WO2023082757A1 - 一种锂过渡金属复合氧化物、电化学装置和电子装置 - Google Patents

一种锂过渡金属复合氧化物、电化学装置和电子装置 Download PDF

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WO2023082757A1
WO2023082757A1 PCT/CN2022/113859 CN2022113859W WO2023082757A1 WO 2023082757 A1 WO2023082757 A1 WO 2023082757A1 CN 2022113859 W CN2022113859 W CN 2022113859W WO 2023082757 A1 WO2023082757 A1 WO 2023082757A1
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transition metal
composite oxide
metal composite
lithium transition
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French (fr)
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王凯
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宁德新能源科技有限公司
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Priority to EP22891564.1A priority Critical patent/EP4350811A1/en
Publication of WO2023082757A1 publication Critical patent/WO2023082757A1/zh
Priority to US18/400,630 priority patent/US20240136518A1/en

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    • 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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    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
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    • 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 field of electrochemical technology, in particular to a lithium transition metal composite oxide, an electrochemical device and an electronic device.
  • Lithium-ion batteries have the advantages of high energy storage density, high open circuit voltage, low self-discharge rate, long cycle life, and good safety. They are widely used in various fields such as portable electric energy storage, electronic equipment, and electric vehicles. However, higher requirements are also placed on the overall performance of lithium-ion batteries, such as good cycle performance at high voltages (eg greater than 4.2V).
  • the purpose of this application is to provide a lithium transition metal composite oxide, an electrochemical device and an electronic device, so as to improve the cycle performance of the electrochemical device under high voltage.
  • the first aspect of the present application provides a lithium transition metal composite oxide, wherein the lithium transition metal composite oxide has a twin structure, the twin structure includes a first crystal region and a second crystal region, the first crystal region and the second crystal region There is a grain boundary between the two crystal regions, the first crystal region includes a first region within 20nm from the grain boundary, the second crystal region includes a second region within 20nm from the grain boundary, the transition metal layer in the first region and the second
  • the included angle between the transition metal layers in the region is 65° to 80°.
  • the transition metal layer in the first region includes at least one of Co, Mn, or Ni. In some embodiments of the present application, the transition metal layer in the second region includes at least one of Co, Mn, or Ni.
  • the main bodies of the first region and the second region are layered oxide materials containing Co/Ni/Mn, and they will fuse and grow to form twin boundaries under the action of high temperature; the first region and the second region include The above-mentioned transition metal elements all present a layered structure, and the two are connected by twins, which is a connection method with the lowest energy, which is conducive to the stability of the structure.
  • the grain boundaries include element A including at least one of Mg, Al, Ti, Zr, La, Nb, Hf, Zn, Y, or F.
  • element A including at least one of Mg, Al, Ti, Zr, La, Nb, Hf, Zn, Y, or F.
  • the first region includes a third region within 10 nm from the grain boundary and a fourth region from 10 nm to 20 nm from the grain boundary, based on the total moles of Co, Mn and Ni in the third region, the third The mole percentage of element A in the region is X; based on the total moles of Co, Mn and Ni in the fourth region, the mole percentage of element A in the fourth region is Y, satisfying: X/Y ⁇ 2.
  • X is from 0.2% to 2.5%. At this time, the structural stability near the grain boundary in the first crystal region can be better ensured.
  • the area ratio of the second crystal region is 30% to 60%.
  • the lithium transition metal composite oxide includes a substrate and a first layer on the surface of the substrate, the first layer including metal fluoride.
  • the first layer includes metal fluoride, side reactions between the surface of the matrix and the electrolyte can be suppressed, and the stability of the surface structure of the lithium transition metal composite oxide can be improved, thereby improving the cycle performance of the electrochemical device.
  • the lithium transition metal composite oxide satisfies at least one of the following characteristics: (a) the metal fluoride includes at least one of CoF 2 , CoF 3 , CoFO, MgF 2 , NaF or AlF 3 species; (b) the thickness of the first layer is 1nm to 8nm.
  • the lithium transition metal composite oxide satisfies at least one of the characteristics (a) to (b), it is beneficial to improve the cycle performance of the electrochemical device.
  • the second aspect of the present application provides an electrochemical device, which includes a positive electrode sheet, the positive electrode sheet includes a positive electrode material layer, the positive electrode material layer includes a positive electrode active material, and the positive electrode active material includes the lithium transition metal in any of the foregoing embodiments composite oxides.
  • the electrochemical device is fully loaded and then disassembled to obtain the positive electrode sheet, and a disc with a diameter of 1.4 cm in the positive electrode sheet is assembled with lithium metal to form a button battery, and the button battery is charged to 4.7V, wherein the included angle ⁇ in the lithium transition metal composite oxide is 70° to 86°.
  • the electrochemical device is fully loaded and disassembled to obtain the positive pole piece, and two discs with a diameter of 1.4 cm in the positive pole piece are taken and assembled with lithium metal to form the first button battery and the second battery respectively.
  • the included angle between the layer and the transition metal layer in the second region is ⁇ ;
  • the angle between them is ⁇ , satisfying:
  • the number of particles of the positive electrode active material with a twin crystal structure accounts for 35% to 75%.
  • the ratio of the number of particles of the positive electrode active material having a twin crystal structure within the above-mentioned range is beneficial to improve the rate performance and cycle performance of the electrochemical device.
  • the electrochemical device further includes an electrolytic solution
  • the electrolytic solution includes a fluorocarbonate compound
  • the mass percentage of the fluorocarbonate compound is 0.05% to 15% based on the mass of the electrolytic solution.
  • the introduction of the fluorocarbonate compound can form a protective layer at the interface where the twin crystal structure is split, reduce the side reaction between the lithium transition metal composite oxide and the electrolyte, and thereby improve the cycle performance of the electrochemical device.
  • the fluorocarbonate compound includes monofluoroethylene carbonate, difluoroethylene carbonate, 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate , 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylcarbonate At least one of ethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate or trifluoromethylethylene carbonate A sort of.
  • a third aspect of the present application provides an electronic device, which includes the electrochemical device in any one of the foregoing embodiments.
  • the application provides a lithium transition metal composite oxide, an electrochemical device, and an electronic device.
  • the lithium transition metal composite oxide has a twin structure, and the twin structure includes a first crystal region and a second crystal region, and the first crystal region and the second crystal region There is a grain boundary between the two crystal regions, the first crystal region includes a first region within 20nm from the grain boundary, the second crystal region includes a second region within 20nm from the grain boundary, the transition metal layer in the first region and the second
  • the included angle between the transition metal layers in the region is 65° to 80°.
  • Fig. 1 is the scanning electron microscope picture of positive pole piece section in embodiment 1-1;
  • Fig. 2 is the scanning electron micrograph of the lithium transition metal composite oxide with twin crystal structure in the positive pole piece section in embodiment 1-1;
  • Fig. 3 is the positive pole piece obtained by dismantling the electrochemical device in Example 1-1 after being fully charged, the positive pole piece and lithium metal are assembled into a button battery, and when it is charged to 4.7V, the lithium transition metal composite oxide is obtained.
  • Fig. 4 is a graph showing the variation of the capacity retention rate of the electrochemical devices in Example 1-1 and Comparative Example 1-1 with the number of cycles.
  • a lithium-ion battery is used as an example of an electrochemical device to explain the present application, but the electrochemical device of the present application is not limited to the lithium-ion battery.
  • positive electrode active materials with twin structure such as lithium cobaltate
  • twin structure can provide multi-directional migration paths for lithium ions, which is beneficial to improve the rate performance of electrochemical devices.
  • the twin structure is unstable under high voltage, especially at the grain boundary, which is prone to cracking, causing side reactions between the material and the electrolyte, thereby affecting the cycle performance of the electrochemical device, which is difficult to meet the needs of practical applications.
  • the first aspect of the present application provides a lithium transition metal composite oxide, wherein the lithium transition metal composite oxide has a twin structure, the twin structure includes a first crystal region and a second crystal region, the first crystal region and the second crystal region There is a grain boundary between the two crystal regions, the first crystal region includes a first region within 20nm from the grain boundary, the second crystal region includes a second region within 20nm from the grain boundary, the transition metal layer in the first region and the second
  • the included angle between the transition metal layers in the region is 65° to 80°.
  • the included angle may be 65°, 70°, 75°, 80° or any range therebetween.
  • Lithium transition metal composite oxides can be used as positive electrode active materials in electrochemical devices.
  • the inventors of the present application have found that by adjusting the angle between the first region and the second region to be 65° to 80°, the charging and discharging can be reduced.
  • the stress and strain between the first crystal region and the second crystal region during the process can improve the stability of the twin crystal structure, thereby improving the cycle performance of the electrochemical device under high voltage.
  • the first grain region refers to a region where the transition metal layer in the crystal structure has the same orientation on one side of the twin grain boundary
  • the second grain region refers to a region where the twin grain boundary is different from the first grain region.
  • the transition metal layers in the crystal structure have regions of the same orientation.
  • the above included angle refers to the included angle formed when the orientation of the transition metal layer in the first region and the orientation of the transition metal layer in the second region respectively extend to intersect at the grain boundary.
  • the above-mentioned included angle means that after the electrochemical device is fully charged, the positive electrode sheet is disassembled, and the lithium transition metal composite oxide in the positive electrode sheet is In the object, the angle between the transition metal layer in the first region and the transition metal layer in the second region.
  • the transition metal layer in the first region includes at least one of Co, Mn, or Ni. In some embodiments of the present application, the transition metal layer in the second region includes at least one of Co, Mn, or Ni. Both the transition metal layer in the first region and the second region include the above transition metal, which is beneficial to improve the interfacial compatibility between the first region and the second region, thereby improving the stability of the twin structure.
  • the grain boundaries include element A including at least one of Mg, Al, Ti, Zr, La, Nb, Hf, Zn, Y, or F.
  • element A including at least one of Mg, Al, Ti, Zr, La, Nb, Hf, Zn, Y, or F.
  • element A includes Mg
  • O at the grain boundary can form Mg-O bonds with Mg, which improves the stability of the O structure; for example, when element A includes F, it can form a local disordered structure, disperse stress, and reduce Risk of cracking of the twin structure.
  • the mole percentage of element A in the grain boundary is 0.2% to 2.5%.
  • the mass percentage of element A can be 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, or any range therebetween.
  • the first region includes a third region within 10 nm from the grain boundary and a fourth region from 10 nm to 20 nm from the grain boundary, based on the total moles of Co, Mn and Ni in the third region, the third The molar percentage of element A in the region is X; based on the total moles of Co, Mn and Ni in the fourth region, the molar percentage of element A in the fourth region is Y, satisfying: X/Y ⁇ 2, preferably 2 ⁇ X/Y ⁇ 12. The value of X/Y can be 2, 3, 4, 5, 6, 7, 8, 9, 10 or any range therebetween.
  • X is from 0.2% to 2.5%.
  • the value of X can be 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, or any range therebetween.
  • X is 0.2% to 2.5%, which is more conducive to improving the structural stability near the grain boundary in the first crystal region, reducing the risk of twin structure cracking, thereby improving the structural stability of lithium transition metal composite oxides under high voltage .
  • the present application has no particular limitation on the value of Y, as long as X/Y ⁇ 2 is satisfied, for example, 0% ⁇ Y ⁇ 1.0%.
  • the area ratio of the second crystal region is 30% to 60%.
  • the area ratio of the second crystal region can be 30%, 35%, 40%, 45%, 50%, 55%, 60%, or any range therebetween.
  • the lithium transition metal composite oxide includes a substrate and a first layer on the surface of the substrate, the first layer including metal fluoride.
  • the inventors of the present application have found that when the lithium-transition metal composite oxide has a first layer, and the first layer includes metal fluoride, side reactions between the surface of the substrate and the electrolyte can be suppressed, and the surface structure of the lithium-transition metal composite oxide can be improved. stability, thereby improving the cycle performance of electrochemical devices.
  • the metal fluoride includes at least one of CoF 2 , CoF 3 , CoFO, MgF 2 , NaF, or AlF 3 .
  • the first layer has a thickness of 1 nm to 8 nm.
  • the thickness of the first layer may be 1 nm, 2 nm, 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm or any range therebetween.
  • the preparation method of the lithium transition metal composite oxide may include but not limited to the following steps: the transition metal source, The doping element sources are mixed and configured into an aqueous solution, and precipitates are obtained by co-precipitation, and then calcined once, ground and sieved to obtain the first intermediate product; then the first intermediate product is mixed with the lithium source and then calcined twice, ground through sieve to obtain the second intermediate product; then mix the second intermediate product with the dopant element source, perform three calcinations, grind and sieve to obtain the lithium transition metal composite oxide.
  • T1 and time t1 of primary calcination the temperature T2 and time t2 of secondary calcination, the temperature T3 and time t3 of tertiary calcination, as long as the purpose of this application can be achieved, for example, T1 is 500 ° C To 1000°C, t1 is 5h to 15h; T2 is 800°C to 1500°C, t2 is 5h to 15h; T3 is 500°C to 1000°C, t3 is 5h to 15h.
  • Lithium transition metal composite oxides include Li x Ni y Co z Mn k Z q O 2 ⁇ a T a , wherein Z includes B, Mg, Al, Si, P, S, Ti, Cr, Fe, Cu, Zn, At least one of Ga, Y, Zr, Mo, Ag, W, In, Sn, Sb, La, Nb, Hf or Ce, T is halogen; where, 0.2 ⁇ x ⁇ 1.2, 0 ⁇ y ⁇ 1, 0 ⁇ z ⁇ 1, 0 ⁇ k ⁇ 1, 0 ⁇ q ⁇ 1, and y, z, k are not 0 at the same time, and 0 ⁇ a ⁇ 1.
  • the second aspect of the present application provides an electrochemical device, which includes a positive electrode sheet, the positive electrode sheet includes a positive electrode material layer, the positive electrode material layer includes a positive electrode active material, and the positive electrode active material includes the lithium transition metal in any of the foregoing embodiments composite oxides.
  • the lithium transition metal composite oxide provided by the present application has good structural stability, so the electrochemical device provided by the present application has good cycle performance.
  • the electrochemical device is fully loaded and then disassembled to obtain the positive electrode sheet, and a disc with a diameter of 1.4 cm in the positive electrode sheet is assembled with lithium metal to form a button battery, and the button battery is charged to 4.7V, wherein the included angle ⁇ in the lithium transition metal composite oxide is 70° to 86°.
  • the included angle in the lithium transition metal composite oxide is 70°, 72°, 75°, 78°, 80°, 82°, 85°, 86° or any range therebetween.
  • the angle in the lithium transition metal composite oxide is within the above range, indicating that the angle between the transition metal layer in the first region and the transition metal layer in the second region changes at high voltage Smaller, it can improve the stability of the twin structure, thereby improving the cycle performance of the electrochemical device under high voltage.
  • the electrochemical device is fully loaded and disassembled to obtain the positive pole piece, and two discs with a diameter of 1.4 cm in the positive pole piece are taken and assembled with lithium metal to form the first button battery and the second battery respectively.
  • the included angle between the layer and the transition metal layer in the second region is ⁇ ;
  • the angle between them is ⁇ , which satisfies:
  • may be 0.1°, 0.5°, 1°, 2°, 3°, 4°, 5° or any range therebetween.
  • assembly methods known in the art can be used for assembly.
  • the number of particles of the positive electrode active material with a twin crystal structure accounts for 35% to 75%.
  • the proportion of the number of particles of the positive electrode active material with twin structure is 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, or any range therebetween.
  • the positive electrode active material may also include positive electrode active materials known in the art, for example, may include but not limited to lithium nickel cobalt manganate, lithium nickel cobalt aluminate, lithium iron phosphate, lithium cobaltate , lithium manganese oxide or lithium iron manganese phosphate at least one.
  • the electrochemical device includes an electrolyte
  • the electrolyte includes a fluorocarbonate compound
  • the mass percentage of the fluorocarbonate compound is 0.05% to 15% based on the mass of the electrolyte.
  • the mass percentage of the fluorocarbonate compound can be 0.05%, 0.5%, 1%, 5%, 10%, 15%, or any range therebetween.
  • the inventors of the present application have found that the introduction of fluorocarbonate compounds can form a protective layer at the interface where the twin crystal structure is cracked, reducing the side reaction between the lithium transition metal composite oxide and the electrolyte, thereby improving the performance of the electrochemical device. cycle performance.
  • the fluorocarbonate compound includes monofluoroethylene carbonate, difluoroethylene carbonate, 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate , 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylcarbonate At least one of ethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate or trifluoromethylethylene carbonate A sort of.
  • the cathode material layer includes a binder.
  • the binder may include, but is not limited to, polyacryl alcohol, sodium polyacrylate, potassium polyacrylate, lithium polyacrylate, polyimide, polyimide, polyamideimide, butyl Styrene rubber (SBR), polyvinyl alcohol (PVA), polyvinylidene fluoride, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl butyral (PVB), water-based acrylic resin, carboxylate At least one of methylcellulose (CMC) or sodium carboxymethylcellulose (CMC-Na).
  • the positive electrode sheet usually includes a positive current collector.
  • the positive current collector is not particularly limited, as long as the purpose of this application can be achieved, for example, it may include but not limited to aluminum foil, aluminum alloy foil, or a composite current collector.
  • the thickness of the positive electrode collector there is no particular limitation on the thickness of the positive electrode collector, as long as the purpose of the present application can be achieved, for example, the thickness is 8 ⁇ m to 12 ⁇ m.
  • the positive electrode material layer may be provided on one or both surfaces along the thickness direction of the positive electrode current collector. It should be noted that the "surface” here may refer to the entire area of the positive electrode collector or a partial area of the positive electrode collector. This application is not particularly limited, as long as the purpose of this application can be achieved.
  • a conductive agent may also be included in the positive electrode material layer, and the present application has no special limitation on the conductive agent, as long as the purpose of the application can be realized, for example, it may include but not limited to conductive carbon black (Super P), carbon nanotubes (CNTs), carbon fiber, flake graphite, Ketjen black, graphene, metal material or conductive polymer.
  • the aforementioned carbon nanotubes may include, but are not limited to, single-walled carbon nanotubes and/or multi-walled carbon nanotubes.
  • the aforementioned carbon fibers may include, but are not limited to, vapor grown carbon fibers (VGCF) and/or carbon nanofibers.
  • the above metal material may include but not limited to metal powder and/or metal fiber, specifically, the metal may include but not limited to at least one of copper, nickel, aluminum or silver.
  • the aforementioned conductive polymer may include but not limited to at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene or polypyrrole.
  • the positive electrode may further include a conductive layer located between the positive electrode current collector and the positive electrode material layer.
  • the present application has no particular limitation on the composition of the conductive layer, which may be a commonly used conductive layer in the field, for example, may include but not limited to the above-mentioned conductive agent and the above-mentioned binder.
  • the electrochemical device of the present application also includes a negative electrode sheet.
  • the negative electrode sheet usually includes a negative electrode collector and a negative electrode material layer arranged on the surface of the negative electrode collector.
  • the application has no special restrictions on the negative electrode collector, as long as the purpose of the application can be achieved.
  • it may include but not limited to copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam or composite current collectors.
  • the thickness of the negative electrode collector there is no particular limitation on the thickness of the negative electrode collector, as long as the purpose of the present application can be achieved, for example, the thickness is 4 ⁇ m to 12 ⁇ m.
  • the negative electrode material layer may be provided on one or both surfaces along the thickness direction of the negative electrode current collector.
  • the "surface” here may be the entire area of the negative electrode collector, or a partial area of the negative electrode collector. This application is not particularly limited, as long as the purpose of this application can be achieved.
  • the negative electrode material layer includes negative electrode active materials, wherein the negative electrode active material is not particularly limited, as long as the purpose of the application can be achieved, for example, it can include but not limited to natural graphite, artificial graphite, mesophase micro carbon spheres, hard Carbon, soft carbon, silicon, silicon-carbon composite, Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO 2 , lithiated TiO 2 -Li 4 Ti 5 O 12 or Li with spinel structure - at least one of Al alloys.
  • the negative electrode active material is not particularly limited, as long as the purpose of the application can be achieved, for example, it can include but not limited to natural graphite, artificial graphite, mesophase micro carbon spheres, hard Carbon, soft carbon, silicon, silicon-carbon composite, Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO 2 , lithiated TiO 2 -Li 4 Ti 5 O 12 or Li with spinel structure
  • the negative electrode material layer may also include a conductive agent.
  • the present application has no special limitation on the conductive agent, as long as the purpose of the present application can be achieved, for example, it may include but not limited to at least one of the above-mentioned conductive agents.
  • the negative electrode material layer may also include a binder, and the present application has no special restrictions on the binder, as long as the purpose of the application can be achieved, for example, it may include but not limited to at least one of the above-mentioned binders .
  • the negative electrode sheet may further include a conductive layer located between the negative electrode current collector and the negative electrode material layer.
  • the present application has no particular limitation on the composition of the conductive layer, which may be a commonly used conductive layer in the field, and the conductive layer may include but not limited to the above-mentioned conductive agent and the above-mentioned binder.
  • the electrochemical device of the present application also includes a separator, which is not particularly limited in the present application, as long as the purpose of the application can be achieved, such as but not limited to polyethylene (PE), polypropylene (PP), polytetrafluoroethylene Ethylene-based polyolefin (PO) separator, polyester film (such as polyethylene terephthalate (PET) film), cellulose film, polyimide film (PI), polyamide film (PA) , spandex, aramid film, woven film, nonwoven film (non-woven fabric), microporous film, composite film, separator paper, rolled film or spinning film, preferably PP.
  • a separator which is not particularly limited in the present application, as long as the purpose of the application can be achieved, such as but not limited to polyethylene (PE), polypropylene (PP), polytetrafluoroethylene Ethylene-based polyolefin (PO) separator, polyester film (such as polyethylene terephthalate (PET) film),
  • the separator of the present application may have a porous structure, and the pore size is not particularly limited as long as the purpose of the present application can be achieved, for example, the pore size may be 0.01 ⁇ m to 1 ⁇ m.
  • the thickness of the isolation film is not particularly limited, as long as the purpose of the present application can be achieved, for example, the thickness may be 5 ⁇ m to 500 ⁇ m.
  • a separator may include a substrate layer and a surface treatment layer.
  • the substrate layer can be a non-woven fabric, film or composite film with a porous structure, and the material of the substrate layer can include but not limited to polyethylene, polypropylene, polyethylene terephthalate or polyimide at least one.
  • a polypropylene porous film, a polyethylene porous film, a polypropylene non-woven fabric, a polyethylene non-woven fabric, or a polypropylene-polyethylene-polypropylene porous composite film may be used.
  • at least one surface of the substrate layer is provided with a surface treatment layer, and the surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by mixing a polymer and an inorganic material.
  • Inorganic layer may include but not limited to inorganic particles and inorganic layer binder, the present application has no particular limitation on inorganic particles, as long as the purpose of this application can be achieved, for example, may include but not limited to alumina, silicon oxide, Magnesium oxide, titanium oxide, hafnium oxide, tin oxide, cerium oxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide or at least one of barium sulfate.
  • the present application has no particular limitation on the inorganic layer binder, for example, it may include but not limited to polyvinylidene fluoride, copolymer of vinylidene fluoride-hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, At least one of polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polymethylmethacrylate, polytetrafluoroethylene or polyhexafluoropropylene.
  • polyvinylidene fluoride copolymer of vinylidene fluoride-hexafluoropropylene
  • polyamide polyacrylonitrile
  • polyacrylate polyacrylic acid
  • the polymer layer contains a polymer, and the polymer material may include but not limited to polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinyl pyrrolidone, polyvinyl ether, polyvinylidene fluoride At least one of ethylene or poly(vinylidene fluoride-hexafluoropropylene).
  • the electrolytic solution may also include a non-aqueous solvent and a lithium salt.
  • the present application has no special limitation on the non-aqueous solvent, as long as the purpose of the present application can be achieved, for example, it may include but not limited to at least one of carbonate compounds, carboxylate compounds, ether compounds or other organic solvents.
  • the above-mentioned carbonate compound may include, but not limited to, at least one of a chain carbonate compound or a cyclic carbonate compound.
  • Chain carbonate compound can include but not limited to dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethylene propyl carbonate (EPC) or at least one of methyl ethyl carbonate (MEC).
  • the above-mentioned cyclic carbonate may include but not limited to ethylene carbonate (EC), vinylene carbonate (VC), propylene carbonate (PC), butylene carbonate (BC) or vinyl ethylene carbonate (VEC). at least one of .
  • carboxylate compounds may include but are not limited to methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, ⁇ -butyl At least one of lactone, decanolactone, valerolactone, mevalonolactone or caprolactone.
  • the aforementioned ether compounds may include, but are not limited to, dibutyl ether, tetraglyme, diglyme, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxy At least one of methoxyethane, 2-methyltetrahydrofuran or tetrahydrofuran.
  • the above-mentioned other organic solvents may include but not limited to dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2- At least one of pyrrolidone, formamide, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, trioctyl phosphate or phosphoric acid ester.
  • This application has no special restrictions on lithium salts, as long as the purpose of this application can be achieved, for example, it may include but not limited to LiPF 6 , LiBF 4 , LiAsF 6 , LiClO 4 , LiB(C 6 H 5 ) 4 , LiCH 3 SO 3. At least one of LiCF 3 SO 3 , LiN(SO 2 CF 3 ) 2 , LiC(SO 2 CF 3 ) 3 , LiSiF 6 , LiBOB or lithium difluoroborate.
  • the lithium salt comprises LiPF 6 .
  • the electrochemical device of the present application is not particularly limited, and it may include any device that undergoes an electrochemical reaction.
  • the electrochemical device may include, but is not limited to, a lithium metal secondary battery, a lithium ion secondary battery (lithium ion battery), a lithium polymer secondary battery, or a lithium ion polymer secondary battery, among others.
  • the preparation process of electrochemical devices is well known to those skilled in the art, and the present application is not particularly limited.
  • it may include but not limited to the following steps: stack the positive electrode sheet, separator and negative electrode sheet in sequence, and as required Winding, folding and other operations to obtain the electrode assembly with a winding structure, put the electrode assembly into the packaging bag, inject the electrolyte into the packaging bag and seal it, and obtain an electrochemical device; or, put the positive electrode sheet, separator and negative electrode
  • the pole pieces are stacked in order, and then the four corners of the entire laminated structure are fixed with adhesive tape to obtain the electrode assembly of the laminated structure.
  • the electrode assembly is placed in the packaging bag, and the electrolyte is injected into the packaging bag and sealed to obtain an electrochemical device.
  • overcurrent prevention elements, guide plates, etc. can also be placed in the packaging bag as needed, so as to prevent pressure rise and overcharge and discharge inside the electrochemical device.
  • a third aspect of the present application provides an electronic device, which includes the electrochemical device in any one of the foregoing embodiments.
  • the electrochemical device provided by the present application has good cycle performance, so the electronic device provided by the present application has a long service life.
  • the electronic device 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-based computers, mobile computers, e-book players, cellular phones, portable fax machines, portable copiers, portable printers, headsets, VCRs, LCD TVs, portable cleaners, portable CD players, mini discs, transceivers, electronic organizers, calculators, memory cards, portable tape recorders, radios, backup power supplies, motors, cars, motorcycles, power-assisted bicycles, bicycles, Lighting appliances, toys, game consoles, clocks, electric tools, flashlights, cameras, large household storage batteries and lithium-ion capacitors, etc.
  • the application provides a lithium transition metal composite oxide, an electrochemical device, and an electronic device.
  • the lithium transition metal composite oxide has a twin structure, and the twin structure includes a first crystal region and a second crystal region, and the first crystal region and the second crystal region There is a grain boundary between the two crystal regions, the first crystal region includes a first region within 20nm from the grain boundary, the second crystal region includes a second region within 20nm from the grain boundary, the transition metal layer in the first region and the second The included angle between the transition metal layers in the region is 65° to 80°.
  • the angle between the transition metal layers of the first region and the second region can be 65° to 80°, the stress and strain between the first crystal region and the second crystal region can be reduced during charge and discharge, and the twinning can be improved.
  • the stability of the structure thereby improving the cycle performance of the electrochemical device under high voltage.
  • the lithium-ion battery was fully charged to 3.0V at a current density of 10mA/cm 2 , and after standing for 10min, the positive pole piece was disassembled in the glove box; the positive pole piece was transferred to a scanning electron microscope equipped with a focused ion beam (model : FEI Vion Plasma FIB) cavity, processing samples that can be used for transmission scanning electron microscope (STEM, model: FEI Titan3G2 60-300) analysis, the surface of the sample is required to be protected by Pt, and processed with Ga ion beam, and the thickness of the sample should not exceed 100nm ; and clean with low voltage mode to remove residual surface of sample processing.
  • STEM transmission scanning electron microscope
  • the sample is observed under STEM, and at a suitable magnification, an electron microscope photo including the lattice fringes of the first region in the first crystal region and the lattice fringes of the second region in the second crystal region is taken, and the crystal lattice in the first region is measured by image processing software.
  • the angle between the lattice fringes and the lattice fringes in the second region at the grain boundary is the angle between the transition metal layer in the first region and the transition metal layer in the second region after full discharge.
  • the X-ray Energy Spectroscopy (EDS) function is used to collect data at a suitable magnification to obtain the grain boundary of the positive electrode active material, the element content in the third region and the fourth region in the first region. Collect at least 3 different locations and take the average as the final result.
  • the electrolyte is the basic electrolyte in the following example 1-1, and the injection volume is 50 ⁇ L
  • the button battery Charge and discharge to 4.5V and 4.7V respectively, disassemble the button battery, and measure the angle between the transition metal layer in the first area and the transition metal layer in the second area according to the above steps, so that the calculation can be obtained
  • An inductively coupled plasma spectrometer was used to test the contents of different elements in the positive electrode active material.
  • FIG. 1 shows the scanning electron microscope image of the cross section of the positive pole piece in Example 1-1.
  • Fig. 2 shows the scanning electron micrograph of the lithium transition metal composite oxide with twin crystal structure in the cross-section of the positive electrode sheet in Example 1-1, as can be seen from the figure, the positive electrode active material contains lithium with twin crystal structure Transition metal composite oxide particles.
  • Figure 3 shows that the electrochemical device in Example 1-1 is fully charged and disassembled to obtain the positive pole piece, and the positive pole piece and lithium metal are assembled into a button battery, and when charged to 4.7V, the obtained lithium transition metal composite In the TEM image of the oxide, the angle ⁇ between the transition metal layer in the first region and the transition metal layer in the second region is 78°.
  • Positive electrode active material conductive carbon black
  • binder polyvinylidene fluoride according to a mass ratio of 97:1.4:1.6
  • NMP N-methylpyrrolidone
  • the positive electrode slurry is evenly coated on one surface of the positive electrode current collector aluminum foil, and dried to obtain a positive electrode sheet coated with a positive electrode material layer on one side. Repeat the above steps on the other surface of the aluminum foil to obtain a positive electrode sheet coated with a positive electrode material layer on both sides. Then, the positive electrode sheet is obtained after cold pressing and cutting.
  • the negative active material artificial graphite Mix the negative active material artificial graphite, the binder styrene-butadiene rubber (SBR), and the thickener sodium carboxymethyl cellulose in a mass ratio of 97:2:1, add deionized water, and stir evenly under the action of a vacuum mixer , to obtain the negative electrode slurry, wherein the solid content of the negative electrode slurry is 75%.
  • the negative electrode slurry is uniformly coated on one surface of the negative electrode current collector copper foil, and dried to obtain a negative electrode sheet coated with a negative electrode material layer on one side. Repeat the above steps on the other surface of the copper foil to obtain a negative electrode sheet coated with a negative electrode material layer on both sides. Then, the negative electrode sheet is obtained after cold pressing and cutting.
  • a porous PE film with a thickness of 7 ⁇ m was used.
  • the above-prepared positive electrode sheet, separator, and negative electrode sheet are stacked in sequence, and wound to obtain an electrode assembly.
  • step (1) of ⁇ Preparation of positive electrode active material> the molar ratio of Co, Mg, and Al is 97:0.8:2.2, pH is adjusted to above 8.9, T1 is 780°C, T2 in step (2) is 1050°C, t2 is 16h, except that the mass ratio of the second intermediate product to Al 2 O 3 and MgO in step (3) is 100:0.1:0.5, the rest is the same as in Example 1-1.
  • step (1) of ⁇ Preparation of positive electrode active material> the molar ratio of Co, Mg, and Al is 99:0.3:0.7, T1 is 550°C, and t1 is 6h, the second intermediate product and Al 2 in step (3) O 3 and the mass ratio of MgO are except that 100:0.1:0.5, all the other are identical with embodiment 1-1.
  • step (3) the second intermediate product and TiO 2 are mixed according to the mass ratio Except for mixing at 100:0.05, the rest is the same as in Example 1-1.
  • step (1) of ⁇ preparation of positive electrode active material> CoSO 4 and ZnSO 4 are mixed with Co, Zn molar ratio is 99.7:0.3, and in step (3), the second intermediate product and ZnO are mixed according to the mass ratio of 100:0.01 is the same as Example 1-1 except for mixing.
  • T1 is 800°C and t1 is 18h in step (1) of ⁇ Preparation of positive electrode active material>
  • T2 is 1050°C in step (2)
  • the number of moles of Li in Li 2 CO 3 is the same as that of Co
  • Mg and Al except that the ratio of the sum of moles is 1.06:1, the rest are the same as in Example 1-1.
  • Example 1-1 Except preparing positive electrode active material according to the following steps, all the other are the same as Example 1-1:
  • Example 1-1 Except preparing positive electrode active material according to the following steps, all the other are the same as Example 1-1:
  • Example 1-1 to Example 1-3, Comparative Example 1-1 and Comparative Example 1-2 From Example 1-1 to Example 1-3, Comparative Example 1-1 and Comparative Example 1-2, it can be seen that when the included angle of the lithium transition metal composite oxide is within the scope of the application, the obtained lithium ion battery The cycle performance at high voltage is better than that of the Li-ion battery obtained in the comparative example.
  • the capacity retention rate of Example 1-1 is always higher than that of Comparative Example 1-1; and after 100 cycles, the capacity retention rate of Example 1-1 Much higher than Comparative Example 1-1. This is because the angle between the transition metal layer in the first region and the second region is within the above range, which can reduce the stress and strain between the first crystal region and the second crystal region during charge and discharge, thereby improving the twin structure.
  • Example 1-1 to Example 1-3, Comparative Example 1-1 and Comparative Example 1-2 that the lithium transition metal composite oxides in Example 1-1 to Example 1-3, which The degree of angle change between 4.7V and 4.5V
  • Example 1-1 to Example 1-3 is more excellent than that of Comparative Example 1-1 and Comparative Example 1-2, which is due to the transition metals in the first region and the second region
  • the angle between the layers is within the above range, the lithium ion transfer barrier at this interface is lower, and the transfer impedance is smaller, thereby improving the dynamic performance of the twin structure, which in turn makes the lithium ion battery have a better rate. performance.
  • Example 1-1 Example 2-1 to Example 2-8, it can be seen that when X/Y ⁇ 2, the obtained lithium ion battery has good cycle performance, which is due to the fact that the first crystal region is close to the crystal There are relatively more elements A at the boundary, which is more conducive to improving the structural stability near the grain boundary in the first crystal region and reducing the risk of twin structure cracking, thereby improving the structure of lithium transition metal composite oxides under high voltage. stability.
  • element A contains F element, and the resulting lithium-ion battery can have more excellent cycle performance. This is because element A contains F.
  • it can form a local disordered structure and disperse stress, thereby reducing twinning.
  • the risk of crystal structure cracking on the other hand, it can improve the stability of the O structure at the grain boundary and reduce the risk of deterioration at the grain boundary.
  • Example 1-1 From Example 1-1, Example 3-1 and Example 3-2, it can be seen that when the ratio of the number of positive electrode active material particles with a twin crystal structure is within the scope of the application, the obtained lithium ion battery can have both Good cycle performance and rate performance.
  • Example 1-1 78 / / 80 Example 4-1 78 1.8 MgF2 83.5
  • Example 4-2 78 5.2 MgF2 87
  • Example 4-3 78 7.7 MgF2 86.6
  • Example 1-1, Example 4-1 to Example 4-3 it can be seen from Example 1-1, Example 4-1 to Example 4-3 that when a fluorocarbonate compound is further added to the electrolyte, the cycle performance of the lithium-ion battery at high voltage can be further improved.
  • the particle surface of the positive electrode active material can react with the fluorocarbonate compound to form a protective layer of metal fluoride, which improves the stability of the surface structure of the positive electrode active material particle; on the other hand, The introduction of the fluorocarbonate compound can form a protective layer at the interface where the twin crystal structure is split, reduce the side reaction between the lithium transition metal composite oxide and the electrolyte, and thereby improve the cycle performance of the electrochemical device.

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Abstract

提供了一种锂过渡金属复合氧化物、电化学装置和电子装置，锂过渡金属复合氧化物具有孪晶结构，孪晶结构包括第一晶区和第二晶区，第一晶区和第二晶区之间具有晶界，第一晶区包括距离晶界20nm以内的第一区域，第二晶区包括距离晶界20nm以内的第二区域，第一区域中的过渡金属层和第二区域中的过渡金属层之间的夹角为65°至80°。通过调控第一区域和第二区域过渡金属层之间的夹角为65°至80°，能够提高孪晶结构的稳定性，从而提高电化学装置在高电压下的循环性能。

Description

一种锂过渡金属复合氧化物、电化学装置和电子装置
本申请要求于2021年11月11日提交中国专利局、申请号为202111333551.6、发明名称为“一种锂过渡金属复合氧化物、电化学装置和电子装置”的中国专利申请的优先权，其全部内容通过引用结合在本申请中。
技术领域
本申请涉及电化学技术领域，特别是涉及一种锂过渡金属复合氧化物、电化学装置和电子装置。
背景技术
锂离子电池具有储能密度大、开路电压高、自放电率低、循环寿命长、安全性好等优点，广泛应用于便携式电能储存、电子设备、电动汽车等各个领域。但也对锂离子电池的综合性能提出更高的要求，例如在高电压(例如大于4.2V)下具有良好的循环性能等。
发明内容
本申请的目的在于提供一种锂过渡金属复合氧化物、电化学装置和电子装置，以提高电化学装置在高电压下的循环性能。
本申请的第一方面提供了一种锂过渡金属复合氧化物，其中，锂过渡金属复合氧化物具有孪晶结构，孪晶结构包括第一晶区和第二晶区，第一晶区和第二晶区之间具有晶界，第一晶区包括距离晶界20nm以内的第一区域，第二晶区包括距离晶界20nm以内的第二区域，第一区域中的过渡金属层和第二区域中的过渡金属层之间的夹角为65°至80°。通过调控第一区域和第二区域过渡金属层之间的夹角为65°至80°，能够降低充放电过程中第一晶区和第二晶区之间的应力和应变，提高孪晶结构的稳定性，进而提高电化学装置在高电压下的循环性能。
在本申请的一些实施方案中，第一区域中的过渡金属层包括Co、Mn或Ni中的至少一种。在本申请的一些实施方案中，第二区域中的过渡金属层包括Co、Mn或Ni中的至少一种。第一区域和第二区域的主体都是包含Co/Ni/Mn的层状氧化物材料，它们之间在高温的作用下会相互融合并生长形成孪晶界；第一区域和第二区域包括上述过渡金属元素，并且均呈现层状结构，两者之间通过孪晶的方式连接，是一种能量最低的连接方式，有利于结构的稳定性。
在本申请的一些实施方案中，晶界包含元素A，元素A包括Mg、Al、Ti、Zr、La、 Nb、Hf、Zn、Y或F中的至少一种。通过包含上述元素A，能够修饰第一晶区和第二晶区之间的晶界，提高晶界结构的稳定性，从而降低孪晶结构开裂的风险。
在本申请的一些实施方案中，第一区域包括距离晶界10nm以内的第三区域和距离晶界10nm至20nm的第四区域，基于第三区域中Co、Mn和Ni的摩尔总数，第三区域中元素A的摩尔百分含量为X；基于第四区域中Co、Mn和Ni的摩尔总数，第四区域中元素A的摩尔百分含量为Y，满足：X/Y≥2。此时，更有利于提高第一晶区中靠近晶界处的结构稳定性，降低孪晶结构开裂的风险，从而提高锂过渡金属复合氧化物在高电压下的结构稳定性。
在本申请的一些实施方案中，X为0.2％至2.5％。此时，能够更好地保证第一晶区中靠近晶界处的结构稳定性。
在本申请的一些实施方案中，在锂过渡金属复合氧化物的截面中，基于截面的面积，第二晶区的面积占比为30％至60％。通过调控第二晶区的面积占比在上述范围内，有利于改善电化学装置的倍率性能和循环性能。
在本申请的一些实施方案中，锂过渡金属复合氧化物包括基体和位于基体表面的第一层，第一层包括金属氟化物。第一层包括金属氟化物时，可以抑制基体表面与电解液发生副反应，提高锂过渡金属复合氧化物表面结构的稳定性，从而提高电化学装置的循环性能。
在本申请的一些实施方案中，锂过渡金属复合氧化物满足以下特征中的至少一种：(a)金属氟化物包括CoF 2、CoF 3、CoFO、MgF 2、NaF或AlF 3中的至少一种；(b)第一层的厚度为1nm至8nm。当锂过渡金属复合氧化物满足特征(a)至(b)中的至少一种时，均有利于提高电化学装置的循环性能。
本申请的第二方面提供了一种电化学装置，其包括正极极片，正极极片包括正极材料层，正极材料层包括正极活性材料，正极活性材料包括前述任一实施方案中的锂过渡金属复合氧化物。
在本申请的一些实施方案中，将电化学装置满放后拆解得到正极极片，取正极极片中直径为1.4cm的圆片与锂金属组装成扣式电池，将扣式电池充电至4.7V，其中，锂过渡金属复合氧化物中的夹角β为70°至86°。
在本申请的一些实施方案中，将电化学装置满放后拆解得到正极极片，取正极极片中直径为1.4cm的两个圆片与锂金属分别组装成第一扣式电池和第二扣式电池，将第一扣式电池充电至4.5V，将第二扣式电池充电至4.7V，其中，第一扣式电池的锂过渡金属复合氧 化物中，第一区域中的过渡金属层和第二区域中的过渡金属层之间的夹角为α；第二扣式电池的锂过渡金属复合氧化物中，第一区域中的过渡金属层和第二区域中的过渡金属层之间的夹角为β，满足：|β-α|≤5°。当电化学装置满足上述特征时，表明锂过渡金属复合氧化物在充放电过程中，第一区域和第二区域间的应变较小，孪晶结构具有较好的稳定性。
在本申请的一些实施方案中，基于正极活性材料的颗粒数，具有孪晶结构的正极活性材料颗粒数占比为35％至75％。通过具有孪晶结构的正极活性材料的颗粒数占比在上述范围内，有利于提高电化学装置的倍率性能和循环性能。
在本申请的一些实施方案中，电化学装置还包括电解液，电解液包括氟代碳酸酯化合物，基于电解液的质量，氟代碳酸酯化合物的质量百分含量为0.05％至15％。氟代碳酸酯化合物的引入，可以在孪晶结构裂开的界面处形成保护层，减小锂过渡金属复合氧化物与电解液的副反应，从而提高电化学装置的循环性能。
在本申请的一些实施方案中，氟代碳酸酯化合物包括单氟代碳酸乙烯酯、双氟代碳酸乙烯酯、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-甲基亚乙酯或碳酸三氟甲基亚乙酯中的至少一种。
本申请的第三方面提供了一种电子装置，其包括前述任一实施方案中的电化学装置。
本申请提供一种锂过渡金属复合氧化物、电化学装置和电子装置，锂过渡金属复合氧化物具有孪晶结构，孪晶结构包括第一晶区和第二晶区，第一晶区和第二晶区之间具有晶界，第一晶区包括距离晶界20nm以内的第一区域，第二晶区包括距离晶界20nm以内的第二区域，第一区域中的过渡金属层和第二区域中的过渡金属层之间的夹角为65°至80°。通过调控第一区域和第二区域之间的夹角为65°至80°，能够提高孪晶结构的稳定性，从而提高电化学装置在高电压下的循环性能。
附图说明
为了更清楚地说明本申请实施例和现有技术的技术方案，下面对实施例和现有技术中所需要使用的附图作简单地介绍，显而易见地，下面描述中的附图仅仅是本申请的一些实施例，对于本领域普通技术人员来讲，在不付出创造性劳动的前提下，还可以根据这些附图获得其他的附图。
图1为实施例1-1中正极极片截面的扫描电镜图；
图2为实施例1-1中正极极片截面中具有孪晶结构的锂过渡金属复合氧化物的扫描电 镜图；
图3为实施例1-1中电化学装置满放后拆解得到正极极片，将正极极片与锂金属组装成扣式电池，充电至4.7V时，得到的锂过渡金属复合氧化物的透射电镜图；
图4为实施例1-1和对比例1-1中电化学装置的容量保持率随循环圈数的变化曲线图。
具体实施方式
为使本申请的目的、技术方案、及优点更加清楚明白，以下参照附图并举实施例，对本申请进一步详细说明。显然，所描述的实施例仅仅是本申请一部分实施例，而不是全部的实施例。基于本申请中的实施例，本领域普通技术人员在没有作出创造性劳动前提下所获得的所有其他实施例，都属于本申请保护的范围。
需要说明的是，本申请的具体实施方式中，以锂离子电池作为电化学装置的例子来解释本申请，但是本申请的电化学装置并不仅限于锂离子电池。
本申请的发明人研究发现，具有孪晶结构的正极活性材料，例如钴酸锂，其中，孪晶结构可以为锂离子提供多方位的迁移路径，从而有利于提高电化学装置的倍率性能。但是，孪晶结构在高电压下不稳定，尤其是晶界处，容易开裂，使材料与电解液发生副反应，从而影响电化学装置的循环性能，难以满足实际应用中的需求。
本申请的第一方面提供了一种锂过渡金属复合氧化物，其中，锂过渡金属复合氧化物具有孪晶结构，孪晶结构包括第一晶区和第二晶区，第一晶区和第二晶区之间具有晶界，第一晶区包括距离晶界20nm以内的第一区域，第二晶区包括距离晶界20nm以内的第二区域，第一区域中的过渡金属层和第二区域中的过渡金属层之间的夹角为65°至80°。例如，夹角可以为65°、70°、75°、80°或为其间的任意范围。锂过渡金属复合氧化物可以作为正极活性材料用于电化学装置中，本申请的发明人发现，通过调控第一区域和第二区域之间的夹角为65°至80°，能够降低充放电过程中第一晶区和第二晶区之间的应力和应变，提高孪晶结构的稳定性，进而提高电化学装置在高电压下的循环性能。在本申请中，第一晶区是指在孪晶晶界某一侧，晶体结构中的过渡金属层具有相同取向的区域，第二晶区是指孪晶晶界不同于第一晶区的另一侧，晶体结构中的过渡金属层具有相同取向的区域。上述夹角是指将第一区域中的过渡金属层取向与第二区域中的过渡金属层取向分别延伸至在晶界处相交时，所形成的夹角。另外，若锂过渡金属复合氧化物作为正极活性材料存在于电化学装置中，上述夹角是指将电化学装置满放后，拆解得到正极极片，正极极片中的锂过渡金属复合氧化物中，第一区域中的过渡金属层和第二区域中的过渡金属层之间的夹角。
在本申请的一些实施方案中，第一区域中的过渡金属层包括Co、Mn或Ni中的至少一种。在本申请的一些实施方案中，第二区域中的过渡金属层包括Co、Mn或Ni中的至少一种。通过第一区域和第二区域中的过渡金属层均包括上述过渡金属，有利于提高第一区域和第二区域之间的界面相容性，从而提高孪晶结构的稳定性。
在本申请的一些实施方案中，晶界包含元素A，元素A包括Mg、Al、Ti、Zr、La、Nb、Hf、Zn、Y或F中的至少一种。本申请的发明人发现，通过包含上述元素A，能够修饰第一晶区和第二晶区之间的晶界，提高晶界结构的稳定性，从而降低孪晶结构开裂的风险。例如，当元素A包括Mg，晶界处的O能够与Mg形成Mg-O键，提高O结构的稳定性；例如，当元素A包括F，可以形成局部的无序结构，分散应力，从而降低孪晶结构开裂的风险。
在本申请的一些实施方案中，基于晶界中Co、Mn和Ni的摩尔总数，晶界中元素A的摩尔百分含量为0.2％至2.5％。例如，元素A的质量百分含量可以为0.2％、0.25％、0.3％、0.35％、0.4％、0.45％、0.5％、1.0％、1.5％、2.0％、2.5％或为其间的任意范围。通过调控元素A的摩尔百分含量在上述范围内，有利于提高晶界结构的稳定性，从而降低孪晶结构开裂的风险，进而提高电化学装置在高电压下的循环性能。
在本申请的一些实施方案中，第一区域包括距离晶界10nm以内的第三区域和距离晶界10nm至20nm的第四区域，基于第三区域中Co、Mn和Ni的摩尔总数，第三区域中元素A的摩尔百分含量为X；基于第四区域中Co、Mn和Ni的摩尔总数，第四区域中元素A的摩尔百分含量为Y，满足：X/Y≥2，优选为2≤X/Y≤12。X/Y的值可以为2、3、4、5、6、7、8、9、10或为其间的任意范围。
在本申请的一些实施方案中，X为0.2％至2.5％。例如，X的值可以为0.2％、0.25％、0.3％、0.35％、0.4％、0.45％、0.5％、1.0％、1.5％、2.0％、2.5％或为其间的任意范围。X为0.2％至2.5％，更有利于提高第一晶区中靠近晶界处的结构稳定性，降低孪晶结构开裂的风险，从而提高锂过渡金属复合氧化物在高电压下的结构稳定性。本申请对Y的值没有特别限制，只要满足X/Y≥2即可，例如，0％＜Y≤1.0％。
在本申请的一些实施方案中，在锂过渡金属复合氧化物的截面中，基于截面的面积，第二晶区的面积占比为30％至60％。例如，第二晶区的面积占比可以为30％、35％、40％、45％、50％、55％、60％或为其间的任意范围。通过调控第二晶区的面积占比在上述范围内，有利于改善电化学装置的倍率性能和循环性能。
在本申请的一些实施方案中，锂过渡金属复合氧化物包括基体和位于基体表面的第一层，第一层包括金属氟化物。本申请的发明人发现，当锂过渡金属复合氧化物具有第一层，且第一层包括金属氟化物时，可以抑制基体表面与电解液发生副反应，提高锂过渡金属复合氧化物表面结构的稳定性，从而提高电化学装置的循环性能。
在本申请的一些实施方案中，金属氟化物包括CoF 2、CoF 3、CoFO、MgF 2、NaF或AlF 3中的至少一种。
在本申请的一些实施方案中，第一层的厚度为1nm至8nm。例如，第一层的厚度可以为1nm、2nm、3nm、4nm、5nm、6nm、7nm、8nm或为其间的任意范围。通过调控第一层的厚度在上述范围内，有利于提高电化学装置的循环性能和倍率性能。
本申请对锂过渡金属复合氧化物的制备方法没有特别限制，只要能实现本申请的目的即可，例如，锂过渡金属复合氧化物的制备方法可以包括但不限于以下步骤：将过渡金属源、掺杂元素源混合并配置成水溶液，通过共沉淀法得到沉淀，然后进行一次煅烧，研磨过筛，得到第一中间产物；然后将第一中间产物与锂源混合后进行二次煅烧，研磨过筛，得到第二中间产物；然后将第二中间产物与掺杂元素源混合后进行三次煅烧，研磨过筛，即得到锂过渡金属复合氧化物。本申请对一次煅烧的温度T1和时间t1、二次煅烧的温度T2和时间t2、三次煅烧的温度T3和时间t3没有特别限制，只要能实现本申请的目的即可，例如，T1为500℃至1000℃，t1为5h至15h；T2为800℃至1500℃，t2为5h至15h；T3为500℃至1000℃，t3为5h至15h。
锂过渡金属复合氧化物包括Li xNi yCo zMn kZ qO 2±aT a，其中，Z包括B、Mg、Al、Si、P、S、Ti、Cr、Fe、Cu、Zn、Ga、Y、Zr、Mo、Ag、W、In、Sn、Sb、La、Nb、Hf或Ce中的至少一种，T为卤素；其中，0.2<x≤1.2、0≤y≤1、0≤z≤1、0≤k≤1、0≤q≤1，且y、z、k不同时为0，以及0≤a≤1。
本申请的第二方面提供了一种电化学装置，其包括正极极片，正极极片包括正极材料层，正极材料层包括正极活性材料，正极活性材料包括前述任一实施方案中的锂过渡金属复合氧化物。本申请提供的锂过渡金属复合氧化物具有良好的结构稳定性，从而本申请提供的电化学装置具有良好的循环性能。
在本申请的一些实施方案中，将电化学装置满放后拆解得到正极极片，取正极极片中直径为1.4cm的圆片与锂金属组装成扣式电池，将扣式电池充电至4.7V，其中，锂过渡金属复合氧化物中的夹角β为70°至86°。例如，锂过渡金属复合氧化物中的夹角为70°、72°、 75°、78°、80°、82°、85°、86°或为其间的任意范围。当充电至4.7V时，锂过渡金属复合氧化物中的夹角在上述范围内，表明第一区域中的过渡金属层和第二区域中的过渡金属层之间的夹角在高电压下变化较小，能够提高孪晶结构的稳定性，从而提高电化学装置在高电压下的循环性能。
在本申请的一些实施方案中，将电化学装置满放后拆解得到正极极片，取正极极片中直径为1.4cm的两个圆片与锂金属分别组装成第一扣式电池和第二扣式电池，将第一扣式电池充电至4.5V，将第二扣式电池充电至4.7V，其中，第一扣式电池的锂过渡金属复合氧化物中，第一区域中的过渡金属层和第二区域中的过渡金属层之间的夹角为α；第二扣式电池的锂过渡金属复合氧化物中，第一区域中的过渡金属层和第二区域中的过渡金属层之间的夹角为β，满足：|β-α|≤5°，说明锂过渡金属复合氧化物在充放电过程的高电压段，第一区域和第二区域间的应变较小，孪晶结构具有较好的稳定性。例如，|β-α|可以为0.1°、0.5°、1°、2°、3°、4°、5°或为其间的任意范围。本申请对扣式电池的组装方法没有特别限制，可以采用本领域已知的组装方式进行组装。
在本申请的一些实施方案中，基于正极活性材料的颗粒数，具有孪晶结构的正极活性材料颗粒数占比为35％至75％。例如，具有孪晶结构的正极活性材料的颗粒数占比为35％、40％、45％、50％、55％、60％、65％、70％、75％或为其间的任意范围。通过调控具有孪晶结构的正极活性材料的颗粒数占比在上述范围内，有利于提高电化学装置的倍率性能和循环性能。
在本申请的一些实施方案中，正极活性材料还可以包括本领域已知的正极活性材料，例如，可以包括但不限于镍钴锰酸锂、镍钴铝酸锂、磷酸铁锂、钴酸锂、锰酸锂或磷酸锰铁锂中的至少一种。
在本申请的一些实施方案中，电化学装置包括电解液，电解液包括氟代碳酸酯化合物，基于电解液的质量，氟代碳酸酯化合物的质量百分含量为0.05％％至15％。例如，氟代碳酸酯化合物的质量百分含量可以为0.05％、0.5％、1％、5％、10％、15％或为其间的任意范围。本申请的发明人发现，氟代碳酸酯化合物的引入，可以在孪晶结构裂开的界面处形成保护层，减小锂过渡金属复合氧化物与电解液的副反应，从而提高电化学装置的循环性能。
在本申请的一些实施方案中，氟代碳酸酯化合物包括单氟代碳酸乙烯酯、双氟代碳酸乙烯酯、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-甲基亚乙酯或碳酸三氟甲基亚乙酯中的至少一种。
在本申请的一些实施方案中，正极材料层包括粘结剂。在本申请的一些实施方案中，粘结剂可以包括但不限于聚丙烯醇、聚丙烯酸钠、聚丙烯酸钾、聚丙烯酸锂、聚酰亚胺、聚酰亚胺、聚酰胺酰亚胺、丁苯橡胶(SBR)、聚乙烯醇(PVA)、聚偏氟乙烯、聚偏二氟乙烯(PVDF)、聚四氟乙烯(PTFE)、聚乙烯醇缩丁醛(PVB)、水性丙烯酸树脂、羧甲基纤维素(CMC)或羧甲基纤维素钠(CMC-Na)中的至少一种。
正极极片通常包括正极集流体，在本申请中，正极集流体没有特别限制，只要能够实现本申请目的即可，例如可以包括但不限于铝箔、铝合金箔或复合集流体等。在本申请中，对正极集流体的厚度没有特别限制，只要能够实现本申请目的即可，例如厚度为8μm至12μm。在本申请中，正极材料层可以设置于沿正极集流体厚度方向的一个表面或两个表面上。需要说明，这里的“表面”可以是正极集流体的全部区域，也可以是正极集流体的部分区域，本申请没有特别限制，只要能实现本申请目的即可。
在本申请中，正极材料层中还可以包括导电剂，本申请对导电剂没有特别限制，只要能够实现本申请目的即可，例如可以包括但不限于导电炭黑(Super P)、碳纳米管(CNTs)、碳纤维、鳞片石墨、科琴黑、石墨烯、金属材料或导电聚合物中的至少一种。上述碳纳米管可以包括但不限于单壁碳纳米管和/或多壁碳纳米管。上述碳纤维可以包括但不限于气相生长碳纤维(VGCF)和/或纳米碳纤维。上述金属材料可以包括但不限于金属粉和/或金属纤维，具体地，金属可以包括但不限于铜、镍、铝或银中的至少一种。上述导电聚合物可以包括但不限于聚亚苯基衍生物、聚苯胺、聚噻吩、聚乙炔或聚吡咯中的至少一种。
任选地，正极还可以包括导电层，导电层位于正极集流体和正极材料层之间。本申请对导电层的组成没有特别限制，可以是本领域常用的导电层，例如可以包括但不限于上述导电剂和上述粘结剂。
本申请的电化学装置还包括负极极片，负极极片通常包括负极集流体和设置在负极集流体表面的负极材料层，本申请对负极集流体没有特别限制，只要能够实现本申请目的即可，例如，可以包括但不限于铜箔、铜合金箔、镍箔、不锈钢箔、钛箔、泡沫镍、泡沫铜或复合集流体等。在本申请中，对负极集流体的厚度没有特别限制，只要能够实现本申请目的即可，例如厚度为4μm至12μm。在本申请中，负极材料层可以设置在沿负极集流体厚度方向的一个表面或两个表面上。需要说明，这里的“表面”可以是负极集流体的全部区域，也可以是负极集流体的部分区域，本申请没有特别限制，只要能实现本申请目的即可。
本申请中，负极材料层包括负极活性材料，其中，负极活性材料没有特别限制，只要能实现本申请的目的即可，例如可以包括但不限于天然石墨、人造石墨、中间相微碳球、硬碳、软碳、硅、硅-碳复合物、Li-Sn合金、Li-Sn-O合金、Sn、SnO、SnO 2、尖晶石结构的锂化TiO 2-Li 4Ti 5O 12或Li-Al合金中的至少一种。
在本申请中，负极材料层中还可以包括导电剂，本申请对导电剂没有特别限制，只要能够实现本申请目的即可，例如可以包括但不限于上述导电剂中的至少一种。
在本申请中，负极材料层中还可以包括粘结剂，本申请对粘结剂没有特别限制，只要能够实现本申请目的即可，例如可以包括但不限于上述粘结剂中的至少一种。
任选地，负极极片还可以包括导电层，导电层位于负极集流体和负极材料层之间。本申请对导电层的组成没有特别限制，可以是本领域常用的导电层，导电层可以包括但不限于上述导电剂和上述粘结剂。
本申请的电化学装置还包括隔离膜，本申请对隔离膜没有特别限制，只要能够实现本申请目的即可，例如可以包括但不限于聚乙烯(PE)、聚丙烯(PP)、聚四氟乙烯为主的聚烯烃(PO)类隔膜、聚酯膜(例如聚对苯二甲酸二乙酯(PET)膜)、纤维素膜、聚酰亚胺膜(PI)、聚酰胺膜(PA)、氨纶、芳纶膜、织造膜、非织造膜(无纺布)、微孔膜、复合膜、隔膜纸、碾压膜或纺丝膜中的至少一种，优选为PP。本申请的隔离膜可以具有多孔结构，孔径的尺寸没有特别限制，只要能实现本申请的目的即可，例如，孔径的尺寸可以为0.01μm至1μm。在本申请中，隔离膜的厚度没有特别限制，只要能实现本申请的目的即可，例如厚度可以为5μm至500μm。
例如，隔离膜可以包括基材层和表面处理层。基材层可以为具有多孔结构的无纺布、膜或复合膜，基材层的材料可以包括但不限于聚乙烯、聚丙烯、聚对苯二甲酸乙二醇酯或聚酰亚胺中的至少一种。任选地，可以使用聚丙烯多孔膜、聚乙烯多孔膜、聚丙烯无纺布、聚乙烯无纺布或聚丙烯-聚乙烯-聚丙烯多孔复合膜。任选地，基材层的至少一个表面上设置有表面处理层，表面处理层可以是聚合物层或无机物层，也可以是混合聚合物与无机物所形成的层。
无机物层可以包括但不限于无机颗粒和无机物层粘结剂，本申请对无机颗粒没有特别限制，只要能实现本申请的目的即可，例如，可以包括但不限于氧化铝、氧化硅、氧化镁、氧化钛、二氧化铪、氧化锡、二氧化铈、氧化镍、氧化锌、氧化钙、氧化锆、氧化钇、碳化硅、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。本申请对无机物 层粘结剂没有特别限制，例如，可以包括但不限于聚偏氟乙烯、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、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。聚合物层中包含聚合物，聚合物的材料可以包括但不限于聚酰胺、聚丙烯腈、丙烯酸酯聚合物、聚丙烯酸、聚丙烯酸盐、聚乙烯呲咯烷酮、聚乙烯醚、聚偏氟乙烯或聚(偏氟乙烯-六氟丙烯)中的至少一种。
在本申请中，电解液还可以包括非水溶剂和锂盐。本申请对非水溶剂没有特别限制，只要能实现本申请的目的即可，例如，可以包括但不限于碳酸酯化合物、羧酸酯化合物、醚化合物或其它有机溶剂中的至少一种。上述碳酸酯化合物可以包括但不限于链状碳酸酯化合物或环状碳酸酯化合物中的至少一种。上述链状碳酸酯化合物可以包括但不限于碳酸二甲酯(DMC)、碳酸二乙酯(DEC)、碳酸二丙酯(DPC)、碳酸甲丙酯(MPC)、碳酸乙丙酯(EPC)或碳酸甲乙酯(MEC)中的至少一种。上述环状碳酸酯可以包括但不限于碳酸乙烯酯(EC)、碳酸亚乙烯酯(VC)、碳酸亚丙酯(PC)、碳酸亚丁酯(BC)或碳酸乙烯基亚乙酯(VEC)中的至少一种。上述羧酸酯化合物可以包括但不限于甲酸甲酯、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、甲瓦龙酸内酯或己内酯中的至少一种。上述醚化合物可以包括但不限于二丁醚、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-甲基四氢呋喃或四氢呋喃中的至少一种。上述其它有机溶剂可以包括但不限于二甲亚砜、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、磷酸三辛酯或磷酸酯中的至少一种。
本申请对锂盐没有特别限制，只要能实现本申请的目的即可，例如，可以包括但不限于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或二氟硼酸锂中的至少一种。优选地，锂盐包括LiPF 6。
本申请的电化学装置没有特别限制，其可以包括发生电化学反应的任何装置。在一些实施方案中，电化学装置可以包括但不限于：锂金属二次电池、锂离子二次电池(锂离子电池)、锂聚合物二次电池或锂离子聚合物二次电池等。
电化学装置的制备过程为本领域技术人员所熟知的，本申请没有特别的限制，例如，可以包括但不限于以下步骤：将正极极片、隔离膜和负极极片按顺序堆叠，并根据需要将其卷绕、折叠等操作得到卷绕结构的电极组件，将电极组件放入包装袋内，将电解液注入 包装袋并封口，得到电化学装置；或者，将正极极片、隔离膜和负极极片按顺序堆叠，然后用胶带将整个叠片结构的四个角固定好得到叠片结构的电极组件，将电极组件置入包装袋内，将电解液注入包装袋并封口，得到电化学装置。此外，也可以根据需要将防过电流元件、导板等置于包装袋中，从而防止电化学装置内部的压力上升、过充放电。
本申请的第三方面提供了一种电子装置，其包括前述任一实施方案中的电化学装置。本申请提供的电化学装置具有良好的循环性能，从而本申请提供的电子装置具有较长的使用寿命。
本申请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。
本申请提供一种锂过渡金属复合氧化物、电化学装置和电子装置，锂过渡金属复合氧化物具有孪晶结构，孪晶结构包括第一晶区和第二晶区，第一晶区和第二晶区之间具有晶界，第一晶区包括距离晶界20nm以内的第一区域，第二晶区包括距离晶界20nm以内的第二区域，第一区域中的过渡金属层和第二区域中的过渡金属层之间的夹角为65°至80°。通过调控第一区域和第二区域的过渡金属层之间的夹角为65°至80°，能够降低充放电过程中第一晶区和第二晶区之间的应力和应变，提高孪晶结构的稳定性，进而提高电化学装置在高电压下的循环性能。
实施例
以下，举出实施例及对比例来对本申请的实施方式进行更具体地说明。各种的试验及评价按照下述的方法进行。另外，只要无特别说明，“份”、“％”为质量基准。
测试方法和设备：
容量保持率测试：
在25℃的环境中，将锂离子电池在0.2C的充电电流下进行恒流充电，直到上限电压为4.6V，然后恒压充电至电流小于50μA，然后在0.2C的放电电流下进行恒流放电，直到最终电压为3.0V，记录首次循环的放电容量。然后以相同的步骤进行100次的充电和放电 循环，记录第100次循环的放电容量，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％。
倍率性能测试：
在25℃的环境中，将锂离子电池在0.2C的充电电流下进行恒流充电，直到上限电压为4.6V，然后恒压充电至电流小于50μA，然后在0.2C的放电电流下进行恒流放电，直到最终电压为3.0V，记录0.2C放电容量。然后，重复上述恒流恒压充电过程，在2C的放电电流下进行恒流放电，直到最终电压为3.0V，记录2C放电容量。倍率性能＝2C放电容量/0.2C放电容量×100％。
夹角、元素含量的测试：
将锂离子电池在10mA/cm 2的电流密度下满放至3.0V，并且静置10min后在手套箱内拆解获得正极极片；将正极极片转移至配备聚焦离子束的扫描电镜(型号：FEI Vion Plasma FIB)腔体内，加工得到可用于透射扫描电镜(STEM，型号：FEI Titan3G2 60-300)分析的样品，要求样品表面用Pt保护，并且用Ga离子束加工，样品厚度不超过100nm；并且用低电压模式进行清洗，除去样品加工的残留表面。将样品在STEM下观察，在合适的倍率下，拍摄包含第一晶区中第一区域和第二晶区中第二区域晶格条纹的电镜照片，利用图像处理软件测量第一区域中的晶格条纹和第二区域中的晶格条纹在晶界处的夹角，此即为满放后第一区域中的过渡金属层和第二区域中的过渡金属层之间的夹角。同时，在合适的倍率下利用X射线能谱分析(EDS)功能进行数据采集，获得正极活性材料晶界、第一区域中的第三区域和第四区域内的元素含量。采集至少3处不同位置，取平均值作为最终结果。
取上述正极极片中直径为1.4cm的圆片与锂金属组装成扣式电池，其中，电解液为下述实施例1-1中的基础电解液，注液量为50μL，将扣式电池分别充放电至4.5V和4.7V，拆解扣式电池，同样按上述步骤，测量第一区域中的过渡金属层和第二区域中的过渡金属层之间的夹角，从而可计算获得|β-α|。
采用电感耦合等离子光谱发生仪测试正极活性材料中不同元素的含量。
图1示出了实施例1-1中正极极片截面的扫描电镜图。图2示出了实施例1-1中正极极片截面中具有孪晶结构的锂过渡金属复合氧化物的扫描电镜图，从图中可以看出，正极活性材料中包含具有孪晶结构的锂过渡金属复合氧化物颗粒。图3示出了实施例1-1中的电化学装置满放后拆解得到正极极片，将正极极片与锂金属组装成扣式电池，充电至4.7V时，得到的锂过渡金属复合氧化物的透射电镜图，第一区域中的过渡金属层和第二区域中的过渡金属层之间的夹角β为78°。
第一层厚度测试：
将样品在STEM下观察，在合适的倍率下，拍摄颗粒边缘包含第一层的电镜照片，在第一层表面随机选取5个测量点，利用图像处理软件测量各测量点至基体表面的最小距离，取平均值作为第一层的厚度。
颗粒数占比测试：
在正极极片的截面照片中，随机选取长度为500μm的区域，统计其中具有孪晶结构的正极活性材料颗粒数占总颗粒数的比例，作为颗粒数占比。
第二晶区面积占比测试：
将样品在STEM下观察，在合适的倍率下，拍摄截面的电镜照片，利用图像处理软件计算第二晶区的面积为S2，截面的总面积为S，第二晶区面积占比为S2/S。
实施例1-1
<正极活性材料的制备>
(1)将CoSO 4、MgSO 4和Al(NO 3) 3按照Co、Mg、Al摩尔比为98.2:0.8:1混合配置水溶液，加入氨水和碳酸铵，将pH调节至8.5以上，通过沉淀工艺获得碳酸盐沉淀；在60℃烘箱内烘烤，并控制碳酸盐沉淀的水含量不低于7％。然后放入马弗炉中，在空气气氛中进行一次煅烧，煅烧温度T1为750℃，煅烧时间t1为12h，空气流速为10L/min，然后研磨过筛得到第一中间产物。
(2)将第一中间产物与Li 2CO 3混合，放入马弗炉中，在空气气氛中进行二次煅烧，煅烧温度T2为1000℃，煅烧时间t2为12h，空气流速为10L/min；然后研磨过筛得到第二中间产物。其中，Li 2CO 3中Li的摩尔数与Co、Mg和Al的摩尔数之和的比值为1.05:1。
(3)将第二中间产物与Al 2O 3和MgO按照质量比为100:0.1:0.05进行混合，放入马弗炉中，在空气气氛中进行三次煅烧，煅烧温度T3为600℃，煅烧时间t3为8h，空气流速为10L/min；然后研磨过筛得到正极活性材料。
<正极极片的制备>
将正极活性材料、导电剂导电炭黑、粘结剂聚偏二氟乙烯按照质量比为97:1.4:1.6进行混合，加入N-甲基吡咯烷酮(NMP)，在真空搅拌机作用下搅拌均匀，获得正极浆料，其中正极浆料的固含量为70％。将正极浆料均匀涂覆于正极集流体铝箔的一个表面上，烘干，得到单面涂覆有正极材料层的正极极片。在铝箔的另一个表面上重复以上步骤，即得 到双面涂覆有正极材料层的正极极片。然后经过冷压、裁切后得到正极极片。
<负极极片的制备>
将负极活性材料人造石墨、粘结剂丁苯橡胶(SBR)、增稠剂羧甲基纤维素钠按照质量比为97:2:1进行混合，加入去离子水，在真空搅拌机作用下搅拌均匀，获得负极浆料，其中负极浆料的固含量为75％。将负极浆料均匀涂覆于负极集流体铜箔的一个表面上，烘干，得到单面涂覆有负极材料层的负极极片。在铜箔的另一个表面上重复以上步骤，即得到双面涂覆有负极材料层的负极极片。然后经过冷压、裁切后得到负极极片。
<电解液的制备>
在干燥的氩气气氛手套箱中，将PC、EC、DEC按照质量比1:1:1混合得到有机溶剂，然后向有机溶剂中加入锂盐LiPF 6溶解并混合均匀，得到基础电解液。其中，LiPF 6在电解液中的质量浓度为12.5％。
<隔离膜的制备>
采用厚度为7μm的多孔PE薄膜。
<锂离子电池的制备>
将上述制备得到的正极极片、隔离膜、负极极片按顺序叠好，卷绕得到电极组件。将电极组件置于铝塑膜包装袋中，干燥后注入电解液，经过真空封装、静置、化成、脱气、切边等工序得到锂离子电池。
实施例1-2
除了在<正极活性材料的制备>的步骤(1)中Co、Mg、Al摩尔比为97:0.8:2.2、pH调节至8.9以上、T1为780℃，步骤(2)中T2为1050℃、t2为16h，步骤(3)中第二中间产物与Al 2O 3和MgO的质量比为100:0.1:0.5以外，其余与实施例1-1相同。
实施例1-3
除了在<正极活性材料的制备>的步骤(1)中Co、Mg、Al摩尔比为99:0.3:0.7、T1为550℃、t1为6h，步骤(3)中第二中间产物与Al 2O 3和MgO的质量比为100:0.1:0.5以外，其余与实施例1-1相同。
实施例2-1
除了在<正极活性材料的制备>的步骤(1)中Co、Mg、Al摩尔比为98.7:0.3:1、并在一次煅烧时加入Co摩尔数0.5％的MgO，步骤(3)中第二中间产物与Al 2O 3和MgO的质量比为100:0.1:0.1以外，其余与实施例1-1相同。
实施例2-2
除了在<正极活性材料的制备>的步骤(1)中将CoSO 4和Al(NO 3) 3按照Co、Al摩尔比为99:1混合配置水溶液、一次煅烧时加入Co摩尔数0.8％的MgO，步骤(3)中第二中间产物与Al 2O 3和MgO的质量比为100:0.1:0.15以外，其余与实施例1-1相同。
实施例2-3
除了在<正极活性材料的制备>的步骤(1)中Co、Mg、Al摩尔比为98.5:0.5:1以外，其余与实施例1-1相同。
实施例2-4
除了在<正极活性材料的制备>的步骤(1)中将CoSO 4和TiO 2以Co、Ti摩尔比为99.7:0.3混合，且步骤(3)中将第二中间产物与TiO 2按照质量比为100:0.05进行混合以外，其余与实施例1-1相同。
实施例2-5
除了在<正极活性材料的制备>的步骤(1)中将CoSO 4和Nb 2O 5以Co、Nb摩尔比为99.7:0.3混合，且步骤(3)中将第二中间产物与Nb 2O 5按照质量比为100:0.01进行混合以外，其余与实施例1-1相同。
实施例2-6
除了在<正极活性材料的制备>的步骤(1)中将CoSO 4和ZnSO 4以Co、Zn摩尔比为99.7:0.3混合，且步骤(3)中将第二中间产物与ZnO按照质量比为100:0.01进行混合以外，其余与实施例1-1相同。
实施例2-7
除了在<正极活性材料的制备>的步骤(1)中将CoSO 4和NH 4F以Co、F摩尔比为99.7:0.3混合，且步骤(3)中将第二中间产物与NH 4F按照质量比为100:0.01进行混合以外，其余与实施例1-1相同。
实施例2-8
除了在<正极活性材料的制备>的步骤(1)中将CoSO 4、MgSO 4、Al(NO 3) 3和NH 4F以Co、Mg、Al、F摩尔比为99.5:0.1:0.1:0.3混合以外，其余与实施例1-1相同。
实施例3-1
除了在<正极活性材料的制备>的步骤(2)中T2为950℃、t2为6h、空气流速为5L/min以外，其余与实施例1-1相同。
实施例3-2
除了在<正极活性材料的制备>的步骤(1)中T1为800℃、t1为18h，步骤(2)中T2为1050℃、Li 2CO 3中Li的摩尔数与Co、Mg和Al的摩尔数之和的比值为1.06:1以外，其余与实施例1-1相同。
实施例4-1
除了在<电解液的制备>的步骤中在基础电解液的基础上进一步添加单氟代碳酸乙烯酯(FEC)，其中，基于电解液的总质量，FEC的质量百分含量为0.5％以外，其余与实施例1-1相同。
实施例4-2
除了在<电解液的制备>的步骤中在基础电解液的基础上进一步添加单氟代碳酸乙烯酯(FEC)和双氟代碳酸乙烯酯(DFEC)，其中，基于电解液的总质量，FEC的质量百分含量为2.5％、DFEC的质量百分含量为2.5％以外，其余与实施例1-1相同。
实施例4-3
除了在<电解液的制备>的步骤中在基础电解液的基础上进一步添加单氟代碳酸乙烯酯(FEC)和双氟代碳酸乙烯酯(DFEC)，其中，基于电解液的总质量，FEC的质量百分含量为5％、DFEC的质量百分含量为5％以外，其余与实施例1-1相同。
对比例1-1
除了按照以下步骤制备正极活性材料以外，其余与实施例1-1相同：
(1)将CoSO 4、MgSO 4和Al(NO 3) 3按照Co、Mg、Al摩尔比为98.2:0.8:1混合配置水溶液，加入氨水和碳酸铵，将pH调节至8.0以上，通过沉淀工艺获得碳酸盐沉淀；在60℃烘箱内烘烤，并控制碳酸盐沉淀的水含量不低于7％。然后放入马弗炉中，在空气气氛中进行一次煅烧，煅烧温度T1为720℃，煅烧时间t1为12h，空气流速为10L/min，然后研磨过筛得到第一中间产物。
(2)将第一中间产物与Li 2CO 3混合，放入马弗炉中，在空气气氛中进行二次煅烧，煅烧温度T2为950℃，煅烧时间t2为12h，空气流速为10L/min；然后研磨过筛得到正极活性材料。其中，Li 2CO 3中Li的摩尔数与Co、Mg和Al的摩尔数之和的比值为1.05:1。
对比例1-2
除了按照以下步骤制备正极活性材料以外，其余与实施例1-1相同：
(1)将CoSO 4、MgSO 4和Al(NO3) 3按照Co、Mg、Al摩尔比为98.2:0.8:1混合配置 水溶液，加入氨水和碳酸铵，将pH调节至8.5以上，通过沉淀工艺获得碳酸盐沉淀；在120℃烘箱内烘烤，并控制碳酸盐沉淀的水含量不低于7％。然后放入马弗炉中，在空气气氛中进行一次煅烧，煅烧温度T1为950℃，煅烧时间t1为8h，空气流速为30L/min，然后研磨过筛得到第一中间产物。
(2)将第一中间产物与LiOH混合，放入马弗炉中，在空气气氛中进行二次煅烧，煅烧温度T2为900℃，煅烧时间t2为12h，空气流速为30L/min；然后研磨过筛得到正极活性材料。其中，LiOH中Li的摩尔数与Co、Mg和Al的摩尔数之和的比值为1.05:1。
各实施例和对比例的测试结果如表1至表4所示。
表1
Figure PCTCN2022113859-appb-000001
从实施例1-1至实施例1-3、对比例1-1和对比例1-2可以看出，当锂过渡金属复合氧化物的夹角在本申请的范围内，得到的锂离子电池在高电压下的循环性能优于对比例中得到的锂离子电池。从图4中可以看出，锂离子电池在循环过程中，实施例1-1的容量保持率始终高于对比例1-1；且在循环100圈后，实施例1-1的容量保持率远高于对比例1-1。这是由于第一区域和第二区域过渡金属层之间的夹角在上述范围内，能够降低充放电过程中第一晶区和第二晶区之间的应力和应变，从而提高孪晶结构的稳定性，进而提高电化学装置在高电压下的循环性能。从实施例1-1至实施例1-3、对比例1-1和对比例1-2还可以看出，实施例1-1至实施例1-3中的锂过渡金属复合氧化物，其4.7V和4.5V的夹角变化度数|(β-α)|较小，表明实施例中的锂过渡金属复合氧化物在充放电过程的高电压段，其第一晶区和第二晶区之间的应变较小，孪晶结构的稳定性较好。
从表1中还可以看出，实施例1-1至实施例1-3的倍率性能较对比例1-1和对比例1-2更优异，这是由于第一区域和第二区域过渡金属层之间的夹角在上述范围内时，锂离子在此界面传递的势垒更低，传输阻抗更小，从而提升了孪晶结构的动力学性能，进而使得锂离子电池具备更好的倍率性能。
表2
Figure PCTCN2022113859-appb-000002
从实施例1-1、实施例2-1至实施例2-8可以看出，X/Y≥2时，得到的锂离子电池具有良好的循环性能，这是由于第一晶区中靠近晶界处具有相对较多的元素A，更有利于提高第一晶区中靠近晶界处的结构稳定性，降低孪晶结构开裂的风险，从而提高锂过渡金属复合氧化物在高电压下的结构稳定性。另外，可以看出，元素A包含F元素，得到的锂离子电池能够具有更加优异的循环性能，这是由于元素A包括F，一方面，可以形成局部的无序结构，分散应力，从而降低孪晶结构开裂的风险；另一方面，能够提升晶界处O结构的稳定性，降低晶界处劣化的风险。
表3
  4.7V夹角β 颗粒数占比(％) 容量保持率(％) 倍率性能(％)
实施例1-1 78 55 80 93
实施例3-1 78 36 70 86
实施例3-2 78 73 72 95
从实施例1-1、实施例3-1和实施例3-2可以看出，当具有孪晶结构的正极活性材料颗粒数占比在本申请的范围内，得到的锂离子电池能够兼具良好的循环性能和倍率性能。
表4
  4.7V夹角β 第一层厚度(nm) 金属氟化物 容量保持率(％)
实施例1-1 78 / / 80
实施例4-1 78 1.8 MgF 2 83.5
实施例4-2 78 5.2 MgF 2 87
实施例4-3 78 7.7 MgF 2 86.6
从实施例1-1、实施例4-1至实施例4-3可以看出，当进一步在电解液中添加氟代碳酸酯化合物，可以进一步提高锂离子电池在高电压下的循环性能。这是由于，一方面，在充放电过程中，正极活性材料的颗粒表面可以与氟代碳酸酯化合物反应形成金属氟化物的保护层，提高正极活性材料颗粒表面结构的稳定性；另一方面，氟代碳酸酯化合物的引入，可以在孪晶结构裂开的界面处形成保护层，减小锂过渡金属复合氧化物与电解液的副反应，从而提高电化学装置的循环性能。
以上所述仅为本申请的较佳实施例，并不用以限制本申请，凡在本申请的精神和原则之内，所做的任何修改、等同替换、改进等，均应包含在本申请保护的范围之内。

Claims (14)

  1. 一种锂过渡金属复合氧化物，其中，所述锂过渡金属复合氧化物具有孪晶结构，所述孪晶结构包括第一晶区和第二晶区，所述第一晶区和所述第二晶区之间具有晶界，所述第一晶区包括距离所述晶界20nm以内的第一区域，所述第二晶区包括距离所述晶界20nm以内的第二区域，所述第一区域中的过渡金属层和所述第二区域中的过渡金属层之间的夹角为65°至80°。
  2. 根据权利要求1所述的锂过渡金属复合氧化物，其中，所述锂过渡金属复合氧化物满足以下特征中的至少一者：
    (1)所述第一区域中的过渡金属层包括Co、Mn或Ni中的至少一种；
    (2)所述第二区域中的过渡金属层包括Co、Mn或Ni中的至少一种；
    (3)所述晶界包含元素A，所述元素A包括Mg、Al、Ti、Zr、La、Nb、Hf、Zn、Y或F中的至少一种。
  3. 根据权利要求2所述的锂过渡金属复合氧化物，其中，所述第一区域包括距离所述晶界10nm以内的第三区域和距离所述晶界10nm至20nm的第四区域，基于所述第三区域中Co、Mn和Ni的摩尔总数，所述第三区域中元素A的摩尔百分含量为X；基于所述第四区域中Co、Mn和Ni的摩尔总数，所述第四区域中元素A的摩尔百分含量为Y，满足：X/Y≥2。
  4. 根据权利要求3所述的锂过渡金属复合氧化物，其中，X为0.2％至2.5％。
  5. 根据权利要求1所述的锂过渡金属复合氧化物，其中，在所述锂过渡金属复合氧化物的截面中，基于所述截面的面积，所述第二晶区的面积占比为30％至60％。
  6. 根据权利要求1所述的锂过渡金属复合氧化物，其中，所述锂过渡金属复合氧化物包括基体和位于所述基体表面的第一层，所述第一层包括金属氟化物。
  7. 根据权利要求6所述的锂过渡金属复合氧化物，其中，所述锂过渡金属复合氧化物满足以下特征中的至少一者：
    (a)所述金属氟化物包括CoF 2、CoF 3、CoFO、MgF 2、NaF或AlF 3中的至少一种；
    (b)所述第一层的厚度为1nm至8nm。
  8. 一种电化学装置，其包括正极极片，所述正极极片包括正极材料层，所述正极材料层包括正极活性材料，所述正极活性材料包括权利要求1至7中任一项所述的锂过渡金属复合氧化物。
  9. 根据权利要求8所述的电化学装置，其中，将所述电化学装置满放后拆解得到所述正极极片，取所述正极极片中直径为1.4cm的两个圆片与锂金属分别组装成第一扣式电池和第二扣式电池，将所述第一扣式电池充电至4.5V，将所述第二扣式电池充电至4.7V，其中，所述第一扣式电池中，所述锂过渡金属复合氧化物中的所述夹角为α；所述第二扣式电池中，所述锂过渡金属复合氧化物中的所述夹角为β，满足：|β-α|≤5°。
  10. 根据权利要求9所述的电化学装置，其中，β为70°至86°。
  11. 根据权利要求8所述的电化学装置，其中，基于所述正极活性材料的颗粒数，具有孪晶结构的正极活性材料颗粒数占比为35％至75％。
  12. 根据权利要求8所述的电化学装置，其还包括电解液，所述电解液包括氟代碳酸酯化合物，基于所述电解液的质量，所述氟代碳酸酯化合物的质量百分含量为0.05％至15％。
  13. 根据权利要求12所述的电化学装置，所述氟代碳酸酯化合物包括单氟代碳酸乙烯酯、双氟代碳酸乙烯酯、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-甲基亚乙酯或碳酸三氟甲基亚乙酯中的至少一种。
  14. 一种电子装置，其包括权利要求8至13中任一项所述的电化学装置。
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