阅读说明：本技术 磷掺杂硅基锂离子电池负极材料及其制备方法和应用 (Phosphorus-doped silicon-based lithium ion battery cathode material and preparation method and application thereof ) 是由 潘明军 刘柏男 罗飞 于 2020-04-27 设计创作，主要内容包括：本发明涉及一种磷掺杂硅基锂离子电池负极材料及其制备方法和应用,磷掺杂硅基负极材料为粉体材料,粉末电导为3.0S/cm-6.0S/cm；磷掺杂硅基负极材料包括：90wt％-99.49wt％的硅基粉体材料、0.01wt％-3wt％的掺杂在硅基粉体材料中的含磷掺杂材料和0.5wt％-7wt％的软碳材料；硅基粉体材料具体为含有电化学活性粉体材料,包括纳米硅碳复合材料、氧化亚硅、改性氧化亚硅、掺杂氧化亚硅、无定型硅合金中的一种或者几种；含磷掺杂材料包括磷酸二氢钠、磷酸三钾、五氧化二磷、焦磷酸钠,焦磷酸钾,偏磷酸钠中的一种或多种；软碳材料包覆在硅基粉体材料外表面,构成所述磷掺杂硅基负极材料的包覆碳层。(The invention relates to a phosphorus-doped silicon-based lithium ion battery cathode material and a preparation method and application thereof, wherein the phosphorus-doped silicon-based lithium ion battery cathode material is a powder material, and the powder conductance is 3.0S/cm-6.0S/cm; the phosphorus doped silicon-based negative electrode material comprises: 90 to 99.49 weight percent of silicon-based powder material, 0.01 to 3 weight percent of phosphorus-containing doping material doped in the silicon-based powder material and 0.5 to 7 weight percent of soft carbon material; the silicon-based powder material is specifically an electrochemical active powder material, and comprises one or more of a nano silicon-carbon composite material, silicon monoxide, modified silicon monoxide, doped silicon monoxide and amorphous silicon alloy; the phosphorus-containing doping material comprises one or more of sodium dihydrogen phosphate, tripotassium phosphate, phosphorus pentoxide, sodium pyrophosphate, potassium pyrophosphate and sodium metaphosphate; the soft carbon material is coated on the outer surface of the silicon-based powder material to form a coated carbon layer of the phosphorus-doped silicon-based negative electrode material.)

1. The phosphorus-doped silicon-based negative electrode material is characterized by being a powder material, wherein the powder conductance is 3.0S/cm-6.0S/cm; the phosphorus doped silicon-based negative electrode material comprises: 90 to 99.49 weight percent of silicon-based powder material, 0.01 to 3 weight percent of phosphorus-containing doping material doped in the silicon-based powder material and 0.5 to 7 weight percent of soft carbon material;

the silicon-based powder material specifically contains an electrochemical active powder material, and comprises one or more of a nano silicon-carbon composite material, silicon monoxide, modified silicon monoxide, doped silicon monoxide and amorphous silicon alloy;

the phosphorus-containing doping material comprises one or more of sodium dihydrogen phosphate, tripotassium phosphate, phosphorus pentoxide, sodium pyrophosphate, potassium pyrophosphate and sodium metaphosphate;

the soft carbon material is coated on the outer surface of the silicon-based powder material to form a coated carbon layer of the phosphorus-doped silicon-based negative electrode material.

2. The phosphorus-doped silicon-based anode material according to claim 1, wherein the phosphorus-doped silicon-based anode material comprises: 92-98 wt% of silicon-based powder material, 0.01-2 wt% of phosphorus-containing doping material and 1-6 wt% of soft carbon material.

3. The phosphorus-doped silicon-based negative electrode material as claimed in claim 1, wherein the reaction temperature of the coating process of forming the soft carbon material coated on the outer surface of the silicon-based powder material is not higher than 1000 ℃.

4. A method for preparing a phosphorus doped silicon based anode material according to any of the claims 1 to 3, characterized in that the method comprises:

mixing a phosphorus-containing doping material and a silicon-based powder material in a required proportion, and preparing to obtain a primary product; the silicon-based powder material specifically contains an electrochemical active powder material, and comprises one or more of a nano silicon-carbon composite material, silicon monoxide, modified silicon monoxide, doped silicon monoxide and amorphous silicon alloy; the phosphorus-containing doping material comprises one or more of sodium dihydrogen phosphate, tripotassium phosphate, phosphorus pentoxide, sodium pyrophosphate, potassium pyrophosphate and sodium metaphosphate;

and (3) placing the initial product in a high-temperature rotary furnace, heating to 800-1000 ℃ in the atmosphere of protective gas argon, introducing an organic gas source for chemical vapor deposition, preserving heat for 2-4 hours, closing the organic gas source, and cooling to obtain the phosphorus-doped silicon-based negative electrode material.

5. The method according to claim 4, wherein the method for preparing the initial product comprises: spray drying, mechanical mixing, mechanical ball milling, and chemical vapor deposition.

6. The method of claim 4, wherein the organic gas source comprises: one or more of methane, acetylene, propylene and propane.

7. A negative electrode sheet for a lithium battery, characterized in that it comprises the phosphorus-doped silicon-based negative electrode material according to any one of claims 1 to 3.

8. A lithium battery comprising the negative electrode sheet as claimed in claim 7.

9. The lithium battery of claim 8, comprising: any one of a lithium ion battery, a lithium ion supercapacitor, a lithium sulfur battery, and an all solid-state lithium battery.

10. The lithium battery of claim 8, wherein the lithium battery is used in a power battery for a vehicle.

Technical Field

The invention relates to the technical field of materials, in particular to a phosphorus-doped silicon-based lithium ion battery cathode material and a preparation method and application thereof.

Background

Among lithium ion negative electrode materials, silicon is one of negative electrode materials having a great potential at present. Compared with the traditional graphite negative electrode (372mAh/g), the silicon negative electrode has higher theoretical specific capacity (4200 mAh/g). Although the silicon-based anode material can achieve satisfactory energy density at present, the technical bottleneck of the material also exists at the same time. 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. The conductivity of the silicon-based negative electrode material is closely related to the rate capability of the lithium ion battery material. In terms of the current situation, the high-rate lithium ion battery material can greatly increase the cruising ability of an automobile, and meanwhile, the high-rate performance can enable the automobile to have higher charging rate and higher acceleration performance, so that a consumer has more comfortable driving experience. However, poor electron conductivity of the silicon-based material itself affects the charge and discharge rate of the battery.

Researchers have carried out a series of improvement measures aiming at the defects of the silicon-based negative electrode material. The problem group of Wang Dianlong teaching of Harbin Industrial university (Journal of Materials Chemistry A,2014,2, 3521-. Electrochemical tests show that the capacity of the lithium ion battery is quickly attenuated after the current density is increased. The main reason is that the ion conductance limits the improvement of the rate capability of the silicon oxide.

Disclosure of Invention

The embodiment of the invention provides a phosphorus-doped silicon-based negative electrode material and a preparation method and application thereof, wherein a small amount of doped phosphorus atoms replace part of silicon atoms, 4 of outer-layer electrons of the phosphorus atoms form covalent bonds with silicon, so that a freely moving electron appears, the concentration of the free electron is higher, and the conductivity of the silicon-based material is increased; a part of phosphorus atoms can enter the carbon layer to interact with the soft carbon material, so that the effect of further improving the powder conductivity is achieved; the carbon layer is used for limiting the volume expansion effect of the material while high powder conductivity is obtained, so that the silicon-based material can fully exert the advantage of high capacity. The phosphorus-doped silicon-based negative electrode material provided by the invention has a more stable structure, and phosphorus atoms and silicon are not easy to generate side reaction, so that the irreversible capacity is favorably reduced, and the cycle efficiency is improved.

In a first aspect, an embodiment of the present invention provides a phosphorus-doped silicon-based negative electrode material, where the phosphorus-doped silicon-based negative electrode material is a powder material, and a powder conductance is 3.0S/cm to 6.0S/cm; the phosphorus doped silicon-based negative electrode material comprises: 90 to 99.49 weight percent of silicon-based powder material, 0.01 to 3 weight percent of phosphorus-containing doping material doped in the silicon-based powder material and 0.5 to 7 weight percent of soft carbon material;

the silicon-based powder material specifically contains an electrochemical active powder material, and comprises one or more of a nano silicon-carbon composite material, silicon monoxide, modified silicon monoxide, doped silicon monoxide and amorphous silicon alloy;

the phosphorus-containing doping material comprises one or more of sodium dihydrogen phosphate, tripotassium phosphate, phosphorus pentoxide, sodium pyrophosphate, potassium pyrophosphate and sodium metaphosphate;

the soft carbon material is coated on the outer surface of the silicon-based powder material to form a coated carbon layer of the phosphorus-doped silicon-based negative electrode material.

Preferably, the phosphorus doped silicon-based negative electrode material comprises: 92-98 wt% of silicon-based powder material, 0.01-2 wt% of phosphorus-containing doping material and 1-6 wt% of soft carbon material.

Preferably, in the phosphorus-doped silicon-based negative electrode material, the reaction temperature in the coating process of coating the soft carbon material on the surface of the silicon-based powder material is not higher than 1000 ℃.

In a second aspect, an embodiment of the present invention provides a preparation method of the phosphorus-doped silicon-based anode material according to the first aspect, where the preparation method includes:

mixing a phosphorus-containing doping material and a silicon-based powder material in a required proportion, and preparing to obtain a primary product; the silicon-based powder material specifically contains an electrochemical active powder material, and comprises one or more of a nano silicon-carbon composite material, silicon monoxide, modified silicon monoxide, doped silicon monoxide and amorphous silicon alloy; the phosphorus-containing doping material comprises one or more of sodium dihydrogen phosphate, tripotassium phosphate, phosphorus pentoxide, sodium pyrophosphate, potassium pyrophosphate and sodium metaphosphate;

and (3) placing the initial product in a high-temperature rotary furnace, heating to 800-1000 ℃ in the atmosphere of protective gas argon, introducing an organic gas source for chemical vapor deposition, preserving heat for 2-4 hours, closing the organic gas source, and cooling to obtain the phosphorus-doped silicon-based negative electrode material.

Preferably, the method for preparing the primary product specifically comprises: spray drying, mechanical mixing, mechanical ball milling, and chemical vapor deposition.

Preferably, the organic gas source comprises: one or more of methane, acetylene, propylene and propane.

In a third aspect, an embodiment of the present invention provides a negative electrode plate of a lithium battery, including the phosphorus-doped silicon-based negative electrode material described in the first aspect.

In a fourth aspect, an embodiment of the present invention provides a lithium battery, including the negative electrode tab of the third aspect.

Preferably, the lithium battery includes: any one of a lithium ion battery, a lithium ion supercapacitor, a lithium sulfur battery, and an all solid-state lithium battery.

Preferably, the lithium battery is used for a power battery for a vehicle.

The embodiment of the invention provides a phosphorus-doped silicon-based negative electrode material and a preparation method and application thereof, wherein a small amount of doped phosphorus atoms replace part of silicon atoms, 4 of outer-layer electrons of the phosphorus atoms form covalent bonds with silicon, so that a freely moving electron appears, the concentration of the free electron is higher, and the conductivity of the silicon-based material is increased; a part of phosphorus atoms can enter the carbon layer to interact with the soft carbon material, so that the effect of further improving the powder conductivity is achieved; the carbon layer is used for limiting the volume expansion effect of the material while high powder conductivity is obtained, so that the silicon-based material can fully exert the advantage of high capacity. The phosphorus-doped silicon-based negative electrode material provided by the invention has a more stable structure, and phosphorus atoms and silicon are not easy to generate side reaction, so that irreversible capacity is reduced, and the cycle efficiency is improved.

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 powder conductance diagram of phosphorus doped silicon-based anode materials provided in examples 1-5 of the present invention;

fig. 2 is a graph comparing the powder conductance of phosphorus doped silicon based anode materials provided in example 1 of the present invention and comparative examples 1 to 4;

fig. 3 is a Scanning Electron Microscope (SEM) image of the phosphorus doped silicon-based negative electrode material provided in example 1 of the present invention;

fig. 4 is an SEM image of the phosphorus doped silicon-based negative electrode material provided in example 1 of the present invention;

fig. 5 is an X-ray diffraction (XRD) pattern of the phosphorus-doped silicon-based anode material provided in example 1 of the present invention;

fig. 6 is an XRD pattern of the phosphorus doped silicon-based anode material provided in example 2 of the present invention;

fig. 7 is an XRD pattern of the phosphorus doped silicon-based anode material provided in example 3 of the present invention;

fig. 8 is an XRD pattern of the phosphorus doped silicon based anode material provided in comparative example 1 of the present invention;

fig. 9 is a graph comparing the cycling performance of button half cells of phosphorus doped silicon based anode material of example 1 and nitrogen doped silicon based anode material of comparative example 4 provided by the present invention;

fig. 10 is a comparison graph of the cycling performance of the button half cell of the phosphorus doped silicon-based negative electrode material of example 1 and the boron doped silicon-based negative electrode material of comparative example 5.

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 phosphorus-doped silicon-based negative electrode material is a powder material, and the powder conductance is 3.0S/cm-6.0S/cm; the phosphorus doped silicon-based negative electrode material comprises: 90 to 99.49 weight percent of silicon-based powder material, 0.01 to 3 weight percent of phosphorus-containing doping material doped in the silicon-based powder material and 0.5 to 7 weight percent of soft carbon material; the silicon-based powder material is specifically an electrochemical active powder material, and comprises one or more of a nano silicon-carbon composite material, silicon monoxide, modified silicon monoxide, doped silicon monoxide and amorphous silicon alloy;

the phosphorus-containing doping material comprises one or more of sodium dihydrogen phosphate, tripotassium phosphate, phosphorus pentoxide, sodium pyrophosphate, potassium pyrophosphate and sodium metaphosphate;

the soft carbon material is coated on the outer surface of the silicon-based powder material to form a coated carbon layer of the phosphorus-doped silicon-based negative electrode material.

Preferably, in the phosphorus-doped silicon-based negative electrode material, the silicon-based powder material accounts for 92 wt% -98 wt%, the phosphorus-doped material accounts for 0.01 wt% -2 wt%, and the soft carbon material accounts for 1 wt% -6 wt%.

In the phosphorus-doped silicon-based negative electrode material, the reaction temperature is not higher than 1000 ℃ in the coating process of coating the soft carbon material on the surface of the silicon-based powder material. In the process, phosphorus introduced by doping is gradually diffused into the silicon cathode material in the sintering process at 800-1000 ℃ to replace partial silicon atoms to form substitutional doping, so that the concentration of vacancy carriers in the silicon material can be effectively improved, and the intrinsic electronic conductivity of the silicon material is improved; and a part of phosphorus atoms can enter the carbon layer to interact with the soft carbon material, so that the effect of further improving the powder conductivity is achieved.

The phosphorus-doped silicon-based negative electrode material provided by the invention can be used for preparing a negative electrode plate of a lithium battery, the loaded negative electrode plate can be used for lithium batteries such as lithium ion batteries, lithium ion super capacitors, lithium sulfur batteries and all-solid-state lithium batteries, and the material has excellent long-cycle performance at high temperature by adopting phosphorus doping, and is particularly suitable for long-endurance large-scale vehicle power batteries.

The phosphorus-doped silicon-based negative electrode material can be prepared according to the following method.

Mixing a phosphorus-containing doping material and a silicon-based powder material in a required proportion, and preparing to obtain a primary product; and (3) placing the initial product in a high-temperature rotary furnace, heating to 800-1000 ℃ in the atmosphere of protective gas argon, introducing an organic gas source for chemical vapor deposition, keeping the temperature for 2-4 hours, closing the organic gas source, and cooling to obtain the phosphorus-doped silicon-based negative electrode material.

The method for preparing the initial product specifically comprises the following steps: spray drying, mechanical mixing, mechanical ball milling, and chemical vapor deposition.

The silicon-based powder material is specifically an electrochemical active powder material, and comprises one or more of a nano silicon-carbon composite material, silicon monoxide, modified silicon monoxide, doped silicon monoxide and amorphous silicon alloy; the phosphorus-containing doping material comprises one or more of sodium dihydrogen phosphate, tripotassium phosphate, phosphorus pentoxide, sodium pyrophosphate, potassium pyrophosphate and sodium metaphosphate; the organic gas source comprises: one or more of methane, acetylene, propylene and propane. The mixing proportion of the materials is based on the component proportion of the phosphorus doped silicon-based anode material to be finally realized.

The embodiment of the invention provides a phosphorus-doped silicon-based negative electrode material, wherein a small amount of doped phosphorus atoms replace part of silicon atoms, 4 outer electrons of the phosphorus atoms form covalent bonds with silicon, so that a freely moving electron appears, the concentration of the free electron is higher, and the conductivity of the silicon-based material is increased; a part of phosphorus atoms can enter the carbon layer to interact with the soft carbon material, so that the effect of further improving the powder conductivity is achieved; the carbon layer is used for limiting the volume expansion effect of the material while high powder conductivity is obtained, so that the silicon-based material can fully exert the advantage of high capacity. The phosphorus-doped silicon-based negative electrode material provided by the invention has a more stable structure, and phosphorus atoms and silicon are not easy to generate side reaction, so that irreversible capacity is reduced, and the cycle efficiency is improved.

In order to better understand the technical solutions provided by the present invention, the following description respectively describes specific processes for preparing a phosphorus-doped silicon-based negative electrode material by applying the method provided by the above embodiments of the present invention, and a method for applying the same to a secondary battery and battery characteristics.

Example 1

This example 1 provides a soft carbon coated phosphorus doped silicon based anode material.

The soft carbon-coated phosphorus-doped silicon-based negative electrode material of this example was designated as sample # 1. Consists of 95 wt% of silicon oxide, 2 wt% of tripotassium phosphate and 3 wt% of soft carbon coated outside.

The preparation process comprises the following steps: mechanically mixing tripotassium phosphate and silicon monoxide according to the proportion to obtain a primary product, then placing the primary product in a high-temperature rotary furnace under the argon atmosphere, heating to 1000 ℃, and mixing the primary product with the silicon monoxide according to the volume ratio of 1: 1, introducing argon and propylene with the same quantity as the argon for chemical vapor deposition, preserving heat for 2 hours, closing an air source and cooling to obtain a cathode material sample No. 1.

Mixing the obtained negative electrode material, conductive additive carbon black and adhesive (1: 1 of sodium cellulose and styrene butadiene rubber) according to a ratio of 95: 2: 3, weighing well. The slurry preparation was carried out in a beater 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 an 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. The reversible capacity of C/10 was 1822mAh/g, the initial efficiency was 78.5%.

The phosphorus doped silicon-based anode material of the present example was subjected to a powder conductivity test, and the result was 3.7S/cm.

Example 2

This example 2 provides a soft carbon coated phosphorus doped silicon based anode material.

The soft carbon-coated phosphorus-doped silicon-based negative electrode material of this example was denoted as sample # 2. Consists of 93.8 wt% doped silica, 2.4 wt% phosphorus pentoxide and 3.8 wt% soft carbon coating.

The preparation process comprises the following steps: carrying out mechanical ball milling on phosphorus pentoxide and doped silicon monoxide according to the proportion to obtain a primary product, then placing the primary product in a high-temperature rotary furnace under the argon atmosphere, heating to 1000 ℃, and mixing the primary product with the mixed silicon monoxide according to the volume ratio of 1: 1, introducing propane with the same quantity as the argon gas for chemical vapor deposition, preserving the heat for 2.5 hours, closing a gas source and cooling to obtain a sample No. 2.

The preparation of the negative pole piece and the process of battery assembly and test are the same as example 1, and the test result shows that the reversible capacity of C/10 is 1805mAh/g, and the initial efficiency is 77.7%.

The phosphorus doped silicon-based anode material of the present example was subjected to a powder conductivity test, and the result was 3.9S/cm.

Example 3

This example 3 provides a soft carbon coated phosphorus doped silicon based anode material.

The soft carbon-coated phosphorus-doped silicon-based negative electrode material of this example was denoted as sample # 3. Consists of 96.5 wt% of modified silica, 0.8 wt% of sodium pyrophosphate and 2.7 wt% of soft carbon coated outside.

The preparation process comprises the following steps: carrying out spray drying on sodium pyrophosphate and modified silicon oxide according to the proportion to obtain an initial product, then placing the initial product in a high-temperature rotary furnace under the argon atmosphere, heating to 950 ℃, and mixing the initial product with the modified silicon oxide according to the volume ratio of 1: 1 introducing a methane and propylene mixed gas with the same quantity as the argon gas for chemical vapor deposition, preserving the heat for 3 hours, closing a gas source and cooling to obtain a sample No. 3. Wherein in the mixed gas, the ratio of methane to propylene is 2: 1.

the preparation of the negative pole piece and the process of battery assembly and test are the same as example 1, and the test result shows that the reversible capacity of C/10 is 1718mAh/g, and the initial efficiency is 76.9%.

The phosphorus doped silicon-based anode material of the present example was subjected to a powder conductivity test, and the result was 3.8S/cm.

Example 4

This example 4 provides a soft carbon coated phosphorus doped silicon based anode material.

The soft carbon-coated phosphorus-doped silicon-based negative electrode material of this example was denoted as sample # 4. Consists of 95.5 wt% of modified silica, 1.5 wt% of potassium pyrophosphate and 3.0 wt% of soft carbon coated outside.

The preparation process comprises the following steps: mechanically mixing potassium pyrophosphate and modified silicon monoxide after mechanical ball milling in the proportion to obtain a primary product, then placing the primary product in a high-temperature rotary furnace under the argon atmosphere, heating to 850 ℃, and mixing according to the volume ratio of 1: 1 introducing a methane and propylene mixed gas with the same quantity as the argon gas for chemical vapor deposition, preserving the heat for 2.5 hours, closing a gas source and cooling to obtain a sample No. 4. Wherein in the mixed gas, the ratio of methane to propylene is 1: 1. the preparation of the negative pole piece and the process of battery assembly and test are the same as example 1, and the test result shows that the reversible capacity of C/10 is 1688mAh/g, and the initial efficiency is 76.8%.

The phosphorus doped silicon-based anode material of the present example was subjected to a powder conductivity test, and the result was 3.4S/cm.

Example 5

This example 5 provides a soft carbon coated phosphorus doped silicon based anode material.

The soft carbon-coated phosphorus-doped silicon-based negative electrode material of this example was denoted as sample # 5. Consists of 97.0 wt% of amorphous silicon alloy, 0.4 wt% of sodium metaphosphate and 2.6 wt% of soft carbon coated outside.

The preparation process comprises the following steps: and (2) carrying out spray drying on sodium metaphosphate and amorphous silicon alloy according to the proportion to obtain a primary product, then placing the primary product in a high-temperature rotary furnace under the argon atmosphere, heating to 900 ℃, and mixing the primary product with the amorphous silicon alloy according to the volume ratio of 1: 1, introducing acetylene with the same quantity as the argon gas for chemical vapor deposition, preserving the heat for 3 hours, closing an air source and cooling to obtain a sample No. 5.

The preparation of the negative pole piece and the process of battery assembly and test are the same as example 1, and the test result shows that the reversible capacity of C/10 is 1679mAh/g, and the initial efficiency is 77.1%.

The phosphorus doped silicon-based anode material of the present example was subjected to a powder conductivity test, and the result was 3.0S/cm.

For better comparison, we prepared a comparative sample as follows.

Comparative example 1

This comparative example provides a lithium ion battery negative electrode material, sample # 6, of 95 wt% silica, 1.7 wt% tripotassium phosphate, and 3.3 wt% soft carbon coating, comparable to example 1.

The preparation process comprises the following steps: mechanically mixing the silicon oxide and the tripotassium phosphate according to the proportion to obtain a primary product, then placing the primary product in a high-temperature rotary furnace, raising the temperature to 700 ℃ in an argon atmosphere, and mixing the materials according to a volume ratio of 1: 1, introducing propylene with the same quantity as the argon gas for chemical vapor deposition, preserving the heat for 3 hours, closing a gas source and cooling to obtain a sample No. 6.

The procedures of preparation of the negative pole piece, battery assembly and test are the same as example 1, and the test result shows that the reversible capacity of C/10 is 1533mAh/g, and the initial efficiency is 74.6%.

The negative electrode material of this comparative example was subjected to a powder conductivity test, and the result was 2.1S/cm.

Comparative example 2

This comparative example provides a lithium ion battery negative electrode material, sample # 7, of 94.7 wt% silica, 2 wt% tripotassium phosphate, and 3.3 wt% soft carbon coating, comparable to example 1.

The preparation process comprises the following steps: mechanically mixing the silicon oxide and the tripotassium phosphate according to the proportion to obtain a primary product, then placing the primary product in a high-temperature rotary furnace, raising the temperature to 1050 ℃ under the argon atmosphere, and mixing the primary product with the silicon oxide and the tripotassium phosphate according to the volume ratio of 1: 1, introducing propylene with the same quantity as the argon gas for chemical vapor deposition, preserving the heat for 2 hours, closing a gas source and cooling to obtain a sample No. 7.

The preparation of the negative pole piece and the process of battery assembly and test are the same as example 1, and the test result shows that the reversible capacity of C/10 is 1541mAh/g, and the initial efficiency is 75.7%.

The negative electrode material of this comparative example was subjected to a powder conductivity test, and the result was 3.2S/cm.

Comparative example 3

A comparative example provides a negative electrode material for a lithium ion battery, sample # 8, which is a comparative example to example 1 and consists of 94.4 wt% of silica, 2 wt% of tripotassium phosphate, and 3.6 wt% of soft carbon coated thereon.

The preparation process comprises the following steps: mechanically mixing the silicon monoxide and the tripotassium phosphate according to the proportion to obtain a primary product, then placing the primary product in a high-temperature rotary furnace to heat the primary product to 1350 ℃ in an argon atmosphere, and mixing the primary product and the tripotassium phosphate according to a volume ratio of 1: 1, introducing propylene with the same quantity as the argon gas for chemical vapor deposition, preserving the heat for 1.8 hours, closing a gas source and cooling to obtain a sample No. 8.

The preparation of the negative pole piece and the process of battery assembly and test are the same as example 1, and the test result shows that the reversible capacity of C/10 is 1492mAh/g, and the initial efficiency is 74.3%.

The negative electrode material of this comparative example was subjected to a powder conductivity test, and the result was 2.4S/cm.

Comparative example 4

A comparative example provides a negative electrode material for a lithium ion battery, sample # 9, of 94.8 wt% silica, 2.2 wt% melamine, and 3.0 wt% soft carbon coating, as compared to example 1.

The preparation process comprises the following steps: mechanically mixing melamine and silicon monoxide according to the proportion to obtain a primary product, then placing the primary product in a high-temperature rotary furnace to raise the temperature to 1000 ℃ in an argon atmosphere, and mixing the melamine and the silicon oxide according to a volume ratio of 1: 1, introducing propylene with the same quantity as the argon gas for chemical vapor deposition, preserving the heat for 2 hours, closing a gas source and cooling to obtain a sample No. 9.

The preparation of the negative electrode piece and the process of battery assembly and test are the same as example 1, and the test result shows that the reversible capacity of C/10 is 1608mAh/g, and the initial efficiency is 76.1%.

The negative electrode material of this comparative example was subjected to a powder conductivity test, and the result was 3.3S/cm.

Comparative example 5

A comparative example provides a negative electrode material for a lithium ion battery, sample # 10, of 94.2 wt% silica, 2.4 wt% sodium borate and 3.4 wt% soft carbon coated, as compared to example 1.

The preparation process comprises the following steps: mechanically mixing sodium borate and silicon monoxide according to the proportion to obtain an initial product, then placing the initial product in a high-temperature rotary furnace in an argon atmosphere, heating to 1000 ℃, and mixing the initial product and the silicon oxide according to a volume ratio of 1: 1, introducing propylene with the same quantity as the argon gas for chemical vapor deposition, preserving the heat for 2 hours, closing a gas source and cooling to obtain a sample No. 10.

The preparation of the negative pole piece and the process of battery assembly and test are the same as example 1, and the test result shows that the reversible capacity of C/10 is 1640mAh/g, and the initial efficiency is 76.4%.

The negative electrode material of this comparative example was subjected to a powder conductivity test, and the result was 3.0S/cm.

The negative electrode materials of examples 1 to 5 and comparative examples 1 to 5 were subjected to initial efficiency, 0.1C reversible capacity, powder conductivity, and other index tests, and the results are shown in table 1.

TABLE 1

As can be seen from the data in table 1, in the same situation, the silicon-based negative electrode materials in examples 1 to 5 are modified by the phosphorus doping method, and both the powder conductance and the specific charge capacity are high. The comparative examples 1 to 5 adopt phosphorus doping at different temperatures to modify the silicon-based anode material, and the examples show that the improvement effect on the powder conductivity after the phosphorus doping is obvious within the given temperature range of 800-. When the temperature is low, 700 ℃, referring to comparative example 1, the disproportionation reaction is not yet significant, and only a part of the simple substance of silicon is produced, so the first cycle efficiency is low. At this temperature, the phosphorus atoms have not migrated so much that the improvement effect on the powder conductivity is poor. When the temperature exceeds 1000 c, referring to comparative example 2 and comparative example 3, the powder conductance and the initial efficiency tend to decrease. At high temperatures, carbon reacts with silicon to form silicon carbide, which results in a reduction in capacity and a decrease in powder conductance. In comparison with example 1 and comparative example 4, the phosphorus doping and the nitrogen doping both belong to N-type doping, and have very high powder conductivity, which indicates that the N-type doping of the silicon-based material can obviously improve the rate performance. From the viewpoint of cycle performance, the cycle performance of comparative example 4 is significantly inferior to that of example 1, because nitrogen and silicon generate part of silicon nitride at high temperature, and the silicon nitride itself has a rigid structure so that the material is easily broken and pulverized during volume expansion, thereby reducing the capacity and cycle performance of the lithium ion battery.

In the applicant's on-line patent application CN202010153328.2, we improve silicon-based negative electrode materials by carbon coating and boron doping, and the obtained lithium ion negative electrode material has excellent properties of high capacity and high powder conductivity. However, in subsequent studies, it was found that sodium borate is likely to produce a part of boron oxide under the action of high temperature, and boron oxide displaces a part of silicon atoms to form an inert substance, resulting in an increase in irreversible capacity and a decrease in cycle performance. This deficiency can be ameliorated by using phosphorus doping. Comparative example 5 and example 1 were compared, comparative example 5 being doped with P-type boron and example 1 being doped with N-type phosphorus. By comparison, the cycle performance and reversible capacity of the N-type phosphorus doped silicon-based negative electrode material are better than those of the P-type boron doped silicon-based negative electrode material. Therefore, the phosphorus-doped silicon-based negative electrode material is more biased to a large-scale power battery for long-endurance in the application field of lithium ion batteries, and boron doping is more suitable for miniaturized products such as high-rate mobile phone quick-charging lithium ion batteries.

Moreover, in subsequent researches, we also found that high-temperature doping is beneficial to improving the powder conductivity of the negative electrode material, but the powder conductivity is improved due to the influence of an excessively high temperature, and the temperature boundary of the high-temperature doping is 1000 ℃. When the preparation temperature is higher than 1000 ℃, a silicon carbide phase is generated at high temperature. The silica material undergoes disproportionation reaction at a temperature higher than 600 ℃ to produce silica and amorphous silicon. With the increase of the temperature, the amorphous silicon crystal grains grow slowly to generate the crystalline silicon. And the capacity of the lithium ion battery is partially contributed by the simple substance of silicon. After the temperature is higher than 1000 ℃, part of silicon and carbon react to generate silicon carbide, so that the capacity of the silicon-based cathode material is reduced, and the electrical conductivity of the silicon carbide is poor, so that the improvement of the electrical conductivity of the whole cathode material is influenced.

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.