dew point of -40℃, 6.4g of graphite, 3g of silica, 0.4g of fibrous binder (PTFE), and 0.2g of conductive carbon black (SP) were mechanically dispersed at 18000rpm for 15min. After stirring, an agglomerated mixture was obtained. The mixture was then heated and rolled at 140℃ once to obtain a smooth active material layer. The surface capacity of the active material layer was 5mAh / cm². 2 Carbon nanotube-synthesized carbon felt is used as the current collector and is rolled and compounded with the obtained active material layer. The roller temperature is 120℃ and the rolling is performed twice to obtain a silicon negative electrode sheet.

[0072] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A silicon negative electrode sheet, characterized in that, include: An active material layer, wherein the active material layer contains silicon material, a conductive agent, and a fibrous binder; The current collector is attached to the upper and lower surfaces of the active material layer by hot-pressing composite bonding. The current collector is made of carbon felt material, which is perforated to obtain the current collector with a porosity of 20% to 50% and a pore size of less than 30 μm.

2. The silicon negative electrode sheet according to claim 1, characterized in that, The areal capacity of the active material layer is 3~6 mAh / cm³. 2 , The silicon material includes one or more of pure silicon, silicon suboxide, silicon oxide, pre-lithiated silicon, and silicon-carbon composite materials. The conductive agent includes one or more of conductive graphite, carbon black, carbon fiber, carbon nanotubes, and graphene. The fibrous binder includes polytetrafluoroethylene, copolymers of other monomers and tetrafluoroethylene, or mixtures thereof, wherein the other monomers include ethylene or hexafluoropropylene.

3. The silicon negative electrode sheet according to claim 1, characterized in that, The carbon felt material includes one or more of carbon fibers, carbon nanotubes, and carbon foam, wherein the carbon nanotubes include single-walled carbon nanotubes, multi-walled carbon nanotubes, or mixtures thereof.

4. A method for preparing a silicon negative electrode sheet, characterized in that, Includes the following steps: S1, providing a current collector, the current collector being made of carbon felt material, the carbon felt material being perforated to a standard of 20%~50% porosity and pore size less than 30μm, to obtain the current collector; S2, providing an active material layer, the active material layer containing silicon material, conductive agent and fibrous binder; S3, the current collector is attached to the upper and lower surfaces of the active material layer and hot-pressed to obtain a silicon negative electrode sheet.

5. The method for preparing the silicon negative electrode sheet according to claim 4, characterized in that, Step S1 specifically includes: A carbon felt material is provided, the carbon felt material comprising one or more of carbon fibers, carbon nanotubes, and carbon foam, the carbon nanotubes comprising single-walled carbon nanotubes, multi-walled carbon nanotubes, or mixtures thereof.

6. The method for preparing the silicon negative electrode sheet according to claim 4, characterized in that, Step S2 includes: The silicon material, conductive agent, and fibrous binder are dry-mixed to obtain a mixture. The mixture is hot-rolled to obtain the active material layer, wherein the mass ratio of the silicon material, conductive agent and fibrous binder is (0.1~90):(0.1~10):(0.2~20).

7. The method for preparing the silicon negative electrode sheet according to claim 6, characterized in that, In step S2, the dry mixing is carried out in a drying room with a dew point temperature ≤ 30℃. The silicon material includes one or more of pure silicon, silicon suboxide, silicon oxide, pre-lithiated silicon, and silicon-carbon composite materials. The conductive agent includes one or more of conductive graphite, carbon black, carbon fiber, carbon nanotubes, and graphene. The fibrous binder comprises polytetrafluoroethylene, copolymers of other monomers and tetrafluoroethylene, or mixtures thereof, wherein the other monomers include ethylene or hexafluoropropylene, and in step S2, the areal capacity of the active material layer is 3~6 mAh / cm³. 2 .

8. The method for preparing the silicon negative electrode sheet according to claim 6, characterized in that, In step S3, the hot pressing composite is performed by one or more hot rolling processes.

9. The method for preparing the silicon negative electrode sheet according to claim 8, characterized in that, In steps S2 and S3, the temperature of the hot roller pressing is 1°C to 20°C higher than the glass transition temperature of the fiberized binder, and the roller pressing pressure is 1 to 5 MPa.

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