Preparation method of phosphorus-doped silicon-based composite negative electrode material, product and application thereof

Abstract

The application discloses a preparation method of a phosphorus-doped silicon-based composite negative electrode material, which comprises the following steps: (1) mixing phosphorus source gas, carbon source gas and silicon source gas under an inert atmosphere at room temperature to obtain mixed gas; in the mixed gas, the volume percentage of the phosphorus source gas is 0.1-3.0%, the volume percentage of the carbon source gas is 15-28%, and the balance is the silicon source gas; (2) introducing the mixed gas into a deposition furnace in which a base material is placed, and obtaining an intermediate product after heat deposition; and (3) performing carbon coating treatment on the intermediate product, and obtaining the phosphorus-doped silicon-based composite negative electrode material after post-treatment. The application discloses the preparation method of the phosphorus-doped silicon-based composite negative electrode material, and the lithium ion battery assembled by using the prepared negative electrode material has excellent cycle stability, high reversible specific capacity and high initial coulomb efficiency.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium battery negative electrode materials, and particularly relates to a preparation method of a phosphorus-doped silicon-based composite negative electrode material, a product thereof and application. BACKGROUND

[0002] Silicon is considered as the most promising candidate to replace graphite. It is the second most abundant element in the earth's crust, environmentally friendly, and has an ultra-high theoretical capacity (4200 mAh / g). However, the severe volume change during lithium intercalation / deintercalation causes serious adverse consequences, resulting in very poor cycle stability. Although compared with silicon element, the volume expansion of silicon monoxide material during lithium intercalation is greatly reduced, and also has a high theoretical specific capacity (>2000 mAh / g), but the first coulombic efficiency of silicon monoxide is too low (less than 76%), which limits its wider application; and compared with silicon monoxide, the silicon-carbon product on the market has the characteristics of high initial efficiency and high capacity, but its cycle performance is far inferior to that of silicon monoxide; therefore, it is an urgent matter to prepare a silicon-based negative electrode material with high capacity, high initial efficiency and cycle performance.

[0003] A preparation method of a phosphorus-doped porous carbon negative electrode material with improved first coulombic efficiency is disclosed in Chinese patent document CN 107623118 A. Elemental red phosphorus is used as a phosphorus source, an organic carbon source is dispersed in water to form a slurry, and then the slurry is mixed uniformly with the red phosphorus, dried, and then calcined in a sealed tank filled with a protective atmosphere, and then further calcined in an inert atmosphere tube furnace to prepare a phosphorus-doped porous carbon negative electrode material. The technical solution uses phosphorus as a doping element, and claims that it can improve the reversible specific capacity of the carbon material and significantly improve the first coulombic efficiency of the material. The preparation method disclosed in the technical solution is simple, but liquid-solid mixing is used, which cannot guarantee the uniformity of doping, and therefore affects the consistency of the preparation method; and the first coulombic efficiency of the material obtained by the method is only 71% at most, which is insufficient to meet market demand.

[0004] A phosphorus-doped soft carbon-coated silicon-based lithium ion negative electrode material, its preparation method and application are disclosed in Chinese patent document CN 113809311 A. A phosphorus-doped silicon-based lithium ion negative electrode material is prepared by mixing a phosphorus-containing gas source or a high-boiling phosphorus-containing compound with a preheated silicon source vapor at 1200-1700°C for 1-24h. The silicon source vapor is a mixture of silicon vapor and silicon dioxide vapor. The phosphorus-doped silicon-based lithium ion negative electrode material is obtained by cooling the intermediate product to room temperature, breaking and sieving the material, and analyzing and testing the sieved material. The material that meets the preset conditions for uniform doping is coated with carbon to obtain the phosphorus-doped silicon-based lithium ion negative electrode material. In this technical solution, the reaction substances are fully contacted by gas-phase mixing reaction of the phosphorus-containing substance with silicon vapor and silicon dioxide vapor, resulting in a lithium ion battery negative electrode material with uniform bulk doping. The obtained material has higher cycle stability and more excellent consistency. However, the first efficiency of the phosphorus-doped silicon negative electrode material obtained by this method is only 80.6%, and there is no obvious product advantage. More importantly, the energy consumption of this technical solution is very high. The temperature required for preheating silicon and silicon dioxide to form vapor is at least 1350°C, the gas-phase mixing reaction is carried out at a high temperature of 1200-1700°C, and the carbon coating in the later stage also needs to be carried out at a high temperature of 800-1000°C. Therefore, this technical solution is not suitable for large-scale industrial production. SUMMARY

[0005] To solve the above problems in the prior art, the application discloses a preparation method of a phosphorus-doped silicon-based composite negative electrode material. The lithium ion battery assembled by the prepared negative electrode material has excellent cycle stability, high reversible specific capacity and high first coulomb efficiency.

[0006] The specific technical solution is as follows:

[0007] A preparation method of a phosphorus-doped silicon-based composite negative electrode material, comprising the following steps:

[0008] (1) Under an inert atmosphere, mix a phosphorus source gas, a carbon source gas and a silicon source gas at room temperature to obtain a mixed gas;

[0009] In the mixed gas, the volume percentage of the phosphorus source gas is 0.1-3.0%, the volume percentage of the carbon source gas is 15-28%, and the balance is the silicon source gas, based on a total volume of 100%;

[0010] (2) Introduce the mixed gas into a deposition furnace containing a base material, and obtain an intermediate product after heat deposition;

[0011] (3) Perform carbon coating treatment on the intermediate product, and then perform post-treatment to obtain the phosphorus-doped silicon-based composite negative electrode material.

[0012] The application discloses a preparation method of a phosphorus-doped silicon-based composite negative electrode material. The phosphine which is gaseous at normal temperature is used as a phosphorus source, and a gaseous carbon source is additionally introduced. The gaseous carbon source is mixed with a gaseous silicon source at room temperature to obtain a mixed gas. In a gas deposition reaction process, the carbon and the phosphorus are bonded with the silicon source material respectively, and pyrolysis and dehydrogenation are performed. Finally, the phosphorus-doped silicon-based composite negative electrode material is prepared through carbon coating treatment.

[0013] It is found through experiments that the doping of phosphorus atoms in the preparation method can significantly reduce the average particle size of silicon primary grains. The introduction of the gaseous carbon source can produce mutual coordination with the doped phosphorus atoms, which is helpful to the cracking of the phosphorus source gas and the doping of the phosphorus source. When the gaseous carbon source, the gaseous silicon source and the phosphorus source gas are mixed and finally prepared through the above series of processes, the phosphorus-doped silicon-based composite negative electrode material has excellent cycle stability, reversible specific capacity and initial coulombic efficiency.

[0014] It is found through experiments that the combination of only the phosphorus source gas and the silicon source gas or the combination of only the carbon source gas and the silicon source gas cannot obtain the above-mentioned synergistic effect.

[0015] It is found through further experiments that even if the combination of the phosphorus source gas, the carbon source gas and the silicon source gas is used, the lithium ion battery with excellent cycle stability, high reversible specific capacity and initial coulombic efficiency cannot be prepared if the volume ratio of the three is not within the above-mentioned range.

[0016] In step (1):

[0017] The phosphorus source gas is selected from phosphine.

[0018] The carbon source gas is selected from alkane gases which can be cracked at 400-800 DEG C; preferably selected from ethylene, propylene, acetylene and the like.

[0019] The silicon source gas is selected from one or more of silane, dichlorodihydrogen silicon, trichlorohydrogen silicon and silicon tetrachloride.

[0020] In step (2):

[0021] The total flow rate of the mixed gas is 0.1-50 L / min; preferably 20-50 L / min; further preferably 25-30 L / min.

[0022] The base material is selected from one or more of hard carbon, conductive carbon black, carbon nanotube and graphene; the mass of the added base material accounts for 0.1-20.0 wt% of the total mass of the final product.

[0023] Preferably, the D50 of the base material is less than 200 nm.

[0024] The temperature of the thermal deposition is 400-800 DEG C.

[0025] In step (3) :

[0026] The intermediate product is subjected to crushing, grading and magnetic removal treatment, and then subjected to carbon coating treatment.

[0027] Preferably, the particle size concentration (SPAN value) of the intermediate product subjected to crushing, grading and magnetic removal treatment is ≤1.5, and the average particle size is ≤10 μm; further preferably, the SPAN value is ≤1.2.

[0028] In step (3) :

[0029] The carbon coating treatment is selected from one or more of gas phase carbon coating, liquid phase carbon coating and solid phase carbon coating.

[0030] The carbon source used in the gas phase carbon coating is a hydrocarbon gas, such as ethylene, propylene, acetylene, etc., and the specific carbon coating process uses conventional technical means in the art.

[0031] The carbon source used in the liquid phase carbon coating is a carbon-containing high molecular polymer, such as liquid epoxy resin, petroleum residue, liquid asphalt, etc., and the specific carbon coating process uses conventional technical means in the art.

[0032] The carbon source used in the solid phase carbon coating is asphalt, and the specific carbon coating process uses conventional technical means in the art.

[0033] The temperature of the carbon coating treatment is selected from 600-1000℃; and is adjusted adaptively according to the type of the carbon source used.

[0034] In step (3) :

[0035] The post-treatment includes breaking up and sieving, and the specific operations are conventional technical means in the art. For example, the breaking up method uses a spiral breaking up method.

[0036] Preferably, the mesh size used in the sieving is 100-800 mesh.

[0037] On the basis of the above process and raw materials, preferably:

[0038] In step (1), in the mixed gas, the volume ratio of the phosphorus source gas is 0.5-3.0%, the volume ratio of the carbon source gas is 15-25%, and the balance is the silicon source gas.

[0039] Further preferably:

[0040] In the mixed gas, the volume ratio of the phosphorus source gas is 0.5-1.5%, the volume ratio of the carbon source gas is 15-25%, and the balance is the silicon source gas.

[0041] More preferably, the phosphorus source gas, the carbon source gas and the silicon source gas are mixed at a volume ratio of 1.5:25:73.5 at room temperature.

[0042] Most preferably, the silicon source is selected from trichlorosilane; it has been found that, under the above further preferred volume ratio, the lithium ion battery assembled using the phosphorus-doped silicon-based composite negative electrode material ultimately prepared by using trichlorosilane as the silicon source has the best cycle stability, reversible specific capacity and initial coulombic efficiency.

[0043] The application further discloses a phosphorus-doped silicon-based composite negative electrode material prepared by the method.

[0044] The application further discloses application of the phosphorus-doped silicon-based composite negative electrode material prepared by the method in a lithium ion battery; it has been found that the lithium ion battery assembled using the negative electrode material has excellent cycle stability, high reversible specific capacity and high initial coulombic efficiency.

[0045] Compared with the prior art, the application has the following beneficial effects:

[0046] The application discloses a preparation method of a phosphorus-doped silicon-based composite negative electrode material.

[0047] The lithium ion battery assembled using the phosphorus-doped silicon-based composite negative electrode material prepared by the method has excellent cycle stability, a capacity retention rate of more than 80% after 100 cycles, a maximum capacity retention rate of 88%, a capacity retention rate of more than 70% after 500 cycles, a maximum capacity retention rate of 75.5%, high reversible specific capacity (more than 1800 mAh / g) and high initial coulombic efficiency (not less than 90%). BRIEF DESCRIPTION OF DRAWINGS

[0048] Figure 1 Mapping images of the intermediate product prepared in Example 1;

[0049] Figures 2 to 4 are respectively Si element, C element and P element distribution maps in the image range of Figure 1

[0050] Figure 5 is an SEM image of the phosphorus-doped silicon-based composite negative electrode material prepared in Example 1.

[0051] Figure 6 is a TEM image of the phosphorus-doped silicon-based composite negative electrode material prepared in Example 1. DETAILED DESCRIPTION

[0052] ​The specific implementation methods of the present invention will be further described below with reference to examples. It should be noted that the specific implementation methods described herein are only for illustration and explanation of the present invention and are not limited to the present invention.

[0053] Example 1

[0054] (1) Under an argon atmosphere, phosphine, ethylene and silane are thoroughly mixed at room temperature in a volume ratio of 1.5:25:73.5 to obtain a mixed gas.

[0055] (2) The mixed gas was introduced into a deposition furnace containing 100 grams of hard carbon microspheres with a D50 of about 100 nm and the temperature was set to 500 °C at a total gas flow rate of 25 L / min. The gas was continuously introduced until the hard carbon microsphere particles nucleated and grew on the surface, depositing a phosphorus-doped silicon-carbon deposition layer. The gas was kept for 10 h.

[0056] (3) The deposition furnace is cooled down, and the material is crushed and graded after exiting the furnace to obtain uniform particles with D50 less than 5μm and SPAN value less than 1.2. After magnetic treatment, intermediate products are obtained.

[0057] (4) Under an argon atmosphere, the intermediate product is fed into a chemical vapor deposition furnace and heated to 800°C at 5°C / min. Acetylene gas is introduced at a flow rate of 1L / min for gas phase pyrolysis deposition of carbon coating. The carbon coating amount is controlled to be 4wt% of the total mass of the final product. After deposition, the temperature is lowered to room temperature, the material is taken out, broken up and sieved to finally obtain phosphorus-doped silicon-based composite anode material.

[0058] Figure 1 The mapping image of the intermediate product prepared in step (3) of this embodiment, and the Si element ( ) within the image range. Figure 2 ), C element ( Figure 3 ) and the distribution map of element P ( Figure 4 ),observe Figures 2 to 4 It can be observed that the intermediate product prepared in this embodiment has been successfully doped with both C and P elements, and the two elements are uniformly dispersed in the intermediate product.

[0059] Figure 5 This is an SEM image of the final product prepared in this embodiment. Observing this image, it can be seen that the final product prepared in this embodiment is a regular sphere with a relatively uniform particle size distribution.

[0060] Figure 6 This is a TEM image of the final product prepared in this embodiment. Observing this image, it can be seen that the surface of the negative electrode material prepared in this embodiment is coated with a uniform carbon layer.

[0061] Example 2

[0062] The preparation process is basically the same as that in Example 1, except that in step (1), the volume ratio of phosphine, ethylene and silane is replaced by 3:15:82.

[0063] Example 3

[0064] The preparation process is basically the same as that in Example 1, except that in step (1), the volume ratio of phosphine, ethylene and silane is replaced by 0.5:25:74.5.

[0065] Comparative Example 1

[0066] The preparation process is basically the same as that in Example 1, except that in step (1), the volume ratio of phosphine, ethylene and silane is replaced by 5:25:70.

[0067] Comparative Example 2

[0068] The preparation process is basically the same as that in Example 1, except that in step (1), only a mixture gas of ethylene and silane with a volume ratio of 25:75 is added.

[0069] Comparative Example 3

[0070] The preparation process is basically the same as that in Example 1, except that in step (1), the volume ratio of phosphine, ethylene and silane is replaced by 2:30:68.

[0071] Comparative Example 4

[0072] The preparation process is basically the same as that in Example 1, except that in step (1), the volume ratio of phosphine, ethylene and silane is replaced by 2:13:85.

[0073] Comparative Example 5

[0074] The preparation process is basically the same as that in Example 1, except that in step (1), only a mixture gas of phosphine and silane with a volume ratio of 2:98 is added.

[0075] Example 4

[0076] (1) Under an argon atmosphere, phosphine, propylene and dichlorodihydrogen silicon are mixed at a volume ratio of 1.5:25:73.5 at room temperature to obtain a mixed gas.

[0077] (2) The mixed gas is introduced into a deposition furnace with a total gas flow rate of 30 L / min and a temperature of 400°C, and the graphene microspheres with a D50 of about 100 nm are placed in the furnace for 100 grams. The gas is continuously introduced until the graphene microsphere particles continuously nucleate and grow on the surface, and a phosphorus-doped silicon-carbon deposition layer is deposited. The gas introduction time is 13h.

[0078] Steps (3) to (4) are exactly the same as in Example 1.

[0079] Example 5

[0080] (1) Under an argon atmosphere, phosphine, acetylene and trichlorosilane were mixed at a volume ratio of 1.5:25:73.5 at room temperature to obtain a mixed gas.

[0081] (2) The mixed gas was introduced into a deposition furnace in which 100 grams of electrically conductive carbon black microspheres with a D50 of about 100 nm were placed and the temperature was set to 800°C at a total gas flow rate of 30 L / min, and the gas was continuously introduced until the surface of the electrically conductive carbon black microspheres was continuously nucleated and grew, and a phosphorus-doped silicon-carbon deposition layer was deposited, and the gas introduction time was 5 h.

[0082] Steps (3) to (4) are exactly the same as in Example 1.

[0083] Application Example

[0084] The negative electrode materials prepared in each example and each comparative example were assembled into batteries.

[0085] Under a nitrogen protective atmosphere, the conductive agent SuperP and carboxymethyl cellulose sodium CMC were mixed and dispersed with deionized water, then the negative electrode material was added, stirred at 2000 rpm for 10 min, then the aqueous binder AONE (purchased from Shenzhen Yinxin New Material Co., Ltd.) was added, stirred at 2000 rpm for 10 min, to obtain a negative electrode slurry. The mass ratio of the negative electrode material, conductive agent SuperP, carboxymethyl cellulose sodium CMC, and binder AONE (dry weight) was 70:15:5:10, and the solid content of the slurry was 15 wt%.

[0086] The above negative electrode slurry was coated on the current collector copper foil, dried at 80°C under a relative vacuum of -0.1 Mpa for 30 min, then roll-pressed at room temperature, and the areal density was 9.1 mg / cm 2 Then it was punched and cut into a circular sheet with a diameter of 14 mm to make an electrode sheet.

[0087] The counter electrode was a lithium sheet CR2016 (purchased from Shenzhen Yongxingye Equipment Technology Co., Ltd.) with a diameter of 16 mm.

[0088] The assembly of the button cell was carried out in a glove box under an argon atmosphere, and the moisture value and oxygen value in the glove box were less than 0.01 ppm. The button cell was assembled in the order of "negative shell-gasket-lithium sheet-electrolyte-separator-electrolyte-electrode sheet-positive shell", wherein the electrolyte was composed of ethylene carbonate (EC), methyl ethyl carbonate (EMC) and diethyl carbonate (DEC) (EC: EMC: DEC volume ratio = 1:1:1) containing 1.0 M LiPF6.

[0089] The diameter of the electrode sheet was 14 mm, the diameter of the lithium sheet was 16 mm, the diameter of the separator was 19 mm, and the size of the battery shell (positive shell and negative shell) was 20 mm. The separator was a ceramic-coated separator film (purchased from Shanghai Enxin New Material Technology Co., Ltd.) with a thickness of 12 μm. The assembled button cell was placed in the mold groove of a hydraulic sealing machine (purchased from Shenzhen Kejing Zhida Technology Co., Ltd.), locked, and the pressure was > 500 kg / cm 2 Then it was unlocked and the sealed button cell was taken out.

[0090] During the assembly of the battery, five button cells were prepared for each test group, and five groups of data were tested, and the average value of the five groups of data was taken as the final performance.

[0091] Performance test:

[0092] XRD-D2 PHASER of Bruker was used for phase analysis detection, and Scherrer formula was used for calculation to test the particle size of the silicon primary grains.

[0093] Phenom Generation 5 of Thermo Fisher was used for morphology test.

[0094] German Eltra high-frequency infrared carbon and sulfur analyzer was used to test the carbon content.

[0095] German Elementar organic element analyzer was used to test the phosphorus content.

[0096] The battery cycle performance was tested on a Blue Electric Battery Test System CT2001A device, specifically:

[0097] The charge-discharge cycle characteristics of the button cells were detected by the above blue electric test cabinet at 25℃. First, discharge at 0.1C to 0.005V, then discharge at 0.08C to 0.001V, discharge at 0.05C to 0.001V, discharge at 0.02C to 0.001V, and stand for 10min; then charge at 0.1C to 1.5V, stand for 10min, record the charge-discharge capacity after the first cycle, and calculate the first coulombic efficiency; cycle 100 times according to the above method, record the charge-discharge capacity after 100 times, and calculate the capacity retention rate after 100 cycles; the test and calculation process of the capacity retention rate after 500 cycles are the same, and the test results are shown in Table 1 below.

[0098] Table 1

[0099]

[0100] 1. The mass content of phosphorus element in the intermediate product prepared for each example or each comparative example;

[0101] 2. The mass content of carbon element in the intermediate product prepared for each example or each comparative example;

[0102] 3. The average particle size of silicon primary grains of the intermediate product prepared for each example or each comparative example.

[0103] By comparing the changes of the phosphorus content and the carbon content in Table 1, it can be known that the method disclosed in the application can controllably prepare the phosphorus content and the carbon content in the product. By comparing the average particle size of silicon primary grains in Example 1 and Comparative Examples 2 and 3, it can be known that the introduction of phosphorus element can effectively reduce the average particle size of silicon primary grains.

[0104] According to the above examples, the application can be well implemented. It should be noted that, based on the above design, to solve the same technical problem, even if some non-substantial changes or embellishments are made on the application, the essence of the technical solution adopted is still the same as the application, so it should also be within the protection scope of the application.

Claims

1. A method for preparing a phosphorus-doped silicon-based composite negative electrode material, characterized in that, The method comprises the following steps: (1) under an inert atmosphere, mixing a phosphorus source gas, a carbon source gas and a silicon source gas at room temperature to obtain a mixed gas; The phosphorus source gas is selected from phosphine; The carbon source gas is selected from alkane gas that can be cracked at 400-800℃; The silicon source gas is selected from one or more of silane, dichlorosilane, trichlorosilane and silicon tetrachloride; In the mixed gas, the volume percentage of the phosphorus source gas is 0.5-3.0%, the volume percentage of the carbon source gas is 15-25%, and the balance is the silicon source gas, based on a total volume of 100%; (2) introducing the mixed gas into a deposition furnace in which a base material is placed, and obtaining an intermediate product after thermal deposition; The base material is selected from one or more of hard carbon, conductive carbon black, carbon nanotube and graphene; (3) performing carbon coating treatment on the intermediate product, and obtaining the phosphorus-doped silicon-based composite negative electrode material after post-treatment; The lithium ion battery assembled by using the phosphorus-doped silicon-based composite negative electrode material has a capacity retention rate of 70% or more after 500 cycles, a reversible specific capacity of more than 1800 mAh / g, and a first coulombic efficiency of not less than 90%.

2. The method for preparing the phosphorus-doped silicon-based composite anode material according to claim 1, characterized in that, In step (2): The total flow rate of the mixed gas is 0.1-50 L / min; The temperature of the thermal deposition is 400-800℃.

3. The method of claim 1, wherein the phosphorus-doped silicon-based composite negative electrode material is prepared by the following steps of: (a) mixing a silicon-based material, a carbon-based material, and a phosphorus source to form a mixture; (b) heating the mixture to form a phosphorus-doped silicon-based composite negative electrode material. In step (3): The intermediate product is subjected to carbon coating treatment after being crushed, classified and subjected to magnetic removal; The particle size concentration of the intermediate product after being crushed, classified and subjected to magnetic removal is ≤1.5, and the average particle size is ≤10 μm.

4. The method for preparing the phosphorus-doped silicon-based composite anode material according to claim 1, characterized in that, In step (3): The carbon coating treatment is selected from one or more of gas-phase carbon coating, liquid-phase carbon coating and solid-phase carbon coating; The temperature of the carbon coating treatment is selected from 600-1000℃.

5. The method for preparing the phosphorus-doped silicon-based composite anode material according to claim 1, characterized in that, In step (3): The post-treatment comprises dispersing and sieving.

6. The method for preparing the phosphorus-doped silicon-based composite negative electrode material according to any one of claims 1-5, characterized in that: In step (2), the total flow rate of the mixed gas is 20-50 L / min.

7. The method for preparing the phosphorus-doped silicon-based composite negative electrode material according to claim 6, characterized in that: The phosphorus source gas, the carbon source gas and the silicon source gas are mixed at a volume ratio of 1.5:25:73.5 at room temperature in the mixed gas; The silicon source gas is selected from trichlorosilane.

8. A phosphorus-doped silicon-based composite negative electrode material prepared by the method according to any one of claims 1-7.

9. Application of the phosphorus-doped silicon-based composite negative electrode material according to claim 8 in a lithium ion battery.

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