Negative electrode materials, negative electrode sheets, secondary batteries and electronic devices

Abstract

The application provides a negative electrode material, a negative electrode sheet, a secondary battery and an electronic device, and belongs to the technical field of batteries. The negative electrode material provided by the application comprises a silicon-based material and a first coating layer partially coated on the surface of the silicon-based material; the first coating layer comprises a conductive agent and a fluoride; the mass percentage content of silicon elements is A%, and the mass percentage content of fluorine elements is B% based on the mass of the negative electrode material; 24<=A / B<=4800. The negative electrode material of the application can improve the conductivity of the negative electrode material by using the silicon-based material in combination with the conductive agent and the fluoride in the first coating layer, so that the secondary battery has a higher initial coulomb efficiency; by controlling the mass ratio of fluorine elements and silicon elements in the negative electrode material, the fluoride and the silicon-based material can generate a more stable solid electrolyte interface film, the interface stability of the negative electrode material is improved, and the cycle stability and swelling inhibition performance of the secondary battery are improved.

Description

Technical Field

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

[0002] With the increasing demand for large-scale energy storage, electric vehicles, and portable electronic devices, developing energy storage devices with higher energy density has become a top priority. Rechargeable batteries are widely used in various fields due to their long cycle life and environmentally friendly characteristics. However, graphite, as a traditional anode material for rechargeable batteries, has limited its further application due to its low capacity (372 mAh / g) and safety concerns such as active material precipitation. Therefore, developing anode materials with high energy density and high safety has become crucial for the current development of rechargeable battery technology.

[0003] Compared to carbon-based materials such as graphite, elemental silicon has an extremely high theoretical specific capacity (Li). 15 Si4 (3579 mAh / g) and a suitable operating voltage (<0.5V vs. Li / Li) + Silicon is considered the most promising alternative to graphite as an anode material. However, the huge volume expansion and low conductivity of elemental silicon during alloying / dealloying severely limit its large-scale application in secondary batteries.

[0004] To address these issues, existing technologies primarily employ methods such as silicon nanostructuring, constructing porous silicon or silicon-carbon anode materials, and introducing transition metal oxides. While silicon nanostructuring and porous silicon can alleviate the volume expansion problem of elemental silicon to some extent, their high specific surface area and low tap density limit their large-scale application. Although silicon-carbon composites and the introduction of transition metal oxides can reduce the volume expansion of silicon, the mechanical properties and chemical stability of carbon and metal oxides are not outstanding, and therefore cannot achieve an ideal buffering effect. Summary of the Invention

[0005] To address the aforementioned issues, this application provides a negative electrode material, a negative electrode sheet, a secondary battery, and an electronic device, which can provide higher specific capacity and conductivity, reduce volume expansion during charging and discharging, and improve the energy density and cycle performance of the secondary battery.

[0006] Firstly, this application provides a negative electrode material, comprising a silicon-based material and a first coating layer partially covering the surface of the silicon-based material; the first coating layer comprises a conductive agent and a fluoride; based on the mass of the negative electrode material, the mass percentage of silicon is A%, the mass percentage of fluorine is B%, and 24 ≤ A / B ≤ 4800. The negative electrode material of this application uses a silicon-based material as its core, which can improve the energy density of the secondary battery. Combined with the conductive agent and fluoride in the first coating layer, it can improve the conductivity of the negative electrode material, enabling the secondary battery to have a higher initial coulombic efficiency. Furthermore, by controlling the mass content of fluorine and silicon in the negative electrode material within the above-mentioned range, the fluoride and silicon-based material can form a more stable solid electrolyte interphase (SEI) film, improving the interfacial stability of the negative electrode material and enhancing the cycle stability and expansion suppression performance of the secondary battery.

[0007] In some implementations, the negative electrode material satisfies at least one of the following conditions:

[0008] (1) 31≤A / B≤99; By adjusting the mass ratio of fluorine and silicon elements within this range, the film quality of the SEI film can be further improved, the negative electrode material can maintain high cycle stability, and the expansion suppression performance of the secondary battery can be optimized.

[0009] (2) 40.5≤A≤59.8; Controlling the silicon content within this range can enable the anode material to exhibit higher specific capacity and cycle performance.

[0010] (3) 0.01≤B≤2; controlling the fluorine content within this range can enable the anode material to exhibit higher cycle performance and first coulombic efficiency.

[0011] (4) Based on the mass of the anode material, the mass percentage of carbon element is C%, 41≤C≤59.5%; controlling the carbon element content within this range can enable the anode material to have higher cycle performance and specific capacity.

[0012] In some embodiments, the average particle size of the negative electrode material is D μm, where 4 ≤ D ≤ 13. Controlling the average particle size of the negative electrode material within this range enables the negative electrode material to achieve a suitable specific surface area, reduces electrolyte consumption, and also helps to improve the compaction density of the negative electrode material. In addition, it can also have higher ionic conductivity and rate performance.

[0013] In some implementations, 0.1 ≤ B × D ≤ 19.7. Controlling the value of B × D to meet this range can promote close coordination of the components in the negative electrode material, thereby improving the initial coulombic efficiency and cycle performance of the secondary battery.

[0014] In some embodiments, based on the area of ​​the negative electrode material, the area ratio of the conductive agent is S1%, and the area ratio of the fluoride is S2%, with 0.5 ≤ S1 ≤ 5 and 80.5 ≤ S2 ≤ 89.4. Adjusting the area ratios of the conductive agent and fluoride in the negative electrode material to meet these ranges can improve the synergistic effect between the conductive agent and the fluoride, which is beneficial for increasing the capacity of the negative electrode material. Simultaneously, it can further improve the initial coulombic efficiency and cycle performance of the secondary battery.

[0015] In some embodiments, the area ratio of the first coating layer is S0% based on the area of ​​the negative electrode material, where 85.4 ≤ S0 ≤ 95.5%. This application regulates the area of ​​the first coating layer to further improve the initial coulombic efficiency, cycle performance, and swelling suppression performance of the secondary battery.

[0016] In some implementations, the negative electrode material satisfies at least one of the following conditions:

[0017] (1) The silicon-based material includes a porous carbon skeleton and silicon located on the surface and inside the porous carbon skeleton; the silicon-based material can better cooperate with the first coating layer to improve the cycle performance and expansion suppression performance of the secondary battery.

[0018] (2) The conductive agent includes a fibrous conductive agent; the average diameter of the fibrous conductive agent is y nm, 0.5≤y≤19.6; the average length of the fibrous conductive agent is z nm, 508≤z≤996; the use of fibrous conductive agent in this application can further improve the conductivity of the negative electrode material. By controlling its average diameter and average length within the above range, the uniformity of surface charge distribution and long-range conductivity of the negative electrode material can be further improved, so that the secondary battery exhibits higher initial coulombic efficiency and cycle performance.

[0019] (3) The fluoride has the structure shown in Formula I: R1-R2; in Formula I, R1 is selected from at least one of C3 to C15 perfluoroalkyl groups, and R2 is selected from at least one of substituted or unsubstituted C1 to C3 alkoxy groups, substituted or unsubstituted C1 to C3 silyl groups, substituted or unsubstituted C1 to C3 alkyl groups, substituted or unsubstituted C1 to C3 alkenyl groups, substituted or unsubstituted C1 to C3 alkynyl groups, mercapto groups, hydroxyl groups, and halogen atoms; when substituted, the substituent is selected from at least one of C1 to C3 alkyl groups, C1 to C3 alkoxy groups, mercapto groups, hydroxyl groups, and halogen atoms. Using the above-mentioned perfluoroalkyl group in combination with the R2 group can improve the stability of the SEI film and further enhance the cycle performance and swelling suppression performance of the secondary battery.

[0020] In some embodiments, the conductive agent includes at least one of single-walled carbon nanotubes or multi-walled carbon nanotubes. The use of single-walled or multi-walled carbon nanotubes can improve the conductivity of the anode material, and in combination with the fluoride of this application, can further improve the cycle stability of the anode material.

[0021] In some embodiments, the fluoride includes at least one selected from heptadecafluorodecyltrimethoxysilane, perfluorooctyltrimethoxysilane, perfluorodecylethylene, perfluorobutylethylene, perfluorooctylethylene, perfluorohexylethylene, and perfluorodecyl mercaptan. The use of these fluorides can promote improved interfacial stability during cycling, thereby enhancing the cycle performance and anti-swelling properties of the secondary battery.

[0022] Secondly, this application provides a negative electrode sheet, which includes any of the negative electrode materials provided in the first aspect of this application.

[0023] In some embodiments, a negative electrode sheet and a lithium metal sheet are used to fabricate a coin cell, which is then charged and discharged at a constant current of 0.05C. The lithium intercalation potential is 0.6V to 1.2V, and the depth of discharge at the lithium intercalation potential is 0.02% to 1%. The negative electrode sheet fabricated from the negative electrode material of this application has a lower lithium intercalation potential and a lower depth of discharge, resulting in a lower initial coulombic efficiency.

[0024] Thirdly, this application provides a secondary battery, including any of the negative electrode sheets provided in the second aspect of this application.

[0025] Fourthly, this application provides an electronic device including the secondary battery provided in the third aspect of this application.

[0026] Based on the above-mentioned negative electrode material, negative electrode sheet, secondary battery and electronic device of this application, by coating the silicon-based material with a first coating layer composed of conductive agent and fluoride, the conductivity and structural stability of the negative electrode material can be improved at the same time. In addition, it can also promote the formation of a more stable SEI film, so that the secondary battery can still have excellent cycle capacity retention rate and expansion suppression performance at high energy density, thereby extending the battery's range and service life. Attached Figure Description

[0027] Figure 1 The charge-discharge curve of the negative electrode material provided in Example 1;

[0028] Figure 2 A partially enlarged view of the charge-discharge curve of the negative electrode material provided in Example 1;

[0029] Figure 3 The image shows the SEM image of the negative electrode material provided in Example 1. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0031] In a first aspect, this application provides a negative electrode material, comprising a silicon-based material and a first coating layer partially coated on the surface of the silicon-based material; the first coating layer comprises a conductive agent and a fluoride; based on the mass of the negative electrode material, the mass percentage of silicon is A%, the mass percentage of fluorine is B%, and 24 ≤ A / B ≤ 4800. This application uses a conductive agent and a fluoride to coat the silicon-based material, which can form a conductive network structure on the surface of the negative electrode material, improve the conductivity of the negative electrode material, improve electron conduction performance, and, in combination with the silicon-based material, can increase the energy density of the secondary battery, while also promoting the ion transport rate of the secondary battery during charge and discharge, and improving the initial coulombic efficiency. By controlling the mass ratio of silicon and fluorine in the negative electrode material to satisfy the above relationship, the fluoride coating of the silicon-based material promotes the formation of a stable solid electrolyte interphase (SEI) film, reducing capacity decay during secondary battery cycling and improving cycle performance. The network structure formed by the two can ensure strong mechanical strength and structural stability. After coating the silicon-based material, it can also absorb and release the stress generated by the volume expansion of the latter, reducing the volume expansion of the secondary battery during charging and discharging, reducing the risk of material cracking and performance degradation caused by volume expansion, thereby extending the service life of the secondary battery.

[0032] In some embodiments, the mass percentage content of silicon and fluorine in the negative electrode material satisfies 24 ≤ A / B ≤ 4800, preferably 31 ≤ A / B ≤ 99. For example, the value of A / B is 24, 31, 37, 39, 45, 47, 51, 54, 58, 63, 65, 69, 72, 77, 79, 83, 87, 91, 93, 99, 438, 782, 1198, 1645, 1964, 2259, 2708, 3047, 3331, 3954, 4197, 4469, 4800, or a value within any two of these ranges. Controlling the content of silicon and fluorine within the above range can improve the compatibility between fluoride and silicon-based materials, further improving the capacity retention and volume stability of the secondary battery during cycling.

[0033] In some embodiments, 40.5 ≤ A ≤ 59.8, for example, A can be a value within the range of 40.5, 41.6, 43.3, 45.0, 46.6, 48.0, 49.9, 51.1, 53.1, 54.6, 57.5, 59.1, 59.5, 59.8, or any combination of these values. Controlling the silicon content in the negative electrode material within the above range, in combination with fluorides, can improve the specific capacity of the negative electrode material, reduce the volume expansion effect, and improve the volume stability of the negative electrode material during cycling, thereby enhancing the energy density and cycle performance of the secondary battery.

[0034] In some embodiments, 0.01 ≤ B ≤ 2, for example, B can be a value within the range of 0.01, 0.17, 0.32, 0.49, 0.625, 0.66, 0.80, 1.04, 1.17, 1.32, 1.41, 1.61, 1.71, 1.94, 2, or any combination of these values. Controlling the fluorine content in the negative electrode material within the above range can improve the stability of the SEI film, reduce side reactions between the silicon-based material and the electrolyte, and improve the volume stability of the silicon-based material, further enhancing the initial coulombic efficiency, cycle performance, and expansion suppression performance of the secondary battery.

[0035] In some embodiments, the mass percentage of carbon element is C%, based on the mass of the negative electrode material, with 41 ≤ C ≤ 59.5%. Exemplarily, C can be a value within the range of 41, 41.7, 43.2, 44.9, 46.9, 48.5, 49.9, 51.2, 52.8, 55.0, 57.0, 58.9, 59.4, 59.5, or any combination thereof. Regulating the carbon element content in the negative electrode material within the above range enhances the conductivity of the negative electrode material and also acts as a buffer to improve the structural stability of the negative electrode material. Combined with the aforementioned silicon and fluorine elements, it can improve the stability of the SEI film, thereby contributing to higher capacity retention and volume stability of the secondary battery during cycling.

[0036] This application does not impose any particular restrictions on the method for controlling the mass percentage of silicon, fluorine, and carbon elements in the negative electrode material, as long as the purpose of this application can be achieved. For example, the mass percentage of silicon can be controlled by controlling the silicon content in the silicon-based material or by changing the proportion of silicon-based material added, and the mass percentage of fluorine can be controlled by controlling the proportion of fluoride added.

[0037] The elemental content (silicon, fluorine, and carbon) of the anode material in this application can be tested using methods known in the art. For example, the elemental content of the anode material sample can be quantitatively tested using a Shimadzu / Kratos X-ray photoelectron spectrometer AXIS SUPRA+.

[0038] In some embodiments, the average particle size of the negative electrode material is D μm, where 4 ≤ D ≤ 13. For example, D can be 4, 4.8, 5.5, 6.2, 6.9, 7.8, 8.3, 9.3, 10.3, 10.7, 11.4, 12.6, 12.9, 13, or any value within the range of any two of these values. Based on controlling the elemental content of the aforementioned negative electrode material, this application further regulates the particle size within the above-mentioned range, enabling the negative electrode material to have a suitable specific surface area. This is beneficial for improving the synergistic effect between the elements, thereby reducing the occurrence of side reactions and electrolyte consumption during cycling. It also helps to improve the ionic conductivity of the negative electrode material, enhancing the cycle performance and initial coulombic efficiency of the secondary battery.

[0039] The average particle size of the negative electrode material in this application can be tested using methods known in the art. For example, it can be obtained using a method including the following steps: selecting a sample area on the negative electrode sheet, taking a SEM image of the sample area using a scanning electron microscope, then using image analysis software to randomly select 10 particles of the negative electrode material as samples from the SEM image, calculating the area of ​​each of these negative electrode material samples, and then, assuming the negative electrode material samples are spherical, calculating the particle size R (diameter) of each of these negative electrode material samples using the following formula: R = 2 × (S / π) 1 / 2 Where S is the area of ​​the negative electrode material sample. The particle size R of the above negative electrode material sample is calculated from the three SEM images, and the particle sizes of the resulting 30 (10×3) negative electrode material samples are arithmetically averaged to obtain the average particle size of the negative electrode material to be tested.

[0040] In some embodiments, 0.1 ≤ B × D ≤ 19.7. Exemplarily, the value of B × D can be 0.1, 1.7, 2, 3.4, 5.2, 6.5, 8.5, 9.6, 11.1, 13, 13.3, 14.1, 15, 17.1, 17.5, 18.3, 19.7, or a range of any two of these values. By adjusting the average particle size and fluorine content of the negative electrode material to conform to the above relationship, the interfacial stability between the negative electrode material and the electrolyte can be further improved, the interfacial resistance reduced, and the structural stability of the negative electrode material enhanced, thereby improving the initial coulombic efficiency, cycle performance, and expansion suppression performance of the secondary battery.

[0041] In some embodiments, based on the area of ​​the negative electrode material, the area ratio of the conductive agent is S1%, the area ratio of the fluoride is S2%, 0.5≤S1≤5, and 80.5≤S2≤89.4. Exemplarily, S1 can be a value within the range of 0.5, 0.9, 1.2, 1.7, 2.0, 2.4, 2.9, 3, 3.2, 3.4, 3.8, 4.3, 4.6, 5, or any two of these values; S2 can be a value within the range of 80.5, 80.8, 81.6, 82.6, 83.4, 84.1, 84.9, 85, 85.6, 86.9, 87.6, 88.7, 89.1, 89.4, or any two of these values. When the area ratio of conductive agent and fluoride in the negative electrode material is controlled within the above-mentioned range, it can promote better cooperation between the two, improve the conductivity of the conductive network on the surface of the negative electrode material, and help improve the film formation quality of the SEI film, reduce side reactions and capacity decay during the charging and discharging process of the secondary battery, and further improve the initial coulombic efficiency and cycle performance. In addition, the cooperation between conductive agent and fluoride can also further improve the mechanical strength and structural stability of the first coating layer, reduce the volume expansion of the negative electrode material during the alloying process, and improve the expansion suppression performance of the secondary battery.

[0042] This application does not impose any particular limitation on the method for controlling the area ratio of conductive agents and fluorides in the negative electrode material. Methods known in the art can be used, such as adjusting the mass content of the conductive agent and fluoride, or adjusting the dispersion time of the conductive agent and fluoride while keeping their mass content constant. The longer the dispersion time of the conductive agent, the larger its corresponding area ratio; the longer the dispersion time of the fluoride, the larger its corresponding area ratio. The testing of the area ratio of conductive agents and fluorides in the negative electrode material in this application can be performed using methods known in the art, such as a method including the following steps: obtaining a SEM image of the sample area in the negative electrode material using a scanning electron microscope; processing the SEM image using ImageJ image analysis software to identify and calculate the area of ​​the conductive agent; performing EDS elemental surface scanning on the SEM image to obtain an area scan image of fluorine; processing the area scan image of fluorine using ImageJ image analysis software to sum the areas of fluorine to obtain the area of ​​fluorine. In this application, the area of ​​fluorine represents the area of ​​the fluoride.

[0043] In some embodiments, the area ratio of the first coating layer is S0% based on the area of ​​the negative electrode material, where 85.4 ≤ S0 ≤ 95.5. For example, S0 is a value within the range of 85.4, 86.0, 86.4, 87.3, 87.7, 89.2, 89.9, 90.7, 91.2, 91.8, 92.5, 93.4, 94.3, 95.3, 95.5, or any combination of these values. Adjusting the area ratio of the first coating layer in the negative electrode material within the above range can improve the compatibility between the first coating layer and the silicon-based material, enhance the stability of the SEI film and its interface with the negative electrode material, and thus improve the initial coulombic efficiency, cycle performance, and expansion suppression performance of the secondary battery.

[0044] In this application, the silicon-based material may be any material known in the art, such as silicon-carbon materials, silicon-oxygen materials, and silicon. In some preferred embodiments, the silicon-based material comprises a porous carbon framework and silicon located on the surface and inside the porous carbon framework. This type of silicon-carbon composite material can better cooperate with the first coating layer. Through the cooperation of the porous carbon framework and the first coating layer, silicon is multiplely fixed and supported, which can further limit the expansion effect during silicon alloying, improve the expansion suppression performance and cycle stability of the secondary battery, and also help to improve the overall conductivity of the negative electrode material, promote the insertion and extraction of active materials, and improve the energy density and initial coulombic efficiency of the secondary battery.

[0045] The silicon-carbon composite material used in this application can be prepared by methods known in the art. This application does not impose any particular limitation, as long as the purpose of this application can be achieved. For example, it may be prepared by chemical vapor deposition of silicon source and carbon source.

[0046] In some embodiments, the conductive agent includes a fibrous conductive agent; the average diameter of the fibrous conductive agent is y nm, 0.5 ≤ y ≤ 19.6; the average length of the fibrous conductive agent is z nm, 508 ≤ z ≤ 996. For example, y can be a value within the range of 0.5, 2.1, 3.2, 5.2, 5.8, 7.1, 9.2, 10.4, 12.8, 13.8, 14.1, 16.1, 17.5, 19.1, 19.6, or any combination thereof; z can be a value within the range of 508, 514, 570, 607, 636, 677, 717, 763, 788, 809, 865, 907, 938, 967, 996, or any combination thereof. The use of a fibrous conductive agent in this application can further optimize the conductive network structure of the first coating layer, improving the initial coulombic efficiency and cycle performance of the secondary battery. By controlling the average diameter and average length of the fibrous conductive agent, and combining it with fluorides, the structural stability of the negative electrode material can be improved, the fixation and coating effect on silicon-based materials can be enhanced, the volume expansion of the negative electrode material can be slowed down, and the cycle performance and expansion suppression performance of the secondary battery can be further improved.

[0047] In some embodiments, the fluoride has the structure shown in Formula I. Formula I: R1-R2, where R1 is selected from at least one of C3 to C15 perfluoroalkyl groups, and R2 is selected from at least one of substituted or unsubstituted C1 to C3 alkoxy groups, substituted or unsubstituted C1 to C3 silyl groups, substituted or unsubstituted C1 to C3 alkyl groups, substituted or unsubstituted C1 to C3 alkenyl groups, substituted or unsubstituted C1 to C3 alkynyl groups, mercapto groups, hydroxyl groups, and halogen atoms; when substituted, the substituent is selected from at least one of C1 to C3 alkyl groups, C1 to C3 alkoxy groups, mercapto groups, hydroxyl groups, and halogen atoms. This application further modifies the fluoride to include the aforementioned perfluoroalkyl groups, which can promote the formation of a more stable SEI film. The combination of the aforementioned R2 group with the perfluoroalkyl group can further improve the interfacial stability of the negative electrode material during cycling, thereby improving the cycle performance and swelling suppression performance of the secondary battery.

[0048] In this application, perfluoroalkyl refers to an alkyl group in which all hydrogen atoms are replaced by fluorine atoms; silyl refers to an alkyl group containing silicon atoms; and halogen atoms include at least one of fluorine, chlorine, bromine, or iodine atoms. In some preferred embodiments, in Formula I, R1 is selected from at least one of C4 to C12 perfluoroalkyl groups, and R2 is selected from at least one of C1 to C3 alkoxy, trimethoxysilyl, C1 to C3 alkenyl, mercapto, or halogen atoms. Fluorides containing these groups can further improve the stability of the SEI film and optimize the cycle performance and swelling suppression performance of the secondary battery.

[0049] In some embodiments, the conductive agent includes at least one of single-walled carbon nanotubes or multi-walled carbon nanotubes. The use of single-walled or multi-walled carbon nanotubes can further improve the conductivity of the negative electrode material. In combination with the fluoride of this application, it can optimize the structural stability of the first coating layer, further improve the cycle stability of the negative electrode material, and enable the secondary battery to exhibit higher cycle performance and swelling suppression performance.

[0050] In some embodiments, the fluoride includes at least one selected from heptadecafluorodecyltrimethoxysilane, perfluorooctyltrimethoxysilane, perfluorodecylethylene, perfluorobutylethylene, perfluorooctylethylene, perfluorohexylethylene, and perfluorodecyl mercaptan. Using these fluorides in conjunction with conductive agents and silicon-based materials in the negative electrode material can further enhance interfacial stability during cycling, thereby improving the cycle performance and swelling suppression performance of the secondary battery.

[0051] In some embodiments, the negative electrode material is prepared by a method comprising the following steps:

[0052] S1: Provides silicon-carbon materials;

[0053] S2: The conductive agent and the fluoride are first dispersed in a solvent to obtain a dispersion system; wherein the solvent includes at least one of water, ethanol, propanol, butanol, ethylene glycol, propylene glycol, dimethyl methanol, dimethyl sulfoxide, and ethyl acetate.

[0054] S3: The silicon-carbon material in S1 is added to the dispersion system in S2 for a second dispersion treatment, and then dried to obtain the negative electrode material of this application.

[0055] This application does not impose any particular restrictions on the specific parameters of the first dispersion treatment, the second dispersion treatment, and the drying treatment in the preparation method of the negative electrode material, as long as the purpose of this application can be achieved. In particular, there are no particular restrictions on the order of addition of the conductive agent and the fluoride during the first dispersion treatment, as long as the purpose of this application can be achieved. For example, the order of addition of the conductive agent and the fluoride can be adjusted to give them different first dispersion treatment times, thereby controlling the area ratio of the conductive agent and the fluoride in the first coating layer.

[0056] Secondly, this application provides a negative electrode sheet, which includes any of the negative electrode materials provided in the first aspect of this application.

[0057] In some embodiments, a coin cell is fabricated by combining a negative electrode sheet and a lithium metal sheet. A constant current charge-discharge test is performed at 0.05C, resulting in a lithium intercalation potential of 0.6V to 1.2V and a depth of discharge of 0.02% to 1% at which the lithium intercalation potential occurs. When a coin cell containing the negative electrode material of this application is fabricated using a lithium metal sheet as the counter electrode, a constant current charge-discharge test is performed at 0.05C. During the discharge to 5mV, a lithium intercalation plateau appears in the voltage range of 1.2V to 0.6V, for example, a lithium intercalation potential of 0.6V, 0.62V, 0.66V, 0.72V, 0.76V, 0.79V, 0.83V, 0.92V, 0.94V, 0.97V, 1.03V, 1.10V, 1.14V, 1.16V, 1.2V, or any value within the range of any two of these values. The depth of discharge at which the lithium intercalation potential occurs in this application is 0.02% to 1%, for example, a depth of discharge of 0.02%, 0.09%, 0.12%, 0.24%, 0.29%, 0.35%, 0.47%, 0.48%, 0.55%, 0.69%, 0.72%, 0.85%, 0.91%, 0.97%, 1%, or any value within the range of any two of these values. Using the aforementioned lower lithium intercalation potential and depth of discharge in this application can reduce the amount of active material intercalated and deintercalated during charging and discharging, thereby reducing structural changes in the negative electrode material and electrolyte consumption, which in turn helps to improve the cycle performance and swelling suppression performance of the secondary battery.

[0058] In this application, the negative electrode material is included in the negative electrode flux layer of the negative electrode sheet. The negative electrode sheet of this application also includes a negative electrode current collector. In this application, the negative electrode flux layer can be disposed on one surface in the thickness direction of the negative electrode current collector, or on both surfaces in the thickness direction of the negative electrode current collector. It should be noted that the "surface" here can be the entire area of ​​the negative electrode current collector or only a part of it; this application has no particular limitation, as long as the purpose of this application is achieved. This application has no particular limitation on the thickness of the negative electrode flux layer, as long as the purpose of this application is achieved. For example, the thickness of a single-sided negative electrode flux layer can be from 30 μm to 160 μm.

[0059] This application does not impose any particular limitation on the negative electrode current collector, as long as it achieves the purpose of this application. For example, the negative electrode current collector may comprise copper foil, aluminum foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, foamed nickel, foamed copper, composite current collectors (e.g., carbon-copper composite current collector, nickel-copper composite current collector, titanium-copper composite current collector), a polymer substrate coated with a conductive metal, or any combination thereof. This application does not impose any particular limitation on the thickness of the negative electrode current collector, as long as it achieves the purpose of this application. For example, the thickness of the negative electrode current collector may be from 4 μm to 10 μm.

[0060] In this application, the negative electrode binder layer may further include a negative electrode binder, which may include, but is not limited to, at least one of polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyacrylic acid, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, or nylon.

[0061] In this application, the negative electrode binder layer may further include a conductive agent. This application does not particularly limit the type of conductive agent in the negative electrode binder layer, as long as it achieves the purpose of this application. For example, the conductive agent may include, but is not limited to, carbon-based materials, metal-based materials, conductive polymers, and mixtures thereof. In some embodiments, the carbon-based material is selected from natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, or any combination thereof. In some embodiments, the metal-based material is selected from metal powder, metal fiber, copper, nickel, aluminum, or silver. In some embodiments, the conductive polymer is a polyphenylene derivative. This application does not particularly limit the mass ratio of the negative electrode material, conductive agent, and negative electrode binder in the negative electrode binder layer, as long as it achieves the purpose of this application. For example, the loading of the negative electrode material in the negative electrode sheet is 1.0 mg / cm³. 2 Up to 1.5 mg / cm 2 .

[0062] Thirdly, this application provides a secondary battery, including any of the negative electrode sheets provided in the second aspect of this application.

[0063] The secondary battery in this application is not particularly limited, and may include, but is not limited to, lithium-ion secondary batteries (lithium-ion batteries), sodium-ion batteries, etc.

[0064] The secondary battery of this application also includes a positive electrode sheet. This application does not impose any particular limitation on the positive electrode sheet, as long as it achieves the purpose of this application. For example, the positive electrode sheet includes a positive current collector and a positive electrode flux layer located on at least one surface of the positive current collector. The aforementioned "positive electrode flux layer located on at least one surface of the positive current collector" means that the positive electrode flux layer can be located on one surface of the positive current collector along its own thickness direction, or it can be located on two surfaces of the positive current collector along its own thickness direction. It should be noted that the "surface" here can be the entire surface area of ​​the positive current collector, or it can be a partial surface area of ​​the positive current collector; this application does not impose any particular limitation, as long as it achieves the purpose of this application.

[0065] This application does not impose any particular restrictions on the positive electrode current collector, as long as it can achieve the purpose of this application. For example, the positive electrode current collector may include aluminum foil, aluminum alloy foil, or composite current collectors (such as aluminum-carbon composite current collectors). Composite current collectors can be formed by forming metallic materials (copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys, etc.) on a polymer substrate.

[0066] The positive electrode mixture layer of this application includes a positive electrode material. This application does not particularly limit the type of positive electrode material, as long as it can achieve the purpose of this application. For example, the positive electrode material may include lithium nickel cobalt manganese oxide (LiNi). 0.90 Co 0.05 Mn 0.05 At least one of the following: O2 (NCM955), NCM811, NCM622, NCM523, NCM111; lithium nickel cobalt aluminum oxide; lithium iron phosphate; lithium vanadium phosphate; lithium cobalt phosphate; lithium manganese phosphate; lithium manganese iron phosphate; lithium-rich manganese-based materials; lithium cobalt oxide (LiCoO2); lithium iron silicate; lithium vanadium silicate; lithium cobalt silicate; lithium manganese silicate; spinel-type lithium manganese oxide; spinel-type lithium nickel manganese oxide; and lithium titanate. In this application, the cathode material may also contain non-metallic elements, such as at least one of fluorine, phosphorus, boron, chlorine, silicon, or sulfur. In this application, there are no particular limitations on the thickness of the cathode current collector and the cathode flux layer, as long as the purpose of this application is achieved. For example, the thickness of the cathode current collector is 5 μm to 20 μm, and the thickness of the single-sided cathode flux layer is 30 μm to 120 μm.

[0067] In this application, the positive electrode binder layer may further include a positive electrode binder and a conductive agent. This application does not impose any particular limitation on the type of positive electrode binder in the positive electrode binder layer, as long as it achieves the purpose of this application. For example, the positive electrode binder may include, but is not limited to, at least one of polyvinylidene fluoride, polytetrafluoroethylene, polyolefins, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, modified polyvinylidene fluoride, modified styrene-butadiene rubber (SBR), or polyurethane. In some embodiments, the polyolefin binder includes at least one of polyethylene, polypropylene, polyolefin ester, polyolefin alcohol, or polyacrylic acid.

[0068] This application does not impose any particular limitation on the type of conductive agent in the positive electrode binder layer, as long as it achieves the purpose of this application. For example, the conductive agent can be the same type as the conductive agent in the negative electrode binder layer described above. In some embodiments, the conductive agent includes carbon-based materials, such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, or carbon fiber; metal-based materials, such as metal powder or metal fiber of copper, nickel, aluminum, silver, etc.; conductive polymers, such as polyphenylene derivatives; or mixtures thereof. This application does not impose any particular limitation on the mass ratio of positive electrode material, conductive agent, and positive electrode binder in the positive electrode binder layer. Those skilled in the art can select according to actual needs, as long as it achieves the purpose of this application. For example, the loading of positive electrode material in the positive electrode sheet is 4.0 mg / cm³. 2 Up to 10.0 mg / cm 2 .

[0069] In this application, the secondary battery also includes an electrolyte. According to some embodiments of this application, the electrolyte includes lithium salts and non-aqueous solvents. The lithium salt may include, but is not limited to, at least one of: lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium difluorophosphate (LiPO2F2), lithium bis(trifluoromethanesulfonyl)imide LiN(CF3SO2)2 (LiTFSI), lithium bis(fluorosulfonyl)imide Li(N(SO2F)2)(LiFSI), lithium bis(oxalatoborate)borate LiB(C2O4)2 (LiBOB), lithium difluorooxalatoborate LiBF2(C2O4)(LiDFOB), LiNO3, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiC(SO2CF3)3, Li2SiF6, lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), or lithium difluoroborate. This application does not limit the content of lithium salts in the electrolyte, as long as the purpose of this application is achieved. This application does not impose any particular limitation on non-aqueous solvents, as long as they can achieve the purpose of this application. For example, non-aqueous solvents may include, but are not limited to, at least one of carbonate compounds, carboxylic acid ester compounds, ether compounds, or other organic solvents. The aforementioned carbonate compounds may include, but are not limited to, at least one of chain carbonate compounds, cyclic carbonate compounds, or fluorinated carbonate compounds. The aforementioned chain carbonate compounds may include, but are not limited to, at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, or methyl ethyl carbonate (EMC). The aforementioned cyclic carbonates may include, but are not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate, or vinyl ethylene carbonate. Fluorocarbonate compounds may include, but are not limited to, at least one of fluoroethylene carbonate, 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, or trifluoromethylethylene carbonate. The aforementioned carboxylic acid ester compounds may include, but are not limited to, at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanolactone, valproic acid lactone, or caprolactone. The aforementioned ether compounds may include, but are not limited to, at least one of 1,3-dioxapentane (DOL), ethylene glycol dimethyl ether (1,2-dimethoxyethane, DME), dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-diethoxyethane, 1-ethoxy-1-methoxyethane, 2-methyltetrahydrofuran, or tetrahydrofuran.The other organic solvents mentioned above may include, but are not limited to, at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolium ketone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, or trioctyl phosphate.

[0070] The secondary battery of this application also includes a separator. The material and shape of the separator used in the secondary battery of this application are not particularly limited, and can be any technology disclosed in the prior art. In some embodiments, the separator comprises a polymer or inorganic material formed from a material stable to the electrolyte of this application.

[0071] For example, the separator may include a substrate layer and a surface treatment layer. The substrate layer is a nonwoven fabric, membrane, or composite membrane with a porous structure, and the material of the substrate layer is selected from at least one of polyethylene, polypropylene, polyethylene terephthalate, and polyimide. Specifically, a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite membrane may be selected.

[0072] A surface treatment layer is disposed on at least one surface of the substrate layer. The surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by a mixture of polymer and inorganic material. The inorganic layer includes inorganic particles and a binder. The inorganic particles are selected from at least one of alumina, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, and barium sulfate. The binder is selected from at least one of polyvinylidene fluoride, a copolymer of polyvinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl alkoxy, polymethyl methacrylate, polytetrafluoroethylene, and polyhexafluoropropylene. The polymer layer contains a polymer, and the polymer material is selected from at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl alkoxy, polyvinylidene fluoride, and poly(vinylidene fluoride-hexafluoropropylene).

[0073] The secondary battery of this application also includes a packaging bag for containing the positive electrode, negative electrode, separator, and electrolyte, as well as other components known in the art for secondary batteries. This application does not limit the aforementioned other components. This application does not impose any particular limitation on the packaging bag; it can be any packaging bag known in the art, as long as it can achieve the purpose of this application.

[0074] The preparation process of the secondary battery described in this application is well known to those skilled in the art, and this application has no particular limitations. For example, it may include, but is not limited to, the following steps: stacking the positive electrode, separator, and negative electrode in sequence, and performing operations such as winding and folding as needed to obtain a wound electrode assembly; placing the electrode assembly in a packaging bag; injecting electrolyte into the packaging bag and sealing it to obtain a secondary battery; or stacking the positive electrode, separator, and negative electrode in sequence, and then fixing the four corners of the entire stacked structure with tape to obtain a stacked electrode assembly; placing the electrode assembly in a packaging bag; injecting electrolyte into the packaging bag and sealing it to obtain a secondary battery. In addition, overcurrent protection components, conductive plates, etc., may be placed in the packaging bag as needed to prevent the internal pressure of the secondary battery from rising and overcharging / discharging.

[0075] Fourthly, this application provides an electronic device including the secondary battery provided in the third aspect of this application.

[0076] The electronic device described in this application is not particularly limited and can be any electronic device known in the prior art. For example, the electronic device may include, but is not limited to, laptops, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, household large-capacity batteries, and lithium-ion capacitors.

[0077] The following specific embodiments illustrate the solution of this application. Unless otherwise specified, the raw materials used in the following embodiments are all from commercially available products, and the apparatus or equipment used are all purchased from conventional market sales channels. Various tests and evaluations were conducted according to the methods described below. Furthermore, unless otherwise specified, "parts" and "%" are quality standards.

[0078] Example 1

[0079] This embodiment provides a negative electrode material, including a silicon-based material and a first coating layer partially covering the surface of the silicon-based material. The first coating layer includes a conductive agent and a fluoride. Based on the mass of the negative electrode material, the mass percentage of silicon A% is 48%, the mass percentage of fluorine B% is 1%, and the mass percentage of carbon C% is 51%, where A / B = 48.

[0080] The average particle size Dμm of the negative electrode material is 10μm, where B×D=10.

[0081] The conductive agent is single-walled carbon nanotubes, with an average diameter y nm of 2 nm and an average length z nm of 800 nm.

[0082] SEM images of the sample region in the negative electrode material were obtained using a scanning electron microscope. The SEM images were processed using ImageJ image analysis software to identify and calculate the area of ​​the conductive agent. EDS elemental surface scanning was performed on the sample region to obtain a surface scan image of fluorine. The area of ​​fluorine was then summed using ImageJ image analysis software to obtain the area of ​​fluorine. In this application, the area of ​​fluorine represents the area of ​​the fluoride.

[0083] The SEM image of the sample area on the surface of the negative electrode material in this embodiment was obtained by scanning electron microscopy (SEM), as shown below. Figure 3 As shown. The image was processed using the image analysis software ImageJ, and carbon nanotubes (CNTs) were manually identified and counted. Then, the length and width of each CNT were measured, and the area of ​​each CNT (length multiplied by width) was added together to obtain the total coverage area of ​​the CNTs. The area ratio of the total coverage area of ​​the CNTs to the total area of ​​the sample region was then used to obtain the area ratio of the conductive agent.

[0084] By performing an EDS elemental surface scan on the aforementioned sample area, an area scan image of fluorine can be obtained. The area of ​​fluorine is then summed using ImageJ image analysis software to obtain the total area of ​​fluorine. In this application, the area of ​​fluorine represents the area of ​​the fluoride. The area ratio of the fluoride coverage area to the total area of ​​the sample area is then calculated. The sum of the area ratios of the conductive agent and the fluoride is denoted as the area ratio of the first coating layer in the negative electrode material in this embodiment.

[0085] Based on the area of ​​the negative electrode material, the area ratio of the first coating layer is 88%, of which the area ratio of the conductive agent S1% is 3% and the area ratio of the fluoride S2% is 85%.

[0086] The negative electrode material in this embodiment is prepared using a method including the following steps:

[0087] S1: Provide a silicon-based material; the silicon-based material includes a porous carbon framework and silicon located on the surface and inside the porous carbon framework.

[0088] S2: The conductive agent and fluoride are first dispersed in a solvent for 4 hours to obtain a dispersion system; wherein the solvent includes ethanol and butanol (mass ratio of 1:1);

[0089] S3: Add the silicon-based material in S1 to the dispersion system in S2 for a second dispersion treatment of 4 hours, and then dry it at 200°C for 4 hours to obtain the anode material of this application.

[0090] Preparation of the negative electrode sheet: The negative electrode material prepared above was used as the active material, acetylene black as the conductive agent, and sodium alginate as the binder. The mass ratio of active material, acetylene black, and sodium alginate was 70:20:10. The active material and acetylene black were thoroughly mixed and ground uniformly. Sodium alginate aqueous solution was added in proportion and stirred for 4 hours to obtain a negative electrode mixture slurry. Finally, the negative electrode mixture slurry was uniformly coated onto copper foil and vacuum dried at 70℃ for 12 hours. After cold pressing, the negative electrode sheet was obtained. The loading of the active material was 1.2 mg / cm³. 2 .

[0091] Preparation of the positive electrode sheet: Super-P was used as the conductive agent and PVDF as the binder, with a mass ratio of active material (LiFePO4), Super-P, and PVDF of 70:20:10. The active material and Super-P were thoroughly mixed in the specified ratio and ground uniformly. A 10wt.% PVDF solution was then added and stirred for 4 hours to obtain a positive electrode mixture slurry. Finally, the positive electrode mixture slurry was uniformly coated onto aluminum foil and vacuum dried at 70℃ for 12 hours. After cold pressing, the positive electrode sheet was obtained. The loading of the active material was 8 mg / cm³. 2 .

[0092] Electrolyte preparation:

[0093] Using ethylene carbonate and dimethyl carbonate (EC and DMC, volume ratio 1:1) as the base solvent, 1 mol / L LiPF6 and 5 vol% fluoroethylene carbonate (FEC) were added to the base solvent to obtain the electrolyte.

[0094] Preparation of the diaphragm:

[0095] A 25μm microporous single-layer polypropylene (PP) membrane was used as the separator.

[0096] Preparation of secondary batteries:

[0097] The negative electrode sheet is cut into a circular electrode sheet with a diameter of 10mm. The lithium metal sheet and the negative electrode sheet are used as the counter electrode and assembled into a button half cell in a glove box.

[0098] Alternatively, the positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. This is then wound to obtain a bare cell. The bare cell is placed in outer packaging, injected with electrolyte, sealed, and undergoes processes such as formation, degassing, and edge trimming to obtain a lithium-ion battery.

[0099] The coin cell half-cell was placed on a blue electric current tester for testing. A constant current charge-discharge test was performed at a current of 0.05C, and the resulting charge-discharge curve is shown below. Figure 1 As shown, the portion of the charge-discharge curve showing the lithium intercalation potential is magnified as follows: Figure 2 As shown, the lithium intercalation potential ranges from 0.6V to 1.2V, and the discharge curve exhibits a lithium intercalation plateau. The depth of discharge at the lithium intercalation potential is 0.6%.

[0100] Test method:

[0101] Specific capacity testing of negative electrode materials

[0102] The lithium-ion battery was tested using a blue electrode tester. The test procedure was as follows: Step 1: Discharge at 0.05C to 0V; Step 2: Rest for 5 minutes; Step 3: Discharge at 50μA to 0V; Step 4: Rest for 5 minutes; Step 5: Discharge at 20μA to 0V; Step 6: Rest for 5 minutes; Step 7: Charge at 0.1C to 2V; Step 8: Rest for 5 minutes. Steps 1 to 8 were repeated twice. Then, the battery was discharged at 1C to 0V, rested for 5 minutes, and charged at 0.1C to 2V, ending the test. The cumulative capacity of the first, third, and fifth discharge stages in the first cycle is the discharge capacity. Charging at 0.1C to 2.0V gives the charging capacity. Dividing the charging capacity by the weight of the negative electrode material gives the specific capacity of the negative electrode material. Dividing the charging capacity by the discharge capacity gives the initial coulombic efficiency.

[0103] Cyclic capacity retention and expansion rate tests:

[0104] The lithium-ion battery was placed in a constant temperature chamber at 25℃±1℃ for 30 minutes, then charged at a constant current of 0.5C to 4.45V, and then charged at a constant voltage of 4.45V to 0.025C. After being placed in a constant temperature chamber for 5 minutes, it was discharged at 0.5C to 3.0V. This constitutes one charge-discharge cycle. The initial cycle discharge capacity C0 and initial thickness T0 of the lithium-ion battery were recorded. This cycle was then repeated 500 times. The cycle discharge capacity C1 and the thickness T1 after the 500th cycle were recorded. The 500-cycle capacity retention rate = C1 / C0 × 100%. The expansion rate = (T1-T0) / T0 × 100%.

[0105] The anode materials in the following examples and comparative examples differ from those in Example 1 only in that the mass percentages of silicon, fluorine, and / or carbon in the anode materials, as well as the average particle size, are adjusted according to Table 1. When adjusting the element content, only the amounts of silicon-based material, fluoride, and conductive agent added are changed accordingly. In Comparative Example 1, the amount of fluorine added to the anode material is 0, but fluoride is added to the same anode mixture slurry as in Example 1 to ensure that the mass percentage of fluoride in the anode sheets of Comparative Example 1 and Example 1 is the same.

[0106] Table 1

[0107]

[0108]

[0109] As shown in Table 1, the application employs a first coating layer comprising a conductive agent and a fluoride to encapsulate the silicon-based material, which improves the specific capacity and initial coulombic efficiency of the anode material. Specifically, controlling the mass ratio of silicon to fluorine in the anode material to satisfy 24 ≤ A / B ≤ 4800 enhances the cycle capacity retention of the secondary battery and reduces volume expansion. In particular, adjusting the above relationship to satisfy 31 ≤ A / B ≤ 99 further improves the capacity retention and volume stability of the secondary battery during cycling.

[0110] In particular, when the mass contents of silicon, fluorine and carbon in the negative electrode material are adjusted to meet the following conditions: 40.5≤A≤59.8, 0.01≤B≤2, 41≤C≤59.5, the energy density, initial coulombic efficiency, cycle performance and expansion suppression performance of the secondary battery can be further improved.

[0111] Specifically, when the value of B×D is adjusted to satisfy 0.1≤B×D≤19.7, the cycle performance, initial coulombic efficiency, and expansion suppression performance of the secondary battery can be improved. Furthermore, by adjusting the average particle size of the negative electrode material to satisfy 4≤D≤13, it can be made to have a suitable specific surface area, thereby obtaining higher cycle performance and initial coulombic efficiency.

[0112] Specifically, the charge-discharge curve of the negative electrode material of this application shows a lithium intercalation potential of 0.6V to 1.2V, and a depth of discharge of 0.02% to 1% at which the lithium intercalation potential is achieved. The aforementioned lithium intercalation potential and depth of discharge can further improve the cycle performance and swelling suppression performance of the secondary battery.

[0113] The anode materials in the following embodiments differ from those in Example 1 only in that the average diameter and average length of the conductive agent, the type of fluoride, and the area ratio of the conductive agent and the fluoride are adjusted according to Table 2. The types of fluorides are: F1: heptadecafluorodecyltrimethoxysilane; F2: perfluorooctyltrimethoxysilane; F3: perfluorohexylethylene; F4: perfluorodecylthiol.

[0114] Table 2

[0115]

[0116]

[0117] As shown in Table 2, adjusting the area ratio of conductive agent and fluoride in the first coating layer to satisfy 0.5≤S1≤5 and 80.5≤S2≤89.4 can further improve the initial coulombic efficiency, cycle performance and swelling suppression performance of the secondary battery.

[0118] In particular, when the average diameter of the conductive agent satisfies 0.5≤y≤19.6 and the average length of the conductive agent satisfies 508≤z≤996, the conductivity and structural stability of the negative electrode material can be improved, thereby optimizing the initial coulombic efficiency, cycle performance and expansion suppression performance of the secondary battery.

[0119] In particular, the combination of the fluoride provided in this application with silicon-based materials can further improve the cycle performance and expansion suppression performance of secondary batteries.

[0120] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the principles of this application should be included within the protection scope of this application.

Claims

1. A negative electrode material, characterized by, comprise a silicon-based material and a first coating layer partially coated on a surface of the silicon-based material; the first coating layer comprises a conductive agent and a fluoride; a mass percentage of silicon is A%, and a mass percentage of fluorine is B%, based on a mass of the negative electrode material, and 24≤A / B≤4800.

2. The negative electrode material according to claim 1, characterized in that, The negative electrode material satisfies at least one of the following conditions: (1) 31≤A / B≤99; （2）40.5≤A≤59.8； （3）0.01≤B≤2； (4) a mass percentage of carbon is C%, based on a mass of the negative electrode material, and 41≤C≤59.

5.

3. The negative electrode material according to claim 1, characterized in that, The negative electrode material has an average particle size of D μm, and 4≤D≤13; and / or, 0.1≤B×D≤19.

7.

4. The negative electrode material according to any one of claims 1 to 3, characterized in that, An area percentage of the conductive agent is S1%, and an area percentage of the fluoride is S2%, based on an area of the negative electrode material, and 0.5≤S1≤5 and 80.5≤S2≤89.4; and / or, An area percentage of the first coating layer is S0%, based on an area of the negative electrode material, and 85.4≤S0≤95.

5.

5. The negative electrode material according to any one of claims 1 to 3, characterized in that, The negative electrode material satisfies at least one of the following conditions: (1) the silicon-based material comprises a porous carbon skeleton and silicon located on a surface and inside of the porous carbon skeleton; (2) the conductive agent comprises a fibrous conductive agent; an average diameter of the fibrous conductive agent is y nm, and 0.5≤y≤19.6; an average length of the fibrous conductive agent is z nm, and 508≤z≤996; (3) the fluoride has a structure shown in Formula I; R1-R2 Formula I; in Formula I, R1 is selected from at least one of C3 to C15 perfluoroalkyl groups, and R2 is selected from at least one of substituted or unsubstituted C1 to C3 alkoxy groups, substituted or unsubstituted C1 to C3 silyl groups, substituted or unsubstituted C1 to C3 alkyl groups, substituted or unsubstituted C1 to C3 alkenyl groups, substituted or unsubstituted C1 to C3 alkynyl groups, a mercapto group, a hydroxyl group, and a halogen atom; when substituted, the substituent is selected from at least one of C1 to C3 alkyl groups, C1 to C3 alkoxy groups, a mercapto group, a hydroxyl group, and a halogen atom.

6. The negative electrode material according to claim 5, characterized in that, The conductive agent comprises at least one of single-walled carbon nanotubes or multi-walled carbon nanotubes; and / or, The fluoride comprises at least one of heptadecafluorodecyltrimethoxysilane, perfluorooctyltrimethoxysilane, perfluorodecylvinyl, perfluorobutylvinyl, perfluorooctylvinyl, perfluorohexylvinyl, and perfluorodecyl mercaptan.

7. A negative electrode sheet characterized by comprising: The negative electrode material comprises any one of claims 1 to 6.

8. The negative electrode sheet according to claim 7, characterized by The negative electrode material is prepared into a button cell with a lithium metal sheet, and constant current charging and discharging is performed at a current of 0.05C, a lithium intercalation potential is 0.6V to 1.2V, and a discharge depth when the lithium intercalation potential appears is 0.02% to 1%.

9. A secondary battery characterized by comprising: The negative electrode sheet comprises claim 7 or 8.

10. An electronic device, comprising: The secondary battery comprises claim 9.

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