Positive pole piece, secondary battery and electronic device

Abstract

The invention provides a positive pole piece, a secondary battery and an electronic device, the positive pole piece comprises a positive pole current collector and a positive pole material layer arranged on at least one surface of the positive pole current collector, the positive pole material layer comprises a positive pole active material, a positive pole binder, a positive pole conductive agent and an additive, the additive is at least one of a compound shown in a formula I and a compound shown in a formula II, based on the mass of the positive electrode material layer, the mass percentage content of the additive is W%, and 0.02 < = W < = 2.5; the porosity of the positive pole piece is P%, and P is greater than or equal to 12 and less than or equal to 25. According to the present invention, the positive electrode plate meets the above characteristics, such that the positive electrode plate has high porosity and low lithium ion diffusion impedance under the high compaction density condition, and the secondary battery has high energy density and good dynamic performance.

Description

Technical Field

[0001] The present application relates to the field of electrochemistry technology, and particularly to a positive electrode sheet, a secondary battery and an electronic device. Background Art

[0002] With the development of the lithium-ion battery industry, the market's requirements for the kinetic performance and energy density of lithium-ion batteries are also getting higher and higher. Effective methods for improving the energy density of lithium-ion batteries include increasing the coating areal density of the electrode sheet and enhancing the compaction density of the electrode sheet. By increasing the coating areal density of the electrode sheet, the use of the current collector and the separator can be reduced, so as to achieve the purpose of reducing the thickness of the lithium-ion battery and increasing the volume energy density of the lithium-ion battery. By increasing the compaction density of the electrode sheet, the thickness of a single-layer electrode sheet can be reduced, and the purpose of reducing the thickness of the lithium-ion battery and increasing the volume energy density of the lithium-ion battery can also be achieved.

[0003] However, with the increase in the coating areal density of the electrode sheet and the enhancement of the compaction density of the electrode sheet, since the increase in the coating areal density of the electrode sheet leads to an increase in the electrode sheet thickness, the lithium-ion migration path will increase. At the same time, due to the decrease in the porosity of the electrode sheet caused by the high compaction density of the electrode sheet and the increase in the tortuosity of the electrode sheet, the lithium-ion migration rate will become slower, which will affect the kinetic performance of the lithium-ion battery. Therefore, there is an urgent need to provide a lithium-ion battery that has a relatively high energy density and good kinetic performance at the same time. Summary of the Invention

[0004] The purpose of the present application is to provide a positive electrode sheet, a secondary battery and an electronic device, and the secondary battery has a relatively high energy density and good kinetic performance at the same time. The specific technical solutions are as follows:

[0005] In the first aspect of the present application, a positive electrode sheet is provided. The positive electrode sheet includes a positive current collector and a positive electrode material layer provided on at least one surface of the positive current collector. The positive electrode material layer includes a positive active material, a positive binder, a positive conductive agent and an additive, and the additive is at least one of a compound of formula I and a compound of formula II.

[0006]

[0007] Wherein, 9≤n≤20, R1 is selected from H, Li, Ca, Mg, Zn, Al, Fe, Ba or Co, and R2 is selected from C9 to C 20Alkenylene group. Based on the mass of the positive electrode material layer, the mass percentage content of the additive is W%, where 0.02 ≤ W ≤ 2.5. The porosity of the positive electrode sheet is P%, where 12 ≤ P ≤ 25. The inventors have found through research that by adding the additive, namely the above-mentioned compound of formula I and / or compound of formula II, the above additive can act as a dispersant. On the one hand, during the mixing of the components of the positive electrode slurry, the additive can use the steric hindrance effect to improve the distribution of the positive electrode conductive agent and the positive electrode binder, and preferably reduce the agglomeration of the positive electrode conductive agent and the positive electrode binder, so that the mixed phase (CBD carbon glue phase) of the positive electrode conductive agent and the positive electrode binder evenly covers the surface of the positive electrode active material particles and between the positive electrode active material particles, which is beneficial to improving the efficiency of lithium ions being deintercalated from and intercalated into the positive electrode active material; the CBD carbon glue phase evenly covers between the positive electrode active material particles, reducing the possibility of agglomeration of the positive electrode conductive agent and the positive electrode binder, and can optimize the porosity distribution of the positive electrode sheet. The reduction of the agglomeration points of the positive electrode conductive agent and the positive electrode binder generates larger pores in the positive electrode material layer, which is beneficial to improving the diffusion impedance of lithium ions in the positive electrode sheet. When the porosity of the positive electrode sheet is too small, for example, less than 12%, the electrolyte infiltration is insufficient and the lithium ion migration path is narrow, affecting the kinetic performance of the secondary battery; when the porosity of the positive electrode sheet is too large, for example, greater than 25%, the contact resistance between the particles in the positive electrode material layer will increase, affecting the kinetic performance of the secondary battery. On the other hand, the additive has special functional groups and has a relatively high affinity with the solvent in the electrolyte, which can preferably assist the solvent molecules in desolvation, further improving the diffusion impedance of lithium ions, and is beneficial to improving the charge and discharge performance of the secondary battery in a low-temperature environment and a high-rate environment. When the mass percentage content of the additive is too small, for example, less than 0.02%, it cannot effectively improve the agglomeration of the positive electrode conductive agent and the positive electrode binder, affecting the kinetic performance and energy density of the secondary battery; when the mass percentage content of the additive is too large, for example, greater than 2.5%, the positive electrode material layer is more likely to detach from the surface of the positive electrode current collector, affecting the kinetic performance of the secondary battery. Therefore, by controlling the positive electrode sheet to meet the above characteristics, the positive electrode sheet can have a relatively high porosity and a relatively low lithium ion diffusion impedance under high tap density conditions, and the secondary battery has a relatively high energy density and good kinetic performance at the same time.

[0008] In an embodiment of the present application, 0.03 ≤ W ≤ 0.8. By controlling the value of W within the above range, the mass percentage content of the additive can be further optimized, the distribution of the positive electrode conductive agent and the positive electrode binder can be further improved, the agglomeration of the positive electrode conductive agent and the positive electrode binder can be reduced, and the porosity distribution of the positive electrode sheet can be optimized, so as to better improve the transport impedance of lithium ions in the positive electrode sheet and further enhance the cycle performance of the secondary battery. Therefore, the secondary battery has a higher energy density and better kinetic performance at the same time.

[0009] In an embodiment of the present application, the tap density of the positive electrode material layer is PD g / cm 3 , 3.0 ≤ PD ≤ 4.5, preferably, 3.8 ≤ PD ≤ 4.4. By adjusting the tap density of the positive electrode material layer within the above range, under the condition that the positive electrode material layer has a relatively high tap density, the positive active material particles are packed more closely, which can optimize the porosity of the positive electrode material layer, further improve the lithium ion transport impedance in the positive electrode sheet, so that the secondary battery has a relatively high energy density while also having good kinetic performance.

[0010] In an embodiment of the present application, the coating weight of the positive electrode material layer is CW, 0.018 g / cm 2 ≤ CW ≤ 0.039 g / cm 2 . By adjusting the coating weight of the positive electrode material layer within the above range, under the condition that the positive electrode sheet has a relatively high coating weight of the positive electrode material layer, there are more positive active material particles in the same area, and while the energy density of the secondary battery is relatively large, the lithium ion diffusion impedance in the positive electrode sheet is relatively large. The addition of the additive can better improve the distribution of the positive electrode conductive agent and the positive electrode binder, make the mixed phase of the positive electrode conductive agent and the positive electrode binder cover the surface of the positive active material particles and between the positive active material particles more uniformly, better improve the lithium ion diffusion impedance, and preferably improve the cycle performance of the secondary battery. Therefore, the secondary battery has a relatively high energy density while also having good kinetic performance.

[0011] In an embodiment of the present application, the thickness of the positive electrode material layer is H1 μm, 30 ≤ H1 ≤ 110, preferably, 40 ≤ H1 ≤ 80. The thickness of the above positive electrode material layer refers to the thickness of the single-sided positive electrode material layer after cold pressing. By adjusting the thickness of the positive electrode material layer within the above range, under the condition that the positive electrode material layer is relatively thick, the number of positive active material particles per unit volume is relatively large, and while the energy density of the secondary battery is relatively large, the lithium ion diffusion impedance in the positive electrode sheet is relatively large. The addition of the additive can better improve the distribution of the positive electrode conductive agent and the positive electrode binder, make the mixed phase of the positive electrode conductive agent and the positive electrode binder cover the surface of the positive active material particles and between the positive active material particles more uniformly, better improve the lithium ion diffusion impedance, and preferably improve the cycle performance of the secondary battery. Therefore, the secondary battery has a relatively high energy density while also having good kinetic performance.

[0012] In one embodiment of the present application, the compound of Formula I includes at least one of undecanoic acid, lauric acid, tridecanoic acid, myristic acid, pentadecanoic acid, palmitic acid, margaric acid, stearic acid, lithium stearate, calcium stearate, magnesium stearate, zinc stearate, aluminum stearate, iron stearate, barium stearate or cobalt stearate; preferably at least one of palmitic acid, stearic acid, lithium stearate, magnesium stearate or iron stearate. By selecting the above-mentioned compound of Formula I, the compound of Formula I has better grease-like lubrication characteristics, can be more evenly distributed between the positive electrode active material particles, has a higher affinity with the solvent in the electrolyte, can better assist the solvent molecules in desolvation, further improve the diffusion impedance of lithium ions, can improve the charge and discharge performance of the secondary battery under low-temperature environment and high-rate environment, and further enhance the cycle performance of the secondary battery. Therefore, the secondary battery has a high energy density and good kinetic performance at the same time.

[0013] In one embodiment of the present application, the compound of Formula II includes at least one of myristoleic acid, oleic acid or octadecenoic acid. By selecting the above-mentioned compound of Formula II, the compound of Formula II has better grease-like lubrication characteristics, can be more evenly distributed between the positive electrode active material particles, has a higher affinity with the solvent in the electrolyte, can better assist the solvent molecules in desolvation, further improve the diffusion impedance of lithium ions, can improve the charge and discharge performance of the secondary battery under low-temperature environment and high-rate environment, and further enhance the cycle performance of the secondary battery. Therefore, the secondary battery has a high energy density and good kinetic performance at the same time.

[0014] In one embodiment of the present application, the melting point of the additive is Tm °C, 50 ≤ Tm ≤ 230, preferably, 65 ≤ Tm ≤ 190. By selecting the additive within the above melting point range, the selected additive has better dispersibility and lubricity, can further improve the lubricity of the positive electrode sheet and the dispersion performance of the conductive agent and the binder, so that the secondary battery has a high energy density and good kinetic performance at the same time.

[0015] In one embodiment of the present application, the true density of the additive is p g / cm 3 , 0.7 ≤ p ≤ 1.3, preferably, 0.85 ≤ p ≤ 1.15. Or it is a range composed of any two of the above values. By selecting the additive within the above true density range, the selected additive has better thermal stability and mechanical stability, and at the same time, the appropriate true density can further improve the solubility and dispersibility of the additive, so that the secondary battery has a high energy density and good kinetic performance at the same time.

[0016] In an embodiment of the present application, there is a first decomposition peak at 150°C to 220°C and / or a second decomposition peak at 250°C to 350°C in the thermogravimetric curve of the positive electrode sheet. The first decomposition peak at 150°C to 220°C is the thermal decomposition peak of the acid additive, and the second decomposition peak at 250°C to 350°C is the thermal decomposition peak of the salt additive. The thermogravimetric curve of the positive electrode sheet satisfies the above characteristics, indicating that the additives in the positive electrode material layer include acid additives and salt additives. The addition of the above two types of additives can better improve the distribution of the positive electrode conductive agent and the positive electrode binder during the mixing of the components of the positive electrode slurry by using the steric hindrance effect, and better reduce the agglomeration of the positive electrode conductive agent and the positive electrode binder, so that the mixed phase of the positive electrode conductive agent and the positive electrode binder uniformly covers the surface of the positive electrode active material particles and between the positive electrode active material particles. It can optimize the porosity distribution of the positive electrode sheet, improve the diffusion impedance of lithium ions in the positive electrode sheet, and improve the cycle performance of the secondary battery. Therefore, the secondary battery has a higher energy density and better kinetic performance at the same time.

[0017] In an embodiment of the present application, the positive electrode material layer includes an upper layer, a middle layer, and a lower layer with equal thickness arranged in sequence along the thickness direction. The thermal weight loss rates of the upper layer, the middle layer, and the lower layer are M1%, M2%, and M3% respectively, 0 ≤ |M1 - M2| ≤ 0.8, 0 ≤ |M1 - M3| ≤ 0.8. Preferably, 0 ≤ |M1 - M2| ≤ 0.6, 0 ≤ |M1 - M3| ≤ 0.6. By controlling the structure and characteristics of the positive electrode material layer to meet the above range, the difference in the thermal weight loss rates between the upper layer, the middle layer, and the lower layer in the positive electrode material layer is relatively appropriate, indicating that the distribution of the positive electrode binder in the positive electrode material layer is relatively uniform. The addition of the additive can better improve the floating of the positive electrode binder during coating and drying, and better reduce the possibility of the decrease in the content of the positive electrode binder between the positive electrode current collector and the positive electrode material layer, so that there is a high adhesive force between the positive electrode material layer and the positive electrode current collector. At the same time, the uniformly distributed positive electrode binder is beneficial to reducing the polymerization of the positive electrode binder and the conductive agent, thereby increasing the porosity and ionic conductivity of the surface layer of the positive electrode sheet. Therefore, the secondary battery has a higher energy density and better kinetic performance at the same time.

[0018] In an embodiment of the present application, based on the mass of the positive electrode material layer, the mass percentage content of the positive electrode binder is X%, 0.6 ≤ X ≤ 2.5. By controlling the mass percentage content of the positive electrode binder within the above range, the positive electrode binder has an appropriate mass percentage content, which can enable a high adhesive force between the positive electrode material layer and the positive electrode current collector, and further improve the cycle performance of the secondary battery.

[0019] In an embodiment of the present application, the positive electrode binder includes at least one of polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, fluorinated acrylate resin, polyvinylidene fluoride-hexafluoropropylene copolymer, polyvinyl alcohol, polyacrylonitrile, starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, carboxymethyl cellulose, styrene-butadiene rubber, fluororubber, or various copolymers thereof. By selecting the above positive electrode binder, the secondary battery has high mechanical stability and thermal stability during the cycling process, improving the cycling efficiency and safety performance of the secondary battery, and further improving the energy density of the secondary battery.

[0020] In an embodiment of the present application, 10 ≤ X / W ≤ 120. By regulating the value of X / W within the above range, a suitable content of the positive electrode binder is combined with a suitable content of the additive, which can better improve the distribution of the positive electrode conductive agent and the positive electrode binder by using the steric hindrance effect during the mixing of the components of the positive electrode slurry, better reduce the agglomeration of the positive electrode conductive agent and the positive electrode binder, and make the mixed phase of the positive electrode conductive agent and the positive electrode binder evenly cover the surface of the positive electrode active material particles and between the positive electrode active material particles. Further optimize the porosity distribution of the positive electrode sheet, improve the diffusion impedance of lithium ions in the positive electrode sheet, and improve the cycling performance of the secondary battery. Therefore, the secondary battery has good kinetic performance while having a high energy density.

[0021] In an embodiment of the present application, the adhesion between the positive electrode material layer and the positive electrode current collector is F N / m, and F ≥ 25. By regulating the adhesion between the positive electrode material layer and the positive electrode current collector within the above range, the positive electrode material layer and the positive electrode current collector have a high adhesion, further improving the cycling performance of the secondary battery.

[0022] In an embodiment of the present application, the particle size of the positive electrode active material satisfies: 0.25 ≤ Dv10 / Dv50 ≤ 0.5, preferably, 0.33 ≤ Dv10 / Dv50 ≤ 0.45. When the particle size of the positive electrode active material satisfies the above characteristics, the positive electrode active material has a suitable particle size ratio, the large-particle and small-particle positive electrode active materials are blended, the positive electrode active materials are packed more tightly, the tap density of the positive electrode active material itself is high, and the tap density of the positive electrode sheet is high, so that the secondary battery has a high energy density.

[0023] In an embodiment of the present application, the thickness of the positive electrode current collector is H2 μm, where 7 ≤ H2 ≤ 20, and preferably, 8 ≤ H2 ≤ 12. The thickness of the positive electrode current collector described above refers to the thickness of the positive electrode current collector before cold pressing. By controlling the thickness of the positive electrode current collector within the above range, the positive electrode current collector can have good strength and ductility, and at the same time, the secondary battery can also have a high energy density.

[0024] In an embodiment of the present application, the positive electrode active material includes at least one of lithium cobaltate, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminate, or lithium iron phosphate. The above-mentioned lithium nickel cobalt manganese oxide may include LiNi 0.95 Co 0.03 Mn 0.02 O2(Ni95), LiNi 0.91 Co 0.03 Mn 0.06 O2(Ni91), LiNi 0.8 Co 0.1 Mn 0.1 O2(NCM811), LiNi 0.6 Co 0.2 Mn 0.2 O2(NCM622), LiNi 0.5 Co 0.2 Mn 0.3 O2(NCM523) or LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2(NCM111) or at least one of them. By selecting the above positive electrode active material, the secondary battery has a high energy density while also having good cycling performance and safety performance.

[0025] The second aspect of the present application provides a secondary battery, which includes the positive electrode sheet in any of the foregoing embodiments. Therefore, the secondary battery provided by the present application has a high energy density while also having good cycling performance and safety performance.

[0026] The third aspect of the present application provides an electronic device, which includes the secondary battery in any of the foregoing embodiments. Therefore, the electronic device provided by the present application has a high energy density while also having good cycling performance and safety performance.

[0027] Advantages of the present application:

[0028] The present application provides a positive electrode sheet, a secondary battery, and an electronic device. The positive electrode sheet includes a positive electrode current collector and a positive electrode material layer provided on at least one surface of the positive electrode current collector. The positive electrode material layer includes a positive electrode active material, a positive electrode binder, a positive electrode conductive agent, and an additive. The additive is at least one of a compound of formula I and a compound of formula II. Based on the mass of the positive electrode material layer, the mass percentage content of the additive is W%, and 0.02 ≤ W ≤ 2.5; the porosity of the positive electrode sheet is P%, and 12 ≤ P ≤ 25. When the positive electrode sheet satisfies the above characteristics, the secondary battery has a relatively high energy density and good kinetic performance.

[0029] Of course, it is not necessary for any product or method implementing the present application to simultaneously achieve all the above-mentioned advantages. Detailed implementation manners

[0030] The technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all of the embodiments. All other embodiments obtained by those skilled in the art based on the present application belong to the scope of protection of the present application.

[0031] It should be noted that in the specific implementation manners of the present application, a lithium-ion battery is taken as an example of the secondary battery to explain the present application. However, the secondary battery of the present application is not limited to lithium-ion batteries.

[0032] The first aspect of the present application provides a positive electrode sheet. The positive electrode sheet includes a positive electrode current collector and a positive electrode material layer provided on at least one surface of the positive electrode current collector. The positive electrode material layer includes a positive electrode active material, a positive electrode binder, a positive electrode conductive agent, and an additive. The additive is at least one of a compound of formula I and a compound of formula II.

[0033]

[0034] Among them, 9 ≤ n ≤ 20, R1 is selected from H, Li, Ca, Mg, Zn, Al, Fe, Ba, or Co, and R2 is selected from C9 to C 20alkenylene group. Exemplarily, the value of n can be 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19 or 20. Based on the mass of the positive electrode material layer, the mass percentage content of the additive is W%, and 0.02 ≤ W ≤ 2.5. Exemplarily, the value of W can be 0.02, 0.03, 0.05, 0.07, 0.09, 0.1, 0.3, 0.5, 0.7, 1, 1.3, 1.5, 1.7, 1.9, 2.1, 2.3, 2.5 or a range composed of any two of the above numerical values. The porosity of the positive electrode plate is P%, and 12 ≤ P ≤ 25. Exemplarily, the value of P can be 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25 or a range composed of any two of the above numerical values. The above-mentioned "positive electrode material layer provided on at least one surface of the positive electrode current collector" means that the positive electrode material layer can be provided on one surface of the positive electrode current collector along its own thickness direction, or can be provided on two surfaces of the positive electrode current collector along its own thickness direction. It should be noted that the "surface" here can be the entire area of the positive electrode current collector or a partial area of the positive electrode current collector, and there is no special limitation in this application as long as the purpose of this application can be achieved.

[0035] The inventors' research found that by adding additives, namely the above-mentioned compound of Formula I and / or the compound of Formula II, to the positive electrode material layer, the above-mentioned additives can act as dispersants. On the one hand, during the mixing of the components of the positive electrode slurry, the additives can utilize the steric hindrance effect to improve the distribution of the positive electrode conductive agent and the positive electrode binder, and preferably reduce the agglomeration of the positive electrode conductive agent and the positive electrode binder, so that the mixed phase (CBD carbon glue phase) of the positive electrode conductive agent and the positive electrode binder evenly covers the surface of the positive electrode active material particles and between the positive electrode active material particles. The CBD carbon glue phase evenly covering the surface of the positive electrode active material particles can reduce the possibility of overcoating of the positive electrode active material caused by the agglomeration of the positive electrode conductive agent and the positive electrode binder, which is beneficial to improving the efficiency of lithium ion extraction and insertion from the positive electrode active material; the CBD carbon glue phase evenly covering between the positive electrode active material particles and reducing the possibility of agglomeration of the positive electrode conductive agent and the positive electrode binder can optimize the porosity distribution of the positive electrode sheet. The reduction of the agglomeration points of the positive electrode conductive agent and the positive electrode binder generates larger pores in the positive electrode material layer, which is beneficial to improving the diffusion impedance of lithium ions in the positive electrode sheet. When the porosity of the positive electrode sheet is too small, for example, less than 12%, the electrolyte infiltration is insufficient and the lithium ion migration path is narrow, affecting the kinetic performance of the secondary battery; when the porosity of the positive electrode sheet is too large, for example, greater than 25%, the contact resistance between the particles in the positive electrode material layer will increase, affecting the kinetic performance of the secondary battery. On the other hand, the additives have special functional groups and have a relatively high affinity with the solvent in the electrolyte, which can preferably assist the solvent molecules to desolvate, further improve the diffusion impedance of lithium ions, and is beneficial to improving the charge and discharge performance of the secondary battery under low-temperature and high-rate environments, and at the same time is beneficial to improving the increase in impedance during the cycling of the secondary battery, thereby enhancing the cycling performance of the secondary battery. When the mass percentage content of the additive is too small, for example, less than 0.02%, it cannot effectively improve the agglomeration of the positive electrode conductive agent and the positive electrode binder, affecting the cycling performance and energy density of the secondary battery; when the mass percentage content of the additive is too large, for example, greater than 2.5%, the positive electrode material layer is more likely to detach from the surface of the positive electrode current collector, affecting the cycling performance of the secondary battery. Therefore, by controlling the positive electrode sheet to meet the above characteristics, the positive electrode sheet can have a relatively high porosity and a relatively low lithium ion diffusion impedance under the condition of high tap density, and the secondary battery has a relatively high energy density and good kinetic performance at the same time.

[0036] In an embodiment of the present application, 0.03 ≤ W ≤ 0.8. Exemplarily, the value of W can be 0.03, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8 or a range composed of any two of the above numerical values. By adjusting the value of W within the above range, the mass percentage content of the additive can be further optimized, the distribution of the cathode conductive agent and the cathode binder can be further improved, the agglomeration of the cathode conductive agent and the cathode binder can be reduced, and the porosity distribution of the cathode electrode sheet can be optimized, so as to better improve the lithium ion transfer impedance in the cathode electrode sheet and further enhance the cycling performance of the secondary battery. Therefore, the secondary battery has a higher energy density and better kinetic performance at the same time.

[0037] In an embodiment of the present application, the tap density of the cathode material layer is PD g / cm 3 , 3.0 ≤ PD ≤ 4.5. Preferably, 3.8 ≤ PD ≤ 4.4. Exemplarily, the value of PD can be 3.0, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 4.0, 4.1, 4.2, 4.3, 4.4, 4.5 or a range composed of any two of the above numerical values. By adjusting the tap density of the cathode material layer within the above range, under the condition that the cathode material layer has a high tap density, the cathode active material particles are packed more closely, the porosity of the cathode material layer can be optimized, and the lithium ion transfer impedance in the cathode electrode sheet can be further improved, so that the secondary battery has a high energy density and good kinetic performance at the same time.

[0038] In an embodiment of the present application, the coating weight of the cathode material layer is CW, 0.018 g / cm 2 ≤ CW ≤ 0.039 g / cm 2 . Exemplarily, the value of CW can be 0.018, 0.021, 0.023, 0.025, 0.027, 0.029, 0.031, 0.033, 0.035, 0.037, 0.039 or a range composed of any two of the above numerical values. By adjusting the coating weight of the cathode material layer within the above range, under the condition that the cathode electrode sheet has a high coating weight of the cathode material layer, there are more cathode active material particles in the same area, the energy density of the secondary battery is larger while the diffusion impedance of lithium ions in the cathode electrode sheet is larger. The addition of the additive can better improve the distribution of the cathode conductive agent and the cathode binder, make the mixed phase of the cathode conductive agent and the cathode binder more evenly cover the surface of the cathode active material particles and between the cathode active material particles, better improve the diffusion impedance of lithium ions, and preferably improve the cycling performance of the secondary battery. Therefore, the secondary battery has a higher energy density and better kinetic performance at the same time.

[0039] In an embodiment of the present application, the thickness of the positive electrode material layer is H1 μm, where 30 ≤ H1 ≤ 110, and preferably, 40 ≤ H1 ≤ 80. Exemplarily, the value of H1 can be 30, 40, 50, 60, 70, 80, 90, 100, 110, or a range composed of any two of the above numerical values. The thickness of the above positive electrode material layer refers to the thickness of the single-sided positive electrode material layer after cold pressing. By adjusting the thickness of the positive electrode material layer within the above range, when the positive electrode material layer is relatively thick, the number of positive electrode active material particles per unit volume is relatively large, and while the energy density of the secondary battery is relatively large, the diffusion impedance of lithium ions in the positive electrode sheet is relatively large. The addition of the additive can better improve the distribution of the positive electrode conductive agent and the positive electrode binder, make the mixed phase of the positive electrode conductive agent and the positive electrode binder more evenly cover the surface of the positive electrode active material particles and between the positive electrode active material particles, better improve the diffusion impedance of lithium ions, and preferably improve the cycle performance of the secondary battery. Therefore, the secondary battery has a higher energy density and better kinetic performance at the same time.

[0040] In an embodiment of the present application, the compound of formula I includes at least one of undecanoic acid, lauric acid, tridecanoic acid, myristic acid, pentadecanoic acid, palmitic acid, margaric acid, stearic acid, lithium stearate, calcium stearate, magnesium stearate, zinc stearate, aluminum stearate, iron stearate, barium stearate, or cobalt stearate; preferably at least one of palmitic acid, stearic acid, lithium stearate, magnesium stearate, or iron stearate. By selecting the above compound of formula I, the compound of formula I has better grease-like lubrication characteristics, the compound of formula I can be more evenly distributed between the positive electrode active material particles, has a relatively high affinity with the solvent in the electrolyte, can better assist the solvent molecules in desolvation, further improve the diffusion impedance of lithium ions, and can improve the charge and discharge performance of the secondary battery in a low-temperature environment and a high-rate environment, and further improve the cycle performance of the secondary battery. Therefore, the secondary battery has a relatively high energy density and better kinetic performance at the same time.

[0041] In an embodiment of the present application, the compound of formula II includes at least one of myristoleic acid, oleic acid, or oleic acid. By selecting the above compound of formula II, the compound of formula II has better grease-like lubrication characteristics, the compound of formula II can be more evenly distributed between the positive electrode active material particles, has a relatively high affinity with the solvent in the electrolyte, can better assist the solvent molecules in desolvation, further improve the diffusion impedance of lithium ions, and can improve the charge and discharge performance of the secondary battery in a low-temperature environment and a high-rate environment, and further improve the cycle performance of the secondary battery. Therefore, the secondary battery has a relatively high energy density and better kinetic performance at the same time.

[0042] In one embodiment of the present application, the melting point of the additive is Tm °C, where 50 ≤ Tm ≤ 230, and preferably, 65 ≤ Tm ≤ 190. Exemplarily, the value of Tm can be 50, 55, 60, 65, 70, 90, 110, 150, 170, 190, 210, 230, or a range composed of any two of the above numerical values. By selecting the additive within the above melting point range, the selected additive has better dispersibility and lubricity, and can further improve the lubricity of the positive electrode sheet and the dispersion performance of the conductive agent and the binder, so that the secondary battery has a high energy density and good kinetic performance at the same time.

[0043] In one embodiment of the present application, the true density of the additive is p g / cm 3 , where 0.7 ≤ p ≤ 1.3, and preferably, 0.85 ≤ p ≤ 1.15. Exemplarily, the value of p can be 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 1.0, 1.05, 1.1, 1.15, 1.2, 1.25, 1.3, or a range composed of any two of the above numerical values. Or a range composed of any two of the above numerical values. By selecting the additive within the above true density range, the selected additive has better thermal stability and mechanical stability. At the same time, the appropriate true density can further improve the solubility and dispersibility of the additive, so that the secondary battery has a high energy density and good kinetic performance at the same time.

[0044] In one embodiment of the present application, there is a first decomposition peak at 150 °C to 220 °C and / or a second decomposition peak at 250 °C to 350 °C in the thermogravimetric curve of the positive electrode sheet. The first decomposition peak at 150 °C to 220 °C is the thermal decomposition peak of the acid additive, and the second decomposition peak at 250 °C to 350 °C is the thermal decomposition peak of the salt additive. The fact that the thermogravimetric curve of the positive electrode sheet satisfies the above characteristics indicates that the additives in the positive electrode material layer include acid additives and salt additives. The addition of the above two types of additives can better improve the distribution of the positive electrode conductive agent and the positive electrode binder by using the steric hindrance effect during the mixing of the components of the positive electrode slurry, and can better reduce the agglomeration of the positive electrode conductive agent and the positive electrode binder, so that the mixed phase of the positive electrode conductive agent and the positive electrode binder evenly covers the surface of the positive electrode active material particles and between the positive electrode active material particles. It can optimize the porosity distribution of the positive electrode sheet, improve the diffusion impedance of lithium ions in the positive electrode sheet, and improve the cycle performance of the secondary battery. Therefore, the secondary battery has a high energy density and good kinetic performance at the same time.

[0045] In an embodiment of the present application, the positive electrode material layer includes an upper layer, a middle layer, and a lower layer that are arranged in sequence along the thickness direction and have equal thicknesses. The lower layer is closer to the current collector side than the upper layer. The thermal weight loss rates of the upper layer, the middle layer, and the lower layer are M1%, M2%, and M3% respectively. 0 ≤ |M1 - M2| ≤ 0.8, 0 ≤ |M1 - M3| ≤ 0.8. Preferably, 0 ≤ |M1 - M2| ≤ 0.6, 0 ≤ |M1 - M3| ≤ 0.6. Exemplarily, the value of |M1 - M2| can be 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8 or a range composed of any two of the above numerical values; the value of |M1 - M3| can be 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8 or a range composed of any two of the above numerical values. By regulating the structure and characteristics of the positive electrode material layer to meet the above range, the difference in thermal weight loss rates between the upper layer, the middle layer, and the lower layer in the positive electrode material layer is more appropriate, indicating that the distribution of the positive electrode binder in the positive electrode material layer is relatively uniform. The addition of the additive can better improve the floating of the positive electrode binder during coating and drying, and better reduce the possibility of the decrease in the content of the positive electrode binder between the positive electrode current collector and the positive electrode material layer, so that there is a high adhesive force between the positive electrode material layer and the positive electrode current collector. At the same time, the uniformly distributed positive electrode binder is beneficial to reducing the polymerization of the positive electrode binder and the conductive agent, thereby increasing the porosity and ionic conductivity of the surface layer of the positive electrode sheet. Therefore, the secondary battery has a higher energy density and better kinetic performance at the same time.

[0046] In an embodiment of the present application, based on the mass of the positive electrode material layer, the mass percentage content of the positive electrode binder is X%, 0.6 ≤ X ≤ 2.5. Exemplarily, the value of X can be 0.6, 0.7, 0.9, 1.1, 1.3, 1.5, 1.7, 1.9, 2.1, 2.3, 2.5 or a range composed of any two of the above numerical values. By regulating the mass percentage content of the positive electrode binder within the above range, the positive electrode binder has an appropriate mass percentage content, which can enable a high adhesive force between the positive electrode material layer and the positive electrode current collector, and further improve the cycle performance of the secondary battery.

[0047] In an embodiment of the present application, the positive electrode binder includes at least one of polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, fluorinated acrylate resin, polyvinylidene fluoride-hexafluoropropylene copolymer, polyvinyl alcohol, polyacrylonitrile, starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, carboxymethyl cellulose, styrene-butadiene rubber, fluororubber, or various copolymers thereof. By selecting the above positive electrode binder, the adhesion between the positive electrode material layer and the positive electrode current collector can be improved preferably, so that the secondary battery has high mechanical stability and thermal stability during the cycling process, the cycling efficiency and safety performance of the secondary battery are improved, and the energy density of the secondary battery is further improved.

[0048] In an embodiment of the present application, 10 ≤ X / W ≤ 120. Exemplarily, the value of X / W can be 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, or a range composed of any two of the above numerical values. By adjusting the value of X / W within the above range, a suitable content of the positive electrode binder is combined with a suitable content of the additive, and the additive can better improve the distribution of the positive electrode conductive agent and the positive electrode binder by using the steric hindrance effect during the mixing of the components of the positive electrode slurry, better reduce the agglomeration of the positive electrode conductive agent and the positive electrode binder, and make the mixed phase of the positive electrode conductive agent and the positive electrode binder uniformly cover the surface of the positive electrode active material particles and between the positive electrode active material particles. Further optimize the porosity distribution of the positive electrode sheet, improve the diffusion impedance of lithium ions in the positive electrode sheet, and improve the cycling performance of the secondary battery. Therefore, the secondary battery has high energy density and good kinetic performance at the same time.

[0049] In an embodiment of the present application, the adhesion between the positive electrode material layer and the positive electrode current collector is F N / m, and F ≥ 25. Exemplarily, the value of F can be 25, 27, 29, 30, 35, 37, 39, 40, 50, 60, 70, 80, 90, 100, 110, 120, or a range composed of any two of the above numerical values. By adjusting the adhesion between the positive electrode material layer and the positive electrode current collector within the above range, the positive electrode material layer and the positive electrode current collector have high adhesion, and the cycling performance of the secondary battery is further improved.

[0050] In an embodiment of the present application, the particle size of the positive electrode active material satisfies: 0.25 ≤ Dv10 / Dv50 ≤ 0.5. Preferably, 0.33 ≤ Dv10 / Dv50 ≤ 0.45. Exemplarily, the value of Dv10 / Dv50 can be 0.25, 0.30, 0.33, 0.35, 0.37, 0.39, 0.41, 0.43, 0.45, 0.47, 0.5 or a range composed of any two of the above numerical values. When the particle size of the positive electrode active material satisfies the above characteristics, the positive electrode active material has a suitable grading ratio. The large-particle and small-particle positive electrode active materials are blended, and the positive electrode active materials are stacked more closely, and the tap density of the positive electrode active material itself is relatively high, so that the tap density of the positive electrode sheet is relatively high, thereby enabling the secondary battery to have a relatively high energy density. In the present application, 3.0 μm ≤ Dv10 ≤ 10.5 μm, and 6.8 μm ≤ Dv50 ≤ 19.6 μm.

[0051] In the present application, Dv10 refers to the particle size that reaches 10% of the cumulative volume when measured from the small particle size in the particle size distribution based on the volume of the material; Dv50 refers to the particle size that reaches 50% of the cumulative volume when measured from the small particle size in the particle size distribution based on the volume of the material.

[0052] In an embodiment of the present application, the thickness of the positive electrode current collector is H2 μm, 7 ≤ H2 ≤ 20. Preferably, 8 ≤ H2 ≤ 12. Exemplarily, the value of H2 can be 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 or a range composed of any two of the above numerical values. The thickness of the positive electrode current collector refers to the thickness of the positive electrode current collector before cold pressing. By adjusting the thickness of the positive electrode current collector within the above range, the positive electrode current collector can have good strength and ductility, and at the same time, the secondary battery can also have a relatively high energy density.

[0053] In an embodiment of the present application, the positive electrode active material includes at least one of lithium cobaltate, lithium nickel cobalt manganate, lithium nickel cobalt aluminate, or lithium iron phosphate. The above lithium nickel cobalt manganate may include LiNi 0.95 Co 0.03 Mn 0.02 O2(Ni95), LiNi 0.91 Co 0.03 Mn 0.06 O2(Ni91), LiNi 0.8 Co 0.1 Mn 0.1 O2(NCM811), LiNi 0.6 Co 0.2 Mn 0.2 O2(NCM622), LiNi 0.5 Co 0.2 Mn0.3 O2(NCM523) or LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 At least one of O2(NCM111). By selecting the above-mentioned positive electrode active material, the secondary battery has a high energy density while also having good cycle performance and safety performance.

[0054] This application has no particular limitation on the method for regulating the mass percentage content of the regulating additive, as long as the purpose of this application can be achieved. For example, the mass percentage content of the additive can be regulated by regulating the addition amount of the additive.

[0055] In this application, the tap density of the positive electrode material layer can be regulated by means known to those skilled in the art. For example, the tap density of the positive electrode material layer can be regulated by regulating the cold pressing pressure during the cold pressing process. Exemplarily, when other conditions remain unchanged, increasing the cold pressing pressure increases the tap density of the positive electrode material layer; decreasing the cold pressing pressure decreases the tap density of the positive electrode material layer.

[0056] In this application, the coating weight of the positive electrode material layer can be regulated by means known to those skilled in the art. For example, when the positive electrode slurry is coated on the surface of the positive electrode current collector, on the basis of a certain solid content of the positive electrode slurry, increasing the coating amount of the positive electrode slurry increases the coating weight of the positive electrode material layer. This application has no particular limitation as long as the purpose of this application can be achieved.

[0057] This application has no particular limitation on the method for regulating the thickness of the positive electrode material layer, as long as the purpose of this application can be achieved. For example, the thickness of the positive electrode material layer can be regulated by regulating the tap density of the positive electrode material layer.

[0058] This application has no particular limitation on the method for regulating the mass percentage content of the positive electrode binder, as long as the purpose of this application can be achieved. For example, the mass percentage content of the positive electrode binder can be regulated by regulating the addition amount of the positive electrode binder.

[0059] This application has no particular limitation on the method for regulating the value of X / W, as long as the purpose of this application can be achieved. For example, the value of X / W can be regulated by regulating the respective values of X and W, and the regulation method is as described above.

[0060] This application has no particular limitation on the method for regulating the adhesion between the positive electrode material layer and the positive electrode current collector, as long as the purpose of this application can be achieved. For example, the adhesion between the positive electrode material layer and the positive electrode current collector can be regulated by regulating the addition amount of the positive electrode binder and / or the additive.

[0061] The present application has no particular limitation on the method for regulating the particle sizes Dv10 and Dv50 of the positive electrode active material, as long as the object of the present application can be achieved. Exemplarily, the Dv10 and Dv50 of the positive electrode active material can be regulated by grinding the positive electrode active material. For example, the Dv10 of the positive electrode active material can be regulated by regulating the grinding time; the Dv50 of the positive electrode active material can be regulated by regulating the grinding time. Exemplarily, when other conditions remain unchanged, by extending the grinding time, the Dv10 of the positive electrode active material decreases, and the Dv50 of the positive electrode active material decreases; by shortening the grinding time, the Dv10 of the positive electrode active material increases, and the Dv50 of the positive electrode active material increases.

[0062] The present application has no particular limitation on the method for regulating the value of Dv10 / Dv50, as long as the object of the present application can be achieved. For example, the value of Dv10 / Dv50 can be regulated by regulating the respective values of Dv10 and Dv50, and the regulation method is as described above.

[0063] The present application has no particular limitation on the method for regulating the thickness of the positive electrode current collector, as long as the object of the present application can be achieved. For example, commercially available positive electrode current collectors with different thicknesses can be selected.

[0064] The present application has no particular limitation on the positive electrode current collector, as long as the object of the present application can be achieved. For example, it can include aluminum foil, aluminum alloy foil, or a composite current collector (such as an aluminum-carbon composite current collector), etc.

[0065] The positive electrode material layer of the present application further includes a positive electrode conductive agent. The present application has no particular limitation on the positive electrode conductive agent, as long as the object of the present application can be achieved. For example, the positive electrode conductive agent can include, but is not limited to, at least one of conductive carbon black, carbon nanotubes (CNTs), carbon fibers, flake graphite, graphene, metal materials, or conductive polymers. The above-mentioned conductive carbon black can include, but is not limited to, at least one of Super P, acetylene black, or Ketjen black. The above-mentioned carbon nanotubes can include, but is not limited to, single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The above-mentioned carbon fibers can include, but is not limited to, vapor-grown carbon fibers (VGCF) and / or nanofibers. The above-mentioned metal materials can include, but is not limited to, metal powders and / or metal fibers. Specifically, the metal can include, but is not limited to, at least one of copper, nickel, aluminum, or silver. The above-mentioned conductive polymers can include, but is not limited to, at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene, or polypyrrole. The present application has no particular limitation on the mass percentage contents of the positive electrode active material and the positive electrode conductive agent in the positive electrode material layer, and those skilled in the art can select according to actual needs as long as the object of the present application can be achieved.

[0066] The second aspect of the present application provides a secondary battery, which includes the positive electrode sheet in any of the foregoing embodiments. Therefore, the secondary battery provided by the present application has a relatively high energy density, good cycle performance, and safety performance.

[0067] In the present application, the secondary battery further includes a negative electrode sheet. The negative electrode sheet includes a negative electrode current collector and a negative electrode material layer provided on at least one surface of the negative electrode current collector. The above-mentioned "negative electrode material layer provided on at least one surface of the negative electrode current collector" means that the negative electrode material layer can be provided on one surface of the negative electrode current collector along its own thickness direction, or can be provided on two surfaces of the negative electrode current collector along its own thickness direction. It should be noted that the "surface" here can be the entire area of the negative electrode current collector or a partial area of the negative electrode current collector. There is no special limitation in the present application as long as the purpose of the present application can be achieved.

[0068] There is no special limitation on the negative electrode current collector in the present application as long as the purpose of the present application can be achieved. For example, it can include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, or composite current collector, etc.

[0069] The negative electrode material layer of the present application includes a negative electrode active material. There is no special limitation on the negative electrode active material in the present application as long as the purpose of the present application can be achieved. For example, the negative electrode active material can include natural graphite, artificial graphite, mesophase microcarbon microbeads (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composite, SiO x (0.5 < x < 1.6), Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, spinel-structured lithium titanate Li4Ti5O 12 , Li-Al alloy, or at least one of metallic lithium. The negative electrode material layer of the present application further includes a negative electrode binder and a negative electrode conductive agent. There is no special limitation on the negative electrode binder and the negative electrode conductive agent in the negative electrode material layer in the present application as long as the purpose of the present application can be achieved. For example, the negative electrode binder can be at least one of the above-mentioned positive electrode binders, and the negative electrode conductive agent can be at least one of the above-mentioned positive electrode conductive agents. There is no special limitation on the mass ratio of the negative electrode active material, the negative electrode binder, and the negative electrode conductive agent in the negative electrode material layer. Those skilled in the art can select according to actual needs as long as the purpose of the present application can be achieved.

[0070] There is no special limitation on the thickness of the negative electrode current collector in the present application as long as the purpose of the present application can be achieved. For example, the thickness of the negative electrode current collector is 4 μm to 20 μm. There is no special limitation on the thickness of the negative electrode material layer in the present application as long as the purpose of the present application can be achieved. For example, the thickness of the single-sided negative electrode material layer is 30 μm to 250 μm.

[0071] Optionally, the negative electrode sheet may further include a conductive layer, which is located between the negative electrode current collector and the negative electrode material layer. The present application has no particular limitation on the composition of the conductive layer, and it may be a commonly used conductive layer in the art. The conductive layer includes a conductive agent and a binder. The present application has no particular limitation on the conductive agent and the binder in the conductive layer, and it may be at least one of the above-mentioned negative electrode conductive agents and the above-mentioned negative electrode binders. The present application has no particular limitation on the mass ratio of the conductive agent and the binder in the conductive layer, and those skilled in the art can select according to actual needs as long as the purpose of the present application can be achieved.

[0072] In the present application, the secondary battery further includes an electrolyte. The electrolyte includes a lithium salt and a non-aqueous solvent. The lithium salt may include various lithium salts commonly used in the art, such as at least one of LiPF6, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, Li2SiF6, lithium bis(oxalato)borate (LiBOB), or lithium difluoroborate. The present application has no particular limitation on the non-aqueous solvent, as long as the object 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 carbonate compounds may include but are not limited to at least one of linear carbonate compounds, cyclic carbonate compounds, or fluorinated carbonate compounds. The above linear carbonate compounds may include but are not limited to at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), or ethyl methyl carbonate (EMC). The above cyclic carbonate compounds may include but are not limited to at least one of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), or vinylene ethylene carbonate (VEC). The above fluorinated carbonate compounds may include but are not limited to at least one of fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, or trifluoromethyl ethylene carbonate. The above carboxylate compounds may include but are not limited to at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanolide, valerolactone, or caprolactone. The above ether compounds may include but are not limited to at least one of dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1-ethoxy-1-methoxyethane, 2-methyltetrahydrofuran, or tetrahydrofuran. The above other organic solvents may include but are not limited to at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, or trioctyl phosphate. The present application has no particular limitation on the mass percentage content of the lithium salt and the non-aqueous solvent, as long as the object of the present application can be achieved.

[0073] In the present application, the secondary battery further includes a separator. The separator is used to separate the positive electrode plate and the negative electrode plate, prevent internal short circuit of the secondary battery, allow electrolyte ions to pass through freely, and does not affect the progress of the electrochemical charge and discharge process. There is no particular limitation on the separator in the present application as long as the object of the present application can be achieved. For example, the material of the separator may include, but is not limited to, at least one of polyolefins (PO) based on polyethylene (PE) and polypropylene (PP), polyesters (for example, polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex or aramid; the type of the separator may include at least one of a woven film, a non-woven film, a microporous film, a composite film, a rolled film or a spun film.

[0074] In the present application, the separator may include a base film and a surface treatment layer. The base film may be a non-woven fabric or a composite film having a porous structure, and the material of the base film may include at least one of polyethylene, polypropylene, polyethylene terephthalate or polyimide. Optionally, a polypropylene porous film, a polyethylene porous film, a polypropylene non-woven fabric, a polyethylene non-woven fabric or a polypropylene-polyethylene-polypropylene porous composite film may be used. Optionally, a surface treatment layer is provided on at least one surface of the base film, and the surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by mixing a polymer and an inorganic substance. For example, the inorganic layer includes inorganic particles and a separator binder. There is no particular limitation on the above-mentioned inorganic particles in the present application. For example, it may include at least one of alumina, silica, magnesia, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide or barium sulfate. There is no particular limitation on the above-mentioned separator binder in the present application. For example, it may be at least one of the aforementioned positive electrode binders. The polymer layer contains a polymer, and the material of the polymer includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyvinylpyrrolidone, polyethylene ether, polyvinylidene fluoride or poly(vinylidene fluoride-hexafluoropropylene).

[0075] The secondary battery of the present application further includes a packaging bag for accommodating the positive electrode plate, the separator, the negative electrode plate and the electrolyte, as well as other components known in the art in the secondary battery. There is no limitation on the above-mentioned other components in the present application. There is no particular limitation on the packaging bag in the present application. It may be a packaging bag well-known in the art as long as the object of the present application can be achieved.

[0076] There is no particular limitation on the type of the secondary battery in the present application, and it may include any device that undergoes an electrochemical reaction. In the present application, the secondary battery may include, but is not limited to: lithium metal secondary batteries, lithium ion secondary batteries (lithium ion batteries), lithium polymer secondary batteries or lithium ion polymer secondary batteries, etc.

[0077] The preparation process of the secondary battery of the present application is well-known to those skilled in the art, and there is no special limitation in the present application. For example, it may include but is not limited to the following steps: stacking the positive electrode sheet, the separator, and the negative electrode sheet in sequence, and winding, folding, etc. as needed to obtain a wound structure electrode assembly, putting the electrode assembly into a packaging bag, injecting electrolyte into the packaging bag and sealing it to obtain a secondary battery; or, stacking the positive electrode sheet, the separator, and the negative electrode sheet in sequence, and then fixing the four corners of the entire laminated structure with tape to obtain a laminated structure electrode assembly, putting the electrode assembly into a packaging bag, injecting electrolyte into the packaging bag and sealing it to obtain a secondary battery. In addition, an overcurrent protection element, a guide plate, etc. may be placed in the packaging bag as needed to prevent the pressure inside the secondary battery from rising and overcharging / discharging. Among them, the packaging bag is a known packaging bag in the art, and the present application does not limit this.

[0078] The third aspect of the present application provides an electronic device, which includes the secondary battery in any of the foregoing embodiments. Therefore, the electronic device provided by the present application has high energy density while also having good cycle performance and safety performance.

[0079] The present application does not particularly limit the type of the electronic device, and it may be any electronic device known in the prior art. In some embodiments, the electronic device may include but is not limited to a laptop computer, a pen-input computer, a mobile computer, an e-book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a head-mounted stereo earphone, a video recorder, a liquid crystal TV, a portable cleaner, a portable CD player, a mini disc, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, an automobile, a motorcycle, a moped, a bicycle, a lighting fixture, a toy, a game console, a clock, a power tool, a flashlight, a camera, a large household battery, and a lithium-ion capacitor, etc.

[0080] Examples

[0081] Hereinafter, examples and comparative examples are given to more specifically illustrate the embodiments of the present application. Various tests and evaluations are carried out according to the following methods. In addition, unless otherwise specified, "parts" and "%" are based on mass.

[0082] Testing methods and equipment:

[0083] Testing of the type and mass percentage content of additives:

[0084] (1) Disassemble the lithium-ion battery, take out the positive electrode sheet, soak the positive electrode sheet with N-methylpyrrolidone (NMP), centrifuge and take the upper solution for drying to obtain a mixture of the positive electrode binder, the positive electrode conductive agent, and the additive;

[0085] (2) Take the mixture obtained in step (1) and perform thermogravimetric (TG, the instrument model is synchronous thermal analyzer STA449F3) test analysis. The test temperature is from 25°C to 600°C, and calculate the weight loss. Among them, the weight percentage of the decomposed substance between 25°C and 400°C is the mass percentage content of the additive.

[0086] (3) By performing infrared test on the mixture obtained in step (1), in the infrared spectrum of the additive, there are infrared characteristic peaks located at 1710 cm -1 to 1725 cm -1 , 2500 cm -1 to 3300 cm -1 ; If in the infrared spectrum of the above mixture, there are infrared characteristic peaks located at 1710 cm -1 to 1725 cm -1 , 2500 cm -1 to 3300 cm -1 , then the positive electrode material layer contains the additive.

[0087] (4) By performing DSC melting point test on the mixture obtained in step (1), if there is only a characteristic melting peak between 60°C and 80°C, it indicates that the additive in the positive electrode material layer is stearic acid; if there are only characteristic melting peaks between 100°C and 120°C and between 200°C and 230°C, it indicates that the additive in the positive electrode material layer is stearate; if there are characteristic melting peaks between 60°C and 80°C and between 100°C and 120°C and between 200°C and 230°C, it indicates that the additive in the positive electrode material layer is stearate and stearic acid.

[0088] Particle size (Dv50 / Dv10) test:

[0089] (1) Turn on the device: First, turn on the sample injection system of the device, turn on the optical path system and the computer, and preheat the device for 30 min.

[0090] (2) Clean only the sample injection system: Fill the syringe with water, adjust the rotation speed to the maximum and clean for 5 s, then adjust the rotation speed to 0. Repeat the cleaning 3 times to ensure the syringe is clean.

[0091] (3) Enter the "Manual Measurement" interface and set the material name, refractive index, material type, test time, test times, etc. at one time.

[0092] (4) Click "start" on the electrode to perform light alignment and background light measurement.

[0093] (5) Disperse the positive electrode material in an aqueous solution (10 mL), and test it using a laser diffraction / scattering particle size distribution analyzer (Master Sizer 3000). Add the sample to the sample cell. The light obscuration will increase as the amount of sample added increases. When the light obscuration increases to 8% - 12%, stop adding the sample. Wait until the light obscuration stabilizes (generally, it does not fluctuate for 30 s), then click "start" to begin testing the particle size. After the test is completed, obtain Dv10 and Dv50.

[0094] (6) Three parallel samples need to be tested. Calculate the average values of Dv10 and Dv50 respectively, and calculate the value of Dv10 / Dv50.

[0095] Adhesion test:

[0096] (1) Take the dried electrode sheet, and use a blade to cut a specimen with a width of 30 mm and a length of 100 - 160 mm.

[0097] (2) Stick the special double-sided tape on the steel plate, with the tape width of 20 mm and a length of 90 - 150 mm.

[0098] (3) Stick the electrode sheet specimen cut in step (1) on the double-sided tape, with the test surface facing down.

[0099] (4) Insert a paper tape with the same width as the electrode sheet and a length greater than the specimen length by 80 - 200 mm under the electrode sheet, and fix it with crepe glue.

[0100] (5) Turn on the power of the Sansi tensile testing machine. The indicator light will be on. Adjust the limit block to the appropriate position.

[0101] (6) Fix the sample prepared in (4) on the test bench, set the speed at 10 mm / min, the test range at 0 - 40 mm, and start pulling the paper sheet at 90° until the test is completed.

[0102] (7) Save the test data according to the software prompt. After the test is completed, take out the electrode sheet and turn off the instrument.

[0103] Compaction density test of the positive electrode material layer:

[0104] Disassemble the lithium-ion battery, take out the positive electrode sheet. After cleaning the positive electrode sheet with DMC, dry the positive electrode sheet. Select the area on the positive electrode sheet that includes the double-sided positive electrode material layer, and use a cutting machine to cut 10 small round pieces with an area of 1540.25 mm 2 . Weigh them and take the average value M; then use a micrometer to measure the thickness of the small round pieces and take the average value H3. Then wipe off the positive electrode material layer on the 10 small round pieces, weigh them and take the average value m; then use a micrometer to measure the thickness of the positive electrode current collector and take the average value h. The compaction density PD of the positive electrode material layer = (M - m) / [1540.25×(H3 - h)].

[0105] Thermogravimetric test:

[0106] Disassemble the lithium-ion battery, take out the positive electrode plate, wash the positive electrode plate with DMC, and then dry the positive electrode plate. Divide the positive electrode material layer into three layers, namely the upper layer, the middle layer and the lower layer, with a thickness ratio of 1:1:1. Use a small knife to scrape off the powder of the positive electrode material layer of the three layers respectively. Weigh 2 mg of powder samples for each layer and put them into a small crucible of a thermogravimetric analyzer (TG, model: INESA TGA-2000, Shanghai Electric Analytical Instrument Factory). Turn on the thermogravimetric analyzer, open N2 and purge the thermogravimetric analyzer with N2 at a speed of 20 mL / min. Set the programmed temperature range from 25 °C to 500 °C, and the heating rate is 5 °C / min. Wait until the program is completed, and output the thermogravimetric curves of the upper layer, the middle layer and the lower layer, and obtain the thermogravimetric loss rates of the upper layer, the middle layer and the lower layer as M1, M2 and M3 respectively.

[0107] Porosity test of positive electrode plate:

[0108] According to "Determination of Apparent Density, True Density and Porosity of Iron Ore" (GB / T 24586-2009), the test steps are as follows:

[0109] (1) Use a punching machine to punch the positive electrode plate into small round pieces with a diameter of 10 mm or 14 mm. The ports of the round pieces are neat, and the number of round pieces ≥ 40;

[0110] (2) Measure the thickness of the small round pieces with a micrometer and take the average value;

[0111] (3) Place the small round pieces in the test chamber of the tester, and open the test software to conduct the test;

[0112] (4) Output the test report and confirm the porosity data;

[0113] (5) Repeat steps (1) to (4) 3 times, increase the parallel sample test, and take the average value as the porosity of the positive electrode plate.

[0114] Melting point test:

[0115] Use a differential scanning calorimeter (DSC) to test the melting point of the additive. Use an aluminum crucible for the test, the weight of the additive sample is 10 mg, the test temperature range is from room temperature to 400 °C, and the heating rate is 10 °C / min to conduct the melting point test.

[0116] True density test:

[0117] (1) Place the additive sample in the sample cup, ensure that the surface of the sample is flat, and measure the sample mass m.

[0118] (2) Put the sample cup into the gas displacement instrument, and introduce helium gas to completely displace the air in the sample with helium gas.

[0119] (3) Calculate the true volume V of the sample by measuring the volume change of helium gas between the sample and the reference sample.

[0120] (4) Obtain the true density of the additive by calculation: Use the formula (\rho=\frac{m}{V}), where m is the sample mass and V is the true volume of the sample.

[0121] Low-temperature (-20 °C) discharge test:

[0122] Charge the secondary battery at a constant current of 0.2C to the set value at 25 °C (the voltage set value is 4.55V when the positive electrode active material is lithium cobaltate, 4.2V when the positive electrode active material is lithium nickel cobalt manganese oxide and lithium manganate, and 3.6V when the positive electrode active material is lithium iron phosphate), then charge at a constant voltage until the cut-off current is 0.05C, let it stand for 10 min, and then discharge at 0.2C to the set value (the voltage set value is 2.8V when the positive electrode active material is lithium cobaltate, 3.0V when the positive electrode active material is lithium nickel cobalt manganese oxide and lithium manganate, and 2.5V when the positive electrode active material is lithium iron phosphate). At this time, the measured discharge capacity is C0;

[0123] Then charge at a constant current of 0.2C to the voltage set value at -25 °C (the voltage set value is 4.55V when the positive electrode active material is lithium cobaltate, 4.2V when the positive electrode active material is lithium nickel cobalt manganese oxide and lithium manganate, and 3.6V when the positive electrode active material is lithium iron phosphate), charge at a constant voltage until the cut-off current is 0.05C, let it stand for 10 min, then place the secondary battery in a high and low temperature chamber at -20 °C for 4 h, and then discharge at a constant current of 0.2C to the set value (the voltage set value is 2.8V when the positive electrode active material is lithium cobaltate, 3.0V when the positive electrode active material is lithium nickel cobalt manganese oxide and lithium manganate, and 2.5V when the positive electrode active material is lithium iron phosphate); at this time, the measured discharge capacity at -20 °C is C1. Calculate the ratio of the capacity discharged from the 100% SOC state to the corresponding capacity at the cut-off voltage to the original capacity C0, which is the -20 °C discharge capacity ratio.

[0124] Rate discharge test:

[0125] The secondary battery was placed in an incubator at 25 °C and left to stand for 30 min to bring the secondary battery to a constant temperature of 25 °C. It was charged at a constant current of 0.2C until the voltage reached the set value (when the positive electrode active material was lithium cobaltate, the set voltage value was 4.55V; when the positive electrode active material was lithium nickel cobalt manganate and lithium manganate, the set voltage value was 4.2V; when the positive electrode active material was lithium iron phosphate, the set voltage value was 3.6V), then charged at a constant voltage until the cut-off current was 0.05C, and then discharged at a constant current of 0.2C until the voltage reached the set value (the set value was the same as described above), and the discharge capacity was recorded as the initial capacity D0. Then it was charged at a constant current of 0.2C until the voltage reached the set value (the set value was the same as described above), and charged at a constant voltage until the cut-off current was 0.05C. It was discharged at a constant current of 2.0C until the voltage reached the set value (the set value was the same as described above), and the discharge capacity was recorded as the remaining capacity D1. The 2C discharge rate = D1 / D0 × 100%.

[0126] Example 1-1

[0127] <Preparation of the positive electrode plate>

[0128] After mixing lithium cobaltate (LiCoO2), the positive electrode conductive agent acetylene black, the positive electrode binder polyvinylidene fluoride (PVDF), and the additive stearic acid in a weight ratio of 97.52:1.3:1.1:0.08, N-methylpyrrolidone (NMP) was added as a solvent and stirred and mixed evenly to obtain a positive electrode slurry, where the solid content of the positive electrode slurry was 70 wt%. The positive electrode slurry was evenly coated on one surface of a positive electrode current collector aluminum foil with a thickness of 12 μm and dried at 120 °C for 1 h to obtain a positive electrode plate with a single-sided coated positive electrode material layer; among them, the coating weight CW of the positive electrode material layer was 0.025 g / cm 2 . Then the above steps were repeated on the other surface of the aluminum foil to obtain a positive electrode plate with a double-sided coated positive electrode material layer. It was dried under vacuum conditions at 120 °C for 1 h, and then after cold pressing, slicing, and slitting, a positive electrode plate with a specification of 74 mm × 867 mm was obtained. Among them, the compaction density PD of the positive electrode material layer was 4.25 g / cm 3 , and the thickness H1 of the positive electrode material layer after cold pressing was 58.8 μm.

[0129] <Preparation of the negative electrode plate>

[0130] The artificial graphite as the negative electrode active material, sodium carboxymethyl cellulose (CMC-Na) as the negative electrode binder, and styrene-butadiene rubber (SBR) as the negative electrode binder are mixed in a weight ratio of 95:2:3, and then deionized water is added as a solvent and stirred and mixed evenly to obtain a negative electrode slurry, where the solid content of the negative electrode slurry is 75 wt%. The negative electrode slurry is evenly coated on one surface of a negative electrode current collector copper foil with a thickness of 12 μm and dried at 120°C to obtain a negative electrode sheet with a negative electrode material layer with a thickness of 120 μm coated on one side. The above steps are repeated on the other surface of the copper foil to obtain a negative electrode sheet with a negative electrode material layer coated on both sides. It is dried under vacuum conditions at 120°C for 1 h, and then after cold pressing, slicing, and slitting, a negative electrode sheet with a specification of 78 mm × 875 mm is obtained. Among them, the compaction density of the negative electrode material layer is 1.75 g / cm 3 .

[0131] <Preparation of electrolyte>

[0132] In an argon atmosphere glove box with a water content of less than 10 ppm, ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) are mixed in a weight ratio of 1:1:1 to obtain a base solvent, and then lithium salt lithium hexafluorophosphate (LiPF6) is added and mixed evenly to obtain an electrolyte. Based on the mass of the electrolyte, the mass percentage content of the lithium salt is 12.5%, and the balance is the base solvent.

[0133] <Preparation of separator>

[0134] A polyethylene (PE) film with a thickness of 15 μm is used.

[0135] <Preparation of lithium-ion battery>

[0136] The positive electrode sheet, separator, negative electrode sheet, and separator prepared above are stacked in sequence, and the separator is placed in the middle of the positive electrode sheet and the negative electrode sheet to play an isolation role, and then wound to obtain an electrode assembly. After welding the electrode tabs, the electrode assembly is placed in an aluminum-plastic film packaging bag, dried, injected with electrolyte, and then subjected to vacuum packaging, standing, formation, degassing, and edge trimming processes to obtain a lithium-ion battery.

[0137] Examples 1-2 to Examples 1-30

[0138] Except for adjusting the relevant preparation parameters according to Table 1, the rest are the same as in Example 1-1.

[0139] Comparative Examples 1 to Comparative Examples 7

[0140] Except for adjusting the relevant preparation parameters according to Table 1, the rest are the same as in Example 1-1.

[0141] Examples 2-1 to Examples 2-4

[0142] Except that the coating weight of the positive electrode material layer is adjusted by adjusting the coating amount of the positive electrode paste as shown in Table 2, the rest is the same as in Example 1-1.

[0143] Examples 2-5 to 2-10

[0144] Except that the compaction density of the positive electrode material layer is adjusted by adjusting the cold pressing pressure during the cold pressing process as shown in Table 2, the rest is the same as in Example 1-1.

[0145] Examples 2-11 to 2-13

[0146] Except that the relevant preparation parameters are adjusted according to Table 2, the rest is the same as in Example 1-1.

[0147] The preparation parameters and electrical performance parameters of each example and comparative example are shown in Tables 1 to 3.

[0148]

[0149]

[0150]

[0151]

[0152]

[0153] It can be seen from Examples 1-1 to 1-30 and Comparative Examples 1 to 7 that when the positive electrode material layer includes the above additives and the mass percentage content of the additives, and the porosity of the positive electrode sheet is regulated within the scope of the present application, the lithium-ion battery including the above positive electrode sheet has a high discharge capacity ratio at -20 °C and a high 2C discharge rate, indicating that the lithium-ion battery of the embodiment of the present application has good kinetic performance while having a high energy density. In Comparative Example 1, the positive electrode material layer does not include the above additives; in Comparative Examples 2, 3, 6, and 7, the mass percentage content of the additives is not within the scope of the present application; in Comparative Examples 4 and 5, the porosity of the positive electrode sheet is not within the scope of the present application. The discharge capacity ratio at -20 °C and the 2C discharge rate of the lithium-ion batteries of the comparative examples are low, indicating that the lithium-ion batteries of Comparative Examples 1 to 7 have a low energy density and poor kinetic performance.

[0154] The type of the positive electrode binder can affect the energy density and kinetic performance of the lithium-ion battery. As can be seen from Example 1-1, Examples 1-17 to 1-18, by regulating the type of the positive electrode binder within the scope of this application, the lithium-ion battery has a high discharge capacity ratio at -20°C and a high 2C discharge rate, indicating that the lithium-ion battery has good kinetic performance while having a high energy density.

[0155] The mass percentage content of the positive electrode binder can affect the energy density and kinetic performance of the lithium-ion battery. As can be seen from Example 1-1, Examples 1-19 to 1-20, by regulating the mass percentage content of the positive electrode binder within the scope of this application, the lithium-ion battery has a high discharge capacity ratio at -20°C and a high 2C discharge rate, indicating that the lithium-ion battery has good kinetic performance while having a high energy density.

[0156] The ratio of the mass percentage content of the positive electrode binder to the mass percentage content of the additive can affect the energy density and kinetic performance of the lithium-ion battery. As can be seen from Example 1-1, Examples 1-21 to 1-22, by regulating the ratio of the mass percentage content of the positive electrode binder to the mass percentage content of the additive within the scope of this application, the lithium-ion battery has a high discharge capacity ratio at -20°C and a high 2C discharge rate, indicating that the lithium-ion battery has good kinetic performance while having a high energy density.

[0157] The particle size of the positive electrode active material can affect the energy density and kinetic performance of the lithium-ion battery. As can be seen from Example 1-1, Examples 1-23 to 1-26, by regulating the characteristics of the particle size of the positive electrode active material within the scope of this application, the lithium-ion battery has a high discharge capacity ratio at -20°C and a high 2C discharge rate, indicating that the lithium-ion battery has good kinetic performance while having a high energy density.

[0158] The type of the positive electrode active material can affect the energy density and kinetic performance of the lithium-ion battery. As can be seen from Example 1-1, Example 1-27, by regulating the type of the positive electrode active material within the scope of this application, the lithium-ion battery has a high discharge capacity ratio at -20°C and a high 2C discharge rate, indicating that the lithium-ion battery has good kinetic performance while having a high energy density.

[0159] Table 3

[0160]

[0161] The coating weight of the positive electrode material layer usually affects the energy density and kinetic performance of the positive electrode sheet. It can be seen from Examples 1-1, 2-1 to 2-4 that by adjusting the coating weight of the positive electrode material layer within the scope of this application, the lithium-ion battery has a high discharge capacity ratio at -20°C and a high 2C discharge rate, indicating that the lithium-ion battery has good kinetic performance while having a high energy density.

[0162] The tap density of the positive electrode material layer usually affects the energy density and kinetic performance of the positive electrode sheet. It can be seen from Examples 1-1, 2-5 to 2-10 that by adjusting the tap density of the positive electrode material layer within the scope of this application, the lithium-ion battery has a high discharge capacity ratio at -20°C and a high 2C discharge rate, indicating that the lithium-ion battery has good kinetic performance while having a high energy density.

[0163] The thickness of the positive electrode material layer usually affects the energy density and kinetic performance of the positive electrode sheet. It can be seen from Examples 1-1, 2-1 to 2-10 that by adjusting the thickness of the positive electrode material layer within the scope of this application, the lithium-ion battery has a high discharge capacity ratio at -20°C and a high 2C discharge rate, indicating that the lithium-ion battery has good kinetic performance while having a high energy density.

[0164] The thickness of the positive current collector usually affects the energy density and kinetic performance of the lithium-ion battery. It can be seen from Examples 1-1, 2-11 to 2-13 that by adjusting the thickness of the positive current collector within the scope of this application, the lithium-ion battery has a high discharge capacity ratio at -20°C and a high 2C discharge rate, indicating that the lithium-ion battery has good kinetic performance while having a high energy density.

[0165] It should be noted that in this article, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the term "comprising", "including" or any other variation thereof is intended to cover non-exclusive inclusion, so that a process, method or article including a series of elements not only includes those elements, but also includes other elements not explicitly listed, or also includes elements inherent to such process, method or article.

[0166] Each embodiment in this specification is described in a related manner. The same or similar parts between each embodiment can be referred to each other, and the key points of each embodiment are the differences from other embodiments.

[0167] The above are only the preferred embodiments of the present application and are not intended to limit the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present application shall be included within the scope of protection of the present application.

Claims

1. A positive electrode plate, the positive electrode plate comprising a positive current collector and a positive electrode material layer provided on at least one surface of the positive current collector, the positive electrode material layer comprising a positive electrode active material, a positive electrode binder, a positive electrode conductive agent, and an additive, the additive being at least one of a compound of formula I and a compound of formula II, Among them, 9 ≤ n ≤ 20, R1 is selected from H, Li, Ca, Mg, Zn, Al, Fe, Ba or Co, and R2 is selected from C9 to C 20 alkenylene; Based on the mass of the positive electrode material layer, the mass percentage content of the additive is W%, 0.02 ≤ W ≤ 2.5; The porosity of the positive electrode plate is P%, 12 ≤ P ≤ 25.

2. The positive electrode sheet according to claim 1, wherein 0.03≤W≤0.8。 3. The positive electrode sheet according to claim 1, wherein, The tap density of the positive electrode material layer is PD g / cm 3 , and 3.0 ≤ PD ≤ 4.

5.

4. The positive electrode sheet according to claim 1, wherein, The coating weight of the positive electrode material layer is CW, 0.018 g / cm 2 ≤ CW ≤ 0.039 g / cm 2 .

5. The positive electrode sheet according to claim 1, wherein, The thickness of the positive electrode material layer is H1 μm, 30 ≤ H1 ≤ 110.

6. The positive electrode sheet according to claim 1, wherein, The compound of formula I includes at least one of undecanoic acid, lauric acid, tridecanoic acid, myristic acid, pentadecanoic acid, palmitic acid, margaric acid, stearic acid, lithium stearate, calcium stearate, magnesium stearate, zinc stearate, aluminum stearate, iron stearate, barium stearate, or cobalt stearate.

7. The positive electrode sheet according to claim 6, wherein, The compound of formula I includes at least one of palmitic acid, stearic acid, lithium stearate, magnesium stearate, or iron stearate.

8. The positive electrode sheet according to claim 1, wherein, The compound of formula II includes at least one of myristoleic acid, oleic acid, or octadecenoic acid.

9. The positive electrode sheet according to claim 1, wherein, The melting point of the additive is Tm °C, 50 ≤ Tm ≤ 230.

10. The positive electrode sheet according to claim 1, wherein, The true density of the additive is p g / cm 3 , where 0.7 ≤ p ≤ 1.

3.

11. The positive electrode sheet according to claim 1, wherein, There is a first decomposition peak at 150 °C to 220 °C and / or a second decomposition peak at 250 °C to 350 °C in the thermogravimetric curve of the positive electrode plate.

12. The positive electrode sheet according to claim 1, wherein, The positive electrode material layer includes an upper layer, a middle layer, and a lower layer that are arranged in sequence along the thickness direction and have equal thicknesses. The thermal weight loss rates of the upper layer, middle layer, and lower layer are M1%, M2%, and M3% respectively, 0 ≤ |M1 - M2| ≤ 0.8, 0 ≤ |M1 - M3| ≤ 0.

8.

13. The positive electrode sheet according to claim 1, wherein, Based on the mass of the positive electrode material layer, the mass percentage content of the positive electrode binder is X%, 0.6 ≤ X ≤ 2.

5.

14. The positive electrode sheet according to claim 13, wherein, The positive electrode binder includes at least one of polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride - tetrafluoroethylene - propylene terpolymer, vinylidene fluoride - hexafluoropropylene - tetrafluoroethylene terpolymer, tetrafluoroethylene - hexafluoropropylene copolymer, fluorinated acrylate resin, polyvinylidene fluoride - hexafluoropropylene copolymer, polyvinyl alcohol, polyacrylonitrile, starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polyethylene, polypropylene, ethylene - propylene - diene polymer (EPDM), sulfonated EPDM, carboxymethyl cellulose, styrene - butadiene rubber, fluororubber, or various copolymers thereof.

15. The positive electrode sheet according to claim 13, wherein, 10 ≤ X / W ≤ 120.

16. The positive electrode sheet according to claim 1, wherein, The adhesion between the positive electrode material layer and the positive current collector is F N / m, F ≥ 25.

17. The positive electrode sheet according to claim 1, wherein, The particle size of the positive electrode active material satisfies: 0.25 ≤ Dv10 / Dv50 ≤ 0.

5.

18. The positive electrode sheet according to claim 1, wherein, The thickness of the positive current collector is H2 μm, 7 ≤ H2 ≤ 20.

19. The positive electrode plate according to claim 1, which satisfies at least one of the following characteristics: (1) The tap density of the positive electrode material layer is PD g / cm 3 , 3.8 ≤ PD ≤ 4.4; (2) The thickness of the positive electrode material layer is H1 μm, 40 ≤ H1 ≤ 80; (3) The melting point of the additive is Tm °C, 65 ≤ Tm ≤ 190; (4) The true density of the additive is p g / cm 3 , 0.85 ≤ p ≤ 1.15; (5) The particle size of the positive electrode active material satisfies: 0.33 ≤ Dv10 / Dv50 ≤ 0.45; (6) The thickness of the positive current collector is H2 μm, 8 ≤ H2 ≤ 12; (7) The positive electrode active material includes at least one of lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, or lithium iron phosphate; (8) The positive electrode material layer includes an upper layer, a middle layer, and a lower layer that are arranged in sequence along the thickness direction and have equal thicknesses. The thermal weight loss rates of the upper layer, the middle layer, and the lower layer are M1%, M2%, and M3% respectively, and 0 ≤ |M1 - M2| ≤ 0.6, 0 ≤ |M1 - M3| ≤ 0.

6.

20. A secondary battery, comprising the positive electrode tab according to any one of claims 1 to 19.

21. An electronic device, comprising the secondary battery according to claim 20.

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