A surface modification modified lithium-rich manganese-based positive electrode material and a preparation method thereof

Abstract

The application discloses a surface modification modified lithium-rich manganese-based positive electrode material, and a preparation method thereof. The lithium-rich manganese-based positive electrode material is coated with a fast ion conductor coating layer and a spinel structure layer rich in oxygen vacancies. The spinel structure layer is in-situ generated on the surface of the lithium-rich manganese-based positive electrode material, and the fast ion conductor coating layer is coated on the surface of the spinel structure layer. The application can improve the electrical properties of the lithium-rich manganese-based positive electrode material, including improving the initial specific discharge capacity and coulombic efficiency, and improving the cycle stability and rate characteristics, so that the lithium-rich manganese-based positive electrode material can meet the development requirements of high-power electronic devices, such as electric vehicles.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of battery materials, and particularly relates to a lithium-rich manganese-based positive electrode material and a preparation method thereof. BACKGROUND

[0002] In recent years, in order to realize the sustainable development of energy, resources and environment in human society development, seeking clean, efficient and sustainable traffic mode has become a research hotspot, and the development of new energy vehicles has become an important strategic measure to cope with climate change. The power battery as one of the cores of new energy vehicles, the performance of the battery directly determines the driving range, safety performance and cost of electric vehicles. But even if the energy density of ternary battery is higher, the driving range of electric vehicles is generally not more than 500km, so developing higher specific energy lithium ion battery materials to solve the range anxiety problem of electric vehicles is a hot topic in the research of power battery.

[0003] The layered lithium-rich manganese-based positive electrode material xLi2MnO3·(1-x)LiMO2(0

[0004] To overcome the above-mentioned shortcomings, researchers have adopted various optimization methods such as ion doping, surface coating, surface pretreatment, etc. Among them, surface pretreatment can reduce the first irreversible capacity loss of the material by activating the Li2MnO3 phase in the lithium-rich manganese-based material, but the side effect is that the surface structure of the material is greatly affected after treatment, which may reduce the cycle stability and rate performance of the material. For example, Denis et al. used (NH4)2SO4 to treat lithium-rich manganese-based positive electrode materials to activate the Li2MnO3 phase on the surface of the material. The surface of the lithium-rich manganese-based positive electrode material treated formed a spinel layer, and the first discharge specific capacity was 270 mAh / g at a current density of 300 mAh / g. The first coulombic efficiency was improved from 76% to 95%, but the cycle stability of the material was not improved. Surface coating can effectively inhibit the side reaction between the positive electrode material surface and the electrolyte, and improve the cycle stability of the material. For example, patent CN109509874A discloses a preparation method of molybdenum trioxide coated lithium-rich manganese-based positive electrode material. The lithium-rich manganese-based material is mixed with ammonium molybdate by wet method, and then dried by water bath and high temperature heat treatment to obtain the modified lithium-rich manganese-based material. Although the oxide coating layer obtained by this method can improve the cycle stability, it does not effectively eliminate the residual lithium on the surface of the material, and the inhibition effect on the side reaction of the electrode surface is limited. Moreover, molybdenum trioxide as an inert coating often hinders the charge transfer of the electrode material and reduces the mass energy density of the electrode active material, so it has certain limitations in application.

[0005] Therefore, for lithium-rich manganese-based positive electrode materials, it is imperative to comprehensively improve their various electrochemical performances (such as discharge specific capacity, coulombic efficiency, cycle stability, etc.). SUMMARY

[0006] The technical problem to be solved by the present application is to overcome the deficiencies and defects mentioned in the above background art, and to provide a surface modified lithium-rich manganese-based positive electrode material with excellent discharge specific capacity, coulombic efficiency and cycle stability, and a preparation method thereof. To solve the above technical problems, the technical solution proposed by the present application is:

[0007] A surface modified lithium-rich manganese-based positive electrode material, which has a structure from inside to outside as lithium-rich manganese-based positive electrode material, spinel structure layer rich in oxygen vacancies, and fast ion conductor coating layer. The spinel structure layer is generated in situ on the surface of the lithium-rich manganese-based positive electrode material, and the fast ion conductor coating layer is coated on the surface of the spinel structure layer. The fast ion conductor coating layer is obtained by the reaction of a niobium-containing compound with residual lithium on the surface of the lithium-rich manganese-based positive electrode material. The molecular formula of the fast ion conductor coating layer is LiNbO3.

[0008] Preferably, the lithium-rich manganese-based positive electrode material has a molecular formula of xLi2MnO3·(1-x)LiMO2, wherein M is one or more of transition metals Ni, Co, and Mn, and 0

[0009] Preferably, the lithium-rich manganese-based positive electrode material has a particle size of 5-20 μm, the spinel structure layer has a thickness of 1-5 nm, and the fast ion conductor coating layer has a thickness of 1-5 nm. The thickness of the spinel phase and the coating layer is relatively thin at 1-5 nm, because the surface residual lithium is less, the ammonium niobium oxalate hydrate added is less, the content of generated NH3 is also less, and the thickness of the formed coating layer and spinel phase is also relatively low. The thickness of the coating layer should not be too high, otherwise the proportion of active material will be reduced, and the specific discharge capacity of the material will be reduced.

[0010] In the present application, specifically, the fast ion conductor coating layer is formed by the reaction of niobium pentoxide produced by high-temperature thermal decomposition of ammonium niobium oxalate hydrate (chemical formula (NH4) x [NbO(C2O4)3]·yH2O) and residual lithium on the surface of the material, and is formed by sintering, and has a chemical formula of LiNbO3. The spinel structure layer (which can be LiMn2O4) rich in oxygen vacancies is formed by the reaction of ammonia gas produced by high-temperature thermal decomposition of ammonium niobium oxalate hydrate and Li2MnO3 components in the material, and the reaction formula is as follows:

[0011] 2NH3(g)+6Li2MnO3(s)→6LiMnO2(s)+3Li2O(s)+3H2O(g)+N2(g);

[0012] 6LiMnO2(s)+2O lattice →2LiMn2O4(s)+2Li2MnO3(s)+2O vacancy .

[0013] As a general technical concept, the present application also provides a preparation method of the above-mentioned surface-modified lithium-rich manganese-based positive electrode material, comprising the following steps:

[0014] (1) uniformly mixing the lithium-rich manganese-based positive electrode material with ammonium niobium oxalate hydrate, calcining under an inert atmosphere, and then naturally cooling to room temperature, and then removing excess reaction residues by washing, suction filtering, and drying to obtain a pretreated lithium-rich manganese-based positive electrode material;

[0015] (2) calcining the pretreated lithium-rich manganese-based positive electrode material obtained in step (1), and naturally cooling to room temperature to obtain a surface-modified lithium-rich manganese-based positive electrode material.

[0016] The step sintering of the ammonium niobate oxalate hydrate added in the application can produce some impurities while forming the spinel phase and the fast ion conductor coating layer, and the water washing can remove the impurities, but the water washing can affect the crystallinity of the material, and the secondary sintering can ensure the crystallinity of the material and prevent the water washing from destroying the crystal structure of the material.

[0017] In the preparation method, preferably, the added mass of the ammonium niobate oxalate hydrate is 1-10% of the mass of the lithium-rich manganese-based positive electrode material. Controlling the mass ratio can ensure the formation of the spinel phase and the lithium niobate coating layer with a suitable thickness, and a high mass ratio can lead to an excessively thick coating layer and possible impurities, and a low mass ratio can lead to an excessively thin coating layer and even the failure to form the spinel phase, and the modification effect is not obvious.

[0018] More preferably, the molecular formula of the lithium-rich manganese-based positive electrode material is Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2, the molecular formula of the ammonium niobate oxalate hydrate is (NH4)3NbO(C2O4)3·4H2O, and the added mass of the ammonium niobate oxalate hydrate is 5% of the mass of the lithium-rich manganese-based positive electrode material. The reaction of the above lithium-rich manganese-based positive electrode material with the (NH4)3NbO(C2O4)3·4H2O with a specific mass, combined with the regulation of the calcination temperature, can control the reaction process, and finally obtain the LiNbO3 with the spinel phase and the fast ion conductor coating layer uniformly coated and the fast ion conductor coating layer with higher purity and less impurities, which is beneficial to ensure the electrochemical performance of the material.

[0019] In the preparation method, preferably, in the step (1), the calcination temperature is 500-800℃, the calcination time is 3-7h, and the heating rate is 1-5℃ / min. More preferably, the temperature is increased to 650℃ at a heating rate of 3℃ / min and kept at this temperature for 5h. The above temperature needs to ensure that the ammonium niobate oxalate hydrate can be decomposed, and the spinel phase and lithium niobate are generated at the same time. A temperature that is too low can cause the ammonium niobate oxalate hydrate to be unable to decompose, and the spinel phase and lithium niobate cannot be generated. A temperature that is too high can cause the ammonium niobate oxalate hydrate to decompose too quickly, and the ammonia gas is lost too quickly, resulting in too little and uneven generation of the spinel phase. In addition, a temperature that is too high can also make the lithium-rich manganese-based material particles more dense, increasing the lithium ion diffusion resistance.

[0020] In the above preparation method, preferably, in the step (2), the calcination temperature is 200-600℃, the calcination time is 2-5h, and the temperature rising rate is 1-5℃ / min. More preferably, the temperature is raised to 450℃ at a temperature rising rate of 3℃ / min and kept at this temperature for 3h. The sintering step is to ensure the crystallinity of the material, prevent the water washing from damaging the crystal structure of the material, and re-sintering to make the material have better crystallinity. If the sintering temperature is too low or the time is too short, the purpose of improving the crystallinity cannot be achieved, and if the sintering temperature is too high or the time is too long, the material may become more dense, increasing the ion deintercalation resistance.

[0021] In the above preparation method, preferably, in the step (1), the inert atmosphere is argon, nitrogen or a mixed atmosphere of argon and nitrogen, and the washing is performed by using pure water, anhydrous ethanol or a mixed solution of pure water and anhydrous ethanol.

[0022] Compared with the surface coating or surface pretreatment commonly used to improve only part of the electrical properties of the positive electrode material, the surface modification method of the present application is simple in process and can comprehensively improve the various electrochemical properties of the lithium-rich manganese-based positive electrode material, including improving the initial discharge specific capacity and coulombic efficiency of the material, and improving the cycle stability and rate characteristics. Specifically, the present application uses a lithium-rich manganese-based positive electrode material xLi2MnO3·(1-x)LiMO2 as a raw material, uniformly mixes it with a surface modifier ammonium niobate oxalate hydrate, and then sintering in an inert atmosphere to prepare a surface-modified lithium-rich manganese-based positive electrode material by using the thermal decomposition characteristics of the ammonium niobate oxalate hydrate. That is, the ammonium niobate oxalate hydrate material is thermally decomposed to generate NH3 and Nb2O5 at high temperature, and in an inert atmosphere, NH3 can react with the lithium-rich manganese-based positive electrode material to form a spinel phase rich in oxygen vacancies on the surface thereof. And the Nb2O5 generated by decomposition can react with the residual lithium on the surface of the lithium-rich manganese-based positive electrode material and generate a LiNbO3 coating layer with good lithium ion conductivity on the surface thereof.

[0023] Compared with the prior art, the present application has the following advantages:

[0024] 1. The surface-modified lithium-rich manganese-based cathode material of the present invention comprises, from the inside out, a lithium-rich manganese-based cathode material, a spinel structure layer rich in oxygen vacancies, and a fast-ion conductor coating layer. The spinel structure layer has a three-dimensional framework structure for fast lithium-ion transport channels, which, combined with abundant oxygen vacancies, can jointly improve the diffusion rate of lithium ions. Simultaneously, the abundant oxygen vacancy distribution can suppress the loss of lattice oxygen in the material's surface structure, effectively preventing the lithium-rich manganese-based cathode material from releasing large amounts of oxygen under high operating voltages, thus damaging the crystal structure and improving the stability of the material's surface structure, thereby effectively improving the cycle stability of the lithium-rich manganese-based cathode material. Furthermore, the formation of the spinel phase causes the material to release some capacity at around 2.7V, thereby effectively improving the discharge specific capacity and initial coulombic efficiency of the lithium-rich manganese-based battery cathode material, and reducing the irreversible capacity during the first cycle. The LiNbO3 coating layer, with its good lithium-ion conductivity, can improve the lithium-ion conductivity of the lithium-rich manganese-based cathode material, accelerate lithium-ion migration, and improve its rate performance. Meanwhile, the coating layer physically blocks the contact between the lithium-rich manganese-based material and the electrolyte, reducing side reactions between the active material and the electrolyte and oxygen evolution during the activation process, thereby improving the cycle stability of the material.

[0025] 2. In this invention, ammonium niobate oxalate hydrate is used to modify the surface of lithium-rich manganese-based cathode material to obtain a surface-modified lithium-rich manganese-based cathode material. The Nb2O5 generated by the decomposition of ammonium niobate oxalate hydrate reacts with the residual lithium on the surface of the lithium-rich manganese-based cathode material, effectively reducing the residual lithium on the surface and improving the cycle stability.

[0026] 3. The surface modification method of the present invention treats lithium-rich manganese-based cathode materials, which can comprehensively improve the various electrical properties of the materials, including improving the initial discharge specific capacity and coulombic efficiency, while improving their cycle stability and rate characteristics, so that they can meet the development requirements of high-power electronic devices such as electric vehicles.

[0027] 4. The preparation method of the present invention has a simple process flow, is easy to operate, is environmentally friendly, and is suitable for large-scale industrial production. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1 The XRD patterns and partial magnified views of the surface-modified lithium-rich manganese-based cathode material prepared in Example 1 and the unmodified lithium-rich manganese-based material in Comparative Example 1 are shown.

[0030] Figure 2 SEM image (a) and EDS surface scan image (b) of the surface modification modified lithium-rich manganese-based positive electrode material prepared in Example 1.

[0031] Figure 3 The first charge-discharge curve of the surface modification modified lithium-rich manganese-based positive electrode material prepared in Example 1 and the unmodified lithium-rich manganese-based material in Comparative Example 1 assembled in a button cell at a 0.1C discharge rate.

[0032] Figure 4 The cycle performance graph of the surface modification modified lithium-rich manganese-based positive electrode material prepared in Example 1 and the unmodified lithium-rich manganese-based material in Comparative Example 1 assembled in a button cell at a 1C discharge rate.

[0033] Figure 5 The rate performance graph of the surface modification modified lithium-rich manganese-based positive electrode material prepared in Example 1 and the unmodified lithium-rich manganese-based material in Comparative Example 1 assembled in a button cell. DETAILED DESCRIPTION

[0034] In order to facilitate the understanding of the present application, the following will be a more comprehensive and detailed description of the present application in conjunction with the drawings and preferred embodiments of the specification, but the protection scope of the present application is not limited to the following specific embodiments.

[0035] Unless otherwise defined, all the professional terms used in the following have the same meaning as understood by those skilled in the art. The professional terms used in this paper are only for the purpose of describing specific embodiments and are not intended to limit the protection scope of the present application.

[0036] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present application can be purchased from the market or can be prepared by existing methods.

[0037] Example 1:

[0038] A preparation method of a surface modification modified lithium-rich manganese-based positive electrode material, comprising the following steps:

[0039] (1) 1 g of lithium-rich manganese-based positive electrode material (Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2) and 0.05 g of ammonium niobium oxalate hydrate ((NH4)3NbO(C2O4)3·4H2O) are uniformly mixed by grinding, and the mixture is placed in a tube furnace in an argon atmosphere, heated to 650℃ at a heating rate of 3℃ / min and kept at this temperature for 5h, then naturally cooled to room temperature, washed with deionized water and filtered 3 times to remove excess reaction residues, and dried to obtain a pretreated lithium-rich manganese-based positive electrode material.

[0040] (2) The pretreated lithium-rich manganese-based positive electrode material obtained in step (1) is placed in a muffle furnace in an air atmosphere, heated to 450°C at a heating rate of 3°C / min and kept at this temperature for calcination for 3h, and then naturally cooled to room temperature to obtain a surface-modified modified lithium-rich manganese-based positive electrode material.

[0041] Assembly of the battery: 0.2000g of the surface-modified modified lithium-rich manganese-based positive electrode material obtained in this example is weighed, 0.0250g of conductive carbon black is added as a conductive agent and 0.0250g of PVDF (polyvinylidene fluoride) is added as a binder, the mixture is uniformly mixed and then coated on an aluminum foil to form a positive electrode sheet, a CR2025 button cell is assembled in a vacuum glove box with a lithium metal sheet as the negative electrode, Celgard2300 as the separator, 1 mol / L LiPF6 / EC:DMC (volume ratio 1:1) as the electrolyte.

[0042] As shown in Figure 1 , the XRD pattern of the surface-modified modified lithium-rich manganese-based positive electrode material prepared in this example and the unmodified lithium-rich manganese-based material in Comparative Example 1 are both typical α-NaFeO2layered structures, and both have superlattice diffraction peaks corresponding to Lli2MnO3components in the 20°-25° region, and the crystal structure of the material before and after surface modification has not changed. In addition, compared with the unmodified material, the surface-modified modified material XRD pattern observed LiNbO3characteristic peaks near 23° and 33°, and spinel phase characteristic peaks near 36°.

[0043] As shown in Figure 2 (a), the surface-modified modified lithium-rich manganese-based positive electrode material prepared in this example has a good spherical morphology, with a particle size of about 15μm. EDS energy spectrum analysis of the material is shown in Figure 2 (b), and the Nb element is uniformly distributed on the surface of the spherical particles, which indicates that the LiNbO3coating layer is uniformly coated on the surface of the lithium-rich manganese-based material.

[0044] As shown in Figure 3 , the battery assembled in this example has a first discharge specific capacity of 295.7mAh / g at 0.1C in the voltage range of 2.0-4.8V, a first coulombic efficiency of 88.48%, and a discharge platform corresponding to the spinel phase at about 2.7V.

[0045] As shown in Figure 4 , the battery assembled in this example has a capacity retention rate of 90.77% after 100 cycles at a 1C charge-discharge rate in the voltage range of 2.0-4.8V.

[0046] As shown in Figure 5As shown, the battery assembled in this embodiment has a discharge specific capacity of 289.6, 270.4, 248.9, 230.7, 208.9, 153.2 mAh / g at 0.1, 0.2, 1, 2, 5C under the voltage range of 2.0-4.8V.

[0047] Example 2:

[0048] A preparation method of a surface modification modified lithium-rich manganese-based positive electrode material, comprising the following steps:

[0049] (1) 1 g of a lithium-rich manganese-based positive electrode material (Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2) and 0.03 g of ammonium niobate oxalate hydrate ((NH4)3NbO(C2O4)3·4H2O) are uniformly mixed by grinding, the mixture is placed in a tube furnace in an argon atmosphere, heated to 650°C at a heating rate of 3°C / min and kept at this temperature for 5 h, and then naturally cooled to room temperature, washed and filtered with deionized water for 3 times to remove excess reaction residues, and dried to obtain a pretreated lithium-rich manganese-based positive electrode material.

[0050] (2) The pretreated lithium-rich manganese-based positive electrode material obtained in step (1) is placed in a muffle furnace in an air atmosphere, heated to 450°C at a heating rate of 3°C / min and kept at this temperature for 3 h, and then naturally cooled to room temperature to obtain a surface modification modified lithium-rich manganese-based positive electrode material.

[0051] Battery assembly: 0.2000 g of the surface modification modified lithium-rich manganese-based positive electrode material obtained in this embodiment is weighed, 0.0250 g of conductive carbon black is added as a conductive agent and 0.0250 g of PVDF (polyvinylidene fluoride) is added as a binder, uniformly mixed, and then coated on an aluminum foil to form a positive electrode sheet, a metal lithium sheet is used as a negative electrode, Celgard2300 is used as a separator, 1 mol / L LiPF6 / EC:DMC (volume ratio 1:1) is used as an electrolyte, and a CR2025 button cell is assembled in a vacuum glove box.

[0052] The battery assembled in this embodiment has a first discharge capacity of 289.4 mAh / g at 0.1C under the voltage range of 2.0-4.8V, a first coulombic efficiency of 87.32%, a capacity retention rate of 88.63% after 100 cycles at 1C charge-discharge rate, and a discharge specific capacity of 281.4, 267.2, 237.9, 225.2, 197.6, 145.8 mAh / g at 0.1, 0.2, 1, 2, 5C under the charge-discharge rate.

[0053] Example 3:

[0054] A preparation method of a surface modification modified lithium-rich manganese-based positive electrode material, comprising the following steps:

[0055] (1) 1 g of a lithium-rich manganese-based positive electrode material (Li 1.2 Ni 0.2 Mn 0.6 O2) is uniformly mixed with 0.05 g of ammonium niobate oxalate hydrate (NH4NbO(C2O4)2·5H2O) by grinding, and the mixture is placed in a tube furnace in an argon atmosphere, heated to 650°C at a heating rate of 3°C / min, and kept at this temperature for 5 h of calcination, and then naturally cooled to room temperature, washed and filtered with deionized water for 3 times to remove excess reaction residues, and dried to obtain a pretreated lithium-rich manganese-based positive electrode material.

[0056] (2) The pretreated lithium-rich manganese-based positive electrode material obtained in step (1) is placed in a muffle furnace in an air atmosphere, heated to 450°C at a heating rate of 3°C / min, and kept at this temperature for 3 h of calcination, and then naturally cooled to room temperature to obtain a surface modification modified lithium-rich manganese-based positive electrode material.

[0057] Battery assembly: 0.2000 g of the surface modification modified lithium-rich manganese-based positive electrode material obtained in this example is weighed, 0.0250 g of conductive carbon black is added as a conductive agent and 0.0250 g of PVDF (polyvinylidene fluoride) is added as a binder, uniformly mixed, and then coated on an aluminum foil to form a positive electrode sheet, and a CR2025 button cell is assembled in a vacuum glove box with a lithium metal sheet as a negative electrode, Celgard2300 as a separator, and 1 mol / L LiPF6 / EC:DMC (volume ratio 1:1) as an electrolyte.

[0058] The battery assembled in this example has a first discharge capacity of 283.4 mAh / g at 0.1C under a voltage range of 2.0-4.8V, a first coulombic efficiency of 83.67%, a capacity retention rate of 87.28% after 100 cycles at a 1C charge-discharge rate, and a discharge specific capacity of 271.4, 254.8, 221.8, 198.5, 178.4, and 137.8 mAh / g at 0.1, 0.2, 1, 2, 5C, respectively.

[0059] Example 4:

[0060] A preparation method of a surface modification modified lithium-rich manganese-based positive electrode material, comprising the following steps:

[0061] (1) 1 g of a lithium-rich manganese-based positive electrode material (Li 1.2 Ni 0.13 Co 0.13 Mn 0.54O2) with 0.05 g ammonium niobate oxalate hydrate ((NH4)3NbO(C2O4)3·4H2O) using a mixer, and the mixture was placed in a tube furnace in a nitrogen atmosphere, heated to 750°C at a heating rate of 5°C / min and kept at this temperature for 5 h, and then naturally cooled to room temperature. After being washed with deionized water and anhydrous ethanol alternately for 3 times, the excess reaction residues were removed, and the product was dried to obtain a pretreated lithium-rich manganese-based positive electrode material.

[0062] (2) The pretreated lithium-rich manganese-based positive electrode material obtained in step (1) was placed in a muffle furnace in an air atmosphere, heated to 450°C at a heating rate of 3°C / min and kept at this temperature for 3 h, and then naturally cooled to room temperature to obtain a surface-modified modified lithium-rich manganese-based positive electrode material.

[0063] Battery assembly: 0.2000 g of the surface-modified modified lithium-rich manganese-based positive electrode material obtained in this example was weighed, 0.0250 g of conductive carbon black was added as a conductive agent and 0.0250 g of PVDF (polyvinylidene fluoride) was added as a binder, and the mixture was uniformly mixed and coated on an aluminum foil to form a positive electrode sheet. A CR2025 button cell was assembled in a vacuum glove box with a lithium metal sheet as the negative electrode, Celgard2300 as the separator, and 1 mol / L LiPF6 / EC:DMC (volume ratio 1:1) as the electrolyte.

[0064] The battery assembled in this example had a first discharge capacity of 279.4 mAh / g at 0.1C in the voltage range of 2.0-4.8V, a first coulombic efficiency of 83.74%, a capacity retention rate of 90.09% after 100 cycles at a 1C charge-discharge rate, and a specific discharge capacity of 273.2, 260.6, 241.7, 218.7, 185.3 and 153.2 mAh / g at 0.1, 0.2, 1, 2, 5C and 0.1C, respectively.

[0065] Example 5:

[0066] A method for preparing a surface-modified modified lithium-rich manganese-based positive electrode material, comprising the following steps:

[0067] (1) 1 g of a lithium-rich manganese-based positive electrode material (Li 1.2 Ni 0.13 Co 0.13 Mn 0.54O2) with 0.05 g ammonium niobate oxalate hydrate ((NH4)3NbO(C2O4)3·4H2O) were mixed uniformly in a mixer, and the mixture was placed in a tube furnace in a nitrogen atmosphere, heated to 650°C at a heating rate of 3°C / min, and kept at this temperature for 5 h, and then naturally cooled to room temperature. After washing with deionized water and suction filtration for 3 times, the excess reaction residues were removed, and the product was dried to obtain a pretreated lithium-rich manganese-based positive electrode material.

[0068] (2) The pretreated lithium-rich manganese-based positive electrode material obtained in step (1) was placed in a tube furnace in an oxygen atmosphere, heated to 300°C at a heating rate of 5°C / min, and kept at this temperature for 4 h, and then naturally cooled to room temperature to obtain a surface-modified modified lithium-rich manganese-based positive electrode material.

[0069] Battery assembly: 0.2000 g of the surface-modified modified lithium-rich manganese-based positive electrode material obtained in this example was weighed, 0.0250 g of conductive carbon black was added as a conductive agent, and 0.0250 g of PVDF (polyvinylidene fluoride) was added as a binder, and the mixture was uniformly mixed and coated on an aluminum foil to form a positive electrode sheet. In a vacuum glove box, a lithium metal sheet was used as the negative electrode, Celgard 2300 was used as the separator, 1 mol / L LiPF6 / EC:DMC (volume ratio 1:1) was used as the electrolyte, and a CR2025 button cell was assembled.

[0070] The battery assembled in this example had a first discharge capacity of 287.3 mAh / g at 0.1C in the voltage range of 2.0-4.8V, a first coulombic efficiency of 87.43%, a capacity retention rate of 86.243% after 100 cycles at a 1C charge-discharge rate, and a discharge specific capacity of 281.5, 261.6, 239.9, 219.5, 190.3, and 143.5 mAh / g at 0.1, 0.2, 1, 2, 5C, and 0.1C, respectively.

[0071] Comparative Example 1:

[0072] A method for preparing a lithium-rich manganese-based positive electrode material, comprising the following steps:

[0073] A lithium-rich manganese-based positive electrode material (Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2) was directly assembled into a half-cell to test the performance;

[0074] Battery assembly: Weigh 0.2000g of the lithium-rich manganese-based positive electrode material of this comparative example, add 0.0250g of conductive carbon black as a conductive agent and 0.0250g of PVDF (polyvinylidene fluoride) as a binder, mix evenly and coat it on aluminum foil to form a positive electrode sheet. In a vacuum glove box, use a lithium metal sheet as the negative electrode, Celgard2300 as the separator, and 1mol / L LiPF6 / EC:DMC (volume ratio 1:1) as the electrolyte to assemble a CR2025 coin cell.

[0075] like Figure 3 As shown, the battery assembled in this comparative example has an initial discharge specific capacity of 275.1 mAh / g and an initial coulombic efficiency of 79.81% in the voltage range of 2.0-4.8V at 0.1C. The discharge curve does not have a discharge plateau corresponding to spinel.

[0076] like Figure 4 As shown, the battery assembled in this comparative example retains 73.93% of its capacity after 100 cycles at a 1C charge / discharge rate within a voltage range of 2.0-4.8V.

[0077] like Figure 5 As shown, the battery assembled in this comparative example has a discharge specific capacity of 275.1, 249.5, 226.7, 202.6, 168.9, and 105.0 mAh / g at charge / discharge rates of 0.1, 0.2, 1, 2, and 5C within a voltage range of 2.0-4.8V.

[0078] Comparative Example 2:

[0079] A method for preparing a lithium-rich manganese-based cathode material includes the following steps:

[0080] Untreated lithium-rich manganese-based cathode material (Li 1.2 Ni 0.2 Mn 0.6 O2) was directly assembled into a half-cell for performance testing;

[0081] Battery assembly: Weigh 0.2000g of the lithium-rich manganese-based positive electrode material obtained in this comparative example, add 0.0250g of conductive carbon black as a conductive agent and 0.0250g of PVDF (polyvinylidene fluoride) as a binder, mix evenly and coat it on aluminum foil to form a positive electrode sheet. In a vacuum glove box, use a lithium metal sheet as the negative electrode, Celgard 2300 as the separator, and 1mol / L LiPF6 / EC:DMC (volume ratio 1:1) as the electrolyte to assemble a CR2025 coin cell.

[0082] The battery assembled in the present comparative example has a first discharge capacity of 278.6 mAh / g at 0.1C in the voltage range of 2.0-4.8V, a first coulombic efficiency of 80.53%, a capacity retention rate of 72.50% after 100 cycles at 1C charge-discharge rate, and a discharge specific capacity of 269.4, 248.0, 208.8, 183.9, 153.0 and 121.7 mAh / g at 0.1, 0.2, 1, 2, 5C and 0.1C, respectively.

[0083] Comparative Example 3

[0084] A preparation method of a lithium-rich manganese-based positive electrode material, comprising the following steps:

[0085] (1) 1 g of the lithium-rich manganese-based positive electrode material (Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2) was placed in a tube furnace in an argon atmosphere, heated to 650℃ at a heating rate of 3℃ / min and kept at this temperature for 5h, and then naturally cooled to room temperature. The pre-treated lithium-rich manganese-based positive electrode material was obtained by washing and filtering with deionized water for 3 times to remove excess reaction residues and drying.

[0086] (2) The pre-treated lithium-rich manganese-based positive electrode material obtained in step (1) was placed in a muffle furnace in an air atmosphere, heated to 450℃ at a heating rate of 3℃ / min and kept at this temperature for 3h, and then naturally cooled to room temperature to obtain the lithium-rich manganese-based positive electrode material.

[0087] Battery assembly: 0.2000 g of the lithium-rich manganese-based positive electrode material obtained in the present comparative example was weighed, 0.0250 g of conductive carbon black was added as a conductive agent and 0.0250 g of PVDF (polyvinylidene fluoride) was added as a binder, and the mixture was uniformly mixed and coated on an aluminum foil to prepare a positive electrode sheet. A CR2025 button cell was assembled in a vacuum glove box with a lithium metal sheet as the negative electrode, Celgard2300 as the separator, 1 mol / L LiPF6 / EC:DMC (volume ratio 1:1) as the electrolyte.

[0088] The battery assembled in the present comparative example has a first discharge capacity of 278.6 mAh / g at 0.1C in the voltage range of 2.0-4.8V, a first coulombic efficiency of 80.53%, a capacity retention rate of 72.50% after 100 cycles at 1C charge-discharge rate, and a discharge specific capacity of 269.4, 248.0, 208.8, 183.9, 153.0 and 121.7 mAh / g at 0.1, 0.2, 1, 2, 5C and 0.1C, respectively.

Claims

1. A method for preparing a surface-modified lithium-rich manganese-based cathode material, characterized in that, The surface-modified lithium-rich manganese-based cathode material consists of, from the inside out, a lithium-rich manganese-based cathode material, a spinel structure layer rich in oxygen vacancies, and a fast ion conductor coating layer. The spinel structure layer is generated in situ on the surface of the lithium-rich manganese-based cathode material, and the fast ion conductor coating layer is coated on the surface of the spinel structure layer. The fast ion conductor coating layer is obtained by reacting a niobium-containing compound with residual lithium on the surface of the lithium-rich manganese-based cathode material. The molecular formula of the fast ion conductor coating layer is LiNbO3. The preparation method includes the following steps: (1) The lithium-rich manganese-based cathode material is mixed evenly with ammonium niobate oxalate hydrate, calcined under an inert atmosphere, and then cooled to room temperature. After cleaning and drying, the pretreated lithium-rich manganese-based cathode material is obtained. The calcination temperature is 500-800℃, the calcination time is 3-7h, and the heating rate is 1-5℃ / min. (2) The pretreated lithium-rich manganese-based cathode material obtained in step (1) is calcined and cooled to room temperature to obtain a surface-modified lithium-rich manganese-based cathode material; the calcination temperature is 200-600℃, the calcination time is 2-5h, and the heating rate is 1-5℃ / min. The mass of the ammonium niobate oxalate hydrate added is 1-10% of the mass of the lithium-rich manganese-based cathode material.

2. The preparation method according to claim 1, characterized in that, The molecular formula of the lithium-rich manganese-based cathode material is xLi₂MnO₃·(1-x)LiMO₂, where M is one or more transition metals Ni, Co, and Mn, and 0 <x<1。 3. The preparation method according to claim 1, characterized in that, The lithium-rich manganese-based cathode material has a particle size of 5-20 μm, the spinel structure layer has a thickness of 1-5 nm, and the fast ion conductor coating layer has a thickness of 1-5 nm.

4. The preparation method according to claim 1, characterized in that, The molecular formula of the lithium-rich manganese-based cathode material is Li. 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2, wherein the molecular formula of the ammonium niobate oxalate hydrate is (NH4)3NbO(C2O4)3·4H2O, and the mass of the ammonium niobate oxalate hydrate added is 5% of the mass of the lithium-rich manganese-based cathode material.

5. The preparation method according to claim 1, characterized in that, In step (1), the calcination temperature is 650℃, the calcination time is 5h, and the heating rate is 3℃ / min.

6. The preparation method according to any one of claims 1-5, characterized in that, In step (1), the inert atmosphere is argon, nitrogen or a mixture of argon and nitrogen, and the cleaning is performed using pure water, anhydrous ethanol or a mixture of pure water and anhydrous ethanol.

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