Positive electrode active material, preparation method thereof and battery

Abstract

The invention relates to a positive active material, a preparation method thereof and a battery, and belongs to the technical field of batteries. V ions in the lithium ferrovanadium phosphate active material enter LFP crystal lattices through doping to replace Fe < 2 + > sites to form lattice defects, and in order to maintain electric neutrality, the system spontaneously generates additional free electrons, so that the electronic conductivity is increased, and the rate performance of the lithium ferrovanadium phosphate active material applied to a battery is facilitated. And meanwhile, on the basis of doping the V element, the mass content of iron phosphide in the lithium ferrovanadium phosphate active material is controlled to be less than or equal to 800ppb, so that the probability of side reaction with an electrolyte when the lithium ferrovanadium phosphate active material is applied to a battery can be reduced, and the cycle performance is facilitated. And the lithium iron vanadium phosphate active material has two particles with specific volume median particle sizes, so that a relatively good particle size grading relationship can be formed, the lithium iron vanadium phosphate active material has relatively high compaction density, and the volume energy density of the lithium iron vanadium phosphate active material when the lithium iron vanadium phosphate active material is applied to a battery is facilitated.

Description

Technical Field

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

[0002] Lithium vanadium iron phosphate (LFVP) cathode active materials have become one of the most important cathode materials in the fields of power batteries and energy storage batteries due to their excellent safety, long cycle life, and low cost. However, current LFVP cathode active materials struggle to simultaneously achieve high electronic conductivity, low impurities, and high compaction density. Summary of the Invention

[0003] This application provides a positive electrode active material that can simultaneously achieve high electronic conductivity, low impurities, and high compaction density.

[0004] In a first aspect, embodiments of this application provide a positive electrode active material, which includes a lithium vanadium iron phosphate active material. The molar ratio of V element and non-lithium site metal element in the lithium vanadium iron phosphate active material is 0.001~0.005:1. The mass content of iron phosphide in the lithium vanadium iron phosphate active material is ≤800ppb. The lithium vanadium iron phosphate active material includes a first particle and a second particle. The median volumetric particle size of the first particle is ≤2.8μm and the median volumetric particle size of the second particle is ≤0.8μm.

[0005] In the technical solution of this application embodiment, the V ions in the lithium vanadium iron phosphate active material are introduced into the LFP lattice to replace Fe ions through doping. 2+ The presence of sites and lattice defects allows the system to spontaneously generate additional free electrons to maintain electron neutrality, thereby increasing its electronic conductivity and improving its rate performance in batteries. Simultaneously, by controlling the iron phosphide content in the lithium vanadium iron phosphate active material to ≤800 ppb while doping with V, the probability of side reactions with the electrolyte during battery application is reduced, improving cycle performance. Furthermore, this lithium vanadium iron phosphate active material has two specific median particle sizes, forming a good particle size distribution and resulting in high compaction density, which is beneficial for its volumetric energy density in batteries. Ultimately, this lithium vanadium iron phosphate active material achieves a balance of high electronic conductivity, low impurities, and high compaction density, enabling batteries using it as the positive electrode active material to exhibit good rate performance, cycle performance, and volumetric energy density.

[0006] As an optional implementation method, lithium vanadium iron phosphate active materials include Li a Fe 1-x-y V x M yPO4, wherein 0.9≤a≤1.1, 0.002≤x≤0.01, 0≤y≤0.098, 0.002≤x+y≤0.01, and M includes at least one of Ti, Sn, Sb, Mo, and Bi.

[0007] In the above implementation process, Li a Fe 1-x-y V x M y PO4 has good electronic conductivity and ion diffusion rate, which is beneficial to its rate performance when applied to batteries.

[0008] As an optional implementation, the compaction density of the vanadium iron phosphate active material at 3t is ≥2.7g / cm³. 3 .

[0009] In the above implementation process, the compaction density of the vanadium iron phosphate active material at 3t is controlled to be ≥2.7g / cm³. 3 This allows the battery to have a good volumetric energy density when it is applied to a battery.

[0010] As an optional implementation, the ratio of the number of the first particle to the number of the second particle is 1:1 to 6.

[0011] In the above implementation process, by controlling the first and second particles within a suitable quantity range, the active material of lithium vanadium iron phosphate can have a higher compaction density.

[0012] As an optional implementation, the ratio of the first particle to the second particle is 1:3 to 6.

[0013] As an optional implementation, the lithium vanadium iron phosphate active material has a core-shell structure, wherein the core of the core-shell structure includes the active material body, and the active material body includes Li a Fe 1-x-y V x M y PO4, wherein 0.9≤a≤1.1, 0.002≤x≤0.01, 0≤y≤0.098, 0.002≤x+y≤0.01, M includes at least one of Ti, Sn, Sb, Mo, and Bi, the shell includes a first shell and a second shell, the first shell is disposed between the core and the second shell, the material of the first shell includes carbon materials, and the electronic conductivity of the second shell is ≥1×10⁻⁶. 3 S / cm, ionic conductivity of the second shell ≥ 8 × 10 -4 S / cm.

[0014] In the above implementation process, by coating the core active material with a carbon material with good electronic conductivity as the first shell layer and a second shell layer with good electronic and ionic conductivity, the entire lithium vanadium iron phosphate active material has good electronic and ionic conductivity, which is beneficial to its rate performance when applied to batteries.

[0015] As an optional implementation, the material of the second shell includes a highly ionicly conductive material and a highly conductive electronic material, wherein the ionic conductivity of the highly ionicly conductive material is ≥1×10⁻⁶. -3 S / cm, electronic conductivity of high-conductivity electronic materials ≥1×10 4 S / cm.

[0016] In the above implementation process, high ion conductivity materials have good ion conduction performance and high electronic conduction performance. Combining high ion conductivity materials and high electronic conduction materials to form a second shell can help improve the electronic conductivity and ion conductivity of the entire lithium vanadium iron phosphate active material, thereby improving its rate performance when applied to batteries.

[0017] As an optional implementation, the mass ratio of highly conductive ion material to highly conductive electronic material is 80~90:10~20.

[0018] In the above implementation process, by controlling the mass ratio of high ion conductivity material to high electronic conductivity material to be 80~90:10~20, the second shell layer can simultaneously possess electronic conductivity and ion conductivity, which is beneficial to improving the electronic conductivity and ion conductivity of the entire lithium vanadium iron phosphate active material.

[0019] As an alternative implementation, the high-conductivity ion material includes at least one of garnet-type solid electrolyte, NASICON-type solid electrolyte, or perovskite-type solid electrolyte.

[0020] In the above implementation process, high ion-conducting materials such as garnet-type solid electrolytes, NASICON-type solid electrolytes, or perovskite-type solid electrolytes have good ion conduction capabilities, which is beneficial to improving the ion conduction performance of the second shell.

[0021] As an alternative implementation, the garnet-type solid electrolyte includes lithium lanthanum zirconium oxide (Li7La3Zr2O) 12 (abbreviated as LLZO); NASICON-type solid electrolytes include lithium aluminum titanium phosphate (LiTi) 1.3 Al 0.3 Ti 1.7 (PO4)3, abbreviated as LATP, lithium titanium germanium phosphate (Li 1.3 Al 0.3 Ge 1.7(PO4)3, abbreviated as LAGP) or lithium zirconium silicon phosphorus oxide (Li3Zr2Si2PO) 12 At least one of the following: (abbreviated as LZSP); perovskite solid electrolytes include lithium lanthanum titanium oxide (LLTO).

[0022] In the above implementation process, solid electrolyte materials such as lithium lanthanum zirconium oxide, lithium titanium aluminum phosphate, lithium titanium germanium phosphate, lithium zirconium silicon phosphorus oxide, and lithium lanthanum titanium oxide have good ion conduction capabilities, which is beneficial to improving the ion conduction performance of the second shell.

[0023] As an optional implementation, the highly conductive electronic material includes TaN. x , where x < 1 in at least one of them.

[0024] During the above implementation process, TaN x Highly conductive electronic materials have good electronic conductivity, which is beneficial for improving the electronic conductivity of the second shell.

[0025] As an optional implementation, the thickness of the first shell layer is 3nm to 5nm.

[0026] In the above implementation process, by controlling the thickness of the first shell layer to be 3nm~5nm, the active material of lithium vanadium iron phosphate has both good electronic conductivity and high volumetric capacity.

[0027] As an optional implementation, the thickness of the second shell is 3nm~4nm.

[0028] In the above implementation process, by controlling the thickness of the second shell layer to be 3nm~4nm, the active material of lithium vanadium iron phosphate has good electronic conductivity, ionic conductivity, performance stability and high volumetric capacity.

[0029] Secondly, embodiments of this application provide a method for preparing a positive electrode active material, the method comprising: An iron source, a lithium source, a phosphorus source, and a first shell source are mixed to obtain a sintering precursor; the iron source includes at least two types of iron sources. The sintering precursor is subjected to a first sintering to obtain an intermediate product; the first sintering includes a first-stage sintering and a second-stage sintering; the holding temperature of the first-stage sintering is 300℃~450℃, and the gas pressure of the second-stage sintering is 1MPa~5MPa. The intermediate product and additives are mixed and subjected to a second sintering to obtain the positive electrode active material. The additives include a first additive and a second additive. The first additive contains chlorine and the second additive contains vanadium. The molar ratio of vanadium to intermediate product in the second additive is 0.001~0.005:1.

[0030] In the technical solution of this application embodiment, by using at least two iron sources to form sintering precursors, particles of two different sizes can be sintered, forming a particle size distribution that is beneficial for improving the compaction density of the positive electrode active material. Simultaneously, during the first sintering, a stage of sintering is performed at a low temperature to remove volatile components from the sintering precursors, reducing the probability of them damaging the material structure during subsequent sintering. Then, a second stage of sintering is performed under high pressure, allowing the sintering precursors to come into close contact, promoting grain growth and fusion, and forming intermediate products with suitable particle sizes. This results in the final lithium iron phosphate vanadium phosphate active material having particles of two suitable sizes, forming a good gradation relationship and giving it a better compaction density. Furthermore, during the second sintering process, the intermediate products and vanadium chloride are sintered together. Vanadium chloride can react with iron phosphide in the intermediate products to form volatile chlorides, reducing the amount of iron phosphide. The vanadium in the vanadium chloride can be incorporated into the material, improving its electronic conductivity and ion diffusion rate.

[0031] As an alternative implementation, the iron source includes at least two of ferric phosphate, ferrous oxalate, ferric oxide, ferric hydroxide, or iron powder.

[0032] In the above implementation process, by selecting at least two of the following as iron sources: ferric phosphate, ferrous oxalate, ferric oxide, ferric hydroxide, or iron powder, particles with two median volume sizes can be sintered to form particles with particle size distribution, which is beneficial to improving the compaction density of the positive electrode active material.

[0033] As an optional implementation, the lithium source includes at least one of lithium carbonate, lithium hydroxide, or lithium acetate.

[0034] As an optional implementation, the phosphorus source includes at least one of ammonium dihydrogen phosphate or phosphoric acid.

[0035] As an optional implementation, the first shell source includes a carbon source, which includes at least one of glucose, fructose, sucrose, citric acid, tartaric acid, ascorbic acid, or polyethylene glycol.

[0036] In the above implementation process, the first shell layer is formed by using glucose, fructose, sucrose, citric acid, tartaric acid, ascorbic acid or polyethylene glycol as carbon sources. The raw materials are easy to obtain and the preparation process is relatively simple, which helps to control the manufacturing cost of lithium iron phosphate active materials and thus facilitates their industrial production.

[0037] As an optional implementation, the mass of the first shell source is 5% to 12% of the sum of the masses of the iron source, lithium source and phosphorus source.

[0038] In the above implementation process, the appropriate proportion of the first shell source can form a first shell of suitable thickness, thereby enabling the lithium vanadium iron phosphate active material to have both good electronic conductivity and high volumetric capacity.

[0039] As an optional implementation, the median particle size of the sintering precursor is 300 nm to 450 nm.

[0040] In the above-mentioned process, sintering precursors with appropriate particle size can facilitate the formation of lithium vanadium iron phosphate active materials with appropriate particle size, thereby increasing the compaction density of lithium vanadium iron phosphate active materials.

[0041] As an optional implementation, the heating rate of a sintering stage is 1℃ / min to 3℃ / min.

[0042] In the above-mentioned process, a suitable sintering heating rate can help form active materials of vanadium iron phosphate with good compaction density.

[0043] As an optional implementation method, the holding time for one sintering stage is 1h to 3h.

[0044] In the above implementation process, a suitable sintering and holding time can form active materials with good compaction density, such as vanadium iron phosphate, with less energy consumption and lower time cost.

[0045] As an optional implementation, the sintering atmosphere is at least one of nitrogen atmosphere or inert gas atmosphere.

[0046] In the above implementation process, using a nitrogen atmosphere or an inert gas atmosphere as the sintering atmosphere for one stage can help reduce the probability of side reactions occurring throughout the sintering process.

[0047] As an optional implementation, the gas pressure during the first sintering stage is 0.08MPa~0.12MPa.

[0048] In the above implementation process, sintering near atmospheric pressure is beneficial for the discharge of volatile components in the sintering precursor, reducing the probability of them damaging the material structure during subsequent sintering.

[0049] As an optional implementation method, the holding temperature for the two-stage sintering is 700℃~840℃.

[0050] In the above implementation process, a suitable two-stage sintering temperature is beneficial for the full formation of lithium vanadium iron phosphate active materials.

[0051] As an optional implementation method, the heating rate of the two-stage sintering is 3℃ / min to 5℃ / min.

[0052] In the above implementation process, a suitable two-stage sintering heating rate can help form active materials of vanadium iron phosphate with good compaction density.

[0053] As an optional implementation method, the holding time for the two-stage sintering is 8h~12h.

[0054] In the above implementation process, a suitable second-stage sintering and holding time can form vanadium iron phosphate active materials with good compaction density with less energy consumption and lower time cost.

[0055] As an optional implementation, the first additive includes at least one of vanadium chloride, titanium chloride, tin chloride, antimony chloride, molybdenum chloride, or bismuth chloride. In the above-mentioned process, compounds containing chlorine, such as vanadium chloride, titanium chloride, tin chloride, antimony chloride, molybdenum chloride, or bismuth chloride, can react with iron phosphide in the intermediate product to form volatile chlorides, thereby reducing the amount of iron phosphide. Furthermore, the metal elements contained therein can be incorporated into the material, thereby improving its electronic conductivity and ion diffusion rate.

[0056] As an optional implementation, the second additive includes vanadium chloride.

[0057] In the above-mentioned process, vanadium-containing compounds such as vanadium chloride can dope vanadium into the material, thereby improving its electronic conductivity and ion diffusion rate.

[0058] As an optional implementation, the holding temperature for the second sintering is 600℃~750℃.

[0059] In the above process, a suitable second sintering holding temperature can effectively remove iron phosphide from the intermediate product, while allowing the metal elements in the chloride compound to be incorporated into the material, thereby improving the electronic conductivity and ion diffusion rate.

[0060] As an optional implementation, the heating rate of the second sintering is 2℃ / min to 5℃ / min.

[0061] In the above implementation process, a suitable two-stage sintering heating rate can help remove iron phosphide from the intermediate product and facilitate the doping of metal elements from chlorine compounds into the material, thereby improving electronic conductivity and ion diffusion rate.

[0062] As an optional implementation method, the holding time for the second sintering is 2h to 8h.

[0063] In the above implementation process, a suitable two-stage sintering holding time can remove iron phosphide from the intermediate product and complete the doping of metal elements in the chloride compound with less energy consumption and lower time cost.

[0064] As an optional implementation, prior to the second sintering, the second shell source, intermediate product, and additives are mixed. The material of the second shell includes a highly ionicly conductive material and a highly conductive electronic material, wherein the ionic conductivity of the highly ionicly conductive material is ≥1×10⁻⁶. -3 S / cm, electronic conductivity of high-conductivity electronic materials ≥1×10 4 S / cm.

[0065] In the above implementation process, high-conductivity ion materials have good ion conduction performance, and high-conductivity electronic materials have good electronic conduction performance. Combining high-conductivity ion materials and high-conductivity electronic materials to form a second shell can help improve the electronic and ion conductivity of the entire lithium vanadium iron phosphate active material, thereby improving its rate performance when applied to batteries.

[0066] As an optional implementation, the mass ratio of the second shell source to the intermediate product is 1 to 3:100.

[0067] In the above implementation process, the appropriate proportion of the second shell source can form a second shell of suitable thickness, thereby enabling the active materials of vanadium iron phosphate to have good electronic conductivity, ionic conductivity, performance stability and high volumetric capacity.

[0068] Thirdly, this application provides a battery, which includes a positive electrode sheet, a positive electrode sheet including a positive electrode active material layer, a positive electrode active material layer including a positive electrode active material, and the positive electrode active material including the positive electrode active material provided in the first aspect or the positive electrode active material prepared by the preparation method of the positive electrode active material provided in the second aspect. Attached Figure Description

[0069] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0070] Figure 1 This is a flowchart illustrating the methods provided in some embodiments of this application.

[0071] Figure 2 This is a SEM image of the positive electrode active material provided in Example 1 of this application.

[0072] Figure 3 This is a TEM image of the positive electrode active material provided in Example 1 of this application.

[0073] Figure 4This is a SEM image of the positive electrode active material used in Comparative Example 1 of this application. Detailed Implementation

[0074] The present application is hereby disclosed in detail with appropriate reference to the accompanying drawings. However, some unnecessary details may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of essentially the same structures may be omitted. This is to avoid making the following description unnecessarily lengthy and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand the present application and are not intended to limit the subject matter of the claims.

[0075] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60~120 and 80~110 are listed for a specific parameter, it is also expected that ranges of 60~110 and 80~120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1~3, 1~4, 1~5, 2~3, 2~4, and 2~5. In this application, unless otherwise stated, the numerical range "a~b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0~5" indicates that all real numbers between "0~5" have been listed in this article; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0076] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0077] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0078] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, if a method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, if a method may also include step (c), it means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc. In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined. In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0079] In the description of the embodiments of this application, the term "multiple" refers to two or more (including two), similarly, "multiple sets" refers to two or more (including two sets), and "multiple pieces" refers to two or more (including two pieces).

[0080] Currently, judging from market trends, the application of batteries is becoming increasingly widespread. Batteries are not only used in energy storage power systems such as hydropower, thermal power, wind power, and solar power plants, but also widely used in electric vehicles such as electric bicycles, electric motorcycles, and electric cars, as well as in military equipment and aerospace. With the continuous expansion of the application areas of power batteries, the market demand for them is also constantly increasing.

[0081] Among the positive electrode active materials for batteries, lithium iron phosphate (LiFePO4, LFP) has become one of the most important positive electrode materials in the fields of power batteries and energy storage batteries due to its excellent safety, long cycle life, and low cost. Its inherent drawback, namely its poor electronic and ionic conductivity, affects its rate performance.

[0082] Doping with vanadium iron phosphate (V) can significantly improve the electronic and ionic conductivity of lithium iron phosphate cathode active materials. However, V-doped LFP cathode active materials tend to have more uniform particle size, which negatively impacts their compaction density. Furthermore, current methods for controlling the compaction density of LFP cathode active materials often lead to an increase in impurities that favor iron phosphide. Therefore, current LFP cathode active materials struggle to simultaneously achieve high electronic conductivity, low impurities, and high compaction density.

[0083] To improve the performance of lithium vanadium iron phosphate cathode active materials, this application provides a cathode active material that can balance high electronic conductivity, low impurities, and high compaction density.

[0084] This application provides a positive electrode active material, including a lithium vanadium iron phosphate (LFP) active material. The molar ratio of V to non-lithium site metal elements in the LFP active material is 0.001~0.005:1. The mass content of iron phosphide in the LFP active material is ≤800 ppb, and the compaction density of the LFP active material at 3t is ≥2.7 g / cm³. 3 The active material of lithium vanadium iron phosphate includes a first particle and a second particle, wherein 0.8μm < the median volume diameter of the first particle ≤ 2.8μm and 0.2μm ≤ the median volume diameter of the second particle ≤ 0.8μm.

[0085] Among them, lithium vanadium iron phosphate active materials refer to modified or unmodified lithium vanadium iron phosphate active materials, and the modification includes element doping or coating.

[0086] The core and shell composition of lithium vanadium iron phosphate active materials can be determined by inductively coupled plasma atomic emission spectrometry (ICP) combined with SEM and EDS tests.

[0087] The content of iron phosphide in lithium iron phosphate active materials can be tested by utilizing the relatively active chemical properties of Fe2P, which can be dissolved by dilute acids to generate ferrous ions (Fe2P). + LiFePO4 is very stable under these conditions, exhibiting almost no solubility. The active material, vanadium iron phosphate, was immersed in dilute acid, then filtered to obtain a solution. The Fe content was determined using ICP, and the Fe2P content was calculated.

[0088] The median volumetric particle size of the first and second particles in lithium vanadium iron phosphate active materials is the Dv50 of the first and second particles. Dv50 represents the particle size corresponding to 50% of the cumulative amount in the volumetric particle size distribution chart. The volumetric particle size distribution chart, also known as the differential particle size distribution chart, is a curve plotted with particle size on the x-axis and the differential distribution of particle size at different dimensions on the y-axis. It can accurately reflect the particle size distribution characteristics of the material. A laser particle size analyzer can be used to determine the volumetric particle size distribution of the material and plot the interval particle size distribution curve. When measuring the median particle size of the positive active material in the positive active material layer of the positive electrode sheet, the positive active material layer can be removed, immersed in the solvent NMP, and the binder in the positive active material layer can be washed out to obtain the powder material of the positive active material layer. After drying the powder material, it can be detected by a laser particle size analyzer of model Mastersizer3000 to obtain the cumulative particle size distribution map. The Dv50 of the first and second particles in the lithium vanadium iron phosphate active material can be obtained from the peaks in the cumulative particle size distribution map.

[0089] In this positive electrode active material, the V ions in the lithium vanadium iron phosphate active material are introduced into the LFP lattice to replace Fe ions. 2+ The presence of lattice defects at specific sites allows the system to spontaneously generate additional free electrons to maintain electrical neutrality, thereby increasing its electronic conductivity and improving its rate performance in batteries. Furthermore, by controlling the iron phosphide content in the lithium vanadium iron phosphate active material to ≤800 ppb while doping with V, the probability of side reactions with the electrolyte during battery application is reduced, improving cycle performance. This lithium vanadium iron phosphate active material also features two specific median volumetric particle sizes, forming a favorable particle size distribution. The first particle provides skeletal support, while the second fills the gaps between the first particles. This combination results in a high compaction density, which is beneficial for its volumetric energy density in batteries. Ultimately, this lithium vanadium iron phosphate active material achieves a balance of high electronic conductivity, low impurities, and high compaction density, enabling batteries using it as a cathode active material to exhibit good rate performance, cycle performance, and volumetric energy density.

[0090] For example, the molar ratio of V element and non-lithium site metal element in lithium vanadium iron phosphate active materials can be 0.001:1, 0.002:1, 0.003:1, 0.004:1, 0.005:1, etc., or any value in the range of 0.001 to 0.005:1. The iron phosphide content in lithium vanadium iron phosphate active materials can be 800 ppb, 750 ppb, 700 ppb, 650 ppb, 600 ppb, 550 ppb, 500 ppb, 450 ppb, 400 ppb, 350 ppb, 300 ppb, 250 ppb, 200 ppb, 150 ppb, 100 ppb, 50 ppb, 49 ppb, 48 ppb, 47 ppb, 46 ppb, 45 ppb, 44 ppb, 43 ppb, 42 ppb, 41 ppb, 40 ppb, 39 ppb, 38 ppb, 37 ppb, 36 ppb, 35 ppb, etc., or any value within the range of ≤800 ppb. The median volumetric diameter of the first particle can be 1.1 μm, 1.2 μm, 1.4 μm, 1.6 μm, 1.8 μm, 2 μm, 2.2 μm, 2.4 μm, 2.6 μm, 2.8 μm, 3 μm, etc., or any value within the range of >1 μm to 3 μm. The median volumetric diameter of the second particle can be 0.2 μm, 0.4 μm, 0.6 μm, 0.8 μm, 1 μm, etc., or any value within the range of 0.2 μm to 1 μm.

[0091] In some embodiments, lithium vanadium iron phosphate active materials include Li a Fe 1-x-y V x M y PO4, wherein 0.9≤a≤1.1, 0.002≤x≤0.01, 0≤y≤0.098, 0.002≤x+y≤0.01, and M includes at least one of Ti, Sn, Sb, Mo, and Bi. Li a Fe 1-x-y V x M y PO4 has good electronic conductivity and ion diffusion rate, which is beneficial to its rate performance when applied to batteries.

[0092] In some embodiments, the compaction density of lithium iron vanadium phosphate active materials at 3t is ≥2.7g / cm³. 3 .

[0093] The compaction density of lithium vanadium iron phosphate active materials at 3t can be tested by: compacting the lithium vanadium iron phosphate active materials under a pressure of 3t, then testing its mass and volume, and finally obtaining the compaction density of the lithium vanadium iron phosphate active materials using the formula: compaction density = mass / volume.

[0094] By controlling the compaction density of lithium iron phosphate vanadium phosphate active materials at 3t to ≥2.7g / cm³, 3 This allows the battery to have a good volumetric energy density when it is applied to a battery.

[0095] For example, the compaction density of lithium iron phosphate active materials at 3t can be 2.7 g / cm³. 3 2.71 g / cm 3 2.72 g / cm 3 2.73 g / cm 3 2.74 g / cm 3 2.75 g / cm 3 2.76 g / cm 3 2.77 g / cm 3 2.78 g / cm 3 2.79 g / cm 3 2.8 g / cm 3 2.81 g / cm 3 2.82 g / cm 3 2.83 g / cm 3 2.84 g / cm 3 2.85 g / cm 3 etc., it can also be ≥2.7g / cm 3 Any value within the range.

[0096] In some embodiments, the ratio of the number of the first particle to the number of the second particle is 1:1 to 6.

[0097] The number of the first and second particles can be determined using a Mastersizer3000 laser particle size analyzer.

[0098] By controlling the number of first and second particles within an appropriate range, the first particles provide skeletal support, while the second particles fill the gaps between the first particles. This combination allows the lithium vanadium iron phosphate active material to achieve a higher compaction density. Furthermore, the appropriate number of first and second particles promotes the migration rate of the active metal and provides a suitable specific surface area, allowing for a larger contact area with the electrolyte, thus facilitating the construction of the conductive network.

[0099] For example, the ratio of the first particle to the second particle can be 1:1, 1:1.5, 1:2, 1:2.5, 1:3, 1:3.5, 1:4, 1:4.5, 1:5, 1:5.5, 1:6, etc., or any value within the range of 1:1 to 6. Optionally, the ratio of the first particle to the second particle can be 1:3 to 6.

[0100] In some embodiments, lithium vanadium iron phosphate-based active materials have a core-shell structure, wherein the core of the core-shell structure includes the active material body, and the active material body includes Li a Fe 1-x-y V x M y PO4, wherein 0.9≤a≤1.1, 0.002≤x≤0.01, 0≤y≤0.098, 0.002≤x+y≤0.01, M includes at least one of Ti, Sn, Sb, Mo, and Bi, the shell includes a first shell and a second shell, the first shell is disposed between the core and the second shell, the material of the first shell includes carbon materials, and the electronic conductivity of the second shell is ≥1×10⁻⁶. 3 S / cm, ionic conductivity of the second shell ≥ 8 × 10 -4 S / cm. The conductive network constructed by the first shell is responsible for electron transport and facilitates a more uniform and dense coating of the second shell. The second shell also serves as a high-speed ion-electron dual conductive network. The composite shells together construct an efficient charge transport channel. Electrons are rapidly transported to the reaction interface through the carbon network of the first shell, while lithium ions and electrons are rapidly replenished and migrated out through the second shell. The two are efficiently coupled at the interface, which greatly reduces electrochemical polarization, improves reaction kinetics, and effectively enhances rate performance.

[0101] The material of the first shell layer can be obtained through ICP testing. Carbon materials have good electronic conductivity and are relatively easy to prepare, which helps control the manufacturing cost of lithium iron phosphate active materials, thus facilitating their industrial production.

[0102] The electronic conductivity of the second shell can be obtained by using a four-probe method, applying a constant current, measuring the voltage drop, and calculating the resistivity based on the sample thickness and electrode contact area. The ionic conductivity of the second shell can be obtained by electrochemical impedance spectroscopy (EIS): the composite material is prepared into a dense tablet, coated with inert metal electrodes on both sides, and the impedance spectrum is measured. The volume resistance is obtained through equivalent circuit fitting, and the ionic conductivity is calculated. Alternatively, the material and amount of the second shell can be obtained through ICP testing, and a sample with the same composition as the second shell can be prepared. The electronic and ionic conductivity of the second shell can then be obtained using the aforementioned four-probe method and EIS.

[0103] In the above implementation process, by coating the core active material with a carbon material with good electronic conductivity as the first shell layer and a second shell layer with good electronic and ionic conductivity, the entire lithium vanadium iron phosphate active material has good electronic and ionic conductivity, which is beneficial to its rate performance when applied to batteries.

[0104] For example, the electronic conductivity of the second shell can be 1×10⁻⁶. 3 S / cm, 5×10 3 S / cm, 1×10 4 S / cm, 5×10 4 S / cm, 1×10 5 S / cm, 5×10 5 S / cm, 1×10 6 S / cm, 5×10 6 S / cm, etc., can also be ≥1×10 3 Any value within the range of S / cm. The ionic conductivity of the second shell can be 8 × 10⁻⁶. -4 S / cm, 1×10 -3 S / cm, 5×10 -3 S / cm, 1×10 -2 S / cm, 5×10 -2 S / cm, which can also be ≥8×10 -4 Any value within the range of S / cm.

[0105] In some embodiments, the material of the second shell includes a highly ionicly conductive material and a highly ionicly conductive material, wherein the ionic conductivity of the highly ionicly conductive material is ≥1×10⁻⁶. -3 S / cm, electronic conductivity of high-conductivity electronic materials ≥1×10 4 S / cm. The material of the second shell can be obtained through ICP detection. Highly conductive ionic materials have good ion conductivity, and highly conductive electronic materials have good electronic conductivity. Combining highly conductive ionic materials and highly conductive electronic materials to form the second shell can improve the electronic and ionic conductivity of the entire lithium vanadium iron phosphate active material, thereby improving its rate performance when applied to batteries.

[0106] In some embodiments, the mass ratio of the highly conductive ion material to the highly conductive electronic material is 80~90:10~20.

[0107] The quality of highly conductive ionic materials and highly conductive electronic materials can be obtained through ICP testing.

[0108] By controlling the mass ratio of high ion conductivity material to high electronic conductivity material to be 80~90:10~20, the second shell can simultaneously possess electronic and ion conductivity properties, which is beneficial to improving the electronic and ion conductivity of the entire lithium vanadium iron phosphate active material.

[0109] For example, the mass ratio of the highly conductive ion material to the highly conductive electronic material can be 80:20, 81:19, 82:18, 83:17, 84:16, 85:15, 86:14, 87:13, 88:12, 89:11, 90:10, etc., or any value within the range of 80~90:10~20.

[0110] In some embodiments, the highly ion-conducting material includes at least one of garnet-type solid-state electrolytes, NASICON-type solid-state electrolytes, or perovskite-type solid-state electrolytes. Highly ion-conducting materials such as garnet-type solid-state electrolytes, NASICON-type solid-state electrolytes, or perovskite-type solid-state electrolytes possess good ion conductivity, which is beneficial for improving the ion conductivity of the second shell. Optionally, the garnet-type solid-state electrolyte includes lithium lanthanum zirconium oxide (Li7La3Zr2O3). 12 (abbreviated as LLZO); NASICON-type solid electrolytes include lithium aluminum titanium phosphate (LiTi) 1.3 Al 0.3 Ti 1.7 (PO4)3, abbreviated as LATP, lithium titanium germanium phosphate (Li 1.3 Al 0.3 Ge 1.7 (PO4)3, abbreviated as LAGP) or lithium zirconium silicon phosphorus oxide (Li3Zr2Si2PO) 12 At least one of the following: lithium lanthanum titanium oxide (LZSP); perovskite solid electrolytes include lithium lanthanum titanium oxide (LLTO). Solid electrolyte materials such as lithium lanthanum zirconium oxide, lithium titanium aluminum phosphate, lithium titanium germanium phosphate, lithium zirconium silicon phosphorus oxide, and lithium lanthanum titanium oxide have good ion conductivity, which is beneficial for improving the ion conductivity of the second shell.

[0111] In some embodiments, the highly conductive electronic material includes TaN x Where x < 1, at least one of them. TaN x Highly conductive electronic materials have good electronic conductivity, which is beneficial for improving the electronic conductivity of the second shell.

[0112] In some embodiments, the thickness of the first shell layer is 3 nm to 5 nm. The thickness of the first shell layer can be obtained by measuring the TEM of the lithium vanadium iron phosphate active material. By controlling the thickness of the first shell layer to be 3 nm to 5 nm, the lithium vanadium iron phosphate active material can possess both good electronic conductivity and high volumetric capacity.

[0113] For example, the thickness of the first shell layer can be 3 nm, 3.2 nm, 3.4 nm, 3.6 nm, 3.8 nm, 4 nm, 4.2 nm, 4.6 nm, 4.8 nm, 5 nm, etc., or it can be any value in the range of 3 nm to 5 nm.

[0114] In some embodiments, the thickness of the second shell layer is 3 nm to 4 nm. The thickness of the second shell layer can be obtained by measuring the TEM test on the lithium vanadium iron phosphate active material. By controlling the thickness of the second shell layer to 3 nm to 4 nm, the lithium vanadium iron phosphate active material can possess good electronic conductivity, ionic conductivity, performance stability, and high volumetric capacity.

[0115] For example, the thickness of the second shell can be 3 nm, 3.2 nm, 3.4 nm, 3.6 nm, 3.8 nm, 4 nm, etc., or it can be any value in the range of 3 nm to 4 nm.

[0116] Having introduced the composition and structure of the positive electrode active material, the preparation method of the positive electrode active material will be described in detail below.

[0117] Please see Figure 1 , Figure 1 This is a flowchart illustrating the method provided in some embodiments of this application. Embodiments of this application provide a method for preparing a positive electrode active material, the method comprising: S100. Mix the iron source, lithium source, phosphorus source and the first shell source to obtain the sintering precursor.

[0118] In some embodiments, the iron source includes at least two iron sources. By using at least two iron sources to form the sintering precursor, particles with two median volumetric sizes can ultimately be sintered, resulting in a particle size distribution that is beneficial for improving the compaction density of the cathode active material. Further, the iron source includes at least two of ferric phosphate, ferrous oxalate, ferric oxide, ferric hydroxide, or iron powder. By selecting at least two of ferric phosphate, ferrous oxalate, ferric oxide, ferric hydroxide, or iron powder as the iron source, particles with two median volumetric sizes can ultimately be sintered, resulting in a particle size distribution that is beneficial for improving the compaction density of the cathode active material.

[0119] In some embodiments, the lithium source includes at least one of lithium carbonate, lithium hydroxide, or lithium acetate.

[0120] In some embodiments, the phosphorus source includes at least one of ammonium dihydrogen phosphate or phosphoric acid.

[0121] In some embodiments, the first shell source includes a carbon source, which may include at least one selected from glucose, fructose, sucrose, citric acid, tartaric acid, ascorbic acid, or polyethylene glycol. Using glucose, fructose, sucrose, citric acid, tartaric acid, ascorbic acid, or polyethylene glycol as a carbon source to form the first shell provides readily available raw materials and a relatively simple preparation process, which helps control the manufacturing cost of lithium vanadium iron phosphate active materials, thereby facilitating their industrial production.

[0122] In some embodiments, the mass of the first shell source is 5% to 12% of the sum of the masses of the iron source, lithium source, and phosphorus source. A suitable proportion of the first shell source allows for the formation of a first shell of appropriate thickness, thereby enabling the lithium iron phosphate vanadium phosphate active material to possess both good electronic conductivity and high volumetric capacity. For example, the mass of the first shell source can be 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, 10.5%, 11%, 11.5%, 12%, etc., of the sum of the masses of the iron source, lithium source, and phosphorus source, or any value within the range of 5% to 12%.

[0123] In some embodiments, the median particle size of the sintering precursor is 300 nm to 450 nm.

[0124] The particle size of the sintering precursor can be obtained using a Mastersizer3000 laser particle size analyzer.

[0125] A sintering precursor with a suitable particle size can facilitate the formation of lithium vanadium iron phosphate active materials with a suitable particle size, thereby improving the compaction density of the lithium vanadium iron phosphate active materials. For example, the median particle size of the sintering precursor can be 300 nm, 310 nm, 320 nm, 330 nm, 340 nm, 350 nm, 360 nm, 370 nm, 380 nm, 390 nm, 400 nm, 410 nm, 420 nm, 430 nm, 440 nm, 450 nm, etc., or it can be any value in the range of 300 nm to 450 nm.

[0126] Specifically, in this embodiment, the preparation process of the sintering precursor can be as follows: Iron source A and iron source B are compounded in a certain molar ratio (e.g., 9~1:1~9) (iron source A and iron source B are each independently selected from any two of ferric phosphate, ferrous oxalate, ferric oxide, ferric hydroxide, and iron powder), and a lithium source (e.g., one or more of lithium carbonate, lithium hydroxide, and lithium acetate), a phosphorus source (e.g., one or more of ammonium dihydrogen phosphate and phosphoric acid), and a carbon source (e.g., one or more of glucose, fructose, sucrose, citric acid, tartaric acid, ascorbic acid, and polyethylene glycol) are added. After pure water sand milling and spray drying, the sintering precursor is obtained. Among them, the mass of carbon source is 5~12 wt% of the sum of the masses of lithium source, iron source, and phosphorus source; the D50 of the sand milling slurry is 300nm~450nm, and the solid content is 25%~45%; the inlet air temperature of spray drying is 170℃~220℃, and the outlet air temperature is 90℃~110℃.

[0127] S200. The sintering precursor is subjected to a first sintering to obtain an intermediate product.

[0128] In some embodiments, the first sintering includes a first-stage sintering and a second-stage sintering; the holding temperature of the first-stage sintering is 300℃~450℃, and the gas pressure of the second-stage sintering is 1MPa~5MPa. During the first sintering, a first-stage sintering is performed at a low temperature to remove volatile components from the sintering precursor, reducing the probability of these components damaging the material structure during subsequent sintering. Then, a second-stage sintering is performed under high pressure to ensure close contact between the sintering precursors, promoting grain growth and fusion, forming intermediate products with suitable particle sizes. This results in the final lithium vanadium iron phosphate active material having two types of particles with suitable particle sizes, forming a good gradation relationship, and giving it a good compaction density. For example, the holding temperature for the first stage of sintering can be 300℃, 310℃, 320℃, 330℃, 340℃, 350℃, 360℃, 370℃, 380℃, 390℃, 400℃, 410℃, 420℃, 430℃, 440℃, 450℃, etc., or any value within the range of 300℃ to 450℃. The gas pressure for the second stage of sintering can be 1MPa, 1.5MPa, 2MPa, 2.5MPa, 3MPa, 3.5MPa, 4MPa, 4.5MPa, 5MPa, etc., or any value within the range of 1MPa to 5MPa.

[0129] In some embodiments, the heating rate of a single sintering stage is 1°C / min to 3°C / min. A suitable heating rate for a single sintering stage is beneficial for forming active materials of lithium vanadium iron phosphate with good compaction density. For example, the heating rate of a single sintering stage can be 1°C / min, 1.2°C / min, 1.4°C / min, 1.6°C / min, 1.8°C / min, 2°C / min, 2.2°C / min, 2.4°C / min, 2.6°C / min, 2.8°C / min, 3°C / min, etc., or any value within the range of 1°C / min to 3°C / min.

[0130] In some embodiments, the holding time for a single sintering stage is 1 to 3 hours. A suitable holding time for a single sintering stage can form vanadium iron phosphate active materials with good compaction density with less energy consumption and lower time costs. For example, the holding time for a single sintering stage can be 1 hour, 1.2 hours, 1.4 hours, 1.6 hours, 1.8 hours, 2 hours, 2.2 hours, 2.4 hours, 2.6 hours, 2.8 hours, 3 hours, etc., or any value within the range of 1 hour to 3 hours.

[0131] In some embodiments, the sintering atmosphere for a single stage is at least one of a nitrogen atmosphere or an inert gas atmosphere. By using a nitrogen atmosphere or an inert gas atmosphere as the sintering atmosphere for a single stage, it is beneficial to reduce the probability of side reactions occurring throughout the sintering process. For example, the inert gas atmosphere may be an argon atmosphere.

[0132] In some embodiments, the gas pressure for a single sintering stage is 0.08 MPa to 0.12 MPa. Performing a single sintering stage near atmospheric pressure facilitates the removal of volatile components from the sintering precursor, reducing the probability of these components damaging the material structure during subsequent sintering processes. For example, the gas pressure for a single sintering stage can be 0.08 MPa, 0.09 MPa, 0.1 MPa, 0.11 MPa, 0.12 MPa, etc., or any value within the range of 0.08 MPa to 0.12 MPa.

[0133] In some embodiments, the holding temperature for the two-stage sintering is 700℃~840℃. A suitable two-stage sintering temperature is beneficial for the full formation of lithium vanadium iron phosphate-based active materials. The holding temperature for the two-stage sintering can be 700℃, 710℃, 720℃, 730℃, 740℃, 750℃, 760℃, 770℃, 780℃, 790℃, 800℃, 810℃, 820℃, 830℃, 840℃, etc., or any value within the range of 700℃~840℃.

[0134] In some embodiments, the heating rate of the two-stage sintering is 3℃ / min to 5℃ / min. A suitable heating rate for the two-stage sintering is beneficial for forming active materials of lithium vanadium iron phosphate with good compaction density. The heating rate of the two-stage sintering can be 3℃ / min, 3.2℃ / min, 3.4℃ / min, 3.6℃ / min, 3.8℃ / min, 4℃ / min, 4.2℃ / min, 4.4℃ / min, 4.6℃ / min, 4.8℃ / min, 5℃ / min, etc., or any value within the range of 3℃ / min to 5℃ / min.

[0135] In some embodiments, the holding time for the second-stage sintering is 8 to 12 hours. A suitable holding time for the second-stage sintering can form vanadium iron phosphate active materials with good compaction density with less energy consumption and lower time costs. For example, the holding time for the first-stage sintering can be 8 hours, 8.5 hours, 9 hours, 9.5 hours, 10 hours, 10.5 hours, 11 hours, 11.5 hours, 12 hours, etc., or any value within the range of 8 hours to 12 hours.

[0136] Specifically, in this embodiment, the preparation process of the intermediate product can be as follows: the sintering precursor is placed in a pressurized atmosphere sintering furnace for a first sintering. The first sintering includes two stages: a first-stage sintering (low-temperature sintering): the temperature is increased to 300℃~450℃ at a heating rate of 1℃ / min~3℃ / min and held for 1 hour~3 hours under normal pressure in an atmosphere of N2 or Ar. A second-stage sintering (pressurized sintering): the temperature is increased to 790℃~840℃ at a heating rate of 3℃ / min~5℃ / min and held for 8 hours~12 hours, while a pressure of 1MPa~5 MPa is applied to the furnace.

[0137] S300. The intermediate product and additives are mixed and then subjected to a second sintering to obtain the positive electrode active material.

[0138] In some embodiments, the additives include a first additive and a second additive, wherein the first additive contains chlorine and the second additive contains vanadium. During the second sintering process, the intermediate product and the additives containing chlorine and vanadium are sintered together. The first additive containing chlorine reacts with the iron phosphide in the intermediate product to form volatile chlorides, thereby reducing the amount of iron phosphide. The second additive containing vanadium incorporates vanadium into the material, improving its electronic conductivity and ion diffusion rate.

[0139] In some embodiments, the molar ratio of vanadium to intermediate product in the second additive is 0.001 to 0.01:1. For example, the molar ratio of vanadium to intermediate product in the second additive can be 0.001:1, 0.002:1, 0.003:1, 0.004:1, 0.005:1, etc., or any value within the range of 0.001 to 0.005:1.

[0140] In some embodiments, the first additive includes at least one of vanadium chloride, titanium chloride, tin chloride, antimony chloride, molybdenum chloride, or bismuth chloride. Chlorine compounds such as vanadium chloride, titanium chloride, tin chloride, antimony chloride, molybdenum chloride, or bismuth chloride can react with iron phosphide in the intermediate product to form volatile chlorides, thereby reducing the amount of iron phosphide. Furthermore, the metal elements contained therein can be incorporated into the material, improving its electronic conductivity and ion diffusion rate.

[0141] In some embodiments, the second additive includes vanadium chloride. Vanadium-containing compounds such as vanadium chloride can dope vanadium into materials, thereby improving their electronic conductivity and ion diffusion rate.

[0142] In some embodiments, the holding temperature for the second sintering is 600℃~750℃. A suitable second sintering holding temperature can effectively remove iron phosphide from the intermediate product, while simultaneously allowing the metal elements in the chloride compound to be incorporated into the material, thereby improving electronic conductivity and ion diffusion rate. For example, the holding temperature for the second sintering can be 600℃, 610℃, 620℃, 630℃, 640℃, 650℃, 660℃, 670℃, 680℃, 690℃, 700℃, 710℃, 720℃, 730℃, 740℃, 750℃, etc., or any value within the range of 600℃~750℃.

[0143] In some embodiments, the heating rate of the second sintering stage is 2°C / min to 5°C / min. A suitable heating rate for the second-stage sintering stage can facilitate the removal of iron phosphide from the intermediate products and promote the doping of metal elements from chloride compounds into the material, thereby improving electronic conductivity and ion diffusion rate. For example, the heating rate for the second-stage sintering can be 2°C / min, 2.5°C / min, 2.4°C / min, 2.6°C / min, 2.8°C / min, 3°C / min, 3.2°C / min, 3.4°C / min, 3.6°C / min, 3.8°C / min, 4°C / min, 4.2°C / min, 4.4°C / min, 4.6°C / min, 4.8°C / min, 5°C / min, etc., or any value within the range of 2°C / min to 5°C / min.

[0144] In some embodiments, the holding time for the second sintering is 2 hours to 8 hours. A suitable holding time for the two-stage sintering can remove iron phosphide from the intermediate product and complete the doping of metal elements in the chloride compound with less energy consumption and lower time costs. For example, the holding time for the first-stage sintering can be 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, 4.5 hours, 5 hours, 5.5 hours, 6 hours, 6.5 hours, 7 hours, 7.5 hours, 8 hours, etc., or any value within the range of 2 hours to 8 hours.

[0145] In some embodiments, prior to the second sintering, the second shell source, intermediate product, and additives are mixed. The material of the second shell includes a highly ionicly conductive material and a highly conductive electronic material, wherein the ionic conductivity of the highly ionicly conductive material is ≥1×10⁻⁶. -3 S / cm, electronic conductivity of high-conductivity electronic materials ≥1×10 4 S / cm. Highly conductive ionic materials have good ion conductivity, while highly conductive electronic materials have good electronic conductivity. Combining highly conductive ionic materials and highly conductive electronic materials to form a second shell can improve the electronic and ionic conductivity of the entire lithium vanadium iron phosphate active material, thereby improving its rate performance when applied to batteries.

[0146] In some embodiments, the mass ratio of the second shell source to the intermediate product is 1 to 3:100. A suitable proportion of the second shell source allows for the formation of a second shell of appropriate thickness, thereby enabling the lithium vanadium iron phosphate active material to possess good electronic conductivity, ionic conductivity, performance stability, and high volumetric capacity. For example, the mass ratio of the second shell source to the intermediate product can be 1:100, 1.2:100, 1.4:100, 1.6:100, 1.8:100, 2:100, 2.2:100, 2.4:100, 2.6:100, 2.8:100, 3:100, etc., or any value within the range of 1 to 3:100.

[0147] Specifically, in this embodiment, the preparation process of the positive electrode active material can be as follows: The intermediate product, additives (selected from one or more of the chlorides of V and the chlorides of Ti, Sn, Sb, Mo, and Bi), and LLZO-TaN composite powder (LLZO to TaN mass ratio of 80~90:20~10, LLZO particle size range: 30 nm~70 nm, TaN particle size range: 15 nm~30 nm) are thoroughly mixed using a high-speed mixer. Then, the mixture is placed in a sintering furnace and heated to 600-750℃ at a heating rate of 2-5℃ / min, and held at that temperature for 2-8 hours. The mass ratio of LLZO-TaN composite powder to the first sintering product is 1~3:100. The high-speed mixer mixing process involves processing at 300 rpm for 3 min, 900 rpm for 3 min, and 1200 rpm for 20 min.

[0148] This application also provides a battery, which includes a positive electrode sheet, a positive electrode active material layer, and a positive electrode active material layer, which includes a positive electrode active material. The positive electrode active material includes the positive electrode active material provided above or a positive electrode active material prepared by the method provided above.

[0149] The following examples will describe one or more embodiments in more detail. Of course, these examples do not limit the scope of the one or more embodiments.

[0150] Example 1 A positive electrode active material, the preparation process of which is as follows: (1) Iron source ferric phosphate (FePO4) and ferrous oxalate (FeC2O4) are mixed in a molar ratio of 8:2. Lithium source lithium carbonate, phosphorus source ammonium dihydrogen phosphate, first shell source (i.e. carbon source) glucose (the mass of carbon source is 8 wt% of the sum of the masses of lithium source, iron source and phosphorus source) and pure water are added and mixed. The solid content is controlled to be 30%. Then, the mixture is sand-milled and spray-dried to obtain the sintering precursor.

[0151] (2) The sintering precursor is subjected to a first sintering to obtain an intermediate product. The first sintering includes: placing the sintering precursor in a pressurized atmosphere sintering furnace for sintering. The first sintering includes a first-stage sintering and a second-stage sintering. The first-stage sintering process is: heating to 400°C at a heating rate of 2°C / min and holding for 2 hours at atmospheric pressure and N2 atmosphere; the second-stage sintering process is: heating to 820°C at a heating rate of 5°C / min and holding for 10 hours, while applying a pressure of 3 MPa to the furnace.

[0152] (3) The intermediate product, additives, and second shell source are thoroughly mixed using a high-speed mixer and subjected to a second sintering to obtain the positive electrode active material; wherein, the additives include a first additive and a second additive, both of which are VCl3, and the molar ratio of VCl3 to the intermediate product is 0.005:1), and the second shell source is LLZO-TaN. x Composite powder (LLZO and TaN) x (The mass ratio is 80:20) The second sintering process is as follows: the temperature is increased to 680℃ at a heating rate of 3℃ / min and held for 5 hours.

[0153] Example 2 The preparation method of the positive electrode active material in Example 2 is basically the same as that in Example 1. The difference is that the composition and amount of additives in the second sintering are changed: the first additive includes TiCl4 and VCl3, the second additive includes VCl3, and the molar ratio of TiCl4, VCl3 and intermediate product is 0.0025:0.0025:1. All other contents are the same as in Example 1.

[0154] Example 3 The preparation method of the positive electrode active material in Example 3 is basically the same as that in Example 1, except that the composition and amount of additives in the second sintering are changed: the first additive includes SnCl2 and VCl3, the second additive includes VCl3, and the molar ratio of SnCl2, VCl3 and intermediate product is 0.0025:0.0025:1.

[0155] Example 4 The preparation method of the positive electrode active material in Example 4 is basically the same as that in Example 1, except that the molar ratio of ferric phosphate to ferrous oxalate is changed to 5:5 during the preparation of the sintering precursor.

[0156] Example 5 The preparation method of the positive electrode active material in Example 5 is basically the same as that in Example 1, except that the material of the solid electrolyte is changed to LLTO (Li3La2TiO3).

[0157] Example 6 The preparation method of the positive electrode active material in Example 6 is basically the same as that in Example 1, except that the amount of LLZO and TaN is changed during the second sintering. x The mass ratio is 90:10.

[0158] Example 7 The preparation method of the positive electrode active material in Example 7 is basically the same as that in Example 1, except that the mass of the carbon source is changed to 5 wt% of the sum of the masses of the lithium source, iron source and phosphorus source.

[0159] Example 8 The preparation method of the positive electrode active material in Example 8 is basically the same as that in Example 1, except that the gas pressure of the two-stage sintering is changed to 1 MPa.

[0160] Example 9 The preparation method of the positive electrode active material in Example 9 is basically the same as that in Example 1, except that the gas pressure of the second-stage sintering is changed to 5 MPa.

[0161] Example 10 The preparation method of the positive electrode active material in Example 10 is basically the same as that in Example 1, except that the sintering temperature of one stage is changed to 450°C.

[0162] Example 11 The preparation method of the positive electrode active material in Example 11 is basically the same as that in Example 1, except that the sintering temperature of one stage is changed to 300°C.

[0163] Example 12 The preparation method of the positive electrode active material in Example 12 is basically the same as that in Example 1, except that the amount of VCl3 added is changed and the molar ratio of VCl3 to intermediate product is 0.0025:1.

[0164] Example 13 The preparation method of the positive electrode active material in Example 13 is basically the same as that in Example 1, except that the amount of VCl3 added is changed and the molar ratio of VCl3 to intermediate product is 0.001:1.

[0165] Comparative Example 1 The preparation methods of the positive electrode active material in Comparative Example 1 and Example 1 are basically the same, except that VCl3 is replaced with TiCl4.

[0166] Comparative Example 2 The preparation method of the positive electrode active material in Comparative Example 2 is basically the same as that in Example 1, except that VCl3 is replaced with SnCl2.

[0167] Comparative Example 3 The preparation method of the positive electrode active material of Comparative Example 3 is basically the same as that of Example 1, except that the holding temperature of the second stage sintering in the first sintering is changed to 680°C and no additives are used.

[0168] Comparative Example 4 The preparation method of the positive electrode active material in Comparative Example 4 is basically the same as that in Example 1, except that the Fe source in the precursor preparation process is changed to ferrous oxalate.

[0169] Comparative Example 5 The preparation method of the positive electrode active material of Comparative Example 5 is basically the same as that of Example 1, except that VCl3 in the second sintering process is changed to NH4VO3.

[0170] Comparative Example 6 The preparation method of the positive electrode active material of Comparative Example 6 is basically the same as that of Example 1, except that the amount of VCl3 added is changed and the molar ratio of VCl3 to intermediate product is 0.0005:1.

[0171] Comparative Example 7 The preparation method of the positive electrode active material of Comparative Example 7 is basically the same as that of Example 1, except that the amount of VCl3 added is changed and the molar ratio of VCl3 to intermediate product is 0.008:1.

[0172] Comparative Example 8 The preparation method of the positive electrode active material of Comparative Example 8 is basically the same as that of Example 1, except that the first sintering is different. The first sintering process is as follows: the sintering precursor is placed in a pressurized atmosphere sintering furnace for sintering, and the temperature is raised to 820°C at a heating rate of 5°C / min and held for 12 hours at normal pressure and N2 atmosphere.

[0173] Comparative Example 9 The preparation method of the positive electrode active material of Comparative Example 9 is basically the same as that of Example 1, except that the gas pressure of the second-stage sintering is changed to atmospheric pressure.

[0174] Comparative Example 10 The preparation method of the positive electrode active material of Comparative Example 10 is basically the same as that of Example 1, except that the gas pressure of the two-stage sintering is changed to 7 MPa.

[0175] Comparative Example 11 The preparation method of the positive electrode active material of Comparative Example 11 is basically the same as that of Example 1, except that the sintering temperature of one stage is changed to 250°C.

[0176] Comparative Example 12 The preparation method of the positive electrode active material of Comparative Example 12 is basically the same as that of Example 1, except that the sintering temperature of one stage is changed to 820°C.

[0177] The main parameter controls for each embodiment and comparative example are shown in Table 1 below: The positive electrode active materials provided in each embodiment and comparative example were tested, including: Particle size and quantity testing: The results were obtained using a Mastersizer3000 laser particle size analyzer.

[0178] Material testing of the first and second shells: obtained using ICP testing.

[0179] The thickness of the first and second shell layers was measured using cross-sectional SEM.

[0180] Electronic and ionic conductivity tests of the second shell: After obtaining the material and quantity of the second shell through ICP testing, a sample with the same composition as the second shell was prepared. Then, the electronic and ionic conductivity of the second shell were obtained using the aforementioned four-probe method and electrochemical impedance spectroscopy. The four-probe method involved applying a constant current, measuring the voltage drop, and calculating the resistivity based on the sample thickness and electrode contact area. Electrochemical impedance spectroscopy involved preparing the composite material into a dense tablet, coating both sides with inert metal electrodes, measuring the impedance spectrum, obtaining the volume resistance through equivalent circuit fitting, and calculating the ionic conductivity.

[0181] Compacted density test of positive electrode active material: The positive electrode active material was tested using a powder compaction density meter. The test pressure was 220 MPa and the holding time was 15 s.

[0182] Fe2P content test in positive electrode active material: Take 1g of the sample to be tested, add the prepared 1M / L dilute hydrochloric acid solution, heat and stir at 50℃ for 5min, filter, dilute the filtrate to volume and detect the Fe element content by ICP, and calculate the Fe2P content in the sample.

[0183] The test results are shown in Table 1 below: Table 1

[0184] Continued from Table 1

[0185] Continued from Table 1

[0186] In the table, " / " indicates that the substance was not added or that the value does not exist.

[0187] As can be seen from the table above, the positive electrode active material prepared by the method provided in the embodiments of this application can achieve a balance of high electronic conductivity, low impurities, and high compaction density.

[0188] A comparison of the data from Examples 1 to 3 shows that the proposed cathode active material can effectively improve the compaction density and reduce the impurity content while maintaining V doping. In particular, co-doping with V and Ti enables the cathode active material to achieve a compaction density of 2.79 g / cm³. 3The impurity content was controlled at 37 ppb. The reason is speculated to be that V and Ti, as high-valence ions, enter the crystal lattice, causing lattice distortion, increasing the lithium-ion diffusion channels, and introducing more holes and electrons, thereby improving the electronic and ionic conductivity of the material and significantly improving cycle performance and rate performance. The introduction of Ti can inhibit excessive particle growth, making some particles smaller, and V doping will lower the energy barrier for crystal nucleation, making some particles more inclined to grow. The combination of these factors causes differences in particle size and increases the compaction density.

[0189] A comparison of the data from Examples 1 and 4 shows that by controlling the iron source ratio, the positive electrode active material can have a better particle size distribution (i.e., satisfying 0.8μm < the median volume diameter of the first particle ≤ 2.8μm, 0.2μm ≤ the median volume diameter of the second particle ≤ 0.8μm, and the ratio of the number of the first particle to the number of the second particle is 1:1~6), which is beneficial to improving the compaction density.

[0190] A comparison of the data from Examples 1 and 5 shows that using different solid electrolyte materials as high-conductivity ion-coating materials can effectively improve the ionic conductivity of the positive electrode active material.

[0191] A comparison of the data from Examples 1 and 6 shows that by controlling the ratio of highly conductive ion-carrying material to highly conductive electronic material in the second shell within a suitable range, the second shell can simultaneously possess good electron transport and ion transport capabilities, which is beneficial to the electronic conductivity and ion conductivity of the positive electrode active material.

[0192] A comparison of the data from Examples 1 and 7 shows that controlling the thickness of the first shell layer within a suitable range can improve the electronic conductivity of the positive electrode active material.

[0193] A comparison of the data from Examples 1 and 8 to 9 shows that by controlling the gas pressure during the second-stage sintering in the first sintering process within a suitable range, the positive electrode active material can have a better particle size distribution (i.e., satisfying 0.8μm < the median volumetric particle size of the first particle ≤ 2.8μm, 0.2μm ≤ the median volumetric particle size of the second particle ≤ 0.8μm, and the ratio of the number of the first particle to the number of the second particle is 1:1~6), which is beneficial to improving the compaction density.

[0194] A comparison of the data from Examples 1 and 10 to 11 shows that by controlling the sintering temperature of the first sintering stage within a suitable range, the positive electrode active material can have a better particle size distribution (i.e., satisfying 0.8μm < the median volume diameter of the first particle ≤ 2.8μm, 0.2μm ≤ the median volume diameter of the second particle ≤ 0.8μm, and the ratio of the number of the first particle to the number of the second particle is 1:1~6), which is beneficial to improving the compaction density.

[0195] By comparing the data from Examples 1 and 12 to 13, it can be seen that as the doping amount gradually increases, the impurity content in the positive electrode active material gradually decreases. By controlling the doping amount within the range of 1000ppm to 5000ppm, the impurity content in the positive electrode active material is controlled below 761ppm.

[0196] The positive electrode active materials prepared in each embodiment and comparative example were used to prepare batteries. The preparation process is as follows: [Preparation of button cells] At 25℃ and normal pressure (0.1MPa), positive electrode active material, conductive carbon black, and binder polyvinylidene fluoride (PVDF) in a mass percentage ratio of 90:5:5 were added to N-methylpyrrolidone solvent and thoroughly mixed to obtain a positive electrode active slurry. This slurry was then coated onto an aluminum foil surface, dried, and cold-pressed to obtain a positive electrode sheet. The thickness of the positive electrode active layer was 100μm, and the areal density was 1.4g / cm³. 2 The compacted density is 2.5 g / cm³. 3 Then, the positive electrode sheet was punched into a small disc with a diameter of 12 mm using a film punch. After drying and weighing, it was assembled into a coin cell using a 2025 coin cell case, with a Li metal disc as the negative electrode and polyethylene (PE) as the separator, and electrolyte in a glove box under Ar protective atmosphere. The electrolyte included lithium salt and organic solvent. The lithium salt was lithium hexafluorophosphate (LiPF6) with a concentration of 1 mol / L. The solvent included ethylene carbonate (EC), dimethyl carbonate (DMC), and diethyl carbonate (DEC) in a volume ratio of 1:1:1.

[0197] The batteries using the positive electrode active materials provided in each embodiment and comparative example were tested, including: Rate performance and capacity retention tests: The positive electrode active materials prepared in each example and comparative example were assembled into coin cells, and then charge-discharge tests were performed in the Blue Battery Test System. The test voltage was 2.0V-3.75V, the cutoff current was 0.05C, and the cycles were performed as follows: 0.1C charge-discharge for 2 cycles (activation), 0.5C charge-discharge for 2 cycles, 0.5C charge-1C discharge for 2 cycles, and 0.5C charge-5C discharge for 2 cycles, where 1C = 160mAh / g. The energy density and the 1C and 5C rates were recorded, and the test results are summarized in Table 2. The cycle was continued for 500 cycles, and the capacity retention rate on the 500th cycle was recorded.

[0198] The results are shown in Table 2 below: Table 2

[0199] As can be seen from the table above, the battery using the positive electrode active material provided in the embodiments of this application can have both good rate performance and cycle performance.

[0200] Appendix Figures 2 to 4 Detailed explanation: Figure 2 The image shows a SEM image of the lithium iron vanadium phosphate cathode material in Example 1. Figure 2 It can be seen that lithium vanadium iron phosphate cathode material is composed of particles of two sizes, with smaller particles accounting for a higher proportion and having a better compaction density.

[0201] Figure 3 The TEM image of the lithium vanadium iron phosphate cathode material in Example 1 clearly shows the first and second coating layers.

[0202] Figure 4 The image shows the SEM image of the cathode material in Comparative Example 1. It is generally composed of large particles with a small number of small particles and poor compaction density.

[0203] The above are merely specific embodiments of this application and are not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A positive electrode active material, characterized in that, The positive electrode active material includes lithium vanadium iron phosphate active material, wherein the molar ratio of V element and non-lithium site metal element in the lithium vanadium iron phosphate active material is 0.001~0.005:1, the mass content of iron phosphide in the lithium vanadium iron phosphate active material is ≤800ppb, and the lithium vanadium iron phosphate active material includes a first particle and a second particle, wherein 0.8μm < the median volume diameter of the first particle ≤2.8μm, and 0.2μm ≤ the median volume diameter of the second particle ≤0.8μm.

2. The positive electrode active material according to claim 1, characterized in that, The lithium iron phosphate active material includes Li a Fe 1-x-y V x M y PO4, wherein 0.9≤a≤1.1, 0.002≤x≤0.01, 0≤y≤0.098, 0.002≤x+y≤0.01, and M includes at least one of Ti, Sn, Sb, Mo, and Bi.

3. The positive electrode active material according to claim 1 or 2, characterized in that, The compaction density of the vanadium iron phosphate active material at 3t is ≥2.7g / cm³. 3 ; and / or The ratio of the first particle to the second particle is 1:1 to 6; optionally, the ratio of the first particle to the second particle is 1:3 to 6.

4. The positive electrode active material according to claim 1 or 2, characterized in that, The lithium iron phosphate vanadium phosphate active material has a core-shell structure. The core of the core-shell structure includes the active material body, which includes Li. a Fe 1-x- y V x M y PO4, wherein 0.9≤a≤1.1, 0.002≤x≤0.01, 0≤y≤0.098, 0.002≤x+y≤0.01, M includes at least one of Ti, Sn, Sb, Mo, and Bi, the shell includes a first shell and a second shell, the first shell is disposed between the core and the second shell, the material of the first shell includes carbon material, and the electronic conductivity of the second shell is ≥1×10⁻⁶. 3 S / cm, the ionic conductivity of the second shell is ≥8×10 -4 S / cm.

5. The positive electrode active material according to claim 4, characterized in that, The second shell layer comprises a highly ionicly conductive material and a highly conductive electronic material, wherein the highly ionicly conductive material has an ionic conductivity ≥ 1 × 10⁻⁶. -3 S / cm, the electronic conductivity of the highly conductive electronic material is ≥1×10⁻⁶. 4 S / cm.

6. The positive electrode active material according to claim 5, characterized in that, The mass ratio of the highly conductive ion material to the highly conductive electronic material is 80~90:10~20; The highly conductive ion-conducting material includes at least one of garnet-type solid electrolyte, NASICON-type solid electrolyte, or perovskite-type solid electrolyte; optionally, the garnet-type solid electrolyte includes lithium lanthanum zirconium oxide; the NASICON-type solid electrolyte includes at least one of lithium titanium aluminum phosphate, lithium titanium germanium phosphate, or lithium zirconium silicon phosphorus oxide; the perovskite-type solid electrolyte includes lithium lanthanum titanium oxide; and / or, The high-conductivity electronic material includes TaN. x , where x < 1.

7. The positive electrode active material according to any one of claims 4 to 6, characterized in that, The thickness of the first shell layer is 3nm~5nm; and / or, The thickness of the second shell is 3nm~4nm.

8. A method for preparing a positive electrode active material, characterized in that, The method includes: An iron source, a lithium source, a phosphorus source, and a first shell source are mixed to obtain a sintering precursor; the iron source includes at least two types of iron sources. The sintering precursor is subjected to a first sintering to obtain an intermediate product; the first sintering includes a first-stage sintering and a second-stage sintering; the holding temperature of the first-stage sintering is 300℃~450℃, and the gas pressure of the second-stage sintering is 1MPa~5MPa. The intermediate product and the additives are mixed and subjected to a second sintering to obtain a positive electrode active material; the additives include a first additive and a second additive, the first additive contains chlorine, the second additive contains vanadium, and the molar ratio of vanadium to the intermediate product in the second additive is 0.001~0.005:

1.

9. The method for preparing the positive electrode active material according to claim 8, characterized in that, The iron source includes at least two of ferric phosphate, ferrous oxalate, ferric oxide, ferric hydroxide, or iron powder; and / or, The lithium source includes at least one of lithium carbonate, lithium hydroxide, or lithium acetate; and / or, The phosphorus source includes at least one of ammonium dihydrogen phosphate or phosphoric acid; and / or, The first shell source includes a carbon source, which includes at least one selected from glucose, fructose, sucrose, citric acid, tartaric acid, ascorbic acid, or polyethylene glycol; and / or, The mass of the first shell source is 5% to 12% of the sum of the masses of the iron source, the lithium source, and the phosphorus source; and / or, The median particle size of the sintered precursor is 300 nm to 450 nm; and / or The heating rate of the sintering section is 1℃ / min to 3℃ / min; and / or, The holding time for the first sintering stage is 1 hour to 3 hours; and / or, The sintering atmosphere is at least one of nitrogen or an inert gas atmosphere; and / or, The gas pressure during the sintering of the aforementioned section is 0.08 MPa to 0.12 MPa; and / or, The holding temperature for the two-stage sintering is 700℃~840℃; and / or, The heating rate for the two-stage sintering is 3℃ / min to 5℃ / min; and / or, The holding time for the two-stage sintering is 8h~12h; and / or, The first additive includes at least one of vanadium chloride, titanium chloride, tin chloride, antimony chloride, molybdenum chloride, or bismuth chloride; and / or, The second additive includes vanadium chloride; and / or, The second sintering holding temperature is 600℃~750℃; and / or, The heating rate for the second sintering is 2℃ / min to 5℃ / min; and / or, The holding time for the second sintering is 2 hours to 8 hours; and / or, Prior to the second sintering, the process further includes mixing the second shell source, the intermediate product, and the additives. The material of the second shell includes a highly ionicly conductive material and a highly ionicly conductive material, wherein the highly ionicly conductive material has an ionic conductivity ≥ 1 × 10⁻⁶. - 3 S / cm, the electronic conductivity of the highly conductive electronic material is ≥1×10⁻⁶. 4 S / cm; and / or The mass ratio of the second shell source to the intermediate product is 1~3:

100.

10. A battery, characterized in that, The battery includes a positive electrode sheet, the positive electrode sheet includes a positive active material layer, the positive active material layer includes a positive active material, and the positive active material includes the positive active material prepared by any one of claims 1 to 7 or any one of claims 8 to 9.

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