Lithium cobalt oxide cathode material, electrochemical device, electronic device and mobile device

Abstract

The embodiments of the present application provide a lithium cobalt oxide cathode material, which includes a core and a shell layer coated on the core. The core includes a lithium cobalt oxide material; the shell layer includes a first coating layer, a transition layer, and a second coating layer; the first coating layer includes a metal fluoride A b F c , 0 < b ≤ 1, 0 < c ≤ 4, and A is a metal or metalloid element that can satisfy that the bond energy of A-O is greater than the bond energy of Co-O; the second coating layer includes a polyanionic compound Li x M’ y D z , 0

Description

Technical Field

[0001] The embodiments of the present application relate to the technical field of secondary batteries, and in particular, to a lithium cobalt oxide cathode material, an electrochemical device, an electronic device, and a mobile device. Background Art

[0002] The growing demand for long-lasting and durable electronic devices has driven the development of high-energy-density lithium-ion batteries. Currently, the key to increasing the energy density of high-energy-density lithium-ion batteries lies in increasing the specific capacity of the cathode material, including the development of new high-specific-capacity cathode materials and the expansion of the charging window of commercial cathode materials. For the commercially available lithium cobalt oxide LiCoO 2 (LCO) cathode material, expanding the charging voltage window is an effective strategy to increase its specific capacity. The reversible capacity of LCO is 140 mAh g at 4.2 V -1 , and a reversible capacity of about 220 mAh g can be achieved at 4.6 V -1 . However, although the increase in the voltage window increases the reversible capacity of LCO, it sacrifices its thermal stability and cycling stability, making high-voltage LCO unable to meet the requirements of people for the safety and durability of electronic devices.

[0003] The poor thermal stability of high-voltage LCO mainly comes from two aspects: on the one hand, highly delithiated Li x CoO 2 is metastable, and continuously extracting lithium ions from the material will lead to the formation of lattice oxygen with insufficient coordination. At high temperatures, these lattice oxygen with insufficient coordination will break the bond with the transition metal (Co) and form O 2 molecules, which will then leave the LCO host structure. On the other hand, the large-scale insertion and extraction of lithium ions is accompanied by severe interfacial side reactions between Li x CoO 2 and the electrolyte. The side reactions accumulate to form a highly reducing environment, which will reduce the formation energy and migration barrier of oxygen vacancies, thereby driving the release of more lattice oxygen on the LCO surface and generating defects on the electrode. The release of lattice oxygen causes the structural degradation of LCO. In addition, the released oxygen reacts with the combustible electrolyte at high temperatures to generate a large amount of heat and other gases, causing thermal runaway.

[0004] Therefore, there is an urgent need to develop a lithium cobalt oxide cathode material that can reduce the irreversible release of lattice oxygen at high voltages and has good thermal stability and cycling stability. Summary of the Invention

[0005] In view of this, the embodiments of the present application provide a lithium cobalt oxide cathode material. By coating a shell layer on the lithium cobalt oxide core, the irreversible release of lattice oxygen in the lithium cobalt oxide can be effectively reduced, and the thermal stability and cycling stability of the lithium cobalt oxide material can be improved.

[0006] In the first aspect of the embodiments of the present application, a lithium cobalt oxide cathode material is provided. The lithium cobalt oxide cathode material includes a core and a shell layer coated on the core. The core includes a lithium cobalt oxide material; the shell layer includes a first coating layer on the core, a second coating layer on the first coating layer, and a transition layer between the first coating layer and the second coating layer;

[0007] The first coating layer includes a metal fluoride, and the metal fluoride is represented as A b F c , where 0 < b ≤ 1, 0 < c ≤ 4, and A is a metal or metalloid element that can satisfy that the bond energy of A-O is greater than the bond energy of Co-O;

[0008] The second coating layer includes a polyanionic compound, and the polyanionic compound is represented as Li x M’ y D z , where 0 < x ≤ 4, 0 ≤ y ≤ 4, 0 < z ≤ 3, M’ represents a metal or metalloid element that can satisfy that the bond energy of M’-O is greater than the bond energy of Co-O, and D represents a polyanion group;

[0009] The transition layer includes the materials of the first coating layer and the second coating layer.

[0010] For the lithium cobalt oxide cathode material of the embodiments of the present application, by sequentially forming a first coating layer, a transition layer, and a second coating layer outside the lithium cobalt oxide material core, the irreversible release of lattice oxygen in the lithium cobalt oxide can be effectively reduced, and the thermal stability and cycle stability of the lithium cobalt oxide material can be improved. Specifically, for the metal fluoride in the first coating layer, since the bond energy of the A-O bond formed by the A metal ions and oxygen ions therein is greater than the bond energy of Co-O, it can meet the requirement of binding the lattice oxygen on the surface of the lithium cobalt oxide core, and F can occupy the O of lithium cobalt oxide 2-The lattice position stabilizes the octahedral framework structure of lithium cobaltate, thereby stabilizing the lattice oxygen. Moreover, the electronegativity of F is 3.98, which is greater than that of O (3.44), and it can form a strong bond with Co, inhibit the dissolution of transition metal Co, and improve the stability of the lithium cobaltate material. For the polyanionic compound of the second coating layer, due to the strong chemical stability of the polyanionic group, it can effectively inhibit the side reactions at the cathode-electrolyte interface, thereby hindering the catalytic effect of the interface reaction on the release of lattice oxygen. And M' is a metal or metalloid element with an M'-O bond energy greater than that of Co-O, which can meet the requirement of binding the lattice oxygen on the surface of the lithium cobaltate core, inhibit the release of lattice oxygen, and improve the stability of the lithium cobaltate material. The transition layer, as the structural connection layer between the first coating layer and the second coating layer, helps to improve the binding tightness between the two, preventing the second coating layer from falling off and failing during cycling. The existence of the transition layer can also increase the diffusion barrier of lattice oxygen, further preventing the escape of lattice oxygen, improving the stability of the cathode material, and reducing the risk of thermal runaway caused by the reaction of the released oxygen of the cathode material with the electrolyte.

[0011] In some embodiments of the present application, A is selected from one or more of Al, As, Ag, Au, Ba, Be, B, Ca, Ce, Cs, Cr, Cm, Cd, Dy, Er, Eu, Gd, Ge, Hf, Ir, Fe, La, Lu, Mg, Mn, Mo, Nd, Np, Nb, Os, Pr, Pm, Pd, Pt, Re, Ru, Rh, Sm, Sc, Sr, Ta, Tm, Tc, Sn, Ti, W, V, Y, Zr.

[0012] In some embodiments of the present application, M' is selected from one or more of Al, As, Ag, Au, Ba, Be, B, Ca, Ce, Cs, Cr, Cm, Cd, Dy, Er, Eu, Gd, Ge, Hf, Ir, Fe, La, Lu, Mg, Mn, Mo, Nd, Np, Nb, Os, Pr, Pm, Pd, Pt, Re, Ru, Rh, Sm, Sc, Sr, Ta, Tm, Tc, Sn, Ti, W, V, Y, Zr.

[0013] In an embodiment of the present application, A is a metal or metalloid element that can satisfy an A-O bond energy greater than 500 kJ / mol; M' is a metal or metalloid element that can satisfy an M'-O bond energy greater than 500 kJ / mol. The greater the A-O and M'-O bond energies, the stronger the ability to bind lattice oxygen, and thus the better the stability of the lithium cobaltate cathode material can be maintained.

[0014] In the embodiments of the present application, D is selected from an oxygen-containing acid radical of phosphorus, an oxygen-containing acid radical of silicon, an oxygen-containing acid radical of boron, or an oxygen-containing acid radical of tungsten. These oxygen-containing acid radicals all have a small energy convex hull, which can meet the requirement of strong chemical stability to inhibit interfacial side reactions, thereby hindering the catalytic effect of the interfacial reaction on the release of lattice oxygen.

[0015] In the embodiments of the present application, the chemical formula of the transition layer is aA b F c ·(1 - a)Li x M’ y D z , where 0 < a < 1.

[0016] In the embodiments of the present application, along the direction from the first coating layer to the second coating layer, in the transition layer, the material content of the first coating layer gradually decreases, and the material content of the second coating layer gradually increases. Such a distribution is beneficial to improving the bonding tightness of the second coating layer on the surface of the first coating layer, and at the same time can better improve the lattice oxygen diffusion barrier.

[0017] In the embodiments of the present application, in order to preferably inhibit the escape of lattice oxygen in lithium cobaltate and inhibit the dissolution of Co, while ensuring good lithium ion transmission performance, the molar percentage of the metal fluoride of the first coating layer relative to the lithium cobaltate material of the core is 0.1 mol% - 4.0 mol%.

[0018] In the embodiments of the present application, in order to maintain a stable contact interface between the lithium cobaltate cathode material and the electrolyte, and preferably inhibit the escape of lattice oxygen in lithium cobaltate, while ensuring good lithium ion transmission performance, the molar percentage of the polyanionic compound of the second coating layer relative to the lithium cobaltate material of the core is 0.1 mol% - 4.0 mol%.

[0019] In the embodiments of the present application, in order to achieve a strong binding of the first coating layer to the surface lattice oxygen, the thickness of the first coating layer is greater than or equal to 3 nm. In the embodiments of the present application, in order to enable the second coating layer to effectively inhibit the interfacial side reaction at the cathode - electrolyte interface and the catalytic effect of the interfacial reaction on the release of lattice oxygen, the thickness of the second coating layer is greater than or equal to 5 nm.

[0020] In the embodiments of the present application, in order to make the first coating layer and the second coating layer form a tighter connection and improve the lattice oxygen diffusion barrier, the thickness of the transition layer is greater than or equal to 3 nm.

[0021] In the embodiments of the present application, considering that the coating layer material does not have electrochemical activity, in order to better ensure the performance of the specific capacity of the lithium cobaltate material, the total thickness of the first coating layer, the transition layer, and the second coating layer is less than or equal to 20 nm.

[0022] In the embodiment of the present application, the shell layer further includes a diffusion layer disposed between the inner core and the first coating layer, and the diffusion layer includes the material of the inner core and the material of the first coating layer. The existence of the diffusion layer can effectively confine the lattice oxygen in the bulk of lithium cobaltate, stabilize the octahedral framework structure of lithium cobaltate, and further improve the lattice oxygen stability. The existence of the diffusion layer can also improve the binding tightness between the inner core and the first coating layer.

[0023] In the embodiment of the present application, the thickness of the diffusion layer is 2 nm - 80 nm.

[0024] In some embodiments of the present application, the chemical formula of the diffusion layer is Li x A y Co (1-x’-3y’) / 3 O (1-z’) / 2 F z’ , where 0 ≤ x' ≤ 1, 0 ≤ y' ≤ 1, 0 ≤ z' ≤ 1.

[0025] In some embodiments of the present application, the chemical formula of the lithium cobaltate material is LiCo 1-x ”M x ”O 2-y ”Y y ”, where 0 ≤ x'' ≤ 0.4, 0 ≤ y'' ≤ 0.2, M represents one or more of Na, Mg, Al, Si, K, Ca, Ti, Cr, Mn, Fe, Ni, Cu, Zn; Y represents one or more of F, S, P.

[0026] In the embodiment of the present application, the lithium cobaltate cathode material is applied in a high-voltage lithium-ion battery system with a cut-off voltage of 4.5 V - 4.7 V, and the irreversible release amount of lattice oxygen is less than 20% of the total amount of lattice oxygen. The smaller the irreversible release amount of lattice oxygen, the higher the stability of the lithium cobaltate cathode material during cycling under the high-voltage condition of 4.5 V - 4.7 V.

[0027] In the embodiment of the present application, the exothermic peak temperature of the lithium cobaltate cathode material measured by differential scanning calorimetry is greater than 240 °C. The higher exothermic peak temperature of the lithium cobaltate cathode material indicates that the material has good thermal stability.

[0028] The second aspect of the embodiment of the present application provides a preparation method of a lithium cobaltate cathode material, including:

[0029] Coating a first coating layer material on the surface of the lithium cobaltate material to obtain a first composite material; the first coating layer material includes metal fluoride, and the metal fluoride is represented as A b F c , where 0 < b ≤ 1, 0 < c ≤ 4, and A is a metal or metalloid element that can satisfy that the bond energy of A - O is greater than the bond energy of Co - O;

[0030] Coat a second coating material on the metal fluoride to obtain a second composite material; the second coating material includes a polyanionic compound, and the polyanionic compound is expressed as Li x M’ y D z , where 0 < x ≤ 4, 0 ≤ y ≤ 4, 0 < z ≤ 3, M’ is a metal or metalloid element that can satisfy that the bond energy of M’-O is greater than the bond energy of Co-O, and D represents a polyanionic group;

[0031] Sinter the second composite material in an inert atmosphere to obtain a lithium cobaltate cathode material; the lithium cobaltate cathode material includes a core and a shell layer coating the core, the core includes a lithium cobaltate material, and the shell layer includes a first coating layer on the core, a second coating layer on the first coating layer, and a transition layer between the first coating layer and the second coating layer. The first coating layer includes the metal fluoride, the second coating layer includes the polyanionic compound, and the transition layer includes the materials of the first coating layer and the second coating layer.

[0032] In the embodiment of the present application, the temperature of the sintering treatment is 300°C - 650°C, the time is 3 - 10 h; the heating rate during the sintering treatment is 1 - 5°C / min.

[0033] The preparation method of the lithium cobaltate cathode material in the embodiment of the present application can realize the preparation of the shell layer with a multi-layer structure through a one-time sintering process. The one-time sintering process helps to strengthen the mutual diffusion between the lithium cobaltate base material and the first coating layer, and between the first coating layer and the second coating layer, forming a diffusion layer and a transition layer, thereby improving the ability of the shell layer to inhibit the release of lattice oxygen.

[0034] The third aspect of the embodiment of the present application also provides a positive electrode plate, and the positive electrode plate includes the lithium cobaltate cathode material described in the first aspect of the embodiment of the present application.

[0035] The fourth aspect of the embodiment of the present application also provides an electrochemical device, and the electrochemical device includes the lithium cobaltate cathode material described in the first aspect of the embodiment of the present application. The electrochemical device can be a lithium secondary battery.

[0036] In the embodiment of the present application, the capacity retention rate of the electrochemical device is greater than 70% after 300 cycles at a cut-off voltage of 4.5V - 4.7V and charging at 1.5C / discharging at 0.7C. The electrochemical device has good high-voltage thermal stability and cycle stability.

[0037] An embodiment of the present application further provides an electronic device, which includes a housing, electronic components accommodated in the housing, and the electrochemical device described in the fourth aspect of the embodiments of the present application. The electrochemical device powers the electronic device. By using the high-voltage lithium cobaltate cathode material provided in the embodiments of the present application as the cathode active material of the electrochemical device, the electronic device in the embodiments of the present application can improve the thermal stability, cycle performance, and energy density of the electrochemical device, better meet the requirements of consumer electronic products for good thermal stability, long cycle life, and high energy density of the electrochemical device, and improve the user experience and market competitiveness of electronic products.

[0038] An embodiment of the present application further provides a mobile device, which includes the electrochemical device described in the fourth aspect of the embodiments of the present application. By using the electrochemical device provided in the embodiments of the present application for power supply, the competitiveness of the product can be improved. Description of the Drawings

[0039] Figure 1 It is a schematic structural diagram of the lithium cobaltate cathode material 100 provided in the embodiments of the present application;

[0040] Figure 2 It is a schematic structural diagram of the lithium secondary battery 200 provided in the embodiments of the present application;

[0041] Figure 3 It is a schematic structural diagram of the electronic device 300 provided in the embodiments of the present application;

[0042] Figure 4 It is a schematic structural diagram of the mobile device 400 provided in the embodiments of the present application;

[0043] Figure 5 It is a scanning electron microscope (SEM) result diagram of the lithium cobaltate cathode material of Embodiment 1 of the present application;

[0044] Figure 6 and Figure 7 It is an X-ray energy dispersive spectroscopy (EDS) surface scan result diagram of the lithium cobaltate cathode material of Embodiment 1 of the present application;

[0045] Figure 8 It is a high-resolution transmission electron microscope result diagram of the unmodified LiCoO 2 material of Comparative Example 1;

[0046] Figure 9 It is the high-resolution transmission electron microscope result of the lithium cobaltate cathode material of Example 1;

[0047] Figure 10XRD pattern of the lithium cobalt oxide cathode material of Example 1 of this application;

[0048] Figure 11A is LiCoO of Example 1 2 @AlF 3 @Li 3 PO 4 DSC curve of the cathode material;

[0049] Figure 11B is the DSC curve of the unmodified LiCoO cathode material of Comparative Example 1; 2 DSC curve of the cathode material;

[0050] Figure 11C is the DSC curve of the LiCoO cathode material of Comparative Example 2; 2 @AlF 3 DSC curve of the cathode material;

[0051] Figure 11D is the DSC curve of the LiCoO cathode material of Comparative Example 3; 2 @Li 3 PO 4 DSC curve of the cathode material;

[0052] Figure 12A is the cycling performance curve of the cathode materials of Example 1, Comparative Example 1, Comparative Example 2 and Comparative Example 3;

[0053] Figure 12B is the first charge-discharge curve of the cathode materials of Example 1, Comparative Example 1, Comparative Example 2 and Comparative Example 3;

[0054] Figure 13A is the dQ / dV curve of the unmodified LiCoO cathode material of Comparative Example 1; 2 dQ / dV curve of the cathode material;

[0055] Figure 13B is the dQ / dV curve of the LiCoO cathode material of Comparative Example 2; 2 @AlF 3 dQ / dV curve of the cathode material;

[0056] Figure 13C is the dQ / dV curve of the LiCoO cathode material of Comparative Example 3; 2 @Li 3 PO 4 dQ / dV curve of the cathode material;

[0057] Figure 13D is LiCoO of Example 1 2 @AlF 3 @Li 3 PO4 Capacity-voltage differential curve (dQ / dV) of the positive electrode material. Detailed implementation manners

[0058] Hereinafter, embodiments of the present application will be described with reference to the accompanying drawings in the embodiments of the present application.

[0059] See Figure 1 , Figure 1 is a schematic structural diagram of a lithium cobalt oxide positive electrode material 100 provided in an embodiment of the present application. The lithium cobalt oxide positive electrode material 100 includes a core 10 and a shell layer 20 coated on the core 10. The core 10 includes a lithium cobalt oxide material; the shell layer 20 includes a first coating layer 201 on the core 10, a second coating layer 202 on the first coating layer 201, and a transition layer 203 between the first coating layer 201 and the second coating layer 202.

[0060] In the embodiment of the present application, the first coating layer 201 includes a metal fluoride, and the metal fluoride can be represented as A b F c , where 0 < b ≤ 1, 0 < c ≤ 4, and A is a metal or metalloid element that can satisfy that the bond energy of A-O is greater than the bond energy of Co-O (368 kJ / mol). Specifically, the values of b and c are determined according to the valence of A and F.

[0061] In the embodiment of the present application, the second coating layer 202 includes a polyanionic compound, and the polyanionic compound can be represented as Li x M’ y D z , where 0 < x ≤ 4, 0 ≤ y ≤ 4, 0 < z ≤ 3, M’ is a metal or metalloid element that can satisfy that the bond energy of M’-O is greater than the bond energy of Co-O, and D represents a polyanionic group.

[0062] In the embodiment of the present application, the transition layer 203 includes the materials of the first coating layer and the second coating layer, that is, it includes a metal fluoride and a polyanionic compound.

[0063] The lithium cobaltate cathode material of the embodiment of the present application can effectively reduce the irreversible release of lattice oxygen in lithium cobaltate by successively forming a first coating layer 201, a transition layer 203, and a second coating layer 202 on the surface of the lithium cobaltate material core 10, improve the thermal stability and cycle stability of the lithium cobaltate material, and effectively solve the problems of poor thermal stability and cycle stability caused by the irreversible release of lattice oxygen in the lithium cobaltate material in a highly delithiated state when the voltage window is increased, the catalytic release of lattice oxygen by the cathode - electrolyte interface reaction, the thermal runaway caused by the reaction of the released oxygen with the electrolyte at high temperature, and the structural decline. Specifically, the metal fluoride of the first coating layer 201 can meet the requirement of binding the lattice oxygen on the surface of the lithium cobaltate core because the bond energy of the A - O bond formed by the A metal ion and the oxygen ion in it is greater than the Co - O bond energy, and F can occupy the lattice position of O in lithium cobaltate, stabilizing the octahedral framework structure of lithium cobaltate, and thus playing a role in stabilizing lattice oxygen; moreover, the electronegativity of F is 3.98, which is greater than the electronegativity of O, 3.44, and can strongly bond with Co, inhibiting the dissolution of transition metal Co and improving the stability of the lithium cobaltate material. The polyanionic compound of the second coating layer 202 can effectively inhibit the side reaction at the cathode - electrolyte interface due to the strong chemical stability of the polyanionic group, and thus hinder the catalytic effect of the interface reaction on the release of lattice oxygen; and M' is a metal or metalloid element with an M' - O bond energy greater than the Co - O bond energy, which can meet the requirement of binding the lattice oxygen on the surface of the lithium cobaltate core, inhibit the release of lattice oxygen, and improve the stability of the lithium cobaltate material. The transition layer 203, as the structural connection layer between the first coating layer 201 and the second coating layer 202, helps to improve the binding tightness between the two, preventing the second coating layer 202 from falling off and failing during the cycle; the existence of the transition layer 203 can also increase the diffusion barrier of lattice oxygen, further preventing the escape of lattice oxygen, improving the stability of the cathode material, and reducing the risk of thermal runaway caused by the reaction of the released oxygen of the cathode material with the electrolyte. 2- The lattice position of lithium cobaltate stabilizes the octahedral framework structure of lithium cobaltate, thereby playing a role in stabilizing lattice oxygen; moreover, the electronegativity of F is 3.98, which is greater than the electronegativity of O, 3.44, and can strongly bond with Co, inhibiting the dissolution of transition metal Co and improving the stability of the lithium cobaltate material. The polyanionic compound of the second coating layer 202 can effectively inhibit the side reaction at the cathode - electrolyte interface due to the strong chemical stability of the polyanionic group, and thus hinder the catalytic effect of the interface reaction on the release of lattice oxygen; and M' is a metal or metalloid element with an M' - O bond energy greater than the Co - O bond energy, which can meet the requirement of binding the lattice oxygen on the surface of the lithium cobaltate core, inhibit the release of lattice oxygen, and improve the stability of the lithium cobaltate material. The transition layer 203, as the structural connection layer between the first coating layer 201 and the second coating layer 202, helps to improve the binding tightness between the two, preventing the second coating layer 202 from falling off and failing during the cycle; the existence of the transition layer 203 can also increase the diffusion barrier of lattice oxygen, further preventing the escape of lattice oxygen, improving the stability of the cathode material, and reducing the risk of thermal runaway caused by the reaction of the released oxygen of the cathode material with the electrolyte.

[0064] In the embodiment of the present application, the lithium cobaltate material as the core 10 can be undoped or unmodified lithium cobaltate, that is, LiCoO 2 , or it can be doped lithium cobaltate, or it can also be lithium cobaltate coated with one or more materials such as oxides, fast ion conductors, and conductive polymers. Among them, the oxides can be, for example, Al 2 O 3 , MgO, TiO 2 , ZrO 2 , SnO 2 , Co 3 O 4 , V 2 O 5 , etc.; the fast ion conductor can be an oxide - type solid electrolyte, a sulfide - type solid electrolyte, etc., and specifically, it can be Li 2 ZrO3 , Li 3 BO 3 etc.; The conductive polymer can be, for example, polypyrrole (PPy), polyimide (PI), polyethylene glycol (diol) diacrylate (PEGDA), etc. In some embodiments of the present application, the lithium cobaltate material is undoped or unmodified lithium cobaltate, or doped lithium cobaltate, and the chemical formula of the lithium cobaltate material can be LiCo 1-x ”M x ”O 2-y ”Y y ”, where 0 ≤ x” ≤ 0.4, 0 ≤ y” ≤ 0.2, M represents one or more of Na, Mg, Al, Si, K, Ca, Ti, Cr, Mn, Fe, Ni, Cu, Zn; Y represents one or more of F, S, P. The lithium cobaltate material can be a commercially available product or can be prepared by itself. The particle size of the lithium cobaltate material can be 3 μm - 25 μm.

[0065] In some embodiments of the present application, referring to Figure 1 , the shell layer 20 may further include a diffusion layer 204 disposed between the inner core 10 and the first coating layer 201. The diffusion layer 204 includes the material of the inner core 10 and the material of the first coating layer 201. The diffusion layer 204 is formed by the diffusion of the first coating layer material into the inner core material, and the diffusion layer 204 and the inner core 10 have a continuous lithium cobaltate material bulk phase. In one embodiment, the diffusion layer 204 may include a lithium cobaltate material and metal fluorides distributed in the lithium cobaltate material. In the diffusion layer 204, the metal fluorides diffuse into the lithium cobaltate material bulk phase, and the metal ion A can form an A - O bond with O 2- with a bond energy greater than the Co - O bond energy to bind the lattice oxygen in the lithium cobaltate bulk phase. F - can then occupy the lattice position of O 2- in lithium cobaltate, stabilize the octahedral framework structure of lithium cobaltate, and further inhibit the irreversible phase change from O3 to H1 - 3, further enhancing the lattice oxygen stability. The presence of the diffusion layer 204 can improve the binding tightness between the inner core 10 and the first coating layer 201.

[0066] In the embodiments of the present application, the thickness of the diffusion layer 204 depends on the diffusion ability of elements A and F into the lithium cobaltate inner core. In order to better bind the lattice oxygen in the lithium cobaltate bulk phase and stabilize the octahedral framework structure of lithium cobaltate, the thickness of the diffusion layer 204 can be 2 nm - 80 nm. In some embodiments, the thickness of the diffusion layer is 3 nm - 60 nm; in some embodiments, the thickness of the diffusion layer is 5 nm - 50 nm; in some embodiments, the thickness of the diffusion layer is 8 nm - 20 nm; in some embodiments, the thickness of the diffusion layer is 2 nm - 10 nm.

[0067] In some embodiments of the present application, taking the lithium cobaltate material of the core 10 as the undoped or unmodified lithium cobaltate LiCoO 2 as an example, the chemical formula of the material of the diffusion layer 204 can be Li x A y Co (1-x’-3y’) / 3 O (1-z’) / 2 F z’ , where 0 ≤ x' ≤ 1, 0 ≤ y' ≤ 1, 0 ≤ z' ≤ 1.

[0068] In some embodiments of the present application, among metal fluorides, A is a metal or metalloid element that can satisfy that the bond energy of A-O is greater than 368 kJ / mol. The greater the bond energy of A-O, the stronger the ability to bind lattice oxygen, and thus the better the stability of the lithium cobaltate cathode material can be maintained. In the specific embodiments of the present application, A can be one or more metal elements selected from aluminum Al, arsenic As, silver Ag, gold Au, barium Ba, beryllium Be, boron B, calcium Ca, cerium Ce, cesium Cs, chromium Cr, curium Cm, cadmium Cd, dysprosium Dy, erbium Er, europium Eu, gadolinium Gd, germanium Ge, hafnium Hf, iridium Ir, iron Fe, lanthanum La, lutetium Lu, magnesium Mg, manganese Mn, molybdenum Mo, neodymium Nd, neptunium Np, niobium Nb, osmium Os, praseodymium Pr, promethium Pm, palladium Pd, platinum Pt, rhenium Re, ruthenium Ru, rhodium Rh, samarium Sm, scandium Sc, strontium Sr, tantalum Ta, thulium Tm, technetium Tc, tin Sn, titanium Ti, tungsten W, vanadium V, yttrium Y, zirconium Zr. In some embodiments of the present application, A is a metal or metalloid element that can satisfy that the bond energy of A-O is greater than 500 kJ / mol and is easy to diffuse into the bulk of lithium cobaltate to form a diffusion layer. In some preferred embodiments of the present application, A can be one or more selected from Al, B, Ge, Sc, Ti, W, V, Y, La, Mg, Zr. When the expression "a plurality of" is involved in the present application, "a plurality of" means two or more. In some specific embodiments, the metal fluoride can be, for example, MgF 2 , AlF 3 , CaF 2 , LaF 3 , Al 0.5 La 0.5 F 3 , ZrF 4 and so on.

[0069] In the embodiments of the present application, the main function of the second coating layer is to inhibit the interfacial side reaction and the catalytic effect of the interfacial side reaction on the release of lattice oxygen. This function is mainly achieved through polyanion groups. The introduction of M' enables the second coating layer to also play a role in binding lattice oxygen, thereby further inhibiting the release of lattice oxygen. In some embodiments of the present application, in the polyanion-type compound, M' is a metal or metalloid element that can satisfy that the bond energy of M'-O is greater than 368 kJ / mol. In the specific embodiments of the present application, M' can be one or more selected from Al, As, Ag, Au, Ba, Be, B, Ca, Ce, Cs, Cr, Cm, Cd, Dy, Er, Eu, Gd, Ge, Hf, Ir, Fe, La, Lu, Mg, Mn, Mo, Nd, Np, Nb, Os, Pr, Pm, Pd, Pt, Re, Ru, Rh, Sm, Sc, Sr, Ta, Tm, Tc, Sn, Ti, W, V, Y, Zr. In some embodiments of the present application, M' is a metal or metalloid element that can satisfy that the bond energy of A-O is greater than 500 kJ / mol, and M' is preferably a metal or metalloid element that does not change valence and has strong electrochemical stability in the electrolyte to improve the stability of the lithium cobalt oxide cathode material in the electrolyte. In some preferred embodiments of the present application, M' can be one or more selected from Al, Ba, Be, B, Ca, Mg, La, Sr, Ta, Sn, Ti, W, V, Y, Zr. In some specific embodiments, the polyanion-type compound can be, for example, Li 3 PO 4 、LiTi 2 (PO 4 ) 3 、Li 1.3 Al 0.3 Ge 1.7 (PO 4 ) 3 、Li 3 BO 3 、Li 4 SiO 4 、Li 2 SrSiO 4 、Li 2 WO 4 。

[0070] In the embodiments of the present application, the A element in the first coating layer metal fluoride and the M' element in the second coating layer polyanion-type compound can be the same or different.

[0071] In the embodiment of the present application, the polyanion group is a polyanion group with an energy convex hull less than 0.005 eV / atom. An energy convex hull less than 0.005 eV / atom can meet the requirement of strong chemical stability to inhibit interfacial side reactions, thereby hindering the catalytic effect of the interfacial reaction on the release of lattice oxygen. Preferably, the polyanion group can be selected from an oxygen-containing acid root of phosphorus, an oxygen-containing acid root of silicon, an oxygen-containing acid root of boron, or an oxygen-containing acid root of tungsten. Among them, the oxygen-containing acid root of phosphorus can be PO 4 3- , PO 3 3- , P 2 O 7 4- , the oxygen-containing acid root of silicon can be SiO 4 4- , SiO 3 2- , the oxygen-containing acid root of boron can be BO 3 3- , BO 2 - , the oxygen-containing acid root of tungsten can be WO 4 2- , W 2 O 7 2- .

[0072] In the embodiment of the present application, the chemical formula of the transition layer 203 is aA b F c ·(1 - a)Li x M’ y D z , where 0 < a < 1.

[0073] In the embodiment of the present application, along the direction from the first coating layer 201 to the second coating layer 202, that is, along the direction from the inside to the outside of the lithium cobaltate cathode material 100, the material content of the first coating layer in the transition layer 203 gradually decreases, and the material content of the second coating layer gradually increases. That is, along the direction from the first coating layer 201 to the second coating layer 202, the content of metal fluoride in the transition layer 203 gradually decreases, and the content of polyanion-type compound gradually increases. Such a distribution is beneficial to improving the binding tightness of the second coating layer on the surface of the first coating layer, and at the same time can better improve the lattice oxygen diffusion barrier.

[0074] In order to better inhibit the escape of lattice oxygen in lithium cobaltate and the dissolution of Co, and at the same time ensure good lithium-ion transport performance, in some embodiments of the present application, the molar percentage of the metal fluoride of the first coating layer 201 relative to the lithium cobaltate material of the inner core is 0.1 mol% - 4.0 mol%. That is, the molar percentage of the amount of substance of the metal fluoride of the first coating layer 201 relative to the amount of substance of the lithium cobaltate material of the inner core is 0.1 mol% - 4.0 mol%. Taking the amount of substance of the lithium cobaltate material of the inner core 10 as 100 mol as an example, the amount of substance of the metal fluoride of the first coating layer 201 can be 0.1 mol - 4.0 mol. Specifically, in some embodiments, the molar percentage of the amount of substance of the metal fluoride of the first coating layer 201 relative to the amount of substance of the lithium cobaltate material of the inner core can be 0.1 mol%, 0.5 mol%, 1.0 mol%, 2.0 mol%, 3.0 mol%, 3.5 mol%, 4.0 mol%. In some embodiments of the present application, the molar percentage of the metal fluoride of the first coating layer 201 relative to the lithium cobaltate material of the inner core is preferably 0.5 mol% - 2 mol%. Within this range, the escape of lattice oxygen in lithium cobaltate can be better inhibited on the premise of ensuring lithium-ion transport performance.

[0075] In order to maintain a stable contact interface between the lithium cobaltate cathode material and the electrolyte, and to better inhibit the escape of lattice oxygen in lithium cobaltate, and at the same time ensure good lithium-ion transport performance, in some embodiments of the present application, the molar percentage of the polyanionic compound of the second coating layer 202 relative to the lithium cobaltate material of the inner core is 0.1 mol% - 4.0 mol%. That is, the molar percentage of the amount of substance of the polyanionic compound of the second coating layer 202 relative to the amount of substance of the lithium cobaltate material of the inner core is 0.1 mol% - 4.0 mol%. Taking the amount of substance of the lithium cobaltate material of the inner core 10 as 100 mol as an example, the amount of substance of the polyanionic compound of the second coating layer 202 can be 0.1 mol - 4.0 mol. Specifically, in some embodiments, the molar percentage of the amount of substance of the polyanionic compound of the second coating layer 202 relative to the amount of substance of the lithium cobaltate material of the inner core can be 0.1 mol%, 0.5 mol%, 1.0 mol%, 2.0 mol%, 3.0 mol%, 3.5 mol%, 4.0 mol%. Considering the inhibitory effect of the second coating layer on the cathode material - electrolyte interface reaction, the content of the second coating layer can be appropriately increased. In the preferred embodiments of the present application, the molar percentage of the polyanionic compound of the second coating layer 202 relative to the lithium cobaltate material of the inner core is 1.0 mol% - 3.0 mol%.

[0076] In the embodiments of the present application, the content of metal fluoride in the diffusion layer 204 can be determined by its diffusion performance and the technological process. The molar percentage of the metal fluoride in the diffusion layer 204 relative to the lithium cobaltate material of the inner core can be 0 - 4.0 mol% (excluding 0). In some embodiments, the molar percentages are 0.05%, 0.1 mol%, 0.5 mol%, 1.0 mol%, 2.0 mol%, 3.0 mol%, 3.5 mol%, 4.0 mol%. For the same metal fluoride material, the more the content of the metal fluoride in the diffusion layer 204, the more beneficial it is to stabilize the lattice oxygen. In the embodiments of the present application, the content of the metal fluoride and the polyanionic compound in the transition layer 203 can be determined by the diffusion performance of the materials and the process. The molar percentage of the metal fluoride relative to the lithium cobaltate material of the inner core can be 0 - 4.0 mol% (excluding 0), and the molar percentage of the polyanionic compound relative to the lithium cobaltate material of the inner core can be 0 - 4.0 mol% (excluding 0). In some embodiments, the molar percentages of the two materials can be 0.05%, 0.1 mol%, 0.5 mol%, 1.0 mol%, 2.0 mol%, 3.0 mol%, 3.5 mol%, 4.0 mol% respectively.

[0077] In the embodiments of the present application, to achieve a strong binding of the surface lattice oxygen by the first coating layer 201, the thickness of the first coating layer 201 can be set to 3 nm - 12 nm. In some embodiments, the thickness of the first coating layer 201 can be 4 nm - 11 nm. In some embodiments, the thickness of the first coating layer 201 can be 5 nm - 10 nm. In some embodiments, the thickness of the first coating layer 201 can be 6 nm - 9 nm.

[0078] In the embodiments of the present application, the second coating layer 202 is located on the outermost layer of the entire lithium cobaltate material. In order to enable the second coating layer 201 to effectively inhibit the side reaction at the positive electrode - electrolyte interface and the catalytic effect of the interface reaction on the release of lattice oxygen, the thickness of the second coating layer 202 can be set to 5 nm - 14 nm. In some embodiments, the thickness of the second coating layer 202 can be 6 nm - 13 nm. In some embodiments, the thickness of the second coating layer 202 can be 7 nm - 12 nm. In some embodiments, the thickness of the second coating layer 202 can be 8 nm - 11 nm.

[0079] In the embodiments of the present application, in order to enable the first coating layer 201 and the second coating layer 202 to form a tighter connection and increase the diffusion barrier of the lattice oxygen, the thickness of the transition layer 203 can be set to 3 nm - 12 nm. In some embodiments, the thickness of the transition layer 203 can be 4 nm - 11 nm. In some embodiments, the thickness of the transition layer 203 can be 5 nm - 10 nm. In some embodiments, the thickness of the transition layer 203 can be 6 nm - 9 nm.

[0080] In addition, considering that the coating material is not electrochemically active, in order to better ensure the performance of the specific capacity of the lithium cobaltate material, the total thickness of the first coating layer 201, the second coating layer 202, and the transition layer 203 is not greater than 20 nm. In some embodiments, the total thickness of the three layers can be 11 nm - 20 nm.

[0081] The lithium cobaltate cathode material of the embodiment of the present application is applied in a lithium-ion battery system with a voltage of 3.0 - (4.5 - 4.7) V, and the irreversible release amount of lattice oxygen is less than 20% of the total amount of lattice oxygen. The smaller the irreversible release amount of lattice oxygen, the higher the stability of the lithium cobaltate cathode material during cycling under the voltage condition of 3.0 - (4.5 - 4.7) V. Specifically, the irreversible release amount of lattice oxygen in lithium cobaltate can be 19%, 18%, 17%, 16%, 15%, 14%, 13%, 12%, 11%, or 10% or less of the total amount of lattice oxygen. Among them, the irreversible release amount of lattice oxygen can be obtained by differential electrochemical mass spectrometry (DEMS).

[0082] In the embodiment of the present application, the exothermic peak temperature of the lithium cobaltate cathode material measured by differential scanning calorimetry is greater than 240 °C. In some embodiments, the exothermic peak temperature of the lithium cobaltate cathode material measured by differential scanning calorimetry is greater than 270 °C. The exothermic peak of pure undoped or unmodified lithium cobaltate LiCoO 2 is 218.9 °C. After coating the lithium cobaltate material with the shell material of the present application, the exothermic peak temperature of the obtained lithium cobaltate cathode material increases significantly, indicating an improvement in the thermal stability of the material.

[0083] The embodiment of the present application also provides a preparation method for the above-mentioned lithium cobaltate cathode material. This preparation method has low raw material costs, a simple process, is easy to operate, and is suitable for large-scale production. The preparation method specifically may include:

[0084] Step S01: Coating a first coating layer material on the surface of the lithium cobaltate material to obtain a first composite material; the first coating layer material includes metal fluoride, and the metal fluoride is represented as A b F c , where 0 < b ≤ 1, 0 < c ≤ 4, and A is a metal or metalloid element that can satisfy that the bond energy of A - O is greater than the bond energy of Co - O;

[0085] Step S02: Coating a second coating layer material on the metal fluoride to obtain a second composite material; the second coating layer material includes a polyanion-type compound, and the polyanion-type compound is represented as Li x M’ y D z, where \(0 \lt x \leq 4\), \(0 \leq y \leq 4\), \(0 \lt z \leq 3\), \(M'\) is a metal or metalloid element that can satisfy that the bond energy of \(M' - O\) is greater than the bond energy of \(Co - O\), and \(D\) represents a polyanion group;

[0086] Step S03: Sinter the second composite material in an inert atmosphere to obtain a lithium cobalt oxide cathode material; the obtained lithium cobalt oxide cathode material includes a core and a shell layer covering the core. The core includes a lithium cobalt oxide material, and the shell layer includes a first coating layer on the core, a second coating layer on the first coating layer, and a transition layer between the first coating layer and the second coating layer. The first coating layer includes a metal fluoride, the second coating layer includes a polyanion-type compound, and the transition layer includes the first coating layer material and the second coating layer material.

[0087] In the embodiment of the present application, in step S01, coating the first coating layer material on the surface of the lithium cobalt oxide material to obtain the first composite material specifically may include:

[0088] Mix the lithium cobalt oxide material with the raw materials of the first coating layer. The raw materials of the first coating layer include a metal source and a fluorine source. The metal source is the raw material including metal A, and specifically may include one or more of hydroxides, carbonates, nitrates, oxalates, acetates, sulfates, fluorine-containing salts of Al, As, Ag, Au, Ba, Be, B, Ca, Ce, Cs, Cr, Cm, Cd, Dy, Er, Eu, Gd, Ge, Hf, Ir, Fe, La, Lu, Mg, Mn, Mo, Nd, Np, Nb, Os, Pr, Pm, Pd, Pt, Re, Ru, Rh, Sm, Sc, Sr, Ta, Tm, Tc, Sn, Ti, W, V, Y, Zr; the fluorine source may include one or more of NH 4 F, NH 4 HF 2 or the like.

[0089] In the embodiment of the present application, the mixing method of mixing the lithium cobalt oxide material with the raw materials of the first coating layer may be one or more of a liquid phase method, a solid phase method, and other methods. The liquid phase method may be one or more selected from a liquid phase reaction method, a sol-gel method, and a solvothermal method. The solid phase method may be one or more selected from a mechanical stirring method, a high-energy ball milling method, and a mechanical fusion method. Other methods may be one or more selected from an atomic layer deposition method, a chemical vapor deposition method, a magnetron sputtering method, a vacuum thermal deposition method, a plasma sputtering method, a microwave reaction method, an in-situ growth method, an epitaxial growth method, and a high-temperature sintering method.

[0090] In one embodiment, the solvent used in the liquid phase method is selected from one or more of water, ethanol, and acetone. The solvent and the lithium cobalt oxide material LiCo 1-x ”M x ”O 2-y ”Yy The weight ratio of " is (1 - 100):1, the reaction temperature is 30°C - 100°C, and the stirring time is 2h - 20h. The evaporation-drying method of the mixed material can be one or more of drying with a water bath stirrer, drying after centrifugation, and drying in an oven, with a temperature of 60°C - 100°C and a time of 2h - 20h.

[0091] In one embodiment, the solid-phase mixing time in the solid-phase method is 2h - 20h, and the reaction temperature is 30°C - 100°C.

[0092] In the embodiment of the present application, in step S02, coating a second coating layer material on the metal fluoride to obtain the second composite material may specifically include:

[0093] Mixing the first mixed material with the raw materials of the second coating layer. The raw materials of the second coating layer can directly select the required polyanionic compound (Li x M’ y D z ), or can be selected from the lithium source, metal source, and polyanionic group source required for synthesizing the polyanionic compound. Among them, the lithium source can be selected from one or more of hydroxides, carbonates, nitrates, oxalates, acetates, sulfates, phosphates, and fluorine-containing salts of Li. The metal source is the raw material containing metal M’, and specifically can include one or more of hydroxides, carbonates, nitrates, oxalates, acetates, sulfates, phosphates, and fluorine-containing salts of Al, As, Ba, Be, B, Ca, Ce, Cs, Cr, Cm, Dy, Er, Eu, Gd, Ge, Hf, Fe, La, Lu, Mg, Mn, Mo, Nd, Np, Nb, Pr, Pm, Sm, Sc, Sr, Ta, Tm, Sn, Ti, W, V, Y, Zr. The polyanionic group (D) source includes one or more of the oxygen-containing acid roots of phosphorus, the oxygen-containing acid roots of silicon, the oxygen-containing acid roots of boron, and the oxygen-containing acid roots of tungsten. Among them, the oxygen-containing acid roots of phosphorus can be selected from one or more of NH 4 H 2 PO 4 , (NH 4 ) 2 HPO 4 , H 3 PO 4 , NH 4 H 2 PO 3 , (NH 4 ) 2 HPO 3 , H 3 PO 3 ; the oxygen-containing acid roots of silicon are selected from H 2 SiO 3 , C 8 H 20 O4 One or more of Si(TEOS); the oxygen-containing acid source of boron is selected from H 3 BO 3 , HBO 2 ; the oxygen-containing acid source of tungsten is selected from WO 3 , H 2 WO 4 , (NH 4 ) 2 WO 4 one or more of them.

[0094] In the embodiments of the present application, the mixing method of mixing the first composite material with the raw material of the second coating layer can be one or more of the liquid phase method, the solid phase method and other methods. The liquid phase method can be one or more of the liquid phase reaction method, the sol-gel method, and the solvothermal method. The solid phase method can be one or more of the mechanical stirring method, the high-energy ball milling method, and the mechanical fusion method. Other methods can be one or more of the atomic layer deposition method, the chemical vapor deposition method, the magnetron sputtering method, the vacuum thermal deposition method, the plasma sputtering method, the microwave reaction method, the in-situ growth method, the epitaxial growth method, and the high-temperature sintering method.

[0095] In one embodiment, the solvent used in the liquid phase method is selected from one or more of water, ethanol, and acetone. The weight ratio of the solvent to the first composite material is (1-100):1, the reaction temperature is 30°C-100°C, and the stirring time is 2h-20h. The evaporation method of the mixed material can be one or more of drying with a water bath stirrer, drying after centrifugation, and drying in an oven, the temperature is 60°C-100°C, and the time is 2h-20h.

[0096] In one embodiment, the solid phase mixing time in the solid phase method is 2h-20h, and the reaction temperature is 30°C-100°C.

[0097] In the embodiment of the present application, in step S03, the second composite material is sintered in an inert atmosphere, which may be argon, nitrogen, etc. To ensure the formation of the required phase structure of the coating layer, ensure the tight bonding between the core and the coating layer, and between the coating layers, and achieve a uniform and continuous coating layer thickness, the sintering temperature and the holding time are set in the embodiment of the present application. The sintering temperature may be 300°C - 650°C, and the holding time is 3h - 10h. Specifically, since too fast heating rate will generate large stresses at the interfaces between the phases, the heating rate is set to 1°C / min - 5°C / min in the sintering process of the embodiment of the present application. In some embodiments, the sintering temperature may specifically be 300°C, 350°C, 400°C, 450°C, 500°C, 550°C, 600°C, 650°C; the holding time may specifically be 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h; the heating rate may specifically be 1°C / min, 2°C / min, 3°C / min, 4°C / min, 5°C / min.

[0098] After sintering is completed, the powder is collected after natural cooling, and after ball milling treatment, the lithium cobalt oxide cathode material is obtained. In one embodiment, the ball-to-material ratio for ball milling is (1 - 3):1, the rotation speed is 50 - 150 r / min, and the ball milling time is 0.5 - 2h. Specifically, the ball-to-material ratio for ball milling may be 1:1, 2:1, 3:1, and the rotation speed may be 50 r / min, 100 r / min, 150 r / min. The lithium cobalt oxide cathode material obtained after sintering is completed includes a lithium cobalt oxide core, a first coating layer coated on the lithium cobalt oxide core, a second coating layer coated on the first coating layer, and also includes a diffusion layer and a transition layer formed after high-temperature sintering. The diffusion layer is located between the lithium cobalt oxide core and the first coating layer. The diffusion layer is formed by the diffusion of the first coating layer material to the surface layer of the lithium cobalt oxide material, that is, the part of the surface layer of the lithium cobalt oxide material where the first coating layer material is diffused constitutes the diffusion layer, and the part of the lithium cobalt oxide material inside where the first coating layer material is not diffused constitutes the core; the transition layer is located between the first coating layer and the second coating layer, and the transition layer includes the first coating layer material and the second coating layer material. Along the direction from the first coating layer to the second coating layer, the content of the first coating layer material in the transition layer gradually decreases, and the content of the second coating layer material gradually increases. The specific distribution form of the materials in the transition layer and the content of each material can be controlled according to the diffusion performance of each coating raw material and controlling the sintering parameters in the sintering process. The content of the first coating layer material in the diffusion layer can also be controlled according to the diffusion performance of the coating raw material and controlling the sintering parameters in the sintering process.

[0099] This application can realize the preparation of a multi-layer coating layer through a single sintering process. The single sintering process helps to strengthen the mutual diffusion between the lithium cobalt oxide substrate material and the first coating layer, as well as between the first coating layer and the second coating layer, forming a diffusion layer and a transition layer, thereby improving the ability of the shell layer to inhibit the release of lattice oxygen.

[0100] In the embodiment of this application, in step S01, the lithium cobalt oxide material can be undoped or unmodified lithium cobalt oxide, that is, LiCoO 2 , or it can be doped lithium cobalt oxide, or it can also be lithium cobalt oxide coated with one or more materials such as oxides, fast ion conductors, and conductive polymers. In some embodiments of this application, the chemical formula of the lithium cobalt oxide material can be LiCo 1-x ”M x ”O 2-y ”Y y ”, where 0 ≤ x” ≤ 0.4, 0 ≤ y” ≤ 0.2, M represents one or more of Na, Mg, Al, Si, K, Ca, Ti, Cr, Mn, Fe, Ni, Cu, Zn; Y represents one or more of F, S, P. The lithium cobalt oxide material can be a commercially available product or can be obtained by self-preparation.

[0101] Taking the preparation of the LiCo 1-x ”M x ”O 2-y ”Y y ” lithium cobalt oxide material as an example, its preparation method can include:

[0102] Step S101: Prepare a mixture of a lithium source, a cobalt source, and a metal salt; where the lithium source can be selected from one or more of lithium hydroxide, lithium carbonate, lithium nitrate, lithium acetate, and lithium oxalate, the cobalt source can be selected from one or more of cobalt tetroxide, cobalt nitrate, cobalt oxalate, and cobalt acetate, the metal salt is a metal salt containing M, and the metal salt can be selected from one or more of hydroxides, carbonates, nitrates, oxalates, acetates, sulfates, and fluorides of Na, Mg, Al, Si, K, Ca, Ti, Cr, Mn, Fe, Ni, Cu, Zn;

[0103] Step S102: Sinter the mixture obtained in step S101 to obtain a crude product, and crush the crude product to obtain the lithium cobalt oxide material LiCo 1-x ”M x ”O 2-y ”Y y ”. Among them, the sintering temperature is 800°C - 1100°C, the heating rate is 0.1°C / min - 10°C / min, and the holding time is 6h - 24h.

[0104] The embodiment of the present application also provides a positive electrode sheet for a battery. The positive electrode sheet for the battery includes the lithium cobaltate positive electrode material described above in the embodiment of the present application. In one embodiment, the positive electrode sheet for the battery includes a positive electrode current collector and a positive electrode active layer disposed on the positive electrode current collector. The positive electrode active layer includes a positive electrode active material, a conductive agent, and a binder. The positive electrode current collector includes, but is not limited to, a metal foil or an alloy foil. The metal foil may be, for example, an aluminum foil, and the aluminum foil may specifically be a flat aluminum foil or a foam aluminum. The thickness of the positive electrode current collector may be 5 μm to 20 μm. The positive electrode active material includes the lithium cobaltate positive electrode material described above in the embodiment of the present application. In some embodiments, the positive electrode active material may also include other positive electrode active materials. The other positive electrode active materials include, but are not limited to, lithium cobaltate (LiCoO 2 ), lithium iron phosphate (LiFePO 4 ), lithium nickel cobalt manganese oxide (LiNi 0.6 Co 0.2 Mn 0.2 ), polyanionic lithium compound LiM x (PO 4 ) y (where M is Ni, Co, Mn, Fe, Ti, V, 0 ≤ x ≤ 5, 0 ≤ y ≤ 5), etc. The binder may specifically include, but is not limited to, one or more of polyvinylidene fluoride, polytetrafluoroethylene, epoxy resin, polyvinyl alcohol, carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), and sodium alginate. The conductive agent may specifically include, but is not limited to, one or more of graphite, expanded graphite, carbon nanotubes, carbon fibers, activated carbon, amorphous carbon, conductive carbon black, acetylene black, and Super P. The method for preparing the positive electrode sheet for the battery may include: mixing the positive electrode active material, the conductive agent, and the binder to form a slurry; coating the slurry on the positive electrode current collector, drying, and then rolling to obtain the positive electrode sheet for the battery.

[0105] See Figure 2, the embodiment of the present application further provides an electrochemical device 200, which can specifically be a lithium secondary battery. The lithium secondary battery includes a positive electrode 101, a negative electrode 102, an electrolyte 103 disposed between the positive electrode 101 and the negative electrode 102, a separator 104, and corresponding connecting accessories and circuits. The positive electrode includes the battery positive electrode sheet in the above embodiment of the present application. The negative electrode may include a negative electrode current collector and a negative electrode material layer provided on the negative electrode current collector. The negative electrode current collector includes but is not limited to metal foil or alloy foil. The metal foil can be, for example, copper foil, and the copper foil can specifically be flat copper foil or foam copper. The thickness of the negative electrode current collector can be 5μm - 20μm. The negative electrode material layer includes negative electrode active materials, and the negative electrode active materials include but are not limited to one or more of metallic lithium, lithium alloy, lithium titanate, natural graphite, artificial graphite, mesocarbon microbeads, amorphous carbon, carbon fiber, carbon nanotube, hard carbon, soft carbon, graphene, graphene oxide, silicon, silicon carbide compound, silicon oxide compound, silicon metal compound, tin-based compound. The electrolyte includes a lithium salt and a solvent, and the solvent can include one or more of carbonate solvents, carboxylate solvents, and ether solvents. The separator can be a polymer separator, non-woven fabric, etc., including but not limited to single-layer PP (polypropylene), single-layer PE (polyethylene), double-layer PP / PE, double-layer PP / PP, and triple-layer PP / PE / PP separators.

[0106] For the lithium secondary battery of the embodiment of the present application, its shape has no particular limitation and can be cylindrical, button (coin type), flat, square, etc. The lithium secondary battery provided by the embodiment of the present application can be used in terminal consumer products, such as mobile phones, tablet computers, mobile power supplies, portable machines, laptop computers, digital cameras, and other wearable or movable electronic devices, as well as products such as drones and automobiles, to improve product performance.

[0107] The lithium secondary battery provided by the embodiment of the present application has good thermal stability and cycle stability in the voltage range of 3.0 - (4.5 - 4.7) V (indicating that the starting voltage for charging is 3.0V and the cut-off voltage is 4.5V - 4.7V). In some embodiments, when the lithium secondary battery is in an environment of 25°C and in the voltage range of 3.0 - (4.5 - 4.7) V, the capacity retention rate after 300 cycles of charging at 1.5C / discharging at 0.7C is greater than 70%. In some embodiments, when the lithium secondary battery is in an environment of 25°C and in the voltage range of 3.0 - (4.5 - 4.7) V, the capacity retention rate after 300 cycles of charging at 1.5C / discharging at 0.7C is greater than 85%. In some embodiments, when the lithium secondary battery is in an environment of 25°C and in the voltage range of 3.0 - (4.5 - 4.7) V, the capacity retention rate after 300 cycles of charging at 1.5C / discharging at 0.7C is greater than 90%.

[0108] See Figure 3, Embodiment of the present application further provides an electronic device 300, which may include various consumer electronic products, such as mobile phones, tablet computers, mobile power supplies, portable computers, laptop computers, and other wearable or movable electronic devices, televisions, DVD players, video recorders, video cameras, radios, tape recorders, component stereos, record players, CD players, home office equipment, home electronic health care equipment, and automotive and other electronic products. The electronic device 300 includes a housing 301 and electronic components (not shown in the figure) and a battery 302 accommodated in the housing 301. The battery 302 powers the electronic device 300, and the battery 302 includes the lithium secondary battery in the embodiment of the present application. The housing 301 may include a front cover assembled on the front side of the terminal and a rear case assembled on the rear side, and the battery 302 may be fixed to the inner side of the rear case. By using the high-voltage lithium cobaltate cathode material provided in the embodiment of the present application as the cathode active material of the battery, the electronic device 300 in the embodiment of the present application can improve the thermal stability, cycle performance, and energy density of the battery, better meet the requirements of consumer electronic products for good thermal stability, long cycle life, and high energy density of the battery, and improve the user experience and market competitiveness of electronic products.

[0109] See Figure 4 , Embodiment of the present application further provides a mobile device 400, which includes the electrochemical device 200 provided in the embodiment of the present application. Specifically, the mobile device 400 may include a vehicle body 401, a moving component 402, and a driving component 403, and the driving component 403 includes the electrochemical device 200 provided in the embodiment of the present application. The mobile device 400 may be various movable devices for loading, transporting, assembling, disassembling, security, etc., and may be various forms of vehicles. The electrochemical device 200 may provide electrical energy for the mobile device 400 to drive its movement.

[0110] The following further describes the embodiments of the present application through multiple embodiments.

[0111] Embodiment 1

[0112] (1) Preparation of lithium cobaltate material LiCoO 2

[0113] Take Li 2 CO 3 , Co 3 O 4 , and charge materials according to the molar ratio of lithium to cobalt of 1.06:1. After stirring and mixing evenly, place them in a muffle furnace or sintering furnace for temperature sintering. Keep the temperature at 1050 °C for 12 h, collect the product after natural cooling, and perform crushing and collection to obtain unmodified lithium cobaltate LiCoO 2 primary particles.

[0114] (2) Preparation of lithium cobaltate cathode material LiCoO2 @AlF 3 @Li 3 PO 4

[0115] Weigh 0.194 g of Al(NO 3 ) 3 ·9H 2 O and dissolve it in 100 mL of deionized water. Stir magnetically for 30 min at room temperature to completely dissolve it to obtain Solution A; weigh 0.058 g of NH 4 F and dissolve it in 100 mL of deionized water. Stir magnetically for 30 min at room temperature to completely dissolve it to obtain Solution B; weigh 10 g of LiCoO 2 prepared in step (1) and place it in Solution A. Stir magnetically for 30 min at room temperature to completely disperse LiCoO 2 in Solution A; then transfer Solution A to an oil bath at 80 °C. After the temperature of Solution A stabilizes, use a peristaltic pump to dropwise add Solution B to Solution A under magnetic stirring, so that AlF 3 nucleates and grows uniformly on the surface of LiCoO 2 particles. After stirring dry at 80 °C, collect the powder, and the required time is 8 h; then dry the collected powder in a blast drying oven at 80 °C for 12 h to obtain the first composite material;

[0116] Then weigh 0.059 g of Li 3 PO 4 and the first composite material and place them in a ball milling jar. The ball-to-material ratio is 5:1, the rotation speed is 150 r / min, and dry ball mill for 3 h to make the two fully mixed and uniform to obtain the second composite material;

[0117] Collect the second composite material and place it in a tube furnace for sintering. The sintering conditions are: under an argon atmosphere, heat from room temperature to 600 °C at a heating rate of 4 °C / min, hold for 5 h, and then naturally cool to room temperature to obtain the lithium cobalt oxide cathode material LiCoO 2 @AlF 3 @Li 3 PO 4 . This lithium cobalt oxide cathode material includes a lithium cobalt oxide core and an AlF 3 diffusion layer, an AlF 3 layer, an AlF 3 and a transition layer of Li 3 PO 4 formed successively on the surface of the lithium cobalt oxide core, and a Li 3 PO 4 layer.

[0118] Preparation of Lithium Secondary Battery

[0119] Weigh 0.16 g of the obtained lithium cobalt oxide cathode material LiCoO 2 @AlF 3 @Li 3 PO 4 , 0.02 g of acetylene black as a conductive agent, 0.02 g of polyvinylidene fluoride (PVDF) as a binder. After grinding evenly, add an appropriate amount of N-methylpyrrolidone (NMP) and continue grinding until it becomes a paste. Then coat it evenly on the aluminum foil with a coating thickness of 150 μm, and dry it in vacuum at 110 °C for 12 h. After pressing, obtain the positive electrode sheet. Use a lithium metal sheet as the negative electrode, and use a commercial PE separator and 1 mol / L LiPF 6 / (EC + DEC) electrolyte (volume ratio 1:1) to assemble a 2032-type button cell in a glove box under argon protection.

[0120] Comparative Example 1

[0121] Use the unmodified LiCoO 2 cathode material prepared in step (1) of Example 1 of this application as the positive electrode active material, and assemble a 2032-type button cell in the same method as in Example 1.

[0122] Comparative Example 2

[0123] Coat the surface of the unmodified LiCoO 2 cathode material prepared in step (1) of Example 1 of this application with AlF 3 to obtain LiCoO 2 @AlF 3 cathode material. Use the LiCoO 2 @AlF 3 cathode material as the positive electrode active material, and assemble a 2032-type button cell in the same method as in Example 1.

[0124] Comparative Example 3

[0125] Coat the surface of the unmodified LiCoO 2 cathode material prepared in step (1) of Example 1 of this application with Li 3 PO 4 to obtain LiCoO 2 @Li 3 PO 4 cathode material. Use the LiCoO 2 @Li 3 PO 4 cathode material as the positive electrode active material, and assemble a 2032-type button cell in the same method as in Example 1.

[0126] This application is about the lithium cobalt oxide cathode material LiCoO 2 @AlF 3 @Li3 PO 4 and the unmodified LiCoO of Comparative Example 1 2 materials were subjected to the following characterization tests:

[0127] 1. The elemental composition of the cathode material was characterized using an Inductive Coupled Plasma Emission Spectrometer (ICP). The results are shown in Table 1.

[0128] Table 1 Unmodified LiCoO 2 materials and LiCoO 2 @AlF 3 @Li 3 PO 4 ICP results

[0129]

[0130] From the Inductive Coupled Plasma Emission Spectroscopy (ICP) results in Table 1, it can be known that 0.4386 mol% AlF 3 and 0.4616 mol% Li 3 PO 4 were successfully coated on the surface of the lithium cobalt oxide material, which is very close to the initially set stoichiometric ratio (0.5 mol%).

[0131] 2. The morphology of the cathode material was characterized using a Scanning Electron Microscope (SEM). Figure 5 This is the Scanning Electron Microscope (SEM) result of the lithium cobalt oxide cathode material of Example 1 of this application. From Figure 5 it can be seen that a complete granular lithium cobalt oxide cathode material was obtained.

[0132] 3. Energy Eispersive X-ray Spectroscopy (EDS) was used to qualitatively analyze the elemental composition of the cathode material. Figure 6 and Figure 7 are the EDS surface scan results of the lithium cobalt oxide cathode material of Example 1. Figure 6 The results show the presence of the elements Al, F, and P in the coating material, further confirming the presence of the coating. Further, Figure 7 the surface scan results prove the uniform distribution of the elements Al, F, and P on the particle surface, reflecting the uniformity of the coating.

[0133] 4. The positive electrode material was scanned using a High Resolution Transmission Electron Microscope (HRTEM). Figure 8 and Figure 9 are the high-resolution transmission electron microscope scanning results of the unmodified LiCoO in Comparative Example 1 2 material and the lithium cobalt oxide positive electrode material of Example 1, respectively. Among them, Figure 8 a) in is the line scan result, and b) and c) are the area scan results. Figure 9 a) in is the line scan result, and b) and c) are the area scan results. Figure 8 The white line marked in b) in is the line scan range of a), Figure 9 The white line marked in b) in is the line scan range of a). Figure 8 The high-resolution transmission line scan and area scan results of a), b), and c) in show that only the presence of Co element was detected in the unmodified LiCoO 2 material. While Figure 9 the high-resolution transmission area scan results of b) and c) in show the distribution of P element, Al element, and Co element, and the distribution between elements corresponds to Li 3 PO 4 , AlF 3 and LiCoO 2 distribution. Combining with Figure 9 the line scan result of a) in further shows the element distribution within the range of 20 nm from the material surface, that is, along the direction from the AlF 3 coating layer to the Li 3 PO 4 coating layer, the material content of AlF 3 in the transition layer gradually decreases, and the material content of Li 3 PO 4 gradually increases, and it is confirmed that the diffusion layer Li x Al y Co (1-x-3y) / 3 O (1-z) / 2 F z exists between the first coating layer and the lithium cobalt oxide substrate material, and its thickness is 3 nm - 4 nm. The thickness of the first coating layer AlF 3 is 3 nm - 4 nm. The thickness of the first coating layer AlF 3 and the second coating layer Li 3 PO 4 the transition layer Li x Al (1-x) / 3 (PO 4 ) (1-y) / 3 F y is 4 nm - 5 nm, and the second coating layer Li3 PO 4 The coating thickness of PO is 5 nm - 6 nm.

[0134] 5. The crystal structure of the cathode material was analyzed using an X-ray diffractometer (XRD). Figure 10 This is the X-ray diffraction pattern of the lithium cobalt oxide cathode material of Example 1 of this application. Among them Figure 10 a) is the complete pattern, and b) and c) are the partially enlarged patterns. As can be seen from Figure 10 a), the diffraction peaks of the lithium cobalt oxide material before and after coating did not change, and both conform to the hexagonal layered structure of lithium cobalt oxide, with the space group of R-3m. This indicates that multiple coatings will not change the crystal structure of lithium cobalt oxide. To further confirm the presence of LiCoO 2 @AlF 3 @Li 3 PO 4 AlF 3 and Li 3 PO 4 in LiCoO 2 @AlF 3 @Li 3 PO 4 the XRD diffraction pattern was magnified for observation, as shown in Figure 10 b) and c). The partially enlarged patterns show that LiCoO 2 @AlF 3 @Li 3 PO 4 has a diffraction peak of AlF at ~59.1°, which matches the standard PDF card PDF#44-0231 of AlF. At ~38.4° and ~38.6°, there are diffraction peaks of Li 3 PO 3 , which matches the standard PDF card PDF#15-0760 of Li 3 PO 4 . This indicates the formation of the AlF 3 and Li 4 PO 2 @AlF 3 @Li 3 PO 4 coating layer. 3 and Li 3 PO 4 coating layer.

[0135] 6. Differential scanning calorimetry (DSC) was used to analyze LiCoO of Example 1 2 @AlF 3 @Li 3 PO 4Positive electrode material, unmodified LiCoO of Comparative Example 1 2 Positive electrode material, and LiCoO of Comparative Example 2 2 @AlF 3 Positive electrode material, LiCoO of Comparative Example 3 2 @Li 3 PO 4 The thermal stability of the positive electrode material was evaluated. The specific evaluation method was as follows: The assembled button cells of Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3 were charged at a constant current of 0.1C, and the cut-off voltage for charging was 4.65V. Then, the fully charged battery was taken to the glove box for disassembly, and during this process, ceramic tweezers were used to prevent the battery from discharging. The positive electrode sheet wetted by the electrolyte in the battery was taken out, and under the protection of Ar gas, it was heated from room temperature of 25°C to 400°C at a rate of 5°C / min, obtaining the differential scanning calorimetry (DSC) curves as shown in Figure 11A 、 Figure 11B 、 Figure 11C 、 Figure 11D . Among them, Figure 11A is the DSC curve of the LiCoO 2 @AlF 3 @Li 3 PO 4 positive electrode material; Figure 11B is the DSC curve of the unmodified LiCoO 2 positive electrode material of Comparative Example 1; Figure 11C is the DSC curve of the LiCoO 2 @AlF 3 positive electrode material of Comparative Example 2; Figure 11D is the DSC curve of the LiCoO 2 @Li 3 PO 4 positive electrode material of Comparative Example 3.

[0136] For highly delithiated lithium cobaltate, the higher the exothermic peak temperature (oxygen release temperature), the better the lattice oxygen stability of the material. From the DSC curves of Figure 11A 、 Figure 11B 、 Figure 11C 、 Figure 11D , it can be seen that compared with the unmodified LiCoO 2 positive electrode material, LiCoO 2 @AlF 3 (the exothermic peak increased from 218.9°C to 244.1°C, with an increase of +25.2°C) and LiCoO 2 @Li 3 PO 4(The exothermic peak temperature increases from 218.9 °C to 227.7 °C, with an increase of +8.8 °C), and the exothermic peak temperatures have all increased, which verifies the beneficial effect of the AlF 3 and Li 3 PO 4 coating layer in suppressing the release of lattice oxygen. For AlF 3 , the reason for the improved thermal stability is that the Al-O bond is larger than the Co-O bond, and Al 3+ will tightly combine with the O 2- in the core layer, and F - can occupy the lattice position of O 2- in the shell layer, stabilizing the octahedral framework structure of the core layer. Both anions and cations play a role in binding the lattice oxygen of the lithium cobaltate base material. For Li 3 PO 4 , the reason for the improved thermal stability is that the polyanion group with high chemical stability can reduce the interfacial reaction between the LiCoO 4 3- base material and the electrolyte, and inhibit the catalytic effect of the electrolyte on the release of lattice oxygen on the surface of the LiCoO 2 base material. Further, LiCoO 2 @AlF 2 @Li 3 @Li 3 PO 4 (The exothermic peak temperature increases from 218.9 °C to 275.2 °C, with an increase of +56.3 °C) increases the exothermic peak temperature far more than LiCoO 2 @AlF 3 (+25.2 °C) and LiCoO 2 @Li 3 PO 4 (+8.73 °C), which shows the beneficial effect of the diffusion layer and the transition layer in the LiCoO 2 @AlF 3 @Li 3 PO 4 cathode material in suppressing the release of lattice oxygen. Among them, the diffusion layer strengthens the strength of the oxygen octahedral framework and increases the formation energy of surface oxygen vacancies, and the transition layer further increases the diffusion barrier of lattice oxygen. Therefore, the multi-layer coating structure designed in this application has a better effect in improving thermal stability than a single coating layer and a simple superposition of two coating layers.

[0137] 7. For the LiCoO 2 @AlF 3 @Li 3 PO 4 cathode material in Example 1, the unmodified LiCoO 2Positive electrode material, and LiCoO of Comparative Example 2 2 @AlF 3 Positive electrode material, LiCoO of Comparative Example 3 2 @Li 3 PO 4 The electrochemical performance of the positive electrode material was evaluated. The specific method was as follows: The assembled batteries of Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3 were subjected to constant current charge and discharge tests on a Neware charge and discharge tester. The voltage range was 3 - 4.65 V, the test temperature was 25 °C, and the test procedure was to charge and discharge at 0.1 C for the first cycle, and then test at 1.5 C charging / 0.7 C discharging (1 C = 140 mA / g).

[0138] The cycle performance and the first cycle voltage curve of the positive electrode material are as Figure 12A and Figure 12B shown, where Figure 12A is the cycle performance curve of the positive electrode material, Figure 12B is the first cycle voltage curve of the positive electrode material. The statistical results of the first cycle Coulombic efficiency and capacity retention rate are shown in Table 2. It can be seen from Figure 12A that compared with the unmodified LiCoO 2 positive electrode material, the modified materials of Example 1, Comparative Example 2, and Comparative Example 3 all showed significant improvements in the first cycle Coulombic efficiency and capacity retention rate. In addition, for LiCoO 2 @AlF 3 @Li 3 PO 4 multi-layer coating, the improvement effect on the capacity retention rate of the LiCoO 2 substrate material is better than that of single AlF 3 coating and single Li 3 PO 4 coating, which reflects the more excellent high-voltage structure stability of the multi-layer coating. In the high-voltage LiCoO 2 positive electrode material, the irreversible release of lattice oxygen triggers oxygen vacancies and causes the reduction of cations, ultimately leading to the loss of cations and the decline of the structure. Since the multi-layer coating retains the advantages of single coating and also plays the role of strengthening the strength of the oxygen octahedron framework in the diffusion layer and further increasing the diffusion barrier of lattice oxygen in the transition layer, the multi-layer coating material has more excellent lattice oxygen stability and structure stability. It can be seen from Figure 12B that compared with Comparative Example 1, Comparative Example 2, and Comparative Example 3, Example 1 shows the largest first cycle Coulombic efficiency and the highest first discharge specific capacity, indicating that the LiCoO 2 @AlF 3 @Li 3 PO 4 of Example 1 of this application has the most excellent electrochemical reversibility.

[0139] Table 2 Electrochemical performance results

[0140]

[0141] The differential capacity-voltage curve (dQ / dV) of the positive electrode material is as Figure 13A 、 Figure 13B 、 Figure 13C 、 Figure 13D shown, where Figure 13A is the differential capacity-voltage curve (dQ / dV) of the unmodified LiCoO 2 positive electrode material of Comparative Example 1; Figure 13B is the differential capacity-voltage curve (dQ / dV) of the LiCoO 2 @AlF 3 positive electrode material of Comparative Example 2; Figure 13C is the differential capacity-voltage curve (dQ / dV) of the LiCoO 2 @Li 3 PO 4 positive electrode material of Comparative Example 3; Figure 13D is the differential capacity-voltage curve (dQ / dV) of the LiCoO 2 @AlF 3 @Li 3 PO 4 positive electrode material of Example 1. As the cycling progresses, the reduction peaks of all samples show a shift towards lower potentials, i.e., the voltage decay phenomenon. The voltage decay of high-voltage lithium cobaltate is related to the irreversible release of lattice oxygen in the material during highly delithiated states. The irreversibly released lattice oxygen promotes the migration of cations and activates the low-potential Co 2+ / Co 3+ redox couple for charge compensation, resulting in voltage decay of the material. That is to say, the greater the shift of the reduction peak of the material, the more serious the voltage decay.

[0142] Compare the shift amounts of the reduction peaks of the four materials during the 6th to 300th cycles (the shift amount is the difference between the reduction peak potential at the 6th cycle and the reduction peak potential at the 300th cycle). From Figure 13A 、 Figure 13B 、 Figure 13C 、 Figure 13D results, it can be seen that compared with the unmodified LiCoO 2 positive electrode material (reduction peak shift of 160.6 mV), LiCoO 2 @AlF 3 (reduction peak shift of 101.4 mV), LiCoO 2 @Li 3 PO 4(The voltage decay phenomenon with a reduction peak shift of 111.0 mV) is improved, which is related to the strengthening of the Al-O bond in the material to bind lattice oxygen, and PO 4 3- reducing the catalytic effect of the interface side reaction on the release of lattice oxygen. And LiCoO 2 @AlF 3 @Li 3 PO 4 (The voltage decay degree with a reduction peak shift of 58.2 mV) is further reduced compared with single coating, which indicates that the multi-layer coating not only retains the beneficial effect of the single coating layer on inhibiting the irreversible release of lattice oxygen, but the diffusion layer and the transition layer also play an important role in inhibiting the release of lattice oxygen. Among them, the diffusion layer increases the formation energy of oxygen vacancies in the base material, and the transition layer further increases the diffusion barrier of lattice oxygen.

[0143] The lithium cobalt oxide cathode material of Example 1 of this application includes a multi-layer coating layer composed of AlF 3 and Li 3 PO 4 specifically including an AlF 3 diffusion layer, an AlF 3 layer, AlF 3 and Li 3 PO 4 transition layer and a Li 3 PO 4 layer. The thicknesses of the four coating layers are 2-3 nm, 3-4 nm, 4-5 nm and 5-6 nm respectively. By precisely controlling the thickness of each coating layer, the inhibitory effect on the irreversible release of lattice oxygen can be fully exerted, and the thermal stability of the lithium cobalt oxide material in the high delithiated state can be improved. In Example 1 of this application, the preparation of the multi-layer coating layer composed of AlF 3 and Li 3 PO 4 can be realized by the liquid phase method plus a one-time sintering (inert atmosphere) process. The one-time sintering process helps to strengthen the mutual diffusion between the lithium cobalt oxide base material and the first coating layer, and between the first coating layer and the second coating layer, forming a diffusion layer and a transition layer. By controlling conditions such as the sintering temperature and sintering time, precise regulation of the element content and thickness of each layer can be achieved, and the process is simple and controllable.

[0144] Example 2

[0145] (1) Prepare the aluminum-doped lithium cobalt oxide material LiAl 0.05 Co 0.95 O 2

[0146] Respectively take Li 2 CO 3 , Co 3 O4 and Al(OH) 3 , according to the molar ratio of lithium, cobalt, and aluminum of 1.06:1:0.05 for feeding, after stirring and mixing evenly, it is placed in a muffle furnace or sintering furnace and kept at 1050 °C for 12 h. After natural cooling, the product is collected and crushed to obtain aluminum-doped lithium cobaltate LiAl 0.05 Co 0.95 O 2 primary particles.

[0147] (2) Preparation of lithium cobaltate cathode material LiAl 0.05 Co 0.95 O 2 @AlF 3 @LiTi 2 (PO 4 ) 3

[0148] First, weigh 0.194 g of Al(NO 3 ) 3 ·9H 2 O and dissolve it in 100 mL of deionized water. Magnetically stir it for 30 min at room temperature to completely dissolve it to obtain solution A; weigh 0.058 g of NH 4 F and dissolve it in 100 mL of deionized water. Magnetically stir it for 30 min at room temperature to completely dissolve it to obtain solution B; weigh 10 g of the LiAl 0.05 Co 0.95 O 2 prepared in step (1) and place it in solution A. Magnetically stir it for 30 min at room temperature to completely disperse LiAl 0.05 Co 0.95 O 2 in solution A; then transfer solution A to an 80 °C oil bath. After the temperature of solution A is stable, use a peristaltic pump to dropwise add solution B to solution A under magnetic stirring, so that AlF 3 nucleates and grows uniformly on the surface of LiAl 0.05 Co 0.95 O 2 particles. After stirring and drying at 80 °C, collect the powder, and the required time is 8 h; then dry the collected powder in an 80 °C forced-air drying oven for 12 h to obtain the first composite material;

[0149] Next, weigh 0.128 g of LiTi 2 (PO 4 ) 3 and the first composite material and place them in a ball milling jar. The ball-to-material ratio is 5:1, the rotation speed is 150 r / min, and dry ball milling is carried out for 3 h to make the two fully mixed evenly to obtain the second composite material;

[0150] The second composite material was collected and sintered in a tube furnace under the following conditions: in an argon atmosphere, it was heated from room temperature to 600 °C at a heating rate of 4 °C / min, held for 8 h, and then naturally cooled to room temperature; the lithium cobalt oxide cathode material LiAl was obtained. 0.05 Co 0.95 O 2 @AlF 3 @LiTi 2 (PO 4 ) 3 , the lithium cobalt oxide cathode material includes a LiAl 0.05 Co 0.95 O 2 core, and an AlF 0.05 Co 0.95 O 2 diffusion layer, an AlF 3 layer, an AlF 3 layer, and an AlF 3 and a LiTi 2 (PO 4 ) 3 transition layer, and a LiTi 2 (PO 4 ) 3 layer formed in sequence on the surface of the LiAl 3 diffusion layer has a thickness of 5 nm - 6 nm, the first coating layer of AlF 3 has a thickness of 3 nm - 4 nm, the first coating layer of AlF 3 and the second coating layer of LiTi 2 (PO 4 ) 3 have a transition layer thickness of 5 nm - 6 nm, and the second coating layer of LiTi 2 (PO 4 ) 3 has a coating thickness of 6 nm - 7 nm.

[0151] The LiAl 0.05 Co 0.95 O 2 @AlF 3 @LiTi 2 (PO 4 ) 3 cathode material prepared in Example 2 of this application was used as the cathode active material, and a 2032-type button battery was assembled in the same manner as in Example 1.

[0152] Comparative Example 4

[0153] The aluminum-doped lithium cobalt oxide LiAl 0.05 Co 0.95 O 2 prepared in Example 2 was surface-coated with AlF 3, to obtain LiAl 0.05 Co 0.95 O 2 @AlF 3 The cathode material, using LiAl 0.05 Co 0.95 O 2 @AlF 3 The cathode material as the cathode active material, assembled into a 2032-type button battery in the same manner as in Example 1.

[0154] Comparative Example 5

[0155] The lithium cobaltate doped with aluminum prepared in Example 2, LiAl 0.05 Co 0.95 O 2 was surface-coated with LiTi 2 (PO 4 ) 3 , to obtain LiAl 0.05 Co 0.95 O 2 @LiTi 2 (PO 4 ) 3 The cathode material, using LiAl 0.05 Co 0.95 O 2 @LiTi 2 (PO 4 ) 3 The cathode material as the cathode active material, assembled into a 2032-type button battery in the same manner as in Example 1.

[0156] Using the same method as in Example 1, constant current charge and discharge tests, differential scanning calorimetry (DSC) tests, etc. were performed on the cathode materials and batteries of Example 2 and Comparative Examples 4-5. Among them, the thermal stability results of the cathode materials are shown in Table 3, and the electrochemical performance results are shown in Table 4.

[0157] Table 3 Thermal stability results of cathode materials

[0158] Example Positive electrode material composition Exothermic peak temperature (°C) Example 2 <![CDATA[LiAl 0.05 Co 0.95 O 2 @AlF 3 @LiTi 2 (PO 4 ) 3 > 277.2 Comparative Example 4 <![CDATA[LiAl 0.05 Co 0.95 O 2 @AlF 3 > 245.2 Comparative Example 5 <![CDATA[LiAl 0.05 Co 0.95 O 2 @LiTi 2 (PO 4 ) 3 > 235.2 Comparative Example 1 <![CDATA[Unmodified LiCoO 2 material]]> 218.9

[0159] Table 4 Electrochemical performance results of cathode materials

[0160]

[0161] Compared with Example 1, in this example, the LiCoO 2 material was doped with Al, which helps to improve the stability of the lattice oxygen in the LiCoO 2 bulk structure. In this example, LiTi 2 (PO 4 )3 As the outermost coating layer, due to the strong binding force between Ti and O, the introduction of Ti element helps to further improve the stability of lattice oxygen.

[0162] Example 3

[0163] Prepare lithium cobalt oxide cathode material LiCoO 2 @Al 0.5 La 0.5 F 3 @Li 1.3 Al 0.3 Ge 1.7 (PO 4 ) 3

[0164] Weigh 0.194 g of Al(NO 3 ) 3 ·9H 2 O and weigh 0.394 g of La(NO 3 ) 3 ·6H 2 O and dissolve them in 100 mL of deionized water. Stir magnetically for 30 min at room temperature to completely dissolve them to obtain solution A; weigh 0.116 g of NH 4 F and dissolve it in 100 mL of deionized water. Stir magnetically for 30 min at room temperature to completely dissolve it to obtain solution B; weigh 20 g of the lithium cobalt oxide material LiCoO 2 prepared in Example 1 and place it in solution B. Stir magnetically for 30 min at room temperature to completely disperse LiCoO 2 in solution B; then transfer solution B to an 80 °C oil bath. After the temperature of solution B is stable, use a peristaltic pump to dropwise add solution A to solution B under magnetic stirring, so that Al 0.5 La 0.5 F 3 nucleates and grows uniformly on the surface of LiCoO 2 particles. After drying at 80 °C for 8 h, collect the powder. Subsequently, dry the collected powder in a blast drying oven at 80 °C for 12 h to obtain the first composite material;

[0165] Next, weigh 0.425 g of Li 1.3 Al 0.3 Ge 1.7 (PO 4 ) 3 and the first composite material and place them in a ball milling jar. The ball-to-material ratio is 5:1, the rotation speed is 150 r / min, and dry ball milling is carried out for 4 h to make the two fully mixed and uniform to obtain the second composite material;

[0166] The second composite material was collected and sintered in a tube furnace under the following conditions: in an argon atmosphere, it was heated from room temperature to 650 °C at a heating rate of 2 °C / min, held for 10 h, and then naturally cooled to room temperature to obtain the lithium cobalt oxide cathode material LiCoO 2 @Al 0.5 La 0.5 F 3 @Li 1.3 Al 0.3 Ge 1.7 (PO 4 ) 3 , and the lithium cobalt oxide cathode material includes a lithium cobalt oxide core, and an Al 0.5 La 0.5 F 3 diffusion layer, an Al 0.5 La 0.5 F 3 layer, an Al 0.5 La 0.5 F 3 and Li 1.3 Al 0.3 Ge 1.7 (PO 4 ) 3 transition layer, and a Li 1.3 Al 0.3 Ge 1.7 (PO 4 ) 3 layer. The thickness of the Al 0.5 La 0.5 F 3 diffusion layer is 8 nm - 9 nm, the thickness of the first coating layer Al 0.5 La 0.5 F 3 is 5 nm - 6 nm, the thickness of the transition layer between the first coating layer Al 0.5 La 0.5 F 3 and the second coating layer Li 1.3 Al 0.3 Ge 1.7 (PO 4 ) 3 is 5 nm - 6 nm, and the coating thickness of the second coating layer Li 1.3 Al 0.3 Ge 1.7 (PO 4 ) 3 is 7 nm - 8 nm.

[0167] Comparative Example 6

[0168] The lithium cobalt oxide LiCoO used in Example 3 was surface-coated with Al 2 surface0.5 La 0.5 F 3 , obtain LiCoO 2 @Al 0.5 La 0.5 F 3 As the cathode material, LiCoO 2 @Al 0.5 La 0.5 F 3 The cathode material is used as the cathode active material, and a 2032-type button battery is assembled in the same method as in Example 1.

[0169] Comparative Example 7

[0170] The lithium cobaltate LiCoO used in Example 3 2 is surface-coated with Li 1.3 Al 0.3 Ge 1.7 (PO 4 ) 3 , obtain LiCoO 2 @Li 1.3 Al 0.3 Ge 1.7 (PO 4 ) 3 As the cathode material, LiCoO 2 @Li 1.3 Al 0.3 Ge 1.7 (PO 4 ) 3 The cathode material is used as the cathode active material, and a 2032-type button battery is assembled in the same method as in Example 1.

[0171] The same method as in Example 1 is used to conduct constant current charge and discharge tests, differential scanning calorimetry (DSC) tests, etc. on the cathode materials and batteries of Example 3 and Comparative Examples 6-7. Among them, the thermal stability results of the cathode materials are shown in Table 5, and the electrochemical performance results are shown in Table 6.

[0172] Table 5 Thermal Stability Results of Cathode Materials

[0173] Example Positive electrode material composition Exothermic peak temperature (°C) Example 3 <![CDATA[LiCoO 2 @Al 0.5 La 0.5 F 3 @Li 1.3 Al 0.3 Ge 1.7 (PO 4 ) 3 > 276.7 Comparative Example 6 <![CDATA[LiCoO 2 @Al 0.5 La 0.5 F 3 > 245.5 Comparative Example 7 <![CDATA[LiCoO 2 @Li 1.3 Al 0.3 Ge 1.7 (PO 4 ) 3 > 230.8 Comparative Example 1 <![CDATA[Unmodified LiCoO 2 material]]> 218.9

[0174] Table 6 Electrochemical Performance Results of Cathode Materials

[0175]

[0176] Compared with Example 1, the first coating layer in this example uses fluorides of Al and La. The La-O bond is stronger than the Al-O bond, and the binding of lattice oxygen is more obvious. At the same time, La can stabilize the octahedral framework of the layered structure; Li 1.3Al 0.3 Ge 1.7 (PO 4 ) 3 In the second coating layer, Al and Ge make the phosphate more stable and effectively resist the catalytic effect of the interfacial reaction on the lattice oxygen.

[0177] Example 4

[0178] Prepare the lithium cobalt oxide cathode material LiCoO 2 @MgF 2 @Li 3 BO 3

[0179] Weigh 0.264 g of Mg(NO 3 ) 2 ·6H 2 O and dissolve it in 100 mL of deionized water. Stir magnetically for 30 min at room temperature to completely dissolve it to obtain solution A; weigh 0.116 g of NH 4 F and dissolve it in 100 mL of deionized water. Stir magnetically for 30 min at room temperature to completely dissolve it to obtain solution B; weigh 20 g of the commercially available 4.48 V lithium cobalt oxide material LiCoO 2 and place it in solution B. Stir magnetically for 30 min at room temperature to completely disperse LiCoO 2 in solution B; then transfer solution B to an 80 °C oil bath. After the temperature of solution B is stable, use a peristaltic pump to dropwise add solution A to solution B under magnetic stirring, so that MgF 2 nucleates and grows uniformly on the surface of LiCoO 2 particles. After drying at 80 °C for 8 h, collect the powder. Subsequently, dry the collected powder in a blast drying oven at 80 °C for 12 h to obtain the first composite material;

[0180] Next, weigh 0.082 g of Li 3 BO 3 and the first composite material and place them in a ball milling jar. The ball-to-material ratio is 4:1, the rotation speed is 150 r / min, and dry ball mill for 2 h to make the two fully mixed and uniform to obtain the second composite material.

[0181] Collect the second composite material and place it in a tube furnace for sintering. The sintering conditions are: under an argon atmosphere, heat from room temperature to 500 °C at a heating rate of 4 °C / min, hold for 6 h, and then naturally cool to room temperature to obtain the lithium cobalt oxide cathode material LiCoO 2 @MgF 2 @Li 3 BO 3 , and this lithium cobalt oxide cathode material includes a lithium cobalt oxide core and MgF formed successively on the surface of the lithium cobalt oxide core 2Diffusion layer, MgF 2 layer, MgF 2 and Li 3 BO 3 transition layer of and Li 3 BO 3 layer. The thickness of the MgF 2 diffusion layer is 2 nm - 3 nm, and the thickness of the first coating layer MgF 2 is 3 nm - 4 nm. The thickness of the transition layer between the first coating layer MgF 2 and the second coating layer Li 3 BO 3 is 3 nm - 4 nm, and the coating thickness of the second coating layer Li 3 BO 3 is 5 nm - 6 nm.

[0182] Using the LiCoO 2 @MgF 2 @Li 3 BO 3 positive electrode material prepared in Example 4 of this application as the positive electrode active material, and assembling it into a 2032-type button battery in the same method as in Example 1.

[0183] Comparative Example 8

[0184] Using the commercial 4.48 V lithium cobaltate material LiCoO 2 used in Example 4 as the positive electrode active material, and assembling it into a 2032-type button battery in the same method as in Example 1.

[0185] Comparative Example 9

[0186] Coating the surface of the commercial 4.48 V lithium cobaltate material LiCoO 2 used in Example 4 with MgF 2 to obtain the LiCoO 2 @MgF 2 positive electrode material. Using the LiCoO 2 @MgF 2 positive electrode material as the positive electrode active material, and assembling it into a 2032-type button battery in the same method as in Example 1.

[0187] Comparative Example 10

[0188] Coating the surface of the commercial 4.48 V lithium cobaltate material LiCoO 2 used in Example 4 with Li 3 BO 3 to obtain the LiCoO 2 @Li 3 BO 3 positive electrode material. Using the LiCoO 2 @Li3 BO 3 As the positive electrode active material, the positive electrode material was assembled into a 2032 type button battery by the same method as in Example 1.

[0189] The positive electrode materials and batteries of Example 4 and Comparative Examples 8-10 were tested by constant current charge and discharge test, differential scanning calorimetry (DSC) test, etc. using the same method as in Example 1. Among them, the thermal stability results of the positive electrode materials are shown in Table 7 as shown, and the electrochemical performance results are shown in Table 8.

[0190] Table 7 Thermal stability results of the positive electrode material

[0191] Example Positive electrode material composition Exothermic peak temperature (°C) Example 4 <![CDATA[LiCoO 2 @MgF 2 @Li 3 BO 3 > 263.2 Comparative Example 9 <![CDATA[LiCoO 2 @MgF 2 > 237.5 Comparative Example 10 <![CDATA[LiCoO 2 @Li 3 BO 3 > 231.1 Comparative Example 8 <![CDATA[Commercial LiCoO 2 Material]]> 225.4

[0192] Table 8 Electrochemical performance results of the positive electrode material

[0193]

[0194] In this example, commercial 4.48V lithium cobaltate material was used as the base material, which is helpful for batch scale-up experiments. Using MgF 2 and Li 3 BO 3 coating the lithium cobaltate material can effectively improve the thermal stability and electrochemical performance of the material.

[0195] Example 5

[0196] Prepare lithium cobaltate positive electrode material LiCoO 2 @MgF 2 @Li 4 SiO 4

[0197] Weigh 0.264 g of Mg(NO 3 ) 2 ·6H 2 O and dissolve it in 100 mL of deionized water. Stir magnetically at room temperature for 30 min to completely dissolve it to obtain solution A; weigh 0.116 g of NH 4 F and dissolve it in 100 mL of deionized water. Stir magnetically at room temperature for 30 min to completely dissolve it to obtain solution B; weigh 20 g of the LiCoO prepared in Example 1 2 and place it in solution B. Stir magnetically at room temperature for 30 min to completely disperse LiCoO 2 in solution B; then transfer solution B to an 80 °C oil bath. After the temperature of solution B is stable, use a peristaltic pump to dropwise add solution A to solution B under magnetic stirring, so that MgF 2 is formed on LiCoO 2Nucleation and growth occur uniformly on the particle surface. After drying by stirring at 80 °C, the powder is collected, and the required time is 8 h. Subsequently, the collected powder is dried in a forced-air drying oven at 80 °C for 12 h to obtain the first composite material.

[0198] Next, the sol-gel method is used to prepare the second composite material. Dissolve 0.270 g of CH 3 COOLi and 0.213 g of Si(OC 2 H 5 ) 4 in ethanol. Let the solution stand for two days to form a Li 4 SiO 4 sol solution. Add the first composite material to the Li 4 SiO 4 sol solution. Stir the mixture and gently heat it to 60 °C until the solvent completely evaporates.

[0199] Collect the second composite material and sinter it in a tube furnace. The sintering conditions are as follows: in an argon atmosphere, heat from room temperature to 550 °C at a heating rate of 3 °C / min, hold for 10 h, and then cool naturally to room temperature to obtain the lithium cobalt oxide cathode material LiCoO 2 @MgF 2 @Li 4 SiO 4 . This lithium cobalt oxide cathode material includes a lithium cobalt oxide core, and a MgF 2 diffusion layer, a MgF 2 layer, a MgF 2 and a Li 4 SiO 4 transition layer, and a Li 4 SiO 4 layer formed successively on the surface of the lithium cobalt oxide core. The thickness of the MgF 2 diffusion layer is 2 nm - 3 nm, the thickness of the first coating layer MgF 2 is 3 nm - 4 nm, the thickness of the transition layer between the first coating layer MgF 2 and the second coating layer Li 4 SiO 4 is 3 nm - 4 nm, and the coating thickness of the second coating layer Li 4 SiO 4 is 5 nm - 6 nm.

[0200] Use the LiCoO 2 @MgF 2 @Li 4 SiO 4 cathode material prepared in Example 5 of this application as the cathode active material, and assemble it into a 2032-type button battery in the same method as in Example 1.

[0201] Comparative Example 11

[0202] The lithium cobalt oxide LiCoO used in Example 5 2 was surface-coated with MgF 2 , obtaining LiCoO 2 @MgF 2 as the cathode material. The LiCoO 2 @MgF 2 cathode material was used as the cathode active material, and a 2032-type button battery was assembled in the same manner as in Example 1.

[0203] Comparative Example 12

[0204] The lithium cobalt oxide LiCoO used in Example 5 2 was surface-coated with Li 4 SiO 4 , obtaining LiCoO 2 @Li 4 SiO 4 as the cathode material. The LiCoO 2 @Li 4 SiO 4 cathode material was used as the cathode active material, and a 2032-type button battery was assembled in the same manner as in Example 1.

[0205] The same method as in Example 1 was used to perform constant current charge-discharge tests, differential scanning calorimetry (DSC) tests, etc. on the cathode materials and batteries of Example 5 and Comparative Examples 11-12. Among them, the thermal stability results of the cathode materials are shown in Table 9, and the electrochemical performance results are shown in Table 10.

[0206] Table 9 Thermal Stability Results of Cathode Materials

[0207] Example Positive electrode material composition Exothermic peak temperature (°C) Example 5 <![CDATA[LiCoO 2 @MgF 2 @Li 4 SiO 4 > 253.1 Comparative Example 11 <![CDATA[LiCoO 2 @MgF 2 > 240.3 Comparative Example 12 <![CDATA[LiCoO 2 @Li 4 SiO 4 > 232.5 Comparative Example 1 <![CDATA[Unmodified LiCoO 2 material]]> 218.9

[0208] Table 10 Electrochemical Performance Results of Cathode Materials

[0209]

[0210]

[0211] Compared with Example 1, in this example, Li 4 SiO 4 was used as the outermost coating layer. Since the tetrahedron constructed by SiO 4 4- has a stable orthorhombic structure, it can well inhibit the interfacial reaction and reduce the catalysis of the interfacial reaction on the release of lattice oxygen.

[0212] Example 6

[0213] Preparation of lithium cobalt oxide cathode material LiCoO 2 @LaF 3 @Li 2 SrSiO 4

[0214] Weigh 0.394 g of La(NO 3 ) 3 ·6H 2 O and dissolve it in 100 mL of deionized water. Stir magnetically for 30 min at room temperature to completely dissolve it to obtain solution A; weigh 0.058 g of NH 4 F and dissolve it in 100 mL of deionized water. Stir magnetically for 30 min at room temperature to completely dissolve it to obtain solution B; weigh 10 g of LiCoO prepared in Example 1 2 and place it in solution A. Stir magnetically for 30 min at room temperature to completely disperse LiCoO 2 in solution A; then transfer solution A to an 80 °C oil bath. After the temperature of solution A is stable, use a peristaltic pump to dropwise add solution B to solution A under magnetic stirring, so that LaF 3 nucleates and grows uniformly on the surface of LiCoO 2 particles. After drying by stirring at 80 °C, collect the powder, and the required time is 8 h; then dry the collected powder in a blast drying oven at 80 °C for 12 h to obtain the first composite material;

[0215] Next, weigh 0.097 g of Li 2 SrSiO 4 and the first composite material and place them in a ball milling jar. The ball-to-material ratio is 5:1, the rotation speed is 150 r / min, and dry ball milling is carried out for 3 h to make the two fully mixed and uniform to obtain the second composite material;

[0216] Collect the second composite material and place it in a tube furnace for sintering. The sintering conditions are: under an argon atmosphere, heat from room temperature to 650 °C at a heating rate of 1 °C / min, hold for 10 h, and then naturally cool to room temperature to obtain the lithium cobalt oxide cathode material LiCoO 2 @LaF 3 @Li 2 SrSiO 4 . This lithium cobalt oxide cathode material includes a lithium cobalt oxide core, and a LaF 3 diffusion layer, a LaF 3 layer, a LaF 3 and a transition layer of Li 2 SrSiO 4 as well as a Li 2 SrSiO 4 layer formed in sequence on the surface of the lithium cobalt oxide core. The thickness of the LaF 3 diffusion layer is 3 nm - 4 nm, and the first coating layer LaF3 has a thickness of 4 nm - 5 nm, and the first coating layer LaF 3 and the second coating layer Li 2 SrSiO 4 The thickness of the transition layer between them is 5 nm - 6 nm, and the coating thickness of the second coating layer Li 2 SrSiO 4 is 6 nm - 7 nm.

[0217] Comparative Example 13

[0218] The lithium cobaltate LiCoO used in Example 6 2 was surface-coated with LaF 3 to obtain LiCoO 2 @LaF 3 cathode material. The LiCoO 2 @LaF 3 cathode material was used as the cathode active material, and a 2032-type button battery was assembled in the same manner as in Example 1.

[0219] Comparative Example 14

[0220] The lithium cobaltate LiCoO used in Example 6 2 was surface-coated with Li 2 SrSiO 4 to obtain LiCoO 2 @Li 2 SrSiO 4 cathode material. The LiCoO 2 @Li 2 SrSiO 4 cathode material was used as the cathode active material, and a 2032-type button battery was assembled in the same manner as in Example 1.

[0221] The cathode materials and batteries of Example 6 and Comparative Examples 13 - 14 were tested by constant current charge and discharge test, differential scanning calorimetry (DSC) test, etc. using the same method as in Example 1. Among them, the thermal stability results of the cathode materials are shown in Table 11, and the electrochemical performance results are shown in Table 12.

[0222] Table 11 Thermal Stability Results of Cathode Materials

[0223] Example Positive electrode material composition Exothermic peak temperature (°C) Example 6 <![CDATA[LiCoO 2 @LaF 3 @Li 2 SrSiO 4 > 259.9 Comparative Example 13 <![CDATA[LiCoO 2 @LaF 3 > 242.3 Comparative Example 14 <![CDATA[LiCoO 2 @Li 2 SrSiO 4 > 233.1 Comparative Example 1 <![CDATA[Unmodified LiCoO 2 material]]> 218.9

[0224] Table 12 Electrochemical Performance Results of Cathode Materials

[0225]

[0226] Compared with Example 1, in this example, La with stronger bonding ability to lattice oxygen is used in the first coating layer, which can further improve the stability of lattice oxygen. At the same time, Li is adopted in this example. 2 SrSiO 4 is used as the second coating layer. In addition to SiO 4 4- The constructed tetrahedron has a very stable structure, which can effectively inhibit the interfacial reaction. The introduction of Sr also further strengthens the stability of the second coating layer and improves the binding force on lattice oxygen.

[0227] Example 7

[0228] Prepare the lithium cobalt oxide cathode material LiCoO 2 @ZrF 4 @Li 2 WO 4

[0229] Weigh 0.439 g of Zr(NO 3 ) 4 ·5H 2 O and dissolve it in 100 mL of deionized water. Stir magnetically at room temperature for 30 min to completely dissolve it to obtain Solution A; weigh 0.151 g of NH 4 F and dissolve it in 100 mL of deionized water. Stir magnetically at room temperature for 30 min to completely dissolve it to obtain Solution B; weigh 20 g of the lithium cobalt oxide material LiCoO 2 prepared in Example 1 and place it in Solution B. Stir magnetically at room temperature for 30 min to completely disperse LiCoO 2 in Solution B; then transfer Solution B to an 80°C oil bath. After the temperature of Solution B is stable, use a peristaltic pump to dropwise add Solution A to Solution B under magnetic stirring, so that Al 0.5 La 0.5 F 3 nucleates and grows uniformly on the surface of LiCoO 2 particles. After drying at 80°C for 8 h, collect the powder. Subsequently, dry the collected powder in an 80°C forced-air drying oven for 12 h to obtain the first composite material;

[0230] Then weigh 0.237 g of WO 3 and 0.086 g of LiOH·H 2 O and place them in a ball milling jar with the first composite material. The ball-to-material ratio is 5:1, the rotation speed is 150 r / min, and dry ball milling is carried out for 5 h to make the two fully mixed and uniform to obtain the second composite material;

[0231] The second composite material was collected and sintered in a tubular furnace under the following sintering conditions: in an argon atmosphere, heated from room temperature to 650 °C at a heating rate of 2 °C / min, held for 10 h, and then naturally cooled to room temperature to obtain the lithium cobalt oxide cathode material LiCoO 2 @ZrF 4 @Li 2 WO 4 , the lithium cobalt oxide cathode material includes a lithium cobalt oxide core, and a ZrF 4 diffusion layer, a ZrF 4 layer, a ZrF 4 and Li 2 WO 4 transition layer and a Li 2 WO 4 layer formed in sequence on the surface of the lithium cobalt oxide core. The thickness of the ZrF 4 diffusion layer is 7 nm - 8 nm, the thickness of the first coating layer ZrF 4 is 3 nm - 4 nm, the thickness of the transition layer between the first coating layer ZrF 4 and the second coating layer Li 2 WO 4 is 5 nm - 6 nm, and the coating thickness of the second coating layer Li 2 WO 4 is 7 nm - 8 nm.

[0232] Comparative Example 15

[0233] The surface of the lithium cobalt oxide LiCoO used in Example 7 was coated with ZrF 2 , to obtain the LiCoO 4 @ZrF 2 cathode material. The LiCoO 4 @ZrF 2 cathode material was used as the positive electrode active material, and a 2032-type button battery was assembled in the same manner as in Example 1. 4

[0234] Comparative Example 16

[0235] The surface of the lithium cobalt oxide LiCoO used in Example 7 was coated with Li 2 , to obtain the LiCoO 2 @Li 4 WO 2 cathode material. The LiCoO 2 WO 4 @Li 2 cathode material was used as the positive electrode active material, and a 2032-type button battery was assembled in the same manner as in Example 1. 2 WO 4

[0236] ​​The same method as in Example 1 was used to conduct constant current charge-discharge tests, differential scanning calorimetry (DSC) tests, etc. on the cathode materials and batteries of Example 7 and Comparative Examples 15-16. Among them, the thermal stability results of the cathode materials are shown in Table 13, and the electrochemical performance results are shown in Table 14.

[0237] Table 13 Thermal Stability Results of Cathode Materials

[0238] Example Positive electrode material composition Exothermic peak temperature (°C) Example 7 <![CDATA[LiCoO 2 @ZrF 4 @Li 2 WO 4 > 254.6 Comparative Example 15 <![CDATA[LiCoO 2 @ZrF 4 > 240.3 Comparative Example 16 <![CDATA[LiCoO 2 @Li 2 WO 4 > 235.7 Comparative Example 1 <![CDATA[Unmodified LiCoO 2 material]]> 218.9

[0239] Table 14 Electrochemical Performance Results of Cathode Materials

[0240]

[0241] Compared with Example 1, in this example, the first coating layer uses a fluoride of Zr, and the strong bonding ability of Zr and O further enhances the binding of lattice oxygen. In addition, the second coating layer uses Li 2 WO 4 , WO 4 2- The strong stability further inhibits the catalytic effect of the interfacial reaction on the release of lattice oxygen.

[0242] Example 8

[0243] Prepare lithium cobalt oxide cathode material LiCoO 2 @ZrF 4 @Li 1.85 Y 0.05 WO 4

[0244] Weigh 0.439 g of Zr(NO 3 ) 4 ·5H 2 O and dissolve it in 100 mL of deionized water. Stir magnetically at room temperature for 30 min to completely dissolve it to obtain Solution A; weigh 0.151 g of NH 4 F and dissolve it in 100 mL of deionized water. Stir magnetically at room temperature for 30 min to completely dissolve it to obtain Solution B; weigh 20 g of the lithium cobalt oxide material LiCoO 2 prepared in Example 1 and place it in Solution B. Stir magnetically at room temperature for 30 min to completely disperse LiCoO 2 in Solution B; then transfer Solution B to an 80 °C oil bath. After the temperature of Solution B is stable, use a peristaltic pump to dropwise add Solution A to Solution B under magnetic stirring, so that Al 0.5 La 0.5 F 3 on LiCoO 2Nucleation and growth occur uniformly on the particle surface. After drying by stirring at 80 °C, the powder is collected, and the required time is 8 h. Subsequently, the collected powder is dried in a forced-air drying oven at 80 °C for 12 h to obtain the first composite material;

[0245] Next, 0.237 g of WO 3 , 0.006 g of Y 2 O 3 and 0.079 g of LiOH·H 2 O are placed in a ball-milling jar with the first composite material. The ball-to-material ratio is 5:1, the rotation speed is 150 r / min, and dry ball milling is carried out for 8 h to make the two fully mixed and uniform, obtaining the second composite material;

[0246] The second composite material is collected and sintered in a tubular furnace. The sintering conditions are as follows: in an argon atmosphere, it is heated from room temperature to 650 °C at a heating rate of 1 °C / min, held for 10 h, and then naturally cooled to room temperature to obtain the lithium cobalt oxide cathode material LiCoO 2 @ZrF 4 @Li 1.85 Y 0.05 WO 4 . This lithium cobalt oxide cathode material includes a lithium cobalt oxide core, and a ZrF 4 diffusion layer, a ZrF 4 layer, a ZrF 4 and Li 1.85 Y 0.05 WO 4 transition layer, and a Li 1.85 Y 0.05 WO 4 layer formed successively on the surface of the lithium cobalt oxide core. The thickness of the ZrF 4 diffusion layer is 7 nm - 8 nm, the thickness of the first coating layer ZrF 4 is 3 nm - 4 nm, the thickness of the transition layer between the first coating layer ZrF 4 and the second coating layer Li 1.85 Y 0.05 WO 4 is 5 nm - 6 nm, and the coating thickness of the second coating layer Li 1.85 Y 0.05 WO 4 is 8 nm - 9 nm.

[0247] Comparative Example 17

[0248] The surface of the lithium cobalt oxide LiCoO 2 used in Example 8 is coated with ZrF 4 to obtain the LiCoO 2 @ZrF 4 cathode material. The LiCoO 2 @ZrF4 The positive electrode material, as the positive electrode active material, was assembled into a 2032-type button battery in the same manner as in Example 1.

[0249] Comparative Example 18

[0250] The lithium cobaltate LiCoO used in Example 8 2 was surface-coated with Li 1.85 Y 0.05 WO 4 to obtain LiCoO 2 @Li 1.85 Y 0.05 WO 4 as the positive electrode material. The LiCoO 2 @Li 1.85 Y 0.05 WO 4 positive electrode material, as the positive electrode active material, was assembled into a 2032-type button battery in the same manner as in Example 1.

[0251] The positive electrode materials and batteries of Example 8 and Comparative Examples 17-18 were tested by constant current charge and discharge test, differential scanning calorimetry (DSC) test, etc. using the same method as in Example 1. Among them, the thermal stability results of the positive electrode materials are shown in Table 15, and the electrochemical performance results are shown in Table 16.

[0252] Table 15 Thermal Stability Results of Positive Electrode Materials

[0253] Example Positive electrode material composition Exothermic peak temperature (°C) Example 8 <![CDATA[LiCoO 2 @ZrF 4 @Li 1.85 Y 0.05 WO 4 > 257.9 Comparative Example 15 <![CDATA[LiCoO 2 @ZrF 4 > 240.3 Comparative Example 16 <![CDATA[LiCoO 2 @Li 1.85 Y 0.05 WO 4 > 236.8 Comparative Example 1 <![CDATA[Unmodified LiCoO 2 material]]> 218.9

[0254] Table 16 Electrochemical Performance Results of Positive Electrode Materials

[0255]

[0256] Compared with Example 1, in this example, the first coating layer uses a fluoride of Zr, and the strong bonding ability between Zr and O further enhances the binding of lattice oxygen. In addition, the second coating layer uses Li 1.85 Y 0.05 WO 4 WO 4 2- The strong stability of further inhibits the catalytic effect of the interfacial reaction on the release of lattice oxygen. The introduction of Y further enhances the structural stability of the second coating layer and increases the binding force on lattice oxygen.

[0257] The lithium cobalt oxide cathode material provided by the embodiments of the present application has a shell structure with multiple layers of coating on the surface. Compared with the cathode material with a single-layer coating in the comparative example, the synergistic effect of the multi-layer coating modification effectively enhances the binding of the lattice oxygen of the lithium cobalt oxide base material in the high delithiation state, improves the diffusion barrier of the lattice oxygen, and improves the thermal stability and cycle stability of the high-voltage lithium cobalt oxide cathode material. Specific manifestations are as follows. For example, the test results of differential scanning calorimetry (DSC) show that, compared with the unmodified LiCoO 2 material (exothermic peak at 218.93 °C), the thermal stability of the multi-layer coated material LiCoO 2 @AlF 3 @Li 3 PO 4 in Example 1 is greatly improved (exothermic peak at 275.2 °C); the results of the capacity-voltage differential curve (dQ / dV) show that, compared with the unmodified LiCoO 2 material, the voltage decay of the multi-layer coated material LiCoO 2 @AlF 3 @Li 3 PO 4 in Example 1 is greatly reduced (the degree of reduction peak shift decreases from 160.6 mV to 58.2 mV); the results of the constant current charge-discharge test show that, compared with the unmodified LiCoO 2 sample (the capacity retention rate after 300 cycles is 6.94%), the capacity retention rate of the multi-layer coated material LiCoO 2 @AlF 3 @Li 3 PO 4 in Example 1 is greatly improved (the capacity retention rate after 300 cycles is 86.66%).

Claims

1. A lithium cobalt oxide cathode material, characterized in that, the lithium cobalt oxide cathode material includes a core and a shell layer coated on the core, the core includes a lithium cobalt oxide material; the shell layer includes a first coating layer on the core, a second coating layer on the first coating layer, and a transition layer between the first coating layer and the second coating layer; The first coating layer includes metal fluoride, and the metal fluoride is represented as A b F c , where 0 < b ≤ 1, 0 < c ≤ 4, and A is a metal element that can satisfy that the bond energy of A-O is greater than the bond energy of Co-O; The second coating layer includes a polyanionic compound, which is represented as Li x M’ y D z , where 0 < x ≤ 4, 0 ≤ y ≤ 4, 0 < z ≤ 3, M’ represents a metal or metalloid element that can satisfy that the bond energy of M’-O is greater than the bond energy of Co-O, and D represents a polyanion group; the transition layer includes the material of the first coating layer and the material of the second coating layer.

2. The lithium cobalt oxide cathode material according to claim 1, characterized in that, A is a metal element that can satisfy that the bond energy of A-O is greater than 500 kJ / mol; M' is a metal or metalloid element that can satisfy that the bond energy of M'-O is greater than 500 kJ / mol.

3. The lithium cobalt oxide cathode material according to claim 1 or 2, characterized in that, The chemical formula of the transition layer is aA b F c ·(1 - a)Li x M’ y D z , where 0 < a < 1.

4. The lithium cobalt oxide cathode material according to claim 1, characterized in that, along the direction from the first coating layer to the second coating layer, in the transition layer, the content of the material of the first coating layer gradually decreases, and the content of the material of the second coating layer gradually increases.

5. The lithium cobalt oxide cathode material according to claim 1, characterized in that, the molar percentage of the metal fluoride of the first coating layer relative to the lithium cobalt oxide material of the core is 0.1 mol%-4.0 mol%.

6. The lithium cobalt oxide cathode material according to claim 1, characterized in that, the molar percentage of the polyanionic compound of the second coating layer relative to the lithium cobalt oxide material of the core is 0.1 mol%-4.0 mol%.

7. The lithium cobalt oxide cathode material according to claim 1, characterized in that, the thickness of the first coating layer is greater than or equal to 3 nm; the thickness of the second coating layer is greater than or equal to 5 nm.

8. The lithium cobalt oxide cathode material according to claim 1, characterized in that, the thickness of the transition layer is greater than or equal to 3 nm.

9. The lithium cobalt oxide cathode material according to claim 1, characterized in that, the total thickness of the first coating layer, the transition layer, and the second coating layer is less than or equal to 20 nm.

10. The lithium cobalt oxide cathode material according to claim 1, characterized in that, the shell layer further includes a diffusion layer between the core and the first coating layer, and the diffusion layer includes the material of the core and the material of the first coating layer.

11. The lithium cobalt oxide cathode material according to claim 10, characterized in that, the thickness of the diffusion layer is 2 nm-80 nm.

12. The lithium cobalt oxide cathode material according to claim 10 or 11, characterized in that, The chemical formula of the diffusion layer is Li x A y Co (1-x’-3y’) / 3 O (1-z’) / 2 F z’ , where 0 ≤ x’ ≤ 1, 0 ≤ y’ ≤ 1, and 0 ≤ z’ ≤ 1.

13. The lithium cobalt oxide cathode material according to claim 1, characterized in that, A is selected from one or more of Al, As, Ag, Au, Ba, Be, Ca, Ce, Cs, Cr, Cm, Cd, Dy, Er, Eu, Gd, Ge, Hf, Ir, Fe, La, Lu, Mg, Mn, Mo, Nd, Np, Nb, Os, Pr, Pm, Pd, Pt, Re, Ru, Rh, Sm, Sc, Sr, Ta, Tm, Tc, Sn, Ti, W, V, Y, Zr.

14. The lithium cobaltate cathode material according to claim 1 or 13, characterized in that, M' is selected from one or more of Al, As, Ag, Au, Ba, Be, B, Ca, Ce, Cs, Cr, Cm, Cd, Dy, Er, Eu, Gd, Ge, Hf, Ir, Fe, La, Lu, Mg, Mn, Mo, Nd, Np, Nb, Os, Pr, Pm, Pd, Pt, Re, Ru, Rh, Sm, Sc, Sr, Ta, Tm, Tc, Sn, Ti, W, V, Y, Zr.

15. The lithium cobaltate cathode material according to claim 1, characterized in that, D is selected from an oxygen-containing acid radical of phosphorus, an oxygen-containing acid radical of silicon, an oxygen-containing acid radical of boron or an oxygen-containing acid radical of tungsten.

16. The lithium cobaltate cathode material according to claim 1, characterized in that, when the lithium cobaltate cathode material is applied in a lithium ion battery system with a cut-off voltage of 4.5V - 4.7V, the irreversible release amount of lattice oxygen is less than 20% of the total amount of lattice oxygen.

17. The lithium cobaltate cathode material according to claim 1, characterized in that, the exothermic peak temperature of the lithium cobaltate cathode material measured by differential scanning calorimetry is greater than 240°C.

18. A positive electrode sheet, characterized in that, the positive electrode sheet includes the lithium cobaltate cathode material according to any one of claims 1 - 17.

19. An electrochemical device, characterized in that, the electrochemical device includes the lithium cobaltate cathode material according to any one of claims 1 - 17.

20. The electrochemical device according to claim 19, characterized in that, when the electrochemical device is charged at 1.5C / discharged at 0.7C for 300 cycles at a cut-off voltage of 4.5V - 4.7V, the capacity retention rate is greater than 70%.

21. An electronic device, characterized in that, the electronic device includes a housing, electronic components accommodated in the housing, and the electrochemical device according to claim 19 or 20, and the electrochemical device supplies power to the electronic device.

22. A mobile device, characterized in that, the mobile device includes the electrochemical device according to claim 19 or 20.

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