Positive electrode material, and preparation method therefor and use thereof

Abstract

A positive electrode material, and a preparation method therefor and the use thereof. The chemical general formula of the positive electrode material is LiaFebMncMx(PO4)d, where 0.990≤a≤1.1, 0.9≤b+c≤1.1, 0.95≤d≤1.1, 0.001≤x≤0.03, and 0.9≤b+c+x≤1.1. Crystals of the positive electrode material can preferentially grow along an ac crystal plane, wherein the ratio of the size of the positive electrode material along an a direction to the size of the positive electrode material along a b direction is 0.4542-0.4756; and the ratio of the size of the positive electrode material along a c direction to the size of the positive electrode material along the b direction is 0.5869-0.6172. The size of the crystals of the positive electrode material along the b direction is relatively small, and since the ac plane is perpendicular to the migration direction of lithium ions, the positive electrode material preferentially grows along the ac plane, thereby shortening the diffusion distance of lithium ions and improving the cycling performance of the positive electrode material.

Description

Positive electrode material, preparation method and application thereof

[0001] This disclosure claims priority to the Chinese patent application filed with the China Patent Office on October 27, 2023, with application number 202311412581.5, the entire contents of which are incorporated by reference into this disclosure. Technical Field

[0002] The present disclosure relates to the field of battery technology, and in particular to a positive electrode material and a preparation method and application thereof. Background Art

[0003] Lithium-ion batteries are a new generation of green, high-energy batteries, increasingly playing a vital role in various fields. The cathode material of a lithium-ion battery is a crucial component, determining its energy density, lifespan, and safety, and therefore playing a central role in the battery. As electric vehicles demand ever-increasing range, the performance requirements for cathode materials are also increasing. However, existing cathode materials suffer from poor cycling performance during charge and discharge, limiting the potential for improved lithium-ion battery performance.

[0004] Summary of the Invention

[0005] The present disclosure provides a positive electrode material, a preparation method thereof, and an application thereof.

[0006] In a first aspect, the present disclosure provides a positive electrode material, the chemical formula of which is Li a Fe b Mn c M x (PO4) d , wherein M comprises at least one element selected from Ti, V, Mg, Zr, Co, In, Ni, and Nb, 0.990≤a≤1.1, 0.9≤b+c≤1.1, 0.95≤d≤1.1, 0.001≤x≤0.03, and 0.9≤b+c+x≤1.1. Crystals of the positive electrode material can preferentially grow along the ac crystal plane. The ratio of the size of the positive electrode material along the a-direction to the size of the positive electrode material along the b-direction is 0.4542 to 0.4756; and the ratio of the size of the positive electrode material along the c-direction to the size of the positive electrode material along the b-direction is 0.5869 to 0.6172.

[0007] In the embodiment of the present disclosure, by introducing the M element into the positive electrode material, the positive electrode material can be preferentially grown on the specified ac crystal plane to shorten the size of the positive electrode material crystal along the b direction. Since the ac plane is perpendicular to the direction of lithium ion migration, the bc plane and the b direction are parallel to the lithium ion transmission channel. In addition, by controlling 0.001≤x≤0.03, the M element is appropriately doped, and the cycle performance of the positive electrode material is improved while ensuring that the positive electrode material has high electrochemical properties. In the embodiment of the present disclosure, by modifying the positive electrode material and controlling the degree of coordination between the doping element and the anion, the positive electrode material can be preferentially grown along the ac plane, shortening the lithium ion diffusion distance, which is beneficial to lithium ion migration, thereby improving the ion transmission rate and electron transmission rate of the positive electrode material, and the cycle performance of the positive electrode material is effectively improved.

[0008] In one possible embodiment, the ratio of the diffraction peak area of ​​the (020) crystal plane of the positive electrode material to the diffraction peak area of ​​the (200) crystal plane is 3.011 to 3.500, wherein the (020) crystal plane corresponds to the ac crystal plane. The larger the ratio of the diffraction peak area of ​​the (020) crystal plane of the positive electrode material to the diffraction peak area of ​​the (200) crystal plane, the better the cycle performance of the positive electrode material. The present disclosure designs the structure of the positive electrode material and controls the ratio of the diffraction peak area of ​​the (020) crystal plane of the positive electrode material to the diffraction peak area of ​​the (200) crystal plane within an appropriate range, so that the crystal structure of the positive electrode material grows along a specific ac crystal plane, thereby significantly improving the cycle performance of the positive electrode material.

[0009] In one possible embodiment, the M includes at least two elements selected from Ti, V, Mg, Zr, Co, In, Ni, and Nb. M is selected from a variety of metals to help comprehensively improve the performance of the positive electrode material.

[0010] In one possible embodiment, the at least two elements include at least one of Ti and Nb. Doping the positive electrode material with Ti helps improve the battery's charge and discharge performance. Doping the positive electrode material with Nb helps improve the structural stability of the positive electrode material. In the disclosed embodiments, M includes at least one of Ti and Nb, which can further enhance the performance of the positive electrode material.

[0011] In one possible embodiment, the molar ratio of the Ti and / or Nb element to the M element is (0.5-1): 1. In the disclosed embodiment, a higher proportion of the Ti element and / or Nb element in the M element is more conducive to improving the charge and discharge performance and structural stability of the positive electrode material, and the positive electrode material has more excellent performance.

[0012] In one possible embodiment, the positive electrode material is obtained by doping the M element at the Mn position of lithium manganese iron phosphate. In the present disclosure, doping the M element at the Mn position facilitates the preferential growth of the positive electrode material along the ac plane, shortening the lithium ion diffusion distance and improving the cycling performance of the positive electrode material. In addition, doping the M element at the Mn position can increase the molar ratio of Fe to Mn in the positive electrode material, resulting in higher cycling stability of the positive electrode material.

[0013] In a second aspect, the present disclosure provides a method for preparing a positive electrode material, the method comprising:

[0014] dissolving a lithium source, an iron source, and a manganese source in a solvent to obtain a first slurry;

[0015] dissolving a phosphorus source and a dopant in a solvent to obtain a second slurry;

[0016] mixing the second slurry and the first slurry to obtain a mixed slurry;

[0017] heating the mixed slurry to obtain a precursor;

[0018] The precursor is sintered and ground to obtain the positive electrode material.

[0019] In a possible implementation, the mixing of the second slurry and the first slurry includes:

[0020] The second slurry is divided into n portions, and the n portions of the second slurry are sequentially added to the first slurry at intervals; wherein n is a positive integer and is greater than or equal to 2.

[0021] The preparation method of the positive electrode material provided by the present disclosure is conducive to the preparation of Li a Fe b Mn c M x (PO4) d positive electrode materials, thereby improving the cycle performance of the positive electrode materials.

[0022] In a third aspect, the present disclosure provides a positive electrode plate, which includes the positive electrode material as described above, or includes the positive electrode material prepared by the preparation method of the positive electrode material as described above.

[0023] In a fourth aspect, the present disclosure provides a secondary battery comprising a negative electrode plate, a separator, and the positive electrode plate as described above. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the technical solutions in the embodiments of the present disclosure, the drawings required for use in the embodiments of the present disclosure will be described below.

[0025] FIG1 is an XRD structure diagram of differently doped positive electrode materials provided in one embodiment of the present disclosure. DETAILED DESCRIPTION

[0026] The technical solutions in the embodiments of the present disclosure will be described below in conjunction with the drawings in the embodiments of the present disclosure. Obviously, the described embodiments are only part of the embodiments of the present disclosure, rather than all the embodiments.

[0027] As used herein, the terms "first," "second," and the like are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of the technical features being referenced. Thus, a feature identified as "first" or "second" may explicitly or implicitly include one or more of the features. Throughout this disclosure, unless otherwise specified, "plurality" means two or more.

[0028] In addition, in this article, directional terms such as "upper" and "lower" are defined relative to the orientation of the structure schematically placed in the accompanying drawings. It should be understood that these directional terms are relative concepts. They are used for relative description and clarification, and they can change accordingly according to changes in the orientation of the structure.

[0029] For ease of understanding, the English abbreviations and related technical terms involved in the embodiments of the present disclosure are first explained and described below.

[0030] XRD: short for X-ray Diffraction.

[0031] In the existing technology, lithium iron phosphate (LFP) and lithium manganese iron phosphate (LMFP) are usually selected as positive electrode materials. As a low-cost, high-safety olivine lithium iron phosphate (LFP) is considered to be one of the most competitive materials. However, as people's requirements for the cruising range of electric vehicles are getting higher and higher, the operating voltage and energy density of lithium iron phosphate can no longer meet the needs. Lithium manganese iron phosphate (LMFP), which also has an olivine structure, is a solid solution positive electrode material formed by combining the high energy density of lithium manganese phosphate and the special effects of lithium iron phosphate. However, lithium manganese iron phosphate has the problem of extremely low electronic conductivity and ionic conductivity when used on a large scale, and the dissolution of Mn during the charge and discharge process of lithium manganese iron phosphate makes it difficult to improve its cycle capacity.

[0032] The present disclosure provides a positive electrode material, the chemical formula of the positive electrode material is Li a Fe b Mn c M x (PO4) dWherein, M comprises at least one element selected from Ti, V, Mg, Zr, Co, In, Ni, and Nb, and 0.990≤a≤1.1, 0.9≤b+c≤1.1, 0.95≤d≤1.1, 0.001≤x≤0.03, and 0.9≤b+c+x≤1.1. Crystals of the positive electrode material can preferentially grow along the ac crystal plane. The ratio of the size of the positive electrode material along the a-direction to the size of the positive electrode material along the b-direction is 0.4542 to 0.4756, and the ratio of the size of the positive electrode material along the c-direction to the size of the positive electrode material along the b-direction is 0.5869 to 0.6172.

[0033] In the present disclosure, the positive electrode material is used to provide active lithium ions for the lithium ion battery, and the active lithium ions migrate between the positive electrode material and the negative electrode of the battery, thereby realizing the charging and discharging of the battery. The chemical formula of the positive electrode material is Li a Fe b Mn c M x (PO4) d , wherein Li represents lithium element, Fe represents iron element, Mn represents manganese element, P represents phosphorus element, and O represents oxygen element.

[0034] M is selected from one or more elements of Ti, V, Mg, Zr, Co, In, Ni, and Nb. For example, M is selected from one element of Ti, V, Mg, Zr, Co, In, Ni, and Nb, and the general chemical formula of the positive electrode material can be Li a Fe b Mn c Ti x (PO4) d 、Li a Fe b Mn c V x (PO4) d 、Li a Fe b Mn c Mg x (PO4) d 、Li a Fe b Mn c Zr x (PO4) d 、Li a Fe b Mn c Co x (PO4) d 、Li a Fe b Mn c In x (PO4) d 、Lia Fe b Mn c Ni x (PO4) d 、Li a Fe b Mn c Nb x (PO4) d .

[0035] When M is selected from a plurality of elements selected from Ti, V, Mg, Zr, Co, In, Ni, and Nb, the general chemical formula of the positive electrode material can be expressed as Li a Fe b Mn c M x1 M' x2 (PO4) d , where x1+x2=x. Or the general chemical formula of the positive electrode material can be expressed as Li a Fe b Mn c M x1 M' x2 M” x3 (PO4) d , where x1+x2+x3=x.

[0036] In the embodiment of the present disclosure, by introducing the M element into the positive electrode material, the positive electrode material can be preferentially grown on a specified ac crystal plane to shorten the size of the positive electrode material crystal along the b direction. The ac plane is perpendicular to the lithium ion migration direction, and the bc plane and the b direction are parallel to the lithium ion transmission channel. Generally speaking, the greater the doping amount of the M element, the higher the concentration of breakable Li-O bonds, the shorter the b-axis length of the positive electrode material crystal, and the higher the cycle performance of the positive electrode material. If the doping amount of the M element exceeds the upper limit, an impurity phase will be generated inside the positive electrode material crystal, thereby affecting the electrochemical properties of the positive electrode material. In the present disclosure, by controlling 0.001≤x≤0.03, the M element is appropriately doped, and the cycle performance of the positive electrode material is improved while ensuring that the positive electrode material has high electrochemical properties.

[0037] In the present disclosure, the ratio of the size of the positive electrode material along the a direction to the size of the positive electrode material along the b direction is 0.4542~0.4756. The larger the ratio of the size of the positive electrode material along the a direction to the size of the positive electrode material along the b direction, the smaller the size of the positive electrode material along the b direction, indicating that the positive electrode material preferentially grows along the ac plane, shortening the size of the positive electrode material along the b direction, shortening the lithium ion diffusion distance, and thus improving the cycle performance of the positive electrode material.

[0038] The ratio of the size of the positive electrode material along the c-direction to the size of the positive electrode material along the b-direction is 0.5869-0.6172, and the ratio of the size of the positive electrode material along the c-direction to the size of the positive electrode material along the b-direction is 0.5869-0.6172. A larger ratio of the size of the positive electrode material along the c-direction to the size of the positive electrode material along the b-direction indicates that the size of the positive electrode material along the b-direction is smaller, indicating that the positive electrode material preferentially grows along the ac plane, shortening the size of the positive electrode material along the b-direction, thereby shortening the lithium ion diffusion distance and improving the cycling performance of the positive electrode material.

[0039] In the disclosed embodiments, by modifying the cathode material and controlling the degree of coordination between the doping element and the anion, the cathode material is preferentially grown along the ac plane, shortening the lithium ion diffusion distance and facilitating lithium ion migration, thereby increasing the ion and electron transport rates of the cathode material. This effectively improves the cycling performance of the cathode material.

[0040] In one embodiment, the ratio of the size of the positive electrode material along the a-direction to the size of the positive electrode material along the b-direction is 0.4542, 0.4550, 0.4600, 0.4650, 0.4700 or 0.4756.

[0041] In one embodiment, the ratio of the size of the positive electrode material along the c-direction to the size of the positive electrode material along the b-direction is 0.5869, 0.5900, 0.5950, 0.6000, 0.6100 or 0.6172.

[0042] In one possible implementation, the ratio of the diffraction peak area of ​​the (020) crystal plane of the positive electrode material to the diffraction peak area of ​​the (200) crystal plane is 3.011 to 3.500, wherein the (020) crystal plane corresponds to the ac crystal plane. The (020) crystal plane is perpendicular to the direction of lithium ion migration. The (200) crystal plane corresponds to the bc plane, that is, the (200) crystal plane is parallel to the lithium ion transmission channel. When the positive electrode material is characterized by X-ray diffraction (XRD), the ratio of the peak area of ​​the diffraction peak corresponding to the (020) crystal plane to the peak area of ​​the diffraction peak corresponding to the (200) crystal plane in the XRD spectrum of the positive electrode material can be used to evaluate the strength of the preferential growth of the positive electrode material. The peak area of ​​the diffraction peak corresponding to the (020) crystal plane can be expressed as A020, and the peak area of ​​the diffraction peak corresponding to the (200) crystal plane can be expressed as A200. The size of the A020 / A200 ratio can be understood as the length of the b-axis in the unit cell parameters. The larger the A020 / A200 ratio, the shorter the b-axis length, the smaller the lithium ion insertion and extraction resistance, and the better the cycle performance of the positive electrode material.

[0043] Please refer to Figure 1, which is an XRD structure diagram of different doped cathode materials provided by one embodiment of the present disclosure. a Fe b Mn c (PO4)d In the embodiment of the present disclosure, the general chemical formula of the positive electrode material is Li a Fe b Mn c M x (PO4) d , and M is selected from Ti and Co, or M is selected from Nb and Mg, or M is selected from Nb, Mg and V, the (020) crystal plane diffraction peak area of ​​the positive electrode material increases, and the ratio of the (020) crystal plane diffraction peak area to the (200) crystal plane diffraction peak area increases.

[0044] In the disclosed embodiments, a larger ratio of the diffraction peak area of ​​the (020) crystal plane of the positive electrode material to the diffraction peak area of ​​the (200) crystal plane indicates that the positive electrode material can preferentially grow along the ac plane, thereby shortening the lithium ion diffusion distance and improving the cycling performance of the positive electrode material. In the disclosed embodiments, by designing the structure of the positive electrode material and regulating the ratio of the diffraction peak area of ​​the (020) crystal plane of the positive electrode material to the diffraction peak area of ​​the (200) crystal plane within the range of 3.011 to 3.500, the crystal structure of the positive electrode material grows along a specific ac crystal plane, significantly improving the cycling performance of the positive electrode material.

[0045] In one possible implementation, the ratio of the (020) crystal plane diffraction peak area to the (200) crystal plane diffraction peak area of ​​the positive electrode material is 3.011, 3.050, 3.100, 3.150, 3.200, 3.250, 3.300, 3.350, 3.400, 3.450, and 3.500.

[0046] In one embodiment, M includes at least two elements selected from Ti, V, Mg, Zr, Co, In, Ni, and Nb. For example, when M is selected from two elements selected from Ti, V, Mg, Zr, Co, In, Ni, and Nb, the general chemical formula of the positive electrode material may be:

[0047] Li a Fe b Mn c Nb x1 Mg x2 (PO4) d 、Li a Fe b Mn c Nb x1 Ti x2 (PO4) d 、Li a Fe b Mn c Nb x1 V x2 (PO4) d、Li a Fe b Mn c Nb x1 Co x2 (PO4) d 、Li a Fe b Mn c Ti x1 Co x2 (PO4) d 、Li a Fe b Mn c Ti x1 Ni x2 (PO4) d 、Li a Fe b Mn c Ti x1 Mg x2 (PO4) d 、Li a Fe b Mn c V x1 Mg x2 (PO4) d 、Li a Fe b Mn c In x1 Co x2 (PO4) d .

[0048] When M is selected from two or more elements selected from Ti, V, Mg, Zr, Co, In, Ni, and Nb, the general chemical formula of the positive electrode material may be:

[0049] Li a Fe b Mn c Nb x1 Mg x2 Zr x3 (PO4) d 、Li a Fe b Mn c Nb x1 Ti x2 Zr x3 (PO4) d 、Li a Fe b Mn c Nb x1 V x2 Ni x3 (PO4) d 、Lia Fe b Mn c Nb x1 Co x2 Ni x3 (PO4) d 、Li a Fe b Mn c Ti x1 Co x2 V x3 (PO4) d 、Li a Fe b Mn c Ti x1 Ni x2 V x3 (PO4) d 、Li a Fe b Mn c Ti x1 Mg x2 Nb x3 (PO4) d 、Li a Fe b Mn c V x1 Mg x2 Nb x3 (PO4) d 、Li a Fe b Mn c In x1 Co x2 Nb x3 Ti x4 (PO4) d .

[0050] In the disclosed embodiments, M is selected from a variety of metals, which contributes to a comprehensive improvement in the performance of the positive electrode material. For example, Ti contributes to improving the battery's charge-discharge performance, while Nb contributes to improving the positive electrode material's structural stability. When both Ti and Nb are selected as M, not only can the battery's charge-discharge performance be improved, but the positive electrode material's structural stability can also be enhanced, resulting in a positive electrode material with even superior performance.

[0051] In one possible implementation, the at least two elements include at least one of Ti and Nb. When the Ti and / or Nb elements are directionally doped into the Mn position, since the ionic radius of Ti and Nb is smaller than the ionic radius of Mn, the original MnO6 octahedron undergoes lattice distortion and contraction, the Li-O bond becomes longer, the energy required for bond breaking is reduced, and the resistance to lithium ion deintercalation from the lattice is reduced, thereby improving the ion transfer rate and electron transfer rate of the positive electrode material. In addition, doping the Ti element in the positive electrode material helps to improve the charge and discharge performance of the battery. Doping the Nb element in the positive electrode material is beneficial to improving the structural stability of the positive electrode material. In the embodiment of the present disclosure, M includes at least one of Ti and Nb, which can better improve the performance of the positive electrode material.

[0052] In one embodiment, M includes Ti and M includes at least one element selected from V, Mg, Zr, Co, In, and Ni. For example, M includes Ti and Co. The positive electrode material provided by the embodiments of the present disclosure has better charge and discharge performance.

[0053] In one embodiment, M includes Nb and M includes at least one element selected from V, Mg, Zr, Co, In, and Ni. For example, M includes Nb and Mg. The structure of the positive electrode material provided by the embodiment of the present disclosure is more stable.

[0054] In one embodiment, M includes Nb and Ti. The positive electrode material provided by the embodiment of the present disclosure has better charge and discharge performance and higher structural stability.

[0055] In one embodiment, M includes Nb, Ti, and M includes at least one element selected from V, Mg, Zr, Co, In, and Ni. For example, M includes Nb, Ti, and Mg. The cathode material provided by the embodiments of the present disclosure has superior overall performance.

[0056] In one possible implementation, the molar ratio of Ti and / or Nb to M is (0.5-1):1. When M is selected from Ti and other non-Nb elements, the molar ratio of Ti to M is (0.5-1):1. Exemplarily, when M is selected from Ti and Co, the ratio of the amount of Ti to the sum of the amounts of Ti and Co is (0.5-1):1.

[0057] Similarly, when M is selected from Nb and other non-Ti elements, the molar ratio of Nb to M is (0.5-1): 1. For example, when M is selected from Nb and Co, the ratio of the amount of Nb to the sum of the amounts of Nb and Co is (0.5-1): 1.

[0058] Similarly, when M is selected from Ti, Nb, and other non-Ti elements, the molar ratio of Ti and Nb to M is (0.5-1): 1. Exemplarily, when M is selected from Ti, Nb, and Co, the ratio of the sum of the amounts of Ti and Nb to the sum of the amounts of Ti, Nb, and Co is (0.5-1): 1.

[0059] If the content of Ti and / or Nb is too low, the effect on improving the charge-discharge performance and structural stability of the positive electrode material is not significant. In the embodiments disclosed herein, a higher proportion of Ti and / or Nb in the M element is more conducive to improving the charge-discharge performance and structural stability of the positive electrode material, resulting in a positive electrode material with more excellent performance.

[0060] In one embodiment, the molar ratio of Ti and / or Nb elements to M may be 0.5:1, 0.55:1, 0.6:1, 0.65:1, 0.7:1, 0.75:1, 0.8:1, 0.85:1, 0.9:1, 0.95:1, or 1:1.

[0061] In one possible implementation, the positive electrode material is obtained by doping the M element at the Mn position of lithium manganese iron phosphate. In the embodiment of the present disclosure, the M element replaces at least part of the Mn element in the lithium manganese iron phosphate and is doped at the Mn position of the lithium manganese iron phosphate. The doped M element occupies the Mn position, and the M element is selectively doped at the Mn position. By controlling the degree of coordination between the doping element and the anion, the directional orientation growth of the Mn position doping is controlled. On the one hand, it is beneficial for the positive electrode material to better grow preferentially along the ac plane, so that the lithium ion diffusion distance is shortened, so as to improve the cycle performance of the positive electrode material. On the other hand, doping the M element at the Mn position can increase the molar ratio of the Fe element and the Mn element in the positive electrode material, so that the positive electrode material is more inclined to the characteristics of lithium iron phosphate, and the positive electrode material has higher cycle stability.

[0062] In one embodiment, Ti or Nb is doped into the Mn site, the relative strength of the (020) crystal plane increases, the A020 / A200 ratio becomes larger, the b-axis of the positive electrode material crystal is shortened, and the cycle performance of the positive electrode material is improved.

[0063] In other embodiments, the M element may also be doped at other locations. In one embodiment, the interior or exterior surface of the positive electrode material further includes a conductive material. The conductive material may be a carbon material. The conductive material enhances the conductivity of the positive electrode material and accelerates electron transfer, reducing the polarizability of the positive electrode material, thereby improving the rate capability and cycle performance of the positive electrode material.

[0064] For example, in one embodiment, the conductive material is doped with Li a Feb Mn c M x (PO4) d interior.

[0065] In one embodiment, the positive electrode material is a core-shell structure, and the core of the positive electrode material is Li a Fe b Mn c M x (PO4) d The outer shell of the positive electrode material is a conductive material coating layer, which is coated on the Li a Fe b Mn c M x (PO4) d In one embodiment, the conductive material is also doped into the Li a Fe b Mn c M x (PO4) d Inside the kernel.

[0066] The present disclosure provides a method for preparing a positive electrode material, which includes steps S1, S2, S3, S4, and S5. The specific steps are as follows:

[0067] Step S1, dissolving a lithium source, an iron source, and a manganese source in a solvent to obtain a first slurry;

[0068] Step S2, dissolving the phosphorus source and the dopant in a solvent to obtain a second slurry;

[0069] Step S3, mixing the second slurry and the first slurry to obtain a mixed slurry;

[0070] Step S4, heating the mixed slurry to obtain a precursor;

[0071] Step S5: sintering the precursor and grinding it to obtain the positive electrode material.

[0072] Among them, in step S1 and step S2, the lithium source, iron source, manganese source, phosphorus source and dopant are used to prepare Li a Fe b Mn c M x (PO4) d The raw materials disclosed herein have a purity of lithium source, iron source, manganese source, phosphorus source and dopant greater than or equal to 99%. The lithium source, iron source, manganese source, phosphorus source and dopant are prepared in the following molar ratios: Li ion: Fe ion: Mn ion: M ion: PO4 3-=a:b:c:x:d are weighed, and the lithium source, iron source, and manganese source are dispersed in a solvent to obtain a first slurry, so that the lithium source, iron source, and manganese source are evenly mixed. The phosphorus source and the dopant are dispersed in a solvent to obtain a second slurry, so that the phosphorus source and the dopant are evenly mixed. The solvents in step S1 and step S2 can be the same or different. The solvents in step S1 and step S2 can be one or more of deionized water, anhydrous ethanol, or process alcohol. In one embodiment, after the lithium source, iron source, and manganese source in step S1 are added to the solvent, they can be evenly mixed by ball milling. In one embodiment, in step S2, after the phosphorus source and the dopant are added to the solution, liquid phase ball milling can also be used to mix them. The liquid phase ball milling method can make the raw materials mix more evenly.

[0073] In step S3, the first slurry and the second slurry are mixed to facilitate the subsequent preparation of the positive electrode material.

[0074] In step S4, the mixed slurry is heated to evaporate the solvent in the mixed slurry, thereby obtaining a solid precursor for subsequent sintering to prepare a positive electrode material.

[0075] In step S5, the precursor is sintered, that is, various raw materials of the positive electrode material are sintered to form a molecular formula Li a Fe b Mn c M x (PO4) d positive electrode material.

[0076] In one embodiment, step S5 includes two sintering processes. The first sintering process is as follows: the precursor is heated to 300°C to 500°C at 1°C / min to 5°C / min and kept at this temperature for 4 to 6 hours. The second sintering process is as follows: the product of the first sintering process is heated to 650°C to 900°C at 1°C / min to 5°C / min and kept at this temperature for 8 to 12 hours; the product is cooled to room temperature and the obtained sample is ground to obtain Mn-doped Li-ion battery with preferential growth on the crystal surface. a Fe b Mn c M x (PO4) d positive electrode material.

[0077] In one embodiment, when the positive electrode material is also coated with a carbon layer, step S4 includes: adding a carbon source to the mixed slurry, mixing the mixture evenly, and then heating the mixture to obtain a precursor.

[0078] In one embodiment, the mixing of the second slurry and the first slurry, i.e., step S3, includes: dividing the second slurry into n parts, and adding n parts of the second slurry to the first slurry in sequence; wherein n is a positive integer and is greater than or equal to 2. Exemplarily, n is 3, the second slurry can be divided into three equal parts, and the second slurry is added to the first slurry three times, each time at a certain interval, such as 2 hours. In the embodiment of the present disclosure, the second slurry is added to the first slurry in batches, which is conducive to the preparation of a positive electrode material with preferential growth of the crystal plane. In particular, the more fractions the second slurry is divided into, that is, the larger the value of n, the more complete the reaction of manganese (Mn) position substitution, and the more obvious the effect of the oriented growth of the positive electrode material along the ac plane.

[0079] The preparation method of the positive electrode material provided by the present disclosure is conducive to the preparation of Li a Fe b Mn c M x (PO4) d positive electrode materials, thereby improving the cycle performance of the positive electrode materials.

[0080] In one embodiment, the lithium source is one or more of lithium carbonate, lithium oxalate, and lithium acetate.

[0081] In one embodiment, the phosphorus source is one or more of phosphoric acid, ammonium phosphate, and ammonium dihydrogen phosphate.

[0082] In one embodiment, the manganese source is one or more of manganese carbonate, manganese oxalate, and manganese acetate.

[0083] In one embodiment, the iron source is one or more of ferrous oxalate, ferrous acetate, ferric phosphate and ferric nitrate.

[0084] In one embodiment, the dopant, ie, the M source, is an oxide of the corresponding doping element, such as vanadium oxide for V doping and nickel oxide for Ni doping.

[0085] In one embodiment, the carbon source is one or more of glucose, sucrose, citric acid, acetylene black and polyethylene glycol.

[0086] The present disclosure provides a positive electrode plate, which includes the positive electrode material as described above, or includes the positive electrode material prepared by the preparation method of the positive electrode material as described above.

[0087] The present disclosure provides a secondary battery, which includes a negative electrode sheet, a separator, and the positive electrode sheet as described above.

[0088] In order to illustrate the beneficial effects of the disclosed method, the present invention also provides the following examples and comparative examples:

[0089] Example 1

[0090] Example 1 provides a positive electrode material, the chemical formula of the positive electrode material is LiFe 0.6 Mn 0.38 Ti 0.02 PO4 / C, where the positive electrode material is LiFe 0.6 Mn 0.38 Ti 0.02 The ratio of the diffraction peak area of ​​(020) crystal plane to the diffraction peak area of ​​(200) crystal plane of PO4 is 3.158, and the ratio of the diffraction peak area of ​​LiFe 0.6 Mn 0.38 Ti 0.02 The ratio of the size of PO4 along the a-direction to the size along the b-direction is 0.4670, and the size of LiFe 0.6 Mn 0.38 Ti 0.02 The ratio of the size of PO4 along the c-direction to the size along the b-direction is 0.5889.

[0091] The preparation method of the positive electrode material provided in Example 1 is:

[0092] Step 1: Lithium source, iron source, manganese source, phosphorus source and dopant are mixed in the molar ratio of Li ion: Fe ion: Mn ion: M: PO4. 3- =1:0.6:0.38:0.02:1, the lithium source, iron source and manganese source are preferentially dissolved in the solvent, and the mixture is ball-milled for 3 hours to mix and disperse, and the resulting slurry is the first slurry.

[0093] Step 2: Prepare a solution system containing a phosphorus source and a doping element, namely, a second slurry.

[0094] Step 3: Divide the second slurry into three equal parts and add them into the first slurry three times (each time with an interval of 2 hours).

[0095] Step 4: Add the carbon source to the mixed slurry, mix well, and then heat (80° C.) to evaporate the solvent to obtain a solid block precursor.

[0096] Step 5: Heat the precursor to 350°C at a rate of 3°C / min, keep warm for 6 hours, heat it to 720°C at a rate of 3°C / min, and keep warm for 10 hours; cool it to room temperature, and grind the obtained sample to obtain the positive electrode material.

[0097] Example 2

[0098] Example 2 provides a positive electrode material. The difference from the positive electrode material in Example 1 is that the positive electrode material provided in Example 2 has a general chemical formula of LiFe 0.6 Mn 0.38 Ti 0.01 Co 0.01 PO4 / C.

[0099] Example 3

[0100] Example 3 provides a positive electrode material. The difference from the positive electrode material in Example 1 is that the positive electrode material provided in Example 3 has a chemical formula of LiFe 0.6 Mn 0.38 Nb 0.01 Mg 0.01 PO4 / C.

[0101] Example 4

[0102] Example 4 provides a positive electrode material. The difference from the positive electrode material in Example 1 is that the positive electrode material provided in Example 4 has a chemical formula of LiFe 0.6 Mn 0.38 Nb 0.005 Mg 0.005 V 0.01 PO4 / C.

[0103] Example 5

[0104] Example 5 provides a positive electrode material. The difference from the positive electrode material in Example 1 is that the positive electrode material provided in Example 5 has a general chemical formula of LiFe 0.6 Mn 0.38 Mg 0.01 V 0.01 PO4 / C.

[0105] Example 6

[0106] Example 6 provides a positive electrode material. The difference from the positive electrode material in Example 2 is that the positive electrode material provided in Example 6 has a general chemical formula of LiFe 0.6 Mn 0.38 Ti 0.015 Co 0.005 PO4 / C.

[0107] Example 7

[0108] Example 7 provides a positive electrode material, which is different from the positive electrode material in Example 1 in that, in the positive electrode material provided by Example 7, the ratio of the (020) crystal plane diffraction peak area to the (200) crystal plane diffraction peak area of ​​the positive electrode material is 3.2321.

[0109] Example 8

[0110] Example 8 provides a positive electrode material, which is different from the positive electrode material in Example 1 in that, in the positive electrode material provided in Example 8, the ratio of the size of the positive electrode material along the a direction to the size of the positive electrode material along the b direction is 0.4694, and the ratio of the size of the positive electrode material along the c direction to the size of the positive electrode material along the b direction is 0.5997.

[0111] Comparative Example 1

[0112] Comparative Example 1 provides a positive electrode material, which is different from the positive electrode material in Example 1 in that the positive electrode material provided in Comparative Example 1 has a chemical formula of LiFe 0.5 Mn 0.5 PO4.

[0113] The preparation method of the positive electrode material provided in Comparative Example 1 is:

[0114] Step 1: Lithium source, iron source, manganese source, phosphorus source and dopant are mixed in the molar ratio of Li ion: Fe ion: Mn ion: PO4. 3- =1:0.5:0.5:1 weighing,

[0115] The lithium source, iron source and manganese source are preferentially dissolved in a solvent, and after mixing and dispersing by ball milling for 3 hours, the obtained slurry is the first slurry.

[0116] Step 2: Prepare another solution system containing a phosphorus source, namely, a second slurry.

[0117] Step 3: Divide the second slurry into three equal parts and add them into the first solution three times (each time with an interval of 2 hours).

[0118] Step 4: Add the carbon source to the mixed slurry, mix well, and then heat (80° C.) to evaporate the solvent to obtain a solid block precursor.

[0119] Step 5: Heat the precursor to 350°C at a rate of 3°C / min, keep warm for 6 hours, heat it to 720°C at a rate of 3°C / min, and keep warm for 10 hours; cool it to room temperature, and grind the obtained sample to obtain the positive electrode material.

[0120] Comparative Example 2

[0121] The preparation method of the positive electrode material provided in Comparative Example 2 is:

[0122] Step 1: Lithium source, iron source, manganese source, phosphorus source and dopant are mixed in the molar ratio of Li ion: Fe ion: Mn ion: M: PO4. 3- =1:0.6:0.38:0.02:1 were weighed and dispersed in a solvent, and after ball milling for 3 hours, a mixed slurry was obtained.

[0123] Step 2: Add a carbon source to the mixed slurry, mix well again, heat to 80° C., and evaporate the solvent to obtain a solid block precursor.

[0124] Step 3: Heat the precursor to 350°C at a rate of 3°C / min, keep it warm for 6 hours, then heat it to 720°C at a rate of 3°C / min, keep it warm for 10 hours; cool it to room temperature, and grind the obtained sample to obtain the positive electrode material.

[0125] Comparative Example 3

[0126] The preparation method of the positive electrode material provided in Comparative Example 3 is:

[0127] Step 1: Lithium source, iron source, manganese source, phosphorus source and dopant are mixed in the molar ratio of Li ion: Fe ion: Mn ion: M: PO4. 3- =1:0.6:0.38:0.02:1, the lithium source, iron source and manganese source are preferentially dissolved in the solvent, and the mixture is ball-milled for 3 hours to mix and disperse, and the resulting slurry is the first slurry.

[0128] Step 2: Prepare a solution system containing a phosphorus source and a doping element, namely, a second slurry.

[0129] Step 3: Add the second slurry into the first slurry at one time.

[0130] Step 4: Add the carbon source to the mixed slurry, mix well, and then heat (80° C.) to evaporate the solvent to obtain a solid block precursor.

[0131] Step 5: Heat the precursor to 350°C at a rate of 3°C / min, keep warm for 6 hours, then heat to 720°C at a rate of 3°C / min, keep warm for 10 hours; cool to room temperature, grind the obtained sample to obtain the positive electrode material.

[0132] The positive electrode materials provided in Examples 1 to 8 and the positive electrode materials provided in Comparative Examples 1 to 3 were assembled into positive electrode sheets and lithium-ion batteries respectively according to the following methods:

[0133] Positive electrode: The positive electrode material, polyvinylidene fluoride, and SP-Li were mixed with ball milling in a mass ratio of 80:8:12 to obtain a positive electrode slurry. The positive electrode slurry was coated on the surface of aluminum foil, vacuum dried at 110°C overnight, and roller pressed to obtain a positive electrode sheet.

[0134] Negative electrode: Graphite, carboxymethyl cellulose (CMC), SBR, and SP were mixed in a mass ratio of 95.8:1.2:2:1 and ball-milled to obtain a negative electrode slurry. The negative electrode slurry was coated on the surface of copper foil and vacuum-dried at 110°C overnight to obtain a negative electrode sheet.

[0135] Electrolyte: Ethylene carbonate and ethyl methyl carbonate were mixed in a volume ratio of 3:7, and LiPF6 was added to form an electrolyte. The concentration of LiPF6 was 1 mol / L.

[0136] Diaphragm: Polypropylene microporous separator;

[0137] Lithium-ion battery assembly: Assemble button-type lithium-ion full batteries in an inert atmosphere glove box in the order of graphite negative electrode sheet - diaphragm - electrolyte - positive electrode sheet.

[0138] The electrochemical performance of each lithium-ion battery assembled in the above lithium-ion battery embodiment was tested as shown in Table 1, and all were tested at a rate of 0.5C. The test results are shown in Table 1 below:

[0139] Table 1 Performance test results

[0140] Wherein, a / b represents the ratio of the a-direction size to the b-direction size of the positive electrode material, and c / b represents the ratio of the c-direction size to the b-direction size of the positive electrode material.

[0141] As can be seen from the test results of Examples 1-8 and Comparative Example 1 in Table 1, the a / b and c / b ratios of the positive electrode materials provided in the embodiments of the present disclosure are in the ranges of 0.4542-0.4756 and 0.5869-0.6172, respectively. Furthermore, the a / b and c / b ratios of the positive electrode materials provided in the embodiments of the present disclosure are greater than those in Comparative Example 1, respectively. This indicates that the positive electrode materials in the present disclosure preferentially grow along the ac plane, thereby shortening the relative size in the b direction. Regarding the A020 / A200 ratio, the A020 / A200 ratios in the embodiments of the present disclosure are in the range of 3.011-3.500, and are both greater than those in Comparative Example 1. This indicates that the crystal structure of the positive electrode materials in the present disclosure grows along specific ac crystal planes, significantly improving the cycling performance of the positive electrode materials.

[0142] It can be seen from Examples 1 and 2 that, compared with when M is taken from Mn and Ti, when M is taken from Mn, Ti and Co, the value of a / b decreases, the value of c / b increases, and A020 / A200 increases. The positive electrode material provided in Example 2 has a higher capacity retention rate, indicating that by selecting different M element doping, the size of the positive electrode material can be adjusted to obtain a positive electrode material with better performance.

[0143] It can be seen from Example 1 and Example 3 that compared with M taken from Mn and Ti, when M is taken from Mn, Nb and Mg, the a / b value of the positive electrode material increases, the c / b value increases, and A020 / A200 increases, and the capacity retention rate is significantly improved.

[0144] As can be seen from Examples 1 and 4, compared to when M is selected from Mn and Ti, when M is selected from Mn, Nb, Mg, and V, the a / b value and c / b value of the positive electrode material increase, and the A020 / A200 increases, and the capacity retention rate is significantly improved. This indicates that by regulating the doping of different elements, the size of the positive electrode material can be controlled to obtain a positive electrode material with better performance.

[0145] As can be seen from Examples 1 and 5, compared to when M is selected from Mn and Ti, when M is selected from Mn, Mg, and V, the a / b value and c / b value of the positive electrode material increase, and the A020 / A200 increases, and the capacity retention rate is significantly improved. This indicates that by regulating the doping of different elements, the size of the positive electrode material can be controlled to obtain a positive electrode material with better performance.

[0146] As can be seen from Examples 1 and 6, compared to when M is selected from Mn and Ti, when M is selected from Mn, Ti, and Co, the a / b value of the positive electrode material decreases, the c / b value increases, and the A020 / A200 increases, resulting in a significant improvement in capacity retention. This indicates that by regulating the doping of different elements, the size of the positive electrode material can be controlled to obtain a positive electrode material with even better performance.

[0147] It can be seen from Example 1 and Example 7 that, under the same conditions, increasing the value of A020 / A200 can increase the capacity retention rate of the positive electrode material.

[0148] It can be seen from Example 1 and Example 8 that, under the same conditions, increasing the ratio of a / b and increasing the ratio of c / b can increase the capacity retention rate of the positive electrode material.

[0149] As can be seen from Example 1 and Comparative Example 2, during the preparation of the positive electrode material, the positive electrode material obtained in Comparative Example 2, which directly mixes all the raw materials, evaporates the solvent, and sinters, has smaller a / b values, c / b values, and A020 / A200 values, and a significantly lower capacity retention rate. In Example 1 of the present disclosure, by optimizing the preparation steps and strictly controlling the order of adding the various raw materials, the crystals of the positive electrode material preferentially grow along the ac plane, resulting in a positive electrode material with higher capacity retention rate and better performance.

[0150] As can be seen from Example 1 and Comparative Example 3, during the preparation of the positive electrode material, the second slurry in Comparative Example 3 was added to the first slurry all at once, and the a / b value, c / b value, and A020 / A200 value of the obtained positive electrode material were all small, and the capacity retention rate was significantly lower. In Example 1 of the present disclosure, the second slurry was added to the first slurry in batches, the manganese (Mn) site substitution reaction was more complete, the effect of the positive electrode material oriented along the ac plane was obvious, the capacity retention rate of the positive electrode material was higher, and the performance was more excellent.

[0151] The above is a detailed introduction to the positive electrode materials, preparation methods and applications provided in the embodiments of the present disclosure. Specific examples are used herein to illustrate the principles and embodiments of the present disclosure. The description of the above embodiments is only used to help understand the methods and core ideas of the present disclosure. At the same time, for those skilled in the art, according to the ideas of the present disclosure, there may be changes in the specific embodiments and application scopes. In summary, the contents of this specification should not be understood as limiting the present disclosure.

Claims

1. A positive electrode material, characterized in that: The chemical formula of the positive electrode material is Li a Fe b Mn c M x (PO4) d , wherein M includes at least one element selected from Ti, V, Mg, Zr, Co, In, Ni, and Nb, 0.990≤a≤1.1, 0.9≤b+c≤1.1, 0.95≤d≤1.1, 0.001≤x≤0.03, and 0.9≤b+c+x≤1.1; The crystals of the positive electrode material can preferentially grow along the ac crystal plane, and the ratio of the size of the positive electrode material along the a direction to the size of the positive electrode material along the b direction is 0.4542-0.4756; the ratio of the size of the positive electrode material along the c direction to the size of the positive electrode material along the b direction is 0.5869-0.6172.

2. The positive electrode material according to claim 1, characterized in that The ratio of the diffraction peak area of ​​the (020) crystal plane to the diffraction peak area of ​​the (200) crystal plane of the positive electrode material is 3.011-3.500, wherein the (020) crystal plane corresponds to the ac crystal plane.

3. The positive electrode material according to claim 1, characterized in that The M includes at least two elements of Ti, V, Mg, Zr, Co, In, Ni, and Nb.

4. The positive electrode material according to claim 3, characterized in that The M includes the Ti element and M includes at least one element of V, Mg, Zr, Co, In, and Ni.

5. The positive electrode material according to claim 3, characterized in that The M includes Nb element and M includes at least one element of V, Mg, Zr, Co, In, and Ni.

6. The positive electrode material according to claim 3, characterized in that The at least two elements include at least one of Ti and Nb.

7. The positive electrode material according to claim 3, characterized in that M includes Nb element and Ti element, and M includes at least one element of V, Mg, Zr, Co, In, and Ni.

8. The positive electrode material according to claim 1, characterized in that The molar ratio of the Ti and / or Nb element to the M is (0.5-1):

1.

9. The positive electrode material according to claim 1, characterized in that The positive electrode material is obtained by doping the M element at the Mn position of lithium manganese iron phosphate.

10. The positive electrode material according to claim 1, characterized in that The interior or exterior surface of the positive electrode material also includes a conductive material.

11. The positive electrode material according to claim 10, characterized in that The positive electrode material is a core-shell structure, and the core of the positive electrode material is the Li a Fe b Mn c M x (PO4) d The outer shell of the positive electrode material is the conductive material coating layer, and the conductive material coating layer is coated on the Li a Fe b Mn c M x (PO4) d The outer surface of the core.

12. The positive electrode material according to claim 10, characterized in that The conductive material is a carbon material.

13. A method for preparing a positive electrode material, characterized in that: The preparation method of the positive electrode material comprises: Dissolving a lithium source, an iron source, and a manganese source in a solvent to obtain a first slurry; dissolving a phosphorus source and a dopant in a solvent to obtain a second slurry; mixing the second slurry and the first slurry to obtain a mixed slurry; heating the mixed slurry to obtain a precursor; The precursor is sintered and ground to obtain the positive electrode material.

14. The method for preparing the positive electrode material according to claim 13, characterized in that: The mixing of the second slurry and the first slurry comprises: The second slurry is divided into n portions, and the n portions of the second slurry are sequentially added to the first slurry at intervals; wherein n is a positive integer and is greater than or equal to 2.

15. The method for preparing the positive electrode material according to claim 13, characterized in that: The sintering of the precursor includes two sintering processes, and the temperatures of the two sintering processes are different.

16. The method for preparing the positive electrode material according to claim 15, characterized in that: The first stage of sintering includes: heating the precursor to 300° C. to 500° C. at a rate of 1° C. / min to 5° C. / min, and keeping the temperature for 4 hours to 6 hours.

17. The method for preparing the positive electrode material according to claim 16, characterized in that: The second stage sintering comprises: heating the product of the first stage sintering to 650° C. to 900° C. at 1° C. / min to 5° C. / min, and keeping the temperature for 8 hours to 12 hours.

18. The method for preparing the positive electrode material according to claim 13, characterized in that: The positive electrode material is also coated with a carbon layer. The heating of the mixed slurry includes: adding a carbon source to the mixed slurry, mixing evenly and then heating to obtain the precursor. The carbon source is one or more of glucose, sucrose, citric acid, acetylene black and polyethylene glycol.

19. A positive electrode plate, characterized in that: The positive electrode plate includes the positive electrode material according to any one of claims 1 to 12, or includes the positive electrode material prepared by the method for preparing the positive electrode material according to any one of claims 13 to 18.

20. A secondary battery, characterized in that: The secondary battery comprises a negative electrode sheet, a separator and the positive electrode sheet as claimed in claim 19.

Images