Iron phosphate material, lithium iron phosphate positive electrode material as well as preparation method and application of iron phosphate material and lithium iron phosphate positive electrode material

Abstract

The invention provides an iron phosphate material, a lithium iron phosphate positive electrode material and a preparation method and application thereof, and belongs to the technical field of secondary batteries, the iron phosphate material comprises iron phosphate dihydrate particles, and the iron phosphate dihydrate particles comprise a first doping element, a second doping element and a third doping element; in the direction from the center of the iron phosphate dihydrate particle to the outer side of the iron phosphate dihydrate particle, the iron phosphate dihydrate particle sequentially comprises a first doped region, a second doped region and a third doped region, the first doped element is located in the first doped region, the second doped element is located in the second doped region, and the third doped element is located in the third doped region. According to the invention, layered doping is carried out on iron phosphate dihydrate through elements with different ion radiuses and action effects, so that the discharge performance of the lithium iron phosphate positive electrode material prepared by using the iron phosphate dihydrate as the precursor at a low temperature is remarkably improved.

Description

Technical Field

[0001] This application belongs to the field of secondary battery technology, and in particular relates to an iron phosphate material, a lithium iron phosphate cathode material, their preparation methods and applications. Background Technology

[0002] Lithium iron phosphate (LiFePO4) is known for its high voltage, high energy density, environmental friendliness, and good safety performance as a cathode material for secondary batteries. It occupies an important position in the electric vehicle market, such as its application as a secondary battery in the field of new energy vehicles.

[0003] Lithium iron phosphate (LFP) rechargeable batteries experience a significant reduction in lifespan below 0°C, even below -20°C. At low temperatures, the interfacial charge transfer resistance and diffusion resistance of the rechargeable battery increase significantly, and the polarization also increases markedly, making it easier to reach the cutoff voltage and leading to a decrease in energy density. Current efforts to improve the low-temperature performance of LFP rechargeable batteries through doping and secondary carbon coating have not yielded significant results, and the electrochemical performance of LFP at low temperatures remains far from meeting everyday needs.

[0004] Therefore, it is necessary to propose an iron phosphate material, a lithium iron phosphate cathode material, and their preparation methods and applications to improve the electrochemical performance of lithium iron phosphate at low temperatures. Summary of the Invention

[0005] In view of the technical problems existing in the background art, this application provides an iron phosphate material, a lithium iron phosphate cathode material, a preparation method thereof, and its application, aiming to solve the technical problem that the electrochemical performance of existing lithium iron phosphate at low temperatures needs to be improved.

[0006] In a first aspect, embodiments of this application provide an iron phosphate material, comprising: iron phosphate dihydrate particles, wherein the iron phosphate dihydrate particles include a first doping element, a second doping element, and a third doping element; wherein, in the direction from the center of the iron phosphate dihydrate particles to the outer side of the iron phosphate dihydrate particles, the iron phosphate dihydrate particles sequentially include a first doping region, a second doping region, and a third doping region, wherein the first doping element is located in the first doping region, the second doping element is located in the second doping region, and the third doping element is located in the third doping region, wherein the first doping element is selected from at least one of cerium, lanthanum, and tin, the second doping element is selected from at least one of manganese and vanadium, and the third doping element is selected from at least one of titanium, magnesium, zirconium, and yttrium.

[0007] In the technical solution of this application embodiment, iron phosphate dihydrate is doped in different regions by doping with doping elements of different ionic radii and effects. This allows the doping elements in different doping regions to synergistically exert their respective properties and jointly improve the low-temperature discharge performance of lithium iron phosphate cathode materials made from it as a precursor. Specifically, the first doping element in the first doping region is selected from rare earth elements or tin elements. When lithium iron phosphate is formed from iron phosphate material, the first doping region is a lithium-rich region. The catalytic effect of rare earth elements or tin elements ensures the sufficient and rapid intercalation and deintercalation of excess lithium ions, improving the discharge performance of the lithium iron phosphate cathode material. The second doping element in the second doping region is selected from metal elements with high valence states. This helps to slightly increase the deformation of the intermediate layer during the lithium ion intercalation and deintercalation process, enlarge the ion diffusion channels, further facilitate the extraction of lithium ions, and improve the discharge performance of the lithium iron phosphate cathode material. The third doping element in the third doping region has the functions of resisting over-sintering, refining grains, suppressing crystal transformation, and avoiding the generation of large single crystal particles, ensuring that the primary particles of the lithium iron phosphate cathode material are small enough, thus improving the discharge performance of the lithium iron phosphate cathode material.

[0008] In some embodiments, the chemical formula of the iron phosphate material is: Fe 1-a-b-m A a B b M m PO4, where 0.0019≤a≤0.007, 0.0088≤b≤0.017, 0.0049≤m≤0.018, A is selected from at least one of cerium, lanthanum, and tin, B is selected from at least one of manganese and vanadium, and M is selected from at least one of titanium, magnesium, zirconium, and yttrium; the average particle size of the primary particles of the iron phosphate material is 160nm~240nm; among the primary particles of the iron phosphate material, the proportion of primary particles with a particle size less than or equal to 0.2μm is 55.06%~64.8%, the proportion of primary particles with a particle size greater than 0.2μm and less than or equal to 0.4μm is 32.43%~42.0%, the proportion of primary particles with a particle size greater than 0.4μm and less than or equal to 0.6μm is 1.3%~6.4%, and the proportion of primary particles with a particle size greater than 0.6μm is 0.31%~1.4%.

[0009] In this embodiment, when the doping amounts of the first, second, and third doping elements meet the above-mentioned ranges, it not only facilitates the full and rapid intercalation and deintercalation of lithium ions when the iron phosphate material is applied to lithium iron phosphate cathode materials, but also helps to resist over-sintering, refine grains, suppress crystal transformation, and avoid the generation of large single crystal particles during the formation of lithium iron phosphate materials using iron phosphate materials as raw materials. This significantly improves the low-temperature discharge performance of lithium iron phosphate cathode materials formed from iron phosphate materials. When the average particle size of the primary particles of the iron phosphate material in this application meets the above-mentioned ranges, it is beneficial to obtain iron phosphate materials with smaller and more suitable particle sizes. Based on this, it is beneficial to obtain lithium iron phosphate cathode materials with suitable particle sizes, thereby facilitating the effective diffusion of lithium ions within the lithium iron phosphate cathode material under low-temperature conditions, enhancing the electrochemical activity of the lithium iron phosphate cathode material in low-temperature environments, and improving the electrochemical performance of the lithium iron phosphate cathode material in low-temperature environments. When the particle size distribution of the primary particles of the iron phosphate material meets the above range, the primary particle size of the iron phosphate material is small and the distribution is concentrated. This is beneficial to obtaining lithium iron phosphate cathode material with small and concentrated primary particle size, which improves the electrochemical performance of lithium iron phosphate cathode material in low temperature environment, while optimizing the consistency of performance such as discharge performance of lithium iron phosphate particles in lithium iron phosphate cathode material.

[0010] Secondly, embodiments of this application provide a lithium iron phosphate cathode material, comprising: lithium iron phosphate particles and a carbon coating layer, wherein the carbon coating layer coats the surface of the lithium iron phosphate particles; wherein the lithium iron phosphate particles include a first doping element, a second doping element, and a third doping element; in the direction from the center of the lithium iron phosphate particles to the coating layer, the lithium iron phosphate particles sequentially include a fourth doping region, a fifth doping region, and a sixth doping region, wherein the first doping element is located in the fourth doping region, the second doping element is located in the fifth doping region, and the third doping element is located in the sixth doping region, wherein the first doping element is selected from at least one of cerium, lanthanum, and tin, the second doping element is selected from at least one of manganese and vanadium, and the third doping element is selected from at least one of titanium, magnesium, zirconium, and yttrium.

[0011] In the technical solution of this application embodiment, lithium iron phosphate particles are partitioned and doped with doping elements of different ionic radii and effects. The catalytic effect of the first doping element promotes the full and complete insertion and extraction of excess lithium ions in the fourth doping region. The second doping element with a high valence state expands the ion diffusion channel, which is conducive to the extraction of internal lithium ions. The third doping element has the effects of resisting over-sintering, refining grains, inhibiting crystal transformation, and avoiding the generation of large single crystal particles, so that the primary particles of the lithium iron phosphate cathode material are small enough. The doping elements in different doping regions work together to exert their respective performance and jointly improve the discharge performance of the lithium iron phosphate cathode material at low temperature.

[0012] In some embodiments, the chemical formula of the lithium iron phosphate cathode material is: LiFe1-a-b-m A a B b M m PO4 / C, where 0.0019≤a≤0.007, 0.0088≤b≤0.017, 0.0049≤m≤0.018, A is selected from at least one of cerium, lanthanum, and tin, B is selected from at least one of manganese and vanadium, and M is selected from at least one of titanium, magnesium, zirconium, and yttrium; the compaction density of the lithium iron phosphate cathode material is 2.55 g / cm³. 3 ~2.65g / cm 3 .

[0013] In this embodiment, when the doping amounts of the first, second, and third doping elements meet the aforementioned ranges, it not only facilitates the full and rapid insertion and extraction of lithium ions, but also helps to resist over-sintering, refine grains, suppress crystal transformation, and avoid the generation of large single crystal particles, thereby significantly improving the low-temperature discharge performance of the lithium iron phosphate cathode material. The lithium iron phosphate cathode material has a high compaction density, which is beneficial for improving the energy density of lithium iron phosphate secondary batteries. Furthermore, because the lithium iron phosphate cathode material of this application combines high compaction density and good low-temperature performance, it is beneficial for better addressing the problem of poor battery life caused by low temperatures, improving the temperature adaptability of secondary batteries, and promoting the wider application of secondary batteries.

[0014] In some embodiments, the average particle size of the primary particles in the lithium iron phosphate cathode material is 330 nm to 360 nm; in the lithium iron phosphate cathode material, the proportion of particles with a particle size less than or equal to 0.2 μm is 48.2% to 63.6%, the proportion of particles with a particle size greater than 0.2 μm and less than or equal to 0.4 μm is 21.3% to 32.5%, the proportion of particles with a particle size greater than 0.4 μm and less than or equal to 0.6 μm is 7.3% to 17.4%, and the proportion of particles with a particle size greater than 0.6 μm and less than or equal to 0.2 μm is 330 nm to 360 nm. The proportion of particles with a diameter of 0.8 μm is 2.4%~4.7%, the proportion of particles with a diameter greater than 0.8 μm and less than or equal to 1 μm is 0.48%~1.56%, the proportion of particles with a diameter greater than 1 μm and less than or equal to 2 μm is 1.5%~5.2%, and the proportion of particles with a diameter greater than 2 μm and less than or equal to 5 μm is 1.3%~1.9%; the D50 particle size of the lithium iron phosphate cathode material is 1.35 μm~1.65 μm; the specific surface area of ​​the lithium iron phosphate cathode material is 12 m². 2 / g~15m 2 / g; The powder resistivity of lithium iron phosphate cathode material is 10Ω. cm~15Ω cm; the mass fraction of the carbon coating layer in the lithium iron phosphate cathode material is 1.35%~1.43%; the free lithium content in the lithium iron phosphate cathode material is 150ppm~220ppm.

[0015] In this embodiment, when the average particle size of the primary particles of the lithium iron phosphate cathode material meets the above-mentioned range, it has a smaller primary particle size and the particle size of the primary particles is more concentrated. This is beneficial for the close contact and uniform arrangement between the lithium iron phosphate cathode material particles, as well as the effective diffusion of lithium ions inside the lithium iron phosphate cathode material under low-temperature conditions, thereby improving the electrochemical activity and electrochemical performance of the lithium iron phosphate cathode material under low-temperature conditions. When the particle size distribution of the lithium iron phosphate cathode material meets the above-mentioned range, on the one hand, the particle size distribution is uniform and the overall finished particle size is small, and the internal arrangement of the lithium iron phosphate cathode material is more uniform, which helps to form a balanced voltage platform and keep the secondary battery stable during operation; on the other hand, the presence of large particles of a certain size is beneficial to improving the compaction density and energy density per unit volume. This application utilizes the gradation effect between particles of different sizes of lithium iron phosphate cathode material, which is beneficial to improving the compaction density of lithium iron phosphate cathode material and improving the stress between the particles of lithium iron phosphate cathode material, thereby enhancing the structural stability of lithium iron phosphate cathode material and extending the cycle life of lithium iron phosphate cathode material. When the D50 particle size of the lithium iron phosphate (LFP) cathode material meets the above-mentioned range, it possesses a suitable D50 particle size, which not only helps to shorten the lithium-ion diffusion path and improve the capacity and rate performance of the LFP cathode material, but also improves the fluidity and dispersibility of the electrode slurry when the LFP cathode material is applied to the cathode sheet, resulting in more uniform coating during cathode sheet preparation, which is beneficial for large-scale production. When the specific surface area of ​​the LFP cathode material meets the above-mentioned range, it helps to have an appropriate number of active sites, improving the electrochemical activity of LFP and enhancing the electrochemical performance of the LFP cathode material at low temperatures. When the powder resistivity of the LFP cathode material meets the above-mentioned range, its low powder resistivity is beneficial to improving the conductivity of the LFP cathode material, increasing the electron transport speed, improving the charge and discharge efficiency of the LFP cathode material, and enhancing the rate performance, cycle life, and safety of the LFP cathode material. When the mass fraction of the carbon coating in the lithium iron phosphate cathode material meets the above-mentioned range, it is beneficial to form a continuous and uniform carbon coating on the surface of the lithium iron phosphate particles, reducing the resistance of the lithium iron phosphate cathode material, improving its electronic conductivity, and thus enhancing its charge-discharge performance and rate performance. When the free lithium content in the lithium iron phosphate cathode material meets the above-mentioned range, the moderate free lithium content can provide an additional lithium source within the electrode material, which helps to improve the initial charge-discharge efficiency and reversible capacity of the secondary battery.

[0016] Thirdly, embodiments of this application provide a method for preparing a lithium iron phosphate cathode material, comprising the following steps: Provide iron phosphate materials; Lithium iron phosphate material, lithium source, first organic carbon source, second organic carbon source and first solvent are mixed, and then dried and sintered to obtain lithium iron phosphate cathode material; wherein, The iron phosphate material includes iron phosphate dihydrate particles, which include a first doping element, a second doping element, and a third doping element. Along the direction from the center of the iron phosphate dihydrate particle to its outer side, the iron phosphate dihydrate particle sequentially includes a first doping region, a second doping region, and a third doping region. The first doping element is located within the first doping region, the second doping element is located within the second doping region, and the third doping element is located within the third doping region. The first doping element is selected from at least one of cerium, lanthanum, and tin; the second doping element is selected from at least one of manganese and vanadium; and the third doping element is selected from at least one of titanium, magnesium, zirconium, and yttrium. The molecular weight of the first organic carbon source is less than the molecular weight of the second organic carbon source.

[0017] In the technical solution of this application embodiment, on the one hand, lithium iron phosphate cathode material is prepared using the above-mentioned partitioned doped iron phosphate material as a precursor. The first doping element is used to improve the catalytic effect and promote the full and rapid insertion and extraction of lithium ions. The second doping element is used to expand the ion diffusion channel, which is conducive to the extraction of internal lithium ions. The third doping element is used to resist over-sintering, refine grains, suppress crystal transformation, and avoid the generation of large single crystal particles, so that the primary particles of the lithium iron phosphate cathode material are small enough. The doping elements in different doping regions exert their respective properties and jointly improve the low-temperature discharge performance of lithium iron phosphate secondary batteries. On the other hand, lithium iron phosphate is layered with organic carbon sources of different molecular weights. The carbon source with a smaller molecular weight is used to effectively coat and disperse the lithium iron phosphate particles. The carbon source with a larger molecular weight is used to promote the fusion of some lithium iron phosphate particles and form agglomerates. The carbon source with a larger molecular weight is decomposed and then used for secondary coating to improve the integrity of the coating layer. Thus, while increasing the compaction density, excellent discharge performance is maintained. In this way, a lithium iron phosphate cathode material with high compaction density and high discharge performance under low temperature conditions is prepared, which is conducive to promoting the development of secondary batteries with longer battery life at low temperatures.

[0018] In some embodiments, the preparation steps of the iron phosphate material include: The first ferrous source, the first phosphorus source, the first dopant, the first oxidant, and the second solvent are subjected to a first reaction treatment to obtain a first reaction slurry; The first reaction slurry, the second ferrous source, the second phosphorus source, the second dopant, and the second oxidant are processed by the second reaction to obtain the second reaction slurry; The second reaction slurry, the third ferrous source, the third phosphorus source, the third dopant, and the third oxidant are processed by the third reaction to obtain the third reaction slurry; The third reaction slurry, after aging and post-treatment, yields iron phosphate material; among which, The first dopant is at least one of the following: oxides, hydroxides, chlorides, nitrates, sulfates, carbonates, and oxalates of cerium, lanthanum, and / or tin; The second dopant is at least one of the following: oxides, hydroxides, chlorides, nitrates, sulfates, carbonates, oxalates, and oxyacids of manganese and / or vanadium. The third dopant is at least one of the following: oxides, hydroxides, chlorides, nitrates, sulfates, carbonates, and oxalates of titanium, magnesium, zirconium, and / or yttrium.

[0019] In this embodiment, a mixture of ferrous source, phosphorus source, dopant, oxidant, and solvent is reacted to form an internal doped compound. The cations in the dopant and ferrous ions participate in the precipitation reaction. The iron source, dopant, phosphorus source, and oxidant are added in batches according to a certain ratio to form a hierarchical lithium iron phosphate material. The catalytic effect of the first dopant promotes the full and rapid insertion and extraction of lithium ions. The second dopant expands the ion diffusion channel, which is beneficial for the extraction of internal lithium ions. The third dopant plays a role in resisting over-sintering, refining grains, inhibiting crystal transformation, and avoiding the formation of large single crystal particles. This ensures that the primary particles of the lithium iron phosphate cathode material are small enough, and that the dopant elements at different levels work together to exert their respective performances, ultimately improving the low-temperature discharge performance of the prepared lithium iron phosphate.

[0020] In some embodiments, the first ferrous source, the second ferrous source, and the third ferrous source are each independently selected from at least one of ferrous sulfate, ferrous chloride, ferrous nitrate, and ferrous acetate; the first phosphorus source, the second phosphorus source, and the third phosphorus source are each independently selected from at least one of phosphoric acid, ammonium phosphate, ammonium monohydrogen phosphate, ammonium dihydrogen phosphate, sodium phosphate, sodium monohydrogen phosphate, sodium dihydrogen phosphate, potassium phosphate, potassium monohydrogen phosphate, and potassium dihydrogen phosphate; the first oxidant, the second oxidant, and the third oxidant are each independently selected from at least one of hydrogen peroxide, sodium peroxide, potassium peroxide, and oxygen; the molar ratio of the first ferrous source to the first phosphorus source and the first dopant in the first dopant is 1:(1.3~2.5):(0.01~0.07); the molar ratio of the first ferrous source to the first oxidant is 1:(3.2~7.3); the molar ratio of the second ferrous source to the second ...3.2~7.3); the molar ratio of the second ferrous source to the second phosphorus source and the first dopant in the first dopant is 1:(3.2~7.3); the molar ratio of the second ferrous source to the second phosphorus source and the first dopant in the first dopant is 1:(3.2~7.3); the molar ratio of the second ferrous source to the second phosphorus source and the first dopant in the first dopan The molar ratio of the second dopant element in the two dopants is 1:(1.1~2.75):(0.01~0.04); the molar ratio of the second ferrous source to the second oxidant is 1:(4.8~13.2); the molar ratio of the third ferrous source to the third phosphorus source and the third dopant element in the third dopant is 1:(1.6~3.95):(0.01~0.1); the molar ratio of the third ferrous source to the third oxidant is 1:(2~3.9); the molar ratio of the first ferrous source to the second and third ferrous sources is (10~15):(40~70):(15~50); the molar ratio of the first phosphorus source to the second and third phosphorus sources is (20~30):(55~140):(55~140); the molar ratio of the first oxidant to the second and third oxidants is 1:(3~8):(0.5~3).

[0021] In this embodiment, the aforementioned ferrous source, phosphorus source, and oxidant have the advantages of wide selection and low cost, which is beneficial for large-scale industrial production. When the molar ratio of the first ferrous source to the first phosphorus source and the first dopant element meets the above-mentioned range, it is conducive to the complete precipitation of iron and the first dopant element, avoiding excessively small particle size caused by excessive nucleation, and obtaining iron phosphate material with a more suitable particle size. When the molar ratio of the first ferrous source to the first oxidant meets the above-mentioned range, it is conducive to improving the reaction rate and the degree of reaction of ferrous ions, and fully converting ferrous ions into ferric ions. When the molar ratio of the second ferrous source to the second phosphorus source and the second dopant element meets the above-mentioned range, it is conducive to the complete precipitation of iron and the second dopant element, avoiding excessively small particle size caused by excessive nucleation, and obtaining iron phosphate material with a more suitable particle size. When the molar ratio of the second ferrous source to the second oxidant meets the above-mentioned range, it is conducive to improving the reaction rate and the degree of reaction of ferrous ions, and fully converting ferrous ions into ferric ions. When the molar ratio of the third ferrous source to the third phosphorus source and the third dopant element meets the above-mentioned range, it is beneficial for the complete precipitation of iron and the third dopant element, avoiding excessively small particle size caused by excessive nucleation, and obtaining iron phosphate material with a more suitable particle size. When the molar ratio of the third ferrous source to the third oxidant meets the above-mentioned range, the reaction rate slows down and the reaction is more complete, thereby improving the iron-phosphorus ratio. When the molar ratio of the first ferrous source to the second and third ferrous sources meets the above-mentioned range, it is beneficial to adjust the size of the first, second, and third doped regions of the iron phosphate material, allowing the dopants in different doped regions to fully exert their respective functions, which is conducive to the discharge performance of lithium iron phosphate material. When the molar ratio of the first phosphorus source to the second and third phosphorus sources meets the above-mentioned range, in combination with the ferrous salts and oxidants at each stage, it is beneficial for the complete precipitation of dopants and the on-demand precipitation of iron, thereby obtaining iron phosphate material with a more suitable particle size and iron-phosphorus ratio. When the molar ratio of the first oxidant to the second and third oxidants meets the above range, it can be combined with ferrous salts and phosphorus sources at each stage to better control the reaction rate and oxidation degree of ferrous iron at each stage, thereby obtaining iron phosphate materials with more suitable particle size and iron-phosphorus ratio.

[0022] In some embodiments, the step of obtaining a first reaction slurry by treating a first ferrous source, a first phosphorus source, a first dopant, a first oxidant, and a second solvent through a first reaction includes: providing a first solution containing a first ferrous source, a second solution containing a first phosphorus source and a first dopant, and a third solution containing a first oxidant; mixing the second solution and the third solution into the first solution at a first mixing temperature and a first mixing time to obtain a first mixture; and obtaining the first reaction slurry from the first mixture at a first reaction temperature and after a first reaction time; wherein the first mixing temperature is 15°C to 35°C, the first mixing time is 40 min to 50 min, the first reaction temperature is 35°C to 55°C, and the first reaction time is 20 min to 40 min. The step of obtaining a second reaction slurry by subjecting a first reaction slurry, a second ferrous source, a second phosphorus source, a second dopant, and a second oxidant to a second reaction treatment includes: providing a fourth solution containing a second ferrous source, a fifth solution containing a second phosphorus source and a second dopant, and a sixth solution containing a second oxidant; mixing the fourth solution with the first reaction slurry at a second mixing temperature and a second mixing time to obtain a second mixture; mixing the fifth solution and the sixth solution at a third mixing temperature and a third mixing time to obtain a third mixture; and obtaining the second reaction slurry from the third mixture at a second reaction temperature and a second reaction time; wherein the second mixing temperature is 40℃~60℃, the second mixing time is 10min~30min, the third mixing temperature is 45℃~65℃, the third mixing time is 10min~30min, the second reaction temperature is 55℃~75℃, and the second reaction time is 20min~40min. The step of obtaining a third reaction slurry by subjecting the second reaction slurry, the third ferrous source, the third phosphorus source, the third dopant, and the third oxidant to a third reaction treatment includes: providing a seventh solution containing the third ferrous source, a third dopant, an eighth solution containing the third phosphorus source, and a ninth solution containing the third oxidant; mixing the seventh solution, the third dopant, and the second reaction slurry at a fourth mixing temperature and a fourth mixing time to obtain a fourth mixture; and mixing the eighth solution and the ninth solution at a fifth mixing temperature and a fifth mixing time to obtain the fourth mixture to obtain the third reaction slurry; wherein the fourth mixing temperature is 55℃~75℃, the fourth mixing time is 10min~20min, the fifth mixing temperature is 50℃~75℃, and the fifth mixing time is 30min~40min; The step of obtaining ferric phosphate material by aging and post-treatment of the third reaction slurry includes: mixing the third reaction slurry with a pH adjuster to obtain a fifth mixture with a pH of 1.1 to 1.4; reacting the fifth mixture at a third reaction temperature for a third reaction time to obtain a fourth reaction slurry with a pH of 1.7 to 1.9; and post-treatment of the fourth reaction slurry to obtain ferric phosphate material; wherein the third reaction temperature is 90℃ to 100℃ and the third reaction time is 1h to 3h.

[0023] In this embodiment, a second solution containing a first phosphorus source and a first dopant is mixed with a third solution containing a first oxidant at a first mixing temperature and within a first mixing time, and then mixed with a first solution containing a first ferrous source. The first phosphorus source and the first dopant are pre-mixed to form seed crystals, which then react with the first ferrous source. This helps to better control the doping position of the first dopant element and avoids the problem of insufficient reaction and difficulty in control during the co-precipitation process of the first dopant element and the first ferrous source due to significant competition. At the first reaction temperature and within the first reaction time, the cations in the dopant and ferrous ions co-precipitate to form a monolayer of doped amorphous iron phosphate, resulting in a first reaction slurry containing monolayer doped amorphous iron phosphate. When the first mixing temperature and the first mixing time meet the above range, it helps to control the reaction rate, allowing the reactants sufficient time to diffuse uniformly and improving the particle size and uniformity of iron phosphate particles. When the first reaction temperature and the first reaction time meet the above range, the reaction rate is increased, promoting the formation of iron phosphate particles, while simultaneously regulating the growth uniformity and crystal structure integrity of iron phosphate particles, thereby improving the capacity of the lithium iron phosphate cathode material.

[0024] A fourth solution containing a second ferrous source is mixed with a first reaction slurry at a second mixing temperature and a second mixing time to obtain a second mixture. A fifth solution containing a second phosphorus source and a second dopant is mixed with a sixth solution containing a second oxidant at a third mixing temperature and a third mixing time to form the second mixture. The second phosphorus source and the second dopant are pre-mixed to form seed crystals, which then react with the second ferrous source. This facilitates better control of the doping position of the second dopant element and avoids the problem of insufficient reaction and difficulty in control during the co-precipitation process of the second dopant element and the second ferrous source due to significant competition. The third mixture is then processed at the second reaction temperature and after a second reaction time, utilizing monolayer doping. Amorphous iron phosphate is used as a seed crystal to continue growth, resulting in a second reaction slurry containing double-layer doped amorphous iron phosphate. When the second mixing temperature and the second mixing time meet the above range, it is beneficial to achieve sufficient mixing between the fourth solution and the first reaction slurry. When the third mixing temperature and the third mixing time meet the above range, it is beneficial to control the reaction rate, allowing the reactants sufficient time to diffuse uniformly, thereby improving the particle size and uniformity of the iron phosphate particles. When the second reaction temperature and the second reaction time meet the above range, it increases the reaction rate, promotes the formation of iron phosphate particles, and simultaneously regulates the growth uniformity and crystal structure integrity of the iron phosphate particles, thereby improving the capacity of the lithium iron phosphate cathode material.

[0025] The seventh solution with a third ferrous source, the third dopant, and the second reaction slurry are mixed at a fourth mixing temperature and a fourth mixing time to obtain a fourth mixture. The eighth solution with a third phosphorus source and the ninth solution with a third oxidant are mixed at a fifth mixing temperature and a fifth mixing time to obtain the fourth mixture. Using double-layer doped amorphous iron phosphate as seed crystals, the mixture continues to grow to obtain a third reaction slurry containing triple-layer doped amorphous iron phosphate. When the fourth mixing temperature and the fourth mixing time meet the above range, it is beneficial to achieve sufficient mixing of the seventh solution, the third dopant, and the second reaction slurry. When the fifth mixing temperature and the fifth mixing time meet the above range, it is beneficial to allow the reactants sufficient time to diffuse uniformly, increase the reaction rate, avoid the formation of crystal nuclei, regulate the growth consistency of iron phosphate particles, obtain iron phosphate materials with suitable particle size, and improve the capacity of lithium iron phosphate cathode materials.

[0026] The third reaction slurry is mixed with a pH adjuster to obtain a fifth mixture. The pH of the fifth mixture is 1.1~1.4, which is conducive to promoting the formation of ferric phosphate. The fifth mixture is subjected to the third reaction temperature and the third reaction time to convert the three-layer doped amorphous ferric phosphate into three-layer doped crystalline ferric phosphate dihydrate, resulting in a fourth reaction slurry containing three-layer doped crystalline ferric phosphate dihydrate. The fourth reaction slurry is then post-processed to obtain ferric phosphate material. When the third reaction temperature and the third reaction time meet the above range, it is conducive to complete crystal transformation and avoids changes in crystal morphology due to excessively high temperature, which would affect the stability of the product.

[0027] In some embodiments, the molar ratio of iron in the iron phosphate material to lithium in the lithium source is 1:(1.03~1.06); the difference between the molecular weight of the second organic carbon source and the molecular weight of the first organic carbon source is greater than or equal to 800; the molecular weight of the first organic carbon source is less than or equal to 200, and the molecular weight of the second organic carbon source is greater than or equal to 1000 and less than or equal to 12000; the first organic carbon source is at least one of glycerol or diglycerol; the mass of the first organic carbon source is 2.1%~3.7% of the mass of the iron phosphate material; the second organic carbon source is at least one of β-cyclodextrin or polyethylene glycol; the mass of the second organic carbon source is 8.3%~9.2% of the mass of the iron phosphate material. The steps of mixing iron phosphate material, lithium source, first organic carbon source, second organic carbon source and first solvent include: mixing iron phosphate material, lithium source, first organic carbon source, second organic carbon source and first solvent to obtain a mixed slurry with a solid content of 47.5%~49.3%; and grinding the mixed slurry to obtain a grinding slurry with a D50 particle size of 0.32μm~0.38μm for the solid particles in the grinding slurry. The step of mixing iron phosphate material, lithium source, first organic carbon source, second organic carbon source and first solvent includes: mixing iron phosphate material, lithium source, iron supplementing agent, first organic carbon source, second organic carbon source and first solvent to obtain grinding slurry; wherein, the iron supplementing agent is at least one of ferrous oxalate, ferric citrate and ferric dihydrogen phosphate; the mass of the iron supplementing agent is 0.8% to 1.2% of the mass of iron phosphate material; The steps of mixing iron phosphate material, lithium source, first organic carbon source, second organic carbon source and first solvent, followed by drying and sintering to obtain lithium iron phosphate cathode material include: mixing iron phosphate material, lithium source, first organic carbon source, second organic carbon source and first solvent to obtain a grinding slurry; drying the grinding slurry to obtain a dried material with a D50 particle size of 0.55μm~0.8μm; obtaining the lithium iron phosphate cathode material by sintering the dried material at a first sintering temperature for a first holding time, and then at a second sintering temperature for a second holding time; the first sintering temperature is 800℃~820℃, the first holding time is 0.5h~4h, the second sintering temperature is 780℃~805℃, and the second holding time is 7h~12h.

[0028] In this embodiment, when the molar ratio of iron in the iron phosphate material to lithium in the lithium source meets the above-mentioned range, an appropriate excess of lithium source ensures sufficient free lithium is generated, thereby increasing the material's capacity and avoiding waste caused by excessive lithium source. When the difference between the molecular weight of the second organic carbon source and the molecular weight of the first organic carbon source meets the above-mentioned range, or when the molecular weights of the second and first organic carbon sources respectively meet the above-mentioned ranges, it is beneficial to better utilize the respective roles of the first and second organic carbon sources, obtaining a lithium iron phosphate cathode material that balances high compaction density and excellent discharge performance. The first organic carbon source has the advantages of small molecular weight and low melting point, which is beneficial for better coating and dispersion of lithium iron phosphate particles. When the amount of the first organic carbon source added meets the above-mentioned range, it is beneficial for sufficient coating of lithium iron phosphate particles and sufficient dispersion between them. The second organic carbon source has the characteristic of high decomposition temperature, which makes it easy to bond some lithium iron phosphate particles during sintering and promotes the fusion of bonded lithium iron phosphate particles to form agglomerates, thereby increasing the compaction density of the lithium iron phosphate cathode material. When the amount of the second organic carbon source added meets the above range, it helps to generate an appropriate amount of agglomerates, thereby improving the compaction density of the lithium iron phosphate cathode material without affecting its electrochemical performance.

[0029] When the solid content of the mixed slurry meets the above-mentioned range, it not only facilitates more uniform mixing of the components in the mixed slurry, thereby improving the consistency of the lithium iron phosphate cathode material, but also helps to shorten the drying time and reduce energy consumption. When the D50 particle size of the solid particles in the grinding slurry meets the above-mentioned range, it helps to adjust the particle size of the iron phosphate dihydrate particles participating in the sintering process, thereby helping to improve the electrochemical performance and performance consistency of the lithium iron phosphate cathode material.

[0030] Adding the above-mentioned amount of iron supplementer appropriately replenishes iron, regulates the proportion of iron in the lithium iron phosphate cathode material, and improves the charging specific capacity of the lithium iron phosphate cathode material. The above-mentioned iron supplementer has the advantages of wide availability and low cost, and can be used to prepare lithium iron phosphate cathode material by solid-state sintering with iron phosphate material, lithium source, and organic carbon source, and improve the iron-phosphorus ratio of lithium iron phosphate cathode material.

[0031] When the D50 particle size of the dried material meets the above-mentioned range, it is beneficial to the full formation of lithium iron phosphate cathode material grains during sintering, and the resulting primary particles of lithium iron phosphate cathode material are smaller and more concentrated. When the first sintering temperature, first holding time, second sintering temperature, and second holding time meet the above-mentioned range, it is beneficial to control the carbon coating process in conjunction with the different decomposition temperatures of the first and second organic carbon sources. While effectively coating and dispersing lithium iron phosphate particles using the first organic carbon source, the second organic carbon source promotes the fusion of some lithium iron phosphate particles and the formation of agglomerates, thereby improving the compaction density of the lithium iron phosphate cathode material while maintaining excellent discharge performance.

[0032] Fourthly, embodiments of this application provide a positive electrode sheet, which includes a lithium iron phosphate positive electrode material prepared by the preparation method of the lithium iron phosphate positive electrode material of the second aspect of this application or the lithium iron phosphate positive electrode material of the third aspect of this application.

[0033] In the technical solution of this application embodiment, the positive electrode sheet contains the above-mentioned positive electrode material, and thus has good electrochemical performance at low temperature and higher volumetric energy density.

[0034] Fifthly, embodiments of this application provide a secondary battery, which includes the positive electrode sheet of the fourth aspect of this application.

[0035] In the technical solution of this application embodiment, the secondary battery includes the above-mentioned positive electrode sheet, and thus has good electrochemical performance at low temperature and higher volumetric energy density.

[0036] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

[0037] To more clearly illustrate the technical solutions of this application, the accompanying drawings used in this application will be briefly described below. Obviously, the drawings described below are merely some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without any creative effort.

[0038] Figure 1 This is a process flow diagram of one embodiment of the preparation method of lithium iron phosphate cathode material provided in this application; Figure 2 This is a scanning electron microscope image of the lithium iron phosphate cathode material provided in Embodiment 5 of this application; Figure 3 This is a particle size distribution diagram of the lithium iron phosphate cathode material provided in Example 5 of this application, based on scanning electron microscopy. Figure 4 This is a scanning electron microscope image of the lithium iron phosphate cathode material provided in Comparative Example 1 of this application; Figure 5 This is a particle size distribution diagram of the lithium iron phosphate cathode material provided in Comparative Example 1 of this application based on scanning electron microscopy. Figure 6 This is a cross-sectional EDS elemental analysis diagram of the lithium iron phosphate cathode material provided in Example 5 of this application; Figure 7 This is a cross-sectional EDS elemental analysis diagram of the lithium iron phosphate cathode material provided in Comparative Example 1 of this application. Detailed Implementation

[0039] The embodiments of the technical solution of this application will now be described in detail with reference to the accompanying drawings. These embodiments are only used to more clearly illustrate the technical solution of this application and are therefore merely examples, and should not be used to limit the scope of protection of this application.

[0040] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0041] 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.

[0042] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0043] 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.

[0044] 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).

[0045] In the description of the embodiments of this application, unless otherwise specified, "content" refers to the mass percentage of the tested element, molecule or ion in the sample.

[0046] In the description of the embodiments of this application, unless otherwise specified, "ppm" means the mass of the tested element, molecule or ion in parts per million of the sample mass.

[0047] In the description of the embodiments of this application, unless otherwise specified, the solvent used to form the solution, slurry, etc., and the washing water used for rinsing are each independently selected from at least one of distilled water, deionized water, pure water, and ultrapure water.

[0048] In existing technologies, the performance of lithium iron phosphate (LFP) at low temperatures limits its development. Currently, the main methods to improve the low-temperature discharge performance of LFP are doping and secondary carbon coating, but the improvement is still not significant. Increasing the doping amount helps to improve the low-temperature electrochemical performance of LFP materials; however, when high doping amounts are combined with traditional preparation processes, it is often difficult to achieve the preparation of LFP cathode materials with high compaction density, resulting in poor battery life for LFP secondary batteries in winter.

[0049] To address the issue of insufficient low-temperature electrochemical performance of existing lithium iron phosphate (LFP) batteries, this application provides an iron phosphate material, an LFP cathode material, its preparation method, and its applications. On one hand, this application significantly improves the low-temperature discharge performance of LFP cathode materials prepared using iron phosphate dihydrate as a precursor by partitioning it with elements of different ionic radii and effects. On the other hand, the partial gradation effect of small particle bonding to form larger particles not only minimizes the impact on the capacity of the LFP cathode material but also significantly increases the compaction density and energy density per unit volume. The combination of these two factors further enhances the low-temperature performance of LFP secondary batteries while significantly improving their range due to the higher compaction density, thus ensuring better adaptability and wider deployment of electric vehicles and promoting the development of electric vehicles with longer ranges.

[0050] In a first aspect, embodiments of this application provide an iron phosphate material, comprising: iron phosphate dihydrate particles, each particle including a first dopant element, a second dopant element, and a third dopant element; wherein, in the direction from the center of the iron phosphate dihydrate particle to its outer side, the iron phosphate dihydrate particle sequentially includes a first doped region, a second doped region, and a third doped region, wherein the first dopant element is located within the first doped region, the second doped element is located within the second doped region, and the third doped element is located within the third doped region; the first doped element is selected from at least one of cerium, lanthanum, and tin; the second doped element is selected from at least one of manganese and vanadium; and the third doped element is selected from at least one of titanium, magnesium, zirconium, and yttrium. It should be noted that adjacent two or more doped regions can be completely separated, or some regions can overlap. For example, the boundary between the first and second doped regions may simultaneously contain both the first and second doped elements, and the boundary between the second and third doped regions may simultaneously contain both the second and third doped elements.

[0051] In the technical solution of this application embodiment, iron phosphate dihydrate is doped in different regions by doping with doping elements of different ionic radii and effects. This allows the doping elements in different doping regions to synergistically exert their respective properties and jointly improve the low-temperature discharge performance of lithium iron phosphate cathode materials made from it as a precursor. Specifically, the first doping element in the first doping region is selected from rare earth elements or tin elements. When lithium iron phosphate is formed from iron phosphate material, the first doping region is a lithium-rich region. The catalytic effect of rare earth elements or tin elements ensures the sufficient and rapid intercalation and deintercalation of excess lithium ions, improving the discharge performance of the lithium iron phosphate cathode material. The second doping element in the second doping region is selected from metal elements with high valence states. This helps to slightly increase the deformation of the intermediate layer during the lithium ion intercalation and deintercalation process, enlarge the ion diffusion channels, further facilitate the extraction of lithium ions, and improve the discharge performance of the lithium iron phosphate cathode material. The third doping element in the third doping region has the functions of resisting over-sintering, refining grains, suppressing crystal transformation, and avoiding the generation of large single crystal particles, ensuring that the primary particles of the lithium iron phosphate cathode material are small enough, thus improving the discharge performance of the lithium iron phosphate cathode material.

[0052] Furthermore, in some embodiments, the chemical formula of the iron phosphate material is: Fe 1-a-b-m A a B b M m PO4, where 0.0019 ≤ a ≤ 0.007, 0.0088 ≤ b ≤ 0.017, 0.0049 ≤ m ≤ 0.018, A is selected from at least one of cerium, lanthanum, and tin, B is selected from at least one of manganese and vanadium, and M is selected from at least one of titanium, magnesium, zirconium, and yttrium. As an example, the chemical formula of iron phosphate materials may include, but is not limited to: Fe 0.967 Ce 0.004 Mn 0.012 Mg 0.006 PO4, Fe 0.963 Sn 0.004 Mn 0.012 Ti 0.006 PO4, Fe 0.958 Sn 0.007 Mn 0.011 V 0.0053 Mg 0.009 PO4, Fe 0.964 La 0.0005 Ce 0.0015 Mn 0.009 Zr 0.005 PO4, Fe 0.968 La 0.007 Mn 0.016 Y 0.018 PO4, Fe 0.95 La 0.001 Ce 0.001 Sn 0.003 Mn0.015 Ti 0.003 Zr 0.003 Mg 0.003 PO4, Fe 0.95 La 0.003 Sn 0.004 Mn 0.016 Zr 0.006 Mg 0.00 3PO4, Fe 0.972 Sn 0.007 Mn 0.011 V 0.0053 Mg 0.009 PO4, Fe 0.95 Sn 0.007 Mn 0.011 V 0.0053 Mg 0.009 PO4, Fe 0.97 Sn 0.007 Mn 0.011 V 0.0053 Mg 0.009 PO4, Fe 0.96 Sn 0.007 Mn 0.011 V 0.0053 Mg 0.009 PO4, Fe 0.962 Sn 0.007 Mn 0.011 V 0.0053 Mg 0.009 PO4, Fe 0.973 Sn 0.007 Mn 0.011 V 0.0053 Mg 0.009 PO4, etc.

[0053] Specifically, the values ​​of 'a' include, but are not limited to, 0.0019, 0.003, 0.004, 0.005, 0.006, and 0.007; the values ​​of 'b' include, but are not limited to, 0.0088, 0.01, 0.011, 0.012, 0.013, 0.014, 0.015, 0.016, and 0.017; and the values ​​of 'm' include, but are not limited to, 0.0049, 0.006, 0.008, 0.01, 0.012, 0.014, 0.016, and 0.018.

[0054] In the technical solution of this application embodiment, when the doping amounts of the first, second, and third doping elements meet the above-mentioned ranges, it not only facilitates the full and rapid intercalation and deintercalation of lithium ions when iron phosphate material is applied to lithium iron phosphate cathode material, but also helps to resist over-sintering, refine grains, suppress crystal transformation, and avoid the generation of large single crystal particles during the formation of lithium iron phosphate material using iron phosphate material as raw material, thereby significantly improving the low-temperature discharge performance of lithium iron phosphate cathode material formed using iron phosphate material as raw material. If the doping amounts of the first, second, and third doping elements are too low, it will not be conducive to better exerting the role of each doping element; if the doping amount of the first doping element is too high, it will lead to a low iron-phosphorus ratio and a reduction in lithium ions; if the doping amount of the second doping element is too high, it will lead to excessive deformation, and the crystal structure will be easily destroyed during the charging and discharging process; if the doping amount of the third doping element is too high, it will not only lead to the generation of magnetic foreign matter, but also lead to poor particle fusion performance, making it difficult to control the crushed particle size, thereby resulting in a low compaction density.

[0055] Furthermore, in some embodiments, the iron-to-phosphorus ratio of the iron phosphate material is 0.950 to 0.973, including but not limited to 0.950, 0.955, 0.960, 0.965, 0.97, 0.973, etc., preferably 0.950 to 0.968.

[0056] In the technical solution of this application embodiment, when the iron-to-phosphorus ratio of the iron phosphate material meets the above-mentioned range, the phosphorus element in the iron phosphate structure is excessive, resulting in more defects. This improves the conductivity and ion mobility of the lithium iron phosphate cathode material obtained from iron phosphate material, thereby enhancing the low-temperature discharge performance of the lithium iron phosphate cathode material. When the iron-to-phosphorus ratio of the iron phosphate material meets the above-mentioned range, excessive defects and impurities are avoided from damaging the overall structure of the iron phosphate material, thus preventing a decrease in the cycle stability and long-term reliability of the lithium iron phosphate cathode material obtained from iron phosphate material.

[0057] Furthermore, in some embodiments, the average particle size of the primary particles of the iron phosphate material is 160 nm to 240 nm.

[0058] In the technical solution of this application embodiment, when the average particle size of the primary particles of the iron phosphate material meets the above-mentioned range, it is beneficial to obtain iron phosphate material with a smaller and more suitable particle size, and on this basis, it is beneficial to obtain lithium iron phosphate cathode material with a suitable particle size. This is beneficial to the effective diffusion of lithium ions inside the lithium iron phosphate cathode material under low temperature conditions, thereby improving the electrochemical activity of the lithium iron phosphate cathode material under low temperature conditions and improving the electrochemical performance of the lithium iron phosphate cathode material under low temperature conditions.

[0059] Furthermore, in some embodiments, in the primary particles of the iron phosphate material, the proportion of primary particles with a particle size of 0.2 μm or less is 55.06% to 64.8%, the proportion of primary particles with a particle size greater than 0.2 μm and less than or equal to 0.4 μm is 32.43% to 42.0%, the proportion of primary particles with a particle size greater than 0.4 μm and less than or equal to 0.6 μm is 1.3% to 6.4%, and the proportion of primary particles with a particle size greater than 0.6 μm is 0.31% to 1.4%. In a preferred embodiment, the primary particles of the iron phosphate material have the following proportions: particles with a diameter of 0.2 μm or less account for 55.06% to 64.53%; particles with a diameter greater than 0.2 μm and less than or equal to 0.4 μm account for 33.69% to 38.74%; particles with a diameter greater than 0.4 μm and less than or equal to 0.6 μm account for 1.3% to 6.4%; and particles with a diameter greater than 0.6 μm account for 0.31% to 1.4%.

[0060] In the technical solution of this application embodiment, when the particle size distribution of the primary particles of the iron phosphate material meets the above range, the primary particle size of the iron phosphate material is small and the distribution is concentrated, which is beneficial to obtain lithium iron phosphate cathode material with small and concentrated primary particle size. This improves the electrochemical performance of lithium iron phosphate cathode material in low temperature environment, while optimizing the consistency of performance such as discharge performance of lithium iron phosphate particles in lithium iron phosphate cathode material.

[0061] Secondly, embodiments of this application provide a lithium iron phosphate cathode material, comprising: lithium iron phosphate particles and a carbon coating layer, wherein the carbon coating layer coats the surface of the lithium iron phosphate particles; wherein the lithium iron phosphate particles include a first doping element, a second doping element, and a third doping element; in the direction from the center of the lithium iron phosphate particle to the coating layer, the lithium iron phosphate particles sequentially include a fourth doping region, a fifth doping region, and a sixth doping region, wherein the first doping element is located in the fourth doping region, the second doping element is located in the fifth doping region, and the third doping element is located in the sixth doping region; the first doping element is selected from at least one of cerium, lanthanum, and tin, the second doping element is selected from at least one of manganese and vanadium, and the third doping element is selected from at least one of titanium, magnesium, zirconium, and yttrium. It should be noted that adjacent two or more doping regions can be completely separated, or some regions can overlap. For example, the boundary between the fourth and fifth doping regions may simultaneously contain both the fourth and fifth doping elements, and the boundary between the fifth and sixth doping regions may simultaneously contain both the fifth and sixth doping elements.

[0062] In the technical solution of this application embodiment, lithium iron phosphate particles are partitioned and doped with doping elements of different ionic radii and effects. The catalytic effect of the first doping element promotes the full and complete insertion and extraction of excess lithium ions in the fourth doping region. The second doping element with a high valence state expands the ion diffusion channel, which is conducive to the extraction of internal lithium ions. The third doping element has the effects of resisting over-sintering, refining grains, inhibiting crystal transformation, and avoiding the generation of large single crystal particles, so that the primary particles of the lithium iron phosphate cathode material are small enough. The doping elements in different doping regions work together to exert their respective performance and jointly improve the discharge performance of the lithium iron phosphate cathode material at low temperature.

[0063] Furthermore, in some embodiments, the chemical formula of the lithium iron phosphate cathode material is: LiFe 1-a-b-m A a B b M m PO4 / C, and 0.0019≤a≤0.007, 0.0088≤b≤0.017, 0.0049≤m≤0.018, where A is selected from at least one of cerium, lanthanum, and tin, B is selected from at least one of manganese and vanadium, and M is selected from at least one of titanium, magnesium, zirconium, and yttrium.

[0064] Specifically, the values ​​of 'a' include, but are not limited to, 0.0019, 0.003, 0.004, 0.005, 0.006, and 0.007; the values ​​of 'b' include, but are not limited to, 0.0088, 0.01, 0.011, 0.012, 0.013, 0.014, 0.015, 0.016, and 0.017; and the values ​​of 'm' include, but are not limited to, 0.0049, 0.006, 0.008, 0.01, 0.012, 0.014, 0.016, and 0.018. As an example, the chemical formula of lithium iron phosphate cathode materials can include, but is not limited to, LiFe... 0.971 Ce 0.004 Mn 0.012 Mg 0.006 PO4@C, LiFe 0.968 Sn 0.004 Mn 0.012 Ti 0.006 PO4@C, LiFe 0.962 Sn 0.007 Mn 0.011 V 0.0053 Mg 0.009 PO4@C, LiFe 0.966 Sn 0.007 Mn 0.01 1V 0.0053 Mg 0.009 PO4@C, LiFe 0.963 Sn 0.007 Mn0.011 V 0.0053 Mg 0.009 PO4@C、LiFe 0.961 Sn 0.007 Mn 0.011 V 0.0053 Mg 0.009 PO4@C、LiFe 0.967 La 0.0005 Ce 0.0015 Mn 0.009 Zr 0.005 PO4@C、LiFe 0.973 La 0.007 Mn 0.016 Y 0.018 PO4@C、LiFe 0.958 La 0.001 Ce 0.001 Sn 0.003 Mn 0.015 Ti 0.003 Zr 0.003 Mg 0.003 PO4@C、LiFe 0.955 La 0.003 Sn 0.004 Mn 0.016 Zr 0.006 Mg 0.003 PO4@C、LiFe 0.976 Sn 0.007 Mn 0.011 V 0.0053 Mg 0.009 PO4@C、LiFe 0.953 Sn 0.007 Mn 0.011 V 0.0053 Mg 0.009 PO4@C、LiFe 0.976 Sn 0.007 Mn 0.011 V 0.0053 Mg 0.009 PO4@C、LiFe 0.964 Sn 0.007 Mn 0.011 V 0.0053 Mg 0.009 PO4@C、LiFe 0.97 Sn 0.007 Mn 0.011 V 0.0053 Mg 0.009 PO4@C、LiFe 0.978 Sn 0.007 Mn 0.011 V 0.0053 Mg 0.009 PO4@C、LiFe0.96 3Sn 0.007 Mn 0.011 V 0.0053 Mg 0.009 PO4@C, LiFe 0.961 Sn 0.007 Mn 0.011 V 0.0053 Mg 0.009 PO4@C, LiFe 0.964 Sn 0.007 Mn 0.011 V 0.0053 Mg 0.009 PO4@C, LiFe 0.967 Sn 0.007 Mn 0.011 V 0.0053 Mg 0.009 PO4@C, etc.

[0065] In the technical solution of this application embodiment, when the doping amounts of the first, second, and third doping elements meet the above-mentioned ranges, it is not only beneficial to the full and rapid insertion and extraction of lithium ions, but also beneficial to resisting over-sintering, refining grains, suppressing crystal transformation, and avoiding the generation of large single crystal particles, thereby significantly improving the low-temperature discharge performance of lithium iron phosphate cathode materials. If the doping amounts of the first, second, and third doping elements are too low, it will not be conducive to the full play of the role of each doping element; if the doping amount of the first doping element is too high, it is easy to lead to a low iron-phosphorus ratio and a reduction in lithium ions; if the doping amount of the second doping element is too high, it is easy to lead to excessive deformation of the iron phosphate lattice structure, and the charge-discharge process is prone to damage to the crystal structure; if the doping amount of the third doping element is too high, it is not only easy to lead to the generation of magnetic foreign matter, but also to the deterioration of particle fusion performance, making it difficult to control the overall particle size of the lithium iron phosphate cathode material, thereby leading to a low compaction density.

[0066] Furthermore, in some embodiments, the compaction density of the lithium iron phosphate cathode material is 2.55 g / cm³. 3 ~2.65g / cm 3 including but not limited to 2.55g / cm³ 3 2.57g / cm 3 2.59g / cm 3 2.61 g / cm 3 2.63 g / cm 3 2.65g / cm 3 wait.

[0067] In the technical solution of this application embodiment, when the compaction density of the lithium iron phosphate cathode material meets the above range, it has a high compaction density, which is beneficial to improve the energy density of the lithium iron phosphate secondary battery. At the same time, since the lithium iron phosphate cathode material of this application has both high compaction density and good low-temperature performance, it is beneficial to better improve the problem of poor battery life caused by low temperature, improve the temperature adaptability of the secondary battery, and promote the wider application of the secondary battery.

[0068] Furthermore, in some embodiments, the average particle size of the primary particles of the lithium iron phosphate cathode material is 330nm~360nm, including but not limited to 330nm, 335nm, 340nm, 345nm, 350nm, 355nm, 360nm, etc.

[0069] In the technical solution of this application embodiment, when the average particle size of the primary particles of the lithium iron phosphate cathode material meets the above range, it has a smaller primary particle size and the particle size of the primary particles is more concentrated, which is conducive to the close contact and uniform arrangement between the lithium iron phosphate cathode material particles, as well as the effective diffusion of lithium ions inside the lithium iron phosphate cathode material under low temperature conditions, thereby improving the electrochemical activity of the lithium iron phosphate cathode material under low temperature conditions and improving the electrochemical performance of the lithium iron phosphate cathode material under low temperature conditions.

[0070] Furthermore, in some embodiments, in the lithium iron phosphate cathode material, the proportion of particles with a diameter of 0.2 μm or less is 48.2% to 63.6%, the proportion of particles with a diameter greater than 0.2 μm and less than or equal to 0.4 μm is 21.3% to 32.5%, the proportion of particles with a diameter greater than 0.4 μm and less than or equal to 0.6 μm is 7.3% to 17.4%, the proportion of particles with a diameter greater than 0.6 μm and less than or equal to 0.8 μm is 2.4% to 4.7%, the proportion of particles with a diameter greater than 0.8 μm and less than or equal to 1 μm is 0.48% to 1.56%, the proportion of particles with a diameter greater than 1 μm and less than or equal to 2 μm is 1.5% to 5.2%, and the proportion of particles with a diameter greater than 2 μm and less than or equal to 5 μm is 1.3% to 1.9%. It is understandable that primary particles refer to crystal particles that have not agglomerated, while large particles formed by the aggregation of several primary particles are called secondary particles. The term "particles" mentioned here refers to the proportion of all particles, including primary and secondary particles. In a preferred embodiment, the lithium iron phosphate cathode material comprises particles with a diameter of 0.2 μm or less, accounting for 49.3% to 59.8%; particles with a diameter greater than 0.2 μm and less than or equal to 0.4 μm, accounting for 23.1% to 31.5%; particles with a diameter greater than 0.4 μm and less than or equal to 0.6 μm, accounting for 7.3% to 16.9%; particles with a diameter greater than 0.6 μm and less than or equal to 0.8 μm, accounting for 2.45% to 4.7%; particles with a diameter greater than 0.8 μm and less than or equal to 1 μm, accounting for 0.48% to 1.56%; particles with a diameter greater than 1 μm and less than or equal to 2 μm, accounting for 1.5% to 5.01%; and particles with a diameter greater than 2 μm and less than or equal to 5 μm, accounting for 1.31% to 1.81%.

[0071] In the technical solution of this application embodiment, when the particle size distribution of the lithium iron phosphate cathode material meets the above-mentioned range, on the one hand, the particle size distribution is uniform and the secondary particle size is small, resulting in a more uniform internal arrangement of the lithium iron phosphate cathode material, which helps to form a balanced voltage platform and keep the secondary battery stable during operation; on the other hand, the presence of large particles of a certain size is beneficial to improving the compaction density and energy density per unit volume. This application utilizes the gradation effect between secondary particles of different sizes in the lithium iron phosphate cathode material, which is beneficial to improving the compaction density of the lithium iron phosphate cathode material and improving the stress between the particles, thereby enhancing the structural stability of the lithium iron phosphate cathode material and extending its cycle life.

[0072] Furthermore, in some embodiments, the D50 particle size of the lithium iron phosphate cathode material is 1.35μm~1.65μm, including but not limited to 1.35μm, 1.4μm, 1.45μm, 1.5μm, 1.55μm, 1.6μm, 1.65μm, etc.

[0073] In the technical solution of this application embodiment, when the D50 particle size of the lithium iron phosphate cathode material meets the above range, it has a moderate D50 particle size, which not only helps to shorten the lithium ion diffusion path and improve the capacity and rate performance of the lithium iron phosphate cathode material, but also helps to improve the fluidity and dispersion of the electrode slurry when the lithium iron phosphate cathode material is applied to the cathode sheet, making the coating more uniform and consistent when preparing the cathode sheet, which is beneficial to large-scale production.

[0074] Furthermore, in some embodiments, the specific surface area of ​​the lithium iron phosphate cathode material is 12 m². 2 / g~15m 2 / g, including but not limited to 12m 2 / g、13m 2 / g, 13.37m 2 / g, 13.4m 2 / g, 13.5m 2 / g、14m 2 / g, 14.5m 2 / g, 15m 2 / g, etc., preferably 13.37m 2 / g~15m 2 / g.

[0075] In the technical solutions of this application embodiment, when the specific surface area of ​​the lithium iron phosphate cathode material meets the above-mentioned range, it helps the lithium iron phosphate cathode material to have an appropriate number of active sites, improves the electrochemical activity of lithium iron phosphate, and improves the electrochemical performance of the lithium iron phosphate cathode material at low temperatures.

[0076] Furthermore, in some embodiments, the resistivity of the lithium iron phosphate cathode material powder is 10Ω. cm~15Ω cm, including but not limited to 10Ω cm, 11Ω cm, 12Ω cm, 13Ω cm, 14Ω cm, 15Ω cm, etc., preferably 10Ω cm~13.17Ω cm.

[0077] In the technical solution of this application embodiment, when the powder resistivity of the lithium iron phosphate cathode material meets the above range, its powder resistivity is low, which is beneficial to improve the conductivity of the lithium iron phosphate cathode material, increase the electron transport speed, improve the charge and discharge efficiency of the lithium iron phosphate cathode material, and enhance the rate performance, cycle life and safety of the lithium iron phosphate cathode material.

[0078] Furthermore, in some embodiments, the mass fraction of the carbon coating layer in the lithium iron phosphate cathode material is 1.35% to 1.43%, including but not limited to 1.35%, 1.37%, 1.38%, 1.39%, 1.40%, 1.41%, 1.42%, 1.43%, etc., preferably 1.35% to 1.42%.

[0079] In the technical solution of this application embodiment, when the mass fraction of the carbon coating layer in the lithium iron phosphate cathode material meets the above range, it is beneficial to form a continuous and uniform carbon coating layer on the surface of lithium iron phosphate particles, reduce the resistance of the lithium iron phosphate cathode material, improve the electronic conductivity of the lithium iron phosphate cathode material, and thus improve the charge-discharge performance and rate performance of the lithium iron phosphate cathode material.

[0080] Furthermore, in some embodiments, the free lithium content in the lithium iron phosphate cathode material is 150ppm to 220ppm, including but not limited to 150ppm, 160ppm, 170ppm, 180ppm, 190ppm, 200ppm, 210ppm, 220ppm, etc., preferably 156ppm to 206ppm.

[0081] In the technical solution of this application embodiment, during the charging and discharging process of the lithium iron phosphate cathode material, the consumption of some lithium ions due to the polarization internal resistance and the depletion of the separator leads to a decrease in the charging specific capacity. When the free lithium content in the lithium iron phosphate cathode material meets the above-mentioned range, the free lithium content is moderate and can provide an additional lithium source inside the electrode material, which helps to improve the initial charging and discharging efficiency and reversible capacity of the secondary battery. If the free lithium content in the lithium iron phosphate cathode material is too low, the reactive lithium content is low, and the charging specific capacity of lithium iron phosphate is low; if the free lithium content in the lithium iron phosphate cathode material is too high, it will lead to a high level of ferric phosphide magnetic foreign matter in the lithium iron phosphate cathode material, reducing the capacity of the lithium iron phosphate cathode material.

[0082] Thirdly, embodiments of this application provide a method for preparing a lithium iron phosphate cathode material, comprising the following steps: Provide iron phosphate materials; Lithium iron phosphate material, lithium source, first organic carbon source, second organic carbon source and first solvent are mixed, and then dried and sintered to obtain lithium iron phosphate cathode material; wherein, The iron phosphate material includes iron phosphate dihydrate particles, which include a first doping element, a second doping element, and a third doping element. Along the direction from the center of the iron phosphate dihydrate particle to its outer side, the iron phosphate dihydrate particle sequentially includes a first doping region, a second doping region, and a third doping region. The first doping element is located within the first doping region, the second doping element is located within the second doping region, and the third doping element is located within the third doping region. The first doping element is selected from at least one of cerium, lanthanum, and tin; the second doping element is selected from at least one of manganese and vanadium; and the third doping element is selected from at least one of titanium, magnesium, zirconium, and yttrium. The molecular weight of the first organic carbon source is less than the molecular weight of the second organic carbon source.

[0083] In the technical solution of this application embodiment, on the one hand, lithium iron phosphate cathode material is prepared using the above-mentioned partitioned doped iron phosphate material as a precursor. The first doping element is used to improve the catalytic effect and promote the full and rapid insertion and extraction of lithium ions. The second doping element is used to expand the ion diffusion channel, which is conducive to the extraction of internal lithium ions. The third doping element is used to resist over-sintering, refine grains, suppress crystal transformation, and avoid the generation of large single crystal particles, so that the primary particles of the lithium iron phosphate cathode material are small enough. The doping elements in different doping regions exert their respective performances and jointly improve the low-temperature discharge performance of the lithium iron phosphate secondary battery. On the other hand, lithium iron phosphate is layered and coated using organic carbon sources of different molecular weights. The carbon source with a smaller molecular weight is used to effectively coat and disperse the lithium iron phosphate particles. The carbon source with a larger molecular weight is used to promote the fusion of some lithium iron phosphate particles and form agglomerates. The carbon source with a larger molecular weight is decomposed and then used for secondary coating to improve the integrity of the coating layer. Thus, while improving the compaction density, excellent discharge performance is maintained. In this way, a lithium iron phosphate cathode material with high compaction density and high discharge performance at low temperature is prepared, which is conducive to promoting the development of secondary batteries with longer endurance at low temperature. The first organic carbon source has a lower molecular weight and a lower melting point, which will first form a carbon coating layer, playing a good role in coating and dispersing small particles. The growth rate of lithium iron phosphate will be inhibited after coating. The second organic carbon source has a higher molecular weight and a higher decomposition temperature. During the melting process, it will bind the lithium iron phosphate particles together. The contact parts of the lithium iron phosphate particles will gradually fuse and generate some agglomerates. At the same time, the second organic carbon source will decompose and then coat them again, improving the integrity of the coating layer.

[0084] Meanwhile, compared with the conventional method of preparing lithium iron phosphate cathode materials using anhydrous iron phosphate as a precursor, this application uses iron phosphate dihydrate as a precursor, which makes the slurry grinding process easier and less damaging to the primary particles. It avoids the problem of increasing grinding time to achieve the target particle size and the resulting peeling of the doped layer into a single or double layer, which is conducive to further improving the lithium ion intercalation effect and high-rate discharge performance.

[0085] Furthermore, compared with modification methods that directly dope lithium iron phosphate, this application first prepares doped iron phosphate and then uses the doped iron phosphate as a precursor to prepare lithium iron phosphate. This not only makes the distribution of doping elements more uniform, but also effectively improves the ionic conductivity of the material and avoids crystal defects and side reactions caused by high doping.

[0086] Furthermore, in some embodiments, the preparation steps of the iron phosphate material include: The first ferrous source, the first phosphorus source, the first dopant, the first oxidant, and the second solvent are subjected to a first reaction treatment to obtain a first reaction slurry; The first reaction slurry, the second ferrous source, the second phosphorus source, the second dopant, and the second oxidant are processed by the second reaction to obtain the second reaction slurry; The second reaction slurry, the third ferrous source, the third phosphorus source, the third dopant, and the third oxidant are processed by the third reaction to obtain the third reaction slurry; The third reaction slurry, after aging and post-treatment, yields iron phosphate material; among which, The first dopant is at least one of the following: oxides, hydroxides, chlorides, nitrates, sulfates, carbonates, and oxalates of cerium, lanthanum, and / or tin; The second dopant is at least one of the following: oxides, hydroxides, chlorides, nitrates, sulfates, carbonates, oxalates, and oxyacids of manganese and / or vanadium. The third dopant is at least one of the following: oxides, hydroxides, chlorides, nitrates, sulfates, carbonates, and oxalates of titanium, magnesium, zirconium, and / or yttrium.

[0087] In the technical solution of this application embodiment, by mixing and reacting ferrous source, phosphorus source, dopant, oxidant and solvent, the cations in the dopant and ferrous ions participate in the precipitation reaction to form an internal doped compound; by adding iron source, dopant element, phosphorus source and oxidant in batches in proportion, a hierarchical iron phosphate material is formed. The catalytic effect of the first dopant element promotes the full and rapid insertion and extraction of lithium ions. The second dopant element expands the ion diffusion channel, which is conducive to the extraction of internal lithium ions. The third dopant element plays a role in resisting over-sintering, refining grains, inhibiting crystal transformation and avoiding the generation of large single crystal particles, so that the primary particles of the lithium iron phosphate cathode material are small enough, ensuring that the dopant elements at different levels work together and exert their respective performance, and finally jointly improve the low-temperature discharge performance of the prepared lithium iron phosphate.

[0088] Furthermore, in some embodiments, the first ferrous source, the second ferrous source, and the third ferrous source are each independently selected from at least one of ferrous sulfate, ferrous chloride, ferrous nitrate, and ferrous acetate.

[0089] Furthermore, in some embodiments, the first phosphorus source, the second phosphorus source, and the third phosphorus source are each independently selected from at least one of phosphoric acid, ammonium phosphate, ammonium monohydrogen phosphate, ammonium dihydrogen phosphate, sodium phosphate, sodium monohydrogen phosphate, sodium dihydrogen phosphate, potassium phosphate, potassium monohydrogen phosphate, and potassium dihydrogen phosphate.

[0090] Furthermore, in some embodiments, the first oxidant, the second oxidant, and the third oxidant are each independently selected from at least one of hydrogen peroxide, sodium peroxide, potassium peroxide, and oxygen.

[0091] In the technical solutions of this application embodiment, the above-mentioned ferrous source, phosphorus source and oxidant have the advantages of wide selection and low cost, which is conducive to large-scale industrial production.

[0092] Further, in some embodiments, the molar ratio of the first ferrous source to the first phosphorus source and the first dopant element in the first dopant is 1:(1.3~2.5):(0.01~0.07), including but not limited to 1:1.3:0.01, 1:1.5:0.03, 1:1.7:0.05, 1:1.9:0.035, 1:2.1:0.04, 1:2.3:0.05, 1:2.5:0.05, 1:2.5:0.07, etc. The preferred molar ratio of the first ferrous source to the first phosphorus source and the first dopant element in the first dopant is 1:(1.3~2.5):(0.01~0.05).

[0093] In the technical solution of this application embodiment, when the molar ratio of the first ferrous source to the first phosphorus source and the first dopant element meets the above range, it is beneficial to the complete precipitation of iron element and the first dopant element, avoids excessive nucleation causing the particle size to be too small, and obtains iron phosphate material with a more suitable particle size.

[0094] Furthermore, in some embodiments, the molar ratio of the first ferrous source to the first oxidant is 1:(3.2~7.3), including but not limited to 1:3.2, 1:3.5, 1:4.2, 1:4.9, 1:5.6, 1:6.2, 1:6.7, 1:7, 1:7.3, etc., preferably 1:(3.2~6.7).

[0095] In the technical solution of this application embodiment, when the molar ratio of the first ferrous source to the first oxidant meets the above range, it is beneficial to improve the reaction rate and the degree of reaction of ferrous ions, and to fully convert ferrous ions into ferric ions.

[0096] Further, in some embodiments, the molar ratio of the second ferrous source to the second phosphorus source and the second dopant element in the second dopant is 1:(1.1~2.75):(0.01~0.04), including but not limited to 1:1.1:0.01, 1:1.1:0.04, 1:1.5:0.01, 1:1.6:0.02, 1:1.7:0.025, 1:1.8:0.03, 1:1.9:0.04, 1:2.75:0.01, 1:2.75:0.02, 1:2.75:0.04, etc., preferably 1:(1.5~1.9):(0.01~0.04).

[0097] In the technical solution of this application embodiment, when the molar ratio of the second ferrous source to the second phosphorus source and the second dopant element meets the above range, it is beneficial to the complete precipitation of iron element and the second dopant element, avoids excessive nucleation and resulting in excessively small particle size, and obtains iron phosphate material with a more suitable particle size.

[0098] Furthermore, in some embodiments, the molar ratio of the second ferrous source to the second oxidant is 1:(4.8~13.2), including but not limited to 1:4.8, 1:5.1, 1:5.4, 1:5.7, 1:6.0, 1:6.3, 1:6.5, 1:7, 1:8, 1:9, 1:10, 1:12, 1:13, 1:13.2, etc., preferably 1:(4.8~6.5).

[0099] In the technical solution of this application embodiment, when the molar ratio of the second ferrous source to the second oxidant meets the above range, it is beneficial to improve the reaction rate and the degree of reaction of ferrous ions, and to fully convert ferrous ions into ferric ions.

[0100] Furthermore, in some embodiments, the molar ratio of the third ferrous source to the third phosphorus source and the third dopant element in the third dopant is 1:(1.6~3.95):(0.01~0.1), including but not limited to 1:1.6:0.01, 1:1.6:0.05, 1:1.6:0.1, 1:2.5:0.01, 1:2.8:0.015, 1:3.2:0.02, 1:3.6:0.03, 1:3.9:0.1, 1:3.95:0.02, etc., preferably 1:(2.5~3.9):(0.01~0.1).

[0101] In the technical solution of this application embodiment, when the molar ratio of the third ferrous source to the third phosphorus source and the third dopant element meets the above range, it is beneficial to the complete precipitation of iron element and the third dopant element, avoids excessive nucleation and resulting in excessively small particle size, and obtains iron phosphate material with a more suitable particle size.

[0102] Furthermore, in some embodiments, the molar ratio of the third ferrous source to the third oxidant is 1:(2~3.9), including but not limited to 1:2, 1:2.3, 1:2.5, 1:2.7, 1:2.9, 1:3.1, 1:3.3, 1:3.6, 1:3.9, etc., preferably 1:(2.3~3.9).

[0103] In the technical solution of this application embodiment, when the molar ratio of the third ferrous source to the third oxidant meets the above range, the reaction rate slows down and the reaction is more complete, thereby increasing the iron-phosphorus ratio.

[0104] Furthermore, in some embodiments, the molar ratio of the first ferrous source to the second and third ferrous sources is (10~15):(40~70):(15~50).

[0105] In the technical solution of this application embodiment, when the molar ratio of the first ferrous source to the second and third ferrous sources meets the above range, it is beneficial to adjust the size of the first doped region, the second doped region and the third doped region of the lithium iron phosphate material, so that the doping elements in different doped regions can give full play to their respective functions, which helps the discharge performance of the lithium iron phosphate material.

[0106] Furthermore, in some embodiments, the molar ratio of the first phosphorus source to the second and third phosphorus sources is (20~30):(55~140):(55~140), preferably (20~30):(60~110):(60~135).

[0107] In the technical solution of this application embodiment, when the molar ratio of the first phosphorus source to the second phosphorus source and the third phosphorus source meets the above range, it is conducive to the full precipitation of dopant elements and the on-demand precipitation of iron elements when combined with ferrous salts and oxidants at each stage, thereby obtaining iron phosphate material with more suitable particle size and more suitable iron-phosphorus ratio.

[0108] Furthermore, in some embodiments, the molar ratio of the first oxidant to the second and third oxidants is 1:(3~8):(0.5~3), preferably (10~20):(60~80):(10~30).

[0109] In the technical solution of this application embodiment, when the molar ratio of the first oxidant to the second oxidant and the third oxidant meets the above range, it is combined with the ferrous salt and phosphorus source at each stage to better control the reaction rate and the degree of oxidation of ferrous iron at each stage, so as to obtain iron phosphate material with more suitable particle size and more suitable iron-phosphorus ratio.

[0110] Furthermore, in some embodiments, the molar ratio of the total iron content in the first ferrous source, the second ferrous source, and the third ferrous source to the total phosphorus content in the first phosphorus source, the second phosphorus source, and the third phosphorus source is 1:(2~2.5), including but not limited to 1:2, 1:2.1, 1:2.2, 1:2.3, 1:2.4, 1:2.5, etc.; the molar ratio of the total iron content in the first ferrous source, the second ferrous source, and the third ferrous source to the total oxidant content in the first oxidant, the second oxidant, and the third oxidant is 1:(4.3~4.8), including but not limited to 1:4.3, 1:4.4, 1:4.5, 1:4.6, 1:4.7, 1:4.8, etc.

[0111] In the technical solution of this application embodiment, when the molar ratio of the total iron content in the first ferrous source, the second ferrous source, and the third ferrous source to the total phosphorus content in the first phosphorus source, the second phosphorus source, and the third phosphorus source, and the total oxidant content in the first oxidant, the second oxidant, and the third oxidant meets the above range, the addition of total phosphorus is relatively high, which is beneficial to ensure a lower pH value, reduce the formation of ferric hydroxide, improve the purity of ferric phosphate, reduce the formation of impurities, thereby improving the conductivity and ion mobility of the lithium iron phosphate cathode material, and thus improving the low-temperature discharge performance of the lithium iron phosphate cathode material; the addition of total oxidant is relatively low, which is beneficial to reduce the oxidation of ferrous ions and introduce more defects, thereby improving the conductivity and ion mobility of the lithium iron phosphate cathode material, and thus improving the low-temperature discharge performance of the lithium iron phosphate cathode material.

[0112] Further, in some embodiments, the step of treating the first ferrous source, the first phosphorus source, the first dopant, the first oxidant, and the second solvent with a first reaction to obtain a first reaction slurry includes: providing a first solution containing the first ferrous source, a second solution containing the first phosphorus source and the first dopant, and a third solution containing the first oxidant; mixing the second solution and the third solution with the first solution at a first mixing temperature and a first mixing time to obtain a first mixture; and obtaining the first reaction slurry from the first mixture at the first reaction temperature and after a first reaction time; wherein the first mixing temperature is 15°C to 35°C, including but not limited to 15°C, 20°C, 22°C, and 24°C. The temperatures are 26℃, 28℃, 30℃, 35℃, etc., preferably 20℃~30℃; the first mixing time is 40min~50min, including but not limited to 40min, 42min, 44min, 46min, 48min, 50min, etc.; the first reaction temperature is 35℃~55℃, including but not limited to 35℃, 40℃, 42℃, 44℃, 46℃, 48℃, 50℃, 55℃, etc., preferably 40℃~50℃; the first reaction time is 20min~40min, including but not limited to 20min, 24min, 28min, 32min, 36min, 40min, etc. The step of obtaining a second reaction slurry by subjecting a first reaction slurry, a second ferrous source, a second phosphorus source, a second dopant, and a second oxidant to a second reaction treatment includes: providing a fourth solution containing a second ferrous source, a fifth solution containing a second phosphorus source and a second dopant, and a sixth solution containing a second oxidant; mixing the fourth solution with the first reaction slurry at a second mixing temperature and a second mixing time to obtain a second mixture; mixing the fifth solution and the sixth solution with the second mixture at a third mixing temperature and a third mixing time to obtain a third mixture; and obtaining the second reaction slurry from the third mixture at a second reaction temperature and after a second reaction time; wherein the second mixing temperature is 40℃~60℃, including but not limited to 40℃, 45℃, 47℃, 49℃, 51℃, 53℃, 55℃, 60℃, etc., preferably 45℃~55℃; and the second mixing time is 10min~30min, including but not limited to 10min, 12min, etc. The mixing temperatures are 10 min to 30 min, including but not limited to 45℃, 50℃, 52℃, 54℃, 56℃, 58℃, 60℃, and 65℃, preferably 50℃ to 60℃; the mixing times are 10 min to 30 min, including but not limited to 10 min, 14 min, 18 min, 22 min, 26 min, and 30 min; the second reaction temperature is 60℃ to 70℃, including but not limited to 55℃, 60℃, 62℃, 64℃, 66℃, 68℃, 70℃, and 75℃, preferably 60℃ to 70℃; the second reaction time is 20 min to 40 min, including but not limited to 20 min, 24 min, 28 min, 32 min, 36 min, and 40 min. The step of obtaining a third reaction slurry by subjecting the second reaction slurry, the third ferrous source, the third phosphorus source, the third dopant, and the third oxidant to a third reaction treatment includes: providing a seventh solution containing the third ferrous source, a third dopant, an eighth solution containing the third phosphorus source, and a ninth solution containing the third oxidant; mixing the seventh solution, the third dopant, and the second reaction slurry at a fourth mixing temperature and a fourth mixing time to obtain a fourth mixture; and mixing the eighth solution and the ninth solution at a fifth mixing temperature and a fifth mixing time to obtain the fourth mixture, thereby obtaining the third reaction slurry; wherein the fourth mixing temperature is 55℃~75℃, including but not limited to 55℃, 60℃, 62℃, and 64℃. The mixing temperatures are 66℃, 68℃, 70℃, 75℃, etc., preferably 60℃~70℃; the fourth mixing time is 10min~20min, including but not limited to 10min, 12min, 14min, 16min, 18min, 20min, etc.; the fifth mixing temperature is 50℃~75℃, including but not limited to 50℃, 55℃, 58℃, 60℃, 62℃, 65℃, 68℃, 70℃, 75℃, etc., preferably 55℃~70℃; the fifth mixing time is 30min~40min, including but not limited to 30min, 32min, 34min, 36min, 38min, 40min, etc. The step of obtaining ferric phosphate material by aging and post-treatment of the third reaction slurry includes: mixing the third reaction slurry with a pH adjuster to obtain a fifth mixture, the pH value of the fifth mixture being 1.1~1.4, including but not limited to 1.1, 1.2, 1.3, 1.4, etc.; the fifth mixture being reacted at a third reaction temperature and for a third reaction time to obtain a fourth reaction slurry, the pH value of the fourth reaction slurry being 1.7~1.9, including but not limited to 1.7, 1.75, 1.8, 1.85, 1.9, etc.; the fourth reaction slurry being post-treated to obtain ferric phosphate material; wherein, the third reaction temperature is 90℃~100℃, including but not limited to 90℃, 92℃, 94℃, 96℃, 98℃, 100℃, etc.; the third reaction time is 1h~3h, including but not limited to 1h, 1.5h, 2h, 2.5h, 3h, etc.

[0113] In the technical solution of this application embodiment, a second solution containing a first phosphorus source and a first dopant is mixed with a third solution containing a first oxidant at a first mixing temperature and within a first mixing time to a first solution containing a first ferrous source. The first phosphorus source and the first dopant are pre-mixed to form seed crystals, which then react with the first ferrous source. This helps to better control the doping position of the first dopant element and avoids the problem of insufficient reaction and difficulty in control during the co-precipitation process of the first dopant element and the first ferrous source due to significant competition. The first mixture at the first reaction temperature and within the first reaction time causes the cations in the dopant to co-precipitate with the ferrous ions to form a monolayer doped amorphous iron phosphate, resulting in a first reaction slurry containing a monolayer doped amorphous iron phosphate. When the first mixing temperature and the first mixing time meet the above range, it helps to control the reaction rate, allowing the reactants sufficient time to diffuse uniformly and improving the particle size and uniformity of the iron phosphate particles. When the first reaction temperature and the first reaction time meet the above range, the reaction rate is increased, promoting the formation of iron phosphate particles, while simultaneously regulating the growth uniformity and crystal structure integrity of the iron phosphate particles, thereby improving the capacity of the lithium iron phosphate cathode material.

[0114] A fourth solution containing a second ferrous source is mixed with a first reaction slurry at a second mixing temperature and a second mixing time to obtain a second mixture. A fifth solution containing a second phosphorus source and a second dopant is mixed with a sixth solution containing a second oxidant at a third mixing temperature and a third mixing time to form the second mixture. The second phosphorus source and the second dopant are pre-mixed to form seed crystals, which then react with the second ferrous source. This facilitates better control of the doping position of the second dopant element and avoids the problem of insufficient reaction and difficulty in control during the co-precipitation process of the second dopant element and the second ferrous source due to significant competition. The third mixture is then processed at the second reaction temperature and after a second reaction time, utilizing monolayer doping. Amorphous iron phosphate is used as a seed crystal to continue growth, resulting in a second reaction slurry containing double-layer doped amorphous iron phosphate. When the second mixing temperature and the second mixing time meet the above range, it is beneficial to achieve sufficient mixing between the fourth solution and the first reaction slurry. When the third mixing temperature and the third mixing time meet the above range, it is beneficial to control the reaction rate, allowing the reactants sufficient time to diffuse uniformly, thereby improving the particle size and uniformity of the iron phosphate particles. When the second reaction temperature and the second reaction time meet the above range, it increases the reaction rate, promotes the formation of iron phosphate particles, and simultaneously regulates the growth uniformity and crystal structure integrity of the iron phosphate particles, thereby improving the capacity of the lithium iron phosphate cathode material.

[0115] The seventh solution with a third ferrous source, the third dopant, and the second reaction slurry are mixed at a fourth mixing temperature and a fourth mixing time to obtain a fourth mixture. The eighth solution with a third phosphorus source and the ninth solution with a third oxidant are mixed at a fifth mixing temperature and a fifth mixing time to obtain the fourth mixture. Using double-layer doped amorphous iron phosphate as seed crystals, the mixture continues to grow to obtain a third reaction slurry containing triple-layer doped amorphous iron phosphate. When the fourth mixing temperature and the fourth mixing time meet the above range, it is beneficial to achieve sufficient mixing of the seventh solution, the third dopant, and the second reaction slurry. When the fifth mixing temperature and the fifth mixing time meet the above range, it is beneficial to allow the reactants sufficient time to diffuse uniformly, increase the reaction rate, avoid the formation of crystal nuclei, regulate the growth consistency of iron phosphate particles, obtain iron phosphate materials with suitable particle size, and improve the capacity of lithium iron phosphate cathode materials.

[0116] The third reaction slurry is mixed with a pH adjuster to obtain a fifth mixture. The pH of the fifth mixture is 1.1~1.4, which is conducive to promoting the formation of ferric phosphate. The fifth mixture, at the third reaction temperature and after the third reaction time, converts the three-layer doped amorphous ferric phosphate into three-layer doped crystalline ferric phosphate dihydrate, resulting in a fourth reaction slurry containing three-layer doped crystalline ferric phosphate dihydrate. The fourth reaction slurry is then post-processed to obtain ferric phosphate material. When the third reaction temperature and the third reaction time meet the above range, it is conducive to complete crystal transformation and avoids changes in crystal morphology due to excessively high temperature, which would affect the stability of the product.

[0117] This application ensures a high iron-to-phosphorus ratio and a low impurity content by adjusting the mixing temperature, mixing time, reaction temperature, reaction time, and the ratio of iron source, phosphorus source, and oxidant at each stage, thereby reducing crystal defects and improving the low-temperature discharge performance of lithium iron phosphate cathode materials.

[0118] In the technical solution of this application, it should be noted that the second and third solutions are mixed with the first solution at a first mixing temperature and within a first mixing time to obtain a first mixture; the fifth and sixth solutions are mixed with the second mixture at a third mixing temperature and within a third mixing time to obtain a third mixture; and the eighth and ninth solutions are mixed with the fourth mixture at a fifth mixing temperature and within a fifth mixing time to obtain a third reaction slurry, all in a simultaneous addition manner. In the process of mixing the seventh solution, the third dopant, and the second reaction slurry at a fourth mixing temperature and within a fourth mixing time to obtain a fourth mixture, the third dopant can be pre-mixed into the seventh solution or added separately. All mixing and reaction processes are carried out under stirring conditions. Post-processing includes, but is not limited to, pressure filtration, washing, and drying, which are prior art and will not be described further in this invention.

[0119] Furthermore, in some embodiments, in the first solution containing the first ferrous source, the concentration of ferrous ions is 1 mol / L to 2 mol / L, including but not limited to 1 mol / L, 1.2 mol / L, 1.4 mol / L, 1.6 mol / L, 1.8 mol / L, 2 mol / L, etc.; in the second solution containing the first phosphorus source and the first dopant, PO4... 3- The concentration of the first dopant is 1 mol / L to 3 mol / L, including but not limited to 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L, 3 mol / L, etc.; the concentration of the first dopant is 0.007 mol / L to 0.105 mol / L, including but not limited to 0.007 mol / L, 0.01 mol / L, 0.03 mol / L, 0.05 mol / L, 0.07 mol / L, 0.09 mol / L, 0.105 mol / L; in the third solution containing the first oxidant, the mass fraction of the first oxidant is 25% to 30%, including but not limited to 25%, 26%, 27%, 28%, 29%, 30%, etc.

[0120] Furthermore, in some embodiments, in the fourth solution containing the second ferrous source, the concentration of ferrous ions is 1 mol / L to 2 mol / L, including but not limited to 1 mol / L, 1.2 mol / L, 1.4 mol / L, 1.6 mol / L, 1.8 mol / L, 2 mol / L, etc.; in the fifth solution containing the second phosphorus source and the second dopant, PO4 3- The concentration of the first oxidant is 1 mol / L to 3 mol / L, including but not limited to 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L, 3 mol / L, etc.; the concentration of the second dopant is 0.008 mol / L to 0.06 mol / L, including but not limited to 0.008 mol / L, 0.01 mol / L, 0.02 mol / L, 0.03 mol / L, 0.04 mol / L, 0.05 mol / L, 0.06 mol / L; in the sixth solution containing the second oxidant, the mass fraction of the second oxidant is 25% to 30%, including but not limited to 25%, 26%, 27%, 28%, 29%, 30%, etc.

[0121] Furthermore, in some embodiments, in the seventh solution containing a third ferrous source, the concentration of ferrous ions is 1 mol / L to 2 mol / L, including but not limited to 1 mol / L, 1.2 mol / L, 1.4 mol / L, 1.6 mol / L, 1.8 mol / L, 2 mol / L, etc.; in the eighth solution containing a third phosphorus source, PO4... 3-The concentration is 1 mol / L to 3 mol / L, including but not limited to 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L, 3 mol / L, etc.; in the ninth solution containing the third oxidant, the mass fraction of the second oxidant is 25% to 30%, including but not limited to 25%, 26%, 27%, 28%, 29%, 30%, etc.

[0122] Furthermore, in some embodiments, the first solution having a first ferrous source, the fourth solution having a second ferrous source, and the seventh solution having a third ferrous source are obtained by dissolving titanium dioxide byproducts in water, followed by alkali precipitation, and finally removing impurities by pressure filtration; wherein the mass fraction of ferrous sulfate in the titanium dioxide byproducts is 80%~92%, including but not limited to 80%, 82%, 84%, 86%, 88%, 90%, 92%, etc.; the dissolution temperature is 50℃~80℃, including but not limited to 50℃, 60℃, 70℃, etc. The temperature is 80℃, etc.; the base is at least one of sodium hydroxide or potassium hydroxide; in the first solution having a first ferrous source, the fourth solution having a second ferrous source, and the seventh solution having a third ferrous source, the concentration of ferrous ions is 1 mol / L to 2 mol / L, including but not limited to 1 mol / L, 1.2 mol / L, 1.4 mol / L, 1.6 mol / L, 1.8 mol / L, 2 mol / L, etc., and the pH is 2.8 to 3.2, including but not limited to 2.8, 2.9, 3.0, 3.1, 3.2, etc.

[0123] In the technical solution of this application embodiment, titanium dioxide by-products are used as raw materials, which can not only produce ferrous solutions with appropriate concentration and pH value, but also realize resource recycling, reduce production costs, and have high environmental benefits.

[0124] Furthermore, in some embodiments, the second solution having a first phosphorus source and a first dopant is obtained by mixing the first phosphorus source solution and the first dopant; the fifth solution having a second phosphorus source and a second dopant is obtained by mixing the second phosphorus source solution and the second dopant; wherein, the first phosphorus source solution, the second phosphorus source solution, and the eighth solution having a third phosphorus source are obtained by dissolving and filtering industrial monoammonium phosphate and then adjusting the pH to neutral with ammonia water; in the first phosphorus source solution and the second phosphorus source solution, PO4... 3- The concentration is 1 mol / L to 3 mol / L, including but not limited to 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L, 3 mol / L, etc.

[0125] Furthermore, in some embodiments, the molar ratio of iron in the iron phosphate material to lithium in the lithium source is 1:(1.03~1.06).

[0126] In the technical solution of this application embodiment, when the molar ratio of iron in the iron phosphate material to lithium in the lithium source meets the above range, the lithium source is appropriately in excess, which can ensure the generation of sufficient free lithium, thereby improving the capacity of the material and avoiding waste caused by excessive lithium source.

[0127] Furthermore, in some embodiments, the difference between the molecular weight of the second organic carbon source and the molecular weight of the first organic carbon source is greater than or equal to 800.

[0128] In the technical solution of this application embodiment, when the difference between the molecular weight of the second organic carbon source and the molecular weight of the first organic carbon source meets the above-mentioned range, it is beneficial to better exert the respective roles of the first organic carbon source and the second organic carbon source, and obtain a lithium iron phosphate cathode material that takes into account both high actual density and excellent discharge performance.

[0129] Furthermore, in some embodiments, the molecular weight of the first organic carbon source is less than or equal to 200, and the molecular weight of the second organic carbon source is greater than or equal to 1000 and less than or equal to 12000, including but not limited to 1000, 2000, 4000, 6000, 8000, 10000, 12000, etc.

[0130] In the technical solution of this application embodiment, when the molecular weight of the second organic carbon source and the molecular weight of the first organic carbon source respectively meet the above-mentioned range, it is beneficial to better exert the respective roles of the first organic carbon source and the second organic carbon source, and obtain a lithium iron phosphate cathode material that takes into account both high solid density and excellent discharge performance.

[0131] Furthermore, in some embodiments, the first organic carbon source is at least one of glycerol or diglycerol.

[0132] In the technical solution of this application embodiment, the first organic carbon source has the advantages of small molecular weight and low melting point, which is beneficial to the full coating of lithium iron phosphate particles and the full dispersion between lithium iron phosphate particles.

[0133] Furthermore, in some embodiments, the mass of the first organic carbon source is 2.1% to 3.7% of the mass of the iron phosphate material, including but not limited to 2.1%, 2.3%, 2.5%, 2.7%, 2.9%, 3.1%, 3.3%, 3.5%, 3.7%, etc.

[0134] In the technical solution of this application embodiment, when the amount of the first organic carbon source added meets the above range, it can play a better coating and dispersion role for small particles, and avoid the problem that excessive addition will cause the carbon coating layer to be too thick, hindering the transport of lithium ions and generating inactive impurities, which will lead to a decrease in the capacity of lithium iron phosphate secondary batteries.

[0135] Furthermore, in some embodiments, the second organic carbon source is at least one of β-cyclodextrin or polyethylene glycol.

[0136] In the technical solution of this application embodiment, the second organic carbon source has the characteristic of high decomposition temperature, which makes it easy to bond some lithium iron phosphate particles during sintering and promotes the fusion of the bonded lithium iron phosphate particles to form agglomerates, thereby increasing the compaction density of the lithium iron phosphate cathode material.

[0137] Furthermore, in some embodiments, the mass of the second organic carbon source is 8.3% to 9.2% of the mass of the iron phosphate material, including but not limited to 8.3%, 8.4%, 8.6%, 8.8%, 9%, 9.2%, etc.

[0138] In the technical solution of this application embodiment, when the amount of the second organic carbon source added meets the above range, it helps to generate an appropriate amount of agglomerates, thereby improving the compaction density of the lithium iron phosphate cathode material without affecting its electrochemical performance.

[0139] Furthermore, in some embodiments, the step of mixing the iron phosphate material, the lithium source, the first organic carbon source, the second organic carbon source, and the first solvent includes: Iron phosphate material, lithium source, first organic carbon source, second organic carbon source and first solvent are mixed to obtain a mixed slurry. The solid content of the mixed slurry is 47.5%~49.3%, including but not limited to 47.5%, 48%, 48.5%, 49%, 49.3% etc. After the mixed slurry is ground, a grinding slurry is obtained. The D50 particle size of the solid particles in the grinding slurry is 0.32μm~0.38μm, including but not limited to 0.32μm, 0.33μm, 0.34μm, 0.35μm, 0.36μm, 0.37μm, 0.38μm, etc.

[0140] In the technical solutions of this application embodiment, when the solid content of the mixed slurry meets the above-mentioned range, it not only facilitates more uniform mixing of the components in the mixed slurry, thereby improving the consistency of the lithium iron phosphate cathode material, but also helps to shorten the drying time and reduce energy consumption. When the D50 particle size of the solid particles in the grinding slurry meets the above-mentioned range, it helps to adjust the particle size of the iron phosphate dihydrate particles participating in the sintering process, thereby helping to improve the electrochemical performance and performance consistency of the lithium iron phosphate cathode material.

[0141] In the technical solutions of this application embodiment, the solid content of the mixed slurry refers to the mass fraction of solid particles in the mixed slurry.

[0142] Furthermore, in some embodiments, the step of mixing the iron phosphate material, lithium source, first organic carbon source, second organic carbon source and first solvent includes: mixing the iron phosphate material, lithium source, iron supplement, first organic carbon source, second organic carbon source and first solvent to obtain a grinding slurry.

[0143] In the technical solution of this application embodiment, by adding an iron supplement, the iron-phosphorus ratio of the lithium iron phosphate cathode material can be controlled, thereby improving the charging specific capacity of the lithium iron phosphate cathode material.

[0144] Furthermore, in some embodiments, the iron supplement is at least one of ferrous oxalate, ferric citrate, and ferric dihydrogen phosphate.

[0145] In the technical solution of this application embodiment, the above-mentioned iron supplement has the advantages of wide availability and low cost, and can appropriately supplement iron elements, regulate the proportion of iron elements in lithium iron phosphate cathode materials, and improve the charging specific capacity of lithium iron phosphate.

[0146] Furthermore, in some embodiments, the mass of the iron supplement is 0.8% to 1.2% of the mass of the iron phosphate material, including but not limited to 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, etc.

[0147] In the technical solution of this application embodiment, the above-mentioned amount of iron supplementer is added to appropriately supplement iron elements, regulate the proportion of iron elements in the lithium iron phosphate cathode material, and improve the charging specific capacity of the lithium iron phosphate cathode material.

[0148] Further, in some embodiments, the step of mixing the iron phosphate material, lithium source, first organic carbon source, second organic carbon source, and first solvent, followed by drying and sintering to obtain the lithium iron phosphate cathode material includes: Iron phosphate material, lithium source, first organic carbon source, second organic carbon source and first solvent are mixed to obtain grinding slurry; The grinding slurry is dried to obtain a dried material with a D50 particle size of 0.55μm~0.8μm, including but not limited to 0.55μm, 0.60μm, 0.65μm, 0.70μm, 0.75μm, 0.8μm, etc. The dried material is sintered at the first sintering temperature and after the first holding time, and then sintered at the second sintering temperature and after the second holding time to obtain lithium iron phosphate cathode material; The first sintering temperature is 800℃~820℃, including but not limited to 800℃, 803℃, 804℃, 806℃, 808℃, 810℃, 812℃, 815℃, 820℃, etc., preferably 803℃~812℃; the first holding time is 0.5h~4h, including but not limited to 0.5h, 1h, 1.5h, 2h, 2.5h, 3h, 4h, etc., preferably 1h~3h; the second sintering temperature is 780℃~805℃, including but not limited to 780℃, 790℃, 792℃, 794℃, 796℃, 798℃, 800℃, 805℃, etc., preferably 790℃~800℃; the second holding time is 7h~12h, including but not limited to 7h, 8h, 9h, 10h, 11h, 12h, etc.

[0149] In the technical solution of this application embodiment, when the D50 particle size of the dried material meets the above-mentioned range, it is beneficial to the full formation of lithium iron phosphate cathode material grains during sintering, and the primary particle size of the formed lithium iron phosphate cathode material is small and concentrated. When the first sintering temperature, first holding time, second sintering temperature, and second holding time meet the above-mentioned range, it is beneficial to control the carbon coating process in conjunction with the different decomposition temperatures of the first organic carbon source and the second organic carbon source. While effectively coating and dispersing lithium iron phosphate particles using the first organic carbon source, the second organic carbon source promotes the fusion of some lithium iron phosphate particles and the formation of agglomerates, thereby improving the compaction density of the lithium iron phosphate cathode material while maintaining excellent discharge performance. Specifically, using a higher first sintering temperature and a shorter first holding time can promote particle fusion and ensure the strength of the large particles formed by bonding, thereby improving the compaction density; subsequently, using a lower second sintering temperature and a longer second holding time can avoid the occurrence of side reactions and promote more complete crystallization of lithium iron phosphate crystals.

[0150] Furthermore, in some embodiments, the drying process of the grinding slurry includes the steps of removing liquid from the grinding slurry and controlling the particle size of the solid particles after liquid removal. The dried material obtained by drying the grinding slurry has a D50 particle size of 0.55 μm to 0.8 μm and a D100 of 6.50 to 9.0 μm.

[0151] In the technical solution of this application embodiment, when the D50 particle size and D100 particle size of the dried material meet the above range, it helps to adjust the particle size of the iron phosphate dihydrate particles participating in the sintering process, and ensures that some large fused particles that are not completely crushed are distributed, thereby improving the compaction density of the lithium iron phosphate cathode material.

[0152] Furthermore, in some embodiments, the drying process employs spray drying to remove liquid from the grinding slurry, with an inlet air temperature of 200°C to 260°C and an outlet air temperature of 85°C to 105°C.

[0153] In some embodiments, the particle size of the solid particles after the liquid has been removed from the grinding slurry is controlled by pulverization.

[0154] Furthermore, in some embodiments, the dried material is heated to a first sintering temperature at a first heating rate, held at the first sintering temperature for a first holding time, then cooled to a second sintering temperature at a first cooling rate, held at the second sintering temperature for a second holding time, and finally cooled to the furnace exit temperature at a second cooling rate. After a second pulverization process, lithium iron phosphate cathode material is obtained. The first heating rate is 5~10℃ / min, the first cooling rate is 3~7℃ / min, the second cooling rate is 8~12℃ / min, and the furnace exit temperature is <100℃. The D50 particle size of the material after the second pulverization process is 1.35μm~1.65μm.

[0155] In the technical solution of this application embodiment, when the first heating rate meets the above range, it is beneficial to improve the carbon layer decomposition rate; when the first cooling rate meets the above range, it is beneficial to promote the fusion of some particles; when the second cooling rate meets the above range, the cooling rate is faster, which on the one hand helps to form smaller crystal particles, thereby increasing the specific surface area of ​​the material, and on the other hand avoids the problem that slow cooling may lead to the generation of additional impurity phases, affecting the electrochemical performance of the material; the second pulverization process is used to perform slight pulverization to avoid the lithium iron phosphate particles being too large.

[0156] Furthermore, in some embodiments, the sintering atmosphere is a protective atmosphere. This invention does not limit the type of protective atmosphere; those skilled in the art can select one according to the actual situation, such as nitrogen, argon, etc.

[0157] In the technical solution of this application embodiment, the use of a protective atmosphere can prevent the oxidation of raw materials and the generation of unnecessary byproducts that could affect the performance of lithium iron phosphate cathode materials.

[0158] Fourthly, embodiments of this application provide a positive electrode sheet, which includes a lithium iron phosphate positive electrode material prepared by the preparation method of the lithium iron phosphate positive electrode material of the second aspect of this application or the lithium iron phosphate positive electrode material of the third aspect of this application.

[0159] In the technical solution of this application embodiment, the positive electrode sheet contains the above-mentioned positive electrode material, and thus has good electrochemical performance at low temperature and higher volumetric energy density.

[0160] Fifthly, embodiments of this application provide a secondary battery, which includes the positive electrode sheet of the fourth aspect of this application.

[0161] In the technical solution of this application embodiment, the secondary battery includes the above-mentioned positive electrode sheet, and thus has good electrochemical performance at low temperature and higher volumetric energy density.

[0162] The following are some specific embodiments. It should be noted that the embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0163] I. Preparation Method Example 1 (1) The titanium dioxide byproduct was heated and dissolved, and precipitated by adding a 5% sodium hydroxide solution. The precipitate was removed by pressure filtration to obtain a ferrous solution with an iron ion concentration of 1.5 mol / L (i.e., the iron source solution) and a pH of 3.0. Industrial monoammonium phosphate was dissolved and filtered, and then ammonia was added to adjust the pH to neutral to obtain a phosphorus source solution, in which PO4 ions were added. 3- The concentration is 2 mol / L; (2) Based on a total amount of 1 mol of iron, 0.1 mol of iron source solution (i.e., a ferrous solution containing 0.1 mol of ferrous ions, hereinafter the same) is first added to the reactor as the base material. 0.2 mol of phosphorus source solution (i.e., a phosphorus source solution containing 0.2 mol of phosphate ions, hereinafter the same) and 0.004 mol of cerium nitrate are mixed to obtain a second solution. The second solution is then mixed with a third solution (containing 0.47 mol of hydrogen peroxide) which accounts for 10% of the total hydrogen peroxide solution (mass fraction of 27%). The above-mentioned substrate was slowly added dropwise at 25°C for 45 minutes to carry out the synthesis reaction. After the addition was complete, the first mixture was stirred at 45°C for 30 minutes to obtain the first reaction slurry. Then, 0.5 mol of iron source solution was added to the first reaction slurry at 50°C for 15 minutes to obtain the second mixture. 0.8 mol of phosphorus source solution and 0.012 mol of manganese oxalate were mixed to obtain the fifth solution. The fifth solution was then mixed with a sixth solution (containing 2.82 mol of hydrogen peroxide) which accounted for 60% of the total hydrogen peroxide mass. l) The synthesis reaction is carried out by slowly adding the solution dropwise to the second mixture at 55°C over a period of 20 minutes. After the addition is complete, a third mixture is obtained. The third mixture is then heated to 65°C and stirred continuously for 30 minutes to obtain a second reaction slurry. Finally, the remaining iron source solution (seventh solution) and 0.006 mol of magnesium oxide are added to the second reaction slurry at 65°C over a period of 15 minutes to obtain a fourth mixture. An eighth solution (containing 1.2 mol of phosphate ions) is then slowly added dropwise to the fourth mixture. The ninth solution (containing 1.41 mol of hydrogen peroxide) was added at 60°C for 35 minutes. After the addition was complete, the third reaction slurry was obtained. Phosphoric acid was added to the third reaction slurry to adjust the pH to 1.3. The temperature was then raised to 95°C and the reaction was stirred for 2 hours until the pH reached 1.8. The mixture was then filtered, rinsed (until the conductivity of the wash water was less than or equal to 150 uS / cm), and flash-evaporated (until the moisture content of the material was less than or equal to 1.5%) to obtain ferric phosphate dihydrate (i.e., ferric phosphate material).

[0164] (3) The iron phosphate dihydrate prepared in step (2), lithium carbonate (1.03 times the amount of lithium in iron phosphate dihydrate), ferrous oxalate (0.8% by mass of iron phosphate dihydrate), dipropylene glycol (2.3% by mass of iron phosphate dihydrate), and β-cyclodextrin (molecular weight 1135) (8.8% by mass of iron phosphate dihydrate) are mixed with pure water to obtain a mixed slurry with a solid content of 48%. The slurry is then ground to obtain a solid particle size D50 of 0.35 μm by sand milling. The material was spray-dried (inlet air temperature 240℃, outlet air temperature 95℃) and pulverized to obtain a dried material with a D50 particle size of 0.60μm and a D100 of 7.9μm. Then, under a nitrogen protective atmosphere, the temperature was increased to 806℃ at 8℃ / min and held for 2h. Then, the temperature was decreased to 796℃ at 5℃ / min and held for 8.4h. Finally, the temperature was decreased to below 100℃ at 10℃ / min and removed from the furnace. The material was then pulverized a second time to a D50 particle size of 1.43μm to obtain the lithium iron phosphate cathode material.

[0165] Example 2 (1) The titanium dioxide byproduct was heated and dissolved, and precipitated by adding a 5% sodium hydroxide solution. The precipitate was removed by pressure filtration to obtain a ferrous solution with an iron ion concentration of 1.5 mol / L (i.e., the iron source solution) and a pH of 3.0. Industrial monoammonium phosphate was dissolved, filtered, and then ammonia was added to adjust the pH to neutral to obtain a phosphorus source solution, in which PO4 ions were added. 3- The concentration is 2 mol / L; (2) Based on a total amount of 1 mol of iron, 0.13 mol of iron source solution (i.e., ferrous solution containing 0.13 mol of ferrous ions, hereinafter the same) is first added to the reactor as the base material. Then, 0.2 mol of phosphorus source solution (i.e., phosphorus source solution containing 0.2 mol of phosphate ions, hereinafter the same) and 0.004 mol of stannous sulfate are mixed to obtain a second solution. The second solution and a third solution (0.47 mol of hydrogen peroxide) accounting for 10% of the total hydrogen peroxide solution (mass fraction of 27%) are simultaneously and slowly added dropwise to the above base material at 25°C for a synthesis reaction. The addition time is 45 min. After the addition is completed, the first mixture is stirred at 45°C for 30 min to obtain a first reaction slurry. Then, 0.5 mol of iron source solution is added to the first reaction slurry at 45°C for 30 min to obtain a second mixture. Then, 0.8 mol of phosphorus source solution and 0.016 mol of manganese oxalate are mixed to obtain a fifth solution. The fifth solution and a third solution (0.47 mol of hydrogen peroxide) accounting for 10% of the total hydrogen peroxide solution are added dropwise to the above base material for a synthesis reaction. A sixth solution containing 60% hydrogen (2.82 mol of hydrogen peroxide) was slowly added dropwise to the second mixture at 55°C for 20 min to carry out the synthesis reaction. After the addition was complete, a third mixture was obtained. The third mixture was heated to 65°C and stirred continuously for 30 min to obtain a second reaction slurry. Finally, the remaining iron source solution (seventh solution) and 0.006 mol of titanium oxide were added to the second reaction slurry at 65°C over 15 min to obtain a fourth mixture. An eighth solution (1 mol of phosphate ions) and a ninth solution (1.41 mol of hydrogen peroxide) were slowly added dropwise to the fourth mixture at 60°C over 35 min to obtain a third reaction slurry. Phosphoric acid was added to the third reaction slurry to adjust the pH to 1.1, and then the temperature was raised to 90°C and stirred continuously for 3 h until the pH reached 1.7. The mixture was then filtered, rinsed, and flash-evaporated to obtain ferric phosphate dihydrate (i.e., ferric phosphate material).

[0166] (3) The iron phosphate dihydrate prepared in step (2), lithium carbonate (1.03 times the amount of lithium in iron phosphate dihydrate), ferrous oxalate (0.8% by mass of iron phosphate dihydrate), dipolyglycerol (2.3% by mass of iron phosphate dihydrate), and β-cyclodextrin (molecular weight 1135) (8.8% by mass of iron phosphate dihydrate) are mixed with pure water to obtain a mixed slurry with a solid content of 48%. The slurry is then ground to obtain a grinding slurry with a solid particle size D50 of 0.33 μm by sand milling. The material was spray-dried (inlet air temperature 240℃, outlet air temperature 95℃) and pulverized to obtain a dried material with a D50 particle size of 0.58μm and a D100 of 7.5μm. Then, under a nitrogen protective atmosphere, the temperature was increased to 806℃ at 8℃ / min and held for 2h. Then, the temperature was decreased to 796℃ at 5℃ / min and held for 8.4h. Finally, the temperature was decreased to below 100℃ at 10℃ / min and removed from the furnace. The material was then pulverized a second time to a D50 particle size of 1.41μm to obtain the lithium iron phosphate cathode material.

[0167] Example 3 (1) The titanium dioxide byproduct was heated and dissolved, and precipitated by adding a 5% sodium hydroxide solution. The precipitate was removed by pressure filtration to obtain a ferrous solution with an iron ion concentration of 1.5 mol / L (i.e., the iron source solution) and a pH of 3.0. Industrial monoammonium phosphate was dissolved, filtered, and then ammonia was added to adjust the pH to neutral to obtain a phosphorus source solution, in which PO4 ions were added. 3- The concentration is 2 mol / L; (2) Based on a total amount of 1 mol of iron, firstly, 0.15 mol of iron source solution (i.e., a ferrous solution containing 0.15 mol of ferrous ions, hereinafter the same) is added to the reactor as the base material. Then, 0.3 mol of phosphorus source solution (i.e., a phosphorus source solution containing 0.3 mol of phosphate ions, hereinafter the same) and 0.007 mol of stannous sulfate are mixed to obtain a second solution. The second solution is then mixed with a third solution (hydrogen peroxide solution) that accounts for 20% of the total hydrogen peroxide solution (mass fraction of 27%). The amount of hydrogen sulfide (0.86 mol) was added dropwise at 25°C for 45 min to carry out the synthesis reaction. After the addition was complete, the first mixture was stirred at 45°C for 30 min to obtain the first reaction slurry. Then, 0.5 mol of iron source solution was added to the first reaction slurry at 50°C for 15 min to obtain the second mixture. 0.9 mol of phosphorus source solution and manganese oxalate and ammonium metavanadate in a mass ratio of 2:1 (the sum of the amounts of manganese oxalate and ammonium metavanadate was 0.016 mol) were added. The fifth solution is obtained by mixing the first solution (mol) with the sixth solution (60% of the total hydrogen peroxide mass, 2.58 mol of hydrogen peroxide). The fifth solution and the sixth solution (60% of the total hydrogen peroxide mass, 2.58 mol of hydrogen peroxide) are simultaneously and slowly added dropwise to the second mixture at 55°C for 20 min to carry out the synthesis reaction. After the addition is complete, the third mixture is obtained. The third mixture is heated to 65°C and stirred continuously for 30 min to obtain the second reaction slurry. Finally, the remaining iron source solution (seventh solution) and 0.009 mol of magnesium oxide are added to the second reaction slurry at 65°C. After 15 minutes, a fourth mixture was obtained. An eighth solution (0.9 mol of phosphate ions) and a ninth solution (0.86 mol of hydrogen peroxide) were slowly added dropwise to the fourth mixture at 60°C for 35 minutes. After the addition was complete, a third reaction slurry was obtained. Phosphoric acid was added to the third reaction slurry to adjust the pH to 1.4. The temperature was then raised to 95°C and the reaction was continued for 2 hours until the pH reached 1.9. The mixture was then filtered, rinsed, and flash-evaporated to obtain ferric phosphate dihydrate (i.e., ferric phosphate material).

[0168] (3) The iron phosphate dihydrate prepared in step (2), lithium carbonate (1.03 times the amount of lithium in iron phosphate dihydrate), ferrous oxalate (0.8% by mass of iron phosphate dihydrate), dipolyglycerol (2.3% by mass of iron phosphate dihydrate), and β-cyclodextrin (molecular weight 1135) (8.8% by mass of iron phosphate dihydrate) are mixed with pure water to obtain a mixed slurry with a solid content of 48%. The slurry is then ground to obtain a grinding slurry with a solid particle size D50 of 0.33 μm by sand milling. The material was spray-dried (inlet air temperature 240℃, outlet air temperature 95℃) and pulverized to obtain a dried material with a D50 particle size of 0.61μm and a D100 of 7.2μm. Then, under a nitrogen protective atmosphere, the temperature was increased to 806℃ at 8℃ / min and held for 2h. Then, the temperature was decreased to 796℃ at 5℃ / min and held for 8.4h. Finally, the temperature was decreased to below 100℃ at 10℃ / min and removed from the furnace. The material was then pulverized a second time to a D50 particle size of 1.37μm to obtain the lithium iron phosphate cathode material.

[0169] Example 4 The difference from Example 3 is that step (3) is as follows: (3) The mixture prepared in step (2) of Example 3, lithium carbonate (1.04 times the amount of lithium in dihydrate), ferric dihydrogen phosphate (1.2% by mass of ferric dihydrate), dipolyglycerol (2.7% by mass of ferric dihydrate), and β-cyclodextrin (molecular weight 1135) (8.5% by mass of ferric dihydrate) were mixed with pure water to obtain a mixed slurry with a solid content of 49.3%. The slurry was then ground to obtain a grinding slurry with a solid particle size D50 of 0.32 μm by sand milling. The material was then spray-dried (inlet air temperature 200℃, outlet air temperature 85℃) and pulverized to obtain a dried material with a D50 of 0.57μm and a D100 of 6.5μm. It was then heated to 806℃ at a rate of 8℃ / min under a nitrogen protective atmosphere and held for 2 hours. Then it was cooled to 796℃ at a rate of 5℃ / min and held for 8.4 hours. Finally, it was cooled to below 100℃ at a rate of 10℃ / min and removed from the furnace. It was then pulverized a second time to a D50 particle size of 1.38μm to obtain the lithium iron phosphate cathode material.

[0170] Example 5 The difference from Example 3 is that step (3) is as follows: (3) The mixture prepared in step (2) of Example 3, lithium carbonate (1.04 times the amount of lithium in dihydrate), ferric dihydrogen phosphate (1.2% by mass of ferric dihydrate), dipolyglycerol (3.1% by mass of ferric dihydrate), and β-cyclodextrin (molecular weight 1135) (8.3% by mass of ferric dihydrate) were mixed with pure water to obtain a mixed slurry with a solid content of 48%. The slurry was then milled to obtain a grinding slurry with a solid particle size D50 of 0.37 μm. The material was then spray-dried (inlet air temperature 220℃, outlet air temperature 90℃) and pulverized to obtain a dried material with a D50 of 0.80μm and a D100 of 8.9μm. Then, under a nitrogen protective atmosphere, the temperature was increased to 812℃ at 8℃ / min and held for 2h. Then, the temperature was decreased to 796℃ at 5℃ / min and held for 8.4h. Finally, the temperature was decreased to below 100℃ at 10℃ / min and removed from the furnace. The material was then pulverized a second time to a D50 particle size of 1.35μm to obtain the lithium iron phosphate cathode material.

[0171] Example 6 The difference from Example 3 is that step (3) is as follows: (3) The iron phosphate dihydrate prepared in step (2) of Example 3, lithium carbonate (1.05 times the amount of iron phosphate dihydrate), ferric dihydrogen phosphate (1.2% by mass of iron phosphate dihydrate), glycerol (2.6% by mass of iron phosphate dihydrate), and β-cyclodextrin (molecular weight 1135) (8.7% by mass of iron phosphate dihydrate) were mixed with pure water to obtain a mixed slurry with a solid content of 47.5%. The slurry was then milled to obtain a grinding slurry with a solid particle size D50 of 0.36 μm. The material was then spray-dried (inlet air temperature 240℃, outlet air temperature 95℃) and pulverized to obtain a dried material with a D50 of 0.78μm and a D100 of 8.3μm. Then, under a nitrogen protective atmosphere, the temperature was increased to 809℃ at 8℃ / min and held for 2h. Then, the temperature was decreased to 798℃ at 5℃ / min and held for 8.4h. Finally, the temperature was decreased to below 100℃ at 10℃ / min and removed from the furnace. The material was then pulverized a second time to a D50 particle size of 1.39μm to obtain the lithium iron phosphate cathode material.

[0172] Example 7 (1) The titanium dioxide byproduct was heated and dissolved, and precipitated by adding a 5% sodium hydroxide solution. The precipitate was removed by pressure filtration to obtain a ferrous solution with an iron ion concentration of 1 mol / L (i.e., the iron source solution) and a pH of 2.8. Industrial monoammonium phosphate was dissolved and filtered, and then ammonia was added to adjust the pH to neutral to obtain a phosphorus source solution, in which PO4 ions were added. 3- The concentration is 1 mol / L; (2) Based on a total amount of 1 mol of iron, firstly, 0.14 mol of iron source solution (i.e., a ferrous solution containing 0.14 mol of ferrous ions, the same below) is added to the reactor as the base material. Then, 0.28 mol of phosphorus source solution (i.e., a phosphorus source solution containing 0.28 mol of phosphate ions, the same below), 0.0005 mol of lanthanum nitrate, and 0.0015 mol of cerium nitrate are added to obtain a second solution. The second solution is then combined with a third solution, which accounts for 20% of the total hydrogen peroxide solution (mass fraction 25%). A solution (0.936 mol of hydrogen peroxide) was slowly added dropwise to the above-mentioned substrate at 20°C for 40 min. After the addition was complete, the first mixture was stirred at 40°C for 20 min to obtain the first reaction slurry. Then, 0.7 mol of iron source solution was added to the first reaction slurry at 45°C for 10 min to obtain the second mixture. 1.1 mol of phosphorus source solution and 0.009 mol of manganese oxalate were mixed to obtain the fifth solution. The fifth solution and the sixth solution (3.384 mol of hydrogen peroxide, accounting for 71% of the total hydrogen peroxide mass) were simultaneously and slowly added dropwise to the second mixture at 50°C for 10 min to obtain the third mixture. The third mixture was heated to 60°C and stirred continuously for 20 min to obtain the second reaction slurry. Finally, the remaining iron source solution (seventh solution) and 0.005 mol of zirconium oxide were added to the second reaction slurry at 60°C for 10 min to obtain the second mixture. The fourth mixture was then slowly added dropwise to the eighth solution (0.62 mol of phosphate ions) and the ninth solution (0.48 mol of hydrogen peroxide) at a temperature of 55°C for 40 min. After the addition was complete, the third reaction slurry was obtained. Phosphoric acid was added to the third reaction slurry to adjust the pH to 1.1. The temperature was then raised to 90°C and the reaction was stirred for 3 h until the pH reached 1.7. The mixture was then filtered, rinsed, and flash-evaporated to obtain ferric phosphate dihydrate (i.e., ferric phosphate material).

[0173] (3) The iron phosphate dihydrate prepared in step (2), lithium carbonate (1.03 times the amount of lithium in iron phosphate dihydrate), ferric citrate (0.8% by mass of iron phosphate dihydrate), glycerol (2.1% by mass of iron phosphate dihydrate), and polyethylene glycol (8.3% by mass of iron phosphate dihydrate) (molecular weight 8000) were mixed with pure water to obtain a mixed slurry with a solid content of 47.5%. The slurry was then adjusted by sand milling to obtain a grinding slurry with a solid particle size D50 of 0.32 μm. The material was spray-dried (inlet air temperature 200℃, outlet air temperature 85℃) and pulverized to obtain a dried material with a D50 particle size of 0.55μm and a D100 particle size of 6.5μm. Then, under a nitrogen protective atmosphere, the temperature was increased to 803℃ at 5℃ / min and held for 3h. Then, the temperature was decreased to 790℃ at 7℃ / min and held for 7h. Finally, the temperature was decreased to below 100℃ at 8℃ / min and removed from the furnace. The material was then pulverized a second time to a D50 particle size of 1.47μm to obtain the lithium iron phosphate cathode material.

[0174] Example 8 (1) The titanium dioxide byproduct was heated and dissolved, and precipitated by adding a 5% sodium hydroxide solution. The precipitate was removed by pressure filtration to obtain a ferrous solution with an iron ion concentration of 2 mol / L (i.e., the iron source solution) and a pH of 3.2. Industrial monoammonium phosphate was dissolved and filtered, and then ammonia was added to adjust the pH to neutral to obtain a phosphorus source solution, in which PO4 ions were added. 3- The concentration is 3 mol / L; (2) Based on a total amount of 1 mol of iron, 0.15 mol of iron source solution (i.e., ferrous solution containing 0.15 mol of ferrous ions, hereinafter the same) is first added to the reactor as the base material. 0.2 mol of phosphorus source solution (i.e., phosphorus source solution containing 0.2 mol of phosphate ions, hereinafter the same) and 0.007 mol of lanthanum nitrate are added to obtain the second solution. The second solution and the third solution (0.48 mol of hydrogen peroxide) which account for 10% of the total hydrogen peroxide solution (mass fraction of 30%) are simultaneously and slowly added dropwise to the above base material at 25°C for 45 min. After the addition is completed, the first mixture is stirred at 50°C for 40 min to obtain the first reaction slurry. Then, 0.66 mol of iron source solution is added to the first reaction slurry at 45°C for 20 min to obtain the second mixture. 1.08 mol of phosphorus source solution and 0.016 mol of manganese oxalate are mixed to obtain the fifth solution. The fifth solution and the third solution (10% of the total hydrogen peroxide mass fraction of 30%) are added dropwise to obtain the second mixture. 80% of the sixth solution (containing 3.84 mol of hydrogen peroxide) was slowly added dropwise to the second mixture at 60°C for 15 min. After the addition was complete, a third mixture was obtained. The third mixture was heated to 70°C and stirred continuously for 40 min to obtain a second reaction slurry. Finally, the remaining iron source solution (the seventh solution) and 0.018 mol of yttrium oxide were added dropwise to the second reaction slurry at 60°C over 20 min to obtain a fourth mixture. The eighth solution (containing 0.72 mol of phosphate ions) and the ninth solution (containing 0.48 mol of hydrogen peroxide) were slowly added dropwise to the fourth mixture at 65°C over 30 min to obtain a third reaction slurry. Phosphoric acid was added to the third reaction slurry to adjust the pH to 1.4. The mixture was then heated to 100°C and stirred continuously for 1 h until the pH reached 1.9. After pressure filtration, rinsing, and flash evaporation, ferric phosphate dihydrate (i.e., ferric phosphate material) was obtained.

[0175] (3) The iron phosphate dihydrate prepared in step (2), lithium carbonate (1.03 times the amount of lithium in iron phosphate dihydrate), ferric citrate (1% by mass of iron phosphate dihydrate), glycerol (3.7% by mass of iron phosphate dihydrate), and polyethylene glycol (8.5% by mass of iron phosphate dihydrate) (molecular weight 8000) are mixed with pure water to obtain a mixed slurry with a solid content of 48.4%. The slurry is then adjusted by sand milling to obtain a grinding slurry with a solid particle size D50 of 0.35 μm, and then sprayed. The material was dried by mist drying (inlet air temperature 220℃, outlet air temperature 90℃) and pulverized to obtain a dried material with a D50 particle size of 0.65μm and a D100 of 7.3μm. Then, under a nitrogen protective atmosphere, the temperature was increased to 805℃ at 10℃ / min and held for 1.5h. Then, the temperature was decreased to 800℃ at 5℃ / min and held for 9h. Finally, the temperature was decreased to below 100℃ at 12℃ / min and removed from the furnace. The material was then pulverized a second time to a D50 particle size of 1.51μm to obtain the lithium iron phosphate cathode material.

[0176] Example 9 (1) The titanium dioxide byproduct was heated and dissolved, and precipitated by adding a 5% sodium hydroxide solution. The precipitate was removed by pressure filtration to obtain a ferrous solution with an iron ion concentration of 1 mol / L (i.e., the iron source solution) and a pH of 3.2. Industrial monoammonium phosphate was dissolved, filtered, and then ammonia was added to adjust the pH to neutral to obtain a phosphorus source solution, in which PO4 ions were added. 3- The concentration is 2.5 mol / L; (2) Based on a total amount of 1 mol of iron, 0.12 mol of iron source solution (i.e., ferrous solution containing 0.12 mol of ferrous ions, hereinafter the same) is first added to the reactor as the base material. 0.3 mol of phosphorus source solution (i.e., phosphorus source solution containing 0.3 mol of phosphate ions, hereinafter the same) and 0.001 mol of lanthanum nitrate, 0.001 mol of cerium nitrate, and 0.003 mol of stannous sulfate are added to obtain a second solution. The second solution is then combined with a third solution (12% by mass of the total hydrogen peroxide solution (mass fraction of 30%)) to obtain a third solution. Hydrogen peroxide (0.516 mol) was slowly added dropwise to the above-mentioned substrate at 30°C for 50 min to carry out the synthesis reaction. After the addition was complete, the first mixture was stirred at 45°C for 20 min to obtain the first reaction slurry. Then, 0.45 mol of iron source solution was added to the first reaction slurry at 55°C for 10 min to obtain the second mixture. 0.85 mol of phosphorus source solution and 0.015 mol of manganese oxalate were mixed to obtain the fifth solution. The fifth solution was then mixed with the sixth solution, which accounted for 60% of the total hydrogen peroxide mass. The solution (2.58 mol of hydrogen peroxide) was slowly added dropwise to the second mixture at 58°C for 25 min to carry out the synthesis reaction. After the addition was complete, a third mixture was obtained. The third mixture was heated to 70°C and stirred continuously for 25 min to obtain the second reaction slurry. Finally, the remaining iron source solution (seventh solution) and 0.003 mol of titanium oxide, 0.003 mol of magnesium oxide, 0.003 mol of zirconium oxide, and 0.003 mol of yttrium oxide were added to the second reaction slurry at 70°C. The addition time was... After 10 minutes, a fourth mixture was obtained. The eighth solution (1.35 mol of phosphate ions) and the ninth solution (1.204 mol of hydrogen peroxide) were slowly added dropwise to the fourth mixture at 55°C for 35 minutes. After the addition was complete, a third reaction slurry was obtained. Phosphoric acid was added to the third reaction slurry to adjust the pH to 1.3. The temperature was then raised to 98°C and the reaction was continued with stirring for 1.5 hours until the pH reached 1.8. The mixture was then filtered, rinsed, and flash-evaporated to obtain ferric phosphate dihydrate (i.e., ferric phosphate material).

[0177] (3) The mixture prepared in step (2) consists of lithium carbonate (1.06 times the amount of lithium in dihydrate), ferric citrate (0.8% by mass of ferric phosphate dihydrate), glycerol (2.5% by mass of ferric phosphate dihydrate), and polyethylene glycol (9.2% by mass of ferric phosphate dihydrate, with a molecular weight of 8000). Pure water is added and stirred until homogeneous to obtain a mixed slurry with a solid content of 47.9%. This slurry is then milled to obtain a grinding slurry with a solid particle size (D50) of 0.32 μm. Subsequently, the mixture is further processed... The material was spray-dried (inlet air temperature 250℃, outlet air temperature 100℃) and pulverized to obtain a dried material with a D50 particle size of 0.7μm and a D100 particle size of 8.6μm. Then, under a nitrogen protective atmosphere, the temperature was increased to 809℃ at 5℃ / min and held for 2.5h. Then, the temperature was decreased to 794℃ at 4℃ / min and held for 10h. Finally, the temperature was decreased to below 100℃ at 8℃ / min and removed from the furnace. The material was then pulverized a second time to a D50 particle size of 1.59μm to obtain the lithium iron phosphate cathode material.

[0178] Example 10 (1) The titanium dioxide byproduct was heated and dissolved, and precipitated by adding a 5% sodium hydroxide solution. The precipitate was removed by pressure filtration to obtain a ferrous solution with an iron ion concentration of 1.5 mol / L (i.e., the iron source solution) and a pH of 3.0. Industrial monoammonium phosphate was dissolved and filtered, and then ammonia was added to adjust the pH to neutral to obtain a phosphorus source solution, in which PO4 ions were added. 3- The concentration is 2 mol / L; (2) Based on a total amount of 1 mol of iron, 0.1 mol of iron source solution (i.e., ferrous solution containing 0.1 mol of ferrous ions, hereinafter the same) is first added to the reactor as the base material. 0.25 mol of phosphorus source solution (i.e., phosphorus source solution containing 0.25 mol of phosphate ions, hereinafter the same), 0.003 mol of lanthanum nitrate, and 0.004 mol of stannous sulfate are added to obtain a second solution. The second solution is then combined with a third solution (hydrogen peroxide solution) comprising 10% of the total hydrogen peroxide solution (mass fraction 27%). The first mixture (0.43 mol of hydrogen peroxide) is slowly added dropwise to the above-mentioned substrate at 25°C for 40 min. After the addition is complete, the first mixture is stirred at 50°C for 30 min to obtain the first reaction slurry. Then, 0.4 mol of iron source solution is added to the first reaction slurry at 55°C for 20 min to obtain the second mixture. A fifth solution is obtained by mixing 0.6 mol of phosphorus source solution and 0.016 mol of manganese oxalate. This fifth solution, along with a sixth solution (2.58 mol of hydrogen peroxide, accounting for 60% of the total hydrogen peroxide mass), is slowly added dropwise to the second mixture at 52°C for 30 min to obtain the third mixture. The third mixture is then heated to 60°C and stirred continuously for 35 min to obtain the second reaction slurry. Finally, the remaining iron source solution (seventh solution), 0.003 mol of magnesium oxide, and 0.006 mol of zirconium oxide are added to the second reaction slurry at 70°C for 20 min to obtain the second mixture. The fourth mixture; the eighth solution (1.25 mol of phosphate ions) and the ninth solution (1.29 mol of hydrogen peroxide) were slowly added dropwise to the fourth mixture at a temperature of 70°C for 35 min. After the addition was complete, the third reaction slurry was obtained. Phosphoric acid was added to the third reaction slurry to adjust the pH to 1.2, and then the temperature was raised to 95°C and the reaction was stirred for 2 h until the pH reached 1.9. The mixture was then filtered, rinsed, and flash-evaporated to obtain ferric phosphate dihydrate (i.e., ferric phosphate material).

[0179] (3) The iron phosphate dihydrate prepared in step (2), lithium carbonate (1.06 times the amount of lithium in iron phosphate dihydrate), ferrous oxalate (0.8% by mass of iron phosphate dihydrate), glycerol (2.9% by mass of iron phosphate dihydrate), and polyethylene glycol (8.9% by mass of iron phosphate dihydrate, molecular weight 12000) were mixed with pure water to obtain a mixed slurry with a solid content of 49.3%. The slurry was then adjusted by sand milling to obtain a grinding slurry with a solid particle size D50 of 0.38 μm. The material was spray-dried (inlet air temperature 260℃, outlet air temperature 105℃) and pulverized to obtain a dried material with a D50 particle size of 0.8μm and a D100 particle size of 9μm. Then, under a nitrogen protective atmosphere, the temperature was increased to 812℃ at 10℃ / min and held for 1h. Then, the temperature was decreased to 798℃ at 3℃ / min and held for 12h. Finally, the temperature was decreased to below 100℃ at 12℃ / min and removed from the furnace. The material was then pulverized a second time to a D50 particle size of 1.65μm to obtain the lithium iron phosphate cathode material.

[0180] Example 11 (1) The titanium dioxide byproduct was heated and dissolved, and precipitated by adding a 5% sodium hydroxide solution. The precipitate was removed by pressure filtration to obtain a ferrous solution with an iron ion concentration of 1.5 mol / L (i.e., the iron source solution) and a pH of 3.0. Industrial monoammonium phosphate was dissolved, filtered, and then ammonia was added to adjust the pH to neutral to obtain a phosphorus source solution, in which PO4 ions were added. 3- The concentration is 2 mol / L; (2) Based on a total amount of 1 mol of iron, firstly, 0.15 mol of iron source solution (i.e., a ferrous solution containing 0.15 mol of ferrous ions, hereinafter the same) is added to the reactor as the base material. Then, 0.18 mol of phosphorus source solution (i.e., a phosphorus source solution containing 0.18 mol of phosphate ions, hereinafter the same) and 0.007 mol of stannous sulfate are added to obtain a second solution. The second solution is then combined with a third solution (containing 20% ​​of the total hydrogen peroxide solution (mass fraction of 27%)) to form a third solution (containing 20% ​​of the total hydrogen peroxide solution (mass fraction of 27%). The amount of substance (0.86 mol) was added dropwise at 25°C for 45 min to carry out the synthesis reaction. After the addition was complete, the first mixture was stirred at 45°C for 30 min to obtain the first reaction slurry. Then, 0.5 mol of iron source solution was added to the first reaction slurry at 50°C for 15 min to obtain the second mixture. 0.56 mol of phosphorus source solution and 0.016 mol of manganese oxalate and ammonium metavanadate in a mass ratio of 2:1 were mixed to obtain the fifth solution. The fifth solution was then reacted with the total peroxide... A sixth solution (containing 2.58 mol of hydrogen peroxide) with 60% hydrogen mass was slowly added dropwise to the second mixture at 55°C for 20 min to carry out the synthesis reaction. After the addition was complete, a third mixture was obtained. The third mixture was heated to 65°C and stirred continuously for 30 min to obtain a second reaction slurry. Finally, the remaining iron source solution (seventh solution) and 0.009 mol of magnesium oxide were added to the second reaction slurry at 65°C over 15 min to obtain a fourth mixture. An eighth solution (containing 0.56 mol of phosphate ions) and a ninth solution (containing 0.86 mol of hydrogen peroxide) were slowly added dropwise to the fourth mixture at 60°C over 35 min to obtain a third reaction slurry. Phosphoric acid was added to the third reaction slurry to adjust the pH to 1.4, and then the temperature was raised to 95°C and stirred continuously for 2 h until the pH reached 2.0. The mixture was then filtered, rinsed, and flash-evaporated to obtain ferric phosphate dihydrate (i.e., ferric phosphate material).

[0181] (3) The mixture prepared in step (2) consists of lithium carbonate (1.04 times the amount of lithium in dihydrate), ferric dihydrogen phosphate (1.2% by mass of ferric dihydrate), dipolyglycerol (3.1% by mass of ferric dihydrate), and β-cyclodextrin (molecular weight 1135) (8.3% by mass of ferric dihydrate) with pure water. The mixture is stirred until homogeneous to obtain a slurry with a solid content of 48%. This slurry is then milled to obtain a grinding slurry with a solid particle size (D50) of 0.34 μm. The material was then spray-dried (inlet air temperature 220℃, outlet air temperature 90℃) and pulverized to obtain a dried material with a D50 of 0.77μm and a D100 of 8.4μm. Then, under a nitrogen protective atmosphere, the temperature was increased to 812℃ at 8℃ / min and held for 2 hours. Then, the temperature was decreased to 796℃ at 5℃ / min and held for 8.4 hours. Finally, the temperature was decreased to below 100℃ at 10℃ / min and removed from the furnace. The material was then pulverized a second time to a D50 particle size of 1.37μm to obtain the lithium iron phosphate cathode material.

[0182] Example 12 (1) The titanium dioxide byproduct was heated and dissolved, and precipitated by adding a 5% sodium hydroxide solution. The precipitate was removed by pressure filtration to obtain a ferrous solution with an iron ion concentration of 1.5 mol / L (i.e., the iron source solution) and a pH of 3.0. Industrial monoammonium phosphate was dissolved, filtered, and then ammonia was added to adjust the pH to neutral to obtain a phosphorus source solution, in which PO4 ions were added. 3- The concentration is 2 mol / L; (2) Based on a total amount of 1 mol of iron, firstly, 0.15 mol of iron source solution (i.e., ferrous solution containing 0.15 mol of ferrous ions, the same below) is added to the reactor as the base material. Then, 0.46 mol of phosphorus source solution (i.e., phosphorus source solution containing 0.46 mol of phosphate ions, the same below) and 0.007 mol of stannous sulfate are added to obtain the second solution. The second solution is combined with a third solution (the amount of hydrogen peroxide is 20% of the total hydrogen peroxide solution (mass fraction of 27%)) to form a third solution (the amount of hydrogen peroxide is 20% of the total hydrogen peroxide solution (mass fraction of 27%). Simultaneously, 0.86 mol of a phosphorus source solution was slowly added dropwise to the above-mentioned substrate at 25°C for 45 min to carry out the synthesis reaction. After the addition was complete, the first mixture was stirred at 45°C for 30 min to obtain the first reaction slurry. Then, 0.5 mol of iron source solution was added to the first reaction slurry at 50°C for 15 min to obtain the second mixture. 1.37 mol of phosphorus source solution and 0.016 mol of manganese oxalate and ammonium metavanadate in a mass ratio of 2:1 were mixed to obtain the fifth solution. The fifth solution was then mixed with... A hydrogen peroxide solution with a total hydrogen peroxide mass of 60% (2.58 mol of hydrogen peroxide) was slowly added dropwise to the second mixture at 55°C for 20 min to carry out the synthesis reaction. After the addition was complete, a third mixture was obtained. The third mixture was heated to 65°C and stirred continuously for 30 min to obtain a second reaction slurry. Finally, the remaining iron source solution (seventh solution) and 0.009 mol of magnesium oxide were added to the second reaction slurry at 65°C over 15 min to obtain the second reaction slurry. The fourth mixture was then slowly added dropwise to the eighth solution (1.37 mol of phosphate ions) and the ninth solution (0.86 mol of hydrogen peroxide) at a temperature of 60°C for 35 min. After the addition was complete, the third reaction slurry was obtained. Phosphoric acid was added to the third reaction slurry to adjust the pH to 1.4. The temperature was then raised to 95°C and the reaction was stirred for 2 h until the pH reached 1.9. The mixture was then filtered, rinsed, and flash-evaporated to obtain ferric phosphate dihydrate (i.e., ferric phosphate material).

[0183] (3) The mixture prepared in step (2) consists of lithium carbonate (1.04 times the amount of lithium in dihydrate), ferric dihydrogen phosphate (1.2% by mass of ferric dihydrate), dipolyglycerol (3.1% by mass of ferric dihydrate), and β-cyclodextrin (molecular weight 1135) (8.3% by mass of ferric dihydrate) with pure water. The mixture is stirred until homogeneous to obtain a slurry with a solid content of 48%. This slurry is then milled to obtain a grinding slurry with a solid particle size (D50) of 0.34 μm. The material was then spray-dried (inlet air temperature 220℃, outlet air temperature 90℃) and pulverized to obtain a dried material with a D50 of 0.78μm and a D100 of 8.6μm. Then, under a nitrogen protective atmosphere, the temperature was increased to 812℃ at 8℃ / min and held for 2 hours. Then, the temperature was decreased to 796℃ at 5℃ / min and held for 8.4 hours. Finally, the temperature was decreased to below 100℃ at 10℃ / min and removed from the furnace. The material was then pulverized a second time to a D50 particle size of 1.36μm to obtain the lithium iron phosphate cathode material.

[0184] Example 13 (1) The titanium dioxide byproduct was heated and dissolved, and precipitated by adding a 5% sodium hydroxide solution. The precipitate was removed by pressure filtration to obtain a ferrous solution with an iron ion concentration of 1.5 mol / L (i.e., the iron source solution) and a pH of 3.0. Industrial monoammonium phosphate was dissolved, filtered, and then ammonia was added to adjust the pH to neutral to obtain a phosphorus source solution, in which PO4 ions were added. 3- The concentration is 2 mol / L; (2) Based on a total amount of 1 mol of iron, firstly, 0.15 mol of iron source solution (i.e., ferrous solution containing 0.15 mol of ferrous ions, hereinafter the same) is added to the reactor as the base material. Then, 0.3 mol of phosphorus source solution (i.e., phosphorus source solution containing 0.3 mol of phosphate ions, hereinafter the same) and 0.007 mol of stannous sulfate are added to obtain the second solution. The second solution is then combined with a third solution (hydrogen peroxide solution) that accounts for 20% of the total hydrogen peroxide solution (mass fraction of 27%). The amount of hydrogen (0.7 mol) was added dropwise at 25°C for 45 min to carry out the synthesis reaction. After the addition was complete, the mixture was stirred at 45°C for 30 min to obtain the first reaction slurry. Then, 0.5 mol of iron source solution was added to the first reaction slurry at 50°C over a period of 15 min to obtain the second mixture. A fifth solution was obtained by mixing 0.9 mol of phosphorus source solution with 0.016 mol of manganese oxalate and ammonium metavanadate in a mass ratio of 2:1. The fifth solution, comprising 60% of the total hydrogen peroxide mass, was then added to the first reaction slurry. The sixth solution (containing 2.1 mol of hydrogen peroxide) was slowly added dropwise to the second mixture at 55°C for 20 min to carry out the synthesis reaction. After the addition was complete, the third mixture was obtained. The third mixture was heated to 65°C and stirred continuously for 30 min to obtain the second reaction slurry. Finally, the remaining iron source solution (the seventh solution) and 0.009 mol of magnesium oxide were added to the second reaction slurry at 65°C over 15 min to obtain the fourth mixture. The eighth solution (containing 0.9 mol of phosphate ions) and the ninth solution (containing 0.7 mol of hydrogen peroxide) were slowly added dropwise to the fourth mixture at 60°C over 35 min to obtain the third reaction slurry. Phosphoric acid was added to the third reaction slurry to adjust the pH to 1.4. The mixture was then heated to 95°C and stirred continuously for 2 h until the pH reached 2.0. After pressure filtration, rinsing, and flash evaporation, ferric phosphate dihydrate (i.e., ferric phosphate material) was obtained.

[0185] (3) The mixture prepared in step (2) consists of lithium carbonate (1.04 times the amount of lithium in dihydrate), ferric dihydrogen phosphate (1.2% by mass of ferric dihydrate), dipolyglycerol (3.1% by mass of ferric dihydrate), and β-cyclodextrin (molecular weight 1135) (8.3% by mass of ferric dihydrate) with pure water. The mixture is stirred until homogeneous to obtain a slurry with a solid content of 48%. This slurry is then milled to obtain a grinding slurry with a solid particle size (D50) of 0.34 μm. The material was then spray-dried (inlet air temperature 220℃, outlet air temperature 90℃) and pulverized to obtain a dried material with a D50 of 0.79μm and a D100 of 8.7μm. Then, under a nitrogen protective atmosphere, the temperature was increased to 812℃ at 8℃ / min and held for 2 hours. Then, the temperature was decreased to 796℃ at 5℃ / min and held for 8.4 hours. Finally, the temperature was decreased to below 100℃ at 10℃ / min and removed from the furnace. The material was then pulverized a second time to a D50 particle size of 1.36μm to obtain the lithium iron phosphate cathode material.

[0186] Example 14 (1) The titanium dioxide byproduct was heated and dissolved, and precipitated by adding a 5% sodium hydroxide solution. The precipitate was removed by pressure filtration to obtain a ferrous solution with an iron ion concentration of 1.5 mol / L (i.e., the iron source solution) and a pH of 3.0. Industrial monoammonium phosphate was dissolved, filtered, and then ammonia was added to adjust the pH to neutral to obtain a phosphorus source solution, in which PO4 ions were added. 3- The concentration is 2 mol / L; (2) Based on a total amount of 1 mol of iron, firstly, 0.15 mol of iron source solution (i.e., a ferrous solution containing 0.15 mol of ferrous ions, hereinafter the same) is added to the reactor as the base material. Then, 0.3 mol of phosphorus source solution (i.e., a phosphorus source solution containing 0.3 mol of phosphate ions, hereinafter the same) and 0.007 mol of stannous sulfate are added to obtain a second solution. The second solution is then combined with a third solution (containing 1.1 mol of hydrogen peroxide) which accounts for 20% of the total hydrogen peroxide solution (mass fraction of 27%). Simultaneously, 0.5 mol of iron source solution was slowly added dropwise to the above-mentioned substrate at 25°C for 45 min to carry out the synthesis reaction. After the addition was completed, the first mixture was stirred at 45°C for 30 min to obtain the first reaction slurry. Then, 0.5 mol of iron source solution was added to the first reaction slurry at 50°C for 15 min to obtain the second mixture. 0.9 mol of phosphorus source solution and 0.016 mol of manganese oxalate and ammonium metavanadate in a mass ratio of 2:1 were mixed to obtain the fifth solution. The fifth solution and the sixth solution (6.6 mol of hydrogen peroxide) accounting for 60% of the total hydrogen peroxide mass were simultaneously and slowly added dropwise to the above-mentioned second mixture at 55°C for 20 min to carry out the synthesis reaction. After the addition was completed, the third mixture was obtained. The third mixture was then... The mixture was heated to 65℃ and stirred continuously for 30 minutes to obtain a second reaction slurry. Finally, the remaining iron source solution (seventh solution) and 0.009 mol of magnesium oxide were added to the second reaction slurry at 65℃ over a period of 15 minutes to obtain a fourth mixture. The eighth solution (0.9 mol of phosphate ions) and the ninth solution (1.1 mol of hydrogen peroxide) were slowly added dropwise to the fourth mixture at 60℃ over a period of 35 minutes to obtain a third reaction slurry. Phosphoric acid was added to the third reaction slurry to adjust the pH to 1.4, and then the temperature was raised to 95℃ and the reaction was stirred for 2 hours until the pH reached 2.0. The mixture was then filtered, rinsed, and flash-evaporated to obtain ferric phosphate dihydrate (i.e., ferric phosphate material).

[0187] (3) The mixture prepared in step (2) consists of lithium carbonate (1.04 times the amount of lithium in dihydrate), ferric dihydrogen phosphate (1.2% by mass of ferric dihydrate), dipolyglycerol (3.1% by mass of ferric dihydrate), and β-cyclodextrin (molecular weight 1135) (8.3% by mass of ferric dihydrate) with pure water. The mixture is stirred until homogeneous to obtain a slurry with a solid content of 48%. This slurry is then milled to obtain a grinding slurry with a solid particle size (D50) of 0.37 μm. The material was then spray-dried (inlet air temperature 220℃, outlet air temperature 90℃) and pulverized to obtain a dried material with a D50 of 0.77μm and a D100 of 8.7μm. Next, under a nitrogen protective atmosphere, the temperature was increased to 812℃ at 8℃ / min and held for 2 hours. Then, the temperature was decreased to 796℃ at 5℃ / min and held for 8.4 hours. Finally, the temperature was decreased to below 100℃ at 10℃ / min and removed from the furnace. The material was then pulverized a second time to a D50 particle size of 1.39μm to obtain the lithium iron phosphate cathode material.

[0188] Example 15 (1) The titanium dioxide byproduct was heated and dissolved, and precipitated by adding a 5% sodium hydroxide solution. The precipitate was removed by pressure filtration to obtain a ferrous solution with an iron ion concentration of 1.5 mol / L (i.e., the iron source solution) and a pH of 3.0. Industrial monoammonium phosphate was dissolved, filtered, and then ammonia was added to adjust the pH to neutral to obtain a phosphorus source solution, in which PO4 ions were added. 3- The concentration is 2 mol / L; (2) Based on a total amount of 1 mol of iron, firstly, 0.15 mol of iron source solution (i.e., ferrous solution containing 0.15 mol of ferrous ions, the same below) is added to the reactor as the base material. Then, 0.3 mol of phosphorus source solution (i.e., phosphorus source solution containing 0.3 mol of phosphate ions, the same below) and 0.007 mol of stannous sulfate are added to obtain the second solution. The second solution is combined with a third solution (the amount of hydrogen peroxide is 20% of the total hydrogen peroxide solution (mass fraction of 27%)) to form a third solution (the amount of hydrogen peroxide is 20% of the total hydrogen peroxide solution (mass fraction of 27%). Simultaneously, 0.86 mol of a phosphorus source solution (containing 0.86 mol of manganese oxalate and ammonium metavanadate in a 2:1 mass ratio) was slowly added dropwise to the above-mentioned substrate at 15°C for 45 min to carry out the synthesis reaction. After the addition was completed, the first mixture was stirred at 35°C for 30 min to obtain the first reaction slurry. Then, 0.5 mol of an iron source solution was added to the first reaction slurry at 40°C for 15 min to obtain the second mixture. 0.9 mol of a phosphorus source solution and 0.016 mol of manganese oxalate and ammonium metavanadate in a 2:1 mass ratio were mixed to obtain the fifth solution. The fifth solution and the sixth solution (containing 2.58 mol of hydrogen peroxide, accounting for 60% of the total hydrogen peroxide mass) were simultaneously and slowly added dropwise to the above-mentioned second mixture at 45°C for 20 min to carry out the synthesis reaction. After the addition was completed, the third mixture was obtained. The third mixture was heated to 55°C and stirred continuously for 30 min to obtain the second reaction slurry. Finally, the remaining iron source solution (the seventh solution) and 0.009 mol of magnesium oxide were added to the second reaction slurry at 55°C for 15 min to obtain the second mixture. The fourth mixture was then slowly added dropwise to the eighth solution (0.9 mol of phosphate ions) and the ninth solution (0.86 mol of hydrogen peroxide) at a temperature of 50°C for 35 min. After the addition was complete, the third reaction slurry was obtained. Phosphoric acid was added to the third reaction slurry to adjust the pH to 1.4. The temperature was then raised to 85°C and the reaction was stirred for 2 h until the pH reached 1.8. The mixture was then filtered, rinsed, and flash-evaporated to obtain ferric phosphate dihydrate (i.e., ferric phosphate material).

[0189] (3) The mixture prepared in step (2) consists of lithium carbonate (1.04 times the amount of lithium in dihydrate), ferric dihydrogen phosphate (1.2% by mass of ferric dihydrate), dipolyglycerol (3.1% by mass of ferric dihydrate), and β-cyclodextrin (molecular weight 1135) (8.3% by mass of ferric dihydrate) with pure water. The mixture is stirred until homogeneous to obtain a slurry with a solid content of 48%. This slurry is then milled to obtain a grinding slurry with a solid particle size (D50) of 0.36 μm. The material was then spray-dried (inlet air temperature 220℃, outlet air temperature 90℃) and pulverized to obtain a dried material with a D50 of 0.79μm and a D100 of 8.3μm. Then, under a nitrogen protective atmosphere, the temperature was increased to 812℃ at 8℃ / min and held for 2 hours. Then, the temperature was decreased to 796℃ at 5℃ / min and held for 8.4 hours. Finally, the temperature was decreased to below 100℃ at 10℃ / min and removed from the furnace. The material was then pulverized a second time to a D50 particle size of 1.38μm to obtain the lithium iron phosphate cathode material.

[0190] Example 16 (1) The titanium dioxide byproduct was heated and dissolved, and precipitated by adding a 5% sodium hydroxide solution. The precipitate was removed by pressure filtration to obtain a ferrous solution with an iron ion concentration of 1.5 mol / L (i.e., the iron source solution) and a pH of 3.0. Industrial monoammonium phosphate was dissolved, filtered, and then ammonia was added to adjust the pH to neutral to obtain a phosphorus source solution, in which PO4 ions were added. 3- The concentration is 2 mol / L; (2) Based on a total amount of 1 mol of iron, firstly, 0.15 mol of iron source solution (i.e., ferrous solution containing 0.15 mol of ferrous ions, the same below) is added to the reactor as the base material. Then, 0.3 mol of phosphorus source solution (i.e., phosphorus source solution containing 0.3 mol of phosphate ions, the same below) and 0.007 mol of stannous sulfate are added to obtain the second solution. The second solution is combined with the third solution (the amount of hydrogen peroxide is 20% of the total hydrogen peroxide solution (mass fraction of 27%)) to form a solution of 20% of the total hydrogen peroxide solution (mass fraction of 27%). Simultaneously, 0.86 mol of a phosphorus source solution (containing 0.86 mol of manganese oxalate and ammonium metavanadate in a 2:1 mass ratio) was slowly added dropwise to the above-mentioned substrate at 35°C for 45 min to carry out the synthesis reaction. After the addition was completed, the first mixture was stirred at 55°C for 30 min to obtain the first reaction slurry. Then, 0.5 mol of an iron source solution was added to the first reaction slurry at 60°C for 15 min to obtain the second mixture. 0.9 mol of a phosphorus source solution and 0.016 mol of manganese oxalate and ammonium metavanadate in a 2:1 mass ratio were mixed to obtain the fifth solution. The fifth solution and the sixth solution (containing 2.58 mol of hydrogen peroxide, accounting for 60% of the total hydrogen peroxide mass) were simultaneously and slowly added dropwise to the above-mentioned second mixture at 65°C for 20 min to carry out the synthesis reaction. After the addition was completed, the third mixture was obtained. The third mixture was heated to 75°C and stirred continuously for 30 min to obtain the second reaction slurry. Finally, the remaining iron source solution (the seventh solution) and 0.009 mol of magnesium oxide were added to the second reaction slurry at 75°C for 15 min to obtain the fourth mixture. Mixture; slowly add solution eight (0.9 mol of phosphate ions) and solution nine (0.86 mol of hydrogen peroxide) dropwise to the above fourth mixture at a temperature of 75°C for 35 min. After the addition is complete, a third reaction slurry is obtained. Add phosphoric acid to the third reaction slurry to adjust the pH to 1.4, then raise the temperature to 100°C and continue stirring for 2 h until the pH reaches 2.1. Filter, rinse, and flash evaporate to obtain ferric phosphate dihydrate (i.e., ferric phosphate material).

[0191] (3) The mixture prepared in step (2) consists of lithium carbonate (1.04 times the amount of lithium in dihydrate), ferric dihydrogen phosphate (1.2% by mass of ferric dihydrate), dipolyglycerol (3.1% by mass of ferric dihydrate), and β-cyclodextrin (molecular weight 1135) (8.3% by mass of ferric dihydrate) with pure water. The mixture is stirred until homogeneous to obtain a slurry with a solid content of 48%. This slurry is then milled to obtain a grinding slurry with a solid particle size (D50) of 0.36 μm. The material was then spray-dried (inlet air temperature 220℃, outlet air temperature 90℃) and pulverized to obtain a dried material with a D50 of 0.80μm and a D100 of 8.6μm. Then, under a nitrogen protective atmosphere, the temperature was increased to 812℃ at 8℃ / min and held for 2 hours. Then, the temperature was decreased to 796℃ at 5℃ / min and held for 8.4 hours. Finally, the temperature was decreased to below 100℃ at 10℃ / min and removed from the furnace. The material was then pulverized a second time to a D50 particle size of 1.39μm to obtain the lithium iron phosphate cathode material.

[0192] Example 17 The only difference from Example 5 is that step (3) is as follows: (3) The mixture prepared in step (2) consists of lithium carbonate (1.04 times the amount of lithium in dihydrate), ferric dihydrogen phosphate (1.2% by mass of ferric dihydrate), dipolyglycerol (3.1% by mass of ferric dihydrate), and β-cyclodextrin (8.3% by mass of ferric dihydrate) with pure water. The mixture is stirred and mixed evenly to obtain a slurry with a solid content of 48%. The slurry is then milled to obtain a grinding slurry with a solid particle size D50 of 0.35 μm. The material was spray-dried (inlet air temperature 220℃, outlet air temperature 90℃) and pulverized to obtain a dried material with a D50 of 0.76μm and a D100 of 9.0μm. Then, under a nitrogen protective atmosphere, the temperature was increased to 800℃ at 8℃ / min and held for 0.5h. Then, the temperature was decreased to 796℃ at 5℃ / min and held for 8.4h. Finally, the temperature was decreased to below 100℃ at 10℃ / min and removed from the furnace. The material was then pulverized a second time to a D50 particle size of 1.38μm to obtain the lithium iron phosphate cathode material.

[0193] Example 18 The only difference from Example 5 is that step (3) is as follows: (3) The mixture prepared in step (2) consists of lithium carbonate (1.04 times the amount of lithium in dihydrate), ferric dihydrogen phosphate (1.2% by mass of ferric dihydrate), dipolyglycerol (3.1% by mass of ferric dihydrate), and β-cyclodextrin (molecular weight 1135) (8.3% by mass of ferric dihydrate) with pure water. The mixture is stirred until homogeneous to obtain a slurry with a solid content of 48%. This slurry is then milled to obtain a grinding slurry with a solid particle size (D50) of 0.34 μm. The material was then spray-dried (inlet air temperature 220℃, outlet air temperature 90℃) and pulverized to obtain a dried material with a D50 of 0.78μm and a D100 of 8.4μm. Next, under a nitrogen protective atmosphere, the temperature was increased to 820℃ at 8℃ / min and held for 4 hours. Then, the temperature was decreased to 796℃ at 5℃ / min and held for 8.4 hours. Finally, the temperature was decreased to below 100℃ at 10℃ / min and removed from the furnace. The material was then pulverized a second time to a D50 particle size of 1.38μm to obtain the lithium iron phosphate cathode material.

[0194] Example 19 The only difference from Example 5 is that step (3) is as follows: (3) The iron phosphate dihydrate prepared in step (2), lithium carbonate (1.04 times the amount of lithium in iron phosphate dihydrate), ferric dihydrogen phosphate (1.2% by mass of iron phosphate dihydrate), dipolyglycerol (3.1% by mass of iron phosphate dihydrate), and β-cyclodextrin (molecular weight 1135) (8.3% by mass of iron phosphate dihydrate) are mixed with pure water to obtain a mixed slurry with a solid content of 48%. The slurry with a solid particle size D50 of 0.36 μm is obtained by sand milling. The material was then spray-dried (inlet air temperature 220℃, outlet air temperature 90℃) and pulverized to obtain a dried material with a D50 of 0.79μm and a D100 of 8.3μm. Next, under a nitrogen protective atmosphere, the temperature was increased to 812℃ at 8℃ / min and held for 2 hours. Then, the temperature was decreased to 780℃ at 5℃ / min and held for 6 hours. Finally, the temperature was decreased to below 100℃ at 10℃ / min and removed from the furnace. The material was then pulverized a second time to a D50 particle size of 1.36μm to obtain the lithium iron phosphate cathode material.

[0195] Example 20 The only difference from Example 5 is that step (3) is as follows: (3) The iron phosphate dihydrate prepared in step (2), lithium carbonate (1.04 times the amount of lithium in iron phosphate dihydrate), ferric dihydrogen phosphate (1.2% by mass of iron phosphate dihydrate), dipolyglycerol (3.1% by mass of iron phosphate dihydrate), and β-cyclodextrin (molecular weight 1135) (8.3% by mass of iron phosphate dihydrate) are mixed with pure water to obtain a mixed slurry with a solid content of 48%. The slurry with a solid particle size D50 of 0.34 μm is obtained by sand milling. The material was then spray-dried (inlet air temperature 220℃, outlet air temperature 90℃) and pulverized to obtain a dried material with a D50 of 0.78μm and a D100 of 8.9μm. Next, under a nitrogen protective atmosphere, the temperature was increased to 812℃ at 8℃ / min and held for 2 hours. Then, the temperature was decreased to 805℃ at 5℃ / min and held for 14 hours. Finally, the temperature was decreased to below 100℃ at 10℃ / min and removed from the furnace. The material was then pulverized a second time to a D50 particle size of 1.41μm to obtain the lithium iron phosphate cathode material.

[0196] Comparative Example 1 (1) The titanium dioxide byproduct was heated and dissolved, and precipitated by adding a 5% sodium hydroxide solution. The precipitate was removed by pressure filtration to obtain a ferrous solution with an iron ion concentration of 1.5 mol / L (i.e., the iron source solution) and a pH of 3.0. Industrial monoammonium phosphate was dissolved, filtered, and then ammonia was added to adjust the pH to neutral to obtain a phosphorus source solution, in which PO4 ions were added. 3- The concentration is 2 mol / L; (2) Based on 1 mol of iron, 1 mol of iron source solution was first added to the reactor as the base material. Then, a mixture of 0.007 mol of stannous sulfate, 0.016 mol of manganese oxalate and ammonium metavanadate in a mass ratio of 2:1 and 0.009 mol of magnesium oxide were added to 2.1 mol of phosphorus source solution. Then, phosphorus source solution and 4.3 mol of hydrogen peroxide solution with a mass fraction of 27% were slowly added dropwise at a temperature of 60°C for 120 min. After the addition was completed, phosphoric acid was added to adjust the pH to 1.4. Then, the temperature was raised to 95°C and the reaction was stirred for 2 h until the pH reached 1.9. After pressure filtration, rinsing and flash evaporation, ferric phosphate dihydrate (i.e., ferric phosphate material) was obtained.

[0197] (3) The mixture prepared in step (2) consists of lithium carbonate (1.04 times the amount of lithium in dihydrate), ferric dihydrogen phosphate (1.2% by mass of ferric dihydrate), dipolyglycerol (3.1% by mass of ferric dihydrate), and β-cyclodextrin (8.3% by mass of ferric dihydrate) with pure water. The mixture is stirred until homogeneous to obtain a slurry with a solid content of 48%. This slurry is then milled to obtain a grinding slurry with a solid particle size (D50) of 0.33 μm. The material was then spray-dried (inlet air temperature 220℃, outlet air temperature 90℃) and pulverized to obtain a dried material with a D50 of 0.80μm and a D100 of 8.7μm. Then, under a nitrogen protective atmosphere, the temperature was increased to 812℃ at 8℃ / min and held for 2 hours. Then, the temperature was decreased to 796℃ at 5℃ / min and held for 8.4 hours. Finally, the temperature was decreased to below 100℃ at 10℃ / min and removed from the furnace. The material was then pulverized a second time to a D50 particle size of 1.38μm to obtain the lithium iron phosphate cathode material.

[0198] Comparative Example 2 (1) The titanium dioxide byproduct was heated and dissolved, and precipitated by adding a 5% sodium hydroxide solution. The precipitate was removed by pressure filtration to obtain a ferrous solution with an iron ion concentration of 1.5 mol / L (i.e., the iron source solution) and a pH of 3.0. Industrial monoammonium phosphate was dissolved, filtered, and then ammonia was added to adjust the pH to neutral to obtain a phosphorus source solution, in which PO4 ions were added. 3- The concentration is 2 mol / L; (2) Based on a total amount of 1 mol of iron, firstly, 0.15 mol of iron source solution (i.e., a ferrous solution containing 0.15 mol of ferrous ions, hereinafter the same) is added to the reactor as the base material. Then, 0.3 mol of phosphorus source solution (i.e., a phosphorus source solution containing 0.3 mol of phosphate ions, hereinafter the same) and 0.007 mol of stannous sulfate are added to obtain a second solution. The second solution is then combined with a third solution (containing 0.86 mol of hydrogen peroxide) which accounts for 20% of the total hydrogen peroxide solution (mass fraction of 27%). l) Simultaneously, the above-mentioned substrate is slowly added dropwise at 25°C for 45 min to carry out the synthesis reaction. After the addition is complete, the first mixture is stirred at 45°C for 30 min to obtain the first reaction slurry. Then, 0.5 mol of iron source solution is added to the first reaction slurry at 50°C for 15 min to obtain the second mixture. Then, 0.9 mol of phosphorus source solution and 0.016 mol of manganese oxalate and ammonium metavanadate in a mass ratio of 2:1 are mixed to obtain the fifth solution. The fifth solution is then mixed with 60% of the total hydrogen peroxide mass... The sixth solution (containing 2.58 mol of hydrogen peroxide) was slowly added dropwise to the second mixture at 55°C for 20 min to carry out the synthesis reaction. After the addition was complete, the third mixture was obtained. The third mixture was heated to 65°C and stirred continuously for 30 min to obtain the second reaction slurry. Finally, the remaining iron source solution (the seventh solution) and 0.009 mol of magnesium oxide were added to the second reaction slurry at 65°C over 15 min to obtain the fourth mixture. The fourth mixture was then slowly added dropwise... The eighth solution (containing 0.9 mol of phosphate ions) and the ninth solution (containing 0.86 mol of hydrogen peroxide) were added at a temperature of 60°C for 35 min. After the addition was complete, a third reaction slurry was obtained. Phosphoric acid was added to the third reaction slurry to adjust the pH to 1.4. The temperature was then raised to 95°C and the reaction was stirred for 2 h until the pH reached 1.9. The mixture was then filtered, rinsed, and flash-evaporated to obtain ferric phosphate dihydrate. The ferric phosphate dihydrate was heated to 550°C at a rate of 3°C / min under a nitrogen atmosphere and held for 5 h. After the holding period, the temperature was lowered to below 100°C at a rate of 5°C / min to obtain anhydrous ferric phosphate (i.e., ferric phosphate material).

[0199] (3) The anhydrous iron phosphate prepared in step (2), lithium carbonate (1.04 times the amount of anhydrous iron phosphate), ferric dihydrogen phosphate (1.2% by mass of anhydrous iron phosphate), diglycerol (3.1% by mass of anhydrous iron phosphate), and β-cyclodextrin (molecular weight 1135) (8.3% by mass of anhydrous iron phosphate) prepared in step (2) are mixed evenly with pure water to obtain a mixed slurry with a solid content of 48%. The slurry is then adjusted by sand milling to obtain a grinding slurry with a solid particle size D50 of 0.36 μm. The material was then spray-dried (inlet air temperature 220℃, outlet air temperature 90℃) and pulverized to obtain a dried material with a D50 of 0.79μm and a D100 of 8.8μm. Then, under a nitrogen protective atmosphere, the temperature was increased to 812℃ at 8℃ / min and held for 2 hours. Then, the temperature was decreased to 796℃ at 5℃ / min and held for 8.4 hours. Finally, the temperature was decreased to below 100℃ at 10℃ / min and removed from the furnace. The material was then pulverized a second time to a D50 particle size of 1.38μm to obtain the lithium iron phosphate cathode material.

[0200] Comparative Example 3 (1) The titanium dioxide byproduct was heated and dissolved, and precipitated by adding a 5% sodium hydroxide solution. The precipitate was removed by pressure filtration to obtain a ferrous solution with an iron ion concentration of 1.5 mol / L (i.e., the iron source solution) and a pH of 3.0. Industrial monoammonium phosphate was dissolved, filtered, and then ammonia was added to adjust the pH to neutral to obtain a phosphorus source solution, in which PO4 ions were added. 3- The concentration is 2 mol / L; (2) Based on a total amount of 1 mol of iron, firstly, add 0.15 mol of iron source solution (i.e., a ferrous solution containing 0.15 mol of ferrous ions, the same below) to the reactor as the base material. Then, add 0.3 mol of phosphorus source solution (i.e., a phosphorus source solution containing 0.3 mol of phosphate ions, the same below) and 20% of the total hydrogen peroxide solution (mass fraction of 27%) of a hydrogen peroxide solution (the amount of hydrogen peroxide is 0.86). Simultaneously, 0.5 mol of iron source solution was slowly added dropwise at 25℃ for 45 min to carry out the synthesis reaction. After the addition was completed, the mixture was stirred at 45℃ for 30 min to obtain the first reaction slurry. Then, 0.5 mol of iron source solution was added to the first reaction slurry at 50℃ over a period of 15 min. Next, 0.9 mol of phosphorus source solution and 2.58 mol of hydrogen peroxide solution (60% of the total hydrogen peroxide mass) were simultaneously and slowly added dropwise at 55℃ for 20 min to carry out the synthesis reaction. After the addition was completed, the temperature was raised to 65℃ and the mixture was stirred continuously for 30 min to obtain the second reaction slurry. Finally, the mixture was added in one go... The remaining iron source solution was added to the second reaction slurry at 65℃ over a period of 15 minutes. Then, the remaining phosphorus source solution (0.9 mol of phosphate ions) and the remaining hydrogen peroxide solution (0.86 mol of hydrogen peroxide) were slowly added dropwise at 60℃ over a period of 35 minutes. After the addition was complete, the third reaction slurry was obtained. Phosphoric acid was added to the third reaction slurry to adjust the pH to 1.4. The temperature was then raised to 95℃ and the reaction was stirred for 2 hours until the pH reached 2.0. The mixture was then filtered, rinsed, and flash-evaporated to obtain pure iron phosphate dihydrate (i.e., iron phosphate material).

[0201] (3) Add the pure iron phosphate dihydrate prepared in step (2), lithium carbonate (1.04 times the amount of lithium in iron phosphate dihydrate), stannous sulfate (0.007 times the amount of ferric phosphate dihydrate), manganese oxalate and ammonium metavanadate (2:1 mass ratio, 0.016 times the amount of ferric phosphate dihydrate), magnesium oxide (0.009 times the amount of ferric phosphate dihydrate), ferric dihydrogen phosphate (1.2% by mass of ferric phosphate dihydrate), dipolyglycerol (3.1% by mass of ferric phosphate dihydrate), and β-cyclodextrin (molecular weight 1135) (8.3% by mass of ferric phosphate dihydrate) to pure water and stir until homogeneous. A mixed slurry with a solid content of 48% was obtained. The slurry was then milled to obtain a solid particle size (D50) of 0.34 μm. Subsequently, it was spray-dried (inlet air temperature 220℃, outlet air temperature 90℃) and pulverized to obtain a dried material with a D50 of 0.77 μm and a D100 of 8.5 μm. Then, under a nitrogen protective atmosphere, the temperature was increased to 812℃ at 8℃ / min and held for 2 hours. Then, the temperature was decreased to 796℃ at 5℃ / min and held for 8.4 hours. Finally, the temperature was decreased to below 100℃ at 10℃ / min and removed from the furnace. The material was then pulverized a second time to a D50 particle size of 1.36 μm to obtain the lithium iron phosphate cathode material.

[0202] Comparative Example 4 The difference from Example 5 is that step (3) is as follows: (3) The iron phosphate dihydrate prepared in step (2), lithium carbonate (1.04 times the amount of iron phosphate dihydrate), ferric dihydrogen phosphate (1.2% by mass of iron phosphate dihydrate), and β-cyclodextrin (molecular weight 1135) (11.4% by mass of iron phosphate dihydrate) were mixed with pure water to obtain a mixed slurry with a solid content of 48%. The slurry was then ground to obtain a solid particle size D50 of 0.33 μm by sand milling, and then spray dried. The inlet air temperature is 220℃ and the outlet air temperature is 90℃. The material is then pulverized to obtain a dry material with a D50 of 0.79μm and a D100 of 8.5μm. The material is then heated to 812℃ at 8℃ / min under a nitrogen protective atmosphere and held for 2 hours. Then, it is cooled to 796℃ at 5℃ / min and held for 8.4 hours. Finally, it is cooled to below 100℃ at 10℃ / min and removed from the furnace. The material is then pulverized a second time to a D50 particle size of 1.35μm to obtain the lithium iron phosphate cathode material.

[0203] Comparative Example 5 Compared with Example 5, the difference is that step (3) is as follows: (3) The mixture prepared in step (2) consists of lithium carbonate (1.04 times the amount of lithium in dihydrate), ferric dihydrogen phosphate (1.2% by mass of ferric dihydrate), and glycerol (11.4% by mass of ferric dihydrate) mixed with pure water to obtain a slurry with a solid content of 48%. This slurry is then milled to obtain a grinding slurry with a solid particle size (D50) of 0.35 μm. Finally, it is spray-dried (inlet air temperature is...). The material was pulverized at 220℃ (outlet air temperature was 90℃) to obtain a dry material with a D50 of 0.80μm and a D100 of 8.6μm. Then, under a nitrogen protective atmosphere, the temperature was increased to 812℃ at 8℃ / min and held for 2 hours. Then, the temperature was decreased to 796℃ at 5℃ / min and held for 8.4 hours. Finally, the temperature was decreased to below 100℃ at 10℃ / min and removed from the furnace. The material was then pulverized a second time to a D50 particle size of 1.37μm to obtain the lithium iron phosphate cathode material.

[0204] Comparative Example 6 Compared with Example 5, the difference is that step (3) is as follows: (3) The mixture prepared in step (2) consists of lithium carbonate (1.04 times the amount of lithium in dihydrate), ferric dihydrogen phosphate (1.2% by mass of ferric dihydrate), sucrose (3.1% by mass of ferric dihydrate), and β-cyclodextrin (molecular weight 1135) (8.3% by mass of ferric dihydrate) with pure water. The mixture is stirred until homogeneous to obtain a slurry with a solid content of 48%. This slurry is then milled to obtain a grinding slurry with a solid particle size (D50) of 0.34 μm. Subsequently... The material was spray-dried (inlet air temperature 220℃, outlet air temperature 90℃) and pulverized to obtain a dried material with a D50 of 0.78μm and a D100 of 8.7μm. Then, under a nitrogen protective atmosphere, the temperature was increased to 812℃ at 8℃ / min and held for 2h. Then, the temperature was decreased to 796℃ at 5℃ / min and held for 8.4h. Finally, the temperature was decreased to below 100℃ at 10℃ / min and removed from the furnace. The material was then pulverized a second time to a D50 particle size of 1.35μm to obtain the lithium iron phosphate cathode material.

[0205] II. Testing Methods (1) Performance testing of iron phosphate materials and lithium iron phosphate cathode materials 1. SEM test: The morphology of lithium iron phosphate cathode material was characterized by field emission scanning electron microscopy.

[0206] 2. Elemental distribution: The cross-section of the lithium iron phosphate cathode material was characterized using energy-dispersive X-ray spectroscopy.

[0207] 3. Elemental content: The elemental content in iron phosphate and lithium iron phosphate materials was tested using inductively coupled plasma atomic emission spectrometry. The iron-to-phosphorus ratio of the iron phosphate material was determined by chemical titration.

[0208] 4. Particle size distribution of primary particles in iron phosphate material: obtained by SEM testing and analysis using Nano Measurer 1.2 software.

[0209] 5. Average particle size of primary particles of iron phosphate material: obtained by SEM testing and analysis using Nano Measurer 1.2 software.

[0210] 6. Average primary grain size of lithium iron phosphate cathode material: obtained by SEM testing and analysis using Nano Measurer 1.2 software.

[0211] 7. Particle size distribution of secondary particles in lithium iron phosphate cathode material: obtained by SEM testing and analysis using NanoMeasurer 1.2 software.

[0212] 8. D50 particle size of lithium iron phosphate cathode material: measured by Malvern laser particle size analyzer.

[0213] 9. Compacted density: Tested using a compaction density meter with a test pressure of 3T and a compaction time of 30S.

[0214] 10. Powder resistivity: Tested using the four-probe method at a pressure of 8 MPa.

[0215] 11. BET specific surface area: determined by gas adsorption BET method.

[0216] 12. Free Li: Measured by automatic potentiometric titration.

[0217] (2) Performance testing of secondary batteries The lithium iron phosphate cathode materials prepared in each embodiment and comparative example were mixed with ultrafine carbon powder (Super P, SP) and polyvinylidene fluoride in a mass ratio of 90:5:5, respectively. Then, N-methylpyrrolidone (NMP) was added to form a slurry, which was then coated onto aluminum foil, dried, and pressed into sheets. The lithium sheet was used as the negative electrode, polyethylene as the separator, lithium hexafluorophosphate (LiPF6) as the lithium salt, and ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) in a volume ratio of 1:1:1 as organic solvents to dissolve the lithium salt in the organic solvents to prepare an electrolyte with a concentration of 1M. A button cell was then prepared. The first charge specific capacity and the first discharge specific capacity were measured at a 1C rate at room temperature and -20°C, with a voltage range of 2.50~3.65 V.

[0218] III. Analysis of Test Results for Each Embodiment and Comparative Example Table 1. Particle size distribution of iron phosphate materials

[0219] Table 2 Particle size distribution of lithium iron phosphate cathode material

[0220] Table 3 Chemical formulas and iron-phosphorus ratios of iron phosphate materials and lithium iron phosphate cathode materials

[0221] Table 4. Physicochemical Properties of Lithium Iron Phosphate Cathode Materials

[0222] Table 5 Electrochemical performance test of lithium iron phosphate secondary batteries

[0223] Please refer to Table 2. In the lithium iron phosphate cathode materials prepared in each embodiment, the particle size of the secondary particles is mainly distributed in the range of 0.6 μm and above, and the proportion of primary particles in this range is relatively small. Through the gradation effect between different particle sizes, it is beneficial to improve the compaction density.

[0224] Please refer to Table 3. The methods of each embodiment can produce iron phosphate materials (Fe) conforming to the following chemical formula. 1-a-b- m A a B b M m PO4, and 0.0019≤a≤0.007, 0.0088≤b≤0.017, 0.0049≤m≤0.018) and lithium iron phosphate cathode material (LiFe 1-a-b-m A a B b M mThe iron-phosphorus ratio of lithium iron phosphate (LiFePO4 / C) is 0.0019 ≤ a ≤ 0.007, 0.0088 ≤ b ≤ 0.017, and 0.0049 ≤ m ≤ 0.018, and the iron-phosphorus ratio of the LiFePO4 material is controlled between 0.950 and 0.973. It is understandable that LiFePO4 cathode materials are prepared using LiFePO4 as a precursor, so the iron-phosphorus ratio in its material structure is mainly determined by LiFePO4. The iron-phosphorus ratio in the chemical formula of LiFePO4 cathode materials should be consistent with that of LiFePO4. However, in actual tests of the iron-phosphorus ratio of the products, since the iron-phosphorus ratio of LiFePO4 is obtained by chemical titration, while that of LiFePO4 cathode materials is obtained by ICP inductively coupled plasma atomic emission spectrometry, the measured value of the iron-phosphorus ratio of LiFePO4 cathode materials will be slightly higher than that of LiFePO4. Therefore, there is a certain difference in the elemental ratio shown in their chemical formulas.

[0225] Please refer to Table 4. As can be seen from Table 4, the lithium iron phosphate cathode material prepared in the embodiments of this application has a higher compaction density, indicating that the fused large particles designed in this application have achieved a better gradation effect; the free lithium content is also significantly higher, indicating that the lithium iron phosphate cathode material prepared in this application has better charge and discharge performance, and higher initial charge and discharge efficiency and reversible capacity.

[0226] Please refer to Table 5. As can be seen from Table 5, compared with the lithium iron phosphate prepared in the comparative example, the lithium iron phosphate cathode material prepared in this application has a slightly higher 1C charging specific capacity and an average 1C discharging specific capacity that is nearly 10 mAh / g higher. The low-temperature discharge performance at -20℃ is more than 20 mAh / g higher. It can be seen that the lithium iron phosphate prepared in this application has a higher low-temperature discharge efficiency and obvious advantages in charge and discharge efficiency at both room temperature and low temperature. This indicates that the layered doping and layered coating designed in this scheme have a good promoting effect on the performance of lithium iron phosphate.

[0227] Furthermore, comparing Example 5 with Comparative Examples 1 and 3, compared with Comparative Example 1, which incorporates all doping elements in one step without partitioned doping, and Comparative Example 3, which does not perform element doping, Example 5 exhibits significantly higher room temperature 1C charge / discharge specific capacity, room temperature 1C first discharge efficiency, -20℃ 1C charge / discharge specific capacity, and -20℃ 1C first discharge efficiency. This indicates that partitioned doping in iron phosphate dihydrate helps the doping elements in different doping regions to synergize and exert their respective properties, jointly improving the discharge performance of lithium iron phosphate cathode materials prepared using it as a precursor at room temperature or low temperature. Comparing Example 5 with Comparative Example 2, the various electrochemical performances of Comparative Example 2 showed a certain decline, indicating that compared with preparing lithium iron phosphate cathode materials using anhydrous iron phosphate as raw material, preparing lithium iron phosphate cathode materials using dihydrate iron phosphate is more conducive to improving its product performance. Comparing Example 5 with Comparative Examples 4 to 6 illustrates that layered coating of lithium iron phosphate is achieved using organic carbon sources of different molecular weights. The carbon source with a smaller molecular weight effectively coats and disperses the lithium iron phosphate particles, while the carbon source with a larger molecular weight promotes the fusion of some lithium iron phosphate particles and the formation of aggregates. The carbon source with a larger molecular weight is decomposed and then used for secondary coating, which improves the integrity of the coating layer. This helps to maintain excellent discharge performance while increasing the compaction density, thereby preparing a lithium iron phosphate cathode material with high compaction density and high discharge performance under low temperature conditions.

[0228] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. An iron phosphate material, characterized in that, The iron phosphate material comprises: iron phosphate dihydrate particles, the iron phosphate dihydrate particles comprising a first doping element, a second doping element and a third doping element; wherein, in the direction from the center of the iron phosphate dihydrate particles to the outside of the iron phosphate dihydrate particles, the iron phosphate dihydrate particles comprise a first doping region, a second doping region and a third doping region in sequence, the first doping element is located in the first doping region, the second doping element is located in the second doping region, and the third doping element is located in the third doping region, the first doping element is selected from at least one of cerium, lanthanum and tin, the second doping element is selected from at least one of manganese and vanadium, and the third doping element is selected from at least one of titanium, magnesium, zirconium and yttrium.

2. The iron phosphate material of claim 1, wherein, The chemical formula of the iron phosphate material is: Fe 1-a-b- m A a B b M m PO4, and 0.0019≤a≤0.007, 0.0088≤b≤0.017, 0.0049≤m≤0.018, A is selected from at least one of cerium, lanthanum, tin, B is selected from at least one of manganese, vanadium, M is selected from at least one of titanium, magnesium, zirconium, yttrium; and / or, The average particle size of the primary particles of the iron phosphate material is 160 nm to 240 nm; and / or; In the primary particles of the iron phosphate material, the number fraction of primary particles with a particle size of 0.2 μm or less is 55.06% to 64.8%, the number fraction of primary particles with a particle size of greater than 0.2 μm and less than or equal to 0.4 μm is 32.43% to 42.0%, the number fraction of primary particles with a particle size of greater than 0.4 μm and less than or equal to 0.6 μm is 1.3% to 6.4%, and the number fraction of primary particles with a particle size of greater than 0.6 μm is 0.31% to 1.4%.

3. A lithium iron phosphate cathode material, characterized in that, The iron phosphate lithium material comprises: iron phosphate lithium particles and a carbon coating layer, the carbon coating layer being coated on the surface of the iron phosphate lithium particles; wherein, the iron phosphate lithium particles comprise a first doping element, a second doping element and a third doping element; in the direction from the center of the iron phosphate lithium particles to the coating layer, the iron phosphate lithium particles comprise a fourth doping region, a fifth doping region and a sixth doping region in sequence, the first doping element is located in the fourth doping region, the second doping element is located in the fifth doping region, and the third doping element is located in the sixth doping region, the first doping element is selected from at least one of cerium, lanthanum and tin, the second doping element is selected from at least one of manganese and vanadium, and the third doping element is selected from at least one of titanium, magnesium, zirconium and yttrium.

4. The lithium iron phosphate cathode material of claim 3, wherein, The chemical formula of the lithium iron phosphate positive electrode material is: LiFe 1-a-b-m A a B b M m PO4 / C, and 0.0019≤a≤0.007, 0.0088≤b≤0.017, 0.0049≤m≤0.018, A is selected from at least one of cerium, lanthanum, and tin, B is selected from at least one of manganese and vanadium, and M is selected from at least one of titanium, magnesium, zirconium, and yttrium; and / or, The compaction density of the lithium iron phosphate positive electrode material is 2.55 g / cm 3 2.65 g / cm 3 .

5. The lithium iron phosphate cathode material of claim 3, wherein the lithium iron phosphate cathode material has a particle size distribution such that at least 90% of the particles have a size of less than 20 microns. The average particle size of the primary particles of the iron phosphate lithium positive electrode material is 330 nm to 360 nm; and / or, The D50 particle size of the iron phosphate lithium positive electrode material is 1.35 μm to 1.65 μm; and / or, The D50 particle size of the iron phosphate lithium positive electrode material is 1.35 μm to 1.65 μm; and / or, The number of particles with a particle size of 0.2 μm or less accounts for 48.2% to 63.6%, the number of particles with a particle size of greater than 0.2 μm and 0.4 μm or less accounts for 21.3% to 32.5%, the number of particles with a particle size of greater than 0.4 μm and 0.6 μm or less accounts for 7.3% to 17.4%, the number of particles with a particle size of greater than 0.6 μm and 0.8 μm or less accounts for 2.4% to 4.7%, the number of particles with a particle size of greater than 0.8 μm and 1 μm or less accounts for 0.48% to 1.56%, the number of particles with a particle size of greater than 1 μm and 2 μm or less accounts for 1.5% to 5.2%, and the number of particles with a particle size of greater than 2 μm and 5 μm or less accounts for 1.3% to 1.9%; and / or, The specific surface area of the lithium iron phosphate positive electrode material is 12 m 2 / g~15 m 2 / g; and / or, The powder resistivity of the lithium iron phosphate positive electrode material is 10 Ω cm 15 Ω cm; and / or, The mass fraction of the carbon coating layer in the lithium iron phosphate positive electrode material is 1.35% to 1.43%; and / or, The free lithium content in the lithium iron phosphate positive electrode material is 150 ppm to 220 ppm.

6. A method for preparing a lithium iron phosphate cathode material, characterized in that, The method comprises the following steps: Providing a lithium iron phosphate material; The lithium iron phosphate positive electrode material is obtained by mixing the lithium iron phosphate material, a lithium source, a first organic carbon source, a second organic carbon source and a first solvent, drying treatment and sintering treatment; wherein, The lithium iron phosphate material comprises iron phosphate dihydrate particles, and the iron phosphate dihydrate particles comprise a first doping element, a second doping element and a third doping element; in the direction from the center of the iron phosphate dihydrate particles to the outside of the iron phosphate dihydrate particles, the iron phosphate dihydrate particles sequentially comprise a first doping region, a second doping region and a third doping region, the first doping element is located in the first doping region, the second doping element is located in the second doping region, and the third doping element is located in the third doping region, the first doping element is selected from at least one of cerium, lanthanum and tin, the second doping element is selected from at least one of manganese and vanadium, and the third doping element is selected from at least one of titanium, magnesium, zirconium and yttrium; The molecular weight of the first organic carbon source is less than the molecular weight of the second organic carbon source.

7. The method of claim 6, wherein the lithium iron phosphate cathode material is prepared by the steps of: The preparation steps of the lithium iron phosphate material comprise: ​ The first reaction treatment is performed on a first ferrous source, a first phosphorus source, a first dopant, a first oxidant and a second solvent to obtain a first reaction slurry; The second reaction treatment is performed on the first reaction slurry, a second ferrous source, a second phosphorus source, a second dopant and a second oxidant to obtain a second reaction slurry; The third reaction treatment is performed on the second reaction slurry, a third ferrous source, a third phosphorus source, a third dopant and a third oxidant to obtain a third reaction slurry; The third reaction slurry is subjected to aging treatment and post-treatment to obtain the lithium iron phosphate material; wherein, The first dopant is at least one of an oxide, a hydroxide, a chloride, a nitrate, a sulfate, a carbonate and an oxalate of cerium, lanthanum and / or tin; The second dopant is at least one of an oxide, a hydroxide, a chloride, a nitrate, a sulfate, a carbonate, an oxalate and a salt of an oxyacid of manganese and / or vanadium. The third dopant is at least one of titanium, magnesium, zirconium and / or yttrium oxide, hydroxide, chloride, nitrate, sulfate, carbonate, oxalate.

8. The method for preparing the lithium iron phosphate cathode material according to claim 7, characterized in that, The first ferrous source, the second ferrous source and the third ferrous source are independently selected from at least one of ferrous sulfate, ferrous chloride, ferrous nitrate, ferrous acetate; and / or, The first phosphorus source, the second phosphorus source and the third phosphorus source are independently selected from at least one of phosphoric acid, ammonium phosphate, monoammonium phosphate, diammonium phosphate, sodium phosphate, monosodium phosphate, disodium phosphate, potassium phosphate, monopotassium phosphate, dipotassium phosphate; and / or, The first oxidizing agent, the second oxidizing agent and the third oxidizing agent are independently selected from at least one of hydrogen peroxide, sodium peroxide, potassium peroxide, oxygen; and / or, The molar ratio of the first ferrous source to the first phosphorus source, the first doping element in the first dopant is 1: (1.3~2.5): (0.01~0.07); and / or, The molar ratio of the first ferrous source to the first oxidizing agent is 1: (3.2~7.3); and / or, The molar ratio of the second ferrous source to the second phosphorus source, the second doping element in the second dopant is 1: (1.1~2.75): (0.01~0.04); and / or, The molar ratio of the second ferrous source to the second oxidizing agent is 1: (4.8~13.2); and / or, The molar ratio of the third ferrous source to the third phosphorus source, the third doping element in the third dopant is 1: (1.6~3.95): (0.01~0.1); and / or, The molar ratio of the third ferrous source to the third oxidizing agent is 1: (2~3.9); and / or, The molar ratio of the first ferrous source to the second ferrous source, the third ferrous source is (10~15): (40~70): (15~50); and / or, The molar ratio of the first phosphorus source to the second phosphorus source, the third phosphorus source is (20~30): (55~140): (55~140); and / or, The molar ratio of the first oxidizing agent to the second oxidizing agent, the third oxidizing agent is 1: (3~8): (0.5~3).

9. The method of claim 7, wherein the lithium iron phosphate cathode material is prepared by the steps of: The first ferrous source, the first phosphorus source, the first dopant, the first oxidizing agent and the second solvent are subjected to a first reaction process to obtain a first reaction slurry, including: providing a first solution with the first ferrous source, a second solution with the first phosphorus source and the first dopant, and a third solution with the first oxidizing agent; mixing the second solution and the third solution into the first solution at a first mixing temperature for a first mixing time to obtain a first mixture; subjecting the first mixture to a first reaction temperature for a first reaction time to obtain the first reaction slurry; wherein the first mixing temperature is 15~35℃, the first mixing time is 40~50min, the first reaction temperature is 35~55℃, and the first reaction time is 20~40min; ​ The step of subjecting the first reaction slurry, the second ferrous source, the second phosphorus source, the second dopant and the second oxidizing agent to a second reaction treatment to obtain a second reaction slurry comprises: providing a fourth solution containing the second ferrous source, a fifth solution containing the second phosphorus source and the second dopant, and a sixth solution containing the second oxidizing agent; mixing the fourth solution with the first reaction slurry at a second mixing temperature for a second mixing time to obtain a second mixture; mixing the fifth solution and the sixth solution into the second mixture at a third mixing temperature for a third mixing time to obtain a third mixture; and subjecting the third mixture to a second reaction treatment at a second reaction temperature for a second reaction time to obtain the second reaction slurry; wherein the second mixing temperature is 40-60°C, the second mixing time is 10-30 minutes, the third mixing temperature is 45-65°C, the third mixing time is 10-30 minutes, the second reaction temperature is 55-75°C, and the second reaction time is 20-40 minutes; The step of subjecting the second reaction slurry, the third ferrous source, the third phosphorus source, the third dopant and the third oxidizing agent to a third reaction treatment to obtain a third reaction slurry comprises: providing a seventh solution containing the third ferrous source, the third dopant, an eighth solution containing the third phosphorus source, and a ninth solution containing the third oxidizing agent; mixing the seventh solution, the third dopant and the second reaction slurry at a fourth mixing temperature for a fourth mixing time to obtain a fourth mixture; and mixing the eighth solution and the ninth solution into the fourth mixture at a fifth mixing temperature for a fifth mixing time to obtain the third reaction slurry; wherein the fourth mixing temperature is 55-75°C, the fourth mixing time is 10-20 minutes, the fifth mixing temperature is 50-75°C, and the fifth mixing time is 30-40 minutes. The step of subjecting the third reaction slurry to aging treatment and post-treatment to obtain a ferric phosphate material comprises: mixing the third reaction slurry with a pH adjuster to obtain a fifth mixture, wherein the pH of the fifth mixture is 1.1-1.4; subjecting the fifth mixture to a third reaction treatment at a third reaction temperature for a third reaction time to obtain a fourth reaction slurry, wherein the pH of the fourth reaction slurry is 1.7-1.9; and subjecting the fourth reaction slurry to post-treatment to obtain the ferric phosphate material; wherein the third reaction temperature is 90-100°C, and the third reaction time is 1-3 hours.

10. The method of claim 6, wherein the lithium iron phosphate cathode material is prepared by the steps of: The molar ratio of iron in the ferric phosphate material to lithium in the lithium source is 1:(1.03-1.06); and / or, ​ The difference between the molecular weight of the second organic carbon source and the molecular weight of the first organic carbon source is greater than or equal to 800; and / or, The molecular weight of the first organic carbon source is less than or equal to 200, and the molecular weight of the second organic carbon source is greater than or equal to 1000 and less than or equal to 12000; and / or, The first organic carbon source is at least one of glycerol or dimerized glycerol; and / or, The first organic carbon source is at least one of glycerol or dimerized glycerol; and / or, The mass of the first organic carbon source is 2.1% to 3.7% of the mass of the iron phosphate material; and / or, The second organic carbon source is at least one of β-cyclodextrin or polyethylene glycol; and / or, The mass of the second organic carbon source is 8.3% to 9.2% of the mass of the iron phosphate material; And / or, The step of mixing the iron phosphate material, the lithium source, the first organic carbon source, the second organic carbon source, and the first solvent includes: The mixing of the iron phosphate material, the lithium source, the first organic carbon source, the second organic carbon source, and the first solvent obtains a mixed slurry, and the solid content of the mixed slurry is 47.5% to 49.3%; After the mixed slurry is subjected to a grinding treatment, a ground slurry is obtained, and the D50 particle size of the solid particles in the ground slurry is 0.32 μm to 0.38 μm; and / or, The step of mixing the iron phosphate material, the lithium source, the first organic carbon source, the second organic carbon source, and the first solvent includes: The mixing of the iron phosphate material, the lithium source, the iron supplement, the first organic carbon source, the second organic carbon source, and the first solvent obtains a ground slurry; wherein the iron supplement is at least one of ferrous oxalate, ferric citrate, and ferrous phosphate dihydrogen, and the mass of the iron supplement is 0.8% to 1.2% of the mass of the iron phosphate material; and / or, The step of mixing the iron phosphate material, the lithium source, the first organic carbon source, the second organic carbon source, and the first solvent, and then subjecting to a drying treatment and a sintering treatment, to obtain the lithium iron phosphate positive electrode material, includes: The mixing of the iron phosphate material, the lithium source, the first organic carbon source, the second organic carbon source, and the first solvent obtains a ground slurry; The ground slurry is subjected to a drying treatment to obtain a dried material, and the D50 particle size of the dried material is 0.55 μm to 0.8 μm; The dried material is subjected to a first sintering temperature for a first holding time, and then subjected to a second sintering temperature for a second holding time, to obtain the lithium iron phosphate positive electrode material; wherein The first sintering temperature is 800°C to 820°C, the first holding time is 0.5 h to 4 h, the second sintering temperature is 780°C to 805°C, and the second holding time is 7 h to 12 h.

11. A positive electrode sheet characterized by comprising: The positive electrode sheet includes the lithium iron phosphate positive electrode material of any one of claims 3 to 5 or the lithium iron phosphate positive electrode material prepared by the method of any one of claims 6 to 10.

12. A secondary battery characterized by comprising: The secondary battery includes the positive electrode sheet of claim 11.

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