A negative electrode material, a secondary battery, and an electrical device.

Abstract

This application belongs to the field of new energy battery technology, specifically relating to a negative electrode material, a secondary battery, and an electrical device. This application provides a negative electrode material comprising a porous carbon matrix and a silicon-based material distributed within at least a portion of the pores of the porous carbon matrix; the negative electrode material satisfies the relationship 0.2 < X < 20, where X = D / (S × J), Dμm is the volume median particle size Dv50 of the negative electrode material, and Sm... 2 / g represents the specific surface area of ​​the negative electrode material, and Jnm represents the silicon crystal size of the Si(111) crystal plane in the negative electrode material. The negative electrode material provided in this application has excellent capacity, first-efficiency, rate performance, and cycle performance.

Description

Technical Field

[0001] This application belongs to the field of new energy battery technology, specifically relating to a negative electrode material, a secondary battery, and an electrical device. Background Technology

[0002] Currently, there are higher requirements for the driving range of lithium-ion batteries. However, the energy density of mainstream lithium-ion batteries is insufficient to meet the growing demand of electric vehicles and large-scale energy storage. Compared with cathode materials, anode materials have greater potential for capacity improvement. Among them, silicon has become a relatively ideal anode material due to its high theoretical specific capacity (3579mAh / g), low lithium intercalation potential, and abundant reserves in the earth's crust. However, silicon is prone to huge volume expansion during lithiation / delithiation, leading to particle pulverization and unusability. At the same time, the breakage of silicon causes the anode solid electrolyte membrane (SEI membrane) to continuously rupture and regenerate, consuming a large number of lithium ions. In addition, silicon has poor conductivity and is prone to a large number of side reactions with the electrolyte, leading to electrolyte oxidation and decomposition, excessive growth of the SEI membrane, and damage to the silicon material structure, which seriously affects the cycle stability of the battery.

[0003] Existing technologies improve the structural stability of silicon-carbon materials by coating them with a carbon coating layer. However, carbon-coated silicon-based materials have poor kinetic properties, and the SEI film formed on the surface has poor stability, resulting in limited improvement in cycle performance. Summary of the Invention

[0004] Therefore, the technical problem to be solved by this application is to overcome the poor cycle performance of silicon-based materials in the prior art.

[0005] Therefore, this application provides the following technical solution.

[0006] In a first aspect, this application provides a negative electrode material, including a porous carbon matrix and a silicon-based material distributed within at least a portion of the pores of the porous carbon matrix; The negative electrode material satisfies the relationship 0.2 < X < 20, X = D / (S × J); Wherein, D μm is the value of the volume median particle size Dv50 of the negative electrode material; S m 2 / g is the numerical value of the specific surface area of ​​the negative electrode material; J nm is the numerical value of the silicon crystal size of the Si(111) crystal plane in the negative electrode material.

[0007] In one optional embodiment, the full width at half maximum (FWHM) of the Si(111) crystal plane diffraction peaks in the diffraction pattern obtained by XRD diffraction testing of the negative electrode material is 0.025 rad to 0.3 rad.

[0008] In one optional embodiment, the porous carbon matrix includes micropores, ultramicropores, and mesopores. In the porous carbon matrix, with the total pore volume as 100%, the volume ratio of pores smaller than 1 nm is <20%, and the volume ratio of pores larger than 10 nm is <5%.

[0009] In one optional embodiment, when a negative electrode sheet made of the aforementioned negative electrode material is used as a half-cell for a 0.1C / 0.1C cycle charge-discharge test, the obtained delithiation dQ / dV-V curve satisfies I1 / I2 < 1. Where I1 represents the intensity of the delithiation oxidation peak at 0.40V~0.45V in the delithiation dQ / dV-V curve; I2 represents the intensity of the delithiation oxidation peak at 0.30V~0.35V in the delithiation dQ / dV-V curve; The upper and lower limit voltages for the cyclic charge-discharge test are 0.005V to 2V.

[0010] In one optional embodiment, the porous carbon matrix has a pore volume ≥ 0.5 cm³. 3 / g; and / or, the average pore size of the porous carbon matrix is ​​0.1nm~5nm.

[0011] In one alternative embodiment, the negative electrode material satisfies at least one of the following conditions: A. 1≤J≤5; B. 2 ≤ D ≤ 15; C. 0.1≤S≤6.

[0012] In one alternative embodiment, the negative electrode material satisfies at least one of the following conditions: ①Based on the total mass of the negative electrode material, the porous carbon matrix accounts for 40% to 60% of the mass; ②Based on the total mass of the negative electrode material, the mass percentage of the silicon-based material is 40% to 60%.

[0013] In one alternative embodiment, the negative electrode material further includes a microporous carbon layer disposed on at least a portion of the surface of the porous carbon matrix, wherein the mass percentage of the microporous carbon layer is ≤10% based on the total mass of the negative electrode material.

[0014] Secondly, this application provides a secondary battery, including a negative electrode sheet, wherein the negative electrode sheet includes the negative electrode material described in the first aspect.

[0015] Thirdly, this application provides an electrical device including the secondary battery described in the second aspect, wherein the secondary battery serves as the power supply for the electrical device.

[0016] In the silicon-based anode material provided in this application, the porous carbon matrix is ​​prepared by high-temperature carbonization of one or more organic carbon materials such as phenolic resin, sucrose, glucose, starch, coconut shell, and nut shell.

[0017] The technical solution of this application has the following advantages: The negative electrode material provided in this application includes a porous carbon matrix and a silicon-based material distributed within at least a portion of the pores of the porous carbon matrix; the negative electrode material satisfies the relationship 0.2 < X < 20, X = D / (S × J). In this case, the silicon crystal size J of the Si(111) crystal plane in the negative electrode material has better compatibility with the median particle size D and specific surface area S of the negative electrode material. While fully utilizing the capacity of the silicon-based material, it can also effectively suppress the volume expansion of the silicon-based material, improving the cycle performance and capacity of the battery; and shorten the migration path of lithium ions in the negative electrode material, reducing side reactions, thereby improving the rate performance and first-time efficiency of the battery. Detailed Implementation

[0018] The following embodiments are provided to better understand this application and are not limited to the preferred embodiments described herein. They do not constitute a limitation on the content and scope of protection of this application. Any product that is the same as or similar to this application, derived by anyone under the guidance of this application or by combining features of this application with other prior art, falls within the scope of protection of this application.

[0019] Where specific experimental steps or conditions are not specified in the embodiments, they can be performed according to the conventional experimental steps or conditions described in the literature in this field. Existing technologies use carbon coating to modify silicon-based materials. This can improve the conductivity of silicon-based materials using carbon, and also use the carbon coating layer to restrict the volume expansion of silicon and reduce the contact between silicon and the electrolyte. However, the kinetic performance of the carbon coating layer is poor, and the SEI film formed on the surface of the silicon-based material has poor stability, resulting in poor battery cycle performance.

[0020] In a first aspect, this application provides a negative electrode material, including a porous carbon matrix and a silicon-based material distributed within at least a portion of the pores of the porous carbon matrix; The negative electrode material satisfies the relationship 0.2 < X < 20, X = D / (S × J); Wherein, D μm is the value of the volume median particle size Dv50 of the negative electrode material; S m 2 / g is the numerical value of the specific surface area of ​​the negative electrode material; J nm is the numerical value of the silicon crystal size of the Si(111) crystal plane in the negative electrode material.

[0021] This study found that a single silicon-based material contains both crystalline and amorphous silicon regions. By performing XRD characterization on the silicon-based material in the anode material and calculating the dimensions of multiple crystalline silicon regions in the silicon-based material using the Scherrer equation, the size of the Si(111) crystal plane silicon crystals in the anode material can be obtained. Furthermore, this study found that by controlling the size of the Si(111) crystal plane silicon crystals, the median particle size, and the specific surface area of ​​the anode material to satisfy 0.2 < X < 20, the anode material exhibits better structural stability and conductivity. This is because, at this point, the size of the Si(111) crystal plane silicon crystals in the anode material has better compatibility with the median particle size and specific surface area of ​​the anode material. While fully utilizing the capacity of the silicon-based material, it can also effectively suppress the volume expansion of the silicon-based material, improving the cycle performance and capacity of the battery; and shortening the migration path of lithium ions in the anode material, reducing side reactions, thereby improving the rate performance and first-time efficiency of the battery. For example, X can be a range of any one or any two of the following: 0.21, 0.3, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 19.9.

[0022] The volume median particle size Dv50 of the negative electrode material can be determined using conventional methods in the art: laser particle size analysis, for example, using a Malvern particle size analyzer.

[0023] The specific surface area S of the negative electrode material can be determined using conventional methods in the art: it is obtained through a fully automated physical adsorption analyzer. Specifically, the sample to be tested is dried and degassed at high temperature to remove moisture and adsorbed gases from the sample pores. The pretreated sample is then placed in the sample cell of a gas adsorption analyzer, and vacuum degassing is performed to remove adsorbed gases from the sample surface and pores. Pure nitrogen gas is then introduced into the sample tube at liquid nitrogen temperature for adsorption. After adsorption is complete, the nitrogen pressure is gradually reduced, and the desorption amount is recorded. The instrument automatically records the nitrogen adsorption and desorption amounts. The adsorption isotherm is analyzed using BET (Brunor-Emmett-Teller) theory or other appropriate models to calculate the specific surface area.

[0024] In one optional embodiment, the full width at half maximum (FWHM) of the Si(111) crystal plane diffraction peak in the diffraction pattern obtained by XRD diffraction testing of the negative electrode material is 0.025 rad to 0.3 rad. This indicates that the silicon in the negative electrode material has a low degree of crystallinity and the silicon grain size is small, which can effectively reduce the degree of volume expansion, improve the structural stability of the negative electrode material, fully utilize the capacity, and improve the first-efficiency, cycle, and rate performance of the battery. For example, the FWHM of the Si(111) crystal plane diffraction peak can be any one or any two of the following values: 0.025 rad, 0.05 rad, 0.1 rad, 0.15 rad, 0.2 rad, 0.25 rad, and 0.3 rad.

[0025] In one optional embodiment, the porous carbon matrix includes micropores, ultramicropores, and mesopores. In the porous carbon matrix, with the total pore volume as 100%, the volume percentage of pores smaller than 1 nm is <20%, and the volume percentage of pores larger than 10 nm is <5%. By controlling the volume percentage of pores smaller than 1 nm in the porous carbon matrix to <20%, electrolyte side reactions and the consumption of active lithium ions can be reduced. This avoids the problem of excessively large pore volumes smaller than 1 nm leading to difficulty in lithium ion insertion / extraction and the occurrence of "dead lithium," while simultaneously improving the lithium ion insertion / extraction rate of the anode material, which is beneficial to the battery's first-efficiency performance, cycle life, and rate performance. Furthermore, the porous carbon matrix is ​​predominantly composed of pores between 1 nm and 10 nm, reserving expansion space for silicon-based materials. This prevents the silicon-based materials from pulverizing and failing due to excessive stress during charging and discharging, thus improving the battery's cycle performance. The pore distribution in the porous carbon matrix can be obtained by removing the silicon component from the silicon-carbon material through acid or alkali etching, followed by pore structure analysis of the remaining porous carbon material.

[0026] In one optional embodiment, when a negative electrode sheet made of the aforementioned negative electrode material is used as a half-cell for a 0.1C / 0.1C cycle charge-discharge test, the obtained delithiation dQ / dV-V curve satisfies I1 / I2 < 1. Wherein, I1 represents the delithiation oxidation peak intensity at 0.40V~0.45V in the delithiation dQ / dV-V curve; I2 represents the delithiation oxidation peak intensity at 0.30V~0.35V in the delithiation dQ / dV-V curve; the upper and lower limit voltages of the cycle charge-discharge test are 0.005V~2V.

[0027] Furthermore, this study found that when I1 / I2 < 1, the degree of silicon floating on the surface of the negative electrode material is relatively small. At this time, the silicon-based material is uniformly deposited inside the porous carbon matrix, providing a buffer space for the volume expansion of the silicon-based material, reducing the volume expansion effect of the material, and further improving the cycle performance of the battery. For example, I1 / I2 can be any one or any two of the following: 0.5, 0.6, 0.7, 0.8, 0.9, and 0.99.

[0028] In one optional embodiment, the porous carbon matrix has a pore volume ≥ 0.5 cm³. 3 / g, especially meeting 0.5cm 3 / g~1.3cm 3 / g can further suppress the volume expansion of silicon-based materials, improve the structural stability of anode materials, and benefit the cycle performance of batteries.

[0029] The pore volume of the porous carbon matrix can be measured using conventional methods in the art: acid or alkali etching removes the silicon component from the silicon-carbon material, and then pore structure analysis is performed on the remaining porous carbon material to measure the pore volume of the porous carbon matrix. For example, the pore volume of the porous carbon matrix can be 0.5 cm³. 3 / g, 0.6cm 3 / g, 0.7cm 3 / g, 0.8cm 3 / g, 0.9cm 3 / g, 1cm 3 / g, 1.1cm 3 / g, 1.2cm 3 / g, 1.3cm 3 / g, 1.4cm 3 / g, 1.5cm 3 The range of one or both of the values ​​in / g.

[0030] In one optional embodiment, the average pore size of the porous carbon matrix is ​​0.1 nm to 5 nm, thereby effectively controlling the size of the silicon-based material. This effectively suppresses the volume expansion of the silicon-based material, reduces side reactions, improves the structural stability of the anode material, and increases the lithium-ion insertion / extraction rate, which is beneficial to the battery's first-cycle efficiency, cycle life, and rate performance. The average pore size of the porous carbon matrix can be measured using conventional methods in the art: the sample to be tested is dried and degassed at high temperature to remove moisture and adsorbed gases from the sample pores. The pretreated sample is then placed in the sample cell of a gas adsorption analyzer, and vacuum degassing is performed to remove adsorbed gases from the sample surface and pores. Pure nitrogen gas is then introduced into the sample tube at liquid nitrogen temperature for adsorption. After adsorption is complete, the nitrogen pressure is gradually reduced, and the desorption amount is recorded. The instrument automatically records the nitrogen adsorption and desorption amounts. Adsorption isotherms can be analyzed using BET (Brunor-Emmett-Teller) theory or other suitable models, and the average pore size of the material can be obtained by methods such as BJH or HK. For example, the average pore size of the porous carbon matrix can be any one or any two of 0.1 nm, 0.5 nm, 1 nm, 2 nm, 3 nm, 4 nm, and 5 nm.

[0031] In one alternative embodiment, the negative electrode material satisfies at least one of the following conditions: A. 1≤J≤5; B. 2 ≤ D ≤ 15; C. 0.1≤S≤6.

[0032] This further enhances the structural stability of the anode material, allowing it to accommodate the volume expansion of the silicon-based material, which is beneficial for the battery's cycle performance. Further limiting the median particle size (Dv50) of the anode material to 2μm~15μm shortens the ion migration path, improves the packing density and structural stability of the anode material, minimizes expansion, and thus enhances the battery's electrochemical performance; the specific surface area of ​​the anode material meets the requirement of 0.1m². 2 / g~6m 2 / g, side reactions are reduced, which is beneficial to the first efficiency, rate and cycle performance of the battery; the silicon crystal size of the Si(111) crystal plane of the negative electrode material meets the requirements of 1 nm~5 nm, thereby reducing the volume expansion of silicon-based materials, improving the stability of the negative electrode material, and improving the cycle performance of the battery.

[0033] For example, D μm can be a range of any one or any two of 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, and 15μm.

[0034] For example, S m 2 / g can be 0.1m 2 / g、1m 2 / g、2m 2 / g、3m 2 / g、4m 2 / g、5m 2 / g、6m 2 The range of one or both of the values ​​in / g.

[0035] For example, J nm can be a range of any one or any two of 1 nm, 2 nm, 3 nm, 4 nm, and 5 nm.

[0036] In one alternative embodiment, the negative electrode material satisfies at least one of the following conditions: ①Based on the total mass of the negative electrode material, the porous carbon matrix accounts for 40% to 60% of the mass; thus, the structural stability of the negative electrode material can be improved, and the volume expansion of the silicon-based material can be effectively suppressed, thereby improving the rate and cycle performance of the battery.

[0037] ②Based on the total mass of the negative electrode material, the mass percentage of the silicon-based material is 40% to 60%. Reducing the volume expansion of the silicon-based material while ensuring battery capacity is beneficial to the battery's cycle and rate performance.

[0038] In one optional embodiment, the negative electrode material further includes a microporous carbon layer disposed on at least a portion of the surface of the porous carbon matrix. The mass percentage of the microporous carbon layer is ≤10% based on the total mass of the negative electrode material. By controlling the mass percentage of the microporous carbon layer, the structural stability of the negative electrode material can be improved, side reactions can be reduced, and kinetics can be enhanced, which is beneficial to the battery's capacity, rate capability, and cycle performance.

[0039] In this application, the mass ratio of microporous carbon layer, porous carbon matrix and silicon-based material in the negative electrode material can be tested using methods and equipment known in the art, such as by TG-DTA testing method.

[0040] For example, the mass percentage of the microporous carbon layer relative to the mass of the negative electrode material can be any one or any two of the following: 1%, 2%, 3%, 4%, 5%, 5%, 6%, 7%, 8%, 9%, and 10%. For example, the mass percentage of the porous carbon matrix relative to the mass of the negative electrode material can be any one or any two of the following: 40%, 45%, 50%, 55%, and 60%. For example, the mass percentage of the silicon-based material relative to the mass of the negative electrode material can be any one or any two of the following: 40%, 45%, 50%, 55%, and 60%.

[0041] In one optional embodiment, after three cycles of 0.1C / 0.1C charge-discharge testing with the negative electrode sheet made of the aforementioned negative electrode material as a half-cell, and after reaching 100% SOC, the thickness expansion rate of the disassembled negative electrode sheet is <100%. This indicates that the negative electrode sheet made of the negative electrode material provided in this application has excellent structural stability and low expansion, which is beneficial to the cycle performance of the battery.

[0042] Secondly, this application provides a secondary battery, including a negative electrode sheet, the negative electrode sheet comprising the negative electrode material as described in the first aspect.

[0043] It is understandable that the secondary battery provided in this application has excellent cycle performance due to the presence of the negative electrode material in the first aspect.

[0044] Thirdly, this application provides an electrical device including the secondary battery described in the second aspect, wherein the secondary battery serves as the power supply for the electrical device.

[0045] It is understood that the electrical equipment provided in this application has excellent cycle performance due to the presence of the secondary battery in the second aspect.

[0046] Fourthly, this application provides a method for preparing a negative electrode material, comprising the following steps: (1) The porous carbon precursor is carbonized and activated to obtain porous carbon; (2) Introduce carbon source gas and perform CVD pre-deposition on the above porous carbon to obtain a porous carbon matrix; (3) Place the porous carbon matrix obtained in step (2) in a CVD furnace, introduce silicon-containing gas to perform silicon deposition, and obtain a silicon-carbon precursor; (4) The silicon-carbon precursor is coated with carbon under an inert atmosphere to obtain the negative electrode material.

[0047] In one optional embodiment, the carbonization step includes: a first sintering and a second sintering in an inert atmosphere; in one optional embodiment, the temperature of the first sintering is 200℃~400℃, and the time of the first sintering is 0.5h~3h; in one optional embodiment, the temperature of the second sintering is 600℃~1000℃, and the time of the second sintering is 3h~5h.

[0048] In one optional embodiment, the activation step includes: activating the device by introducing carbon dioxide or water vapor, and in another optional embodiment, the activation time is 5h to 8h.

[0049] In one optional embodiment, the activation process further includes air jet milling and sieving to initially control the particle size of the porous carbon, thereby ensuring that the volume median particle size Dv50 of the negative electrode material meets the requirements of 2μm~15μm.

[0050] In one optional embodiment, the pre-deposition time is 0.2h to 2h.

[0051] In one optional embodiment, the pre-deposition temperature is 400°C to 500°C.

[0052] In one optional embodiment, the flow rate of the carbon source gas is 6 L / min to 10 L / min.

[0053] In one optional embodiment, the carbon source gas includes acetylene gas. Step (2) can adjust the pore size inside the porous carbon matrix so that the porous carbon matrix includes micropores, ultramicropores, and mesopores.

[0054] In one optional embodiment, the silicon-containing gas comprises a mixture of nitrogen and silane; in another optional embodiment, the volume ratio of nitrogen to silane is 1:(2~4).

[0055] In one optional embodiment, the silicon deposition temperature is 400°C to 650°C, preferably 400°C to 500°C.

[0056] In one alternative embodiment, the silicon deposition time is 5h to 18h.

[0057] In one optional embodiment, the carbon coating step includes: first heating to a first temperature, then introducing a first gas, the first gas comprising a mixture of nitrogen and acetylene gas, wherein in one optional embodiment, the volume ratio of nitrogen to acetylene gas in the mixture is (3~5):1.

[0058] In one optional embodiment, the first temperature is 450°C to 700°C, and preferably, the first temperature is 500°C to 600°C.

[0059] In one optional implementation, the time for introducing the first gas is 2h to 8h.

[0060] The silicon crystal size J of the Si(111) crystal plane in the negative electrode material can be controlled by adjusting at least one of the following: the second sintering temperature in step (1), the activation time, the pre-deposition time in step (2), the silicon deposition temperature in step (3), and the first temperature in step (4).

[0061] The specific surface area S of the negative electrode material can be controlled by adjusting at least one of the following: the temperature of the second sintering in step (1), the activation time in step (1), the first temperature in step (4), and / or the time of introducing the first gas.

[0062] In one optional embodiment, the preparation steps of the negative electrode material include: (1) Carbonize and activate the porous carbon precursor. During the process, an inert atmosphere is used for protection. First, the temperature is raised to 200℃~400℃ and held for 0.5h~3h. Then, the temperature is raised to 800℃ for carbonization and held for 3h~5h. Subsequently, carbon dioxide or water vapor is introduced for activation treatment for 5h~8h to obtain porous carbon.

[0063] (2) Introduce carbon source gas and perform CVD pre-deposition on the above porous carbon, so that the carbon source gas is deposited in the micropores of the porous carbon for a deposition time of 0.3h~0.5h to obtain a porous carbon matrix.

[0064] (3) Place the porous carbon matrix obtained in step (2) in a CVD furnace, introduce a mixture of nitrogen and silane into the furnace for silicon deposition, the volume ratio of nitrogen to silane is 1:(2~4), the deposition temperature is 400℃~500℃, the deposition time is 8h~10h, and a silicon-carbon precursor is obtained.

[0065] (4) Under an inert atmosphere, the furnace is heated to 500℃~600℃, and a mixture of nitrogen and acetylene is introduced into the furnace to carbonize the silicon-carbon precursor for 3~4 hours. Then, the acetylene is stopped, and the furnace is allowed to cool down naturally to room temperature under an inert atmosphere to obtain the negative electrode material.

[0066] In one alternative embodiment, the porous carbon precursor includes one or more of the following: phenolic resin, sucrose, glucose, starch, coconut shell, nut shell, etc.

[0067] Example 1 This embodiment provides a method for preparing a negative electrode material, including the following steps: (1) Under an inert atmosphere, the phenolic resin (Nantong Runfeng, 9003-35-4) was first heated to 300℃ and kept at that temperature for 1 hour; then heated to 800℃ and kept at that temperature for 4 hours. Then carbon dioxide was introduced for activation treatment, and the activation time was 6 hours. The mixture was then pulverized by airflow and sieved to obtain porous carbon. (2) The porous carbon was pre-deposited by CVD. The relative pressure was adjusted to 3 kPa and the carbon source gas (acetylene gas) flow rate was 8 L / min. The deposition time was 0.5 h and the deposition temperature was 450 °C to obtain a porous carbon matrix. (3) The porous carbon matrix is ​​placed in a CVD furnace, and a mixture of nitrogen and silane is introduced into the furnace for silicon deposition. The volume ratio of nitrogen to silane is 1:3, the deposition temperature is 500℃, and the deposition time is 10h to obtain a silicon-carbon precursor. (4) Under an inert atmosphere, the furnace is heated to 550°C and a mixture of nitrogen and acetylene gas (volume ratio of 4:1) is introduced into the furnace to carbon-coat the silicon-carbon precursor to obtain a microporous carbon layer. The coating time is 4 hours. The acetylene gas is then stopped and the furnace is allowed to cool naturally to room temperature under an inert atmosphere to obtain the negative electrode material. The median particle size D of the negative electrode material is 8.2 μm.

[0068] The characterization results of the porous carbon matrix and the anode material are shown in Table 1-2; where D μm refers to the volume median particle size Dv50 of the anode material, and S m 2 / g refers to the specific surface area of ​​the negative electrode material, J nm refers to the silicon crystal size of the Si(111) crystal plane in the negative electrode material, the mass ratio of the microporous carbon layer refers to the percentage of the mass of the microporous carbon layer in the total mass of the negative electrode material, the mass ratio of the porous carbon matrix refers to the percentage of the mass of the porous carbon matrix in the total mass of the negative electrode material, the mass ratio of the silicon-based material refers to the percentage of the mass of the silicon-based material in the total mass of the negative electrode material, and the peak intensity ratio refers to the peak intensity of the delithiation oxidation at 0.45V and the peak intensity of the delithiation oxidation at 0.35V in the dQ / dV-V curve obtained by performing 0.1C / 0.1C cycle charge-discharge tests (upper and lower limit voltages are 0.005V~2V) on coin half-cells made from the negative electrode sheets prepared in each embodiment and comparative example.

[0069] Example 2 The preparation method of the negative electrode material in this embodiment is basically the same as that in embodiment 1, except that the carbon source deposition time in step (2) is changed to 1 hour.

[0070] Example 3 The method for preparing a negative electrode material in this embodiment is basically the same as that in Example 1, except that the carbon source deposition time in step (2) is changed to 0.2h.

[0071] Example 4 The method for preparing a negative electrode material in this embodiment is basically the same as that in Example 1, except that in step (1), the temperature is raised to 600°C instead of 800°C in Example 1.

[0072] Example 5 The method for preparing a negative electrode material in this embodiment is basically the same as that in Example 1, except that in step (1), the temperature is raised to 1000℃ instead of 800℃ in Example 1.

[0073] Example 6 The preparation method of the negative electrode material in this embodiment is basically the same as that in Example 1, except that the deposition time in step (3) is changed to 18h.

[0074] Example 7 The method for preparing a negative electrode material in this embodiment is basically the same as that in Example 1, except that the deposition time in step (3) is changed to 5h.

[0075] Example 8 The method for preparing a negative electrode material in this embodiment is basically the same as that in Example 1, except that in step (4), the temperature is raised to 700°C instead of 550°C in Example 1.

[0076] Example 9 The method for preparing a negative electrode material in this embodiment is basically the same as that in Example 1, except that in step (4), the temperature is raised to 450°C instead of 550°C in Example 1.

[0077] The preparation methods and parameter settings of Examples 10-11 are basically the same as those of Example 1. The differences are shown in Tables 1 and 2.

[0078] Example 12 The preparation method of the negative electrode material in this embodiment is basically the same as that in Example 1, except that the parameters of the negative electrode material are different, as shown in Tables 1 and 2. Step (4) is different: heating to 500℃ instead of heating to 550℃ in Example 1; coating time of 8h instead of coating time of 4h in Example 1.

[0079] Example 13 The preparation method of the negative electrode material in this embodiment is basically the same as that in Example 1, except that the parameters of the negative electrode material are different, as shown in Tables 1 and 2. Step (1) is different: the activation time is 2 hours instead of 6 hours in Example 1; Step (4) is different: heating to 600℃ instead of heating to 550℃ in Example 1; coating time of 2h instead of coating time of 4h in Example 1.

[0080] Example 14 The method for preparing the negative electrode material in this embodiment is basically the same as that in Example 1, except that the parameters of the negative electrode material are different. Please refer to Tables 1 and 2. Step (1) is different: the temperature is raised to 900℃ instead of 800℃ in Example 1; the activation time is 8h instead of 6h in Example 1; Step (2) is different: the deposition time is 2 hours instead of the 0.5 hours in Example 1; Step (3) is different: the deposition temperature is 650℃ instead of 500℃ in Example 1.

[0081] Example 15 The method for preparing the negative electrode material in this embodiment is basically the same as that in Example 1, except that the parameters of the negative electrode material are different. Please refer to Tables 1 and 2. Step (1) is different: the temperature is raised to 700℃ instead of 800℃ in Example 1; the activation time is 5h instead of 6h in Example 1; Step (2) is different: the deposition time is 0.3 h instead of the 0.5 h deposition time in Example 1; Step (3) is different: the deposition temperature is 450℃ instead of 500℃ in Example 1.

[0082] Comparative Example 1 The preparation method of the negative electrode material in this comparative example is basically the same as that in Example 1, except that step (2) is not performed, and steps (3)-(4) are different: In step (3), the deposition temperature is 550°C instead of 500°C in Example 1. In step (4), the coating time of 1 hour is replaced by the coating time of 4 hours in Example 1.

[0083] Comparative Example 2 The preparation method of the negative electrode material in this comparative example is basically the same as that in Example 1, except that the parameters of the negative electrode material are different, as shown in Tables 1 and 2. Step (1) is different: the temperature is raised to 900℃ instead of 800℃ in Example 1; the activation time is 9h instead of 6h in Example 1; Step (2) is different: the deposition time is 2 hours instead of the 0.5 hours in Example 1; Step (3) is different: the deposition temperature is 650℃ instead of 500℃ in Example 1.

[0084] Comparative Example 3 The preparation method of the negative electrode material in this comparative example is basically the same as that in Example 1, except that the parameters of the negative electrode material are different, as shown in Tables 1 and 2. Step (1) is different: the temperature is raised to 700℃ instead of 800℃ in Example 1; the activation time is 5h instead of 6h in Example 1; Step (2) is different: the deposition time is 0.3 h instead of the 0.5 h deposition time in Example 1; Step (3) is different: the deposition temperature is 450℃ instead of 500℃ in Example 1.

[0085] Test case This test case provides the performance of the batteries in various embodiments and comparative examples, as detailed below: Method for preparing a coin cell battery: 1) Preparation of the negative electrode sheet: The negative electrode material, conductive agent (carbon black), and binder (polyvinylidene fluoride, PVDF) prepared in the above examples and comparative examples are mixed in a mass ratio of 8:1:1. 20wt% of the solvent (N-methylpyrrolidone, NMP) of the total mixed powder is added dropwise, and the mixture is stirred until homogeneous to prepare a negative electrode slurry. The negative electrode slurry is then uniformly coated onto the negative electrode current collector (copper foil), with a coating surface density of approximately 4 mg / cm². 2 The coated negative electrode sheet is dried to remove the solvent. The dried negative electrode sheet is then rolled and slit to complete the fabrication of the coin cell negative electrode sheet.

[0086] 2) Button cell fabrication: The prepared negative electrode, separator, electrolyte, and lithium sheet are placed in a casing, sealed, and pressed to obtain a CR2032 button cell. The separator is a PP / PE composite separator. The electrolyte composition is: ethylene carbonate / dimethyl carbonate / ethyl methyl carbonate (volume ratio 1:1:1) solution with 5 wt% FEC (fluoroethylene carbonate) and 1 mol / L lithium hexafluorophosphate as the lithium salt.

[0087] 1) First-cycle reversible capacity test method: After the button cell is assembled, ① first discharge: discharge at a constant current of 0.1C to 0.01V, and record the discharge specific capacity as Q1; ② then charge: charge at a constant current of 0.1C to 2V, and record the charging specific capacity as Q2; the charging specific capacity recorded as Q2 is the first-cycle reversible capacity; 2) First-cycle coulombic efficiency: After the button cell is assembled, ① first discharge: discharge at a constant current of 0.1C to 0.01V, and the discharge specific capacity is recorded as Q1; ② then charge: charge at a constant current of 0.1C to 2V, and the charging specific capacity is recorded as Q2; the first coulombic efficiency is the value of Q2 / Q1*100%; 3) 100-cycle capacity retention rate: ① Discharge: Discharge at a constant current of 0.1C to 0.01V, and record the discharge specific capacity as Q1; ② Charge: Charge at a constant current of 0.1C to 2V, and record the charging specific capacity as Q2; Repeat steps ① and ② for 100 cycles, and the charging capacity is Q100. Q100 / Q2*100% is the 100-cycle capacity retention rate.

[0088] 4) Rate performance: ① Discharge: Constant current discharge from 0.1C to 0.01V, discharge specific capacity is denoted as Q. X放 (X is the charge / discharge rate); ② Charging: Charge at a constant current of 0.1C to 2V, and obtain the charging specific capacity, denoted as Q. X充 Adjust the current to 0.5C / 1C / 2C / 3C / 4C respectively, and repeat steps ① and ②. Q 4C放 / Q 0.1C放*100% represents the rate performance at 4C.

[0089] The specific test results are as follows.

[0090] Table 1 Characterization results of porous carbon matrix

[0091] Table 2 Characterization results of anode materials

[0092] Table 3 Performance test results of the examples and comparative examples

[0093] The data above shows that the application of the anode material of this application can help improve the first-cycle reversible capacity, first-cycle coulombic efficiency, rate capability, and cycle performance of secondary batteries.

[0094] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A negative electrode material, characterized in that, It includes a porous carbon matrix and a silicon-based material distributed within at least a portion of the pores of the porous carbon matrix; The negative electrode material satisfies the relationship 0.2 < X < 20, X = D / (S × J); Wherein, D μm is the value of the volume median particle size Dv50 of the negative electrode material; S m 2 / g is the numerical value of the specific surface area of ​​the negative electrode material; J nm is the numerical value of the silicon crystal size of the Si(111) crystal plane in the negative electrode material.

2. The negative electrode material according to claim 1, characterized in that, In the diffraction pattern obtained by XRD diffraction test of the negative electrode material, the full width at half maximum (FWHM) of the Si(111) crystal plane diffraction peak is 0.025 rad to 0.3 rad.

3. The negative electrode material according to claim 1, characterized in that, The porous carbon matrix includes micropores, ultramicropores, and mesopores. In the porous carbon matrix, with the total pore volume as 100%, the volume ratio of pores smaller than 1 nm is <20%, and the volume ratio of pores larger than 10 nm is <5%.

4. The negative electrode material according to claim 1, characterized in that, In the 0.1C / 0.1C cycle charge-discharge test conducted using the negative electrode sheet made of the aforementioned negative electrode material as a half-cell, the obtained delithiation dQ / dV-V curve satisfies I1 / I2 < 1; Where I1 represents the intensity of the delithiation oxidation peak at 0.40V~0.45V in the delithiation dQ / dV-V curve; I2 represents the intensity of the delithiation oxidation peak at 0.30V~0.35V in the delithiation dQ / dV-V curve; The upper and lower limit voltages for the cyclic charge-discharge test are 0.005V to 2V.

5. The negative electrode material according to claim 1, characterized in that, The porous carbon matrix has a pore volume ≥ 0.5 cm³. 3 / g; and / or, the average pore size of the porous carbon matrix is ​​0.1nm~5nm.

6. The negative electrode material according to any one of claims 1 to 5, characterized in that, The negative electrode material satisfies at least one of the following conditions: A. 1≤J≤5; B. 2 ≤ D ≤ 15; C. 0.1≤S≤6.

7. The negative electrode material according to claim 6, characterized in that, The negative electrode material satisfies at least one of the following conditions: ①Based on the total mass of the negative electrode material, the porous carbon matrix accounts for 40% to 60% of the mass; ②Based on the total mass of the negative electrode material, the mass percentage of the silicon-based material is 40% to 60%.

8. The negative electrode material according to claim 7, characterized in that, The negative electrode material further includes a microporous carbon layer disposed on at least a portion of the surface of the porous carbon matrix, wherein the mass percentage of the microporous carbon layer is ≤10% based on the total mass of the negative electrode material.

9. A secondary battery, characterized in that, It includes a negative electrode sheet, wherein the negative electrode sheet comprises the negative electrode material as described in any one of claims 1 to 8.

10. An electrical appliance, characterized in that, The device includes the secondary battery as described in claim 9, wherein the secondary battery serves as the power supply for the electrical equipment.

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