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 additive, the mass percentage content of the positive pole additive is m% based on the mass of the positive pole material layer, m is larger than or equal to 0.1 and smaller than or equal to 0.5, and the positive pole additive comprises at least one of a structural formula shown in a formula (I) or a structural formula shown in a formula (II). The secondary battery provided by the invention has good high-temperature cycle performance.

Description

Technical Field

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

[0002] Secondary batteries, such as lithium-ion batteries, are widely used in fields such as smart phones, wearable devices, consumer drones, and electric vehicles due to their advantages of high energy density, long cycle life, and no memory effect. With the wide application of lithium-ion batteries in the above fields, the market's requirements for the high-temperature cycle performance of lithium-ion batteries are getting higher and higher. However, at high temperatures, the positive electrode active material in the lithium-ion battery will undergo a phase change and release active oxygen, thereby affecting the high-temperature cycle performance of the lithium-ion battery. Summary of the Invention

[0003] The purpose of this application is to provide a positive electrode plate, a secondary battery, and an electronic device to improve the high-temperature cycle performance of the secondary battery. The specific technical solutions are as follows:

[0004] In the first aspect of this application, a positive electrode plate is provided, which 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 additive. Based on the mass of the positive electrode material layer, the mass percentage content of the positive electrode additive is m%, where 0.1 ≤ m ≤ 0.5. The positive electrode additive includes at least one of the structural formulas shown in formula (I) or formula (II).

[0005]

[0006] R 1 to R 2 Each independently selects from a hydrogen atom, a nitrogen atom, a hydroxyl group, an alkyl group of C 1 to C 18 or a linear or cyclic alkyl group of C 3 to C 18 containing an ester group; R 3 to R 6 Each independently selects from a hydrogen atom, a hydroxyl group, an alkyl group of C 1 to C 18 or a linear or cyclic alkyl group of C 1 to C 18 containing an ester group or an ether bond. By introducing the above positive electrode additive into the positive electrode plate and regulating the mass percentage content m% of the positive electrode additive within the scope of this application, the positive electrode additive can capture free radicals, convert the oxygen free radicals generated by the positive electrode active material and the small molecule free radicals generated by the electrolyte into stable small molecule substances, reduce the chain decomposition reaction of the electrolyte, and thus improve the high-temperature cycle performance of the secondary battery on the basis of the secondary battery having good kinetic performance and high energy density.

[0007] In some embodiments of the present application, 0.15 ≤ m ≤ 0.3. By regulating the value of m within the above range, it is beneficial to further improve the high-temperature cycle performance of the secondary battery on the basis of the secondary battery having good kinetic performance and high energy density.

[0008] In some embodiments of the present application, R 1 to R 2 are each independently selected from a hydrogen atom, an alkyl group having C 3 to C 10 and a chain alkyl group having C 3 to C 10 and containing an ester group; R 3 to R 6 are each independently selected from a hydrogen atom, a chain alkyl group having C 1 to C 5 and a chain or cyclic alkyl group having C 1 to C 10 and containing an ester group or an ether bond. R 1 to R 6 being selected from the above groups is beneficial to further improve the high-temperature cycle performance of the secondary battery on the basis of the secondary battery having good kinetic performance and high energy density.

[0009] In some embodiments of the present application, the positive electrode material layer contains nitrogen element, and based on the mass of the positive electrode material layer, the mass percentage content of nitrogen element in the positive electrode material layer is 0.1% to 0.3%. The nitrogen element in the positive electrode material layer is derived from the positive electrode additive. By regulating the mass percentage content of nitrogen element in the positive electrode material layer within the above range, the mass percentage content of the positive electrode additive is within a suitable range, thereby being beneficial to improving the high-temperature cycle performance of the secondary battery, while having good kinetic performance and high energy density.

[0010] In some embodiments of the present application, the positive electrode additive includes at least one of a polymer of succinic acid and 4-hydroxy-2,2,6,6-tetramethyl-1-piperidinol, N,N-bis(2,2,6,6-tetramethyl-4-piperidyl)-1,6-hexanediamine, pentaerythritol tetra[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], butyl hydroxyanisole or dibutyl hydroxytoluene. Selecting the above positive electrode additive is beneficial to further improving the high-temperature cycle performance of the secondary battery on the basis of the secondary battery having good kinetic performance and high energy density.

[0011] In some embodiments of the present application, the positive electrode plate satisfies at least one of the following characteristics: (1) The infrared spectrum of the positive electrode material layer is at 1200 cm -1 to 1350 cm -1There are characteristic peaks; (2) The infrared spectrum of the positive electrode material layer has characteristic peaks between 1000 cm -1 and 1199 cm -1 . The positive electrode sheet satisfying the above characteristics is beneficial to improving the high-temperature cycle performance of the secondary battery, and at the same time has good kinetic performance and high energy density.

[0012] In some embodiments of the present application, the positive electrode sheet satisfies at least one of the following characteristics: (1) The transmittance of the characteristic peak at 1200 cm -1 to 1350 cm -1 of the infrared spectrum of the positive electrode material layer is I 1 , 30% ≤ I 1 ≤ 80%; (2) The transmittance of the characteristic peak at 1000 cm -1 to 1199 cm -1 of the infrared spectrum of the positive electrode material layer is I 2 , 60% ≤ I 2 ≤ 70%. The positive electrode sheet satisfying the above characteristics is beneficial to further improving the high-temperature cycle performance of the secondary battery, and at the same time has good kinetic performance and high energy density.

[0013] In some embodiments of the present application, the thickness of the positive electrode material layer is H μm, 10 ≤ H ≤ 50. By controlling the thickness H of the positive electrode material layer within the above range, it is beneficial to improve the kinetic performance and high-temperature cycle performance of the secondary battery, and is also beneficial to improving the energy density of the secondary battery.

[0014] In some embodiments of the present application, the sheet resistance of the positive electrode sheet is R Ω, and the thickness of the positive electrode material layer is H μm, 0.05 ≤ R ≤ 0.5, 0.5 ≤ R × H ≤ 8. The values of the sheet resistance R of the positive electrode sheet and R × H within the above range are beneficial to improving the kinetic performance and high-temperature cycle performance of the secondary battery, and are also beneficial to improving the energy density of the secondary battery.

[0015] The second aspect of the present application provides a secondary battery, which includes the positive electrode sheet provided by the first aspect of the present application. The secondary battery of the present application has good high-temperature cycle performance and kinetic performance.

[0016] The third aspect of the present application provides an electronic device, which includes the secondary battery provided by the second aspect of the present application. The electronic device of the present application has a long service life and good performance.

[0017] Advantages of the present application:

[0018] The present application provides a positive electrode plate, a secondary battery, and an electronic device. The positive electrode plate 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 additive. Based on the mass of the positive electrode material layer, the mass percentage content of the positive electrode additive is m%, where 0.1 ≤ m ≤ 0.5. The positive electrode additive includes at least one of the structural formulas shown in Formula (I) or Formula (II). By introducing the above positive electrode additive into the positive electrode plate and controlling the mass percentage content m% of the positive electrode additive within the scope of the present application, the positive electrode additive can capture free radicals, convert the oxygen free radicals generated by the positive electrode active material and the small molecule free radicals generated by the electrolyte into stable small molecule substances, and reduce the chain decomposition reaction of the electrolyte. Thus, on the basis that the secondary battery has good kinetic performance and high energy density, the high-temperature cycle performance of the secondary battery is improved.

[0019] Of course, it is not necessary for any product or method implementing the present application to simultaneously achieve all the above-mentioned advantages. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, other embodiments can also be obtained based on these drawings.

[0021] Figure 1 It is the infrared spectrum diagram of the positive electrode material layer of Embodiment 11 of the present application. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0022] The following will clearly and completely describe the technical solutions in the present application in conjunction with the embodiments of the present application and the drawings. Obviously, the described embodiments are only some embodiments of the present application, rather than all embodiments. All other embodiments obtained by those skilled in the art based on the present application fall within the scope of protection of the present application.

[0023] It should be noted that in the specific embodiments 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.

[0024] At high temperatures, the structural phase change of the positive electrode active material in the secondary battery intensifies, releasing active oxygen, which decomposes the electrolyte into active small molecule free radicals, thereby affecting the high-temperature cycling performance of the secondary battery. Existing technologies usually improve the above problems by coating the positive electrode active material or introducing electrolyte additives into the electrolyte. However, for the solution of coating the positive electrode active material, the coating layer will reduce the reactive area of the positive electrode active material, affect the utilization of the specific capacity of the positive electrode active material, reduce the energy density of the secondary battery, and also cause the kinetic performance of the secondary battery to decline. For the solution of introducing electrolyte additives into the electrolyte, since active oxygen is generated from the positive electrode active material, a relatively large amount of electrolyte additives needs to be added and the action efficiency is lower for the electrolyte additives to play a role. Moreover, when the active oxygen in the positive electrode plate interacts with the additives in the electrolyte, the active oxygen has entered the electrolyte and partially oxidized it, affecting the electrochemical performance of the secondary battery. Therefore, the effect of improving the high-temperature cycling performance of the secondary battery is poor.

[0025] Based on this, in the first aspect of the present application, a positive electrode plate is provided, which 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 additive. Based on the mass of the positive electrode material layer, the mass percentage content of the positive electrode additive is m%, 0.1 ≤ m ≤ 0.5. Preferably, 0.15 ≤ m ≤ 0.3. For example, the value of m can be 0.10, 0.15, 0.18, 0.20, 0.22, 0.25, 0.28, 0.30, 0.35, 0.40, 0.45, 0.50 or a range composed of any two of these values. The positive electrode additive includes at least one of the structural formulas shown in formula (I) or formula (II):

[0026]

[0027] R 1 to R 2 each independently selected from a hydrogen atom, a nitrogen atom, a hydroxyl group, a C 1 to C 18 alkyl group, a C 3 to C 18 chain or cyclic alkyl group containing an ester group; R 3 to R 6 each independently selected from a hydrogen atom, a hydroxyl group, a C 1 to C 18 alkyl group, a C 1 to C 18 chain or cyclic alkyl group containing an ester group or an ether bond. The present application defines C 1 to C 18There is no particular limitation on the structure of the alkyl group in the alkyl group, as long as the object of the present application can be achieved. For example, the above alkyl group can be a linear alkyl group or a cyclic alkyl group. The present application relates to C containing an ester group 3 to C 18 There is no particular limitation on the position of the ester group in the linear alkyl group or cyclic alkyl group, or on the position of the ester group or ether bond in the C 1 to C 18 linear alkyl group or cyclic alkyl group, as long as the object of the present application can be achieved. For example, the above ester group or ether bond can be located in the middle of the linear alkyl group or at the end of the linear alkyl group.

[0028] In the present application, by introducing the above positive electrode additive into the positive electrode sheet and controlling the mass percentage content m% of the positive electrode additive within the scope of the present application, the positive electrode additive can capture free radicals, convert the oxygen free radicals generated by the positive electrode active material and the small molecule free radicals (such as alkyl free radicals) generated by the electrolyte into stable small molecule substances, and reduce the chain decomposition reaction of the electrolyte. Specifically, the structural formula shown in formula (I) contains a hindered amine structure, and the hindered amine structure can absorb energy and be converted into a stable nitroxide free radical. The above nitroxide free radical can capture free radicals (such as oxygen free radicals, alkyl free radicals) to convert them into stable small molecule substances, and has a regeneration function, and can be reconverted into a nitroxide free radical in the subsequent process for repeated use many times, with a relatively high action efficiency; the structural formula shown in formula (II) contains a hindered phenol structure, and the phenolic group (-OH) has a hydrogen donating ability and can provide hydrogen atoms to free radicals (such as alkyl free radicals) to form a stable phenoxyl free radical and terminate the chain reaction of free radicals, reducing the chain decomposition reaction of the electrolyte. At the same time, the positive electrode additive of the present application exists on the surface of the positive electrode active material and is insoluble in the electrolyte, can directly and rapidly absorb the active oxygen generated by the structural phase change of the positive electrode active material, reduce the risk of active oxygen entering the electrolyte and partially oxidizing it, has a higher action efficiency, and has a better effect on improving the high-temperature cycle performance of the secondary battery. And because the positive electrode additive can directly act on the positive electrode active material, the addition amount can be relatively small, the coating on the surface of the positive electrode active material is less, the reaction active area of the positive electrode active material is larger, and the specific capacity can also be exerted to a greater extent, and the influence on the kinetic performance and energy density of the secondary battery is smaller. Therefore, the present application can improve the high-temperature cycle performance of the secondary battery on the basis of the secondary battery having good kinetic performance and high energy density. In the present application, high temperature means a temperature greater than or equal to 45 °C, and the positive electrode additive can be obtained by purchase.

[0029] When the value of m is too small, for example, less than 0.1, the mass percentage content of the positive electrode additive is too small, and the number of free radicals that can be captured is less. The positive electrode additive is not in time to convert oxygen free radicals into stable small molecule substances, and the presence of oxygen free radicals still has a great influence on the decomposition of the electrolyte, so the effect of improving the high-temperature cycle performance of the secondary battery is poor. When the value of m is too large, for example, greater than 0.5, the mass percentage content of the positive electrode additive is too large, and the surface of the positive electrode active material is coated more, and the reaction active area of the positive electrode active material is smaller, which affects the kinetic performance and high-temperature cycle performance of the secondary battery.

[0030] In the present application, the positive electrode additive includes at least one of the structural formulas shown in formula (I) or formula (II). The above structural formula may refer to the molecular structural formula of a compound, that is, the positive electrode additive includes at least one of the compounds shown in formula (I) or formula (II); the above structural formula may also refer to a structural fragment, that is, the molecular structural formula of the positive electrode additive includes at least one of the structural fragments shown in formula (I) or formula (II). In some embodiments, the positive electrode additive includes at least one of the compounds shown in formula (I) or formula (II). In other embodiments, the positive electrode additive includes at least one of the structural fragments shown in formula (I) or formula (II).

[0031] In some embodiments, compared with a secondary battery in which the positive electrode sheet does not include a positive electrode additive, the capacity retention rate of the secondary battery of the present application after 500 cycles at a high temperature (for example, 45 °C) can be increased by more than 3%.

[0032] In some embodiments of the present application, R 1 to R 2 are each independently selected from a hydrogen atom, an alkyl group having 1 3 to 6 10 carbon atoms, or a chain alkyl group having 2 3 to 6 10 carbon atoms and containing an ester group; R 3 to R 6 are each independently selected from a hydrogen atom, a chain alkyl group having 1 1 to 6 5 carbon atoms, a chain alkyl group having 2 1 to 6 10 carbon atoms and containing an ester group or an ether bond, or a cyclic alkyl group having 3 1 to 6 6 carbon atoms. That R 1 to R 6 are selected from the above groups is beneficial to further improving the high-temperature cycle performance of the secondary battery on the basis of the secondary battery having good kinetic performance and high energy density.

[0033] In some embodiments of the present application, the positive electrode material layer contains nitrogen element, and based on the mass of the positive electrode material layer, the mass percentage content of nitrogen element in the positive electrode material layer is 0.1% to 0.3%. For example, the mass percentage content of nitrogen element in the positive electrode material layer can be 0.10%, 0.12%, 0.15%, 0.17%, 0.20%, 0.22%, 0.25%, 0.28%, 0.30% or a range composed of any two of these values. The nitrogen element in the positive electrode material layer is derived from the positive electrode additive. By controlling the mass percentage content of nitrogen element in the positive electrode material layer within the above range and the mass percentage content of the positive electrode additive within a suitable range, it is beneficial for the generated nitrogen oxygen free radicals to play a role, converting the oxygen free radicals generated by the positive electrode active material and the small molecule free radicals (such as alkyl free radicals) generated by the electrolyte into stable small molecule substances, reducing the chain decomposition reaction of the electrolyte, thereby being beneficial to improving the high-temperature cycle performance of the secondary battery, while having good kinetic performance and high energy density.

[0034] In the present application, the mass percentage content of nitrogen element in the positive electrode material layer can be controlled by controlling the type of the positive electrode additive and the mass percentage content of the positive electrode additive. For example, when other conditions remain unchanged, the higher the nitrogen content of the positive electrode additive, the greater the mass percentage content of nitrogen element in the positive electrode material layer; the lower the nitrogen content of the positive electrode additive, the smaller the mass percentage content of nitrogen element in the positive electrode material layer. When other conditions remain unchanged, the greater the mass percentage content of the positive electrode additive, the greater the mass percentage content of nitrogen element in the positive electrode material layer; the smaller the mass percentage content of the positive electrode additive, the smaller the mass percentage content of nitrogen element in the positive electrode material layer.

[0035] In some embodiments of the present application, the positive electrode additive includes at least one of the polymer of succinic acid and 4-hydroxy-2,2,6,6-tetramethyl-1-piperidino, N,N-bis(2,2,6,6-tetramethyl-4-piperidyl)-1,6-hexanediamine, pentaerythritol tetra[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], butyl hydroxyanisole or dibutyl hydroxytoluene. Selecting the above positive electrode additive is beneficial to further improve the high-temperature cycle performance of the secondary battery on the basis of the secondary battery having good kinetic performance and high energy density.

[0036] In some embodiments, the molar ratio of succinic acid monomer to 4-hydroxy-2,2,6,6-tetramethyl-1-piperidinol monomer in the polymer of succinic acid and 4-hydroxy-2,2,6,6-tetramethyl-1-piperidinol is 1:1, and its molecular structural formula is shown as follows. The present application has no particular limitation on the degree of polymerization n of the above polymer, as long as the object of the present application can be achieved. For example, the degree of polymerization n can be from 2 to 100, and the value of the degree of polymerization n can be 2, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100 or a range composed of any two of these numerical values.

[0037]

[0038] In some embodiments of the present application, the infrared spectrum of the positive electrode material layer has a characteristic peak between 1200 cm -1 and 1350 cm -1 . The characteristic peak in the infrared spectrum between 1200 cm -1 and 1350 cm -1 corresponds to the C-N bond in the structural formula shown in formula (I). The infrared spectrum of the positive electrode material layer satisfies the above characteristics, indicating that there is a positive electrode additive containing the structural formula shown in formula (I) in the positive electrode material layer. The nitroxyl radicals generated by it can capture free radicals (for example, oxygen free radicals, alkyl free radicals) and convert them into stable small molecule substances, reducing the chain decomposition reaction of the electrolyte, thereby being beneficial to improving the high-temperature cycle performance of the secondary battery, while having good kinetic performance and high energy density.

[0039] In some embodiments of the present application, the transmittance of the characteristic peak at 1200 cm -1 to 1350 cm -1 of the infrared spectrum of the positive electrode material layer is I 1 , 30% ≤ I 1 ≤ 80%. For example, the value of I 1 can be 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80% or a range composed of any two of these numerical values. The value of I 1 within the above range indicates that the mass percentage content of the positive electrode additive containing the structural formula shown in formula (I) is within a suitable range. The nitroxyl radicals generated by the positive electrode additive have a small impact on the kinetic performance of the secondary battery on the premise of meeting the demand for converting oxygen free radicals, thereby being beneficial to improving the high-temperature cycle performance of the secondary battery, while having good kinetic performance and high energy density.

[0040] In some embodiments of the present application, the infrared spectrum of the positive electrode material layer is between 1000 cm -1 and 1199 cm -1There are characteristic peaks. In the infrared spectrum, the characteristic peak at 1000 cm -1 to 1199 cm -1 corresponds to the C-OH bond in the structural formula shown in Formula (II). The infrared spectrum of the positive electrode material layer satisfies the above characteristics, indicating that there is a positive electrode additive containing the structural formula shown in Formula (II) in the positive electrode material layer, which can provide hydrogen atoms to free radicals (for example, alkyl free radicals), form stable phenoxy free radicals and terminate the chain reaction of free radicals, reduce the chain decomposition reaction of the electrolyte, and thus is beneficial to improving the high-temperature cycle performance of the secondary battery, while having good kinetic performance and high energy density.

[0041] In some embodiments of the present application, the transmittance of the characteristic peak at 1000 cm -1 to 1199 cm -1 in the infrared spectrum of the positive electrode material layer is I 2 , 60% ≤ I 2 ≤ 70%. For example, the value of I 2 can be 60%, 63%, 65%, 68%, 70% or a range composed of any two of these values. When the value of I 2 is within the above range, it indicates that the mass percentage content of the positive electrode additive containing the structural formula shown in Formula (II) is within a suitable range, which is beneficial for the phenol group to play a role and takes into account both kinetic performance and high-temperature cycle performance, and thus is beneficial to improving the high-temperature cycle performance of the secondary battery, while having good kinetic performance and high energy density.

[0042] In some embodiments, there are characteristic peaks in the infrared spectrum of the positive electrode material layer between 1200 cm -1 and 1350 cm -1 as well as between 1000 cm -1 and 1199 cm -1 . The infrared spectrum of the positive electrode material layer satisfies the above characteristics, indicating that there are positive electrode additives containing the structural formula shown in Formula (I) and the structural formula shown in Formula (II) simultaneously in the positive electrode material layer, which is beneficial to further improving the high-temperature cycle performance of the secondary battery, while having good kinetic performance and high energy density.

[0043] In some embodiments, the transmittance of the characteristic peak at 1200 cm -1 to 1350 cm -1 in the infrared spectrum of the positive electrode material layer is I 1 , 30% ≤ I 1 ≤ 80%, and the transmittance of the characteristic peak at 1000 cm -1 to 1199 cm -1 is I 2 , 60% ≤ I 2 ≤ 70%. For example, I 1The value can be 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80% or a range composed of any two of these values. I 2 The value can be 60%, 63%, 65%, 68%, 70% or a range composed of any two of these values. I 1 and I 2 When the value is within the above range, it is beneficial to improve the high-temperature cycle performance of the secondary battery, and at the same time, the kinetic performance is good and the energy density is high.

[0044] In some embodiments of the present application, the thickness of the positive electrode material layer is H μm, where 10 ≤ H ≤ 50. For example, the value of H can be 10, 15, 20, 25, 30, 35, 40, 45, 50 or a range composed of any two of these values. By regulating the thickness H of the positive electrode material layer within the above range, the path for lithium ions to migrate from the electrolyte to the inside of the positive electrode material layer during charge and discharge is shorter, which is beneficial to reducing the internal resistance of the positive electrode plate, thereby beneficial to improving the kinetic performance and high-temperature cycle performance of the secondary battery, and also beneficial to increasing the energy density of the secondary battery. In the present application, the above thickness refers to the single-sided thickness of the positive electrode material layer.

[0045] In the present application, the thickness of the positive electrode material layer can be regulated by regulating the single-sided coating surface density and the compaction density of the positive electrode material layer. For example, when other conditions remain unchanged, as the single-sided coating surface density of the positive electrode material layer increases, the thickness of the positive electrode material layer increases; when the single-sided coating surface density of the positive electrode material layer decreases, the thickness of the positive electrode material layer decreases. When other conditions remain unchanged, as the compaction density of the positive electrode material layer increases, the thickness of the positive electrode material layer decreases; when the compaction density of the positive electrode material layer decreases, the thickness of the positive electrode material layer increases.

[0046] In some embodiments of the present application, the sheet resistance of the positive electrode plate is R Ω, and the thickness of the positive electrode material layer is H μm, where 0.05 ≤ R ≤ 0.5 and 0.5 ≤ R × H ≤ 8. For example, the value of R can be 0.05, 0.10, 0.15, 0.20, 0.25, 0.30, 0.35, 0.40, 0.45, 0.50 or a range composed of any two of these values, and the value of R × H can be 0.5, 1, 2, 3, 4, 5, 6, 7, 8 or a range composed of any two of these values. When the sheet resistance R of the positive electrode plate and the value of R × H are within the above range, it is beneficial to improve the transport rate of electrons in the positive electrode plate, thereby beneficial to improving the kinetic performance and high-temperature cycle performance of the secondary battery, and also beneficial to increasing the energy density of the secondary battery.

[0047] In the present application, the positive electrode plate includes a positive electrode current collector and a positive electrode material layer disposed on at least one surface of the positive electrode current collector. The above-mentioned "positive electrode material layer disposed on at least one surface of the positive electrode current collector" means that the positive electrode material layer can be disposed on one surface of the positive electrode current collector along its own thickness direction, or can be disposed on both 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. There is no special limitation in the present application as long as the purpose of the present application can be achieved.

[0048] In the present application, the positive electrode material layer includes a positive electrode active material. Based on the mass of the positive electrode material layer, the mass percentage content of the positive electrode active material is 84% to 99%. For example, the mass percentage content of the positive electrode active material can be any range composed of two values among 84%, 86%, 88%, 90%, 92%, 94%, 96%, 99%. There is no special limitation on the positive electrode active material in the present application as long as the purpose of the present application can be achieved. For example, the positive electrode active material can include, but is not limited to, at least one of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminate, lithium iron phosphate, lithium-rich manganese-based material, lithium cobalt oxide (LiCoO 2 ), lithium manganese oxide, lithium manganese iron phosphate or lithium titanate. The above-mentioned lithium nickel cobalt manganese oxide can include LiNi 0.95 Co 0.03 Mn 0.02 O 2 (Ni95), LiNi 0.91 Co 0.03 Mn 0.06 O 2 (Ni91), LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811), LiNi 0.6 Co 0.2 Mn 0.2 O 2 (NCM622), LiNi 0.5 Co 0.2 Mn 0.3 O 2 (NCM523) or LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O 2 (NCM111) and the like.

[0049] The positive electrode material layer may further include a positive electrode conductive agent and a positive electrode binder. Based on the mass of the positive electrode material layer, the mass percentage content of the positive electrode conductive agent is 0.2% to 8%, and the mass percentage content of the positive electrode binder is 0.2% to 8%. For example, the mass percentage content of the positive electrode conductive agent may be 0.2%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, or a range composed of any two of these values, and the mass percentage content of the positive electrode binder may be 0.2%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, or a range composed of any two of these values. The present application does not particularly limit the types of the positive electrode conductive agent and the positive electrode binder, as long as the object of the present application can be achieved. For example, the positive electrode conductive agent may 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 conductive carbon black may include, but is not limited to, at least one of acetylene black or Ketjen black. The above carbon nanotubes may include, but are not limited to, single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The above carbon fibers may include, but is not limited to, vapor-grown carbon fibers (VGCF) and / or nanofibers. The above metal materials may include, but are not limited to, metal powders and / or metal fibers. Specifically, the metal may include, but is not limited to, at least one of copper, nickel, aluminum, or silver. The above conductive polymers may include, but is not limited to, at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene, or polypyrrole. For example, the positive electrode binder may include, but is not limited to, at least one of polyacrylic acid, sodium polyacrylate, potassium polyacrylate, lithium polyacrylate, polyvinyl alcohol, carboxymethyl cellulose, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, polyimide, polyamideimide, styrene-butadiene rubber, or polyvinylidene fluoride.

[0050] The present application does not particularly limit the positive electrode current collector, as long as the object of the present application can be achieved. For example, it may include aluminum foil, aluminum alloy foil, or a composite current collector (such as an aluminum-carbon composite current collector), etc. The present application does not particularly limit the thickness of the positive electrode current collector, as long as the object of the present application can be achieved. For example, the thickness of the positive electrode current collector may be 6 μm to 25 μm.

[0051] Optionally, the positive electrode sheet may further include a conductive layer, and the conductive layer is located between the positive electrode current collector and the positive electrode material layer. The present application does not particularly limit the composition of the conductive layer, and it may be a commonly used conductive layer in the art. For example, the conductive layer includes a conductive layer conductive agent and a conductive layer binder. The present application does not particularly limit the conductive layer conductive agent and the conductive layer binder in the conductive layer. For example, the conductive layer conductive agent may be at least one of the above positive electrode conductive agents, and the conductive layer binder may be at least one of the above positive electrode binders.

[0052] The second aspect of the present application provides a secondary battery, which includes the positive electrode sheet provided by the first aspect of the present application. The secondary battery of the present application has good high-temperature cycling performance and kinetic performance.

[0053] The secondary battery further includes a negative electrode sheet, which includes a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector. The above "the negative electrode sheet includes a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector" means that the negative electrode material layer can be disposed on one surface of the negative electrode current collector along its own thickness direction, or can be disposed 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 surface of the negative electrode current collector, or can be a partial area of the surface of the negative electrode current collector. The present application has no special limitation, as long as the purpose of the present application can be achieved.

[0054] The present application has no special limitation on the negative electrode current collector, 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. Exemplarily, the composite current collector can be a lithium-copper composite current collector, a carbon-copper composite current collector, a nickel-copper composite current collector or a titanium-copper composite current collector, etc.

[0055] The negative electrode material layer of the present application includes a negative electrode active material. The present application has no special limitation on the negative electrode active material, as long as the purpose of the present application can be achieved. For example, the negative electrode active material can include but is not limited to natural graphite, artificial graphite, mesophase carbon microspheres, hard carbon, soft carbon, silicon, silicon-carbon composite, Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO 2 and lithiated TiO with a spinel structure 2 -Li 4 Ti 5 O 12 or at least one of Li-Al alloy.

[0056] The negative electrode material layer of the present application can further include a negative electrode conductive agent and a negative electrode binder. For example, the negative electrode conductive agent can be at least one of the above positive electrode conductive agents, and the negative electrode binder can be at least one of the above positive electrode binders. The present application has no special limitation on the mass ratio of the negative electrode active material, the negative electrode conductive agent and the negative electrode binder 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.

[0057] The present application has no special limitation on the thickness of the negative electrode material layer and the thickness of the negative electrode current collector, as long as the purpose of the present application can be achieved. For example, the single-sided thickness of the negative electrode material layer can be 80 μm to 100 μm, and the thickness of the negative electrode current collector can be 4 μm to 15 μm.

[0058] 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 does not particularly limit the composition of the conductive layer, and it may be a commonly used conductive layer in the art. For example, the conductive layer includes a conductive agent for the conductive layer and a binder for the conductive layer. The present application does not particularly limit the conductive agent for the conductive layer and the binder for the conductive layer in the conductive layer. For example, the conductive agent for the conductive layer may be at least one of the above-mentioned conductive agents for the positive electrode, and the binder for the conductive layer may be at least one of the above-mentioned binders for the positive electrode.

[0059] In the present application, the secondary battery further includes a separator. The present application does not particularly limit the separator, as long as it can achieve the purpose of the present application. For example, the material of the separator may include, but is not limited to, at least one of polyolefins (PO) mainly composed of polyethylene (PE) and polypropylene (PP), polyester (e.g., 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.

[0060] In some embodiments, the separator may include a substrate layer and a surface treatment layer. The substrate layer may be a non-woven fabric or a composite film having a porous structure, and the material of the substrate layer 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.

[0061] Optionally, a surface treatment layer is provided on at least one surface of the substrate layer, and the surface treatment layer may be a polymer layer, an inorganic layer, or a layer formed by mixing a polymer and an inorganic substance.

[0062] In some embodiments, the inorganic layer includes ceramic particles and an inorganic layer binder. The present application does not particularly limit the ceramic particles. For example, the ceramic particles may include at least one of silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, aluminum hydroxide, magnesium hydroxide, calcium hydroxide or barium sulfate. The present application does not particularly limit the inorganic layer binder. For example, the inorganic layer binder may be at least one of the above-mentioned binders for the positive electrode. In some embodiments, the polymer layer includes a polymer, and the material of the polymer may include, but is not limited to, at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyethylene ether, polyvinylidene fluoride or poly(vinylidene fluoride-hexafluoropropylene).

[0063] In this application, the thickness of the separator film is not particularly limited as long as the object of this application can be achieved. For example, the thickness of the separator film can be 3 μm to 30 μm.

[0064] In this application, the secondary battery further includes an electrolyte, and the electrolyte includes a lithium salt and a non-aqueous solvent.

[0065] This application does not particularly limit the lithium salt as long as the object of this application can be achieved. For example, the lithium salt can include but is not limited to LiPF 6 , LiBF 4 , LiAsF 6 , LiClO 4 , LiB(C 6 H 5 ) 4 , LiCH 3 SO 3 , LiCF 3 SO 3 , LiN(SO 2 CF 3 ) 2 , LiC(SO 2 CF 3 ) 3 , Li 2 SiF 6 , at least one of lithium bis(oxalato)borate (LiBOB) or lithium difluoroborate. This application does not particularly limit the content of the lithium salt in the electrolyte as long as the object of this application can be achieved.

[0066] This application does not particularly limit the non-aqueous solvent as long as the object of this application can be achieved. For example, the non-aqueous solvent can include but is not limited to at least one of carbonate compounds, carboxylate compounds, ether compounds, or other organic solvents.

[0067] The above-mentioned 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-mentioned 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 methyl ethyl carbonate (MEC). The above-mentioned 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-mentioned fluorinated carbonate compounds may include, but are not limited to, at least one of fluorinated ethylene 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-mentioned carboxylic ester compounds may include, but are not limited to, at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanolide, valerolactone, or caprolactone. The above-mentioned 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-mentioned other organic solvents may include, but are not limited to, at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methylsulfolane, 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 content of the non-aqueous solvent in the electrolyte as long as the object of the present application can be achieved.

[0068] The secondary battery further includes a housing for accommodating the positive electrode plate, the separator, the negative electrode plate, and the electrolyte, as well as other components known in the field of secondary batteries. The present application does not limit the above-mentioned other components. The present application has no particular limitation on the housing, and it can be a housing well-known in the art as long as the object of the present application can be achieved. For example, the housing can be a hard shell housing or a flexible housing. The material of the hard shell housing can be metal. The present application does not limit the type of metal, and a metal hard shell housing known in the art can be used as long as the object of the present application can be achieved. The flexible housing can be a metal plastic film, such as an aluminum plastic film, a steel plastic film, etc.

[0069] The secondary battery of the present application is not particularly limited and may include any device that undergoes an electrochemical reaction. In some embodiments, the secondary battery may include, but is not limited to, a lithium-ion secondary battery (lithium-ion battery), a lithium polymer secondary battery, or a lithium-ion polymer secondary battery, etc.

[0070] The preparation process of the secondary battery of the present application is well-known to those skilled in the art and is not particularly limited in the present application. For example, the preparation process of the secondary battery may include, but is not limited to, the following steps: stacking a positive electrode sheet, a separator, a negative electrode sheet, and a separator in sequence, and winding, folding, etc. as needed to obtain a wound electrode assembly, placing the electrode assembly into a housing, injecting an electrolyte into the housing and sealing it to obtain a secondary battery; or stacking a positive electrode sheet, a separator, a negative electrode sheet, and a separator in sequence, and then fixing the four corners of the entire laminated structure with tape to obtain a laminated electrode assembly, placing the electrode assembly into a housing, injecting an electrolyte into the housing and sealing it to obtain a secondary battery. In addition, an overcurrent protection element, a guide plate, etc. may be placed in the housing as needed to prevent the pressure inside the secondary battery from rising and overcharging / discharging.

[0071] The third aspect of the present application provides an electronic device that includes the secondary battery provided in the second aspect of the present application. The electronic device of the present application has a long service life and good performance.

[0072] The electronic device of the present application is not particularly limited and 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 headset stereo, a video recorder, a liquid crystal TV, a portable cleaner, a portable CD player, a minidisc, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power source, a motor, a car, a motorcycle, a moped, a bicycle, a lighting fixture, a toy, a game console, a clock, a power tool, a flash, a camera, a large household battery, and a lithium-ion capacitor, etc.

[0073] Examples

[0074] 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.

[0075] Testing method and device:

[0076] Test for the mass percentage content of nitrogen element in the positive electrode material layer

[0077] Under the condition of 25°C ± 3°C, after discharging the lithium-ion battery at 0.5C to 3V, the positive electrode plate was disassembled, and the residual electrolyte on the surface of the positive electrode plate was wiped off with lint-free paper. The surface of the positive electrode plate perpendicular to the thickness direction was observed using a scanning electron microscope (SEM) in backscattering mode, and the above surface of the positive electrode plate was scanned using an energy-dispersive X-ray spectrometer (EDS) to obtain the mass percentage content of nitrogen element in the positive electrode material layer.

[0078] Infrared spectrum test

[0079] Under the condition of 25°C ± 3°C, after discharging the lithium-ion battery at 0.5C to 3V, the positive electrode plate was disassembled, and after wiping off the residual electrolyte on the surface of the positive electrode plate with lint-free paper, it was placed in an oven at 85°C for drying. The positive electrode plate was subjected to diffuse reflectance infrared test using an infrared spectrometer, and the test parameters were a light wave wavelength of 2.5 μm to 25 μm and a frequency of 4000 cm -1 to 400 cm -1 , and the absorption spectrum generated by the light wave irradiating the positive electrode plate is the infrared spectrum, where the transmittance of the characteristic peak at 1200 cm -1 to 1350 cm -1 is I 1 , and the transmittance of the characteristic peak at 1000 cm -1 to 1199 cm -1 is I 2 .

[0080] Thickness test

[0081] Under the condition of 25°C ± 3°C, after discharging the lithium-ion battery at 0.5C to 3V, the positive electrode plate was disassembled, and the residual electrolyte on the surface of the positive electrode plate was wiped off with lint-free paper. The positive electrode plate was cut using plasma to obtain a cross-section along the thickness direction. Then, a scanning electron microscope (SEM) was used to observe the above cross-section, 15 test points were selected, the interval between adjacent test points was 2 mm, the thickness of the single-sided positive electrode material layer at the above test points was measured, and the average value was calculated as the thickness of the positive electrode material layer.

[0082] Membrane resistance test

[0083] Under the condition of 25°C ± 3°C, after charging the lithium-ion battery at 0.5C to 4.53V, the positive electrode plate was disassembled, and the residual electrolyte on the surface of the positive electrode plate was wiped off with lint-free paper. The obtained positive electrode plate was placed in an environment with a humidity of 10% for 30 min, and then it was sealed and transferred to the membrane resistance test location. The membrane resistance of the positive electrode plate was tested using a BER1200 model membrane resistance tester, the interval between adjacent test points was 2 mm to 3 mm, 15 test points at different positions were tested, and the average resistance of all test points was recorded as the membrane resistance R of the positive electrode plate. Among them, the test parameters were: the indenter area was 153.94 mm2 , with a pressure of 3.5 t and a holding time of 50 s.

[0084] Rate performance test

[0085] Under the condition of 25 °C, after the lithium-ion battery is left standing for 5 min, it is charged at a constant current of 0.7 C to 4.53 V, charged at a constant voltage of 4.53 V to 0.05 C, left standing for 5 min, and then discharged at a constant current of 0.2 C to 3.0 V. The discharge capacity of the lithium-ion battery at this time is measured and recorded as the 0.2 C discharge capacity. Then, after leaving it standing for 5 min, it is charged at a constant current of 0.7 C to 4.53 V, charged at a constant voltage of 4.53 V to 0.05 C, left standing for 5 min, and then discharged at a constant current of 2 C to 3.0 V. The discharge capacity of the lithium-ion battery at this time is measured and recorded as the 2 C discharge capacity. 2C discharge capacity / 0.2C discharge capacity (%) = 2C discharge capacity / 0.2C discharge capacity × 100%. The rate performance and kinetic performance of the lithium-ion battery are evaluated by 2C discharge capacity / 0.2C discharge capacity. The larger the 2C discharge capacity / 0.2C discharge capacity, the better the rate performance and kinetic performance of the lithium-ion battery; the smaller the 2C discharge capacity / 0.2C discharge capacity, the worse the rate performance and the kinetic performance of the lithium-ion battery.

[0086] High-temperature cycle performance test

[0087] Under the condition of 45 °C, the lithium-ion battery is charged at a constant current of 0.5 C to a voltage of 4.53 V, charged at a constant voltage of 4.53 V to a current of 0.025 C, and then discharged at a constant current of 0.5 C to a voltage of 3.0 V. The discharge capacity of the lithium-ion battery at this time is measured and recorded as the discharge capacity of the first cycle. Then, 500 cycles are carried out according to the above charge and discharge steps, and the discharge capacity of the 500th cycle is measured. 45 °C cycle 500 times capacity retention rate (%) = discharge capacity of the 500th cycle / discharge capacity of the first cycle × 100%.

[0088] Example 1

[0089] <Preparation of the positive electrode sheet>

[0090] The positive electrode active material lithium cobaltate (LiCoO 2) The polymer of succinic acid and 4-hydroxy-2,2,6,6-tetramethyl-1-piperidinol as a positive electrode additive (the molecular structural formula is shown below, the degree of polymerization n = 30), the positive electrode conductive agent Super P, and the positive electrode binder polyvinylidene fluoride are mixed according to the mass ratio of 97.6∶0.3∶0.9∶1.2. N-methylpyrrolidone (NMP) is added as a solvent to prepare a slurry with a solid content of 75 wt%. After vacuum stirring evenly, the positive electrode slurry is obtained. The positive electrode slurry is evenly coated on one surface of a positive electrode current collector aluminum foil with a thickness of 10 μm and dried at 90 °C to obtain a positive electrode sheet with a single-sided coated positive electrode material layer. Then, the above steps are repeated on the other surface of the aluminum foil to obtain a positive electrode sheet with a double-sided coated positive electrode material layer. After drying at 90 °C, it is cold-pressed, and then cut and welded with electrode tabs to obtain a positive electrode sheet with a specification of 74 mm × 867 mm for use. Among them, the single-sided coating surface density of the positive electrode material layer is 0.160 mg / mm 2 , and the thickness of the single-sided positive electrode material layer is shown in Table 1.

[0091]

[0092] <Preparation of negative electrode sheet>

[0093] The artificial graphite as the negative electrode active material, styrene-butadiene rubber as the negative electrode binder, and acetylene black as the negative electrode conductive agent are mixed according to the mass ratio of 97.4∶1.4∶1.2. Deionized water is added as a solvent to prepare a slurry with a solid content of 45 wt%. After vacuum stirring evenly, the negative electrode slurry is obtained. The negative electrode slurry is evenly coated on one surface of a negative electrode current collector copper foil with a thickness of 6 μm and dried at 90 °C to obtain a negative electrode sheet with a single-sided coated negative electrode material layer. Then, the above steps are repeated on the other surface of the copper foil to obtain a negative electrode sheet with a double-sided coated negative electrode material layer. After drying at 90 °C, it is cold-pressed, and then cut and welded with electrode tabs to obtain a negative electrode sheet with a specification of 78 mm × 875 mm for use. Among them, the thickness of the single-sided negative electrode material layer is 54.5 μm, and the compaction density of the negative electrode material layer is 1.7 g / cm 3 .

[0094] <Separator>

[0095] A polyethylene porous polymer film with a thickness of 5 μm (manufacturer: Celgard Separator Co., Ltd., USA) is used as the separator.

[0096] <Preparation of electrolyte>

[0097] In a glove box with an argon atmosphere where the water content is less than 10 ppm, ethylene carbonate (EC), propylene carbonate (PC), and diethyl carbonate (DEC) are evenly mixed according to the mass ratio of 10∶30∶60 to obtain a basic solvent, and the lithium salt LiPF6 Stir evenly to obtain the electrolyte. Among them, based on the total mass of the electrolyte, the mass percentage of the lithium salt LiPF 6 is 12.5%, and the balance is the base solvent.

[0098] <Preparation of Lithium-Ion Batteries>

[0099] Stack the positive electrode plate, separator, negative electrode plate, and separator in sequence, with the separator in the middle of the positive electrode plate and the negative electrode plate to play an isolation role, and wind to obtain the electrode assembly. Put the electrode assembly into an aluminum-plastic film packaging bag, remove moisture at 80 °C, inject the prepared electrolyte, and obtain a lithium-ion battery through vacuum packaging, standing, forming, and shaping processes. Among them, the upper limit voltage of forming is 4.53 V, the forming temperature is 85 °C, and the forming time is 60 min.

[0100] Examples 2 to 13

[0101] Except for adjusting the corresponding preparation parameters according to Table 1, the rest are the same as in Example 1. Among them, when the mass percentage m% of the positive electrode additive changes, the mass percentage of the positive electrode active material changes accordingly, and the mass percentages of the positive electrode conductive agent and the positive electrode binder remain unchanged. The thickness H of the positive electrode material layer is regulated by controlling the single-sided coating surface density of the positive electrode material layer. The mass ratio of the two positive electrode additives in Example 8 and Example 10 is 1:1. The positive electrode additive in Example 12 uses the compound shown in formula (Ⅲ), and the positive electrode additive in Example 13 uses the compound shown in formula (Ⅳ).

[0102]

[0103] Comparative Example 1

[0104] Except for not adding a positive electrode additive in <Preparation of the Positive Electrode Plate>, the positive electrode active material lithium cobaltate (LiCoO 2 ), the positive electrode conductive agent conductive carbon black (Super P), and the positive electrode binder polyvinylidene fluoride are mixed in a mass ratio of 97.9:0.9:1.2, the rest are the same as in Example 1.

[0105] Comparative Example 2 to Example 3

[0106] Except for adjusting the corresponding preparation parameters according to Table 1, the rest are the same as in Example 1. Among them, when the mass percentage of the positive electrode additive changes, the mass percentage of the positive electrode active material changes accordingly, and the mass percentages of the positive electrode conductive agent and the positive electrode binder remain unchanged.

[0107] The preparation parameters and performance parameters of each example and comparative example are shown in Table 1.

[0108]

[0109] It can be seen from Examples 1 to 13 and Comparative Examples 1 to 3 that by introducing a cathode additive within the scope of this application into the cathode electrode sheet and regulating the mass percentage content m% of the cathode additive within the scope of this application, the 2C discharge capacity / 0.2C discharge capacity and the capacity retention rate after 500 cycles at 45 °C of the lithium-ion battery are larger, indicating that the kinetic performance and high-temperature cycling performance of the lithium-ion battery of this application are good. In Comparative Example 1, the cathode electrode sheet does not include a cathode additive. In Comparative Examples 2 and 3, the mass percentage content m% of the cathode additive in the cathode electrode sheet is not within the scope of this application. The 2C discharge capacity / 0.2C discharge capacity of the lithium-ion battery is smaller, and the capacity retention rate after 500 cycles at 45 °C is smaller, indicating that the kinetic performance and / or high-temperature cycling performance of the lithium-ion battery are poor.

[0110] The mass percentage content m% of the cathode additive generally affects the kinetic performance and high-temperature cycling performance of the lithium-ion battery. It can be seen from Examples 1 to 4 and Comparative Examples 1 to 3 that when the value of m is too small, such as in Comparative Examples 1 and 2, the capacity retention rate after 500 cycles at 45 °C of the lithium-ion battery is smaller; when the value of m is too large, such as in Comparative Example 3, the 2C discharge capacity / 0.2C discharge capacity and the capacity retention rate after 500 cycles at 45 °C of the lithium-ion battery are smaller, indicating that the kinetic performance and / or high-temperature cycling performance of the lithium-ion battery are poor. When the value of m is within the scope of this application, the 2C discharge capacity / 0.2C discharge capacity and the capacity retention rate after 500 cycles at 45 °C of the lithium-ion battery are larger, indicating that the kinetic performance and high-temperature cycling performance of the lithium-ion battery of this application are good.

[0111] The thickness H of the cathode material layer generally affects the kinetic performance and high-temperature cycling performance of the lithium-ion battery. It can be seen from Example 1 and Examples 5 to 7 that when the value of H is within the scope of this application, the 2C discharge capacity / 0.2C discharge capacity and the capacity retention rate after 500 cycles at 45 °C of the lithium-ion battery are larger, indicating that the kinetic performance and high-temperature cycling performance of the lithium-ion battery of this application are good.

[0112] The type of the cathode additive generally affects the kinetic performance and high-temperature cycling performance of the lithium-ion battery. It can be seen from Example 1 and Examples 8 to 13 that by selecting the cathode additive within the scope of this application, the 2C discharge capacity / 0.2C discharge capacity and the capacity retention rate after 500 cycles at 45 °C of the lithium-ion battery are larger, indicating that the kinetic performance and high-temperature cycling performance of the lithium-ion battery of this application are good.

[0113] Figure 1 is the infrared spectrogram of the cathode material layer of Example 11 of this application. From Figure 1 it can be seen that the infrared spectrum of the cathode material layer is at 1100 cm-1 There is a characteristic peak at, and at 1100 cm -1 The transmittance I of the characteristic peak at 2 is 60%. The above characteristic peak corresponds to the C-OH bond in the structural formula shown in the positive electrode additive formula (II). It should be noted that in this text, the term "comprising", "including" or any other variant 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 expressly listed, or also includes elements inherent to such process, method or article.

[0114] Each embodiment in this specification is described in a related manner. For the same and similar parts between the embodiments, reference can be made to each other. Each embodiment focuses on the differences from other embodiments.

[0115] 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 sheet, comprising a positive electrode current collector and a positive electrode material layer disposed on at least one surface of the positive electrode current collector, wherein the positive electrode material layer comprises a positive electrode additive, and the mass percentage of the positive electrode additive is m%, based on the mass of the positive electrode material layer, 0.1≤m≤0.5, and the positive electrode additive comprises at least one of the structural formula represented by formula (I) or the structural formula represented by formula (II), R1 to R2 are each independently selected from a hydrogen atom, a nitrogen atom, a hydroxyl group, a C1 to C 18 Alkyl, C3 to C containing ester group 18 A chain alkyl or a cyclic alkyl; R3 to R6 are each independently selected from a hydrogen atom, a hydroxyl group, a C1 to C 18 an alkyl group, a C1 to C 18 A chain alkyl group or a cyclic alkyl group.

2. The positive electrode sheet according to claim 1, wherein: 0.15≤m≤0.3。 3. The positive electrode sheet according to claim 1, wherein: R1 to R2 are each independently selected from a hydrogen atom, a C3 to C 10 Alkyl, C3 to C containing ester group 10 R3 to R6 are each independently selected from a hydrogen atom, a C1 to C5 chain alkyl group, a C1 to C5 chain alkyl group containing an ester group or an ether bond, 10 A chain alkyl group or a cyclic alkyl group.

4. The positive electrode sheet according to claim 1, wherein: The positive electrode material layer contains nitrogen. Based on the mass of the positive electrode material layer, the mass percentage of the nitrogen in the positive electrode material layer is 0.1% to 0.3%.

5. The positive electrode sheet according to claim 1, wherein: The positive electrode additive includes at least one of a polymer of succinic acid and 4-hydroxy-2,2,6,6-tetramethyl-1-piperidinol, N,N-bis(2,2,6,6-tetramethyl-4-piperidinyl)-1,6-hexanediamine, pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, butylated hydroxyanisole or dibutylated hydroxytoluene.

6. The positive electrode sheet according to any one of claims 1 to 5, wherein: The positive electrode sheet satisfies at least one of the following characteristics: (1) The infrared spectrum of the positive electrode material layer is at 1200 cm -1 Up to 1350cm -1 There are characteristic peaks between them; (2) The infrared spectrum of the positive electrode material layer is at 1000 cm -1 Up to 1199cm -1 There are characteristic peaks between them.

7. The positive electrode sheet according to claim 6, wherein: The positive electrode sheet satisfies at least one of the following characteristics: (1) The infrared spectrum of the positive electrode material layer is at 1200 cm -1 Up to 1350cm -1 The transmittance of the characteristic peak is I1, 30%≤I1≤80%; (2) The infrared spectrum of the positive electrode material layer is at 1000 cm -1 Up to 1199cm -1 The transmittance of the characteristic peak is I2, 60%≤I2≤70%.

8. The positive electrode sheet according to any one of claims 1 to 5, wherein: The thickness of the positive electrode material layer is H μm, 10≤H≤50.

9. The positive electrode sheet according to any one of claims 1 to 5, wherein: The film resistance of the positive electrode plate is RΩ, the thickness of the positive electrode material layer is Hμm, 0.05≤R≤0.5, 0.5≤R×H≤8. 10 . A secondary battery comprising the positive electrode sheet according to claim 1 . 11 . An electronic device comprising the secondary battery according to claim 10 .

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