Composite negative electrode material, preparation method thereof, and lithium ion secondary battery

Abstract

The present application relates to the field of anode materials, and provides a composite anode material, a preparation method thereof, and a lithium-ion secondary battery. The composite anode material includes primary particles and a protective layer. Among them, the primary particles include a framework, and the framework includes a main framework located inside the primary particles and a plurality of branches extending from the main framework to the surface of the primary particles. The protective layer is located on the surface of the framework. The primary particles are of a macroporous structure, and pores are formed inside the primary particles, and the pores extend to the surface of the primary particles. The protective layer wraps the surface of the framework, or the protective layer wraps the framework and fills the pore structure. The composite anode material, the preparation method thereof, and the lithium-ion secondary battery of the present application have low cost and can be produced on a large scale, and can effectively improve the charge-discharge cycle performance of the anode material.

Description

Technical Field

[0001] This application relates to the technical field of anode materials. Specifically, it relates to a composite anode material, a preparation method thereof, and a lithium-ion secondary battery. Background Art

[0002] The new energy industry is one of the seven key emerging industries supported in China. Greatly increasing the application ratio of new energy vehicles and new energy, and promoting green and low-carbon industries such as new energy vehicles, new energy, and energy conservation and environmental protection to become pillar industries have become the strategic development plans of China. With the rapid development of the electric vehicle industry, there is an urgent need to develop lithium-ion batteries with higher energy density. The anode is an important part of a lithium-ion battery. However, the theoretical capacity of graphite anodes is only 372 mAh / g, and the capacity utilization has reached its limit, making it difficult to meet the long-range requirements of electric vehicles. Therefore, designing and developing new high-capacity anode materials is the core and key to breaking through high specific energy power batteries. Anode materials such as Si, Ge, Sn, Sb, and B have attracted wide attention and research because of their high specific capacity and are preferred anode materials for realizing high specific energy batteries. However, these anode materials have a large volume expansion (>300%) during the lithium insertion / extraction process, and will powder and fall off from the current collector during charge and discharge, resulting in the loss of electrical contact between the active material and the current collector, leading to poor electrochemical performance, capacity decay, and decreased cycle stability, making it difficult to obtain commercial applications. Summary of the Invention

[0003] In view of this, this application proposes a composite anode material and a preparation method thereof. The composite anode material can reduce volume expansion and thus effectively improve the charge and discharge cycle performance of the material.

[0004] A composite anode material, the composite anode material includes primary particles and a protective layer; wherein, the primary particles include a skeleton, the skeleton includes a main skeleton located inside the primary particles and a plurality of branches extending from the main skeleton to the surface of the primary particles; the protective layer is located on the surface of the skeleton.

[0005] In the above solution, compared with the secondary porous structure formed by the accumulation of nanoparticles, the negative electrode material of the present application has the advantage of a more stable integrated structure, and can have a smaller specific surface area and a higher porosity at the same time. The negative electrode material of the present application is a single complete particle, and the entire skeleton is connected, enhancing the electron conduction and ion diffusion of the material, and can effectively release the stress after lithiation, avoiding the pulverization of the material caused by stress concentration. For the negative electrode material assembled by primary particles, due to the obvious grain boundaries between the particles, the lithiation stress is concentrated, the particles are broken, and the entire structure is damaged, ultimately leading to the deterioration of the electrochemical performance. The protective layer formed on the surface of the negative electrode material skeleton can further improve the conductivity and cycle stability of the negative electrode material, and at the same time further alleviate the volume expansion of the negative electrode material, thereby further enhancing the conductivity and rate performance of the negative electrode material.

[0006] In a feasible implementation manner, the composite negative electrode material includes at least one of the following a to e:

[0007] a. The main skeleton is a three-dimensional network structure;

[0008] b. Each single branch is a separate crystal grain;

[0009] c. Each single branch is a separate crystal grain, and the size of the crystal grain is 30nm - 100nm;

[0010] d. The maximum width of the cross-section of the branch is 20nm - 350nm, and the maximum length of the cross-section of the branch is 50nm - 2500nm;

[0011] e. The branch is selected from at least one of rod-shaped nanoparticles, nanosheets, nanowires, and nanotubes.

[0012] In a feasible implementation manner, the primary particle is a macroporous structure, and pores are formed inside the primary particle, and the pores extend to the surface of the primary particle.

[0013] In a feasible implementation manner, the diameter of the pore is 10nm - 150nm; the depth of the pore is 50nm - 1500nm.

[0014] In a feasible implementation manner, through holes are formed inside the primary particle, and the porosity of the primary particle is not less than 30%.

[0015] In a feasible implementation manner, the protective layer is also filled in the pores or the through holes.

[0016] In a feasible implementation manner, the protective layer includes at least one of a carbon layer, a metal oxide layer, and a metal nitride layer; and / or

[0017] The protective layer includes a carbon layer, and the carbon layer is an amorphous carbon layer and / or a graphite carbon layer. Based on the composite anode material with a mass percentage of 100%, when the carbon layer is only located on the surface of the framework, the mass percentage of carbon is 5% - 25%; when the carbon layer is located on the surface of the framework and fills the pores or the through holes, based on the composite anode material with a mass percentage of 100%, the mass percentage of carbon is 25% - 75% and does not include 25%; and / or

[0018] The protective layer includes a metal oxide layer, and the metal elements of the metal oxide layer include at least one of Si, Sn, Ge, Li, V, Al, Fe, and Zn. Based on the composite anode material with a mass percentage of 100%, when the metal oxide layer is only located on the surface of the framework, the mass percentage of the metal oxide is 5% - 25%; when the metal oxide layer is located on the surface of the framework and fills the pores or the through holes, based on the composite anode material with a mass percentage of 100%, the mass percentage of the metal oxide is 25% - 75% and does not include 25%; and / or

[0019] The protective layer includes a metal nitride layer, and the metal elements in the metal nitride layer include at least one of Ti, V, Nb, Ta, W, and Zr. Based on the composite anode material with a mass percentage of 100%, when the metal nitride layer is only located on the surface of the framework, the mass percentage of the metal nitride is 5% - 25%; when the metal nitride is located on the surface of the framework and fills the pores or the through holes, based on the composite anode material with a mass percentage of 100%, the mass percentage of the metal nitride is 25% - 75% and does not include 25%.

[0020] In a feasible implementation manner, the composite anode material includes at least one of the following a - j:

[0021] a. The primary particles are selected from at least one of silicon, germanium, antimony, tin, and boron;

[0022] b. The median particle size of the primary particles is 0.2 μm - 15 μm;

[0023] c. The specific surface area of the primary particles is 5 m2 / g - 100 m2 / g;

[0024] d. The porosity of the primary particles is 30% - 70%;

[0025] e. The tapped density of the primary particle powder is 0.2 g / cm3 - 0.8 g / cm3;

[0026] f. The compacted density of the primary particle powder is 1.2 g / cm3 - 1.8 g / cm3;

[0027] g. The median particle size of the composite anode material is 0.1 μm to 15 μm;

[0028] h. The specific surface area of the composite anode material is 1 m2 / g to 150 m2 / g;

[0029] i. The porosity of the composite anode material is 10% to 70%;

[0030] j. The thickness of the protective layer on the surface of the framework is 1 nm to 300 nm.

[0031] The present application provides a method for preparing a composite anode material, and the method includes the following steps:

[0032] Placing a mixture containing an N-M alloy and a carbon-containing ammonium salt in a protective atmosphere for a displacement reaction to obtain a reaction product, the reaction product including an oxide of M and a nitride of M; and

[0033] Removing the oxide of M and the nitride of M to obtain a composite anode material;

[0034] Wherein, N in the N-M alloy includes at least one of silicon, germanium, antimony, tin, and boron, and M in the N-M alloy includes at least one of magnesium, aluminum, calcium, and zinc.

[0035] In the above solution, the present application uses a carbon-containing ammonium salt as a carbon source and an N-M alloy to prepare a composite anode material by a one-step composite method under high temperature conditions. Compared with the two-step composite method, it can effectively improve the preparation efficiency and the process is simple.

[0036] In a feasible implementation manner, the method includes at least one of the following features a to e:

[0037] a. The particle size of the N-M alloy is 0.2 μm to 15 μm;

[0038] b. The molar ratio of the N-M alloy to the carbon-containing ammonium salt in the mixture is 1:(0.1-10);

[0039] c. The carbon-containing ammonium salt includes at least one of ammonium carbonate, ammonium bicarbonate, and ammonium carbamate;

[0040] d. The mixture further includes a carbon-containing ammonium salt decomposition inhibitor; and / or

[0041] The molar ratio of the N-M alloy to the carbon-containing ammonium salt decomposition inhibitor is 1:(0.2-10); and / or, the ammonium salt decomposition inhibitor includes carbonate and / or bicarbonate;

[0042] e. The mixture further includes a molten salt medium; and / or

[0043] The molar ratio of the N-M alloy to the molten salt medium is 1:(0.1 - 10); and / or

[0044] The molten salt medium includes at least one of ammonium halide salts and halide salts; and / or

[0045] The chemical formula of the ammonium halide salt is NH 4 Y, where Y includes at least one of Cl, Br, F, and I.

[0046] In a feasible implementation manner, the preparation method includes at least one of the following features a to g:

[0047] a. The reaction temperature of the displacement reaction is 200°C to 950°C, and the heat preservation time is 1 h to 24 h;

[0048] b. The reaction heating rate of the displacement reaction is 1°C / min to 20°C / min;

[0049] c. The protective atmosphere includes at least one of helium, neon, argon, krypton, and xenon;

[0050] d. The method for removing the oxide of M and the nitride of M includes pickling;

[0051] e. The method for removing the oxide of M and the nitride of M includes pickling, and the acid solution used for pickling includes at least one of hydrochloric acid, nitric acid, and sulfuric acid;

[0052] f. The method for removing the oxide of M and the nitride of M includes pickling, and the mass concentration of the acid solution used for pickling is 1 mol / L to 5 mol / L;

[0053] g. The method for removing the oxide of M and the nitride of M includes pickling, and the pickling time is 1 h to 10 h.

[0054] On the other hand, the present application also provides a method for preparing a composite negative electrode material, including the following steps:

[0055] Placing a mixture containing an N-M alloy and a transition metal halide in a protective atmosphere for a displacement reaction to obtain a reaction product, the reaction product including a halide of M and a transition metal; and

[0056] Removing the halide of M and the transition metal in the reaction product to obtain an N material, the N material being primary particles, and the primary particles including a skeleton, the skeleton including a main skeleton located inside the primary particles and a plurality of branches extending from the main skeleton to the surface of the primary particles; and

[0057] A metal oxide layer is formed on the surface of the skeleton of the N material to obtain a composite negative electrode material;

[0058] Among them, N in the N-M alloy includes at least one of silicon, germanium, antimony, tin, and boron, and M in the N-M alloy includes at least one of magnesium, aluminum, calcium, and zinc.

[0059] The composite negative electrode material obtained by this preparation method has a metal oxide layer formed on the surface of the N material. The metal oxide layer has advantages such as good rigidity and excellent compactness, and can effectively inhibit the destruction of the entire structure caused by the volume expansion of N, reduce the volume expansion of the material, and at the same time avoid the contact between the electrolyte and the N material, reduce side reactions, and improve the initial efficiency of the entire composite material.

[0060] On the other hand, the present application also provides a preparation method of a composite negative electrode material, including the following steps:

[0061] A mixture containing an N-M alloy and a transition metal halide is placed in a protective atmosphere for a displacement reaction to obtain a reaction product, and the reaction product includes a halide of M and a transition metal; and

[0062] The halide of M and the transition metal are removed to obtain an N material. The N material is a primary particle, and the primary particle includes a skeleton. The skeleton includes a main skeleton located inside the primary particle and a plurality of branches extending from the main skeleton to the surface of the primary particle;

[0063] A metal oxide layer is formed on the surface of the skeleton of the N material to obtain a composite; and

[0064] The composite is heat-treated in a protective atmosphere and then nitrided to obtain a composite negative electrode material;

[0065] Among them, N in the N-M alloy includes at least one of silicon, germanium, antimony, tin, and boron, and M in the N-M alloy includes at least one of magnesium, aluminum, calcium, and zinc.

[0066] By coating a metal oxide layer on the surface of the skeleton of the negative electrode material N and then heat-treating in a protective atmosphere, it is ensured that the oxide is transformed from amorphous to crystalline under high temperature and normal pressure. Further, through nitriding treatment, the metal oxide layer on the surface of the inner core is nitrided into a metal nitride. In this solution, the metal nitride layer not only has good rigidity but also excellent electrical conductivity, can effectively relieve the volume expansion of silicon, increase the electrical conductivity of the material, improve the rate performance of the material, reduce the irreversible capacity loss of the material, and bring high capacity.

[0067] In a feasible implementation manner, the preparation method includes at least one of the following features a to h:

[0068] a. The chemical formula of the transition metal halide is ABx, where x = 2 or 3, A includes at least one of Sn, Cu, Fe, Zn, Co, Mn, Cr, and Ni, and B includes at least one of Cl, F, and Br;

[0069] b. The method for forming the metal oxide layer includes at least one of hydrothermal method, sol-gel method, precipitation method, chemical vapor deposition method, magnetron sputtering, and solid-phase reaction method;

[0070] c. The metal elements in the metal oxide layer include at least one of Si, Sn, Ge, Li, V, Al, Fe, and Zn;

[0071] d. The temperature of the displacement reaction is 500°C - 1100°C, and the heat preservation time is 1h - 48h;

[0072] e. The heat treatment temperature is 500°C - 800°C, and the heat preservation time is 1h - 24h; and / or, the protective atmosphere includes at least one of helium, neon, argon, krypton, and xenon;

[0073] f. The method for removing the halides of the transition metals A and M is pickling;

[0074] g. The nitriding treatment is carried out at 400°C - 950°C for 2h - 24h;

[0075] h. The atmosphere for the nitriding treatment adopts at least one of ammonia atmosphere and nitrogen atmosphere.

[0076] A lithium-ion secondary battery, which includes the composite negative electrode material described above or the negative electrode material prepared by the preparation method of the composite negative electrode material. Description of the Drawings

[0077] Figure 1a It is a schematic structural diagram of the composite negative electrode material provided for an embodiment;

[0078] Figure 1b It is a schematic structural diagram of the composite negative electrode material provided for another embodiment;

[0079] Figure 2 It is a schematic synthesis flow diagram of the composite negative electrode material provided for this embodiment;

[0080] Figure 3a It is a scanning electron microscope picture of the silicon-carbon composite negative electrode material provided for this embodiment;

[0081] Figure 3b It is another scanning electron microscope picture of the silicon-carbon composite negative electrode material provided for this embodiment;

[0082] Figure 4Raman graph of the silicon-carbon composite anode material provided in this embodiment;

[0083] Figure 5 XRD graph of the silicon-carbon composite anode material provided in this embodiment;

[0084] Figure 6 Cycling performance curve graph of the silicon-carbon composite anode material provided in this embodiment. Specific implementation manners

[0085] The following are the preferred implementation manners of the embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principles of the embodiments of the present invention, 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 invention.

[0086] "Dealloying" herein refers to a method of selectively removing one or more components in an alloy through a chemical or electrochemical corrosion process. The dealloying process involves the removal of old lattice sites and the formation of new lattice sites, and also involves the nucleation and growth of new crystals. Among them, the formation of the nanoporous structure during the dealloying process is closely related to the atomic-level reorganization at the alloy / solution interface, and the reorganization process is completed through the surface diffusion of undissolved metal atoms and vacancies. Moreover, the speed of surface diffusion has an important impact on the size of the ligaments / channels in the finally formed nanoporous metal.

[0087] The embodiments of the present application provide a composite anode material. Specifically, as Figure 1a shown, the composite anode material includes primary particles and a protective layer 20;

[0088] Among them, the primary particles include a framework, and the framework includes a main framework 11 located inside the primary particles and a plurality of branches 12 extending from the main framework 11 to the surface of the primary particles; the protective layer 20 is located on the surface of the framework.

[0089] Please further refer to Figure 1a , the primary particles of this embodiment are of a macroporous structure, and pore channels 13 are formed inside the primary particles, and the pore channels 13 extend to the surface of the primary particles. Among them, according to the definition of the International Union of Pure and Applied Chemistry (IUPAC), pores with a diameter greater than 50 nm are called macropores.

[0090] The main framework inside the primary particles of the anode material of this embodiment and the plurality of branches extending from the main framework to the surface of the primary particles are an integral body. The entire framework structure enhances the electronic conduction and ion diffusion of the material, and can effectively release the stress after lithiation, avoiding the concentration of stress at the grain boundaries and causing the material to crack and pulverize.

[0091] The pore structure where the pores of the negative electrode material extend to the surface of the primary particles has the following advantages: First, while improving the lithium storage performance, it reduces the swelling of the lithium battery. It can not only relieve the volume expansion during the lithium intercalation process, but also provide space for internal expansion during lithiation, enabling the electrode material to expand inward after lithiation and reducing the thickness of the entire electrode film, greatly improving the safety of the lithium-ion battery. Second, it provides channels for the electrolyte to flow, facilitating the contact of the electrolyte. The pore structure can also bring a higher tap density and increase the volumetric energy density of the battery.

[0092] Moreover, compared with the secondary porous structure formed by the accumulation of nanoparticles, the negative electrode material of this embodiment has the advantage of a more stable integrated structure and can have both a smaller specific surface area and a higher porosity. The present invention is a single complete particle with the entire skeleton connected, enhancing the electron conduction and ion diffusion of the material, and can effectively release the stress after lithiation, avoiding material pulverization caused by stress concentration. For the porous material assembled by secondary particles, due to the obvious grain boundaries between the particles, it leads to stress concentration during lithiation, particle fragmentation, and the destruction of the entire structure, ultimately resulting in the deterioration of the electrochemical performance.

[0093] The protective layer located on the surface of the skeleton can improve the conductivity and stability, facilitate the entry and exit of lithium ions, and improve the rate performance of the negative electrode material.

[0094] In some embodiments, the main skeleton is a three-dimensional network structure;

[0095] In some embodiments, a single branch is a separate grain; there is no obvious grain boundary between the branch and the main skeleton, and the grains are dispersed on the surface of the primary particle. In the prior art solutions, the branches on the secondary particles of porous silicon are mainly composed of multiple small grains with many grain boundaries. Compared with this structure, the branches on the primary particles in this embodiment are a single large grain without excessive grain boundaries. After lithiation, the stress can be better dispersed, avoiding material damage caused by stress concentration; at the same time, the crystal plane curves of a single grain are the same, which is more conducive to reducing the relative volume expansion in a certain direction of the material, while the structure composed of multiple small grains has a relatively large volume expansion and relatively poor structural stability, resulting in poor cycle stability.

[0096] Specifically, the size of the grain is 30nm - 100nm; exemplarily, the size of the grain can be 30nm, 45nm, 50nm, 60nm, 75nm, 100nm.

[0097] Among them, further referring to Figure 1a , the maximum width 11W of the cross-section of the branch is 20nm - 350nm, and the maximum length 11L of the cross-section of the branch is 50nm - 2500nm;

[0098] Exemplarily, the maximum width 11W of the branch cross-section can be, for example, 20 nm, 40 nm, 80 nm, 100 nm, 150 nm, 200 nm, 250 nm, 300 nm or 350 nm, and the maximum length 11L of the branch cross-section can be, for example, 50 nm, 100 nm, 200 nm, 300 nm, 400 nm, 500 nm, 800 nm, 1000 nm, 1500 nm, 2000 nm or 2500 nm, which is not limited herein.

[0099] In some embodiments, the branch is selected from at least one of rod-shaped nanoparticles, nanosheets, nanowires and nanotubes.

[0100] In some embodiments, the diameter of the pore 13 measured by the mercury intrusion test method is 10 nm - 150 nm; the depth of the pore is 50 nm - 1500 nm. Exemplarily, the pore diameter can specifically be 10 nm, 50 nm, 60 nm, 80 nm, 100 nm or 150 nm, which is not limited herein. The depth of the pore 13 can specifically be 50 nm, 100 nm, 200 nm, 300 nm, 400 nm, 500 nm, 800 nm or 1000 nm, which is not limited herein.

[0101] In some embodiments, the protective layer includes at least one of a carbon layer, a metal oxide layer, and a metal nitride layer;

[0102] In some embodiments, the carbon layer is an amorphous carbon layer and / or a graphite carbon layer;

[0103] In some embodiments, the carbon layer is only located on the surface of the framework. Based on the mass percentage of the composite anode material being 100%, the mass percentage of carbon is 5% - 25%; specifically, it can be 5%, 8%, 10%, 12%, 15%, 18%, 20% or 25%, which is not limited herein.

[0104] In some embodiments, the thickness of the carbon layer is 1 nm - 300 nm.

[0105] In some embodiments, referring to Figure 1b , when the content of the protective layer is relatively high, the protective layer also fills the pores, which can further enhance the conductivity and structural stability.

[0106] Specifically, the carbon layer also fills the pores; the carbon filled in the pore structure can provide more ion and electron transport paths, has good carbon conductivity, is beneficial to the entry and exit of lithium ions, improves the rate performance of the material, and can further improve the stability.

[0107] In some embodiments, when the carbon layer is located on the surface of the framework and fills the pores, based on the mass percentage of the composite anode material being 100%, the mass percentage of carbon is 25% to 75% and does not include 25%; specifically, it can be 25%, 28%, 30%, 35%, 40%, 45%, 50% or 75%, which is not limited herein.

[0108] In some embodiments, the protective layer includes a metal oxide layer, and the metal elements of the metal oxide layer include at least one of Si, Sn, Ge, Li, V, Al, Fe, and Zn; the metal oxide layer has advantages such as good rigidity and excellent compactness, and can effectively inhibit the destruction of the entire structure caused by the volume expansion of N, reduce the volume expansion of the material, avoid contact between the electrolyte and the N material at the same time, reduce side reactions, and improve the initial efficiency of the entire composite material.

[0109] Based on the mass percentage of the composite anode material being 100%, when the metal oxide layer is only located on the surface of the framework, the mass percentage of the metal oxide is 5% to 25%;

[0110] When the metal oxide layer is located on the surface of the framework and fills the pores, based on the mass percentage of the composite anode material being 100%, the mass percentage of the metal oxide is 25% to 75% and does not include 25%;

[0111] The protective layer includes a metal nitride layer, and the metal elements in the metal nitride layer include at least one of Ti, V, Nb, Ta, W, and Zr; the metal nitride layer not only has good rigidity but also excellent electrical conductivity, can effectively relieve the volume expansion of silicon, increase the electrical conductivity of the material, improve the rate performance of the material, reduce the irreversible capacity loss of the material, and bring high capacity.

[0112] Based on the mass percentage of the composite anode material being 100%, when the metal nitride layer is only located on the surface of the framework, the mass percentage of the metal nitride is 5% to 25%;

[0113] When the metal nitride is located on the surface of the framework and fills the pores, based on the mass percentage of the composite anode material being 100%, the mass percentage of the metal nitride is 25% to 75% and does not include 25%.

[0114] Through holes are formed inside the primary particles of one embodiment, and the porosity of the primary particles is not less than 30%. The primary particles of this embodiment have a high porosity, which can effectively alleviate the volume expansion of the negative electrode material by more than 300%. Combining the advantages of the macroporous through-structure, the pore structure after lithiation can also be kept intact. The porosity of the prior art is low and there are many micropores and mesopores, which cannot meet the huge volume expansion of the negative electrode material (such as silicon). After the holes are filled after lithiation, due to electrochemical sintering, the holes are finally blocked and the porous structure cannot be maintained.

[0115] Furthermore, the porosity of the primary particles is 30% - 70%, such as 30%, 35%, 40%, 50%, 55%, 60% or 70%, etc., and preferably 40% - 60%.

[0116] As Figure 1b shown, in some embodiments, the carbon layer is also filled in the through holes; the carbon filled in the through holes can provide more ion and electron transmission paths, has good carbon conductivity, is beneficial to the entry and exit of lithium ions, improves the rate performance of the material, and can further improve the stability.

[0117] In some embodiments, when the carbon layer is located on the surface of the framework and fills the through holes, based on the mass percentage content of the composite negative electrode material being 100%, the mass percentage content of carbon is 25% - 75% and does not include 25%; specifically, it can be 25%, 28%, 30%, 35%, 40%, 45%, 50% or 75%, which is not limited herein.

[0118] In some embodiments, the protective layer is a metal oxide layer, and the metal elements of the metal oxide layer include at least one of oxides of Si, Sn, Ge, Li, V, Al, Fe and Zn.

[0119] Based on the mass percentage content of the composite negative electrode material being 100%, when the oxide layer is located on the surface of the framework and fills the through holes, the mass percentage content of the metal oxide is 25% - 75% and does not include 25%.

[0120] In some embodiments, the protective layer is a metal nitride layer, and the metal elements in the metal nitride layer include at least one of Ti, V, Nb, Ta, W and Zr.

[0121] In some embodiments, when the metal nitride layer is located on the surface of the framework and fills the through holes, the mass percentage content of the metal nitride is 25% - 75% and does not include 25%.

[0122] In some embodiments, the primary particles are selected from at least one of silicon, germanium, tin, boron, and antimony; their skeletons can be silicon skeletons, germanium skeletons, tin skeletons, boron skeletons, antimony skeletons, etc.; for example, if the primary particles are selected from silicon materials, the primary particles include a silicon skeleton, including a main skeleton located inside the primary particles and multiple branches extending from the main skeleton to the surface of the primary particles. The skeleton structures of germanium, boron, tin, and antimony are similar to the above-mentioned silicon skeleton structure.

[0123] In some embodiments, the median particle size of the primary particles is 0.2 μm to 15 μm, such as 0.2 μm, 1 μm, 3 μm, 5 μm, 8 μm, 10 μm, 12 μm, or 15 μm, etc. Preferably, it is 0.5 μm to 10 μm, and more preferably 1 μm to 5 μm.

[0124] In some embodiments, the specific surface area of the primary particles is 5 m 2 / g to 100 m 2 / g, such as 5 m 2 / g, 10 m 2 / g, 20 m 2 / g, 30 m 2 / g, 40 m 2 / g, 50 m 2 / g, 60 m 2 / g, 80 m 2 / g, or 100 m 2 / g, etc. Preferably, it is 10 m 2 / g to 50 m 2 / g.

[0125] In some embodiments, the tapped density of the powder of the primary particles is 0.2 g / cm 3 to 0.8 g / cm 3 , such as 0.2 g / cm 3 , 0.3 g / cm 3 , 0.5 g / cm 3 , 0.6 g / cm 3 , 0.7 g / cm 3 , or 0.8 g / cm 3 , etc. Preferably, it is 0.4 g / cm 3 to 0.7 g / cm 3 .

[0126] In some embodiments, the compressibility of the powder of the primary particles is 1.2 g / cm 3 to 1.8 g / cm 3 , such as 1.2 g / cm 3 , 1.3 g / cm 3 , 1.4 g / cm 3 , 1.5 g / cm 3, 1.6 g / cm 3 or 1.8 g / cm 3 etc., preferably 1.4 g / cm 3 ~1.7 g / cm 3 ;

[0127] In some embodiments, the median particle size of the composite negative electrode material is 0.1 μm to 15 μm. Optionally, the median particle size of the composite negative electrode material can specifically be 0.1 μm, 0.5 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm or 10 μm, etc., which is not limited herein. The median particle size of the composite negative electrode material is preferably 0.5 μm to 10 μm, and more preferably 1 μm to 8 μm.

[0128] In some embodiments, the specific surface area ratio of the composite negative electrode material is 1 m 2 / g~150 m 2 / g. Optionally, the specific surface area ratio of the composite negative electrode material can be 1 m 2 / g, 5 m 2 / g, 10 m 2 / g, 20 m 2 / g, 30 m 2 / g, 40 m 2 / g, 50 m 2 / g, 60 m 2 / g, 70 m 2 / g, 100 m 2 / g, 120 m 2 / g or 150 m 2 / g, etc., which is not limited herein; the specific surface area ratio of the composite negative electrode material is preferably 1 m 2 / g~50 m 2 / g. It can be understood that the smaller the specific surface area, the better. An excessively large specific surface area is likely to cause the formation of the SEI film, consume too much irreversible lithium salt, and reduce the initial efficiency of the battery. Considering the cost of the preparation process, the specific surface area is controlled at 10 m 2 / g~50 m 2 / g.

[0129] In some embodiments, the porosity of the composite negative electrode material is 10% to 70%, such as 10%, 30%, 35%, 40%, 50%, 55%, 60% or 70%, etc., and is preferably 40% to 60%.

[0130] When the protective layer is a carbon layer, a preparation method of a composite negative electrode material in an embodiment is as Figure 2 shown, and the method includes the following steps S100 to S400:

[0131] S100. Prepare the N-M alloy;

[0132] S200. Mix the N-M alloy with the ammonium carbonate salt to obtain a mixture;

[0133] S300. Carry out a displacement reaction on the mixture under a protective atmosphere to obtain a reaction product, where the reaction product includes the nitride of M and the oxide of M;

[0134] S400. Remove the oxide of M and the nitride of M to obtain a composite anode material.

[0135] The obtained composite anode material includes primary particles and a carbon layer; among them, the primary particles include a framework, and the framework includes a main framework located inside the primary particles and multiple branches extending from the main framework to the surface of the primary particles; the carbon layer is located on the surface of the framework.

[0136] The primary particles are of a macroporous structure, and pores are formed inside the primary particles, and the pores extend to the surface of the primary particles.

[0137] And through holes are formed inside the primary particles, and the porosity of the primary particles is not less than 30%.

[0138] In this solution, the anode material is prepared by a one-step composite method. At high temperature, the N-M alloy directly reacts with the ammonium carbonate salt to remove the metal components in the N-M alloy, and at the same time, a carbon layer is in-situ deposited on the surface of the N material. After pickling, a composite anode material is obtained. The overall reaction is mild and there are no by-products. The N material structure is complete and stable, and the carbon layer is evenly deposited. The raw materials participating in the reaction are all common alloys, ammonium salts and common inorganic compounds, which can reduce costs.

[0139] The following is a specific description of the preparation method of the composite anode material;

[0140] Step S100. Prepare the N-M alloy;

[0141] In some embodiments, the N in the N-M alloy includes at least one of Si, Ge, Sn, B, and Sb; the M in the N-M alloy includes at least one of Mg, Al, Zn, and Ca. In a specific example, the N-M alloy can be a Si-Mg alloy, a Si-Al alloy, a Ge-Mg alloy, a Ge-Al alloy, etc. Different types of alloys can obtain different-shaped branches, including at least one of rod-shaped nanoparticles, nanosheets, nanowires, and nanotubes.

[0142] In some embodiments, the preparation method of the N-M alloy is to mix N powder and active metal M and then heat and react under a protective gas to obtain the N-M alloy.

[0143] Among them, the powder particle size of the N powder is 0.2 μm to 15 μm, specifically, it can be 0.2 μm, 0.5 μm, 1 μm, 3 μm, 5 μm, 8 μm, 10 μm, 15 μm, etc., which are not limited herein.

[0144] The powder particle size of the active metal M is 0.1 μm to 80 μm, specifically, it can be 0.1 μm, 5 μm, 10 μm, 20 μm, 40 μm, 50 μm, 80 μm, etc., which are not limited herein.

[0145] The molar ratio of the N powder to the active metal M is 1:(1 - 3), specifically, it can be 1:1, 1:1.5, 1:2, 1:2.5, or 1:3, which are not limited herein.

[0146] In some embodiments, the temperature of the heating reaction is 400 - 900 °C. For example, it can be 400 °C, 500 °C, 600 °C, 700 °C, 800 °C, or 900 °C.

[0147] The heat preservation time of the heating reaction is 2 h to 8 h. For example, it can be 2 h, 4 h, 6 h, or 8 h, which are not limited herein.

[0148] The heating rate of the heating reaction is 1 °C / min to 10 °C / min. For example, it can be 1 °C / min, 3 °C / min, 5 °C / min, 8 °C / min, or 10 °C / min, which are not limited herein.

[0149] In this application, by controlling parameters such as the N powder particle size, active metal particle size, reaction temperature, and reaction time, it is beneficial to the formation of the silicon alloy and improves the doping uniformity of the metal elements in the silicon alloy.

[0150] Of course, the N-M alloy can also be prepared by other preparation methods, such as high-energy ball milling, vacuum smelting, and hot press sintering, etc. It can be understood that the N-M alloy can be obtained commercially, and in this case, step S100 can be omitted.

[0151] In some embodiments, the mass percentage content of N in the N-M alloy is 15% - 60%. Optionally, the mass percentage content of N can be 15%, 20%, 30%, 40%, 50%, or 60%, which are not limited herein. In specific embodiments, the N-M alloy can be at least one of a silicon-magnesium alloy, a silicon-aluminum alloy, a silicon-calcium alloy, and a silicon-zinc alloy. It can be understood that the pore size and porosity of the three-dimensional pores of the N material can be changed by controlling the composition of the N-M alloy. Generally, the higher the N content in the N-M alloy, the smaller the pore size. The pore depth can be changed by controlling the heating reaction time and reaction temperature. Generally, the longer the reaction time and the higher the reaction temperature, the deeper the pore depth.

[0152] In specific embodiments, the method further includes:

[0153] The obtained N-M alloy is pulverized, and the particle size of the N-M alloy powder is adjusted to 0.2 μm to 15 μm. For example, it can be 0.2 μm, 0.5 μm, 1 μm, 2 μm, 5 μm, 10 μm or 15 μm, which is not limited herein.

[0154] Specifically, the equipment for the pulverization treatment includes at least one of a planetary ball mill, a sand mill and a jet mill. It can be understood that the smaller the particle size of the silicon alloy, the larger its specific surface area, and the reaction can be more sufficient during the dealloying heat treatment.

[0155] S200. Mix the N-M alloy and the carbon-containing ammonium salt to obtain a mixture;

[0156] It should be noted that the carbon-containing ammonium salt refers to a salt containing carbon and ammonium ions.

[0157] In some specific embodiments, the molar ratio of the N-M alloy to the carbon-containing ammonium salt in the mixture is 1:(0.1-10). Specifically, it can be 1:0.1, 1:0.5, 1:1, 1:2, 1:4, 1:5, 1:7 or 1:10, which is not limited herein.

[0158] Specifically, the carbon-containing ammonium salt includes at least one of ammonium carbonate, ammonium bicarbonate and ammonium carbamate; ammonium carbonate, ammonium bicarbonate and ammonium carbamate are thermally unstable and easily decompose into ammonia and carbon dioxide. Therefore, during the reaction process, an ammonium salt inhibitor is added to the mixture to inhibit the high-temperature decomposition of the ammonium salt.

[0159] In some specific embodiments, the molar ratio of the N-M alloy to the ammonium salt decomposition inhibitor is 1:(0.2-10). For example, it can be 1:0.2, 1:0.5, 1:1, 1:2, 1:4, 1:5, 1:7 or 1:10, which is not limited herein.

[0160] In some of these embodiments, the ammonium salt decomposition inhibitor includes a carbonate and / or a bicarbonate.

[0161] Among them, the chemical formula of the carbonate is M y CO 3 , and the chemical formula of the bicarbonate is M(HCO 3 ) y , M includes at least one of Na, K, Li, Mg, Ca, Zn, and Ba, and y = 1 or 2.

[0162] It can be understood that the bicarbonate is unstable at high temperatures and easily decomposes into a carbonate, carbon dioxide and water. The decomposed carbon dioxide gas, inorganic salt and water are harmless to the environment and absorb part of the reaction energy to inhibit the decomposition reaction of the ammonium salt at high temperatures.

[0163] In some of the embodiments, in order to improve the reaction completeness, a molten salt medium is further added. Optionally, the molten salt medium includes at least one of an ammonium halide salt and a halide salt.

[0164] The molar ratio of the NM alloy to the ammonium halide salt is 1:(0.1-10), specifically 1:0.1, 1:0.5, 1:1, 1:2, 1:4, 1:5, 1:7 or 1:10, which is not limited here. The chemical formula of the ammonium halide salt is NH 4 Y, wherein Y includes at least one of Cl, Br, F and I.

[0165] An ammonium salt decomposition inhibitor and an appropriate amount of molten salt medium (ammonium halide salt) are added to the reaction. On the one hand, the ammonium salt decomposition inhibitor can be used to inhibit the decomposition of the ammonium salt, so that it remains in a high-temperature liquid state, which is conducive to the ammonium salt slowly reacting with the alloy from the outside to the inside to achieve the purpose of dealloying. At the same time, it gradually flows into the pore structure of the silicon material and serves as a liquid template for the connected skeleton, which facilitates the gradual and uniform deposition of carbon in the pore structure of the silicon material, thereby enhancing the conductivity and structural stability of the entire composite structure. On the other hand, the molten salt can increase the solubility of the ammonium salt therein, promote the full reaction, ensure the high-temperature liquid environment when the alloy powder reacts with the ammonium salt and the uniformity of the reaction temperature, avoid the destruction of the porous structure due to excessive local temperature, and improve the yield and purity.

[0166] After adding the corresponding ammonium halide as the molten salt medium, the high-temperature liquid environment and the uniformity of the reaction temperature when the alloy powder reacts with the ammonium salt can be further guaranteed, avoiding the destruction of the porous structure due to excessive local temperature. The obtained negative electrode material has excellent stability, uniform carbon composite structure, and exhibits excellent electrochemical properties.

[0167] Similarly, the molar ratio of the NM alloy to the halide is 1:(0.1-10), specifically 1:0.1, 1:0.5, 1:1, 1:2, 1:4, 1:5, 1:7 or 1:10, which is not limited here. The halide chemical formula is MYa, where a=1, M includes at least one of Na, K, Li, Mg, Ca, Zn and Ba, and Y includes at least one of Cl, Br, F and I.

[0168] S300, subjecting the mixture to a replacement reaction under a protective atmosphere to obtain a reaction product, wherein the reaction product includes a nitride of M and an oxide of M.

[0169] This reaction can be called a dealloying reaction.

[0170] The reaction products of the substitution reaction include nitrides of M, oxides of M, carbon and N. For example, the NM alloy is a silicon-magnesium alloy, the ammonium salt is ammonium carbonate, and the chemical reaction formula for dealloying is: 5Mg2 Si + 2(NH 4 ) 2 CO 3 → 5Si + 2C + 4MgO + 2Mg 3 N 2 + 2H 2 O + 6H 2 , after the reaction, remove the metal oxides (MgO) and nitrides (Mg 3 N 2 ) in the reaction products, and a composite anode material can be obtained.

[0171] It can be understood that when an ammonium salt is selected to participate in the dealloying process, the ammonium salt is in a molten state during the reaction process, providing a connected liquid template for the formation of the connected silicon skeleton and ensuring the continuity of the pore structure of the silicon skeleton; in addition, the ammonium salt serves as a carbon source, and the carbon layer formed after the reaction is continuously filled in the pore structure to form a three-dimensional conductive carbon network structure. Since the reaction is relatively mild at high temperatures, the carbon-oxygen bonds in the ammonium salt can be broken and reorganized orderly to form a carbon layer, improving the conductivity and being more conducive to the entry and exit of lithium ions, thereby improving the rate performance of the material.

[0172] In a specific embodiment, the dealloying heat treatment is carried out under a vacuum condition, and the vacuum degree is 1 Pa to 20 kPa. It can be understood that in the embodiments of the present application, the dealloying heat treatment is carried out in a high-temperature vacuum environment, which improves the reaction rate and makes the reaction safer.

[0173] In order for the mixture to react fully, the temperature of the dealloying heat treatment is 200 °C to 950 °C, for example, it can be 200 °C, 300 °C, 400 °C, 600 °C, 800 °C or 950 °C.

[0174] The heat preservation time of the dealloying heat treatment is 1 h to 24 h, for example, it can be 1 h, 3 h, 6 h, 9 h, 12 h, 15 h, 18 h or 24 h, and no limitation is made here.

[0175] The heating rate of the dealloying heat treatment is 1 °C / min to 20 °C / min, for example, it can be 1 °C / min, 5 °C / min, 10 °C / min, 15 °C / min or 20 °C / min. Thereby effectively improving the reaction efficiency.

[0176] It can be understood that within the above-mentioned suitable heat treatment temperature, time, and heating rate ranges, it is helpful to improve the dealloying efficiency and helpful for the N-M alloy to form an N skeleton structure during the dealloying process. In order to improve the safety of the reaction, the dealloying heat treatment is carried out under the protection of a protective gas, and the protective gas includes at least one of nitrogen, helium, neon, argon, and xenon. The flow rate of the protective gas can be controlled at 1 L / min to 10 L / min to improve the safety of the reaction.

[0177] S400. Remove the oxide and nitride of M to obtain a composite anode material.

[0178] As an optional technical solution of the present application, the removal method includes pickling. Pickling the reaction product can remove the oxide and nitride of M in the reaction product.

[0179] The mass concentration of the acid solution is 1 mol / L to 5 mol / L. For example, it can be 1 mol / L, 2 mol / L, 3 mol / L, 4 mol / L, or 5 mol / L. Of course, the mass concentration of the acid solution can also be adjusted according to actual needs and is not limited herein.

[0180] The duration of the pickling is 1 h to 10 h. For example, it can be 1 h, 3 h, 5 h, 7 h, or 10 h. In this embodiment, the pickling product can still be recycled.

[0181] When the protective layer is a metal oxide layer, the preparation method of the composite anode material includes the following steps S100' to S500':

[0182] S100'. Prepare an N-M alloy;

[0183] S200'. Mix the N-M alloy with a transition metal halide to obtain a mixture;

[0184] S300'. Place the mixture in a protective atmosphere for a displacement reaction to obtain a reaction product. The reaction product includes a halide of M and a transition metal;

[0185] S400'. Remove the halide of M and the transition metal in the reaction product to obtain an N material; the N material is a primary particle, and the primary particle includes a framework. The framework includes a main framework located inside the primary particle and a plurality of branches extending from the main framework to the surface of the primary particle;

[0186] S500'. Form a metal oxide layer on the surface of the framework of the N material to obtain a composite anode material.

[0187] The obtained composite anode material includes primary particles and a metal oxide layer; wherein, the primary particles include a framework. The framework includes a main framework located inside the primary particle and a plurality of branches extending from the main framework to the surface of the primary particle; the metal oxide layer is located on the surface of the framework.

[0188] It can be understood that the primary particle is a macroporous structure, and pores are formed inside the primary particle, and the pores extend to the surface of the primary particle.

[0189] It can also be understood that through holes are formed inside the primary particle, and the porosity of the primary particle is not less than 30%.

[0190] The following is a specific description of the preparation method of the composite negative electrode material;

[0191] S100′. Prepare the N-M alloy;

[0192] In some embodiments, N in the N-M alloy includes at least one of Si, Ge, Sn, B, and Sb; M in the N-M alloy includes at least one of Mg, Al, Zn, and Ca. In a specific example, the N-M alloy can be a Si-Mg alloy, a Si-Al alloy, a Ge-Mg alloy, a Ge-Al alloy, etc. Different types of alloys can obtain different-shaped branches, including at least one of rod-shaped nanoparticles, nanosheets, nanowires, and nanotubes.

[0193] Specifically, the preparation method of the N-M alloy is the same as that in step S100; details are not described here;

[0194] S200′. Mix the N-M alloy with a transition metal halide to obtain a mixture;

[0195] In some embodiments, the chemical formula of the transition metal halide is ABx, where x = 2 or 3, A includes at least one of Sn, Cu, Fe, Zn, Co, Mn, Cr, and Ni, and B includes at least one of Cl, F, and Br;

[0196] Among them, the molar ratio of the N-M alloy to the transition metal halide is 1:(0.1 - 2).

[0197] It can be understood that the mixture can be obtained commercially, and in this case, step S200′ can be omitted.

[0198] S300′. Place the mixture in a protective atmosphere for a displacement reaction to obtain a reaction product, and the reaction product includes a halide of M and a transition metal;

[0199] In some embodiments, the temperature of the displacement reaction is 500°C - 1100°C, which can be 500°C, 600°C, 700°C, 800°C, 900°C, 1000°C, or 1100°C.

[0200] The reaction time is 1h - 48h, such as 1h, 5h, 10h, 15h, 20h, 25h, 30h, 35h, or 45h, etc.

[0201] The gas of the protective atmosphere includes at least one of helium, neon, argon, krypton, and xenon;

[0202] S400′. Remove the halide of M and the transition metal from the reaction product to obtain N material; the N material is primary particles, and the primary particles include a framework, and the framework includes a main framework located inside the primary particles and a plurality of branches extending from the main framework to the surface of the primary particles;

[0203] The removal method is the same as that in step S400 and will not be described in detail here.

[0204] S500′. Form a metal oxide layer on the surface of the framework structure of the N material to obtain a composite negative electrode material.

[0205] In some embodiments, the method for forming the metal oxide layer includes at least one of hydrothermal method, sol-gel method, precipitation method, chemical vapor deposition method, magnetron sputtering and solid-phase reaction method;

[0206] The metal elements in the metal oxide layer include at least one of Si, Sn, Ge, Li, V, Al, Fe and Zn.

[0207] When the protective layer is a metal nitride layer, the preparation method of the composite negative electrode material includes the following steps S100″ to S600″:

[0208] S100″. Prepare N-M alloy;

[0209] S200″. Mix the N-M alloy with a transition metal halide to obtain a mixture;

[0210] S300″. Place the mixture in a protective atmosphere for a displacement reaction to obtain a reaction product, and the reaction product includes the halide of M and the transition metal;

[0211] S400″. Remove the halide of M and the transition metal from the reaction product to obtain N material, the N material is primary particles, and the primary particles include a framework, and the framework includes a main framework located inside the primary particles and a plurality of branches extending from the main framework to the surface of the primary particles;

[0212] S500″. Form a metal oxide layer on the surface of the N material to obtain a composite;

[0213] S600″. Heat-treat the composite in a protective atmosphere and then perform nitriding treatment to obtain a composite negative electrode material.

[0214] The obtained composite negative electrode material includes primary particles and a metal nitride layer; wherein, the primary particles include a framework, and the framework includes a main framework located inside the primary particles and a plurality of branches extending from the main framework to the surface of the primary particles; the metal nitride layer is located on the surface of the framework.

[0215] It can be understood that the primary particles have a macroporous structure, and pores are formed inside the primary particles and extend to the surface of the primary particles.

[0216] It can also be understood that through holes are formed inside the primary particles, and the porosity of the primary particles is not less than 30%.

[0217] Among them, steps S100″ to S500″ are the same as steps S100′ to S500′ and will not be described in detail here.

[0218] In some embodiments, the heat treatment temperature is 500°C - 800°C, and the holding time is 1h - 24h;

[0219] In some embodiments, the protective atmosphere includes at least one of helium, neon, argon, krypton, and xenon;

[0220] In some embodiments, the nitriding treatment is carried out at 400°C - 950°C for 2h - 24h;

[0221] The atmosphere for the nitriding treatment is at least one of ammonia atmosphere and nitrogen atmosphere;

[0222] The embodiment of the present invention also provides a lithium-ion secondary battery, including the above composite negative electrode material or a negative electrode material prepared according to the preparation method of the above composite negative electrode material.

[0223] The embodiments of the present invention will be further described below in multiple embodiments. Among them, the embodiments of the present invention are not limited to the following specific embodiments. Within the scope of the main rights unchanged, appropriate changes can be made for implementation.

[0224] Example 1

[0225] The preparation method of the silicon-carbon composite negative electrode material in this embodiment includes the following steps:

[0226] (1) Mix silicon powder with a particle size of 1μm and magnesium powder in a molar ratio of 1:2 evenly, then put them into a vacuum furnace, evacuate to 10Pa, and heat at a heating rate of 3°C / min to 600°C under the protection of argon inert gas and hold for 6h to fully react to obtain a silicon-magnesium alloy; after ball-milling the silicon-magnesium alloy, 1μm silicon-magnesium alloy powder is obtained.

[0227] (2) Mix 1mol of silicon-magnesium alloy powder, 1mol of ammonium carbonate, 1mol of sodium carbonate, and 1mol of ammonium chloride evenly, and then add 1.5mol of sodium chloride to obtain a mixture.

[0228] (3) After mixing the obtained mixture evenly, put it into a sealed stainless-steel reactor. Heat the reactor in an argon atmosphere at a heating rate of 3 °C / min to 750 °C, then hold the temperature for 8 h to allow sufficient reaction to obtain a reaction product.

[0229] (4) After subjecting the reaction product to mechanical stirring and pickling treatment with 1 mol / L hydrochloric acid solution for 2 h, perform suction filtration, washing, and drying to obtain a silicon-carbon composite anode material.

[0230] After testing, the tap density of the prepared silicon composite anode material is 0.73 g / cm 3 , the powder compaction density is 1.2 g / cm 3 , the porosity is 50%, the specific surface area is 18 m 2 / g, and the carbon content is 12%.

[0231] Figures 3a to 3b is the scanning electron microscope image of the silicon-carbon composite anode material in this example; Figure 4 is the Raman diagram of the silicon-carbon composite anode material in this example; Figure 5 is the XRD pattern of the silicon-carbon composite anode material in this example; Figure 6 The cycle performance curve of the silicon-carbon composite anode material in this example, with a charge-discharge current of 0.5C.

[0232] As Figures 3a to 3b can be seen from the scanning electron microscope image in

[0233] Figure 5 , the prepared silicon material is primary particles. The primary particles include a silicon skeleton, and the silicon skeleton includes a main skeleton located inside the primary particles and multiple branches extending from the main skeleton to the surface of the primary particles; the primary particles are macroporous structures, and pore channels are formed inside the primary particles. The pore channels extend to the surface of the primary particles, and a layer of graphite carbon layer is wrapped on the surface of the silicon skeleton. The thickness of the carbon layer is 25 nm, the branches of the skeleton are rod-shaped nanosilicon, the average diameter of the pore channels is about 80 nm, and the depth of the pore channels is about 250 nm.

[0233] Figure 5 's Raman spectrum further proves the existence of a 2D peak near 2680 cm -1 , which is a characteristic peak of graphite, further indicating that the in-situ generated carbon is graphite-like carbon, with better conductivity and stability. From Figure 5 's XRD pattern, it can be seen that the three strong peaks at 28.4°, 47.3°, and 56.1° correspond to the three strong peaks of silicon (JCPDS No.27-1402), and there are basically no impurity phases;

[0234] Figure 6It can be seen that the lithium-ion battery prepared from the silicon-carbon composite anode material has excellent cycling performance. At a high current of 0.5C, after 1200 cycles, the capacity is still 897 mAh / g. Therefore, the silicon-carbon composite anode material prepared according to the method provided in this application has at least the advantage of high charge-discharge cycle stability.

[0235] Example 2

[0236] The preparation method of the silicon-carbon composite anode material in this example includes the following steps:

[0237] (1) Mix 1.5-μm silicon powder and zinc powder evenly at a molar ratio of 1:2.2, put them into a vacuum furnace, evacuate to 10 Pa, and heat to 650 °C at a heating rate of 5 °C / min under the protection of argon inert gas, then keep it warm for 3 h to make them react fully to obtain silicon-zinc alloy. The vacuum degree remains unchanged during the reaction process; mill the silicon-zinc alloy to obtain 1-μm silicon-zinc alloy powder;

[0238] (2) Mix 1 mol of silicon-zinc alloy powder, 3 mol of ammonium carbamate, 1 mol of potassium carbonate, and 1.5 mol of ammonium chloride evenly, and then add 1.5 mol of sodium chloride to obtain a mixture.

[0239] (3) Put the obtained mixture into a sealed stainless-steel reaction kettle, heat the reaction kettle to 800 °C at a heating rate of 3 °C / min in an argon atmosphere, and keep it warm for 8 h to make it react fully to obtain a reaction product;

[0240] (4) Put the reaction product into a 2-L 1-mol / L hydrochloric acid solution for mechanical stirring and pickling treatment for 3 h, then filter, wash, and dry to obtain a silicon composite anode material.

[0241] After testing, the tap density of the prepared silicon composite anode material is 0.77 g / cm 3 , the powder compact density is 1.26 g / cm 3 , the porosity is 52%, the specific surface area is 25 m 2 / g, and the carbon content is 15%.

[0242] The silicon-carbon composite material includes a silicon material and a carbon layer. The silicon material is a primary particle, and the primary particle includes a silicon skeleton. The silicon skeleton includes a main skeleton located inside the primary particle and multiple branches extending from the main skeleton to the surface of the primary particle; the branches are rod-shaped nano-silicon particles; the primary particle has a macroporous structure, and pores are formed inside the primary particle. The pores extend to the surface of the primary particle, and the surface of the silicon skeleton is coated with an amorphous carbon layer. The thickness of the carbon layer is 15 nm, the average diameter of the pores is about 80 nm, and the depth of the pores is about 300 nm.

[0243] Example 3

[0244] The preparation method of the silicon-carbon composite anode material of this embodiment includes the following steps:

[0245] (1) Mix 2-μm silicon powder and magnesium powder evenly at a molar ratio of 1:2.8, then put them into a vacuum furnace. Pump the vacuum to 10 Pa, and heat them to 620 °C at a heating rate of 5 °C / min under the protection of argon inert gas, and keep them at this temperature for 4 h to fully react to obtain a silicon-magnesium alloy. The vacuum degree remains unchanged during the reaction process; ball-mill the silicon-magnesium alloy to obtain 2-μm silicon-magnesium alloy powder;

[0246] (2) Mix 1 mol of silicon-magnesium alloy powder, 5 mol of ammonium carbamate, 2 mol of ammonium bicarbonate, and 2.5 mol of ammonium bromide evenly, and then add 1.5 mol of potassium chloride to obtain a mixture.

[0247] (3) Put the obtained mixture into a sealed stainless-steel reaction kettle, heat the reaction kettle to 820 °C at a heating rate of 3 °C / min in an argon atmosphere, and keep it at this temperature for 8 h to fully react to obtain a reaction product;

[0248] (4) Put the reaction product into a 3-L 1-mol / L hydrochloric acid solution for mechanical stirring and pickling treatment for 3 h, then filter, wash, and dry to obtain a silicon composite anode material.

[0249] After testing, the tapped density of the prepared silicon composite anode material is 0.45 g / cm 3 , the powder compacted density is 1.09 g / cm 3 , the porosity is 65%, the specific surface area is 53 m 2 / g, and the carbon content is 38%.

[0250] The silicon-carbon composite material includes a silicon material and a carbon layer. The silicon material is a primary particle. The primary particle includes a silicon skeleton. The silicon skeleton includes a main skeleton located inside the primary particle and multiple branches extending from the main skeleton to the surface of the primary particle; the branches are nano-silicon wafers; the primary particle is a macroporous structure, and pores are formed inside the primary particle. The pores extend to the surface of the primary particle, and the surface of the silicon skeleton is coated with an amorphous carbon layer. The thickness of the carbon layer is 25 nm; and the pores are filled with a carbon material; the average diameter of the pores is about 50 nm, and the depth of the pores is about 500 nm.

[0251] Example 4

[0252] The preparation method of the silicon-carbon composite anode material of this embodiment includes the following steps:

[0253] (1) Mix 3-μm silicon powder and aluminum powder evenly at a molar ratio of 1:3, then put them into a vacuum furnace. Evacuate to 10 Pa, and heat at a heating rate of 5 °C / min under the protection of argon inert gas to 660 °C, then hold for 3 h to make them react fully to obtain silicon-aluminum alloy. The vacuum degree remains unchanged during the reaction process; Ball-mill the silicon-aluminum alloy to obtain 3-μm silicon-aluminum alloy powder;

[0254] (2) Mix 1 mol of silicon-aluminum alloy powder, 4.5 mol of ammonium carbamate, 1.8 mol of ammonium carbonate and 2.2 mol of ammonium bromide evenly, and then add 1.5 mol of sodium chloride to obtain a mixture.

[0255] (3) Put the obtained mixture into a sealed stainless-steel reaction kettle, heat the reaction kettle in an argon atmosphere at a heating rate of 2 °C / min to 810 °C, and then hold for 8 h to make it react fully to obtain a reaction product;

[0256] (4) Put the reaction product into a 4-L 1-mol / L hydrochloric acid solution for mechanical stirring and pickling treatment for 3 h, then filter, wash and dry to obtain a silicon composite anode material.

[0257] After testing, the tap density of the prepared silicon composite anode material is 0.58 g / cm 3 , the powder compact density is 1.12 g / cm 3 , the porosity is 32%, the specific surface area is 60 m 2 / g, and the carbon content is 40%.

[0258] The silicon-carbon composite material includes silicon material and a carbon layer. The silicon material is primary particles, and the primary particles include a silicon skeleton. The silicon skeleton includes a main skeleton located inside the primary particles and multiple branches extending from the main skeleton to the surface of the primary particles; The branches are rod-shaped nanosilicon particles; The primary particles are macroporous structures, and pore channels are formed inside the primary particles. The pore channels extend to the surface of the primary particles, and the surface of the silicon skeleton is coated with a carbon layer which is a graphite carbon layer. The thickness of the carbon layer is 50 nm and the pore channels are filled with carbon materials; The average diameter of the pore channels is about 150 nm, and the depth of the pore channels is about 1000 nm.

[0259] Example 5:

[0260] (1) Mix 2-μm silicon powder and magnesium powder evenly at a molar ratio of 1:1.8, then put them into a vacuum furnace. Evacuate to 10 Pa, and heat at a heating rate of 5 °C / min under the protection of argon inert gas to 650 °C, then hold for 3 h to make them react fully to obtain silicon-magnesium alloy. The vacuum degree remains unchanged during the reaction process; Ball-mill the silicon-magnesium alloy to obtain 3-μm silicon-magnesium alloy powder;

[0261] (2) Mix 1 mol of silicon-magnesium alloy powder evenly with 1.5 mol of ammonium carbamate, 0.8 mol of ammonium carbonate, and 1.2 mol of ammonium bromide, and then add 0.5 mol of sodium chloride to obtain a mixture.

[0262] (3) After mixing the obtained mixture evenly, put it into a sealed stainless-steel reaction kettle. Heat the reaction kettle in an argon atmosphere at a heating rate of 4 °C / min to 750 °C and keep it warm for 8 h to make it react fully to obtain a reaction product.

[0263] (4) Put the reaction product into a 2 L 1 mol / L hydrochloric acid solution and carry out mechanical stirring and pickling treatment for 3 h, then filter, wash, and dry to obtain a silicon composite anode material.

[0264] After testing, the tap density of the prepared silicon composite anode material is 0.8 g / cm 3 , the powder compact density is 1.38 g / cm 3 , the porosity is 30%, the specific surface area is 10 m 2 / g, and the carbon content is 5%.

[0265] The silicon-carbon composite material includes a silicon material and a carbon layer. The silicon material is a primary particle. The primary particle includes a silicon skeleton. The silicon skeleton includes a main skeleton located inside the primary particle and multiple branches extending from the main skeleton to the surface of the primary particle. The primary particle is a macroporous structure, and pores are formed inside the primary particle. The pores extend to the surface of the primary particle, and the carbon layer wrapped on the surface of the silicon skeleton is graphite carbon, and the thickness of the carbon layer is 5 nm. The average diameter of the pores is about 20 nm, and the depth of the pores is about 60 nm.

[0266] Example 6

[0267] A preparation method of a germanium-carbon composite anode material includes the following steps:

[0268] (1) Mix germanium powder with a particle size of 1.5 μm and aluminum powder evenly at a molar ratio of 1:3, put them into an atmosphere furnace, and heat them to 480 °C at a heating rate of 5 °C / min under the protection of argon inert gas and keep it warm for 6 h to make them react fully to obtain a germanium-aluminum alloy. After ball-milling the germanium-aluminum alloy, germanium-aluminum alloy powder with a particle size of 0.5 μm is obtained.

[0269] (2) Mix 1 mol of germanium-aluminum alloy powder evenly with 2.5 mol of ammonium carbamate, 1.8 mol of ammonium carbonate, and 2.2 mol of ammonium bromide, and then add 1.5 mol of sodium chloride to obtain a mixture.

[0270] (3) After mixing the obtained mixture evenly, put it into a sealed stainless-steel reaction kettle. Heat the reaction kettle in an argon atmosphere at a heating rate of 4 °C / min to 780 °C and keep it warm for 8 h to make it react fully to obtain a reaction product.

[0271] (4) The reaction product is put into a 2 L 1 mol / L hydrochloric acid solution and mechanically stirred for pickling treatment for 3 h, then filtered, washed, and dried to obtain the germanium-carbon composite anode material.

[0272] The median particle size of the obtained germanium-carbon composite anode material is about 0.6 μm, and the tapped density is 0.78 g / cm 3 , and the pressed density is 1.1 g / cm 3 , the specific surface area is 16 m 2 / g, the porosity is 24%, and the mass percentage content of carbon is 75%.

[0273] The germanium-carbon composite material includes germanium material and a carbon layer. The germanium material is primary particles. The primary particles include a germanium skeleton. The germanium skeleton includes a main skeleton located inside the primary particles and multiple branches extending from the main skeleton to the surface of the primary particles; the branches are rod-shaped nanoparticles; the primary particles are macroporous structures, and pores are formed inside the primary particles. The pores extend to the surface of the primary particles, and a carbon layer with a thickness of 80 nm wraps the surface of the germanium skeleton; the average diameter of the pores is about 100 nm, and the depth of the pores is about 800 nm.

[0274] Example 7

[0275] A preparation method of a germanium-carbon composite anode material, comprising the following steps:

[0276] (1) Germanium powder with a particle size of 1.5 μm and magnesium powder are mixed evenly at a molar ratio of 1:2.5 and then put into an atmosphere furnace. Under the protection of argon inert gas, it is heated to 480 °C at a heating rate of 5 °C / min and kept warm for 6 h to fully react to obtain a germanium-magnesium alloy; the germanium-magnesium alloy is ball-milled to obtain germanium-magnesium alloy powder with a particle size of 0.5 μm;

[0277] (2) 1 mol of germanium-magnesium alloy powder, 1.5 mol of ammonium carbamate, 0.8 mol of ammonium carbonate, and 1.2 mol of ammonium bromide are mixed evenly, and then 0.5 mol of sodium chloride is added to obtain a mixture.

[0278] (3) The obtained mixture is mixed evenly and then put into a sealed stainless steel reaction kettle. The reaction kettle is heated to 750 °C at a heating rate of 4 °C / min in an argon atmosphere and kept warm for 8 h to fully react to obtain a reaction product;

[0279] (4) The reaction product is put into a 2 L 1 mol / L hydrochloric acid solution and mechanically stirred for pickling treatment for 3 h, then filtered, washed, and dried to obtain the germanium-carbon composite anode material.

[0280] The median particle size of the obtained germanium-carbon composite anode material is about 0.6 μm, and the tapped density is 0.88 g / cm 3, the compaction density is 1.3 g / cm 3 , the specific surface area is 11 m 2 / g, the porosity is 44%, and the mass percentage content of carbon is 25%.

[0281] The germanium-carbon composite material includes germanium material and a carbon layer. The germanium material is primary particles, and the primary particles include a germanium skeleton. The germanium skeleton includes a main skeleton located inside the primary particles and multiple branches extending from the main skeleton to the surface of the primary particles; the branches are rod-shaped nanoparticles; the primary particles are macroporous structures, and pores are formed inside the primary particles. The pores extend to the surface of the primary particles, and a carbon layer with a thickness of 50 nm wraps the surface of the germanium skeleton; the average diameter of the pores is about 60 nm, and the depth of the pores is about 1500 nm.

[0282] Example 8

[0283] A preparation method of a silicon composite anode material includes the following steps:

[0284] (1) Mix 1.5 μm silicon powder and magnesium powder evenly at a molar ratio of 1:2.5, then put them into an atmosphere furnace, and heat them to 600 °C at a heating rate of 5 °C / min under the protection of argon inert gas and keep them at this temperature for 6 h to fully react to obtain a silicon-magnesium alloy; ball-mill the silicon-magnesium alloy to obtain 0.5 μm silicon-magnesium alloy powder;

[0285] (2) Mix 1 mol of the silicon-magnesium alloy powder, 1 mol of copper chloride (CuCl 2 ) and 1 mol of sodium chloride (NaCl) evenly to obtain a mixture;

[0286] (3) Put the obtained mixture into an argon atmosphere and heat it to 750 °C at a heating rate of 3 °C / min, then keep it at this temperature for 8 h to fully react to obtain a reaction product; put the reaction product into a 2 L 1 mol / L hydrochloric acid solution and carry out mechanical stirring and pickling treatment for 3 h, then filter, wash, and dry to obtain a silicon anode material with a skeleton structure;

[0287] (4) Dissolve 1 mol of the above silicon anode material and 0.7 g of cellulose in 500 ml of absolute ethanol and disperse them evenly to obtain a mixed solution.

[0288] (5) Dropwise add 3 g of tetrabutyl titanate into the above mixed solution, heat it to 80 °C, then stir it rapidly for 3 hours and then filter, and vacuum dry it at 60 °C for 24 hours to obtain a titanium oxide precursor-coated silicon-magnesium alloy composite;

[0289] (6) Heat the above composite in an argon atmosphere to 750 °C at a heating rate of 3 °C / min and keep it at this temperature for 8 h to fully react to obtain a silicon / titanium oxide composite anode material.

[0290] The median particle size of the obtained composite anode material is about 0.6 μm, the specific surface area is 44 m 2 / g, the porosity is 43%, and the mass percentage content of titanium oxide is 12%.

[0291] The composite material includes a silicon material and a titanium oxide layer. The silicon material is a primary particle, and the primary particle includes a silicon skeleton. The silicon skeleton includes a main skeleton located inside the primary particle and a plurality of branches extending from the main skeleton to the surface of the primary particle; the branches are rod-shaped nanoparticles; the primary particle is a macroporous structure, and pores are formed inside the primary particle. The pores extend to the surface of the primary particle, and the surface of the silicon skeleton is coated with a titanium oxide layer; the average diameter of the pores is about 100 nm, and the depth of the pores is about 700 nm.

[0292] Example 9

[0293] A method for preparing a silicon composite anode material, comprising the following steps:

[0294] (1) Mix 1.5-μm silicon powder and magnesium powder evenly at a molar ratio of 1:2.5, then put them into an atmosphere furnace, and heat them to 600 °C at a heating rate of 5 °C / min under the protection of argon inert gas and keep them warm for 6 h to fully react to obtain a silicon-magnesium alloy; ball-mill the silicon-magnesium alloy to obtain 0.5-μm silicon-magnesium alloy powder;

[0295] (2) Mix 1 mol of the silicon-magnesium alloy powder, 1 mol of copper chloride (CuCl 2 ) and 1 mol of sodium chloride (NaCl) evenly to obtain a mixture;

[0296] (3) Put the obtained mixture into an argon atmosphere and heat it to 750 °C at a heating rate of 3 °C / min, then keep it warm for 8 h to fully react to obtain a reaction product; put the reaction product into a 2-L 1-mol / L hydrochloric acid solution and carry out mechanical stirring and pickling treatment for 3 h, then filter, wash, and dry to obtain a silicon anode material with a skeleton structure;

[0297] (4) Disperse 1 mol of the above silicon anode material and 0.7 g of cellulose evenly in 500 ml of absolute ethanol to obtain a mixed solution.

[0298] (5) Dropwise add 3 g of tetrabutyl titanate into the above mixed solution, heat it to 80 °C, then stir rapidly for 3 hours and then filter, and vacuum dry at 60 °C for 24 hours to obtain a titanium oxide precursor-coated silicon-magnesium alloy composite;

[0299] (6) Put the above complex into a tubular atmosphere furnace, heat it to 650 °C at a heating rate of 3 °C / min in an argon atmosphere, keep it for 5 h to allow sufficient reaction, then change the argon to ammonia, raise the temperature to 800 °C, and keep it for 8 h to obtain a silicon / titanium nitride composite anode material;

[0300] The median particle size of the obtained composite anode material is about 0.7 μm, the specific surface area is 40 m 2 / g, the porosity is 48%, and the mass percentage content of titanium nitride is 32%.

[0301] The composite material includes a silicon material and a titanium nitride layer. The silicon material is a primary particle, and the primary particle includes a silicon skeleton. The silicon skeleton includes a main skeleton located inside the primary particle and a plurality of branches extending from the main skeleton to the surface of the primary particle; the branches are nanowires; the primary particle has a macroporous structure, and pores are formed inside the primary particle. The pores extend to the surface of the primary particle, and the surface of the silicon skeleton is coated with a titanium nitride layer; the average diameter of the pores is about 58 nm, and the depth of the pores is about 1000 nm.

[0302] Example 10

[0303] A preparation method of a silicon composite anode material, comprising the following steps:

[0304] (1) Mix 1.5-μm silicon powder and magnesium powder evenly at a molar ratio of 1:2.5, put them into an atmosphere furnace, heat them to 600 °C at a heating rate of 5 °C / min under the protection of argon inert gas, and keep them for 6 h to allow sufficient reaction to obtain a silicon-magnesium alloy; ball-mill the silicon-magnesium alloy to obtain 0.5-μm silicon-magnesium alloy powder;

[0305] (2) Mix 1 mol of silicon-magnesium alloy powder, 1 mol of copper chloride (CuCl 2 ) and 1 mol of sodium chloride (NaCl) evenly to obtain a mixture;

[0306] (3) Put the obtained mixture into an argon atmosphere, heat it to 700 °C at a heating rate of 3 °C / min, and keep it for 6 h to allow sufficient reaction to obtain a reaction product; put the reaction product into a 2 L 1 mol / L hydrochloric acid solution, stir it mechanically for pickling treatment for 3 h, then filter, wash, and dry to obtain a silicon anode material with a skeleton structure;

[0307] (4) Prepare vanadium pentoxide-coated silicon anode material through a sol-gel process. First, prepare 500 ml of an alcohol solution of vanadium triisopropoxide with a concentration of 0.15 M / L, add 30 ml of acetylacetone to obtain a mixed solution; add 0.5 mol of silicon anode material powder to the above mixed solution, stir for 36 hours, and disperse evenly to obtain a sol.

[0308] (5) The sol is subjected to suction filtration and vacuum dried at 60 °C for 24 hours to obtain a vanadium pentoxide precursor-coated silicon anode material composite;

[0309] (6) The above composite is placed in a tube furnace and heated to 600 °C at a heating rate of 3 °C / min in an argon atmosphere and held for 3 h to allow sufficient reaction. Then, the argon is replaced with ammonia and the temperature is raised to 750 °C and held for 8 h to obtain a silicon / vanadium nitride composite anode material.

[0310] The median particle size of the obtained composite anode material is about 0.6 μm, the specific surface area is 51 m 2 / g, the porosity is 40%, and the mass percentage content of vanadium nitride is 25%.

[0311] The composite material includes a silicon material and a vanadium nitride layer. The silicon material is primary particles, and the primary particles include a silicon skeleton. The silicon skeleton includes a main skeleton located inside the primary particles and multiple branches extending from the main skeleton to the surface of the primary particles; the branches are rod-shaped nanoparticles; the primary particles are macroporous structures, and pores are formed inside the primary particles. The pores extend to the surface of the primary particles, and the surface of the silicon skeleton is coated with a vanadium nitride layer; the average diameter of the pores is about 100 nm, and the depth of the pores is about 900 nm.

[0312] Comparative Example 1:

[0313] (1) Silicon powder with a particle size of 1 μm and magnesium powder are mixed evenly at a molar ratio of 1:2 and placed in a vacuum furnace. The vacuum is pumped to 10 Pa, and it is heated to 600 °C at a heating rate of 3 °C / min under the protection of argon inert gas and held for 6 h to allow sufficient reaction to obtain a silicon-magnesium alloy; the silicon-magnesium alloy is ball-milled to obtain 1-μm silicon-magnesium alloy powder.

[0314] (2) 1 mol of the silicon-magnesium alloy powder is mixed evenly with 1 mol of ammonium carbonate, 1 mol of sodium carbonate, and 1 mol of ammonium chloride to obtain a mixture.

[0315] (3) The obtained mixture is mixed evenly and placed in a sealed stainless-steel reaction kettle. The reaction kettle is heated to 750 °C at a heating rate of 3 °C / min in an argon atmosphere and held for 8 h to allow sufficient reaction to obtain a reaction product;

[0316] (4) The reaction product is mechanically stirred and pickled with 1 mol / L hydrochloric acid solution for 2 h, then suction filtered, washed, and dried to obtain a silicon-carbon composite anode material.

[0317] Comparative Example 2

[0318] (1) Mix silicon powder with a particle size of 1 μm and magnesium powder evenly at a molar ratio of 1:2, then put them into a vacuum furnace. Evacuate to 10 Pa, and heat at a heating rate of 3 °C / min under the protection of argon inert gas to 600 °C, then hold for 6 h to make them react fully to obtain a silicon-magnesium alloy; ball-mill the silicon-magnesium alloy to obtain silicon-magnesium alloy powder with a particle size of 1 μm.

[0319] (2) After mixing 1 mol of silicon-magnesium alloy powder, 1 mol of ammonium carbonate and 1 mol of ammonium chloride evenly, add 1.5 mol of sodium chloride to obtain a mixture.

[0320] (3) Put the obtained mixture into a sealed stainless-steel reaction kettle, heat the reaction kettle in an argon atmosphere at a heating rate of 3 °C / min to 750 °C, then hold for 8 h to make it react fully to obtain a reaction product;

[0321] (4) After pickling the reaction product with mechanical stirring in 1 mol / L hydrochloric acid solution for 2 h, filter, wash and dry to obtain a silicon-carbon composite anode material.

[0322] Comparative Example 3

[0323] Use the silicon-carbon composite anode material SiO / C. The median particle size of the silicon-carbon composite anode material is 1.5 μm. The inner core of the composite material is a porous silicon structure composed of nano-silicon particles, and the outer shell is wrapped by a carbon layer; among them, the mass percentage content of carbon is 22%, the specific surface area is 38 m 2 / g, and the porosity of the silicon-carbon composite anode material is 67%. It is the SiOx / C anode material, where x = 1.0.

[0324] Performance test:

[0325] Make lithium-ion batteries with the anode materials prepared in Examples 1-10 and Comparative Examples 1-3, the same cathode material and current collector, and conduct battery performance tests. The test items include discharge specific capacity, initial Coulomb efficiency, capacity after 1200 cycles at 0.5C, and capacity retention rate after 1200 cycles at 0.5C. The sample numbers are S1-S10 and R1-R3, and the performance parameters of the samples are shown in Table 1:

[0326] Table 1. Performance comparison result table

[0327]

[0328]

[0329] As can be seen from the above-mentioned examples and comparative examples, the composite anode materials provided in Examples 1, 2, 5, and 6 have a three-dimensional pore structure, and the carbon layer is coated on the surface of the anode material skeleton. The composite anode materials provided in Examples 3 and 4 have a three-dimensional pore structure, and the carbon layer is coated on the surface of the anode material skeleton and filled into the three-dimensional pore structure, having good structural stability. The through pore structure can provide space for internal expansion during the process of lithium insertion and extraction in the anode material, and can also serve as a channel for electrolyte flow, reducing the expansion of lithium batteries while improving the lithium storage performance of silicon and increasing the capacity retention rate of the battery.

[0330] In Comparative Example 1, no molten salt medium was added during the preparation process, and the local temperature of the high-temperature liquid environment during the reaction of the alloy powder with the ammonium salt was too high, resulting in the destruction of some three-dimensional pore structures and poor charge-discharge cycle stability of the battery. In Comparative Example 2, no ammonium salt decomposition inhibitor was added during the preparation process. During the reaction, the ammonium salt decomposed into ammonia and carbon dioxide, and it was difficult to uniformly deposit and form a carbon layer on the surface of the silicon material or in the three-dimensional pores, resulting in a decrease in the carbon content of the final anode material, poor electrical conductivity of the anode material, and weak volume expansion inhibition performance, leading to poor long-cycle performance.

[0331] According to the above-mentioned examples and test results, the battery made of the silicon-carbon composite anode material prepared in this application has good charge-discharge cycle stability, high capacity, and high cycle life. In summary, the preparation method of the porous silicon-carbon composite anode material provided in this application is simple and easy to operate, the preparation process is safe and efficient; the manufacturing cost is effectively reduced, suitable for mass production; the prepared product is used as a battery electrode, having good charge-discharge cycle performance.

[0332] 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 composite anode material, characterized in that, the composite anode material comprises primary particles and a protective layer; wherein, the primary particles comprise a framework, the framework comprises a main framework located inside the primary particles and a plurality of branches extending from the main framework to the surface of the primary particles, the main framework is a three-dimensional network structure, and a single branch is an individual crystal grain, and the size of the crystal grain is 30nm - 100nm; the primary particles are of a macroporous structure, pores are formed inside the primary particles, the pores extend to the surface of the primary particles, the porosity of the primary particles is 30% - 70%, the diameter of the pores is 10nm - 150nm; the depth of the pores is 50nm - 1500nm; the protective layer comprises a carbon layer, and the carbon layer is located on the surface of the framework and fills the pores; the porosity of the composite anode material is 24% - 65%.

2. The composite anode material according to claim 1, characterized in that, the composite anode material comprises at least one of the following a - b: a. The maximum width of the cross-section of the branch is 20nm - 350nm, and the maximum length of the cross-section of the branch is 50nm - 2500nm; b. The branch is selected from at least one of rod-shaped nanoparticles, nanosheets, nanowires and nanotubes.

3. The composite anode material according to claim 1, characterized in that, the carbon layer is an amorphous carbon layer and / or a graphite carbon layer. Based on the composite anode material with a mass percentage of 100%, the mass percentage of carbon is 25% - 75% and does not include 25%.

4. The composite anode material according to any one of claims 1 - 3, characterized in that, the composite anode material comprises at least one of the following a - h: a. The primary particles are selected from at least one of silicon, germanium, antimony, tin, and boron; b. The median particle size of the primary particles is 0.2µm - 15µm; c. The specific surface area of the primary particles is 5 m 2 / g to 100 m 2 / g; d. The tapped density of the primary particle powder is 0.2 g / cm 3 ~ 0.8 g / cm 3 ; e. The powder compaction density of the primary particles is 1.2 g / cm 3 ~ 1.8 g / cm 3 ; f. The median particle size of the composite anode material is 0.1µm - 15µm; g. The specific surface area of the composite anode material is 1 m 2 / g to 150 m 2 / g; h. The thickness of the protective layer located on the surface of the framework is 1nm - 300nm.

5. A preparation method of the composite anode material according to any one of claims 1 - 4, characterized in that, the method comprises the following steps: Placing a mixture containing an N-M alloy, a carbon-containing ammonium salt, a carbon-containing ammonium salt decomposition inhibitor and a molten salt medium in a protective atmosphere for a displacement reaction, the reaction temperature of the displacement reaction is 200°C - 950°C, the holding time is 1h - 24h, and the reaction heating rate is 1°C / min - 20°C / min to obtain a reaction product, the reaction product comprises an oxide of M and a nitride of M; and Removing the oxide of M and the nitride of M by pickling to obtain the composite anode material; wherein, N in the N-M alloy is selected from at least one of silicon, germanium, antimony, tin, and boron, and M in the N-M alloy is selected from at least one of magnesium, aluminum, calcium, and zinc.

6. The preparation method of the composite anode material according to claim 5, characterized in that, the method comprises at least one of the following features a - e: a. The particle size of the N-M alloy is 0.2 µm to 15 µm; b. The molar ratio of the N-M alloy to the ammonium carbonate salt mixture is 1:(0.1 - 10); c. The ammonium carbonate salt is selected from at least one of ammonium carbonate, ammonium bicarbonate, and ammonium carbamate; d. The molar ratio of the N-M alloy to the ammonium salt decomposition inhibitor is 1:(0.2 - 10); and / or, the ammonium salt decomposition inhibitor is selected from carbonate and / or bicarbonate; e. The molar ratio of the N-M alloy to the molten salt medium is 1:(0.1 - 10); and / or The molten salt medium is selected from ammonium halide salts; the chemical formula of the ammonium halide salt is NH 4 Y, where Y is selected from at least one of Cl, Br, F, and I.

7. The preparation method of the composite negative electrode material according to claim 5, characterized in that, the preparation method includes at least one of the following features a to d: a. The gas of the protective atmosphere is selected from at least one of helium, neon, argon, krypton, and xenon; b. The acid solution used for pickling is selected from at least one of hydrochloric acid, nitric acid, and sulfuric acid; c. The mass concentration of the acid solution used for pickling is 1 mol / L to 5 mol / L; d. The pickling time is 1 h to 10 h.

8. A lithium-ion secondary battery, characterized in that, the lithium-ion secondary battery includes the composite negative electrode material according to any one of claims 1 to 4 or the negative electrode material prepared by the preparation method of the composite negative electrode material according to any one of claims 5 to 7.

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