Negative electrode slurry, negative electrode sheet, all-solid-state battery and preparation method thereof

Abstract

The present invention provides a negative electrode slurry, a negative electrode plate, an all-solid-state battery, and a preparation method thereof. The negative electrode slurry comprises first micron silicon particles, second micron silicon particles, third micron silicon particles, a solvent, and a first binder. The particle size of the first micron silicon particles is less than the particle size of the second micron silicon particles, which is less than the particle size of the third micron silicon particles. The difference in particle size between the first and second micron silicon particles is between 0.5 and 2.5 μm. The difference in particle size between the second and third micron silicon particles is between 2 and 19 μm. The negative electrode plate prepared using the negative electrode slurry of the present invention not only has a low plate expansion rate and a high silicon content, but also exhibits excellent electrochemical performance in all-solid-state batteries. Furthermore, the micron silicon particles are widely available and more environmentally friendly. The negative electrode plate can be prepared using a simple preparation method, resulting in lower product manufacturing costs and promising prospects for industrial application.

Description

Technical Field

[0001] The present invention relates to the field of all-solid-state lithium-ion batteries, and in particular to a negative electrode slurry, a negative electrode sheet, an all-solid-state battery and a preparation method thereof. Background Art

[0002] As the graphite negative electrode in lithium-ion batteries has reached its theoretical capacity (375mAh / g), the energy density of the battery has gradually decreased. Silicon materials have received widespread attention due to their high gram capacity (4200mAh / g), wide source of raw materials and environmental friendliness. Usually, silicon negative electrodes are only used as an additive to increase capacity and mixed with graphite negative electrodes, while pure silicon negative electrodes have not yet been commercially applied. This is mainly because pure silicon negative electrodes easily generate Li during the lithium insertion process. 3.75 Si alloy, which causes its volume to change and can expand to 300% of its original volume. During the charge and discharge process of the battery, the silicon electrode can cause the solid electrolyte interface film on the silicon surface to continuously rupture and form, and can also cause the negative electrode active material to separate from the current collector, resulting in rapid decay of the negative electrode capacity and poor battery cycle performance. Therefore, compared with traditional liquid lithium-ion batteries, silicon negative electrodes are more suitable for all-solid-state batteries. This is mainly based on the fact that all-solid-state batteries use solid electrolytes instead of liquid electrolytes, and the silicon negative electrode only contacts the surface of the solid electrolyte, so there will be no rupture and formation of a large number of solid electrolyte interface films on the surface of silicon particles.

[0003] In the prior art, in order to alleviate the problem of silicon negative electrode expansion, the methods used mainly include using complex silicon nanostructures and combining carbon composite materials with elastic adhesive matrices or polymers to prepare silicon negative electrode plates. However, the plates prepared by this method have low compactness and the preparation methods are often complicated and costly, making them impractical for large-scale application, thereby hindering the commercial application of silicon negative electrodes. A Chinese invention patent (application number: CN201910534209.9) discloses an all-solid-state battery using a silicon negative electrode and a sulfide solid electrolyte. It mainly prepares a composite silicon negative electrode by mixing silicon with a sulfide electrolyte to alleviate the volume expansion problem of silicon. However, the effective silicon content of the composite silicon negative electrode during operation is less than 60wt%, which makes it impossible to exert the high capacity characteristics of the silicon material, reduces the energy density of the all-solid-state battery, and also increases the amount of sulfide electrolyte used, resulting in a significant increase in cost.

[0004] In summary, the silicon anode materials prepared in the prior art have problems such as severe volume expansion, low silicon content, or high production costs during specific applications. Based on this, there is an urgent need to provide a silicon anode material to improve the above problems. Summary of the Invention

[0005] The main purpose of the present invention is to provide a negative electrode slurry, a negative electrode plate, an all-solid-state battery and a preparation method thereof, so as to solve the problems of existing silicon negative electrodes, such as severe volume expansion, low silicon content of the material, or high preparation cost of the material itself.

[0006] To achieve the above-mentioned object, according to one aspect of the present invention, a negative electrode slurry is provided, which includes first micron silicon particles, second micron silicon particles, third micron silicon particles, a solvent and a first binder; wherein the particle size of the first micron silicon particles is less than the particle size of the second micron silicon particles and is less than the particle size of the third micron silicon particles, and the difference in particle size between the first micron silicon particles and the second micron silicon particles is between 0.5 and 2.5 μm; and the difference in particle size between the second micron silicon particles and the third micron silicon particles is between 2 and 19 μm.

[0007] Furthermore, the particle size of the first micron silicon particles is 0.3-0.7 μm, the particle size of the second micron silicon particles is 1-2 μm, and the particle size of the third micron silicon particles is 4-20 μm; preferably, the weight ratio of the first micron silicon particles, the second micron silicon particles and the third micron silicon particles is (0.1-10):(0.1-50):(50-90); further preferably, the weight ratio of the first micron silicon particles, the second micron silicon particles and the third micron silicon particles is (5-10):(30-50):(50-65).

[0008] Furthermore, the ratio of the total weight of the first micron silicon particles, the second micron silicon particles and the third micron silicon particles to the weight of the first binder is (90-99.9):(0.1-10); preferably, the ratio of the total weight of the first micron silicon particles, the second micron silicon particles and the third micron silicon particles to the weight of the first binder is (95-99.9):(0.1-5).

[0009] Furthermore, the first binder is selected from one or more of PVDF, SBS, NBR, PAA, CMC or PTFE; the solvent is preferably selected from one or more of N-methylpyrrolidone, cyclohexane, toluene, benzene, methyl ethyl ketone, ethyl acetate, dichloroethane or water; and the amount of the solvent is preferably 0.8 to 1.5 times the total weight of the first micron silicon particles, the second micron silicon particles and the third micron silicon particles.

[0010] According to another aspect of the present invention, a negative electrode plate is provided. The negative electrode plate is obtained by first drying and forming the above-mentioned negative electrode slurry.

[0011] Furthermore, the porosity of the negative electrode sheet is 20-60%, preferably 40-50%; the silicon loading of the negative electrode sheet is preferably 0.2-5.0 mg / cm 2 , more preferably 0.8 to 1.8 mg / cm 2; The thickness of the negative electrode sheet is preferably 10 to 50 μm, more preferably 20 to 30 μm.

[0012] Furthermore, the first drying process temperature is 70-120° C., and the process time is 8-15 hours.

[0013] According to another aspect of the present invention, an all-solid-state battery is provided, which includes a positive electrode sheet, a solid electrolyte layer and a negative electrode sheet stacked in sequence, and the negative electrode sheet is the above-mentioned negative electrode sheet.

[0014] Furthermore, the positive electrode active material in the positive electrode sheet includes a base material and a coating layer coated on the outer surface of the base material; preferably, the base material has a structural formula of LiNi x Co y Mn z M n O2, wherein 0.7≤x≤0.92, 0≤y≤0.2, 0≤z≤0.2, 0≤n≤0.2, and x+y+z+n=1; M is selected from one or more of Al, Mg, Fe, Ti, V, Zr, La, Mo, Zn, Cu or Y.

[0015] Furthermore, the material of the coating layer is selected from LiNbO3, Li 1.3 Al 0.3 Ti 1.7 (PO4)3, Li3BO3, LiPO3, Li2ZrO3, Li7La3Zr2O 12 , Li2TiO3, LiTaO3 or Al2O3; preferably, the positive electrode active material is granular, and the average particle size of the positive electrode active material is 1 to 15 μm.

[0016] Furthermore, the material of the solid electrolyte layer is a sulfide solid electrolyte and / or a halide solid electrolyte; preferably, the sulfide solid electrolyte is selected from Li6PS5Cl, Li6PS5Cl 0.5 Br 0.5 、Li 9.54 Si 1.74 P 1.44 S 11.7 Cl 0.3 、Li 10 GeP2S 12 、Li7P3S 11 、LiPON、Li 10 SnP2S 12, LiS-SiS2 or one or more of xLi2S·yP2S5, wherein 100≥x≥70, 30≥y≥0; more preferably, the halide solid electrolyte is selected from one or more of Li3InCl6, Li3YBr6, Li3InBr6, Li2ZrCl6, Li3ErCl6 or Li3YCl6.

[0017] According to another aspect of the present invention, a method for preparing an all-solid-state battery is provided, which comprises the following steps: step S1, providing the above-mentioned negative electrode plate, wherein the negative electrode plate has a first surface and a second surface arranged opposite to each other; step S2, arranging a solid electrolyte layer on the first surface of the negative electrode plate; step S3, arranging a positive electrode plate on the outer surface of the solid electrolyte layer away from the first surface.

[0018] Furthermore, in step S2, the material of the solid electrolyte layer is first mixed with the second binder to obtain a mixed slurry, and then the mixed slurry is coated on the first surface of the negative electrode plate, and the solid electrolyte layer is formed after a second drying; preferably, the material of the solid electrolyte layer is granular, and the average particle size of the material of the solid electrolyte layer is 1 to 100 μm; preferably, the weight ratio of the material of the solid electrolyte layer to the second binder is (90 to 100): (0.1 to 10); preferably, the treatment temperature of the second drying is 60 to 80°C, and the treatment time is 12 to 24 hours.

[0019] The negative electrode plate prepared by using the negative electrode slurry of the present invention not only has a low plate expansion rate and a high silicon content, but also the all-solid-state battery also exhibits excellent electrochemical performance. The micron silicon particles have a wider source and are more environmentally friendly. The negative electrode plate can be prepared by a simple preparation method, the product manufacturing cost is lower, and the industrial application prospect is better. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The accompanying drawings, which constitute part of this application, are intended to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are intended to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

[0021] Figure 1 A schematic structural diagram of an all-solid-state battery in one embodiment of the present invention is shown.

[0022] The above drawings include the following reference numerals:

[0023] 10. Positive electrode; 20. Solid electrolyte layer; 30. Negative electrode;

[0024] 11. First current collector; 12. Positive electrode active material layer;

[0025] 31. Negative electrode active material layer; 32. Second current collector. DETAILED DESCRIPTION

[0026] It should be noted that, in the absence of conflict, the embodiments and features of the embodiments in this application can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0027] As described in the background technology section of the present invention, the silicon negative electrode materials prepared in the prior art have problems such as severe volume expansion, low silicon content, or high preparation cost during specific applications. To address this problem, the present invention provides a negative electrode slurry, which includes first micron silicon particles, second micron silicon particles, third micron silicon particles, a solvent, and a first binder; wherein the particle size of the first micron silicon particles is less than the particle size of the second micron silicon particles and less than the particle size of the third micron silicon particles, and the particle size difference between the first micron silicon particles and the second micron silicon particles is between 0.5 and 2.5 μm; and the particle size difference between the second micron silicon particles and the third micron silicon particles is between 2 and 19 μm.

[0028] Although silicon has a high gram capacity, the negative electrode sheet usually made of pure silicon material will form Li when lithium is inserted. 3.75 Si alloy, the volume expansion of the alloy is greater than 300%. In this way, in liquid lithium ions, the silicon negative electrode will continue to change in volume during the charge and discharge process, which will cause the solid electrolyte interface film on the silicon surface to continuously break and form, and will also cause the active material to separate from the current collector, causing the negative electrode capacity to decay rapidly and the cycle performance to be substandard. Therefore, in the prior art, silicon negative electrodes are usually only used as an additive to increase capacity and mixed with graphite negative electrodes, such as the commonly used composite silicon carbon (for example: S i / C or SiO / C) negative electrode material.

[0029] The present invention unexpectedly uses micron silicon particles of different particle sizes to cooperate with each other to form the above-mentioned negative electrode slurry. When the negative electrode slurry is subsequently formed into a negative electrode sheet (described in detail below), a suitable porous structure can be formed in the negative electrode sheet, thereby causing the negative electrode sheet to have a porous structure with excellent performance. Such a porous structure can enable the negative electrode sheet to significantly alleviate the lateral volume expansion change of the negative electrode sheet when lithium is inserted at a high silicon content (silicon content is higher than 99wt%, gram capacity is higher than 2500mAh / g), thereby avoiding cracking or pulverization of the negative electrode sheet, thereby enabling the all-solid-state battery to simultaneously take into account better capacity performance, cycle performance and energy density. At the same time, the above-mentioned micron silicon particles are relatively wide in source, more environmentally friendly, and the negative electrode sheet can be prepared by a simple preparation method, with lower product manufacturing costs and better prospects for industrial application.

[0030] In order to further obtain a negative electrode sheet with better structural performance and to slow down the lateral volume expansion change of the negative electrode material when lithium is inserted, the particle size of the first micron silicon particles is preferably 0.3-0.7 μm, the particle size of the second micron silicon particles is 1-2 μm, and the particle size of the third micron silicon particles is 4-20 μm. Based on this, the negative electrode sheet obtained subsequently has a more suitable porosity, and the battery can simultaneously take into account better capacity performance, cycle performance and energy density. Further preferably, the weight ratio of the first micron silicon particles, the second micron silicon particles and the third micron silicon particles is (0.1-10): (0.1-50): (50-90), and more preferably (5-10): (30-50): (50-65). In order to further improve the stability and performance uniformity of the negative electrode sheet, the ratio of the total weight of the first micron silicon particles, the second micron silicon particles and the third micron silicon particles to the weight of the first binder is preferably (90-99.9): (0.1-10).

[0031] To further improve the stability, dispersion uniformity, and safety of the negative electrode slurry and ensure better adhesion between micron silicon particles of different particle sizes, thereby enhancing electrochemical performance, the first binder is preferably selected from one or more of PVDF, SBS, NBR, PAA, CMC, or PTFE. Furthermore, the solvent is preferably selected from one or more of NMP, cyclohexane, toluene, benzene, methyl ethyl ketone, ethyl acetate, or ethylene dichloride. More preferably, the amount of solvent used is 0.8 to 1.5 times the total weight of the first, second, and third micron silicon particles.

[0032] In an optional embodiment, those skilled in the art can obtain the above-mentioned negative electrode slurry by the following preparation method: first dissolve the above-mentioned binder in a solvent to prepare a glue solution, then mix micron silicon particles of different particle sizes, and finally add the glue solution to the mixture to form the above-mentioned negative electrode slurry.

[0033] The present invention provides a negative electrode plate, which is obtained by first drying and forming the above-mentioned negative electrode slurry. Based on the reasons mentioned above, the negative electrode plate of the present invention has a porous structure with excellent performance. Such a porous structure can enable the negative electrode plate to significantly alleviate the lateral volume expansion change of the negative electrode plate when lithium is inserted under high silicon content (silicon content is higher than 99wt%, gram capacity is higher than 2500mAh / g), thereby avoiding cracking or pulverization of the negative electrode plate, and thus enabling the all-solid-state battery to take into account better capacity performance, cycle performance and energy density at the same time. At the same time, the above-mentioned micron silicon particles are relatively wide in source and more environmentally friendly. By using them as raw materials for preparing negative electrode plates, negative electrode plates can be prepared by a simple preparation method, and the product manufacturing cost is lower and the industrial application prospect is better.

[0034] Specifically, those skilled in the art can obtain the above-mentioned negative electrode sheet by the following preparation method: coating the above-mentioned negative electrode slurry on copper foil with a scraper to form a film, and then further performing a first drying on the film to obtain the negative electrode sheet.

[0035] In a preferred embodiment, in order to better alleviate the lateral volume expansion change of the negative electrode material during lithium insertion, thereby avoiding cracking or pulverization of the negative electrode material and further improving the capacity performance and cycle performance of the all-solid-state battery, the porosity of the negative electrode sheet is preferably 20-60%, more preferably 40-50%; the silicon loading of the negative electrode sheet is 0.2-5.0 mg / cm 2 , more preferably 0.8 to 1.8 mg / cm 2 The silicon content of the negative electrode sheet mentioned above is relatively high in this application, so the thickness can be smaller than that of products with the same area and capacity. On the basis of slowing down the volume expansion of the negative electrode material in the longitudinal direction of the battery, the applicant, in order to further promote the interface contact between the negative electrode sheet and the current collector and the solid electrolyte membrane, preferably sets the thickness of the negative electrode sheet to 10 to 50 μm, and more preferably to 20 to 30 μm.

[0036] To further improve the stability of the negative electrode sheet and the electrochemical performance of the battery, the negative electrode slurry is first dried and formed to obtain the negative electrode sheet. Preferably, the first drying treatment temperature is 70-120° C. and the treatment time is 8-15 hours.

[0037] Another aspect of the present invention provides an all-solid-state battery, which comprises a positive electrode sheet, a solid electrolyte layer, and a negative electrode sheet stacked in sequence, wherein the negative electrode sheet is the negative electrode sheet provided above. The all-solid-state battery has the characteristics of small volume expansion change, high silicon content, and excellent cycle performance and electrochemical performance, such as Figure 1 As shown, the all-solid-state battery includes a positive electrode sheet 10, a solid electrolyte layer 20, and a negative electrode sheet 30. The positive electrode sheet 10 includes a first current collector 11 and a positive electrode active material 12; the negative electrode sheet 30 includes a negative electrode active material 31 and a second current collector 32.

[0038] In a preferred embodiment, in order to further improve the electrochemical performance and cycle performance of the battery, the positive electrode active material in the positive electrode sheet of the all-solid-state battery includes a base material and a coating layer coated on the outer surface of the base material, and the preferred structural formula of the base material is LiNi x Co y Mn z M nO2, wherein 0.7≤x≤0.92, 0≤y≤0.2, 0≤z≤0.2, 0≤n≤0.2, and satisfying x+y+z+n=1; M is selected from one or more of Al, Mg, Fe, Ti, V, Zr, La, Mo, Zn, Cu or Y. In order to further improve the performance of the positive electrode sheet and make it cooperate with the negative electrode sheet and the solid electrolyte layer to make the battery chemical performance better, the material of the coating layer is preferably selected from LiNbO3, Li 1.3 Al 0.3 Ti 1.7 (PO4)3, Li3BO3, LiPO3, Li2ZrO3, Li7La3Zr2O 12 , Li2TiO3, LiTaO3 or Al2O3. It is further preferred that the positive electrode active material is in a granular form, and the average particle size of the positive electrode active material is 1 to 15 μm.

[0039] In order to further improve the electrochemical properties and cycle performance of the battery, the material of the solid electrolyte layer is preferably a sulfide solid electrolyte and / or a halide solid electrolyte; more preferably, the sulfide solid electrolyte is selected from Li6PS5Cl, Li6PS5Cl 0.5 Br 0.5 、Li 9.54 Si 1.74 P 1.44 S 11.7 Cl 0.3 、Li 10 GeP2S 12 、Li7P3S 11 、LiPON、Li 10 SnP2S 12 , LiS-SiS2 or one or more of xLi2S·yP2S5, wherein 100≥x≥70, 30≥y≥0; more preferably, the halide solid electrolyte is selected from one or more of Li3InCl6, Li3YBr6, Li3InBr6, Li2ZrCl6, Li3ErCl6 or Li3YCl6.

[0040] Another aspect of the present invention also provides a method for preparing an all-solid-state battery, which comprises the following steps: step S1, providing the above-mentioned negative electrode plate, wherein the negative electrode plate has a first surface and a second surface arranged opposite to each other; step S2, arranging a solid electrolyte layer on the first surface of the negative electrode plate; step S3, arranging a positive electrode plate on the outer surface of the solid electrolyte layer away from the first surface.

[0041] Those skilled in the art can first select a negative electrode sheet having a first surface and a second surface arranged opposite each other, then coat a solid electrolyte layer on the first surface of the negative electrode sheet, and finally place a positive electrode sheet on the outer surface of the solid electrolyte layer away from the first surface, assemble it into an all-solid-state battery by compaction, and press the all-solid-state battery at 300-400 MPa for 2-10 minutes to obtain the final all-solid-state battery. The all-solid-state battery prepared in this way, in which the solid electrolyte layer is coated on the negative electrode sheet, can further reduce the amount of the second binder used compared to traditional solid electrolyte film formation alone, thereby achieving higher ionic conductivity and further enabling the all-solid-state battery to have better rate performance at room temperature.

[0042] To further improve the chemical properties and cycle performance of all-solid-state batteries, in step S2 of preparing the all-solid-state battery, the material for the solid electrolyte layer is first mixed with a second binder to form a mixed slurry. The mixed slurry is then coated on the first surface of the negative electrode plate and subjected to a second drying step to form the solid electrolyte layer. Preferably, the weight ratio of the solid electrolyte layer material to the second binder is (90-100):(0.1-10), the solid electrolyte layer material is granular, and the average particle size of the solid electrolyte layer material is 1-100 μm; more preferably, the second drying process temperature is 60-80°C and the treatment time is 12-24 hours.

[0043] The present application is further described in detail below with reference to specific embodiments. These embodiments should not be construed as limiting the scope of protection claimed in this application.

[0044] Example 1

[0045] Negative electrode slurry: the particle size of the first micron silicon particles is 0.7μm, the particle size of the second micron silicon particles is 1.7μm, and the particle size of the third micron silicon particles is 10.0μm. The particle size difference between the first micron silicon particles and the second micron silicon particles is 1.0μm, and the particle size difference between the second micron silicon particles and the third micron silicon particles is 8.3μm; the weight ratio of the first micron silicon particles, the second micron silicon particles and the third micron silicon particles is 7:40:53, the solvent type is NMP, the first binder type is PVDF, the ratio of the total weight of the first micron silicon particles, the second micron silicon particles and the third micron silicon particles to the weight of the first binder is 99:1, and the amount of solvent used is 1 times the total weight of the first micron silicon particles, the second micron silicon particles and the third micron silicon particles.

[0046] Preparation steps of the negative electrode sheet: take the above-mentioned negative electrode slurry, then use a doctor blade to coat it into a film, and perform the first drying in a vacuum drying oven at a treatment temperature of 90°C and a treatment time of 12 hours to obtain a negative electrode sheet.

[0047] Preparation steps for the solid electrolyte layer: The solid electrolyte is a sulfide solid electrolyte with a Li6PS5Cl structure. The solid electrolyte layer material has a particle size of 15μm, and the secondary binder is SBS. First, the solid electrolyte layer material is mixed with the secondary binder to form a mixed slurry. This mixed slurry is then applied to the first surface of the negative electrode sheet. After a second drying step, the solid electrolyte layer is formed. The weight ratio of the solid electrolyte layer material to the secondary binder is 98:2. The secondary drying step is performed at 80°C for 12 hours.

[0048] Preparation steps of positive electrode sheet: the positive electrode matrix material structure is LiNi 0.8 Co 0.1 Mn 0.1 O3, the coating layer material is LiNbO3, the positive electrode active material particle size is 5μm, the third binder is SBS, and the conductive agent is VCGF carbon. Take the above-mentioned positive electrode material, the material in the solid electrolyte layer, and the conductive agent and stir them in a mixer for the first time to obtain a mixed material. The first stirring speed is 1200rpm and the first stirring time is 0.2h. Then, the third binder is dissolved in anisole to obtain a third binder solution. The third binder solution is added to the above-mentioned mixed material and stirred for the second time to form a coating slurry. Among them, the second stirring speed is 1200rpm and the second stirring time is 0.15h. Then, use a scraper to coat the film and dry it in a vacuum drying oven at 80°C for 12h.

[0049] The all-solid-state battery preparation steps are as follows: the positive electrode sheet and the negative electrode sheet coated with a solid electrolyte layer are cut into small discs with a diameter of 10 mm. The negative electrode sheet coated with the solid electrolyte layer directly faces the positive electrode sheet and is compacted to form an all-solid-state lithium-ion battery. The all-solid-state battery is first pressed at 400 MPa for 5 minutes, and then the electrochemical performance is tested at 80 MPa.

[0050] Example 2

[0051] The only difference from Example 1 is that the particle size of the first micron silicon particles is 0.5 μm, the particle size of the second micron silicon particles is 1 μm, and the particle size of the third micron silicon particles is 20 μm. The particle size difference between the first micron silicon particles and the second micron silicon particles is 0.5 μm, and the particle size difference between the second micron silicon particles and the third micron silicon particles is 19 μm.

[0052] Example 3

[0053] The only difference from Example 1 is that the particle size of the first micron silicon particles is 0.3 μm, the particle size of the second micron silicon particles is 1 μm, and the particle size of the third micron silicon particles is 4 μm. The particle size difference between the first micron silicon particles and the second micron silicon particles is 0.7 μm, and the particle size difference between the second micron silicon particles and the third micron silicon particles is 3 μm.

[0054] Example 4

[0055] The only difference from Example 1 is that the weight ratio of the first micron silicon particles, the second micron silicon particles and the third micron silicon particles is 3:25:72.

[0056] Example 5

[0057] The only difference from Example 1 is that the weight ratio of the first micron silicon particles, the second micron silicon particles and the third micron silicon particles is 3:15:82.

[0058] Example 6

[0059] The only difference from Example 1 is that the weight ratio of the first micron silicon particles, the second micron silicon particles and the third micron silicon particles is 8:40:52.

[0060] Comparative Example 1

[0061] The only difference from Example 1 is that the negative electrode slurry only includes micron silicon particles with a particle size of 1.7 μm.

[0062] Comparative Example 2

[0063] The only difference from Example 1 is that the first micron silicon particles in the negative electrode slurry are 0.7 μm, and the second micron silicon particles are 1.7 μm.

[0064] Comparative Example 3

[0065] The only difference from Example 1 is that the particle size of the first micron silicon particles is 0.7 μm, the particle size of the second micron silicon particles is 5.7 μm, and the particle size of the third micron silicon particles is 30.7 μm. The particle size difference between the first micron silicon particles and the second micron silicon particles is 5 μm; the particle size difference between the second micron silicon particles and the third micron silicon particles is 25 μm.

[0066] Comparative Example 4

[0067] The only difference from Example 1 is that the particle size of the first micron silicon particles is 0.7 μm, the particle size of the second micron silicon particles is 0.75 μm, and the particle size of the third micron silicon particles is 1.25 μm. The particle size difference between the first micron silicon particles and the second micron silicon particles is 0.05 μm; the particle size difference between the second micron silicon particles and the third micron silicon particles is 0.5 μm.

[0068] Comparative Example 5

[0069] The only difference from Example 1 is that the negative electrode slurry only includes micron silicon particles with a particle size of 0.7 μm.

[0070] Comparative Example 6

[0071] The only difference from Example 1 is that the negative electrode slurry only includes micron silicon particles with a particle size of 4.0 μm.

[0072] Comparative Example 7

[0073] The only difference from Example 1 is that the weight ratio of the first micron silicon particles, the second micron silicon particles and the third micron silicon particles is 25:60:15.

[0074] Performance testing:

[0075] (1) Electrochemical performance test

[0076] The all-solid-state battery was tested for charge and discharge performance at a 0.1C rate, with a test voltage range of 2.5-4.2V and a test temperature of 30°C. This mainly included testing the all-solid-state battery's initial efficiency, 0.1C discharge specific capacity, and cycle performance (capacity retention after 100 cycles at 0.1C).

[0077] (2) Porosity test

[0078] It is calculated by the ratio of true density to theoretical density. The specific formula is as follows:

[0079] Porosity = 1-(real density / theoretical density), where the real density is the ratio of the mass of the active material layer on the electrode to the volume of the active material layer, and the theoretical density is the theoretical density of high-purity silicon material (2.34 g / cm 3 ).

[0080] (3) Silicon loading

[0081] The negative electrode sheet is cut into discs with a diameter of 10 mm to obtain mass m1, and the same size of plain foil (without negative electrode material) is cut to obtain mass m2. The silicon loading is equal to the mass difference between mass m1 and mass m2, multiplied by the proportion of silicon in the sum of silicon and binder to obtain the silicon loading.

[0082] (4) Pole thickness expansion rate

[0083] The expansion rate of the negative electrode is measured by a professional expansion force testing equipment, an in-situ expansion analysis system, the equipment model is swe2110, and the test conditions are: measurement under a constant pressure of 628kg.

[0084] The specific test results of the negative electrode sheets and all-solid-state batteries prepared in the above embodiments and comparative examples are shown in Table 1.

[0085] Table 1

[0086]

[0087] From the above description, it can be seen that the above embodiments of the present invention achieve the following technical effects:

[0088] From the test data of Examples 1, 2, 3 and Comparative Examples 1, 2, 5, and 6, it can be found that when the negative electrode slurry of the present invention is used, which includes first micron silicon particles, second micron silicon particles, third micron silicon particles, a solvent, and a first binder, and the particle size of the first micron silicon particles is less than the particle size of the second micron silicon particles and less than the particle size of the third micron silicon particles, the prepared negative electrode sheet has a low sheet expansion rate and excellent electrochemical performance, and the micron silicon particles are widely available and more environmentally friendly. The negative electrode sheet can be prepared by a simple preparation method, and the product manufacturing cost is lower and the industrial application prospect is better. However, when only micron silicon particles of one particle size are used (Comparative Examples 1, 5, and 6) and micron silicon particles of two particle sizes are used (Comparative Example 2), due to the singleness of the silicon particle size or the small difference in the particle size of the two silicon particles, the sheet porosity is low, resulting in a significantly increased expansion rate of the obtained negative electrode sheet, and ultimately poor electrochemical performance.

[0089] From the test data of Examples 1, 2, 3 and Comparative Examples 3 and 4, it can be found that when the preparation method of the present invention is adopted, wherein the particle size difference between the first micron silicon particles and the second micron silicon particles is between 0.5 and 2.5 μm; the particle size difference between the second micron silicon particles and the third micron silicon particles is between 2 and 19 μm, and the particle size of the first micron silicon particles is 0.3 to 0.7 μm, the particle size of the second micron silicon particles is 1 to 2 μm, and the particle size of the third micron silicon particles is 4 to 20 μm, the prepared negative electrode pole piece has a lower pole piece expansion rate and excellent electrochemical performance, and the micron silicon particles are from a wider source and are more environmentally friendly. The negative electrode pole piece can be prepared by a simple preparation method, the product manufacturing cost is lower, and the industrial application prospect is better. However, when the particle sizes of the three types of micron silicon particles used are not within the above range, or the particle sizes of the first micron silicon particles and the second micron silicon particles, as well as the particle size difference between the second micron silicon particles and the third micron silicon particles are not within the above range (for example, Comparative Examples 3 and 4), the porosity in the electrode will be reduced due to the silicon particles being too small or too large, resulting in a significantly increased expansion rate of the negative electrode and poor electrochemical performance.

[0090] From the test data of Examples 4, 5, 6 and Comparative Example 7, it can be found that when the preparation method of the present invention is adopted, wherein the weight ratio of the first micron silicon particles, the second micron silicon particles and the third micron silicon particles is in the range of (0.1-10): (0.1-50): (50-90) (for example, 3:25:72 in Example 4 and 3:15:82 in Example 5), the prepared negative electrode pole piece has a lower pole piece expansion rate and better electrochemical performance, especially when the weight ratio of the first micron silicon particles, the second micron silicon particles and the third micron silicon particles is in the range of (5-10): (30-50): (50-65) (for example, 8:40:52 in Example 6), the prepared negative electrode slurry pole piece has a lower expansion rate and excellent electrochemical performance, and the negative electrode pole piece can be prepared only by a simple preparation method, the product manufacturing cost is lower, and the industrial application prospect is better. However, when the weight ratio of the first micron silicon particles, the second micron silicon particles and the third micron silicon particles is outside the range of (0.1-10):(0.1-50):(50-90) (for example, 25:60:15 in Comparative Example 7), the silicon particles with large particle size and the silicon particles with small particle size are not well matched, and a suitable porosity cannot be formed, resulting in a significantly increased expansion rate of the obtained negative electrode plate and poor electrochemical performance.

[0091] In summary, the negative electrode plate prepared by the negative electrode slurry of the present invention has a lower plate expansion rate, a higher silicon content of the plate, and the battery exhibits excellent electrochemical performance. In addition, the source of micron silicon particles is wider and more environmentally friendly. The negative electrode plate can be prepared by a simple preparation method, the product manufacturing cost is lower, and the industrial application prospect is better.

[0092] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A negative electrode slurry, characterized in that: The negative electrode slurry includes first micron silicon particles, second micron silicon particles, third micron silicon particles, a solvent and a first binder; The particle size of the first micron silicon particles is less than the particle size of the second micron silicon particles, which is less than the particle size of the third micron silicon particles. The difference in particle size between the first micron silicon particles and the second micron silicon particles is between 0.5 and 2.5 μm. The difference in particle size between the second micron silicon particles and the third micron silicon particles is between 2 and 19 μm. The particle size of the first micron silicon particles is 0.3-0.7 μm, the particle size of the second micron silicon particles is 1-2 μm, and the particle size of the third micron silicon particles is 4-20 μm; The weight ratio of the first micron silicon particles, the second micron silicon particles and the third micron silicon particles is (0.1-10):(0.1-50):(50-90).

2. The negative electrode slurry according to claim 1, characterized in that The weight ratio of the first micron silicon particles, the second micron silicon particles and the third micron silicon particles is (5-10):(30-50):(50-65).

3. The negative electrode slurry according to claim 1, characterized in that The ratio of the total weight of the first micron silicon particles, the second micron silicon particles, and the third micron silicon particles to the weight of the first binder is (90-99.9):(0.1-10).

4. The negative electrode slurry according to claim 1, characterized in that The ratio of the total weight of the first micron silicon particles, the second micron silicon particles, and the third micron silicon particles to the weight of the first binder is (95-99.9):(0.1-5).

5. The negative electrode slurry according to any one of claims 1 to 4, characterized in that The first binder is selected from one or more of PVDF, SBS, NBR, PAA, CMC or PTFE.

6. The negative electrode slurry according to any one of claims 1 to 4, characterized in that The solvent is selected from one or more of N-methylpyrrolidone, cyclohexane, toluene, benzene, methyl ethyl ketone, ethyl acetate, ethylene dichloride or water.

7. The negative electrode slurry according to any one of claims 1 to 4, characterized in that The amount of the solvent used is 0.8 to 1.5 times the total weight of the first micron silicon particles, the second micron silicon particles, and the third micron silicon particles.

8. A negative electrode plate, characterized in that: The negative electrode sheet is obtained by first drying and forming the negative electrode slurry according to any one of claims 1 to 7.

9. The negative electrode sheet according to claim 8, characterized in that: The porosity of the negative electrode sheet is 20-60%.

10. The negative electrode sheet according to claim 8, characterized in that: The porosity of the negative electrode sheet is 40-50%.

11. The negative electrode sheet according to claim 8, characterized in that: The silicon loading of the negative electrode plate is 0.2-5.0 mg / cm 2 .

12. The negative electrode sheet according to claim 8, characterized in that: The silicon loading of the negative electrode plate is 0.8-1.8 mg / cm 2 .

13. The negative electrode sheet according to claim 8, characterized in that: The thickness of the negative electrode plate is 10-50 μm.

14. The negative electrode sheet according to claim 8, characterized in that: The thickness of the negative electrode plate is 20-30 μm.

15. The negative electrode sheet according to any one of claims 8 to 14, characterized in that: The first drying process is performed at a temperature of 70-120° C. and for a time of 8-15 hours.

16. An all-solid-state battery comprising a positive electrode sheet, a solid electrolyte layer, and a negative electrode sheet stacked in sequence, characterized in that: The negative electrode sheet is the negative electrode sheet according to any one of claims 8 to 15.

17. The all-solid-state battery according to claim 16, characterized in that: The positive electrode active material in the positive electrode plate includes a base material and a coating layer coated on the outer surface of the base material.

18. The all-solid-state battery according to claim 17, characterized in that: The structural formula of the matrix material is LiNi x Co y Mn z M n O2, wherein 0.7≤x≤0.92, 0≤y≤0.2, 0≤z≤0.2, 0≤n≤0.2, and x+y+z+n=1; M is selected from one or more of Al, Mg, Fe, Ti, V, Zr, La, Mo, Zn, Cu or Y.

19. The all-solid-state battery according to claim 17, characterized in that: The material of the coating layer is selected from LiNbO3, Li 1.3 Al 0.3 Ti 1.7 (PO4)3, Li3BO3, LiPO3, Li2ZrO3, Li7La3Zr2O 12 , one or more of Li2TiO3, LiTaO3 or Al2O3.

20. The all-solid-state battery according to claim 17, characterized in that The positive electrode active material is in a granular form, and the average particle size of the positive electrode active material is 1 to 15 μm.

21. The all-solid-state battery according to claim 16, wherein: The material of the solid electrolyte layer is a sulfide solid electrolyte and / or a halide solid electrolyte.

22. The all-solid-state battery according to claim 21, characterized in that The sulfide solid electrolyte is selected from Li6PS5Cl, Li6PS5Cl 0.5 Br 0.5 、Li 9.54 Si 1.74 P 1.44 S 11.7 Cl 0.3 、Li 10 GeP2S 12 、Li7P3S 11 、LiPON、Li 10 SnP2S 12 , LiS-SiS2 or xLi2S•yP2S5, wherein 100≥x≥70, 30≥y≥0.

23. The all-solid-state battery according to claim 21, characterized in that The halide solid electrolyte is selected from one or more of Li3InCl6, Li3YBr6, Li3InBr6, Li2ZrCl6, Li3ErCl6 or Li3YCl6.

24. A method for preparing an all-solid-state battery according to any one of claims 16 to 23, characterized in that: The preparation method comprises the following steps: Step S1, providing a negative electrode sheet according to any one of claims 8 to 15, wherein the negative electrode sheet has a first surface and a second surface disposed opposite to each other; Step S2, providing a solid electrolyte layer on the first surface of the negative electrode plate; Step S3: arranging a positive electrode sheet on the outer surface of the solid electrolyte layer away from the first surface.

25. The method for preparing an all-solid-state battery according to claim 24, wherein: In step S2, the material of the solid electrolyte layer is first mixed with a second binder to obtain a mixed slurry, and then the mixed slurry is coated on the first surface of the negative electrode plate, and the solid electrolyte layer is formed after a second drying.

26. The method for preparing an all-solid-state battery according to claim 25, wherein: The material of the solid electrolyte layer is in a granular form, and the average particle size of the material of the solid electrolyte layer is 1 to 100 μm.

27. The method for preparing an all-solid-state battery according to claim 25, wherein: The weight ratio of the material of the solid electrolyte layer to the second binder is (90-100):(0.1-10).

28. The method for preparing an all-solid-state battery according to claim 25, wherein: The second drying process is performed at a temperature of 60-80° C. and for a time of 12-24 hours.

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