Positive electrode composite material and preparation method thereof, positive electrode active material and preparation method and application thereof

Abstract

The invention provides a positive electrode composite material and a preparation method thereof, and a positive electrode active material and a preparation method and application thereof. The specific coating layers are formed on the surfaces of the inner cores of the positive electrode composite material and the positive electrode active material, so that the high-temperature performance of the final battery can be effectively improved, the direct-current internal resistance of the battery is reduced, and the electrochemical performance of the whole battery is optimized. Moreover, the positive electrode composite material and the positive electrode active material provided by the embodiment of the invention are also easy to prepare, the process reliability is high, the production cost is relatively low, and the positive electrode composite material has a relatively good market prospect.

Description

Technical Field

[0001] The present application relates to the technical field of battery materials, and in particular to positive electrode composite materials and preparation methods thereof, positive electrode active materials and preparation methods and applications thereof. Background Art

[0002] With the continuous development of new energy technologies, the application scenarios of lithium-ion batteries are increasing, and the market's performance requirements for lithium-ion batteries are also getting higher and higher. Among the commonly used positive electrode materials for lithium-ion batteries, materials such as lithium iron manganese phosphate are gradually favored by the market due to their better electrochemical performance. However, under high temperature conditions, the capacity decay of the above materials is more obvious, which seriously affects the high temperature cycle performance and storage performance of the battery. The industry has tried to use coating, doping, and particle morphology control to improve the high temperature performance of the above materials, but the related technical solutions have problems such as high cost, difficulty in preparation, or poor results. Summary of the invention

[0003] In view of this, the embodiments of the present application provide a positive electrode composite material and a preparation method thereof, a positive electrode active material and a preparation method and application thereof. The positive electrode composite material and positive electrode active material provided in the embodiments of the present application are not only easy to prepare and have low cost, but also have good electrochemical performance, especially in terms of high temperature storage performance of the full battery, and have a good market prospect.

[0004] In a first aspect, an embodiment of the present application provides a positive electrode composite material, comprising a core having positive electrode activity and a first coating layer, a transition layer and a second coating layer sequentially coated on the surface of the core; the first coating layer comprises a carbon material, the second coating layer comprises a metal oxide, and the transition layer comprises a material of the first coating layer and a material of the second coating layer;

[0005] The metal in the metal oxide includes one or more of Ca, Mg and Ba.

[0006] The above-mentioned metal oxide has a certain alkalinity, and the second coating layer formed by it can play the role of an alkaline insulating layer, thereby improving the electrochemical performance of the material, including high-temperature cycle performance and high-temperature storage performance, and reducing the battery DC internal resistance of the final battery. More importantly, the transition layer contains the materials of the first coating layer and the second coating layer at the same time, which can be used as a bridge to effectively improve the bonding force between the first coating layer and the second coating layer, and can effectively weaken the interface mutation between the first coating layer and the second coating layer, thereby effectively improving the structural stability of the positive electrode composite material during battery cycling and storage, and is more conducive to the transmission of active ions, and thus is beneficial to the high-temperature long-cycle performance and long-term high-temperature storage performance of the final battery.

[0007] Furthermore, when the material of the inner core includes at least one of lithium manganese iron phosphate, nickel cobalt manganese ternary, and lithium manganate, the above-mentioned first coating layer, transition layer, and second coating layer can also effectively inhibit the dissolution of the Mn element, weaken the Jahn-Teller distortion effect of the above-mentioned materials in the inner core, thereby reducing the DC internal resistance of the battery during the cycle, and is beneficial to improving the high-temperature cycle performance and high-temperature storage performance of the material.

[0008] A second aspect of the embodiment of the present application provides a method for preparing a positive electrode composite material, comprising:

[0009] Mixing a core precursor, an inorganic base and an organic base salt to obtain a mixture; the inorganic base includes one or more of calcium hydroxide, barium hydroxide and magnesium hydroxide; the organic base salt includes one or more of an organic calcium salt, an organic magnesium salt and an organic barium salt with a pH value of 7 to 10; the material of the core precursor includes a core precursor and carbon;

[0010] The mixture is sintered to transform the core precursor into a core coated with a first coating layer, and a transition layer and a second coating layer stacked in sequence are formed on the surface of the first coating layer to obtain a positive electrode composite material; the first coating layer includes a carbon material, the second coating layer includes a metal oxide, and the transition layer includes the material of the first coating layer and the material of the second coating layer; the core has positive electrode activity.

[0011] The inorganic base of the specific type and the organic alkali salt of the specific pH value are easy to mix evenly, and are easy to form a uniform composite alkali layer wrapped on the surface of the core precursor. When the mixture is sintered, under the action of high temperature, in the chemical system of the present application, the inorganic base in the composite alkali layer reacts chemically with the organic alkali salt to generate metal oxides, and at the same time, the organic ions in the organic alkali salt are carbonized to form carbon materials. This part of the carbon material interacts with the carbon material in the core precursor, and a part of the metal oxide is entrained to form a transition layer containing both carbon materials and metal oxides, while most of the metal oxides generated by the inorganic base and the organic alkali salt at high temperature are coated on the surface of the transition layer away from the core. The above preparation method has strong process reliability, low preparation cost, and is suitable for large-scale industrial production.

[0012] A third aspect of an embodiment of the present application provides a positive electrode active material, comprising a core with positive electrode activity and a carbon layer and a composite alkali layer sequentially coated on the surface of the core, the composite alkali layer comprising an inorganic base and an organic alkali salt; wherein the inorganic base comprises one or more of calcium hydroxide, barium hydroxide and magnesium hydroxide, and the organic alkali salt comprises one or more of organic calcium salts, organic magnesium salts and organic barium salts with a pH value of 7 to 10.

[0013] Under the combination of specific inorganic bases and organic alkali salts, the above-mentioned composite alkali layer has a suitable alkalinity, which can be used as an alkaline isolation layer to reduce the damage of substances in the battery system to the core, thereby improving the electrochemical performance of the battery. In addition, the above-mentioned inorganic base is easy to be evenly mixed with the above-mentioned organic alkali salt, so that the uniformity of the composite alkali layer is high, the risk of the above-mentioned composite alkali layer absorbing water is small, the risk of side reactions with the core material is small, and the risk of side reactions with the electrolyte and other substances in the battery is small, which can fully reduce the risk of the composite alkali layer absorbing water or reacting with other substances to cause the battery performance to deteriorate. Further, when the core material includes at least one material of lithium manganese iron phosphate, nickel cobalt manganese ternary, and lithium manganate, the above-mentioned composite alkali layer can also effectively inhibit the dissolution of the Mn element, weaken the Jahn-Teller distortion effect of the above-mentioned materials in the core, thereby reducing the DC internal resistance of the battery during the cycle, and is conducive to improving the high-temperature cycle performance and high-temperature storage performance of the positive electrode active material.

[0014] A fourth aspect of the present application provides a method for preparing a positive electrode active material, comprising:

[0015] Mixing core material particles, an inorganic base and an organic base salt to coat the surface of the core material particles with a composite base layer to obtain a positive electrode active material;

[0016] The core material particles include a material with positive electrode activity; the inorganic base includes one or more of calcium hydroxide, barium hydroxide and magnesium hydroxide; and the organic base salt includes one or more of an organic calcium salt, an organic magnesium salt and an organic barium salt with a pH value of 7 to 10.

[0017] The preparation method has strong process reliability, low preparation cost and is suitable for large-scale industrial production.

[0018] The fifth aspect of the embodiments of the present application provides a positive electrode plate, comprising the positive electrode composite material provided in the first aspect of the embodiments of the present application, and / or the positive electrode active material provided in the third aspect of the embodiments of the present application.

[0019] A sixth aspect of the embodiments of the present application provides a secondary battery, comprising the positive electrode plate provided in the fifth aspect of the embodiments of the present application. DETAILED DESCRIPTION

[0020] Lithium-ion batteries are one of the most widely used energy storage systems. For example, they are widely used in consumer electronics, electric vehicles, and grid-scale energy storage systems. Among the commonly used positive electrode materials for lithium-ion batteries, lithium iron manganese phosphate (LFMP) materials have gradually gained market favor due to their superior electrochemical performance, but the above materials still have some application shortcomings. For example, the capacity decay is more obvious under high temperature conditions, which seriously affects the high-temperature cycle performance and high-temperature storage performance of the battery. Taking LFMP materials as an example, the root causes of the above phenomena generally include: 1) Structural distortion caused by the Jahn-Teller effect. The distortion will cause drastic changes in the volume of the material. Repeated stress changes will cause the material particles to loosen, thereby increasing the charge transfer resistance of the positive electrode and slowing down the transmission rate of electrons in the positive electrode membrane; 2) The dissolution of the Mn element causes lattice defects, which affects Li + migration, and also caused the loss of electroactive substances; and in the liquid batteries currently used in commercial applications, the small amount of water H 2 O will react with fluorine-containing electrolyte lithium salt to produce HF, which will accelerate the dissolution of Mn element.

[0021] In related technologies, coating, doping and particle morphology control are often used to improve the high-temperature performance of the above materials. However, the solutions of related technologies have problems such as high cost, difficulty in preparation, or poor effect.

[0022] In order to solve the above technical problems, the embodiment of the present application provides a positive electrode composite material, comprising a core with positive electrode activity and a first coating layer, a transition layer and a second coating layer sequentially coated on the surface of the core; the first coating layer comprises a carbon material, the second coating layer comprises a metal oxide, and the transition layer comprises a material of the first coating layer and a material of the second coating layer;

[0023] The metal in the metal oxide includes one or more of Ca, Mg and Ba. It is understandable that in some embodiments of the present application, the metal oxide includes one or more of calcium oxide, magnesium oxide and barium oxide; in some possible embodiments, the metal oxide may include, for example, a composite metal oxide, such as calcium magnesium hydroxide.

[0024] The above-mentioned metal oxide has a certain alkalinity, and the second coating layer formed by it can play the role of an alkaline insulating layer, which can effectively inhibit the side reactions between the core material and other substances in the battery system (for example, HF), thereby improving the electrochemical performance of the material. Specifically, when the core material includes at least one of lithium manganese iron phosphate, nickel cobalt manganese ternary, and lithium manganate, the dissolution of the Mn element of the core material can be effectively inhibited, and the Jahn-Teller distortion effect of the above-mentioned material can be effectively weakened, thereby reducing the DC internal resistance of the battery during the cycle, and improving the high-temperature cycle performance and high-temperature storage performance of the material. The first coating layer and the transition layer can also play a certain physical isolation role, assisting in inhibiting the dissolution of the Mn element and the Jahn-Teller distortion effect. More importantly, the transition layer contains the materials of both the first coating layer and the second coating layer, which can act as a bridge to effectively enhance the bonding force between the first coating layer and the second coating layer, and can effectively weaken the interface mutation between the first coating layer and the second coating layer, thereby effectively improving the structural stability of the positive electrode composite material during battery cycling and storage, and is more conducive to the transmission of active ions, thereby facilitating the high-temperature and long-cycle performance of the final battery and long-term high-temperature storage performance.

[0025] In addition, the first coating layer includes a carbon material, which is beneficial to improving the electronic conductivity of the positive electrode composite material and the rate performance of the final battery. In the embodiment of the present application, scanning electron microscope-energy dispersive spectroscopy (SEM-EDS) can be used to characterize the presence of the first coating layer, the second coating layer and the transition layer.

[0026] In the embodiments of the present application, the material with positive electrode activity refers to a material that can release and embed active ions during the battery charging and discharging process; in the present application, the active ions include alkali metal ions, specifically including but not limited to lithium ions.

[0027] In some embodiments of the present application, the material of the core has the ability to deintercalate lithium ions; the material of the core includes at least one of lithium iron manganese phosphate (LFMP) materials, nickel cobalt manganese ternary materials (NMP), and lithium manganate materials. The above-mentioned lithium iron manganese phosphate materials include doped or undoped lithium iron manganese phosphate, wherein the doped lithium iron manganese phosphate can be, for example, doped with at least one element in the positions of Li, Mn, Fe, P, and O; the doped elements can be any element known in the art that can be doped in the above corresponding positions, and the doping elements in the Mn position can be, for example, other transition metal elements other than Mn and Fe, and the doping elements in the phosphorus position can be, for example, B elements, etc. In some embodiments of the present application, the Jahn-Teller distortion effect of the LFMP material can be further weakened by regulating the Mn element content in the LFMP material. Similarly, the NMP material includes doped or undoped NMP, and the doped elements can be any element known in the art that can be doped in the above-mentioned materials. The lithium manganese oxide material includes doped or undoped lithium manganese oxide, which can be any well-known doped lithium manganese oxide in the art. The doping elements can be, for example, Al, Cr, Fe, etc., so as to further weaken the Jahn-Teller distortion effect of the lithium manganese oxide. This application does not impose any limitation on this.

[0028] In some embodiments of the present application, the particle size of the kernel is 50nm to 500nm. Controlling the particle size of the kernel within the above range is conducive to controlling the deintercalation path of the active ions within a shorter range, thereby facilitating the rapid deintercalation of the active ions in the positive electrode composite material and the performance of the battery's rate performance. In addition, it is also beneficial to ensure that the electrochemical capacity of the positive electrode composite material particles is at a higher level; when the material of the kernel includes NMP materials, LFMP materials, and lithium manganate materials, it is also beneficial to inhibit the dissolution of the Mn element. Specifically, the particle size of the kernel can be, for example, 50nm, 80nm, 100nm, 120nm, 150nm, 180nm, 200nm, 220nm, 250nmm, 280nm, 300nm, 320nm, 350nm, 380nm, 400nm, 420nm, 450nm, 480nm, 500nm, etc.

[0029] In some embodiments of the present application, the thickness of the first coating layer is 1nm to 5nm. In the positive electrode composite material with a special structure provided in the embodiment of the present application, the thickness of the first coating layer is controlled within the above range. First, it is conducive to ensuring the uniformity of the first coating layer, which can effectively improve the electronic conductivity of the positive electrode composite material, and is also conducive to the deintercalation / embedding of active ions. It can also provide a certain physical isolation effect of the electrolyte, which is conducive to inhibiting the dissolution of manganese elements, thereby more conducive to improving the comprehensive electrochemical performance of the positive electrode composite material. Specifically, the thickness of the first coating layer can be, for example, 1nm, 1.2nm, 1.8nm, 2nm, 2.2nm, 2.5nm, 2.8nm, 3nm, 3.2nm, 3.5nm, 3.8nm, 4nm, 4.2nm, 4.5nm, 4.8nm, 5nm, etc.

[0030] In some embodiments of the present application, the thickness of the second coating layer is 0.5nm to 2nm. The second coating layer of suitable thickness can effectively resist the infringement of impurities such as HF in the battery system on the core material, which is beneficial to suppress the dissolution of manganese elements, and can also reduce the risk of reduced battery capacity due to poor conductivity of metal oxides. In addition, controlling the thickness of the second coating layer within the above range is also beneficial to improve the surface uniformity of the coating layer of the positive electrode composite material. Specifically, the thickness of the second coating layer can be, for example, 0.5nm, 0.6nm, 0.7nm, 0.8nm, 0.9nm, 1nm, 1.1nm, 1.2nm, 1.3nm, 1.4nm, 1.5nm, 1.6nm, 1.7nm, 1.8nm, 1.9nm, 2nm, etc.

[0031] In some embodiments of the present application, the thickness of the transition layer is ≤0.5nm. Specifically, the thickness of the transition layer can be, for example, 0.01nm, 0.02nm, 0.05nm, 0.1nm, 0.2nm, 0.3nm, 0.4nm, 0.5nm, etc. Controlling the thickness of the transition layer within the above range is beneficial to improving the bonding force between the first coating layer and the second coating layer (for example, it is beneficial for the material of the transition layer to form a chemical bond with the materials of the first coating layer and the second coating layer), improving the structural stability of the positive electrode composite material, and is also more conducive to optimizing the interface between the first coating layer and the second coating layer.

[0032] In some embodiments of the present application, the transition layer includes a carbon material and a metal oxide dispersed in the carbon material. In some specific embodiments, the metal oxide is evenly dispersed in the carbon material. In this way, the uniformity of the transition layer is high, which is conducive to optimizing the comprehensive performance of the positive electrode composite material.

[0033] In some specific embodiments, the thickness of the first coating layer is 1nm to 5nm, the thickness of the second coating layer is 0.5nm to 2nm, and the thickness of the transition layer is ≤0.5nm. In the cathode composite material with a special structure provided in the embodiments of the present application, the thickness of each of the three layers is controlled within the above range, which is more conducive to the synergistic effect between the three layers, and thus more conducive to the high temperature cycle performance and high temperature storage performance of the cathode composite material.

[0034] In the embodiment of the present application, a high-resolution transmission electron microscope (TEM) may be used to characterize the thicknesses of the first coating layer, the transition layer, and the second coating layer.

[0035] Accordingly, the present embodiment provides a method for preparing a positive electrode composite material, which can be used to prepare the positive electrode composite material provided in the present embodiment, comprising:

[0036] S1, mixing a core precursor, an inorganic base and an organic base salt to obtain a mixture; the inorganic base includes one or more of calcium hydroxide, barium hydroxide and magnesium hydroxide, and the organic base salt includes one or more of an organic calcium salt, an organic magnesium salt and an organic barium salt with a pH value of 7 to 10; the core precursor includes a core precursor material and carbon;

[0037] S2. Sintering the mixture to transform the core precursor into a core coated with a first coating layer, and forming a transition layer and a second coating layer stacked in sequence on the surface of the first coating layer to obtain a positive electrode composite material; the first coating layer includes a carbon material, the second coating layer includes a metal oxide, and the transition layer includes the material of the first coating layer and the material of the second coating layer; the core has positive electrode activity.

[0038] In step S1, the inorganic base of the specific type and the organic alkali salt of the specific pH value are easy to mix evenly, and are easy to form a uniform composite alkali layer wrapped on the surface of the core precursor. In step S2, when the mixture is sintered, under the action of high temperature, in the chemical system of the present application, the inorganic base in the composite alkali layer reacts chemically with the organic alkali salt to generate metal oxides, and the organic ions in the organic alkali salt are carbonized to form carbon materials. This part of the carbon material interacts with the carbon material in the core precursor, and a part of the metal oxide is entrained to form a transition layer containing both carbon materials and metal oxides, while most of the metal oxides generated by the inorganic base and the organic alkali salt at high temperature are coated on the surface of the transition layer away from the core. In addition, when the core precursor is sintered, the core precursor material is further crystallized, and the morphology is further regularized to form a core with positive electrode activity, and a positive electrode composite material is obtained in which the core surface is sequentially coated with a first coating layer, a transition layer and a second coating layer. In addition, the above-mentioned preparation method has strong process reliability, low preparation cost, and is suitable for large-scale industrial production.

[0039] In some embodiments of the present application, the core precursor, inorganic base and organic base salt can be mixed in a mixer. The crystallinity of the core precursor material is not as high as that of the core material obtained after sintering, and the morphology regularity is relatively low, but the chemical composition is basically the same.

[0040] In some embodiments of the present application, the organic calcium salt includes calcium lactate, the organic magnesium salt includes magnesium lactate, and the organic barium salt includes barium lactate. The above-mentioned lactic acid organic metal alkali salt is easier to mix evenly with the inorganic base, and the two cooperate with each other, which is more conducive to the metal oxide and the carbon material under the action of high temperature, and further more conducive to obtaining the stacked transition layer and the second coating layer.

[0041] In some embodiments of the present application, the mass ratio of the organic alkali salt to the inorganic base is 1: (5-20). Controlling the mass ratio of the two within the above range is more conducive to obtaining the second coating layer and the transition layer of the target thickness. For example, the thickness of the second coating layer is 0.5nm-2nm, and the thickness of the transition layer is ≤0.5nm. In addition, it is also beneficial to obtain a transition layer in which metal oxides are uniformly dispersed in the carbon material, thereby being more conducive to improving the comprehensive electrochemical performance of the positive electrode composite material. Specifically, the mass ratio of the organic alkali salt to the inorganic base can be, for example, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, 1:11, 1:12, 1:13, 1:14, 1:15, 1:16, 1:17, 1:18, 1:19, 1:20, etc. In some specific embodiments, the ratio of the sum of the masses of calcium hydroxide, barium hydroxide and magnesium hydroxide to the mass of the lactic acid metal alkali salt is 1: (5-20).

[0042] In some embodiments of the present application, based on the mass of the core precursor, the mass proportion of the organic alkali salt is 0.05% to 0.1%, and the mass proportion of the inorganic base is 0.5% to 1%. In this way, it is more conducive to controlling the thickness of the transition layer and the second coating layer within the target range, so that the content of the metal oxide in the positive electrode composite material is controlled within a more suitable range, which is conducive to optimizing the electrochemical performance of the final positive electrode composite material. Specifically, based on the mass of the core precursor, the mass proportion of the organic alkali salt can be, for example, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.1%, and the mass proportion of the inorganic base can be, for example, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, etc.

[0043] In some embodiments of the present application, in step S2, the sintering temperature is 700℃~850℃, and the sintering insulation time is 8h~10h. In the chemical system of the preparation method of the present application, the sintering parameters of step S2 are controlled within the above range, which is more conducive to obtaining a uniform transition layer and a second coating layer, and it is easier to form a chemical bond between the materials of the transition layer and the second coating layer. In addition, the above sintering conditions are also more conducive to the crystallization and shaping of the core precursor material in the core precursor. Specifically, the sintering temperature of step S2 can be, for example, 700℃, 720℃, 750℃, 780℃, 800℃, 820℃, 850℃, etc., and the sintering insulation time can be, for example, 6h, 7h, 8h, 9h, 10h. In some specific embodiments of the present application, the heating rate of sintering in step S2 is 5℃ / min~10℃ / min. Specifically, the heating rate of sintering in step S2 can be, for example, 5°C / min, 6°C / min, 7°C / min, 8°C / min, 9°C / min, or 10°C / min.

[0044] In some embodiments of the present application, in step S1, the preparation of the core precursor includes:

[0045] S11, weighing corresponding element sources according to the molar ratio of each element of the material of the core to be prepared; dispersing the above-mentioned element sources and carbon source in a medium, mixing, and obtaining a first material after drying;

[0046] S12, subjecting the first material to high temperature treatment under a protective atmosphere to obtain a core precursor.

[0047] In the above step S11, the above-mentioned element sources can be commonly used element sources in the industry for preparing active metal ion positive electrode active materials (e.g., lithium ion positive electrode active materials), and the carbon source can be any carbon source known in the art for preparing active metal ion positive electrode active materials (e.g., lithium ion positive electrode active materials), including but not limited to one or more of glucose, sucrose, starch, and citric acid. It is understandable that, considering the possible loss of active metal sources, the alkali metal source can be appropriately excessive, for example, the lithium source can be excessive by 10wt%.

[0048] In some embodiments of the present application, a person skilled in the art can determine the relative amount of the carbon source and each element source according to the thickness of the first coating layer of the target. In some embodiments of the present application, based on the mass of the lithium source, the mass content of the carbon source can be, for example, 8% to 12%. Specifically, based on the mass of the lithium source, the mass content of the carbon source can be, for example, 8%, 9%, 10%, 11%, 12%, etc.

[0049] In some embodiments of the present application, the medium in step S11 may be, for example, ethanol, but is not limited thereto.

[0050] In some embodiments of the present application, the drying in step S11 can be, for example, spray drying, and the spray drying can adopt any known process parameters in the field, and the present application does not limit this. In some specific embodiments, after the above-mentioned spray drying, the particle morphology of the first material is also controlled, so as to facilitate the control of the core particle size in the positive electrode composite material within the range of 50nm to 500nm. In some embodiments of the present application, in step S12, after the high temperature treatment, the material obtained after the high temperature treatment is also crushed to obtain a core precursor.

[0051] In some embodiments of the present application, the protective atmosphere in step S12 includes nitrogen, argon, etc. The high temperature treatment can be performed in a tube furnace.

[0052] In some embodiments of the present application, in step S12, the temperature of the high temperature treatment is 400°C to 500°C, the holding time is 8h to 10h, and the heating rate is 5°C / min to 10°C / min. This is conducive to obtaining a core precursor with a target microstructure and chemical composition.

[0053] An embodiment of the present application also provides a positive electrode active material, including a core with positive electrode activity and a carbon layer and a composite alkali layer sequentially coated on the surface of the core from the inside to the outside, the composite alkali layer including an inorganic base and an organic alkali salt; wherein the inorganic base includes one or more of calcium hydroxide, barium hydroxide and magnesium hydroxide; the organic alkali salt includes one or more of organic calcium salts, organic magnesium salts and organic barium salts with a pH value of 7 to 10; the core has the ability to deintercalate lithium ions.

[0054] Under the combination of specific inorganic alkali and organic alkali salt, the above-mentioned composite alkali layer has a suitable alkalinity, which can be used as an alkaline insulating layer to reduce the damage of the substances in the battery system to the core, especially to inhibit the side reaction of HF with the core material, thereby improving the electrochemical performance of the material. Specifically, when the core material is at least one of LFMP, nickel-cobalt-manganese ternary, and lithium manganate, the dissolution of the Mn element of the core material can be effectively inhibited, and the Jahn-Teller distortion effect of LFMP materials and lithium manganate materials can be effectively weakened, thereby reducing the DC internal resistance of the battery during the cycle process, improving the high-temperature cycle performance and high-temperature storage performance of the material. In addition, the above-mentioned inorganic alkali is easy to be evenly mixed with the above-mentioned organic alkali salt, so that the uniformity of the composite alkali layer is high (including composition uniformity and thickness uniformity), the above-mentioned composite alkali layer has a small risk of absorbing water, a small risk of side reactions with the core material, and a small risk of side reactions with the electrolyte and other substances in the battery, which can fully reduce the risk of the composite alkali layer absorbing water or reacting with other substances to cause the battery performance to deteriorate.

[0055] Similarly, the carbon layer can also play a certain physical isolation role, helping to inhibit the dissolution of Mn elements and the Jahn-Teller distortion effect. The carbon layer can also improve the electronic conductivity of the positive electrode active material.

[0056] In some embodiments of the present application, the core has the ability to deintercalate lithium ions; the core material includes at least one of lithium iron manganese phosphate (LFMP) materials, nickel cobalt manganese ternary materials (NMP), and lithium manganate materials. For details, please refer to the description of the positive electrode composite material section above, which will not be repeated here.

[0057] In some embodiments of the present application, the organic calcium salt includes calcium lactate, the organic magnesium salt includes magnesium lactate, and the organic barium salt includes barium lactate. Compared with other types of organic calcium salts, organic magnesium salts, and organic barium salts, calcium lactate, magnesium lactate, and barium lactate have a higher degree of coordination with the hydroxides corresponding to the above elements, are easier to form a uniform composite alkali layer, and can control the alkalinity of the composite alkali layer within a suitable range, or in other words, can achieve similar or better high-temperature performance of the positive electrode active material when the thickness of the composite alkali layer is smaller.

[0058] In some embodiments of the present application, the mass ratio of the organic alkali salt to the inorganic alkali is 1: (5-20). Controlling the mass ratio of the two within the above range is more conducive to obtaining a composite alkali layer of suitable alkalinity and is more conducive to improving the high temperature performance of the positive electrode active material. Specifically, the mass ratio of the organic alkali salt to the inorganic alkali can be, for example, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, 1:11, 1:12, 1:13, 1:14, 1:15, 1:16, 1:17, 1:18, 1:19, 1:20, etc. In some specific embodiments, the sum of the masses of calcium hydroxide, barium hydroxide and magnesium hydroxide and the mass ratio of lactic acid metal alkali salts is 1: (5-20). In the embodiment of the present application, the mass content of the elements in the inorganic alkali and organic alkali salt in the composite alkali layer can be determined by inductively coupled plasma (ICP), and then the mass ratio of the inorganic alkali and the organic alkali salt can be calculated.

[0059] In some embodiments of the present application, the particle size of the core is 50nm to 500nm. Controlling the particle size of the core within the above range is conducive to controlling the deintercalation path of the active ions within a shorter range, thereby facilitating the rapid deintercalation of the active ions in the positive electrode active material and the performance of the battery's rate performance. In addition, it is also beneficial to ensure that the electrochemical capacity of the positive electrode active material particles is at a higher level; when the material of the core includes at least one of NMP materials, LFMP materials, and lithium manganate materials, it is also beneficial to assist in suppressing the dissolution of the Mn element. Specifically, the particle size of the core can be, for example, 50nm, 80nm, 100nm, 120nm, 150nm, 180nm, 200nm, 220nm, 250nm, 280nm, 300nm, 320nm, 350nm, 380nm, 400nm, 420nm, 450nm, 480nm, 500nm, etc.

[0060] In some embodiments of the present application, the thickness of the carbon layer is 1nm to 5nm. In this way, firstly, it is conducive to ensuring the uniformity of the carbon layer, which can effectively improve the electronic conductivity of the positive electrode active material, and is also conducive to the extraction / embedding of active ions, which is conducive to inhibiting the dissolution of manganese elements, and can also provide a certain physical isolation effect of the electrolyte, thereby being more conducive to improving the comprehensive electrochemical performance of the positive electrode active material. Specifically, the thickness of the carbon layer can be, for example, 1nm, 1.2nm, 1.8nm, 2nm, 2.2nm, 2.5nm, 2.8nm, 3nm, 3.2nm, 3.5nm, 3.8nm, 4nm, 4.2nm, 4.5nm, 4.8nm, 5nm, etc.

[0061] In some embodiments of the present application, the thickness of the composite alkali layer is 1nm to 5nm. A composite alkali layer of suitable thickness can effectively resist the damage of impurities such as HF in the battery system to the core material, and can also reduce the risk of reduced battery capacity due to the non-conductivity of the composite alkali. In addition, controlling the thickness of the composite alkali layer within the above range is conducive to inhibiting the dissolution of manganese elements and improving the surface uniformity of the coating layer of the positive electrode active material. Specifically, the thickness of the composite alkali layer can be, for example, 1nm, 1.2nm, 1.8nm, 2nm, 2.2nm, 2.5nm, 2.8nm, 3nm, 3.2nm, 3.5nm, 3.8nm, 4nm, 4.2nm, 4.5nm, 4.8nm, 5nm, etc.

[0062] In some embodiments of the present application, based on the mass of the core, the mass proportion of the organic alkali salt is 0.05% to 0.1%, and the mass proportion of the inorganic alkali is 0.5% to 1%. In this way, it is beneficial to obtain a positive electrode active material with better high-temperature cycle performance and high-temperature storage performance, and it is also beneficial to the performance of the rate performance of the positive electrode active material, and it is also beneficial to obtain a uniform, appropriately thick, and relatively dense composite alkali coating layer. Specifically, based on the mass of the core, the mass proportion of the organic alkali salt can be, for example, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.1%, and the mass proportion of the inorganic alkali can be, for example, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, etc.

[0063] The present application also provides a method for preparing a positive electrode active material, comprising:

[0064] S1', mixing core material particles, an inorganic base and an organic base salt to coat the surface of the core material particles with a composite base layer to obtain a positive electrode active material;

[0065] The core material particles include a material with positive electrode activity and a carbon layer coated on the surface thereof; the inorganic base includes one or more of calcium hydroxide, barium hydroxide and magnesium hydroxide; the organic base salt includes one or more of organic calcium salt, organic magnesium salt and organic barium salt with a pH value of 7 to 10.

[0066] The preparation method has strong process reliability, simple operation, low cost and is suitable for large-scale industrial production.

[0067] In some embodiments of the present application, in step S1', core material particles, inorganic base and organic base salt are added to a ball mill according to a preset mass ratio, and then a dispersion medium is added for ball milling. After ball milling, drying and crushing are performed in sequence to obtain a positive electrode active material.

[0068] In some embodiments of the present application, in step S1', the speed of ball milling is 400rmp~450rmp, and the ball milling time is 6h~8h. In this way, it is beneficial to coat the surface of the core material particles with the composite alkali and improve the uniformity of the composite alkali layer. Specifically, 100g of core material particles and 100g of ball milling beads can be added to a 500g ball milling jar, and then a preset mass ratio of composite alkali is added for ball milling. Specifically, in step S1', the speed of ball milling can be, for example, 400rmp, 410rmp, 420rmp, 430rmp, 440rmp, 450rmp, and the ball milling time can be, for example, 6h, 7h, 8h.

[0069] In some embodiments of the present application, in step S1', the dispersion medium may be, for example, ethanol.

[0070] In some embodiments of the present application, in step S1', the organic calcium salt includes calcium lactate, the organic magnesium salt includes magnesium lactate, and the organic barium salt includes barium lactate.

[0071] In some embodiments of the present application, in step S1', the core material has lithium ion deintercalation capability, including at least one of lithium iron manganese phosphate (LFMP) materials, nickel cobalt manganese ternary materials (NMP), and lithium manganate materials.

[0072] In some embodiments of the present application, in step S1', the thickness of the carbon layer is 1nm-5nm, and the particle size of the core material particles excluding the carbon layer is 50nm-500nm. In the embodiment of the present application, a laser particle size analyzer can be used to test the particle size of the core material particles, and a high-power transmission TEM can be used to test the thickness of the carbon layer.

[0073] In some embodiments of the present application, in step S1', the preparation of the core material particles includes:

[0074] (1) Weighing corresponding element sources according to the molar ratio of each element of the core material to be prepared; dispersing the above-mentioned element sources and a carbon source in a medium, mixing, and drying to obtain a second material;

[0075] (2) sintering the second material for the first time under a protective atmosphere to obtain a first precursor;

[0076] (3) mixing the first precursor with a certain amount of carbon source in a medium, mixing them evenly, and then drying and shaping to obtain a second precursor;

[0077] (4) The second precursor is sintered for a second time under a protective atmosphere, and core material particles are obtained after crushing.

[0078] The above-mentioned element sources can be the element sources commonly used in the industry for preparing lithium-ion positive electrode active materials, and the carbon source can be any carbon source known in the art for preparing positive electrode active materials, including but not limited to one or more of glucose, sucrose, starch, and citric acid. It is understandable that, considering the possible loss of active ion sources, for example, the loss of lithium sources, the lithium source can be appropriately excessive, for example, an excess of 10wt%. Specifically, taking LFMP materials as an example, the iron source includes but is not limited to one or more of ferric sulfate, anhydrous ferric chloride, and ferroferric oxide; the manganese source includes but is not limited to one or more of manganese nitrate, tetrahydrated manganese acetate, and manganese dioxide; the lithium source includes but is not limited to one or more of lithium dihydrogen phosphate, lithium hydroxide, and lithium carbonate; the phosphorus source includes but is not limited to one of ammonium dihydrogen phosphate and lithium dihydrogen phosphate.

[0079] In some embodiments of the present application, those skilled in the art can determine the relative amounts of the carbon source and each element source according to the thickness of the target carbon layer. For example, the mass content of the carbon source is 8%-12% of the mass of the lithium source.

[0080] In some embodiments of the present application, the medium in step (1) and step (3) may be, for example, ethanol, but is not limited thereto.

[0081] In some embodiments of the present application, in step (1), a sand milling process can be used to mix the element sources and the carbon source.

[0082] In some embodiments of the present application, the drying in step (1) and step (3) can be, for example, spray drying. The spray drying can adopt any known process parameters in the art, and the present application does not impose any limitation on this.

[0083] In some embodiments of the present application, the crushing in step (4) can be performed by air jet milling.

[0084] In some embodiments of the present application, in step (2), the temperature of the first sintering is 400°C to 500°C, the insulation time is 8h to 10h, and the heating rate is 5°C / min to 10°C / min.

[0085] In some embodiments of the present application, in step (4), the temperature of the second sintering is 700°C to 850°C, the insulation time of the second sintering is 8h to 10h, and the heating rate is 5°C / min to 10°C / min.

[0086] The embodiments of the present application also provide a positive electrode plate, comprising the aforementioned positive electrode composite material provided in the embodiments of the present application, and / or, comprising the aforementioned positive electrode active material provided in the embodiments of the present application.

[0087] Due to the positive electrode composite material and / or positive electrode active material provided in the embodiments of the present application, the positive electrode plate can be used to provide a secondary battery with better high-temperature cycle performance, better high-temperature storage performance, and lower DC internal resistance.

[0088] In some embodiments of the present application, the positive electrode plate includes a current collector and a positive electrode material layer arranged on at least one side of the current collector, and the positive electrode material includes the aforementioned positive electrode active material and / or the aforementioned positive electrode composite material provided in the embodiments of the present application.

[0089] In the embodiment of the present application, when positive electrode material layers are provided on both sides of the current collector, the positive electrode material layer on one side may include the aforementioned positive electrode active material and / or the aforementioned positive electrode composite material, or the positive electrode material layers on both sides may include the aforementioned positive electrode active material and / or the aforementioned positive electrode composite material.

[0090] In some embodiments of the present application, the positive electrode material layer further includes a conductive agent, a binder, etc. The present application does not limit the type and mass ratio of the conductive agent and the binder, and they can be any conductive agent and binder suitable for lithium-ion battery positive electrodes in the field.

[0091] In some embodiments of the present application, the binder includes PVDF5130 and PVDF9100 in a mass ratio of (15-20):(2-8), wherein PVDF is polyvinylidene fluoride.

[0092] In some embodiments of the present application, the conductive agent may be one or more of Super P and KS-6.

[0093] In some embodiments of the present application, the positive electrode material layer may also include any other active material known in the art that is suitable for corresponding types of active metal ion batteries (eg, lithium ion batteries), which can be determined by technicians in the art according to actual production needs.

[0094] In the embodiments of the present application, the mass proportion of the positive electrode active material and the positive electrode composite material in the positive electrode material layer is not limited, and technicians in the field can determine it according to actual production needs.

[0095] In the embodiment of the present application, the current collector can be any current collector suitable for the positive electrode of a corresponding type of active metal ion battery (eg, lithium ion battery) in the art.

[0096] The embodiment of the present application also provides a positive electrode slurry, including a solvent, a binder and a conductive agent dispersed in the solvent, and the aforementioned positive electrode active material and / or the aforementioned positive electrode composite material provided in the embodiment of the present application.

[0097] In some embodiments of the present application, the above-mentioned solvent may be, for example, N-methylpyrrolidone (NMP).

[0098] In some embodiments of the present application, the room temperature viscosity of the positive electrode slurry is 8000 mPa·s to 10000 mPa·s, which is beneficial to the preparation and quality of the positive electrode sheet, and further to the performance of the final battery.

[0099] In some embodiments of the present application, the preparation of the positive electrode slurry includes:

[0100] Add the binder into a solvent (e.g., NMP), and stir under vacuum at a revolution speed of 15 rpm and a rotation speed of 3000 rpm for 3 h to obtain a glue solution;

[0101] According to the preset mass ratio, the above-mentioned positive electrode active material and / or the above-mentioned positive electrode composite material, as well as the glue are added into the ball mill, the rotation speed of the ball mill is 400 rpm, the ball milling time is 6 hours, and after mixing evenly, the conductive agent is added and the ball milling is carried out at a ball milling speed of 400 rpm for 2 hours.

[0102] The embodiment of the present application also provides a secondary battery, including the positive electrode plate provided in the embodiment of the present application.

[0103] In some embodiments of the present application, the secondary battery includes the aforementioned positive electrode sheet, negative electrode sheet, and an electrolyte located in the positive electrode sheet and the negative electrode sheet. In some specific embodiments, the above electrolyte includes a liquid electrolyte. In some specific embodiments, the secondary battery is a liquid battery.

[0104] In the embodiment of the present application, when the secondary battery includes multiple positive electrode plates, each positive electrode plate can be the positive electrode plate provided in the embodiment of the present application, or a part of the positive electrode plates can be the positive electrode plates provided in the embodiment of the present application, and the others can be any positive electrode plates known in the art that are suitable for the positive electrode of the corresponding type of active metal ion battery (for example, lithium ion battery).

[0105] Due to the use of the positive electrode plate provided in the embodiment of the present application, the secondary battery has excellent high-temperature cycle performance, high-temperature storage performance and low DC internal resistance, and has a better market prospect.

[0106] In the embodiment of the present application, the secondary battery may be a laminated battery or a wound battery.

[0107] The technical solution of the present application is further illustrated by multiple embodiments below.

[0108] Example 1

[0109] (1) According to the lithium manganese iron phosphate to be prepared, 24.42 g of a lithium source (lithium hydroxide), 15.99 g of an iron source (ferric sulfate), 55.78 g of a manganese source (manganese nitrate) and 115.03 g of a phosphorus source (ammonium dihydrogen phosphate) were weighed, and dispersed with 1.95 g of a carbon source (glucose) in ethanol, and sand-milled to make the materials evenly mixed, and then spray-dried to dry the materials and control the particle morphology to obtain a first material; wherein, based on the mass of lithium hydroxide, the mass content of the carbon source is 8 wt.%.

[0110] (2) placing the first material in a tube furnace for high temperature treatment under a nitrogen atmosphere, wherein the high temperature treatment temperature is 450° C., the heat preservation time is 8 h, and the heating rate is 5° C. / min, to obtain a core precursor;

[0111] (3) 100 g of the core precursor, 0.6 g of calcium hydroxide, and 0.06 g of calcium lactate were mixed evenly and sintered at a temperature of 780°C for 10 h at a heating rate of 5°C / min to obtain a positive electrode composite material. The average particle size of the core was 150 nm, the thickness of the first coating layer was 3 nm, the thickness of the transition layer was 0.5 nm, and the thickness of the second coating layer was 2 nm.

[0112] Example 2

[0113] The only difference from Example 1 is that in step (3), calcium hydroxide is 1.0 g and calcium lactate is 0.06 g. The particle size of the core of the positive electrode composite material is 140 nm, the thickness of the first coating layer is 3 nm, the thickness of the transition layer is 0.7 nm, and the thickness of the second coating layer is 3 nm.

[0114] Example 3

[0115] The only difference from Example 1 is that in step (3), calcium hydroxide is 0.6 g and calcium lactate is 0.1 g. The particle size of the core of the positive electrode composite material is 145 nm, the thickness of the first coating layer is 3 nm, the thickness of the transition layer is 0.56 nm, and the thickness of the second coating layer is 2.5 nm.

[0116] Example 4

[0117] (1) According to the lithium manganese iron phosphate to be prepared, 24.42g of lithium source (lithium hydroxide), 15.99g of iron source (ferrous sulfate), 55.78g of manganese source (manganese nitrate) and 115.03g of phosphorus source (ammonium dihydrogen phosphate) were weighed, and dispersed with 0.975g of carbon source (glucose) in ethanol, and sand milled to make the materials mix evenly, and then spray dried the materials and adjusted the particle morphology to obtain the first material; wherein, based on the mass of lithium hydroxide, the mass content of the carbon source is 8wt.%.

[0118] (2) Under a nitrogen atmosphere, the second material is placed in a tube furnace for a first sintering, the high temperature treatment temperature is 450° C., the heat preservation time is 8 h, and the heating rate is 5° C. / min, to obtain a first precursor;

[0119] (3) dispersing 100 g of the first precursor and 0.975 g of a carbon source (glucose) in ethanol, performing sand milling, spray drying, and particle morphology shaping to obtain a second precursor;

[0120] (4) Under nitrogen, the second precursor is sintered for a second time in a tubular furnace, and then the material is ground by a jet mill to obtain core material particles; the second sintering temperature is 780°C, the insulation time is 10 hours, and the heating rate is 5°C / min.

[0121] (5) Weigh 100 g of ball milling beads in a 500 g ball milling jar, and use ethanol to mill 100 g of core particle material, 0.6 g of calcium hydroxide, and 0.06 g of calcium lactate. The speed of the ball milling is 400 rpm, the ball milling time is 6 hours, and the positive electrode active material is obtained by drying and crushing. The particle size of the core is 200 nm, the thickness of the carbon layer is 4 nm, and the thickness of the composite base layer is 3.5 nm.

[0122] Example 5

[0123] The only difference from Example 4 is that in step (3), calcium hydroxide is 1.0 g and calcium lactate is 0.06 g. The particle size of the core of the positive electrode active material is 180 nm, the thickness of the carbon layer is 4 nm, and the thickness of the composite alkali layer is 4 nm.

[0124] Example 6

[0125] The only difference from Example 4 is that in step (3), calcium hydroxide is 0.6 g and calcium lactate is 0.10 g. The particle size of the core of the positive electrode active material is 190 nm, the thickness of the carbon layer is 4 nm, and the thickness of the composite alkali layer is 3.8 nm.

[0126] Comparative Example 1

[0127] (1) According to the lithium manganese iron phosphate to be prepared, 24.42 g of a lithium source (lithium hydroxide), 15.99 g of an iron source (ferric sulfate), 55.78 g of a manganese source (manganese nitrate) and 115.03 g of a phosphorus source (ammonium dihydrogen phosphate) were weighed and dispersed in ethanol with 0.975 g of a carbon source (glucose);

[0128] (2) Under a nitrogen atmosphere, the second material is placed in a tube furnace for a first sintering, the high temperature treatment temperature is 450° C., the heat preservation time is 8 h, and the heating rate is 5° C. / min, to obtain a first precursor;

[0129] (3) dispersing 100 g of the first precursor and 0.975 g of a carbon source (glucose) in ethanol, performing sand milling, spray drying, and particle morphology shaping to obtain a second precursor;

[0130] (4) Under nitrogen, the second precursor is sintered for a second time in a tubular furnace, and then the material is ground by a jet mill to obtain lithium manganese iron phosphate @C; wherein the second sintering temperature is 780°C, the insulation time is 10 hours, and the heating rate is 5°C / min.

[0131] Comparative Example 2

[0132] (1) According to the lithium manganese iron phosphate to be prepared, 24.42 g of a lithium source (lithium hydroxide), 15.99 g of an iron source (ferric sulfate), 55.78 g of a manganese source (manganese nitrate) and 115.03 g of a phosphorus source (ammonium dihydrogen phosphate) were weighed and dispersed in ethanol with 0.975 g of a carbon source (glucose).

[0133] (2) Under a nitrogen atmosphere, the second material is placed in a tube furnace for a first sintering, the high temperature treatment temperature is 450° C., the heat preservation time is 8 h, and the heating rate is 5° C. / min, to obtain a first precursor;

[0134] (3) dispersing 100 g of the first precursor and 0.975 g of a carbon source (glucose) in ethanol, performing sand milling, spray drying, and particle morphology shaping to obtain a second precursor;

[0135] (4) Under nitrogen, the second precursor is sintered for a second time in a tubular furnace, and then the material is ground by a jet mill to obtain core material particles; the second sintering temperature is 780°C, the insulation time is 10 hours, and the heating rate is 5°C / min.

[0136] (5) Weigh 100 g of ball mill beads into a 500 g ball mill jar, and ball mill 100 g of the core particle material and 0.01 g of LiOH with ethanol at a ball mill speed of 400 rpm for 6 h. Dry and crush the mixture to obtain lithium manganese iron phosphate @C @LiOH of Comparative Example 2.

[0137] Comparative Example 3

[0138] The only difference from Example 1 is that in step (3), calcium lactate is replaced by calcium dihydrogen phosphate.

[0139] Comparative Example 4

[0140] The only difference from Example 4 is that in step (3), calcium lactate is replaced by calcium dihydrogen phosphate.

[0141] Preparation of test cells

[0142] (1) The positive electrode materials prepared in the above-mentioned embodiments and comparative examples were respectively dispersed in NMP with a binder and a conductive agent, and stirred evenly to obtain a positive electrode slurry. In each positive electrode slurry, the mass ratio of positive electrode material: binder: conductive agent was 96:2.5:0.7, the conductive agent was Super P and KS-6 with a mass ratio of 1:0.33, and the binder was PVDF5130:PVDF9100 with a mass ratio of 9:1.

[0143] (2) The above-mentioned positive electrode slurries are respectively coated on the opposite sides of the positive electrode collector (specifically aluminum foil) to form a positive electrode material layer, and dried at 100° C. to obtain positive electrode sheets of each embodiment and comparative example, and the single-sided surface density of each positive electrode sheet is controlled to be the same.

[0144] (3) Multiple positive electrode sheets of various embodiments and comparative examples are alternately stacked with separators and graphite negative electrode sheets, and a battery is prepared by lamination, wherein the positive and negative electrode sheets are alternately arranged, and adjacent positive and negative electrode sheets are separated by separators to obtain a dry battery cell. The dry battery cell is placed in an aluminum-plastic film outer packaging, injected with electrolyte SW2001A, and then vacuum-sealed to obtain a laminated soft-pack full battery of each embodiment and comparative example. Among them, the negative electrode sheet includes a copper foil and a negative electrode active material layer arranged on the surface of the copper foil, and the mass ratio of graphite: SFG-6: SBR: CMC in the negative electrode active material layer is 1:3:1.6:1.

[0145] Performance Testing

[0146] (1) High temperature cycle test: First, the battery cell was charged and discharged at 1C at room temperature of 25°C, and then placed at 40°C. After 500 cycles of 1C charge and discharge in the electrochemical window of 2V to 4.25V, the retention rate of the 500th cycle capacity was calculated. The calculation formula is as follows: 500th cycle capacity retention rate (%) = (500th cycle discharge capacity / 1st cycle discharge capacity) × 100%. The results are summarized in Table 1.

[0147] (2) High temperature storage test: First, the battery cell is discharged at room temperature of 25°C at 1C, and the discharge capacity of the last cycle is recorded as D 0 The battery cell was fully charged at 1C, and then placed in a 60°C oven for 28 days. The battery cell was then taken out and cooled to room temperature to test the discharge capacity and recovery capacity, which were recorded as D 1 and D 2 , then the cell high temperature storage capacity retention rate is calculated as: D 1 / D 0 Calculation of cell high temperature storage capacity recovery rate: D 2 / D 0 , the results are summarized in Table 1.

[0148] (3) DC internal resistance test: After 500 cycles, the battery is adjusted to 50% SOC, 1C 10s discharge, and the discharge resistance is tested. Resistance DCIR = (V 0 -V 10 ) / I, where V 0 is the potential before discharge, V 10 is the potential at 10s of discharge, I is the discharge current 1C, and the results are summarized in Table 1.

[0149] (4) Specific test of Mn dissolution: Weigh 5.0000g±0.0100g of the sample to be tested into a 0.008mol / 150mL beaker of hydrochloric acid and seal it with polyethylene film again. Place the sample in a magnetic stirrer and stir it at 880rpm for 30min. After stirring, place it in water at room temperature for 30min, then dilute it to 50mL, and finally test the dissolution amount of Mn element on the machine. The results are summarized in Table 1.

[0150] (5) Mn platform ratio test: Connect the divided cells to the battery test cabinet, set the voltage platform to 3.6 V, measure and calculate the Mn platform ratio, and read the readings; the results are summarized in Table 1.

[0151] Table 1

[0152]

[0153] It can be seen from the data of the embodiments and comparative examples in Table 1 that the positive electrode composite material and positive electrode active material provided in the embodiments of the present application have both excellent high-temperature cycle performance and high-temperature storage performance, and the manganese dissolution amount is significantly reduced, the proportion of the Mn platform is effectively improved, and the DC internal resistance of the battery is also low. Referring to the data of the comparative example, it is not difficult to find that although the positive electrode active material of comparative example 1 also has an alkali coating layer, the material of its alkali coating layer is LiOH, and the performance of the final battery is not significantly improved. Comparative Examples 3 and 4 respectively replace the organic alkali salts specified in the embodiments of the present application with dihydrogen phosphate. After there is no compounding of inorganic alkali and specific organic alkali salts in the system, the high temperature performance of the battery is still poor, and the inhibitory effect on manganese dissolution is poor, and the DC internal resistance of the battery is also significantly higher than that of the embodiment.

[0154] The above is an exemplary embodiment of the present application. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made thereto without departing from the principles of the present application. These improvements and modifications are also considered to be within the scope of protection of the present application.

Claims

1. A positive electrode composite material, characterized in that: It comprises a core with positive electrode activity and a first coating layer, a transition layer and a second coating layer sequentially coated on the surface of the core; the first coating layer comprises a carbon material, the second coating layer comprises a metal oxide, and the transition layer comprises a material of the first coating layer and a material of the second coating layer; The metal in the metal oxide includes one or more of Ca, Mg and Ba.

2. The positive electrode composite material according to claim 1, characterized in that: The transition layer includes a carbon material and a metal oxide dispersed in the carbon material.

3. The positive electrode composite material according to claim 1 or 2, characterized in that: The particle size of the core is 50nm to 500nm; and / or, The thickness of the first coating layer is 1 nm to 5 nm; and / or, The thickness of the second coating layer is 0.5 nm to 2 nm; and / or, The thickness of the transition layer is ≤0.5 nm.

4. The positive electrode composite material according to any one of claims 1 to 3, characterized in that: The material of the core includes one or more of lithium iron manganese phosphate materials, nickel cobalt manganese ternary materials, and lithium manganate materials.

5. A method for preparing a positive electrode composite material, characterized in that: include: Mixing a core precursor, an inorganic base and an organic base salt to obtain a mixture; the inorganic base includes one or more of calcium hydroxide, barium hydroxide and magnesium hydroxide; the organic base salt includes one or more of organic calcium salt, organic magnesium salt and organic barium salt with a pH value of 7 to 10; the material of the core precursor includes a core precursor material and carbon; The mixture is sintered to transform the core precursor into a core coated with a first coating layer, and a transition layer and a second coating layer stacked in sequence are formed on the surface of the first coating layer to obtain a positive electrode composite material; the first coating layer includes a carbon material, the second coating layer includes a metal oxide, and the transition layer includes the material of the first coating layer and the material of the second coating layer; the core has positive electrode activity.

6. The method for preparing the positive electrode composite material according to claim 5, characterized in that: The organic calcium salt includes calcium lactate, the organic magnesium salt includes magnesium lactate, and the organic barium salt includes barium lactate; and / or, the mass ratio of the organic alkali salt to the inorganic base is 1:(5-20); and / or, based on the mass of the core precursor, the mass proportion of the organic alkali salt is 0.05%-0.1%, and the mass proportion of the inorganic base is 0.5%-1%; And / or, the sintering temperature is 700° C. to 850° C., and the insulation time is 8 h to 10 h.

7. A positive electrode active material, characterized in that: It comprises a core with positive electrode activity and a carbon layer and a composite alkali layer sequentially coated on the surface of the core, wherein the composite alkali layer comprises an inorganic base and an organic alkali salt; wherein the inorganic base comprises one or more of calcium hydroxide, barium hydroxide and magnesium hydroxide, and the organic alkali salt comprises one or more of organic calcium salt, organic magnesium salt and organic barium salt with a pH value of 7 to 10.

8. The positive electrode active material according to claim 7, characterized in that The organic calcium salt comprises calcium lactate, the organic magnesium salt comprises magnesium lactate, and the organic barium salt comprises barium lactate; and / or, The mass ratio of the organic base salt to the inorganic base is 1:(5-20); and / or, based on the mass of the core, the mass percentage of the inorganic base is 0.5%-1%, and the mass percentage of the organic base salt is 0.05%-1%; and / or, The thickness of the carbon layer is 1 nm to 5 nm; and / or, The thickness of the composite alkali layer is 1 nm to 5 nm; and / or, The particle size of the core is 50nm to 500nm.

9. The positive electrode active material according to claim 7 or 8, characterized in that: The material of the core includes one or more of lithium iron manganese phosphate materials, nickel cobalt manganese ternary materials, and lithium manganate materials.

10. A method for preparing a positive electrode active material, characterized in that: include: Mixing core material particles, an inorganic base and an organic base salt to coat the surface of the core material particles with a composite base layer to obtain a positive electrode active material; Among them, the core material particles include materials with positive electrode activity; the inorganic base includes one or more of calcium hydroxide, barium hydroxide and magnesium hydroxide, and the organic alkali salt includes one or more of organic calcium salts, organic magnesium salts and organic barium salts with a pH value of 7 to 10.

11. A positive electrode sheet, characterized in that: The method comprises the positive electrode composite material as claimed in any one of claims 1 to 4, and / or the positive electrode active material as claimed in any one of claims 7 to 9.

12. A secondary battery, characterized in that: Comprising the positive electrode sheet as claimed in claim 11.

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