CN113809310A - Boron-doped soft carbon-coated silicon-based lithium ion negative electrode material and preparation method and application thereof - Google Patents

Boron-doped soft carbon-coated silicon-based lithium ion negative electrode material and preparation method and application thereof Download PDF

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CN113809310A
CN113809310A CN202010543274.0A CN202010543274A CN113809310A CN 113809310 A CN113809310 A CN 113809310A CN 202010543274 A CN202010543274 A CN 202010543274A CN 113809310 A CN113809310 A CN 113809310A
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潘明军
刘柏男
罗飞
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Tianmulake Excellent Anode Materials Co Ltd
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    • H—ELECTRICITY
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    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
    • H01M4/386—Silicon or alloys based on silicon
    • 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
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • 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
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
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    • H01M4/625—Carbon or graphite
    • 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 boron-doped soft carbon-coated silicon-based lithium ion negative electrode material and a preparation method and application thereof. Taking a boron-containing gas source or a high-boiling point boron-containing compound as a doping material, and carrying out gas-phase mixing reaction on vapor of the doping material and preheated silicon source vapor at 1200-1700 ℃ for 1-24 hours to obtain a boron-doped silicon protoxide material; wherein the silicon source vapor is a mixed vapor of silicon vapor and silicon dioxide vapor; the boron-containing gas source is a gaseous boron-containing compound at normal temperature, and the high-boiling point boron-containing compound is a liquid or solid boron-containing compound at normal temperature; cooling the boron-doped silicon oxide material to room temperature, discharging, crushing and screening; performing a flight time secondary ion mass spectrometry test on the crushed and screened material to determine whether the doping uniformity of boron doped in the silicon monoxide meets a preset condition; and (3) carrying out carbon coating on the material with the doping uniformity meeting the preset condition to obtain the boron-doped silicon-based lithium ion battery cathode material.

Description

Boron-doped soft carbon-coated silicon-based lithium ion negative electrode material and preparation method and application thereof
Technical Field
The invention relates to the technical field of material preparation, in particular to a boron-doped soft carbon-coated silicon-based lithium ion negative electrode material and a preparation method and application thereof.
Background
With the rapid development of new energy automobiles, higher requirements on the performance of power batteries are put forward in the industry. The anode and cathode materials determine the key components of the energy density, power density, cycle life, high and low temperature performance and safety performance of the power battery, and the main function of the lithium ion battery is to enable lithium ions to be freely deintercalated and realize the charging and discharging functions of the battery. The requirements of the lithium ion battery cathode material at least meet the following points: 1. a lower chemical potential; 2. good conductivity; 3. good cycle stability and safety; 4. inexpensive raw materials, and the like.
The cathode material is one of the most critical materials of the lithium ion battery technology. The graphite negative electrodes currently on the market have reached their technical bottleneck due to their low gram capacity. And silicon is one of the most promising lithium ion negative electrode materials to replace it. The silicon-based negative electrode material has a series of defects of volume expansion effect, poor conductivity and the like, and practical application of the silicon-based negative electrode material is limited.
Patent CN106654194A provides a method for preparing an element-doped silicon oxide negative electrode material of a lithium ion battery. The doped metal and the non-metal elements are combined, the defects of the anode material are constructed through the non-metal, the intrinsic ion transmission capability of the material is improved, meanwhile, the conductivity of the material is improved through the metal and SiOx mixed conductive network, a certain position is reserved for volume expansion, and the high specific capacity and the excellent cycle performance can be realized. However, the preparation method adopts liquid-solid phase mixing, and the uniformity of bulk phase doping cannot be guaranteed, so that the consistency of the material obtained by the preparation method is influenced, and the cycle performance of the material is possibly influenced.
Disclosure of Invention
The embodiment of the invention provides a boron-doped soft carbon-coated silicon-based lithium ion negative electrode material, and a preparation method and application thereof.
In a first aspect, an embodiment of the present invention provides a method for preparing a boron-doped soft carbon-coated silicon-based lithium ion negative electrode material, including:
taking a boron-containing gas source or a high-boiling point boron-containing compound as a doping material, and carrying out gas-phase mixing on vapor of the doping material and preheated silicon source vapor at 1200-1700 ℃ for reaction for 1-24 hours to obtain a boron-doped silicon protoxide material; wherein the silicon source vapor is a mixed vapor of silicon vapor and silicon dioxide vapor; the boron-containing gas source is a gaseous boron-containing compound at normal temperature, and the high-boiling point boron-containing compound is a liquid or solid boron-containing compound at normal temperature;
cooling the boron-doped silicon oxide material to room temperature, discharging, crushing and screening;
performing a flight time secondary ion mass spectrometry test on the crushed and screened material to determine whether the doping uniformity of boron doped in the silicon monoxide meets a preset condition;
and (3) carrying out carbon coating on the material with the doping uniformity meeting the preset condition to obtain the boron-doped silicon-based lithium ion cathode material.
Preferably, the boron-containing gas source specifically comprises: one or more of diborane, boron trichloride, or boron trifluoride;
the high boiling point boron-containing compound specifically includes: decaborane, boric acid or sodium borohydride.
Preferably, the vapour of the doping material is obtained by heating the doping material to a temperature of 25 ℃ to 800 ℃.
Preferably, the silicon source vapor and the silicon dioxide vapor in the silicon source vapor are in a molar ratio of silicon: silica 1: 1 and mixing.
Preferably, the mass of boron atoms in the doping material is 100ppm to 100000ppm of the total mass of silicon and silicon dioxide in the silicon source vapor.
Preferably, the preset conditions are specifically as follows: in the process of the flight time secondary ion mass spectrometry analysis and test, the fluctuation range of the boron atom concentration is within +/-50% in all the particle sputtering time periods.
Preferably, the carbon coating specifically comprises: placing the material with the doping uniformity meeting the preset condition in a rotary furnace, heating to 800-1000 ℃ under the protective atmosphere, introducing an organic gas source for chemical vapor deposition, keeping the temperature for 2-4 hours, and then closing the organic gas source for cooling; wherein the organic gas source specifically comprises: one or more of methane, acetylene, propylene or propane.
In a second aspect, an embodiment of the present invention provides a lithium ion battery negative electrode material, including the boron-doped soft carbon-coated silicon-based lithium ion negative electrode material prepared by the preparation method in the first aspect.
In a third aspect, an embodiment of the present invention provides a lithium battery pole piece, where the lithium battery pole piece includes the lithium ion battery negative electrode material described in the second aspect.
In a fourth aspect, an embodiment of the present invention provides a lithium battery, where the lithium battery includes the lithium battery pole piece of the third aspect.
According to the preparation method of the boron-doped soft carbon-coated silicon-based lithium ion negative electrode material, the lithium ion battery negative electrode material with uniform phase doping is obtained through gas-phase reaction, the obtained material has higher cycle stability, and meanwhile, the material consistency is more excellent.
Drawings
The technical solutions of the embodiments of the present invention are further described in detail with reference to the accompanying drawings and embodiments.
Fig. 1 is a flowchart of a method for preparing a boron-doped soft carbon-coated silicon-based lithium ion negative electrode material according to an embodiment of the invention;
fig. 2 is a time-of-flight secondary ion mass spectrum of the boron-doped silicon-based lithium ion battery negative electrode material provided in example 1 of the present invention;
fig. 3 is a time-of-flight secondary ion mass spectrum of the uniform boron-doped silicon-based lithium ion battery negative electrode material provided in comparative example 1 of the present invention;
fig. 4 is a time-of-flight secondary ion mass spectrum of the uniform boron-doped silicon-based lithium ion battery negative electrode material provided in comparative example 2 of the present invention;
fig. 5 is a comparison of the time-of-flight secondary ion mass spectrograms of the uniform boron-doped silicon-based lithium ion battery anode materials provided in example 1 and comparative examples 1-2 of the present invention.
Detailed Description
The invention is further illustrated by the following figures and specific examples, but it should be understood that these examples are for the purpose of illustration only and are not to be construed as in any way limiting the present invention, i.e., as in no way limiting its scope.
The preparation method of the boron-doped soft carbon-coated silicon-based lithium ion negative electrode material disclosed by the invention comprises the following steps as shown in figure 1:
step 110, taking a boron-containing gas source or a high-boiling point boron-containing compound as a doping material, and carrying out gas-phase mixing reaction on vapor of the doping material and preheated silicon source vapor at 1200-1700 ℃ for 1-24 hours to obtain a boron-doped silicon protoxide material;
wherein the vapor of the doping material is obtained by heating the doping material to 25 ℃ -800 ℃.
In the doping material, the boron-containing gas source is a gaseous boron-containing compound at normal temperature, and specifically can comprise one or more of diborane, boron trichloride or boron trifluoride; the high-boiling point boron-containing compound is a liquid or solid boron-containing compound at normal temperature, and specifically may include one or more of decaborane, boric acid, or sodium borohydride.
The silicon source vapor is a mixed vapor of silicon vapor and silicon dioxide vapor, preferably in a molar ratio of silicon: silica 1: 1 and mixing.
The mass of boron atoms in the doping material accounts for 100ppm-100000ppm of the total mass of silicon and silicon dioxide in the silicon source steam.
Step 120, cooling the boron-doped silicon monoxide material to room temperature, discharging, crushing and screening;
130, performing a flight time secondary ion mass spectrometry test on the crushed and sieved material to determine whether the doping uniformity of boron doped in the silicon monoxide meets a preset condition;
the preset conditions in this step are specifically: in the process of the flight time secondary ion mass spectrometry analysis and test, the fluctuation range of the boron atom concentration is within +/-50% in all the particle sputtering time periods. If this condition is satisfied, it is considered to be acceptable, and the next carbon coating is performed.
And 140, performing carbon coating on the material with the doping uniformity meeting the preset condition to obtain the boron-doped silicon-based lithium ion negative electrode material.
The carbon coating specifically comprises the following steps: placing the material with the doping uniformity meeting the preset condition in a rotary furnace, heating to 800-1000 ℃ under the protective atmosphere, introducing an organic gas source for chemical vapor deposition, keeping the temperature for 2-4 hours, and then closing the organic gas source for cooling;
wherein, the organic gas source specifically includes: one or more of methane, acetylene, propylene or propane.
According to the preparation method, the lithium ion battery cathode material with uniform phase doping is obtained through gas phase reaction, the obtained material has higher cycling stability, and meanwhile, the consistency of the material is more excellent.
The boron-doped soft carbon-coated silicon-based lithium ion negative electrode material prepared by the preparation method of the embodiment can be used as a lithium ion battery negative electrode material and applied to a lithium battery pole piece and a lithium battery.
In order to better understand the technical solutions provided by the present invention, the following description respectively describes specific processes for preparing a negative electrode material of a lithium battery by using the methods provided by the above embodiments of the present invention, and a method for applying the negative electrode material to a lithium battery and battery characteristics by using the negative electrode material.
Example 1
1.4kg of silicon powder and 3kg of silica were placed in a high-temperature reaction furnace and heated to steam, while 13.4L (12.7 g in terms of mass) of diborane was slowly introduced under an argon-protected atmosphere, reacted at 1500 ℃ for 4 hours, and cooled to room temperature. And detecting the crushed material by a time-of-flight secondary ion mass spectrometer (TOF-SIMS). Fig. 2 is a time-of-flight secondary ion mass spectrum of the boron-doped silicon-based lithium ion battery negative electrode material provided in embodiment 1 of the present invention, and it can be known that the boron atom concentration fluctuation is uniformly distributed within the etching time, within the defined range ± 50%.
Placing 2kg of qualified materials in a rotary furnace, heating to 1000 ℃ under the protective argon atmosphere, and mixing the materials according to the volume ratio of 1: 2 introducing argon and acetylene mixed gas for chemical vapor deposition, keeping the temperature for 2 hours, closing an organic gas source, and cooling to obtain the uniform boron-doped soft carbon-coated silicon-based lithium ion battery cathode material, wherein the boron content in the obtained cathode material is 0.11%.
Mixing the obtained negative electrode material, conductive additive carbon black and adhesive 1: 1, and the sodium cellulose and styrene butadiene rubber in a mass ratio of 95%: 2%: 3% are weighed out. And (5) placing the mixture into a beater to prepare the pulp at room temperature. And uniformly coating the prepared slurry on a copper foil. Drying in a forced air drying oven at 50 deg.C for 2 hr, cutting into 8 × 8mm pole pieces, and vacuum drying in a vacuum drying oven at 100 deg.C for 10 hr. And transferring the dried pole piece into a glove box for standby use to assemble a battery.
The simulated cell was assembled in a glove box containing a high purity Ar atmosphere using lithium metal as the counter electrode and 1 mole of LiPF6The solution in ethylene carbonate EC/dimethyl carbonate DMC was used as electrolyte to assemble a battery. And (3) carrying out a constant-current charge-discharge mode test by using a charge-discharge instrument, wherein the discharge cutoff voltage is 0.005V, the charge cutoff voltage is 1.5V, the first-week charge-discharge test is carried out at a current density of C/10, and the second-week discharge test is carried out at a current density of C/10.
Example 2
2.8kg of silicon powder and 6kg of silicon dioxide are placed in a high-temperature reaction furnace and heated to steam, 3.2L (3 g in terms of mass) of diborane is slowly introduced under the argon protection environment, the reaction is carried out for 8 hours at 1200 ℃, and the reaction is cooled to room temperature. And after the discharged material is crushed, the material is qualified by TOF-SIMS detection. Placing 2kg of qualified materials in a rotary furnace, heating to 850 ℃ under the protective argon atmosphere, and mixing the materials according to the volume ratio of 1: 2 introducing argon and mixed gas of propylene and acetylene for chemical vapor deposition, wherein the volume ratio of propylene to acetylene is 1: 1, keeping the temperature for 4 hours, closing an organic gas source, and cooling to obtain the uniform boron-doped soft carbon-coated silicon-based lithium ion battery cathode material, wherein the boron content in the obtained cathode material is 0.013%.
The preparation process of the negative electrode plate, the battery assembly and the battery test method are the same as those in example 1.
Example 3
7kg of silicon powder and 15kg of silicon dioxide are placed in a high-temperature reaction furnace and heated to steam, 35L (141 g in terms of mass) of boron trichloride is slowly introduced under the protection of argon gas, the reaction is carried out for 18 hours at 1300 ℃, and the reaction is cooled to room temperature. And after the discharged material is crushed, the material is qualified by TOF-SIMS detection. Placing 2kg of qualified materials in a rotary furnace, heating to 900 ℃ under the protective argon atmosphere, and mixing the materials according to the volume ratio of 1: 1, introducing argon and propylene with the same quantity as the argon for chemical vapor deposition, preserving the heat for 2.5 hours, closing an organic gas source, and cooling to obtain the uniform boron-doped soft carbon-coated silicon-based lithium ion battery cathode material, wherein the boron content in the obtained cathode material is 0.059%.
The preparation process of the negative electrode plate, the battery assembly and the battery test method are the same as those in example 1.
Example 4
2.8kg of silicon powder and 6kg of silicon dioxide are placed in a high-temperature reaction furnace and heated to steam, and 910g of sodium borohydride is heated to 550 ℃ to steam at the same time, and after the steam is mixed with each other, the silicon powder and the silicon dioxide react for 7 hours at 1600 ℃, and then the silicon powder and the silicon dioxide are cooled to room temperature. And after the discharged material is crushed, the material is qualified by TOF-SIMS detection. Placing 2kg of qualified materials in a rotary furnace, heating to 900 ℃ under the protective argon atmosphere, and mixing the materials according to the volume ratio of 1: 1, introducing argon and acetylene with the same quantity as the argon for chemical vapor deposition, keeping the temperature for 3 hours, closing an organic gas source, and cooling to obtain the uniform boron-doped soft carbon-coated silicon-based lithium ion battery cathode material, wherein the boron content in the obtained cathode material is 2.9%.
The preparation process of the negative electrode plate, the battery assembly and the battery test method are the same as those in example 1.
Example 5
1.4kg of silicon powder and 3kg of silicon dioxide are placed in a high-temperature reaction furnace and heated to steam, and at the same time, 210g of sodium borohydride is heated to 550 ℃ to steam, and the steam is mixed with each other, reacted at 1500 ℃ for 3.5 hours, and cooled to room temperature. And after the discharged material is crushed, the material is qualified by TOF-SIMS detection. Placing 2kg of qualified materials in a rotary furnace, heating to 1000 ℃ under the protective argon atmosphere, and mixing the materials according to the volume ratio of 1: 1 introducing argon and mixed gas of acetylene and propane which is equal to the argon for carrying out chemical vapor deposition, wherein the volume ratio of the acetylene to the propane in the mixed gas is 3: 1, preserving the heat for 3 hours, closing an organic gas source, and cooling to obtain the uniform boron-doped soft carbon-coated silicon-based lithium ion battery cathode material, wherein the boron content in the obtained cathode material is 1.4%.
The preparation process of the negative electrode plate, the battery assembly and the battery test method are the same as those in example 1.
Example 6
2.8kg of silicon powder and 6kg of silicon dioxide are placed in a high-temperature reaction furnace and heated to steam, simultaneously, 8L (32.2 g in terms of mass) of boron trichloride is slowly introduced under the argon protection environment, the reaction is carried out for 8 hours at 1400 ℃, and the reaction is cooled to room temperature. And after the discharged material is crushed, the material is qualified by TOF-SIMS detection. Placing 2kg of qualified materials in a rotary furnace, heating to 950 ℃ under the protective argon atmosphere, and mixing the materials according to the volume ratio of 1: 2, introducing argon and acetylene to carry out chemical vapor deposition, keeping the temperature for 2.5 hours, closing an organic gas source, and cooling to obtain the uniform boron-doped soft carbon-coated silicon-based lithium ion battery cathode material, wherein the boron content in the obtained cathode material is 0.033%.
The preparation process of the negative electrode plate, the battery assembly and the battery test method are the same as those in example 1.
Example 7
1.4kg of silicon powder and 3kg of silicon dioxide are placed in a high-temperature reaction furnace and heated to become steam, at the same time, 10g of decaborane is heated to 230 ℃ to become steam, the steam is mixed with each other, then the reaction is carried out for 3 hours at 1700 ℃, and the reaction is cooled to the room temperature. And after the discharged material is crushed, the material is qualified by TOF-SIMS detection. Placing 2kg of qualified materials in a rotary furnace, heating to 1000 ℃ under the protective argon atmosphere, and mixing the materials according to the volume ratio of 1: 2 introducing argon and acetylene to carry out chemical vapor deposition, preserving the heat for 2 hours, closing an organic gas source, and cooling to obtain the uniform boron-doped soft carbon-coated silicon-based lithium ion battery cathode material, wherein the boron content in the obtained cathode material is 0.2%.
The preparation process of the negative electrode plate, the battery assembly and the battery test method are the same as those in example 1.
Example 8
2.8kg of silicon powder and 6kg of silicon dioxide were placed in a high temperature reaction furnace and heated to become vapor, while 5g of decaborane was heated to 230 ℃ to become vapor, the vapors were mixed with each other and reacted at 1700 ℃ for 9 hours, and cooled to room temperature. And after the discharged material is crushed, the material is qualified by TOF-SIMS detection. Placing 2kg of qualified materials in a rotary furnace, heating to 1000 ℃ under the protective argon atmosphere, and mixing the materials according to the volume ratio of 1: 1, introducing argon and propylene to carry out chemical vapor deposition, preserving the heat for 2 hours, closing an organic gas source, and cooling to obtain the uniform boron-doped soft carbon-coated silicon-based lithium ion battery cathode material, wherein the boron content in the obtained cathode material is 0.05%.
The preparation process of the negative electrode plate, the battery assembly and the battery test method are the same as those in example 1.
Comparative example 1
This comparative example provides a lithium ion battery negative electrode material that is comparable to example 1. Mechanically mixing 2kg of silicon monoxide and 7.6g of sodium borohydride, testing by a time of flight secondary ion mass spectrometer (TOF-SIMS), placing the mixture in a rotary furnace, heating to 1000 ℃ under an argon protection environment, and mixing the materials according to a volume ratio of 1: 1: 1, introducing argon gas and propylene and methane gas which are respectively equal to the argon gas in quantity to carry out chemical vapor deposition, keeping the temperature for 2 hours, closing an organic gas source and cooling to obtain the negative electrode material of the lithium ion battery for comparison, wherein the boron content in the obtained negative electrode material is 0.11%.
The preparation process of the negative electrode plate, the battery assembly and the battery test method are the same as those in example 1.
Comparative example 2
Comparative example 2 provides a negative electrode material for a lithium ion battery, compared to example 1. 2kg of silica and 7.6g of sodium borohydride are uniformly mixed by water, and the mixture is spray-dried to obtain the composite silica raw material. After the composite silicon monoxide raw material is subjected to the detection of a time-of-flight secondary ion mass spectrometer (TOF-SIMS), the composite silicon monoxide raw material is placed in a rotary furnace and heated to 1000 ℃ under the argon protection environment, and the mass ratio of the composite silicon monoxide raw material to the argon protection material is 1: 1: 1, introducing argon gas and propylene and methane gas which are respectively equal to the argon gas in quantity to carry out chemical vapor deposition, keeping the temperature for 2 hours, closing an organic gas source and cooling to obtain the negative electrode material of the lithium ion battery for comparison, wherein the boron content in the obtained negative electrode material is 0.11%.
The preparation process of the negative electrode plate, the battery assembly and the battery test method are the same as those in example 1.
The above negative electrode materials of examples 1 to 8 and comparative examples 1 to 2 were subjected to index tests of initial efficiency, reversible capacity at 0.1C, cycle performance at 0.1C magnification, and the like, and the results are shown in table 1.
Figure BDA0002539788500000101
TABLE 1
As can be seen from the data in table 1, in the same case, the gas phase mixing technology is adopted in examples 1 to 8 to modify the silicon-based negative electrode material, and the gas phase mass transfer is uniform, so that the lithium battery has good performance consistency, and the charging specific capacity and the cycle performance are both high. Comparative examples 1-2 adopt solid phase coating and liquid phase coating respectively to carry out silicon-based negative electrode material modification, and it can be seen from comparative example 1 that the cycle stability is not good in the long-cycle process, which is mainly due to insufficient contact of the solid phase coating and the presence of an incompletely reacted activation region. Comparative example 2, in which liquid phase coating was used, the doping was relatively more uniform than comparative example 1, but since liquid phase coating was performed using an aqueous phase, the silica contacted a large amount of oxygen dissolved in water, causing partial oxidation of the surface, and the first efficiency and capacity were reduced.
In addition, fig. 5 is a comparison of the flight time secondary ion mass spectrograms of the uniform boron doped silicon-based lithium ion battery anode materials provided in example 1 and comparative examples 1-2 of the present invention. It can be seen from comparison that, in comparative examples 1-2, the fluctuation range of boron atoms is initially uniform by using the solid phase coating and the liquid phase coating respectively, but as the etching time increases, when the material is etched, due to the defect of non-bulk phase doping, boron atoms are not dispersed in the material, so that the boron atom concentration gradually becomes zero. And because the mode of vapor reaction is adopted, corresponding boron atoms enter the interior of the silicon oxide material when the silicon oxide is generated, so that the boron atoms are uniformly distributed in the whole material from inside to outside.
According to the preparation method of the boron-doped soft carbon-coated silicon-based lithium ion negative electrode material, the lithium ion battery negative electrode material with uniform phase doping is obtained through gas-phase reaction, the obtained material has higher cycle stability, and meanwhile, the material consistency is more excellent.
The above-mentioned embodiments are intended to illustrate the objects, technical solutions and advantages of the present invention in further detail, and it should be understood that the above-mentioned embodiments are merely exemplary embodiments of the present invention, and are not intended to limit the scope of the present invention, and any modifications, equivalent substitutions, improvements and the like made within the spirit and principle of the present invention should be included in the scope of the present invention.

Claims (10)

1. A preparation method of a boron-doped soft carbon-coated silicon-based lithium ion negative electrode material is characterized by comprising the following steps:
taking a boron-containing gas source or a high-boiling point boron-containing compound as a doping material, and carrying out gas-phase mixing reaction on vapor of the doping material and preheated silicon source vapor at 1200-1700 ℃ for 1-24 hours to obtain a boron-doped silicon protoxide material; wherein the silicon source vapor is a mixed vapor of silicon vapor and silicon dioxide vapor; the boron-containing gas source is a gaseous boron-containing compound at normal temperature, and the high-boiling point boron-containing compound is a liquid or solid boron-containing compound at normal temperature;
cooling the boron-doped silicon oxide material to room temperature, discharging, crushing and screening;
performing a flight time secondary ion mass spectrometry test on the crushed and screened material to determine whether the doping uniformity of boron doped in the silicon monoxide meets a preset condition;
and (3) carrying out carbon coating on the material with the doping uniformity meeting the preset condition to obtain the boron-doped silicon-based lithium ion cathode material.
2. The method according to claim 1, wherein the boron-containing gas source specifically comprises: one or more of diborane, boron trichloride, or boron trifluoride;
the high boiling point boron-containing compound specifically includes: decaborane, boric acid or sodium borohydride.
3. The method for preparing according to claim 1, wherein the vapor of the doping material is obtained by heating the doping material to 25 ℃ -800 ℃.
4. The method of claim 1, wherein the silicon source vapor comprises silicon vapor and silicon dioxide vapor in a molar ratio of silicon: silica 1: 1 and mixing.
5. The method according to claim 1, wherein the mass of boron atoms in the doping material is 100ppm to 100000ppm based on the total mass of silicon and silicon dioxide in the silicon source vapor.
6. The preparation method according to claim 1, wherein the preset conditions are specifically: in the process of the flight time secondary ion mass spectrometry analysis and test, the fluctuation range of the boron atom concentration is within +/-50% in all the particle sputtering time periods.
7. The preparation method according to claim 1, wherein the carbon coating is specifically: placing the material with the doping uniformity meeting the preset condition in a rotary furnace, heating to 800-1000 ℃ under the protective atmosphere, introducing an organic gas source for chemical vapor deposition, keeping the temperature for 2-4 hours, and then closing the organic gas source for cooling; wherein the organic gas source specifically comprises: one or more of methane, acetylene, propylene or propane.
8. The negative electrode material of the lithium ion battery is characterized in that the negative electrode material is the boron-doped soft carbon-coated silicon-based lithium ion negative electrode material prepared by the preparation method of any one of claims 1 to 7.
9. A lithium battery pole piece, characterized in that the lithium battery pole piece comprises the lithium ion battery negative electrode material of the claim 8.
10. A lithium battery comprising a lithium battery electrode sheet according to claim 9.
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