WO2020258996A1 - 一种低产气高容量的三元正极材料 - Google Patents

一种低产气高容量的三元正极材料 Download PDF

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WO2020258996A1
WO2020258996A1 PCT/CN2020/084336 CN2020084336W WO2020258996A1 WO 2020258996 A1 WO2020258996 A1 WO 2020258996A1 CN 2020084336 W CN2020084336 W CN 2020084336W WO 2020258996 A1 WO2020258996 A1 WO 2020258996A1
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coating layer
positive electrode
cathode material
electrode material
substrate
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PCT/CN2020/084336
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English (en)
French (fr)
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杜锐
王嗣慧
刘勇超
罗炽
赵德宇
柳娜
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宁德时代新能源科技股份有限公司
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Priority to EP20833684.2A priority Critical patent/EP3930052A4/en
Publication of WO2020258996A1 publication Critical patent/WO2020258996A1/zh
Priority to US17/518,744 priority patent/US11569510B2/en
Priority to US18/087,064 priority patent/US20230126587A1/en

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    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/628—Inhibitors, e.g. gassing inhibitors, corrosion inhibitors
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    • 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
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    • 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
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    • 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
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    • 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
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    • C01P2004/50—Agglomerated particles
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    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
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    • C01P2004/61—Micrometer sized, i.e. from 1-100 micrometer
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    • C01P2004/60—Particles characterised by their size
    • C01P2004/62—Submicrometer sized, i.e. from 0.1-1 micrometer
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    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
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    • C01P2006/80—Compositional purity
    • H—ELECTRICITY
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    • 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 disclosure relates to the field of electrochemistry, in particular to a ternary cathode material with low gas production and high capacity and an electrochemical energy storage device.
  • Lithium-ion batteries have the advantages of high specific energy, wide application temperature range, low self-discharge rate, long cycle life, good safety performance, and no pollution, and have now been used in various fields. Lithium-ion batteries have been gradually tried all over the world as the energy system of automobiles to replace traditional diesel locomotives. However, currently commonly used lithium iron phosphate (LiFePO 4 ), low nickel ternary (LiNi 1/3 Co 1/3 Mn 1/3 O 2 ), etc., due to the nature of the material itself, cannot fully meet the requirements of lithium ion batteries. The energy density requirements of battery cathode materials.
  • high-nickel ternary cathode materials can increase the energy density of batteries. Therefore, high-nickel ternary cathode materials are currently one of the main research objects of power batteries.
  • the direct side reaction between the positive electrode active material and the electrolyte is also significantly intensified, and the high-temperature gas production performance is significantly deteriorated, which is one of the bottlenecks in the commercialization of mass production of batteries.
  • the main means to solve the high temperature gas production performance will lead to different degrees of damage to the cell performance: for example, the reversible gram capacity of the active material decreases, and the cycle performance deteriorates.
  • the purpose of the present disclosure is to provide a ternary cathode material with low gas production and high capacity to solve the problems in the prior art.
  • the present disclosure provides a positive electrode material, including a substrate, the molecular formula of the substrate is Li x Ni y Co z M k Me p O r A m , where 0.95 ⁇ x ⁇ 1.05 , 0.50 ⁇ y ⁇ 0.95, 0 ⁇ z ⁇ 0.2, 0 ⁇ k ⁇ 0.4, 0 ⁇ p ⁇ 0.05, 1 ⁇ r ⁇ 2, 0 ⁇ m ⁇ 2, m+r ⁇ 2, M is selected from Mn and/or Al, Me are selected from one or more combinations of Zr, Zn, Cu, Cr, Mg, Fe, V, Ti, Sr, Sb, Y, W, Nb, and A is selected from N, F, S, Cl One or a combination of one or more of the above; the surface of the substrate is provided with a coating layer, the coating layer includes a coating element selected from Al, Zr, Ba, Zn, Ti, Co, A combination of one or more of W, Y, Si, Sn, B, and P; the nickel el
  • the present disclosure provides an electrochemical energy storage device, including the cathode material described in the present disclosure.
  • the positive electrode material of the present disclosure has good crystal structure stability and surface inertness, and the nickel elution absorbance of the positive electrode material is low, which can effectively inhibit the side reaction between the positive electrode material and the electrolyte, thereby optimizing cycle performance, improving thermal stability and Gas production phenomenon.
  • the lithium ion battery of the present disclosure and its preparation method will be described in detail below.
  • the first aspect of the present disclosure provides a cathode material, including a substrate, the molecular formula of the substrate is Li x Ni y Co z M k Me p O r A m , wherein 0.95 ⁇ x ⁇ 1.05, 0.50 ⁇ y ⁇ 0.95 , 0 ⁇ z ⁇ 0.2, 0 ⁇ k ⁇ 0.4, 0 ⁇ p ⁇ 0.05, 1 ⁇ r ⁇ 2, 0 ⁇ m ⁇ 2, m+r ⁇ 2, M is selected from Mn and/or Al, Me is selected from Zr A combination of one or more of Zn, Cu, Cr, Mg, Fe, V, Ti, Sr, Sb, Y, W, Nb, A is selected from one or more of N, F, S, and Cl A combination of species; the substrate is provided with a coating layer, the coating layer includes a coating element selected from Al, Zr, Ba, Zn, Ti, Co, W, Y, Si, One or a combination of Sn, B, and P; the nickel elution absorbance per unit mass of the positive electrode
  • the method for determining the nickel dissolution absorbance w per unit mass of the positive electrode material may generally include: placing the unit mass of the positive electrode material in an appropriate solution, and measuring the resulting dissolution under a certain wavelength range. The absorbance of the liquid.
  • the method for determining the nickel elution absorbance w per unit mass of the positive electrode material may specifically include the following steps: 1g of the positive electrode material at a pH of 8-11 and a diacetyl oxime concentration of 10 g/ Stored in 10mL ethanol solution of L for 24h, take 5mL supernatant and add deionized water, dilute to 10mL dissolving liquid, and use UV-Vis spectrophotometer to detect the absorbance of the dissolving liquid in the range of 430nm-570nm.
  • the higher the relative content of nickel the larger the gram capacity of the ternary material is, which is more conducive to increasing the energy density of the electrochemical energy storage device.
  • the relative content of nickel increases, it will also It has many negative effects on the overall performance of the electrochemical energy storage device. For example, when the relative content of Ni in the ternary material is high, the layered structure of the ternary material will collapse due to the mixing of Ni 2+ and Li + , making the deintercalation of Li + in the ternary material more and more The more difficult it is, the worse the cycle performance of the electrochemical energy storage device will eventually be.
  • the increase in the relative content of Ni in the ternary material will also reduce the thermal decomposition temperature of the ternary material, resulting in an increase in the amount of heat release and the deterioration of the thermal stability of the ternary material.
  • the relative content of Ni in the ternary material increases, the content of Ni 4+ with strong oxidizing properties will also increase.
  • the electrolyte contacts the ternary material, the electrolyte will interact with the ternary material. More side reactions, and in order to maintain charge balance, the ternary material will release oxygen, which will not only destroy the crystal structure of the ternary material, but also aggravate the flatulence of the electrochemical energy storage device and deteriorate the storage performance of the electrochemical energy storage device.
  • the positive electrode material is doped and surface coated in a high nickel substrate to control the nickel dissolution and absorbance of the positive electrode material in an appropriate range, so that the contact between the electrolyte and the material can be isolated to a certain extent , Thereby optimizing cycle performance, improving thermal stability, reducing the degree of side reactions, and improving gas production.
  • the absorbance of nickel element per unit mass of the cathode material may be w ⁇ 0.7, w ⁇ 0.6, w ⁇ 0.5, w ⁇ 0.4, w ⁇ 0.3, or w ⁇ 0.2.
  • the nickel dissolution absorbance w per unit mass of the positive electrode material exceeds 0.7, it means that the nickel element in the positive electrode material particles is relatively easy to dissolve.
  • the surface of the positive electrode material is prone to side reactions with the electrolyte, which leads to the use of the The gas production of the lithium-ion battery of the cathode material is too high.
  • the lower the nickel elution absorbance per unit mass of the positive electrode material the stronger the stability of the crystal structure, especially the surface crystal structure of the positive electrode material.
  • the theoretical specific surface area BET 1 of the positive electrode material and the real specific surface area BET 2 of the positive electrode material generally satisfy:
  • BET 1 6/( ⁇ D v 50); ⁇ is the true density of the positive electrode material, and the unit of measurement is g/cm 3 ; D v 50 is when the cumulative volume distribution percentage of the positive electrode material reaches 50% The corresponding particle size, the unit of measurement is ⁇ m.
  • the true specific surface area BET 2 of the positive electrode material can be determined by the N 2 adsorption method, and the specific method can be referred to GB/T19587-2004. (BET 2 -BET 1 )/BET 1 represents the degree of deviation between the theoretical specific surface area of the positive electrode material and the actual specific surface area, which can measure the degree of unevenness on the surface of the positive electrode material.
  • the coated cathode material has a flat surface, less concave and convex structure, and a smaller contact area with the electrolyte, which is beneficial to inhibit the dissolution of Ni in the cathode material and ensure good lithium ion transport performance between secondary particles , Taking into account the high temperature gas production and dynamic performance.
  • the substrate may include secondary particles composed of primary particles, the D v 50 of the secondary particles may be 5 ⁇ m to 18 ⁇ m, and the particle size of the primary particles The range can be 0.1 ⁇ m to 1.0 ⁇ m.
  • the D v 50 usually refers to the particle size corresponding to the volume cumulative distribution percentage of the sample reaching 50%.
  • the D v 50 of the secondary particles may be 5 ⁇ m to 18 ⁇ m, 5 ⁇ m to 6 ⁇ m, 6 ⁇ m to 7 ⁇ m, 7 ⁇ m to 8 ⁇ m, 8 ⁇ m to 9 ⁇ m, 9 ⁇ m to 10 ⁇ m, 10 ⁇ m to 11 ⁇ m, 11 ⁇ m to 12 ⁇ m, 12 ⁇ m to 13 ⁇ m, 13 ⁇ m ⁇ 14 ⁇ m, 14 ⁇ m ⁇ 15 ⁇ m, 15 ⁇ m ⁇ 16 ⁇ m, 16 ⁇ m ⁇ 17 ⁇ m, or 17 ⁇ m ⁇ 18 ⁇ m, preferably 8 ⁇ 15 ⁇ m;
  • the particle size range of the primary particles can be 0.1 ⁇ m ⁇ 1 ⁇ m, 0.1 ⁇ m ⁇ 0.9 ⁇ m, 0.2 ⁇ m ⁇ 0.8 ⁇ m, or 0.2 ⁇ m ⁇ 0.5 ⁇ m.
  • the relative amount of fine particles with small particle size has a more significant impact on the residual lithium content and gas production of the positive electrode active material.
  • control of the secondary particle morphology of high-nickel ternary material Li x Ni y Co z M k Me p O r A m or a surface provided with a coating layer Li x Ni y Co z M k Me p O r A m of The D v 50 of primary particles and secondary particles within a certain range can be an effective means to solve the problem of gas production.
  • the BET specific surface area of true positive electrode material 2 may be 0.1m 2 /g ⁇ 1.0m 2 / g, 0.1m 2 /g ⁇ 0.2m 2 / g, 0.2m 2 /g ⁇ 0.3m 2/ g, 0.3m 2 /g ⁇ 0.4m 2/ g, 0.4m 2 /g ⁇ 0.5m 2/ g, 0.5m 2 /g ⁇ 0.6m 2/ g, 0.6m 2 / g to 0.7m 2/ g, 0.7m 2 / g to 0.8m 2 / g, 0.8m 2 / g to 0.9m 2 / g, or 0.9m 2 / g to 1.0m 2/ g.
  • the specific surface area of a suitable positive electrode material can make the contact area between the electrolyte and the positive electrode active material smaller, which is beneficial to inhibit side reactions, avoid corrosion of the electrolyte and damage the crystal structure of the positive electrode active material, which will increase the flatulence of the electrochemical energy storage device.
  • it can be beneficial to use less auxiliary materials to meet the relatively strong adsorption performance of the positive electrode active material, the binder, and the conductive agent when mixing to form the positive electrode slurry, thereby helping to improve the electrochemical storage.
  • the energy density of the energy device is beneficial to use less auxiliary materials to meet the relatively strong adsorption performance of the positive electrode active material, the binder, and the conductive agent when mixing to form the positive electrode slurry, thereby helping to improve the electrochemical storage.
  • the substrate may include single crystal or single crystal-like particles.
  • the particle size D v 50 of the substrate may be 1 ⁇ m to 6 ⁇ m, 1 ⁇ m to 2 ⁇ m, 2 ⁇ m to 3 ⁇ m, 3 ⁇ m to 4 ⁇ m, 4 ⁇ m to 5 ⁇ m, or 5 ⁇ m to 6 ⁇ m, preferably, the particle size D v 50 of the substrate is 2 ⁇ m to 5 ⁇ m.
  • the single crystal or quasi-single crystal particles generally refer to a positive electrode material composed of a complete single particle or agglomeration of less than ten particles.
  • the real specific surface area BET 2 of the positive electrode material may be 0.5m 2 /g ⁇ 1.5m 2/ g, 0.5m 2 /g ⁇ 0.6m 2/ g , 0.6m 2 /g ⁇ 0.7m 2/ g, 0.7m 2 /g ⁇ 0.8m 2/ g, 0.8m 2 /g ⁇ 0.9m 2/ g, 0.9m 2 /g ⁇ 1.0m 2/ g, 1.0 m 2 /g ⁇ 1.1m 2/ g, 1.1m 2 /g ⁇ 1.2m 2/ g, 1.2m 2 /g ⁇ 1.3m 2/ g, 1.3m 2 /g ⁇ 1.4m 2/ g, or 1.4m 2 /g ⁇ 1.5m 2/ g.
  • the positive electrode material when the positive electrode material includes particles with a single crystal or quasi-single crystal structure with the above-mentioned particle size and BET within the above-mentioned range, the surface and internal crystal structure of the positive electrode material are more complete, and the contact area with the electrolyte is more complete. Smaller, it helps to improve the elution of nickel on the particle surface.
  • the unit volume content Mv of the coating element in the positive electrode material may be 0.4 mg/cm 3 ⁇ 15 mg/cm 3 , 0.4 mg/cm 3 ⁇ 0.6 mg/cm 3 , 0.6mg/cm 3 ⁇ 0.8mg/cm 3 , 0.8mg/cm 3 ⁇ 1mg/cm 3 , 1mg/cm 3 ⁇ 2mg/cm 3 , 2mg/cm 3 ⁇ 4mg/cm 3 , 4mg/cm 3 ⁇ 6mg /cm 3 , 6 mg/cm 3 to 8 mg/cm 3 , 8 mg/cm 3 to 10 mg/cm 3 , or 10 mg/cm 3 to 15 mg/cm 3 , preferably 0.8 mg/cm 3 to 10 mg/cm 3 .
  • the appropriate content of the coating element can usually ensure that the surface modification and polarization problems of the positive electrode material are compatible in systems with different volume particle size distributions, effectively improving the gas generation problems of high-capacity batteries, and optimizing cycle and rate performance.
  • the coating element usually exists in the form of an oxide.
  • the coating layer may include one or a combination of the oxides of the above-mentioned coating elements, or include the above-mentioned coating elements , Lithium-containing oxides of lithium elements, which specifically include but are not limited to aluminum oxide, zirconium oxide, zinc oxide, titanium oxide, silicon oxide, tin oxide, tungsten oxide, yttrium oxide, cobalt oxide, barium oxide, phosphorous oxide, Boron, and lithium aluminum oxide, lithium zirconium oxide, lithium zinc oxide, lithium magnesium oxide, lithium tungsten oxide, lithium yttrium oxide, lithium cobalt oxide, lithium barium oxide, lithium phosphorus oxide, or lithium boron One or more combinations of oxides.
  • Lithium-containing oxides of lithium elements which specifically include but are not limited to aluminum oxide, zirconium oxide, zinc oxide, titanium oxide, silicon oxide, tin oxide, tungsten oxide, yttrium oxide, cobalt oxide, barium oxide, phosphorous oxide, Boron, and lithium aluminum oxide, lithium zircon
  • the coating layer may include an inner coating layer, and the inner coating layer may be located inside the substrate, and may be located on at least part of the surface of the primary particles,
  • the inner coating layer includes a coating element, and the coating element of the inner coating layer may be selected from Al, Zr, Ba, Zn, Ti, Co, W, Y, Si, Sn, B, P, etc.
  • the substrate includes secondary particles composed of primary particles, so at least part of the coating layer may be located between the primary particles in the secondary particles, that is, at least part of the coating layer is located inside the secondary particles.
  • the surface of the primary particles, this part of the coating layer can be considered as the inner coating layer.
  • the inner coating layer may include oxides of coating elements, that is, at least part of the coating elements in the inner coating layer may be in the form of oxides or lithium-containing oxides, and specifically may be Including but not limited to aluminum oxide, zirconium oxide, zinc oxide, titanium oxide, silicon oxide, tin oxide, tungsten oxide, yttrium oxide, cobalt oxide, barium oxide, phosphorus oxide or boron oxide, and lithium aluminum oxide, lithium zirconium oxide , Lithium zinc oxide, lithium magnesium oxide, lithium tungsten oxide, lithium yttrium oxide, lithium cobalt oxide, lithium barium oxide, lithium phosphorus oxide or lithium boron oxide, etc. .
  • the secondary particles are formed by close packing of several primary particles, the volume of the secondary particles will expand and contract during the cycle, resulting in an increase in the spacing between the primary particles in the secondary particles, and a large number of unpackaged particles are exposed. Fresh surface covered, so there is a risk of side reactions with the electrolyte.
  • the coating layer is provided on the surface of the secondary particles, at least a part of the surface of the primary particles or the grain boundaries between adjacent primary particles are further coated, which can enhance the internal Density, increase the force between the internal primary particles, and further optimize the gas production problem in the circulation process.
  • the coating layer may include an outer coating layer, and the outer coating layer may generally be located on the surface of the secondary particle and/or the surface of the substrate.
  • the coating layer includes a coating element, and the coating element of the outer coating layer can be selected from one or more of Al, Zr, Ba, Zn, Ti, Co, W, Y, Si, Sn, B, P, etc. kind of combination.
  • the substrate includes secondary particles composed of primary particles, at least part of the coating layer may be located on the surface of the secondary particles, and the coating element in the oxide coating layer may be on the surface of the secondary particles. Surface distribution of secondary particles.
  • the outer coating layer may include oxides of coating elements, that is, at least part of the coating elements in the outer coating layer may exist in the form of oxides or lithium-containing oxides, and specifically may include but Not limited to aluminum oxide, zirconium oxide, zinc oxide, titanium oxide, silicon oxide, tin oxide, tungsten oxide, yttrium oxide, cobalt oxide, barium oxide, phosphorus oxide, boron oxide, and lithium aluminum oxide, lithium zirconium oxide, and lithium One or more combinations of zinc oxide, lithium magnesium oxide, lithium tungsten oxide, lithium yttrium oxide, lithium cobalt oxide, lithium barium oxide, lithium phosphorus oxide, or lithium boron oxide.
  • the outer coating layer is the part that mainly plays a role in reducing the contact area between the substrate and the electrolyte.
  • the presence of the outer coating layer can effectively modify the surface of the high nickel positive electrode material and reduce the positive electrode material and the electrolyte.
  • the side reaction of the battery can effectively suppress the gas generation phenomenon of the battery.
  • the coating layer may contain at least two or more of the above-mentioned coating elements, more specifically, it may contain at least two or more of the oxides formed by the above-mentioned coating elements, Therefore, the adhesion stability of the coating layer on the surface of the substrate can be improved, so that the coating layer has a certain ion conductivity and conductivity, and the influence of the coating layer on the polarization problem of the positive electrode material can be reduced.
  • the outer coating layer may include a continuous and/or discontinuous coating layer.
  • the continuous coating layer can form a relatively complete protection for the surface of the substrate, which is beneficial to stabilize the surface structure of the positive electrode material, inhibit the amount of nickel eluted from the positive electrode material, and inhibit the side reaction of the electrolyte; but the continuous coating layer needs to have a good Electronic conduction and ion conduction performance to avoid increasing the impedance of the pole piece and deteriorating the dynamic performance of the battery.
  • the advantage of the discontinuous coating layer is to reduce the proportion of the coating layer on the surface of the substrate and retain more ion transport channels, but the improvement effect of the structural stability of the substrate surface is slightly worse than that of the continuous coating layer.
  • the outer coating layer may include a continuous first coating layer and a discontinuous second coating layer, and may be a composite of two forms.
  • the second coating layer may be located on the surface of the first coating layer, or between the first coating layer and the substrate.
  • the area of the discontinuous second coating layer of a single unit is generally smaller than the area of the first coating layer of a single unit.
  • the second covering layer and the first covering layer may include different covering elements, so that the covering of the discontinuous covering layer The coating material and the coating material of the continuous coating layer are at least partially different.
  • the content of the coating element in the outer coating layer may account for more than 60 wt%, more than 70 wt%, and 80 wt% of the total mass of the coating element in the positive electrode material. Above, 90wt% or more, preferably 80wt% to 98wt%.
  • the coating elements are mainly distributed on the surface of the secondary particles, and the mass distributed on the surface of the secondary particles accounts for the positive electrode active material. When the total mass of the coating elements exceeds a certain proportion, the surface modification of the high nickel cathode material is relatively more significant, and the gas production suppression effect on the battery is also better.
  • the substrate is a lithium transition metal oxide with a relatively high nickel content.
  • y preferably satisfies 0.50 ⁇ y ⁇ 0.90, more preferably 0.70 ⁇ y ⁇ 0.90
  • z preferably satisfies 0 ⁇ z ⁇ 0.15, more preferably 0.05 ⁇ z ⁇ 0.15
  • k preferably satisfies 0 ⁇ k ⁇ 0.2, more preferably 0.05 ⁇ k ⁇ 0.2
  • p preferably satisfies 0 ⁇ p ⁇ 0.03 , More preferably 0 ⁇ p ⁇ 0.025.
  • the molecular formula of the substrate Li x Ni y Co z M k Me p O r A m may include, but is not limited to, LiNi 1/3 Co 1/3 Mn 1/3 O 2 , LiNi 0.5 Co 0.2 Mn 0.3 O 2 , LiNi 0.5 Co 0.25 Mn 0.25 O 2 , LiNi 0.55 Co 0.15 Mn 0.3 O 2 , LiNi 0.55 Co 0.1 Mn 0.35 O 2 , LiNi 0.55 Co 0.05 Mn 0.4 O 2 , LiNi 0.6 Co 0.2 Mn 0.2 O 2 , LiNi 0.65 Co 0.15 Mn 0.2 O 2 , LiNi 0.65 Co 0.12 Mn 0.23 O 2 , LiNi 0.65 Co 0.1 Mn 0.25 O 2 , LiNi 0.65 Co 0.05 Mn 0.3 O 2 , LiNi 0.75 Co 0.1 Mn 0.15 O 2 , LiNi 0.8 Co 0.1 Mn 0.1 O 2.
  • LiNi 0.85 Co 0.05 Mn 0.1 O 2 LiNi 0.88 Co 0.05 Mn 0.07 O 2 , LiNi 0.9 Co 0.05 Mn 0.05 O 2, etc.
  • the above substances can also be partially substituted by doping element Me and/or doping element A The modified substance.
  • the method for measuring the residual lithium on the surface of the positive electrode material can refer to the GBT 9725-2007 general rule of chemical reagent potentiometric titration.
  • the content of Li 2 CO 3 in the residual lithium on the surface of the positive electrode material is generally less than 3000 ppm.
  • the The content of Li 2 CO 3 in the residual lithium on the surface of the positive electrode material is less than 2000 ppm.
  • the content of LiOH in the residual lithium on the surface of the positive electrode material (that is, the content of LiOH in the residual lithium on the surface of the positive electrode material relative to the total mass of the positive electrode material) is less than 5000 ppm, preferably, the residual lithium on the surface of the positive electrode material
  • the content of LiOH is less than 4000 ppm.
  • the Li 2 CO 3 remaining on the surface of the ternary material will decompose to produce CO 2 , because the CO 2 gas will cause a pressure difference with the temperature difference (especially when the reaction is accompanied by a thermal reaction When it occurs), the flatulence of the electrochemical energy storage device is intensified, and the storage performance of the electrochemical energy storage device is deteriorated.
  • Providing a coating layer on the surface of the substrate can reduce the residual lithium content (such as LiOH, Li 2 CO 3, etc.) on the surface of the positive electrode active material to a certain extent, thereby achieving the purpose of improving the storage performance of the electrochemical energy storage device.
  • providing a coating layer on the surface of the substrate can also reduce the probability of side reactions between the substrate and the electrolyte due to direct contact, thereby reducing the amount of oxygen released by the positive electrode active material to balance the charge during the charge and discharge process. And this brings the risk of collapse of the crystal structure.
  • the content of Li 2 CO 3 is generally lower than LiOH
  • the residual lithium (LiOH, Li 2 O) on the surface easily reacts with moisture in the air, CO 2 and the like, and the reaction product is Li 2 CO 3 and the like. The higher the Li 2 CO 3 , the more violent the reaction, and the more serious the gas production problem of the battery produced accordingly.
  • the second aspect of the present disclosure provides a method for detecting the nickel elution absorbance per unit mass of the cathode material provided in the first aspect of the present disclosure, including:
  • UV-Vis ultraviolet-visible light
  • the result of the measurement can be used as the absorbance of nickel dissolution of the cathode material
  • the color developer is selected from diacetyl oxime.
  • the main solvent can be one or a combination of ethanol, water, and acetone, so that a reaction medium can be provided to react and complex the dissolved nickel with the color developer.
  • the color development enhancer may include but is not limited to one or a combination of ammonia, NaOH, KOH, etc., so as to provide a suitable pH for the reaction, enhance the sensitivity of color development and increase the speed of color development.
  • the pH of the solution A may be 8-11. After the positive electrode material is in full contact with the solution A, after soaking and standing still, the upper clear solution B is taken.
  • the solution B usually contains nickel diacetyl oxime.
  • the nickel element absorbance of the positive electrode material is obtained by detecting the solution B or the diluent of the solution B using a spectrophotometer.
  • the wavelength range of the absorbance test can be 430 nm to 500 nm.
  • the absorbance can be tested under the condition of a wavelength of 470 nm.
  • the method for detecting the nickel elution absorbance of the positive electrode material may specifically include the following steps:
  • the nickel dissolution absorbance of the positive electrode material is detected by an ultraviolet-visible spectrophotometer, which has high sensitivity and accuracy, and can intuitively reflect the structural stability of the positive electrode material crystal, especially the crystal surface; There is no need to perform a long-term cycle test of the battery, and the gas generation problem of the cathode material can be quickly reflected.
  • an ultraviolet-visible spectrophotometer which has high sensitivity and accuracy, and can intuitively reflect the structural stability of the positive electrode material crystal, especially the crystal surface; There is no need to perform a long-term cycle test of the battery, and the gas generation problem of the cathode material can be quickly reflected.
  • the outer electrons of the atom selectively absorb electromagnetic waves of certain wavelengths to form an atomic absorption spectrum.
  • the electron energy level in the molecule undergoes a transition to produce an electronic spectrum located in the ultraviolet and visible light parts. .
  • the degree of absorption is only related to the concentration of the solution.
  • the high nickel material contains a large amount of nickel.
  • the battery cell of the material is stored in a fully charged state. Because the high oxidation of the material promotes the oxidation and decomposition of the electrolyte, a large amount of gas is generated.
  • the surface coating method can isolate the electrolyte and the material to a certain extent. Contact, thereby reducing the degree of side reactions, thereby improving gas production. If the raw materials are not made into batteries, the gas production performance of high nickel materials can be judged, which can undoubtedly effectively reduce the evaluation cost and provide a quick and effective method for material screening.
  • Solid materials have a certain degree of solubility in liquids, the dissolution rate of materials is reduced, and the ion concentration in the solution is low. According to this principle, by immersing the high-nickel material in a liquid and detecting the concentration of the dissolved nickel, the difference in gas production of the material can be judged.
  • the third aspect of the present disclosure provides the preparation method of the cathode material provided in the first aspect of the present disclosure, including:
  • a coating layer is formed on the surface of the substrate.
  • the method for preparing the cathode material may include: providing a substrate.
  • the method for providing the substrate should be known to those skilled in the art.
  • it may include: mixing and sintering the raw materials of the substrate to provide the substrate.
  • the raw material of the substrate may include a ternary material precursor of nickel, cobalt, manganese and/or aluminum, a lithium source, a source of M, a source of Me, a source of A, etc., and the ratio between the raw materials is usually based on the elements in the substrate. The proportion of the ratio.
  • the ternary material precursor may include, but is not limited to, the ternary material precursor may include, but is not limited to, Ni 1/3 Co 1/3 Mn 1/3 (OH) 2 , Ni 0.5 Co 0.2 Mn 0.3 (OH) 2 , Ni 0.5 Co 0.25 Mn 0.25 (OH) 2 , Ni 0.55 Co 0.15 Mn 0.3 (OH) 2 , Ni 0.55 Co 0.1 Mn 0.35 (OH) 2 , Ni 0.55 Co 0.05 Mn 0.4 (OH) 2.
  • the lithium source It may be a lithium-containing compound, and the lithium-containing compound may be a combination of one or more of LiOH ⁇ H 2 O, LiOH, Li 2 CO 3 ,
  • the sintering conditions may be 800° C. and oxygen concentration ⁇ 20%.
  • the particle morphology of the positive electrode material can be adjusted by selecting precursors of different ternary materials and adjusting the synthesis process.
  • the precursors of the ternary materials can be prepared by controlling the reaction time, the pH value during co-precipitation, and the ammonia Concentration, to achieve control of particle size.
  • the method for preparing the positive electrode material may further include: forming a coating layer on the surface of the substrate.
  • the method of forming a coating layer on the surface of the substrate should be known to those skilled in the art.
  • it may include: sintering the substrate in the presence of a compound containing a coating element to form a coating on the surface of the substrate. Cladding.
  • Those skilled in the art can select suitable types, proportions, and sintering conditions of the compound containing the coating element according to parameters such as the composition of the coating layer and the nickel element absorbance of the positive electrode material.
  • the compound containing coating elements may be oxides of these coating elements, and specifically may include but not limited to Al 2 O 3 , ZrO 2 , Ba(NO 3 ) 2 , ZnO, SnO 2 , SiO 2 , A combination of one or more of TiO 2 , Co 2 O 3 , WO 3 , Y 2 O 3 , H 3 BO 3 , P 2 O 5, etc., for another example, the amount of the coating element used may be 0.01wt% ⁇ 0.5wt%, 0.01wt% ⁇ 0.05wt%, 0.05wt% ⁇ 0.1wt%, 0.1wt% ⁇ 0.2wt%, 0.2wt% ⁇ 0.3wt%, 0.3wt% ⁇ 0.4wt% of the material mass , Or 0.4wt% to 0.5wt%.
  • the sintering conditions may be 200°C to 700°C, 200°C to 300°C, 300°C to 400°C, 400°C to 500°C, 500°C to 600°C, Or 600°C ⁇ 700°C high temperature sintering.
  • the fourth aspect of the present disclosure provides an electrochemical energy storage device, including the cathode material provided in the first aspect of the present disclosure.
  • the electrochemical energy storage device may be a super capacitor, a lithium ion battery, a lithium metal battery, or a sodium ion battery.
  • the electrochemical energy storage device is a lithium ion battery is shown, but the present disclosure is not limited thereto.
  • the lithium ion battery may include a positive pole piece, a negative pole piece, a separator separated between the positive pole piece and the negative pole piece, and an electrolyte, wherein the positive pole piece includes The positive active material provided by the first aspect of the present disclosure.
  • the method for preparing the lithium ion battery should be known to those skilled in the art.
  • the positive pole piece, the separator film and the negative pole piece may each be a layered body, which can be cut to a target size in sequence. Stacked, it can also be wound to a target size to form a battery cell, and can be further combined with an electrolyte to form a lithium ion battery.
  • the positive pole piece usually includes a positive current collector and a positive electrode material layer on the positive current collector.
  • the positive electrode material layer may include the first aspect of the present disclosure.
  • a suitable method to prepare the positive electrode sheet for example, it may include the following steps: after mixing the positive electrode material, the binder, and the conductive agent to form a slurry, then coating on the positive electrode current collector.
  • the adhesive usually includes a fluorine-containing polyolefin adhesive.
  • the fluorine-containing polyolefin adhesive Compared with the fluorine-containing polyolefin adhesive, water is usually a good solvent, that is, the fluorine-containing polyolefin adhesive is usually It has good solubility in water.
  • the fluorine-containing polyolefin binder may include but not limited to polyvinylidene fluoride (PVDF), vinylidene fluoride copolymers, etc. or their modifications (for example, carboxylic acid, Modified acrylic acid, acrylonitrile, etc.) derivatives.
  • PVDF polyvinylidene fluoride
  • the mass percentage content of the binder may be due to the poor conductivity of the binder itself, so the amount of the binder cannot be too high.
  • the mass percentage of the binder in the positive electrode active material layer is less than or equal to 2 wt%, so as to obtain a lower pole piece impedance.
  • the conductive agent of the positive pole piece may be various conductive agents suitable for lithium ion (secondary) batteries in the field, for example, may include but not limited to acetylene black, conductive carbon black, carbon fiber (VGCF), carbon nanotube (CNT), Ketjen Black, etc., one or more combinations.
  • the weight of the conductive agent may account for 1 wt% to 10 wt% of the total mass of the positive electrode material layer. More preferably, the weight ratio of the conductive agent to the positive electrode material in the positive pole piece is greater than or equal to 1.5:95.5.
  • the positive electrode current collector of the positive electrode sheet may generally be a layered body, the positive electrode current collector is usually a structure or part that can collect current, and the positive electrode current collector may It is a variety of materials suitable for use as a positive electrode current collector of a lithium ion battery in the field.
  • the positive electrode current collector may include but is not limited to metal foil, and more specifically may include but not limited to copper foil, aluminum foil, and the like.
  • the negative pole piece generally includes a negative current collector and a negative active material layer on the surface of the negative current collector, and the negative active material layer generally includes a negative active material.
  • the negative electrode active material may be various materials suitable for the negative electrode active material of lithium ion batteries in the art, for example, it may include but not limited to graphite, soft carbon, hard carbon, carbon fiber, mesophase carbon microspheres, silicon-based materials , Tin-based materials, lithium titanate, or other metals that can form alloys with lithium, or a combination of one or more of them.
  • the graphite can be selected from one or a combination of artificial graphite, natural graphite and modified graphite;
  • the silicon-based material can be selected from elemental silicon, silicon-oxygen compounds, silicon-carbon composites, and silicon alloys
  • the tin-based material can be selected from one or more combinations of elemental tin, tin oxide compounds, and tin alloys.
  • the negative electrode current collector is usually a structure or part that collects current.
  • the negative electrode current collector can be various materials suitable for use as a lithium ion battery negative current collector in the art.
  • the negative electrode current collector can include but is not limited to Metal foil and the like, more specifically, may include but not limited to copper foil and the like.
  • the isolation film may be various materials suitable for the isolation film of lithium ion batteries in the art, for example, may include but not limited to polyethylene, polypropylene, poly One or more combinations of vinyl fluoride, aramid, polyethylene terephthalate, polytetrafluoroethylene, polyacrylonitrile, polyimide, polyamide, polyester, and natural fibers.
  • the electrolyte may be various electrolyte solutions suitable for lithium ion batteries in the art.
  • the electrolyte usually includes an electrolyte and a solvent, and the electrolyte may generally be Including lithium salt, etc., more specifically, the lithium salt may be an inorganic lithium salt and/or an organic lithium salt, etc., specifically including but not limited to, the lithium salt may be selected from LiPF 6 , LiBF 4 , LiN(SO 2 F) 2 (LiFSI for short), LiN(CF 3 SO 2 ) 2 (LiTFSI for short), LiClO 4 , LiAsF 6 , LiB(C 2 O 4 ) 2 (LiBOB for short), LiBF 2 C 2 O 4 (Abbreviated as LiDFOB) one or more of the combination.
  • LiPF 6 LiBF 4
  • LiN(SO 2 F) 2 LiFSI for short
  • LiN(CF 3 SO 2 ) 2 LiTFSI for short
  • LiClO 4 LiAsF 6
  • the concentration of the electrolyte may be between 0.8 mol/L and 1.5 mol/L.
  • the solvent may be various solvents suitable for the electrolyte of lithium ion batteries in the field.
  • the solvent of the electrolyte is usually a non-aqueous solvent, preferably an organic solvent, and may specifically include but not limited to ethylene carbonate, carbonic acid One or more combinations of propylene, butylene carbonate, pentene carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate, etc., or their halogenated derivatives.
  • the higher the Ni content in the ternary material the larger the gram capacity of the ternary material, which is also conducive to increasing the energy density of the electrochemical energy storage device.
  • the positive electrode activity increases, and the cycle performance is obviously deteriorated.
  • the researchers in this case found that after the traditional coating method treats the ternary material, the surface still contains a large amount of nickel. Therefore, after the battery is fully charged, the high-priced nickel on the surface of the material will contact the electrolyte and cause a large number of side reactions. This leads to poor cycle performance.
  • the positive electrode material of the embodiment of the present disclosure has good crystal structure stability and surface inertness, and the content of the soluble nickel element on the surface of the positive electrode active material is low, which effectively inhibits the side reaction between the positive electrode material and the electrolyte, thereby improving the ternary material High temperature cycle and high temperature storage performance.
  • one or more method steps mentioned in the present disclosure do not exclude that there may be other method steps before and after the combined step or other method steps may be inserted between these explicitly mentioned steps, unless otherwise It should be noted; it should also be understood that the combined connection relationship between one or more devices/devices mentioned in this disclosure does not exclude that there may be other devices/devices before and after the combined device/device or that these are explicitly mentioned Other devices/devices can be inserted between the two devices/devices, unless otherwise specified. Moreover, unless otherwise specified, the number of each method step is only a convenient tool for identifying each method step, and is not intended to limit the arrangement order of each method step or limit the scope of implementation of the present disclosure. The change or adjustment of the relative relationship is If there is no substantial change to the technical content, it should be regarded as the scope of the present disclosure.
  • the nickel sulfate, manganese sulfate, and cobalt sulfate are prepared into a solution with a concentration of 1mol/L according to the molar ratio of Ni:Co:Mn 8:1:1, and the hydroxide co-precipitation technology is used to prepare lithium nickel with a larger particle size.
  • the precursor of transition metal oxide A is Ni 0.8 Co 0.1 Mn 0.1 (OH) 2 .
  • the reaction time is 75h-125h
  • the pH value during co-precipitation is 7.5-8.5
  • the ammonia concentration is 1mol/L.
  • the base material of the ternary material; the cathode material matrix and the alumina additive are placed in the mixing equipment according to the ratio of the coating element content of 3.5mg/cm 3 for mixing, and then placed in the atmosphere furnace for sintering at 450 °C to form Coating layer to obtain the finished cathode material.
  • the prepared cathode material is further prepared into a battery, and the preparation method is as described above.
  • the prepared battery is subjected to performance testing, the specific parameters are shown in Table 1, and the testing results are shown in Table 2.
  • Step 1 Mix the above-mentioned high nickel cathode material, adhesive polyvinylidene fluoride, and conductive agent acetylene black at a mass ratio of 98:1:1, add N-methylpyrrolidone (NMP), and stir evenly under the action of a vacuum mixer Obtain positive electrode slurry; uniformly coat the positive electrode slurry on an aluminum foil with a thickness of 12 ⁇ m, with an areal density of 0.1 mg/mm 2 ⁇ 0.3 mg/mm 2 ;
  • NMP N-methylpyrrolidone
  • Step 2 The coated pole pieces are dried in an oven at 100° C. to 130° C., cold pressed, and slit to obtain positive pole pieces.
  • the organic solvent is a mixed liquid containing ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC), wherein the volume ratio of EC, EMC and DEC is 20:20:60.
  • EC ethylene carbonate
  • EMC ethyl methyl carbonate
  • DEC diethyl carbonate
  • the concentration of lithium salt is 1 mol/L.
  • the positive pole piece, separator film, and negative pole piece in order so that the separator film is located between the positive and negative pole pieces for isolation. After winding it into a square bare cell, it is filled with aluminum plastic film, and then After baking at 80°C to remove water, the corresponding non-aqueous electrolyte is injected and sealed, and the finished battery is obtained after the processes of standing, hot and cold pressing, forming, fixture, and volume division.
  • the preparation method of the positive electrode material of Example 1 is basically the same, except that the coating additive is zirconia, and the content of the coating element is 4.6 mg/cm 3 .
  • the preparation method of the cathode material is basically the same as that of Example 1, except that the coating additive is titanium oxide, and the content of the coating element is 4.3 mg/cm 3 .
  • the preparation method of the positive electrode material of Example 1 is basically the same, except that the coating additive is phosphorus pentoxide, and the content of the coating element is 4.2 mg/cm 3 .
  • the preparation method of the positive electrode material is basically the same as that of Example 1, except that the coating additives are alumina and boron oxide, and the content of the coating element is 4.0 mg/cm 3 .
  • the preparation method of the positive electrode material is basically the same as that of Example 1, except that the coating additives are titanium oxide and boron oxide, and the content of the coating element is 3.8 mg/cm 3 .
  • the preparation method of the positive electrode material is basically the same as that of Example 1, except that the coating additive is boron oxide, and the content of the coating element is 0.4 mg/cm 3 .
  • the preparation method of the cathode material is basically the same as that of Example 1, except that the coating additive is boron oxide, and the content of the coating element is 0.8 mg/cm 3 .
  • the preparation method of the cathode material is basically the same as that of Example 1, except that the coating additive is boron oxide, and the content of the coating element is 10 mg/cm 3 .
  • the preparation method of the positive electrode material is basically the same as that of Example 1, except that the coating additive is boron oxide, and the content of the coating element is 15 mg/cm 3 .
  • the preparation method of the positive electrode material is basically the same as that of Example 7, except that the content of the coating element is 4.7 mg/cm 3 .
  • the preparation method of the positive electrode material is basically the same as that of Example 1, except that the sintering temperature of the precursor and LiOH is 900°C, the obtained positive electrode material is single crystal particles, and the substrate D50 is 6 ⁇ m; the coating additive is boron oxide , The content of coating element is 4.2mg/cm 3 .
  • the preparation method of the positive electrode material of Example 11 is basically the same, except that the substrate D50 is 15 ⁇ m.
  • the preparation method of the positive electrode material of Example 11 is basically the same, except that the substrate D50 is 8 ⁇ m.
  • the preparation method of the positive electrode material of Example 11 is basically the same, except that the substrate D50 is 12 ⁇ m.
  • the preparation method of the positive electrode material of Example 11 is basically the same, except that the substrate D50 is 18 ⁇ m.
  • the preparation method of the cathode material is basically the same as that of Example 11, except that the substrate D50 is 5 ⁇ m.
  • the preparation method of the positive electrode material of Example 12 is basically the same, except that: the substrate D50 is 2 ⁇ m; the content of the coating element boron is 2.1 mg/cm 3 .
  • the preparation method of the positive electrode material is basically the same as that of Example 1, except that no coating treatment is performed.
  • the preparation method of the positive electrode material of Example 1 is basically the same, except that the coating additive is magnesium oxide, and the content of the coating element is 4.7 mg/cm 3 .
  • the preparation method of the positive electrode material of Comparative Example 3 is basically the same, except that the substrate is coated with magnesium oxide, and the content of the coating element is 4.7 mg/cm 3 .
  • the battery After the battery was fully charged to 4.2V at 1C, it was allowed to stand in a thermostat at 80°C for 10 days. The initial volume of the battery and the volume after standing for 10 days were measured by the drainage method to obtain the volume expansion rate of the battery.
  • the volume expansion rate of the battery (%) (volume after standing for 10 days/initial volume-1) ⁇ 100%.
  • the nickel elution absorbance of the positive electrode material was controlled to not exceed 0.7.
  • the nickel elution absorbance of the material is lower, and the crystal structure of the cathode material, especially the stability of the surface crystal structure, is stronger. Therefore, the gram capacity of the cathode material measured by battery discharge is higher, and the high temperature cycle and high temperature volume expansion rate are effectively suppressed.
  • the degree of deviation between the theoretical specific surface area of the positive electrode material and the real specific surface area within a certain range, it is ensured that the particle size and morphological uniformity of the positive electrode material are better, and the surface of the coated positive electrode material is relatively flat and the concave and convex structure is relatively high. Less, the contact area with the electrolyte is small, which is beneficial to inhibit the dissolution of Ni element in the cathode material, while ensuring good lithium ion transmission performance between secondary particles, taking into account high-temperature gas production and dynamic performance.
  • the adhesion stability of the coating layer on the surface of the substrate can be improved, so that the coating layer has a certain degree of ion conductivity and conductivity, and the coating is reduced.
  • the influence of the layer on the polarization of the cathode material is reduced.
  • the proportion of the coating layer on the surface of the substrate can be reduced, and more ion transport channels are retained, but the structural stability of the substrate surface is improved
  • the effect is slightly worse than the continuous coating layer; if double-layer coating is used, high ionic conductivity can be achieved while effective coating, avoiding the deterioration of the battery due to excessive dissolution of nickel in the cathode material during long-term cycling performance.
  • the present disclosure effectively overcomes various shortcomings in the prior art and has a high industrial value.

Abstract

本公开涉及电化学领域，特别是涉及一种正极材料。本公开的正极材料，包括基材，所述基材的分子式为Li xNi yCo zM kMe pO rA m，其中，0.95≤x≤1.05，0.50≤y≤0.95，0≤z≤0.2，0≤k≤0.4，0≤p≤0.05，1≤r≤2，0≤m≤2，m+r≤2；所述基材上设有包覆层，所述包覆层包括包覆元素；单位质量所述正极材料的镍溶出吸光度w≤0.7。

Description

一种低产气高容量的三元正极材料
本公开要求享有2019年06月28日提交的名称为“一种低产气高容量的三元正极材料”的中国专利申请CN201910578176.8的优先权，其全部内容通过引用并入本文中。
技术领域
本公开涉及电化学领域，特别是涉及一种低产气高容量的三元正极材料和电化学储能装置。
背景技术
随着能源危机以及环境问题的不断升级，开发新型绿色能源已迫在眉睫。锂离子电池具有比能量高、应用温度范围宽、自放电率低、循环寿命长、安全性能好、无污染等优点，现已被应用于各个领域中。锂离子电池作为汽车的能源系统取代传统内燃机车已在世界各地逐步尝试。然而目前常用的磷酸铁锂(LiFePO 4)、低镍三元(LiNi 1/3Co 1/3Mn 1/3O 2)等，由于受到材料本身的性质局限，不能完全满足动力电池对锂离子电池正极材料能量密度的需求。提高高镍三元正极材料的镍含量可以提升电池的能量密度，因此，高镍三元正极材料是目前动力电池的主要研究对象之一。但是，随着镍含量的增加，正极活性材料与电解液直接的副反应也明显加剧，高温产气性能明显恶化，是目前电池量产商业化的瓶颈之一。
目前在材料层面，解决高温产气性能的主要手段均会导致电芯性能不同程度的破坏：如，活性材料的可逆克容量降低，循环性能变差等。
发明内容
鉴于以上所述现有技术的缺点，本公开的目的在于提供一种低产气高容量的三元正极材料，用于解决现有技术中的问题。
为实现上述目的及其他相关目的，本公开提供一种正极材料，包括基材，所述基材的分子式为Li xNi yCo zM kMe pO rA m，其中，0.95≤x≤1.05，0.50≤y≤0.95，0≤z≤0.2，0≤k≤0.4，0≤p≤0.05，1≤r≤2，0≤m≤2，m+r≤2，M选自Mn和/或Al，Me选自Zr、Zn、Cu、Cr、Mg、Fe、V、Ti、Sr、Sb、Y、W、Nb中的一种或多种的组合，A选自N、F、S、Cl中的一种或多种的组合；所述基材表面设有包覆层，所述包覆层包括包覆元素，所述包覆元素选自 Al、Zr、Ba、Zn、Ti、Co、W、Y、Si、Sn、B、P中的一种或多种的组合；单位质量所述正极材料的镍溶出吸光度w≤0.7。
另一方面，本公开提供一种电化学储能装置，包括本公开所述的正极材料。
相对于现有技术，本公开具有以下有益效果：
本公开的正极材料具有良好的晶体结构稳定性和表面惰性，正极材料的镍溶出吸光度较低，从而可以有效抑制正极材料与电解液之间的副反应，进而优化循环性能、改善热稳定性和产气现象。
具体实施方式
下面详细说明本公开的锂离子电池及其制备方法。
本公开第一方面提供一种正极材料，包括基材，所述基材的分子式为Li xNi yCo zM kMe pO rA m，其中，0.95≤x≤1.05，0.50≤y≤0.95，0≤z≤0.2，0≤k≤0.4，0≤p≤0.05，1≤r≤2，0≤m≤2，m+r≤2，M选自Mn和/或Al，Me选自Zr、Zn、Cu、Cr、Mg、Fe、V、Ti、Sr、Sb、Y、W、Nb中的一种或多种的组合，A选自N、F、S、Cl中的一种或多种的组合；所述基材上设有包覆层，所述包覆层包括包覆元素，所述包覆元素选自Al、Zr、Ba、Zn、Ti、Co、W、Y、Si、Sn、B、P中的一种或多种的组合；单位质量所述正极材料的镍溶出吸光度w≤0.7。
在本公开的实施例中，单位质量所述正极材料的镍溶出吸光度w的确定方法通常可以包括：将单位质量的所述正极材料置于适当的溶液中，在一定波长范围条件下测量所得溶出液的吸光度。在本公开一具体实施例中，单位质量所述正极材料的镍溶出吸光度w的确定方法具体可以包括如下步骤：将1g所述正极材料在pH为8～11、丁二酮肟浓度为10g/L的10mL乙醇溶液中存储24h，取5mL上层清液加去离子水、稀释为10mL溶出液，采用UV-Vis分光光度计检测所述溶出液在430nm～570nm范围内的吸光度。
在三元材料中，镍元素的相对含量越高，三元材料的克容量通常就越大，越有利于提升电化学储能装置的能量密度，但是随着镍元素相对含量的增加，也会对电化学储能装置的整体性能带来诸多负面效果。例如，当三元材料中Ni元素的相对含量较高时，三元材料的层状结构会因为Ni 2+与Li +的混排而崩塌，使得Li +在三元材料中的脱嵌越来越困难，最终导致电化学储能装置循环性能恶化。再例如，三元材料中Ni元素相对含量的增加，还会降低三元材料的热分解温度，导致放热量增加，三元材料的热稳定性变差。再例如，三元材料中的Ni元素的相对含量增加时，具有强氧化性的Ni 4+的含量也会随之增加，当电解液与三元材料接触时，电解液会与三元材料发生更多副反应，而为了保持电荷平衡， 三元材料会释放出氧气，这样不仅会破坏三元材料的晶体结构，而且会加剧电化学储能装置胀气，恶化电化学储能装置的存储性能。本案研究人员经大量研究发现，将正极材料通过在高镍基材中进行掺杂和表面包覆，控制正极材料的镍溶出吸光度在适当范围，从而可以在一定程度上隔绝电解液和材料的接触，进而优化循环性能、改善热稳定性，并降低副反应程度，改善产气现象。
在本公开的一些实施方式中，单位质量所述正极材料的镍元素吸光度可以为w≤0.7、w≤0.6、w≤0.5、w≤0.4、w≤0.3、或w≤0.2。本公开中当单位质量所述正极材料的镍溶出吸光度w超过0.7时，表示所述正极材料颗粒中的镍元素较易溶出，此时正极材料表面容易与电解液发生副反应，因此导致使用该正极材料的锂离子电池的产气量过高。单位质量所述正极材料的镍溶出吸光度越低，表明该正极材料的晶体结构、尤其表面晶体结构的稳定性越强。
在本公开的实施例所提供的正极材料中，所述正极材料的理论比表面积BET 1与所述正极材料的真实比表面积BET 2通常可以满足：
0.3≤(BET 2-BET 1)/BET 1≤5.5；
其中，BET 1＝6/(ρ×D v50)；ρ为所述正极材料的真实密度，计量单位为g/cm 3；D v50为所述正极材料的体积累计分布百分数达到50％时对应的粒径，计量单位为μm。所述正极材料的真实比表面积BET 2可经N 2吸附法测定，具体方法可以参见GB/T19587-2004。(BET 2-BET 1)/BET 1表示正极材料的理论比表面积与真实比表面积的偏离程度，其可以衡量正极材料表面的凹凸起伏程度。由于材料均匀性是影响正极材料的BET 2的因素之一，所以通过控制正极材料理论比表面积与真实比表面积的偏离程度在一定范围内，可以表明所述正极材料的粒度、形态均匀性较好，包覆后的正极材料表面较平整、凹凸起伏结构较少，与电解液的接触面积较小，有利于抑制正极材料中的Ni元素溶出、同时保证锂离子在二次颗粒间的传输性能良好，兼顾了高温产气和动力学性能。
在本公开的实施例所提供的正极材料中，所述基材可以包括由一次颗粒组成的二次颗粒，所述二次颗粒的D v50可以为5μm～18μm，所述一次颗粒的粒径范围可以为0.1μm～1.0μm。所述D v50通常指样品的体积累计分布百分数达到50％时对应的粒径。具体的，所述二次颗粒的D v50可以为5μm～18μm、5μm～6μm、6μm～7μm、7μm～8μm、8μm～9μm、9μm～10μm、10μm～11μm、11μm～12μm、12μm～13μm、13μm～14μm、14μm～15μm、15μm～16μm、16μm～17μm、或17μm～18μm，优选为8～15μm；所述一次颗粒的粒径范围可以为0.1μm～1μm、0.1μm～0.9μm、0.2μm～0.8μm、或0.2μm～0.5μm。对于镍含量较高的三元材料而言，小粒径微粉的相对数量对正极活性材料的残锂量、产气问题影响更加显著。 因此控制高镍二次颗粒形貌的三元材料Li xNi yCo zM kMe pO rA m或表面设置有包覆层的Li xNi yCo zM kMe pO rA m的一次颗粒和二次颗粒的D v50在一定的范围内，可以是解决其产气问题的一种有效手段。当所述基材包括由一次颗粒组成的二次颗粒时，所述正极材料的真实比表面积BET 2可以为0.1m 2/g～1.0m 2/g、0.1m 2/g～0.2m 2/g、0.2m 2/g～0.3m 2/g、0.3m 2/g～0.4m 2/g、0.4m 2/g～0.5m 2/g、0.5m 2/g～0.6m 2/g、0.6m 2/g～0.7m 2/g、0.7m 2/g～0.8m 2/g、0.8m 2/g～0.9m 2/g、或0.9m 2/g～1.0m 2/g。合适的正极材料的比表面积一方面可以使电解液与正极活性材料的接触面积较少，有利于抑制副反应，避免电解液腐蚀并破坏正极活性材料的晶体结构导致加剧电化学储能装置胀气的问题，另一方面则可以有利于在混合形成正极浆料时，使用较少的辅料即可以满足正极活性材料与粘结剂、导电剂的吸附性能相对较强，由此有利于提升电化学储能装置的能量密度。
在本公开的实施例所提供的正极材料中，所述基材可以包括单晶或类单晶颗粒。当所述基材为单晶或类单晶颗粒时，所述基材的粒径D v50可以为1μm～6μm、1μm～2μm、2μm～3μm、3μm～4μm、4μm～5μm、或5μm～6μm，优选地，所述基材的粒径D v50为2μm～5μm。所述单晶或类单晶颗粒，通常是指颗粒形态为完整的单独一个颗粒组成、或者由少于十个的颗粒团聚而成的正极材料。当所述正极材料包括单晶或类单晶颗粒时，所述正极材料的真实比表面积BET 2可以为0.5m 2/g～1.5m 2/g、0.5m 2/g～0.6m 2/g、0.6m 2/g～0.7m 2/g、0.7m 2/g～0.8m 2/g、0.8m 2/g～0.9m 2/g、0.9m 2/g～1.0m 2/g、1.0m 2/g～1.1m 2/g、1.1m 2/g～1.2m 2/g、1.2m 2/g～1.3m 2/g、1.3m 2/g～1.4m 2/g、或1.4m 2/g～1.5m 2/g。在本公开的实施例中，当正极材料包括上述粒径和BET在上述范围的单晶或类单晶结构的颗粒时，正极材料的表面及内部晶体结构更加完整、且与电解液的接触面积较小，有利于改善颗粒表面的镍元素溶出问题。
在本公开的实施例所提供的正极材料中，所述正极材料中包覆元素的单位体积含量Mv可以为0.4mg/cm 3～15mg/cm 3、0.4mg/cm 3～0.6mg/cm 3、0.6mg/cm 3～0.8mg/cm 3、0.8mg/cm 3～1mg/cm 3、1mg/cm 3～2mg/cm 3、2mg/cm 3～4mg/cm 3、4mg/cm 3～6mg/cm 3、6mg/cm 3～8mg/cm 3、8mg/cm 3～10mg/cm 3、或10mg/cm 3～15mg/cm 3，优选可以为0.8mg/cm 3～10mg/cm 3。合适的包覆元素的含量通常可以保证在不同体积粒径分布的体系下，正极材料的表面改性和极化问题得到兼容，有效改善高容量电池的产气问题、优化循环及倍率性能。所述包覆层中，包覆元素通常以氧化物的形式存在，例如，所述包覆层可以包括上述包覆元素的氧化物中的一种或多种的组合、或者包括上述包覆元素、锂元素的含锂氧化物，具体可以是包括但不限于氧化铝、氧化锆、氧化锌、氧化钛、氧化硅、氧化锡、氧化钨、氧化钇、氧化钴、氧化钡、氧化磷、氧化硼、以及锂铝氧化物、锂锆氧化物、锂 锌氧化物、锂镁氧化物、锂钨氧化物、锂钇氧化物、锂钴氧化物、锂钡氧化物、锂磷氧化物或者锂硼氧化物中的一种或多种的组合。
在本公开的实施例所提供的正极材料中，所述包覆层可以包括内包覆层，所述内包覆层可以位于所述基材内部，且可以位于至少部分的一次颗粒的表面，所述内包覆层包括包覆元素，所述内包覆层的包覆元素可以选自Al、Zr、Ba、Zn、Ti、Co、W、Y、Si、Sn、B、P等中的一种或多种的组合。所述正极材料中，所述基材包括一次颗粒组成的二次颗粒，所以至少部分的包覆层可以位于二次颗粒内的一次颗粒之间，即位于所述二次颗粒内部的、至少部分的一次颗粒的表面，这部分包覆层可以被认为是内包覆层。所述内包覆层中可以包括包覆元素的氧化物，即内包覆层中至少部分的包覆元素可以以其氧化物的形式、或者以其含锂氧化物的形式存在，具体可以是包括但不限于氧化铝、氧化锆、氧化锌、氧化钛、氧化硅、氧化锡、氧化钨、氧化钇、氧化钴、氧化钡、氧化磷或氧化硼、以及锂铝氧化物、锂锆氧化物、锂锌氧化物、锂镁氧化物、锂钨氧化物、锂钇氧化物、锂钴氧化物、锂钡氧化物、锂磷氧化物或锂硼氧化物等中的一种或多种的组合。由于二次颗粒是由若干个一次颗粒紧密堆积形成，所以在循环过程中，二次颗粒会发生体积的膨胀和收缩，导致二次颗粒内部一次颗粒之间的间距增大，暴露出大量未包覆的新鲜表面，因此存在与电解液发生副反应的风险。在本公开的实施例中，在二次颗粒表面设置包覆层的同时，在其内部至少一部分一次颗粒的表面或相邻一次颗粒之间晶界处进一步包覆，可以增强二次颗粒内部的致密度，提高内部一次颗粒之间的作用力，进一步优化循环过程中的产气问题。
在本公开的实施例所提供的正极材料中，所述包覆层可以包括外包覆层，所述外包覆层通常可以位于二次颗粒的表面和/或基材表面，所述外包覆层包括包覆元素，所述外包覆层的包覆元素可以选自Al、Zr、Ba、Zn、Ti、Co、W、Y、Si、Sn、B、P等中的一种或多种的组合。所述正极材料中，所述基材包括一次颗粒组成的二次颗粒，至少部分的包覆层可以位于二次颗粒的表面，所述氧化物包覆层中的包覆元素可以在所述二次颗粒表面分布。所述外包覆层中可以包括包覆元素的氧化物，即外包覆层中至少部分的包覆元素可以以其氧化物、或者以其含锂氧化物的形式存在，具体可以是包括但不限于氧化铝、氧化锆、氧化锌、氧化钛、氧化硅、氧化锡、氧化钨、氧化钇、氧化钴、氧化钡、氧化磷、氧化硼、以及锂铝氧化物、锂锆氧化物、锂锌氧化物、锂镁氧化物、锂钨氧化物、锂钇氧化物、锂钴氧化物、锂钡氧化物、锂磷氧化物或锂硼氧化物等中的一种或多种的组合。所述正极材料中，外包覆层是主要发挥减少基材与电解液接触面积的部分，外包覆层的存在可以有效地对高镍正极材料的表面进行改性，降低正极材料与电解液的副反应，从而可以有效抑制电池的产气现象。
在本公开的实施例所提供的正极材料中，所述包覆层中可以含有至少两种以上的上述包覆元素，更具体可以含有至少两种以上的上述包覆元素所形成的氧化物，从而可以提高包覆层在基材表面附着的稳定性，使包覆层兼具一定的导离子性和导电子性，减少包覆层对正极材料极化问题的影响。
在本公开的实施例所提供的正极材料中，所述外包覆层可以包括连续状和/或非连续状的包覆层。连续状包覆层可以对基材表面形成较完整的保护，有利于稳定正极材料的表面结构、抑制正极材料的镍溶出量、抑制电解液的副反应；但是连续状包覆层需要具有良好的电子导通以及离子导通性能，以避免引起极片的阻抗增加，恶化电池的动力学性能。而非连续状包覆层的优势在于降低包覆层在基材表面的占比，保留较多的离子传输通道，但基材表面的结构稳定性改善效果略差于连续状包覆层。在本公开的一优选实施方式中，所述外包覆层可以包括连续状的第一包覆层与非连续状的第二包覆层，可以是两种形态的复合形态。所述第二包覆层可以位于第一包覆层的表面，也可以位于第一包覆层和基材之间。在本公开的一优选实施例中，单个单元的所述非连续状的第二包覆层的面积通常小于单个单元的第一包覆层的面积。在本公开的另一优选实施方式中，所述外包覆层中，所述第二包覆层和第一包覆层可以包括不同的包覆元素，从而使得非连续状包覆层的包覆物质与连续状包覆层的包覆物质至少部分是不同的。
在本公开的实施例所提供的正极材料中，所述外包覆层中所述包覆元素的含量可以占所述正极材料中总包覆元素质量的60wt％以上、70wt％以上、80wt％以上、90wt％以上，优选可以为80wt％～98wt％。在本公开的实施例中，由于二次颗粒表面最先与电解液接触、相对面积更大，因此包覆元素主要还是在二次颗粒表面分布，在二次颗粒表面分布的质量占正极活性材料中总包覆元素质量的一定比例以上时，相对来说对高镍正极材料表面改性更加显著、对电池的产气抑制效果也更加良好。
在本公开的实施例所提供的正极材料中，所述基材为镍含量较高的锂过渡金属氧化物，在所述基材的分子式中，y优选满足0.50≤y≤0.90，更优选为0.70≤y≤0.90，z优选满足0≤z≤0.15，更优选为0.05≤z≤0.15，k优选满足0≤k≤0.2，更优选为0.05≤k≤0.2，p优选满足0≤p≤0.03，更优选为0≤p≤0.025。具体地，所述基材的分子式Li xNi yCo zM kMe pO rA m可以是包括但不限于LiNi 1/3Co 1/3Mn 1/3O 2、LiNi 0.5Co 0.2Mn 0.3O 2、LiNi 0.5Co 0.25Mn 0.25O 2、LiNi 0.55Co 0.15Mn 0.3O 2、LiNi 0.55Co 0.1Mn 0.35O 2、LiNi 0.55Co 0.05Mn 0.4O 2、LiNi 0.6Co 0.2Mn 0.2O 2、LiNi 0.65Co 0.15Mn 0.2O 2、LiNi 0.65Co 0.12Mn 0.23O 2、LiNi 0.65Co 0.1Mn 0.25O 2、LiNi 0.65Co 0.05Mn 0.3O 2、LiNi 0.75Co 0.1Mn 0.15O 2、LiNi 0.8Co 0.1Mn 0.1O 2、LiNi 0.85Co 0.05Mn 0.1O 2、LiNi 0.88Co 0.05Mn 0.07O 2、LiNi 0.9Co 0.05Mn 0.05O 2等，也可以为上述物质经过掺杂元素Me和/或掺杂元素A进行部分 取代改性后的物质。
在本公开的实施例所提供的正极材料中，所述正极材料表面的残锂的测量方法可以参照GBT 9725-2007化学试剂电位滴定法通则。所述正极材料表面的残锂中Li 2CO 3的含量(即所述正极材料表面的残锂中Li 2CO 3的质量相对于正极材料总质量的含量)通常小于3000ppm，优选地，所述正极材料表面的残锂中Li 2CO 3的含量小于2000ppm。所述正极材料表面的残锂中LiOH的含量(即所述正极材料表面的残锂中LiOH的质量相对于正极材料总质量的含量)小于5000ppm，优选地，所述正极材料表面的残锂中LiOH的含量小于4000ppm。在三元材料的实际生产过程中，由于所使用的原料锂盐可能存在不纯及熔点低的问题，其在较低温度下就会发生熔融、分解和挥发损失，因此在三元材料的制备过程中会加入过量的锂盐以弥补烧结过程中造成的锂损失。三元材料表面存在活性氧阴离子，其会和空气中的CO 2和H 2O反应而生成碳酸根，同时锂离子会从本体迁移到表面并在三元材料表面形成Li 2CO 3，这一过程同时伴随着三元材料表面脱氧而形成结构扭曲的表面氧化物层。另外，三元材料合成中锂盐过量的做法使得多余的锂盐在高温煅烧后的产物主要是Li的氧化物，其与空气中的CO 2和H 2O反应再次生成LiOH和Li 2CO 3，残留在三元材料表面，使三元材料的pH值较高。且在充放电过程中，残留在三元材料表面的Li 2CO 3会发生分解产生CO 2，由于CO 2气体会随着温度的差异而造成气压差(特别是当反应过程中伴随着热反应发生的时候)，因此加剧了电化学储能装置胀气，恶化了电化学储能装置的存储性能。在所述基材的表面设置包覆层可以在一定程度上降低正极活性材料表面残锂(例如LiOH、Li 2CO 3等)含量，达到改善电化学储能装置存储性能的目的。此外在所述基材的表面设置包覆层还可以降低基材与电解液因直接接触而发生副反应的概率，进而可以减少正极活性材料在充放电过程中为了平衡电荷而释放出的氧气量以及由此带来晶体结构崩塌的风险。在本公开的一优选实施方式中，在所述基材的表面设置包覆层而得到的正极材料表面上(即所述外包覆层中)，Li 2CO 3的含量通常低于LiOH，在正极材料表面，表面残锂(LiOH、Li 2O)容易与空气中的水分、CO 2等反应，反应产物为Li 2CO 3等。Li 2CO 3越高，说明反应程度越剧烈，相应制作出的电池的产气问题越严重。
本公开的第二方面提供用于本公开的第一方面所提供的正极材料的单位质量正极材料镍溶出吸光度检测方法，包括：
1)配置含有显色剂、显色增强剂以及主溶剂的溶液A，
2)将所述正极材料加入所述溶液A中，经浸泡、静置，取上层澄清溶液B；
3)采用紫外-可见光(UV-Vis)分光光度计，测试溶液B或溶液B的稀释液的吸光度；
测量所得的结果即可以作为所述正极材料的镍溶出吸光度
所述正极材料的吸光度测试方法中，所述显色剂选自丁二酮肟。所述主溶剂可以是乙醇、水、丙酮中的一种或多种的组合，从而可以提供反应介质使溶出的镍与显色剂反应络合。所述显色增强剂，可以是包括但不限于氨水、NaOH、KOH等中的一种或多种的组合，从而可以提供反应适宜的pH，增强显色的灵敏度和提高显色速度。所述溶液A的pH可以是8～11。当所述正极材料与溶液A充分接触后，经浸泡、静置，取上层澄清溶液B，溶液B中通常含有丁二酮肟镍。所述正极材料的镍元素吸光度通过采用分光光度计对溶液B或溶液B的稀释液进行检测获得。测试吸光度的波长范围可以为430nm～500nm，例如，可以在470nm波长的条件下测试吸光度。
在本公开的一优选实施方式中，所述正极材料的镍溶出吸光度的检测方法具体可以包括如下步骤：
1)以丁二酮肟为显色剂、氨水为显色增强剂、乙醇为主溶剂配置溶液A，所述溶液A中丁二酮肟的浓度为10g/L，所述氨水的浓度为25wt％～28wt％；
2)将1g所述正极材料加入10mL所述溶液A，振荡并静置24h，取5mL上层澄清溶液B；
3)将所述溶液B加去离子水定容至10mL溶液C，采用紫外-可见光分光光度计，在470nm波长测试溶液C的吸光度。
在本公开的实施例中，所述正极材料的镍溶出吸光度通过紫外-可见光分光光度计检测，具有较高的灵敏度和准确性，可以直观的反映正极材料晶体、尤其晶体表面的结构稳定性；无需进行电池的长期循环测试，就可以快速反映正极材料的产气问题。具体来说，当光照射到原子或分子结构时，原子外层电子会选择性地吸收某些波长的电磁波形成原子吸收光谱，分子中的电子能级发生跃迁产生位于紫外及可见光部分的电子光谱。测量某种物质对不同波长单色光的吸收程度，以波长为横坐标，吸光度为纵坐标作图，可得到一条吸收光谱曲线，光吸收程度最大处的波长叫做最大吸收波长。当物质的浓度不同时，光吸收曲线形状相同，最大吸收波长不变，只是对应的吸光度大小不同。而吸光度在锂电池领域中的应用也是根据以上的原理。根据光的吸收定律(朗伯-比尔定律)，溶液对光的吸收程度与溶液浓度、液层厚度及入射光波长等因素有关，如果保持入射光波长和液层厚度不变，那么溶液对光的吸收程度只与溶液浓度有关。高镍材料中含有大量镍元素，材料电芯在满充状态下存储由于材料的高氧化性促进电解液氧化分解，产生大量气体，表面包覆的方法可在一定程度上隔绝电解液与材料的接触，从而降低副反应程度，进而改善产气现象。若在原材料未做成电芯的状态就可以判断高镍材料的产气性能，无疑能够有效降低评估成本，也为材料筛选提供一个快速有效的方法。固体材料在液体中都有一定的溶解度， 材料的溶出速率降低，溶液中的离子浓度低。根据这一原理，将高镍材料置于液体中浸泡，检测溶出的镍的浓度，就可以判断材料的产气差异。
本公开的第三方面提供本公开的第一方面所提供的正极材料的制备方法，包括：
提供基材；
在基材表面形成包覆层。
在本公开的实施例所提供的正极材料的制备方法中，可以包括：提供基材。提供所述基材的方法对于本领域技术人员来说应该是已知的，例如，可以包括：将基材的原料混合、烧结，以提供基材。本领域技术人员可根据基材的元素组成，选择合适的基材的原料和配比。例如，所述基材的原料可以包括镍钴锰和/或铝的三元材料前驱体、锂源、M源、Me源、A源等，各原料之间的比例通常参照基材中各元素的比例进行配比。更具体的，所述三元材料前驱体可以是包括但不限于所述三元材料前驱体可以是包括但不限于Ni 1/3Co 1/3Mn 1/3(OH) 2、Ni 0.5Co 0.2Mn 0.3(OH) 2、Ni 0.5Co 0.25Mn 0.25(OH) 2、Ni 0.55Co 0.15Mn 0.3(OH) 2、Ni 0.55Co 0.1Mn 0.35(OH) 2、Ni 0.55Co 0.05Mn 0.4(OH) 2、Ni 0.6Co 0.2Mn 0.2(OH) 2、Ni 0.65Co 0.15Mn 0.2(OH) 2、Ni 0.65Co 0.12Mn 0.23(OH) 2、Ni 0.65Co 0.1Mn 0.25(OH) 2、Ni 0.65Co 0.05Mn 0.3(OH) 2、Ni 0.75Co 0.1Mn 0.15(OH) 2、Ni 0.8Co 0.1Mn 0.1(OH) 2、Ni 0.88Co 0.05Mn 0.07(OH) 2、0.9Ni 0.8Mn 0.2(OH) 2·0.1Al 2(OH) 3、0.9Ni 0.9Mn 0.1(OH) 2·0.1Al 2(OH) 3、0.9Ni 0.9Co 0.05Mn 0.05(OH) 2·0.1Al 2(OH) 3，所述锂源可以是含锂的化合物，所述含锂化合物可以是包括但不限于LiOH·H 2O、LiOH、Li 2CO 3、Li 2O等中的一种或多种的组合，所述Me源通常可以是含Me元素的化合物，所述含Me元素的化合物可以是含有Zr、Zn、Cu、Cr、Mg、Fe、V、Ti、Sr、Sb、Y、W、Nb中至少一种元素的氧化物、硝酸盐、碳酸盐中的一种或几种，所述A源可以是含A元素的化合物，所述含A元素的化合物可以是含A元素的盐，具体可以是包括但不限于LiF、NaCl、NaBr等中的一种或多种的组合。再例如，所述烧结的条件可以是800℃、氧气浓度≥20％。所述正极材料的颗粒形态可以选择不同三元材料的前驱体以及调节合成工艺进行调整，例如，可以在制备三元材料的前驱体的过程中通过控制反应时间、共沉淀时的pH值、氨浓度，实现对颗粒粒径的控制。
在本公开的实施例所提供的正极材料的制备方法中，还可以包括：在基材表面形成包覆层。在基材表面形成包覆层的方法对于本领域技术人员来说应该是已知的，例如，可以包括：将基材在含包覆元素的化合物存在的条件下烧结，以在基材表面形成包覆层。本领域技术人员可根据包覆层的组成、正极材料的镍元素吸光度等参数，选择合适的含包覆元素的化合物的种类、配比和烧结条件等。例如，所述含包覆元素的化合物可以是这些包覆元素的氧化物，具体可以是包括但不限于Al 2O 3、ZrO 2、Ba(NO 3) 2、ZnO、SnO 2、SiO 2、 TiO 2、Co 2O 3、WO 3、Y 2O 3、H 3BO 3、P 2O 5等中的一种或多种的组合，再例如，所述包覆元素的使用量可以是基材质量的0.01wt％～0.5wt％、0.01wt％～0.05wt％、0.05wt％～0.1wt％、0.1wt％～0.2wt％、0.2wt％～0.3wt％、0.3wt％～0.4wt％、或0.4wt％～0.5wt％，再例如，所述烧结的条件可以是200℃～700℃、200℃～300℃、300℃～400℃、400℃～500℃、500℃～600℃、或600℃～700℃高温烧结。
本公开的第四方面提供一种电化学储能装置，包括本公开的第一方面所提供的正极材料。
在本公开的实施例所提供的电化学储能装置中，需要说明的是，所述电化学储能装置可以为超级电容器、锂离子电池、锂金属电池或钠离子电池等。在本公开的实施例中，仅示出电化学储能装置为锂离子电池的实施例，但本公开不限于此。
在本公开的实施例所提供的锂离子电池中，可以包括正极极片、负极极片、间隔于正极极片和负极极片之间的隔离膜、电解液，其中，所述正极极片包括本公开的第一方面所提供的正极活性材料。制备所述锂离子电池的方法对于本领域技术人员来说应该是已知的，例如，所述正极极片、隔离膜和负极极片各自都可以是层体，从而可以裁剪成目标尺寸后依次叠放，还可以卷绕至目标尺寸，以用于形成电芯，并可以进一步与电解液结合以形成锂离子电池。
在本公开的实施例所提供的锂离子电池中，所述正极极片通常包含正极集流体和位于所述正极集流体上的正极材料层，所述正极材料层可以包括本公开的第一方面所提供的正极材料、粘结剂、导电剂。本领域技术人员可选择合适的方法制备所述正极极片，例如，可以包括如下步骤：将正极材料、粘结剂、导电剂混合形成浆料后，涂布于正极集流体上。所述粘结剂通常包括含氟聚烯烃类粘结剂，相对于所述含氟聚烯烃类粘结剂来说，水通常是良溶剂，即所述含氟聚烯烃类粘结剂通常在水中具有良好的溶解性，例如，所述含氟聚烯烃类粘结剂可以是包括但不限于聚偏氟乙烯(PVDF)、偏氟乙烯共聚物等或它们的改性(例如，羧酸、丙烯酸、丙烯腈等改性)衍生物等。在所述正极材料层中，粘结剂的质量百分比含量可以是由于粘结剂本身的导电性较差，因此粘结剂的用量不能过高。优选地，正极活性物质层中粘结剂的质量百分含量小于等于2wt％，以获得较低的极片阻抗。所述正极极片的导电剂可以是本领域各种适用于锂离子(二次)电池的导电剂，例如，可以是包括但不限于乙炔黑、导电炭黑、碳纤维(VGCF)、碳纳米管(CNT)、科琴黑等中的一种或多种的组合。所述导电剂的重量可以占正极材料层总质量的1wt％～10wt％。更优选地，正极极片中导电剂与正极物质的重量比大于等于1.5：95.5。
在本公开的实施例所提供的锂离子电池中，所述正极极片的正极集流体通常可以为层 体，所述正极集流体通常是可以汇集电流的结构或零件，所述正极集流体可以是本领域各种适用于作为锂离子电池正极集流体的材料，例如，所述正极集流体可以是包括但不限于金属箔等，更具体可以是包括但不限于铜箔、铝箔等。
在本公开的实施例所提供的锂离子电池中，所述负极极片通常包括负极集流体和位于负极集流体表面的负极活性物质层，所述负极活性物质层通常包括负极活性物质。所述负极活性物质可以是本领域各种适用于锂离子电池的负极活性物质的材料，例如，可以是包括但不限于石墨、软碳、硬碳、碳纤维、中间相碳微球、硅基材料、锡基材料、钛酸锂或其他能与锂形成合金的金属等中的一种或多种的组合。其中，所述石墨可选自人造石墨、天然石墨以及改性石墨中的一种或多种的组合；所述硅基材料可选自单质硅、硅氧化合物、硅碳复合物、硅合金中的一种或多种的组合；所述锡基材料可选自单质锡、锡氧化合物、锡合金中的一种或多种的组合。所述负极集流体通常是汇集电流的结构或零件，所述负极集流体可以是本领域各种适用于作为锂离子电池负极集流体的材料，例如，所述负极集流体可以是包括但不限于金属箔等，更具体可以是包括但不限于铜箔等。
在本公开的实施例所提供的锂离子电池中，所述隔离膜可以是本领域各种适用于锂离子电池隔离膜的材料，例如，可以是包括但不限于聚乙烯、聚丙烯、聚偏氟乙烯、芳纶、聚对苯二甲酸乙二醇酯、聚四氟乙烯、聚丙烯腈、聚酰亚胺，聚酰胺、聚酯和天然纤维等中的一种或多种的组合。
在本公开的实施例所提供的锂离子电池中，所述电解液可以是本领域各种适用于锂离子电池的电解液，例如，所述电解液通常包括电解质和溶剂，所述电解质通常可以包括锂盐等，更具体的，所述锂盐可以是无机锂盐和/或有机锂盐等，具体可以是包括但不限于，所述锂盐可选自LiPF 6、LiBF 4、LiN(SO 2F) 2(简写为LiFSI)、LiN(CF 3SO 2) 2(简写为LiTFSI)、LiClO 4、LiAsF 6、LiB(C 2O 4) 2(简写为LiBOB)、LiBF 2C 2O 4(简写为LiDFOB)中的的一种或多种的组合。再例如，所述电解质的浓度可以为0.8mol/L～1.5mol/L之间。所述溶剂可以是本领域各种适用于锂离子电池的电解液的溶剂，所述电解液的溶剂通常为非水溶剂，优选可以为有机溶剂，具体可以是包括但不限于碳酸乙烯酯、碳酸丙烯酯、碳酸丁烯酯、碳酸戊烯酯、碳酸二甲酯、碳酸二乙酯、碳酸二丙酯、碳酸甲乙酯等或它们的卤代衍生物中的一种或多种的组合。
通常来说，在三元材料中Ni的含量越高，三元材料的克容量通常就越大，也越有利于提升电化学储能装置的能量密度，但是随着镍含量的增加，正极活性材料与电解液直接的副反应也明显加剧，循环性能明显恶化。而本案研究人员发现，传统的包覆方法处理三元材料后，表面仍含有大量的镍元素，所以在电池满充后，材料表面的高价镍元素会与电 解液接触会发生大量的副反应，从而导致循环性能变差。本公开的实施例的正极材料具有良好的晶体结构稳定性和表面惰性，正极活性物质表面的可溶出镍元素含量较低，有效抑制正极材料与电解液之间的副反应，从而改善三元材料的高温循环和高温存储性能。
以下通过特定的具体实例说明本公开的实施方式，本领域技术人员可由本说明书所揭露的内容轻易地了解本公开的其他优点与功效。本公开还可以通过另外不同的具体实施方式加以实施或应用，本说明书中的各项细节也可以基于不同观点与应用，在没有背离本公开的精神下进行各种修饰或改变。
须知，下列实施例中未具体注明的工艺设备或装置均采用本领域内的常规设备或装置。
此外应理解，本公开中提到的一个或多个方法步骤并不排斥在所述组合步骤前后还可以存在其他方法步骤或在这些明确提到的步骤之间还可以插入其他方法步骤，除非另有说明；还应理解，本公开中提到的一个或多个设备/装置之间的组合连接关系并不排斥在所述组合设备/装置前后还可以存在其他设备/装置或在这些明确提到的两个设备/装置之间还可以插入其他设备/装置，除非另有说明。而且，除非另有说明，各方法步骤的编号仅为鉴别各方法步骤的便利工具，而非为限制各方法步骤的排列次序或限定本公开可实施的范围，其相对关系的改变或调整，在无实质变更技术内容的情况下，当亦视为本公开可实施的范畴。
实施例1
(1)正极材料的具体制备工艺为：
a.制备基材前驱体：
将硫酸镍、硫酸锰、硫酸钴按Ni：Co：Mn摩尔比8:1:1，配置成浓度为1mol/L的溶液，利用氢氧化物共沉淀技术，制备得到较大粒径的锂镍过渡金属氧化物A的前驱体Ni 0.8Co 0.1Mn 0.1(OH) 2。制备前躯体的过程中，反应时间为75h～125h、共沉淀时的pH值为7.5～8.5、氨浓度为1mol/L。
b.正极材料的制备方法：
将三元材料前驱体Ni 0.8Co 0.1Mn 0.1(OH) 2和LiOH·H 2O置于混料设备中进行混料，然后置于气氛炉中800℃进行烧结，冷却后通过机械研磨即为三元材料的基材；将正极材料基体与氧化铝添加剂按包覆元素含量3.5mg/cm 3的配比置于混料设备中进行混料，然后置于气氛炉中进行烧结450℃，形成包覆层，获得成品的正极材料。
将制备获得的正极材料进一步制备电池，制备方法如上所述。将制备获得的电池进行性能检测，具体的参数如表1所示，检测结果如表2所示。
(2)正极极片的制备
步骤1：将上述高镍正极材料、粘接剂聚偏氟乙烯、导电剂乙炔黑按照质量比98:1:1进行混合，加入N-甲基吡咯烷酮(NMP)，在真空搅拌机作用下搅拌均匀获得正极浆料；将正极浆料均匀涂覆于厚度为12μm的铝箔上，面密度为0.1mg/mm 2～0.3mg/mm 2；
步骤2：将涂覆后的极片经过100℃～130℃烘箱干燥、冷压、分切得到正极极片。
(3)负极极片的制备：
将负极活性材料石墨、增稠剂羧甲基纤维素钠、粘接剂丁苯橡胶、导电剂乙炔黑按照质量比97:1:1:1进行混合，加入去离子水，在真空搅拌机作用下获得负极浆料；将负极浆料均匀涂覆在厚度为8μm的铜箔上，0.05mg/mm 2～0.15mg/mm 2；将铜箔在室温晾干后转移至120℃烘箱干燥1h，对极片反面进行相同工艺处理，然后经过冷压、分切得到负极片。
(4)电解液制备：
有机溶剂为含有碳酸亚乙酯(EC)、碳酸甲乙酯(EMC)和碳酸二乙酯(DEC)的混合液，其中，EC、EMC和DEC的体积比为20:20:60。在含水量<10ppm的氩气气氛手套箱中，将充分干燥的LiPF 6锂盐溶解于有机溶剂中，混合均匀，获得电解液。其中，锂盐的浓度为1mol/L。
(5)隔离膜的制备：
选用12μm厚的聚丙烯隔离膜。
(6)电池的制备：
将正极极片、隔离膜、负极极片按顺序叠好，使隔离膜处于正、负极片之间起到隔离的作用，再卷绕成方形的裸电芯后，装入铝塑膜，然后在80℃下烘烤除水后，注入相应的非水电解液、封口，经静置、热冷压、化成、夹具、分容等工序后，得到成品电池。
实施例2
与实施例1的正极材料的制备方法基本相同，不同之处在于：包覆添加剂为氧化锆，包覆元素含量为4.6mg/cm 3。
实施例3
与实施例1的正极材料的制备方法基本相同，不同之处在于：包覆添加剂为氧化钛，包覆元素含量为4.3mg/cm 3。
实施例4
与实施例1的正极材料的制备方法基本相同，不同之处在于：包覆添加剂为五氧化二磷，包覆元素含量为4.2mg/cm 3。
实施例5
与实施例1的正极材料的制备方法基本相同，不同之处在于：包覆添加剂为氧化铝和氧化硼，包覆元素含量为4.0mg/cm 3。
实施例6
与实施例1的正极材料的制备方法基本相同，不同之处在于：包覆添加剂为氧化钛和氧化硼，包覆元素含量为3.8mg/cm 3。
实施例7
与实施例1的正极材料的制备方法基本相同，不同之处在于：包覆添加剂为氧化硼，包覆元素含量为0.4mg/cm 3。
实施例8
与实施例1的正极材料的制备方法基本相同，不同之处在于：包覆添加剂为氧化硼，包覆元素含量为0.8mg/cm 3。
实施例9
与实施例1的正极材料的制备方法基本相同，不同之处在于：包覆添加剂为氧化硼，包覆元素含量为10mg/cm 3。
实施例10
与实施例1的正极材料的制备方法基本相同，不同之处在于：包覆添加剂为氧化硼，包覆元素含量为15mg/cm 3。
实施例11
与实施例7的正极材料的制备方法基本相同，不同之处在于：包覆元素含量为4.7mg/cm 3。
实施例12
与实施例1的正极材料的制备方法基本相同，不同之处在于：前驱体与LiOH烧结温度为900℃，得到的正极材料为单晶颗粒，且基材D50为6μm；包覆添加剂为氧化硼，包覆元素含量为4.2mg/cm 3。
实施例13
与实施例11的正极材料的制备方法基本相同，不同之处在于：基材D50为15μm。
实施例14
与实施例11的正极材料的制备方法基本相同，不同之处在于：基材D50为8μm。
实施例15
与实施例11的正极材料的制备方法基本相同，不同之处在于：基材D50为12μm。
实施例16
与实施例11的正极材料的制备方法基本相同，不同之处在于：基材D50为18μm。
实施例17
与实施例11的正极材料的制备方法基本相同，不同之处在于：基材D50为5μm。
实施例18
与实施例12的正极材料的制备方法基本相同，不同之处在于：基材D50为2μm；包覆元素硼元素的含量为2.1mg/cm 3。
对比例1
与实施例1的正极材料的制备方法基本相同，不同之处在于：不做包覆处理。
对比例2
与实施例1的正极材料的制备方法基本相同，不同之处在于：包覆添加剂为氧化镁，包覆元素含量为4.7mg/cm 3。
对比例3
与对比例1的正极材料的制备方法基本相同，不同之处在于：基材为D50＝3.5μm的单晶正极材料。
对比例4
与对比例3的正极材料的制备方法基本相同，不同之处在于：对基材进行了氧化镁包覆处理，包覆元素含量为4.7mg/cm 3。
测试方法
(1)单位质量正极材料镍溶出吸光度的检测方法：
1)以丁二酮肟为显色剂、氨水为显色增强剂、乙醇为主溶剂配置溶液A，所述溶液A中丁二酮肟的浓度为10g/L，所述氨水的浓度为25～28wt％；
2)将1g正极材料加入10mL所述溶液A，振荡并静置24h，取5mL上层澄清溶液B；
3)将溶液B加水定容至10mL溶液C，用紫外-可见光分光光度计，在470nm波长测试溶液C的吸光度。
(2)锂离子电池的45℃循环性能测试
在45℃的恒温环境下，在2.8V～4.2V下，按照1C充电至4.2V，然后在4.2V下恒压充电至电流≤0.05mA，静置5min，然后按照1C放电至2.8V，容量记为Dn(n＝0,1,2……)，重复前面过程，直至容量衰减到初始容量的80％，记录该锂离子电池的循环圈数。各实施例和各对比例的检测结果如表2所示。
(3)锂离子电池的放电容量测试
在25℃的恒温环境下，在2.8V～4.2V下，按照1C充电至4.2V，然后在4.2V下恒压充电至电流≤0.05mA，静置5min，然后按照1C放电至2.8V，记录该锂离子电池的容量具体结果如表2所示。
(4)电池的高温产气测试：
将电池以1C满充电至4.2V后，于80℃恒温箱中静置10天。并通过排水法测定电池的初始体积与静置10天后的体积，得到电池的体积膨胀率。
电池的体积膨胀率(％)＝(静置10天后的体积/初始体积-1)×100％。 表1
Figure PCTCN2020084336-appb-000001
表2
Figure PCTCN2020084336-appb-000002
Figure PCTCN2020084336-appb-000003
结合表1和表2数据可知：对比例1～4中，高镍三元正极材料由于包覆物质与基体的结合不牢固、或包覆层结构不致密、或粉体颗粒形貌的凸起起伏过大等，使得单位质量正极材料镍溶出吸光度w均超过0.7，表明正极材料粉体颗粒中的镍元素较易溶出，此时当该正极材料用于锂离子电池时，粉体颗粒表面容易与电解液发生副反应，导致使用该正极材料的锂离子电池的产气量过高、高温循环时的容量衰减较快、循环日历寿命减少。
而在实施例1～18中，通过调节正极材料的包覆物质、包覆层的相对含量、颗粒表面形貌等因素的综合影响，控制正极材料的镍溶出吸光度不超过0.7，由于单位质量正极材料的镍溶出吸光度较低，该正极材料的晶体结构、尤其表面晶体结构的稳定性越强，因此电池放电测出的正极材料克容量较高、高温循环及高温体积膨胀率得到有效抑制。具体的，通过控制正极材料理论比表面积与真实比表面积的偏离程度在一定范围内，保证所述正极材料的粒度、形态均匀性较好，包覆后的正极材料表面较平整、凹凸起伏结构较少，与电解液的接触面积较小，有利于抑制正极材料中的Ni元素溶出、同时保证锂离子在二次颗粒间的传输性能良好，兼顾了高温产气和动力学性能。当所述包覆层中含有至少两种上述包覆元素时，可以提高包覆层在基材表面附着的稳定性，使得包覆层兼具一定的导离子性和导电子性，减少包覆层对正极材料极化问题的影响。在对正极材料进行包覆工艺时，外包覆层为非连续状时，可以降低包覆层在基材表面的占比，保留较多的离子传输通道，但 基材表面的结构稳定性改善效果略差于连续状包覆层；若使用双层包覆时，可以在有效包覆的同时实现高离子导通性能，避免在长期循环过程中，因正极材料镍元素的过量溶出而恶化电池性能。
综上所述，本公开有效克服了现有技术中的种种缺点而具高度产业利用价值。
上述实施例仅例示性说明本公开的原理及其功效，而非用于限制本公开。任何熟悉此技术的人士皆可在不违背本公开的精神及范畴下，对上述实施例进行修饰或改变。因此，举凡所属技术领域中具有通常知识者在未脱离本公开所揭示的精神与技术思想下所完成的一切等效修饰或改变，仍应由本公开的权利要求所涵盖。

Claims (12)

  1. 一种正极材料，包括基材，所述基材的分子式为Li xNi yCo zM kMe pO rA m，其中，0.95≤x≤1.05，0.50≤y≤0.95，0≤z≤0.2，0≤k≤0.4，0≤p≤0.05，1≤r≤2，0≤m≤2，m+r≤2，M选自Mn和/或Al，Me选自Zr、Zn、Cu、Cr、Mg、Fe、V、Ti、Sr、Sb、Y、W、Nb中的一种或多种的组合，A选自N、F、S、Cl中的一种或多种的组合；
    所述基材上设有包覆层，所述包覆层包括包覆元素，所述包覆元素选自Al、Zr、Ba、Zn、Ti、Co、W、Y、Si、Sn、B、P中的一种或多种的组合；
    单位质量所述正极材料的镍溶出吸光度w≤0.7。
  2. 如权利要求1所述的正极材料，其中，所述正极材料的理论比表面积BET 1与所述正极材料的真实比表面积BET 2满足：
    0.3≤(BET 2-BET 1)/BET 1≤5.5；
    其中，BET 1＝6/(ρ×D v50)；
    ρ为所述正极材料的真实密度，计量单位为g/cm 3；
    D v50为所述正极材料的体积累计分布百分数达到50％时对应的粒径，计量单位为μm。
  3. 如权利要求1～2任一权利要求所述的正极材料，其中，所述基材包括由一次颗粒组成的二次颗粒，所述正极材料的真实比表面积BET 2为0.1m 2/g～1.0m 2/g，D v50为5μm～18μm。
  4. 如权利要求1～2任一权利要求所述的正极材料，其中，所述基材包括单晶或类单晶颗粒，所述正极材料的真实比表面积BET 2为0.5m 2/g～1.5m 2/g，D v50为1μm～6μm。
  5. 如权利要求1～4任一权利要求所述的正极材料，其中，所述正极材料中包覆元素的单位体积含量Mv为0.4mg/cm 3～15mg/cm 3，优选为0.8mg/cm 3～10mg/cm 3。
  6. 如权利要求1～5任一权利要求所述的正极材料，其中，所述包覆层包括内包覆层，所述内包覆层位于所述基材内部的、至少部分的一次颗粒的表面，所述内包覆层包括包覆元素，所述内包覆层的包覆元素选自Al、Zr、Ba、Zn、Ti、Co、W、Y、Si、Sn、B、P中的一种或多种的组合。
  7. 如权利要求1～6任一权利要求所述的正极材料，其中，所述包覆层包括外包覆层，所述外包覆层位于所述基材表面，所述外包覆层包括包覆元素，所述外包覆层的包覆元素选自Al、Zr、Ba、Zn、Ti、Co、W、Y、Si、Sn、B、P中的一种或多种的组合。
  8. 如权利要求7所述的正极材料，其中，所述外包覆层包括连续状和/或非连续状的 包覆层；优选地，所述外包覆层包括连续状的第一包覆层与非连续状的第二包覆层；更优选地，所述第二包覆层和第一包覆层包括不同的包覆元素。
  9. 如权利要求1所述的正极材料，其中，在所述基材的分子式中，0.70≤y≤0.90，0≤z≤0.15，0≤k≤0.2，0≤p≤0.03。
  10. 如权利要求1所述的正极材料，其中，在所述正极材料表面的残锂中，Li 2CO 3小于3000ppm，LiOH小于5000ppm。
  11. 如权利要求10所述的正极材料，其中，在所述正极材料表面的残锂中，Li 2CO 3的含量小于LiOH含量。
  12. 一种电化学储能装置，包括如权利要求1～11任一权利要求所述的正极材料。
PCT/CN2020/084336 2019-06-28 2020-04-11 一种低产气高容量的三元正极材料 WO2020258996A1 (zh)

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