WO2022121293A1 - 正极材料、电化学装置和电子装置 - Google Patents

正极材料、电化学装置和电子装置 Download PDF

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WO2022121293A1
WO2022121293A1 PCT/CN2021/104024 CN2021104024W WO2022121293A1 WO 2022121293 A1 WO2022121293 A1 WO 2022121293A1 CN 2021104024 W CN2021104024 W CN 2021104024W WO 2022121293 A1 WO2022121293 A1 WO 2022121293A1
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positive electrode
electrode material
particles
peak
particle size
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PCT/CN2021/104024
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English (en)
French (fr)
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吴霞
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宁德新能源科技有限公司
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Priority to JP2022518858A priority Critical patent/JP7534393B2/ja
Priority to EP21902005.4A priority patent/EP4261952A4/en
Publication of WO2022121293A1 publication Critical patent/WO2022121293A1/zh
Priority to US18/207,899 priority patent/US20230352677A1/en

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    • H—ELECTRICITY
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    • H01M4/36—Selection of substances as active materials, active masses, active liquids
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    • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
    • C01G51/00—Compounds of cobalt
    • C01G51/40—Cobaltates
    • C01G51/42—Cobaltates containing alkali metals, e.g. LiCoO2
    • C—CHEMISTRY; METALLURGY
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    • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
    • C01G53/00—Compounds of nickel
    • C01G53/40—Nickelates
    • C01G53/42—Nickelates containing alkali metals, e.g. LiNiO2
    • C01G53/44—Nickelates containing alkali metals, e.g. LiNiO2 containing manganese
    • C01G53/50—Nickelates containing alkali metals, e.g. LiNiO2 containing manganese of the type [MnO2]n-, e.g. Li(NixMn1-x)O2, Li(MyNixMn1-x-y)O2
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    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
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    • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
    • H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
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    • H01M10/4235—Safety or regulating additives or arrangements in electrodes, separators or electrolyte
    • H—ELECTRICITY
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    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/131—Electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
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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
    • H01M4/485—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of mixed oxides or hydroxides for inserting or intercalating light metals, e.g. LiTi2O4 or LiTi2OxFy
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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
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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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    • C01P2002/70—Crystal-structural characteristics defined by measured X-ray, neutron or electron diffraction data
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    • C01P2004/00—Particle morphology
    • C01P2004/51—Particles with a specific particle size distribution
    • C01P2004/53—Particles with a specific particle size distribution bimodal size distribution
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    • C01P2004/60—Particles characterised by their size
    • C01P2004/61—Micrometer sized, i.e. from 1-100 micrometer
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    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
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    • C01P2006/40—Electric properties
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    • H01M2004/021—Physical characteristics, e.g. porosity, surface area
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    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/028—Positive electrodes
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    • H01M2300/0017—Non-aqueous electrolytes
    • H01M2300/0025—Organic electrolyte
    • H01M2300/0028—Organic electrolyte characterised by the solvent
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • the present application relates to the technical field of electrochemistry, and in particular, to a positive electrode material, an electrochemical device, and an electronic device.
  • electrochemical devices eg, lithium-ion batteries
  • electrochemical devices eg, lithium-ion batteries
  • an important way is to increase the voltage of electrochemical devices.
  • the cathode materials of electrochemical devices have unstable crystal structure at high voltage, the capacity decays rapidly, and the cycle performance is greatly reduced.
  • the lithium cobalt oxide cathode material widely used in electrochemical devices has the R-3m crystal phase structure, and its theoretical capacity is 273.8mAh/g, which has good cycle performance and safety performance.
  • the material market occupies an important position.
  • lithium cobalt oxide materials are developing in the direction of high voltage.
  • lithium cobalt oxide materials have a capacity of only 190mA/g when the charging voltage is 4.5V.
  • lithium ions are extracted from the crystal structure of lithium cobalt oxide to improve the capacity of lithium cobalt oxide materials, but with the further increase of voltage, lithium ions are extracted from the crystal structure of lithium cobalt oxide will lead to a series of irreversible phase transitions, making cobalt oxide
  • the cycle performance and storage performance of lithium cobalt oxide materials are greatly reduced, and the interfacial side reactions increase at high voltages, the dissolution of cobalt metal is serious, the decomposition of electrolyte increases, and the capacity attenuation of lithium cobalt oxide materials is very serious.
  • the present application provides a positive electrode material, an electrochemical device and an electronic device.
  • the positive electrode material in the present application has a stable crystal structure, and the electrochemical device using the positive electrode material can maintain high capacity and good cycle performance under high voltage. .
  • the present application proposes a positive electrode material in some embodiments, the positive electrode material is a particle having a P6 3 mc crystal phase structure; the particle size distribution frequency curve of the positive electrode material includes a first peak and a second peak.
  • This application proposes a positive electrode material composed of particles of different particle sizes.
  • the P6 3 mc phase compound has a special oxygen structure, which is very stable at a high voltage of 4.6V, is friendly to electrolytes, and has excellent cycle performance.
  • the crystal phase structure of P6 3 mc has a unique lithium-deficient structure. During the process of delithiation/intercalation, due to the existence of lithium vacancies in its crystal structure, it has the ability to accommodate additional lithium ions, so it can prevent capacity decay. When the particles are mixed, the kinetic performance of the cathode material is improved, so the P6 3 mc crystal phase structure has a stronger lithium intercalation ability, showing better capacity and better cycle performance.
  • the particle size of the particle represented by the first peak is smaller than the particle size of the particle represented by the second peak, the peak area of the first peak is S1, and the peak area of the second peak is S2, 0 ⁇ S1/S2 ⁇ 1.
  • S1 and S2 respectively represent the content of particles with two different particle sizes, and 0 ⁇ S1/S2 ⁇ 1 indicates that the percentage of particles with smaller particle size is less than 50%, and the particles with smaller particle size are less than 50%. If the percentage is too high, the cycle performance may be degraded. In some embodiments, if there are no particles with smaller particle size, it is not beneficial to improve the compaction density, and it is not beneficial to improve the kinetic performance of the cathode material.
  • the chemical compositions of the first particles and the second particles are different;
  • the first particles include: Li x Na z Co 1-y1 M 1 y1 O 2 , wherein 0.6 ⁇ x ⁇ 0.95, 0 ⁇ y1 ⁇ 0.15 , 0 ⁇ z ⁇ 0.05, M 1 includes at least one of Al, Mg, Ti, Zr, La, Ca, Ge, Nb, Sn or Y;
  • the second particle includes: Li x Na z Co 1-y2 M 2 y2 O 2 , wherein 0.6 ⁇ x ⁇ 0.95, 0 ⁇ y2 ⁇ 0.15, 0 ⁇ z ⁇ 0.05, and M 2 includes at least one of Ni, Mn, Zn or Fe.
  • the first particle and the second particle The chemical composition of the particles is different. According to the performance shortcomings of the particles with different particle sizes, the corresponding chemical composition is selected to make up for the performance shortcomings.
  • the average particle size of the first particles is 3 ⁇ m to 12 ⁇ m, and the average particle size of the second particles is 15 ⁇ m to 30 ⁇ m. In some embodiments, if the average particle size of the first particles and the second particles is too small, the consumption of the electrolyte will increase, and the cycle performance of the positive electrode material will be adversely affected. If the average particle size of the secondary particles is too large, the rate performance may be lowered.
  • the particles of the positive electrode material have pores and cracks inside them. Particles with holes and cracks can fully contact the electrolyte, and when the cathode material expands during the charging and discharging process, the holes and cracks can reduce the internal stress of the cathode material, thereby helping to improve the stability of the crystal structure.
  • the specific surface area of the positive electrode material is 0.1 m 2 /g to 2 m 2 /g. Too small specific surface area is not conducive to rate performance, and too large specific surface area may lead to decreased cycle performance.
  • the positive electrode material is a particle with a P6 3 mc crystal phase structure; the particle size distribution frequency curve of the positive electrode material includes a first peak and a second peak, and the positive electrode material includes: Li x Na z Co 1-y My O 2 , wherein, 0.6 ⁇ x ⁇ 0.95, 0 ⁇ y ⁇ 0.15, 0 ⁇ z ⁇ 0.05, M includes: Al, Mg, Ti, Mn, Fe, Ni, Zn, At least one of Cu, Nb, Cr, Y, or Zr, the particles having the P6 3 mc crystal phase structure have an average particle diameter of 3 ⁇ m to 30 ⁇ m.
  • the positive electrode material can be doped or undoped lithium cobalt oxide material.
  • the doping element in the lithium cobalt oxide can improve the structural stability, but when the content of the doping element is too high, the capacity may be reduced. If the loss is too large, within the range defined in this application, the structural stability can be improved under the condition of ensuring the capacity.
  • the particles of the positive electrode material have pores and cracks inside them. Particles with holes and cracks can fully contact the electrolyte, and when the cathode material expands during the charging and discharging process, the holes and cracks can reduce the internal stress of the cathode material, thereby helping to improve the stability of the crystal structure.
  • the specific surface area of the positive electrode material is 0.1 m 2 /g to 2 m 2 /g. Too small specific surface area is not conducive to rate performance, and too large specific surface area may lead to decreased cycle performance.
  • an electrochemical device including: a positive electrode; a negative electrode; an electrolyte;
  • the active material layer and the positive electrode active material layer include any one of the positive electrode materials described above.
  • the compaction density of the positive electrode active material layer of the electrochemical device is 3 g/cm 3 to 4.35 g/cm 3 .
  • the positive electrode material since the positive electrode material has particles of two different particle sizes, it is beneficial to improve the compaction density of the positive electrode active material layer, but an excessively large compaction density may lead to particle breakage.
  • the electrolyte includes a compound having 2 to 3 cyano groups; wherein the compound having 2 to 3 cyano groups includes a dinitrile compound, a trinitrile compound, an ether dinitrile compound or an ether trinitrile compound. at least one.
  • the bond energy of the carbon-nitrogen triple bond in the cyano group is very high, and it is not easy to be oxidized and has high stability. position, thereby reducing the decomposition of the electrolyte.
  • the compound with 2 to 3 cyano groups can better reduce the reaction between the positive electrode and the electrolyte in the present application, and inhibit gas production.
  • compounds with 2 to 3 cyano groups include glutaronitrile, succinonitrile, adiponitrile, 1,3,6-hexanetricarbonitrile, 1,3,5-pentanetricarbonitrile, 1,3,5-pentanetricarbonitrile, At least one of 2,3-propanetricarbonitrile or 1,2,3-tris(2-cyanoethoxy)propane, wherein the content of the compound having 2 to 3 cyano groups is 0.01wt based on the weight of the electrolyte % to 15wt%.
  • an electronic device is provided, including the electrochemical device according to any one of the above.
  • the electrolyte includes an organic solvent including at least one of ethylene carbonate, diethyl carbonate, propylene carbonate, propyl propionate, or vinylene carbonate.
  • organic solvent can synergize with the cathode material in this paper to stabilize its crystal structure, thereby improving the cycle performance.
  • the cathode materials provided in the examples of the present application have particles with a P63mc crystal phase structure, and the P63mc crystal phase structure has a unique HCP (hexagonal closest packing) oxygen structure.
  • Oxygen structure is stable, electrolyte friendly, and excellent cycle performance.
  • the particle size distribution frequency curve of the positive electrode material includes the first peak and the second peak, indicating that the positive electrode material includes two kinds of particles with different particle sizes, which can improve the processing performance of the material and solve the problem of high formula sedimentation and compaction.
  • the problem of low density, and the crystal phase structure of P63mc itself is a lithium-deficient material.
  • the charging process requires delithium ions to open the channel.
  • the discharge process in addition to accommodating its own lithium ions, it also has the ability to electrochemically intercalate lithium ions, absorb additional lithium ions, and positive electrode materials.
  • the kinetic performance of the cathode material is improved, so the cathode material has a stronger lithium intercalation ability, showing higher capacity and better cycle performance.
  • the lithium cobalt oxide cathode material with R-3m phase in the prior art undergoes an irreversible phase transition (O3 to H1-3, H1-3 to O1) in the crystal structure at high voltages of 4.6V and above, which makes the material cycle performance and safety.
  • the performance is greatly reduced.
  • metal cation bulk doping is generally used to improve the structural stability of the R-3m phase lithium cobalt oxide cathode material.
  • the doping of most elements improves the structural stability of the material by delaying the irreversible phase transition.
  • the effect of this method on improving the structural stability is not obvious when the voltage is higher than 4.6V, and when the doping amount increases, the loss of theoretical capacity will increase. The capacity and cycling performance are maintained while maintaining the stability of the crystal structure at high voltage.
  • some embodiments of the present application propose a positive electrode material, the positive electrode material is a particle with a P6 3 mc crystal phase structure; the particle size distribution frequency curve of the positive electrode material includes a first peak and a second peak , which indicates that there are two kinds of particles with different particle sizes of P6 3 mc crystal phase structure in the cathode material.
  • This application proposes a positive electrode material composed of particles of different particle sizes.
  • the P6 3 mc phase compound has a special HCP oxygen structure, which is very stable at a high voltage of 4.6V, is friendly to electrolytes, and has excellent cycle performance.
  • the particles of the cathode material with different particle sizes, the effect of the particles with different particle sizes can be fully exerted, the processing performance of the material can be improved, the problems of high formula sedimentation and low compaction density can be solved, and the rate performance can be improved.
  • the crystal phase structure of P6 3 mc has a unique lithium-deficient structure, which can prevent capacity fading due to the ability to accommodate additional lithium ions due to the existence of lithium vacancies in its crystal structure during the delithiation/intercalation process.
  • the kinetic performance of the cathode material is improved, so the P6 3 mc crystal phase structure has stronger lithium intercalation ability, showing better capacity and better cycle performance.
  • the particle size of the particle represented by the first peak is smaller than the particle size of the particle represented by the second peak, the peak area of the first peak is S1, and the peak area of the second peak is S2, 0 ⁇ S1/S2 ⁇ 1.
  • S1 and S2 respectively represent the content of particles with two different particle sizes, and 0 ⁇ S1/S2 ⁇ 1 indicates that the percentage of particles with smaller particle size is less than 50%, and the particles with smaller particle size are less than 50%. If the percentage is too high, the cycle performance may be degraded. In some embodiments, if there are no particles with smaller particle size, it is not beneficial to improve the compaction density, and it is not beneficial to improve the kinetic performance of the cathode material.
  • the positive electrode material includes: first particles and second particles; the first particles and the second particles have different chemical compositions.
  • the first particles include: Li x Na z Co 1-y1 M 1 y1 O 2 , wherein 0.6 ⁇ x ⁇ 0.95, 0 ⁇ y1 ⁇ 0.15, 0 ⁇ z ⁇ 0.05, M 1 Including at least one of Al, Mg, Ti, Zr, La, Ca, Ge, Nb, Sn or Y;
  • the second particles include: Li x Na z Co 1-y2 M 2 y2 O 2 , wherein, 0.6 ⁇ x ⁇ 0.95, 0 ⁇ y2 ⁇ 0.15, 0 ⁇ z ⁇ 0.05, M 2 includes at least one of Ni, Mn, Zn or Fe.
  • the performance of particles with different particle sizes is different, the cycle performance of particles with smaller particle size is relatively poor, and the rate performance of particles with larger particle size is relatively poor. Therefore, in some embodiments of the present application, the first The chemical compositions of the first particle and the second particle are different. According to the performance shortcomings of the particles with different particle sizes, the corresponding chemical composition is selected to make up for the shortcomings in performance. For example, doping the first particle with a smaller particle size improves the cycle performance.
  • the second particle with a larger particle size is doped with an element that improves the rate performance, so that the cathode material as a whole shows better rate performance and cycle performance;
  • the average particle size of the first particle is 3 ⁇ m to 12 ⁇ m
  • the average particle diameter of the second particles is 15 ⁇ m to 30 ⁇ m.
  • the first particles are particles represented by the first peak
  • the second particles are particles represented by the second peak
  • both the first particles and the second particles have a P6 3 mc crystal phase structure.
  • the particles of the positive electrode material have pores and cracks inside.
  • the particles with holes and cracks can fully contact the electrolyte, and when the cathode material expands during charging and discharging, the holes and cracks can reduce the internal stress of the cathode material, thereby helping to improve the stability of the crystal structure. sex.
  • the number of holes and cracks on one particle is less than or equal to 50, and if the number is too large, the mechanical strength of the positive electrode material may be insufficient, and crystal collapse is likely to occur.
  • the positive electrode material is a particle with a P6 3 mc crystal phase structure; the particle size distribution frequency curve of the positive electrode material includes a first peak and a second peak, and the positive electrode material includes: Li x Na z Co 1-y My O 2 , wherein, 0.6 ⁇ x ⁇ 0.95, 0 ⁇ y ⁇ 0.15, 0 ⁇ z ⁇ 0.05, M includes: Al, Mg, Ti, Mn, Fe, Ni, Zn, At least one of Cu, Nb, Cr, Y, or Zr, the particles having the P6 3 mc crystal phase structure have an average particle diameter of 3 ⁇ m to 30 ⁇ m.
  • the positive electrode material can be doped or undoped lithium cobalt oxide material.
  • the structural stability can be improved, but when the content of the doping element is too high, it may cause If the capacity loss is too large, within the range defined in the present application, the structural stability can be improved while ensuring the capacity.
  • the particle size of the particles will affect the structural stability and rate capability of the positive electrode material.
  • the first particles with smaller particle size have poorer structural stability than the second particles, and the Compared with the first particle, the second particle with a larger diameter has poorer rate performance, so the first particle can be doped with M 1 that is beneficial to improve the structural stability of the first particle, and the second particle can be doped with M 1 that is beneficial to improving the structural stability of the first particle. M 2 that increases the rate capability of the second particle.
  • the particles of the positive electrode material have pores and cracks inside.
  • the particles with holes and cracks can fully contact the electrolyte, and when the cathode material expands during charging and discharging, the holes and cracks can reduce the internal stress of the cathode material, thereby helping to improve the stability of the crystal structure. sex.
  • the number of holes and cracks on one particle is less than or equal to 50, and if the number is too large, the mechanical strength of the positive electrode material may be insufficient, and crystal collapse is likely to occur.
  • the specific surface area of the positive electrode material is 0.1 m 2 /g to 2 m 2 /g. In some embodiments, when the specific surface area is greater than 2 m 2 /g, the consumption of the electrolyte is accelerated, the stability of the crystal structure is reduced, and the cycle performance may be reduced, which is not conducive to the cycle performance, and when the specific surface area is less than 0.1 m 2 /g May result in poor rate performance.
  • an electrochemical device including: a positive electrode, a negative electrode, an electrolyte, and a separator, and the separator is arranged between the positive electrode and the negative electrode; wherein, the positive electrode comprises a current collector and is arranged on the current collector
  • the positive electrode active material layer includes the positive electrode material in any of the above embodiments.
  • the compaction density of the positive electrode active material layer is 3 g/cm 3 to 4.35 g/cm 3 .
  • the positive electrode material has two kinds of particles with different particle sizes, it is beneficial to improve the compaction density of the positive electrode active material layer. It is 3.80 g/cm 3 or more, the compacted density of the positive electrode active material layer is 4 g/cm 3 or more when compressed under a pressure of 250 MPa, and the compacted density of the positive electrode active material layer is 4.2 g/cm 3 or more when compressed under a pressure of 500 MPa. .
  • the electrochemical device is cycled for 20 cycles at a rate of 1C, and the growth rate of the DC resistance of the electrochemical device is less than or equal to 2%.
  • the growth rate of the DC resistance of the electrochemical device after the cycle is less than or equal to 2%, which can indicate that the positive electrode material of the electrochemical device in the present application has good structural stability, and no obvious change occurs during the cycle. Structural changes will not result in a significant increase in DC resistance.
  • the electrolyte includes a compound having 2 to 3 cyano groups; wherein, the compound having 2 to 3 cyano groups includes a dinitrile compound, a trinitrile compound, an ether dinitrile compound or an ether trinitrile at least one of the compounds.
  • the bond energy of the carbon-nitrogen triple bond in the cyano group is very high, and it is not easy to be oxidized and has high stability. position, thereby reducing the decomposition of the electrolyte.
  • compounds with 2 to 3 cyano groups can better reduce the reaction between the positive electrode and the electrolyte and inhibit gas production.
  • compounds having 2 to 3 cyano groups include glutaronitrile, succinonitrile, adiponitrile, 1,3,6-hexanetricarbonitrile, 1,3,5-pentanetricarbonitrile At least one of , 1,2,3-propanetricarbonitrile or 1,2,3-tris(2-cyanoethoxy)propane, wherein based on the weight of the electrolyte, the content of the compound having 2 to 3 cyano groups 0.01 wt % to 15 wt %.
  • the current collector of the positive electrode can be made of Al foil, of course, other current collectors of the positive electrode commonly used in the art can also be used.
  • the thickness of the current collector of the positive electrode may be 1 ⁇ m to 200 ⁇ m.
  • the positive electrode active material layer may be coated only on a partial area of the current collector of the positive electrode.
  • the thickness of the cathode active material layer may be 10 ⁇ m to 500 ⁇ m. It should be understood that these are exemplary only and other suitable thicknesses may be employed.
  • the release membrane includes at least one of polyethylene, polypropylene, polyvinylidene fluoride, polyethylene terephthalate, polyimide, or aramid.
  • the polyethylene includes at least one selected from high density polyethylene, low density polyethylene or ultra-high molecular weight polyethylene. Especially polyethylene and polypropylene, they have a good effect on preventing short circuits and can improve the stability of the battery through the shutdown effect.
  • the thickness of the isolation film is in the range of about 5 ⁇ m to 500 ⁇ m.
  • the surface of the isolation membrane may further include a porous layer, the porous layer is disposed on at least one surface of the isolation membrane, the porous layer includes inorganic particles and a binder, and the inorganic particles are selected from aluminum oxide (Al 2 O 3 ), Silicon oxide (SiO 2 ), magnesium oxide (MgO), titanium oxide (TiO 2 ), hafnium dioxide (HfO 2 ), tin oxide (SnO 2 ), ceria (CeO 2 ), nickel oxide (NiO), oxide Zinc (ZnO), calcium oxide (CaO), zirconium oxide (ZrO 2 ), yttrium oxide (Y 2 O 3 ), silicon carbide (SiC), boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide or sulfuric acid at least one of barium.
  • the pores of the isolation membrane have diameters in the range of about 0.01 ⁇ m to 1 ⁇ m.
  • the binder of the porous layer is selected from polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, sodium carboxymethyl cellulose, polyamide At least one of vinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene or polyhexafluoropropylene.
  • the porous layer on the surface of the separator can improve the heat resistance, oxidation resistance and electrolyte wettability of the separator, and enhance the adhesion between the separator and the pole piece.
  • the electrochemical device is wound or stacked.
  • the electrochemical device includes a lithium-ion battery, although the present application is not so limited.
  • the electrochemical device may also include an electrolyte.
  • the electrolyte may be one or more of a gel electrolyte, a solid electrolyte, and an electrolytic solution, and the electrolytic solution includes a lithium salt and a non-aqueous solvent.
  • the lithium salt is selected from LiPF6, LiBF4 , LiAsF6, LiClO4 , LiB ( C6H5 ) 4 , LiCH3SO3 , LiCF3SO3 , LiN ( SO2CF3 ) 2 , LiC ( SO2CF3 ) 3 , LiSiF 6 , LiBOB or one or more of lithium difluoroborate.
  • LiPF 6 is chosen as the lithium salt because it can give high ionic conductivity and improve cycle characteristics.
  • the non-aqueous solvent may be a carbonate compound, a carboxylate compound, an ether compound, other organic solvents, or a combination thereof.
  • the carbonate compound may be a chain carbonate compound, a cyclic carbonate compound, a fluorocarbonate compound, or a combination thereof.
  • chain carbonate compounds are diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), methyl carbonate Ethyl esters (MEC) and combinations thereof.
  • chain carbonate compounds are diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), methyl carbonate Ethyl esters (MEC) and combinations thereof.
  • Examples of the cyclic carbonate compound are ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylethylene carbonate (VEC), or a combination thereof.
  • fluorocarbonate compound examples include fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate Fluoroethylene, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-carbonate -Difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, trifluoromethylethylene carbonate, or a combination thereof.
  • FEC fluoroethylene carbonate
  • 1,2-difluoroethylene carbonate 1,1-difluoroethylene carbonate
  • 1,1,2-trifluoroethylene carbonate Fluoroethylene, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-carbonate -Difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene
  • carboxylate compounds are methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, ⁇ -butyrolactone, decolactone, Valerolactone, mevalonolactone, caprolactone, methyl formate, or a combination thereof.
  • ether compounds are dibutyl ether, tetraglyme, diglyme, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxy Ethane, 2-methyltetrahydrofuran, tetrahydrofuran, or a combination thereof.
  • organic solvents examples include dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, methyl amide, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, trioctyl phosphate, and phosphate esters or combinations thereof.
  • Embodiments of the present application also provide electronic devices including the above electrochemical devices.
  • the electronic device in the embodiment of the present application is not particularly limited, and it may be used in any electronic device known in the prior art.
  • electronic devices may include, but are not limited to, notebook computers, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, headsets, VCRs, LCD TVs, portable cleaners, portable CD players, mini discs, transceivers, electronic notepads, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, assisted bicycles, bicycles, Lighting equipment, toys, game consoles, clocks, power tools, flashlights, cameras, large-scale household storage batteries and lithium-ion capacitors, etc.
  • Some embodiments of the present application also propose a method for preparing a positive electrode material, which can be used to prepare the positive electrode material in the above-mentioned embodiments, and the preparation method includes the following steps:
  • Li x Na z Co 1-y My O 2 wherein 0.6 ⁇ x ⁇ 0.95, 0 ⁇ y ⁇ 0.15, 0 ⁇ z ⁇ 0.05, and M is selected from Al, Mg, Ti, Mn, Fe, Ni , at least one of the group consisting of Zn, Cu, Nb, Cr or Zr,
  • Li x Na z Co 1-y1 M 1 y1 O 2 and Li x Na z Co 1-y2 M 2 y2 O 2 are mixed in a certain proportion, wherein Li x Na z Co 1-y2 M 2 y2 O 2 is less than the number of Li x Na z Co 1-y1 M 1 y1 O 2 .
  • Preparation of positive electrode sheet Dissolve the positive electrode material, conductive agent conductive carbon black, and binder polyvinylidene fluoride in N-methylpyrrolidone (NMP) solution in a weight ratio of 97:1.4:1.6 to form a positive electrode slurry material.
  • NMP N-methylpyrrolidone
  • the positive electrode slurry was coated on the positive electrode current collector with a coating weight of 17.2 mg/cm 2 , and the positive electrode sheet was obtained after drying, cold pressing and cutting.
  • the negative electrode material is artificial graphite.
  • the negative electrode material, acrylic resin, conductive carbon black and sodium carboxymethyl cellulose are dissolved in deionized water in a weight ratio of 94.8:4.0:0.2:1.0 to form a negative electrode active material layer slurry, wherein the weight percentage of silicon is 10%.
  • a 10 ⁇ m thick copper foil was used as the negative electrode current collector, and the negative electrode slurry was coated on the negative electrode current collector with a coating weight of 6.27 mg/cm 2 , and dried until the water content of the negative electrode sheet was less than or equal to 300 ppm to obtain a negative electrode active material layer.
  • the negative pole piece is obtained after cutting.
  • the isolation film substrate is polyethylene (PE) with a thickness of 8 ⁇ m, and 2 ⁇ m alumina ceramic layers are coated on both sides of the isolation film substrate, and finally, 2.5 ⁇ m alumina ceramic layers are coated on both sides of the coated ceramic layer. mg of binder polyvinylidene fluoride (PVDF), dried.
  • PE polyethylene
  • PVDF binder polyvinylidene fluoride
  • Preparation of lithium ion battery stack the positive pole piece, the separator and the negative pole piece in order, so that the separator is in the middle of the positive pole piece and the negative pole piece to play a role of isolation, and coil to obtain an electrode assembly.
  • the electrode assembly is placed in the outer packaging aluminum-plastic film, and after dehydration at 80°C, the above electrolyte is injected and packaged, and the lithium ion battery is obtained through the process of forming, degassing, and trimming.
  • the preparation steps of the lithium ion batteries of the examples and the comparative examples are the same, and the difference between the examples and the comparative examples is only in the positive electrode materials used.
  • the specific positive electrode materials used are shown in Tables 1 to 8 below.
  • the test method refers to the particle size distribution laser diffraction method GB/T19077-2016. 1. Test range: 0.02 ⁇ m to 2000 ⁇ m (MS2000); 0.01 ⁇ m to 3500 ⁇ m (MS3000); 2. Detection limit 20nm. Finally, the volume distribution curve of the powder is obtained. It should be noted that the average particle size in this application refers to the particle size corresponding to a sample in the particle size distribution based on volume, when the cumulative particle size distribution percentage reaches 50%.
  • the first charge and discharge are performed, and constant current charging is performed at a charging current of 0.5C (that is, the current value that completely discharges the theoretical capacity within 2h) until the upper limit voltage is 4.8V; then, in Perform constant current discharge at a discharge current of 0.5C until the final voltage is 3V, record the discharge capacity of the first cycle (first cycle discharge capacity); continue to the 100th charge and discharge cycle, record the discharge capacity of the 100th cycle.
  • Capacity retention rate after the 100th cycle discharge capacity at the 100th cycle/discharge capacity at the first cycle ⁇ 100%.
  • the positive electrode material was processed by an ion polishing machine (JEOL-IB-09010CP) to obtain a cross section.
  • JEOL-IB-09010CP Use a scanning electron microscope to photograph the cross-section of the particle at a magnification of not less than 5.0K to obtain a particle image. Holes and cracks can be observed on the cross-sectional image. In the particle cross-section image, the closed areas with different colors from the surrounding areas are the holes and cracks. .
  • the hole selection requirements are as follows: the ratio of the longest axis of the closed region to the longest axis of the particle in a single particle is between 2% and 10%, and the difference between the longest axis and the shortest axis of the closed region is less than 0.5 microns, which is Holes that meet the counting requirements;
  • the requirements for the selection of cracks are as follows: when the ratio of the longest axis of the closed region to the longest axis of the particle in a single particle is not less than 70%, it is a crack that meets the counting requirements.
  • the selection method of the long and short axes connect any two points of the closed curve, the longest distance is the longest axis, and the shortest distance is the shortest axis.
  • a closed area refers to an area enclosed by closed lines in a graph, and the line connecting any point inside the closed area and any point outside the area intersects the boundary of the area.
  • the powder of positive electrode material is analyzed and tested by iCAP7000 ICP detector;
  • NMP can be used to dissolve the pole piece, the powder is filtered and dried, and the iCAP7000 ICP detector is used for elemental analysis and testing.
  • X-ray diffraction test Bruker D8 ADVANCE was used to obtain the XRD diffraction pattern of the cathode material. If the powder cannot be obtained, for the positive pole piece, NMP can be used to dissolve the positive pole piece, filter the powder and dry it, and use XRD to detect the powder.
  • test equipment is: BSD-BET400
  • test process the sample is placed in a system filled with N 2 gas, and the surface of the material is physically adsorbed at the temperature of liquid nitrogen.
  • the physical adsorption is in equilibrium, by measuring the adsorption pressure and the flow rate of the adsorbed gas at equilibrium, the adsorption capacity of the monomolecular layer of the material can be obtained, and then the specific surface area of the sample can be calculated.
  • Compaction density test discharge the lithium-ion battery to 0SOC% (SOC: State Of Charge, state of charge), disassemble the battery, clean, dry, and use an electronic balance to measure the positive electrode of a certain area A (the positive electrode of the current collector). Both sides are coated with a positive electrode active material layer) for weighing, the weight is recorded as W 1 , and the thickness T 1 of the positive electrode is measured using a micrometer.
  • the positive electrode active material layer is washed off with a solvent, dried, and the weight of the positive electrode current collector is measured, denoted as W 2 , and the thickness T 2 of the positive electrode current collector is measured with a micrometer.
  • the weight W 0 and thickness T 0 of the positive electrode active material layer disposed on one side of the positive electrode current collector and the compaction density of the positive electrode active material layer are calculated by the following equations:
  • T 0 (T 1 -T 2 )/2
  • the positive electrode material simultaneously includes Li a1 Na c1 Co 1-b1 M 1 b1 O 2 and Li a2 Na c2 Co 1-b2 M 2 b2 O 2 with a P6 3 mc crystal phase structure, and Li a1 Na c1 Co 1-b1 M
  • Li a1 Na c1 Co 1-b1 M Different sizes of the particles of 1 b1 O 2 and Li a2 Na c2 Co 1-b2 M 2 b2 O 2 can improve the first cycle discharge capacity and cycle capacity, so some embodiments of the present application define that the positive electrode material contains P6 3 mc
  • the particles of the crystal phase structure, and the particle size distribution frequency curve of the positive electrode material includes the first peak and the second peak.
  • the average particle diameter of the first particles is defined to be 3 ⁇ m to 12 ⁇ m, and the average particle diameter of the second particles is 15 ⁇ m to 30 ⁇ m.
  • Example 1-1 Comparing Example 1-1 to Example 1-17, it can be seen that M 1 or M 2 is not used for doping in Example 1-1, while Example 1-2 to Example 1-17 are all doped , the first-cycle discharge capacity and the 100-cycle capacity retention rate of Examples 1-2 to 1-17 are better than those of Example 1-1, so in some examples of this application, the positive electrode material has M 1 or M 2 .
  • Examples 1-18 to 1-19 Zn is used for doping in Example 1-18, and Al is used for doping in Example 1-19, because there are both large particles and small particles with the same chemical composition. Particles, the first cycle discharge capacity and 100 cycle capacity retention rate of Examples 1-18 to 1-19 are better than those of Example 1-1, so the particle size distribution frequency curve of the positive electrode material in some examples in this application The first and second peaks are included on the graph.
  • the positive electrode materials used are all Li x Na z Co 1-y My O 2
  • the crystal phase structures of the positive electrode materials in each of the examples and comparative examples in Table 2 are all for the P6 3 mc.
  • Comparing Example 2-1 and Comparative Example 2-1 to Comparative Example 2-3 it can be seen that, compared with Comparative Example 2-3 without holes and cracks in the positive electrode material, when there is one hole or gap in the positive electrode material, It can improve the first-cycle discharge capacity and the 100-cycle capacity retention rate. When there are holes and cracks in the positive electrode material at the same time, the lithium-ion battery has higher first-cycle discharge capacity and 100-cycle cycle capacity retention rate.
  • the particles defining the positive electrode material in the examples have pores and cracks inside.
  • the positive electrode materials used are all Li x Na z Co 1-y My O 2
  • the crystal phase structures of the positive electrode materials in each of the examples and comparative examples in Table 3 are all for the P6 3 mc.
  • Example 3-1 Comparing Example 3-1, Example 3-2, Comparative Example 3-1 and Comparative Example 3-2, it can be seen that when the specific surface area of the positive electrode material is greater than 2 m 2 /g, the first cycle discharge capacity of the lithium ion battery is relatively high. It is small, and the 100-cycle capacity retention rate is low. When the specific surface area of the positive electrode material is less than or equal to 2m 2 /g, the first-cycle discharge capacity of the lithium-ion battery is higher, and the 100-cycle cycle capacity retention rate is better.
  • the specific surface area of the positive electrode material is defined to be 0.1 m 2 /g to 2 m 2 /g.
  • the positive electrode materials used are all Li x Na z Co 1-y My O 2
  • the crystal phase structures of the positive electrode materials in each of the examples and comparative examples in Table 4 are all P6 3 mc.
  • the main peak range in Table 4 refers to the diffraction angle of the diffraction peak with the strongest intensity in the X-ray diffraction pattern of the positive electrode material
  • the full width at half maximum in Table 4 refers to the diffraction peak of the main peak.
  • Example 4-1 Comparing Example 4-1, Example 4-2, Comparative Example 4-1 and Comparative Example 4-2, it can be seen that when the main peak range is from 18° to 19°, compared with the case where the full width at half maximum is greater than 0.5° , when the full width at half maximum is in the range of 0° to 0.5°, the first-cycle discharge capacity and 100-cycle capacity retention rate of the lithium-ion battery are both high.
  • the diffraction peak with the strongest intensity is The diffraction angles of 18° to 19° range from 18° to 19°, and the FWHM of the most intense diffraction peaks range from 0° to 0.5°.
  • the positive electrode materials used are all Li x Na z Co 1-y My O 2
  • the crystal phase structures of the positive electrode materials in the examples and comparative examples in Table 5 are all for the P6 3 mc.
  • Example 5-1 to Example 5-6 Comparative Example 5-1 and Comparative Example 5-2, it can be seen that the first cycle discharge capacity and 100-cycle cycle capacity of Example 5-1 to Example 5-6 The retention rate is higher than that of Comparative Example 5-1 and Comparative Example 5-2. It can be seen that when the compaction density of the positive active material layer is 3g/ cm3 to 4.35g/ cm3 , it is beneficial to improve the lithium ion Discharge performance and cycle performance of the battery.
  • Comparative Examples 7-1 to 7-8 and Comparative Examples 7-1 and 7-2 that compounds with 2 to 3 cyano groups were added to the electrolyte of lithium ion batteries, and the compounds with 2 to 3 cyano groups were controlled.
  • the mass content of the compound with 2 to 3 cyano groups is in the range of 0.01 wt % to 15 wt %, the first cycle discharge capacity and the 100 cycle capacity retention rate of the lithium ion battery can be improved.

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Abstract

本申请提供一种正极材料、电化学装置和电子装置，本申请在一些实施例中提出一种正极材料，正极材料为P6 3mc晶相结构的颗粒；正极材料的粒度分布频率曲线图上包含第一峰和第二峰。本申请中的正极材料具有稳定的晶体结构，采用该正极材料的电化学装置能够在高电压下保持较高的容量和良好的循环性能。

Description

正极材料、电化学装置和电子装置
相关申请的交叉引用
本申请基于申请号为202011460086.8、申请日为2020年12月11日，名称为“正极材料、电化学装置和电子装置”的中国专利申请提出，并要求该中国专利申请的优先权，该中国专利申请的全部内容在此引入本申请作为参考。
技术领域
本申请涉及电化学技术领域，尤其涉及一种正极材料、电化学装置和电子装置。
背景技术
随着电化学装置(例如，锂离子电池)的发展和进步，对其容量提出了越来越高的要求。为了提高电化学装置的容量，一个重要的途径是提高电化学装置的电压，然而电化学装置的正极材料在高电压下晶体结构不稳定，容量快速衰减，循环性能大幅降低。
目前，电化学装置(例如，锂离子电池)中广泛使用的钴酸锂正极材料为R-3m晶相结构，其理论容量为273.8mAh/g，其具有良好的循环性能和安全性能，在正极材料市场占有重要地位。为了获得更高的比能量，钴酸锂材料正在朝着高电压的方向发展，目前钴酸锂材料在充电电压为4.5V时，容量也仅仅达到190mA/g，人们尝试通过从钴酸锂材料的晶体结构中脱出更多的锂离子从而提高钴酸锂材料的容量，但随着电压的进一步升高，锂离子从钴酸锂的晶体结构中脱出将导致一系列不可逆的相变，使得钴酸锂材料的循环性能和存储性能大大降低，并且在高电压下界面副反应增加，钴金属溶出严重，电解液分解增加，钴酸锂材料的容量衰减十分严重。
发明内容
本申请提供一种正极材料、电化学装置和电子装置，本申请中的正极材料具有稳定的晶体结构，采用该正极材料的电化学装置能够在高电压下保持较高的容量和良好的循环性能。
本申请在一些实施例中提出一种正极材料，正极材料为具有P6 3mc晶相结构的颗粒；正极材料的粒度分布频率曲线图上包含第一峰和第二峰。本申请提出了一种由不同粒径大小颗粒组成的正极材料，一方面，P6 3mc相化合物具有特殊的氧结构，在4.6V的高电压下十分稳定，对电解液友好，循环性能优异。另一方面，通过设计不同粒径的正极材料的颗粒，可以充分发挥不同粒径的颗粒的作用，提高材料的加工性能，解决高配方沉降和压实密度低的问题，有利于提高倍率性能。而且P6 3mc晶相结构具有独特的缺锂结构，在脱锂/嵌锂过程中，由于其晶体结构中存在锂空位，具有容纳额外锂离子的能力，因此能够防止容量衰减，在不同粒径的颗粒混合时，正极材料的动力学性能得以提升，因此P6 3mc晶相结构有更强的嵌锂能力，呈现出更好的容量和更好的循环性能。
在一些实施例中，第一峰所表示的颗粒的粒径小于第二峰所表示的颗粒的粒径，第一峰的峰面积为S1，第二的峰面积为S2，0<S1/S2<1。一些实施例中，S1和S2分别表示了两种不同粒径的颗粒的含量，0<S1/S2<1表明具有较小的粒径的颗粒的百分比小于50％，具有较小粒径的颗粒的百分比如果过高可能会造成循环性能降低。一些实施例中，如果没有具有较小粒径的颗粒，则不利于提高压实密度，并且对提高正极材料的动力学性能不利。
在一些实施例中，第一颗粒与第二颗粒的化学组成不同；第一颗粒包括：Li xNa zCo 1-y1M 1 y1O 2，其中，0.6<x<0.95，0≤y1<0.15，0≤z<0.05，M 1包括Al、Mg、Ti、Zr、La、Ca、Ge、Nb、Sn或Y中的至少一种；第二颗粒包括：Li xNa zCo 1-y2M 2 y2O 2，其中，0.6<x<0.95，0≤y2<0.15，0≤z<0.05，M 2包括Ni、Mn、Zn或Fe中的至少一种。不同粒径的颗粒的性能不同，粒径较小的颗粒的循环性能相对较差，粒径较大的颗粒的倍率性能相对较差，因此，本申请一些实施例中，第一颗粒和第二颗粒的化学组成不同，针对不同粒径的颗粒的性能缺点，选择对应的化学组成，从而弥补性能上的缺点。
一些实施例中，所述第一颗粒的平均粒径为3μm至12μm，所述第二颗粒的平均粒径为15μm至30μm。一些实施例中，如果第一颗粒和第二颗粒的平均粒径过小，会导致电解液的消耗增加，并且不利于正极材料的循环性能， 在另一些实施例中，如果第一颗粒和第二颗粒的平均粒径过大，可能会导致倍率性能降低。
在一些实施例中，正极材料的颗粒内部具有孔洞和裂缝。具有孔洞和裂缝的颗粒能够与电解液充分接触，并且在正极材料充放电的过程中发生膨胀时，孔洞和裂缝能够减少正极材料的内应力，从而有利于提高晶体结构的稳定性。一些实施例中，正极材料的比表面积为0.1m 2/g至2m 2/g。比表面积过小不利于倍率性能，比表面积过大可能导致循环性能下降。
本申请一些实施例中提出的一种正极材料，正极材料为具有P6 3mc晶相结构的颗粒；所述正极材料的粒度分布频率曲线图上包含第一峰和第二峰，正极材料包括：Li xNa zCo 1-yM yO 2，其中，0.6<x<0.95，0≤y<0.15，0≤z<0.05，M包括：Al、Mg、Ti、Mn、Fe、Ni、Zn、Cu、Nb、Cr、Y或Zr中的至少一种，具有P6 3mc晶相结构的颗粒的平均粒径为3μm至30μm。一些实施例中，正极材料可以采用掺杂或未掺杂的钴酸锂材料，钴酸锂中的掺杂元素，可以提高结构稳定性，但掺杂元素的含量过高时，可能会导致容量损失过大，在本申请所限定的范围内，能够在保证容量的情况下提高结构稳定性。
在一些实施例中，正极材料的颗粒内部具有孔洞和裂缝。具有孔洞和裂缝的颗粒能够与电解液充分接触，并且在正极材料充放电的过程中发生膨胀时，孔洞和裂缝能够减少正极材料的内应力，从而有利于提高晶体结构的稳定性。一些实施例中，正极材料的比表面积为0.1m 2/g至2m 2/g。比表面积过小不利于倍率性能，比表面积过大可能导致循环性能下降。
本申请的一些实施例中提出一种电化学装置，包括：正极；负极；电解液；隔离膜，隔离膜设置在正极和负极之间；其中，正极包括集流体和设置在集流体上的正极活性物质层，正极活性物质层包括上述任一项的正极材料。
在一些实施例中，电化学装置正极活性物质层的压实密度为3g/cm 3至4.35g/cm 3。一些实施例中，由于正极材料具有两种不同粒径的颗粒，因此有利于提高正极活性物质层的压实密度，但压实密度过大可能导致颗粒破碎。
在一些实施例中，电解液包括具有2至3个氰基的化合物；其中，具有2至3个氰基的化合物包括二腈化合物、三腈化合物、醚二腈化合物或醚三腈化合物中的至少一种。一些实施例中，氰基中的碳氮三键的键能很高，不易被氧化具有较高的稳定性，同时氰基的配位能力很强，可以和正极材料中 的高价态金属离子配位，从而减少对电解液的分解，相比于单氰化合物，具有2至3个氰基的化合物能够更好的减少本申请中正极与电解液的反应，抑制产气。
在一些实施例中，具有2至3个氰基的化合物包括戊二腈、丁二腈、己二腈、1,3,6-己三甲腈、1,3,5-戊三甲腈、1,2,3-丙三甲腈或1,2,3-三(2-氰基乙氧基)丙烷中至少一种，其中基于电解液重量，具有2至3个氰基的化合物的含量为0.01wt％至15wt％。本申请的一些实施例中提出一种电子装置，包括上述任一项的电化学装置。
在一些实施例中，所述电解液包括有机溶剂，所述有机溶剂包括碳酸乙烯酯、碳酸二乙酯、碳酸亚丙酯、丙酸丙酯或碳酸亚乙烯酯中至少一种。通过上述有机溶剂能和本文中的正极材料协同作用，稳定其晶体结构，从而改善循环性能。
本申请实施例提供的正极材料具有P63mc晶相结构的颗粒，P63mc晶相结构具有独特的HCP(hexagonal closest packing，六方最密堆积)氧结构，在高电压(例如4.6V及以上)循环过程中氧结构稳定，对电解液友好，循环性能优异。本申请中，正极材料的粒度分布频率曲线图上包含第一峰和第二峰，表明正极材料中包括两种不同粒径的颗粒，从而可以提高材料的加工性能，解决高配方沉降、压实密度低的问题，并且P63mc晶相结构本身为缺锂材料，充电过程需要脱锂离子打开通道，放电过程除容纳自身脱出锂离子外，还具有电化学嵌锂能力，吸收额外锂离子，正极材料的大小颗粒混合时，正极材料的动力学性能得到提升，因而正极材料具有更强的嵌锂能力，呈现更高的容量和更好的循环性能。
具体实施方式
下面将更详细地描述本申请的实施例。本申请可以通过各种形式来实现，而且不应该被解释为限于这里阐述的实施例，相反提供这些实施例是为了更加透彻和完整地理解本申请。
现有技术中具有R-3m相的钴酸锂正极材料在4.6V及以上的高电压下晶体结构发生不可逆相变(O3到H1-3，H1-3到O1)，使得材料循环性能和安全性能大大降低，相关技术中一般采用金属阳离子体相掺杂来提高R-3m相 钴酸锂正极材料的结构稳定性，大部分元素的掺杂都是通过推迟不可逆相变来提高材料的结构稳定性，但该方法在高于4.6V电压后对提高结构稳定性的效果不明显，并且当掺杂量增多后，理论容量的损失会增大，因此，相关技术中无法在4.6V及以上的高电压下保持晶体结构稳定性的同时保持容量和循环性能。
为了至少部分解决上述问题，本申请的一些实施例中提出一种正极材料，正极材料为具有P6 3mc晶相结构的颗粒；正极材料的粒度分布频率曲线图上包含第一峰和第二峰，这表明正极材料中具有两种不同粒径的P6 3mc晶相结构的颗粒。
本申请提出了一种由不同粒径大小颗粒组成的正极材料，一方面，P6 3mc相化合物具有特殊的HCP氧结构，在4.6V的高电压下十分稳定，对电解液友好，循环性能优异。另一方面，通过设计不同粒径的正极材料的颗粒，可以充分发挥不同粒径的颗粒的作用，提高材料的加工性能，解决高配方沉降和压实密度低的问题，有利于提高倍率性能。更为重要的是，P6 3mc晶相结构具有独特的缺锂结构，在脱锂/嵌锂过程中，由于其晶体结构中存在锂空位，具有容纳额外锂离子的能力，因此能够防止容量衰减，在不同粒径的颗粒混合时，正极材料的动力学性能得以提升，因此P6 3mc晶相结构有更强的嵌锂能力，呈现出更好的容量和更好的循环性能。
在本申请的一些实施例中，第一峰所表示的颗粒的粒径小于第二峰所表示的颗粒的粒径，第一峰的峰面积为S1，第二的峰面积为S2，0<S1/S2<1。一些实施例中，S1和S2分别表示了两种不同粒径的颗粒的含量，0<S1/S2<1表明具有较小的粒径的颗粒的百分比小于50％，具有较小粒径的颗粒的百分比如果过高可能会造成循环性能降低。一些实施例中，如果没有具有较小粒径的颗粒，则不利于提高压实密度，并且对提高正极材料的动力学性能不利。
在本申请的一些实施例中，正极材料包括：第一颗粒和第二颗粒；第一颗粒与第二颗粒的化学组成不同。在本申请的一些实施例中，第一颗粒包括：Li xNa zCo 1-y1M 1 y1O 2，其中，0.6<x<0.95，0≤y1<0.15，0≤z<0.05，M 1包括Al、Mg、Ti、Zr、La、Ca、Ge、Nb、Sn或Y中的至少一种；第二颗粒包括：Li xNa zCo 1-y2M 2 y2O 2，其中，0.6<x<0.95，0≤y2<0.15，0≤z<0.05，M 2包括Ni、Mn、Zn或Fe中的至少一种。一些实施例中，不同粒径的颗粒的性能不同， 粒径较小的颗粒的循环性能相对较差，粒径较大的颗粒的倍率性能相对较差，因此，本申请一些实施例中，第一颗粒和第二颗粒的化学组成不同，针对不同粒径的颗粒的性能缺点，选择对应的化学组成，从而弥补性能上的缺点，例如在粒径较小的第一颗粒中掺杂提高循环性能的元素，在粒径较大的第二颗粒中掺杂提高倍率性能的元素，从而使得正极材料整体上表现出更好的倍率性能和循环性能；第一颗粒的平均粒径为3μm至12μm，第二颗粒的平均粒径为15μm至30μm。一些实施例中，如果第一颗粒和第二颗粒的平均粒径过小，会导致电解液的消耗增加，并且不利于正极材料的循环性能，在另一些实施例中，如果第一颗粒和第二颗粒的平均粒径过大，可能会导致倍率性能降低。一些实施例中，第一颗粒为第一峰所表示的颗粒，第二颗粒为第二峰所表示的颗粒，第一颗粒和第二颗粒均为P6 3mc晶相结构。
在本申请的一些实施例中，正极材料的颗粒内部具有孔洞和裂缝。一些实施例中，具有孔洞和裂缝的颗粒能够与电解液充分接触，并且在正极材料充放电的过程中发生膨胀时，孔洞和裂缝能够减少正极材料的内应力，从而有利于提高晶体结构的稳定性。在一些实施例中，一个颗粒上的孔洞和裂缝的数量小于或等于50个，数量过多可能导致正极材料的机械强度不够，容易发生晶体坍塌。
本申请一些实施例中提出的一种正极材料，正极材料为具有P6 3mc晶相结构的颗粒；所述正极材料的粒度分布频率曲线图上包含第一峰和第二峰，正极材料包括：Li xNa zCo 1-yM yO 2，其中，0.6<x<0.95，0≤y<0.15，0≤z<0.05，M包括：Al、Mg、Ti、Mn、Fe、Ni、Zn、Cu、Nb、Cr、Y或Zr中的至少一种，具有P6 3mc晶相结构的颗粒的平均粒径为3μm至30μm。
一些实施例中，正极材料可以采用掺杂或未掺杂的钴酸锂材料，通过在钴酸锂中进行掺杂，可以提高结构稳定性，但掺杂元素的含量过高时，可能会导致容量损失过大，在本申请所限定的范围内，能够在保证容量的情况下提高结构稳定性。
一些实施例中，颗粒的粒径会影响正极材料的结构稳定性和倍率性能，一些实施例中，颗粒粒径较小的第一颗粒相比于第二颗粒的结构稳定性较差，颗粒粒径较大的第二颗粒相比于第一颗粒倍率性能较差，因此可以在第一颗 粒中掺杂有利于提高第一颗粒的结构稳定性的M 1，在第二颗粒中掺杂有利于提高第二颗粒的倍率性能的M 2。
在本申请的一些实施例中，正极材料的颗粒内部具有孔洞和裂缝。一些实施例中，具有孔洞和裂缝的颗粒能够与电解液充分接触，并且在正极材料充放电的过程中发生膨胀时，孔洞和裂缝能够减少正极材料的内应力，从而有利于提高晶体结构的稳定性。在一些实施例中，一个颗粒上的孔洞和裂缝的数量小于或等于50个，数量过多可能导致正极材料的机械强度不够，容易发生晶体坍塌。
在本申请的一些实施例中，正极材料的比表面积为0.1m 2/g至2m 2/g。一些实施例中，比表面积大于2m 2/g时，加速对于电解液的消耗，晶体结构的稳定性降低，可能会导致循环性能下降，不利于循环性能，而比表面积小于0.1m 2/g时可能会导致倍率性能较差。
在本申请的一些实施例中还提出一种电化学装置，包括：正极、负极、电解液和隔离膜，隔离膜设置在正极和负极之间；其中，正极包括集流体和设置在集流体上的正极活性物质层，正极活性物质层包括上述任一实施例中的正极材料。
在本申请的一些实施例中，电化学装置，正极活性物质层的压实密度为3g/cm 3至4.35g/cm 3。一些实施例中，由于正极材料具有两种不同粒径的颗粒，因此有利于提高正极活性物质层的压实密度，一些实施例中，以150MPa的压力压缩时的正极活性物质层的压实密度为3.80g/cm 3以上，以250MPa的压力压缩时正极活性物质层的压实密度为4g/cm 3以上，以500MPa的压力压缩时正极活性物质层的压实密度为4.2g/cm 3以上。(c)电化学装置在放电容量不小于200mAh/g时，将电化学装置在1C倍率下循环20圈，电化学装置的直流电阻的增长率小于或等于2％。一些实施例中，电化学装置在循环后的直流电阻的增长率小于或等于2％，可以表明本申请中电化学装置的正极材料具有较好的结构稳定性，在循环过程中未发生明显的结构变化，不会导致直流电阻明显增加。
在本申请的一些实施例中，电解液包括具有2至3个氰基的化合物；其中，具有2至3个氰基的化合物包括二腈化合物、三腈化合物、醚二腈化合物或醚三腈化合物中的至少一种。一些实施例中，氰基中的碳氮三键的键能 很高，不易被氧化具有较高的稳定性，同时氰基的配位能力很强，可以和正极材料中的高价态金属离子配位，从而减少对电解液的分解，相比于单氰化合物，具有2至3个氰基的化合物能够更好的减少正极与电解液的反应，抑制产气。
在本申请的一些实施例中，具有2至3个氰基的化合物包括戊二腈、丁二腈、己二腈、1,3,6-己三甲腈、1,3,5-戊三甲腈、1,2,3-丙三甲腈或1,2,3-三(2-氰基乙氧基)丙烷中至少一种，其中基于电解液重量，具有2至3个氰基的化合物的含量为0.01wt％至15wt％。
在一些实施例中，正极的集流体可以采用Al箔，当然，也可以采用本领域常用的其他正极的集流体。在一些实施例中，正极的集流体的厚度可以为1μm至200μm。在一些实施例中，正极活性物质层可以仅涂覆在正极的集流体的部分区域上。在一些实施例中，正极活性物质层的厚度可以为10μm至500μm。应该理解，这些仅是示例性的，可以采用其他合适的厚度。
在一些实施例中，隔离膜包括聚乙烯、聚丙烯、聚偏氟乙烯、聚对苯二甲酸乙二醇酯、聚酰亚胺或芳纶中的至少一种。例如，聚乙烯包括选自高密度聚乙烯、低密度聚乙烯或超高分子量聚乙烯中的至少一种。尤其是聚乙烯和聚丙烯，它们对防止短路具有良好的作用，并可以通过关断效应改善电池的稳定性。在一些实施例中，隔离膜的厚度在约5μm至500μm的范围内。
在一些实施例中，隔离膜表面还可以包括多孔层，多孔层设置在隔离膜的至少一个表面上，多孔层包括无机颗粒和粘结剂，无机颗粒选自氧化铝(Al 2O 3)、氧化硅(SiO 2)、氧化镁(MgO)、氧化钛(TiO 2)、二氧化铪(HfO 2)、氧化锡(SnO 2)、二氧化铈(CeO 2)、氧化镍(NiO)、氧化锌(ZnO)、氧化钙(CaO)、氧化锆(ZrO 2)、氧化钇(Y 2O 3)、碳化硅(SiC)、勃姆石、氢氧化铝、氢氧化镁、氢氧化钙或硫酸钡中的至少一种。在一些实施例中，隔离膜的孔具有在约0.01μm至1μm的范围的直径。多孔层的粘结剂选自聚偏氟乙烯、偏氟乙烯-六氟丙烯的共聚物、聚酰胺、聚丙烯腈、聚丙烯酸酯、聚丙烯酸、聚丙烯酸盐、羧甲基纤维素钠、聚乙烯呲咯烷酮、聚乙烯醚、聚甲基丙烯酸甲酯、聚四氟乙烯或聚六氟丙烯中的至少一种。隔离膜表面的多孔层可以提升隔离膜的耐热性能、抗氧化性能和电解质浸润性能，增强隔离膜与极片之间的粘接性。
在本申请的一些实施例中，电化学装置为卷绕式或堆叠式。
在一些实施例中，电化学装置包括锂离子电池，但是本申请不限于此。在一些实施例中，电化学装置还可以包括电解质。电解质可以是凝胶电解质、固态电解质和电解液中的一种或多种，电解液包括锂盐和非水溶剂。锂盐选自LiPF 6、LiBF 4、LiAsF 6、LiClO 4、LiB(C 6H 5) 4、LiCH 3SO 3、LiCF 3SO 3、LiN(SO 2CF 3) 2、LiC(SO 2CF 3) 3、LiSiF 6、LiBOB或者二氟硼酸锂中的一种或多种。例如，锂盐选用LiPF 6，因为它可以给出高的离子导电率并改善循环特性。
非水溶剂可为碳酸酯化合物、羧酸酯化合物、醚化合物、其它有机溶剂或它们的组合。
碳酸酯化合物可为链状碳酸酯化合物、环状碳酸酯化合物、氟代碳酸酯化合物或其组合。
链状碳酸酯化合物的实例为碳酸二乙酯(DEC)、碳酸二甲酯(DMC)、碳酸二丙酯(DPC)、碳酸甲丙酯(MPC)、碳酸乙丙酯(EPC)、碳酸甲乙酯(MEC)及其组合。所述环状碳酸酯化合物的实例为碳酸亚乙酯(EC)、碳酸亚丙酯(PC)、碳酸亚丁酯(BC)、碳酸乙烯基亚乙酯(VEC)或者其组合。所述氟代碳酸酯化合物的实例为碳酸氟代亚乙酯(FEC)、碳酸1,2-二氟亚乙酯、碳酸1,1-二氟亚乙酯、碳酸1,1,2-三氟亚乙酯、碳酸1,1,2,2-四氟亚乙酯、碳酸1-氟-2-甲基亚乙酯、碳酸1-氟-1-甲基亚乙酯、碳酸1,2-二氟-1-甲基亚乙酯、碳酸1,1,2-三氟-2-甲基亚乙酯、碳酸三氟甲基亚乙酯或者其组合。
羧酸酯化合物的实例为乙酸甲酯、乙酸乙酯、乙酸正丙酯、乙酸叔丁酯、丙酸甲酯、丙酸乙酯、丙酸丙酯、γ-丁内酯、癸内酯、戊内酯、甲瓦龙酸内酯、己内酯、甲酸甲酯或者其组合。
醚化合物的实例为二丁醚、四甘醇二甲醚、二甘醇二甲醚、1,2-二甲氧基乙烷、1,2-二乙氧基乙烷、乙氧基甲氧基乙烷、2-甲基四氢呋喃、四氢呋喃或者其组合。
其它有机溶剂的实例为二甲亚砜、1,2-二氧戊环、环丁砜、甲基环丁砜、1,3-二甲基-2-咪唑烷酮、N-甲基-2-吡咯烷酮、甲酰胺、二甲基甲酰胺、乙腈、磷酸三甲酯、磷酸三乙酯、磷酸三辛酯、和磷酸酯或者其组合。
本申请的实施例还提供了包括上述电化学装置的电子装置。本申请实施例的电子装置没有特别限定，其可以是用于现有技术中已知的任何电子装置。在一些实施例中，电子装置可以包括，但不限于，笔记本电脑、笔输入型计算机、移动电脑、电子书播放器、便携式电话、便携式传真机、便携式复印机、便携式打印机、头戴式立体声耳机、录像机、液晶电视、手提式清洁器、便携CD机、迷你光盘、收发机、电子记事本、计算器、存储卡、便携式录音机、收音机、备用电源、电机、汽车、摩托车、助力自行车、自行车、照明器具、玩具、游戏机、钟表、电动工具、闪光灯、照相机、家庭用大型蓄电池和锂离子电容器等。
本申请的一些实施例中还提出一种正极材料的制备方法，可以用于制备上述实施例中的正极材料，该制备方法包括如下步骤：
(1)制备Li xNa zCo 1-yM yO 2，其中0.6<x<0.95，0≤y<0.15，0≤z<0.05，M选自由Al、Mg、Ti、Mn、Fe、Ni、Zn、Cu、Nb、Cr或Zr组成的群组中的至少一者，
(2)液相沉淀法加烧结法制备具有不同粒径大小的M 1元素掺杂的(Co 1-y1M 1 y1) 3O 4和M 2元素掺杂的(Co 1-y2M 2 y2) 3O 4前躯体：将可溶性钴盐(例如，氯化钴、醋酸钴、硫酸钴、硝酸钴等)和M盐(例如，硫酸盐等)按照Co与M的摩尔比为(1-y1)：y1和(1-y2):y2的比例加入溶剂(例如，去离子水)中，按0.1mol/L至3mol/L浓度加入沉淀剂(例如碳酸钠、氢氧化钠)和络合剂(例如氨水)，络合剂与沉淀剂的摩尔比为0.1至1，调节pH值(例如，将pH值调节5至9)，使之沉淀；然后将沉淀物在空气下400℃至800℃进行烧结5h至20h，并对烧结产物进行研磨以获得具有不同平均粒径的M 1元素掺杂的(Co 1-y1M 1 y1) 3O 4和M 2元素掺杂的(Co 1-y2M 2 y2) 3O 4前躯体。M 1包括Al、Mg、Ti、Zr、La、Ca、Ge、Nb、Sn或Y中的至少一种；M 2包括Ni、Mn、Zn或Fe中的至少一种
(3)固相烧结法合成Na mCo 1-yM yO 2：M 1元素掺杂的(Co 1-y1M 1 y1) 3O 4和M 2元素掺杂的(Co 1-y2M 2 y2) 3O 4前躯体。粉体与Na 2CO 3粉体按照Na与Co的摩尔比为0.7：1到最大0.74：1的比例进行混合；将混合均匀的粉体在氧气气氛中、700℃至1000℃条件下烧结36h至56h得到P6 3mc结构的Na mCo 1-y1M 1 y1O 2和Na mCo 1-y2M 1 y2O 2，其中0.6<m<1。
(4)离子交换法合成P6 3mc结构的Li xNa zCo 1-yM yO 2正极材料：将Na mCo 1-y1M 1 y1O 2和Na mCo 1-y2M 1 y2O 2与含锂熔盐(例如，硝酸锂、氯化锂、氢氧化锂等)按照Na与Li的摩尔比为0.01至0.2的比例混合均匀，在200℃至400℃、空气气氛中反应2h至8h，反应物经去离子水多次洗涤，待熔盐清洗干净，烘干粉体得到P6 3mc结构的Li xNa zCo 1-y1M 1 y1O 2，其中，0.6<x<0.95，0≤y1<0.15，0≤z<0.05，第二颗粒包括：Li xNa zCo 1-y2M 2 y2O 2，其中，0.6<x<0.95，0≤y2<0.15，0≤z<0.05。
(5)Li xNa zCo 1-y1M 1 y1O 2和Li xNa zCo 1-y2M 2 y2O 2按照一定比例进行混合，其中，Li xNa zCo 1-y2M 2 y2O 2小于Li xNa zCo 1-y1M 1 y1O 2的数量。
下面列举了一些具体实施例和对比例以更好地对本申请进行说明，其中，采用锂离子电池作为示例。
正极极片的制备：将正极材料、导电剂导电炭黑、粘结剂聚偏二氟乙烯按重量比97：1.4：1.6的比例溶于N-甲基吡咯烷酮(NMP)溶液中，形成正极浆料。采用铝箔作为正极集流体，将正极浆料涂覆于正极集流体上，涂布重量为17.2mg/cm 2，经过干燥、冷压、裁切后得到正极极片。
负极极片的制备：负极材料为人造石墨。将负极材料、丙烯酸树脂、导电碳黑和羧甲基纤维素钠按重量比94.8：4.0：0.2：1.0的比例溶于去离子水中，形成负极活性物质层浆料，其中，硅的重量百分比为10％。采用10μm厚度铜箔作为负极集流体，将负极浆料涂覆于负极集流体上，涂布重量为6.27mg/cm 2，干燥至负极极片的含水量小于等于300ppm，得到负极活性物质层。裁切后得到负极极片。
隔离膜的制备：隔离膜基材为8μm厚的聚乙烯(PE)，在隔离膜基材的两侧各涂覆2μm氧化铝陶瓷层，最后在涂布了陶瓷层的两侧各涂覆2.5mg的粘结剂聚偏氟乙烯(PVDF)，烘干。
电解液的制备：在含水量小于10ppm的环境下，将六氟磷酸锂与非水有机溶剂(碳酸乙烯酯(EC)：碳酸二乙酯(DEC)：碳酸亚丙酯(PC)：丙酸丙酯(PP)：碳酸亚乙烯酯(VC)＝20：30：20：28：2，重量比)按重量比8：92配制以形成电解液。
锂离子电池的制备：将正极极片、隔离膜、负极极片按顺序依次叠好，使隔离膜处于正极极片和负极极片中间起到隔离的作用，并卷绕得到电极组 件。将电极组件置于外包装铝塑膜中，在80℃下脱去水分后，注入上述电解液并封装，经过化成，脱气，切边等工艺流程得到锂离子电池。
实施例和对比例的锂离子电池的制备步骤相同，各个实施例和对比例的区别仅在于所采用的正极材料不同，具体采用的正极材料如下表1至表8所示。
下面描述本申请的各个参数的测试方法。
颗粒体积分布测试：
取适量粉体进行超声分散，将分散物放入激光粒度测试仪器(Mastersizer3000)进行测试，测试方法参考粒度分布激光衍射法GB/T19077-2016，1、测试范围：0.02μm至2000μm(MS2000)；0.01μm至3500μm(MS3000)；2、检出限20nm。最后，得到粉体的体积分布曲线。需要说明的是，本申请中的平均粒径是指一个样品在体积基准的粒度分布中，累计粒度分布百分数达到50％时所对应的粒径。
容量保持率测试：
在25℃的环境中，进行第一次充电和放电，在0.5C(即2h内完全放掉理论容量的电流值)的充电电流下进行恒流充电，直到上限电压为4.8V；然后，在0.5C的放电电流下进行恒流放电，直到最终电压为3V，记录首次循环的放电容量(首圈放电容量)；继续进行到第100次充电和放电循环，记录第100次循环的放电容量。按照如下公式计算得到锂离子电池的第100圈循环后的容量保持率：
第100圈循环后的容量保持率＝第100次循环的放电容量/首次循环的放电容量×100％。
孔洞和裂缝测试：
利用离子抛光机(日本电子-IB-09010CP)对正极材料加工，得到断面。利用扫描电子显微镜对其断面进行拍摄，拍摄倍数不低于5.0K，获得颗粒图像，断面图像上可观测到孔洞和裂缝，在颗粒截面图像中，与周围颜色不同的闭合区域即为孔洞和裂缝。
孔洞选取要求为：单个颗粒中闭合区域的最长轴与颗粒最长轴的比介于2％到10％之间，且闭合区域的最长轴与最短轴的差值小于0.5微米，即为符合计数要求的孔洞；
裂缝的选取要求为：单个颗粒中闭合区域的最长轴与颗粒最长轴的比不低于70％时，即为符合计数要求的裂缝。
长短轴的选取方式：连接闭合曲线任意两点，最长的距离即为最长轴，最短的距离即为最短轴。
闭合区域是指图形中由封闭线条围成的一个区，闭合区域内部任何一点与区域外任何一点的连线都和区域的边界相交。
元素组成测试：
对正极材料的粉体采用iCAP7000 ICP检测仪进行元素分析测试；
对于负载有正极材料的极片，可采用NMP溶解极片，过滤取粉体烘干，采用iCAP7000 ICP检测仪进行元素分析测试。
X射线衍射测试：采用Bruker D8 ADVANCE获取正极材料的XRD衍射图谱。若拿不到粉体，针对正极极片，可采用NMP溶解正极极片，过滤取粉体烘干，用XRD检测粉体。
比表面积(BET)测试方法：测试设备为：BSD-BET400；测试过程：将样品放入充满N 2气体体系,材料的表面在液氮温度下发生物理吸附。当该物理吸附处于平衡时,通过测量平衡时的吸附压力和吸附气体的流量,可求出材料的单分子层吸附量,从而计算出试样的比表面积。
压实密度测试：将锂离子电池放电至0SOC％(SOC：State Of Charge，荷电状态)，拆解电池，清洗，烘干，使用电子天平对一定面积A的正极极片(正极集流体的双面涂覆有正极活性物质层)进行称重，重量记为W 1，并使用万分尺测得正极的厚度T 1。使用溶剂洗掉正极活性物质层，烘干，测量正极集流体的重量，记为W 2，并使用万分尺测得正极集流体的厚度T 2。通过下式计算设置在正极集流体一侧的正极活性物质层的重量W 0和厚度T 0以及正极活性物质层的压实密度：
W 0＝(W 1-W 2)/2
T 0＝(T 1-T 2)/2
压实密度＝W 0/(T0×A)。
表1
Figure PCTCN2021104024-appb-000001
Figure PCTCN2021104024-appb-000002
从表1中可以看出，实施例1-1到实施例1-17的首圈放电容量和循环容量中的综合性能优于对比例1-1到对比例1-8，由此可知，在正极材料中同时包括P6 3mc晶相结构的Li a1Na c1Co 1-b1M 1 b1O 2和Li a2Na c2Co 1-b2M 2 b2O 2，且Li a1Na c1Co 1-b1M 1 b1O 2和Li a2Na c2Co 1-b2M 2 b2O 2的颗粒的尺寸不同时能够提高首圈放电容量和循环容量，因此本申请的一些实施例中限定正极材料包含具有P6 3mc晶相结构的颗粒，且正极材料的粒度分布频率曲线图上包含第一峰和第二峰。
对比实施例1-1到实施例1-17、以及对比例1-9和对比例1-10可以看出，当第一颗粒尺寸在3μm至12μm内，当第二颗粒尺寸在15μm至30μm内时，锂离子电池的首圈放电容量不低于239mAh/g且100圈循环容量保持率不低于88％，而当第一颗粒尺寸大于或等于13μm、第二颗粒尺寸大于或等于32μm时，会造成首圈放电容量下降和循环容量保持率下降。因此一些实施例中限定第一颗粒的平均粒径为3μm至12μm，第二颗粒的平均粒径为15μm至30μm。
对比实施例1-1到实施例1-17可以看出，实施例1-1中未使用M 1或M 2进行掺杂，而实施例1-2到实施例1-17均进行了掺杂，实施例1-2到实施例1-17的首圈放电容量和100圈循环容量保持率均优于实施例1-1，因此在本申请中的一些实施例中正极材料中具有M 1或M 2。
实施例1-18至实施例1-19可以看出，实施例1-18中使用Zn进行掺杂，实施例1-19中使用Al进行掺杂，因同时存在化学组成相同的大颗粒和小颗粒，实施例1-18至实施例1-19的首圈放电容量和100圈循环容量保持率均优于实施例1-1，因此本申请中的一些实施例中正极材料的粒度分布频率曲线图上包含第一峰和第二峰。
在表2所示的实施例和对比例中，所采用的正极材料均为Li xNa zCo 1-yM yO 2，表2中各个实施例和对比例的正极材料的晶相结构均为P6 3mc。
表2
Figure PCTCN2021104024-appb-000003
Figure PCTCN2021104024-appb-000004
对比实施例2-1和对比例2-1到对比例2-3可以看出，相比于正极材料中没有孔洞和裂缝的对比例2-3，正极材料中有孔洞或缝隙的一个时，能够提高首圈放电容量和100圈循环容量保持率，当正极材料中同时具有孔洞和裂缝时，锂离子电池具有更高的首圈放电容量和100圈循环容量保持率，因此在本申请的一些实施例中限定正极材料的颗粒内部具有孔洞和裂缝。
在表3所示的实施例和对比例中，所采用的正极材料均为Li xNa zCo 1-yM yO 2，表3中各个实施例和对比例的正极材料的晶相结构均为P6 3mc。
表3
Figure PCTCN2021104024-appb-000005
对比实施例3-1、实施例3-2、对比例3-1和对比例3-2可以看出，当正极材料的比表面积大于2m 2/g时，锂离子电池的首圈放电容量较小，且100圈循环容量保持率较低，当正极材料的比表面积小于或等于2m 2/g时，锂离子电池的首圈放电容量较高，且100圈循环容量保持率较好，因此在本申请的一些实施例中限定正极材料的比表面积为0.1m 2/g至2m 2/g。
在表4所示的实施例和对比例中，采用的正极材料均为Li xNa zCo 1-yM yO 2，表4中各个实施例和对比例的正极材料的晶相结构均为P6 3mc。表4中的主峰范围是指正极材料的X射线衍射图谱中强度最强的衍射峰的衍射角，表4中的半高宽是指主峰的衍射峰。
表4
Figure PCTCN2021104024-appb-000006
对比实施例4-1、实施例4-2、对比例4-1和对比例4-2可以看出，主峰范围在18°至19°时，相比于半高宽为大于0.5°的情况，当半高宽在0°至0.5°范围内时，锂离子电池的首圈放电容量和100圈循环容量保持率均较高，在正极材料的X射线衍射图谱中，强度最强的衍射峰的衍射角在18°至19°范围，强度最强的衍射峰的半高宽在0°至0.5°范围内。
在表5所示的实施例和对比例中，所采用的正极材料均为Li xNa zCo 1-yM yO 2，表5中各个实施例和对比例的正极材料的晶相结构均为P6 3mc。
表5
Figure PCTCN2021104024-appb-000007
对比实施例5-1到实施例5-6，以及对比例5-1和对比例5-2可以看出，实施例5-1到实施例5-6的首圈放电容量和100圈循环容量保持率均高于对比例5-1和对比例5-2，由此可见，当正极活性物质层的压实密度为3g/cm 3至4.35g/cm 3的情况下，有利于提高锂离子电池的放电性能和循环性能。
表6
Figure PCTCN2021104024-appb-000008
Figure PCTCN2021104024-appb-000009
对比实施例7-1到实施例7-8以及对比例7-1和对比例7-2可以看出，在锂离子电池的电解液中加入具有2至3个氰基的化合物，并且控制具有2至3个氰基的化合物的质量含量在0.01wt％至15wt％范围内时，可以提高锂离子电池的首圈放电容量和100圈循环容量保持率。
以上描述仅为本申请的较佳实施例以及对所运用技术原理的说明。本领域技术人员应当理解，本申请中所涉及的公开范围，并不限于上述技术特征的特定组合而成的技术方案，同时也应涵盖由上述技术特征或其等同特征进行任意组合而形成的其它技术方案。例如上述特征与本申请中公开的具有类似功能的技术特征进行互相替换而形成的技术方案。

Claims (15)

  1. 一种正极材料，其特征在于，
    所述正极材料包括具有P6 3mc晶相结构的颗粒；
    所述正极材料的粒度分布频率曲线图上包含第一峰和第二峰。
  2. 根据权利要求1所述的正极材料，其特征在于，所述第一峰所表示的颗粒的粒径小于第二峰所表示的颗粒的粒径，所述第一峰的峰面积为S1，所述第二的峰面积为S2，0<S1/S2<1。
  3. 根据权利要求1所述的正极材料，其特征在于，
    所述正极材料包括：第一颗粒和第二颗粒；
    所述第一颗粒包括：Li xNa zCo 1-y1M 1 y1O 2，其中，0.6<x<0.95，0≤y1<0.15，0≤z<0.05，M 1包括Al、Mg、Ti、Zr、La、Ca、Ge、Nb、Sn或Y中的至少一种；
    所述第二颗粒包括：Li xNa zCo 1-y2M 2 y2O 2，其中，0.6<x<0.95，0≤y2<0.15，0≤z<0.05，M 2包括Ni、Mn、Zn或Fe中的至少一种。
  4. 根据权利要求3所述的正极材料，其特征在于，所述第一颗粒的平均粒径为3μm至12μm。
  5. 根据权利要求3所述的正极材料，其特征在于，所述第二颗粒的平均粒径为15μm至30μm。
  6. 根据权利要求1所述正极材料，其特征在于，所述正极材料的颗粒内部具有孔洞和裂缝。
  7. 根据权利要求1所述正极材料，其特征在于，所述正极材料的比表面积为0.1m 2/g至2m 2/g。
  8. 一种正极材料，其特征在于，所述正极材料包括具有P6 3mc晶相结构的颗粒；
    所述正极材料的粒度分布频率曲线图上包含第一峰和第二峰，
    所述正极材料包括：Li xNa zCo 1-yM yO 2，其中，0.6<x<0.95，0≤y<0.15，0≤z<0.05，M包括：Al、Mg、Ti、Mn、Fe、Ni、Zn、Cu、Nb、Cr、Y或Zr中的至少一种。
  9. 根据权利要求8所述正极材料，其特征在于，所述具有P6 3mc晶相结构的颗粒的平均粒径为3μm至30μm。
  10. 一种电化学装置，其特征在于，包括：
    正极；负极；电解液；隔离膜，所述隔离膜设置在所述正极和所述负极之间；
    其中，所述正极包括集流体和设置在所述集流体上的正极活性物质层，所述正极活性物质层包括如权利要求1至9中任一项所述的正极材料。
  11. 根据权利要求10所述的电化学装置，其特征在于，所述正极活性物质层的压实密度为3g/cm 3至4.35g/cm 3。
  12. 根据权利要求10所述的电化学装置，其特征在于，所述电解液包括具有2至3个氰基的化合物，基于所述电解液的重量，所述具有2至3个氰基的化合物的含量为0.01wt％至15wt％。
  13. 根据权利要求12所述的电化学装置，其特征在于，所述具有2至3个氰基的化合物包括二腈化合物、三腈化合物、醚二腈化合物或醚三腈化合物中的至少一种。
  14. 根据权利要求12所述的电化学装置，其特征在于，所述具有2至3个氰基的化合物包括戊二腈、丁二腈、己二腈、1,3,6-己三甲腈、1,3,5-戊三甲腈、1,2,3-丙三甲腈或1,2,3-三(2-氰基乙氧基)丙烷中至少一种。
  15. 一种电子装置，其特征在于，包括权利要求10至15任一项所述的电化学装置。
PCT/CN2021/104024 2020-12-11 2021-07-01 正极材料、电化学装置和电子装置 WO2022121293A1 (zh)

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