Positive electrode material, preparation method thereof and lithium battery containing positive electrode material

Abstract

The invention discloses a positive electrode material, a preparation method thereof and a lithium battery containing the positive electrode material. The positive electrode material has a core-shell structure, a core layer is a secondary microsphere formed by gathering primary particles, the primary particles are strip-shaped, and a shell layer is a compound composed of lithium, phosphorus and IVB elements. The positive electrode material provided by the invention has relatively high discharge capacity, excellent rate capability and cycling stability, and can be used in a high-performance lithium battery.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of lithium batteries, in particular to a positive electrode material, a preparation method thereof and a lithium battery comprising the positive electrode material. BACKGROUND

[0002] With the popularization of electric vehicles, the market has higher and higher requirements for the performance of electric vehicles, such as the cruising range, service life, charging and discharging rate, etc. The performance of electric vehicles is mainly determined by lithium batteries, and the performance of lithium batteries is mainly determined by the positive electrode material used, etc. Among commercialized positive electrode materials, ternary positive electrode materials composed of lithium nickel cobalt manganese oxide or lithium nickel cobalt aluminum oxide have higher theoretical specific capacity compared with other positive electrode materials, and are generally used in electric vehicles with long cruising range.

[0003] Among ternary positive electrode materials, different elements play different roles. Nickel mainly plays a role in capacity, cobalt can improve the rate performance of the material, and manganese or aluminum mainly stabilizes the skeleton structure of the material and improves the stability of the material. In order to meet the increasing demand for the cruising range of electric vehicles, the nickel content in ternary positive electrode materials is continuously increasing. However, the continuous increase of the nickel content in the material leads to the decrease of the content of other elements such as cobalt and manganese, resulting in serious decline of the rate performance of the material and rapid deterioration of the cycle stability, which is difficult to meet the comprehensive requirements of high-performance electric vehicles for the capacity, rate and cycle of the positive electrode material.

[0004] Therefore, it is urgent to solve the problem that the rate performance and cycle performance of high-nickel-content positive electrode materials are difficult to be considered due to the capacity improvement. SUMMARY

[0005] The present application provides a positive electrode material, a preparation method thereof and a lithium battery comprising the positive electrode material, aiming at the problem that the capacity, rate and cycle performance of ternary positive electrode materials in the prior art are difficult to be considered. The positive electrode material of the present application has high discharge specific capacity, excellent rate performance and cycle stability when applied in lithium batteries.

[0006] The first aspect of the present application provides a positive electrode material, which has a core-shell structure, the core layer is a secondary microsphere formed by aggregation of primary particles, the primary particles are in a strip shape, and the shell layer is a compound composed of lithium, phosphorus and a group IVB element.

[0007] In the above technical solution, the chemical formula of the compound composed of lithium, phosphorus and a group IVB element is LiM2(PO4)3, wherein M is a group IVB element; preferably, the compound is selected from at least one of lithium zirconium phosphate, lithium titanium phosphate and lithium hafnium phosphate.

[0008] In the above technical solution, the mass of the core layer is 100 parts, and the mass of the shell layer is greater than 0 parts and not higher than 5 parts.

[0009] In the technical solution, the chemical general formula of the core layer in the positive electrode material is Li a Ni x Co y M z N p O2, wherein 0.9≤a≤1.2, 0≤x≤1, 0≤y≤1, 0≤z≤1, 0<p≤0.1, the values of x, y and z are not 0 at the same time, and the values of a, x, y, z and p satisfy the principle of electrical neutrality, M is selected from at least one of group VIIB or group IIIA elements, and N is selected from at least one of group VA elements. Further, the group VIIB element is preferably Mn, the group IIIA element is preferably Al, and the group VA element is selected from at least one of N, P, Sb and Bi.

[0010] In the technical solution, the chemical general formula of the core layer in the positive electrode material is Li a Ni x Co y M z N p O2, wherein 0.6≤x≤1.00, 0≤y≤0.5, 0≤z≤0.5, 0<p≤0.05, the values of x, y and z are not 0 at the same time, preferably the values of y and z are not 0 at the same time, and the values of a, x, y, z and p satisfy the principle of electrical neutrality.

[0011] In the technical solution, the primary particles of the core layer in the positive electrode material are arranged along the radial direction of the secondary microspheres, and the medium particle size of the secondary microspheres is 1.0-20.0 μm. The medium particle size represents the particle size corresponding to the cumulative particle size distribution percentage of 50% of the secondary microspheres.

[0012] In the technical solution, the primary particles of the core layer in the positive electrode material have an aspect ratio of 1.05-20.00, preferably 1.50-10.00, and further preferably 1.50-8.00.

[0013] The second aspect of the present application provides a preparation method of a positive electrode material, comprising:

[0014] (1) mixing a positive electrode material precursor, a lithium source and a modifier containing a group VA element, sintering to obtain an intermediate product;

[0015] (2) mixing the intermediate product prepared in step (1) with a compound composed of lithium, phosphorus and a group IVB element to obtain the positive electrode material.

[0016] In the technical solution, the chemical general formula of the positive electrode material precursor is Ni x Co y M z(OH)2, 0≤x≤1, 0≤y≤1, 0≤z≤1, preferably 0.6≤x≤1.00, 0≤y≤0.5, 0≤z≤0.5, x, y and z are not simultaneously 0, and the values of x, y and z satisfy the principle of electrical neutrality.

[0017] In the technical scheme, the morphology of the positive electrode material precursor is a microsphere formed by stacking the flakes. The average thickness of the flake is 1-500 nm, preferably 1-200 nm.

[0018] In the technical scheme, the lithium source is preferably at least one of lithium nitrate (LiNO3), lithium chloride (LiCl), lithium carbonate (Li2CO3), lithium hydroxide (LiOH), lithium hydroxide monohydrate (LiOH·H2O), lithium oxide (Li2O), lithium acetate (CH3COOLi), and lithium oxalate (Li2C2O4).

[0019] In the technical scheme, the molar ratio of the positive electrode material precursor to the lithium source (calculated as Li element) is 1:(0.90-1.20).

[0020] In the technical scheme, the Group VA element-containing modifier is preferably at least one of a Group VA element-containing nitrate, chloride, carbonate, hydroxide, oxide, acetate, and oxalate.

[0021] In the technical scheme, the molar ratio of the Group VA element-containing modifier (calculated as Group VA element) to the positive electrode material precursor is greater than 0 to 0.1, preferably the molar ratio of the Group VA element-containing modifier (calculated as Group VA element) to the positive electrode material precursor is (0.001-0.05):1.

[0022] In the technical scheme, the sintering is programmed temperature sintering, the heating rate is preferably 0.5-10℃ / min, the sintering temperature is 580-900℃, preferably 600-850℃, the sintering time is 4-48h, preferably 8-24h, and further preferably 12-20h.

[0023] In the technical scheme, the sintering is programmed temperature sintering, the heating rate is preferably 0.5-10℃ / min, the sintering temperature is 580-900℃, preferably 600-850℃, the sintering time is 4-48h, preferably 8-24h, and further preferably 12-20h.

[0024] In the technical scheme, the compound composed of lithium, phosphorus and Group IVB element is at least one of lithium zirconium phosphate, lithium titanium phosphate, and lithium hafnium phosphate.

[0025] In the technical solution, the mass ratio of the compound composed of lithium, phosphorus and the element of the IVB group to the intermediate product is greater than 0 to 0.05, preferably (0.001-0.05):1.

[0026] In the technical solution, the positive electrode material has a core-shell structure, the core layer is a secondary microsphere formed by aggregation of primary particles, the primary particles are in a strip shape, and the shell layer is a compound composed of lithium, phosphorus and the element of the IVB group.

[0027] In the technical solution, in the positive electrode material, the primary particles of the core layer are arranged along the radial direction of the secondary microsphere, and the medium particle size of the secondary microsphere is 1.0-20.0 μm. The medium particle size refers to the particle size corresponding to the cumulative particle size distribution percentage of 50% of the secondary microsphere.

[0028] In the technical solution, in the positive electrode material, the aspect ratio of the primary particles of the core layer is 1.05-20.00, preferably 1.50-10.00, and further preferably 1.50-8.00.

[0029] The third aspect of the present application provides a lithium battery comprising the above positive electrode material and application thereof.

[0030] Compared with the prior art, the present application has the following beneficial effects:

[0031] 1. The positive electrode material of the present application has a core-shell structure, the core layer is a secondary microsphere formed by aggregation of primary particles arranged along the radial direction of the secondary microsphere, the primary particles are in a strip shape, and the shell layer is a compound composed of lithium, phosphorus and the element of the IVB group. The use of the positive electrode material of the present application solves the problem that the discharge capacity, rate and cycle performance of high-nickel positive electrode material are difficult to be considered simultaneously, and has the comprehensive advantages of high discharge capacity, good rate performance and good cycle stability.

[0032] 2. In the preparation process of the positive electrode material of the present application, the flaky positive electrode material precursor, lithium source and VA group element modifier are mixed and sintered to obtain an intermediate product, and then the intermediate product is mixed with a compound composed of lithium, phosphorus and the element of the IVB group to obtain a core-shell positive electrode material. In the sintering process, the flaky morphology of the precursor and the synergistic effect of the modifier containing the VA group element are used to adjust the crystallization process of the primary particles of the positive electrode material, and the sintering temperature and sintering time are controlled, so that the morphology of the primary particles of the obtained positive electrode material is in a strip shape and arranged along the radial direction of the secondary microsphere of the positive electrode material. This composition and structure of the material are more conducive to the diffusion of lithium ions, which can improve the discharge specific capacity and rate performance of the material. The compound composed of lithium, phosphorus and the element of the IVB group is coated on the surface of the intermediate, and the synergistic effect between the components makes the material structure more stable and has better cycle stability.

[0033] 3、The positive electrode material provided by the application can be used in high-performance lithium batteries, and the discharge specific capacity at 1C rate can reach 199.9 mAh / g, and the capacity retention rate after 100 cycles at 1C rate can reach 91.0%. BRIEF DESCRIPTION OF DRAWINGS

[0034] Figure 1 is an SEM image of the positive electrode material prepared in Example 1 of the application;

[0035] Figure 2 is an SEM image of the cross section of the positive electrode material prepared in Example 1 of the application;

[0036] Figure 3 is the charge-discharge curve of the positive electrode material prepared in Example 1 of the application at 1C rate;

[0037] Figure 4 is the cycle stability result of the positive electrode material prepared in Example 1 of the application at 1C rate. DETAILED DESCRIPTION

[0038] The technical solutions of the application will be described in detail below.

[0039] The application provides a positive electrode material, which has a core-shell structure, the core layer is a secondary microsphere formed by aggregation of primary particles, the primary particles are in a strip shape, and the shell layer is a compound composed of lithium, phosphorus and a Group IVB element.

[0040] The positive electrode material provided by the application has a core layer with a mass of 100 parts and a shell layer with a mass of more than 0 parts and not higher than 5 parts in mass parts. As non-limiting examples, for example but not limited to 0.1 parts, 0.2 parts, 0.3 parts, 0.4 parts, 0.5 parts, 0.6 parts, 0.7 parts, 0.8 parts, 0.9 parts, 1 part, 1.5 parts, 2 parts, 2.5 parts, 3 parts, 3.5 parts, 4 parts, 4.5 parts, 5 parts and the like.

[0041] The positive electrode material provided by the application has a core layer with a mass of 100 parts and a shell layer with a mass of more than 0 parts and not higher than 5 parts in mass parts. As non-limiting examples, for example but not limited to 0.1 parts, 0.2 parts, 0.3 parts, 0.4 parts, 0.5 parts, 0.6 parts, 0.7 parts, 0.8 parts, 0.9 parts, 1 part, 1.5 parts, 2 parts, 2.5 parts, 3 parts, 3.5 parts, 4 parts, 4.5 parts, 5 parts and the like. a Ni x Co y M z N p O2, wherein 0.9≤a≤1.2, 0≤x≤1, 0≤y≤1, 0≤z≤1, 0<p≤0.1; preferably 0.6≤x≤1.00, 0≤y≤0.5, 0≤z≤0.5, 0<p≤0.05, further preferably 0.9≤x≤1.00, 0≤y≤0.5, 0≤z≤0.5, x, y and z are not 0 at the same time, preferably x, y and z are not 0 at the same time, and the values of a, x, y, z and p satisfy the principle of electrical neutrality.

[0042] In one embodiment of the present application, preferably, M is selected from Mn and / or Al. That is, preferably, the chemical formula is Li a Ni x Co y M z N p O2the compound is Li a Ni x Co y Mn z N p O2or Li a Ni x Co y Al z N p O2.

[0043] The positive electrode material provided by the present application has a core layer formed by accumulation of primary particles, and the primary particles are arranged along the radial direction of the secondary microspheres. The secondary microspheres have a medium particle size of 1.0-20.0 μm, preferably 5.0-12.0 μm.

[0044] The positive electrode material provided by the present application has primary particles in the shape of a long strip, and the primary particles have an aspect ratio of 1.05-20.0, preferably 1.50-10.00, and further preferably 1.50-8.00. The aspect ratio of the primary particles may, for example, but not limited to, 1.50, 1.55, 1.60, 1.65, 1.70, 1.75, 1.95, 2.20, 2.45, 2.70, 2.95, 3.20, 3.45, 3.70, 3.95, 4.20, 4.45, 4.70, 4.95, 5.20, 5.45, 5.70, 5.95, 6.20, 6.45, 6.70, 6.95, 7.20, 7.45, 7.70, 7.95, 8.00, and any value in the range formed by any two of these values.

[0045] The positive electrode material provided by the present application has a shell layer formed by a compound of lithium, phosphorus and a Group IVB element. The Group IVB element is selected from at least one of titanium, zirconium and hafnium. As a non-limiting example, the compound of lithium, phosphorus and a Group IVB element is at least one of lithium titanium phosphate, lithium zirconium phosphate and lithium hafnium phosphate.

[0046] In one preferred embodiment of the present application, the SEM image of the positive electrode material is shown in Figure 1 From Figure 1 it can be seen that the positive electrode material of the present application is a spherical secondary particle with a medium particle size of 10.8 μm, and the surface of the spherical particle is coated with a shell layer material. The SEM image of the cross section of the positive electrode material is shown in Figure 2 From Figure 2As can be seen, the primary particles present a strip shape, and the primary particles are arranged along the radial direction of the secondary microspheres, and the average aspect ratio of the primary particles is 5.43.

[0047] In the present application, the scanning electron microscope (SEM) is obtained by a scanning electron microscope of ZEISS Merlin model of ZEISS Company, Germany.

[0048] The inventors of the present application have made an in-depth study on the positive electrode material of lithium battery, and have creatively obtained the positive electrode material of lithium battery with the above composition and structural characteristics in the process of preparing the positive electrode material.

[0049] The second aspect of the present application provides a preparation method of the positive electrode material, comprising:

[0050] (1) mixing the positive electrode material precursor, the lithium source and the modifier containing the group VA element, sintering to obtain an intermediate product;

[0051] (2) mixing the intermediate product with a compound composed of lithium, phosphorus and group IVB element to obtain the positive electrode material.

[0052] In the present application, the chemical general formula of the positive electrode material precursor is Ni x Co y M z (OH)2, 0≤x≤1, 0≤y≤1, 0≤z≤1, preferably 0.6≤x≤1.00, 0≤y≤0.5, 0≤z≤0.5, preferably 0.9≤x≤1.00, 0≤y≤0.5, 0≤z≤0.5, the values of x, y and z are not 0 at the same time, and the values of x, y and z satisfy the principle of electrical neutrality.

[0053] As a non-limiting example, the typical chemical general formula of the precursor can be Ni 0.6 Co 0.2 Mn 0.2 (OH)2, Ni 0.8 Co 0.1 Mn 0.1 (OH)2, Ni 0.9 Co 0.05 Mn 0.05 (OH)2, Ni 0.95 Co 0.025 Mn 0.025 (OH)2, Ni 0.8 Co 0.15 Al 0.05(OH)2, etc. The morphology of the positive electrode material precursor is a microsphere formed by stacking of flaky particles, and the thickness of the flaky particles is 1-500 nm, preferably 1-200 nm.

[0054] In the present application, the lithium source can be in the form of a lithium salt, which is preferably at least one selected from the group consisting of lithium nitrate (LiNO3), lithium chloride (LiCl), lithium carbonate (Li2CO3), lithium hydroxide (LiOH), lithium hydroxide monohydrate (LiOH-H2O), lithium oxide (Li2O), lithium acetate (CH3COOLi), and lithium oxalate (Li2C2O4).

[0055] In the present application, the mixing of the positive electrode material precursor and the lithium source can be achieved by using a high-speed mixer, a ball mill, a V-type mixer, mechanical stirring, a plowshare mixer, a double-screw conical mixer, or the like.

[0056] In the present application, the molar ratio of the positive electrode material precursor to the lithium source (in terms of Li element) is 1:(0.90-1.20). As non-limiting examples, when the molar number of the precursor is 1, the molar number of the lithium source (in terms of Li element) can be 0.90, 0.95, 1.00, 1.05, 1.10, 1.15, 1.20, and any value within the range defined by any two of these values.

[0057] In the present application, the Group VA element-containing modifier is preferably at least one selected from the group consisting of Group VA element-containing nitrate, Group VA element-containing chloride, Group VA element-containing carbonate, Group VA element-containing hydroxide, Group VA element-containing oxide, Group VA element-containing acetate, and Group VA element-containing oxalate. As non-limiting examples, the Group VA element-containing modifier can be at least one selected from the group consisting of ammonium nitrate, ammonium chloride, antimony acetate, antimony oxide, bismuth oxalate, bismuth carbonate, phosphorus oxide, and the like.

[0058] In the present application, the molar ratio of the Group VA element-containing modifier (in terms of Group VA element) to the positive electrode material precursor is 0-0.10 and not 0. As non-limiting examples, when the molar number of the precursor is 1, the molar number of the modifier (in terms of Group VA element) can be 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, and any value within the range defined by any two of these values. Preferably, the molar ratio of the Group VA element-containing modifier (in terms of Group VA element) to the precursor is 0.001-0.05.

[0059] In the present application, the sintering is performed in an atmosphere furnace, and the sintering atmosphere can be at least one selected from the group consisting of air, oxygen, and an inert atmosphere such as nitrogen.

[0060] In the present application, the sintering is programmed temperature sintering, the sintering temperature is 580-900℃, such as 580℃, 600℃, 650℃, 700℃, 750℃, 800℃, 850℃, 900℃ and any range between any two values, more preferably, the sintering temperature is 600-850℃; the sintering time is 4-48h, such as 4h, 8h, 12h, 16h, 20h, 24h, 28h, 32h, 36h, 40h, 44h, 48h and any range between any two values, preferably, the sintering time is 8-24h, more preferably, the sintering time is 12-20h.

[0061] In the present application, the pre-sintering is carried out before the sintering, the pre-sintering temperature is 300-580℃, such as 300℃, 350℃, 400℃, 450℃, 500℃, 550℃, 580℃ and any range between any two values, preferably, the pre-sintering temperature is 450-550℃, more preferably, the pre-sintering temperature is 450-530℃; preferably, the pre-sintering time is 1-10h, such as 1h, 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h and any range between any two values, more preferably, the pre-sintering time is 4-8h.

[0062] In the present application, the heating rate of sintering is not particularly limited, preferably 0.5-10℃ / min, such as 0.5℃ / min, 1℃ / min, 2℃ / min, 3℃ / min, 5℃ / min, 10℃ / min and any value in the range between any two of these values.

[0063] In the present application, the mixing of the positive electrode material precursor, lithium source and the VA group element-containing modifier is not particularly limited, which can be realized by high-speed mixer, ball mill, V-type mixer, mechanical stirring, plough mixer, double-helix conical mixer and the like.

[0064] In the present application, the mass ratio of the compound composed of lithium, phosphorus and IVB element to the intermediate product is (0-0.05) and not 0. As a non-limiting example, when the mass fraction of the intermediate product is 1, the mass fraction of the compound composed of lithium, phosphorus and IVB element can be 0.001, 0.002, 0.003, 0.004, 0.005, 0.006, 0.007, 0.008, 0.009, 0.01, 0.015, 0.02, 0.0025, 0.03, 0.035, 0.04, 0.045, 0.05 and any value in the range between any two of these values, preferably, the mass ratio of the modifier to the intermediate product is (0.005-0.05):1.

[0065] In the present application, the mixing of the compound composed of lithium, phosphorus and IVB element with the intermediate product is not particularly limited, and can be achieved by using a high-speed mixer, a ball mill, a V-type mixer, mechanical stirring, a plowshare mixer, a double helix conical mixer, etc.

[0066] The third aspect of the present application provides a lithium battery cathode material prepared by the preparation method described above.

[0067] The properties of the lithium battery cathode material have been described in detail in the first aspect, and will not be repeated here.

[0068] The fourth aspect of the present application provides a lithium battery comprising the cathode material described above and the application thereof. The lithium battery has: a cathode comprising the cathode material described above; an anode; an electrolyte; and a separator. The cathode and the anode can be prepared by coating and drying a composite for forming a cathode active material layer and a composite for forming an anode active material layer on respective current collectors.

[0069] The cathode composite can be prepared by a cathode active material, a conductive agent, a binder and a solvent.

[0070] The conductive agent is not particularly limited in the present application, as long as it has conductivity and remains stable in the charge and discharge range. The conductive agent can be at least one of acetylene black, ketjen black, artificial graphite, natural graphite, carbon tube, graphene, superconducting carbon, carbon nanofiber, carbon dot, aluminum powder, nickel powder, titanium oxide, and conductive polymer.

[0071] The binder provides the adhesion of the cathode active material, the conductive agent and the current collector. The binder can be at least one of polyvinylidene fluoride (PVDF), polyvinyl alcohol (PVA), sodium carboxymethyl cellulose (CMC), styrene butadiene rubber (SBR), water-based acrylic resin, polytetrafluoroethylene (PTFE), polyvinyl butyral (PVB), ethylene-vinyl acetate (EVA), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoroethylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoro-propylene copolymer and fluorine-containing acrylic resin.

[0072] The current collector is not particularly limited in the present application, as long as it has suitable conductivity. The current collector can be aluminum, nickel, copper, titanium, silver, stainless steel and carbon material. The current collector can be processed into various forms such as foil, sheet, film, mesh, hole, non-woven fabric, etc.

[0073] The solvent can be N-methyl pyrrolidone.

[0074] The anode composite can be prepared by an anode active material, a conductive agent, a binder and a solvent.

[0075] The negative active material is not particularly limited, and can be selected according to actual needs. The negative active material can be at least one of artificial graphite, natural graphite, soft carbon, hard carbon, mesocarbon microbeads (MCMB), carbon fiber, lithium metal, silicon, silicon oxide, lithium metal alloy, lithium titanate.

[0076] The conductive agent and the binder of the negative electrode are not particularly limited, and the same type and content as used in the preparation of the positive electrode can be used. The current collector of the negative electrode can also be aluminum, nickel, copper, titanium, silver, stainless steel, and carbon material. The current collector can also be processed into various forms such as foils, sheets, films, nets, holes, non-woven fabrics, etc.

[0077] The electrolyte is a liquid electrolyte, and the liquid electrolyte contains a lithium salt and a solvent, wherein the lithium salt and the solvent are not particularly limited.

[0078] The solvent can be at least one of non-aqueous solvents such as ethylene carbonate (EC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), propylene carbonate (PC), ethyl propyl carbonate (EPC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), methyl formate (MF), ethyl formate (Eft), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), propyl butyrate (BP).

[0079] The lithium salt can be at least one of LiPF6 (lithium hexafluorophosphate), LiBF4 (lithium tetrafluoroborate), LiClO4 (lithium perchlorate), LiAsF6 (lithium hexafluoroarsenate), LiFSI (lithium bisfluorosulfonylimide), LiTFSI (lithium bis-trifluoromethanesulfonylimide), LiTFS (lithium trifluoromethanesulfonate), LiDFOB (lithium difluoro(oxalato)borate), LiBOB (lithium bis(oxalato)borate), LiPO2F2 (lithium difluorophosphate), LiDFOP (lithium difluoro(oxalato)phosphate), LiTFOP (lithium tetrafluoro(oxalato)borate).

[0080] In order to improve the performance of the lithium battery, an additive can also be selectively added to the electrolyte, such as at least one of vinylene carbonate (VC), fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), tris(trimethylsilyl)phosphate (TMSP), sulfonate cyclic quaternary ammonium salt, ethylene sulfite (DTO), dimethyl sulfite (DMS), 1-propene-1,3-sulfonic acid lactone (PST), 4-propyl ethylene sulfite (PEGLST), diethyl sulfite (DES), adiponitrile (ADN), succinonitrile (SN), 1,3-propane sulfonolactone (1,3-PS), vinyl sulfite (DTD), 4-methyl ethylene sulfite (PCS), etc.

[0081] A separator is disposed between the positive and negative electrodes to function as a separator between the positive and negative electrodes. The separator can be a polyolefin such as polyethylene, polypropylene, a composite of polyethylene and polypropylene, a sheet formed of glass fibers, a nonwoven fabric, or the like. When a solid electrolyte is used, the solid electrolyte can also be used as the separator.

[0082] Next, a method for preparing the lithium battery described above will be described. The main steps include: mixing the positive electrode material, the conductive agent, the binder, and the solvent uniformly, coating the mixture on at least one surface of the positive electrode current collector, drying, rolling, and slicing to obtain the positive electrode; mixing the negative electrode material, the conductive agent, the binder, and the solvent uniformly, coating the mixture on at least one surface of the negative electrode current collector, drying, rolling, and slicing to obtain the negative electrode; assembling the positive electrode sheet, the separator, and the negative electrode sheet into a stacked or wound cell, placing the cell in a housing, injecting the electrolyte, and then packaging to obtain the lithium battery.

[0083] In the positive or negative electrode sheet described above, the amounts of the positive or negative electrode material, the conductive agent, and the binder are not specifically limited. For example, the mass content of the lithium battery positive or negative electrode material can be 50%-99%, the mass content of the conductive agent can be 0.5%-25%, and the mass content of the binder can be 0.5%-25%, based on the total amount of the positive or negative electrode material.

[0084] For the same purpose, the mass ratio of the lithium battery positive electrode material, the conductive agent, and the binder in the embodiment of the present application is 90:5:5, the conductive agent is acetylene black, the binder is polyvinylidene fluoride (PVDF), the negative electrode in the coin-type half cell is made of metal lithium, the separator is made of Celllgard 2400 polypropylene separator from the United States, the electrolyte is a liquid electrolyte, the solvent is a mixed solvent of ethylene carbonate (EC) and methyl ethyl carbonate (EMC) in a volume ratio of 3:7, and the solute is lithium hexafluorophosphate LiPF6 with a molar concentration of 1 mol / L.

[0085] The lithium battery in the embodiment of the present application is assembled in an inert atmosphere glove box with a water content and an oxygen content of less than 0.1 ppm. The battery model is not specifically limited, and for the same purpose, the coin-type battery model used in the embodiment of the present application is model 2025, and the electrochemical test conditions are: a temperature of 25°C; and a voltage range of 2.8-4.3 V.

[0086] The present application will be described in detail below through examples.

[0087]

Example 1

[0088] This example is used to illustrate the preparation and evaluation method of the positive electrode material described in the present application.

[0089] (1) Preparation of the positive electrode material

[0090] A precursor with a chemical composition of Ni 0.94 Co 0.03 Mn 0.03 (OH)2, the primary particles of the precursor are flaky with an average thickness of 45 nm. Lithium source LiOH·H2O and Bi2O3 are added to make the molar ratio of Li to the precursor 1.02:1 and the molar ratio of Bi to the precursor 0.02:1. The precursor, the lithium source and Bi2O3 are mixed uniformly and then loaded into a crucible for step sintering. The first step is to increase the temperature from room temperature to 450℃ at a rate of 5℃ / min and keep the temperature for 6h. The second step is to increase the temperature from 450℃ to 750℃ at a rate of 5℃ / min and keep the temperature for 12h. Then the intermediate product is obtained after natural cooling.

[0091] Zirconium lithium phosphate is added to the intermediate product, and the mass ratio of zirconium lithium phosphate to the intermediate product is 3:100. The intermediate product and zirconium lithium phosphate are mixed uniformly to obtain the positive electrode material.

[0092] (2) Evaluation of the positive electrode material

[0093] The SEM image of the positive electrode material is shown in Figure 1 From the image, it can be seen that the positive electrode material with good sphericity can be obtained by using the preparation method provided by the present application. The positive electrode material is a secondary microsphere formed by the accumulation of primary particles. The medium particle size of the secondary microsphere is 10.8μm. The surface of the secondary microsphere obviously contains a coating material. Figure 1 The cross-sectional image of the positive electrode material obtained after focused ion beam cutting is shown in Figure 2 The primary particles of the positive electrode material are long strips, and the primary particles are arranged and distributed along the radial direction of the secondary microsphere. The average aspect ratio of the primary particles is 5.43.

[0094] The above-mentioned positive electrode material, acetylene black and a polyvinylidene fluoride solution with a mass fraction of 10% are mixed uniformly according to a mass ratio of 90:5:5 of the positive electrode material:acetylene black:polyvinylidene fluoride. Then the mixture is coated on an aluminum foil, the solvent is dried, and the slice is obtained to obtain a positive electrode sheet. A lithium sheet is used as a counter electrode, and the above-mentioned positive electrode sheet is assembled into a button lithium battery in a glove box. The button lithium battery has a charge-discharge voltage range of 2.8-4.3V. The discharge specific capacity at 1C rate is 199.9mAh / g, the discharge capacity ratio at 10C rate to 0.1C rate is 75.6%, and the capacity retention rate at 1C rate after 100 cycles is 91.0%.

[0095]

Example 2

[0096] This example is used to illustrate the preparation and evaluation method of the positive electrode material according to the present application.

[0097] (1) Preparation of the positive electrode material

[0098] A precursor with a chemical composition of Ni 0.94 Co 0.03 Mn 0.03 (OH)2, the primary particles of the precursor are flaky with an average thickness of 45 nm, a lithium source LiOH-H2O and Sb2O3 are added to make the molar ratio of Li: precursor 1.05:1 and the molar ratio of Sb: precursor 0.05:1, the precursor, the lithium source and Sb2O3 are mixed uniformly and then loaded into a crucible for step sintering, the first step: from room temperature to 500℃ at a rate of 10℃ / min, holding for 6h, the second step: from 500℃ to 800℃ at a rate of 10℃ / min, holding for 16h, and then naturally cooling to obtain an intermediate product.

[0099] Titanium lithium phosphate is added to the intermediate product, the molar ratio of titanium lithium phosphate to the intermediate product is 4:100, the intermediate product and titanium lithium phosphate are mixed uniformly to obtain the positive electrode material.

[0100] (2) Evaluation of the positive electrode material

[0101] The SEM image of the positive electrode material is similar to Figure 1 The cross-sectional image of the positive electrode material is similar to Figure 2 The primary particles of the positive electrode material are long strip-shaped and the primary particles are arranged and distributed along the radial direction of the secondary microspheres, the average aspect ratio of the primary particles is 4.32. The median size of the secondary microspheres is 9.6μm.

[0102] The lithium battery is prepared according to the method described in Example 1.

[0103] The discharge specific capacity of the button lithium battery is 196.4mAh / g at a 1C rate, the discharge capacity ratio at 10C rate to 0.1C rate is 74.5%, and the capacity retention rate is 90.6% after 100 cycles at a 1C rate.

[0104]

Example 3

[0105] (1) Preparation of the positive electrode material

[0106] A precursor with a chemical composition of Ni 0.94 Co 0.03 Mn 0.03The precursor of (OH)2 is in the form of flakes with an average thickness of 45 nm. Lithium source LiOH·H2O and P2O5 are added to make the molar ratio of Li to precursor 1.08:1 and the molar ratio of P to precursor 0.03:1. The precursor, lithium source and P2O5 are mixed evenly and then placed in a crucible for stepwise sintering. The first step is to heat from room temperature to 530℃ at 5℃ / min and hold for 4 h. The second step is to heat from 530℃ to 730℃ at 10℃ / min and hold for 18 h. After natural cooling, the intermediate product is obtained.

[0107] Lithium hafnium phosphate is added to the intermediate product at a molar ratio of 1:100. After the intermediate product and lithium hafnium phosphate are mixed evenly, the cathode material is obtained.

[0108] (2) Evaluation of cathode materials

[0109] SEM images of cathode materials and Figure 1 Similarly, the cross-sectional view of the cathode material is the same as... Figure 2 Similar. The primary particles of this cathode material are elongated and arranged radially along the secondary microspheres, with an average aspect ratio of 2.95. The secondary microspheres have a medium particle size of 10.3 μm.

[0110] Lithium batteries were prepared according to the method described in Example 1.

[0111] The charge / discharge voltage range of the button-type lithium battery is 2.8-4.3V. The specific capacity at 1C rate is 195.4mAh / g, the capacity ratio at 10C rate to 0.1C rate is 73.7%, and the capacity retention rate after 100 cycles at 1C rate is 89.8%.

[0112]

Example 4

[0113] (1) Preparation of cathode materials

[0114] Take the chemical composition as Ni 0.94 Co 0.03 Al 0.03 The precursor of (OH)2 is in the form of flakes with an average thickness of 60 nm. Lithium source LiOH·H2O and P2O5 are added to make the molar ratio of Li to precursor 1.08:1 and the molar ratio of P to precursor 0.07:1. The precursor, lithium source and P2O5 are mixed evenly and then placed in a crucible for stepwise sintering. The first step is to heat from room temperature to 550℃ at 5℃ / min and hold for 4 h. The second step is to heat from 550℃ to 860℃ at 10℃ / min and hold for 9 h. After natural cooling, the intermediate product is obtained.

[0115] Lithium hafnium phosphate is added to the intermediate product at a molar ratio of 1:100. After the intermediate product and lithium hafnium phosphate are mixed evenly, the cathode material is obtained.

[0116] (2) Evaluation of cathode materials

[0117] SEM images of cathode materials and Figure 1 Similarly, the cross-sectional view of the cathode material is the same as... Figure 2 Similar. The primary particles of this cathode material are elongated and arranged radially along the secondary microspheres, with an average aspect ratio of 1.88. The secondary microspheres have a medium particle size of 10.2 μm.

[0118] Lithium batteries were prepared according to the method described in Example 1.

[0119] The charge / discharge voltage range of the button-type lithium battery is 2.8-4.3V. The specific capacity at 1C rate is 192.4mAh / g, the capacity ratio at 10C rate to 0.1C rate is 69.3%, and the capacity retention rate after 100 cycles at 1C rate is 86.1%.

[0120] Comparative Example 1

[0121] (1) Preparation of cathode materials

[0122] Take the chemical composition as Ni 0.94 Co 0.03 Mn 0.03 The precursor of (OH)2 is in the form of flakes with an average thickness of 45 nm. LiOH·H2O is added to make the molar ratio of Li to precursor 1.02:1. The precursor and lithium source are mixed evenly and then placed in a crucible for stepwise sintering. The first step is to heat the material from room temperature to 450°C at 5°C / min and hold it for 6 h. The second step is to heat the material from 450°C to 750°C at 5°C / min and hold it for 12 h. After natural cooling, the cathode material is obtained.

[0123] (2) Evaluation of cathode materials

[0124] The cross-sectional image of the cathode material shows that the primary particles are short and coarse, with no specific arrangement and exhibiting a disordered stacking state. The average aspect ratio of the primary particles is 1.19. The medium particle size of the secondary microspheres is 9.8 μm.

[0125] Lithium batteries were prepared according to the method described in Example 1.

[0126] The button lithium battery has a charge-discharge voltage range of 2.8-4.3V. The specific discharge capacity at 1C rate is 188.4mAh / g, the discharge capacity ratio at 10C rate to 0.1C rate is 21.2%, and the capacity retention rate after 100 cycles at 1C rate is 75%.

[0127] Comparative Example 2

[0128] (1) Preparation of the positive electrode material

[0129] A precursor with a chemical composition of Ni 0.94 Co 0.03 Mn 0.03 (OH)2was taken, the precursor primary particles were in a sheet shape with an average thickness of 45nm, a lithium source LiOH·H2O was added to make the molar ratio of Li: precursor 1.02:1, the precursor and the lithium source were mixed uniformly and then loaded into a crucible for step sintering, the first step: from room temperature to 450℃ at a rate of 5℃ / min, and kept for 6h, the second step: from 450℃ to 750℃ at a rate of 5℃ / min, and kept for 12h, and then naturally cooled to obtain an intermediate product.

[0130] Zirconium lithium phosphate was added to the intermediate product, the mass ratio of zirconium lithium phosphate to the intermediate product was 3:100, the intermediate product and the zirconium lithium phosphate were mixed uniformly to obtain the positive electrode material.

[0131] (2) Evaluation of the positive electrode material

[0132] The cross-sectional view of the positive electrode material showed that the primary particles of the positive electrode material were short and thick particles, the primary particles had no specific arrangement and were in a disordered stacking state, and the average length-width ratio of the primary particles was 1.21. The median size of the secondary microspheres was 10.5μm.

[0133] The lithium battery was prepared according to the method described in Example 1.

[0134] The button lithium battery has a charge-discharge voltage range of 2.8-4.3V. The specific discharge capacity at 1C rate is 187.5mAh / g, the discharge capacity ratio at 10C rate to 0.1C rate is 36.6%, and the capacity retention rate after 100 cycles at 1C rate is 77.6%.

[0135] Comparative Example 3

[0136] (1) Preparation of the positive electrode material

[0137] Compared with Example 1, the difference was that a precursor with a chemical composition of Ni 0.94 Co 0.03 Mn 0.03 (OH)2was taken, and the precursor morphology was that the primary particles were spindle agglomerated into microspheres.

[0138] (2) Evaluation of the positive electrode material

[0139] The cross-sectional view of the positive electrode material shows that the primary particles of the positive electrode material are short stubby particles, the primary particles have no specific arrangement, and present a state of disordered stacking, and the average aspect ratio of the primary particles is 1.26. The median size of the secondary microspheres is 10.3 μm.

[0140] A lithium battery was prepared according to the method described in Example 1.

[0141] The charge-discharge voltage range of the button lithium battery is 2.8-4.3 V. The specific discharge capacity at 1C rate is 188.9 mAh / g, the ratio of the discharge capacity at 10C rate to that at 0.1C rate is 38.7%, and the capacity retention rate after 100 cycles at 1C rate is 78.1%.

[0142] The above describes the specific embodiments of the present application in detail, but the present application is not limited thereto. Within the technical concept of the present application, various simple modifications can be made to the technical solutions of the present application, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be considered as the disclosed content of the present application and fall within the protection scope of the present application.

Claims

1. A positive electrode material, having a core-shell structure, wherein a core layer is a secondary microsphere formed by aggregation of primary particles, the primary particles are in a strip shape, and a shell layer is a compound composed of lithium, phosphorus and a group IVB element.

2. The positive electrode material of claim 1, wherein, The positive electrode material has a core layer with a mass of 100 parts and a shell layer with a mass of greater than 0 parts and not higher than 5 parts.

3. The positive electrode material of claim 1, wherein, The compound composed of lithium, phosphorus and a group IVB element has a chemical formula of LiM 2 (PO 4 ) 3, wherein M is a group IVB element; preferably, the compound is at least one selected from lithium zirconium phosphate, lithium titanium phosphate and lithium hafnium phosphate.

4. The positive electrode material of claim 1, wherein, The positive electrode material has a core layer with a chemical formula of Li a Ni x Co y M z N p O2, wherein 0.9≤a≤1.2, 0≤x≤1, 0≤y≤1, 0≤z≤1, 0<p≤0.1, preferably 0.6≤x≤1.00, 0≤y≤0.5, 0≤z≤0.5, 0<p≤0.05, x, y and z are not simultaneously 0, preferably y and z are not simultaneously 0, and the values of a, x, y, z and p satisfy the principle of electrical neutrality, M is selected from at least one of group VIIB or group IIIA elements, and N is selected from at least one of group VA elements; preferably, the group VIIB element is preferably Mn, the group IIIA element is preferably Al, and the group VA element is selected from at least one of N, P, Sb and Bi.

5. The cathode material of claim 1, wherein, The primary particles are arranged along a radial direction of the secondary microsphere, and the secondary microsphere has a medium particle size of 1.0-20.0 μm.

6. The cathode material of claim 1, wherein, The primary particles have an aspect ratio of 1.05-20.00, preferably 1.50-10.00, and further preferably 1.50-8.

00. 7.A method for preparing the positive electrode material according to any one of claims 1-6, comprising: (1) mixing a positive electrode material precursor, a lithium source and a group VA element-containing modifier, and sintering to obtain an intermediate product; (2) mixing the intermediate product prepared in step (1) with a compound composed of lithium, phosphorus and a group IVB element to obtain the positive electrode material.

8. The preparation method according to claim 7, characterized in that, The chemical general formula of the positive electrode material precursor is Ni x Co y M z (OH)2, 0≤x≤1, 0≤y≤1, 0≤z≤1, preferably 0.6≤x≤1.00, 0≤y≤0.5, 0≤z≤0.5, the values of x, y and z are not 0 at the same time, and the values of x, y and z satisfy the principle of electrical neutrality.

9. The preparation method according to claim 7, characterized in that, The lithium source is at least one selected from lithium nitrate, lithium chloride, lithium carbonate, lithium hydroxide, lithium hydroxide monohydrate, lithium oxide, lithium acetate and lithium oxalate; and / or, the group VA element-containing modifier is at least one selected from group VA element-containing nitrate, chloride, carbonate, hydroxide, oxide, acetate and oxalate.

10. The preparation method according to claim 7, characterized in that, The molar ratio of the positive electrode material precursor to the lithium source in terms of Li element is 1:(0.90-1.20); and / or, the molar ratio of the group VA element-containing modifier to the positive electrode material precursor in terms of group VA element is greater than 0 to 0.1, preferably (0.001-0.05):1; and / or, the mass ratio of the compound composed of lithium, phosphorus and a group IVB element to the intermediate product is greater than 0 to 0.05, preferably (0.001-0.05):

1.

11. The preparation method according to claim 7, characterized in that, The sintering temperature is 580-900℃, preferably 600-850℃, and the sintering time is 4-48h, preferably 8-24h, and further preferably 12-20h.

12. The method of claim 7, wherein, The positive electrode material precursor has a morphology of microspheres formed by stacking of flakes; the average thickness of the flakes is 1-500nm, preferably 1-200nm. 13.A lithium battery comprising the positive electrode material according to any one of claims 1-6, a negative electrode, a separator and an electrolyte.

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