Secondary battery and electric equipment

Abstract

The invention relates to the technical field of batteries, and discloses a secondary battery and electric equipment.The secondary battery comprises a positive plate, a negative plate, a diaphragm and electrolyte; the positive plate, the negative plate and the diaphragm are laminated or wound to form a battery cell, the number n of layers of the battery cell is more than or equal to 50 and less than or equal to 80, and the thickness of the battery cell is 5-15mm; the electrolyte comprises a solvent, the solvent comprises a linear solvent with 5-6 carbon atoms, the mass ratio of the linear solvent with 5-6 carbon atoms in the electrolyte is S3, and S3 is larger than or equal to 5% and smaller than or equal to 70%; the positive plate comprises a positive current collector and a positive active layer coated on the surface of at least one side of the positive current collector, and the positive active layer comprises a positive active material; the positive electrode active material comprises an Ni element, and the mass ratio of the Ni element in the positive electrode active material is w; 0.3 < = S3 / w < = 1.5. According to the lithium ion battery, gas production of the battery can be well inhibited through optimized matching of the electrolyte and the positive electrode active material in the lithium ion battery, and the risk of thermal runaway is reduced.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of batteries, in particular to a secondary battery and an electric device. BACKGROUND

[0002] Compared with a lithium iron phosphate battery, a ternary lithium battery has higher energy density, smaller volume, can more effectively support long-time power demand of an electric device, and has large-power charging and discharging capacity, and is the most suitable power supply device for low-altitude aircraft, humanoid robots and other devices.

[0003] However, the low-altitude aircraft, humanoid robots and other devices need to perform large-power charging and discharging when working, for example, need to discharge at a rate of 10C or more; when performing large-power charging and discharging, due to the existence of internal resistance, the battery has high temperature rise, and the surface temperature of the battery may reach 40-80 DEG C; and these devices need to work in hot summer, that is, the battery needs to operate in a high-temperature environment; the battery has large temperature rise superimposed on the ambient temperature, and in a serious case, the surface temperature of the battery can reach 80 DEG C or more, so that the battery is more likely to produce gaseous by-products, and in a serious case, explosion and other thermal safety hazards occur, causing serious safety problems. SUMMARY

[0004] Therefore, the application provides a secondary battery to solve the problem of thermal safety hazards caused by the production of gaseous by-products when the battery operates under large-power charging and discharging and high-temperature environment; thereby reducing the production of gaseous by-products and reducing the risk of thermal runaway.

[0005] In a first aspect, the application provides a secondary battery, comprising a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte; the positive electrode sheet, the negative electrode sheet and the separator are formed into an electric core by lamination or winding, the positive electrode sheet comprises a positive electrode current collector and a plurality of positive electrode tabs extending from the positive electrode current collector, the negative electrode sheet comprises a negative electrode current collector and a plurality of negative electrode tabs extending from the negative electrode current collector; the number of layers n of the electric core satisfies: 50≤n≤80, and the thickness of the electric core is 5-15 mm.

[0006] The electrolyte comprises a solvent, the solvent comprises a linear solvent with 5-6 carbon atoms, and the mass fraction of the linear solvent with 5-6 carbon atoms in the electrolyte is S3, and 5%≤S3≤70%; The positive electrode sheet further comprises a positive electrode active layer coated on at least one side surface of the positive electrode current collector, and the positive electrode active layer comprises a positive electrode active material; the positive electrode active material comprises Ni element, and the mass fraction of the Ni element in the positive electrode active material is w; 0.3≤S3 / w≤1.5.

[0007] wherein, for the stacked cell, the number of layers of the cell refers to the number of positive or negative electrode sheets; for the wound cell, the number of layers of the cell refers to the number of folds of the positive or negative electrode sheet.

[0008] In an optional embodiment, 15%≤S3≤50%; and / or, the positive active material is LiNi x Co y Mn z M k O2, wherein 0.3≤x≤0.9, preferably 0.5≤x≤0.8; 0≤y≤1, 0≤z≤1, 0≤k≤0.05, and x+y+z+k=1, M is selected from one or more of Fe, Mg, Cu, Zn, Al, Ti, Sn, B, Ga, Cr, Sr, V, Zr; and / or, the linear solvent of 5-6 carbon atoms includes one or more of diethyl carbonate (DEC), ethyl propyl carbonate, propyl propionate (PP), ethyl butyrate, methyl trimethylacetate, ethyl isobutyrate; and / or, 20%≤w≤55%.

[0009] In an optional embodiment, the solvent further includes a cyclic carbonate, the cyclic carbonate includes at least one of ethylene carbonate (EC) and propylene carbonate (PC), the content of ethylene carbonate (EC) is S1, and the content of propylene carbonate (PC) is S2; 0.01%≤S1≤30%; 0.01%≤S2≤30%; and / or, 0.1≤S1 / S2≤10, preferably 0.15≤S1 / S2≤5; and / or, 10%≤S1+S2≤40%, preferably 15%≤S1+S2≤35%.

[0010] In an optional embodiment, the electrolyte further includes a first additive, the mass ratio of the first additive in the electrolyte is S4, 0.1%≤S4≤6%, preferably 0.5%≤S4≤5%; the first additive includes one or more of 1,3-propane sultone, propylene-1,3-sulfonic acid lactone, ethylene sulfate, ethylene sulfite, thiophene; and / or, the electrolyte further includes a second additive, the mass ratio of the second additive in the electrolyte is S5, 0.1%≤S5≤4%, preferably 0.5%≤S5≤3%; the second additive includes one or more of vinylene carbonate, vinyl ethylene carbonate, fluoroethylene carbonate, difluoroethylene carbonate.

[0011] In an alternative embodiment, the electrolyte further comprises a lithium salt, the lithium salt comprising one or more of lithium hexafluorophosphate (LiPF6), lithium bisfluorosulfonylimide (LiFSI), lithium bis(trifluoromethylsulfonyl)imide (LiTFSI), the mass ratio of the lithium salt in the electrolyte being S6, 8%≤S6≤20%, preferably 10%≤S6≤18%.

[0012] In an alternative embodiment, the separator comprises a base film and a glue layer, the coverage of the glue layer in the separator being m, 20%≤m≤100%, preferably 0.05≤S6 / m≤1. And / or, the porosity of the separator is controlled to be 30%-50%.

[0013] In an alternative embodiment, the doping element in the positive electrode active material comprises Al element, preferably Al and Ti, the doping amount of the doping element in the positive electrode active material being within 1%, preferably the doping content of Al element in the positive electrode active material being 500-3000ppm. And / or, the positive electrode active material is a single crystal material.

[0014] In an alternative embodiment, the average particle size of the positive electrode active material is 3-7 μm, and the particle size distribution is: 1≤Dv10≤3, 4≤Dv50≤6, 8≤Dv90≤15. And / or, the thickness of the single-sided positive electrode active layer in the positive electrode sheet is h1 μm, 55≤h1≤75.

[0015] In an alternative embodiment, the negative electrode sheet comprises a negative electrode current collector and a negative electrode active layer coated on at least one side surface of the negative electrode current collector, the negative electrode active layer comprising a negative electrode active material; The average particle size of the negative electrode active material is 4-8 μm, and the particle size distribution is: 2≤D10≤4, 4≤D50≤8, 9≤D90≤15; and / or, the thickness of the single-sided negative electrode active layer in the negative electrode sheet is h2 μm, 60≤h2≤80. Preferably, 1≤h2 / h1≤1.2.

[0016] In a second aspect, the present application provides a power utilization device comprising the above-mentioned secondary battery.

[0017] Advantages: The secondary battery provided by the application comprises a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte; the positive electrode sheet, the negative electrode sheet and the separator are stacked or wound to form a battery cell, the positive electrode sheet comprises a positive electrode current collector and a plurality of positive electrode tabs extending from the positive electrode current collector, the negative electrode sheet comprises a negative electrode current collector and a plurality of negative electrode tabs extending from the negative electrode current collector; the number of layers n of the battery cell satisfies 50≤n≤80, and the thickness of the battery cell is 5-15 mm; the solvent of the electrolyte comprises a linear solvent with 5-6 carbon atoms in a mass ratio of S3, the positive electrode active material comprises Ni elements in a mass ratio of w, and 5%≤S3≤70%, 0.3≤S3 / w≤1.5 are controlled. The battery cell of the application adopts a multi-tab structure, the number of layers of the battery cell is related to the number of reaction tabs on the side, and the multi-tab structure effectively meets large-rate charging and discharging. By controlling the number of layers and the thickness of the battery cell within a suitable range, the large-rate charging and discharging is met, and the battery cell temperature rise is effectively prevented from being too high, and the safety is improved. At the same time, the linear solvent with 5-6 carbon atoms has a relatively high content of C atoms, a relatively large molecular volume, a relatively stable molecule, a relatively small Brownian motion and a relatively high boiling point, and is not easy to be oxidized to produce gas. At the same time, due to the relatively large molecular volume of the solvent, it is difficult to enter the solvation structure of lithium ions, and when lithium ions are removed or embedded from the active sites of the positive electrode, the solvent will not migrate to the active sites of the positive electrode with the lithium ions, so it will not be oxidized by the positive electrode. In addition, the linear solvent with 5-6 carbon atoms has good oxidation stability itself, and when the molecule is adsorbed on the active sites on the surface of the positive electrode, such as the exposed Ni atoms on the surface of the positive electrode, the molecule will not be oxidized, and other molecules (such as EC molecules in the electrolyte) are also prevented from reacting at the active sites. Therefore, when w is larger, the content of Ni in the positive electrode is higher, and the exposed active sites are more, which is more prone to oxidize the electrolyte; when S3 is smaller, only a small number of Ni active sites are covered by the solvent, causing other components to be oxidized. Therefore, by comprehensively adjusting the mass ratio S3 of the linear solvent with 5-6 carbon atoms in the electrolyte and the mass ratio w of Ni elements in the positive electrode active material, 5%≤S3≤70%, 0.3≤S3 / w≤1.5, the battery gas production can be well inhibited, the battery expansion can be reduced, and the large-rate charging and discharging can be realized by the cooperation of the structure of the battery cell, the positive electrode active material and the solvent composition in the electrolyte, while the temperature rise and the gas production of the side reaction are effectively controlled, and the safety performance is comprehensively improved. DETAILED DESCRIPTION

[0018] In order to make the purpose, technical scheme and advantages of the embodiments of the application clearer, the technical scheme of the embodiments of the application will be described clearly and completely below in combination with the embodiments of the application. Obviously, the described embodiments are part of the embodiments of the application, rather than all the embodiments of the application. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative labor belong to the scope of protection of the application.

[0019] The embodiments of the present application will be described below in conjunction with the following schemes.

[0020] According to the embodiments of the present application, in one aspect, a secondary battery is provided, comprising a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte; the positive electrode sheet, the negative electrode sheet and the separator are stacked or wound to form a battery cell, the positive electrode sheet comprises a positive electrode current collector and a plurality of positive electrode tabs extending from the positive electrode current collector, the negative electrode sheet comprises a negative electrode current collector and a plurality of negative electrode tabs extending from the negative electrode current collector; the number of layers n of the battery cell satisfies: 50≤n≤80, the thickness of the battery cell is 5-15 mm; the electrolyte comprises a solvent, the solvent comprises a linear solvent with 5-6 carbon atoms, the mass proportion of the linear solvent with 5-6 carbon atoms in the electrolyte is S3, 5%≤S3≤70%; the positive electrode sheet comprises a positive electrode current collector and a positive electrode active layer coated on at least one side surface of the positive electrode current collector, the positive electrode active layer comprises a positive electrode active material; the positive electrode active material comprises Ni element, the mass proportion of Ni element in the positive electrode active material is w; 0.3≤S3 / w≤1.5.

[0021] The secondary battery provided by the application, wherein a positive electrode sheet, a negative electrode sheet and a separator are stacked or wound to form a battery cell, the positive electrode sheet comprises a positive electrode current collector and a plurality of positive electrode tabs extending from the positive electrode current collector, the negative electrode sheet comprises a negative electrode current collector and a plurality of negative electrode tabs extending from the negative electrode current collector; the number of layers n of the battery cell satisfies: 50≤n≤80, and the thickness of the battery cell is 5-15 mm; the battery cell of the application adopts a multi-tab structure, the number of layers of the battery cell is related to the number of reaction tabs on the side, and the multi-tab structure effectively meets the large-rate charging and discharging; by controlling the number of layers and the thickness of the battery cell within a suitable range, the large-rate charging and discharging is met, and the temperature rise of the battery cell is effectively prevented, and the safety is improved. Meanwhile, the solvent of the electrolyte comprises a linear solvent with 5-6 carbon atoms with a mass ratio of S3, and the positive electrode active material comprises Ni element with a mass ratio of w, and 5%≤S3≤70%, 0.3≤S3 / w≤1.5 are controlled. The linear solvent with 5-6 carbon atoms has a relatively high content of C atoms, a relatively large molecular volume, a relatively stable molecule, a relatively small Brownian motion and a relatively high boiling point, and is not easy to be oxidized to produce gas; meanwhile, due to the relatively large molecular volume of the solvent, it is difficult to enter the solvation structure of lithium ions, and when lithium ions are removed or embedded from the active sites of the positive electrode, the solvent will not migrate to the active sites of the positive electrode with the lithium ions, so as not to be oxidized by the positive electrode. And, the linear solvent with 5-6 carbon atoms has good oxidation stability itself, when the molecule is adsorbed on the active sites on the surface of the positive electrode, such as the exposed Ni atoms on the surface of the positive electrode, the molecule will not be oxidized, and other molecules (such as EC molecules in the electrolyte) will not react at the active sites. Therefore, the larger w is, the higher the content of Ni in the positive electrode is, the more active sites are exposed, the more likely the electrolyte is oxidized, the more oxidation reactions occur, and the more gas is produced, and the larger the battery expansion rate is; the larger S3 is, the more active sites on the surface of the positive electrode can be covered by the linear solvent with 5-6 carbon atoms, and the linear solvent with 5-6 carbon atoms will not be oxidized, which improves the oxidation resistance of the electrolyte, and the less gas is produced, but the larger S3 is, the larger the impedance is, and the larger the temperature rise is; and the smaller S3 is, the fewer active sites on the surface of the positive electrode are covered by the linear solvent with 5-6 carbon atoms, the more oxidation reactions occur, the more gas is produced, and the larger the battery expansion rate is. Therefore, by comprehensively adjusting the multi-tab structure of the battery cell, the number of layers n of the battery cell, the thickness of the battery cell, the mass ratio S3 of the linear solvent with 5-6 carbon atoms in the electrolyte, and the mass ratio w of Ni element in the positive electrode active material, 50≤n≤80, the thickness of the battery cell is 5-15 mm, 5%≤S3≤70%, and 0.3≤S3 / w≤1.5, the battery gas production can be well inhibited, the temperature rise can be reduced, and the risk of thermal runaway can be reduced.

[0022] As an example, the number of layers n of the battery cell can be 50, 55, 60, 65, 70, 75, 80, or within a range between any two of the above values, the thickness of the battery cell can be 5 mm, 7 mm, 9 mm, 11 mm, 13 mm, 15 mm, or within a range between any two of the above values, the mass fraction S3 of the linear solvent with 5-6 carbon atoms in the electrolyte can be 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, or within a range between any two of the above values; the value of S3 / w can be 0.3, 0.5, 0.8, 1.0, 1.2, 1.5, or within a range between any two of the above values.

[0023] Preferably, 15%≤S3≤50%.

[0024] In an alternative embodiment, the positive active material is LiNi x Co y Mn z M k O2, wherein 0.3≤x≤0.9, preferably 0.5≤x≤0.8, 0≤y≤1, 0≤z≤10≤k≤0.05, and x+y+z+k=1.

[0025] Preferably, M is selected from one or more of Fe, Mg, Cu, Zn, Al, Ti, Sn, B, Ga, Cr, Sr, V, Zr.

[0026] In an alternative embodiment, the linear solvent with 5-6 carbon atoms includes one or more of diethyl carbonate (DEC), ethyl propyl carbonate, propyl propionate (PP), ethyl butyrate, methyl trimethylacetate, ethyl isobutyrate. The specific molecular structure is as follows: , , , , , .

[0027] In an alternative embodiment, 20%≤w≤55%; as an example, the mass fraction w of the Ni element in the positive active material can be 20%, 30%, 40%, 50%, 55%, or within a range between any two of the above values.

[0028] In an alternative embodiment, the solvent of the electrolyte further comprises a cyclic carbonate, the cyclic carbonate comprising at least one of ethylene carbonate EC and propylene carbonate PC; the content of ethylene carbonate EC is S1, 0.01%≤S1≤30%, the content of propylene carbonate PC is S2, 0.01%≤S2≤30%; 10%≤S1+S2≤40%, preferably 15%≤S1+S2≤35%; 0.1≤S1 / S2≤10, preferably 0.15≤S1 / S2≤5.

[0029] Specifically, the cyclic carbonate in the present application has a high dielectric constant, and controlling it in the range can well dissociate lithium salt. This is due to the carbon-based oxygen p orbital of the cyclic carbonate having a lone pair of electrons, which can enter the s orbital of the lithium ion to form coordination, so that the cyclic carbonate is more likely to form a solvation structure with the lithium ion in the electrolyte solution. Specifically, the electrolyte solution in the present application comprises a cyclic solvent and a linear solvent. The cyclic solvent generally has a high dielectric constant and can dissociate lithium salt, and the linear solvent has a low viscosity and good fluidity, so that the lithium ion can be quickly transported. Therefore, in the electrolyte solution, the content of the cyclic carbonate increases, the viscosity increases, and then the compatibility is affected, the impedance increases, the temperature rise is improved, and the lithium is easily precipitated from the negative electrode, which affects the cycle performance; the content of the cyclic carbonate is too low, which cannot dissociate lithium salt, and is more likely to form lithium dendrites, which affects the cycle performance; in summary, by comprehensively controlling the total amount of the cyclic carbonate, i.e., 10%≤S1+S2≤40%, preferably 15%≤S1+S2≤35%, the balance between safety performance and cycle performance can be considered.

[0030] For example, S1+S2 can be set to 10%, 15%, 20%, 25%, 30%, 35%, 50%, or within a range composed of any two of the above values.

[0031] In an alternative embodiment, EC is more likely to be oxidized at the positive electrode among the two cyclic carbonates, because EC and Li + form coordination to form a solvation structure, and migrate together with Li + to the active sites on the positive electrode surface, so that EC contacts the positive electrode surface, and the H on the two methylene groups is oxidized by the TM-O 2 on the positive electrode surface, causing EC to decompose. The molecular structure of propylene carbonate PC is -CH3 instead of H in EC, so that when PC contacts the positive electrode surface, due to the steric hindrance of -CH3, the TM-O 2- inaccessible to the methylene H, thus unable to oxidize PC to cause decomposition. Therefore, the oxidation stability of ethylene carbonate EC is not as good as PC, and EC is more prone to oxidation to produce gas at the positive electrode. Similarly, EC is more prone to reduction reaction at the negative electrode than PC, and after the reduction of EC at the negative electrode, organic matter is generated to form a solid electrolyte interface SEI covering the negative electrode, protecting the negative electrode from the reduction decomposition of other solvents; PC cannot undergo reduction decomposition and cannot form a SEI layer at the negative electrode, and when lithium ions migrate to the surface of the negative electrode together with PC, the negative electrode protection interface is not good enough to protect PC from being embedded in the graphite negative electrode along with the lithium ions, causing the interlayer spacing of the negative electrode graphite particles to increase and the negative electrode structure to be damaged. Therefore, the larger the S1 / S2 value, the more EC there is, the better the protection of the negative electrode, and the better the capacity retention rate of the battery at room temperature, but the battery is more prone to produce gas at high temperature; on the contrary, the smaller the S1 / S2 value, the more PC there is, the electrolyte is not easy to be oxidized at the positive electrode, and the battery is not easy to produce gas at high temperature, but the protection of the negative electrode is not enough, and PC is easy to be embedded in the graphite negative electrode to cause the capacity attenuation of the battery. The present application effectively balances the high-temperature safety performance and cycle performance of the battery system by strictly controlling the amount of EC and PC, specifically, controlling 0.01%≤S1≤30%, 0.01%≤S2≤30%, 0.1≤S1 / S2≤10. Preferably, 0.15≤S1 / S2≤5.

[0032] As an example, the content S1 of the ethylene carbonate can be set to 0.01%, 0.1%, 0.5%, 1%, 5%, 10%, 15%, 20%, 25%, 30% or within a range consisting of any two of the above values; the content S2 of the propylene carbonate can be set to 0.01%, 0.1%, 0.5%, 1%, 5%, 10%, 15%, 20%, 25%, 30% or within a range consisting of any two of the above values; S1 / S2 can be set to 0.1, 0.15, 0.2, 0.5, 1, 1.5, 2, 3, 4, 5, 6, 7, 8, 9, 10 or within a range consisting of any two of the above values.

[0033] In one optional embodiment, the electrolyte further includes a first additive containing sulfur (S). This additive forms an S-containing interface during the oxidation film formation at the positive electrode, and the S-element complexes with the metal elements on the positive electrode surface, reducing the oxidizability of the positive electrode surface. This reduces the oxidation of the electrolyte by the positive electrode, decreases gas production, and consequently reduces the expansion rate. If the amount of the first additive is too small, it will not reduce the oxidation of the electrolyte by the positive electrode, increasing the expansion rate; if the amount of the first additive is too large, it will cause an excessively thick interface layer on the positive electrode surface, increasing battery impedance, decreasing battery kinetic performance, and increasing battery temperature rise. Therefore, the mass percentage (S4) of the first additive in the electrolyte can be controlled, 0.1% ≤ S4 ≤ 6%, preferably 0.5% ≤ S4 ≤ 5%. For example, the first additive includes one or more of 1,3-propanesulfonyl lactone (PS), propylene-1,3-sulfonyl lactone (PST), vinyl sulfate (DTD), methylene disulfonate, vinyl sulfite, thiophene, etc.

[0034] As an example, the mass percentage S4 of the first additive in the electrolyte can be set to 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, or within any two of the above values.

[0035] The content of the first additive needs to be adjusted in conjunction with other components in the electrolyte. Specifically, when S3 is large and S1 / S2 is small, the electrolyte itself has good antioxidant properties, which can reduce S4 to balance the kinetic performance of the battery.

[0036] In one optional embodiment, the electrolyte further includes a second additive, wherein the mass percentage of the second additive in the electrolyte is S5, 0.1% ≤ S5 ≤ 4%, preferably 0.5% ≤ S5 ≤ 3%. For example, the second additive includes one or more of vinylene carbonate, ethylene ethylene carbonate, fluoroethylene carbonate, and difluoroethylene carbonate.

[0037] The second additive of this invention can undergo a reduction reaction at the negative electrode to form a stable SEI film, protecting the negative electrode and preventing other solvents from reducing, decomposing, or embedding into it, thereby improving cycle performance. When the additive content is high, the interface formed at the negative electrode is thicker, resulting in higher battery impedance, decreased high-power charge / discharge performance, and increased temperature rise.

[0038] As an example, the mass percentage S5 of the second additive in the electrolyte can be set to 0.1%, 0.5%, 1%, 2%, 3%, 4%, or within any two of the above values.

[0039] In this invention, when the ratio of S1 to S2 in the electrolyte is small, the PC content in the electrolyte is large. Increasing S5 is beneficial to protect the negative electrode and prevent PC from embedding into the graphite negative electrode.

[0040] In an optional embodiment, the electrolyte further includes a lithium salt, which includes one or more of lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide (LiFSI), and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). The mass percentage of the lithium salt in the electrolyte is S6, where 8% ≤ S6 ≤ 20%, preferably 10% ≤ S6 ≤ 18%.

[0041] In this invention, LiPF6 exhibits good stability and can passivate the positive electrode current collector to prevent corrosion; therefore, LiPF6 is typically used as the main salt. Furthermore, LiFSI has a larger anion size than LiPF6, resulting in higher conductivity, higher transference number, and superior kinetic performance. When LiFSI and LiPF6 are used together, the battery exhibits even better kinetic performance.

[0042] As an example, the mass percentage S6 of the lithium salt in the electrolyte can be set to 8%, 10%, 12%, 14%, 16%, 18%, 20%, or within any two of the above values.

[0043] In one optional embodiment, the diaphragm includes a base membrane and an adhesive layer, wherein the coverage of the adhesive layer in the diaphragm is m, 20%≤m≤100%, preferably 0.05≤S6 / m≤1; and the porosity of the diaphragm is controlled at 30-50%.

[0044] When the adhesive layer coverage in the separator is too low, the bonding performance is poor, affecting the battery's long-cycle performance. Conversely, when the adhesive layer coverage in the separator is high, the electrodes in the battery adhere better, and the transport of lithium ions between the positive electrode, separator, and negative electrode is more stable, ensuring better long-cycle performance. The adhesive layer coverage in this invention is controlled at 20-100%, resulting in good long-cycle performance.

[0045] The adhesion between the separator and the electrode is directly related to the lithium salt concentration in the electrolyte. When the lithium salt content in the electrolyte decreases, the adhesive layer on the separator surface swells better, resulting in better adhesion between the separator and the electrode. However, too low a lithium salt concentration can lead to excessive swelling of the separator adhesive layer, causing it to detach. When the lithium salt content in the electrolyte is too high, it is difficult to swell the adhesive layer in the separator, resulting in poor adhesion between the separator and the electrode. This is because when the lithium salt content is too high, the electrolyte contains a large number of lithium ions. These lithium ions coordinate with solvents in the electrolyte, such as EC and PC, resulting in fewer free PC and EC. With fewer free solvents, the small molecules entering the separator adhesive layer are smaller, making it difficult for the separator adhesive layer molecules to swell. Specifically, a higher S6 / m value indicates a higher lithium salt content, a smaller adhesive layer coverage, and greater difficulty in swelling the separator, leading to poorer separator adhesion. Conversely, a lower S6 / m value results in better adhesion. When the S6 / m value is too low, the lithium salt content is too low, and the adhesive layer coverage is too high, causing a large number of solvent molecules to enter the adhesive layer, leading to excessive swelling and subsequent adhesive layer detachment, resulting in battery failure. This invention achieves better adhesion between the separator and the electrode by comprehensively controlling the lithium salt content and adhesive layer coverage to 0.05 ≤ S6 / m ≤ 1, thus resulting in better electrochemical performance.

[0046] The higher the porosity of the separator, the better the battery's high-power charge and discharge capability. However, excessively high porosity can lead to increased thermal shrinkage of the separator, negatively impacting battery safety. The separator of this invention has a porosity controlled at 30-50%, providing excellent lithium-ion transport capabilities. This allows lithium ions to pass through the separator quickly, reducing transport resistance within the separator.

[0047] As an example, the porosity of the membrane can be set to 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100%, or within any two of the above values; S6 / m can be set to 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, or within any two of the above values.

[0048] Method for detecting coating coverage: The membrane surface is observed using a scanning electron microscope (SEM), and the photographs are processed using image analysis software to accurately calculate the percentage of the coating coverage area to the total area.

[0049] Methods for detecting membrane porosity: The gas (such as helium) specific gravity method is used. By measuring the skeletal volume and geometric volume of the membrane, the proportion of the difference between the two is calculated to obtain the membrane porosity.

[0050] To improve the high-power charging and discharging performance and battery safety, the positive electrode active material used is a ternary material. At the same time, by controlling the morphology, doping elements, particle size and the thickness of the positive electrode active layer, the battery has good high-power charging and discharging performance and high-temperature performance.

[0051] In one optional embodiment, the doping element in the positive electrode active material includes Al, preferably Al and Ti, and the doping amount of the doping element in the positive electrode active material is less than 1%. Preferably, the doping content of Al in the positive electrode active material is 500-3000 ppm.

[0052] In this invention, Al stabilizes the cathode structure, preventing severe phase transitions and oxygen evolution. Al doping effectively reduces electrolyte oxidation and expansion. Simultaneously, doping the cathode with Ti creates a fast-ion conductor at the interface. Through the formation of Li-Ti-O electrostatic interactions, the lithium-ion solvation energy is lowered, enabling rapid lithium-ion transport at the interface and improving fast-charging cycle performance.

[0053] As an example, the doping amount of the dopant element in the positive electrode active material is 0.05%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, or within any two of the above values, and the doping content of Al element in the positive electrode active material is 500 ppm, 800 ppm, 1000 ppm, 1500 ppm, 2000 ppm, 2500 ppm, 3000 ppm, or within any two of the above values.

[0054] Method for detecting the doping amount of doped elements: X-ray energy dispersive spectroscopy is used to scan the surface of the positive electrode to obtain the mass content distribution of various elements.

[0055] In one alternative embodiment, the positive electrode active material is a single-crystal material. This is because single crystals have fewer surface active sites compared to polycrystalline materials, thus reducing the oxidation of the electrolyte.

[0056] In one optional embodiment, the average particle size of the positive electrode active material is 3-7 μm, and its particle size distribution is: 1≤Dv10≤3, 4≤Dv50≤6, 8≤Dv90≤15; the thickness of the positive electrode active layer on one side of the positive electrode sheet is h1μm, and 55≤h1≤75.

[0057] This invention accelerates lithium-ion transport within the cathode by controlling the average particle size and particle size distribution of the positive electrode active material. This results in a shorter transport distance for lithium ions within the ternary cathode particles, reducing diffusion resistance and lowering temperature rise. However, excessively small particle size increases the number of active sites in contact with the electrolyte, increasing gas production and expansion rate. Therefore, controlling the particle size of the positive electrode active material in the cathode sheet balances temperature rise and expansion rate, achieving better cycle performance. Simultaneously, controlling the thickness of the active material on one side of the cathode sheet also enables rapid lithium-ion transport between cathode particles.

[0058] As an example, the average particle size of the positive electrode active material can be set to 3μm, 4μm, 5μm, 6μm, 7μm or within any two of the above values; the Dv10 of the positive electrode active material can be 1μm, 1.5μm, 2μm, 2.5μm, 3μm or within any two of the above values; the Dv50 of the positive electrode active material can be 4μm, 4.5μm, 5μm, 5.5μm, 6μm or within any two of the above values; the Dv90 of the positive electrode active material can be 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm or within any two of the above values; and the thickness h1 of the positive electrode active layer on one side of the positive electrode sheet can be 55μm, 60μm, 65μm, 70μm, 75μm or within any two of the above values.

[0059] In one optional embodiment, the negative electrode sheet includes a negative electrode current collector and a negative electrode active layer coated on at least one side surface of the negative electrode current collector, wherein the negative electrode active layer includes a negative electrode active material. The particle size of the negative electrode active material also affects the content of ethylene carbonate and the second additive in the electrolyte. Smaller particle sizes result in a higher specific surface area of ​​the negative electrode, more exposed active sites, and better fast-charging performance. However, this also increases the demand for ethylene carbonate and the second additive in the electrolyte. Increased active sites on the negative electrode surface require more second additive or ethylene carbonate to form the SEI layer, thereby protecting the negative electrode, increasing impedance, and consequently raising the temperature rise. The negative electrode active material described in this invention has an average particle size of 4-8 μm, with a particle size distribution of: 2≤D10≤4, 4≤D50≤8, 9≤D90≤15; and / or, the thickness of the single-sided negative electrode active layer in the negative electrode sheet is h2μm, 60≤h2≤80.

[0060] To ensure that the movement rates of lithium ions at the positive and negative electrodes are matched, the thickness of the active layers at both electrodes needs to be controlled. Preferably, the thickness of the active layers at both electrodes is controlled to satisfy 1 ≤ h2 / h1 ≤ 1.2. This ensures that the movement speed of lithium ions in the active layers of both electrodes is relatively equal, and the kinetic energy of lithium ion transport at the positive and negative electrodes is matched, preventing lithium ions from accumulating at the negative electrode or causing severe concentration polarization at the positive electrode. Simultaneously, to enable rapid transport of lithium ions from the positive electrode to the negative electrode or vice versa, the separator also needs to be controlled to facilitate rapid transport of lithium ions within the separator.

[0061] As an example, the average particle size of the negative electrode active material can be set to 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, or within any two of the above values; the Dv10 of the negative electrode active material can be 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, or within any two of the above values; and the Dv50 of the negative electrode active material can be 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, or within any two of the above values. Within the negative electrode active material, Dv90 can be 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm or within any two of the above values. The thickness h2 of the single-sided negative electrode active layer in the negative electrode sheet can be 60μm, 65μm, 70μm, 75μm, 80μm or within any two of the above values. h2 / h1 can be 1, 1.1, 1.2 or within any two of the above values.

[0062] Method for detecting the average particle size of negative electrode active material or positive electrode active material: The negative electrode sheet or positive electrode sheet is observed using an electron scanning electron microscope. Five different regions are observed, and four to six different particles are randomly selected from each region, for a total of 30 particles, and their average particle size is measured.

[0063] Methods for detecting Dv10, Dv50, and Dv90 of negative or positive electrode active materials: Obtain the negative or positive electrode active material, and use a laser particle size analyzer to measure the particle size distribution Dv10, Dv50, and Dv90 values.

[0064] Method for detecting the thickness of the negative electrode active layer or the positive electrode active layer: The cross-section of the electrode is observed using an electron scanning electron microscope, and the thickness of the active material of the electrode at 10 different locations is measured and the average value is taken.

[0065] Electrolyte The electrolyte of this invention includes an organic solvent, a lithium salt, and functional additives.

[0066] Other organic solvents include cyclic carbonates and linear solvents with 5-6 carbon atoms. The linear solvents with 5-6 carbon atoms include one or more of diethyl carbonate (DEC), ethyl propyl carbonate, propyl propionate (PP), ethyl butyrate, methyl trimethylacetate, and ethyl isobutyrate. The cyclic carbonates include at least one of ethylene carbonate (EC) and propylene carbonate (PC).

[0067] Lithium salts include one or more of lithium hexafluorophosphate (LiPF6), lithium bisfluorosulfonylimide (LiFSI), and lithium bistrifluoromethylsulfonylimide (LiTFSI).

[0068] Functional additives include first additives, second additives, etc.; second additives include one or more of vinylene carbonate, ethylene ethylene carbonate, fluoroethylene carbonate, difluoroethylene carbonate, etc.; first additives include one or more of 1,3-propane sulpholactone (PS), propenyl-1,3-sulfonyl lactone (PST), vinyl sulfate (DTD), vinyl sulfite, thiophene, etc.

[0069] [Septum] The diaphragm of the present invention is an aqueous diaphragm or an oil-based diaphragm, which includes at least a base membrane and an adhesive layer; the structural features of the diaphragm are adhesive layer + base membrane, adhesive layer + ceramic + base membrane, adhesive layer + ceramic + base membrane + adhesive layer, and adhesive layer + ceramic + base membrane + ceramic + adhesive layer.

[0070] The base membrane can be selected from commonly used base membrane materials in the field, including but not limited to polyethylene (PE), polypropylene (PP), and PE and PP composite membranes.

[0071] The ceramics used include aluminum oxide (Al₂O₃), aluminum hydroxide, magnesium oxide, alumina, zirconium oxide, titanium oxide, and silicon oxide. The ceramic layer thickness is controlled between 1-3 μm. Applying a ceramic layer to the separator effectively suppresses separator shrinkage and prevents short circuits at the positive and negative electrode contacts.

[0072] The adhesive layer is a conventional spray coating layer. Commonly used adhesive layers can be selected from one or more of the following: polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polyacrylic acid resin, polymethyl acrylate, butyl acrylate-acrylonitrile copolymer, polyacrylonitrile, ethylene-acrylic acid copolymer, polyethyl acrylate, or sodium carboxymethyl cellulose.

[0073] The diaphragm of the present invention can be coated on one or both sides using any one of the following coating processes: gravure coating, transfer coating, dip coating, and spray coating.

[0074] [Positive Electrode Tablets] The positive electrode sheet of the present invention includes a positive current collector, a positive active material, a conductive agent, and a binder. The positive electrode sheet includes a positive current collector and a positive active layer disposed on the surface of the positive current collector. The positive active layer includes 90%-99.8% positive active material, 0.1%-5% conductive agent, and 0.1%-5% binder by mass percentage.

[0075] In this invention, the positive current collector is aluminum foil, carbon-coated aluminum foil, or composite aluminum foil.

[0076] The type of positive electrode active material is LiNi x Co y Mn z M k O2, the doping element M is selected from one or more of Fe, Mg, Cu, Zn, Al, Ti, Sn, B, Ga, Cr, Sr, V, Zr, wherein 0.3≤x≤0.9, preferably 0.5≤x≤0.8, 0≤y≤1, 0≤z≤1, 0≤k≤0.05, and x+y+z+k=1; the positive electrode active material is a single crystal material.

[0077] The present invention does not impose any particular limitation on the conductive agent in the positive electrode, which may be selected from the conductive agents commonly used in the art, including but not limited to one or more of acetylene black, conductive carbon black, Ketjen black, conductive graphite, carbon nanotubes, conductive carbon fibers, and graphene.

[0078] The present invention does not impose any particular limitation on the binder in the positive electrode sheet, which may be selected from binders commonly used in the art, including but not limited to one or more of polyvinylidene fluoride, polytetrafluoroethylene, sodium carboxymethyl cellulose, styrene-butadiene rubber, and polyethylene oxide.

[0079] Negative electrode plate The negative electrode sheet of the present invention includes a negative electrode current collector, a negative electrode active material, a conductive agent, and a binder. The negative electrode sheet includes a negative electrode current collector and a negative electrode active layer disposed on the surface of the negative electrode current collector. In the negative electrode active layer, the negative electrode active material accounts for 90 wt%-98.5 wt% of the total mass of the negative electrode active layer, the conductive agent accounts for 0.1 wt%-5 wt% of the total mass of the negative electrode active layer, and the binder accounts for 0.1 wt%-5 wt% of the total mass of the negative electrode active layer.

[0080] According to the battery of the present invention, the negative electrode active material includes at least one of graphite, silicon-based materials, etc.

[0081] According to the battery of the present invention, the conductive agent is selected from at least one of acetylene black, conductive carbon black, Ketjen black, conductive graphite, carbon nanotubes, conductive carbon fibers, and graphene.

[0082] According to the battery of the present invention, the binder is selected from at least one of polytetrafluoroethylene, sodium carboxymethyl cellulose, styrene-butadiene rubber, and polyethylene oxide.

[0083] This invention does not impose any particular limitation on the types of conductive agents and binders in the negative electrode sheet. The selection range can be referred to the types of conductive agents and binders in the positive electrode sheet, which will not be elaborated here.

[0084]

Battery

[0085] Preferably, the battery cell adopts a laminated structure or a multi-tab wound structure, with 50-80 layers and a thickness of 6-14mm. Specifically, the thickness... Width Height is 6-14mm 148-152mm 202-210mm.

[0086] To meet the high-current charging and discharging capabilities of the battery cell, with a constant load current I, the number of winding layers in the cell is n, and the soft tab current i = I / n. The lower the number of winding layers, the higher the current per soft tab. Therefore, too few winding layers lead to excessive temperature rise, affecting the cell's safety performance; while too many layers reduce process yield and increase process costs. If the cell thickness is too small, the cell capacity and energy density are compromised, and the limited number of winding layers has the same impact as "the lower the number of winding layers." Too much thickness results in poor heat dissipation, accumulated internal temperature rise, and reduced cell cycle life. A cell width / height within this range provides good electrolyte wetting (aging) time, DCIR gains, high current diffusion efficiency under high-power operating conditions, and good current density and temperature rise consistency across different areas of the cell surface. Excessive width / height leads to a rapid increase in stress and localized temperature rise, resulting in a decrease in overall cell performance; too little width / height leads to a decrease in cell capacity.

[0087] The lithium-ion battery provided by the present invention will be further described in detail below through specific embodiments.

[0088] Unless otherwise specified, the reagents, materials and instruments used in the following examples are all conventional reagents, materials and instruments in the art, and can be obtained commercially. The reagents involved can also be synthesized by conventional methods in the art.

[0089] According to an embodiment of the present invention, in another aspect, the present invention also provides an electrical device including the above-mentioned secondary battery, wherein the electrical device is a low-altitude aircraft or a humanoid robot.

[0090] Examples and Comparative Examples Example 1 A secondary battery, the specific preparation process of which is as follows: 1. Preparation of the positive electrode: LiNi 0.8 Co 0.1 Mn 0.1 O2 powder, polyvinylidene fluoride, acetylene black, and carbon nanotubes were added to a vacuum mixer in a mass ratio of 96:2:1.5:0.5. N-methylpyrrolidone (NMP) was then added, and the mixture was thoroughly mixed under vacuum until a homogeneous, free-flowing positive electrode slurry with a solid content of 55 wt% was formed. This positive electrode slurry was then uniformly coated onto a 12 μm thick aluminum foil, with a single-sided surface density of 10 mg / cm². 2 After drying and rolling, the thickness h1 of the single-sided positive electrode active layer is controlled to be 65μm, then slitting and punching to obtain the positive electrode sheet; LiNi 0.8 Co 0.1 Mn 0.1 O2 powder is a single-crystal powder, LiNi 0.8 Co 0.1 Mn 0.1 The average particle size of the O2 powder is 5.1 μm, and its particle size distribution is as follows: D10 is 2.8 μm, D50 is 5.13 μm, and D90 is 9.3 μm. The mass percentage w of Ni element in the positive electrode active material is 48.3%.

[0091] 2. Preparation of the negative electrode sheet: Graphite, styrene-butadiene rubber, sodium carboxymethyl cellulose, and acetylene black were added to a vacuum mixer in a mass ratio of 96.5:1:1:1.5. Deionized water was added, and the mixture was thoroughly mixed under vacuum to form a uniform, free-flowing negative electrode slurry with a solid content of 45 wt%. The negative electrode slurry was then uniformly coated onto a 6 μm thick carbon-coated copper foil with a single-sided surface density of 5 mg / cm². 2 After drying and rolling, the thickness of the negative electrode active material on one side is controlled to be 70μm, and then die-cut to obtain the negative electrode sheet; the average particle size of graphite is 6μm, and the particle size distribution is: D10 is 3.5μm, D50 is 6.1μm, and D90 is 10μm.

[0092] 3. Electrolyte preparation: In an argon-filled glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), and methyl ethyl carbonate (EMC) are mixed evenly in a mass ratio of 2:1:3:4. Fully dried lithium hexafluorophosphate (LiPF6) and lithium bis(fluorosulfonyl)imide (LiFSI) are added and stirred to dissolve. The added mass of LiPF6 and LiFSI is 3% and 12% of the total electrolyte mass, respectively. A second additive, vinylene carbonate (VC), is added at 1% of the total electrolyte mass. A first additive, 1,3-propanesulfonyl lactone, is added at 3% of the total electrolyte mass. Lithium difluorophosphate (LiPO2F2) is added at 0.5% of the total electrolyte mass. The mixture is stirred evenly, and after passing moisture and free acid tests, the desired electrolyte is obtained.

[0093] 4. Preparation of the diaphragm containing the adhesive layer: The diaphragm of the present invention is composed of: adhesive layer + ceramic + base membrane + adhesive layer. The base membrane is made of 7μm PP polymer. A 2μm ceramic is coated on one side of the base membrane. A 1μm PVDF adhesive layer is coated on the ceramic surface and the base membrane on the other side. The coverage of the adhesive layer in the diaphragm is 60%, and the porosity of the diaphragm is 40%.

[0094] 5. Preparation of lithium-ion batteries: The above-mentioned positive electrode, negative electrode and separator are wound to obtain a bare cell. The number of layers n of the cell is 65 and the thickness of the cell is about 12mm. The positive electrode sheet includes multiple positive electrode tabs extending from the positive electrode current collector, and the negative electrode sheet includes multiple negative electrode tabs extending from the negative electrode current collector, forming a cell with a multi-tab structure. Hard tabs are welded onto the bare cell. The cell is placed in the battery casing. The above-mentioned electrolyte is injected into the dried and qualified cell. After standing, aging, formation, secondary sealing, aging and sorting processes, the battery is obtained.

[0095] Examples 2-4 The difference from Example 1 lies in the different positive electrode active material, as shown in Table 1 below: Table 1

[0096] Everything else is the same as in Example 1.

[0097] Example 5 A secondary battery, the specific preparation process of which is as follows: 1. Preparation of the positive electrode: LiNi 0.6 Co 0.1 Mn 0.294 Al 0.003 Ti 0.003O2 powder, polyvinylidene fluoride, acetylene black, and carbon nanotubes were added to a vacuum mixer in a mass ratio of 96:2:1.5:0.5. N-methylpyrrolidone (NMP) was then added, and the mixture was thoroughly mixed under vacuum until a homogeneous, free-flowing positive electrode slurry with a solid content of 55 wt% was formed. This positive electrode slurry was then uniformly coated onto a 12 μm thick aluminum foil, with a single-sided surface density of 10 mg / cm². 2 After drying and rolling, the thickness h1 of the single-sided positive electrode active layer is controlled to be 65μm, then slitting and punching to obtain the positive electrode sheet; LiNi 0.6 Co 0.1 Mn 0.394 Al 0.00 3Ti 0.003 O2 powder is a single-crystal powder, LiNi 0.6 Co 0.1 Mn 0.394 Al 0.003 Ti 0.003 The average particle size of the O2 powder is 5.1 μm, and its particle size distribution is as follows: D10 is 2.8 μm, D50 is 5.13 μm, and D90 is 9.3 μm. The mass percentage w of Ni element in the positive electrode active material is about 37%, and the doping amount of Al element in the positive electrode active material is 800 ppm.

[0098] 2. Preparation of the negative electrode sheet: Graphite, styrene-butadiene rubber, sodium carboxymethyl cellulose, and acetylene black were added to a vacuum mixer in a mass ratio of 96.5:1:1:1.5. Deionized water was added, and the mixture was thoroughly mixed under vacuum to form a uniform, free-flowing negative electrode slurry with a solid content of 45 wt%. The negative electrode slurry was then uniformly coated onto a 6 μm thick carbon-coated copper foil with a single-sided surface density of 5 mg / cm². 2 After drying and rolling, the thickness of the negative electrode active material on one side is controlled to be 70μm, and then die-cut to obtain the negative electrode sheet; the average particle size of graphite is 6μm, and the particle size distribution is: D10 is 3.5μm, D50 is 6.1μm, and D90 is 10μm.

[0099] 3. Electrolyte preparation: In an argon-filled glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), and methyl ethyl carbonate (EMC) are mixed evenly in a mass ratio of 2:1:3:4. Fully dried lithium hexafluorophosphate (LiPF6) and lithium bis(fluorosulfonyl)imide (LiFSI) are added and stirred to dissolve. The added mass of LiPF6 and LiFSI is 3% and 12% of the total electrolyte mass, respectively. A second additive, vinylene carbonate (VC), is added at 1% of the total electrolyte mass. A first additive, 1,3-propanesulfonyl lactone, is added at 3% of the total electrolyte mass. Lithium difluorophosphate (LiPO2F2) is added at 0.5% of the total electrolyte mass. The mixture is stirred evenly, and after passing moisture and free acid tests, the desired electrolyte is obtained.

[0100] 4. Preparation of the diaphragm containing the adhesive layer: The diaphragm of the present invention is composed of: adhesive layer + ceramic + base membrane + adhesive layer. The base membrane is made of 7μm PP polymer. A 2μm ceramic is coated on one side of the base membrane. A 1μm PVDF adhesive layer is coated on the ceramic surface and the base membrane on the other side. The coverage of the adhesive layer in the diaphragm is 60%, and the porosity of the diaphragm is 40%.

[0101] 5. Preparation of lithium-ion batteries: The above-mentioned positive electrode, negative electrode and separator are wound to obtain bare cells; hard tabs are welded onto the bare cells and placed in the battery casing; the above-mentioned electrolyte is injected into the dried and qualified cells; after standing, aging, formation, secondary sealing, aging and sorting processes, the battery is obtained.

[0102] Examples 6-12 The difference from Example 5 lies in the composition of the positive electrode active material, as shown in Table 2 below: Table 2

[0103] Everything else is the same as in Example 5.

[0104] Examples 13-17 The difference from Example 5 lies in the content S3 of the linear solvent with 5-6 carbon atoms. Correspondingly, the content of ethyl methyl carbonate (EMC) is adjusted to make its total amount reach 100%, and the composition of the positive electrode active material is changed so that S3 / w is within the range of this invention. The specific settings are shown in Table 3 below: Table 3

[0105] Everything else is the same as in Example 5.

[0106] Examples 18-21 The difference from Example 5 is that the particle sizes of the positive and negative electrode active materials are different, as shown in Table 4 below: Table 4

[0107] Everything else is the same as in Example 5.

[0108] Examples 22-29 The difference from Example 5 lies in the different types and mass percentages of the first additive (S4), the second additive (S5), and the lithium salt (S6) in the electrolyte. Correspondingly, the content of ethyl methyl carbonate (EMC) is adjusted to achieve a total of 100%, as shown in Table 5 below. Table 5

[0109] Everything else is the same as in Example 5.

[0110] Example 30 The difference from Example 5 is that the type of linear solvent with 5-6 carbon atoms is different. In this example, propyl propionate is used instead of diethyl carbonate (DEC). Otherwise, it is the same as Example 5.

[0111] Examples 31-37 The difference from Example 5 is that the types and mass ratios (S1 / S2, S1+S2) of cyclic carbonates in the electrolyte are different. Correspondingly, the content of ethyl methyl carbonate (EMC) is adjusted to make its total amount 100%, as shown in Table 6 below: Table 6

[0112] Everything else is the same as in Example 5.

[0113] Examples 38-39 The difference from Example 5 lies in the different coverage rate m of the adhesive layer in the diaphragm and the different porosity of the diaphragm, and the control of S6 / m within the specified range, as shown in Table 7 below: Table 7

[0114] Everything else is the same as in Example 5.

[0115] Examples 40-41 The difference from Example 5 lies in the different thicknesses of the positive active layer in the positive electrode, the negative active layer in the negative electrode, the cell thickness, and the number of cell layers n. The specific settings are shown in Table 8 below. Table 8

[0116] Everything else is the same as in Example 5.

[0117] The electrochemical performance of the batteries prepared in the examples and comparative examples was tested, and the specific testing process is as follows: 1. Fast charging cycle performance test High-temperature fast-charging cycle performance test: At 45℃, the battery thickness d1 before cycling was measured with vernier calipers. After capacity testing, the battery was charged at 6C constant current and constant voltage to 4.35V, with a cutoff current of 0.05C. Then, it was discharged at 10C constant current to 2.5V, and the initial discharge capacity was recorded. This cycle was repeated for 1000 charge-discharge cycles. The capacity retention rate on the 1000th cycle was calculated, and the battery thermal thickness d2 was recorded. The calculation formula is as follows: Cycle capacity retention rate (%) at week 1000 = (Cycle discharge capacity at week 1000 / Initial cycle discharge capacity) × 100%.

[0118] Battery expansion rate (%) after 1000 cycles = (Battery thickness d2 after 1000 cycles / Battery thickness d1 before cycling) × 100%.

[0119] 2. Battery temperature rise test At 25℃, three temperature sensors were placed at the center of the battery, the positive electrode tab, and the negative electrode tab, respectively, to monitor the real-time temperature. The battery, after being sized, was charged at 1C constant current and constant voltage to 3.65V, with a cutoff current of 0.05C. It was then discharged at 1C constant current to 2.5V, and the initial discharge capacity C0 was recorded. The battery was discharged at 1C to 20% SOC, and after resting for 4 hours, the average temperature T0 of the temperature sensors was recorded. The battery was then charged at 6C to 80% SOC, and the maximum real-time temperature T1 during charging was recorded. The temperature rise T1-T0 was calculated.

[0120] Based on the table below, the results of the experiments conducted on the above groups are shown in Tables 9 and 10.

[0121] Table 9

[0122] Table 10

[0123] Although embodiments of the invention have been described in conjunction with the invention description, those skilled in the art can make various modifications and variations without departing from the spirit and scope of the invention, and such modifications and variations all fall within the scope defined by the appended claims.

Claims

1. A secondary battery, comprising a positive electrode, a negative electrode, a separator, and an electrolyte; characterized in that, The positive electrode, the negative electrode, and the separator are stacked or wound to form a battery cell. The positive electrode includes a positive current collector and a plurality of positive tabs extending from the positive current collector. The negative electrode includes a negative current collector and a plurality of negative tabs extending from the negative current collector. The number of layers n of the battery cell satisfies: 50≤n≤80, and the thickness of the battery cell is 5-15mm. The electrolyte includes a solvent, which includes a linear solvent with 5-6 carbon atoms, and the mass percentage of the linear solvent with 5-6 carbon atoms in the electrolyte is S3, where 5% ≤ S3 ≤ 70%. The positive electrode sheet further includes a positive electrode active layer coated on at least one side of the positive electrode current collector, the positive electrode active layer including a positive electrode active material; the positive electrode active material includes Ni element, and the mass percentage of Ni element in the positive electrode active material is w; 0.3≤S3 / w≤1.

5.

2. The secondary battery according to claim 1, characterized in that, 15％≤S3≤50％； And / or, the positive electrode active material is LiNi x Co y Mn z M k O2, wherein 0.3≤x≤0.9, preferably 0.5≤x≤0.8, 0≤y≤1, 0≤z≤1, 0≤k≤0.05, and x+y+z+k=1, and M is selected from one or more of Fe, Mg, Cu, Zn, Al, Ti, Sn, B, Ga, Cr, Sr, V, and Zr; And / or, the linear solvent with 5-6 carbon atoms includes one or more of diethyl carbonate, ethyl propyl carbonate, propyl propionate, ethyl butyrate, methyl trimethylacetate, and ethyl isobutyrate. And / or, 20% ≤ w ≤ 55%.

3. The secondary battery according to claim 1, characterized in that, The solvent also includes cyclic carbonates, which include at least one of ethylene carbonate and propylene carbonate, wherein the content of ethylene carbonate is S1 and the content of propylene carbonate is S2. 0.01% ≤ S1 ≤ 30%, 0.01% ≤ S2 ≤ 30%; And / or, 0.1≤S1 / S2≤10, preferably, 0.15≤S1 / S2≤5; And / or, 10% ≤ S1 + S2 ≤ 40%, preferably 15% ≤ S1 + S2 ≤ 35%.

4. The secondary battery according to any one of claims 1-3, characterized in that, The electrolyte also includes a first additive, the first additive having a mass percentage of S4 in the electrolyte of 0.1% ≤ S4 ≤ 6%, preferably 0.5% ≤ S4 ≤ 5%; the first additive includes one or more of 1,3-propanesulfonyl lactone, propenyl-1,3-sulfonyl lactone, vinyl sulfate, vinyl sulfite, and thiophene. And / or, the electrolyte further includes a second additive, the second additive having a mass percentage of S5 in the electrolyte of 0.1% ≤ S5 ≤ 4%, preferably 0.5% ≤ S5 ≤ 3%; the second additive includes one or more of vinylene carbonate, ethylene ethylene carbonate, fluoroethylene carbonate, and difluoroethylene carbonate.

5. The secondary battery according to any one of claims 1-4, characterized in that, The electrolyte also includes lithium salts, including one or more of lithium hexafluorophosphate, lithium bisfluorosulfonylimide, and lithium bistrifluoromethylsulfonylimide. The mass percentage of lithium salts in the electrolyte is S6, where 8% ≤ S6 ≤ 20%, preferably 10% ≤ S6 ≤ 18%.

6. The secondary battery according to claim 5, characterized in that, The diaphragm includes a base membrane and an adhesive layer, wherein the coverage of the adhesive layer in the diaphragm is m, 20% ≤ m ≤ 100%, preferably 0.05 ≤ S6 / m ≤ 1; And / or, the porosity of the diaphragm is controlled at 30%-50%.

7. The secondary battery according to any one of claims 1-6, characterized in that, The doping element in the positive electrode active material includes Al, preferably Al and Ti, and the doping amount of the doping element in the positive electrode active material is less than 1%. Preferably, the doping content of Al in the positive electrode active material is 500-3000 ppm. And / or, the positive electrode active material is a single crystal material.

8. The secondary battery according to any one of claims 1-7, characterized in that, The average particle size of the positive electrode active material is 3-7 μm, and its particle size distribution is: 1≤Dv10≤3, 4≤Dv50≤6, 8≤Dv90≤15; And / or, the thickness of the positive active layer on one side of the positive electrode sheet is h1μm, 55≤h1≤75.

9. The secondary battery according to claim 8, characterized in that, The negative electrode sheet includes a negative electrode current collector and a negative electrode active layer coated on at least one side of the negative electrode current collector, wherein the negative electrode active layer includes a negative electrode active material. The average particle size of the negative electrode active material is 4-8 μm, and its particle size distribution is: 2≤D10≤4, 4≤D50≤8, 9≤D90≤15; and / or, the thickness of the negative electrode active layer on one side of the negative electrode sheet is h2μm, 60≤h2≤80; Preferably, 1≤h2 / h1≤1.

2.

10. An electrical appliance, characterized in that, Includes the secondary battery as described in any one of claims 1-9.

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