WO2023056633A1 - 一种电池层状正极材料及其制备方法和应用 - Google Patents

一种电池层状正极材料及其制备方法和应用 Download PDF

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WO2023056633A1
WO2023056633A1 PCT/CN2021/122864 CN2021122864W WO2023056633A1 WO 2023056633 A1 WO2023056633 A1 WO 2023056633A1 CN 2021122864 W CN2021122864 W CN 2021122864W WO 2023056633 A1 WO2023056633 A1 WO 2023056633A1
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positive electrode
electrode material
layered positive
battery
battery layered
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PCT/CN2021/122864
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English (en)
French (fr)
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潘锋
黄伟源
赵庆贺
张明建
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北京大学深圳研究生院
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Priority to CN202180007629.7A priority Critical patent/CN114930576A/zh
Priority to PCT/CN2021/122864 priority patent/WO2023056633A1/zh
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H01M4/366—Composites as layered products
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/50—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese
    • H01M4/505—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese of mixed oxides or hydroxides containing manganese for inserting or intercalating light metals, e.g. LiMn2O4 or LiMn2OxFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/52—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron
    • H01M4/525—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron of mixed oxides or hydroxides containing iron, cobalt or nickel for inserting or intercalating light metals, e.g. LiNiO2, LiCoO2 or LiCoOxFy
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • the present application relates to the field of battery positive electrode materials, in particular to a battery layered positive electrode material and its preparation method and application.
  • lithium-ion batteries The performance of lithium-ion batteries is closely related to the selection, preparation process and performance of electrode materials for batteries.
  • lithium cobalt oxide LiCoO 2 and ternary cathode material Li[Ni x Co y Mn 1-xy ]O 2 (0 ⁇ x ⁇ 1, 0 ⁇ y ⁇ 1) have the characteristics of high capacity, high rate and simple synthesis process.
  • ternary cathode material Li[Ni x Co y Mn 1-xy ]O 2 (0 ⁇ x ⁇ 1, 0 ⁇ y ⁇ 1) have the characteristics of high capacity, high rate and simple synthesis process.
  • Become the positive electrode material of lithium batteries such as 3C digital, unmanned aerial vehicle and electric vehicle power supply.
  • These two types of positive electrode materials have a typical layered structure, that is, a crystal structure in which transition metal layers and lithium layers are alternately stacked.
  • the transition metal layer will slip, stack faults, twist, and even produce microcracks with the cyclical Li + intercalation/extraction process. It is especially serious during high voltage charging and discharging.
  • the slip, stacking fault, distortion and micro-cracks of the transition metal layer lead to the collapse of the interface structure, the pulverization of the active material, and the active Ni/Co ions in the high-valence state cause the interface
  • the intensification of side reactions will eventually lead to an increase in the internal resistance of the battery and a rapid decline in capacity.
  • the more effective strategy currently adopted is to coat the surface of the active material.
  • the interface coating generally has high ion conductivity and can effectively isolate the direct contact between the electrolyte and the active material.
  • the purpose of this application is to provide an improved battery layered positive electrode material and its preparation method and application.
  • One aspect of the present application discloses a battery layered positive electrode material, the crystal structure of the battery layered positive electrode material has a heterogeneous phase structure in which the surface interface layer and the bulk phase layer are pinned into the crystal structure; The heterogeneous phase structure is evenly distributed on the surface of the crystal structure, covering the crystal structure to form a uniform crystal surface layer.
  • the battery layered positive electrode material with a heterogeneous phase structure on the surface of the crystal structure of the present application the heterogeneous phase at the interface is pinned into each layer, which can ensure the stability of each layered phase. It can fundamentally solve the problems of slippage, collapse, distortion and microcracks of each layer of battery layered positive electrode materials; moreover, the crystal surface layer of the coated crystal structure formed by the heterogeneous phase structure can isolate the electrolyte and inhibit the interface side reaction, Solve the problem of rapid capacity decay of battery layered cathode materials. Therefore, the battery layered cathode material of the present application greatly improves the electrochemical performance of the layered cathode material, especially under high voltage (> 4.3V vs.
  • the so-called “heterogeneous phase structure” refers to a structure formed by element replacement or doping on the surface interface of the crystal structure of the battery layered positive electrode material, that is, the element composition is different from that of the battery layered positive electrode material;
  • this "heterogeneous phase structure” is formed by extending the bulk layer lattice of the crystal structure of the battery layered cathode material, and co-lattice with the bulk layer of the crystal structure of the battery layered cathode material Spinel phase or rock salt phase structure.
  • the heterogeneous phase structure of the battery layered positive electrode material of the present application is pinned into each layer of the bulk phase of the crystal structure and the surface interface, and can also build a three-dimensional lithium ion diffusion network to improve Cycling stability, capacity and rate performance.
  • the crystal surface layer of the present application is the surface layer formed by uniformly covering the crystal structure with heterogeneous phase structure; There are essential differences in the surface coating modification of macroscopic cathode materials.
  • the heterogeneous phase structure is a spinel phase or a rock-salt phase structure.
  • the spinel phase structure and the rock-salt phase structure are only heterogeneous phase structures that are pinned into each layer of the crystal structure specifically formed in an implementation mode of the present application, and other heterogeneous phase structures are not excluded .
  • the heterogeneous phase structure is formed by epitaxially growing the bulk phase layer of the crystal structure of the battery layered positive electrode material to the surface interface layer of the crystal structure, that is, the heterogeneous phase structure and Bulk layer co-lattice of crystal structure.
  • co-lattice heterogeneous phase structure is only one implementation of the present application, which is formed by lattice epitaxy of the bulk layer. In theory, as long as a pinned heterogeneous phase structure can be formed, It is not ruled out that other non-co-lattice manners are also possible.
  • the thickness of the crystal surface layer is greater than or equal to 10 nm.
  • the crystal surface layer of the present application is actually the microstructure layer on the surface of the crystal structure formed by the heterogeneous phase structure covering the crystal structure; therefore, the thickness of the crystal surface layer is actually the pinned heterogeneous phase structure pinning. into the depth of each layer of the crystal structure.
  • the thickness of the crystal surface layer is preferably not less than 10 nm in the present application.
  • the battery layered positive electrode material is Li 1+x TMO 2+y , where 0 ⁇ x ⁇ 1, 0 ⁇ y ⁇ 1, and TM is at least one of Co, Mn, Ni and Al .
  • the lithium-ion battery layered positive electrode material is only the battery layered positive electrode material specifically tested in an implementation mode of the present application. According to the inventive concept of the present application, other ion battery layered positive electrode materials are not excluded.
  • the transition metal is at least one of Co, Mn, Ni and Al, which are relatively common layered cathode materials for lithium-ion batteries, and other transition metals are not excluded.
  • the battery layered positive electrode material is at least one of lithium cobalt oxide, high-nickel binary material, high-nickel multi-component material, and lithium-rich manganese positive electrode material; wherein, high nickel means that the nickel content is greater than Or equal to 50%.
  • binary materials and multi-component materials in this application refer to positive electrode materials containing two or more of nickel, cobalt, manganese, aluminum, etc.; that is, binary materials are positive electrode materials containing two of them;
  • a multi-element material includes two or more positive electrode materials, for example, three of them, that is, a ternary material.
  • the battery layered positive electrode material is at least one of LiNi 0.8 Co 0.1 Mn 0.1 O 2 , LiNi 0.5 Co 0.3 Mn 0.2 O 2 and LiCoO 2 .
  • the constituent elements of the crystal surface layer include cations and anions
  • the cations include at least one of Li, Co, Mn, Ni, Al, B, Mg, Ca, and Zn
  • the anions include O and/or F.
  • the content of Al, B, Mg, Ca, Zn and/or fluorine increases gradually from the inside to the outside, and the content of Co, Mn, Ni and/or O gradually decreases from the inside to the outside.
  • the layer of the co-lattice heterogeneous phase structure is mainly the elements in the raw materials used in the pretreatment, and the elements in the battery layered positive electrode material, both of which are in Formed by interdiffusion of anions and cations during heat treatment. Therefore, the constituent elements of the heterogeneous phase structure layer are mainly composed of pretreated raw materials and battery layered cathode materials. It can be understood that although the heterogeneous phase is formed by the epitaxial growth of the bulk phase layer of the crystal structure; however, according to the source of its constituent elements, each element presents a gradient distribution that increases or decreases from the inside to the outside.
  • the constituent elements are mainly Co, Mn, Ni, and O, etc. provided by the battery layered positive electrode material, and their content gradually decreases from the inside to the outside; the constituent elements are mainly Al, B, Mg, Ca, Zn provided by the pretreated raw materials. And fluorine, its content gradually increases from the inside out.
  • from inside to outside means from the bulk phase layer of the crystal structure to the surface layer.
  • the other side of the application discloses the preparation method of the battery layered positive electrode material of the present application, including performing the following treatment on the conventional battery layered positive electrode material to obtain the battery layered positive electrode material with a pinned heterogeneous phase structure in the crystal structure ;
  • Step 1 using at least one of the following methods to pretreat the conventional battery layered positive electrode material,
  • (a) solution soaking method including soaking conventional battery layered positive electrode materials in a solution containing at least one of Li + , borate, Al 3+ , Mg 2+ , Ca 2+ , Zn 2+ and F - , the immersion condition is 0-160°C for 1-24h to obtain the pretreated battery layered positive electrode material;
  • sol-gel method including combining conventional battery layered cathode materials with a sol containing at least one of Li + , borate, Al 3+ , Mg 2+ , Ca 2+ , Zn 2+ and F - The gel is evenly mixed, heated and dried to obtain a pretreated battery layered positive electrode material;
  • (c) ball milling method comprising combining conventional battery layered cathode materials with solid materials containing at least one of Li + , borate, Al 3+ , Mg 2+ , Ca 2+ , Zn 2+ and F - Perform ball milling and mixing to obtain pretreated battery layered positive electrode materials;
  • Step 2 heat-treat the pretreated battery layered positive electrode material obtained in step 1 at 400-700°C for more than the threshold time in an inert atmosphere or a reducing atmosphere, and then control the cooling rate to be less than or equal to 1°C/min, and lower the temperature to At room temperature, a battery layered positive electrode material with a pinned heterogeneous phase structure in the crystal structure and a thickness of the crystal surface layer greater than or equal to 10nm can be obtained; the inert atmosphere is nitrogen or argon atmosphere; the reducing atmosphere is nitrogen+ Hydrogen atmosphere, or argon + hydrogen atmosphere.
  • the layered positive electrode material pretreated in step 1 is heat-treated at a high temperature of 400-700°C for a time exceeding the threshold, and at the same time, the cooling rate is controlled to be less than or equal to 1°C/min. Necessary for a surface heterogeneous phase structure co-latticed with the bulk layered structure.
  • the heat treatment time at high temperature it is possible to realize the diffusion of the superficial replacement metal and fluorine elements to the internal bulk layered structure, and the heterogeneous phase structure co-lattice with the bulk layered structure is gradually formed during the diffusion process; at the same time
  • the slower cooling rate ensures that the heterogeneous phase structure co-lattice with the bulk layered structure can be completely preserved from high temperature to room temperature, and eliminates the internal stress of the material caused by the two-phase co-lattice.
  • the selection of the heat treatment process in step 2 can also make the thickness of the heterogeneous phase structure in the surface region of the layered positive electrode material greater than or equal to 10nm, so as to ensure that the heterogeneity in the surface region has sufficient pinning effect on the layered structure, thereby inhibiting Slip, collapse and microcrack generation of layered structures under high voltage.
  • a thin layer and uniform covering is introduced on the surface of the original layered positive electrode material powder through the solution soaking method, sol-gel method, and ball milling method, but the layer of covering
  • the biggest role is to replace/diffuse elements in the surface area of the material in step 2 to form a surface-interface heterogeneous phase structure layer with a thickness greater than 10nm, which is different from the traditional cladding layer used to conduct lithium and isolate the electrolyte. There is a big difference in effect.
  • step 2 the time of heat treatment in step 2 needs to be long enough, and at the same time, the rate of cooling after heat treatment is slow enough to obtain a uniform heterogeneous structure region with sufficient thickness on the surface, so as to play a role in the high voltage cycle process.
  • the effect on the pinning stability of bulk layered materials is also very different from that of traditional cladding layers.
  • the thickness of the heterogeneous phase region on the surface of the material is less than 10 nm, which is not enough to keep the layered structure of the layered cathode material with a particle size of more than 5 ⁇ m stable under high-voltage charge-discharge conditions , the slip, collapse, and microcracks of the layered structure caused by the large structural stress inside the material are difficult to avoid, and ultimately affect the cycle stability of the layered cathode material.
  • the heterogeneous phase structure on the surface of layered cathode materials is closely related to the heat treatment temperature and time.
  • the cooling rate to be less than 1°C/min
  • the higher the temperature the longer the heat treatment time, the slower the cooling rate, and the higher the temperature.
  • It is easy to form a spinel phase structure on the contrary, it is easy to form a rock-salt phase structure.
  • the rock-salt phase structure can also pin the layers of the crystal structure to ensure the stability of each layer.
  • the conventional battery layered positive electrode material refers to the battery layered positive electrode material whose crystal structure surface is a normal main metal layer; for example, conventional LiCoO 2 , that is, the crystal structure surface is a normal lithium layer, and the normal lithium oxygen structure lithium cobalt oxide.
  • the present application directly performs pretreatment and subsequent heat treatment on the conventional battery layered positive electrode material to obtain the battery layered positive electrode material with a crystal structure surface of the present application having a heterogeneous phase structure co-lattice with the bulk layered structure.
  • Another aspect of the present application discloses the application of the battery layered positive electrode material of the present application in the preparation of power batteries, large-scale energy storage batteries, or lithium-ion batteries for 3C consumer electronics products, drones or electronic cigarettes.
  • the battery layered positive electrode material of the present application has the advantages of high voltage, high reversible charge and discharge capacity, high rate and good cycle stability, and can be better used for power batteries or large-scale energy storage batteries, such as electric vehicles or Power batteries for other medium and large electric equipment.
  • the battery layered positive electrode material of the present application can also be used in lithium-ion batteries of 3C consumer electronics products, unmanned aerial vehicles or electronic cigarettes.
  • Another aspect of the present application discloses a lithium ion battery using the battery layered positive electrode material of the present application.
  • the lithium ion battery of the present application due to the use of the battery layered positive electrode material of the present application, enables the battery to work at a higher charge and discharge voltage, and has a higher reversible charge and discharge capacity and rate, and cycle stability better.
  • the battery layered positive electrode material of the present application has a heterogeneous phase structure pinned into each layer in its crystal structure. Using the pinning effect of the heterogeneous phase structure, on the one hand, it can ensure the stability of each layered phase and solve the crystallization problem. Slip, collapse, distortion, and microcracks of each layer in the structure; on the other hand, the crystal surface layer formed by the heterogeneous phase structure can conduct electricity, conduct lithium, and play a role in isolating the electrolyte at the interface.
  • the battery layered cathode material of the present application also has high capacity, rate and cycle stability at a high voltage greater than 4.3V, and exhibits excellent electrochemical performance under high voltage charge and discharge conditions.
  • the battery layered positive electrode material of the present application has a simple preparation method and is easy to produce on a large scale.
  • Figure 1 is a diagram of the XRD characterization results of LiCoO 2 @LCAF-S in the examples of the present application;
  • Fig. 2 is the surface morphology, element distribution and electron diffraction characteristic analysis results of LiCoO 2 @LCAF-S in the examples of the present application;
  • Figure 3 is a diagram of the rate and cycle performance results of LiCoO 2 @LCAF-S and conventional LiCoO 2 positive electrodes in the range of 3-4.6V vs. Li/Li + in the example of the present application.
  • the left figure shows the comparison of the rate performance of the two,
  • the figure on the right shows the comparison of the cycle stability of the two.
  • the main problem faced by layered cathode materials at high voltage is the accumulation of internal stress caused by a large number of ion intercalation/extraction, which induces the slippage, collapse and crack growth of the layered structure. Therefore, under high voltage, if we want to solve this problem, the most important thing is to propose a strategy to improve the stability of the layered structure.
  • the inventors of the present application creatively propose that, from the perspective of positive electrode material surface structure/element regulation and design, by constructing a surface heterogeneous phase structure, the layered positive electrode material transition group metal layer can be increased under high voltage conditions when a large amount of lithium is delithiated. Structural stability to prevent a large number of irreversible microcrack structural defects and reduce the possibility of rapid decay of layered cathode materials under high pressure.
  • the heterogeneous phase structure formed on the surface of the crystal structure is specifically the spinel phase or rock salt formed by the epitaxial growth of bulk layered materials to the surface interface Phase, this kind of battery layered positive electrode material with crystal structure, because the spinel structure or rock salt phase structure can maintain stability during high voltage charge and discharge, and can provide a three-dimensional lithium ion transport network, so it can effectively suppress high voltage While addressing the problems of slip, collapse, twist, and microcrack formation in the lower transition metal layer, the capacity and rate performance of layered cathode materials are improved.
  • the present application creatively proposes a new battery layered positive electrode material, whose crystal structure has a heterogeneous phase structure in which the surface interface layer and the bulk phase layer are pinned into the crystal structure;
  • the heterogeneous phase structure is evenly distributed on the surface of the crystal structure, covering the crystal structure to form a uniform crystal surface layer.
  • the heterogeneous phase structure grown in the same lattice as the bulk layered structure is very stable. During high-voltage charging and discharging, it can strongly pin the bulk layered structure and effectively inhibit the phase structure. Transition metal layer slippage, collapse, distortion and microcrack formation problems due to evolution. Therefore, the interface optimization strategy of this application can effectively suppress the intensification of side reactions and the rapid increase of internal resistance during high-voltage cycling, thus enabling layered cathode materials to obtain high capacity, rate and cycle stability.
  • lithium cobaltate is used as the raw material, and it is pretreated by solution immersion method, and then the pretreated lithium cobaltate is heat-treated to obtain the spinel with eutectic lattice on the surface of the crystal structure of this example.
  • Lithium cobalt oxide layered cathode material at the stone phase interface is as follows:
  • Step 1 pretreatment, put 0.3mmol of aluminum sulfate into 40mL of deionized water, and stir for 10min to form a clear solution A; 1g of commercial lithium cobaltate (D50 is 10-13 microns, Xiamen Tungsten) and 0.5g poly Put ethylene glycol into solution A and stir for 10 minutes to form black suspension B; put 1.8mmol lithium fluoride into 40mL deionized water and stir for 2 minutes to form solution C; add solution C to the suspension solution drop by drop In B, keep stirring during the dropping process to form a suspension D; transfer the suspension D to a water bath at 60°C for 6 hours of hydrothermal reaction, then filter with suction, and wash with deionized water and absolute ethanol. Dry it in a vacuum oven at 100°C to obtain pretreated lithium cobalt oxide powder.
  • D50 is 10-13 microns, Xiamen Tungsten
  • Step 2 Subsequent heat treatment and sintering, the above pretreated LiCoO 2 powder is heat-treated at 600°C for 24 hours in an air atmosphere, then cooled to room temperature at a controlled cooling rate of 1°C/min, and the obtained powder is sieved through a 100-mesh sieve to obtain LiCoO 2 powder with Li, Al, Co, O, and F composition spinel phases on the surface, marked as LiCoO 2 @LCAF-Spinel-1#.
  • Electrochemical test Using NMP as a solvent, LiCoO 2 @LCAF-Spinel, carbon black and PVDF were uniformly mixed at a mass ratio of 8:1:1 to prepare a positive electrode sheet with an active material loading of about 2.1 mg cm - 2 .
  • XRD analysis results show that the obtained LiCoO 2 @LCAF-Spinel-1# unit cell parameters belong to R-3m, which is a typical lithium cobalt oxide layered structure, as shown in Figure 1.
  • the TEM EDS-mapping elemental analysis results show that there is a gradient layer with a thickness of about 20nm containing Co, Mg, F and O elements, as shown in Figure 2.
  • Further analysis of the electron diffraction characteristics of the interface layer shows that the interface layer with a thickness of about 20 nm exhibits obvious spinel structure characteristics, indicating that there is a layer of spinel containing Li, Co, Mg, O and F on the surface.
  • the structural layer that is, the spinel phase interface layer with a co-lattice on the surface of the crystal structure.
  • the analysis results show that the spinel phase interface of the eutectic lattice is formed by the bulk phase layer of the crystal structure of the battery layered positive electrode material epitaxially growing to the surface interface of the crystal structure according to the same crystal lattice; the eutectic phase interface of the spinel phase interface The spinel of the lattice is pinned into the surface area and the bulk phase layer of the crystal structure; and the spinel of the co-lattice is evenly distributed on the surface interface at the spinel phase interface.
  • the synthesized material is a lithium cobalt oxide layered positive electrode material with surface gradient spinel pinning, that is, the content of metal elements Al and F gradually increases from the inside to the outside, and the content of Co and oxygen increases from the inside to the outside. outside gradually decreases.
  • the electrochemical test results show that the button battery with the positive electrode material LiCoO 2 @LCMF-Spinel-1# and the lithium metal negative electrode, in the 3-4.6V vs.
  • Li/Li + interval charge-discharge cycle process compared with the purchased Without any treatment of LiCoO 2 , the pre-treated and heat-treated LiCoO 2 in this example showed higher rate and cycle stability, and its discharge capacity at 0.1C and 10C current was ⁇ 218mAh/g and ⁇ 109mAh/g, respectively , the capacity retention rate was ⁇ 79.4% after 200 cycles at 45°C under 2C current.
  • lithium cobalt oxide is used as the raw material, and it is pretreated by ball milling, and then the pretreated lithium cobalt oxide is heat-treated to obtain the spinel with eutectic lattice on the surface of the crystal structure of this example.
  • Lithium cobalt oxide layered positive electrode material at the phase interface is as follows:
  • Step 1 pretreatment, 0.3mmol of zinc fluoride (nano powder, D 50 is about 20nm), 0.3mmol of lithium fluoride (nano powder, D 50 is about 15nm) and 10mmol of commercial lithium cobaltate ( D 50 is 10-13 microns, Xiamen Tungsten) Mix evenly, and grind by hand for 60 minutes. Dry the uniformly mixed powder in a vacuum oven at 120°C for more than 12 hours, sieve it through a 100-mesh sieve, and prepare it for later use to obtain a pretreated lithium cobaltate powder containing Li, Co, Zn, O and F on the surface.
  • Step 2 Subsequent heat treatment and sintering.
  • the above pretreated LiCoO 2 powder was heat-treated in a rotary tube furnace at 650°C for 24h in an Ar inert atmosphere, and the cooling rate was controlled to be lower than 1°C/min.
  • the obtained powder was 100 Mesh sieve, marked as LiCoO 2 @LZF-Spinel-2#.
  • the material without step two treatment is marked as LiCoO 2 @LF+AF.
  • Electrochemical test Using NMP as a solvent, LiCoO 2 @LZF-Spinel-2#, carbon black and PVDF were uniformly mixed at a mass ratio of 8:1:1 to prepare a positive electrode sheet with an active material loading of about 2.5 mg cm -2 .
  • XRD analysis results show that the obtained LiCoO 2 @LZF-Spinel-2# unit cell parameters belong to R-3m, which is a typical layered structure of lithium cobalt oxide.
  • the results of TEM EDS-mapping and diffraction analysis show that there is a spinel layer with a thickness of about 25nm on the surface, and the elemental composition of the spinel layer includes Li, Co, Al, O and F, that is, there is a spinel layer on the surface of the material .
  • the analysis of the material that has not been treated in step 2 shows that there are only a few 5-20nm nanoscale lithium fluoride and aluminum fluoride nanoparticle adhesion layers on the surface of the obtained material, and no spinel phase is formed.
  • the electrochemical test results show that the button battery with the positive electrode material LiCoO 2 @LCZF-S and the lithium metal negative electrode, in the 3-4.6V vs.
  • the treated LiCoO 2 and the LiCoO 2 @LF+AF materials without step 2 treatment exhibit higher rate and cycle stability, and their discharge capacities at 0.1C and 10C are ⁇ 220mAh/g and ⁇ 129mAh/g, and the capacity retention rate is 89.4% after 200 cycles at 2C current.
  • the LiCoO 2 @LF+AF material without step 2 treatment has a discharge capacity of ⁇ 201mAh/g and ⁇ 65mAh/g at 0.1C and 10C, respectively, and a capacity retention rate of 59.1 after 200 cycles at 2C %.
  • lithium cobaltate is used as the raw material, and it is pretreated by the sol-gel method, and then the pretreated lithium cobaltate is subjected to subsequent heat treatment, that is, the crystal structure of this example has a co-lattice on the surface.
  • Lithium cobalt oxide layered positive electrode material with spinel phase interface The specific preparation method is as follows:
  • Step 1 Pretreatment, pour 10mmol of commercial lithium cobaltate (D 50 is 10-13 microns, Xiamen Tungsten) and 1g of polyethylene glycol (molecular weight greater than 2000) into 40mL of deionized water, stir well to form a suspension Solution A; add 0.3mmol of magnesium sulfate and 0.3mmol of lithium sulfate to solution A, continue to stir and dissolve to form a suspension solution B; add 0.9mmol of potassium fluoride to 40mL of deionized water to form solution C; dissolve solution C Add it dropwise to solution B, and keep stirring at 90°C until the water evaporates completely; dry the obtained material in a vacuum oven at 120°C for more than 12 hours, pass through a 100-mesh sieve, and set aside.
  • D 50 is 10-13 microns, Xiamen Tungsten
  • Step 2 Subsequent heat treatment and sintering.
  • the powder pretreated in step 1 is heat-treated in a rotary tube furnace at 650°C for 24h under an Ar inert atmosphere, and the cooling rate is controlled to be lower than 1°C/min.
  • Electrochemical test Using NMP as a solvent, LiCoO 2 @LCMF-Spinel-3#, carbon black and PVDF were evenly mixed at a mass ratio of 8:1:1 to prepare a positive electrode sheet with an active material loading of about 2.5 mg cm -2 .
  • XRD analysis results show that the obtained LiCoO 2 @LCMF-Spinel-3# unit cell parameters belong to R-3m, which is a typical layered structure of lithium cobalt oxide.
  • TEM EDS-mapping and diffraction analysis results show that there is a spinel layer with a thickness of about 28nm on the surface, and the elemental composition of the spinel layer includes Li, Co, Al, O and F, that is, the surface of the material has a spinel layer .
  • Electrochemical test results show that the button battery with the positive electrode material LiCoO 2 @LCMF-S and the lithium metal negative electrode, in the 3-4.6V vs.
  • the treated LiCoO 2 showed higher rate and cycle stability. Its discharge capacity at 0.1C and 10C current was ⁇ 225mAh/g and ⁇ 134mAh/g, respectively, and the capacity remained after 200 cycles at 2C current. The rate is 92.3%.
  • LiNi 0.8 Co 0.1 Mn 0.1 O 2 and LiNi 0.5 Co 0.3 Mn 0.2 O 2 were subjected to the pretreatment and subsequent heat treatment of step 1 and step 2, and the obtained materials were respectively marked as NCM811 @LZF-spinel and replacement NCM532 @LZF-spinel. That is, LiNi 0.8 Co 0.1 Mn 0.1 O 2 and LiNi 0.5 Co 0.3 Mn 0.2 O 2 were used to replace the lithium cobaltate in Example 2 in equal amounts, and the rest remained unchanged.
  • the results of XRD analysis showed that the obtained NCM811@LZF-spinel and NCM532@LZF-spinel were typical layered structures.
  • the results of TEM EDS-mapping and diffraction analysis show that there is a spinel phase region with a thickness of about 35nm and 27nm, which is uniformly distributed at the surface interface, and the elemental composition of the spinel phase layer includes Li, Ni , Co, Mn, Zn, O and F. Both materials after step 1 and step 2 showed better rate and cycle stability.
  • the button battery with positive electrode material NCM811@LZF-spinel and lithium metal negative electrode has a discharge capacity of 0.1C and 10C during the charge-discharge cycle of 3-4.3V vs. Li/Li + . ⁇ 215mAh/g and ⁇ 125mAh/g, the capacity retention rate is 89.3% after 200 cycles at 2C current.
  • the button battery with positive electrode material NCM532@LZF-spinel and lithium metal negative electrode has a discharge capacity of 0.1C and 10C during the charge-discharge cycle of 3-4.3V vs. Li/Li + . ⁇ 205mAh/g and ⁇ 113mAh/g, the capacity retention rate is 84.3% after 200 cycles at 2C current.
  • Example 2 Using the same ball milling method and heat treatment as in Example 2, for some typical high-nickel binary materials, such as LiNi 0.8 Co 0.2 O 2 (NC82), LiNi 0.8 Mn 0.2 O 2 (NM82), LiNi 0.6 Co 0.4 O 2 (NC64), LiNi 0.6 Mn 0.4 O 2 (NM64); high nickel ternary materials such as LiNi 0.6 Co 0.2 Mn 0.2 O 2 (NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811), LiNi 0.8 Co 0.1 Al 0.1 O 2 (NCA811); high-nickel multi-component materials, such as LiNi 0.7 Co 0.1 Mn 0.1 Al 0.1 O 2 (NCMA7111) for the pretreatment and subsequent heat treatment of step 1 and step 2, the sample obtained after synthesis is at 3-4.3V Electrochemical tests are carried out in the potential interval of the range, and the obtained results are shown in Table 1,
  • the commercialized LiCoO2 material (D 50 is 10-13 microns, Xiamen tungsten) is subjected to the pretreatment and subsequent heat treatment of step 1 and step 2.
  • the heat treatment temperature/time and cooling time are controlled to obtain spinel phase layers in the surface area with different thicknesses.
  • the heat treatment process conditions are shown in Table 2.
  • Example 2 Using the same method as in Example 2, the 0.1C/10C capacity test and the 200-cycle capacity retention test of 2C cycles were carried out on the cathode material with a co-lattice spinel phase interface on the crystal structure surface prepared in this example. The results are shown in Table 2. .

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Abstract

本申请公开了一种电池层状正极材料及其制备方法和应用。本申请的电池层状正极材料，其晶体结构中具有以钉扎的方式扎入晶体结构的表面界面层和体相层的异质相结构；该异质相结构均匀分布于晶体结构的表面，将晶体结构包覆其中，形成均匀的晶体表层。本申请的电池层状正极材料，其晶体结构中的异质相结构钉扎入晶体结构的各层状相，一方面，能够保障各层状相的稳定，解决晶体结构中各层滑移、坍塌、扭曲和微裂纹的问题；另一方面，异质相结构形成的晶体表层能够导电、导锂，且在界面起到隔离电解液的作用。本申请的电池层状正极材料，在大于4.3V的高电压下具有较高的容量、倍率和循环稳定性，在高电压充放电条件下表现出优异的电化学性能。

Description

一种电池层状正极材料及其制备方法和应用 技术领域
本申请涉及电池正极材料领域，特别是涉及一种电池层状正极材料及其制备方法和应用。
背景技术
随着时代发展，人们对于能源需求的增加，导致能源短缺和环境恶化成为全球性的难题。
当前，化石燃料作为人类主要能源，在使用过程中产生大量的CO 2等温室气体，使地球温度升高，生态环境恶化。基于此，中国提出了“碳达峰”和“碳中和”的国家战略，以实现国家能源利用方式从不可再生化石能源到可再生清洁能源的转变，如风能、太阳能等。这种转变给储能器件的开发及应用提出了机遇和挑战。
锂离子电池自问世以来，由于开路电压高、循环寿命长、功率密度高、自放电少、无记忆效用等优点，不仅在3C应用领域，包括手机、数码相机、笔记本电脑等方面显示出广阔应用前景，而且在电动汽车、无人机、电动船等应用领域也有较多应用。
锂离子电池的性能与电池用电极材料的选择、制备工艺及性能等密切相关。当前，钴酸锂LiCoO 2和三元正极材料Li[Ni xCo yMn 1-x-y]O 2(0<x<1，0<y<1)以高容量、高倍率和合成工艺简单等特性成为3C数码、无人机及电动车动力电源等锂电池的正极材料。这两类正极材料均为典型的层状结构，即过渡族金属层和锂层交替堆叠排列的晶体结构。这两类正极材料的层状结构在充放电过程中，伴随着循环往复的Li +嵌入/脱出过程，过渡族金属层会发生滑移、层错、扭曲、甚至产生微裂纹，这种情况在高电压充放电过程中尤为严重。在循环往复的高电压充放电过程中，过渡族金属层的滑移、层错、扭曲及微裂纹的产生，导致界面结构坍塌、活性材料粉化、及高价态的活性Ni/Co离子导致界面副反应加剧等，最终导致电池内阻增加，容量快速衰减。
为解决以上问题，目前采取的比较有效的策略是在活性材料表面进行包覆处理，该界面包覆层一般具有高的离子电导，且能够有效隔绝电解液与活性材料的直接接触。虽然这些策略能够对抑制副反应、延缓内 阻增加有帮助，但对于解决过渡族金属层滑移、坍塌、扭曲和微裂纹形成的问题，并无显著作用。
因此，如何有效解决过渡族金属层滑移、坍塌、扭曲和微裂纹形成，是从根本上解决电池层状正极材料容量快速衰减的关键，也是本领域的研究重点和难点。
发明内容
本申请的目的是提供一种改进的电池层状正极材料及其制备方法和应用。
本申请采用了以下技术方案：
本申请的一方面公开了一种电池层状正极材料，该电池层状正极材料的晶体结构中具有以钉扎的方式扎入晶体结构的表面界面层和体相层的异质相结构；该异质相结构均匀分布于晶体结构的表面，将晶体结构包覆其中，形成均匀的晶体表层。
需要说明的是，本申请的晶体结构表面具有异质相结构的电池层状正极材料，其界面的异质相以钉扎的方式扎入各层中，能够起到保障各层状相稳定的作用，从根本上解决电池层状正极材料各层滑移、坍塌、扭曲和微裂纹的问题；并且，异质相结构形成的包覆晶体结构的晶体表层能够隔离电解液，抑制界面副反应，解决电池层状正极材料容量快速衰减的问题。因此，本申请的电池层状正极材料极大的提高了层状正极材料的电化学性能，尤其是在高电压(＞4.3V vs.Li/Li +)充放电条件下表现出优异的容量、倍率和循环稳定性。本申请中，所谓“异质相结构”是指，对电池层状正极材料的晶体结构的表面界面进行元素替换或掺杂形成的结构，即元素构成异于电池层状正极材料；本申请的一种实现方式中，这种“异质相结构”是电池层状正极材料的晶体结构的体相层晶格延伸形成的，与电池层状正极材料的晶体结构的体相层共晶格的尖晶石相或岩盐相结构。
还需要说明的是，本申请的电池层状正极材料，其异质相结构以钉扎的形式扎入晶体结构的体相各层和表面界面，还能够构筑形成三维的锂离子扩散网络，提高循环稳定性、容量和倍率性能。可以理解，本申请的晶体表层就是异质相结构均匀包覆晶体结构而形成的表面层；本申请的晶体表层是从微观的晶体结构水平形成的包覆在晶体结构表面的层，与现有的宏观的正极材料表面包覆修饰有本质区别。
本申请的一种实现方式中，异质相结构为尖晶石相或岩盐相结构。
需要说明的是，尖晶石相结构和岩盐相结构只是本申请的一种实现方式中具体形成的钉扎入晶体结构各层的异质相结构，不排除还可以是其他的异质相结构。
本申请的一种实现方式中，异质相结构是由电池层状正极材料的晶体结构的体相层按照其相同晶格外延生长到晶体结构的表面界面层而成，即异质相结构与晶体结构的体相层共晶格。
需要说明的是，共晶格的异质相结构只是本申请的一种实现方式中，由体相层的晶格外延生长而成，理论上来说，只要能够形成钉扎的异质相结构，不排除还可以是其他的非共晶格的方式。
本申请的一种实现方式中，晶体表层的厚度大于或等于10nm。
需要说明的是，本申请的晶体表层实际上就是异质相结构包覆晶体结构形成的位于晶体结构表面的微观结构层；因此，晶体表层的厚度，实际上就是钉扎的异质相结构扎入晶体结构各层的深度。为了确保异质相结构对各层状相的稳定作用，以及晶体表层对电解液的隔绝作用，本申请优选晶体表层的厚度不小于10nm。
本申请的一种实现方式中，电池层状正极材料为Li 1+xTMO 2+y，其中0≤x≤1，0≤y≤1，TM为Co、Mn、Ni和Al的至少一种。
需要说明的是，锂离子电池层状正极材料只是本申请的一种实现方式中具体试验的电池层状正极材料，按照本申请的发明构思，不排除还可以是其他的离子电池层状正极材料。可以理解，过渡金属为Co、Mn、Ni和Al中的至少一种，这些只是比较常见的锂离子电池层状正极材料，不排除还可以是其他的过渡金属。
本申请的一种实现方式中，电池层状正极材料为钴酸锂、高镍二元材料、高镍多元材料、富锂锰正极材料中的至少一种；其中，高镍是指镍含量大于或等于50％。
需要说明的是，本申请的二元材料和多元材料，是指含镍、钴、锰、铝等中的两种或多种的正极材料；即二元材料就是含其中两种的正极材料；多元材料即含其中两种以上的正极材料，例如含其中三种，即三元材料。
本申请的一种实现方式中，电池层状正极材料为LiNi 0.8Co 0.1Mn 0.1O 2、LiNi 0.5Co 0.3Mn 0.2O 2和LiCoO 2中的至少一种。
可以理解，以上几种具体的电池层状正极材料只是本申请的一种实 现方式中具体制备的几种锂离子电池层状正极材料，不排除还可以是其他的电池层状正极材料。
本申请的一种实现方式中，晶体表层的组成元素包括阳离子和阴离子，阳离子包括Li、Co、Mn、Ni、Al、B、Mg、Ca和Zn中的至少一种，阴离子包括O和/或F。
本申请的一种实现方式中，Al、B、Mg、Ca、Zn和/或氟的含量由内而外逐渐升高，Co、Mn、Ni和/或O的含量由内而外逐渐降低。
需要说明的是，在本申请的一种实现方式中，共晶格的异质相结构的层主要是预处理时采用的原材料中的元素，以及电池层状正极材料中的元素，两者在热处理时通过阴阳离子互扩散形成。因此，异质相结构层的组成元素，主要由预处理的原材料和电池层状正极材料组成。可以理解，虽然异质相是由晶体结构的体相层的晶格外延生长而成；但是，根据其组成元素的来源，各元素呈由内而外的升高或降低的梯度分布。例如，组成元素主要由电池层状正极材料提供的Co、Mn、Ni和O等，其含量由内而外逐渐降低；组成元素主要由预处理的原材料提供的Al、B、Mg、Ca、Zn和氟，其含量由内而外逐渐升高。本申请中，由内而外是指由晶体结构的体相层向表层。
本申请的另一面公开了本申请的电池层状正极材料的制备方法，包括对常规的电池层状正极材料进行以下处理，获得晶体结构中具有钉扎的异质相结构的电池层状正极材料；
步骤一，采用以下方法中的至少一种对常规的电池层状正极材料进行预处理，
(a)溶液浸泡法，包括将常规的电池层状正极材料浸泡于含Li +、硼酸根、Al 3+、Mg 2+、Ca 2+、Zn 2+和F -中的至少一种的溶液中，浸泡条件为0-160℃浸泡1-24h，获得预处理的电池层状正极材料；
(b)溶胶凝胶法，包括将常规的电池层状正极材料与含Li +、硼酸根、Al 3+、Mg 2+、Ca 2+、Zn 2+和F -中的至少一种的溶胶凝胶均匀混合，加热烘干，获得预处理的电池层状正极材料；
(c)球磨法，包括将常规的电池层状正极材料与含Li +、硼酸根、Al 3+、Mg 2+、Ca 2+、Zn 2+和F -中的至少一种的固体材料一起进行球磨混料，获得预处理的电池层状正极材料；
步骤二，将步骤一获得的预处理的电池层状正极材料，在惰性气氛或还原性气氛下，400-700℃热处理超过阈值时间，然后，控制降温速率 小于或等于1℃/min，降温至室温，即可获得晶体结构中具有钉扎的异质相结构，且晶体表层的厚度大于或等于10nm的电池层状正极材料；其中，惰性气氛为氮气或氩气气氛；还原性气氛为氮气+氢气气氛，或氩气+氢气气氛。阈值时间满足公式τ＝36-0.04T，其中τ为阈值时间，单位为h；T为热处理温度，单位为℃。也就是说，热处理温度越高，阈值时间越小。
需要说明的是，本申请中，通过将步骤一中预处理的层状正极材料在400-700℃高温下进行超过阈值时间的热处理，同时，控制降温速率小于或等于1℃/min，是形成与体相层状结构共晶格的表面异质相结构的必要条件。通过控制高温下的热处理时间，能够实现表面外加替换金属和氟元素向内部体相层状结构的扩散，与体相层状结构共晶格的异质相结构在该扩散过程中逐步形成；同时较慢的降温速率保证了与体相层状结构共晶格的异质相结构从高温到常温能够完全的保留下来，且消除因两相共晶格带来的材料内应力。本申请中，步骤二中热处理工艺的选择还能够使层状正极材料表面区域的异质相结构厚度大于或等于10nm，以保证表面区域异质相对层状结构具有足够的钉扎作用，从而抑制高电压下层状结构的滑移、坍塌和微裂纹产生。
还需要说明的是，本申请中步骤一中通过溶液浸泡法、溶胶凝胶法、和球磨法，在原始层状正极材料粉末表面引入一层薄层且均匀的覆盖物，但该层覆盖物最大的作用是用于步骤二中对材料表层区域进行元素替换/扩散，以形成厚度大于10nm的表界面异质相结构层，这点与传统的包覆层用于导锂和隔绝电解液的作用有很大的区别。还需要说明的是，步骤二中热处理的时间需要足够长，同时，热处理后降温的速率足够慢，才能获得表面足够厚度的均匀的异质相结构区域，这样才能在高电压循环过程中起到对体相层状材料钉扎稳定的作用，这点与传统的包覆层也有很大区别。如果热处理时间过短或降温速率过快，材料表面的异质相区域的厚度小于10nm，则不足以让粒径尺度超过5μm的层状正极材料的层状结构在高电压充放电条件下保持稳定，材料内部由于大的结构应力导致的层状结构滑移、坍塌、微裂纹很难避免，最终影响到层状正极材料的循环稳定性。
还需要说明的是，层状正极材料表面异质相结构与热处理温度和时间密切相关。一般来说，在满足“400-700℃高温下进行超过阈值时间的热处理，同时，控制降温速率小于1℃/min”的前提下，温度越高，热 处理时间越长，降温速率越慢，越容易形成尖晶石相结构，反之，则容易形成岩盐相结构。岩盐相结构同样能够对晶体结构的各层进行钉扎，起到保障各层稳定的作用。
本申请中，常规的电池层状正极材料是指晶体结构表面为正常的主金属层的电池层状正极材料；例如常规的LiCoO 2，即晶体结构表面为正常的锂层，正常的锂氧结构的钴酸锂。本申请直接对常规的电池层状正极材料进行预处理和后续的热处理，即可获得本申请的晶体结构表面具有与体相层状结构共晶格的异质相结构的电池层状正极材料。
本申请的再一面公开了本申请的电池层状正极材料在制备动力电池、大规模储能电池，或3C消费电子产品、无人机或电子烟的锂离子电池中的应用。
可以理解，本申请的电池层状正极材料具有电压高、可逆充放电容量高、倍率高和循环稳定性好等优点，能够更好的用于动力电池或大规模储能电池，例如电动汽车或其他中大型电动设备的动力电池。同样的，本申请的电池层状正极材料也能够用于3C消费电子产品、无人机或电子烟的锂离子电池。
本申请的再一面公开了一种采用本申请的电池层状正极材料的锂离子电池。
可以理解，本申请的锂离子电池，由于采用本申请的电池层状正极材料，使得电池能够在更高的充放电电压下工作，并且具有更高的可逆充放电容量和倍率，且循环稳定性更好。
本申请的有益效果在于：
本申请的电池层状正极材料，其晶体结构中具有钉扎入各层的异质相结构，利用该异质相结构的钉扎作用，一方面，能够保障各层状相的稳定，解决晶体结构中各层滑移、坍塌、扭曲和微裂纹的问题；另一方面，异质相结构形成的晶体表层能够导电、导锂，并且在界面起到隔离电解液的作用。本申请的电池层状正极材料，在大于4.3V的高电压下也具有较高的容量、倍率和循环稳定性，在高电压充放电条件下表现出优异的电化学性能。此外，本申请的电池层状正极材料制备方法简单，易于大规模工业化生产。
附图说明
图1是本申请实施例中LiCoO 2@LCAF-S的XRD表征结果图；
图2是本申请实施例中LiCoO 2@LCAF-S的表面形貌、元素分布及电子衍射特征分析结果；
图3是本申请实施例中LiCoO 2@LCAF-S与常规LiCoO 2正极在3-4.6V vs.Li/Li +区间的倍率和循环性能结果图，其中，左图为两者倍率性能对比，右图为两者循环稳定性对比。
具体实施方式
近年来，学界和产业界迫切的想通过提高充放电电压的方法实现锂离子电池更大的可逆容量存储，但以钴酸锂LiCoO 2和三元正极材料Li[Ni xCo yMn 1-x-y]O 2(0<x<1，0<y<1)为代表的层状正极活性材料，在高电压(＞4.35V vs.Li/Li +)循环过程中，不仅面临因界面副反应增加导致的电池内阻增加问题，而且，更重要的是，材料体相会产生因相结构演变导致的过渡族金属层滑移、坍塌、扭曲和微裂纹形成的问题，最终导致活性材料粉化。活性材料粉化进一步的促进了活性材料/电解液界面副反应，进一步导致内阻增加，电池性能加速衰减。也就是说，层状正极材料在高电压下面临的主要问题是大量离子嵌入/脱出导致的材料内应力累积诱发层状结构滑移、坍塌和裂纹滋生的问题。因此，高电压下，若想解决该问题，最重要的就是提出提高层状结构稳定性的策略。
基于此，若想提高高电压下锂电池的循环稳定性，仅仅要通过传统的电化学惰性包覆层对层状正极活性材料进行包覆以降低界面副反应，是远远不够的。而且，传统的电化学惰性包覆层，是以牺牲材料可逆容量来获得高循环稳定性，这对产业化应用不利。本申请发明人创造性的提出，从正极材料表面结构/元素调控设计的角度，通过构筑表面异质相结构，增加层状正极材料过渡族金属层在高电压工况条件下、大量脱锂时的结构稳定性，以防止大量不可逆的微裂纹结构缺陷产生，降低层状正极材料在高压下快速衰减的可能性。
以往的研究，主要集中在增加界面离子/电子电导和抑制副反应方面，而针对晶体结构优化提高层状结构稳定性的相关研究很少。本申请研究表明，在晶体结构表面形成的异质相结构，例如，本申请的一种实现方式中，具体是体相层状材料同晶格外延生长到表面界面形成的尖晶石相或岩盐相，这种晶体结构的电池层状正极材料，由于尖晶石结构或岩盐相结构在高电压充放电过程中能够保持稳定，且能够提供一个三维 的锂离子传输网络，因此能够有效抑制高电压下过渡族金属层的滑移、坍塌、扭曲和微裂纹形成问题的同时，提高层状正极材料的容量和倍率性能。
根据以上研究和认识，本申请创造性的提出了一种新的电池层状正极材料，其晶体结构中具有以钉扎的方式扎入晶体结构的表面界面层和体相层的异质相结构；异质相结构均匀分布于晶体结构的表面，将晶体结构包覆其中，形成均匀的晶体表层。
在本申请中，与体相层状结构同晶格外延生长异质相结构非常稳定，在高电压充放电过程中，能对体相层状结构起到强烈钉扎作用，有效抑制因相结构演变导致的过渡族金属层滑移、坍塌、扭曲和微裂纹形成问题。因此，本申请的界面优化策略，能有效抑制高电压循环过程副反应加剧和内阻快速增加问题，因而使层状正极材料在高电压下(＞4.3V vs.Li/Li +)获得高的容量、倍率和循环稳定性。
下面通过具体实施例对本申请作进一步详细说明。以下实施例仅对本申请进行进一步说明，不应理解为对本申请的限制。
实施例一
本例采用市售的商业化钴酸锂为原料，采用溶液浸泡法对其进行预处理，然后对预处理的钴酸锂进行热处理，即获得本例的晶体结构表面具有共晶格的尖晶石相界面的钴酸锂层状正极材料。具体制备方法如下：
步骤一：预处理，将0.3mmol的硫酸铝放入40mL的去离子水中，搅拌10min形成澄清溶液A；将1g的商业化钴酸锂(D50为10-13微米，厦钨)和0.5g聚乙二醇放入溶液A中，搅拌10min，形成黑色的悬浊液B；将1.8mmol的氟化锂放入40mL去离子水中，搅拌2min形成溶液C；将溶液C逐滴加入到悬浊溶液B中，滴加过程中持续搅拌，形成悬浊液D；将该悬浊液D转移至60℃的水浴锅中水热反应6h后，抽滤，采用去离子水及无水乙醇进行清洗，在100℃真空烘箱中烘干，获得预处理的钴酸锂粉末。
步骤二，后续热处理烧结，将上述预处理处理的LiCoO 2粉末，在空气气氛下，600℃热处理24h后，控制降温速率1℃/min降温至常温，将所获得的粉末100目过筛，获得表面带有Li、Al、Co、O和F成分尖晶石相的LiCoO 2粉末，标记为LiCoO 2@LCAF-Spinel-1#。
电化学测试：采用NMP作为溶剂，将LiCoO 2@LCAF-Spinel、炭黑和PVDF以质量比8:1:1的比例均匀混合，制备成正极极片，活性物质载量约为2.1mg cm -2。使用2032纽扣电池制备以锂片作为负极的半电池，使用Celgard 2035隔膜和高电压电解液(质量比LiPF 6:EMC:FEC＝15:55:30)，将该半电池在3-4.6V(vs.Li/Li +)之间循环。
材料表征及电化学结果：XRD分析结果表明，所得LiCoO 2@LCAF-Spinel-1#晶胞参数属于R-3m，为典型的钴酸锂层状结构，如图1所示。TEM EDS-mapping元素分析结果表明，表明存在一层厚度约20nm的成分包含Co、Mg、F和O元素的梯度层，如图2所示。进一步对该界面层的电子衍射特征进行分析，表明该厚度约20nm的界面层表现出明显的尖晶石结构特征，说明表面存在一层成分包含Li、Co、Mg、O和F的尖晶石结构层，即晶体结构表面具有共晶格的尖晶石相界面层。分析结果显示，共晶格的尖晶石相界面是由电池层状正极材料的晶体结构的体相层按照其相同晶格外延生长到晶体结构的表面界面而成；尖晶石相界面中共晶格的尖晶石以钉扎的形式扎入晶体结构的表面区域与体相层；并且，尖晶石相界面中共晶格的尖晶石均匀分布于表面界面。综合多方面结果分析，该合成的材料为表面梯度尖晶石钉扎的钴酸锂层状正极材料，即金属元素Al和F的含量由内而外逐渐升高，Co和氧的含量由内而外逐渐降低。电化学测试结果表明，以正极材料LiCoO 2@LCMF-Spinel-1#和锂金属负极搭配的扣式电池，在3-4.6V vs.Li/Li +区间充放电循环过程中，相比购买的没有经过任何处理的LiCoO 2，本例预处理和热处理的LiCoO 2表现出更高的倍率和循环稳定性，其在0.1C和10C电流下的放电容量分别是～218mAh/g和～109mAh/g，在2C电流下45℃高温循环200圈后容量保持率为～79.4％。
实施例二
本例采用市售的商业化钴酸锂为原料，采用球磨法对其进行预处理，然后对预处理的钴酸锂进行热处理，即获得本例的晶体结构表面具有共晶格的尖晶石相界面的钴酸锂层状正极材料。具体制备方法如下：
步骤一：预处理，将0.3mmol的氟化锌(纳米粉末，D 50约为20nm)、0.3mmol的氟化锂(纳米粉末，D 50约为15nm)与和10mmol的商业化钴酸锂(D 50为10-13微米，厦钨)混合均匀，手工研磨60min。将混合均匀的粉料放在120℃的真空烘箱中干燥12h以上，100目过筛，备用， 即可获得预处理的表面含Li、Co、Zn、O和F的钴酸锂粉末。
步骤二，后续热处理烧结，将上述预处理的LiCoO 2粉末，在Ar惰性气氛下，在旋转管式炉中650℃热处理24h后，控制降温速度低于1℃/min，将所获得的粉末100目过筛，标记为LiCoO 2@LZF-Spinel-2#。作为对比，未经过步骤二处理的材料标记为LiCoO 2@LF+AF。
电化学测试：采用NMP作为溶剂，将LiCoO 2@LZF-Spinel-2#、炭黑和PVDF以质量比8:1:1的比例均匀混合，制备成正极极片，活性物质载量约为2.5mg cm -2。使用2032纽扣电池制备以锂片作为负极的半电池，使用Celgard 2035隔膜和高电压电解液(质量比LiPF 6:EMC:FEC＝15:55:30)，将该半电池在3-4.6V(vs.Li/Li +)之间循环。
材料表征及电化学结果：XRD分析结果表明，所得LiCoO 2@LZF-Spinel-2#晶胞参数属于R-3m，为典型的钴酸锂层状结构。TEM EDS-mapping及衍射分析结果表明，表面存在一层厚度约25nm左右的尖晶石层，尖晶石层的元素成分包括Li、Co、Al、O和F，即材料表面具有尖晶石层。针对未经过步骤二处理的材料分析表明，所得材料表面仅存在若干5-20nm纳米尺度的氟化锂和氟化铝的纳米粒子附着层，而未形成尖晶石相。
电化学测试结果表明，以正极材料LiCoO 2@LCZF-S和锂金属负极搭配的扣式电池，在3-4.6V vs.Li/Li +区间充放电循环过程中，相比购买的没有经过任何处理的LiCoO 2和未经过步骤二处理的LiCoO 2@LF+AF材料，表现出更高的倍率和循环稳定性，其在在0.1C和10C电流下的放电容量分别是～220mAh/g和～129mAh/g，在2C电流下循环200圈后容量保持率为89.4％。未经过步骤二处理的LiCoO 2@LF+AF材料，在在0.1C和10C电流下的放电容量分别是～201mAh/g和～65mAh/g，在2C电流下循环200圈后容量保持率为59.1％。
实施例三
本例采用市售的商业化钴酸锂为原料，采用溶胶凝胶法对其进行预处理，然后对预处理的钴酸锂进行后续热处理，即获得本例的晶体结构表面具有共晶格的尖晶石相界面的钴酸锂层状正极材料。具体制备方法如下：
步骤一：预处理，将10mmol的商业化钴酸锂(D 50为10-13微米，厦钨)和1g的聚乙二醇(分子量大于2000)倒入40mL去离子水中， 搅拌均匀形成悬浊溶液A；在溶液A中加入0.3mmol的硫酸镁和0.3mmol的硫酸锂，持续搅拌溶解形成悬浊溶液B；在40mL的去离子水中加入0.9mmol的氟化钾，形成溶液C；将溶液C逐滴加入到溶液B中，并在90℃下持续搅拌，直至水分蒸发完毕；将所获得的材料进行在120℃的真空烘箱中干燥12h以上，100目过筛，备用。
步骤二，后续热处理烧结，将步骤一预处理后的粉末，在Ar惰性气氛下，在旋转管式炉中650℃热处理24h后，控制降温速度低于1℃/mi n，将所获得的粉末100目过筛，标记为LiCoO 2@LMF-Spinel-3#。
电化学测试：采用NMP作为溶剂，将LiCoO 2@LCMF-Spinel-3#、炭黑和PVDF以质量比8:1:1的比例均匀混合，制备成正极极片，活性物质载量约为2.5mg cm -2。使用2032纽扣电池制备以锂片作为负极的半电池，使用Celgard 2035隔膜和高电压电解液(质量比LiPF 6:EMC:FEC＝15:55:30)，将该半电池在3-4.6V(vs.Li/Li +)之间循环。
材料表征及电化学结果：XRD分析结果表明，所得LiCoO 2@LCMF-Spinel-3#晶胞参数属于R-3m，为典型的钴酸锂层状结构。TEM EDS-mapping及衍射分析结果表明，表面存在一层厚度约28nm左右的尖晶石层，尖晶石层的元素成分包括Li、Co、Al、O和F，即材料表面具有尖晶石层。
电化学测试结果表明，以正极材料LiCoO 2@LCMF-S和锂金属负极搭配的扣式电池，在3-4.6V vs.Li/Li +区间充放电循环过程中，相比购买的没有经过任何处理的LiCoO 2，表现出更高的倍率和循环稳定性，其在在0.1C和10C电流下的放电容量分别是～225mAh/g和～134mAh/g，在2C电流下循环200圈后容量保持率为92.3％。
实施例四
采用与实施例二中相同的球磨法和热处理，对LiNi 0.8Co 0.1Mn 0.1O 2和LiNi 0.5Co 0.3Mn 0.2O 2进行步骤一和步骤二的预处理和后续热处理，所得材料分别标记为NCM811@LZF-spinel和替换NCM532@LZF-spinel。即分别采用LiNi 0.8Co 0.1Mn 0.1O 2和LiNi 0.5Co 0.3Mn 0.2O 2等量替换实施例二的钴酸锂，其余不变。
XRD分析结果表明，所得NCM811@LZF-spinel和NCM532@LZF-spinel为典型层状结构。TEM EDS-mapping及衍射分析结果表明，表明存在一层厚度分别约为35nm和27nm左右的尖晶石相 区域，在表界面处均匀分布，其中，尖晶石相层的元素成分包括Li、Ni、Co、Mn、Zn、O和F。经过步骤一和步骤二处理后的两种材料均表现出了更优异的倍率和循环稳定性。
以正极材料NCM811@LZF-spinel和锂金属负极搭配的扣式电池，在3-4.3V vs.Li/Li +区间充放电循环过程中，其在在0.1C和10C电流下的放电容量分别是～215mAh/g和～125mAh/g，在2C电流下循环200圈后容量保持率为89.3％。
以正极材料NCM532@LZF-spinel和锂金属负极搭配的扣式电池，在3-4.3V vs.Li/Li +区间充放电循环过程中，其在在0.1C和10C电流下的放电容量分别是～205mAh/g和～113mAh/g，在2C电流下循环200圈后容量保持率为84.3％。
实施例五
采用与实施例二中相同的球磨法和热处理，对一些典型的高镍二元材料，例如LiNi 0.8Co 0.2O 2(NC82)、LiNi 0.8Mn 0.2O 2(NM82)、LiNi 0.6Co 0.4O 2(NC64)、LiNi 0.6Mn 0.4O 2(NM64)；高镍三元材料，例如LiNi 0.6Co 0.2Mn 0.2O 2(NCM622)、LiNi 0.8Co 0.1Mn 0.1O 2(NCM811)、LiNi 0.8Co 0.1Al 0.1O 2(NCA811)；高镍多元材料，例如LiNi 0.7Co 0.1Mn 0.1Al 0.1O 2(NCMA7111)进行步骤一和步骤二的预处理和后续热处理，合成完毕后获得的样品在3-4.3V的电位区间进行电化学测试，所得结果表1所示，
表1 采用实施例二方法处理的高镍典型正极材料的电化学性能
Figure PCTCN2021122864-appb-000001
Figure PCTCN2021122864-appb-000002
通过对表1中几种典型高镍材料进行球磨和热处理前后的电化学数据结果分析，可知，表面区域异质相钉扎对所有典型高镍材料的倍率、容量和循环稳定性均具有有益效果。
实施例六
采用与实施例二中相同的球磨法，对商业化LiCoO 2材料(D 50为10-13微米，厦钨)进行步骤一和步骤二的预处理和后续热处理，通过调控步骤二后续热处理工艺中热处理温度/时间及降温控制时间，获得不同厚度的表面区域尖晶石相层。具体的，热处理工艺条件如表2所示。
表2 热处理工艺条件及正极材料性能测试结果
Figure PCTCN2021122864-appb-000003
Figure PCTCN2021122864-appb-000004
采用实施例二相同的方法对本例制备的晶体结构表面具有共晶格的尖晶石相界面的正极材料进行0.1C/10C容量测试和2C循环200圈容量保持率测试，结果如表2所示。
通过对表2中结果的分析，可得到如下结论：
1)对比350-750℃热处理24h，同时降温速率小于1℃/min的6个样品，发现350℃样品表面并未发现明显尖晶石相层。随着热处理温度提高，2C循环200圈容量保持率逐渐提高，但相应的容量和倍率性能降低。
2)对比600℃热处理24h，但降温速率不同的5个样品，发现随着降温速率的提高，材料容量和倍率变化不大，但循环稳定性逐步降低。
3)对比400℃热处理6h、12h和24h，降温速率均低于1℃/min的3个样品，发现，热处理时间延长，尖晶石相层的厚度逐渐增加，但400℃热处理12h的样品尖晶石相厚度仍小于10nm，导致循环稳定性不佳；对比700℃热处理6h、12h和24h，降温速率均低于1℃/min的3个样品，发现，热处理时间延长，尖晶石相层的厚度逐渐增加，700℃热处理超过6h样品表面尖晶石相厚度即可大于10nm，同时在2C循环200圈后容量保持率均大于80％。
4)对于750℃热处理24h，同时降温速率小于1℃/min的样品的电化学数据，发现温度超过700℃，尽管循环稳定性极大提高，但不利于倍率和容量的发挥。
本实施例的结果表明，不同热处理温度下获得“尖晶石相结构厚度大于或等于10nm”的时间阈值是不同的，热处理温度越高，时间阈值越低；原则上，只要满足在特定热处理温度T时，热处理的时间超过阈值时间τ即可，两者满足公式τ＝36-0.04T，其中τ为阈值时间，单位为 h；T为热处理温度，单位为℃。在700℃高温条件下，热处理超过6h即可获得厚度超过10nm的尖晶石相界面层。实际生产过程中，基于能耗问题考虑，我们选取合适的温度和时间对材料进行热处理。因此，优选采用400-700℃热处理超过阈值时间。同时，本实施例的结果表明，降温速率对材料容量和倍率的影响较小，但对材料循环稳定性的影响很大，只有在降温速率低于或等于1℃/min条件下，所获得的层状正极材料的循环稳定性才能得到保证。
以上内容是结合具体的实施方式对本申请所作的进一步详细说明，不能认定本申请的具体实施只局限于这些说明。对于本申请所属技术领域的普通技术人员来说，在不脱离本申请构思的前提下，还可以做出若干简单推演或替换。

Claims (10)

  1. 一种电池层状正极材料，其特征在于：所述电池层状正极材料的晶体结构中具有以钉扎的方式扎入晶体结构的表面界面层和体相层的异质相结构；所述异质相结构均匀分布于晶体结构的表面，将晶体结构包覆其中，形成均匀的晶体表层。
  2. 根据权利要求1所述的电池层状正极材料，其特征在于：所述异质相结构为尖晶石相或岩盐相结构；
    优选的，所述异质相结构是由所述电池层状正极材料的晶体结构的体相层按照其相同晶格外延生长到晶体结构的表面界面层而成，即异质相结构与晶体结构的体相层共晶格。
  3. 根据权利要求1所述的电池层状正极材料，其特征在于：所述晶体表层的厚度大于或等于10nm。
  4. 根据权利要求1-3任一项所述的电池层状正极材料，其特征在于：所述电池层状正极材料为Li 1+xTMO 2+y，其中0≤x≤1，0≤y≤1，TM为Co、Mn、Ni和Al的至少一种。
  5. 根据权利要求4所述的电池层状正极材料，其特征在于：所述电池层状正极材料为钴酸锂、高镍二元材料、高镍多元材料、富锂锰正极材料中的至少一种；
    所述高镍是指镍含量大于或等于50％；
    优选的，所述电池层状正极材料为LiNi 0.8Co 0.1Mn 0.1O 2、LiNi 0.5Co 0.3Mn 0.2O 2和LiCoO 2中的至少一种。
  6. 根据权利要求5所述的电池层状正极材料，其特征在于：所述晶体表层的组成元素包括阳离子和阴离子，所述阳离子包括Li、Co、Mn、Ni、Al、B、Mg、Ca和Zn中的至少一种，所述阴离子包括O和/或F。
  7. 根据权利要求6所述的电池层状正极材料，其特征在于：所述晶体表层中，Al、B、Mg、Ca、Zn和/或氟的含量由内而外逐渐升高，Co、Mn、Ni和/或O的含量由内而外逐渐降低。
  8. 根据权利要求1-7任一项所述的电池层状正极材料的制备方法，其特征在于：包括对常规的电池层状正极材料进行以下处理，获得晶体结构中具有钉扎的异质相结构的电池层状正极材料；
    步骤一，采用以下方法中的至少一种对常规的电池层状正极材料进行预处理，
    (a)溶液浸泡法，包括将常规的电池层状正极材料浸泡于含Li +、硼酸根、Al 3+、Mg 2+、Ca 2+、Zn 2+和F -中的至少一种的溶液中，浸泡条件为0-160℃浸泡1-24h，获得预处理的电池层状正极材料；
    (b)溶胶凝胶法，包括将常规的电池层状正极材料与含Li +、硼酸根、Al 3+、Mg 2+、Ca 2+、Zn 2+和F -中的至少一种的溶胶凝胶均匀混合，加热烘干，获得预处理的电池层状正极材料；
    (c)球磨法，包括将常规的电池层状正极材料与含Li +、硼酸根、Al 3+、Mg 2+、Ca 2+、Zn 2+和F -中的至少一种的固体材料一起进行球磨混料，获得预处理的电池层状正极材料；
    步骤二，将步骤一获得的预处理的电池层状正极材料，在惰性气氛或还原性气氛下，400-700℃热处理超过阈值时间，然后，以小于或等于1℃/min的降温速率降温至室温，即可获得晶体结构中具有钉扎的异质相结构，且晶体表层的厚度大于或等于10nm的电池层状正极材料；
    所述惰性气氛为氮气气氛或氩气气氛；所述还原性气氛为氮气加氢气的气氛，或氩气加氢气的气氛；
    所述阈值时间满足公式τ＝36-0.04T，其中τ为阈值时间，单位为h；T为热处理温度，单位为℃。
  9. 根据权利要求1-7任一项所述的电池层状正极材料在制备动力电池、大规模储能电池，或3C消费电子产品、无人机或电子烟的锂离子电池中的应用。
  10. 一种采用权利要求1-7任一项所述的电池层状正极材料的锂离子电池。
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