WO2017101660A1 - 正极活性材料包覆液及其制备方法以及正极活性材料的包覆方法 - Google Patents

正极活性材料包覆液及其制备方法以及正极活性材料的包覆方法 Download PDF

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WO2017101660A1
WO2017101660A1 PCT/CN2016/107275 CN2016107275W WO2017101660A1 WO 2017101660 A1 WO2017101660 A1 WO 2017101660A1 CN 2016107275 W CN2016107275 W CN 2016107275W WO 2017101660 A1 WO2017101660 A1 WO 2017101660A1
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positive electrode
active material
phosphate
electrode active
coating liquid
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PCT/CN2016/107275
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English (en)
French (fr)
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何向明
吴英强
王莉
李建军
尚玉明
倪欢
渠建春
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江苏华东锂电技术研究院有限公司
清华大学
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Publication of WO2017101660A1 publication Critical patent/WO2017101660A1/zh
Priority to US16/010,409 priority Critical patent/US10714755B2/en

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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
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/628—Inhibitors, e.g. gassing inhibitors, corrosion inhibitors
    • 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
    • C01B25/36—Aluminium phosphates
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
    • C01G53/00—Compounds of nickel
    • C01G53/40—Nickelates
    • C01G53/42—Nickelates containing alkali metals, e.g. LiNiO2
    • C01G53/44—Nickelates containing alkali metals, e.g. LiNiO2 containing manganese
    • C01G53/50—Nickelates containing alkali metals, e.g. LiNiO2 containing manganese of the type [MnO2]n-, e.g. Li(NixMn1-x)O2, Li(MyNixMn1-x-y)O2
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
    • C09D1/00—Coating compositions, e.g. paints, varnishes or lacquers, based on inorganic substances
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
    • H01B1/00—Conductors or conductive bodies characterised by the conductive materials; Selection of materials as conductors
    • 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
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/131—Electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
    • 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
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/80—Particles consisting of a mixture of two or more inorganic phases
    • 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
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/028—Positive electrodes
    • 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
    • H01M4/48—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
    • 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 invention relates to a positive electrode active material coating liquid, a preparation method thereof, and a coating method of a positive electrode active material.
  • the surface of the particle of the positive electrode active material of the lithium ion battery is coated with other materials, which is a common method for modifying the positive electrode active material in the prior art.
  • coating a layer of carbon on the surface of the lithium iron phosphate particles can effectively solve the problem of low conductivity of lithium iron phosphate, and the lithium iron phosphate coated with the carbon layer has good conductivity.
  • the prior art has shown that coating aluminum phosphate on the surface of lithium cobaltate or other positive active material particles can improve the thermal stability of the positive electrode of a lithium ion battery (refer to the literature "Correlation between AlPO 4 nanoparticle coating thickness on LiCoO 2 cathode and Thermal stablility" J. Cho, Electrochimica Acta 48 (2003) 2807-2811 and U.S. Patent No. 7,326,498.
  • the method of coating the positive electrode active material with aluminum phosphate is to first prepare a dispersion formed by dispersing aluminum phosphate particles in water, and adding the positive electrode active material particles to the dispersion of the prepared aluminum phosphate particles, and adsorbing
  • the aluminum phosphate particles are adsorbed on the surface of the large particles of the positive electrode active material, and the water in the dispersion is evaporated to dryness and heat-treated at 700 ° C to form a positive electrode active material having aluminum phosphate particles on the surface.
  • the aluminum phosphate coating layer formed on the surface of the positive electrode active material by the above method is not uniform enough, so that the lithium ion battery to which the positive electrode active material is applied has poor cycle performance.
  • a coating material for a positive electrode active material comprising a solvent and a coating precursor soluble in the solvent, wherein the solvent comprises at least an alcohol solvent, and the coating precursor contains at least formula (1-1) and At least one complex in 1-2),
  • the -OX 1 and -OX 2 are -OH groups or carbonoxy groups.
  • a preparation method of a positive electrode active material coating liquid comprising the following steps:
  • an aluminum salt is added to the phosphate solution, and the aluminum salt is dissolved in the alcohol solvent and reacted with the phosphate compound to obtain a homogeneous clear solution.
  • a method for coating a positive active material comprising the steps of:
  • the solid-liquid mixture is dried and sintered to obtain a positive electrode composite material
  • the positive electrode composite material includes a positive electrode active material and a coating layer coated on the surface of the positive electrode active material.
  • the positive electrode active material coating liquid in the embodiment of the present invention is a homogeneous phase clear solution
  • a coating layer can be formed on the surface of the positive electrode active material particles, so that each positive electrode active material is formed.
  • the surface of the particle is completely covered by the coating layer, and the thickness of the coating layer is thin and uniform.
  • the coating layer can avoid side reaction between the positive electrode active material and the electrolyte, and improve the thermal stability of the battery and the capacity retention performance of the battery.
  • the thickness of the coating layer is thin, the electrochemical performance of the lithium ion battery is not lowered.
  • FIG. 1 is a flow chart of a method for preparing a positive electrode active material coating liquid and a method for coating a positive electrode active material according to an embodiment of the present invention.
  • FIG. 2 is an XRD test diagram of a coating layer obtained by sintering at different temperatures according to an embodiment of the present invention.
  • FIG. 3 is a graph showing charge and discharge voltages of a coated lithium ion battery according to an embodiment of the present invention.
  • FIG. 4 is a graph showing charge and discharge voltages of a lithium ion battery before coating according to an embodiment of the present invention.
  • FIG. 5 is a comparison diagram of cycle performance of a lithium ion battery after coating and before coating according to an embodiment of the present invention.
  • FIG. 6 is a test diagram of safety performance of a lithium ion battery after coating and before coating according to an embodiment of the present invention.
  • the embodiment of the invention first provides a coating solution for a positive electrode active material, comprising a solvent and a coating precursor soluble in the solvent.
  • the positive active material coating liquid is a homogeneous clear solution, and the coated precursor is completely dissolved in the solvent.
  • the solvent includes at least an alcohol solvent, and may further include other solvents capable of being miscible with the alcohol solvent.
  • the solvent in the aluminum phosphate coating liquid may be only an organic solvent, and is preferably only an alcohol solvent.
  • the solvent in the aluminum phosphate coating liquid may also be a combination of an organic solvent and water, preferably a combination of an alcohol solvent and water, and more preferably, the water in the solvent is only introduced from the synthetic raw material of the coated precursor. Crystal water.
  • the coated precursor contains at least one of the complexes of the formulae (1-1) and (1-2).
  • R 1 OH and R 2 OH are alcohol solvent molecules, and may be independently selected from one or more of methanol, ethanol, propanol, n-butanol and isopropanol.
  • x may be 1 to 5
  • y may be 0 to 4
  • x + y 5
  • a may be 1 to 4
  • b may be 0 to 3
  • a + b 4, that is, each aluminum atom and at least An alcohol solvent molecule is complexed and can be coordinated with water molecules.
  • -OX 1 and -OX 2 may be an -OH group or a carbon group corresponding to the alcohol solvent molecule, for example, independently selected from -OH, methoxy, ethoxy, propoxy, butoxy And at least one of isopropoxy groups.
  • the mass fraction of the coated precursor in the positive electrode active material coating liquid is preferably from 1% to 15%.
  • an embodiment of the present invention further provides a method for preparing a positive electrode active material coating liquid, which comprises the following steps:
  • an aluminum salt is added to the phosphate solution, and the aluminum salt is dissolved in the alcohol solvent, and reacted with the phosphate compound to obtain a homogeneous clear solution, that is, the positive electrode active material coating liquid.
  • the alcohol solvent is preferably a composite solvent of one or more of methanol, ethanol, propanol, n-butanol, and isopropyl alcohol.
  • the mass ratio of the phosphate compound to the alcohol solvent is preferably 1:1 to 1:50.
  • the step S1 may further include adding at least one of phosphoric acid and phosphorus pentoxide to the alcohol solvent to react with the alcohol solvent at a temperature of 0 to 80 ° C to form the phosphate compound.
  • the alcohol solvent is capable of completely reacting the phosphoric acid and/or phosphorus pentoxide in excess, preferably in a mass ratio of phosphoric acid and/or phosphorus pentoxide to an alcohol solvent of from 1:1 to 1:50.
  • phosphorus pentoxide is reacted with ethanol, and the reaction occurs as shown in the formulas (2-1) and (2-2).
  • the aluminum salt is an alcohol-soluble aluminum salt, and can dissociate aluminum ions in an alcohol solvent, and is preferably one or more of aluminum chloride, aluminum nitrate, aluminum isopropoxide, and aluminum lactate.
  • the mass ratio of the total amount of the alcohol-soluble aluminum salt to the alcohol solvent is preferably 1:1 to 1:50.
  • the molar ratio of the phosphorus element contained in the phosphate compound to the aluminum element contained in the alcohol-soluble aluminum salt was 1:1.
  • the aluminum salt may or may not have crystal water.
  • the aluminum salt reacts with the phosphate compound in the alcohol solvent, so that the aluminum ion reacts with the hydroxide on the phosphate compound to form a PO-Al structure, and on the other hand, with the alcohol.
  • the solvent molecules are combined to form an ionic solvation to form a complex.
  • the reaction temperature in the step S2 is preferably from 20 ° C to 80 ° C, and the reaction time is preferably from 30 minutes to 10 hours.
  • This step S2 is preferably:
  • the phosphate solution obtained in the step S1 is further mixed with the aluminum salt solution obtained in the step S21, and the aluminum salt is reacted with the phosphate compound to obtain a homogeneous clear solution.
  • the phosphate solution is reacted with an aluminum salt solution, and the reaction occurs as shown in the formulas (2-3) and (2-4).
  • the positive electrode active material coating liquid preferably contains no water or only contains the reaction raw material, ie Crystal water introduced by aluminum salt.
  • the aluminum salt solution, the phosphate solution, and the finally obtained homogeneous clear solution have no water
  • the solvent is only an organic solvent, or only Crystal water introduced by aluminum salt.
  • the coating liquid of the non-aqueous system has a smaller viscosity and surface tension, and the surface coating of the positive electrode active material can be made more uniform.
  • the embodiment of the invention further provides a coating method of the positive electrode active material, and coating the positive electrode active material by using the above positive electrode active material coating liquid, comprising the following steps:
  • the solid-liquid mixture is dried and sintered to obtain a positive electrode composite material
  • the positive electrode composite material includes a positive electrode active material and a coating layer coated on the surface of the positive electrode active material.
  • the positive electrode active material coating liquid is evaporated to dryness, and the product obtained by sintering at different temperatures (400 ° C, 500 ° C, 700 ° C, 900 ° C) is subjected to XRD test to prove that the chemical composition of the coating layer is AlPO 4 .
  • the mass percentage of the coating layer in the positive electrode composite material is preferably from 0.3% to 5%, and the thickness is preferably from 5 nm to 100 nm.
  • the positive active material may be at least one of a lithium-transition metal oxide having a layered structure, a lithium-transition metal oxide having a spinel structure, and a lithium-transition metal oxide having an olivine structure, for example, an olive. Stone type lithium iron phosphate, layered structure lithium cobaltate, layered structure lithium manganate, spinel type lithium manganate, lithium nickel manganese oxide and lithium nickel cobalt manganese oxide.
  • a thin layer of a liquid phase formed by coating a positive electrode active material coating liquid is formed on the surface of the positive electrode active material.
  • the positive electrode active material and the positive electrode active material coating liquid are uniformly mixed and then filtered, so that the solid-liquid mixture is in a slurry state, and the positive electrode active material coating liquid is coated only on the surface of the positive electrode active material, which is favorable for obtaining A positive electrode composite having a thinner cladding layer.
  • the drying may be naturally dried or heated and dried at normal temperature, as long as the solvent in the mixture is removed, and the temperature of the heating and drying is preferably 60 to 100 °C.
  • the sintering is carried out in air to remove organic groups in the coated precursor to form the coating.
  • the sintering temperature is 300 ° C to 800 ° C, and is 400 ° C in this embodiment.
  • the sintering time is preferably from 3 hours to 8 hours.
  • the positive electrode active material coating liquid in the embodiment of the present invention is a homogeneous phase clear solution
  • a coating layer can be formed on the surface of the positive electrode active material particles, so that the surface of each positive electrode active material particle is completely coated. Coating, the coating layer is thin and uniform, and the coating layer can avoid side reaction between the positive electrode active material and the electrolyte, improve the thermal stability of the battery and maintain the capacity of the battery, and on the other hand, the package
  • the coating thickness is thin and does not degrade the electrochemical performance of the lithium ion battery.
  • Phosphorus pentoxide and ethanol are mixed at a molar ratio of 1:10, and stirred at room temperature to completely react phosphorus pentoxide to form a phosphate solution; aluminum nitrate and ethanol are mixed at a molar ratio of 1:10 to make aluminum nitrate Completely dissolved to form an aluminum nitrate solution, the molar ratio of P:Al in the phosphorus pentoxide to aluminum nitrate is 1:1; the phosphate solution is mixed with the aluminum nitrate solution, and the reaction is stirred at 50 ° C to obtain a homogeneously clarified positive electrode. Active material coating liquid.
  • the positive electrode active material coating liquid is mixed with the positive electrode active material LiNi 1/3 Co 1/3 Mn 1/3 O 2 at a mass ratio of 1:5 to 1:2, and the excess liquid phase is filtered and dried at 60 ° C. Sintering in air at 400 ° C to obtain a positive electrode composite material and assembling a lithium ion battery.
  • the uncoated positive electrode active material was assembled into a lithium ion battery, and the other components of the battery and the charge and discharge performance test conditions were the same as in Example 1 except that the positive electrode active material was not coated.
  • the lithium ion battery of Embodiment 1 is subjected to a constant current charge and discharge cycle at different current densities in a voltage range of 4.6 to 3.0 V, which are 0.1 C charge/0.1 C discharge, and 0.2 C charge/1.0 C discharge, respectively. It can be seen that the battery still has a high specific capacity when discharging at a large current, and the attenuation is small after 100 cycles, and has a good capacity retention rate.
  • the lithium ion battery of Comparative Example 1 was subjected to a constant current charge and discharge cycle under the same conditions, and it can be seen that the discharge specific capacity of the battery was significantly reduced at 50 cycles of large current discharge, and the capacity retention rate was poor. . From this, it is understood that the capacity retention of the positive electrode active material by the coating is improved, and the electrochemical performance of the lithium ion battery can be greatly improved.
  • the lithium ion battery of Example 1 and Comparative Example 1 was charged to 10.0 V at a current of 1.0 A to perform an overcharge test of the battery.
  • the battery temperature was measured, and the ratio of Example 1 was observed.
  • the battery temperature of Comparative Example 1 was significantly lowered, and the safety performance of the battery was significantly improved.

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Abstract

本发明涉及一种正极活性材料包覆液的制备方法，包括如下步骤：S1，在醇类溶剂中加入磷酸酯类化合物，得到磷酸酯溶液；以及S2，在该磷酸酯溶液中加入铝盐，该铝盐溶于该醇类溶剂，并与该磷酸酯类化合物反应得到均相的澄清溶液。本发明还涉及一种正极活性材料包覆液及一种正极活性材料的包覆方法。

Description

正极活性材料包覆液及其制备方法以及正极活性材料的包覆方法
相关申请
本发明申请要求2015年12月17日申请的，申请号为201510952129.7，名称为“正极活性材料包覆液及其制备方法以及正极活性材料的包覆方法”的中国专利申请的优先权，在此将其全文引入作为参考。
技术领域
本发明涉及一种正极活性材料包覆液及其制备方法以及正极活性材料的包覆方法。
背景技术
对锂离子电池正极活性材料的颗粒表面采用其它材料形成包覆，是现有技术中对正极活性材料进行改性的常用方法。例如，在磷酸铁锂的颗粒表面包覆一层碳可以有效解决磷酸铁锂导电性较低的问题，使包覆有碳层的磷酸铁锂具有较好的导电性。另外，现有技术已表明，在钴酸锂或其它正极活性材料颗粒表面包覆磷酸铝可以提高锂离子电池正极的热稳定性(请参阅文献“Correlation between AlPO4nanoparticle coating thickness on LiCoO2cathode and thermal stablility”J.Cho,Electrochimica Acta 48(2003)2807-2811及专利号为7,326,498的美国专利)。
现有技术中用磷酸铝包覆正极活性材料的方法是先制备磷酸铝颗粒分散于水中形成的分散液，并将正极活性材料颗粒加入这种制备好的磷酸铝颗粒的分散液中，通过吸附的作用使磷酸铝颗粒吸附在正极活性材料大颗粒表面，再将分散液中的水蒸干，并在700℃下热处理，形成表面具有磷酸铝颗粒的正极活性材料。然而，由于磷酸铝不溶于水，通过上述方法在正极活性材料表面形成的磷酸铝包覆层不够均匀，从而使应用该正极活性材料的锂离子电池循环性能不好。
发明内容
有鉴于此，确有必要提供一种正极活性材料包覆液及其制备方法以及正极活性材料的包覆方法。
一种正极活性材料包覆液，包括溶剂及能够溶于该溶剂的包覆前驱物，其特征在于，该溶剂至少包括醇类溶剂，该包覆前驱物至少含有式(1-1)及(1-2)中的至少一种配合物，
Figure PCTCN2016107275-appb-000001
该R1OH和R2OH为醇类溶剂分子，x为1～5，y为0～4，且x+y＝5，a为1～4，b为0～3，且a+b＝4，该-OX1及-OX2为-OH基或碳氧基团。
一种正极活性材料包覆液的制备方法，包括如下步骤：
S1，在醇类溶剂中加入磷酸酯类化合物，得到磷酸酯溶液；以及
S2，在该磷酸酯溶液中加入铝盐，该铝盐溶于该醇类溶剂，并与该磷酸酯类化合物反应得到均相的澄清溶液。
一种正极活性材料的包覆方法，包括以下步骤：
S1，在醇类溶剂中加入磷酸酯类化合物，得到磷酸酯溶液；
S2，在该磷酸酯溶液中加入铝盐，该铝盐溶于该醇类溶剂，并与该磷酸酯类化合物反应得到均相的澄清溶液；
S3，将正极活性材料与该正极活性材料包覆液混合均匀，得到一固液混合物；以及
S4，将该固液混合物干燥并烧结，得到正极复合材料，该正极复合材料包括正极活性材料及包覆在该正极活性材料表面的包覆层。
相较于现有技术，由于本发明实施例中所述正极活性材料包覆液为一均相澄清溶液，可以较容易地在正极活性材料颗粒表面均形成包覆层，使每个正极活性材料颗粒表面完全被包覆层包覆，包覆层厚度较薄且均匀连续，该包覆层可以避免正极活性材料与电解液之间的副反应，提高了电池的热稳定性以及电池容量保持性能，另一方面由于该包覆层厚度较薄，不会降低锂离子电池的电化学性能。
附图说明
图1是本发明实施例提供的正极活性材料包覆液的制备方法及正极活性材料的包覆方法的流程图。
图2是本发明实施例提供不同温度烧结得到的包覆层的XRD测试图。
图3是本发明实施例提供的包覆后的锂离子电池的充放电电压曲线图。
图4是本发明实施例提供的包覆前的锂离子电池的充放电电压曲线图。
图5是本发明实施例提供的包覆后与包覆前的锂离子电池的循环性能比较图。
图6是本发明实施例提供的包覆后与包覆前的锂离子电池的安全性能测试图。
具体实施方式
以下将结合附图详细说明本发明一种正极活性材料包覆液及其制备方法以及正极活性材料的包覆方法。
本发明实施例首先提供一种正极活性材料包覆液，包括溶剂及能够溶于该溶剂的包覆前驱物。该正极活性材料包覆液为一种均相的澄清溶液，该包覆前驱物完全溶解于该溶剂中。该溶剂至少包括醇类溶剂，并可以进一步包括能够与该醇类溶剂互溶的其他溶剂。
该磷酸铝包覆液中的溶剂可以仅为有机溶剂，优选仅为醇类溶剂。该磷酸铝包覆液中的溶剂也可以为有机溶剂与水的组合，优选为醇类溶剂与水的组合，更优选地，该溶剂中的水仅为从该包覆前驱物的合成原料引入的结晶水。
该包覆前驱物至少含有式(1-1)及(1-2)中的至少一种配合物。
Figure PCTCN2016107275-appb-000002
其中，该R1OH和R2OH为醇类溶剂分子，可独立的选自甲醇、乙醇、丙醇、正丁醇及异丙醇中的一种或多种。x可以为1～5，y可以为0～4，且x+y＝5；a可以为1～4，b可以为0～3，且a+b＝4，即每个铝原子分别与至少一个醇类溶剂分子配合，并可以与水分子配合。-OX1及-OX2可以为-OH基或与该醇类溶剂分子对应的碳氧基团，例如可独立的选自-OH、甲氧基、乙氧基、丙氧基、丁氧基及异丙氧基中的至少一种。
该包覆前驱物在该正极活性材料包覆液中的质量分数优选为1％～15％。
请参阅图1，本发明实施例进一步提供一种上述正极活性材料包覆液的制备方法，该方法包括如下步骤：
S1，在醇类溶剂中加入磷酸酯类化合物，得到磷酸酯溶液；以及
S2，在该磷酸酯溶液中加入铝盐，该铝盐溶于该醇类溶剂，并与该磷酸酯类化合物反应得到均相的澄清溶液，即该正极活性材料包覆液。
该醇类溶剂优选为甲醇、乙醇、丙醇、正丁醇及异丙醇中的一种或一种以上的复合溶剂。
该磷酸酯类化合物通式可以为AnP(O)(OH)m，其中A为与该醇类溶剂分子对应的碳氧基团，如甲氧基、乙氧基、丙氧基、丁氧基及异丙氧基中的至少一种，n＝1～3，m＝0～2，m+n＝3。该磷酸酯类化合物具体可举例为磷酸一甲酯、磷酸二甲酯、磷酸三甲酯、磷酸一乙酯、磷酸二乙酯、磷酸三乙酯、磷酸一丁酯、磷酸一丁酯、磷酸三丁酯、磷酸一异丙酯、磷酸二异丙酯及磷酸三异丙酯中的至少一种。
该磷酸酯类化合物与醇类溶剂的质量比优选为1:1～1:50。
该步骤S1可进一步包括将磷酸和五氧化二磷中至少一种加入该醇类溶剂中在0～80℃温度下与该醇类溶剂发生反应生成该磷酸酯类化合物。该醇类溶剂能够使该磷酸和/或五氧化二磷完全反应并过量，优选为磷酸和/或五氧化二磷与醇类溶剂的质量比为1:1～1:50。
本实施例中采用五氧化二磷与乙醇反应，发生的反应如式(2-1)及(2-2)所示。
Figure PCTCN2016107275-appb-000003
该铝盐为醇溶性铝盐，能够在醇类溶剂中解离出铝离子，优选为氯化铝、硝酸铝、异丙醇铝及乳酸铝中的一种或一种以上。该醇溶性铝盐总的加入量与醇类溶剂质量比优选为1:1～1:50。该磷酸酯类化合物所含的磷元素与醇溶性铝盐所含的铝元素的摩尔比为1:1。该铝盐可以带有或不带有结晶水。
该步骤S2中该铝盐在该醇类溶剂中与该磷酸酯类化合物发生反应，使铝离子一方面与磷酸酯类化合物上的氢氧根反应生成P-O-Al结构，另一方面与醇类溶剂分子配合，发生离子溶剂化(ionic solvation)，形成配合物。该步骤S2的反应温度优选为20℃～80℃，反应时间优选为30分钟～10小时。当该磷酸酯类化合物通式中m＝0，即含有3个酯基取代时，该铝盐引入的结晶水也可以使该磷酸酯类化合物发生水解，得到一个氢氧根，从而可以使上述反应进行。
该步骤S2优选为：
S21,将该铝盐加入到另一醇类溶剂中搅拌至溶解，得到铝盐溶液；以及
S22，将步骤S1得到的所述磷酸酯溶液与步骤S21得到的所述铝盐溶液进一步混合，使该铝盐与该磷酸酯类化合物反应，得到均相的澄清溶液。
本实施例中磷酸酯溶液与铝盐溶液反应，发生的反应如式(2-3)及(2-4)所示。
Figure PCTCN2016107275-appb-000004
由于水对于某些正极活性材料，如高镍含量的三元正极材料及钴酸锂的性能会产生不利影响，该正极活性材料包覆液中优选为不含水，或仅含有由反应原料，即铝盐引入的结晶水。在该正极活性材料包覆液的制备方法中，无论是该铝盐溶液，还是该磷酸酯溶液，以及最后得到的均相澄清溶液中优选为不含水，溶剂仅为有机溶剂，或者仅含有由铝盐引入的结晶水。并且，非水体系的包覆液具有更小的粘度和表面张力，可以使正极活性材料表面包覆更加均匀。
本发明实施例进一步提供一种正极活性材料的包覆方法，应用上述正极活性材料包覆液对正极活性材料进行包覆，包括以下步骤：
S3，将正极活性材料与该正极活性材料包覆液混合均匀，得到一固液混合物；以及
S4，将该固液混合物干燥并烧结，得到正极复合材料，该正极复合材料包括正极活性材料及包覆在该正极活性材料表面的包覆层。
请参阅图2，将该正极活性材料包覆液蒸干后在不同温度(400℃、500℃、700℃、900℃)下烧结得到的产物进行XRD测试可以证明该包覆层的化学成分为AlPO4。
该包覆层在该正极复合材料中的质量百分比优选为0.3％至5％，厚度优选为5nm～100nm。
该正极活性材料可以为层状结构的锂-过渡金属氧化物，尖晶石型结构的锂-过渡金属氧化物以及橄榄石型结构的锂-过渡金属氧化物中的至少一种，例如，橄榄石型磷酸铁锂、层状结构钴酸锂、层状结构锰酸锂、尖晶石型锰酸锂、锂镍锰氧化物及锂镍钴锰氧化物。
在该步骤S3中，该正极活性材料表面形成一层正极活性材料包覆液形成的液相薄层。优选可以将该正极活性材料与该正极活性材料包覆液混合均匀后过滤，使该固液混合物呈浆料态，该正极活性材料包覆液仅包覆在该正极活性材料表面，有利于获得具有较薄包覆层的正极复合材料。
在该步骤S4中，该干燥可为常温自然晾干或加热烘干，只要去除该混合物中的溶剂即可，所述加热烘干的温度优选为60℃～100℃。所述烧结在空气中进行，使该包覆前驱物中的有机基团去除，生成该包覆层。该烧结温度为300℃～800℃，本实施例中为400℃。该烧结时间优选为3小时～8小时。
由于本发明实施例中所述正极活性材料包覆液为一均相澄清溶液，可以较容易地在正极活性材料颗粒表面均形成包覆层，使每个正极活性材料颗粒表面完全被包覆层包覆，包覆层厚度较薄且均匀连续，该包覆层可以避免正极活性材料与电解液之间的副反应，提高了电池的热稳定性以及电池容量保持性能，另一方面由于该包覆层厚度较薄，不会降低锂离子电池的电化学性能。
实施例1
将五氧化二磷与乙醇按照摩尔比1:10的比例混合，在室温搅拌使五氧化二磷完全反应生成磷酸酯溶液；将硝酸铝与乙醇按照摩尔比1:10的比例混合，使硝酸铝完全溶解，生成硝酸铝溶液，该五氧化二磷与硝酸铝中P:Al的摩尔比为1:1；将磷酸酯溶液与该硝酸铝溶液混合，在50℃搅拌反应得到均相澄清的正极活性材料包覆液。
将该正极活性材料包覆液与正极活性材料LiNi1/3Co1/3Mn1/3O2按照质量比1:5～1:2混合，过滤多余液相，在60℃烘干之后在400℃空气中烧结，得到正极复合材料并组装锂离子电池。该锂离子电池中电解液为1.0mol L-1LiPF6(EC/EMC＝3:7，质量比)，负极为金属锂片，进行充放电性能测试。
对比例1
将未包覆的正极活性材料组装锂离子电池，除正极活性材料未进行包覆外，电池的其它组分与充放电性能测试条件与实施例1相同。
请参阅图3，将实施例1的锂离子电池在4.6～3.0V电压范围采用不同电流密度进行恒流充放电循环，分别为0.1C充电/0.1C放电，以及0.2C充电/1.0C放电，可以看到电池在大电流放电时仍然具有较高的比容量，且100次循环后衰减较小，具有较好的容量保持率。
请参阅图4及图5，以相同条件对对比例1的锂离子电池进行恒流充放电循环，可以看到电池在大电流放电50次循环时放电比容量即明显降低，容量保持率较差。由此可知，包覆对正极活性材料的容量保持率改善明显，能够极大的提高锂离子电池的电化学性能。
请参阅图6，将实施例1与对比例1的锂离子电池以1.0A电流充电至10.0V，进行电池的过充电测试，在这一过程对电池温度进行测量，可以看到实施例1比对比例1的电池温度明显降低，对电池的安全性能有明显提升。
另外，本领域技术人员还可在本发明精神内作其它变化，当然这些依据本发明精神所作的变化，都应包含在本发明所要求保护的范围内。

Claims (11)

  1. 一种正极活性材料包覆液，包括溶剂及能够溶于该溶剂的包覆前驱物，其特征在于，该溶剂至少包括醇类溶剂，该包覆前驱物至少含有式(1-1)及(1-2)中的至少一种配合物，
    Figure PCTCN2016107275-appb-100001
    该R1OH和R2OH为醇类溶剂分子，x为1～5，y为0～4，且x+y＝5，a为1～4，b为0～3，且a+b＝4，该-OX1及-OX2为-OH基或碳氧基团。
  2. 如权利要求1所述的正极活性材料包覆液，其特征在于，该R1OH和R2OH独立的选自甲醇、乙醇、丙醇、正丁醇及异丙醇中的至少一种，该-OX1及-OX2独立的选自-OH、甲氧基、乙氧基、丙氧基、丁氧基及异丙氧基中的至少一种。
  3. 如权利要求1所述的正极活性材料包覆液，其特征在于，该磷酸铝包覆液中的溶剂仅为有机溶剂，或者该溶剂中的水仅为从该包覆前驱物的合成原料引入的结晶水。
  4. 如权利要求1所述的正极活性材料包覆液，其特征在于，该包覆前驱物在该正极活性材料包覆液中的质量分数为1％～15％。
  5. 一种正极活性材料包覆液的制备方法，包括如下步骤：
    S1，在醇类溶剂中加入磷酸酯类化合物，得到磷酸酯溶液；以及
    S2，在该磷酸酯溶液中加入铝盐，该铝盐溶于该醇类溶剂，并与该磷酸酯类化合物反应得到均相的澄清溶液。
  6. 如权利要求5所述的正极活性材料包覆液的制备方法，其特征在于，该醇类溶剂为甲醇、乙醇、丙醇、正丁醇及异丙醇中的一种或一种以上的复合溶剂。
  7. 如权利要求5所述的正极活性材料包覆液的制备方法，其特征在于，该磷酸酯类化合物为磷酸一甲酯、磷酸二甲酯、磷酸三甲酯、磷酸一乙酯、磷酸二乙酯、磷酸三乙酯、磷酸一丁酯、磷酸一丁酯、磷酸三丁酯、磷酸一异丙酯、磷酸二异丙酯、磷酸三异丙酯中的至少一种。
  8. 如权利要求5所述的正极活性材料包覆液的制备方法，其特征在于，该铝盐为氯化铝、硝酸铝、异丙醇铝及乳酸铝中的一种或一种以上。
  9. 如权利要求5所述的正极活性材料包覆液的制备方法，其特征在于，该磷酸酯类化合物所含的磷元素与醇溶性铝盐所含的铝元素的摩尔比为1:1。
  10. 如权利要求5所述的正极活性材料包覆液的制备方法，其特征在于，该步骤S2为：
    S21,将该铝盐加入到另一醇类溶剂中搅拌至溶解，得到铝盐溶液；以及
    S22，将步骤S1得到的所述磷酸酯溶液与步骤S21得到的所述铝盐溶液进一步混合，使该铝盐与该磷酸酯类化合物反应，得到均相的澄清溶液。
  11. 一种正极活性材料的包覆方法，包括以下步骤：
    S1，在醇类溶剂中加入磷酸酯类化合物，得到磷酸酯溶液；
    S2，在该磷酸酯溶液中加入铝盐，该铝盐溶于该醇类溶剂，并与该磷酸酯类化合物反应得到均相的澄清溶液；
    S3，将正极活性材料与该正极活性材料包覆液混合均匀，得到一固液混合物；以及
    S4，将该固液混合物干燥并烧结，得到正极复合材料，该正极复合材料包括正极活性材料及包覆在该正极活性材料表面的包覆层。
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