Negative electrode material, preparation method thereof and lithium ion battery

Abstract

The invention provides a negative electrode material and a preparation method thereof, and a lithium ion battery, the negative electrode material comprises a carbon material and a nanometer silicon-based material dispersed in the carbon material, the negative electrode material contains a fluorine element, and the total mass content of the fluorine element in the negative electrode material is A0ppm; in the negative electrode material, the mass content of the fluorine element contained in the nanometer silicon-based material is A1 ppm, and A0-2A1 is larger than or equal to 30 ppm. According to the negative electrode material, the preparation method thereof and the lithium ion battery provided by the invention, the volume expansion of the negative electrode material can be reduced, the structural integrity of the negative electrode material can be maintained in the cyclic charge-discharge process, and the cycle performance is further improved.

Description

Technical Field

[0001] This application relates to the technical field of anode materials, and more specifically, to anode materials, their preparation methods, and lithium-ion batteries. Background Art

[0002] Existing lithium-ion batteries are widely used in electric vehicles and consumer electronics due to their advantages such as high energy density, high output power, long cycle life, and low environmental pollution. Developing lithium-ion batteries with higher energy density is a major trend at present. The cathode material and anode material are the core of the battery, which determine the working efficiency of the battery. Currently, the commercial anode material is graphite, whose capacity has approached the theoretical upper limit, and the room for further improvement is limited. There is an urgent need to develop a new generation of anode materials with high energy density.

[0003] Silicon-based anode materials are generally regarded as the next-generation anode materials for batteries, with advantages such as high capacity, abundant sources, and relative safety. However, silicon-based anode materials have a severe volume expansion effect during the cycling process, resulting in material pulverization, fragmentation, and rapid cycling decay of the material. To address this problem, there are multiple solutions currently, including structural design of silicon, using technical means such as nanosizing and porousization; or improving it through composite coating and other methods.

[0004] However, existing silicon-carbon anode materials will undergo huge volume changes during charge and discharge, leading to capacity attenuation and deterioration of cycling performance. Summary of the Invention

[0005] This application provides an anode material, its preparation method, and a lithium-ion battery, which can effectively inhibit the volume expansion of the anode material, improve the cycling performance of the battery, and the preparation method can reduce the preparation cost.

[0006] In a first aspect, this application provides an anode material, which includes aggregates. The aggregates include a carbon material and a nano-silicon-based material dispersed in the carbon material, and the anode material contains fluorine element, and the total mass content of the fluorine element in the anode material is A 0 ppm;

[0007] In the anode material, the mass content of the fluorine element contained in the nano-silicon-based material is A 1 ppm, A 0 - 2A 1 ≥ 30 ppm.

[0008] In one embodiment, the total mass content of the fluorine element in the anode material is A 0 ppm, and the value range of A 0 is 100 - 10000.

[0009] In one embodiment, the average particle size D of the nano-silicon-based material 50 is 1 nm to 500 nm.

[0010] In one embodiment, the mass content of the nano-silicon-based material in the negative electrode material is 10% to 80%.

[0011] In one embodiment, the nano-silicon-based material includes at least one of elemental silicon, silicon alloy, and silicon oxide material.

[0012] In one embodiment, the mass content of the carbon material in the negative electrode material is 10% to 50%.

[0013] In one embodiment, the carbon material includes at least one of hard carbon and soft carbon.

[0014] In one embodiment, the damage resistance strength of the negative electrode material particles is ≥300 MPa.

[0015] In one embodiment, the negative electrode material further includes a coating layer present on at least a part of the surface of the nano-silicon-based material.

[0016] In one embodiment, the coating layer includes amorphous carbon and a lithium salt dispersed in the amorphous carbon.

[0017] In one embodiment, the lithium salt includes at least one of lithium hydroxide, lithium chloride, lithium carbonate, lithium fluoride, lithium oxide, lithium borohydride, lithium perchlorate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium hexafluorophosphate, lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, lithium bis(difluoromethanesulfonyl)imide, and lithium bis(trifluoromethylsulfonyl)imide, etc.

[0018] In one embodiment, the thickness of the coating layer is 1 nm to 3000 nm.

[0019] In one embodiment, the median particle size of the negative electrode material is 0.5 μm to 30 μm.

[0020] In one embodiment, the specific surface area of the negative electrode material is ≤5 m 2 / g.

[0021] In a second aspect, the present application provides a method for preparing a negative electrode material, the method including the following steps:

[0022] Prepare a first precursor, the first precursor including a nano-silicon-based material;

[0023] Prepare a second precursor, the second precursor including the first precursor and a carbon source;

[0024] Carry out carbonization treatment on the second precursor to obtain a negative electrode material;

[0025] Among them, the first precursor and / or the second precursor include a fluorine-containing compound; the negative electrode material contains fluorine element, and the total mass content of the fluorine element in the negative electrode material is A 0 ppm; in the negative electrode material, the mass content of the fluorine element contained in the nano-silicon-based material is A 1 ppm, A 0 -2A 1 ≥30 ppm.

[0026] In some embodiments, the fluorine-containing compound includes at least one of calcium fluoride, cryolite, aluminum fluoride, sodium fluoride, sodium fluorosilicate, magnesium fluoride, potassium fluoride, lithium fluoride, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium hexafluorophosphate, lithium difluorooxalate borate, fluoroethylene carbonate, lithium bis(difluoromethanesulfonyl)imide, and lithium bis(trifluoromethylsulfonyl)imide.

[0027] In some embodiments, at least one of the first precursor, the second precursor, and the nano-silicon-based material includes a lithium salt.

[0028] In some embodiments, at least one of the first precursor, the second precursor, and the nano-silicon-based material includes a lithium salt, and the lithium salt includes at least one of lithium hydroxide, lithium chloride, lithium carbonate, lithium fluoride, lithium oxide, lithium borohydride, lithium perchlorate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium hexafluorophosphate, lithium bis(oxalato)borate, lithium difluorooxalate borate, lithium bis(difluoromethanesulfonyl)imide, and lithium bis(trifluoromethylsulfonyl)imide, etc.

[0029] In some embodiments, the average particle size D of the nano-silicon-based material 50 is 1 nm to 500 nm.

[0030] In some embodiments, before preparing the first precursor, the method further includes: wet-crushing a mixture of a silicon-based material and a solvent, and drying to obtain a nano-silicon-based material.

[0031] In some embodiments, the step of preparing the first precursor includes: wet-crushing a mixture of a silicon-based material, a fluorine-containing compound, and a solvent, and drying to obtain the first precursor.

[0032] In some embodiments, the step of preparing the first precursor includes: wet-crushing a mixture of a silicon-based material, a fluorine-containing compound, and a solvent, and drying to obtain the first precursor; wherein, the mass content of the fluorine-containing compound added in the first precursor is 0.01% to 3%;

[0033] In some embodiments, the step of preparing the first precursor includes: mixing a nano-silicon-based material, a fluorine-containing compound, and a solvent, and then removing the solvent to obtain the first precursor.

[0034] In some embodiments, the nano-silicon-based material includes at least one of elemental silicon, silicon alloy, and silicon oxide material.

[0035] In some embodiments, the solvent includes an organic solvent.

[0036] In some embodiments, the organic solvent includes at least one of methanol, ethanol, ethylene glycol, propanol, isopropanol, glycerol, n-butanol, isobutanol, pentanol, trifluoroethanol, and trifluoromethanol.

[0037] In some embodiments, the mixing treatment method includes at least one of mechanical stirring, ultrasonic dispersion, and grinding dispersion.

[0038] In some embodiments, the step of preparing the first precursor includes: mixing a nano-silicon-based material, a fluorine-containing compound, and a solvent, and then performing a drying treatment to obtain the first precursor.

[0039] In some embodiments, the temperature of the drying treatment is 40°C to 600°C.

[0040] In some embodiments, the drying treatment time is 1 h to 15 h.

[0041] In some embodiments, the drying treatment method includes at least one of spray drying and freeze drying.

[0042] In some embodiments, the mass content of the lithium salt added to the first precursor is 0.05% to 1%.

[0043] In some embodiments, the step of preparing the second precursor includes: mixing the first precursor, a carbon source, and a fluorine-containing compound to obtain the second precursor.

[0044] In some embodiments, the mass ratio of the first precursor to the carbon source is 100:(10 - 100).

[0045] In some embodiments, the carbon source includes at least one of sucrose, glucose, polyethylene, polyvinyl alcohol, polyethylene glycol, polyaniline, epoxy resin, phenolic resin, furfural resin, acrylic resin, polyethylene oxide, polyvinylidene fluoride, polyacrylonitrile, polyvinyl chloride, and asphalt.

[0046] In some embodiments, the mass content of the fluorine-containing compound added to the second precursor is 0.05% to 3%.

[0047] In some embodiments, the mass content of the lithium salt added to the second precursor is 0.01% to 0.1%.

[0048] In some embodiments, the temperature of the carbonization treatment is 600°C to 1200°C.

[0049] In some embodiments, the time of the carbonization treatment is 1 h to 10 h.

[0050] In some embodiments, the heating rate of the carbonization treatment is 1°C / min to 30°C / min.

[0051] In some embodiments, a protective gas is passed during the carbonization treatment, and the protective gas includes at least one of nitrogen, helium, neon, argon, and krypton.

[0052] In a third aspect, the present application provides a lithium-ion battery, and the lithium-ion battery includes the above-mentioned negative electrode material or the negative electrode material prepared according to the above-mentioned preparation method.

[0053] The technical solution of the present application has at least the following beneficial effects:

[0054] The negative electrode material provided by the present application includes a carbon material and a nano-silicon-based material dispersed in the carbon material, and the negative electrode material contains fluorine element, and the total mass content of the fluorine element in the negative electrode material is A 0 ppm; in the negative electrode material, the mass content of the fluorine element contained in the nano-silicon-based material is A 1 ppm, controlling A 0 -2A 1 ≥30 ppm, it can ensure that the content of fluorine element in the nano-silicon-based material is less than the mass content of fluorine element in the part of the negative electrode material other than the nano-silicon-based material. More fluorine elements exist in the part of the negative electrode material other than the nano-silicon-based material. Fluorine element has strong electronegativity and can be reduced at a lower reduction potential. The content of fluorine element contained in the nano-silicon-based material is less than the content of fluorine element in the part of the negative electrode material other than the nano-silicon-based material. Under this concentration difference gradient, the fluorine element in the part of the negative electrode material other than the nano-silicon-based material can preferentially participate in the formation of the solid electrolyte interface film on the surface of the negative electrode material during the charge and discharge process, optimize the solid electrolyte interface film, reduce the reaction activity between the negative electrode material and the electrolyte, protect the negative electrode material, reduce the occurrence of side reactions, and thus improve the cycle performance of the negative electrode material, especially the long-cycle performance; and can avoid the formation of the solid electrolyte interface film inside the negative electrode material particles and improve the specific capacity of the material.

[0055] The preparation method of the negative electrode material provided by this application first prepares a first precursor containing a nano-silicon-based material, and then carbonizes a second precursor containing the first precursor and a carbon source to obtain the negative electrode material. Among them, a fluorine-containing compound is added to the first precursor and / or the second precursor, so that most of the fluorine elements are located in the part of the negative electrode material other than the nano-silicon-based material, so that A 0 -2A 1 ≥30 ppm is controlled within this range, which can ensure that the content of fluorine elements in the nano-silicon-based material is less than the mass content of fluorine elements in the part of the negative electrode material other than the nano-silicon-based material. More fluorine elements exist in the part of the negative electrode material other than the nano-silicon-based material. Fluorine elements have strong electronegativity and can be reduced at a lower reduction potential. Therefore, the fluorine elements in the part of the negative electrode material other than the nano-silicon-based material can preferentially participate in the formation of the solid electrolyte film on the surface of the negative electrode material during the charge and discharge process, optimize the solid electrolyte film, reduce the reaction activity between the negative electrode material and the electrolyte, protect the negative electrode material, reduce the occurrence of side reactions, and thus improve the cycle performance of the negative electrode material, especially the long-cycle performance; and can avoid the formation of a solid electrolyte film inside the negative electrode material particles and improve the specific capacity of the material. The preparation method provided by this application can be applied to large-scale production, and the prepared negative electrode material can effectively improve the stability of the charge and discharge cycle of the lithium battery and effectively reduce the expansion rate of the negative electrode material. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Figure 1 is a schematic flow chart of the preparation method of the negative electrode material provided by the embodiment of this application;

[0057] Figure 2 is a scanning electron microscope (SEM) picture of the negative electrode material prepared in Example 1 of this application;

[0058] Figure 3 is an X-ray diffraction pattern of the negative electrode material prepared in Example 1 of this application;

[0059] Figure 4 is the first charge-discharge curve of the negative electrode material prepared in Example 1 of this application;

[0060] Figure 5 is the cycle performance curve of the negative electrode material prepared in Example 1 of this application;

[0061] Figure 6 is a detection photo of the scanning transmission electron microscope (STEM-EDX) of the negative electrode material prepared in Example 1 of this application. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0062] The following is the preferred implementation mode of the embodiments of the present application. It should be noted that for those of ordinary skill in the art in the technical field, without departing from the principles of the embodiments of the present application, several improvements and refinements can be made, and these improvements and refinements are also regarded as the protection scope of the embodiments of the present application.

[0063] A negative electrode material of an embodiment, the negative electrode material includes a carbon material and a nano-silicon-based material dispersed in the carbon material, and the negative electrode material contains fluorine element, and the total mass content of the fluorine element in the negative electrode material is A 0 ppm;

[0064] In the negative electrode material, the mass content of the fluorine element contained in the nano-silicon-based material is A 1 ppm, A 0 - 2A 1 ≥ 30 ppm.

[0065] Among them, the mass content of the fluorine element is obtained by the following test method:

[0066] Using ion chromatography, atomic absorption spectrometry, elemental analysis or inductively coupled plasma spectrometry to measure that the total mass content of the fluorine element in the negative electrode material is A 0 ppm;

[0067] Then soak the negative electrode material in a sodium hydroxide solution with a concentration of 8 mol / L until the silicon-based material is removed. The remaining material is washed with deionized water and dried to obtain a composite after removing the silicon-based material; and using ion chromatography, atomic absorption spectrometry, elemental analysis or inductively coupled plasma spectrometry to measure that the mass content of the fluorine element in the composite after removing silicon is A 2 ppm;

[0068] After calculation, in the negative electrode material, the mass content of the fluorine element contained in the nano-silicon is A 1 ppm, A 2 - A 1 = A 0 - A 1 - A 1 = A 0 - 2A 1 .

[0069] The negative electrode material of this embodiment includes a carbon material and a nano-silicon-based material dispersed in the carbon material, and controls A 0 - 2A 1In the range of ≥30 ppm, it can ensure that the content of fluorine element in the nano-silicon-based material is less than the mass content of fluorine element in the part of the negative electrode material other than the nano-silicon-based material. More fluorine elements exist in the part of the negative electrode material other than the nano-silicon-based material. Fluorine element has strong electronegativity and can be reduced at a lower reduction potential. The content of fluorine element contained in the nano-silicon-based material is less than the content of fluorine element in the part of the negative electrode material other than the nano-silicon-based material. Under this concentration difference gradient, it can enable the fluorine element in the part of the negative electrode material other than the nano-silicon-based material to preferentially participate in the formation of the solid electrolyte film on the surface of the negative electrode material during charge and discharge, optimize the solid electrolyte film, reduce the reaction activity between the negative electrode material and the electrolyte, protect the negative electrode material, reduce the occurrence of side reactions, thereby improving the cycle performance of the negative electrode material, especially the long-cycle performance; and can reduce the formation of the solid electrolyte film inside the negative electrode material particles and improve the specific capacity of the material.

[0070] In some embodiments, the carbon material includes at least one of hard carbon and soft carbon. Soft carbon can be amorphous carbon, porous carbon, and hard carbon can be capacitive carbon, activated carbon, etc., which are not limited herein.

[0071] The nano-silicon-based material can be located on the surface of the carbon material, between carbon material particles or embedded in the carbon material. When the carbon material is porous carbon, the nano-silicon-based material can also be located in the pores of the porous carbon.

[0072] In some embodiments, 30 ppm ≤ A 0 - 2A 1 ≤ 7000 ppm, A 0 - 2A 1 Specifically, it can be 30 ppm, 50 ppm, 100 ppm, 150 ppm, 200 ppm, 300 ppm, 400 ppm, 500 ppm, 1000 ppm, 2000 ppm, 3000 ppm, 4000 ppm, 5000 ppm, 6000 ppm or 7000 ppm, etc., which are not limited herein. Preferably, 100 ppm ≤ A 0 - 2A 1 ≤ 1000 ppm. Controlling the value of A 0 - 2A 1 within the above range means that the content of fluorine element on the surface of the nano-silicon-based material is less, and most of the fluorine elements exist in the part of the negative electrode material other than the nano-silicon-based material, which is more conducive to the formation of the solid electrolyte film on the surface of the negative electrode material particles, and the cycle retention rate of the negative electrode material is further optimized.

[0073] In some embodiments, the total mass content of fluorine element in the negative electrode material is A 0 ppm, A 0The value range is 100~10000; A 0 The specific value of can be 100, 200, 500, 1000, 2000, 5000, 8000, 9000 or 10000, etc., and of course it can also be other values ​​within the above range, which is not limited here. Specifically, the total mass content of fluorine element in the negative electrode material can be measured by ion chromatography, atomic absorption spectrometry, elemental analysis or inductively coupled plasma spectrometry.

[0074] In some embodiments, the nano silicon-based material includes at least one of silicon, silicon-oxygen material and silicon alloy. Silicon alloys include silicon-lithium alloys, silicon-magnesium alloys, etc. The silicon-oxygen material can be a silicon-oxygen composite with a molar ratio of silicon atoms to oxygen atoms in the range of 0.1 to 1.9. The silicon-oxygen composite can be Si and SiO 2 complex, or a compound containing a chemical formula of SiO x (0<x<2) substances can also be silicate substances.

[0075] In some embodiments, the average particle size D of the nano-silicon-based material 50 1nm to 500nm. Specifically, it can be 1nm, 5nm, 10nm, 15nm, 20nm, 30nm, 40nm, 50nm, 100nm, 200nm, 300nm, 400nm or 500nm, etc. Of course, it can also be other values ​​within the above range, which is not limited here. Nano silicon-based materials have strong structural stability and can inhibit volume expansion. The average particle size of nano silicon-based materials is controlled within the above range, which can reduce the agglomeration of nano silicon-based materials during the charging and discharging process and reduce production costs. Preferably, the average particle size D of the nano silicon-based material is 50 1nm to 200nm, more preferably 1nm to 100nm.

[0076] In some embodiments, the destructive strength of the negative electrode material particles is ≥300MPa. The destructive strength of the negative electrode material particles can be 300MPa, 310MPa, 320MPa, 350MPa, 380MPa, 390MPa, 400MPa, 450MPa, 480MPa or 500MPa, etc., and of course it can also be other values ​​within the above range, which is not limited here. Because it has strong rigidity and strong particle structure stability, it can resist certain volume expansion stress, thereby reducing expansion and improving battery cycle stability.

[0077] In some embodiments, the mass content of the nano-silicon-based material in the negative electrode material is 10% to 80%, specifically 10%, 20%, 30%, 40%, 50%, 60%, 70% or 80%, etc., which is not limited here.

[0078] ​In some embodiments, the mass content of the carbon material in the anode material is 10% to 50%, specifically it can be 10%, 20%, 25%, 30%, 35%, 40%, 45% or 50%, etc., which is not limited herein.

[0079] Furthermore, the anode material further includes a coating layer present on at least a part of the surface of the nano-silicon-based material. Preferably, the coating layer is distributed on the surface of the nano-silicon-based material.

[0080] In some embodiments, the coating layer includes amorphous carbon.

[0081] In some embodiments, the thickness of the coating layer is 1 nm to 3000 nm. It can be understood that the coating layer coated on the surface of the nano-silicon-based material can reduce the contact between the nano-silicon-based material and the electrolyte, reduce the formation of the passivation film, and improve the reversible capacitance of the battery.

[0082] Specifically, the coating layer is a carbon layer, and the thickness of the carbon layer can be 1 nm, 50 nm, 180 nm, 200 nm, 350 nm, 400 nm, 550 nm, 850 nm, 950 nm, 1050 nm, 1500 nm, 2000 nm, 2500 nm or 3000 nm, etc. Of course, it can also be other values within the above range, which is not limited herein. If the carbon layer is too thick and the carbon proportion is too high, it is not conducive to obtaining a composite material with a high specific capacity; if the carbon layer is too thin, it is not conducive to increasing the conductivity of the anode material and has a weak performance in suppressing the volume expansion of the material, resulting in poor long-cycle performance. Preferably, the thickness of the carbon layer is 50 nm to 800 nm; more preferably, the thickness of the carbon layer is 100 nm to 500 nm.

[0083] In some embodiments, the coating layer includes amorphous carbon and a lithium salt dispersed in the amorphous carbon. The presence of the lithium salt in the coating layer can increase the content of active lithium ions, participate in the formation of the solid electrolyte during the first charge and discharge process, make up for the lack of active lithium ions in the electrolyte, and make up for the irreversible capacity loss, which can effectively improve the first Coulomb efficiency of the material.

[0084] In some embodiments, the lithium salt includes at least one of lithium hydroxide, lithium chloride, lithium carbonate, lithium fluoride, lithium oxide, lithium borohydride, lithium perchlorate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium hexafluorophosphate, lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, lithium bis(difluoromethanesulfonyl)imide and lithium bis(trifluoromethylsulfonyl)imide, etc.

[0085] In some embodiments, the median particle size of the negative electrode material is 0.5 μm to 30 μm. Specifically, it can be 0.5 μm, 1 μm, 5 μm, 8 μm, 10 μm, 13 μm, 15 μm, 18 μm, 20 μm, 25 μm, 30 μm, etc. Of course, it can also be other values within the above range, which are not limited herein. It can be understood that controlling the median particle size of the negative electrode material within the above range is beneficial to improving the cycling performance of the negative electrode material.

[0086] In some embodiments, the specific surface area of the negative electrode material is ≤ 5 m 2 / g. Specifically, it can be 5 m 2 / g, 4.5 m 2 / g, 4 m 2 / g, 3.5 m 2 / g, 3 m 2 / g, 2 m 2 / g, 1 m 2 / g or 0.5 m 2 / g, etc. Of course, it can also be other values within the above range, which are not limited herein. It can be understood that controlling the specific surface area of the negative electrode material within the above range is beneficial to suppressing volume expansion and improving the cycling performance of the negative electrode material.

[0087] In some embodiments, the damage resistance strength of the negative electrode material particles is ≥ 300 MPa. The damage strength of the negative electrode material particles can specifically be 300 MPa, 310 MPa, 320 MPa, 350 MPa, 380 MPa, 390 MPa, 400 MPa, 450 MPa, 480 MPa, 500 MPa, etc. Of course, it can also be other values within the above range, which are not limited herein. Because it has strong rigidity and the particle structure has strong stability, it can resist a certain amount of volume expansion stress, thereby reducing expansion and improving the cycling stability of the battery.

[0088] It should be noted that the negative electrode materials of the above various embodiments can be arbitrarily combined without contradiction, such as combining and limiting the damage resistance strength and specific surface area of the negative electrode material particles, etc.

[0089] On the other hand, the present application provides a method for preparing a negative electrode material, as Figure 1 shown, the method includes the following steps:

[0090] Step S10, preparing a first precursor, the first precursor includes a nano-silicon-based material;

[0091] Step S20, preparing a second precursor, the second precursor includes the first precursor and a carbon source;

[0092] Step S30, performing carbonization treatment on the second precursor to obtain a negative electrode material;

[0093] Among them, the first precursor and / or the second precursor includes a fluorine-containing compound; the negative electrode material contains fluorine element, and the total mass content of fluorine element in the negative electrode material is A 0 ppm; in the negative electrode material, the mass content of fluorine element contained in the nano-silicon-based material is A 1 ppm, A 0 - 2A 1 ≥30 ppm.

[0094] In the preparation method of this embodiment, first prepare a first precursor containing a nano-silicon-based material, and then carbonize a second precursor containing the first precursor and a carbon source to obtain a negative electrode material. Among them, a fluorine-containing compound is added to all the first precursors and / or the second precursors, so that most of the fluorine elements are located in the part of the negative electrode material other than the nano-silicon-based material, so that A 0 - 2A 1 ≥30 ppm is controlled within this range, which can ensure that the content of fluorine element in the nano-silicon-based material is less than the mass content of fluorine element in the part of the negative electrode material other than the nano-silicon-based material. More fluorine elements exist in the part of the negative electrode material other than the nano-silicon-based material. Fluorine element has strong electronegativity and can be reduced at a lower reduction potential. Therefore, the fluorine element in the part of the negative electrode material other than the nano-silicon-based material can preferentially participate in the formation of the solid electrolyte interface film on the surface of the negative electrode material during charge and discharge, optimize the solid electrolyte interface film, reduce the reaction activity between the negative electrode material and the electrolyte, protect the negative electrode material, reduce the occurrence of side reactions, and thus improve the cycle performance of the negative electrode material, especially the long-cycle performance; and can avoid the formation of a solid electrolyte interface film inside the negative electrode material particles and improve the specific capacity of the material. The preparation method provided by this application is applicable to large-scale production, and the prepared negative electrode material can effectively improve the charge and discharge cycle stability of lithium batteries and effectively reduce the expansion rate of the negative electrode material.

[0095] The following specifically introduces the preparation method of this application in combination with examples:

[0096] Before step S10, the method further includes:

[0097] Perform wet pulverization treatment on the mixture of the silicon-based material and the solvent, and dry to obtain a nano-silicon-based material.

[0098] In some embodiments, the solvent includes at least one of methanol, ethanol, ethylene glycol, propanol, isopropanol, glycerol, n-butanol, isobutanol, pentanol, trifluoroethanol, and trifluoromethanol.

[0099] In some embodiments, the drying temperature is 40°C to 600°C, specifically 40°C, 50°C, 80°C, 100°C, 120°C, 250°C, 380°C, 400°C, 500°C, 580°C or 600°C, etc. The drying time is 1h to 15h, specifically 1h, 3h, 5h, 7h, 9h, 10h, 12h or 15h, etc. The drying method can be, for example, oven drying, freeze drying, stirring evaporation, spray drying, etc. The drying process in this embodiment can remove the solvent in the mixture as much as possible.

[0100] Step S10, preparing a first precursor, the first precursor comprising a nano-silicon-based material.

[0101] In some embodiments, step S10 includes: wet-crushing a mixture of silicon-based materials, fluorine-containing compounds and solvents, and drying to obtain a first precursor; wherein the mass content of the fluorine-containing compound added to the first precursor is 0.01% to 3%.

[0102] Specifically, the mass content of the fluorine-containing compound added to the first precursor can be 0.01%, 0.02%, 0.06%, 0.1%, 0.2%, 0.4%, 0.5%, 0.6%, 0.8%, 1%, 1.5%, 2%, 2.5% or 3%, etc., and of course it can also be other values ​​within the above range, which is not limited here.

[0103] In some embodiments, the nano silicon-based material includes at least one of silicon, silicon-oxygen material and silicon alloy. Silicon alloys include silicon-lithium alloys, silicon-magnesium alloys, etc. The silicon-oxygen material can be a silicon-oxygen composite with a molar ratio of silicon atoms to oxygen atoms in the range of 0.1 to 1.9. The silicon-oxygen composite can be Si and SiO 2 complex, or a compound containing a chemical formula of SiO x (0<x<2) substances can also be silicate substances. The chemical formula of silicon-oxygen materials can be SiO x , 0<x<2, silicon oxide material can be SiO, SiO 0.2 、SiO 0.5 、SiO 0.7 、SiO 0.9 、SiO 1.5 、SiO 1.6 or SiO 1.9 Etc.

[0104] In some embodiments, step S10 includes: mixing the nano-silicon-based material, the fluorine-containing compound and the solvent and removing the solvent to obtain a first precursor.

[0105] In some embodiments, the nano-silicon-based material is in the form of particles, and the average particle size of the nano-silicon-based material is from 1 nm to 500 nm. Specifically, it can be 1 nm, 5 nm, 10 nm, 15 nm, 20 nm, 30 nm, 40 nm, 50 nm, 100 nm, 200 nm, 300 nm, 400 nm or 500 nm, etc. Of course, it can also be other values within the above range, which are not limited herein. Through multiple experiments, it is found that the nano-silicon-based material has a high surface energy and is prone to agglomeration during charge and discharge. The structure of the particles is strong, which can inhibit the volume expansion of silicon. If the particle size of the silicon-based material is too small, the production process cost is high. Preferably, the median particle size of the nano-silicon-based material is 1 nm to 200 nm, more preferably 1 nm - 100 nm.

[0106] In some embodiments, the solvent includes an organic solvent; the organic solvent includes at least one of methanol, ethanol, ethylene glycol, propanol, isopropanol, glycerol, n-butanol, isobutanol, pentanol, trifluoroethanol and trifluoromethanol.

[0107] In some embodiments, the mixing treatment method includes at least one of mechanical stirring, ultrasonic dispersion, and grinding dispersion.

[0108] In some embodiments, the specific steps for preparing the first precursor include: mixing the nano-silicon-based material, the fluorine-containing compound and the solvent, and then performing a drying treatment to obtain the first precursor.

[0109] In some embodiments, the mixing treatment method includes at least one of mechanical stirring, ultrasonic dispersion, and grinding dispersion. Preferably, grinding dispersion is adopted, so that the nano-silicon-based material can be dispersed, reducing the agglomeration of the nano-silicon-based material, and the nano-silicon-based material can be dispersed into smaller nano-particles. Preferably, through wet ball milling, the wet ball milling dispersion time can be controlled within 0.5 h to 10 h. Through sufficient grinding, the components can be mixed more evenly, and the particle size of the nano-silicon-based material can reach 1 nm to 500 nm.

[0110] In some embodiments, the dried first precursor can also be dispersed. The dispersion can be grinding dispersion, and the dispersion time is 0.5 h - 9 h. Specifically, it can be 0.5 h, 1.5 h, 2.5 h, 3.5 h, 4.5 h, 5.5 h, 7.5 h or 9 h, etc. The grinding dispersion in this embodiment controls the particle size of the first precursor after dispersion.

[0111] In some embodiments, the fluorine-containing compound includes at least one of calcium fluoride, cryolite, aluminum fluoride, sodium fluoride, sodium fluorosilicate, magnesium fluoride, potassium fluoride, lithium fluoride, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium hexafluorophosphate, lithium difluorooxalate borate, fluorinated ethylene carbonate, lithium bis(difluoromethanesulfonyl)imide and lithium bis(trifluoromethylsulfonyl)imide.

[0112] In some embodiments, the mass content of the fluorine-containing compound added to the first precursor is 0.01% to 3%; specifically, it can be 0.01%, 0.02%, 0.06%, 0.1%, 0.2%, 0.4%, 0.5%, 0.6%, 0.8%, 1%, 1.5%, 2%, 2.5% or 3%, etc. Of course, it can also be other values within the above range, which are not limited herein. Preferably, the mass content of the fluorine-containing compound added to the first precursor is 0.01% to 0.09%. When the fluorine-containing compound can also be used as a lithium salt, such as lithium fluoride, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium hexafluorophosphate, lithium difluorooxalate borate, lithium bis(difluoromethanesulfonyl)imide and lithium bis(trifluoromethylsulfonyl)imide, the control range of its addition amount is based on the fluorine-containing compound.

[0113] In some embodiments, the lithium salt includes at least one of lithium hydroxide, lithium chloride, lithium carbonate, lithium fluoride, lithium oxide, lithium borohydride, lithium perchlorate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium hexafluorophosphate, lithium bis(oxalato)borate, lithium difluorooxalate borate, lithium bis(difluoromethanesulfonyl)imide and lithium bis(trifluoromethylsulfonyl)imide.

[0114] In some embodiments, the mass content of the lithium salt added to the first precursor is 0.05% to 1%, specifically, it can be 0.05%, 0.08%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.8% or 1%, etc. Of course, it can also be other values within the above range, which are not limited herein.

[0115] Step S20: Prepare a second precursor, and the second precursor includes the first precursor and a carbon source.

[0116] In some embodiments, the carbon source includes at least one of sucrose, glucose, polyethylene, polyvinyl alcohol, polyethylene glycol, polyaniline, epoxy resin, phenolic resin, furfural resin, acrylic resin, polyethylene oxide, polyvinylidene fluoride, polyacrylonitrile, polyvinyl chloride and pitch.

[0117] In some embodiments, the mass ratio of the first precursor to the carbon source is 100:(10 - 100); specifically, it can be 100:100, 100:94, 100:80, 100:75, 100:70, 100:50, 100:30, 100:20 or 100:10, etc. The mass ratio of the first precursor to the carbon source should not be too high, which will cause the capacity of the material to decrease. In addition, in some embodiments, if the ratio of non-graphitized carbon is too high, it will also cause the first efficiency of the material to decrease.

[0118] In some embodiments, the step of preparing the second precursor may specifically include: mixing the first precursor, the carbon source and the fluorine-containing compound to obtain the second precursor.

[0119] In some embodiments, the mixing method includes at least one of fusion treatment, kneading and extrusion treatment, and VC mixing.

[0120] In some embodiments, the mass content of the fluorine-containing compound added to the second precursor is 0.05% to 0.9%; specifically, it can be 0.05%, 0.1%, 0.2%, 0.5%, 0.6%, 0.7%, 0.8% or 0.9%, etc. Of course, it can also be other values within the above range, which are not limited herein.

[0121] In some embodiments, the total mass content of the fluorine-containing compound added to the second precursor and / or the first precursor is greater than the mass content of the fluorine-containing compound in the nano-silicon-based material. By controlling the addition amount of the fluorine-containing compound, it is beneficial to make the fluorine element content in the part of the negative electrode material other than the nano-silicon-based material greater than the fluorine element content contained in the nano-silicon-based material. The fluorine element content forms a concentration gradient, which can enable the fluorine element in the part of the negative electrode material other than the nano-silicon-based material to preferentially participate in the formation of the solid electrolyte interface film on the surface of the negative electrode material during charge and discharge, and optimize the solid electrolyte interface film.

[0122] In some embodiments, the second precursor further includes a lithium salt, and the mass content of the lithium salt added to the second precursor is 0.01% to 0.1%. Specifically, it can be 0.01%, 0.02%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09% or 0.1%, etc. Of course, it can also be other values within the above range, which are not limited herein. When the fluorine-containing compound can also be used as a lithium salt, such as lithium fluoride, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium hexafluorophosphate, lithium difluorooxalate borate, lithium bis(difluoromethanesulfonyl)imide and lithium bis(trifluoromethylsulfonyl)imide, the control range of its addition amount is based on the fluorine-containing compound.

[0123] In some embodiments, the mixing method is mechanical fusion, so as to improve the fracture strength of the negative electrode material particles, and then perform carbonization treatment to enhance the stability of the particle structure. At the same time, it can enhance the connection stability between the nano-silicon-based material and the carbon source and reduce the porosity. Of course, in other embodiments, other methods can also be used for mixing treatment, which are not limited herein.

[0124] In some embodiments, the fracture strength of the negative electrode material particles ≥ 300 MPa.

[0125] Step S30: Carbonize the second precursor to obtain a negative electrode material.

[0126] In some embodiments, the temperature of the carbonization treatment is 600°C to 1200°C, for example, it can be 600°C, 700°C, 800°C, 900°C, 1000°C, 1100°C, 1200°C, etc. Preferably, the temperature of the carbonization treatment is 600°C to 1000°C.

[0127] In some embodiments, the time of the carbonization treatment is 1h to 10h, for example, it can be 1h, 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h or 10h, etc.

[0128] In some embodiments, the heating rate during the carbonization treatment is 1°C / min to 30°C / min, specifically, it can be 1°C / min, 5°C / min, 10°C / min, 15°C / min, 20°C / min, 25°C / min or 30°C / min, etc. For example, preferably, the heating rate during the carbonization treatment is 1°C / min to 15°C / min.

[0129] In some embodiments, a protective gas is passed during the carbonization treatment, and the protective gas includes at least one of nitrogen, helium, neon, argon and krypton.

[0130] In some embodiments, after step S30, at least one of crushing, screening and demagnetization is also performed; preferably, after the carbonization treatment, crushing, screening and demagnetization are sequentially performed.

[0131] In some embodiments, the crushing method is any one of a mechanical crusher, a jet mill and a cryogenic crusher.

[0132] In some embodiments, the screening method is any one of a fixed screen, a rotary screen, a resonant screen, a roller screen, a vibrating screen and a chain screen, and the mesh number of the screening is ≥500 mesh. Specifically, the mesh number of the screening can be 500 mesh, 600 mesh, 700 mesh, 800 mesh, etc. Controlling the particle size of the negative electrode material within the above range is beneficial to improving the cycle performance of the negative electrode material.

[0133] In some embodiments, the demagnetization equipment is any one of a permanent magnetic drum separator, an electromagnetic iron remover and a pulsating high gradient magnetic separator. Demagnetization is to finally control the content of magnetic substances in the negative electrode material and avoid the influence of magnetic substances on the discharge effect of the lithium-ion battery and the safety of the battery during use.

[0134] In the present disclosure, the median particle size refers to the average particle size, and its physical meaning is the particle size corresponding to when the cumulative particle size distribution percentage of the particles reaches 50%, which is measured by a Malvern particle size analyzer. The Malvern particle size analyzer uses the light scattering phenomenon of particles and comprehensively calculates the particle size distribution of the measured particles based on the distribution of scattered light energy.

[0135] In some embodiments, the total mass content of fluorine element in the negative electrode material is A 0 ppm, and the value range of A 0 is 100 - 10000; the specific value of A 0 can be specifically 100, 200, 500, 1000, 2000, 5000, 8000, 9000 or 10000, etc. Of course, it can also be other values within the above range, which are not limited herein. Specifically, the total mass content of fluorine element in the negative electrode material can be measured by ion chromatography, atomic absorption spectrometry, elemental analysis or inductively coupled plasma spectrometry.

[0136] This application also provides a lithium-ion battery, including the above-mentioned negative electrode material.

[0137] The following further illustrates the embodiments of this application through multiple examples. Among them, the embodiments of this application are not limited to the following specific examples. Within the scope of the main rights unchanged, appropriate changes can be made for implementation.

[0138] Example 1

[0139] The preparation method of the negative electrode material in this example includes the following steps:

[0140] (1) Wet-crush 100μm of metallic silicon with a ball mill. The solvent is n-hexane. Based on 100% of the mass of nano-silicon, add 0.03% of lithium tetrafluoroborate for mixing. The rotation speed is 500 rpm and the time is 18 h to obtain a slurry containing nano-silicon (D 50 is 180 nm) and lithium tetrafluoroborate.

[0141] (2) Freeze-dry and granulate the slurry to obtain a first precursor;

[0142] (3) Mix the first precursor, pitch and lithium hexafluoroarsenate in a mass ratio of 100:49:0.1 to obtain a second precursor;

[0143] (4) Place the second precursor in a heat treatment furnace for carbonization treatment. The carbonization treatment temperature is 1000°C and keep it for 4 h, then pulverize and screen to obtain the negative electrode material.

[0144] The negative electrode material prepared in this example includes a carbon material and nano-silicon dispersed in the carbon material. The performance test data of the negative electrode material are shown in Table 1. Figure 2 It is the scanning electron microscope (SEM) picture of the negative electrode material prepared in Example 1 of this application.

[0145] Example 2

[0146] (1) Wet grind 20 μm of metallic silicon using a planetary ball mill with butanol as the solvent, a rotation speed of 600 rpm, and a time of 30 h to obtain a slurry containing nano-silicon (D 50 with a size of 130 nm).

[0147] (2) Based on 100% of the mass of the slurry, add 0.4% of lithium hexafluoroarsenate to the slurry for mixing, and then spray dry and granulate to obtain a first precursor;

[0148] (3) Mix the first precursor and phenolic resin in a mass ratio of 100:33 to obtain a second precursor;

[0149] (4) Place the second precursor in a heat treatment furnace for carbonization treatment at a carbonization temperature of 800 °C for 3 h, and then pulverize and screen to obtain the negative electrode material.

[0150] The negative electrode material prepared in this example includes a carbon material and nano-silicon dispersed in the carbon material. The performance test data of the negative electrode material are shown in Table 1.

[0151] Example 3

[0152] (1) Wet grind 10 μm of metallic silicon using a stirred mill with methanol as the solvent, a rotation speed of 400 rpm, and a time of 25 h to obtain a slurry containing nano-silicon (D 50 with a size of 120 nm).

[0153] (2) Based on 100% of the mass of the slurry, add 0.09% of lithium difluorooxalate borate to the slurry for mixing, and then spray dry and granulate to obtain a first precursor;

[0154] (3) Mix the first precursor, phenolic resin, and lithium difluorooxalate borate in a mass ratio of 100:33:0.08 to obtain a second precursor;

[0155] (4) Place the second precursor in a heat treatment furnace for carbonization treatment at a carbonization temperature of 800 °C for 3 h, and then pulverize and screen to obtain the negative electrode material.

[0156] The negative electrode material prepared in this example includes a carbon material and nano-silicon dispersed in the carbon material. The performance test data of the negative electrode material are shown in Table 1.

[0157] Example 4

[0158] (1) Wet grind 100 μm of metallic silicon using a sand mill with tert-butanol as the solvent, a rotation speed of 900 rpm, and a time of 33 h to obtain a slurry containing nano-silicon (D 50 with a size of 80 nm).

[0159] (2) Based on 100% of the mass of the slurry, 0.08% of lithium fluoride is added to the slurry for mixing, and then spray-dried and granulated to obtain the first precursor;

[0160] (3) The first precursor, sucrose, and lithium bis(difluoromethanesulfonyl)imide are mixed in a mass ratio of 100:88:0.1 to obtain the second precursor;

[0161] (4) The second precursor is placed in a heat treatment furnace for carbonization treatment. The carbonization treatment temperature is 780 °C and kept warm for 8 h, and then pulverized and sieved to obtain the anode material.

[0162] The anode material prepared in this example includes carbon materials and nano-silicon dispersed in the carbon materials. The performance test data of the anode material are shown in Table 1.

[0163] Example 5

[0164] (1) 40-μm metallic silicon is wet-pulverized with a sand mill. The solvent is methanol. Based on 100% of the mass of the nano-silicon, 0.06% of lithium difluoro(oxalato)borate is added for mixing. The rotation speed is 1700 rpm and the time is 28 h to obtain a slurry containing nano-silicon (D 50 is 60 nm) and lithium difluoro(oxalato)borate.

[0165] (2) Based on 100% of the mass of the slurry, 0.08% of fluoroethylene carbonate is added to the slurry for mixing, and then freeze-dried and granulated to obtain the first precursor;

[0166] (3) The first precursor and fructose are mixed in a mass ratio of 100:94 to obtain the second precursor;

[0167] (4) The second precursor is placed in a heat treatment furnace for carbonization treatment. The carbonization treatment temperature is 880 °C and kept warm for 4 h, and then pulverized and sieved to obtain the anode material.

[0168] The anode material prepared in this example includes carbon materials and nano-silicon dispersed in the carbon materials. The performance test data of the anode material are shown in Table 1.

[0169] Example 6

[0170] The difference from Example 1 is:

[0171] In step (1), 10-μm silicon oxide material (SiO) is wet-pulverized with a ball mill. The solvent is n-hexane. Based on 100% of the mass of the nano-silicon oxide material, 0.05% of magnesium fluoride is added for mixing. The rotation speed is 500 rpm and the time is 18 h to obtain a slurry containing nano-silicon oxide material (D 50 is 180 nm) and lithium tetrafluoroborate.

[0172] Example 7

[0173] Differing from Example 1:

[0174] In step (1), the 10 μm magnesium silicide alloy was wet milled using a ball mill with n-hexane as the solvent. Based on 100% of the mass of the nanoscale magnesium silicide alloy, 0.03% lithium tetrafluoroborate was added and mixed at a rotation speed of 500 rpm for 18 h to obtain a slurry containing nanoscale magnesium silicide alloy (D 50 being 180 nm) and lithium tetrafluoroborate.

[0175] Example 8

[0176] Differing from Example 1:

[0177] In step (2), based on 100% of the mass of the slurry, 0.08% fluoroethylene carbonate was added to the slurry and mixed, and then freeze-dried and granulated to obtain a first precursor.

[0178] Example 9

[0179] Differing from Example 1:

[0180] In step (3), the first precursor, pitch, and lithium carbonate were mixed in a mass ratio of 100:49:0.05 to obtain a second precursor.

[0181] Example 10

[0182] (1) The 100 μm metallic silicon was wet milled using a ball mill with trifluoroethanol as the solvent. Based on 100% of the mass of the nanoscale silicon, 1% lithium tetrafluoroborate was added and mixed at a rotation speed of 500 rpm for 18 h to obtain a slurry containing nanoscale silicon (D 50 being 180 nm) and lithium tetrafluoroborate.

[0183] (2) The slurry was freeze-dried and granulated to obtain a first precursor;

[0184] (3) The first precursor, pitch, and lithium hexafluoroarsenate were mixed in a mass ratio of 100:49:3 to obtain a second precursor;

[0185] (4) The second precursor was placed in a heat treatment furnace for carbonization treatment at a carbonization temperature of 1000 °C for 4 h, and then pulverized and sieved to obtain the negative electrode material.

[0186] The negative electrode material prepared in this example includes a carbon material and nanoscale silicon dispersed in the carbon material. The performance test data of the negative electrode material are shown in Table 1.

[0187] Comparative Example 1

[0188] The preparation method of the negative electrode material of this comparative example includes the following steps:

[0189] (1) Wet-mill 100-μm metallic silicon using a ball mill with n-hexane as the solvent, at a rotation speed of 500 rpm for 18 h to obtain a slurry containing nano-silicon (D 50 being 180 nm).

[0190] (2) Freeze-dry and granulate the slurry to obtain a first precursor;

[0191] (3) Mix the first precursor and pitch in a mass ratio of 100:49 to obtain a second precursor;

[0192] (4) Place the second precursor in a heat treatment furnace for carbonization treatment at 1000 °C for 4 h, then pulverize and screen to obtain the negative electrode material.

[0193] The negative electrode material prepared in this comparative example includes a carbon material and nano-silicon dispersed in the carbon material. The performance test data of the negative electrode material are shown in Table 1.

[0194] Comparative Example 2

[0195] The preparation method of the negative electrode material of this comparative example includes the following steps:

[0196] (1) Wet-mill 100-μm metallic silicon using a ball mill with n-hexane as the solvent. Based on 100% of the mass of nano-silicon, add 0.03% of lithium tetrafluoroborate for mixing, at a rotation speed of 500 rpm for 18 h to obtain a slurry containing nano-silicon (D 50 being 180 nm) and lithium tetrafluoroborate.

[0197] (2) Freeze-dry and granulate the slurry to obtain a first precursor;

[0198] (3) Mix the first precursor and pitch in a mass ratio of 100:49 to obtain a second precursor;

[0199] (4) Place the second precursor in a heat treatment furnace for carbonization treatment at 1000 °C for 4 h, then pulverize and screen to obtain the negative electrode material.

[0200] The negative electrode material prepared in this comparative example includes a carbon material and nano-silicon dispersed in the carbon material. The performance test data of the negative electrode material are shown in Table 1.

[0201] Comparative Example 3

[0202] The preparation method of the negative electrode material of this comparative example includes the following steps:

[0203] (1) Wet-mill 100 μm of metallic silicon using a ball mill with n-hexane as the solvent. Add 0.02% of lithium tetrafluoroborate based on the mass of the nano-silicon and mix at a rotation speed of 500 rpm for 18 h to obtain a slurry containing nano-silicon (D50 is 180 nm) and lithium tetrafluoroborate.

[0204] (2) Freeze-dry and granulate the slurry to obtain the first precursor.

[0205] (3) Mix the first precursor, asphalt, and lithium difluoro(oxalato)borate in a mass ratio of 100:39:0.02 to obtain the second precursor.

[0206] (4) Place the second precursor in a heat treatment furnace for carbonization treatment at 1000 °C for 4 h, then pulverize and screen to obtain the anode material.

[0207] The anode material prepared in this comparative example includes carbon materials and nano-silicon dispersed in the carbon materials. The performance test data of the anode material are shown in Table 1.

[0208] Test method

[0209] (1) Test for the mass content of fluorine element in the anode material:

[0210] Take 10 g of the anode material and measure the total mass content of fluorine element in the anode material as A ppm by ion chromatography, atomic absorption spectrometry, elemental analysis, or inductively coupled plasma spectrometry. 0 ppm;

[0211] Then soak the anode material in a sodium hydroxide solution with a concentration of 8 mol / L until the silicon-based material is removed. The remaining material is washed and dried with deionized water to obtain a composite after removing the silicon-based material. Measure the mass content of fluorine element in the composite after removing the silicon-based material as A ppm by ion chromatography, atomic absorption spectrometry, elemental analysis, or inductively coupled plasma spectrometry. 2 ppm;

[0212] After calculation, in the anode material, the mass content of fluorine element contained in the nano-silicon-based material is A ppm, A = A - A, then A - A = A - A - A = A - 2A; 1 ppm, A 2 = A 0 - A 1 , then A 2 - A 1 = A 0 - A 1 - A 1 = A 0 - 2A 1 ;

[0213] Measure 5 times using the above-mentioned scheme, and take the average value of the mass content of fluorine elements contained in the nano-silicon-based material. (2) Test method for the median particle size of the negative electrode material:

[0214] The particle size test method refers to GB / T 19077-2016. The median particle size, that is, the average particle size, of the negative electrode material is measured by using a Mastersizer 3000 laser particle size analyzer.

[0215] (3) Test for the damage resistance strength of the negative electrode material particles:

[0216] Extrude the negative electrode material to test the damage strength of a single particle. Test ≥50 negative electrode material particles, and take the average value as the damage resistance strength of the particles.

[0217] (4) Test method for the specific surface area of the negative electrode material:

[0218] Use a Micromeritics Tristar 3020 specific surface area and pore size analyzer to test the specific surface area of the negative electrode material. Weigh a certain mass of powder, perform complete degassing under vacuum heating to remove surface adsorbates, and then use the nitrogen adsorption method. Calculate the specific surface area of the particles through the amount of adsorbed nitrogen.

[0219] (5) Test method for the coating layer thickness of the negative electrode material:

[0220] Use a focused ion beam microscope (FIB-SEM) device to cut the material into sections, and measure the average thickness of the coating layer in the scanning electron microscope image.

[0221] (6) Test for the mass content of carbon material in the negative electrode material:

[0222] The negative electrode material sample is heated and burned at high temperature by a high-frequency furnace under oxygen-rich conditions to oxidize carbon into carbon dioxide. This gas is processed and then enters the corresponding absorption cell to absorb the corresponding infrared radiation and is then converted into a corresponding signal by a detector. This signal is sampled by a computer, linearly corrected, and then converted into a value proportional to the carbon dioxide concentration. Then, the values obtained throughout the analysis process are accumulated. After the analysis is completed, this accumulated value is divided by the weight value in the computer, multiplied by the correction factor, and the blank is deducted to obtain the mass percentage content of carbon material in the sample. Use a high-frequency infrared carbon and sulfur analyzer (model: Shanghai Dekai HCS-140) to test the sample.

[0223] (7) Electrochemical test:

[0224] The following method was used to test the electrochemical cycling performance: The prepared anode material, conductive agent, and binder were dissolved in deionized water and mixed according to a mass percentage of 94:1:5, and the solid content was controlled at 50%. It was coated on a copper foil current collector, vacuum dried, and an anode electrode sheet was obtained. Then, a layered lithium nickel cobalt manganese oxide (abbreviated as NCM) ternary cathode electrode sheet prepared by a traditional and mature process, a 1 mol / L LiPF 6 / ethylene carbonate + dimethyl carbonate + methyl ethyl carbonate (v / v = 1:1:1) electrolyte, a Celgard 2400 separator, and the outer shell were assembled using a conventional production process to obtain a lithium-ion button battery. The initial thickness of the electrode sheet of the lithium-ion battery was measured using a micrometer as H0. The charge-discharge test of the lithium-ion battery was carried out on a LAND battery test system of Wuhan Jinnuo Electronics Co., Ltd. Under normal temperature conditions, a constant current charge-discharge at 0.2C was carried out, and the charge-discharge voltage was limited to 2.75 - 4.2V to obtain the first reversible capacity, the first charge capacity, and the first discharge capacity. The first Coulombic efficiency = the first discharge capacity / the first charge capacity.

[0225] It was cycled 50 times repeatedly, and the thickness of the electrode sheet of the lithium-ion battery at this time was measured using a micrometer as H1. After 50 cycles, the swelling rate = (H1 - H0) / H0 × 100%.

[0226] It was cycled 100 times repeatedly, and the discharge capacity was recorded as the remaining capacity of the lithium-ion battery; the capacity retention rate = the remaining capacity / the initial capacity * 100%.

[0227] The results of the above performance tests are as follows:

[0228] Table 1. Comparison results of anode material performance

[0229]

[0230]

[0231] Figure 3 This is the X-ray diffraction pattern of the anode material prepared in Example 1 of this application; as Figure 3 shown, the X-ray diffraction pattern of the anode material has silicon characteristic peaks. Figure 4 This is the first charge-discharge curve of the anode material prepared in Example 1 of this application; as Figure 4 shown, the first charge-discharge capacity of the anode material is relatively high, and the first Coulombic efficiency can also reach 88.1%. Figure 5 This is the cycling performance curve of the anode material prepared in Example 1 of this application; as Figure 5 shown, the anode material has excellent cycling performance, and the capacity retention rate after 300 cycles is 90.5%. Figure 6 This is the detection photo of the scanning transmission electron microscope (STEM-EDX) of the anode material prepared in Example 1 of this application, asFigure 6 As shown, fluorine elements are mainly distributed in the carbon material on the surface of nano-silicon, specifically Figure 6 the fluorine elements represented by ① to ⑥ in [reference]. The fluorine elements in the carbon material preferentially participate in the formation of the solid electrolyte membrane to optimize the solid electrolyte membrane.

[0232] According to the test data of Examples 1 to 10, more fluorine elements exist in the part of the negative electrode material other than the nano-silicon-based material. Fluorine elements have strong electronegativity and can be reduced at a relatively low reduction potential. Therefore, the fluorine elements in the part of the negative electrode material other than the nano-silicon-based material can participate in the formation of the solid electrolyte membrane during the charge and discharge process, optimize the solid electrolyte membrane, reduce the reaction activity between the negative electrode material and the electrolyte, protect the negative electrode material, reduce the occurrence of side reactions, and thus improve the cycle performance of the negative electrode material. And according to the test data of Examples 1 to 5, A 0 -2 A 1 The greater the difference, the more fluorine elements are present in the part of the negative electrode material other than the nano-silicon-based material, which is more conducive to the formation of the solid electrolyte membrane on the surface of the negative electrode material particles, and the cycle retention rate of the negative electrode material is further optimized.

[0233] In Comparative Example 1, during the preparation of the negative electrode material, no fluorine-containing compound was added. Trace amounts of fluorine mainly originated from the small amount of fluorine doped in the pitch. The total content of fluorine elements in the prepared negative electrode material was insufficient, and there was not enough fluorine element to participate in the formation of the solid electrolyte membrane. The side reaction between the negative electrode material and the electrolyte increased, and the cycle retention rate of the material decreased significantly.

[0234] In Comparative Example 2, during the preparation of the negative electrode material, the amount of the added fluorine-containing compound was insufficient. The total content of fluorine elements in the prepared negative electrode material was insufficient, and most of the fluorine elements were distributed on the surface of the nano-silicon. There was not enough fluorine element on the surface of the negative electrode material to participate in the formation of the solid electrolyte membrane. The side reaction between the negative electrode material and the electrolyte increased, and the cycle retention rate of the material decreased significantly.

[0235] In Comparative Example 3, during the preparation of the negative electrode material, the amount of the fluorine-containing compound added during the preparation of the nano-silicon-based material was greater than the amount of the fluorine-containing compound added during the preparation of the second precursor, resulting in the fluorine element content in the final product nano-silicon being relatively close to the fluorine element content in the carbon material. There was no formation of a fluorine element content gradient difference. There was not enough fluorine element on the surface of the negative electrode material to participate in the formation of the solid electrolyte membrane. The side reaction between the negative electrode material and the electrolyte increased, and the cycle retention rate of the material decreased compared to Example 1.

[0236] Although this application is disclosed above with preferred embodiments, it is not used to limit the claims. Any person skilled in the art can make several possible changes and modifications without departing from the concept of this application. Therefore, the protection scope of this application should be determined by the scope defined by the claims of this application.

Claims

1. A negative electrode material, characterized in that: The negative electrode material includes a carbon material and a nano-silicon-based material dispersed in the carbon material, and the negative electrode material contains fluorine element, and the total mass content of the fluorine element in the negative electrode material is A0 ppm; In the negative electrode material, the mass content of the fluorine element contained in the nano silicon-based material is A1 ppm, A0-2A1≥30ppm.

2. The negative electrode material according to claim 1, characterized in that The negative electrode material meets at least one of the following characteristics: (1) The total mass content of the fluorine element in the negative electrode material is A0 ppm, and the value range of A0 is 100 to 10000; (2) The average particle size D of the nano-silicon-based material 50 1nm~500nm; (3) The mass content of the nano-silicon-based material in the negative electrode material is 10% to 80%; (4) The nano-silicon-based material includes at least one of silicon, silicon alloy and silicon-oxygen material; (5) The mass content of the carbon material in the negative electrode material is 10% to 50%; (6) The carbon material includes at least one of hard carbon and soft carbon; (7) The destructive strength of the negative electrode material particles is ≥300 MPa.

3. The negative electrode material according to claim 1 or 2, characterized in that: The negative electrode material further includes a coating layer present on at least a portion of the surface of the nano-silicon-based material.

4. The negative electrode material according to claim 3, characterized in that The negative electrode material meets at least one of the following characteristics: (1) The coating layer comprises amorphous carbon; (2) The coating layer includes amorphous carbon and lithium salt dispersed in the amorphous carbon; (3) The coating layer includes a lithium salt, and the lithium salt includes at least one of lithium hydroxide, lithium chloride, lithium carbonate, lithium fluoride, lithium oxide, lithium borohydride, lithium perchlorate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium hexafluorophosphate, lithium bis(oxalatoborate), lithium difluorooxalatoborate, lithium bis(difluorosulfonylimide) and lithium bis(trifluoromethylsulfonylimide); (4) The coating layer has a thickness of 1 nm to 3000 nm; (5) The median particle size of the negative electrode material is 0.5 μm to 30 μm; (6) The specific surface area of ​​the negative electrode material is ≤5m 2 / g.

5. A method for preparing a negative electrode material, characterized in that: The method comprises the following steps: preparing a first precursor, wherein the first precursor comprises a nano-silicon-based material; preparing a second precursor, wherein the second precursor comprises the first precursor and a carbon source; Carrying out carbonization of the second precursor to obtain a negative electrode material; Wherein, the first precursor and / or the second precursor comprises a fluorine-containing compound, the negative electrode material contains fluorine element, and the total mass content of the fluorine element in the negative electrode material is A0 ppm; in the negative electrode material, the mass content of the fluorine element contained in the nano-silicon-based material is A1 ppm, A0-2 A1≥30ppm.

6. The preparation method according to claim 5, characterized in that: The method satisfies at least one of the following characteristics: (1) The fluorine-containing compound includes at least one of calcium fluoride, cryolite, aluminum fluoride, sodium fluoride, sodium fluorosilicate, magnesium fluoride, potassium fluoride, lithium fluoride, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium hexafluorophosphate, lithium difluorooxalatoborate, fluoroethylene carbonate, lithium bis(difluorosulfonyl)imide and lithium bis(trifluoromethylsulfonyl)imide; (2) at least one of the first precursor, the second precursor and the nano-silicon-based material includes a lithium salt; (3) at least one of the first precursor, the second precursor and the nano-silicon-based material comprises a lithium salt, and the lithium salt comprises at least one of lithium hydroxide, lithium chloride, lithium carbonate, lithium fluoride, lithium oxide, lithium borohydride, lithium perchlorate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium hexafluorophosphate, lithium bis(oxalatoborate), lithium difluorooxalatoborate, lithium bis(difluorosulfonylimide) and lithium bis(trifluoromethylsulfonylimide); (4) The average particle size D of the nano-silicon-based material 50 It is 1nm~500nm.

7. The preparation method according to claim 6, characterized in that: The method satisfies at least one of the following characteristics: (1) Before preparing the first precursor, the method further comprises: subjecting a mixture of the silicon-based material and the solvent to wet pulverization treatment, and drying to obtain a nano silicon-based material; (2) The step of preparing the first precursor comprises: subjecting a mixture of a silicon-based material, a fluorine-containing compound and a solvent to a wet pulverization process, and drying to obtain the first precursor; (3) The step of preparing the first precursor comprises: subjecting a mixture of a silicon-based material, a fluorine-containing compound and a solvent to wet pulverization treatment, and drying to obtain the first precursor; wherein the mass content of the fluorine-containing compound added to the first precursor is 0.01% to 3%; (4) The step of preparing the first precursor includes: mixing the nano-silicon-based material, the fluorine-containing compound and the solvent and removing the solvent to obtain the first precursor; (5) The step of preparing the first precursor comprises: mixing a nano-silicon-based material, a fluorine-containing compound and a solvent and removing the solvent to obtain the first precursor; wherein the nano-silicon-based material comprises at least one of silicon element, silicon alloy and silicon-oxygen material; (6) The solvent includes an organic solvent; (7) The organic solvent comprises at least one of methanol, ethanol, ethylene glycol, propanol, isopropanol, glycerol, n-butanol, isobutanol, amyl alcohol, trifluoroethanol and trifluoromethanol; (8) The mixing treatment method includes at least one of mechanical stirring, ultrasonic dispersion, and grinding dispersion; (9) The step of preparing the first precursor comprises: mixing the nano-silicon-based material, the fluorine-containing compound and the solvent, and drying the mixture to obtain the first precursor; (10) The drying temperature is 40°C to 600°C; (11) The drying time is 1 hour to 15 hours; (12) The drying method includes at least one of spray drying and freeze drying; (13) The mass content of the lithium salt added to the first precursor is 0.05% to 1%.

8. The preparation method according to claim 6, characterized in that: The method satisfies at least one of the following characteristics: (1) preparing a second precursor, comprising: mixing the first precursor, a carbon source and a fluorine-containing compound to obtain a second precursor; (2) The mass ratio of the first precursor to the carbon source is 100:(10-100); (3) The carbon source includes at least one of sucrose, glucose, polyethylene, polyvinyl alcohol, polyethylene glycol, polyaniline, epoxy resin, phenolic resin, furfural resin, acrylic resin, polyethylene oxide, polyvinylidene fluoride, polyacrylonitrile, polyvinyl chloride and asphalt; (4) The mass content of the fluorine-containing compound added to the second precursor is 0.05% to 3%; (5) The mass content of the lithium salt added to the second precursor is 0.01% to 0.1%.

9. The preparation method according to claim 5, characterized in that: The method satisfies at least one of the following characteristics: (1) The temperature of the carbonization treatment is 600° C. to 1200° C.; (2) The carbonization treatment time is 1 hour to 10 hours; (3) The heating rate of the carbonization treatment is 1°C / min to 30°C / min; (4) The carbonization process is passed through a protective gas, and the protective gas includes at least one of nitrogen, helium, neon, argon and krypton.

10. A lithium ion battery, characterized in that: The lithium ion battery comprises the negative electrode material according to any one of claims 1 to 4 or the negative electrode material prepared by the preparation method according to any one of claims 5 to 9.

Images