WO2024124725A1 - 一种改性磷酸锰铁锂正极材料及其制备方法和应用 - Google Patents

一种改性磷酸锰铁锂正极材料及其制备方法和应用 Download PDF

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WO2024124725A1
WO2024124725A1 PCT/CN2023/082818 CN2023082818W WO2024124725A1 WO 2024124725 A1 WO2024124725 A1 WO 2024124725A1 CN 2023082818 W CN2023082818 W CN 2023082818W WO 2024124725 A1 WO2024124725 A1 WO 2024124725A1
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manganese
positive electrode
optionally
electrode material
lithium
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French (fr)
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温圣耀
张�林
刘范芬
苑丁丁
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湖北亿纬动力有限公司
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    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B25/00—Phosphorus; Compounds thereof
    • C01B25/16—Oxyacids of phosphorus; Salts thereof
    • C01B25/26—Phosphates
    • C01B25/45—Phosphates containing plural metal, or metal and ammonium
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
    • C01G33/00—Compounds of niobium
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/04—Processes of manufacture in general
    • H01M4/0471—Processes of manufacture in general involving thermal treatment, e.g. firing, sintering, backing particulate active material, thermal decomposition, pyrolysis
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/136—Electrodes based on inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H01M4/366—Composites as layered products
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/50—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese
    • H01M4/505—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese of mixed oxides or hydroxides containing manganese for inserting or intercalating light metals, e.g. LiMn2O4 or LiMn2OxFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/5825—Oxygenated metallic salts or polyanionic structures, e.g. borates, phosphates, silicates, olivines
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2002/00—Crystal-structural characteristics
    • C01P2002/50—Solid solutions
    • C01P2002/52—Solid solutions containing elements as dopants
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/40—Electric properties
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/021—Physical characteristics, e.g. porosity, surface area
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/028—Positive electrodes
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • the present application belongs to the technical field of lithium-ion batteries and relates to a modified lithium manganese iron phosphate positive electrode material and a preparation method and application thereof.
  • the cathode materials of lithium-ion power batteries are mainly lithium iron phosphate (LFP) and ternary materials.
  • LFP has gradually become the preferred choice of energy storage and power battery companies due to its advantages such as high cost performance, high safety and small resource bottleneck.
  • it has the problem of low energy density, which has become a key factor restricting the large-scale application of lithium iron phosphate.
  • Lithium manganese iron phosphate is a positive electrode material obtained by adding manganese to LFP.
  • Manganese doping can make LMFP have a higher voltage platform (4.1Vvs3.4V), and the energy density of the battery is increased by about 15%. It is a positive electrode material with great application prospects.
  • LMFP positive electrode materials are still in the early stages of industrialization. The main reason is that LMFP has low electronic conductivity and ion diffusion rate, low first coulomb efficiency, and poor cycle performance, which seriously affects its commercial landing. Therefore, how to improve the electronic conductivity, ion transfer rate and cycle stability of LMFP materials is the current technical key. At present, the effective way to solve this technical problem is to perform lattice doping and double-coating integrated modification on the LMFP material.
  • CN114335480A provides a method for preparing a core-shell carbon-coated doped lithium iron phosphate and its application.
  • the method firstly causes a chelating reaction between an iron source, a transition metal compound and tannic acid, and then The tannic acid-coated transition metal ion-doped lithium iron phosphate precursor is obtained by hydrothermal synthesis reaction with phosphorus source and lithium source, and finally the tannic acid is carbonized by sintering in an inert atmosphere to obtain core-shell carbon-coated doped lithium iron phosphate.
  • the chelating reaction used in this method can inhibit the loss of transition metal ions, and the tannic acid carbonization can inhibit the agglomeration of secondary particles, so that the cathode material obtained can obtain better rate and kinetic performance in application, but the cycle performance has no obvious improvement and cannot meet the needs of power batteries.
  • CN113942990A discloses a carbon-coated and ion-doped lithium manganese iron phosphate positive electrode material prepared by co-precipitation reaction. This method overcomes the problems of uneven element distribution, low compaction density and low specific capacity of the lithium manganese iron phosphate positive electrode material, but the material has poor cycle stability. After the assembled button battery is cycled for 80 weeks at a rate of 1C, the capacity decays to 95.8%.
  • the purpose of the present application is to provide a modified lithium iron manganese phosphate positive electrode material, a preparation method and application thereof.
  • the modified lithium iron manganese phosphate positive electrode material described in the present application is doped with Nb element, and the surface is double-coated with LiNbO 3 and Nb 2 O 5.
  • the coating layer of the modified lithium iron manganese phosphate positive electrode material has good uniformity, consistency and conductivity. LiNbO 3 and Nb 2 O 5 synergistically improve the rate performance and long cycle performance of the LMFP electrode material.
  • an embodiment of the present application provides a modified lithium iron manganese phosphate positive electrode material, comprising a doped lithium iron manganese phosphate core and a coating layer disposed on the surface of the doped lithium iron manganese phosphate core, wherein the doped lithium iron manganese phosphate core comprises Nb element, and the coating layer comprises LiNbO 3 and Nb 2 O 5 .
  • the modified lithium manganese iron phosphate positive electrode material described in the embodiment of the present application is doped with Nb element in the bulk phase and double coated on the surface.
  • NbO 3 and Nb 2 O 5 among which Nb has stronger interatomic force after doping, which can stabilize the lattice structure, improve the dissolution of manganese, reduce Li/Ni mixing, and increase the lithium ion diffusion coefficient;
  • Nb 2 O 5 has strong stability within the working voltage range, which can effectively inhibit the side reactions between the electrode and the electrolyte and enhance the interface stability, thereby improving the cycle stability of the LMFP positive electrode material;
  • LiNbO 3 can not only act as a physical barrier to enhance the interface stability, but also act as a fast ion conductor to promote the rapid conduction of lithium ions.
  • the chemical formula of the doped lithium manganese iron phosphate core is LiNbaMnxFe1 - xPO4 , wherein 0 ⁇ a ⁇ 0.05, 0 ⁇ x ⁇ 1.
  • the coating layer has a thickness of 10-50 nm, for example, 10 nm, 20 nm, 30 nm, 40 nm or 50 nm.
  • the molar mass ratio of LiNbO 3 and Nb 2 O 5 in the coating layer is 1:(0.1-0.4), for example: 1:0.1, 1:0.15, 1:0.2, 1:0.25, 1:0.3, 1:0.35 or 1:0.4, etc.
  • an embodiment of the present application provides a method for preparing the modified lithium manganese iron phosphate positive electrode material as described in the first aspect, the preparation method comprising the following steps:
  • step (2) mixing the calcined material obtained in step (1), LiNbO 3 , and Nb 2 O 5 with an organic solvent and grinding them;
  • step (3) calcining the material obtained by the grinding treatment in step (2) to obtain the modified lithium manganese iron phosphate positive electrode material.
  • Nb-doped LMFP is first synthesized, and then LiNbO 3 and Nb 2 O 5 are mixed in a certain proportion, and then LMFP is dry-mixed with the coating mixture, and then sintered to obtain a doped and double-coated integrated
  • the modified LMFP positive electrode material has a coating layer with good uniformity, consistency and conductivity.
  • the preparation process of this method is simple and controllable, and is easy to mass industrialize.
  • the lithium source in step (1) includes lithium carbonate and/or lithium dihydrogen phosphate.
  • the manganese source includes any one of manganese sulfate, manganese carbonate, manganese nitrate, manganese acetate or manganese oxalate, or a combination of at least two thereof.
  • the iron source includes iron phosphate and/or iron powder.
  • the phosphorus source includes phosphoric acid and/or diammonium phosphate.
  • the niobium source includes any one of niobium oxide, niobium hydroxide, niobium chloride, niobium sulfate, niobium nitrate or niobium acetate, or a combination of at least two thereof.
  • the complexing agent comprises sodium alginate.
  • the drying method in step (1) comprises spray drying.
  • the sintering temperature is 600-900°C, for example, 600°C, 750°C, 800°C, 850°C or 900°C.
  • the sintering treatment time is 6-15 hours, for example: 6 hours, 8 hours, 10 hours, 12 hours or 15 hours.
  • the sintering process atmosphere includes a nitrogen atmosphere.
  • the organic solvent in step (2) comprises ethanol.
  • the grinding speed is 500-1000 rpm, for example, 500 rpm, 600 rpm, 700rpm, 800rpm, 900rpm or 1000rpm etc.
  • the grinding treatment time is 0.3-1 h, for example: 0.3 h, 0.5 h, 0.6 h, 0.8 h or 1 h.
  • the mass ratio of the total mass of LiNbO 3 and Nb 2 O 5 to the mass of the sintered material is 0.1-10:100, for example: 0.1:100, 0.5:100, 1:100, 5:100 or 10:100, etc., preferably 0.5-2:100.
  • the temperature of the calcination treatment in step (3) is 200-650°C, for example, 200°C, 300°C, 400°C, 500°C or 650°C.
  • the calcination treatment time is 2-15 hours, for example: 2 hours, 5 hours, 8 hours, 10 hours or 15 hours.
  • an embodiment of the present application provides a positive electrode plate, wherein the positive electrode plate comprises the modified lithium iron manganese phosphate positive electrode material as described in the first aspect.
  • an embodiment of the present application provides a lithium-ion battery, wherein the lithium-ion battery comprises the positive electrode sheet as described in the third aspect.
  • the modified lithium manganese iron phosphate positive electrode material described in the present application is doped with Nb element, and the surface is double-coated with LiNbO 3 and Nb 2 O 5.
  • the coating layer of the modified lithium manganese iron phosphate positive electrode material has good uniformity, consistency and conductivity. LiNbO 3 and Nb 2 O 5 synergistically improve the rate performance and long cycle performance of the LMFP electrode material.
  • Nb 5+ doped layered transition metal oxide cathode materials can inhibit cation mixing and significantly improve the rate and cycle stability of the material; LiNbO 3 coated modified cathode materials have high lithium ion The conductivity can effectively isolate the organic electrolyte while ensuring that the rate performance of the material will not be reduced. Therefore, constructing Nb 5+ doping and /LiNbO 3 structure will have a synergistic effect and significantly improve the rate, cycle and safety performance.
  • T-Nb 2 O 5 (T-phase niobium oxide) has a special lithium ion transmission channel, and the rate performance is excellent, comparable to the best solid electrolyte.
  • T-phase niobium oxide has been used as a high-rate negative electrode material for lithium batteries.
  • T-Nb 2 O 5 as the niobium source, while constructing Nb 5+ doping/LiNbO 3 coating, the surface of the excess niobium source (T-Nb 2 O 5 ) residual material can continue to serve as a physical protective layer without reducing the rate performance of the material.
  • This embodiment provides a modified lithium iron manganese phosphate positive electrode material, and the modified lithium iron manganese phosphate positive electrode material is prepared by the following method:
  • step (1) LiNbO 3 and Nb 2 O 5 were added into a high-speed mixer at a ratio of 1:0.25 and mixed at a speed of 800 rpm for 0.5 h to obtain a coated mixture.
  • the coated mixture and the calcined material obtained in step (1) were then dispersed in an ethanol solvent, stirred and ground, wherein the coating mixture accounted for 1%, the ball milling speed was 600 rpm, and the ball milling time was 2 h;
  • the coating layer thickness of the modified lithium manganese iron phosphate positive electrode material is 25nm.
  • This embodiment provides a modified lithium iron manganese phosphate positive electrode material, and the modified lithium iron manganese phosphate positive electrode material is prepared by the following method:
  • Example 1 The only difference between this comparative example and Example 1 is that the core is not doped with Nb, and the other conditions and parameters are exactly the same as those in the example.
  • Example 1 The only difference between this comparative example and Example 1 is that LiNbO 3 is not added, and other conditions and parameters are exactly the same as those of the example.
  • the lithium manganese iron phosphate prepared in Examples 1-4 and Comparative Examples 1-3 was selected as the positive electrode material, and the graphite carbon material was selected as the negative electrode material, and the PE/PP polymer material was matched as the separator, and the core was assembled into a roll by winding or lamination, which was encapsulated in an aluminum shell or aluminum-plastic film, and a lithium ion electrolyte composed of EC/EMC and LiPF 6 was injected to assemble into an aluminum shell or soft-pack lithium ion battery.
  • the discharge rate at 3C and the capacity retention rate after 1000 cycles at 1C at 25°C were tested.
  • the test results are shown in Table 1:
  • Example 1 By comparing Example 1 with Examples 3-4, it can be seen that in the modified lithium iron manganese phosphate positive electrode material described in the present application, the mass ratio of LiNbO 3 and Nb 2 O 5 will affect its performance.
  • the mass ratio of LiNbO 3 and Nb 2 O 5 is controlled at 1:(0.1-0.4), the performance of the obtained positive electrode material is better. If the mass proportion of LiNbO 3 is too large, the material stability is poor and the cycle capacity retention rate is low. If the mass proportion of Nb 2 O 5 is too large, the material rate performance is poor.
  • Example 1 By comparing Example 1 with Comparative Example 1, it can be seen that the modified lithium manganese iron phosphate core described in the present application has a strong interatomic force after Nb doping, which can stabilize the lattice structure, improve the dissolution of manganese, reduce Li/Ni mixing, and increase the lithium ion diffusion coefficient.
  • LiNbO 3 can not only serve as a physical barrier to enhance interface stability, but also serve as a fast ion conductor to promote the rapid conduction of lithium ions.
  • Nb 2 O 5 has strong stability within the working voltage range, can effectively inhibit the side reaction between the electrode and the electrolyte and enhance the interface stability, thereby improving the cycle stability of the LMFP positive electrode material.

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Abstract

本申请提供了一种改性磷酸锰铁锂正极材料及其制备方法和应用，所述改性磷酸锰铁锂正极材料包括掺杂型磷酸锰铁锂内核和设置于所述掺杂型磷酸锰铁锂内核表面的包覆层，所述掺杂型磷酸锰铁锂内核包括Nb元素，所述包覆层包括LiNbO3和Nb2O5，本申请所述改性磷酸锰铁锂正极材料的掺杂Nb元素，表面双包覆LiNbO3和Nb2O5，所述改性磷酸锰铁锂正极材料的包覆层具有良好的均匀性、一致性与导电性，LiNbO3和Nb2O5协同提高了LMFP电极材料的倍率性能和长循环性能。

Description

一种改性磷酸锰铁锂正极材料及其制备方法和应用
本申请要求在2022年12月14日提交中国专利局、申请号为202211611334.3的中国专利申请的优先权，以上申请的全部内容通过引用结合在本申请中。
技术领域
本申请属于锂离子电池技术领域，涉及一种改性磷酸锰铁锂正极材料及其制备方法和应用。
背景技术
近年来，新能源汽车蓬勃发展，带动了锂离子动力电池需求的迅速增长。目前，锂离子动力电池的正极材料主要磷酸铁锂(LFP)和三元材料。其中，LFP凭借高性价比、高安全性以及资源瓶颈小等优势，逐渐成为储能和动力电池企业的优先选择，然而其存在能量密度低的问题，这成为制约磷酸铁锂大规模应用的关键因素。
磷酸锰铁锂(LMFP)是在LFP的基础上添加锰元素后获得的一种正极材料，锰的掺杂可使LMFP具有更高的电压平台(4.1Vvs3.4V)，电池的能量密度提升15％左右，是一种具有极大应用前景的正极材料。当前LMFP正极材料还处于产业化初期，其主要原因是LMFP电子导电率和离子扩散速率较低，首次库伦效率低，循环性能差，这严重影响其商业落地。因此，如何提高LMFP材料的电子导电、离子传输速率以及循环稳定性是当前的技术关键。目前，解决该技术问题有效的办法就是对LMFP材料进行晶格掺杂和双包覆一体化修饰。
CN114335480A提供了一种核壳型碳包覆掺杂类磷酸铁锂的制备方法和应用，该方法首先将铁源、过渡金属化合物和单宁酸发生螯合反应，再将此螯合 物与磷源、锂源进行水热合成反应，得到单宁酸包覆过渡金属离子掺杂磷酸铁锂前驱体，最后在惰性气氛下烧结单宁酸碳化得到核壳型碳包覆掺杂类磷酸铁锂。该方法采用的螯合反应可抑制过渡金属离子的流失，单宁酸碳化可抑制二次颗粒的团聚，使得其制得的正极材料在应用中能够获得较好的倍率和动力学性能，但循环性能无明显改善，无法满足动力电池需求。
CN113942990A公开了一种采用共沉淀反应制备碳包覆和离子掺杂的磷酸锰铁锂正极材料，该方法克服了磷酸锰铁锂正极材料元素分布不均匀、压实密度低、比容量不高的问题，但材料的循环稳定性较差，其组装成的扣电在1C倍率下循环80周后，容量衰减至95.8％。
发明内容
以下是对本文详细描述的主题的概述。本概述并非是为了限制权利要求的保护范围。
本申请的目的在于提供一种改性磷酸锰铁锂正极材料及其制备方法和应用，本申请所述改性磷酸锰铁锂正极材料的掺杂Nb元素，表面双包覆LiNbO3和Nb2O5，所述改性磷酸锰铁锂正极材料的包覆层具有良好的均匀性、一致性与导电性，LiNbO3和Nb2O5协同提高了LMFP电极材料的倍率性能和长循环性能。
为达到此目的，本申请采用以下技术方案：
第一方面，本申请实施例提供了一种改性磷酸锰铁锂正极材料，所述改性磷酸锰铁锂正极材料包括掺杂型磷酸锰铁锂内核和设置于所述掺杂型磷酸锰铁锂内核表面的包覆层，所述掺杂型磷酸锰铁锂内核包括Nb元素，所述包覆层包括LiNbO3和Nb2O5。
本申请实施例所述改性磷酸锰铁锂正极材料体相掺杂Nb元素，表面双包覆 LiNbO3和Nb2O5，其中Nb掺杂后具有较强的原子间作用力，可稳定晶格结构，改善锰的溶出，降低Li/Ni混排，提高了锂离子扩散系数；Nb2O5在工作电压范围内具有较强的稳定性，可有效抑制电极与电解液之间的副反应并增强了界面稳定性，提高LMFP正极材料的循环稳定性；LiNbO3既可以作为物理屏障增强界面稳定性，还可以作为快离子导体促进锂离子的快速传导。
在一实施例中，所述掺杂型磷酸锰铁锂内核的化学式为LiNbaMnxFe1-xPO4，其中，0<a≤0.05，0<x<1。
在一实施例中，所述包覆层的厚度为10-50nm，例如：10nm、20nm、30nm、40nm或50nm等。
在一实施例中，所述包覆层中LiNbO3和Nb2O5的摩尔质量比为1:(0.1-0.4)，例如：1:0.1、1:0.15、1:0.2、1:0.25、1:0.3、1:0.35或1:0.4等。
第二方面，本申请实施例提供了一种如第一方面所述改性磷酸锰铁锂正极材料的制备方法，所述制备方法包括以下步骤：
(1)将锂源、锰源、铁源和磷源与溶剂混合得到混合盐溶液，将所述混合盐溶液、铌源和络合剂混合，干燥后经烧结处理得到一烧材料；
(2)将步骤(1)得到的一烧材料、LiNbO3、Nb2O5与有机溶剂混合，进行研磨处理；
(3)对步骤(2)研磨处理得到的物料进行焙烧处理，得到所述改性磷酸锰铁锂正极材料。
本申请实施例先合成掺杂Nb的LMFP，然后将LiNbO3和Nb2O5按一定比例混合，再将LMFP与包覆混合料进行干混，随后烧结处理得到掺杂和双包覆一体化 修饰的LMFP正极材料，制备的包覆层具有良好的均匀性、一致性与导电性，该方法制备过程简单可控，易于大规模工业化生产。
在一实施例中，步骤(1)所述锂源包括碳酸锂和/或磷酸二氢锂。
在一实施例中，所述锰源包括硫酸锰、碳酸锰、硝酸锰、醋酸锰或草酸锰中的任意一种或至少两种的组合。
在一实施例中，所述铁源包括磷酸铁和/或铁粉。
在一实施例中，所述磷源包括磷酸和/或磷酸二氢铵。
在一实施例中，所述混合盐溶液中的各元素摩尔比为Li:Mn:Fe:P＝(1-1.6):x:(1-x):1，0<x<1。
在一实施例中，所述铌源包括氧化铌、氢氧化铌、氯化铌、硫酸铌、硝酸铌或醋酸铌中的任意一种或至少两种的组合。
在一实施例中，所述络合剂包括海藻酸钠。
在一实施例中，步骤(1)所述干燥的方法包括喷雾干燥。
在一实施例中，所述烧结处理的温度为600-900℃，例如：600℃、750℃、800℃、850℃或900℃等。
在一实施例中，所述烧结处理的时间为6-15h，例如：6h、8h、10h、12h或15h等。
在一实施例中，所述烧结处理的气氛包括氮气气氛。
在一实施例中，步骤(2)所述有机溶剂包括乙醇。
在一实施例中，所述研磨处理的速度为500-1000rpm，例如：500rpm、600 rpm、700rpm、800rpm、900rpm或1000rpm等。
在一实施例中，所述研磨处理的时间为0.3-1h，例如：0.3h、0.5h、0.6h、0.8h或1h等。
在一实施例中，所述LiNbO3和Nb2O5的总质量与一烧材料的质量比为0.1-10:100，例如：0.1:100、0.5:100、1:100、5:100或10:100等，优选为0.5-2:100。
在一实施例中，步骤(3)所述焙烧处理的温度为200-650℃，例如：200℃、300℃、400℃、500℃或650℃等。
在一实施例中，所述焙烧处理的时间为2-15h，例如：2h、5h、8h、10h或15h等。
第三方面，本申请实施例提供了一种正极极片，所述正极极片包含如第一方面所述改性磷酸锰铁锂正极材料。
第四方面，本申请实施例提供了一种锂离子电池，所述锂离子电池包含如第三方面所述的正极极片。
相对于相关技术，本申请具有以下有益效果：
(1)本申请所述改性磷酸锰铁锂正极材料的掺杂Nb元素，表面双包覆LiNbO3和Nb2O5，所述改性磷酸锰铁锂正极材料的包覆层具有良好的均匀性、一致性与导电性，LiNbO3和Nb2O5协同提高了LMFP电极材料的倍率性能和长循环性能。
(2)Nb5+掺杂层状过渡金属氧化物正极材料，可抑制阳离子混排，显著提高材料的倍率和循环稳定性；LiNbO3包覆改性正极材料，由于其具有的高锂离子 电导性，可在有效隔绝有机电解液的同时，确保不会降低材料的倍率性能。因此，构建Nb5+掺杂和/LiNbO3结构，将具有协同效应，显著改善倍率、循环及安全性能。T-Nb2O5(T相氧化铌)具有特殊的锂离子传输通道，而倍率性能优异，可媲美最优异的固态电解质，目前T相氧化铌已经用作锂电池高倍率负极材料。采用T-Nb2O5作为铌源，在构建Nb5+掺杂/LiNbO3包覆的同时，使过量的铌源(T-Nb2O5)残留材料的表面，可继续作为物理保护层而不会降低材料的倍率性能。
在阅读并理解了详细描述后，可以明白其他方面。
具体实施方式
实施例1
本实施例提供了一种改性磷酸锰铁锂正极材料，所述改性磷酸锰铁锂正极材料通过如下方法制得：
(1)按照摩尔比Li:Mn:Fe:P＝1.08:0.7:0.3:1称取碳酸锂、硫酸锰、铁粉、磷酸，加入到去离子水中分散搅拌球磨，随后加入氯化铌、海藻酸钠，以1000rpm的搅拌速度搅拌3h后，进行喷雾干燥，放入氮气气氛保护的箱式炉，以5℃的升温速率，升温至780℃，保温10h后，得到一烧材料；
(2)将LiNbO3和Nb2O5按1:0.25的比例加入高混机中进行混合，转速800rpm，高混时间0.5h得到包覆混合料，随后将包覆混合料与步骤(1)得到的一烧材料分散在乙醇溶剂中搅拌研磨，其中包覆混合料占比1％，球磨转速600rpm，球磨时间2h；
(3)在氮气气氛烧结，烧结的升温速率为8℃/min，烧结温度为650℃，煅烧时间为2h，随后在氮气气氛中冷却至室温，获得所述改性磷酸锰铁锂正极 材料，所述改性磷酸锰铁锂正极材料的包覆层厚度为25nm。
实施例2
本实施例提供了一种改性磷酸锰铁锂正极材料，所述改性磷酸锰铁锂正极材料通过如下方法制得：
(1)按照摩尔比Li:Mn:Fe:P＝1.08:0.7:0.3:1称取碳酸锂、硫酸锰、铁粉、磷酸，加入到去离子水中分散搅拌球磨，随后加入氯化铌、海藻酸钠，以1200rpm的搅拌速度搅拌3h后，进行喷雾干燥，放入氮气气氛保护的箱式炉，以8℃的升温速率，升温至790℃，保温9h后，得到一烧材料；
(2)将LiNbO3和Nb2O5按1:0.3的比例加入高混机中进行混合，转速850rpm，高混时间0.5h得到包覆混合料，随后将包覆混合料与步骤(1)得到的一烧材料分散在乙醇溶剂中搅拌研磨，其中包覆混合料占比1％，球磨转速600rpm，球磨时间2h；
(3)在氮气气氛烧结，烧结的升温速率为8℃/min，烧结温度为680℃，煅烧时间为2h，随后在氮气气氛中冷却至室温，获得所述改性磷酸锰铁锂正极材料。
实施例3
本实施例与实施例1区别仅在于，LiNbO3和Nb2O5的质量比为1:0.05，其他条件与参数与实施例1完全相同。
实施例4
本实施例与实施例1区别仅在于，LiNbO3和Nb2O5的质量比为1:0.6，其他条件与参数与实施例1完全相同。
对比例1
本对比例与实施例1区别仅在于，内核中不掺杂Nb，其他条件与参数与实施例完全相同。
对比例2
本对比例与实施例1区别仅在于，不加入LiNbO3，其他条件与参数与实施例完全相同。
对比例3
本对比例与实施例1区别仅在于，不加入Nb2O5，其他条件与参数与实施例完全相同。
性能测试：
选取实施例1-4和对比例1-3制得的磷酸锰铁锂作为正极材料，负极材料选取石墨碳材料，搭配PE/PP高分子材料作为隔膜，采用卷绕或者叠片方式组装成卷芯，封装在铝壳或者铝塑膜中，并注入EC/EMC和LiPF6组成的锂离子电解液，组装成铝壳或软包锂离子电池，测试其在3C下的放电倍率，以及25℃下1C循环1000次后容量保持率，测试结果如表1所示：
表1

由实施例1和实施例3-4对比可得，本申请所述改性磷酸锰铁锂正极材料中，LiNbO3和Nb2O5的质量比会影响其性能，将LiNbO3和Nb2O5的质量比控制在1:(0.1-0.4)，制得正极材料的性能较好，若LiNbO3的质量占比过大，材料稳定性差，循环容量保持率低，若Nb2O5的质量占比过大，材料倍率性能差。
由实施例1和对比例1对比可得，本申请所述改性磷酸锰铁锂内核中Nb掺杂后具有较强的原子间作用力，可稳定晶格结构，改善锰的溶出，降低Li/Ni混排，提高了锂离子扩散系数。
由实施例1和对比例2对比可得，LiNbO3既可以作为物理屏障增强界面稳定性，还可以作为快离子导体促进锂离子的快速传导。
由实施例1和对比例3对比可得，Nb2O5在工作电压范围内具有较强的稳定性，可有效抑制电极与电解液之间的副反应并增强了界面稳定性，提高LMFP正极材料的循环稳定性。

Claims (9)

  1. 一种改性磷酸锰铁锂正极材料，所述改性磷酸锰铁锂正极材料包括掺杂型磷酸锰铁锂内核和设置于所述掺杂型磷酸锰铁锂内核表面的包覆层，所述掺杂型磷酸锰铁锂内核包括Nb元素，所述包覆层包括LiNbO3和Nb2O5。
  2. 如权利要求1所述的改性磷酸锰铁锂正极材料，其中，所述掺杂型磷酸锰铁锂内核的化学式为LiNbaMnxFe1-xPO4，其中，0<a≤0.05，0<x<1。
  3. 如权利要求1或2所述的改性磷酸锰铁锂正极材料，其中，所述包覆层的厚度为10-50nm；
    可选地，所述包覆层中LiNbO3和Nb2O5的质量比为1:(0.1-0.4)。
  4. 一种如权利要求1-3任一项所述改性磷酸锰铁锂正极材料的制备方法，所述制备方法包括以下步骤：
    (1)将锂源、锰源、铁源和磷源与溶剂混合得到混合盐溶液，将所述混合盐溶液、铌源和络合剂混合，干燥后经烧结处理得到一烧材料；
    (2)将步骤(1)得到的一烧材料、LiNbO3、Nb2O5与有机溶剂混合，进行研磨处理；
    (3)对步骤(2)研磨处理得到的物料进行焙烧处理，得到所述改性磷酸锰铁锂正极材料。
  5. 如权利要求4所述的制备方法，其中，步骤(1)所述锂源包括碳酸锂和/或磷酸二氢锂；
    可选地，所述锰源包括硫酸锰、碳酸锰、硝酸锰、醋酸锰或草酸锰中的任意一种或至少两种的组合；
    可选地，所述铁源包括磷酸铁和/或铁粉；
    可选地，所述磷源包括磷酸和/或磷酸二氢铵；
    可选地，所述混合盐溶液中的各元素摩尔比为Li:Mn:Fe:P＝(1-1.6):x:(1-x):1，0<x<1；
    可选地，所述铌源包括氧化铌、氢氧化铌、氯化铌、硫酸铌、硝酸铌或醋酸铌中的任意一种或至少两种的组合；
    可选地，所述络合剂包括海藻酸钠。
  6. 如权利要求4或5所述的制备方法，其中，步骤(1)所述干燥的方法包括喷雾干燥；
    可选地，所述烧结处理的温度为600-900℃；
    可选地，所述烧结处理的时间为6-15h；
    可选地，所述烧结处理的气氛包括氮气气氛。
  7. 如权利要求4-6任一项所述的制备方法，其中，步骤(2)所述有机溶剂包括乙醇；
    可选地，所述研磨处理的速度为500-1000rpm；
    可选地，所述研磨处理的时间为0.3-1h；
    可选地，所述LiNbO3和Nb2O5的总质量与一烧材料的质量比为0.1-10:100，优选为0.5-2:100。
  8. 如权利要求4-7任一项所述的制备方法，其中，步骤(3)所述焙烧处理的温度为200-650℃；
    可选地，所述焙烧处理的时间为2-15h。
  9. 一种正极极片，所述正极极片包含如权利要求1-3任一项所述改性磷酸锰铁锂正极材料。
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