Negative electrode material and preparation method therefor, and lithium-ion battery

Abstract

A negative electrode material and a preparation method therefor, and a lithium-ion battery. The negative electrode material comprises an inner core and a composite layer, which is located on at least part of the surface of the inner core, wherein the inner core comprises graphite, and the composite layer comprises a carbonaceous material and a non-carbonaceous material. As for the negative electrode material, by means of a synergistic effect of the carbonaceous material and the non-carbonaceous material in the composite layer, the specific surface value of the negative electrode material can be reduced, the interface stability of the negative electrode material can be enhanced, the wettability of an electrolyte solution can be improved, an interface side reaction can be reduced, and the lithium ion transport efficiency can be improved, thereby improving the electrochemical performance of the negative electrode material.

Description

Negative electrode material and preparation method thereof, and lithium ion battery

[0001] This application claims priority to the Chinese patent application filed with the State Intellectual Property Office on September 27, 2023, with application number 202311279012.8 and invention name “Negative electrode material and preparation method thereof, lithium-ion battery”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application relates to the technical field of negative electrode materials, and more specifically, to negative electrode materials and preparation methods thereof, and lithium-ion batteries. Background Art

[0003] Lithium-ion batteries have been widely used in portable electronic devices, electric vehicles, drones and other fields due to their advantages such as high energy density, long cycle life, low environmental pollution and no memory effect. In recent years, with the further enrichment of lithium-ion battery application scenarios, the demand for their performance has also increased. The performance indicators of lithium-ion batteries are closely related to the electrode materials, so it is very necessary to further improve the performance of lithium-ion battery negative electrode materials. Graphite materials have been widely used in the field of lithium-ion battery negative electrode materials, but traditional graphite materials still have shortcomings such as poor compatibility with electrolytes and unstable solid electrolyte interface films (SEI), resulting in low initial Coulombic efficiency of the material, poor kinetic transport and continuous attenuation of cycle capacity. Studies have found that the electrochemical properties of graphite materials can be improved by using various modifiers to coat and composite the surface of graphite.

[0004] Currently, coating layers are mainly divided into two categories: carbonaceous materials and non-carbonaceous materials. Carbonaceous material coating often uses asphalt or resin as the coating precursor. Through solid-phase or liquid-phase mixing and high-temperature carbonization treatment, the precursor is converted into soft carbon or hard carbon material and composited on the graphite particles. This can reduce the specific surface area value of the graphite material and improve electrolyte compatibility. However, the product after asphalt or resin carbonization is still essentially a carbon material. At low potentials, it will still undergo irreversible reactions with electrolyte components, causing the graphite material interface layer to continuously decompose and repair and reorganize, resulting in continuous battery capacity decay.

[0005] Therefore, how to enhance the interfacial stability of negative electrode materials and reduce interfacial side reactions is one of the technical problems that still needs to be solved.

[0006] Application Contents

[0007] The purpose of the present application is to provide a negative electrode material and a preparation method thereof, and a lithium-ion battery. The negative electrode material of the present application can reduce the specific surface area value of the negative electrode material, enhance the interface stability of the negative electrode material, improve the electrolyte wettability, reduce interfacial side reactions, and improve the lithium ion transmission efficiency, thereby improving the electrochemical performance of the negative electrode material through the synergistic effect of the carbonaceous material and the non-carbonaceous material in the composite layer.

[0008] In a first aspect, the present application provides a negative electrode material, comprising a core and a composite layer located on at least a portion of the surface of the core, wherein the core comprises graphite, and the composite layer comprises a carbonaceous material and a non-carbonaceous material.

[0009] In some embodiments, the non-carbonaceous material is dispersed in the carbonaceous material.

[0010] In some embodiments, the non-carbonaceous material has the general chemical formula A x B y , wherein 1≤x≤3, 1≤y≤5, element A includes at least one of Li, Na, K, Ca, Mg, Al, Zn, Ti, Nb, Zr, Mo, P, Si and B, and element B includes at least one of B, O, F, Si, P, S, Br and Cl.

[0011] In some embodiments, the graphite includes at least one of natural graphite, artificial graphite, and microcrystalline graphite.

[0012] In some embodiments, the inner core has a median particle size D50, 0.5 μm ≤ D50 ≤ 30 μm.

[0013] In some embodiments, the mass content of carbon in the graphite is ≥80%.

[0014] In some embodiments, the carbonaceous material includes at least one of amorphous carbon and graphitic carbon.

[0015] In some embodiments, the composite layer has a thickness of 1 nm to 200 nm.

[0016] In some embodiments, the non-carbonaceous material includes at least one of LiF, NaF, MgF2, MgO, P2O5, Al2O3, SiO2, and B2O3.

[0017] In some embodiments, the average particle size of the non-carbonaceous material is G, and G is ≤ 150 nm.

[0018] In some embodiments, a mass ratio of the composite layer to the core is C, and 0.01≤C≤0.5.

[0019] In some embodiments, the mass ratio of the carbonaceous material to the non-carbonaceous material is D, and 0.1≤D≤80.

[0020] In some embodiments, the powder conductivity of the core is E1, the powder conductivity of the negative electrode material is E2, the ratio of E2 to E1 is E, and 1<E<1000.

[0021] In some embodiments, the specific surface area of ​​the core is 6 m 2 / g~15m 2 / g.

[0022] In some embodiments, the specific surface area of ​​the negative electrode material is 1 m 2 / g~5m 2 / g.

[0023] In a second aspect, the present application provides a method for preparing a negative electrode material, comprising the following steps:

[0024] preparing a first precursor, the first precursor comprising a core and a polymer layer formed on a surface of the core, wherein the core comprises graphite;

[0025] attaching an inorganic salt on the surface of the first precursor to obtain a second precursor; and

[0026] The second precursor is carbonized to obtain a negative electrode material.

[0027] In some embodiments, the preparation of the first precursor includes the following steps: subjecting a first mixed solution containing graphite and an organic molecular monomer to a polymerization reaction, solid-liquid separation, and drying to obtain the first precursor.

[0028] In some embodiments, attaching an inorganic salt on the surface of the first precursor to obtain a second precursor includes the following steps: drying a second mixed solution containing the first precursor and the inorganic salt to obtain the second precursor.

[0029] In some embodiments, the graphite includes at least one of natural graphite, artificial graphite, and microcrystalline graphite.

[0030] In some embodiments, the graphite has a median particle size of 0.5 μm to 30 μm.

[0031] In some embodiments, the mass ratio of the graphite to the organic molecular monomer is 1:(0.01-0.4).

[0032] In some embodiments, the organic molecular monomer includes at least one of aniline, styrene, fluorostyrene, hydroxyethyl acrylate, acrylate, pyrrole, vinylidene fluoride, tetrafluoroethylene, and dopamine.

[0033] In some embodiments, the first mixed solution and the second mixed solution both include a solvent, and the solvent includes at least one of water, methanol, ethanol, acetone, nitrogen-methyl pyrrolidone, and N,N-dimethylformamide.

[0034] In some embodiments, the first mixed solution further includes an auxiliary agent.

[0035] In some embodiments, the first mixed solution further includes an auxiliary agent, and the mass concentration of the auxiliary agent in the first mixed solution is 0.01 mol / L to 4 mol / L.

[0036] In some embodiments, the first mixed solution further includes an auxiliary agent, the auxiliary agent includes an initiator, and the initiator includes at least one of ammonium persulfate, sodium persulfate, potassium persulfate, aluminum chloride and hydrogen peroxide.

[0037] In some embodiments, the first mixed solution further includes an auxiliary agent, the auxiliary agent includes a catalyst, and the catalyst includes at least one of sodium hydroxide, lithium hydroxide, potassium hydroxide, ammonia water, and sodium carbonate.

[0038] In some embodiments, the first mixed solution further includes an auxiliary agent, wherein the auxiliary agent includes a pH adjuster, and the pH adjuster includes at least one of an acidic pH reagent and an alkaline pH reagent.

[0039] In some embodiments, the first mixed solution further includes an auxiliary agent, the auxiliary agent includes a pH adjuster, and the pH of the first mixed solution is 4-10.

[0040] In some embodiments, the first mixed solution further includes an auxiliary agent, wherein the auxiliary agent includes a pH adjuster, and the pH adjuster includes at least one of hydrochloric acid, sulfuric acid, phosphoric acid, and nitric acid.

[0041] In some embodiments, the first mixed solution further includes an auxiliary agent, the auxiliary agent includes a pH adjuster, and the pH adjuster includes at least one of lithium hydroxide, sodium hydroxide, potassium hydroxide, sodium carbonate, and sodium bicarbonate.

[0042] In some embodiments, the polymerization reaction temperature is 40°C to 100°C.

[0043] In some embodiments, the polymerization reaction time is 3 hours to 48 hours.

[0044] In some embodiments, the polymerization reaction is carried out under stirring.

[0045] In some embodiments, the polymerization reaction is carried out under stirring at a stirring rate of 50 r / min to 1000 r / min.

[0046] In some embodiments, the solid-liquid separation comprises at least one of filtration and centrifugation.

[0047] In some embodiments, the drying comprises at least one of natural volatilization, forced air drying, flash drying, freeze drying, inert atmosphere protection drying, and vacuum drying.

[0048] In some embodiments, the inorganic salt includes at least one of lithium hydroxide, sodium hydroxide, potassium hydroxide, magnesium nitrate, calcium chloride, aluminum nitrate, zinc nitrate, titanium n-propoxide, niobium oxalate, zirconium oxychloride, ammonium molybdate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, sodium metasilicate, sodium borate, ammonium fluoride, titanium oxysulfide, zinc bromide and zirconium chloride.

[0049] In some embodiments, the mass ratio of the first precursor to the inorganic salt is 1:(0.001-0.1).

[0050] In some embodiments, the drying comprises at least one of natural volatilization, forced air drying, flash drying, freeze drying, inert atmosphere drying, and vacuum drying.

[0051] In some embodiments, the drying temperature is 60°C to 600°C.

[0052] In some embodiments, the drying time is 0.5 h to 48 h.

[0053] In some embodiments, the carbonization treatment is performed under a protective atmosphere.

[0054] In some embodiments, the carbonization treatment is performed under a protective atmosphere, and the protective atmosphere includes at least one of nitrogen, helium, neon, argon, and air.

[0055] In some embodiments, the heating rate of the carbonization treatment is 1° C. / min to 20° C. / min.

[0056] In some embodiments, the carbonization treatment is carried out at a holding temperature of 600°C to 2500°C.

[0057] In some embodiments, the carbonization treatment is carried out for a holding time of 0.1 h to 10 h.

[0058] In a third aspect, the present application provides a lithium-ion battery, comprising the negative electrode material described in the first aspect or the negative electrode material prepared by the method for preparing the negative electrode material described in the second aspect.

[0059] Compared with the prior art, the technical solution of this application has at least the following beneficial effects:

[0060] In the negative electrode material provided in the present application, the negative electrode material includes a core and a composite layer located on at least part of the surface of the core, the core includes graphite, and the composite layer includes carbonaceous material and non-carbonaceous material. Through the synergistic effect of the carbonaceous material and the non-carbonaceous material in the composite layer, the specific surface area of ​​the negative electrode material can be reduced, and the high-temperature storage performance and electrode processing performance of the negative electrode material can be improved; it can also improve the interface stability of the negative electrode material, reduce interface side reactions, enhance electrolyte wettability, improve lithium ion transmission efficiency, and improve the reversible capacity, initial efficiency and rate performance of the negative electrode material.

[0061] In the preparation method of the negative electrode material provided in the present application, a first precursor is obtained by subjecting a first mixed solution containing a graphite material and an organic molecular monomer to a polymerization reaction, so that a polymer formed by the polymerization of the organic molecular monomer is composited on the surface of the graphite particles to form a polymer layer, and the polymer has a highly reactive functional group. Then, a second mixed solution containing the first precursor and an inorganic salt is fully mixed and dried, and the inorganic salt in the second mixed solution is hydrolyzed to form inorganic ions. The inorganic ions are grafted and introduced into the polymer layer on the surface of the graphite particles by utilizing the grafting reaction between the highly reactive functional groups in the polymer and the inorganic ions to obtain a second precursor. Finally, the second precursor is carbonized. After the carbonization treatment, the organic molecules in the polymer layer are in situ cracked into carbonaceous materials, and the inorganic ions are in situ converted into non-carbonaceous materials, thereby forming a composite layer containing carbonaceous materials and non-carbonaceous materials on the surface of the graphite particles. The surface of the prepared negative electrode material has a uniformly coated composite layer. Through the synergistic effect of the carbonaceous material and the non-carbonaceous material in the composite layer, the specific surface area of ​​the negative electrode material can be reduced, and the high-temperature storage performance and electrode processing performance of the negative electrode material can be improved; it can also improve the interface stability of the negative electrode material, reduce interface side reactions, enhance the electrolyte wettability, improve the lithium ion transmission efficiency, and enhance the reversible capacity, initial efficiency and rate performance of the negative electrode material. BRIEF DESCRIPTION OF THE DRAWINGS

[0062] The present application is further described below with reference to the accompanying drawings and examples.

[0063] FIG1 is a flow chart of a preparation process of a negative electrode material provided in an embodiment of the present application;

[0064] FIG2 is a schematic diagram of the structure of the negative electrode material provided in an embodiment of the present application;

[0065] FIG3a is a scanning electron microscope image of the negative electrode material prepared in Example 1 of the present application;

[0066] FIG3 b is a scanning electron microscope image of the negative electrode material prepared in Example 1 of the present application at another magnification;

[0067] FIG4 is a scanning electron microscope image of a cross-section of the negative electrode material prepared in Example 1 of the present application. DETAILED DESCRIPTION

[0068] In order to better understand the technical solution of the present application, the embodiments of the present application are described in detail below with reference to the accompanying drawings.

[0069] It should be clear that the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0070] The terms used in the embodiments of the present application are only for the purpose of describing specific embodiments and are not intended to limit the present application. The singular forms "a", "an", "the" and "the" used in the embodiments of the present application and the appended claims are also intended to include plural forms unless the context clearly indicates otherwise.

[0071] It should be understood that the term "and / or" as used herein is merely a description of the relationship between associated objects, indicating that three possible relationships exist. For example, "A and / or B" can represent: A exists alone, A and B exist simultaneously, or B exists alone. Furthermore, the character " / " in this document generally indicates that the associated objects are in an "or" relationship.

[0072] In a first aspect, the present application provides a negative electrode material, as shown in FIG2 , the negative electrode material comprises a core and a composite layer located on at least a portion of the surface of the core, the core comprises graphite, and the composite layer comprises a carbonaceous material and a non-carbonaceous material.

[0073] In the negative electrode material provided in the present application, the negative electrode material includes a core and a composite layer located on at least part of the surface of the core, the core includes graphite, and the composite layer includes carbonaceous material and non-carbonaceous material. Through the synergistic effect of the carbonaceous material and the non-carbonaceous material in the composite layer, the specific surface area of ​​the negative electrode material can be reduced, and the high-temperature storage performance and electrode processing performance of the negative electrode material can be improved; it can also improve the interface stability of the negative electrode material, reduce interface side reactions, enhance electrolyte wettability, improve lithium ion transmission efficiency, and improve the reversible capacity, initial efficiency and rate performance of the negative electrode material.

[0074] In some embodiments, the graphite includes at least one of natural graphite, artificial graphite, and microcrystalline graphite.

[0075] In some embodiments, the median particle size of the inner core is D50, 0.5 μm ≤ D50 ≤ 30 μm, specifically 0.5 μm, 1 μm, 3.5 μm, 5 μm, 8 μm, 10 μm, 12 μm, 15 μm, 18 μm, 19.7 μm, 21.3 μm, 24.5 μm, 26.1 μm, 28.4 μm, 29 μm or 30 μm, etc., of course, it can also be other values ​​within the above range, which is not limited here.

[0076] In some embodiments, the mass content of carbon element in the graphite is ≥80%, specifically 80%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 98% or 99%, etc., and of course it can also be other values ​​within the above range, which is not limited here.

[0077] In some embodiments, the carbonaceous material includes at least one of amorphous carbon and graphite carbon. Specifically, the amorphous carbon includes soft carbon and hard carbon. In some embodiments, the thickness of the composite layer is 1nm to 200nm. Specifically, the thickness of the composite layer can be 1nm, 2nm, 5nm, 10nm, 15nm, 30nm, 50nm, 80nm, 100nm, 110nm, 150nm, 180nm or 200nm, etc., which are not limited here. When the composite layer is thin, it is difficult for the carbonaceous material and the non-carbonaceous material to form a uniform wrapping effect on the surface of the graphite material, resulting in a higher specific surface area of ​​the negative electrode material. When the composite layer is too thick, the interfacial lithium ion transmission efficiency of the negative electrode material is reduced, resulting in a deterioration in the rate performance of the negative electrode material. Therefore, optimizing and controlling the thickness of the composite layer within the range of 1nm to 200nm can reduce the specific surface area of ​​the negative electrode material, improve the high-temperature storage performance and electrode processing performance of the negative electrode material, and at the same time improve the interfacial lithium ion transmission efficiency of the negative electrode material, and improve the first efficiency and rate performance of the negative electrode material.

[0078] In some embodiments, the non-carbonaceous material has the general chemical formula A x B y , wherein 1≤x≤3, 1≤y≤5, element A includes at least one of Li, Na, K, Ca, Mg, Al, Zn, Ti, Nb, Zr, Mo, P, Si and B, and element B includes at least one of B, O, F, Si, P, S, Br and Cl.

[0079] In some embodiments, the A element includes at least one of Li, Na, Mg, Al, P, Si, and B; and the B element is O or F.

[0080] In some embodiments, the non-carbonaceous material is at least one of LiF, NaF, MgF2, MgO, P2O5, Al2O3, SiO2, and B2O3.

[0081] In some embodiments, the non-carbonaceous material is dispersed in the carbonaceous material. It is understood that since the carbonaceous material is formed by carbonization of organic matter, before the organic matter is carbonized, the non-carbonaceous material can attach to the surface or interior of the organic matter in ionic form, achieving uniform compounding and forming a composite layer composed of cross-linked and interspersed non-carbonaceous material and carbonaceous material.

[0082] In some embodiments, the average particle size of the non-carbonaceous material is G, and G≤150nm, specifically 0.5nm, 1nm, 1.5nm, 3.6nm, 4.8nm, 7nm, 8.9nm, 10nm, 11.2nm, 15nm, 20nm, 30nm, 50nm, 80nm, 100nm, 120nm, 140nm or 150nm, etc., but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable. When the average particle size of the non-carbonaceous material in the composite layer is too large, the non-carbonaceous material is difficult to be evenly distributed in the carbonaceous material, resulting in a high specific surface area of ​​the negative electrode material and poor interfacial lithium ion transport performance.

[0083] In this application, an S-4800 scanning electron microscope was used to observe the microscopic morphology of the surface of the negative electrode material and the particle size of the non-carbonaceous material. A 1 μm*1 μm area was randomly selected on a single negative electrode material particle, the particle size distribution of the non-carbonaceous material in the area was statistically analyzed, and the average particle size of the non-carbonaceous material was calculated as G.

[0084] In some embodiments, the mass ratio of the composite layer to the core is C, and 0.01≤C≤0.5. The value of C can specifically be 0.01, 0.03, 0.07, 0.09, 0.1, 0.17, 0.25, 0.3, 0.35, 0.4, 0.42, 0.48 or 0.5, etc., and is not limited here. When the C value is low, the composite layer content in the negative electrode material is small, and it is difficult to form a complete and uniform coating layer on the surface of the core, resulting in a larger specific surface area of ​​the negative electrode material. When the C value is high, the composite layer content in the negative electrode material is large, and the coating layer formed on the surface of the core is thicker, resulting in poor kinetic performance of the negative electrode material and low capacity.

[0085] In some embodiments, the mass ratio of the carbonaceous material to the non-carbonaceous material is D, and 0.1≤D≤80, specifically 0.1, 0.5, 0.8, 1, 5, 10, 18, 24, 30, 35, 40, 50, 62, 74, or 80, etc., of course, it can also be other values ​​within the above range, which is not limited here. When the D value is low, the content of non-carbonaceous material in the composite layer is high, resulting in a larger specific surface area of ​​the negative electrode material. When the D value is high, the content of carbonaceous material in the composite layer is high, resulting in a decrease in the interfacial lithium ion transfer efficiency of the negative electrode material and a deterioration in the rate performance of the negative electrode material.

[0086] In some embodiments, the powder conductivity of the graphite is E1, the powder conductivity of the negative electrode material is E2, the ratio of E2 to E1 is E, and 1<E<1000. The value of E can specifically be 1.01, 5, 10, 50, 100, 150, 200, 300, 400, 500, 600, 700, 800, 900 or 1000, etc., which are not limited here. It should be noted that graphite is the powder conductivity of the uncoated graphite raw material, and the powder conductivity of the negative electrode material refers to the conductivity after the graphite is coated with the composite layer. The value of E can represent the conductivity of the negative electrode material. If the value of E is too small, the conductivity of the negative electrode material is difficult to improve.

[0087] In some embodiments, the specific surface area of ​​the core is 6 m 2 / g~15m 2 / g, specifically 6m 2 / g, 6.8m 2 / g, 7.9m 2 / g, 8.7m 2 / g, 9.5m 2 / g、10m 2 / g, 11.3m 2 / g, 12.4m 2 / g, 13.5m 2 / g、14m 2 / g or 15m 2 / g, etc., and of course, it can also be other values ​​within the above range, which is not limited here.

[0088] In some embodiments, the specific surface area of ​​the negative electrode material is 1 m 2 / g~5m 2 / g, specifically 1m 2 / g, 1.5m 2 / g, 2.3m 2 / g, 2.8m 2 / g、3m 2 / g, 3.5m 2 / g、4m 2 / g, 4.8m 2 / g or 5m 2 / g, etc., and of course, it can also be other values ​​within the above range, which is not limited here.

[0089] In the present application, the negative electrode material includes a core and a composite layer located on at least a portion of the surface of the core. The composite layer is completely and evenly coated on the surface of the core, which can reduce the specific surface area of ​​the negative electrode material and control the specific surface area of ​​the negative electrode material to 1m 2 / g~5m 2 / g range, which is beneficial to improving the high-temperature storage performance and electrode processing performance of the negative electrode material, and further beneficial to improving the cycle performance of the lithium-ion battery made of the negative electrode material.

[0090] In a second aspect, the present application provides a method for preparing a negative electrode material, as shown in FIG1 , comprising the following steps:

[0091] Step S100, preparing a first precursor, wherein the first precursor includes a core and a polymer layer formed on the surface of the core, wherein the core includes graphite;

[0092] Step S200, attaching an inorganic salt to the surface of the first precursor to obtain a second precursor;

[0093] Step S300: carbonizing the second precursor to obtain a negative electrode material.

[0094] In the preparation method of the negative electrode material provided in the present application, a first precursor is obtained by subjecting a first mixed solution containing a graphite material and an organic molecular monomer to a polymerization reaction, so that the polymer formed by the polymerization of the organic molecular monomer is composited on the surface of the graphite particles to form a polymer layer, and the polymer layer has highly reactive functional groups. Then, a second mixed solution containing the first precursor and an inorganic salt is fully mixed and dried, and the inorganic salt in the second mixed solution is hydrolyzed to form inorganic ions. The inorganic ions are grafted and introduced into the polymer layer on the surface of the graphite particles by utilizing the grafting reaction between the highly reactive functional groups in the polymer and the inorganic ions to obtain a second precursor. Finally, the second precursor is carbonized. After the carbonization treatment, the organic molecules in the polymer layer are in situ cracked into carbonaceous materials, and the inorganic ions are in situ converted into non-carbonaceous materials, thereby forming a composite layer containing carbonaceous materials and non-carbonaceous materials on the surface of the graphite particles. The surface of the prepared negative electrode material has a uniformly coated composite layer. Through the synergistic effect of the carbonaceous material and the non-carbonaceous material in the composite layer, the specific surface area of ​​the negative electrode material can be reduced, and the high-temperature storage performance and electrode processing performance of the negative electrode material can be improved; it can also improve the interface stability of the negative electrode material, reduce interface side reactions, enhance electrolyte wettability, improve lithium ion transmission efficiency, and enhance the reversible capacity, initial efficiency, and rate performance of the negative electrode material.

[0095] Step S100 , preparing a first precursor, wherein the first precursor includes a core and a polymer layer formed on a surface of the core, wherein the core includes graphite.

[0096] In some embodiments, preparing a first precursor includes the following steps: subjecting a first mixed solution containing a graphite material and an organic molecular monomer to a polymerization reaction, solid-liquid separation, and drying to obtain a first precursor, wherein the first precursor includes a core and a polymer layer located on the surface of the core, and the core includes graphite.

[0097] In some embodiments, the graphite material includes at least one of natural graphite, artificial graphite, and microcrystalline graphite.

[0098] In some embodiments, the median particle size of the graphite is 0.5 μm to 30 μm. Specifically, it can be 0.5 μm, 1 μm, 3.5 μm, 5 μm, 8 μm, 10 μm, 12 μm, 15 μm, 18 μm, 19.7 μm, 21.3 μm, 24.5 μm, 26.1 μm, 28.4 μm, 29 μm, or 30 μm, etc. Of course, other values ​​within the above range are also possible and are not limited here.

[0099] In some embodiments, the mass ratio of the graphite material and the organic molecular monomer is 1:(0.01~0.4). Specifically, it can be 1:0.01, 1:0.05, 1:0.1, 1:0.15, 1:0.2, 1:0.25, 1:0.3, 1:0.35 or 1:0.4, etc., but it is not limited to the listed values. Other unlisted values ​​within this numerical range are also applicable. Controlling the mass ratio of the graphite material and the organic molecular monomer can reduce the situation where the polymer coating layer is too thick, affecting the capacity; it can also reduce the situation where there is too little polymer and a complete polymer coating layer cannot be formed, thereby affecting the complete uniformity of the coating of the composite layer, which is not conducive to the decrease in the specific surface area of ​​the negative electrode material. The present application ensures the formation of a uniform polymer coating layer on the surface of the graphite particles by controlling the mass ratio of the graphite material and the organic molecular monomer, thereby improving the coating uniformity of the graphite particles and the composite layer.

[0100] In some embodiments, the organic molecular monomer includes at least one of aniline, styrene, fluorostyrene, hydroxyethyl acrylate, acrylate, pyrrole, vinylidene fluoride, tetrafluoroethylene, and dopamine.

[0101] In some embodiments, the first mixed solution and the second mixed solution both include a solvent, and the solvent includes at least one of water, methanol, ethanol, acetone, nitrogen-methyl pyrrolidone, and N,N-dimethylformamide.

[0102] In some embodiments, the first mixed solution further includes an auxiliary agent. It is understood that the addition of the chemical reaction auxiliary agent can promote the polymerization reaction of the organic molecular monomer.

[0103] In some embodiments, the first mixed solution further includes an auxiliary agent, and the mass concentration of the auxiliary agent in the first mixed solution is 0.01mol / L to 4mol / L, specifically 0.01mol / L, 0.05molL, 0.08mol / L, 0.1mol / L, 0.5mol / L, 1mol / L, 1.5mol / L, 1.8mol / L, 2mol / L, 2.5mol / L, 3mol / L, 3.5mol / L or 4mol / L, etc., of course, it can also be other values ​​within the above range, which is not limited here.

[0104] In some embodiments, the first mixed solution further includes an auxiliary agent, the auxiliary agent includes an initiator, and the initiator includes at least one of ammonium persulfate, sodium persulfate, potassium persulfate, aluminum chloride and hydrogen peroxide.

[0105] In some embodiments, the first mixed solution further includes an auxiliary agent, the auxiliary agent includes a catalyst, and the catalyst includes at least one of sodium hydroxide, lithium hydroxide, potassium hydroxide, ammonia water, and sodium carbonate.

[0106] In some embodiments, the first mixed solution further includes an auxiliary agent, which includes a pH regulator, and the pH regulator includes at least one of an acidic pH reagent and an alkaline pH reagent. Specifically, the acidic pH regulator used can be at least one of hydrochloric acid, sulfuric acid, phosphoric acid, and nitric acid, and the alkaline pH regulator used can be at least one of lithium hydroxide, sodium hydroxide, potassium hydroxide, sodium carbonate, and sodium bicarbonate. It should be noted that the pH value of the first mixed solution here is adjusted according to the required polymerization reaction environment of different organic molecular monomers.

[0107] In some embodiments, the first mixed solution further includes an auxiliary agent, which includes a pH regulator. The pH of the first mixed solution is 4 to 10, specifically 4, 5, 6, 7, 8, 9 or 10, etc., but is not limited to the listed values. Other unlisted values ​​within this numerical range are also applicable.

[0108] In some embodiments, the polymerization reaction temperature is 40° C. to 100° C. The polymerization reaction temperature can be 40° C., 45° C., 50° C., 55° C., 60° C., 70° C., 80° C., 90° C., or 100° C., etc., and is not limited here.

[0109] In some embodiments, the polymerization reaction time is 3h to 48h, specifically 3h, 5h, 8h, 12h, 15h, 18h, 20h, 24h, 30h, 36h, 40h, 45h or 48h, etc., and of course other values ​​within the above range can also be used, which is not limited here.

[0110] In some embodiments, the polymerization reaction is carried out under stirring, and the polymer formed by the polymerization of the organic molecular monomers is entangled on the surface of the graphite to form a polymer layer.

[0111] The present application can promote the full polymerization reaction of organic monomer molecules by controlling the temperature, time and amount of chemical reaction aids added in the polymerization reaction. Under stirring, the polymer formed by polymerization can be more evenly wrapped around the surface of graphite.

[0112] In some embodiments, the polymerization reaction is carried out under stirring at a stirring rate of 50 r / min to 1000 r / min, specifically 50 r / min, 100 r / min, 200 r / min, 300 r / min, 400 r / min, 500 r / min, 800 r / min, or 1000 r / min, etc., and other values ​​within the above range are also possible and are not limited here. Controlling the stirring rate within the above range is conducive to more uniform winding of the polymer generated by the polymerization reaction on the surface of the graphite.

[0113] In some embodiments, the polymerization reaction is carried out under ultraviolet light irradiation. It is understood that ultraviolet light irradiation can promote the polymerization reaction of organic molecular monomers.

[0114] In some embodiments, the solid-liquid separation comprises at least one of filtration and centrifugation.

[0115] Step S200: attaching an inorganic salt to the surface of the first precursor to obtain a second precursor.

[0116] In some embodiments, attaching an inorganic salt on the surface of the first precursor to obtain a second precursor includes the following steps: drying a second mixed solution containing the first precursor and the inorganic salt to obtain the second precursor.

[0117] In some embodiments, the inorganic salt includes at least one of lithium hydroxide, sodium hydroxide, potassium hydroxide, magnesium nitrate, calcium chloride, aluminum nitrate, zinc nitrate, titanium n-propoxide, niobium oxalate, zirconium oxychloride, ammonium molybdate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, sodium metasilicate, sodium borate, ammonium fluoride, titanium oxysulfide, zinc bromide, and zirconium chloride.

[0118] In some embodiments, the mass ratio of the first precursor to the inorganic salt is 1:(0.001-0.1), specifically 1:0.001, 1:0.003, 1:0.005, 1:0.01, 1:0.02, 1:0.05, 1:06, 1:0.09 or 1:0.1, etc., but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable. Controlling the mass ratio of the first precursor and the inorganic salt can control the mass ratio of the carbonaceous material and the non-carbonaceous material in the composite layer, thereby reducing the situation where the content of the carbonaceous material in the composite layer is too high, resulting in a larger specific surface area of ​​the negative electrode material; it can also reduce the situation where the content of the non-carbonaceous material in the composite layer is too high, resulting in a decrease in the interfacial lithium ion transmission efficiency of the negative electrode material, causing a deterioration in the rate performance of the negative electrode material. By controlling the mass ratio of the first precursor and the inorganic salt, the present application can ensure that the negative electrode material has a lower specific surface area, and can also improve the interfacial lithium ion transmission efficiency of the negative electrode material and improve the rate performance of the negative electrode material.

[0119] In some embodiments, the drying method includes at least one of natural volatilization, forced air drying, flash drying, freeze drying, inert atmosphere protection drying and vacuum drying.

[0120] In some embodiments, the drying temperature is 60°C to 600°C, specifically 60°C, 100°C, 200°C, 300°C, 400°C, 500°C or 600°C, etc. Of course, it can also be other values ​​within the above range, which is not limited here.

[0121] In some embodiments, the drying time is 0.5h to 48h, specifically 0.5h, 1h, 5h, 10h, 12h, 15h, 18h, 24h, 36h, 45h or 48h, etc. Of course, it can also be other values ​​within the above range, which is not limited here.

[0122] Step S300: carbonizing the second precursor to obtain a negative electrode material.

[0123] In some embodiments, the carbonization treatment is carried out under a protective atmosphere, and the protective atmosphere includes at least one of nitrogen, helium, neon, argon, and air. It is understandable that the introduction of nitrogen, helium, neon, argon, etc. as a protective atmosphere during the carbonization treatment can effectively inhibit the oxidation reaction of the graphite material, reduce the situation where the graphite material is burned at high temperatures, and ensure the stability and uniformity of the carbonization process. It should be noted that during low-temperature heat treatment, for example, when the heat treatment temperature is below 700°C, the introduction of air can promote the beneficial phase change transformation of the surface state of the graphite material, can access oxygen-containing functional groups on the surface of the graphite material, improve the electrolyte wettability and interface stability of the composite graphite negative electrode material, and enhance the electrochemical performance of the composite graphite negative electrode material. Therefore, according to different actual application requirements and carbonization treatment conditions, selecting a suitable atmosphere protection method can effectively control the chemical composition and surface state of the graphite material, thereby adjusting its performance and application effect.

[0124] In some embodiments, the heating rate of the carbonization treatment is 1°C / min to 20°C / min, specifically 1°C / min, 2°C / min, 3°C / min, 4°C / min, 5°C / min, 6°C / min, 7°C / min, 8°C / min, 9°C / min, 10°C / min, 12°C / min, 15°C / min, 18°C / min or 20°C / min, etc. Of course, it can also be other values ​​within the above range, which is not limited here.

[0125] In some embodiments, the holding temperature of the carbonization treatment is 600°C to 2500°C, specifically 600°C, 800°C, 900°C, 1000°C, 1200°C, 1500°C, 1800°C, 2000°C, 2200°C, 2300°C or 2500°C, etc. Of course, it can also be other values ​​within the above range, which is not limited here.

[0126] In some embodiments, the holding time of the carbonization treatment is 0.1h to 10h, specifically 0.1h, 0.5h, 1h, 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h or 10h, etc., and of course it can also be other values ​​within the above range, which is not limited here.

[0127] In a third aspect, the present application provides a lithium-ion battery, comprising the negative electrode material described in the first aspect or the negative electrode material prepared by the method for preparing the negative electrode material described in the second aspect.

[0128] Example

[0129] Example 1

[0130] (1) 100 g of natural graphite was dispersed in 200 ml of deionized water, 5 g of aniline monomer was added, and the mixture was stirred thoroughly to form a first mixed solution.

[0131] (2) The first mixed solution was stirred at 45° C. at a stirring rate of 300 r / min, and 15 ml of an aqueous solution of ammonium persulfate (2 mol / L) was added dropwise thereto. After the mixture was stirred for 120 min to carry out a polymerization reaction, the mixture was filtered and dried to obtain a first precursor, wherein the first precursor included a core and polyaniline located on the surface of the core, and the core included natural graphite.

[0132] (3) 100 g of the first precursor was mixed evenly with 200 ml of deionized water, and then 2.5 g of LiOH.H2O was added and stirred evenly to form a second mixed solution. The second mixed solution was stirred at 90°C to evaporate the solvent and then dried to obtain a second precursor.

[0133] (4) Under a nitrogen atmosphere, the second precursor was heated to 1250°C and carbonized for 4 hours to obtain a negative electrode material.

[0134] The negative electrode material prepared in this embodiment includes a core and a composite layer located on at least a portion of the surface of the core, the composite layer includes hard carbon and lithium oxide (Li2O), and the core includes natural graphite.

[0135] Figure 3a is a scanning electron microscope image of the negative electrode material prepared in Example 1, and Figure 3b is a scanning electron microscope image of the negative electrode material prepared in Example 1 at another magnification. As shown in Figures 3a and 3b, the surface of the negative electrode material particles prepared in Example 1 contains carbonaceous material-non-carbonaceous material nanoparticles co-composite and is smooth overall.

[0136] FIG4 is a scanning electron microscope image of a cross section of the negative electrode material prepared in Example 1. As shown in FIG4 , the thickness of the composite layer of the negative electrode material prepared in Example 1 is about 60 nm.

[0137] Example 2

[0138] (1) 100 g of natural graphite was dispersed in 200 ml of deionized water, 5 g of aniline monomer was added, and the mixture was stirred thoroughly to form a first mixed solution.

[0139] (2) The first mixed solution was stirred at 45° C. at a stirring rate of 300 r / min, and 15 ml of an aqueous solution of ammonium persulfate (2 mol / L) was added dropwise thereto. After the mixture was stirred for 120 min to carry out a polymerization reaction, the mixture was filtered and dried to obtain a first precursor, wherein the first precursor included a core and polyaniline located on the surface of the core, and the core included natural graphite.

[0140] (3) 100 g of the first precursor was mixed evenly with 200 ml of deionized water, and 7.5 g of (NH4)2HPO4 was added and stirred evenly to form a second mixed solution. The second mixed solution was stirred at 90° C. to evaporate the solvent and then dried to obtain a second precursor.

[0141] (4) Under a nitrogen atmosphere, the second precursor was heated to 1250°C and carbonized for 4 hours to obtain a negative electrode material.

[0142] The negative electrode material prepared in this embodiment includes a core and a composite layer located on at least a portion of the surface of the core, the composite layer includes hard carbon and phosphorus pentoxide (P2O5), the core includes natural graphite, and the thickness of the composite layer is about 55 nm.

[0143] Example 3

[0144] (1) 100 g of natural graphite was dispersed in 200 ml of deionized water, 5 g of aniline monomer was added, and the mixture was stirred thoroughly to form a first mixed solution.

[0145] (2) The first mixed solution was stirred at 45° C. at a stirring rate of 300 r / min, and 15 ml of an aqueous solution of ammonium persulfate (2 mol / L) was added dropwise thereto. After the mixture was stirred for 120 min to carry out a polymerization reaction, the mixture was filtered and dried to obtain a first precursor, wherein the first precursor included a core and polyaniline located on the surface of the core, and the core included natural graphite.

[0146] (3) 100 g of the first precursor was mixed evenly with 200 ml of deionized water, and 7.5 g of NH4F was added and stirred evenly to form a second mixed solution. The second mixed solution was stirred at 90° C. to evaporate the solvent and then dried to obtain a second precursor.

[0147] (4) Under a nitrogen atmosphere, the second precursor was heated to 1250°C and carbonized for 4 hours to obtain a negative electrode material.

[0148] The negative electrode material prepared in this embodiment includes a core and a composite layer located on at least a portion of the surface of the core, the composite layer includes hard carbon and carbon fluoride (CF4), the core includes natural graphite, and the thickness of the composite layer is 65 nm.

[0149] It should be noted that the carbon fluoride (CF4) in the composite layer of this embodiment is a fluorine-doped carbon material, that is, the carbon fluoride (CF4) in the composite layer includes carbonaceous materials and non-carbonaceous materials.

[0150] Example 4

[0151] (1) 100 g of natural graphite was dispersed in 200 ml of ethanol, 10 g of styrene monomer was added and stirred thoroughly to form a first mixed solution.

[0152] (2) The first mixed solution was placed at 65° C. and stirred for 120 min to perform a polymerization reaction. The stirring rate was controlled to be 400 r / min, and the mixture was filtered and dried to obtain a first precursor. The first precursor included a core and polystyrene located on the surface of the core, and the core included natural graphite.

[0153] (3) 100 g of the first precursor was mixed evenly with 200 ml of deionized water, and then 2.5 g of LiOH.H2O was added and stirred evenly to form a second mixed solution. The second mixed solution was stirred at 90°C to evaporate the solvent and then dried to obtain a second precursor.

[0154] (4) Under a nitrogen atmosphere, the second precursor was heated to 1250°C and carbonized for 4 hours to obtain a negative electrode material.

[0155] The negative electrode material prepared in this embodiment includes a core and a composite layer located on at least a portion of the surface of the core, the composite layer includes hard carbon and lithium oxide (Li2O), the core includes natural graphite, and the thickness of the composite layer is 55 nm.

[0156] Example 5

[0157] (1) 100 g of natural graphite was dispersed in 200 ml of ethanol, 10 g of fluorostyrene monomer was added, and the mixture was stirred thoroughly to form a first mixed solution.

[0158] (2) The first mixed solution was placed at 65° C. and stirred for 120 min to perform a polymerization reaction. The stirring rate was controlled to be 500 r / min, and the mixture was filtered and dried to obtain a first precursor. The first precursor included a core and polyfluorostyrene located on the surface of the core, and the core included natural graphite.

[0159] (3) 100 g of the first precursor was mixed evenly with 200 ml of deionized water, and then 2.5 g of LiOH.H2O was added and stirred evenly to form a second mixed solution. The second mixed solution was stirred at 90°C to evaporate the solvent and then dried to obtain a second precursor.

[0160] (4) Under a nitrogen atmosphere, the second precursor was heated to 1250°C and carbonized for 4 hours to obtain a negative electrode material.

[0161] The negative electrode material prepared in this embodiment includes a core and a composite layer located on at least a portion of the surface of the core, the composite layer includes hard carbon, lithium fluoride (LiF) and lithium oxide (Li2O), the core includes natural graphite, and the thickness of the composite layer is 55nm.

[0162] Example 6

[0163] (1) 100 g of natural graphite was dispersed in 200 ml of ethanol, 10 g of dopamine monomer was added, and the mixture was stirred thoroughly to form a first mixed solution.

[0164] (2) The first mixed solution was placed at 65° C. and stirred for 180 min to perform a polymerization reaction. The stirring rate was controlled to be 500 r / min, and the mixture was filtered and dried to obtain a first precursor. The first precursor included a core and polyfluorostyrene located on the surface of the core, and the core included natural graphite.

[0165] (3) 100 g of the first precursor was mixed evenly with 200 ml of deionized water, and then 2.5 g of LiOH.H2O was added and stirred evenly to form a second mixed solution. The second mixed solution was stirred at 90°C to evaporate the solvent and then dried to obtain a second precursor.

[0166] (4) Under a nitrogen atmosphere, the second precursor was heated to 1250°C and carbonized for 4 hours to obtain a negative electrode material.

[0167] The negative electrode material prepared in this embodiment includes a core and a composite layer located on at least a portion of the surface of the core, the composite layer includes soft carbon and lithium oxide (Li2O), the core includes graphite, and the thickness of the composite layer is 60 nm.

[0168] Example 7

[0169] (1) 100 g of natural graphite was dispersed in 200 ml of deionized water, 5 g of dopamine was added, and the mixture was stirred thoroughly to form a first mixed solution.

[0170] (2) The first mixed solution was stirred at 40° C. at a stirring rate of 300 r / min, and 15 ml (4 mol / L) of ammonia water was added dropwise thereto as a polymerization catalyst. After the polymerization reaction, the mixture was stirred for 120 min, and filtered and dried to obtain a first precursor. The first precursor included a core and polydopamine located on the surface of the core, and the core included natural graphite.

[0171] (3) 100 g of the first precursor was mixed evenly with 200 ml of deionized water, and then 2.5 g of LiOH.H2O was added and stirred evenly to form a second mixed solution. The second mixed solution was stirred at 90°C to evaporate the solvent and then dried to obtain a second precursor.

[0172] (4) Under a nitrogen atmosphere, the second precursor was heated to 1250°C and carbonized for 4 hours to obtain a negative electrode material.

[0173] The negative electrode material prepared in this embodiment includes a core and a composite layer located on at least a portion of the surface of the core, the composite layer includes hard carbon and lithium oxide (Li2O), the core includes artificial graphite, and the thickness of the composite layer is 50 nm.

[0174] Example 8

[0175] The difference from Example 1 is that (3) 100 g of the first precursor is mixed evenly with 200 ml of deionized water, and then 24.5 g of Al(NO3)3·9H2O is added and stirred evenly to form a second mixed solution. The second mixed solution is stirred at 90°C to evaporate the solvent and then dried to obtain a second precursor.

[0176] The negative electrode material prepared in this embodiment includes a core and a composite layer located on at least a portion of the surface of the core, the composite layer includes hard carbon and aluminum oxide (Al2O3), the core includes graphite, and the thickness of the composite layer is 100 nm.

[0177] Example 9

[0178] The difference from Example 1 is that natural graphite is replaced by artificial graphite with the same particle size distribution, and the other process parameters are exactly the same as those in Example 1.

[0179] The negative electrode material prepared in this embodiment includes a core and a composite layer located on at least a portion of the surface of the core, the composite layer includes hard carbon and lithium oxide (Li2O), the core includes artificial graphite, and the thickness of the composite layer is 70 nm.

[0180] Example 10

[0181] Different from Example 1, (4) the second precursor was heated to 2000° C. under an argon atmosphere and then carbonized for 4 hours to obtain a negative electrode material.

[0182] The negative electrode material prepared in this embodiment includes a core and a composite layer located on at least a portion of the surface of the core, the composite layer includes hard carbon and lithium oxide (Li2O), the core includes natural graphite, and the thickness of the composite layer is 150 nm.

[0183] Example 11

[0184] Different from Example 1, (4) the second precursor is heated to 1600° C. under an argon atmosphere and then carbonized for 4 hours to obtain a negative electrode material.

[0185] The negative electrode material prepared in this embodiment includes a core and a composite layer located on at least a portion of the surface of the core, the composite layer includes hard carbon and lithium oxide (Li2O), the core includes natural graphite, and the thickness of the composite layer is 120 μm.

[0186] Example 12

[0187] The difference from Example 1 is that (1) 100 g of natural graphite is dispersed in 200 ml of deionized water, 5 g of aniline monomer is added and stirred thoroughly to form a first mixed solution, and phosphoric acid solution is added to adjust the pH of the first mixed solution to 4.5.

[0188] The negative electrode material prepared in this embodiment includes a core and a composite layer located on at least a portion of the surface of the core, the composite layer includes hard carbon and lithium oxide (Li2O), and the core includes natural graphite.

[0189] Example 13

[0190] The difference from Example 1 is that (1) 100 g of natural graphite is dispersed in 200 ml of deionized water, 5 g of aniline monomer is added and stirred thoroughly to form a first mixed solution, and sodium hydroxide solution is added to adjust the pH of the first mixed solution to 8.5.

[0191] The negative electrode material prepared in this embodiment includes a core and a composite layer located on at least a portion of the surface of the core, the composite layer includes hard carbon and lithium oxide (Li2O), and the core includes natural graphite.

[0192] Comparative Example 1

[0193] (1) 100 g of natural graphite was dispersed in 200 ml of deionized water, 5 g of aniline monomer was added, and the mixture was stirred thoroughly to form a mixed solution.

[0194] (2) The mixed solution was stirred at 45° C. at a stirring rate of 500 r / min, and 15 ml (2 mol / L) of ammonium persulfate aqueous solution was added dropwise thereto. After the mixture was stirred for 120 min to carry out polymerization reaction, the mixture was filtered and dried to obtain a precursor, wherein the precursor comprises a core and polyaniline located on the surface of the core, and the core comprises natural graphite.

[0195] (3) Under a nitrogen atmosphere, the precursor was heated to 1250°C and carbonized for 4 hours to obtain the negative electrode material.

[0196] The negative electrode material prepared in this comparative example includes a core and a carbon coating layer located on at least a portion of the surface of the core, and the core includes natural graphite.

[0197] Comparative Example 2

[0198] (1) 100 g of natural graphite material was mixed evenly with 200 ml of deionized water, and 2.5 g of LiOH.H2O was added and stirred evenly to form a mixed solution. The mixed solution was stirred and volatilized at 90°C and dried to obtain a precursor.

[0199] (3) Under a nitrogen atmosphere, the precursor was heated to 1250°C and carbonized for 4 hours to obtain the negative electrode material.

[0200] The negative electrode material prepared in this comparative example includes a core and a lithium oxide coating layer located on at least a portion of the surface of the core, and the core includes graphite.

[0201] Comparative Example 3

[0202] (1) Similar to Example 9, 100 g of artificial graphite was dispersed in 200 ml of deionized water, and 5 g of aniline monomer was added and stirred thoroughly to form a mixed solution.

[0203] (2) The mixed solution was stirred at 45° C. at a stirring rate of 300 r / min, and 15 ml (2 mol / L) of ammonium persulfate aqueous solution was added dropwise thereto. After the mixture was stirred for 120 min to carry out polymerization reaction, the mixture was filtered and dried to obtain a precursor, wherein the precursor comprises a core and polyaniline located on the surface of the core, and the core comprises artificial graphite.

[0204] (3) Under a nitrogen atmosphere, the precursor was heated to 1250°C and carbonized for 4 hours to obtain the negative electrode material.

[0205] The negative electrode material prepared in this comparative example includes a core and a carbon coating layer located on at least a portion of the surface of the core, and the core includes artificial graphite.

[0206] Test Method

[0207] (1) Test method for average particle size of negative electrode material:

[0208] The particle size distribution range of the negative electrode material was tested by Malvern laser particle size analyzer.

[0209] (2) Testing method for specific surface area of ​​negative electrode material:

[0210] At constant temperature and low temperature, after measuring the adsorption amount of gas on the solid surface at different relative pressures, the monolayer adsorption amount of the sample is obtained based on the Brownauer-Ettel-Taylor adsorption theory and its formula (BET formula), thereby calculating the specific surface area of ​​the material.

[0211] (3) Observation of the surface smoothness of negative electrode material particles:

[0212] The micromorphology of the surface of the negative electrode material was observed using an S-4800 scanning electron microscope.

[0213] (4) Test method for average particle size of non-carbonaceous materials:

[0214] The microscopic morphology of the surface of the negative electrode material and the particle size of the non-carbonaceous material were observed using an S-4800 scanning electron microscope. A 1 μm*1 μm area was randomly selected on a single negative electrode material particle, and the particle size distribution of the non-carbonaceous material in the area was statistically analyzed. The average particle size of the non-carbonaceous material was calculated as G.

[0215] (5) Test method for thickness of composite layer:

[0216] The graphite particles were cut open using a focused ion beam to obtain a cross section, and the micromorphology of the cross section of the negative electrode material and the thickness of the composite layer were observed using an S-4800 scanning electron microscope.

[0217] (6) Powder conductivity test:

[0218] The powder resistivity test system was used to test the powder conductivity of the negative electrode material.

[0219] (7) Electrochemical performance test

[0220] The negative electrode materials prepared in Examples 1-13 and Comparative Examples 1-3 were dissolved in deionized water at a mass ratio of 96.5:1.5:1, carboxymethyl cellulose, and styrene-butadiene rubber. The solid content was controlled to 50%, and the resulting materials were coated onto a copper foil current collector and vacuum-dried to produce negative electrode sheets. A lithium metal sheet was used as the counter electrode, and button-type batteries were assembled in an argon-filled glove box. Charge and discharge tests were conducted at a current density of 0.1C with a charge and discharge range of 0.01-1.5V. Cyclic charge and discharge were performed to obtain the first reversible specific capacity, first-cycle charge capacity, and first-cycle discharge capacity. First coulombic efficiency = first-cycle discharge capacity / first-cycle charge capacity. Cyclic charge and discharge were performed at different rates to obtain rate performance.

[0221] The above performance test results are detailed in Table 1.

[0222] Table 1. Performance parameters of negative electrode materials and batteries prepared in various examples and comparative examples

[0223] As shown in Table 1, in Examples 1 to 13, a first precursor is obtained by subjecting a first mixed solution containing a graphite material and an organic molecular monomer to a polymerization reaction. The polymer formed by the polymerization of the organic molecular monomer is composited on the surface of the graphite particles to form a polymer layer. The polymer has a highly reactive functional group. A second mixed solution containing the first precursor and an inorganic salt is fully mixed and dried. During the drying process, the inorganic salt in the second mixed solution is hydrolyzed to form inorganic ions. The inorganic ions are grafted into the polymer layer on the surface of the graphite particles by utilizing the grafting reaction between the highly reactive functional groups in the polymer and the inorganic ions to obtain a second precursor. Finally, the second precursor is carbonized. After the carbonization treatment, the organic molecules in the polymer layer are in situ cracked into carbonaceous materials, and the inorganic ions are in situ converted into non-carbonaceous materials, thereby forming a composite layer containing carbonaceous materials and non-carbonaceous materials on the surface of the graphite particles. The surface of the prepared negative electrode material has a uniformly coated composite layer. Through the synergistic effect of the carbonaceous material and the non-carbonaceous material in the composite layer, the specific surface value of the negative electrode material can be reduced, and the high-temperature storage performance and electrode processing performance of the negative electrode material can be improved; it can also improve the interface stability of the negative electrode material, reduce interface side reactions, enhance electrolyte wettability, improve lithium ion transmission efficiency, increase the reversible capacity and initial efficiency of the negative electrode material, and improve the rate performance of the negative electrode material.

[0224] Compared with Example 1, the negative electrode material of Comparative Example 1 directly carbonizes the first precursor during the preparation process, and the coating layer in the prepared negative electrode material is a single carbon coating layer, which is easy to undergo irreversible reaction with the electrolyte components at low potential, resulting in continuous repair and generation of the SEI film, reduced surface and interfacial stability of the negative electrode material, intensified side reactions with the electrolyte, reduced lithium ion transmission efficiency, reduced powder conductivity of the negative electrode material, and reduced reversible capacity, initial efficiency, and rate performance of the material.

[0225] Compared with Example 1, during the preparation process of the negative electrode material of Comparative Example 2, the natural graphite material and the non-carbonaceous material are directly compounded. The coating layer in the prepared negative electrode material is a single non-carbonaceous material coating layer. The specific surface area of ​​the negative electrode material is large, the contact between the material and the electrolyte is increased, the interfacial side reaction is intensified, the surface and interfacial stability of the material is reduced, and the lithium ion transmission efficiency is reduced, resulting in a decrease in the powder conductivity of the negative electrode material, a decrease in its reversible capacity and rate performance, and a significant decrease in the first efficiency.

[0226] Example 9 and Comparative Example 3 use artificial graphite as raw material. Compared with Example 9, the negative electrode material of Comparative Example 3 directly carbonizes the first precursor during the preparation process. The coating layer in the prepared negative electrode material is a single carbon coating layer. The surface stability of the negative electrode material is low, and the side reaction with the electrolyte is more intense at low potential. Its performance indicators such as the first coulombic efficiency, powder conductivity and rate performance all deteriorate to varying degrees.

[0227] The applicant declares that while the above-mentioned embodiments are used to illustrate the detailed process equipment and process flow of the present application, the present application is not limited to the above-mentioned detailed process equipment and process flow, which does not mean that the present application must rely on the above-mentioned detailed process equipment and process flow in order to be implemented. Those skilled in the art should understand that any improvements to the present application, equivalent replacements for the raw materials of the present application's products, addition of auxiliary ingredients, and selection of specific methods, etc., fall within the scope of protection and disclosure of the present application.

Claims

1. A negative electrode material, characterized in that: The negative electrode material comprises a core and a composite layer located on at least a portion of the surface of the core, wherein the core comprises graphite, and the composite layer comprises a carbonaceous material and a non-carbonaceous material.

2. The negative electrode material according to claim 1, characterized in that The non-carbonaceous material is dispersed in the carbonaceous material.

3. The negative electrode material according to claim 1, characterized in that The chemical formula of the non-carbonaceous material is A x B y , wherein 1≤x≤3, 1≤y≤5, the A element includes at least one of Li, Na, K, Ca, Mg, Al, Zn, Ti, Nb, Zr, Mo, P, Si and B, and the B element includes at least one of B, O, F, Si, P, S, Br and Cl.

4. The negative electrode material according to claim 1, characterized in that It meets at least one of the following technical features: (1) The graphite comprises at least one of natural graphite, artificial graphite and microcrystalline graphite; (2) the median particle size of the inner core is D50, 0.5 μm ≤ D50 ≤ 30 μm; (3) The mass content of carbon in the graphite is ≥ 80%; (4) The carbonaceous material includes at least one of amorphous carbon and graphite carbon; (5) The thickness of the composite layer is 1 nm to 200 nm; (6) The non-carbonaceous material includes at least one of LiF, NaF, MgF2, MgO, P2O5, Al2O3, SiO2, and B2O3; (7) The average particle size of the non-carbonaceous material is G, and G≤150nm.

5. The negative electrode material according to any one of claims 1 to 3, characterized in that: It meets at least one of the following technical features: (1) The mass ratio of the composite layer to the core is C, and 0.01≤C≤0.5; (2) The mass ratio of the carbonaceous material to the non-carbonaceous material is D, and 0.1≤D≤80; (3) The powder conductivity of the core is E1, the powder conductivity of the negative electrode material is E2, the ratio of E2 to E1 is E, and 1<E<1000; (4) The specific surface area of ​​the inner core is 6 m 2 / g~15m 2 / g; (5) The specific surface area of ​​the negative electrode material is 1 m 2 / g~5m 2 / g.

6. A method for preparing a negative electrode material, characterized in that: The following steps are involved: preparing a first precursor, the first precursor comprising a core and a polymer layer formed on a surface of the core, wherein the core comprises graphite; Attaching an inorganic salt to the surface of the first precursor to obtain a second precursor; and The second precursor is carbonized to obtain a negative electrode material.

7. The preparation method according to claim 6, characterized in that: The preparation of the first precursor comprises the following steps: The first mixed solution containing graphite and organic molecular monomers is subjected to polymerization reaction, solid-liquid separation and drying to obtain the first precursor.

8. The preparation method according to claim 6, characterized in that: The step of attaching an inorganic salt on the surface of the first precursor to obtain a second precursor includes the following steps: drying a second mixed solution containing the first precursor and the inorganic salt to obtain a second precursor.

9. The preparation method according to claim 7, characterized in that: It meets at least one of the following technical features: (1) The graphite comprises at least one of natural graphite, artificial graphite and microcrystalline graphite; (2) The median particle size of the graphite is 0.5 μm to 30 μm; (3) The mass ratio of the graphite to the organic molecular monomer is 1:(0.01-0.4); (4) The organic molecular monomer includes at least one of aniline, styrene, fluorostyrene, hydroxyethyl acrylate, acrylate, pyrrole, vinylidene fluoride, tetrafluoroethylene and dopamine; (5) Both the first mixed solution and the second mixed solution include a solvent, and the solvent includes at least one of water, methanol, ethanol, acetone, nitrogen methyl pyrrolidone and N,N-dimethylformamide.

10. The preparation method according to claim 7, characterized in that: It meets at least one of the following technical features: (1) The first mixed solution also includes an auxiliary agent; (2) The first mixed solution further includes an auxiliary agent, and the mass concentration of the auxiliary agent in the first mixed solution is 0.01 mol / L to 4 mol / L; (3) The first mixed solution further includes an auxiliary agent, the auxiliary agent includes an initiator, and the initiator includes at least one of ammonium persulfate, sodium persulfate, potassium persulfate, aluminum chloride and hydrogen peroxide; (4) The first mixed solution further includes an auxiliary agent, the auxiliary agent includes a catalyst, and the catalyst includes at least one of sodium hydroxide, lithium hydroxide, potassium hydroxide, ammonia water and sodium carbonate; (5) The first mixed solution further includes an auxiliary agent, wherein the auxiliary agent includes a pH adjuster, and the pH adjuster includes at least one of an acidic pH reagent and an alkaline pH reagent; (6) The first mixed solution further includes an auxiliary agent, wherein the auxiliary agent includes a pH adjuster, and the pH of the first mixed solution is 4 to 10; (7) The first mixed solution further includes an auxiliary agent, wherein the auxiliary agent includes a pH adjuster, and the pH adjuster includes at least one of hydrochloric acid, sulfuric acid, phosphoric acid and nitric acid; (8) The first mixed solution also includes an auxiliary agent, the auxiliary agent includes a pH adjuster, and the pH adjuster includes at least one of lithium hydroxide, sodium hydroxide, potassium hydroxide, sodium carbonate and sodium bicarbonate.

11. The preparation method according to claim 7, characterized in that: It meets at least one of the following technical features: (1) The polymerization reaction temperature is 40°C to 100°C; (2) The polymerization reaction time is 3h to 48h; (3) the polymerization reaction is carried out under stirring; (4) The polymerization reaction is carried out under stirring at a stirring rate of 50 r / min to 1000 r / min; (5) The solid-liquid separation includes at least one of filtration and centrifugation.

12. The preparation method according to claim 8, characterized in that: It meets at least one of the following technical features: (1) The inorganic salt includes at least one of lithium hydroxide, sodium hydroxide, potassium hydroxide, magnesium nitrate, calcium chloride, aluminum nitrate, zinc nitrate, titanium n-propoxide, niobium oxalate, zirconium oxychloride, ammonium molybdate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, sodium metasilicate, sodium borate, ammonium fluoride, titanium oxysulfide, zinc bromide and zirconium chloride; (2) The mass ratio of the first precursor to the inorganic salt is 1:(0.001-0.1); (3) The drying comprises at least one of natural volatilization, forced air drying, flash drying, freeze drying, inert atmosphere drying and vacuum drying; (4) The drying temperature is 60° C. to 600° C.; (5) The drying time is 0.5h to 48h; (6) The carbonization treatment is carried out under a protective atmosphere; (7) The carbonization treatment is carried out under a protective atmosphere, wherein the protective atmosphere comprises at least one of nitrogen, helium, neon, argon and air; (8) The heating rate of the carbonization treatment is 1°C / min to 20°C / min; (9) The heat preservation temperature of the carbonization treatment is 600° C. to 2500° C.; (10) The heat preservation time of the carbonization treatment is 0.1h to 10h.

13. A lithium ion battery, characterized in that: The lithium-ion battery comprises the negative electrode material according to any one of claims 1 to 5 or the negative electrode material prepared by the method for preparing the negative electrode material according to any one of claims 6 to 12.

Images