Positive electrode sheet, secondary battery, and electric device

Abstract

The application provides a positive electrode sheet, a secondary battery and an electric device. The positive electrode sheet comprises a positive electrode current collector, a positive electrode film layer arranged on at least one surface of the positive electrode current collector, and a conductive primer layer between the positive electrode current collector and the positive electrode film layer. The positive electrode film layer comprises a positive electrode active material with a core-shell structure, the positive electrode active material comprises an inner core and a shell covering the inner core, and the conductive primer layer comprises a first polymer, a first water-based binder and a first conductive agent.

Description

TECHNICAL FIELD

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

[0002] In recent years, with the application range of secondary batteries becoming more and more extensive, secondary batteries are widely used in energy storage power supply systems such as hydropower, thermal power, wind power and solar power stations, and in many fields such as electric tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, etc. Due to the great development of secondary batteries, higher requirements are put forward for their energy density, cycle performance, etc.

[0003] The related art improves one or more performances of a secondary battery by setting a conductive primer layer between an active material and a current collector of a positive electrode sheet.

[0004] In order to further improve the performance of the battery, the prior art needs a more optimal positive electrode sheet. SUMMARY

[0005] In view of the above problems, the present application provides a new type of positive electrode sheet, a secondary battery and an electric device. The new type of positive electrode sheet includes a new type of positive electrode active material and a new type of conductive primer layer, which are described below respectively.

[0006] The first aspect of the present application provides a positive electrode sheet, comprising a positive electrode current collector, a positive electrode film layer arranged on at least one surface of the positive electrode current collector, and a conductive primer layer located between the positive electrode current collector and the positive electrode film layer, wherein,

[0007] The positive electrode film layer comprises a positive electrode active material having a core-shell structure, the positive electrode active material comprising an inner core and a shell covering the inner core,

[0008] The inner core comprises Li 1+x Mn 1-y A y P 1-z R z O4, x = -0.100-0.100, y = 0.001-0.500, z = 0.001-0.100, the A is selected from one or more of Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb and Ge, and can be selected from one or more of Fe, Ti, V, Ni, Co and Mg, the R is selected from one or more of B, Si, N and S;

[0009] The shell comprises a first coating layer covering the inner core and a second coating layer covering the first coating layer, wherein,

[0010] The first coating layer comprises pyrophosphate MP2O7 and phosphate XPO4, wherein M and X are each independently selected from one or more of Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb or Al;

[0011] The second coating layer contains carbon;

[0012] The conductive undercoat includes a first polymer, a first water-based binder, and a first conductive agent.

[0013] The first polymer comprises:

[0014] Equation 1 represents the first single-unit cell;

[0015] A second monomer unit selected from at least one of the monomer units represented by Formula 2 and the monomer units represented by Formula 3;

[0016] A third monomer unit selected from at least one of the monomer units represented by Formula 4 and the monomer units represented by Formula 5; and

[0017] The fourth monomer unit represented by Equation 6, R 1 R 2 R 3 Each group independently represents H, carboxyl, ester, and the following substituted or unsubstituted groups: C1–C10 alkyl, C1–C10 alkoxy, C2–C10 alkenyl, C6–C10 aryl, R 4 The following groups, whether substituted or unsubstituted, represent H: alkyl (C1-C10), alkoxy (C1-C10), alkenyl (C2-C10), and aryl (C6-C10).

[0018]

[0019] In some embodiments, based on the total mass of the first polymer,

[0020] The first monomer unit has a mass percentage content of M1, where M1 is 10% to 55%, optionally 25% to 55%; and / or,

[0021] The second monomer unit has a mass percentage content of M2, where M2 is 40%–80%, optionally 50%–70%; and / or,

[0022] The third monomer unit has a mass percentage content of M3, where M3 is 0% to 10%, optionally 0.001% to 2%; and / or,

[0023] The fourth monomer unit has a mass percentage content of M4, where M4 is 0% to 10%, and optionally 0.1% to 1%.

[0024] In some implementations, M3 / (M2+M3) is 0% to 5%, and optionally 0.001% to 1%.

[0025] In some embodiments, the first polymer comprises one or more selected from hydrogenated nitrile butadiene rubber and hydrogenated carboxylated nitrile butadiene rubber; and / or, the weight-average molecular weight of the first polymer is 50,000 to 1,500,000, optionally 200,000 to 400,000.

[0026] In some embodiments, the first waterborne adhesive comprises one or more selected from waterborne polyacrylic resins and their derivatives, waterborne amino-modified polypropylene resins and their derivatives, and polyvinyl alcohol and its derivatives, and optionally includes waterborne acrylic-acrylate copolymers; and / or, the weight-average molecular weight of the first waterborne adhesive is 200,000 to 1,500,000, and optionally 300,000 to 400,000.

[0027] In some embodiments, the first conductive agent includes one or more selected from superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers, and optionally includes one or more selected from carbon nanotubes, graphene, and carbon nanofibers.

[0028] In some embodiments, the total mass of the conductive undercoating is used as the basis for measurement.

[0029] The mass percentage of the first polymer is X1, where X1 is 5% to 20%, optionally 5% to 10%; and / or,

[0030] The first water-based adhesive has a mass percentage content of X2, where X2 is 30% to 80%, optionally 40% to 50%; and / or,

[0031] The mass percentage of the first conductive agent is X3, where X3 is 10% to 50%, and optionally 40% to 50%.

[0032] In some embodiments, the thickness of the conductive undercoat is 1 μm to 20 μm, and optionally 3 μm to 10 μm.

[0033] In some embodiments, the positive electrode film layer further includes one or more selected from wetting agents and dispersants; optionally, the positive electrode film layer also includes both wetting agents and dispersants.

[0034] In some embodiments, the surface tension of the wetting agent is 20 mN / m to 40 mN / m. Optionally, the wetting agent includes at least one of the following functional groups: -CN, -NH2, -NH-, -N-, -OH, -COO-, -C(=O)-OC(=O)-.

[0035] In some embodiments, the wetting agent includes one or more selected from small molecule organic solvents and low molecular weight polymers.

[0036] Optionally, the small molecule organic solvent includes one or more selected from alkanolamines, alcohols, and nitriles; optionally, the alkanolamines have 1 to 16 carbon atoms, and optionally 2 to 6.

[0037] Optionally, the low molecular weight polymer includes one or more selected from maleic anhydride-styrene copolymer, polyvinylpyrrolidone, and polysiloxane. Optionally, the weight average molecular weight of the low molecular weight polymer is below 6000, and optionally is 3000 to 6000.

[0038] In some embodiments, the dispersant comprises a second polymer, and the second polymer comprises:

[0039] The fifth monomer unit represented by Equation 7;

[0040] A sixth monomeric unit selected from at least one of the monomeric units represented by Formula 8 and the monomeric units represented by Formula 9; and

[0041] A seventh monomer unit selected from at least one of the monomer units represented by Formula 10 and the monomer units represented by Formula 11.

[0042]

[0043] In some embodiments, based on the total mass of the second polymer,

[0044] The fifth monomer unit has a mass percentage content of M5, where M5 is 10% to 55%, optionally 25% to 55%; and / or,

[0045] The sixth monomer unit has a mass percentage content of M6, where M6 is 40%–80%, optionally 50%–70%; and / or,

[0046] The seventh monomer unit has a mass percentage content of M7, which is 0% to 10%, and optionally 0.001% to 2%.

[0047] In some implementations, M7 / (M6+M7) is 0% to 5%, and optionally 0.001% to 1%.

[0048] In some embodiments, the second polymer is hydrogenated nitrile butadiene rubber; and / or,

[0049] The weight-average molecular weight of the second polymer is 50,000 to 500,000, and optionally 150,000 to 350,000.

[0050] In some embodiments, based on the total mass of the positive electrode film, the mass percentage content of the dispersant is Y1, where Y1 is 0.05% to 1%, optionally 0.1% to 0.5%; and / or, the mass percentage content of the wetting agent is Y2, where Y2 is 0.05% to 2%, optionally 0.2% to 0.8%.

[0051] In some implementations, Y1 / Y2 is 0.05 to 20, optionally 0.1 to 1, and further 0.3 to 0.8.

[0052] In some embodiments, the mass ratio of the first polymer to the second polymer in the positive electrode sheet is 1.5 to 5, and optionally 2 to 3.

[0053] In some embodiments, the interplanar spacing of the phosphate in the first coating layer is 0.345-0.358 nm, and the included angle of the crystal orientation (111) is 24.25°-26.45°; the interplanar spacing of the pyrophosphate in the first coating layer is 0.293-0.326 nm, and the included angle of the crystal orientation (111) is 26.41°-32.57°.

[0054] In some implementations, in the kernel, the ratio of y to 1-y is 1:10 to 10:1, optionally 1:4 to 1:1; and / or, in the kernel, the ratio of z to 1-z is 1:9 to 1:999, optionally 1:499 to 1:249.

[0055] In some implementations, the coating amount of the first coating layer is greater than 0% by weight and less than or equal to 7% by weight, optionally 4-5.6% by weight, based on the weight of the core.

[0056] In some embodiments, the weight ratio of pyrophosphate to phosphate in the first coating layer is 1:3 to 3:1, and may be selected as 1:3 to 1:1.

[0057] In some embodiments, the crystallinity of the pyrophosphate and the phosphate is each independently 10% to 100%, optionally 50% to 100%.

[0058] In some embodiments, the coating amount of the second coating layer is greater than 0% by weight and less than or equal to 6% by weight, optionally 3-5% by weight, based on the weight of the core.

[0059] In some embodiments, A is selected from at least two of Fe, Ti, V, Ni, Co, and Mg.

[0060] In some embodiments, the Li / Mn antisite defect concentration of the positive electrode active material is less than 4%, and optionally less than 2%.

[0061] In some embodiments, the lattice change rate of the positive electrode active material is less than 6%, and optionally less than 4%.

[0062] In some embodiments, the surface oxygen valence state of the positive electrode active material is below -1.88, and optionally between -1.98 and -1.88.

[0063] In some embodiments, the compaction density of the positive electrode active material at 3 tons is 2.0 g / cm³. 3 The above is optional, 2.2 g / cm³. 3 above.

[0064] In some implementations, the specific surface area of ​​the positive electrode active material is 15 m². 2 / g~25m 2 / g, the coating weight on one side of the positive electrode current collector is 20mg / cm³. 2 ~40mg / cm 2 When the specific surface area of ​​the positive electrode active material is 15m² 2 / g~25m 2 / g, the coating weight on one side of the positive electrode current collector is 20mg / cm³. 2 ~40mg / cm 2 During the coating process, film peeling is prone to occur. This application employs a novel conductive undercoat to increase the adhesion strength between the positive electrode active material layer and the current collector.

[0065] A second aspect of this application provides a secondary battery comprising the positive electrode sheet described in any of the preceding claims.

[0066] A third aspect of this application provides an electrical device including the aforementioned secondary battery.

[0067] The core-shell structured positive electrode active material provided in this application includes a core and a shell covering the core.

[0068] The kernel includes Li 1+x Mn 1-y A y P 1-z R zO4, where x = -0.100 to 0.100, for example, x can be 0.006, 0.004, 0.003, 0.002, 0.001, 0, -0.001, -0.003, -0.004, -0.005, -0.006, -0.007, -0.008, -0.009, -0.10; y = 0.001 to 0.500, for example, y can be 0.1, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45; z = 0.001 to 0. .100, for example, z can be 0.001, 0.002, 0.003, 0.004, 0.005, 0.006, 0.007, 0.008, 0.009, 0.1; A is selected from one or more of Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb and Ge, and can be selected from one or more of Fe, Ti, V, Ni, Co and Mg; R is selected from one or more of B, Si, N and S;

[0069] The shell includes a first covering layer covering the core and a second covering layer covering the first covering layer.

[0070] The first coating layer comprises pyrophosphate MP2O7 and phosphate XPO4, wherein M and X are each independently selected from one or more of Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb or Al;

[0071] The second coating layer contains carbon.

[0072] Unless otherwise stated, in the above chemical formulas, when A consists of two or more elements, the limitation on the range of values ​​for y applies not only to the stoichiometric coefficient of each element as A, but also to the sum of the stoichiometric coefficients of all elements as A. For example, when A consists of two or more elements A1, A2...An, the stoichiometric coefficients y1, y2...yn of each of A1, A2...An must each fall within the range of values ​​for y defined in this application, and the sum of y1, y2...yn must also fall within this range. Similarly, for the case where R consists of two or more elements, the limitation on the range of values ​​for the stoichiometric coefficients of R in this application has the same meaning.

[0073] The inventors of this application discovered in practical operation that manganese dissolution is severe in lithium manganese phosphate cathode active materials during deep charge-discharge processes. Although existing technologies have attempted to coat lithium manganese phosphate with lithium iron phosphate to reduce interfacial side reactions, this coating cannot prevent the migration of dissolved manganese into the electrolyte. After migrating to the negative electrode, the dissolved manganese is reduced to metallic manganese. This generated metallic manganese acts as a "catalyst," catalyzing the decomposition of the SEI film (solid electrolyte interphase) on the negative electrode surface. Some of the byproducts are gases, which can easily cause battery expansion, affecting the safety performance of the secondary battery. Others deposit on the negative electrode surface, hindering the channels for lithium ions to enter and exit the negative electrode, increasing the impedance of the secondary battery and affecting its kinetic performance. Furthermore, to replenish the lost SEI film, the electrolyte and the active lithium inside the battery are continuously consumed, irreversibly affecting the capacity retention rate of the secondary battery.

[0074] After extensive research, the inventors discovered that the problems of severe manganese leaching and high surface reactivity in lithium manganese phosphate cathode active materials may be due to the delithiation of Mn. 3+ The Jiang-Taylor effect and Li + This is caused by changes in channel size. To address this, the inventors modified lithium manganese phosphate to obtain a positive electrode active material that significantly reduces manganese leaching and lattice change rate, thereby exhibiting good cycle performance, high-temperature storage performance, and safety performance.

[0075] like Figure 9 As shown, the lithium manganese phosphate cathode active material of this application has a core-shell structure with two coating layers. The cathode active material includes a core 91 and a shell covering the core. The shell includes a first coating layer 92 covering the core and a second coating layer 93 covering the first coating layer 92. The core comprises Li... 1+x Mn 1-y A y P 1-z R z O4. The element A doping at the manganese sites of lithium manganese phosphate in the core helps reduce the lattice change rate of lithium manganese phosphate during lithium insertion / extraction, improves the structural stability of the lithium manganese phosphate cathode material, greatly reduces manganese dissolution, and lowers the oxygen activity on the particle surface. The element R doping at the phosphorus sites helps change the ease of Mn-O bond length changes, thereby lowering the lithium-ion migration barrier, promoting lithium-ion migration, and improving the rate performance of the secondary battery.

[0076] The first coating layer of the positive electrode active material in this application comprises pyrophosphate and phosphate. Since the migration barrier of transition metals in pyrophosphate is high (>1 eV), the dissolution of transition metals can be effectively suppressed. Phosphate, on the other hand, has excellent lithium-ion conduction capabilities and can reduce surface lithium impurities. Furthermore, since the second coating layer is a carbon-containing layer, it can effectively improve the conductivity and desolvation capability of LiMnPO4. In addition, the "barrier" effect of the second coating layer can further hinder the migration of manganese ions into the electrolyte and reduce the corrosion of the active material by the electrolyte.

[0077] Therefore, by performing specific element doping and surface coating on lithium manganese phosphate, this application can effectively suppress the dissolution of Mn during the lithium insertion / extraction process, while promoting the migration of lithium ions, thereby improving the rate performance of the cell and enhancing the cycle performance and high-temperature performance of the secondary battery.

[0078] Figure 10 This is a comparison of the XRD pattern of Embodiment 1-1 of this application before the first and second coating layers are applied, and the standard XRD pattern of lithium manganese phosphate (00-033-0804). It should be noted that, as... Figure 10 As shown in the figure, by comparing the XRD spectra before and after LiMnPO4 doping in this application, it can be seen that the positions of the main characteristic peaks of the positive electrode active material in this application are basically the same as those of the material before LiMnPO4 doping. This indicates that the doped lithium manganese phosphate positive electrode active material does not have impurity phases, and the improvement in the performance of the secondary battery mainly comes from element doping, rather than impurity phases.

[0079] In some embodiments, optionally, the interplanar spacing of the phosphate in the first coating layer is 0.345-0.358 nm, and the included angle of the crystal orientation (111) is 24.25°-26.45°; the interplanar spacing of the pyrophosphate in the first coating layer is 0.293-0.326 nm, and the included angle of the crystal orientation (111) is 26.41°-32.57°.

[0080] When the interplanar spacing and the angle between the crystal orientation (111) of the phosphate and pyrophosphate in the first coating layer are within the above range, impurity phases in the coating layer can be effectively avoided, thereby improving the specific capacity, cycle performance and rate performance of the material.

[0081] In some embodiments, optionally, in the core, the ratio of y to 1-y is 1:10 to 10:1, optionally 1:4 to 1:1. Here, y represents the sum of the stoichiometric coefficients of the Mn-doped elements. When the above conditions are met, the energy density and cycle performance of the cathode active material can be further improved.

[0082] In some embodiments, optionally, the ratio of z to 1-z in the core is 1:9 to 1:999, optionally 1:499 to 1:249. Here, y represents the sum of the stoichiometric coefficients of the p-site dopants. When the above conditions are met, the energy density and cycle performance of the cathode active material can be further improved.

[0083] In some implementations, optionally, the coating amount of the first coating layer is greater than 0% by weight and less than or equal to 7% by weight, optionally 4-5.6% by weight, based on the weight of the core.

[0084] When the coating amount of the first coating layer is within the above-mentioned range, it can further suppress manganese dissolution and further promote lithium-ion transport. It can also effectively avoid the following situations: if the coating amount of the first coating layer is too small, the pyrophosphate may not sufficiently inhibit manganese dissolution, and the improvement on lithium-ion transport performance may not be significant; if the coating amount of the first coating layer is too large, the coating layer may be too thick, increasing battery impedance and affecting the battery's kinetic performance.

[0085] In some embodiments, optionally, the weight ratio of pyrophosphate to phosphate in the first coating layer is 1:3 to 3:1, and optionally 1:3 to 1:1.

[0086] A proper ratio of pyrophosphate and phosphate is beneficial for fully leveraging their synergistic effect and can effectively avoid the following situations: if there is too much pyrophosphate and too little phosphate, it may lead to an increase in battery impedance; if there is too much phosphate and too little pyrophosphate, the effect of inhibiting manganese dissolution will be insignificant.

[0087] In some embodiments, optionally, the crystallinity of the pyrophosphate and the phosphate is each independently 10% to 100%, optionally 50% to 100%.

[0088] In the first coating layer of the lithium manganese phosphate cathode active material of this application, the presence of pyrophosphate and phosphate with a certain degree of crystallinity helps maintain the structural stability of the first coating layer and reduces lattice defects. This is beneficial in two ways: firstly, it allows the pyrophosphate to fully inhibit manganese dissolution; secondly, it helps the phosphate reduce the surface lithium content and lower the valence state of surface oxygen, thereby reducing interfacial side reactions between the cathode material and the electrolyte, reducing electrolyte consumption, and improving the cycle performance and safety performance of the battery.

[0089] It should be noted that, in this application, the crystallinity of pyrophosphate and phosphate can be adjusted, for example, by adjusting the process conditions of the sintering process, such as sintering temperature and sintering time. The crystallinity of pyrophosphate and phosphate can be measured by methods known in the art, such as X-ray diffraction, density method, infrared spectroscopy, differential scanning calorimetry, and nuclear magnetic resonance absorption method.

[0090] In some implementations, the second coating layer may optionally have a coating amount greater than 0% by weight and less than or equal to 6% by weight, optionally 3-5% by weight, based on the weight of the core.

[0091] The carbon-containing layer, serving as the second coating layer, acts as a barrier, preventing direct contact between the positive electrode active material and the electrolyte, thereby reducing electrolyte corrosion and improving battery safety at high temperatures. Furthermore, its strong conductivity reduces internal resistance, enhancing battery kinetic performance. However, due to the low specific capacity of carbon materials, excessive use of the second coating layer may decrease the overall specific capacity of the positive electrode active material. Therefore, when the coating amount is within the aforementioned range, it can further improve battery kinetic and safety performance without sacrificing the specific capacity of the positive electrode active material.

[0092] In some embodiments, the A may optionally be selected from at least two of Fe, Ti, V, Ni, Co, and Mg.

[0093] Simultaneous doping of two or more of the aforementioned elements at the manganese sites in lithium manganese phosphate cathode active materials is beneficial to enhancing the doping effect. On the one hand, it further reduces the lattice change rate, thereby inhibiting the dissolution of manganese and reducing the consumption of electrolyte and active lithium. On the other hand, it is also beneficial to further reduce surface oxygen activity, reduce interfacial side reactions between cathode active materials and electrolyte, thereby improving the cycle performance and high-temperature storage performance of the battery.

[0094] In some embodiments, the Li / Mn antisite defect concentration of the positive electrode active material is optionally below 4%, and optionally below 2%.

[0095] In the positive electrode active material of this application, the Li / Mn antisite defect refers to the Li / Mn antisite defect in the LiMnPO4 lattice. + and Mn 2+ The positions of Li have been interchanged. + The transmission channel is a one-dimensional channel, Mn 2+ In Li + It is difficult to migrate in the transmission channel, therefore, the Mn of the inversion defect is difficult to migrate. 2+ It will hinder Li + The transport of Li / Mn antisite defects can be improved by controlling the concentration of Li / Mn antisite defects at a low level. In this application, the antisite defect concentration can be determined, for example, according to JIS K 0131-1996.

[0096] In some embodiments, the lattice change rate of the positive electrode active material is optionally less than 6%, and optionally less than 4%.

[0097] The lithium insertion / extraction process in LiMnPO4 is a two-phase reaction. The interfacial stress between the two phases is determined by the rate of lattice change; the smaller the rate of lattice change, the smaller the interfacial stress. + The easier the transmission, the better. Therefore, reducing the lattice change rate of the core will be beneficial for enhancing Li. + This improves the transmission capacity, thereby enhancing the rate performance of secondary batteries.

[0098] In some embodiments, optionally, the average discharge voltage of the positive electrode active material is 3.5V or higher, and the discharge specific capacity is 140mAh / g or higher; optionally, the average discharge voltage is 3.6V or higher, and the discharge specific capacity is 145mAh / g or higher.

[0099] Although the average discharge voltage of undoped LiMnPO4 is above 4.0V, its discharge specific capacity is low, usually less than 120mAh / g, and therefore its energy density is low. By adjusting the lattice change rate through doping, its discharge specific capacity can be greatly improved, and the overall energy density can be significantly increased with a slight decrease in average discharge voltage.

[0100] In some embodiments, the surface oxygen valence state of the positive electrode active material is optionally below -1.88, and optionally between -1.98 and -1.88.

[0101] This is because the higher the valence state of oxygen in a compound, the stronger its ability to gain electrons, i.e., the stronger its oxidizing power. In the lithium manganese phosphate cathode active material of this application, by controlling the surface valence state of oxygen at a low level, the reactivity of the cathode material surface can be reduced, the interfacial side reactions between the cathode material and the electrolyte can be reduced, thereby improving the cycle performance and high-temperature storage performance of the secondary battery.

[0102] In some embodiments, optionally, the compaction density of the positive electrode active material at 3 tons (T) is 2.0 g / cm³. 3 The above is optional, 2.2 g / cm³. 3 above.

[0103] A higher compaction density of the positive electrode active material, i.e., a greater weight of active material per unit volume, is more conducive to improving the volumetric energy density of the battery. In this application, the compaction density can be measured, for example, according to GB / T 24533-2009.

[0104] Regarding the positive electrode sheet provided in this application, it includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector. The positive electrode film layer includes the lithium manganese phosphate positive electrode active material of this application or the lithium manganese phosphate positive electrode active material prepared according to the method of this application, and the content of the positive electrode active material in the positive electrode film layer is more than 10% by weight, based on the total weight of the positive electrode film layer.

[0105] In some embodiments, optionally, the content of the positive electrode active material in the positive electrode film layer is 90-99.5% by weight, based on the total weight of the positive electrode film layer.

[0106] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0107] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0108] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0109] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0110] In some embodiments, the positive electrode film layer of this application comprises 90-99.5% of the lithium manganese phosphate positive electrode active material of this application, 0.4-5.5% of binder, 0.1-2.5% of conductive carbon and 0.001-1% of other additives, based on the total weight of the positive electrode film layer.

[0111] In some embodiments, the positive electrode film layer of this application may optionally include other additives such as dispersants, wetting agents, rheology modifiers, and other additives commonly used in the art.

[0112] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0113] In some embodiments, the coating weight of the positive electrode film in this application is 0.28-0.45 g / 1540.25 mm. 2 The compacted density reaches 2.2-2.8 g / cm³. 3 .

[0114] It should be noted that in this paper, the median particle size Dv 50 This refers to the particle size corresponding to a cumulative volume distribution percentage of the positive electrode active material reaching 50%. In this application, the median particle size Dv of the positive electrode active material... 50 Particle size can be determined using laser diffraction particle size analysis. For example, according to standard GB / T 19077-2016, a laser particle size analyzer (e.g., MalvernMaster Size 3000) can be used for determination.

[0115] In this document, the term "cladding layer" refers to a layer of material covering the core, which may completely or partially cover the core. The use of "cladding layer" is for ease of description only and is not intended to limit the invention. Similarly, the term "thickness of cladding layer" refers to the thickness of the layer of material covering the core in the radial direction of the core.

[0116] In this document, the term "source" refers to a compound that is the source of a certain element. For example, the types of "sources" include, but are not limited to, carbonates, sulfates, nitrates, elements, halides, oxides, and hydroxides.

[0117] Beneficial effects

[0118] One or more embodiments of this application have one or more of the following beneficial effects:

[0119] (1) This application modifies lithium manganese phosphate to obtain a positive electrode active material that significantly reduces manganese dissolution and lattice change rate, thereby exhibiting good cycle performance, high-temperature storage performance, and safety performance. The first coating layer of the positive electrode active material in this application includes pyrophosphate and phosphate. Due to the high migration barrier of transition metals in pyrophosphate (>1eV), the dissolution of transition metals can be effectively suppressed. Phosphate has excellent lithium-ion conduction ability and can reduce the surface lithium content. In addition, since the second coating layer is a carbon-containing layer, it can effectively improve the conductivity and desolvation ability of LiMnPO4. Furthermore, the "barrier" effect of the second coating layer can further hinder the migration of manganese ions into the electrolyte and reduce the corrosion of the active material by the electrolyte. Therefore, by performing specific element doping and surface coating on lithium manganese phosphate, this application can effectively suppress Mn dissolution during the lithium insertion / extraction process while promoting lithium ion migration, thereby improving the rate performance of the cell and enhancing the cycle performance and high-temperature performance of the secondary battery.

[0120] (2) When the BET specific surface area of ​​the positive electrode active material is large and there are many small particles, the bonding strength between the positive electrode active material and the current collector (aluminum foil) is weak, and the film delamination phenomenon occurs during the coating process. This application adopts a novel conductive undercoating to increase the bonding strength between the positive electrode active material layer and the current collector.

[0121] (3) During the process of coating the positive electrode active material slurry (containing solvent N-methylpyrrolidone, abbreviated as NMP) on the conductive base coating surface, the first polymer in the conductive base coating will dissolve again after contacting the solvent NMP, thereby diffusing with the positive electrode active material slurry. After curing, the active material layer can be integrated with the base coating, thereby effectively increasing the bonding strength between the positive electrode film layer and the positive electrode current collector.

[0122] (4) When the first water-based binder in the conductive base coating is an acrylic-acrylate copolymer (weight average molecular weight: 200,000 to 1,500,000), the binder has strong polarity and can achieve good adhesion with the current collector (aluminum foil). In addition, the acrylic-acrylate copolymer has good stability in the electrolyte, high temperature resistance, corrosion resistance, and low electrolyte absorption efficiency (low swelling degree).

[0123] (5) When the conductive agent in the conductive base coating is selected from one or two of carbon black, acetylene black, carbon fiber, graphite and carbon nanotubes, it can reduce the interface resistance, improve the charge and discharge rate performance of the battery and extend the cycle life of the battery. Attached Figure Description

[0124] Figure 1 This is a schematic diagram of the positive electrode sheet according to an embodiment of this application.

[0125] Figure 2 This is a schematic flowchart illustrating the measurement of electrode adhesion force according to an embodiment of this application;

[0126] Figure 3 This is a schematic diagram of a secondary battery according to one embodiment of this application.

[0127] Figure 4 yes Figure 3 An exploded view of a secondary battery according to one embodiment of this application is shown.

[0128] Figure 5 This is a schematic diagram of a battery module according to one embodiment of this application.

[0129] Figure 6 This is a schematic diagram of a battery pack according to one embodiment of this application.

[0130] Figure 7 yes Figure 6 An exploded view of a battery pack according to one embodiment of this application is shown.

[0131] Figure 8 This is a schematic diagram of an electrical device that uses a secondary battery as a power source according to one embodiment of this application.

[0132] Figure 9 This is a schematic diagram of a core-shell structured positive electrode active material according to an embodiment of this application.

[0133] Figure 10 This is a comparison diagram of the XRD spectrum of Example 1-1 of this application before the first and second coating layers are applied, and the standard XRD spectrum of lithium manganese phosphate (00-033-0804).

[0134] Explanation of reference numerals in the attached figures:

[0135] 1 Battery pack; 2 Upper casing; 3 Lower casing; 4 Battery module; 5 Secondary battery; 51 Housing; 52 Electrode assembly; 53 Top cover assembly; 11 Positive current collector; 112 Surface; 12 Conductive base coating; 13 Positive film layer; 510 Steel plate; 520 Double-sided adhesive; 530 Electrode sheet; Detailed Implementation

[0136] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the negative electrode active material and its manufacturing method, positive electrode sheet, negative electrode sheet, secondary battery, battery module, battery pack, and device of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0137] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0138] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0139] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0140] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0141] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0142] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0143] [Rechargeable Battery]

[0144] Secondary batteries, also known as rechargeable batteries or storage batteries, are batteries that can be recharged after being discharged to activate the active materials and continue to be used.

[0145] Typically, a secondary battery consists of a positive electrode, a negative electrode, a separator, and an electrolyte. During charging and discharging, active ions (such as lithium ions) repeatedly insert and extract between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing active ions to pass through. The electrolyte, also positioned between the positive and negative electrodes, mainly serves to conduct active ions.

[0146] [Positive electrode plate]

[0147] A first aspect of this application provides a positive electrode sheet, comprising a positive current collector, a positive electrode film layer disposed on at least one surface of the positive current collector, and a conductive undercoat layer located between the positive current collector and the positive electrode film layer, wherein...

[0148] The positive electrode film layer includes a positive electrode active material with a core-shell structure, wherein the positive electrode active material includes a core and a shell covering the core.

[0149] The kernel includes Li 1+x Mn 1-y A y P 1-z R z O4, x = -0.100 to 0.100, y = 0.001 to 0.500, z = 0.001 to 0.100, wherein A is selected from one or more of Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb and Ge, and may be selected from one or more of Fe, Ti, V, Ni, Co and Mg, wherein R is selected from one or more of B, Si, N and S;

[0150] The shell includes a first covering layer covering the core and a second covering layer covering the first covering layer, wherein,

[0151] The first coating layer comprises pyrophosphate MP2O7 and phosphate XPO4, wherein M and X are each independently selected from one or more of Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb or Al;

[0152] The second coating layer contains carbon;

[0153] The conductive undercoat includes a first polymer, a first water-based binder, and a first conductive agent.

[0154] The first polymer comprises:

[0155] Equation 1 represents the first single-unit cell;

[0156] A second monomer unit selected from at least one of the monomer units represented by Formula 2 and the monomer units represented by Formula 3;

[0157] A third monomer unit selected from at least one of the monomer units represented by Formula 4 and the monomer units represented by Formula 5; and

[0158] The fourth monomer unit represented by Equation 6, R 1 R 2 R 3 Each group independently represents H, carboxyl, ester, and the following substituted or unsubstituted groups: C1–C10 alkyl, C1–C10 alkoxy, C2–C10 alkenyl, C6–C10 aryl, R 4 The following groups, whether substituted or unsubstituted, represent H: alkyl (C1-C10), alkoxy (C1-C10), alkenyl (C2-C10), and aryl (C6-C10).

[0159]

[0160] In the positive electrode sheet based on the above scheme, the positive electrode film layer and the positive electrode current collector have enhanced bonding strength. Without theoretical limitations, during the process of coating the positive electrode active material slurry (containing the solvent N-methylpyrrolidone, abbreviated as NMP) onto the conductive undercoat surface, the first polymer in the conductive undercoat will dissolve again upon contact with the solvent NMP, thereby interdiffusion with the positive electrode active material slurry. After curing, the active material layer can fuse with the undercoat layer, thus effectively increasing the bonding strength between the positive electrode film layer and the positive electrode current collector.

[0161] In some embodiments, the first polymer is a random copolymer.

[0162] Nitrile butadiene rubber (NBR) is a random copolymer formed by the polymerization (e.g., emulsion polymerization) of acrylonitrile and butadiene monomers, with the following general structural formula:

[0163]

[0164] In nitrile rubber, the linkage between butadiene (B) and acrylonitrile (A) units is generally a ternary combination of BAB, BBA, or ABB, ABA, and BBB. However, with increasing acrylonitrile content, a pentagonal linkage of AABAA can also occur, and it can even become the bulk polymer of acrylonitrile. In nitrile rubber, the sequence distribution of butadiene is mainly trans-1,4 structure, and its microstructure is related to the polymerization conditions.

[0165] Hydrogenated nitrile butadiene rubber (HNBR) is a product obtained by adding hydrogen to the carbon-carbon double bonds in the molecular chain of nitrile butadiene rubber until it is partially or completely saturated. The chemical formula of fully saturated hydrogenated nitrile butadiene rubber is as follows:

[0166]

[0167] There are three main methods for preparing hydrogenated nitrile butadiene rubber (HNBR): ethylene-acrylonitrile copolymerization, NBR solution hydrogenation, and NBR emulsion hydrogenation.

[0168] Hydrogenated carboxylated butyl rubber (HXNBR) is a polymer obtained by selectively hydrogenating C=C bonds in the copolymerization of nitrile (e.g., acrylonitrile), conjugated diene (e.g., butadiene) and unsaturated carboxylic acid. The term "hydrogenated carboxylated butyl rubber" refers to hydrogenated nitrile butadiene rubber with the addition of carboxyl groups.

[0169] Esters of unsaturated carboxylic acids are, for example, esters of α,β-unsaturated monocarboxylic acids. Alkyl esters and alkoxyalkyl esters of α,β-unsaturated monocarboxylic acids are acceptable. Alkyl esters of α,β-unsaturated monocarboxylic acids, such as C1-C18 alkyl esters, are also acceptable. Alkyl esters of acrylic acid or methacrylic acid, such as C1-C18 alkyl esters, include methyl acrylate, ethyl acrylate, propyl acrylate, n-butyl acrylate, tert-butyl acrylate, 2-ethylhexyl acrylate, n-dodecyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, and 2-ethylhexyl methacrylate. Alkoxyalkyl esters of α,β-unsaturated monocarboxylic acids are also acceptable. Alkoxyalkyl esters of acrylic acid or methacrylic acid, such as C2-C12-alkoxyalkyl esters of acrylic acid or methacrylic acid, are also highly acceptable. Methoxymethyl acrylate, methoxyethyl acrylate, ethoxyethyl acrylate, and methoxyethyl acrylate are also highly acceptable. Mixtures of alkyl esters (such as those mentioned above) and alkoxyalkyl esters (such as those in the forms mentioned above) may also be used. Hydroxyalkyl acrylates and hydroxyalkyl methacrylates wherein the hydroxyalkyl group has 1-12 carbon atoms may also be used, such as 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, and 3-hydroxypropyl acrylate. Similarly, epoxy-containing esters, such as glycidyl methacrylate, may be used. Cyanoalkyl acrylates and cyanoalkyl methacrylates wherein the cyanoalkyl group has 2-12 carbon atoms may also be used, such as α-cyanoethyl acrylate, β-cyanoethyl acrylate, and cyanobutyl methacrylate. Fluorine-substituted benzyl acrylates or methacrylates may also be used, such as fluorobenzyl acrylate and fluorobenzyl methacrylate. Fluoroalkyl acrylates and methacrylates may also be used, such as trifluoroethyl acrylate and tetrafluoropropyl methacrylate. Amino-containing α,β-unsaturated carboxylic acid esters, such as dimethylaminomethyl acrylate and diethylaminoethyl acrylate, may also be used.

[0170] In some embodiments, based on the total mass of the first polymer,

[0171] The first monomer unit has a mass percentage content of M1, where M1 is 10% to 55%, optionally 25% to 55%; and / or,

[0172] The second monomer unit has a mass percentage content of M2, where M2 is 40%–80%, optionally 50%–70%; and / or,

[0173] The third monomer unit has a mass percentage content of M3, where M3 is 0% to 10%, optionally 0.001% to 2%; and / or,

[0174] The fourth monomer unit has a mass percentage content of M4, where M4 is 0% to 10%, and optionally 0.1% to 1%.

[0175] The conductive undercoat layer based on this scheme can dissolve moderately during the coating process, thereby forming an enhanced bond with the positive electrode film layer.

[0176] In some embodiments, based on the total mass of the first polymer,

[0177] The first monomer unit has a mass percentage content of M1, which is 10% to 55%, optionally 10%-15%, 15%-20%, 20%-25%, 25%-30%, 30%-35%, 35%-40%, 40%-45%, 45%-50%, or 50%-55%; and / or,

[0178] The second monomer unit has a mass percentage content of M2, which is 40% to 80%, optionally 40%-45%, 45%-50%, 50%-55%, 55%-60%, 60%-65%, 65%-70%, 70%-75%, or 75%-80%; and / or,

[0179] The third monomer unit has a mass percentage content of M3, where M3 is 0% to 10%, optionally 0.001%-1%, 1%-2%, 2%-3%, 3%-4%, 4%-5%, 5%-6%, 6%-7%, 7%-8%, 8%-9%, or 9%-10%; and / or,

[0180] The fourth monomer unit has a mass percentage of M4, which is 0%–10%, optionally 0.01%–1%, 1%–2%, 2%–3%, 3%–4%, 4%–5%, 5%–6%, 6%–7%, 7%–8%, 8%–9%, ​​or 9%–10%. The positive electrode sheet based on this scheme is used in a secondary battery, and one or more performance characteristics of the secondary battery are significantly improved. The conductive undercoating layer based on this scheme can dissolve moderately during the coating process, thereby forming a reinforced bond with the positive electrode film layer.

[0181] In some implementations, M3 / (M2+M3) is 0% to 5%, optionally 0.001% to 1%. Positive electrode sheets based on this scheme are used in secondary batteries, resulting in significant improvements in one or more performance characteristics of the secondary battery.

[0182] In some implementations, M3 / (M2+M3) is 0.01%-1%, 1%-2%, 2%-3%, 3%-4%, or 4%-5%.

[0183] In some embodiments, the first polymer comprises one or more selected from hydrogenated nitrile butadiene rubber and hydrogenated carboxylated nitrile butadiene rubber; and / or, the weight-average molecular weight of the first polymer is 50,000 to 1,500,000, optionally 200,000 to 400,000. Positive electrode sheets based on this design are used in secondary batteries, resulting in significant improvements in one or more performance characteristics of the secondary battery.

[0184] In some embodiments, the weight-average molecular weight of the first polymer is 100,000-300,000, 300,000-500,000, 500,000-700,000, 700,000-900,000, 900,000-1,100,000, 1,100,000-1,300,000, or 1,300,000-1,500,000.

[0185] In some embodiments, the first waterborne adhesive comprises one or more selected from waterborne polyacrylic resins and their derivatives, waterborne amino-modified polypropylene resins and their derivatives, and polyvinyl alcohol and its derivatives, optionally including waterborne acrylic-acrylate copolymers; and / or,

[0186] The first aqueous binder has a weight-average molecular weight of 200,000 to 1,500,000, optionally 300,000 to 400,000. Positive electrode sheets based on this design are used in secondary batteries, resulting in significant improvements in one or more performance characteristics of the secondary battery.

[0187] In some embodiments, the weight-average molecular weight of the first aqueous adhesive is 100,000-300,000, 300,000-500,000, 500,000-700,000, 700,000-900,000, 900,000-1,100,000, or 1,100,000-1,300,000.

[0188] In some embodiments, the first conductive agent comprises one or more selected from superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers, and optionally includes one or more selected from carbon nanotubes, graphene, and carbon nanofibers. A positive electrode based on this scheme is used in a secondary battery, and one or more performance characteristics of the secondary battery are significantly improved.

[0189] In some embodiments, the total mass of the conductive undercoating is used as the basis for measurement.

[0190] The mass percentage of the first polymer is X1, where X1 is 5% to 20%, optionally 5% to 10%; and / or,

[0191] The first water-based adhesive has a mass percentage content of X2, where X2 is 30% to 80%, optionally 40% to 50%; and / or,

[0192] The first conductive agent has a mass percentage of X3, where X3 is 10% to 50%, and optionally 40% to 50%. The positive electrode sheet based on this scheme is used in a secondary battery, resulting in a significant improvement in one or more performance characteristics of the secondary battery.

[0193] In some embodiments, the thickness of the conductive undercoat is 1 μm to 20 μm, optionally 3 μm to 10 μm. Positive electrode sheets based on this design are used in secondary batteries, resulting in significant improvements in one or more performance characteristics of the secondary battery.

[0194] In some embodiments, the positive electrode film layer further includes one or more selected from wetting agents and dispersants; optionally, the positive electrode film layer also includes both a wetting agent and a dispersant. Positive electrode sheets based on this design are used in secondary batteries, resulting in significant improvements in one or more performance characteristics of the secondary battery.

[0195] In some embodiments, the surface tension of the wetting agent is 20 mN / m to 40 mN / m. Optionally, the wetting agent includes at least one of the following functional groups: -CN, -NH2, -NH-, -N-, -OH, -COO-, -C(=O)-OC(=O)-. Positive electrode sheets based on this scheme are used in secondary batteries, and one or more performance characteristics of the secondary battery are significantly improved.

[0196] In some implementations, surface tension can be measured using the Wilhelmy Plate Method. Specific test procedures can be found in commonly used standards in the field, such as GB / T / 22237-2008 Surfactants—Determination of surface tension, and ASTM D1331-14. Standard test methods for surface tension and interfacial tension of coating solutions, solvents, surfactant solutions and related materials.

[0197] In some embodiments, the wetting agent includes one or more selected from small molecule organic solvents and low molecular weight polymers.

[0198] Optionally, the small molecule organic solvent includes one or more selected from alkanolamines, alcohols, and nitriles; optionally, the alkanolamines have 1 to 16 carbon atoms, and optionally 2 to 6.

[0199] Optionally, the low molecular weight polymer includes one or more selected from maleic anhydride-styrene copolymer, polyvinylpyrrolidone, and polysiloxane. Optionally, the weight-average molecular weight of the low molecular weight polymer is below 6000, and optionally between 3000 and 6000. The positive electrode sheet based on this design is used in secondary batteries, and one or more performance characteristics of the secondary battery are significantly improved.

[0200] In some embodiments, the dispersant comprises a second polymer, and the second polymer comprises:

[0201] The fifth monomer unit represented by Equation 7;

[0202] A sixth monomeric unit selected from at least one of the monomeric units represented by Formula 8 and the monomeric units represented by Formula 9; and

[0203] A seventh monomer unit selected from at least one of the monomer units represented by Formula 10 and the monomer units represented by Formula 11.

[0204]

[0205] The positive electrode sheet based on this scheme is used in secondary batteries, and one or more of the performance characteristics of the secondary battery are significantly improved.

[0206] In some embodiments, based on the total mass of the second polymer,

[0207] The fifth monomer unit has a mass percentage content of M5, where M5 is 10% to 55%, optionally 25% to 55%; and / or,

[0208] The sixth monomer unit has a mass percentage content of M6, where M6 is 40%–80%, optionally 50%–70%; and / or,

[0209] The seventh monomer unit has a mass percentage content of M7, which is 0% to 10%, and optionally 0.001% to 2%.

[0210] In some embodiments, based on the total mass of the second polymer,

[0211] The fifth monomer unit has a mass percentage content of M5, which is 10% to 55%, optionally 10%-15%, 15%-20%, 20%-25%, 25%-30%, 30%-35%, 35%-40%, 40%-45%, 45%-50%, or 50%-55%; and / or,

[0212] The sixth monomer unit has a mass percentage content of M6, where M6 is 40%–80%, optionally 40%–45%, 45%–50%, 50%–55%, 55%–60%, 60%–65%, 65%–70%, 70%–75%, or 75%–80%; and / or,

[0213] The seventh monomer unit has a mass percentage content of M7, which is 0% to 10%, and optionally 0.01%-1%, 1%-2%, 2%-3%, 3%-4%, 4%-5%, 5%-6%, 6%-7%, 7%-8%, 8%-9%, or 9%-10%.

[0214] In some implementations, M7 / (M6+M7) is 0% to 5%, optionally 0.001% to 1%. Positive electrode sheets based on this scheme are used in secondary batteries, resulting in significant improvements in one or more performance characteristics of the secondary battery.

[0215] In some embodiments, the second polymer is hydrogenated nitrile butadiene rubber; and / or,

[0216] The second polymer has a weight-average molecular weight of 50,000 to 500,000, optionally 150,000 to 350,000. Positive electrode sheets based on this design are used in secondary batteries, resulting in significant improvements in one or more performance characteristics.

[0217] In some embodiments, based on the total mass of the positive electrode film, the mass percentage content of the dispersant is Y1, where Y1 is 0.05% to 1%, optionally 0.1% to 0.5%; and / or, the mass percentage content of the wetting agent is Y2, where Y2 is 0.05% to 2%, optionally 0.2% to 0.8%. Positive electrode sheets based on this scheme are used in secondary batteries, resulting in significant improvements in one or more performance characteristics of the secondary battery.

[0218] In some embodiments, Y1 / Y2 is 0.05 to 20, optionally 0.1 to 1, and further 0.3 to 0.8. Positive electrode sheets based on this scheme are used in secondary batteries, resulting in significant improvements in one or more performance characteristics of the secondary battery.

[0219] In some embodiments, the mass ratio of the first polymer to the second polymer in the positive electrode is 1.5 to 5, optionally 2 to 3. Positive electrode sheets based on this design are used in secondary batteries, resulting in significant improvements in one or more performance characteristics of the secondary battery.

[0220] In some embodiments, the interplanar spacing of the phosphate in the first coating layer is 0.345-0.358 nm, and the included angle of the crystal orientation (111) is 24.25°-26.45°; the interplanar spacing of the pyrophosphate in the first coating layer is 0.293-0.326 nm, and the included angle of the crystal orientation (111) is 26.41°-32.57°. The positive electrode sheet based on this scheme is used in secondary batteries, and one or more performance characteristics of the secondary battery are significantly improved.

[0221] In some embodiments, in the core, the ratio of y to 1-y is 1:10 to 10:1, optionally 1:4 to 1:1; and / or, in the core, the ratio of z to 1-z is 1:9 to 1:999, optionally 1:499 to 1:249. Positive electrode sheets based on this scheme are used in secondary batteries, resulting in significant improvements in one or more performance characteristics of the secondary battery.

[0222] In some embodiments, the coating weight of the first coating layer is greater than 0% by weight and less than or equal to 7% by weight, optionally 4-5.6% by weight, based on the weight of the core. Positive electrode sheets based on this design are used in secondary batteries, resulting in significant improvements in one or more performance characteristics of the secondary battery.

[0223] In some embodiments, the weight ratio of pyrophosphate to phosphate in the first coating layer is 1:3 to 3:1, optionally 1:3 to 1:1. Positive electrode sheets based on this scheme are used in secondary batteries, resulting in significant improvements in one or more performance characteristics of the secondary battery.

[0224] In some embodiments, the crystallinity of the pyrophosphate and phosphate is independently 10% to 100%, optionally 50% to 100%. Positive electrode sheets based on this scheme are used in secondary batteries, resulting in significant improvements in one or more performance characteristics of the secondary battery.

[0225] In some embodiments, the coating amount of the second coating layer is greater than 0% by weight and less than or equal to 6% by weight, optionally 3-5% by weight, based on the weight of the core. Positive electrode sheets based on this design are used in secondary batteries, resulting in significant improvements in one or more performance characteristics of the secondary battery.

[0226] In some embodiments, A is selected from at least two of Fe, Ti, V, Ni, Co, and Mg. Positive electrode sheets based on this design are used in secondary batteries, resulting in significant improvements in one or more performance characteristics of the secondary battery.

[0227] In some embodiments, the Li / Mn antisite defect concentration of the positive electrode active material is below 4%, optionally below 2%. Positive electrode sheets based on this scheme are used in secondary batteries, resulting in significant improvements in one or more performance characteristics of the secondary battery.

[0228] In some embodiments, the lattice change rate of the positive electrode active material is less than 6%, optionally less than 4%. Positive electrode sheets based on this scheme are used in secondary batteries, resulting in significant improvements in one or more performance characteristics of the secondary battery.

[0229] In some embodiments, the surface oxygen valence state of the positive electrode active material is below -1.88, optionally between -1.98 and -1.88. Positive electrode sheets based on this design are used in secondary batteries, resulting in significant improvements in one or more performance characteristics of the secondary battery.

[0230] In some embodiments, the compaction density of the positive electrode active material at 3 tons is 2.0 g / cm³. 3 The above is optional, 2.2 g / cm³. 3 The above describes a method for using positive electrode sheets in secondary batteries, which significantly improves one or more performance characteristics of the secondary batteries.

[0231] In some embodiments, this application provides a secondary battery including the positive electrode sheet described in any of the above embodiments.

[0232] In some embodiments, this application provides an electrical device including the aforementioned secondary battery.

[0233] In some implementations, the positive electrode typically includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, the positive electrode film layer including a positive electrode active material.

[0234] Figure 1 A schematic diagram of a positive electrode sheet according to an embodiment is shown. As shown, a positive electrode sheet includes a positive current collector 11, a positive electrode film layer 13 disposed on at least one surface 112 of the positive current collector 11, and a conductive undercoat layer 12 located between the positive current collector 11 and the positive electrode film layer 13.

[0235] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0236] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0237] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0238] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0239] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0240] [Negative electrode plate]

[0241] The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector, the negative electrode film layer including a negative electrode active material.

[0242] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0243] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0244] In some embodiments, the negative electrode active material may be a negative electrode active material known in the art for use in batteries. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. Silicon-based materials may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0245] In some embodiments, the negative electrode film layer may optionally include a binder. As an example, the binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0246] In some embodiments, the negative electrode film may optionally include a conductive agent. As an example, the conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0247] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0248] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0249] [Electrolytes]

[0250] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific restrictions on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or entirely solid.

[0251] In some embodiments, the electrolyte is liquid and includes an electrolyte salt and a solvent.

[0252] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0253] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0254] In some embodiments, the electrolyte may optionally include additives. As examples, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0255] [Isolation membrane]

[0256] In some embodiments, the secondary battery also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0257] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0258] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0259] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0260] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0261] This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 3 This is an example of a square-structured secondary battery 5.

[0262] In some implementations, refer to Figure 4 The outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 can be placed over the opening to close the receiving cavity. A positive electrode, a negative electrode, and a separator can be formed into an electrode assembly 52 using a winding or stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The secondary battery 5 may contain one or more electrode assemblies 52, which can be selected by those skilled in the art according to specific practical needs.

[0263] In some implementations, the secondary batteries can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery module.

[0264] Figure 5 This is battery module 4, used as an example. (See reference...) Figure 5In battery module 4, multiple secondary batteries 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple secondary batteries 5 can be fixed in place using fasteners.

[0265] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0266] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0267] Figure 6 and Figure 7 This is battery pack 1 as an example. (See reference...) Figure 6 and Figure 7 The battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0268] In addition, this application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack provided in this application. The secondary battery, battery module, or battery pack can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0269] As the electrical device, a secondary battery, battery module, or battery pack can be selected according to its usage requirements.

[0270] Figure 8 This is an example of an electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery for this device, a battery pack or battery module can be used.

[0271] Specific embodiments of novel positive electrode active materials

[0272] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in the art or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially. Unless otherwise specified, the content of each component in the embodiments of this invention is based on the mass of the component excluding crystallization water.

[0273] The sources of raw materials involved in the embodiments of this application are as follows:

[0274] Name Chemical formula Factory Specification Manganese carbonate MnCO3 Shandong Yisha Chemical Industry Co., Ltd. 1Kg Lithium carbonate Li2CO3 Shandong Yisha Chemical Industry Co., Ltd. 1Kg Magnesium carbonate MgCO3 Shandong Yisha Chemical Industry Co., Ltd. 1Kg Zinc carbonate ZnCO3 Wuhan Xinru Chemical Co., Ltd. 25Kg Ferrous carbonate FeCO3 Xi'an Lanzhiguang Fine Materials Co., Ltd. 1Kg Nickel sulfate [NiCO3] Shandong Yisha Chemical Industry Co., Ltd. 1Kg Titanium sulfate Ti(SO4)2 Shandong Yisha Chemical Industry Co., Ltd. 1Kg Cobalt sulfate CoSO4 Xiamen Zhixin Chemical Co., Ltd. 500g Vanadium dichloride [CAT] Shanghai Jinjinyue Industry Co., Ltd. 1Kg Oxalic acid dihydrate [C2H2O4.2H2O] Shanghai Jinjinyue Industry Co., Ltd. 1Kg Ammonium dihydrogen phosphate NH4H2PO4 Shanghai Chengshao Biological Technology Co., Ltd. 500g Sucrose C 12 H 22 O 11 ]]> Shanghai Yuanye Biological Technology Co., Ltd. 100g Sulfuric acid H2SO4 Shenzhen Haishan Biological Technology Co., Ltd. Mass fraction 60% Nitric acid HNO3 Anhui Lingtian Fine Chemical Co., Ltd. Mass fraction 60% Siliconous acid [H2SiO3] Shanghai Yuanye Biological Technology Co., Ltd. 100g Boric acid H3BO3 Changzhou Qidui Chemical Co., Ltd. 1Kg

[0275] Example 1-1

[0276] Preparation of a double-layer coated lithium manganese phosphate cathode active material

[0277] (1) Preparation of co-doped lithium manganese phosphate core

[0278] Preparation of Fe, Co, and V co-doped manganese oxalate: 689.5 g of manganese carbonate (calculated as MnCO3), 455.2 g of ferrous carbonate (calculated as FeCO3), 4.6 g of cobalt sulfate (calculated as CoSO4), and 4.9 g of vanadium dichloride (calculated as VCl2) were thoroughly mixed in a mixer for 6 hours. The mixture was transferred to a reaction vessel, and 5 liters of deionized water and 1260.6 g of oxalic acid dihydrate (calculated as C2H2O4·2H2O) were added. The reaction vessel was heated to 80°C and stirred at 600 rpm for 6 hours until the reaction was terminated (no bubbles were generated), yielding a suspension of Fe, Co, V, and S co-doped manganese oxalate. The suspension was then filtered, and the filter cake was dried at 120°C and then ground to obtain Fe, Co, and V co-doped manganese oxalate dihydrate particles with a median particle size Dv50 of 100 nm.

[0279] Preparation of Fe, Co, V, and S co-doped lithium manganese phosphate: 1793.4 g of manganese oxalate dihydrate particles obtained in the previous step, 369.0 g of lithium carbonate (calculated as Li₂CO₃), 1.6 g of 60% dilute sulfuric acid (calculated as 60% H₂SO₄), and 1148.9 g of ammonium dihydrogen phosphate (calculated as NH₄H₂PO₄) were added to 20 L of deionized water. The mixture was stirred for 10 hours to ensure homogeneity, resulting in a slurry. The slurry was then transferred to a spray dryer for spray drying and granulation. The drying temperature was set at 250 °C, and the drying time was 4 hours to obtain powder. Under a nitrogen (90 vol%) + hydrogen (10 vol%) protective atmosphere, the powder was sintered at 700 °C for 4 hours to obtain 1572.1 g of Fe, Co, V, and S co-doped lithium manganese phosphate.

[0280] (2) Preparation of lithium iron pyrophosphate and lithium iron phosphate

[0281] Preparation of Lithium Iron Pyrophosphate Powder: 4.77 g lithium carbonate, 7.47 g ferrous carbonate, 14.84 g ammonium dihydrogen phosphate, and 1.3 g oxalic acid dihydrate were dissolved in 50 ml deionized water. The pH of the mixture was 5, and the mixture was stirred for 2 hours to allow the reaction mixture to react completely. The resulting solution was then heated to 80 °C and maintained at this temperature for 4 hours to obtain a suspension containing Li₂FeP₂O₇. The suspension was filtered, washed with deionized water, and dried at 120 °C for 4 hours to obtain powder. The powder was sintered at 650 °C under a nitrogen atmosphere for 8 hours, and then naturally cooled to room temperature before grinding to obtain Li₂FeP₂O₇. z FeP2O7 powder.

[0282] Preparation of lithium iron phosphate suspension: 11.1 g lithium carbonate, 34.8 g ferrous carbonate, 34.5 g ammonium dihydrogen phosphate, 1.3 g oxalic acid dihydrate, and 74.6 g sucrose (in C2) were added. 12 H 22 O 11 The solution (hereinafter referred to as "the solution") was dissolved in 150 ml of deionized water to obtain a mixture, which was then stirred for 6 hours to allow the mixture to react fully. The resulting solution was then heated to 120°C and maintained at that temperature for 6 hours to obtain a suspension containing LiFePO4.

[0283] (3) Covering

[0284] 1572.1g of the Fe, Co, V, and S co-doped lithium manganese phosphate and 15.72g of the lithium iron pyrophosphate (Li2FeP2O7) powder were added to the lithium iron phosphate (LiFePO4) suspension prepared in the previous step. After stirring and mixing evenly, the mixture was transferred to a vacuum oven and dried at 150°C for 6 hours. The product was then dispersed by sand milling. After dispersion, the product was sintered at 700°C for 6 hours under a nitrogen atmosphere to obtain the target product, double-layer coated lithium manganese phosphate.

[0285] Preparation of the positive electrode sheet

[0286] The double-layer coated lithium manganese phosphate positive electrode active material, conductive agent acetylene black, and binder polyvinylidene fluoride (PVDF) prepared above were added to N-methylpyrrolidone (NMP) in a weight ratio of 92:2.5:5.5 and stirred until homogeneous to obtain the positive electrode slurry. Then, the positive electrode slurry was prepared at a ratio of 0.280 g / 1540.25 mm. 2 The coating is evenly applied to aluminum foil, and then dried, cold-pressed, and slit to obtain the positive electrode sheet.

[0287] Preparation of the negative electrode sheet

[0288] A negative electrode slurry was prepared by dissolving artificial graphite (anode active material), hard carbon, acetylene black (conductive agent), styrene-butadiene rubber (SBR) (binder), and sodium carboxymethyl cellulose (CMC-Na) (thickener) in deionized water at a weight ratio of 90:5:2:2:1 and stirring until homogeneous. The negative electrode slurry was then prepared at a concentration of 0.117 g / 1540.25 mm. 2 The negative electrode sheet is obtained by uniformly coating the copper foil of the negative electrode current collector, drying, cold pressing, and slitting.

[0289] Preparation of Electrolyte

[0290] In an argon atmosphere glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), ethylene carbonate (EC) / ethyl methyl carbonate (EMC) were mixed uniformly at a volume ratio of 3 / 7 as an organic solvent. 12.5% ​​by weight (based on the weight of the organic solvent) of LiPF6 was added and dissolved in the organic solvent and stirred until homogeneous to obtain the electrolyte.

[0291]

Isolation Film

[0292] The material used was a commercially available PP-PE copolymer microporous film with a thickness of 20 μm and an average pore size of 80 nm (from Zogo Electronics Technology Co., Ltd., model 20).

[0293] [Preparation of a full cell]

[0294] The obtained positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. The electrodes are then wound to obtain a bare cell. The bare cell is placed in an outer packaging, injected with the electrolyte, and sealed to obtain a full battery (hereinafter also referred to as "full battery").

[0295] [Preparation of button cells]

[0296] The double-layer coated lithium manganese phosphate positive electrode active material, PVDF, and acetylene black prepared above were added to NMP at a weight ratio of 90:5:5, and stirred in a drying chamber to form a slurry. The slurry was then coated onto aluminum foil, dried, and cold-pressed to form a positive electrode sheet. The coating amount was 0.02 g / cm³. 2 The compacted density is 2.0 g / cm³. 3 .

[0297] A lithium sheet is used as the negative electrode, and a solution of 1 mol / L LiPF6 in ethylene carbonate (EC) + diethyl carbonate (DEC) + dimethyl carbonate (DMC) in a volume ratio of 1:1:1 is used as the electrolyte. The solution is assembled with the positive electrode prepared above in a button cell to form a button cell (hereinafter also referred to as "button cell").

[0298] Examples 1-2 to 1-6

[0299] In the preparation of the co-doped lithium manganese phosphate core, the preparation conditions of the lithium manganese phosphate core in Examples 1-2 to 1-6 are the same as those in Example 1-1, except that vanadium dichloride and cobalt sulfate are not used, and 463.4 g of ferrous carbonate, 1.6 g of 60% dilute sulfuric acid, 1148.9 g of ammonium dihydrogen phosphate and 369.0 g of lithium carbonate are used.

[0300] In addition, during the preparation of lithium iron pyrophosphate and lithium iron phosphate, and during the coating of the first and second coating layers, the raw materials used were adjusted according to the ratio of the coating amount shown in Table 1 to the coating amount corresponding to Example 1-1, so that the amounts of Li2FeP2O7 / LiFePO4 in Examples 1-2 to 1-6 were 12.6g / 37.7g, 15.7g / 47.1g, 18.8g / 56.5g, 22.0g / 66.0g and 25.1g / 75.4g, respectively, and the amount of sucrose in Examples 1-2 to 1-6 was 37.3g, the other conditions were the same as in Example 1-1.

[0301] Examples 1-7 to 1-10

[0302] Except that the amounts of sucrose used were 74.6g, 149.1g, 186.4g and 223.7g respectively, so that the corresponding coating amounts of the carbon layer as the second coating layer were 31.4g, 62.9g, 78.6g and 94.3g respectively, the conditions of Examples 1-7 to 1-10 were the same as those of Examples 1-3.

[0303] Examples 1-11 to 1-14

[0304] Except for adjusting the amounts of various raw materials according to the coating amounts shown in Table 1 during the preparation of lithium iron pyrophosphate and lithium iron phosphate so that the amounts of Li2FeP2O7 / LiFePO4 are 23.6g / 39.3g, 31.4g / 31.4g, 39.3g / 23.6g and 47.2g / 15.7g respectively, the conditions of Examples 1-11 to 1-14 are the same as those of Examples 1-7.

[0305] Examples 1-15

[0306] Except for the use of 492.80 g ZnCO3 instead of ferrous carbonate in the preparation of the co-doped lithium manganese phosphate core, the conditions of Examples 1-15 were the same as those of Examples 1-14.

[0307] Examples 1-16 to 1-18

[0308] Except that in Examples 1-16, 466.4 g of NiCO3, 5.0 g of zinc carbonate, and 7.2 g of titanium sulfate were used instead of ferrous carbonate in the preparation of the co-doped lithium manganese phosphate core; in Examples 1-17, 455.2 g of ferrous carbonate and 8.5 g of vanadium dichloride were used in the preparation of the co-doped lithium manganese phosphate core; and in Examples 1-18, 455.2 g of ferrous carbonate, 4.9 g of vanadium dichloride, and 2.5 g of magnesium carbonate were used in the preparation of the co-doped lithium manganese phosphate core, the conditions of Examples 1-17 to 1-19 were the same as those of Examples 1-7.

[0309] Examples 1-19 to 1-20

[0310] Except that in Examples 1-19, 369.4 g of lithium carbonate and 1.05 g of 60% dilute nitric acid were used instead of dilute sulfuric acid in the preparation of the co-doped lithium manganese phosphate core, and in Examples 1-20, 369.7 g of lithium carbonate and 0.78 g of silicic acid were used instead of dilute sulfuric acid in the preparation of the co-doped lithium manganese phosphate core, the conditions of Examples 1-19 to 1-20 were the same as those of Examples 1-18.

[0311] Examples 1-21 to 1-22

[0312] Except that in Examples 1-21, 632.0 g of manganese carbonate, 463.30 g of ferrous carbonate, 30.5 g of vanadium dichloride, 21.0 g of magnesium carbonate, and 0.78 g of silicic acid were used in the preparation of the co-doped lithium manganese phosphate core; and in Examples 1-22, 746.9 g of manganese carbonate, 289.6 g of ferrous carbonate, 60.9 g of vanadium dichloride, 42.1 g of magnesium carbonate, and 0.78 g of silicic acid were used in the preparation of the co-doped lithium manganese phosphate core, the conditions of Examples 1-21 to 1-22 were the same as those of Examples 1-20.

[0313] Examples 1-23 to 1-24

[0314] Except for Examples 1-23, which used 804.6 g manganese carbonate, 231.7 g ferrous carbonate, 1156.2 g ammonium dihydrogen phosphate, 1.2 g boric acid (99.5% by mass), and 370.8 g lithium carbonate in the preparation of the co-doped lithium manganese phosphate core, and Examples 1-24, which used 862.1 g manganese carbonate, 173.8 g ferrous carbonate, 1155.1 g ammonium dihydrogen phosphate, 1.86 g boric acid (99.5% by mass), and 371.6 g lithium carbonate in the preparation of the co-doped lithium manganese phosphate core, the conditions of Examples 1-23 to 1-24 were the same as those of Examples 1-22.

[0315] Examples 1-25

[0316] Except for the use of 370.1g of lithium carbonate, 1.56g of silicic acid and 1147.7g of ammonium dihydrogen phosphate in the preparation of the co-doped lithium manganese phosphate core in Examples 1-25, the conditions in Examples 1-25 were the same as those in Examples 1-20.

[0317] Examples 1-26

[0318] Except for the use of 368.3g lithium carbonate, 4.9g dilute sulfuric acid with a mass fraction of 60%, 919.6g manganese carbonate, 224.8g ferrous carbonate, 3.7g vanadium dichloride, 2.5g magnesium carbonate, and 1146.8g ammonium dihydrogen phosphate in the preparation of the co-doped lithium manganese phosphate core in Examples 1-26, the conditions in Examples 1-26 are the same as those in Examples 1-20.

[0319] Examples 1-27

[0320] Except for the use of 367.9g of lithium carbonate, 6.5g of 60% dilute sulfuric acid, and 1145.4g of ammonium dihydrogen phosphate in the preparation of the co-doped lithium manganese phosphate core in Examples 1-27, the conditions in Examples 1-27 were the same as those in Examples 1-20.

[0321] Examples 1-28 to 1-33

[0322] Except for Examples 1-28 to 1-33, which used 1034.5g of manganese carbonate, 108.9g of ferrous carbonate, 3.7g of vanadium dichloride, and 2.5g of magnesium carbonate in the preparation of the co-doped lithium manganese phosphate core, the amounts of lithium carbonate used were 367.6g, 367.2g, 366.8g, 366.4g, 366.0g, and 332.4g, respectively; the amounts of ammonium dihydrogen phosphate used were 1144.5g, 1143.4g, 1142.2g, 1141.1g, 1139.9g, and 1138.8g, respectively; and the amounts of 60% dilute sulfuric acid used were 8.2g, 9.8g, 11.4g, 13.1g, 14.7g, and 16.3g, respectively. The conditions in Examples 1-28 to 1-33 were the same as in Examples 1-20.

[0323] Examples 2-1 to 2-4

[0324] Example 2-1

[0325] Except that in the preparation of lithium iron pyrophosphate (Li2FeP2O7), the sintering temperature in the powder sintering step was 550°C and the sintering time was 1h to control the crystallinity of Li2FeP2O7 to 30%, and in the preparation of lithium iron phosphate (LiFePO4), the sintering temperature in the coating sintering step was 650°C and the sintering time was 2h to control the crystallinity of LiFePO4 to 30%, all other conditions were the same as in Examples 1-1.

[0326] Example 2-2

[0327] Except that in the preparation of lithium iron pyrophosphate (Li2FeP2O7), the sintering temperature in the powder sintering step was 550°C and the sintering time was 2h to control the crystallinity of Li2FeP2O7 to 50%, and in the preparation of lithium iron phosphate (LiFePO4), the sintering temperature in the coating sintering step was 650°C and the sintering time was 3h to control the crystallinity of LiFePO4 to 50%, the other conditions were the same as in Examples 1-1.

[0328] Example 2-3

[0329] Except that in the preparation of lithium iron pyrophosphate (Li2FeP2O7), the sintering temperature in the powder sintering step was 600℃ and the sintering time was 3h to control the crystallinity of Li2FeP2O7 to 70%, and in the preparation of lithium iron phosphate (LiFePO4), the sintering temperature in the coating sintering step was 650℃ and the sintering time was 4h to control the crystallinity of LiFePO4 to 70%, the other conditions were the same as in Examples 1-1.

[0330] Examples 2-4

[0331] Except that in the preparation of lithium iron pyrophosphate (Li2FeP2O7), the sintering temperature in the powder sintering step was 650℃ and the sintering time was 4h to control the crystallinity of Li2FeP2O7 to 100%, and in the preparation of lithium iron phosphate (LiFePO4), the sintering temperature in the coating sintering step was 700℃ and the sintering time was 6h to control the crystallinity of LiFePO4 to 100%, the other conditions were the same as in Examples 1-1.

[0332] Examples 3-1 to 3-12

[0333] Except for the preparation of Fe, Co, and V co-doped manganese oxalate particles, the heating temperature / stirring time in the reactor in Example 3-1 was 60℃ / 120 minutes; the heating temperature / stirring time in the reactor in Example 3-2 was 70℃ / 120 minutes; the heating temperature / stirring time in the reactor in Example 3-3 was 80℃ / 120 minutes; the heating temperature / stirring time in the reactor in Example 3-4 was 90℃ / 120 minutes; the heating temperature / stirring time in the reactor in Example 3-5 was 100℃ / 120 minutes; and the heating temperature / stirring time in the reactor in Example 3-6 was 110℃ / 120 minutes. Example 3 -7 The heating temperature / stirring time in the reactor in Examples 3-7 was 120℃ / 120 minutes; the heating temperature / stirring time in the reactor in Examples 3-8 was 130℃ / 120 minutes; the heating temperature / stirring time in the reactor in Examples 3-9 was 100℃ / 60 minutes; the heating temperature / stirring time in the reactor in Examples 3-10 was 100℃ / 90 minutes; the heating temperature / stirring time in the reactor in Examples 3-11 was 100℃ / 150 minutes; the heating temperature / stirring time in the reactor in Examples 3-12 was 100℃ / 180 minutes. Except for these conditions, the other conditions in Examples 3-1 to 3-12 were the same as in Examples 1-1.

[0334] Examples 4-1 to 4-7

[0335] Examples 4-1 to 4-4: Except that the drying temperature / drying time in the drying step of the preparation of lithium iron pyrophosphate (Li2FeP2O7) was 100℃ / 4h, 150℃ / 6h, 200℃ / 6h and 200℃ / 6h respectively; and the sintering temperature and sintering time in the sintering step of the preparation of lithium iron pyrophosphate (Li2FeP2O7) were 700℃ / 6h, 700℃ / 6h, 700℃ / 6h and 600℃ / 6h respectively, the other conditions were the same as in Examples 1-7.

[0336] Examples 4-5 to 4-7: Except that the drying temperature / drying time in the drying step during the coating process is 150℃ / 6h, 150℃ / 6h and 150℃ / 6h respectively; and the sintering temperature and sintering time in the sintering step during the coating process are 600℃ / 4h, 600℃ / 6h and 800℃ / 8h respectively, the other conditions are the same as in Examples 1-12.

[0337] Comparative Example 1

[0338] Preparation of manganese oxalate: 1149.3 g of manganese carbonate was added to a reaction vessel, along with 5 liters of deionized water and 1260.6 g of oxalic acid dihydrate (calculated as C2H2O4·2H2O, the same below). The reaction vessel was heated to 80°C and stirred at 600 rpm for 6 hours until the reaction was terminated (no more bubbles were generated), resulting in a manganese oxalate suspension. The suspension was then filtered, and the filter cake was dried at 120°C and then ground to obtain manganese oxalate dihydrate particles with a median particle size Dv50 of 100 nm.

[0339] Preparation of carbon-coated lithium manganese phosphate: Take 1789.6g of the above-obtained manganese oxalate dihydrate particles, 369.4g of lithium carbonate (calculated as Li2CO3, the same below), 1150.1g of ammonium dihydrogen phosphate (calculated as NH4H2PO4, the same below) and 31g of sucrose (calculated as C). 12 H 22 O 11 The mixture (hereinafter the same) is added to 20 liters of deionized water, and stirred for 10 hours to ensure uniform mixing, resulting in a slurry. The slurry is then transferred to a spray dryer for spray drying and granulation. The drying temperature is set at 250°C, and the mixture is dried for 4 hours to obtain a powder. Under a protective atmosphere of nitrogen (90 vol%) + hydrogen (10 vol%), the powder is sintered at 700°C for 4 hours to obtain carbon-coated lithium manganese phosphate.

[0340] Comparative Example 2

[0341] Except for the use of 689.5g of manganese carbonate and the addition of 463.3g of ferrous carbonate, the conditions for Comparative Example 2 were the same as those for Comparative Example 1.

[0342] Comparative Example 3

[0343] Except for the use of 1148.9g of ammonium dihydrogen phosphate and 369.0g of lithium carbonate, and the addition of 1.6g of 60% dilute sulfuric acid, the other conditions of Comparative Example 3 were the same as those of Comparative Example 1.

[0344] Comparative Example 4

[0345] Except for the use of 689.5g of manganese carbonate, 1148.9g of ammonium dihydrogen phosphate and 369.0g of lithium carbonate, and the addition of 463.3g of ferrous carbonate and 1.6g of 60% dilute sulfuric acid, the other conditions of Comparative Example 4 were the same as those of Comparative Example 1.

[0346] Comparative Example 5

[0347] Except for the additional step of preparing lithium iron pyrophosphate powder: 9.52 g of lithium carbonate, 29.9 g of ferrous carbonate, 29.6 g of ammonium dihydrogen phosphate, and 32.5 g of oxalic acid dihydrate were dissolved in 50 ml of deionized water. The pH of the mixture was 5, and the mixture was stirred for 2 hours to allow the reaction mixture to react fully. The resulting solution was then heated to 80°C and maintained at that temperature for 4 hours to obtain a suspension containing Li₂FeP₂O₇. The suspension was filtered, washed with deionized water, and dried at 120°C for 4 hours to obtain powder. The powder was sintered at 500°C under a nitrogen atmosphere for 4 hours, and then naturally cooled to room temperature before grinding. The crystallinity of Li₂FeP₂O₇ was controlled to be 5%. Except for the amount of Li₂FeP₂O₇ used when preparing the carbon-coated material, which was 62.8 g, the other conditions of Comparative Example 5 were the same as those of Comparative Example 4.

[0348] Comparative Example 6

[0349] Except for the additional step of preparing a lithium iron phosphate suspension: 14.7 g of lithium carbonate, 46.1 g of ferrous carbonate, 45.8 g of ammonium dihydrogen phosphate, and 50.2 g of oxalic acid dihydrate were dissolved in 500 ml of deionized water, and then stirred for 6 hours to allow the mixture to react fully. The resulting solution was then heated to 120 °C and maintained at that temperature for 6 hours to obtain a suspension containing LiFePO4. In the preparation of lithium iron phosphate (LiFePO4), except for the sintering temperature of 600 °C and the sintering time of 4 h in the coating sintering step to control the crystallinity of LiFePO4 to 8%, and the amount of LiFePO4 used in preparing the carbon-coated material being 62.8 g, the other conditions of Comparative Example 6 were the same as those of Comparative Example 4.

[0350] Comparative Example 7

[0351] Preparation of lithium iron pyrophosphate powder: 2.38 g lithium carbonate, 7.5 g ferrous carbonate, 7.4 g ammonium dihydrogen phosphate, and 8.1 g oxalic acid dihydrate were dissolved in 50 ml deionized water. The pH of the mixture was 5, and the mixture was stirred for 2 hours to allow the reaction mixture to react fully. The resulting solution was then heated to 80 °C and maintained at that temperature for 4 hours to obtain a suspension containing Li₂FeP₂O₇. The suspension was filtered, washed with deionized water, and dried at 120 °C for 4 hours to obtain powder. The powder was sintered at 500 °C under a nitrogen atmosphere for 4 hours, and after naturally cooling to room temperature, it was ground to control the crystallinity of Li₂FeP₂O₇ to 5%.

[0352] Preparation of lithium iron phosphate suspension: 11.1 g lithium carbonate, 34.7 g ferrous carbonate, 34.4 g ammonium dihydrogen phosphate, 37.7 g oxalic acid dihydrate, and 37.3 g sucrose (in C2) were added. 12 H 22 O 11The solution (hereinafter the same) was dissolved in 1500 ml of deionized water and then stirred for 6 hours to allow the mixture to react fully. The resulting solution was then heated to 120°C and maintained at that temperature for 6 hours to obtain a suspension containing LiFePO4.

[0353] 15.7 g of the obtained lithium iron pyrophosphate powder was added to the above-mentioned lithium iron phosphate (LiFePO4) and sucrose suspension. In the preparation process, the sintering temperature in the coating sintering step was 600℃ and the sintering time was 4 h to control the crystallinity of LiFePO4 to 8%. The other conditions of Comparative Example 7 were the same as those of Comparative Example 4, and amorphous lithium iron pyrophosphate, amorphous lithium iron phosphate, and carbon-coated positive electrode active materials were obtained.

[0354] Comparative Examples 8-11

[0355] Except that in the preparation of lithium iron pyrophosphate (Li2FeP2O7), the drying temperature / drying time in the drying step was 80℃ / 3h, 80℃ / 3h, and 80℃ / 3h in Comparative Examples 8-10, respectively; the sintering temperature and sintering time in the sintering step were 400℃ / 3h, 400℃ / 3h, and 350℃ / 2h in Comparative Examples 8-10, respectively; and the drying temperature / drying time in the drying step of lithium iron phosphate (LiFePO4) preparation in Comparative Example 11 was 80℃ / 3h; and the Li2FeP2O7 / LiFePO4 dosage was 47.2g / 15.7g, 15.7g / 47.2g, 62.8g / 0g, and 0g / 62.8g in Comparative Examples 8-11, respectively, all other conditions were the same as in Examples 1-7.

[0356] The preparation of the positive electrode, negative electrode, electrolyte, separator, and battery in the above embodiments and comparative examples are all the same as the processes in Examples 1-1.

[0357] [Relevant Parameter Tests]

[0358] 1. Initial capacity test of button cell batteries:

[0359] At a voltage of 2.5–4.3V, the button cell prepared above is charged to 4.3V at 0.1C, and then charged at 4.3V at a constant voltage until the current is less than or equal to 0.05mA. After standing for 5 minutes, it is discharged to 2.0V at 0.1C. The discharge capacity at this time is the initial specific capacity, denoted as D0.

[0360] 2. Average discharge voltage (V) test of coin cell:

[0361] The coin cells prepared above were placed in a constant temperature environment of 25°C for 5 minutes, discharged at 0.1C to 2.5V, placed in a constant temperature environment for 5 minutes, charged at 0.1C to 4.3V, and then charged at a constant voltage of 4.3V until the current is less than or equal to 0.05mA. After being placed in a constant temperature environment for 5 minutes, they were discharged at 0.1C to 2.5V. The discharge capacity at this time is the initial specific capacity, denoted as D0, and the discharge energy is the initial energy, denoted as E0. The average discharge voltage V of the coin cells is E0 / D0.

[0362] 3. Full battery gas expansion test at 60°C:

[0363] The prepared full cell was stored at 60°C at 100% state of charge (SOC). The open-circuit voltage (OCV) and internal resistance (IMP) of the cell were measured before, during, and after storage to monitor SOC, and the cell volume was also measured. The full cell was removed after every 48 hours of storage, allowed to stand for 1 hour, and then the OCV and IMP were measured. After cooling to room temperature, the cell volume was measured using the displacement method. The displacement method involves first measuring the cell's weight F1 separately using a balance with automatic unit conversion, and then completely immersing the cell in deionized water (with a known density of 1 g / cm³). 3 In the experiment, the weight F2 of the battery cell and the buoyancy F of the battery cell are measured at this time. 浮 That is, F1-F2, and then according to Archimedes' principle, F 浮 =ρ×g×V 排 The cell volume V is calculated to be V = (F1 - F2) / (ρ × g).

[0364] Based on the OCV and IMP test results, the batteries in all embodiments maintained a SOC of over 99% throughout the entire experiment until the end of storage.

[0365] After 30 days of storage, the cell volume was measured, and the percentage increase in cell volume after storage was calculated relative to the cell volume before storage.

[0366] In addition, measure the residual capacity of the battery cell. Charge the full battery at 1C to 4.3V within the range of 2.5V to 4.3V, then charge it at a constant voltage of 4.3V until the current is less than or equal to 0.05mA. Let it stand for 5 minutes, and record the charging capacity at this point as the residual capacity of the battery cell.

[0367] 4. Cyclic performance test of the entire battery at 45°C:

[0368] Under constant temperature conditions of 45℃ and at a voltage range of 2.5–4.3V, the prepared full battery was charged at 1C to 4.3V, and then charged at a constant voltage of 4.3V until the current was less than or equal to 0.05mA. After resting for 5 minutes, it was discharged at 1C to 2.5V, and the discharge capacity at this point was recorded as D0. The aforementioned charge-discharge cycle was repeated until the discharge capacity decreased to 80% of D0. The number of cycles completed at this point was recorded.

[0369] 5. Lattice change rate test:

[0370] Under a constant temperature environment of 25℃, the positive electrode active material sample prepared above was placed in an XRD (model Bruker D8 Discover) and tested at 1° / min. The test data was then organized and analyzed. Referring to the standard PDF card, the lattice constants a0, b0, c0 and v0 were calculated (a0, b0 and c0 represent the length of each aspect of the unit cell, and v0 represents the volume of the unit cell, which can be directly obtained from the XRD refinement results).

[0371] Using the above-described method for preparing coin cells, the positive electrode active material sample was prepared into a coin cell, and the coin cell was charged at a low rate of 0.05C until the current decreased to 0.01C. The positive electrode sheet was then removed from the coin cell and immersed in dimethyl carbonate (DMC) for 8 hours. After drying, the powder was scraped off, and particles with a diameter less than 500 nm were screened out. Samples were taken, and their cell volume v1 was calculated in the same manner as the fresh samples tested above. The lattice change rate (cell volume change rate) before and after complete lithium insertion / extraction is shown in the table.

[0372] 6. Li / Mn inverse defect concentration test:

[0373] The XRD results obtained from the "lattice change rate measurement method" are compared with the PDF (Powder Diffraction File) card of the standard crystal to determine the Li / Mn antisite defect concentration. Specifically, the XRD results obtained from the "lattice change rate measurement method" are imported into the General Structure Analysis System (GSAS) software to automatically obtain refined results, which include the occupancy of different atoms. The Li / Mn antisite defect concentration is then obtained by reading the refined results.

[0374] 7. Transition metal dissolution test:

[0375] The full battery, after being cycled at 45°C until its capacity decayed to 80%, was discharged at a 0.1C rate until the cutoff voltage of 2.0V. Then, the battery was disassembled, the negative electrode was removed, and 30 unit areas (1540.25 mm²) were randomly selected from the negative electrode. 2The discs were tested using an Agilent ICP-OES730 inductively coupled plasma emission spectrometry (ICP). The amounts of Fe (if the Mn site of the positive electrode active material is doped with Fe) and Mn were calculated based on the ICP results, thus determining the amount of Mn (and Mn-doped Fe) dissolved after cycling. The testing standard was based on EPA-6010D-2014.

[0376] 8. Surface oxygen valence state test:

[0377] 5g of the positive electrode active material sample prepared above was used to prepare a coin cell according to the above method. The coin cell was charged at a low rate of 0.05C until the current decreased to 0.01C. Then, the positive electrode sheet of the coin cell was removed and immersed in dimethyl carbonate (DMC) for 8 hours. After drying, the powder was scraped off, and particles with a diameter of less than 500nm were screened out. The obtained particles were measured using electron energy loss spectroscopy (EELS, using a Talos F200S instrument) to obtain the energy loss near-edge structure (ELNES), which reflects the density of states and energy level distribution of the element. Based on the density of states and energy level distribution, the number of occupied electrons was calculated by integrating the valence band density of states data, thereby deducing the valence state of the surface oxygen after charging.

[0378] 9. Compacted density measurement:

[0379] Take 5g of the prepared positive electrode active material powder and place it in a compaction mold (CARVER mold, model 13mm, USA). Then place the mold on a compaction density instrument. Apply a pressure of 3T and read the thickness of the powder under pressure (thickness after depressurization; the area of ​​the container used for testing is 1540.25mm²) on the instrument. 2 The compaction density is calculated using ρ = m / v.

[0380] 10. X-ray diffraction method for testing the crystallinity of pyrophosphate and phosphate.

[0381] Take 5g of the positive electrode active material powder prepared above, and measure the total scattering intensity by X-rays. It is the sum of the scattering intensity of all matter in space. It is only related to the intensity of the primary rays, the chemical structure, and the total number of electrons participating in the diffraction, i.e., the mass, and is not related to the order state of the sample. Then, separate the crystalline scattering and non-crystalline scattering from the diffraction pattern. The crystallinity is the ratio of the scattering of the crystalline part to the total scattering intensity.

[0382] 11. Interplanar spacing and angles

[0383] Take 1g of each of the above-prepared positive electrode active material powders into a 50mL test tube, and inject 10mL of 75% alcohol into the test tube. Then, stir and disperse the mixture thoroughly for 30 minutes. Then, use a clean disposable plastic pipette to take an appropriate amount of the above solution and drop it onto a 300-mesh copper grid. At this time, some powder will remain on the copper grid. Transfer the copper grid along with the sample to the TEM (Talos F200s G2) sample chamber for testing, obtain the original TEM test image, and save the original image format (xx.dm3).

[0384] Open the original image obtained from the TEM test in DigitalMicrograph software and perform a Fourier transform (the software will automatically complete this step after clicking) to obtain the diffraction pattern. Measure the distance from the diffraction spot to the center position in the diffraction pattern to obtain the interplanar spacing. The included angle is calculated according to the Bragg equation.

[0385]

[0386]

[0387]

[0388]

[0389]

[0390]

[0391]

[0392]

[0393]

[0394]

[0395]

[0396] Specific embodiments of the novel conductive undercoating

[0397] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0398] To distinguish them from the specific embodiments of the novel cathode material mentioned above, the specific embodiments of the novel conductive undercoating are numbered with a suffix ['].

[0399] Example 1-1' (Positive electrode active material of Example 1-1)

[0400] 1. Provide the first polymer

[0401] In the following embodiments, the first polymer is a hydrogenated carboxylated acrylonitrile butadiene rubber containing a first monomer unit, a second monomer unit, a third monomer unit, and a fourth monomer unit. The weight percentages of the first monomer unit, the second monomer unit, the third monomer unit, and the fourth monomer unit in the polymer, as well as the weight-average molecular weight of the first polymer, are shown in Table 1P.

[0402] The first monomer unit is the monomer unit represented by Equation 1;

[0403]

[0404] The second monomer unit is selected from at least one of the groups consisting of monomer units represented by Equation 2 and monomer units represented by Equation 3.

[0405] One kind

[0406]

[0407] The third monomer unit is selected from at least one of the groups consisting of monomer units represented by Equation 4 and monomer units represented by Equation 5.

[0408] A sort of;

[0409]

[0410]

[0411] The fourth monomer unit is the monomer unit represented by Equation 6:

[0412]

[0413] In this embodiment, R 1 R 2 and R 3 Both are H, R 4 It is n-butyl.

[0414] Table 1P

[0415]

[0416] 2. Preparation of aluminum foil with conductive undercoating

[0417] The first polymer, the first water-based binder (polyacrylic acid-acrylate copolymer, weight average molecular weight 340,000) and the first conductive agent (SP) are mixed in a weight ratio of 15:40:45, dissolved / dispersed in NMP solvent, and a conductive base coating slurry is prepared.

[0418] A conductive undercoating slurry is applied to both sides of an aluminum foil, and after drying, a conductive undercoating with a thickness of 5 μm is formed on each side. An aluminum foil with a conductive undercoating is obtained.

[0419] 3) Preparation of positive electrode sheet

[0420] The double-layer coated lithium manganese phosphate positive electrode active material of Examples 1-1 above was mixed evenly with the conductive agent acetylene black and the binder polyvinylidene fluoride (PVDF) in an N-methylpyrrolidone solvent system at a weight ratio of 92:2.5:5.5 to obtain a positive electrode slurry. The positive electrode slurry was coated onto both sides of an aluminum foil with a conductive undercoat, dried, and cold-pressed to form a positive electrode film, thus obtaining the positive electrode sheet. The single-sided density of the positive electrode film was 0.025 g / cm³. 2 The compacted density is 2.4 g / cm³. 3 .

[0421] 4) Preparation of negative electrode sheet

[0422] Artificial graphite (negative electrode active material), hard carbon, acetylene black (conductive agent), styrene-butadiene rubber (SBR) (binder), and sodium carboxymethyl cellulose (CMC) (thickener) were mixed evenly in deionized water at a weight ratio of 90:5:2:2:1. The mixture was then coated onto copper foil, dried, and cold-pressed to form a positive electrode film, thus obtaining the negative electrode sheet. The one-sided density of the negative electrode film was 0.013 g / cm³. 2 The compacted density is 1.7 g / cm³. 3 .

[0423] 5) Assembly of the full battery

[0424] Using a porous polyethylene (PE) polymer film as a separator, the positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. The resulting bare cell is then wound up. The bare cell is placed in an outer packaging, infused with electrolyte, and sealed to obtain a full battery (hereinafter referred to as "full battery").

[0425] The weight of the positive electrode active material in a single full cell is 565.66g; the weight of the negative electrode active material is 309.38g.

[0426] Examples 1-2' to 1-33' (Positive electrode active materials of Examples 1-2 to 1-33)

[0427] The difference between Examples 1-2' to 1-33' and Example 1-1' lies in step 3). The parameters of other steps are the same as those in Example 1-1'.

[0428] The positive electrode active materials used in step 3) of Examples 1-2' to 1-33' are the same as those in Examples 1-2 to 1-33 above.

[0429] Examples 2-1' to 2-3' (Positive electrode active materials of Examples 2-1 to 2-3)

[0430] The difference between Examples 2-1' and 2-3' and Example 1-1 is step 3). The parameters of other steps are the same as those in Example 1-1'.

[0431] In step 3), the positive electrode active materials used in Examples 2-1' to 2-3' are the same as those in Examples 2-1 to 2-3 above.

[0432] Comparative Examples 1' to 8' (without conductive undercoat)

[0433] The difference between Comparative Examples 1' to 8' and Examples 1-1' lies in steps 2) and 3). The other step parameters are the same as those in Examples 1-1'.

[0434] In Comparative Examples 1' to 8', in steps 2) and 3), instead of preparing an aluminum foil with a conductive undercoat, the positive electrode slurry was directly coated onto the aluminum foil and dried and cold-pressed to form a positive electrode film, thus obtaining a positive electrode sheet.

[0435] The positive electrode active materials used in Comparative Examples 1 to 7' in step 3) are the same as those used in Comparative Examples 1-1 to 1-7 above.

[0436] Comparative Example 8' uses the same positive electrode active material as in Example 1-1 above in step 3).

[0437] Comparative Example 9' (excluding the first polymer)

[0438] The difference between Comparative Example 9' and Example 1-1' lies in step 2). The other step parameters are the same as those in Example 1-1'.

[0439] In Comparative Example 9', in step 2), the first aqueous binder (polyacrylic acid-acrylate copolymer) and the first conductive agent (SP) were mixed in a weight ratio of 40:45, dissolved / dispersed in deionized water, and a conductive primer slurry was prepared. The conductive primer slurry was coated onto an aluminum foil, and after drying, a conductive primer coating with a thickness of 5 μm was formed. An aluminum foil with a conductive primer coating was obtained.

[0440] Comparative Example 10' (replacing the first polymer with the I polymer)

[0441] The difference between Comparative Example 10' and Example 1-1' lies in step 2). The other step parameters are the same as those in Example 1-1'.

[0442] In Comparative Example 10', in step 2), the first polymer, the first aqueous binder (polyacrylic acid-acrylate copolymer), and the first conductive agent (SP) were mixed in a weight ratio of 15:40:45 and dissolved / dispersed in deionized water to prepare a conductive undercoating slurry. The conductive undercoating slurry was coated onto an aluminum foil, and after drying, a conductive undercoating with a thickness of 5 μm was formed. An aluminum foil with a conductive undercoating was obtained.

[0443] The difference between polymer I and polymer I lies in their composition. The composition and weight-average molecular weight of polymer I are shown in Table 2P below.

[0444] Table 2P

[0445]

[0446] Comparative Example 11' (replacing the first water-based adhesive with the first adhesive)

[0447] The difference between Comparative Example 11' and Example 1-1' lies in step 2). The other step parameters are the same as those in Example 1-1'.

[0448] In Comparative Example 11', in step 2), the first polymer, the first binder (polyacrylic acid, weight average molecular weight 350,000), and the first conductive agent (SP) were mixed in a weight ratio of 15:40:45 and dissolved / dispersed in deionized water to prepare a conductive undercoating slurry. The conductive undercoating slurry was coated onto an aluminum foil, and after drying, a conductive undercoating with a thickness of 5 μm was formed. An aluminum foil with a conductive undercoating was obtained.

[0449] Analysis and testing

[0450] 1. Adhesion test of positive electrode sheet

[0451] Figure 2 (a) through (d) show the flowchart of the peel test. Figure 2 As shown in (a), a steel plate 510 is first provided, with dimensions of 30mm wide × 100mm long. Figure 2 As shown in (b), a double-sided tape 520 is then provided, with dimensions of 20mm wide × 30mm long. The double-sided tape 520 is attached to the steel plate 510, with one wide edge of the double-sided tape 520 aligned with one wide edge of the steel plate 510. Figure 2As shown in (c), a test electrode 530 is then provided, with dimensions of 20mm wide × 180mm long. The test electrode 530 is placed over the double-sided adhesive 520 (aligned on both sides), with the coated side of the electrode 530 facing the double-sided adhesive 520. Because the length of the test electrode 530 is greater than the length of the double-sided adhesive 520, a portion of the test electrode 530 is not bonded to the double-sided adhesive. Figure 2 As shown in (d), the steel plate 510 is fixed on the base of the tensile testing machine. A clamp holds the end of the electrode 530 to be tested that is not bonded to the double-sided adhesive. The clamp is then stretched towards the other end (as indicated by the arrow). The direction of the stretching force is perpendicular to the steel plate 510 and maintains a certain distance from its surface. While stretching the electrode outwards from the paper, the steel plate moves upwards to keep the stretching direction perpendicular to the electrode peeling position. During the stretching process, the electrode 530 is gradually peeled off the steel plate. The stretching speed of the clamp is 50 mm / min. The tension of the clamp is recorded during the stretching process. After the tension stabilizes, a further 40 mm peeling length is performed, and the average tension at this peeling length is taken as the adhesive force (in N).

[0452] 2. Battery DC resistance test

[0453] At 25℃, the battery was charged to 4.3V using a constant current and constant voltage at 1.0C (1.0C refers to the nominal capacity); the battery charge was adjusted to 50% SOC at a 1.0C rate, and after standing for 5 minutes, it was charged to 4C constant current (I m Discharge for 30 seconds (collect voltage data every 1 second), and record the initial voltage U. o and the voltage U after 30 seconds of discharge 30 The DC impedance (DCR) value is calculated using the following formula.

[0454] DC impedance value = (U0 - U 30 ) / I m

[0455] With the DC resistance value of the battery in Example 1-1' being 100%, the changes in other examples and comparative examples relative to Example 1-1' are expressed as percentages.

[0456] 3. Number of cycles in which the battery retains 80% capacity at 45°C (hereinafter referred to as "80% capacity cycles")

[0457] Under constant temperature conditions of 45℃, the full battery was charged at 1C to 4.3V within a range of 2.5V to 4.3V, and then charged at a constant voltage of 4.3V until the current was less than or equal to 0.05mA. After resting for 5 minutes, it was discharged at 1C to 2.5V, and the discharge capacity at this point was recorded as D0. This charge-discharge cycle was repeated until the discharge capacity decreased to 80% of D0. The number of cycles completed at this point was recorded.

[0458] According to the above detection and analysis methods, the bonding force of the positive electrode sheets prepared in Examples 1-1' to 1-33', Examples 2-1' to 2-3' and Comparative Examples 1' to 11' were tested, as were the DC impedance values ​​of the batteries and the number of cycles with 80% capacity retention at 45°C. The results are shown in Table 3P below.

[0459] Table 3P

[0460]

[0461]

[0462]

[0463] As shown in Table 3P, the positive electrode sheets of Examples 1-1' to 1-33' and Examples 2-1' to 2-3' exhibited improved adhesion, and the batteries of Examples 1-1' to 1-33' and Examples 2-1' to 2-3' exhibited reduced DC resistance and improved cycle capacity retention.

[0464] Comparative Example 8' (without conductive primer), Comparative Example 9' (without first polymer), Comparative Example 10' (replacing first polymer with I polymer), and Comparative Example 11' (replacing first water-based adhesive with I adhesive) failed to achieve the above-mentioned improved effect.

[0465] Examples 3-1' to 3-7' (Compositional variations of the first polymer)

[0466] The difference between Examples 3-1' to 3-7' and Example 1-1' lies in step 2). The parameters of other steps are the same as those in Example 1-1'.

[0467] In step 2), the composition of the first polymer used in Examples 3-1' to 3-7' differs from that in Example 1-1', specifically in the weight percentages of the second and third monomer units. The composition of the first polymer in Examples 3-1' to 3-7' is shown in Table 4P below.

[0468] Table 4P

[0469]

[0470] Examples 3-8' to 3-12' (Variations on the thickness of the conductive undercoat)

[0471] The difference between Examples 3-8' to 3-12' and Example 1-1' lies in step 2). The parameters of other steps are the same as those in Example 1-1'.

[0472] In step 2), the thickness of the conductive undercoat in Examples 3-8' to 3-12' is different from that in Examples 1-1, as detailed in Table 5P.

[0473] Table 5P

[0474]

[0475] Examples 3-13' to 3-18' (Variations on the composition of the conductive undercoat)

[0476] The difference between Examples 3-13' to 3-18' and Example 1-1' lies in step 2). The parameters of other steps are the same as those in Example 1-1'.

[0477] In step 2), the conductive base coating composition (the ratio of the first polymer, the first water-based binder, and the first conductive agent) of Examples 3-13' to 3-18' is different from that of Examples 1-1', as detailed in Table 6P.

[0478] Table 6P

[0479]

[0480] According to the above detection and analysis methods, the bonding force of the positive electrode sheet prepared in Examples 1-1', 3-1' to 3-18' above, the DC impedance value of the battery, and the number of cycles with 80% capacity retention at 45°C were tested. The results are shown in Table 7P below.

[0481] Table 7P

[0482] Pole piece adhesion Direct current impedance 80% capacity cycle number Example 1-1' 13 100％ 1650 Example 3-1' 12.7 100％ 1700 Example 3-2' 13 97％ 1688 Example 3-3' 12.5 100％ 1703 Example 3-4' 13.1 99％ 1600 Example 3-5' 13.8 98％ 1660 Example 3-6' 13.9 99％ 1655 Example 3-7' 12 258％ 731 Example 3-8' 8.5 110％ 1540 Example 3-9' 7.3 101％ 1720 Example 3-10' 9.9 100％ 1779 Example 3-11' 21.1 120％ 1600 Example 3-12' 32.5 150％ 1678 Example 3-13' 8.1 100％ 1630 Example 3-14' 10.5 105％ 1680 Example 3-15' 11.6 103％ 1701 Example 3-16' 10.7 145％ 1600 Example 3-17' 14.5 130％ 1635 Example 3-18' 15 110％ 1630

[0483] As shown in Table 7P, the positive electrode sheets of Examples 1-1', 3-1' to 3-18' exhibited good adhesion, and the batteries of Examples 1-1', 3-1' to 3-18' showed reduced DC resistance and improved cycle capacity retention. When the value of M3 / (M2+M3) was 0% to 5%, the mass impedance of the battery showed a significant reduction.

[0484] Examples 4-1' to 4-9'

[0485] The difference between Examples 4-1' to 4-9' and Example 1-1' lies in step 3). The parameters of other steps are the same as those in Example 1-1'.

[0486] In step 3) of Examples 4-1' to 4-9', the double-layer coated lithium manganese phosphate positive electrode active material of Example 1-1 above is mixed evenly with conductive agent acetylene black, binder polyvinylidene fluoride (PVDF), dispersant and wetting agent in an N-methylpyrrolidone solvent system at a weight ratio of (92-Y1-Y2):2.5:5.5:Y1:Y2 to obtain a positive electrode slurry. The positive electrode slurry is coated on both sides of an aluminum foil with a conductive undercoat and dried and cold-pressed to form a positive electrode film, thus obtaining a positive electrode sheet. The single-sided density of the positive electrode film is 0.025 g / cm³. 2 The compacted density is 2.4 g / cm³. 3 .

[0487] The wetting agent in Examples 4-1' to 4-9' was a maleic anhydride-styrene copolymer (molecular weight 5000). The dispersant in Examples 4-1' to 4-9' was a second polymer.

[0488] The second polymer is a hydrogenated nitrile butadiene rubber containing a fifth monomer unit, a sixth monomer unit, and a seventh monomer unit. The weight percentages of the fifth, sixth, and seventh monomer units in the polymer, as well as the weight-average molecular weight of the second polymer, are shown in Table 8P.

[0489] The fifth monomer unit is the monomer unit represented by Equation 1;

[0490]

[0491] The sixth monomer unit is selected from at least one of the monomer units represented by Formula 8 and the monomer units represented by Formula 9.

[0492]

[0493] The seventh monomer unit is selected from at least one of the monomer units represented by Formula 10 and the monomer units represented by Formula 11.

[0494]

[0495] Table 8P

[0496]

[0497] In the positive electrode sheets of Examples 4-1' to 4-9', the mass ratio of the first polymer (from the conductive undercoat) to the second polymer (from the positive electrode film) is 2:1.

[0498] The proportions of dispersant (second polymer) Y1 and wetting agent (maleic anhydride-styrene copolymer) Y2 used in step 3) in Examples 4-1' to 4-9', as well as their ratio Y1 / Y2, are shown in Table 9P below.

[0499] Table 9P

[0500] [Y1] [Y2] [Y1 / Y2] Example 4-1' 0.2 0.3 0.67 Example 4-2' 0.1 0.5 0.20 Example 4-3' 0.5 0.5 1.00 Example 4-4' 1 0.5 2.00 Example 4-5' 0.25 0.05 5.00 Example 4-6' 0.25 0.2 1.25 Example 4-7' 0.25 0.3 0.83 Example 4-8' 0.25 0.8 0.31 Example 4-9' 0.25 2 0.13

[0501] According to the above detection and analysis methods, the bonding force of the positive electrode sheet prepared in Examples 1-1' and 4-1' to 4-9' above, the DC impedance value of the battery, and the number of cycles with 80% capacity retention at 45°C were tested. The results are shown in Table 10P below.

[0502] Table 10P

[0503] Pole piece adhesion Direct current impedance Cycle number Example 1-1' 13 100％ 1650 Example 4-1' 64 93％ 1762 Example 4-2' 60 95％ 1770 Example 4-3' 178 104％ 1310 Example 4-4' 193 160％ 1308 Example 4-5' 105 100％ 1700 Example 4-6' 105 99％ 1830 Example 4-7' 110 98％ 1781 Example 4-8' 108 106％ 1690 Example 4-9' 109 116％ 1410

[0504] As shown in Table 10P, based on the above-mentioned novel conductive undercoating, the combination of a novel positive electrode film containing dispersants and wetting agents can further improve the adhesion of the electrode sheets and / or reduce the DC impedance of the battery and / or improve the cycle performance of the battery.

[0505] Based on the experimental data above, this application provides a novel positive electrode sheet, a secondary battery, and an electrical device. The positive electrode sheet includes a novel positive electrode active material and a novel conductive undercoating.

[0506] The new positive electrode active materials have achieved better performance in one or all of the following aspects: cycle performance, high-temperature storage performance, and safety performance.

[0507] The new conductive undercoat coating achieves superior performance in one or all aspects of providing electrode adhesion, reducing battery DC impedance, and improving battery cycle performance.

[0508] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A positive electrode sheet, comprising a positive current collector, a positive electrode film layer disposed on at least one surface of the positive current collector, and a conductive undercoat layer located between the positive current collector and the positive electrode film layer, wherein, The positive electrode film layer includes a positive electrode active material with a core-shell structure, wherein the positive electrode active material includes a core and a shell covering the core. The kernel includes Li 1+x Mn 1-y A y P 1-z R z O4, x = -0.100~0.100, y = 0.001~0.500, z = 0.001~0.100, wherein A is selected from one or more of Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb and Ge, and R is selected from one or more of B, Si, N and S; The shell includes a first covering layer covering the core and a second covering layer covering the first covering layer, wherein, The first coating layer comprises pyrophosphate MP2O7 and phosphate XPO4, wherein M and X are each independently selected from one or more of Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb or Al; The second coating layer contains carbon; The conductive undercoat includes a first polymer, a first water-based binder, and a first conductive agent. The first polymer comprises: Equation 1 represents the first single-unit cell; A second monomer unit selected from at least one of the monomer units represented by Formula 2 and the monomer units represented by Formula 3; A third monomer unit selected from at least one of the monomer units represented by Formula 4 and the monomer units represented by Formula 5; and The fourth monomer unit represented by Equation 6, R 1 R 2 R 3 Each group independently represents H, carboxyl, ester, and the following substituted or unsubstituted groups: C1-C10 alkyl, C1-C10 alkoxy, C2-C10 alkenyl, C6-C10 aryl, R 4 The following groups, whether substituted or unsubstituted, represent H: alkyl (C1-C10), alkoxy (C1-C10), alkenyl (C2-C10), and aryl (C6-C10). Formula 1 Formula 2 Formula 3 Formula 4 Formula 5 Formula 6; Based on the total mass of the first polymer, the mass percentage of the first monomer unit is M1, where M1 is 10% to 55%; the mass percentage of the second monomer unit is M2, where M2 is 40% to 80%; the mass percentage of the third monomer unit is M3, where M3 is 0.001% to 2%; and the mass percentage of the fourth monomer unit is M4, where M4 is 0.1% to 10%.

2. The positive electrode sheet according to claim 1, wherein, The A is selected from one or more of Fe, Ti, V, Ni, Co and Mg.

3. The positive electrode sheet according to claim 1, wherein, Based on the total mass of the first polymer, The first monomer unit has a mass percentage content of M1, where M1 is 25% to 55%; and / or, The second monomer unit has a mass percentage content of M2, where M2 is 50%~70%; and / or, The mass percentage of the fourth monomer unit is M4, where M4 is 0.1% to 1%.

4. The positive electrode sheet according to claim 1, wherein, M3 / (M2+M3) is 0%~5%.

5. The positive electrode sheet according to claim 1, wherein, M3 / (M2+M3) is 0.001%~1%.

6. The positive electrode sheet according to claim 1, wherein, The first polymer includes one or more of hydrogenated nitrile butadiene rubber and hydrogenated carboxylated nitrile butadiene rubber; and / or, The weight-average molecular weight of the first polymer is 50,000 to 1,500,000.

7. The positive electrode sheet according to claim 1, wherein, The weight-average molecular weight of the first polymer is 200,000 to 400,000.

8. The positive electrode sheet according to claim 1, wherein, The first waterborne adhesive comprises one or more of waterborne polyacrylic acid resin and its derivatives, waterborne amino-modified polypropylene resin and its derivatives, and polyvinyl alcohol and its derivatives; and / or, The weight-average molecular weight of the first water-based adhesive is 200,000 to 1,500,000.

9. The positive electrode sheet according to claim 1, wherein, The first waterborne adhesive comprises a waterborne acrylic-acrylate copolymer; and / or, The weight-average molecular weight of the first water-based adhesive is 300,000 to 400,000.

10. The positive electrode sheet according to claim 1, wherein, The first conductive agent includes one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

11. The positive electrode sheet according to claim 1, wherein, The first conductive agent includes one or more of carbon nanotubes, graphene, and carbon nanofibers.

12. The positive electrode sheet according to claim 1, wherein, Based on the total mass of the conductive undercoating layer The mass percentage of the first polymer is X1, where X1 is 5% to 20%; and / or, The first water-based adhesive has a mass percentage content of X2, where X2 is 30%~80%; and / or, The mass percentage of the first conductive agent is X3, where X3 is 10% to 50%.

13. The positive electrode sheet according to claim 1, wherein, Based on the total mass of the conductive undercoating layer The mass percentage of the first polymer is X1, where X1 is 5% to 10%; and / or, The first water-based adhesive has a mass percentage content of X2, where X2 is 40%~50%; and / or, The mass percentage of the first conductive agent is X3, where X3 is 40%~50%.

14. The positive electrode sheet according to claim 1, wherein, The thickness of the conductive undercoat is 1μm to 20μm.

15. The positive electrode sheet according to claim 1, wherein, The thickness of the conductive undercoat is 3μm to 10μm.

16. The positive electrode sheet according to claim 1, wherein, The positive electrode film layer also includes one or more of the following: wetting agent and dispersant.

17. The positive electrode sheet according to claim 16, wherein, The positive electrode film also includes a wetting agent and a dispersant.

18. The positive electrode sheet according to claim 16, wherein, The surface tension of the wetting agent is 20mN / m to 40mN / m.

19. The positive electrode sheet according to claim 16, wherein, The wetting agent includes at least one of the following functional groups: -CN, -NH2, -NH-, -N-, -OH, -COO-, -C(=O)-OC(=O)-.

20. The positive electrode sheet according to claim 16, wherein, The wetting agent includes one or more of small molecule organic solvents and low molecular weight polymers.

21. The positive electrode sheet according to claim 20, wherein, The small molecule organic solvent includes one or more of the following: alkanolamines, alcohols, and nitriles.

22. The positive electrode sheet according to claim 21, wherein, The alkanolamine compounds have 1 to 16 carbon atoms.

23. The positive electrode sheet according to claim 21, wherein, The alkanolamine compounds have 2 to 6 carbon atoms.

24. The positive electrode sheet according to claim 20, wherein, The low molecular weight polymer includes one or more of maleic anhydride-styrene copolymer, polyvinylpyrrolidone, and polysiloxane.

25. The positive electrode sheet according to claim 20, wherein, The weight-average molecular weight of the low molecular weight polymer is below 6000.

26. The positive electrode sheet according to claim 20, wherein, The weight-average molecular weight of the low molecular weight polymer is 3000~6000.

27. The positive electrode sheet according to claim 16, wherein, The dispersant comprises a second polymer, and the second polymer comprises: The fifth monomer unit represented by Equation 7; A sixth monomeric unit selected from at least one of the monomeric units represented by Formula 8 and the monomeric units represented by Formula 9; and A seventh monomer unit selected from at least one of the monomer units represented by Formula 10 and the monomer units represented by Formula 11. Formula 7 Formula 8 Formula 9 Formula 10 Formula 11.

28. The positive electrode sheet according to claim 27, wherein, Based on the total mass of the second polymer, The fifth monomer unit has a mass percentage content of M5, where M5 is 10% to 55%; and / or, The sixth monomer unit has a mass percentage content of M6, where M6 is 40% to 80%; and / or, The mass percentage of the seventh monomer unit is M7, where M7 is 0% to 10%.

29. The positive electrode sheet according to claim 27, wherein, Based on the total mass of the second polymer, The fifth monomer unit has a mass percentage content of M5, where M5 is 25% to 55%; and / or, The sixth monomer unit has a mass percentage content of M6, where M6 is 50% to 70%; and / or, The seventh monomer unit has a mass percentage content of M7, which is 0.001% to 2%.

30. The positive electrode sheet according to claim 28, wherein, M7 / (M6+M7) is 0% to 5%.

31. The positive electrode sheet according to claim 28, wherein, M7 / (M6+M7) is 0.001%~1%.

32. The positive electrode sheet according to claim 27, wherein, The second polymer is hydrogenated nitrile butadiene rubber; and / or, The weight-average molecular weight of the second polymer is 50,000 to 500,000.

33. The positive electrode sheet according to claim 27, wherein, The weight-average molecular weight of the second polymer is 150,000 to 350,000.

34. The positive electrode sheet according to claim 16, wherein, Based on the total mass of the positive electrode film layer The dispersant has a mass percentage content of Y1, where Y1 is 0.05% to 1%; and / or, The mass percentage of the wetting agent is Y2, and Y2 is 0.05% to 2%.

35. The positive electrode sheet according to claim 16, wherein, Based on the total mass of the positive electrode film layer The dispersant has a mass percentage content of Y1, where Y1 is 0.1% to 0.5%; and / or, The mass percentage of the wetting agent is Y2, and Y2 is 0.2% to 0.8%.

36. The positive electrode sheet according to claim 34, wherein, Y1 / Y2 is 0.05~20.

37. The positive electrode sheet according to claim 34, wherein, Y1 / Y2 is 0.1~1.

38. The positive electrode sheet according to claim 34, wherein, Y1 / Y2 is 0.3~0.

8.

39. The positive electrode sheet according to claim 27, wherein, In the positive electrode sheet, the mass ratio of the first polymer to the second polymer is 1.5 to 5.

40. The positive electrode sheet according to claim 27, wherein, In the positive electrode sheet, the mass ratio of the first polymer to the second polymer is 2 to 3.

41. The positive electrode sheet according to claim 1, wherein, The interplanar spacing of the phosphate in the first coating layer is 0.345-0.358 nm, and the included angle of the crystal orientation (111) is 24.25°-26.45°; the interplanar spacing of the pyrophosphate in the first coating layer is 0.293-0.326 nm, and the included angle of the crystal orientation (111) is 26.41°-32.57°.

42. The positive electrode sheet according to claim 1, wherein, In the kernel, the ratio of y to 1-y is 1:10 to 10:1; and / or, In the kernel, the ratio of z to 1-z is between 1:9 and 1:

999.

43. The positive electrode sheet according to claim 1, wherein, In the kernel, the ratio of y to 1-y is 1:4 to 1:1; and / or, In the kernel, the ratio of z to 1-z is between 1:499 and 1:

249.

44. The positive electrode sheet according to claim 1, wherein, The coating amount of the first coating layer is greater than 0% by weight and less than or equal to 7% by weight, based on the weight of the core.

45. The positive electrode sheet according to claim 1, wherein, The first coating layer has a coating weight of 4-5.6% by weight, based on the weight of the core.

46. ​​The positive electrode sheet according to claim 1, wherein, The weight ratio of pyrophosphate to phosphate in the first coating layer is 1:3 to 3:

1.

47. The positive electrode sheet according to claim 1, wherein, The weight ratio of pyrophosphate to phosphate in the first coating layer is 1:3 to 1:

1.

48. The positive electrode sheet according to claim 1, wherein, The crystallinity of the pyrophosphate and phosphate is independently between 10% and 100%.

49. The positive electrode sheet according to claim 1, wherein, The crystallinity of the pyrophosphate and phosphate is independently between 50% and 100%.

50. The positive electrode sheet according to claim 1, wherein, The second coating layer has a coating amount greater than 0% by weight and less than or equal to 6% by weight, based on the weight of the core.

51. The positive electrode sheet according to claim 1, wherein, The second coating layer has a coating amount of 3-5% by weight, based on the weight of the core.

52. The positive electrode sheet according to claim 1, wherein, The A is selected from at least two of Fe, Ti, V, Ni, Co and Mg.

53. The positive electrode sheet according to claim 1, wherein, The concentration of Li / Mn antisite defects in the positive electrode active material is below 4%.

54. The positive electrode sheet according to claim 1, wherein, The concentration of Li / Mn antisite defects in the positive electrode active material is below 2%.

55. The positive electrode sheet according to claim 1, wherein, The lattice variation rate of the positive electrode active material is less than 6%.

56. The positive electrode sheet according to claim 1, wherein, The lattice change rate of the positive electrode active material is less than 4%.

57. The positive electrode sheet according to claim 1, wherein, The surface oxygen valence state of the positive electrode active material is below -1.

88.

58. The positive electrode sheet according to claim 1, wherein, The surface oxygen valence state of the positive electrode active material is -1.98 to -1.

88.

59. The positive electrode sheet according to any one of claims 1-58, wherein, The compaction density of the positive electrode active material at 3 tons is 2.0 g / cm³. 3 above.

60. The positive electrode sheet according to any one of claims 1-58, wherein, The compaction density of the positive electrode active material at 3 tons is 2.2 g / cm³. 3 above.

61. A secondary battery comprising a positive electrode sheet according to any one of claims 1-60.

62. An electrical device comprising a secondary battery according to claim 61.

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