WO2019080346A1

WO2019080346A1 - Space buffer lithium-doped silicon oxide composite material and preparation method therefor, and lithium-ion battery

Info

Publication number: WO2019080346A1
Application number: PCT/CN2017/118636
Authority: WO
Inventors: 潘芳芳; 单旭意; 肖亚洲; 万爽; 刘俊涛
Original assignee: 中航锂电（洛阳）有限公司
Priority date: 2017-10-23
Filing date: 2017-12-26
Publication date: 2019-05-02
Also published as: CN108232145A; CN108232145B

Abstract

A space buffer lithium-doped silicon oxide composite material and a preparation method therefor, and a lithium-ion battery, relating to the technical field of lithium-ion batteries. The material is a core-shell structure. The core is a lithium-predoped silicon oxide composite material, and the shell is a coating carbon layer. The lithium doping is implemented by converting silicon oxide in the silicon oxide composite material into lithium silicate by means of solid phase reaction during the preparation process. The method for preparing a space buffer lithium-doped silicon oxide composite material comprises: after silicon oxide particle surfaces are coated with a lithium source, a coating carbon layer is formed on the obtained particle surfaces by means of chemical vapor carbon deposition; the obtained coated material is sintered in vacuum or inert atmosphere; the lithium source with which the surfaces are coated reacts with silicon oxide. On one hand, the lithium doping of the silicon oxide material is implemented; on the other hand, the formation of a cavity structure is implemented. The space buffer lithium-doped silicon oxide composite material has the characteristics of high specific capacity, high first-time charging and discharging efficiency, and long service life.

Description

Space buffer, lithium doped silicon oxide composite material and preparation method thereof, lithium ion battery

Technical field

The invention relates to a space buffering, lithium doped silicon oxide composite material, a preparation method thereof and a lithium ion battery, and belongs to the technical field of lithium ion batteries.

Background technique

With the increasing use of lithium-ion batteries in different fields, people have put forward higher requirements for the performance of lithium-ion batteries. In particular, many application fields have higher and higher requirements on the energy density of lithium-ion batteries. Whether it is 3C products or electric vehicles, people expect the energy density of batteries to reach a new order of magnitude, making the product's battery life or The cruising range is no longer a major factor plaguing the product. However, the current energy density of lithium-ion batteries has become more and more difficult, and energy density has become the biggest bottleneck restricting the development of current lithium-ion batteries.

At present, the actual capacity of graphite anodes is close to the theoretical limit, and it is difficult to further increase the material and process optimization. Compared with graphite (372mAh/g), oxy-silica materials with ultra-high theoretical specific capacity have become the most promising alternative for lithium-ion battery carbon-based anodes. However, oxysilylene materials currently face two problems: first, high volume expansion during lithiation, up to 200%; high volume expansion will inevitably lead to material failure, interface degradation and cycle performance degradation. Secondly, oxysilicon oxide has a low initial charge and discharge efficiency (<70%) due to the formation of by-products such as Li ₂ O and Li ₄ SiO ₄ during the first charging process. In the lithium-ion battery system, the first charge and discharge efficiency is mainly determined by the first efficiency of the negative electrode. The first low efficiency of the negative electrode consumes a large amount of active lithium ions during the first charging process, which greatly reduces the battery capacity and energy density.

There have been reports in the prior art that lithium is pre-embedded by a negative electrode to improve first efficiency. LG Company proposed a method to control the lithium-replenishing speed and lithium-replenishing amount by controlling the external short-circuit resistance and short-circuit time, and designed an industrialized electrode lithium-replenishing process to realize continuous production of lithium-filled negative electrode pieces. Specifically, the process is to place a battery composed of a positive electrode, a negative electrode and a separator in an electrolyte reaction cell, and to charge and discharge the negative electrode through a lithium metal electrode to realize pre-intercalation of lithium. JM Energy introduced a lithium electrode in the assembly process of the battery core and welded the tab of the lithium electrode to the negative electrode tab. After the electrolyte was injected, the lithium electrode was short-circuited to the negative electrode to realize lithium replacement.

The Chinese invention patent with the publication No. CN104993098A discloses the application of metallic lithium powder in lithium supplementation of a negative electrode material, which achieves a pre-lithiation process of the negative electrode by uniformly coating lithium powder particles on the surface of the negative electrode tab. However, due to the high activity of lithium metal itself, the above pre-lithiation methods need to be carried out in a dry and oxygen-free environment, which is difficult to operate, and the degree and precision of pre-lithiation are difficult to precisely control.

The Chinese invention patent publication No. CN101047234A discloses a method of solid-phase sintering a silicon oxide powder with a lithium source to achieve pre-expansion and pre-lithiation of the silicon oxide material. The method solves the defects of high expansion and low initial effect of silicon oxide from the material scale, but the lack of internal buffer structure makes the material still face the problem of unstable interface and poor cycle in the process of volume expansion and contraction.

Summary of the invention

It is an object of the present invention to provide a long-life, high-efficiency spatial buffer, lithium-doped silicon oxide composite.

It is still another object of the present invention to provide a method for preparing the above-described space buffered, lithium doped silicon oxide composite material.

It is also an object of the present invention to provide a lithium ion battery using the above spatially buffered, lithium doped silicon oxide composite.

To achieve the above object, the technical solution of the space buffering, lithium doped silicon oxide composite material of the present invention is:

a space buffered, lithium doped silicon oxide composite material, the space buffered, lithium doped silicon oxide composite material is a core-shell structure, and the core is a pre-doped lithium silicon oxide composite material, The shell is a carbon coating.

In the present invention, the pre-doped lithium silicon-oxygen composite material is formed by sintering a lithium source and a silicon oxide at a high temperature (800-1300 ° C), and anion conversion or partial conversion into a gas escape in the lithium source during sintering. Finally, a certain space buffer structure is formed between the core shells, and the space buffer structure is used for buffering the volume change of the silicon oxide material during charge and discharge, and avoiding the volume expansion of the silicon oxide material during the charge and discharge cycle, resulting in a decrease in battery performance. Therefore, in the present invention, the composite material has a space buffer structure between the core and the shell. The pre-doped lithium silicon oxide composite material is formed by sintering a lithium source and a silicon oxide at 800-1300 ° C.

Specifically, the pre-doped lithium silicon oxide composite material comprises a composite formed of lithium silicate, silicon oxide and silicon, and the silicon oxide is disproportionated during high temperature treatment to form a composite structure in which nano silicon is dispersed and distributed in silicon oxide. Further, the outer lithium source reacts with a part of the silicon oxide to form lithium silicate, and finally a composite structure of lithium silicate, silicon oxide and silicon or a composite structure of lithium silicate and silicon is obtained. By lithium doping, the first efficiency of the silicon oxide material as the anode active material of the lithium ion battery can be greatly improved.

Specifically, the pre-doped lithium silicon oxide composite material comprises a mass ratio of lithium silicate, silicon oxide, and silicon of 6-85:0-59:15-35, preferably 10-85:0- 55:15-35, a further optimized solution, the mass ratio of lithium silicate, silicon oxide and silicon is 20-75:5-50:20-30.

The molar ratio of the lithium element to the silicon element in the pre-doped lithium silicon oxide composite material is 0.1 ≤ Li / Si ≤ 2.0, preferably 0.2 ≤ Li / Si ≤ 2.0. Silicon oxide can greatly improve the first efficiency of silicon oxide materials as active materials for lithium ion battery anodes by lithium doping. Preferably, 0.3 < Li / Si ≤ 1.5.

The mass ratio of the coated carbon layer to the pre-doped lithium silicon oxide composite material is 3-40:100. The mass ratio is preferably from 3 to 30:100. The thickness of the carbon coating layer should not be too large, so as not to affect the insertion and extraction of lithium ions in the silicon-based material, and the thickness of the coating layer should not be too small, ensuring the strength while avoiding the reaction of the bareness of the silicon-based material with the electrolyte. . The surface lithium salt of the silicon oxide material acts on the high temperature and the silicon oxide to realize the pre-doped lithium, and the occupied space will be released to form a void as a buffer structure of the silicon oxide as the anode material of the lithium ion battery, that is, the core. The space buffer structure between the shell and the shell is a gap between the core and the shell. The volume ratio of the space buffer structure, that is, the space occupied by the voids to the overall particle (core) of the pre-doped lithium silicon oxide composite material is 1% to 30%. The volume ratio is further preferably from 1% to 15%.

The technical solution of the method for preparing the space buffering, lithium-doped silicon oxide composite material of the invention is:

The method for preparing the space buffering, lithium-doped silicon oxide composite material comprises the following steps:

1) uniformly mixing the silicon oxide with the lithium source to obtain a premixed material;

2) forming a coating carbon layer on the surface of the premixed material particles obtained in step 1) by chemical vapor deposition, to obtain a coating material;

3) The coating material obtained in the step 2) is sintered at 800-1300 ° C for 2-6 h under vacuum or an inert atmosphere.

The oxide of silicon is SiO _x , wherein 0.5 _{≤ x ≤} 1.5. Preferably, the oxide of silicon is silicon oxide (i.e., silicon monoxide, SiO).

The space buffering, lithium-doped silicon oxide composite material of the present invention is prepared by coating a surface of a silicon oxide particle with a lithium source and forming a coating carbon layer on the surface of the obtained particle by chemical vapor deposition; The obtained cladding material is sintered under an inert atmosphere, and the surface layer coated lithium source reacts with the silicon oxide to realize lithium pre-doping while constructing a cavity structure inside the particles by the lithium source itself. The method of the invention realizes lithium doping of the silicon oxide material on the one hand, and effectively realizes the construction of the internal space buffer structure of the silicon oxide composite material on the other hand.

In order to facilitate the coating of the lithium source and the carbon material, a uniform particle silicon oxide material is used as a raw material. The silicon oxide material has a particle diameter of 0.1 to 5.0 μm. Preferably, the silicon oxide material has a particle diameter of 1.0 to 5.0 μm. The particle size distribution is advantageous for improving the electrochemical performance of the finally obtained composite material while effectively avoiding agglomeration between the composite particles.

In order to prevent the electrochemical properties of the finally obtained composite material from being affected by impurities, the purity of the silicon oxide as a raw material is as high as possible. Generally, the purity of the silicon oxide is 99.99% or more. The content of the magnetic substance in the oxide of silicon is 50.0 ppm or less, and the content of the metal foreign matter is 50.0 ppm or less.

The amount of lithium source added is calculated based on the first efficiency and the specific needs of the required space. At the same time, it forms a uniform coating on the surface of the oxide material particles of silicon. In general, the first efficiency is calculated by the molar ratio of the oxide of silicon to the lithium in the lithium source; and the reserved space is mainly regulated by the volume change before and after the reaction of the lithium source and the silicon oxide, wherein the ratio of carbon to hydrogen is higher. The higher the volume of the lithium source during the pre-doped lithium process, the higher the cavity ratio. Preferably, the molar ratio of the silicon oxide material to the surface layer coated lithium source material is 1:0.2-10; the mass ratio of the silicon oxide material to the surface layer coated lithium source material is 10-90:10-90, further It is preferably 10-70: 30-90.

According to the demand for constructing the space buffer structure, the type of the lithium source needs to be an inorganic or organic lithium compound having a high ratio of carbon to hydrogen, and preferably one or more of lithium hydroxide, lithium acetate, lithium oxalate, and lithium oxalate borate. In order to increase the efficiency of mixing and uniformity of mixing of the silicon oxide with the lithium source, the lithium source is an aqueous solution or an organic solution of one or more of lithium hydroxide, lithium acetate, lithium oxalate, and lithium oxalate. The solvent in the organic solution is one of ethanol, acetone, dimethyl carbonate, and dimethyl ether.

The silicon oxide particles are added to an aqueous solution or an organic solution of a lithium source, dispersed and mixed, and then dried to obtain oxide solid particles of silicon coated with a lithium source. The method of mixing the lithium source and the silicon oxide is one of mechanical mixing, liquid phase dispersion, and spray drying. The mechanical mixing device is a ball mill or a fusion machine. Further, the mixing method is preferably spray drying to increase the degree of mixing uniformity and uniform uniformity of the resulting material particles. After drying, the lithium source is wrapped around the surface of the silicon oxide material to form a cladding layer.

The carbon source used in the above chemical vapor deposition is one or more of a gas phase carbon source, a liquid phase carbon source, and a solid phase carbon source; the vapor phase carbon source is one of methane, ethane, ethylene, acetylene or The liquid phase carbon source is one or two of toluene and ethylbenzene; and the solid phase carbon source is one or two of rosin and asphalt. Preferably, the carbon source used for chemical vapor deposition is methane or ethylene.

The temperature of the chemical vapor deposition can be selected depending on the carbon source used. Generally, the temperature of the chemical vapor deposition is 500-700 °C. Chemical vapor deposition can deposit a carbon source on the surface of a pre-doped lithium silicon oxide composite substrate to form a carbon material coating. High temperature refers to the temperature at which carbon deposits on the surface of the substrate. The temperature may further preferably be 550 ° C, 600 ° C, 650 ° C or 700 ° C. In order to facilitate the uniform coating of the carbon layer on the surface of the material, while ensuring the self-supporting strength of the coated carbon layer.

The inert atmosphere mainly provides protection for the reaction. Generally, the inert atmosphere is one or more of Ar, He, and Ne. It is preferably an Ar gas.

In order to ensure that the sintered material has an optimized microstructure, the sintering temperature in the step 3) is preferably from 900 to 1200 °C. In this temperature range, the doping of lithium in the silicon oxide compound is more uniform and stable in the sintered material, and at the same time, it is advantageous to form a space buffer structure inside the material to buffer the expansion of the silicon material during charge and discharge. The temperature may further preferably be 900 ° C, 1000 ° C, 1100 ° C or 1200 ° C. The sintering time is further preferably 2-4 h.

The technical scheme of the lithium ion battery of the present invention is as follows:

A lithium ion battery includes a positive electrode and a negative electrode, wherein the negative electrode includes a negative electrode active material, and the negative electrode active material is the above-mentioned space buffered, lithium doped silicon oxide composite material.

The lithium ion battery includes a positive electrode, a negative electrode, a separator, and an electrolyte. The positive electrode active material used for the positive electrode is one of LCO, LMO, NCM, and NCA. The electrolyte in the electrolytic solution is one of LiPF ₆ and LiTFSI, and the solvent is one or a mixture of two or more of EC, EMC, DMC, PC, and FEC. The separator is one of polypropylene or polyethylene or a composite film of several of them. The cathode, the separator, and the electrolyte in the above lithium ion battery may also be other conventional materials for preparing a lithium ion battery.

The beneficial effects of the invention are:

1) The space buffered, lithium doped silicon oxide composite material of the present invention achieves an effective improvement of the first charge and discharge efficiency of the material by pre-doping lithium of the silicon oxide material.

2) Using chemical vapor deposition method, the carbon layer is uniformly coated in situ on the surface of the particles to increase the conductivity of the material while avoiding the direct contact reaction between the electrolyte and the silicon oxide, and improving the rate characteristics and cycle stability of the material.

3) Through the construction of the internal cavity buffer structure of the particles, many problems such as carbon layer damage, interface degradation and cycle performance degradation caused by volume expansion of the material during charging are effectively alleviated.

4) The space buffered, lithium doped silicon oxide composite material of the present invention has a high specific capacity (>550 mAh/g), high initial charge and discharge efficiency (>89%), and long life.

5) The preparation method of the space buffering and lithium doped silicon oxide composite material of the invention is simple in operation, easy to control, low in production cost, and suitable for industrial production.

DRAWINGS

1 is a schematic diagram of the reaction of the preparation of the space buffered, lithium doped silicon oxide composite of the present invention.

Detailed ways

Embodiments of the present invention will be further described below in conjunction with the accompanying drawings.

The reaction principle of the space buffer and lithium-doped silicon oxide composite material in the following embodiment is as shown in FIG. 1. First, a lithium source is coated on the surface of the silicon oxide 1 to form a uniform lithium source layer 2, and then The surface of the lithium source layer is coated with a high-strength carbon layer 3 by CVD. After high-temperature sintering, lithium ions in the lithium source enter the interior of the silicon oxide particles to achieve pre-doping, and the anions are converted into a large amount in the process. The gas is discharged to obtain a spatially buffered, lithium-doped silicon oxide composite material, wherein 4 is a silicon nanoparticle, 5 is a lithium silicate substrate, and 6 is a cavity structure model (void).

Example 1

The space buffering, lithium-doped silicon oxide composite material of the embodiment has a core-shell structure, the core is a silicon-oxygen composite material pre-doped with lithium, the shell is a coated carbon layer, and a space buffer structure exists between the core shells. The main component of the pre-doped lithium silicon oxide composite material is a mixture of lithium silicate, silicon oxide and silicon. By further characterization, the mass ratio of lithium silicate, silicon oxide and silicon is 6:57:28; the volume of voids in the pre-doped lithium silicon oxide composite is about 3%, and the molar ratio of lithium to silicon The ratio is 1:10. The mass ratio of the carbon coating layer to the pre-doped lithium silicon oxide composite material is 6:100.

The method for preparing the spatially buffered, lithium-doped silicon oxide composite material of the embodiment includes the following steps:

1) 300 g of 99.99% pure silicon oxide (SiO) particles are pulverized by air flow to an average particle size D50 = 1.0 μm, and then the pulverized silicon oxide material is added to a lithium hydroxide aqueous solution having a concentration of 1 mol/L. Ultrasonic dispersion for 8h; the mass ratio of the pulverized silicon oxide material to the lithium hydroxide in the lithium hydroxide aqueous solution is 90:10; the mixture obtained by ultrasonic dispersion is spray-dried, and the premixed material is collected;

2) 150g premixed material is placed in a chemical vapor deposition reactor with an effective volume of 10.0L, and methane is used as a carbon source for vapor phase carbon deposition reaction. The reaction temperature is 600 ° C, the reaction time is 3 h, and the flow rate of methane is 4.0 L. /min, after the reaction, a stable, self-supporting coated carbon layer structure is formed on the surface of the material particles;

3) Switching the methane gas stream into a high-purity argon gas stream as a protective atmosphere, raising the temperature of the reactor to 1000 ° C, and reacting at a high temperature for 3 h. In the process, the silicon monoxide material undergoes self-disproportionation reaction simultaneously with the surface lithium. The chemical reaction of the source realizes the pre-doping of lithium in the silicon-oxygen composite material, and at the same time, the space buffer structure is constructed between the lithium-doped silicon-oxygen negative electrode particles and the surface carbon layer by the lithium source itself, and the product is naturally cooled. To room temperature, 100 g of a space buffered, lithium doped silicon oxide composite was obtained. The void volume ratio of the core pre-doped lithium silicon oxide composite is about 8%.

The lithium ion battery of the embodiment includes a positive electrode sheet, a separator, a negative electrode sheet, and an electrolyte, and the negative electrode sheet includes a negative electrode current collector and a negative electrode material layer coated on the negative electrode current collector, and the negative electrode material layer includes the above space buffering and doping. Lithium silicon oxide composite material.

The method for preparing the lithium ion battery of the embodiment includes the following steps:

The space-buffered, lithium-doped silicon oxide composite material was mixed with the graphite anode material as a negative electrode active material according to a mass ratio of 15:85, and then the negative electrode active material, SP, CMC, and SBR were mass ratio of 85:10: 2:3 was made into a negative electrode slurry, coated on the surface of copper foil, dried at 120 ° C for 4 h, and then pressed into a circular negative pole piece with a diameter of 12 mm;

A lithium-ion battery is used as a counter electrode to assemble a button-type lithium ion secondary battery. The electrolyte used is a non-aqueous electrolyte having a LiPF ₆ concentration of 1 mol/L, and the solvent used for the electrolyte is an EC having a volume ratio of 4:5:1. A mixed solvent composed of DMC and FEC; the separator used was a 24 μm polypropylene separator.

Example 2

The space buffering, lithium-doped silicon oxide composite material of the embodiment has a core-shell structure, the core is a silicon-oxygen composite material pre-doped with lithium, and the shell is a carbon layer; the space buffer structure exists between the core shells . The main component of the pre-doped lithium silicon oxide composite material is a mixture of lithium silicate, silicon oxide and silicon. By further characterization analysis, wherein the mass ratio of lithium silicate, silicon oxide and silicon is 43:32:25; the volume ratio of void volume to pre-doped lithium silicon oxide composite is about 6%, lithium element and silicon element The molar ratio is 4:5. The mass ratio of the carbon coating layer to the pre-doped lithium silicon oxide composite material is 5:100.

1) 300 g of 99.99% pure silicon oxide (SiO) particles are pulverized by air flow to an average particle size D50 = 1.0 μm, and then the pulverized silicon oxide material is added to a lithium hydroxide aqueous solution having a concentration of 1 mol/L. Ultrasonic dispersion for 8h; the mass ratio of the pulverized silicon oxide material to the lithium hydroxide in the lithium hydroxide aqueous solution is 56:44; the mixture obtained by ultrasonic dispersion is spray-dried, and the premixed material is collected;

2) 150g premixed material is placed in a chemical vapor deposition reactor with an effective volume of 10.0L, and methane is used as a carbon source for vapor phase carbon deposition reaction. The reaction temperature is 600 ° C, the reaction time is 2 h, and the flow rate of methane is 4.0 L. /min, after the reaction, a stable, self-supporting coated carbon layer structure is formed on the surface of the material particles;

3) Switching the methane gas stream into a high-purity argon gas stream as a protective atmosphere, raising the temperature of the reactor to 1000 ° C, and reacting at a high temperature for 3 h. In the process, the silicon monoxide material undergoes self-disproportionation reaction simultaneously with the surface lithium. The chemical reaction of the source realizes the pre-doping of lithium in the silicon-oxygen composite material, and at the same time, the space buffer structure is constructed by the lithium source itself consuming between the lithium-doped silicon-oxygen composite material particles and the surface carbon layer, and the product is naturally formed. After cooling to room temperature, the unreacted lithium source was removed by washing with deionized water and ethanol, and dried to obtain 100 g of a space buffered, lithium doped silicon oxide composite material. The void volume ratio of the core pre-doped lithium silicon oxide composite is about 6%.

The mass ratio of lithium silicate, silicon oxide, silicon, the core-shell mass ratio, the void ratio in the pre-doped lithium silicon-oxygen composite, the molar ratio of lithium to silicon, and the SiO _x particles in Examples 3-10 The diameter, the type of lithium source, the CVD carbon source, the silicon oxide to lithium source mass ratio, the carbon deposition temperature, the carbon deposition time, the reaction temperature, and the sintering time are shown in Table 1. The space buffer, lithium-doped silicon oxide Other features of the composite material and the preparation method are the same as those in the first embodiment.

The lithium ion battery of Examples 3-10 can be prepared by the method of the above Example 2, wherein the negative electrode active material correspondingly uses the space buffered, lithium doped silicon oxide composite material of Examples 3-10.

Comparative example 1

The comparative example uses SiO raw material powder as a negative electrode active material directly after carbon coating at 700 ° C and methane as a carbon source, assembling a lithium ion secondary battery, other test conditions of carbon coating, and assembly of a lithium ion secondary battery. The method was the same as in Example 2.

Comparative example 2

In this comparative example, 300 g of SiO2 particles having a purity of 99.99% were flow-pulverized to an average particle size of D50=1.0 μm, and oxypropylene was added to the oxidized hydroxide according to the mass ratio of oxymethylene oxide to lithium hydroxide of 56:44. The lithium aqueous solution (1 mol/L) was ultrasonically dispersed for 8 hours. The mixed solution was spray-dried, and 150 g of the collected powder was placed in a chemical vapor deposition reactor having an effective volume of 10.0 L, using high-purity argon gas as a protective atmosphere, and high-temperature reaction at 1000 ° C for 3 hours to complete the oxidized silica particles. Pre-expansion and pre-doping of lithium. Further, the temperature was lowered to 700 ° C, and high-purity argon gas was switched to methane, and carbon deposition was carried out for 3 hours under a methane flow rate of 4.0 L/min to obtain a pre-doped oxysilylene powder coated with a carbon layer. This material was used as a negative electrode active material, and a lithium ion secondary battery was assembled. Other test conditions were the same as those in Example 2.

Table 1 Material parameters and reaction conditions in Examples 3-10 and Comparative Examples 1-2

In the above table, x = 1 of SiO _x in Example 3-9, and x = 1.05 of SiO _x in Example 10.

In the above table, D1 and D2 refer to Comparative Example 1 and Comparative Example 2, respectively.

In the above embodiments, the core-shell mass ratio can be determined by thermogravimetric analysis and the mass ratio of the lithium silicate, silicon oxide, and silicon is determined by nuclear magnetic resonance spectroscopy (29Si NMR) analysis; pre-doped lithium The proportion of the cavity (void) volume in the silicon oxide composite was measured by a porosity tester.

Test case

The lithium ion batteries of Examples 1-10 and Comparative Examples 1-2 were tested as follows:

Charge/discharge tests were performed on the charge/discharge tester to determine the capacity of the battery and material, the first efficiency, and the full-capacity rebound rate.

Gram capacity, first efficiency, cycle retention test:

1) Constant current charging (0.1C+0.05C+0.01C three-stage constant current to 0.005V to stop charging) @25°C;

2) Constant current discharge (0.1C to 1.5V) @25°C.

The cycle retention test was performed alternately for

steps

1 and 2 for a total of 20 weeks.

Full power rebound rate test:

1) Constant current and constant voltage charging (0.1C+0.05C+0.01C three-stage constant current to 0.005V to stop charging) @25°C;

2) constant current discharge (0.1C to 1.5V) @25 °C;

3) Constant current and constant voltage charging (0.1C+0.05C+0.01C three-stage constant current to 0.005V to stop charging) @25°C.

The battery is disassembled and the thickness of the pole piece is tested.

The test results are shown in Table 2.

Table 2 Electrochemical performance of lithium ion batteries in Examples 1-10 and Comparative Examples 1-2

It can be seen from the above test results that the space buffered, pre-doped lithium silicon oxide composite material of the present invention can be used as a negative electrode material to obtain a lithium ion secondary battery having high capacity, high first effect and long life.

Claims

A space buffered, lithium doped silicon oxide composite material having a core-shell structure, characterized in that the core is a pre-doped lithium silicon oxide composite material, and the shell is a coated carbon layer.
The space buffered lithium-doped silicon oxide composite material according to claim 1, wherein the pre-doped lithium silicon oxide composite material comprises lithium silicate, silicon oxide, silicon, and the lithium silicate. The mass ratio of silicon oxide to silicon is 6-85:0-59:15-35.
The space buffered, lithium doped silicon oxide composite according to claim 1, wherein the core and the shell have a spatial buffer structure.
The space buffered lithium-doped silicon oxide composite material according to claim 1, wherein the pre-doped lithium silicon oxide composite material is sintered by a lithium source and a silicon oxide at 800-1300 ° C. to make.
The space buffered, lithium-doped silicon oxide composite material according to any one of claims 1 to 4, wherein a mass ratio of the coated carbon layer to the pre-doped lithium silicon oxide composite material is 3 -40:100.
The space buffered, lithium-doped silicon oxide composite material according to any one of claims 1 to 4, wherein a molar ratio of lithium element to silicon element in the pre-doped lithium silicon-oxygen composite material : 0.1 ≤ Li / Si ≤ 2.0.
A method for preparing a spatially buffered, lithium-doped silicon oxide composite material, comprising the steps of:

1) uniformly mixing the oxide of silicon and the lithium source to obtain a premixed material; the lithium source is one or more of lithium hydroxide, lithium acetate, lithium oxalate, and lithium oxalate;

2) forming a coating carbon layer on the surface of the premixed material particles obtained in step 1) by chemical vapor deposition, to obtain a coating material;

3) The coating material obtained in the step 2) is sintered at 800-1300 ° C for 2-6 h under vacuum or an inert atmosphere.
The method for preparing a space buffered, lithium-doped silicon oxide composite according to claim 7, wherein the oxide of silicon is SiO x , wherein 0.5 ≤ x ≤ 1.5.
The method for preparing a space buffered, lithium-doped silicon oxide composite according to claim 7, wherein the silicon oxide has a particle diameter of 0.1 to 5.0 μm.
The method for preparing a space buffered, lithium doped silicon oxide composite according to claim 7, wherein the chemical vapor deposition temperature is 500-700 °C.
The method according to claim 7, wherein the inert atmosphere is one or more of Ar, He, and Ne.
The method for preparing a space buffered, lithium-doped silicon oxide composite according to claim 7, wherein the carbon source used in the chemical vapor deposition is a gas phase carbon source, a liquid phase carbon source, and a solid phase carbon. One or more of the sources; the gas phase carbon source is one or more of methane, ethane, ethylene, acetylene; the liquid phase carbon source is one or two of toluene and ethylbenzene; The solid phase carbon source is one or both of rosin and asphalt.
A lithium ion battery comprising a positive electrode and a negative electrode, wherein the negative electrode comprises a negative electrode active material, wherein the negative electrode active material is a space buffer, lithium doped silicon oxide according to any one of claims 1-6 Composite material.