Hollow positive electrode material and preparation method and application thereof

Abstract

The invention discloses a hollow positive electrode material and a preparation method and application thereof. The positive electrode material is a microsphere formed by gathering primary particles, the primary particles are arranged along the radial direction of the microsphere, and the inside of the microsphere has a hollow structure. The positive electrode material disclosed by the invention is applied to a high-performance lithium battery, and the discharge capacity and the cycling stability of the positive electrode material are improved.

Description

Technical Field

[0001] This invention belongs to the field of lithium batteries, specifically relating to a hollow cathode material, its preparation method, and its application. Background Technology

[0002] With the promotion and popularization of new energy vehicles, the market demand for electric vehicles with long range, high power, and long service life is becoming increasingly urgent. The performance of electric vehicles is mainly determined by the lithium batteries they use. Cathode materials are one of the key components of lithium batteries, determining key indicators such as energy density, power density, and cycle life. Among currently commercialized cathode materials such as olivine-structured LiFePO4, spinel-structured LiMn2O4, layered LiCoO2, and layered ternary cathode materials, layered ternary cathode materials have higher theoretical capacity. Their application in lithium batteries can improve the driving range of electric vehicles, making them a research hotspot for high-performance lithium battery cathode materials.

[0003] Layered ternary cathode materials mainly include nickel-cobalt-manganese or nickel-cobalt-aluminum systems. Increasing the nickel content helps improve the specific capacity, increasing the cobalt content helps improve the rate performance, and increasing the manganese and aluminum content mainly improves the stability and safety. While increasing the nickel content improves the discharge capacity of ternary cathode materials, it significantly reduces rate performance and cycle stability. Therefore, it is urgent to address the issues of high-rate discharge capacity and cycle stability of layered ternary cathode materials from a material structure perspective. Summary of the Invention

[0004] This invention addresses the problem of poor discharge capacity and cycle stability of layered ternary cathode materials at high rates in existing technologies, and provides a hollow cathode material, its preparation method, and its applications. The cathode material of this invention simultaneously possesses the advantages of high discharge specific capacity and good cycle stability.

[0005] The first aspect of the present invention provides a hollow cathode material, wherein the cathode material is a microsphere formed by the aggregation of primary particles, wherein the primary particles are arranged along the radial direction of the microsphere and the microsphere has a hollow structure inside.

[0006] In the above technical solution, the outer wall thickness of the positive electrode material accounts for 20%-95% of the total microsphere radius, preferably 30%-90%.

[0007] In the above technical solution, the primary particles are elongated, and the aspect ratio of the elongated particles is 1.05-20.00, preferably 1.50-15.00, and more preferably 3.50-15.00.

[0008] In the above technical solution, the median particle size of the microspheres is 1.0 - 20.0 μm. The median particle size refers to the particle diameter corresponding to when the cumulative particle size distribution percentage of the microspheres reaches 50%.

[0009] In the above technical solution, the chemical composition of the positive electrode material 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, x, y, and z do not all take the value of 0 simultaneously, and the values of a, x, y, z, and p satisfy the principle of electrical neutrality. 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.

[0010] In the above technical solution, the chemical composition of the positive electrode material is Li a Ni x Co y M z N p O2, where 0.5 ≤ x ≤ 0.99, 0 ≤ y ≤ 0.5, 0 ≤ z ≤ 0.5, 0 < p ≤ 0.05, x, y, and z do not all take the value of 0 simultaneously, preferably x, y, and z are not all 0, and the values of a, x, y, z, and p satisfy the principle of electrical neutrality.

[0011] 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.

[0012] 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.

[0013] The second aspect of the present invention provides a preparation method for the above positive electrode material, including:

[0014] Mixing a positive electrode material precursor, a lithium source, and a modifier containing an element in Group VA, and sintering to obtain the positive electrode material.

[0015] In the above technical solution, the chemical composition of the positive electrode material precursor is Ni x Co y M z (OH)2, where 0 ≤ x ≤ 1, 0 ≤ y ≤ 1, 0 ≤ z ≤ 1, preferably 0.5 ≤ x ≤ 0.99, 0 ≤ y ≤ 0.5, 0 ≤ z ≤ 0.5, x, y, and z do not all take the value of 0 simultaneously, and the values of x, y, and z satisfy the principle of electrical neutrality.

[0016] In the above technical solution, the morphology of the cathode material precursor is a microsphere formed by the stacking of sheet-like primary particles. The average thickness of the sheet is 1-500 nm, preferably 1-200 nm.

[0017] In the above technical solution, the porosity of the interior of the cathode material precursor is higher than that of the exterior, i.e., the internal structure is loose and the external structure is dense. Further, the thickness of the external structure accounts for 20%-95% of the total microsphere radius, preferably 30%-90%. Further, the diameter of the precursor microspheres is 1.0-20.0 μm.

[0018] 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).

[0019] 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).

[0020] In the above technical solution, the modifier containing Group VA elements is preferably selected from at least one of nitrates, chlorides, carbonates, hydroxides, oxides, acetates, and oxalates containing Group VA elements.

[0021] In the above technical solution, the molar ratio of the cathode material precursor and the modifier containing Group VA elements (calculated as Group VA elements) is 1:(0-0.1) and not 0, preferably 1:(0.001-0.05).

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

[0023] 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, a pre-sintering temperature of 300-575℃, preferably 450-550℃, more preferably 450-530℃, and a pre-sintering time of 1-10h, preferably 4-8h.

[0024] The third aspect of this invention provides the application of the above-mentioned cathode material in lithium batteries.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] 1. The cathode material of this invention is a microsphere formed by the aggregation of primary particles. The microsphere has a hollow internal structure, and the primary particles are arranged radially along the sphere. Preferably, the primary particles are elongated strips with an aspect ratio of 1.05-20.00. The cathode material of this invention exhibits excellent electrochemical performance, with advantages such as high discharge specific capacity and good cycle stability.

[0027] 2. In the preparation process of the lithium battery cathode material of the present invention, a cathode material precursor with a sheet-like morphology, a lithium source, and a modifier containing a group VA element are mixed and sintered. During the sintering process, the crystallization process of the primary particles of the lithium battery cathode material can be adjusted through the synergistic effect of the sheet-like morphology of the precursor and the modifier containing the group VA element, as well as by controlling the sintering temperature and sintering time. The resulting primary particles of the lithium battery cathode material have an elongated shape and are arranged along the radial direction of the secondary microspheres of the lithium battery cathode material. This composition and structure of the material is conducive to the diffusion of lithium ions and can improve the discharge specific capacity and cycle stability of the material.

[0028] 3. In the preparation process of the lithium battery cathode material of the present invention, a precursor with a large internal porosity, a lithium source, and a modifier containing a group VA element are mixed and sintered. By controlling the internal and external porosity of the precursor, as well as the sintering temperature and sintering time, the crystallization process inside and outside the cathode material can be adjusted to obtain a hollow lithium battery cathode material. This can effectively improve the problem of difficult diffusion of lithium ions inside the cathode material, and at the same time buffer the problem of particle breakage caused by volume expansion and contraction of the cathode material during charging and discharging, thereby improving the discharge specific capacity and cycle stability of the material.

[0029] 4. The lithium battery cathode material provided by this invention can be used in high energy density and high stability lithium batteries. The discharge specific capacity can reach 190.8 mAh / g at 1C rate, and the capacity retention rate can reach 87.6% after 200 cycles at 1C rate. Attached Figure Description

[0030] Figure 1 This is a SEM image of the lithium battery cathode material prepared in Example 1 of the present invention;

[0031] Figure 2 This is a SEM image of a cross-section of the lithium battery cathode material prepared in Example 1 of this invention;

[0032] Figure 3 This is a comparison chart of the cycling results of the lithium battery cathode material prepared in Example 1 of the present invention and the comparative example. Detailed Implementation

[0033] The technical solution of the present invention will be described in detail below.

[0034] In the first aspect of the present invention, a cathode material is provided. The cathode material is a microsphere formed by aggregation of primary particles, wherein the primary particles are arranged along the radial direction of the microsphere, and the microsphere has a hollow structure inside.

[0035] The cathode material provided by the present invention has a chemical composition of 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, and the values of a, x, y, z, and p satisfy the principle of electroneutrality. M is selected from at least one of the elements of Group VIIB or Group IIIA, and N is selected from at least one of the elements of Group VA.

[0036] In one embodiment of the present invention, preferably, M is selected from Mn and / or Al. That is, preferably, the compound with the chemical composition of Li a Ni x Co y M z N p O2 is Li a Ni x Co<— y Mn z N p O2 or Li a Ni x Co y Al z N p O2.

[0037] The cathode material provided by this invention has an outer wall thickness of 20%-95% of the total microsphere particle radius, preferably 30%-90%. This outer wall thickness as a percentage of the total microsphere particle radius is, for example, but not limited to, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 68%, 70%, 75%, 80%, 85%, 90%, 95%, and any value within any range of two of these values. The method for measuring the outer wall thickness as a percentage of the total microsphere particle radius is as follows: First, the cathode material particles are cut with an ion beam, and a cross-sectional SEM image is taken. Then, the outer wall thickness and the total microsphere particle radius are measured using SEM image measurement software. When measuring the outer wall thickness and the total microsphere particle radius, measurements are taken at least five times from different directions on the cross-section of the cathode material particles, and the average values ​​are taken as the outer wall thickness and the microsphere radius, respectively. Furthermore, the average value of the ratio of the outer wall thickness to the radius of the microsphere is selected from more than 5 positive electrode material particles and taken as the proportion of the outer wall thickness to the total radius of the microsphere.

[0038] The cathode material provided by this invention has primary particles with an aspect ratio of 1.05-20.00, preferably 1.5-15.00. The aspect ratio of the primary particles is, for example, but not limited to, 1.05, 1.25, 1.5, 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, and 6. 70, 6.95, 7.20, 7.45, 7.70, 7.95, 8.35, 8.75, 9.25, 9.75, 10.50, 11.00, 11.50, 12.00, 12.50, 13.00, 13.50, 14.00, 14.50, 15.00, and any value within the range formed by any two of these values.

[0039] The cathode material provided by this invention has microspheres with a medium particle size of 1.0-20.0 μm. The medium particle size of the microspheres is, for example, but not limited to, 1.0 μm, 2.0 μm, 3.0 μm, 4.0 μm, 5.0 μm, 6.0 μm, 7.0 μm, 8.0 μm, 9.0 μm, 10.0 μm, 10.5 μm, 10.8 μm, 11.0 μm, 12.0 μm, 13.0 μm, 14.0 μm, 15.0 μm, 20.0 μm, and any value within any range formed by any two of these values. The medium particle size represents the particle size corresponding to a cumulative particle size distribution percentage of 50% for the cathode material microspheres.

[0040] 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 is spherical. The SEM image of a cross-section of the cathode material is shown below. Figure 2 As shown. From Figure 2 As can be seen, the cathode material is formed by the aggregation of primary particles into microspheres. The microspheres have a hollow internal structure, the primary particles are elongated, and the primary particles are arranged along the radial direction of the microspheres.

[0041] In this invention, the scanning electron microscope (SEM) images were obtained using a ZEISS Merlin model scanning electron microscope from the German company ZEISS.

[0042] 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 lithium battery cathode materials. Lithium battery cathode materials with this characteristic composition and structure have higher discharge specific capacity and better cycle stability, and can be used in high-performance lithium batteries.

[0043] A second aspect of the present invention provides a method for preparing the above-mentioned cathode material, comprising:

[0044] The cathode material precursor, lithium source, and modifier containing Group VA elements are mixed and sintered to obtain the lithium battery cathode material.

[0045] In this invention, the chemical composition 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.

[0046] In this invention, the morphology of the cathode material precursor is a secondary microsphere formed by the stacking of sheet-like primary particles. The thickness of the sheet-like particles is 1-500 nm, preferably 1-200 nm. The thickness of the sheet-like particles is, for example, but not limited to, 1 nm, 5 nm, 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, 80 nm, 100 nm, 120 nm, 150 nm, 180 nm, 200 nm, and any value within any two of these values.

[0047] In this invention, the porosity of the interior of the cathode material precursor is higher than that of the exterior. Preferably, the diameter of the precursor microspheres is 1.0-20.0 μm.

[0048] In this invention, the thickness of the external structure of the cathode material precursor accounts for 20%-95% of the total microsphere radius, preferably 30%-90%. The proportion of the external structure thickness of the cathode material precursor to the total microsphere radius is, for example, but not limited to, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, and any value within any two of these ranges. The method for measuring the proportion of the precursor's external structure thickness to the total microsphere radius is as follows: First, the cathode material precursor particles are cut with an ion beam, and a cross-sectional SEM image is taken. Then, the thickness of the external structure and the radius of the entire microsphere particle are measured using SEM image measurement software. After measuring the external structure thickness and the total microsphere particle radius from different directions of the cross-section of the cathode material precursor particle more than five times, the average values ​​are taken as the precursor's external structure thickness and the microsphere particle radius, respectively. Furthermore, the ratio of the external structure thickness to the microsphere radius of five or more cathode material precursor particles is averaged and used as the proportion of the external structure thickness to the total microsphere radius.

[0049] 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).

[0050] 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.

[0051] 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.

[0052] In this invention, the modifier containing a Group VA element is preferably selected from at least one of nitrates, chlorides, carbonates, hydroxides, oxides, acetates, and oxalates containing a Group VA element. As a non-limiting example, the Group VA modifier may be at least one of ammonium nitrate, ammonium chloride, antimony acetate, antimony oxide, bismuth oxalate, bismuth carbonate, phosphorus oxide, etc.

[0053] In this invention, the molar ratio of the cathode material precursor to the modifier containing a Group VA element (calculated as a 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 modifier (calculated as a 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, or any value within any range of any two of these values. Preferably, the molar ratio of the precursor to the modifier containing a Group VA element (calculated as a Group VA element) is 1:(0.001-0.05).

[0054] 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.

[0055] In this invention, the sintering is programmed temperature sintering, and the sintering temperature is 580-900℃, for example, it can be 580℃, 600℃, 650℃, 700℃, 750℃, 800℃, 850℃, 900℃, or any range between any two values. More preferably, the calcination temperature is 600-850℃. 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.

[0056] In this invention, pre-sintering is performed before sintering. The pre-sintering temperature is 300-575℃, for example, it can be 300℃, 350℃, 400℃, 450℃, 500℃, 550℃, 575℃, or any range between any two values. Preferably, the calcination temperature is 450-550℃, and 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.

[0057] 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 any range of any two of these values.

[0058] In this invention, there are no special restrictions on the mixing of the cathode material precursor, lithium source, and modifier containing Group VA elements. It can be achieved by means of high-speed mixer, ball mill, V-type mixer, mechanical stirring, plow mixer, double helix conical mixer, etc.

[0059] The third aspect of the present invention provides a lithium battery cathode material prepared by the preparation method described above.

[0060] The properties of the lithium battery cathode material have already been described in detail in the first aspect and will not be repeated here.

[0061] A fourth aspect of the present invention provides the application of the lithium battery positive electrode material as described above in a lithium battery. The lithium battery comprises: a positive electrode, including the aforementioned lithium battery 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.

[0062] Positive electrode composites can be prepared using positive electrode active materials, conductive agents, binders, and solvents.

[0063] 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.

[0064] 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 lithium battery copolymer, vinylidene fluoride-hexafluoroethylene-tetrafluoroethylene lithium battery polymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylic resin.

[0065] 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.

[0066] The solvent can be N-methylpyrrolidone.

[0067] Anode composites can be prepared using anode active materials, conductive agents, binders, and solvents.

[0068] 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.

[0069] 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.

[0070] The electrolyte of this invention is a liquid electrolyte containing lithium salt and solvent, wherein the lithium salt and solvent are not specifically limited.

[0071] 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).

[0072] 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).

[0073] 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).

[0074] 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.

[0075] The following describes the preparation method of the lithium battery, used to prepare the aforementioned lithium battery. The main steps include: uniformly mixing the lithium battery 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 encapsulating it to obtain the lithium battery.

[0076] In the above-mentioned positive or negative electrode sheets, the amount of positive and negative electrode materials, conductive agents, and binders is not specifically limited. For example, based on the total amount of positive or negative electrode materials, the mass content of the lithium battery 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%.

[0077] For comparison, in the embodiments of the present invention, the mass ratio of the positive electrode material of the lithium battery, the conductive agent, and the binder is 90:5:5. 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.

[0078] 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 restrictions 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.

[0079] The present invention will be described in detail below through embodiments.

[0080]

Example 1

[0081] This embodiment is used to illustrate the method for preparing and evaluating lithium battery cathode materials according to the present invention.

[0082] (1) Preparation of lithium battery cathode materials

[0083] Take the chemical composition as Ni 0.92 Co 0.03 Mn 0.05 10g of (OH)2 precursor was prepared, with primary particles in sheet form and an average sheet thickness of approximately 50nm. The precursor microspheres had a diameter of 10.9μm, and the thickness of the external structure of the precursor accounted for 58% of the total microsphere radius. Lithium sources LiOH·H2O and Bi2O3 were added to achieve a Li:precursor molar ratio of 1.02:1 and a Bi:precursor molar ratio of 0.03:1. After uniformly mixing the precursor, lithium source, and Bi2O3, the mixture was placed in a crucible for stepwise sintering. The first step was pre-sintering: the temperature was increased from room temperature to 450℃ at a rate of 5℃ / min and held for 6h. The second step was sintering: the temperature was increased from 450℃ to 750℃ at a rate of 5℃ / min and held for 12h. After natural cooling, the lithium battery cathode material was obtained.

[0084] (2) Evaluation of lithium battery cathode materials

[0085] The SEM image of the lithium battery cathode material is shown below. Figure 1 As shown in the figure, the cathode material obtained by the preparation method provided by this invention consists of secondary microspheres formed by the stacking of primary particles. The medium particle size of the secondary microspheres is 10.8 μm. Figure 1 The cross-sectional image of the lithium battery cathode material shown is obtained by focused ion beam cutting. Figure 2 As shown, the lithium battery cathode material microspheres have a hollow structure inside, and the thickness of the outer wall of the cathode material accounts for 52% of the total radius of the microspheres. The primary particles are elongated and are arranged radially along the secondary microspheres. The average aspect ratio of the primary particles is 6.87.

[0086] The above-mentioned lithium battery positive electrode material, acetylene black, and 10% (w / w) polyvinylidene fluoride solution were mixed evenly according to a mass ratio of lithium battery positive electrode material: acetylene black: polyvinylidene fluoride 90:5:5. The mixture was then coated onto aluminum foil, the solvent was dried, and the foil was sliced ​​to obtain the positive electrode sheet. Using a lithium sheet as the counter electrode, the positive electrode sheets were assembled into a coin cell lithium battery in a glove box. The charge / discharge voltage range of the coin cell lithium battery is 2.8-4.3V. The specific capacity at 1C rate is 190.8mAh / g, and the capacity retention rate after 200 cycles at 1C rate is 87.6%.

[0087]

Example 2

[0088] This embodiment is used to illustrate the method for preparing and evaluating lithium battery cathode materials according to the present invention.

[0089] (1) Preparation of lithium battery cathode materials

[0090] Take the chemical composition as Ni 0.92 Co 0.03 Mn 0.05 10g of (OH)2 precursor was prepared, with primary particles in sheet form and an average sheet thickness of approximately 50nm. The precursor microspheres had a diameter of 10.5μm, and the thickness of the external structure of the precursor accounted for 76% of the total microsphere radius. Lithium source LiOH·H2O and Sb2O3 were added to achieve a Li:precursor molar ratio of 1.05:1 and a Sb:precursor molar ratio of 0.05:1. After uniformly mixing the precursor, lithium source, and Sb2O3, the mixture was placed in a crucible for stepwise sintering. The first step was pre-sintering: the temperature was increased from room temperature to 500℃ at a rate of 10℃ / min and held for 6 hours. The second step was sintering: the temperature was increased from 500℃ to 800℃ at a rate of 10℃ / min and held for 16 hours. After natural cooling, the lithium battery cathode material was obtained.

[0091] (2) Evaluation of lithium battery cathode materials

[0092] SEM images of lithium battery cathode materials and Figure 1 Similar to, cross-sectional view and Figure 2 Similar. The secondary microspheres have a medium particle size of 10.3 μm. The lithium battery cathode material microspheres have a hollow internal structure, with the outer wall thickness of the cathode material accounting for 73% of the total microsphere radius. The primary particles are elongated and arranged radially along the secondary microspheres, with an average aspect ratio of 5.39.

[0093] Lithium batteries were prepared according to the method described in Example 1.

[0094] The button cell lithium battery has a charge / discharge voltage range of 2.8-4.3V. Its discharge specific capacity at 1C rate is 189.7mAh / g, and its capacity retention rate after 200 cycles at 1C rate is 85.2%.

[0095]

Example 3

[0096] (1) Preparation of lithium battery cathode materials

[0097] Take the chemical composition as Ni 0.8 Co 0.1 Mn 0.1 10g of (OH)2 precursor was prepared, with primary particles in sheet form and an average sheet thickness of approximately 50nm. The precursor microspheres had a diameter of 10.2μm, and the thickness of the external structure of the precursor accounted for 45% of the total microsphere radius. Lithium source LiOH·H2O and P2O5 were added to achieve a Li:precursor molar ratio of 1.08:1 and a P:precursor molar ratio of 0.03:1. The precursor, lithium source, and P2O5 were mixed uniformly and then placed in a crucible for stepwise sintering. The first step was pre-sintering: the temperature was increased from room temperature to 530℃ at a rate of 5℃ / min and held for 4h. The second step was sintering: the temperature was increased from 530℃ to 730℃ at a rate of 10℃ / min and held for 18h. After natural cooling, the lithium battery cathode material was obtained.

[0098] (2) Evaluation of lithium battery cathode materials

[0099] SEM images of lithium battery cathode materials and Figure 1 Similar to, cross-sectional view and Figure 2 Similar. The secondary microspheres have a medium particle size of 9.9 μm. The lithium battery cathode material microspheres have a hollow internal structure, and the outer wall thickness of the cathode material accounts for 39% of the total microsphere radius. The primary particles are elongated and arranged radially along the secondary microspheres, with an average aspect ratio of 3.76.

[0100] Lithium batteries were prepared according to the method described in Example 1.

[0101] The button cell lithium battery has a charge / discharge voltage range of 2.8-4.3V. Its discharge specific capacity at 1C rate is 188.6mAh / g, and its capacity retention rate after 200 cycles at 1C rate is 83.4%.

[0102]

Example 4

[0103] (1) Preparation of lithium battery cathode materials

[0104] Take the chemical composition as Ni 0.92 Co 0.03 Al 0.0510g of (OH)2 precursor was prepared, with primary particles in sheet form and an average sheet thickness of approximately 60nm. The precursor microspheres had a diameter of 10.4μm, and the thickness of the external structure of the precursor accounted for 54% of the total microsphere radius. Lithium source LiOH·H2O and P2O5 were added to achieve a Li:precursor molar ratio of 1.1:1 and a P:precursor molar ratio of 0.07:1. After uniformly mixing the precursor, lithium source, and P2O5, the mixture was placed in a crucible for stepwise sintering. The first step was pre-sintering: the temperature was increased from room temperature to 550℃ at a rate of 5℃ / min and held for 4h. The second step was sintering: the temperature was increased from 550℃ to 880℃ at a rate of 10℃ / min and held for 8h. After natural cooling, the lithium battery cathode material was obtained.

[0105] (2) Evaluation of lithium battery cathode materials

[0106] SEM images of lithium battery cathode materials and Figure 1 Similar to, cross-sectional view and Figure 2 Similar. The secondary microspheres have a medium particle size of 10.2 μm. The lithium battery cathode material microspheres have a hollow internal structure, with the outer wall thickness of the cathode material accounting for 48% of the total microsphere radius. The primary particles are elongated and arranged radially along the secondary microspheres, with an average aspect ratio of 2.95. The lithium battery was prepared according to the method described in Example 1.

[0107] The button cell lithium battery has a charge / discharge voltage range of 2.8-4.3V. Its discharge specific capacity at 1C rate is 187.2mAh / g, and its capacity retention rate after 200 cycles at 1C rate is 79.3%.

[0108]

Example 5

[0109] (1) Preparation of lithium battery cathode materials

[0110] Take the chemical composition as Ni 0.92 Co 0.03 Mn 0.05 10g of (OH)2 precursor was prepared, with primary particles in sheet form and an average sheet thickness of approximately 50nm. The precursor microspheres had a diameter of 10.3μm, and the thickness of the external structure of the precursor accounted for 94% of the total microsphere radius. Lithium source LiOH·H2O and P2O5 were added to achieve a Li:precursor molar ratio of 1.08:1 and a P:precursor molar ratio of 0.03:1. The precursor, lithium source, and P2O5 were mixed uniformly and then placed in a crucible for stepwise sintering. The first step was pre-sintering: the temperature was increased from room temperature to 530℃ at a rate of 5℃ / min and held for 4h. The second step was sintering: the temperature was increased from 530℃ to 730℃ at a rate of 10℃ / min and held for 18h. After natural cooling, the lithium battery cathode material was obtained.

[0111] (2) Evaluation of lithium battery cathode materials

[0112] SEM images of lithium battery cathode materials and Figure 1 Similar to, cross-sectional view and Figure 2 Similar. The secondary microspheres have a medium particle size of 10.1 μm. The lithium battery cathode material microspheres have a hollow internal structure, with the outer wall thickness of the cathode material accounting for 93% of the total microsphere radius. The primary particles are elongated and arranged radially along the secondary microspheres, with an average aspect ratio of 3.59.

[0113] Lithium batteries were prepared according to the method described in Example 1.

[0114] The button cell lithium battery has a charge / discharge voltage range of 2.8-4.3V. Its discharge specific capacity at 1C rate is 186.8mAh / g, and its capacity retention rate after 200 cycles at 1C rate is 71.2%.

[0115] Comparative Example 1

[0116] (1) Preparation of lithium battery cathode materials

[0117] Take the chemical composition as Ni 0.92 Co 0.03 Mn 0.05 10g of (OH)2 precursor, the primary particles are in the form of flakes with an average thickness of about 50nm and a dense internal structure. LiOH·H2O is added to make the molar ratio of Li:precursor 1.02:1. After the precursor and lithium source are mixed evenly, they are placed in a crucible for stepwise sintering. The first step is pre-sintering: the temperature is increased from room temperature to 450℃ at 5℃ / min and held for 6h. The second step is sintering: the temperature is increased from 450℃ to 750℃ at 5℃ / min and held for 12h. After natural cooling, the lithium battery cathode material is obtained.

[0118] (2) Evaluation of lithium battery cathode materials

[0119] SEM images of lithium battery cathode materials and Figure 1 Similar. Cross-sectional images obtained after focused ion beam cutting show that the lithium battery cathode material is dense internally, with short and coarse primary particles that are randomly stacked without a specific arrangement. The average aspect ratio of the primary particles is 1.18. The medium particle size of the secondary microspheres is 9.8 μm.

[0120] Lithium batteries were prepared according to the method described in Example 1.

[0121] The button cell lithium battery has a charge / discharge voltage range of 2.8-4.3V. Its discharge specific capacity at 1C rate is 183.4mAh / g, and its capacity retention rate after 200 cycles at 1C rate is 29.5%.

[0122] Comparative Example 2

[0123] (1) Preparation of lithium battery cathode materials

[0124] Compared with Example 1, the precursor morphology is that the primary particles are microspheres formed by the aggregation of spindle fibers, and the microspheres are dense inside.

[0125] (2) Evaluation of positive materials for lithium batteries

[0126] SEM images of lithium battery cathode materials and Figure 1 Similarly, cross-sectional images obtained after focused ion beam cutting show that the internal structure of this lithium battery cathode material is dense, with short and coarse primary particles that exhibit no specific arrangement and are randomly stacked. The average aspect ratio of the primary particles is 1.21. The medium particle size of the secondary microspheres is 10.3 μm.

[0127] Lithium batteries were prepared according to the method described in Example 1.

[0128] The button cell lithium battery has a charge / discharge voltage range of 2.8-4.3V. Its discharge specific capacity at 1C rate is 184.6mAh / g, and its capacity retention rate after 200 cycles at 1C rate is 35.2%.

[0129] 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 inventive concept, 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 hollow cathode material, characterized in that, The cathode material is a microsphere formed by the aggregation of primary particles, wherein the primary particles are arranged along the radial direction of the microsphere and the microsphere has a hollow structure inside.

2. The cathode material according to claim 1, characterized in that, The chemical composition of the positive electrode material 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, and the values of a, x, y, z, and p satisfy the principle of electrical neutrality; 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.

3. The cathode material according to claim 1, characterized in that, The outer wall thickness of the positive electrode material accounts for 20%-95% of the total radius of the microsphere, preferably 30%-90%. Preferably, the microspheres have a medium particle size of 1.0-20.0 μm.

4. The cathode material according to claim 1, characterized in that, The primary particles are elongated, with an aspect ratio of 1.05-20.00, preferably 1.50-15.

00.

5. A method for preparing the cathode material according to any one of claims 1-4, comprising: The cathode material precursor, lithium source, and modifier containing a group VA element are mixed and sintered to obtain the cathode material.

6. The preparation method according to claim 5, characterized in that, The chemical composition 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 the values ​​of x, y and z are not simultaneously 0, and the values ​​of x, y and z satisfy the principle of electroneutrality; And / or, the lithium source is selected from at least one of lithium nitrate, lithium chloride, lithium carbonate, lithium hydroxide, lithium hydroxide monohydrate, lithium oxide, lithium acetate, and lithium oxalate; And / or, the modifier containing a Group VA element is selected from at least one of nitrates, chlorides, carbonates, hydroxides, oxides, acetates, and oxalates containing a Group VA element.

7. The preparation method according to claim 5, characterized in that, The molar ratio of the cathode material precursor to the lithium source, based on Li element, is 1:(0.90-1.20); And / or, the molar ratio of the cathode material precursor and the modifier containing a Group VA element, calculated based on the Group VA element, is 1:(0-0.1) and not 0, preferably 1:(0.001-0.05).

8. The preparation method according to claim 5, characterized in that, The sintering temperature is 580-900℃, preferably 600-850℃, and the sintering time is 4-48h, preferably 8-24h, and more preferably 12-20h; Preferably, pre-sintering is performed before sintering, with a pre-sintering temperature of 300-575℃, more preferably 450-550℃, and even more preferably 450-530℃, and a pre-sintering time of 1-10h, preferably 4-8h.

9. The preparation method according to claim 5, characterized in that, The morphology of the cathode material precursor is a microsphere formed by the stacking of sheet-like primary particles; the average thickness of the sheet is 1-500 nm, preferably 1-200 nm.

10. The preparation method according to claim 5, characterized in that, The porosity inside the cathode material precursor is higher than the porosity outside. Preferably, the thickness of the outer structure of the precursor accounts for 20%-95% of the total radius of the microsphere, and more preferably 30%-90%. Preferably, the precursor microspheres have a diameter of 1.0-20.0 μm.

11. The application of the cathode material according to any one of claims 1-4 in a lithium battery.

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