Olivine-type cathode material, preparation method and application thereof, and lithium-ion battery

Abstract

The present invention relates to the technical field of lithium-ion batteries, and particularly relates to an olivine-type cathode material, a preparation method and application thereof, and a lithium-ion battery. The olivine-type cathode material includes a lithium phosphate salt as a matrix and a carbon coating layer coated on the matrix; wherein, the matrix has a general formula shown in Formula I: Li a M 1‑ b M’ b P c O4 Formula I, wherein, 0.9 ≤ a ≤ 1.1, 0.95 ≤ b < 1, 0.96 ≤ b / c ≤ 0.99; M is selected from at least one of W, Mg, Nb, V, Ti, Mo, Rh, Os and Ta; M’ is selected from at least one of Mn, Co, Ni and Fe. The olivine-type cathode material provided by the present invention has the characteristics of high conductivity, low powder impedance, high tap density and high particle strength; meanwhile, the lithium-ion battery containing the olivine-type cathode material has high rate performance and low temperature performance.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion batteries, and particularly relates to an olivine-type cathode material, a preparation method and application thereof, and a lithium-ion battery containing the olivine-type cathode material. Background Art

[0002] Since the commercialization of lithium-ion batteries, due to their advantages such as high energy density, good cycle life, high voltage platform, excellent rate performance, and no memory effect, they have been rapidly applied and developed, and are currently widely used in the fields of energy storage, power tools, electric vehicles, military equipment, aerospace, etc.

[0003] As the core factor affecting lithium-ion batteries, the performance of the cathode material directly affects the performance of lithium-ion batteries. Lithium iron phosphate has become one of the main cathode materials currently used due to its advantages such as high safety, long cycle life, low cost, wide raw material sources, and environmental friendliness. Especially after the launch of blade battery technology, it has been warmly welcomed by the market, and its shipments have even exceeded those of ternary materials. However, restricted by its own crystal structure, lithium iron phosphate also has the disadvantages of poor conductivity and slow ion migration rate, which directly affect its rate and low-temperature performance, and this is also the main challenge it currently faces. Summary of the Invention

[0004] The purpose of the present invention is to overcome the problems of poor conductivity and slow ion migration rate existing in the existing lithium iron phosphate, which in turn lead to poor rate performance and low-temperature performance, etc. A new olivine-type cathode material, a preparation method and application thereof, and a lithium-ion battery containing the olivine-type cathode material are provided. The olivine-type cathode material has the characteristics of high conductivity, low powder impedance, high tap density, and large particle strength; at the same time, the lithium-ion battery containing the olivine-type cathode material has excellent rate performance and low-temperature performance.

[0005] In order to achieve the above purpose, in the first aspect of the present invention, an olivine-type cathode material is provided. The olivine-type cathode material includes a lithium phosphate salt as a matrix, and a carbon coating layer coated on the matrix;

[0006] Among them, the matrix has a general formula shown in Formula I: Li a M 1-b M’ b P c O4 Formula I,

[0007] Among them, 0.9 ≤ a ≤ 1.1, 0.95 ≤ b < 1, 0.96 ≤ b / c ≤ 0.99; M is selected from at least one of W, Mg, Nb, V, Ti, Mo, Rh, Os, and Ta; M’ is selected from at least one of Mn, Co, Ni, and Fe.

[0008] Preferably, based on the total weight of the olivine-type cathode material, the content of the carbon coating layer is 1-2.8 wt%.

[0009] Preferably, the C in the carbon coating layer is derived from C1 generated by carbonization of an organic carbon source and C2 derived from an inorganic carbon source, and the weight ratio of C1 to C2 is 6.5:0.9-1.1.

[0010] Preferably, the aspect ratio of the olivine-type cathode material is 0.95-1.05; D 50 is 2-17 μm; K90 is 1-3, where K90 = (D 90 -D 10 ) / D 50 .

[0011] Preferably, the cross-sectional porosity of the olivine-type cathode material is 5-20%.

[0012] Preferably, the specific surface area of the olivine-type cathode material is 7-30 m 2 / g.

[0013] Preferably, the volume resistivity of the olivine-type cathode material ≤ 60 Ω·cm.

[0014] Preferably, the tap density of the olivine-type cathode material is 2-2.4 g / cm 3 .

[0015] Preferably, the change rate of D 50 of the olivine-type cathode material before and after 2T pressure ≤ 3%; the change rate of D 50 before and after 4T pressure ≤ 15%; the change rate of D 50 before and after 6T pressure ≤ 30%.

[0016] The second aspect of the present invention provides a preparation method of an olivine-type cathode material, and the preparation method includes the following steps:

[0017] (1) Mix a phosphate, a lithium source, an organic carbon source, an M source and a solvent, and perform first grinding on the obtained first slurry to obtain a second slurry;

[0018] (2) Mix the second slurry and an inorganic carbon source and then perform second grinding, and dry the obtained third slurry to obtain a spherical or quasi-spherical precursor;

[0019] (3) Sinter the precursor in an inert atmosphere to obtain an olivine-type cathode material.

[0020] Preferably, the phosphate has the general formula shown in Formula II: M’ x P yO4·nH2O of Formula II, wherein M' is selected from at least one of Mn, Co, Ni, and Fe, 0.95 ≤ x < 1, 0.96 ≤ x / y ≤ 0.99, and 0 ≤ n ≤ 2.

[0021] Preferably, the molar ratio of the phosphate based on M', the lithium source based on Li, and the M source based on M is n(M'):n(Li):n(M), wherein 0.95 ≤ n(M') < 1, 0.9 ≤ n(Li) ≤ 1.1, and 0 < n(M) ≤ 0.05.

[0022] The third aspect of the present invention provides an application of the olivine-type cathode material provided in the first aspect, or the olivine-type cathode material prepared by the preparation method provided in the second aspect, in a lithium-ion battery and a vehicle battery.

[0023] The fourth aspect of the present invention provides a lithium-ion battery, which contains the olivine-type cathode material provided in the first aspect, or the olivine-type cathode material prepared by the preparation method provided in the second aspect.

[0024] Compared with the prior art, the present invention has the following advantages:

[0025] (1) The olivine-type cathode material provided by the present invention includes lithium phosphate as a matrix and a carbon coating layer, and the matrix has a specific composition shown in Formula I. By adjusting the types of M and M' and a, b, c in Formula I, the olivine-type cathode material has the characteristics of high conductivity, low powder impedance, high tap density, and high particle strength. In particular, by limiting the content and composition of the carbon coating layer, the performance of the olivine-type cathode material is further improved;

[0026] (2) The preparation method provided by the present invention first adds an organic carbon source and an inorganic carbon source step by step and grinds them, and then obtains a spherical or quasi-spherical precursor after drying, which shortens the lithium ion diffusion distance and improves the lithium ion diffusion rate at low temperature; then sinter the precursor in an inert atmosphere to carbonize the organic carbon source and cooperate with the inorganic carbon source to form a carbon coating layer on the surface of lithium phosphate to obtain an olivine-type cathode material; in particular, according to whether the phosphate contains water, by adjusting the sintering conditions, on the one hand, it solves the defect that the capacity cannot be fully utilized or is insufficient when directly using hydrated phosphate to prepare the cathode material in the prior art, enriching the source of raw materials; on the other hand, it improves the performance of the cathode material; at the same time, this preparation method simplifies the process flow and is convenient for industrial production;

[0027] (3) The cathode material provided by the present invention is applicable to fields such as lithium-ion batteries and vehicle batteries. In particular, the lithium-ion battery containing this olivine-type cathode material has high rate performance and low temperature performance. Description of the Drawings

[0028] Figure 1 It is the SEM image of the olivine-type cathode material Q1 obtained in Example 1;

[0029] Figure 2 It is the sectional view of the olivine-type cathode material Q1 obtained in Example 1. Specific Embodiments

[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] In the present invention, unless otherwise specified, "first", "second" and "third" neither represent the order nor limit each material or step, but are only used to distinguish or indicate that these are not the same material or step. For example, "first slurry", "second slurry" and "third slurry" are only used to indicate that these are not the same slurry; similarly, "first grinding" and "second grinding" are only used to indicate that these are not the same grinding.

[0032] The first aspect of the present invention provides an olivine-type cathode material, and the olivine-type cathode material includes a lithium phosphate salt as a matrix and a carbon coating layer coated on the matrix;

[0033] Wherein, the matrix has the general formula shown in Formula I: Li a M 1-b M’ b P c O4 Formula I,

[0034] Wherein, 0.9 ≤ a ≤ 1.1, 0.95 ≤ b < 1, 0.96 ≤ b / c ≤ 0.99; M is selected from at least one of W, Mg, Nb, V, Ti, Mo, Rh, Os and Ta; M’ is selected from at least one of Mn, Co, Ni and Fe.

[0035] In the present invention, unless otherwise specified, the olivine-type cathode material is simply referred to as the cathode material.

[0036] In some embodiments of the present invention, in Formula I, 0.9 ≤ a ≤ 1.1, 0.95 ≤ b < 1, 0.96 ≤ b / c ≤ 0.99; M is selected from at least one of W, Mg, Nb, V, Ti, Mo, Rh, Os, and Ta; M' is selected from at least one of Mn, Co, Ni, and Fe; preferably, in Formula I, 0.98 ≤ a ≤ 1.08, 0.96 ≤ b ≤ 0.99, 0.96 ≤ b / c ≤ 0.98; M is selected from W and / or Ti; M' is selected from Mn and / or Fe.

[0037] In some embodiments of the present invention, preferably, based on the total weight of the olivine-type cathode material, the content of the carbon coating layer is 1-2.8 wt%, for example, 1 wt%, 1.2 wt%, 1.54 wt%, 1.57 wt%, 1.58 wt%, 1.61 wt%, 1.62 wt%, 1.8 wt%, 2 wt%, 2.2 wt%, 2.55 wt%, 2.8 wt%, and any value within the range composed of any two values, preferably 1.2-2.8 wt%.

[0038] In some embodiments of the present invention, preferably, the C in the carbon coating layer is derived from C1 generated by carbonization of an organic carbon source and C2 derived from an inorganic carbon source, and the weight ratio of C1 to C2 is 5-15:1, for example, 5:1, 6.5:1, 6.7:1, 6.85:1, 6.9:1, 7.05:1, 7.1:1, 8:1, 9:1, 10:1, 11.75:1, 12:1, 15:1, and any value within the range composed of any two values, preferably 6.5-12:1. When the weight ratio of C1 to C2 is within the said range, C1 can reduce ferric iron to ferrous iron while forming a flocculent carbon coating layer on the surface of the matrix. Additionally, C2 can form a fibrous conductive network to link the coated particles and enhance the conductivity between the particles. Thus, spherical particles with appropriate porosity and relatively high particle strength are obtained.

[0039] In some embodiments of the present invention, preferably, the aspect ratio of the olivine-type cathode material is 0.95-1.05, for example, 0.95, 0.96, 0.97, 0.98, 0.99, 1, 1.01, 1.03, 1.05, and any value within the range composed of any two values, preferably 0.96-1.03. In the present invention, the aspect ratio of the olivine-type cathode material, on the one hand, is beneficial to shortening the transmission distance of lithium ions, improving the kinetic performance, and further enhancing the rate performance of the lithium-ion battery containing the cathode material; on the other hand, when the aspect ratio is close to 1, the cathode material is spherical or quasi-spherical, resulting in larger voids between the particles, so that the electrolyte can more easily penetrate, and thus the rate performance and low-temperature performance of the product containing the olivine-type cathode material are improved.

[0040] In the present invention, unless otherwise specified, the aspect ratio refers to the ratio of the longest particle diameter of the olivine-type cathode material to the particle diameter perpendicular to the longest particle diameter.

[0041] In some embodiments of the present invention, preferably, the D 50 of the olivine-type cathode material is 2 - 17 μm, for example, 2 μm, 5 μm, 6.6 μm, 6.8 μm, 6.9 μm, 7.1 μm, 7.4 μm, 7.6 μm, 8 μm, 10 μm, 12 μm, 15 μm, 17 μm, and any value within the range composed of any two of these values, preferably 5 - 15 μm.

[0042] In some embodiments of the present invention, preferably, the K90 of the olivine-type cathode material is 1 - 3, for example, 1, 1.2, 1.56, 1.89, 1.92, 1.98, 2.01, 2.02, 2.21, 2.5, 3, and any value within the range composed of any two of these values, preferably 1 - 2.5, where K90 = (D 90 - D 10 ) / D 50 .

[0043] In some embodiments of the present invention, preferably, the cross-sectional porosity of the olivine-type cathode material is 5 - 20%, for example, 5%, 10%, 11%, 12%, 13%, 14%, 15%, 18%, 20%, and any value within the range composed of any two of these values, preferably 10 - 20%. Adopting the preferred conditions is more conducive to improving the rate performance and low-temperature performance of the product containing the olivine-type cathode material.

[0044] In some embodiments of the present invention, preferably, the specific surface area of the olivine-type cathode material is 7 - 30 m 2 / g, for example, 7 m 2 / g, 9 m 2 / g, 9.3 m 2 / g, 9.6 m 2 / g, 9.7 m 2 / g, 9.8 m 2 / g, 10.2 m 2 / g, 11.6 m 2 / g, 13 m 2 / g, 15 m 2 / g, 18 m 2 / g, 20 m 2 / g, 22.5 m 2 / g, 25 m 2 / g, 30 m 2 / g, and any value within the range formed by any two numerical values, preferably 9 - 25 m 2 / g. Adopting the preferred conditions is beneficial to the immersion in the electrolyte, thereby improving the rate performance and low-temperature performance of the product containing the olivine-type cathode material.

[0045] In some embodiments of the present invention, preferably, the volume resistivity of the olivine-type cathode material is ≤ 60 Ω·cm. For example, 10 Ω·cm, 15 Ω·cm, 20 Ω·cm, 21 Ω·cm, 22 Ω·cm, 23 Ω·cm, 26 Ω·cm, 30 Ω·cm, 40 Ω·cm, 50 Ω·cm, 58 Ω·cm, 60 Ω·cm, and any value within the range formed by any two numerical values, preferably 20 - 60 Ω·cm. In the present invention, the powder impedance of the olivine-type cathode material is small, resulting in good kinetic performance, thereby improving the rate performance of the product containing the olivine-type cathode material.

[0046] In some embodiments of the present invention, preferably, the tap density of the olivine-type cathode material is 2 - 2.4 g / cm 3 , for example, 2 g / cm 3 , 2.1 g / cm 3 , 2.16 g / cm 3 , 2.21 g / cm 3 , 2.23 g / cm 3 , 2.27 g / cm 3 , 2.3 g / cm 3 , 2.31 g / cm 3 , 2.32 g / cm 3 , 2.37 g / cm 3 , 2.4 g / cm 3 , and any value within the range formed by any two numerical values, preferably 2.2 - 2.4 g / cm 3 . In the present invention, the tap density of the olivine-type cathode material is relatively large, which can improve the tap density of the electrode sheet containing the olivine-type cathode material, thereby improving the energy density of the product containing the olivine-type cathode material.

[0047] In some embodiments of the present invention, preferably, the D 50 change rate of the olivine-type cathode material before and after 2T pressure is ≤ 3%. For example, 1%, 1.5%, 1.9%, 2%, 2.1%, 2.3%, 2.5%, 2.9%, 3%, and any value within the range formed by any two numerical values, preferably 1.5 - 3%; the D 50The change rate ≤ 15%, for example, 8%, 10%, 10.8%, 11%, 11.8%, 12.1%, 12.4%, 12.6%, 13%, 14.1%, 15%, and any value within the range composed of any two numerical values, preferably 10 - 15%; the D of the olivine-type cathode material before and after 6T pressure 50 The change rate ≤ 30%, for example, 20%, 22.4%, 25.1%, 25.3%, 25.7%, 25.9%, 26%, 27%, 28.2%, 29%, 30%, and any value within the range composed of any two numerical values, preferably 25 - 30%. Adopting the preferred conditions is more conducive to improving the particle strength of the olivine-type cathode material.

[0048] In the present invention, the D of the olivine-type cathode material before and after 2T pressure 50 The change rate = (D of the olivine-type cathode material before 2T pressure 50 ― D of the olivine-type cathode material before 2T pressure 50 ) / D of the olivine-type cathode material before 2T pressure 50 . Similarly, the D of the olivine-type cathode material before and after 4T pressure 50 The change rate = (D of the olivine-type cathode material before 4T pressure 50 ― D of the olivine-type cathode material before 4T pressure 50 ) / D of the olivine-type cathode material before 4T pressure 50 .

[0049] In the present invention, without special instructions, the particle size parameters (for example, D 50 , D 90 , D 10 ) are measured by the MS 3000 laser particle size analyzer method; the cross-sectional porosity parameter is measured by calculating the porosity of the picture using particle size software after preparing with the IM4000 ion milling equipment and performing scanning electron microscopy testing; the specific surface area parameter is measured by the Tristar 3020 specific surface area analyzer; the volume resistivity parameter is measured by the ST 2722; the tap density parameter is measured by the Sansi Zongheng (UTM7305) tap density meter.

[0050] The second aspect of the present invention provides a preparation method of an olivine-type cathode material, and the preparation method includes the following steps:

[0051] (1) Mix phosphate, lithium source, organic carbon source, M source, and solvent to obtain a first slurry, and perform first grinding on the first slurry to obtain a second slurry;

[0052] (2) Mix the second slurry and inorganic carbon source and then perform second grinding, and dry the obtained third slurry to obtain a spherical or quasi-spherical precursor;

[0053] (3) Sinter the precursor in an inert atmosphere to obtain an olivine-type cathode material.

[0054] The inventors of the present invention have found through research that first, after grinding a first slurry containing phosphate, lithium source, organic carbon source, and M source, an inorganic carbon source is added and ground to the nanoscale (i.e., D 50 = 100 - 300 nm), and after spray drying, a nanoscale precursor is formed to shorten the lithium ion diffusion distance and improve the diffusion rate at low temperatures; then the precursor is sintered under specific conditions, especially by regulating the sintering temperature at each stage, so that phosphate, lithium source, and M source in the precursor in-situ generate lithium phosphate salts with smaller particle sizes, and the organic carbon source is carbonized and combined with the inorganic carbon source to form a carbon coating layer on the surface of the lithium phosphate salt, obtaining an olivine-type cathode material.

[0055] Specifically, the present invention uses a composite carbon source (i.e., organic carbon source and inorganic carbon source) as a coating agent to coat on the surface of the matrix (i.e., lithium phosphate salt). In view of the different carbonization temperatures of various organic carbon sources, thus, based on the carbonization temperatures of different organic carbon sources, by staged sintering and controlling the sintering temperature at each stage, the composite carbon source is carbonized at different sintering stages, and further, lithium phosphate with smaller particle sizes is obtained. Especially when using hydrated phosphate as a raw material, its transformation temperature is close to the carbonization temperature of the organic carbon source. By means of staged sintering and curve adjustment, the transformation and lithiation reactions of the hydrated phosphate can be carried out simultaneously, achieving a win-win effect, and further solving the problem that the capacity cannot be fully exerted or is insufficient when directly using hydrated phosphate to prepare the cathode material in the prior art.

[0056] In some embodiments of the present invention, preferably, in step (1), the phosphate has the general formula shown in Formula II: M’ x P y O4·nH2O Formula II, wherein M’ is selected from at least one of Mn, Co, Ni, and Fe, 0.95 ≤ x < 1, 0.96 ≤ x / y ≤ 0.99, 0 ≤ n ≤ 2. In the present invention, without special instructions, n includes but is not limited to 0, 1, 1.4, 2, etc.

[0057] In some embodiments of the present invention, further preferably, in Formula II, M’ is selected from Mn and / or Fe, 0.96 ≤ x ≤ 0.99, 0.96 ≤ x / y ≤ 0.98.

[0058] In the present invention, unless otherwise specified, the phosphate includes the following two cases: In the first case, in Formula II, when n = 0, M' is selected from at least one of Mn, Co, Ni, and Fe, 0.95 ≤ x < 1, and 0.96 ≤ x / y ≤ 0.99; in the second case, in Formula II, when n ≠ 0, that is, 0 < n ≤ 2, M' is selected from at least one of Mn, Co, Ni, and Fe, 0.95 ≤ x < 1, and 0.96 ≤ x / y ≤ 0.99.

[0059] In some embodiments of the present invention, in step (1), in Formula II, when n = 0, the D of the phosphate 50 is 1 - 8 μm, for example, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 8 μm, and any value within the range composed of any two of these values, preferably 1 - 6 μm; the specific surface area is 6 - 12 m 2 / g, for example, 6 m 2 / g, 7 m 2 / g, 8 m 2 / g, 9 m 2 / g, 10 m 2 / g, 12 m 2 / g, and any value within the range composed of any two of these values, preferably 6 - 10 m 2 / g.

[0060] In some embodiments of the present invention, in step (1), in Formula II, when n ≠ 0, the D of the phosphate 50 is 1 - 8 μm, for example, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 8 μm, and any value within the range composed of any two of these values, preferably 1 - 6 μm; the specific surface area is 30 - 55 m 2 / g, for example, 30 m 2 / g, 35 m 2 / g, 40 m 2 / g, 45 m 2 / g, 50 m 2 / g, 55 m 2 / g, and any value within the range composed of any two of these values, preferably 30 - 50 m 2 / g.

[0061] In some embodiments of the present invention, preferably, in step (1), the molar ratio of the phosphate in terms of M', the lithium source in terms of Li, and the M source in terms of M is n(M'):n(Li):n(M), where 0.95 ≤ n(M') < 1, 0.9 ≤ n(Li) ≤ 1.1, and 0 < n(M) ≤ 0.05; more preferably, 0.96 ≤ n(M') ≤ 0.99, 0.98 ≤ n(Li) ≤ 1.08, and 0.01 ≤ n(M) ≤ 0.04.

[0062] In some embodiments of the present invention, preferably, the lithium source is selected from organic lithium sources and / or inorganic lithium sources; more preferably, the lithium source is selected from at least one of lithium carbonate, lithium hydroxide, lithium phosphate, lithium dihydrogen phosphate, lithium acetate, lithium oxalate, and lithium nitrate.

[0063] In some embodiments of the present invention, preferably, the weight ratio of the organic carbon source to the phosphate is 10 - 15:100, for example, 10:100, 11:100, 12:100, 13:100, 15:100, and any value within the range composed of any two of these values, preferably 10 - 13:100. Using an organic carbon source with a specific weight ratio can improve the electronic conductivity of the material body. When the weight ratio is less than 10:100, the effect is not good, and when the weight ratio is greater than 15:100, the opposite effect occurs.

[0064] In some embodiments of the present invention, preferably, the organic carbon source is selected from sugars, carboxylic acids, and polymers.

[0065] In a specific embodiment of the present invention, preferably, the sugars include, but are not limited to, glucose, sucrose, starch, cellulose, etc.; the carboxylic acids include, but are not limited to, citric acid, oxalic acid, etc.; the polymers have a weight average molecular weight of 1000 - 8000 g / mol and include, but are not limited to, polyethylene glycol, polyvinyl alcohol, polyethylene, etc.

[0066] In a preferred embodiment of the present invention, more preferably, in the organic carbon source, the weight ratio of sugars, carboxylic acids, and polymers is 3 - 8:1:1 - 4, for example, 3:1:1, 3:1:2, 3:1:3, 3:1:4, 4:1:1, 4:1:2, 4:1:3, 4:1:4, 5:1:1, 5:1:2, 5:1:3, 5:1:4, 6:1:1, 6:1:2, 6:1:3, 6:1:4, 7:1:1, 7:1:2, 7:1:3, 7:1:4, 8:1:1, 8:1:2, 8:1:3, 8:1:4, and any value within the range composed of any two of these values.

[0067] In some embodiments of the present invention, preferably, the M source is selected from compounds containing at least one element of W, Mg, Nb, V, Ti, Mo, Rh, Os, and Ta; more preferably, the M source is selected from compounds containing W and / or Ti. In the present invention, when the M source is selected from compounds containing at least two elements of W, Mg, Nb, V, Ti, Mo, Rh, Os, and Ta, the molar ratio of the specific compounds of the multiple M sources is not limited.

[0068] In the present invention, there is a wide selection range for the type of the solvent, as long as the phosphate, lithium source, organic carbon source, and M source can be dissolved in the solvent. Preferably, the solvent includes, but is not limited to, water and ethanol.

[0069] In some embodiments of the present invention, preferably, the solid content in the first slurry is 30-50 wt%, for example, 30 wt%, 35 wt%, 40 wt%, 45 wt%, 50 wt%, and any value within the range composed of any two values.

[0070] In the present invention, the first grinding is rough grinding, that is, making the particles in the first slurry rough. Preferably, the conditions of the first grinding include: the size of the grinding medium > 0.5 mm, preferably 0.7-0.8 mm; the grinding time is 0.1-1.5 h, preferably 0.5-1 h. In the present invention, the grinding medium includes, but is not limited to, zirconia balls.

[0071] In some embodiments of the present invention, preferably, in step (2), the weight ratio of the inorganic carbon source to the phosphate is 0.01-1:100, for example, 0.01:100, 0.05:100, 0.1:100, 0.2:100, 0.3:100, 0.4:100, 0.5:100, 0.6:100, 0.8:100, 1:100, and any value within the range composed of any two values, preferably 0.01-0.6:100.

[0072] According to the present invention, adding an inorganic carbon source as a conductive agent before the second grinding can not only utilize its rich conductive network and strong conductive ability to increase the conductivity between primary particles, but also make it more evenly mixed with the raw materials (i.e., phosphate, lithium source, organic carbon source, M source), and adjust the size of the primary particles during this process so that the particles are not too large; at the same time, the addition of the inorganic carbon source can also improve the adsorption performance of the electrode sheet. For example, carbon nanotubes have a diversion effect on the conductive liquid, making its processing performance better.

[0073] In some embodiments of the present invention, preferably, the inorganic carbon source is selected from at least one of carbon black, carbon nanotubes, conductive graphite, and graphene. Among them, carbon black includes but is not limited to acetylene black, SP, Ketjen black, etc.; carbon nanotubes include but are not limited to single-walled carbon nanotubes and multi-walled carbon nanotubes.

[0074] In the present invention, the second grinding is ultrafine grinding. Preferably, the conditions for the second grinding include: the size of the grinding medium ≤ 0.5 mm, preferably 0.3 - 0.4 mm; the grinding time is 2 - 10 h, preferably 2 - 5 h. Such settings enable the inorganic carbon source to be fully ground to adjust the size and be uniformly mixed with the phosphate, lithium source, organic carbon source, and M source, avoiding poor coating effects due to the large particles of the inorganic carbon source.

[0075] In some embodiments of the present invention, preferably, the D 50 of the particles in the third slurry is 100 - 300 nm, for example, 100 nm, 120 nm, 150 nm, 180 nm, 200 nm, 300 nm, and any value within the range composed of any two values, preferably 100 - 200 nm; the K90 of the particles in the third slurry is 1 - 6, for example, 1, 2, 3, 4, 5, 6, and any value within the range composed of any two values, preferably 1 - 5.

[0076] In the present invention, in step (2), the drying aims to remove the solvent in the third slurry. In the present invention, the drying includes but is not limited to spray drying.

[0077] In some embodiments of the present invention, preferably, the precursor is 2 - 15 μm, for example, 2 μm, 5 μm, 8 μm, 10 μm, 12 μm, 15 μm, and any value within the range composed of any two values, preferably 5 - 15 μm; the specific surface area of the precursor is 20 - 40 m 2 / g, for example, 20 m 2 / g, 25 m 2 / g, 30 m 2 / g, 35 m 2 / g, 40 m 2 / g, and any value within the range composed of any two values, preferably 25 - 35 m 2 / g. Using the preferred conditions is more conducive to shortening the lithium ion transmission distance, improving the kinetic performance, and thus improving the rate performance.

[0078] In the present invention, by controlling the sintering conditions, the lithium phosphate salt in-situ generated from the phosphate, lithium source, and M source in the precursor serves as the matrix, causing the organic carbon source to carbonize and form a carbon coating layer with the inorganic carbon source. Preferably, in step (3), the olivine-type cathode material includes a matrix and a carbon coating layer coated on the matrix; wherein, the matrix has the general formula shown in Formula I: Li a M 1-b M’ b P c O4 Formula I, where 0.9 ≤ a ≤ 1.1, 0.95 ≤ b < 1, 0.96 ≤ b / c ≤ 0.99; M is selected from at least one of W, Mg, Nb, V, Ti, Mo, Rh, Os, and Ta; M’ is selected from at least one of Mn, Co, Ni, and Fe; Further preferably, in Formula I, 0.98 ≤ a ≤ 1.08, 0.96 ≤ b ≤ 0.99, 0.96 ≤ b / c ≤ 0.98; M is selected from W and / or Ti; M’ is selected from Mn and / or Fe.

[0079] In some embodiments of the present invention, preferably, the C in the carbon coating layer is derived from C1 generated by carbonizing the organic carbon source and C2 derived from the inorganic carbon source, and the weight ratio of C1 to C2 is 5-15:1, for example, 5:1, 6.5:1, 6.7:1, 6.85:1, 6.9:1, 7.05:1, 7.1:1, 8:1, 9:1, 10:1, 11.75:1, 12:1, 15:1, and any value within the range composed of any two numerical values, preferably 6.5-12:1.

[0080] In the present invention, unless otherwise specified, the carbon coating layer is derived from an inorganic carbon source and an organic carbon source. Taking the inorganic carbon source as carbon nanotubes as an example, the primary particles in the secondary particles are linked by fibrous carbon nanotubes. This fibrous carbon chain can enhance the entanglement between voids, increase the conductivity between primary particles, and also enhance the strength of the secondary particles. Under the pressurized state, due to the winding of carbon fibers on the surface of the primary particles, even if deformation occurs, it will not break. Therefore, the product of the present invention can have high strength on the premise of having large voids, and at the same time, the tubular structure of the carbon nanotubes can also facilitate the infiltration of the electrolyte.

[0081] In some embodiments of the present invention, preferably, in Formula II, when n = 0, the sintering conditions include: heating at a heating rate of 1-10 °C / min to 420-460 °C, holding for 50-70 min; then heating at a heating rate of 1-10 °C / min to 600-700 °C, holding for 8-10 h.

[0082] In some embodiments of the present invention, preferably, in Formula II, when n≠0, the sintering conditions include: heating at a heating rate of 1-10 °C / min to 420-460 °C, holding for 50-70 min; then heating at a heating rate of 1-10 °C / min to 480-520 °C, holding for 100-140 min; and finally heating at a heating rate of 1-10 °C / min to 600-700 °C, holding for 8-10 h.

[0083] In the present invention, multi-stage sintering is beneficial to the crystal form transformation when using hydrated phosphate as the raw material. Different organic carbon sources will be carbonized in stages, reducing trivalent transition metals to divalent, and forming olivine-type cathode microcrystals with lithium sources and M sources. The mutual cooperation of organic carbon sources and inorganic carbon sources inhibits the movement of microcrystal grain boundaries at different sintering stages, controlling the slow growth of particles.

[0084] In the present invention, without special instructions, the olivine-type cathode material is secondary particles aggregated by primary particles. When the D of primary particles and secondary particles 50 is smaller, it is more beneficial to shorten the transmission distance of lithium ions, improve kinetic performance, and then improve the rate performance. At the same time, when the aspect ratio of secondary particles is close to 1 and the secondary particles are spherical or quasi-spherical, the voids of the secondary particles are larger, that is, the cross-sectional porosity is larger. Therefore, the electrolyte is more likely to penetrate, making the low-temperature rate performance of the product containing the olivine-type cathode material better.

[0085] The third aspect of the present invention provides an application of the olivine-type cathode material provided in the first aspect, or the olivine-type cathode material prepared by the preparation method provided in the second aspect, in lithium-ion batteries and vehicle batteries.

[0086] The fourth aspect of the present invention provides a lithium-ion battery, which includes the olivine-type cathode material provided in the first aspect, or the olivine-type cathode material prepared by the preparation method provided in the second aspect.

[0087] In some embodiments of the present invention, preferably, the 0.1C discharge capacity of the lithium-ion battery containing the olivine-type cathode material > 150 mAh / g, and the 5C discharge capacity > 110 mAh / g.

[0088] The present invention will be described in detail below through examples.

[0089] Particle size parameters (e.g., D 50 , D 90 , D 10 ) are measured by the MS 3000 laser particle size analyzer method;

[0090] The cross-sectional porosity parameter is measured by calculating the porosity of the image using particle size software after preparation with an IM4000 ion milling device and then performing scanning electron microscopy testing.

[0091] The specific surface area parameter is measured using a Tristar 3020 specific surface area analyzer.

[0092] The volume resistivity parameter is measured using an ST2722.

[0093] The compacted density parameter is measured using a Sansi Zongheng (UTM7305) compacted density meter.

[0094] Example 1

[0095] (1) Mix phosphate (Fe x P y O4, x = 0.97, y = 1; D 50 is 1.9 μm; specific surface area is 7.9 m 2 / g), lithium source (lithium carbonate), organic carbon source (weight ratio of glucose, citric acid, and PEG (weight average molecular weight of 2000 g / mol) is 7:1:3), M source (TiO2), and water to obtain a first slurry with a solid content of 45 wt%; wherein, the molar ratio of the phosphate based on Fe, the lithium source based on Li, and the M source based on Ti is 0.97:1.06:0.03; the weight ratio of the organic carbon source to the phosphate is 11:100;

[0096] Perform first grinding on the above first slurry with a zirconia bead size of 0.75 mm and a grinding time of 0.5 h to obtain a second slurry;

[0097] (2) Mix the above second slurry and inorganic carbon source (carbon nanotubes) and then perform second grinding with a zirconia bead size of 0.35 mm and a grinding time of 3.5 h. The D 50 of the particles in the obtained third slurry is 160 nm and K90 is 1.08; wherein, the weight ratio of the above inorganic carbon source to the phosphate is 0.2:100;

[0098] Perform spray drying on the above third slurry to obtain a precursor;

[0099] Among them, the D 50 of the above precursor is 6.1 μm and the specific surface area is 30 m 2 / g;

[0100] (3) Sinter the above precursor in a nitrogen atmosphere, heat it to 440 °C at a heating rate of 1.5 °C / min and hold for 1 h; heat it to 650 °C at a heating rate of 1.5 °C / min and hold for 10 h to obtain the olivine-type cathode material Q1;

[0101] Among them, the composition of the olivine-type cathode material Q1, the content of the carbon coating layer, the aspect ratio, D 50 , K90, cross-sectional porosity, specific surface area, volume resistivity, tap density, 2T D 50 change rate, 4T D 50 change rate, and 6T D 50 change rates are all listed in Table 1.

[0102] Among them, the SEM image of the olivine-type cathode material Q1 is as Figure 1 shown. It can be seen from Figure 1 that the olivine-type cathode material Q1 has a spherical structure.

[0103] Among them, the cross-sectional view of the olivine-type cathode material Q1 is as Figure 2 shown. It can be seen from Figure 2 that the cross-sectional porosity of the olivine-type cathode material Q1 is 12%.

[0104] Example 2

[0105] (1) Mix hydrated phosphate (Fe x P y O4·nH2O, x = 0.97, y = 1, n = 1.4; D 50 is 2.3 μm; specific surface area is 49 m 2 / g), lithium source (lithium carbonate), organic carbon source (weight ratio of glucose, citric acid, and PEG (weight average molecular weight is 2000 g / mol) is 7:1:3), M source (TiO2), and water to obtain a first slurry with a solid content of 45 wt%; among them, the molar ratio of the phosphate in terms of Fe, the lithium source in terms of Li, and the M source in terms of Ti is 0.97:1.06:0.03; the weight ratio of the organic carbon source and the phosphate is 11:100;

[0106] Perform first grinding on the above first slurry, with the zirconia bead size being 0.75 mm and the grinding time being 0.5 h to obtain a second slurry;

[0107] (2) Mix the above second slurry and inorganic carbon source (carbon nanotubes) and then perform second grinding, with the zirconia bead size being 0.35 mm and the time being 3 h. The D 50 of the particles in the obtained third slurry is 160 nm and K90 is 1.06; among them, the weight ratio of the inorganic carbon source and the phosphate is 0.2:100;

[0108] Perform spray drying on the above third slurry to obtain a precursor;

[0109] Among them, the D 50 of the above precursor is 6.8 μm and the specific surface area is 35 m 2 / g;

[0110] (3) Sinter the above precursor in a nitrogen atmosphere, heat it to 440 °C at a heating rate of 1.5 °C / min and keep it at a constant temperature for 1 h; heat it to 500 °C at a heating rate of 1.5 °C / min and keep it at a constant temperature for 2 h; heat it to 650 °C at a heating rate of 1.5 °C / min and keep it at a constant temperature for 10 h to obtain the olivine-type cathode material Q2;

[0111] Among them, the composition of the olivine-type cathode material Q2, the content of the carbon coating layer, the aspect ratio, D 50 , K90, cross-sectional porosity, specific surface area, volume resistivity, tap density, 2T D 50 change rate, 4T D 50 change rate and 6T D 50 change rates are all listed in Table 1.

[0112] Example 3

[0113] (1) Mix phosphate (Fe x P y O4, x = 0.97, y = 1; D 50 is 1.9 μm; the specific surface area is 7.9 m 2 / g), lithium source (lithium carbonate), organic carbon source (weight ratio of glucose: citric acid: PEG (weight average molecular weight is 2000 g / mol) is 7:1:3), M source (TiO2) and water to obtain a first slurry with a solid content of 45 wt%; among them, the molar ratio of the phosphate based on Fe, the lithium source based on Li and the M source based on Ti is 0.97:1.06:0.03; the weight ratio of the organic carbon source and the phosphate is 11:100;

[0114] Perform first grinding on the above first slurry, the zirconia ball size is 0.75 mm, and the grinding time is 0.5 h to obtain a second slurry;

[0115] (2) Mix the above second slurry and inorganic carbon source (carbon nanotubes) and then perform second grinding, the zirconia ball size is 0.35 mm, and the grinding time is 3.5 h. The D 50 of the particles in the obtained third slurry is 200 nm, and K90 is 1.01; among them, the weight ratio of the inorganic carbon source and the phosphate is 0.2:100;

[0116] Perform spray drying on the above third slurry to obtain a precursor;

[0117] Among them, the D 50 of the above precursor is 7 μm, and the specific surface area is 33 m 2 / g;

[0118] (3) Sinter the above precursor in a nitrogen atmosphere, heat it to 440 °C at a heating rate of 1.5 °C / min, and keep it at a constant temperature for 1 h; then heat it to 650 °C at a heating rate of 1.5 °C / min and keep it at a constant temperature for 10 h to obtain the olivine-type cathode material Q3;

[0119] Among them, the composition of the olivine-type cathode material Q3, the content of the carbon coating layer, the aspect ratio, D 50 , K90, cross-sectional porosity, specific surface area, volume resistivity, tap density, 2T D 50 change rate, 4T D 50 change rate and 6T D 50 change rates are all listed in Table 1.

[0120] Example 4

[0121] According to the method of Example 1, the difference is that

[0122] In step (1), replace the M source with WO3. Among them, the molar ratio of the phosphate in terms of Fe, the lithium source in terms of Li, and the M source in terms of W is 0.97:1.06:0.03; under the same other conditions, obtain the olivine-type cathode material Q4;

[0123] Among them, D of the particles in the third slurry 50 is 160 nm and K90 is 1.07;

[0124] Among them, D of the precursor 50 is 6.3 μm and the specific surface area is 31 m 2 / g;

[0125] Among them, the composition of the olivine-type cathode material Q4, the content of the carbon coating layer, the aspect ratio, D 50 , K90, cross-sectional porosity, specific surface area, volume resistivity, tap density, 2T D 50 change rate, 4T D 50 change rate and 6T D 50 change rates are all listed in Table 1.

[0126] Example 5

[0127] According to the method of Example 1, the difference is that

[0128] In step (1), replace the weight ratio of glucose:citric acid:PEG in the organic carbon source with 6:1:2; under the same other conditions, obtain the olivine-type cathode material Q5;

[0129] Among them, D of the particles in the third slurry 50 is 160 nm and K90 is 1.04;

[0130] Among them, D of the precursor 50 is 6.6 μm, and the specific surface area is 30 m 2 / g;

[0131] Among them, the composition of the olivine-type cathode material Q5, the content of the carbon coating layer, the aspect ratio, D 50 , K90, cross-sectional porosity, specific surface area, volume resistivity, tap density, 2T D 50 change rate, 4T D 50 change rate and 6T D 50 change rate are all listed in Table 1.

[0132] Example 6

[0133] According to the method of Example 2, the difference is that

[0134] in step (1), the hydrated phosphate is replaced with hydrated manganese iron phosphate (Mn x1 Fe x2 P y O4·nH2O, x1:x2 = 6:4, x1 + x2 = 0.97, y = 1, n = 1; D 50 is 1.9 μm; the specific surface area is 30 m 2 / g), the weight ratio of the organic carbon source and the phosphate is replaced with 15:100; the M source is replaced with TiO2 and WO3, and the molar ratio of TiO2 and WO3 is 3:1, and the other conditions are the same, to obtain the olivine-type cathode material Q6;

[0135] Among them, D of the particles in the third slurry 50 is 160 nm, and K90 is 1.05;

[0136] Among them, D of the precursor 50 is 6.2 μm, and the specific surface area is 32 m 2 / g;

[0137] Among them, the composition of the olivine-type cathode material Q6, the content of the carbon coating layer, the aspect ratio, D 50 , K90, cross-sectional porosity, specific surface area, volume resistivity, tap density, 2T D 50 change rate, 4T D 50 change rate and 6T D 50 change rate are all listed in Table 1.

[0138] Comparative Example 1

[0139] According to the method of Example 1, the difference is that

[0140] in step (2), the conditions of spray drying are adjusted so that D in the precursor 50is 18 μm, and K90 is 1.63; with the remaining conditions being the same, the olivine-type cathode material DQ1 is obtained;

[0141] Among them, the composition of the olivine-type cathode material DQ1, the content of the carbon coating layer, the aspect ratio, D 50 , K90, the cross-sectional porosity, specific surface area, volume resistivity, tap density, 2T D 50 change rate, 4T D 50 change rate, and 6T D 50 change rates are all listed in Table 1.

[0142] Comparative Example 2

[0143] According to the method of Example 1, the difference is that

[0144] in step (3), heating to 650 °C at a heating rate of 1.5 °C / min is replaced by heating to 720 °C at a heating rate of 1.5 °C / min, and with the remaining conditions being the same, the olivine-type cathode material DQ2 is obtained;

[0145] Among them, the composition of the olivine-type cathode material DQ2, the content of the carbon coating layer, the aspect ratio, D 50 , K90, the cross-sectional porosity, specific surface area, volume resistivity, tap density, 2T D 50 change rate, 4T D 50 change rate, and 6T D 50 change rates are all listed in Table 1.

[0146] Comparative Example 3

[0147] According to the method of Example 1, the difference is that

[0148] in step (2), no inorganic carbon source is added, and with the remaining conditions being the same, the cathode material DQ3 is obtained;

[0149] Among them, D of the particles in the third slurry 50 is 160 nm, and K90 is 1.05;

[0150] Among them, D of the precursor 50 is 6.3 μm, and the specific surface area is 33 m 2 / g;

[0151] Among them, the composition of the cathode material DQ3, the content of the carbon coating layer, the aspect ratio, D 50 , K90, the cross-sectional porosity, specific surface area, volume resistivity, tap density, 2T D 50 change rate, 4T D 50 change rate, and 6T D 50 change rates are all listed in Table 1.

[0152] Comparative Example 4

[0153] According to the method of Example 1, the difference is that

[0154] in step (1), the weight ratio of glucose, citric acid and PEG in the organic carbon source is changed from 7:1:3 to 8:3 for glucose and PEG in the organic carbon source;

[0155] in step (2), no inorganic carbon source is added, and the other conditions are the same, obtaining the positive electrode material DQ4;

[0156] wherein, the D 50 of the particles in the third slurry is 160 nm, and K90 is 1.07;

[0157] wherein, the D 50 of the precursor is 6.6 μm, and the specific surface area is 33.2 m 2 / g;

[0158] wherein, the composition, the content of the carbon coating layer, the aspect ratio, D 50 , K90, the cross-sectional porosity, the specific surface area, the volume resistivity, the tap density, the 2T D 50 change rate, the 4T D 50 change rate and the 6T D 50 change rate of the positive electrode material DQ4 are all listed in Table 1.

[0159] Comparative Example 5

[0160] According to the method of Example 1, the difference is that

[0161] in step (1), no M source (TiO2) is added, and the other conditions are the same, obtaining the positive electrode material DQ5;

[0162] wherein, the D 50 of the particles in the third slurry is 160 nm, and K90 is 1.08;

[0163] wherein, the D 50 of the precursor is 6.2 μm, and the specific surface area is 30 m 2 / g;

[0164] wherein, the composition, the content of the carbon coating layer, the aspect ratio, D 50 , K90, the cross-sectional porosity, the specific surface area, the volume resistivity, the tap density, the 2T D 50 change rate, the 4T D 50 change rate and the 6T D 50 change rate of the positive electrode material DQ5 are all listed in Table 1.

[0165] Table 1

[0166]

[0167] Note: 1 - Content of carbon coating layer, wt%; 2 - C in the carbon coating layer comes from C1 generated by carbonization of organic carbon source and C2 from inorganic carbon source, and the weight ratio of C1 and C2.

[0168] Continued Table 1

[0169]

[0170] It can be seen from the results in Table 1 that, compared with Comparative Examples 3 - 5, the olivine-type cathode material prepared by the preparation method provided by the present invention in Examples 1 - 6 includes a matrix and a carbon coating layer, wherein the matrix satisfies the general formula of Formula I, that is, Li a M 1-b M’ b P c O4, where 0.9 ≤ a ≤ 1.1, 0.95 ≤ b < 1, 0.96 ≤ b / c ≤ 0.99, M is selected from at least one of W, Mg, Nb, V, Ti, Mo, Rh, Os and Ta, and M’ is selected from at least one of Mn, Co, Ni and Fe; the content of the carbon coating layer is 1 - 2.8 wt%; C in the carbon coating layer comes from C1 generated by carbonization of organic carbon source and C2 from inorganic carbon source, and the weight ratio of C1 and C2 is 5 - 15:1.

[0171] Compared with Comparative Examples 1 - 2, the olivine-type cathode material prepared in Examples 1 - 6 satisfies: aspect ratio is 0.95 - 1.05; D 50 is 2 - 17 μm; K90 is 1 - 3; cross-sectional porosity is 5 - 20%; specific surface area is 7 - 30 m 2 / g; volume resistivity ≤ 60 Ω·cm; tap density is 2 - 2.4 g / cm 3 ; 2T D 50 change rate ≤ 3%; 4T D 50 change rate ≤ 15%; 6T D 50 change rate ≤ 30%. Therefore, the olivine-type cathode material provided by the present invention has the characteristics of high conductivity, low powder impedance, high tap density and large particle strength.

[0172] Test Example 1

[0173] Assembled battery: The olivine-type cathode materials, acetylene black, and polyvinylidene fluoride (PVDF) of Examples 1-6 and Comparative Examples 1-5 were mixed in a weight ratio of 90:5:5, coated on aluminum foil and dried. They were stamped into a cathode electrode sheet with a diameter of 12 mm and a thickness of 120 μm under a pressure of 100 MPa, and then the cathode electrode sheet was placed in a vacuum drying oven and dried at 120 °C for 12 h. The anode used a Li metal sheet with a diameter of 17 mm and a thickness of 1 mm; the separator used a 25-μm-thick Celgard 2400 porous membrane; the electrolyte used an equal-volume mixture of 1 mol / L LiPF6, ethylene carbonate (EC), and diethyl carbonate (DEC). The cathode electrode sheet, separator, anode electrode sheet, and electrolyte were assembled into a 2025-type button battery in an Ar gas glove box with a water content and an oxygen content both less than 5 ppm. The assembled button battery was tested for its capacity at 0.1C and 5C rates at 25 °C, and for its capacity at 0.1C rate at -20 °C. The results are shown in Table 2.

[0174] Table 2

[0175]

[0176] From the data in Table 2, it can be seen that compared with Comparative Examples 3-5, the lithium-ion batteries prepared from the olivine-type cathode materials prepared in Examples 1-6 have higher rate performance and low-temperature performance. At the same time, compared with Comparative Examples 1-2, the lithium-ion batteries prepared from the olivine-type cathode materials prepared in Examples 1-6 have higher low-temperature performance.

[0177] Therefore, the lithium-ion batteries prepared from the olivine-type cathode materials provided by the present invention have both higher rate performance and low-temperature performance.

[0178] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited thereto. Within the scope of the technical concept 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, The lithium iron phosphate cathode material includes lithium phosphate as the matrix and a carbon coating layer coated on the matrix; Among them, the matrix has the general formula shown in Formula I: Li a M 1-b M’ b P c O4 Formula I wherein, 0.9 ≤ a ≤ 1.1, 0.95 ≤ b < 1, 0.96 ≤ b / c ≤ 0.99; M is selected from at least one of W, Mg, Nb, V, Ti, Mo, Rh, Os, and Ta; M' is selected from Fe; wherein, C in the carbon coating layer is derived from C1 generated by carbonization of an organic carbon source and C2 derived from an inorganic carbon source, and the weight ratio of C1 to C2 is 5 - 10:1; Among them, the lithium iron phosphate cathode material is prepared by the following method: (1) Mix a phosphate, a lithium source, an organic carbon source, an M source and a solvent, and subject the obtained first slurry to first grinding to obtain a second slurry; (2) Mix the second slurry and an inorganic carbon source and then perform second grinding, and dry the obtained third slurry to obtain a spherical or quasi-spherical precursor; (3) Sinter the precursor in an inert atmosphere to obtain the lithium iron phosphate cathode material; among them, the phosphate has the general formula of Formula II: M’ x P y O4·nH2O (II), 0.95 ≤ x < 1, 0.96 ≤ x / y ≤ 0.99, 0 ≤ n ≤ 2.

2. The lithium iron phosphate cathode material according to claim 1, wherein, In formula I, 0.98 ≤ a ≤ 1.08, 0.96 ≤ b ≤ 0.99, 0.96 ≤ b / c ≤ 0.98; M is selected from W and / or Ti; and / or, based on the total weight of the lithium iron phosphate cathode material, the content of the carbon coating layer is 1 - 2.8 wt%; and / or, C in the carbon coating layer is derived from C1 generated by carbonization of an organic carbon source and C2 derived from an inorganic carbon source, and the weight ratio of C1 to C2 is 6.5 - 10:

1.

3. The lithium iron phosphate cathode material according to claim 2, wherein, Based on the total weight of the lithium iron phosphate cathode material, the content of the carbon coating layer is 1.2 - 2.8 wt%.

4. The lithium iron phosphate cathode material according to any one of claims 1-3, wherein, The aspect ratio of the lithium iron phosphate cathode material is 0.95 - 1.05; D 50 is 2 - 17 µm; K90 is 1 - 3, where K90 = (D 90 - D 10 ) / D 50 ; and / or, the cross-sectional porosity of the lithium iron phosphate cathode material is 5 - 20%; and / or, the specific surface area of the lithium iron phosphate cathode material is 7-30 m 2 / g; and / or, the volume resistivity of the lithium iron phosphate cathode material is ≤ 60 Ω∙cm; And / or, the tap density of the lithium iron phosphate cathode material is 2-2.4 g / cm 3 ; And / or, the D change rate of the lithium iron phosphate cathode material before and after 2T pressure 50 ≤ 3%; the D change rate before and after 4T pressure 50 ≤ 15%; the D change rate before and after 6T pressure 50 ≤ 30%.

5. The lithium iron phosphate cathode material according to claim 4, wherein the aspect ratio of the lithium iron phosphate cathode material is 0.96 - 1.03; D 50 is 5 - 15 µm; K90 is 1 - 2.5, wherein, K90=(D 90 -D 10 ) / D 50 ; and / or, the cross-sectional porosity of the lithium iron phosphate cathode material is 10 - 20%; and / or, the specific surface area of the lithium iron phosphate cathode material is 9-25m 2 / g; and / or, the volume resistivity of the lithium iron phosphate cathode material is 20 - 60 Ω∙cm; And / or, the tap density of the lithium iron phosphate cathode material is 2.2-2.4 g / cm 3 ; and / or, the change rate of the lithium iron phosphate cathode material before and after 2T pressure for D 50 is 1.5 - 3%; the change rate of D before and after 4T pressure 50 is 10 - 15%; the change rate of D before and after 6T pressure 50 is 25 - 30%.

6. A method for preparing the lithium iron phosphate cathode material according to claim 1, characterized in that, The preparation method includes the following steps: (1) Mix phosphate, a lithium source, an organic carbon source, an M source, and a solvent, and grind the obtained first slurry for the first time to obtain a second slurry; (2) Mix the second slurry and an inorganic carbon source, then grind for the second time, and dry the obtained third slurry to obtain a spherical or quasi-spherical precursor; (3) Sinter the precursor in an inert atmosphere to obtain the lithium iron phosphate cathode material; Among them, the phosphate has a general formula shown in Formula II: M’ x P y O4·nH2O (II), 0.95 ≤ x < 1, 0.96 ≤ x / y ≤ 0.99, 0 ≤ n ≤ 2, and M’ is selected from Fe.

7. The preparation method according to claim 6, wherein, In step (1), in formula II, 0.96 ≤ x ≤ 0.99, 0.96 ≤ x / y ≤ 0.

98.

8. The preparation method according to claim 7, wherein, In Formula II, when n = 0, D of the phosphate 50 is 1 - 8 µm; the specific surface area is 6 - 12 m 2 / g; or In Formula II, when n≠0, D of the phosphate 50 is 1-8 µm; the specific surface area is 30-55 m 2 / g; and / or, the molar ratio of the phosphate in terms of M', the lithium source in terms of Li, and the M source in terms of M is n(M'):n(Li):n(M), wherein, 0.95 ≤ n(M') < 1, 0.9 ≤ n(Li) ≤ 1.1, 0 < n(M) ≤ 0.

05.

9. The preparation method according to claim 8, wherein, In formula II, when n = 0, D of the phosphate 50 is 1 - 6 µm; the specific surface area is 6 - 10 m 2 / g; or In Formula II, when n ≠ 0, D of the phosphate 50 is 1 - 6 µm; the specific surface area is 30 - 50 m 2 / g; and / or, the molar ratio of the phosphate in terms of M', the lithium source in terms of Li, and the M source in terms of M is n(M'):n(Li):n(M), wherein, 0.96 ≤ n(M') ≤ 0.99, 0.98 ≤ n(Li) ≤ 1.08, 0.01 ≤ n(M) ≤ 0.

04.

10. The preparation method according to claim 6, wherein, In step (1), the lithium source is selected from an organic lithium source and / or an inorganic lithium source; and / or, the weight ratio of the organic carbon source to the phosphate is 10 - 15:100; and / or, the organic carbon source is selected from sugars, carboxylic acids, and polymers; and / or, the M source is selected from compounds containing at least one element of W, Mg, Nb, V, Ti, Mo, Rh, Os, and Ta; And / or, the solid content in the first slurry is 30-50 wt%; And / or, the conditions of the first grinding include: the size of the grinding medium > 0.5 mm; The grinding time is 0.1-1.5 h.

11. According to the preparation method described in claim 10, wherein The lithium source is selected from at least one of lithium carbonate, lithium hydroxide, lithium phosphate, lithium dihydrogen phosphate, lithium acetate, lithium oxalate and lithium nitrate; And / or, the weight ratio of the organic carbon source to the phosphate is 10-13:100; And / or, in the organic carbon source, the weight ratio of saccharides, carboxylic acids and polymers is 3-8:1:1-4; And / or, the conditions of the first grinding include: the size of the grinding medium is 0.7-0.8 mm; The grinding time is 0.5-1 h.

12. The preparation method according to claim 6, wherein, In step (2), the weight ratio of the inorganic carbon source to the phosphate is 0.01-1:100; And / or, the inorganic carbon source is selected from at least one of carbon black, carbon nanotubes, conductive graphite and graphene; And / or, the conditions of the second grinding include: the size of the grinding medium ≤ 0.5 mm; the grinding time is 2-10 h; and / or, the D of the particles in the third slurry 50 is 100 - 300 nm; K90 is 1 - 6; and / or, D of the precursor 50 is 2 - 15 µm; the specific surface area is 20 - 40 m 2 / g.

13. The preparation method according to claim 12, wherein, In step (2), the weight ratio of the inorganic carbon source to the phosphate is 0.01-0.6:100; And / or, the conditions of the second grinding include: the size of the grinding medium is 0.3-0.4 mm; the grinding time is 2-5 h; And / or, D of the particles in the third slurry 50 is 100 - 200 nm; K90 is 1 - 5; and / or, D of the precursor 50 is 5 - 15 µm; the specific surface area is 25 - 35 m 2 / g.

14. The preparation method according to claim 6, wherein In formula II, when n = 0, the sintering conditions include: heating to 420-460 °C at a heating rate of 1-10 °C / min, holding for 50-70 min; then heating to 600-700 °C at a heating rate of 1-10 °C / min, holding for 8-10 h; or, When n ≠ 0, the sintering conditions include: heating to 420-460 °C at a heating rate of 1-10 °C / min, holding for 50-70 min; then heating to 480-520 °C at a heating rate of 1-10 °C / min, holding for 100-140 min; finally heating to 600-700 °C at a heating rate of 1-10 °C / min, holding for 8-10 h.

15. Application of the lithium iron phosphate cathode material according to any one of claims 1-5 in a lithium ion battery and a vehicle battery.

16. A lithium-ion battery, characterized in that, The lithium ion battery includes: the lithium iron phosphate cathode material according to any one of claims 1-5.

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