CN115347151A

CN115347151A - Composite negative electrode material, preparation method thereof and lithium ion secondary battery

Info

Publication number: CN115347151A
Application number: CN202110468548.9A
Authority: CN
Inventors: 安威力; 何鹏; 任建国; 贺雪琴
Original assignee: BTR New Material Group Co Ltd; Dingyuan New Energy Technology Co Ltd
Current assignee: BTR New Material Group Co Ltd; Dingyuan New Energy Technology Co Ltd
Priority date: 2021-04-28
Filing date: 2021-04-28
Publication date: 2022-11-15

Abstract

The application relates to the field of negative electrode materials, and provides a composite negative electrode material, a preparation method thereof and a lithium ion secondary battery, wherein the composite negative electrode material comprises primary particles and a protective layer; wherein the primary particle comprises a backbone comprising a main backbone located inside the primary particle and a plurality of branches extending from the main backbone to the surface of the primary particle; the protective layer is positioned on the surface of the framework; the primary particles are of a macroporous structure, and pore channels are formed in the primary particles and extend to the surfaces 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 negative electrode material, the preparation method thereof and the lithium ion secondary battery are low in cost and capable of realizing large-scale production, and the charge-discharge cycle performance of the negative electrode material can be effectively improved.

Description

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

Technical Field

The application relates to the technical field of negative electrode materials, in particular to a composite negative electrode material, a preparation method thereof and a lithium ion secondary battery.

Background

The new energy industry is one of the emerging industries supported by seven major keys in China. The application ratio of the new energy automobile and the new energy is greatly improved, and green and low-carbon industries such as the new energy automobile, the new energy and energy conservation and environmental protection are promoted to become a post industry, so that the post industry becomes strategic development planning in China. With the rapid development of the electric automobile industry, the development of a lithium ion battery with higher energy density is urgently needed. The negative electrode is an important component of the lithium ion battery, but the theoretical capacity of the graphite negative electrode is only 372mAh/g, the capacity exertion reaches the upper limit, and the long endurance requirement of the electric automobile is difficult to meet. Therefore, the design and development of new high-capacity negative electrode materials are the core and key for breaking through high-specific-energy power batteries. Negative electrode materials such as Si, ge, sn, sb, and B are preferred negative electrode materials for realizing high specific energy batteries due to their high specific capacities, and also have attracted extensive attention and research. However, these negative electrode materials have large volume expansion (> 300%) during lithium intercalation, and may be pulverized and fall off from the current collector during charging and discharging, so that the electrical contact between the active material and the current collector is lost, resulting in poor electrochemical performance, capacity fading, and reduced cycling stability, and thus are difficult to be commercially applied.

Disclosure of Invention

In view of this, the present application provides a composite negative electrode material and a preparation method thereof, where the composite negative electrode material can reduce volume expansion, and further can effectively improve charge-discharge cycle performance of the material.

A composite anode material includes primary particles and a protective layer; wherein the primary particle comprises a backbone comprising a main backbone located inside the primary particle and a plurality of branches extending from the main backbone to the surface of the primary particle; the protective layer is located on the surface of the framework.

In the above scheme, compared with a secondary porous structure formed by stacking nanoparticles, the cathode material has the advantage of more stable integrated structure, and can have smaller specific surface area and higher porosity. The negative electrode material is a complete particle, the whole framework is connected, electrons of the reinforcing material are transmitted to the negative electrode material and are diffused with ions, stress after lithiation can be effectively released, stress concentration is avoided, material pulverization is avoided, the negative electrode material assembled by the primary particles is broken by the particles due to the fact that obvious crystal boundaries exist between the particles, lithiation stress concentration is caused, and the electrochemical performance is finally deteriorated due to the fact that the whole structure is damaged. The protective layer formed on the surface of the negative electrode material framework can further improve the conductivity and the cycling stability of the negative electrode material, and simultaneously further relieve the volume expansion of the negative electrode material, so that the conductivity and the rate performance of the negative electrode material are further improved.

In one possible embodiment, the composite anode material includes at least one of the following a to e:

a. the main framework is a three-dimensional net structure;

b. a single said branch is an individual die;

c. the single branch is an independent crystal grain, and the size of the crystal grain is 30nm-100nm;

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

e. the branches are selected from at least one of rod-shaped nanoparticles, nanosheets, nanowires and nanotubes.

In one possible embodiment, the primary particle has a macroporous structure, and the inside of the primary particle is formed with a pore channel extending to the surface of the primary particle.

In one possible embodiment, the diameter of the pore channel is 10nm to 150nm; the depth of the pore channel is 50nm-1500nm.

In one possible embodiment, the primary particle has through holes formed therein, and the porosity of the primary particle is not less than 30%.

In a possible embodiment, the protective layer is further filled in the hole or the through hole.

In one possible embodiment, the protective layer includes at least one of a carbon layer, a metal oxide layer, and a metal nitride layer; and/or

The protective layer comprises a carbon layer, the carbon layer is an amorphous carbon layer and/or a graphite carbon layer, and when the mass percentage of the composite anode material is 100%, the carbon content percentage of the carbon layer is 5% -25% when the carbon layer is only positioned on the surface of the framework; when the carbon layer is positioned on the surface of the framework and filled in the pore channel or the through hole, the carbon content is 25-75% and does not include 25% by mass based on 100% by mass of the composite anode material; and/or

The protective layer comprises a metal oxide layer, the metal element of the metal oxide layer comprises at least one of Si, sn, ge, li, V, al, fe and Zn, and when the mass percentage of the composite negative electrode material is 100%, the mass percentage of the metal oxide layer is 5% -25% when the metal oxide layer is only positioned on the surface of the framework; when the metal oxide layer is positioned on the surface of the framework and is filled in the pore channel or the through hole, the mass percentage of the metal oxide is 25-75% and not 25% based on 100% of the composite negative electrode material; and/or

The protective layer comprises a metal nitride layer, the metal element in the metal nitride layer comprises at least one of Ti, V, nb, ta, W and Zr, and when the mass percentage of the composite negative electrode material is 100%, the mass percentage of the metal nitride layer is 5-25% when the metal nitride layer is only positioned on the surface of the framework; when the metal nitride is positioned on the surface of the framework and filled in the pore channel or the through hole, the mass percentage of the metal nitride is 25-75% and does not include 25% by taking the mass percentage of the composite negative electrode material as 100%.

In one possible embodiment, the composite anode material includes at least one of the following a to j:

a. the primary particles are selected from at least one of silicon, germanium, antimony, tin and boron;

b. the median particle diameter of the primary particles is 0.2-15 μm;

c. the specific surface area of the primary particles is 5m 2/g-100 m2/g;

d. the porosity of the primary particles is 30-70%;

e. the tap density of the powder of the primary particles is 0.2g/cm < 3 > -0.8 g/cm < 3 >;

f. the powder compaction density of the primary particles is 1.2g/cm < 3 > -1.8 g/cm < 3 >;

g. the median particle size of the composite negative electrode material is 0.1-15 mu m;

h. the specific surface area of the composite negative electrode material is 1m 2/g-150 m2/g;

i. the porosity of the composite negative electrode material is 10-70%;

j. the thickness of the protective layer on the surface of the framework is 1 nm-300 nm.

The application provides a preparation method of a composite anode material, which comprises the following steps:

placing a mixture containing N-M alloy and carbon-containing ammonium salt in a protective atmosphere for a displacement reaction to obtain a reaction product, wherein the reaction product comprises an oxide of M and a nitride of M; and

removing the oxide of M and the nitride of M to obtain a composite cathode material;

wherein N in the N-M alloy comprises at least one of silicon, germanium, antimony, tin and boron, and M in the N-M alloy comprises at least one of magnesium, aluminum, calcium and zinc.

In the scheme, the composite anode material is prepared by adopting the one-step composite method under the high-temperature condition by taking the carbon-containing ammonium salt as the carbon source and the N-M alloy, compared with the two-step composite method, the preparation efficiency can be effectively improved, and the process is simple.

In a possible embodiment, the method comprises at least one of the following features a to e:

a. the grain diameter of the N-M alloy is 0.2-15 mu M;

b. the molar ratio of the mixed N-M alloy and the carbon-containing ammonium salt is 1 (0.1-10);

c. the carbon-containing ammonium salt comprises at least one of ammonium carbonate, ammonium bicarbonate and ammonium carbamate;

d. the mixture further comprises a carbonaceous ammonium salt decomposition inhibitor; and/or

The molar ratio of the N-M alloy to the carbonaceous ammonium salt decomposition inhibitor is 1 (0.2-10); and/or, the ammonium salt decomposition inhibitor comprises a carbonate and/or bicarbonate;

e. the mixture further comprises a molten salt medium; and/or

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

The molten salt medium comprises at least one of ammonium halide salt and halogenated salt; and/or

The chemical formula of the halogenated ammonium salt is NH ₄ Y, wherein Y comprises at least one of Cl, br, F and I.

In a possible embodiment, the preparation method comprises at least one of the following features a to g:

a. the reaction temperature of the replacement reaction is 200-950 ℃, and the heat preservation time is 1-24 h;

b. the reaction heating rate of the displacement reaction is 1-20 ℃/min;

c. the protective atmosphere comprises at least one of helium, neon, argon, krypton and xenon;

d. the method for removing the oxide of M and the nitride of M comprises acid washing;

e. the method for removing the oxide of M and the nitride of M comprises acid washing, wherein an acid solution adopted by the acid washing comprises at least one of hydrochloric acid, nitric acid and sulfuric acid;

f. the method for removing the oxide of M and the nitride of M comprises acid washing, wherein the mass concentration of an acid solution adopted by the acid washing is 1-5 mol/L;

g. the method for removing the oxide of M and the nitride of M comprises acid washing, wherein the acid washing time is 1-10 h.

On the other hand, the application also provides a preparation method of the composite anode material, which comprises the following steps:

placing a mixture containing N-M alloy and transition metal halide in a protective atmosphere for a displacement reaction to obtain a reaction product, wherein the reaction product comprises M halide and transition metal; and

removing halides and transition metals of M in the reaction product to obtain N materials, wherein the N materials are primary particles, the primary particles comprise a framework, and the framework comprises a main framework positioned inside the primary particles and a plurality of branches extending from the main framework to the surfaces of the primary particles; and

forming a metal oxide layer on the surface of the framework of the N material to obtain a composite negative electrode material;

The composite negative electrode material obtained by the preparation method has the advantages that the metal oxide layer is formed on the surface of the N material, the metal oxide layer has the advantages of good rigidity, excellent compactness and the like, the whole structure damage caused by the volume expansion of N can be effectively inhibited, the volume expansion of the material is reduced, meanwhile, the contact between electrolyte and the N material is avoided, the side reaction is reduced, and the first effect of the whole composite material is improved.

In another aspect, the present application further provides a preparation method of the composite anode material, including the following steps:

placing a mixture containing N-M alloy and transition metal halide in a protective atmosphere for displacement reaction to obtain a reaction product, wherein the reaction product comprises M halide and transition metal; and

removing the halide and the transition metal of the M to obtain an N material, wherein the N material is a primary particle, the primary particle comprises a framework, and the framework comprises a main framework positioned inside the primary particle and a plurality of branches extending from the main framework to the surface of the primary particle;

forming a metal oxide layer on the surface of the framework of the N material to obtain a compound; and

carrying out heat treatment on the composite under a protective atmosphere and then carrying out nitridation treatment to obtain a composite negative electrode material;

After a metal oxide layer is coated on the surface of a framework of a negative electrode material N, the heat treatment is carried out in a protective atmosphere, so that the oxide is converted from amorphous into crystal at high temperature and under normal pressure. The metal oxide layer on the surface of the inner core is further nitrided into metal nitride through nitridation treatment. In the scheme, the metal nitride layer has good rigidity and excellent conductivity, can effectively relieve the volume expansion of silicon, simultaneously increases the conductivity of the material, improves the multiplying power of the material, reduces the irreversible capacity loss of the material and brings high capacity.

In one possible embodiment, the production method comprises at least one of the following features a to h:

a. the transition metal halide has a chemical formula ABx, wherein x =2 or 3, A comprises at least one of Sn, cu, fe, zn, co, mn, cr and Ni, and B comprises at least one of Cl, F and Br;

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

c. the metal element in the metal oxide layer includes at least one of Si, sn, ge, li, V, al, fe and Zn;

d. the temperature of the replacement reaction is 500-1100 ℃, and the heat preservation time is 1-48 h;

e. the heat treatment temperature is 500-800 ℃, and the heat preservation time is 1-24 h; and/or the protective atmosphere comprises at least one of helium, neon, argon, krypton and xenon;

f. the method for removing the halides of the transition metals A and M is acid washing;

g. the nitridation treatment is carried out for 2 to 24 hours at the temperature of 400 to 950 ℃;

h. the nitriding atmosphere is at least one of an ammonia gas atmosphere and a nitrogen gas atmosphere.

A lithium ion secondary battery comprises the composite negative electrode material or the negative electrode material prepared by the preparation method of the composite negative electrode material.

Drawings

Fig. 1a is a schematic structural diagram of a composite anode material according to an embodiment;

fig. 1b is a schematic structural diagram of a composite anode material according to another embodiment;

fig. 2 is a schematic view of a synthetic process of the composite anode material provided in this embodiment;

fig. 3a is a scanning electron microscope picture of the silicon-carbon composite anode material provided in this embodiment;

fig. 3b is another scanning electron microscope picture of the silicon-carbon composite anode material provided in this embodiment;

fig. 4 is a raman chart of the silicon-carbon composite anode material provided in the present embodiment;

fig. 5 is an XRD pattern of the silicon-carbon composite anode material provided in this example;

fig. 6 is a graph showing cycle performance of the silicon-carbon composite anode material provided in this embodiment.

Detailed Description

While the following is a description of the preferred embodiments of the present invention, it should be noted that those skilled in the art can make various modifications and improvements without departing from the principle of the embodiments of the present invention, and such modifications and improvements are considered to be within the scope of the embodiments of the present invention.

As used herein, "dealloying" refers to a process in which one or more elements of an alloy are selectively removed by 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, wherein the formation of a nanoporous structure in the dealloying process is closely related to the recombination of atomic levels on an alloy/solution interface, the recombination process is completed through the surface diffusion of undissolved metal atoms and vacancies, and the speed of the surface diffusion has an important influence on the size of ligaments/channels in the finally formed nanoporous metal.

The embodiment of the present application provides a composite negative electrode material, specifically, as shown in fig. 1a, the composite negative electrode material includes primary particles and a protective layer 20;

wherein the primary particle comprises a skeleton, the skeleton comprises a main skeleton 11 positioned inside the primary particle and a plurality of branches 12 extending from the main skeleton 11 to the surface of the primary particle; the protective layer 20 is located on the surface of the skeleton.

Referring further to fig. 1a, the primary particle of this embodiment has a macroporous structure, wherein the primary particle has a pore channel 13 formed therein, and the pore channel 13 extends to the surface of the primary particle. Among them, those having a pore diameter of more than 50nm are called macropores according to the definition of the International Union of Pure and Applied Chemistry (IUPAC).

The main framework inside the primary particles of the negative electrode material and the plurality of branches extending from the main framework to the surfaces of the primary particles are integrated, the electronic conduction and the ion diffusion of the whole framework structure reinforced material can effectively release the stress after lithiation, and the material fracture and pulverization caused by the concentration of the stress at a crystal boundary are avoided.

The pore channel structure of the cathode material extending to the surface of the primary particles has the following advantages: 1. the expansion of the lithium battery can be reduced while the lithium storage performance is improved. The volume expansion in the lithium intercalation process can be relieved, and an internal expansion space is provided for lithiation, so that the electrode material is expanded inwards after lithiation to reduce the thickness of the whole electrode film, and the safety of the lithium ion battery is greatly improved. 2. And a channel for flowing the electrolyte is provided, so that the contact of the electrolyte is facilitated. The pore structure can also bring higher tap density, and can increase the volume energy density of the battery.

Compared with a secondary porous structure formed by accumulating nano particles, the cathode material has the advantage of more stable integrated structure, and can have smaller specific surface area and higher porosity. The invention is a porous material which is formed by the primary integral particles and the whole framework which are connected, the electron transfer and the ion diffusion of the reinforced material can effectively release the stress after lithiation, and avoid the material pulverization caused by stress concentration.

The protective layer positioned on the surface of the framework can improve the conductivity and stability, is beneficial to the access of lithium ions and improves the multiplying power performance of the cathode material.

In some embodiments, the backbone is a three-dimensional network;

in some embodiments, the single branch is a separate grain; compared with the structure, the branch on the primary particle in the embodiment is a single large grain without excessive crystal boundaries, so that the stress can be well dispersed after lithiation, and the damage of the material caused by stress concentration is avoided; meanwhile, the crystal face curves of a single crystal grain are the same, so that the relative volume expansion of the material in a certain direction is reduced, the structure formed by a plurality of small crystal grains has relatively large volume expansion, and meanwhile, the structural stability is relatively poor, so that the circulation stability is poor.

Specifically, the size of the crystal grains is 30nm-100nm; illustratively, the size of the grains may be 30nm, 45nm, 50nm, 60nm, 75nm, 100nm.

Wherein, with further reference to FIG. 1a, the maximum width 11W of the cross-section of the branch is from 20nm to 350nm, and the maximum length 11L of the cross-section of the branch is from 50nm to 2500nm;

illustratively, the maximum width 11W of the cross section of the branch may be, for example, 20nm, 40nm, 80nm, 100nm, 150nm, 200nm, 250nm, 300nm or 350nm, and the maximum length 11L of the cross section of the branch may be, for example, 50nm, 100nm, 200nm, 300nm, 400nm, 500nm, 800nm, 1000nm, 1500nm, 2000nm or 2500nm, without limitation.

In some embodiments, the branches are selected from at least one of rod-like nanoparticles, nanoplates, nanowires, and nanotubes.

In some embodiments, the diameter of the channels 13 is from 10nm to 150nm as measured by mercury intrusion test methods; the depth of the pore channel is 50nm-1500nm. Illustratively, the diameter of the pore channel may be 10nm, 50nm, 60nm, 80nm, 100nm or 150nm, but is not limited thereto. The depth of the pore channel 13 may be 50nm, 100nm, 200nm, 300nm, 400nm, 500nm, 800nm or 1000nm, but is not limited thereto.

In some embodiments, the protective layer comprises at least one of a carbon layer, a metal oxide layer, a metal nitride layer;

in some embodiments, the carbon layer is an amorphous carbon layer and/or a graphitic carbon layer;

in some embodiments, the carbon layer is only positioned on the surface of the skeleton, and the carbon content is 5-25% by mass based on 100% by mass of the composite negative electrode material; specifically, it may be 5%, 8%, 10%, 12%, 15%, 18%, 20% or 25%, and is not limited herein.

In some embodiments, the carbon layer has a thickness of 1nm to 300nm.

In some embodiments, referring to fig. 1b, when the content of the protective layer is higher, the protective layer also fills the pores, which may further enhance the electrical conductivity and the structural stability.

Specifically, the carbon layer is also filled in the pore channel; the carbon filled in the pore structure can provide more ion and electron transmission paths, has good carbon conductivity, is beneficial to the entering and exiting of lithium ions, improves the rate capability of the material, and can further improve the stability.

In some embodiments, when the carbon layer is located on the surface of the skeleton and fills the pore channels, the carbon content is 25% to 75% and not 25% by mass of the composite anode material of 100%; specifically, the concentration may be 25%, 28%, 30%, 35%, 40%, 45%, 50%, or 75%, which is not limited herein.

In some embodiments, the protective layer comprises a metal oxide layer, the metal element of the metal oxide layer comprising at least one of Si, sn, ge, li, V, al, fe, and Zn; the metal oxide layer has the advantages of good rigidity, excellent compactness and the like, can effectively inhibit the volume expansion of N to cause the damage of the whole structure, reduces the volume expansion of the material, avoids the contact of electrolyte and the N material, reduces side reaction and improves the first effect of the whole composite material.

When the mass percentage of the composite negative electrode material is 100%, when the metal oxide layer is only positioned on the surface of the framework, the mass percentage of the metal oxide is 5% -25%;

when the metal oxide layer is positioned on the surface of the framework and filled in the pore channel, the mass percentage of the metal oxide is 25-75% and not 25% based on 100% of the mass percentage of the composite negative electrode material;

the protective layer comprises a metal nitride layer, and the metal element in the metal nitride layer comprises at least one of Ti, V, nb, ta, W and Zr; the metal nitride layer has good rigidity and excellent conductivity, can effectively relieve the volume expansion of silicon, simultaneously increases the conductivity of the material, improves the multiplying power of the material, reduces the irreversible capacity loss of the material and brings high capacity.

When the mass percentage of the composite negative electrode material is 100%, the mass percentage of the metal nitride layer is 5% -25% when the metal nitride layer is only positioned on the surface of the framework;

when the metal nitride is positioned on the surface of the framework and filled in the pore channel, the mass percentage of the metal nitride is 25-75% and not 25% by taking the mass percentage of the composite negative electrode material as 100%.

In one embodiment, the primary particle has a through-hole formed therein, and the porosity of the primary particle is not less than 30%. The primary particles of the embodiment have high porosity, can effectively relieve volume expansion of more than 300% of the negative electrode material, and combine the advantages of a macroporous through structure, the pore structure after lithiation can also be kept intact, the porosity in the prior art is low, and more micropores and mesopores exist, so that the huge volume expansion of the negative electrode material (such as silicon) cannot be met, and after the pores are filled, the pores are finally filled due to electrochemical sintering after lithiation, so that the porous structure cannot be kept.

Further, the porosity of the primary particles is 30% to 70%, for example 30%, 35%, 40%, 50%, 55%, 60%, or 70%, and preferably 40% to 60%.

As shown in fig. 1b, in some embodiments, a carbon layer is also filled in the via hole; the carbon filled in the through hole can provide more ion and electron transmission paths, has good carbon conductivity, is beneficial to the entering and exiting of lithium ions, improves the multiplying power performance of the material, and can further improve the stability.

In some embodiments, when the carbon layer is located on the surface of the skeleton and fills the through holes, the carbon content is 25 to 75% by mass and does not include 25% by mass, based on 100% by mass of the composite anode material; specifically, the concentration may be 25%, 28%, 30%, 35%, 40%, 45%, 50% or 75%, and is not limited herein.

In some embodiments, the protective layer is a metal oxide layer, the metal element of the metal oxide layer includes at least one of oxides of Si, sn, ge, li, V, al, fe, and Zn,

when the composite negative electrode material is counted by 100% by mass, when the oxide layer is positioned on the surface of the framework and filled in the through hole, the metal oxide is 25% -75% by mass and does not include 25%;

in some embodiments, the protective layer is a metal nitride layer, and the metal element in the metal nitride layer includes at least one of Ti, V, nb, ta, W, and Zr;

in some embodiments, when the metal nitride layer is located on the surface of the framework and fills the through hole, the metal nitride content is 25% to 75% by mass, and not 25%.

In some embodiments, the primary particles are selected from at least one of silicon, germanium, tin, boron, and antimony; the framework can be a silicon framework, a germanium framework, a tin framework, a boron framework, an antimony framework and the like; if the primary particle is selected from the silicon material, the primary particle comprises a silicon skeleton, a main skeleton positioned in the primary particle and a plurality of branches extending from the main skeleton to the surface of the primary particle. The framework structures of germanium, boron, tin and antimony are similar to the silicon framework structure described above.

In some embodiments, the primary particles have a median particle diameter of 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, and the like. Preferably 0.5 to 10 μm, and more preferably 1 to 5 μm.

In some embodiments, the primary particles have a specific surface area of 5m ² /g～100m ² In g, e.g. 5m ² /g、10m ² /g、20m ² /g、30m ² /g、40m ² /g、50m ² /g、60m ² /g、80m ² In g or 100m ² And/g, etc. Preferably 10m ² /g～50m ² /g。

In some embodiments, the primary particles have a powder tap density of 0.2g/cm ³ ～0.8g/cm ³ E.g. 0.2g/cm ³ 、0.3g/cm ³ 、0.5g/cm ³ 、0.6g/cm ³ 、0.7g/cm ³ Or 0.8g/cm ³ And the like. Preferably 0.4g/cm ³ ～0.7g/cm ³ 。

In some embodiments, the primary particles have a powder compaction density of 1.2g/cm ³ ～1.8g/cm ³ E.g. 1.2g/cm ³ 、1.3g/cm ³ 、1.4g/cm ³ 、1.5g/cm ³ 、1.6g/cm ³ Or 1.8g/cm ³ Etc., preferably 1.4g/cm ³ ～1.7g/cm ³ ；

In some embodiments, the median particle size of the composite negative electrode material is 0.1 μm to 15 μm, and optionally, the median particle size of the composite negative electrode material may be specifically 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, and the like, which is not limited herein. The median particle diameter of the composite negative electrode material is preferably 0.5 to 10 μm, more preferably 1 to 8 μm.

In some casesIn one embodiment, the specific surface area ratio of the composite anode material is 1m ² /g～150m ² (ii) in terms of/g. Alternatively, the specific surface area ratio of the composite anode material may be 1m ² /g、5m ² /g、10m ² /g、20m ² /g、30m ² /g、40m ² /g、50m ² /g、60m ² /g、70m ² /g、100m ² /g、120m ² G or 150m ² (iv)/g, etc., without limitation; the specific surface area ratio of the composite anode material is preferably 1m ² /g～50m ² (ii) in terms of/g. Understandably, the smaller the specific surface area is, the better, the larger the specific surface area is, the SEI film formation is easily caused by the overlarge specific surface area, the irreversible lithium salt is consumed too much, the first efficiency of the battery is reduced, and the specific surface area is controlled to be 10m by comprehensively considering the cost of the preparation process ² /g～50m ² /g。

In some embodiments, the porosity of the composite anode material is 10% to 70%, such as 10%, 30%, 35%, 40%, 50%, 55%, 60%, or 70%, etc., preferably 40% to 60%.

When the protective layer is a carbon layer, a method for preparing a composite anode material according to an embodiment, as shown in fig. 2, includes the following steps S100 to S400:

s100, preparing an N-M alloy;

s200, mixing the N-M alloy with the carbon-containing ammonium salt to obtain a mixture;

s300, performing a displacement reaction on the mixture in a protective atmosphere to obtain a reaction product, wherein the reaction product comprises nitride of M and oxide of M;

and S400, removing the oxide of the M and the nitride of the M to obtain the composite negative electrode material.

The obtained composite anode material comprises primary particles and a carbon layer; the primary particle comprises a skeleton, wherein the skeleton comprises a main skeleton positioned inside the primary particle and a plurality of branches extending from the main skeleton to the surface of the primary particle; the carbon layer is positioned on the surface of the framework.

The primary particles are of a macroporous structure, and pore channels are formed in the primary particles and extend to the surfaces of the primary particles.

And through holes are formed in the primary particles, and the porosity of the primary particles is not lower than 30%.

According to the scheme, the cathode material is prepared through a one-step compounding method, the N-M alloy and the carbon-containing ammonium salt directly react at high temperature, metal components in the N-M alloy are removed, meanwhile, a carbon layer is generated on the surface of the N material through in-situ deposition, the composite cathode material is obtained after acid cleaning, the overall reaction is mild, no by-product is generated, the N material is complete and stable in structure, and the carbon layer is uniformly deposited. The raw materials participating in the reaction are common alloy, ammonium salt and common inorganic compound, so that the cost can be reduced.

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

s100, preparing an N-M alloy;

in some embodiments, N in the N-M alloy comprises 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 specific examples, the N-M alloy may be a Si-Mg alloy, a Si-Al alloy, a Ge-Mg alloy, a Ge-Al alloy, or the like. Different types of alloys can obtain branches with different shapes, including at least one of rod-shaped nano particles, nano sheets, nano wires and nano tubes.

In some embodiments, the N-M alloy is prepared by mixing N powder and an active metal M and then heating and reacting under a protective gas to obtain the N-M alloy.

The particle size of the N powder is 0.2 μm to 15 μm, and specifically, it may be 0.2 μm, 0.5 μm, 1 μm, 3 μm, 5 μm, 8 μm, 10 μm, or 15 μm, and the like, which is not limited herein.

The particle size of the active metal M powder is 0.1 μ M to 80 μ M, and specifically, it may be 0.1 μ M, 5 μ M, 10 μ M, 20 μ M, 40 μ M, 50 μ M or 80 μ M, and the like, and is not limited herein.

The molar ratio of the N powder to the active metal M is 1: (1 to 3), specifically 1:1, 1.5, 1:2, 1.5 or 1:3, but not limited thereto.

In some embodiments, the temperature of the heating reaction is 400-900 ℃, for example 400 ℃, 500 ℃, 600 ℃, 700 ℃, 800 ℃ or 900 ℃.

The holding time for the heating reaction is 2h to 8h, for example, 2h, 4h, 6h or 8h, which is not limited herein.

The heating rate of the heating reaction is 1 ℃/min to 10 ℃/min, and may be, for example, 1 ℃/min, 3 ℃/min, 5 ℃/min, 8 ℃/min or 10 ℃/min, without limitation.

In the application, parameters such as the particle size of the N powder, the particle size of the active metal, the reaction temperature, the reaction time and the like are controlled, so that the generation of the silicon alloy is facilitated, and the doping uniformity of metal elements of the silicon alloy is improved.

Of course, the N-M alloy can also be prepared by other preparation methods, such as: high-energy ball milling, vacuum smelting, hot-pressing sintering and the like. It is understood that the N-M alloy may be commercially available, and step S100 may be omitted.

In some embodiments, the content of N in the N-M alloy is 15% to 60% by mass, and optionally, the content of N may be 15%, 20%, 30%, 40%, 50%, or 60% by mass, which is not limited herein. In a particular embodiment, the N-M alloy may be at least one of a silicon magnesium alloy, a silicon aluminum alloy, a silicon calcium alloy, a silicon zinc alloy, for example. It will be appreciated that the pore size and porosity of the three-dimensional channels of the N material can be varied by controlling the composition of the N-M alloy, with the higher the N content in the N-M alloy generally, the smaller the pore size. The heating reaction time and reaction temperature can be controlled to vary the depth of the pores, generally the longer the reaction time and the higher the reaction temperature, the deeper the depth of the pores.

In a specific embodiment, the method further comprises:

the obtained N-M alloy is pulverized to adjust the particle size of the N-M alloy powder to 0.2 to 15 μ M, which may be, for example, 0.2, 0.5, 1, 2, 5, 10 or 15 μ M, but is not limited thereto.

Specifically, the crushing treatment equipment comprises at least one of a planetary ball mill, a sand mill and an air flow crusher. It is understood that the smaller the grain size of the silicon alloy, the larger the specific surface area thereof, and the more sufficient the reaction can be made at the time of the dealloying heat treatment.

the carbonaceous ammonium salt refers to a salt containing carbon and an ammonium ion.

In some embodiments, the molar ratio of the N-M alloy to the carbonaceous ammonium salt is 1 (0.1-10), and may be 1.

Specifically, the carbonaceous 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, and therefore an ammonium salt inhibitor is further added to the mixture during the reaction to inhibit the decomposition of the ammonium salt at high temperature.

In some embodiments, the molar ratio of N-M alloy and ammonium salt decomposition inhibitor is 1 (0.2-10), and may be, for example, 1.

In some of these embodiments, the ammonium salt decomposition inhibitor comprises a carbonate and/or bicarbonate salt.

Wherein the carbonate has the chemical formula of M _y CO ₃ The bicarbonate has the formula M (HCO) ₃ ) _y M includes at least one of Na, K, li, mg, ca, zn, and Ba, y =1 or 2.

Understandably, the bicarbonate is unstable at high temperature and is easy to decompose into carbonate, carbon dioxide and water, the decomposed carbon dioxide gas, inorganic salt and water have no harm to the environment, partial reaction energy is absorbed, and the decomposition reaction of ammonium salt at high temperature is inhibited.

In some embodiments, in order to improve the reaction abundance, a molten salt medium is further added, and optionally, the molten salt medium comprises at least one of an ammonium halide salt and a halide salt.

The molar ratio of the N-M alloy to the ammonium halide salt is 1 (0.1-10), and specifically can be 1. The chemical formula of the halogenated ammonium salt is NH ₄ Y, wherein Y comprises at least one of Cl, br, F and I.

An ammonium salt decomposition inhibitor and a proper amount of molten salt medium (halogenated ammonium salt) are added in the reaction, on one hand, the ammonium salt decomposition inhibitor can inhibit the decomposition of the ammonium salt, so that the ammonium salt is kept in a high-temperature liquid state, the ammonium salt can slowly react with the alloy from outside to inside to achieve the aim of dealloying, and simultaneously, the ammonium salt gradually flows into the pore channel structure of the silicon material to serve as a liquid template of a connected framework, so that carbon is gradually and uniformly deposited in the pore channel structure of the silicon material, and the conductivity and the structural stability of the whole composite structure are enhanced; on the other hand, the molten salt can increase the solubility of the ammonium salt in the molten salt, promote the reaction to be fully carried out, ensure the high-temperature liquid environment and the uniformity of the reaction temperature when the alloy powder reacts with the ammonium salt, avoid the damage of a porous structure caused by overhigh local temperature, and improve the yield and the purity.

After the corresponding ammonium halide is added as a molten salt medium, the high-temperature liquid environment and the uniformity of the reaction temperature in the reaction of the alloy powder and the ammonium salt can be further ensured, the porous structure damage caused by overhigh local temperature is avoided, and the prepared cathode material has excellent stability, uniform carbon composite structure and excellent electrochemical performance.

Likewise, the molar ratio of the N-M alloy to the halide is 1: (0.1-10), specifically, 1.1, 1.5, 1:1, 1:2, 1:4, 1:5, 1:7 or 1. Wherein the halide has a chemical formula of MYa, wherein a =1,M comprises at least one of Na, K, li, mg, ca, zn and Ba, and Y comprises at least one of Cl, br, F and I.

S300, carrying out replacement reaction on the mixture in a protective atmosphere to obtain a reaction product, wherein the reaction product comprises nitride of M and oxide of M.

This reaction may be referred to as a dealloying reaction.

Wherein, the reaction product of the replacement reaction comprises M nitride, M oxide, carbon and N simple substance. Illustratively, the N-M alloy is a silicon-magnesium alloy, the ammonium salt is ammonium carbonate, and the chemical reaction formula for dealloying is: 5Mg ₂ Si+2(NH ₄ ) ₂ CO ₃ →5Si+2C+4MgO+2Mg ₃ N ₂ +2H ₂ O+6H ₂ After the reaction, removing the reaction productMetal oxide (MgO) and nitride (Mg) ₃ N ₂ ) And obtaining the composite cathode material.

Understandably, the ammonium salt is selected to participate in the process of dealloying, the ammonium salt is in a molten state in the reaction process, a connected liquid template is provided for the formation of a connected silicon framework, and the continuity of the pore channel structure of the silicon framework is ensured; in addition, ammonium salt is used as a carbon source, and a carbon layer formed after reaction is also continuously filled in the pore structure to form a three-dimensional conductive carbon network structure. Because the reaction is mild at high temperature, the carbon-oxygen bond in the ammonium salt can be orderly recombined after being broken to form a carbon layer, so that the conductivity is improved, the lithium ion can enter and exit more favorably, and the multiplying power of the material is improved.

In a specific embodiment, the dealloying heat treatment is performed under vacuum conditions, with a vacuum of 1Pa to 20KPa. As can be understood, the alloying heat treatment is carried out under the high-temperature vacuum environment, the reaction rate is improved, and the reaction is safer.

The temperature of the dealloying heat treatment is 200 to 950 ℃ for the mixture to react sufficiently, and may be, for example, 200 ℃, 300 ℃, 400 ℃, 600 ℃, 800 ℃ or 950 ℃.

The holding time of the dealloying heat treatment is 1h to 24h, for example, 1h, 3h, 6h, 9h, 12h, 15h, 18h or 24h, which is not limited herein.

The heating rate of the dealloying heat treatment is 1 ℃/min to 20 ℃/min, and may be, for example, 1 ℃/min, 5 ℃/min, 10 ℃/min, 15 ℃/min or 20 ℃/min. Thereby effectively improving the reaction efficiency.

It can be understood that within the temperature, time and temperature rise rate range of the proper heat treatment, the dealloying efficiency is improved, and the N-M alloy is helped to form an N framework structure in the dealloying process. In order to increase the safety of the reaction, the dealloying heat treatment is carried out under the protection of a protective gas comprising at least one of nitrogen, helium, neon, argon, hernia. The flow of the protective gas can be controlled to be 1L/min-10L/min so as to improve the safety of the reaction.

As an optional technical solution of the present application, the removing method includes acid washing, and the reaction product is acid washed, so that the oxide and nitride of M in the reaction product can be removed.

The mass concentration of the acid solution is 1mol/L to 5mol/L, and may be, for example, 1mol/L, 2mol/L, 3mol/L, 4mol/L, or 5mol/L. It is needless to say that the mass concentration of the acid solution may be adjusted according to actual requirements, and is not limited herein.

The acid washing time is 1h to 10h, and may be 1h, 3h, 5h, 7h or 10h, for example. In this example, the acid-washed product can still be recovered for recycling.

When the protective layer is a metal oxide layer, the preparation method of the composite negative electrode material comprises the following steps of S100 'to S500':

s100', preparing an N-M alloy;

s200', mixing the N-M alloy with a transition metal halide to obtain a mixture;

s300', placing the mixture in a protective atmosphere for a displacement reaction to obtain a reaction product, wherein the reaction product comprises M halide and transition metal;

s400', removing halide and transition metal of M in the reaction product to obtain an N material; the N material is a primary particle, the primary particle comprises a skeleton, and the skeleton comprises a main skeleton positioned inside the primary particle and a plurality of branches extending from the main skeleton to the surface of the primary particle;

s500', forming a metal oxide layer on the surface of the framework of the N material to obtain the composite cathode material.

The obtained composite negative electrode material comprises primary particles and a metal oxide layer; the primary particle comprises a skeleton, wherein the skeleton comprises a main skeleton positioned inside the primary particle and a plurality of branches extending from the main skeleton to the surface of the primary particle; the metal oxide layer is positioned on the surface of the framework.

It is understood that the primary particles have a macroporous structure, and the inside of the primary particles is formed with pores extending to the surface of the primary particles.

It is also understood that the primary particle has through-holes formed therein, and the porosity of the primary particle is not less than 30%.

s100', preparing an N-M alloy;

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 specific examples, the N-M alloy may be a Si-Mg alloy, a Si-Al alloy, a Ge-Mg alloy, a Ge-Al alloy, or the like. Different types of alloys can obtain branches with different shapes, including at least one of rod-shaped nano particles, nano sheets, nano wires and nano tubes.

Specifically, the preparation method of the N-M alloy is the same as the step S100; will not be described in detail herein;

s200', mixing the N-M alloy with a transition metal halide to obtain a mixture;

in some embodiments, the transition metal halide has the formula ABx, wherein x =2 or 3, a comprises at least one of Sn, cu, fe, zn, co, mn, cr, and Ni, and B comprises at least one of Cl, F, and Br;

wherein the molar ratio of the N-M alloy to the transition metal halide is 1 (0.1-2).

It is understood that the mixture may be obtained commercially, in which case step S200' may be omitted.

S300', placing the mixture in protective atmosphere for replacement reaction to obtain a reaction product, wherein the reaction product comprises halide of M and transition metal;

in some embodiments, the temperature of the metathesis reaction is from 500 ℃ to 1100 ℃, and can be 500 ℃, 600 ℃, 700 ℃, 800 ℃, 900 ℃, 1000 ℃, or 1100 ℃.

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

The gas of the protective atmosphere comprises at least one of helium, neon, argon, krypton and xenon;

the removing method is the same as step S400, and will not be described in detail here.

S500', forming a metal oxide layer on the surface of the skeleton structure of the N material to obtain the composite cathode material.

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

the metal element in the metal oxide layer includes at least one of Si, sn, ge, li, V, al, fe, and Zn.

When the protective layer is a metal nitride layer, the preparation method of the composite negative electrode material comprises the following steps of S100-S600':

s100', preparing an N-M alloy;

s200', mixing the N-M alloy with a transition metal halide to obtain a mixture;

s300' placing the mixture in protective atmosphere for replacement reaction to obtain a reaction product, wherein the reaction product comprises M halide and transition metal;

s400', removing halide and transition metal of M in the reaction product to obtain an N material, wherein the N material is primary particles, the primary particles comprise a framework, and the framework comprises a main framework positioned in the primary particles and a plurality of branches extending from the main framework to the surfaces of the primary particles;

s500', forming a metal oxide layer on the surface of the N material to obtain a compound;

and S600', performing heat treatment on the composite in a protective atmosphere, and then performing nitriding treatment to obtain the composite cathode material.

The obtained composite negative electrode material comprises primary particles and a metal nitride layer; the primary particle comprises a skeleton, wherein the skeleton comprises a main skeleton positioned inside the primary particle and a plurality of branches extending from the main skeleton to the surface of the primary particle; the metal nitride layer is positioned on the surface of the framework.

It is understood that the primary particle has a macroporous structure, and the inside of the primary particle is formed with a pore passage extending to the surface of the primary particle.

The steps S100 'to S500' are the same as the steps S100 'to S500', and will not be described in detail.

In some embodiments, the heat treatment temperature is 500 ℃ to 800 ℃, and the holding time is 1h to 24h;

in some embodiments, the protective atmosphere comprises at least one of helium, neon, argon, krypton, and xenon;

in some embodiments, the nitriding treatment is incubated at 400 ℃ to 950 ℃ for 2h to 24h;

the nitriding atmosphere adopts at least one of ammonia gas atmosphere and nitrogen gas atmosphere;

the embodiment of the invention also provides a lithium ion secondary battery which comprises the composite negative electrode material or the negative electrode material prepared by the preparation method of the composite negative electrode material.

The following examples are intended to illustrate the invention in more detail. The embodiments of the present invention are not limited to the following specific embodiments. The present invention can be modified and implemented as appropriate within the scope of the main claim.

Example 1

The preparation method of the silicon-carbon composite anode material of the embodiment comprises the following steps:

(1) Uniformly mixing silicon powder with the particle size of 1 mu m and magnesium powder according to the molar ratio of 1:2, putting the mixture into a vacuum furnace, vacuumizing the vacuum furnace to 10Pa, heating the mixture to 600 ℃ at the heating rate of 3 ℃/min under the protection of argon inert gas, and preserving the heat for 6 hours to fully react to obtain silicon-magnesium alloy; and ball-milling the silicon-magnesium alloy to obtain 1 micron silicon-magnesium alloy powder.

(2) 1mol of silicon-magnesium alloy powder, 1mol of ammonium carbonate, 1mol of sodium carbonate and 1mol of ammonium chloride are mixed uniformly, and then 1.5mol of sodium chloride is added to obtain a mixture.

(3) Uniformly mixing the obtained mixture, putting the mixture into a sealed stainless steel reaction kettle, heating the reaction kettle to 750 ℃ at a heating rate of 3 ℃/min in an argon atmosphere, and then preserving heat for 8 hours to fully react to obtain a reaction product;

(4) And mechanically stirring and pickling the reaction product in 1mol/L hydrochloric acid solution for 2 hours, and then performing suction filtration, washing and drying to obtain the silicon-carbon composite negative electrode material.

The tap density of the prepared silicon composite anode material is 0.73g/cm through testing ³ The powder compacted density is 1.2g/cm ³ Porosity of 50% and specific surface area of 18m ² (ii)/g, carbon content 12%.

FIGS. 3a to 3b are scanning electron microscope images of the silicon-carbon composite negative electrode material in this embodiment; FIG. 4 is a Raman diagram of the silicon-carbon composite anode material of the present example; FIG. 5 is an XRD spectrum of the silicon-carbon composite anode material in the present example; fig. 6 shows the cycle performance curve of the silicon-carbon composite negative electrode material in this example, and the charge and discharge current is 0.5C.

As can be seen from the scanning electron microscope images in fig. 3a to 3b, the prepared 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 a plurality of branches extending from the main skeleton to the surface of the primary particle; the primary particles are of a macroporous structure, a pore channel is formed inside the primary particles, the pore channel extends to the surface of the primary particles, the surface of a silicon framework is coated with a graphite carbon layer, the thickness of the carbon layer is 25nm, branches of the framework are rod-shaped nanometer silicon, the average diameter of the pore channel is about 80nm, and the depth of the pore channel is about 250nm.

The Raman spectrum of FIG. 5 is further demonstrated at 2680cm ^-1 A2D peak exists nearby, which is a characteristic peak of graphite, and further shows that the in-situ generated carbon is graphite-like carbon and has better conductivity and stability. From the XRD pattern of FIG. 5, it can be seen that the three intensity peaks at 28.4 °, 47.3 ° and 56.1 ° correspond to the three intensity peaks of silicon (JCPDS No. 27-1402), substantially free of impuritiesPhase (1);

in fig. 6, it can be seen that the lithium ion battery prepared from the silicon-carbon composite negative electrode material has high cycle performance, and has a capacity of 897mAh/g after 1200 cycles under a large current of 0.5C. Therefore, the silicon-carbon composite negative electrode material prepared by the method at least has the advantage of high charge-discharge cycle stability.

Example 2

The preparation method of the silicon-carbon composite anode material comprises the following steps:

(1) Uniformly mixing 1.5-micron silicon powder and zinc powder according to a molar ratio of 1:2.2, putting the mixture into a vacuum furnace, vacuumizing the vacuum furnace to 10Pa, heating the mixture to 650 ℃ at a heating rate of 5 ℃/min under the protection of argon inert gas, and then preserving the heat for 3 hours to ensure that the mixture fully reacts to obtain a silicon-zinc alloy, wherein the vacuum degree is kept unchanged all the time in the reaction process; ball-milling the silicon-zinc alloy to obtain 1 mu m silicon-zinc alloy powder;

(2) 1mol of silicon-zinc alloy powder, 3mol of ammonium carbamate, 1mol of potassium carbonate and 1.5mol of ammonium chloride are uniformly mixed, and then 1.5mol of sodium chloride is added to obtain a mixture.

(3) Uniformly mixing the obtained mixture, putting the mixture into a sealed stainless steel reaction kettle, heating the reaction kettle to 800 ℃ at a heating rate of 3 ℃/min in an argon atmosphere, and then preserving heat for 8 hours to fully react to obtain a reaction product;

(4) And (3) placing the reaction product into 2L of 1mol/L hydrochloric acid solution, mechanically stirring, pickling for 3h, and performing suction filtration, washing and drying to obtain the silicon composite negative electrode material.

Through tests, the tap density of the prepared silicon composite anode material is 0.77g/cm ³ The powder compacted density is 1.26g/cm ³ Porosity 52%, specific surface area 25m ² Per g, carbon content 15%.

The silicon-carbon composite material comprises a silicon material and a carbon layer, wherein the silicon material is primary particles, the primary particles comprise a silicon framework, and the silicon framework comprises a main framework positioned inside the primary particles and a plurality of branches extending from the main framework to the surfaces of the primary particles; the branches are rod-shaped silicon nanoparticles; the primary particles are of a macroporous structure, the pores are formed in the primary particles, the pores extend to the surfaces of the primary particles, the surface of the silicon framework is coated with the carbon layer which is amorphous carbon, the thickness of the carbon layer is 15nm, the average diameter of the pores is about 80nm, and the depth of the pores is about 300nm.

Example 3

(1) Uniformly mixing silicon powder with the particle size of 2 microns and magnesium powder according to the mol ratio of 1; ball-milling the silicon-magnesium alloy to obtain 2 mu m silicon-magnesium alloy powder;

(2) 1mol of silicon-magnesium alloy powder, 5mol of ammonium carbamate, 2mol of ammonium bicarbonate and 2.5mol of ammonium bromide are uniformly mixed, and then 1.5mol of potassium chloride is added to obtain a mixture.

(3) Uniformly mixing the obtained mixture, putting the mixture into a sealed stainless steel reaction kettle, heating the reaction kettle to 820 ℃ at the heating rate of 3 ℃/min in the argon atmosphere, and then preserving heat for 8 hours to fully react to obtain a reaction product;

(4) And (3) placing the reaction product into 3L of 1mol/L hydrochloric acid solution, mechanically stirring, carrying out acid washing treatment for 3h, and carrying out suction filtration, washing and drying to obtain the silicon composite negative electrode material.

Through tests, the tap density of the prepared silicon composite anode material is 0.45g/cm ³ The powder compacted density is 1.09g/cm ³ The porosity was 65%, the specific surface area was 53m ² Per g, carbon content 38%.

The silicon-carbon composite material comprises a silicon material and a carbon layer, wherein the silicon material is primary particles, the primary particles comprise a silicon framework, and the silicon framework comprises a main framework positioned inside the primary particles and a plurality of branches extending from the main framework to the surfaces of the primary particles; branching into nanometer silicon chips; the primary particles are of a macroporous structure, pore channels are formed in the primary particles, the pore channels extend to the surfaces of the primary particles, the surfaces of the silicon frameworks are wrapped by carbon layers which are amorphous carbon layers, and the thickness of each carbon layer is 25nm; and the pore canal is filled with carbon material; the average diameter of the channels is about 50nm and the depth of the channels is about 500nm.

Example 4

(1) Uniformly mixing 3 mu m of silicon powder and aluminum powder according to a molar ratio of 1:3, putting the mixture into a vacuum furnace, vacuumizing to 10Pa, heating to 660 ℃ at a heating rate of 5 ℃/min under the protection of argon inert gas, and preserving heat for 3 hours to ensure that the mixture fully reacts to obtain silicon-aluminum alloy, wherein the vacuum degree is kept unchanged all the time in the reaction process; ball-milling the silicon-aluminum alloy to obtain silicon-aluminum alloy powder with the particle size of 3 mu m;

(2) 1mol of silicon-aluminum alloy powder, 4.5mol of ammonium carbamate, 1.8mol of ammonium carbonate and 2.2mol of ammonium bromide are mixed uniformly, and then 1.5mol of sodium chloride is added to obtain a mixture.

(3) Uniformly mixing the obtained mixture, putting the mixture into a sealed stainless steel reaction kettle, heating the reaction kettle to 810 ℃ at the heating rate of 2 ℃/min in the argon atmosphere, and then preserving heat for 8 hours to fully react to obtain a reaction product;

(4) And (3) placing the reaction product into 4L of 1mol/L hydrochloric acid solution, mechanically stirring, carrying out acid washing treatment for 3h, and carrying out suction filtration, washing and drying to obtain the silicon composite negative electrode material.

Through tests, the tap density of the prepared silicon composite anode material is 0.58g/cm ³ The powder compacted density is 1.12g/cm ³ The porosity was 32%, and the specific surface area was 60m ² (iv)/g, carbon content 40%.

The silicon-carbon composite material comprises a silicon material and a carbon layer, wherein the silicon material is primary particles, the primary particles comprise a silicon framework, and the silicon framework comprises a main framework positioned inside the primary particles and a plurality of branches extending from the main framework to the surfaces of the primary particles; the branches are rod-shaped silicon nanoparticles; the primary particles are of a macroporous structure, a pore channel is formed inside the primary particles, the pore channel extends to the surface of the primary particles, the surface of the silicon framework is wrapped by a carbon layer which is a graphite carbon layer, the thickness of the carbon layer is 50nm, and the pore channel is filled with a carbon material; the average diameter of the channels is about 150nm and the depth of the channels is about 1000nm.

Example 5:

(1) Uniformly mixing silicon powder with the particle size of 2 microns and magnesium powder according to the molar ratio of 1.8, putting the mixture into a vacuum furnace, vacuumizing the vacuum furnace to 10Pa, heating the mixture to 650 ℃ at the heating rate of 5 ℃/min under the protection of argon inert gas, and then preserving the heat for 3 hours to ensure that the mixture fully reacts to obtain silicon-magnesium alloy, wherein the vacuum degree is kept unchanged all the time in the reaction process; ball-milling the silicon-magnesium alloy to obtain 3 mu m silicon-magnesium alloy powder;

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

(3) Uniformly mixing the obtained mixture, putting the mixture into a sealed stainless steel reaction kettle, heating the reaction kettle to 750 ℃ at the heating rate of 4 ℃/min in the argon atmosphere, and then preserving heat for 8 hours to fully react to obtain a reaction product;

Through tests, the tap density of the prepared silicon composite anode material is 0.8g/cm ³ The powder compacted density is 1.38g/cm ³ The porosity was 30%, and the specific surface area was 10m ² (ii)/g, carbon content 5%.

The silicon-carbon composite material comprises a silicon material and a carbon layer, wherein the silicon material is primary particles, the primary particles comprise silicon skeletons, and the silicon skeletons comprise main skeletons positioned in the primary particles and a plurality of branches extending from the main skeletons to the surfaces of the primary particles; the primary particles are of a macroporous structure, pore channels are formed in the primary particles, the pore channels extend to the surfaces of the primary particles, the carbon layer wrapped on the surface of the silicon framework is graphite carbon, and the thickness of the carbon layer is 5nm; the average diameter of the channels is about 20nm and the depth of the channels is about 60nm.

Example 6

A preparation method of a germanium-carbon composite negative electrode material comprises the following steps:

(1) Uniformly mixing germanium powder with the diameter of 1.5 microns and aluminum powder according to the molar ratio of 1:3, putting the mixture into an atmosphere furnace, heating the mixture to 480 ℃ at the heating rate of 5 ℃/min under the protection of argon inert gas, and then preserving heat for 6 hours to fully react to obtain germanium-aluminum alloy; performing ball milling on the germanium-aluminum alloy to obtain germanium-aluminum alloy powder with the particle size of 0.5 mu m;

(2) 1mol of germanium-aluminum alloy powder, 2.5mol of ammonium carbamate, 1.8mol of ammonium carbonate and 2.2mol of ammonium bromide are mixed uniformly, and then 1.5mol of sodium chloride is added to obtain a mixture.

(3) Uniformly mixing the obtained mixture, putting the mixture into a sealed stainless steel reaction kettle, heating the reaction kettle to 780 ℃ at the heating rate of 4 ℃/min in the argon atmosphere, and then preserving heat for 8 hours to fully react to obtain a reaction product;

(4) And (3) placing the reaction product into 2L of 1mol/L hydrochloric acid solution, mechanically stirring, carrying out acid washing treatment for 3h, and carrying out suction filtration, washing and drying to obtain the germanium-carbon composite negative electrode material.

The obtained germanium-carbon composite negative electrode material has a median particle diameter of about 0.6 μm and a tap density of 0.78g/cm ³ Compacted density 1.1g/cm ³ A specific surface area of 16m ² The porosity is 24 percent, and the mass percent content of carbon is 75 percent.

The germanium-carbon composite material comprises a germanium material and a carbon layer, wherein the germanium material is a primary particle, the primary particle comprises a germanium skeleton, and the germanium skeleton comprises a main skeleton positioned in 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 particles are of a macroporous structure, pore channels are formed inside the primary particles, the pore channels extend to the surfaces of the primary particles, and the surfaces of the germanium frameworks are wrapped with carbon layers with the thickness of 80 nm; the average diameter of the channels is about 100nm and the depth of the channels is about 800nm.

Example 7

(1) Uniformly mixing germanium powder with the particle size of 1.5 mu m and magnesium powder according to the mol ratio of 1:2.5, putting the mixture into an atmosphere furnace, heating the mixture to 480 ℃ at the heating rate of 5 ℃/min under the protection of argon inert gas, and preserving heat for 6 hours to fully react to obtain germanium-magnesium alloy; ball-milling the germanium-magnesium alloy to obtain germanium-magnesium alloy powder with the particle size of 0.5 mu m;

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

The obtained germanium-carbon composite negative electrode material has a median particle diameter of about 0.6 μm and a tap density of 0.88g/cm ³ Compacted density of 1.3g/cm ³ Specific surface area of 11m ² The porosity is 44%, and the carbon content is 25% by mass.

The germanium-carbon composite material comprises a germanium material and a carbon layer, wherein the germanium material is a primary particle, the primary particle comprises a germanium skeleton, and the germanium skeleton comprises a main skeleton positioned in the primary particle and a plurality of branches extending from the main skeleton to the surface of the primary particle; branching into rod-shaped nanoparticles; the primary particles are of a macroporous structure, a pore channel is formed inside the primary particles, the pore channel extends to the surface of the primary particles, and the surface of the germanium framework is wrapped with a carbon layer with the thickness of 50nm; the average diameter of the channels was about 60nm and the depth of the channels was about 1500nm.

Example 8

A preparation method of a silicon composite anode material comprises the following steps:

(1) Uniformly mixing 1.5 mu m silicon powder and magnesium powder according to the mol ratio of 1:2.5, putting the mixture into an atmosphere furnace, heating the mixture to 600 ℃ at the heating rate of 5 ℃/min under the protection of argon inert gas, and then preserving heat for 6h to ensure that the mixture fully reacts to obtain silicon-magnesium alloy; ball-milling the silicon-magnesium alloy to obtain 0.5 mu m silicon-magnesium alloy powder;

(2) 1mol of silicon-magnesium alloy powder and 1mol of copper chloride (CuCl) ₂ ) Uniformly mixing the mixture and 1mol of sodium chloride (NaCl) to obtain a mixtureA compound;

(3) Placing the obtained mixture into an argon atmosphere, heating to 750 ℃ at a heating rate of 3 ℃/min, and then preserving heat for 8 hours to fully react to obtain a reaction product; placing the reaction product into 2L of 1mol/L hydrochloric acid solution, mechanically stirring, pickling for 3h, and performing suction filtration, washing and drying to obtain a silicon negative electrode material with a skeleton structure;

(4) 1mol of the silicon negative electrode material and 0.7g of cellulose are dissolved in 500ml of absolute ethyl alcohol to be uniformly dispersed to obtain a mixed solution.

(5) Dropwise adding 3g of tetrabutyl titanate into the mixed solution, heating to 80 ℃, rapidly stirring for 3 hours, carrying out suction filtration, and carrying out vacuum drying at 60 ℃ for 24 hours to obtain a titanium oxide precursor coated silicon-magnesium alloy compound;

(6) And heating the composite to 750 ℃ at the heating rate of 3 ℃/min in the argon atmosphere, and then preserving heat for 8 hours to fully react to obtain the silicon/titanium oxide composite negative electrode material.

The median diameter of the obtained composite anode material is about 0.6 μm, and the specific surface area is 44m ² The porosity was 43%, and the titanium oxide content was 12% by mass.

The composite material comprises a silicon material and a titanium oxide layer, wherein the silicon material is primary particles, the primary particles comprise a silicon framework, and the silicon framework comprises a main framework positioned inside the primary particles and a plurality of branches extending from the main framework to the surfaces of the primary particles; branching into rod-shaped nanoparticles; the primary particles are of a macroporous structure, pore channels are formed in the primary particles, the pore channels extend to the surfaces of the primary particles, and the surfaces of the silicon frameworks are wrapped by titanium oxide layers; the average diameter of the channels is about 100nm and the depth of the channels is about 700nm.

Example 9

(2) 1mol of silicon-magnesium alloy powder and 1mol of copper chloride (CuCl) ₂ ) Uniformly mixing the mixture and 1mol of sodium chloride (NaCl) to obtain a mixture;

(6) Putting the compound into a tubular atmosphere furnace, heating to 650 ℃ at a heating rate of 3 ℃/min in an argon atmosphere, preserving heat for 5 hours to enable the compound to fully react, then changing argon into ammonia gas, heating to 800 ℃, and preserving heat for 8 hours to obtain a silicon/titanium nitride composite negative electrode material;

the obtained composite anode material has a median particle diameter of about 0.7 μm and a specific surface area of 40m ² The porosity is 48%, and the mass percentage content of the titanium nitride is 32%.

The composite material comprises a silicon material and a titanium nitride layer, wherein the silicon material is primary particles, the primary particles comprise a silicon framework, and the silicon framework comprises a main framework positioned inside the primary particles and a plurality of branches extending from the main framework to the surfaces of the primary particles; the branches are nanowires; the primary particles are of a macroporous structure, pore channels are formed in the primary particles, the pore channels extend to the surfaces of the primary particles, and the surfaces of the silicon frameworks are wrapped with titanium nitride layers; the average diameter of the channels was about 58nm and the depth of the channels was about 1000nm.

Example 10

(3) Putting the obtained mixture into an argon atmosphere, heating to 700 ℃ at a heating rate of 3 ℃/min, and then preserving heat for 6 hours to fully react to obtain a reaction product; placing the reaction product into 2L of 1mol/L hydrochloric acid solution, mechanically stirring, pickling for 3h, and performing suction filtration, washing and drying to obtain a silicon negative electrode material with a skeleton structure;

(4) Preparing a silicon cathode material wrapped by vanadium pentoxide through a sol-gel process, firstly preparing 500ml of 0.15M/L alcohol solution of triisopropoxyl vanadium oxide, and adding 30ml of acetylacetone to obtain a mixed solution; and adding 0.5mol of silicon negative electrode material powder into the mixed solution, stirring for 36 hours, and uniformly dispersing to obtain sol.

(5) Carrying out suction filtration on the sol, and carrying out vacuum drying for 24 hours at the temperature of 60 ℃ to obtain a vanadium pentoxide precursor-coated silicon negative electrode material compound;

(6) And (3) putting the compound into a tubular atmosphere furnace, heating to 600 ℃ at the heating rate of 3 ℃/min in the argon atmosphere, preserving heat for 3h to enable the compound to fully react, then replacing argon with ammonia, heating to 750 ℃ and preserving heat for 8h to obtain the silicon/vanadium nitride composite negative electrode material.

The median diameter of the obtained composite anode material is about 0.6 μm, and the specific surface area is 51m ² The porosity is 40 percent, and the mass percent content of vanadium nitride is 25 percent.

The composite material comprises a silicon material and a vanadium nitride layer, wherein the silicon material is primary particles, the primary particles comprise a silicon framework, and the silicon framework comprises a main framework positioned inside the primary particles and a plurality of branches extending from the main framework to the surfaces of the primary particles; branching into rod-shaped nanoparticles; the primary particles are of a macroporous structure, a pore channel is formed inside the primary particles, the pore channel extends to the surface of the primary particles, and the surface of the silicon framework is wrapped by a vanadium nitride layer; the average diameter of the channels is about 100nm and the depth of the channels is about 900nm.

Comparative example 1:

(1) Uniformly mixing silicon powder with the particle size of 1 mu m and magnesium powder according to the mol ratio of 1:2, putting the mixture into a vacuum furnace, vacuumizing the vacuum furnace to 10Pa, heating the mixture to 600 ℃ at the heating rate of 3 ℃/min under the protection of argon inert gas, and preserving the heat for 6 hours to ensure that the mixture is fully reacted to obtain silicon-magnesium alloy; and ball-milling the silicon-magnesium alloy to obtain 1 micron silicon-magnesium alloy powder.

(2) Uniformly mixing 1mol of silicon-magnesium alloy powder with 1mol of ammonium carbonate, 1mol of sodium carbonate and 1mol of ammonium chloride to obtain a mixture.

Comparative example 2

(2) 1mol of silicon-magnesium alloy powder, 1mol of ammonium carbonate and 1mol of ammonium chloride are mixed uniformly, and then 1.5mol of sodium chloride is added to obtain a mixture.

Comparative example 3

The composite material adopts a silicon-carbon composite cathode material SiO/C, the median particle size of the silicon-carbon composite cathode material is 1.5 mu m, the inner core of the composite material is a porous silicon structure accumulated by nano silicon particles, and the shell of the composite material is wrapped by a carbon layer; wherein the carbon content is 22 percent by mass, and the specific surface area is 38m ² The porosity of the silicon-carbon composite negative electrode material is 67 percent. Namely SiOx/C anode material, where x =1.0.

And (3) performance testing:

the negative electrode materials prepared in the embodiments 1 to 10 and the comparative examples 1 to 3, the same positive electrode material and the current collector are prepared into a lithium ion battery, and the battery performance test is performed, wherein the test items comprise specific discharge capacity, first coulombic efficiency, capacity after 1200 cycles of 0.5C cycle and capacity retention rate after 1200 cycles of 0.5C cycle, the sample numbers are S1 to S10 and R1 to R3, and the performance parameters of the samples are as shown in Table 1:

TABLE 1 Performance comparison results Table

It can be known from the above examples and comparative examples that the composite negative electrode materials provided in examples 1, 2, 5, and 6 have a three-dimensional pore structure, the carbon layer is coated on the surface of the skeleton of the negative electrode material, the composite negative electrode materials provided in examples 3 and 4 have a three-dimensional pore structure, the carbon layer is coated on the surface of the skeleton of the negative electrode material and filled in the three-dimensional pore structure, and the through pore structure has good structural stability, can provide a space for internal expansion in the lithium desorption and insertion process of the negative electrode material, and can be used as a passage for electrolyte flow, thereby improving the lithium storage performance of silicon, reducing the expansion of a lithium battery, and improving the capacity retention rate of the battery.

Comparative example 1 no molten salt medium is added in the preparation process, and local temperature of high-temperature liquid environment is too high when the alloy powder reacts with ammonium salt, so that part of three-dimensional pore structure is damaged, and the charge-discharge cycle stability of the battery is poor. Comparative example 2 no ammonium salt decomposition inhibitor was added during the preparation process, ammonium salt was decomposed into ammonia and carbon dioxide during the reaction process, and it was difficult to uniformly deposit and form a carbon layer on the surface or in the three-dimensional pore channels of the silicon material, so that the carbon content of the final negative electrode material was reduced, the conductivity of the negative electrode material was poor, the volume expansion inhibition performance was weak, and the price of the long cycle performance was poor.

According to the embodiments and the test results, the battery prepared from the silicon-carbon composite negative electrode material has the advantages of good charge-discharge cycle stability, high capacity and long cycle life. In summary, the preparation method of the porous silicon-carbon composite anode material provided by the application is simple and easy to operate, and the preparation process is safe and efficient; the manufacturing cost is effectively reduced, and the method is suitable for quantitative production; the prepared product is used as a battery pole piece and has better charge-discharge cycle performance.

Although the present application has been described with reference to preferred embodiments, it is not intended to limit the scope of the claims, and many possible variations and modifications may be made by one skilled in the art without departing from the spirit of the application.

Claims

1. The composite negative electrode material is characterized by comprising primary particles and a protective layer; wherein the primary particle comprises a backbone comprising a main backbone located inside the primary particle and a plurality of branches extending from the main backbone to the surface of the primary particle; the protective layer is located on the surface of the framework.

2. The composite anode material according to claim 1, wherein the composite anode material comprises at least one of the following a to e:

a. the main framework is a three-dimensional net structure;

b. a single said branch is an individual die;

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;

e. the branch is selected from at least one of a rod-shaped nanoparticle, a nano sheet, a nano wire and a nano tube.

3. The composite anode material according to claim 1, wherein the primary particles have a macroporous structure, and pore channels are formed in the primary particles and extend to the surfaces of the primary particles.

4. The composite anode material of claim 3, wherein the diameter of the pore channel is 10nm to 150nm; the depth of the pore channel is 50nm-1500nm.

5. The composite anode material according to claim 1, wherein through holes are formed inside the primary particles, and a porosity of the primary particles is not less than 30%.

6. The composite anode material according to claim 3 or 5, wherein the protective layer is further filled in the pore channel or the through hole.

7. The composite anode material according to claim 1 or 6, wherein the protective layer comprises at least one of a carbon layer, a metal oxide layer, and a metal nitride layer; and/or

The protective layer comprises a metal oxide layer, the metal element of the metal oxide layer comprises at least one of Si, sn, ge, li, V, al, fe and Zn, and when the mass percentage of the composite negative electrode material is 100%, the mass percentage of the metal oxide layer is 5% -25% when the metal oxide layer is only positioned on the surface of the framework; when the metal oxide layer is positioned on the surface of the framework and is filled in the pore channel or the through hole, the mass percentage of the metal oxide is 25-75% and does not include 25% by taking the mass percentage of the composite negative electrode material as 100%; and/or

The protective layer comprises a metal nitride layer, the metal element in the metal nitride layer comprises at least one of Ti, V, nb, ta, W and Zr, and when the composite negative electrode material is calculated by taking the mass percentage of 100%, the metal nitride layer is only positioned on the surface of the framework, the mass percentage of the metal nitride is 5-25%; when the metal nitride is positioned on the surface of the framework and filled in the pore channel or the through hole, the mass percentage of the metal nitride is 25-75% and does not include 25% by taking the mass percentage of the composite negative electrode material as 100%.

8. The composite anode material according to any one of claims 1 to 7, wherein the composite anode material comprises at least one of the following a to j:

b. the median particle diameter of the primary particles is 0.2-15 μm;

c. the specific surface area of the primary particles is 5m ² /g～100m ² /g；

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

e. the tap density of the primary particles is 0.2g/cm ³ ～0.8g/cm ³ ；

f. Powder compacted density of the primary particlesIs 1.2g/cm ³ ～1.8g/cm ³ ；

h. the specific surface area of the composite negative electrode material is 1m ² /g～150m ² /g；

i. The porosity of the composite negative electrode material is 10-70%;

9. A preparation method of the composite anode material is characterized by comprising the following steps:

placing a mixture containing N-M alloy and carbon-containing ammonium salt in a protective atmosphere to carry out a displacement reaction to obtain a reaction product, wherein the reaction product comprises an oxide of M and a nitride of M; and

10. The method for producing the composite anode material according to claim 9, characterized by comprising at least one of the following features a to e:

a. the grain diameter of the N-M alloy is 0.2-15 mu M;

e. the mixture further comprises a molten salt medium; and/or

11. The method according to claim 10, characterized by comprising at least one of the following features a to g:

b. the reaction heating rate of the displacement reaction is 1-20 ℃/min;

c. the gas of the protective atmosphere comprises at least one of helium, neon, argon, krypton and xenon;

e. the method for removing the oxide of M and the nitride of M comprises acid washing, wherein the acid solution adopted by the acid washing comprises at least one of hydrochloric acid, nitric acid and sulfuric acid;

12. The preparation method of the composite anode material is characterized by comprising the following steps of:

13. The preparation method of the composite anode material is characterized by comprising the following steps of:

14. The production method according to claim 12 or 13, characterized by comprising at least one of the following features a to h:

c. the metal element in the metal oxide layer comprises at least one of Si, sn, ge, li, V, al, fe and Zn;

g. the nitridation treatment is carried out for 2 to 24 hours at the temperature of 400 to 950 ℃.

15. A lithium ion secondary battery comprising the composite anode material according to any one of claims 1 to 8 or the anode material produced by the method for producing the composite anode material according to any one of claims 9 to 14.