Composite negative electrode material, preparation method thereof, negative electrode sheet, secondary battery and electric device

Abstract

The application belongs to the technical field of lithium ion batteries, and particularly relates to a composite negative electrode material, a preparation method thereof, a negative electrode sheet, a secondary battery and an electric device; the composite negative electrode material comprises a core and a coating layer coated on the outer surface of the core; the core comprises porous carbon and nano-silicon loaded on the porous carbon; lithium is distributed between the core and the coating layer; the application realizes lithium supplement by reducing organic lithium in volatile organic lithium solution and distributing the organic lithium on the surface of particles by introducing organic gas and inert gas into the volatile organic lithium solution; lithium is located on the outside of silicon-carbon material, effectively compensates for the loss of lithium ions caused by the formation of a solid electrolyte interface (SEI) film during the cycle process of the battery, effectively improves the initial efficiency of the silicon-carbon negative electrode material, and the lithium is also wrapped by the carbon material, which significantly improves the chemical stability of the lithium in air.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of secondary batteries, in particular to a composite negative electrode material, a preparation method thereof, a negative electrode sheet, a secondary battery and an electric device. BACKGROUND

[0002] At present, the negative electrode material of lithium ion batteries mainly adopts traditional graphite material. However, silicon-based materials are gradually increasing the proportion of use in negative electrode materials due to their significant specific capacity advantage. Silicon-based negative electrode materials are mainly divided into silicon-oxygen and silicon-carbon two technical routes. Among them, the silicon-carbon negative electrode material is a composite of nano-silicon and graphite. This material utilizes the high specific capacity characteristics of nano-silicon, and through the composite with graphite, the volume change of silicon in the charging and discharging process can be relieved to a certain extent, and the structural stability and cycle performance of the material are improved.

[0003] The silicon-carbon prepared by the prior art has too low carbon matrix first effect, resulting in low silicon-carbon first effect, loss of cathode capacity, and with the increasing demand for ED, high first-effect deposition-type silicon-carbon material is more and more competitive. If the silicon content is forcibly increased to improve the first effect, the expansion will increase, and the material is more likely to fail during use. The first effect of the negative electrode material is a key problem in lithium ion batteries, and is also a bottleneck restricting the further development of the current material.

[0004] Therefore, it is urgent to develop a composite negative electrode material that can effectively improve the first effect of the silicon-carbon negative electrode material. SUMMARY

[0005] The present application aims at the deficiencies of the prior art, and provides a composite negative electrode material that can effectively improve the first effect of the silicon-carbon negative electrode material.

[0006] To achieve the above-mentioned purpose, the present application adopts the following technical solutions:

[0007] A composite negative electrode material, comprising a core and a coating layer coated on the outer surface of the core, wherein the core comprises porous carbon and nano-silicon loaded on the porous carbon, and lithium is distributed between the core and the coating layer.

[0008] Preferably, the particle size D50 of the porous carbon is R1 μm, the particle size D50 of the nano-silicon particles is R2 nm, and the content of the nano-silicon is B% of the mass of the silicon-carbon, wherein 2.8 < (R1-R2) x B% < 3.5. When the value of the relationship (R1-R2) x B% is too small, the material first effect is low, the cathode capacity is low, and the cost of the battery increases. When the value of the relationship (R1-R2) x B% is too large, the material expands greatly, the stress is large during expansion, the damage to the porous carbon matrix is serious, and the material is more likely to be pulverized and fail.

[0009] Preferably, the coating layer is a carbon coating layer.

[0010] Preferably, the particle size D50 of the porous carbon is 7-9 μm. If the particle size is too small, the yield will be low and the cost will be increased. If the particle size is too large, the diffusion impedance of lithium ions in the particles will be large and the rate capability will be poor.

[0011] Preferably, the particle size D50 of the nano-silicon particles is 1-3 nm. If the particle size of the nano-silicon is too small, the interface between silicon and carbon will be more, the lithium ion transfer interface will be more, the impedance will be larger, and the polarization of the material during use will be larger. If the size of the nano-silicon is too large, the uniformity of lithium intercalation in the silicon will be poorer, the nano-silicon will be more prone to breakage, and the degree of expansion will be increased.

[0012] Preferably, the pore volume of the porous carbon is 0.6-1.0 cm 3 / g, and the pore distribution structure is as follows: the proportion of micropores is 80-90%, the proportion of mesopores is 8-15%, and the proportion of macropores is 1-5%, wherein the pore size of the micropores is ≤2 nm, the pore size of the mesopores is 2-50 nm, and the pore size of the macropores is ≥50 nm.

[0013] In addition, the application also provides a preparation method of the composite negative electrode material.

[0014] S1, carbonizing a carbon source under the protection of an inert gas to obtain a carbon matrix;

[0015] S2, performing pore forming and purification on the carbon matrix to obtain a porous carbon matrix;

[0016] S3, vapor depositing silicon on the porous carbon matrix to obtain the inner core;

[0017] S4, vapor depositing lithium on the inner core to obtain an inner core with lithium element distributed on the surface;

[0018] S5, vapor depositing carbon on the inner core obtained in S4 to form a carbon coating layer, thereby obtaining the composite negative electrode material.

[0019] Preferably, the carbonization of S1 includes carbonizing the carbon source at 900-1200℃ for 3-6 h.

[0020] Preferably, in step S1, the carbon source is obtained by carbonizing biomass such as coconut shell, rice husk, and kudzu, or a carbon source such as a phenolic resin-based carbon source, an epoxy resin-based carbon source, petroleum coke, and anthracite. The resin-based carbon source is beneficial to improving the structural stability of the material and improving the pressure resistance of the material.

[0021] In step S1, if the temperature and reaction time are lower than the preset range, the carbon source cannot be carbonized better, there are too many heteroatoms, and the material has low primary efficiency. If the temperature and reaction time are higher than the preset range, the resulting carbon source structure is loose, has poor structural stability, and the material has poor pressure resistance. Controlling the temperature and reaction time in the preset range can reduce heteroatoms while enhancing the stability of the formed carbon structure, ensuring the structural stability and primary efficiency of the material.

[0022] Preferably, the pore forming of S2 includes mixing the carbon matrix with a pore forming agent, calcining at 850-1000℃ for 1-2h.

[0023] Preferably, the purification of S2 includes acid washing and water washing to neutralize the calcined product, and then calcining at 500-600℃ for 3-4h.

[0024] Preferably, the pore forming agent of S2 is an alkaline pore forming agent.

[0025] Preferably, the pore forming agent includes at least one of sodium hydroxide and potassium hydroxide.

[0026] Preferably, the concentration of the pore forming agent is 1-2mol / L.

[0027] Preferably, the addition amount of the pore forming agent is 8%-15% of the mass of the carbon matrix.

[0028] In step S2, many impurity substances and heteroatoms are generated during the pore forming process, so the resulting product needs to be purified by acid dissolution and the excess residual alkali needs to be washed and neutralized. If the reaction time is too short, there will be too many heteroatoms, and if the reaction time is too long, the porous carbon structure will have poor stability. By high-temperature heating to purify the carbon matrix, the content of heteroatoms, especially oxygen atoms, is reduced (<2%), and the primary efficiency of the material in battery applications is improved.

[0029] Preferably, the vapor deposition of silicon of S3 includes placing the porous carbon matrix in a reaction device, introducing a first mixed gas containing a first protective gas and a silicon source gas, and performing vapor deposition of silicon on the porous carbon matrix.

[0030] Preferably, the conditions for vapor deposition of silicon are 350-450℃ for 1-3h.

[0031] Preferably, the content of the first protective gas is 10%-30% of the volume of the first mixed gas; preferably, the silicon source gas includes silane gas.

[0032] Preferably, the first protective gas comprises at least one of helium, nitrogen, argon and krypton. Among them, the silane gas is reduced into nanosilicon by being introduced into the porous carbon, and the nanosilicon grows in the porous carbon, and the size is limited by the pore size of the porous carbon and the reaction temperature and time. If the reaction temperature is too low, it is difficult to reduce silane, and the production capacity is low. If the reaction temperature is too high, it will cause the nanosilicon to be converted from amorphous silicon to crystalline silicon, resulting in anisotropic expansion, increasing the expansion rate of the material and easily generating chemically inert silicon carbide. If the reaction time is too short, the silicon cannot be completely deposited inside, and if the reaction time is too long, the silicon is easy to accumulate on the surface, increase the material expansion, and shorten the service life.

[0033] Preferably, the vapor deposition lithium of S4 comprises introducing a second mixed gas containing a second protective gas and a carbon source gas into an organic lithium solution, heating the reaction to obtain an organic lithium gas, and then introducing the organic lithium gas into a reaction device containing the inner core to perform vapor deposition lithium on the inner core to obtain an inner core with lithium element distributed on the surface.

[0034] Preferably, the heating reaction condition of S4 is 300-400℃ for 1-3h.

[0035] Preferably, the organic lithium solution is at least one of n-butyllithium, methanolic lithium, sec-butyllithium and diisopropylamino lithium.

[0036] Preferably, the carbon source gas of S4 comprises at least one of acetylene, ethylene and methane.

[0037] Preferably, the flow rate of the organic lithium gas is 0.1-0.3m / s.

[0038] Preferably, the second protective gas comprises at least one of helium, nitrogen, argon and krypton.

[0039] In step S4, lithium is supplemented by gas phase deposition, which greatly improves the uniformity of lithium supplementation compared to solid phase or liquid phase blending lithium supplementation, and the amount of lithium supplementation can be controlled by controlling the flow rate of the mixed gas. The organic gas and inert gas are introduced into the volatile organic lithium solution, so that the organic lithium is reduced and distributed on the surface of the particles to supplement lithium. Lithium element is located on the outside of the silicon-carbon material, effectively compensating for the loss of lithium ions caused by the formation of solid electrolyte interface (SEI) film during the cycle process, and can effectively improve the initial efficiency of the silicon-carbon negative electrode material. When the reaction temperature is too low, the organic lithium will not be completely decomposed, and the lithium supplementation efficiency will be low. When the reaction temperature is too high, the amorphous silicon will become crystalline silicon, and the expansion and kinetic performance of the crystalline silicon are not as good as those of the amorphous silicon. When the reaction time is too short, the organic lithium will not be completely decomposed, and the lithium supplementation efficiency will be low. When the reaction time is too long, the amorphous silicon will become crystalline silicon, and the expansion and kinetic performance of the crystalline silicon are not as good as those of the amorphous silicon. When the flow rate of organic lithium gas is too low, the reservation will not be sufficient, and when the flow rate of organic lithium gas is too high, the fluidized state will be unstable, and the pre-lithium will be uneven.

[0040] Preferably, the gas phase deposition carbon of S5 comprises introducing a carbon source gas into a reaction device containing the core obtained in S4, and performing gas phase deposition carbon on the core.

[0041] Preferably, the carbon source gas of S5 comprises acetylene.

[0042] Preferably, the conditions for the gas phase deposition carbon are 550-600℃, and the deposition time is 1-3h.

[0043] When the deposition temperature is too high, chemical inert silicon carbide is easily generated, and when the deposition temperature is too low, the organic gas and organic lithium are difficult to be reduced. When the reaction time is too short, the organic gas will not be fully reacted, the obtained coated carbon layer will contain impurity atoms, and the initial efficiency of the material will be reduced. When the reaction time is too long, the amorphous silicon in the silicon-carbon material will become crystalline silicon, and the expansion and kinetic performance of the crystalline silicon are not as good as those of the amorphous silicon.

[0044] In addition, the application also provides a negative electrode sheet comprising the composite negative electrode material.

[0045] In addition, the application also provides a secondary battery comprising an electric core wound by a negative electrode sheet, a positive electrode sheet and a separator, and an electrolyte, and a shell packaging the electric core and the electrolyte, wherein the negative electrode sheet is the above-mentioned negative electrode sheet.

[0046] In addition, the application also provides an electric device comprising the above-mentioned secondary battery.

[0047] Compared with the prior art, the beneficial effects of the present application are that: the present application realizes lithium supplement by reducing organic lithium in the volatile organic lithium solution and distributing it on the surface of the particles by introducing organic gas and inert gas. Lithium is located on the outside of the silicon-carbon material, effectively compensating for the loss of lithium ions caused by the formation of the solid electrolyte interface (SEI) film during the cycle process, effectively improving the initial efficiency of the silicon-carbon negative electrode material, and the lithium element is wrapped by the carbon material, significantly improving its chemical stability in air. BRIEF DESCRIPTION OF DRAWINGS

[0048] Figure 1 The structure schematic diagram of the composite negative electrode material of an embodiment of the present application.

[0049] Among them, 1-pore; 2-porous carbon; 3-lithium particles; 4-carbon coating layer. DETAILED DESCRIPTION

[0050] In order to make the technical solutions and advantages of the present application clearer, the technical solutions of the present application will be described clearly and completely below in combination with specific embodiments. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0051] According to the first aspect of the present application, the present application provides a composite negative electrode material, comprising a core and a coating layer wrapped on the outer surface of the core, the core comprising porous carbon and nano-silicon loaded on the porous carbon, and lithium element being distributed between the core and the coating layer.

[0052] In some embodiments, the particle size D50 of the porous carbon is R1 μm, the particle size D50 of the nano-silicon particles is R2 nm, and the content of the nano-silicon is B% of the mass of the silicon-carbon, wherein 2.8<(R1-R2)xB%<3.5, for example, it can be 2.9, 3.0, 3.1, 3.2, 3.3, 3.4, etc.

[0053] In some embodiments, the coating layer is a carbon coating layer.

[0054] In some embodiments, the particle size D50 of the porous carbon is 7-9 μm, for example, it can be 7 μm, 8 μm, 9 μm.

[0055] In some embodiments, the particle size D50 of the nano-silicon particles is 1-3 nm, for example, it can be 1.5 nm, 2 nm, 2.2 nm.

[0056] In some embodiments, the pore volume of the porous carbon is 0.6-1.0 cm 3 / g, for example, it can be 0.6 cm3 / g, 0.7 cm 3 / g, 0.8 cm 3 / g, 0.9 cm 3 / g, 1.0 cm 3 / g; the pore distribution structure is: the proportion of micropores is 80-90%, the proportion of mesopores is 8-15%, and the proportion of macropores is 1-5%, wherein the pore size of the micropores is ≤2 nm, the pore size of the mesopores is 2-50 nm, and the pore size of the macropores is ≥50 nm.

[0057] According to a second aspect of the present application, the present application provides a preparation method of a composite negative electrode material, comprising the following steps:

[0058] S1, carbonizing a carbon source under the protection of inert gas to obtain a carbon matrix;

[0059] S2, performing pore forming and purification on the carbon matrix to obtain a porous carbon matrix;

[0060] S3, vapor depositing silicon on the porous carbon matrix to obtain the inner core;

[0061] S4, vapor depositing lithium on the inner core to obtain an inner core with lithium element distributed on the surface;

[0062] S5, vapor depositing carbon on the inner core obtained in S4 to form a carbon coating layer, thereby obtaining the composite negative electrode material.

[0063] In some embodiments, the carbonization of step S1 comprises carbonizing the carbon source at 900-1200℃ for 3-6h, and the carbonization temperature may, for example, be 900℃, 1000℃, 1100℃, or 1200℃, and the carbonization time may, for example, be 3h, 4h, 5h, or 6h.

[0064] In some embodiments, in step S1, the carbon source is obtained by carbonizing biomass such as coconut shell, rice husk, and luffa, or carbon sources such as phenolic resin-based carbon source, epoxy resin-based carbon source, petroleum coke, and anthracite.

[0065] In some embodiments, the pore forming of S2 comprises mixing the carbon matrix with a pore former, calcining at 850-1000℃ for 1-2h, and the calcination temperature may, for example, be 850℃, 900℃, 950℃, or 1000℃, and the calcination time may, for example, be 1h, 1.5h, or 2h.

[0066] In some embodiments, the purification of S2 comprises performing acid washing and water washing to neutralization on the calcination product, then calcining at 500-600℃ for 3-4h, and crushing. The calcination temperature may, for example, be 500℃, 550℃, or 600℃, and the calcination time may, for example, be 3h, 3.5h, or 4h.

[0067] In some embodiments, the pore-forming agent of S2 is a basic pore-forming agent.

[0068] In some embodiments, the pore-forming agent comprises at least one of sodium hydroxide and potassium hydroxide.

[0069] In some embodiments, the concentration of the pore-forming agent is 1-2 mol / L, for example, it can be 1 mol / L or 2 mol / L.

[0070] In some embodiments, the amount of the pore-forming agent added is 8%-15% of the mass of the carbon matrix, for example, it can be 8%, 9%, 10%, 11%, 12%, 13%, 14%, or 15%.

[0071] In some embodiments, the vapor-deposited silicon of S3 comprises placing the porous carbon matrix in a reaction device, introducing a first mixed gas containing a first protective gas and a silicon source gas, and performing vapor deposition of silicon on the porous carbon matrix.

[0072] In some embodiments, the conditions for vapor-deposited silicon are 350-450℃, for example, it can be 350℃, 400℃, or 450℃, and the deposition time is 1-3h, for example, it can be 1h, 1.5h, 2h, or 3h.

[0073] In some embodiments, the content of the first protective gas is 10%-30% of the volume of the first mixed gas, for example, it can be 10%, 15%, 20%, 25%, or 30%.

[0074] In some embodiments, the silicon source gas comprises silane gas; preferably, the first protective gas comprises at least one of helium, nitrogen, argon, and krypton.

[0075] In some embodiments, the vapor-deposited lithium of S4 comprises introducing a second mixed gas containing a second protective gas and a carbon source gas into an organic lithium solution, heating the reaction to obtain an organic lithium gas, and then introducing the organic lithium gas into a reaction device containing the inner core to perform vapor deposition of lithium on the inner core to obtain an inner core with lithium single atoms distributed on the surface.

[0076] In some embodiments, the heating reaction conditions of S4 are 300-400℃, for example, it can be 300℃, 350℃, or 400℃, and the reaction time is 1-3h, for example, it can be 1h, 1.5h, 2h, or 3h.

[0077] In some embodiments, the organic lithium solution is at least one of n-butyllithium, methyllithium, sec-butyllithium, and diisopropylamino lithium.

[0078] In some embodiments, the carbon source gas of S4 comprises at least one of acetylene, ethylene, and methane.

[0079] In some embodiments, the flow rate of the organic lithium gas is 0.1-0.3 m / s, for example, can be 0.1 m / s, 0.2 m / s, 0.3 m / s.

[0080] In some embodiments, the second protective gas comprises at least one of helium, nitrogen, argon and krypton.

[0081] In some embodiments, the vapor-deposited carbon of S5 comprises introducing a carbon source gas into a reaction device containing the core obtained in S4, and vapor-depositing carbon on the core.

[0082] In some embodiments, the carbon source gas of S5 comprises acetylene.

[0083] In some embodiments, the conditions for vapor-depositing carbon are 550-600℃, for example, can be 550℃, 580℃, 600℃, and depositing for 1-3 h, for example, can be 1 h, 1.5 h, 2 h, 3 h.

[0084] According to a third aspect of the present application, the present application provides a negative electrode sheet, comprising a negative electrode current collector and a negative electrode active material layer coated on at least one surface of the negative electrode current collector, wherein the negative electrode active material layer comprises the composite negative electrode material described above.

[0085] According to a fourth aspect of the present application, the present application provides a secondary battery, comprising an electrode core wound by a negative electrode sheet, a positive electrode sheet and a separator, and an electrolyte, and a shell encapsulating the electrode core and the electrolyte, wherein the negative electrode sheet is the negative electrode sheet described above.

[0086] According to a fifth aspect of the present application, the present application provides an electric device comprising the secondary battery described above.

[0087] The positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector, wherein the positive electrode active material layer comprises a positive electrode active material, which can be one or more of a combination of compounds represented by the chemical formulae Li a Ni x Co y M z O 2-b N b The positive electrode active material can also be one or more of a combination of compounds represented by the chemical formulae LiCoO2, LiNiO2, LiVO2, LiCrO2, LiMn2O4, LiCoMnO4, Li2NiMn3O8, LiNi 0.5 Mn 1.5LiCoP04, LiMnP04, LiFeP04, LiNiP04, LiCoFSO4, CuS2, FeS2, MoS2, NiS, TiS2, etc. The positive active material can also be modified, and the method for modifying the positive active material should be known to those skilled in the art, for example, the positive active material can be modified by coating, doping, etc., and the material used for modification can be a combination of one or more of Al, B, P, Zr, Si, Ti, Ge, Sn, Mg, Ce, W, etc. The positive current collector is usually a structure or part that collects current, and the positive current collector can be various materials suitable for use as a positive current collector of a lithium ion battery in the art, for example, the positive current collector can be a combination of one or more of metal foil, etc., and more specifically can be a combination of one or more of aluminum foil, etc.

[0088] The separator can be various materials suitable for use as a separator of a secondary battery in the art, for example, can be a combination of one or more of polyethylene, polypropylene, polyvinylidene fluoride, aramid, polyethylene terephthalate, polytetrafluoroethylene, polyacrylonitrile, polyimide, polyamide, polyester, and natural fiber, etc.

[0089] The secondary battery also includes an electrolyte, which includes an organic solvent, an electrolyte lithium salt, and an additive. The electrolyte lithium salt can be LiPF6 and / or LiBOB used in a high-temperature electrolyte; can be at least one of LiBF4, LiBOB, LiPF6 used in a low-temperature electrolyte; can be at least one of LiBF4, LiBOB, LiPF6, LiTFSI used in an overcharge-preventing electrolyte; can be at least one of LiC104, LiAsF6, LiCF3SO3, LiN(CF3SO2)2. The organic solvent can be a cyclic carbonate, including PC, EC; can be a chain carbonate, including DFC, DMC, or EMC; can be a carboxylic acid ester, including MF, MA, EA, MP, etc. The additive includes at least one of a film-forming additive, a conductive additive, a flame-retardant additive, an overcharge-preventing additive, an additive for controlling the content of H2O and HF in the electrolyte, an additive for improving low-temperature performance, a multifunctional additive, etc.

[0090] The application will be further described in conjunction with the specific embodiments, but the embodiments of the application are not limited thereto.

[0091] Example 1

[0092] Preparation of the negative material:

[0093] As Figure 1As shown, the composite negative electrode material provided by the embodiment includes an inner core 2 and a coating layer 4 coated on the outer surface of the inner core 2, the inner core 2 includes porous carbon and nano-silicon loaded on the porous carbon, and lithium element 3 is distributed between the inner core 2 and the coating layer 4.

[0094] The preparation method of the composite negative electrode material includes the following steps:

[0095] S1, place the carbon source at a temperature of 1000℃, introduce nitrogen, heat for 3 hours to obtain a carbon matrix; wherein the carbon source is phenol formaldehyde resin (purchased from Shaoguan Derui Chemical Industry Co., Ltd., CAS: 9003-35-4).

[0096] S2, mix the carbon matrix with potassium hydroxide and then place it in a constant temperature device to calcine at 850℃ for 1.5h, after the reaction is completed, perform acid washing, water washing to neutral, drying, calcining at 500℃ for 4h, and crushing to obtain a porous carbon matrix; wherein the concentration of potassium hydroxide is 1mol / L, and the addition amount of potassium hydroxide accounts for 9% of the mass of the carbon matrix. The porous carbon matrix has a pore volume of 0.8cm 3 / g, a particle size D50 of 8.5μm, and a pore distribution ratio of 85% micropores, 10% mesopores, and 5% macropores.

[0097] S3, place the porous carbon matrix in a rotary furnace, introduce a first mixed gas to react to obtain a porous carbon matrix with deposited nano-silicon; wherein the first mixed gas is a mixed gas of nitrogen and silane, the volume ratio of nitrogen accounts for 25% of the volume of the first mixed gas, the reaction temperature is 400℃, and the reaction time is 2h.

[0098] S4, place the porous carbon matrix with deposited nano-silicon in a rotary furnace, introduce a second mixed gas into an organic lithium solution to heat and react to obtain an organic lithium gas, and then introduce the organic lithium gas into the rotary furnace to react; wherein the second mixed gas is a mixed gas of nitrogen and acetylene (the volume ratio of nitrogen to acetylene is 1:3), the organic lithium solution is n-butyllithium, the reaction temperature is 360℃, the reaction time is 2h, and the gas flow rate is 0.2m / s.

[0099] S5, after the reaction is completed, stop introducing the organic lithium gas, introduce an organic gas to react, and obtain the composite negative electrode material after the reaction is completed; wherein the organic gas is acetylene, the reaction temperature is 550℃, and the reaction time is 2h.

[0100] The porous carbon has a particle size D50 of 8.5μm, the nano-silicon particles have a particle size D50 of 1.8nm, and the content of the nano-silicon is 46% of the mass of silicon-carbon.

[0101] Example 2

[0102] The difference from Example 1 is that in Step S4 of this example, the gas flow rate is 0.2 m / s, the reaction temperature is 300°C, and the reaction time is 1 hour.

[0103] The rest is the same as Example 1, and will not be repeated here.

[0104] Example 3

[0105] The difference from Example 1 is that in Step S4 of this example, the gas flow rate is 0.3 m / s, the reaction temperature is 300°C, and the reaction time is 1 hour.

[0106] The rest is the same as Example 1, and will not be repeated here.

[0107] Example 4

[0108] The difference from Example 1 is that in Step S4 of this example, the gas flow rate is 0.2 m / s, the reaction temperature is 360°C, and the reaction time is 1 hour.

[0109] The rest is the same as Example 1, and will not be repeated here.

[0110] Example 5

[0111] The difference from Example 1 is that in Step S4 of this example, the gas flow rate is 0.1 m / s, the reaction temperature is 300°C, and the reaction time is 1 hour.

[0112] The rest is the same as Example 1, and will not be repeated here.

[0113] Example 6

[0114] The difference from Example 1 is that in Step S4 of this example, the gas flow rate is 0.2 m / s, the reaction temperature is 360°C, and the reaction time is 3 hours.

[0115] The rest is the same as Example 1, and will not be repeated here.

[0116] Example 7

[0117] The difference from Example 1 is that in Step S4 of this example, the gas flow rate is 0.2 m / s, the reaction temperature is 400°C, and the reaction time is 1 hour.

[0118] The rest is the same as Example 1, and will not be repeated here.

[0119] Comparative Example 1

[0120] The difference from Example 1 is that in Step S4 of this example, the mixed gas does not pass through the organic lithium solution, the gas flow rate is 0.2 m / s, the reaction temperature is 400°C, and the reaction time is 1 hour, and the reaction time in Step S5 is 1 hour.

[0121] The rest is the same as Example 1, which will not be repeated here.

[0122] Comparative Example 2

[0123] Different from Example 1, in the step S4 of the present comparative example, the mixed gas does not pass through the organic lithium solution, the gas flow rate is 0.2 m / s, the reaction temperature is 400℃, the reaction time is 2 hours, and the reaction time in the step S5 is 2 hours.

[0124] The rest is the same as Example 1, which will not be repeated here.

[0125] Comparative Example 3

[0126] Different from Example 1, in the step S4 of the present comparative example, the reaction temperature is 200℃.

[0127] The rest is the same as Example 1, which will not be repeated here.

[0128] Comparative Example 4

[0129] Different from Example 1, in the step S4 of the present comparative example, the reaction temperature is 500℃.

[0130] The rest is the same as Example 1, which will not be repeated here.

[0131] Comparative Example 5

[0132] Different from Example 1, in the step S4 of the present comparative example, the reaction time is 0.5 hours, and the gas flow rate is 0.1 m / s.

[0133] The rest is the same as Example 1, which will not be repeated here.

[0134] Comparative Example 6

[0135] Different from Example 1, in the step S4 of the present comparative example, the reaction time is 4 hours, and the gas flow rate is 0.1 m / s.

[0136] The rest is the same as Example 1, which will not be repeated here.

[0137] Comparative Example 7

[0138] Different from Example 1, in the step S4 of the present comparative example, the organic lithium gas flow rate is 0.5 m / s.

[0139] The rest is the same as Example 1, which will not be repeated here.

[0140] Comparative Example 8

[0141] Different from Example 1, in the step S5 of the present comparative example, the carbon-coated reaction time is 4h.

[0142] The rest is the same as Example 1, which will not be repeated here.

[0143] Comparative Example 9

[0144] Different from Example 1, the pore-forming in step S2 of the present comparative example is not followed by purification treatment (i.e. no water washing and calcination treatment).

[0145] The rest is the same as Example 1, which will not be repeated here.

[0146] Comparative Example 10

[0147] Different from Example 1, the preparation process of the composite anode material of the present comparative example does not contain step S5.

[0148] The rest is the same as Example 1, which will not be repeated here.

[0149] The anode materials of the above examples and comparative examples are further applied to the preparation of lithium ion batteries, and the specific preparation method comprises:

[0150] S1, preparation of the positive electrode sheet: the positive electrode active material lithium cobaltate, the conductive agent conductive carbon black, and the binder polyvinylidene fluoride are mixed in a mass ratio of 97:1.5:1.5, N-methyl pyrrolidone (NMP) is added, and the mixture is stirred uniformly under the action of a vacuum stirrer to obtain a positive electrode slurry, wherein the solid content of the positive electrode slurry is 75wt%. The positive electrode slurry is uniformly coated on one surface of an aluminum foil with a thickness of 8μm, and the aluminum foil is dried at 125℃ for 1h to obtain a positive electrode sheet coated with a positive electrode material layer on one side. The above steps are repeated on the other surface of the aluminum foil, i.e. a positive electrode sheet coated with a positive electrode material layer on both sides is obtained. Then, after cold pressing, sheet cutting, and slitting, the positive electrode is dried at 125℃ under vacuum conditions for 2h to obtain a positive electrode with a specification of 65mm×860mm.

[0151] S2, preparation of the negative electrode sheet: the negative electrode material, CMC, PAA, and CNT are mixed in a mass ratio of negative electrode material: CMC: PAA: CNT = 80:9:10:1, deionized water is added, and the mixture is stirred uniformly under the action of a vacuum stirrer to obtain a negative electrode slurry, wherein the solid content of the negative electrode slurry is 45wt%. The negative electrode slurry is uniformly coated on one surface of a copper foil with a thickness of 6μm, and the copper foil is dried at 120℃ to obtain a negative electrode coated with a negative electrode material layer on one side. The above steps are repeated on the other surface of the aluminum foil, i.e. a negative electrode coated with a negative electrode material layer on both sides is obtained. Then, after cold pressing, sheet cutting, and slitting, the negative electrode is dried at 120℃ under vacuum conditions for 2h to obtain a negative electrode with a specification of 69mm×868mm.

[0152] S3, preparation of electrolyte: in an argon atmosphere glove box with water content <10 ppm, EC, PC and DMC were mixed according to the mass ratio of 3:2:4 to obtain an organic solvent, and then lithium salt lithium hexafluorophosphate was added to the organic solvent to obtain the electrolyte. The concentration of lithium salt is 1 mol / L.

[0153] S4, assembly of lithium ion battery: the above prepared positive electrode, separator (PE) and negative electrode were stacked in order, and the separator was placed between the positive electrode and the negative electrode to play a role of isolation, and the electrode assembly was obtained by winding. The electrode assembly was placed in an aluminum plastic film packaging bag, dried, and then injected with electrolyte, and then subjected to vacuum packaging, standing, formation, degassing, edge cutting and other processes to obtain a lithium ion battery.

[0154] Performance test

[0155] The capacity and initial efficiency test steps are 0.1C discharge to 0.05V, 5min standby, 0.01C discharge to 0.05V, 5min standby, 0.1C charge to 1.5V, 5min standby.

[0156] The test results are shown in Table 1.

[0157] Table 1

[0158]

[0159]

[0160] Note: The more the amount of carbon coating and the longer the carbon coating time, the less likely the material to produce gas during the stirring coating process, which is beneficial to improve the processing performance of the material. However, the more the amount of carbon coating and the longer the carbon coating time, the capacity and initial efficiency of the material will decrease.

[0161] As can be seen from the comparison of the experimental data of Examples 1-7 and Comparative Examples 1-10 in Table 1, the present application realizes lithium supplementation by introducing organic gas and inert gas into volatile organic lithium solution, so that organic lithium is reduced and distributed on the surface of the particles. Lithium element is located on the outside of the silicon-carbon material, effectively compensating for the loss of lithium ions caused by the formation of solid electrolyte interface (SEI) film during the cycle process, which can effectively improve the initial efficiency and capacity of the silicon-carbon negative electrode material, and the lithium element is also wrapped by the carbon material, which significantly improves its chemical stability in air.

[0162] The data comparison of Example 1 and Comparative Examples 1-2 shows that the initial capacity and capacity of the conventional silicon-carbon material prepared without lithium supplement are low. The data comparison of Example 1 and Comparative Examples 3-6 shows that the lithium supplement time and temperature have certain influence on the performance of the material. When the lithium supplement time is too long, the amorphous silicon will become crystalline silicon, and the expansion and kinetics of the crystalline silicon are not as good as those of the amorphous silicon. When the lithium supplement time is too short, the lithium supplement efficiency is low. When the lithium supplement temperature is too high, the amorphous silicon will become crystalline silicon, and the expansion and kinetics of the crystalline silicon are not as good as those of the amorphous silicon. When the lithium supplement temperature is too low, the organic lithium is not completely decomposed, and the lithium supplement efficiency is low. The data comparison of Example 1 and Comparative Example 7 shows that when the flow rate of the organic lithium gas is too large, the fluidized state will be unstable, and the pre-lithiation will be uneven.

[0163] According to the disclosure and teaching of the above description, those skilled in the art of the present application can also make changes and modifications to the above embodiments. Therefore, the present application is not limited to the above specific embodiments, and any obvious improvements, replacements or modifications made by those skilled in the art on the basis of the present application all fall within the protection scope of the present application. In addition, although some specific terms are used in the present specification, these terms are only for convenience of description and do not constitute any limitation on the present application.

Claims

1. A composite negative electrode material, characterized in that, It includes a core and a coating layer covering the outer surface of the core. The core includes porous carbon and nano-silicon supported on the porous carbon. Elemental lithium is distributed between the core and the coating layer. The preparation of composite anode materials includes the following steps: S1. Carbonize the carbon source under inert gas protection to obtain a carbon matrix; S2. Pore-forming and purifying the carbon matrix to obtain a porous carbon matrix. The purification in S2 includes acid washing and water washing of the calcined product until neutral, followed by calcination at 500-600℃ for 3-4 hours. S3. Silicon is vapor-deposited on the porous carbon matrix to obtain the core; S4. Lithium is vapor-deposited on the core to obtain a core with elemental lithium distributed on its surface. The vapor-deposit lithium in S4 includes passing a second mixed gas containing a second protective gas and a carbon source gas into an organic lithium solution, heating and reacting to obtain organic lithium gas, and then passing the organic lithium gas into a reaction device containing the core to perform vapor-deposit lithium on the core to obtain a core with elemental lithium distributed on its surface. The heating reaction conditions of S4 are 300-400℃ for 1-3 hours, and the flow rate of the organic lithium gas is 0.1-0.3 m / s. S5. Carbon is vapor-deposited on the core obtained in S4. The conditions for vapor-depositing carbon are 550-600℃ for 1-3 hours to form a carbon coating layer, thereby obtaining the composite anode material.

2. The composite negative electrode material according to claim 1, characterized in that, The porous carbon has a particle size D50 of R1 μm, the nano-silicon is nano-silicon particles with a particle size D50 of R2 nm, and the nano-silicon content is B% of the mass of silicon-carbon, wherein 2.8 < (R1-R2) × B% < 3.

5.

3. The composite negative electrode material according to claim 1, characterized in that, The porous carbon has a particle size D50 of 7-9 μm, and the nano-silicon particles have a particle size D50 of 1-3 nm.

4. The composite negative electrode material according to claim 1, characterized in that, The porous carbon has a pore volume of 0.6-1.0 cm³. 3 / g, the pore distribution structure is as follows: micropores account for 80-90%, mesopores account for 8-15%, and macropores account for 1-5%, of which the pore diameter of micropores is ≤2nm, the pore diameter of mesopores is 2-50nm, and the pore diameter of macropores is ≥50nm.

5. The composite negative electrode material according to claim 1, characterized in that, The carbonization of S1 includes carbonizing the carbon source at 900-1200℃ for 3-6 hours; And / or, the pore-forming process of S2 includes mixing a carbon matrix with a pore-forming agent and calcining at 850-1000℃ for 1-2 hours, wherein the pore-forming agent is an alkaline pore-forming agent, the concentration of the pore-forming agent is 1-2 mol / L, and the amount of the pore-forming agent added is 8%-15% of the mass of the carbon matrix; And / or, the vapor deposition of silicon in S3 includes placing a porous carbon substrate in a reaction apparatus, introducing a first mixed gas containing a first protective gas and a silicon source gas, and performing vapor deposition of silicon on the porous carbon substrate. The conditions for vapor deposition of silicon are deposition at 350-450°C for 1-3 hours, the content of the first protective gas is 10%-30% of the volume of the first mixed gas, the silicon source gas includes silane gas, and the first protective gas includes at least one of helium, nitrogen, argon and krypton. And / or, the organic lithium solution of S4 is at least one of n-butyllithium, lithium methoxide, sec-butyllithium and diisopropylaminolithium, the carbon source gas of S4 includes at least one of acetylene, ethylene and methane, and the second protective gas includes at least one of helium, nitrogen, argon and krypton. And / or, the carbon deposition in S5 includes passing a carbon source gas into a reaction apparatus containing the core obtained in S4, and performing carbon deposition in the core, wherein the carbon source gas in S5 includes acetylene.

6. A negative electrode sheet, characterized in that, Includes the composite anode material as described in any one of claims 1-5.

7. A secondary battery, characterized in that, Includes the negative electrode sheet as described in claim 6.

8. An electrical device, characterized in that, Includes the secondary battery as described in claim 7.

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