Mixed negative electrode material, negative electrode and lithium ion secondary battery thereof

Abstract

The invention provides a mixed negative electrode material. The mixed negative electrode material comprises a silicon carbon material and a graphitized material, the silicon-carbon material takes porous carbon as a matrix, and a silicon layer and an ordered layered carbon layer are sequentially deposited on the surface of the porous carbon matrix; the compaction density of the mixed negative electrode material is 1.0-2.0 g / cm < 3 > and the conductivity is 0.80-118 S / cm under the pressure of more than or equal to 5 Mpa; the ratio of the mass ratio of the graphitized material to the mass ratio of the silicon-carbon material is greater than or equal to 1.6 and less than or equal to 8.5, and the particle size Dv10 of the mixed negative electrode material is 1.1-5.2 mu m; dv50 is 5.3 [mu] m to 16 [mu] m; dv90 is from 16 [mu] m to 35 [mu] m; the porosity of the mixed negative electrode material is 0.005%-0.1%; the specific surface area is 1.2-3.2 m < 2 > / g, and the surface of the negative electrode is provided with a cutting area. The problems that the negative electrode interface stability is reduced, the impedance is increased, the lithium ion conducting capacity is low, and the battery cycle performance is poor are solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium ion secondary batteries, in particular to a mixed negative electrode material, a negative electrode and a lithium ion secondary battery thereof. BACKGROUND

[0002] With the rapid development of lithium ion batteries for many years, the requirements for high energy density and fast charging of lithium ion batteries are increasing to meet various application needs, including portable electronic products and electric vehicles and various application scenarios. Silicon-carbon materials stand out with their high lithiation capacity, excellent safety performance and high abundance. The use of graphite negative electrode material mixed with silicon-carbon material can significantly improve the energy density of lithium ion batteries and is expected to have large-scale commercial prospects. However, the vulnerability of silicon-carbon material leads to the generation of new interfaces, volume expansion, and deterioration of the contact interface with electrolyte, conductive agent and binder. At the same time, there is a phenomenon that the contact area between electrolyte and negative electrode material is small and the wettability is poor. This phenomenon further reduces the stability of the negative electrode interface, increases the impedance, and increases the diffusion barrier, which reduces the lithium ion conducting ability, resulting in poor battery cycle life and poor rate performance. The physical cutting method can increase the specific surface area of the negative electrode material in contact with the electrolyte, but this method has obvious defects. The cutting process generates local concentrated heat, which causes thermal damage to the negative active material and reduces the content of active silicon. At this time, the lithium ion conducting ability cannot be improved well. In view of this, the mixed negative electrode material needs to be improved and developed, and it should be suitable for physical cutting, so as to obtain a negative electrode material with high electrical conductivity, good cycle performance and good rate performance, a negative electrode and a lithium ion secondary battery. SUMMARY

[0003] The present application discloses a mixed negative electrode material, a negative electrode and a lithium ion secondary battery thereof, which increases the specific surface area of the mixed negative electrode material by cutting the surface of the electrode, optimizes the contact between the electrolyte and the mixed negative electrode material, accelerates lithium migration, and improves the efficiency of lithium ion conduction. At the same time, the high thermal conductivity and low resistance characteristics of the horizontal layered carbon microcrystals in silicon-carbon are used to transfer the cutting heat horizontally to graphite, reduce the vertical heat into the silicon-carbon interior, reduce the damage to active silicon and the generation of crystalline silicon, and generate a small amount of crystalline silicon to cover the cutting wound, reduce the exposure of active silicon and lithium loss, and further prolong the cycle life of the battery.

[0004] The present application is realized by the following technical solutions:

[0005] The present application first provides a mixed negative electrode material, which comprises silicon-carbon material and graphitized material.

[0006] The silicon-carbon material has a porous carbon as a matrix, and a silicon layer and an ordered layered carbon layer are sequentially deposited on the surface of the porous carbon matrix.

[0007] The compaction density of the mixed negative electrode material at ≥5Mpa is 1.0-2.0g / cm 3 , and the electrical conductivity is 0.80-188S / cm;

[0008] The mass ratio of the graphitized material of the mixed negative electrode material is ≥ the mass ratio of the silicon-carbon material, and satisfies 1.6≤mass ratio of graphitized material / mass ratio of silicon-carbon material≤8.5;

[0009] The mass ratio of the graphitized material is the mass ratio of the graphitized material to the negative electrode active material (graphitized material and silicon-carbon material);

[0010] The mass ratio of the silicon-carbon material is the mass ratio of the silicon-carbon material to the negative electrode active material (graphitized material and silicon-carbon material);

[0011] The particle size Dv10 of the mixed negative electrode material is 1.1μm-5.2μm;

[0012] The particle size Dv50 of the mixed negative electrode material is 5.3μm-16μm;

[0013] The particle size Dv90 of the mixed negative electrode material is 16μm-35μm;

[0014] The porosity of the mixed negative electrode material is 0.005%-0.1%;

[0015] The specific surface area of the mixed negative electrode material satisfies 1.2-3.2m 2 / g.

[0016] The surface of the mixed negative electrode electrode coated with the silicon-carbon material and the graphitized material has a cutting region.

[0017] As a further scheme, the depth of the cutting region of the surface of the mixed negative electrode electrode is 8-45μm, and the depth of the cutting region is < the negative electrode slurry coating thickness of the mixed negative electrode electrode ≤164μm; the width of the cutting region of the mixed negative electrode electrode is 45-240μm.

[0018] As a further scheme, the true density of the mixed negative electrode material is 2.05cm 3 / g-2.26cm 3 / g.

[0019] As a further scheme, the particle size range of the mixed negative electrode material is 0.9μm-37μm.

[0020] As a further preferred scheme, the particle size range of the mixed negative electrode material is 1.2μm-31μm.

[0021] As a further solution, the compaction density of the mixed negative electrode material at ≥ 100 MPa is 1.2-2.0 g / cm 3 .

[0022] The application also provides a preparation method of a mixed negative electrode including the mixed negative electrode material, including the following steps:

[0023] S1: Pre-mixing the graphitized material and the silicon-carbon material according to the target mass ratio and the particle size distribution range to obtain a mixed negative electrode material;

[0024] S2: Mixing and stirring the mixed negative electrode material, the negative electrode adhesive material, the negative electrode conductor material and the solvent to obtain a composite negative electrode slurry;

[0025] S3: Coating the composite negative electrode slurry on a foil, drying to remove the solvent, rolling, drying, and die cutting to obtain a mixed negative electrode;

[0026] S4: Physically cutting the surface of the negative electrode;

[0027] The silicon-carbon material satisfies one or more of the following characteristics:

[0028] (1) The silicon-carbon material has an electrical resistivity of 0.02-15 Ω*cm at a compaction density of 1.0-1.6 g / cm 3 .

[0029] (2) The silicon-carbon material has an electrical conductivity value / compaction density value ≥ 1, with the electrical conductivity unit being S / cm and the compaction density unit being g / cm 3 .

[0030] (3) The silicon-carbon material has a reversible deformation amount / maximum deformation amount in the range of 21%-45% at 30-300 MPa.

[0031] The graphitized material satisfies one or more of the following characteristics:

[0032] (1) The specific surface area of the graphitized material is 1.0-3.2 m 2 / g.

[0033] (2) The Dv50 of the graphitized material is 10 μm-18 μm.

[0034] (3) The OI value of the graphitized material at a compaction density of 1.75 g / cm 3 is < 10.5.

[0035] As a further preferred solution, the porous carbon satisfies one or more of the following conditions:

[0036] (1) The pore volume of the porous carbon is 0.55-1.15 cm3 / g,

[0037] (2) the particle size of the porous carbon is 2 μm to 30 μm;

[0038] (3) the D peak area Ad in the Raman spectrum of the porous carbon is 1180 cm -1 to 1400 cm -1 , the G peak area Ag is 1400 cm -1 to 1650 cm -1 , and the ratio Ag / Ad satisfies 0.507 to 2.370.

[0039] As a further solution, in the silicon-carbon material, the mass ratio of the silicon layer to the porous carbon is 1:(0.75 to 2.4).

[0040] As a further solution, the carbon content of the ordered layered carbon layer deposited on the surface of the porous carbon substrate accounts for 0.2 to 5 wt% of the silicon-carbon material.

[0041] As a further preferred solution, the ordered layered carbon layer has a thickness of 2 to 94 nm.

[0042] As a further solution, the premixing method of the S1 mixed negative electrode material is:

[0043] The graphitized material and the silicon-carbon material are respectively sieved according to the particle size intervals of lower limit of particle size to Dv10, Dv10 to Dv50 (not including Dv10), Dv50 to Dv90 (not including Dv50), and Dv90 to upper limit of particle size (not including Dv90), the four parts of materials sieved above are mixed according to the particle number ratio of 1:4:4:1, and then the graphitized material and the silicon-carbon material are mixed according to the target mass ratio to obtain the mixed negative electrode material.

[0044] As a further preferred solution, the preparation method of the silicon-carbon material in S1 is: a gas-phase silicon source is deposited in the porous carbon by chemical vapor deposition, carbon deposition coating is performed at high temperature to form an ordered layered carbon layer, which is the silicon-carbon material.

[0045] As a further solution, the porous carbon is hard carbon or soft carbon obtained by carbonization and activation of at least one of phenolic resin, coconut shell, and tar.

[0046] As a further solution, the carbonization temperature of the phenolic resin, coconut shell, and tar is 600 to 1000°C, and the carbonization time is 4 to 10 h.

[0047] As a further solution, the gas-phase silicon source includes at least one of monosilane, disilane, trichlorosilane, dichlorosilane, or trichlorosilane.

[0048] As a further aspect, the temperature of the chemical vapor deposition is 350-760°C.

[0049] As a further aspect, the carbon source for the ordered layered carbon layer deposited on the surface of the porous carbon substrate comprises at least one of nanographite sheets, nanotubes, nanocarbon fibers, ethylene, butyne, acetylene or propyne.

[0050] As a further aspect, the temperature of the carbon deposition coating is 420-600°C.

[0051] As a further preferred aspect, the temperature of the carbon deposition coating is 480°C.

[0052] As a further aspect, the graphitized material is obtained by carbonization, graphitization, granulation and coating of one or more of needle tar, coal tar, pitch tar, petroleum coke.

[0053] As a further aspect, the carbonization temperature of the graphitized material precursor is 420-1260°C, and the carbonization time is 3-10h.

[0054] As a further aspect, in S4, the surface of the negative electrode is subjected to photon beam cutting, and the cutting is performed by a high-temperature photon beam perpendicular to the surface of the negative electrode, resulting in a cutting region, and the cutting region contains the cut silicon-carbon material.

[0055] As a further aspect, the temperature of the photon beam cutting is 800-2000°C.

[0056] As a further preferred aspect, the temperature of the photon beam cutting is 1000-1800°C.

[0057] The application also provides a lithium ion secondary battery comprising the mixed negative electrode material or the mixed negative electrode prepared by the preparation method of the mixed negative electrode material.

[0058] As a further aspect, the lithium ion secondary battery comprises a negative electrode comprising the mixed negative electrode material, a positive electrode, an electrolyte and a separator.

[0059] As a further aspect, the negative electrode is a foil comprising a mixed negative electrode coating.

[0060] As a further aspect, the positive electrode is a foil comprising a positive electrode coating.

[0061] The positive electrode coating comprises a positive electrode material, an electrolyte, a positive electrode adhesive material and a positive electrode conductor material; and the mixed negative electrode coating comprises the mixed negative electrode material, a negative electrode conductor material and a negative electrode adhesive material.

[0062] The application further provides a preparation method of a lithium ion secondary battery containing the mixed negative electrode material, comprising the following steps:

[0063] S1: adding a positive electrode adhesive material, a positive electrode conductor material, a solvent and an electrolyte into the positive electrode material, and mixing and kneading to obtain a positive electrode slurry;

[0064] S2: coating the positive electrode slurry on a foil, drying to remove the solvent, rolling, drying, and die cutting to obtain a positive electrode;

[0065] S3: laminating the positive electrode, a separator and a negative electrode, welding a tab, casing, injecting liquid, forming, and distributing to obtain the lithium ion secondary battery.

[0066] The application has the following characteristics and advantages:

[0067] (1) In the application, the graphite material and the silicon-carbon material are combined, the contact area between the negative electrode materials is increased, the pressure at the contact position is reduced, the silicon-carbon material of the negative electrode is more evenly distributed, after lithiation, the uniform contact of the graphite ensures isotropic expansion, thereby enhancing the overall integrity of the mixed negative electrode material and the structural stability of the negative electrode.

[0068] (2) The silicon-carbon material of the negative electrode is mechanically reinforced, the resistivity is reduced, the conductivity is increased, the particle size crack is reduced and the electron path is enhanced, thereby reducing the surface tension and slowing down the crack propagation. This significantly reduces the crushing and expansion of the negative electrode; reduces the contact impedance, weakens the diffusion barrier, and improves the lithium ion conducting ability.

[0069] (3) By cutting the graphite material and the silicon-carbon material on the surface of the negative electrode, the specific surface area of the negative electrode can be increased, the contact with the electrolyte can be increased, the lithium migration distance and the diffusion resistance can be reduced, the lithium can be quickly inserted and removed, the local electrolyte aggregation can be prevented, the contact between the silicon-carbon material and the graphitized material and the electrolyte can be optimized, and the interface can be improved.

[0070] (4) In order to reduce the loss of the silicon-carbon material in the cutting, the graphite microcrystal development degree of the ordered layered carbon layer in the silicon-carbon material is good, has high thermal conductivity and low resistance characteristics, and the ordered layered carbon layer is distributed horizontally, the horizontal heat transfer of the cutting heat is better, the longitudinal heat conduction performance to the inside of the silicon-carbon material is weakened, the secondary heat transfer efficiency to the contacted graphitized material is higher, the further cutting in the inside of the silicon-carbon material is reduced, the cutting loss of the active silicon and the further formation of the crystalline silicon are reduced, part of the crystalline silicon is added to the cut silicon-carbon negative electrode, the crystalline silicon covers the exposed area of the cut silicon-carbon negative electrode, the exposure of the active silicon is reduced, the consumption of lithium is further reduced, and the cycle life of the battery is improved. BRIEF DESCRIPTION OF DRAWINGS

[0071] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed to be used in the embodiments or prior art description will be briefly introduced as follows. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without any creative effort based on these drawings.

[0072] Figure 1 The figure of the conductivity value change of the mixed negative electrode material in example 1 under different compaction densities;

[0073] Figure 2 The figure of the compaction density change of the mixed negative electrode material in example 1 under different pressures

[0074] Figure 3 The figure of the resistivity change of the silicon-carbon material in example 1 under different pressures;

[0075] Figure 4 The figure of the conductivity value change of the silicon-carbon material in example 1 under different compaction densities;

[0076] Figure 5 The transmission electron microscope figure of the silicon-carbon material in example 1;

[0077] Figure 6 The transmission electron microscope figure of the surface cutting area of the mixed negative electrode material in example 1;

[0078] Figure 7 The surface schematic diagram of the mixed negative electrode material cut by the photon beam in example 1;

[0079] Figure 8 The lateral heat conduction schematic diagram of the silicon-carbon material cut by the photon beam in example 1 DETAILED DESCRIPTION

[0080] In order to facilitate the understanding of the present application, the present application will be described more fully below, and the embodiments of the present application are given, but the scope of the present application is not limited by this.

[0081] The present application discloses a kind of mixed negative electrode material, negative electrode and its lithium ion secondary battery for the problems in prior art, the specific surface area of the mixed negative electrode material is increased by cutting electrode surface, its contact with electrolyte is optimized, lithium migration is accelerated, lithium ion conducting efficiency is improved, simultaneously, the high heat conduction low resistance characteristics of the lateral layered carbon microcrystal in silicon-carbon are used, cutting heat is transferred to graphite in lateral, reduce the heat vertically in-depth silicon-carbon internal, reduce active silicon damage and crystalline silicon generation, the trace crystalline silicon generated covers cutting wound surface, reduce active silicon exposure and lithium loss, in turn, the cycle life of battery is prolonged.

[0082] The present application is realized by the following technical solutions:

[0083] The application first provides a mixed negative electrode material, comprising a silicon-carbon material and a graphitized material;

[0084] The silicon-carbon material takes porous carbon as a matrix, and a silicon layer and an ordered layered carbon layer are sequentially deposited on the surface of the porous carbon matrix;

[0085] The compaction density of the mixed negative electrode material under ≥5Mpa is 1.0-2.0g / cm 3 , and the electrical conductivity is 0.80-188S / cm;

[0086] The mass ratio of the graphitized material in the mixed negative electrode material is ≥ the mass ratio of the silicon-carbon material, and satisfies 1.6≤mass ratio of graphitized material / mass ratio of silicon-carbon material≤8.5;

[0087] The mass ratio of the graphitized material is the mass ratio of the graphitized material in the negative electrode active material (graphitized material and silicon-carbon material);

[0088] The mass ratio of the silicon-carbon material is the mass ratio of the silicon-carbon material in the negative electrode active material (graphitized material and silicon-carbon material);

[0089] The particle size Dv10 of the mixed negative electrode material is 1.1μm-5.2μm;

[0090] The particle size Dv50 of the mixed negative electrode material is 5.3μm-16μm;

[0091] The particle size Dv90 of the mixed negative electrode material is 16μm-35μm;

[0092] The porosity of the mixed negative electrode material is 0.005%-0.1%;

[0093] The specific surface area of the mixed negative electrode material satisfies 1.2-3.2m 2 / g;

[0094] The surface of the mixed negative electrode electrode coated with the silicon-carbon material and the graphitized material has a cutting area.

[0095] The application takes porous carbon as a matrix, and a silicon-carbon material with a silicon layer and an ordered layered carbon layer deposited on the surface of the porous carbon matrix in sequence is mixed with graphitized material to obtain a mixed negative electrode material, and the structural characteristics of the silicon-carbon material with the high-thermal-conductivity and low-resistance ordered layered carbon layer on the surface of the silicon-carbon material enable the heat cut on the surface of the negative electrode to be transferred to the graphitized material in a horizontal direction, reduces the heat penetrating into the interior of the silicon-carbon material in a vertical direction, reduces the damage to active silicon and the generation of crystalline silicon, solves the problem of active silicon loss in the process of cutting the surface of the negative electrode, and can improve the wettability of the electrolyte on the surface of the negative electrode, and the electrolyte spreads on the surface of the electrode at a faster speed, and the efficient network system provided by the efficient contact between the ordered layered carbon layer of the silicon-carbon material and the graphitized material also provides an efficient network system for the conduction of electrons.

[0096] The application can obtain a mixed negative electrode with high compaction, low porosity and low specific surface area by controlling the compaction density, the mass ratio of the silicon-carbon material and the graphitized material in the mixed negative electrode material, the particle size distribution of the mixed negative electrode material, the porosity of the mixed negative electrode material and the specific surface area of the mixed negative electrode material, effectively improves the conductivity of the battery while reducing the impedance of the battery, and improves the cycle performance and rate performance of the battery. On the one hand, the suitable compaction density provides sufficient space for electron conduction, the micro-pores reserved under the higher compaction density provide sufficient ion channels and ensure sufficient electrolyte immersion space, and also ensure sufficient structural support strength; on the other hand, the conductivity is also related to the particle size distribution of the mixed negative electrode material, when the particle size range and the particle size distribution of the mixed negative electrode material are within a certain range, the contact area between the particles increases, at this time, the electron transfer path is shortened, and the conductivity is improved; on the other hand, the low porosity is a direct result of the high compaction density and the optimized particle size distribution range, which reflects that the proportion of solid materials in the electrode is high, and the invalid space is small, which not only strengthens the electron conduction network, but also reduces the tortuosity of ion transmission, which is beneficial to the improvement of the conductivity, strengthens the electron conduction and optimizes the ion transmission path; in addition, the low specific surface area means that the active interface of the mixed negative electrode material exposed to the electrolyte is reduced, and a more stable and thinner interface layer is beneficial to maintaining efficient ion transmission across the interface, thereby improving the overall ion conductivity and long-term cycle stability of the electrode; in addition, by controlling the mass ratio of the silicon-carbon material and the graphitized material in the mixed negative electrode material, the graphitized particles can form a rigid constraint network to absorb the expansion stress of the silicon particles, and a higher mass ratio of the silicon-carbon material provides higher specific capacity, improves the capacity density of the battery, and balances the mechanical strength and electrochemical performance of the electrode.

[0097] Specifically, the compaction density of the mixed negative electrode material can be controlled mainly in the following aspects. Firstly, when the particle sizes Dv10, Dv50 and Dv90 of the mixed negative electrode material are limited within a certain range, the upper limit of Dv90 can control the particle size and proportion of large particles at the same time, prevent the formation of too large pores locally, and thus ensure the uniform infiltration of electrolyte in the electrode, while the sizes of Dv50 and Dv10 are optimized. Under this particle size distribution system, by controlling the sizes of the median particle size and the fine particle size, the large particles and small particles are reasonably distributed, the large particles form a skeleton, and the small particles effectively fill the gaps between the large particles. This optimized particle gradation is the material basis for achieving ideal compaction density and pore structure. In addition, the compaction density is also related to the pressure. When the pressure is increased, the compaction density shows an upward trend. However, too high pressure may damage the structure of the mixed negative electrode material. In addition, the compaction density is also related to the porosity of the mixed negative electrode material of the application. When the porosity meets certain conditions, a suitable compaction density control range is provided, which avoids the problems of broken electronic conduction network caused by too high porosity and too low compaction density, and blocked ion transport path and unable to release silicon expansion stress caused by too low porosity and too high compaction density. On the basis of the above, a suitable compaction density can be obtained, which significantly improves the electrical conductivity of the electrode, enhances the structural stability of the electrode, and finally realizes higher rate performance and longer cycle life.

[0098] The particle size distribution of the mixed negative electrode material in the application can be realized by conventional means. The silicon-carbon material and the graphitized material can be mixed according to a certain mixing ratio and manner to obtain the ideal mixed negative electrode material particle size range. The silicon-carbon material or the graphitized material is sieved according to the particle size size distribution requirements, the negative electrode material in different particle size size ranges is sieved out, each part of the negative electrode material after sieving is mixed according to the target ratio, and then the silicon-carbon material and the graphitized material in the mixed negative electrode material are mixed according to a certain mass ratio.

[0099] The mass proportion of the graphitized material in the mixed negative electrode material obtained by the application is greater than or equal to the mass proportion of the silicon-carbon material, and satisfies 1.6≤mass proportion of graphitized material / mass proportion of silicon-carbon material≤8.5. This design can realize the reasonable matching of the graphitized material and the silicon-carbon material by the mass proportion of the mixed negative electrode material, ensure the fast transmission of electrons and excellent interface contact characteristics, and balance the structural strength, specific capacity, electrolyte infiltration capacity of the mixed negative electrode material, thereby improving the electrical conductivity.

[0100] In addition, the application can also control the porosity and specific surface area of the mixed negative electrode material within a certain range, and under a certain porosity and specific surface area, sufficient active sites are provided for the electrode, while the mechanical strength of the electrode is also considered, the surface tension of the negative electrode material is reduced, and the porosity and specific surface area of the mixed negative electrode material are also related to the compaction density and particle size distribution of the mixed negative electrode material as described above. Under a certain compaction density and particle size distribution, appropriate voids and specific surface area are provided. Avoid the problem of increasing porosity when the compaction density is too low and the particle size is large.

[0101] As a further solution, the cutting area depth of the surface of the mixed negative electrode is 8-45 μm, and the cutting area depth < the negative electrode paste coating thickness of the mixed negative electrode ≤ 164 μm; the cutting area width of the mixed negative electrode is 45-240 μm.

[0102] The cutting area existing on the surface of the negative electrode can increase the specific surface area of the negative electrode, increase the contact with the electrolyte, reduce the lithium migration distance and diffusion resistance, and can quickly embed lithium and lithium, prevent local electrolyte aggregation, optimize the contact of silicon-carbon material, graphitized material and electrolyte, and improve the interface; to reduce the loss of silicon-carbon material in cutting: the graphitized microcrystalline development degree of the ordered layered carbon layer in the silicon-carbon material is good, has high thermal conductivity and low resistance characteristics, and the ordered layered carbon layer is distributed horizontally, the horizontal transfer of cutting heat is better, the longitudinal thermal conductivity to the inside of the silicon-carbon material is weakened, the secondary heat transfer efficiency to the contacted graphitized material is higher, the melting and crystallization of active silicon inside the silicon-carbon material is reduced, and the cutting loss and further formation of crystalline silicon of active silicon are reduced; part of the silicon-carbon negative electrode cut increases the crystalline silicon, the crystalline silicon covers the exposed area of the mixed negative electrode material cut, reduces the exposure of active silicon, and can further reduce the consumption of lithium and improve the cycle life of the battery.

[0103] As a further solution, the true density of the mixed negative electrode material is 2.05 cm 3 / g-2.26 cm 3 / g.

[0104] As a further solution, the particle size range of the mixed negative electrode material is 0.9 μm-37 μm.

[0105] As a further preferred solution, the particle size range of the mixed negative electrode material is 1.2 μm-31 μm.

[0106] As a further solution, the compaction density of the mixed negative electrode material under ≥100 Mpa is 1.2-2.0 g / cm 3 .

[0107] The application can further obtain the mixed negative electrode material satisfying the above performance parameters through material design of the silicon-carbon material and the graphitized material. Specifically, the mixed negative electrode material satisfying the above performance parameters can be obtained by optimizing the resistivity, the electrical conductivity, the reversible deformation variable / the maximum deformation variable range of the silicon-carbon material at a high compaction density, and the specific surface area, the Dv50 range, and the OI value at a high compaction density of the graphitized material.

[0108] The application also provides a preparation method of a mixed negative electrode including the mixed negative electrode material, including the following steps:

[0109] S1: pre-mixing the graphitized material and the silicon-carbon material according to a target mass ratio and a particle size distribution range to obtain a mixed negative electrode material;

[0110] S2: mixing and stirring the mixed negative electrode material, a negative electrode adhesive material, a negative electrode conductor material, and a solvent to obtain a composite negative electrode slurry;

[0111] S3: coating the composite negative electrode slurry on a foil, drying to remove the solvent, rolling, drying, and die cutting to obtain a mixed negative electrode;

[0112] S4: physically cutting the surface of the negative electrode;

[0113] As a further scheme, the silicon-carbon material satisfies one or more of the following characteristics:

[0114] (1) the silicon-carbon material has a resistivity of 0.02-15 Ω*cm at a compaction density of 1.0-1.6 g / cm 3 ;

[0115] (2) the silicon-carbon material has an electrical conductivity value / compaction density value of ≥1, the electrical conductivity unit is S / cm, and the compaction density unit is g / cm 3 ;

[0116] (3) the silicon-carbon material has a reversible deformation variable / the maximum deformation variable range of 21%-45% at 30-300 MPa.

[0117] At a higher compaction density, the resistivity of the silicon-carbon material can be controlled within a certain range, the ratio of the electrical conductivity to the compaction density is optimized, the mixed negative electrode material after mixing of the silicon-carbon material and the graphitized material satisfies the above performance, the higher reversible deformation variable range under a high pressure provides sufficient operation space for the high pressure condition in the compaction process of the mixed negative electrode material, and the higher reversible deformation variable range also provides stress absorption for the expansion of the silicon-carbon material, thereby ensuring that the prepared mixed negative electrode material satisfies the above characteristics.

[0118] As a further preferred embodiment, the graphitized material satisfies one or more of the following characteristics:

[0119] (1) The specific surface area of ​​the graphitized material is 1.0–3.2 m². 2 / g.

[0120] (2) The Dv50 of the graphitized material is 10μm to 18μm.

[0121] (3) The graphitized material has a content of 1.75 g / cm³. 3 The OI value at the compacted density is <10.5.

[0122] This invention utilizes different raw materials for carbonization of graphitized materials, controlling the carbonization temperature and time to obtain graphitized materials that meet the aforementioned specific surface area, particle size distribution, and OI value at a certain compaction density. These characteristics of the graphitized materials can create a complementary filling effect with the aforementioned silicon-carbon materials, thereby increasing the compaction density and conductivity of the composite anode material. When the specific surface area of ​​the graphitized material is within a certain range, a higher contact area between the graphitized material and the silicon-carbon material can be achieved, further improving conductivity. The OI value of the graphitized material at a certain compaction density determines the degree of graphitization order. When the OI value is relatively low, it indicates a higher degree of crystal disorder in the graphitized material. This results in better effective contact between the graphitized material and the silicon-carbon material, promoting multi-directional lithium-ion diffusion and further enhancing conductivity.

[0123] Furthermore, the present invention can further control the material performance parameters of the porous carbon matrix, silicon layer and ordered layered carbon layer in the preparation of silicon-carbon materials, so as to obtain silicon-carbon materials that meet the above performance parameters.

[0124] As a further embodiment, the porous carbon satisfies one or more of the following conditions:

[0125] (1) The pore volume of the porous carbon is 0.55–1.15 cm³. 3 / g,

[0126] (2) The particle size of the porous carbon is 2μm to 30μm;

[0127] (3) The area of ​​peak D, Ad, in the Raman spectrum of the porous carbon is 1180 cm⁻¹. -1 From 1400cm -1 The corresponding area and peak area Ag of G are 1400 cm⁻¹ -1 From 1650cm -1 The corresponding area, and the Ag / Ad ratio satisfies 0.507 to 2.370.

[0128] The ratio of the G peak and the D peak area (Ag / Ad) in the Raman spectrum reflects the carbonization degree and the structural defect density of the porous carbon material, and the Ag / Ad ratio in the range of 0.507-2.370 indicates that the porous carbon has moderate carbon microcrystal order, the moderate order degree guarantees the good intrinsic conductivity of the pore wall, and at the same time maintains the necessary structural activity to facilitate the deposition and combination of silicon.

[0129] The present application can obtain the ideal Ag / Ad ratio by controlling the carbonization temperature of the raw materials of different kinds of porous carbon, and the structural characteristics of the porous carbon, thereby indirectly affecting the conductivity of the silicon-carbon material.

[0130] As a further scheme, in the silicon-carbon material, the mass ratio of the silicon layer to the porous carbon is 1:(0.75-2.4).

[0131] As a further scheme, the carbon content of the ordered layered carbon layer deposited on the surface of the porous carbon substrate accounts for 0.2-5wt% of the silicon-carbon material.

[0132] By depositing an ordered layered carbon layer on the surface of the porous carbon and controlling the carbon content of the ordered carbon layer, the resistivity of the mixed negative electrode material can be further reduced, the conductivity can be improved, an efficient electron seepage network of the silicon-carbon material and the graphitized material in the negative electrode is established, the electrical contact capacity is enhanced, the polarization of the mixed negative electrode material is well reduced, the good electron and ion contact network of the negative electrode is ensured, the high proportion of silicon in the silicon-carbon material enhances the rate performance of the negative electrode, the distributed porous carbon in the silicon-carbon material strengthens the toughness and pressure resistance of the silicon-carbon material, the brittleness is reduced, and the interface stability of the mixed negative electrode material is increased. In the silicon-carbon material, the mass ratio of silicon to porous carbon can be controlled by the temperature of gas phase deposition. The carbon content of the ordered layered carbon layer deposited on the surface of the porous carbon substrate accounts for the mass ratio of the silicon-carbon material, which can be controlled by the temperature during the carbon deposition coating process.

[0133] As a further preferred scheme, the ordered layered carbon layer has a thickness of 2-94nm.

[0134] As a further scheme, the premixing method of the S1 mixed negative electrode material is:

[0135] The graphitized material and the silicon-carbon material are respectively sieved according to the particle size interval of the lower limit of the particle size-Dv10, Dv10-Dv50 (not including Dv10), Dv50-Dv90 (not including Dv50), and Dv90-the upper limit of the particle size (not including Dv90), the four parts of the materials sieved above are mixed according to the particle number ratio of 1:4:4:1, and then the graphitized material and the silicon-carbon material are mixed according to the target mass ratio to obtain the mixed negative electrode material.

[0136] As a further preferred aspect, the method for preparing the silicon-carbon material in S1 comprises: depositing a gas-phase silicon source in the porous carbon by chemical vapor deposition, and performing carbon deposition coating at a high temperature to form an ordered layered carbon layer, i.e., the silicon-carbon material.

[0137] As a further aspect, the porous carbon is hard carbon or soft carbon obtained by carbonization and activation of at least one of phenolic resin, coconut shell, and tar.

[0138] As a still further aspect, the carbonization temperature of the phenolic resin, coconut shell, and tar is 600-1000℃, and the carbonization time is 4-10h.

[0139] As one of the exemplary aspects, different carbonization temperatures and carbonization times of the porous carbon raw materials of different origins can obtain porous carbons with different structural characteristics. The carbonization temperature is a key factor for driving the conversion of organic matter into carbon material and affecting the order degree of carbon microcrystal. A lower temperature is conducive to obtaining porous carbon with developed pores and high specific surface area. A higher temperature can promote the ordering and recombination of carbon structure, reduce defects, and enhance the mechanical strength and intrinsic conductivity of the pore wall. The carbonization time has a certain contribution to the fullness of pyrolysis reaction and the uniformity of structural evolution. By selecting different raw materials and carbonizing at appropriate temperatures and times, the desired particle size and particle size distribution range of the porous carbon can be obtained, and the area ratio of G peak to D peak in the Raman spectrum can be obtained.

[0140] As a further aspect, the gas-phase silicon source comprises at least one of monosilane, disilane, trichlorosilane, dichlorosilane, or trichlorosilane.

[0141] As a further aspect, the temperature of the chemical vapor deposition is 350-760℃.

[0142] In the present application, the temperature of the chemical vapor deposition has a certain influence on the mass ratio of silicon to porous carbon in the silicon-carbon material. With the increase of the temperature of the gas-phase deposition, the silicon-carbon ratio in the silicon-carbon material shows a trend of first increasing and then decreasing, which is related to the silicon hydride cracking efficiency and the silicon-carbon interdiffusion degree at different temperatures. This may be due to the fact that in the relatively low temperature range, the increase of the silicon hydride cracking efficiency is the dominant factor, while in the higher temperature range, the silicon-carbon interdiffusion and reaction consumption become the dominant factors, which together lead to the non-monotonic change of the silicon content.

[0143] As a further aspect, the carbon source for the deposition of the ordered layered carbon layer on the surface of the porous carbon substrate comprises at least one of nano-graphite sheet, nano-tube, nano-carbon fiber, ethylene, butyne, acetylene, or propyne.

[0144] As a further aspect, the temperature of the carbon deposition coating is 420-600℃.

[0145] As a further preferred aspect, the temperature of the carbon deposition coating is 480℃.

[0146] In the present application, the carbon deposition time or deposition temperature can be controlled to promote the formation of a thicker and denser carbon coating layer on the surface of the porous carbon substrate. The coating layer is mainly composed of pyrolytic carbon, and the degree of carbon deposition coating increases with increasing temperature. By adjusting the temperature and time parameters, the mass fraction of the carbon in the coating layer can be increased, thereby accurately controlling its mass fraction in the final silicon-carbon material.

[0147] As a further aspect, the graphitized material is obtained by carbonization, graphitization, granulation, and coating of one or more of needle-shaped tar, coal tar, pitch tar, and petroleum coke.

[0148] As a further aspect, the carbonization temperature of the graphitized material precursor is 420-1260℃, and the carbonization time is 3-10h.

[0149] The carbonization temperature and time of the raw material of the graphitized material have certain effects on the specific surface area, particle size distribution, and OI value of the graphitized material. When the carbonization temperature is too high and the time is too long, the structure of the graphitized material may be affected, thereby affecting the specific surface area and OI value of the graphitized material. By selecting appropriate graphitized material raw materials and treating them at appropriate carbonization temperatures and times, an ideal specific surface area and an ideal graphitized material particle size distribution can be obtained, and a lower OI value indicates that the crystal arrangement is multi-directional, the crystal structure is not easily damaged during particle compaction, the structure is more complete, a continuous conductive network is provided, the silicon expansion stress is uniformly distributed in the mixed negative electrode, a buffer is formed between the graphitized material and the silicon-carbon material, and the damage of the silicon expansion to the compacted structure can be alleviated.

[0150] As a further preferred aspect, the S2 is a pre-mixture of the negative electrode conductor material and the mixed negative electrode material; 30%-70% of the negative electrode adhesive material a, 30%-70% of the negative electrode adhesive material b, and a solvent are mixed and kneaded for 0.5-3h; the remaining negative electrode adhesive material a, the negative electrode conductor material, the remaining negative electrode adhesive material b, and the solvent are further mixed and stirred for 0.5-3h to control the solid content at 30%-55%; the negative electrode adhesive material c and the solvent are further stirred for 0.5-3h to control the solid content at 25%-48% and the fineness at ≤45μm, thereby obtaining the mixed negative electrode slurry;

[0151] As a further preferred place, the S2 is to pre-mix the negative electrode conductor material, the mixed negative electrode material; add 50% of the negative electrode adhesive material a, 50% of the negative electrode adhesive material b, the solvent is mixed and kneaded for 90min; add the rest of the negative electrode adhesive material a, the negative electrode conductor material, the rest of the negative electrode adhesive material b, the solvent is mixed and stirred for 120min, control the solid content at 45%; add the adhesive material c, the solvent is stirred for 60min, control the solid content at 40%, the fineness is ≤45μm, get the composite negative electrode slurry;

[0152] As a further scheme, the S3 is that the surface density of the negative electrode slurry coated on the foil is 0.003-0.024g / cm 2 .

[0153] As a further scheme, in the S4, the negative electrode surface is cut by a photon beam, and the cutting is performed by a high-temperature photon beam perpendicular to the negative electrode surface, resulting in a cutting area, and the cutting area has a cut silicon-carbon material;

[0154] The cutting area on the negative electrode surface can increase the specific surface area of the negative electrode, increase the contact with the electrolyte, reduce the lithium migration distance and diffusion resistance, quickly embed and extract lithium, prevent local electrolyte aggregation, optimize the contact between the silicon-carbon material and the graphitized material and the electrolyte, and improve the interface; to reduce the loss of silicon-carbon material in cutting: the ordered layered carbon layer in the silicon-carbon material has good graphitic microcrystalline development, high thermal conductivity, and low resistance characteristics, and the ordered layered carbon layer is distributed horizontally, the horizontal transfer of cutting heat is better, the longitudinal thermal conductivity to the inside of the silicon-carbon material is weakened, the secondary heat transfer efficiency to the contacted graphitized material is higher, the melting and crystallization of active silicon inside the silicon-carbon material is reduced, and the cutting loss and further formation of crystalline silicon of active silicon are reduced; part of the cut silicon-carbon negative electrode has crystalline silicon, the crystalline silicon covers the exposed area of the mixed negative electrode material, reduces the exposure of active silicon, and can further reduce the consumption of lithium and improve the cycle life of the battery.

[0155] As a further scheme, the temperature of the photon beam cutting is 800-2000℃.

[0156] As a further preferred scheme, the temperature of the photon beam cutting is 1000-1800℃.

[0157] If the cutting temperature is too high, the cutting is too deep and too wide, and more mixed negative electrode material (graphitized material + silicon-carbon material) will be lost, causing lithium precipitation on the cell interface, rapid capacity reduction, cycle deterioration, easy shedding of negative electrode material on the negative electrode surface, and higher cutting temperature and cutting power when cutting too deep, which can easily cause excessive crystalline silicon to be generated.

[0158] The application also provides a lithium ion secondary battery comprising the mixed negative electrode material or the mixed negative electrode prepared by the preparation method of the mixed negative electrode.

[0159] The lithium ion secondary battery comprises a negative electrode comprising the mixed negative electrode material, a positive electrode, an electrolyte, and a separator.

[0160] As a further solution, the negative electrode is a foil comprising a mixed negative electrode coating.

[0161] As a further solution, the positive electrode is a foil comprising a positive electrode coating.

[0162] The positive electrode coating comprises a positive electrode material, an electrolyte, a positive electrode adhesive material, and a positive electrode conductor material; and the mixed negative electrode coating comprises the mixed negative electrode material, a negative electrode conductor material, and a negative electrode adhesive material.

[0163] As a further solution, the positive electrode material is selected from one or more of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminate, lithium nickel cobalt manganese aluminate, lithium-rich manganese-based material, lithium iron phosphate, lithium manganese phosphate, lithium iron manganese phosphate, lithium manganese oxide, lithium cobalt oxide, and lithium nickel manganese oxide.

[0164] As a further solution, the electrolyte is selected from one or more of lithium lanthanum zirconate (LLZO), lithium lanthanum tantalate (LLTO), lithium lanthanum zirconium tantalate (LLZTO), lithium aluminum titanium phosphate (LATP), lithium aluminum germanium phosphate (LAGP), polyethylene oxide (PEO), polyacrylonitrile (PAN), polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), polymethyl methacrylate (PMMA), lithium indium chloride (Li3InCl6), lithium indium bromide (Li3InBr6), lithium yttrium chloride (LiYCl), lithium yttrium bromide (LiYBr), lithium phosphorus sulfide chloride (LiPSCl), and lithium germanium phosphide (LiGePS).

[0165] As a further solution, the positive electrode conductor material and the negative electrode conductor material are each independently selected from one or more of conductive carbon black, conductive Ketjen black, conductive acetylene black, conductive graphene, single-walled carbon nanotubes, multi-walled carbon nanotubes, and oligo-walled carbon nanotubes.

[0166] As a further solution, the positive electrode adhesive material and the negative electrode adhesive material are each independently selected from one or more of polyacrylic acid metal salt and / or polyacrylate derivative, polystyrene and its derivatives, carboxyalkyl cellulose and its derivatives, and polyvinylidene fluoride, polyacrylic block copolymer derivative.

[0167] As a further aspect, the polyacrylic acid metal salt and / or polyacrylate derivative is selected from one or more of polyacrylic acid sodium, polyacrylic acid lithium, polymethyl methacrylate, polyethyl methacrylate;

[0168] As a further aspect, the polystyrene and its derivatives is selected from one or more of polystyrene-butadiene, polystyrene-butadiene-methyl / ethyl / propyl acrylate, polystyrene-butadiene-acrylic acid-methyl / ethyl / propyl acrylate, polystyrene-butadiene-acrylic acid sodium / lithium-methyl / ethyl / propyl acrylate-acrylonitrile.

[0169] As a further aspect, the carboxyalkyl cellulose salt and its derivatives is selected from one or more of carboxymethyl cellulose, carboxymethyl cellulose lithium, carboxymethyl cellulose sodium.

[0170] As a further aspect, the polyacrylic acid block copolymer derivative is selected from one or more of polyacrylic acid sodium / lithium-methyl / ethyl / propyl acrylate, polyacrylic acid sodium / lithium-acrylonitrile, polyacrylic acid sodium / lithium-butadiene-acrylonitrile, polyacrylic acid sodium / lithium-methyl / ethyl / propyl acrylate-acrylonitrile-styrene.

[0171] The negative electrode binder material includes a negative electrode binder material a, a negative electrode binder material b, and a negative electrode binder material c.

[0172] As a further preferred aspect, the negative electrode binder material a is selected from one or more of polyacrylic acid metal salt and / or polyacrylate derivative;

[0173] The negative electrode binder material b is selected from one or more of carboxyalkyl cellulose and its derivatives;

[0174] The negative electrode binder material c is selected from one or more of polyacrylic acid block copolymer derivative.

[0175] As a further aspect, a solvent is also used in the process of preparing the mixed negative electrode coating or the positive electrode coating, and the solvent is selected from one or more of N-methyl pyrrolidone, dimethyl carbonate, diethyl carbonate, ethylene carbonate, water, ethanol.

[0176] As a further aspect, the mass ratio of the positive electrode material, the positive electrode conductor material, the positive electrode binder material, and the electrolyte in the positive electrode coating is (90-99.3):(0.05-6):(0.6-10):(0.02-0.8).

[0177] As a further preferred aspect, the mass ratio of the positive electrode material, the conductor material, the positive electrode binder material, and the electrolyte in the positive electrode coating is 97:1.2:1.7:0.1.

[0178] As a further solution, the mass ratio of the mixed negative electrode material, the conductor material, the negative electrode adhesive material in the mixed negative electrode coating is (90-98.6):(0.2-10):(1.2-8).

[0179] As a further preferred solution, the mass ratio of the mixed negative electrode material, the negative electrode conductor material, the negative electrode adhesive material in the mixed negative electrode coating is 96.6:3:0.4.

[0180] As a further solution, the negative electrode thickness is 60-185 μm;

[0181] The electrolyte and the separator are not limited and can be any lithium ion battery electrolyte and lithium ion battery separator.

[0182] The application also provides a preparation method of a lithium ion secondary battery containing the mixed negative electrode material, comprising:

[0183] S1: adding a positive electrode adhesive material, a positive electrode conductor material, a solvent and an electrolyte to a positive electrode material and mixing to obtain a positive electrode slurry;

[0184] S2: coating the positive electrode slurry on a foil, drying to remove the solvent, rolling, drying, and die cutting to obtain a positive electrode;

[0185] S3: laminating the positive electrode, a separator and a negative electrode, welding a tab, casing, injecting a liquid, forming and dividing to obtain the lithium ion secondary battery.

[0186] As a further solution, in S1, the positive electrode conductor material and the positive electrode material are premixed, 30-70% of the positive electrode adhesive material and the solvent are added and mixed for 0.5-3 h for kneading, the remaining positive electrode adhesive material, positive electrode conductor material, solvent and electrolyte are added and mixed for 0.5-3 h for stirring, the solid content is controlled to be 65-85%, and the solvent is added and stirred for 0.5-3 h, the solid content is controlled to be 60-80%, and the fineness is ≤45 μm, to obtain the positive electrode slurry;

[0187] As a further solution, in S1, the positive electrode conductor material and the positive electrode material are premixed, 50% of the positive electrode adhesive material and the solvent are added and mixed for 90 min for kneading, the remaining positive electrode adhesive material, positive electrode conductor material, solvent and electrolyte are added and mixed for 90 min for stirring, the solid content is controlled to be 82%, and the solvent is added and stirred for 60 min, the solid content is controlled to be 70%, and the fineness is ≤12 μm, to obtain the positive electrode slurry;

[0188] As a further solution, in S2, the surface density of the positive electrode slurry coated on the foil is 0.011-0.070 g / cm 2 .

[0189] As a specific example of the implementation of the present application, the following detailed case is provided:

[0190] Example 1

[0191] (1) Screen the graphitized material and silicon-carbon material according to 1.2-4.2 μm, 4.2-11 μm, 11-22 μm, and 22-31 μm, respectively. Mix the screened materials according to a particle number ratio of 1:4:4:1, and then mix the graphitized material and silicon-carbon material according to a mass ratio of 8:2 to obtain a mixed negative electrode material. The compaction density of the mixed negative electrode material is 1.2 g / cm 3 : The porosity of the mixed negative electrode material is 0.08%; and the specific surface area of the mixed negative electrode material is 2.4 m 2 / g.

[0192] (2) Pre-mix the conductive acetylene black and the mixed negative electrode material; add 50% lithium polyacrylate, 50% lithium carboxymethyl cellulose, and N-methyl pyrrolidone for kneading for 90 min; then add the remaining 50% lithium polyacrylate, single-walled carbon nanotubes, and N-methyl pyrrolidone for stirring for 120 min, with the solid content controlled at 45%; then add lithium polyacrylate-butadiene-acrylonitrile and N-methyl pyrrolidone for stirring for 60 min, with the solid content controlled at 40% and the fineness controlled at ≤45 μm, to obtain a composite negative electrode slurry;

[0193] The mass ratio of the graphitized negative electrode + silicon-carbon negative electrode, conductor material, and adhesive material in the composite negative electrode slurry is controlled at 96.6:3:0.4.

[0194] Pre-mix polyvinylidene fluoride and lithium cobaltate, add 50% polyvinylidene fluoride and N-methyl pyrrolidone for kneading for 90 min, then add the remaining 50% polyvinylidene fluoride, multi-walled carbon nanotubes, N-methyl pyrrolidone, and lithium titanium aluminum phosphate for stirring for 90 min, with the solid content controlled at 82%, and then add N-methyl pyrrolidone for stirring for 60 min, with the solid content controlled at 70% and the fineness controlled at ≤12 μm, to obtain a positive electrode slurry;

[0195] The mass ratio of the positive electrode material, conductor material, adhesive material, and electrolyte in the positive electrode slurry is controlled at 97:1.2:1.7:0.1.

[0196] Coat the composite negative electrode slurry on a foil, with the surface density controlled at 0.006 g / cm 2 , dry to remove the solvent, roll, dry, and die-cut to obtain a composite negative electrode;

[0197] Photon beam cutting: cutting with a photon beam of 1400℃ perpendicular to the surface of the negative electrode, controlling the depth of the cutting area of the surface of the negative electrode = 20 μm < the thickness of the negative electrode paste coating of the negative electrode = 80 μm, the width of the cutting area of the negative electrode = 120 μm.

[0198] (4) The positive electrode paste is coated on the foil, and the areal density is controlled at 0.019 g / cm 2 , solvent is removed by drying, rolling, drying, and die cutting to obtain the positive electrode;

[0199] (5) The positive electrode sheet, the separator, and the negative electrode sheet are stacked, the tab is welded, the shell is assembled, the liquid is injected, and the formation is performed: 0.1C charging to 3.5V + 0.5C charging to 4.0V; the capacity is divided: 0.5C charging to 4.5V, 0.5C discharging to 3.0V, which is a secondary battery.

[0200] The silicon-carbon material in the mixed negative electrode material satisfies the following conditions: a pressure of 40 MPa, at which the resistivity is 2.5 Ω*cm; the conductivity value of the silicon-carbon material / the compaction density value = 3.3, and the compaction density is 1.2 g / cm 3 ; the reversible deformation amount / the maximum deformation amount of the silicon-carbon material at 300 MPa is in the range of 29%;

[0201] The preparation method of the silicon-carbon material specifically comprises: depositing methylsilane in porous carbon with a pore volume of 0.92 cm 3 / g by chemical vapor deposition at a temperature of 480℃, and the mass ratio of silicon to carbon in the porous carbon is 1:(1.05); performing carbon deposition coating on the porous carbon by 4.5wt% ethyne + 1.5wt% nanometer carbon tube + 94wt% argon, to form an ordered layered carbon layer with a thickness of about 40 nm, and the carbon content of the carbon deposition coating accounts for 0.8wt% of the silicon-carbon material.

[0202] The porous carbon is hard carbon obtained by carbonization and activation of phenolic resin at 820℃ for 7h; the pore volume of the porous carbon is 0.92 cm 3 / g, and the particle size of the porous carbon is 3.0 μm-25 μm; the D peak area (1180 cm -1 -1400 cm -1 ) Ad and the G peak area (1400 cm -1 -1650 cm -1 ) Ag in the Raman spectrum of the porous carbon are 0.776.

[0203] The graphitized material is obtained by needle-shaped tar carbonization, graphitization, granulation, and coating, and satisfies the graphitized material with a specific surface area of 1.5 m 2 / g, a Dv50 of 13 μm, and an OI value of 8.5 at a compaction density of 1.75 g / cm 3 .

[0204] The carbonization temperature and carbonization time of the needle-shaped tar of the graphitized material precursor are 840°C and 6h, respectively.

[0205] Example 2

[0206] The difference from Example 1 is that:

[0207] The carbonization temperature and carbonization time of the coal tar of the graphitized material precursor are 650°C and 4h, respectively, and the specific surface area of the graphitized material obtained at this time is 1.3m 2 / g, the DV50 of the graphitized material is 15μm, and the OI value of the graphitized material at a compacted density of 1.75g / cm 3 is 9.4.

[0208] Example 3

[0209] The difference from Example 1 is that:

[0210] The carbonization temperature and carbonization time of the pitch tar of the graphitized material precursor are 1010°C and 8h, respectively, and the specific surface area of the graphitized material obtained at this time is 2.4m 2 / g, the DV50 of the graphitized material is 11μm, and the OI value of the graphitized material at a compacted density of 1.75g / cm 3 is 7.6. The mass ratio of the graphitized material / silicon-carbon material = 10:2.

[0211] Example 4

[0212] The difference from Example 1 is that:

[0213] The carbonization temperature and carbonization time of the petroleum coke of the graphitized material precursor are 760°C and 6h, respectively, and the specific surface area of the graphitized material obtained at this time is 1.4m 2 / g, the DV50 of the graphitized material is 14μm, and the OI value of the graphitized material at a compacted density of 1.75g / cm 3 is 8.8. The mass ratio of the graphitized material / silicon-carbon material = 8.

[0214] Example 5

[0215] The difference from Example 1 is that

[0216] Photon beam cutting: cutting is performed with a photon beam of 1200°C vertically to the surface of the negative electrode, and the cutting region depth of the surface of the negative electrode is controlled = 18μm < the negative paste coating thickness of the negative electrode = 80μm, and the cutting region width of the negative electrode is 50μm.

[0217] Example 6

[0218] The difference from Example 1 is that:

[0219] Photon beam cutting: cutting is performed perpendicularly to the surface of the negative electrode using a photon beam at 1500°C, the depth of the cutting region of the surface of the negative electrode is controlled to be = 23 μm < the negative electrode slurry coating thickness of the negative electrode = 80 μm, and the width of the cutting region of the negative electrode is 80 μm.

[0220] Example 7:

[0221] The difference from Example 1 is that:

[0222] Photon beam cutting: cutting is performed perpendicularly to the surface of the negative electrode using a photon beam at 1600°C, the depth of the cutting region of the surface of the negative electrode is controlled to be = 27 μm < the negative electrode slurry coating thickness of the negative electrode = 80 μm, and the width of the cutting region of the negative electrode is 200 μm.

[0223] Example 8:

[0224] The difference from Example 1 is that:

[0225] The difference from Example 1 is that the porous carbon is hard carbon obtained by carbonization of phenol formaldehyde resin at 1000°C for 9 h and activation; the pore volume of the porous carbon is 0.58 m 3 / g, the particle size of the porous carbon is 2.0 μm to 19 μm; the D peak area (1180 cm -1 to 1400 cm -1 ) Ad, the G peak (1400 cm -1 to 1650 cm -1 ) Ag, and the Ag / Ad ratio = 0.589.

[0226] The silicon-carbon material in the mixed negative electrode material satisfies the following conditions: pressure 40 MPa, at which the resistivity is 3.6 Ω*cm; the conductivity value of the silicon-carbon material / the compacted density value = 2.9, and the compacted density is 1.2 g / cm 3 ; the reversible deformation amount / the maximum deformation amount of the silicon-carbon material at 300 MPa is in the range of 31%.

[0227] The graphitized material and the silicon-carbon material are sieved into 1.2 to 2.2 μm, 2.2 to 5.9 μm, 5.9 to 17 μm, and 17 to 31 μm, respectively.

[0228] The compacted density of the mixed negative electrode material is 2.0 g / cm 3 ; and the porosity of the mixed negative electrode material is 0.005%.

[0229] Example 9:

[0230] The difference from Example 1 is that:

[0231] The porous carbon is hard carbon obtained by carbonization and activation of phenolic resin at 950℃ for 7h; the pore volume of the porous carbon is 0.65m 3 / g, the particle size of the porous carbon is 2.3μm-21μm; the D peak area (1180cm -1 to 1400cm -1 corresponding area) Ad, the G peak (1400cm -1 to 1650cm -1 corresponding area) Ag, and the ratio of Ag / Ad is 0.591.

[0232] The silicon-carbon material in the mixed negative electrode material satisfies the following conditions: the pressure is 40MPa, at this time, the resistivity is 3.4Ω*cm; the conductivity value of the silicon-carbon material / the compacted density value is 3.0, and the compacted density is 1.2g / cm 3 ; the reversible deformation amount / the maximum deformation amount of the silicon-carbon material at 300MPa is in the range of 30%.

[0233] The graphitized material and the silicon-carbon material are respectively sieved according to 1.2-2.4μm, 2.4-7μm, 7-18μm, and 18-31μm.

[0234] The compacted density of the mixed negative electrode material is 1.8g / cm 3 ; the porosity of the mixed negative electrode material is 0.01%.

[0235] Example 10:

[0236] The difference from Example 1 is that:

[0237] The porous carbon is hard carbon obtained by carbonization and activation of phenolic resin at 900℃ for 7h; the pore volume of the porous carbon is 0.73m 3 / g, the particle size of the porous carbon is 2.9μm-24μm; the D peak area (1180cm -1 to 1400cm -1 corresponding area) Ad, the G peak (1400cm -1 to 1650cm-1 corresponding area) Ag, and the ratio of Ag / Ad is 0.612.

[0238] The silicon-carbon material in the mixed negative electrode material satisfies the following conditions: the pressure is 40MPa, at this time, the resistivity is 3.2Ω*cm; the conductivity value of the silicon-carbon material / the compacted density value is 3.1, and the compacted density is 1.2g / cm 3 ; the reversible deformation amount / the maximum deformation amount of the silicon-carbon material at 300MPa is in the range of 30%.

[0239] The graphitized material and the silicon-carbon material are sieved according to 1.2-3 μm, 3-8.3 μm, 8.3-19 μm, and 19-31 μm, respectively.

[0240] The compacted density of the mixed negative electrode material is 1.6 g / cm 3 The porosity of the mixed negative electrode material is 0.03%.

[0241] Example 11:

[0242] The difference from Example 1 is that:

[0243] The porous carbon is hard carbon obtained by carbonization and activation of phenolic resin at 750°C for 4 h; the pore volume of the porous carbon is 1.15 m 3 / g, and the particle size of the porous carbon is 4.6 μm-29 μm; the D peak area (1180 cm -1 -1400 cm -1 corresponding area) Ad, the G peak (1400 cm -1 -1650 cm-1 corresponding area) Ag, and the Ag / Ad ratio is 0.654.

[0244] The silicon-carbon material in the mixed negative electrode material satisfies the following conditions: pressure 40 MPa, at which the resistivity is 3.1 Ω*cm; the silicon-carbon material conductivity value / compacted density value=3.1, and the compacted density is 1.2 g / cm 3 The reversible deformation amount / maximum deformation amount of the silicon-carbon material at 300 MPa is in the range of 30%.

[0245] The graphitized material and the silicon-carbon material are sieved according to 1.2-4.8 μm, 4.8-14 μm, 14-28 μm, and 28-35 μm, respectively.

[0246] The compacted density of the mixed negative electrode material is 1.1 g / cm 3 The porosity of the mixed negative electrode material is 0.09%.

[0247] Example 12:

[0248] The difference from Example 1 is that:

[0249] The porous carbon is hard carbon obtained by carbonization and activation of phenolic resin at 700°C for 3 h; the pore volume of the porous carbon is 1.23 m 3 / g, and the particle size of the porous carbon is 5.0 μm-35 μm; the D peak area (1180 cm -1 -1400 cm -1 corresponding area) Ad, the G peak (1400 cm -1Ag, Ag / Ad ratio = 0.631;

[0250] The silicon-carbon material in the mixed negative electrode material satisfies the following conditions: pressure 40 MPa, resistivity 3.3 Ω*cm; silicon-carbon material conductivity value / compaction density value = 2.9, compaction density 1.2 g / cm 3 ; the reversible deformation amount / maximum deformation amount of the silicon-carbon material at 300 MPa is in the range of 30%;

[0251] The graphitized material and the silicon-carbon material are sieved according to 1.2-5.1 μm, 5.1-15.5 μm, 15.5-33 μm, and 33-35 μm, respectively.

[0252] The compaction density of the mixed negative electrode material is 1.0 g / cm 3 ; the porosity of the mixed negative electrode material is 0.1%.

[0253] Example 13:

[0254] The difference from Example 1 is that:

[0255] The silicon-carbon material preparation method specifically includes: depositing silane in a porous carbon with a pore volume of 0.85 cm 3 / g by chemical vapor deposition at a temperature of 570°C, and the mass ratio of silicon to carbon in the porous carbon is 1:(1.08)

[0256] The silicon-carbon material in the mixed negative electrode material satisfies the following conditions: pressure 40 MPa, resistivity 2.4 Ω*cm; silicon-carbon material conductivity value / compaction density value = 3.5, compaction density 1.3 g / cm 3 ; the reversible deformation amount / maximum deformation amount of the silicon-carbon material at 300 MPa is in the range of 27%;

[0257] Example 14:

[0258] The difference from Example 1 is that:

[0259] The silicon-carbon material preparation method specifically includes: depositing silane in a porous carbon with a pore volume of 0.85 cm 3 / g by chemical vapor deposition at a temperature of 750°C, and the mass ratio of silicon to carbon in the porous carbon is 1:0.75

[0260] The silicon-carbon material in the mixed negative electrode material satisfies the following conditions: pressure 40 MPa, resistivity 2.2 Ω*cm; silicon-carbon material conductivity value / compaction density value = 3.8, compaction density 1.4 g / cm 3 ; the reversible deformation amount / maximum deformation amount of the silicon-carbon material at 300 MPa is in the range of 25%;

[0261] Example 15:

[0262] The difference from Example 1 is that:

[0263] The method for preparing the silicon-carbon material specifically comprises: depositing dichlorodihydrogen silicon in a porous carbon with a pore volume of 0.85 cm 3 / g at a temperature of 570 DEG C by chemical vapor deposition, and the mass ratio of silicon to carbon in the porous carbon is 1:1.03;

[0264] The silicon-carbon material in the mixed negative electrode material satisfies the following conditions: pressure 40 MPa, resistivity 2.0 Ω*cm; the conductivity value of the silicon-carbon material / the compactness value of the silicon-carbon material = 4.2, and the compactness of the silicon-carbon material is 1.5 g / cm 3 ; the reversible deformation range of the silicon-carbon material at 300 MPa / the maximum deformation range is 24%;

[0265] Example 16:

[0266] The difference from Example 1 is that:

[0267] The porous carbon is a hard carbon obtained by carbonizing phenol formaldehyde resin at 700 DEG C for 6 h and activating; the pore volume of the porous carbon is 1.14 cm 3 / g, and / or, the particle size of the porous carbon is 3.5 μm-28 μm; the D peak area (1180 cm -1 -1400 cm -1 of the Raman spectrum of the porous carbon) Ad, the G peak (1400 cm -1 -1650 cm -1 of the Raman spectrum of the porous carbon) Ag, and the Ag / Ad ratio = 0.624;

[0268] The silicon-carbon material in the mixed negative electrode material satisfies the following conditions: pressure 40 MPa, resistivity 1.8 Ω*cm; the conductivity value of the silicon-carbon material / the compactness value of the silicon-carbon material = 5.6, and the compactness of the silicon-carbon material is 1.6 g / cm 3 ; the reversible deformation range of the silicon-carbon material at 300 MPa / the maximum deformation range is 23%;

[0269] Example 17:

[0270] The difference from Example 1 is that:

[0271] The porous carbon is a hard carbon obtained by carbonizing coconut shell at 1000 DEG C for 8 h and activating; the pore volume of the porous carbon is 0.82 cm 3 / g, and / or, the particle size of the porous carbon is 3.0 μm-25 μm; the D peak area (1180 cm -1 -1400 cm -1 of the Raman spectrum of the porous carbon) Ad, the G peak (1400 cm -1from 1650 cm -1 Ag, Ag / Ad ratio = 0.663;

[0272] The silicon-carbon material in the mixed negative electrode material satisfies the following conditions: pressure 40 MPa, resistivity 2.7 Ω*cm; silicon-carbon material conductivity value / compaction density value = 3.3, compaction density 1.3 g / cm 3 ; the silicon-carbon material has a reversible deformation range / maximum deformation range of 29% at 300 MPa;

[0273] Example 18:

[0274] The difference from Example 1 is that:

[0275] The porous carbon is a hard carbon obtained by carbonization and activation of tar at 900℃ for 7h; the porous carbon has a pore volume of 1.02 cm 3 / g, and / or, the porous carbon has a particle size of 4.5 μm to 29 μm; the porous carbon has a D peak area (1180 cm -1 to 1400 cm -1 , a G peak (1400 cm -1 to 1650 cm -1 , and an Ag peak (1650 cm 3 Ag, Ag / Ad ratio = 0.675;

[0276] The silicon-carbon material in the mixed negative electrode material satisfies the following conditions: pressure 40 MPa, resistivity 3.6 Ω*cm; silicon-carbon material conductivity value / compaction density value = 3.3, compaction density 1.4 g / cm 3 ; the silicon-carbon material has a reversible deformation range / maximum deformation range of 29% at 300 MPa;

[0277] Example 19:

[0278] The difference from Example 1 is that:

[0279] The porous carbon is coated with ethyne 4.5wt% + 1.5wt% nanometer carbon tube + argon 94wt% carbon deposition, forming an ordered layered carbon layer with a thickness of about 30 nm, and the carbon content of the carbon deposition coating accounts for 0.6wt% of the silicon-carbon material.

[0280] The silicon-carbon material in the mixed negative electrode material satisfies the following conditions: pressure 40 MPa, resistivity 2.3 Ω*cm; silicon-carbon material conductivity value / compaction density value = 3.2, compaction density 1.2 g / cm 3 ; the silicon-carbon material has a reversible deformation range / maximum deformation range of 29% at 300 MPa;

[0281] Example 20:

[0282] The difference with example 1 is that:

[0283] The porous carbon is carbon deposited coated with acetylene 4.5wt% + 1.5wt% nanotubes + argon 94wt%, forming an ordered laminar carbon layer of thickness of about 50 nm, the carbon deposited coated carbon content of 1.4wt% of the silicon-carbon material.

[0284] The silicon-carbon material in the mixed anode material meets the following conditions: pressure 40 MPa, resistivity 2.1 Ω*cm; silicon-carbon material conductivity value / compaction density value = 3.4, compaction density 1.2 g / cm 3 ; the silicon-carbon material at 300 MPa, the reversible deformation / maximum deformation range is 27%;

[0285] Example 21:

[0286] The difference with example 1 is that:

[0287] The porous carbon is carbon deposited coated with acetylene 4.5wt% + 1.5wt% nanotubes + argon 94wt%, forming an ordered laminar carbon layer of thickness of about 67 nm, the carbon deposited coated carbon content of 2.6wt% of the silicon-carbon material.

[0288] The silicon-carbon material in the mixed anode material meets the following conditions: pressure 40 MPa, resistivity 1.9 Ω*cm; silicon-carbon material conductivity value / compaction density value = 3.9, compaction density 1.2 g / cm 3 ; the silicon-carbon material at 300 MPa, the reversible deformation / maximum deformation range is 25%;

[0289] Example 22:

[0290] The difference with example 1 is that:

[0291] The porous carbon is carbon deposited coated with acetylene 4.5wt% + 1.5wt% nanotubes + argon 94wt%, forming an ordered laminar carbon layer of thickness of about 93 nm, the carbon deposited coated carbon content of 4.8wt% of the silicon-carbon material.

[0292] The silicon-carbon material in the mixed anode material meets the following conditions: pressure 40 MPa, resistivity 1.7 Ω*cm; silicon-carbon material conductivity value / compaction density value = 5.9, compaction density 1.2 g / cm 3 ; the silicon-carbon material at 300 MPa, the reversible deformation / maximum deformation range is 23%;

[0293] Comparative example 1:

[0294] The difference with example 1 is that:

[0295] The carbonization temperature and carbonization time of the needle-shaped tar precursor of the graphitized material are 350 DEG C and 3h respectively, and the specific surface area of the obtained graphitized material is 0.8m 2 / g, the DV50 of the graphitized material is 6.5μm, and the OI value of the graphitized material under the compaction density of 1.75g / cm 3 is 12.1.

[0296] The porous carbon is a hard carbon obtained by carbonization and activation of phenolic resin at 1900 DEG C for 11h; the pore volume of the porous carbon is 1.32cm 3 / g, the particle size of the porous carbon is 0.5μm-19μm; the D peak area (1180cm -1 -1400cm -1 , the G peak area (1400cm -1 -1650cm -1 , and the Ag / Ad ratio is 0.89.

[0297] The silicon-carbon material in the mixed negative electrode material satisfies the following conditions: pressure 40MPa, resistivity 13.6Ω*cm; the conductivity value / specific density value of the silicon-carbon material is 1.5, and the specific density is 1.2g / cm 3 ; the reversible deformation amount / maximum deformation amount of the silicon-carbon material under 300MPa is in the range of 12%.

[0298] The graphitized material and the silicon-carbon material are respectively sieved according to 0.5-1.3μm, 1.3-5.3μm, 5.3-15μm, and 15-20μm.

[0299] Comparative Example 2:

[0300] The difference from Example 1 is that:

[0301] The method for preparing the silicon-carbon material specifically comprises: depositing methylsilane in the porous carbon with a pore volume of 0.85cm 3 / g by chemical vapor deposition at a temperature of 280 DEG C, and the mass ratio of silicon to carbon in the porous carbon is 1:3.2.

[0302] The silicon-carbon material in the mixed negative electrode material satisfies the following conditions: pressure 40MPa, resistivity 15.6Ω*cm; the conductivity value / specific density value of the silicon-carbon material is 1.3, and the specific density is 1.2g / cm 3 ; the reversible deformation amount / maximum deformation amount of the silicon-carbon material under 300MPa is in the range of 17%.

[0303] Comparative Example 3:

[0304] The difference from Example 1 is that:

[0305] The porous carbon is coated with 4.5wt%+1.5wt% nanometer carbon tube+94wt% argon carbon deposition, and the content forms an ordered layered carbon layer with a thickness of about 1nm, and the carbon content of the carbon deposition coating accounts for 0.05wt% of the silicon-carbon material.

[0306] The silicon-carbon material in the mixed negative electrode material meets the following conditions: pressure 40MPa, resistivity 15.5Ω*cm; silicon-carbon material conductivity value / compaction density value=1.2, compaction density 1.2g / cm 3 ; the reversible deformation amount / maximum deformation amount of the silicon-carbon material at 300MPa is in the range of 16%

[0307] Comparative Example 4:

[0308] The difference from Example 1 is that the porous carbon is a hard carbon obtained by carbonization of phenolic resin at 500°C for 3h and activation; the pore volume of the porous carbon is 1.32cm 3 / g, and the particle size of the porous carbon is 7.0μm-40μm; the D peak area (1180cm -1 -1400cm -1 ) Ad, G peak (1400cm -1 -1650cm -1 ) Ag, and the Ag / Ad ratio is 0.492 in the Raman spectrum of the porous carbon.

[0309] The graphitized material and the silicon-carbon material are sieved into 1.2-7.5μm, 7.5-17μm, 17-38μm, and 38-43um, respectively, and the above sieved materials are mixed in a particle number ratio of 1:4:4:1, and then the graphitized material and the silicon-carbon material are mixed in a mass ratio of 8:2 to obtain a mixed negative electrode material, and the compaction density of the mixed negative electrode material is 0.9g / cm 3 ; the porosity of the mixed negative electrode material is 0.15%;

[0310] Comparative Example 5:

[0311] The difference from Example 1 is that there is no photon beam cutting.

[0312] Comparative Example 6:

[0313] The difference from Example 1 is that the graphitized material and the silicon-carbon material are mixed in a mass ratio of 2:3 to obtain a mixed negative electrode material

[0314] Comparative Example 7:

[0315] The difference from Example 1 is that the graphitization material and silicon-carbon material are sieved into 3.4-7.4 μm, 7.4-19 μm, 19-39 μm, and 39-42 μm, respectively, and the materials sieved above are mixed in a particle number ratio of 1:4:4:1, respectively,

[0316] The mixed negative electrode materials prepared in Examples 1-22 and Comparative Examples 1-7 are tested as follows:

[0317] (1) Cycle test:

[0318] The secondary batteries of each of the above examples and comparative examples are subjected to the following charge and discharge in an indoor environment at 25±1°C and a relative humidity of less than 65% without being clamped by a jig: 3.0C CC (constant current) to 4.05V, standing for 300s; 2.9C CC to 4.15V, CV (constant voltage) to 2.30C, standing for 300s; 2.50C CC to 4.25V, CV to 1.80C, standing for 300s; 2.0C CC to 4.40V, CV to 1.55C, standing for 300s; 1.55C CC to 4.50V, CV to 1.20C, standing for 300s; 0.5C DC to 3.0V. Continue 3.40C CC to 4.05V. Record the discharge capacity at 0.5C DC to 3.0V in the first week as C0.5. When the discharge capacity at 0.5C DC to 3.0V of each group of secondary batteries satisfies = 80% x C0.5, stop the charge and discharge, and record the number of charge and discharge cycles of the secondary batteries of each of the examples and comparative examples.

[0319] (2) Impedance DCIR test: the secondary battery is charged at 0.5C current to 3.95V, and stands for 300s; ② continue discharging at 0.1C current for 10s, and record the voltage at which the discharging stops; ③ discharge at 1C current for 1s, and record the voltage at which the discharging stops; ④ DCR = (voltage at which the discharging stops in the third step - voltage at which the discharging stops in the second step) / 0.9C;

[0320] (3) 0.2C, 0.5C, 1.0C, 2.0C rate test: the secondary batteries of each of the above examples and comparative examples are subjected to the following charge and discharge:

[0321] 0.5C CC (constant current) to 4.5V, CV (constant voltage) to 0.25C, standing for 300s; 0.2C DC to 3.0V, standing for 300s, and record the discharge capacity at 0.2C R0.2;

[0322] 0.5C CC (constant current) to 4.5V, CV (constant voltage) to 0.25C, rest for 300s; 0.5C DC to 3.0V, rest for 300s, record 0.5C discharge capacity R0.5;

[0323] 0.5C CC (constant current) to 4.5V, CV (constant voltage) to 0.25C, rest for 300s; 1.0C DC to 3.0V, rest for 300s, record 1.0C discharge capacity R1.0;

[0324] 0.5C CC (constant current) to 4.5V, CV (constant voltage) to 0.25C, rest for 300s; 2.0C DC to 3.0V, rest for 300s, record 2.0C discharge capacity R2.0;

[0325] Rate count: 0.5C rate = R0.5 / R0.2, 1.0C rate = R1.0 / R0.2, 2.0C rate = R2.0 / R0.2.

[0326] The test results are shown in the following table:

[0327]

[0328]

[0329] As can be seen from the comparison of Examples 1-22 and Comparative Examples 1-7, when the mixed negative electrode material in the application simultaneously uses silicon-carbon material with silicon layer and ordered layered carbon layer deposited in sequence and graphitized material, and the mass ratio of the two materials is limited within a certain range, and the compaction density, electrical conductivity, particle size distribution and porosity of the mixed negative electrode material are limited within a certain range, on this basis, the high thermal conductivity and low resistance characteristics of the transverse layered carbon microcrystals in the silicon-carbon can be used to transfer the cutting heat horizontally to the graphite, reduce the vertical deepening of the heat into the silicon-carbon, reduce the damage of active silicon and the generation of crystalline silicon, the generated trace amount of crystalline silicon covers the cutting wound, reduces the exposure of active silicon and lithium loss, and further prolongs the cycle life of the battery.

[0330] As can be seen from the comparison of Example 1 and Comparative Example 1, when the carbonization temperature of the graphitized material precursor is low, and the carbonization temperature of the raw material of the porous carbon is high, both of which are not within the limited range of the application, the graphitized material and the porous silicon-carbon material obtained at this time do not have good parameters, such as large particle size of the graphitized material, at this time, the graphitized material has a compaction density of 1.75g / cm3, which is less than the compaction density of the porous silicon-carbon material, and the compaction density of the porous silicon-carbon material is 2.05g / cm3, which is less than the compaction density of the graphitized material, and the electrical conductivity of the graphitized material is 1.5x10-4S / cm, which is less than the electrical conductivity of the porous silicon-carbon material, and the electrical conductivity of the porous silicon-carbon material is 2.5x10-4S / cm, which is less than the electrical conductivity of the graphitized material, and the particle size of the graphitized material is 20-30μm, which is larger than the particle size of the porous silicon-carbon material, and the particle size of the porous silicon-carbon material is 10-20μm, which is less than the particle size of the graphitized material, and the porosity of the graphitized material is 0.3g / cm3, which is less than the porosity of the porous silicon-carbon material, and the porosity of the porous silicon-carbon material is 0.5g / cm3, which is less than the porosity of the graphitized material. 3The OI value at the compaction density is high, which indicates that the graphitized material is irregular and has a high degree of defects at this time, and the microstructure of the graphitized material exhibits significant non-uniformity - disordered carbon phase and highly oriented crystal domains coexist, resulting in an increase in the diffusion energy barrier of lithium ions between crystal planes, reducing the electrochemical performance of the battery.

[0331] As can be seen from the comparison of Example 1 and Comparative Examples 2-3, by controlling the temperature of the deposition of the gas-phase silicon source, the carbon content of the ordered layered carbon layer can be controlled to further reduce the resistivity of the mixed negative electrode material, improve the electrical conductivity, establish an efficient electronic percolation network of the silicon-carbon material and the graphitized material in the negative electrode, enhance the electrical contact ability, well reduce the polarization of the mixed negative electrode material, ensure the good electronic and ionic contact network of the negative electrode, the high proportion of silicon in the silicon-carbon material enhances the rate performance of the negative electrode, and the distributed porous carbon in the silicon-carbon material strengthens the toughness, compression resistance and reduces the brittleness of the silicon-carbon material, and the interface stability of the mixed negative electrode material is increased. The mass ratio of silicon to porous carbon in the silicon-carbon material can be controlled by the temperature of the gas-phase deposition. The mass ratio of the carbon content of the ordered layered carbon layer deposited on the surface of the porous carbon matrix to the silicon-carbon material can be controlled by the temperature during the carbon deposition coating process. When the mass ratio of the carbon content of the ordered layered carbon layer deposited on the surface of the porous carbon matrix to the silicon-carbon material is not within the limited range, the content of the surface ordered layered carbon layer may be insufficient to laterally transfer cutting heat to graphite, resulting in more crystalline silicon, which is not conducive to reducing the impedance of the battery.

[0332] As can be seen from the comparison of Example 1 and Comparative Example 4, the resistivity of the silicon-carbon material prepared in Comparative Example 4 is high, the ratio of the electrical conductivity to the compaction density is less than 1, and the reversible deformation range of the silicon-carbon material is low. This is because the phenolic resin used as the porous carbon raw material is subjected to a carbonization reaction at a lower temperature and for a shorter time. Due to incomplete carbonization, the pore volume of the porous carbon material obtained at this time is large, the particle size of the porous carbon is large, the value of Ag / Ad is small, the silicon-carbon material obtained has a high defect density, and the volume expansion of the silicon-carbon material is significant, which is not conducive to improving the cycle performance of the battery.

[0333] As can be seen from the comparison of Example 1 and Comparative Example 5, as shown in Figures 6 to 8 the negative electrode subjected to photon beam cutting, when the mixed negative electrode material composed of the graphitized material and the silicon-carbon material with ordered layered carbon layer is used, the structure avoids the problem of crystalline silicon formed in the cutting area due to the concentration of cutting heat, increases the specific surface area of the negative electrode, improves the contact between the negative active material and the electrolyte, improves the interface, reduces the interface impedance, and also reduces the consumption of lithium, prolongs the service life of the battery, thereby improving the cycle performance and rate performance of the battery.

[0334] As can be seen from the comparison of Example 1 and Comparative Example 6, when the mass ratio of graphitized material / silicon-carbon material is within the limited range, the reasonable combination of the graphitized material and the silicon-carbon material is achieved, the fast electron transmission and excellent interface contact characteristics are ensured, and the structural strength, specific capacity, and electrolyte wettability of the mixed negative electrode material are balanced, thereby improving the electrical conductivity.

[0335] As can be seen from the comparison of Example 1 and Comparative Example 7, when the graphitized material and the silicon-carbon material are mixed, the particle size of the screened particles is not mixed according to the limited range of the present application, at this time, due to the lack of ideal compaction density and pore structure of the material basis, the structural stability of the electrode is poor, which is not conducive to achieving higher rate performance and longer cycle life.

[0336] As can be seen from the comparison of Examples 1-2 and Examples 3-4, the present application can further optimize the mass ratio of graphitized material and silicon-carbon material to achieve a reasonable combination of graphitized material and silicon-carbon material, ensure fast electron transmission and excellent interface contact characteristics, and balance the structural strength, specific capacity, and electrolyte wettability of the mixed negative electrode material, thereby improving the electrical conductivity.

[0337] As can be seen from the comparison of Examples 1-2 and Examples 5-7, during the cutting operation on the surface of the negative electrode, by controlling the temperature of the photon beam cutting, and limiting the depth and width of the cutting area within a certain range, the problem of losing too much mixed negative electrode material due to cutting too deep and too wide is avoided, which causes the lithium precipitation at the interface of the battery, rapid capacity reduction, cycle deterioration, and easy shedding of the negative electrode material on the surface of the negative electrode. In addition, cutting too deep requires higher cutting temperature and cutting power, which can easily lead to the problem of excessive crystalline silicon generation. At the same time, the problem of limited improvement of the battery electrochemical performance due to too low cutting temperature, cutting depth, and cutting width is also avoided.

[0338] As can be seen from the comparison of Examples 1-2 and Examples 8-12, by optimizing the carbonization temperature and time of the porous carbon raw material within a certain range, the particle size range of the porous carbon can be further optimized within a certain range, and the Ag / Ad value of the porous carbon can be further improved. At this time, the structure of the obtained porous carbon material is more complete, the defects are less, and the order degree is higher. On this basis, the graphitized material and the silicon-carbon material are mixed within a certain particle size range, at this time, the mixed negative electrode material can obtain good porosity under a certain compaction density. From the particle size range of the mixed negative electrode material, the compaction density, and the order degree of the porous carbon in the mixed negative electrode material, the electrochemical performance of the battery is improved.

[0339] As can be seen from the comparison of Examples 1-2 and Examples 13-15, when different gas-phase silicon sources are selected for deposition on the porous carbon, the mass ratio of silicon to the porous carbon of the obtained silicon-carbon material is different as the deposition temperature of the gas-phase silicon source is increased.

[0340] As can be seen from the comparison of Examples 1-2 and Examples 16-18, when different types of porous carbon raw materials are selected and different carbonization temperatures are used, different pore volumes are obtained, and porous carbons with different particle sizes are formed. In this case, the Ag / Ad is also different, and the porous carbon material obtained on this basis also exhibits certain differences in conductivity and resistivity at different compaction densities, thereby indirectly affecting the electrochemical performance of the final mixed negative electrode material.

[0341] As can be seen from the comparison of Examples 1-2 and Examples 19-22, when the porous carbon is coated by carbon deposition, the mass ratio of the carbon content in the silicon-carbon material is different when the carbon deposition coating is performed, and the thickness of the preferred layered carbon layer on the surface of the silicon-carbon material is different. In this case, the resistivity of the silicon-carbon material increases first and then decreases with the increase of the thickness, and the ratio of the conductivity to the compaction density increases first and then decreases, so when the surface of the silicon-carbon material is coated by carbon deposition, the ordered layered carbon layer on the surface is limited within a certain range, and good electrochemical performance can be obtained.

[0342] As can be seen from the comparison of Example 1 and Example 2, as in Example 1, the lower the OI value of the graphitized material, the higher the degree of disorder of the crystal of the graphitized material, and the better the effective contact between the graphitized material and the silicon-carbon material is achieved, which promotes the multi-directional diffusion of lithium ions and further enhances the cycle performance of the electrode.

[0343] Figure 1 The compaction density of the mixed negative electrode material of Example 1 is 1.0-2.0 g / cm 3 , and the conductivity is 0.80-118 S / cm. Figure 2 The compaction density of the mixed negative electrode material of Example 1 at ≥100 MPa is 1.2-2.0 g / cm 3 . Figure 3 As can be seen, the resistivity of the silicon-carbon material of Example 1 at 40 MPa is 2.5 Ω*cm, Figure 4 As can be seen, the conductivity value / compaction density value of the silicon-carbon material of Example 1 is 3.3, and Figure 5 As can be seen, the transmission electron microscope image of the silicon-carbon material of Example 1 shows that it has a high compaction density and a low porosity.

[0344] In summary, in the present application, the graphite material and silicon-carbon material are combined, the contact area between the negative electrode materials is increased, the pressure at the contact position is reduced, the silicon-carbon material of the negative electrode is more evenly distributed, after lithiation, the uniform contact of the graphite ensures isotropic expansion, thereby enhancing the overall integrity of the mixed negative electrode material and the structural stability of the negative electrode. The silicon-carbon material of the negative electrode is mechanically enhanced, the resistivity is reduced, the conductivity is increased, the particle size cracks are reduced and the electron path is enhanced, thereby reducing the surface tension and slowing down the crack propagation. This significantly reduces the pulverization and expansion of the negative electrode; reduces the contact impedance, weakens the diffusion barrier, and improves the lithium ion conductivity. By cutting the graphite material and silicon-carbon material on the surface of the negative electrode, the specific surface area of the negative electrode can be increased, the contact with the electrolyte can be increased, the lithium migration distance and diffusion impedance can be reduced, the lithium can be quickly inserted and extracted, the local electrolyte accumulation can be prevented, the contact between the silicon-carbon material, the graphitized material and the electrolyte can be optimized, and the interface can be improved; in order to reduce the loss of the silicon-carbon material during cutting, the graphite crystallites in the ordered layered carbon layer of the silicon-carbon material have good development degree, high thermal conductivity and low resistance characteristics, and the ordered layered carbon layer is distributed horizontally, the horizontal transfer of cutting heat is better, the longitudinal thermal conductivity to the inside of the silicon-carbon material is weakened, the secondary heat transfer efficiency to the contacted graphitized material is higher, the further cutting of the silicon-carbon material inside is reduced, the cutting loss of active silicon and the further formation of crystalline silicon are reduced; the cut silicon-carbon negative electrode has part of crystalline silicon, the crystalline silicon covers the exposed area of the cut silicon-carbon negative electrode, the exposure of active silicon is reduced, the consumption of lithium is further reduced, and the battery cycle life is improved.

[0345] It should be noted that the above only describes the preferred embodiments of the present application and should not be used to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application should be included in the protection scope of the present application.

Claims

1. A mixed negative electrode material, characterized by, The silicon-carbon material and the graphitized material are included. The silicon-carbon material is based on a porous carbon, and a silicon layer and an ordered layered carbon layer are sequentially deposited on the surface of the porous carbon substrate. The compaction density of the mixed negative electrode material is 1.0-2.0 g / cm3 under ≥5 MPa 3 , and the conductivity is 0.80-118 S / cm. The mass ratio of the graphitized material to the silicon-carbon material is greater than or equal to 1.6 and less than or equal to 8.

5. The particle size Dv10 of the mixed negative electrode material is 1.1 μm to 5.2 μm. The particle size Dv50 of the mixed negative electrode material is 5.3 μm to 16 μm. The particle size Dv90 of the mixed negative electrode material is 16 μm to 35 μm. The porosity of the mixed negative electrode material is 0.005% to 0.1%. The specific surface area of the mixed negative electrode material is 1.2 m 2 / g~3.2 m 2 / g; The mixed negative electrode has a cutting area on the surface of the mixed negative electrode coated with the silicon-carbon material and the graphitized material.

2. The mixed anode material of claim 1, wherein, The depth of the cutting area on the surface of the mixed negative electrode is 8 μm to 45 μm, and the depth of the cutting area is less than the negative electrode slurry coating thickness of the mixed negative electrode, which is less than or equal to 164 μm; and the width of the cutting area of the mixed negative electrode is 45 μm to 240 μm.

3. The mixed anode material of claim 1, wherein, The true density of the mixed negative electrode material is 2.05 cm 3 / g ~ 2.26 cm 3 / g; Preferably, the particle size of the mixed negative electrode material is 0.9 μm to 37 μm. Further preferably, the particle size of the mixed negative electrode material is 1.2 μm to 31 μm. Preferably, the mixed anode material has a compaction density of 1.2 to 2.0 g / cm3 at > 100 MPa 3 .

4. A method for producing a mixed negative electrode comprising the mixed negative material according to any one of claims 1 to 3, characterized by, The method comprises the following steps: S1: Pre-mixing the graphitized material and the silicon-carbon material according to the target mass ratio and the particle size distribution range to obtain a mixed negative electrode material; S2: Mixing and stirring the mixed negative electrode material, a negative electrode adhesive material, a negative electrode conductor material, and a solvent to obtain a composite negative electrode slurry; S3: Coating the composite negative electrode slurry on a foil, drying to remove the solvent, rolling, drying, and die cutting to obtain a mixed negative electrode; S4: Physically cutting the surface of the negative electrode; The silicon-carbon material satisfies the following characteristics: the silicon-carbon material has a compaction density of 1.0-1.6 g / cm 3 The silicon-carbon material has a resistivity of 0.02-15 Ω*cm; the silicon-carbon material has a conductivity value / compaction density value≥1; the silicon-carbon material has a reversible deformation amount / maximum deformation amount in the range of 21%-45% under 30-300 MPa. The graphitized material satisfies the following characteristics: the specific surface area of the graphitized material is 1.0 to 3.2 m 2 / g; the Dv50 of the graphitized material is 10 μm to 18 μm; the OI value of the graphitized material at a compaction density of 1.75 g / cm 3 < 10.

5.

5. The method of claim 4, wherein the mixture of the negative electrode is prepared by mixing the active material, the conductive material, and the binder in a solvent. The porous carbon satisfies one or more of the following characteristics: (1) the porous carbon has a pore volume of 0.55 cm 3 / g to 1.15 cm 3 / g; (2) The particle size of the porous carbon is 2 μm to 30 μm; (3) the D peak area Ad in a Raman spectrum of the porous carbon is 1180 cm -1 from 1400 cm -1 the corresponding area, the G peak area Ag is 1400 cm -1 from 1650 cm -1 the corresponding area, and the Ag / Ad ratio satisfies 0.507-2.

370.

6. The method of claim 4, wherein the mixture of the negative electrode is prepared by mixing the active material, the conductive material, and the binder in a solvent. In the silicon-carbon material, the mass ratio of the silicon layer to the porous carbon is 1:(0.75-2.4); Preferably, the carbon content of the ordered layered carbon layer deposited on the surface of the porous carbon substrate accounts for 0.2-5 wt% of the silicon-carbon material. Further preferably, the ordered layered carbon layer has a thickness of 2-94 nm.

7. The method for preparing the mixed negative electrode according to claim 4, wherein The method for preparing the silicon-carbon material in S1 is as follows: depositing a gas-phase silicon source on the porous carbon by chemical vapor deposition, and performing carbon deposition coating at a high temperature to form an ordered layered carbon layer, which is the silicon-carbon material. Preferably, the porous carbon is hard carbon or soft carbon obtained by carbonization and activation of at least one of phenolic resin, coconut shell, and tar; the carbonization temperature of the phenolic resin, coconut shell, and tar is 600-1000 °C, and the carbonization time is 4-10 h. Preferably, the gas-phase silicon source includes at least one of monosilane, disilane, trichlorosilane, dichlorosilane, or trichlorosilane; and the temperature of the chemical vapor deposition is 350 °C to 760 °C. Preferably, the carbon source of the ordered layered carbon layer deposited on the surface of the porous carbon substrate comprises at least one of nano-graphite flake, nanotube, nanocarbon fiber, ethylene, butyne, acetylene or propyne; the carbon deposition coating temperature is 420-600°C; Further preferably, the carbon deposition coating temperature is 480°C.

8. The method of claim 4, wherein the mixture of the negative electrode is prepared by mixing the active material, the conductive material, and the binder in a solvent. The graphitized material is obtained by carbonization, graphitization, granulation and coating of one or more of needle-like tar, coal tar, pitch tar, petroleum coke; Preferably, the carbonization temperature of the graphitized material precursor is 420-1260°C, and the carbonization time is 3-10h.

9. The method of claim 4, wherein the mixture of the negative electrode is prepared by mixing the active material, the conductive material, and the binder in a solvent. In the S4, the method for physically cutting the surface of the negative electrode is: The surface of the negative electrode is cut by a photon beam, and the cutting is performed by a high-temperature photon beam perpendicular to the surface of the negative electrode, and the surface of the negative electrode has a cutting area; The temperature of the photon beam cutting is 800-2000°C; Preferably, the temperature of the photon beam cutting is 1000-1800°C.

10. A lithium ion secondary battery comprising the mixed negative material of any one of claims 1-3 or the mixed negative electrode prepared by the preparation method of any one of claims 4-9.

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