CN111009647A

CN111009647A - Lithium borosilicate alloy cathode active material of lithium secondary battery, cathode, preparation and application thereof

Info

Publication number: CN111009647A
Application number: CN201911256941.0A
Authority: CN
Inventors: 杨娟; 唐晶晶; 周向阳; 任永鹏; 周昊宸; 王鹏; 胡挺杰; 邹蔼婷
Original assignee: Hunan Chenyu Fuji New Energy Technology Co ltd; Central South University
Current assignee: Hunan Chenyu Fuji New Energy Technology Co ltd
Priority date: 2019-12-10
Filing date: 2019-12-10
Publication date: 2020-04-14
Anticipated expiration: 2039-12-10
Also published as: CN111009647B

Abstract

The invention belongs to the technical field of lithium secondary battery cathode materials, and particularly discloses a lithium borosilicate alloy cathode active material for a lithium secondary battery, which comprises a porous silicon framework and active lithium and Li-B-Si clusters which are compounded in the porous silicon framework and exist in an alloy form. The invention also discloses a preparation method of the lithium borosilicate alloy cathode active material, a cathode containing the lithium borosilicate alloy cathode active material and a lithium secondary battery. The invention discovers that the negative active material with the special structure and the special components has excellent first reversible capacity, coulombic efficiency and cycling stability.

Description

Lithium borosilicate alloy cathode active material of lithium secondary battery, cathode, preparation and application thereof

Technical Field

The invention belongs to the technical field of lithium ion battery electrode materials, and particularly relates to a lithium borosilicate alloy cathode and a preparation method thereof.

Background

With the continuous update of consumer electronic products and the increasing development of electric automobiles, the demand for new generation of high specific energy lithium ion batteries is increasing, and the development of cathode materials of the batteries from embedded carbon-based materials (with a theoretical capacity of 372mAh/g) to lithiatable metal materials, metal compounds and composite materials with high theoretical capacity is promoted. Wherein, silicon has the advantages of high theoretical capacity (4211mAh/g), good safety performance, wide source and the like, and becomes the mainstream of the research of novel cathode materials at home and abroad at present. However, when silicon is used as a negative electrode, the conductivity and the lithium ion diffusion coefficient are both low, so that the internal resistance is large and the rate performance is poor; the lithium ion causes a large volume change (about 300%) during insertion, and causes the phenomena of silicon particle breakage, pulverization, falling off, etc., the internal structure of the electrode is damaged, and the capacity is rapidly reduced.

In order to improve the characteristics of the silicon cathode, the general idea is to slow down the huge volume change of the silicon material in the process of lithium intercalation/deintercalation and improve the conductivity and the structural stability of the material. The prior art means is mainly to carry out nano-crystallization of silicon materials and various composite and porous structure designs on the basis of nano-crystallization. Patent CN106784707 discloses a method for preparing a nano silicon-carbon composite lithium ion battery cathode material, which is obtained by using micron silicon, organic matter and carbon source as raw materials and adopting the technical scheme of ball milling, granulation, high-temperature sintering and mixing with graphite, and overcomes the expansion of silicon material in the charging and discharging processes. Patent CN 105070894 discloses a porous silicon-based composite negative electrode material for lithium ion batteries, which is obtained by etching silicon alloy particles to obtain amorphous porous silicon, and further mixing and sintering the amorphous porous silicon with a carbon source.

However, the large specific surface area of nano-silicon and porous silicon results in large initial irreversible capacity loss, large consumption of electrolyte and lithium ions in the positive electrode material, low charge-discharge efficiency and poor stability, reduced energy density and cycle life of the battery, and is not favorable for commercial application. Therefore, reducing the irreversible capacity loss of the nano-silicon and improving the coulombic efficiency are the keys of practical application of the silicon negative electrode. The lithium-silicon alloy cathode formed by the metal lithium and the silicon can effectively reduce the irreversible capacity loss and improve the coulomb efficiency. The lithium-silicon alloy can be manufactured by a high-temperature melting method or a powder metallurgy method, however, because the metal lithium has extremely high activity, the requirements on oxygen partial pressure and water partial pressure in the manufacturing process are high, the process is complex, the cost is high, and the lithium-silicon alloy is not suitable for mass production. In addition, when the lithium-silicon alloy is applied to a lithium secondary battery, certain lithium dendrite problem still exists, and the problem of silicon expansion and pulverization is inevitable at the same time, so that the cycle performance of the battery is poor.

Disclosure of Invention

The present invention has been made in view of the disadvantages of the prior art, and a first object of the present invention is to provide a lithium borosilicate alloy negative electrode active material for a lithium secondary battery (also referred to as a lithium borosilicate alloy negative electrode active material or a negative electrode active material for short in the present invention) for improving the problems of volume expansion, poor conductivity and high irreversible capacity of a silicon negative electrode.

A second object of the present invention is to provide a lithium borosilicate alloy negative electrode containing the lithium borosilicate alloy negative electrode active material. The lithium-boron-silicon alloy cathode is stable in structure, so that a lithium ion battery prepared from the cathode has high first coulombic efficiency and good cycle performance.

The third purpose of the invention is to provide a preparation method of the lithium borosilicate alloy cathode. The preparation method of the lithium borosilicate alloy cathode is simple in process, low in preparation cost, capable of realizing large-scale production and good in commercial application prospect.

A fourth object of the present invention is to provide a lithium secondary battery comprising the lithium borosilicate alloy negative electrode.

A lithium-boron-silicon alloy cathode active material comprises a porous silicon skeleton, and active lithium and Li-B-Si clusters which are compounded in the porous silicon skeleton and exist in an alloy form.

The invention discovers that the negative active material with the special structure and the special components has excellent first reversible capacity, coulombic efficiency and cycling stability.

Preferably, the lithium borosilicate alloy negative active material has a nano-porous structure on a porous silicon framework, is a mesoporous cross-linked structure, has an average pore diameter of 2-50 nm and a specific surface area of 10-200 m²g^-1。

Preferably, the mass ratio of Li to Si of the lithium borosilicate alloy negative electrode active material is 1 (1-100), and the mass ratio of Li to B is 1 (0.1-2). Preferably, in the lithium borosilicate alloy negative electrode active material, the lithium content is 15-30 wt%; the content of B is 0.3-2%.

Preferably, the lithium borosilicate alloy negative electrode active material is characterized in that the mass content of Li-B-Si clusters is 1-20%; preferably 1 to 7%.

The invention provides a preferable lithium borosilicate alloy cathode which comprises Li, B and Si, wherein the mass ratio of Li to Si is 1 (1-100), and the mass ratio of Li to B is 1 (0.1-2); the lithium borosilicate alloy is composed of a boron-doped porous silicon skeleton and lithium embedded by a physical or electrochemical method, the lithium-embedded silicon and the lithium form the lithium silicon alloy, and uniformly dispersed Li-B-Si stable inert clusters are formed in the alloy. The mass content of the material is 1-20%. (ii) a The boron-doped porous silicon skeleton has a nano porous structure which is a mesoporous cross-linked structure, and the average pore diameter is within2 to 50nm, and a specific surface area of 10 to 200m²g^-1。

The second purpose of the invention is to provide a preparation method of the lithium borosilicate alloy negative electrode active material, which comprises the following steps:

step (1): dissolving a liquid silicon source and a boron-containing compound in an organic dispersion liquid, stirring uniformly, adding an auxiliary acid, mixing to obtain a mixed solution, then adding an alkali liquor for reaction, and carrying out solid-liquid separation after the reaction is finished to obtain a precursor;

step (2): uniformly mixing a precursor, a metal M reducing agent, a metal N salt and a nonionic surfactant, and then carrying out a first-stage reaction at 300-400 ℃ under the protection of an inert atmosphere; then heating to 550-850 ℃ to perform a second stage reaction, and washing the obtained powder with dilute acid after the reaction is finished, chemically modifying and washing to obtain the boron-doped porous silicon skeleton;

the metal M is a metal capable of reducing silicon oxide;

the metal N is alkali metal and/or alkaline earth metal;

and (3): and lithiating the boron-doped porous silicon skeleton to obtain the lithium-doped porous silicon lithium battery.

Researches show that the negative active material of the Li-B-Si cluster in the porous silicon framework in the in-situ dispersion distribution can be successfully obtained by performing in-situ doping on silicon dioxide through B in the step (1), matching with a two-stage sintering process under the assistance of metal M-metal N salt and a non-ionic surfactant in the step (2), and further lithiating, and has excellent structural stability, excellent first reversible capacity, coulombic efficiency and cycling stability.

The inventor researches and discovers that: (1) the material with Li-B-Si clusters dispersed and distributed in situ in the cathode framework structure can unexpectedly have excellent first reversible capacity, coulombic efficiency and cycling stability; (2) the in-situ doping of B is combined with a two-stage sintering process under the assistance of a novel nonionic surfactant, so that the structure and component characteristics of the negative active material obtained by lithiation can be unexpectedly utilized, and the electrical property of the obtained material can be unexpectedly and remarkably improved.

Preferably, the liquid silicon source is one or more of sodium silicate, potassium silicate, ethyl orthosilicate and methyl orthosilicate, and preferably, the liquid silicon source is ethyl orthosilicate. The mass fraction of the silicon source in the mixed solution is 1-35%.

Preferably, the boron-containing compound is one or more of boric acid, sodium borate and borax; boric acid is more preferred.

Preferably, the weight ratio of boron to silicon in the boron-containing compound and the liquid silicon source is (5-50): 100.

Preferably, the auxiliary acid is one or more of hydrochloric acid, sulfuric acid and nitric acid.

The concentration of the auxiliary acid to the hydrogen ion in the volume of the mixed solution is 0.001 to 0.1 mol/L.

The organic dispersant is one or more of ethanol, methanol and glycol.

The alkali liquor is ammonia water and a diluent thereof; preferably a solution comprising ammonia, deionized water, an organic dispersion; the volume ratio of the ammonia water, the deionized water and the organic dispersion liquid is 1 (1-5) to 1-5.

The liquid phase synthesis environment (reaction environment after adding alkali) is mechanical stirring, magnetic stirring or vacuum impregnation, and the reaction temperature range is 20-80 ℃.

Preferably, the metal M reducing agent is one or more of potassium, calcium, sodium, magnesium and aluminum.

Preferably, the mass ratio of the metal M reducing agent to the precursor is (0.5-2): 1.

The salt of the metal N is a chloride salt of the metal N; preferably, the alkali metal chloride is selected from one or more of lithium chloride, sodium chloride and potassium chloride; the alkaline earth metal chloride is selected from one or more of magnesium chloride, calcium chloride and barium chloride.

Preferably, the mass ratio of the metal N salt to the precursor is (1-20): 1; more preferably 10-15: 1.

Preferably, the nonionic surfactant is selected from one or more of polyoxyethylene polyoxypropylene ether block copolymer, polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer and sodium polyacrylate.

Preferably, the mass ratio of the nonionic surfactant to the precursor is (0.01-0.1): 1; more preferably 0.02 to 0.08: 1.

The inert atmosphere is argon or nitrogen.

Under the action of the components, the invention is further matched with the two-stage reaction under the temperature condition, which is beneficial to further improving the performance of the material and improving the electrical properties such as multiplying power, cycle performance and the like of the subsequently prepared negative electrode.

Preferably, the temperature of the first-stage reaction is 350-400 ℃.

Preferably, the time of the first stage reaction is 1-6 h.

Preferably, the temperature of the second-stage reaction is 700-850 ℃.

Preferably, the time of the second stage reaction is 2-12 h.

After the reaction is finished, washing with dilute acid, then carrying out chemical modification treatment, then washing for the second time, and drying to obtain the catalyst.

Preferably, the diluted acid is one or more of hydrochloric acid, sulfuric acid and nitric acid, the concentration is 0.5-2 mol/L, and the reaction (washing) time is 1-12 h.

Preferably, the chemical modifier is hydrofluoric acid or alkali solution. The alkali liquor is one or two of sodium hydroxide solution and potassium hydroxide solution, the mass fraction of the alkali liquor is 1-40%, and the reaction time is 0.1-6 h. The mass fraction of the hydrofluoric acid is 1-10%, and the reaction time is 0.1-3 h.

After the treatment with the chemical modifier, the mixture is subjected to a second washing step by using solvents such as ethanol and water. Washing, separating and drying to obtain the product.

Preferably, the boron-doped porous silicon skeleton is a mesoporous cross-linked structure, the average pore diameter is 2-50 nm, and the specific surface area is 10-200 m²g^-1(ii) a Preferably, the doping amount of B is 0.1-5%.

In the invention, in the step (3), the boron-doped porous silicon skeleton prepared under the special conditions can be lithiated by adopting the existing method. In the present invention, the negative active material with high electrical properties can be unexpectedly lithiated due to the special process conditions of step (1) and step (2).

The invention also provides a lithium borosilicate alloy negative electrode, which comprises a current collector and a negative electrode material compounded on the surface of the current collector, wherein the negative electrode material comprises the lithium borosilicate alloy negative electrode active material, a conductive agent and a binder.

In the present invention, the current collector may be any negative current collector known in the art. The conductive agent and binder may also be any available material known to those skilled in the art. And the dosage of the conductive agent, the adhesive and the active material can be selectively adjusted according to the existing theory.

For example, the mass content of the active material in the negative electrode sheet is 60 to 99%. The negative electrode binder can be one or more of polyvinylidene fluoride, carboxymethyl cellulose, styrene butadiene rubber, polytetrafluoroethylene, polyacrylic acid, polyvinyl alcohol and sodium alginate, and the mass content of the negative electrode binder is 0.1-20%. The negative electrode conductive agent can be one or more selected from graphite, acetylene black, conductive carbon black, carbon nano tubes, carbon fibers, graphene, copper powder and nickel powder, and the mass content of the negative electrode conductive agent is 0.1-20%. The solvent refers to an organic solvent such as N-methylpyrrolidone or water that can dissolve the binder in the case where the binder is in a solid state. The negative electrode current collector may be one selected from copper foil, nickel foam, copper foam, and carbon foam; the technical parameters of coating, drying and rolling are known to the person skilled in the art.

The invention also provides a preparation method of the lithium borosilicate alloy cathode, which can be obtained by directly pulping and compounding the cathode active material, the conductive agent and the binder on the surface of a cathode current collector; or preparing a boron-doped porous silicon skeleton, slurrying and compounding the boron-doped porous silicon skeleton, a conductive agent and a binder on the surface of the negative current collector, and performing lithiation treatment to obtain the lithium ion battery.

Preferably, the preparation method of the lithium borosilicate alloy negative electrode comprises the following steps:

step (a): obtaining the boron-doped porous silicon skeleton through the step (1) and the step (2);

step (b): slurrying the boron-doped porous silicon skeleton, the conductive agent and the binder, compounding the slurried materials on the surface of a current collector, drying the slurried materials to obtain a silicon negative electrode sheet precursor, embedding lithium into the silicon negative electrode sheet precursor, and carrying out lithiation reaction to obtain the lithium-boron-silicon alloy negative electrode.

The boron-doped porous silicon skeleton can be prepared into the cathode plate precursor by adopting the conventional materials and methods.

Preferably, lithium is intercalated into the boron-doped porous silicon skeleton by a physical lithium intercalation alloying method or an electrochemical lithium intercalation alloying method, and a lithiation reaction is carried out. Research shows that the negative electrode of the invention can further exert the characteristics of the material of the invention by adopting a physical lithium intercalation alloying or electrochemical lithium intercalation alloying method, and is beneficial to further improving the structural stability and the electrical property of the negative electrode after lithiation.

Preferably: the physical lithium-embedding alloying method is to scrape and coat metal lithium powder or cling lithium foil to the silicon negative plate precursor wetted by lithium-containing organic electrolyte and to mechanically press. For example, in the physical lithium intercalation alloying method, when the metal lithium powder is used as a lithium source, the particle size of the metal lithium powder is 0.1-100 μm, and the mass ratio of the addition amount to silicon is 1 (1-100); when the metal lithium foil is used as a lithium source, the thickness of the metal lithium foil is 0.01-2 mm; the lithium salt of the lithium-containing organic electrolyte can be one or more selected from lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium trifluoromethanesulfonate and lithium bis (trifluoromethanesulfonyl) imide, and the concentration of the lithium salt is 0.5-2 mol/L; the solvent of the lithium-containing organic electrolyte can be one or more selected from ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate; the water content and the oxygen content in the inert atmosphere for controlling the moisture are both less than 1 ppm; the mechanical pressing range is 0.1-100 MPa, and the lithiation time is 0.5-100 h.

Preferably: the electrochemical lithium intercalation alloying adopts a two-electrode mode, metal lithium is taken as a sacrificial anode, a silicon negative plate precursor is taken as a cathode, a lithium-containing organic electrolyte is inserted after the two electrodes are connected, and the electrochemical lithiation process of the silicon electrode is carried out by controlling the voltage in an inert atmosphere of controlling moisture.

Preferably, the electrochemical lithium intercalation alloying power supply mode is direct current deposition or pulse electrodeposition, the cut-off potential is 0.01-0.5V, the current density is 10-1000 mA/gSi, and the lithiation time is 0.1-50 h.

The preparation method of the lithium borosilicate alloy negative electrode comprises the following steps:

dissolving a certain proportion of liquid silicon source and boron-containing compound in an organic dispersion liquid, uniformly stirring, adding auxiliary acid, reacting in a liquid phase for 2-5 h, taking out, and cooling to room temperature; then adding a uniform mixed solution of ammonia water, deionized water and organic dispersion liquid which are prepared according to a certain proportion, continuously stirring and reacting for 2-5 h at room temperature, and then carrying out solid-liquid separation; and repeatedly washing the obtained precipitate with ethanol and water, separating and drying to obtain a precursor.

Secondly, grinding the precursor obtained in the first step, a metal reducing agent and alkali metal chloride and/or alkaline earth metal chloride according to a certain proportion until the precursor, the metal reducing agent and the alkali metal chloride and/or the alkaline earth metal chloride are uniformly mixed, sealing the mixture in a stainless steel reactor, firstly preserving the heat of the reactor for 1-6 h at 300-400 ℃ under the protection of inert atmosphere, then preserving the heat for 2-12 h at 550-850 ℃, and then naturally cooling; after the reaction is finished, washing the obtained powder with dilute acid, hydrofluoric acid or alkali liquor, ethanol and water, separating and drying to obtain the boron-doped porous silicon material (boron-doped porous silicon skeleton).

And thirdly, manufacturing the boron-doped porous silicon material obtained in the second step into a negative plate by adopting various pole plate manufacturing methods commonly used in the field, for example, the boron-doped porous silicon material is used as an active substance, a binder and a conductive agent are added according to a certain proportion, the mixture is uniformly mixed in a solvent, the mixture is coated on a negative current collector, and the negative plate is formed after drying and rolling.

Fourthly, lithium intercalation alloying is carried out on the negative pole piece prepared in the third step by adopting a physical or electrochemical method to obtain a lithium borosilicate alloy negative pole; preferably, the physical lithium-embedding alloying method comprises the steps of scraping and coating metal lithium powder or clinging a lithium foil to a silicon negative plate wetted by lithium-containing organic electrolyte, and mechanically pressing under an inert atmosphere with controlled moisture; the electrochemical lithium intercalation alloying preferably adopts a two-electrode mode, metal lithium is taken as a sacrificial anode, a silicon negative plate is taken as a cathode, a lithium-containing organic electrolyte is inserted after the two electrodes are connected, and the electrochemical lithiation process of the silicon electrode is carried out by controlling the voltage in an inert atmosphere of controlling moisture.

A sixth object of the present invention is to provide a lithium secondary battery, wherein the negative electrode comprises the lithium borosilicate alloy negative electrode active material.

Preferably, the negative electrode of the lithium secondary battery is the lithium borosilicate alloy negative electrode.

The invention utilizes the special crystal structure characteristics of boron-doped silicon oxide, adjusts the microscopic appearance of a reduction product by controlling the intervention behavior of boron in metal reduction, and realizes the simple, convenient and controllable preparation of the nano porous silicon material; further utilizes the chemical reaction characteristics between lithium and silicon and lithium and boron, and adopts a physical or electrochemical lithiation method to realize the high-efficiency alloying of lithium in the porous silicon. The high-performance cathode suitable for the lithium ion battery is prepared by regulating and controlling the components and the structure of the lithium-silicon alloy.

The basic principle of the implementation of the technical scheme of the invention is as follows: firstly, silicon compound is taken as raw material, boron compound is added as structure regulator, boron enters into hydrolysate silicon oxide in a coprecipitation mode, the intervention of boron influences the connection mode and the structure base type of silica backbone, and boron-doped silicon oxide (B-SiO) with special crystal structure is formed₂) (ii) a Then, a specific temperature rising system is adopted to carry out metal reduction on the B-SiO₂Obtaining boron-doped silicon (B-Si) with a porous structure by the microstructure adjusting effect of boron in the reduction process; finally, B-Si is made into an electrode to carry out physical or electrochemical lithiation, the lithiation degree is controlled, Li and Si form lithium-silicon alloy, meanwhile, because the element B can react with metallic Li under specific conditions to generate non-integral ratio metal boride, the structure of the metal boride changes with the number of B atoms in the composition, and therefore, Li-B-Si stable clusters which are uniformly dispersed can be formed in the alloy by controlling the reaction conditions, and finally, the lithium-boron-silicon alloy cathode (B-Li) with a stable nano-porous structure is formed_xSi)。

Compared with the prior art, the lithium borosilicate alloy cathode has the following characteristics and advantages:

(1) boron is introduced in the silicon reduction process, so that the appearance and structure of the silicon alloy can be adjusted, and the boron in the silicon lattice is synchronously doped in situ; boron doped in the silicon has stronger interaction with lithium, and can form uniformly dispersed Li-B-Si inert atom clusters in the silicon to maintain the structural stability of the alloy cathode.

(2) The silicon substrate with the high specific surface area can effectively reduce the current density in the charging and discharging process, and has bulk alloying-dealloying reaction with the metal lithium, thereby effectively avoiding the phenomenon of uneven deposition/dissolution of the lithium and the safety problem caused by the heterogeneity of the space structure of the conventional three-dimensional current collector.

(3) The lithium component has a supplementary effect on irreversible lithium loss during first charge and discharge, active lithium is removed after discharge to leave nano porous silicon containing Li-B-Si stable clusters, good conductivity and stable structure are still maintained, and electrode volume change in the subsequent circulation process is relieved.

(4) The invention innovatively facilitates lithiation to obtain a material with high structural stability and high electrical property through B in-situ doping-metal N salt + nonionic surfactant assisted two-stage metal reduction reaction;

(5) the method has the advantages of rich raw material sources, simple and convenient process, strong operability, flexibility, controllability and high practical application value.

Drawings

FIG. 1 is a schematic diagram of a lithium borosilicate alloy cathode structure

FIG. 2 SEM photograph of boron-doped silicon particles prepared in example 1

Detailed Description

The specific procedures of the present invention are illustrated below by way of examples, it being understood that these examples are intended to illustrate the invention and are not intended to limit the scope of the invention in any way. Various procedures and methods not described in detail herein are conventional methods well known in the art.

Example 1

According to the mass ratio of the element boron to the silicon in the compound as 1: 5, dissolving boric acid and ethyl orthosilicate in ethanol with the volume 10 times that of the boric acid and the ethyl orthosilicate, uniformly stirring for 10min, adding 0.06mol/L hydrochloric acid solution with the relative total volume of 0.5, uniformly stirring for 3h at 60 ℃, and cooling to room temperature; then, mixing the components in a volume ratio of 1: 1, adding a mixed solution of ammonia water, deionized water and absolute ethyl alcohol (the volume ratio is 1: 2: 3), stirring and reacting for 3 hours at room temperature, carrying out solid-liquid separation, repeatedly washing the obtained precipitate with ethanol and water, and separating and drying to obtain a precursor.

1g of the precursor is taken, ground with 1g of magnesium powder, 10g of sodium chloride powder and 0.05g of polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer (P123) to be uniformly mixed, sealed in a stainless steel reactor, heated to 350 ℃ at a heating rate of 3 ℃/min in a horizontally placed tube furnace under the argon atmosphere, kept for 2h, then heated to 700 ℃, kept for 5h and then naturally cooled; immersing the reaction product in 2mol/L hydrochloric acid, stirring for 6h, and treating with 5% HF acid for 30min after separation; and finally, washing with ethanol and water, separating and drying to obtain the boron-doped porous silicon material. The appearance of the sample was observed by scanning electron microscopy, see figure 2. The boron-doped porous silicon material prepared by the embodiment has a spherical porous structure, the particle diameter is about 850nm, the pore structure distribution is tested by nitrogen adsorption and desorption, the average size of pore channels is 33nm, and the specific surface area is 120m²g^-1。

Mixing the obtained porous silicon material with conductive carbon black and sodium alginate according to the mass ratio of 6: 2: 2, uniformly mixing, preparing slurry by taking deionized water as a solvent, coating the slurry on a copper foil, and drying to prepare a lithium ion battery negative electrode plate; a lithium foil with the thickness of 0.05mm is closely attached to a silicon negative electrode sheet wetted by a lithium-containing organic electrolyte, and the electrolyte consists of 1mol/L lithium hexafluorophosphate, ethylene carbonate and diethyl carbonate (the volume ratio of the solvent is 1: 1); and mechanically pressing under 20MPa in an inert atmosphere (the water and oxygen content are less than 1ppm) with controlled moisture, and lithiating for 50 hours to obtain the lithium-boron-silicon alloy negative plate. The mass content of lithium and silicon in the lithium-boron-silicon alloy is tested by adopting a gas volumetric method (based on the principle that hydrogen is replaced by active lithium and absolute ethyl alcohol through reaction), the mass content of boron in the lithium-boron-silicon alloy is tested by adopting ICP-AES (inductively coupled plasma-atomic emission Spectrometry), and the mass fraction of lithium in the lithium-boron-silicon alloy is 28%, the mass fraction of boron in the lithium-boron-silicon alloy is 1.2%, and the balance is a silicon simple substance.

Assembling the lithium borosilicate alloy negative plate into a CR2032 type lithium ion button cell, and detecting the electrochemical performance at room temperature in a voltage range of 0.01-1.2V, wherein the current density of a charge and discharge test is 200 mA/g. The first reversible capacity is recorded to be 1810mAh/g, the coulombic efficiency is 95%, and the capacity retention rate is 92% after 100 times of circulation. After the 10 th complete discharge (delithiation), the residual lithium content in the active material in the test electrode was 0.76 wt%, and the content of inert Li-B-Si clusters not participating in the reaction was calculated to be 5 wt%.

Example 2

According to the mass ratio of the element boron to the silicon in the compound as 1: dissolving sodium borate and sodium silicate in 10 times of ethanol by volume, uniformly stirring for 10min, adding 0.1mol/L hydrochloric acid solution with the relative total volume of 0.6, uniformly stirring at 60 ℃ for 3h, and cooling to room temperature; then, according to the volume ratio of 3: 2 adding a mixed solution of ammonia water, deionized water and absolute ethyl alcohol (volume ratio is 1: 2: 3), stirring and reacting for 3 hours at room temperature, carrying out solid-liquid separation, repeatedly washing the obtained precipitate with ethanol and water, and carrying out separation and drying to obtain a precursor.

1g of the precursor is taken, ground with 1g of magnesium powder, 10g of sodium chloride powder and 0.05g of polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer (P123) to be uniformly mixed, sealed in a stainless steel reactor, heated to 350 ℃ at a heating rate of 3 ℃/min in a horizontally placed tube furnace under the argon atmosphere, kept for 2h, then heated to 700 ℃, kept for 5h and then naturally cooled; immersing the reaction product in 2mol/L hydrochloric acid, stirring for 6h, and treating with 5% HF acid for 30min after separation; and finally, washing with ethanol and water, separating and drying to obtain the boron-doped porous silicon material. The boron-doped porous silicon material prepared by the embodiment has a particle diameter of about 670nm, and adopts nitrogen adsorption and desorption to test the pore structure distribution, wherein the average pore size is 18nm, and the specific surface area is 89m²g^-1。

Mixing the obtained porous silicon material with conductive carbon black and sodium alginate according to the mass ratio of 6: 2: 2, uniformly mixing, preparing slurry by taking deionized water as a solvent, coating the slurry on a copper foil, and drying to prepare a lithium ion battery negative electrode plate; a lithium foil with the thickness of 0.05mm is closely attached to a silicon negative electrode sheet wetted by a lithium-containing organic electrolyte, and the electrolyte consists of 1mol/L lithium hexafluorophosphate, ethylene carbonate and diethyl carbonate (the volume ratio of the solvent is 1: 1); and mechanically pressing under 20MPa in an inert atmosphere (the water and oxygen content are less than 1ppm) with controlled moisture, and lithiating for 50 hours to obtain the lithium-boron-silicon alloy negative plate. The mass content of lithium and silicon in the lithium-boron-silicon alloy is tested by adopting a gas volumetric method (based on the principle that hydrogen is replaced by active lithium and absolute ethyl alcohol through reaction), the mass content of boron in the lithium-boron-silicon alloy is tested by adopting ICP-AES (inductively coupled plasma-atomic emission Spectrometry), and the mass fraction of lithium in the lithium-boron-silicon alloy is 26%, the mass fraction of boron in the lithium-boron-silicon alloy is 0.34%, and the balance is a silicon simple substance.

Assembling the lithium borosilicate alloy negative plate into a CR2032 type lithium ion button cell, and detecting the electrochemical performance at room temperature in a voltage range of 0.01-1.2V, wherein the current density of a charge and discharge test is 200 mA/g. The first reversible capacity was recorded as 1720mAh/g, the coulombic efficiency was 94%, and the capacity retention after 100 cycles was 90%. After the 10 th complete discharge (delithiation), the residual lithium content in the active material in the test electrode was 0.2 wt%, and the content of inert Li-B-Si clusters not participating in the reaction was calculated to be 1.2 wt%.

Example 3

Taking 1g of the precursor, grinding 1g of magnesium powder, 12g of sodium chloride powder and 0.05g of polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer (P123) to be uniformly mixed, sealing in a stainless steel reactor, heating to 400 ℃ at a heating rate of 5 ℃/min in a horizontally placed tube furnace under the argon atmosphere, preserving heat for 1.5h, then heating to 800 ℃, preserving heat for 3.5h, and naturally cooling; reaction ofImmersing the product in 2mol/L hydrochloric acid, stirring for 6h, separating, and treating with 10% NaOH alkali for 30 min; and finally, washing with ethanol and water, separating and drying to obtain the boron-doped porous silicon material. The boron-doped porous silicon material prepared by the embodiment has a particle diameter of about 800nm, and adopts nitrogen adsorption and desorption to test the pore structure distribution, wherein the average pore size is 27nm, and the specific surface area is 156m²g^-1。

Mixing the obtained porous silicon material with conductive carbon black and sodium alginate according to the mass ratio of 6: 2: 2, uniformly mixing, preparing slurry by taking deionized water as a solvent, coating the slurry on a copper foil, and drying to prepare a lithium ion battery negative electrode plate; a lithium foil with the thickness of 0.05mm is closely attached to a silicon negative electrode sheet wetted by a lithium-containing organic electrolyte, and the electrolyte consists of 1mol/L lithium hexafluorophosphate, ethylene carbonate and diethyl carbonate (the volume ratio of the solvent is 1: 1); and mechanically pressing under 20MPa in an inert atmosphere (the water and oxygen content are less than 1ppm) with controlled moisture, and lithiating for 50 hours to obtain the lithium-boron-silicon alloy negative plate. The mass content of lithium and silicon in the lithium-boron-silicon alloy is tested by adopting a gas volumetric method (based on the principle that hydrogen is replaced by active lithium and absolute ethyl alcohol through reaction), the mass content of boron in the lithium-boron-silicon alloy is tested by adopting ICP-AES (inductively coupled plasma-atomic emission Spectrometry), and the mass fraction of lithium in the lithium-boron-silicon alloy is 27%, the mass fraction of boron in the lithium-boron-silicon alloy is 0.9%, and the balance is a silicon simple substance.

Assembling the lithium borosilicate alloy negative plate into a CR2032 type lithium ion button cell, and detecting the electrochemical performance at room temperature in a voltage range of 0.01-1.2V, wherein the current density of a charge and discharge test is 200 mA/g. The first reversible capacity was recorded as 1780mAh/g, the coulombic efficiency was 95%, and the capacity retention rate was 91% after 100 cycles. After the 10 th complete discharge (delithiation), the residual lithium content in the active material in the test electrode was 0.58 wt%, and the content of inert Li-B-Si clusters not participating in the reaction was calculated to be 3.8 wt%.

Example 4

Compared with example 1, the difference is only that direct current is adopted to deposit lithium, specifically:

1g of the precursor is taken, ground with 1g of magnesium powder, 10g of sodium chloride powder and 0.05g of polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer (P123) to be uniformly mixed, sealed in a stainless steel reactor, heated to 350 ℃ at a heating rate of 3 ℃/min in a horizontally placed tube furnace under the argon atmosphere, kept for 2h, then heated to 700 ℃, kept for 5h and then naturally cooled; immersing the reaction product in 2mol/L hydrochloric acid, stirring for 6h, and treating with 5% HF acid for 30min after separation; and finally, washing with ethanol and water, separating and drying to obtain the boron-doped porous silicon material. The boron-doped porous silicon material prepared by the embodiment has a particle diameter of about 850nm, and adopts nitrogen adsorption and desorption to test the pore structure distribution, wherein the average pore size is 33nm, and the specific surface area is 120m²g^-1。

Mixing the obtained porous silicon material with conductive carbon black and sodium alginate according to the mass ratio of 6: 2: 2, uniformly mixing, preparing slurry by taking deionized water as a solvent, coating the slurry on a copper foil, and drying to prepare a lithium ion battery negative electrode plate; the silicon negative plate is used as a cathode, metal lithium is used as a sacrificial anode, and a lithium-containing organic electrolyte is inserted after connection, wherein the electrolyte consists of 1mol/L lithium hexafluorophosphate, ethylene carbonate and diethyl carbonate (the volume ratio of the solvent is 1: 1); and (3) carrying out direct current deposition in an inert atmosphere (the water and oxygen content is less than 1ppm) with controlled moisture, wherein the cut-off potential is 0.01V, the current density is 100mA/gSi, and the electrodeposition time is 15h, so as to obtain the lithium-boron-silicon alloy negative plate. The mass content of lithium and silicon in the lithium-boron-silicon alloy is tested by adopting a gas volumetric method (based on the principle that hydrogen is replaced by active lithium and absolute ethyl alcohol through reaction), the mass content of boron in the lithium-boron-silicon alloy is tested by adopting ICP-AES (inductively coupled plasma-atomic emission Spectrometry), and the mass fraction of lithium in the lithium-boron-silicon alloy is measured to be 19%, the mass fraction of boron in the lithium-boron-silicon alloy is measured to be 1.3%, and the balance is a silicon simple substance.

Assembling the lithium borosilicate alloy negative plate into a CR2032 type lithium ion button cell, and detecting the electrochemical performance at room temperature in a voltage range of 0.01-1.2V, wherein the current density of a charge and discharge test is 200 mA/g. The first reversible capacity is 1730mAh/g, the coulombic efficiency is 93 percent, and the capacity retention rate is 90 percent after 100 times of circulation. After the 10 th complete discharge (delithiation), the residual lithium content in the active material in the test electrode was 0.78 wt%, and the content of inert Li-B-Si clusters not participating in the reaction was calculated to be 5.1 wt%.

Example 5

Compared with the example 1, the main difference is that the nonionic surfactant is changed into the following specific components:

Taking 1g of the precursor, grinding the precursor, 1g of magnesium powder, 10g of sodium chloride powder and 0.02g of polyoxyethylene polyoxypropylene ether block copolymer (F127) until the mixture is uniformly mixed, sealing the mixture in a stainless steel reactor, heating the mixture to 350 ℃ at a heating rate of 3 ℃/min in a horizontally placed tubular furnace under the atmosphere of argon, preserving the heat for 2 hours, then heating the mixture to 700 ℃, preserving the heat for 5 hours, and naturally cooling the mixture; immersing the reaction product in 2mol/L hydrochloric acid, stirring for 6h, and treating with 5% HF acid for 30min after separation; and finally, washing with ethanol and water, separating and drying to obtain the boron-doped porous silicon material. The boron-doped porous silicon material prepared by the embodiment has a particle diameter of about 750nm, and adopts nitrogen adsorption and desorption to test the pore structure distribution, wherein the average pore size is 25nm, and the specific surface area is 145m²g^-1。

Mixing the obtained porous silicon material with conductive carbon black and sodium alginate according to the mass ratio of 6: 2: 2, uniformly mixing, preparing slurry by taking deionized water as a solvent, coating the slurry on a copper foil, and drying to prepare a lithium ion battery negative electrode plate; a lithium foil with the thickness of 0.05mm is closely attached to a silicon negative electrode sheet wetted by a lithium-containing organic electrolyte, and the electrolyte consists of 1mol/L lithium hexafluorophosphate, ethylene carbonate and diethyl carbonate (the volume ratio of the solvent is 1: 1); and mechanically pressing under 20MPa in an inert atmosphere (the water and oxygen content are less than 1ppm) with controlled moisture, and lithiating for 50 hours to obtain the lithium-boron-silicon alloy negative plate. The mass content of lithium and silicon in the lithium-boron-silicon alloy is tested by adopting a gas volumetric method (based on the principle that hydrogen is replaced by active lithium and absolute ethyl alcohol through reaction), the mass content of boron in the lithium-boron-silicon alloy is tested by adopting ICP-AES (inductively coupled plasma-atomic emission Spectrometry), and the mass fraction of lithium in the lithium-boron-silicon alloy is 24%, the mass fraction of boron in the lithium-boron-silicon alloy is 1.5%, and the balance is a silicon simple substance.

Assembling the lithium borosilicate alloy negative plate into a CR2032 type lithium ion button cell, and detecting the electrochemical performance at room temperature in a voltage range of 0.01-1.2V, wherein the current density of a charge and discharge test is 200 mA/g. The first reversible capacity is 1750mAh/g, the coulombic efficiency is 94%, and the capacity retention rate is 93% after 100 cycles. After the 10 th complete discharge (delithiation), the residual lithium content in the active material in the test electrode was 0.95 wt%, and the content of inert Li-B-Si clusters not participating in the reaction was calculated to be 6.3 wt%.

Example 6

Grinding 1g of the precursor, 1g of magnesium powder, 10g of sodium chloride powder and 0.08g of sodium polyacrylate until the mixture is uniformly mixed, sealing the mixture in a stainless steel reactor, heating the mixture to 350 ℃ in a horizontally placed tubular furnace at the heating rate of 3 ℃/min under the argon atmosphere for 2 hours, and then heating the mixture to 70 DEG CKeeping the temperature at 0 ℃ for 5h, and then naturally cooling; immersing the reaction product in 2mol/L hydrochloric acid, stirring for 6h, and treating with 5% HF acid for 30min after separation; and finally, washing with ethanol and water, separating and drying to obtain the boron-doped porous silicon material. The particle diameter of the boron-doped porous silicon material prepared by the embodiment is about 920nm, the pore structure distribution is tested by nitrogen adsorption and desorption, the average size of pore channels is 46nm, and the specific surface area is 95m²g^-1。

Mixing the obtained porous silicon material with conductive carbon black and sodium alginate according to the mass ratio of 6: 2: 2, uniformly mixing, preparing slurry by taking deionized water as a solvent, coating the slurry on a copper foil, and drying to prepare a lithium ion battery negative electrode plate; a lithium foil with the thickness of 0.05mm is closely attached to a silicon negative electrode sheet wetted by a lithium-containing organic electrolyte, and the electrolyte consists of 1mol/L lithium hexafluorophosphate, ethylene carbonate and diethyl carbonate (the volume ratio of the solvent is 1: 1); and mechanically pressing under 20MPa in an inert atmosphere (the water and oxygen content are less than 1ppm) with controlled moisture, and lithiating for 50 hours to obtain the lithium-boron-silicon alloy negative plate. The mass content of lithium and silicon in the lithium-boron-silicon alloy is tested by adopting a gas volumetric method (based on the principle that hydrogen is replaced by active lithium and absolute ethyl alcohol through reaction), the mass content of boron in the lithium-boron-silicon alloy is tested by adopting ICP-AES (inductively coupled plasma-atomic emission Spectrometry), and the mass fraction of lithium in the lithium-boron-silicon alloy is measured to be 18%, the mass fraction of boron in the lithium-boron-silicon alloy is measured to be 0.7%, and the balance is a silicon simple substance.

Assembling the lithium borosilicate alloy negative plate into a CR2032 type lithium ion button cell, and detecting the electrochemical performance at room temperature in a voltage range of 0.01-1.2V, wherein the current density of a charge and discharge test is 200 mA/g. The first reversible capacity is recorded to be 1810mAh/g, the coulombic efficiency is 95%, and the capacity retention rate is 92% after 100 times of circulation. After the 10 th complete discharge (delithiation), the residual lithium content in the active material in the test electrode was 0.55 wt%, and the content of inert Li-B-Si clusters not participating in the reaction was calculated to be 3.6 wt%.

Comparative example 1

Compared with the embodiment 1, the difference is that boron doping is not carried out, specifically:

taking 1g of solid spherical silicon dioxide powder with the diameter of 0.5-1 mu m as a precursor, uniformly mixing the solid spherical silicon dioxide powder with 1g of magnesium powder, 10g of sodium chloride powder and 0.05g of polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer (P123), sealing the mixture in a stainless steel reactor, heating to 700 ℃ at the heating rate of 5 ℃/min in a horizontally placed tubular furnace in the argon atmosphere, preserving the temperature for 6h, and then naturally cooling; immersing the reaction product in 2mol/L hydrochloric acid, stirring for 6h, and treating with 5% HF acid for 30min after separation; and finally, washing with ethanol and water, separating and drying for 12 hours to obtain the non-boron-doped silicon material.

Mixing the obtained boron-free silicon material with conductive carbon black and sodium alginate according to the mass ratio of 6: 2: 2, uniformly mixing, preparing slurry by taking deionized water as a solvent, coating the slurry on a copper foil, and drying to prepare a lithium ion battery negative electrode plate; a lithium foil with the thickness of 0.05mm is closely attached to a silicon negative electrode sheet wetted by a lithium-containing organic electrolyte, and the electrolyte consists of 1mol/L lithium hexafluorophosphate, ethylene carbonate and diethyl carbonate (the volume ratio of the solvent is 1: 1); and mechanically pressing under 20MPa in an inert atmosphere (the water and oxygen content are less than 1ppm) with controlled moisture, and lithiating for 50 hours to obtain the lithium-silicon alloy negative plate.

And assembling the lithium-silicon alloy negative plate into a lithium ion button cell to detect the electrochemical performance, wherein the charge-discharge test current density is 200 mA/g. The first reversible capacity is recorded to be 1350mAh/g, the coulombic efficiency is recorded to be 93 percent, and the capacity retention rate is recorded to be 76 percent after 100 times of circulation.

Comparative example 2

Compared with example 1, the difference is that no lithiation treatment is performed, specifically:

1g of the precursor is taken, ground with 1g of magnesium powder, 10g of sodium chloride powder and 0.05g of polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer (P123) to be uniformly mixed, sealed in a stainless steel reactor, heated to 350 ℃ at a heating rate of 3 ℃/min in a horizontally placed tube furnace under the argon atmosphere, kept for 2h, then heated to 700 ℃, kept for 5h and then naturally cooled; immersing the reaction product in 2mol/L hydrochloric acid, stirring for 6h, and treating with 5% HF acid for 30min after separation; and finally, washing with ethanol and water, separating and drying to obtain the boron-doped porous silicon material.

Mixing the obtained porous silicon material with conductive carbon black and sodium alginate according to the mass ratio of 6: 2: 2, uniformly mixing, preparing slurry by taking deionized water as a solvent, coating the slurry on a copper foil, and drying to prepare a lithium ion battery negative electrode plate; and assembling the negative plate into a lithium ion button cell to detect the electrochemical performance, wherein the charge-discharge test current density is 200 mA/g. The first reversible capacity was recorded as 1420mAh/g, the coulombic efficiency was 71%, and the capacity retention after 100 cycles was 87%.

Comparative example 3

Compared with the example 1, the difference is that the two-stage heat treatment is not carried out, specifically:

1g of the precursor is taken, ground with 1g of magnesium powder, 10g of sodium chloride powder and 0.05g of polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer (P123) to be uniformly mixed, sealed in a stainless steel reactor, heated to 700 ℃ at the heating rate of 3 ℃/min in a horizontally placed tube furnace under the argon atmosphere, and naturally cooled after heat preservation for 5 hours; immersing the reaction product in 2mol/L hydrochloric acid, stirring for 6h, and treating with 5% HF acid for 30min after separation; and finally, washing with ethanol and water, separating and drying to obtain the boron-doped porous silicon material.

Mixing the obtained porous silicon material with conductive carbon black and sodium alginate according to the mass ratio of 6: 2: 2, uniformly mixing, preparing slurry by taking deionized water as a solvent, coating the slurry on a copper foil, and drying to prepare a lithium ion battery negative electrode plate; a lithium foil with the thickness of 0.05mm is closely attached to a silicon negative electrode sheet wetted by a lithium-containing organic electrolyte, and the electrolyte consists of 1mol/L lithium hexafluorophosphate, ethylene carbonate and diethyl carbonate (the volume ratio of the solvent is 1: 1); and mechanically pressing under 20MPa in an inert atmosphere (the water and oxygen content are less than 1ppm) with controlled moisture, and lithiating for 50 hours to obtain the negative plate.

And assembling the negative plate into a CR2032 type lithium ion button cell, and detecting the electrochemical performance at a voltage range of 0.01-1.2V at room temperature, wherein the charge-discharge test current density is 200 mA/g. The first reversible capacity is recorded to be 1330mAh/g, the coulombic efficiency is 79 percent, and the capacity retention rate is 77 percent after 100 times of circulation. After the 10 th complete discharge (delithiation), the residual lithium content in the active material in the test electrode was 0.14 wt%, and the content of inert Li-B-Si clusters not participating in the reaction was calculated to be 0.9 wt%.

Comparative example 4

The difference from example 1 is that the heat treatment control conditions are not within specific ranges, specifically:

Taking 1g of the precursor, grinding 1g of magnesium powder, 10g of sodium chloride powder and 0.05g of polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer (P123) to be uniformly mixed, sealing in a stainless steel reactor, heating to 550 ℃ at a heating rate of 3 ℃/min in a horizontally placed tubular furnace under an air atmosphere, keeping the temperature for 2h, then continuously heating to 900 ℃ under an argon atmosphere, keeping the temperature for 3h, and then naturally cooling; immersing the reaction product in 2mol/L hydrochloric acid, stirring for 6h, and treating with 5% HF acid for 30min after separation; and finally, washing with ethanol and water, separating and drying to obtain the boron-doped porous silicon material.

And assembling the negative plate into a CR2032 type lithium ion button cell, and detecting the electrochemical performance at a voltage range of 0.01-1.2V at room temperature, wherein the charge-discharge test current density is 200 mA/g. The first reversible capacity was recorded as 1420mAh/g, the coulombic efficiency was 80%, and the capacity retention rate was 62% after 100 cycles. After the 10 th complete discharge (delithiation), the residual lithium content in the active material in the test electrode was 0.11 wt%, and the content of inert Li-B-Si clusters not participating in the reaction was calculated to be 0.7 wt%.

Comparative example 5

Compared with the example 1, the difference is that the nonionic surfactant is not added, and specifically comprises the following components:

Taking 1g of the precursor, grinding the precursor, 1g of magnesium powder and 10g of sodium chloride powder to be uniformly mixed, sealing the mixture in a stainless steel reactor, heating the mixture to 350 ℃ at a heating rate of 3 ℃/min in a horizontally placed tube furnace under the atmosphere of argon, preserving the heat for 2 hours, then heating the mixture to 700 ℃, preserving the heat for 5 hours, and naturally cooling the mixture; immersing the reaction product in 2mol/L hydrochloric acid, stirring for 6h, and treating with 5% HF acid for 30min after separation; and finally, washing with ethanol and water, separating and drying to obtain the boron-doped porous silicon material.

And assembling the negative plate into a CR2032 type lithium ion button cell, and detecting the electrochemical performance at a voltage range of 0.01-1.2V at room temperature, wherein the charge-discharge test current density is 200 mA/g. The first reversible capacity is 1160mAh/g, the coulombic efficiency is 79 percent, and the capacity retention rate is 63 percent after 100 cycles. After the 10 th complete discharge (delithiation), the residual lithium content in the active material in the test electrode was 0.12 wt%, and the content of inert Li-B-Si clusters not participating in the reaction was calculated to be 0.8 wt%.

Comparative example 6

Compared with the embodiment 1, the difference is that boron is not adopted, and other elements are adopted for doping, specifically:

according to the mass ratio of the element boron to the silicon in the compound as 1: 5 dissolving phosphoric acid and ethyl orthosilicate in ethanol with the volume 10 times that of the mixture, uniformly stirring the mixture for 10min, adding 0.06mol/L hydrochloric acid solution with the relative total volume of 0.5, uniformly stirring the mixture for 3h at the temperature of 60 ℃, and cooling the mixture to room temperature; then, mixing the components in a volume ratio of 1: 1, adding a mixed solution of ammonia water, deionized water and absolute ethyl alcohol (the volume ratio is 1: 2: 3), stirring and reacting for 3 hours at room temperature, carrying out solid-liquid separation, repeatedly washing the obtained precipitate with ethanol and water, and separating and drying to obtain a precursor.

1g of the precursor is taken, ground with 1g of magnesium powder, 10g of sodium chloride powder and 0.05g of polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer (P123) to be uniformly mixed, sealed in a stainless steel reactor, heated to 350 ℃ at a heating rate of 3 ℃/min in a horizontally placed tube furnace under the argon atmosphere, kept for 2h, then heated to 700 ℃, kept for 5h and then naturally cooled; immersing the reaction product in 2mol/L hydrochloric acid, stirring for 6h, and treating with 5% HF acid for 30min after separation; and finally, washing with ethanol and water, separating and drying to obtain the phosphorus-doped porous silicon material.

And assembling the negative plate into a CR2032 type lithium ion button cell, and detecting the electrochemical performance at a voltage range of 0.01-1.2V at room temperature, wherein the charge-discharge test current density is 200 mA/g. Recording the first reversible capacity of 920mAh/g, the coulombic efficiency of 80 percent and the capacity retention rate of 67 percent after 100 times of circulation.

Comparative example 7

Compared with the embodiment 1, the difference is that the doping content of the B element is not in a specific range, specifically:

according to the mass ratio of the element boron to the silicon in the compound as 1: 25 dissolving boric acid and ethyl orthosilicate in ethanol with the volume 10 times that of the boric acid and ethyl orthosilicate, uniformly stirring for 10min, adding 0.06mol/L hydrochloric acid solution with the relative total volume of 0.5, uniformly stirring for 3h at 60 ℃, and cooling to room temperature; then, mixing the components in a volume ratio of 1: 1, adding a mixed solution of ammonia water, deionized water and absolute ethyl alcohol (the volume ratio is 1: 2: 3), stirring and reacting for 3 hours at room temperature, carrying out solid-liquid separation, repeatedly washing the obtained precipitate with ethanol and water, and separating and drying to obtain a precursor.

Mixing the obtained porous silicon material with conductive carbon black and sodium alginate according to the mass ratio of 6: 2: 2, uniformly mixing, preparing slurry by taking deionized water as a solvent, coating the slurry on a copper foil, and drying to prepare a lithium ion battery negative electrode plate; a lithium foil with the thickness of 0.05mm is closely attached to a silicon negative electrode sheet wetted by a lithium-containing organic electrolyte, and the electrolyte consists of 1mol/L lithium hexafluorophosphate, ethylene carbonate and diethyl carbonate (the volume ratio of the solvent is 1: 1); and mechanically pressing under 20MPa in an inert atmosphere (the water and oxygen content are less than 1ppm) with controlled moisture, and lithiating for 50 hours to obtain the lithium-boron-silicon alloy negative plate. The mass content of boron in the lithium borosilicate alloy is 0.06 percent by adopting ICP-AES test.

Assembling the lithium borosilicate alloy negative plate into a CR2032 type lithium ion button cell, and detecting the electrochemical performance at room temperature in a voltage range of 0.01-1.2V, wherein the current density of a charge and discharge test is 200 mA/g. The first reversible capacity was recorded as 1380mAh/g, the coulombic efficiency as 81%, and the capacity retention after 100 cycles as 72%. After the 10 th complete discharge (delithiation), the residual lithium content in the active material in the test electrode was less than 0.1 wt%, and the content of inert Li-B-Si clusters not participating in the reaction was calculated to be less than 0.6 wt%.

Claims

1. The lithium borosilicate alloy cathode active material of the lithium secondary battery is characterized by comprising a porous silicon framework, and active lithium and Li-B-Si clusters which are compounded in the porous silicon framework and exist in an alloy form.

2. The lithium borosilicate alloy negative active material for lithium secondary battery according to claim 1, wherein said negative active material comprises a mixture of a lithium borosilicate alloy and a boron silicateThe porous silicon skeleton has a nano porous structure which is a mesoporous cross-linked structure, the average pore diameter is 2-50 nm, and the specific surface area is 10-200 m²g^-1。

3. The lithium borosilicate alloy negative active material for a lithium secondary battery according to claim 2, wherein the mass ratio of Li to Si is 1 (1 to 100) and the mass ratio of Li to B is 1 (0.1 to 2).

4. The lithium borosilicate alloy negative electrode active material for a lithium secondary battery according to claim 1, wherein the mass content of the Li-B-Si cluster is 1 to 20%.

5. A method for preparing the lithium borosilicate alloy negative active material of the lithium secondary battery as claimed in any one of claims 1 to 4, which comprises the following steps:

the metal M is a metal capable of reducing silicon oxide; the metal N is alkali metal and/or alkaline earth metal;

6. The method for preparing the boron-doped porous silicon skeleton of the lithium secondary battery as claimed in claim 5, wherein the liquid silicon source is one or more of sodium silicate, potassium silicate, ethyl orthosilicate and methyl orthosilicate;

preferably, the boron-containing compound is one or more of boric acid, sodium borate and borax;

preferably, the weight ratio of boron to silicon in the boron-containing compound and the liquid silicon source is (1-50): 100;

7. The method for preparing the boron-doped porous silicon framework of the lithium secondary battery as claimed in claim 5, wherein the metal M reducing agent is one or more of potassium, calcium, sodium, magnesium and aluminum;

the salt of the metal N is a chloride salt of the metal N; preferably, the salt of the metal N is selected from one or more of lithium chloride, sodium chloride and potassium chloride; the alkaline earth metal chloride is selected from one or more of magnesium chloride, calcium chloride and barium chloride;

preferably, the mass ratio of the metal N salt to the precursor is (1-20): 1;

preferably, the mass ratio of the metal M reducing agent to the precursor is (0.5-2): 1;

preferably, the nonionic surfactant is selected from one or more of polyoxyethylene polyoxypropylene ether block copolymer, polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer and sodium polyacrylate;

preferably, the mass ratio of the nonionic surfactant to the precursor is (0.01-0.1): 1;

preferably, the chemical modifier is hydrofluoric acid or alkali liquor;

8. The lithium borosilicate alloy negative electrode of the lithium secondary battery is characterized by comprising a current collector and a negative electrode material compounded on the surface of the current collector, wherein the negative electrode material comprises a conductive agent and a binder; the lithium borosilicate alloy anode active material prepared by the preparation method of any one of claims 1 to 4 or the lithium borosilicate alloy anode active material prepared by the preparation method of any one of claims 5 to 7 is further included.

9. The method of making a lithium borosilicate alloy negative electrode for a lithium secondary battery as claimed in claim 8, comprising the steps of:

step (a): obtaining the boron-doped porous silicon skeleton by adopting the steps (1) and (2) of the preparation method of any one of claims 5 to 7;

step (b): slurrying the boron-doped porous silicon skeleton, the conductive agent and the binder, compounding the slurried boron-doped porous silicon skeleton, the conductive agent and the binder on the surface of a current collector, drying the slurried boron-doped porous silicon skeleton and the slurry to obtain a silicon negative electrode sheet precursor, embedding lithium into the silicon negative electrode sheet precursor, and carrying out lithiation reaction to obtain the lithium borosilicate alloy negative electrode;

preferably, lithium is inserted into the boron-doped porous silicon framework by adopting a physical lithium insertion alloying or electrochemical lithium insertion alloying method, and lithiation reaction is carried out;

preferably: the physical lithium-embedding alloying method is that metal lithium powder is scraped or lithium foil is clung to the silicon negative plate precursor wetted by lithium-containing organic electrolyte, and mechanical pressing is carried out;

10. A lithium secondary battery, characterized in that its negative electrode comprises the lithium borosilicate alloy negative electrode active material according to any one of claims 1 to 4, or the lithium borosilicate alloy negative electrode active material prepared by the preparation method according to any one of claims 5 to 7;

preferably, the negative electrode is the lithium borosilicate alloy negative electrode according to claim 8 or the lithium borosilicate alloy negative electrode prepared by the preparation method according to claim 9.