CN112234174B

CN112234174B - Lithium ion battery cathode material and preparation method thereof

Info

Publication number: CN112234174B
Application number: CN202011097928.8A
Authority: CN
Inventors: 徐泉; 刘柱; 李阁; 闫明妍; 程晓彦; 赵岸光
Original assignee: Jiangxi Yijin New Energy Technology Co ltd
Current assignee: Jiangxi Yijin New Energy Technology Co ltd
Priority date: 2020-10-14
Filing date: 2020-10-14
Publication date: 2022-02-22
Anticipated expiration: 2040-10-14
Also published as: CN112234174A

Abstract

The invention relates to a lithium ion battery cathode material and a preparation method thereof. The lithium ion battery cathode material has a three-layer core-shell structure and consists of an inner core material, a silicon oxide intermediate layer and a carbon-coated outer layer. The surface of the core material is pretreated by non-oxidizing atmosphere, and a specific temperature gradient is formed by heating and the silicon oxide steam, so that the nano silicon oxide layer is deposited on the surface. By adjusting the thickness of the element-doped carbon coating layer and the thickness of the silicon monoxide deposition layer, the lithium ion battery cathode material with high electronic conductance, low volume expansion, excellent cycle performance and rate capability is obtained. The preparation method comprises the following steps: 1) putting a material capable of generating the silicon monoxide steam into a reaction bin, putting a core material into a rotary collecting bin, vacuumizing and heating; 2) depositing the silica on the surface of the core material in a gas phase manner; 3) and after cooling, carrying out carbon coating on the materials in the collecting bin.

Description

Lithium ion battery cathode material and preparation method thereof

Technical Field

The invention belongs to the technical field of batteries, and particularly relates to a lithium ion battery cathode material, a preparation method and a preparation method thereof.

Background

In recent years, with the excessive exploitation and utilization of non-renewable energy, the problems of energy shortage and environmental pollution become more serious. The application of the lithium ion battery technology with the characteristics of high energy density, long cycle life and environmental friendliness is an effective method for relieving energy and environmental problems.

Lithium ion batteries have been widely used in power batteries, portable devices, and large-scale energy storage fields. Most of commercial lithium batteries adopt a graphite system as a negative electrode, and the development of the lithium battery towards a high specific energy direction is limited due to the lower theoretical lithium storage capacity of the graphite negative electrode. With the current mature graphite-like carbon negative electrode material, the lithium intercalation capability is basically fully exerted, and the aim is difficult to achieve. In recent years, researchers have conducted a great deal of exploratory work around lithium ion battery cathode materials, and research shows that many novel cathode materials have large theoretical capacity and huge volume expansion, such as silicon-based cathodes, germanium-based cathodes and tin-based cathodes. The severe volume expansion of high capacity negative electrode materials presents new problems for batteries compared to the volume expansion rate of less than 10% of conventional graphite.

With the progress of research, researchers have found that a silicon oxide negative electrode material in a high capacity negative electrode can buffer volume expansion and easily realize excellent cycle stability due to the generation of lithium oxide and lithium silicate protective layers during charge and discharge. At present, carbon-coated silicon monoxide materials produced intermittently are usually mixed with other negative electrode materials to improve the energy density of the lithium ion battery, however, the particles are very easy to be pulverized and broken in the process of lithium intercalation and deintercalation of the silicon monoxide due to the large particle size of the common mechanical mixing mode, the battery capacity is rapidly attenuated, and the advantage of compounding the negative electrode materials and the silicon monoxide materials cannot be effectively exerted.

The invention uniformly coats the silicon monoxide on the surface of the inner core material by a vapor deposition mode to form a nano-scale coating layer, thereby effectively overcoming the defects of poor conductivity and large volume change inherent in the silicon monoxide and simultaneously improving the reversible capacity of the cathode material. The even cladding of carbon-layer forms stable nucleocapsid structure at the surface, can effectively improve negative electrode material's electron conductivity on the one hand, and on the other hand can effectually alleviate the volume expansion of material, promotes the circulation stability of material. The negative electrode material and the silicon monoxide material are compounded in the same production equipment, the preparation method is simple and effective, the industrial large-scale production is facilitated, and the preparation method has wide application prospect.

Disclosure of Invention

The invention provides a negative electrode material with a core-shell structure, which is coated by a silicon monoxide and a carbon coating layer. Combining core material (metal and its metal oxide, nonmetal) with SiO_xThe advantages of the cathode material improve the energy density and the cycle life of the cathode material of the current lithium ion battery.

In order to achieve the purpose, the invention adopts the following technical scheme:

the invention provides a lithium ion battery cathode material which is characterized by having a core-shell structure and comprising a core material, a middle layer and an outer shell layer from inside to outside; wherein the middle layer is silicon oxide, the carbon coating layer is an outer shell layer, and the core material is metal or metal oxide thereof or nonmetal.

In the preferred technical scheme of the invention:

the non-metals include, but are not limited to, soft carbon, hard carbon, crystalline graphite, cryptocrystalline graphite, synthetic graphite, conductive graphite, single crystal silicon, polycrystalline silicon, amorphous silicon, or metallic silicon. Preferably crystalline flake graphite; the average particle size of the non-metallic material is 2-50 μm, preferably 5-15 μm. The carbon has a particle size of 2 to 20 μm, preferably 5 to 15 μm.

The metal and its metal oxide is selected from one of titanium, iron, manganese, germanium, tin and its oxide. Preferably, the metal and its metal oxide are germanium, tin and its oxides.

The silicon monoxide can be expressed as SiO_x，0<x<2, the x values are average values. Preferably 0.8. ltoreq. x.ltoreq.1.6.

The mass of the negative electrode material is 100%, wherein the mass percent of the core material is 50-95%, the mass percent of the silica is 3-50%, and the mass percent of the carbon coating layer is 1-15%. Preferably, the mass percent of the core material is 75-90%, the mass percent of the silica is 5-20%, and the mass percent of the carbon coating layer is 3-8%.

Preferably, the negative electrode material of the present invention has a median particle diameter of 1 to 25 μm, preferably a median particle diameter of 4 to 16 μm.

The principle of the invention is that the silicon monoxide is coated on the surface of the pretreated core material in a vapor deposition mode, and the cathode material is obtained after the outer surface is coated with carbon. The advantages of the silica cathode material and the core material are combined to prepare the lithium ion battery cathode material with good cycle stability, excellent conductivity, low expansibility and high energy density.

The shell carbon coating layer has a flexible buffer effect, relieves the volume expansion of the silicon monoxide layer through a sliding effect, and improves the electronic conductance of the material. Through adjusting carbon coating and nitrogenize the suboxide layer cladding thickness, produced multilayer cladding synergism unexpectedly, the shell is dredged, and the intermediate level restriction has restricted the volume expansion of material when guaranteeing that the whole material has good electric conductivity, has increased substantially the cycle stability of material, promotes battery life.

The invention also provides a preparation method of the lithium ion battery cathode material, which comprises the following steps:

adding the powder of the sub-silicon oxide or the powder of the silicon powder and the silicon dioxide which are uniformly mixed according to a certain mass ratio into a vacuum reaction bin, and adding the core material into a rotary collecting bin;

heating the materials in the vacuum reaction bin, simultaneously carrying out heat preservation on the heating rotary collection bin, so that the materials in the reaction bin enter the rotary collection bin in a steam form and are deposited on the surface of the inner core material;

3) and after cooling, carrying out carbon coating on the materials in the rotary collecting bin.

The core material is at least one of nonmetal, metal and metal oxide.

Preferably, in the step 1), the core material is pretreated in a rotary collecting bin, wherein the pretreatment means that the core material is pretreated in Ar: H₂According to the volume ratio (70-80): (20-30) is pre-activated at the temperature of 100-300 ℃, and the gas is fully treated on the core material in the rotary bin through high-temperature and rotary rotation, so that the surface activity of the core material is favorably adjusted, and the stability and uniformity of the deposition of the silicon monoxide on the surface of the core material are improved.

Preferably, the raw material in the step 1) is nano-scale, namely nano-silica, or a mixture of nano-silica powder and nano-silica according to a mass ratio of 1: 1.8-3.

The mass ratio of the nano-silica or the mixture of the nano-silica powder and the nano-silica to the core material in the vacuum reaction bin in the step 1) is 0.06-0.5: 1.

More preferably, the mass ratio of the nano-sized silica to the core material is 0.08-0.2:1, and if the mass ratio is more than 0.2:1, the formed silica layer is too thick, so that the electronic conductivity of the whole material is reduced, the expansion effect of the silica is obvious, and the cycling stability and the first library efficiency of the material are reduced. If the mass ratio is less than 0.08:1, the produced silicon protoxide layer is too thin to form effective coating, cannot generate synergistic effect with a carbon coating layer to limit volume expansion, and simultaneously has low material capacity and no high specific capacity advantage.

Specifically, the amorphous silica coating layer formed in a vacuum high-temperature state by adjusting the ratio of the raw material to the core material has a system in which reduced-state silicon, oxidized-state silicon and transition-state silicon are simultaneously present. The amorphous silicon monoxide structure is beneficial to the diffusion of lithium ions, has no obvious volume expansion in the charging and discharging process, is beneficial to forming a synergistic effect with the carbon coating layer to relieve the overall volume expansion of the material, and improves the cycling stability of the material.

The temperature of the rotary collecting bin and the vacuum reaction bin in the step 2) have temperature gradient. Namely, the temperature of the vacuum reaction chamber is 500-850 ℃ higher than that of the rotary collection chamber. Specifically, the temperature of the rotary collection bin is 800 ℃ in 600-.

Particularly, in a high-temperature high-vacuum environment, the temperature gradient of 500-850 ℃ is formed between the reaction bin and the rotary collection bin, so that the high-temperature silicon oxide steam can rapidly enter the rotary collection bin with a low temperature, and the silicon oxide steam can enter and disperse in the rotary collection bin to form a uniform coating layer. The coating layer of the silicon oxide is more uniform, the dispersibility is good, the thickness of the silicon oxide layer is proper, the energy density of the battery is ensured, and the expansion is effectively relieved.

The vacuum reaction bin and the rotary collecting bin are respectively arranged, so that the temperature can be respectively controlled, the temperature gradient can be accurately controlled, and the vapor deposition process is facilitated. Different from static sintering, the invention adopts dynamic uniform coating, and the materials are in a rotary cabin with a rotary function, so that the deposition process is carried out under the rotary dynamic state, and the coating layer is more uniform and stable. In addition, the invention has the advantages that the production of the raw materials to the finished product is realized, the whole process is carried out in a closed device, the introduction of impurities into the exposed air is reduced, the purity of the cathode coating material is improved, the continuous non-intermittent operation can be realized, the time required by temperature rise and temperature drop in the same operation chamber is reduced, the process is greatly simplified, the energy consumption is reduced, and the industrial large-scale production is facilitated.

Preferably, the suitable thickness of the layer of silicon oxide is 150-300nm, more preferably 80-220 nm.

If the thickness of the silicon oxide layer is larger than 300nm, the generated silicon oxide layer is too thick, the electronic conductivity of the whole material is reduced, the expansion effect of the silicon oxide is obvious, and the cycling stability and the efficiency of the material are reduced. If the thickness of the silicon oxide layer is less than 150nm, the produced silicon oxide layer is too thin to form an effective coating, cannot generate a synergistic effect with a carbon coating layer to limit volume expansion, and simultaneously has low material capacity and no high specific capacity advantage.

More preferably, after the step 2) of depositing the silicon monoxide, the material of the rotary collecting bin is modified before the step 3) of carbon coating.

The modification treatment is nitriding treatment or boronizing treatment. Specifically, the modification treatment is carried out on the deposition material obtained in the step 2) at the temperature of 100-600 ℃. The modification treatment is to modify the surface of the deposition material by one or two atoms of nitrogen and boron.

The nitrogen source is one or more of ammonia gas, melamine, urea, polyacrylonitrile and amino acid, and the boron source is one or more of boric acid and borane.

Preferably, the modification treatment is ammonia treatment at the temperature of 200-600 ℃, ammonia is introduced, the flow rate is controlled to be 10-20L/min, and the treatment is kept for 30-90 min.

More preferably, the ammonia gas treatment process is carried out at 250-400 ℃ and the treatment time is 40-60 min.

The ammonia gas treatment can form a small amount of silicon nitrogen compounds on the surface of a silicon oxide deposition layer in a high-temperature process to form a high-conductivity surface, the small amount of nitrogen also occupies space, the intercalation space provided for subsequent carbon coating is matched with the dynamic feeding process of a rotary bin by utilizing the anchoring effect, the matching embedding of a carbon material and the silicon oxide is facilitated, and the expansion of a battery material is effectively inhibited.

Optionally, the modification treatment is boronization treatment, and boric acid is introduced for treatment for 30-60min at 200-500 ℃ under the condition of carrier gas.

Wherein the carrier gas can be nitrogen or argon, and the gas flow rate is 10-20L/min. Boron not only forms a high-conductivity surface on a silicon oxide deposition layer, improves the vacancy current-carrying capacity by utilizing the advantage of atomic radius, but also greatly improves the stability of the electrochemical structure of the carbon layer, is beneficial to the matching coating of the carbon material and the silicon oxide by utilizing the dynamic feeding and coating processes of the rotary bin, and effectively inhibits the expansion of the battery material.

The carbon coating layer in the step 3) can be one or more of an amorphous carbon coating layer, a graphene coating layer or a carbon nanotube coating layer.

Preferably, the carbon coating layer is a graphene coating layer, the coating thickness is 10-35nm, and more preferably, the coating thickness of the graphene coating layer is 20-30 nm. A mode of vertically growing graphene on the surface is adopted, a conductive network is formed on the surface of the silicon oxide, the lithium ion migration rate is favorably improved, and a small amount of nitrogen and boron elements in the silicon oxide can further provide effective embedding points to form a high-conductivity surface coating.

Specifically, the thickness of the carbon coating layer is adjusted by regulating and controlling the carbon source ratio. And combining the obtained silicon oxide coating layer by temperature gradient deposition to obtain the material with a double-coated three-layer structure. The flexible carbon coating layer and the rigid silicon oxide coating layer have a synergistic effect in a certain proportion, so that the cycling stability of the battery can be greatly improved.

Specifically, the carbon coating layer may be formed by a vapor deposition method, a solid phase coating method, or a liquid phase coating method; the solid phase coating agent is one or more of coal tar pitch, petroleum pitch, needle coke or petroleum coke, and the temperature of the solid phase coating is 400-800 ℃, preferably 500-750 ℃; the solid phase coating time is 1-5h, preferably 2-3 h; the gas source of the chemical vapor deposition method is one or the combination of two of acetylene, methane, propane, butane, benzene and toluene; the temperature of the chemical vapor deposition coating is 600-1000 ℃, and preferably 600-950 ℃; the coating time of the chemical vapor deposition method is 1-8h, and preferably 2-4 h.

Compared with the prior art, the composite graphite cathode of the lithium ion battery provided by the invention has the following advantages:

the invention generates silicon monoxide (SiO) by vacuum high temperature_x) The steam forms a deposition layer on the surface of the inner core material, and the carbon layer uniformly coats the outermost layer. The lithium ion battery cathode material with good cycle performance, low expansion and high energy density is obtained. The problems of structural damage caused by mechanical mixing of the conventional cathode material (metal or metal oxide or nonmetal thereof) and the silicon-oxygen cathode material, low coulombic efficiency caused by uneven mixing and poor cycle performance are solved.

(2) The lithium ion battery cathode material prepared by the invention has the following structure from outside to inside: the carbon coating layer, the silicon monoxide and the core material form the cathode material with a core-shell structure. The carbon layer is uniformly coated on the surface of the whole particle, so that the conductivity of the material is improved, and the expansion of the material is effectively relieved.

(3) The lithium ion battery cathode material prepared by the invention has a simple and efficient preparation method. The raw materials are fed into the vacuum furnace equipment to produce finished products. The method effectively reduces the material loss in the process of compounding the silicon-based negative electrode material and the negative electrode material (metal and metal oxide thereof, and non-metal oxide) in the prior art, simplifies the process, realizes continuous production, reduces the introduction of impurities exposed in the air, is environment-friendly, saves energy, and is beneficial to industrial large-scale preparation.

(4) According to the invention, by controlling the adding proportion and the adding amount of the raw materials, the size and the layer thickness of three layers of the core-shell structure can be effectively controlled, the uniformity and the effectiveness of the coating structure are adjusted, and the conductivity of the cathode material is improved. The preparation of the silica layer through the pretreatment of the core material and the vacuum high temperature is more favorable for forming a uniform amorphous silica layer and is favorable for the transition of lithium ions.

(5) In a high-temperature high-vacuum environment, the reaction bin and the rotary collecting bin form a temperature gradient of more than 500 ℃, so that the silicon monoxide vapor can enter and disperse in the rotary collecting bin more conveniently, and the silicon monoxide coating layer is more uniform and has good dispersibility.

(6) The invention adopts dynamic uniform coating, the materials are in a rotary cabin with a rotary function, so that the deposition process is carried out under the rotary dynamic state, and the coating layer is more uniform and stable. The continuous bin heating is beneficial to reducing air exposure, and the intermittent process has higher working efficiency than the prior intermittent process.

(7) Modification treatment is adopted between the silicon oxide coating and the carbon coating, and particularly, the vacancy current-carrying capacity is improved and the electronic conductivity is improved under the occupying anchoring action of nitrogen and boron during nitridation and boronization treatment. Meanwhile, the coating of the carbon material on the silicon oxide is facilitated to make up the defects, the expansion of the battery material is effectively inhibited, and the cycling stability of the battery is improved.

Drawings

Fig. 1 is a schematic diagram of a negative electrode material of a lithium ion battery according to the present invention.

Fig. 2 is an X-ray diffraction spectrum of the negative electrode material of the lithium ion battery prepared in example 1 of the present invention.

Fig. 3 is a charge-discharge curve of the negative electrode material of the lithium ion battery prepared in example 1 of the present invention.

Fig. 4 is a cycle performance diagram of a negative electrode material of a lithium ion battery prepared in example 1 of the present invention.

Detailed Description

The present invention will be further described with reference to the following examples, but the present invention is not limited to the following examples.

The experimental methods described in the following examples are all conventional methods unless otherwise specified; the reagents and materials are commercially available, unless otherwise specified.

Example 1

According to the mass ratio of the silicon monoxide to the crystalline flake graphite of 0.1:1, 1kg of the silicon monoxide and 10kg of the crystalline flake graphite are respectively added into a vacuum reaction bin and a rotary collecting bin. Ar is H at 200 DEG C₂The volume ratio is 7: 3, pretreating the flake graphite at 200 ℃.

And (2) heating to 1360 ℃ under the condition of vacuum degree of 60pa, preserving heat for 5h, and sublimating the silicon monoxide powder under the conditions of high temperature and vacuum. At the same time, the collection chamber was heated to 800 ℃ and held warm. And the silicon oxide vapor enters a rotary collecting bin and is deposited on the surface of the scale graphite.

In the rotary cabin, ammonia gas is introduced for 50min at a rate of 10L/min and at a temperature of 300 ℃.

After cooling, introducing nitrogen with the flow of 20L/min into the rotary collecting bin, and heating to 975 ℃; and then acetylene with the flow rate of 20L/min is introduced to crack the materials at high temperature, and the materials in the rotary collecting bin are coated with pyrolytic carbon for 1.5 h.

The lithium ion battery cathode material with the core material of crystalline flake graphite is obtained. The thickness of the carbon coating layer is 20nm, and the thickness of the silicon oxide coating layer is 220 nm.

Example 2

The lithium ion battery negative electrode material of the invention is prepared according to the same method as the embodiment 1, except that: respectively adding 2kg of silicon monoxide and 10kg of crystalline flake graphite according to the mass ratio of 0.2:1 of the silicon monoxide and the pretreated flake graphite in the step (1). The thickness of the carbon coating layer is 20nm, and the thickness of the silicon oxide coating layer is 300 nm.

Example 3

The lithium ion battery negative electrode material of the invention is prepared according to the same method as the embodiment 1, except that: and (4) cooling according to the step (3), introducing nitrogen with the flow rate of 20L/min into the rotary collecting bin, and heating to 975 ℃. And introducing acetylene with the flow of 10L/min to crack the acetylene at high temperature, and carrying out pyrolytic carbon coating on the material in the rotary collecting bin for 1.5 h. The thickness of the carbon coating layer is 10nm, and the thickness of the silicon oxide coating layer is 200 nm.

Example 4

The lithium ion battery negative electrode material of the invention is prepared according to the same method as the embodiment 1, except that: cooling and cooling in the step (3), introducing nitrogen with the flow of 20L/min into the rotary collecting bin, and heating to 975 ℃. And introducing acetylene with the flow of 30L/min to crack the materials at high temperature, and carrying out pyrolytic carbon coating on the materials in the rotary collecting bin for 1.5 h. The thickness of the carbon coating layer is 30nm, and the thickness of the silicon oxide coating layer is 200 nm.

Example 5

The lithium ion battery negative electrode material of the invention is prepared according to the same method as the embodiment 1, except that: respectively taking the mixed powder of the nano silicon powder and the nano silicon dioxide according to the mass ratio of 1:2 of the nano silicon powder to the nano silicon dioxide in the step (1), and controlling the ratio of the silicon monoxide: the mass ratio of the core material is still 0.1: 1. Ar is H at 200 DEG C₂7: 3, pretreating the flake graphite. The thickness of the carbon coating layer is 20nm, and the thickness of the silicon oxide coating layer is 200 nm.

Example 6

The lithium ion battery negative electrode material of the invention is prepared according to the same method as the embodiment 1, except that: and (2) heating to 1360 ℃ under the condition of vacuum degree of 60pa, preserving heat for 5h, and sublimating the silicon monoxide powder under the conditions of high temperature and vacuum. The silicon oxide vapor enters a rotary collecting bin at the pretreatment temperature (200 ℃) and is deposited on the surface of the scale graphite. The thickness of the carbon coating layer is 20nm, and the thickness of the silicon oxide coating layer is 50 nm.

Example 7

The lithium ion battery negative electrode material of the invention is prepared according to the same method as the embodiment 1, except that: according to the step (1), 1kg of silicon monoxide and 10kg of crystalline flake graphite are respectively added into a vacuum reaction bin and a rotary collecting bin according to the mass ratio of 0.1:1, so that the pretreatment process of an inner core is omitted, and the deposition of the silicon monoxide is directly carried out. The thickness of the carbon coating layer is 20nm, and the thickness of the silicon oxide coating layer is 200 nm.

Example 8

The lithium ion battery negative electrode material of the invention is prepared according to the same method as the embodiment 5, except that: and (4) introducing methane with the flow rate of 20L/min and hydrogen with the flow rate of 1L/min into the step (3) to crack the methane and the hydrogen at high temperature, and coating the materials in the rotary collection bin with vertically grown graphene. The other steps are the same as the example 1, and the lithium ion battery cathode material is prepared. The thickness of the graphene coating layer is 20nm, and the thickness of the silicon oxide coating layer is 200 nm.

Example 9

The lithium ion battery negative electrode material of the invention is prepared according to the same method as the embodiment 1, except that: and (3) after the silicon monoxide is deposited on the surface of the scale graphite in the step (2), immediately performing carbon coating in the step (3), and omitting the nitriding treatment process. The thickness of the carbon coating layer is 20nm, and the thickness of the silicon oxide coating layer is 230 nm.

Example 10

The lithium ion battery negative electrode material of the invention is prepared according to the same method as the embodiment 1, except that: according to the step (1), 4kg of silicon monoxide and 10kg of crystalline flake graphite are respectively added into a vacuum reaction bin and a rotary collecting bin according to the mass ratio of 0.4:1, the thickness of a carbon coating layer is 20nm, and the thickness of the silicon monoxide coating layer is 380 nm.

Example 11

The lithium ion battery negative electrode material of the invention is prepared according to the same method as the embodiment 1, except that: changing the nitriding treatment into the boronizing treatment: in a rotary cabin, nitrogen is used as a carrier, the flow rate is 10L/min, the temperature is maintained at 400 ℃, and boric acid is introduced for 40 min.

Example 12

The lithium ion battery negative electrode material of the invention is prepared according to the same method as the embodiment 1, except that: and (3) replacing the flake graphite in the step (1) with silicon.

Example 13

The lithium ion battery negative electrode material of the invention is prepared according to the same method as the embodiment 1, except that: and (3) replacing the flake graphite in the step (1) with tin dioxide.

Example 14

The lithium ion battery negative electrode material of the invention is prepared according to the same method as the embodiment 1, except that: and (3) replacing the flake graphite in the step (1) with germanium oxide.

Comparative example 1

And mixing the silicon oxide particles with the carbon coating layer thickness of 20nm according to the mass ratio of 0.1: and 1, mechanically mixing with the flake graphite to obtain the mechanically mixed negative electrode material.

Application example

The electrochemical performance of the lithium ion battery negative electrode materials prepared in the above examples and comparative examples was tested according to the following method: mixing the prepared lithium ion battery negative electrode material, carbon black, carboxymethyl cellulose (CMC) and Styrene Butadiene Rubber (SBR) composite binder in a mass ratio of 80:10:10 to prepare slurry (wherein the mass ratio of the CMC to the SBR is 1:1), uniformly coating the slurry on a copper foil current collector, and performing vacuum drying for 12 hours to prepare a working electrode; with lithium foil as counter electrode and a glass fiber membrane (from Whatman, UK) as separator, 1mol L^-1LiPF6 (the solvent is a mixed solution of ethylene carbonate and dimethyl carbonate with the volume ratio of 1:1) is used as an electrolyte, VC with the volume fraction of 1% and FEC with the volume fraction of 5% are added into the electrolyte, and the button cell is assembled in a German Braun inert gas glove box in an argon atmosphere.

And (3) carrying out charge and discharge tests on the assembled battery on a LAND charge and discharge tester.

Electrochemical analysis and test are carried out on the lithium ion battery negative electrode material prepared in the example 1, the charging and discharging interval is 0-2V, and the compaction density is 1.51g cm^-3At a current density of 0.2C (mA g)^-1) The capacity of the material can reach 504.8mA h g by charging and discharging^-1The first-turn coulombic efficiency is 90.2%, and the capacity retention rate is 98.1% after 100 cycles, which proves that the cathode material obtained by the invention has higher capacity and excellent cycle performance.

TABLE 1 electrochemical Performance test results for lithium ion Battery cathode materials

As can be seen from the data in Table 1, the invention controls the addition proportion and the dosage of the raw materials and combines the process conditions of specific dynamic coating to control the coating of the silicon monoxide on the surface of the core material in a vapor deposition mode to form a more uniform and stable silicon monoxide coating, the embedding matching degree of the two coatings is improved through modification treatment, and finally the size and the layer thickness of the three layers of the core-shell structure are effectively controlled through coating the carbon layer on the surface, so that the uniformity and the effectiveness of the coating structure are adjusted, and the battery capacity and the cycle stability are balanced. The lithium battery cathode material prepared by the method has excellent comprehensive performance, the first reversible specific capacity of more than 500mAh/g, the retention rate of more than 97 percent after 100 circles, high energy density and excellent cycle performance. And silica: the mass ratio of the core material and the thickness of each layer of the core-shell material have certain influence on the electrode material, if the content of silicon oxide is too much, although the first specific capacity is increased, the first storage and the cycling stability are obviously reduced, and the electrical efficiency is poorer.

The applicant states that the present invention is illustrated by the above examples to show the detailed process equipment and process flow of the present invention, but the present invention is not limited to the above detailed process equipment and process flow, i.e. it does not mean that the present invention must rely on the above detailed process equipment and process flow to be implemented. It should be understood by those skilled in the art that any modification of the present invention, equivalent substitutions of the raw materials of the product of the present invention, addition of auxiliary components, selection of specific modes, etc., are within the scope and disclosure of the present invention.

Claims

1. A preparation method of a lithium ion battery negative electrode material is provided with a three-layer core-shell structure, wherein an inner core is one of nonmetal, metal and metal oxide, a middle layer is a silicon oxide deposition layer, a carbon coating layer is an outer shell layer, and the preparation method of the lithium ion battery negative electrode material comprises the following steps:

1) adding silicon monoxide powder or powder obtained by uniformly mixing silicon and silicon dioxide in a certain mass ratio into a vacuum reaction bin, and adding a pretreated core material into a rotary collecting bin, wherein the pretreatment refers to that the core material is in Ar: H₂According to the volume ratio (70-80):(20-30) in a proportion of pre-activation at 100-300 ℃;

2) heating the materials in the vacuum reaction bin, and simultaneously preserving the heat of the rotary collection bin to ensure that the silicon monoxide enters the rotary collection bin in a steam form and is deposited on the surface of the inner core material;

3) after cooling, carrying out carbon coating on the materials in the rotary collecting bin;

the temperature of the vacuum reaction bin is 500-850 ℃ higher than that of the rotary collection bin;

and after the step 2) of the deposition of the silicon monoxide, before the step 3) of the carbon coating, modifying the material of the rotary collecting bin, wherein the modification is to perform ammonia gas treatment at the temperature of 200-600 ℃, introducing ammonia gas, controlling the flow rate to be 10-20L/min, and keeping the treatment for 30-90 min.

2. The method of claim 1, wherein the ratio of the silica powder, or silicon and silicon dioxide, to the core material in step 1) is 0.06-0.5:1 by mass.

3. The method of claim 2, wherein the ratio of the silica powder, or silicon and silicon dioxide, to the core material in step 1) is 0.08 to 0.2:1 by mass.

4. The method according to claim 1, wherein the vacuum reaction chamber is heated in step 2) with a vacuum degree of 0.01 to 500 Pa; the temperature of the vacuum reaction chamber is 1000-1600 ℃, and the heat preservation time is 3-30 h.

5. The method as claimed in claim 4, wherein the temperature of the vacuum reaction chamber in step 2) is 1300-1400 ℃, and the holding time is 10-25 h.

6. The method as set forth in claim 5, wherein the temperature of the rotary collecting bin in the step 2) is 500-1000 ℃.

7. The method as set forth in claim 6, wherein the temperature of the rotary collecting bin in the step 2) is 600-800 ℃.

8. The method according to claim 1, wherein the mass percent of the inner core is 75-90%, the mass percent of the silicon oxide deposition layer is 5-20%, and the mass percent of the carbon coating layer is 3-8%, based on 100% of the mass of the negative electrode material.