Composite coated modified positive electrode material, preparation method thereof and secondary battery

Abstract

The invention discloses a composite coated modified positive electrode material, a preparation method thereof and a secondary battery, the composite coated modified positive electrode material provided by the invention comprises a positive electrode material and a composite coating layer on the surface of the positive electrode material, and the composite coating layer is composed of a fast ion conductor and a conductive polymer. The used fast ion conductor is a self-synthesized fast ion conductor and has the characteristics of stable crystal lattice, low surface brittleness and high ionic conductivity, the fast ion conductor and the conductive polymer are simultaneously coated on the surface of the positive electrode material to form a composite coating layer, and an electron-ion double-conduction transmission network is formed on the surface of the positive electrode material; the interface stability of the positive electrode material is enhanced, the volume expansion effect is relieved, and the electrochemical performance of the positive electrode material is comprehensively and effectively improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of battery materials, in particular to a composite-coated modified positive electrode material, a preparation method thereof and a secondary battery. BACKGROUND

[0002] Lithium ion batteries have been widely used in electric vehicles (EV) and hybrid electric vehicles (HEV). In the past decade, driven by the progress in the field of new energy materials, improving the energy density and designing high-energy-density battery systems have become the focus of current industry research, and the positive electrode material has become a key factor determining its performance. Especially, medium-high nickel positive electrode materials have high specific capacity and other characteristics, and have become the primary choice for designing high-energy-density lithium ion batteries. However, there are problems such as Li-Ni mixing, H2-H3 phase transition and oxygen precipitation under long-time high-current conditions, and the interface phase reaction leads to the generation of HF, which poses a safety problem. These problems hinder the further application of medium-high nickel materials in high-energy-density battery systems. SUMMARY

[0003] The present application aims to overcome the above-mentioned deficiencies in the prior art and provide a composite-coated modified positive electrode material, a preparation method thereof and a secondary battery.

[0004] The present application solves the technical problem by using the following technical solution.

[0005] The present application provides a composite-coated modified positive electrode material, which comprises a positive electrode material and a composite coating layer on the surface of the positive electrode material, the composite coating layer being composed of a fast ion conductor and a conductive polymer, the general formula of the fast ion conductor being: Li5A2B 0.5 C 1-x D x Si2O 12 , wherein: A comprises at least one of Al 3+ , Ca 3+ , Sc 3+ and Y 3+ , B comprises at least one of Mg 2+ , Zn 2+ , Cu 2+ and Ca 2+ , C comprises at least one of Sn 4+ , Ce 4+ and Ge 4+ , D comprises at least one of Zr 4+ , Hf 4+ and Ti 4+ , and the doping amount of the doping element D is 0.1-10wt% of Li5A2B 0.5 CSi2O 12 .

[0006] The application further provides a preparation method of the composite-coated modified positive electrode material.

[0007] The application further provides a secondary battery, wherein the positive electrode of the secondary battery comprises the composite-coated modified positive electrode material.

[0008] The application has the following beneficial effects:

[0009] The application provides a composite-coated modified positive electrode material, a preparation method thereof and a secondary battery. A fast ion conductor with characteristics of stable crystal lattice, low surface brittleness and high ion conductivity is self-synthesized, and the fast ion conductor is coated on the surface of a positive electrode material together with a conductive polymer to form a composite coating layer. The composite fast ion conductor formed by the combination of the fast ion conductor and the conductive polymer can form an "electron-ion" double-continuous transmission network on the surface of the positive electrode material, which can simultaneously consider the ion conductivity and electronic conductivity of the material. In addition, the flexible and dense coating layer formed by the conductive polymer and the fast ion conductor blocks the invasion of the electrolyte, reduces the direct reaction between the positive electrode material and the electrolyte, and effectively improves the overall performance of the electrode material. BRIEF DESCRIPTION OF DRAWINGS

[0010] In order to more clearly illustrate the technical solutions of the embodiments of the application, the following will briefly introduce the drawings needed to be used in the embodiments. It should be understood that the following drawings only show some of the embodiments of the application, and therefore should not be considered as a limitation to the scope. For those skilled in the art, other related drawings can also be obtained without creative labor on the basis of these drawings.

[0011] Figure 1 The preparation flow chart of the composite-coated modified positive electrode material in the application;

[0012] Figure 2 The scanning electron microscope image of the sample in Example 1;

[0013] Figure 3 The transmission electron microscope image of the sample in Example 1;

[0014] Figure 4 The half-cell cycle performance (5C rate 200 cycles) of Example 1 and Comparative Example 1. DETAILED DESCRIPTION

[0015] In order to make the purposes, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below. If the specific conditions are not specified in the embodiments, the conventional conditions or the conditions suggested by the manufacturers are adopted. If the manufacturers of the reagents or instruments are not specified, the conventional products that can be commercially purchased are adopted.

[0016] The composite-coated modified positive electrode material, the preparation method thereof and the secondary battery provided by the embodiments of the present application will be described in detail below.

[0017] In the first aspect, the embodiments of the present application provide a composite-coated modified positive electrode material, which comprises a positive electrode material and a composite coating layer on the surface of the positive electrode material, and the composition of the composite coating layer is a fast ion conductor and a conductive polymer, and the general formula of the fast ion conductor is Li5A2B 0.5 C 1-x D x Si2O 12 , wherein A comprises at least one of Al 3+ , Ca 3+ , Sc 3+ and Y 3+ , B comprises at least one of Mg 2+ , Zn 2+ , Cu 2+ and Ca 2+ , C comprises at least one of Sn 4+ , Ce 4+ and Ge 4+ , D comprises at least one of Zr 4+ , Hf 4+ and Ti 4+ , and the doping amount of the doping element D is 0.1-10wt% of Li5A2B 0.5 CSi2O 12 .

[0018] The middle and high nickel positive electrode material has the characteristics of high specific capacity, and becomes the primary choice for designing high energy density lithium ion batteries at present. However, there are problems such as Li-Ni mixing, H2-H3 phase change and oxygen precipitation under long time and large current conditions, and HF is generated due to interface reaction, which has safety hazards. These problems hinder the further application of middle and high nickel positive electrode materials in high specific energy battery systems. The common modification method is to coat the surface of the middle and high nickel material with a nano-scale additive, and form a coating layer by high temperature calcination, so as to isolate the interface reaction between the positive electrode material and the electrolyte, and reduce the residual alkali of the positive electrode material. The fast ion conductor has the characteristics of high ionic conductivity, low interface impedance and excellent chemical stability, which effectively improves the overall rate and cycle performance of the battery. However, the common fast ion conductor has certain surface brittleness and poor interface compatibility with the middle and high nickel material, so that the common fast ion conductor coated modification of the middle and high nickel positive electrode material has limited application under high rate and long cycle conditions.

[0019] To overcome the above problems existing in the prior art, the embodiment of the present application provides a composite coated modified positive electrode material, which comprises a positive electrode material and a composite coating layer on the surface of the positive electrode material, the composition of the composite coating layer is a fast ion conductor and a conductive polymer, the general formula of the fast ion conductor is: Li5A2B 0.5 C 1- x D x Si2O 12 , wherein: A comprises at least one of Al 3+ , Ca 3+ , Sc 3+ and Y 3+ , B comprises at least one of Mg 2+ , Zn 2+ , Cu 2+ and Ca 2+ , C comprises at least one of Sn 4+ , Ce 4+ and Ge 4+ , D comprises at least one of Zr 4+ , Hf 4+ and Ti 4+ , and the doping amount of the doping element D is Li5A2B 0.5 CSi2O 120.1-10wt%. The composite coating modified positive electrode material, the fast ion conductor in the composite coating layer coated on the surface of the positive electrode material is a self-synthesized fast ion conductor, the particle strength is enhanced by introducing A, B and C elements in the oxide, and the lattice strength is further stabilized by adding a doped doping element D to further reduce the surface brittleness of the fast ion conductor. The conductive polymer has the flexibility of the polymer material and the conductivity of the conductor, and coating it on the surface of the positive electrode material can realize multiple performance improvement, such as strengthening electronic conduction, blocking interface reaction, buffering volume change and improving structural stability. In the present application, the combination of fast ion conductor and conductive polymer can improve the problems of poor interface compatibility of fast ion conductor and lithium nickel cobalt manganese oxide, and the combination of fast ion conductor and conductive polymer can form a composite fast ion conductor with the advantages of both fast ion conductor and conductive polymer, which can be uniformly coated with lithium nickel cobalt manganese oxide to effectively reduce the residual alkali on the surface of the positive electrode material. In addition, the composite fast ion conductor formed by the combination of fast ion conductor and conductive polymer can form an "electron-ion" double continuous transmission network on the surface of the positive electrode material, which can simultaneously consider the ion conductivity and electronic conductivity of the material, effectively improve the overall performance of the electrode material, and the flexibility of the conductive polymer can buffer the mechanical stress caused by the volume change, and the rigid structure of the fast ion conductor can maintain the overall stability of the coating layer, which is especially suitable for positive electrode materials with severe volume change during charging and discharging, and can effectively improve the electrochemical performance of medium-high nickel materials under high rate and long cycle conditions.

[0020] In some optional embodiments, the positive electrode material is a bulk phase doped positive electrode material, and the composition of the bulk phase doped positive electrode material is: LiNi x Co y Mn z M a O2, wherein x+y+z+a=1, M is a dopant, M is selected from one or more of Ti, Al, Ta, Zr, W and Nb, the value of M is 0.1-10wt%, the particle size D 50 of the positive electrode material is 6-10um.

[0021] The embodiment of the present application provides a composite coating modified positive electrode material, which stabilizes the crystal structure, controls the electronic conductivity, optimizes the ion transmission channel by bulk phase doping of the positive electrode material, and effectively improves the lithium ion transmission rate, reduces the Ni / Li disorder, reduces the side reaction between the surface of the positive electrode material and the electrolyte, improves the particle strength, improves the rate and cycle performance of the material, and optimizes the good rate and cycle performance of the sample under large current conditions.

[0022] In some alternative embodiments, the conductive polymer comprises at least one of PAN, PEO, PEG, PVA, PANI, PPy, poly(3,4-ethylenedioxythiophene).

[0023] In some alternative embodiments, the molar ratio of the fast ionic conductor to the conductive polymer in the coating layer is (3:1)~(0.5:1), the coating amount of the coating layer is 0.1~7wt% of the total mass of the positive electrode material, and the thickness of the coating layer is 0.1~50nm.

[0024] In the second aspect, the embodiments of the present application provide a preparation method of the composite coating modified positive electrode material, comprising the following steps: mixing the composite fast ionic conductor and the positive electrode material, and then stirring and mixing coating in the presence of an initiator to obtain the composite coating modified positive electrode material.

[0025] In some alternative embodiments, the preparation of the fast ionic conductor comprises the following steps: ball-milling Li source, Al source, Mg source, Sn source and Si oxide, and Zr-containing compound according to a proportion, and then placing them in a box furnace to perform heat preservation and drying under the condition of air compression, collecting the fast ionic conductor when the temperature drops to room temperature;

[0026] Preferably, the rotation speed of the ball-milling mixing is 400~800rpm / min, and the time is 8~16 hours.

[0027] Preferably, the temperature rising rate in the drying process is 1~10℃ / min, the temperature is 200~600℃, and the heat preservation time is 4~10 hours.

[0028] In some alternative embodiments, the preparation of the composite fast ionic conductor comprises the following steps: ball-milling the fast ionic conductor and the conductive polymer, and then drying to obtain the composite fast ionic conductor.

[0029] Preferably, the molar ratio of the fast ionic conductor to the conductive polymer in the coating layer is (3:1)~(0.5:1), the rotation speed of the ball-milling mixing is 600~1200rpm / min, and the time is 3~10 hours.

[0030] Preferably, the temperature in the drying process is 60~100℃, and the heat preservation time is 6~12 hours.

[0031] In some alternative embodiments, the preparation of the positive electrode material comprises the following steps: ball-milling a hydroxide precursor, a lithium source and a M-containing compound, and then performing calcination under an oxygen-containing atmosphere, and then crushing after cooling to obtain the positive electrode material.

[0032] Preferably, the mass ratio of the hydroxide precursor to the lithium source is 1:(1.1-1);

[0033] Preferably, the rotation speed of the ball milling is 200-350 rpm / min, and the time is 1-4 hours.

[0034] Preferably, the calcination temperature is 600-1000℃, the time is 6-15 hours, and the heating rate during the calcination is 1-8℃ / min.

[0035] In some alternative embodiments, the preparation of the composite-coated modified cathode material comprises the following steps: after mixing the composite fast ionic conductor with the cathode material, adding a solvent and an initiator, stirring to mix and coat, drying after the mixing and coating, and cooling and sieving to obtain the composite-coated modified cathode material.

[0036] Preferably, the initiator is azobisisobutyronitrile, and the amount of the initiator is 0.5-4wt% of the total mass of the composite fast ionic conductor and the cathode material.

[0037] Preferably, the solvent is dimethylformamide, and the solid content of the mixture after adding the solvent is 60%.

[0038] Preferably, the rotation speed of the mixing and coating is 400-800 rpm / min, and the time is 6-10 hours.

[0039] Preferably, the temperature during the drying is 60-100℃, and the holding time is 8-16 hours.

[0040] In a third aspect, the embodiments of the present application provide a secondary battery, wherein the cathode of the secondary battery comprises the composite-coated modified cathode material described above.

[0041] The present application will be further described below with reference to the embodiments.

[0042] A preparation method of a composite-coated modified cathode material is shown in Figure 1 , which comprises the following steps:

[0043] 1. Fast ionic conductor Li5Al2Mg 0.5 Sn 1-x Zr x Si2O 12 Preparation: according to the corresponding proportions, add Li source, Al source, Mg source, Sn source and Si oxide, and dopant Zr compound (the doping amount is 0.1-10wt%, based on Li5Al2Mg 0.5 SnSi2O 12The mixture is ball-milled in a ball mill tank at a speed of 400-800 rpm / min for 8-16 hours, and then the mixture is placed in a box furnace, and heated at a speed of 1-10 ℃ / min under the condition of air supply, and kept at 200-600 ℃ for 4-10 hours, and the product is collected when the temperature drops to room temperature.

[0044] 2. Preparation of composite fast ionic conductor: according to Li5Al2Mg 0.5 Sn 1-x Zr x Si2O 12 The corresponding sample is weighed in a molar ratio of 3:1-0.5:1 to PEO, preferably 1:1. The corresponding sample is added to a ball mill tank and ball-milled at a speed of 600-1200 rpm / min for 3-10 hours. The mixture is placed in a vacuum drying oven at 60-100 ℃ for 6-12 hours to obtain the composite fast ionic conductor.

[0045] 3. Preparation of nickel-cobalt-manganese lithium: according to Ni x Co y Mn z (OH)2 (wherein x+y+z=1) and lithium source in a ratio of 1:1.05-1:1.08, preferably 1:1.06, and adding a doping additive (one or more of TiO2, α-Al2O3, Ta2O5, ZrO2, WO3 and NbO2), ball-milling the mixture at a speed of 200-350 rpm / min for 1-4 hours. The sample is placed in a box furnace and calcined at 600-1000 ℃ in an oxygen atmosphere for 6-15 hours, and the heating rate is 1-8 ℃ / min. The product is broken and sieved to obtain a one-fired sample of lithium nickel-cobalt-manganese oxide, and the particle size D 50 is 6-10 μm.

[0046] 4. Preparation of composite fast ionic conductor-coated nickel-cobalt-manganese lithium: 0.1-7 wt% of composite fast ionic conductor (based on the mass of nickel-cobalt-manganese lithium) is weighed, preferably 1-5 wt%. The corresponding nickel-cobalt-manganese lithium product and composite fast ionic conductor are added to a ball mill tank, and 0.5-4 wt% of initiator azobisisobutyronitrile (based on the total mass of the sample) and solvent dimethylformamide (60% solid content of the sample) are added. The mixture is coated at a speed of 400-800 rpm / min for 6-10 hours. The sample is collected in a vacuum drying oven at 60-100 ℃ for 8-16 hours after the coating is completed. The product is sieved and collected, and the coating thickness is controlled to be 0.1-50 nm.

[0047] Example 1:

[0048] A preparation method of a composite-coated modified positive electrode material, comprising the following steps:

[0049] 1. Li5Al2Mg 0.5 Sn 1-x Zr x Si2O 12 / PEO preparation: Li5Al2Mg 0.5 SnSi2O 12 SnSi2O 0.5 SnSi2O 12 SnSi2O 0.5 SnSi2O 12 SnSi2O 0.5 Sn 1-x Zr x Si2O 12 / PEO composite fast ionic conductor.

[0050] 2. LiNi 0.7 Co 0.1 Mn 0.2 O2 sample preparation: Ni 0.7 Co 0.1 Mn 0.2 (OH)2(D 50 (OH)2(D 0.7 Co 0.1 Mn 0.2 (OH)2(D 0.7 Co 0.1 Mn 0.2 O2 sintered sample.

[0051] 3. Li5Al2Mg 0.5 Sn 1-x Zrx Si2O 12 Composite fast ionic conductor coated LiNi 0.7 Co 0.1 Mn 0.2 O2Sample preparation: 3wt% Li5Al2Mg 0.5 Sn 1-x Zr x Si2O 12 / PEO coated LiNi 0.7 Co 0.1 Mn 0.2 O2mass basis) and a certain amount of LiNi 0.7 Co 0.1 Mn 0.2 O2fired sample, a certain mass of azobisisobutyronitrile (2wt% of the total mass of the sample) and dimethylformamide (solid content 60%) were added, 0.5mm zirconium beads were added, and the mixture was ball milled at 500rpm / min for 6 hours, then the mixed sample was collected and dried in a vacuum drying oven at 70°C for 12 hours, and after the furnace temperature dropped, the Li5Al2Mg 0.5 SnSi2O 12 -Zr / PEO coated LiNi 0.7 Co 0.1 Mn 0.2 O2sample.

[0052] Example 2:

[0053] A preparation method of a composite coated modified positive electrode material, comprising the following steps:

[0054] 1. Ni 0.7 Co 0.1 Mn 0.2 (OH)2(D 50 Particle size 9.2±0.5μm) and LiOH were mixed in a ratio of 1:1.06, and 2wt% TiO2, 1wt% α-Al2O3 and 0.4wt% Ta2O5 (based on the mass of Ni 0.7 Co 0.1 Mn 0.2 (OH)2mass basis) were ball milled in a ball mill jar at a speed of 250rpm / min for 2 hours, then the sample was placed in a box furnace, oxygen was introduced, the heating rate was 5°C / min, and the temperature was kept at 750°C for 10 hours, then the LiNi 0.7 Co 0.1 Mn 0.2 O2fired sample.

[0055] 3. 2wt% Li5Al2Mg 0.5 Sn 1-x Zrx Si2O 12 / PEO (with LiNi 0.7 Co 0.1 Mn 0.2 O2 mass basis) and a certain amount of LiNi 0.7 Co 0.1 Mn 0.2 O2 calcined sample, a certain mass of azobisisobutyronitrile (2wt% of the total mass of the sample) and dimethylformamide (solid content 60%) were added, 0.5mm zirconium beads were added, and the mixture was ball milled at 500rpm / min for 6 hours, then the mixed sample was collected and dried in a vacuum drying oven at 70°C for 12 hours, and after the furnace temperature dropped, the finished product of Example 2 was obtained by sieving.

[0056] Example 3:

[0057] A preparation method of a composite coated modified positive electrode material, comprising the following steps:

[0058] 1. Ni 0.7 Co 0.1 Mn 0.2 (OH)2 (D 50 The particle size was 9.2±0.5μm) and Li2CO3 were mixed in a ratio of 1:1.06, and 1wt% TiO2, 2wt% α-Al2O3 and 0.5wt% Ta2O5 (based on the mass of Ni 0.7 Co 0.1 Mn 0.2 (OH)2 mass basis) were ball milled in a ball mill jar at a speed of 250rpm / min for 2 hours, then the sample was placed in a box furnace, oxygen was introduced, the heating rate was 5°C / min, and the temperature was kept at 900°C for 10 hours, after the furnace temperature dropped, LiNi 0.8 Co 0.1 Mn 0.1 O2 calcined sample.

[0059] 2. 1wt% Li5Al2Mg 0.5 Sn 1-x Zr x Si2O 12 / PEO (with Ni 0.7 Co 0.1 Mn 0.2 (OH)2 mass basis) and a certain amount of LiNi 0.7 Co 0.1 Mn 0.2O2 calcined sample, a certain amount of azobisisobutyronitrile (2wt% of the total mass of the sample) and dimethylformamide (60% solid content) were added, 0.5mm zirconium beads were added, and the mixture was ball-milled at 500rpm / min for 6 hours. Then the mixed sample was collected and dried in a vacuum drying oven at 70°C for 12 hours. After the furnace temperature decreased, the product of Example 3 was obtained by sieving.

[0060] Comparative Example 1:

[0061] A preparation method of a composite-coated modified positive electrode material, comprising the following steps:

[0062] 1. Ni 0.7 Co 0.1 Mn 0.2 (OH)2(D 50 The LiNi 0.7 Co 0.1 Mn 0.2 (OH)2was mixed in a ratio of 1:1.06, and 1wt% TiO2, 2wt% α-Al2O3 and 0.5wt% Ta2O5 were added (based on the mass of LiNi 0.7 Co 0.1 Mn 0.2 O2 calcined sample.

[0063] 2. 1.5wt% H3BO3, 0.8wt% ZrO2 and 2wt% LiF (based on the mass of LiNi 0.7 Co 0.1 Mn 0.2 O2 calcined sample, and a certain amount of LiNi 0.7 Co 0.1 Mn 0.2 O2 calcined sample was ball-milled at a speed of 300rpm / min for 2 hours, and then the sample was placed in a box furnace, compressed air was introduced, the temperature was raised at a rate of 5°C / min, and the sample was kept at 350°C for 6 hours. After the furnace temperature decreased, LiNi 0.7 Co 0.1 Mn 0.2 O2 calcined sample.

[0064] Comparative Example 2:

[0065] A preparation method of a composite-coated modified positive electrode material, comprising the following steps:

[0066] 1. Ni 0.7 Co 0.1Mn 0.2 (OH)2(D 50 Particle size 9.2±0.5 μm) and LiOH were mixed in a ratio of 1:1.06, and 2wt% TiO2, 1wt% α-Al2O3, and 0.4wt% Ta2O5 (in terms of LiNi 0.7 Co 0.1 Mn 0.2 (OH)2mass as a basis) were ball-milled in a ball mill jar at a rotation speed of 250 rpm / min for 2 hours, and then the sample was placed in a box furnace, oxygen was introduced, the temperature was raised at a rate of 5°C / min, and the sample was kept at 750°C for 10 hours. After the furnace temperature dropped, the LiNi 0.7 Co 0.1 Mn 0.2 O2fired sample.

[0067] 2. 0.7wt% NbO2, 1.2wt% WO3, and 0.9wt% β-Al2O3 (in terms of LiNi 0.7 Co 0.1 Mn 0.2 O2fired sample mass as a basis) and a certain amount of LiNi 0.7 Co 0.1 Mn 0.2 O2fired sample were ball-milled at a rotation speed of 300 rpm / min for 2 hours, and then the sample was placed in a box furnace, compressed air was introduced, the temperature was raised at a rate of 5°C / min, and the sample was kept at 350°C for 6 hours. After the furnace temperature dropped, the LiNi 0.7 Co 0.1 Mn 0.2 O2fired sample.

[0068] Comparative Example 3:

[0069] A method for preparing a composite-coated modified positive electrode material, comprising the following steps:

[0070] 1. Ni 0.7 Co 0.1 Mn 0.2 (OH)2(D 50 Particle size 9.2±0.5 μm) and Li2CO3 were mixed in a ratio of 1:1.06, and 1wt% TiO2, 2wt% α-Al2O3, and 0.5wt% Ta2O5 (in terms of LiNi 0.7 Co 0.1 Mn 0.2 (OH)2mass as a basis) were ball-milled in a ball mill jar at a rotation speed of 250 rpm / min for 2 hours, and then the sample was placed in a box furnace, oxygen was introduced, the temperature was raised at a rate of 5°C / min, and the sample was kept at 900°C for 10 hours. After the furnace temperature dropped, the LiNi0.8 Co 0.1 Mn 0.1 O2 - as-sintered sample.

[0071] 2. Weigh 1.5wt% Y2O3, 1.0wt% LiF and 2.2wt% H3BO3 (as LiNi 0.7 Co 0.1 Mn 0.2 O2 - as-sintered sample mass as reference) and a certain mass of LiNi 0.7 Co 0.1 Mn 0.2 O2 - as-sintered sample, ball-mill the mixture at 300 rpm / min for 2 hours, then place the sample in a box furnace, pass compressed air, the heating rate is 5°C / min, keep the temperature at 350°C for 6 hours, sieve after the furnace temperature drops to get LiNi 0.6 Co 0.2 Mn 0.2 O2 - as-sintered sample.

[0072] Comparative Example 4:

[0073] Similar to the steps of Example 1, the only difference is that the coating material is 10wt% Li5Al2Mg 0.5 Sn 1- x Zr x Si2O 12 / PEO.

[0074] Comparative Example 5:

[0075] Similar to the steps of Example 1, the only difference is that no coating treatment is performed, only the matrix material.

[0076] Comparative Example 6:

[0077] Similar to the steps of Example 1, the only difference is that no PEO polymer is added and only 3wt% Li5Al2Mg 0.5 Sn 1-x Zr x Si2O 12 is coated.

[0078] Comparative Example 7:

[0079] Similar to the steps of Example 1, the only difference is that no ZrO2 is added and only 3wt% Li5Al2Mg 0.5 SnSi2O 12 / PEO is coated.

[0080] Detection:

[0081] The examples and comparative examples were used as positive electrode materials (area density: 10.5 mg / cm³). 2 Using commercial lithium foil as the negative electrode, 1 mol / L LiPF6 as the electrolyte, DMC:EC:EMC = 1:1:1, and Celgard 2250 as the separator, coin cells were assembled. The test voltage range was 3.0 to 4.4V. The cells were tested at 0.1C to 10C and cycled at 5C.

[0082] Table 1 shows the rate performance test results of the half-cells of the examples and comparative examples, Table 2 shows the cycle performance summary of the half-cells of the examples and comparative examples (5C rate 200 cycles), and Table 3 shows the total alkali data of the examples and comparative examples.

[0083] Table 1

[0084]

[0085] Table 2

[0086] Sample Name Initial Capacity (mAh / g) Capacity after cycling (mAh / g) Capacity retention (%) Example 1 163.21 146.10 89.52 Example 2 157.34 137.20 87.20 Example 3 153.77 136.61 88.84 Comparative Example 1 152.11 88.81 58.39 Comparative Example 2 146.12 77.56 53.08 Comparative Example 3 150.82 79.15 52.48 Comparative Example 4 121.70 62.34 51.22 Comparative Example 5 113.40 35.66 31.45 Comparative Example 6 118.60 74.30 62.65 Comparative Example 7 109.40 57.89 52.92

[0087] Table 3

[0088]

[0089] Based on the performance data in Table 1-3 and Figures 2-4 The microstructure and electrochemical characterization results show that the embodiments of the present invention successfully prepared a lithium nickel cobalt manganese oxide cathode material coated with a composite fast ion conductor using a wet coating process. The conductive coating on the NCM substrate surface achieved a homogeneous, dense, and continuous coating. Figure 2 , 3 SEM / TEM images); electrochemical tests ( Figure 4 This indicates that the sample from Example 1 retained 146.10 mAh g after 200 cycles at 5C. -1 Its high reversible specific capacity is significantly better than that of Comparative Example 1 (88.81 mAh g). -1 Meanwhile, the composite fast ion conductor coating significantly improved the material's initial coulombic efficiency and rate performance (Tables 1 and 2), and effectively suppressed side reactions at the electrode / electrolyte interface by reducing the residual alkali content on the material surface (such as Li2CO3, LiOH, etc., Table 3). Furthermore, comparative studies of key components and process parameters showed that: 1) the coating thickness needs optimization; excessive thickness (Comparative Examples 4-5) will hinder ion diffusion and degrade performance, while the absence of a coating (related comparative examples) leads to performance degradation due to HF corrosion caused by high residual alkali content; 2) essential polymer binders such as PEO (Comparative Example 6) can strengthen the coating-substrate interface bonding and prevent coating peeling during cycling; 3) the included ZrO2 component (Comparative Example 7) can effectively suppress lithium ion deposition and cation (Ni) deposition.2+ Li + )mixing. In summary, the composite fast ion conductor coating layer described in the present application significantly improves the rate performance and cycle stability of nickel-cobalt-lithium manganate positive electrode material through the synergistic effects of optimizing interface stability, enhancing ion conduction and providing structural support, etc.

[0090] The above only for the preferred embodiments of the present application, and is not intended to limit the present application, for those skilled in the art, the present application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. within the spirit and principles of the present application, should be included in the protection scope of the present application.

Claims

1. A composite coating-modified positive electrode material, characterized by, The composite-coated modified positive electrode material comprises a positive electrode material and a composite coating layer on the surface of the positive electrode material, the composite coating layer is composed of a fast ion conductor and a conductive polymer, the general formula of the fast ion conductor is: Li5A2B 0.5 C 1-x D x Si2O 12 , wherein: A comprises at least one of Al 3+ , Ca 3+ , Sc 3+ and Y 3+ , B comprises at least one of Mg 2+ , Zn 2+ , Cu 2+ and Ca 2+ , C comprises at least one of Sn 4+ , Ce 4+ and Ge 4+ , D comprises at least one of Zr 4+ , Hf 4+ and Ti 4+ , and the doping amount of the doping element D is 0.1-10wt% of the mass of Li5A2B 0.5 CSi2O 12 .

2. The composite coating-modified cathode material of claim 1, wherein, The positive electrode material is a bulk-doped positive electrode material, the bulk-doped positive electrode material has a composition of: LiNi x Co y Mn z M a O2, wherein x+y+z+a=1, M is a dopant, M is selected from one or more of Ti, Al, Ta, Zr, W and Nb, M has a value of 0.1-10wt%, and the particle size D 50 of the positive electrode material is 6-10μm.

3. The composite coating-modified cathode material of claim 1, wherein, The conductive polymer includes at least one of PAN, PEO, PEG, PVA, PANI, PPy, poly(3,4-ethylenedioxythiophene).

4. The composite coating-modified cathode material of claim 1, wherein, The molar ratio of the fast ion conductor to the conductive polymer in the coating layer is (3:1) to (0.5:1), the coating amount of the coating layer is 0.1 to 7 wt% of the total mass of the positive electrode material, and the thickness of the coating layer is 0.1 to 50 nm.

5. A method of producing a composite coating-modified positive electrode material according to any one of claims 1 to 4, characterized by, The preparation of the composite coating modified positive electrode material includes the following steps:

6. The production method according to claim 5, characterized by, The preparation of the fast ion conductor includes the following steps: The Li source, the Al source, the Mg source, the Sn source, and the Si oxide, and the Zr-containing compound are ball-milled in proportion, and then are placed in a box furnace for heat preservation and drying under the condition of compressed air being introduced, and the fast ion conductor is collected after the temperature is reduced to room temperature; Preferably, the rotation speed of the ball-milling is 400 to 800 rpm / min, and the time is 8 to 16 hours; Preferably, the temperature rising rate in the drying process is 1 to 10 ℃ / min, the temperature is 200 to 600 ℃, and the heat preservation time is 4 to 10 hours.

7. The preparation method according to claim 5, characterized in that, The preparation of the composite fast ion conductor includes the following steps: the fast ion conductor and the conductive polymer are ball-milled and then dried to obtain the composite fast ion conductor; Preferably, the molar ratio of the fast ion conductor to the conductive polymer in the coating layer is (3:1) to (0.5:1); the rotation speed of the ball-milling is 600 to 1200 rpm / min, and the time is 3 to 10 hours; Preferably, the temperature in the drying process is 60 to 100 ℃, and the heat preservation time is 6 to 12 hours.

8. The production method according to claim 5, characterized by, The preparation of the positive electrode material includes the following steps: The hydroxide precursor, the lithium source, and the M-containing compound are ball-milled, and then are calcined in an oxygen-containing atmosphere, and then the positive electrode material is obtained after being broken by cooling; Preferably, the mass ratio of the hydroxide precursor to the lithium source is 1:(1.1 to 1); Preferably, the rotation speed of the ball-milling is 200 to 350 rpm / min, and the time is 1 to 4 hours; Preferably, the calcination temperature is 600 to 1000 ℃, the time is 6 to 15 hours, and the temperature rising rate in the calcination process is 1 to 8 ℃ / min.

9. The production method according to claim 5, characterized by, The preparation of the composite coating modified positive electrode material includes the following steps: The composite fast ion conductor and the positive electrode material are mixed, a solvent and an initiator are added, and then stirring is performed for mixing and coating, and then drying is performed after the mixing and coating, and the composite coating modified positive electrode material is obtained after being cooled and sieved; Preferably, the initiator is azobisisobutyronitrile, and the amount of the initiator is 0.5 to 4 wt% of the total mass of the composite fast ion conductor and the positive electrode material; Preferably, the solvent is dimethylformamide, and the solid content of the mixture after the solvent is added is 60%; Preferably, the rotation speed of the mixing and coating is 400 to 800 rpm / min, and the time is 6 to 10 hours; Preferably, the temperature in the drying process is 60 to 100 ℃, and the heat preservation time is 8 to 16 hours.

10. A secondary battery characterized by The positive electrode of the secondary battery comprises the composite-coated modified positive electrode material according to any one of claims 1-4 or the composite-coated modified positive electrode material prepared by the preparation method according to any one of claims 5-9. The positive electrode of the secondary battery comprises the composite-coated modified positive electrode material according to any one of claims 1-4 or the composite-coated modified positive electrode material prepared by the preparation method according to any one of claims 5-9.

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