WO2024026713A1 - 用于锂二次电池的正极活性材料及其制备方法 - Google Patents

用于锂二次电池的正极活性材料及其制备方法 Download PDF

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WO2024026713A1
WO2024026713A1 PCT/CN2022/109897 CN2022109897W WO2024026713A1 WO 2024026713 A1 WO2024026713 A1 WO 2024026713A1 CN 2022109897 W CN2022109897 W CN 2022109897W WO 2024026713 A1 WO2024026713 A1 WO 2024026713A1
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active material
single crystal
particularly preferably
bet
particles
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PCT/CN2022/109897
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English (en)
French (fr)
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张学全
王竞鹏
陈彦彬
刘亚飞
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北京当升材料科技股份有限公司
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • 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

Definitions

  • the present invention relates to a positive electrode active material, a preparation method thereof, and a lithium secondary battery including the positive electrode active material.
  • Lithium-ion battery is a green secondary battery with outstanding advantages such as high operating voltage, high energy density, good cycle life, small self-discharge, and no memory effect, and has been developing rapidly.
  • NCM layered ternary materials
  • the reaction between the highly active Ni 4+ generated during the charging process and the electrolyte will generate a NiO-like rock salt phase, seriously damaging the structure of the layered material, causing the cathode structure to collapse, and thus inducing transition metal ion dissolution, phase transformation and lattice oxygen precipitation.
  • the "secondary particles" of current conventional polycrystalline NCM are usually composed of many nanoscale “primary particles”. Changes in lattice parameters during the charge and discharge process will lead to the formation of microcracks in the secondary particles.
  • microcracks will expose fresh interfaces inside the secondary particles, further accelerating performance degradation. It is worth noting that the higher the nickel content, the more obvious the damage effect of cracks. To sum up, the main reason for the decline in cycle life of NCM, especially high-nickel NCM, is microcracks. Cracks will cause the thermal stability, structural stability and cycle stability of the cathode material to simultaneously decrease.
  • Patent CN 109962221 B uses agglomerate-blended single-crystal materials.
  • the main components are single-crystal lithium iron manganese phosphate materials and agglomerated multi-element materials.
  • Multi-element and lithium iron manganese phosphate belong to two different cathode materials. Their test voltages and The scope of use is different, so forcibly mixing the two materials together will inevitably sacrifice their respective advantages and cause a waste of resources.
  • the patent number CN 107154491 B mixes two materials with different conductivity, taking into account the capacity of the two materials respectively, but does not consider the impact of the Ni content of the two different materials on the final product. The two materials are mixed together. The materials are mixed together and their particle size protection range is relatively wide, making it difficult to determine the effect of the final product.
  • the purpose of the present invention is to overcome the shortcomings of the existing technology and effectively improve the defects of low capacity and poor circulation of the blended product.
  • the present invention effectively increases the capacity of the cathode active material by setting the Ni content of small particles to be higher than that of large particles; in addition, by preparing large polycrystalline particles and small single crystal particles, and controlling their different surface characteristics, the invention effectively suppresses polycrystalline large particles.
  • the generation of particle micro-cracks thereby improves the stability of the cathode active material during long-term cycling.
  • the cathode active material provided by the invention has the properties of high compaction, high capacity and high stability.
  • the present invention provides a positive active material for a lithium secondary battery, characterized in that the positive active material includes polycrystalline particles represented by Formula A1 and single crystal particles represented by Formula A2
  • A1 Li 1+a1 Ni x1 Co y1 M z1 M′ 1-x1-y1-z1 O 2
  • A2 Li 1+a2 Ni x2 Co y2 M z2 M′ 1-x2-y2-z2 O 2
  • M is one or two elements selected from Mn and Al,
  • M' is one or more selected from B, F, Mg, Si, P, Ca, Ti, V, Cr, Fe, Ga, Sr, Y, Zr, Nb, Mo, Sn, Ba, La, Ce, Elements of W, –0.03 ⁇ a1 ⁇ 0.20, 0.30 ⁇ x1 ⁇ 0.99, 0 ⁇ y1 ⁇ 0.30, 0 ⁇ z1 ⁇ 0.30, 0 ⁇ 1–x1–y1–z1 ⁇ 0.10, –0.03 ⁇ a2 ⁇ 0.20, 0.31 ⁇ x2 ⁇ 1.00, 0 ⁇ y2 ⁇ 0.30, 0 ⁇ z2 ⁇ 0.30, 0 ⁇ 1–x2–y2–z2 ⁇ 0.10, the condition is: 0 ⁇ x2–x1 ⁇ 0.5.
  • the present invention also provides a method for preparing a cathode active material, which includes the following steps:
  • M is one or two elements selected from Mn and Al,
  • M' is one or more selected from B, F, Mg, Si, P, Ca, Ti, V, Cr, Fe, Ga, Sr, Y, Zr, Nb, Mo, Sn, Ba, La, Ce, Elements of W, 0.30 ⁇ x1 ⁇ 0.99, 0 ⁇ y1 ⁇ 0.30, 0 ⁇ z1 ⁇ 0.30, 0 ⁇ 1–x1–y1–z1 ⁇ 0.10, 0.31 ⁇ x2 ⁇ 1.00, 0 ⁇ y2 ⁇ 0.30, 0 ⁇ z2 ⁇ 0.30, 0 ⁇ 1–x2–y2–z2 ⁇ 0.10, the condition is: 0 ⁇ x2–x1 ⁇ 0.5;
  • step iv) blending the polycrystalline particles of step ii) and the single crystal particles of step iii) to obtain the cathode active material.
  • the present invention also provides a lithium secondary battery including the positive active material according to the present invention or the positive active material prepared by the preparation method according to the present invention.
  • Figures 1 to 3 show respectively SEM photos of the large polycrystalline particles A1 and the small single crystal particles A2 in Example 1 and after blending the two;
  • Figure 4 shows the charge and discharge curves of Example 1, Comparative Example 1, and Comparative Example 2;
  • Figure 5 shows the cycle life of Example 1, Comparative Example 1, and Comparative Example 2.
  • the present invention relates to a positive active material for a lithium secondary battery, characterized in that the positive active material includes polycrystalline particles represented by formula A1 and single crystal particles represented by formula A2
  • A1 Li 1+a1 Ni x1 Co y1 M z1 M′ 1-x1-y1-z1 O 2
  • A2 Li 1+a2 Ni x2 Co y2 M z2 M′ 1-x2-y2-z2 O 2
  • M is one or two elements selected from Mn and Al,
  • M' is one or more selected from B, F, Mg, Si, P, Ca, Ti, V, Cr, Fe, Ga, Sr, Y, Zr, Nb, Mo, Sn, Ba, La, Ce,
  • W -0.03 ⁇ a1 ⁇ 0.20, preferably -0.01 ⁇ a1 ⁇ 0.14, more preferably 0 ⁇ a1 ⁇ 0.10, particularly preferably 0.01 ⁇ a1 ⁇ 0.08, 0.30 ⁇ x1 ⁇ 0.99, preferably 0.57 ⁇ x1 ⁇ 0.99, more preferably 0.72 ⁇ x1 ⁇ 0.99, particularly preferably 0.80 ⁇ x1 ⁇ 0.99, 0 ⁇ y1 ⁇ 0.30, preferably 0 ⁇ y1 ⁇ 0.21, more preferably 0 ⁇ y1 ⁇ 0.15, particularly preferably 0 ⁇ y1 ⁇ 0.10, 0 ⁇ z1 ⁇ 0.30, preferably 0 ⁇ z1 ⁇ 0.18, more preferably 0 ⁇ z1 ⁇ 0.11, particularly preferably 0 ⁇ z1 ⁇ 0.06, 0 ⁇ 1–x1–y1–z1 ⁇ 0.10, preferably 0 ⁇ 1
  • a2>a1 preferably 0.01 ⁇ a2–a1 ⁇ 0.20, more preferably 0.01 ⁇ a2–a1 ⁇ 0.12, particularly preferably 0.01 ⁇ a2–a1 ⁇ 0.07, especially Preferably, it is 0.01 ⁇ a2–a1 ⁇ 0.04.
  • the polycrystalline particles have a particle size D 50 of 6 to 30 ⁇ m, preferably 8 to 25 ⁇ m, more preferably 9 to 20 ⁇ m, particularly preferably 10 to 18 ⁇ m.
  • the particle size D 50 of the single crystal particles is 0.1 to 10 ⁇ m, preferably 0.5 to 8.0 ⁇ m, more preferably 1.0 to 6.0 ⁇ m, particularly preferably 1.5 to 4.5 ⁇ m. .
  • the content of the polycrystalline particles is 20 to 90%, preferably 45 to 85%, more preferably 50 to 80% based on the weight of the cathode active material. , particularly preferably 60 to 80%, and the content of the single crystal particles is 10 to 80%, preferably 10 to 70%, more preferably 15 to 60%, particularly preferably 20 to 40%.
  • the polycrystalline particles have a coating layer comprising at least one coating element selected from the group consisting of: B, F, Mg, Al, Si, P, Ca, Ti, V, Cr, Fe, Ga, Sr, Y, Zr, Nb, Mo, Sn, Ba, La, Ce, W, wherein the content of the coating element is 0.1 to 0.1 based on the polycrystalline particles.
  • the single crystal particles have a coating layer containing at least one coating element selected from the following group: B, F, Mg, Al, Si, P , Ca, Ti, V, Cr, Fe, Ga, Sr, Y, Zr, Nb, Mo, Sn, Ba, La, Ce, W, wherein based on the single crystal particles, the content of the coating element is 0.1 to 2 mol%, preferably about 1 mol%; the condition is that the coating layer of the polycrystalline particles contains a coating element different from the coating element of the coating layer of the single crystal particle.
  • the specific surface area before and after BET of the cathode active material before and after sintering in an air atmosphere at 600° C. for 8 hours satisfies:
  • the present invention uses single crystal particles with rounded surfaces and polycrystalline particles with high particle strength, combined with a preferred blending ratio, to control the finished material to expose a stable crystal structure, thereby causing the surface pores of the finished product to change during the further sintering process. rate is lower.
  • the specific surface area before and after BET of the polycrystalline particles before and after sintering in an air atmosphere at 600° C. for 8 hours satisfies:
  • it is 40% ⁇ ( after BET – before BET) / before BET ⁇ 20%.
  • Polycrystalline particles are composed of multiple nanoscale particles.
  • the BET of the material needs to be controlled within a certain range. Normally, after high-temperature sintering, the BET of the material will be further reduced.
  • the present invention can play a good surface and interface protection role by controlling the crystallinity and orientation of the nanocrystal grains on the surface of the material, combined with in-situ molten surface treatment. And it was unexpectedly discovered that the BET on the surface of the material increased instead of falling. The inventor further discovered that after polycrystalline particles with such surface BET properties are blended with single crystal particles, the cathode material exhibits relatively excellent pressure resistance characteristics and better discharge capacity and cycle performance.
  • the specific surface area before and after BET of the single crystal particles before and after sintering in an air atmosphere at 600° C. for 8 hours satisfies:
  • it is 0 ⁇ ( before BET- after BET)/ before BET ⁇ 10%.
  • the single crystal particles of the present invention have a relatively stable structure due to their good crystallinity and rounded surface. During the high-temperature sintering process, the material does not collapse and close to a large extent, and its BET changes relative to the BET of unsintered materials. smaller.
  • the positive active material does not contain nickel-free active materials, such as lithium iron manganese phosphate.
  • the cathode active material is composed of polycrystalline particles represented by Formula A1 and single crystal particles represented by Formula A2.
  • the present invention also relates to a method for preparing a cathode active material, which includes the following steps:
  • M is one or two elements selected from Mn and Al,
  • M' is one or more selected from B, F, Mg, Si, P, Ca, Ti, V, Cr, Fe, Ga, Sr, Y, Zr, Nb, Mo, Sn, Ba, La, Ce,
  • W 0.30 ⁇ x1 ⁇ 0.99, preferably 0.57 ⁇ x1 ⁇ 0.99, more preferably 0.72 ⁇ x1 ⁇ 0.99, particularly preferably 0.80 ⁇ x1 ⁇ 0.99, 0 ⁇ y1 ⁇ 0.30, preferably 0 ⁇ y1 ⁇ 0.21, More preferably, 0 ⁇ y1 ⁇ 0.15, particularly preferably 0 ⁇ y1 ⁇ 0.10, 0 ⁇ z1 ⁇ 0.30, preferably 0 ⁇ z1 ⁇ 0.18, more preferably 0 ⁇ z1 ⁇ 0.11, particularly preferably 0 ⁇ z1 ⁇ 0.06, 0 ⁇ 1–x1–y1–z1 ⁇ 0.10, preferably 0 ⁇ 1–x1–y1–z1 ⁇ 0.08, more preferably 0 ⁇ 1–x1–y1–z1 ⁇ 0.05, particularly preferably 0 ⁇ 1–x1– y1
  • ii) Mix the lithium source and the polycrystalline particle precursor according to the molar ratio r1, and optionally mix M' as a doping element, where 0.97 ⁇ r1 ⁇ 1.20, preferably 0.99 ⁇ r1 ⁇ 1.14, and more preferably 1.00 ⁇ r1 ⁇ 1.10, particularly preferably 1.01 ⁇ r1 ⁇ 1.08; and then perform primary sintering in a sintering atmosphere of air or oxygen, preferably oxygen, at a sintering temperature T1, where 600°C ⁇ T1 ⁇ 1000°C, preferably 675°C ⁇ T1 ⁇ 875°C, more preferably 690°C ⁇ T1 ⁇ 800°C, particularly preferably 690°C ⁇ T1 ⁇ 780°C; and then crushed to obtain polycrystalline particles;
  • iii) Mix the lithium source and the single crystal particle precursor according to the molar ratio r2, and optionally mix M' as a doping element, where 0.97 ⁇ r2 ⁇ 1.20, preferably 0.98 ⁇ r2 ⁇ 1.16, and more preferably 0.99 ⁇ r2 ⁇ 1.14, particularly preferably 1.00 ⁇ r2 ⁇ 1.08; and then perform primary sintering in a sintering atmosphere of air or oxygen, preferably oxygen, at a sintering temperature T2, where 650°C ⁇ T2 ⁇ 1050°C, preferably 730°C ⁇ T2 ⁇ 930°C, more preferably 750°C ⁇ T2 ⁇ 930°C, particularly preferably 750°C ⁇ T2 ⁇ 900°C; then single crystal particles are obtained by crushing; and
  • step iv) blending the polycrystalline particles of step ii) and the single crystal particles of step iii) to obtain the cathode active material.
  • r2>r1 preferably 0.01 ⁇ r2–r1 ⁇ 0.20, more preferably 0.01 ⁇ r2–r1 ⁇ 0.12, particularly preferably 0.01 ⁇ r2–r1 ⁇ 0.07, particularly preferably 0.01 ⁇ r2–r1 ⁇ 0.04.
  • the polycrystalline particle precursor has a particle size D 50 of 6.5 to 30.5 ⁇ m, preferably 8.5 to 25.5 ⁇ m, more preferably 9.5 to 20.5 ⁇ m, particularly preferably 10.5 to 18.5 ⁇ m.
  • the polycrystalline particles have a particle size D 50 of 6 to 30 ⁇ m, preferably 8 to 25 ⁇ m, more preferably 9 to 20 ⁇ m, particularly preferably 10 to 18 ⁇ m.
  • the particle size D 50 of the single crystal particle precursor is from 0.1 to 30.5 ⁇ m, preferably from 1.0 to 17.3 ⁇ m, more preferably from 1.0 to 9.3 ⁇ m, particularly preferably from 1.0 to 6.0 ⁇ m.
  • the particle size D 50 of the single crystal particles is 0.1 to 10 ⁇ m, preferably 0.5 to 8.0 ⁇ m, more preferably 1.0 to 6.0 ⁇ m, particularly preferably 1.5 to 4.5 ⁇ m.
  • the content of the polycrystalline particles is 20 to 90%, preferably 45 to 85%, more preferably 50 to 80%, especially based on the weight of the cathode active material. It is preferably 60 to 80%, and the content of the single crystal particles is 10 to 80%, preferably 10 to 70%, more preferably 15 to 60%, particularly preferably 20 to 40%.
  • the polycrystalline particles are mixed with a coating precursor comprising at least one coating element selected from the group: B, F, Mg, Al, Si, P, Ca, Ti, V, Cr, Fe, Ga, Sr, Y, Zr, Nb, Mo, Sn, Ba, La, Ce, W, and then in air or oxygen at sintering temperature T3 , preferably perform secondary sintering in an oxygen sintering atmosphere to obtain secondary sintered polycrystalline particles, where 250°C ⁇ T3 ⁇ 800°C, preferably 250°C ⁇ T3 ⁇ 600°C, more preferably 250°C ⁇ T3 ⁇ 480°C, particularly preferably 250°C ⁇ T3 ⁇ 400°C, wherein the content of the coating element is 0.1 to 2 mol%, preferably about 1 mol%, based on the polycrystalline particles; and/or, the The single crystal particles are mixed with a coating precursor containing at least one coating element selected from the group consisting of: B, F, Mg, Al, Si, P, Ca, Ti, V, Cr, Fe
  • the present invention also relates to a lithium secondary battery including the positive active material according to the present invention or the positive active material produced by the preparation method according to the present invention.
  • a 10.5 ⁇ m polycrystalline cathode precursor composed of Ni 0.83 Co 0.11 Mn 0.06 (OH) 2 and a 4 ⁇ m single crystal cathode precursor composed of Ni 0.86 Co 0.08 Mn 0.06 (OH) 2 were separately prepared using a liquid phase co-precipitation method.
  • LiOH and Ni 0.83 Co 0.11 Mn 0.06 (OH) 2 are mixed according to a molar ratio of 1.08.
  • the mixed material is sintered for the first time in an oxygen atmosphere.
  • the sintering temperature is 750°C. After sintering, the material is crushed. After crushing, Boric acid containing 1 mol% B was added to the material for the second sintering.
  • the sintering temperature was 400°C, and a polycrystalline large particle material with D 50 of 10.0 ⁇ m was obtained, as shown in Figure 1. When the polycrystalline material was treated at 600°C for 8 hours, its BET increased with a change rate of 35%.
  • LiOH and Ni 0.86 Co 0.08 Mn 0.06 (OH) 2 are mixed according to a molar ratio of 1.12.
  • the mixed material is sintered for the first time in an oxygen atmosphere.
  • the sintering temperature is 812°C. After sintering, the material is crushed. After crushing, The material is added with Al 2 O 3 containing 1 mol% of Al and then undergoes second sintering. The sintering temperature is 620°C, and finally a single crystal small particle material with D 50 of 3.5 ⁇ m is obtained, as shown in Figure 2.
  • the single crystal material was treated at 600°C for 8 hours, and its BET decreased with a change rate of 2%.
  • a 10.5 ⁇ m polycrystalline cathode precursor composed of Ni 0.83 Co 0.11 Mn 0.06 (OH) 2 and a 4 ⁇ m single crystal cathode precursor composed of Ni 0.86 Co 0.08 Mn 0.06 (OH) 2 were separately prepared using a liquid phase co-precipitation method.
  • LiOH and Ni 0.83 Co 0.11 Mn 0.06 (OH) 2 are mixed according to a molar ratio of 1.06.
  • the mixed material is sintered for the first time in an oxygen atmosphere.
  • the sintering temperature is 745°C. After sintering, the material is crushed. After crushing, Boric acid containing 0.8 mol% B was added to the material for second sintering.
  • the sintering temperature was 380°C to obtain a polycrystalline large particle material with D 50 of 10.0 ⁇ m. When the polycrystalline material was treated at 600°C for 8 hours, its BET increased with a change rate of 24%.
  • LiOH and Ni 0.86 Co 0.08 Mn 0.06 (OH) 2 are mixed according to a molar ratio of 1.12.
  • the mixed material is sintered for the first time in an oxygen atmosphere.
  • the sintering temperature is 812°C. After sintering, the material is crushed. After crushing, The material is added with Al 2 O 3 containing 1.2 mol% of Al and then undergoes second sintering. The sintering temperature is 610°C, and finally a single crystal small particle material with D 50 of 3.5 ⁇ m is obtained.
  • the single crystal material was treated at 600°C for 8 hours, and its BET decreased with a change rate of 3%.
  • the above-mentioned large polycrystalline particles and small single crystal particles were mixed at a mass ratio of 8:2 to obtain a positive electrode active material for lithium secondary batteries.
  • the positive electrode active material was treated at 600°C for 8 hours, and its BET change rate increased by 19%.
  • a 10.5 ⁇ m polycrystalline cathode precursor composed of Ni 0.86 Co 0.11 Mn 0.03 (OH) 2 and a 4 ⁇ m single crystal cathode precursor composed of Ni 0.88 Co 0.08 Mn 0.04 (OH) 2 were separately prepared using a liquid phase co-precipitation method.
  • LiOH and Ni 0.86 Co 0.11 Mn 0.03 (OH) 2 are mixed according to a molar ratio of 1.06.
  • the mixed material is sintered for the first time in an oxygen atmosphere.
  • the sintering temperature is 725°C. After sintering, the material is crushed. After crushing, Boric acid containing 0.8 mol% B was added to the material for second sintering.
  • the sintering temperature was 380°C to obtain a polycrystalline large particle material with D 50 of 10.0 ⁇ m. When the polycrystalline material was treated at 600°C for 8 hours, its BET increased with a change rate of 26%.
  • LiOH and Ni 0.88 Co 0.08 Mn 0.04 (OH) 2 are mixed according to a molar ratio of 1.11.
  • the mixed material is sintered for the first time in an oxygen atmosphere.
  • the sintering temperature is 805°C. After sintering, the material is crushed. After crushing, The material is added with Al 2 O 3 containing 1.0 mol% of Al and then undergoes second sintering. The sintering temperature is 610°C, and finally a single crystal small particle material with D 50 of 3.5 ⁇ m is obtained.
  • the single crystal material was treated at 600°C for 8 hours, and its BET decreased with a change rate of 2%.
  • the above-mentioned large polycrystalline particles and small single crystal particles are mixed at a mass ratio of 7:3 to obtain a positive electrode active material for lithium secondary batteries.
  • the positive active material was treated at 600°C for 8 hours, its BET change rate increased by 20%.
  • a 10.5 ⁇ m polycrystalline cathode precursor composed of Ni 0.86 Co 0.11 Mn 0.03 (OH) 2 and a 4 ⁇ m single crystal cathode precursor composed of Ni 0.88 Co 0.08 Mn 0.04 (OH) 2 were separately prepared using a liquid phase co-precipitation method.
  • the mixed material is sintered for the first time in an oxygen atmosphere.
  • the sintering temperature is 685°C. After sintering, the material is crushed. After crushing, Boric acid containing 0.8 mol% B was added to the material for second sintering.
  • the sintering temperature was 380°C to obtain a polycrystalline large particle material with D 50 of 10.0 ⁇ m. When the polycrystalline material was treated at 600°C for 8 hours, its BET increased with a change rate of 26%.
  • LiOH and Ni 0.88 Co 0.08 Mn 0.04 (OH) 2 are mixed according to a molar ratio of 1.11.
  • the mixed material is sintered for the first time in an oxygen atmosphere.
  • the sintering temperature is 805°C. After sintering, the material is crushed. After crushing, The material is added with Al 2 O 3 containing 1.0 mol% of Al and then undergoes second sintering. The sintering temperature is 610°C, and finally a single crystal small particle material with D 50 of 3.5 ⁇ m is obtained.
  • the single crystal material was treated at 600°C for 8 hours, and its BET decreased with a change rate of 2%.
  • the above-mentioned large polycrystalline particles and small single crystal particles are mixed at a mass ratio of 3:7 to obtain a cathode active material for lithium secondary batteries.
  • the positive active material was treated at 600°C for 8 hours, its BET change rate increased by 6%.
  • a 10.5 ⁇ m polycrystalline cathode precursor composed of Ni 0.88 Co 0.10 Mn 0.02 (OH) 2 and a 4 ⁇ m single crystal cathode precursor composed of Ni 0.90 Co 0.08 Mn 0.02 (OH) 2 were separately prepared using a liquid phase co-precipitation method.
  • LiOH and Ni 0.88 Co 0.10 Mn 0.02 (OH) 2 are mixed according to a molar ratio of 1.08.
  • the mixed material is sintered for the first time in an oxygen atmosphere.
  • the sintering temperature is 780°C. After sintering, the material is crushed. After crushing, Boric acid containing 1 mol% B was added to the material for second sintering.
  • the sintering temperature was 400°C to obtain a polycrystalline large particle material with D 50 of 10.0 ⁇ m. When the polycrystalline material was treated at 600°C for 8 hours, its BET increased with a change rate of 32%.
  • LiOH and Ni 0.90 Co 0.08 Mn 0.02 (OH) 2 are mixed according to a molar ratio of 1.12.
  • the mixed material is sintered for the first time in an oxygen atmosphere.
  • the sintering temperature is 812°C. After sintering, the material is crushed. After crushing, The material is added with Al 2 O 3 containing 1 mol% of Al and then undergoes second sintering. The sintering temperature is 620°C, and finally a single crystal small particle material with D 50 of 3.5 ⁇ m is obtained.
  • the single crystal material was treated at 600°C for 8 hours, and its BET decreased with a change rate of 2%.
  • the above-mentioned large polycrystalline particles and small single crystal particles are mixed at a mass ratio of 7:3 to obtain a positive electrode active material for lithium secondary batteries.
  • the positive active material was treated at 600°C for 8 hours, its BET change rate increased by 22%.
  • a 10.5 ⁇ m polycrystalline cathode precursor composed of Ni 0.83 Co 0.11 Mn 0.06 (OH) 2 and a 4 ⁇ m single crystal cathode precursor composed of Ni 0.86 Co 0.08 Mn 0.06 (OH) 2 were separately prepared using a liquid phase co-precipitation method.
  • LiOH and Ni 0.83 Co 0.11 Mn 0.06 (OH) 2 are mixed according to a molar ratio of 1.08.
  • the mixed material is sintered for the first time in an oxygen atmosphere.
  • the sintering temperature is 750°C. After sintering, the material is crushed. After crushing, Boric acid containing 1 mol% B was added to the material for second sintering.
  • the sintering temperature was 400°C to obtain a polycrystalline large particle material with D 50 of 10.0 ⁇ m. When the polycrystalline material was treated at 600°C for 8 hours, its BET increased with a change rate of 35%.
  • LiOH and Ni 0.86 Co 0.08 Mn 0.06 (OH) 2 are mixed according to a molar ratio of 1.12.
  • the mixed material is sintered for the first time in an oxygen atmosphere.
  • the sintering temperature is 812°C.
  • the material is crushed.
  • the material contains B 0.4 mol% boric acid and then undergoes second sintering at a sintering temperature of 400°C to finally obtain a single crystal small particle material with D 50 of 3.5 ⁇ m.
  • the single crystal material was treated at 600°C for 8 hours, and its BET increased with a change rate of 9%.
  • the above-mentioned large polycrystalline particles and small single crystal particles are mixed at a mass ratio of 7:3 to obtain a positive electrode active material for lithium secondary batteries.
  • the positive active material was treated at 600°C for 8 hours, its BET change rate increased by 27%.
  • a 10.5 ⁇ m polycrystalline cathode precursor composed of Ni 0.83 Co 0.11 Mn 0.06 (OH) 2 and a 4 ⁇ m single crystal cathode precursor composed of Ni 0.86 Co 0.08 Mn 0.06 (OH) 2 were separately prepared using a liquid phase co-precipitation method.
  • LiOH and Ni 0.83 Co 0.11 Mn 0.06 (OH) 2 are mixed according to a molar ratio of 1.08.
  • the mixed material is sintered for the first time in an oxygen atmosphere.
  • the sintering temperature is 750°C. After sintering, the material is crushed. After crushing, Boric acid containing 0.5 mol% B was added to the material for second sintering.
  • the sintering temperature was 400°C to obtain a polycrystalline large particle material with D 50 of 10.0 ⁇ m. When the polycrystalline material was treated at 600°C for 8 hours, its BET increased with a change rate of 11%.
  • LiOH and Ni 0.86 Co 0.08 Mn 0.06 (OH) 2 are mixed according to a molar ratio of 1.12.
  • the mixed material is sintered for the first time in an oxygen atmosphere.
  • the sintering temperature is 812°C. After sintering, the material is crushed. After crushing, The material is added with Al 2 O 3 containing 1 mol% of Al and then undergoes second sintering. The sintering temperature is 620°C, and finally a single crystal small particle material with D 50 of 3.5 ⁇ m is obtained.
  • the single crystal material was treated at 600°C for 8 hours, and its BET decreased with a change rate of 2%.
  • the above-mentioned large polycrystalline particles and small single crystal particles are mixed at a mass ratio of 7:3 to obtain a positive electrode active material for lithium secondary batteries.
  • the positive active material was treated at 600°C for 8 hours, its BET change rate increased by 7%.
  • a 10.5 ⁇ m polycrystalline cathode precursor composed of Ni 0.83 Co 0.11 Mn 0.06 (OH) 2 and a 4 ⁇ m single crystal cathode precursor composed of Ni 0.86 Co 0.08 Mn 0.06 (OH) 2 were separately prepared using a liquid phase co-precipitation method.
  • LiOH and Ni 0.83 Co 0.11 Mn 0.06 (OH) 2 are mixed according to a molar ratio of 1.08.
  • the mixed material is sintered for the first time in an oxygen atmosphere.
  • the sintering temperature is 750°C. After sintering, the material is crushed. After crushing, Al 2 O 3 containing 1 mol% of Al was added to the material for second sintering.
  • the sintering temperature was 620°C, and a polycrystalline large particle material with D 50 of 10.0 ⁇ m was obtained.
  • the polycrystalline material was treated at 600°C for 8 hours, and its BET decreased with a change rate of 3%.
  • LiOH and Ni 0.86 Co 0.08 Mn 0.06 (OH) 2 are mixed according to a molar ratio of 1.12.
  • the mixed material is sintered for the first time in an oxygen atmosphere.
  • the sintering temperature is 812°C. After sintering, the material is crushed. After crushing, The material is added with Al 2 O 3 containing 1 mol% of Al and then undergoes second sintering. The sintering temperature is 620°C, and finally a single crystal small particle material with D 50 of 3.5 ⁇ m is obtained.
  • the single crystal material was treated at 600°C for 8 hours, and its BET decreased with a change rate of 2%.
  • the above-mentioned large polycrystalline particles and small single crystal particles are mixed at a mass ratio of 7:3 to obtain a positive electrode active material for lithium secondary batteries.
  • the cathode active material was treated at 600°C for 8 hours, and its BET change rate was reduced by 3%.
  • a 10.5 ⁇ m polycrystalline cathode precursor composed of Ni 0.83 Co 0.11 Mn 0.06 (OH) 2 and a 4 ⁇ m single crystal cathode precursor composed of Ni 0.86 Co 0.08 Mn 0.06 (OH) 2 were separately prepared using a liquid phase co-precipitation method.
  • LiOH and Ni 0.83 Co 0.11 Mn 0.06 (OH) 2 are mixed according to a molar ratio of 1.08.
  • the mixed material is sintered for the first time in an oxygen atmosphere.
  • the sintering temperature is 750°C. After sintering, the material is crushed. After crushing, Boric acid containing 0.5 mol% B was added to the material for second sintering.
  • the sintering temperature was 400°C to obtain a polycrystalline large particle material with D 50 of 10.0 ⁇ m. When the polycrystalline material was treated at 600°C for 8 hours, its BET increased with a change rate of 11%.
  • LiOH and Ni 0.86 Co 0.08 Mn 0.06 (OH) 2 are mixed according to a molar ratio of 1.12.
  • the mixed material is sintered for the first time in an oxygen atmosphere.
  • the sintering temperature is 812°C.
  • the material is crushed.
  • the material contains B 0.4 mol% boric acid and then undergoes second sintering at a sintering temperature of 400°C to finally obtain a single crystal small particle material with D 50 of 3.5 ⁇ m.
  • the single crystal material was treated at 600°C for 8 hours, and its BET increased with a change rate of 9%.
  • the above-mentioned large polycrystalline particles and small single crystal particles are mixed at a mass ratio of 7:3 to obtain a positive electrode active material for lithium secondary batteries.
  • the positive active material was treated at 600°C for 8 hours, its BET change rate increased by 10%.
  • a 10.5 ⁇ m polycrystalline cathode precursor composed of Ni 0.83 Co 0.11 Mn 0.06 (OH) 2 and a 4 ⁇ m single crystal cathode precursor composed of Ni 0.84 Co 0.08 Mn 0.08 (OH) 2 were separately prepared using a liquid phase co-precipitation method.
  • LiOH and Ni 0.83 Co 0.11 Mn 0.06 (OH) 2 are mixed according to a molar ratio of 1.08.
  • the mixed material is sintered for the first time in an oxygen atmosphere.
  • the sintering temperature is 750°C. After sintering, the material is crushed. After crushing, Boric acid containing 0.5 mol% B was added to the material for second sintering.
  • the sintering temperature was 400°C to obtain a polycrystalline large particle material with D 50 of 10.0 ⁇ m. When the polycrystalline material was treated at 600°C for 8 hours, its BET increased with a change rate of 35%.
  • the mixed material is sintered for the first time in an oxygen atmosphere.
  • the sintering temperature is 812°C.
  • the material is crushed.
  • the material contains B 0.4 mol% boric acid and then undergoes second sintering at a sintering temperature of 400°C to finally obtain a single crystal small particle material with D 50 of 3.5 ⁇ m.
  • the single crystal material was treated at 600°C for 8 hours, and its BET decreased with a change rate of 2%.
  • the above-mentioned large polycrystalline particles and small single crystal particles are mixed at a mass ratio of 7:3 to obtain a positive electrode active material for lithium secondary batteries.
  • the positive active material was treated at 600°C for 8 hours, its BET change rate increased by 24%.
  • a 10.5 ⁇ m polycrystalline cathode precursor composed of Ni 0.83 Co 0.11 Mn 0.06 (OH) 2 and a 4 ⁇ m single crystal cathode precursor composed of Ni 0.80 Co 0.11 Mn 0.09 (OH) 2 were separately prepared using a liquid phase co-precipitation method.
  • LiOH and Ni 0.83 Co 0.11 Mn 0.06 (OH) 2 are mixed according to a molar ratio of 1.08.
  • the mixed material is sintered for the first time in an oxygen atmosphere.
  • the sintering temperature is 750°C. After sintering, the material is crushed. After crushing, Boric acid containing 1 mol% B was added to the material for second sintering.
  • the sintering temperature was 400°C to obtain a polycrystalline large particle material with D 50 of 10.0 ⁇ m. When the polycrystalline material was treated at 600°C for 8 hours, its BET increased with a change rate of 35%.
  • the mixed material is sintered for the first time in an oxygen atmosphere.
  • the sintering temperature is 820°C.
  • the material is crushed.
  • the material is added with Al 2 O 3 containing 1 mol% of Al and then undergoes second sintering.
  • the sintering temperature is 620°C, and finally a single crystal small particle material with D 50 of 3.5 ⁇ m is obtained.
  • the single crystal material was treated at 600°C for 8 hours, and its BET decreased with a change rate of 2%.
  • the above-mentioned large polycrystalline particles and small single crystal particles are mixed at a mass ratio of 7:3 to obtain a positive electrode active material for lithium secondary batteries.
  • the cathode active material was treated at 600°C for 8 hours, and its BET increased by 25%.
  • a 10.5 ⁇ m polycrystalline cathode precursor composed of Ni 0.83 Co 0.11 Mn 0.06 (OH) 2 and a 4 ⁇ m single crystal cathode precursor composed of Ni 0.83 Co 0.11 Mn 0.06 (OH) 2 were separately prepared using a liquid phase co-precipitation method.
  • LiOH and Ni 0.83 Co 0.11 Mn 0.06 (OH) 2 are mixed according to a molar ratio of 1.08.
  • the mixed material is sintered for the first time in an oxygen atmosphere.
  • the sintering temperature is 750°C. After sintering, the material is crushed. After crushing, Boric acid containing 1 mol% B was added to the material for second sintering.
  • the sintering temperature was 400°C to obtain a polycrystalline large particle material with D 50 of 10.0 ⁇ m. When the polycrystalline material was treated at 600°C for 8 hours, its BET increased with a change rate of 35%.
  • the mixed material is sintered for the first time in an oxygen atmosphere.
  • the sintering temperature is 816°C. After sintering, the material is crushed. After crushing, The material is added with Al 2 O 3 containing 1 mol% of Al and then undergoes second sintering. The sintering temperature is 620°C, and finally a single crystal small particle material with D 50 of 3.5 ⁇ m is obtained.
  • the single crystal material was treated at 600°C for 8 hours, and its BET decreased with a change rate of 2%.
  • the above-mentioned large polycrystalline particles and small single crystal particles are mixed at a mass ratio of 7:3 to obtain a positive electrode active material for lithium secondary batteries.
  • the cathode active material was treated at 600°C for 8 hours, and its BET increased by 25%.
  • Tri-star 3020 specific surface meter for testing, weigh 3 grams of sample, and install the sample tube to the vacuum connector on the degassing station. Set the heating temperature to 300°C and the degassing time to 120 minutes. After degassing is completed, cool the sample tube. Input the mass of the empty sample tube and the mass of the degassed sample and sample tube in the tester software interface, record the specific surface area data output after calculation by the software (BET method), and complete the test of the specific surface area of the cathode material sample;
  • the composite nickel-cobalt-manganese multi-component cathode active material for non-aqueous electrolyte secondary batteries, acetylene black and polyvinylidene fluoride (PVDF) are mixed and then coated on aluminum foil and dried. Assemble the dried positive electrode sheet, separator, negative electrode sheet and electrolyte into a 2025 button battery in an Ar gas glove box with a water content and oxygen content of less than 5 ppm.
  • First discharge capacity test method After making the button battery, place it for 2 hours. After the open circuit voltage stabilizes, charge the positive electrode with a current density of 0.1C to a cut-off voltage of 4.3V, then charge at a constant voltage for 30 minutes, and then discharge at the same current density. to the cut-off voltage of 3.0V; do it again in the same way, and use the discharge capacity as the first discharge capacity.
  • Figure 4 shows the charge and discharge curves of button batteries prepared from the cathode materials in Example 1 and Comparative Examples 1 and 2. It can be seen that the cathode material in Example 1 has a higher first discharge capacity than the Comparative Example.
  • the lithium nickel cobalt manganate cathode material, graphite anode material, carbon black conductive agent, and binder PVDF into a vacuum oven at 120°C to dry for 12 hours.
  • the slurry is coated on the aluminum foil using a lithium battery coater and dried, the pole pieces are cut using a pole piece slitting machine, and the pole pieces are rolled using a pole piece roller press.
  • small-grain single-crystal materials can enter the gaps between large polycrystalline particles and form a synergistic effect of mutual support and gap-filling with large-grain polycrystals, effectively increasing the compaction density of the material;

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Abstract

正极活性材料、其制备方法以及包含正极活性材料的锂二次电池，正极活性材料包含式Li1+a1Nix1Coy1Mz1M'1-x1-y1-z1O 2表示的多晶颗粒和式Li1+a2Nix2Coy2Mz2M'1-x2-y2-z2O2表示的单晶颗粒，其中，M为一种或两种选自Mn、Al的元素，M'为一种或多种选自B、F、Mg、Si、P、Ca、Ti、V、Cr、Fe、Ga、Sr、Y、Zr、Nb、Mo、Sn、Ba、La、Ce、W的元素，–0.03≤a1≤0.20，0.30≤x1≤0.99，0≤y1≤0.30，0≤z1≤0.30，0≤1–x1–y1–z1≤0.10，–0.03≤a2≤0.20，0.31≤x2≤1.00，0≤y2≤0.30，0≤z2≤0.30，0≤1–x2–y2–z2≤0.10，0<x2–x1≤0.5。

Description

用于锂二次电池的正极活性材料及其制备方法 技术领域
本发明涉及正极活性材料、其制备方法以及包含所述正极活性材料的锂二次电池。
背景技术
近年来，随着能源和环境危机加重，风能、太阳能等自然能源得到大力发展，但是这些能源的使用效率低下，不能满足大规模的能源使用缺口。锂离子电池是一种绿色二次电池，具有工作电压高、能量密度大、循环寿命好、自放电小、无记忆效应等突出优点，得到迅猛发展。
在锂离子电池领域，层状三元材料(NCM)由于其具有较高的比容量和稳定性，极具发展潜力。但是，随着NCM中镍含量的提升，材料的稳定性逐渐下降。在充电过程中产生的高活性Ni 4+与电解液的反应会生成类NiO岩盐相，严重破坏层状材料的结构，导致正极结构坍塌，进而诱发过渡金属离子溶解、相转变和晶格氧析出。目前常规的多晶NCM的“二次颗粒”通常由许多纳米级“一次粒子”组成，在充放电过程中因晶格参数发生变化，会导致二次颗粒微裂纹的形成。形成的微裂纹会暴露二次颗粒内部的新鲜界面，进一步加速性能衰减。值得注意的是，镍含量越高，裂纹的破坏效果越明显。综上所述，NCM尤其是高镍NCM循环寿命下降的主要原因是微裂纹，裂纹会造成正极材料的热稳定性、结构稳定性和循环稳定性同时降低。
目前为了改善高镍多晶材料微裂纹的产生，多数研究采用包覆和掺杂等技术改进大颗粒的强度，但是在制作成电池的过程中，压实密度很难提升。同等镍含量下，多晶小颗粒容量相比大颗粒会高，但是循环和产气性能都有所下降。单晶小颗粒形貌和多晶小颗粒形貌不同，其颗粒 强度相对较高，但是容量和产气性能也难以达到理想水平，筛分和制浆也存在较大的问题。
专利CN 109962221 B采用团聚体掺混类单晶材料，主要成分为单晶类磷酸锰铁锂材料和团聚类多元材料，多元和磷酸锰铁锂属于两种不同的正极材料，其测试电压和使用范围都不相同，所以强行把两种材料混在一起，难免会牺牲各自的优势，造成资源浪费。专利号为CN 107154491 B的专利将两种不同电导的材料混合在一起，分别考虑了两种材料的容量，但是并未考虑两种不同材料的Ni含量对最终产品带来的影响，将两种材料混合在一起，其粒度保护范围也相对较宽，最终产品的效果难以确定。
发明内容
本发明的目的在于克服现有技术的不足，有效改善掺混产品容量低、循环差的缺陷。本发明通过设置小颗粒Ni含量高于大颗粒Ni含量，有效地提升正极活性材料的容量；此外，通过制备多晶大颗粒和单晶小颗粒，控制其不同的表面特性，有效抑制多晶大颗粒微裂纹的产生，从而改善正极活性材料在长期循环过程中的稳定性。本发明提供的正极活性材料具有高压实、高容量、高稳定的性质。
一方面，本发明提供用于锂二次电池的正极活性材料，其特征在于，所述正极活性材料包含式A1表示的多晶颗粒和式A2表示的单晶颗粒
A1：Li 1+a1Ni x1Co y1M z1M′ 1-x1-y1-z1O 2
A2：Li 1+a2Ni x2Co y2M z2M′ 1-x2-y2-z2O 2
其中，
M为一种或两种选自Mn、Al的元素，
M′为一种或多种选自B、F、Mg、Si、P、Ca、Ti、V、Cr、Fe、Ga、Sr、Y、Zr、Nb、Mo、Sn、Ba、La、Ce、W的元素， –0.03≤a1≤0.20，0.30≤x1≤0.99，0≤y1≤0.30，0≤z1≤0.30，0≤1–x1–y1–z1≤0.10，–0.03≤a2≤0.20，0.31≤x2≤1.00，0≤y2≤0.30，0≤z2≤0.30，0≤1–x2–y2–z2≤0.10，其条件是：0<x2–x1≤0.5。
另一方面，本发明还提供制备正极活性材料的方法，其包括以下步骤：
i)采用液相共沉淀法分别制备式A3表示的多晶颗粒前驱体和式A4表示的单晶颗粒前驱体
A3：Ni x1Co y1M z1M′ 1-x1-y1-z1(OH) 2
A4：Ni x2Co y2M z2M′ 1-x2-y2-z2(OH) 2
其中，
M为一种或两种选自Mn、Al的元素，
M′为一种或多种选自B、F、Mg、Si、P、Ca、Ti、V、Cr、Fe、Ga、Sr、Y、Zr、Nb、Mo、Sn、Ba、La、Ce、W的元素，0.30≤x1≤0.99，0≤y1≤0.30，0≤z1≤0.30，0≤1–x1–y1–z1≤0.10，0.31≤x2≤1.00，0≤y2≤0.30，0≤z2≤0.30，0≤1–x2–y2–z2≤0.10，其条件是：0<x2–x1≤0.5；
ii)将锂源与所述多晶颗粒前驱体按照摩尔比r1进行混合，任选混入M′作为掺杂元素，其中0.97≤r1≤1.20；然后在烧结温度T1下于空气或氧气的烧结气氛中进行初次烧结，其中600℃≤T1≤1000℃；然后经破碎得到多晶颗粒；
iii)将锂源与所述单晶颗粒前驱体按照摩尔比r2进行混合，任选混入M′作为掺杂元素，其中0.97≤r2≤1.20；然后在烧结温度T2下于空气或氧气的烧结气氛中进行初次烧结，其中650℃≤T2≤1050℃；然后经破碎得到单晶颗粒；及
iv)将步骤ii)的所述多晶颗粒与步骤iii)的所述单晶颗粒进行掺混得到所述正极活性材料。
再一方面，本发明还提供锂二次电池，其包含根据本发明的正极活性材料或通过根据本发明的制备方法制得的正极活性材料。
附图说明
图1至3所示分别为实施例1中的多晶大颗粒A1和单晶小颗粒A2及两者掺混后的SEM照片；
图4所示为实施例1、对比例1、对比例2的充放电曲线；及
图5所示为实施例1、对比例1、对比例2的循环寿命。
具体实施方式
若没有另外说明，将在此提及的所有的出版物、专利申请、专利及其他参考文献的全部内容出于所有目的明确地引入本申请作为参考，如同充分地阐述。
除非另有定义，在此使用的所有的技术和科学术语具有与本发明所属技术领域的普通技术人员通常的理解相同的含义。若有冲突，则以本说明书为准，包括定义。
若数量、浓度或其他数值或参数作为范围、优选的范围或者一系列优选的上限和优选的下限给出，则应当理解为特别地公开了由任意一对的任意范围上限或优选的数值与任意范围下限或优选的数值形成的所有的范围，无论这些范围是否被分别地公开。在此提及数值的范围时，除非另有说明，意味着该范围包括其端点以及在该范围内的所有的整数和分数。
一方面，本发明涉及用于锂二次电池的正极活性材料，其特征在于，所述正极活性材料包含式A1表示的多晶颗粒和式A2表示的单晶颗粒
A1：Li 1+a1Ni x1Co y1M z1M′ 1-x1-y1-z1O 2
A2：Li 1+a2Ni x2Co y2M z2M′ 1-x2-y2-z2O 2
其中，
M为一种或两种选自Mn、Al的元素，
M′为一种或多种选自B、F、Mg、Si、P、Ca、Ti、V、Cr、Fe、Ga、Sr、Y、Zr、Nb、Mo、Sn、Ba、La、Ce、W的元素，–0.03≤a1≤0.20，优选为–0.01≤a1≤0.14，更优选为0≤a1≤0.10，特别优选为0.01≤a1≤0.08，0.30≤x1≤0.99，优选为0.57≤x1≤0.99，更优选为0.72≤x1≤0.99，特别优选为0.80≤x1≤0.99，0≤y1≤0.30，优选为0≤y1≤0.21，更优选为0≤y1≤0.15，特别优选为0≤y1≤0.10，0≤z1≤0.30，优选为0≤z1≤0.18，更优选为0≤z1≤0.11，特别优选为0≤z1≤0.06，0≤1–x1–y1–z1≤0.10，优选为0≤1–x1–y1–z1≤0.08，更优选为0≤1–x1–y1–z1≤0.05，特别优选为0≤1–x1–y1–z1≤0.03，–0.03≤a2≤0.20，优选为–0.02≤a2≤0.16，更优选为–0.01≤a2≤0.14，特别优选为0≤a2≤0.08，0.31≤x2≤1.00，优选为0.59≤x2≤0.995，更优选为0.75≤x2≤0.995，特别优选为0.81≤x2≤0.995，0≤y2≤0.30，优选为0≤y2≤0.21，更优选为0≤y2≤0.15，特别优选为0≤y2≤0.10，0≤z2≤0.30，优选为0≤z2≤0.18，更优选为0≤z2≤0.11，特别优选为0≤z2≤0.08，0≤1–x2–y2–z2≤0.10，优选为0≤1–x2–y2–z2≤0.08，更优选为0≤1–x2–y2–z2≤0.05，特别优选为0≤1–x2–y2–z2≤0.03， 其条件是：0<x2–x1≤0.5，优选为0.01≤x2–x1≤0.27，更优选为0.01≤x2–x1≤0.20，进一步优选为0.015≤x2–x1≤0.20，特别优选为0.02≤x2–x1≤0.15。
依照根据本发明的正极活性材料的一个实施方案，a2>a1，优选为0.01≤a2–a1≤0.20，更优选为0.01≤a2–a1≤0.12，特别优选为0.01≤a2–a1≤0.07，尤其优选为0.01≤a2–a1≤0.04。
依照根据本发明的正极活性材料的另一个实施方案，所述多晶颗粒的粒度D 50为6至30μm，优选为8至25μm，更优选为9至20μm，特别优选为10至18μm。
依照根据本发明的正极活性材料的另一个实施方案，所述单晶颗粒的粒度D 50为0.1至10μm，优选为0.5至8.0μm，更优选为1.0至6.0μm，特别优选为1.5至4.5μm。
依照根据本发明的正极活性材料的另一个实施方案，基于所述正极活性材料的重量，所述多晶颗粒的含量为20至90％，优选为45至85％，更优选为50至80％，特别优选为60至80％，所述单晶颗粒的含量为10至80％，优选为10至70％，更优选为15至60％，特别优选为20至40％。
依照根据本发明的正极活性材料的另一个实施方案，所述多晶颗粒具有包含至少一种选自以下组中的包覆元素的包覆层：B、F、Mg、Al、Si、P、Ca、Ti、V、Cr、Fe、Ga、Sr、Y、Zr、Nb、Mo、Sn、Ba、La、Ce、W，其中基于所述多晶颗粒，所述包覆元素的含量为0.1至2摩尔％，优选为约1摩尔％；和/或，所述单晶颗粒具有包含至少一种选自以下组中的包覆元素的包覆层：B、F、Mg、Al、Si、P、Ca、Ti、V、Cr、Fe、Ga、Sr、Y、Zr、Nb、Mo、Sn、Ba、La、Ce、W，其中基于所述单晶颗粒，所述包覆元素的含量为0.1至2摩尔％，优选为约1摩尔％；其条件是：所述多晶颗粒的包覆层所包含的包覆元素不同于所述单晶颗粒的包覆层所包含的包覆元素。
依照根据本发明的正极活性材料的另一个实施方案，所述正极活性材料在600℃下于空气气氛中烧结8小时前后的比表面积BET 前和BET 后满足：
|BET 后–BET 前|/BET 前≤50％，
优选为|BET 后–BET 前|/BET 前≤30％。
本发明使用表面圆润的单晶颗粒和颗粒强度高的多晶颗粒，结合优选的掺混比例，控制成品材料暴露出稳定的晶体结构，从而使该成品在进一步烧结过程中，其表面孔隙的变化率较低。
依照根据本发明的正极活性材料的另一个实施方案，所述多晶颗粒在600℃下于空气气氛中烧结8小时前后的比表面积BET 前和BET 后满足：
(BET 后–BET 前)/BET 前≥15％，
优选为40％≥(BET 后–BET 前)/BET 前≥20％。
多晶颗粒是由多个纳米级颗粒组成的，为了保持较好的循环性能，纳米颗粒表面的空隙不能过多，材料的BET需要控制在一定的范围内。通常情况下，经过高温烧结，材料的BET会进一步降低，但是本发明通过控制材料表面纳米晶粒的结晶性及取向，结合原位熔融态的表面处理，能起到良好的表界面保护作用，并且意外发现使得材料表面的BET不降反升。本发明人进一步发现，具有此表面BET性质的多晶颗粒在和单晶颗粒掺混后，正极材料表现出较为优异的抗压特性和较好的放电容量和循环性能。
依照根据本发明的正极活性材料的另一个实施方案，所述单晶颗粒在600℃下于空气气氛中烧结8小时前后的比表面积BET 前和BET 后满足：
(BET 前–BET 后)/BET 前≤15％，
优选为0≤(BET 前–BET 后)/BET 前≤10％。
本发明的单晶颗粒由于结晶性良好且表面圆润等特点，使其结构较为稳定，材料在高温烧结过程中，并未出现很大程度的坍塌及闭合，其BET相对于未烧结材料的BET变化较小。
依照根据本发明的正极活性材料的另一个实施方案，所述正极活性材料不包含无镍的活性材料，例如磷酸锰铁锂。
依照根据本发明的正极活性材料的另一个实施方案，所述正极活性材料由式A1表示的多晶颗粒和式A2表示的单晶颗粒组成。
另一方面，本发明还涉及制备正极活性材料的方法，其包括以下步骤：
i)采用液相共沉淀法分别制备式A3表示的多晶颗粒前驱体和式A4表示的单晶颗粒前驱体
A3：Ni x1Co y1M z1M′ 1-x1-y1-z1(OH) 2
A4：Ni x2Co y2M z2M′ 1-x2-y2-z2(OH) 2
其中，
M为一种或两种选自Mn、Al的元素，
M′为一种或多种选自B、F、Mg、Si、P、Ca、Ti、V、Cr、Fe、Ga、Sr、Y、Zr、Nb、Mo、Sn、Ba、La、Ce、W的元素，0.30≤x1≤0.99，优选为0.57≤x1≤0.99，更优选为0.72≤x1≤0.99，特别优选为0.80≤x1≤0.99，0≤y1≤0.30，优选为0≤y1≤0.21，更优选为0≤y1≤0.15，特别优选为0≤y1≤0.10，0≤z1≤0.30，优选为0≤z1≤0.18，更优选为0≤z1≤0.11，特别优选为0≤z1≤0.06，0≤1–x1–y1–z1≤0.10，优选为0≤1–x1–y1–z1≤0.08，更优选为0≤1–x1–y1–z1≤0.05，特别优选为0≤1–x1–y1–z1≤0.03，0.31≤x2≤1.00，优选为0.59≤x2≤0.995，更优选为0.75≤x2≤0.995，特别优选为0.81≤x2≤0.995， 0≤y2≤0.30，优选为0≤y2≤0.21，更优选为0≤y2≤0.15，特别优选为0≤y2≤0.10，0≤z2≤0.30，优选为0≤z2≤0.18，更优选为0≤z2≤0.11，特别优选为0≤z2≤0.08，0≤1–x2–y2–z2≤0.10，优选为0≤1–x2–y2–z2≤0.08，更优选为0≤1–x2–y2–z2≤0.05，特别优选为0≤1–x2–y2–z2≤0.03，其条件是：0<x2–x1≤0.5，优选为0.01≤x2–x1≤0.27，更优选为0.01≤x2–x1≤0.20，进一步优选为0.015≤x2–x1≤0.20，特别优选为0.02≤x2–x1≤0.15；
ii)将锂源与所述多晶颗粒前驱体按照摩尔比r1进行混合，任选混入M′作为掺杂元素，其中0.97≤r1≤1.20，优选为0.99≤r1≤1.14，更优选为1.00≤r1≤1.10，特别优选为1.01≤r1≤1.08；然后在烧结温度T1下于空气或氧气、优选为氧气的烧结气氛中进行初次烧结，其中600℃≤T1≤1000℃，优选为675℃≤T1≤875℃，更优选为690℃≤T1≤800℃，特别优选为690℃≤T1≤780℃；然后经破碎得到多晶颗粒；
iii)将锂源与所述单晶颗粒前驱体按照摩尔比r2进行混合，任选混入M′作为掺杂元素，其中0.97≤r2≤1.20，优选为0.98≤r2≤1.16，更优选为0.99≤r2≤1.14，特别优选为1.00≤r2≤1.08；然后在烧结温度T2下于空气或氧气、优选为氧气的烧结气氛中进行初次烧结，其中650℃≤T2≤1050℃，优选为730℃≤T2≤930℃，更优选为750℃≤T2≤930℃，特别优选为750℃≤T2≤900℃；然后经破碎得到单晶颗粒；及
iv)将步骤ii)的所述多晶颗粒与步骤iii)的所述单晶颗粒进行掺混得到所述正极活性材料。
依照根据本发明的方法的一个实施方案，r2>r1，优选为0.01≤r2–r1≤0.20，更优选为0.01≤r2–r1≤0.12，特别优选为 0.01≤r2–r1≤0.07，尤其优选为0.01≤r2–r1≤0.04。
依照根据本发明的方法的另一个实施方案，所述多晶颗粒前驱体的粒度D 50为6.5至30.5μm，优选为8.5至25.5μm，更优选为9.5至20.5μm，特别优选为10.5至18.5μm。所述多晶颗粒的粒度D 50为6至30μm，优选为8至25μm，更优选为9至20μm，特别优选为10至18μm。
依照根据本发明的方法的另一个实施方案，所述单晶颗粒前驱体的粒度D 50为0.1至30.5μm，优选为1.0至17.3μm，更优选为1.0至9.3μm，特别优选为1.0至6.0μm。所述单晶颗粒的粒度D 50为0.1至10μm，优选为0.5至8.0μm，更优选为1.0至6.0μm，特别优选为1.5至4.5μm。
依照根据本发明的方法的另一个实施方案，基于所述正极活性材料的重量，所述多晶颗粒的含量为20至90％，优选为45至85％，更优选为50至80％，特别优选为60至80％，所述单晶颗粒的含量为10至80％，优选为10至70％，更优选为15至60％，特别优选为20至40％。
依照根据本发明的方法的另一个实施方案，在步骤iv)之前，将所述多晶颗粒与包含至少一种选自以下组中的包覆元素的包覆前驱体进行混合：B、F、Mg、Al、Si、P、Ca、Ti、V、Cr、Fe、Ga、Sr、Y、Zr、Nb、Mo、Sn、Ba、La、Ce、W，然后在烧结温度T3下于空气或氧气、优选为氧气的烧结气氛中进行二次烧结，得到经二次烧结的多晶颗粒，其中250℃≤T3≤800℃，优选为250℃≤T3≤600℃，更优选为250℃≤T3≤480℃，特别优选为250℃≤T3≤400℃，其中基于所述多晶颗粒，所述包覆元素的含量为0.1至2摩尔％，优选为约1摩尔％；和/或，将所述单晶颗粒与包含至少一种选自以下组中的包覆元素的包覆前驱体进行混合：B、F、Mg、Al、Si、P、Ca、Ti、V、Cr、Fe、Ga、Sr、Y、Zr、Nb、Mo、Sn、Ba、La、Ce、W，然后在烧结温度T4下于空气或氧气、优选为氧气的烧结气氛中进行二次烧结，得到经二次烧结的单晶颗粒，其中300℃≤T4≤900℃，优选为460℃≤T4≤800℃，更优选为550℃≤T4≤750℃，特别优选为600℃≤T4≤750℃，其中基于所述 单晶颗粒，所述包覆元素的含量为0.1至2摩尔％，优选为约1摩尔％；其条件是：所述多晶颗粒的包覆前驱体所包含的包覆元素不同于所述单晶颗粒的包覆前驱体所包含的包覆元素。
另一方面，本发明还涉及锂二次电池，其包含根据本发明的正极活性材料或通过根据本发明的制备方法制得的正极活性材料。
实施例
实施例1
首先采用液相共沉淀方法单独制备组成为Ni 0.83Co 0.11Mn 0.06(OH) 2的10.5μm多晶正极前驱体和组成为Ni 0.86Co 0.08Mn 0.06(OH) 2的4μm单晶正极前驱体。
将LiOH与Ni 0.83Co 0.11Mn 0.06(OH) 2按照摩尔比为1.08混合，混合后的物料在氧气气氛下进行第一次烧结，烧结温度为750℃，烧结后对物料进行破碎，破碎后的物料加入含B 1mol％的硼酸进行第二烧结，烧结温度为400℃，得到D 50为10.0μm多晶大颗粒材料，如图1所示。该多晶材料在600℃下处理8小时，其BET增大，变化率为35％。
将LiOH与Ni 0.86Co 0.08Mn 0.06(OH) 2按照摩尔比为1.12混合，混合后的物料在氧气气氛下进行第一次烧结，烧结温度为812℃，烧结后对物料进行破碎，破碎后的物料加入含Al 1mol％的Al 2O 3后进行第二烧结，烧结温度为620℃，最终得到D 50为3.5μm单晶小颗粒材料，如图2所示。该单晶材料在600℃下处理8小时，其BET减小，变化率为2％。
将上述多晶大颗粒和单晶小颗粒按照质量比7:3进行混合，得到用于锂二次电池的正极活性材料，如图3所示。该正极活性材料在600℃下处理8小时，其BET变化率为增大24％。
实施例2
首先采用液相共沉淀方法单独制备组成为Ni 0.83Co 0.11Mn 0.06(OH) 2的10.5μm多晶正极前驱体和组成为Ni 0.86Co 0.08Mn 0.06(OH) 2的4μm单晶正极前驱体。
将LiOH与Ni 0.83Co 0.11Mn 0.06(OH) 2按照摩尔比为1.06混合，混合后的物料在氧气气氛下进行第一次烧结，烧结温度为745℃，烧结后对物料进行破碎，破碎后的物料加入含B 0.8mol％的硼酸进行第二烧结，烧结温度为380℃，得到D 50为10.0μm多晶大颗粒材料。该多晶材料在600℃下处理8小时，其BET增大，变化率为24％。
将LiOH与Ni 0.86Co 0.08Mn 0.06(OH) 2按照摩尔比为1.12混合，混合后的物料在氧气气氛下进行第一次烧结，烧结温度为812℃，烧结后对物料进行破碎，破碎后的物料加入含Al 1.2mol％的Al 2O 3后进行第二烧结，烧结温度为610℃，最终得到D 50为3.5μm单晶小颗粒材料。该单晶材料在600℃下处理8小时，其BET减小，变化率为3％。
将上述多晶大颗粒和单晶小颗粒按照质量比8:2进行混合，得到用于锂二次电池的正极活性材料。该正极活性材料在600℃下处理8小时，其BET变化率为增大19％。
实施例3
首先采用液相共沉淀方法单独制备组成为Ni 0.86Co 0.11Mn 0.03(OH) 2的10.5μm多晶正极前驱体和组成为Ni 0.88Co 0.08Mn 0.04(OH) 2的4μm单晶正极前驱体。
将LiOH与Ni 0.86Co 0.11Mn 0.03(OH) 2按照摩尔比为1.06混合，混合后的物料在氧气气氛下进行第一次烧结，烧结温度为725℃，烧结后对物料进行破碎，破碎后的物料加入含B 0.8mol％的硼酸进行第二烧结，烧结温度为380℃，得到D 50为10.0μm多晶大颗粒材料。该多晶材料在600℃下处理8小时，其BET增大，变化率为26％。
将LiOH与Ni 0.88Co 0.08Mn 0.04(OH) 2按照摩尔比为1.11混合，混合后的物料在氧气气氛下进行第一次烧结，烧结温度为805℃，烧结后对物料进行破碎，破碎后的物料加入含Al 1.0mol％的Al 2O 3后进行第二烧结，烧结温度为610℃，最终得到D 50为3.5μm单晶小颗粒材料。该单晶材料在600℃下处理8小时，其BET减小，变化率为2％。
将上述多晶大颗粒和单晶小颗粒按照质量比7:3进行混合，得到用于锂二次电池的正极活性材料。该正极活性材料在600℃下处理8小时，其BET变化率为增大20％。
实施例4
首先采用液相共沉淀方法单独制备组成为Ni 0.86Co 0.11Mn 0.03(OH) 2的10.5μm多晶正极前驱体和组成为Ni 0.88Co 0.08Mn 0.04(OH) 2的4μm单晶正极前驱体。
将LiOH与Ni 0.86Co 0.11Mn 0.03(OH) 2按照摩尔比为1.06混合，混合后的物料在氧气气氛下进行第一次烧结，烧结温度为685℃，烧结后对物料进行破碎，破碎后的物料加入含B 0.8mol％的硼酸进行第二烧结，烧结温度为380℃，得到D 50为10.0μm多晶大颗粒材料。该多晶材料在600℃下处理8小时，其BET增大，变化率为26％。
将LiOH与Ni 0.88Co 0.08Mn 0.04(OH) 2按照摩尔比为1.11混合，混合后的物料在氧气气氛下进行第一次烧结，烧结温度为805℃，烧结后对物料进行破碎，破碎后的物料加入含Al 1.0mol％的Al 2O 3后进行第二烧结，烧结温度为610℃，最终得到D 50为3.5μm单晶小颗粒材料。该单晶材料在600℃下处理8小时，其BET减小，变化率为2％。
将上述多晶大颗粒和单晶小颗粒按照质量比3:7进行混合，得到用于锂二次电池的正极活性材料。该正极活性材料在600℃下处理8小时，其BET变化率为增大6％。
实施例5
首先采用液相共沉淀方法单独制备组成为Ni 0.88Co 0.10Mn 0.02(OH) 2的10.5μm多晶正极前驱体和组成为Ni 0.90Co 0.08Mn 0.02(OH) 2的4μm单晶正极前驱体。
将LiOH与Ni 0.88Co 0.10Mn 0.02(OH) 2按照摩尔比为1.08混合，混合后的物料在氧气气氛下进行第一次烧结，烧结温度为780℃，烧结后对物料进行破碎，破碎后的物料加入含B 1mol％的硼酸进行第二烧结，烧结温度为400℃，得到D 50为10.0μm多晶大颗粒材料。该多晶材料在600℃下处理8小时，其BET增大，变化率为32％。
将LiOH与Ni 0.90Co 0.08Mn 0.02(OH) 2按照摩尔比为1.12混合，混合后的物料在氧气气氛下进行第一次烧结，烧结温度为812℃，烧结后对物料进行破碎，破碎后的物料加入含Al 1mol％的Al 2O 3后进行第二烧结，烧结温度为620℃，最终得到D 50为3.5μm单晶小颗粒材料。该单晶材料在600℃下处理8小时，其BET减小，变化率为2％。
将上述多晶大颗粒和单晶小颗粒按照质量比7:3进行混合，得到用于锂二次电池的正极活性材料。该正极活性材料在600℃下处理8小时，其BET变化率为增大22％。
实施例6
首先采用液相共沉淀方法单独制备组成为Ni 0.83Co 0.11Mn 0.06(OH) 2的10.5μm多晶正极前驱体和组成为Ni 0.86Co 0.08Mn 0.06(OH) 2的4μm单晶正极前驱体。
将LiOH与Ni 0.83Co 0.11Mn 0.06(OH) 2按照摩尔比为1.08混合，混合后的物料在氧气气氛下进行第一次烧结，烧结温度为750℃，烧结后对物料进行破碎，破碎后的物料加入含B 1mol％的硼酸进行第二烧结，烧结温度为400℃，得到D 50为10.0μm多晶大颗粒材料。该多晶材料在600℃下处理8小时，其BET增大，变化率为35％。
将LiOH与Ni 0.86Co 0.08Mn 0.06(OH) 2按照摩尔比为1.12混合，混合后的物料在氧气气氛下进行第一次烧结，烧结温度为812℃，烧结后对物料进行破碎，破碎后的物料含B 0.4mol％的硼酸后进行第二烧结，烧结温度为400℃，最终得到D 50为3.5μm单晶小颗粒材料。该单晶材料在600℃下处理8小时，其BET增加，变化率为9％。
将上述多晶大颗粒和单晶小颗粒按照质量比7:3进行混合，得到用于锂二次电池的正极活性材料。该正极活性材料在600℃下处理8小时，其BET变化率为增大27％。
实施例7
首先采用液相共沉淀方法单独制备组成为Ni 0.83Co 0.11Mn 0.06(OH) 2的10.5μm多晶正极前驱体和组成为Ni 0.86Co 0.08Mn 0.06(OH) 2的4μm单晶正极前驱体。
将LiOH与Ni 0.83Co 0.11Mn 0.06(OH) 2按照摩尔比为1.08混合，混合后的物料在氧气气氛下进行第一次烧结，烧结温度为750℃，烧结后对物料进行破碎，破碎后的物料加入含B 0.5mol％的硼酸进行第二烧结，烧结温度为400℃，得到D 50为10.0μm多晶大颗粒材料。该多晶材料在600℃下处理8小时，其BET增大，变化率为11％。
将LiOH与Ni 0.86Co 0.08Mn 0.06(OH) 2按照摩尔比为1.12混合，混合后的物料在氧气气氛下进行第一次烧结，烧结温度为812℃，烧结后对物料进行破碎，破碎后的物料加入含Al 1mol％的Al 2O 3后进行第二烧结，烧结温度为620℃，最终得到D 50为3.5μm单晶小颗粒材料。该单晶材料在600℃下处理8小时，其BET减小，变化率为2％。
将上述多晶大颗粒和单晶小颗粒按照质量比7:3进行混合，得到用于锂二次电池的正极活性材料。该正极活性材料在600℃下处理8小时，其BET变化率为增大7％。
实施例8
首先采用液相共沉淀方法单独制备组成为Ni 0.83Co 0.11Mn 0.06(OH) 2的10.5μm多晶正极前驱体和组成为Ni 0.86Co 0.08Mn 0.06(OH) 2的4μm单晶正极前驱体。
将LiOH与Ni 0.83Co 0.11Mn 0.06(OH) 2按照摩尔比为1.08混合，混合后的物料在氧气气氛下进行第一次烧结，烧结温度为750℃，烧结后对物料进行破碎，破碎后的物料加入含Al 1mol％的Al 2O 3进行第二烧结，烧结温度为620℃，得到D 50为10.0μm多晶大颗粒材料。该多晶材料在600℃下处理8小时，其BET减小，变化率为3％。
将LiOH与Ni 0.86Co 0.08Mn 0.06(OH) 2按照摩尔比为1.12混合，混合后的物料在氧气气氛下进行第一次烧结，烧结温度为812℃，烧结后对物料进行破碎，破碎后的物料加入含Al 1mol％的Al 2O 3后进行第二烧结，烧结温度为620℃，最终得到D 50为3.5μm单晶小颗粒材料。该单晶材料在600℃下处理8小时，其BET减小，变化率为2％。
将上述多晶大颗粒和单晶小颗粒按照质量比7:3进行混合，得到用于锂二次电池的正极活性材料。该正极活性材料在600℃下处理8小时，其BET变化率为减小3％。
实施例9
首先采用液相共沉淀方法单独制备组成为Ni 0.83Co 0.11Mn 0.06(OH) 2的10.5μm多晶正极前驱体和组成为Ni 0.86Co 0.08Mn 0.06(OH) 2的4μm单晶正极前驱体。
将LiOH与Ni 0.83Co 0.11Mn 0.06(OH) 2按照摩尔比为1.08混合，混合后的物料在氧气气氛下进行第一次烧结，烧结温度为750℃，烧结后对物料进行破碎，破碎后的物料加入含B 0.5mol％的硼酸进行第二烧结，烧结温度为400℃，得到D 50为10.0μm多晶大颗粒材料。该多晶材料在600℃下处理8小时，其BET增大，变化率为11％。
将LiOH与Ni 0.86Co 0.08Mn 0.06(OH) 2按照摩尔比为1.12混合，混合后的物料在氧气气氛下进行第一次烧结，烧结温度为812℃，烧结后对物料进行破碎，破碎后的物料含B 0.4mol％的硼酸后进行第二烧结，烧结温度为400℃，最终得到D 50为3.5μm单晶小颗粒材料。该单晶材料在600℃下处理8小时，其BET增加，变化率为9％。
将上述多晶大颗粒和单晶小颗粒按照质量比7:3进行混合，得到用于锂二次电池的正极活性材料。该正极活性材料在600℃下处理8小时，其BET变化率为增大10％。
实施例10
首先采用液相共沉淀方法单独制备组成为Ni 0.83Co 0.11Mn 0.06(OH) 2的10.5μm多晶正极前驱体和组成为Ni 0.84Co 0.08Mn 0.08(OH) 2的4μm单晶正极前驱体。
将LiOH与Ni 0.83Co 0.11Mn 0.06(OH) 2按照摩尔比为1.08混合，混合后的物料在氧气气氛下进行第一次烧结，烧结温度为750℃，烧结后对物料进行破碎，破碎后的物料加入含B 0.5mol％的硼酸进行第二烧结，烧结温度为400℃，得到D 50为10.0μm多晶大颗粒材料。该多晶材料在600℃下处理8小时，其BET增大，变化率为35％。
将LiOH与Ni 0.84Co 0.08Mn 0.08(OH) 2按照摩尔比为1.12混合，混合后的物料在氧气气氛下进行第一次烧结，烧结温度为812℃，烧结后对物料进行破碎，破碎后的物料含B 0.4mol％的硼酸后进行第二烧结，烧结温度为400℃，最终得到D 50为3.5μm单晶小颗粒材料。该单晶材料在600℃下处理8小时，其BET减小，变化率为2％。
将上述多晶大颗粒和单晶小颗粒按照质量比7:3进行混合，得到用于锂二次电池的正极活性材料。该正极活性材料在600℃下处理8小时，其BET变化率为增大24％。
对比例1
首先采用液相共沉淀方法单独制备组成为Ni 0.83Co 0.11Mn 0.06(OH) 2的10.5μm多晶正极前驱体和组成为Ni 0.80Co 0.11Mn 0.09(OH) 2的4μm单晶正极前驱体。
将LiOH与Ni 0.83Co 0.11Mn 0.06(OH) 2按照摩尔比为1.08混合，混合后的物料在氧气气氛下进行第一次烧结，烧结温度为750℃，烧结后对物料进行破碎，破碎后的物料加入含B 1mol％的硼酸进行第二烧结，烧结温度为400℃，得到D 50为10.0μm多晶大颗粒材料。该多晶材料在600℃下处理8小时，其BET增大，变化率为35％。
将LiOH与Ni 0.80Co 0.11Mn 0.09(OH) 2按照摩尔比为1.12混合，混合后的物料在氧气气氛下进行第一次烧结，烧结温度为820℃，烧结后对物料进行破碎，破碎后的物料加入含Al 1mol％的Al 2O 3后进行第二烧结，烧结温度为620℃，最终得到D 50为3.5μm单晶小颗粒材料。该单晶材料在600℃下处理8小时，其BET减小，变化率为2％。
将上述多晶大颗粒和单晶小颗粒按照质量比7:3进行混合，得到用于锂二次电池的正极活性材料。该正极活性材料在600℃下处理8小时，其BET增大25％。
对比例2
首先采用液相共沉淀方法单独制备组成为Ni 0.83Co 0.11Mn 0.06(OH) 2的10.5μm多晶正极前驱体和组成为Ni 0.83Co 0.11Mn 0.06(OH) 2的4μm单晶正极前驱体。
将LiOH与Ni 0.83Co 0.11Mn 0.06(OH) 2按照摩尔比为1.08混合，混合后的物料在氧气气氛下进行第一次烧结，烧结温度为750℃，烧结后对物料进行破碎，破碎后的物料加入含B 1mol％的硼酸进行第二烧结，烧结温度为400℃，得到D 50为10.0μm多晶大颗粒材料。该多晶材料在600℃下处理8小时，其BET增大，变化率为35％。
将LiOH与Ni 0.83Co 0.11Mn 0.06(OH) 2按照摩尔比为1.12混合，混合后的物料在氧气气氛下进行第一次烧结，烧结温度为816℃，烧结后对物料进行破碎，破碎后的物料加入含Al 1mol％的Al 2O 3后进行第二烧结，烧结温度为620℃，最终得到D 50为3.5μm单晶小颗粒材料。该单晶材料在600℃下处理8小时，其BET减小，变化率为2％。
将上述多晶大颗粒和单晶小颗粒按照质量比7:3进行混合，得到用于锂二次电池的正极活性材料。该正极活性材料在600℃下处理8小时，其BET增大25％。
比表面积测量：
使用Tri-star 3020比表面仪进行测试，称取3克样品，将样品管安装到脱气站口上真空接头上。设定加热温度300℃，脱气时间120min，脱气结束后，将样品管冷却。在测试仪软件界面输入空样品管质量和脱气后样品及样品管的质量，记录经软件计算后输出的比表面积数据(BET法)，完成正极材料样品比表面积的测试；
粒度测量：
使用Mastersizer2000激光粒度仪进行测试。修改软件中“测量”中测试次数项的“样品测试时间”和“背景测试时间”为6秒；测量循环项的循环次数为3次，延迟时间为5秒，点击从测量中创建平均结果记录。其次，点击“开始”自动进行测量背景；自动测量完成后，先加入40毫升焦磷酸钠，然后用药品匙加入少量样品，直到遮光度达到目视10至20％区域的1/2处时点击“开始”，最终记录三次结果和平均值。
制备扣式电池：
首先，将非水系电解质二次电池用复合镍钴锰多元正极活性材料、乙炔黑及聚偏二氟乙烯(PVDF)，混合后涂覆在铝箔上并进行烘干处理。 将烘干完的正极极片、隔膜、负极极片及电解液在水含量与氧含量均小于5ppm的Ar气手套箱内组装成2025型扣式电池。
首次放电容量测试方法：制作扣式电池后放置2小时，开路电压稳定后，对正极的电流密度为0.1C的方式充电至截止电压4.3V，再恒压充电30min，随后以同样的电流密度放电至截止电压3.0V；按同样的方式再进行1次，将放电容量作为首次放电容量。图4示出实施例1、对比例1和2中正极材料制备得到扣式电池的充放电曲线，可以看到实施例1中正极材料相比对比例具有更高的首次放电容量。
制备全电池及产气测试：
将镍钴锰酸锂正极材料、石墨负极材料、炭黑导电剂、粘结剂PVDF放入120℃的真空烘箱中干燥12小时。将烘干后的正极材料、炭黑导电剂、PVDF、NMP混合均匀，调制成正极浆料。将该浆料使用锂电池涂布机涂布到铝箔上并干燥，使用极片分切机对极片进行裁切，使用极片辊压机对极片进行辊压。
将950克干燥后的人造石墨、13克Super-P、14克CMC、46克SBR溶液和1200克去离子水混合均匀，调制成负极浆料。将该浆料使用锂电池涂布机涂布到铜箔上并干燥。将涂布完成得到的负极片使用真空烘箱进行干燥，使用极片分切机对极片进行裁切，使用极片辊压机对极片进行辊压。
将上述正极片和负极片采用常规制作方法进行卷绕制作，并注入电解液，制作成全电池。测量全电池经过化成之后的初始厚度，在45℃恒温箱中放置7天之后，再次测试全电池厚度，用厚度的增加率表征全电池中正极材料的产气。图5示出实施例1、对比例1和2中正极材料制作的全电池的循环寿命变化，可见实施例1中正极材料制得的全电池具有更好的稳定性，循环寿命更长。
Figure PCTCN2022109897-appb-000001
Figure PCTCN2022109897-appb-000002
本发明提供的正极活性材料及其锂离子电池获得以下有益的效果：
1)与多晶类材料相比，相同镍含量的单晶具有更好的循环寿命和更低的产气性能，因此单晶的加入可以有效改善掺混后材料的循环和产气等性能；
2)单晶材料因其特殊的单晶形貌，克容量发挥与相同镍含量的多晶相比偏低，因此本发明采用略高镍含量的单晶，弥补其克容量低的短板，同时其循环和产气等性能与低镍含量的多晶保持同一水平；
3)掺混后小颗粒单晶材料可以进入到多晶大颗粒的间隙中，和大颗粒多晶形成相互支撑和填隙的协同效应，有效提高材料的压实密度；
4)在以单晶小颗粒为主的体系中加入少量大粒径多晶球形颗粒，可以有效改善单晶材料流动性差，不易筛分、制浆等问题。
虽然描述了特定的实施方案，这些实施方案仅以示例性的方式给出，并不意味着限制本发明的范围。所附的权利要求及其等价物意味着覆盖落入本发明的范围和精神之内的所有的修改、替换和改变方案。

Claims (28)

  1. 用于锂二次电池的正极活性材料，其特征在于，所述正极活性材料包含式A1表示的多晶颗粒和式A2表示的单晶颗粒
    A1：Li 1+a1Ni x1Co y1M z1M′ 1-x1-y1-z1O 2
    A2：Li 1+a2Ni x2Co y2M z2M′ 1-x2-y2-z2O 2
    其中，
    M为一种或两种选自Mn、Al的元素，
    M′为一种或多种选自B、F、Mg、Si、P、Ca、Ti、V、Cr、Fe、Ga、Sr、Y、Zr、Nb、Mo、Sn、Ba、La、Ce、W的元素，
    –0.03≤a1≤0.20，优选为–0.01≤a1≤0.14，更优选为0≤a1≤0.10，特别优选为0.01≤a1≤0.08，
    0.30≤x1≤0.99，优选为0.57≤x1≤0.99，更优选为0.72≤x1≤0.99，特别优选为0.80≤x1≤0.99，
    0≤y1≤0.30，优选为0≤y1≤0.21，更优选为0≤y1≤0.15，特别优选为0≤y1≤0.10，
    0≤z1≤0.30，优选为0≤z1≤0.18，更优选为0≤z1≤0.11，特别优选为0≤z1≤0.06，
    0≤1–x1–y1–z1≤0.10，优选为0≤1–x1–y1–z1≤0.08，更优选为0≤1–x1–y1–z1≤0.05，特别优选为0≤1–x1–y1–z1≤0.03，
    –0.03≤a2≤0.20，优选为–0.02≤a2≤0.16，更优选为–0.01≤a2≤0.14，特别优选为0≤a2≤0.08，
    0.31≤x2≤1.00，优选为0.59≤x2≤0.995，更优选为0.75≤x2≤0.995，特别优选为0.81≤x2≤0.995，
    0≤y2≤0.30，优选为0≤y2≤0.21，更优选为0≤y2≤0.15，特别优选为0≤y2≤0.10，
    0≤z2≤0.30，优选为0≤z2≤0.18，更优选为0≤z2≤0.11，特别优选为0≤z2≤0.08，
    0≤1–x2–y2–z2≤0.10，优选为0≤1–x2–y2–z2≤0.08，更优选为0≤1–x2–y2–z2≤0.05，特别优选为0≤1–x2–y2–z2≤0.03，
    其条件是：0<x2–x1≤0.5，优选为0.01≤x2–x1≤0.27，更优选为0.01≤x2–x1≤0.20，进一步优选为0.015≤x2–x1≤0.20，特别优选为0.02≤x2–x1≤0.15。
  2. 根据权利要求1所述的正极活性材料，其特征在于，a2>a1，优选为0.01≤a2–a1≤0.20，更优选为0.01≤a2–a1≤0.12，特别优选为0.01≤a2–a1≤0.07，尤其优选为0.01≤a2–a1≤0.04。
  3. 根据权利要求1或2所述的正极活性材料，其特征在于，所述多晶颗粒的粒度D 50为6至30μm，优选为8至25μm，更优选为9至20μm，特别优选为10至18μm。
  4. 根据权利要求1至3之一所述的正极活性材料，其特征在于，所述单晶颗粒的粒度D 50为0.1至10μm，优选为0.5至8.0μm，更优选为1.0至6.0μm，特别优选为1.5至4.5μm。
  5. 根据权利要求1至4之一所述的正极活性材料，其特征在于，基于所述正极活性材料的重量，所述多晶颗粒的含量为20至90％，优选为45至85％，更优选为50至80％，特别优选为60至80％。
  6. 根据权利要求1至5之一所述的正极活性材料，其特征在于，基于所述正极活性材料的重量，所述单晶颗粒的含量为10至80％，优选为10至70％，更优选为15至60％，特别优选为20至40％。
  7. 根据权利要求1至6之一所述的正极活性材料，其特征在于，所述多晶颗粒具有包含至少一种选自以下组中的包覆元素的包覆层：B、F、Mg、Al、Si、P、Ca、Ti、V、Cr、Fe、Ga、Sr、Y、Zr、Nb、Mo、Sn、Ba、La、Ce、W，其中基于所述多晶颗粒，所述包覆元素的含量为0.1至2摩尔％，优选为约1摩尔％。
  8. 根据权利要求1至7之一所述的正极活性材料，其特征在于，所述单晶颗粒具有包含至少一种选自以下组中的包覆元素的包覆层：B、F、Mg、Al、Si、P、Ca、Ti、V、Cr、Fe、Ga、Sr、Y、Zr、Nb、Mo、Sn、Ba、La、Ce、W，其中基于所述单晶颗粒，所述包覆元素的含量为0.1至2摩尔％，优选为约1摩尔％。
  9. 根据权利要求1至8之一所述的正极活性材料，其特征在于，所述多晶颗粒和所述单晶颗粒分别具有包含至少一种选自以下组中的包覆元素的包覆层：B、F、Mg、Al、Si、P、Ca、Ti、V、Cr、Fe、Ga、Sr、Y、Zr、Nb、Mo、Sn、Ba、La、Ce、W，其中分别基于所述多晶颗粒和所述单晶颗粒，所述包覆元素的含量为0.1至2摩尔％，优选为约1摩尔％。
  10. 根据权利要求9所述的正极活性材料，其特征在于，所述多晶颗粒的包覆层所包含的包覆元素不同于所述单晶颗粒的包覆层所包含的包覆元素。
  11. 根据权利要求1至10之一所述的正极活性材料，其特征在于，所述正极活性材料在600℃下于空气气氛中烧结8小时前后的比表面积BET 前和BET 后满足：
    |BET 后–BET 前|/BET 前≤50％，
    优选为|BET 后–BET 前|/BET 前≤30％。
  12. 根据权利要求1至11之一所述的正极活性材料，其特征在于，所述多晶颗粒在600℃下于空气气氛中烧结8小时前后的比表面积BET 前和BET 后满足：
    (BET 后–BET 前)/BET 前≥15％，
    优选为40％≥(BET 后–BET 前)/BET 前≥20％。
  13. 根据权利要求1至12之一所述的正极活性材料，其特征在于，所述单晶颗粒在600℃下于空气气氛中烧结8小时前后的比表面积BET 前和BET 后满足：
    (BET 前–BET 后)/BET 前≤15％，
    优选为0≤(BET 前–BET 后)/BET 前≤10％。
  14. 根据权利要求1至13之一所述的正极活性材料，其特征在于，所述正极活性材料不包含无镍的活性材料，例如磷酸锰铁锂。
  15. 根据权利要求1至14之一所述的正极活性材料，其特征在于，所述正极活性材料由式A1表示的多晶颗粒和式A2表示的单晶颗粒组成。
  16. 制备正极活性材料的方法，其包括以下步骤：
    i)采用液相共沉淀法分别制备式A3表示的多晶颗粒前驱体和式A4表示的单晶颗粒前驱体
    A3：Ni x1Co y1M z1M′ 1-x1-y1-z1(OH) 2
    A4：Ni x2Co y2M z2M′ 1-x2-y2-z2(OH) 2
    其中，
    M为一种或两种选自Mn、Al的元素，
    M′为一种或多种选自B、F、Mg、Si、P、Ca、Ti、V、Cr、Fe、Ga、Sr、Y、Zr、Nb、Mo、Sn、Ba、La、Ce、W的元素，
    0.30≤x1≤0.99，优选为0.57≤x1≤0.99，更优选为0.72≤x1≤0.99，特别优选为0.80≤x1≤0.99，
    0≤y1≤0.30，优选为0≤y1≤0.21，更优选为0≤y1≤0.15，特别优选为0≤y1≤0.10，
    0≤z1≤0.30，优选为0≤z1≤0.18，更优选为0≤z1≤0.11，特别优选为0≤z1≤0.06，
    0≤1–x1–y1–z1≤0.10，优选为0≤1–x1–y1–z1≤0.08，更优选为0≤1–x1–y1–z1≤0.05，特别优选为0≤1–x1–y1–z1≤0.03，
    0.31≤x2≤1.00，优选为0.59≤x2≤0.995，更优选为0.75≤x2≤0.995，特别优选为0.81≤x2≤0.995，
    0≤y2≤0.30，优选为0≤y2≤0.21，更优选为0≤y2≤0.15，特别优选为0≤y2≤0.10，
    0≤z2≤0.30，优选为0≤z2≤0.18，更优选为0≤z2≤0.11，特别优选为0≤z2≤0.08，
    0≤1–x2–y2–z2≤0.10，优选为0≤1–x2–y2–z2≤0.08，更优选为0≤1–x2–y2–z2≤0.05，特别优选为0≤1–x2–y2–z2≤0.03，
    其条件是：0<x2–x1≤0.5，优选为0.01≤x2–x1≤0.27，更优选为0.01≤x2–x1≤0.20，进一步优选为0.015≤x2–x1≤0.20，特别优选为0.02≤x2–x1≤0.15；
    ii)将锂源与所述多晶颗粒前驱体按照摩尔比r1进行混合，任选混入M′作为掺杂元素，其中0.97≤r1≤1.20，优选为0.99≤r1≤1.14，更优选为1.00≤r1≤1.10，特别优选为1.01≤r1≤1.08；然后在烧结温度T1下于空气或氧气、优选为氧气的烧结气氛中进行初次烧结，其中600℃≤T1≤1000℃，优选为675℃≤T1≤875℃，更优选为690℃≤T1≤800℃，特别优选为690℃≤T1≤780℃；然后经破碎 得到多晶颗粒；
    iii)将锂源与所述单晶颗粒前驱体按照摩尔比r2进行混合，任选混入M′作为掺杂元素，其中0.97≤r2≤1.20，优选为0.98≤r2≤1.16，更优选为0.99≤r2≤1.14，特别优选为1.00≤r2≤1.08；然后在烧结温度T2下于空气或氧气、优选为氧气的烧结气氛中进行初次烧结，其中650℃≤T2≤1050℃，优选为730℃≤T2≤930℃，更优选为750℃≤T2≤930℃，特别优选为750℃≤T2≤900℃；然后经破碎得到单晶颗粒；及
    iv)将步骤ii)的所述多晶颗粒与步骤iii)的所述单晶颗粒进行掺混得到所述正极活性材料。
  17. 根据权利要求16所述的方法，其特征在于，r2>r1，优选为0.01≤r2–r1≤0.20，更优选为0.01≤r2–r1≤0.12，特别优选为0.01≤r2–r1≤0.07，尤其优选为0.01≤r2–r1≤0.04。
  18. 根据权利要求16或17所述的方法，其特征在于，所述多晶颗粒前驱体的粒度D 50为6.5至30.5μm，优选为8.5至25.5μm，更优选为9.5至20.5μm，特别优选为10.5至18.5μm。
  19. 根据权利要求16至18之一所述的方法，其特征在于，所述多晶颗粒的粒度D 50为6至30μm，优选为8至25μm，更优选为9至20μm，特别优选为10至18μm。
  20. 根据权利要求16至19之一所述的方法，其特征在于，所述单晶颗粒前驱体的粒度D 50为0.1至30.5μm，优选为1.0至17.3μm，更优选为1.0至9.3μm，特别优选为1.0至6.0μm。
  21. 根据权利要求16至20之一所述的方法，其特征在于，所述单晶颗粒的粒度D 50为0.1至10μm，优选为0.5至8.0μm，更优选为1.0至6.0μm，特别优选为1.5至4.5μm。
  22. 根据权利要求16至21之一所述的方法，其特征在于，基于所述正极活性材料的重量，所述多晶颗粒的含量为20至90％，优选为45至85％，更优选为50至80％，特别优选为60至80％。
  23. 根据权利要求16至22之一所述的方法，其特征在于，基于所述正极活性材料的重量，所述单晶颗粒的含量为10至80％，优选为10至70％，更优选为15至60％，特别优选为20至40％。
  24. 根据权利要求16至23之一所述的方法，其特征在于，在步骤iv)之前，将所述多晶颗粒与包含至少一种选自以下组中的包覆元素的包覆前驱体进行混合：B、F、Mg、Al、Si、P、Ca、Ti、V、Cr、Fe、Ga、Sr、Y、Zr、Nb、Mo、Sn、Ba、La、Ce、W，然后在烧结温度T3下于空气或氧气、优选为氧气的烧结气氛中进行二次烧结，得到经二次烧结的多晶颗粒，其中250℃≤T3≤800℃，优选为250℃≤T3≤600℃，更优选为250℃≤T3≤480℃，特别优选为250℃≤T3≤400℃，其中基于所述多晶颗粒，所述包覆元素的含量为0.1至2摩尔％，优选为约1摩尔％。
  25. 根据权利要求16至24之一所述的方法，其特征在于，在步骤iv)之前，将所述单晶颗粒与包含至少一种选自以下组中的包覆元素的包覆前驱体进行混合：B、F、Mg、Al、Si、P、Ca、Ti、V、Cr、Fe、Ga、Sr、Y、Zr、Nb、Mo、Sn、Ba、La、Ce、W，然后在烧结温度T4下于空气或氧气、优选为氧气的烧结气氛中进行二次烧结，得到经二次 烧结的单晶颗粒，其中300℃≤T4≤900℃，优选为460℃≤T4≤800℃，更优选为550℃≤T4≤750℃，特别优选为600℃≤T4≤750℃，其中基于所述单晶颗粒，所述包覆元素的含量为0.1至2摩尔％，优选为约1摩尔％。
  26. 根据权利要求16至25之一所述的方法，其特征在于，在步骤iv)之前，将所述多晶颗粒与包含至少一种选自以下组中的包覆元素的包覆前驱体进行混合：B、F、Mg、Al、Si、P、Ca、Ti、V、Cr、Fe、Ga、Sr、Y、Zr、Nb、Mo、Sn、Ba、La、Ce、W，然后在烧结温度T3下于空气或氧气、优选为氧气的烧结气氛中进行二次烧结，得到经二次烧结的多晶颗粒，其中250℃≤T3≤800℃，优选为250℃≤T3≤600℃，更优选为250℃≤T3≤480℃，特别优选为250℃≤T3≤450℃，另外将所述单晶颗粒与包含至少一种选自以下组中的包覆元素的包覆前驱体进行混合：B、F、Mg、Al、Si、P、Ca、Ti、V、Cr、Fe、Ga、Sr、Y、Zr、Nb、Mo、Sn、Ba、La、Ce、W，然后在烧结温度T4下于空气或氧气、优选为氧气的烧结气氛中进行二次烧结，得到经二次烧结的单晶颗粒，其中250℃≤T4≤900℃，优选为250℃≤T4≤750℃，更优选为250℃≤T4≤700℃，特别优选为300℃≤T4≤700℃，其中分别基于所述多晶颗粒和所述单晶颗粒，所述包覆元素的含量为0.1至2摩尔％，优选为约1摩尔％。
  27. 根据权利要求26所述的方法，其特征在于，所述多晶颗粒的包覆前驱体所包含的包覆元素不同于所述单晶颗粒的包覆前驱体所包含的包覆元素。
  28. 锂二次电池，其包含根据权利要求1至13之一所述的正极活性材料或通过根据权利要求16至27之一所述的方法制得的正极活性材料。
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