Positive electrode active material and preparation method therefor, positive electrode sheet, and battery

Abstract

The present application relates to the technical field of batteries, and provides a positive electrode active material and a preparation method therefor, a positive electrode sheet, and a battery. The positive electrode active material comprises a ternary material and lithium manganese iron phosphate, wherein the mass of lithium manganese iron phosphate is A and the total mass of the ternary material and lithium manganese iron phosphate is B, both of which satisfy: 0<A / B<50%; and lithium manganese iron phosphate is of a hollow spherical structure, and has a median particle size of 0.5-3 μm.

Description

A positive electrode active material and its preparation method, positive electrode sheet and battery

[0001] This application claims priority to Chinese Patent Application No. 202411817186.X, filed on December 10, 2024, the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of battery technology, specifically to a positive electrode active material and its preparation method, a positive electrode slurry, a positive electrode sheet, and a battery. Background Technology

[0003] Due to the scarcity of cobalt and nickel, the upstream raw materials in the new energy industry chain (cobalt and nickel account for 0.43% and 0.01% of the national non-ferrous metal mineral resources, respectively), the cost of ternary materials is relatively high. Compared to the precious metals cobalt and nickel in ternary materials, lithium manganese iron phosphate (LFP) mainly contains manganese and iron, which have lower market prices, thus ensuring lower costs. Furthermore, from a structural perspective, compared to layered ternary materials, LFP with its olivine structure is more stable during charging and discharging; even if all lithium ions are released during charging, structural collapse will not occur. Simultaneously, phosphorus (P) atoms in LFP form PO4 tetrahedra through strong covalent bonds with PO, making it difficult for oxygen atoms to escape from the structure. This also contributes to the high safety and stability of LFP. Currently, most ternary materials on the market have a cycle life of 1000-2000 cycles, which is relatively short. In contrast, LFP, with its more stable olivine structure, can achieve a cycle life of over 2000 cycles, demonstrating excellent cycle performance. In addition, the particle size of conventional ternary materials is generally 6 to 10 micrometers. Due to the large particle size, the lithium-ion diffusion path is long, resulting in relatively poor high-rate performance. However, ternary materials have a high specific capacity, i.e., a high energy density.

[0004] Based on the advantages and disadvantages of ternary materials and lithium manganese iron phosphate, they are usually blended to reduce costs. Invention Overview

[0005] In related technologies, single-crystal ternary materials and single-crystal lithium manganese iron phosphate are usually mixed. Although this can reduce costs, it is difficult to achieve electrochemical performance such as rate performance and cycle performance.

[0006] This application provides a positive electrode active material, including ternary materials and lithium manganese iron phosphate;

[0007] Among them, the mass of lithium manganese iron phosphate is A, and the total mass of ternary materials and lithium manganese iron phosphate is B, satisfying: 0 < A / B < 50%;

[0008] Lithium manganese iron phosphate has a hollow spherical structure, and its median particle size is 0.5μm-3μm.

[0009] This application also provides a method for preparing a positive electrode active material, used to prepare the positive electrode active material as described above, comprising:

[0010] We provide ternary materials and lithium manganese iron phosphate;

[0011] Ternary materials and lithium manganese iron phosphate are mixed in a certain proportion to obtain positive electrode active materials.

[0012] This application also provides a positive electrode sheet, including a positive electrode foil and a positive electrode active layer coated on the positive electrode foil;

[0013] The positive electrode active layer includes the positive electrode active material as described above;

[0014] And / or, positive electrode active materials prepared by the methods described above.

[0015] This application also provides a battery, including the positive electrode as described above. Beneficial effects

[0016] The positive electrode active material provided in this application includes a ternary material and lithium manganese iron phosphate (LMP). The mass of LMP is A, and the total mass of the ternary material and LMP is B, satisfying 0 < A / B < 50%. LMP has a hollow spherical structure with a median particle size of 0.5 μm-3 μm. By adding LMP to the positive electrode active material, the amount of ternary material used can be reduced, thereby lowering the cost of the positive electrode active material. The hollow spherical structure and median particle size of LMP in the 0.5 μm-3 μm range give it excellent rate performance. Ensuring that the mass A of LMP and the total mass B of the ternary material and LMP satisfy 0 < A / B < 50% allows for a reduction in the cost of the positive electrode active material while maintaining high rate performance, cycle performance, and energy density, thus improving overall electrochemical performance.

[0017] The method for preparing positive electrode active materials provided in this application involves mixing ternary materials and lithium manganese iron phosphate to form positive electrode active materials, and the preparation process is simple.

[0018] The positive electrode provided in this application embodiment, by including the positive electrode active material described above, can achieve a balance between high rate performance, cycle performance and energy density, thereby improving the overall electrochemical performance.

[0019] The battery provided in this application embodiment, by including the positive electrode as described above, can achieve a balance between high rate performance, cycle performance, and energy density, thereby improving the overall electrochemical performance. Attached Figure Description

[0020] Figure 1 is a schematic diagram of the synthesis process of hollow spherical lithium manganese iron phosphate in the embodiments of this application;

[0021] Figure 2 is an analysis chart of the test results of the 3C capacity retention rate in Comparative Example 1;

[0022] Figure 3 is an analysis chart of the test results of the 3C capacity retention rate in Comparative Example 2;

[0023] Figure 4 is an analysis chart of the test results of 3C capacity retention rate in Embodiment 1 of this application;

[0024] Figure 5 is an analysis diagram of the cycle performance test results of Embodiment 1 of this application. Embodiments of the present invention

[0025] In a first aspect, embodiments of this application provide a positive electrode active material comprising a ternary material and lithium manganese iron phosphate (LMP). The mass of LMP is A, and the total mass of the ternary material and LMP is B, satisfying 0 < A / B < 50%. LMP has a hollow spherical structure with a median particle size of 0.5 μm-3 μm. By adding LMP to the positive electrode active material, the amount of ternary material used can be reduced, thereby lowering the cost of the positive electrode active material. The hollow spherical structure and median particle size of LMP within the 0.5 μm-3 μm range provide excellent rate performance. Ensuring that the mass A of LMP and the total mass B of the ternary material and LMP satisfy 0 < A / B < 50% allows for a reduction in the cost of the positive electrode active material while maintaining high rate performance, cycle performance, and energy density, thus improving overall electrochemical performance.

[0026] Hollow spherical lithium manganese iron phosphate (LMP) provides a wide and smooth diffusion channel. Compared to solid LMP, the hollow spherical LMP reduces the diffusion distance of lithium ions within the material, thereby increasing the diffusion rate. When used in batteries, hollow spherical LMP can withstand volume changes during charge and discharge, thus helping to maintain the material's cycle stability. Due to the increased lithium-ion diffusion rate, hollow spherical LMP can respond quickly to current changes during charge and discharge, exhibiting excellent rate performance.

[0027] The lithium manganese iron phosphate provided in this application has a hollow spherical structure and a small particle size, with a median particle size of 0.5 μm-3 μm. This shortens the diffusion distance of lithium ions within the material, allowing the battery to respond quickly to changes in current when applied to batteries, thereby improving the battery's rate performance. The smaller particle size also helps reduce the agglomeration of the positive electrode active material, improving dispersibility and stability.

[0028] This application embodiment combines lithium manganese iron phosphate that meets the above conditions with ternary materials to form a positive electrode active material. This can reduce costs while maintaining high rate performance, cycle performance and energy density, thereby improving the overall electrochemical performance of the positive electrode active material when applied to batteries.

[0029] In some embodiments, the specific surface area of ​​lithium manganese iron phosphate is 11 m². 2 / g-21m 2 / g.

[0030] By setting the specific surface area of ​​lithium manganese iron phosphate within the aforementioned range, it is beneficial to improve the insertion and extraction reactions of lithium ions, thereby increasing the energy density of the material and the driving range of the battery. It also shortens the diffusion path of lithium ions within the material, increasing the diffusion rate and thus improving rate performance. Within this specific surface area, agglomeration can also be reduced, improving dispersibility and stability, thereby extending the cycle life of the battery.

[0031] In some embodiments, the tap density of lithium manganese iron phosphate is 0.3 g / cm³. 3 -0.8g / cm 3 .

[0032] In some embodiments, the molecular formula of the ternary material is LiNi. a Co b Mn c M d O2; where a+b+c+d=1, a≥0.5, b≤0.3, 0≤d≤0.05. M is selected from at least one of Zr, Sr, W, B, Nb, Al, Mg and Ti.

[0033] The high nickel (Ni) content in ternary materials helps improve specific capacity and energy density, while reducing the cost per watt-hour; therefore, a ≥ 0.5 is set. Cobalt (Co) is expensive; by rationally controlling its content, costs can be reduced while maintaining high performance.

[0034] Doping with elements such as Zr, Sr, W, B, Nb, Al, Mg, and Ti can enhance the electrochemical performance of ternary materials. Specifically, zirconium (Zr) doping helps improve the stability and mechanical strength of ternary materials, effectively resisting damage caused by volume expansion and contraction; strontium (Sr) doping increases the volume of primary particles and unit cells in ternary materials, thereby increasing the compaction density and improving the volumetric energy density of the battery; tungsten (W) and boron (B) doping helps optimize the crystal structure of ternary materials, improving their stability and performance; niobium (Nb) doping improves the cycle performance and thermal stability of nickel-rich ternary materials; aluminum (Al) doping helps improve the battery capacity and cycle stability of ternary materials, as aluminum has high electrochemical activity and can provide more lithium insertion sites, thus increasing the battery's energy storage capacity; magnesium (Mg) and titanium (Ti) doping helps improve the structural and thermal stability of ternary materials, contributing to improved battery safety and cycle life.

[0035] By setting d≤0.05, the doping element does not significantly alter the main structure of the ternary material, maintaining its original stability and reliability. Furthermore, the amount of doping element added is relatively small, achieving the desired effect while reducing costs.

[0036] In some embodiments, the median particle size of the ternary material is 3 μm-10 μm. By setting the median particle size of the ternary material within this range, the lithium-ion diffusion path within the ternary material particles is relatively short, which helps to improve the lithium-ion diffusion efficiency, thereby improving the charge-discharge performance of the battery. The particle sizes of the ternary material and lithium manganese iron phosphate are relatively close, which helps to achieve uniform stress dispersion within the positive electrode active material and reduces capacity decay caused by volume changes.

[0037] In some embodiments, lithium manganese iron phosphate includes a lithium manganese iron phosphate body and a carbon coating layer covering the lithium manganese iron phosphate body.

[0038] By adding a carbon coating, the electronic conductivity of the lithium manganese iron phosphate (LFP) battery can be improved, the internal resistance of the battery can be reduced, and thus the power density and energy density of the battery can be increased. The carbon coating also helps to form a conductive network on the surface of the LFP battery, thereby improving electron transport efficiency and reducing polarization during battery charging and discharging. Furthermore, the carbon coating can also act as a protective layer for the LFP battery, reducing the corrosive effects of substances such as hydrofluoric acid in the electrolyte, and it can also enhance the structural stability of the LFP battery, improving cycle performance.

[0039] Secondly, embodiments of this application provide a method for preparing a positive electrode active material, used to prepare the positive electrode active material as described above, comprising:

[0040] We provide ternary materials and lithium manganese iron phosphate;

[0041] Ternary materials and lithium manganese iron phosphate are mixed in a certain proportion to obtain positive electrode active materials.

[0042] This application's embodiments involve blending ternary materials and lithium manganese iron phosphate to form a positive electrode active material, a simple preparation process. The beneficial effects of the obtained positive electrode active material have been described above and will not be repeated here.

[0043] In some embodiments, prior to providing the ternary material and lithium manganese iron phosphate, the method further includes: preparing lithium manganese iron phosphate.

[0044] The preparation of lithium manganese iron phosphate includes:

[0045] A phosphoric acid solution was added to a lithium source solution to carry out a reaction, resulting in a hollow spherical lithium phosphate precursor.

[0046] Ferrous salt, manganese salt and lithium phosphate precursor are dispersed in a solvent, and after reaction, lithium manganese iron phosphate precursor is formed.

[0047] The lithium manganese iron phosphate precursor was sintered for the first time to obtain lithium manganese iron phosphate.

[0048] Specifically, this application describes the preparation of hollow spherical lithium manganese iron phosphate using a liquid-phase method. As shown in Figure 1, phosphoric acid is first reacted with a lithium source to form a hollow spherical lithium phosphate precursor. Then, ferrous salt, manganese salt, and the lithium phosphate precursor are dispersed in a solvent. Iron and manganese ions are then bonded to the hollow spherical lithium phosphate precursor via a solvothermal method. Due to the gaps between different monomers in the lithium phosphate precursor, iron and manganese ions can easily enter the interior of the hollow spheres, thus forming the lithium manganese iron phosphate precursor. After sintering, the lithium manganese iron phosphate precursor exhibits improved crystallinity, enhanced interparticle bonding, and optimized microstructure, resulting in stable lithium manganese iron phosphate.

[0049] For example, ferrous salt, manganese salt, and lithium phosphate precursor are dispersed in ethylene glycol solvent. Since lithium phosphate is insoluble in ethylene glycol, it maintains a hollow spherical structure during the reaction. Furthermore, because lithium phosphate and lithium manganese iron phosphate have the same orthogonal system, a structural transformation occurs during the reaction, resulting in hollow spherical lithium manganese iron phosphate.

[0050] The method for preparing lithium manganese iron phosphate provided in this application can produce lithium manganese iron phosphate with a hollow spherical structure and a small particle size, which has excellent rate performance.

[0051] In some embodiments, a phosphoric acid solution is added to a lithium source solution to react and obtain a hollow spherical lithium phosphate precursor, comprising:

[0052] Add phosphoric acid solution to lithium hydroxide solution, stir at room temperature for 2-4 hours, and filter to obtain the first filtrate;

[0053] After drying the first filter material, a hollow spherical lithium phosphate precursor was obtained.

[0054] Lithium phosphate can be formed by reacting phosphoric acid in a phosphoric acid solution with lithium hydroxide in a lithium hydroxide solution. The lithium phosphate then self-assembles in the solution to form hollow spherical lithium manganese iron phosphate. The preparation of hollow spherical lithium phosphate involves mild reaction conditions and a simple process.

[0055] The molar ratio of phosphoric acid to lithium hydroxide can be set to 1:3 to form lithium phosphate (Li3PO4), thereby improving the utilization rate of phosphoric acid and lithium hydroxide.

[0056] In some embodiments, the molar ratio of ferrous salt to manganese salt is 1:9 to 9:1. The molar ratio of ferrous salt to manganese salt can be set as needed. It is understood that by setting the ratio of the two, different lithium manganese iron phosphates can be obtained, thus changing the ratio of iron (Fe) and manganese (Mn) elements in lithium manganese iron phosphate.

[0057] That is, the molecular formula of the obtained lithium manganese iron phosphate is LiMn x Fe y PO4, 0<x<1, 0<y<1, 0<x+y≤1.

[0058] In some embodiments, the sum of the amounts of ferrous salt and manganese salt is in a 1:1 ratio to the amount of lithium phosphate precursor. By setting the above ratio, the utilization rate of ferrous salt, manganese salt, and lithium phosphate precursor can be improved.

[0059] In some embodiments, the lithium manganese iron phosphate precursor is subjected to a first sintering, including:

[0060] The lithium manganese iron phosphate precursor was sintered for 5-8 hours in a protective atmosphere at a temperature of 150℃-200℃.

[0061] Sintering under a protective atmosphere can prevent oxidation of the lithium phosphate precursor with oxygen during sintering, thus improving sintering stability. By controlling the sintering temperature at 150℃-200℃, the lithium manganese iron phosphate precursor can undergo dehydration and recrystallization reactions. Sintering for 5-8 hours ensures sufficient reaction, thereby forming a stable lithium manganese iron phosphate structure.

[0062] In some embodiments, after sintering the lithium manganese iron phosphate precursor, the method further includes:

[0063] The sintered lithium manganese iron phosphate precursor was mixed with a carbon source and a first additive to obtain a coating material.

[0064] The coating material is sintered a second time to obtain lithium manganese iron phosphate with a carbon coating layer.

[0065] By mixing a carbon source and a first additive with the sintered lithium manganese iron phosphate precursor and performing a second sintering, a carbon coating layer can be formed on the surface of the lithium manganese iron phosphate.

[0066] In some embodiments, the carbon source accounts for 10%-20% of the mass of the coating material. By controlling the mass percentage of the carbon source in the coating material within the above range, it is helpful to form a carbon coating layer of appropriate thickness.

[0067] In some embodiments, the carbon source includes at least one of glucose, sucrose, and polyethylene glycol.

[0068] In some embodiments, the first additive comprises at least one of Mg, Ti, Nb, Nd, Zr and Al, and the addition ratio of the first additive is 0ppm-6000ppm.

[0069] The conductivity of the carbon coating can be improved, the ion diffusion performance optimized, the structural stability enhanced, and the energy density increased by adding a first additive containing at least one of Mg, Ti, Nb, Nd, Zr, and Al.

[0070] By setting the addition ratio of the first additive to 0ppm-6000ppm, the effect of the first additive can be brought into play, and the phenomenon of clogging of lithium-ion diffusion channels caused by excessive addition of the first additive can be reduced, thus ensuring the structural stability and electrochemical performance of the material.

[0071] In some embodiments, the coating material is subjected to a second sintering, including:

[0072] The coating material is sintered at a temperature of 550℃-750℃ for 5-8 hours.

[0073] A second sintering process at 500℃-750℃ enables the carbon source to undergo a carbonization reaction, forming a compact carbon coating layer that adheres tightly to the surface of lithium manganese iron phosphate. This improves the conductivity and structural stability of the carbon coating layer. Setting the sintering time to 5-8 hours helps ensure a tight bond between the carbon coating layer and the lithium manganese iron phosphate, and avoids performance degradation caused by excessively long sintering times.

[0074] In some embodiments, prior to providing the ternary material and lithium manganese iron phosphate, the following are also included:

[0075] Preparation of ternary materials.

[0076] The preparation of ternary materials includes:

[0077] The ternary material precursor, lithium carbonate, and the second additive are mixed to obtain the first mixture;

[0078] Under an oxygen-containing atmosphere, the first mixture is subjected to a third sintering to obtain the first sintered material;

[0079] The first sintering material is crushed to obtain a ternary material.

[0080] The ratio of the ternary material precursor, lithium carbonate, and the second additive can be adjusted as needed. The ternary material precursor mainly consists of nickel, cobalt, and manganese, and is the core component of the ternary material. Lithium carbonate, as the lithium source, reacts with the ternary material precursor during sintering to form lithium nickel cobalt manganese oxide. Adding the second additive can improve the conductivity, structural stability, and cycle performance of the ternary material.

[0081] In some embodiments, the second additive contains at least one of Zr, Sr, W, B, Nb, Al, Mg and Ti.

[0082] In some embodiments, the first mixture is subjected to a third sintering under an oxygen-containing atmosphere, comprising:

[0083] The first mixture is sintered in a sintering furnace under an atmosphere with an oxygen concentration of ≥95%.

[0084] During the sintering process, the sintering furnace is first heated from room temperature to 450℃-600℃ at a heating rate of 5℃ / min and held for 3h-5h. Then, the sintering furnace is heated to 700℃-900℃ at a heating rate of 5℃ / min and held for 6h-10h.

[0085] In an oxygen-rich atmosphere (oxygen concentration ≥95%), a stable oxidizing environment is formed, which helps ternary materials form ideal crystal and layered structures during sintering, thereby improving their electrochemical performance. During sintering, the furnace is first heated from room temperature to 450℃-600℃ at a rate of 5℃ / min and held for 3-5 hours. This slow heating rate allows the material to gradually adapt to the temperature change. Holding at 450℃-600℃ for 3-5 hours allows for the decomposition of the ternary precursor, the melting of lithium carbonate, and partial reactions. Then, the temperature is raised again and held at 700℃-900℃ for 6-10 hours. This prolonged high-temperature holding promotes ion diffusion and reactions within the material, fostering a more complete and denser crystal structure. Simultaneously, the high-temperature holding also improves the crystallinity and purity of the ternary material, further enhancing its electrochemical performance.

[0086] Thirdly, embodiments of this application provide a positive electrode sheet, including a positive electrode foil and a positive electrode active layer coated on the positive electrode foil;

[0087] The positive electrode active layer includes the positive electrode active material as described above;

[0088] And / or, positive electrode active materials prepared by the methods described above.

[0089] The positive electrode sheet provided in this application embodiment also has the beneficial effects of the above-mentioned positive electrode active material, which will not be repeated here.

[0090] In some embodiments, the positive electrode sheet includes a positive electrode foil, a positive electrode active material, a positive electrode conductive agent, a positive electrode binder, and a dispersant.

[0091] The positive electrode foil can be carbon-coated aluminum foil, the thickness of which can be 6μm-20μm and the thickness of which can be greater than 0μm and less than or equal to 1.5μm.

[0092] The carbon-coated aluminum foil comprises aluminum foil and a carbon coating layer applied to the aluminum foil. The carbon coating layer optimizes the surface properties of the aluminum foil, allowing the positive electrode slurry to adhere tightly and uniformly to the foil, reducing ineffective space and thus improving the battery's energy density. Setting the aluminum foil thickness between 6μm and 20μm ensures sufficient mechanical strength while reducing battery weight, further enhancing energy density. The carbon coating layer thickness is set within the range of greater than 0μm and less than or equal to 1.5μm, resulting in an ultra-thin and uniform coating that contributes to improved overall battery performance.

[0093] The mass ratio of positive electrode active material, positive electrode conductive agent, positive electrode binder, and positive electrode dispersant is (95-98):(0.5-2.5):(1-3):(0-1). The positive electrode active material is a key component for energy storage and release in the battery. A higher proportion of positive electrode active material helps improve the battery's energy density, increasing the energy storage capacity of the battery within the same volume or mass, thus extending its service life. An appropriate amount of positive electrode conductive agent helps form an effective conductive network, reducing the battery's internal resistance and increasing electron and ion transport rates, thereby enhancing the battery's charge and discharge performance. The positive electrode binder plays a crucial role in maintaining the structural integrity and stability of the positive electrode sheet. By controlling the addition ratio of the positive electrode binder within a suitable range, it is possible to ensure that the positive electrode active material does not detach during the expansion and contraction of the charge and discharge process, maintaining structural stability and thus improving the battery's cycle life and safety. The dispersant helps improve the flowability of the positive electrode slurry, ensuring that the positive electrode active material is evenly distributed.

[0094] In some embodiments, the positive electrode conductive agent includes at least one of carbon nanotubes, graphene, and acetylene black. Carbon nanotubes possess high electrical conductivity, and using them as a positive electrode conductive agent helps reduce battery internal resistance and improve battery charge-discharge efficiency. Furthermore, carbon nanotubes exhibit good mechanical strength and flexibility, capable of withstanding volume changes in the positive electrode active material during charge-discharge, reducing the risk of particle breakage and structural damage to the positive electrode active material, thereby improving battery cycle stability. When used as a positive electrode conductive agent, the amount of carbon nanotubes added can be reduced, helping to increase the proportion of positive electrode active material added, thus increasing the battery's energy density. Graphene has a large specific surface area, which helps to form electrolyte storage voids, increasing the contact area between the positive electrode active material and the electrolyte, thereby enhancing battery charge-discharge efficiency. Graphene also possesses excellent mechanical properties, which can improve the volumetric energy density of the positive electrode sheet, increase the bendability and peel strength of the positive electrode sheet, thereby improving the overall stability of the battery. In addition, graphene has good thermal conductivity, which can reduce the battery's thermal resistance and improve its thermal stability. Acetylene black has moderate thermal conductivity, low nitrogen cost, and good mechanical stability, which can inhibit material shedding and damage.

[0095] In some embodiments, the positive electrode binder includes at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), and polyacrylic acid (PAA). PVDF possesses excellent chemical stability and corrosion resistance, ensuring reliability and safety during use. PVDF also exhibits good high-voltage resistance, remaining stable under high voltage conditions without oxidation or deterioration. It has good solubility and dissolution rate, enabling uniform dispersion onto the positive electrode slurry and positive electrode sheet surface, thus forming a uniform adhesive layer. Furthermore, its high flexibility and adhesion strength reduce the shedding of the positive electrode active material during repeated expansion and contraction. PTFE exhibits excellent corrosion resistance, strong stability, and good high-temperature stability, allowing for long-term use at high temperatures without decomposition. PAA possesses good adhesion, connecting with functional groups on the surface of the positive electrode active material through hydrogen bonds, thereby forming a stable adhesive layer and helping to prevent the shedding and pulverization of the positive electrode active material. PAA also effectively suppresses the volume expansion of the positive electrode active material during charge and discharge, thus extending the battery's cycle life. Furthermore, PAA itself has a small coefficient of volume expansion and a large coefficient of thermal diffusivity, making it suitable as a positive electrode binder, which ensures good safety of the battery when used under high power charging and discharging and high temperature conditions.

[0096] Fourthly, embodiments of this application provide a battery including the positive electrode as described above.

[0097] The battery provided in this application embodiment also has the beneficial effects of the above-mentioned positive electrode active material, which will not be repeated here.

[0098] In some embodiments, the battery further includes a negative electrode, an electrolyte, and a separator.

[0099] The negative electrode sheet comprises negative electrode foil, negative electrode active material, negative electrode conductive agent, and negative electrode binder. The negative electrode foil is made of copper foil or copper mesh, with a thickness of 4μm-12μm. Copper foil and copper mesh possess excellent conductivity and low resistivity, enabling rapid conduction of current within the battery. Using them as negative electrode foil provides an efficient conductive channel for the insertion and extraction of lithium ions, thereby improving the battery's charge and discharge efficiency and response speed. The high mechanical strength of copper foil and copper mesh protects the internal battery structure, increasing its stability and strength. By controlling the thickness of the negative electrode foil to 4μm-12μm, both structural strength and the energy density of the battery can be increased by reducing the mass of the negative electrode foil.

[0100] The negative electrode conductive agent is at least one of carbon nanotubes, carbon black, and acetylene black. The advantages of carbon nanotubes and acetylene black have been described in the section on positive electrode conductive agents; their application in negative electrode conductive agents offers similar advantages and will not be repeated here. Carbon black possesses excellent conductivity, which can improve the conductivity of the negative electrode sheet, reduce battery internal resistance, and allow for uniform dispersion within the negative electrode active material, forming a conductive network, accelerating electron transport rates, and improving battery performance. By using carbon black as the negative electrode conductive agent, conductivity can be significantly improved with a relatively low addition amount, facilitating an increase in the amount of negative electrode active material added to the negative electrode sheet. Furthermore, carbon black exhibits excellent chemical and physical stability, low cost, and good compatibility with other materials.

[0101] The electrolyte comprises an electrolyte, an organic solvent, and additives. The electrolyte is at least one of lithium hexafluorophosphate (LIPF6), lithium bis(fluorosulfonyl)imide (LiFSI), and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). The organic solvent comprises at least one of ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), polycarbonate (PC), and ethyl methyl carbonate (EMC). The additives comprise at least one of vinylene carbonate (VC), ethylene sulfate (DTD), methanedisulfonate (MMDS), lithium bis(oxalato)borate (LiBOB), and 1,3-propanesulfonyl lactone (PS), with the additive content ranging from 0.2% to 1.5% of the total electrolyte mass.

[0102] The diaphragm comprises a base membrane and a diaphragm coating applied to the base membrane. The base membrane is made of polypropylene (PP) or polyethylene (PE). The diaphragm coating is made of at least one of alumina, boehmite, magnesium hydroxide, and barium sulfate. The base membrane has a thickness of 5 μm–16 μm, the diaphragm coating has a thickness of 0.5 μm–5 μm, and the tensile strength of the diaphragm is greater than 200 MPa.

[0103] The vehicle provided in this application embodiment also has the beneficial effects of the above-mentioned positive electrode active material, which will not be repeated here.

[0104] The embodiments of this application are described 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.

[0105] It should be noted that, except for the conditions stated in the embodiments and comparative examples, the conditions in the embodiments and comparative examples are the same.

[0106] Example 1

[0107] In this embodiment: the positive electrode active material in the positive electrode sheet includes 10% LiMn. 0.6 Fe 0.4 PO4 and 90% LiNi 0.8 Co 0.1 Mn 0.1 O2; the negative electrode active material is graphite; the electrolyte is LiPF6; the separator is a 12μm PP membrane. The positive electrode, negative electrode, electrolyte, and separator are assembled to obtain a 2Ah lithium-ion battery.

[0108] Among them, LiMn 0.6 Fe 0.4 PO4 has a hollow spherical structure, while LiMn 0.6 Fe 0.4 The median particle size of PO4 is 1.5 μm, and the specific surface area is 15 m². 2 / g, tap density is 0.7g / cm³ 3 LiNi 0.8 Co 0.1 Mn 0.1 The median particle size of O2 is 8 μm.

[0109] Example 2

[0110] In this embodiment: the positive electrode active material in the positive electrode sheet includes 20% LiMn. 0.6 Fe 0.4 PO4 and 80% LiNi 0.8 Co 0.1 Mn 0.1 O2; the negative electrode active material is graphite; the electrolyte is LiPF6; the separator is a 12μm PP membrane. The positive electrode, negative electrode, electrolyte, and separator are assembled to obtain a 2Ah lithium-ion battery.

[0111] Among them, LiMn 0.6 Fe 0.4PO4 has a hollow spherical structure, while LiMn 0.6 Fe 0.4 The median particle size of PO4 is 1.5 μm, and the specific surface area is 15 m². 2 / g, tap density is 0.7g / cm³ 3 LiNi 0.8 Co 0.1 Mn 0.1 The median particle size of O2 is 8 μm.

[0112] Example 3

[0113] In this embodiment: the positive electrode active material in the positive electrode sheet includes 30% LiMn. 0.6 Fe 0.4 PO4 and 70% LiNi 0.8 Co 0.1 Mn 0.1 O2; the negative electrode active material is graphite; the electrolyte is LiPF6; the separator is a 12μm PP membrane. The positive electrode, negative electrode, electrolyte, and separator are assembled to obtain a 2Ah lithium-ion battery.

[0114] Among them, LiMn 0.6 Fe 0.4 PO4 has a hollow spherical structure, while LiMn 0.6 Fe 0.4 The median particle size of PO4 is 1.5 μm, and the specific surface area is 15 m². 2 / g, tap density is 0.7g / cm³ 3 LiNi 0.8 Co 0.1 Mn 0.1 The median particle size of O2 is 8 μm.

[0115] Example 4

[0116] In this embodiment: the positive electrode active material in the positive electrode sheet includes 40% LiMn. 0.6 Fe 0.4 PO4 and 60% LiNi 0.8 Co 0.1 Mn 0.1 O2; the negative electrode active material is graphite; the electrolyte is LiPF6; the separator is a 12μm PP membrane. The positive electrode, negative electrode, electrolyte, and separator are assembled to obtain a 2Ah lithium-ion battery.

[0117] Among them, LiMn 0.6 Fe 0.4 PO4 has a hollow spherical structure, while LiMn 0.6 Fe 0.4The median particle size of PO4 is 1.5 μm, and the specific surface area is 15 m². 2 / g, tap density is 0.7g / cm³ 3 LiNi 0.8 Co 0.1 Mn 0.1 The median particle size of O2 is 8 μm.

[0118] Example 5

[0119] In this embodiment: the positive electrode active material in the positive electrode sheet includes 5% LiMn. 0.5 Fe 0.5 PO4 and 95% LiNi 0.8 Co 0.1 Mn 0.1 O2; the negative electrode active material is graphite; the electrolyte is LiPF6; the separator is a 12μm PP membrane. The positive electrode, negative electrode, electrolyte, and separator are assembled to obtain a 2Ah lithium-ion battery.

[0120] Among them, LiMn 0.5 Fe 0.5 PO4 has a hollow spherical structure, while LiMn 0.5 Fe 0.5 The median particle size of PO4 is 0.8 μm, and the specific surface area is 18 m². 2 / g, tap density is 0.6g / cm³ 3 LiNi 0.5 Co 0.2 Mn 0.3 The median particle size of O2 is 6 μm.

[0121] Example 6

[0122] In this embodiment: the positive electrode active material in the positive electrode sheet includes 45% LiMn. 0.5 Fe 0.5 PO4 and 55% LiNi 0.8 Co 0.1 Mn 0.1 O2; the negative electrode active material is graphite; the electrolyte is LiPF6; the separator is a 12μm PP membrane. The positive electrode, negative electrode, electrolyte, and separator are assembled to obtain a 2Ah lithium-ion battery.

[0123] Among them, LiMn 0.5 Fe 0.5 PO4 has a hollow spherical structure, while LiMn 0.5 Fe 0.5 The median particle size of PO4 is 0.8 μm, and the specific surface area is 18 m². 2 / g, tap density is 0.6g / cm³3 LiNi 0.5 Co 0.2 Mn 0.3 The median particle size of O2 is 6 μm.

[0124] Comparative Example 1

[0125] In this embodiment: the positive electrode active material is 100% LiNi. 0.8 Co 0.1 Mn 0.1 O2; the negative electrode active material is graphite; the electrolyte is LiPF6; the separator is a 12μm PP membrane. The positive electrode, negative electrode, electrolyte, and separator are assembled to obtain a 2Ah lithium-ion battery.

[0126] Among them, LiNi 0.8 Co 0.1 Mn 0.1 The median particle size of O2 is 8 μm.

[0127] Comparative Example 2

[0128] In this embodiment: the positive electrode active material is 100% LiMn. 0.6 Fe 0.4 PO4; the negative electrode active material is graphite; the electrolyte is LiPF6; the separator is a 12μm PP membrane. The positive electrode, negative electrode, electrolyte, and separator are assembled to obtain a 2Ah lithium-ion battery.

[0129] Among them, LiMn 0.6 Fe 0.4 PO4 has a hollow spherical structure, while LiMn 0.6 Fe 0.4 The median particle size of PO4 is 1.5 μm, and the specific surface area is 15 m². 2 / g, tap density is 0.7g / cm³ 3 .

[0130] Comparative Example 3

[0131] In this embodiment: the positive electrode active material in the positive electrode sheet includes 50% LiMn. 0.6 Fe 0.4 PO4 and 50% LiNi 0.8 Co 0.1 Mn 0.1 O2; the negative electrode active material is graphite; the electrolyte is LiPF6; the separator is a 12μm PP membrane. The positive electrode, negative electrode, electrolyte, and separator are assembled to obtain a 2Ah lithium-ion battery.

[0132] Among them, LiMn0.6 Fe 0.4 PO4 has a hollow spherical structure, while LiMn 0.6 Fe 0.4 The median particle size of PO4 is 1.5 μm, and the specific surface area is 15 m². 2 / g, tap density is 0.7g / cm³ 3 LiNi 0.8 Co 0.1 Mn 0.1 The median particle size of O2 is 8 μm.

[0133] Comparative Example 4

[0134] In this embodiment: the positive electrode active material in the positive electrode sheet includes 70% LiMn. 0.6 Fe 0.4 PO4 and 30% LiNi 0.8 Co 0.1 Mn 0.1 O2; the negative electrode active material is graphite; the electrolyte is LiPF6; the separator is a 12μm PP membrane. The positive electrode, negative electrode, electrolyte, and separator are assembled to obtain a 2Ah lithium-ion battery.

[0135] Among them, LiMn 0.6 Fe 0.4 PO4 has a hollow spherical structure, while LiMn 0.6 Fe 0.4 The median particle size of PO4 is 1.5 μm, and the specific surface area is 15 m². 2 / g, tap density is 0.7g / cm³ 3 LiNi 0.8 Co 0.1 Mn 0.1 The median particle size of O2 is 8 μm.

[0136] The batteries assembled in Examples 1-6 and Comparative Examples 1-4 were tested for 0.1C specific capacity, 3C capacity retention, and energy density. The results are shown in Table 1.

[0137] Table 1. Comparison of battery performance test results in different embodiments and comparative examples.

[0138]

[0139] As shown in Table 1, in Comparative Example 1, the positive electrode active material is 100% ternary material, and the 3C capacity retention rate is 57.82% (as shown in Figure 2). In Comparative Example 2, the positive electrode active material is 100% lithium manganese iron phosphate, and the 3C capacity retention rate is 92.96% (as shown in Figure 3). The rate performance of the battery in Comparative Example 2 is better than that in Comparative Example 1, mainly because lithium manganese iron phosphate has a hollow spherical structure and a small particle size, which shortens the lithium extraction and insertion path during charging and discharging, thus improving the rate performance.

[0140] Comparing Examples 1-6 with Comparative Examples 1-4, it was found that mixing a certain proportion of lithium manganese iron phosphate into the positive electrode active material can improve its rate performance on the basis of using ternary materials alone. Moreover, as the mixing proportion of lithium manganese iron phosphate increases, the rate performance of the battery gradually increases. When the lithium manganese iron phosphate blending ratio is 10%, the 3C capacity retention rate of the battery is 62.30% (Example 1, as shown in Figure 4), which is 4.5% higher than that of a battery using 100% ternary materials; when the lithium manganese iron phosphate blending ratio is 20%, the 3C capacity retention rate of the battery is 68.45% (Example 2), which is 10.6% higher than that of a battery using 100% ternary materials; when the lithium manganese iron phosphate blending ratio is 30%, the 3C capacity retention rate of the battery is 72.18% (Example 3), which is 14.4% higher than that of a battery using 100% ternary materials; when the lithium manganese iron phosphate blending ratio is 40%, the 3C capacity retention rate of the battery is 76.50% (Example 4), which is 18.7% higher than that of a battery using 100% ternary materials; when the lithium manganese iron phosphate blending ratio is 5%, the 3C capacity retention rate of the battery is 63%. The 3C capacity retention rate was 79.68% (Example 5) when the lithium manganese iron phosphate (LFP) content was 45%, which is 5.7% higher than that of a battery using 100% LFP. When the positive electrode active material was 100% LFP, the 3C capacity retention rate was 92.96% (Comparative Example 2), which is 35.1% higher than that of a battery using 100% LFP. When the LFP content was 50%, the 3C capacity retention rate was 80.82% (Comparative Example 3), which is 23.0% higher than that of a battery using 100% LFP. When the LFP content was 70%, the 3C capacity retention rate was 89.10% (Comparative Example 4), which is 31.3% higher than that of a battery using 100% LFP.

[0141] However, the actual specific capacity of the battery using 100% lithium manganese iron phosphate was 145 mAh / g (Comparative Example 2), which is 52 mAh / g lower than the actual specific capacity of 197 mAh / g (Comparative Example 1) when using 100% ternary materials. As the proportion of lithium manganese iron phosphate increases, the actual specific capacity of the battery will decrease. When the lithium manganese iron phosphate blending amount is 10%, the 0.1C specific capacity of the battery is 192 mAh / g (Example 1), which is 5 mAh / g lower than the specific capacity of the battery using 100% ternary materials; when the lithium manganese iron phosphate blending amount is 20%, the 0.1C specific capacity of the battery is 186 mAh / g (Example 2), which is 11 mAh / g lower than the specific capacity of the battery using 100% ternary materials; when the lithium manganese iron phosphate blending amount is 30%, the 0.1C specific capacity of the battery is 180 mAh / g (Example 3), which is 17 mAh / g lower than the specific capacity of the battery using 100% ternary materials; when the lithium manganese iron phosphate blending amount is 40%, the 0.1C specific capacity of the battery is 171 mAh / g (Example 4), which is 26 mAh / g lower than the specific capacity of the battery using 100% ternary materials. When the lithium manganese iron phosphate blending amount is 5%, the 0.1C specific capacity of the battery is 191 mAh / g (Example 5), which is 6 mAh / g lower than the specific capacity of the battery using 100% ternary materials; when the lithium manganese iron phosphate blending amount is 45%, the 0.1C specific capacity of the battery is 169 mAh / g (Example 6), which is 28 mAh / g lower than the specific capacity of the battery using 100% ternary materials; when the lithium manganese iron phosphate blending ratio is 50%, the 0.1C specific capacity of the battery is 167 mAh / g (Comparative Example 3), which is 30 mAh / g lower than the specific capacity of the battery using 100% ternary materials; when the lithium manganese iron phosphate blending ratio is 70%, the 0.1C specific capacity of the battery is 158 mAh / g (Comparative Example 4), which is 39 mAh / g lower than the specific capacity of the battery using 100% ternary materials.

[0142] Furthermore, incorporating a certain proportion of lithium manganese iron phosphate into the positive electrode active material can improve the energy density of the battery compared to using lithium manganese iron phosphate alone. Moreover, the energy density gradually increases with the increase in the proportion of ternary materials. When the proportion of lithium manganese iron phosphate is 10% and the proportion of ternary materials is 90%, the energy density of the battery is 262 Wh / kg (Example 1), which is 62 Wh / kg higher than that of a battery using only lithium manganese iron phosphate. The energy density of the battery was 256 Wh / kg when the lithium iron phosphate blending ratio was 20% and the ternary material blending ratio was 80% (Example 2), which is 56 Wh / kg higher than the battery using only lithium iron phosphate; when the lithium iron phosphate blending ratio was 30% and the ternary material blending ratio was 70%, the energy density of the battery was 250 Wh / kg (Example 3), which is 50 Wh / kg higher than the battery using only lithium iron phosphate; when the lithium iron phosphate blending ratio was 40% and the ternary material blending ratio was 60%, the energy density of the battery was 243 Wh / kg (Example 4), which is 43 Wh / kg higher than the battery using only lithium iron phosphate; when the lithium iron phosphate blending ratio was 5% and the ternary material blending ratio was 95%, the energy density of the battery was... The energy density of the battery was 259 Wh / kg (Example 5), which is 59 Wh / kg higher than that of the battery using only lithium manganese iron phosphate; when the blending ratio of lithium manganese iron phosphate was 45% and the blending ratio of ternary material was 55%, the energy density of the battery was 241 Wh / kg (Example 6), which is 41 Wh / kg higher than that of the battery using only lithium manganese iron phosphate; when the blending ratio of lithium manganese iron phosphate was 50% and the blending ratio of ternary material was 50%, the energy density of the battery was 237 Wh / kg (Comparative Example 3), which is 37 Wh / kg higher than that of the battery using only lithium manganese iron phosphate; when the blending ratio of lithium manganese iron phosphate was 70% and the blending ratio of ternary material was 30%, the energy density of the battery was 233 Wh / kg (Comparative Example 4), which is 33 Wh / kg higher than that of the battery using only lithium manganese iron phosphate.

[0143] In addition, lithium manganese iron phosphate has an olivine structure and has better cycle performance. In Example 1, by mixing 10% lithium manganese iron phosphate into the positive electrode active material, the number of cycles can reach more than 2000 cycles (as shown in Figure 5).

[0144] In summary, this application, by including both ternary materials and hollow spherical lithium manganese iron phosphate as the positive electrode active material, can save costs by doping hollow spherical lithium manganese iron phosphate into the ternary material and controlling the doping ratio of lithium manganese iron phosphate in the positive electrode active material within the range of greater than 0% and less than 50%, while simultaneously taking into account rate performance, cycle performance, and energy density, thus ensuring comprehensive electrochemical performance.

Claims

1. A positive electrode active material, comprising a ternary material and lithium manganese iron phosphate; in, The mass of the lithium manganese iron phosphate is A, and the total mass of the ternary material and the lithium manganese iron phosphate is B, satisfying: 0 < A / B < 50%; The lithium manganese iron phosphate has a hollow spherical structure, and the median particle size of the lithium manganese iron phosphate is 0.5μm-3μm.

2. The positive electrode active material according to claim 1, wherein, The specific surface area of ​​the lithium manganese iron phosphate is 11 m². 2 / g-21m 2 / g; 3. The positive electrode active material according to claim 1 or 2, wherein, The tap density of the lithium manganese iron phosphate is 0.3 g / cm³. 3 -0.8g / cm 3 .

4. The positive electrode active material according to any one of claims 1-3, wherein, The molecular formula of the ternary material is LiNi. a Co b Mn c M d O2; where a+b+c+d=1, a≥0.5, b≤0.3, 0≤d≤0.05; M is selected from at least one of Zr, Sr, W, B, Nb, Al, Mg and Ti.

5. The positive electrode active material according to any one of claims 1-4, wherein, The median particle size of the ternary material is 3 μm - 10 μm.

6. The positive electrode active material according to any one of claims 1-5, wherein, The lithium manganese iron phosphate includes a lithium manganese iron phosphate body and a carbon coating layer covering the lithium manganese iron phosphate body.

7. A method for preparing a positive electrode active material, used to prepare the positive electrode active material as described in any one of claims 1-6, comprising: We provide ternary materials and lithium manganese iron phosphate; The ternary material and the lithium manganese iron phosphate are mixed in a certain proportion to obtain the positive electrode active material.

8. The method for preparing the positive electrode active material according to claim 7, wherein, Prior to providing the ternary material and lithium manganese iron phosphate, the method also includes: Prepare the lithium manganese iron phosphate; The preparation of the lithium manganese iron phosphate includes: A phosphoric acid solution was added to a lithium source solution to carry out a reaction, resulting in a hollow spherical lithium phosphate precursor. Ferrous salt, manganese salt and lithium phosphate precursor are dispersed in a solvent, and after reaction, lithium manganese iron phosphate precursor is formed. The lithium manganese iron phosphate precursor was sintered for the first time to obtain lithium manganese iron phosphate.

9. The method for preparing the positive electrode active material according to claim 8, wherein, The step of adding a phosphoric acid solution to a lithium source solution and reacting to obtain a hollow spherical lithium phosphate precursor includes: The phosphoric acid solution was added to the lithium hydroxide solution, stirred at room temperature for 2-4 hours, and filtered to obtain the first filtrate. After drying the first filter material, a hollow spherical lithium phosphate precursor is obtained.

10. The method for preparing the positive electrode active material according to claim 8 or 9, wherein, The molar ratio of the ferrous salt to the manganese salt is 1:9-9:1; 11. The method for preparing the positive electrode active material according to any one of claims 8-10, wherein, The sum of the amounts of the ferrous salt and the manganese salt is in a 1:1 ratio to the amount of the lithium phosphate precursor.

12. The method for preparing the positive electrode active material according to any one of claims 8-11, wherein, The first sintering of the lithium manganese iron phosphate precursor includes: The lithium manganese iron phosphate precursor was sintered for 5-8 hours in a protective atmosphere at a temperature of 150℃-200℃.

13. The method for preparing the positive electrode active material according to any one of claims 8-12, wherein, After sintering the lithium manganese iron phosphate precursor, the process further includes: The sintered lithium manganese iron phosphate precursor is mixed with a carbon source and a first additive to obtain a coating material. The coating material is sintered a second time to obtain the lithium manganese iron phosphate with a carbon coating layer.

14. The method for preparing the positive electrode active material according to claim 13, wherein, In the coating material, the carbon source accounts for 10%-20% by mass; 15. The method for preparing the positive electrode active material according to claim 13 or 14, wherein, In the coating material, the first additive contains at least one of Mg, Ti, Nb, Nd, Zr and Al, and the addition ratio of the first additive is 0ppm-6000ppm.

16. The method for preparing the positive electrode active material according to any one of claims 13-15, wherein, The second sintering of the coating material includes: The coating material is sintered at a temperature of 550℃-750℃ for 5h-8h.

17. The method for preparing the positive electrode active material according to any one of claims 7-16, wherein, Prior to providing the ternary material and lithium manganese iron phosphate, the method also includes: Prepare the ternary material; The preparation of the ternary material includes: The ternary material precursor, lithium carbonate, and the second additive are mixed to obtain the first mixture; Under an oxygen-containing atmosphere, the first mixture is subjected to a third sintering to obtain the first sintered material; The first sintered material is crushed to obtain the ternary material.

18. The method for preparing the positive electrode active material according to claim 17, wherein, The third sintering of the first mixture under an oxygen-containing atmosphere includes: The first mixture was sintered in a sintering furnace under an atmosphere with an oxygen concentration of ≥95%. During the sintering process, the sintering furnace is first heated from room temperature to 450℃-600℃ at a heating rate of 5℃ / min and held for 3h-5h. Then, the sintering furnace is heated to 700℃-900℃ at a heating rate of 5℃ / min and held for 6h-10h.

19. A positive electrode sheet, comprising a positive electrode foil and a positive electrode active layer coated on the positive electrode foil; in, The positive electrode active layer comprises the positive electrode active material as described in any one of claims 1-6; And / or, the positive electrode active material prepared by the method for preparing the positive electrode active material according to any one of claims 7-18.

20. A battery comprising the positive electrode as claimed in claim 19.

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