A modified lithium cobalt oxide cathode material, a preparation method and application thereof

Abstract

The application discloses a modified lithium cobaltate positive electrode material, a preparation method and application thereof, and relates to the technical field of lithium batteries. By coating a cobalt-aluminum oxide coating layer on the lithium cobaltate core, the cobalt-aluminum oxide coating layer has a high specific surface area, can be fully contacted with an electrolyte solution, and has good electronic conductivity, so that the rate performance of the positive electrode material can be effectively improved. The cobalt-aluminum oxide coating layer can effectively reduce the contact between the lithium cobaltate core and the electrolyte solution, the occurrence of surface side reactions and the dissolution of cobalt, and is beneficial to improving the cycle stability of the positive electrode material.

Description

TECHNICAL FIELD

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

[0002] Lithium cobalt oxide as an important positive electrode material has high energy density and relatively high electrochemical performance, but there are problems such as capacity attenuation, structure damage and safety hazards in the cycle process. Therefore, improving the performance of lithium cobalt oxide positive electrode material and improving its cycle stability and safety have become a research hotspot in the field of batteries.

[0003] Surface coating of lithium cobalt oxide can improve the cycle stability and safety to some extent, but the traditional coating material cannot significantly improve the electronic / ionic conductivity and cannot improve the structural stability of the lithium cobalt oxide positive electrode material, and the cycle stability also needs to be further improved.

[0004] In view of this, the present application is proposed. SUMMARY

[0005] The purpose of the present application is to provide a modified lithium cobalt oxide positive electrode material, a preparation method and application thereof, aiming to significantly improve the cycle stability of the lithium cobalt oxide positive electrode material.

[0006] The present application is realized as follows:

[0007] In a first aspect, the present application provides a modified lithium cobalt oxide positive electrode material, comprising a lithium cobalt oxide core and a cobalt aluminum oxide coating layer coated on the lithium cobalt oxide core. In an optional embodiment, the mass fraction of cobalt in the modified lithium cobalt oxide positive electrode material is 59.29%-60.10%, and the mass fraction of aluminum is 0.11%-0.82%;

[0008] The specific surface area of the modified lithium cobalt oxide positive electrode material is 0.55m 2 / g-0.65m 2 / g.

[0009] Preferably, the cobalt aluminum oxide coating layer is formed by a CoAl-MOF material;

[0010] Preferably, a lithium cobalt oxide intermediate layer is formed between the lithium cobalt oxide core and the cobalt aluminum oxide coating layer, and the lithium cobalt oxide intermediate layer is generated by reaction of a cobalt oxide compound derived from the CoAl-MOF material.

[0011] In a second aspect, the present application provides a preparation method of the modified lithium cobalt oxide positive electrode material of the foregoing embodiment, comprising: forming a cobalt aluminum oxide coating layer on a lithium cobalt oxide core.

[0012] In an optional embodiment, the CoAl-MOF material is prepared by using a cobalt salt, an aluminum salt, an organic ligand and a solvent as raw materials; and the lithium cobaltate, the lithium carbonate and the CoAl-MOF material are mixed and sintered.

[0013] In an optional embodiment, the lithium cobaltate, the lithium carbonate and the CoAl-MOF material are ground and then sintered, and the sintering temperature is controlled to be 700-900°C and the sintering time is controlled to be 3-8h.

[0014] Preferably, the sintering temperature is 730-780°C and the sintering time is 4-6h.

[0015] Preferably, the mass ratio of the CoAl-MOF material to the lithium cobaltate is (1-8):100, and more preferably (4-6):100.

[0016] Preferably, the molar ratio of lithium cobalt in the lithium carbonate and the CoAl-MOF material is controlled to be (1.01-1.05):1 by adjusting the amount of the lithium carbonate.

[0017] In an optional embodiment, the preparation process of the CoAl-MOF material comprises: mixing a cobalt salt, an aluminum salt, an organic ligand and a solvent to obtain a mixed solution, and reacting the mixed solution in a reaction kettle at 120-150°C for 12-36h.

[0018] Preferably, the reaction temperature of the mixed solution is 135-145°C and the reaction time is 20-30h.

[0019] Preferably, after the reaction is completed, washing and drying are performed.

[0020] In an optional embodiment, the molar ratio of cobalt, aluminum and the organic ligand is controlled to be (5-10):(5-10):(7-15), and preferably (6-8):(6-8):(7-9), by adjusting the amount of the cobalt salt, the aluminum salt and the organic ligand.

[0021] Preferably, the organic ligand is selected from any one of terephthalic acid, trimesic acid, 2-methyl terephthalic acid, 2,2-bipyridine and 4,4-bipyridine.

[0022] Preferably, the cobalt salt is selected from at least one of cobalt nitrate, cobalt chloride and cobalt sulfate.

[0023] Preferably, the aluminum salt is selected from at least one of aluminum nitrate and aluminum chloride.

[0024] Preferably, the solvent is a mixed solvent formed by N,N-dimethylformamide, ethanol and water, and the volume ratio of N,N-dimethylformamide, ethanol and water is (10-20):(0.5-1.5):1, and more preferably (15-17):(0.8-1.2):1.

[0025] In a third aspect, the present application provides a positive electrode sheet comprising the modified lithium cobalt oxide positive electrode material according to any one of the preceding embodiments or the modified lithium cobalt oxide positive electrode material prepared by the method according to any one of the preceding embodiments.

[0026] In a fourth aspect, the present application provides a secondary battery comprising the positive electrode sheet according to the preceding embodiment.

[0027] In a fifth aspect, the present application provides an electric device comprising the secondary battery according to the preceding embodiment.

[0028] The present application has the following beneficial effects: by coating a cobalt aluminum oxide coating layer on the lithium cobalt oxide core, the cobalt aluminum oxide coating layer has a high specific surface area, can be in full contact with the electrolyte solution, and has good electronic conductivity, which can effectively improve the rate performance of the positive electrode material. The cobalt aluminum oxide coating layer can effectively reduce the contact between the lithium cobalt oxide core and the electrolyte solution, the occurrence of surface side reactions and the dissolution of cobalt, which is conducive to improving the cycle stability of the positive electrode material. BRIEF DESCRIPTION OF DRAWINGS

[0029] In order to more clearly illustrate the technical solutions of the embodiments of the present 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 embodiments of the present application, and therefore should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can also be obtained without creative labor on the basis of these drawings.

[0030] Figure 1 XRD powder diffraction pattern of Example 1;

[0031] Figure 2 SEM pattern of Example 1;

[0032] Figure 3 Cycle stability test result pattern of Example 1, Example 2, Example 3, Example 4, Example 5, Example 6, Example 7, Comparative Example 1 and Comparative Example 2 at 0.1C. DETAILED DESCRIPTION

[0033] In order to make the purpose, technical solutions and advantages of the embodiments of the present application more clear, the technical solutions in the embodiments of the present application will be described clearly and completely. The specific conditions are not specified in the embodiments, which are carried out according to the conventional conditions or the conditions recommended by the manufacturer. The reagents or instruments used are not specified by the manufacturer, which are all conventional products that can be purchased on the market.

[0034] The embodiments of the present application provide a preparation method of a modified lithium cobalt oxide positive electrode material, which prepares a modified lithium cobalt oxide positive electrode material with a lithium cobalt oxide core and a cobalt aluminum oxide coating layer. Specifically, the method comprises the following steps:

[0035] S1, preparing CoAl-MOF material

[0036] The CoAl-MOF material is obtained by combining aluminum and cobalt with the organic ligand through a solvothermal method, by taking a cobalt salt, an aluminum salt, an organic ligand, and a solvent as raw materials.

[0037] MOF (metal organic framework) and its derivatives have the characteristics of high porosity and controllable structure. The application of MOF derivatives to the coating modification of lithium cobalt oxide positive electrode materials can effectively improve the capacity attenuation and structural stability of lithium cobalt oxide. Compared with traditional coating materials, MOF derivatives have higher specific surface area and controllable pore size, so they can achieve more precise coating effect and improve electronic / ionic conductivity. In addition, MOF derivatives also have good chemical stability and environmental friendliness, which can effectively reduce environmental pollution.

[0038] In some embodiments, the preparation process of the CoAl-MOF material includes: mixing a cobalt salt, an aluminum salt, an organic ligand, and a solvent to obtain a mixed solution, and reacting the mixed solution in a reaction kettle at 120-150℃ for 12-36h to obtain a CoAl-MOF material with a framework structure. Preferably, the reaction temperature of the mixed solution is 135-145℃, and the reaction time is 20-30h. By further optimizing the reaction temperature and time, the reaction can be fully carried out.

[0039] Specifically, the reaction temperature of the mixed solution can be 120℃, 125℃, 130℃, 135℃, 140℃, 145℃, 150℃, etc., and the reaction time can be 12h, 15h, 20h, 25h, 30h, 36h, etc.

[0040] In some embodiments, by adjusting the amount of the cobalt salt, the aluminum salt, and the organic ligand, the molar ratio of cobalt, aluminum, and organic ligand is (5-10):(5-10):(7-15), preferably (6-8):(6-8):(7-9). By adjusting the molar ratio of cobalt, aluminum, and organic ligand, the content of aluminum in the coating layer is further adjusted, and the electrochemical performance of the modified lithium cobalt oxide positive electrode material is improved.

[0041] Specifically, by adjusting the amount of the cobalt salt, the aluminum salt, and the organic ligand, the molar ratio of cobalt, aluminum, and organic ligand can be 5:5:7, 6:6:8, 7:7:9, 8:8:11, 9:9:13, 10:10:15, etc. The molar ratio of cobalt and aluminum is not limited to 1:1, but can be 1:(0.5-2), all of which are within the protection scope of the present application.

[0042] In some embodiments, the organic ligand is selected from any one of terephthalic acid, trimesic acid, 2-methyl terephthalic acid, bipyridine and tetrapyridine, preferably terephthalic acid (BDC, C8H6O4). The cobalt salt is selected from any one of cobalt nitrate, cobalt chloride and cobalt sulfate, preferably cobalt nitrate hexahydrate (Co(NO3)2·6H2O). The aluminum salt is selected from any one of aluminum nitrate and aluminum chloride, preferably aluminum nitrate nonahydrate (Al(NO3)3·9H2O).

[0043] In some embodiments, the solvent is a mixed solvent formed by N,N-dimethylformamide (DMF, C3H7NO), ethanol and water, and the volume ratio of N,N-dimethylformamide, ethanol and water is (10-20):(0.5-1.5):1, preferably (15-17):(0.8-1.2):1, such as 10:0.5:1, 12:0.7:1, 14:0.8:1, 16:1.0:1, 18:1.2:1, 20:1.5:1, etc.

[0044] In other embodiments, the solvent can also be a single solvent, and the specific type is not limited as long as it can well dissolve the reaction raw materials.

[0045] In some embodiments, the mixed solution can be stirred uniformly before the reaction, and the stirring speed can be controlled to be 100-300 rpm, and the stirring time can be 20-40 min. The reaction process can be incubated in an oven with a temperature meeting the requirements, and after the reaction is completed, it is naturally cooled to room temperature, and then washed and dried. The reagent used for washing is not limited, which can be ethanol and water, but is not limited thereto; the washing method is not limited, which can adopt the method of suction filtration. After washing, drying is performed, and the drying temperature can be 70-90°C, and the drying time can be 10-15 h.

[0046] S2, forming a cobalt aluminum oxide coating layer

[0047] The lithium cobaltate, lithium carbonate and CoAl-MOF material are mixed and sintered, after sintering, the CoAl-MOF material forms a cobalt aluminum metal oxide, and a coating layer is formed on the lithium cobaltate; the lithium carbonate reacts with the cobalt oxide compound formed by the CoAl-MOF material during the sintering process to newly generate a layer of LiCoO2, the layer of LiCoO2 is embedded on the surface of the crystal lattice of the core lithium cobaltate and is tightly combined with the derived porous Al2O3 through the skeleton of the precursor MOF, and finally a dense and continuous porous coating layer is formed on the surface of the core, thereby optimizing the electrochemical performance and structural stability of the lithium cobaltate positive electrode material.

[0048] In some embodiments, the lithium cobaltate, lithium carbonate and CoAl-MOF material are ground before sintering, and the raw materials are mixed uniformly by grinding to improve the uniformity of the product after sintering. The sintering temperature is controlled to be 700-900 DEG C, and the sintering time is 3-8 h; preferably, the sintering temperature is 730-780 DEG C, and the sintering time is 4-6 h. By further controlling the sintering temperature and time, a uniform modified lithium cobaltate positive electrode material is obtained.

[0049] Specifically, the sintering temperature can be 700 DEG C, 730 DEG C, 750 DEG C, 780 DEG C, 800 DEG C, 850 DEG C, 900 DEG C, etc., and the sintering time can be 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, etc. The ground material can be loaded into an alumina crucible and then transferred to a muffle furnace for sintering. The sintering atmosphere can be air, and after sintering, the MOF derivative coated lithium cobaltate positive electrode material is naturally cooled to room temperature.

[0050] In some embodiments, the mass ratio of the CoAl-MOF material to the lithium cobaltate is (1-8):100, preferably (4-6):100; and the molar ratio of lithium to cobalt in the lithium carbonate and the CoAl-MOF material is (1.01-1.05):1 by adjusting the amount of lithium carbonate. By controlling the amounts of lithium cobaltate, lithium carbonate and CoAl-MOF material, the electrochemical performance of the modified lithium cobaltate positive electrode material obtained can be further improved.

[0051] Specifically, the mass ratio of the modified lithium cobaltate positive electrode material can be 1:100, 2:100, 3:100, 4:100, 5:100, 6:100, 7:100, 8:100, etc.; and the molar ratio of lithium to cobalt in the total sintering raw materials can be 1.01:1, 1.02:1, 1.03:1, 1.04:1, 1.05:1, etc. by adjusting the amount of lithium carbonate.

[0052] It should be noted that the lithium cobaltate can be a commercially available material or prepared by a conventional method. For example, the lithium cobaltate can be prepared by a high-temperature solid-phase method. Specifically, a cobalt source and a lithium source are mixed uniformly according to the ratio, calcined at a high temperature, and then crushed and sieved to obtain the lithium cobaltate. The cobalt source can be tricobalt tetroxide, and the lithium source can be lithium carbonate. The molar ratio of lithium to cobalt is 1.05-1.1:1, and the high-temperature calcination conditions are calcination at 900-1200 DEG C for 6-30 h.

[0053] The embodiment of the present application also provides a modified lithium cobaltate positive electrode material, which comprises a lithium cobaltate core and a cobalt aluminum oxide coating layer coated on the lithium cobaltate core. The cobalt aluminum oxide coating layer can effectively reduce the contact between the lithium cobaltate core and the electrolyte solution, the occurrence of surface side reactions and the dissolution of cobalt, and is beneficial to improving the cycle stability of the positive electrode material.

[0054] The specific surface area of the cobalt-aluminum oxide coating layer is 0.55 m 2 / g-0.65 m 2 The bimetallic oxide obtained by the MOF self-sacrifice template method has a porous structure of the MOF precursor, a large specific surface area, can be fully contacted with the electrolyte solution, and has good electronic conductivity and ion conductivity, so that the rate performance of the positive electrode material can be effectively improved.

[0055] In the optional embodiment, the mass fraction of cobalt in the modified lithium cobalt oxide positive electrode material is 59.29%-60.10%, and the mass fraction of aluminum is 0.11%-0.82%.

[0056] In some embodiments, the cobalt-aluminum oxide coating layer is formed by the CoAl-MOF material, the cobalt-aluminum oxide coating layer is derived from the bimetallic MOF, the oxides of cobalt and aluminum interact through the MOF skeleton, and the oxide coating layer formed in situ on the surface of the positive electrode material has a shorter electron / ion transmission distance compared with other coating layers, can improve the interface resistance, and improve the electrochemical performance. In addition, the oxide coating layer formed in situ on the surface of the positive electrode material is uniformly distributed and has a stable structure, can effectively reduce the contact between the positive electrode material and the electrolyte solution, the occurrence of surface side reactions and the dissolution of cobalt, and improve the cycle stability of the positive electrode material.

[0057] In some embodiments, a lithium cobalt oxide intermediate layer is formed between the lithium cobalt oxide core and the cobalt-aluminum oxide coating layer, and the lithium cobalt oxide intermediate layer is generated by the reaction of the cobalt oxide compound derived from the CoAl-MOF material. The oxide coating layer is tightly combined with the positive electrode material through the newly generated LiCoO2 intermediate layer, has the characteristics of large specific surface area, high porosity and good ion conductivity, can improve the structural stability and cycle stability of the lithium cobalt oxide positive electrode material, and slow down the capacity decay in the cycle process.

[0058] The embodiment of the present application provides a positive electrode sheet, which comprises the modified lithium cobalt oxide positive electrode material or the modified lithium cobalt oxide positive electrode material prepared by the preparation method, and can further comprise a positive electrode current collector, a positive electrode active coating layer is formed on at least one surface of the positive electrode current collector, and the lithium cobalt oxide positive electrode material exists in the positive electrode active coating layer as a positive electrode active material.

[0059] The embodiment of the present application provides a secondary battery, which comprises the positive electrode sheet, and can further comprise a negative electrode sheet, an electrolyte, a separator and the like to form a complete battery structure, and has good cycle performance.

[0060] Specifically, the specific types of the negative electrode sheet, the electrolyte and the separator are not limited, and can be the materials commonly used in lithium cobalt oxide batteries. In the charging and discharging process of the secondary battery, active ions are embedded and removed between the positive electrode sheet and the negative electrode sheet, and the electrolyte plays a role in conducting ions between the positive electrode sheet and the negative electrode sheet.

[0061] In other embodiments, it can also not be in the form of a secondary battery, but can be in the form of a battery module, a battery pack, etc.

[0062] The embodiment of the present application provides a kind of electric device, including above-mentioned secondary battery, utilize secondary battery as the energy storage unit of electric device.The electric device can be but not limited to mobile device (such as mobile phone, notebook computer etc.), electric vehicle (such as pure electric vehicle, hybrid electric vehicle, plug-in hybrid electric vehicle, electric bicycle, electric scooter, electric golf cart, electric truck etc.), electric train, ship and satellite, energy storage system etc.

[0063] The features and performances of the present application are further described in detail below in conjunction with embodiments.

[0064] Embodiment 1

[0065] The embodiment provides a preparation method of modified lithium cobalt oxide positive electrode material, comprising the following steps:

[0066] (1) CoAl-MOF precursor material is prepared by solvothermal method

[0067] Mix 64 mL of N,N-dimethylformamide (DMF, C3H7NO), 4 mL of anhydrous ethanol and 4 mL of deionized water into a 100 mL polytetrafluoroethylene reactor liner, then weigh 262.6 mg of aluminum nitrate nonahydrate (Al(NO3)3·9H2O), 203.6 mg of cobalt nitrate hexahydrate (Co(NO3)2·6H2O) and 124.6 mg of terephthalic acid (BDC, C8H6O4) into the above mixed solution respectively.

[0068] Put the obtained mixed solution into an electromagnetic stirrer to stir at a speed of 200 rpm for 30 min until the mixture is uniform, then load it into a reactor and put it into a 140°C oven for 24 h. After the heat preservation is completed, the reactor is placed at room temperature to cool naturally, then the precipitate is filtered and washed with anhydrous ethanol and deionized water until clean, and then dried in a 80°C vacuum drying box for 12 h to obtain a CoAl-MOF precursor material.

[0069] (2) Lithium cobalt oxide material is prepared by high-temperature solid-phase method

[0070] Weigh 1.94 g of lithium carbonate and 4.01 g of tricobalt tetraoxide into a ball mill for ball milling, move the uniformly mixed material into an alumina crucible and put it into a muffle furnace for calcination at 950°C for 8 h, cool to room temperature, then crush, grind and sieve to obtain a lithium cobalt oxide material.

[0071] (3) Form a cobalt-aluminum oxide coating layer

[0072] Take 3 g of lithium cobalt oxide, 0.15 g of CoAl-MOF (i.e. the coating amount is 5 wt%) and 0.023 g of lithium carbonate into a mortar and grind for 30 min, then load into an alumina crucible and put into a muffle furnace for calcination. Heat to 750°C at a heating rate of 5°C / min and calcine for 5 h to obtain a CoAl-MOF derivative in-situ coated lithium cobalt oxide positive electrode material.

[0073] The XRD diffraction pattern and micro-morphology of the modified lithium cobalt oxide positive electrode material prepared in this example are shown in Figure 1 and Figure 2 It can be seen from Figure 1 that there is a diffraction peak at 2θ = 18.93° for the (003) crystal plane of lithium cobalt oxide, and other diffraction peaks correspond one by one to the standard card, proving that the obtained material is still lithium cobalt oxide. It can be seen from Figure 2 that the particle size of the modified lithium cobalt oxide positive electrode material prepared is 13-20 μm.

[0074] Example 2

[0075] Example 2 differs from Example 1 only in that the amount of CoAl-MOF precursor material added in step (3) is 3 wt%, specifically, take 3 g of lithium cobalt oxide, 0.09 g of CoAl-MOF and 0.014 g of lithium carbonate into a mortar and grind for 30 min, then load into an alumina crucible and put into a muffle furnace for calcination.

[0076] Example 3

[0077] Example 4 differs from Example 1 only in that the amount of CoAl-MOF precursor material added in step (3) is 4 wt%, specifically, take 3 g of lithium cobalt oxide, 0.12 g of CoAl-MOF and 0.018 g of lithium carbonate into a mortar and grind for 30 min, then load into an alumina crucible and put into a muffle furnace for calcination.

[0078] Example 4

[0079] Example 4 differs from Example 1 only in that the amount of CoAl-MOF precursor material added in step (4) is 6 wt%, specifically, take 3 g of lithium cobalt oxide, 0.18 g of CoAl-MOF and 0.028 g of lithium carbonate into a mortar and grind for 30 min, then load into an alumina crucible and put into a muffle furnace for calcination.

[0080] Example 5

[0081] Example 5 differs from Example 1 only in the amount of CoAl-MOF precursor material added in step (4) (8 wt%), specifically 3 g of lithium cobaltate, 0.24 g of CoAl-MOF, and 0.039 g of lithium carbonate were weighed into a mortar and ground for 30 min to mix uniformly, then loaded into an alumina crucible and placed in a muffle furnace for calcination.

[0082] Example 6

[0083] Example 6 differs from Example 1 only in that the molar ratio of cobalt to aluminum is controlled to be 2:1 during the preparation of the CoAl-MOF precursor material. The specific steps are as follows: Specifically, 175.1 mg of aluminum nitrate nonahydrate (Al(N03)3-9H20), 271.5 mg of cobalt nitrate hexahydrate (Co(N03)2-6H20), and 124.6 mg of terephthalic acid were weighed into a mixed solution.

[0084] Example 7

[0085] Example 7 differs from Example 1 only in that the molar ratio of cobalt to aluminum is controlled to be 1:2 during the preparation of the CoAl-MOF precursor material. The specific steps are as follows: Specifically, 350.1 mg of aluminum nitrate nonahydrate (Al(N03)3-9H20), 135.7 mg of cobalt nitrate hexahydrate (Co(N03)2-6H20), and 124.6 mg of terephthalic acid were weighed into a mixed solution.

[0086] Comparative Example 1

[0087] This comparative example provides a preparation method of a modified lithium cobaltate positive electrode material, specifically the preparation of a lithium cobaltate positive electrode material coated with an Al-MOF derivative. The specific steps are as follows:

[0088] (1) Preparation of Al-MOF precursor by solvothermal method

[0089] Mix 64 mL of N,N-dimethylformamide (DMF, C3H7NO), 4 mL of anhydrous ethanol, and 4 mL of deionized water into a 100 mL polytetrafluoroethylene reactor inner liner, then weigh 525.2 mg of aluminum nitrate nonahydrate (Al(N03)3-9H20) and 124.6 mg of terephthalic acid (BDC, C8H6O4) into the above mixed solution.

[0090] Put the resulting mixed solution into an electromagnetic stirrer and stir at a speed of 200 rpm for 30 min until it is mixed uniformly, then load it into a reactor and place it in a 140°C oven for 24 h. After the heat preservation is completed, the reactor is placed at room temperature to cool naturally, then the precipitate is washed clean with anhydrous ethanol and deionized water, and is placed in a 80°C vacuum drying oven for 12 h to obtain the Al-MOF precursor material.

[0091] (2) Preparation of lithium cobalt oxide material by high-temperature solid-phase method

[0092] The same as step (2) of Example 1.

[0093] (3) Forming a coating layer

[0094] 3 g of lithium cobalt oxide and 0.15 g of Al-MOF were weighed into a mortar and ground for 30 min to mix uniformly, then loaded into an alumina crucible and placed in a muffle furnace for calcination. The temperature was raised to 750°C at a rate of 5°C / min and calcined for 5 h to obtain an Al-MOF derivative coated lithium cobalt oxide positive electrode material.

[0095] Comparative Example 2

[0096] This comparative example provides a preparation method of a modified lithium cobalt oxide positive electrode material, specifically a preparation of a lithium cobalt oxide positive electrode material coated with a Co-MOF derivative. The specific steps are as follows:

[0097] (1) Preparation of Co-MOF precursor by solvothermal method

[0098] 64 mL of N,N-dimethylformamide (DMF, C3H7NO), 4 mL of anhydrous ethanol, and 4 mL of deionized water were mixed into a 100 mL polytetrafluoroethylene reactor inner liner, and then 370.2 mg of cobalt nitrate hexahydrate (Co(NO3)2·6H2O) and 124.6 mg of terephthalic acid (BDC, C8H6O4) were weighed into the above mixed solution.

[0099] The obtained mixed solution was placed on an electromagnetic stirrer and stirred at a speed of 200 rpm for 30 min until it was mixed uniformly, then loaded into a reactor and placed in a 140°C oven for 24 h. After the heat preservation was completed, the reactor was taken out and naturally cooled to room temperature, then the precipitate was filtered and washed with anhydrous ethanol and deionized water, and placed in a 80°C vacuum drying box for drying for 12 h to obtain a Co-MOF precursor material.

[0100] (2) Preparation of lithium cobalt oxide material by high-temperature solid-phase method

[0101] The same as step (2) of Example 1.

[0102] (3) Forming a coating layer

[0103] 3 g of lithium cobalt oxide, 0.15 g of Co-MOF precursor material, and 0.052 g of lithium carbonate were weighed into a mortar and ground for 30 min to mix uniformly, then loaded into an alumina crucible and placed in a muffle furnace for calcination. The temperature was raised to 750°C at a rate of 5°C / min and calcined for 5 h to obtain a Co-MOF derivative coated lithium cobalt oxide positive electrode material.

[0104] Test Example 1

[0105] The electrochemical performance of the modified lithium cobalt oxide cathode material prepared in the test examples and the comparative examples was tested, and the results are shown in Table 1 and Figure 3 .

[0106] Test method: the active material: acetylene black: PVDF obtained in the examples and the comparative examples were mixed at a mass ratio of 8:1:1 to form a slurry, which was then coated on an aluminum foil to form a cathode, and a metal lithium was used as an anode to assemble a coin-type half-cell. The electrochemical performance of the half-cell was tested at 25℃, 3.0-4.55V and 0.1C.

[0107] Table 1: results of lithium cobalt oxide half-cell performance test

[0108]

[0109] In Examples 1-5, Example 1 showed the optimal discharge specific capacity, first efficiency and capacity retention rate, indicating that the cathode material with a coating amount of 5wt% was optimal. The performance of the seven examples was better than that of the comparative example, indicating that the Al2O3 coating layer obtained by using the bimetallic CoAl-MOF as a precursor was closely combined with the generated intermediate layer LiCoO2 through the structure of the precursor MOF, achieving a better coating effect and enhancing the structural stability of the lithium cobalt oxide cathode material.

[0110] The above is only a preferred embodiment 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 shall be included in the protection scope of the present application.

Claims

1. A modified lithium cobalt oxide cathode material, characterized in that, The modified lithium cobalt oxide cathode material comprises a lithium cobalt oxide core and a cobalt-aluminum oxide coating layer coated on the lithium cobalt oxide core. The mass fraction of cobalt in the modified lithium cobalt oxide cathode material is 59.29%-60.10%, and the mass fraction of aluminum is 0.11%-0.82%. The cobalt-aluminum oxide coating layer is formed by a CoAl-MOF material. A lithium cobalt oxide intermediate layer is formed between the lithium cobalt oxide core and the cobalt-aluminum oxide coating layer, and the lithium cobalt oxide intermediate layer is generated by the reaction of a cobalt oxide compound derived from the CoAl-MOF material and lithium carbonate.

2. The modified lithium cobalt oxide cathode material of claim 1, wherein, The specific surface area of the modified lithium cobalt oxide positive electrode material is 0.55m 2 / g-0.65m 2 / g.

3. A method for producing the modified lithium cobalt oxide cathode material according to claim 1 or 2, characterized in that, The preparation method comprises the following steps: The cobalt-aluminum oxide coating layer is formed on the lithium cobalt oxide core. A CoAl-MOF material is prepared by taking a cobalt salt, an aluminum salt, an organic ligand and a solvent as raw materials, and lithium cobalt oxide, lithium carbonate and the CoAl-MOF material are mixed and sintered.

4. The production method according to claim 3, characterized by, After the lithium cobalt oxide, lithium carbonate and the CoAl-MOF material are ground, sintering is performed, and the sintering temperature is controlled to be 700-900°C, and the sintering time is controlled to be 3-8h.

5. The preparation method according to claim 4, characterized in that, The sintering temperature is 730-780°C, and the sintering time is 4-6h.

6. The preparation method according to claim 3, characterized in that, The mass ratio of the CoAl-MOF material to lithium cobalt oxide is (1-8):

100.

7. The preparation method according to claim 6, characterized in that, The mass ratio of the CoAl-MOF material to lithium cobalt oxide is (4-6):

100.

8. The preparation method according to claim 3, characterized in that, The molar ratio of lithium to cobalt in lithium carbonate and the CoAl-MOF material is (1.01-1.05):1 by adjusting the amount of lithium carbonate.

9. The preparation method according to claim 3, characterized in that, The preparation process of the CoAl-MOF material comprises the following steps: the cobalt salt, the aluminum salt, the organic ligand and the solvent are mixed to obtain a mixed solution, and the mixed solution is reacted in a reaction kettle at 120-150°C for 12-36h.

10. The preparation method according to claim 9, characterized in that, The reaction temperature of the mixed solution is 135-145°C, and the reaction time is 20-30h.

11. The preparation method according to claim 9, characterized in that, After the reaction is completed, washing and drying are performed.

12. The method of claim 9, wherein, The molar ratio of cobalt, aluminum and the organic ligand is (5-10):(5-10):(7-15) by adjusting the amount of the cobalt salt, the aluminum salt and the organic ligand.

13. The method of claim 12, wherein, The molar ratio of cobalt, aluminum and the organic ligand is (6-8):(6-8):(7-9) by adjusting the amount of the cobalt salt, the aluminum salt and the organic ligand.

14. The method of claim 13, wherein, The organic ligand is selected from any one of terephthalic acid, trimesic acid, 2-methyl terephthalic acid, bipyridine and tetrapyridine.

15. The preparation method according to claim 13, characterized in that, The cobalt salt is selected from at least one of cobalt nitrate, cobalt chloride and cobalt sulfate.

16. The method of claim 13, wherein, The aluminum salt is selected from at least one of aluminum nitrate and aluminum chloride.

17. The preparation method according to claim 9, characterized in that, The solvent is a mixed solvent formed by N,N-dimethylformamide, ethanol and water, and the volume ratio of N,N-dimethylformamide, ethanol and water is (10-20):(0.5-1.5):

1.

18. The method of claim 17, wherein, The volume ratio of N,N-dimethylformamide, ethanol and water is (15-17):(0.8-1.2):

1.

19. A positive electrode sheet characterized by comprising: The modified lithium cobalt oxide cathode material prepared by the preparation method of any one of claims 3-18.

20. A secondary battery characterized by comprising: The positive electrode sheet of claim 19.

21. An electrical device, comprising: The secondary battery of claim 20.

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