WO2021082314A1 - 锂离子电池的正极材料及其制备方法 - Google Patents

锂离子电池的正极材料及其制备方法 Download PDF

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WO2021082314A1
WO2021082314A1 PCT/CN2020/077203 CN2020077203W WO2021082314A1 WO 2021082314 A1 WO2021082314 A1 WO 2021082314A1 CN 2020077203 W CN2020077203 W CN 2020077203W WO 2021082314 A1 WO2021082314 A1 WO 2021082314A1
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positive electrode
electrode material
aluminum
titanium
core
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PCT/CN2020/077203
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English (en)
French (fr)
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江卫军
乔齐齐
许鑫培
施泽涛
马加力
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蜂巢能源科技有限公司
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    • 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
    • H01M4/52—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron
    • H01M4/525—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron of mixed oxides or hydroxides containing iron, cobalt or nickel for inserting or intercalating light metals, e.g. LiNiO2, LiCoO2 or LiCoOxFy
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
    • C01G53/00—Compounds of nickel
    • C01G53/006—Compounds containing, besides nickel, two or more other elements, with the exception of oxygen or hydrogen
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • 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
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/624—Electric conductive fillers
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/01—Particle morphology depicted by an image
    • 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
    • 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

  • This application relates to the technical field of lithium ion batteries. Specifically, this application relates to a cathode material of a lithium ion battery and a preparation method thereof.
  • the cobalt-free materials composed of LiNi 0.9 Mn 0.1 O 2 and LiNi 0.9 Al 0.1 O 2 have first charge and discharge coulombic efficiencies of 85.9% and 84.9%, respectively, while LiNi containing cobalt
  • the first charge-discharge Coulombic efficiency of 0.9 Co 0.05 Al 0.05 O 2 can reach 89%.
  • the cobalt-free material with the composition of LiNi 0.7 Mn 0.3 O 2 has a first charge-discharge coulombic efficiency of 71-75%.
  • the present application designs a preparation method for improving the first coulombic efficiency of the cobalt-free nickel-manganese cathode material by co-coating.
  • this application proposes a positive electrode material for a lithium ion battery.
  • the positive electrode material has a core-shell structure, and the material forming the outer shell of the core-shell structure is formed of a compound of titanium and a compound of aluminum, and the compound of titanium includes titanium dioxide and tetrabutyl titanate
  • the aluminum compound includes at least one of aluminum oxide, aluminum hydroxide, and aluminum ethoxide.
  • cathode material according to the foregoing embodiments of the present application may also have the following additional technical features:
  • the titanium compound is titanium dioxide
  • the aluminum compound is alumina
  • the material forming the inner core of the core-shell structure is layered lithium nickel manganate.
  • the specific surface area of the positive electrode material is 0.1-0.5 m 2 /g.
  • the particle size D50 of the positive electrode material is 3-15 microns.
  • the present application proposes a method for preparing the above-mentioned cathode material of a lithium ion battery.
  • the method includes: (1) providing a core; (2) performing a coating treatment on the surface of the core to obtain the positive electrode material with a core-shell structure, wherein the coating
  • the processed raw materials include titanium compounds and aluminum compounds.
  • the inventor found through research that by adopting the preparation method of the embodiments of the present application, by co-coating titanium and aluminum on the outer surface of the inner core of the positive electrode material, a positive electrode material with reduced surface impedance and improved first charge and discharge Coulomb efficiency can be obtained, and the preparation The method is easy to operate and has the potential for large-scale industrial production.
  • preparation method according to the foregoing embodiment of the present application may also have the following additional technical features:
  • the step (1) includes: (1-1) mixing lithium hydroxide with nickel manganese hydroxide to obtain a first mixture; (1-2) performing a first mixture on the first mixture Calcining treatment and crushing treatment to obtain the inner core.
  • the step (2) includes: (2-1) mixing the inner core with nano-titania and nano-alumina to obtain a second mixture; (2-2) performing the second mixture The second calcination process is used to obtain the positive electrode material.
  • the content of titanium element is 0.15-0.25 wt%
  • the content of aluminum element is 0.05-0.15 wt%.
  • the first calcination treatment is reacted at 720-870 degrees Celsius for 8-12 hours, and the second calcination treatment is reacted at 300-600 degrees Celsius for 4-8 hours.
  • FIG. 1 is a schematic diagram of a cross-sectional structure of a cathode material with a core-shell structure according to an embodiment of the present application;
  • FIG. 2 is a comparison diagram of charge and discharge curves of a positive electrode material before and after coating according to an embodiment of the present application
  • FIG. 3 is a comparison diagram of the cycle curves of the positive electrode material before and after coating according to an embodiment of the present application
  • FIG. 4 is a schematic flow chart of a method for preparing a cathode material according to an embodiment of the present application
  • Figure 5 is an electron micrograph of the core of an embodiment of the application before (a) (b) and (c) (d) after coating;
  • Figure 6 is an elemental analysis diagram of the core of an embodiment of the present application before (a) and after (b) coating.
  • this application proposes a positive electrode material for a lithium ion battery.
  • the positive electrode material has a core-shell structure, that is, the outer shell 200 covers the inner core 100, and the material of the outer shell 200 forming the core-shell structure is composed of a compound of titanium (Ti) and a compound of aluminum (Al).
  • the compound of titanium includes at least one of titanium dioxide and tetrabutyl titanate
  • the compound of aluminum includes at least one of aluminum oxide, aluminum hydroxide, and aluminum ethoxide.
  • the inventor of the present application discovered during the research that the first charge-discharge reversibility of the cobalt-free nickel-manganese binary layered cathode material is poor, and the first charge-discharge coulombic efficiency is generally lower than 86%, which will affect the cobalt-free The energy density of the nickel-manganese cathode material. Therefore, the inventors tried to coat titanium and aluminum together on the surface of layered lithium nickel manganese oxide and other materials.
  • the coating of titanium can solve the conductivity of the positive electrode material, and the coating of aluminum can improve the cycle stability of the positive electrode material and reduce Gas production, so that the coated shell can reduce the surface impedance of the positive electrode material, thereby improving the coulombic efficiency of the first charge and discharge of the positive electrode material.
  • the titanium compound can be titanium dioxide (TiO 2 ), and the aluminum compound is aluminum oxide (Al 2 O 3 ).
  • TiO 2 titanium dioxide
  • Al 2 O 3 aluminum oxide
  • titanium dioxide and titanium dioxide can not only reduce the surface impedance of the positive electrode material, but also The casing 200 composed of titanium dioxide and titanium dioxide reduces the gas production of the positive electrode material and increases its cycle life.
  • Li x Ni a Mn b O 2 lithium nickel manganese oxide
  • the specific surface area of the positive electrode material may be 0.1 to 0.5 m 2 /g, and the particle size D50 of the positive electrode material is 3 to 15 microns, that is, when the cumulative particle size distribution percentage of the positive electrode material reaches 50% The corresponding particle size is 3-15 microns.
  • the preparation of the positive electrode material particles with the above-mentioned particle size and specific surface area can make the first charge and discharge Coulomb efficiency and energy density of the binary layered positive electrode material without cobalt higher.
  • the content of titanium element can be 0.15 to 0.25 wt%
  • the content of aluminum element can be 0.05 to 0.15 wt%. In this way, it is only necessary to coat the outer surface of the inner core 100 with the above content of titanium.
  • the compound and the aluminum compound can increase the first efficiency of the cathode material by 4%.
  • the 50-week cycle retention rate of the uncoated positive electrode material is 98.8%, while the 50-week cycle retention rate of the coated positive electrode material reaches 99.7%.
  • the first efficiency of the uncoated cathode material is only 85.5%, and the first efficiency of the coated cathode material is 89.5%, indicating that the first efficiency of Ti and Al is increased by 4%.
  • the discharge capacity of the uncoated and coated cathode materials at 0.1C is 176.0 and 184.2mAh/g, respectively, indicating that the 0.1C capacity of the coated cathode material has increased by 8.2mAh/g; the uncoated cathode material
  • the discharge capacity under 1C condition was 158.6mAh/g, and the 1C discharge capacity after coating reached 163.7mAh/g, indicating that the 1C capacity of the positive electrode material after coating increased by 5.1mAh/g. Therefore, it is shown that the co-coating of Ti and Al improves the capacity and first-time efficiency of the cathode material.
  • the present application proposes a positive electrode material, the outer surface of the core material is co-coated with titanium and aluminum, and the coating of titanium can solve the conductivity of the positive electrode material, and the coating of aluminum
  • the coating can improve the cycle stability of the positive electrode material and reduce the gas production, so that the coated shell can reduce the surface impedance of the positive electrode material, thereby improving the first charge and discharge coulombic efficiency of the positive electrode material.
  • the present application proposes a method for preparing the above-mentioned cathode material of a lithium ion battery.
  • the method includes:
  • step S100 may include: S110 firstly combine lithium hydroxide (LiOH) with nickel manganese hydroxide (Ni a Mn b (OH) 2 , where 0.55 ⁇ a ⁇ 0.95 and 0.05 ⁇ b ⁇ 0.45) Mixing, for example, use high-speed mixing equipment to mix for 5-20 minutes, or use laboratory 5L equipment with a rotation speed of 2000-3000rpm, or use laboratory 100L equipment with a rotation speed of 800-900rpm, and the material filling efficiency in the equipment is 30-70%, in this way, the first mixture can be obtained; S120 then performs the first calcining treatment and crushing treatment on the first mixture to obtain the inner core 100.
  • LiOH lithium hydroxide
  • Ni a Mn b (OH) 2 nickel manganese hydroxide
  • step S100 may include: S110 firstly combine lithium hydroxide (LiOH) with nickel manganese hydroxide (Ni a Mn b (OH) 2 , where 0.55 ⁇ a ⁇ 0.95 and 0.05 ⁇ b ⁇ 0.4
  • the first calcination treatment may be a reaction at 720-870 degrees Celsius for 8-12 hours, for example, in an oxygen atmosphere with a concentration greater than 95% at 720-870 degrees Celsius for 8-12 hours, In this way, after calcination under the above-mentioned conditions, continuous use of rollers or other mechanical crushing methods, layered lithium nickel manganate particles sieved with 300-400 mesh can be obtained.
  • S200 Perform coating treatment on the surface of the core to obtain a positive electrode material with a core-shell structure.
  • a coating treatment is performed on the surface of the core 100 to obtain a positive electrode material having a core-shell structure, wherein the raw material for the coating treatment includes a compound of titanium (Ti) and a compound of aluminum (Al).
  • step S200 may include: S210 continue to mix the inner core with nano titanium dioxide (TiO 2 ) and nano alumina (Al 2 O 3 ) using high-speed mixing equipment to obtain a second mixture; S230 The mixture is subjected to a second calcination treatment to obtain a positive electrode material.
  • the inner core can be coated by a dry method, and the positive electrode material whose outer surface is co-coated with titanium dioxide and aluminum oxide has lower surface impedance and higher first charge and discharge coulombic efficiency.
  • the content of titanium is 0.15 to 0.25 wt%
  • the content of aluminum is 0.05 to 0.15 wt%
  • the molar ratio of titanium to aluminum is controlled within the range 0.5 ⁇ 1.5, the best ratio is 1.
  • the nanoparticles in the above-mentioned ratio range can be uniformly attached to the outer surface of the core 100, and the surface impedance of the positive electrode material can be reduced after the above-mentioned calcination treatment.
  • the second calcination treatment may be a reaction at 300-600 degrees Celsius for 4-8 hours.
  • the coated second mixture is treated at a high temperature of 300-600 degrees Celsius for 4-8 hours.
  • the high temperature treatment adopts an oxygen atmosphere with a concentration range of 20-100%.
  • the inventors performed scanning electron microscopy (SEM) observations on the positive electrode material before and after the coating.
  • SEM scanning electron microscopy
  • FIG. 5 where (a) and (b) of FIG. 5 are the morphology of the core 100 before coating.
  • Figure 5 (c) and (d) show the morphology of the positive electrode material after coating. It can be seen from Fig. 5 that the SEM photograph clearly shows the presence of coating on the surface of the coated positive electrode material.
  • the inventor continued to perform elemental analysis (EDS-ICP) on the particles in the SEM field of view, and the EDS diagram of the positive electrode material before and after the coating is shown in Figure 6, where (a ) Represents the core 100 before coating, and (b) of FIG. 6 represents the positive electrode material after coating, and the abscissa in FIG. 6 is energy.
  • the ICP results of the positive electrode materials before and after coating are shown in Table 2.
  • the present application proposes a preparation method.
  • a preparation method By co-coating titanium and aluminum on the outer surface of the inner core of the positive electrode material, a positive electrode with reduced surface impedance and improved first charge and discharge Coulomb efficiency can be obtained.
  • the preparation method is easy to operate and has the potential for large-scale industrial production.
  • first and second are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of indicated technical features. Therefore, the features defined with “first” and “second” may explicitly or implicitly include at least one of the features. In the description of the present application, "a plurality of” means at least two, such as two, three, etc., unless specifically defined otherwise.

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Abstract

本申请提出了锂离子电池的正极材料及其制备方法。该锂离子电池的正极材料具有核壳结构，形成核壳结构的外壳的材料由钛的化合物和铝的化合物组成，且钛的化合物包括二氧化钛和钛酸四丁酯中的至少一种，铝的化合物包括氧化铝、氢氧化铝和乙醇铝中的至少一种。本申请所提出的正极材料，其内核材料外表面共包覆有钛和铝，而钛的包覆可解决正极材料的导电性，铝的包覆可提高正极材料的循环稳定性并降低产气量，从而包覆的外壳能够降低正极材料的表面阻抗，进而提高正极材料的首次充放电库伦效率。

Description

锂离子电池的正极材料及其制备方法
优先权信息
本申请请求2019年10月29日向中国国家知识产权局提交的、专利申请号为201911040257.9的发明的专利申请的优先权和权益，并且通过参照在先文本的全文并入此处。
技术领域
本申请涉及锂离子电池技术领域，具体的，本申请涉及锂离子电池的正极材料及其制备方法。
背景技术
虽然目前研究发现，无钴的高镍正极材料具有容量高、成本较低等优势，但是不含钴的二元层状材料首次充放电可逆性却较差，会导致首次充放电的库伦效率较低，从而影响材料的能量密度。
根据加拿大学者J.R.Dahn在2019年发表的文献，组成为LiNi 0.9Mn 0.1O 2和LiNi 0.9Al 0.1O 2的无钴材料，其首次充放电库伦效率分别为85.9％和84.9％，而含钴的LiNi 0.9Co 0.05Al 0.05O 2的首次充放电库伦效率可达到89％。另外，在江西理工大学的2017届硕士生罗垂意的论文中，组成为LiNi 0.7Mn 0.3O 2的无钴材料的首次充放电库伦效率为71～75％。
首次充放电库伦效率的降低会导致材料的能量密度降低。因此，为开发高能量密度的无钴化正极材料，就需要开发新的技术来提升首次充放电库伦效率。
发明内容
本申请是基于发明人的下列发现而完成的：
为了解决无钴的正极材料的首次充放电库伦效率较低的问题，本申请设计一种通过共包覆提高无钴的镍锰正极材料的首次库伦效率的制备方法。
在本申请的第一方面，本申请提出了一种锂离子电池的正极材料。
根据本申请的实施例，所述正极材料具有核壳结构，形成所述核壳结构的外壳的材料由钛的化合物和铝的化合物形成，且所述钛的化合物包括二氧化钛和钛酸四丁酯中的至少一种，所述铝的化合物包括氧化铝、氢氧化铝和乙醇铝中的至少一种。
发明人经过研究发现，本申请实施例的正极材料，其内核材料外表面共包覆有钛和铝， 而钛的包覆可解决正极材料的导电性，铝的包覆可提高正极材料的循环稳定性并降低产气量，从而包覆的外壳能够降低正极材料的表面阻抗，进而提高正极材料的首次充放电库伦效率。
另外，根据本申请上述实施例的正极材料，还可以具有如下附加的技术特征：
根据本申请的实施例，所述钛的化合物为二氧化钛，且所述铝的化合物为氧化铝。
根据本申请的实施例，形成所述核壳结构的内核的材料为层状镍锰酸锂。
根据本申请的实施例，所述正极材料的比表面积为0.1～0.5m 2/g。
根据本申请的实施例，所述正极材料的颗粒粒度D50为3～15微米。
在本申请的第二方面，本申请提出了一种制备上述的锂离子电池的正极材料的方法。
根据本申请的实施例，所述方法包括：(1)提供内核；(2)在所述内核的表面进行包覆处理，以获得具有核壳结构的所述正极材料，其中，所述包覆处理的原料包括钛的化合物和铝的化合物。
发明人经过研究发现，采用本申请实施例的制备方法，通过在正极材料的内核外表面共同包覆钛和铝，可获得表面阻抗降低、首次充放电库伦效率提高的正极材料，并且，该制备方法的操作简便且具有大批量产业化生产的潜力。
另外，根据本申请上述实施例的制备方法，还可以具有如下附加的技术特征：
根据本申请的实施例，所述步骤(1)包括：(1-1)将氢氧化锂与氢氧化镍锰混合，获得第一混合物；(1-2)对所述第一混合物进行第一煅烧处理并破碎处理，以获得所述内核。
根据本申请的实施例，所述步骤(2)包括：(2-1)将所述内核与纳米二氧化钛、纳米氧化铝混合，获得第二混合物；(2-2)对所述第二混合物进行第二煅烧处理，以获得所述正极材料。
根据本申请的实施例，在所述第二混合物中，钛元素的含量为0.15～0.25wt％，铝元素的含量为0.05～0.15wt％。
根据本申请的实施例，所述第一煅烧处理在720～870摄氏度下反应8～12小时，且所述第二煅烧处理在300～600摄氏度下反应4～8小时。
本申请的附加方面和优点将在下面的描述中部分给出，部分将从下面的描述中变得明显，或通过本申请的实践了解到。
附图说明
本申请的上述的方面结合下面附图对实施例的描述进行解释，其中：
图1是本申请一个实施例的具有核壳结构的正极材料的截面结构示意图；
图2是本申请一个实施例的正极材料在包覆前和包覆后的充放电曲线对比图；
图3是本申请一个实施例的正极材料在包覆前和包覆后的循环曲线对比图；
图4是本申请一个实施例的制备正极材料的方法流程示意图；
图5是本申请一个实施例的内核在包覆前(a)(b)和包覆后(c)(d)的电镜照片；
图6是本申请一个实施例的内核在包覆前(a)和包覆后(b)的元素分析图。
具体实施方式
下面详细描述本申请的实施例，本技术领域人员会理解，下面实施例旨在用于解释本申请，而不应视为对本申请的限制。除非特别说明，在下面实施例中没有明确描述具体技术或条件的，本领域技术人员可以按照本领域内的常用的技术或条件或按照产品说明书进行。
在本申请的一个方面，本申请提出了一种锂离子电池的正极材料。
根据本申请的实施例，参考图1，正极材料具有核壳结构，即外壳200包覆内核100，且形成核壳结构的外壳200的材料由钛(Ti)的化合物和铝(Al)的化合物组成，且钛的化合物包括二氧化钛和钛酸四丁酯中的至少一种，而铝的化合物包括氧化铝、氢氧化铝和乙醇铝中的至少一种。本申请的发明人在研究过程中发现，无钴的镍锰二元层状正极材料的首次充放电可逆性较差，且首次充放电库伦效率一般低于86％，进而会影响到无钴的镍锰正极材料的能量密度。所以，发明人尝试在层状镍锰酸锂等材料的表面共同包覆钛和铝，而钛的包覆可解决正极材料的导电性，铝的包覆可提高正极材料的循环稳定性并降低产气量，从而包覆的外壳能够降低正极材料的表面阻抗，进而提高正极材料的首次充放电库伦效率。
在本申请的一些实施例中，钛的化合物可以选择二氧化钛(TiO 2)，且铝的化合物为氧化铝(Al 2O 3)，如此，二氧化钛和二氧化钛不仅能降低正极材料的表面阻抗，还可通过二氧化钛和二氧化钛组成的外壳200降低正极材料的产气量并提高其循环寿命。
在本申请的一些实施例中，形成核壳结构的内核的材料可为层状镍锰酸锂(Li xNi aMn bO 2，其中，1<x<1.10、1:1<a:b<19:1且a+b＝1)，如此，钛和铝形成的外壳200可包覆无钴的层状镍锰酸锂材料形成的内核100，从而降低正极材料的表面阻抗，进而提高不含钴的二元层状正极材料的首次充放电库伦效率。
在本申请的一些具体示例中，正极材料的比表面积可以为0.1～0.5m 2/g，且正极材料的颗粒粒度D50为3～15微米，即正极材料的累计粒度分布百分数达到50％时所对应的粒径在3～15微米。如此，制备出上述粒度尺寸和比表面积的正极材料颗粒，可使不含钴的二元层 状正极材料的首次充放电库伦效率和能量密度都更高。
在本申请的一些具体示例中，钛元素的含量可以为0.15～0.25wt％，铝元素的含量可以为0.05～0.15wt％，如此，只需在内核100的外表面包覆上述含量的钛的化合物和铝的化合物，就可以将正极材料的首次效率提高了4％。
具体的，发明人对无钴正极材料LiNi 0.75Mn 0.25O 2在包覆前后，分别测试了首周充放电曲线，如图2所示，且将包覆前后的正极材料组装成纽扣电池后进行50次循环性能测试，其结果如图3所示，并且，包覆前后的正极材料的扣电数据可参考表1。从图2可看出，不包覆的正极材料在0.1C条件下的首周充电比容量为205.9mAh/g，而放电比容量为176.0mAh/g，而包覆二氧化钛和氧化铝后的正极材料在0.1C条件下的首周充电比容量为205.8mAh/g，放电比容量为184.2mAh/g。从图3可看出，不包覆的正极材料的50周循环保持率为98.8％，而包覆后的正极材料50周循环保持率达到99.7％。而从表1可看出，不包覆的正极材料的首次效率仅为85.5％，包覆后的正极材料首次效率为89.5％，说明在Ti和Al的共包覆后首次效率提高了4％；不包覆和包覆的正极材料在0.1C条件下的放电容量分别为176.0和184.2mAh/g，说明包覆后正极材料的0.1C容量提高了8.2mAh/g；不包覆的正极材料在1C条件下的放电容量为158.6mAh/g，而包覆后1C放电容量达到163.7mAh/g，说明包覆后正极材料的1C容量提高了5.1mAh/g。因此，都说明Ti和Al的共包覆提高了正极材料的容量和首次效率。
表1.包覆前后的正极材料的扣电数据对比
样品 0.1C容量(mAh/g) 首次效率(％) 1C容量(mAh/g) 50周循环容量保持率(％)
不包覆 176.0 85.5 158.6 98.8
包覆后 184.2 89.5 163.7 99.7
综上所述，根据本申请的实施例，本申请提出了一种正极材料，其内核材料外表面共包覆有钛和铝，而钛的包覆可解决正极材料的导电性，铝的包覆可提高正极材料的循环稳定性并降低产气量，从而包覆的外壳能够降低正极材料的表面阻抗，进而提高正极材料的首次充放电库伦效率。
在本申请的另一个方面，本申请提出了一种制备上述的锂离子电池的正极材料的方法。根据本申请的实施例，参考图4，方法包括：
S100：提供内核。
在该步骤中，可直接提供内核100，具体的，内核100可以由层状镍锰酸锂形成的。在本申请的一些实施例中，步骤S100可以包括：S110先将氢氧化锂(LiOH)与氢氧化镍锰(Ni aMn b(OH) 2，其中，0.55≤a≤0.95且0.05≤b≤0.45)混合，具体例如采用高速混合设备混合5～20分钟，或者采用转速在2000～3000rpm的实验室5L设备，或者采用转速在 800～900rpm的实验室100L设备，且设备中的物料填充效率在30-70％，这样可以获得第一混合物；S120然后对第一混合物进行第一煅烧处理并破碎处理，以获得内核100。
在本申请的一些具体示例中，第一煅烧处理可以是在720～870摄氏度下反应8～12小时，具体例如在浓度大于95％的氧气氛围中于720～870摄氏度下反应8～12小时，如此，采用上述条件煅烧后，继续采用对辊或者其他机械的破碎方式，可获得300-400目过筛后的层状镍锰酸锂颗粒。
S200：在内核的表面进行包覆处理，以获得具有核壳结构的正极材料。
在该步骤中，在内核100的表面进行包覆处理，以获得具有核壳结构的正极材料，其中，包覆处理的原料包括钛(Ti)的化合物和铝(Al)的化合物。
在本申请的一些实施例中，步骤S200可以包括：S210将内核与纳米二氧化钛(TiO 2)、纳米氧化铝(Al 2O 3)采用高速混合设备继续混合，获得第二混合物；S230对第二混合物进行第二煅烧处理，以获得正极材料。如此，可以通过干法包覆内核，且外表面共包覆二氧化钛和氧化铝的正极材料的表面阻抗更低且首次充放电库伦效率更高。
在本申请的一些实施例中，在第二混合物中，钛元素的含量为0.15～0.25wt％，铝元素的含量为0.05～0.15wt％，并且，钛元素与铝元素的摩尔比范围控制在0.5～1.5，最好的比例为1。如此，采用颗粒尺寸在10～100nm(最好在50nm以下)，可使上述比例范围的纳米颗粒均匀地附着在内核100的外表面，然后经过上述煅烧处理以后可使正极材料的表面阻抗降低。
在本申请的一些实施例中，第二煅烧处理可以是在300～600摄氏度下反应4～8小时，具体例如将包覆好的第二混合物，在300～600度高温下处理4～8小时，且高温处理采用浓度范围在20～100％的氧气氛围。如此，经过包覆和煅烧的步骤之后，再通过300～400目筛分可获得粒度分布D50在3～15微米的正极材料。
具体的，发明人分别对包覆前后的正极材料进行扫描电子显微镜(SEM)的观察，可参考图5，其中，图5的(a)和(b)为包覆前内核100的形貌，图5的(c)和(d)为包覆后正极材料的形貌。从图5可看出，SEM照片清楚地显示出包覆后的正极材料表面存在包覆物。为了进一步表征包覆物的存在，发明人继续对SEM视野中的颗粒进行元素分析(EDS-ICP)，且包覆前后的正极材料的EDS图如图6所示，其中，图6的(a)表示包覆前内核100，而图6的(b)表示包覆后正极材料，且图6中的横坐标为能量(energy)。并且，包覆前后的正极材料的ICP结果如表2所示。
表2.包覆前后的正极材料的ICP数据
Figure PCTCN2020077203-appb-000001
Figure PCTCN2020077203-appb-000002
综上所述，根据本申请的实施例，本申请提出了一种制备方法，通过在正极材料的内核外表面共同包覆钛和铝，可获得表面阻抗降低、首次充放电库伦效率提高的正极材料，并且，该制备方法的操作简便且具有大批量产业化生产的潜力。
在本申请的描述中，需要理解的是，术语“中心”、“纵向”、“横向”、“长度”、“宽度”、“厚度”、“上”、“下”、“前”、“后”、“左”、“右”、“竖直”、“水平”、“顶”、“底”、“内”、“外”、“顺时针”、“逆时针”、“轴向”、“径向”、“周向”等指示的方位或位置关系为基于附图所示的方位或位置关系，仅是为了便于描述本申请和简化描述，而不是指示或暗示所指的装置或元件必须具有特定的方位、以特定的方位构造和操作，因此不能理解为对本申请的限制。
此外，术语“第一”、“第二”仅用于描述目的，而不能理解为指示或暗示相对重要性或者隐含指明所指示的技术特征的数量。由此，限定有“第一”、“第二”的特征可以明示或者隐含地包括至少一个该特征。在本申请的描述中，“多个”的含义是至少两个，例如两个，三个等，除非另有明确具体的限定。
在本说明书的描述中，参考术语“一个实施例”、“一些实施例”、“示例”、“具体示例”、或“一些示例”等的描述意指结合该实施例或示例描述的具体特征、结构、材料或者特点包含于本申请的至少一个实施例或示例中。在本说明书中，对上述术语的示意性表述不必须针对的是相同的实施例或示例。而且，描述的具体特征、结构、材料或者特点可以在任一个或多个实施例或示例中以合适的方式结合。此外，在不相互矛盾的情况下，本领域的技术人员可以将本说明书中描述的不同实施例或示例以及不同实施例或示例的特征进行结合和组合。
尽管上面已经示出和描述了本申请的实施例，可以理解的是，上述实施例是示例性的，不能理解为对本申请的限制，本领域的普通技术人员在本申请的范围内可以对上述实施例进行变化、修改、替换和变型。

Claims (10)

  1. 一种锂离子电池的正极材料，其特征在于，所述正极材料具有核壳结构，形成所述核壳结构的外壳的材料由钛的化合物和铝的化合物组成，且所述钛的化合物包括二氧化钛和钛酸四丁酯中的至少一种，所述铝的化合物包括氧化铝、氢氧化铝和乙醇铝中的至少一种。
  2. 根据权利要求1所述的正极材料，其特征在于，所述钛的化合物为二氧化钛，且所述铝的化合物为氧化铝。
  3. 根据权利要求1所述的正极材料，其特征在于，形成所述核壳结构的内核的材料为层状镍锰酸锂。
  4. 根据权利要求1所述的正极材料，其特征在于，所述正极材料的比表面积为0.1～0.5m 2/g。
  5. 根据权利要求1所述的正极材料，其特征在于，所述正极材料的颗粒粒度D50为3～15微米。
  6. 一种制备权利要求1～5中任一项所述的锂离子电池的正极材料的方法，其特征在于，包括：
    (1)提供内核；
    (2)在所述内核的表面进行包覆处理，以获得具有核壳结构的所述正极材料，其中，所述包覆处理的原料包括钛的化合物和铝的化合物。
  7. 根据权利要求6所述的方法，其特征在于，所述步骤(1)包括：
    (1-1)将氢氧化锂与氢氧化镍锰混合，获得第一混合物；
    (1-2)对所述第一混合物进行第一煅烧处理并破碎处理，以获得所述内核。
  8. 根据权利要求7所述的方法，其特征在于，所述步骤(2)包括：
    (2-1)将所述内核与纳米二氧化钛、纳米氧化铝混合，获得第二混合物；
    (2-2)对所述第二混合物进行第二煅烧处理，以获得所述正极材料。
  9. 根据权利要求8所述的方法，其特征在于，在所述第二混合物中，钛元素的含量为0.15～0.25wt％，铝元素的含量为0.05～0.15wt％。
  10. 根据权利要求8所述的方法，其特征在于，所述第一煅烧处理在720～870摄氏度下反应8～12小时，且所述第二煅烧处理在300～600摄氏度下反应4～8小时。
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