Negative electrode material, secondary battery, and electric device

Abstract

The invention belongs to the technical field of batteries, and particularly relates to a negative electrode material, a secondary battery and electric equipment. The second coating layer with the porous carbon material in the negative electrode material provides a sufficient buffer space for volume expansion of silicon, so that cracks and pulverization of the negative electrode material are effectively reduced, and the structural integrity of the negative electrode material is further ensured. And meanwhile, the solid electrolyte arranged in the second coating layer can maintain the smoothness of an ion transmission path in the silicon expansion process, so that the rate capability and the quick charge performance of the battery are ensured. Besides, a third coating layer (SEI film) formed by the ionic liquid has good ionic conductivity, and dynamic covalent bonds existing in some ionic liquids can be fractured and recombined under the action of external stress, so that a self-repairing function is realized. Therefore, when cracks are generated on the surface of the negative electrode material due to volume expansion, the third coating layer can quickly repair the cracks, prevent electrolyte permeation and lithium dendrite growth and inhibit side reactions.

Description

Technical Field

[0001] This application belongs to the field of battery technology, specifically relating to a negative electrode material, a secondary battery, and an electrical device. Background Technology

[0002] Silicon-based materials are favored as anode materials due to their high theoretical specific capacity, low delithiation potential, abundant reserves, and environmental friendliness. However, silicon-based materials undergo volume expansion of up to 300%-400% during charge and discharge. This drastic volume change leads to severe cracking and pulverization of the anode material, thereby compromising the integrity of the anode structure. Moreover, the cracks caused by volume expansion block ion transport pathways, resulting in poor rate performance and fast-charging performance of the battery. Furthermore, repeated volume expansion and contraction cause the solid electrolyte interphase (SEI) film on the surface of the anode to continuously rupture and regenerate, consuming electrolyte and lithium source, exacerbating side reactions, and ultimately leading to a sharp reduction in battery cycle life and coulombic efficiency. Summary of the Invention

[0003] This application aims to provide an anode material, a secondary battery, and an electrical device to solve the problem of cracking and pulverization of silicon-based anode materials caused by volume expansion during charging and discharging.

[0004] To address the aforementioned technical problems, this application provides a negative electrode material, comprising: a core, including silicon particles; a first coating layer disposed on at least a portion of the surface of the core, the first coating layer comprising a conductive material; a second coating layer disposed on at least a portion of the surface of the first coating layer, the second coating layer comprising a porous carbon material and a solid electrolyte; and a third coating layer disposed on at least a portion of the surface of the second coating layer, the third coating layer comprising an ionic liquid.

[0005] In one embodiment, the first coating layer and the second coating layer have a porous structure.

[0006] In one embodiment, the average pore size of the first coating layer is smaller than the average pore size of the second coating layer, and the solid electrolyte is distributed in the pores of the second coating layer.

[0007] In one embodiment, the average particle size of the silicon particles is 50 nm to 200 nm; and / or the average particle size of the anode material is 5 μm to 20 μm.

[0008] In one embodiment, the average particle size of the silicon particles is 100 nm to 150 nm; and / or the average particle size of the anode material is 8 μm to 15 μm.

[0009] In one embodiment, at least one of the following is satisfied: A. The average pore size of the first coating layer is 2nm~10nm; B. The porosity of the first coating layer is 40%~60%; C. The average pore size of the second coating layer is 15nm~30nm; D. The porosity of the second coating layer is 50%~70%.

[0010] In one embodiment, the conductive material includes metallic conductive materials and / or carbonaceous conductive materials.

[0011] In one embodiment, at least one of the following is satisfied: a. Conductive metallic materials include at least one of the following: copper, aluminum, copper alloys, and aluminum alloys; b. Carbonaceous conductive materials include at least one of the following: graphite, graphene, carbon nanotubes, carbon black, and carbon fiber; c. Porous carbon materials include at least one of the following: porous soft carbon, porous hard carbon; d. Solid electrolytes include at least one of the following: inorganic solid electrolytes and organic solid electrolytes.

[0012] In one embodiment, the conductive material is a mixture of metallic conductive material and carbonaceous conductive material; wherein the mass ratio of metallic conductive material to carbonaceous conductive material is 1: (2.3~9).

[0013] In one embodiment, at least one of the following is satisfied: ①. Inorganic solid electrolytes include at least one of the following: oxide solid electrolytes, sulfide solid electrolytes, nitride solid electrolytes, phosphide solid electrolytes, and halide solid electrolytes; ②. Organic solid electrolytes include at least one of the following: polymer solid electrolytes and gel polymer electrolytes; ③. The average particle size of the solid electrolyte is greater than the average pore size of the first coating layer and smaller than the average pore size of the second coating layer; ④. The solid electrolyte accounts for 70% to 90% of the porous volume in the second coating layer. In one embodiment, at least one of the following is satisfied: I. The thickness of the first coating layer is 5nm~15nm; II. The thickness of the second coating layer is 50 nm to 150 nm; III. The thickness of the third coating layer is 3nm~10nm; IV. The ionic liquid includes at least one of the following: phenylboronic acid-functionalized imidazole ionic liquid (PBA-IL) or furanylimidazolium Diels-Alder adduct.

[0014] This application also provides a secondary battery, including a negative electrode sheet, the negative electrode sheet including a negative current collector and an active material layer disposed on at least one surface of the negative current collector; wherein the active material layer contains the aforementioned negative electrode material.

[0015] This application also provides an electrical device, which includes a secondary battery; wherein the secondary battery is used to provide electrical energy to the electrical device.

[0016] This application protects a negative electrode material. Because the first coating layer contains a conductive material, it ensures the conductivity of the negative electrode material. The porous carbon material in the negative electrode material provides ample buffer space for the volume expansion of silicon, effectively reducing cracking and pulverization, thus ensuring the integrity of the negative electrode structure. Simultaneously, the solid electrolyte in the second coating layer maintains unobstructed ion transport paths during silicon expansion, ensuring the battery's rate performance and fast-charging performance. Furthermore, the third coating layer (SEI film) formed by the ionic liquid has good ionic conductivity, and the dynamic covalent bonds in the ionic liquid can break and recombine under external stress, achieving a self-repair function. Therefore, when cracks appear on the surface of the negative electrode material due to volume expansion, the third coating layer can quickly repair the cracks, prevent electrolyte penetration and lithium dendrite growth, suppress side reactions, and ultimately ensure the battery's cycle life and coulombic efficiency.

[0017] Additional aspects and advantages of this application 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 this application. Detailed Implementation

[0018] The embodiments of this application will now be described in detail. Examples of these embodiments are shown, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to reference are exemplary and are only used to explain this application, and should not be construed as limiting this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

[0019] The terms "first" and "second" in the specification and claims of this application may explicitly or implicitly include one or more of the features. In the description of this application, unless otherwise stated, "multiple" means two or more. Furthermore, "and / or" in the specification and claims indicates at least one of the connected objects, and the character " / " generally indicates that the preceding and following objects are in an "or" relationship.

[0020] In the description of the present application, it should be understood that the orientation or positional relationship indicated by the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as a limitation on the present application.

[0021] In the description of the present application, it should be noted that unless otherwise clearly specified and limited, the terms "mounted", "connected", and "coupled" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present application can be understood according to specific situations.

[0022] The present application provides a negative electrode material, including: a core including silicon particles; a first coating layer provided on at least part of the surface of the core, the first coating layer containing a conductive material; a second coating layer provided on at least part of the surface of the first coating layer, the second coating layer containing a porous carbon material and a solid electrolyte; a third coating layer provided on at least part of the surface of the second coating layer, the third coating layer containing an ionic liquid. [[ID=,7]]

[0023] The porous carbon material in the second coating layer of the negative electrode material provides sufficient buffer space for the volume expansion of silicon, effectively reducing cracks and pulverization of the negative electrode material, and thus ensuring the integrity of the negative electrode structure. At the same time, the solid electrolyte provided in the second coating layer can always maintain the ion transmission path unblocked during the silicon expansion process, and thus ensure the rate performance and fast charging performance of the battery. In addition, the third coating layer (SEI film) formed by the ionic liquid has good ionic conductivity, and the dynamic covalent bonds in the ionic liquid can be broken and recombined under the action of external stress to achieve a self-repair function. Therefore, when cracks are generated on the surface of the negative electrode material due to volume expansion, the third coating layer can quickly repair the cracks, prevent electrolyte penetration and lithium dendrite growth, inhibit the occurrence of side reactions, and ensure the cycle life and Coulomb efficiency of the battery. In the present application, the silicon particles can be one of silicon oxide materials (SiOx, where 0 < x ≤ 2) and elemental silicon.

[0024] In some embodiments, the first coating layer and the second coating layer have a porous structure. In one embodiment, the average pore size of the first coating layer is smaller than the average pore size of the second coating layer, and the solid electrolyte is distributed in the pores of the second coating layer.

[0025] The porous structure of the first and second coating layers can further provide expansion space for the silicon particles in the core, thereby effectively improving the structural stability of the anode material.

[0026] The average pore size of the first coating layer is smaller than that of the second coating layer. During lithium intercalation, the volume expansion of silicon particles is transmitted from the inside to the outside. The first coating layer is in direct contact with the silicon particle core and requires a denser microporous structure to disperse stress and provide an electronic conduction channel. The second coating layer, on the other hand, requires larger pores to accommodate a greater volume expansion. Therefore, setting a dense-loose pore gradient structure from the inside to the outside can not only absorb the volume expansion of silicon particles in stages and reduce cracking and pulverization of the negative electrode material, but also avoid stress concentration or pore collapse caused by a single pore size design. This improves the cycle stability of the negative electrode material and enhances the cycle life of the battery.

[0027] In one embodiment, the average pore size of the first coating layer is 2nm to 10nm. This first coating layer is adjacent to the silicon particles and needs to provide high electronic conductivity and initial stress buffering. Therefore, a pore size within this range can reduce electrolyte penetration and decrease side reactions between silicon and the electrolyte. Simultaneously, this pore structure can initially absorb the volume expansion stress of the silicon particles through elastic deformation, preventing cracks from directly extending to the outer layer. Furthermore, this pore structure can also act as an "ion sieve," slowing the entry of electrolyte solvent molecules and reducing excessive growth of the SEI film.

[0028] In one embodiment, the average pore size of the second coating layer is 15nm~30nm. This pore size provides ample space for greater volume expansion of silicon particles. The pore size is much larger than the Debye radius of lithium ions, significantly reducing ion transport resistance. Combined with the filled solid electrolyte, this forms a continuous and efficient ion transport path. Simultaneously, the pore walls of this porous structure act as a mechanical framework, maintaining the overall structural stability of the negative electrode material and suppressing cracking and pulverization of the negative electrode material during cycling.

[0029] Specifically, the average pore size of the first coating layer is any one or any two of 2nm, 4nm, 6nm, 8nm, and 10nm, and the average pore size of the second coating layer is any one or any two of 15nm, 20nm, 25nm, and 30nm.

[0030] In one embodiment, the porosity of the first coating layer is 40% to 60%. This first coating layer directly coats the silicon particles and needs to simultaneously meet the requirements for electron conduction and initial volume expansion buffering. At the same time, a porosity within this range can reduce the direct penetration of electrolyte to the silicon surface, lowering the probability of excessive SEI film growth and side reactions.

[0031] In one embodiment, the porosity of the second coating layer is 50% to 70%. The second coating layer needs to provide sufficient space for the significant volume expansion of silicon particles, therefore its porosity is higher than that of the first coating layer. Furthermore, the 50% to 70% porosity ensures both pore connectivity and maintains the mechanical strength of the pore walls, preventing pore collapse during cycling and preserving the structural integrity of the negative electrode material.

[0032] Specifically, the porosity of the first coating layer is 40%, 45%, 50%, 55%, 60% or any value within the above range, and the porosity of the second coating layer is any one or any two of 50%, 55%, 60%, 65%, 70%.

[0033] In one embodiment, the average particle size of the silicon particles is 50 nm to 200 nm. The volumetric expansion stress of silicon particles is positively correlated with their particle size; reducing the particle size can significantly reduce expansion stress and crack propagation driving force. Particle sizes within this range can achieve a balance between nanoscale effects and actual fabrication processes. Simultaneously, this particle size range can buffer expansion through its own deformation and the synergistic effect of adjacent channels, reducing cracking and pulverization of the anode material. Furthermore, it can avoid the surge in specific surface area and exacerbation of side reactions caused by excessively small particles.

[0034] Specifically, the average particle size of the silicon particles is within the range of any one or both of 50nm, 100nm, 150nm, and 200nm. In one embodiment, the average particle size of the silicon particles is 100nm to 150nm.

[0035] In one embodiment, the average particle size of the negative electrode material is 5 μm to 20 μm. An average particle size within this range can reduce localized stress concentration during charging and discharging, prevent particle breakage and excessive SEI film growth, thereby extending the battery's cycle life.

[0036] Specifically, the average particle size of the negative electrode material is any one or any two of 5μm, 10μm, 15μm, and 20μm. In one embodiment, the average particle size of the negative electrode material is 8μm to 15μm.

[0037] In one embodiment, the conductive material includes a metallic conductive material and / or a carbonaceous conductive material. In some embodiments, the metallic conductive material includes at least one of the following: copper, aluminum, copper alloys, and aluminum alloys; in some embodiments, the carbonaceous conductive material includes at least one of the following: graphite, graphene, carbon nanotubes, carbon black, and carbon fibers.

[0038] Metal atoms have few outermost electrons, and the binding force between them and the atomic nucleus is weak. Therefore, in metal crystals, these outer electrons are not bound by individual atoms and become free electrons. When an external electric field is applied, these free electrons overcome the obstruction of a few impurities and defects in the crystal under the action of the electric field force and move in a directional manner in the opposite direction of the electric field, forming an electric current.

[0039] In carbonaceous conductive materials, carbon atoms form a conjugated π-bond system through specific bonding—carbon atoms adopt sp² hybridization, and the remaining unhybridized p electrons overlap and are no longer bound by individual carbon atoms, forming freely moving delocalized electrons. These delocalized electrons need to transfer charge through continuous conductive channels to form an electric current.

[0040] The aforementioned conductive materials possess excellent conductivity and are structurally stable, making them resistant to reaction with the electrolyte. This allows them to maintain the electronic conductivity of the negative electrode material over a long period.

[0041] When the conductive material is a mixture of metallic conductive material and carbonaceous conductive material, the mass ratio of metallic conductive material to carbonaceous conductive material is 1:(2.3~9).

[0042] In one embodiment, the conductive material is a mixture of metallic conductive material and carbonaceous conductive material, wherein the mass ratio of the metallic conductive material to the carbonaceous conductive material is any one or both of the following: 1:2.3, 1:5, 1:7, and 1:9. The mixed conductive material can achieve good conductivity while also having a higher proportion of carbonaceous conductive material, which can reduce the weight of the negative electrode material and improve the specific capacity of the secondary battery.

[0043] In one embodiment, the porous carbon material includes at least one of the following: porous soft carbon and porous hard carbon. The porous structure of porous soft carbon and porous hard carbon facilitates ion diffusion and charge storage, while also effectively absorbing particle expansion stress, improving the cycle stability and charge-discharge performance of the battery. Furthermore, soft carbon and hard carbon are widely available and easily obtained.

[0044] In one embodiment, the solid electrolyte includes at least one of the following: an inorganic solid electrolyte and an organic solid electrolyte.

[0045] Inorganic solid electrolytes typically possess high ionic conductivity and good chemical stability. In one embodiment, the inorganic solid electrolyte may be selected from oxide-based solid electrolytes, such as Li7La3Zr2O.12 At least one of the following: (LLZO), Li3PO4-based materials (such as Li3PO4-Li2S-SiO2), LiTaO3, and LiNbO3; sulfide solid electrolytes, such as the Li2S-P2S5 system (such as Li7P3S). 11 ), Li 10 GeP2S 12 At least one of (LGPS), Li3PS4, and doped / modified materials (such as Li3PS4-LiI); halide solid electrolytes, such as Li a At least one of the following: MX4 (Li2MnCl4, Li2ZnCl4), Li3MX6 (Li3YCl6, Li3YBr6), Li6MX8 (Li6CoCl8), and Li3LaCl6.

[0046] In one embodiment, the organic solid electrolyte includes a polymer solid electrolyte and a gel polymer electrolyte. In one embodiment, the polymer solid electrolyte includes at least one of polyethylene oxide (PEO), polypropylene oxide (PPO), polyacrylonitrile (PAN), and polymethyl methacrylate (PMMA). In one embodiment, the gel polymer electrolyte includes polyacrylic acid gel and PMMA-based gel. In one embodiment, the organic solid electrolyte can also be an ionic liquid-based solid electrolyte, which is formed by solidifying an ionic liquid as the conductive medium with a polymer or other carrier. Electrolytes composed of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and lithium hexafluorophosphate (LiPF6) ionic liquids and polymers belong to this category, possessing both high ionic conductivity and thermal stability. In one embodiment, the organic solid electrolyte can also be a modified polymer electrolyte, which is a modified solid electrolyte material obtained through copolymerization, crosslinking, or elemental modification, such as fluorinated polyether electrolytes modified with fluorine-containing groups, and polypropylene carbonate (PPC), which can optimize room-temperature ionic conductivity and interfacial compatibility.

[0047] In one embodiment, the average particle size of the solid electrolyte is larger than the average pore size of the first coating layer and smaller than the average pore size of the second coating layer. This design ensures that the solid electrolyte is relatively uniformly distributed in the pores of the second coating layer, forming a continuous ion transport network.

[0048] In one embodiment, the solid electrolyte occupies 70% to 90% of the porous volume in the second coating layer. The second coating layer simultaneously serves as a buffer for volume expansion and for ion transport. This filling ratio ensures that the electrolytes within the pores are in contact with each other, meaning that the ion transport channels are not interrupted during cycling, and even after silicon volume expansion, a low ion transport resistance is maintained. Simultaneously, it reduces direct contact between the liquid electrolyte and the active material, suppressing side reactions and abnormal SEI film growth.

[0049] In one embodiment, the thickness of the first coating layer is controlled between 5 nm and 15 nm. Within this range, good conductivity and microporous structure can be guaranteed, while the energy density of the material will not be reduced due to excessive coating layer thickness.

[0050] In one embodiment, the thickness of the second coating layer is 50nm~150nm. This thickness design ensures the formation of a sufficient network of mesopores and macropores, providing ample space for volume expansion and guaranteeing the mechanical strength of the second coating layer to prevent structural collapse of the negative electrode material during cycling.

[0051] In one embodiment, the thickness of the third coating layer is 3nm to 10nm. This range ensures ion conduction while also providing crack self-healing and flexibility. Specifically, the thickness of the first coating layer is any one or any two of 5nm, 8nm, 12nm, and 15nm; the thickness of the second coating layer is any one or any two of 50nm, 80nm, 130nm, and 150nm; and the thickness of the third coating layer is any one or any two of 3nm, 5nm, 7nm, and 10nm.

[0052] In one embodiment, the ionic liquid includes at least one of the following: a phenylboronic acid-functionalized imidazole ionic liquid, or a furanylimidazolium Diels-Alder adduct (such as furanylimidazolium-5-carboxylate). The aforementioned ionic liquid can fracture and reform under external stress, achieving a self-healing function. When cracks appear on the surface of the negative electrode material due to volume expansion, the aforementioned ionic liquid can rapidly repair the cracks, inhibit electrolyte penetration, and suppress the occurrence of side reactions.

[0053] The second coating layer of porous carbon material in the anode material protected in this application provides ample and gradient-distributed buffer space for the volume expansion of silicon, effectively reducing cracking and pulverization of the anode material and thus ensuring the structural integrity of the anode material. Simultaneously, the solid electrolyte disposed in the second coating layer can maintain unobstructed ion transport pathways during silicon particle expansion, thereby ensuring the battery's rate performance and fast-charging performance. Furthermore, the SEI film formed by the self-healing ionic liquid can dynamically repair surface cracks and inhibit repeated rupture and regeneration of the SEI film, thereby reducing the occurrence of side reactions and ultimately ensuring the battery's cycle life and coulombic efficiency.

[0054] The negative electrode material of this application has a three-layer coating structure of "core - first coating layer - second coating layer - third coating layer", and a solid electrolyte is filled in the porous structure of the second coating layer. The preparation method includes the following main steps: 1. Preparation of the first coating layer Specifically, the process includes: drying silicon particles and cooling them to room temperature; mixing silicon particles, carbon nanotubes, dispersants, and organic solutions to obtain a suspension; drying the suspension to obtain a dry powder; and carbonizing the dry powder to obtain a composite precursor.

[0055] The conditions for drying silicon particles include: a vacuum drying oven temperature of 120~180℃ and a drying time of 4~6 hours.

[0056] The organic solvent includes ethanol, and the ratio of silicon particles, carbon nanotubes, dispersant and ethanol is 100:(3~10):(0.5~20):(100~300).

[0057] The parameters for stirring the mixture include: stirring speed of 200~400 rpm and stirring time of 3~6 h.

[0058] The conditions for drying the suspension include: vacuum drying temperature of 80~100℃ and vacuum drying time of 8~12h.

[0059] The composite precursor is obtained by carbonizing the dried powder, including: placing the dried powder in a tube furnace under argon protection, heating it to 850-950℃ at a rate of 7-9℃ / min, carbonizing for 2-4 hours, and then cooling to obtain the composite precursor.

[0060] 2. Preparation of the second coating layer Specifically, this involves mixing a composite precursor, a carbon source (such as pitch or sucrose), and polymethyl methacrylate (PMMA) microspheres, and then carbonizing them to obtain carbonized particles; finally, etching the carbonized particles to obtain particles with a second coating layer.

[0061] The mixing ratio of the composite precursor, carbon source, and polymethyl methacrylate (PMMA) microspheres is 100:(15-40):(8-20).

[0062] The carbonization treatment conditions include: carbonization temperature of 600~800℃ and carbonization time of 4~8 hours.

[0063] The carbonized particles are etched, including etching the carbonized particles with HF for 30-45 minutes to obtain particles with a second coating layer.

[0064] 3. Filling with solid electrolyte Specifically, this includes: preparing a solid electrolyte solution; immersing particles with a second coating layer in the solid electrolyte solution, and obtaining particles filled with solid electrolyte after drying.

[0065] The preparation of solid electrolytes includes: dissolving solid electrolyte particles in a solvent to obtain a solid electrolyte solution.

[0066] The solvent is N-methylpyrrolidone (NMP), and the concentration of the solid electrolyte solution particles is 0.1~0.5 g / mL.

[0067] The soaking time is 2 to 5 hours.

[0068] The drying conditions include: a drying temperature of 90-110℃ and a drying time of 7-9 hours.

[0069] 4. Preparation of the third coating layer Specifically, the process includes: dissolving the ionic liquid in a solvent to obtain an ionic liquid monomer solution; dispersing the particles after filling with solid electrolyte in step 3 in the ionic liquid monomer solution (the mass ratio of the particles after filling with solid electrolyte to the ionic liquid is 100:(5~18)), and adding an initiator to carry out a free radical polymerization reaction to obtain particles with a third coating layer; and pulverizing and sieving the particles with the third coating layer to obtain the negative electrode material.

[0070] The solvent in the ionic liquid monomer solution is dimethylformamide (DMF) or dimethyl sulfoxide (DMSO), and the concentration range of the ionic liquid is 0.01 g / mL to 1.0 g / mL.

[0071] The initiator includes azobisisobutyronitrile (AIBN), and the initiator accounts for 0.57% to 1% of the mass of the ionic liquid.

[0072] The free radical polymerization reaction is carried out at a temperature of 70-90℃ for 6-10 hours.

[0073] The sieve used for sieving is 300 mesh, and the average particle size of the negative electrode material is 5-20 μm.

[0074] This application also provides a secondary battery, including a negative electrode sheet, the negative electrode sheet including a negative current collector and an active material layer disposed on at least one surface of the negative current collector; wherein the active material layer contains the aforementioned negative electrode material.

[0075] This application also provides an electrical device, which includes a secondary battery; wherein the secondary battery is used to provide electrical energy to the electrical device.

[0076] To better explain this solution, embodiments and comparative examples are also provided below.

[0077] Example 1 The preparation of secondary batteries includes: 1. Preparation of negative electrode sheet 1.1 Silicon particles (SiO2) were placed in a vacuum drying oven and dried at 160°C for 5 hours to remove surface adsorbed water, thus obtaining dried silicon particles. The silicon particles, graphene, and dispersant were added to 80 mL of ethanol in a ratio of 80:7:13 and stirred at 300 rpm for 5 hours to obtain a mixed suspension. The suspension was vacuum dried at 90°C for 10 hours to obtain a dried powder. The dried powder was placed in an argon-protected tube furnace and heated to 900°C at a rate of 8°C / min for 3 hours to carbonize. After cooling, a composite precursor was obtained.

[0078] 1.2. The composite precursor, asphalt, and PMMA microspheres were mixed, and the mixture was carbonized at 700℃ for 6 hours and etched with HF for 40 minutes to form a second coating layer with a network structure. A solid electrolyte solution was obtained by dissolving a solid electrolyte in N-methylpyrrolidone (NMP) with a concentration of 0.3 g / mL. The particles of the second coating layer were immersed in the solid electrolyte solution, vacuum impregnated for 3 hours, and then dried in a 100℃ drying oven for 8 hours to obtain particles filled with solid electrolyte.

[0079] 1.3. The particles filled with solid electrolyte were dispersed in an ionic liquid solution (concentration 12%), and azobisisobutyronitrile (AIBN) was added as an initiator. After free radical polymerization at 80°C for 8 hours, particles with a third coating layer were formed. The particles with the third coating layer were pulverized and passed through a 300-mesh sieve to obtain the negative electrode material.

[0080] 1.4. Dry mix the above-mentioned negative electrode material with conductive carbon black for 10 minutes; then, add deionized water and binder (sodium carboxymethyl cellulose and styrene-butadiene rubber in a 1:1 mass ratio) to adjust the solid content to 55 wt%; then, stir at high speed for 30 minutes, ultrasonically disperse for 15 minutes, and vacuum degas for 20 minutes to obtain a slurry. The mass ratio of negative electrode material to conductive carbon black binder in the slurry is 85:5:10; then, coat the slurry onto a 10 μm copper foil and vacuum dry at 110℃ for 12 hours; finally, roll-press to a compaction density of 1.6 g / cm³. 3 Cut into 15mm diameter round pieces.

[0081] The anode material contains silicon particles with an average particle size of 50 nm; the first coating layer is made of copper with a thickness of 5 nm, an average pore size of 2 nm, and a porosity of 40%; the second coating layer is made of porous soft carbon with a thickness of 50 nm, an average pore size of 15 nm, and a porosity of 50%; the solid electrolyte accounts for 70% of the porous volume in the second coating layer and is LiTaO3; the third coating layer has a thickness of 3 nm and the ionic liquid is phenylboronic acid-functionalized imidazole ionic liquid (PBA-IL).

[0082] 2. Preparation of the positive electrode: NCM811 and conductive carbon black were mixed; then, polyvinylidene fluoride and NMP solution were added, and the solid content was adjusted to 70 wt%. The mixture was then vacuum stirred and degassed for 30 minutes, controlling the slurry viscosity to approximately 2300 mPa·s. The mass ratio of NCM811, conductive carbon black, and polyvinylidene fluoride in the slurry was 96:2:2. The slurry was then uniformly coated onto a 12 μm aluminum foil and vacuum dried at 120℃ for 12 hours. Finally, it was rolled to a compaction density of 3.5 g / cm³. 3 It is cut into 14mm diameter round pieces.

[0083] 3. Preparation of electrolyte: Mix ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a volume ratio of 3:3:4. Then, add 1.0 M LiPF6 and stir magnetically until completely dissolved. Next, add 1 wt% vinylene carbonate (VC) and 1 wt% fluoroethylene carbonate (FEC) and continue stirring for 30 minutes. Finally, filter through a 0.2 μm polytetrafluoroethylene (PTFE) membrane and let stand for 2 hours before use.

[0084] 4. Button cell battery assembly: In the glove box, stack the positive electrode, separator, and negative electrode in sequence; then, add 100 μL of electrolyte to ensure full wetting; finally, place the gasket and spring, press and seal, and let stand for 24 hours before conducting electrochemical tests.

[0085] Example 2 The difference from Example 1 is that in step 1.1, the average particle size of the silicon particles in the negative electrode material is adjusted from 50nm to 200nm.

[0086] Example 3 The difference from Example 1 is that in step 1.1, the average particle size of the silicon particles in the negative electrode material is adjusted from 50nm to 100nm.

[0087] Example 4 The difference from Example 1 is that in step 1.1, the material of the first coating layer is changed from graphene to carbon nanotubes.

[0088] Example 5 The difference from Example 1 is that in step 1.1, the thickness of the first coating layer is adjusted from 5 nm to 15 nm by adjusting the content of the suspension components.

[0089] Example 6 The difference from Example 1 is that in step 1.1, the thickness of the first coating layer is adjusted from 5 nm to 10 nm by adjusting the content of the suspension components.

[0090] Examples 7-10 The difference from Example 1 is that in step 1.1, the average pore size and porosity of the first coating layer are adjusted by adjusting the carbonization process parameters. Example 11 The difference from Example 1 is that in step 1.2, the carbonization temperature is adjusted, and the material of the second coating layer is changed from porous soft carbon to porous hard carbon.

[0091] Example 12 The difference from Example 1 is that in step 1.2, the thickness of the second coating layer is adjusted from 50 nm to 150 nm by adjusting the content of the components in the mixture.

[0092] Example 13 The difference from Example 1 is that in step 1.2, the thickness of the second coating layer is adjusted from 50 nm to 100 nm by adjusting the content of the components in the mixture.

[0093] Examples 14-17 The difference from Example 1 is that in step 1.2, the average pore size and porosity of the second coating layer are adjusted by adjusting the carbonization and etching process parameters.

[0094] Example 18 The difference from Example 1 is that in step 1.2, the solid electrolyte accounts for 90% of the porous volume in the second coating layer by adjusting the impregnation time from 70%.

[0095] Example 19 The difference from Example 1 is that in step 1.2, the solid electrolyte accounts for 80% of the porous volume in the second coating layer by adjusting the impregnation time from 70%.

[0096] Example 20 The difference from Example 1 is that in step 1.2, the solid electrolyte is changed from LiTaO3 to lithium polyoxyethylene trifluoromethanesulfonate.

[0097] Example 21 The difference from Example 1 is that in step 1.3, the thickness of the third coating layer is adjusted from 3 nm to 10 nm by adjusting the free radical polymerization reaction parameters.

[0098] Example 22 The difference from Example 1 is that in step 1.3, the thickness of the third coating layer is adjusted from 3 nm to 5 nm by adjusting the free radical polymerization reaction parameters.

[0099] Example 23 The difference from Example 1 is that in step 1.3, the ionic liquid is changed from phenylboronic acid functionalized imidazole ionic liquid (PBA-IL) to furanylimidazolium-5-carboxylate.

[0100] Comparative Example The difference from Example 1 is that a layer of soft carbon material is coated on the surface of elemental silicon particles as a negative electrode material, the average particle size of the silicon particles is 50 nm, and the thickness of the carbon coating layer is 50 nm.

[0101] The following performance tests were performed on the coin cells obtained in the above embodiments and comparative examples. Tables 1 and 2 are parameter tables for the negative electrode materials corresponding to each example, and Table 3 is a performance data table for the initial coulombic efficiency, capacity retention rate of the battery after 300 cycles, and expansion rate of the negative electrode sheet for the coin cells corresponding to each example.

[0102] I. Initial Coulomb Efficiency Test Method: The prepared coin cells were left to stand at a constant temperature of 25°C for 12 hours to ensure sufficient electrolyte immersion. They were then charged at a constant current rate of 0.1C until the upper limit voltage of 4.25V was reached, and the initial charge capacity was recorded. Subsequently, the coin cells were discharged at a constant current rate of 0.1C until the lower limit voltage of 2V was reached, and the initial discharge capacity was recorded. The initial coulombic efficiency was calculated as (initial discharge capacity / initial charge capacity) * 100%.

[0103] II. Test methods for battery capacity retention and negative electrode expansion rate after 300 cycles: The prepared coin cells were placed at a constant temperature of 25℃ for 12 hours to ensure full immersion in the electrolyte. The coin cells were then charged at a constant current rate of 1C until the upper limit voltage of 4.25V was reached. Subsequently, the coin cells were discharged at a constant current rate of 1C until the lower limit voltage of 2V was reached. This charge-discharge cycle was repeated 300 times. Battery capacity retention after 300 cycles = (Battery discharge capacity on the 300th cycle / Battery discharge capacity on the 1st cycle) * 100%.

[0104] 3. After the battery has undergone the above 300 cycles, disassemble the battery in the glove box and remove the negative electrode. Clean it with DMC and vacuum dry it (drying temperature 60℃, time 2 hours). Use a laser thickness gauge to measure the thickness of the negative electrode at different positions (at least 5 points) and record the average thickness H300 after the cycle. Compare it with the initial average thickness H1 before the cycle. The expansion rate of the negative electrode is calculated as (H300-H1) / H1*100%.

[0105] Table 1. Parameter table of the negative electrode material for each example.

[0106] Table 2 shows the parameters of the anode materials for each example.

[0107] Table 3 Battery Performance Test Data

[0108] As can be seen from the data in Tables 1-3 above, using the negative electrode material of this application is beneficial to reducing the first irreversible capacity loss of the battery, while also suppressing the expansion of the negative electrode sheet and improving the cycle life of the battery.

[0109] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0110] Although embodiments of this application 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 this application, the scope of which is defined by the claims and their equivalents.

Claims

1. A negative electrode material, characterized in that, include: The core, including silicon particles; A first coating layer is disposed on at least a portion of the surface of the core, the first coating layer comprising a conductive material; A second coating layer is disposed on at least a portion of the surface of the first coating layer, the second coating layer comprising a porous carbon material and a solid electrolyte; A third coating layer is disposed on at least a portion of the surface of the second coating layer, the third coating layer comprising an ionic liquid.

2. The negative electrode material according to claim 1, characterized in that, The first coating layer and the second coating layer have a porous structure.

3. The negative electrode material according to claim 2, characterized in that, The average pore size of the first coating layer is smaller than that of the second coating layer, and the solid electrolyte is distributed in the pores of the second coating layer.

4. The negative electrode material according to claim 1, characterized in that, The average particle size of the silicon particles is 50 nm to 200 nm; and / or the average particle size of the negative electrode material is 5 μm to 20 μm.

5. The negative electrode material according to claim 4, characterized in that, The average particle size of the silicon particles is 100nm~150nm; and / or the average particle size of the negative electrode material is 8μm~15μm.

6. The negative electrode material according to claim 2, characterized in that, Meet at least one of the following: A. The average pore size of the first coating layer is 2nm~10nm; B. The porosity of the first coating layer is 40%~60%; C. The average pore size of the second coating layer is 15nm~30nm; D. The porosity of the second coating layer is 50%~70%.

7. The negative electrode material according to claim 1, characterized in that, The conductive material includes metallic conductive materials and / or carbonaceous conductive materials.

8. The negative electrode material according to claim 7, characterized in that, Meet at least one of the following: a. The metallic conductive material includes at least one of the following: copper, aluminum, copper alloy, and aluminum alloy; b. The carbonaceous conductive material includes at least one of the following: graphite, graphene, carbon nanotubes, carbon black, and carbon fiber; c. The porous carbon material includes at least one of the following: porous soft carbon, porous hard carbon; d. The solid electrolyte includes at least one of the following: inorganic solid electrolyte, organic solid electrolyte.

9. The negative electrode material according to claim 7, characterized in that, The conductive material is a mixture of the metallic conductive material and the carbonaceous conductive material; The mass ratio of the metallic conductive material to the carbonaceous conductive material is 1:(2.3~9).

10. The negative electrode material according to claim 8, characterized in that, Meet at least one of the following: ①. The inorganic solid electrolyte includes at least one of the following: oxide solid electrolyte, sulfide solid electrolyte, nitride solid electrolyte, phosphide solid electrolyte, and halide solid electrolyte; ②. The organic solid electrolyte includes at least one of the following: polymer solid electrolyte, gel polymer electrolyte; ③. The average particle size of the solid electrolyte is greater than the average pore size of the first coating layer and smaller than the average pore size of the second coating layer; ④. The solid electrolyte accounts for 70% to 90% of the porous volume in the second coating layer.

11. The negative electrode material according to claim 1, characterized in that, Meet at least one of the following: I. The thickness of the first coating layer is 5nm~15nm; II. The thickness of the second coating layer is 50 nm to 150 nm; III. The thickness of the third coating layer is 3nm~10nm; IV. The ionic liquid includes at least one of the following: phenylboronic acid-functionalized imidazole ionic liquid, furanylimidazolium Diels-Alder adduct.

12. A secondary battery, characterized in that, It includes a negative electrode sheet, the negative electrode sheet including a negative current collector and an active material layer disposed on at least one surface of the negative current collector; The active material layer comprises the negative electrode material according to any one of claims 1 to 11.

13. An electrical appliance, characterized in that, The electrical equipment includes the secondary battery as described in claim 12; The secondary battery is used to provide power to the electrical equipment.

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