Positive electrode material, preparation method thereof and application of positive electrode material in lithium battery

Abstract

The invention discloses a positive electrode material, a preparation method thereof and application of the positive electrode material in a lithium battery. The positive electrode material comprises a matrix and a modification additive, the matrix is a secondary microsphere formed by aggregation of primary particles, and the primary particles are strip-shaped; the general chemical formula of the modification auxiliary agent is LiAeB1-ePO4, and 0 lt; lt, lt; 1, A is selected from at least one of VIIB group elements, and B is selected from at least one of VIII group elements. By adopting the positive electrode material disclosed by the invention, the oxygen release temperature of the positive electrode material can be remarkably increased, the heat release of reaction with electrolyte is greatly reduced, and the positive electrode material can be used in a high-safety lithium battery.

Description

Technical Field

[0001] The present invention belongs to the field of lithium batteries, and particularly relates to a cathode material, a preparation method thereof, and an application thereof in lithium batteries. Background Art

[0003] Compared with fuel vehicles, the driving range of new energy vehicles is relatively short, which affects the actual use experience of new energy vehicles. Therefore, researchers have been constantly working on developing high-energy-density power batteries to improve the driving range of new energy vehicles. The driving range of power batteries is mainly determined by the cathode materials used. Currently, commercially available cathode materials mainly include LiFePO4 with an olivine structure, LiMn2O4 with a spinel structure, LiCoO2 with a layered structure, and ternary cathode materials with a layered structure, etc. Among them, the ternary cathode materials with a layered structure have a high theoretical specific capacity and are preferred cathode materials for high-energy-density power batteries.

[0004] However, with the increase in the specific capacity of ternary cathode materials, the activity of the materials becomes higher and the safety becomes worse. Specifically, the oxygen release temperature of the materials becomes lower, and the heat release amount when reacting with the electrolyte becomes larger. The frequent safety accidents of new energy vehicle spontaneous combustion have severely restricted the large-scale application of high-energy-density cathode materials, and it is urgent to solve the problem of poor safety of ternary cathode materials. Summary of the Invention

[0005] Aiming at the problem of poor safety of ternary cathode materials in the prior art, the present invention provides a cathode material, a preparation method thereof, and an application thereof in lithium batteries. The cathode material of the present invention has excellent safety performance when applied in lithium batteries, specifically manifested as a high oxygen release temperature of the material and a low heat release amount when reacting with the electrolyte.

[0006] The first aspect of the present invention provides a cathode material, which includes a matrix and a modification additive. The matrix is a secondary microsphere formed by the aggregation of primary particles, and the primary particles are strip-shaped; the chemical general formula of the modification additive is LiA e B 1-e PO4, where 0 < e < 1, A is selected from at least one of the elements in Group VIIB, and B is selected from at least one of the elements in Group VIII.

[0007] In the above technical solution, the chemical general formula of the matrix is Li a Ni x Co y M z N pO2, where 0.9 ≤ a ≤ 1.2, 0 ≤ x ≤ 1, 0 ≤ y ≤ 1, 0 ≤ z ≤ 1, 0 < p ≤ 0.1. Preferably, 0.5 ≤ x ≤ 0.99, 0 ≤ y ≤ 0.5, 0 ≤ z ≤ 0.5, 0 < p ≤ 0.05. The values of x, y, and z are not all 0 at the same time, and the values of a, x, y, z, and p satisfy the principle of electroneutrality. Preferably, M is selected from at least one of the elements in Group VIIB or Group IIIA, and N is selected from at least one of the elements in Group VA.

[0008] In the above technical solution, the element in Group VIIB is preferably Mn, the element in Group IIIA is preferably Al, and the element in Group VA is selected from at least one of N, P, Sb, and Bi.

[0009] In the above technical solution, M is preferably at least one of Mn and Al, and N is preferably at least one of P, Sb, and Bi.

[0010] In the above technical solution, the Group VIIB element is preferably Mn, and the Group VIII element is preferably Fe.

[0011] In the above technical solution, A is preferably Mn, and B is preferably Fe.

[0012] In the above technical solution, for the positive electrode material, by mass parts:

[0013] Matrix: 100 parts;

[0014] The modifying assistant is more than 0 parts and less than or equal to 30 parts.

[0015] In the above technical solution, the positive electrode material has a core-shell structure, the core layer is the matrix, and the shell layer is the modifying assistant.

[0016] In the above technical solution, the core-shell structure is that the shell layer coats the core layer in a discontinuous island shape. Discontinuous island coating means that the modifying assistant does not form a dense and continuous coating layer on the surface of the positive electrode material (matrix), and the modifying assistant can coat the surface of the positive electrode material in the form of single particles or agglomerates of a certain number.

[0017] In the above technical solution, the matrix is a secondary microsphere formed by the aggregation of primary particles, where the primary particles are arranged along the radial direction of the secondary microsphere, and the median size of the secondary microsphere is 1.0 - 20.0 μm. The median size represents the particle size corresponding to when the cumulative particle size distribution percentage of the secondary microsphere reaches 50%.

[0018] In the above technical solution, the aspect ratio of the primary particle is 1.05 - 20.00, preferably 1.50 - 10.00, and more preferably 4.00 - 8.00.

[0019] A second aspect of the present invention provides a method for preparing the above-mentioned cathode material, comprising:

[0020] (1) Mix the cathode material precursor, lithium source and group VA element source, and sinter to obtain the matrix;

[0021] (2) The matrix obtained in step (1) is mixed with the modified additive to obtain the cathode material.

[0022] In the above technical solution, the general chemical formula of the cathode material precursor is Ni. x Co y M z (OH)2, 0≤x≤1, 0≤y≤1, 0≤z≤1, preferably 0.5≤x≤0.99, 0≤y≤0.5, 0≤z≤0.5, where x, y and z are not simultaneously 0, and the values ​​of x, y and z satisfy the principle of electroneutrality.

[0023] In the above technical solution, the morphology of the cathode material precursor is microspheres formed by the stacking of sheets. The average thickness of the sheets is 1-500 nm, preferably 1-200 nm.

[0024] In the above technical solution, the lithium source is preferably selected from 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).

[0025] In the above technical solution, the molar ratio of the cathode material precursor to the lithium source (calculated as Li element) is 1:(0.90-1.20).

[0026] In the above technical solution, the Group VA element source is preferably selected from at least one of the Group VA elements, including nitrates, chlorides, carbonates, hydroxides, oxides, acetates, and oxalates.

[0027] In the above technical solution, the molar ratio of the cathode material precursor to the Group VA element source (based on the Group VA element) is 1:(0-0.1) and not 0. Preferably, the molar ratio of the cathode material precursor to the Group VA element source (based on the Group VA element) is 1:(0.001-0.05).

[0028] In the above technical solution, the sintering is programmed temperature sintering, the heating rate is preferably 0.5-10℃ / min, the sintering temperature is 680-1000℃, preferably 720-900℃, and the sintering time is 4-48h, preferably 8-24h, and more preferably 12-20h.

[0029] In the above technical solution, pre-sintering is performed before sintering. Pre-sintering is programmed temperature rise sintering, with a preferred heating rate of 0.5-10℃ / min. The pre-sintering temperature is 300-650℃, preferably 450-550℃, and more preferably 450-530℃. The pre-sintering time is 1-10h, preferably 4-8h.

[0030] In the above technical solution, the mass ratio of the matrix to the modifying agent is 1:(0-0.30) and not 0. Preferably, the mass ratio of the matrix to the modifying agent is 1:(0.01-0.30).

[0031] The third aspect of this invention provides the application of the above-mentioned cathode material in lithium batteries.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] 1. The cathode material of this invention comprises a matrix and a modifying agent. The matrix is ​​formed by the aggregation of primary particles arranged radially along secondary microspheres. The primary particles are elongated strips with an aspect ratio of 1.05-20.0. Simultaneously, the matrix surface is coated with a non-continuous island-like structure formed by a compound composed of lithium, phosphorus, Group VIIB elements, and Group VIII elements as a modifying agent. The cathode material of this invention exhibits good safety performance, a higher oxygen release temperature, and lower heat release during reaction with the electrolyte.

[0034] 2. The inventors discovered that by first mixing a sheet-like cathode material precursor, a lithium source, and a Group VA element source, and then sintering the resulting matrix, the crystallization process of the primary cathode material particles can be regulated during sintering through the synergistic effect of the sheet-like morphology of the precursor and the Group VA element source, as well as by controlling the sintering temperature and time. The resulting primary cathode material particles exhibit an elongated shape and are arranged radially along the secondary microspheres of the cathode material. Then, a compound composed of lithium, phosphorus, Group VIIB elements, and Group VIII elements is coated onto the surface of the matrix to form a discontinuous island-like coating layer. The elongated primary particle structure in the cathode material of this invention exhibits good stability, and combined with the discontinuous island-like coating layer, it can significantly improve the safety of the material.

[0035] 3. The cathode material provided by this invention can be used in high-safety lithium batteries. The secondary oxygen release temperature of the cathode material can reach 238.2℃, and the total heat release from the reaction with the electrolyte can be reduced to 898.2J / g. Attached Figure Description

[0036] Figure 1 This is a SEM image of the positive electrode material prepared in Example 1 of this invention;

[0037] Figure 2 This is a SEM image of a cross-section of the positive electrode material obtained in Example 1 of this invention;

[0038] Figure 3 This is the exothermic curve of the positive electrode material prepared in Example 1 of the present invention and Comparative Example 1 when reacting with the electrolyte in the charged state. Detailed implementation manners

[0039] The technical solution of the present invention will be described in detail below.

[0040] The first aspect of the present invention provides a positive electrode material, which includes a matrix and a modification additive. The matrix includes Li a Ni x Co y M z N p O2, M is selected from at least one of the elements in Group VIIB or Group IIIA, N is selected from at least one of the elements in Group VA, and the chemical general formula of the modification additive is LiA e B 1-e PO4 (0 < e < 1), A is selected from at least one of the elements in Group VIIB, and B is selected from at least one of the elements in Group VIII.

[0041] For the positive electrode material provided by the present invention, the chemical general formula of the matrix is Li a Ni x Co y M z N p O2, where 0.9 ≤ a ≤ 1.2, 0 ≤ x ≤ 1, 0 ≤ y ≤ 1, 0 ≤ z ≤ 1, 0 < p ≤ 0.1, preferably 0.5 ≤ x ≤ 0.99, 0 ≤ y ≤ 0.5, 0 ≤ z ≤ 0.5, 0 < p ≤ 0.05. The values of x, y, and z are not all 0 at the same time. Preferably, the values of x, y, and z are all not 0, and the values of a, x, y, z, and p satisfy the principle of electrical neutrality.

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

[0043] In one embodiment of the present invention, preferably, A is Mn and B is Fe. That is, preferably, the modification additive is LiMn e Fe 1-e PO4 (0 < e < 1).

[0044] The lithium battery cathode material provided by this invention, in parts by mass:

[0045] The matrix is ​​100 parts;

[0046] The modifying agent is greater than 0 parts and less than 30 parts. As a non-limiting example, such as, but not limited to, 1 part, 2 parts, 3 parts, 4 parts, 5 parts, 6 parts, 7 parts, 8 parts, 9 parts, 10 parts, 11 parts, 12 parts, 13 parts, 14 parts, 15 parts, 20 parts, 25 parts, 30 parts, and any value within the range formed by any two of these values.

[0047] The cathode material provided by this invention has a core-shell structure, with the core layer serving as the matrix and the shell layer as a modifying agent. The modifying agent forms a discontinuous island-like coating layer on the surface of the matrix.

[0048] The cathode material provided by the present invention has a matrix of secondary microspheres formed by the aggregation of primary particles. The secondary microspheres have a medium particle size of 1.0-20.0 μm, and the primary particles are arranged along the radial direction of the secondary microspheres.

[0049] The positive electrode material provided by this invention has primary particles in the form of elongated strips. The aspect ratio of the primary particles is 1.05-20.00, preferably 1.50-10.00, and more preferably 1.50-8.00. As non-limiting examples, the aspect ratios of the primary particles are 1.50, 1.55, 1.60, 1.65, 1.70, 1.75, 1.95, 2.20, 2.45, and 2.70. 2.95, 3.20, 3.45, 3.70, 3.95, 4.00, 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 within the range formed by any two of these values.

[0050] In a preferred embodiment of the present invention, the SEM image of the positive electrode material is as follows: Figure 1 As shown. From Figure 1 As can be seen from the image, the cathode material of this invention consists of spherical secondary particles with a medium particle size of 10.8 μm. The surface of the spherical particles contains discontinuous island-shaped coating modifiers. A SEM image of the cross-section of the cathode material is shown below. Figure 2 As shown. From Figure 2 As can be seen, the primary particles are elongated and arranged along the radial direction of the secondary microspheres.

[0051] In this invention, the scanning electron microscope (SEM) images were obtained using a ZEISS Merlin model scanning electron microscope from the German company ZEISS.

[0052] Through in-depth research on lithium battery cathode materials, the inventors of this invention have creatively obtained lithium battery cathode materials with the above-mentioned composition and structural characteristics during the preparation of cathode materials. Cathode materials with this characteristic composition and structure have higher oxygen release temperature and lower heat release in the side reaction with electrolyte, and can be used in high-safety lithium batteries.

[0053] A second aspect of the present invention provides a method for preparing the above-mentioned cathode material, comprising:

[0054] (1) Mix the cathode material precursor, lithium source and group VA element source, and sinter to obtain the matrix;

[0055] (2) The matrix is ​​mixed with the modified additive to obtain the cathode material.

[0056] In this invention, the general chemical formula of the cathode material precursor is Ni. x Co y M z (OH)₂, 0≤x≤1, 0≤y≤1, 0≤z≤1, preferably 0.5≤x≤0.99, 0≤y≤0.5, 0≤z≤0.5, where x, y, and z are not simultaneously 0, and the values ​​of x, y, and z satisfy the electroneutrality principle. As a non-limiting example, a typical chemical composition of the precursor could be Ni. 0.5 Co 0.2 Mn 0.3 (OH)2, 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 cathode material precursor is a microsphere formed by the stacking of sheets, the thickness of which is 1-500 nm, preferably 1-200 nm. As a non-limiting example, the thickness of the sheets is 1 nm, 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, 120 nm, 140 nm, 160 nm, 180 nm, 200 nm, and any value within the range formed by any two of these values.

[0057] In this invention, the lithium source may exist in the form of a lithium salt, which is preferably selected from 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).

[0058] In this invention, the mixing of the cathode material precursor and the lithium source can be achieved by means of a high-speed mixer, ball mill, V-type mixer, mechanical stirring, plow mixer, double helix conical mixer, etc.

[0059] In this invention, the molar ratio of the cathode material precursor to the lithium source (calculated as Li) is 1:(0.90-1.20). As a non-limiting example, when the number of moles of the precursor is 1, the number of moles of the lithium source (calculated as Li) can be 0.90, 0.95, 1.00, 1.05, 1.10, 1.15, 1.20, or any value within the range formed by any two of these values.

[0060] In this invention, the Group VA element source is preferably selected from at least one of nitrates, chlorides, carbonates, hydroxides, oxides, acetates, and oxalates containing Group VA elements. As a non-limiting example, the modifier containing Group VA elements may be at least one of ammonium nitrate, ammonium chloride, antimony acetate, antimony oxide, bismuth oxalate, bismuth carbonate, phosphorus oxide, etc.

[0061] In this invention, the molar ratio of the cathode material precursor to the Group VA element source (based on the Group VA element) is 1:(0-0.1) and not 0. As a non-limiting example, when the number of moles of the precursor is 1, the number of moles of the Group VA element source (based on the 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 formed by any two of these values. Preferably, the molar ratio of the precursor to the Group VA element source (based on the Group VA element) is 1:(0.001-0.05).

[0062] In this invention, sintering is carried out in an atmosphere furnace, and the sintering atmosphere can be at least one of air, oxygen, and an inert atmosphere (such as nitrogen).

[0063] In this invention, the sintering is programmed temperature sintering, and the sintering temperature is 680-1000℃, for example, it can be 680℃, 700℃, 750℃, 800℃, 850℃, 900℃, 950℃, 1000℃, or any range between any two values. More preferably, the sintering temperature is 720-900℃. The sintering time is 4-48h, for example, it can be 4h, 8h, 12h, 16h, 20h, 24h, 28h, 32h, 36h, 40h, 44h, 48h, or any range between any two values. Preferably, the sintering time is 8-24h, and more preferably, the sintering time is 12-20h.

[0064] In this invention, pre-sintering is performed before sintering. The pre-sintering temperature is 300-650℃, for example, it can be 300℃, 350℃, 400℃, 450℃, 500℃, 550℃, 600℃, 650℃, or 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, for example, it can be 1h, 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h, or any range between any two values. More preferably, the pre-sintering time is 4-8h.

[0065] In this invention, there is no particular limitation on the heating rate of sintering, but it is preferably 0.5-10℃ / min, for example 0.5℃ / min, 1℃ / min, 2℃ / min, 3℃ / min, 5℃ / min, 10℃ / min, and any value within the range formed by any two of these values.

[0066] In this invention, there are no special restrictions on the mixing of the cathode material precursor, lithium source, and group VA element source, and it can be achieved by means of high-speed mixer, ball mill, V-type mixer, mechanical stirring, plow mixer, double helix conical mixer, etc.

[0067] In this invention, the mass ratio of the matrix to the modifying agent is 1:(0-0.30) and not 0. As a non-limiting example, when the mass number of the matrix is ​​1, the mass number of the modifying agent can be 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.10, 0.11, 0.12, 0.13, 0.14, 0.15, 0.20, 0.25, 0.30, or any value within a range formed by any two of these values. Preferably, the mass ratio of the matrix to the modifying agent is 1:(0.01-0.30).

[0068] The third aspect of the present invention provides a lithium battery cathode material prepared by the preparation method described above.

[0069] The properties of the lithium battery cathode material have already been described in detail in the first aspect and will not be repeated here.

[0070] A fourth aspect of the present invention provides the application of the positive electrode material as described above in a lithium battery. The lithium battery comprises: a positive electrode, including the aforementioned positive electrode material; a negative electrode; an electrolyte; and a separator. The positive and negative electrodes can be prepared by coating and drying a composite for forming a layer containing a positive electrode active material and a composite for forming a layer containing a negative electrode active material onto their respective current collectors.

[0071] Positive electrode composites can be prepared using positive electrode active materials, conductive agents, binders, and solvents.

[0072] This invention does not impose specific limitations on the conductive agent, as long as it is conductive and remains stable within the charge-discharge range. The conductive agent can be at least one of acetylene black, Ketjen black, artificial graphite, natural graphite, carbon nanotubes, graphene, superconducting carbon, carbon nanofibers, carbon dots, aluminum powder, nickel powder, titanium dioxide, and conductive polymers.

[0073] The binder provides adhesion between the positive electrode active material, the conductive agent, and the current collector. The binder can be at least one of the following: polyvinylidene fluoride (PVDF), polyvinyl alcohol (PVA), sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), waterborne acrylic resin, polytetrafluoroethylene (PTFE), polyvinyl butyral (PVB), ethylene-vinyl acetate (EVA), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoroethylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylic resin.

[0074] This invention does not impose specific limitations on the current collector, as long as it has suitable conductivity. The current collector can be made of aluminum, nickel, copper, titanium, silver, stainless steel, or carbon materials. The current collector can be processed into various forms such as foil, sheet, film, mesh, perforated, or nonwoven fabric.

[0075] The solvent can be N-methylpyrrolidone.

[0076] Anode composites can be prepared using anode active materials, conductive agents, binders, and solvents.

[0077] This invention does not impose any special restrictions on the negative electrode active material, and it can be selected according to actual needs. The negative electrode active material can be at least one of the following: artificial graphite, natural graphite, soft carbon, hard carbon, mesophase microspheres (MCMB), carbon fiber, lithium metal, silicon, silicon oxide, lithium metal alloy, and lithium titanate.

[0078] The conductive agent and binder of the negative electrode in this invention are not particularly limited and can be of the same type and content as those used in the preparation of the positive electrode. The current collector of the negative electrode can also be made of aluminum, nickel, copper, titanium, silver, stainless steel, and carbon materials. The current collector can also be processed into various forms such as foil, sheet, film, mesh, perforated, and non-woven fabric.

[0079] The electrolyte of this invention is a liquid electrolyte containing lithium salt and solvent, wherein the lithium salt and solvent are not specifically limited.

[0080] The solvent can be a non-aqueous solvent, such as at least one of ethylene carbonate (EC), diethyl carbonate (DEC), methyl ethyl 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), and propyl butyrate (BP).

[0081] The lithium salt can be at least one of LiPF6 (lithium hexafluorophosphate), LiBF4 (lithium tetrafluoroborate), LiClO4 (lithium perchlorate), LiAsF6 (lithium hexafluoroarsenate), LiFSI (lithium bis(fluorosulfonyl)imide), LiTFSI (lithium bis(trifluoromethanesulfonyl)imide), LiTFS (lithium trifluoromethanesulfonate), LiDFOB (lithium difluorooxalate borate), LiBOB (lithium bis(oxalate borate), LiPO2F2 (lithium difluorophosphate), LiDFOP (lithium difluorooxalate phosphate), and LiTFOP (lithium tetrafluorooxalate borate).

[0082] To improve the performance of lithium batteries, additives can be selectively added to the electrolyte, such as vinylene carbonate (VC), fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), tris(trimethylsilane) phosphate (TMSP), sulfonate cyclic quaternary ammonium salts, ethylene sulfite (DTO), dimethyl sulfite (DMS), 1-propylene-1,3-sulfonyl lactone (PST), 4-propyl ethylene sulfate (PEGLST), diethyl sulfite (DES), adiponitrile (ADN), succinate (SN), 1,3-propane sulfonyl lactone (1,3-PS), vinyl sulfate (DTD), and 4-methyl ethylene sulfate (PCS).

[0083] A separator is placed between the positive and negative electrodes to isolate them. The separator can be made of polyolefins, such as polyethylene, polypropylene, or a composite of polyethylene and polypropylene, or it can be a sheet formed of glass fiber or a non-woven fabric. When using a solid electrolyte, the solid electrolyte can also be used as the separator.

[0084] The following describes the preparation method of the lithium battery, used to prepare the aforementioned lithium battery. The main steps include: uniformly mixing the positive electrode material, conductive agent, binder, and solvent, coating it onto at least one surface of the positive electrode current collector, drying, rolling, and slicing it for use as the positive electrode; uniformly mixing the negative electrode material, conductive agent, binder, and solvent, coating it onto at least one surface of the negative electrode current collector, drying, rolling, and slicing it for use as the negative electrode; assembling the positive electrode sheet, separator, and negative electrode sheet into a stacked or wound cell, placing the cell in a casing, injecting electrolyte, and then encapsulating it to obtain the lithium battery.

[0085] In the above-mentioned positive or negative electrode sheet, the amount of positive and negative electrode materials, conductive agent and binder is not specifically limited. For example, based on the total amount of positive or negative electrode materials, the mass content of the positive or negative electrode materials 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%.

[0086] For comparison, in the embodiments of the present invention, the mass ratio of positive electrode material: conductive agent: binder is 92:3:5. The conductive agent is acetylene black, the binder is polyvinylidene fluoride (PVDF), the negative electrode in the coin cell is lithium metal, the separator is Celllgard 2400 polypropylene separator from the United States, the electrolyte is liquid electrolyte, the solvent is a mixture of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 3:7, the solute is lithium hexafluorophosphate (LiPF6), and the molar concentration is 1 mol / L.

[0087] The lithium batteries in this embodiment of the invention are assembled in an inert atmosphere glove box, where the moisture and oxygen content is below 0.1 ppm. There are no particular limitations on the battery model; for comparison, the coin cell model used in this embodiment is 2025, and the electrochemical testing conditions are: temperature 25°C; voltage range 2.8-4.3V.

[0088] In this embodiment of the invention, the exothermic temperature and heat of reaction between the positive electrode material and the electrolyte are tested as follows: The positive electrode material is assembled into a 2025 coin cell according to the aforementioned method. After charging the battery to 4.3V, the battery is disassembled to obtain the charged positive electrode sheet. The positive electrode sheet is placed in a gold-plated stainless steel crucible, and electrolyte is added to the crucible. The mass of the electrolyte is 45% of the mass of the electrode sheet. After sealing the gold-plated stainless steel crucible, it is placed in a differential scanning calorimeter for testing. The equilibrium temperature is 50℃, the heating rate is 10℃ / min, and the maximum temperature is 350℃. The differential scanning calorimeter used in this invention is a TA DSC25 from the USA.

[0089] The present invention will be described in detail below through embodiments.

[0090]

Example 1

[0091] This embodiment is used to illustrate the method for preparing and evaluating cathode materials according to the present invention.

[0092] (1) Preparation of cathode materials

[0093] Take the chemical composition as Ni 0.8 Co 0.1 Mn 0.1 10g of (OH)2 precursor (sheet form, average thickness 45nm) was added to a lithium source LiOH·H2O and Bi2O3, such that the molar ratio of Li to precursor was 1.02:1 and the molar ratio of Bi to precursor was 0.02:1. The precursor, lithium source and Bi2O3 were mixed evenly and then placed in a crucible for stepwise sintering. The first step was pre-sintering: the temperature was increased from room temperature to 450℃ at 5℃ / min and held for 6h. The second step was sintering: the temperature was increased from 450℃ to 750℃ at 5℃ / min and held for 12h. After that, it was naturally cooled to obtain the matrix.

[0094] Adding the modifier LiFe to the matrix 0.25 Mn 0.75 PO4, with a mass ratio of matrix to modifier of 1:0.15, is mixed evenly to obtain the cathode material.

[0095] (2) Evaluation of cathode materials

[0096] The SEM image of the cathode material is as follows: Figure 1 As shown in the figure, the preparation method provided by this invention can yield a cathode material with good sphericity. The matrix of this cathode material is a secondary microsphere formed by the stacking of primary particles. The medium particle size of the secondary microspheres is 10.8 μm. Modifying agents form discontinuous island-like coatings on the surface of the secondary microspheres. Figure 1 The cross-sectional image of the cathode material obtained by focused ion beam cutting is shown below. Figure 2 As shown, the primary particles of the cathode material matrix are elongated and arranged radially along the secondary microspheres, with an average aspect ratio of 5.71.

[0097] Take the above-mentioned positive electrode material, acetylene black and 10% polyvinylidene fluoride solution, mix them evenly according to the mass ratio of positive electrode material: acetylene black: polyvinylidene fluoride 92:3:5, coat them on aluminum foil, dry the solvent and cut them into pieces to obtain the positive electrode sheet. Use a lithium sheet as the counter electrode and assemble the above positive electrode sheet into a button lithium battery in a glove box.

[0098] Take the above-mentioned button cell, charge it to 4.3V, disassemble the battery to obtain the charged positive electrode sheet, place it in a gold-plated stainless steel crucible, add electrolyte to the crucible, the mass of the electrolyte is 45% of the mass of the electrode sheet, seal the gold-plated stainless steel crucible and place it in a differential scanning calorimeter for testing, the equilibrium temperature is 50℃, the heating rate is 10℃ / min, the maximum temperature is 350℃, the secondary oxygen release temperature of the positive electrode material is 238.3℃, and the total heat release with electrolyte is 898.2J / g.

[0099]

Example 2

[0100] This embodiment is used to illustrate the method for preparing and evaluating cathode materials according to the present invention.

[0101] (1) Preparation of cathode materials

[0102] Take the chemical composition as Ni 0.8 Co 0.1 Mn 0.1 10g of (OH)2 precursor (sheet form, average thickness 45nm) was added to a lithium source LiOH·H2O and Sb2O3, such that the molar ratio of Li to precursor was 1.05:1 and the molar ratio of Sb to precursor was 0.05:1. The precursor, lithium source and Sb2O3 were mixed evenly and then placed in a crucible for stepwise sintering. The first step was pre-sintering: the temperature was increased from room temperature to 500℃ at 10℃ / min and held for 6h. The second step was sintering: the temperature was increased from 500℃ to 800℃ at 10℃ / min and held for 16h. After that, it was naturally cooled to obtain the matrix.

[0103] Adding the modifier LiFe to the matrix 0.5 Mn 0.5 PO4, with a mass ratio of matrix to modifier of 1:0.1, is used to obtain the cathode material after the matrix and modifier are mixed evenly.

[0104] (2) Evaluation of cathode materials

[0105] SEM images of cathode materials and Figure 1 Similar to, cross-sectional view and 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 4.56. The secondary microspheres have a medium particle size of 10.2 μm.

[0106] A lithium battery was prepared according to the method described in Example 1, and its safety was tested with the electrolyte.

[0107] The secondary oxygen release temperature of the cathode material is 236.5℃, and the total heat release with the electrolyte is 905.8J / g.

[0108]

Example 3

[0109] (1) Preparation of cathode materials

[0110] Take the chemical composition as Ni 0.8 Co 0.15 Al 0.05 10g of (OH)2 precursor (sheet form, average thickness 50nm) was added to a lithium source LiOH·H2O and P2O5, such that the molar ratio of Li to precursor was 1.08:1 and the molar ratio of P to precursor was 0.04:1. The precursor, lithium source and P2O5 were mixed evenly and then placed in a crucible for stepwise sintering. The first step was pre-sintering: the temperature was increased from room temperature to 550℃ at 5℃ / min and held for 4h. The second step was sintering: the temperature was increased from 550℃ to 730℃ at 10℃ / min and held for 18h. After that, it was naturally cooled to obtain the matrix.

[0111] Adding the modifier LiFe to the matrix 0.75 Mn 0.25 PO4, with a mass ratio of matrix to modifier of 1:0.05, is mixed evenly to obtain the cathode material.

[0112] (2) Evaluation of cathode materials

[0113] SEM images of cathode materials and Figure 1 Similar to, cross-sectional view and 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 3.02. The secondary microspheres have a medium particle size of 10.5 μm.

[0114] A lithium battery was prepared according to the method described in Example 1, and its safety was tested with the electrolyte.

[0115] The secondary oxygen release temperature of the cathode material is 234.2℃, and the total heat release with the electrolyte is 957.4J / g.

[0116]

Example 4

[0117] (1) Preparation of cathode materials

[0118] Take the chemical composition as Ni 0.8 Co 0.15 Al 0.0510g of (OH)2 precursor (sheet form, average thickness 50nm) was added to a lithium source LiOH·H2O and P2O5, such that the molar ratio of Li to precursor was 1.08:1 and the molar ratio of P to precursor was 0.04:1. The precursor, lithium source and P2O5 were mixed evenly and then placed in a crucible for stepwise sintering. The first step was pre-sintering: the temperature was increased from room temperature to 620℃ at 5℃ / min and held for 2h. The second step was sintering: the temperature was increased from 620℃ to 860℃ at 10℃ / min and held for 7h. After that, it was naturally cooled to obtain the matrix.

[0119] Adding the modifier LiFe to the matrix 0.75 Mn 0.25 PO4, with a mass ratio of matrix to modifier of 1:0.05, is mixed evenly to obtain the cathode material.

[0120] (2) Evaluation of cathode materials

[0121] SEM images of cathode materials and Figure 1 Similar to, cross-sectional view and 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 1.93. The secondary microspheres have a medium particle size of 10.1 μm.

[0122] A lithium battery was prepared according to the method described in Example 1, and its safety was tested with the electrolyte.

[0123] The secondary oxygen release temperature of the cathode material is 231.7℃, and the total heat release with the electrolyte is 1128.9J / g.

[0124] Comparative Example 1

[0125] (1) Preparation of cathode materials

[0126] Take the chemical composition as Ni 0.8 Co 0.1 Mn 0.1 10g of (OH)2 precursor (sheet-like, average thickness 45nm) was added to a lithium source LiOH·H2O to make the molar ratio of Li:precursor 1.02:1. The precursor and lithium source were mixed evenly and then placed in a crucible for stepwise sintering. The first step was pre-sintering: the temperature was increased from room temperature to 450℃ at 5℃ / min and held for 6h. The second step was sintering: the temperature was increased from 450℃ to 750℃ at 5℃ / min and held for 12h. After that, it was naturally cooled to obtain the cathode material.

[0127] (2) Evaluation of cathode materials

[0128] SEM images of the cathode material show that no island-like coatings have formed on the substrate surface. Cross-sectional images obtained by focused ion beam cutting show that the primary particles of this cathode material are short and coarse, exhibiting a disordered stacking without a specific arrangement. The average aspect ratio of the primary particles is 1.19. The medium-sized secondary microspheres have a particle size of 9.8 μm.

[0129] A lithium battery was prepared according to the method described in Example 1, and its safety was tested with the electrolyte.

[0130] The secondary oxygen release temperature of the cathode material is 224.4℃, and the total heat release with the electrolyte is 1365.6J / g.

[0131] Comparative Example 2

[0132] (1) Preparation of cathode materials

[0133] Take the chemical composition as Ni 0.8 Co 0.1 Mn 0.1 10g of (OH)2 precursor (sheet-like, average thickness 45nm) was added to a lithium source LiOH·H2O and Bi2O3, such that the molar ratio of Li to precursor was 1.02:1 and the molar ratio of Bi to precursor was 0.02:1. The precursor, lithium source and Bi2O3 were mixed evenly and then placed in a crucible for stepwise sintering. The first step was pre-sintering: the temperature was increased from room temperature to 450℃ at 5℃ / min and held for 6h. The second step was sintering: the temperature was increased from 450℃ to 750℃ at 5℃ / min and held for 12h. After natural cooling, the cathode material was obtained.

[0134] (2) Evaluation of cathode materials

[0135] SEM images of the cathode material show no island-like coating on its surface. Cross-sectional images obtained by focused ion beam cutting of the cathode material show that the primary particles are elongated strips, arranged radially along the secondary microspheres, with an average aspect ratio of 5.59. The secondary microspheres have a medium particle size of 10.7 μm.

[0136] A lithium battery was prepared according to the method described in Example 1, and its safety was tested with the electrolyte.

[0137] The secondary oxygen release temperature of the cathode material is 230.5℃, and the total heat release with the electrolyte is 1203.2J / g.

[0138] Comparative Example 3

[0139] (1) Preparation of cathode materials

[0140] Take the chemical composition as Ni 0.8 Co 0.1 Mn0.1 10g of (OH)2 precursor (sheet form, average thickness 45nm) was added to a lithium source LiOH·H2O to make the molar ratio of Li:precursor 1.02:1. The precursor and lithium source were mixed evenly and then placed in a crucible for stepwise sintering. The first step was pre-sintering: the temperature was increased from room temperature to 450℃ at 5℃ / min and held for 6h. The second step was sintering: the temperature was increased from 450℃ to 750℃ at 5℃ / min and held for 12h. After that, it was naturally cooled to obtain the matrix.

[0141] Adding the modifier LiFe to the matrix 0.25 Mn 0.75 PO4, with a mass ratio of matrix to modifier of 1:0.15, is mixed evenly to obtain the cathode material.

[0142] (2) Evaluation of cathode materials

[0143] SEM images of cathode materials and Figure 1 Similar. Cross-sectional images obtained after focused ion beam cutting show that the primary particles of this cathode material are short and coarse, with no specific arrangement and exhibiting a disordered stacking state. The average aspect ratio of the primary particles is 1.23. The medium particle size of the secondary microspheres is 10.1 μm.

[0144] A lithium battery was prepared according to the method described in Example 1, and its safety was tested with the electrolyte.

[0145] The secondary oxygen release temperature of the cathode material is 224.6℃, and the total heat release with the electrolyte is 1229.1J / g.

[0146] Comparative Example 4

[0147] (1) Preparation of cathode materials

[0148] Compared with Example 1, the difference is that the precursor morphology is microspheres formed by the aggregation of spindle fibers in the primary particles.

[0149] (2) Evaluation of cathode materials

[0150] SEM images of cathode materials and Figure 1 Similarly, cross-sectional images obtained after focused ion beam cutting show that the primary particles of this cathode material are short and coarse, with no specific arrangement and exhibiting a disordered stacking state. The average aspect ratio of the primary particles is 1.27. The medium particle size of the secondary microspheres is 9.9 μm.

[0151] A lithium battery was prepared according to the method described in Example 1, and its safety was tested with the electrolyte.

[0152] The secondary oxygen release temperature of the cathode material is 225.1℃, and the total heat release with the electrolyte is 1218.4J / g.

[0153] The specific embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, including combining the various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A cathode material, comprising a matrix and a modifying agent, wherein the matrix is ​​a secondary microsphere formed by the aggregation of primary particles, wherein the primary particles are elongated; and the modifying agent has the general chemical formula LiA. e B 1-e PO4, of which, 0 < e < 1, A is selected from at least one of the elements in Group VIIB, and B is selected from at least one of the elements in Group VIII.

2. The cathode material according to claim 1, characterized in that, The median particle size of the secondary microspheres is 1.0 - 20.0 μm, and the primary particles are arranged along the radial direction of the secondary microspheres.

3. The cathode material according to claim 1 or 2, characterized in that, The aspect ratio of the primary particles is 1.05 - 20.00, preferably 1.50 - 10.

00.

4. The cathode material according to claim 1, characterized in that, The chemical general formula of the matrix is Li a Ni x Co y M z N p O2, where 0.9 ≤ a ≤ 1.2, 0 ≤ x ≤ 1, 0 ≤ y ≤ 1, 0 ≤ z ≤ 1, 0 < p ≤ 0.

1. Preferably, 0.5 ≤ x ≤ 0.99, 0 ≤ y ≤ 0.5, 0 ≤ z ≤ 0.5, 0 < p ≤ 0.

05. The values of x, y, and z are not simultaneously 0, and the values of a, x, y, z, and p satisfy the principle of electroneutrality; preferably, M is selected from at least one of the elements in Group VIIB or Group IIIA, and N is selected from at least one of the elements in Group VA.

5. The positive electrode material according to claim 1, characterized in that, For the positive electrode material, in parts by mass: Matrix 100 parts; The modification aid is more than 0 parts and not more than 30 parts.

6. The cathode material according to claim 1, characterized in that, The positive electrode material has a core-shell structure, the core layer is the matrix, and the shell layer is the modification aid; preferably, the core-shell structure is such that the shell layer coats the core layer in a discontinuous island-like manner.

7. The preparation method of 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 source, and sintering to obtain a matrix; (2) Mixing the matrix obtained in step (1) with a modification aid to obtain a positive electrode material.

8. The preparation method according to claim 7, characterized in that, The general chemical formula of the cathode material precursor is Ni. x Co y M z (OH)2, 0≤x≤1, 0≤y≤1, 0≤z≤1, preferably 0.5≤x≤0.99, 0≤y≤0.5, 0≤z≤0.5, where x, y and z are not simultaneously 0, and the values ​​of x, y and z satisfy the principle of electroneutrality.

9. The preparation method according to claim 7, characterized in that, The molar ratio of the positive electrode material precursor and the lithium source in terms of Li element is 1:(0.90 - 1.20); and / or, the molar ratio of the positive electrode material precursor and the Group VA element source in terms of the Group VA element is 1:(0 - 0.1) and not 0, preferably 1:(0.001 - 0.05); and / or, the mass ratio of the matrix and the modification aid is 1:(0 - 0.30) and not 0, preferably 1:(0.01 - 0.30).

10. The preparation method according to claim 7, characterized in that, The sintering temperature is 680 - 1000 °C, preferably 720 - 900 °C, the sintering time is 4 - 48 h, preferably 8 - 24 h, and more preferably 12 - 20 h.

11. The preparation method according to claim 7, characterized in that, Pre-sintering is carried out before the sintering, the pre-sintering temperature is 300 - 650 °C, preferably 450 - 550 °C, more preferably 450 - 530 °C, and the pre-sintering time is 1 - 10 h, preferably 4 - 8 h.

12. The preparation method according to claim 7, characterized in that, The morphology of the positive electrode material precursor is microspheres formed by stacking flakes; the average thickness of the flakes is 1 - 500 nm, preferably 1 - 200 nm.

13. The application of the positive electrode material according to any one of claims 1 - 6 in a lithium battery.

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