Secondary battery and electrical device

Abstract

Provided are a secondary battery and an electrical device, relating to the technical field of secondary batteries. The secondary battery comprises a negative electrode sheet and an electrolyte; a negative active material in the negative electrode sheet has a graphitization degree of G; the electrolyte comprises 1,3-propane sultone and fluoroethylene carbonate; and based on the mass of the electrolyte, the mass percentage of 1,3-propane sultone is X%, and the mass percentage of fluoroethylene carbonate is Y%, wherein X>0.2×G+Y and 1.2≤Y≤4.2. The secondary battery can ameliorate the problem of low-temperature lithium precipitation, and the cycle performance of the battery is improved.

Description

Secondary batteries and electrical equipment

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to Chinese patent application number 2023114903633, filed with the Chinese Patent Office on November 9, 2023, entitled “Secondary Batteries and Electrical Equipment,” the entire contents of which are incorporated by reference into this application. Technical Field

[0003] The present application relates to the technical field of secondary batteries, and in particular to a secondary battery and an electrical device. Background Art

[0004] Lithium-ion secondary batteries are now widely used in our daily lives, including consumer products such as mobile phones, computers, tablets, wristbands, smartwatches, and electronic door locks, as well as power products such as electric vehicles, energy storage, power tools, and drones. These batteries are now integrated into every aspect of our lives. At the same time, the service life of lithium-ion secondary batteries is becoming increasingly important, with consumers demanding batteries with long lifespans. Long-life batteries are characterized by excellent cycle performance, which is directly related to consumer experience. Excellent cycle performance can extend the lifespan of electric vehicles, extend their service life, enable energy storage batteries to operate for extended periods without replacement, and provide mobile phones with extended battery life, reducing the need for frequent battery replacements. Furthermore, battery cycle performance is correlated with battery cost. For the same price, a higher number of cycles means lower per-cycle costs, leading to a market preference for products with better cycle performance at the same price point. This is crucial given the actual operating conditions of electric vehicles and energy storage batteries. To meet market demand, lithium-ion batteries with excellent cycle performance are needed. Therefore, the cycle performance of the negative electrode active material needs to be improved, as does the system design. The negative electrode active materials of existing lithium-ion batteries are usually improved in terms of cycle life by coating treatment, raw material and particle size design, etc. However, these methods are relatively complicated to process the negative electrode active materials.

[0005] Application Contents

[0006] In view of this, the present application provides a secondary battery and an electrical device, which can improve the problem of low-temperature lithium deposition in the battery and enhance the cycle performance of the battery.

[0007] In a first aspect of the present application, a secondary battery is provided, comprising a negative electrode plate and an electrolyte, wherein the negative electrode active material in the negative electrode plate has a graphitization degree G, and the electrolyte comprises 1,3-propane sultone and fluoroethylene carbonate. Based on the mass of the electrolyte, the mass percentage of 1,3-propane sultone is X%, and the mass percentage of fluoroethylene carbonate is Y%, wherein X>0.2×G+Y, and 1.2≤Y≤4.2.

[0008] In the above technical solution, the research found that the degree of graphitization of the negative electrode active material affects the interlayer spacing of the active material graphite, and the interlayer spacing affects the intercalation and deintercalation of active ions (such as lithium ions), which in turn affects the cycle performance of the secondary battery. Therefore, the cycle performance of the secondary battery can be improved by regulating the range of graphitization. The degree of graphitization is related to the interlayer spacing of the negative electrode active material. The interlayer spacing of the negative electrode active material affects the degree of reaction between the negative electrode active material and the electrolyte, which in turn affects the intercalation / deintercalation of active ions in another dimension, affecting the cycle performance and low-temperature lithium precipitation performance of the secondary battery. Therefore, in the present application, based on the mass of the electrolyte, the mass percentage of fluoroethylene carbonate is between 1.2% and 4.2%, which can promote the film formation of the negative electrode, and the impedance of the negative electrode film formation is low and the kinetics are very good, but its addition will produce side reactions; therefore, further adding 1,3-propane sultone to the electrolyte, and X>0.2×G+Y, can inhibit the occurrence of side reactions to a certain extent, and make the film formation quality of the positive and negative electrodes higher, so that the cycle performance and low-temperature lithium precipitation performance of the secondary battery are better.

[0009] In some embodiments, 1.7≤X≤5.1. While satisfying X>0.2×G+Y, the mass percentage of 1,3-propane sultone is between 1.7% and 5.1% based on the mass of the electrolyte. This can improve the coordination between 1,3-propane sultone and fluoroethylene carbonate, thereby further improving the film formation quality of the positive and negative electrodes, and alleviating the side reaction problems of the secondary battery, further improving the cycle performance and low-temperature lithium deposition performance of the secondary battery. Optionally, 1.8≤X≤4.1.

[0010] In some embodiments, 91.8% < G ≤ 97%. The negative electrode active material has a high degree of graphitization, which reduces the degree of side reactions with the electrolyte and forms a thinner SEI film. However, due to the high degree of graphitization, the interlayer spacing is small, and lithium insertion causes the interlayer spacing to expand significantly, making the SEI film prone to rupture and making it difficult for lithium ions to be inserted / extracted. Therefore, the mass percentage of 1,3-propane sultone X% and the mass percentage of fluoroethylene carbonate Y% in the electrolyte are controlled to satisfy: X>0.2×G+Y, 1.2≤Y≤4.2, which can make the film formation stability of the SEI film better, facilitate the interfacial diffusion of lithium ions, thereby improving the insertion / extraction of lithium ions at low temperatures, and further improving the cycle performance and low-temperature lithium precipitation performance of the secondary battery. Optionally, 93.5% ≤ G ≤ 96%.

[0011] In some embodiments, 1.4≤Y≤3.5. Based on the mass of the electrolyte, the weight percentage of fluoroethylene carbonate is between 1.4% and 3.5%. When combined with 1,3-propane sultone, this can further improve the film formation stability of the SEI film on the surface of the negative electrode active material, improve the problem of lithium deposition at low temperatures, and thus further improve the cycle performance and low-temperature lithium deposition performance of the secondary battery.

[0012] In some embodiments, the negative electrode active material satisfies: 0.05≤CD / (372×G)×Z 50 ≤0.1, where the powder compaction density of the negative electrode active material is CD g / cm 3 In the volume-based particle size distribution of the negative electrode active material, the particle size at which the volume accumulation reaches 50% from the small particle size side is Z 50 μm. Studies have found that the degree of graphitization will affect the compaction density of the negative electrode active material, and the particle size Z 50 It also affects the compaction density of the active material. Therefore, the negative electrode active material satisfies 0.06≤CD / (372×G)×Z 50 ≤0.1, which can further improve the low-temperature lithium deposition performance of the secondary battery and improve the cycle performance of the secondary battery. Optionally, 0.06≤CD / (372×G)×Z 50 ≤0.095.

[0013] In some embodiments, 1.7≤CD≤2.0, the compaction density of the negative electrode active material is 1.7 g / cm 3 ~2.0g / cm 3 The cycle performance and low temperature performance of the secondary battery can be further improved.

[0014] In some embodiments, 7≤Z 50≤15. In the volume-based particle size distribution of the negative electrode active material, the particle size that reaches 50% of the volume accumulation from the small particle size side is 7μm to 15μm, which can improve the overall performance of the negative electrode active material and further improve the performance of the secondary battery.

[0015] In some embodiments, the negative electrode active material satisfies: 3.5≤(Z 90 / Z 10 )×ET≤20, where the specific surface area of ​​the negative electrode active material is Tm 2 / g, in the volume-based particle size distribution of the negative electrode active material, the particle size at which the volume accumulation reaches 10% from the small particle size side is Z 10 μm, the particle size that reaches 90% of the volume accumulation is Z 90 μm, in the particle size distribution based on the number of negative electrode active materials, the particle size that reaches 10% of the cumulative number from the small particle size side is Eμm. The graphitization degree G of the negative electrode active material will affect the specific surface area T of the negative electrode active material, thereby affecting the reactive surface between the electrolyte and the negative electrode active material. The particle distribution of the negative electrode active material will also affect the reactive surface. Therefore, based on the definition of the graphitization degree G and the electrolyte additive, the negative electrode active material satisfies: 3.5≤(Z 90 / Z 10 )×ET≤20, which can further improve the low-temperature lithium deposition performance of the secondary battery and improve the cycle performance of the secondary battery. 90 / Z 10 )×ET≤13.

[0016] In some embodiments, 3≤Z 10 ≤8. In the volume-based particle size distribution of the negative electrode active material, the particle size that reaches 10% of the cumulative volume from the small particle size side is 5μm to 10μm, which can improve the overall performance of the negative electrode active material and further improve the performance of the secondary battery.

[0017] In some embodiments, 20≤Z 90 ≤35. In the volume-based particle size distribution of the negative electrode active material, the particle size at which 90% of the volume accumulation is achieved, starting from the small particle size side, is 20 μm to 35 μm, which can further improve the cycle performance of the secondary battery.

[0018] In some embodiments, 1 ≤ E ≤ 5. In the number-based particle size distribution of the negative electrode active material, the particle size that reaches 10% of the cumulative number from the small particle size side is 1 μm to 5 μm, which can improve the overall performance of the negative electrode active material and further improve the performance of the secondary battery.

[0019] In some embodiments, 1≤T≤5. The specific surface area of ​​the negative electrode active material is 1m 2 / g~2m 2 / g, which can further improve the cycle and low-temperature performance of the secondary battery. In some embodiments, the particle sphericity S of the negative electrode active material satisfies: 0.4≤S≤0.95. The particle morphology of the negative electrode active material will also have a certain impact on the electrical performance of the secondary battery. The sphericity of the particles is conducive to reducing the reactive surface of the particles, improving the cycle performance and low-temperature lithium precipitation performance. On the basis of limiting the graphitization degree G and the electrolyte additives, the sphericity S of the negative electrode active material satisfies: 0.4≤S≤0.95, which can further improve the cycle performance and low-temperature lithium precipitation performance of the battery. Optionally, 0.48≤S≤0.7.

[0020] In some embodiments, the intensity ratio of the Raman spectrum D peak to the G peak of the negative electrode active material Id / Ig satisfies: 0.2≤Id / Ig≤0.6, where Id represents the intensity of the Raman spectrum at 1300 cm -1 ~1400cm -1 The characteristic peak intensity at 1525 cm - 1 ~1625cm -1 The characteristic peak intensity at . Optionally, 0.2≤Id / Ig≤0.4. The degree of graphitization G of the negative electrode active material will affect the surface defectivity of the material. At a lower degree of graphitization G, the surface defectivity of the negative electrode active material is relatively large, which will affect the battery's cycle performance and low-temperature lithium deposition performance to a certain extent. Therefore, on the basis of limiting the degree of graphitization G and the electrolyte additives, the negative electrode active material satisfies: 0.2≤Id / Ig≤0.6, which can further improve the low-temperature lithium deposition performance of the secondary battery and improve the cycle performance of the secondary battery.

[0021] In some embodiments, the negative electrode active material includes at least one of natural graphite or artificial graphite.

[0022] In some embodiments, the compaction density of the negative electrode sheet satisfies: 1.3 g / cm 3 ≤PD≤1.78g / cm 3 The degree of graphitization will affect the compaction density of the negative electrode active material powder, and thus affect the compaction density of the electrode sheet. On the basis of limiting the graphitization degree G of the negative electrode active material and the electrolyte additives, the compaction density of the negative electrode sheet meets the following requirements: 1.30g / cm 3 ≤PD≤1.78g / cm 3 , which can make the electrolyte infiltration better and facilitate the deintercalation and extraction of lithium ions, thereby further improving the battery's cycle performance and low-temperature performance.

[0023] In some embodiments, the negative electrode pole piece has an OI value of 6 ≤ ≤ 18. The graphitization degree G of the negative electrode active material also affects the OI value of the pole piece. The higher the graphitization degree G, the greater the OI value. Based on the defined graphitization degree G and the electrolyte additives, a negative electrode pole piece having an OI value of 6 ≤ ≤ 18 can enable lithium ions to be intercalated and deintercalated in all directions, further improving the battery's cycling performance and low-temperature performance. Alternatively, the OI value is 7 ≤ ≤ 15.

[0024] In a second aspect of the present application, an electrical device is provided, comprising the secondary battery provided in any one of the first aspects above. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without creative work.

[0026] FIG1 is a cycle performance diagram of the lithium-ion batteries provided in Example 1 and Comparative Example 1 of the present application. DETAILED DESCRIPTION

[0027] The present application provides a secondary battery, comprising a negative electrode plate and an electrolyte, wherein the negative electrode active material in the negative electrode plate has a graphitization degree G, and the electrolyte comprises 1,3-propane sultone and fluoroethylene carbonate. Based on the mass of the electrolyte, the mass percentage of 1,3-propane sultone is X%, and the mass percentage of fluoroethylene carbonate is Y%, wherein X>0.2×G+Y, and 1.2≤Y≤4.2.

[0028] The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer located on one or both surfaces of the negative electrode current collector. The "surface" here can be the entire area of ​​the negative electrode current collector or a portion of the negative electrode current collector. This application is not particularly limited as long as the purpose of this application can be achieved. The negative electrode active material can refer to: a secondary battery is disassembled to obtain a negative electrode sheet, the negative electrode active material layer on the negative electrode sheet is scraped off, and then fired in an air atmosphere at a temperature of 400°C. The final powder material is the negative electrode active material.

[0029] The negative electrode active material has a graphitization degree G, which can be detected by XRD and then calculated.

[0030] Since the degree of graphitization of the negative electrode active material affects the interlayer spacing of the active material graphite, the interlayer spacing affects the intercalation and deintercalation of active ions (such as lithium ions), which in turn affects the cycle performance of the secondary battery, the cycle performance of the secondary battery can be improved by regulating the range of graphitization. The degree of graphitization is related to the interlayer spacing of the negative electrode active material. The interlayer spacing of the negative electrode active material affects the degree of reaction between the negative electrode active material and the electrolyte, which in turn affects the intercalation / deintercalation of active ions in another dimension, affecting the cycle performance and low-temperature lithium precipitation performance of the secondary battery. Therefore, in this application, based on the mass of the electrolyte, the mass percentage of fluoroethylene carbonate is between 1.2% and 4.2%, which can promote the formation of the negative electrode film, and the impedance of the negative electrode film formation is low and the kinetics are very good, but its addition will produce side reactions; therefore, further adding 1,3-propane sultone to the electrolyte, and X>0.2×G+Y, can inhibit the generation of side reactions to a certain extent, and make the film formation quality of the positive and negative electrodes higher, so that the cycle performance and low-temperature lithium precipitation performance of the secondary battery are better. As an example, the mass percentage of fluoroethylene carbonate is 1.2%, 1.5%, 2%, 2.2%, 2.5%, 2.8%, 3%, 3.2%, 3.5%, 3.8%, 4%, 4.2%, or a value within a range consisting of any two of these values. Optionally, 1.4≤Y≤3.5.

[0031] In some embodiments, the electrolyte comprises 1,3-propane sultone and fluoroethylene carbonate. Based on the mass of the electrolyte, the mass percentage of 1,3-propane sultone is X% and the mass percentage of fluoroethylene carbonate is Y%, wherein X>0.2×G+Y, 1.2≤Y≤4.2, and 1.7≤X≤5.1. While satisfying X>0.2×G+Y, the mass percentage of fluoroethylene carbonate is between 1.2% and 4.2%, and the mass percentage of 1,3-propane sultone is between 1.7% and 5.1%. This can improve the coordination between 1,3-propane sultone and fluoroethylene carbonate, further improve the film formation quality of the positive and negative electrodes, alleviate the side reaction problems of the secondary battery, and further improve the cycle performance and low-temperature lithium deposition performance of the secondary battery.

[0032] As an example, based on the mass of the electrolyte, the mass percentage of 1,3-propane sultone is 1.7%, 2.0%, 2.2%, 2.5%, 2.8%, 3%, 3.2%, 3.5%, 3.8%, 4%, 4.2%, 4.5%, 4.8%, 5.1%, or a value within a range consisting of any two of these values. Optionally, the mass percentage of 1,3-propane sultone is 1.8% to 4.1%.

[0033] In some embodiments, the electrolyte comprises 1,3-propane sultone and fluoroethylene carbonate, with the mass percentage of 1,3-propane sultone being X% and the mass percentage of fluoroethylene carbonate being Y%, based on the mass of the electrolyte, where X > 0.2 × G + Y, 1.2 ≤ Y ≤ 4.2, and 91.8% < G ≤ 97%. A high degree of graphitization in the negative electrode active material reduces the degree of side reactions with the electrolyte, resulting in a thinner SEI film. However, a high degree of graphitization results in a smaller interlayer spacing, which expands significantly upon lithium insertion, making the SEI film susceptible to rupture and hindering the insertion / extraction of lithium ions. Therefore, controlling X > 0.2 × G + Y, 1.2 ≤ Y ≤ 4.2, and the degree of graphitization of the negative electrode active material to between 91.8% and 97% can improve the film formation stability of the SEI film, facilitate interfacial diffusion of lithium ions, and thus enhance the insertion / extraction of lithium ions at low temperatures, further improving the cycling performance and low-temperature lithium deposition performance of the secondary battery.

[0034] As an example, the degree of graphitization G of the negative electrode active material is 91.8%, 92%, 92.2%, 92.5%, 92.8%, 93%, 93.2%, 93.5%, 94%, 94.5%, 95%, 95.5%, 96%, 96.5%, 97%, 97.5%, 98%, 98.5%, 99%, 99.5%, or a value within a range consisting of any two of these values. Optionally, 93.5%≤G≤96%.

[0035] In the present application, the mass percentage of each component in the electrolyte is usually controlled when the electrolyte is configured. After the battery has been charged and discharged, the components in the electrolyte may change slightly, but still within the aforementioned range. The mass percentage of each component in the electrolyte of the present application can also be the mass percentage of the electrolyte in the battery after disassembly after charging and discharging. The detection method can be: first discharge the battery, place it in a drying oven after the discharge is completed, cut off the tabs and packaging bag, and then place it in a centrifuge for centrifugation to extract the electrolyte in the battery. The extracted electrolyte is analyzed for components using a gas chromatograph-mass spectrometer to obtain the additive components and mass percentages in the electrolyte. The mass percentages of each component are calculated based on the mass test of the electrolyte.

[0036] In the present application, other components may be added to the electrolyte. The electrolyte lithium salt also includes a lithium salt and a non-aqueous solvent. The lithium salt may include at least one of LiPF6, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, Li2SiF6, lithium bis(oxalatoborate) (LiBOB), or lithium difluoroborate. The present application does not particularly limit the mass percentage of the lithium salt in the electrolyte, as long as the purpose of the present application can be achieved. As an example, based on the mass of the electrolyte, the mass percentage of the lithium salt is 10%-15%. The electrolyte may further include a sodium salt and a non-aqueous solvent, or the electrolyte may further include a lithium salt and a non-aqueous solvent. The sodium salt may include at least one of NaPF6, NaClO4, NaBCl4, NaSO3CF3, or Na(CH3)C6H4SO3. The present application does not particularly limit the concentration of the sodium salt in the electrolyte, as long as the objectives of the present application are achieved. For example, the sodium salt may be present in an amount of 2% to 15% by weight based on the mass of the electrolyte.

[0037] The present application has no special restrictions on the above-mentioned non-aqueous solvent, as long as the purpose of the present application can be achieved, for example, it may include but is not limited to at least one of carbonate compounds, carboxylate compounds, ether compounds or other organic solvents; the above-mentioned carbonate compounds may include but are not limited to at least one of chain carbonate compounds, cyclic carbonate compounds or fluorocarbonate compounds; the above-mentioned chain carbonate compounds may include but are not limited to at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC) or methylethyl carbonate (MEC); the above-mentioned cyclic carbonates may include but are not limited to at least one of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC) or vinylethylene carbonate (VEC); the fluorocarbonate compounds may include but are not limited to 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, carbon At least one of 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 above-mentioned carboxylic acid ester compound may include but is not limited to methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanolactone, valerolactone or at least one of caprolactone; the above-mentioned ether compound may include but is not limited to at least one of dibutyl ether, tetraglyme, diglyme, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1-ethoxy-1-methoxyethane, 2-methyltetrahydrofuran or tetrahydrofuran; the above-mentioned other organic solvents may include but are not limited to at least one of dimethyl sulfoxide, 1,2-dioxolane, cyclopentane, methylcyclopentane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate or trioctyl phosphate.

[0038] In some embodiments, the negative electrode active material includes at least one of natural graphite or artificial graphite.

[0039] In some embodiments, the negative electrode active material satisfies: 0.05≤CD / (372×G)×Z 50 ≤0.1, where the powder compaction density of the negative electrode active material is CD g / cm 3 In the volume-based particle size distribution of the negative electrode active material, the particle size at which the volume accumulation reaches 50% from the small particle size side is Z 50 μm. Studies have found that the degree of graphitization will affect the compaction density of the negative electrode active material, and the particle size Z 50It also affects the compaction density of the active material. Therefore, the negative electrode active material satisfies 0.05≤CD / (372×G)×Z 50 ≤0.1, which can further improve the low-temperature lithium deposition performance of the secondary battery and improve the cycle performance of the secondary battery.

[0040] CD / (372×G)×Z 50 In the formula, the unit of compacted density is g / cm 3 In the volume-based particle size distribution of the negative electrode active material, the particle size at which the volume accumulation reaches 50% from the small particle size side is Dv50, and its unit is μm, that is, Z 50 μm. In this formula, only values ​​with these units are considered, while the units themselves are ignored.

[0041] As an example, CD / (372×G)×Z 50 The value of is 0.05, 0.055, 0.06, 0.07, 0.08, 0.09, 0.095, 0.1 or a value within the range of any two of these values. Optionally, 0.06≤CD / (372×G)×Z 50 ≤0.095

[0042] In some embodiments, based on the mass of the electrolyte, the electrolyte comprises X% by mass of 1,3-propane sultone and Y% by mass of fluoroethylene carbonate, X>0.2×G+Y, 1.2≤Y≤4.2, and the powder compaction density of the negative electrode active material is 1.7 g / cm 3 ~2.0g / cm 3 Within this range, the cycle performance and low-temperature lithium deposition performance of the secondary battery can be further improved.

[0043] As an example, the powder compaction density of the negative electrode active material is 1.7 g / cm 3 , 1.72g / cm 3 , 1.74g / cm 3 , 1.76g / cm 3 , 1.78g / cm 3 , 1.8g / cm 3 , 1.82g / cm 3 、1.84g / cm 3 , 1.86g / cm 3 , 1.88g / cm 3 , 1.9g / cm 3 , 1.92g / cm 3 , 1.94g / cm 3 , 1.96g / cm 3 , 1.98g / cm 3, 2.0g / cm 3 Or a value within a range consisting of any two of these values.

[0044] In some embodiments, in the volume-based particle size distribution of the negative electrode active material, the particle size that reaches 50% of the volume accumulation from the small particle size side is in the range of 7 μm to 15 μm (Z 50 The thickness of the negative electrode active material is 35 μm to 45 μm), which can improve the comprehensive performance of the negative electrode active material and further improve the performance of the secondary battery.

[0045] As an example, in the volume-based particle size distribution of the negative electrode active material, from the small particle size side, the particle size at which the volume accumulation reaches 50% is 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm or a value within a range consisting of any two of these values.

[0046] In some embodiments, the negative electrode active material satisfies: 3.5≤(Z 90 / Z 10 )×ET≤20, where the specific surface area of ​​the negative electrode active material is Tm 2 / g, in the volume-based particle size distribution of the negative electrode active material, the particle size at which the volume accumulation reaches 10% from the small particle size side is Z 10 μm, the particle size that reaches 90% of the volume accumulation is Z 90 μm, in the particle size distribution based on the number of negative electrode active materials, the particle size that reaches 10% of the cumulative number from the small particle size side is Eμm. The graphitization degree G of the negative electrode active material will affect the specific surface area T of the negative electrode active material, thereby affecting the reactive surface between the electrolyte and the negative electrode active material. The particle distribution of the negative electrode active material will also affect the reactive surface. Therefore, based on the definition of the graphitization degree G and the electrolyte additive, the negative electrode active material satisfies: 3.5≤(Z 90 / Z 10 )×ET≤15, which can further improve the low-temperature lithium deposition performance of the secondary battery and enhance the cycle performance of the secondary battery.

[0047] (Z 90 / Z 10 )×ET formula, in the volume-based particle size distribution of the negative electrode active material, the particle size that reaches 10% of the volume accumulation from the small particle size side is Dv10, and its unit is μm, that is, Z 10 μm; In the volume-based particle size distribution of the negative electrode active material, the particle size that reaches 90% of the volume accumulation from the small particle size side is Dv90, and its unit is μm, that is, Z 90μm; In the particle size distribution based on the number of negative electrode active materials, the particle size that reaches 10% of the cumulative number from the small particle size side is Dn10, and its unit is μm, that is, Eμm; The specific surface area of ​​the negative electrode active material BET is Tm 2 / g. When calculating in this formula, only the values ​​with these units are considered, and the units themselves are ignored.

[0048] As an example, (Z 90 / Z 10 )×ET is 3.5, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 17, 20 or a value within the range of any two of these values. 90 / Z 10 )×ET≤13.

[0049] In some embodiments, in the volume-based particle size distribution of the negative electrode active material, the particle size that reaches 90% of the volume accumulation is within the range of 20 μm to 35 μm (Z 90 The thickness of the secondary battery is 20 μm to 35 μm), which can further improve the cycle performance and low-temperature lithium deposition performance of the secondary battery.

[0050] As an example, in the volume-based particle size distribution of the negative electrode active material, from the small particle size side, the particle size at which 90% of the volume accumulation is reached is 20 μm, 23 μm, 25 μm, 27 μm, 29 μm, 31 μm, 32 μm, 33 μm, 34 μm, 35 μm or a value within a range consisting of any two of these values.

[0051] In some embodiments, in the volume-based particle size distribution of the negative electrode active material, the particle size that reaches 10% of the volume accumulation from the small particle size side is in the range of 3 μm to 8 μm (Z 10 The thickness of the secondary battery is 3 μm to 8 μm), which can further improve the cycle performance and low-temperature lithium deposition performance of the secondary battery.

[0052] As an example, in the volume-based particle size distribution of the negative electrode active material, from the small particle size side, the particle size reaching 10% of the volume accumulation is 3μm, 4μm, 5μm, 5.5μm, 6μm, 7μm, 7.5μm, 8μm or a value within the range of any two of these values.

[0053] In some embodiments, in the particle size distribution based on the number of negative electrode active materials, starting from the small particle size side, the particle size of 10% of the cumulative number is in the range of 1 μm to 5 μm (E μm is 1 μm to 5 μm), which can further improve the cycle performance and low-temperature lithium deposition performance of the secondary battery.

[0054] As an example, in the particle size distribution based on the number of the negative electrode active material, from the small particle size side, the particle size at which the cumulative number of 10% is reached is 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, or a value within a range consisting of any two of these values.

[0055] In some embodiments, the value of E is less than Z 10 The value of can further improve the low-temperature lithium deposition performance of the secondary battery and improve the cycle performance of the secondary battery.

[0056] In some embodiments, the specific surface area of ​​the negative electrode active material is 1.0 m 2 / g~5.0m 2 / g range, the comprehensive performance of the negative electrode active material can be improved, and the performance of the secondary battery can be further improved.

[0057] As an example, the specific surface area of ​​the negative electrode active material is 1.0 m 2 / g, 1.4m 2 / g, 1.6m 2 / g, 2.0m 2 / g, 2.4m 2 / g, 3.2m 2 / g, 3.8m 2 / g, 4.1m 2 / g, 5.0m 2 / g or a value within a range consisting of any two of these values.

[0058] In some embodiments, the particle sphericity S of the negative electrode active material satisfies the following conditions: 0.4 ≤ S ≤ 0.95. The particle morphology of the negative electrode active material also has a certain impact on the electrical performance of the secondary battery. Spherical particles can help reduce the reactive surface area of ​​the particles, improving cycling performance and low-temperature lithium deposition performance. Based on the defined graphitization degree G and electrolyte additives, the sphericity S of the negative electrode active material satisfies the following conditions: 0.4 ≤ S ≤ 0.95, which can further improve the battery's cycling performance and low-temperature lithium deposition performance.

[0059] As an example, the particle sphericity S of the negative electrode active material is 0.4, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, or a value within a range consisting of any two of these values. Optionally, 0.48≤S≤0.7.

[0060] In some embodiments, the intensity ratio of the Raman spectrum D peak to the G peak of the negative electrode active material Id / Ig satisfies: 0.2≤Id / Ig≤0.6, where Id represents the intensity of the Raman spectrum at 1300 cm -1 ~1400cm-1 The characteristic peak intensity at 1525 cm - 1 ~1625cm -1 The characteristic peak intensity at . The degree of graphitization G of the negative electrode active material affects the material's surface defectivity. At lower degrees of graphitization G, the surface defectivity of the negative electrode active material is relatively large, which will to some extent affect the battery's cycling performance and low-temperature lithium deposition performance. Therefore, based on the defined degree of graphitization G and electrolyte additives, the negative electrode active material satisfies the following conditions: 0.2 ≤ Id / Ig ≤ 0.6, which can further improve the low-temperature lithium deposition performance and enhance the secondary battery's cycling performance.

[0061] As an example, the negative electrode active material has a Raman spectrum D peak to G peak intensity ratio Id / Ig of 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, or a value within a range consisting of any two of these values. Optionally, 0.2≤Id / Ig≤0.4.

[0062] In the present application, the negative electrode active material includes graphite, and the preparation method of graphite includes: (1) selecting petroleum coke (petroleum coke is required to have a volatile content of less than 13% by mass and a sulfur content of less than 2% by mass) as the artificial graphite raw material, first crushing the petroleum coke to a Dv50 of 7μm to 12μm, and then subjecting it to a pre-carbonization treatment at a treatment temperature of 800℃ to 1200℃ and a treatment time of ≥8h, and the volatile content after treatment is less than 5% by mass. (2) After the pre-carbonization treatment, mixing with asphalt (the asphalt addition amount is 1% to 5% by mass of the petroleum coke) and granulating, the granulation time is 1h to 3h, and the granulation temperature is 150℃ to 450℃. The granulation size and powder compaction are controlled by controlling the granulation time and granulation temperature. (3) After granulation, the mixture is evenly mixed and graphitized. The degree of graphitization is controlled by adjusting the graphitization temperature and time, and needs to be determined in combination with the tap density of the powder before graphitization. The graphitization temperature is 2000℃~3000℃, and the holding time is 12h~72h. When the graphitization degree is low, the graphitization temperature is also low and the holding time is reduced. When the graphitization degree is high, the graphitization temperature is high and the holding time is increased. The tap density of the material after granulation will also affect the graphitization effect. When the tap density is high, the temperature should be appropriately increased and the holding time should be increased. When the tap density is low, the temperature should be appropriately reduced and the holding time should be reduced. Under the same graphitization degree requirement, the tap density is different, and the graphitization temperature and holding time can also be adjusted. (4) After the graphitization is completed, the particles are shaped and graded to obtain graphite. The shaping time is 2h~8h, and the classification yield is 80%~100%.

[0063] In some embodiments, the compaction density of the negative electrode sheet satisfies: 1.3 g / cm3 ≤PD≤1.78g / cm 3 The degree of graphitization will affect the compaction density of the negative electrode active material powder, and thus affect the compaction density of the electrode sheet. On the basis of limiting the graphitization degree G of the negative electrode active material and the electrolyte additives, the compaction density of the negative electrode sheet meets the following requirements: 1.3g / cm 3 ≤PD≤1.78g / cm 3 , which can make the electrolyte infiltration better and facilitate the deintercalation and extraction of lithium ions, thereby further improving the battery's cycle performance and low-temperature performance.

[0064] As an example, the compaction density of the negative electrode sheet is 1.30 g / cm 3 , 1.35g / cm 3 , 1.40g / cm 3 , 1.45g / cm 3 , 1.50g / cm 3 , 1.55g / cm 3 , 1.60g / cm 3 , 1.65g / cm 3 , 1.70g / cm 3 , 1.75g / cm 3 , 1.78g / cm 3 Or a value within a range consisting of any two of these values.

[0065] In some embodiments, the negative electrode pole piece has an OI value of 6 ≤ ≤ 18. A portion of the negative electrode pole piece (including the negative electrode current collector and the negative electrode active material layer) is cut away, and XRD data of the negative electrode pole piece is measured with reference to JB / T 4220-2011 to obtain the peak area of ​​the 004 peak and the peak area of ​​the 110 peak. The OI value of the negative electrode pole piece = 004 peak area / 110 peak area. The 004 peak area is the characteristic peak area of ​​the XRD diffraction pattern line at 53° to 57°, and the 110 peak area is the characteristic peak area of ​​the XRD diffraction pattern line at 75° to 79°.

[0066] The graphitization degree G of the negative electrode active material will also affect the OI value of the electrode. The higher the graphitization degree, the greater the OI value. On the basis of limiting the graphitization degree G and the electrolyte additives, the negative electrode plate 6≤OI value≤18 can enable lithium ions to be deintercalated in all directions, which can further improve the battery's cycle performance and low-temperature performance.

[0067] As an example, the OI value of the negative electrode plate is 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, or a value within a range consisting of any two of these values. Optionally, 7≤OI value≤15.

[0068] As an example, the preparation method of the negative electrode plate includes: mixing the negative electrode active material (artificial graphite), additives (such as conductive agents), binders (such as styrene-butadiene rubber), and thickeners (such as sodium carboxymethyl cellulose) in a certain ratio, wherein the mass proportion of the additive is 1% to 3%, the mass proportion of the negative electrode active material is 90% to 97%, the mass proportion of the binder styrene-butadiene rubber is 1.2% to 2.2%, and the mass proportion of the thickener sodium carboxymethyl cellulose is 0.5% to 1.5%, and the mass ratio of the four components adds up to 100%, and then fully stirring and mixing in an appropriate amount of water solvent to form a uniform negative electrode slurry, coating the slurry on the negative electrode collector, drying, and cold pressing to obtain the negative electrode plate.

[0069] As an example, the negative electrode active material layer on the negative electrode sheet is scraped off and then calcined at 400° C. in an air atmosphere to obtain a powder material as the negative electrode active material.

[0070] The present application does not particularly limit the negative electrode current collector, as long as it can achieve the objectives of the present application. For example, the negative electrode current collector may comprise aluminum foil, copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, or a polymer substrate coated with a conductive metal. The conductive metal includes, but is not limited to, copper, nickel, or titanium, and the polymer substrate material includes, but is not limited to, at least one of polyethylene, polypropylene, ethylene-propylene copolymer, polyethylene terephthalate, polyethylene naphthalate, and poly(p-phenylene terephthalamide).

[0071] In this application, there is no particular limitation on the thickness of the negative electrode current collector and the negative electrode active material layer, as long as the purpose of this application can be achieved. For example, the thickness of the negative electrode current collector is 4 μm to 12 μm, and the thickness of the negative electrode active material layer on one side of the negative electrode current collector is 30 μm to 130 μm.

[0072] In certain embodiments, the present application has no particular restrictions on the above-mentioned binding agent, as long as the purpose of the present application can be achieved. For example, the binding agent may include but is not limited to polypropylene alcohol, sodium polyacrylate, potassium polyacrylate, lithium polyacrylate, polyimide, polyamide-imide, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl pyrrolidone, polyethylene, polypropylene, epoxy resin, nylon, styrene-butadiene rubber (SBR), polyvinyl alcohol (PVA), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl butyral, water-based acrylic resin, carboxymethyl cellulose (CMC) or sodium carboxymethyl cellulose (CMC-Na) etc. at least one.

[0073] In some embodiments, the negative electrode sheet can be prepared according to conventional methods in the art. For example, the graphite, conductive agent, binder, and thickener described above are dispersed in a solvent, which can be N-methylpyrrolidone (NMP) or deionized water, to form a uniform negative electrode slurry. The negative electrode slurry is then coated on the negative electrode current collector, and the negative electrode sheet is obtained through drying, cold pressing, and other processes.

[0074] Among them, the conductive agent may include but is not limited to carbon materials, metals or conductive polymers; carbon materials may include at least one of conductive carbon black (Super P), carbon nanotubes (CNTs), carbon nanofibers, carbon dots or graphene; metals may include metal powders or metal fibers of copper, iron, aluminum, etc.; conductive polymers may include at least one of polythiophene, polypyrrole, polyaniline, polyphenylene and polyphenylene ethylene.

[0075] The aforementioned negative electrode sheet, positive electrode sheet, electrolyte and separator are combined to form a secondary battery. The secondary battery has good cycle performance and low-temperature lithium deposition performance.

[0076] In some embodiments, the secondary battery may be a lithium ion secondary battery or a sodium ion secondary battery.

[0077] In some embodiments, the positive electrode plate in the present application includes a positive electrode current collector and a positive electrode active material layer provided on at least one surface of the positive electrode current collector and including a positive electrode active material; wherein the positive electrode current collector can be aluminum foil, foamed aluminum, an aluminum composite current collector (a current collector with a polymer support layer in the middle and an aluminum metal layer on both surfaces of the support layer), nickel foil, foamed nickel, etc.; the positive electrode active material can be lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium cobalt oxide, lithium iron phosphate, lithium manganese oxide, Prussian white, Prussian blue, etc.

[0078] For example, the isolation film can be made of various materials, such as PP (polypropylene), PE (polyethylene), etc.

[0079] The present application also provides an electrical device comprising the aforementioned secondary battery. The electrical device provided in the present application has a long service life due to the inclusion of the aforementioned secondary battery having high energy density, low-temperature lithium deposition performance, and cycle performance.

[0080] In some embodiments, the electrical devices may include, but are not limited to, mobile phones, laptop computers, headphones, video recorders, calculators, vehicles, ships, spacecraft, power tools, electric toys, etc. The present application does not impose any special restrictions on the above-mentioned electrical devices.

[0081] To make the purpose, technical solutions and advantages of the examples of the present application clearer, the technical solutions in the examples of the present application will be described clearly and completely below. Where specific conditions are not specified in the examples, conventional conditions or conditions recommended by the manufacturer are used. Where the manufacturer of the reagents or instruments is not specified, they are all conventional products that can be purchased commercially.

[0082] Example 1-1

[0083] (1) Preparation of artificial graphite

[0084] Petroleum coke (with a volatile content of 10.0% by mass and a sulfur content of 1.2% by mass) was crushed to a Dv50 of 9.0 μm and then pre-carbonized at 1000°C for 10 hours. After this treatment, it was mixed with asphalt (the asphalt addition amount was 3% of the mass of the petroleum coke) and granulated at 300°C for 2 hours. After granulation, it was graphitized at 2900°C for 28 hours. It was then shaped for 4 hours with a classification yield of 90%, resulting in artificial graphite, a negative electrode active material.

[0085] (2) Preparation of negative electrode sheet

[0086] The negative electrode active material, artificial graphite, the additive conductive carbon black (Super P), the binder styrene-butadiene rubber (SBR), and the thickener sodium carboxymethyl cellulose (CMC) were mixed in a specific ratio: 95% artificial graphite, 1.5% additive, 2.0% SBR, and 1.5% CMC. The mixture was then thoroughly stirred in an appropriate amount of deionized water to form a negative electrode slurry with a solid content of 40 wt%. The mixture was then mixed evenly. The negative electrode slurry was evenly coated on both surfaces of a 6 μm thick copper foil for the negative electrode current collector. The foil was then dried at 85°C for 4 hours to produce a negative electrode sheet with a single-sided negative electrode active material layer of 50 μm. After cold pressing, cutting, and slitting, the sheet was dried under vacuum at 120°C for 12 hours to obtain a negative electrode sheet measuring 76.6 mm x 875 mm.

[0087] (3) Preparation of positive electrode sheet

[0088] Lithium iron phosphate, acetylene black (a conductive agent), and polyvinylidene fluoride (PVDF) (a binder) were mixed in a certain ratio, with the weight proportion of lithium iron phosphate being 96.3%, the weight proportion of the conductive agent being 2.2%, and the weight proportion of PVDF being 1.5%. N-methylpyrrolidone (NMP) was added as a solvent and stirred evenly to prepare a positive electrode slurry with a solid content of 72 wt%. The positive electrode slurry was evenly coated on both surfaces of a 13 μm thick positive electrode current collector aluminum foil and dried at 85°C to obtain a positive electrode sheet with a single-sided positive electrode active material layer thickness of 80 μm. After cold pressing, cutting, and slitting, the sheet was dried under vacuum at 85°C for 4 hours to obtain a positive electrode sheet with a size of 74 mm × 867 mm.

[0089] (4) Preparation of electrolyte

[0090] 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:PC:EMC:DEC = 1:3:3:3. 1,3-Propane sultone and fluoroethylene carbonate were then added, dissolved, and thoroughly stirred. Lithium salt LiPF6 was then added and mixed uniformly to obtain an electrolyte. The mass percentage of LiPF6 was 11.0%, the mass percentage of 1,3-Propane sultone was 2.1%, and the mass percentage of fluoroethylene carbonate was 1.9%. The mass percentages of each component were calculated based on the mass of the electrolyte.

[0091] (5) Preparation of isolation membrane

[0092] A polyethylene film with a thickness of 8 μm (supplied by Celgard) was used as the separator.

[0093] (6) Preparation of lithium-ion batteries

[0094] The positive electrode sheet, separator, and negative electrode sheet are stacked in order, with the separator positioned between the positive and negative electrodes to provide insulation. The electrodes are then wound to form an electrode assembly. After welding the tabs, the electrode assembly is packaged in an aluminum-plastic film bag and dried in an 80°C vacuum oven for 12 hours to remove moisture. The prepared electrolyte is then injected and the lithium-ion battery is produced through vacuum packaging, standing, formation, degassing, and shaping.

[0095] The differences between Examples 1-2 to 1-15, and Comparative Examples 1-1 to 1-2 and Example 1-1 are: different graphitization treatment conditions, different mass percentages of 1,3-propane sultone, and different mass percentages of fluoroethylene carbonate. See Table 1 for details.

[0096] The performance of the lithium-ion batteries provided in Examples 1-1 to 1-15 and Comparative Examples 1-1 to 1-2 was tested as shown in Table 1. The specific methods are as follows:

[0097] (1) 1000-cycle capacity retention rate (%)

[0098] Temperature: 45°C;

[0099] 1. 0.5C DC to 2.5V (not the first discharge);

[0100] 2. ---Rest 10 minutes;

[0101] 3. 0.5C CC to 3.6V, CV to 0.05C;

[0102] 4. ---Rest 10 minutes;

[0103] 5. 0.5C DC to 2.5V (first discharge);

[0104] 6. Repeat steps 2-5 1000 times;

[0105] 7. The capacity retention rate after 1000 cycles is calculated as: 1000th discharge / first discharge × 100%.

[0106] (2) Low temperature lithium deposition performance

[0107] The lithium-ion battery under test is tested at -5°C, left to rest for 5 minutes, and then charged at a constant current of 1.6C to 3.60V. Then, it is charged at a constant voltage of 3.60V to 0.05C; left to rest for 5 minutes, and then discharged at a constant current of 1.0C to 2.5V, and left to rest for 5 minutes. After repeating the above charge and discharge process 10 times, the battery is fully charged, disassembled in a dry room, and photographed to record the state of the negative electrode. The degree of lithium plating is determined based on the state of the negative electrode after full charge and disassembly. If the entire negative electrode appears golden yellow and the gray area is less than 5%, it is judged that there is no lithium plating. If the gray area of ​​the negative electrode exceeds 5%, it is judged that lithium plating has occurred.

[0108] (3) Parameters of the negative electrode

[0109] Discharge the battery first. After discharge, place it in a drying oven, cut off the tabs and packaging bag, and take out the negative electrode.

[0110] (3.1)OI value

[0111] The (004) and (110) diffraction patterns of the negative electrode active material layer were measured in accordance with the Mechanical Industry Standard of the People's Republic of China, JB / T 4220-2011, "Method for Determination of Lattice Parameters of Artificial Graphite." The experimental conditions were as follows: CuKα radiation was used for X-rays, and CuKα radiation was removed by a filter or monochromator. The operating voltage of the X-ray tube was 30 kV to 35 kV, and the operating current was 15 mA to 20 mA. The scanning speed of the counter was 1 / 4° / min. When recording the 004 diffraction pattern, the scanning range of the diffraction angle 2θ was 53° to 57°. When recording the 110 diffraction pattern, the scanning range of the diffraction angle 2θ was 75° to 79°. The peak area obtained from the (004) diffraction pattern was recorded as C004. The peak area obtained from the (110) diffraction pattern was recorded as C110. Calculate the ratio of C004 / C110 of the negative electrode active material, which is the OI value of the negative electrode sheet.

[0112] (3.2) Compacted density

[0113] Compaction density = mass / volume × 100%. Take the negative electrode sheet, and then use a sheet punching machine to punch out small discs. The radius of the small disc is 1 cm. The punched small disc is double-sided. Test its double-sided thickness L cm. Weigh the mass of the small disc mg. Then soak and wash the small disc with soapy water to remove the active material layer, leaving only a clean small disc copper foil. Test the copper foil thickness L1 and weigh the copper foil weight m1 g. Then calculate the compaction density according to the formula PD = (m-m1) / ((3.14×12)×(L-L1)). Repeat the operation 5 times and take the average value to obtain the compaction density PD of the negative electrode sheet.

[0114] (4) Parameters of negative electrode active materials

[0115] The negative electrode active material layer on the disassembled negative electrode sheet is scraped off, and then fired at 400°C in an air atmosphere for 4 hours. The final powder material obtained is the negative electrode active material.

[0116] (4.1) Graphitization degree G test

[0117] High-purity silicon powder was used as the standard sample. The negative electrode active material sample and the silicon standard sample were mixed in a weight ratio of 5:1. The XRD test obtained the 002 peak of graphite and the 111 peak of silicon. The 002 peak of graphite obtained by the test was calibrated. The calibrated 002 crystal plane spacing d 002 The graphitization degree of the negative electrode active material is indirectly calculated using the formula G = (0.344-d 002 ) / (0.344-0.3354), 0.3440 represents the interlayer spacing of completely ungraphitized carbon, and 0.3354 represents the interlayer spacing of ideal graphite, both in nm.

[0118] (4.2) Powder compaction density CD g / cm 3 test

[0119] The powder compaction density test standard refers to GB / T 24533-2009, "Graphite-Based Anode Materials for Lithium-Ion Batteries." The specific test method is: Weigh 1.0000±0.0500g of the negative electrode active material sample and place it in a test mold (CARVER#3619 (13mm)). The sample is then placed in a 5.0-ton Sansi Zongheng UTM7305 test apparatus with a pressure increase rate of 10mm / min, a pressure increase hold time of 30s, a pressure relief rate of 30mm / min, and a pressure relief hold time of 10s. The compaction density is calculated as: Compacted density = material mass / (material load area × sample thickness).

[0120] (4.3) Particle size distribution Dv10(Z 10 μm)、Dv50(Z 50 μm)、Dv90(Z 90 μm), Dn10 (Eμm) test

[0121] The particle size test method refers to GB / T 19077-2016. The specific process is to weigh 0.8g of the negative electrode active material sample and mix it evenly with 20mL of deionized water and a trace amount of dispersant. After placing it in an ultrasonic device for 5 minutes, the solution is poured into the sampling system Hydro 2000SM for testing. The test equipment used is the Mastersizer 3000 produced by Malvern. During the test, when the laser beam passes through the dispersed particle sample, the particle size measurement is completed by measuring the intensity of the scattered light. The data is then used to analyze and calculate the particle size distribution that forms the scattering spectrum. The refractive index of the particles used in the test is 1.8. One sample is tested three times, and the particle size is finally taken as the average of the three tests.

[0122] (4.4) Specific surface area BET (T m 2 / g)test

[0123] The test method for specific surface area refers to GB / T 19587-2017. The specific process is to weigh 0.5g to 2g of the negative electrode active material sample (the sample weight should at least cover 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 12mm). After pre-treatment at 200°C for 2h, it is placed 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.

[0124] (4.5) Sphericity S

[0125] The negative electrode active material particles are thoroughly diluted with alcohol and then coated onto copper foil or silicon wafers. After drying, they are observed using a scanning electron microscope (SEM). Optical or SEM images are taken, and the images are then analyzed for particle sphericity. Particle size is defined as the ratio of the circular perimeter of the particle's equivalent projected area to the actual perimeter of its projection. The SEM magnification is 1000x, and the number of particles within the image is no less than 100. The average sphericity of these particles is calculated to determine the particle sphericity S of the active material.

[0126] Table 1

[0127] From the comparison of Examples 1-1 to 1-15 and Comparative Examples 1-1 to 1-2, it can be seen that in the lithium-ion battery of the present application, the mass percentage content of 1,3-propane sultone X% and the mass percentage content of fluoroethylene carbonate Y% in the electrolyte satisfy X>0.2×G+Y, 1.2≤Y≤4.2, which can improve the low-temperature lithium precipitation problem of the battery and improve the cycle performance of the battery.

[0128] A comparison of Examples 1-1 to 1-15 shows that the mass percentage of fluoroethylene carbonate is between 1.4% and 3.5%, which can further improve the battery's cycle performance while meeting the battery's low-temperature lithium deposition performance. Furthermore, the electrolyte contains X% by mass of 1,3-propane sultone and Y% by mass of fluoroethylene carbonate, where X > 0.2 × G + Y, and the mass percentage of fluoroethylene carbonate is between 1.4% and 2.4%, which can further improve the battery's cycle performance.

[0129] Comparison of Examples 1-6 to 1-8 shows that, when the degree of graphitization and the mass percentage of fluoroethylene carbonate are the same, the mass percentage of 1,3-propane sultone is higher (

[0130] The difference between Example 2-1 to Example 2-5 and Example 1-1 is that the mass percentage of the volatile matter of the petroleum coke is different, and the Dv50 size of the petroleum coke after crushing is different. See Table 2 for details.

[0131] The performance was tested according to the aforementioned method, and the results are shown in Table 2.

[0132] Table 2

[0133] Comparison of Example 1-1 with Example 2-1 to Example 2-5 shows that the negative electrode active material of the battery satisfies 0.05≤CD / (372×G)×Z 50≤0.1, which can further improve the cycle performance of the battery. The degree of graphitization will affect the compaction density of the negative electrode active material, and the particle size Z 50 It also affects the compaction density of the active material. Therefore, the negative electrode active material satisfies 0.05≤CD / (372×G)×Z 50 ≤0.1, which can further improve the low-temperature lithium deposition performance of the secondary battery and improve the cycle performance of the secondary battery.

[0134] The differences between Example 3-1 to Example 3-6 and Example 2-4 are: different amounts of asphalt added, different granulation times and different granulation temperatures, see Table 3 for details.

[0135] The performance was tested according to the aforementioned method, and the results are shown in Table 3.

[0136] Table 3

[0137] Comparison of Example 2-4 with Example 3-1 to Example 3-6 shows that the negative electrode active material of the battery satisfies 3.5≤(Z 90 / Z 10 )×ET≤20, which can further improve the cycle performance of the battery. The graphitization degree G of the negative electrode active material will affect the specific surface area T of the negative electrode active material, thereby affecting the reactive surface between the electrolyte and the negative electrode active material. The particle distribution of the negative electrode active material will also affect the reactive surface. Therefore, on the basis of limiting the graphitization degree G and the electrolyte additives, the negative electrode active material satisfies: 3.5≤(Z 90 / Z 10 )×ET≤20, which can further improve the low-temperature lithium deposition performance of the secondary battery and improve the cycle performance of the secondary battery.

[0138] The difference between Example 4-1 to Example 4-6 and Example 3-5 is that the shaping time and the classification yield are different, see Table 4 for details.

[0139] The performance was tested according to the aforementioned method, and the results are shown in Table 4.

[0140] Table 4

[0141] Comparing Examples 3-5 with Examples 4-1 to 4-6, it can be seen that the negative electrode active material of the battery satisfies 0.4≤S≤0.95, which can further improve the cycle performance of the battery. The particle morphology of the negative electrode active material will also have a certain impact on the electrical performance of the secondary battery. The spherical shape of the particles is conducive to reducing the reactive surface of the particles, improving the cycle performance and low-temperature lithium precipitation performance. On the basis of limiting the graphitization degree G and the electrolyte additives, the sphericity S of the negative electrode active material satisfies: 0.4≤S≤0.95, which can further improve the cycle performance and low-temperature lithium precipitation performance of the battery. The negative electrode active material satisfies 0.2≤Id / Ig≤0.6, which can improve the cycle performance of the battery; on the basis of limiting the graphitization degree G and the electrolyte additives, the negative electrode active material satisfies: 0.2≤Id / Ig≤0.6, which can further improve the low-temperature lithium precipitation performance of the secondary battery and improve the cycle performance of the secondary battery.

[0142] The difference between Example 5-1 to Example 5-6 and Example 4-5 is that the pressing conditions of the negative electrode sheets are different, which ultimately results in different OI values ​​and compaction densities of the negative electrode sheets. Please refer to Table 5 for details.

[0143] The performance was tested according to the aforementioned method, and the results are shown in Table 5.

[0144] Table 5

[0145] Comparison between Example 4-5 and Example 5-1 to Example 5-6 shows that the negative electrode sheet of the battery meets the compaction density of 1.30 g / cm 3 ≤PD≤1.78g / cm 3 , can improve the cycle performance of the battery; the negative electrode of the battery meets the OI value ≤ 18, which can improve the cycle performance of the battery. This is because the compaction density of the electrode meets 1.30g / cm 3 ≤PD≤1.78g / cm 3 , which can make the electrolyte infiltration effect better, make it easier to realize lithium ion deintercalation, and the electronic conductivity effect is also better; in addition, the OI value of 6≤the electrode piece≤18 can make the orientation distribution of the negative electrode active material on the negative electrode current collector more uniform, and deintercalation can be realized in all directions, thereby improving the cycle performance of the battery.

[0146] The embodiments described above are only some of the embodiments of the present application, rather than all of the embodiments. The detailed description of the embodiments of the present application is not intended to limit the scope of the application claimed for protection, but only represents selected embodiments of the present application.

Claims

1. A secondary battery, characterized in that: The invention comprises a negative electrode plate and an electrolyte, wherein the negative electrode active material in the negative electrode plate has a graphitization degree G, and the electrolyte comprises 1,3-propane sultone and fluoroethylene carbonate. Based on the mass of the electrolyte, the mass percentage of the 1,3-propane sultone is X%, and the mass percentage of the fluoroethylene carbonate is Y%, wherein X>0.2×G+Y, and 1.2≤Y≤4.

2.

2. The secondary battery according to claim 1, characterized in that: 1.7≤X≤5.1 or 91.8%<G≤97%.

3. The secondary battery according to claim 1 or 2, characterized in that: The secondary battery satisfies at least one of the following conditions: 1)93.5％≤G≤96％； 2) 1.8 ≤ X ≤ 4.1; or 3)1.4≤Y≤3.5。 4. The secondary battery according to any one of claims 1 to 3, characterized in that: The negative electrode active material satisfies at least one of the following conditions: 4) 0.05 ≤ CD / (372×G)×Z 50 ≤0.1, wherein the powder compaction density of the negative electrode active material is CD g / cm 3 In the volume-based particle size distribution of the negative electrode active material, the particle size at which the volume accumulation reaches 50% from the small particle size side is Z 50 μm; optionally, 0.06≤CD / (372×G)×Z 50 ≤0.095; or 5)3.5≤(Z 90 / Z 10 )×ET≤20, wherein the specific surface area of ​​the negative electrode active material is Tm 2 / g, in the volume-based particle size distribution of the negative electrode active material, the particle size that reaches 10% of the volume accumulation from the small particle size side is Z 10 μm, the particle size that reaches 90% of the volume accumulation is Z 90 μm, in the particle size distribution based on the number of the negative electrode active material, the particle size that reaches 10% of the cumulative number from the small particle size side is Eμm; optionally, 5≤(Z 90 / Z 10 )×ET≤13.

5. The secondary battery according to any one of claims 1 to 4, characterized in that: The negative electrode active material satisfies at least one of the following conditions: 6) The particle sphericity S of the negative electrode active material satisfies: 0.4≤S≤0.95; optionally, 0.48≤S≤0.7; or 7) The intensity ratio of the D peak to the G peak of the Raman spectrum of the negative electrode active material satisfies the condition: 0.2≤Id / Ig≤0.6, where Id represents the intensity of the Raman spectrum at 1300cm -1 ~1400cm -1 The characteristic peak intensity at 1525cm -1 ~1625cm -1 Characteristic peak intensity at; preferably, 0.2≤Id / Ig≤0.

4.

6. The secondary battery according to any one of claims 1 to 5, characterized in that: The negative electrode active material satisfies at least one of the following conditions: 8) The powder compaction density of the negative electrode active material is CD g / cm 3 , 1.7≤CD≤2.0; or 9) In the volume-based particle size distribution of the negative electrode active material, the particle size at which the volume accumulation reaches 50% from the small particle size side is Z 50 μm, 7≤Z 50 ≤15.

7. The secondary battery according to any one of claims 1 to 6, characterized in that: The negative electrode active material satisfies at least one of the following conditions: 10) In the particle size distribution based on the number of the negative electrode active material, the particle size that reaches 10% of the cumulative number from the small particle size side is E μm, 1≤E≤5; 11) In the volume-based particle size distribution of the negative electrode active material, the particle size that reaches 90% of the volume accumulation from the small particle size side is Z 90 μm, 20≤Z 90 ≤35; or 12) In the volume-based particle size distribution of the negative electrode active material, the particle size that reaches 10% of the volume accumulation from the small particle size side is Z 10 μm, 3≤Z 10 ≤8.

8. The secondary battery according to any one of claims 1 to 7, characterized in that: The negative electrode sheet satisfies at least one of the following conditions: 13) The compaction density of the negative electrode sheet meets the following requirements: 1.30 g / cm 3 ≤PD≤1.78g / cm 3 ;or 14) The OI value of the negative electrode plate satisfies: 6≤OI value≤18.

9. The secondary battery according to any one of claims 1 to 8, characterized in that: The negative electrode active material includes at least one of natural graphite or artificial graphite.

10. An electrical device, characterized in that: The invention comprises the secondary battery according to any one of claims 1 to 9.

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