Negative electrode active material, negative electrode sheet, secondary battery, and electronic device

Abstract

A negative electrode active material, a negative electrode plate, a secondary sheet, and an electronic device. The negative electrode active material comprises: a graphite particle and a silicon carbide layer arranged on the surface of the graphite particle, wherein the mass percentage content Y% of silicon in the negative electrode active material and the average height Lc nm of the negative electrode active material in a c-axis direction meet 0.3 × (32 - Lc) ≤ Y ≤ 0.9 × (32 - Lc). By means of the arrangement of the silicon carbide layer on the surface of the graphite particle in the negative electrode active particle and the control of the thickness of the silicon carbide layer in the negative electrode active material on the basis of the average height of the graphite particle in the c-axis direction, a reaction between the graphite particle and an electrolyte can be effectively reduced, the consumption of active ions is reduced, and the first coulombic efficiency of a battery is improved.

Description

Negative electrode active material, negative electrode sheet, secondary battery and electronic device

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to Chinese patent application 202311527450.1, filed on November 16, 2023, entitled “Negative Electrode Active Material, Negative Electrode Sheet, Secondary Battery and Electronic Device,” the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present application relates to the field of battery technology, and in particular to a negative electrode active material, a negative electrode plate, a secondary battery and an electronic device. Background Art

[0004] Secondary batteries, such as lithium-ion batteries, are widely used in digital electronics, energy storage, drones, power tools, and electric vehicles due to their high energy density, long cycle life, high safety, and fast charging capabilities. Currently, the primary active material in the negative electrode of lithium-ion batteries is graphite. However, during the formation process, a solid electrolyte interface (SEI) film forms, leading to a loss of active lithium ions and a decrease in the battery's initial coulombic efficiency (ICE). Therefore, there is a need to improve this ICE.

[0005] Summary of the Invention

[0006] The present application provides a negative electrode active material, a negative electrode plate, a secondary battery and an electronic device, aiming to improve the first coulombic efficiency of the battery by reducing the side reaction between the negative electrode active material and the electrolyte.

[0007] In a first aspect, the present application provides a negative electrode active material, comprising: graphite particles, and a silicon carbide layer disposed on the surface of the graphite particles, wherein the mass percentage Y% of silicon in the negative electrode active material and the average height Lc nm of the negative electrode active material along the c-axis direction satisfy: 0.3×(32-Lc)≤Y≤0.9×(32-Lc).

[0008] According to the present application, by setting a silicon carbide layer on the surface of graphite particles and controlling the thickness of the silicon carbide layer in the negative electrode active material based on the average height of the graphite particles along the c-axis direction, the reaction between the graphite particles and the electrolyte can be effectively reduced, the consumption of active ions can be reduced, and the first coulombic efficiency of the battery can be improved.

[0009] In some embodiments, the thickness of the silicon carbide layer is 5 nm to 100 nm, preferably 15 nm to 40 nm.

[0010] In some embodiments, the crystal phase of silicon carbide in the silicon carbide layer is β-phase silicon carbide.

[0011] In some embodiments, the specific surface area BET m 2 / g and the mass percentage Y% of silicon in the negative electrode active material satisfies: 1.2≤BET-0.3×Y≤2.0.

[0012] In some embodiments, the powder compaction density of the negative electrode active material under the test condition of 5 tons of pressure is P g / cm 3 The mass percentage Y% of silicon in the negative electrode active material satisfies: 1.80≤P+0.08×Y≤2.10.

[0013] In some embodiments, the volume particle size of the negative electrode active material satisfies: 0.2≤(Dv90-Dv50) / Dv99≤0.5.

[0014] In some embodiments, the Raman spectrum D peak intensity of the negative electrode active material is d and the Raman spectrum G peak intensity I of the negative electrode active material g Satisfaction: I d / I g <0.5.

[0015] In some embodiments, the tap density of the negative electrode active material is TD g / cm 3 Satisfies: 0.7≤TD≤1.2.

[0016] In some embodiments, the orientation index (OI) value of the negative electrode active material is ≤6.

[0017] In a second aspect, the present application provides a negative electrode plate, comprising: a negative electrode film layer, wherein the negative electrode film layer comprises the negative electrode active material according to any embodiment of the first aspect.

[0018] In some embodiments, the compaction density of the negative electrode sheet is PD g / cm 3 Meets: 1.45≤PD≤1.75.

[0019] In some embodiments, the porosity K% of the negative electrode sheet satisfies: 25≤K≤40.

[0020] In a third aspect, the present application provides a secondary battery, comprising: a negative electrode sheet according to any embodiment of the second aspect.

[0021] In a fourth aspect, the present application provides an electronic device comprising: a secondary battery according to any embodiment of the third aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the present application.

[0023] FIG1 is a SEM photograph of the negative electrode active material in one embodiment of the present application.

[0024] FIG. 2 is an Si element spectrum of an EDS element test of a negative electrode active material in an embodiment of the present application. DETAILED DESCRIPTION

[0025] The various embodiments or implementation schemes in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments.

[0026] Throughout this specification, reference to terms such as "one embodiment," "some embodiments," "illustrative embodiments," "examples," "specific examples," or "some examples" means that a specific feature, structure, material, or characteristic described in conjunction with an embodiment or example is included in at least one embodiment or example of the present application. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

[0027] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of the technical features being referred to. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of such features. Throughout the description of this application, "plurality" means at least two, for example, two, three, etc., unless otherwise specifically defined.

[0028] In this application, batteries may include lithium-ion secondary batteries, lithium-ion primary batteries, lithium-sulfur batteries, sodium-lithium-ion batteries, sodium-ion batteries, or magnesium-ion batteries, and the embodiments of this application are not limited thereto. Batteries may be cylindrical, flat, rectangular, or in other shapes, and the embodiments of this application are not limited thereto.

[0029] As described in the background art above, negative electrode active materials represented by graphite consume active ions due to the formation of SEI film during the formation process, resulting in a decrease in the first coulombic efficiency of the battery.

[0030] Based on the above problems, the related technologies mainly adopt methods such as increasing the particle size of the negative electrode active material and particle shaping to reduce the amount of active ions consumed to improve the coulombic efficiency of the battery. However, the above methods will affect the dynamic performance of the battery, the improvement effect is limited and the cost is high.

[0031] Based on this, the present application provides a negative electrode active material, a negative electrode plate, a secondary battery, and an electronic device. The negative electrode active material is not easily reactive with the electrolyte, which can reduce the consumption of active ions during the formation process, thereby improving the initial coulombic efficiency of the battery. The following describes the implementation methods of the present application in detail.

[0032] negative electrode active material

[0033] In a first aspect, the present application provides a negative electrode active material comprising: graphite particles, and a silicon carbide layer disposed on the surface of the graphite particles, wherein the mass percentage Y% of silicon in the negative electrode active material and the average height Lc nm of the negative electrode active material along the c-axis direction satisfy: 0.3×(32-Lc)≤Y≤0.9×(32-Lc).

[0034] According to the present application, the structure of the negative electrode active material is to set a silicon carbide layer on the surface of the graphite particles. The silicon carbide layer on the surface of the negative electrode active material can effectively reduce the contact between the active surface of the graphite particles and the electrolyte, thereby reducing the formation of the SEI film, reducing the consumption of active ions, and improving the first coulombic efficiency (first efficiency) of the battery. At the same time, since silicon carbide has good active ion deintercalation performance, the silicon carbide layer on the surface does not significantly affect the kinetic performance of the battery; the mass percentage Y% of silicon in the negative electrode active material and the average height Lc nm of the negative electrode active material along the c-axis direction satisfy: 0.3×(32-Lc)≤Y≤0.9×(32-Lc). It can be understood that the mass percentage of silicon in the negative electrode active material is positively correlated with the content of silicon carbide in the negative electrode active material. Since the main material of the negative electrode active material is graphite particles, the average height Lc of the negative electrode active material along the c-axis direction is 0.3×(32-Lc). The main influencing factor of nm is the average height of the graphite particles along the c-axis. The higher Lc, that is, the higher the average height of the graphite particles along the c-axis, the higher the crystallinity of the graphite particles, the better its stability, and a thinner silicon carbide layer can effectively reduce the reaction between the graphite particles and the electrolyte. In addition, when the crystallinity of the graphite particles is high, the volume expansion rate of the embedded active ions is large. Due to the high rigidity of the silicon carbide layer, the thickness of the silicon carbide layer should not be too large to accommodate the volume expansion of the graphite particles with high crystallinity, improve the stability of the negative electrode active material, and thus reduce the reduction in the first efficiency caused by the rupture of the silicon carbide layer. Based on this, it is necessary to select an appropriate silicon carbide content according to the average height Lc of the negative electrode active material along the c-axis to improve the first efficiency of the battery. In addition, since the height of highly crystalline graphite particles along the c-axis is about 32 nm, the battery has a higher first efficiency when the mass percentage Y% of silicon in the negative electrode active material and the average height Lc nm of the negative electrode active material along the c-axis satisfy: 0.3×(32-Lc)≤Y≤0.9×(32-Lc). It should also be noted that the Lc nm of the negative electrode active material satisfies 0<Lc<32. It is worth mentioning that, since the silicon carbide layer has good thermal stability, the negative electrode active material can also effectively improve the thermal runaway temperature of the battery by reducing the contact between the graphite particles and the electrolyte. The mass percentage of silicon in the negative electrode active material has a meaning well known in the art and can be detected according to known methods and instruments. As an example, the mass percentage of silicon in the negative electrode active material can be detected according to GB / T 17359-2012, specifically: under the requirements of the standard experimental environment and the test standards, the negative electrode active material is placed in the sample chamber of the scanning electron microscope according to the standard operating procedures, the test position is magnified and observed using an acceleration voltage of 15kV, and the mass percentage of silicon in the sample is quantitatively detected using an X-ray energy spectrum analyzer.

[0035] The average height of the negative electrode active material along the c-axis direction has a meaning well known in the art and can be detected according to known methods and instruments. As an example, the average height of the negative electrode active material along the c-axis direction can be detected by X-ray powder diffraction (XRD) test. Specifically, the negative electrode active material is tested using an X-ray powder diffractometer (XRD, instrument model: Bruker D8 ADVANCE), the target material is Cu Kα; the voltage and current are 40KV / 40mA, the scanning angle range is 5° to 80°, the scanning step length is 0.00836°, and the time per step is 0.3s. The X-ray diffraction pattern of the negative electrode active material is obtained, and the half-maximum width of the 002 peak (the full width at 50% between the lowest and highest points of the peak intensity of the 002 peak) is obtained. The average height Lc of the negative electrode active material along the c-axis direction is calculated according to Lc=Kλ / α(2θ) / cosα. nm, where K = Scherrer constant (K = 0.9), α is the half-peak width of the 002 peak, λ is the wavelength (0.154056), and θ is the angle of the maximum peak intensity position of the 002 peak.

[0036] In some embodiments, the thickness of the silicon carbide layer is 5 nm to 100 nm.

[0037] In some of the above embodiments, the thickness of the silicon carbide layer is further limited. Since the silicon carbide layer has strong rigidity, the thickness of the silicon carbide layer will affect the powder compaction density of the negative electrode active material, making it easier to crush. Therefore, it should not be too thick. At the same time, a silicon carbide layer of appropriate thickness can further improve the thermal stability of the negative electrode active material, thereby further improving the thermal runaway temperature of the battery. For example, the thickness of the silicon carbide layer can be 5nm, 10nm, 15nm, 20nm, 25nm, 30nm, 35nm, 40nm, 45nm, 50nm, 55nm, 60nm, 65nm, 70nm, 75nm, 80nm, 85nm, 90nm, 95nm, 100nm, or within the range composed of any of the above values. It should also be noted that graphite particles with appropriate crystallinity can be selected based on the thickness of the appropriate silicon carbide layer to further improve the initial effect and thermal reliability of the battery.

[0038] The thickness of the silicon carbide layer has a well-known meaning in the art and can be detected using methods and instruments known in the art. As an example, the sample can be observed using a projection electron microscope to observe and calculate the thickness of the silicon carbide therein.

[0039] In some embodiments, the crystalline phase of silicon carbide in the silicon carbide layer is β-phase silicon carbide. The metallographic phase of silicon carbide can be β-phase, which not only has good mechanical properties but also has excellent active ion intercalation and deintercalation capabilities, thereby improving the initial efficiency of the battery without significantly affecting the battery's kinetic performance.

[0040] In some embodiments, the specific surface area BET m of the negative electrode active material is 2 / g and the mass percentage content Y% of silicon in the negative electrode active material satisfies: 1.2≤BET-0.3×Y≤2.0.

[0041] In some of the above embodiments, the relationship between the specific surface area of ​​the negative electrode active material and the mass percentage of silicon in the negative electrode active material is further defined. Since a silicon carbide layer is provided on the surface of the graphite particles, the adsorption capacity of nitrogen will be enhanced, thereby increasing the specific surface area of ​​the negative electrode active material. Generally, the higher the mass percentage of silicon in the negative electrode active material, that is, the greater the silicon carbide content, the larger the specific surface area of ​​the negative electrode active material. Since the specific surface area of ​​the graphite particles will affect the uniformity of silicon carbide deposition, after a large number of experiments, the influence factor of the mass percentage of silicon in the negative electrode active material on the specific surface area of ​​the negative electrode active material is determined to be 0.3, that is, BET-0.3×Y can be approximately understood as the specific surface area of ​​the graphite particles. By controlling the specific surface area of ​​the graphite particles, the silicon carbide layer on the surface can be made more uniform. When the negative electrode active material satisfies 1.2≤BET-0.3×Y≤2.0, the negative electrode active material consumes less active ions during the battery formation process, thereby further improving the first effect of the battery. For example, BET-0.3×Y may be 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, or any range thereof.

[0042] The specific surface area of ​​the negative electrode active material has a meaning well known in the art and can be detected according to methods and instruments known in the art. As an example, it can be detected with reference to GB / T 19587-2017, specifically: weigh 1 to 8 g of the sample (the sample weight should be at least 1 / 3 of the volume of the sphere) and place it in a 1 / 2-inch long tube with a bulb (the diameter of the spherical part is 12 mm). After pre-treatment at 200°C for 2 hours, place it in the test equipment TriStar3030 (Machinery, USA) for testing. The adsorption gas used is N2 (purity: 99.999%). The test conditions are carried out at 77K, and the specific surface area is measured by the BET calculation method.

[0043] In some embodiments, the powder compaction density of the negative electrode active material under the test condition of 5 tons of pressure is P g / cm 3 The mass percentage Y% of silicon in the negative electrode active material satisfies: 1.80≤P+0.08×Y≤2.10.

[0044] In some of the above embodiments, the relationship between the powder compaction density of the negative electrode active material under the test condition of a pressure of 5 tons and the mass percentage of silicon in the negative electrode active material is further defined. As mentioned above, since the silicon carbide layer has strong rigidity, the thickness of the silicon carbide layer will affect the powder compaction density of the negative electrode active material. The greater the silicon carbide content, the smaller the powder compaction density. After a large number of experiments, the influence factor of the mass percentage of silicon in the negative electrode active material on the powder compaction density of the negative electrode active material under the test condition of a pressure of 5 tons was determined to be 0.08, that is, P+0.08×Y can be approximately understood as the powder compaction density of graphite particles. By controlling the powder compaction density of graphite particles, the stability of the negative electrode active material can be further improved. When the negative electrode active material satisfies 1.80≤P+0.08×Y≤2.10, the negative electrode active material is less likely to deform and is not easy to break during the cold pressing process, further improving the initial effect of the battery. For example, P+0.08×Y can be 1.80, 1.85, 1.90, 1.95, 2.00, 2.05, 2.10, or any range thereof. More preferably, 1.95≤P+0.08×Y≤2.05.

[0045] The powder compaction density of the negative electrode active material under the test condition of a pressure of 5 tons has a meaning well known in the art and can be tested according to methods and instruments known in the art. As an example, it can be tested with reference to GB / T 24533-2009, specifically: weighing 1.0000±0.0500g of the sample is placed in a test mold (CARVER#3619 (13mm), and then placing the sample in the test equipment, the test equipment is Sansi Zongheng UTM7305, the test tonnage is 5 tons, the pressure increase rate is 10mm / min, the pressure increase holding time is 30s, the pressure relief rate is 30mm / min, and the pressure relief holding time is 10s. The calculation formula of compaction density is: compaction density = negative electrode material mass / negative electrode material force area / sample thickness.

[0046] In some embodiments, the volume particle size of the negative electrode active material satisfies: 0.2≤(Dv90-Dv50) / Dv99≤0.5.

[0047] In some of the above embodiments, the volume particle size distribution of the negative electrode active material is further limited. Generally, if the particle size distribution of the negative electrode active material is too wide, it is not conducive to the processing performance and coulombic efficiency of the negative electrode active material, and if it is too narrow, it is not conducive to further improving the compaction density of the negative electrode sheet. Therefore, when the volume particle size of the negative electrode active material satisfies 0.2≤(Dv90-Dv50) / Dv99≤0.5, the first efficiency of the battery can be further improved. For example, (Dv90-Dv50) / Dv99 can be 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, or within the range of any of the above values.

[0048] The volume particle sizes Dv50, Dv90, and Dv99 of the negative electrode active material have well-known meanings in the art and can be measured using methods and instruments known in the art. For example, GB / T 19077-2016 can be used for measurement. Specifically, 1 g of sample is weighed and mixed evenly with 20 mL of deionized water and a trace amount of dispersant. The mixture is then ultrasonicated for 5 minutes, and the solution is then poured into a sample injection system, a Hydro2000SM, for measurement using a Malvern Mastersizer 3000. During the measurement process, the intensity of scattered light as a laser beam passes through the dispersed particle sample is measured. This data is then used to analyze and calculate the particle size distribution, which forms the scattering spectrum. The particles used in the test have a refractive index of 1.8. Each sample is tested three times, and the particle size is calculated as the average of these three measurements to determine Dv50, Dv90, and Dv99, respectively.

[0049] In some embodiments, the Raman spectrum D peak intensity I of the negative electrode active material is d and the Raman spectrum G peak intensity I of the negative electrode active material g Satisfaction: I d / I g <0.5.

[0050] In some of the above embodiments, the defectivity of the negative electrode active material is further defined. d / I g The value can represent the degree of defect of the negative electrode active material. d / I g The larger the value, the higher the degree of surface defects of the negative electrode active material, which will increase the side reaction with the electrolyte, thereby affecting the initial efficiency of the battery. d / I g When the ratio is less than 0.5, the initial efficiency of the battery can be further improved.

[0051] Raman spectrum D peak intensity I of negative electrode active material d and the Raman spectrum G peak intensity I of the negative electrode active materialg The detection method has a well-known meaning in the art and can be performed according to methods and instruments known in the art. As an example, a laser microconfocal Raman spectrometer (Raman, HR Evolution, HORIBA Scientific Instruments Division) is used to scan the sample particles to obtain the D peak and G peak of all particles within the area. The data is processed using LabSpec software to obtain the peak intensities of the D peak and G peak of each particle, which are I d and I g , I d / I g The frequency of Id / Ig was statistically analyzed with a step size of 0.02 to obtain a normal distribution graph, and the average value of Id / Ig was calculated, which is the intensity ratio of the D peak to the G peak of the active material. d / I g The laser wavelength of the Raman spectrometer can be in the range of 532nm to 785nm. Among them, the D peak is generally at 1350cm -1 Nearby, caused by the radial breathing mode of the symmetric stretching vibration of sp2 carbon atoms in the aromatic ring (structural defect); G peak: appears at 1575cm -1 Nearby, it is caused by the stretching vibration between sp2 carbon atoms, which corresponds to the vibration of E2g optical phonon in the center of the Brillouin zone (in-plane vibration of carbon atoms).

[0052] In some embodiments, the tap density of the negative electrode active material is TD g / cm 3 Satisfies: 0.7≤TD≤1.2.

[0053] In some of the above embodiments, the tap density of the negative electrode active material is further limited. The tap density will affect the processing performance of the negative electrode active material. 3 When 0.7≤TD≤1.2 is satisfied, the negative electrode active material has better processability and the performance of the resulting negative electrode sheet is more stable. For example, TD can be 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, or any range thereof.

[0054] The tap density of negative electrode active materials has a well-known meaning in the art and can be measured using methods and instruments known in the art. As an example, 50g of powder is weighed and placed into a graduated cylinder. The cylinder is then mounted on an instrument and vibrated. After vibration, the volume is visually measured based on the height of the powder surface, and the tap density is calculated. The test equipment used may be a Dandong Better BT-301.

[0055] In some embodiments, the orientation index (OI) value of the negative electrode active material is ≤6.

[0056] In some of the above-mentioned embodiments, the orientation index (OI) value of the negative electrode active material is further limited. A larger OI value indicates a higher orientation index of the negative electrode active material. A high orientation index results in a relatively single direction for the active ions to be intercalated and deintercalated in the negative electrode active material, which is not conducive to the intercalation and deintercalation of the active ions, thereby affecting the battery's kinetic performance. Therefore, when the OI value of the negative electrode active material is ≤6, the battery's kinetic performance is better.

[0057] The orientation degree OI value of the negative electrode active material has a meaning well known in the art and can be measured according to methods and instruments known in the art. As an example, the (004) plane diffraction line pattern and the (110) plane diffraction line pattern in the X-ray diffraction spectrum of the negative electrode active material layer can be measured with reference to the industry standard JB / T 4220-2011. The specific test conditions are as follows: X-rays are CuKα radiation, and the CuKα radiation is removed by a filter or a monochromator. The operating voltage of the X-ray tube is (30-35) kV, and the operating current is (15-20) mA. The scanning speed of the counter is 1 / 4° / min. When recording the 004 diffraction line pattern, the scanning range of the diffraction angle 2θ is 53° to 57°. When recording the 110 diffraction line pattern, the scanning range of the diffraction angle 2θ is 75° to 79°. The peak area obtained from the (004) plane diffraction line pattern is recorded as C004. The peak area obtained from the (110) plane diffraction line pattern is recorded as C110. The ratio of C004 / C110 of the negative electrode active material is calculated, which is the OI value of the negative electrode active material.

[0058] Method for preparing negative electrode active material

[0059] The negative electrode active material of the first aspect can be prepared using methods and instruments known in the art. As an example, it can be prepared by the following method:

[0060] Preparation of graphite particles: Petroleum coke can be selected as the raw material for graphite particles, and the sulfur content of petroleum coke is less than 1%. The petroleum coke is crushed to a Dv50 of 9-12μm, and then pre-carbonized at a temperature of 900-1100℃ and a treatment time of ≥6h. The treated sample continues to be graphitized. The graphitization process is to control the temperature and time of graphitization. The graphitization temperature is controlled at 2700-3000℃, and the holding time is controlled at 36-72h. After graphitization is completed, it is shaped and graded to narrow its particle size range. The shaping and grading time is 3-8h. According to the actual powder parameter requirements, different yields are adjusted. The grading yield is controlled at 50%-90% to obtain graphite particles. It can be understood that different graphite particles can be obtained by controlling the above process parameters.

[0061] Preparation of the negative electrode active material: Suitable graphite particles are coated by vapor deposition. The vapor deposition temperature is selected to be 900-1200°C, argon (Ar) is used as the carrier gas, and silane and acetylene are used as the reaction gases. The flow rate ratio of silane to acetylene is controlled at 5:4. The flow rate of silane is controlled at 25-75 sccm, and the flow rate of acetylene is controlled at 20-60 sccm. The deposition time is controlled at 3-15 hours. By controlling the gas flow rate and reaction time, the thickness of the silicon carbide layer deposited on the graphite particle surface can be controlled.

[0062] Figure 1 is a SEM image of the negative electrode active material in one embodiment of the present application. Its morphology is not significantly different from that of general graphite particles, indicating that the silicon carbide layer does not significantly affect the morphology of the graphite particles. Figure 2 is an EDS elemental analysis of the Si element spectrum of the negative electrode active material in one embodiment of the present application. Red indicates the presence of Si elements. It can be seen that the graphite particles are fully coated with silicon carbide, indicating that the deposition effect of silicon carbide is good.

[0063] In a second aspect, the present application provides a negative electrode plate, comprising: a negative electrode film layer, wherein the negative electrode film layer comprises the negative electrode active material according to any embodiment of the first aspect.

[0064] According to the present application, since the negative electrode plate includes the silicon-carbon negative electrode material of any embodiment of the first aspect, it has the beneficial effects of the first aspect.

[0065] In some embodiments, the compacted density of the negative electrode sheet is PD g / cm 3 Meets: 1.45≤PD≤1.75.

[0066] In some of the above embodiments, the compaction density of the negative electrode plate is further limited. If the compaction density is too high, the negative electrode active material may rupture and form microcracks, resulting in an increase in the film-forming reaction surface, affecting the first effect of the battery. If the compaction density is too low, the contact between the negative electrode active materials is poor, and the electronic conductivity is reduced, which also affects the first effect of the battery. When the compaction density of the negative electrode plate satisfies 1.45≤PD≤1.75, the first effect of the battery is further improved.

[0067] In some embodiments, the porosity K% of the negative electrode sheet satisfies: 25≤K≤40.

[0068] In some of the above embodiments, the porosity of the negative electrode sheet is further limited. It can be understood that the porosity is related to the wetting performance of the electrolyte, that is, it will affect the transmission of active ions and also affect the electron transmission between the negative electrode active materials. When the porosity of the negative electrode sheet satisfies 25≤K≤40, the initial performance of the battery is further improved.

[0069] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer base layer and a metal layer formed on at least one surface of the polymer base material. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer base material (such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0070] In some embodiments, the negative electrode film layer may further include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0071] In some embodiments, the negative electrode film layer may further include a conductive agent, which may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0072] In some embodiments, the negative electrode film layer may optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0073] In some embodiments, the negative electrode sheet can be prepared by the following method: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode current collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0074] In a third aspect, the present application provides a secondary battery, comprising: a negative electrode sheet according to any embodiment of the second aspect.

[0075] According to the present application, the battery includes the negative electrode sheet of any embodiment of the second aspect, so the battery has the beneficial effects of the second aspect.

[0076] Typically, a battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator.

[0077]

Positive electrode

[0078] The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer provided on at least one surface of the positive electrode current collector, wherein the positive electrode film layer includes a positive electrode active material.

[0079] As an example, the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive electrode current collector.

[0080] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0081] In some embodiments, the positive electrode active material may adopt the positive electrode active material for batteries that is well known in the art. As an example, the positive electrode active material may include at least one of the following materials: lithium-containing phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, the present application is not limited to these materials, and other traditional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also referred to as NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also referred to as NCM 523 ), LiNi 0.5 Co 0.25 Mn 0.25 O2 (also referred to as NCM 211 ), LiNi 0.6 Co 0.2 Mn 0.2 O2 (also referred to as NCM 622 ), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also referred to as NCM 811 ), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al0.05 O2) and its modified compounds. Examples of olivine-structured lithium-containing phosphates may include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon.

[0082] In some embodiments, the positive electrode film layer may further optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0083] In some embodiments, the positive electrode film layer may further include a conductive agent. For example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0084] In some embodiments, the positive electrode sheet can be prepared by the following method: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode current collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0085]

Negative electrode

[0086] Select according to any embodiment of the second aspect.

[0087] [Diaphragm]

[0088] The separator is placed between the positive and negative electrodes to prevent short circuits between the positive and negative electrodes while allowing active ions to pass through. This application does not impose any particular restrictions on the type of separator; any known porous separator with good chemical and mechanical stability can be used.

[0089] In some embodiments, the material of the separator can be selected from one or more of, but not limited to, glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. Alternatively, the separator can be made of polyethylene and / or polypropylene. The separator can be a single-layer film or a multi-layer composite film. When the separator is a multi-layer composite film, the materials of each layer can be the same or different. In some embodiments, the separator can also be provided with a ceramic coating or a metal oxide coating.

[0090]

Electrolyte

[0091] The electrolyte plays a role in conducting active ions between the positive electrode and the negative electrode. The electrolyte that can be used in the secondary electrolyte of this application can be an electrolyte known in the prior art.

[0092] In some embodiments, the electrolyte may include an organic solvent, an electrolyte salt, and optional additives. The types of the organic solvent, the lithium salt, and the additives are not particularly limited and may be selected according to needs.

[0093] In some embodiments, the secondary battery is a lithium-ion battery, and the electrolyte salt may include a lithium salt. As an example, the lithium salt includes, but is not limited to, at least one of LiPF6 (lithium hexafluorophosphate), LiBF4 (lithium tetrafluoroborate), LiClO4 (lithium perchlorate), LiFSI (lithium bis(trifluoromethanesulfonyl imide), LiTFSI (lithium bis(trifluoromethanesulfonyl imide), LiTFS (lithium trifluoromethanesulfonate), LiDFOB (lithium difluorooxalatoborate), LiBOB (lithium dioxalatoborate), LiPO2F2 (lithium difluorophosphate), LiDODFP (lithium difluorooxalatophosphate), and LiOTFP (lithium tetrafluorooxalatophosphate). The above lithium salts can be used alone or in combination.

[0094] In some embodiments, the secondary battery is a sodium ion battery, and the electrolyte salt may include a sodium salt. As an example, the sodium salt may be selected from at least one of NaPF6, NaClO4, NaBCl4, NaSO3CF3, and Na(CH3)C6H4SO3.

[0095] In some embodiments, as an example, the organic solvent includes but is not limited to ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), cyclopentane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS) and diethyl sulfone (ESE). The above organic solvents can be used alone or in combination. Alternatively, two or more organic solvents are used in combination.

[0096] In some embodiments, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high or low temperature performance, etc.

[0097] As an example, the additive includes but is not limited to at least one of fluoroethylene carbonate (FEC), vinylene carbonate (VC), vinyl ethylene carbonate (VEC), diethylene sulfate (DTD), propylene sulfate, vinyl sulfite (ES), 1,3-propane sultone (PS), 1,3-propene sultone (PST), sulfonate cyclic quaternary ammonium salt, succinic anhydride, succinonitrile (SN), adiponitrile (AND), tris(trimethylsilyl) phosphate (TMSP), and tris(trimethylsilyl) borate (TMSB).

[0098] The electrolyte solution can be prepared according to conventional methods in the art. For example, an organic solvent, an electrolyte salt, and optional additives can be uniformly mixed to obtain the electrolyte solution. The order in which the materials are added is not particularly limited. For example, the electrolyte salt and optional additives can be added to the organic solvent and mixed uniformly to obtain the electrolyte solution; alternatively, the electrolyte salt can be first added to the organic solvent, and then the optional additives can be added to the organic solvent and mixed uniformly to obtain the electrolyte solution.

[0099] electronic devices

[0100] In a fourth aspect, the present application provides an electronic device, comprising: a secondary battery according to any embodiment of the third aspect.

[0101] According to the present application, since the electronic device includes the secondary battery of any embodiment of the third aspect, the electronic device has the beneficial effects of the third aspect.

[0102] The electronic device of the present application is not particularly limited and can be any electronic device known in the prior art. In some embodiments, the electronic device can include, but is not limited to, a laptop computer, a pen-type computer, a mobile computer, an e-book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a head-mounted stereo headset, a video recorder, an LCD television, a portable cleaner, a portable CD player, a mini-disc, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, a car, a motorcycle, a power-assisted bicycle, a bicycle, a lighting fixture, a toy, a game console, a clock, a power tool, a flashlight, a camera, a large household battery, and a lithium-ion capacitor.

[0103] Below, the embodiment of the present application is described. The embodiment described below is exemplary and is only used to explain the present application, and is not to be construed as limiting the present application. Where specific techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. Reagents or instruments used that do not specify the manufacturer are conventional products that can be obtained commercially.

[0104] Test of the first coulombic efficiency of the battery: The assembled lithium-ion battery was subjected to formation and capacity tests, and charged at a rate of 0.2C until the voltage reached 3.6V and the current was less than 0.05C, and the charging capacity Q1 was obtained. Then, it was allowed to stand for 5 minutes and discharged at a rate of 0.2C until the voltage reached 2.5V, and the discharge capacity Q2 was obtained. The first coulombic efficiency = Q2 / Q1×100%.

[0105] Battery thermal runaway temperature test: First, fully charge the battery and then place it in a high-temperature chamber. The starting temperature of the high-temperature chamber is 25°C. The temperature is heated at a heating rate of 5°C / min to the set temperature, which is 120-180°C. The temperature is then kept warm for 60 minutes. If the battery smokes, catches fire, or even explodes, it is determined to be thermal runaway. Otherwise, it is determined that thermal runaway has not occurred.

[0106] Example 1-1

[0107] Preparation of graphite particles: Petroleum coke is selected as the raw material for graphite particles, with a sulfur content of 0.8%. The petroleum coke is crushed to a Dv50 of 10μm and then pre-carbonized at 950°C for 8 hours. The treated sample is then graphitized. The graphitization process involves controlling the graphitization temperature and time. The graphitization temperature is controlled at 2900°C and the holding time is controlled at 48 hours. After graphitization, the sample is shaped and graded to narrow the particle size range. The shaping and grading time is 4 hours, and the grading yield is controlled at 65%, resulting in graphite particles.

[0108] Preparation of the negative electrode active material: The prepared graphite particles were coated by vapor deposition at a temperature of 1000°C, using argon (Ar) as the carrier gas and silane and acetylene as the reactant gases, with a flow rate ratio of 5:4. The silane flow rate was controlled at 45 sccm, the acetylene flow rate at 36 sccm, and the deposition time at 4 hours to obtain the negative electrode active material. Some of its parameters are shown in Table 1.

[0109] Preparation of negative electrode sheet: The negative electrode active material, conductive carbon, binder styrene butadiene rubber (abbreviated as SBR), and thickener sodium carboxymethyl cellulose (abbreviated as CMC) are mixed in a certain ratio, wherein the mass ratio of conductive carbon is 1.5%, the mass ratio of negative electrode active material is 96%, the mass ratio of binder styrene butadiene rubber (abbreviated as SBR) is 1.5%, and the mass ratio of thickener sodium carboxymethyl cellulose (abbreviated as CMC) is 1.0%. Then, the mixture is fully stirred and mixed in an appropriate amount of deionized water solvent to form a uniform negative electrode slurry. The slurry is coated on the current collector Cu foil, dried, and cold pressed to obtain the negative electrode sheet.

[0110] Preparation of positive electrode sheet: Lithium iron phosphate is selected as the positive electrode active material, and it is thoroughly stirred and mixed with the conductive agent acetylene black and the binder polyvinylidene fluoride (abbreviated as PVDF) in a weight ratio of 96.3:2.2:1.5 in an appropriate amount of N-methylpyrrolidone (abbreviated as NMP) solvent to form a uniform positive electrode slurry; this slurry is coated on the current collector Al foil, dried and cold pressed to obtain a positive electrode sheet.

[0111] Preparation of the electrolyte: In a dry argon atmosphere glove box, ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a mass ratio of EC:EMC:DEC = 1:3:3:3. 1,3-Propane sultone was then added, dissolved, and thoroughly stirred. LiPF6 was then added and mixed until uniformly distributed to obtain an electrolyte. The mass percentage of LiPF6 was 11.0%, and the mass percentage of 1,3-Propane sultone was 2.9%. The mass percentages of each substance were calculated based on the mass of the electrolyte.

[0112] Preparation of isolation membrane: 8 μm PE porous polymer film was selected as the isolation membrane.

[0113] Preparation of lithium-ion battery: Take the above-mentioned negative electrode sheet and positive electrode sheet and wind them together with the separator, place them in an aluminum-plastic film, then inject liquid, let it stand, and form it to make a lithium-ion secondary battery.

[0114] The first coulombic efficiency and thermal runaway temperature of the above lithium-ion battery were tested, and the results are shown in Table 1.

[0115] Examples 1-2 to 1-9, Comparative Examples 1 to 6

[0116] This is similar to Example 1-1, except that the thickness of the silicon carbide layer of the negative electrode active material, Lc, and Y are changed by controlling the graphitization process and vapor deposition conditions. The graphitization temperature and time affect the size of Lc. Increasing the temperature and holding time increases Lc, while conversely, decreasing it. Specific parameters are shown in Table 1.

[0117] The first coulombic efficiency and thermal runaway temperature of the above lithium-ion battery were tested, and the results are shown in Table 1.

[0118] Table 1

[0119] According to Table 1, the first-effect and thermal runaway temperatures of the lithium-ion batteries obtained in each Example were higher than those in each Comparative Example, indicating that the negative electrode active material provided in this application can effectively improve the first-effect and thermal stability of the battery. In each Comparative Example, since Lc and Y did not meet the requirements, this may result in the silicon carbide layer being unable to effectively protect the negative electrode active material, or the silicon carbide layer being unable to adapt well to the expansion of the graphite particles, resulting in rupture, which in turn leads to a decrease in the first-effect and thermal runaway temperatures.

[0120] Examples 2-1 to 2-7

[0121] The method is substantially the same as Example 1-1, except that the BET and Y of the negative electrode active material are changed by controlling the vapor deposition conditions. The specific parameters are shown in Table 2.

[0122] The first coulombic efficiency and thermal runaway temperature of the above lithium-ion battery were tested, and the results are shown in Table 2.

[0123] Table 2

[0124] According to Table 2, the relationship between the specific surface area of ​​the negative electrode active material and the mass percentage of silicon will also affect the first efficiency and thermal runaway temperature of the battery. When BET-0.3Y meets 1.2~2, the first efficiency and thermal runaway temperature of the battery are better.

[0125] Examples 3-1 to 3-6

[0126] It is roughly the same as Example 2-3, except that: by controlling the crushing size of petroleum coke, the deposition process and the vapor deposition conditions, the P and Y of the negative electrode active material are changed. The specific parameters are shown in Table 3.

[0127] The first coulombic efficiency and thermal runaway temperature of the above lithium-ion battery were tested, and the results are shown in Table 3.

[0128] Table 3

[0129] According to Table 3, the relationship between the powder compaction density of the negative electrode active material and the mass percentage of silicon will also affect the first effect and thermal runaway temperature of the battery. When P+0.08Y meets 1.8~2.1, the first effect and thermal runaway temperature of the battery are better. Furthermore, when P+0.08Y meets 1.95~2.05, the first effect and thermal runaway temperature of the battery are even better.

[0130] Examples 4-1 to 4-6

[0131] The same as Example 3-4, except that the shaping time and classification yield of the graphitized material are controlled and adjusted to change the (Dv90-Dv50) / Dv99 and I d / I g , the specific parameters are shown in Table 4.

[0132] The first coulombic efficiency and thermal runaway temperature of the above lithium-ion battery were tested, and the results are shown in Table 4.

[0133] Table 4

[0134] According to Table 4, the particle size distribution and surface defect of the negative electrode active material will also affect the first efficiency and thermal runaway temperature of the battery. When 0.2≤(Dv90-Dv50) / Dv99≤0.5, the first efficiency and thermal runaway temperature of the battery are better. d / I g When the value is less than 0.5, the battery's first efficiency and thermal runaway temperature are better.

[0135] Examples 5-1 to 5-6

[0136] This is similar to Example 4-5, except that the TD and OI of the negative electrode active material can be modified by controlling the shaping and classification yield and classification frequency (the classification frequency affects the particle size distribution; a lower frequency results in a wider particle size distribution). Removing more fine powder reduces the yield but increases the TD of the negative electrode active material. A wider particle size distribution can reduce the OI of the active material. Specific parameters are shown in Table 5.

[0137] The first coulombic efficiency and thermal runaway temperature of the above lithium-ion battery were tested, and the results are shown in Table 5.

[0138] Table 5

[0139] According to Table 5, the tap density and OI value of the negative electrode active material will also affect the first efficiency and thermal runaway temperature of the battery. When 0.7≤TD≤1.2, the first efficiency and thermal runaway temperature of the battery are better, and when the OI value is ≤6, the first efficiency and thermal runaway temperature of the battery are better.

[0140] Examples 6-1 to 6-6

[0141] It is roughly the same as Example 5-5, except that the PD and K of the negative electrode are changed. The specific parameters are shown in Table 6.

[0142] The first coulombic efficiency and thermal runaway temperature of the above lithium-ion battery were tested, and the results are shown in Table 6.

[0143] Table 6

[0144] According to Table 6, the compaction density and porosity of the negative electrode sheet will also affect the first effect and thermal runaway temperature of the battery. When 1.45≤PD≤1.75, the first effect and thermal runaway temperature of the battery are better, and when 25≤K≤40, the first effect and thermal runaway temperature of the battery are better.

[0145] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some or all of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A negative electrode active material, wherein: include: Graphite particles, and a silicon carbide layer disposed on the surface of the graphite particles, wherein the mass percentage Y% of silicon in the negative electrode active material and the average height Lc nm of the negative electrode active material along the c-axis direction satisfy: 0.3×(32-Lc)≤Y≤0.9×(32-Lc).

2. The negative electrode active material according to claim 1, wherein The thickness of the silicon carbide layer is 5 nm to 100 nm, preferably 15 nm to 40 nm. The crystal phase of silicon carbide in the silicon carbide layer is β-phase silicon carbide.

3. The negative electrode active material according to claim 1 or 2, wherein The specific surface area BETm of the negative electrode active material 2 / g and the mass percentage content Y% of silicon in the negative electrode active material satisfies: 1.2≤BET-0.3×Y≤2.

0.

4. The negative electrode active material according to any one of claims 1 to 3, wherein The powder compaction density of the negative electrode active material under the test condition of 5 tons of pressure is P g / cm 3 The mass percentage Y% of silicon in the negative electrode active material satisfies: 1.80≤P+0.08×Y≤2.

10.

5. The negative electrode active material according to any one of claims 1 to 4, wherein The volume particle size of the negative electrode active material satisfies: 0.2≤(Dv90-Dv50) / Dv99≤0.

5.

6. The negative electrode active material according to any one of claims 1 to 5, wherein The negative electrode active material satisfies at least one of the following conditions: (1) The Raman spectrum D peak intensity I of the negative electrode active material d and the Raman spectrum G peak intensity I of the negative electrode active material g Satisfaction: I d / I g <0.5; (2) The tap density of the negative electrode active material TD g / cm 3 Satisfies: 0.7≤TD≤1.2; or (3) The orientation degree OI value of the negative electrode active material is ≤6.

7. A negative electrode sheet, wherein: include: A negative electrode film layer, comprising the negative electrode active material according to any one of claims 1 to 6.

8. The negative electrode sheet according to claim 7, wherein: The negative electrode sheet satisfies at least one of the following conditions: (4) The compaction density of the negative electrode sheet is PD g / cm 3 Satisfies: 1.45≤PD≤1.75; or (5) The porosity K% of the negative electrode sheet satisfies: 25≤K≤40.

9. A secondary battery, wherein: include: A positive electrode sheet, an electrolyte and a negative electrode sheet according to claim 7 or 8.

10. An electronic device, wherein: include: The secondary battery according to claim 9.

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