Negative plate, battery, battery pack and electric equipment

Abstract

The invention discloses a negative plate, a battery, a battery pack and electric equipment, the negative plate comprises a silicon material and three-dimensional graphene, the three-dimensional graphene comprises first three-dimensional graphene and second three-dimensional graphene, the D50 particle size of the first three-dimensional graphene is d1, the D50 particle size of the second three-dimensional graphene is d2, and d1 and d2 meet the following conditions: d1 is more than or equal to 3 microns and less than or equal to 10 microns, and d2 is more than 0 microns and less than or equal to 3 microns. According to reasonable particle size matching of the negative plate, the first three-dimensional graphene and the second three-dimensional graphene, reduction of the preparation difficulty of the negative plate is facilitated, the production cost of the negative plate and the lithium ion battery is reduced, meanwhile, the porosity of the electrode is increased, the tortuosity is reduced, the compaction and reversible resilience performance and the conductive contact site of the electrode plate are improved, and the lithium ion battery has a good application prospect. Reliable elastic electric connection is provided for the breathing expansion process in the battery circulation process, and the capacity and the circulation performance of the battery are improved.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and in particular to a negative electrode, a battery, a battery pack, and an electrical device. Background Technology

[0002] In related technologies, silicon-containing anodes are commonly used in lithium-ion batteries. However, silicon-containing anodes are prone to volume expansion during battery cycling, causing the active material particles to gradually detach from the external conductive network, forming "islands" and resulting in rapid capacity and cycle life degradation. Therefore, the related technologies for anode sheets need further improvement. Summary of the Invention

[0003] The present invention aims to at least solve one of the technical problems existing in the prior art. To this end, the first objective of the present invention is to provide a negative electrode.

[0004] According to a first aspect of the present invention, the negative electrode sheet includes: silicon material and three-dimensional graphene, wherein the three-dimensional graphene includes: a first three-dimensional graphene and a second three-dimensional graphene, wherein the D50 particle size of the first three-dimensional graphene is d1, and the D50 particle size of the second three-dimensional graphene is d2, wherein d1 and d2 satisfy: 3μm≤d1≤10μm, 0μm<d2≤3μm.

[0005] According to embodiments of the present invention, the negative electrode sheet employs silicon material and first and second three-dimensional graphene with different particle sizes. This allows the first three-dimensional graphene to fully exert its supporting role while preventing the sharp edges of the rigid silicon material surface from scratching the separator and causing a short circuit during hot pressing. The second three-dimensional graphene can fully fill the gaps in the first three-dimensional graphene, playing a synergistic role in pore filling. This provides a buffer space for the expansion of the silicon-based material, reduces the short-circuit rate, and increases the compaction density of the negative electrode sheet. Therefore, the reasonable particle size combination of the first and second three-dimensional graphene helps reduce the manufacturing difficulty of the negative electrode sheet and lowers the production cost of the negative electrode sheet and its lithium-ion battery. Simultaneously, it increases the porosity of the electrode, reduces tortuosity, improves the compaction, reversible resilience, and conductive contact sites of the electrode sheet, providing a reliable elastic electrical connection for the breathing expansion process during battery cycling, and improving the battery's capacity and cycle performance.

[0006] According to some embodiments of the present invention, d1 and d2 satisfy: d1 / d2≥8.

[0007] According to some embodiments of the present invention, the weight ratio of the first three-dimensional graphene to the second three-dimensional graphene satisfies: 1:(0.33~3).

[0008] According to some embodiments of the present invention, the specific surface area of ​​the three-dimensional graphene is a, wherein a satisfies: a < 200 g / m² 2.

[0009] According to some embodiments of the present invention, the three-dimensional graphene has a coating layer, the precursor of which includes at least one coated graphene selected from sugars, polymers, and bitumen.

[0010] According to some embodiments of the present invention, the negative electrode further includes a lithiophilic material disposed within the pores of the three-dimensional graphene, wherein the mass percentage of the lithiophilic material is 0.01% to 1%.

[0011] According to some embodiments of the present invention, the lithiophilic material includes at least one of C3N4, zinc oxide, copper oxide, lithium nitride, lithium phosphide, lithium lanthanum zirconium tantalum oxide, and lithium aluminum titanium phosphate.

[0012] According to some embodiments of the present invention, the proportion of the three-dimensional graphene in the negative electrode material is w, wherein w satisfies: 3% ≤ w ≤ 15%.

[0013] According to some embodiments of the present invention, w satisfies: 5% ≤ w ≤ 10%.

[0014] According to some embodiments of the present invention, the silicon material comprises silicon carbon and / or silicon oxide.

[0015] According to some embodiments of the present invention, the negative electrode sheet comprises, by weight percentage: 3% to 15% three-dimensional graphene, 50% to 90% silicon material and additives, wherein the additives include binders and / or conductive agents.

[0016] A battery according to a second aspect of the present invention includes: a negative electrode sheet, wherein the negative electrode sheet is the same as the negative electrode sheet described in the first aspect of the present invention.

[0017] A battery pack according to a third aspect of the present invention includes at least one battery according to the second aspect of the present invention described above.

[0018] An electrical appliance according to a fourth aspect of the present invention includes at least one battery pack according to the third aspect of the present invention described above.

[0019] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Detailed Implementation

[0020] The negative electrode sheet according to the first aspect of the present invention is described in detail below.

[0021] The negative electrode sheet according to a first aspect of the present invention comprises: silicon material and three-dimensional graphene. The three-dimensional graphene is prepared by plasma-enhanced chemical vapor deposition (PECVD). Specifically, the three-dimensional graphene is graphene with a three-dimensional structure formed by the disordered overlapping of two-dimensional graphene sheets. Therefore, the three-dimensional graphene has advantages such as good conductivity, high porosity, excellent mechanical tensile properties, and elasticity. More specifically, the three-dimensional graphene has high porosity, high oil absorption value (200 / 100g to 900g / 100g), high conductivity (conductivity 20S / cm to 200S / cm), and high elasticity (reversible compression rebound ratio 4% to 20%, higher than the reversible compression rebound performance of graphite).

[0022] Adding three-dimensional graphene to silicon materials facilitates the construction of nanoporous negative electrode sheets, improves their elasticity, maintains the continuity of the conductive network, and thus reduces the formation of "islands." Because silicon materials are highly rigid and have poor elasticity, the composite with three-dimensional graphene helps improve the reversible compression recovery performance of the negative electrode sheet, absorbs expansion due to breathing, and improves cycle performance. It can also effectively mitigate the damage to the separator caused by the rigid silicon material during battery hot pressing.

[0023] The three-dimensional graphene comprises two types: a first three-dimensional graphene and a second three-dimensional graphene. The first three-dimensional graphene has a D50 particle size of d1, and the second three-dimensional graphene has a D50 particle size of d2. d1 and d2 satisfy the following conditions: 3μm ≤ d1 ≤ 10μm, 0μm < d2 ≤ 3μm. The D50 particle size is also known as the median particle size or average particle size. This configuration results in a relatively large and reasonable particle size for the first three-dimensional graphene, which allows it to fully exert its supporting function while preventing the sharp edges of the rigid silicon material surface from scratching the separator and causing a short circuit during hot pressing. The second three-dimensional graphene has a relatively small and reasonable particle size, allowing it to fully fill the gaps in the first three-dimensional graphene, reducing the short-circuit rate, increasing the compaction density of the negative electrode, and simultaneously increasing the number of conductive contact sites. Therefore, the aforementioned three-dimensional graphene can synergistically fill pores, further increasing the porosity of the electrode, reducing tortuosity, and improving the electrode's compaction, reversible resilience, and conductive contact sites, providing a reliable elastic electrical connection for the breathing expansion process during battery cycling. The appropriate particle size combination of the first and second three-dimensional graphene can further enhance the electrode's reversible compression resilience and conductive contact sites, providing a reliable elastic electrical connection for the breathing expansion process during battery cycling.

[0024] According to embodiments of the present invention, the negative electrode sheet employs silicon material and first and second three-dimensional graphene with different particle sizes. This allows the first three-dimensional graphene to fully exert its supporting role while preventing the sharp edges of the rigid silicon material surface from scratching the separator and causing a short circuit during hot pressing. The second three-dimensional graphene can fully fill the gaps in the first three-dimensional graphene, playing a synergistic role in pore filling. This provides a buffer space for the expansion of the silicon-based material, reduces the short-circuit rate, and increases the compaction density of the negative electrode sheet. Therefore, the reasonable particle size combination of the first and second three-dimensional graphene helps reduce the manufacturing difficulty of the negative electrode sheet and lowers the production cost of the negative electrode sheet and its lithium-ion battery. Simultaneously, it increases the porosity of the electrode, reduces tortuosity, improves the compaction, reversible resilience, and conductive contact sites of the electrode sheet, providing a reliable elastic electrical connection for the breathing expansion process during battery cycling, and improving the battery's capacity and cycle performance.

[0025] According to some embodiments of the present invention, d1 and d2 satisfy: d1 / d2≥8. Therefore, the particle size distribution of the first three-dimensional graphene and the second three-dimensional graphene is more reasonable, which is beneficial to fully utilizing the functions of the first three-dimensional graphene and the second three-dimensional graphene, thereby improving the compaction of the negative electrode and providing buffer space for the expansion of silicon-based materials.

[0026] According to some embodiments of the present invention, the weight ratio of the first three-dimensional graphene and the second three-dimensional graphene satisfies 1:(0.33~3). Therefore, by setting the weight ratio of the first three-dimensional graphene and the second three-dimensional graphene to 1:(0.33~3), the risk of agglomeration of the three-dimensional graphene is reduced, the dispersion uniformity of the three-dimensional graphene is improved, and the conductivity of the negative electrode is enhanced, thereby improving the cycle performance of the battery.

[0027] According to some embodiments of the present invention, the specific surface area of ​​the three-dimensional graphene is a, wherein a satisfies: a < 200 g / m² 2 Understandably, the specific surface area of ​​three-dimensional graphene refers to the sum of the specific surface areas of the first and second three-dimensional graphene. When the specific surface area of ​​three-dimensional graphene is greater than 200 g / m²... 2At this stage, the larger specific surface area of ​​three-dimensional graphene increases the contact area between it and the electrolyte, easily leading to a larger SEI (solid electrolyte interphase), which increases the consumption of active lithium and affects the initial efficiency of the negative electrode. Simultaneously, the larger surface area also occupies more space, resulting in a lower packing density of three-dimensional graphene, thus reducing the energy stored per unit volume of three-dimensional graphene and affecting the battery's energy density. Furthermore, to achieve a larger specific surface area, the pores of three-dimensional graphene may be overly complex or too small, lengthening the lithium-ion transport path, increasing transport resistance, and affecting the rapid storage and release of lithium ions, i.e., impacting the battery's rate performance. Therefore, by setting the specific surface area of ​​three-dimensional graphene to a < 200 g / m², [further optimization is needed]. 2 This reduces the adsorption and consumption of lithium ions, which helps to improve the energy density of the battery, reduce the transport resistance of lithium ions, and enable rapid storage and release of lithium ions. At the same time, it reduces the agglomeration of three-dimensional graphene, enhances the uniformity of the electrode slurry, and improves the feasibility of the process.

[0028] The three-dimensional graphene has a coating layer, and the precursor of the coating layer is at least one of sugars, polymers, and pitch. Therefore, by using sugars, polymers, and / or pitch to coat the three-dimensional graphene, its specific surface area can be controlled to be <200 g / m². 2 This can significantly reduce the side reactions caused by the high specific surface area of ​​graphene. For example, the specific surface area of ​​uncoated graphene is >600 g / m³. 2 Strong adsorption between particles leads to particle agglomeration and difficulty in dispersion; furthermore, the high specific surface area increases the contact area with the electrolyte, and the larger SEI area increases the consumption of active lithium, affecting the first-time efficiency of the anode. Reducing the specific surface area of ​​three-dimensional graphene can reduce the adsorption and consumption of lithium ions. This invention reduces the specific surface area by coating with sugars, polymers, and / or pitch, thereby reducing the agglomeration of graphene particles, enhancing the uniformity of the electrode slurry, improving process feasibility, and improving the first-time efficiency of the anode. The coated graphene has a certain structural strength, which can alleviate the volume expansion caused by silicon material expansion.

[0029] Furthermore, combining the advantages of high electrical conductivity, large specific surface area, and high mechanical strength of three-dimensional graphene with the strong stability and excellent electrochemical performance of coating layers using sugars, polymers, and / or pitch as precursors, facilitates the rapid transport of lithium ions, i.e., promotes the rapid diffusion of charge carriers (such as lithium ions), thereby improving the rate performance and cycle stability of the battery. The coating layers using sugars, polymers, and / or pitch as precursors protect the graphene structure from physical and chemical damage during electrochemical cycling, reducing the stacking and re-aggregation between three-dimensional graphene sheets and maintaining the porosity and high specific surface area of ​​the three-dimensional graphene. Simultaneously, the coating layers using sugars, polymers, and / or pitch as precursors to coat the graphene can reduce side reactions between the three-dimensional graphene and the electrolyte, prevent electrolyte decomposition, and extend the battery's lifespan. Specifically, graphene coated with sugars, polymers, and / or pitch can be achieved by: thoroughly dispersing and mixing graphene with a solution containing carbon sources such as sugars, polymers, and / or pitch, and then performing heat treatment in an inert atmosphere, converting the organic matter into carbon through a high-temperature pyrolysis process, thereby achieving the coating of graphene.

[0030] Furthermore, the negative electrode also includes a lithiophilic material disposed within the pores of the three-dimensional graphene. The lithiophilic material helps enhance the adsorption of lithium ions by the three-dimensional graphene, promoting rapid diffusion of lithium ions within its structure, thereby improving the battery's charge / discharge rate and power density. By placing the lithiophilic material within the pores of the three-dimensional graphene, the negative electrode can be stabilized, the formation of lithium dendrites can be suppressed, side reactions can be reduced, and the battery's safety and cycle stability can be improved. Specifically, the lithiophilic material can be introduced into the pores of the three-dimensional graphene through pre-deposition. This allows for the construction of a porous, highly elastic, nano-sized electrode while inducing uniform lithium deposition, reducing the tortuosity of lithium ion transport, lowering the risk of lithium plating, improving the liquid absorption and retention capacity of the negative electrode, and reducing expansion.

[0031] The mass percentage of the lithiophilic material is 0.01% to 1%. Therefore, the addition amount of lithiophilic material is reasonable, which is beneficial for fully leveraging the ability of three-dimensional graphene to adsorb lithium ions and promote the rapid diffusion of lithium ions within its structure, thereby improving the charge / discharge rate and power density of the battery. At the same time, it avoids waste of lithiophilic material, which helps control the cost of the lithium-ion battery anode. Furthermore, the lithiophilic material within the above mass range fills the pores of the three-dimensional graphene, and the lithium content increases the elasticity of the graphene, while the expansion and contraction of the silicon material provides a buffer stress, thus increasing the stability of the anode structure.

[0032] Furthermore, the lithiophilic materials include at least one of C3N4, zinc oxide, copper oxide, lithium nitride, lithium phosphide, lithium lanthanum zirconium tantalum oxide, and lithium aluminum titanium phosphate. Among these, C3N4, zinc oxide, copper oxide, lithium nitride, lithium phosphide, lithium lanthanum zirconium tantalum oxide, and lithium aluminum titanium phosphate all possess high lithium-ion conductivity, chemical stability, thermal stability, and mechanical strength. Therefore, using at least one of C3N4, zinc oxide, copper oxide, lithium nitride, lithium phosphide, lithium lanthanum zirconium tantalum oxide, and lithium aluminum titanium phosphate as the lithiophilic material is beneficial for lithium-ion transport, avoids side reactions when the lithiophilic material directly contacts the lithium metal anode, improves battery safety, and extends the lifespan of the lithium-ion battery.

[0033] According to some embodiments of the present invention, the proportion of three-dimensional graphene in the negative electrode material is w, where w satisfies: 3% ≤ w ≤ 15%. When the proportion of three-dimensional graphene in the negative electrode material is less than 3%, there is less three-dimensional graphene, resulting in poor improvement of the reversible compression resilience of the negative electrode sheet and a weaker effect on improving the expansion and cycle performance of the negative electrode. When the proportion of three-dimensional graphene in the negative electrode material is greater than 15%, there is more three-dimensional graphene, increasing the cost of the negative electrode sheet and increasing the side reactions of the negative electrode, which easily affects the electrochemical performance of the negative electrode. Therefore, by setting the proportion of three-dimensional graphene in the negative electrode material to 3% ≤ w ≤ 15%, it is beneficial to improve the reversible compression resilience of the negative electrode sheet, improve the expansion and cycle performance of the negative electrode, and at the same time, it is beneficial to reduce the cost of the negative electrode sheet. It can be understood that the negative electrode material refers to all materials that make up the negative electrode active material layer. That is, the proportion of three-dimensional graphene in the negative electrode material refers to the proportion of three-dimensional graphene in the total mass of the negative electrode material layer.

[0034] Preferably, the proportion of three-dimensional graphene in the negative electrode material is 5% ≤ w ≤ 10%. The effect of three-dimensional graphene is optimized, thereby improving the cycle performance of lithium-ion batteries.

[0035] According to some embodiments of the present invention, the silicon material includes silicon-carbon and / or silicon-oxygen. Silicon-carbon possesses high hardness, good thermal stability, chemical inertness, and thermal conductivity, while maintaining good electrical conductivity even at high temperatures. Silicon-oxygen possesses high theoretical specific capacity, low lithiation potential, and good cycle stability. Therefore, using silicon-carbon and / or silicon-oxygen as the silicon material is beneficial for improving the energy efficiency and cycle stability of the battery, and extending the lifespan of the lithium-ion battery.

[0036] The silicon material can be silicon suboxide, but it is not limited to this.

[0037] According to some embodiments of the present invention, the negative electrode sheet comprises, by weight percentage: 3% to 15% three-dimensional graphene, 50% to 90% silicon material, and additives. Thus, the ratio of three-dimensional graphene, silicon material, and additives is more reasonable. The additives are used to thoroughly mix the silicon material and three-dimensional graphene, thereby optimizing the reversible compression resilience and conductive contact sites of the negative electrode sheet, providing a reliable elastic electrical connection for the breathing expansion process during battery cycling.

[0038] The additives include binders and / or conductive agents. The amount of additives added can range from 3 wt% to 15 wt%, without specific limitations. Binders can form a strong bond between components such as silicon materials and three-dimensional graphene, improving the uniformity of the negative electrode. Conductive agents can be used to improve the conductivity of the negative electrode, allowing current to pass through it effectively.

[0039] The binder may be at least one of polyacrylic acid, sodium alginate, and polyimide. The conductive agent may be single-walled carbon nanotubes or graphite, but is not limited thereto.

[0040] According to some embodiments of the present invention, the negative electrode sheet further includes a current collector, and the negative electrode material is disposed on the current collector to form a negative electrode active material layer. The negative electrode active material layer includes silicon material, three-dimensional graphene, optional binder, and optional conductive agent.

[0041] According to some embodiments of the present invention, a method for preparing a negative electrode sheet includes the following steps:

[0042] Three-dimensional graphene is dispersed, a binder is added, it is dispersed again, silicon material is added and kneaded; a conductive agent is added, and then a solvent is added to adjust the viscosity before coating it onto a current collector, thus obtaining the final product.

[0043] The method for preparing the negative electrode sheet according to the embodiments of the present invention is relatively simple, which is conducive to improving the production efficiency of the negative electrode sheet, reducing the cost of the negative electrode sheet, and thus enhancing the market competitiveness of the negative electrode sheet.

[0044] For example, the preparation method may include the following steps: ① Pre-dispersing the three-dimensional graphene slurry using a high-pressure homogenizing device; ② Adding 3wt% to 15wt% of a binder (at least one of polyacrylic acid, sodium alginate, and polyimide), and dispersing it for 30 min using a dual planetary device to form a three-dimensional graphene dispersion liquid; ③ Adding silicon material (silicon suboxide and / or silicon carbon active material) to the prepared three-dimensional graphene dispersion liquid and kneading it for 90 min; ④ Adding 3wt% to 15wt% of a conductive agent (SWCNT, single-walled carbon nanotubes); ⑤ Finally, adding a solvent (N-methylpyrrolidone and water) to adjust the viscosity and then coating it onto a copper foil.

[0045] According to the preparation method of a specific embodiment of the present invention, three-dimensional graphene can be thoroughly mixed with silicon-based materials, introducing a lithium-affinity three-dimensional elastic conductive framework between the silicon-based material particles. As lithium insertion into the silicon particles proceeds, the silicon particles expand, and the elastic layer can be compressed to buffer the expansion; during delithiation, the excellent reversible elasticity maintains the electrical connection. During high-current charging and discharging, it can also reduce local current density and help to uniformly deposit lithium metal in porous structures.

[0046] A battery according to a second aspect of the present invention includes: a negative electrode sheet, wherein the negative electrode sheet is the same as the negative electrode sheet described in the first aspect of the present invention.

[0047] The battery according to the embodiments of the present invention is beneficial to improving the charging and discharging performance of the battery, extending the battery's service life, and enhancing the battery's market competitiveness.

[0048] A battery pack according to a third aspect of the present invention includes at least one battery according to the second aspect of the present invention described above.

[0049] The battery pack according to embodiments of the present invention is beneficial to improving the applicability of the battery pack and enhancing its market competitiveness.

[0050] An electrical appliance according to a fourth aspect of the present invention includes at least one battery pack according to the third aspect of the present invention described above.

[0051] The electrical equipment according to the embodiments of the present invention is beneficial to improving the operational stability of the electrical equipment and enhancing the user experience.

[0052] The embodiments of the present invention are described in detail below. It should be noted that the embodiments described below are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention. In addition, unless otherwise specified, all reagents used in the following embodiments are commercially available or can be synthesized according to the methods described herein or known to others. For reaction conditions not listed, they are also readily available to those skilled in the art.

[0053] 1. Production of positive electrode plates

[0054] 960g of positive electrode active material ternary 622 (NCMLi) 0.13 Ni 0.6 Co 0.2 Mn 0.2 O2 (96%), 30g binder PVDF (polyvinylidene fluoride) (3%), 5g acetylene black (0.5%), and 5g conductive agent CNT (carbon nanotubes) (0.5%) were added to 2000g solvent NMP (nitrogen methyl pyrrolidone) and then stirred in a vacuum mixer to form a stable and uniform positive electrode slurry.

[0055] A slot coating machine is used to uniformly and intermittently coat the positive electrode slurry onto both sides of an aluminum foil (160 mm wide and 16 μm thick). The foil is then dried at 393 K and pressed into a sheet using a roller press. The positive electrode sheet is then cut into rectangular sheets measuring 43 mm * 56 mm, and tabs are spot-welded to the width direction.

[0056] 2. Fabrication of the negative electrode

[0057] Example 1

[0058] A 6% polyacrylic acid / sodium alginate binder was dispersed using a dual planetary mixer for 30 min. Then, 8 wt% of three-dimensional graphene with mixed particle sizes of 5 μm and 0.6 μm (containing 0.5% lithium-affinity copper oxide in the interstices of the graphene) was added and stirred to obtain a three-dimensional graphene conductive slurry. The weight ratio of 5 μm to 0.6 μm three-dimensional graphene was 1:1.

[0059] Then, 80 wt% silicon carbide powder was added and kneaded. The resulting silicon carbide powder had a particle size D50 of 8 μm. 6% single-walled carbon nanotube conductive agent was added and dispersed for 30 min. Finally, NMP and water were added to adjust the viscosity. The mixture was then coated onto an 8 μm thick copper foil and baked in a tunnel oven at 65℃~105℃, achieving a coating density of approximately 62 g / m². 2 After rolling, the thickness of the negative electrode sheet is about 60μm.

[0060] Example 2

[0061] Example 2 is basically the same as Example 1, except that 3wt% of three-dimensional graphene with mixed particle sizes of 5μm and 0.6μm is added, and the content of single-walled carbon nanotube conductive agent is adjusted so that the overall mass of the negative electrode material is 100%.

[0062] Example 3

[0063] Example 3 is basically the same as Example 1, except that 5 wt% of three-dimensional graphene with a mixed particle size of 5 μm and 0.6 μm is added, and the content of single-walled carbon nanotube conductive agent is adjusted so that the overall mass of the negative electrode material is 100%.

[0064] Example 4

[0065] Example 4 is basically the same as Example 1, except that 10wt% of three-dimensional graphene with mixed particle sizes of 5μm and 0.6μm is added, and the content of single-walled carbon nanotube conductive agent is adjusted so that the overall mass of the negative electrode material is 100%.

[0066] Example 5

[0067] Example 5 is basically the same as Example 1, except that 15wt% of three-dimensional graphene with mixed particle sizes of 5μm and 0.6μm is added, and the content of single-walled carbon nanotube conductive agent is adjusted so that the overall mass of the negative electrode material is 100%.

[0068] Example 6

[0069] Example 6 is basically the same as Example 1, except that 8 wt% of three-dimensional graphene with a mixed particle size of 8 μm and 0.3 μm is added.

[0070] Example 7

[0071] Example 7 is basically the same as Example 1, except that 8 wt% of three-dimensional graphene with mixed particle sizes of 10 μm and 3 μm is added.

[0072] Example 8

[0073] Example 8 is basically the same as Example 1, except that the weight ratio of 5μm three-dimensional graphene to 0.6μm three-dimensional graphene is 1:3.

[0074] Example 9

[0075] Example 9 is basically the same as Example 1, except that the weight ratio of 5μm three-dimensional graphene to 0.6μm three-dimensional graphene is 3:1.

[0076] Example 10

[0077] Example 10 is basically the same as Example 1, except that the lithiophilic material is lithium nitride.

[0078] Example 11

[0079] Example 11 is basically the same as Example 1, except that 8 wt% of three-dimensional graphene with a mixed particle size of 9 μm and 0.2 μm is added.

[0080] Example 12

[0081] Example 12 is basically the same as Example 1, except that 8 wt% of three-dimensional graphene with mixed particle sizes of 3 μm and 0.4 μm is added.

[0082] Comparative Example 1

[0083] Polyacrylic acid / sodium alginate binder was dispersed using a (6%) dual planetary mixer for 30 minutes. 8 wt% carbon black and graphite conductive agent were added and stirred to obtain a conductive slurry. Then, 80 wt% silicon carbide powder was added and kneaded. 6% single-walled carbon nanotube conductive agent was added and dispersed for 30 minutes. Finally, NMP and water were added to adjust the viscosity. The slurry was coated onto an 8 μm thick copper foil and baked in a tunnel oven at 65℃~105℃, achieving a coating density of approximately 62 g / m².2 After rolling, the thickness of the negative electrode sheet is about 60μm.

[0084] Comparative Example 2

[0085] Polyacrylic acid / sodium alginate binder was dispersed using a (6%) dual planetary mixer for 30 min. 8 wt% of 5 μm particle size three-dimensional graphene slurry was added and stirred to obtain a three-dimensional graphene conductive slurry. Silicon carbide powder was then added and kneaded. 6% single-walled carbon nanotube conductive agent was added and dispersed for 30 min. Finally, NMP and water were added to adjust the viscosity. The mixture was coated onto an 8 μm thick copper foil and baked in a tunnel oven at 65℃~105℃, achieving a coating density of approximately 62 g / m². 2 After rolling, the electrode thickness is approximately 60 μm.

[0086] Comparative Example 3

[0087] A polyacrylic acid / sodium alginate binder was dispersed using a (6%) dual planetary mixer for 30 min. 8 wt% of 0.6 μm particle size three-dimensional graphene slurry was added and stirred to obtain a three-dimensional graphene conductive slurry. Then, 80 wt% silicon carbide powder was added and kneaded. 6% single-walled carbon nanotube conductive agent was added and dispersed for 30 min. Finally, NMP and water were added to adjust the viscosity. The mixture was coated onto an 8 μm thick copper foil and baked in a tunnel oven at 65℃~105℃, achieving a coating density of approximately 62 g / m². 2 After rolling, the electrode thickness is approximately 60 μm.

[0088] Comparative Example 4

[0089] Comparative Example 4 is basically the same as Example 1, except that 8 wt% of three-dimensional graphene with a mixed particle size of 15 μm and 0.3 μm is added.

[0090] Comparative Example 5

[0091] Comparative Example 5 is basically the same as Example 1, except that 8 wt% of three-dimensional graphene with mixed particle sizes of 25 μm and 4 μm is added.

[0092] Performance testing

[0093] Reversible compression rebound rate test: After rolling, the negative electrode sheet was cut to a size of 45*58mm. The reversible compression rebound performance of the negative electrode sheet was tested using an in-situ dilatometer, with a pressure range of 0MPa to 5MPa. The starting point of the 15th roll was used as the initial thickness h0, and the thickness at the end of the pressurization at 4MPa was used as h1. The reversible compression rebound rate % = (h0-h1) / h0. Better reversible compression rebound performance improves the expansion and cycle performance of the negative electrode.

[0094] Battery unit current surface density expansion test: A 43*56mm positive electrode sheet was prepared and assembled with negative electrodes and PE separators obtained in each example and comparative example. The electrolyte was 1mol / L LiPF6, and the EC to EMC volume ratio was 1:1. The expansion performance of the corresponding battery formation stage was tested. The battery was stabilized at a constant pressure of 2MPa for 10h in an in-situ dilatometer, and the thickness H0 was recorded. Constant current charging and discharging was performed at 0.05C, with a voltage window of 2.2V to 4.2V. The dimensional change H1 in the thickness direction of the battery during charging was collected using the in-situ dilatometer. Battery unit current density expansion = (H1-H0) / (0.05C discharge capacity / positive electrode area). The measurement of battery unit current density expansion shows that a smaller unit current density expansion is beneficial in reducing the risk of battery capacity and cycle degradation.

[0095] Table 1. Test results of Examples 1-12 and Comparative Examples 1-5

[0096]

[0097]

[0098] As can be seen from Table 1, compared with Comparative Examples 1-5, the reversible compression rebound rate of Examples 1-12 has been improved, and the unit current density conversion expansion of Examples 1-12 has been reduced.

[0099] In the description of this specification, references to terms such as "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example.

[0100] Although embodiments of the invention have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

Claims

1. A negative electrode sheet, characterized in that, Comprise: Silicon material and three-dimensional graphene, wherein the three-dimensional graphene comprises: first three-dimensional graphene and second three-dimensional graphene, wherein the D50 particle size of the first three-dimensional graphene is d1, the D50 particle size of the second three-dimensional graphene is d2, and the d1, d2 satisfy: 3 μm≤d1≤10 μm, 0 μm 2. The negative electrode sheet according to claim 1, characterized by The d1, d2 satisfy: d1 / d2≥8.

3. The negative electrode sheet according to claim 1, characterized by The weight ratio of the first three-dimensional graphene and the second three-dimensional graphene satisfies: 1:(0.33-3).

4. The negative electrode sheet according to claim 1, characterized by The specific surface of the three-dimensional graphene is a, wherein the a satisfies: a < 200 g / m 2 .

5. The negative electrode sheet according to claim 1, wherein The three-dimensional graphene has a coating layer, and a precursor of the coating layer comprises at least one of sugar, polymer and pitch.

6. The negative electrode sheet according to claim 1, characterized by Also include: Lithiophilic material, the lithiophilic material is arranged in the pore of the three-dimensional graphene, and the mass fraction of the lithiophilic material is 0.01%-1%.

7. The negative electrode sheet according to claim 6, characterized by The lithiophilic material includes at least one of C3N4, zinc oxide, copper oxide, lithium nitride, lithium phosphide, lithium lanthanum zirconium tantalum oxide and lithium aluminum titanium phosphate.

8. The negative electrode sheet according to any one of claims 1 to 7, wherein The proportion of the three-dimensional graphene in the negative electrode material of the negative electrode sheet is w, wherein the w satisfies: 3%≤w≤15%.

9. The negative electrode sheet according to claim 8, characterized by The w satisfies: 5%≤w≤10%.

10. The negative electrode sheet according to any one of claims 1 to 7, wherein The silicon material includes silicon carbon and / or silicon oxygen.

11. The negative electrode sheet according to any one of claims 1 to 7, wherein In mass percentage, it comprises 3%-15% of three-dimensional graphene, 50%-90% of silicon material and additives, wherein the additives include binder and / or conductive agent.

12. A battery, characterized by Comprise: The negative electrode sheet is the negative electrode sheet according to any one of claims 1-11.

13. A battery pack, characterized by Comprise at least one battery according to claim 12.

14. An electrical device, characterized by Comprise at least one battery pack according to claim 13 or the battery according to claim 12.

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