Iron phosphate and its preparation methods, lithium iron phosphate materials, lithium-ion batteries, and electrical devices.

Abstract

This application belongs to the field of iron phosphate preparation technology, specifically relating to iron phosphate and its preparation method, lithium iron phosphate materials, lithium-ion batteries, and electrical devices. The iron phosphate comprises iron phosphate particles, which include the compound shown in Formula 1: Fe x M y Formula 1 for PO4, where 0.9 ≤ x ≤ 1, 0 ≤ y ≤ 0.1, and M includes at least one of Ti, Zr, V, W, Nb, Mg, and Sr; the structural porosity coefficient Q of iron phosphate satisfies: 150 × 10⁻⁶. ‑6 m 3 / g≤Q≤450×10 ‑6 m 3 / g, the porosity N satisfies: 10%≤N≤45%; where, the structural porosity coefficient Q=Dv50×S; porosity N=Vh / (Vh+Vs). The iron phosphate of this application has the characteristics of large particle size, high specific surface area, and loose porous structure. The lithium iron phosphate material obtained from this precursor has excellent electrochemical performance.

Description

Technical Field

[0001] This application belongs to the field of iron phosphate preparation technology, specifically relating to iron phosphate and its preparation method, lithium iron phosphate materials, lithium-ion batteries, and electrical devices. Background Technology

[0002] In the mainstream preparation process of lithium iron phosphate (LFP), iron phosphate, as the core precursor, directly affects the subsequent composite sintering effect with lithium and carbon sources due to its morphology, particle uniformity, and reactivity. It is a key raw material determining the electrochemical performance and batch stability of the finished LFP product. However, currently available iron phosphate is mostly in amorphous blocky or fine-particle agglomerate structure, with poor morphological order and insufficient particle uniformity. This results in poor compatibility with lithium and carbon sources, easily causing uneven subsequent synthesis reactions and reducing the performance of the finished material. Therefore, iron phosphate requires further improvement. Summary of the Invention

[0003] This invention aims to at least partially solve one of the technical problems in related technologies. To this end, this invention proposes a type of lithium iron phosphate with large particle size, high specific surface area, and loose porous structure. Lithium iron phosphate materials obtained from this precursor exhibit excellent electrochemical performance.

[0004] A first aspect of this application provides an iron phosphate compound comprising iron phosphate particles, said iron phosphate particles comprising a compound of Formula 1: Fe x M y PO4 Formula 1 Wherein, 0.9≤x≤1, 0≤y≤0.1, and M includes at least one of Ti, Zr, V, W, Nb, Mg, and Sr; The structural porosity coefficient Q of the iron phosphate satisfies: 150 × 10 -6 m 3 / g≤Q≤450 ×10 -6 m 3 / g; The porosity N of the iron phosphate satisfies: 10% ≤ N ≤ 45%; The structural porosity coefficient Q = Dv50 × S, where Dv50 is the median particle size of the iron phosphate in µm, and S is the specific surface area of ​​the iron phosphate in m². 2 / g; Porosity N = Vh / (Vh + Vs), where Vh is the pore volume of the iron phosphate and Vs is the skeletal volume of the iron phosphate.

[0005] When the iron phosphate in this application simultaneously meets the aforementioned ranges for structural porosity coefficient Q and porosity N, it possesses both a large macroscopic particle size and a loose, porous internal structure. The resulting lithium iron phosphate material exhibits excellent rate performance and cycle stability. The larger macroscopic particle size indicates that iron phosphate has a large specific surface area, which facilitates the formation of a more uniform contact interface when iron phosphate is mixed with lithium and carbon sources during lithium iron phosphate material preparation, reducing agglomeration problems caused by particle size differences. On the other hand, the loose, porous internal structure significantly increases the reaction contact area through well-developed pore channels, effectively improving the reaction inhomogeneity problems caused by traditional amorphous blocky or fine-particle agglomeration structures. This significantly enhances the compatibility of iron phosphate with lithium and carbon sources, resulting in a more complete and uniform lithiation reaction. Sufficient pore space allows for the construction of smooth and efficient lithium-ion transport pathways, effectively reducing electrode polarization and ultimately significantly improving the rate discharge capability and long-term cycle stability of lithium iron phosphate materials. Furthermore, introducing elements such as Ti, Zr, V, W, Nb, Mg, and Sr during the iron phosphate synthesis stage, compared to adding them during the lithium iron phosphate cathode stage, can better improve the electronic conductivity and lithium-ion diffusion performance of LiFePO4, thereby further enhancing the rate performance of lithium iron phosphate materials. In summary, this application improves the overall performance of lithium iron phosphate materials by limiting the structural porosity coefficient Q and porosity N within a specific range and synergistically combining them with element M doping.

[0006] According to an embodiment of this application, the iron phosphate satisfies: 200 × 10 -6 m 3 / g≤Q≤350 ×10 -6 m 3 / g.

[0007] According to an embodiment of this application, the Dv50 of the iron phosphate satisfies: 10µm≤Dv50≤40µm, preferably 15µm≤Dv50≤30µm.

[0008] According to an embodiment of this application, the specific surface area S of the iron phosphate satisfies: 7m² 2 / g≤S≤25 m 2 / g, preferably 9m 2 / g ≤S≤18 m 2 / g.

[0009] According to embodiments of this application, the iron phosphate satisfies at least one of the following conditions: 0.75≤K90≤1.75; The pore volume ratio Z of the iron phosphate satisfies 50% < Z ≤ 85%; 10%≤ΔDv50≤25%; Wherein, K90 = (R90 - R10) / R50, R10 is the pore diameter corresponding to the cumulative pore volume of the iron phosphate reaching 10% of the total pore volume, R50 is the pore diameter corresponding to the cumulative pore volume of the iron phosphate reaching 50% of the total pore volume, and R90 is the pore diameter corresponding to the cumulative pore volume of the iron phosphate reaching 90% of the total pore volume. Z = Volume of open aperture / (Volume of open aperture + Volume of closed aperture) × 100%; The iron phosphate was subjected to fracturing treatment under a pressure of 3.5T. The particle size change rate ΔDv50 = (Dv50 before fracturing - Dv50 after fracturing) / (Dv50 before fracturing) × 100%.

[0010] According to embodiments of this application, the iron phosphate satisfies at least one of the following conditions: 0.05cm 3 / g≤Vh≤0.15cm 3 / g; 0.2cm 3 / g≤Vs≤0.3cm 3 / g; 20nm≤R10≤40nm; 50nm≤R50≤80nm; 90nm≤R90≤150nm.

[0011] A second aspect of this application provides a method for preparing the ferric phosphate described in the first aspect, comprising: Provide a first solution containing ferrous dihydrogen phosphate; The first solution and the oxidant are mixed and oxidized at a first temperature T1 for a first time t1 to obtain the first slurry of ferric phosphate dihydrate. The first solution, the oxidant, and the optional M source are added to the first slurry of ferric phosphate dihydrate in a parallel flow, and mixed at a second temperature T2 for a second time t2 to obtain the second slurry of ferric phosphate dihydrate. The second slurry of ferric phosphate dihydrate was sequentially subjected to pressure filtration, washing, drying, and calcination to obtain ferric phosphate. Wherein, the second temperature T2 < the first temperature T1, and the second time t2 > the first time t1.

[0012] The preparation method of this application adopts the iron method process route, designs a two-stage reaction mechanism, and synthesizes large-particle porous lithium iron phosphate materials by precisely adjusting key process parameters. Moreover, this method does not require the use of commonly used organic dispersants, pore-forming templates and other non-phosphorus and iron system raw materials, the raw material control is simple, the impurity level of the finished product is low, the raw materials are easy to obtain, the process route is simple and clear, and it can be quickly introduced and applied on the basis of existing mature processes.

[0013] According to embodiments of this application, the above method satisfies at least one of the following conditions: 60≤T1<90℃; 0.5h≤t1≤3h; 40≤T2<70℃; 2h≤t2≤10h.

[0014] According to an embodiment of this application, providing a first solution containing ferrous dihydrogen phosphate includes: Iron and phosphoric acid with a mass concentration of 10% to 50% are mixed and reacted at a temperature of 25℃ ≤ T < 75℃ for 1 to 10 hours to obtain the first solution containing ferrous dihydrogen phosphate.

[0015] According to embodiments of this application, the above method satisfies at least one of the following conditions: The oxidant includes hydrogen peroxide; The M source includes at least one of the following: an oxide of M, a nitrate containing M, a sulfate containing M, and a chloride containing M; The molar ratio of Fe in the iron, P in the phosphoric acid, and the oxidant is 1:2.3~3.0:0.5-0.75.

[0016] According to embodiments of this application, the above method satisfies at least one of the following conditions: The calcination temperature is 600℃~750℃, preferably 625℃~675℃; The calcination time is 2h to 12h, preferably 4h to 8h.

[0017] A third aspect of this application provides a lithium iron phosphate material, wherein the raw materials for preparing the lithium iron phosphate material include the iron phosphate described in the first aspect or the iron phosphate prepared by the method described in the second aspect. This lithium iron phosphate material exhibits excellent electrochemical performance, excellent high-rate charge / discharge capability, and high particle uniformity. Its application in lithium-ion batteries can effectively improve the rate performance and cycle performance of lithium-ion batteries.

[0018] A fourth aspect of this application provides a lithium-ion battery comprising the lithium iron phosphate material described in the third aspect. This lithium-ion battery includes all the features and advantages of the aforementioned iron phosphate or lithium iron phosphate material, which will not be elaborated upon here.

[0019] A fifth aspect of this application provides an electrical device comprising the aforementioned lithium-ion battery. This electrical device incorporates all the features and advantages of the aforementioned iron phosphate or lithium iron phosphate materials, which will not be elaborated upon here. Attached Figure Description

[0020] Figure 1This is a frontal SEM image of the iron phosphate from Example 1 of this application.

[0021] Figure 2 This is a cross-sectional SEM image of the iron phosphate in Example 1 of this application.

[0022] Figure 3 This is a frontal SEM image of iron phosphate from Comparative Example 1 of this application.

[0023] Figure 4 This is a cross-sectional SEM image of iron phosphate from Comparative Example 1 of this application.

[0024] Figure 5 These are the 1C charge / discharge curves of lithium iron phosphate in Example 1 and Comparative Example 1 of this application.

[0025] Figure 6 These are the 5C charge-discharge curves of lithium iron phosphate in Example 1 and Comparative Example 1 of this application.

[0026] Figure 7 These are the 10C charge-discharge curves of lithium iron phosphate in Example 1 and Comparative Example 1 of this application.

[0027] Figure 8 These are the cumulative pore size distribution curves of iron phosphate in Example 1 and Comparative Example 1 of this application. Detailed Implementation

[0028] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0029] Phosphorus-based cathode materials are currently the most commercially viable and mature cathode material system, with lithium iron phosphate (LiFePO4) being the core representative. LiFePO4 cathode materials possess significant advantages such as long cycle life and excellent safety performance, and are now widely used in automotive power batteries, energy storage batteries, and other fields. Their industrial-scale preparation process is highly mature. Iron phosphate, as the core precursor for lithium iron phosphate production, is an indispensable key raw material in the current mainstream lithium iron phosphate synthesis process.

[0030] The current mainstream preparation process for lithium iron phosphate (LFP) involves mixing iron phosphate with lithium sources such as lithium carbonate and carbon sources, along with functional additives, and then processing this mixture through grinding, spraying, sintering, and crushing to obtain the LFP cathode material. In this process, the structural properties of iron phosphate play a decisive role in the synthesis efficiency and final performance of LFP. When iron phosphate has a larger reaction contact area, it can effectively shorten the lithium-ion diffusion path, enabling the lithiation reaction to be fully completed under low-temperature, short-time conditions, avoiding the Fe2+ degradation caused by high-temperature, long-time sintering. 3+The formation of impurity phases (such as Fe2O3 and Li3Fe2(PO4)3) and the problem of lithium iron phosphate antisite defects significantly improve the initial coulombic efficiency of cathode materials. Simultaneously, the excellent pore structure and large contact area enable uniform dispersion of the carbon source, greatly improving the uniformity and quality of carbon coating. However, currently commercially available conventional lithium iron phosphate materials are mostly amorphous blocky or small particle agglomerates with poor particle morphology regularity and structural consistency, making it difficult to ensure the uniformity of subsequent lithiation reactions and carbon coating treatment, thus limiting further improvements in the electrochemical performance of lithium iron phosphate materials.

[0031] Based on the above, in a first aspect, this application proposes ferric phosphate, comprising ferric phosphate particles, said ferric phosphate particles comprising the compound shown in Formula 1: Fe x M y PO4 Formula 1 Wherein, 0.9≤x≤1, 0≤y≤0.1, and M includes at least one of Ti, Zr, V, W, Nb, Mg, and Sr; The structural porosity coefficient Q of the iron phosphate satisfies: 150 × 10 -6 m 3 / g≤Q≤450 ×10 -6 m 3 / g, specifically, the structural porosity coefficient Q can be 150 × 10 -6 m 3 / g, 200 ×10 -6 m 3 / g, 250 ×10 -6 m 3 / g, 300 ×10 - 6 m 3 / g, 350 ×10 -6 m 3 / g, 400 ×10 -6 m 3 / g, 450 ×10 -6 m 3 / g or any two of the above; the porosity N of the iron phosphate satisfies: 10%≤N≤45%, specifically, the porosity N can be 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45% or any two of the above.

[0032] When the iron phosphate of this application simultaneously meets the aforementioned ranges for both the structural porosity coefficient Q and porosity N, it possesses both a large macroscopic particle size and a loose, porous internal structure. The lithium iron phosphate material prepared from this material exhibits excellent rate performance and cycle life. Specifically, the structural porosity coefficient Q is dimensionally equivalent to the reciprocal of density; a larger Q value indicates a lower bulk density and more developed internal porosity in the iron phosphate. When the Q value is controlled within the aforementioned range, it indicates that the iron phosphate has a large macroscopic particle size and a loose, porous internal structure. Porosity N directly reflects the pore volume ratio; iron phosphate meeting the above range exhibits significant porous and loose characteristics as well as a well-developed pore structure. When iron phosphate simultaneously meets the structural porosity coefficient Q and porosity N ranges defined in this application, the larger macroscopic particles indicate that iron phosphate has a larger specific surface area. This is beneficial for forming a more uniform contact interface when iron phosphate is mixed with lithium sources, carbon sources, etc., during the preparation of lithium iron phosphate materials, reducing agglomeration problems caused by particle size differences. On the other hand, the internal loose and porous structure can significantly increase the reaction contact area through well-developed pore channels, thereby effectively improving the reaction inhomogeneity problem caused by traditional amorphous blocky or fine particle agglomeration structures. This significantly improves the compatibility of iron phosphate with lithium sources and carbon sources, resulting in a more complete and uniform lithiation reaction. Sufficient pore space can construct a smooth and efficient lithium-ion transport pathway, effectively reducing the degree of electrode polarization, and ultimately greatly improving the rate discharge capability and long-cycle stability of lithium iron phosphate materials. Furthermore, introducing elements such as Ti, Zr, V, W, Nb, Mg, and Sr during the iron phosphate synthesis stage, compared to adding them during the lithium iron phosphate cathode stage, can better improve the electronic conductivity and lithium-ion diffusion performance of LiFePO4, thereby further enhancing the rate performance of lithium iron phosphate materials. In summary, this application improves the overall performance of lithium iron phosphate materials by limiting the structural porosity coefficient Q and porosity N within a specific range and synergistically combining them with element M doping.

[0033] It should be noted that since the specific surface area S includes both the outer surface area of ​​the particles and the inner surface area of ​​the pores, when the particle size is large and the pores are not well-developed, the Q value may mainly reflect the contribution of the outer surface area. In this case, porosity N needs to be combined to accurately characterize the degree of internal looseness and porosity. Therefore, by simultaneously limiting Q and N, iron phosphate with both a large macroscopic particle size and a well-developed pore structure can be screened more accurately.

[0034] If the Q value is too large, it indicates that the structure of iron phosphate may be too loose and the mechanical strength of the particles may be insufficient. During the subsequent grinding process of preparing lithium iron phosphate materials, the structure will break down too quickly and cannot fully combine with the lithium source, carbon source, etc., thus affecting the performance of lithium iron phosphate materials. If the Q value is too small, it indicates that the bulk density of iron phosphate is too high, which may result in fewer pores. During the subsequent lithiation reaction, the lithium source and carbon source will have difficulty penetrating, which may easily lead to uneven reaction.

[0035] If the N value is too large, it indicates that the porosity of iron phosphate is too high, which may lead to a decrease in mechanical strength. During the subsequent grinding process of lithium iron phosphate material preparation, the structure breaks down too quickly and cannot fully combine with lithium source, carbon source, etc. If the N value is too small, it indicates that the porosity of iron phosphate is too low, the pores are underdeveloped, and the specific surface area is low, which may lead to local unevenness and incomplete lithiation reaction.

[0036] The structural porosity coefficient Q = Dv50 × S, where Dv50 is the median particle size of the iron phosphate, and S is the specific surface area of ​​the iron phosphate. Dv50 represents the volume of particles smaller than or larger than this diameter that account for 50% of the total particle volume, and the unit is µm. Dv50 can be measured using a laser particle size analyzer, and S can be measured using a specific surface area analyzer, with the unit being m. 2 / g.

[0037] According to embodiments of this application, the Dv50 of the iron phosphate satisfies: 10µm ≤ Dv50 ≤ 40µm, specifically 15µm ≤ Dv50 ≤ 30µm. As a specific example, the Dv50 of the iron phosphate can be 10µm, 12µm, 15µm, 18µm, 21µm, 24µm, 27µm, 30µm, 33µm, 35µm, 38µm, 40µm, or any range between two of these. Within the above range, during the lithiation reaction, the iron phosphate particles have a high degree of particle size matching with the lithium source, carbon source, etc., resulting in high mixing uniformity and a more complete and uniform lithiation reaction.

[0038] According to an embodiment of this application, the specific surface area S of the iron phosphate satisfies: 7m² 2 / g≤S≤25 m 2 / g, specifically 9m 2 / g ≤S≤18 m 2 / g. As a specific example, the S in ferric phosphate can be 7m. 2 / g、9m 2 / g、12m 2 / g, 15m 2 / g、18m 2 / g、22m 2 / g、25m 2 / g or any combination thereof. Within the above range, a suitable specific surface area can provide sufficient contact interface, allowing for a more complete and uniform lithiation reaction.

[0039] Porosity N = Vh / (Vh + Vs), where Vh is the pore volume of the iron phosphate and Vs is the skeletal volume of the iron phosphate. Porosity N can be obtained by true density measurement.

[0040] According to an embodiment of this application, the pore volume Vh of the ferric phosphate pores satisfies: 0.05 cm³. 3 / g≤Vh≤0.15cm 3 / g, specifically, Vh can be 0.05cm 3 / g, 0.08cm 3 / g, 0.1cm 3 / g, 0.13cm 3 / g, 0.15cm 3 / g or a range between / g and either / g or any two of the above ranges. Within this range, it indicates that the iron phosphate contains well-developed and interconnected pores, ensuring that the subsequent lithiation reaction proceeds fully and uniformly.

[0041] According to an embodiment of this application, the skeleton volume Vs of ferric phosphate satisfies: 0.2 cm³. 3 / g≤Vs≤0.3cm 3 / g, specifically, Vs can be 0.2cm 3 / g, 0.22cm 3 / g, 0.24cm 3 / g, 0.26cm 3 / g, 0.28cm 3 / g, 0.3cm 3 / g or any two of the above ranges. Within the above range, ferric phosphate can have strong mechanical strength and maintain a complete particle morphology.

[0042] According to an embodiment of this application, the iron phosphate satisfies: 200 × 10 -6 m 3 / g≤Q≤350×10 -6 m 3 / g. Within the above range, lithium iron phosphate combines large macroscopic particle size with a loose and porous internal structure, which can further improve the overall performance of lithium iron phosphate materials.

[0043] According to embodiments of this application, 0.75 ≤ K90 ≤ 1.75. Specifically, K90 can be 0.75, 1, 1.25, 1.50, 1.75, or any two of these ranges. Within this range, it indicates that the pore size distribution of iron phosphate is concentrated and uniform, with a low proportion of extreme pore volumes for both ultra-large and ultra-fine pores, reflecting the uniformity of the internal pores. If K90 is too large, it indicates that the internal pore size distribution of iron phosphate is not concentrated, the proportion of extreme pore sizes increases, and the uniformity of the pore structure decreases. If K90 is too small, it indicates that the internal pore size distribution of iron phosphate is too concentrated, the pore connectivity is limited, which is not conducive to the efficient lithiation reaction.

[0044] K90 = (R90 - R10) / R50, where R10 represents the pore diameter when the cumulative pore volume in the ferric phosphate reaches 10% of the total pore volume, R50 represents the pore diameter when the cumulative pore volume in the ferric phosphate reaches 50% of the total pore volume, and R90 represents the pore diameter when the cumulative pore volume in the ferric phosphate reaches 90% of the total pore volume. R90, R10, and R50 can be calculated using a surface area analyzer based on the BJH model.

[0045] According to embodiments of this application, 20nm ≤ R10 ≤ 40nm. Specifically, R10 can be 20nm, 25nm, 30nm, 35nm, 40nm, or any combination thereof. Within this range, it indicates that a certain proportion of small-diameter pores exist within the iron phosphate.

[0046] According to embodiments of this application, 50nm ≤ R50 ≤ 80nm. Specifically, R50 can be a range of 50nm, 55nm, 60nm, 65nm, 70nm, 75nm, 80nm, or any two of these ranges. Within this range, it indicates that there is a certain proportion of appropriately sized pores within the iron phosphate.

[0047] According to embodiments of this application, 90nm ≤ R90 ≤ 150nm. Specifically, R90 can be 90nm, 100nm, 110nm, 120nm, 130nm, 140nm, 150nm, or any range between two of these. Within the above range, it indicates that there is a certain proportion of relatively large-diameter pores inside the iron phosphate.

[0048] According to an embodiment of this application, the open-pore volume ratio Z of the iron phosphate satisfies 50% < Z ≤ 85%, and the open-pore volume ratio Z = open-pore volume / (open-pore volume + closed-pore volume) × 100%. The sum of the open-pore volume and the closed-pore volume is consistent with the aforementioned pore volume Vh of the iron phosphate. Specifically, the open-pore volume ratio Z of the iron phosphate can be 50%, 60%, 70%, 80%, 85%, or any two of these ranges. Within the above range, the proportion of open pores inside the iron phosphate is relatively high, the internal open pores are well-developed and have good connectivity; the overall structure presents a loose and porous microstructure. The open-pore volume and closed-pore volume can be obtained by N2 adsorption-desorption isotherm testing. If the Z value is too large, the proportion of open pores inside the iron phosphate is too high, the skeletal support is insufficient, which may lead to a decrease in the mechanical strength of the iron phosphate. If the Z value is too small, there are too many closed-pore structures inside the iron phosphate, the pore connectivity is poor, which leads to uneven and incomplete subsequent lithiation reaction.

[0049] According to the embodiments of this application, 10% ≤ ΔDv50 ≤ 25%, specifically, ΔDv50 can be 10%, 13%, 16%, 19%, 22%, 25%, or any two of these ranges. Within this range, it is demonstrated that iron phosphate, while possessing a loose and porous structure, maintains a certain compressive strength. During subsequent mixing and grinding, efficient control and rapid homogenization of the slurry particle size can be achieved, while maintaining a moderate integrity of the particle structure. This ensures uniform contact and thorough mixing of iron phosphate with the lithium and carbon sources, laying the foundation for preparing lithium iron phosphate materials with excellent consistent performance.

[0050] The iron phosphate was subjected to fracturing treatment at a pressure of 3.5T. The particle size change rate ΔDv50 = (Dv50 before fracturing - Dv50 after fracturing) / (Dv50 before fracturing) × 100%.

[0051] A second aspect of this application provides a method for preparing the ferric phosphate described in the first aspect, comprising: S10: Provides a first solution containing ferrous dihydrogen phosphate.

[0052] According to embodiments of this application, providing a first solution containing ferrous dihydrogen phosphate comprises: mixing elemental iron and phosphoric acid with a mass concentration of 10% to 50% at a temperature of 25°C ≤ T < 75°C for 1 to 10 hours to obtain the first solution containing ferrous dihydrogen phosphate. Within the above conditions, the above process can achieve a mild, sufficient, and controllable reaction between iron and phosphoric acid, generating high-purity, single-component ferrous dihydrogen phosphate, reducing the formation of impurity phases, and providing a basis for obtaining ferric phosphate with better consistency.

[0053] According to embodiments of this application, elemental iron can be provided in the form of iron blocks, iron filings, iron powder, etc.

[0054] According to an embodiment of this application, after the oxidation reaction is completed, the process further includes filtering the first solution containing ferrous dihydrogen phosphate. Unreacted excess reduced iron powder, insoluble impurities, and suspended solids are filtered out, leaving only a clear and pure ferrous dihydrogen phosphate filtrate.

[0055] S20: Mix the first solution and the oxidant, and carry out the oxidation reaction at the first temperature T1 for the first time t1 to obtain the first slurry of ferric phosphate dihydrate (FePO4·2H2O).

[0056] In this step, the first solution and the oxidant are mixed. The ferrous dihydrogen phosphate in the first solution undergoes an oxidation reaction with the oxidant to obtain ferric phosphate dihydrate with a pure phase, regular morphology, and uniform particle size. This ferric phosphate dihydrate product has superior overall performance and can be used directly as a seed crystal in subsequent growth processes. It can effectively guide the orderly crystallization and growth of subsequent raw materials, providing a good foundation for the preparation of ferric phosphate with high regularity and high performance consistency.

[0057] According to embodiments of this application, the oxidant includes hydrogen peroxide. Hydrogen peroxide has strong oxidizing properties, and the oxidation product in the oxidation reaction is only water, without introducing foreign impurity ions, making it green and environmentally friendly. The oxidation reaction is: 2Fe(H2PO4)2 + H2O2 + 2H2O → 2FePO4·2H2O↓ + 2H3PO4. According to embodiments of this application, the molar ratio of Fe in the iron, P in the phosphoric acid, and the oxidant is 1:2.3~3.0:0.5-0.75. This ratio ensures sufficient dissolution of the iron and the Fe... 2+ Completely oxidized to Fe 3+ This yields high-purity iron phosphate.

[0058] According to embodiments of this application, 60℃≤T1<90℃. Specifically, the first temperature T1 can be 60℃, 65℃, 70℃, 75℃, 80℃, 85℃, 89℃, or any two of these ranges. Within the above range, the reaction system is homogeneous and the oxidation reaction is accelerated, thereby stably generating iron phosphate dihydrate crystals with pure phase, uniform particle size, and regular morphology.

[0059] According to the embodiments of this application, 0.5h ≤ t1 ≤ 3h. Specifically, the first time t1 can be 0.5h, 1h, 1.5h, 2h, 2.5h, 3h, or any two of these ranges. Within this range, the oxidation reaction can proceed fully while ensuring sufficient crystallization of ferric phosphate dihydrate without excessive growth, resulting in ferric phosphate dihydrate crystals with few structural defects, high purity, small size, and uniform particle size. These crystals can efficiently induce the directional and uniform growth of subsequent raw materials on the seed crystal surface, ensuring the regularity and consistency of the morphology of subsequent precursor particles.

[0060] S30: The first solution, the oxidant, and the optional M source are added to the first ferric phosphate dihydrate slurry in a parallel flow, and mixed at a second temperature T2 for a second time t2 to obtain a second ferric phosphate dihydrate slurry. The second temperature T2 < the first temperature T1, and the second time t2 > the first time t1.

[0061] In this step, the first slurry of ferric phosphate dihydrate prepared in the aforementioned steps is used as a seed crystal. At the same time, the raw materials are fed in a co-current manner to ensure that the reactants are in uniform contact at a constant ratio. This enables rapid and uniform nucleation and controlled growth under high temperature and short time conditions, resulting in ferric phosphate dihydrate particles with pure phase, regular morphology, and uniform particle size.

[0062] It is understandable that steps S10 and S20 are the preparation processes for iron phosphate dihydrate seed crystals. These processes are carried out in a batch-step manner: first, elemental iron reacts with phosphoric acid to prepare a first solution, providing a stable reaction basis for subsequent oxidation; then, under relatively high temperature and short time conditions, the first solution, oxidant, and M source are mixed, reducing the non-uniformity of seed crystal size caused by the reaction, and resulting in a more ordered crystal structure with fewer defects. In step S30, using the iron phosphate dihydrate seed crystal as a substrate, raw materials are added continuously in a parallel flow manner, and crystal growth is carried out under relatively low temperature and long time conditions, ultimately obtaining large-particle iron phosphate with a loose structure and high porosity. Specifically, during seed crystal preparation, high temperature accelerates the oxidation reaction rate and increases the kinetics of seed crystal nucleation, enabling the system to simultaneously and in batches generate a large number of uniformly distributed crystal nuclei. Simultaneously, high temperature helps eliminate intermediate or impurity phases, resulting in pure, uniformly sized seed crystals; while the shorter reaction time ensures that the system only completes crystal nucleus generation, resulting in small, uniform crystal sizes and good dispersibility. In step S30, the lower crystal growth temperature can effectively reduce the kinetic rate of the raw materials. At the same time, the feed is fed in a co-current manner, so that the concentration of raw material ions in the reactor is always kept at a constant level, maintaining the system in a stable state of low supersaturation. This reduces the possibility of the formation of new crystal nuclei and ensures that crystal growth only occurs on the surface of the original seed crystals. The long growth process allows iron and phosphorus ions to slowly, orderly, and layer by layer deposit on the seed crystal surface, achieving the construction of uniform and interconnected pores and a loose porous structure. This results in the final obtained iron phosphate dihydrate crystal particles with uniform growth, fewer defects, and a more concentrated particle size distribution.

[0063] According to an embodiment of this application, 40℃≤T2<70℃. Specifically, the second temperature T2 can be 40℃, 45℃, 50℃, 55℃, 60℃, 65℃, 69℃, or any two of these ranges. Within this range, the kinetic rate of the raw materials can be effectively reduced, maintaining the system in a stable state with low supersaturation, thereby reducing the possibility of new crystal nuclei forming and ensuring that crystal growth occurs only on the surface of the existing seed crystals.

[0064] According to an embodiment of this application, 2h ≤ t2 ≤ 10h. Specifically, the second time t2 can be 2h, 4h, 6h, 8h, 10h, or any two of these ranges. Within the above range, iron-phosphorus ions are deposited slowly, orderly, and layer by layer on the seed crystal surface, achieving a fully ordered arrangement of the crystal lattice. This results in uniform growth of the final iron phosphate dihydrate crystal particles, fewer defects, and a more concentrated particle size distribution.

[0065] According to embodiments of this application, the M source includes at least one of the following: an oxide of M, a nitrate containing M, a sulfate containing M, and a chloride containing M. The aforementioned M source has good water solubility, which facilitates uniform reaction in a liquid-phase system, and the raw materials are widely available and easily obtained.

[0066] According to the embodiments of this application, the amount of M source added can be determined according to the chemical formula of the target iron phosphate. Specifically, the actual feeding ratio can be flexibly adjusted according to process requirements.

[0067] S40: The second slurry of ferric phosphate dihydrate is sequentially subjected to pressure filtration, washing, drying, and calcination to obtain ferric phosphate. Pressure filtration and washing separate the ferric phosphate dihydrate product and remove impurity ions adhering to the surface of the ferric phosphate dihydrate product through washing. After drying, the surface moisture is removed. After calcination of the ferric phosphate dihydrate to remove the bound water, ferric phosphate is obtained.

[0068] According to embodiments of this application, the drying process includes, but is not limited to, flash drying. For example, the washed product is dried at an inlet air temperature of 280°C-450°C and an outlet air temperature of 105°C-130°C. Drying can remove moisture from the surface of ferric phosphate dihydrate.

[0069] According to embodiments of this application, the calcination temperature is 600℃~750℃, specifically 625℃~675℃. As an example, the calcination temperature can be 600℃, 610℃, 620℃, 625℃, 650℃, 660℃, 670℃, 675℃, 700℃, 725℃, 750℃, or any range between two of these. Within the above range, the bound water of ferric phosphate dihydrate can be sufficiently removed without damaging the structure of ferric phosphate dihydrate or causing abnormal grain growth.

[0070] According to embodiments of this application, the calcination time is 2h to 12h, specifically 4h to 8h. As an example, the calcination time can be 2h, 4h, 6h, 8h, 10h, 12h, or any range between two of these. Within this range, the bound water of ferric phosphate dihydrate can be sufficiently removed, ensuring the purity and structural stability of the ferric phosphate phase.

[0071] A third aspect of this application provides a lithium iron phosphate material, wherein the raw materials for preparing the lithium iron phosphate material include the iron phosphate described in the first aspect or the iron phosphate prepared by the method described in the second aspect. This lithium iron phosphate material exhibits excellent electrochemical performance, high-rate charge / discharge capability, and high particle uniformity. Its application in lithium-ion batteries can effectively improve the rate performance of lithium-ion batteries.

[0072] According to embodiments of this application, a method for preparing lithium iron phosphate includes: mixing iron phosphate, lithium salt, optional carbon source, and dopant, followed by grinding, spraying, and sintering to obtain lithium iron phosphate material. Specific operations can be performed using conventional techniques.

[0073] According to embodiments of this application, the dopants include TiO2, TiOSO4, ZrO2, Zr(NO3)4, V2O5, WO3, Nb2O5, MgO, MgSO4, SrSO4, etc. These dopants can provide doping elements such as Ti, Zr, V, W, Nb, Mg, and Sr, which can improve the electronic conductivity and lithium-ion diffusion performance of LiFePO4, thereby enhancing the rate performance of lithium iron phosphate materials.

[0074] According to embodiments of this application, the carbon source includes at least one of inorganic carbon sources and organic carbon sources. Inorganic carbon sources include, but are not limited to, carbon black, conductive carbon, acetylene black, graphene, etc.; organic carbon sources include, but are not limited to, glucose, sucrose, fructose, starch, citric acid, urea, polyvinyl alcohol (PVA), polyethylene glycol (PEG), cellulose, etc.

[0075] A fourth aspect of this application provides a lithium-ion battery comprising the lithium iron phosphate material described in the third aspect. This lithium-ion battery includes all the features and advantages of the aforementioned iron phosphate or lithium iron phosphate material, which will not be elaborated upon here.

[0076] According to an embodiment of this application, the lithium-ion battery includes a positive electrode, a negative electrode, an electrolyte, and a separator.

[0077] According to an embodiment of this application, the positive electrode sheet includes a positive current collector and a positive electrode dressing layer disposed on at least one side surface of the positive current collector. The positive electrode dressing layer includes a positive electrode material, a positive electrode conductive agent, and a positive electrode binder.

[0078] According to embodiments of this application, the positive current collector includes a metal foil; as a specific example, this application uses aluminum foil.

[0079] According to embodiments of this application, the positive electrode conductive agent includes at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes (CNTs), graphene, and Super P.

[0080] According to embodiments of this application, the positive electrode binder includes at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), and a terpolymer of PVDF-tetrafluoroethylene-propylene.

[0081] According to an embodiment of this application, the lithium-ion battery further includes a negative electrode sheet, the negative electrode sheet including a negative electrode current collector and a negative electrode coating layer disposed on at least one side surface of the negative electrode current collector, the negative electrode coating layer including a negative electrode active material.

[0082] According to embodiments of this application, the negative electrode sheet includes, but is not limited to, a lithium metal sheet.

[0083] According to embodiments of this application, the negative electrode active material includes silicon-based materials and carbon materials.

[0084] According to embodiments of this application, the negative electrode sheet further includes at least one of a negative electrode binder, a negative electrode conductive agent, and a thickener.

[0085] According to embodiments of this application, the negative electrode binder includes at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), and polyacrylamide (PAM).

[0086] According to embodiments of this application, the negative electrode conductive agent includes at least one of superconducting carbon, acetylene black, carbon black, and graphene.

[0087] According to embodiments of this application, the thickener includes sodium carboxymethyl cellulose (CMC-Na).

[0088] According to the embodiments of this application, in the above-mentioned lithium-ion battery, the electrolyte can be a liquid electrolyte (i.e., an electrolyte solution) or a solid electrolyte.

[0089] According to an embodiment of this application, the electrolyte is an electrolyte solution. In this case, the positive electrode, the negative electrode, and the separator are all immersed in the electrolyte solution. During the charging and discharging process of the battery, active ions are inserted and extracted back and forth between the positive electrode and the negative electrode. The electrolyte solution plays the role of conducting ions between the positive electrode and the negative electrode. The separator is disposed between the positive electrode and the negative electrode and mainly plays the role of preventing short circuits between the positive electrode and the negative electrode, while allowing active ions to pass through.

[0090] According to an embodiment of this application, the electrolyte is a solid electrolyte. In this case, the positive electrode, negative electrode, electrolyte, and separator can be manufactured into a battery cell through a winding or stacking process, and the battery cell can be housed in an outer package. The positive and negative electrode sheets are alternately stacked, and the electrolyte and battery separator are disposed between adjacent positive and negative electrode sheets.

[0091] According to embodiments of this application, the diaphragm can be made of various porous structures with good stability, such as polyethylene diaphragms, polypropylene diaphragms, PE ceramic-coated diaphragms, etc.

[0092] A fifth aspect of this application provides an electrical device comprising the aforementioned lithium-ion battery. This electrical device incorporates all the features and advantages of the aforementioned iron phosphate or lithium iron phosphate materials, which will not be elaborated upon here.

[0093] It is understood that there are no particular restrictions on the specific type of electrical device; it can be any device that uses a lithium-ion battery as a power source or energy storage unit. For example, electrical devices include, but are not limited to, electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), mobile terminals (such as mobile phones, laptops, game consoles, wearable devices, etc.), drones, aerospace equipment, satellites, ships, energy storage systems, and so on.

[0094] It is understandable that, in addition to the lithium-ion battery mentioned above, the electrical device also includes necessary structures and components, all of which can be made with reference to conventional technologies. For example, an electric vehicle may include a body, chassis, tires, navigation system, radar system, steering system, braking system, lubrication system, cooling system, driving system, etc., which will not be described in detail here.

[0095] The embodiments of this application are described in detail below.

[0096] Example 1 Preparation of ferric phosphate: 85% phosphoric acid was diluted with a certain amount of pure water by stirring to obtain 25% phosphoric acid. A certain amount of reduced iron powder was added to the 25% dilute phosphoric acid solution at a Fe:P molar ratio of 1:3. The mixture was stirred at 45℃ for 2 hours. The reaction solution was then filtered to obtain the corresponding ferrous phosphate solution.

[0097] The ferrous phosphate solution obtained in the previous step was introduced into the first reaction vessel. Hydrogen peroxide was added as an oxidant according to the ratio of n(H2O2):n(Fe)=0.65:1. The first reaction time was set to t1=1h and the first reaction temperature was set to T1=85℃. The reaction yielded the first slurry of ferric phosphate dihydrate.

[0098] The first slurry of ferric phosphate dihydrate obtained in the previous step was introduced into the second reactor as a seed liquid. Ferrous phosphate solution, hydrogen peroxide, and TiO2 aqueous suspension were introduced in a parallel flow according to the ratio of n(H2O2):n(Fe):n(TiO2) = 0.65:1:0.03. The second reaction time t2 was set to 5 hours, and the second reaction temperature T2 was set to 60°C. Overflow was continued to obtain the second slurry of ferric phosphate dihydrate.

[0099] The second slurry of ferric phosphate dihydrate obtained in the previous step was subjected to pressure filtration and washing with twice the amount of pure water. After washing, the filter cake was sent to a flash dryer with the inlet air temperature set at 280℃ and the outlet air temperature at 105℃. After drying, the corresponding dried ferric phosphate dihydrate was obtained.

[0100] The dried ferric phosphate dihydrate obtained in the previous step was calcined at 650°C for 4 hours to obtain ferric phosphate FePO4.

[0101] Preparation of the cathode material: The obtained iron phosphate, lithium carbonate, glucose, and titanium dioxide were added to deionized water in a molar ratio of 1:1:0.25:0.005 to form an initial slurry. This slurry was then ground to a specific particle size (D) using a sand mill. 50 After reaching a depth of 0.3µm, the powder is spray-dried, and then sintered at 780℃ for 10 hours in a nitrogen atmosphere to obtain the corresponding lithium iron phosphate cathode material (LiFePO4 / C).

[0102] Fabrication of button cells: First, a non-aqueous electrolyte secondary battery composite lithium iron phosphate positive electrode active material (the above-mentioned lithium iron phosphate positive electrode material), acetylene black and polyvinylidene fluoride (PVDF) are mixed in a mass ratio of 95%:2.5%:2.5%, coated on aluminum foil and dried. The positive electrode is then stamped into a positive electrode sheet with a diameter of 12mm and a thickness of 120μm under a pressure of 100MPa. The positive electrode sheet is then placed in a vacuum drying oven and dried at 120℃ for 12h.

[0103] The negative electrode uses a Li metal sheet with a diameter of 17 mm and a thickness of 1 mm; The diaphragm uses a 25μm thick porous polyethylene membrane; The electrolyte used is a 1 mol / L mixture of LiPF6, ethylene carbonate (EC), and diethyl carbonate (DEC) in a 1:1 volume ratio. The positive electrode, separator, negative electrode, and electrolyte were assembled into a 2025 coin cell in an Ar gas glove box with a water content and oxygen content of less than 5 ppm. The cell at this stage was considered an unactivated cell. The specific parameters of Examples 1-33 and Comparative Examples 1-6 are shown in Table 1, and other parameters are the same as those of Example 1.

[0104] Performance testing: (1) Porosity N test method (true density analyzer method): AccuPyc II 1345 fully automatic gas replacement method true density analyzer is used. After the instrument starts cavity calibration, the sample cup is taken out, a certain amount of sample is weighed and its mass is recorded (the volume is about 4 / 5 of the sample chamber volume). Then the sample cup is put into the instrument, the sample cover and the sealing cover are put on. After confirming that there is no error, click to start the measurement program. The fully automatic gas replacement method is used to obtain the test sample pore volume Vh and the skeleton volume test value Vs. The calculation formula of the porosity N of the test material is: test sample pore volume Vh / (test sample pore volume Vh + skeleton volume test value Vs) × 100%.

[0105] (2) Pore size testing method: Using an ASAP 2460 surface area analyzer, a certain mass of positive electrode active material was taken and dehydrated and degassed in a sealed tube at 300℃. Then, it was transferred to a surface area testing bottle. Nitrogen was used as the adsorption gas. The amount of nitrogen adsorbed by the material under different nitrogen pressures from vacuum to nitrogen saturated vapor pressure was tested and recorded to obtain the adsorption isotherm curve. Based on the BJH model, the pore size and corresponding volume ratio of the positive electrode active material can be calculated to obtain R10, R50, and R90. K90 = (R90 - R10) / R50.

[0106] (3) Pore volume test: Based on the N2 adsorption-desorption isotherm test and analysis, the pore volume was obtained using a Tristar 3020 surface analyzer from Micromeritics. Using a conventional measuring device (Tristar 3020), N2 was gradually added to the test material after the physical adsorption components had been removed, starting under vacuum. The pressure change caused by N2 adsorption was calculated using the constant volume method, and the amount of N2 adsorbed was obtained according to the gas equation. Thus, the N2 adsorption isotherm from 0 atm to 0.995 atm was obtained at liquid nitrogen temperature. After reaching 0.995 atm, the N2 pressure was gradually reduced to 0 atm to obtain the N2 desorption isotherm from 0.995 atm to 0 atm, and the N2 adsorption-desorption isotherms were obtained by summing them up. Among them, the N2 adsorption-desorption isotherm analysis is: the pore volume is obtained by calculating the amount of N2 adsorbed when the relative pressure (p / p0) of the N2 adsorption isotherm is 0.995. The percentage of the pore volume with open holes, Z = (open hole volume / (open hole volume + closed hole volume)) × 100%. The sum of the open hole volume and the closed hole volume is the pore volume of the test sample pores measured above.

[0107] (4) Test method for specific surface area S of materials: Using a TriStar specific surface area analyzer, weigh a certain mass of sample, and slowly pour the weighed sample into the bottom of the sample tube using a funnel. After the sample is added, immediately cover the sample tube with a stopper; set the program so that the sample is first aspirated and then degassed. On the software interface, click "sample analysis" to start automatic measurement and obtain the specific surface area S value of the sample, in m². 2 / g.

[0108] (5) Particle size test method: Using Malvern Mastersizer-3000 laser particle size analyzer, set the parameters and measurement background, add solid particles in the 10%-20% shading range, click test, and obtain the corresponding particle size test result Dv50, in µm.

[0109] (6) Structural porosity coefficient Q: Q=Dv50×S.

[0110] (7) Test method for particle size change during fracturing: A Shimadzu MCT-210 micro compression tester was used to perform particle fracturing with a pressure of 3.5T. A Malvern Mastersizer-3000 laser particle size analyzer was used to test the particle size Dv50 before and after fracturing, and the particle size change rate ΔDv50 was calculated based on the test results.

[0111] (8) 1C, 5C, 10C discharge capacity: Using activated batteries, at a current density of 1C and a voltage range of 2.0 to 3.8V, at a temperature of 25°C, the corresponding discharge capacity was tested according to the discharge rate conditions of 1C, 5C, and 10C, and the charge-discharge curves were plotted.

[0112] (9) Cycle retention rate: At a temperature of 45°C, the discharge capacity retention rate is statistically analyzed after 80 cycles of continuous charge and discharge at a current density of 1C in the voltage range of 2.0V-3.75V.

[0113] Table 1

[0114] Table 2

[0115] Table 3

[0116] Figure 1 , Figure 2 The images are front and cross-sectional SEM images of ferric phosphate from Example 1. Figure 3 , Figure 4 The images are SEM images of the front and cross-section of iron phosphate for comparative example 1. Figure 8 These are the cumulative pore size distribution curves of the iron phosphate in Example 1 and Comparative Example 1. The comparison shows that the iron phosphate in this application has a larger particle size, a loose and porous internal structure, and a uniform distribution, while the iron phosphate in Comparative Example 1 has fewer pores and a larger distribution variation.

[0117] Figure 5 , 6 Figures 7 and 8 show the 1C, 5C, and 10C charge-discharge curves of lithium iron phosphate prepared from iron phosphate in Example 1 and Comparative Example 1, respectively. The comparison of the charge-discharge curves at different rates shows that the lithium iron phosphate prepared from the iron phosphate of this application exhibits higher discharge capacity and voltage retention at different rates (1C, 5C, 10C), demonstrating superior rate performance compared to the comparative sample.

[0118] As can be seen from Tables 1-3, compared with Comparative Examples 1-33 and Comparative Examples 1-6, the iron phosphate of this application has the structural characteristics of being porous, having a high specific surface area, and having a large particle size, and has better rate performance and cycle performance than Comparative Examples 1-6.

[0119] Compared with Example 1, Comparative Example 1 shows that the porosity N and the structural looseness coefficient Q are both smaller in Comparative Example 1, indicating that the bulk density of iron phosphate is relatively high, the porosity is less, and the lithium ion transport channels are too narrow. At the same time, too few pores will also make the pores easy to be blocked by interface by-products, ultimately resulting in poor rate performance and cycle stability.

[0120] Although Comparative Example 2 has a suitable porosity N, the structural porosity coefficient Q is too small, indicating that the bulk density of lithium iron phosphate is too high, which may result in fewer pores. This reduces the internal diffusion rate of lithium ions and lacks sufficient structural deformation buffer space. The volume expansion and contraction during charging and discharging can easily cause internal stress accumulation, gradually destroying the microstructure of lithium iron phosphate material, and ultimately causing the cycle performance and rate performance of lithium iron phosphate material to decline simultaneously.

[0121] Although Comparative Example 3 has a suitable porosity N, its structural looseness coefficient Q is too large, indicating that the lithium iron phosphate material has too many internal pores and an overly loose overall structure, resulting in insufficient particle mechanical strength. This makes it prone to structural deformation and powder degradation during charge-discharge cycles, thus leading to poor cycle performance. In Comparative Example 6, both porosity N and structural looseness coefficient Q are too large, further worsening the cycle performance.

[0122] While Comparative Examples 4 and 5 possess suitable porosity coefficients (Q values), the excessively low porosity (N) in Comparative Example 4 results in overly narrow lithium-ion transport channels. Under high-current conditions, lithium-ion migration is hindered, polarization intensifies, and the 10C rate discharge capability significantly decreases. Simultaneously, the pores are easily blocked by interfacial byproducts, ultimately leading to poor cycle stability. In contrast, the excessively high porosity (N) in Comparative Example 5 results in an excessively long lithium-ion transport path, increasing interfacial transport resistance. This not only significantly reduces the 10C rate discharge capability but also increases the contact area between the electrolyte and the active material, exacerbating interfacial side reactions and causing simultaneous degradation in cycle performance.

[0123] Through the above embodiments and comparative examples, it is demonstrated that the iron phosphate of this application possesses structural characteristics of being porous, having a high specific surface area, and a large particle size. The lithium iron phosphate cathode material prepared from this precursor exhibits excellent rate performance and cycle performance, meeting the application requirements of next-generation lithium iron phosphate materials for high-rate charge and discharge at the battery level.

[0124] The terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0125] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0126] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A type of iron phosphate, characterized in that, Includes iron phosphate particles, said iron phosphate particles comprising the compound shown in Formula 1: Fe x M y PO4 Formula 1 Wherein, 0.9≤x≤1, 0≤y≤0.1, and M includes at least one of Ti, Zr, V, W, Nb, Mg, and Sr; The structural porosity coefficient Q of the iron phosphate satisfies: 150 × 10 -6 m 3 / g≤Q≤450×10 -6 m 3 / g; The porosity N of the iron phosphate satisfies: 10% ≤ N ≤ 45%; The structural porosity coefficient Q = Dv50 × S, where Dv50 is the median particle size of the iron phosphate (µm), and S is the specific surface area of ​​the iron phosphate (m²). 2 / g; Porosity N = Vh / (Vh + Vs), where Vh is the pore volume of the iron phosphate and Vs is the skeletal volume of the iron phosphate.

2. The iron phosphate according to claim 1, characterized in that, The iron phosphate satisfies: 200 × 10 -6 m 3 / g≤Q≤350 ×10 -6 m 3 / g.

3. The ferric phosphate according to claim 1 or 2, characterized in that, At least one of the following conditions must be met: 0.75≤K90≤1.75； The pore volume ratio Z of the iron phosphate satisfies 50% < Z ≤ 85%; 10%≤ΔDv50≤25%; Wherein, K90 = (R90 - R10) / R50, R10 is the pore diameter corresponding to the cumulative pore volume of the iron phosphate reaching 10% of the total pore volume, R50 is the pore diameter corresponding to the cumulative pore volume of the iron phosphate reaching 50% of the total pore volume, and R90 is the pore diameter corresponding to the cumulative pore volume of the iron phosphate reaching 90% of the total pore volume. Z = Volume of open aperture / (Volume of open aperture + Volume of closed aperture) × 100%; The iron phosphate was subjected to fracturing treatment under a pressure of 3.5T. The particle size change rate ΔDv50 = (Dv50 before fracturing - Dv50 after fracturing) / (Dv50 before fracturing) × 100%.

4. The ferric phosphate according to claim 3, characterized in that, At least one of the following conditions must be met: 0.05cm 3 / g≤Vh≤0.15cm 3 / g; 0.2cm 3 / g≤Vs≤0.3cm 3 / g; 20nm≤R10≤40nm; 50nm≤R50≤80nm; 90nm≤R90≤150nm.

5. A method for preparing ferric phosphate according to any one of claims 1 to 4, characterized in that, include: Provide a first solution containing ferrous dihydrogen phosphate; The first solution and the oxidant are mixed and oxidized at a first temperature T1 for a first time t1 to obtain the first slurry of ferric phosphate dihydrate. The first solution, the oxidant, and the optional M source are added to the first slurry of ferric phosphate dihydrate in a parallel flow, and mixed at a second temperature T2 for a second time t2 to obtain the second slurry of ferric phosphate dihydrate. The second slurry of ferric phosphate dihydrate was sequentially subjected to pressure filtration, washing, drying, and calcination to obtain ferric phosphate. Wherein, the second temperature T2 < the first temperature T1, and the second time t2 > the first time t1.

6. The method according to claim 5, characterized in that, At least one of the following conditions must be met: 60≤T1＜90℃； 0.5h≤t1≤3h; 40≤T2＜70℃； 2h≤t2≤10h.

7. The method according to claim 5, characterized in that, The provision of the first solution containing ferrous dihydrogen phosphate includes: Iron and phosphoric acid with a mass concentration of 10% to 50% are mixed and reacted at a temperature of 25℃ ≤ T < 75℃ for 1 to 10 hours to obtain the first solution containing ferrous dihydrogen phosphate.

8. The method according to claim 7, characterized in that, At least one of the following conditions must be met: The oxidant includes hydrogen peroxide; The M source includes at least one of the following: an oxide of M, a nitrate containing M, a sulfate containing M, and a chloride containing M; The molar ratio of Fe in the iron, P in the phosphoric acid, and the oxidant is 1:2.3~3.0:0.5~0.

75.

9. The method according to claim 5, characterized in that, At least one of the following conditions must be met: The calcination temperature is 600℃~750℃, preferably 625℃~675℃; The calcination time is 2h to 12h, preferably 4h to 8h.

10. A lithium iron phosphate material, characterized in that, The raw materials for preparing the lithium iron phosphate material include the iron phosphate as described in any one of claims 1 to 4.

11. A lithium-ion battery, characterized in that, Including the lithium iron phosphate material as described in claim 10.

12. An electrical appliance, characterized in that, Including the lithium-ion battery as described in claim 11.

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