Negative electrode material and preparation method therefor

Abstract

Provided are a negative electrode material (100) and a preparation method therefor. The negative electrode material (100) comprises a silicon-carbon core (101) and a coating layer (102) arranged on the surface of the silicon-carbon core (101). The silicon-carbon core (101) comprises porous carbon and a silicon-based material deposited on the porous carbon. The ratio of the mass content of the silicon-based material to the total pore volume of the porous carbon in the negative electrode material (100) is within a first value range, and a differential value obtained by differentiating the voltage with the charge-discharge capacity at 0.45 V in a charge-discharge curve of the negative electrode material (100) is within a second value range, so that the negative electrode material (100) has high capacity, low expansion performance, and high conductivity, wherein the unit of the total pore volume of the porous carbon is cm3 / g. For the negative electrode material (100), by controlling the ratio of the mass content of the silicon-based material to the total pore volume of the porous carbon in the negative electrode material (100) within a certain value range, the negative electrode material (100) can have high capacity and also has low expansion performance and high conductivity, thereby improving the cycle performance and rate performance of the negative electrode material (100).

Description

Negative electrode material and preparation method thereof

[0001] The present application claims priority to the Chinese patent application No. 202411056908.4, filed on July 31, 2024, and entitled "Negative electrode material and preparation method thereof", the whole content of which is incorporated herein by reference. TECHNICAL FIELD

[0002] The embodiments of the present application relate to the technical field of negative electrode materials, in particular to a negative electrode material and a preparation method thereof. BACKGROUND

[0003] The silicon negative electrode material has high capacity (theoretical capacity 4200mAh / g), but also faces the problems of poor cycle performance, easy pulverization of powder, poor conductivity, low rate performance and the like caused by huge volume expansion. In order to improve the shortcomings of the silicon negative electrode material, the industry uses a gas deposition method to deposit a silicon material on a porous carbon to form a silicon-carbon material, which improves the cycle performance and rate performance to a certain extent. However, with the increasing performance requirements of products, the cycle performance and rate performance of the silicon-carbon material still need to be continuously optimized. SUMMARY

[0004] In view of this, the embodiments of the present application provide a negative electrode material and a preparation method thereof. The negative electrode material includes a porous carbon and a deposited silicon-based material. The ratio of the mass content of the silicon-based material to the total pore volume of the porous carbon in the negative electrode material is controlled in a specific value range, and the differential value of the differential of the charge and discharge capacity with respect to the voltage in the charge and discharge curve of the negative electrode material is controlled to be a small value. This is conducive to the negative electrode material to obtain higher capacity while better balancing low expansion performance and high conductivity, thereby improving the cycle performance and rate performance of the negative electrode material.

[0005] In a first aspect, the embodiments of the present application provide a negative electrode material. The negative electrode material includes a silicon-carbon inner core and a coating layer arranged on the surface of the silicon-carbon inner core. The silicon-carbon inner core includes a porous carbon and a silicon-based material deposited on the porous carbon. The ratio of the mass content of the silicon-based material to the total pore volume of the porous carbon in the negative electrode material is within a first value range. The differential value dQ / dV of the differential of the charge and discharge capacity with respect to the voltage at 0.45V in the charge and discharge curve of the negative electrode material is within a second value range, so that the negative electrode material has high capacity, low expansion performance and high conductivity. The total pore volume of the porous carbon is in cm 3 / g.

[0006] The negative electrode material provided by the embodiments of the present application comprises porous carbon and deposited silicon-based material, the ratio of the mass content of the silicon-based material to the total pore volume of the porous carbon in the negative electrode material is controlled to be within a certain value range, and the differential value of the differential of the charge and discharge capacity with respect to the voltage in the charge and discharge curve of the negative electrode material is controlled to be within a certain value range, so that the negative electrode material can obtain a suitable silicon content under a specific total pore volume of the porous carbon, the negative electrode material can have as high silicon content as possible to obtain relatively higher capacity, and the problem of reduction of the structural stability and conductivity of the material due to the enrichment of silicon outside the pores of the porous carbon can be effectively avoided, thereby facilitating the negative electrode material to obtain higher capacity while better balancing low expansion performance and high conductivity, and further improving the cycle performance and rate performance of the negative electrode material.

[0007] In an embodiment of the present application, a negative electrode material is provided, the negative electrode material comprises a silicon-carbon inner core and a coating layer arranged on the surface of the silicon-carbon inner core, the silicon-carbon inner core comprises porous carbon and a silicon-based material deposited on the porous carbon, the ratio of the mass content of the silicon-based material to the total pore volume of the porous carbon in the negative electrode material is within a first value range, and the differential value dQ / dV of the differential of the charge and discharge capacity with respect to the voltage at 0.45 V in the charge and discharge curve of the negative electrode material is within a second value range. The first value range is greater than 0.40 and less than or equal to 0.58.

[0008] The above suitable ratio range facilitates the silicon to be maintained at a high content while realizing the concentrated distribution of the silicon in the pores of the porous carbon, so that the negative electrode material can better balance high capacity, high initial efficiency, low expansion performance and high conductivity.

[0009] In an embodiment of the present application, a negative electrode material is provided, the negative electrode material comprises a silicon-carbon inner core and a coating layer arranged on the surface of the silicon-carbon inner core, the silicon-carbon inner core comprises porous carbon and a silicon-based material deposited on the porous carbon, the ratio of the mass content of the silicon-based material to the total pore volume of the porous carbon in the negative electrode material is within a first value range, and the differential value dQ / dV of the differential of the charge and discharge capacity with respect to the voltage at 0.45 V in the charge and discharge curve of the negative electrode material is within a second value range. The second value range is less than 1.7.

[0010] The Dq / Dv value of the above negative electrode material is at a smaller value, the enrichment of the silicon on the surface of the porous carbon is less, the silicon is more uniformly dispersed, the expansion of the negative electrode material is lower, and the stability is higher.

[0011] In an embodiment of the present application, the first value range is greater than 0.40 and less than or equal to 0.58, and the second value range is less than 1.7.

[0012] The negative electrode material in the embodiments of the present application controls the ratio of the mass content of the silicon-based material to the total pore volume of the porous carbon within a suitable specific value range, and controls the differential value of the charge-discharge capacity with respect to voltage in the charge-discharge curve of the negative electrode material within a suitable specific value range, so that the negative electrode material can obtain the optimal silicon content under a specific total pore volume of the porous carbon. In this way, the negative electrode material can have as high a silicon content as possible to obtain relatively higher capacity, and can better avoid the problem of reduced material structural stability and conductivity due to the enrichment of silicon outside the pores of the porous carbon, so that the negative electrode material can better balance low expansion performance and high conductivity while obtaining higher capacity, thereby improving the cycle performance and rate performance of the negative electrode material.

[0013] In the embodiments of the present application, the first value range is greater than 0.50 and less than 0.58. The above suitable ratio range is beneficial to maintaining a high content of silicon while achieving the concentrated distribution of silicon within the pores of the porous carbon, so that the negative electrode material can better balance high capacity, high initial efficiency, low expansion performance and high conductivity.

[0014] In the embodiments of the present application, the second value range is less than 1.6. When the Dq / Dv value of the negative electrode material is smaller, the enrichment of silicon on the surface of the porous carbon is less, the silicon is more uniformly dispersed, the expansion of the negative electrode material is lower, and the stability is higher.

[0015] In the embodiments of the present application, in the porous carbon, the total volume of the openings with an opening diameter ≤3nm accounts for more than or equal to 90% of the total opening volume. That is, among all the openings in the porous carbon, the total volume of the openings with an opening diameter ≤3nm accounts for more than or equal to 90%. The openings with an opening diameter ≤3nm have stronger adsorption capacity for silane, which is beneficial to maintaining a relatively strong adsorption potential benchmark for the porous carbon. Therefore, controlling the smaller pores with a pore diameter ≤3nm at a relatively high proportion can make the opening diameter distribution of the porous carbon narrower and the effective deposition pore proportion larger (the proportion of openings that can effectively adsorb silane and make it deposit to form silicon is larger), thereby facilitating effective in-pore adsorption, and better limiting the particle size of the deposited silicon-based material in the openings by using the threshold effect of the pore diameter, and further improving the low expansion performance and high conductivity of the negative electrode material.

[0016] In the embodiments of the present application, in the porous carbon, the total volume of the openings with an opening diameter of 1nm-3nm accounts for more than or equal to 50% of the total opening volume. That is, among all the openings in the porous carbon, the total volume of the openings with an opening diameter of 1nm-3nm accounts for more than or equal to 50%. Controlling the openings with an opening diameter of 1nm-3nm at a relatively high proportion is beneficial to maintaining a relatively strong adsorption potential benchmark for the porous carbon, and is beneficial to achieving effective adsorption and deposition of silane molecules in the pores.

[0017] In the embodiments of the present application, the total pore volume of the porous carbon is 0.4cm3 / g-1.0cm 3 / g. The porous carbon has a suitable total pore volume, which is conducive to maintaining the stability of the carbon skeleton structure of the porous carbon and enabling the porous carbon to adsorb more silicon to improve the capacity.

[0018] In the embodiments of the present application, the mass content of the silicon-based material in the negative electrode material is greater than or equal to 42%. The silicon-based material has a high capacity, and a large mass content of the silicon-based material deposited in the negative electrode material is conducive to improving the capacity of the negative electrode material, thereby improving the overall capacity of the battery and better meeting the high-capacity demand of the battery market.

[0019] In consideration of the structural stability of the porous carbon skeleton of the negative electrode material and the conductivity of the negative electrode material, in the embodiments of the present application, the mass content of the silicon-based material in the negative electrode material is 47%-54%.

[0020] In the embodiments of the present application, the coating layer comprises a carbon material and / or a fast ion conductor; and / or, the mass content of the coating layer in the negative electrode material is less than or equal to 3%. The coating layer can protect the silicon deposited on the porous carbon, alleviate the volume expansion of the silicon, and at the same time improve the conductivity. By keeping the coating layer at a low proportion, the influence on the structural performance of the core body can be reduced while achieving the above effects.

[0021] In the embodiments of the present application, the electrical conductivity of the negative electrode material is greater than or equal to 1 S / cm. The negative electrode material of the present application has a high electrical conductivity, which can improve the transmission speed of metal ions, reduce the internal resistance of the battery, and improve the charge and discharge performance of the battery.

[0022] In the embodiments of the present application, the expansion rate of a single particle of the negative electrode material after complete lithiation is less than or equal to 90%. The negative electrode material has a low expansion rate, which can have strong structural stability, thereby improving the cycle performance of the battery.

[0023] In the embodiments of the present application, the reversible capacity of the negative electrode material is greater than 1200 mAh / g. The negative electrode material has a high reversible capacity, which can improve the overall capacity of the battery and improve the initial coulombic efficiency.

[0024] In the embodiments of the present application, the specific surface area of the negative electrode material is less than 10 m 2 / g. The specific surface area of the negative electrode material is controlled at a relatively small value, which is conducive to controlling the side reaction at a low level while obtaining a certain negative electrode reaction rate, thereby avoiding excessive side reactions from affecting the cycle performance and high-temperature performance.

[0025] In the embodiments of the present application, the capacity retention rate of a half-cell cycled 100 times with a negative electrode composed of the negative electrode material as an active material as the negative electrode and a lithium sheet as the counter electrode is greater than or equal to 80%. The negative electrode material has excellent cycle performance, which can improve the cycle performance of the battery.

[0026] The second aspect of the embodiments of the present application provides a preparation method of a negative electrode material, comprising:

[0027] The porous carbon is placed in a reaction furnace, heated to a first temperature, and a silicon-based material raw gas is introduced according to the ratio of the mass content of the silicon-based material in the negative electrode material to the total pore volume of the porous carbon being within a first value range, so that the silicon-based material is deposited on the porous carbon to obtain a silicon-carbon core; wherein the unit of the total pore volume of the porous carbon is cm 3 / g;

[0028] The reaction furnace is heated to a second temperature, and a coating layer raw gas is introduced to deposit a coating layer on the surface of the silicon-carbon core to obtain a negative electrode material, and the differential value dQ / dV of the charging and discharging capacity at 0.45V to voltage in the charging and discharging curve of the negative electrode material is within a second value range, so that the negative electrode material has high capacity, low expansion performance and high conductivity.

[0029] In the embodiments of the present application, the first value range is greater than 0.40 and less than or equal to 0.58. This suitable ratio range is beneficial to the concentration distribution of silicon in the pores of the porous carbon while maintaining a high content of silicon, so that the negative electrode material can better balance high capacity, high initial efficiency, low expansion performance and high conductivity.

[0030] In the embodiments of the present application, the second value range is less than 1.7. When the Dq / Dv value of the negative electrode material is smaller, the enrichment of silicon on the surface of the porous carbon is less, the silicon is more uniformly dispersed, the expansion of the negative electrode material is lower, and the stability is higher.

[0031] In the embodiments of the present application, the silicon-based material raw gas is a mixed gas of silane and diluent gas, and the volume fraction of silane in the mixed gas of silane and diluent gas is greater than or equal to 10%; the flow rate of the introduced silane is 0.01L / min-20L / min. During the vapor deposition process, the silane in the introduced mixed gas of silane and diluent gas is controlled at a higher content, which is beneficial to improving the deposition efficiency.

[0032] In the embodiments of the present application, the first temperature is 380℃-485℃; during the process of introducing the silicon-based material raw gas to deposit the silicon-based material on the porous carbon, the reaction furnace is rotated at a speed of 20-100s / revolution, and the temperature is maintained for 1-5h. The suitable temperature setting is beneficial to the adsorption, cracking, nucleation and growth of the silicon-based material raw gas on the porous carbon.

[0033] In the embodiment of the present application, the second temperature is 500-800°C; in the process of introducing the cladding layer raw material gas to deposit the cladding layer on the surface of the silicon-carbon inner core, the reaction furnace is rotated at a speed of 20-100s / revolution, and heat preservation is performed for 1-3h. The suitable temperature setting is beneficial to pyrolysis of the carbon source to form a carbon layer.

[0034] The preparation method of the negative electrode material in the embodiment of the present application controls the amount of the silicon-based material deposited in a specific range according to the total pore volume of the porous carbon, which is beneficial to maintaining a certain adsorption difference inside and outside the pores of the porous carbon. In the deposition process, silane is preferentially adsorbed and cracked inside the pores, avoiding enrichment of silicon on the surface of the porous carbon. The negative electrode material has high capacity, low swelling performance and high conductivity, and can obtain a negative electrode material with low swelling performance and high conductivity while maintaining a high silane introduction concentration to ensure high production efficiency.

[0035] The third aspect of the embodiment of the present application provides a negative electrode sheet, which comprises the negative electrode material of the first aspect of the embodiment of the present application. The negative electrode sheet is used in a battery, which can improve the performance of the battery.

[0036] The fourth aspect of the embodiment of the present application provides a battery, which comprises the negative electrode sheet of the third aspect of the embodiment of the present application or the negative electrode material of the first aspect. The battery is used in an electric device such as an electronic device, which can improve the performance of the device.

[0037] The embodiment of the present application also provides an electric device, which comprises the battery of the fourth aspect. The battery provides electric energy for the electric device. The battery provided by the embodiment of the present application can improve the performance of the electric device and the competitiveness of the product.

[0038] The embodiment of the present application also provides an energy storage device, which comprises the battery of the fourth aspect. The battery stores electric energy for the energy storage device. BRIEF DESCRIPTION OF DRAWINGS

[0039] FIG. 1 is a structural schematic diagram of the negative electrode material 100 provided by the embodiment of the present application;

[0040] FIG. 2 is a schematic diagram of deposition of silicon on the porous carbon;

[0041] FIG. 3 is a flowchart of a preparation method of a negative electrode material provided by the embodiment of the present application;

[0042] FIG. 4 is a schematic diagram of the cross-sectional structure of the negative electrode sheet 200 provided by the embodiment of the present application;

[0043] FIG. 5 is a schematic diagram of the structure of the battery 300 provided by the embodiment of the present application;

[0044] FIG. 6 is a schematic diagram of the structure of the electric device 400 provided by the embodiment of the present application. DETAILED DESCRIPTION

[0045] The embodiments of the present application will be described below in conjunction with the accompanying drawings of the embodiments of the present application.

[0046] The positive and negative electrode materials in the battery are the main factors affecting the energy storage performance. The current commercial positive electrode material lithium cobalt oxide LCO has basically reached its use limit. The capacity and rate performance of the negative electrode are crucial to the overall performance of the battery. However, the actual use capacity of the current commercial graphite negative electrode is 360 mAh / g, which is close to its theoretical value (372 mAh / g). The silicon negative electrode material has a high theoretical capacity (4200 mAh / g), but it will undergo severe volume expansion and contraction during the lithium intercalation and deintercalation reaction, resulting in structure damage and pulverization, and poor cycle performance. In addition, the silicon negative electrode material has poor electrical conductivity and low rate performance compared with graphite and other negative electrode materials. In order to improve the expansion performance and electrical conductivity of the silicon negative electrode material, the industry usually uses a vapor deposition method to deposit silicon material on porous carbon to form a silicon-carbon material, which improves the cycle performance and rate performance to a certain extent. However, with the increasing performance requirements of products, the cycle performance and rate performance of the silicon-carbon material still need to be continuously optimized. Therefore, the embodiments of the present application provide a negative electrode material, which includes porous carbon and deposited silicon. By controlling the ratio of the mass content of the silicon-based material to the total pore volume of the porous carbon in the negative electrode material within a specific value range, and controlling the differential value of the differential of the charge and discharge capacity with respect to the voltage in the charge and discharge curve of the negative electrode material to be a small value, the negative electrode material can better balance the low expansion performance and high electrical conductivity while improving the silicon content to obtain high capacity, thereby improving the cycle performance and rate performance of the negative electrode material.

[0047] Referring to FIG. 1, FIG. 1 is a structural schematic diagram of a negative electrode material 100 provided by the embodiments of the present application. The negative electrode material 100 includes a silicon-carbon inner core 101 and a coating layer 102 arranged on the surface of the silicon-carbon inner core 101. The silicon-carbon inner core 101 includes porous carbon and a silicon-based material deposited on the porous carbon. The ratio of the mass content of the silicon-based material to the total pore volume of the porous carbon in the negative electrode material 100 is within a first value range. The differential value dQ / dV of the differential of the charge and discharge capacity with respect to the voltage at 0.45 V in the charge and discharge curve of the negative electrode material 100 is within a second value range. The unit of the total pore volume of the porous carbon is cm 3 / g.

[0048] It should be noted that FIG. 1 only shows the cross-sectional structure of the negative electrode material 100 to show the positional relationship between the silicon-carbon inner core and the coating layer, and does not limit the actual shape of the negative electrode material 100.

[0049] The Dq / Dv value of the negative electrode material 100 can reflect the silicon enrichment degree of the surface of the porous carbon (i.e., outside the pores) in the negative electrode material 100. The smaller the Dq / Dv value, the smaller the silicon enrichment degree of the surface of the porous carbon, the more silicon is deposited in the pores. The larger the Dq / Dv value, the larger the silicon enrichment degree of the surface of the porous carbon, the more serious the surface silicon enrichment, and the less silicon is deposited in the pores. The Dq / Dv value is the differential value of the differential of the charge and discharge capacity to the voltage in the charge and discharge curve of the negative electrode material 100.

[0050] The negative electrode material 100 provided by the embodiments of the present application includes porous carbon and deposited silicon-based material. By controlling the ratio of the mass content of the silicon-based material to the total pore volume of the porous carbon within a certain value range and controlling the differential value of the differential of the charge and discharge capacity to the voltage in the charge and discharge curve of the negative electrode material within a certain value range, the negative electrode material 100 can obtain a suitable silicon content under a certain total pore volume of the porous carbon. In this way, the negative electrode material 100 can have as high a silicon content as possible to obtain a relatively higher capacity, and can effectively avoid the problem of reduced material structural stability and conductivity due to the enrichment of silicon outside the pores of the porous carbon, thereby facilitating the negative electrode material 100 to obtain a higher capacity while better balancing low swelling performance and high conductivity, and further improving the cycle performance and rate performance of the negative electrode material.

[0051] The negative electrode material 100 provided by the embodiments of the present application can utilize the adsorption capacity of the mesopores of the porous carbon, and through gas phase deposition, silane molecules and the like are adsorbed into the pores, and after cracking, nucleation and growth, the structure of the porous carbon in which the silicon-based material is deposited is finally obtained. The higher the mass content of the silicon-based material in the negative electrode material 100, the higher the capacity and the initial efficiency will be. However, under a certain total pore volume of the porous carbon, the mass content of the silicon-based material is relatively too high, which will cause the deposition of silicon outside the pores of the porous carbon, i.e. on the surface of the porous carbon, so as to intensify the swelling and reduce the conductivity. In the embodiments of the present application, the first value range is greater than 0.40 and less than or equal to 0.58. In the embodiments of the present application, the second value range is less than 1.7. In this way, it is beneficial to maintain a suitable silicon mass content according to the total pore volume of the porous carbon, so that the negative electrode material has low swelling performance and high conductivity. Specifically, by controlling the ratio of the mass content of the silicon-based material in the negative electrode material 100 to the total pore volume of the porous carbon in a certain value range greater than 0.40 and less than or equal to 0.58, and by controlling the differential value of the differential of the charge-discharge capacity at 0.45V to the voltage in the charge-discharge curve of the negative electrode material in a certain value range less than 1.7, the negative electrode material can have the most suitable silicon content under a certain total pore volume of the porous carbon, so that the negative electrode material can have as high a silicon content as possible to obtain a relatively higher capacity, and can better avoid the problem of reducing the structural stability and conductivity of the material due to the enrichment of silicon outside the pores of the porous carbon, so that the negative electrode material can better balance the low swelling performance and the high conductivity while obtaining a higher capacity, and further improve the cycle performance and the rate performance of the negative electrode material.

[0052] Referring to FIG. 2, FIG. 2 is a schematic diagram of the deposition of silicon on the porous carbon. Based on the skeleton of the porous carbon 11, the silane is adsorbed into the pores 110 of the porous carbon 11 under high temperature conditions, and then the process of silane cracking, silicon nucleation and growth is experienced to complete the deposition of silicon in the pores. When the adsorption and growth rate of the silane on the surface of the porous carbon is greater than or equal to the adsorption and growth rate of the silane in the pores of the porous carbon, the enrichment of silicon on the surface of the porous carbon will be caused, and therefore, in order to avoid the enrichment of silicon on the surface of the porous carbon, it is necessary to keep the adsorption and growth rate of the silane in the pores of the porous carbon always greater than the adsorption and growth rate of the silane on the surface of the porous carbon. The negative electrode material 100 of the embodiments of the present application is beneficial to keeping a certain pore specific surface area by controlling the ratio of the mass content of the silicon-based material to the total pore volume of the porous carbon in a certain value range, and promoting the heterogeneous cracking of the silane to preferentially form in the inner wall of the pores of the porous carbon, so that the silicon is deposited in the pores and the swelling is limited, and at the same time, the insulating rich-silicon layer does not damage the conductive network of the porous carbon, and therefore, the negative electrode material can have low swelling performance and high conductivity.

[0053] The negative electrode material 100 provided by the embodiments of the present application can maintain a certain content of silicon according to a certain total pore volume of the porous carbon, and the time and flow rate of the input of the silane gas during the deposition process can be controlled, so that the enrichment of silicon on the surface of the porous carbon can be realized without reducing the concentration of the input silane gas and the deposition temperature, and the high silane deposition efficiency can be maintained while the enrichment of silicon on the surface of the porous carbon is controlled.

[0054] In some embodiments of the present application, the differential value of the charge-discharge capacity with respect to the voltage in the charge-discharge curve of the negative electrode material 100 is less than 1.6. In the negative electrode material of the embodiments of the present application, the Dq / Dv value of the negative electrode material is small, the enrichment of silicon on the surface of the porous carbon is small, the silicon is more uniformly dispersed, the expansion of the negative electrode material is lower, and the stability is higher.

[0055] In some embodiments of the present application, the ratio of the mass content of the silicon-based material to the total pore volume of the porous carbon in the negative electrode material 100 may, for example, but not limited to, be 0.41, 0.43, 0.45, 0.48, 0.50, 0.51, 0.52, 0.53, 0.54, 0.55, 0.56, 0.57, or 0.58. In some embodiments of the present application, the ratio of the mass content of the silicon-based material to the total pore volume of the porous carbon in the negative electrode material 100 is greater than 0.50 and less than 0.58. The above suitable ratio range is beneficial to maintaining a high content of silicon while realizing the concentrated distribution of silicon in the pores of the porous carbon, so that the negative electrode material 100 can better balance high capacity, high initial efficiency, low expansion performance, and high conductivity performance.

[0056] In the embodiments of the present application, taking the mass content of the silicon-based material in the negative electrode material 100 as 48% and the total pore volume of the porous carbon as 0.9 cm 3 / g as an example, the ratio of the mass content of the silicon-based material to the total pore volume of the porous carbon in the negative electrode material 100 is calculated as 0.48 / 0.9 = 0.53.

[0057] In some embodiments of the present application, the total volume of the pores with an opening diameter of 1-3 nm accounts for greater than or equal to 50% of the total pore volume in the porous carbon, i.e., the total volume of the pores with an opening diameter of 1-3 nm accounts for greater than or equal to 50% of all the pores in the porous carbon. Controlling the pores with an opening diameter of 1-3 nm to a high proportion is conducive to maintaining a strong adsorption potential reference of the porous carbon and conducive to achieving effective adsorption and deposition of silane molecules in the pores. In some embodiments, the total volume of the pores with an opening diameter of 1-3 nm accounts for 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, or 100% of the total pore volume in the porous carbon. Correspondingly, in some embodiments of the present application, the total volume of the pores with an opening diameter of <1 nm accounts for ≤40% of the total pore volume in the porous carbon. In this way, the mass proportion of the silicon-based material in the negative electrode material 100 can be increased, thereby increasing the reversible capacity of the negative electrode material 100 and the energy density of the battery.

[0058] In some embodiments of the present application, the total volume of the pores with an opening diameter of 1-3 nm accounts for greater than or equal to 50% of the total pore volume in the porous carbon, i.e., the total volume of the pores with an opening diameter of 1-3 nm accounts for greater than or equal to 50% of all the pores in the porous carbon. Controlling the pores with an opening diameter of 1-3 nm to a high proportion is conducive to maintaining a strong adsorption potential reference of the porous carbon and conducive to achieving effective adsorption and deposition of silane molecules in the pores. In some embodiments, the total volume of the pores with an opening diameter of 1-3 nm accounts for 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, or 100% of the total pore volume in the porous carbon. Correspondingly, in some embodiments of the present application, the total volume of the pores with an opening diameter of <1 nm accounts for ≤40% of the total pore volume in the porous carbon. In this way, the mass proportion of the silicon-based material in the negative electrode material 100 can be increased, thereby increasing the reversible capacity of the negative electrode material 100 and the energy density of the battery.

[0059] In some embodiments of the present application, the total volume of the pores with an opening diameter of 1-3 nm accounts for greater than or equal to 50% of the total pore volume in the porous carbon, i.e., the total volume of the pores with an opening diameter of 1-3 nm accounts for greater than or equal to 50% of all the pores in the porous carbon. Controlling the pores with an opening diameter of 1-3 nm to a high proportion is conducive to maintaining a strong adsorption potential reference of the porous carbon and conducive to achieving effective adsorption and deposition of silane molecules in the pores. In some embodiments, the total volume of the pores with an opening diameter of 1-3 nm accounts for 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, or 100% of the total pore volume in the porous carbon. Correspondingly, in some embodiments of the present application, the total volume of the pores with an opening diameter of <1 nm accounts for ≤40% of the total pore volume in the porous carbon. In this way, the mass proportion of the silicon-based material in the negative electrode material 100 can be increased, thereby increasing the reversible capacity of the negative electrode material 100 and the energy density of the battery.

[0060] In some embodiments of the present application, the total volume of the pores with an opening diameter of 1-3 nm accounts for greater than or equal to 50% of the total pore volume in the porous carbon, i.e., the total volume of the pores with an opening diameter of 1-3 nm accounts for greater than or equal to 50% of all the pores in the porous carbon. Controlling the pores with an opening diameter of 1-3 nm to a high proportion is conducive to maintaining a strong adsorption potential reference of the porous carbon and conducive to achieving effective adsorption and deposition of silane molecules in the pores. In some embodiments, the total volume of the pores with an opening diameter of 1-3 nm accounts for 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, or 100% of the total pore volume in the porous carbon. Correspondingly, in some embodiments of the present application, the total volume of the pores with an opening diameter of <1 nm accounts for ≤40% of the total pore volume in the porous carbon. In this way, the mass proportion of the silicon-based material in the negative electrode material 100 can be increased, thereby increasing the reversible capacity of the negative electrode material 100 and the energy density of the battery.

[0061] Openings refer to cavities and channels in the porous solid that are in communication with the outside world. In the embodiments of the present application, the opening size and distribution of the openings in the porous carbon can be determined by gas adsorption-desorption testing. The gas used in the gas adsorption-desorption testing can be, but is not limited to, nitrogen, carbon dioxide, argon, etc. For example, in nitrogen adsorption-desorption testing, the degassing time is kept ≥ 30 min and the degassing temperature is ≥ 100℃ during the testing process, and the adsorption-desorption curve of the porous carbon is obtained, so that the opening size distribution of the openings in the porous carbon can be obtained. Based on the principle of gas adsorption-desorption testing (closed pores cannot be tested), the opening size of each opening specifically refers to the opening size measured by gas adsorption-desorption testing, which can be considered as the maximum transverse size of the opening. Specifically, the shape of the opening can be spherical, spherical-like, strip-shaped, irregular, etc.

[0062] In some embodiments of the present application, the silicon-based material deposited on the porous carbon is a nano-silicon-based material particle, which can be one or more of silicon element, doped silicon, and silicon alloy. In some embodiments, the nano-silicon-based material particle is silicon element. In some embodiments, the size of the nano-silicon-based material particle in at least one direction is ≤ 2 nm. Smaller silicon size is more conducive to inhibiting the volume change of the negative electrode material 100 during the battery cycle.

[0063] In the embodiments of the present application, part or all of the openings in the porous carbon are deposited with silicon-based material, and there can be some openings in the porous carbon that are not deposited with silicon-based material. The silicon-based material deposited on the porous carbon is concentrated in the openings, and a small amount of silicon-based material can be deposited outside the pores. There can also be a small amount of closed pores in the porous carbon. Closed pores refer to cavities and channels in the porous solid that are not in communication with the outside world. There is no silicon in the closed pores.

[0064] In the embodiments of the present application, the total pore volume of the porous carbon is 0.4 cm 3 / g-1.0 cm 3 / g. In some embodiments, the total pore volume of the porous carbon is 0.4 cm 3 / g, 0.5 cm 3 / g, 0.6 cm 3 / g, 0.7 cm 3 / g, 0.8 cm 3 / g, 0.9 cm 3 / g, 1.0 cm 3 / g. The porous carbon has a suitable total pore volume, which is conducive to maintaining the stability of the carbon skeleton structure and also enables the absorption of more silicon to improve the capacity. In the embodiments of the present application, the total pore volume of the porous carbon can be determined by gas adsorption-desorption testing.

[0065] For the negative electrode material 100 of the embodiments of the present application, the total pore volume of the porous carbon and the pore size distribution of the open pores can be determined by gas adsorption / desorption test after removing the coating layer 102 and the deposited silicon. In the embodiments of the present application, the distribution of silicon in the negative electrode material 100 can be characterized by energy dispersive spectrometer (EDS) test.

[0066] In the embodiments of the present application, the mass content of the silicon-based material in the negative electrode material 100 is greater than or equal to 42%. The silicon-based material has high capacity, and a large mass content of the deposited silicon-based material in the negative electrode material 100 is beneficial to improve the capacity of the negative electrode material 100, thereby improving the overall capacity of the battery and better meeting the high-capacity demand of the battery market. Considering the structural stability of the porous carbon framework of the negative electrode material of the present application and the conductivity of the negative electrode material, in some embodiments of the present application, the mass content of the silicon-based material in the negative electrode material 100 is controlled to be 42%-54%. In some embodiments, the mass content of the silicon-based material in the negative electrode material 100 is 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, or 54%.

[0067] In the embodiments of the present application, the coating layer 102 comprises a carbon material and / or a fast ion conductor. The carbon material can be amorphous carbon. In some embodiments, the carbon material is low-temperature pyrolytic carbon of organic matter. The fast ion conductor can be any fast ion conductor material known in the art. Taking the fast ion conductor material for lithium ion battery as an example, it includes but is not limited to Li3N, Li 14 Zn, etc. Taking the fast ion conductor for sodium ion battery as an example, it includes but is not limited to Na3Zr2Si2PO 12 , Na2O·Al2O3, etc. The coating layer 102 can protect the silicon deposited on the porous carbon, alleviate the volume expansion of silicon, and improve the conductivity.

[0068] In some embodiments, the coating layer 102 is a carbon coating layer; in some embodiments, the coating layer 102 is a fast-ion-conductor coating layer; in some embodiments, the coating layer 102 comprises a carbon coating layer and a fast-ion-conductor coating layer arranged in a stack; in some embodiments, the coating layer 40 is a composite coating layer, and the material of the composite coating layer comprises carbon material and fast-ion-conductor. The carbon coating layer can improve the electronic conductivity of the negative electrode material 100 and can contribute to the capacity, and the fast-ion-conductor coating layer can improve the ionic conductivity of the negative electrode material 100, thereby improving the rate performance of the battery and improving the fast-charging performance of the battery; the composite coating layer can improve the electronic conductivity and ionic conductivity of the negative electrode material 100 at the same time. In addition, the coating layer 102 can serve as a physical barrier to protect the silicon-based material deposited on the porous carbon and reduce the risk of the silicon-based material being exposed on the surface of the negative electrode material 100, thereby reducing the side reactions (for example, the side reactions between the silicon-based material and the electrolyte in a liquid battery) during the battery cycle, thereby improving the interface stability of the negative electrode material 100 and facilitating the performance of the battery. Furthermore, the coating layer can also inhibit and relieve the expansion of the silicon-carbon core, thereby further reducing the expansion rate of the negative electrode material 100 during the charge and discharge cycle.

[0069] In some embodiments of the present application, the carbon coating layer and the fast-ion-conductor coating layer are formed on the surface of the porous carbon in sequence, or the fast-ion-conductor coating layer and the carbon coating layer are formed on the surface of the porous carbon in sequence. Those skilled in the art can select according to the actual application.

[0070] In some embodiments of the present application, the mass ratio of the coating layer 102 in the negative electrode material 100 is less than or equal to 3%. Keeping the coating layer 102 at a low proportion can reduce the impact on the structure and performance of the silicon-carbon core 101 while achieving the above effects. In some embodiments, the mass ratio of the coating layer 102 in the negative electrode material 100 is 0.5%, 1%, 1.5%, 2%, 2.5%, or 3%.

[0071] In some embodiments of the present application, the thickness of the coating layer 102 is ≤20 nm. Controlling the thickness within the above range can achieve the physical isolation effect, and at the same time, the diffusion path of ions or electrons in the negative electrode material 100 is short, which can ensure that the rate performance of the final battery is good. Specifically, the thickness of the coating layer 102 can be, but is not limited to, 1 nm, 2 nm, 5 nm, 8 nm, 10 nm, 12 nm, 15 nm, 18 nm, 20 nm, etc.

[0072] In some embodiments, at least part of the surface of the silicon-carbon core 101 is covered by the coating layer 102; in other embodiments, the entire surface of the silicon-carbon core 101 is covered by the coating layer 102. The coating layer 102 can be partially filled in the open pores of the porous carbon.

[0073] In some embodiments of the present application, the D50 of the negative electrode material 100 can be in the range of 2 μm-15 μm. In some embodiments, the D50 of the negative electrode material 100 is in the range of 7 μm-8 μm. Specifically, the D50 of the negative electrode material 100 can be, but is not limited to, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, etc. The negative electrode material has a suitable D50 size, which is beneficial to the electrochemical performance of the battery. The D50 refers to the particle size corresponding to the cumulative particle size distribution percentage of 50% of the negative electrode material 100, which can be tested by a laser particle size analyzer.

[0074] In embodiments of the present application, the electrical conductivity of the negative electrode material 100 is greater than or equal to 1 S / cm. According to the present application, the content of silicon is maintained at a certain value based on the total pore volume of the porous carbon, which can obtain effective deposition in the pores and avoid the deposition of silicon on the surface of the porous carbon to reduce the electrical conductivity. The negative electrode material 100 of the present application has a high electrical conductivity, which can improve the transmission speed of metal ions, reduce the internal resistance of the battery, and improve the charge and discharge performance of the battery. In some embodiments, the electrical conductivity of the negative electrode material 100 is greater than or equal to 1.1 S / cm. The electrical conductivity of the negative electrode material 100 can be tested by a powder conductivity tester.

[0075] In embodiments of the present application, the expansion rate of the single particle of the negative electrode material 100 after complete lithiation is less than or equal to 90%. The negative electrode material 100 has a low expansion rate, which can have strong structural stability, thereby improving the cycle performance of the battery. In some embodiments, the expansion rate of the single particle of the negative electrode material 100 after complete lithiation is 10%-90%. In some embodiments, the expansion rate of the single particle of the negative electrode material 100 after complete lithiation is 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%. The size of the single particle before and after lithiation can be observed by in-situ lithium intercalation to obtain the size of the single particle before and after lithiation, and then the expansion rate of the single particle after complete lithiation is calculated by the formula: expansion rate=(change in size of single particle before and after lithiation / size of single particle before lithiation) x 100%. The in-situ lithium intercalation can be carried out by in-situ scanning electron microscope (SEM) and transmission electron microscope (TEM) in combination with an electrochemical system.

[0076] In this embodiment, the expansion rate of the negative electrode sheet prepared by the negative electrode material 100 after complete lithiation is less than or equal to 80%. In some embodiments, the expansion rate of the negative electrode sheet prepared by the negative electrode material 100 after complete lithiation is 10%, 20%, 30%, 40%, 50%, 60%, 70%, 75%, or 80%.

[0077] In this embodiment, the reversible capacity of the negative electrode material is greater than 1200 mAh / g. The high reversible capacity of the negative electrode material can improve the overall capacity of the battery and enhance the first-pass coulombic efficiency. In some embodiments, the reversible capacity of the negative electrode material is 1300 mAh / g, 1400 mAh / g, 1500 mAh / g, 1600 mAh / g, 1700 mAh / g, 1800 mAh / g, 1900 mAh / g, 2000 mAh / g, 2100 mAh / g, or 2200 mAh / g. In some embodiments, the reversible capacity of the negative electrode material is greater than 1700 mAh / g.

[0078] In this embodiment, the specific surface area of ​​the negative electrode material is less than 10m². 2 / g. In some embodiments, the specific surface area of ​​the negative electrode material is 0.5m². 2 / g-9m 2 / g. In some embodiments, the specific surface area of ​​the negative electrode material is 1m². 2 / g-5m 2 / g. For example, the specific surface area of ​​the negative electrode material can be 0.5m². 2 / g、1m 2 / g、2m 2 / g、3m 2 / g、4m 2 / g、5m 2 / g、6m 2 / g、7m 2 / g、8m 2 / g、9m 2 / g. Controlling the specific surface area of ​​the anode material to a relatively small value is beneficial for achieving a certain anode reaction rate while keeping side reactions at a low level, thus avoiding excessive side reactions that could affect cycle performance and high-temperature performance.

[0079] In some embodiments, the capacity retention rate of the half-cell after 100 cycles is greater than or equal to 80%. In some embodiments, the capacity retention rate of the half-cell after 100 cycles is greater than or equal to 85%. In some embodiments, the capacity retention rate of the half-cell after 100 cycles is greater than or equal to 90%. In some embodiments, the capacity retention rate of the half-cell after 100 cycles is greater than or equal to 95%. For example, the capacity retention rate of the half-cell after 100 cycles is 80%, 85%, 90%, 95%, 96%, 97%, 98%. In some embodiments, the first coulombic efficiency of the half-cell at 0.15V is greater than or equal to 80%. For example, the first coulombic efficiency of the half-cell at 0.15V is 80%, 85%, 90%.

[0080] The negative electrode material 100 of the present application can be directly or after chemical decomposition (e.g., dissolving silicon) to characterize the material phase, structure, elements and corresponding content and distribution. X-ray photoelectron spectroscopy (XPS), energy dispersive spectrometer (EDS), X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), gas adsorption-desorption curve analysis and other technologies can be used.

[0081] Referring to FIG. 3, the present application also provides a preparation method of the above-mentioned negative electrode material, comprising:

[0082] S101, place the porous carbon in the reaction furnace, heat to a first temperature, and according to the ratio of the mass content of the silicon-based material in the negative electrode material to the total pore volume of the porous carbon, pass the silicon-based material raw gas within the first value range to make the silicon-based material deposit on the porous carbon, to obtain a silicon-carbon core; wherein the unit of the total pore volume of the porous carbon is cm 3 / g;

[0083] S102, heat the reaction furnace to a second temperature, and pass the coating layer raw gas to make the silicon-carbon core surface deposit to form a coating layer, to obtain a negative electrode material, and the differential value dQ / dV of the charge-discharge capacity at 0.45V in the charge-discharge curve of the negative electrode material is within the second value range, so that the negative electrode material has high capacity, low expansion performance and high conductivity.

[0084] Step S101 is a process of chemical vapor deposition of silicon-based material on the porous carbon to obtain the silicon-carbon core, i.e. a silicon infiltration process, and the chemical vapor deposition is specifically a chemical vapor infiltration (CVI) process.

[0085] In the embodiments of the present application, the first value range is greater than 0.40 and less than or equal to 0.58. In the embodiments of the present application, the second value range is less than 1.7. In step S101, taking the mixture of silane and diluent gas as the raw material gas of silicon-based material for depositing silicon as an example, according to the ratio of the mass content of silicon-based material in the negative electrode material to the total pore volume of the porous carbon being greater than 0.40 and less than or equal to 0.58, the specific operation is as follows: according to the total pore volume of the porous carbon added in the reaction furnace, the mass content of silicon in the negative electrode material is calculated, and then the amount of silane required to be introduced is calculated according to the mass content, and the total amount of the mixture of silane and diluent gas required to be introduced is further obtained. For example, the total pore volume of the porous carbon added in the reaction furnace is 0.8 cm 3 / g, and the ratio of the target value of the mass content of silicon in the negative electrode material to the total pore volume of the porous carbon is 0.6, then the mass content of silicon in the negative electrode material is 48%, and the amount of silane required to be introduced is calculated according to the mass content, and the amount of silane required to be introduced is calculated according to the silane utilization rate (silicon-based raw material gas utilization rate) being greater than or equal to 90%. For example, the amount of silane required to be introduced can be calculated according to the silane utilization rate being 90%-95%, and specifically, the amount of silane required to be introduced can be calculated according to the silane utilization rate being 90%, 91%, 92%, 93%, 94%, or 95%. The silane utilization rate (silicon-based raw material gas utilization rate) is set according to the actual situation. Since the actual amount of silane introduced = the introduction flow rate of silane * the introduction time, the amount of silane introduced can be adjusted by adjusting the introduction flow rate and the introduction time.

[0086] It can be understood that when the silicon-based material is doped silicon, a doping raw material gas is also introduced during the deposition process; when the silicon-based material is a silicon alloy, an alloy raw material gas is also introduced during the deposition process.

[0087] The smaller the ratio of the mass content of silicon-based material in the negative electrode material to the total pore volume of the porous carbon, the more favorable the increase in the adsorption difference of the porous carbon inside and outside the pores, but the capacity and the initial efficiency will be reduced. Considering the capacity, low swelling performance and high conductivity performance, the ratio of the mass content of silicon-based material in the negative electrode material to the total pore volume of the porous carbon can be controlled in the range of greater than 0.50 and less than or equal to 0.58.

[0088] In step S101, the porous carbon can be selected according to the total pore volume, pore size distribution, and the like as described in the foregoing sections herein, which will not be repeated here. The reaction furnace can be a rotary furnace. The porous carbon can be placed in the reaction furnace, and a protective gas (e.g., nitrogen, argon) can be introduced to remove air, and the temperature can be raised to the first temperature under the protection of the protective gas.

[0089] In the mixed gas of silane and diluent gas, the diluent gas is a high-purity gas that does not contain components that change silane over time. In the mixed gas of silane and diluent gas, the silane can be monosilane (SiH4), disilane (Si2H6), or the like; and the diluent gas can be argon, nitrogen, or the like.

[0090] In the embodiments of the present application, the volume fraction of silane in the mixed gas of silane and diluent gas is greater than or equal to 10%. In the vapor deposition process, the silane in the mixed gas of silane and diluent gas introduced is controlled at a relatively high content, which is beneficial to improve the deposition efficiency. In some embodiments, the volume fraction of silane in the mixed gas of silane and diluent gas can be 10%-70%. In some embodiments, the volume fraction of silane in the mixed gas of silane and diluent gas is 10%, 20%, 30%, 40%, 50%, 60%, or 70%. In some embodiments, the volume fraction of silane in the mixed gas of silane and diluent gas is 30%-50%. According to the present application, the content of silicon is controlled according to the total pore volume of the porous carbon, and in the deposition process, without reducing the concentration of the introduced silane gas or reducing the deposition temperature, a higher deposition rate can be obtained while maintaining a relatively high silane concentration and a relatively high temperature, and the enrichment of silicon on the surface of the porous carbon can be controlled.

[0091] In the embodiments of the present application, in the process of introducing the mixed gas of silane and diluent gas to deposit the silicon-based material on the porous carbon, the flow rate of the introduced silane is 0.01 L / min-20 L / min. Exemplarily, the flow rate of the introduced silane is 0.01 L / min, 0.05 L / min, 0.08 L / min, 0.1 L / min, 0.5 L / min, 1 L / min, 3 L / min, 5 L / min, 8 L / min, 10 L / min, 12 L / min, 15 L / min, 18 L / min, or 20 L / min.

[0092] In the embodiments of the present application, the first temperature during the silicon deposition process is 380-485°C. The suitable temperature setting is conducive to the adsorption, cracking, nucleation and growth of silane. Exemplarily, the first temperature can be 380°C, 390°C, 400°C, 420°C, 450°C, 460°C, 470°C, 480°C, 485°C. The temperature rising rate when rising to the first temperature can be 2-10°C / min, for example, 2°C / min, 5°C / min, 10°C / min, and during this period, argon can be introduced at a flow rate of 0.2-0.8 L / min, for example, 0.2 L / min, 0.5 L / min, 0.8 L / min.

[0093] In some embodiments of the present application, during the process of introducing the mixed gas of silane and diluent gas to deposit silicon on the porous carbon, the reaction furnace is rotated at a speed of 20-100 s / revolution, and is kept at temperature for 1-5 h to achieve better silicon deposition effect. In some embodiments, the reaction furnace is rotated at a speed of 20 s / revolution, 50 s / revolution, 80 s / revolution, 100 s / revolution. In some embodiments, the reaction furnace is kept at temperature for 1 h, 2 h, 3 h, 4 h, 5 h. After the silicon deposition is completed, the introduction of silane gas is stopped.

[0094] Step S102 is the process of chemical vapor deposition to form a coating layer on the silicon-carbon core. In the embodiments of the present application, the coating layer raw gas is a mixed gas of carbon source gas and diluent gas, and the carbon source gas can be, for example, acetylene, ethylene, propylene, etc., and the diluent gas can be, for example, argon, nitrogen, etc. In the mixed gas of carbon source gas and diluent gas, the volume fraction of carbon source gas is 30-50%, for example, 30%, 35%, 40%, 45%, 50%. During the deposition process, the utilization rate of the coating layer raw gas is 10-60%, and specifically, for example, it can be 10%, 20%, 30%, 40%, 50%, 60%.

[0095] In step S102, the second temperature can be 500-800°C. The suitable temperature setting is conducive to the pyrolysis of carbon source to form a carbon layer. Exemplarily, the second temperature can be 500°C, 550°C, 600°C, 650°C, 700°C, 750°C, 800°C. The temperature rising rate when rising to the second temperature can be 2-10°C / min, for example, 2°C / min, 5°C / min, 10°C / min. Before and during the process of rising the reaction furnace to the second temperature, argon can be introduced at a flow rate of 0.5-1.5 L / min, for example, 0.5 L / min, 1.0 L / min, 1.5 L / min.

[0096] During the process of introducing the coating layer raw gas to deposit a coating layer on the surface of the silicon-carbon core, the flow rate of the coating layer raw gas introduced is 0.01-20 L / min.

[0097] In some embodiments of the present application, during the process of introducing the coating layer raw material gas to deposit the coating layer on the surface of the silicon-carbon core, the reaction furnace is rotated at a speed of 20-100s / revolution, and the temperature is maintained for 1-3h. In some embodiments, the reaction furnace is rotated at a speed of 20s / revolution, 50s / revolution, 80s / revolution or 100s / revolution. In some embodiments, the temperature is maintained for 1h, 2h or 3h.

[0098] In step S102, the proportion of the deposited coating layer in the negative electrode material is controlled to be less than or equal to 3%.

[0099] The preparation method of the negative electrode material provided in the embodiments of the present application controls the amount of the deposited silicon-based material in a specific range according to the total pore volume of the porous carbon, which is beneficial to maintaining a certain adsorption difference inside and outside the pores of the porous carbon. During the deposition process, silane is preferentially adsorbed and cracked inside the pores, avoiding the enrichment of silicon on the surface of the porous carbon. As a result, the negative electrode material has high capacity, low swelling performance and high conductivity. In the case of maintaining a high silane introduction concentration to ensure high production efficiency, the negative electrode material with low swelling performance and high conductivity can be obtained.

[0100] Referring to FIG. 4, FIG. 4 is a schematic diagram of the cross-sectional structure of the negative electrode sheet 200 provided in the embodiments of the present application. The negative electrode sheet 200 includes a current collector 201 and a negative electrode active layer 202 disposed on the current collector 201. The current collector 201 can be a metal foil, such as a copper foil, an aluminum foil, a gold foil, a platinum foil, etc. The negative electrode active layer 202 includes the negative electrode material 100 described above in the embodiments of the present application. The negative electrode active layer 202 includes a negative electrode active material, a conductive agent and a binder. The negative electrode active material can include only the negative electrode material 100, or can include the negative electrode material 100 and other negative electrode active materials. The other negative electrode active materials can include one or more of a carbon-based negative electrode active material, a silicon-based negative electrode active material and a phosphorus-based negative electrode active material. The negative electrode sheet 200 includes the negative electrode material 100 provided in the embodiments of the present application, which is beneficial to improving the capacity of the negative electrode sheet 200, while obtaining high cycle retention rate and rate performance. The binder can be, for example, sodium carboxymethyl cellulose (CMC-Na), styrene butadiene rubber (SBR), polyacrylic acid (PAA), lithium polyacrylate (LiPAA), etc. The conductive agent can be, for example, Super P carbon black, amorphous carbon, carbon nanotubes, carbon fibers, graphene, etc.

[0101] Referring to FIG. 5, FIG. 5 is a schematic diagram of the structure of the battery 300 provided in the embodiments of the present application. The battery 300 includes a positive electrode 301, a negative electrode 302, an electrolyte 304 located between the positive electrode 301 and the negative electrode 302, and corresponding circuits. The negative electrode 302 includes the negative electrode sheet 200 described above in the embodiments of the present application.

[0102] In the embodiments of the present application, the battery 300 can be a secondary battery, specifically, but not limited to, a lithium ion secondary battery or a sodium ion secondary battery. The battery 300 can be a liquid battery, a solid battery or a semi-solid battery. In some embodiments of the present application, the battery 300 is a liquid battery, the electrolyte 304 is a liquid electrolyte, and the battery 300 further comprises a separator 303 between the positive electrode 301 and the negative electrode 302. In some embodiments of the present application, the battery 300 is a solid battery, and the electrolyte 304 is a solid electrolyte.

[0103] The positive electrode 301 can be various commercially available or self-prepared battery positive electrodes, which are not particularly limited in the present application. The separator 303 includes, but is not limited to, a single-layer polypropylene (PP) separator, a single-layer polyethylene (PE) separator, a double-layer PP / PE separator, a double-layer PP / PP separator, a three-layer PP / PE / PP separator, and a ceramic-coated PE separator.

[0104] As shown in FIG. 5, the reaction principle of the battery 300 is as follows: during charging, metal ions (such as lithium ions) are released from the positive electrode 301 and migrate to the negative electrode 302 through the electrolyte 304 (liquid electrolyte), while electrons (e-) flow from the positive electrode 301 to the negative electrode 302 through the external circuit, the open-circuit voltage of the battery 300 increases, and the electrical energy is stored; during discharging, metal ions (such as lithium ions) are released from the negative electrode 302 and return to the positive electrode 301 through the electrolyte 304, and the corresponding electrons (e-) migrate from the negative electrode 302 to the positive electrode 301 through the external circuit, the voltage decreases, and the electrical energy is released. In FIG. 5, the solid arrows represent the charging process, and the dashed arrows represent the discharging process. Relatively speaking, the more the number of metal ion migration and the faster the migration speed, the higher the capacity and rate performance of the battery.

[0105] The battery provided by the embodiments of the present application adopts the negative electrode material provided by the embodiments of the present application, which can improve the structural stability and rate performance of the negative electrode material while maintaining high specific capacity, thereby being beneficial to the improvement of long cycle stability and fast charging performance of the battery. The battery provided by the embodiments of the present application can be used in terminal devices, such as consumer electronic products, for example, mobile phones, earphones, tablet computers, mobile power sources, portable computers, notebook computers and other wearable or mobile electronic devices, and can also be used in vehicle (for example, electric vehicles, electric bicycles, etc.), unmanned aerial vehicles, energy storage devices, power stations, base stations and other equipment products, so as to improve the performance of the products.

[0106] Referring to FIG. 6, FIG. 6 is a structural schematic diagram of an electric device 400 provided by an embodiment of the present application. The electric device 400 includes a shell 411 and electronic components and the battery 300 as described above in the embodiments of the present application accommodated in the shell 411, and the battery 300 supplies power to the electronic components. In the present application, the electric device 400 can be any device using electricity, which can be a consumer electronic product such as a mobile phone, a tablet computer, a desktop computer, a notebook computer, a mobile power supply, a portable computer, a smart screen, a display, a sound system, a vehicle-mounted product, and other wearable or movable electronic devices (for example, glasses, watches, bracelets, earphones, etc.), or a vehicle (for example, a power automobile, an electric bicycle, etc.), a ship, an aerospace device, a drone, a power station, a base station, and other device products. The battery provided by the embodiments of the present application can improve the performance of the electric device and improve the competitiveness of the product.

[0107] The embodiments of the present application also provide an energy storage device, which includes a receiving cavity and a battery accommodated in the receiving cavity, and the battery stores electric energy for the energy storage device.

[0108] The embodiments of the present application also provide an energy storage system, which includes an energy storage device and a power converter electrically connected, and the power converter is used for power conversion processing of voltage and / or current, and the changed voltage and / or current are input to the energy storage device.

[0109] The technical solutions of the present application will be further described in the following embodiments.

[0110] Embodiment 1

[0111] In this embodiment, 40 g of porous carbon with a total pore volume of 0.81 cm 3 / g is selected. In all the openings in the porous carbon, the total volume ratio of the openings with an opening diameter ≤ 3 nm is greater than or equal to 90%, the total volume ratio of the openings with an opening diameter of 1-3 nm is greater than or equal to 50%, the mass content of silicon in the negative electrode material is 44.3%, the ratio of the mass content of silicon in the negative electrode material to the total pore volume of the porous carbon (hereinafter referred to as RSP) is 0.547, and the mass content of the coating layer in the negative electrode material is 2%. The 40 g of porous carbon is placed in a rotary furnace, heated to 400℃ at a rate of 5℃ / min, and then a mixture gas of silane with a volume fraction of 30% (the dilution gas is argon) is introduced. The rotary furnace rotates at a speed of 20 s / revolution, and the temperature is maintained for 1.8 h. After the temperature maintenance is completed, the silane gas is turned off, and after 30 min, the rotary furnace is heated to 600℃ at a rate of 5℃ / min, a mixture gas of acetylene with a volume fraction of 30% (the dilution gas is argon) is introduced, and the rotary furnace rotates at a speed of 20 s / revolution. The temperature is maintained for 1 h. The utilization rate of silane is 92%.

[0112] Embodiment 2

[0113] The difference from Example 1 is that the mass content of silicon in the negative electrode material is different from that of Example 1, the corresponding RSP ratio is different, the concentration of monosilane in the silicon deposition process is unchanged, and the time of introducing the monosilane mixed gas is regulated.

[0114] Example 3

[0115] The difference from Example 1 is that the total pore volume of the porous carbon selected in this example is 0.89 cm 3 / g, the mass content of silicon in the negative electrode material is 47.8%, the corresponding RSP ratio is 0.537, the concentration of monosilane in the silicon deposition process is unchanged, and the time of introducing the monosilane mixed gas is regulated.

[0116] Example 4

[0117] The difference from Example 3 is that the mass content of silicon in the negative electrode material is different from that of Example 3, the corresponding RSP ratio is different, the concentration of monosilane in the silicon deposition process is unchanged, and the time of introducing the monosilane mixed gas is regulated.

[0118] Example 5

[0119] The difference from Example 1 is that the total pore volume of the porous carbon selected in this example is 0.95 cm 3 / g, the mass content of silicon in the negative electrode material is 50.3%, the corresponding RSP ratio is 0.529, the concentration of monosilane in the silicon deposition process is unchanged, and the time of introducing the monosilane mixed gas is regulated.

[0120] Examples 6-7

[0121] The difference from Example 5 is that the mass content of silicon in the negative electrode material is different from that of Example 5, the corresponding RSP ratio is different, the concentration of monosilane in the silicon deposition process is unchanged, and the time of introducing the monosilane mixed gas is regulated.

[0122] Comparative Examples 1-3

[0123] The difference from Example 1 is that the mass content of silicon in the negative electrode material is different from that of Example 1, the corresponding RSP ratio is different, the concentration of monosilane in the silicon deposition process is unchanged, and the time of introducing the monosilane mixed gas is regulated.

[0124] Comparative Examples 4-6

[0125] The difference from Example 3 is that the mass content of silicon in the negative electrode material is different from that of Example 3, the corresponding RSP ratio is different, the concentration of monosilane in the silicon deposition process is unchanged, and the time of introducing the monosilane mixed gas is regulated.

[0126] Comparative Examples 7-8

[0127] The difference from Example 5 is that the mass content of silicon in the negative electrode material is different from that of Example 5, the corresponding RSP ratio is different, the concentration of monosilane in the silicon deposition process is unchanged, and the time of introducing the monosilane mixed gas is regulated.

[0128] The negative electrode materials obtained in Examples 1-7 and Comparative Examples 1-8 were subjected to silicon content determination, conductivity test and expansion performance test, respectively. The content of silicon element in the negative electrode material was determined by thermogravimetric analysis (TGA), and the conductivity of the negative electrode material was tested by a powder resistivity tester. The specific parameter values are shown in Table 1.

[0129] The negative electrode materials obtained in Examples 1-7 and Comparative Examples 1-8 were mixed with conductive agent (Super P carbon black) and binder (sodium carboxymethyl cellulose) in a mass ratio of 8:1:1 in an aqueous solvent to obtain negative electrode slurry after stirring uniformly. The negative electrode slurry was coated on a copper foil, vacuum dried at 110°C for 12h, and then rolled to obtain a negative electrode sheet. A metal lithium sheet was used as a counter electrode, a commercial PE separator and a 1mol / L LiPF6 electrolyte of EC (ethylene carbonate) and DEC (diethyl carbonate) in a volume ratio of 1:1 were used, and a 2032 type button cell was assembled in an argon glove box.

[0130] The batteries prepared in Examples 1-7 and Comparative Examples 1-8 were placed in an electrochemical test cabinet, and discharged at 0.1C to 0.005V at 25°C, and then rested for 5min. The discharge was continued at 0.02C to 0.005V and rested for 5min, and then charged at 0.1C to 1.5V. The cycle test was carried out, and the reversible capacity, the first coulombic efficiency, the dQ / dV value at 0.45V, and the cycle capacity retention rate of the battery after 100 cycles of the negative electrode material were calculated. The reversible capacity is the first discharge reversible capacity of the negative electrode material. The first coulombic efficiency = first discharge capacity / first charge capacity*100%.

[0131] The initial thickness of each negative electrode sheet obtained in Examples 1-7 and Comparative Examples 1-8 was tested at 25°C. Then the button cells obtained in Examples 1-7 and Comparative Examples 1-8 were charged to 0.005V to make the negative electrode full lithium state, disassembled, and the thickness of the negative electrode sheet was tested. The thickness increment of the negative electrode sheet was recorded, and the expansion rate of the negative electrode sheet was calculated. The expansion rate of the negative electrode sheet = thickness increment of the negative electrode sheet / initial thickness of the negative electrode sheet*100%, and the results are shown in Table 1.

[0132] Table 1

[0133] From the results of Table 1, it can be seen that according to the specific pore volume of the porous carbon, the RSP ratio of the negative electrode material of Examples 1-7 is controlled to be less than 0.58, the dQ / dV value at 0.45 V is less than 1.7, and the conductivity and cycle retention rate of the corresponding negative electrode material are greatly improved compared with the comparative examples with the same total pore volume. Compared with Comparative Examples 1-8, the negative electrode material of Examples 1-7 has relatively larger reversible specific capacity and first coulombic efficiency under the premise of high conductivity and good cycle performance.

[0134] It should be understood that the first, second, and various numerical designations referred to herein are only for the convenience of differentiation and do not limit the scope of the present application.

[0135] In the present application, "and / or" describes the association relationship of associated objects, which means that there can be three kinds of relationships, for example, A and / or B, which can represent the following cases: A exists alone, A and B exist together, and B exists alone, where A and B can be singular or plural. The character " / " generally represents an "or" relationship between the associated objects before and after it.

[0136] In the present application, "at least one" means one or more, and "multiple" means two or more. "At least one of the following" or the like means any combination of these items, including any combination of single item or multiple items. For example, "at least one of a, b, or c", or "at least one of a, b, and c", can mean a, b, c, a-b (i.e., a and b), a-c, b-c, or a-b-c, where a, b, and c can be single or multiple.

[0137] In the present application, "-" represents a range value, including the end point values at both ends. For example, the value of a can be 0.5-15, which means that the value of a can be between 0.5 and 15, and includes the end point values 0.5 and 15.

[0138] It should be understood that in various embodiments of the present application, the size of the sequence number of the above processes does not mean the order of execution, and part or all of the steps can be executed in parallel or in sequence, and the execution order of each process should be determined according to its function and inherent logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

Claims

1. A negative electrode material, characterized by, The negative electrode material comprises a silicon-carbon inner core and a coating layer arranged on the surface of the silicon-carbon inner core, the silicon-carbon inner core comprises porous carbon and a silicon-based material deposited on the porous carbon, the ratio of the mass content of the silicon-based material to the total pore volume of the porous carbon in the negative electrode material is within a first value range, and the differential value dQ / dV of the charging-discharging capacity at 0.45 V to voltage in the charging-discharging curve of the negative electrode material is within a second value range, so that the negative electrode material has high capacity, low expansion performance and high conductivity. 3 / g.

2. The negative electrode material of claim 1, wherein, The first value range is greater than 0.40 and less than or equal to 0.

58.

3. The negative electrode material of claim 2, wherein, The first value range is greater than 0.50 and less than 0.

58.

4. The negative electrode material of any one of claims 1 to 3, wherein The second value range is less than 1.

7.

5. The negative electrode material of claim 4, wherein the carbon-based material is selected from the group consisting of graphite, carbon black, and carbon nanotubes. The second value range is less than 1.

6.

6. The negative electrode material of any one of claims 1 to 5, wherein, In the porous carbon, the proportion of the total volume of the open pores with an opening diameter of less than or equal to 3 nm to the total open pore volume is greater than or equal to 90%.

7. The negative electrode material of claim 6, wherein the carbon-based material is selected from the group consisting of graphite, carbon black, and carbon nanotubes. In the porous carbon, the proportion of the total volume of the open pores with an opening diameter of 1 nm to 3 nm to the total open pore volume is greater than or equal to 50%.

8. The negative electrode material of any one of claims 1 to 7, wherein, The total pore volume of the porous carbon is 0.4 cm 3 / g-1.0 cm 3 / g.

9. The negative electrode material of any one of claims 1-8, wherein, The mass content of the silicon-based material in the negative electrode material is greater than or equal to 42%.

10. The negative electrode material of claim 9, wherein the carbon-based material is selected from the group consisting of graphite, carbon black, and carbon nanotubes. The mass content of the silicon-based material in the negative electrode material is 47% to 54%.

11. The negative electrode material of any one of claims 1-10, wherein, The coating layer comprises a carbon material and / or a fast ion conductor; and / or, the mass proportion of the coating layer in the negative electrode material is less than or equal to 3%.

12. The negative electrode material of any one of claims 1-11, wherein, The electrical conductivity of the negative electrode material is greater than or equal to 1 S / cm.

13. The negative electrode material of any one of claims 1-12, wherein, The expansion rate of a single particle of the negative electrode material after complete lithiation is less than or equal to 90%.

14. The negative electrode material of any one of claims 1-13, wherein, The reversible capacity of the negative electrode material is greater than 1200 mAh / g.

15. The negative electrode material of any one of claims 1-14, wherein, The specific surface area of the negative electrode material is less than 10 m 2 / g.

16. The negative electrode material of any one of claims 1-15, wherein, The capacity retention rate of a half-cell cycled 100 times with a negative electrode composed of the negative electrode material as an active material and a lithium sheet as a counter electrode is greater than or equal to 80%.

17. A method for preparing a negative electrode material, characterized in that, Comprise: The porous carbon is placed in a reaction furnace, heated to a first temperature, and according to the ratio of the mass content of the silicon-based material in the negative electrode material to the total pore volume of the porous carbon within a first value range, a silicon-based material raw gas is introduced to deposit the silicon-based material on the porous carbon to obtain a silicon-carbon core; wherein the total pore volume of the porous carbon is cm 3 / g. The reaction furnace is heated to a second temperature, and a coating layer raw material gas is introduced to deposit a coating layer on the surface of the silicon-carbon core, thereby obtaining a negative electrode material. In the charge-discharge curve of the negative electrode material, the differential value dQ / dV of the charge-discharge capacity at 0.45 V with respect to the voltage is within a second value range, so that the negative electrode material has high capacity, low expansion performance and high conductivity.

18. The production method according to claim 17, wherein The first value range is greater than 0.40 and less than or equal to 0.

58.

19. The production method according to claim 17 or 18, wherein The second value range is less than 1.

7.

20. The production method according to any one of claims 17 to 19, wherein The silicon-based material raw material is a mixed gas of silane and diluent gas, and the volume fraction of silane in the mixed gas of silane and diluent gas is greater than or equal to 10%; the flow rate of silane is 0.01 L / min to 20 L / min.

21. The method of manufacturing according to any one of claims 17-20, wherein, The first temperature is 380°C to 485°C; during the process of introducing the silicon-based material raw material gas and depositing the silicon-based material on the porous carbon, the reaction furnace is rotated at a speed of 20 to 100 s / revolution, and the temperature is maintained for 1 to 5 h.

22. The preparation method according to any one of claims 17-21, characterized in that, The second temperature is 500°C to 800°C; during the process of introducing the coating layer raw material gas and depositing the coating layer on the surface of the silicon-carbon core, the reaction furnace is rotated at a speed of 20 to 100 s / revolution, and the temperature is maintained for 1 to 3 h.

23. A negative electrode sheet characterized by comprising: The negative electrode sheet comprises the negative electrode material according to any one of claims 1 to 16.

24. A battery, characterized by The battery comprises the negative electrode sheet according to claim 23; or comprises the negative electrode material according to any one of claims 1 to 16.

25. An electrical device, comprising: The electrical equipment comprises the battery according to claim 24.

26. An energy storage device, comprising: The energy storage device comprises the battery according to claim 24.

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