Modified positive electrode material and preparation method and application thereof

Abstract

The application provides a modified positive electrode material and a preparation method and application thereof, and belongs to the technical field of lithium ion battery materials; the modified positive electrode material provided by the application comprises a positive electrode material base body and a coating layer arranged on the surface of the positive electrode material base body; the coating layer comprises a fluorine-containing polymer, a metal oxide and an MBene nano material; the modified positive electrode material provided by the application has excellent charge-discharge performance and cycle performance under a high cut-off voltage; and the raw materials used in the preparation method of the modified positive electrode material are cheap and easy to obtain, the operation is simple, and no other impurity ions are introduced, which is beneficial to actual production.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium ion battery materials, and particularly relates to a modified positive electrode material and a preparation method and application thereof. BACKGROUND

[0002] Lithium ion batteries are the most widely used battery type in recent years, and have good use prospects due to the advantages of high energy density, small self-discharge and no memory effect. A lithium ion battery is composed of a positive electrode, a negative electrode, a separator and an electrolyte. Since the energy density of the negative electrode material is much higher than that of the positive electrode, how to improve the energy density of the positive electrode material has become a research hotspot. Layered lithium cobaltate is one of the most commonly used commercial lithium ion battery positive electrode materials, and is favored due to its high energy density. However, the actual capacity of lithium cobaltate material is proportional to the cut-off voltage, and when the cut-off voltage reaches 4.2V, the actual capacity of lithium cobaltate is half of the theoretical capacity, and 50% of lithium ions are released, and the crystal structure changes. In the current research, the cut-off voltage of lithium cobaltate is increased from 4.2V to 4.5V, which can obtain higher battery capacity, but the too high cut-off voltage causes irreversible phase transition of lithium cobaltate positive electrode material, and leads to transition metal dissolution and oxygen evolution, resulting in the decline of battery cycle performance and safety. SUMMARY

[0003] The purpose of the present application is to overcome the shortcomings of the prior art and provide a modified positive electrode material with excellent electrochemical performance and cycle performance and high energy density under high cut-off voltage environment, and a preparation method and application thereof.

[0004] To achieve the above-mentioned purpose, in the first aspect of the present application, the present application provides a modified positive electrode material, which comprises a positive electrode material substrate and a coating layer arranged on the surface of the positive electrode material substrate, wherein the coating layer comprises a fluorine-containing polymer and a metal oxide coated MBene nanomaterial.

[0005] The modified positive electrode material provided by the application can effectively improve the cycle performance and electrochemical performance of a lithium ion battery under high cut-off voltage when applied to the preparation of the lithium ion battery. Specifically, the fluorine ion in the fluorine-containing polymer can synergize with the MBene in the metal oxide coated MBene nanomaterial, improving the thermal stability and high-pressure stability of the coating layer of the modified positive electrode material, so that the structure of the modified positive electrode material is stable under high temperature and high pressure, thereby ensuring excellent cycle performance under high cut-off voltage. Second, MBene and metal-fluorine combination open double lithium ion diffusion channels, that is, the free metal ion can synergize with MBene after combining with the fluorine ion, greatly improving the migration rate of lithium ions. Third, the hydrogen bonds generated between MBene and the fluorine-containing polymer and the introduction of the metal oxide coated MBene can reduce the agglomeration of MBene, making the coating layer more uniform as a whole, and further improving the comprehensive performance of the lithium ion prepared subsequently. Fourth, the advantages of the fluorine-containing polymer and the metal oxide coated MBene nanomaterial in the coating layer are retained, so that the lithium ion battery prepared has excellent electronic conductivity and ionic conductivity. Fifth, the coating layer in the application can also avoid the corrosion of the positive electrode material matrix caused by direct contact with the electrolyte, and the fluorine ion in the fluorine-containing polymer and the metal ion in the metal oxide can inhibit the generation of hydrogen fluoride in the electrolyte after entering the electrolyte, and can also inhibit the polarization of the positive electrode material matrix, thereby protecting the positive electrode material.

[0006] In an embodiment, the mass percentage of the coating layer is 0.5-1.5% based on the modified positive electrode material.

[0007] The application research found that when the mass percentage of the coating layer is 0.5-1.5%, the thickness of the coating layer obtained is within the range given by the application, and the modified positive electrode material obtained is applied to the preparation of a lithium ion battery, the lithium ion battery obtained has good cycle performance under high cut-off voltage, and the charge-discharge performance of the lithium ion battery obtained is excellent and the specific capacity is high.

[0008] In a second aspect of the application, the application provides a preparation method of the modified positive electrode material, which comprises the following steps:

[0009] (1) Preparation of positive electrode material matrix: mix lithium source and cobalt source, sinter, cool, and crush to obtain a positive electrode material matrix;

[0010] (2) Preparation of the fluorine-containing polymer: the fluorine-containing diol compound, the carbonate-based compound and the catalyst are mixed to perform a polymerization reaction, and then filtered, washed and dried to obtain the fluorine-containing polymer;

[0011] (3) Preparation of the metal oxide coated MBene nanomaterial: the metal oxide is added into a first organic solvent, and then the MBene nanoparticles are added to perform a coating reaction, and then dried to obtain the metal oxide coated MBene nanomaterial;

[0012] (4) Preparation of the modified positive electrode material: the fluorine-containing polymer and the metal oxide coated MBene nanomaterial are added into a second organic solvent to disperse, and then the second organic solvent dispersion liquid of the positive electrode material matrix is added, followed by stirring, evaporation and drying to obtain a powder; the powder is subjected to a fusion reaction to obtain the modified positive electrode material.

[0013] The preparation method of the positive electrode material provided by the application is simple in operation and easy to produce in practice, and the modified positive electrode material can be effectively prepared by using the preparation method.

[0014] In an embodiment, the fluorine-containing diol compound includes at least one of 3,3,3-trifluoro-1,2-propanediol, octafluoro-1,6-hexanediol, 2,3,5,6-tetrafluorophtaldehyde, 4,4,4-trifluoro-3-(trifluoromethyl)-1,3-butanediol, and 2,2,3,3-tetrafluoro-1,4-butanediol.

[0015] In an embodiment, the fluorine-containing diol compound is 3,3,3-trifluoro-1,2-propanediol.

[0016] The selection of the fluorine-containing diol compound will affect the synergistic effect with the MBene, thereby affecting the cycle performance of the product. When the fluorine-containing diol compound is further selected to be the above-mentioned compound, especially 3,3,3-trifluoro-1,2-propanediol, the cycle performance of the lithium ion battery prepared by using the obtained product under high cut-off voltage is more excellent.

[0017] In an embodiment, the carbonate-based compound includes at least one of diethyl carbonate, dimethyl carbonate, diphenyl carbonate, ethylene carbonate and propylene carbonate.

[0018] In an embodiment, the carbonate-based compound is diethyl carbonate.

[0019] In an embodiment, the catalyst includes an organic tin catalyst.

[0020] Exemplarily, the organic tin catalyst includes at least one of dibutyltin dilaurate and dibutyltin dimethoxide.

[0021] In an embodiment, the organotin catalyst is dibutyltin dilaurate.

[0022] In an embodiment, the metal oxide comprises at least one of MgO, AI2O3, TiO2.

[0023] In an embodiment, the metal oxide is MgO.

[0024] The present application research found that the selection of metal oxide will not only affect the action of metal oxide and MBene, but also affect the action of MBene and fluorine-containing polymer, when the further metal oxide is the above type of substance, especially MgO, the product obtained can greatly improve the migration rate of lithium ions, thereby improving the charge-discharge performance and specific capacity of lithium ion battery; and the above type of metal ion and fluoride ion can enter the electrolyte to inhibit the generation of hydrogen fluoride, further improving the cycle performance of the lithium ion battery prepared subsequently.

[0025] In an embodiment, the MBene nanoparticles comprise at least one of Mo2B nanoparticles, CrB nanoparticles, TiB nanoparticles, MnB nanoparticles.

[0026] In an embodiment, the MBene nanoparticles are Mo2B nanoparticles.

[0027] The present application research found that the selection of MBene nanoparticles not only can itself play better conductivity characteristics, but also will act together with metal oxide and fluorine-containing polymer to affect the specific capacity and energy density of the lithium ion battery prepared, and also affect the cycle performance of lithium ions; when the further selection of MBene nanoparticles is the above type of substance, especially Mo2B nanoparticles, the comprehensive effect of the product obtained is more excellent.

[0028] In an embodiment, the average diameter of the MBene nanoparticles is 50-200 nm.

[0029] The present application research found that the average diameter of MBene nanoparticles will affect the coating reaction with metal oxide, when the further selection of the average diameter of MBene nanoparticles is 50-200 nm, the comprehensive performance of the product prepared is more excellent.

[0030] In an embodiment, the first organic solvent comprises at least one of ethylene glycol, propylene glycol, and glycerol.

[0031] In an embodiment, the first organic solvent is ethylene glycol.

[0032] In an embodiment, the second organic solvent comprises at least one of styrene, ethanol, and ethylene glycol ether.

[0033] In an embodiment, the second organic solvent is ethanol.

[0034] The present application has found that when the first and second organic solvents are selected as above, a well-dispersed solution can be obtained, and the selected organic solvents are pollution-free and safe.

[0035] In an embodiment, the lithium source comprises Li2CO3, and the cobalt source comprises Co3O4.

[0036] In an embodiment, in step (1), the molar ratio of lithium ions to cobalt ions in the lithium source and the cobalt source is (0.9-1.05):(1-1.1).

[0037] In an embodiment, in step (1), when the lithium source and the cobalt source are mixed, the rotation speed of the mixing is 300-650 rpm, and the mixing time is 0.5-2 h.

[0038] In an embodiment, in step (1), the sintering temperature is 750-1050℃, the sintering time is 6-12 h, and the temperature rising rate during sintering is 3-6℃ / min.

[0039] The present application has found that when the parameters in step (1) are within the above ranges, the corresponding positive electrode material matrix can be obtained.

[0040] In an embodiment, in step (2), the mass ratio of the fluorine-containing diol compound, the carbonate-based compound, and the catalyst is (0.9-1.1):(0.5-1):(0.15-0.35).

[0041] In an embodiment, in step (2), the temperature of the polymerization reaction is 120-200℃.

[0042] In an embodiment, in step (2), the polymerization reaction is carried out in an inert gas environment; the inert gas comprises at least one of Ar, Kr, and Xe, and preferably, the inert gas is Ar.

[0043] In an embodiment, in step (2), the polymerization reaction is carried out by first reacting at room temperature, and then continuing the reaction by reducing the pressure to 10-100 pa.

[0044] In an embodiment, in step (2), the drying temperature is 60-100℃, and the drying time is 6-15 h.

[0045] The application researches and finds that when the parameters in step (2) are selected within the above range, the obtained fluorine-containing polymer applied to the preparation of modified positive electrode materials has more excellent comprehensive performance.

[0046] In an embodiment, in step (3), the mass ratio of the metal oxide and the MBene nanoparticles is (0.011-0.013):1.

[0047] In an embodiment, in step (3), the mass ratio of the metal oxide and the MBene nanoparticles is 0.012:1.

[0048] The application researches and finds that the metal oxide and the MBene nanoparticles can affect the thickness of the core-shell structure of the metal oxide coated MBene nanomaterial, thereby affecting the performance of the metal oxide coated MBene nanomaterial, and when the mass ratio of the two is further selected within the above range, especially the above point value, the comprehensive effect of the obtained product is more excellent.

[0049] In an embodiment, in step (3), the temperature of the coating reaction is 60-90℃, the time is 6-12h, and the rotation speed is 300-600rpm.

[0050] In an embodiment, in step (3), the drying temperature is 60-100℃.

[0051] The application researches and finds that when the parameters of the coating reaction of the metal oxide and the MBene nanoparticles are within the above range, a well-coated metal oxide coated MBene nanomaterial can be obtained, thereby helping to achieve excellent performance of the modified positive electrode material.

[0052] In an embodiment, in step (4), the mass ratio of the positive electrode material matrix, the fluorine-containing polymer, and the metal oxide coated MBene nanomaterial is 1:0.01:(0.0001-0.001).

[0053] The application researches and finds that when the mass ratio of the positive electrode material matrix, the fluorine-containing polymer, and the metal oxide coated MBene nanomaterial is within the above given range, the coating layer of the obtained product and the parameters of the coating layer and the positive electrode material matrix will be within the range given by the application, thereby ensuring that the product has excellent comprehensive effect.

[0054] In an embodiment, in step (4), the fusion reaction time is 10-60min, and the rotation speed is 3000-4000rpm.

[0055] In an embodiment, in step (4), the stirring speed for dispersing the fluorine-containing polymer and the metal oxide coated MBene nanomaterial into the second organic solvent is 300-600 rpm, and the stirring time is 20-40 min.

[0056] In an embodiment, in step (4), the stirring speed for evaporating the solvent is 300-700 rpm, the time is 8-16 h, and the temperature is 50-80℃.

[0057] In an embodiment, in step (4), the drying temperature is 60-100℃, and the time is 6-12 h.

[0058] The present application has found that when the parameters in step (4) are within the ranges given above, the modified positive electrode material with excellent comprehensive effect can be prepared.

[0059] In a third aspect of the present application, the present application provides the use of the modified positive electrode material in the preparation of a lithium ion battery.

[0060] Compared with the prior art, the present application has the following beneficial effects:

[0061] The modified positive electrode material provided by the present application introduces a coating layer including a fluorine-containing polymer and a metal oxide coated MBene nanomaterial on the surface of the positive electrode material matrix, and the obtained modified positive electrode material has good ion diffusion rate and electrical conductivity, and can maintain structural stability at high pressure and high temperature, so that the modified positive electrode material has excellent charge and discharge performance and cycle performance at high cut-off voltage. Moreover, the raw materials used in the preparation method of the modified positive electrode material provided by the present application are cheap and easy to obtain, the operation is simple, and no other impurity ions are introduced, which is beneficial to actual production. BRIEF DESCRIPTION OF DRAWINGS

[0062] Figure 1 A scanning electron microscope image of the modified positive electrode material prepared in Example 1;

[0063] Figure 2 An XRD pattern of the modified positive electrode material prepared in Example 1. DETAILED DESCRIPTION

[0064] For the purpose of better illustrating the object, technical scheme and advantages of the present application, the present application will be further described below in combination with specific embodiments.

[0065] The reagents, methods and equipment used in the present application are all conventional reagents, methods and equipment in the art unless otherwise specified.

[0066] Example 1

[0067] The embodiment of the present application provides a modified positive electrode material, the modified positive electrode material comprises a positive electrode material matrix and a coating layer coated on the surface of the positive electrode material matrix, the coating layer comprises a fluorine-containing polymer and a metal oxide coated MBene nanomaterial, and the positive electrode material matrix is a lithium cobaltate material.

[0068] The preparation method of the modified positive electrode material comprises the following steps:

[0069] (1) Preparation of the positive electrode material matrix: 400g of lithium source (lithium carbonate) and cobalt source (tricobalt tetroxide) with a lithium cobalt molar ratio of 1.05:1 are mixed in a high-speed mixer at a rotating speed of 300rpm for 1h, then the uniformly mixed material is placed into a box furnace and heated to 1030 DEG C at a heating rate of 3 DEG C / min and sintered for 10h, after the material is cooled, crushing is performed, and the positive electrode material matrix is obtained;

[0070] (2) Preparation of the fluorine-containing polymer: fluorine-containing diol (3,3,3-trifluoro-1,2-propanediol), carbonate-based compound (diethyl carbonate) and catalyst (dibutyltin dilaurate) are weighed according to a mass ratio of 1:0.91:0.25, and then the materials are simultaneously added into a reaction kettle, Ar gas is introduced to completely discharge the air in the reaction kettle, then the temperature is raised to 120 DEG C for high-temperature reaction for 10h (at normal pressure), then the temperature is raised to 190 DEG C, and the gas pressure is reduced to 70pa for reaction for 2.5h, a fluorine-containing polymer mixture is obtained, the mixture is washed with deionized water, and then dried at 80 DEG C for 10h, and the fluorine-containing polymer (polytrifluoromethyl ethyl carbonate) is obtained;

[0071] (3) Preparation of the metal oxide coated MBene nanomaterial: 0.12g of metal oxide (MgO) is added into 50mL of a first organic solvent (ethylene glycol), after stirring and mixing uniformly, a mixed solution is obtained, 10g of MBene nanoparticles (Mo2B nanoparticles, with an average diameter of 100nm) is added into the mixed solution, stirring is carried out on a constant-temperature magnetic stirrer at 60 DEG C and 450rpm for 8h, a MgO-MBene mixed solution of the MgO coated MBene nanomaterial is obtained, then the dry powder is obtained after drying for 8h in a constant-temperature oven at 85 DEG C to remove the excess solvent, and the MgO coated MBene nanomaterial is obtained after crushing the powder;

[0072] (4) Preparation of modified positive electrode material: 3g of polytrifluoromethyl ethyl carbonate was added to 60mL of the second organic solvent (absolute ethanol), followed by 0.15g of MgO-coated MBene nanomaterial, and stirred at a speed of 500rpm for 30min; then 300mL of the absolute ethanol solution of the lithium cobalt oxide positive electrode material matrix (300g) prepared in step (1) was added, and stirred at 65℃ and 600rpm until it was evaporated, dried at 85℃ for 8h after evaporation, and a powder was obtained; finally, the powder was fused by a mechanical fusion machine at a speed of 3500rpm for 30min, and a modified positive electrode material was obtained.

[0073] Example 2

[0074] The modified positive electrode material provided by the embodiment of the present application is different from the embodiment 1 only in the preparation method;

[0075] The preparation method of the modified positive electrode material comprises the following steps:

[0076] (1) Preparation of positive electrode material matrix: 400g of lithium source (lithium carbonate) and cobalt source (tricobalt tetroxide) with a lithium-cobalt molar ratio of 0.9:1.1 were mixed in a high-speed mixer at a speed of 300rpm for 1h, and then the mixed material was placed in a box furnace and heated to 750℃ at a heating rate of 6℃ / min for sintering for 12h. After the material was cooled, it was crushed to obtain a positive electrode material matrix;

[0077] (2) Preparation of fluorine-containing polymer: the fluorine-containing diol (3,3,3-trifluoro-1,2-propanediol), carbonate compound (diethyl carbonate) and catalyst (dibutyltin dilaurate) were weighed according to a mass ratio of 1:0.78:0.35, and then added to the reaction kettle at the same time. After the air in the reaction kettle was completely discharged by introducing Ar gas, the temperature was raised to 120℃ for high-temperature reaction for 10 hours (at normal pressure), and then the temperature was raised to 190℃ and the gas pressure was reduced to 70pa for reaction for 2.5h. A fluorine-containing polymer mixture was obtained. After the mixture was washed with deionized water and dried at 80℃ for 10h, a fluorine-containing polymer (polytrifluoromethyl ethyl carbonate) was obtained;

[0078] (3) Preparation of metal oxide coated MBene nanomaterial: 0.12 g of metal oxide (MgO) was added to 50 mL of the first organic solvent (ethylene glycol), and after stirring and mixing uniformly, a mixed solution was obtained. 10 g of MBene nanoparticles (Mo2B nanoparticles, with an average diameter of 100 nm) was added to the mixed solution, and stirring was performed on a constant temperature magnetic stirrer at 90°C and 350 rpm for 6 h to obtain a mixed solution of MgO coated MBene nanomaterial MgO-MBene. After that, the solution was dried in an 85°C constant temperature oven for 8 h to remove the excess solvent, and a dry powder was obtained. After the powder was crushed, the MgO coated MBene nanomaterial was obtained.

[0079] (4) Preparation of modified positive electrode material: 3 g of polytrifluoromethyl ethyl carbonate was added to 60 mL of the second organic solvent (absolute ethanol), and then 0.15 g of MgO coated MBene nanomaterial was added. Stirring was performed at a speed of 300 rpm for 40 min. Then, 300 mL of the absolute ethanol solution of the lithium cobaltate positive electrode material substrate (300 g) prepared in step (1) was added, and stirring was performed at 80°C and 300 rpm for 8 h. After evaporation, drying was performed at 85°C for 8 h to obtain a powder. Finally, the powder was fused by a mechanical fusion machine at a speed of 3500 rpm for 30 min to obtain the modified positive electrode material.

[0080] Example 3

[0081] The embodiment of the present application provides a modified positive electrode material, and the only difference between the modified positive electrode material and the embodiment 1 is that in step (4), the mass of the lithium cobaltate positive electrode material substrate added is changed to 626.85 g, so that the mass percentage of the coating layer is 0.5% based on the modified positive electrode material.

[0082] Example 4

[0083] The embodiment of the present application provides a modified positive electrode material, and the only difference between the modified positive electrode material and the embodiment 1 is that in step (4), the mass of the lithium cobaltate positive electrode material substrate added is changed to 206.85 g, so that the mass percentage of the coating layer is 1.5% based on the modified positive electrode material.

[0084] Example 5

[0085] The embodiment of the present application provides a modified positive electrode material, and the only difference between the modified positive electrode material and the embodiment 1 is that in step (4), the mass of the lithium cobaltate positive electrode material substrate added is changed to 1046.85 g, so that the mass percentage of the coating layer is 0.3% based on the modified positive electrode material.

[0086] Example 6

[0087] The embodiment of the present application provides a modified positive electrode material, and the only difference between the modified positive electrode material and the embodiment 1 is that in step (4), the mass of the added lithium cobaltate positive electrode material matrix is 171.85g, so that the mass percentage of the coating layer is 1.8% according to the modified positive electrode material.

[0088] Embodiment 7

[0089] The embodiment of the present application provides a modified positive electrode material, and the only difference between the modified positive electrode material and the embodiment 1 is that the fluorine-containing diol used is 2,3,5,6-tetrafluorop-xyleneglycol.

[0090] Embodiment 8

[0091] The embodiment of the present application provides a modified positive electrode material, and the only difference between the modified positive electrode material and the embodiment 1 is that the carbonate-based compound used is propylene carbonate.

[0092] Embodiment 9

[0093] The embodiment of the present application provides a modified positive electrode material, and the only difference between the modified positive electrode material and the embodiment 1 is that the metal oxide used is Al2O3.

[0094] Embodiment 10

[0095] The embodiment of the present application provides a modified positive electrode material, and the only difference between the modified positive electrode material and the embodiment 1 is that the MBene nanoparticles used are MnB nanoparticles.

[0096] Embodiment 11

[0097] The embodiment of the present application provides a modified positive electrode material, and the only difference between the modified positive electrode material and the embodiment 1 is that in step (3), the mass of the metal oxide is 0.10g.

[0098] Embodiment 12

[0099] The embodiment of the present application provides a modified positive electrode material, and the only difference between the modified positive electrode material and the embodiment 1 is that in step (3), the mass of the metal oxide is 0.14g.

[0100] Embodiment 13

[0101] The embodiment of the present application provides a modified positive electrode material, and the only difference between the modified positive electrode material and the embodiment 1 is that in step (3), the stirring is performed on a constant-temperature magnetic stirrer at 50 DEG C and 450rpm for 8h.

[0102] Embodiment 14

[0103] The modified positive electrode material of the embodiment of the present application has only one difference from the embodiment 1, which is that in step (3), the powder is stirred for 8 h on a constant temperature magnetic stirrer at 100 ℃ and 450 rpm.

[0104] Embodiment 15

[0105] The modified positive electrode material of the embodiment of the present application has only one difference from the embodiment 1, which is that in step (4), the powder is fused for 30 min by a mechanical fusion machine at a rotation speed of 2000 rpm.

[0106] Embodiment 16

[0107] The modified positive electrode material of the embodiment of the present application has only one difference from the embodiment 1, which is that in step (4), the powder is fused for 30 min by a mechanical fusion machine at a rotation speed of 5000 rpm.

[0108] Comparative Example 1

[0109] The modified positive electrode material of the comparative example of the present application has only one difference from the embodiment 1, which is that there is no step (3) and in step (4), the metal oxide is directly added; that is, in step (4), 3 g of polytrifluoromethyl ethyl carbonate is added into 60 mL of the second organic solvent (absolute ethanol), then 0.15 g of MBene nanoparticles (Mo2B nanoparticles, with an average diameter of 100 nm) is added, and stirred for 30 min at a rotation speed of 500 rpm; then 300 mL of the absolute ethanol solution of the lithium cobaltate positive electrode material matrix (300 g) prepared in step (1) is added, and stirred at 65 ℃ and 600 rpm to evaporate for 12 h, dried at 85 ℃ for 8 h to obtain a powder; finally, the powder is fused for 30 min by a mechanical fusion machine at a rotation speed of 3500 rpm to obtain the modified positive electrode material.

[0110] Comparative Example 2

[0111] The modified positive electrode material of the comparative example of the present application has only one difference from the embodiment 1, which is that there is no step (3) and in step (4), the metal oxide is directly added; that is, in step (4), 3 g of polytrifluoromethyl ethyl carbonate is added into 60 mL of the second organic solvent (absolute ethanol), then 0.15 g of MgO is added, and stirred for 30 min at a rotation speed of 500 rpm; then 300 mL of the absolute ethanol solution of the lithium cobaltate positive electrode material matrix (300 g) prepared in step (1) is added, and stirred at 65 ℃ and 600 rpm to evaporate for 12 h, dried at 85 ℃ for 8 h to obtain a powder; finally, the powder is fused for 30 min by a mechanical fusion machine at a rotation speed of 3500 rpm to obtain the modified positive electrode material.

[0112] Comparative Example 3

[0113] The present invention provides a modified cathode material in comparative example. The only difference between the modified cathode material and Example 1 is that no metal oxide is added to coat MBene nanomaterials. That is, in step (4), 3.15g of polytrifluoromethyl ethyl carbonate is added to 60mL of the second organic solvent (anhydrous ethanol); then 300mL of anhydrous ethanol solution of the lithium cobalt oxide cathode material matrix (300g) prepared in step (1) is added, and the mixture is stirred and evaporated to dryness at 65℃ and 600rpm for 12h. After evaporation, the mixture is dried at 85℃ for 8h to obtain powder; finally, the powder is fused by mechanical fusion machine at a speed of 3500rpm for 30min to obtain the modified cathode material.

[0114] Comparative Example 4

[0115] The present invention provides a modified cathode material in comparative example, the only difference between the modified cathode material and Example 1 is that only step (1) is present.

[0116] Example of effect

[0117] This invention investigates the performance of the modified cathode materials prepared in Examples 1-16 and Comparative Examples 1-4. The modified cathode materials prepared in Examples 1-16 and Comparative Examples 1-4, along with the binder PVDF and the conductive agent, were mixed in a mass ratio of 95:2.5:2.5 to obtain a cathode slurry, which was then coated onto the surface of aluminum foil to obtain a cathode sheet. Lithium metal was used as the anode, and the electrolyte ratio was 1.15M LiPF6EC:DMC (1:1 vo 1%). The resulting coin cells were assembled. The coin cells were tested at 25°C with a test voltage of 3–4.6V. The one-week capacity and 50-week capacity retention were tested, and the results are shown in Table 1.

[0118] Table 1

[0119]

[0120]

[0121] As shown in Table 1, when the technical solution provided by this invention is adopted, the obtained product has excellent charge-discharge performance and energy density, and excellent cycle performance, which is significantly improved compared with the untreated cathode material in Comparative Example 4. Specifically, the obtained product has a charge specific capacity of over 207.5 mAh / g, a discharge specific capacity of over 170.3 mAh / g, an initial efficiency of over 81.1%, and a 50-cycle retention rate of over 76.4%. The scanning electron microscope image of the modified cathode material prepared in Example 1 is shown below. Figure 1 As shown, the XRD pattern is as follows Figure 2 As shown;

[0122] As can be seen from Examples 1 and 3-6, the mass percentage of the modified cathode material coating layer affects the electrochemical performance; as can be seen from Examples 1 and 7-10, the specific selection of the coating material also affects the overall performance of the product; as can be seen from Examples 1 and 11-12, the mass ratio of metal oxide to MBene nanoparticles also affects the overall performance of the product; as can be seen from Examples 1 and 13-16, the parameters in the preparation process of the modified cathode material also affect the overall performance of the product.

[0123] As can be seen from Example 1 and Comparative Example 1, when the MBene nanoparticles introduced into the coating layer are not coated with metal oxide, the overall performance of the obtained product shows a significant downward trend. As can be seen from Example 1 and Comparative Example 2, when the coating layer does not contain MBene nanoparticles but contains metal oxide, the charge-discharge specific capacity, initial efficiency, and 50-cycle retention rate of the obtained product all decrease significantly. As can be seen from Example 1 and Comparative Example 3, when the coating layer of the modified cathode material contains only fluoropolymer, the obtained product cannot achieve the effect of the present invention.

Claims

1. A modified positive electrode material comprising a positive electrode material base and a coating layer provided on the surface of the positive electrode material base, characterized in that, The coating layer comprises fluorine-containing polymer, metal oxide coated MBene nanomaterials; The fluorine-containing polymer is formed by polymerization reaction of fluorine-containing diol compound, carbonate-based compound and catalyst.

2. The modified cathode material of claim 1, wherein, The mass percentage of the coating layer is 0.5-1.5% based on the modified positive electrode material.

3. The method for producing a modified cathode material according to any one of claims 1 to 2, wherein The preparation method comprises the following steps: (1) Preparation of positive electrode material substrate: mix lithium source and cobalt source, then sinter, cool, and crush to obtain positive electrode material substrate; (2) Preparation of fluorine-containing polymer: mix fluorine-containing diol compound, carbonate-based compound and catalyst, then perform polymerization reaction, and then filter, wash and dry to obtain fluorine-containing polymer; (3) Preparation of metal oxide coated MBene nanomaterials: add metal oxide into first organic solvent, then add MBene nanoparticles, and then perform coating reaction, and then dry to obtain metal oxide coated MBene nanomaterials; (4) Preparation of modified positive electrode material: add fluorine-containing polymer and metal oxide coated MBene nanomaterials into second organic solvent for dispersion, then add second organic solvent dispersion liquid of positive electrode material substrate, and then perform stirring and dry distillation and drying to obtain powder; and then perform fusion reaction of the powder to obtain modified positive electrode material.

4. The production method according to claim 3, characterized by, At least one of the following (a)-(h) is satisfied: (a) The fluorine-containing diol compound comprises at least one of 3,3,3-trifluoro-1,2-propanediol, octafluoro-1,6-hexanediol, 2,3,5,6-tetrafluorophtaldehyde, 4,4,4-trifluoro-3-(trifluoromethyl)-1,3-butanediol, and 2,2,3,3-tetrafluoro-1,4-butanediol; (b) The carbonate-based compound comprises at least one of diethyl carbonate, dimethyl carbonate, diphenyl carbonate, ethylene carbonate, and propylene carbonate; (c) The catalyst comprises organic tin catalyst; (d) The metal oxide comprises at least one of MgO, Al2O3, and TiO2; (e) The MBene nanoparticles comprise at least one of Mo2B nanoparticles, CrB nanoparticles, TiB nanoparticles, and MnB nanoparticles; (f) The first organic solvent comprises at least one of ethylene glycol, propylene glycol, and glycerol; (g) The second organic solvent comprises at least one of styrene, ethanol, and ethylene glycol ether; (h) The lithium source comprises Li2CO3, and the cobalt source comprises Co3O4.

5. The preparation method according to claim 3, characterized in that, In step (2), the mass ratio of fluorine-containing diol compound, carbonate-based compound and catalyst is (0.9-1.1):(0.5-1):(0.15-0.35). And / or, in step (2), the temperature of the polymerization reaction is 120-200℃.

6. The preparation method according to claim 3, characterized in that, In step (3), the mass ratio of metal oxide and MBene nanoparticles is (0.011-0.013):

1.

7. The preparation method according to claim 3, characterized in that, In step (3), the temperature of the coating reaction is 60-90℃, the time is 6-12h, and the rotation speed is 300-600rpm.

8. The preparation method according to claim 3, characterized in that, In step (4), the mass ratio of the positive electrode material base, the fluorine-containing polymer and the metal oxide coated MBene nanomaterial is 1:0.01:(0.0001-0.001).

9. The preparation method according to claim 3, characterized in that, In step (4), the time of the fusion reaction is 10-60 min, and the rotation speed is 3000-4000 rpm.

10. Use of the modified positive electrode material according to any one of claims 1-2 in the preparation of a lithium ion battery.

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