A cobalt-free positive electrode material, a positive electrode sheet including the cobalt-free positive electrode material, and a battery

Abstract

The present application relates to the technical field of lithium ion batteries, in particular to a cobalt-free positive electrode material, a positive electrode sheet comprising the cobalt-free positive electrode material and a battery. The cobalt-free positive electrode material comprises a base, a first coating layer and a second coating layer. The base comprises a material with a chemical formula of Li(Ni x Mn 1‑x M 1 y M 2 z )O2; the first coating layer comprises a material with a chemical formula of Li(MnM 1 y M 2 z )2O4; and the second coating layer comprises niobium tungsten oxide. Wherein, 0.6≤x≤0.9, 0 1 and M 2 are the same or different, and are independently selected from at least one of Al, Mg, Ti, Zr, B, Y, W, Sr, La, Mo, Nb and V. The coating structure comprises a protective inner layer (the first coating layer) with a spinel phase structure and an outer layer (the second coating layer) with excellent electrical conductivity, which can improve the kinetic performance of the battery while stabilizing the surface / interface structure and improving the cycle performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium ion batteries, in particular to a cobalt-free positive electrode material, a positive electrode sheet comprising the cobalt-free positive electrode material and a battery. BACKGROUND

[0002] Since Sony commercialized lithium ion batteries in 1991, lithium ion batteries have been widely used in consumer electronics and electric vehicles due to their high energy density, long cycle life and environmental friendliness.

[0003] As an important component of lithium ion batteries, positive electrode materials have a great impact on the cost and performance of lithium ion batteries. Commercialized material ternary positive electrode material Li[Ni x Co y Mn 1-x-y ]O2(NCM) has advantages such as high discharge capacity and high energy density, and has become a hot spot in the research and application of lithium ion battery positive electrode materials. However, the increasing demand for ternary materials has accelerated the consumption of global cobalt reserves, and the tightening of cobalt supply chain has significantly increased the price of cobalt. The use of low-estimated / cobalt-free positive electrodes can significantly reduce the dependence on cobalt and meet the growing demand for lithium ion batteries, and low-cost low-estimated / cobalt-free positive electrode materials have become the mainstream trend of future lithium battery industry development.

[0004] The presence of Co 3+ in ternary materials can maintain good kinetic performance and rate discharge capacity, and can also reduce cation mixing and stabilize the layered structure. The low content of cobalt in the low-estimated / cobalt-free positive electrode material can reduce the electronic conductivity of the material, thereby reducing the rate performance and low-temperature performance. The cobalt-free positive electrode material increases the nickel content of the system to improve the energy density, but there is a strong negative correlation between the discharge capacity and the cycle stability. The decrease of the non-active Mn 4+ content for stabilizing the delithiated structure leads to the decrease of cycle stability.

[0005] Most of the currently developed cobalt-free materials are polycrystalline materials, and intergranular and intragranular cracks occur at high voltage, exposing a large number of fresh surfaces inside the secondary particles. The activity of lattice oxygen in the outer layer of the primary particles after material pulverization is high, and the oxygen release behavior will be greatly intensified, resulting in a decrease in structural stability and capacity fading. SUMMARY

[0006] In order to improve the deficiencies of the prior art, the present application provides a cobalt-free positive electrode material, a positive electrode sheet comprising the cobalt-free positive electrode material and a battery. The cobalt-free positive electrode material of the present application has a stable surface / interface structure, which can significantly improve the rate performance, cycle performance and safety performance of the battery when used in the battery.

[0007] To solve the above technical problems, the technical scheme provided by the present application is as follows:

[0008] A cobalt-free positive electrode material, comprising a substrate, a first coating layer and a second coating layer, the substrate comprises a material with a chemical formula of Li(Ni x Mn 1-x M 1 y M 2 z )O2; the first coating layer comprises a material with a chemical formula of Li(MnM 1 y M 2 z )2O4; the second coating layer comprises niobium tungsten oxide; wherein, 0.6≤x≤0.9, 0<y≤0.02, 0<z≤0.02; M 1 and M 2 are the same or different, and are independently selected from at least one of Al, Mg, Ti, Zr, B, Y, W, Sr, La, Mo, Nb and V.

[0009] According to the embodiment of the present application, the crystal structure of the cobalt-free positive electrode material is a single crystal structure, which can solve the repeated formation of micro-cracks in the cycle process of the polycrystalline cobalt-free positive electrode material, and improve the cycle performance and safety performance of the cobalt-free positive electrode material.

[0010] According to the embodiment of the present application, the first coating layer is coated on the surface of the substrate, and the coating is complete coating or partial coating.

[0011] According to the embodiment of the present application, the second coating layer is coated on the outer surface of the first coating layer, and the coating is complete coating or partial coating.

[0012] According to the embodiment of the present application, the chemical formula of the niobium tungsten oxide is Nb 18 W 16 O 93 or Nb 16 W5O 55 The present application adopts the method of coating the surface of the substrate with niobium tungsten oxide, which is beneficial to form the first coating layer with a spinel phase structure and the second coating layer with fast ion conductor performance on the surface of the substrate, and improves the lithium ion diffusion migration rate and kinetic performance of the cobalt-free positive electrode material.

[0013] According to an embodiment of the present application, the median particle size of the niobium tungsten oxide is 50-200 nm, for example 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, 110 nm, 120 nm, 130 nm, 140 nm, 150 nm, 160 nm, 170 nm, 180 nm, 190 nm or 200 nm.

[0014] According to an embodiment of the present application, the Li(Ni x Mn 1-x M 1 y M 2 z )O2 has a layered structure.

[0015] According to an embodiment of the present application, the Li(MnM 1 y M 2 z )2O4 has a spinel structure. The present application uses Li(MnM 1 y M 2 z )2O4 material with a spinel structure, which can stabilize the surface / interface structure of the positive electrode material and improve the cycle performance of the battery. Meanwhile, the present application uses the effect of co-doping (M 1 and M 2 ) to stabilize the structure of the positive electrode material. The high-valence cation doping can solve the collapse problem of Li(Ni x Mn 1-x M 1 y M 2 z )O2 layered structure, thereby improving the stability and long cycle performance of the layered structure.

[0016] According to an embodiment of the present application, the thickness of the first coating layer is 5-20 nm, for example 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, 10 nm, 11 nm, 12 nm, 13 nm, 14 nm, 15 nm, 16 nm, 17 nm, 18 nm, 19 nm or 20 nm.

[0017] According to an embodiment of the present application, the thickness of the second coating layer is 5-10 nm, for example 5 nm, 6 nm, 7 nm, 8 nm, 9 nm or 10 nm.

[0018] According to an embodiment of the present application, the mass of the first coating layer accounts for 0.02wt% to 2.5wt% of the total mass of the cobalt-free cathode material, for example, 0.02wt%, 0.03wt%, 0.05wt%, 0.08wt%, 0.1wt%, 0.2wt%, 0.3wt%, 0.4wt%, 0.5wt%, 0.6wt%, 0.7wt%, 0.8wt%, 0.9wt%, 1.0wt%, 1.1wt%, 1.2wt%, 1.3wt%, 1.4wt%, 1.5wt%, 1.6wt%, 1.7wt%, 1.8wt%, 1.9wt%, 2.0wt%, 2.1wt%, 2.2wt%, 2.3wt%, 2.4wt% or 2.5wt%.

[0019] According to an embodiment of the present application, the mass of the second coating layer accounts for 0.02wt% to 2.5wt% of the total mass of the cobalt-free cathode material, for example, 0.02wt%, 0.03wt%, 0.05wt%, 0.08wt%, 0.1wt%, 0.2wt%, 0.3wt%, 0.4wt%, 0.5wt%, 0.6wt%, 0.7wt%, 0.8wt%, 0.9wt%, 1.0wt%, 1.1wt%, 1.2wt%, 1.3wt%, 1.4wt%, 1.5wt%, 1.6wt%, 1.7wt%, 1.8wt%, 1.9wt%, 2.0wt%, 2.1wt%, 2.2wt%, 2.3wt%, 2.4wt% or 2.5wt%.

[0020] According to an embodiment of the present application, the median particle size of the cobalt-free cathode material is 2μm to 5μm.

[0021] The present application also provides a preparation method of the above-mentioned cobalt-free cathode material, which comprises the following steps:

[0022] (1) mixing a Ni x Mn 1-x (OH)2 precursor, a lithium salt, a compound containing metal element M 1 and a compound containing metal element M 2 , and performing first sintering to prepare a Li(Ni 1 Mn 2 x Mn 1- x M 1 y M 2 z )O2;

[0023] ​(2) mixing Nb2O5 and WO3, and then performing calcination and nanometer processing in sequence to obtain a niobium-tungsten oxide coating agent;

[0024] (3) mixing Li(Ni x Mn 1-x M 1 y M 2 z )O2 of step (1) with the niobium-tungsten oxide coating agent of step (2), and performing second sintering to obtain an intermediate;

[0025] (4) mixing the intermediate of step (3) with the niobium-tungsten oxide coating agent of step (2), and performing third sintering to obtain the cobalt-free positive electrode material.

[0026] According to the embodiment of the present application, in step (1), the Ni x Mn 1-x (OH)2 precursor is prepared by a coprecipitation method.

[0027] Exemplarily, the Ni x Mn 1-x (OH)2 precursor is prepared by the following method:

[0028] The soluble nickel salt, the soluble manganese salt and ammonia water are mixed, the pH of the reaction solution is adjusted to 11.0-12.0, and a coprecipitation reaction is performed to prepare the Ni x Mn 1-x (OH)2 precursor.

[0029] The temperature of the coprecipitation reaction is 50-70℃, and the time is 30-50h.

[0030] The mass concentration of the ammonia water is 10-18%.

[0031] The molar ratio of Ni 2+ and the soluble manganese salt Mn 2+ in the soluble nickel salt is x:1-x.

[0032] The coprecipitation reaction is performed under nitrogen gas protection.

[0033] According to the embodiment of the present application, in step (1), the lithium salt is selected from lithium carbonate and / or lithium hydroxide.

[0034] According to the embodiment of the present application, in step (1), the doping metal element M 1 and the doping metal element M 2 are defined as above.

[0035] According to an embodiment of the present application, in step (1), the compound containing the metal element M 1 is selected from oxides containing the metal element M 1 .

[0036] According to an embodiment of the present application, in step (1), the first sintering is performed at a temperature of 900°C to 1200°C for a holding time of 3h to 12h, at a temperature increase rate of 2°C / min to 5°C / min, in a pure oxygen atmosphere.

[0037] According to an embodiment of the present application, in step (1), the molar content ratio of Ni x and Mn 1-x in the Ni 2+ Mn 2+ (OH)2 precursor to the molar content of M 1 in the compound containing the metal element M 1 is 100:(0 to 2), excluding 100:0.

[0038] According to an embodiment of the present application, in step (1), the molar content ratio of Ni x and Mn 1-x in the Ni 2+ Mn 2+ (OH)2 precursor to the molar content of M 2 in the compound containing the metal element M 2 is 100:(0 to 2), excluding 100:0.

[0039] According to an embodiment of the present application, in step (1), the molar content ratio of Ni x and Mn 1-x in the Ni 2+ Mn 2+ (OH)2 precursor to the molar content of Li + in the lithium salt is (0.96 to 1.10):1.

[0040] According to an embodiment of the present application, in step (2), the molar ratio of Nb in Nb2O5 to W in WO3 is 18:16 or 16:5.

[0041] According to an embodiment of the present application, in step (2), the calcination is performed at a temperature of 1100°C to 1300°C for a time of 3h to 12h.

[0042] According to an embodiment of the present application, in step (2), the nanofabrication is performed by a ball milling process.

[0043] According to an embodiment of the present application, in step (2), the median particle size of the niobium tungsten oxide coating agent is 50-200 nm, for example, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, 110 nm, 120 nm, 130 nm, 140 nm, 150 nm, 160 nm, 170 nm, 180 nm, 190 nm or 200 nm.

[0044] According to an embodiment of the present application, in step (3), the temperature rising rate of the second sintering is 2-8°C / min, the temperature of the second sintering is 800-900°C, the time of the second sintering is 6-12 h, and the atmosphere of the second sintering is an oxygen-containing atmosphere.

[0045] According to an embodiment of the present application, in step (3), the mass ratio of the Li(Ni x Mn 1-x M 1 y M 2 z )O2 of step (1) to the niobium tungsten oxide coating agent of step (2) is 1:0.5%-1.5%.

[0046] According to an embodiment of the present application, in step (3), the added niobium tungsten oxide coating agent is calcined at a temperature of 800-900°C, and the niobium tungsten oxide itself will undergo a decomposition reaction, catalyzing the surface layer effect of the Li(Ni 1 Mn 2 M x Mn 1-x M 1 y M 2 z )O2 of the doped metal element M 1 y M 2 z )2O4 with a spinel structure, to maintain a more stable structure.

[0047] According to an embodiment of the present application, in step (4), the temperature rising rate of the third sintering is 2-8°C / min, the temperature of the third sintering is 600-800°C, the time of the third sintering is 6-12 h, and the atmosphere of the third sintering is an oxygen-containing atmosphere.

[0048] According to an embodiment of the present application, in step (4), the mass ratio of the intermediate obtained in step (3) to the niobium tungsten oxide coating agent of step (2) is 1:0.2%-0.6%.

[0049] According to an embodiment of the present application, in step (4), the niobium tungsten oxide coating agent is added and calcination is performed at a temperature of 600-800°C, so that a layer of niobium tungsten oxide with a fast ion conductor structure is formed on the surface of the material.

[0050] The present application also provides a positive electrode sheet comprising the cobalt-free positive electrode material described above.

[0051] According to an embodiment of the present application, the positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer coated on at least one side surface of the positive electrode current collector, wherein the positive electrode active material layer comprises the cobalt-free positive electrode material described above.

[0052] According to an embodiment of the present application, the positive electrode active material layer further comprises a conductive agent. In some embodiments, the conductive agent is selected from one or more of conductive carbon black, acetylene black, ketjen black, carbon fiber, graphene, single-walled carbon nanotube, and multi-walled carbon nanotube.

[0053] According to an embodiment of the present application, the positive electrode active material layer further comprises a binder. In some embodiments, the binder is selected from one or more of carboxymethyl cellulose, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyethylene, polyvinyl alcohol, polyvinyl chloride, polyvinyl fluoride, polyvinyl pyrrolidone, polytetrafluoroethylene, polypropylene, butadiene rubber, epoxy resin, butadiene rubber binder, and acrylonitrile-based binder.

[0054] According to an embodiment of the present application, the mass percentage of each component in the positive electrode active material layer is as follows:

[0055] 91-97.5wt% of the cobalt-free positive electrode material, 0.5-4wt% of the conductive agent, and 2-5wt% of the binder.

[0056] The present application also provides a battery comprising the cobalt-free positive electrode material described above, or a battery comprising the positive electrode sheet described above.

[0057] According to an embodiment of the present application, the battery is a lithium ion battery.

[0058] On the one hand, the cobalt-free positive electrode material is prone to phase change and lattice oxygen loss under high voltage, and the lattice structure phase and thermal stability are seriously deteriorated, the present application adopts a double-coating technology to form a special structure of the coating structure outside the substrate, the coating structure includes a protective inner layer (the first coating layer) with a spinel phase structure and an outer layer (the second coating layer) with excellent conductivity, which can stabilize the surface / interface structure and improve the cycle performance, and at the same time, the dynamic performance of the battery can be improved. On the other hand, the cobalt-free positive electrode material will produce a series of side reactions with the electrolyte under high voltage, the interface stability is poor, and the electrochemical performance such as cycle stability and high-temperature storage performance is greatly affected. The high-valence metal ion is doped, and the synergistic effect of multi-element doping can overcome the structural defects of the cobalt-free positive electrode material, and the electrochemical performance of the cobalt-free positive electrode material can be improved from multiple aspects, and the discharge specific capacity and cycle performance of the cobalt-free positive electrode material are improved.

[0059] The beneficial effects of the present application are as follows:

[0060] The present application provides a cobalt-free positive electrode material, a positive electrode sheet comprising the cobalt-free positive electrode material and a battery.

[0061] 1. The present application coats niobium tungsten oxide on the surface of the substrate material Li(Ni x Mn 1-x M 1 y M 2 z )O2, high ionic radius W 6+ and Nb 5+ can increase the interlayer spacing, the synergistic effect of Nb, W and O can form part of lithium vacancies and electron vacancies, which can effectively improve the bulk phase conductivity and grain boundary conductivity of the cobalt-free positive electrode material of the present application; the existence of lithium vacancies can establish a more smooth channel for the transmission of lithium ions, which can further improve the diffusion and migration rate of lithium ions, thereby improving the rate performance of the cobalt-free positive electrode material.

[0062] 2. The present application coats Li(MnM x Mn 1-x M 1 y M 2 z )2O4 with a spinel phase structure on the surface of the substrate material Li(Ni 1 y M 2 z )O2, the spinel phase structure of Li(MnM 1 y M 2 z)2O4 can improve the thermal stability and structural stability of the cobalt-free positive electrode material, effectively inhibiting the surface structure degradation phenomenon; at the same time, it can reduce the direct contact of the cobalt-free positive electrode material with the electrolyte, improve the interface stability, ensure the structural morphology of the cobalt-free positive electrode material to be complete, and achieve the effects of stabilizing the surface / interface structure and improving the cycle performance.

[0063] 3. The structure of the main body is stabilized by using the co-doping effect. The introduction of high-valence ions leads to charge compensation of the positive electrode structure, thereby generating holes. The generated holes make it easier for electrons to transition from the valence band to the conduction band, thereby enhancing the electronic conductivity and lithium ion diffusion capacity of the material. The transition metal ion is doped and embedded in the cobalt-free positive electrode material, thereby inhibiting the phase transition of the deep delithiation state structure, solving the problem of collapse of the layered structure caused by Li / Ni mixing, and making it a high-performance positive electrode material with stable structure.

[0064] 4. Single crystal route. In the cycle process, intercrystalline cracks and secondary ball structure collapse will inevitably occur in conventional polycrystalline materials, thereby causing serious performance decline. The cobalt-free positive electrode material of the present application has a single crystal structure, which has fewer grain boundaries and a complete crystal structure, can greatly inhibit the intercrystalline cracks caused by anisotropic stress in the long-term cycle process and the oxygen release and particle pulverization of the positive electrode in the cycle process, and improve the cycle performance and safety performance of the cobalt-free positive electrode material. BRIEF DESCRIPTION OF DRAWINGS

[0065] Figure 1 is the XRD pattern of the cobalt-free positive electrode material of embodiment 1 of the present application;

[0066] Figure 2 is the SEM pattern of the cobalt-free positive electrode material of embodiment 1 of the present application;

[0067] Figure 3 is the test data of the coin cell assembled by the cobalt-free positive electrode material of embodiment 1 of the present application;

[0068] Figure 4 is the 45℃ cycle capacity retention rate graph of the lithium ion battery assembled by the cobalt-free positive electrode material of embodiment 1 of the present application;

[0069] Figure 5 is a structural schematic diagram of the cobalt-free positive electrode material of embodiment 1 of the present application. DETAILED DESCRIPTION

[0070] The present application will be further described in detail below in conjunction with specific embodiments. It should be understood that the following embodiments are only exemplary to illustrate and explain the present application, and should not be interpreted as limiting the scope of protection of the present application. Any technology realized based on the above description of the present application is covered within the scope intended to be protected by the present application.

[0071] The experimental methods used in the following examples are conventional methods unless otherwise specified; the reagents, materials, etc. used in the following examples are commercially available unless otherwise specified.

[0072] Example 1

[0073] I. Preparation of the positive electrode material

[0074] 1). Synthesis of Ni 0.65 Mn 0.35 (OH)2precursor by co-precipitation, wherein NiSO4, MnSO4and ammonia are co-precipitated according to a molar ratio n(Ni):n(Mn) = 65:35, to obtain a Ni 0.65 Mn 0.35 (OH)2precursor; the reaction temperature is 50°C, and the reaction time is 36 h; ammonia is added to adjust the pH of the reaction solution to 11.2, and nitrogen is continuously introduced into the reaction kettle; the Ni 0.65 Mn 0.35 (OH)2precursor is mixed with LiOH according to a molar ratio of the sum of the molar contents of Ni 2+ and Mn 2+ to the molar content of Li + (Ni 2+ + Mn 2+ ):Li + = 1:1.02, and the Ni 0.65 Mn 0.35 (OH)2precursor, ZrO2and TiO2are mixed according to a molar ratio (Ni 2+ + Mn 2+ ):Zr 2+ :Ti 2+ = 100:0.5:0.5, uniformly mixed, and then subjected to first sintering at a sintering temperature of 1080°C for 4 h, to obtain Li(Ni 0.65 Mn 0.35 Ti 0.005 Zr 0.005 )O2.

[0075] 2). Nb2O5and WO3are mixed according to a molar ratio n(Nb):n(W) = 18:16, and then subjected to sintering and ball milling in sequence, to obtain a niobium-tungsten oxide coating agent Nb 18 W 16 O 93 with a particle size of 80 nm; the sintering temperature is 1200°C, and the time is 4 h;

[0076] 3). Li(Ni 0.65 Mn 0.35 Ti 0.005 Zr 0.005O2 and niobium tungsten oxide coating agent Nb 18 W 16 O 93 Sintering temperature is 860℃, and time is 8h; the intermediate is coated with niobium tungsten oxide and lithium nickel manganese cobalt oxide Li(Ni 0.65 Mn 0.35 Ti 0.005 Zr 0.005 O2 together, and decomposes into the intermediate coated with Li(MnTi 0.005 Zr 0.005 )2O4 coating layer at high temperature;

[0077] 4). The intermediate obtained above is mixed with niobium tungsten oxide coating agent Nb 18 W 16 O 93 Sintering temperature is 680℃, and time is 8h.

[0078] II. Assembling of button cell: the cobalt-free positive electrode material, conductive agent and PVDF are weighed and uniformly mixed according to the mass ratio of 90:5:5, and are dispersed with N-methyl pyrrolidone (NMP) solvent to form a slurry; the slurry is uniformly coated on an aluminum foil and dried at 80℃ for 12h to obtain a positive electrode sheet; the dried positive electrode sheet is cut into a round sheet after rolling and is placed in a glove box for standby. The round sheet prepared above is used as a positive electrode, lithium metal is used as a negative electrode, Celgard 2400 (microporous polypropylene film) is used as a separator, and 1mol / L LiPF6+(EC:EMC:DMC=1:1:1) is used as an electrolyte to assemble a 2032 type button cell.

[0079] III. Assembling of lithium ion battery:

[0080] (1) Preparation of positive electrode sheet

[0081] The positive electrode material, binder, conductive carbon black SP and carbon nanotube CNT prepared above are mixed according to the weight ratio of 96:2:1.5:0.5, N-methyl pyrrolidone (NMP) is added, and the mixture is stirred into a uniform and flowable positive electrode slurry under the action of a vacuum stirrer; N-methyl pyrrolidone (NMP) is added to adjust the solid content of the positive electrode slurry; the positive electrode slurry is uniformly coated on a 12um aluminum foil, and the coating surface density is controlled at 15.0mg / cm2; the coated aluminum foil is baked in an oven with different temperature gradients in five stages, and the baked electrode sheet is rolled twice, and the rolled electrode sheet is cut and ultrasonically welded to obtain the required positive electrode sheet.

[0082] (2) Preparation of negative electrode sheet

[0083] The negative electrode active material graphite, thickener sodium carboxymethyl cellulose (CMC-Na), binder styrene-butadiene rubber (SBR), and conductive agent acetylene black (SP) were mixed in a weight ratio of 96.5:1.0:1.0:1.5, and deionized water was added as a solvent. The mixture was stirred in a vacuum mixer to obtain a negative electrode slurry. The negative electrode slurry was uniformly coated onto copper foil. The coated copper foil was baked in an oven with three different temperature gradients. The baked electrode was then rolled twice. After rolling, the electrode was slit and super-welded to obtain the desired negative electrode.

[0084] (3) Electrolyte preparation and separator preparation

[0085] The electrolyte uses a commercially available electrolyte, with ethylene carbonate, propylene carbonate, and diethyl carbonate in a mass ratio of 1:1:1 as the solvent, and 1 mol / L lithium hexafluorophosphate (LiPF6) as the lithium salt. Film-forming additives and high-voltage additives are also added to the composition. A 7+3μm hybrid coating membrane (polypropylene substrate + PVDF & ceramic hybrid coating) is selected as the separator.

[0086] (4) Preparation of lithium-ion batteries

[0087] The prepared positive electrode sheet, separator, and negative electrode sheet are stacked in sequence. The positive electrode is connected to aluminum tabs via aluminum foil sheets, and the negative electrode is connected to nickel tabs via copper foil sheets, thus preparing a multi-tab type battery cell. Two layers of separator sheets wrap the negative electrode sheet, and the positive electrode sheet is placed on the separator sheets, ensuring that the separator sheets are between the positive and negative electrodes to isolate and subsequently transport lithium ions. Then, the cells are wound to obtain bare cells without electrolyte filling. The bare cells are heat-sealed in a shell made of aluminum-plastic film, and electrolyte is injected into the bare cells with a moisture content of <200ppm after baking. After vacuum sealing, hot and cold pressing, formation, shaping, and sorting, a lithium-ion battery is obtained.

[0088] Figure 1 The image shows the XRD pattern of the cobalt-free cathode material in Example 1. Figure 1 The results show that the prepared material is a solid solution material, and no other impurity phases appear in the structure, which belongs to the layered ternary cathode material spectrum.

[0089] Figure 2 Here is a SEM image of the cobalt-free cathode material from Example 1. Figure 2 As can be seen, the prepared particles are single-crystal particles with a relatively smooth and rounded surface and good surface coating effect. The median particle size of the cobalt-free cathode material is 2μm to 5μm.

[0090] Figure 3 The test data for the coin cell assembled with the cobalt-free cathode material of Example 1 shows that its specific capacity at 0.1C discharge is 196.2 mAh / g, indicating that the cathode material has a high specific capacity.

[0091] Figure 4 This is a graph showing the 45°C cycle capacity retention of the lithium-ion battery assembled with the cobalt-free cathode material of Example 1; from Figure 4 As can be seen, the capacity retention rate after 1000 battery cycles is 88.2%, indicating that the cathode material has excellent cycle performance.

[0092] Figure 5 This is a schematic diagram of the structure of the cobalt-free cathode material in Example 1. From... Figure 5 As can be seen from Example 1, the cathode material prepared has a multilayer structure, including a cobalt-free cathode material matrix, a protective inner layer (intermediate layer) with a spinel phase structure, and an outer layer (outer layer) with excellent conductivity.

[0093] Example 2

[0094] I. Preparation of cathode materials

[0095] 1) Ni was synthesized using a co-precipitation method. 0.7 Mn 0.3 The (OH)₂ precursor was obtained by co-precipitation of NiSO₄, MnSO₄, and ammonia water in a molar ratio of n(Ni):n(Mn) = 70:30 to yield Ni. 0.7 Mn 0.3 (OH)₂ precursor; reaction temperature 65℃, reaction time 48h; ammonia water added to adjust the pH of the reaction solution to 11.5, nitrogen gas continuously purged into the reactor; Ni 0.7 Mn 0.3 (OH)₂ precursor reacts with LiOH in Ni 2+ and Mn 2+ The sum of the molar contents of Li + The ratio of the molar contents of Ni is the molar ratio (Ni 2+ +Mn 2+ ):Li + Mix Ni at a ratio of 1:1.05. 0.7 Mn 0.3 (OH)2 precursor, Al2O3 and ZrO2 in molar ratio (Ni 2+ +Mn 2+ ):Al 3+ :Zr 2+ The mixture was prepared by mixing the components in a ratio of 100:0.6:0.5, followed by a first sintering at 1050℃ for 6 hours to obtain Li(Ni) alloy. 0.7 Mn 0.3 Al 0.006 Zr 0.005 O2;

[0096] 2). The Nb2O5 and WO3 are mixed in a molar ratio of n(Nb):n(W)=18:16, and then sintering calcination and ball milling are sequentially performed to obtain the niobium tungsten oxide coating agent Nb 18 W 16 O 93 at a sintering temperature of 1250°C for 4h;

[0097] 3). The Li(Ni 0.7 Mn 0.3 Al 0.006 Zr 0.005 )O2 and the niobium tungsten oxide coating agent Nb 18 W 16 O 93 are mixed in a mass ratio of 1:0.75% and uniformly mixed, and then second sintering is performed to obtain an intermediate; the sintering temperature is 880°C, and the sintering time is 7h; the niobium tungsten oxide and the Li(Ni 0.7 Mn 0.3 Al 0.006 Zr 0.005 )O2 jointly act, and are decomposed at high temperature into the intermediate with a spinel phase structure coating layer;

[0098] 4). The intermediate obtained above and the niobium tungsten oxide coating agent Nb 18 W 16 O 93 are mixed in a mass ratio of 1:0.3% and uniformly mixed, and then third sintering is performed to obtain the cobalt-free positive electrode material; the sintering temperature is 700°C, and the sintering time is 8h.

[0099] II. Assembling of button cell: the steps are as in Example 1.

[0100] III. Assembling of lithium ion battery: the steps are as in Example 1.

[0101] Example 3

[0102] I. Preparation of positive electrode material

[0103] 1). The Ni 0.75 Mn 0.25 (OH)2 precursor is synthesized by a coprecipitation method, and NiSO4, MnSO4 and ammonia are coprecipitated in a molar ratio of n(Ni):n(Mn)=75:25 to obtain the Ni 0.75 Mn 0.25 (OH)2 precursor; the reaction temperature is 60°C, and the reaction time is 42h; ammonia is added to adjust the pH of the reaction solution to 11.8, and nitrogen is continuously introduced into the reaction kettle; the Ni 0.75 Mn 0.25 (OH)2 precursor and Li2CO3 are mixed in a mass ratio of Ni 2+ and Mn2+ the sum of the molar contents of Li + the ratio of the molar contents of Li 2+ +Mn 2+ ):Li + = 1:1.05, and then mixed, the Ni 0.75 Mn 0.25 (OH)2 precursor, Y2O3 and TiO2 were mixed in a molar ratio (Ni 2+ +Mn 2+ ):Y 3+ :Ti 2+ = 100:0.5:0.4, uniformly mixed, and then first sintered at a sintering temperature of 1000°C for 8h; to obtain Li(Ni 0.75 Mn 0.25 Y 0.005 Ti 0.004 )O2;

[0104] 2). The Nb2O5 and WO3 were mixed in a molar ratio n(Nb):n(W) = 16:5, and then sequentially sintered, calcined and ball-milled to obtain a niobium tungsten oxide coating agent Nb 16 W5O 55 with a particle size of 100nm; the sintering temperature was 1200°C for 5h;

[0105] 3). The Li(Ni 0.75 Mn 0.25 Y 0.005 Ti 0.004 )O2 and the niobium tungsten oxide coating agent Nb 16 W5O 55 were mixed uniformly in a mass ratio of 1:1%, and then second sintered to obtain an intermediate; the sintering temperature was 860°C for 8h; the niobium tungsten oxide and the Li(Ni 0.75 Mn 0.25 Y 0.005 Ti 0.004 )O2 jointly acted, and were decomposed at high temperature into an intermediate with a spinel phase structure coating layer;

[0106] 4). The above obtained intermediate and the niobium tungsten oxide coating agent Nb 16 W5O 55 were mixed uniformly in a mass ratio of 1:0.5%, and then third sintered to obtain the cobalt-free positive electrode material; the sintering temperature was 720°C for 8h.

[0107] II. Assembling of button cell: the steps were as in Example 1.

[0108] III. Assembling of lithium ion battery: the steps were as in Example 1.

[0109] Example 4

[0110] I. Preparation of the positive electrode material

[0111] 1). Synthesis of Ni 0.6 Mn 0.4 (OH)2precursor by co-precipitation method, NiSO4, MnSO4and ammonia were co-precipitated according to the molar ratio n(Ni):n(Mn) = 60:40, and Ni 0.6 Mn 0.4 (OH)2precursor was obtained; the reaction temperature was 60°C, and the reaction time was 50 h; ammonia was added to adjust the pH of the reaction solution to 11.0, and nitrogen was continuously introduced into the reaction kettle; the Ni 0.6 Mn 0.4 (OH)2precursor was mixed with LiOH according to the molar ratio of the sum of the molar contents of Ni 2+ and Mn 2+ to the molar content of Li + , i.e. (Ni 2+ + Mn 2+ ):Li + = 1:1.025, the Ni 0.6 Mn 0.4 (OH)2precursor, WO3and ZrO2were mixed according to the molar ratio (Ni 2+ + Mn 2+ ):W 3+ :Zr 2+ = 100:0.5:0.5, and after uniform mixing, first sintering was performed at a sintering temperature of 1120°C for 4 h; Li(Ni 0.6 Mn 0.4 W 0.005 Zr 0.005 )O2was prepared;

[0112] 2). Nb 16 W5O 55 , a niobium tungsten oxide coating agent, was obtained by mixing Nb2O5and WO3according to the molar ratio n(Nb):n(W) = 16:5, and then sequentially performing sintering calcination and ball milling treatment; the sintering temperature was 1200°C, and the time was 5 h;

[0113] 3). Li(Ni 0.6 Mn 0.4 W 0.005 Zr 0.005 )O2was mixed with the niobium tungsten oxide coating agent Nb 16 W5O 55 according to the mass ratio of 1:0.8%, and after uniform mixing, second sintering was performed to obtain an intermediate; the sintering temperature was 880°C, and the time was 5 h; the niobium tungsten oxide and Li(Ni0.6 Mn 0.4 W 0.005 Zr 0.005 )O2cooperate and decompose into an intermediate at high temperature, which has a spinel phase structure coating layer;

[0114] 4). The intermediate obtained above is mixed with the niobium tungsten oxide coating agent Nb 16 W5O 55 at a mass ratio of 1:0.4%, and uniformly mixed to perform third sintering to obtain the cobalt-free positive electrode material; the sintering temperature is 720°C, and the time is 8h.

[0115] II. Assembling of button cell: the steps are as in Example 1.

[0116] III. Assembling of lithium ion battery: the steps are as in Example 1.

[0117] Comparative Example 1

[0118] I. Preparation of positive electrode material

[0119] 1). Synthesizing Ni 0.7 Mn 0.3 (OH)2precursor by co-precipitation method, and co-precipitating NiSO4, MnSO4and ammonia water at a molar ratio of n(Ni):n(Mn) = 70:30 to obtain Ni 0.7 Mn 0.3 (OH)2precursor; the reaction temperature is 65°C, and the reaction time is 48h; ammonia water is added to adjust the pH of the reaction solution to 11.5, and nitrogen gas is continuously introduced into the reaction kettle; the Ni 0.7 Mn 0.3 (OH)2precursor is mixed with LiOH at a molar ratio of the sum of the molar contents of Ni 2+ and Mn 2+ to the molar content of Li + , i.e. (Ni 2+ + Mn 2+ ):Li + = 1:1.02, and the Ni 0.7 Mn 0.3 (OH)2precursor, Y2O3and ZrO2are mixed at a molar ratio of (Ni 2+ + Mn 2+ ):Y 3+ :Ti 2+ = 100:0.6:0.5, uniformly mixed, and then subjected to first sintering at a sintering temperature of 1080°C for 6h; to obtain Li(Ni 0.7 Mn 0.3 Y 0.006 Zr 0.005 )O2.

[0120] 2). Li(Ni 0.7 Mn 0.3 Y 0.006 Zr 0.005 )O2 and Al2O3 coating agent were mixed uniformly according to the mass ratio of 1:0.3%, and the third sintering was carried out to obtain the cobalt-free positive electrode material; the sintering temperature was 720°C, and the time was 8h.

[0121] II. Assembling of button cell: the steps were as in Example 1.

[0122] III. Assembling of lithium ion battery: the steps were as in Example 1.

[0123] Test example

[0124] a. Discharge gram capacity test:

[0125] The button cells of the examples and comparative examples were tested for charging performance at a temperature of 25±5°C, and the test process was as follows:

[0126] 1) The button cell was activated for 24h;

[0127] 2) 0.1C constant current charging to 4.45V, with a cutoff current of 0.05C;

[0128] 3) Rest for 10 minutes;

[0129] 4) 0.1C constant current discharging to the lower limit voltage 2.8V.

[0130] The discharge gram capacity of the positive electrode material was calculated, and the results were shown in Table 1.

[0131] b. Rate test (25°C, 2C / 0.33C):

[0132] The lithium ion batteries of the examples and comparative examples were tested for rate performance at a temperature of 25±2°C, and the test process was as follows:

[0133] 1) Capacity test by 0.2C / 0.2C cycling for three times in a 25±2°C environment;

[0134] 2) 0.5C discharging to the lower limit voltage (2.8V);

[0135] 3) Rest for 30min;

[0136] 4) 0.5C constant current charging to the upper limit voltage (4.4V) and then constant voltage charging, with a cutoff current of 0.05C;

[0137] 5) Rest for 30min;

[0138] 6) nC discharge to lower limit voltage, wherein nC = 0.2C / 0.33C / 0.5C / 0.7C / 1C / 1.5C / 2C / 3C / 5C;

[0139] 7) Repeat steps 3-6 to complete the discharge steps for all rates.

[0140] The rate performance of the battery (rate = 2C discharge capacity / 0.33C discharge capacity) was calculated, and the results are shown in Table 1.

[0141] c. Cycle capacity test

[0142] The lithium ion batteries of the examples and comparative examples were tested for cycle performance at 25±2℃ and 45±2℃, respectively. The test process included:

[0143] 1) The battery cell was placed in an environment of 25±2℃ (45±2℃);

[0144] 2) 0.5C discharge to lower limit voltage (2.8V), and stand for 30 min;

[0145] 3) 1C charge to upper limit voltage (4.4V), with a cutoff current of 0.05C;

[0146] 4) Stand for 30 min;

[0147] 5) 1C discharge to lower limit voltage (2.8V), and stand for 30 min;

[0148] 6) 1C charge to upper limit voltage (4.4V), with a cutoff current of 0.05C, and stand for 30 min;

[0149] Repeat steps 5-6 for 1000 cycles.

[0150] Capacity retention formula: the first cycle test capacity is denoted as A1, and the test capacity after 1000 cycles is denoted as A2; the capacity retention rate = A2 / A1 x 100%, and the specific test results are shown in Table 1.

[0151] d. Low temperature performance test (-20℃ / 25℃)

[0152] Test the state voltage, internal resistance, and thickness of the lithium ion battery at 25℃±2℃.

[0153] 1) Stand for 30 min at 25±2℃;

[0154] 2) 0.5C discharge to lower limit voltage 2.8V;

[0155] 3) Stand for 4h;

[0156] 4) 1C charge to upper limit voltage 4.4V, with a cutoff current of 0.05C;

[0157] 5) 4h rest;

[0158] 6) 4h rest at different temperature (25℃ / 45℃ / 0℃ / -10℃ / -20℃) and discharged at 1C to 2.8V;

[0159] 7) 4h rest at 25±2℃;

[0160] Repeat steps 4-7 until all temperature discharge tests are completed.

[0161] The rate capability of the battery was calculated (Rate = Discharge capacity at -20℃ / Discharge capacity at 25℃), and the results are shown in Table 1.

[0162] e. Thermal decomposition temperature test - DSC test

[0163] The lithium ion cell was fully charged to 4.4V at 0.33C rate, and disassembled in a glove box filled with argon to recover the positive electrode sheet, and the electrode sheet was washed with dimethyl carbonate (DMC) and dried. The positive electrode sheet and electrolyte were placed together in a high-pressure crucible of a thermal analysis instrument, 1 mol / L LiPF6(EC:DMC:DMC=1:1:1) was used as electrolyte, and the positive electrode sheet and electrolyte were prepared according to 1mg:0.6μL. The thermal analysis test temperature range was 25-500℃, and the heating rate was 5℃ / min.

[0164] Table 1 Battery performance of Examples 1-4 and Comparative Example 1

[0165]

[0166] The above describes embodiments of the present application. However, the present application is not limited to the above-described embodiments. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application should be included in the scope of protection of the present application.

Claims

1. A cobalt-free cathode material, characterized in that, The cobalt-free positive electrode material comprises a base body, a first coating layer and a second coating layer, the base body comprises a material with a chemical formula of Li(Ni x Mn 1-x M 1 y M 2 z )O2; the first coating layer comprises a material with a chemical formula of Li(MnM 1 y M 2 z )2O4; the second coating layer comprises niobium tungsten oxide; wherein 0.6≤x≤0.9, 0<y≤0.02, 0<z≤0.02; M 1 and M 2 are the same or different, and are independently selected from at least one of Al, Mg, Ti, Zr, B, Y, W, Sr, La, Mo, Nb and V. The chemical formula of the niobium tungsten oxide is Nb 18 W 16 O 93 or Nb 16 W5O 55 ; The preparation method of the cobalt-free positive electrode material comprises the following steps: (3) mixing Li(Ni x Mn 1-x M 1 y M 2 z )O2 with a niobium tungsten oxide coating agent, and performing second sintering to obtain an intermediate body; (4) mixing the intermediate obtained in step (3) with a niobium tungsten oxide coating agent, and performing third sintering to obtain the cobalt-free positive electrode material; In step (3), the temperature of the second sintering is 800-900°C, the time of the second sintering is 6-12h, and the atmosphere of the second sintering is an oxygen-containing atmosphere. In step (4), the temperature of the third sintering is 600-800°C, the time of the third sintering is 6-12h, and the atmosphere of the third sintering is an oxygen-containing atmosphere.

2. The cobalt-free cathode material of claim 1, wherein, The crystal structure of the cobalt-free positive electrode material is a single crystal structure.

3. The cobalt-free cathode material of claim 1 or 2, wherein, The first coating layer is coated on the surface of the substrate, and the second coating layer is coated on the outer surface of the first coating layer, and the coating is complete coating or partial coating.

4. The cobalt-free cathode material of claim 1, wherein, The median particle size of the niobium tungsten oxide is 50-200nm.

5. The cobalt-free cathode material of claim 1, wherein, Li(Ni x Mn 1-x M 1 y M 2 z )O2 has a layered structure; and / or, the Li(MnM 1 y M 2 z )2O4 has a spinel phase structure.

6. The cobalt-free cathode material of claim 1, wherein, The thickness of the first coating layer is 5-20nm; And / or, the thickness of the second coating layer is 5-10nm.

7. The cobalt-free cathode material of claim 1 or 6, wherein, The mass of the first coating layer accounts for 0.02wt%-2.5wt% of the total mass of the cobalt-free positive electrode material; And / or, the mass of the second coating layer accounts for 0.02wt%-2.5wt% of the total mass of the cobalt-free positive electrode material.

8. The cobalt-free cathode material of claim 1, wherein, The preparation method of the cobalt-free positive electrode material comprises the following steps: (1) Ni x Mn 1-x (OH)₂ precursor, lithium salt, containing metal element M 1 Compounds and compounds containing the metal element M 2 The compounds were mixed and subjected to a first sintering process to prepare the doped metal element M. 1 and doped metal element M 2 Li(Ni) x Mn 1-x M 1 y M 2 z O2; (2) mixing Nb2O5 and WO3, and then performing calcination and nanomachining in sequence to obtain a niobium tungsten oxide coating agent.

9. The cobalt-free cathode material of claim 8, wherein, In step (2), the molar ratio of Nb in Nb2O5 to W in WO3 is 18:16 or 16:5; And / or, in step (2), the temperature of the calcination is 1100-1300°C, and the time is 3-12h; And / or, in step (2), the nanomachining is ball milling treatment; And / or, in step (2), the median particle size of the niobium tungsten oxide coating agent is 50-200nm.

10. The cobalt-free cathode material of claim 1, wherein, In step (3), the heating rate of the second sintering is 2-8°C / min, And / or, in step (3), the mass ratio of Li(Ni x Mn 1-x M 1 y M 2 z )O2 to the niobium tungsten oxide coating agent is 1:0.5%~1.5%.

11. The cobalt-free cathode material of claim 1, wherein, In step (4), the heating rate of the third sintering is 2-8°C / min, And / or, in step (4), the mass ratio of the intermediate obtained in step (3) to the niobium tungsten oxide coating agent is 1:0.2%-0.6%.

12. A positive electrode sheet characterized by comprising: The positive electrode sheet comprises the cobalt-free positive electrode material according to any one of claims 1-11.

13. The positive electrode sheet according to claim 12, characterized by The positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer coated on at least one side surface of the positive electrode current collector, and the positive electrode active material layer comprises the cobalt-free positive electrode material.

14. A battery comprising the cobalt-free positive electrode material according to any one of claims 1-11; or, the battery comprises the positive electrode sheet according to claim 12 or 13.

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