CN112103480A - Treatment method of pre-lithiated SiOx negative electrode material - Google Patents

Treatment method of pre-lithiated SiOx negative electrode material Download PDF

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CN112103480A
CN112103480A CN202010813573.1A CN202010813573A CN112103480A CN 112103480 A CN112103480 A CN 112103480A CN 202010813573 A CN202010813573 A CN 202010813573A CN 112103480 A CN112103480 A CN 112103480A
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negative electrode
electrode material
lithiated
siox
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CN112103480B (en
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陈鹏
褚春波
张耀
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Xinwangda Power Technology Co ltd
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Sunwoda Electric Vehicle Battery Co Ltd
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H01M4/366—Composites as layered products
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
    • H01M10/4235—Safety or regulating additives or arrangements in electrodes, separators or electrolyte
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/483—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides for non-aqueous cells
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/027—Negative electrodes
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Abstract

The invention relates to a processing method of a pre-lithiated SiOx negative electrode material. A method of treating a pre-lithiated SiOx negative electrode material, comprising the steps of: mixing the pre-lithiated SiOx negative electrode material with a first solid compound to obtain a first mixture, wherein X is more than 0 and less than 2, and the first solid compound is selected from at least one of ammonium fluoride and ammonium phosphate; and under the atmosphere of protective gas, carrying out heat preservation sintering on the first mixture at the temperature of 50-300 ℃ to obtain a first pre-lithium silicon negative electrode material. The processing method of the pre-lithiated SiOx negative electrode material can improve the stability of the pre-lithiated SiOx negative electrode material.

Description

Treatment method of pre-lithiated SiOx negative electrode material
Technical Field
The invention relates to the technical field of batteries, in particular to a method for processing a pre-lithiated SiOx negative electrode material.
Background
Along with the requirement of people on the endurance mileage of the electric automobile, the energy density of a battery system of a passenger car needs to be continuously improved, and the traditional graphite cathode can not meet the energy density requirement of the current power battery. The silicon-based negative electrode has higher gram capacity, so the silicon-based negative electrode becomes an important research material.
Compared with pure Si cathode, silicon oxide SiOxThe material has higher gram capacity, lower expansion and better cycle life, and is considered as the next generation cathode material. However, conventional silicon oxide compounds SiOxThe problem of low first effect seriously restricts the commercial application of the silicon oxide compound, and the first effect of the silicon oxide compound is improved at present mainly by two modes, namely pole piece end design and lithium supplement and extraction through the pole piece endThe first effect is improved, one is to supplement lithium during the synthesis of the material end, and the first effect is improved. The metal lithium powder that lithium was adopted is mended to utmost point piece end exists detonation, explosion safety risk, and metal lithium powder all has the contact injury risk to operating personnel respiratory track, eyes and skin in addition. In contrast, end-of-material lithium supplementation may radically avoid the above-mentioned risks faced by cell manufacturers. However, the stability of the pre-lithiated SiOx negative electrode material formed by lithium-supplementing at the material end is poor.
Disclosure of Invention
Therefore, a method for processing the pre-lithiated SiOx negative electrode material is needed to obtain a pre-lithiated SiOx negative electrode material with better stability.
A method of treating a pre-lithiated SiOx negative electrode material, comprising the steps of:
mixing a pre-lithiated SiOx negative electrode material with a first solid compound to obtain a first mixture, wherein 0 & lt X & lt 2, and the first solid compound is selected from at least one of ammonium fluoride and ammonium phosphate;
and under the atmosphere of protective gas, carrying out heat preservation sintering on the first mixture at the temperature of 50-300 ℃ to obtain a first pre-lithium silicon negative electrode material.
According to the processing method of the pre-lithiated SiOx negative electrode material, the pre-lithiated SiOx negative electrode material is reacted with ammonium fluoride and/or ammonium phosphate at a high temperature, and alkaline substances such as lithium oxide and lithium hydroxide on the surface of the pre-lithiated SiOx negative electrode material are converted into LiF or lithium phosphate, so that the problem of the alkaline substances on the surface layer of the lithium SiOx negative electrode material is radically solved, and the stability of the pre-lithiated SiOx negative electrode material is improved; meanwhile, by controlling the using amount of the ammonium fluoride or the ammonium phosphate, an artificial inorganic SEI film is formed on the surface of the pre-lithiated SiOx negative electrode material, and the artificial SEI film is compact, controllable in thickness and hydrophobic, so that the dissolution rate of the lithium silicate of the inner core can be inhibited, and the stability of the pre-lithiated SiOx negative electrode material is improved.
In one embodiment, the mass ratio of the pre-lithiated SiOx negative electrode material to the first solid compound is 100:0.1 to 100: 10.
In one embodiment, in the step of sintering the first mixture at 50-300 ℃, the heating rate is 5-50 ℃/min, and the heat preservation time is 1-24 h.
In one embodiment, the pre-lithiated SiOx negative electrode material has a particle size of 1 μm to 10 μm.
In one embodiment, the carbon coating amount of the pre-lithiated SiOx negative electrode material is 0.1 wt% to 6 wt%.
In one embodiment, the step of sintering the first mixture at 50-300 ℃ under a thermal insulation condition to obtain the first pre-lithium silicon negative electrode material further comprises:
mixing the first pre-lithium silicon negative electrode material with a second solid compound to obtain a second mixture, wherein the second solid compound is at least one selected from nitrogen-containing organic matters and boron oxides;
and under the atmosphere of protective gas, carrying out heat preservation sintering on the second mixture at the temperature of 100-600 ℃ to obtain a second pre-lithium silicon negative electrode material.
In one embodiment, the mass ratio of the first pre-lithium silicon negative electrode material to the second solid compound is 100: 0.1-100: 6.
In one embodiment, in the step of sintering the second mixture at 100-600 ℃, the heating rate is 5-50 ℃/min, and the heat preservation time is 1-24 h.
In one embodiment, the step of sintering the second mixture at 100-600 ℃ under heat preservation specifically comprises: and carrying out heat preservation sintering on the second mixture at the temperature of 450-550 ℃.
In one embodiment, the nitrogen-containing organic compound is selected from at least one of fatty amine and aniline.
Detailed Description
The present invention may be embodied in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.
An embodiment of a method of treating a pre-lithiated SiOx negative electrode material, comprises the steps of:
step S110: the pre-lithiated SiOx negative electrode material is mixed with a first solid compound to obtain a first mixture.
Wherein, in SiOx, X is more than 0 and less than 2. Such as SiO.
Specifically, the first solid compound is at least one selected from ammonium fluoride and ammonium phosphate.
Further, the mass ratio of the pre-lithiated SiOx negative electrode material to the first solid compound is 100: 0.1-100: 10.
Specifically, the particle size of the pre-lithiated SiOx negative electrode material is 1 μm to 10 μm. The particle size is too small, the specific surface area is too large, the side reaction is too large, and the electrical property is deteriorated; the particle size is too large, the silicon cathode dynamics is influenced, and in addition, the large particles are slow in stress release, local stress concentration is caused, the interface is deteriorated, and the electrical property of the silicon cathode is deteriorated.
Specifically, the carbon coating amount of the pre-lithiated SiOx negative electrode material is 0.1 wt% -6 wt%. The coating effect cannot be achieved due to the excessively low carbon coating amount; too high, deteriorating the gram capacity and high temperature performance of the silicon negative electrode.
The silicate phase formed by pre-lithium on the inner core of the pre-lithiated SiOx negative electrode material has certain solubility in water, and the dissolution of the lithium silicate can cause the alkalinity of negative electrode slurry, deteriorate the stability of the negative electrode slurry and influence the coating of the negative electrode slurry; meanwhile, the surface layer of the pre-lithiated SiOx negative electrode material is provided with lithium oxide, lithium hydroxide and lithium carbonate which are formed after pre-lithiation, and the pre-lithiated SiOx negative electrode material is sensitive to air and presents strong basicity in water-based slurry, so that the stability of the negative electrode slurry is deteriorated. In addition, the pre-lithiated SiOx negative electrode material has high core activity, and can slowly react with deionized water in the negative electrode slurry to generate gas, so that the electrical property of the negative electrode material is deteriorated.
Among them, the pre-lithiated SiOx negative electrode material can be obtained by being purchased on the market or by being prepared. In this example, a pre-lithiated SiOx negative electrode material was obtained by preparation.
In one embodiment, the pre-lithiated SiOx negative electrode material is prepared by a method selected from one of a thermodynamic heating method, a wet doping method, and an electrochemical deposition method.
Specifically, the thermodynamic heating method is to react SiOx with metallic lithium or a lithium-containing compound by heating. Among them, the lithium-containing compound includes lithium oxide, lithium carbonate, lithium hydroxide, and the like.
Specifically, the wet doping method is to react SiOx with an organic solution containing metallic lithium at normal temperature.
Specifically, the electrochemical deposition method is to perform lithium deposition on the surface of SiOx.
Step S120: and under the atmosphere of protective gas, carrying out heat preservation sintering on the first mixture at the temperature of 50-300 ℃ to obtain a first pre-lithium silicon negative electrode material.
Further, the step of sintering the first mixture at 50-300 ℃ under heat preservation specifically comprises: and (3) carrying out heat preservation sintering on the first mixture at the temperature of 150-200 ℃. Specifically, the protective gas is nitrogen.
By adopting a solid heating decomposition method, an acidic substance generated by the first solid compound neutralizes an alkaline substance on the surface layer of the pre-lithiated SiOx negative electrode material, and a layer of LiF or Li with controllable thickness and ion conduction is formed on the surface layer of the pre-lithiated SiOx negative electrode material3PO4. By reasonably controlling the dosage of the solid compound, no additional solid waste slag is generated.
Further, in the step of sintering the first mixture at the temperature of 50-300 ℃, the heating rate is 5-50 ℃/min, and the heat preservation time is 1-24 h. The heating rate is 5 ℃/min to 50 ℃/min, the composition and the proportion of silicate crystal phase in the silicon negative electrode are influenced, and the electrochemical performance of the silicon negative electrode is improved; the heat preservation time is 1-24 h, the size of the silicon crystal grains of the inner core and the size of the silicate crystal grains are influenced, and the electrochemical performance of the silicon cathode is improved.
The step of sintering the first mixture at 50-300 ℃ to obtain the first pre-lithium silicon negative electrode material further includes:
step S130: and mixing the first pre-lithium silicon negative electrode material with a second solid compound to obtain a second mixture.
Wherein the second solid compound is at least one selected from nitrogen-containing organic substances and boron oxides. Further, the nitrogen-containing organic substance is selected from at least one of aliphatic amine and aniline to form a nitrogen-doped carbon coating layer. In one embodiment, the aniline is melamine.
In one embodiment, the oxide of boron is boron trioxide. So as to form a boron-doped carbon coating layer, improve the electrical conductivity of the silicon cathode and improve the cycle.
Further, the mass ratio of the first pre-lithium silicon negative electrode material to the second solid compound is 100: 0.1-100: 6. The content of the second solid compound is too low, so that the conductivity of the silicon cathode is improved to be limited, and the carbon coating effect cannot be realized; the content of the second solid compound is too high, which affects the gram capacity exertion of the silicon negative electrode and in addition deteriorates the high temperature performance.
Step S140: and (3) carrying out heat preservation sintering on the second mixture at the temperature of 100-600 ℃ in the atmosphere of protective gas to obtain a second pre-lithium silicon negative electrode material.
Further, the step of sintering the second mixture at 100-600 ℃ under heat preservation specifically comprises: and carrying out heat preservation sintering on the second mixture at the temperature of 450-550 ℃. Specifically, the protective gas is nitrogen.
Further, in the step of sintering the second mixture at the temperature of 100-600 ℃, the heating rate is 5-50 ℃/min, and the heat preservation time is 1-24 h. The heating rate is 5 ℃/min to 50 ℃/min, the composition and the proportion of silicate crystal phase in the silicon negative electrode are influenced, and the electrochemical performance of the silicon negative electrode is improved; the heat preservation time is 1-24 h, the size of the silicon crystal grains of the inner core and the size of the silicate crystal grains are influenced, and the electrochemical performance of the silicon cathode is improved.
Regulating and controlling the type of the core silicate crystalline phase of the pre-lithiated SiOx negative electrode material by controlling the heating temperature, the heating rate and the heat preservation time, namely, converting the lithium orthosilicate phase into the lithium metasilicate phase and the lithium disilicate phase; meanwhile, element doping is carried out on the inner core of the pre-lithiated SiOx negative electrode material, so that the intrinsic conductivity of the pre-lithiated silicon negative electrode is improved, and the processing performance and the electrochemical performance of the pre-lithiated silicon negative electrode are improved. Wherein, the element doping mainly refers to nitrogen element and boron element doping.
The processing method of the pre-lithiated SiOx negative electrode material at least has the following advantages:
1) according to the processing method of the pre-lithiated SiOx negative electrode material, the pre-lithiated SiOx negative electrode material is reacted with ammonium fluoride or ammonium phosphate at a high temperature, and alkaline substances such as lithium oxide and lithium hydroxide on the surface of the pre-lithiated SiOx negative electrode material are converted into LiF or lithium phosphate, so that the problem of the alkaline substances on the surface layer of the lithium SiOx negative electrode material is radically solved, and the stability of the pre-lithiated SiOx negative electrode material is improved; meanwhile, by controlling the using amount of the ammonium fluoride or the ammonium phosphate, a layer of artificial inorganic SEI is formed on the surface of the pre-lithiated SiOx negative electrode material, the artificial SEI is compact, the thickness is controllable and hydrophobic, the dissolution rate of the lithium silicate in the inner core can be inhibited, and the stability of the pre-lithiated SiOx negative electrode material is improved.
2) The processing method of the pre-lithiation SiOx negative electrode material forms a layer of artificial inorganic SEI on the surface of the pre-lithiation SiOx negative electrode material, and radically solves the problem of material processing caused by strong basicity on the surface of the pre-lithiation SiOx negative electrode material. In addition, the artificial SEI can reduce the first irreversible lithium consumption, and the artificial SEI is resistant to electrolyte corrosion, so that the first effect and the electrochemical properties of the pre-lithiated SiOx negative electrode material, such as cycle life and storage life, can be further improved.
3) The method for treating the pre-lithiated SiOx negative electrode material does not generate a large amount of industrial waste acid or waste water, does not form toxic organic waste liquid, and is environment-friendly.
4) According to the processing method of the pre-lithiation SiOx negative electrode material, the silicate crystal phase of the core of the pre-lithiation SiOx negative electrode material is regulated and controlled by controlling the heat treatment temperature and the heating rate, lithium orthosilicate with high water solubility is converted into lithium metasilicate or lithium disilicate with low water solubility, the dissolution of the lithium metasilicate phase is fundamentally inhibited, the dissolution rate of the lithium metasilicate is radically reduced, and the structural stability and the electrical conductivity of the pre-lithiation SiOx negative electrode material are improved; in addition, the lithium metasilicate phase is electrochemically inert, so that the side reaction of the material in the circulating process or high-temperature storage can be reduced, the structural stability of the material is maintained, and the method is beneficial to prolonging the circulating life of the material and improving the high-temperature storage performance.
In addition, when the silicate crystal phase is regulated and controlled by controlling the heat treatment temperature, a nitrogen-containing organic matter or a boron-containing compound with low decomposition temperature is added to form a nitrogen-doped pre-lithiated SiOx negative electrode material core or a boron-doped pre-lithiated SiOx negative electrode material core, so that the intrinsic electronic conductivity of the material is improved; in addition, the low decomposition temperature reduces the large growth risk of silicon crystal grains, improves the intrinsic electronic conductivity of the silicon cathode, improves the electrical property of the material and promotes the quick charge property of the material; meanwhile, a carbon coating protective layer is formed on the surface LiF outer core or the lithium phosphate outer core to form double-layer coating, so that the electrical property of the silicon-based negative electrode is improved.
5) The surface of the pre-lithiated SiOx negative electrode material is alkaline, and the material can react with water and carbon dioxide in the air irreversibly when stored at normal humidity, so that the performance of the material is deteriorated. The method comprises the steps of reacting a pre-lithiated SiOx negative electrode material with ammonium fluoride or ammonium phosphate at a high temperature, converting alkaline substances lithium oxide and lithium hydroxide on the surface of the pre-lithiated SiOx negative electrode material into LiF or lithium phosphate, radically solving the problem of the alkaline substances on the surface layer of the lithium SiOx negative electrode material, and forming a compact artificial inorganic protective layer on the surface layer, wherein the protective layer is hydrophobic, electrochemically stable, and stable to air, does not deteriorate the electrical property of the material when stored conventionally, and reduces the storage requirement of the pre-lithiated SiOx negative electrode material.
6) By the processing method of the pre-lithiated SiOx negative electrode material, the strong alkaline substances on the surface layer of the pre-lithiated SiOx negative electrode material are removed, and the pH value of the material is reduced, so that the alkalinity of the negative electrode slurry is reduced, the stability of the negative electrode slurry is improved, the processability of the negative electrode slurry is improved, the excellent rate of a negative electrode plate is improved, and the manufacturing cost of a battery cell is reduced. In addition, compared with alkaline slurry, the neutral slurry has lower corrosion to the pipeline of the equipment.
The following are specific examples:
example 1
The treatment method of the prelithiated SiOx negative electrode material of this example is as follows:
1) 100g of 6 μm SiO with 10g of Li2O mechanical ball milling and mixing for 3h, and then roasting for 2h at 500 ℃ under the protection of nitrogen in an inert atmosphere to obtain a pre-lithiated SiOx negative electrode material, which is recorded as a sample S1;
taking S1100 g with the particle size of 6 μm and the carbon coating amount of 3 wt%, taking NH4F 5g，Stirring for 1h at room temperature, uniformly mixing, then placing the mixed sample in a tubular furnace, introducing nitrogen at a nitrogen introduction rate of 50mL/min, starting heating to 190 ℃ after introducing nitrogen for half an hour, controlling the temperature rise rate at 30 ℃/min, keeping the temperature for 0.5h after raising the temperature to 190 ℃, grinding and screening the obtained powder, and finally obtaining a pre-lithiation SiOx negative electrode material with a surface coated with a layer of LiF, wherein the sample is marked as D1.
Example 2
The treatment method of the prelithiated SiOx negative electrode material of this example is as follows:
mixing 10g of biphenyl with 100g of tetrahydrofuran, then adding 0.5g of metal lithium powder to obtain an organic solution containing metal lithium, then adding 10g of 6-micron SiO, stirring for 12 hours, filtering, and washing with tetrahydrofuran to obtain a pre-lithiated SiOx negative electrode material, wherein the sample is marked as S2;
taking S2100 g with particle size of 6 μm and carbon coating amount of 3 wt%, taking NH4And F5 g, stirring for 1h at room temperature, uniformly mixing, then placing the mixed sample in a tube furnace, introducing nitrogen at a nitrogen introduction rate of 50mL/min, starting heating to 190 ℃ after introducing nitrogen for half an hour, controlling the heating rate at 30 ℃/min, keeping the temperature for 0.5h after heating to 190 ℃, grinding and screening the obtained powder, and finally obtaining the pre-lithiated SiOx negative electrode material with the surface coated with a layer of LiF, wherein the sample is marked as D2.
Example 3
The treatment method of the prelithiated SiOx negative electrode material of this example is as follows:
mixing 100g of 6-micron SiO negative electrode and 5g of metal lithium powder, adding 100g of electrolyte, and standing at normal temperature for 12 hours to obtain a pre-lithiated SiOx negative electrode material, wherein the sample S3 is obtained, the solute of the electrolyte is 1.2mol/L lithium hexafluorophosphate, and the solvent is ethylene carbonate EC;
taking S3100 g with particle size of 6 μm and carbon coating amount of 3 wt%, taking NH4F5 g, stirring for 1h at room temperature, uniformly mixing, then placing the mixed sample in a tube furnace, introducing nitrogen at a nitrogen introduction rate of 50mL/min, starting heating to 190 ℃ after introducing nitrogen for half an hour, controlling the heating rate at 30 ℃/min, keeping the temperature for 0.5h after heating to 190 ℃, and grinding and screening the obtained powderAnd finally obtaining the pre-lithiated SiOx negative electrode material with the surface coated with one layer of LiF, and marking as a sample D3.
Example 4
The method of treating the prelithiated SiOx negative electrode material of this example was substantially the same as the method of treating the prelithiated SiOx negative electrode material of example 1, except that NH was used4Replacement of F with ammonium phosphate (NH)4)3PO4And the sample is recorded as D4.
Example 5
The method of treating the prelithiated SiOx negative electrode material of this example was substantially the same as the method of treating the prelithiated SiOx negative electrode material of example 2, except that NH was used4Replacement of F with ammonium phosphate (NH)4)3PO4And the sample is recorded as D5.
Example 6
The method of treating the prelithiated SiOx negative electrode material of this example was substantially the same as the method of treating the prelithiated SiOx negative electrode material of example 3, except that NH was used4Replacement of F with ammonium phosphate (NH)4)3PO4And the sample is recorded as D6.
Example 7
The treatment method of the prelithiated SiOx negative electrode material of this example is as follows:
taking 100g of the D1 sample in example 1, taking 10g of the melamine sample, stirring for 1h, uniformly mixing, then placing the mixed sample in a tube furnace, introducing nitrogen at a nitrogen introduction rate of 50mL/min, starting heating to 190 ℃ after introducing nitrogen for half an hour, controlling the heating rate at 5 ℃/min, heating to 600 ℃, preserving heat for 8h, grinding and screening the obtained powder, and finally obtaining the nitrogen-doped and surface layer second layer carbon-coated pre-lithiated SiOx negative electrode material, which is recorded as D7.
Example 8
The treatment method of the prelithiated SiOx negative electrode material of this example is as follows:
taking 100g of the D1 sample in example 1, taking 20g of the melamine sample, stirring for 1h, uniformly mixing, then placing the mixed sample in a tube furnace, introducing nitrogen at a nitrogen introduction rate of 50mL/min, starting heating to 190 ℃ after introducing nitrogen for half an hour, controlling the heating rate at 5 ℃/min, heating to 600 ℃, preserving heat for 8h, grinding and screening the obtained powder, and finally obtaining the nitrogen-doped and surface layer second layer carbon-coated pre-lithiated SiOx negative electrode material, which is recorded as D8.
Example 9
The treatment method of the prelithiated SiOx negative electrode material of this example is as follows:
taking 100g of the D1 sample in example 1, taking 20g of the melamine sample, stirring for 1h, uniformly mixing, then placing the mixed sample in a tube furnace, introducing nitrogen at a nitrogen introduction rate of 50mL/min, starting heating to 190 ℃ after introducing nitrogen for half an hour, controlling the heating rate at 5 ℃/min, heating to 500 ℃, preserving heat for 8h, grinding and screening the obtained powder, and finally obtaining the nitrogen-doped and surface layer second layer carbon-coated pre-lithiated SiOx negative electrode material, which is recorded as D9.
Example 10
The treatment method of the prelithiated SiOx negative electrode material of this example is as follows:
taking 100g of the D1 sample in example 1, taking 20g of the melamine sample, stirring for 1h, uniformly mixing, then placing the mixed sample in a tube furnace, introducing nitrogen at a nitrogen introduction rate of 50mL/min, starting heating to 190 ℃ after introducing nitrogen for half an hour, controlling the heating rate at 5 ℃/min, raising the temperature to 560 ℃, preserving heat for 8h, grinding and screening the obtained powder, and finally obtaining the nitrogen-doped and surface layer second layer carbon-coated pre-lithiated SiOx negative electrode material, which is recorded as D10.
Example 11
The treatment method of the prelithiated SiOx negative electrode material of this example is as follows:
taking 100g of the D1 sample in example 1, taking 20g of the melamine sample, stirring for 1h, uniformly mixing, then placing the mixed sample in a tube furnace, introducing nitrogen at a nitrogen introduction rate of 50mL/min, starting heating to 190 ℃ after introducing nitrogen for half an hour, controlling the heating rate at 30 ℃/min, raising the temperature to 560 ℃, preserving heat for 8h, grinding and screening the obtained powder, and finally obtaining the nitrogen-doped and surface layer second layer carbon-coated pre-lithiated SiOx negative electrode material, which is recorded as D11.
Example 12
The treatment method of the prelithiated SiOx negative electrode material of this example is as follows:
taking 100g of the D1 sample in example 1, taking 20g of the melamine sample, stirring for 1h, uniformly mixing, then placing the mixed sample in a tube furnace, introducing nitrogen at a nitrogen introduction rate of 50mL/min, starting heating to 190 ℃ after introducing nitrogen for half an hour, controlling the heating rate at 30 ℃/min, raising the temperature to 560 ℃, preserving heat for 5h, grinding and screening the obtained powder, and finally obtaining the nitrogen-doped and surface layer second layer carbon-coated pre-lithiated SiOx negative electrode material, which is recorded as D12.
And (3) testing:
the pre-lithiated SiOx negative electrode materials prepared in examples 1 to 12 and S1, S2 and S3 were subjected to material pH, surface lithium carbonate and lithium hydroxide detection, recording the reaction time with water, and full electrical performance detection of soft packages of charging CR2032 and 3Ah, with the test results shown in table 1;
the button cell comprises a negative electrode, a conductive agent SP, a modified polyacrylic acid (93: 3: 4), an active substance, a pre-lithiated SiOx negative electrode material, a negative electrode gram capacity and a first effect which are charge capacity/discharge capacity are mainly tested;
the negative electrode of the soft package battery is prepared from an active substance, a conductive agent SP and modified polyacrylic acid (93: 3: 4), wherein the soft package battery mainly represents the cycle life and the negative electrode thickness expansion, and the active substance is composed of a 15% pre-lithiated SiOx negative electrode material and 85% artificial graphite.
1) The pH value of the material is tested according to the general rule of GB/T9724-;
2) the test of the lithium content, the lithium hydroxide content and the lithium carbonate content on the surface of the material refers to a general method for measuring the acidity and the alkalinity of GB/T9736-;
3) the powder resistance test refers to the carbon composite lithium iron phosphate anode material for GB/T30835-;
3) the reaction time t of the material with water is recorded: the time t for which 5g of the powder was added to 100mL of water when t was 0 was recorded and the occurrence of bubbles was observed.
4) First charge gram capacity and first effect test:
after the button cell is assembled, discharging: 0.2C DC to5mV, 0.1C DC to5mV, 0.05C DC to5mV, 0.02C DC to5mV, 0.01C DC to5mV, and the specific discharge capacity is recorded as Q1; charging: 0.1 CC to 2V, charge capacity is denoted as Q2; q2 is first charge gram capacity; the first effect of power-on is abbreviated as ICE, which is Q2/Q1.
5) Capacity retention rate test:
charging: 1C CC to 4.2V, Rest 10 min; discharging: 1C DC to 2.5V, Rest 0min, and discharge capacity denoted as Qn (n ═ 1,2,3 · · 200); thirdly, repeating the steps of firstly, secondly, 200 circles. The capacity retention rate of the full-electric 200-turn capacitor is as follows: Q200/Q1.
6) Volume expansion test:
circulating 200 circles of electric cores, disassembling at full power, with micrometer caliper thickness d2, fresh pole piece rolling thickness d1, full charge expansion calculation at full power 200 circles: (d2-d1)/(d 1-8).
7) Rate of capacity fade loss
Capacity fade loss ratio (pre-exposure capacity-post-exposure capacity)/pre-exposure capacity.
TABLE 1
Figure BDA0002631883520000131
Figure BDA0002631883520000141
From table 1, the pre-lithiated SiOx negative electrode material has no post-treatment process, has strong surface basicity and high pH, and causes decrease in gram volume and first effect due to storage in air. The capacity loss of the comparative examples 1-3 is 9% -10%, the capacity fading rate of the post-processed examples 1-12 is 0.1% -0.9%, the fading rate of the comparative examples is 10-1000 times of that of the examples, and obviously, the stability of the pre-lithiated SiOx negative electrode material is improved by the post-processing.
Through the surface treatment of ammonium fluoride or ammonium phosphate, the pH is reduced by 3 points, the surface alkaline substance lithium hydroxide is reduced to more than 80%, the lithium carbonate content is reduced by more than 90%, the stability in water is improved by more than 10 times, and the gas production starting time is prolonged by more than 10 times, which indicates that the pre-lithiated SiOx negative electrode material prepared in the examples 1-12 has better stability. In addition, a layer of artificial SEI is formed on the surface layer by the treatment of the ammonium fluoride or ammonium phosphate, so that the air stability is improved, and the first effect and the cycle life are improved.
From the data in Table 1, through heat treatment and nitrogen doping, the conductance of D7-D12 powder is improved, the pH value shows a reduction trend, and the alkali content in the surface layer is kept at a lower level without obvious change; the heat treatment regulates and controls the silicate phase of the inner core of the silicon cathode, the water resistance is improved, and the time for generating bubbles in water is prolonged by more than 2 times; the pH is reduced, the conductivity is improved, and silicate regulation and control are performed, so that the cycle life and the volume expansion of the pre-lithium silicon cathode are improved.
From D7-D8, the appropriate increase in the amount of nitrogen doping can increase the conductivity of the silicon cathode, thereby increasing the capacity performance and the cycle life.
From D8 to D10, too high a heat treatment temperature is disadvantageous in terms of cycle life and expansion, and proper temperature control improves cycle life.
From D10-D11, the temperature rise rate affects the crystalline phase of the silicon core, thereby affecting the water resistance of the silicon core, properly increasing the rate, more favorably converting the crystalline phase of the silicon core into silicate with strong water resistance, improving the water resistance of the silicon core, maintaining the structural stability of silicon in the circulating process and prolonging the circulating life of the silicon core due to the electrochemical inertia of the silicate with strong water resistance.
From D11-D12, the heat treatment time also influences the electrical performance of the pre-lithiated silicon negative electrode, and the proper time reduction is beneficial to prolonging the cycle life of the silicon negative electrode.
The technical features of the embodiments described above may be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the embodiments described above are not described, but should be considered as being within the scope of the present specification as long as there is no contradiction between the combinations of the technical features.
The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.

Claims (10)

1. A method of pre-lithiating a SiOx negative electrode material, comprising the steps of:
mixing a pre-lithiated SiOx negative electrode material with a first solid compound to obtain a first mixture, wherein 0 & lt X & lt 2, and the first solid compound is selected from at least one of ammonium fluoride and ammonium phosphate;
and under the atmosphere of protective gas, carrying out heat preservation sintering on the first mixture at the temperature of 50-300 ℃ to obtain a first pre-lithium silicon negative electrode material.
2. The method of claim 1, wherein a mass ratio of the pre-lithiated SiOx negative electrode material to the first solid compound is 100:0.1 to 100: 10.
3. The method for processing the pre-lithiated SiOx negative electrode material according to claim 1, wherein in the step of sintering the first mixture at a temperature of 50 ℃ to 300 ℃, the temperature increase rate is 5 ℃/min to 50 ℃/min, and the temperature keeping time is 1h to 24 h.
4. The method of treating a pre-lithiated SiOx negative electrode material of claim 1, wherein the pre-lithiated SiOx negative electrode material has a particle size of 1 μ ι η to 10 μ ι η.
5. The method of claim 1, wherein the carbon coating of the pre-lithiated SiOx negative electrode material is between 0.1 wt% and 6 wt%.
6. The method of claim 1, wherein the step of sintering the first mixture at 50-300 ℃ to obtain a first pre-lithiated SiOx negative electrode material is further followed by:
mixing the first pre-lithium silicon negative electrode material with a second solid compound to obtain a second mixture, wherein the second solid compound is at least one selected from nitrogen-containing organic matters and boron oxides;
and under the atmosphere of protective gas, carrying out heat preservation sintering on the second mixture at the temperature of 100-600 ℃ to obtain a second pre-lithium silicon negative electrode material.
7. The method for treating the pre-lithiated SiOx negative electrode material of claim 6, wherein a mass ratio of the first pre-lithiated silicon negative electrode material to the second solid compound is 100:0.1 to 100: 6.
8. The method for processing the pre-lithiated SiOx negative electrode material according to claim 6, wherein in the step of sintering the second mixture at a temperature of 100 ℃ to 600 ℃, the temperature increase rate is 5 ℃/min to 50 ℃/min, and the temperature keeping time is 1h to 24 h.
9. The method for treating the pre-lithiated SiOx negative electrode material according to claim 6, wherein the step of sintering the second mixture at 100 ℃ to 600 ℃ under a constant temperature is specifically as follows: and carrying out heat preservation sintering on the second mixture at the temperature of 450-550 ℃.
10. The method of treating the pre-lithiated SiOx negative electrode material of claim 6, wherein the nitrogen-containing organic compound is selected from at least one of an aliphatic amine and aniline.
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