A high energy density lithium ion battery silicon-based negative electrode composite slurry and preparation method thereof

Abstract

The present invention discloses a high-energy-density lithium-ion battery silicon-based negative electrode composite slurry and a preparation method thereof. The silicon-based negative electrode composite slurry includes components such as a silicon-based main material, a resin binder, an SBR binder, a CMC powder binder, a granular conductive agent, a linear conductive agent, a liquid conductive agent, a dispersant, and a solvent. During the slurrying process, the present invention develops a suitable preparation method for the silicon system, which is not easy to knead and clump. The clustering and kneading of the silicon-based main material is achieved by gradually increasing the solid content of the slurry. The prepared slurry has excellent stability and is not easy to settle. The main material particles and the conductive agent in the obtained composite slurry are evenly dispersed, and a stable three-dimensional conductive network can be formed. The diaphragm resistivity is low, which provides a good path for electronic conduction and is of great application value in silicon-based negative electrode systems with high expansion rates. In addition, the preparation method provided by the present invention has a simple process, does not require complex mechanical equipment, can be mass-produced, and has good industrial application prospects.

Description

Technical Field

[0001] The present invention belongs to the field of lithium-ion battery slurry preparation technology, and specifically relates to a high-energy-density lithium-ion battery silicon-based negative electrode composite slurry and a preparation method thereof. Background Art

[0002] Currently, graphite, the mainstream anode material for commercial lithium-ion batteries, has a theoretical capacity of 372 mAh / g. Even the most advanced artificial graphite in the industry has an actual capacity of only 340-355 mAh / g. Its development potential has reached a bottleneck and it is no longer able to meet the demand for small size and high energy density in lithium-ion batteries. Among various anode materials, Si and SiOx anodes have extremely high lithium storage capacity (pure Si has a theoretical capacity of 4200 mAh / g) and are abundant in resources. SiOx also has a high capacity of 1400-1500 mAh / g, making it the most competitive alternative to graphite as anode material for next-generation lithium-ion batteries.

[0003] However, the high expansion and contraction coefficient of silicon-based negative electrodes causes them to continuously pulverize during the lithium insertion and extraction cycle, which destroys the overall structure of the material, continuously consumes active lithium, and causes a rapid degradation of cycle performance, which limits its large-scale application. Therefore, a large number of researchers are committed to the structural design and synthesis of Si-based materials, mostly based on suppressing the expansion of Si materials and taking advantage of the small volume effect of nanomaterials. When the Si particle size is less than 150nm, it is less likely to expand and crack, thereby significantly improving its cycle performance. However, the processing performance of nano-sized Si / SiOx is difficult to meet commercial requirements, so the Si / SiOx currently used in commercial applications is generally micron-sized.

[0004] In addition, the current commercial negative electrodes are all Si-doped graphite materials, and their slurry dispersion process is also based on the graphite CMC / SBR or PAA silicon-carbon system, which can basically follow the graphite pulping process. However, for the pure Si / SiOx negative electrode system, the difficulties in preparing the slurry are as follows: ① Compared with graphite, Si / SiOx has poor flexibility and smaller particles, high surface energy, and it is difficult to disperse the agglomerates evenly; ② Its inherent low conductivity leads to high resistivity, so a large amount of conductive agent is required, and the dispersion of the conductive agent becomes difficult; ③ Due to the lack of graphite support, the pure Si / SiOx system has high expansion and requires a high proportion of polymer binder. Increasing the binder content is not conducive to the dispersion of the main material particles. In addition, the slurry has high viscosity and low solid content, which easily forms micelles and particles, affecting the coating interface. Therefore, there are many application difficulties in the pulping process for the pure Si / SiOx system.

[0005] Currently, numerous patents and literature reports on slurry preparation processes using graphite CMC / SBR or PAA silicon-carbon systems, characterized by low binder content and high solids content. These slurries produced by these processes are characterized by poor stability, prone to sedimentation, and rheological anomalies. Furthermore, the formation of graphite-like clumping during the slurry preparation process for pure silicon anodes is difficult, significantly hindering the wetting and dispersion of dry powder. The quality of electrode slurry preparation directly impacts electrode performance, particularly for pure Si / SiOx anode systems. Addressing these slurry preparation challenges for pure Si / SiOx anode systems is a pressing technical challenge. Summary of the Invention

[0006] In view of the shortcomings of the existing technology, one of the purposes of the present invention is to provide a high-energy-density lithium-ion battery silicon-based negative electrode composite slurry, which has good post-coating processing performance and uniform coating surface density, while improving the rate and cycle performance of silicon-based high-energy-density lithium-ion batteries.

[0007] A second objective of the present invention is to provide a method for preparing the aforementioned silicon-based negative electrode composite slurry. During the slurrying process, the present invention achieves clumping and kneading of the pure silicon negative electrode by gradually increasing the slurry solids content. This improves the dispersion issues encountered in pure Si / SiOx negative electrode slurrying, resulting in a stable, rheologically normal negative electrode slurry that facilitates the high-capacity characteristics of pure Si / SiOx active materials. A specific process is provided to address the difficulties in slurrying with high conductive agent and binder content. This method is applicable to any micron-sized Si and SiOx material system.

[0008] To achieve the above object, the technical solution adopted by the present invention is:

[0009] A high-energy-density silicon-based negative electrode composite slurry for lithium-ion batteries, comprising the following components by weight: 21.0% to 28.5% of a silicon-based main material, 30% to 45% of a resin binder, 0.5% to 2% of an SBR binder, 1.5% to 2% of a CMC powder binder, 0.5% to 1.0% of a granular conductive agent, 1.0% to 1.5% of a linear conductive agent, 25% to 35% of a liquid conductive agent, 0.5% to 2.0% of a dispersant, and 5% to 20.0% of a solvent, the total weight of the above components being 100%. Preferably, the silicon-based main material includes at least one of Si and SiOx; the granular conductive agent includes at least one of Super P Li, acetylene black, LITX 300, and carbon black (Ketjen black carbon ECP600JD); the linear conductive agent includes at least one of carbon nanotube powder, VGCF, and carbon nanotube conductive paste; the liquid conductive agent includes at least one of graphene conductive paste and carbon nanotube conductive paste; the dispersant includes at least one of 1-3 butanediol, EC, PC, and isopropyl alcohol.

[0010] The method for preparing the high energy density lithium-ion battery silicon-based negative electrode composite slurry comprises the following steps:

[0011] Step 1: Weigh the silicon-based material to 91% to 96% of its total mass, then add it and a granular conductive agent to a dual planetary mixing tank. Start the orbital motion, close the dispersion shaft, and stir evenly to obtain a mixed powder. Preferably, the orbital speed is 20 to 40 rpm. Avoid vacuum during this process and maintain atmospheric pressure.

[0012] Step 2: Add CMC powder binder to deionized water and disperse at high speed to form a CMC binder solution. A resin binder is then added in proportion and dispersed at high speed under vacuum to form a mixed solution. Preferably, the CMC binder solution has a solids content of 0.5-1.2% and a viscosity of 3,000-9,000 mPas; the resin binder has a solids content of 8-10%; and the mass ratio of the CMC binder solution to the resin binder is 1:3-1:5.

[0013] Step 3: Add the conductive agent to the mixed adhesive solution from Step 2, then fully disperse it at high speed. Test the fineness of the composite conductive adhesive slurry until it reaches ≤5 μm, thereby obtaining a composite conductive adhesive slurry for later use. Preferably, the revolution speed is 60-80 rpm, the dispersion speed is 3500-4500 rpm, the vacuum level is <-90 kPa, the viscosity of the composite conductive adhesive slurry is controlled between 6000 and 9000 mPas, and the solids content is 5% to 8%.

[0014] Step 4: Add the composite conductive adhesive slurry in step 3 to the mixed powder in step 1 at one time, adjust the solid content to about 60%, stir and disperse for a period of time until the slurry becomes a paste slurry with good fluidity; then evenly add the remaining part of the silicon-based main material to the paste slurry, stir while adding, adjust the solid content to about 68%, close the cylinder and stir and disperse for a period of time until the slurry becomes a very viscous paste slurry, at this time the slurry does not form a complete clumping situation; finally, continue to add the remaining silicon-based main material to the viscous paste slurry, stir while adding, adjust the solid content to 72-74%, close the cylinder and stir for a period of time, scrape the wall slightly, at this time a dough-like state can be formed, continue to turn on the stirring, low-speed dispersion, fully knead and soak for a period of time to obtain a dough-like material. Preferably, the revolution speed is 20-40 rpm, the wall scraping number is greater than 2 times, the revolution speed after scraping is 40-60 rpm, the dispersion speed is 2500-3500 rpm, and the vacuum degree is less than -90 kPa.

[0015] Step 5: Add the liquid conductive agent, dispersant, and deionized water to the dough-like material in step 4, dilute the slurry while stirring and dispersing at high speed, dilute to a solid content of 27-33%, continue to add the SBR binder, rotate and stir evenly, control the slurry viscosity, solid content, and fineness, then rotate at a low speed under vacuum to defoam, pass through a 200-mesh screen, and obtain the target slurry. Preferably, the revolution speed is 20-40 rpm, the dispersion speed is 500-1500 rpm, the vacuum degree is less than -90 kPa, the defoaming time is 3-6 hours, the slurry viscosity is controlled at 2500-4500 mpas, the solid content is 25.5%-31.5%, and the fineness is less than 10 μm.

[0016] The beneficial effects produced by the present invention are as follows:

[0017] (1) Based on the industry's demand for high-energy-density lithium-ion batteries, a pure Si / SiOx negative electrode slurry process and slurry are provided. The high conductive agent and high binder ratio of the pure silicon system are difficult to disperse, and the low solid content is easy to settle. The dispersibility of the main material and the conductive agent is improved, and the slurry has good stability and is not easy to settle. There is no abnormal viscosity and rheology even after long-term standing, and the stability is good. Traditional graphite needs to add powder and liquid in one step to form a kneading cluster. This is based on the oily surface characteristics of graphite. The solid content can be easily controlled by the amount of solvent added during the slurrying process. Therefore, after the powder is added in one step, the kneading solid content can be controlled by adding solvent by judging whether a kneading cluster is formed. It is basically adjusted from high solid content to low solid content, and there is no need to adjust the solid content by distribution. The main material (Si or SiOx) of the silicon negative electrode has a high polarity on the surface and is easy to absorb the binder liquid. The colloids after agglomeration are very sticky and easily adhere to the stirring shaft and the cylinder body. The internal cohesion is not enough to make it spontaneously agglomerate. When the solid content is high at the beginning, dry material appears. Because it will not spontaneously agglomerate, the dry material forms a dead zone. The dry material has not been in contact with the dispersion shaft during the stirring process, resulting in uneven dispersion. Therefore, the traditional method of adjusting the solid content from high to low can easily cause the silicon-based main material to form large pieces of dry material. The dry material cannot agglomerate even when the liquid is continuously added, resulting in poor slurry dispersion, high fineness, and many coating scratches. The present invention uses the method of increasing the solid content by reverse gradient for the first time to achieve agglomeration and kneading of the pure silicon negative electrode, so that the silicon negative electrode is fully soaked, kneaded and dispersed evenly, and the coating surface density can be lower than 100g / m 2 , achieving the coating requirements of high gram capacity and low surface density. The coated electrode has high adhesion, is not easy to fall off, and has low impedance. The membrane prepared by coating the slurry can be used on soft-pack batteries with an energy density greater than 400Wh / Kg.

[0018] (2) The silicon-based negative electrode composite slurry provided in the present invention contains a variety of conductive agents such as granular conductive agents, linear conductive agents and liquid conductive agents, among which the granular conductive agents and linear conductive agents can form a three-dimensional conductive network, which is evenly coated on the surface of the silicon-based main material without agglomeration, which provides great help in improving the material capacity and cycle performance; in addition, due to the high proportion of binder in the silicon-based negative electrode composite slurry, the diaphragm resistivity is higher than that of traditional graphite, and it also affects Li diffusion. The highly dispersed conductive agent provided by the present invention can suppress the high resistivity caused by the high proportion of binder.

[0019] (3) It fills the gap in the current industry for pure silicon system negative electrode slurry preparation, and the slurry preparation process is simple and easy to operate. The traditional double planetary mixer can meet the slurry preparation requirements. Compared with traditional graphite and silicon carbon slurry preparation, it does not require new changes to the equipment and can be mass-produced, with excellent industrial application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a SEM image of the electrode prepared in Example 1;

[0021] Figure 2 The figure is a summary of the stability test results of the composite slurries prepared in various embodiments and comparative examples. DETAILED DESCRIPTION

[0022] The present invention will be further described below with reference to the embodiments so that those skilled in the art can better understand the present invention and implement it, but the embodiments are not intended to limit the present invention.

[0023] In addition, unless otherwise specified, the preparation processes in the following embodiments are conventional means in the prior art in this field, and therefore, they are not described in detail; the mixing equipment used in the embodiments is a double planetary slurry mixing equipment, "revolution speed" refers to the speed of the revolution shaft, and the dispersion speed refers to the speed of the dispersion shaft.

[0024] The specific information of some raw materials used in the following examples and comparative examples is as follows: the supplier of the resin binder is produced by Sumitomo Chemical of Japan, model number is AQUACHARGE SW100; the supplier of the SiOx main material is the silicon oxide negative electrode produced by Lanxi Zhide of China, model number is S0212; the above raw materials are only for full disclosure and are not limitations of the present invention. The purpose of the present invention can be achieved by using other raw materials with similar properties, and they all fall within the scope of protection of the present invention.

[0025] Example 1

[0026] Step 1: Add 5 kg of pure SiOx main material and 0.012 kg of conductive carbon material Super P Li into a double planetary stirring tank, rotate at 40 rpm, stir for 1 hour, and stir evenly at normal pressure to obtain a mixed powder;

[0027] Step 2: Take 0.5 kg of CMC powder and add it to deionized water, and disperse it at high speed to prepare a CMC adhesive solution. The solid content and viscosity of the CMC adhesive solution are 0.8% and 7654 mpas respectively; then take 3 kg of CMC adhesive solution and add it to 10 kg of resin adhesive, and the solid content of the resin adhesive is 10%, and then disperse it at high speed under vacuum to prepare a mixed adhesive solution;

[0028] Step 3: Add 110g of carbon nanotube powder to 10kg of the mixed glue solution from step 2, and then fully disperse it at high speed, with an orbital speed of 80rpm, a dispersion speed of 4500rpm, a vacuum degree of <-90kPa, a conductive paste viscosity of 8650mpas, and a solid content of 7.2%. The fineness of the composite conductive adhesive paste is tested, and the fineness is ≤5μm, which is set aside.

[0029] Step 4: Take 5Kg of the composite conductive adhesive slurry in step 3 and add it to the mixed powder in step 1 at one time, adjust the solid content to about 60%, the revolution speed is 40rpm, the dispersion speed is 2500rpm, stir and disperse for 20min until the slurry becomes a paste with good fluidity; then add 160g of pure SiOx powder evenly to the paste slurry, stir while adding, the revolution speed is 40rpm, adjust the solid content to about 68%, the revolution speed is 40rpm, the dispersion speed is 2500rpm, stir and disperse for a period of time until the slurry becomes a very viscous paste, at this time the slurry does not form a complete agglomeration; finally, continue to add 80g of pure SiOx powder evenly to the viscous paste slurry, stir while adding, adjust the solid content to about 72%, the revolution speed is 40rpm, the dispersion speed is 2500rpm, stir the cylinder for 30min, scrape the wall 2 times, at this time a dough-like state can be formed, continue to turn on the stirring, low-speed dispersion, and fully knead for 3h;

[0030] Step 5: Add 85g of graphene conductive slurry, 105g of tri-butylene glycol dispersant, and 7.2kg of deionized water to step 4, dilute the slurry while stirring and dispersing at high speed, with an orbital speed of 40rpm and a dispersion speed of 1500rpm to dilute to a solid content of 30.05%, continue to add 145g of SBR, stir evenly at an orbital speed of 40rpm, control the slurry viscosity, solid content, and fineness, then defoam under vacuum at low speed, and pass through a 200-mesh sieve to obtain the target slurry.

[0031] The obtained negative electrode composite slurry was coated on the surface of copper foil using transfer coating, and then rolled to obtain the electrode after drying; the coating surface density was 92g / m2 , compacted density 1.45g / m 3 The obtained electrode was tested by SEM, and the results are as follows. Figure 1 shown.

[0032] Figure 1 The two pictures on the left and right are SEM pictures of the same sample at different magnifications. Figure 1 It can be seen that the conductive agent is evenly distributed and the binder is evenly coated on the surface of the particles without clumping, which helps to enhance the electrical performance and long-term cycle stability of the silicon negative electrode particles.

[0033] Example 2

[0034] Step 1: Add 5 kg of pure SiOx main material and 0.012 kg of conductive carbon material Super P Li into a double planetary stirring tank, rotate at 40 rpm, stir for 1 hour, and stir evenly at normal pressure to obtain a mixed powder;

[0035] Step 2: Take 0.7 kg of CMC powder and add it to deionized water, and disperse it at high speed to prepare a CMC adhesive solution. The solid content and viscosity of the CMC adhesive solution are 0.6% and 3687 mpas respectively; then take 3 kg of CMC adhesive solution and add it to 8 kg of resin adhesive. The solid content of the resin adhesive is 10%, and then disperse it at high speed under vacuum to prepare a mixed adhesive solution;

[0036] Step 3: Add 110g of carbon nanotube conductive paste to 10kg of the mixed glue solution from step 2, and then fully disperse it at high speed, with an orbital speed of 80rpm, a dispersion speed of 4500rpm, a vacuum degree of <-90kPa, a conductive paste viscosity of 7634mpas, and a solid content of 6.94%. The fineness of the composite conductive adhesive paste is tested, and the fineness is ≤5μm, and it is set aside.

[0037] Step 4: Take 5.5Kg of the composite conductive adhesive slurry in step 3 and add it to the mixed powder in step 1 at one time, adjust the solid content to about 60%, the revolution speed is 40rpm, the dispersion speed is 2500rpm, stir and disperse for 20min until the slurry becomes a paste with good fluidity; then add 160g of pure SiOx powder evenly to the paste slurry, stir while adding, the revolution speed is 40rpm, adjust the solid content to about 68%, the revolution speed is 40rpm, the dispersion speed is 2500rpm, stir and disperse for a period of time until the slurry becomes a very viscous paste, at this time the slurry does not form a complete agglomeration; finally, continue to add 80g of pure SiOx powder evenly to the viscous paste slurry, stir while adding, adjust the solid content to about 72%, the revolution speed is 40rpm, the dispersion speed is 2500rpm, stir the cylinder for 30min, scrape the wall 2 times, at this time a dough-like state can be formed, continue to turn on the stirring, low-speed dispersion, and fully knead for 3h;

[0038] Step 5: Add 115g of graphene conductive slurry, 130g of tri-butylene glycol dispersant, and 7.5kg of deionized water to step 4, dilute the slurry while stirring and dispersing at high speed, with an orbital speed of 40rpm and a dispersion speed of 1500rpm to dilute to a solid content of 29.85%, continue to add 156g of SBR, stir evenly at an orbital speed of 40rpm, control the slurry viscosity, solid content, and fineness, then defoam under vacuum at low speed, and pass through a 200-mesh sieve to obtain the target slurry.

[0039] The obtained negative electrode composite slurry was coated on the surface of copper foil using transfer coating, and then rolled to obtain the electrode after drying; the coating surface density was 100g / m 2 , compacted density 1.4g / m 3 .

[0040] Example 3

[0041] Step 1: Add 6 kg of pure SiOx main material and 0.026 kg of conductive carbon material Ketjen Black Carbon ECP600JD into a double planetary mixing tank, rotate at 40 rpm, stir for 1 hour, and stir evenly at normal pressure to obtain a mixed powder;

[0042] Step 2: Take 0.5 kg of CMC powder and add it to deionized water, and disperse it at high speed to prepare a CMC adhesive solution. The solid content and viscosity of the CMC adhesive solution are 0.8% and 8967 mpa respectively; then take 3 kg of CMC adhesive solution and add it to 10 kg of resin adhesive, and the solid content of the resin adhesive is 10%, and then disperse it at high speed under vacuum to prepare a mixed adhesive solution;

[0043] Step 3: Add 110g of VGCF powder to 10kg of the mixed glue solution from step 2, and then fully disperse it at high speed, with an orbital speed of 80rpm, a dispersion speed of 4500rpm, a vacuum degree of <-90kPa, a conductive paste viscosity of 6998mpas, and a solid content of 7.15%. The fineness of the composite conductive adhesive paste was tested, and the fineness was ≤5μm, and it was set aside.

[0044] Step 4: Take 5.3Kg of the composite conductive adhesive slurry in step 3 and add it to the mixed powder in step 1 at one time, adjust the solid content to about 60%, the revolution speed is 40rpm, the dispersion speed is 2500rpm, stir and disperse for 20min until the slurry becomes a paste with good fluidity; then add 160g of pure SiOx powder evenly to the paste slurry, stir while adding, the revolution speed is 40rpm, adjust the solid content to about 68%, the revolution speed is 40rpm, the dispersion speed is 2500rpm, stir and disperse for a period of time until the slurry becomes a very viscous paste, at this time the slurry does not form a complete agglomeration; finally, continue to add 80g of pure SiOx powder evenly to the viscous paste slurry, stir while adding, adjust the solid content to about 72%, the revolution speed is 40rpm, the dispersion speed is 2500rpm, stir the cylinder for 30min, scrape the wall 2 times, at this time a dough-like state can be formed, continue to turn on the stirring, low-speed dispersion, and fully knead for 3h;

[0045] Step 5: Add 109g of graphene conductive slurry, 95g of PC, and 8.4kg of deionized water to step 4, dilute the slurry while stirring and dispersing at high speed, with an orbital speed of 40rpm and a dispersion speed of 1500rpm to dilute to a solid content of 27.89%, continue to add 134g of SBR, stir evenly at an orbital speed of 40rpm, control the slurry viscosity, solid content, and fineness, then defoam under vacuum at low speed, and pass through a 200-mesh sieve to obtain the target slurry.

[0046] The obtained negative electrode composite slurry was coated on the surface of copper foil using transfer coating, and then rolled to obtain the electrode after drying; the coating surface density was 92g / m 2 , compacted density 1.45g / m 3 .

[0047] Comparative Example 1

[0048] Step 1: Add 5 kg of pure SiOx main material and 0.012 kg of conductive carbon material Super P Li into a double planetary stirring tank, rotate at 40 rpm, stir for 1 hour, and stir evenly at normal pressure to obtain a mixed powder;

[0049] Step 2: Take 0.5 kg of CMC powder and add it to deionized water, and disperse it at high speed to prepare CMC adhesive solution. The solid content and viscosity of the CMC adhesive solution are 0.8% and 7568 mpas respectively; then take 3 kg of CMC adhesive solution and add it to 10 kg of resin adhesive, and the solid content of the resin adhesive is 10%, and then disperse it at high speed under vacuum to prepare a mixed adhesive solution;

[0050] Step 3: Add 110g of carbon nanotube powder to 10kg of the mixed glue solution from step 2, and then fully disperse it at high speed, with an orbital speed of 80rpm, a dispersion speed of 4500rpm, a vacuum degree of <-90kPa, a conductive paste viscosity of 8497mpas, and a solid content of 7.2%. The fineness of the composite conductive adhesive paste was tested, and the fineness was ≤5μm, and it was set aside.

[0051] Step 4: Take 5 kg of the composite conductive adhesive slurry prepared in step 3 and add it to the mixed powder prepared in step 1 at one time, adjust the solid content to about 72%, rotate at 40 rpm, disperse at 2500 rpm, and stir the mixture for 3 hours.

[0052] Step 5: Add 85g of graphene conductive slurry, 105g of tri-butylene glycol dispersant, and 7.2kg of deionized water to step 4, dilute the slurry while stirring and dispersing at high speed, with an orbital speed of 40rpm and a dispersion speed of 1500rpm to dilute to a solid content of 30.05%, continue to add 145g of SBR, stir evenly at an orbital speed of 40rpm, control the slurry viscosity, solid content, and fineness, then defoam under vacuum at low speed, and pass through a 200-mesh sieve to obtain the target slurry.

[0053] The obtained negative electrode composite slurry was coated on the surface of copper foil using transfer coating, and then rolled to obtain the electrode after drying; the coating surface density was 92g / m 2 , compacted density 1.45g / m 3 .

[0054] Comparative Example 2

[0055] Step 1: Add 6 kg of pure SiOx main material and 0.026 kg of conductive carbon material Ketjen Black Carbon ECP600JD into a double planetary mixing tank, rotate at 40 rpm, stir for 1 hour, and stir evenly at normal pressure to obtain a mixed powder;

[0056] Step 2: Take 0.5 kg of CMC powder and add it to deionized water, and disperse it at high speed to prepare a CMC adhesive solution. The solid content and viscosity of the CMC adhesive solution are 0.8% and 8856 mpas respectively; then take 3 kg of CMC adhesive solution and add it to 10 kg of resin adhesive, and the solid content of the resin adhesive is 10%, and then disperse it at high speed under vacuum to prepare a mixed adhesive solution;

[0057] Step 3: Add 110g of VGCF powder to 10kg of the mixed glue solution from step 2, and then fully disperse it at high speed, with an orbital speed of 80rpm, a dispersion speed of 4500rpm, a vacuum degree of <-90kPa, a conductive paste viscosity of 6785mpas, and a solid content of 7.15%. The fineness of the composite conductive adhesive paste was tested, and the fineness was ≤5μm, and it was set aside.

[0058] Step 4: Take 5.3 kg of the composite conductive adhesive slurry prepared in step 3 and add it to the mixed powder prepared in step 1 at one time, adjust the solid content to about 72%, rotate at 40 rpm, disperse at 2500 rpm, and stir the mixture for 3 hours.

[0059] Step 5: Add 109g of graphene conductive slurry, 95g of PC, and 8.4kg of deionized water to step 4, dilute the slurry while stirring and dispersing at high speed, with an orbital speed of 40rpm and a dispersion speed of 1500rpm to dilute to a solid content of 27.89%, continue to add 134g of SBR, stir evenly at an orbital speed of 40rpm, control the slurry viscosity, solid content, and fineness, then defoam under vacuum at low speed, and pass through a 200-mesh sieve to obtain the target slurry.

[0060] The obtained negative electrode composite slurry was coated on the surface of copper foil using transfer coating, and then rolled to obtain the electrode after drying; the coating surface density was 92g / m 2 , compacted density 1.45g / m 3 .

[0061] Performance testing

[0062] The stability test of the composite slurry prepared in Examples 1 to 3 and Comparative Examples 1 to 2 was carried out. The viscosity was measured every 1 hour. The upper slurry was taken for testing. The results are as follows: Figure 2 As shown. Figure 2 It can be seen that the slurry prepared by the present invention is more stable than the slurry prepared in the comparative example.

[0063] The resistivity, adhesion and peel strength of the electrodes prepared in the above examples and comparative examples were tested, and the results are shown in Table 1 below:

[0064] Table 1

[0065] Resistivity Ω·cm Adhesion force N / m Peel strength N / m Example 1 15.34 154.29 198.56 Example 2 23.56 123.19 156.34 Example 3 13.56 134.56 178.56 Comparative Example 1 95.45 98.16 154.25 Comparative Example 2 100.34 100.45 134.83

[0066] It can be seen from the table that the film resistivity, electrode adhesion and electrode peel strength of the electrodes prepared in Examples 1-3 are better than those of the comparative example, indicating that the slurry mixing process is more conducive to the dispersion of the binder and the conductive agent, and significantly improves the physical and chemical properties of the electrode.

[0067] Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

Claims

1. A method for preparing a high energy density lithium-ion battery silicon-based negative electrode composite slurry, characterized in that: The following steps are involved: Step 1: Weigh 91% to 96% of the total mass of the silicon-based main material, and then mix it with a granular conductive agent to obtain a mixed powder; Step 2: Add CMC powder binder into water to prepare CMC binder solution, and then add resin binder to prepare mixed solution; Step 3: Add a linear conductive agent to the mixed glue solution and mix until the fineness of the material is ≤5μm to obtain a composite conductive adhesive slurry; Step 4: Add all the composite conductive adhesive slurry to the mixed powder in step 1, adjust the solid content to 60%, and mix to make the slurry into a paste slurry with good fluidity; then add the remaining part of the silicon-based main material to the paste slurry to adjust its solid content to 68%, and mix to make the slurry into a viscous paste slurry. At this time, the slurry does not form a complete clumping situation; continue to add the remaining silicon-based main material to the viscous paste slurry, adjust its solid content to 72-74%, and mix to obtain a dough-like material; Step 5: Add liquid conductive agent, dispersant, and deionized water to the dough-like material, and mix them simultaneously to adjust the solid content to 27-33%. Then add SBR binder, mix evenly, and defoam to obtain the target slurry, i.e., silicon-based negative electrode composite slurry. The silicon-based negative electrode composite slurry comprises the following components by weight percentage: 21.0% to 28.5% of a silicon-based main material, 30% to 45% of a resin binder, 0.5% to 2% of an SBR binder, 1.5% to 2% of a CMC powder binder, 0.5% to 1.0% of a granular conductive agent, 1.0% to 1.5% of a linear conductive agent, 25% to 35% of a liquid conductive agent, 0.5% to 2.0% of a dispersant, and 5% to 20.0% of a solvent. The total weight of the above components is 100%. The silicon-based main material includes at least one of Si and SiOx.

2. The method for preparing a high energy density lithium-ion battery silicon-based negative electrode composite slurry according to claim 1, characterized in that: The granular conductive agent includes at least one of Super P Li, acetylene black, and LITX 300.

3. The method for preparing a high energy density lithium-ion battery silicon-based negative electrode composite slurry according to claim 1, characterized in that: The linear conductive agent includes at least one of carbon nanotube powder, VGCF, and carbon nanotube conductive paste.

4. The method for preparing a high energy density lithium-ion battery silicon-based negative electrode composite slurry according to claim 1, characterized in that: The liquid conductive agent includes at least one of graphene conductive paste and carbon nanotube conductive paste.

5. The method for preparing a high energy density lithium-ion battery silicon-based negative electrode composite slurry according to claim 1, characterized in that: The dispersant includes at least one of 1-3 butanediol, EC, PC, and isopropyl alcohol.

6. The method for preparing a high energy density lithium-ion battery silicon-based negative electrode composite slurry according to claim 1, characterized in that: In step 2, the solid content of the CMC adhesive solution is 0.5-1.2%, and the viscosity is 3000-9000 mpas; the solid content of the resin adhesive is 8-10%; and the mass ratio of the CMC adhesive solution to the resin adhesive is 1:3-1:

5.

7. The method for preparing a high energy density lithium-ion battery silicon-based negative electrode composite slurry according to claim 1, characterized in that: In step three, the composite conductive adhesive slurry has a viscosity of 6000 to 9000 mpas and a solid content of 5% to 8%.

8. The method for preparing a high energy density lithium-ion battery silicon-based negative electrode composite slurry according to claim 1, characterized in that: In step five, the viscosity of the silicon-based negative electrode composite slurry is 2500-4500 mpas, and the solid content is 25.5%-31.5%.

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