Mixed conductor layer coated silicon monoxide negative electrode material and preparation method thereof

Abstract

The invention relates to a mixed conductor layer coated silicon monoxide negative electrode material, the material comprises a pre-lithiated SiOx material, the surface of the pre-lithiated SiOx material is provided with a coating layer, and the coating layer structure is an amorphous carbon layer in which lithium ion conduction active sites are uniformly dispersed. The preparation method of the material comprises the following steps: preparing a precursor-coated SiOx material: adding SiOx / C particles into a precursor solution, and adopting a coating process to obtain the precursor-coated SiOx material; preparing a chemical pre-lithiation agent solution; lithiation reduction: soaking the precursor coated SiOx material in a pre-lithiation agent solution, stirring for a period of time in an inert atmosphere, and then washing and drying to obtain a lithiated SiOx material; and heat treatment: calcining the lithiated SiOx material, and then carrying out heat preservation to obtain the mixed conductor layer coated pre-lithiated SiOx material.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to a mixed conductor layer-coated silicon monoxide negative electrode material and a preparation method thereof. Background Art

[0002] Silicon (Si) negative electrode materials are considered to be the most promising materials to replace traditional graphite negative electrodes because of their high theoretical specific capacity (4200mAh / g), environmental friendliness, and abundant reserves. However, Si undergoes a huge volume change (about 300%) during the lithium storage process, which leads to problems such as electrode pulverization, current collector shedding, and unstable SEI, which seriously restricts its commercialization process. SiOx negative electrode materials form inert lithium products (lithium silicate or lithium oxide) during the first lithium insertion reaction, which can buffer the volume expansion of the material during the charge and discharge process and improve the cycle stability of the material. Compared with single Si, the cycle stability of SiOx has been greatly improved. However, SiOx materials still have a certain volume expansion phenomenon during the charge and discharge process, resulting in unsatisfactory cycle performance. In addition, due to the generation of inert substances that consume part of the limited active lithium, the first coulomb efficiency of SiOx materials is low, affecting the energy density of the battery. Pre-lithiation technology can greatly improve the first coulomb efficiency of SiOx, thereby improving the energy density of the entire battery. Commonly used pre-lithiation technologies include electrochemical pre-lithiation, chemical pre-lithiation, direct contact pre-lithiation with lithium metal, and direct addition of pre-lithiation reagents.

[0003] At present, the improvement of the electrode reaction kinetics of SiOx materials after pre-lithiation has only improved the electronic conductivity of the materials, and there is a lack of research on the modification of lithium ion conductivity. Furthermore, in the existing research on improving both the electronic conductivity and lithium ion conductivity of pre-lithiation SiOx materials, not only is the process complicated, but the two components in the mixed conductive layer of electrons / ions are unevenly dispersed, which is not conducive to the synergistic improvement of electronic / ionic conductivity, resulting in poor electrochemical performance of the current pre-lithiation SiOx materials, especially poor rate and low temperature performance.

[0004] Patent CN113823772A discloses a double conductive layer coated pre-lithium SiOx material, wherein the inner coating layer is an electronic conductive coating layer and the outer coating layer is a lithium ion conductive coating layer. The double conductive layer not only has a significant effect on restricting the expansion of the SiOx material, but also can improve the electrode reaction kinetics of the pre-lithium SiOx material to a certain extent. However, the inner and outer double-layer structure of the electronic and ion conductive layers is not conducive to exerting the synergistic characteristics of the electronic / lithium ion conductors. The lithium conductivity in the electronic conductive layer is poor, or the electron conductivity in the ion conductive layer is poor, which restricts the improvement of the performance of the pre-lithium SiOx material.

[0005] Secondly, the gas production problem of existing pre-lithium SiOx materials is still serious and has not been well solved. The reason is that it is currently difficult to achieve continuous and uniform coating of pre-lithium SiOx materials to avoid direct contact with water during slurry adjustment. For example, patent CN105932224A discloses a modified silicon-based negative electrode material embedded with lithium ions. The preparation method is to use a lithium-aromatic hydrocarbon complex solution to pre-lithium a carbon-coated silicon-based oxide negative electrode material, thereby improving the first coulomb efficiency of the negative electrode material. However, the prepared material contains a large amount of residual alkaline substances such as LiOH and Li2CO3 on the surface of the exposed pre-lithium SiOx material, which leads to excessive alkalinity of the slurry during the slurry adjustment process, resulting in gas production, resulting in excessive porosity and resistance of the pole piece, and poor electrochemical performance.

[0006] Therefore, there is a need for a pre-lithium SiOx material with a mixed conductor surface coating having excellent electronic / ionic conductive properties. Summary of the invention

[0007] The present invention provides a mixed conductor layer coated silicon oxide negative electrode material, the material comprises a pre-lithium SiOx material, the surface of the pre-lithium SiOx material has a coating layer, and the coating layer structure is an amorphous carbon layer with lithium ion conductive active sites uniformly dispersed inside.

[0008] Furthermore, the lithium ion conductive active site comprises a fast lithium ion conductor or a material with a low lithium ion diffusion barrier, and the lithium ion conductivity of the fast lithium ion conductor is not less than 10 -7 S / cm, and the lithium ion diffusion barrier of the low lithium ion diffusion barrier material is not higher than 0.3 eV.

[0009] At the same time, the present invention provides a method for preparing a mixed conductor layer-coated silicon oxide negative electrode material, comprising the following steps:

[0010] Preparing a precursor-coated SiOx material: adding SiOx / C particles to a precursor solution and adopting a coating process to obtain a precursor-coated SiOx material;

[0011] Prepare chemical pre-lithium solution;

[0012] Lithiation reduction: The precursor-coated SiOx material is immersed in a pre-lithium solution, stirred for a certain period of time under an inert atmosphere, and then washed and dried to obtain a lithiated SiOx material;

[0013] Heat treatment: The lithiated SiOx material is calcined and then kept warm to obtain a mixed conductor layer coated pre-lithiated SiOx material.

[0014] Furthermore, for the selection of precursors, based on first principle calculations, the lowest unoccupied molecular orbital potential (LUMO) is selected to be lower than the HOMO value of the chemical pre-lithium agent, and the lithium reduction product contains a lithium compound, wherein the lithium ion conductivity of the lithium compound is not less than 10 -7 S / cm or the lithium ion diffusion barrier of its low lithium ion diffusion barrier material is not higher than 0.3eV.

[0015] Furthermore, the precursor includes one or more of the following substances:

[0016] a. After the lithium reduction reaction with the chemical pre-lithium agent, it can generate a lithium ion conductivity of not less than 10 -7 S / cm ionic conductor;

[0017] b. After the lithium reduction reaction with the chemical pre-lithium agent, a reduction product with a lithium ion diffusion barrier of no more than 0.3 eV can be generated;

[0018] c. After lithium reduction reaction with chemical pre-lithium agent, linear polymer can be generated;

[0019] d. After lithium reduction reaction with chemical pre-lithium agent, lithium ion conductor and linear polymer can be generated simultaneously.

[0020] Furthermore, the ion conductor is Li3PO4, Li3BO3 or LiAlO2.

[0021] Furthermore, the reduction product is LiF.

[0022] Furthermore, the coating process is a liquid phase coating process, and the liquid phase coating process is liquid phase mixing combined with rotary evaporation or liquid phase mixing combined with spray drying;

[0023] Alternatively, the coating process is a solid phase coating process, and the solid phase coating process is one of sand milling mixing, VC mixing, hot kneading, and mechanical fusion.

[0024] Furthermore, the chemical pre-lithium agent solution is prepared by using metallic lithium, aromatic hydrocarbons and solvents.

[0025] Furthermore, the aromatic hydrocarbon is selected from one or more of biphenyl-type aromatic compounds such as biphenyl and 4-methylbiphenyl, condensed ring aromatic hydrocarbons and their derivatives; the solvent is selected from one or more of ethylene glycol dimethyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, and tetrahydropyran.

[0026] The pre-lithium SiOx material of the present invention has a surface coating layer structure in which fast lithium ion conduction active sites are uniformly dispersed inside an amorphous carbon layer. The mixed conductor coating layer is beneficial to accelerating the conduction of electrons and lithium ions, improving the electrode reaction kinetics of the pre-lithium SiOx material, and improving the material rate performance. On the other hand, the continuous and uniform conductive coating layer not only effectively avoids direct contact between the pre-lithium SiOx and the electrolyte, thereby improving the material's resistance to electrolyte corrosion, but also helps to homogenize the surface current density and electrode reaction degree of the pre-lithium SiOx, eliminates the structural stress generated by uneven volume expansion, and improves the material's structure and cycle stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a schematic diagram of the structure of the mixed conductor layer coated silicon monoxide negative electrode material of the present invention;

[0028] Figure 2 This is the first charge and discharge curve of the silicon oxide negative electrode material before and after the mixed conductor layer is coated;

[0029] Figure 3 It is the cycling performance of silicon oxide negative electrode material before and after coating with mixed conductor layer. DETAILED DESCRIPTION

[0030] See also Figure 1 The pre-lithium SiOx material of the present invention has a surface coating layer structure in which fast lithium ion conduction active sites are uniformly dispersed inside an amorphous carbon layer. The mixed conductor coating layer is beneficial to accelerating the conduction of electrons and lithium ions, improving the electrode reaction kinetics of the pre-lithium SiOx material, and improving the material rate performance; on the other hand, the continuous and uniform conductive coating layer not only effectively avoids direct contact between the pre-lithium SiOx and the electrolyte, thereby improving the material's resistance to electrolyte corrosion, but also helps to homogenize the surface current density and electrode reaction degree of the pre-lithium SiOx, eliminate the structural stress caused by uneven volume expansion, and improve the material's structure and cycle stability.

[0031] The lithium ion conductive active sites include fast lithium ion conductors or materials with low lithium ion diffusion barrier, wherein the lithium ion conductivity of the fast lithium ion conductor is not less than 10 -7 S / cm, and the lithium ion diffusion barrier of the low lithium ion diffusion barrier material is not higher than 0.3 eV.

[0032] In order to realize the above structure, the main idea adopted by the present invention is: select a specific precursor to coat the SiOx material to obtain the precursor-coated SiOx material; then perform a pre-lithiation operation on the material, and during the pre-lithiation process, the precursor is in situ converted into a coating layer of "fast ion conductor + amorphous carbon", and finally a mixed conductor layer is obtained to continuously coat the pre-lithiation SiOx material.

[0033] Specifically, the present invention provides a method for manufacturing a pre-lithium SiOx material having a surface coating layer of a mixed conductor (capable of simultaneously conducting fast electrons and lithium ions) with excellent electronic and ionic conductivity, comprising the following steps:

[0034] S1: preparing precursor-coated SiOx material: adding SiOx / C particles to the precursor solution and adopting a coating process to obtain the precursor-coated SiOx material;

[0035] For the selection of precursors, based on first-principles calculations, lithium compounds with low lowest unoccupied molecular orbital potential (LUMO) and low ion migration activation energy in lithium reduction products are screened. Among them, LUMO is lower than the HOMO value of the chemical pre-lithium agent, and the lithium ion conductivity of the lithium compound is not less than 10 -7 S / cm, or the lithium ion diffusion barrier of its low lithium ion diffusion barrier material is not higher than 0.3eV.

[0036] Specifically, the precursor includes one or more of the following:

[0037] a. After the lithium reduction reaction with chemical pre-lithium agent, it can generate Li3PO4, Li3BO3 or LiAlO2 with high lithium ion conductivity (not less than 10 -7 S / cm) ion conductor;

[0038] b. After the lithium reduction reaction with the chemical pre-lithium agent, a reduction product such as LiF with a low lithium ion diffusion barrier (not higher than 0.3 eV) can be generated;

[0039] Higher lithium ion conductivity can effectively increase the transfer rate of lithium ions within SiOx particles and between particles, accelerating the electrode reaction kinetics; while lower lithium ion diffusion barriers can effectively prevent the local accumulation of lithium ions on the surface of particles and the formation of lithium dendrites, thereby improving battery safety performance.

[0040] c. After lithium reduction reaction with chemical pre-lithium agent, linear polymer can be generated;

[0041] d. After the lithium reduction reaction with the chemical pre-lithium agent, lithium ion conductors and linear polymers can be generated simultaneously;

[0042] The linear structure of the polymer molecules is conducive to a closer fit to the SiOx material, and during the calcination process, a carbon coating layer is formed that tightly wraps the pre-lithium SiOx material through a carbonization reaction.

[0043] The coating process is a liquid phase coating process or a solid phase coating process, which is determined by the specific precursor material. For soluble precursor materials, liquid phase coating is preferred, such as liquid phase mixing and stirring + rotary evaporation or liquid phase mixing and stirring + spray drying. For insoluble precursor materials, solid phase coating is preferred, such as sand milling, VC mixing, hot kneading, mechanical fusion, etc.

[0044] S2: preparing a chemical pre-lithium agent solution: the chemical pre-lithium agent solution has a half-wave potential of 0.02 to 1.5 V, preferably 0.05 to 0.6 V.

[0045] The chemical lithium agent solution is prepared from metallic lithium, aromatic hydrocarbons and solvents. The aromatic hydrocarbon substances include biphenyl, 4-methylbiphenyl and other biphenyl-type aromatic compounds, naphthalene, anthracene and other condensed ring aromatic hydrocarbons and their derivatives. Solvents include ethylene glycol dimethyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, tetrahydropyran and the like. The molar ratio of metallic lithium to aromatic hydrocarbons is 1:1 to 10, and the concentration of the lithium-aromatic hydrocarbon complex in the solvent after the complexation reaction is 0.2 to 3 mol / L.

[0046] S3: Lithiation reduction: The precursor-coated SiOx material is immersed in a pre-lithiation agent solution, stirred for a certain period of time under an inert atmosphere and a certain temperature, and then washed and dried to obtain a lithiated SiOx material.

[0047] By utilizing the strong reducing property of the chemical pre-lithiation agent, the SiOx material is subjected to a lithium reduction reaction. The reaction in this step is Li-AC+SiOx=Li-SiOx+AC, and the lithiated SiOx material can be obtained. At the same time, the lithium reduction will generate a mixed conductive coating layer. Here, AC represents an aromatic hydrocarbon substance.

[0048] Specifically, the stirring temperature ranges from 5 to 80° C., preferably from 20 to 50° C. The stirring time ranges from 1 to 50 hours, preferably from 5 to 25 hours. The washing method includes: high-speed centrifugal washing and suction filtration washing.

[0049] S4: Heat treatment: calcining the lithiated SiOx material and then keeping it warm to obtain a mixed conductor layer coated pre-lithiated SiOx material.

[0050] During the calcination process, the following reaction will occur: Li-SiOx = lithium silicate + Si, where lithium silicate includes Li2SiO3, Li2Si2O5, Li4SiO4, Li8SiO6, etc. At the same time, the polymer in the mixed conductive coating layer after reduction in step S3 is converted into carbon. The final material form is a pre-lithium SiOx material with a surface coating layer. The surface coating layer structure is an amorphous carbon layer with fast lithium ion conduction active points evenly dispersed inside. The mixed conductor coating layer is conducive to accelerating the conduction of electrons and lithium ions.

[0051] Specifically, during the heat treatment process, the environment is an inert gas atmosphere (such as argon) with a flow rate of 0.1 to 2 L / min; heating rate: 1 to 10°C / min, temperature: 600 to 1000°C, and insulation time 0.5 to 10 hours.

[0052] Several embodiments are given below to explain the preparation method in detail:

[0053] Embodiment 1:

[0054] Fluorinated ethylene carbonate was selected as the precursor and dissolved in dimethyl carbonate at a volume ratio of 1:50. SiO x / C particles, wherein fluoroethylene carbonate and SiO x The mass ratio of the C / C particles was 1:5, stirred for 1 h, and then the solvent was removed by rotary evaporation to obtain the precursor-coated SiOx material;

[0055] A 1 mol / L 4-methylbiphenyl-2-methyltetrahydrofuran solution was prepared, and a metal lithium sheet was added thereto, wherein the molar ratio of the lithium sheet to the 4-methylbiphenyl was 4:1, and the chemical pre-lithium agent solution was obtained after being fully stirred for 2 hours.

[0056] Press SiO x The precursor-coated SiOx material was added to the chemical pre-lithium agent in a ratio of 10:1 between the mass ratio of C particles and metallic lithium, and stirred in a water bath at 45°C for 15 hours; the solution was then removed by centrifugal washing, dried at 60°C, and finally the dried material was placed in a tubular furnace for calcination at 600°C for 4 hours.

[0057] Fluorinated ethylene carbonate undergoes a reduction reaction under the action of a chemical pre-lithium solution to form LiF and a polymer layer. The former is uniformly dispersed in the polymer layer in the form of nanocrystals, and in the subsequent heat treatment process, it is carbonized to form a mixed conductive coating layer containing LiF and C. This coating layer not only effectively prevents direct contact between the pre-lithium SiOx / C material and the electrolyte to avoid electrode side reactions, but also its good electronic and lithium ion conductivity can effectively improve the electrode reaction kinetics of the material, thereby improving the rate characteristics of the material.

[0058] Example 2

[0059] Lithium difluorophosphate and vinylene carbonate were selected as precursors and dissolved in dimethyl carbonate at a volume ratio of 1:50. SiO x / C particles, wherein lithium difluorophosphate and vinylene carbonate are combined with SiO x The mass ratio of the C / C particles was 1:5, stirred for 1 h, and then the solvent was removed by spray drying to obtain the precursor-coated SiOx material;

[0060] A biphenyl-tetrahydrofuran solution with a concentration of 1 mol / L is prepared, and a metal lithium sheet is added thereto. The molar ratio of the lithium sheet to the 4-methylbiphenyl is 4:1, and the chemical pre-lithium agent solution is obtained after being fully stirred for 2 hours.

[0061] Press SiO x The precursor-coated SiOx material was added to the chemical pre-lithium agent in a ratio of 10:1 between the mass ratio of C particles and metallic lithium, and stirred in a water bath at 45°C for 15 hours; the solution was then removed by centrifugal washing, and the material was dried at 60°C. Finally, the dried material was placed in a tubular furnace for calcination at 700°C for 6 hours.

[0062] Example 3

[0063] Ethylene carbonate and vinylene carbonate were selected as precursors and dissolved in dimethyl carbonate at a volume ratio of 1:50. SiO x / C particles, wherein ethylene carbonate and ethylene carbonate and SiO x The mass ratio of the C / C particles was 1:5, stirred for 1 h, and then the solvent was removed by spray drying to obtain the precursor-coated SiOx material;

[0064] A 1 mol / L 4-methylbiphenyl-tetrahydrofuran solution was prepared, and a metal lithium sheet was added thereto, wherein the molar ratio of the lithium sheet to the 4-methylbiphenyl was 4:1, and the chemical pre-lithium agent solution was obtained after being fully stirred for 2 hours.

[0065] Press SiO x The precursor-coated SiOx material was added to the chemical pre-lithium agent in a ratio of 10:1 between the mass ratio of C particles and metallic lithium, and stirred in a water bath at 45°C for 15 hours; the solution was then removed by centrifugal washing, and the material was dried at 60°C. Finally, the dried material was placed in a tubular furnace for calcination at 600°C for 6 hours.

[0066] Example 4

[0067] Vinylene carbonate was selected as the precursor and dissolved in dimethyl carbonate at a volume ratio of 1:50. SiO x / C particles, wherein tri(pentafluorophenyl)borane and vinylene carbonate are reacted with SiO x The mass ratio of the C / S particles was 1:5, and the mixture was stirred for 1 h, and then the solvent was removed by rotary evaporation to obtain a precursor-coated SiOx material;

[0068] A 1 mol / L 4-methylbiphenyl-tetrahydrofuran solution was prepared, and a metal lithium sheet was added thereto, wherein the molar ratio of the lithium sheet to the 4-methylbiphenyl was 4:1, and the chemical pre-lithium agent solution was obtained after being fully stirred for 2 hours.

[0069] Press SiO x The precursor-coated SiOx material was added to the chemical pre-lithium agent in a ratio of 10:1 between the mass ratio of C particles and metallic lithium, and stirred in a water bath at 45°C for 15 hours; the solution was then removed by centrifugal washing, dried at 60°C, and finally the dried material was placed in a tubular furnace for calcination at 800°C for 4 hours.

[0070] Comparative Example 1

[0071] In the present invention, the SiOx material is coated with a precursor, and then the material is pre-lithiated. During the pre-lithiation process, the precursor is in situ converted into a coating layer of "fast ion conductor + amorphous carbon", and finally a mixed conductor layer is obtained to continuously coat the pre-lithiation SiOx material. For comparison, the SiOx / C material is directly reacted with a chemical pre-lithiation agent without being coated with a precursor material for comparison.

[0072] A 1 mol / L 4-methylbiphenyl-2-methyltetrahydrofuran solution was prepared, and a metal lithium sheet was added thereto, wherein the molar ratio of the lithium sheet to the 4-methylbiphenyl was 4:1, and the chemical pre-lithium agent solution was obtained after being fully stirred for 2 hours.

[0073] SiOx / C particles were added to the chemical pre-lithium agent at a mass ratio of 10:1 to metallic lithium, and stirred in a water bath at 45°C for 15 hours; the solution was then removed by centrifugal washing, dried at 60°C, and finally the dried material was placed in a tubular furnace for calcination at 600°C for 4 hours.

[0074] Comparative Example 2

[0075] The calcination process is crucial to the formation of the mixed conductive coating. During the calcination process, the polymer is transformed in situ to form carbon, which ensures the excellent electronic conductivity of the mixed conductive coating. In this comparative example, after washing and drying the lithiation reaction product, the battery is directly assembled without calcining the powder.

[0076] Fluorinated ethylene carbonate was selected as the precursor and dissolved in dimethyl carbonate at a volume ratio of 1:50. SiO x / C particles, wherein fluoroethylene carbonate and SiO x The mass ratio of the C / S particles was 1:5, and the mixture was stirred for 1 h, and then the solvent was removed by rotary evaporation to obtain a precursor-coated SiOx material;

[0077] A 1 mol / L 4-methylbiphenyl-2-methyltetrahydrofuran solution was prepared, and a metal lithium sheet was added thereto, wherein the molar ratio of the lithium sheet to the 4-methylbiphenyl was 4:1, and the chemical pre-lithium agent solution was obtained after being fully stirred for 2 hours.

[0078] The precursor-coated SiOx material was added to the chemical pre-lithium agent at a mass ratio of SiOx / C particles to metallic lithium of 10:1, and stirred in a water bath at 45°C for 15 hours; the solution was then removed by centrifugal washing and dried at 60°C.

[0079] After mixing the negative electrode materials, conductive agent SP, carbon nanotubes, and binder (mass ratio CMC:SBR=3:8) provided in Examples 1-4 and Comparative Examples 1 and 2 at a mass ratio of 85:4.8:0.2:10, the mixed slurry was evenly coated on the upper surface of the Cu foil and vacuum dried for 2 hours, and the electrode sheet was rolled at a compaction density of 1.2g / cm3 to obtain a negative electrode sheet. Lithium flakes were used as counter electrodes, 1mol / L LiPF6 / DMC+DEC+EC (volume ratio of 1:1:1) was used as electrolyte, 10% FEC was used as electrolyte additive, and glass fiber membrane was used as a diaphragm, and button cells were assembled in a gas glove box with an argon atmosphere.

[0080] The button cells assembled from Examples 1-4 and Comparative Examples 1-2 were subjected to electrochemical analysis tests. The charge and discharge range was 0.005-1.5V, the first week of charge and discharge tests were conducted at a current density of 0.05C, and the second week and subsequent discharge tests were conducted at a current density of 0.5C. The electrochemical performance is shown in Table 1.

[0081] Table 1 Electrochemical performance test results

[0082]

[0083]

[0084] like Figure 2 As shown in Figure 3, by comparing Example 1 with Comparative Example 1, the first coulombic efficiency is slightly reduced because of the introduction of inactive substances such as LiF, but the capacity retention rate is greatly improved. This is because a coating layer of "fast ion conductor + amorphous carbon" is constructed to improve its conductivity and improve the electrochemical performance.

[0085] Comparing Example 1 with Comparative Example 2, Comparative Example 2 was not subjected to calcination stabilization treatment, resulting in the presence of more active lithium, which reacted with air or water during the subsequent coating process, causing its electrochemical performance to deteriorate.

[0086] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A mixed conductor layer coated with silicon oxide negative electrode material, It is characterized in that The material comprises a pre-lithium SiOx material, the surface of the pre-lithium SiOx material has a coating layer, and the coating layer structure is an amorphous carbon layer with lithium ion conductive active sites uniformly dispersed inside.

2. The mixed conductor layer coated silicon monoxide negative electrode material according to claim 1, It is characterized in that The lithium ion conductive active site comprises a fast lithium ion conductor or a material with a low lithium ion diffusion barrier, and the lithium ion conductivity of the fast lithium ion conductor is not less than 10 -7 S / cm, and the lithium ion diffusion barrier of the low lithium ion diffusion barrier material is not higher than 0.3 eV.

3. A method for preparing a mixed conductor layer coated with silicon oxide negative electrode material, It is characterized in that The following steps are involved: Preparing a precursor-coated SiOx material: adding SiOx / C particles to a precursor solution and adopting a coating process to obtain a precursor-coated SiOx material; Prepare chemical pre-lithium solution; Lithiation reduction: The precursor-coated SiOx material is immersed in a pre-lithium solution, stirred for a certain period of time under an inert atmosphere, and then washed and dried to obtain a lithiated SiOx material; Heat treatment: The lithiated SiOx material is calcined and then kept warm to obtain a mixed conductor layer coated pre-lithiated SiOx material.

4. The preparation method according to claim 3, It is characterized in that For the selection of precursors, based on first principle calculations, the lowest unoccupied molecular orbital potential (LUMO) is selected to be lower than the HOMO value of the chemical pre-lithium agent, and the lithium reduction product contains a lithium compound, wherein the lithium ion conductivity of the lithium compound is not less than 10 -7 S / cm or the lithium ion diffusion barrier of its low lithium ion diffusion barrier material is not higher than 0.3eV.

5. The preparation method according to claim 3, It is characterized in that The precursor includes one or more of the following substances: a. After the lithium reduction reaction with the chemical pre-lithium agent, it can generate a lithium ion conductivity of not less than 10 -7 S / cm ionic conductor; b. After the lithium reduction reaction with the chemical pre-lithium agent, a reduction product with a lithium ion diffusion barrier of no more than 0.3 eV can be generated; c. After lithium reduction reaction with chemical pre-lithium agent, linear polymer can be generated; d. After lithium reduction reaction with chemical pre-lithium agent, lithium ion conductor and linear polymer can be generated simultaneously.

6. The preparation method according to claim 5, It is characterized in that The ion conductor is Li 3 PO 4 , Li 3 BO 3 or LiAlO 2 .

7. The preparation method according to claim 5, It is characterized in that The reduction product is LiF.

8. The preparation method according to claim 3, It is characterized in that The coating process is a liquid phase coating process, and the liquid phase coating process is liquid phase mixing combined with rotary evaporation or liquid phase mixing combined with spray drying; Alternatively, the coating process is a solid phase coating process, and the solid phase coating process is one of sand milling mixing, VC mixing, hot kneading, and mechanical fusion.

9. The preparation method according to claim 3, It is characterized in that The chemical pre-lithium agent solution is prepared from metallic lithium, aromatic hydrocarbons and solvents.

10. The preparation method according to claim 9, It is characterized in that The aromatic hydrocarbon is selected from one or more of biphenyl-type aromatic compounds such as biphenyl and 4-methylbiphenyl, condensed ring aromatic hydrocarbons and their derivatives; the solvent is selected from one or more of ethylene glycol dimethyl ether, tetrahydrofuran, 2-methyltetrahydrofuran and tetrahydropyran.

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