Composite positive electrode active material and preparation method thereof, positive electrode and battery

Abstract

The embodiment of the invention discloses a composite positive electrode active material and a preparation method thereof, a positive electrode and a battery, and belongs to the technical field of batteries, and the composite positive electrode active material comprises lithium manganese iron phosphate and a first solid electrolyte. Wherein the mass percent of the first solid electrolyte in the composite positive electrode active material is 5-9%; the particle size D50 of the lithium manganese iron phosphate is A, the particle size D10 of the first solid electrolyte is B, the particle size D50 of the first solid electrolyte is C, (B-A) / 3 is more than 0 and less than 1.5, and (C-A) / 7 is more than 1.2 and less than 3.5. According to the composite positive electrode active material provided by the embodiment of the invention, the defects of a lithium manganese iron phosphate system can be improved, the conductivity is improved, the rate capability is ensured, manganese precipitation in lithium manganese iron phosphate is reduced, the cycling stability is enhanced, and the electrochemical performance of a battery in a wide temperature range application scene is expanded.

Description

Technical Field

[0001] This application relates to the field of battery technology, specifically to a composite positive electrode active material and its preparation method, a positive electrode, and a battery. Background Technology

[0002] Currently, lithium-ion battery technology is rapidly developing towards higher energy density, higher safety, and lower cost. Lithium manganese iron phosphate (LMFP) exhibits significant advantages due to its olivine-type structure. The introduction of manganese increases the voltage platform to 4.1V, and its theoretical energy density is 15% higher than that of lithium iron phosphate (LFP). While inheriting the stable olivine-type structure of lithium iron phosphate (LFP), LMFP forms a solid solution by partially replacing iron sites with manganese, resulting in higher thermal stability. The thermal stability of lithium manganese iron phosphate (LMFP) is mainly reflected in the following aspects: First, the strong Fe-O covalent bond, similar to that of LFP, effectively suppresses oxygen release at high temperatures and maintains framework stability. Second, the introduction of Mn-O bonds does not destroy the original structure's anti-pyrolysis characteristics; LMFP still maintains a thermal runaway initiation temperature above 250℃, comparable to LFP, fundamentally ensuring the thermal safety of the battery system. This allows LMFP batteries to exhibit the same level of safety performance as LFP in extreme tests such as nail penetration and overcharge, significantly outperforming layered ternary materials. Furthermore, the raw material composition of LMFP is only 60% of that of ternary materials, containing no precious metals such as cobalt or nickel. However, the LMFP material system has the following inherent defects: extremely low electronic conductivity (only 10⁻⁹). S (on the order of / cm), severely limiting rate performance; Mn 3+ The Jahn-Teller effect can cause lattice distortion, leading to the precipitation of Mn ions. In addition, the two-phase reaction mechanism during charging and discharging can generate significant polarization voltage, which limits its performance in wide temperature range applications. Summary of the Invention

[0003] This application provides a composite positive electrode active material and its preparation method, a positive electrode, and a battery, aiming to solve the problems of low conductivity, easy precipitation of manganese ions, and limited performance in a wide temperature range of lithium manganese phosphate.

[0004] According to a first aspect of this application, a composite positive electrode active material is provided, comprising lithium manganese iron phosphate and a first solid electrolyte; The mass percentage of the first solid electrolyte in the composite positive electrode active material is 5%-9%; the particle size D50 of lithium manganese iron phosphate is A, the particle size D10 of the first solid electrolyte is B, and the particle size D50 of the first solid electrolyte is C, satisfying: 0 < (BA) / 3 < 1.5, and 1.2 < (CA) / 7 < 3.5.

[0005] The composite cathode and active material provided in this application includes lithium manganese iron phosphate and a first solid electrolyte, with the first solid electrolyte comprising 5%-9% by mass in the cathode active material. This improves the conductivity of the composite cathode active material, reduces interfacial impedance, and enhances the conductivity of the lithium manganese iron phosphate cathode system. By ensuring that the particle sizes D50A of lithium manganese iron phosphate, D10B of the first solid electrolyte, and D50C of the first solid electrolyte satisfy 0 < (BA) / 3 < 1.5 and 1.2 < (CA) / 7 < 3.5, a good stacking effect between lithium manganese iron phosphate and the first solid electrolyte is achieved. This results in a tightly packed structure where lithium manganese iron phosphate coats the surface of the first solid electrolyte, increasing the compaction density, ensuring the energy density of the cathode, and forming a good conductive network. This improves the low conductivity of lithium manganese iron phosphate and enhances the rate performance of the cathode. Simultaneously, the introduction of the first solid electrolyte stabilizes the crystal structure of lithium manganese iron phosphate, reduces manganese precipitation, and the high mechanical strength of the first solid electrolyte helps suppress lithium dendrite growth, enhances cycle stability, and extends battery life. By introducing a first solid electrolyte into the composite cathode active material, the liquid electrolyte in the battery can be at least partially replaced, reducing the risk of thermal runaway, improving the low-temperature capacity retention rate of the battery, and expanding the electrochemical performance of the battery in a wide temperature range application scenario. In other words, the composite cathode active material provided in this application embodiment can improve the defects of the lithium manganese iron phosphate system, increase conductivity, ensure rate performance, reduce manganese deposition in lithium manganese iron phosphate, enhance cycle stability, and expand the electrochemical performance of the battery in a wide temperature range application scenario.

[0006] Optionally, the particle size D10 of the first solid electrolyte is 2μm-5μm, the particle size D50 is 8μm-20μm, and the particle size D90 is 40μm-80μm; And / or, the particle size D50 of lithium manganese iron phosphate is 0.7μm-1.7μm, and the particle size D90 is 2μm-15μm.

[0007] By ensuring that the particle sizes D10, D50, and D90 of the first solid electrolyte are within the aforementioned ranges, a good stacking effect can be achieved. Small-sized first solid electrolyte particles can fill the gaps between large-sized first solid electrolyte particles, forming a continuous conductive network, shortening the lithium-ion migration path, and reducing the interface resistance. Medium-sized first solid electrolyte particles serve as a framework to support the structure of the positive electrode active layer and ensure the porosity of the positive electrode active layer. Large-sized first solid electrolyte particles form fast ion channels, accelerating the ion transport rate.

[0008] By ensuring that the particle sizes D50 and D90 of lithium manganese iron phosphate (LFP) fall within the aforementioned ranges, a good stacking effect can be achieved between LFP and the first solid electrolyte. This allows LFP particles to coat the surface of the first solid electrolyte, resulting in a relatively short diffusion path for lithium ions within the particles. This enables rapid insertion and extraction of lithium ions into the cathode material, improving the battery's charge and discharge rate and enhancing its rate performance. Smaller LFP particle sizes provide a larger specific surface area, offering more active sites for lithium ion insertion and extraction, thus contributing to increased battery capacity and energy density. Furthermore, the smaller particle size allows for a tighter packing structure on the first solid electrolyte surface, facilitating electron conduction between LFP particles and between LFP and the first solid electrolyte particles, improving the conductivity of the cathode and thereby enhancing the battery's charge and discharge efficiency.

[0009] Optionally, the first solid electrolyte includes at least one of an oxide solid electrolyte, a polymer solid electrolyte, and a sulfide solid electrolyte; And / or, the molar ratio of manganese to iron in lithium manganese iron phosphate is 1:1.

[0010] Oxide solid electrolytes (such as lithium lanthanum zirconium oxide and lithium aluminum titanium phosphate) possess high ionic conductivity and good thermal stability, as well as high mechanical strength, which helps ensure the stability and safety of battery operation in high-temperature environments. Furthermore, oxide solid electrolytes exhibit high tolerance to air and electrolyte components, reducing the occurrence of side reactions. Polymer solid electrolytes (such as polyethylene oxide) possess good flexibility and plasticity, improving interfacial contact with lithium manganese iron phosphate and reducing interfacial impedance. Polymer solid electrolytes also exhibit strong stability. Sulfide solid electrolytes (such as lithium phosphorus sulfide and lithium sulfide-phosphorus sulfide composites Li₂S-P₂S₅) have ionic conductivity approaching or even exceeding that of liquid electrolytes, compensating for the insufficient conductivity of lithium manganese iron phosphate, and also possess good mechanical properties.

[0011] By setting the molar ratio of manganese to iron in lithium manganese iron phosphate to 1:1, it helps to increase the compaction density, reduce the voltage plateau, and facilitate the formation of a stable solid solution structure. This effectively reduces structural distortion caused by the Jahn-Teller effect, thereby improving the cycle life of the battery.

[0012] According to a second aspect of this application, a method for preparing a composite positive electrode active material is also provided, comprising: Lithium manganese iron phosphate and the first solid electrolyte were ball-milled and mixed to obtain a composite positive electrode active material; The mass percentage of the first solid electrolyte in the composite positive electrode active material is 5%-9%; the particle size D50 of lithium manganese iron phosphate is A, the particle size D10 of the first solid electrolyte is B, and the particle size D50 of the first solid electrolyte is C, satisfying: 0 < (BA) / 3 < 1.5, and 1.2 < (CA) / 7 < 3.5.

[0013] The method for preparing the composite positive electrode active material provided in this application has all the beneficial effects of the composite positive electrode active material mentioned above. Furthermore, by using ball milling and mixing, lithium manganese iron phosphate and the first solid electrolyte in the composite positive electrode active material can form a core-shell structure, which has excellent stacking effect and ensures the performance of the composite positive electrode active material.

[0014] According to a third aspect of this application, a positive electrode is also provided, comprising the composite positive electrode active material as described above, and / or a composite positive electrode active material prepared by the method described above.

[0015] The positive electrode provided in this application has all the beneficial effects of the above-mentioned composite positive electrode active material, which will not be repeated here.

[0016] Optionally, the positive electrode includes a positive current collector and a positive active layer coated on at least one side of the positive current collector; the positive active layer includes a composite positive active material, a first conductive agent, and a first binder; The mass ratio of the composite positive electrode active material, the first conductive agent, and the first binder is (96%-98.5%):(0.5%-1.5%):(1%-2.5%). And / or, the areal density of the positive electrode on one side is 180 g / m². 2 -250g / m 2 ; And / or, the porosity of the positive electrode active layer is 29%-31%.

[0017] By maintaining the mass ratio of the composite positive electrode active material, the first conductive agent, and the first binder within the aforementioned range, the proportion of the composite positive electrode active material can be guaranteed, ensuring the energy density of the battery. Furthermore, the first solid electrolyte and the first conductive agent construct a good conductive network, compensating for the poor conductivity of lithium manganese iron phosphate and maintaining the structural stability of the positive electrode active layer. Maintaining the areal density of the positive electrode within the aforementioned range allows for a balance between the battery's energy density and power density. Maintaining the porosity of the positive electrode active layer within the aforementioned range provides sufficient lithium-ion transport channels, accelerating lithium-ion transport performance and ensuring the wettability of the electrolyte to the positive electrode active layer.

[0018] According to a fourth aspect of this application, a battery is also provided, including the positive electrode as described above, and further including a separator and a negative electrode; The separator is located on the side of the positive electrode closer to the positive electrode active layer; the negative electrode is located on the side of the separator away from the positive electrode.

[0019] The battery provided in this application has all the beneficial effects of the batteries described above, which will not be repeated here.

[0020] Optionally, the separator includes a base membrane and a solid electrolyte layer disposed on the side of the base membrane near the negative electrode, wherein the solid electrolyte layer includes a second solid electrolyte.

[0021] By setting a solid electrolyte layer on the membrane, the second solid electrolyte in the solid electrolyte layer can maintain high ionic conductivity at low temperatures, reducing the ion conduction obstruction caused by the increased viscosity of the liquid electrolyte at low temperatures. Setting a solid electrolyte layer on the side of the base membrane near the negative electrode helps to construct a gradient ion transport channel and reduce low-temperature impedance.

[0022] Optionally, the second solid electrolyte includes at least one of an oxide solid electrolyte, a polymer solid electrolyte, and a sulfide solid electrolyte; And / or, the thickness of the solid electrolyte layer is 1μm-2μm.

[0023] Oxide solid electrolytes (such as lithium lanthanum zirconium oxide and lithium aluminum titanium phosphate) possess high ionic conductivity and good thermal stability, as well as high mechanical strength, which helps ensure the stability and safety of battery operation in high-temperature environments. Furthermore, oxide solid electrolytes exhibit high tolerance to air and electrolyte components, reducing the occurrence of side reactions. Polymer solid electrolytes (such as polyethylene oxide) possess good flexibility and plasticity, improving interfacial contact with lithium manganese iron phosphate and reducing interfacial impedance. Polymer solid electrolytes also exhibit strong stability. Sulfide solid electrolytes (such as lithium phosphorus sulfide and lithium sulfide-phosphorus sulfide composites Li₂S-P₂S₅) have ionic conductivity approaching or even exceeding that of liquid electrolytes, compensating for the insufficient conductivity of lithium manganese iron phosphate, and also possess good mechanical properties.

[0024] By controlling the thickness of the solid electrolyte layer to 1μm-2μm, the lithium-ion migration path can be shortened, the battery internal resistance can be reduced, the proportion of inactive materials can be decreased, the energy density can be increased, and good mechanical and safety performance can be guaranteed at the same time.

[0025] Optionally, the battery's CB value is 1-1.14.

[0026] By keeping the battery's CB value (the ratio of negative electrode capacity to positive electrode capacity) within this range, it is possible to ensure that the negative electrode provides sufficient lithium vacancies to receive active lithium ions, thereby reducing lithium deposition.

[0027] Optionally, the battery is a semi-solid-state battery or a solid-state battery.

[0028] Compared to liquid lithium batteries, semi-solid-state batteries or solid-state batteries, which replace at least part of the liquid electrolyte with a solid electrolyte, have higher mechanical strength, reduce the risk of short circuits, and ensure capacity retention at low temperatures. The addition of a solid electrolyte can compensate for the low conductivity of lithium manganese iron phosphate, improve energy density, extend cycle life, and ensure battery performance over a wide temperature range.

[0029] Optionally, the battery is a semi-solid-state battery; the battery also includes an electrolyte, and the electrolyte filling coefficient in the battery is 2.5g / Ah-2.8g / Ah.

[0030] By adding a first solid electrolyte to the composite cathode material, it is possible to replace part of the liquid electrolyte in the battery, thereby enabling the battery to maintain good electrochemical performance even with a low liquid filling coefficient. Due to the low liquid filling coefficient, the risk of thermal runaway can be reduced, the low-temperature capacity retention rate of the battery can be improved, and the electrochemical performance of the battery can be expanded in a wide temperature range application scenario. Attached Figure Description

[0031] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0032] Figure 1 This is a graph showing the relationship between the areal density growth rate and capacity growth rate of the composite positive electrode active material provided in the embodiments of this application under different first solid electrolyte addition ratios; Figure 2 This is a graph showing the energy density growth rate of the composite positive electrode active material provided in the embodiments of this application under different proportions of the first solid electrolyte. Detailed Implementation

[0033] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0034] This application provides a battery and an electrical device. Detailed descriptions are provided below. It should be noted that the order of description of the following embodiments is not intended to limit the preferred order of the embodiments. Furthermore, in the description of this application, the term "comprising" means "including but not limited to". The terms first, second, third, etc., are used merely as illustrative and do not impose numerical requirements or establish an order. Various embodiments of the present invention may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a rigid limitation on the scope of the invention; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single digits within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Additionally, whenever a numerical range is indicated herein, it means including any referenced number (fraction or integer) within the indicated range.

[0035] In a first aspect, embodiments of this application provide a composite positive electrode active material, including lithium manganese iron phosphate and a first solid electrolyte; The mass percentage of the first solid electrolyte in the composite positive electrode active material is 5%-9%; the particle size D50 of lithium manganese iron phosphate is A, the particle size D10 of the first solid electrolyte is B, and the particle size D50 of the first solid electrolyte is C, satisfying: 0 < (BA) / 3 < 1.5, and 1.2 < (CA) / 7 < 3.5.

[0036] The composite cathode and active material provided in this application include lithium manganese iron phosphate and a first solid electrolyte, with the first solid electrolyte comprising 5%-9% by mass in the composite cathode active material. This improves the conductivity of the composite cathode active material, reduces interfacial impedance, and enhances the conductivity of the lithium manganese iron phosphate cathode system. By ensuring that the particle sizes D50A of lithium manganese iron phosphate, D10B of the first solid electrolyte, and D50C of the first solid electrolyte satisfy 0 < (BA) / 3 < 1.5 and 1.2 < (CA) / 7 < 3.5, a good stacking effect between lithium manganese iron phosphate and the first solid electrolyte is achieved. This results in a tightly packed structure where lithium manganese iron phosphate coats the surface of the first solid electrolyte, increasing the compaction density, ensuring the energy density of the cathode, and forming a good conductive network. This improves the low conductivity of lithium manganese iron phosphate and enhances the rate performance of the cathode. Simultaneously, the introduction of the first solid electrolyte stabilizes the crystal structure of lithium manganese iron phosphate, reduces manganese precipitation, and the high mechanical strength of the first solid electrolyte helps suppress lithium dendrite growth, enhances cycle stability, and extends battery life. By introducing a first solid electrolyte into the composite cathode active material, the liquid electrolyte in the battery can be at least partially replaced, reducing the risk of thermal runaway, improving the low-temperature capacity retention rate of the battery, and expanding the electrochemical performance of the battery in a wide temperature range application scenario. In other words, the composite cathode active material provided in this application embodiment can improve the defects of the lithium manganese iron phosphate system, increase conductivity, ensure rate performance, reduce manganese deposition in lithium manganese iron phosphate, enhance cycle stability, and expand the electrochemical performance of the battery in a wide temperature range application scenario.

[0037] In lithium iron phosphate (LFP) batteries, the development of high-compaction processes for high energy density requires LFP materials, leading to poor liquid absorption and retention, which limits the development of LFP batteries. Furthermore, LFP battery solutions struggle to meet market demands for high energy density and high safety performance in lithium batteries. Among various technologies, lithium manganese iron phosphate (LMFP) stands out as the most economical solution for meeting high energy density requirements due to its superior energy density and significant cost advantages. However, LMFP itself suffers from low electronic conductivity, manganese ion deposition, and unstable performance in wide-temperature applications.

[0038] The composite positive electrode active material provided in this application, by introducing a first solid electrolyte and making the first solid electrolyte and lithium manganese iron phosphate form a grade, controls the appropriate addition ratio of the first solid electrolyte, makes up for the defects of lithium manganese iron phosphate itself, improves conductivity, ensures rate performance, reduces manganese precipitation in lithium manganese iron phosphate, enhances cycle stability, and expands the electrochemical performance of the battery in a wide temperature range application scenario.

[0039] It is understood that this application ensures a good gradation effect between lithium manganese iron phosphate and the first solid electrolyte by meeting the requirements of 0 < (BA) / 3 < 1.5 and 1.2 < (CA) / 7 < 3.5. This allows lithium manganese iron phosphate to coat the surface of the first solid electrolyte, forming a core-shell structured composite positive electrode active material (particle size D50 of 150μm-210μm). The presence of the first solid electrolyte significantly improves the conductivity of lithium manganese iron phosphate and gives the positive electrode active layer suitable porosity. The particle size is tested using a Malvern laser particle size analyzer. The testing principle is laser diffraction and scattering; after laser irradiation of particles, some light is scattered. By measuring the light intensity at different angles through the relationship between the scattering angle θ and the particle size, the particle size distribution can be obtained.

[0040] In some embodiments, the particle size D10 of the first solid electrolyte is 2 μm-5 μm, the particle size D50 is 8 μm-20 μm, and the particle size D90 is 40 μm-80 μm.

[0041] By ensuring that the particle sizes D10, D50, and D90 of the first solid electrolyte are within the aforementioned ranges, a good stacking effect can be achieved. Small-sized first solid electrolyte particles can fill the gaps between large-sized first solid electrolyte particles, forming a continuous conductive network, shortening the lithium-ion migration path, and reducing the interface resistance. Medium-sized first solid electrolyte particles serve as a framework to support the structure of the positive electrode active layer and ensure the porosity of the positive electrode active layer. Large-sized first solid electrolyte particles form fast ion channels, accelerating the ion transport rate.

[0042] For example, the particle size D10 of the first solid electrolyte can be 2 μm, 3 μm, 4 μm or 5 μm, the particle size D50 can be 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm or 20 μm, and the particle size D90 can be 40 μm, 45 μm, 50 μm, 55 μm, 60 μm, 65 μm, 70 μm, 75 μm or 80 μm.

[0043] In some embodiments, the particle size D50 of lithium manganese iron phosphate is 0.7 μm-1.7 μm, and the particle size D90 is 2 μm-15 μm. By ensuring that the particle sizes D50 and D90 of lithium manganese iron phosphate are within the aforementioned ranges, a good stacking effect can be achieved between lithium manganese iron phosphate and the first solid electrolyte. This allows the lithium manganese iron phosphate particles to coat the surface of the first solid electrolyte, resulting in a relatively short diffusion path for lithium ions within the particles. This enables lithium ions to rapidly insert and extract into the cathode material, improving the battery's charge and discharge rate and enhancing its rate performance. Smaller particle sizes of lithium manganese iron phosphate provide a larger specific surface area, offering more active sites for lithium ion insertion and extraction, thus contributing to increased battery capacity and energy density. Furthermore, the smaller particle sizes allow for a tighter stacking structure on the surface of the first solid electrolyte, facilitating electron conduction between lithium manganese iron phosphate particles and between lithium manganese iron phosphate particles and the first solid electrolyte particles, improving the conductivity of the cathode and thereby increasing the battery's charge and discharge efficiency.

[0044] For example, the particle size D50 of lithium manganese iron phosphate can be 0.7μm, 0.8μm, 0.9μm, 1μm, 1.1μm, 1.2μm, 1.3μm, 1.4μm, 1.5μm, 1.6μm or 1.7μm, and the particle size D90 can be 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm or 15μm.

[0045] In some embodiments, the first solid electrolyte includes at least one of an oxide solid electrolyte, a polymer solid electrolyte, and a sulfide solid electrolyte.

[0046] Oxide solid electrolytes (such as lithium lanthanum zirconium oxide and lithium aluminum titanium phosphate) possess high ionic conductivity and good thermal stability, as well as high mechanical strength, which helps ensure the stability and safety of battery operation in high-temperature environments. Furthermore, oxide solid electrolytes exhibit high tolerance to air and electrolyte components, reducing the occurrence of side reactions. Polymer solid electrolytes (such as polyethylene oxide) possess good flexibility and plasticity, improving interfacial contact with lithium manganese iron phosphate and reducing interfacial impedance. Polymer solid electrolytes also exhibit strong stability. Sulfide solid electrolytes (such as lithium phosphorus sulfide and lithium sulfide-phosphorus sulfide composites Li₂S-P₂S₅) have ionic conductivity approaching or even exceeding that of liquid electrolytes, compensating for the insufficient conductivity of lithium manganese iron phosphate, and also possess good mechanical properties.

[0047] For example, the first solid electrolyte can be lithium lanthanum zirconium oxide (LLZO). LLZO has a cubic structure, a high Young's modulus, and can support a higher compaction density. LLZO also exhibits high stability to moisture and air, and excellent electrical conductivity, which can compensate for the shortcomings of lithium manganese iron phosphate, such as low conductivity, low compaction density, and sensitivity to moisture. In addition, LLZO has a lower cost, which helps to reduce battery costs.

[0048] In some embodiments, the molar ratio of manganese to iron in lithium manganese iron phosphate is 1:1.

[0049] By setting the molar ratio of manganese to iron in lithium manganese iron phosphate to 1:1, it helps to increase the compaction density, reduce the voltage plateau, and facilitate the formation of a stable solid solution structure. This effectively reduces structural distortion caused by the Jahn-Teller effect, thereby improving the cycle life of the battery.

[0050] Secondly, embodiments of this application also provide a method for preparing a composite positive electrode active material, comprising: Lithium manganese iron phosphate and the first solid electrolyte were ball-milled and mixed to obtain a composite positive electrode active material; The mass percentage of the first solid electrolyte in the composite positive electrode active material is 5%-9%; the particle size D50 of lithium manganese iron phosphate is A, the particle size D10 of the first solid electrolyte is B, and the particle size D50 of the first solid electrolyte is C, satisfying: 0 < (BA) / 3 < 1.5, and 1.2 < (CA) / 7 < 3.5.

[0051] The method for preparing the composite positive electrode active material provided in this application has all the beneficial effects of the composite positive electrode active material mentioned above. Furthermore, by using ball milling and mixing, lithium manganese iron phosphate and the first solid electrolyte in the composite positive electrode active material can form a core-shell structure, which has excellent stacking effect and ensures the performance of the composite positive electrode active material.

[0052] For example, mixing lithium manganese iron phosphate and the first solid electrolyte in a ball mill at 21 R / min for 1 hour can ensure the mixing effect and form a good stacking effect.

[0053] In some embodiments, prior to ball milling and mixing the lithium manganese iron phosphate and the first solid electrolyte, the method further includes: The lithium manganese iron phosphate and the first solid electrolyte were dried.

[0054] By drying the lithium manganese iron phosphate and the first solid electrolyte before ball milling, the risk of agglomeration during ball milling can be reduced.

[0055] For example, lithium manganese iron phosphate and the first solid electrolyte were dried at 105°C for 2 hours.

[0056] Thirdly, this application also provides a positive electrode, including the composite positive electrode active material as described above, and / or a composite positive electrode active material prepared by the method described above.

[0057] The positive electrode provided in this application has all the beneficial effects of the above-mentioned composite positive electrode active material, which will not be repeated here.

[0058] In some embodiments, the positive electrode includes a positive current collector and a positive active layer coated on at least one side of the positive current collector; the positive active layer includes a composite positive active material, a first conductive agent, and a first binder. The mass ratio of the composite positive active material, the first conductive agent, and the first binder is (96%-98.5%):(0.5%-1.5%):(1%-2.5%).

[0059] By ensuring that the mass ratio of the composite positive electrode active material, the first conductive agent, and the first binder is within the aforementioned range, the proportion of the composite positive electrode active material can be guaranteed, thus ensuring the energy density of the battery. Furthermore, by constructing a good conductive network through the first solid electrolyte and the first conductive agent, the poor conductivity of lithium manganese iron phosphate can be compensated for, and the structural stability of the positive electrode active layer can be maintained.

[0060] In some embodiments, the areal density of the positive electrode on one side is 180 g / m². 2 -250g / m 2 By keeping the surface density of the positive electrode within the above range, the energy density and power density of the battery can be balanced.

[0061] For example, the areal density of the positive electrode on one side can be 180 g / m². 2 190g / m 2 200g / m 2 210g / m 2 220g / m 2 230g / m 2 240g / m 2 Or 250g / m 2 .

[0062] In some embodiments, the porosity of the positive electrode active layer is 29%-31%.

[0063] By keeping the porosity of the positive electrode active layer within the above range, sufficient lithium-ion transport channels can be provided, accelerating lithium-ion transport performance and ensuring the wetting performance of the electrolyte on the positive electrode active layer.

[0064] For example, the porosity of the positive electrode active layer can be 29%, 30%, or 31%.

[0065] For example, the preparation method of the positive electrode can be as follows: The composite positive electrode active material, the first conductive agent and the first binder are dispersed in N-methylpyrrolidone solvent and stirred to obtain a positive electrode slurry. The positive electrode slurry is coated on the surface of the positive electrode current collector to obtain a positive electrode.

[0066] The first conductive agent can be conductive carbon black (SP), carbon nanotubes (CNT), or acetylene black; the first binder can be polyvinylidene fluoride (PVDF); and the positive electrode current collector can be an aluminum foil with a thickness of 9μm-12μm or a carbon-coated aluminum foil with a thickness of 9μm-12μm.

[0067] Fourthly, this application also provides a battery, including a positive electrode as described above, and further including a separator and a negative electrode. The separator is located on the side of the positive electrode close to the positive electrode active layer; the negative electrode is located on the side of the separator opposite to the positive electrode.

[0068] The battery provided in this application has all the beneficial effects of the batteries described above, which will not be repeated here.

[0069] In some embodiments, the separator includes a base membrane and a solid electrolyte layer disposed on the side of the base membrane near the negative electrode, wherein the solid electrolyte layer includes a second solid electrolyte.

[0070] By setting a solid electrolyte layer on the membrane, the second solid electrolyte in the solid electrolyte layer can maintain high ionic conductivity at low temperatures, reducing the ion conduction obstruction caused by the increased viscosity of the liquid electrolyte at low temperatures. Setting a solid electrolyte layer on the side of the base membrane near the negative electrode helps to construct a gradient ion transport channel and reduce low-temperature impedance.

[0071] In some embodiments, the second solid electrolyte includes at least one of an oxide solid electrolyte, a polymer solid electrolyte, and a sulfide solid electrolyte.

[0072] Oxide solid electrolytes (such as lithium lanthanum zirconium oxide and lithium aluminum titanium phosphate) possess high ionic conductivity and good thermal stability, as well as high mechanical strength, which helps ensure the stability and safety of battery operation in high-temperature environments. Furthermore, oxide solid electrolytes exhibit high tolerance to air and electrolyte components, reducing the occurrence of side reactions. Polymer solid electrolytes (such as polyethylene oxide) possess good flexibility and plasticity, improving interfacial contact with lithium manganese iron phosphate and reducing interfacial impedance. Polymer solid electrolytes also exhibit strong stability. Sulfide solid electrolytes (such as lithium phosphorus sulfide and lithium sulfide-phosphorus sulfide composites Li₂S-P₂S₅) have ionic conductivity approaching or even exceeding that of liquid electrolytes, compensating for the insufficient conductivity of lithium manganese iron phosphate, and also possess good mechanical properties.

[0073] In some embodiments, the thickness of the solid electrolyte layer is 1 μm-2 μm.

[0074] By controlling the thickness of the solid electrolyte layer in the separator to 1μm-2μm, the lithium-ion migration path can be shortened, the battery internal resistance can be reduced, the proportion of inactive materials can be reduced, the energy density can be increased, and good mechanical and safety performance can be guaranteed at the same time.

[0075] For example, the thickness of the solid electrolyte layer can be 1 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm or 2 μm.

[0076] For example, the method for preparing the thickness of the solid electrolyte layer can be as follows: Solid electrolyte, polyvinylidene fluoride (PVDF), and N-methylpyrrolidone (NMP) are added to a mixer in a ratio of (30-45%):(10-15%):(40-60%). The mixing speed is 1500 r / min - 2500 r / min, and the slurry viscosity is controlled at 500 mPa*s - 3000 mPa*s. The slurry is then coated onto the prepared diaphragm base membrane.

[0077] In some embodiments, the negative electrode includes a negative electrode current collector and a negative electrode active layer coated on at least one side of the negative electrode current collector. The negative electrode active layer includes a composite negative electrode active material, a second conductive agent, and a second binder. The composite negative electrode active material includes graphite and a third solid electrolyte, wherein the third solid electrolyte accounts for 1.0% of the composite negative electrode active material by mass.

[0078] For example, the preparation method of the composite negative electrode active material can be as follows: Graphite and a third solid electrolyte were ball-milled and mixed to obtain a composite negative electrode active material.

[0079] The negative electrode can be prepared as follows: The composite negative electrode active material, the second conductive agent, and the second binder are dispersed in a solvent and stirred to obtain a negative electrode slurry. The negative electrode slurry is coated on one side of the negative electrode current collector and then dried and cold-pressed to obtain the negative electrode.

[0080] The second conductive agent can be conductive carbon black (SP) or AB05, the second binder can be styrene-butadiene rubber (SBR), and the negative electrode current collector can be a copper foil of 4.5μm-6μm.

[0081] In some embodiments, the CB value of the battery is 1-1.14.

[0082] By keeping the battery's CB value (the ratio of negative electrode capacity to positive electrode capacity) within this range, it is possible to ensure that the negative electrode provides sufficient lithium vacancies to receive active lithium ions, thereby reducing lithium deposition.

[0083] For example, the CB value of the battery can be 1, 1.02, 1.04, 1.05, 1.06, 1.08, 1.1, 1.12 or 1.14.

[0084] In some embodiments, the mass ratio of the composite negative electrode active material, the second conductive agent, and the second binder is (96%-97.5%):(0.5%-1.5%):(1%-2%).

[0085] By ensuring the mass ratio of the composite negative electrode active material, the second conductive agent, and the second binder is within the above range, it is possible to guarantee the battery energy density while forming a good conductive network and structural stability.

[0086] The third solid electrolyte includes at least one of oxide solid electrolytes, polymer solid electrolytes, and sulfide solid electrolytes.

[0087] Oxide solid electrolytes (such as lithium lanthanum zirconium oxide and lithium aluminum titanium phosphate) possess high ionic conductivity and good thermal stability, as well as high mechanical strength, which helps ensure the stability and safety of battery operation in high-temperature environments. Furthermore, oxide solid electrolytes exhibit high tolerance to air and electrolyte components, reducing the occurrence of side reactions. Polymer solid electrolytes (such as polyethylene oxide) possess good flexibility and plasticity, improving interfacial contact with lithium manganese iron phosphate and reducing interfacial impedance. Polymer solid electrolytes also exhibit strong stability. Sulfide solid electrolytes (such as lithium phosphorus sulfide and lithium sulfide-phosphorus sulfide composites Li₂S-P₂S₅) have ionic conductivity approaching or even exceeding that of liquid electrolytes, compensating for the insufficient conductivity of lithium manganese iron phosphate, and also possess good mechanical properties.

[0088] In some embodiments, the battery is a semi-solid-state battery or a solid-state battery.

[0089] Compared to liquid lithium batteries, semi-solid-state batteries or solid-state batteries, which replace at least part of the liquid electrolyte with a solid electrolyte, have higher mechanical strength, reduce the risk of short circuits, and ensure capacity retention at low temperatures. The addition of a solid electrolyte can compensate for the low conductivity of lithium manganese iron phosphate, improve energy density, extend cycle life, and ensure battery performance over a wide temperature range.

[0090] In some embodiments, the battery is a semi-solid-state battery. The battery also includes an electrolyte, the electrolyte filling ratio of which is 2.5 g / Ah to 2.8 g / Ah.

[0091] By adding a first solid electrolyte to the composite cathode material, it is possible to replace part of the liquid electrolyte in the battery, thereby enabling the battery to maintain good electrochemical performance even with a low liquid filling coefficient. Due to the low liquid filling coefficient, the risk of thermal runaway can be reduced, the low-temperature capacity retention rate of the battery can be improved, and the electrochemical performance of the battery can be expanded in a wide temperature range application scenario.

[0092] For example, the electrolyte injection ratio in the battery can be 2.5 g / Ah, 2.6 g / Ah, 2.7 g / Ah, or 2.8 g / Ah.

[0093] In some embodiments, the electrolyte includes a lithium salt, a solvent, a crosslinking agent, and an initiator. The lithium salt includes lithium hexafluorophosphate, and the solvent includes at least one selected from ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate.

[0094] For example, the volume ratio of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate can be (15~35):(0~30):(0~40); the ratio of crosslinking agent to initiator can be (2-10):(1-5). The crosslinking agent can be a Doveryl crosslinking agent, such as 2,2'-(2,2,3,3,4,4,5,5-octafluorohexane-1,6-diyl)bis(ethylene oxide) (OFHDBO) or 1,6-bis(acryloyloxy)-2,2,3,3,4,4,5,5-octafluorohexane (OFHDODA). The initiator can be azobisisobutyronitrile (AIBN) or benzoyl peroxide (BPO).

[0095] For example, the battery assembly method can be as follows: The positive electrode, negative electrode, and separator are cut, die-cut, and slit. Then, the slit positive electrode, negative electrode, and separator are stacked, assembled, and dried to obtain a stacked core. The stacked cores are placed into the casing, electrolyte is injected, and the battery is left at 45°C for 24-48 hours to obtain the battery. The battery is subjected to formation and capacity testing, charged at 0.05C for 2-4 hours, 0.1C for 2-4 hours, and 0.15C for 1-3 hours. After formation, the battery is subjected to a side compressive force of 300kgf-1000kgf at 60℃-80℃ and left to stand for 60 minutes. Capacity testing is then performed by charging at 0.2C to 4.2V, discharging at 0.33C to 2.5V, and charging at 0.33C to 3.5V.

[0096] The embodiments of this application are further illustrated below with reference to specific examples. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of this application. Experimental methods in the following embodiments that do not specify specific conditions are generally performed according to the conditions recommended by the manufacturer.

[0097] Composite positive electrode active materials were prepared according to the following mass percentages of the first solid electrolyte in the composite positive electrode active material: 0%, 0.2%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, and 15%, respectively. The preparation method of the composite positive electrode active material is as follows: lithium manganese iron phosphate and the first solid electrolyte are dried at 105℃ for 2h, and then the lithium manganese iron phosphate and lithium lanthanum zirconium oxide are ball-milled and mixed in a ball mill at 21R / min for 1h to obtain the composite positive electrode active material; wherein, the first solid electrolyte is lithium lanthanum zirconium oxide, the particle size D10 of lithium lanthanum zirconium oxide is 3μm, the particle size D50 is 14μm, the particle size D90 is 60μm, and the particle size D50 of lithium manganese iron phosphate is 1.2μm and the particle size D90 is 9μm.

[0098] The compaction density, areal density, specific capacity, and capacity of different composite cathode active materials were tested, and the areal density growth rate, capacity growth rate, and energy density growth rate relative to 0% of the first solid electrolyte addition were calculated. The results are shown in Table 1. Figure 1 and Figure 2 As shown: Table 1

[0099] From Table 1 and Figures 1-2 It can be seen that as the proportion of the first solid electrolyte in the composite cathode active material increases, a scissor-like difference emerges between the areal density growth rate and the capacity growth rate. When the mass percentage of the first solid electrolyte is 5%, the ratio of the areal density growth rate to the capacity decay rate is basically the same. When the mass percentage of the first solid electrolyte is greater than 5%, a higher areal density is required to replenish the capacity. And from... Figure 2 As can be seen from the energy density growth curve, when the mass percentage of the first solid electrolyte is greater than 9%, the energy density decreases.

[0100] Therefore, in this embodiment of the application, the mass percentage of the first solid electrolyte in the composite positive electrode active material is set to 5%-9%, which can take into account good overall electrochemical performance.

[0101] This application also includes the following embodiments and comparative examples: Example 1 (1) Lithium manganese iron phosphate and lithium lanthanum zirconium oxide were dried at 105℃ for 2h, and then the lithium manganese iron phosphate and lithium lanthanum zirconium oxide were ball-milled and mixed at 21R / min for 1h to obtain a composite positive electrode active material; wherein, the mass percentage of lithium lanthanum zirconium oxide in the composite positive electrode active material was 7%, the particle size D10 of lithium lanthanum zirconium oxide was 3μm, the particle size D50 was 14μm, the particle size D90 was 60μm, the particle size D50 of lithium manganese iron phosphate was 1.2μm, and the particle size D90 was 9μm; (2) The composite positive electrode active material, the first conductive agent and the first binder are added to N-methylpyrrolidone in a mass ratio of 97%:1%:2% to obtain a positive electrode slurry. The positive electrode slurry is coated on one side of the positive electrode current collector and then dried and cold-pressed to obtain the positive electrode. The first conductive agent is SP+CNT (the mass ratio of SP and CNT is 0.5%:0.5%), the first binder is PVDF, and the positive electrode current collector is a carbon-coated aluminum foil with a thickness of 12μm. (3) The negative electrode active material, the second conductive agent and the second binder are added to N-methylpyrrolidone in a mass ratio of 97%:1%:2% to obtain a negative electrode slurry. The negative electrode slurry is coated on one side of the negative electrode current collector, and the negative electrode is obtained after drying and cold pressing. The negative electrode active material is graphite, the second conductive agent is SP, the second binder is SBR, and the negative electrode current collector is a copper foil with a thickness of 4.5 μm. (4) After stacking the positive electrode, separator and negative electrode, put them into the casing and inject electrolyte to obtain the battery; wherein, the separator is a 7+2 separator (7μm thick base film + 2μm thick ceramic coating).

[0102] Example 2 The difference between this embodiment and Embodiment 1 is that the mass percentage of lithium lanthanum zirconium oxide in the composite positive electrode active material is 5%, while the other conditions remain the same as in Embodiment 1.

[0103] Example 3 The difference between this embodiment and Embodiment 1 is that the mass percentage of lithium lanthanum zirconium oxide in the composite positive electrode active material is 9%, while the other conditions remain the same as in Embodiment 1.

[0104] Example 4 The difference between this embodiment and Example 1 is that the particle size D10 of lithium lanthanum zirconium oxide is 5 μm, the particle size D50 is 20 μm, and the particle size D90 is 70 μm; the particle size D50 of lithium manganese iron phosphate is 1.2 μm, and the particle size D90 is 9 μm. All other conditions are the same as in Example 1.

[0105] Example 5 The difference between this embodiment and Example 1 is that the particle size D10 of lithium lanthanum zirconium oxide is 4.5 μm, the particle size D50 is 17 μm, and the particle size D90 is 75 μm; the particle size D50 of lithium manganese iron phosphate is 1.2 μm, and the particle size D90 is 9 μm. All other conditions are the same as in Example 1.

[0106] Example 6 The difference between this embodiment and Embodiment 1 is that the negative electrode active material is a composite negative electrode active material composed of graphite and lithium aluminum titanium phosphorus oxide, and the mass percentage of lithium aluminum titanium phosphorus oxide in the composite negative electrode active material is 1%. All other conditions are the same as in Embodiment 1.

[0107] Example 7 The difference between this embodiment and Embodiment 1 is that the diaphragm includes a base membrane and a solid electrolyte layer coated on one side of the diaphragm. The solid electrolyte layer includes LATP solid electrolyte, and the thickness of the solid electrolyte layer is 1.5 μm. All other conditions are the same as in Embodiment 1.

[0108] Example 8 The difference between this embodiment and Embodiment 1 is that: the negative electrode active material is a composite negative electrode active material composed of graphite and lithium aluminum titanium phosphorus oxide, and the mass percentage of lithium aluminum titanium phosphorus oxide in the composite negative electrode active material is 1.5%; the separator includes a base film and a solid electrolyte layer coated on one side of the separator, wherein the solid electrolyte layer includes LLZO solid electrolyte, and the thickness of the solid electrolyte layer is 1.5 μm, and the other conditions are consistent with those in Embodiment 1.

[0109] In this embodiment, the preparation method of the negative electrode active material is the same as that in Example 6, and the preparation method of the separator is the same as that in Example 7.

[0110] Comparative Example 1 The difference between this comparative example and Example 1 is that the mass percentage of lithium lanthanum zirconium oxide in the composite positive electrode active material is 0.5%, while all other conditions remain the same as in Example 1.

[0111] Comparative Example 2 The difference between this comparative example and Example 1 is that the mass percentage of lithium lanthanum zirconium oxide in the composite positive electrode active material is 3%, while the other conditions are the same as in Example 1.

[0112] Comparative Example 3 The difference between this comparative example and Example 1 is that the mass percentage of lithium lanthanum zirconium oxide in the composite positive electrode active material is 12%, while the other conditions are the same as in Example 1.

[0113] Comparative Example 4 The difference between this embodiment and Example 1 is that the particle size D10 of lithium lanthanum zirconium oxide is 8 μm, the particle size D50 is 30 μm, and the particle size D90 is 90 μm; the particle size D50 of lithium manganese iron phosphate is 1.2 μm, and the particle size D90 is 9 μm. All other conditions are the same as in Example 1.

[0114] The batteries from Examples 1-8 and Comparative Examples 1-4 were subjected to capacity testing. The batteries were charged at 0.05C for 2-4 hours, 0.1C for 2-4 hours, and 0.15C for 1-3 hours. After capacity testing, the batteries were subjected to a side pressure of 300 kgf-1000 kgf at 60°C-80°C and left to stand for 60 minutes. The batteries were then charged at 0.2C to 4.2V, discharged at 0.33C to 2.5V, and charged at 0.33C to 3.5V.

[0115] The electrochemical performance of the batteries in Examples 1-8 and Comparative Examples 1-4 was then tested. Capacity retention at -20℃, -40℃, and after 200 cycles were tested. The method for testing the -20℃ capacity retention was as follows: the battery was placed in an environment of 25℃, charged at 0.33CCCV with a cut-off current of 0.05C for three cycles at standard capacity, then fully charged at 0.33CCCV, placed at -20℃ for 4 hours, and then discharged at 0.33C to 2.0V. The method for testing the -40℃ capacity retention was as follows: the battery was placed in an environment of 25℃, charged at 0.33CCCV with a cut-off current of 0.05C for three cycles at standard capacity, then fully charged at 0.33CCCV, placed at -40℃ for 4 hours, and then discharged at 0.33C to 2.0V. The test method for 200-cycle capacity retention is as follows: The battery is placed in an environment of 25℃ and charged at 0.33CCCV with a cutoff current of 0.05C for three cycles at standard capacity. The capacity of the third cycle is recorded as Q0. The cell is then fully charged at 0.5CCCV, allowed to rest for 10 minutes, discharged at a constant current of 1C to 2.5V, and allowed to rest for 10 minutes. This process is repeated every 50 cycles, with 0.33CCCV standard capacity tests performed and the results recorded as Q1, Q2, Q3...Q 200 Calculate Q 200 The ratio of Q0 to Q0. The test results are shown in Table 2: Table 2

[0116] As shown in Table 2, compared to Comparative Examples 1-4, the batteries obtained in Examples 1-8 of this application maintain good capacity retention at -20℃ and -40℃, and exhibit high capacity retention after 200 cycles. This is mainly because Examples 1-8 of this application form a composite positive electrode active material by compounding lithium manganese iron phosphate and a solid electrolyte, and by rationally setting the particle size of lithium manganese iron phosphate and the solid electrolyte, thereby improving the defects of the lithium manganese iron phosphate system, increasing conductivity, ensuring rate performance, and enhancing cycle stability.

[0117] The foregoing has provided a detailed description of a composite positive electrode active material and its preparation method, as well as the positive electrode and battery, provided in the embodiments of this application. Specific examples have been used to illustrate the principles and implementation methods of this application. The descriptions of the above embodiments are only for the purpose of helping to understand the methods and core ideas of this application. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this application. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A composite positive electrode active material, characterized in that, Including lithium manganese iron phosphate and the first solid electrolyte; Wherein, the mass percentage of the first solid electrolyte in the composite positive electrode active material is 5%-9%; the particle size D50 of the lithium manganese iron phosphate is A, the particle size D10 of the first solid electrolyte is B, and the particle size D50 of the first solid electrolyte is C, satisfying: 0 < (BA) / 3 < 1.5, and 1.2 < (CA) / 7 < 3.

5.

2. The composite positive electrode active material according to claim 1, characterized in that, The particle size D10 of the first solid electrolyte is 2μm-5μm, the particle size D50 is 8μm-20μm, and the particle size D90 is 40μm-80μm; And / or, the particle size D50 of the lithium manganese iron phosphate is 0.7μm-1.7μm, and the particle size D90 is 2μm-15μm.

3. The composite positive electrode active material according to claim 1 or 2, characterized in that, The first solid electrolyte includes at least one of oxide solid electrolyte, polymer solid electrolyte, and sulfide solid electrolyte; And / or, the molar ratio of manganese to iron in the lithium manganese iron phosphate is 1:

1.

4. A method for preparing a composite positive electrode active material, characterized in that, include: Lithium manganese iron phosphate and the first solid electrolyte were ball-milled and mixed to obtain a composite positive electrode active material; Wherein, the mass percentage of the first solid electrolyte in the composite positive electrode active material is 5%-9%; the particle size D50 of the lithium manganese iron phosphate is A, the particle size D10 of the first solid electrolyte is B, and the particle size D50 of the first solid electrolyte is C, satisfying: 0 < (BA) / 3 < 1.5, and 1.2 < (CA) / 7 < 3.

5.

5. A positive electrode, characterized in that, Includes the composite positive electrode active material as described in any one of claims 1-3, and / or the composite positive electrode active material prepared by the method described in claim 4.

6. The positive electrode according to claim 5, characterized in that, The positive electrode includes a positive electrode current collector and a positive electrode active layer coated on at least one side of the positive electrode current collector; the positive electrode active layer includes the composite positive electrode active material, a first conductive agent, and a first binder; The mass ratio of the composite positive electrode active material, the first conductive agent, and the first binder is (96%-98.5%):(0.5%-1.5%):(1%-2.5%). And / or, the areal density of the positive electrode on one side is 180 g / m³. 2 -250g / m 2 ; And / or, the porosity of the positive electrode active layer is 29%-31%.

7. A battery, characterized in that, It includes the positive electrode as described in claim 5 or 6, and also includes a separator and a negative electrode; The membrane is located on the side of the positive electrode closer to the positive electrode active layer; the negative electrode is located on the side of the membrane away from the positive electrode.

8. The battery according to claim 7, characterized in that, The diaphragm includes a base membrane and a solid electrolyte layer disposed on the base membrane near the negative electrode side, wherein the solid electrolyte layer includes a second solid electrolyte.

9. The battery according to claim 8, characterized in that, The second solid electrolyte includes at least one of oxide solid electrolyte, polymer solid electrolyte, and sulfide solid electrolyte; And / or, the thickness of the solid electrolyte layer is 1μm-2μm.

10. The battery according to any one of claims 7-9, characterized in that, The CB value of the battery is 1-1.

14.

11. The battery according to any one of claims 7-9, characterized in that, The battery is a semi-solid-state battery or a solid-state battery.

12. The battery according to claim 11, characterized in that, The battery is a semi-solid-state battery; the battery also includes an electrolyte, and the electrolyte injection coefficient in the battery is 2.5g / Ah-2.8g / Ah.

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