Lithium iron phosphate cathode material, its preparation method, and lithium-ion battery

Abstract

The present invention relates to the technical field of preparing lithium ion cathode materials, and discloses a lithium iron phosphate cathode material, a preparation method thereof, and a lithium ion battery. Through XRD testing, the lithium iron phosphate cathode material has diffraction characteristic peaks at 2θ A1 = 29.4 - 29.6°, 2θ A2 = 29.8 - 30° and 2θ A3 = 43.8 - 43.9°. The lithium iron phosphate cathode material has specific diffraction characteristic peaks through XRD testing, so that the lithium iron phosphate cathode material has a high tap density, and further significantly improves the electrochemical properties such as the capacity and cycle performance of the lithium ion battery assembled from the lithium iron phosphate cathode material.

Description

Technical Field

[0001] The present invention relates to the technical field of preparing lithium-ion cathode materials, and particularly relates to a lithium iron phosphate cathode material, a preparation method thereof, and a lithium-ion battery. Background Art

[0002] Lithium-ion batteries are a type of green secondary battery, having prominent advantages such as high voltage, large energy density, good cycle performance, small self-discharge, and no memory effect. Since their successful development in the 1990s, they have been rapidly applied and developed. In recent years, the application scope of lithium-ion batteries has become increasingly extensive, including energy storage power systems such as hydroelectric, thermal, wind, and solar power stations, as well as multiple fields such as power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, and aerospace. Among them, lithium iron phosphate cathode materials have become one of the most promising lithium-ion battery cathode materials due to advantages such as stable structure, rich resources, long cycle life, good safety, environmental friendliness, and a theoretical capacity as high as 170 mAh / g.

[0003] There are many preparation methods for lithium iron phosphate cathode materials, which can generally be divided into liquid-phase methods and solid-phase methods. Among them, liquid-phase methods include low-temperature synthesis methods such as chemical precipitation method, hydrothermal method, and sol-gel method. Solid-phase methods include high-temperature solid-phase sintering method, carbothermal reduction method, microwave sintering method, etc. No matter which synthesis method is used, it needs to be considered from aspects such as cost, ease of process control, and performance when practiced in industrial production. The quality of lithium iron phosphate cathode materials has a direct impact on the performance of batteries such as energy density, cycle life, and safety.

[0004] With the rapid development of the energy storage and power battery industries, new requirements and challenges are put forward for lithium iron phosphate cathode materials. At present, the research on high-compactness lithium iron phosphate materials and their precursor iron phosphate materials is relatively extensive. CN116553507A discloses a high-compactness lithium iron phosphate material and a densification treatment process for its precursor. Take the lithium iron phosphate precursor material, transport it to a plasma flame through an inert gas atmosphere for melting treatment to form spherical single crystals, place them in a graphite sintering furnace, heat and sinter, and then introduce superheated steam; under the heat preservation state, introduce a carbon-containing gas to form a thin carbon coating on the surface of the spherical single crystals, and cool to obtain the high-compactness lithium iron phosphate material. This method has a complex preparation process, is not easy to regulate, consumes a large amount of energy, and lacks product uniformity and stability.

[0005] CN112408351A discloses a preparation method of high-compactness iron phosphate and lithium iron phosphate. A trivalent iron source slurry is prepared and divided into two parts. A mixed solution of phosphoric acid and liquid alkali is added to one part and reacted. When the mixed slurry turns white, the other part is added to the mixed slurry and reacted. Finally, washing, filtration, drying and calcination are carried out to obtain high-compactness iron phosphate. The preparation process of this method is not easy to control. At the same time, simply regulating the stacking mode and particle size distribution of the secondary particles of iron phosphate cannot fundamentally improve the tap density of the lithium iron phosphate material. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to overcome the deficiencies of the prior art and provide a lithium iron phosphate cathode material, its preparation method, and a lithium ion battery. The lithium iron phosphate cathode material has specific diffraction characteristic peaks through XRD testing, so that the lithium iron phosphate cathode material has a high tap density, and further significantly improves the electrochemical properties such as the capacity and cycle performance of the lithium ion battery assembled from the lithium iron phosphate cathode material.

[0007] The first aspect of the present invention provides a lithium iron phosphate cathode material, wherein, through XRD testing, the cathode material has diffraction characteristic peaks at 2θ A1 = 29.4 - 29.6°, 2θ A2 = 29.8 - 30° and 2θ A3 = 43.8 - 43.9°.

[0008] The second aspect of the present invention provides a preparation method of a lithium iron phosphate cathode material, wherein the preparation method includes the following steps:

[0009] (1) Mix a ferric phosphate precursor, a lithium source, a carbon source, an optional metal source M, and an optional Mn source with a liquid medium, grind them into a slurry, and then dry to obtain a dried material;

[0010] (2) Under a protective atmosphere, calcine the dried material to obtain a sintered material;

[0011] (3) Crush and screen the sintered material to obtain the lithium iron phosphate cathode material;

[0012] Among them, the ferric phosphate precursor has diffraction characteristic peaks at 2θ a1 = 16.2 - 16.9°, 2θ a2 = 27.3 - 28.1°, 2θ a3 = 29.0 - 29.7° and 2θ a4 = 30.2 - 30.9° through XRD testing; the ferric phosphate precursor has diffraction characteristic peaks at 2θ b1 = 20 - 20.7°, 2θ b2= 21.5 - 22.2°, 2θ b3 = 23.4 - 24°, 2θ b4 Diffraction characteristic peaks exist at = 25.5 - 26.2°;

[0013] For the iron phosphate precursor, the integral area A(2θ ai ) of the diffraction characteristic peak at ai and the integral area A(2θ bj ) of the diffraction characteristic peak at bj satisfy:

[0014] where i is an integer from 1 to 4 and j is an integer from 1 to 4.

[0015] The third aspect of the present invention provides a lithium iron phosphate cathode material prepared by the above preparation method.

[0016] The fourth aspect of the present invention provides a lithium-ion battery, wherein the lithium-ion battery includes the above lithium iron phosphate cathode material.

[0017] Through the above technical solutions, the lithium iron phosphate cathode material, its preparation method and application, and the lithium-ion battery provided by the present invention achieve the following beneficial effects:

[0018] The lithium iron phosphate cathode material provided by the present invention has specific diffraction characteristic peaks through XRD testing, enabling the cathode material to have a high tap density. When used in a lithium-ion battery, it can effectively improve the electrochemical performance of the lithium-ion battery, showing higher capacity, energy efficiency, lower internal resistance, and better cycling performance.

[0019] Furthermore, the content of Fe2P in the lithium iron phosphate cathode material provided by the present invention is low, which can further improve the capacity and energy density of the cathode material, reduce side reactions with the electrolyte, and improve the service life and safety of the lithium-ion battery containing the cathode material.

[0020] Furthermore, the lithium iron phosphate cathode material provided by the present invention includes a matrix and a carbon coating layer coated on the surface of the matrix, and the carbon coating layer is uniformly coated on the surface of the matrix, thereby further improving the capacity, energy efficiency, and cycling performance of the lithium-ion battery containing the cathode material, while further reducing the internal resistance.

[0021] Specifically, the lithium iron phosphate cathode material provided by the present invention has a high tap density of 2.63 g / cm 3 , enabling the 0.1C discharge specific capacity of the lithium-ion battery containing the cathode material to reach 160 mAh / g, the capacity retention rate after 200 cycles at room temperature to be 97%, and the 1C energy efficiency to reach 95%, showing excellent electrochemical performance.

[0022] In addition, the present invention provides the corresponding relationship between the c / a value of the unit cell parameter of the iron phosphate precursor and the tap density of lithium iron phosphate, providing a basis for the development of raw materials and the design of products.

[0023] In the preparation method of the lithium iron phosphate cathode material provided by the present invention, on the one hand, by using a precursor material with a specific XRD structure, there are certain defects in the structure of the iron phosphate precursor, which can play the role of a flux during the sintering process of the precursor, reducing the sintering temperature. On the other hand, by optimizing the grinding, spraying, and sintering process conditions, a lithium iron phosphate cathode material with high tap density and good electrochemical performance is prepared.

[0024] In addition, the preparation method of the lithium iron phosphate precursor of the present invention only optimizes the process parameters and does not require any adjustment to the existing production line. The entire process is non-toxic and harmless, with a simple process, easily available raw materials, low equipment requirements, easy to promote and apply, and can be widely used in the industrial production of lithium iron phosphate cathode materials. Description of the Drawings

[0025] Figure 1 XRD pattern of the iron phosphate precursor prepared in Preparation Example 1 of the present invention.

[0026] Figure 2 SEM image of the iron phosphate precursor prepared in Preparation Example 1 of the present invention.

[0027] Figure 3 XRD patterns of the lithium iron phosphate cathode materials prepared in Example 1 and Example 2 of the present invention.

[0028] Figure 4 SEM image of the lithium iron phosphate cathode material prepared in Example 1 of the present invention.

[0029] Figure 5 Charge-discharge performance chart of the lithium-ion battery assembled from the lithium iron phosphate cathode materials of Example 1 and Example 2. Detailed Description of the Invention

[0030] In the ranges disclosed herein, the endpoints and any values are not limited to the exact ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values, they can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

[0031] The first aspect of the present invention provides a lithium iron phosphate cathode material, characterized in that by XRD testing, the cathode material has 2θ A1 = 29.4 - 29.6°, 2θA2 = 29.8 - 30° and 2θ A3 Diffraction characteristic peaks exist at = 43.8 - 43.9°.

[0032] In the present invention, when the lithium iron phosphate cathode material is tested by XRD, specific diffraction characteristic peaks exist at specific 2θ, enabling the cathode material to have a high tap density. When used in a lithium-ion battery, it can effectively improve the electrochemical performance of the lithium-ion battery, showing higher capacity, energy efficiency, lower internal resistance, and better cycling performance.

[0033] Furthermore, through XRD testing, the cathode material has diffraction characteristic peaks at 2θ B1 = 25.4 - 25.5°, 2θ B2 = 35.9 - 36° and 2θ B3 = 60.7 - 60.8°.

[0034] According to the present invention, the ratio of the peak intensity I(2θ A2 ) of the diffraction characteristic peak at 2θ A2 in the cathode material to the peak intensity I(2θ B3 ) of the diffraction characteristic peak at 2θ B3 is 0.25 ≤ I(2θ A2 ) / I(2θ B3 ) ≤ 0.27.

[0035] In the present invention, when the ratio of the peak intensity I(2θ A2 ) of the diffraction characteristic peak at 2θ A2 in the cathode material to the peak intensity I(2θ B3 ) of the diffraction characteristic peak at 2θ B3 satisfies the above range, the cathode material can exhibit a relatively high tap density at a relatively low temperature.

[0036] In the present invention, the ratio of the peak intensity I(2θ A2 ) of the diffraction characteristic peak at 2θ A2 in the cathode material to the peak intensity I(2θ B3 ) of the diffraction characteristic peak at 2θ B3 is 0.25 ≤ I(2θ A2 ) / I(2θ B3 ) ≤ 0.27. For example, it can be 0.250, 0.251, 0.252, 0.253, 0.254, 0.255, 0.256, 0.257, 0.258, 0.259, 0.260, 0.261, 0.262, 0.263, 0.264, 0.265, 0.266, 0.267, 0.268, 0.269, 0.27, and any range composed of any two values. Preferably, 0.26 ≤ I(2θA2 ) / I(2θ B3 ) ≤ 0.27

[0037] According to the present invention, the positive electrode material includes a matrix and a carbon coating layer coated on the surface of the matrix;

[0038] wherein, the matrix has the composition shown in Formula I:

[0039] Li 1+a Fe b M c Mn d (PO4) 1-2w (P2O7) w Formula I;

[0040] wherein, -0.1 ≤ a ≤ 0.1, 0 ≤ b ≤ 1, 0 ≤ c ≤ 0.5, 0 ≤ d ≤ 1, 0.03 ≤ w ≤ 0.09;

[0041] M is selected from at least one of La, Ce, Cr, Mo, Ca, Hf, Ti, Fe, Zn, Y, Zr, W, Nb, Sm, Co, Ni, V, Mg, Na, B, and Al.

[0042] In the present invention, the lithium iron phosphate positive electrode material provided by the present invention includes a matrix and a carbon coating layer coated on the surface of the matrix, and the carbon coating layer is uniformly coated on the surface of the matrix, thereby further improving the capacity, energy efficiency, and cycle performance of the lithium ion battery including the positive electrode material, while further reducing the internal resistance.

[0043] Further, M is selected from at least one of Al, Zr, W, Fe, Co, V, and Ti.

[0044] In the present invention, -0.1 ≤ a ≤ 0.1. For example, it can be -0.09, -0.08, -0.07, -0.06, -0.05, -0.04, -0.03, -0.02, -0.01, 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, and the ranges composed of any two values. Preferably, -0.05 ≤ a ≤ 0.05; 0 ≤ b ≤ 1. For example, it can be 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, and the ranges composed of any two values. Preferably, 0.5 ≤ b ≤ 1; 0 ≤ c ≤ 0.5. For example, it can be 0, 0.001, 0.002, 0.003, 0.004, 0.005, 0.006, 0.007, 0.008, 0.009, 0.01, 0.011, 0.012, 0.013, 0.014, 0.015, 0.016, 0.017, 0.018, 0.019, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, and the ranges composed of any two values. Preferably, 0.001 ≤ c ≤ 0.1; 0 ≤ d ≤ 1. For example, it can be 0, 0.1, 0.2, 0.3, 0.4, 0.5, and the ranges composed of any two values. Preferably, 0 ≤ d ≤ 0.5; 0.03 ≤ w ≤ 0.09. For example, it can be 0.03, 0.031, 0.032, 0.033, 0.034, 0.035, 0.036, 0.037, 0.038, 0.039, 0.04, 0.041, 0.042, 0.043, 0.044, 0.045, 0.046, 0.047, 0.048, 0.049, 0.05, 0.051, 0.052, 0.053, 0.054, 0.055, 0.056, 0.057, 0.058, 0.059, 0.06, 0.061, 0.062, 0.063, 0.064, 0.065, 0.066, 0.067, 0.068, 0.069, 0.07, 0.071, 0.072, 0.073, 0.074, 0.075, 0.076, 0.077, 0.078, 0.079, 0.08, 0.081, 0.082, 0.083, 0.084, 0.085, 0.086, 0.087, 0.088, 0.089, 0.09, and the ranges composed of any two values. Preferably, 0.04 ≤ w ≤ 0.08.

[0045] According to the present invention, based on the total weight of the positive electrode material, the content of the carbon coating layer is 0.5 - 2 wt%.

[0046] In the present invention, the content of the carbon coating layer is 0.5-2 wt%, for example, it can be 0.5 wt%, 0.6 wt%, 0.7 wt%, 0.8 wt%, 0.9 wt%, 1 wt%, 1.1 wt%, 1.2 wt%, 1.3 wt%, 1.4 wt%, 1.5 wt%, 1.6 wt%, 1.7 wt%, 1.8 wt%, 1.9 wt%, 2 wt%, and the range composed of any two values. Preferably, based on the total weight of the positive electrode material, the content of the carbon coating layer is 1-1.5 wt%.

[0047] According to the present invention, the lithium iron phosphate positive electrode material has a secondary particle structure formed by primary particles, and the median particle size D of the primary particles 50 is 0.2-2 μm.

[0048] In the present invention, the median particle size D of the primary particles 50 is 0.2-2 μm, for example, it can be 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm, 2 μm, and the range composed of any two values. Preferably, the median particle size D of the primary particles 50 is 0.5-1.5 μm.

[0049] According to the present invention, the tap density of the lithium iron phosphate positive electrode material is 2.5-2.7 g / cm 3 .

[0050] In the present invention, when the tap density of the lithium iron phosphate positive electrode material satisfies the above range, the tap density is relatively high, further reducing the internal resistance of contact between material particles and improving the energy density of the material.

[0051] In the present invention, the tap density of the lithium iron phosphate positive electrode material is 2.5-2.7 g / cm 3 , for example, it can be 2.5 g / cm 3 , 2.51 g / cm 3 , 2.52 g / cm 3 , 2.53 g / cm 3 , 2.54 g / cm 3 , 2.55 g / cm 3 , 2.56 g / cm 3 , 2.57 g / cm 3 , 2.58 g / cm 3 , 2.59 g / cm 3 , 2.6 g / cm3 , 2.61 g / cm 3 , 2.62 g / cm 3 , 2.63 g / cm 3 , 2.64 g / cm 3 , 2.65 g / cm 3 , 2.66 g / cm 3 , 2.67 g / cm 3 , 2.68 g / cm 3 , 2.69 g / cm 3 , 2.7 g / cm 3 , and the range composed of any two values. Preferably, the tap density of the lithium iron phosphate cathode material is 2.55 - 2.65 g / cm 3 .

[0052] According to the present invention, the tap density of the lithium iron phosphate cathode material is 0.6 - 1.1 g / cm 3 .

[0053] In the present invention, when the tap density of the lithium iron phosphate cathode material satisfies the above range, there is an obvious grading between particles, improving the processing performance of the material.

[0054] In the present invention, the tap density of the lithium iron phosphate cathode material is 0.6 - 1.1 g / cm 3 , for example, it can be 0.6 g / cm 3 , 0.61 g / cm 3 , 0.62 g / cm 3 , 0.63 g / cm 3 , 0.64 g / cm 3 , 0.65 g / cm 3 , 0.66 g / cm 3 , 0.67 g / cm 3 , 0.68 g / cm 3 , 0.69 g / cm 3 , 0.7 g / cm 3 , 0.71 g / cm 3 , 0.72 g / cm 3 , 0.73 g / cm 3 , 0.74 g / cm 3 , 0.75 g / cm 3 , 0.76 g / cm 3 , 0.77 g / cm 3 , 0.78 g / cm 3 , 0.79 g / cm 3 , 0.8 g / cm 3 , 0.81 g / cm 3, 0.82 g / cm 3 , 0.83 g / cm 3 , 0.84 g / cm 3 , 0.85 g / cm 3 , 0.86 g / cm 3 , 0.87 g / cm 3 , 0.88 g / cm 3 , 0.89 g / cm 3 , 0.9 g / cm 3 , 0.91 g / cm 3 , 0.92 g / cm 3 , 0.93 g / cm 3 , 0.94 g / cm 3 , 0.95 g / cm 3 , 0.96 g / cm 3 , 0.97 g / cm 3 , 0.98 g / cm 3 , 0.99 g / cm 3 , 1 g / cm 3 , 1.1 g / cm 3 , and ranges formed by any two values. Preferably, the tap density of the lithium iron phosphate cathode material is 0.7 - 1 g / cm 3 .

[0055] According to the present invention, the specific surface area of the lithium iron phosphate cathode material is 8 - 20 m 2 / g.

[0056] In the present invention, the specific surface area of the lithium iron phosphate cathode material is 8 - 20 m 2 / g, for example, it can be 8 m 2 / g, 9 m 2 / g, 10 m 2 / g, 11 m 2 / g, 12 m 2 / g, 13 m 2 / g, 14 m 2 / g, 15 m 2 / g, 16 m 2 / g, 17 m 2 / g, 18 m 2 / g, 19 m 2 / g, 20 m 2 / g, and ranges formed by any two values. Preferably, the specific surface area of the lithium iron phosphate cathode material is 10 - 15 m 2 / g.

[0057] According to the present invention, the volume resistivity of the lithium iron phosphate cathode material is 1 - 100 Ω·cm.

[0058] In the present invention, the volume resistivity of the lithium iron phosphate cathode material is 1-100 Ω·cm. For example, it can be 1 Ω·cm, 2 Ω·cm, 3 Ω·cm, 4 Ω·cm, 5 Ω·cm, 6 Ω·cm, 7 Ω·cm, 8 Ω·cm, 9 Ω·cm, 10 Ω·cm, 12 Ω·cm, 14 Ω·cm, 16 Ω·cm, 18 Ω·cm, 20 Ω·cm, 22 Ω·cm, 24 Ω·cm, 26 Ω·cm, 28 Ω·cm, 30 Ω·cm, 35 Ω·cm, 40 Ω·cm, 45 Ω·cm, 50 Ω·cm, 55 Ω·cm, 60 Ω·cm, 65 Ω·cm, 70 Ω·cm, 75 Ω·cm, 80 Ω·cm, 85 Ω·cm, 90 Ω·cm, 95 Ω·cm, 100 Ω·cm, and the range composed of any two values. Preferably, the volume resistivity of the lithium iron phosphate cathode material is 10-60 Ω·cm.

[0059] According to the present invention, the Fe2P content of the lithium iron phosphate cathode material is ≤100 ppb.

[0060] In the present invention, the lithium iron phosphate cathode material has a low content of Fe2P, which can further improve the capacity and energy density of the cathode material, reduce the side reaction with the electrolyte, and improve the service life and safety of the lithium ion battery containing the cathode material.

[0061] In the present invention, the Fe2P content of the lithium iron phosphate cathode material is ≤100 ppb. For example, it can be 100 ppb, 99 ppb, 98 ppb, 97 ppb, 96 ppb, 95 ppb, 94 ppb, 93 ppb, 92 ppb, 91 ppb, 90 ppb, 85 ppb, 80 ppb, 75 ppb, 70 ppb, 65 ppb, 60 ppb, 55 ppb, 50 ppb, 45 ppb, 40 ppb, 35 ppb, 30 ppb, 25 ppb, 20 ppb, 15 ppb, 10 ppb, 5 ppb, 0 ppb, and the range composed of any two values. Preferably, the Fe2P content of the lithium iron phosphate cathode material is ≤90 ppb.

[0062] According to the present invention, the numerical values of the Fe2P content, volume resistivity and tap density of the lithium iron phosphate cathode material satisfy the following relationship:

[0063] MI = 77.13PD - 0.03R - 107.7

[0064] Wherein, R is the volume resistivity of the lithium iron phosphate cathode material, Ω·cm;

[0065] PD is the tap density of the lithium iron phosphate cathode material, g / cm3 ;

[0066] MI is the Fe₂P content of the lithium iron phosphate cathode material, in ppb.

[0067] In the present invention, when the Fe₂P content, volume resistivity, and tap density of the cathode material satisfy the above relationships, it is possible to prepare a cathode material with a relatively high tap density at a relatively low temperature, and the cathode material has good electrical properties.

[0068] According to the present invention, the tap density of the lithium iron phosphate cathode material and the peak intensity I(2θ A2 ) of the diffraction characteristic peak at 2θ of the cathode material measured by XRD satisfy the following relationship: A2 )

[0069] PD = 0.084I(2θ A2 );

[0070] wherein, PD is the tap density of the lithium iron phosphate cathode material, in g / cm 3 ;

[0071] I(2θ A2 ) is the peak intensity I(2θ A2 ) of the diffraction characteristic peak at 2θ in the XRD diffraction pattern of the lithium iron phosphate cathode material. A2 )

[0072] In the present invention, the inventors have found through research that the tap density of the lithium iron phosphate cathode material and the peak intensity I(2θ A2 ) of the diffraction characteristic peak at 2θ in the cathode material satisfy the above relationship, and by regulating the peak intensity of the diffraction characteristic peak at 2θ, the tap density of the cathode material can be further identified. A2 ) A2

[0073] The second aspect of the present invention provides a method for preparing a lithium iron phosphate cathode material, characterized in that the preparation method includes the following steps:

[0074] (1) Mix a ferric phosphate precursor, a lithium source, a carbon source, optionally a metal source M, and optionally a Mn source with a liquid medium, grind them into a slurry, and then dry to obtain a dried material;

[0075] (2) Under a protective atmosphere, calcine the dried material to obtain a sintered material;

[0076] (3) Crush and screen the sintered material to obtain the lithium iron phosphate cathode material;

[0077] wherein, the ferric phosphate precursor is tested by XRD at 2θ a1= 16.2 - 16.9°, 2θ a2 = 27.3 - 28.1°, 2θ a3 = 29.0 - 29.7° and 2θ a4 Diffraction characteristic peaks exist at = 30.2 - 30.9°; the iron phosphate precursor shows diffraction characteristic peaks at 2θ b1 = 20 - 20.7°, 2θ b2 = 21.5 - 22.2°, 2θ b3 = 23.4 - 24°, 2θ b4 Diffraction characteristic peaks exist at = 25.5 - 26.2°;

[0078] In the iron phosphate precursor, the integral area A(2θ ai ) of the diffraction characteristic peak at 2θ ai and the integral area A(2θ bj ) of the diffraction characteristic peak at 2θ bj satisfy:

[0079] where i is an integer from 1 to 4 and j is an integer from 1 to 4.

[0080] In the present invention, by using a precursor material with a specific XRD structure, the structure of the iron phosphate precursor has certain defects, which can act as a flux during the sintering process of the precursor, reducing the sintering temperature while increasing the tap density of the prepared lithium iron phosphate cathode material.

[0081] Furthermore, in the iron phosphate precursor,

[0082] According to the present invention, the lattice parameters of the a-axis and c-axis of the iron phosphate precursor measured by XRD satisfy: 2.2306 ≤ c / a ≤ 2.2330.

[0083] In the present invention, selecting an iron phosphate precursor with the above specific c / a value of the lattice parameter can achieve a higher tap density at a lower temperature while reducing the content of iron phosphide in lithium iron phosphate, thereby improving the capacity and energy density of the cathode material prepared from the precursor, reducing side reactions with the electrolyte, and improving the service life and safety of the battery.

[0084] In the present invention, the crystal structure of the iron phosphate precursor is hexagonal system with the space group of P3121.

[0085] In the present invention, the point group structure of the iron phosphate precursor shows an equivalent arrangement on the a-axis and b-axis. The c-axis is the upright crystal axis.

[0086] In the present invention, the unit cell parameters of the a-axis and c-axis of the iron phosphate precursor measured by XRD satisfy: 2.2306 ≤ c / a ≤ 2.2330. For example, it can be 2.2306, 2.2307, 2.2308, 2.2309, 2.231, 2.2311, 2.2312, 2.2313, 2.2314, 2.2315, 2.2316, 2.2317, 2.2318, 2.2319, 2.232, 2.2321, 2.2322, 2.2323, 2.2324, 2.2325, 2.2326, 2.2327, 2.2328, 2.2329, 2.2330, and the ranges composed of any two values. Preferably, 2.231 ≤ c / a ≤ 2.2326.

[0087] According to the present invention, the iron phosphate precursor has the composition shown in Formula II:

[0088] (Fe 1-y M y PO4) 1-6x [Fe4(P2O7)3] x Formula II,

[0089] where 0.01 ≤ x ≤ 0.03, 0 ≤ y ≤ 0.1, and M is selected from at least one of Al, Mg, Ca, Sr, V, Cr, Y, Mo, Nb, W, La, Sm, Co, Ni, Cu, Zn, Zr, and Ti.

[0090] Further, 0.01 ≤ x ≤ 0.02, 0 < y ≤ 0.05, and M is selected from at least one of Al, Mg, Co, Ni, Cu, Zn, Zr, and Ti.

[0091] According to the present invention, in the iron phosphate precursor, the molar ratio of the metal element to the phosphorus element n(Me) / n(P) is 0.96 - 0.98.

[0092] In the present invention, when the molar ratio of the metal element to the phosphorus element in the iron phosphate precursor satisfies the above range, the precursor has certain structural defects, and the excessive phosphorus acts as a flux, which can reduce the sintering temperature and improve the tap density of the prepared lithium iron phosphate cathode material.

[0093] Further, in the iron phosphate precursor, the molar ratio of the metal element to the phosphorus element n(Me) / n(P) is 0.96 - 0.97.

[0094] According to the present invention, the median particle size D of the iron phosphate precursor 50 is 1 - 25 μm.

[0095] In the present invention, when the median particle size of the iron phosphate precursor meets the above range, it is beneficial to improve the grinding efficiency during the preparation of the cathode material and reduce energy consumption.

[0096] In the present invention, the median particle size D of the iron phosphate precursor 50 is 1 - 25 μm. For example, it can be 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, 21 μm, 22 μm, 23 μm, 24 μm, 15 μm, and the range composed of any two values. Preferably, the median particle size D of the iron phosphate precursor 50 is 2 - 20 μm.

[0097] According to the present invention, the primary particle size of the iron phosphate precursor is 20 - 200 nm.

[0098] In the present invention, when the primary particle size of the iron phosphate precursor meets the above range, the primary particles are uniform and dense, which is beneficial to obtaining a high - tap - density lithium iron phosphate cathode material.

[0099] In the present invention, the primary particle size of the iron phosphate precursor is 20 - 200 nm. For example, it can be 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, 55 nm, 60 nm, 65 nm, 70 nm, 80 nm, 85 nm, 90 nm, 95 nm, 100 nm, 110 nm, 120 nm, 130 nm, 140 nm, 150 nm, 160 nm, 170 nm, 180 nm, 190 nm, 200 nm, and the range composed of any two values. Preferably, the primary particle size of the iron phosphate precursor is 50 - 150 nm.

[0100] According to the present invention, the tap density of the iron phosphate precursor is 0.8 - 1.3 g / cm 3 .

[0101] In the present invention, when the tap density of the iron phosphate precursor meets the above range, it indicates that the precursor has a high density, which is beneficial to further improving the tap density of the lithium iron phosphate cathode material.

[0102] In the present invention, the tap density of the iron phosphate precursor is 0.8 - 1.3 g / cm 3 , for example, it can be 0.8 g / cm 3 , 0.81 g / cm 3 , 0.82 g / cm 3 , 0.83 g / cm 3 , 0.84 g / cm3 , 0.85 g / cm 3 , 0.86 g / cm 3 , 0.87 g / cm 3 , 0.88 g / cm 3 , 0.89 g / cm 3 , 0.9 g / cm 3 , 0.91 g / cm 3 , 0.92 g / cm 3 , 0.93 g / cm 3 , 0.94 g / cm 3 , 0.95 g / cm 3 , 0.96 g / cm 3 , 0.97 g / cm 3 , 0.98 g / cm 3 , 0.99 g / cm 3 , 1 g / cm 3 , 1.11 g / cm 3 , 1.12 g / cm 3 , 1.13 g / cm 3 , 1.14 g / cm 3 , 1.15 g / cm 3 , 1.16 g / cm 3 , 1.17 g / cm 3 , 1.18 g / cm 3 , 1.19 g / cm 3 , 1.2 g / cm 3 , 1.21 g / cm 3 , 1.22 g / cm 3 , 1.23 g / cm 3 , 1.24 g / cm 3 , 1.25 g / cm 3 , 1.26 g / cm 3 , 1.27 g / cm 3 , 1.28 g / cm 3 , 1.29 g / cm 3 , 1.3 g / cm 3 , and a range composed of any two values. Preferably, the tapped density of the iron phosphate precursor is 0.9 - 1.2 g / cm 3 .

[0103] According to the present invention, the specific surface area of the iron phosphate precursor is 6 - 10 m 2 / g.

[0104] In the present invention, when the specific surface area of the iron phosphate precursor satisfies the above range, the precursor has a high reaction activity. When preparing the lithium iron phosphate cathode material therefrom, it is beneficial to the diffusion of lithium ions and improves the charge and discharge capacity.

[0105] In the present invention, the specific surface area of the iron phosphate precursor is 6-10 m 2 / g, and can be, for example, 6 m 2 / g, 6.1 m 2 / g, 6.2 m 2 / g, 6.3 m 2 / g, 6.4 m 2 / g, 6.5 m 2 / g, 6.6 m 2 / g, 6.7 m 2 / g, 6.8 m 2 / g, 6.9 m 2 / g, 7 m 2 / g, 7.1 m 2 / g, 7.2 m 2 / g, 7.3 m 2 / g, 7.4 m 2 / g, 7.5 m 2 / g, 7.6 m 2 / g, 7.7 m 2 / g, 7.8 m 2 / g, 7.9 m 2 / g, 8 m 2 / g, 8.1 m 2 / g, 8.2 m 2 / g, 8.3 m 2 / g, 8.4 m 2 / g, 8.5 m 2 / g, 8.6 m 2 / g, 8.7 m 2 / g, 8.8 m 2 / g, 8.9 m 2 / g, 9 m 2 / g, 9.1 m 2 / g, 9.2 m 2 / g, 9.3 m 2 / g, 9.4 m 2 / g, 9.5 m 2 / g, 9.6 m 2 / g, 9.7 m 2 / g, 9.8 m 2 / g, 9.9 m 2 / g, 10 m 2 / g, and the range composed of any two values. Preferably, the specific surface area of the iron phosphate precursor is 6.5-9.5 m2 / g.

[0106] According to the present invention, the content of sulfur in the iron phosphate precursor is ≤ 400 ppm.

[0107] In the present invention, when the content of sulfur in the iron phosphate precursor meets the above range, lattice distortion caused by impurity ions can be effectively avoided, and the low-temperature performance and cycle performance of the positive electrode material prepared therefrom can be improved.

[0108] In the present invention, the content of sulfur in the iron phosphate precursor is ≤ 400 ppm, and can be, for example, 400 ppm, 350 ppm, 300 ppm, 250 ppm, 200 ppm, 150 ppm, 100 ppm, 50 ppm, 40 ppm, 30 ppm, 25 ppm, 20 ppm, 15 ppm, 10 ppm, 5 ppm, 0 ppm, and the ranges composed of any two values. Preferably, the content of sulfur in the iron phosphate precursor is ≤ 200 ppm.

[0109] In the present invention, there is no particular limitation on the source of the iron phosphate precursor, as long as the iron phosphate precursor has the structural features defined in the present invention.

[0110] In order to further ensure and improve the electrochemical performance of the lithium iron phosphate positive electrode material, preferably, the iron phosphate precursor of the present invention is prepared according to the following steps:

[0111] S1. Dissolve an iron source and an M source in water to form a mixed salt solution A1;

[0112] S2. Dissolve a phosphorus source in water, add a pH regulator to form a phosphorus source solution A2;

[0113] S3. Mix the mixed salt solution A1, the phosphorus source solution A2, and an oxidant A3, and carry out a synthesis reaction, and optionally add an auxiliary agent;

[0114] S4. Filter and wash the product of step S3 to obtain a filter cake B1. Pulp the filter cake, and after obtaining a slurry, optionally add an auxiliary agent, adjust the pH value, carry out an aging and crystal transformation reaction, and then filter and wash to obtain a filter cake B3;

[0115] S5. Calcinate the filter cake to obtain an iron phosphate precursor;

[0116] Among them, the pH value of the phosphorus source solution A2 is 0.5 - 2.5;

[0117] The conditions of the aging and crystal transformation reaction include: the reaction temperature is 70 - 90 °C, the heating rate is 1 - 3 °C / min, and the reaction time is 1 - 3 h;

[0118] The calcination conditions include: the calcination temperature is 500 - 800 °C, the heating rate is 3 - 8 °C / min, and the calcination time is 2 - 4 h.

[0119] In the present invention, by controlling the pH value of the phosphorus source solution, the aging and crystal transformation reaction, and the calcination conditions, the prepared iron phosphate precursor simultaneously includes an iron phosphate phase and an iron pyrophosphate phase, and the diffraction intensity of the characteristic peaks of the iron pyrophosphate phase and the iron phosphate phase, as well as the unit cell parameters of the iron phosphate precursor, satisfy a specific range. Specifically, when the iron phosphate precursor described in the first aspect of the present invention is used to prepare a lithium iron phosphate cathode material, it can reduce the sintering temperature while increasing the tap density of the lithium iron phosphate cathode material.

[0120] Specifically, the pH value of the phosphorus source solution is controlled to regulate the oxidation precipitation reaction to generate amorphous iron phosphate; then, the aging temperature, heating rate, and aging time in the aging and crystal transformation stage are regulated to complete the crystal transformation reaction from amorphous iron phosphate to iron phosphate dihydrate, realizing the regulation of the crystallinity and unit cell parameters of iron phosphate dihydrate; finally, the calcination temperature, heating rate, and calcination time in the calcination stage are regulated to complete the dehydration and crystal transformation reaction from iron phosphate dihydrate to anhydrous iron phosphate, controlling the doping of iron pyrophosphate in the iron phosphate, and realizing the regulation of the crystallinity and unit cell parameters of anhydrous iron phosphate.

[0121] In the present invention, there are no specific limitations on the mixing method of the mixed salt solution A1, the phosphorus source solution A2, and the oxidant A3, nor on the timing of adding the auxiliary agent, as long as the mixed salt solution A1, the phosphorus source solution A2, and the antioxidant A3 can be fully mixed evenly, or the aging and crystal transformation reaction can be carried out optionally in the presence of the auxiliary agent.

[0122] In a specific embodiment of the present invention, the mixed salt solution A1, the phosphorus source solution A2, and the oxidant A3 are added to the reaction kettle in a co-current manner for the synthesis reaction.

[0123] In a specific embodiment of the present invention, first, the mixed salt solution A1 and the oxidant A3 are fully reacted, and then they are added to the reaction kettle in a co-current manner with the phosphorus source solution A2 for the synthesis reaction.

[0124] In a specific embodiment of the present invention, the mixed salt solution A1 is used as the bottom liquid, and the phosphorus source solution A2 and the oxidant A3 are added to the reaction kettle in a co-current manner for the synthesis reaction.

[0125] In the present invention, the pH value of the phosphorus source solution A2 is 0.5 - 2.5, for example, it can be 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, 2.1, 2.2, 2.3, 2.4, 2.5, and the range composed of any two values. In a preferred embodiment of the present invention, the pH value of the phosphorus source solution A2 is 1 - 2.

[0126] In the present invention, the conditions of the aging and crystal transformation reaction include: the reaction temperature is 70 - 90 °C, for example, it can be 70 °C, 75 °C, 80 °C, 85 °C, 90 °C, and the range composed of any two values; the heating rate is 1 - 3 °C / min, for example, it can be 1 °C / min, 1.5 °C / min, 2 °C / min, 2.5 °C / min, 3 °C / min, and the range composed of any two values; the reaction time is 1 - 3 h, for example, it can be 1 h, 1.5 h, 2 h, 2.5 h, 3 h, and the range composed of any two values. In a preferred embodiment of the present invention, the conditions of the aging and crystal transformation reaction include: the reaction temperature is 80 - 85 °C, the heating rate is 2 - 3 °C / min, and the reaction time is 1 - 2 h.

[0127] In the present invention, the conditions of the calcination include: the calcination temperature is 500 - 800 °C, for example, it can be 500 °C, 550 °C, 600 °C, 650 °C, 700 °C, 750 °C, 800 °C, and the range composed of any two values; the heating rate is 3 - 8 °C / min, for example, it can be 3 °C / min, 3.5 °C / min, 4 °C / min, 4.5 °C / min, 5 °C / min, 5.5 °C / min, 6 °C / min, 6.5 °C / min, 7 °C / min, 7.5 °C / min, 8 °C / min, and the range composed of any two values; the calcination time is 2 - 4 h, for example, it can be 2 h, 2.5 h, 3 h, 3.5 h, 4 h, and the range composed of any two values. In a preferred embodiment of the present invention, the conditions of the calcination include: the calcination temperature is 600 - 750 °C, the heating rate is 3 - 5 °C / min, and the calcination time is 2 - 3 h;

[0128] According to the present invention, in step (4), the pH value is adjusted to 1 - 2.5, for example, it can be 1, 1.5, 2, 2.5, and the range composed of any two values, preferably to 1 - 2.

[0129] In the present invention, for step (4), there is no particular limitation on the way to adjust the pH value. In order not to introduce impurities, preferably, phosphoric acid is added to adjust the pH value.

[0130] According to the present invention, in step (1), the concentration of the mixed salt solution A1 is 0.1 - 4 mol / L, for example, it can be 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L, 3 mol / L, 3.5 mol / L, 4 mol / L, and the range composed of any two values, and preferably 0.2 - 2 mol / L.

[0131] In the present invention, no specific limitation is imposed on the type of the iron source. The iron source includes but is not limited to divalent iron salts. Preferably, the divalent iron salt is selected from at least one of ferrous sulfate, ferrous chloride, ferrous nitrate, and ferrous acetate.

[0132] In the present invention, no specific limitation is imposed on the type of the M source. The M source is a compound capable of providing M element selected from at least one of Mn, Al, Mg, Co, Ni, Cu, Zn, Zr, and Ti, including but not limited to oxides containing M, salts containing M, etc.

[0133] In the present invention, in step S1, the iron source and the M source satisfy 0 ≤ n(M) / [n(Fe) + n(M)] ≤ 0.1, and preferably, 0 < n(M) / [n(Fe) + n(M)] ≤ 0.05.

[0134] In the present invention, the concentration of the phosphorus source solution A2 is 0.2 - 20 mol / L, for example, it can be 0.2 mol / L, 0.4 mol / L, 0.6 mol / L, 0.8 mol / L, 1 mol / L, 1.2 mol / L, 1.4 mol / L, 1.6 mol / L, 1.8 mol / L, 2 mol / L, 3 mol / L, 4 mol / L, 5 mol / L, 6 mol / L, 7 mol / L, 8 mol / L, 9 mol / L, 10 mol / L, 11 mol / L, 12 mol / L, 13 mol / L, 14 mol / L, 15 mol / L, 16 mol / L, 17 mol / L, 18 mol / L, 19 mol / L, 20 mol / L, and the range composed of any two values, and preferably 1 - 15 mol / L.

[0135] In the present invention, no specific limitation is imposed on the type of the phosphorus source. The phosphorus source includes but is not limited to at least one of phosphoric acid, sodium dihydrogen phosphate, disodium hydrogen phosphate, ammonium dihydrogen phosphate, and diammonium hydrogen phosphate. Preferably, the phosphorus source is selected from at least one of phosphoric acid, sodium dihydrogen phosphate, and ammonium dihydrogen phosphate.

[0136] In the present invention, the type of the pH regulator is not specifically limited, and its function is to adjust the pH of the solution. The pH regulator is an acid solution or an alkali solution. Preferably, the pH regulator is selected from at least one of sodium hydroxide, ammonia water, sulfuric acid, hydrochloric acid and nitric acid.

[0137] In the present invention, in step S3, the dosages of the mixed salt solution A1 and the phosphorus source solution A2 are such that n(P):n(Fe) is 1-3:1, preferably 1-1.5:1.

[0138] In the present invention, in step S3, the dosages of the mixed salt solution A1 and the oxidant A3 are such that n(oxidant):n(Fe) is 1-5:1, preferably 1-3:1.

[0139] In the present invention, the type of the oxidant is not specifically limited. The oxidant includes but is not limited to hydrogen peroxide, ozone, sodium persulfate, ammonium persulfate, sodium hypochlorite, sodium ferrate. Preferably, the oxidant is selected from at least one of hydrogen peroxide, sodium persulfate and ammonium persulfate.

[0140] In the present invention, the conditions of the synthesis reaction include: the reaction temperature is 25-60 °C, for example, it can be 25 °C, 30 °C, 35 °C, 40 °C, 45 °C, 50 °C, 55 °C, 60 °C, and the range composed of any two values; the reaction time is 1-6 h, for example, it can be 1 h, 1.5 h, 2 h, 2.5 h, 3 h, 3.5 h, 4 h, 4.5 h, 5 h, 5.5 h, 6 h, and the range composed of any two values.

[0141] Further, the conditions of the synthesis reaction include: the reaction temperature is 40-60 °C, and the reaction time is 1-3 h.

[0142] In the present invention, during the preparation process of the iron phosphate precursor, adding an auxiliary agent in the aging and crystal transformation stage or the synthesis reaction stage can induce the deposition and arrangement of crystal nuclei, make the secondary particles of the precursor denser, and at the same time can help remove sulfur impurities in the crystal lattice, thereby affecting the unit cell parameters.

[0143] In the present invention, the auxiliary agent is selected from at least one of sodium hexadecyl benzene sulfonate, sodium dodecyl benzene sulfonate, triethanolamine, ethylene glycol, polyvinyl pyrrolidone, polyethylene glycol, wood cellulose and carboxymethyl cellulose. Preferably, the auxiliary agent is selected from at least one of sodium hexadecyl benzene sulfonate, polyethylene glycol, wood cellulose and carboxymethyl cellulose.

[0144] In the present invention, based on the total amount of the iron source and the M source, the dosage of the auxiliary agent is 0.1 wt% - 1 wt%, for example, it can be 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%, 0.6 wt%, 0.7 wt%, 0.8 wt%, 0.9 wt%, 1 wt%, and the range composed of any two values, and preferably 0.1 wt% - 0.5 wt%.

[0145] In the present invention, when the dosage of the auxiliary agent is controlled to meet the above range, it can induce the deposition and arrangement of crystal nuclei, make the secondary particles denser, and at the same time help to remove sulfur impurities in the lattice, thereby further modulating the unit cell parameters in the precursor.

[0146] In the present invention, there is no special requirement for the washing method in step S4, and it can be carried out according to the conventional washing method in the art. Preferably, a washing liquid is used, preferably pure water at 20 - 90 °C, and more preferably pure water at 30 - 60 °C for washing.

[0147] According to the present invention, the dosages of the iron phosphate precursor, the lithium source, the metal source M, and the Mn source are such that:

[0148] n(Li):n(Fe):n(M):n(Mn) = 1 + a:b:c:d, where -0.1 ≤ a ≤ 0.1, 0 ≤ b ≤ 1, 0 ≤ c ≤ 0.5, 0 ≤ d ≤ 1.

[0149] In the present invention, there is no particular limitation on the specific dosage of the metal source M, as long as the dosages of the metal source M and the iron phosphate precursor are such that the content c of the M element in the cathode material satisfies 0 ≤ c ≤ 0.5.

[0150] Further, the dosages of the iron phosphate precursor, the lithium source, the metal source M, and the Mn source are such that:

[0151] n(Li):n(Fe):n(M):n(Mn) = 1 + a:b:c:d, where -0.05 ≤ a ≤ 0.05, 0.5 ≤ b ≤ 1, 0.001 ≤ c ≤ 0.1, 0 ≤ d ≤ 0.5.

[0152] According to the present invention, based on the total mass of the iron phosphate precursor, the dosage of the carbon source is 8 wt% - 18 wt%, for example, it can be 8 wt%, 9 wt%, 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt%, 15 wt%, 16 wt%, 17 wt%, 18 wt%, and the range composed of any two values, and preferably 10 wt% - 15 wt%.

[0153] In the present invention, the type of the liquid medium is not specifically limited as long as a uniform slurry can be formed. For example, the liquid medium is selected from at least one of water, methanol, ethanol, propanol, ethylene glycol, isopropanol, benzyl alcohol, acetone, benzene, toluene, methyl ether, ethyl ether, acetic acid, xylene, tetrahydrofuran, dimethyl carbonate, N-methylpyrrolidone, propylene carbonate, triethylamine, triethanolamine, N,N-dimethylformamide, N,N-diethylformamide, acetonitrile and ethylene glycol dimethyl ether. The amount of the liquid medium is also not specifically limited as long as a uniform slurry can be formed.

[0154] In the present invention, the type of the lithium source is not particularly limited. For example, the lithium source is selected from at least one of lithium oxide, lithium hydroxide, lithium chloride, lithium nitrate, lithium nitrite, lithium formate, lithium acetate, lithium oxalate, lithium carbonate, lithium phosphate, lithium hydrogen phosphate and lithium dihydrogen phosphate. Preferably, the lithium source is selected from at least one of lithium hydroxide, lithium carbonate and lithium dihydrogen phosphate.

[0155] In the present invention, the type of the carbon source is not particularly limited. For example, the carbon source is selected from at least one of glucose, sucrose, fructose, cellulose, starch, citric acid, polyacrylic acid, phenolic resin, polyethylene glycol, dopamine, graphene and carbon nanotubes. Preferably, the carbon source is selected from at least one of glucose, sucrose, starch, graphene and polyethylene glycol.

[0156] In the present invention, the type of the metal source M is not particularly limited as long as a compound capable of providing element M can be provided. For example, the metal source M is selected from at least one of oxalate, nitrate, acetate, oxide, hydroxide, carbonate, phosphate, metal cluster, metal complex and carboxylate capable of providing element M.

[0157] In the present invention, the type of the Mn source is not particularly limited. For example, the Mn source is selected from at least one of manganese sulfate, manganese nitrate, manganese acetate, manganese chloride and manganese oxide.

[0158] In the present invention, the grinding method and conditions are not particularly limited as long as the mixture of the iron phosphate precursor, lithium source, carbon source, Mn source, metal source M and the liquid medium can be sufficiently ground so that the median particle size D of the ground slurry 50 is 50 - 2000 nm, preferably 100 - 1000 nm.

[0159] In a specific embodiment of the present invention, the grinding conditions include: ball milling at a speed of 100 - 600 rpm for 1 - 24 h using a planetary ball mill; and / or ball milling at a speed of 300 - 3000 rpm for 0.5 - 10 h using a stirred mill and / or a sand mill.

[0160] According to the present invention, the solid content of the slurry is 10-70 wt%, preferably 20-60 wt%.

[0161] According to the present invention, the drying method is spray drying.

[0162] According to the present invention, the conditions of the spray drying include: the inlet air temperature is 190-280 °C, and the outlet air temperature is 60-120 °C.

[0163] Further, the conditions of the spray drying include: the inlet air temperature is 200-270 °C, and the outlet air temperature is 70-110 °C.

[0164] In the present invention, in step (1), the median particle size D of the spray-dried material 50 is 5-50 μm, preferably 8-40 μm; the specific surface area is 5-15 m 2 / g, preferably 8-13 m 2 / g; the apparent density is 0.3-1 g / cm 3 , preferably 0.5-0.8 g / cm 3 ; the moisture content ≤ 5%, preferably ≤ 3%.

[0165] According to the present invention, in step (2), the conditions of the calcination treatment include: the calcination temperature is 500-900 °C, for example, it can be 500 °C, 550 °C, 600 °C, 650 °C, 700 °C, 750 °C, 800 °C, 850 °C, 900 °C, and the range composed of any two values; the calcination time is 4-20 h, for example, it can be 4 h, 5 h, 6 h, 7 h, 8 h, 9 h, 10 h, 11 h, 12 h, 13 h, 14 h, 15 h, 16 h, 17 h, 18 h, 19 h, 20 h, and the range composed of any two values.

[0166] In the present invention, under the above conditions, the calcination treatment can make the prepared cathode material particles uniform and round in size, and the carbon coating layer has a moderate thickness, further improving the electronic conductivity and processing performance of the cathode material.

[0167] Further, in step (2), the conditions of the calcination treatment include: the calcination temperature is 600-800 °C; the calcination time is 6-15 h.

[0168] In the present invention, the protective atmosphere is selected from nitrogen and / or argon.

[0169] In the present invention, in step (3), the comminution equipment is selected from a jet mill and / or a mechanical grinder.

[0170] The third aspect of the present invention provides a lithium iron phosphate cathode material prepared by the above preparation method.

[0171] In the fourth aspect of the present invention, a lithium-ion battery is provided, wherein the lithium-ion battery pack includes the above-mentioned lithium iron phosphate cathode material.

[0172] In the present invention, when the above-mentioned lithium iron phosphate cathode material is applied to a lithium-ion battery, it can effectively improve the electrochemical performance of the lithium-ion battery, showing higher capacity, energy efficiency, lower internal resistance, and better cycling performance.

[0173] In the present invention, the lithium-ion battery prepared with the lithium iron phosphate cathode material has a 0.1C capacity ≥ 158 mAh / g, preferably ≥ 160 mAh / g.

[0174] In the present invention, the lithium-ion battery prepared with the lithium iron phosphate cathode material has a 0.5C capacity ≥ 151 mAh / g, preferably ≥ 152 mAh / g.

[0175] In the present invention, the lithium-ion battery prepared with the lithium iron phosphate cathode material has a 1C capacity ≥ 143.5 mAh / g, preferably ≥ 145.5 mAh / g.

[0176] In the present invention, the lithium-ion battery prepared with the lithium iron phosphate cathode material has a 1C @ 200-week cycling capacity retention rate ≥ 97%.

[0177] In the present invention, the lithium-ion battery prepared with the lithium iron phosphate cathode material has a first-week energy efficiency ≥ 90%, preferably ≥ 91%.

[0178] The present invention will be described in detail below through examples. In the following examples,

[0179] The crystallographic properties such as the unit cell parameters of the iron phosphate precursor were measured by a Rigaku SmartLab X-ray diffractometer. The voltage was set at 40 kV, the current at 40 mA, the step size at 0.005°, the height-limiting slit at 10 mm, the divergence slit at 1 / 2°, the anti-scattering slit at 8 mm, the receiving slit open, and the test scanning 2θ angle was set from 10° to 80°, continuously scanned in 1D mode at a scanning speed of 1.2° / min.

[0180] The contents of various elements in the iron phosphate precursor and the lithium iron phosphate cathode material were measured by an Agilent 5800 ICP-OES spectrometer. The argon partial pressure gauge was controlled at 80 - 100 psi, the liquid argon booster valve compressed the control pressure above 200 psi, nitrogen was 60 - 100 psi, and compressed air was 80 - 100 psi; when making the standard curve, three-point calibration was required according to the concentration of the sample, and the coefficient of the standard curve was above 0.9999.

[0181] The median particle size of the iron phosphate precursor and the lithium iron phosphate cathode material was tested using a Malvern laser particle size analyzer Mastersizer 3000. A certain amount of sodium pyrophosphate dispersant was added, and the sample was added until the obscuration was in the range of 10%-20%. After ultrasonic treatment for 3 minutes, the test was started, and the average value of three tests was taken as the measured value of the median particle size.

[0182] The primary particle size of the iron phosphate precursor was tested using a scanning electron microscope of model S-4800 from HITACHI, Japan. The test voltage was 1 kV - 5 kV, and the test magnification was 1 k - 30 k.

[0183] The tapped density of the iron phosphate precursor material was tested using a tapped density tester of model BT-30 from Becton Dickinson. The number of vibrations was set to 3000 times, and the vibration frequency was 250 times / min.

[0184] The specific surface area of the iron phosphate precursor and the lithium iron phosphate cathode material was tested using a specific surface area analyzer of model Tristar II 3020 from Micromertics, USA. The degassing temperature was set to 300 °C, and the degassing time was 120 min.

[0185] The tap density of the lithium iron phosphate cathode material was measured using a tap density meter of model MCP-PD51 from Mitsubishi Chemical, Japan. 1 ± 0.01 g of the sample was weighed, and a pressure of 3 T was selected for the test.

[0186] The volume resistivity of the lithium iron phosphate cathode material was tested using a powder compaction resistance meter of model MCP-PD51 from Mitsubishi Chemical, Japan. The four-probe method was used to measure the volume resistivity under a pressure of 20 kN.

[0187] The raw materials used in the examples and comparative examples were all commercially available products.

[0188] Preparation Example - Preparation of Iron Phosphate Precursor

[0189] Preparation Example 1

[0190] S1. According to the molar ratio of n(Fe):n(Ti) = 0.99:0.01, a certain mass of ferrous sulfate and titanium oxysulfate were weighed and dissolved in deionized water to prepare a 2 mol / L mixed salt solution A1.

[0191] S2. A certain mass of concentrated phosphoric acid was weighed, and the pH of the solution was adjusted to 2 with 30% sodium hydroxide to prepare a 2 mol / L phosphorus source solution A2.

[0192] S3. A certain amount of the mixed salt solution A1, the phosphorus source solution A2, and 30% hydrogen peroxide A3 were added in parallel to the reaction kettle for a synthesis reaction. The reaction temperature was 40 °C, and the reaction time was 1 h.

[0193] S4. After the reaction is completed, filter and wash the reaction slurry to obtain a filter cake. Pulp the filter cake, add the obtained slurry to a reaction kettle, add 0.1 wt% of lignocellulose based on the total mass of ferrous sulfate and titanyl sulfate, add phosphoric acid to adjust the pH to 1.5, control the heating rate at 2 °C / min, the aging temperature at 82 °C, and the aging time at 2 h. After the reaction is completed, filter and wash the reaction slurry to obtain a filter cake.

[0194] S5. Calcinate the filter cake at high temperature for dehydration, control the heating rate at 3 °C / min, the calcination temperature at 700 °C, and the calcination time at 3 h to obtain an anhydrous iron phosphate precursor P1. Its composition is (Fe 0.99 Ti 0.01 PO4) 0.91 [Fe4(P2O7)3] 0.015 , where x = 0.015 and y = 0.01.

[0195] Figure 1 is the XRD pattern of the iron phosphate precursor P1. It can be seen from Figure 1 that the precursor material has diffraction characteristic peaks at 2θ a1 = 16.2 - 16.9°, 2θ a2 = 27.3 - 28.1°, 2θ a3 = 29.0 - 29.7° and 2θ a4 = 30.2 - 30.9°. There are characteristic peaks at 2θ b1 = 20 - 20.7°, 2θ b2 = 21.5 - 22.2°, 2θ b3 = 23.4 - 24°, 2θ b4 = 25.5 - 26.2°. It is speculated that the iron phosphate precursor contains a ferric pyrophosphate phase. Through calculation, it is found that

[0196] Figure 2 is the SEM image of the iron phosphate precursor P1. It can be seen from Figure 2 that the primary particles are uniform and dense, and the difference between particles is reduced during the calcination stage, which can effectively improve the tap density of the cathode material.

[0197] Preparation Example 2

[0198] S1. The same as Preparation Example 1.

[0199] S2. The same as Preparation Example 1.

[0200] S3. The same as Preparation Example 1.

[0201] S4. The same as Preparation Example 1.

[0202] S5. Calcinate the filter cake at high temperature for dehydration, control the heating rate at 5 °C / min, the calcination temperature at 650 °C, and the calcination time at 2 h to obtain anhydrous iron phosphate P2. Its composition is: (Fe 0.99 Ti 0.01 PO4) 0.886 [Fe4(P2O7)3] 0.019 , where x = 0.019 and y = 0.01.

[0203] Preparation Example 3

[0204] S1. The same as Preparation Example 1.

[0205] S2. The same as Preparation Example 1.

[0206] S3. The same as Preparation Example 1.

[0207] S4. After the reaction is completed, filter and wash the reaction slurry to obtain a filter cake. Pulverize the filter cake, add the obtained slurry to the reaction kettle, add 0.1 wt% of lignocellulose based on the total mass of ferrous sulfate and titanyl sulfate, adjust the pH to 1.5 with phosphoric acid, control the heating rate at 3 °C / min, the aging temperature at 80 °C, and the aging time at 1 h. After the reaction is completed, filter and wash the reaction slurry to obtain a filter cake.

[0208] S5. The same as Example 1 to obtain anhydrous iron phosphate precursor P3. Its composition is: (Fe 0.99 Ti 0.01 PO4) 0.904 [Fe4(P2O7)3] 0.016 , where x = 0.016 and y = 0.01.

[0209] Preparation Example 4

[0210] S1. The same as Preparation Example 1.

[0211] S2. Weigh a certain mass of concentrated phosphoric acid, add sodium hydroxide with a concentration of 30% to adjust the pH of the solution to 1.5, and prepare a 2 mol / L phosphorus source solution.

[0212] S3. The same as Preparation Example 1.

[0213] S4. The same as Preparation Example 1.

[0214] S5. The same as Preparation Example 1. Obtain anhydrous iron phosphate precursor P4. Its composition is: (Fe 0.99 Ti 0.01 PO4) 0.898 [Fe4(P2O7)3] 0.017 , where x = 0.017 and y = 0.01.

[0215] Preparation Example 5

[0216] S1. The same as Preparation Example 1.

[0217] S2. Weigh a certain mass of ammonium dihydrogen phosphate, dissolve it in deionized water, add dilute sulfuric acid with a concentration of 30% to adjust the pH of the solution to 2, and prepare a 2 mol / L phosphorus source solution.

[0218] S3. The same as Preparation Example 1.

[0219] S4. The same as Preparation Example 1.

[0220] S5. The same as Preparation Example 1 to obtain an anhydrous iron phosphate precursor P5. Its composition is: (Fe 0.99 Ti 0.01 PO4) 0.91 [Fe4(P2O7)3] 0.015 , where x = 0.015 and y = 0.01.

[0221] Preparation Example 6

[0222] S1. The same as Preparation Example 1.

[0223] S2. Weigh a certain mass of ammonium dihydrogen phosphate, dissolve it in deionized water, add dilute sulfuric acid with a concentration of 30% to adjust the pH of the solution to 2, and prepare a 2 mol / L phosphorus source solution.

[0224] S3. The same as Preparation Example 1.

[0225] S4. After the reaction, add 0.1 wt% of lignocellulose based on the total mass of ferrous sulfate and titanyl sulfate, add phosphoric acid to adjust the pH to 1.5, control the heating rate at 2 °C / min, the aging temperature at 82 °C, and the aging time at 2 h. After the reaction, filter and wash the reaction slurry to obtain a filter cake. S5. The same as Example 1 to obtain an anhydrous iron phosphate precursor P6. Its composition is: (Fe 0.99 Ti 0.01 PO4) 0.91 [Fe4(P2O7)3] 0.015 , where x = 0.015 and y = 0.01.

[0226] Preparation Example 7

[0227] S1. Weigh a certain mass of ferrous sulfate and dissolve it in deionized water to prepare a 2 mol / L salt solution.

[0228] S2. The same as Preparation Example 1.

[0229] S3. The same as Preparation Example 1.

[0230] S4: The same as Preparation Example 1.

[0231] S5: The same as Preparation Example 1 to obtain an anhydrous iron phosphate precursor P7. Its composition is: (FePO4) 0.88 [Fe4(P2O7)3] 0.02 , where x = 0.02 and y = 0.

[0232] Comparative Preparation Example 1

[0233] S1: The same as Preparation Example 1.

[0234] S2: The same as Preparation Example 1.

[0235] S3: The same as Preparation Example 1.

[0236] S4: The same as Preparation Example 1.

[0237] S5: The filter cake is calcined at high temperature for dehydration, controlling the heating rate at 2 °C / min, the calcination temperature at 850 °C, and the calcination time at 5 h to obtain an anhydrous iron phosphate precursor DP1. Its composition is: (Fe 0.99 Ti 0.01 PO4) 0.958 [Fe4(P2O7)3] 0.007 , where x = 0.007 and y = 0.01.

[0238] Comparative Preparation Example 2

[0239] S1: The same as Preparation Example 1.

[0240] S2: The same as Preparation Example 1.

[0241] S3: The same as Preparation Example 1.

[0242] S4: After the reaction is completed, the reaction slurry is filtered and washed to obtain a filter cake. The filter cake is slurried, and the resulting slurry is added to a reaction kettle. Wood cellulose is added, and phosphoric acid is added to adjust the pH to 1.5. The heating rate is controlled at 0.5 °C / min, the aging temperature is 95 °C, and the aging time is 4 h. After the reaction is completed, the reaction slurry is filtered and washed to obtain a filter cake..

[0243] S5: The same as Preparation Example 1 to obtain an anhydrous iron phosphate precursor DP2. Its composition is: (Fe 0.99 Ti 0.01 PO4) 0.946 [Fe4(P2O7)3] 0.009 , where x = 0.009 and y = 0.01.

[0244] Comparative Preparation Example 3

[0245] S1: The same as Preparation Example 1.

[0246] S2. Similar to Preparation Example 1, except that a certain mass of concentrated phosphoric acid was weighed, and the pH of the solution was adjusted to 3 with 30% sodium hydroxide, and a 2 mol / L phosphorus source solution was prepared.

[0247] S3. The same as Preparation Example 1.

[0248] S4. The same as Preparation Example 1.

[0249] S5. The filter cake was calcined at high temperature for dehydration, controlling the heating rate at 3 °C / min, the calcination temperature at 700 °C, and the calcination time at 3 h to obtain an anhydrous iron phosphate precursor DP3, the composition of which was: (Fe 0.99 Ti 0.01 PO4) 0.952 [Fe4(P2O7)3] 0.008 , where x = 0.008 and y = 0.01.

[0250] The physical and chemical indexes of the lithium iron phosphate precursor prepared in the preparation example are shown in Table 1.

[0251] Table 1

[0252] Ratio * Lattice parameter c / a <![CDATA[D 50 > TD BET Me / P Unit / / μm <![CDATA[g / cm 3 > <![CDATA[m 2 / g]]> / Preparation Example 1 1.5％ 2.2322 10.36 1.15 7.6 0.97 Preparation Example 2 1.9％ 2.2313 10.08 1.18 6.9 0.962 Preparation Example 3 1.6％ 2.2318 9.98 1.18 7.5 0.968 Preparation Example 4 1.7％ 2.2315 10.56 1.14 7.8 0.966 Preparation Example 5 1.5％ 2.2322 10.23 1.16 7.9 0.97 Preparation Example 6 1.5％ 2.2322 10.16 1.15 7.7 0.97 Preparation Example 7 1.5％ 2.2321 10.26 1.15 7.7 0.971 Comparative Preparation Example 1 0.70％ 2.2338 10.87 1.37 5.3 0.986 Comparative Preparation Example 2 0.90％ 2.2335 11.34 1.33 5.8 0.982 Comparative Preparation Example 3 0.80％ 2.2336 10.86 1.35 5.5 0.984

[0253] * means

[0254] Example - for preparing lithium iron phosphate cathode material

[0255] Example 1

[0256] (1) The feeding amounts of iron phosphate precursor P1, lithium carbonate, and titanium oxide were such that n(Fe):n(Li):n(Ti) = 0.961:1.04:0.019, and they were mixed with pure water. Glucose was added in an amount of 12 wt% based on the mass of the iron phosphate precursor P1, and the solid content was controlled at 40 wt%. The mixture was uniformly mixed by mechanical stirring to obtain a slurry; the slurry was ground by a sand mill (conditions: rotation speed 800 rpm), and the median particle size D 50 of the slurry was 380 nm; the ground slurry was spray-dried and granulated, controlling the inlet air temperature at 235 °C and the outlet air temperature at 85 °C to obtain a spray-dried material;

[0257] (2) Under a N2 atmosphere, the spray-dried material was sintered, controlling the heating rate at 2 °C / min, the calcination temperature at 770 °C, and the calcination time at 9 h to obtain a sintered material;

[0258] (3) The sintered material was pulverized by air flow and sieved to obtain a lithium iron phosphate cathode material A1.

[0259] The lithium iron phosphate positive electrode material A1 includes a substrate and a carbon coating layer coated on the surface of the substrate, wherein the composition of the substrate is Li 1.04 (Fe 0.961 Ti 0.019 )(PO4) 0.91 (P2O7) 0.045 .

[0260] XRD of lithium iron phosphate cathode material A1 is as follows Figure 3 As shown by Figure 3 It can be seen that the positive electrode material has a A1 =29.4-29.6°, 2θ A2 =29.8-30° and 2θ A3 =43.8-43.9°, and there is a characteristic diffraction peak at 2θ B1 =25.4-25.5°, 2θ B2 =35.9-36° and 2θ B3 =60.7-60.8°, there is a characteristic diffraction peak. Through analysis, it is speculated that there is lithium iron pyrophosphate phase in the positive electrode material A1. A2 The peak intensity of the diffraction characteristic peak at I(2θ A2 ) and 2θ B3 The peak intensity of the diffraction characteristic peak at I(2θ B3 ) ratio I(2θ A2 ) / I(2θ B3 ) is 0.255. At the same time, the compaction density of the lithium iron phosphate positive electrode material A1 is consistent with the 2θ measured by XRD of the positive electrode material A2 The peak intensity of the diffraction characteristic peak at I(2θ A2 ) satisfies the following relationship:

[0261] PD=0.084I(2θ A2 )+0.377.

[0262] Example 2

[0263] (1) The same as Example 1, except that the iron phosphate precursor P2 is used to replace the iron phosphate precursor P1, the iron phosphate precursor P2, lithium carbonate, and titanium oxide are added so that n(Fe):n(Li):n(Ti)=0.953:1.04:0.019, and are mixed with pure water to obtain a spray-dried material;

[0264] (2) Same as Example 1.

[0265] (3) The same as in Example 1, a lithium iron phosphate positive electrode material A2 is obtained. The lithium iron phosphate positive electrode material A2 includes a substrate and a carbon coating layer coated on the surface of the substrate, wherein the composition of the substrate is Li 1.04 (Fe 0.953Ti 0.019 )(PO4) 0.886 (P2O7) 0.057 。

[0266] It can be seen from the XRD analysis that for the cathode material A2, the peak intensity I(2θ A2 ) of the diffraction characteristic peak at 2θ A2 ) and the peak intensity I(2θ B3 ) of the diffraction characteristic peak at 2θ B3 ) have a ratio I(2θ A2 ) / I(2θ B3 ) of 0.267. At the same time, the tap density of the lithium iron phosphate cathode material A2 and the peak intensity I(2θ A2 ) of the diffraction characteristic peak at 2θ A2 ) measured by XRD for the cathode material satisfy the following relationship:

[0267] PD = 0.084I(2θ A2 ).

[0268] Example 3

[0269] (1) The same as Example 1, except that the iron phosphate precursor P3 is used to replace the iron phosphate precursor P1. The feeding amounts of the iron phosphate precursor P3, lithium carbonate, and titanium oxide are such that n(Fe):n(Li):n(Ti) = 0.959:1.04:0.019, and they are mixed with pure water to obtain a spray-dried material;

[0270] (2) The same as Example 1.

[0271] (3) The same as Example 1 to obtain the lithium iron phosphate cathode material A3. The lithium iron phosphate cathode material A3 includes a matrix and a carbon coating layer covering the surface of the matrix. Among them, the composition of the matrix is

[0272] Li 1.04 (Fe 0.959 Ti 0.019 )(PO4) 0.904 (P2O7) 0.048 。

[0273] It can be seen from the XRD analysis that for the cathode material A3, the peak intensity I(2θ A2 ) of the diffraction characteristic peak at 2θ A2 ) and the peak intensity I(2θ B3 ) of the diffraction characteristic peak at 2θ B3 ) have a ratio I(2θ A2 ) / I(2θ B3 ) of 0.264. At the same time, the tap density of the lithium iron phosphate cathode material A3 and the 2θ A2The peak intensity I(2θ A2 ) of the diffraction characteristic peak at the position satisfies the following relationship:

[0274] PD = 0.084I(2θ A2 ) + 0.377.

[0275] Example 4

[0276] (1) The same as Example 1, except that iron phosphate precursor P4 is used to replace iron phosphate precursor P1. The feeding amounts of iron phosphate precursor P4, lithium carbonate, and titanium oxide are such that n(Fe):n(Li):n(Ti) = 0.957:1.04:0.019, and they are mixed with pure water to obtain a spray-dried material;

[0277] (2) The same as Example 1.

[0278] (3) The same as Example 1 to obtain lithium iron phosphate cathode material A4. Lithium iron phosphate cathode material A4 includes a matrix and a carbon coating layer coated on the surface of the matrix. Among them, the composition of the matrix is

[0279] Li 1.04 (Fe 0.957 Ti 0.019 )(PO4) 0.898 (P2O7) 0.051 .

[0280] It can be known through XRD analysis that the ratio I(2θ A2 ) of the peak intensity I(2θ A2 ) of the diffraction characteristic peak at 2θ B3 to the peak intensity I(2θ B3 ) of the diffraction characteristic peak at 2θ A2 ) / I(2θ B3 ) is 0.266. At the same time, the tap density of lithium iron phosphate cathode material A4 and the peak intensity I(2θ A2 ) of the diffraction characteristic peak at 2θ A2 ) measured by XRD for the cathode material satisfy the following relationship:

[0281] PD = 0.084I(2θ A2 ) + 0.377.

[0282] Example 5

[0283] (1) The same as Example 1, except that iron phosphate precursor P5 is used to replace iron phosphate precursor P1. The feeding amounts of iron phosphate precursor P5, lithium carbonate, and titanium oxide are such that n(Fe):n(Li):n(Ti) = 0.961:1.04:0.019, and they are mixed with pure water to obtain a spray-dried material;

[0284] (2) is the same as Example 1.

[0285] (3) is the same as Example 1, obtaining lithium iron phosphate cathode material A5. The lithium iron phosphate cathode material A5 includes a matrix and a carbon coating layer coated on the surface of the matrix. Among them, the composition of the matrix is Li 1.04 (Fe 0.961 Ti 0.019 )(PO4) 0.91 (P2O7) 0.045 .

[0286] It can be known through XRD analysis that the intensity I(2θ A2 ) of the diffraction characteristic peak at 2θ in the cathode material A5 and the intensity I(2θ A2 ) of the diffraction characteristic peak at 2θ B3 satisfy the following relationship: I(2θ B3 ) / I(2θ A2 ) = 0.254. At the same time, the tap density of the lithium iron phosphate cathode material A5 and the intensity I(2θ B3 ) of the diffraction characteristic peak at 2θ measured by XRD of the cathode material satisfy the following relationship: A2 PD = 0.084I(2θ A2 ) + 0.377.

[0287] PD = 0.084I(2θ A2 ) + 0.377.

[0288] Example 6

[0289] (1) is the same as Example 1, except that iron phosphate precursor P6 is used to replace iron phosphate precursor P1. The feeding amounts of iron phosphate precursor P6, lithium carbonate, and titanium oxide are such that n(Fe):n(Li):n(Ti) = 0.961:1.04:0.019, and they are mixed with pure water to obtain a spray-dried material;

[0290] (2) is the same as Example 1.

[0291] (3) is the same as Example 1, obtaining lithium iron phosphate cathode material A6. The lithium iron phosphate cathode material A6 includes a matrix and a carbon coating layer coated on the surface of the matrix. Among them, the composition of the matrix is

[0292] Li 1.04 (Fe 0.961 Ti 0.019 )(PO4) 0.91 (P2O7) 0.045 .

[0293] It can be known through XRD analysis that the intensity I(2θ A2 ) of the diffraction characteristic peak at 2θ in the cathode material A6 and the intensity I(2θ A2) with 2θ B3 The peak intensity I(2θ B3 ) of the diffraction characteristic peak at A2 ) / I(2θ B3 ) is 0.253. Meanwhile, the tap density of the lithium iron phosphate cathode material A6 and the peak intensity I(2θ A2 ) of the diffraction characteristic peak at 2θ measured by XRD of the cathode material satisfy the following relationship: A2

[0294] PD = 0.084I(2θ A2 ) + 0.377.

[0295] Example 7

[0296] (1) It is the same as Example 1; the difference is that the iron phosphate precursor P7 is used to replace the iron phosphate precursor P1, and the feeding amounts of the iron phosphate precursor P7, lithium carbonate, and titanium oxide are such that n(Fe):n(Li):n(Ti) = 0.960:1.04:0.019, and they are mixed with pure water to obtain a spray-dried material;

[0297] (2) It is the same as Example 1.

[0298] (3) It is the same as Example 1 to obtain the lithium iron phosphate cathode material A7. The lithium iron phosphate cathode material A7 includes a matrix and a carbon coating layer coated on the surface of the matrix, wherein the composition of the matrix is

[0299] Li 1.04 (Fe 0.960 Ti 0.019 )(PO4) 0.88 (P2O7) 0.06 .

[0300] Through XRD analysis, it can be known that the ratio of the peak intensity I(2θ A2 ) of the diffraction characteristic peak at 2θ in the cathode material A7 to the peak intensity I(2θ A2 ) of the diffraction characteristic peak at 2θ B3 is I(2θ B3 ) / I(2θ A2 ) / I(2θ B3 ) = 0.254. Meanwhile, the tap density of the lithium iron phosphate cathode material A7 and the peak intensity I(2θ A2 ) of the diffraction characteristic peak at 2θ measured by XRD of the cathode material satisfy the following relationship: A2

[0301] PD = 0.084I(2θ A2 ) + 0.377.

[0302] Example 8 ​​

[0303] (1) The same as Example 1, except that the median particle size D of the slurry is controlled 50 to be 450 nm; a spray-dried material is obtained;

[0304] (2) The same as Example 1;

[0305] (3) The same as Example 1, and lithium iron phosphate cathode material A8 is obtained. The lithium iron phosphate cathode material A8 includes a matrix and a carbon coating layer coated on the surface of the matrix. Among them, the composition of the matrix is Li 1.04 (Fe 0.961 Ti 0.019 )(PO4) 0.91 (P2O7) 0.045 .

[0306] It can be known through XRD analysis that the intensity I(2θ A2 ) of the diffraction characteristic peak at 2θ of the cathode material A8 and the intensity I(2θ A2 ) of the diffraction characteristic peak at 2θ B3 satisfy the following relationship: I(2θ B3 ) / I(2θ A2 ) is 0.25. At the same time, the tap density of the lithium iron phosphate cathode material A8 and the intensity I(2θ B3 ) of the diffraction characteristic peak at 2θ measured by XRD of the cathode material satisfy the following relationship: A2 PD = 0.084I(2θ A2 ) + 0.377.

[0307] PD = 0.084I(2θ A2 ).

[0308] Example 9

[0309] (1) The same as Example 1, except that the median particle size D of the slurry is controlled 50 to be 300 nm; a spray-dried material is obtained;

[0310] (2) The same as Example 1;

[0311] (3) The same as Example 1, and lithium iron phosphate cathode material A9 is obtained. The lithium iron phosphate cathode material A9 includes a matrix and a carbon coating layer coated on the surface of the matrix. Among them, the composition of the matrix is

[0312] Li 1.04 (Fe 0.961 Ti 0.019 )(PO4) 0.91 (P2O7) 0.045 .

[0313] It can be known through XRD analysis that at 2θ of the cathode material A9 A2The peak intensity I(2θ A2 ) of the diffraction characteristic peak at B3 and the peak intensity I(2θ B3 ) of the diffraction characteristic peak at 2θ A2 ) have a ratio of I(2θ B3 ) / I(2θ A2 ) of 0.251. At the same time, the tap density of the lithium iron phosphate cathode material A9 and the peak intensity I(2θ A2 ) of the diffraction characteristic peak at 2θ

[0314] measured by XRD of the cathode material satisfy the following relationship: A2 PD = 0.084I(2θ

[0315] Example 10

[0316] (1) is the same as Example 1.

[0317] (2) is the same as Example 1, except that the sintering temperature is 760 °C.

[0318] (3) is the same as Example 1. The lithium iron phosphate cathode material A10 is obtained. The lithium iron phosphate cathode material A10 includes a matrix and a carbon coating layer coated on the surface of the matrix. Among them, the composition of the matrix is

[0319] Li 1.04 (Fe 0.961 Ti 0.019 )(PO4) 0.91 (P2O7) 0.045 .

[0320] It can be seen from XRD analysis that the ratio of the peak intensity I(2θ A2 ) of the diffraction characteristic peak at 2θ A2 in the cathode material A10 to the peak intensity I(2θ B3 ) of the diffraction characteristic peak at 2θ B3 is I(2θ A2 ) / I(2θ B3 ) = 0.252. At the same time, the tap density of the lithium iron phosphate cathode material A10 and the peak intensity I(2θ A2 ) of the diffraction characteristic peak at 2θ A2 measured by XRD of the cathode material satisfy the following relationship:

[0321] PD = 0.084I(2θ A2 ) + 0.377.

[0322] Example 11

[0323] (1) is the same as Example 1.

[0324] (2) Same as Example 1, except that the calcination temperature is 780°C.

[0325] (3) Same as Example 1. Obtain lithium iron phosphate positive electrode material A11. The lithium iron phosphate positive electrode material A11 includes a substrate and a carbon coating layer coated on the surface of the substrate, wherein the composition of the substrate is

[0326] Li 1.04 (Fe 0.961 Ti 0.019 )(PO4) 0.91 (P2O7) 0.045 .

[0327] XRD analysis shows that the 2θ A2 The peak intensity of the diffraction characteristic peak at I(2θ A2 ) and 2θ B3 The peak intensity of the diffraction characteristic peak at I(2θ B3 ) ratio I(2θ A2 ) / I(2θ B3 ) is 0.255. At the same time, the compaction density of the lithium iron phosphate positive electrode material A11 is consistent with the 2θ measured by XRD of the positive electrode material A2 The peak intensity of the diffraction characteristic peak at I(2θ A2 ) satisfies the following relationship:

[0328] PD=0.084I(2θ A2 )+0.377.

[0329] Example 12

[0330] (1) Same as Example 1.

[0331] (2) Same as Example 1, except that the calcination temperature is 900°C.

[0332] (3) Same as Example 1. Obtain lithium iron phosphate positive electrode material A12. The lithium iron phosphate positive electrode material A12 includes a substrate and a carbon coating layer coated on the surface of the substrate, wherein the composition of the substrate is

[0333] Li 1.04 (Fe 0.961 Ti 0.019 )(PO4) 0.91 (P2O7) 0.045 .

[0334] XRD analysis shows that the 2θ A2 The peak intensity of the diffraction characteristic peak at I(2θ A2 ) and 2θ B3 The peak intensity of the diffraction characteristic peak at I(2θ B3) The ratio I(2θ A2 ) / I(2θ B3 ) is 0.266. Meanwhile, the tap density of the lithium iron phosphate cathode material A12 and the peak intensity I(2θ A2 ) of the diffraction characteristic peak at 2θ of the cathode material measured by XRD satisfy the following relationship: A2 )

[0335] PD = 0.084I(2θ A2 ) + 0.377.

[0336] Example 13

[0337] (1) Similar to Example 1, the feeding amounts of the iron phosphate precursor P1, lithium carbonate, titanium oxide, and manganese oxide are such that n(Fe):n(Li):n(Ti):n(Mn) = 0.961:1.04:0.01:0.01, and they are mixed with pure water to obtain a spray-dried material;

[0338] (2) Similar to Example 1.

[0339] (3) Similar to Example 1, the lithium iron phosphate cathode material A13 is obtained. The lithium iron phosphate cathode material A13 includes a matrix and a carbon coating layer coated on the surface of the matrix, wherein the composition of the matrix is Li 1.04 (Fe 0.961 Ti 0.01 Mn 0.01 )(PO4) 0.91 (P2O7) 0.045 .

[0340] It can be known through XRD analysis that the ratio of the peak intensity I(2θ A2 ) of the diffraction characteristic peak at 2θ in the cathode material A13 to the peak intensity I(2θ A2 ) of the diffraction characteristic peak at 2θ B3 is I(2θ B3 ) / I(2θ A2 ) / I(2θ B3 ) is 0.254. Meanwhile, the tap density of the lithium iron phosphate cathode material A13 and the peak intensity I(2θ A2 ) of the diffraction characteristic peak at 2θ of the cathode material measured by XRD satisfy the following relationship: A2 )

[0341] PD = 0.084I(2θ A2 ) + 0.377.

[0342] Comparative Example 1

[0343] (1) The same as Example 1, except that iron phosphate precursor DP1 is used to replace iron phosphate precursor P1. The feeding amounts of iron phosphate precursor DP1, lithium carbonate, and titanium oxide are such that n(Fe):n(Li):n(Ti) = 0.976:1.04:0.019, and they are mixed with pure water to obtain a spray-dried material;

[0344] (2) The same as Example 1.

[0345] (3) The same as Example 1 to obtain lithium iron phosphate cathode material D1. Lithium iron phosphate cathode material D1 includes a matrix and a carbon coating layer coated on the surface of the matrix. Among them, the composition of the matrix is Li 1.04 (Fe 0.976 Ti 0.019 )(PO4) 0.958 (P2O7) 0.021 .

[0346] It can be seen from XRD analysis that there are no diffraction characteristic peaks in the cathode material D1 at 2θ A1 = 29.4 - 29.6°, 2θ A2 == 29.8 - 30°, 2θ A3 = 43.8 - 43.9°.

[0347] Comparative Example 2

[0348] (1) The same as Example 1, except that iron phosphate precursor DP2 is used to replace iron phosphate precursor P1. The feeding amounts of iron phosphate precursor DP2, lithium carbonate, and titanium oxide are such that n(Fe):n(Li):n(Ti) = 0.999:1.04:0.019, and they are mixed with pure water to obtain a spray-dried material;

[0349] (2) The same as Example 1.

[0350] (3) The same as Example 1 to obtain lithium iron phosphate cathode material D2. Lithium iron phosphate cathode material D2 includes a matrix and a carbon coating layer coated on the surface of the matrix. Among them, the composition of the matrix is Li 1.04 (Fe 0.999 Ti 0.019 )(PO4) 0.946 (P2O7) 0.027 .

[0351] It can be seen from XRD analysis that there are no diffraction characteristic peaks in the cathode material D2 at 2θ A1 = 29.4 - 29.6°, 2θ A2 == 29.8 - 30°, 2θ A3 = 43.8 - 43.9°.

[0352] Comparative Example 3

[0353] (1) It is the same as Example 1, except that iron phosphate precursor DP3 is used to replace iron phosphate precursor P1. The feeding amounts of iron phosphate precursor DP3, lithium carbonate, and titanium oxide are such that n(Fe):n(Li):n(Ti) = 0.998:1.04:0.019, and they are mixed with pure water to obtain a spray-dried material;

[0354] (2) It is the same as Example 1.

[0355] (3) It is the same as Example 1 to obtain lithium iron phosphate cathode material D3. Lithium iron phosphate cathode material D3 includes a matrix and a carbon coating layer coated on the surface of the matrix. Among them, the composition of the matrix is Li 1.04 (Fe 0.998 Ti 0.019 )(PO4) 0.952 (P2O7) 0.024 .

[0356] It can be known through XRD analysis that the cathode material D3 has no diffraction characteristic peaks at 2θ A1 = 29.4 - 29.6°, 2θ A2 == 29.8 - 30°, 2θ A3 = 43.8 - 43.9°.

[0357] Comparative Example 4

[0358] (1) It is the same as Example 1, except that iron phosphate precursor DP1 is used to replace iron phosphate precursor P1. The feeding amounts of iron phosphate precursor DP1, lithium carbonate, and titanium oxide are such that n(Fe):n(Li):n(Ti) = 0.976:1.04:0.019, and they are mixed with pure water to obtain a spray-dried material;

[0359] (2) It is the same as Example 1, except that the calcination temperature is 795 °C.

[0360] (3) It is the same as Example 1 to obtain lithium iron phosphate cathode material D4. Lithium iron phosphate cathode material D4 includes a matrix and a carbon coating layer coated on the surface of the matrix. Among them, the composition of the matrix is Li1.04(Fe 0.976 Ti 0.019 )(PO4) 0.958 (P2O7) 0.021 .

[0361] It can be known through XRD analysis that the cathode material D4 has no diffraction characteristic peaks at 2θ A1 = 29.4 - 29.6°, 2θ A2 == 29.8 - 30°, 2θ A3 = 43.8 - 43.9°.

[0362] Comparative Example 5

[0363] (1) The same as Example 1.

[0364] (2) The same as Example 1, except that the calcination temperature is 480 °C.

[0365] (3) The same as Example 1. The lithium iron phosphate cathode material D5 was obtained. The lithium iron phosphate cathode material D5 includes a matrix and a carbon coating layer coated on the surface of the matrix. Among them, the composition of the matrix is

[0366] Li 1.04 (Fe 0.961 Ti 0.019 )(PO4) 0.91 (P2O7) 0.045 .

[0367] It can be known from XRD analysis that the cathode material D5 has no diffraction characteristic peaks at 2θ A1 = 29.4 - 29.6 °, 2θ A2 = 29.8 - 30 °, 2θ A3 = 43.8 - 43.9 °.

[0368] In the examples and comparative examples, the median particle size, specific surface area, apparent density and moisture content of the spray-dried material are shown in Table 2.

[0369] Table 2

[0370] <![CDATA[D 50 > BET Bulk density Moisture content Unit μm <![CDATA[m 2 / g]]> <![CDATA[g / cm 3 > ％ Example 1 23.2 11.0 0.62 2.2 Example 2 22.5 10.5 0.63 2.3 Example 3 23.3 10.8 0.60 2.3 Example 4 22.6 12.2 0.62 2.2 Example 5 23.5 10.8 0.62 2.4 Example 6 23.6 11.5 0.59 2.0 Example 7 22.9 12.0 0.61 2.3 Example 8 22.5 12.2 0.58 2.2 Example 9 23.8 11.5 0.59 2.4 Example 10 23.5 11.2 0.59 2.4 Example 11 23 11.8 0.59 2.4 Example 12 23.3 11.5 0.69 2.2 Example 13 23.3 11.6 0.62 2.2 Comparative Example 1 22.3 11.5 0.62 2.1 Comparative Example 2 23.0 11.1 0.60 1.9 Comparative Example 3 23.8 11.5 0.61 2.3 Comparative Example 4 22.2 11.8 0.58 2.4 Comparative Example 5 23.3 9 0.62 2.2

[0371] Examples

[0372] The physical and chemical indexes of the lithium iron phosphate cathode material are shown in Table 2.

[0373] Table 2 continued

[0374] <![CDATA[D 50 1 > PD Carbon coating layer BET Volume resistivity <![CDATA[Fe2P content]]> <![CDATA[I(2θ A2 ) / I(2θ B3 )]]> Unit μm <![CDATA[g / cm 3 > ％ <![CDATA[m 2 / g]]> Ω·cm ppb Example 1 1.35 2.52 1.31 11.2 20 80 0.255 Example 2 1.33 2.63 1.33 11.3 19 86 0.267 Example 3 1.38 2.60 1.29 11.4 18 85 0.264 Example 4 1.40 2.61 1.28 11.5 21 85 0.266 Example 5 1.38 2.52 1.29 11.3 18 78 0.254 Example 6 1.41 2.51 1.28 11.1 19 76 0.253 Example 7 1.39 2.51 1.29 11 20 79 0.254 Example 8 1.38 2.59 1.34 10.8 21 82 0.25 Example 9 1.40 2.48 1.23 12 19 78 0.251 Example 10 1.36 2.45 1.33 11.5 22 71 0.252 Example 11 1.42 2.55 1.28 11 15 90 0.255 Example 12 1.62 2.68 1.28 9.5 36 2220 0.266 Example 13 1.33 2.50 1.28 11.5 18 81 0.254 Comparative Example 1 1.36 2.40 1.30 11.3 22 70 / Comparative Example 2 1.35 2.42 1.30 11.5 18 75 / Comparative Example 3 1.35 2.41 1.31 10.8 19 66 / Comparative Example 4 1.38 2.50 1.29 11.2 9 1520 / Comparative Example 5 0.88 2.02 1.66 14.8 45 20 /

[0375] 1 Refers to the average particle size of the primary particles.

[0376] For the lithium iron phosphate cathode materials prepared in Examples 1 - 11, Example 14 and Comparative Examples 1 - 3, Comparative Example 5, the numerical values of the Fe2P content, volume resistivity and tap density satisfy the following relationship. The three satisfy the relationship: MI = 77.13PD - 0.03R - 107.7.

[0377] Test Example

[0378] This test example is used to illustrate the electrode material, electrode, lithium ion battery and their preparation methods.

[0379] (1) Preparation of the positive electrode sheet: The lithium iron phosphate positive electrode materials, conductive agent carbon nanotubes, and NMP solution of binder PVDF obtained in the above-mentioned examples and comparative examples were mixed at a mass ratio of 90:5:5. The specific method is as follows: The dried positive electrode material and conductive agent were ground in a mortar for 15 minutes. After grinding evenly, the PVDF solution (mass fraction 5%) was added according to the ratio, and stirred on a magnetic stirrer for 6 hours; the obtained paste-like slurry was evenly coated on the current collector aluminum foil, then dried in a vacuum drying oven at 60 °C for 20 hours, and then stamped into a positive electrode sheet with a diameter of 12 mm and a thickness of 120 μm under a pressure of 100 MPa. The positive electrode sheet was placed in a vacuum drying oven at 120 °C and dried for 12 h.

[0380] (2) Battery assembly: A metal lithium sheet with a diameter of 17 mm and a thickness of 1 mm was used as the negative electrode, a polyethylene porous membrane with a thickness of 25 μm and an alumina ceramic layer coated on the surface was used as the separator, and an equal-volume mixture of 1 mol / L LiPF6, ethylene carbonate (EC), and diethyl carbonate (DEC) was selected as the electrolyte. The positive electrode sheet, separator, negative electrode sheet, and electrolyte were assembled into a 2025-type button cell in an Ar gas glove box with a water content and oxygen content both less than 5 ppm.

[0381] (3) Electrochemical performance test: The battery was subjected to charge and discharge tests using a LAND CT2001A charge and discharge tester from Wuhan Lanbo Electronics Co., Ltd. The charge and discharge voltage range was 2.5 to 3.75 V. The specific capacity of the assembled lithium-ion battery was tested at rates of 0.1C and 1C respectively, and the cycle performance was tested at a rate of 1C. The test results are shown in Table 3.

[0382] Table 3

[0383]

[0384]

[0385] From the results of Table 2 and Table 3, it can be seen that when the peak intensity I(2θ A2 ) of the diffraction characteristic peak at 2θ A2 ) and the peak intensity I(2θ B3 ) of the diffraction characteristic peak at 2θ B3 ) satisfy the ratio I(2θ A2 ) / I(2θ B3 ) ≥ 0.26, the positive electrode material exhibits a higher tap density, better electrochemical performance, and less Fe2P content is generated.

[0386] Figure 1 This is the XRD pattern of the iron phosphate precursor prepared in Preparation Example 1 of the present invention. It can be seen from Figure 1 that at 2θ a1= 16.2 - 16.9°, 2θ a2 = 27.3 - 28.1°, 2θ a3 = 29 - 29.7° and 2θ a4 Diffraction characteristic peaks exist at = 30.2 - 30.9°, which proves that the iron phosphate precursor contains the iron pyrophosphate phase.

[0387] Figure 2 This is the SEM image of the iron phosphate precursor prepared in Preparation Example 1 of the present invention. Figure 2 It can be seen that the average primary particle size of the iron phosphate precursor is 150 nm.

[0388] Figure 3 This is the XRD pattern of the lithium iron phosphate cathode material prepared in Example 1 and Example 2 of the present invention. Figure 3 It can be seen that at 2θ A1 = 29.50°, 2θ A2 = 29.93°, 2θ A3 Diffraction characteristic peaks exist at = 43.85°, which proves that the cathode material contains the lithium iron pyrophosphate phase.

[0389] Figure 4 This is the SEM image of the lithium iron phosphate cathode material prepared in Example 1 of the present invention. The cathode material has a secondary particle structure formed by primary particles.

[0390] Figure 5 This is the charge-discharge performance graph of the lithium-ion battery assembled from the lithium iron phosphate cathode materials of Example 1 and Example 2. Figure 5 It can be seen that Example 2 has higher charge capacity and discharge capacity.

[0391] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited thereto. Within the technical concept scope of the present invention, various simple modifications can be made to the technical solutions of the present invention, including any other suitable combination of each technical feature. These simple modifications and combinations should also be regarded as the content disclosed by the present invention and fall within the protection scope of the present invention.

Claims

1. A lithium iron phosphate cathode material, characterized in that, Through XRD testing, the cathode material has diffraction characteristic peaks at 2θ A1 = 29.4 - 29.6°, 2θ A2 = 29.8 - 30° and 2θ A3 = 43.8 - 43.9°; The positive electrode material includes a matrix and a carbon coating layer coated on the surface of the matrix; Among them, the matrix has the composition shown in Formula I: Li 1+a Fe b M c Mn d (PO4) 1-2w (P2O7) w Formula I; where, -0.1 ≤ a ≤ 0.1, 0 ≤ b ≤ 1, 0 ≤ c ≤ 0.5, 0 ≤ d ≤ 1, 0.03 ≤ w ≤ 0.09; M is selected from at least one of La, Ce, Cr, Mo, Ca, Hf, Ti, Fe, Zn, Y, Zr, W, Nb, Sm, Co, Ni, V, Mg, Na, B, and Al; The Fe2P content of the lithium iron phosphate positive electrode material is ≤90 ppb.

2. The lithium iron phosphate cathode material according to claim 1, wherein, Through XRD testing, the cathode material has diffraction characteristic peaks at 2θ B1 = 25.4 - 25.5°, 2θ B2 = 35.9 - 36° and 2θ B3 = 60.7 - 60.8°.

3. The lithium iron phosphate cathode material according to claim 1 or 2, wherein, The peak intensity I(2θ A2 ) of the diffraction characteristic peak at 2θ A2 and the peak intensity I(2θ B3 ) of the diffraction characteristic peak at 2θ B3 satisfy 0.25 ≤ I(2θ A2 ) / I(2θ B3 ) ≤ 0.

27.

4. The lithium iron phosphate cathode material according to claim 3, wherein, The peak intensity I(2θ A2 ) of the diffraction characteristic peak at 2θ A2 in the positive electrode material and the peak intensity I(2θ B3 ) of the diffraction characteristic peak at 2θ B3 satisfy 0.26 ≤ I(2θ A2 ) / I(2θ B3 ) ≤ 0.

27.

5. The lithium iron phosphate cathode material according to claim 1 or 2, wherein M is selected from at least one of Al, Zr, W, Co, V, and Ti; And / or, based on the total weight of the positive electrode material, the content of the carbon coating layer is 0.5-2 wt%.

6. The lithium iron phosphate cathode material according to claim 5, wherein Based on the total weight of the positive electrode material, the content of the carbon coating layer is 1-1.5 wt%.

7. The cathode material according to claim 1 or 2, wherein The lithium iron phosphate cathode material has a secondary particle structure formed by primary particles, and the median particle size D 50 of the primary particles is 0.2 - 2 μm; and / or, the tap density of the lithium iron phosphate cathode material is 2.5-2.7 g / cm 3 ; And / or, the tap density of the lithium iron phosphate cathode material is 0.6-1.1 g / cm 3 ; and / or, the specific surface area of the lithium iron phosphate cathode material is 8-20 m 2 / g; And / or, the volume resistivity of the lithium iron phosphate positive electrode material is 1-100 Ω·cm.

8. The positive electrode material according to claim 7, wherein, The numerical values of the Fe2P content, volume resistivity, and tap density of the lithium iron phosphate positive electrode material satisfy the following relationship: MI = 77.13PD - 0.03R - 107.7 Among them, R is the volume resistivity of the lithium iron phosphate positive electrode material, Ω·cm; PD is the tap density of the lithium iron phosphate cathode material, g / cm 3 ; MI is the Fe2P content of the lithium iron phosphate positive electrode material, ppb; and / or, the tap density of the lithium iron phosphate cathode material and the peak intensity I(2θ A2 ) of the diffraction characteristic peak at 2θ of the cathode material measured by XRD A2 satisfy the following relationship: PD = 0.084 I(2θ A2 ) + 0.377; Among them, PD is the tap density of the lithium iron phosphate cathode material, g / cm 3 ; I(2θ A2 ) is the peak intensity I(2θ A2 ) of the diffraction characteristic peak at 2θ A2 ) in the XRD diffraction pattern of the lithium iron phosphate cathode material.

9. A preparation method of a lithium iron phosphate cathode material, characterized in that, The preparation method includes the following steps: (1) Mix the iron phosphate precursor, lithium source, carbon source, optionally metal source M, and optionally Mn source with a liquid medium, grind them into a slurry, and then dry to obtain a dried material; (2) Under a protective atmosphere, calcine the dried material to obtain a sintered material; (3) Crush and screen the sintered material to obtain the lithium iron phosphate positive electrode material; Among them, the iron phosphate precursor has diffraction characteristic peaks at 2θ a1 = 16.2 - 16.9°, 2θ a2 = 27.3 - 28.1°, 2θ a3 = 29 - 29.7° and 2θ a4 = 30.2 - 30.9° as determined by XRD test; the iron phosphate precursor has diffraction characteristic peaks at 2θ b1 = 20 - 20.7°, 2θ b2 = 21.5 - 22.2°, 2θ b3 = 23.4 - 24°, 2θ b4 = 25.5 - 26.2° as determined by XRD test; The integral area A(2θ ai ) of the diffraction characteristic peak at 2θ ai and the integral area A(2θ bj ) of the diffraction characteristic peak at 2θ bj satisfy the following: = 1% - 3%, where i is an integer from 1 to 4 and j is an integer from 1 to 4; In step (2), the temperature of the calcination treatment is greater than or equal to 500 °C; The iron phosphate precursor has the composition shown in Formula II: (Fe 1-y M y PO4) 1-6x [Fe4(P2O7)3] x Formula II wherein, 0.01 ≤ x ≤ 0.02, 0 ≤ y ≤ 0.1, and M is selected from at least one of Al, Mg, Co, Ni, Cu, Zn, Zr, and Ti.

10. The preparation method according to claim 9, wherein The lattice parameters of the a-axis and c-axis of the iron phosphate precursor measured by XRD satisfy: 2.231 ≤ c / a ≤ 2.2326; And / or, in the iron phosphate precursor, the molar ratio n(Me) / n(P) of the metal element to the phosphorus element is 0.960-0.980; And / or, the median particle size D of the iron phosphate precursor 50 is 1 - 25 μm; And / or, the primary particle size of the iron phosphate precursor is 20-200 nm; and / or, the tap density of the iron phosphate precursor is 0.8-1.3 g / cm 3 ; and / or, the specific surface area of the iron phosphate precursor is 6-10 m 2 / g; And / or, the sulfur content in the iron phosphate precursor is ≤400 ppm.

11. The preparation method according to claim 9 or 10, wherein In step (2), the temperature of the calcination treatment is 500-900 °C; And / or, the time of the calcination treatment is 4-20 h.

12. According to the preparation method described in claim 11, wherein, In step (2), the temperature of the calcination treatment is 600-800 °C; And / or, the time of the calcination treatment is 6-15 h.

13. The preparation method according to claim 9 or 10, wherein, The dosages of the iron phosphate precursor, the lithium source, the metal source M, and the Mn source are such that: n(Li): n(Fe): n(M): n(Mn) = 1 + a:b:c:d , where, -0.1 ≤ a ≤ 0.1, 0 ≤ b ≤ 1, 0 ≤ c ≤ 0.5, 0 ≤ d ≤ 1; And / or, based on the total mass of the iron phosphate precursor, the dosage of the carbon source is 8 wt%-18 wt%; and / or, the median particle size D of the slurry 50 is 50 - 2000 nm; And / or, the solid content of the slurry is 10-70 wt%; And / or, the drying method is spray drying; And / or, the conditions of the spray drying include: inlet air temperature 190-280 °C, outlet air temperature 60-120 °C.

14. The preparation method according to claim 13, wherein, -0.05≤ a ≤0.05，0.5≤ b ≤1，0.001≤ c ≤0.1，0≤ d ≤0.5。 15. The preparation method according to claim 9 or 10, wherein, The metal source M is selected from at least one of oxalates, nitrates, acetates, oxides, hydroxides, carbonates, phosphates, metal clusters, metal complexes, and carboxylates that can provide element M; And / or, the carbon source is selected from at least one of glucose, sucrose, fructose, cellulose, starch, citric acid, polyacrylic acid, phenolic resin, polyethylene glycol, dopamine, graphene and carbon nanotubes.

16. The lithium iron phosphate cathode material prepared by the preparation method according to any one of claims 9-15.

17. A lithium-ion battery, characterized in that, The lithium ion battery includes the lithium iron phosphate cathode material according to any one of claims 1-8 and 16.

Images