CN113830771B

CN113830771B - Oxygen-pore double-gradual-change silicon oxide material and preparation and application thereof

Info

Publication number: CN113830771B
Application number: CN202111010358.9A
Authority: CN
Inventors: 周向清; 周昊辰; 王鹏; 周进辉
Original assignee: Hunan Chenyu Fuji New Energy Technology Co ltd
Current assignee: Hunan Chenyu Fuji New Energy Technology Co ltd
Priority date: 2021-08-31
Filing date: 2021-08-31
Publication date: 2023-07-11
Anticipated expiration: 2041-08-31
Also published as: CN113830771A

Abstract

The invention belongs to the technical field of battery cathode materials, and particularly discloses an oxygen-pore double-gradual change silicon oxide material which is a porous silicon oxide material with a pore structure and oxygen content in bidirectional gradual change distribution along the radial direction of material particles; wherein the oxygen content gradually decreases from inside to outside; the pore structure gradually increases from inside to outside. In addition, the invention also provides a preparation method of the material and application of the material in a battery cathode. The research of the invention discovers that the material with the special bidirectional gradient distribution structure has the characteristics of large reversible capacity, excellent multiplying power performance, high first efficiency, stable circulation and the like.

Description

Oxygen-pore double-gradual-change silicon oxide material and preparation and application thereof

Technical Field

The invention belongs to the technical field of lithium battery electrode materials, and particularly relates to a porous silica composite anode material with a radial gradual change structure and a preparation method thereof.

Background

When silicon is used as the negative electrode of the lithium ion battery, the silicon has the advantages of high theoretical capacity, good safety performance, wide sources and the like. However, silicon has a large volume expansion and low intrinsic conductivity during charge and discharge, resulting in poor cycle and rate performance of the battery. In the silicon compound, the theoretical specific capacity of silicon monoxide (SiO) is higher, and the SiO can react with lithium ions to generate an electrochemical inert matrix in the first charge and discharge process, so that the volume expansion problem is effectively relieved, and the cycle performance of the battery is improved. However, the high consumption of lithium ions also makes the first coulombic efficiency of silicon monoxide low. Therefore, in the field of silicon-based negative electrode materials, the technical emphasis and difficulty are focused on how to maintain the cycling stability of the silicon-based negative electrode and improve the first coulombic efficiency.

In general, the oxygen content (SiO _x X is more than 0 and less than 1), which is favorable for improving the first coulombic efficiency, and maintaining a certain oxygen content is favorable for improving the cycle stability, so that the accurate control of oxygen elements in the silicon-based negative electrode is particularly important, and the preparation of the silicon-based material with proper oxygen content and oxygen distribution is a key for obtaining the material with high capacity, high cycle stability and high coulombic efficiency. However, the technical difficulty in precisely controlling the oxygen content of silicon oxygen compounds is great, in particular in controlling the oxygen content to relatively low levels. The main reasons are that the reduction degree of the silicon oxide is difficult to control, the silicon oxide is easy to directly reduce into a silicon simple substance, the local heat is too large in the reduction process, and the sintering agglomeration of the reduction product is easy to cause. Furthermore, the distribution state of oxygen elements in individual particles has no relevant research report on the electrochemical performance effect of materials. On the other hand, the electron conductivity of the silicon oxide is lower than that of the silicon simple substance, so that the rate performance of the battery is reduced, and the porous structure is beneficial to shortening the electron and ion transmission paths and improving the reaction kinetics of the battery. Therefore, developing new oxygen content and distribution control techniques and particle porosification processes are important solutions to obtain high quality silicon oxide anode materials.

Disclosure of Invention

Aiming at overcoming the defects of the prior art, the invention solves the problems of poor cycle performance of a silicon anode material and low first coulombic efficiency of a silicon monoxide anode material, and the first aim of the invention is to provide an oxygen-hole double-gradual-change silicon oxide material with a radial gradual-change structure, which aims at improving the electrochemical performances such as first efficiency, cycle stability and the like.

The second aim of the invention is to provide the oxygen-hole double-gradual-change silicon oxide material with a radial gradual-change structure prepared by a low-temperature heat treatment-buffer etching combined method, and aims to obtain the negative electrode active material with large reversible capacity, excellent multiplying power performance, high first efficiency and cycle stability through a brand new preparation thought.

The third object of the invention is to provide the application of the oxygen-pore double gradual change silicon oxide material as a cathode active material.

A fourth object of the present invention is to provide a negative electrode material comprising the oxygen-pore double graded silica material and a lithium secondary battery.

An oxygen-pore double gradual change silicon oxide material is a porous silicon oxide material with a pore structure and oxygen content in a bidirectional gradual change distribution along the radial direction of material particles; wherein the oxygen content gradually decreases from inside to outside; the pore structure gradually increases from inside to outside.

The invention provides a new material of a bidirectional gradual change structure with gradually decreasing oxygen content from inside to outside and gradually increasing pore structure from inside to outside, and researches show that the material of the special bidirectional gradual change distribution structure has the characteristics of large reversible capacity, excellent rate performance, high first efficiency, stable circulation and the like.

In the invention, the chemical formula of the porous silica material is SiO _x X is more than 0 and less than 1. The gradual change distribution of the oxygen content refers to gradual decrease of the x value along the radial direction of the material particles from inside to outside.

Preferably, the mass percentage of the oxygen in the center of the particle ranges from 20 to 35%, the mass percentage of the oxygen in the surface ranges from 1 to 15%, and the total oxygen content ranges from 10 to 30%, preferably from 15 to 25%.

In the invention, the gradual distribution of the pore structure means that the pore content and the pore diameter are distributed radially.

In the invention, the pore structures are distributed radially and gradually decrease from outside to inside.

Preferably, the total specific surface area of the oxygen-pore double graded silica material is 50-200m ² Preferably 100 to 200m ² And/g. The average pore diameter is 1 to 100nm, preferably 10 to 50nm.

The oxygen-pore double gradual change silicon oxide material is micron-sized particles, preferably, the D50 is 1-30 mu m; further preferably 5 to 10. Mu.m.

The invention also provides a preparation method of the oxygen-pore double gradual change silicon oxide material; the method comprises the following steps:

step (1):

performing secondary heat treatment on the silicon monoxide fine powder in a reducing atmosphere to obtain a reduction product with gradually-distributed oxygen; wherein the temperature of the first-stage reduction is 300-400 ℃; the temperature of the second-stage reduction is 500-900 ℃;

step (2):

placing the reduction product in a buffer etching solution for buffer etching;

the buffer etching solution is a buffer solution containing fluorine source, weak acid and weak base salt;

step (3):

go to step (2): adding a metal salt dispersion liquid into the buffer etching system, mixing to obtain a base liquid, and then adding an oxidant and an organic matter into the base liquid under stirring to perform pore-forming etching;

step (4):

and (3) after the reaction is finished, carrying out solid-liquid separation, washing and drying to obtain the oxygen-pore double gradual change silicon oxide material.

In the prior art, silicon monoxide or silicon is generally adopted as a cathode active material for providing high capacity, and the silicon monoxide has stable circulation performance but low efficiency for the first time; silicon is first more efficient but has poor cycling stability. If the oxygen content in the silicon oxide is controlled to be low and has a proper distribution state, it is expected to obtain a silicon-based active material having stable cycle performance and high first efficiency. However, in the prior art, there is no thought or means for precisely controlling the oxygen content and distribution state in the silicon oxide, which is mainly because the reduction degree of the silicon oxide is difficult to control, and the silicon oxide is easily reduced into a simple substance of silicon directly. Therefore, the invention provides the cooperative process of two-stage reduction-buffer etching-metal catalytic etching, which innovatively carries out radial diffusion of oxygen through the heat treatment in the step (1), carries out radial distribution control of oxygen content by utilizing the etching speed difference of etching liquid on silicon oxides with different oxygen contents in the buffer etching environment in the step (2), and further carries out construction of a radial hole structure under the metal auxiliary effect in the step (3); according to the research of the invention, the cooperation of the two-stage reduction-buffer etching-metal catalytic etching process is further matched with the cooperative control of materials and conditions in each stage, so that the distribution state of oxygen content in a product along the radial direction of particles can be unexpectedly controlled, the radial porous structure of silicon oxide is realized, and the cooperation of the oxygen content and the pore structure which are radially distributed can be realized, so that the anode active material with excellent first-circle coulomb efficiency, high cycle stability and rate characteristics can be unexpectedly obtained.

In the present invention, the particle size of the fine powder of SiO is not particularly limited, and may be, for example, 30 μm or less; preferably less than or equal to 10mm; further preferably 5 to 10. Mu.m.

The silicon monoxide fine powder can be a direct commercial product, or can be obtained by crushing and crushing cheaper materials such as commercial silicon monoxide bulk materials.

In the invention, the two-stage reduction-buffer etching-metal catalytic etching process is combined and cooperated, and the further combined control of the processing conditions (such as a two-stage reduction mechanism, a buffer etching system, a metal etching system and a process) on the cooperated process is a key for successfully constructing the oxygen-hole bidirectional gradual change structure, improving the material capacity, the first-circle coulomb efficiency and the circulation stability.

In the invention, the two-stage heat treatment is innovatively adopted, so that oxygen elements in particles can be diffused from inside to outside, the oxygen content in the particles is lower, the oxygen content on the surfaces of the particles is higher, and then the buffer etching is further combined, the difference of etching speeds of etching liquid on silicon oxides with different oxygen contents is utilized to wash out the silicon oxides with high oxygen content on the surfaces of the particles, and the silicon oxides with low oxygen content in the particles are reserved, thereby effectively controlling the radial distribution of the oxygen content in the particles, and realizing the distribution state of decreasing the oxygen content from inside to outside.

Preferably, the reducing atmosphere is a hydrogen-containing atmosphere; preferably hydrogen, or a hydrogen-shielding gas mixture; the shielding gas is at least one of nitrogen and inert gas.

Further preferably, the content of hydrogen in the reducing atmosphere is 5 to 20% by volume; more preferably 10 to 20v%.

Preferably, the temperature of the primary reduction is 350 to 400 ℃.

Preferably, the temperature is raised to a first-stage reduction temperature at a heating rate of 2-5 ℃/min, and the heat preservation time of the first-stage reduction is preferably 2-4 h;

preferably, the temperature of the two-stage reduction is 700 to 900 ℃.

Preferably, the temperature is increased to a second-stage reduction temperature at a heating rate of 5-10 ℃/min; preferably, the time for the second reduction is 2-4 hours.

In the invention, a buffer etching mode is innovatively adopted, so that the material with the oxygen gradual change structure can be better constructed.

In the present invention, the solvent of the buffer solution is, for example, water.

Preferably, in step (2), the fluorine source is capable of ionizing F ^- Preferably HF, naF, KF, NH) ₄ F.

Preferably, the weak acid is an organic acid, more preferably a unit-ternary organic carboxylic acid; acetic acid is more preferable.

Preferably, the weak base salt is an ammonium ion salt; preferably at least one of ammonium fluoride, ammonium chloride, ammonium nitrate, ammonium sulfate.

Preferably, in the buffer etching solution, the mass concentration of the fluorine source is 5-30%, preferably 10-15wt.%; the mass concentration of weak acid is 5-20%; the mass concentration of the weak alkali salt is 1-15%, preferably 1-10wt.%, and more preferably 5-10%; the balance being a solvent such as water.

Preferably, the pH of the buffer etching solution is 2-6.

Preferably, the buffer etching solution is an aqueous solution for dissolving hydrofluoric acid, acetic acid and ammonium fluoride, wherein the mass percentage concentration of the hydrofluoric acid is 5-15 wt%, the mass percentage concentration of the acetic acid is 5-20 wt%, and the mass percentage concentration of the ammonium fluoride is 1-10 wt%; the balance being a solvent such as water.

Preferably, the solid-to-liquid ratio of the reduction product and the buffer etching solution is 0.01 to 0.5g/mL, more preferably 0.1 to 0.3g/mL;

preferably, the temperature of the buffer etching stage is not particularly required, and may be, for example, room temperature, preferably 20 to 30 ℃, and the reaction time is not particularly required, and may be, for example, 2 to 5 hours.

In the invention, the metal salt dispersion liquid containing organic matters is further added into the reaction system in the step (2), and the F and the oxidant are subjected to double-mechanism cooperative controllable etching under the assistance of two sections of organic matters and metal catalysis by matching with the oxidant and the organic matters which are input subsequently, so that the radial controllable holes of the silicon are facilitated, the oxygen gradual change distribution structure is facilitated to be maintained, and the performance of the prepared material is facilitated to be improved.

In the invention, in the step (3): the metal salt dispersion liquid is an aqueous solution in which metal salts and water-soluble organic matters are dissolved; preferably, the metal salt is a water-soluble salt of a metal ion capable of catalyzing silicon etching; preferably a water-soluble salt of at least one metal element of Ag, cu, au, ni, fe, pt; further preferred are nitrates of the metal ions;

preferably, the water-soluble organic matter is an organic solvent which can be miscible with water, preferably a C1-C4 unit or a polyol; further preferred is ethanol;

preferably, the concentration of the metal salt in the metal salt dispersion is in the range of 0.01 to 1mol/L, preferably 0.1 to 0.5mol/L; in the solvent of water-soluble organic matter and water, the weight percentage of the water-soluble organic matter is 1-50%, preferably 10-40%;

preferably, the volume ratio of the metal salt dispersion liquid to the buffer etching system in the step (2) is 1:10-1:1;

preferably, the oxidant is H ₂ O ₂ 、HNO ₃ 、KClO ₃ 、KMnO ₄ At least one of (a) and (b);

preferably, the organic matter is a water-miscible organic solvent, preferably a C1-C4 unit or a polyol; further preferred is ethanol;

preferably, the oxidant is 2-5% of the volume of the buffer etching system in the step (2), and the addition amount of the organic matters is 5-10% of the volume of the buffer etching system in the step (2);

preferably, the input speed of the oxidant and the organic matters to the base solution is 5-20mL/min;

preferably, the reaction temperature of the pore-forming treatment is not particularly limited, and may be, for example, 25 to 60℃and the reaction time may be adjusted as required, for example, 0.5 to 1 hour.

In the step (4), washing the solid obtained by solid-liquid separation with water, washing with acid, washing with water again to neutrality, recovering to obtain solid, and then drying and scattering to obtain the oxygen-pore double gradual change silicon oxide material;

preferably, the acid washing is a nitric acid solution washing.

step (a): crushing and crushing commercial silicon monoxide block materials serving as raw materials to reduce the particle size of the silicon monoxide block to below 30 mu m to obtain silicon monoxide fine powder;

step (b): performing two-stage heat treatment on the silicon monoxide fine powder in a reducing atmosphere; preferably, the second-stage heat treatment in the step (b) is to heat up to 300-400 ℃ at a heating rate of 2-5 ℃/min, keep the temperature for 2-4 hours, and continuously heat up to 500-900 ℃ at a heating rate of 5-10 ℃/min, and keep the temperature for 2-4 hours; the reducing atmosphere is preferably hydrogen-argon mixed gas, and the percentage content of hydrogen is 5-20%.

Step (c): carrying out buffer etching on the heat treatment product, wherein the etching solution comprises a mixed aqueous solution of hydrofluoric acid, acetic acid and ammonium fluoride, and stirring for reaction to obtain a dispersion liquid A; in the etching liquid component in the step (c), the mass percentage concentration of hydrofluoric acid is 5-15%, the mass percentage concentration of acetic acid is 5-20%, the mass percentage concentration of ammonium fluoride is 1-10%, the reaction temperature is 20-30 ℃ and the reaction time is 2-5 hours.

Step (d): adding a metal salt dispersion liquid into the dispersion liquid A, performing radial pore-forming etching, slowly adding hydrogen peroxide and ethanol in continuous stirring, and stirring for reaction to obtain a dispersion liquid B; preferably, the metal salt dispersion liquid in the step (d) is one or two organic dispersion liquid of silver nitrate and copper nitrate, and the concentration is 0.01-1mol/L; further preferably, the metal salt dispersion liquid is an organic dispersion liquid of silver nitrate, and the concentration is 0.1-0.5mol/L; the organic dispersion liquid is an aqueous solution of organic matters, the mass content of the organic matters is 1-50%, and the organic matters are one or more of methanol, ethanol and isopropanol; preferably, the rate of slowly adding hydrogen peroxide and ethanol in the step (d) is 5-20mL/min, the adding amount of the hydrogen peroxide is 2-5% relative to the volume of the dispersion liquid A, the adding amount of the ethanol is 5-10% relative to the volume of the dispersion liquid A, the reaction temperature is 25-60 ℃, and the reaction time is 0.5-1 hour.

Step (e): and (3) carrying out suction filtration on the dispersion liquid B to obtain powder slurry, then washing with water, pickling, washing with water again to neutrality, and carrying out filtration, drying and scattering to obtain the oxygen-pore double gradual change silicon oxide material. Preferably, nitric acid with the concentration of 1-5mol/L is used for pickling in the step (e), the washing time is more than 30min, deionized water is used for washing to be neutral, and then filtering, drying (drying) and crushing (scattering) are carried out, so that the product is obtained. The drying mode is preferably vacuum drying, the drying temperature is 60-105 ℃, and the drying time is 12-24 hours.

In the technical scheme of the invention, silicon monoxide is used as a raw material, and two-stage heat treatment under a reducing atmosphere is adopted to control the diffusion of oxygen elements in particles from inside to outside so as to form a material composition with low-oxygen-content silicon oxide inside and high-oxygen-content silicon oxide on the surface. And then deoxidizing from outside to inside by buffer etching and pore-forming from outside to inside by radial etching respectively. In the buffer etching step, the combination of hydrogen fluoride, acetic acid and ammonium fluoride is beneficial to stabilizing the etching reaction process, adjusting the etching reaction rate, controlling the etching depth and degree, and providing a flat surface for the next radial etching; and hydrogen peroxide and ethanol in the radial etching step are continuously added dropwise, so that the contact between metal and silicon can be effectively improved, and a uniformly distributed radial duct structure is obtained. And then filtering, drying, scattering and other conventional procedures in the field to finally form the porous silica powder material with the radial gradual oxygen content and the pore structure.

The breaking-up equipment can be selected from common breaking-up equipment including jaw crushers, cone crushers, hammer crushers, roller crushers, jet crushers, planetary ball mills, and the particle size of the broken-up material is in submicron to micron order.

The invention also provides application of the oxygen-pore double gradual change silicon oxide material serving as a negative electrode active material.

The application of the invention is preferably used as a negative electrode active material of a lithium secondary battery.

The preferred application is as a negative electrode active material for compounding with a conductive agent and a binder to prepare a negative electrode material. The conductive agent and the binder are all materials known in the industry.

In a further preferred application, the negative electrode material is applied to the surface of a negative electrode current collector to prepare a negative electrode. The negative electrode material of the present invention may be formed on the current collector by an existing conventional method, for example, by a coating method. The current collector is any material known in the industry.

In a further preferred application, the negative electrode and positive electrode, separator and electrolyte are assembled into a lithium secondary battery.

The invention also provides a lithium secondary battery cathode material, which comprises the oxygen-pore double gradual change silicon oxide material;

preferably, a conductive agent and a binder are also included.

The invention also provides a lithium secondary battery which comprises the oxygen-pore double gradual change silicon oxide material.

A preferred lithium secondary battery, wherein the negative electrode of the lithium secondary battery comprises the oxygen-pore double graded silica material.

The technical scheme of the invention has the beneficial effects that:

(1) The porous silica gradually decreases in oxygen content from the inside of the particles to the surface of the particles, the oxygen content in the center is close to that of silicon monoxide, the oxygen content in the surface is close to that of a silicon simple substance, and the distribution of oxygen elements can enable the material to have high structural stability in the process of charging and discharging, and stable SEI films are arranged on the outside, so that the cycling stability and the first coulombic efficiency of the battery are improved.

(2) The porous silica has rich pore canal structures in the particles, the pore canal is formed by metal ion etching reaction, the pore canal has a radial structure from the surface to the center, and the pore canal is matched with the radial distribution of oxygen content, so that electrolyte can be fully infiltrated into the particles, and the multiplying power performance of the battery is effectively improved.

(3) The porous silica negative electrode has the comprehensive electrochemical properties of high capacity, long service life, high initial coulombic efficiency and good multiplying power characteristic.

(4) The main raw materials of silicon monoxide and auxiliary materials are wide in sources and low in cost, and the adopted processes of crushing, heat treatment, wet etching and the like are simple and convenient, strong in operability, easy to realize large-scale production and good in practical prospect.

Drawings

Fig. 1: EXAMPLE 1 Cross-sectional scanning Electron micrograph of powder Material (product of step (1)) after heat treatment and oxygen element distribution

Fig. 2: scanning electron micrograph of oxygen-pore double graded silica Material in example 1

Fig. 3: EXAMPLE 1X-ray diffraction pattern of an oxygen-pore double graded silica material

Detailed Description

The following examples illustrate specific steps of the invention, but are not intended to limit the scope of the invention in any way. Various processes and methods not described in detail herein are conventional methods well known in the art.

In the following cases, unless specifically stated otherwise, the hydrogen peroxide is H ₂ O ₂ A solution with the mass content of 20-30%;

example 1

Step (1): silicon monoxide with an average particle size of 5mm is taken as a raw material, and silicon monoxide fine powder with an average particle size of 6 mu m is obtained through crushing and grinding. And (3) carrying out secondary heat treatment on the silicon monoxide fine powder in a hydrogen-argon reducing atmosphere containing 10% of hydrogen, heating to 350 ℃ at a heating rate of 3 ℃/min, preserving heat for 3 hours, continuously heating to 700 ℃ at a heating rate of 7 ℃/min, and preserving heat for 3 hours.

Step (2): and placing the obtained heat treatment product into etching solution and carrying out buffer etching for 3 hours at 25 ℃ to obtain dispersion liquid A, wherein the etching solution comprises 10wt.% of hydrofluoric acid, 10wt.% of acetic acid and 5wt.% of ammonium fluoride, and the solid-liquid ratio is 0.1g/ml.

Step (3): to the dispersion A, 0.2mol/L of an organic dispersion of silver nitrate (the organic dispersion is a mixed solution of ethanol and water, wherein the ethanol content is 20wt.% (based on the total weight of ethanol and water), and the addition amount of the organic dispersion is 1/5 of the volume of the dispersion A) was added. While stirring continuously, hydrogen peroxide accounting for 3% of the volume of the dispersion A and ethanol accounting for 6% of the volume of the dispersion A are slowly added at a speed of 10mL/min, and stirring reaction is carried out at 25 ℃ for 40min to obtain a dispersion B.

Step (4): and (3) carrying out suction filtration on the dispersion liquid B to obtain powder, then carrying out primary washing by using deionized water, washing by using 2mol/L nitric acid for 1 hour, finally washing to be neutral by using deionized water, filtering, carrying out vacuum drying at 80 ℃ for 20 hours, and scattering the material by using a jet mill to obtain the oxygen-pore double gradual change silicon oxide material.

Structural analysis:

the distribution of oxygen elements in the particles of the powder material after heat treatment is observed by adopting a double-beam scanning electron microscope energy spectrum, and the oxygen content of a region 10 is 28wt.%, the oxygen content of a region 11 is 39wt.%, and the oxygen content of a region 12 is 55wt.%, which shows that the oxygen elements realize gradual diffusion from inside to outside in radial direction after two-stage heat treatment; the oxygen content of the material after heat treatment was 36wt.% as measured by an oxygen nitrogen analyzer, and the oxygen content of the final product was 21wt.%; the oxygen content is effectively reduced through buffer etching; observing the appearance of the final product by adopting a scanning electron microscope, wherein the average particle diameter of particles is 6 mu m, and the surface of the particles is in a uniform porous honeycomb shape as shown in figure 2; detecting the final product phase by X-ray diffraction, wherein the main component of the powder comprises a silicon-oxygen compound with lower oxygen content as shown in figure 3; the nitrogen adsorption and desorption test is adopted to test the pore structure distribution, the average size of pore channels is 28nm, and the specific surface area is 163m ² /g。

Electrochemical performance measurement:

according to GB/T38823-2020, the porous silica (oxygen-pore double gradual change silica material) electrode is used as a working electrode, metal lithium is used as a negative electrode, and 1mol/L LiPF ₆ The EC/DEC (volume ratio 1:1) +FEC (5%) is electrolyte, the PE-PP composite film is diaphragm, the CR2025 button cell is assembled in a dry glove box filled with argon, electrochemical performance detection is carried out in a voltage interval of 0.005-1.5V at room temperature, and the charge-discharge test current density is 500mA/g. The first reversible capacity was recorded as 1820mAh/g, coulomb efficiency 85%, capacity retention after 100 cycles 90%.

Example 2

In step (1), the silicon monoxide fine powder was subjected to the second heat treatment in a reducing atmosphere of hydrogen-argon containing 5% of hydrogen, and the temperature was raised to 300℃at a heating rate of 2℃per minute, kept for 2 hours, and then raised to 500℃at a heating rate of 5℃per minute, and kept for 2 hours, which was different from example 1.

In this example, the average size of the sample pore canal is 23nm, and the specific surface area is 178m ² /g; oxygen content was 27wt.%. And assembling the silicon negative electrode plate into a lithium ion button cell, and detecting electrochemical performance at room temperature in a voltage range of 0.005-1.5V, wherein the charge-discharge test current density is 500mA/g. The first reversible capacity is 1630mAh/g, the coulomb efficiency is 79%, and the capacity retention rate is 93% after 100 times of circulation.

Example 3

In step (1), the silicon monoxide fine powder was subjected to the second heat treatment in a reducing atmosphere of argon hydrogen containing 20% of hydrogen, and the temperature was raised to 400℃at a temperature-raising rate of 5℃per minute, kept for 4 hours, and then raised to 900℃at a temperature-raising rate of 10℃per minute, and kept for 4 hours, which was different from example 1.

In this example, the average size of the sample pore canal is 35nm, and the specific surface area is 132m ² /g; oxygen content was 18wt.%. And assembling the silicon negative electrode plate into a lithium ion button cell, and detecting electrochemical performance at room temperature in a voltage range of 0.005-1.5V, wherein the charge-discharge test current density is 500mA/g. The first reversible capacity was recorded as 1950mAh/g, coulombic efficiency 87%, and capacity retention 85% after 100 cycles.

Example 4

The difference from example 1 is that the buffer etching system is different, and in step (2), the etching solution is a mixed aqueous solution of 5wt.% hydrofluoric acid, 5wt.% acetic acid, and 1wt.% ammonium fluoride. The etching temperature was 20℃and the time was 2 hours.

In this example, the average size of the sample pore canal is 19nm, and the specific surface area is 185m ² /g; oxygen content was 25wt.%. And assembling the silicon negative electrode plate into a lithium ion button cell, and detecting electrochemical performance at room temperature in a voltage range of 0.005-1.5V, wherein the charge-discharge test current density is 500mA/g. RecordingThe first reversible capacity is 1710mAh/g, the coulomb efficiency is 80%, and the capacity retention rate is 91% after 100 cycles.

Example 5

The difference from example 1 is that the buffer etching system is different, and in step (2), the etching solution is a mixed aqueous solution of 15wt.% hydrofluoric acid, 20wt.% acetic acid, and 10wt.% ammonium fluoride, and the etching temperature is 30 ℃ and the etching time is 5 hours.

In this example, the average size of the sample pore canal is 21nm, and the specific surface area is 180m ² /g; oxygen content was 20wt.%. And assembling the silicon negative electrode plate into a lithium ion button cell, and detecting electrochemical performance at room temperature in a voltage range of 0.005-1.5V, wherein the charge-discharge test current density is 500mA/g. The first reversible capacity is recorded to be 1860mAh/g, the coulomb efficiency is 85%, and the capacity retention rate is 90% after 100 times of circulation.

Example 6

Compared with example 1, the difference is only that the metal etching process is different, in the step (3), 0.5mol/L of silver nitrate organic dispersion liquid (the organic dispersion liquid is a mixed solution of ethanol and water, wherein the ethanol content is 30 wt.%) is added into the dispersion liquid A, the temperature of the system is controlled to be 60 ℃, and hydrogen peroxide accounting for 5% of the volume of the dispersion liquid A and 10% of ethanol are slowly added at a speed of 20mL/min in continuous stirring, and the dispersion liquid B is obtained after stirring and reacting for 1 hour. The other steps are the same as in example 1.

In this example, the average particle diameter of the sample particles was 6. Mu.m, the average pore size was 56nm, and the specific surface area was 79m ² /g; oxygen content was 17wt.%. And assembling the silicon negative electrode plate into a lithium ion button cell, and detecting electrochemical performance at room temperature in a voltage range of 0.005-1.5V, wherein the charge-discharge test current density is 500mA/g. The first reversible capacity was recorded as 2030mAh/g, coulomb efficiency was 84%, and capacity retention after 100 cycles was 83%.

Example 7

In step (3), an organic dispersion of 0.1mol/L copper nitrate (the organic dispersion is a mixed solution of isopropyl alcohol and water, wherein the isopropyl alcohol content is 10 wt.%) was added to the dispersion A, the temperature of the solution was controlled to 25℃and hydrogen peroxide and ethanol which account for 2% of the volume of the dispersion A were slowly added at a rate of 5mL/min with continuous stirring, and the reaction was carried out for 30 minutes to obtain a dispersion B, which was different from example 1 only in the metal etching process.

In this example, the average particle diameter of the sample particles was 6. Mu.m, the average pore size was 8nm, and the specific surface area was 102m ² /g; oxygen content was 22wt.%. And assembling the silicon negative electrode plate into a lithium ion button cell, and detecting electrochemical performance at room temperature in a voltage range of 0.005-1.5V, wherein the charge-discharge test current density is 500mA/g. The first reversible capacity is 1790mAh/g, the coulomb efficiency is 85%, and the capacity retention rate is 89% after 100 cycles.

Comparative example 1

The only difference compared to example 1 is that the heat treatment mechanism of step (1) is changed, i.e. a single-stage heat reduction treatment is used, and the other steps are the same as in example 1: the step (1) of the comparison case is as follows: silicon monoxide with an average particle size of 5mm is taken as a raw material, and silicon monoxide fine powder with an average particle size of 6 mu m is obtained through crushing and grinding. And (3) carrying out heat treatment on the silicon monoxide fine powder in a hydrogen-argon reducing atmosphere containing 10% of hydrogen, heating to 700 ℃ at a heating rate of 3 ℃/min, and preserving heat for 3 hours to obtain a heat treatment product. The subsequent procedure is as in example 1.

The electrochemical properties of the resulting material were measured as in example 1, and the measurement results were: the first reversible capacity is 1120mAh/g, the coulomb efficiency is 65%, and the capacity retention rate is 78% after 100 times of circulation.

Comparative example 2

The only difference compared to example 1 is that the heat treatment mechanism of step (1) is changed, and the other steps are the same as example 1: the step (1) of the present case is: and (3) carrying out two-stage heat treatment on the silicon monoxide fine powder in a hydrogen-argon reducing atmosphere containing 10% of hydrogen, heating to 500 ℃ at a heating rate of 3 ℃/min, preserving heat for 3 hours, and continuously heating to 1000 ℃ at a heating rate of 7 ℃/min, and preserving heat for 3 hours. The resulting heat-treated product was subjected to subsequent treatment in accordance with the procedure of example 1.

The electrochemical properties of the resulting material were measured as in example 1, and the measurement results were: the first reversible capacity is 1250mAh/g, the coulomb efficiency is 71%, and the capacity retention rate is 75% after 100 times of circulation.

Comparative example 3

The difference from example 1 is that buffer etching (changing the composition of the etching liquid) is not used in the step (2) and the other steps are the same as in example 1. The step (2) of the present case is: the resulting heat-treated product was subjected to buffer etching at 25℃for 3 hours, the etching solution composition was 15wt.% hydrofluoric acid solution (F-content was the same as in example 1), and the subsequent steps were the same as in example 1.

The electrochemical properties of the resulting material were measured as in example 1, and the measurement results were: the first reversible capacity is 1280mAh/g, the coulomb efficiency is 73%, and the capacity retention rate is 65% after 100 times of circulation.

Comparative example 4

The difference from example 1 is that the buffer etchant component ratio in step (2) is changed so as not to meet the requirement, and the other steps are the same as in example 1. The step (2) of the present case is: the etching solution was a mixed aqueous solution of 10wt.% hydrofluoric acid, 2wt.% acetic acid, and 0.5wt.% ammonium fluoride. The subsequent procedure is as in example 1.

The electrochemical properties of the resulting material were measured as in example 1, and the measurement results were: the first reversible capacity is 1020mAh/g, the coulomb efficiency is 72%, and the capacity retention rate is 67% after 100 times of circulation.

Comparative example 5

The difference compared with example 1 is that the radial etching of step (3) is not performed, and the other steps are the same as in example 1. In the case, the dispersion liquid A obtained in the step (2) is directly filtered to obtain powder, then the powder is subjected to preliminary washing by deionized water, the powder is washed by 2mol/L nitric acid for 1 hour, finally the powder is washed to be neutral by the deionized water, and the powder is filtered and dried in vacuum at 80 ℃ for 20 hours, and then the powder is scattered by an air flow pulverizer to obtain the silicon oxide material.

The electrochemical properties of the resulting material were measured as in example 1, and the measurement results were: the first reversible capacity is 890mAh/g, the coulomb efficiency is 67%, and the capacity retention rate is 80% after 100 times of circulation.

Comparative example 6

The difference compared to example 1 is only that the process conditions of the radial etching of step (3) are changed (the radial etching step does not use slow addition of ethanol for modification), and the other steps are the same as example 1. The step (3) of the present case is:

to the dispersion A, an organic dispersion of 0.2mol/L silver nitrate was added, and radial etching was performed at 25℃and the organic dispersion was a mixed solution of ethanol and water, wherein the ethanol content was 20wt.%. While stirring continuously, hydrogen peroxide accounting for 3% of the volume of the dispersion liquid A is slowly added at a speed of 10mL/min, and the mixture is stirred and reacted for 40min to obtain a dispersion liquid B. Dispersion B was treated as in example 1.

And (3) carrying out suction filtration on the dispersion liquid B to obtain powder slurry, then carrying out primary washing by using deionized water, washing by using 2mol/L nitric acid for 1 hour, finally washing to be neutral by using deionized water, filtering, carrying out vacuum drying at 80 ℃ for 20 hours, and scattering the materials by using a jet mill to obtain the silicon oxide material.

The electrochemical properties of the resulting material were measured as in example 1, and the measurement results were: the first reversible capacity is 990mAh/g, the coulomb efficiency is 70%, and the capacity retention rate is 76% after 100 cycles.

Claims

1. An oxygen-pore double gradual change silicon oxide material is characterized in that the porous silicon oxide material has a pore structure and oxygen content which are in bidirectional gradual change distribution along the radial direction of material particles; wherein the oxygen content gradually decreases from inside to outside; gradually increasing the pore structure from inside to outside;

the mass percentage of the oxygen in the center of the particle ranges from 20 to 35 percent, the mass percentage of the oxygen on the surface ranges from 1 to 15 percent, and the total oxygen content ranges from 10 to 30 percent;

total specific surface area of oxygen-pore double gradual change silicon oxide material 50-200m ² /g, average pore size of 1-100 nm;

the oxygen-pore double gradual change silicon oxide material is micron-sized particles.

2. The oxygen-porous double graded silica material of claim 1 wherein the oxygen-porous double graded silica material has a D50 of 1 to 30 μm.

3. The oxygen-porous double graded silica material of claim 1 wherein the oxygen-porous double graded silica material has a D50 of 5 to 10 μm.

4. A method for preparing the oxygen-pore double graded silica material according to any one of claims 1 to 3, comprising the steps of:

step (1):

step (2):

placing the reduction product in a buffer etching solution for buffer etching;

the buffer etching solution is a buffer solution containing fluorine source, weak acid and weak base salt; the fluorine source is HF, naF, KF, (NH) ₄ At least one of F; the weak acid is a unit-ternary organic carboxylic acid; the weak alkali salt is ammonium ion salt;

step (3):

adding a metal salt dispersion liquid into the buffer etching system in the step (2), mixing to obtain a base liquid, and then adding an oxidant and an organic matter into the base liquid under stirring to perform pore-forming etching; the metal salt is water soluble salt of at least one metal element in Ag, cu, au, fe, ni, pt; the oxidant is H ₂ O ₂ 、HNO ₃ 、KClO ₃ 、KMnO ₄ At least one of (a) and (b); the organic matter is C ₁ ~C ₄ A monohydric or polyhydric alcohol;

step (4):

5. The method for producing an oxygen-porous double graded silica material according to claim 4, wherein in the step (1), the particle size of the fine powder of SiO is 30 μm or less.

6. The method for producing an oxygen-pore double graded silica material according to claim 4, wherein the reducing atmosphere is an atmosphere containing hydrogen.

7. The method for producing an oxygen-pore double graded silica material according to claim 6, wherein the reducing atmosphere is hydrogen gas or a mixed atmosphere of hydrogen gas and a protective gas.

8. The method for producing an oxygen-pore double graded silica material according to claim 6, wherein the hydrogen gas content is 5 to 20% by volume in the reducing atmosphere.

9. The method for producing an oxygen-porous double graded silica material according to claim 4, wherein the temperature is raised to a first reduction temperature at a temperature-raising rate of 2 to 5 ℃/min.

10. The method for preparing an oxygen-pore double graded silica material according to claim 9, wherein the one-stage reduction heat preservation time is 2-4 hours.

11. The method for producing an oxygen-porous double graded silica material according to claim 4, wherein the temperature is raised to the two-stage reduction temperature at a temperature-raising rate of 5 to 10 ℃/min.

12. The method for preparing an oxygen-pore double graded silica material according to claim 11, wherein the second reduction time is 2 to 4 hours.

13. The method for preparing an oxygen-pore double graded silica material according to claim 4, wherein the weak acid is acetic acid.

14. The method for preparing an oxygen-pore double graded silica material according to claim 4, wherein the weak alkali salt is at least one of ammonium fluoride, ammonium chloride, ammonium nitrate, and ammonium sulfate.

15. The method for preparing an oxygen-pore double graded silica material according to claim 4, wherein the mass concentration of the fluorine source in the buffer etching solution is 5-30%; the mass concentration of weak acid is 5-20%; the mass concentration of the weak alkali salt is 1-15%.

16. The method for preparing an oxygen-pore double graded silica material according to claim 4, wherein the pH of the buffered etching solution is 2-6.

17. The method for preparing an oxygen-pore double graded silica material according to claim 16, wherein the buffer etching solution is an aqueous solution in which hydrofluoric acid, acetic acid and ammonium fluoride are dissolved, wherein the concentration of hydrofluoric acid is 5-15 wt%, the concentration of acetic acid is 5-20 wt%, and the concentration of ammonium fluoride is 1-10 wt%.

18. The method for preparing an oxygen-pore double graded silica material according to claim 4, wherein the solid-to-liquid ratio of the reduction product and the buffer etching solution is 0.01-0.5 g/mL.

19. The method for preparing an oxygen-pore double graded silica material according to claim 18, wherein the temperature of the buffer etching stage is 20-30 ℃ and the reaction time is 2-5 hours.

20. The method for preparing an oxygen-pore double graded silica material according to claim 4, wherein the metal salt is nitrate of at least one metal element of Ag, cu, au, fe, ni, pt.

21. The method for preparing an oxygen-pore double graded silica material according to claim 4, wherein the organic substance is ethanol.

22. The method for producing an oxygen-porous double graded silica material according to claim 4, wherein the concentration of the metal salt in the metal salt dispersion is 0.01 to 1mol/L.

23. The method for preparing an oxygen-pore double graded silica material according to claim 22, wherein the volume ratio of the metal salt dispersion liquid to the buffer etching system in the step (2) is 1:10-1:1.

24. The method for preparing an oxygen-pore double graded silica material according to claim 4, wherein the oxidant is 2-5% of the buffer etching system volume in the step (2), and the organic matter is added in an amount of 5-10% relative to the metal salt dispersion volume.

25. The method for preparing an oxygen-pore double graded silica material according to claim 24, wherein the input speed of the oxidizing agent and the organic matter to the base solution is 5-20mL/min.

26. The method for preparing an oxygen-pore double graded silica material according to claim 4, wherein the reaction temperature during the pore-forming treatment is 25-60 ℃ and the reaction time is 0.5-1 hour.

27. The method for producing an oxygen-pore double graded silica material according to claim 4, wherein in the step (4), the solid obtained by solid-liquid separation is washed with water, washed with acid, washed with water again to neutrality, recovered to obtain a solid, and then dried and scattered to obtain the oxygen-pore double graded silica material.

28. The method for preparing an oxygen-pore double graded silica material according to claim 27, wherein the acid washing is a nitric acid solution washing.

29. Use of the oxygen-pore double graded silica material according to any one of claims 1 to 3 or the oxygen-pore double graded silica material prepared by the preparation method according to any one of claims 4 to 28 as a negative electrode active material.

30. The use according to claim 29 as a negative electrode active material for lithium secondary batteries.

31. The use according to claim 30 as a negative electrode active material for compounding with a conductive agent, a binder to produce a negative electrode material.

32. The use according to claim 31, wherein the negative electrode material is applied to the surface of a negative electrode current collector to produce a negative electrode.

33. The use of claim 32, wherein the negative and positive electrodes, separator and electrolyte are assembled into a lithium secondary battery.

34. A negative electrode material for a lithium secondary battery, characterized by comprising the oxygen-pore double graded silica material according to any one of claims 1 to 3 or the oxygen-pore double graded silica material produced by the production method according to any one of claims 4 to 28.

35. The negative electrode material for a lithium secondary battery according to claim 34, further comprising a conductive agent and a binder.

36. A lithium secondary battery comprising the oxygen-pore double graded silica material according to any one of claims 1 to 3 or the oxygen-pore double graded silica material produced by the production method according to any one of claims 4 to 28.

37. The lithium secondary cell of claim 36, wherein the negative electrode comprises the oxygen-pore double graded silica material.

38. The lithium secondary battery according to claim 37, wherein the negative electrode material comprises the oxygen-pore double graded silica material.