Lithium-rich manganese-based positive electrode material with surface oriented in-situ proton exchange function and preparation method of lithium-rich manganese-based positive electrode material

Abstract

The invention discloses a surface oriented in-situ proton exchange lithium-rich manganese-based positive electrode material and a preparation method thereof, and belongs to the technical field of lithium battery materials, and the preparation method of the material comprises the following steps: carrying out vacuum drying on a lithium-rich manganese-based precursor, uniformly mixing the dried powder and a lithium source according to a molar ratio of 1: (1.2-1.5), and sintering; uniformly dispersing the sintered material and dry ice or oxalic acid or carbonic acid in a constant-temperature liquid phase (ethanol or acetone or deionized water) according to a mass ratio of 1: (0.001-0.200), controlling the temperature of a constant-temperature water bath to be 25-100 DEG C, controlling the pH value of the solution to be 8.0-11.0 to obtain a dispersion liquid, and performing vacuum drying; and then re-sintering and cooling to room temperature to obtain the product. The prepared material has high first coulombic efficiency, stable cycle performance, excellent rate capability and low voltage attenuation, and has the remarkable advantages of simple and convenient synthesis process, short flow and low cost.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium battery materials, and in particular to a surface-oriented in-situ proton exchange lithium-rich manganese-based positive electrode material and a preparation method thereof. Background Art

[0002] In the process of electric energy gradually replacing part of fossil energy, lithium-ion batteries have become one of the effective means to solve today's energy problems due to their advantages such as high energy conversion efficiency, high energy density, good stability, long life and low self-discharge.

[0003] Compared with traditional lithium cobalt oxide, lithium iron phosphate, and other ternary cathode materials, lithium-rich manganese-based cathode materials have significant advantages such as high energy density, high charge and discharge specific capacity, low environmental pollution, and low cost. They are strong competitors for the next generation of commercial lithium-ion battery cathode materials. In terms of its phase composition, lithium-rich manganese-based cathode materials can be considered to be composed of Li 2 MnO 3 and LiTMO 2 (TM = Ni, Co, Mn) two-phase composition. Due to the high manganese content in the material, it is similar to LiCoO 2 Compared with ternary materials, in addition to low cost, it also has the significant advantages of low environmental harm and high recycling value.

[0004] At present, the commercialization difficulties of lithium-rich manganese-based cathode materials are mainly the capacity decay caused by the large irreversible capacity of the first cycle of charge and discharge, the safety problems caused by the release of lattice oxygen, and the electrochemical structure change reflected by the voltage drop during the electrochemical cycle at a certain rate. The reasons for the above problems are as follows: during the charging process, the lattice oxygen O 2- Oxidized to form irreversible oxygen (O 2 ), where O 2 The oxygen escapes and gradually transforms the layered cathode material into the spinel phase and the surface rock salt phase. This part of irreversible oxygen will also react with the electrolyte to generate CO 2 , which not only consumes the electrolyte, but also produces CO after reacting with the electrolyte. 2 Moreover, the process of transition metal (TM) migration to the Li layer through the tetrahedral sites in the transition metal layer will also cause the material to further transform into a spinel structure, thereby reducing the overall electronic conductivity of the material. Therefore, solving the release of lattice oxygen and the migration of transition metals is one of the effective means to improve the electrochemical performance of lithium-rich materials.

[0005] In order to solve the above problems, those skilled in the art have made a lot of efforts, such as:

[0006] CN107180961A discloses a method of using dry ice as a precipitant to adjust the pH of aluminate during dissolution, promote the uniform deposition of aluminum ions on the surface of lithium-rich manganese-based positive electrode materials, and form an aluminum oxide coating layer. During the first charge and discharge cycle, the presence of the coating layer effectively inhibits the escape of lattice oxygen and reduces the irreversible capacity. 2 O 3 The coating layer can increase the first coulombic efficiency of the material from 67% to 85%. However, the patent application lacks long-term performance tests for high cycle numbers (such as >100 times), and therefore fails to fully verify the long-term impact of alumina coating modification on the electrochemical stability of the electrode material.

[0007] CN118039848A discloses a method for preparing a cobalt-free lithium-rich manganese-based precursor by coprecipitation, using spray drying to evenly distribute cobalt nanoparticles on the surface of the precursor, and then using laser melting technology to achieve cobalt element lattice doping and precursor single crystal preparation. The single crystal, grain boundary melting and quenching achieve high mechanical strength and high compaction density, and high-temperature decomposition of cobalt hydroxide to form a dense cobalt oxide coating layer to achieve high cycle stability. The patented preparation process also uses pH regulators such as oxalic acid, chelating agents such as aminotrimethylenephosphonic acid, complexing agents such as disodium ethylenediaminetetraacetic acid, and octylphenol polyoxyethylene ether as non-ionic surfactants, all as additives for densification of the coating. However, the patent application does not provide sufficient characterization methods such as infrared spectroscopy and X-ray diffraction to prove the comprehensive influence of the coordination effect of the polymer compound added to the mixed solution and the lithium-rich manganese-based positive electrode material on the material properties. In addition, the modification strategy of single crystallization and quenching reaction proposed in this patent application to improve the mechanical strength of the interface and prevent interface collapse did not provide relevant rate performance data, and therefore could not fully prove the structural stability under high voltage or high rate (≥1C).

[0008] CN115050959A discloses a modification method for directly treating the surface of lithium-rich manganese-based positive electrode materials using oxalic acid. + / Li + During the replacement reaction, Ni elements on the surface of the material are extracted to reconstruct the Mn-rich surface design and improve the structural stability. However, after the oxalic acid modification, the patented process uses argon as the protective gas and performs re-sintering at 900°C. The re-sintering temperature is high, the secondary growth of the grains is large, the burn-off rate is large, and oxygen vacancies cannot be fully formed, which is not conducive to the formation of a highly ordered crystal phase spinel structure. Moreover, re-sintering at 900°C may cause grain boundary melting to destroy the original Mn-rich surface atomic arrangement and Li + / Ni + Mixed.

[0009] CN103137963A discloses a preparation scheme for modifying lithium-rich manganese-based positive electrode materials using one or more solutions of water, nitric acid, sulfuric acid, hydrochloric acid, hydrofluoric acid, acetic acid, oxalic acid and citric acid. This patent application first uses an acid mixed solution to pre-treat the lithium-rich manganese-based positive electrode material, and then immerses the treated material in a lithium-containing solution for secondary lithium replenishment to repair the defects caused by the primary acid treatment, and finally performs re-sintering to form lithium ion deintercalation channels, thereby improving the initial coulombic efficiency and cycle performance. However, the intrinsic surface defects obtained by acid treatment modification in this patent application can form ion transmission channels, which has the advantage of increasing the lithium ion diffusion rate. Therefore, lithium replenishment by secondary immersion may cause Li + Too high a concentration increases the diffusion resistance of lithium ions, thereby reducing the initial coulombic efficiency. In addition, the patent application does not provide relevant data or characterization to prove or suggest that the Li-containing ions coated on the surface of the lithium-rich manganese-based positive electrode material can be impregnated with secondary impregnation. + The compound replaces the H in the material during the previous proton exchange process. + .

[0010] CN110931775A discloses a modification scheme of lithium-rich manganese-based positive electrode materials by fumigation modification using an acid aqueous solution. This scheme also uses acid vapor to achieve H + / Li + The proton exchange forms an ion transfer channel while forming a spinel surface structure doped with trace amounts of Ni and Co. This modification scheme can not only improve the ion transfer efficiency, but also improve the electrochemical stability of the material surface. However, in this patent, it is very difficult to perform defect treatment or proton exchange reaction on the material surface by evaporating the acid vapor formed in a constant temperature water bath at 40°C-60°C. Compared with the liquid phase acid treatment method, the effect of the fumigation method on improving material performance is almost kept within the error range. Not only that, the patent application does not provide long cycle (more than 100 cycles) data and relevant data on the atomic percentage content, and there is not enough data to prove whether the proton exchange reaction occurs. Summary of the invention

[0011] One of the purposes of the present invention is to provide a lithium-rich manganese-based positive electrode material with surface-oriented in-situ proton exchange to solve the above-mentioned problems.

[0012] In order to achieve the above-mentioned purpose, the technical solution adopted by the present invention is as follows: a lithium-rich manganese-based positive electrode material with surface-oriented in-situ proton exchange, the general structural formula of the lithium-rich manganese-based positive electrode material before surface-oriented in-situ proton exchange is: αLi 2 MnO 3 (1-α)LiTMO2, wherein TM = Ni, Co or Mn, 0<α<1; the general structure after the surface directed in-situ proton exchange is: αLi 2(1−β1)H 2β1 MnO 3 ·(1−α)Li (1−β2) H β2 TMO 2 @C(θwt%), where TM=Ni, Co or Mn, C represents carbon element, 0<α<1, 0≤β1<1, 0≤β2<1, 0≤θ≤20.

[0013] The second object of the present invention is to provide a method for preparing the above-mentioned surface-oriented in-situ proton exchanged lithium-rich manganese-based positive electrode material, the technical scheme adopted is as follows:

[0014] (1) vacuum drying the lithium-rich manganese-based precursor to obtain a dry powder;

[0015] (2) mixing the dry powder obtained in step (1) and a lithium source in a molar ratio of 1:(1.2-1.5) and sintering to obtain a lithium-rich manganese-based positive electrode material;

[0016] (3) The lithium-rich manganese-based positive electrode material obtained in step (2) and dry ice or oxalic acid or carbonic acid are uniformly dispersed in a constant temperature liquid phase in a mass ratio of 1:(0.001-0.200), the constant temperature liquid phase temperature is controlled at 25-100° C., the solution pH is controlled at 8.0-11.0, and then vacuum dried; then sintered again, and naturally cooled to room temperature to obtain a lithium-rich manganese-based positive electrode material with surface directional in-situ proton exchange.

[0017] As a preferred technical solution, in step (1), the lithium-rich manganese-based precursor is Mn 0.54 Ni 0.13 Co 0.13 CO 3 、Ni x Co y Mn z CO 3 or Ni x Co y Mn z (OH) 2 , where 0 <x<0.5,0<y<0 .5,0 .5<z<1。

[0018] As a preferred technical solution, in step (1), the vacuum drying conditions are: temperature 70-90°C, vacuum degree 0-1 Bar.

[0019] As a preferred technical solution, in step (2), the lithium source is lithium hydroxide or lithium carbonate.

[0020] As a preferred technical solution, in step (2), the sintering conditions are: pre-sintering at 400-500°C for 4-8h, heating to 800-950°C for sintering for 12-15h, and naturally cooling to room temperature.

[0021] As a preferred technical solution, in step (3), the lithium-rich manganese-based positive electrode material and oxalic acid or dry ice or carbonic acid are uniformly dispersed in a constant temperature liquid phase.

[0022] As a preferred technical solution, in step (3), the constant temperature liquid phase is selected from ethanol, acetone or deionized water, and the temperature of the constant temperature liquid phase is controlled at 25-100°C by means of a constant temperature water bath, and the pH of the solution is controlled at 8.0-11.0.

[0023] As a preferred technical solution, in step (3), the re-sintering conditions are: sintering at 400-550°C for 2-6 hours and then naturally cooling to room temperature.

[0024] First, from the perspective of reaction mechanism and material electrochemical properties:

[0025] The present invention is mainly based on the method that dry ice, carbonic acid or oxalic acid is dissolved in a liquid solvent (ethanol or acetone or deionized water) to produce H + Or under certain conditions (dry ice, carbonic acid can decompose to produce CO at room temperature 2 Oxalic acid decomposes at 189.5°C or produces CO at high pressure or other conditions below 189.5°C. 2 ) CO produced by decomposition 2 The H generated by dissolving in a liquid solvent + In situ proton exchange reaction with lithium-rich manganese-based cathode materials on the surface + Replace Li + At the same time, oxygen vacancies and Li + Vacancies are beneficial to the subsequent electrochemical cycle process Li + The reinsertion of Li 2 MnO 3 The lattice distortion caused by phase activation means that the transformation of lithium-rich manganese-based layered oxides to spinel during charging and discharging is no longer accompanied by superlattice distortion, and the electrochemical structure is highly stable.

[0026] In addition, dry ice, carbonic acid or oxalic acid decomposes under certain conditions to produce CO 2 The in-situ proton exchange reaction with the lithium-rich manganese-based positive electrode material in the liquid phase solvent is accompanied by a coating process of a thin carbon layer on the surface, which provides a benign channel for the diffusion of ions and electrons in the lithium-rich manganese-based positive electrode material. Under the above synergistic effect, the first coulomb efficiency of the lithium-rich manganese-based positive electrode material is improved and its voltage decay is suppressed. Specifically, the present invention mainly utilizes the CO generated by the decomposition of dry ice, etc. 2H generated in a liquid solvent (pure water or ethanol or acetone) + Li-rich manganese-based cathode materials and their Li 2 MnO 3 The following reactions occur:

[0027] (1)

[0028] (2)

[0029] (3)

[0030] (4)

[0031] The above reactions are accompanied by the in-situ generation of oxygen vacancies, spinel structures and a thin carbon layer-coated system on the material surface.

[0032] Secondly, from the energy point of view: Reaction (3) and reaction (4) describe the proton exchange process and Li + With H 2 O dissolution or removal, where Li 2 MnO 3 The activation barrier of the phase is very low; and the transformed H[Li 1 / 3 Mn 2 / 3 ]O 2 The shear modulus of the phase is much lower than that of Li 2 MnO 3 , the subsequent dissolution of H[Li 1 / 3 Mn 2 / 3 ]O 2 The reaction free energy (per proton) is also slightly smaller than the original protonation reaction. This means that the bonds in the layered structure can be readjusted from Li elements to H elements by the movement of interlayer spacing or interlayer shearing without significantly distorting the structure. Therefore, the prepared material has excellent rate performance, high first coulombic efficiency, and low voltage decay.

[0033] Compared with CN107180961A, in addition to the patent's suppression of lattice oxygen escape and the formation of a surface coating layer to improve the first coulomb efficiency, this application does not use metal elements for surface reconstruction, but uses a one-step method to use dry ice, oxalic acid, and carbonic acid to form carbon dioxide in the reaction to form a carbon layer liquid phase coating, which greatly improves the interface conductivity of the primary particles. In addition, this application comprehensively verifies the dynamic reaction process of dry ice, oxalic acid, carbonic acid and lithium-rich manganese-based positive electrode materials from the perspective of proton and ion reaction mechanisms and binding energy, and has undergone 200-cycle long cycle stability verification (the discharge specific capacity of 6.0wt% oxalic acid modified after 200 cycles is 158.2mah / g).

[0034] Compared with CN118039848A, in addition to the use of a coating layer in the patent to improve the structural stability during a long cycle, the present application synthesizes a precursor containing nickel, cobalt, and manganese in situ. Since the in-situ synthesis of a layered structure precursor containing cobalt elements can more fully suppress the irreversible phase change of the layered positive electrode material, the present application has better structural stability and rate performance (discharge capacity greater than 185mah / g at 1C), and the above patent does not provide rate performance test data. Not only that, the above patent uses a mixed solution of oxalic acid, aminotrimethylenephosphonic acid, etc. to adjust the pH as a means to increase the density of the cobalt hydroxide coating layer, and the synthesis path is complicated. In this application, oxalic acid, dry ice and carbonic acid are treated in one step to directly generate a carbon coating layer. In addition, the reaction conditions such as pH and temperature for the proton exchange reaction in this application are also completely different from those in the above patent.

[0035] Compared with CN115050959A, in addition to using oxalic acid for proton exchange modification as in the patent, the present application uses an oxygen atmosphere to sinter at 400-550°C for 2-6 hours and then re-sinter the oxalic acid-modified lithium-rich manganese-based positive electrode material at a low temperature and low heating rate. Compared with the argon re-sintering environment used in CN115050959A, the oxygen atmosphere is conducive to the generation of sufficient and uniform oxygen vacancies on the surface of the material after proton exchange, increasing H + / Li + Mixing and increasing the lithium ion transmission channel, through the comparison of electrochemical data, it can be proved that compared with CN115050959A (the discharge capacity of 200 cycles treated with 0.1 mol / L oxalic acid at 1C is about 180 mAh / g, and the first coulombic efficiency is 82%), it has higher discharge capacity and first coulombic efficiency (the discharge capacity of 200 cycles treated with dry ice at 1C in this application is 199.1 mAh / g, and the first coulombic efficiency is 90.4%), which can further prove that oxygen vacancies play an important role in improving the first coulombic efficiency and rate performance of materials. In addition, this application also expands the modification scheme of carbonic acid and dry ice for materials, both of which have ideal electrochemical properties.

[0036] Compared with CN110931775A, this application also uses proton exchange reaction to treat the surface defects of lithium-rich manganese-based positive electrode materials. Since CN110931775A does not prove through data or characterization that proton exchange reaction and oxalic acid and defect reaction on the surface of lithium-rich manganese-based positive electrode materials can occur through acid vapor fumigation. Figure 3-Figure 5 As shown, the present application more rigorously uses EDS elemental analysis to prove the introduction of the C element coating layer and rigorously proves through detailed electrochemical data that the introduction of defects such as oxygen vacancies can improve the structural stability of the material in long electrochemical cycles.

[0037] Compared with CN103137963A, the present invention does not need to be immersed in Li-containing water for a second time after acid treatment. + Re-li + In addition, this application uses carbonic acid and dry ice for proton exchange reaction. In addition, this application only uses one-step acid treatment to significantly improve the material's first coulombic efficiency (from 85.1% to more than 89%), 200-cycle long cycle capacity retention rate at 1C (from 69.6 to more than 74%) and other comprehensive electrochemical data. In addition, Figure 5 , Figure 6 The EDS elemental analysis further proves that through the reaction of solutions such as carbonic acid, a thin carbon layer can be introduced on the surface of the material while forming oxygen vacancies, thereby increasing the electronic conductivity. Compared with CN103137963A, it proves that the electrochemical performance and structural stability of the material can be greatly improved without the need for secondary impregnation to supplement lithium.

[0038] Compared with the prior art, the advantages of the present invention are: the present invention can obtain a lithium-rich manganese-based positive electrode material with simultaneous surface-oriented in-situ proton exchange by treating the lithium-rich manganese-based positive electrode material only by a one-step method, and the obtained material is significantly improved in terms of the first coulombic efficiency, cycle capacity retention rate, and voltage attenuation, and has the significant advantages of simple preparation process, short synthesis process, low cost, and low pollution. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 This is a SEM image of the precursor material of Example 1 of the present invention;

[0040] Figure 2 This is a SEM image of the material obtained in Example 1 of the present invention;

[0041] Figure 3 This is the EDS element distribution diagram of Example 1 of the present invention;

[0042] Figure 4 This is the EDS element distribution diagram of Example 2 of the present invention;

[0043] Figure 5 This is the EDS element distribution diagram of Example 3 of the present invention;

[0044] Figure 6 This is the EDS element distribution diagram of Example 4 of the present invention;

[0045] Figure 7 This is the EDS element distribution diagram of Comparative Example 1 of the present invention. DETAILED DESCRIPTION

[0046] The present invention will be further described below in conjunction with the accompanying drawings.

[0047] Embodiment 1:

[0048] In this embodiment, dry ice is taken as an example:

[0049] 0.1 mol of Mn 0.54 Ni 0.13 Co 0.13 CO 3 The mixture was uniformly dispersed in deionized water, and evaporated to dryness at 90°C and 500rpm with stirring to obtain a dry lithium manganese-based cathode material precursor powder; the precursor was mixed with lithium hydroxide at a molar ratio of 1:1.39; then heated to 550°C in an oxygen atmosphere at a heating rate of 2°C / min and sintered for 4h, and heated to 900°C at a heating rate of 2°C / min and sintered for 15h. After cooling to room temperature, the sintered lithium-rich manganese-based cathode material and dry ice were uniformly dispersed in 60°C constant temperature deionized water at a mass ratio of 1:0.06, vacuum dried, and then heated to 550°C in an oxygen atmosphere at a heating rate of 2°C / min and sintered for 4h. After cooling to room temperature, the SEM image of the surface-oriented in-situ proton exchange modified lithium-rich manganese-based cathode material was obtained. Figure 1 As shown. The chemical formula of the obtained material is: Li 1.15 H 0.05 Ni 0.13 Co 0.13 Mn 0.54 O 2 @C.

[0050] Embodiment 2:

[0051] In order to prove that the lithium-rich manganese-based positive electrode material treated with oxalic acid can also realize the present invention, the difference between this embodiment and embodiment 1 is that oxalic acid is used instead of solid dry ice as the modifying material of the lithium-rich manganese-based positive electrode material matrix; the rest is the same as embodiment 1, and the chemical formula of the obtained material is: Li 1.13 H 0.07 Ni 0.13 Co 0.13 Mn 0.54 O 2 @C.

[0052] Embodiment 3:

[0053] In order to prove that the lithium-rich manganese-based positive electrode material treated with carbonic acid can also realize the present invention, the difference between this embodiment and embodiment 1 is that carbonic acid is used instead of solid dry ice as the modifying material of the lithium-rich manganese-based positive electrode material matrix; the rest is the same as embodiment 1, and the chemical formula of the obtained material is: Li 1.12 H 0.08 Ni 0.13 Co 0.13 Mn 0.54 O 2 @C.

[0054] Embodiment 4:

[0055] In order to prove that different proportions of solid dry ice can realize the present invention, in this embodiment, the sintered lithium-rich manganese-based positive electrode material and dry ice are uniformly dispersed in 60°C constant temperature deionized water at a mass ratio of 1:0.08; the rest is the same as in Example 1, and the chemical formula of the obtained material is: Li 1.13 H 0.07 Ni 0.13 Co 0.13 Mn 0.54 O 2 @C.

[0056] Embodiment 5:

[0057] In order to prove that different proportions of solid dry ice can realize the present invention, in this embodiment, the sintered lithium-rich manganese-based positive electrode material and dry ice are uniformly dispersed in 60°C constant temperature deionized water at a mass ratio of 1:0.10; the rest is the same as in Example 1, and the chemical formula of the obtained material is: Li 1.1 H 0.1 Ni 0.13 Co 0.13 Mn 0.54 O 2 @C.

[0058] Embodiment 6:

[0059] In order to prove that different re-sintering conditions (sintering temperature, sintering time, heating rate) can realize the present invention, the difference between this embodiment and embodiment 1 is that the sintering conditions are heated to 500°C at a heating rate of 2°C / min in an oxygen atmosphere and re-sintered for 4h; the rest are the same as embodiment 1, and the chemical formula of the obtained material is Li 1.15 H 0.05 Ni 0.13 Co 0.13 Mn 0.54 O 2 @C.

[0060] Example 7 In order to prove that the present invention can be realized with constant temperature liquid phases of different temperatures or types, this embodiment differs from Embodiment 1 in that the liquid phase temperature is 80° C., and the other conditions are exactly the same as those of Embodiment 1. Example 8

[0061] In order to prove that the present invention can be realized with constant temperature liquid phases of different temperatures or types, this embodiment differs from Embodiment 2 in that the liquid phase temperature is 60° C., the constant temperature liquid phase is ethanol, and the other conditions are exactly the same as those in Embodiment 2. Example 9

[0062] In order to prove that the present invention can be realized with constant temperature liquid phases of different temperatures or types, this embodiment is different from Embodiment 3 in that the liquid phase temperature is 55° C., the constant temperature liquid phase is acetone, and the other conditions are exactly the same as those in Embodiment 1.

[0063] It should be noted that the boiling point of ethanol at room temperature is 78°C, and the boiling point of acetone is 56.1°C. The materials prepared in the above embodiments using deionized water or ethanol or acetone as the constant temperature liquid phase and performing proton exchange at a temperature below the boiling point also have the same mechanism and performance.

[0064] Comparative Example 1:

[0065] In order to demonstrate the importance of pre-treating the lithium-rich manganese-based cathode material matrix with solid dry ice or oxalic acid, this comparative example does not add solid dry ice or oxalic acid for pre-treatment, that is: 0.1 mol Mn 0.54 Ni 0.13 Co 0.13 CO 3 Dissolve in 30 ml of deionized water and disperse evenly, stir and evaporate at 90°C; mix the lithium-rich manganese-based cathode material precursor with lithium hydroxide at a molar ratio of 1:1.39; then heat to 550°C in an oxygen atmosphere at a heating rate of 2°C / min and sinter for 4 hours, heat to 900°C at a heating rate of 2°C / min and sinter for 15 hours, and cool to room temperature to obtain the obtained material. The chemical formula of the obtained material is Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O 2 .

[0066] Comparative Example 2:

[0067] In order to prove that only oxalic acid or carbonic acid or solid dry ice can achieve the modification scheme of the present invention, in this comparative example, the sintered lithium-rich manganese-based positive electrode material and hydrochloric acid are uniformly dispersed in 50°C ethanol at a mass ratio of 1:0.06 to carry out a one-step proton exchange reaction; the rest is the same as comparative example 1. The chemical formula of the obtained material is Li 1.15H0.05 Ni 0.13 Co 0.13 Mn 0.54 O 2 .

[0068] Comparative Example 3:

[0069] In order to prove that only oxalic acid or carbonic acid or solid dry ice can achieve the modification scheme of the present invention, in this comparative example, the sintered lithium-rich manganese-based positive electrode material and citric acid are uniformly dispersed in 50°C ethanol at a mass ratio of 1:0.06 to carry out a one-step proton exchange reaction; the rest is the same as comparative example 1. The chemical formula of the obtained material is Li 1.14H0.06 Ni0.13 Co 0.13 Mn 0.54 O 2 .

[0070] It should be noted that although comparative examples 2 and 3 used hydrochloric acid or citric acid for one-step proton exchange reaction, they could not achieve thin carbon layer coating. 2 Source, it is impossible to produce carbon coating like Examples 1-6, so the first coulombic efficiency and long cycle performance of the comparative material are not ideal compared with the examples.

[0071] Performance test case

[0072] The modified lithium-rich manganese-based positive electrode material obtained in the above examples and comparative examples was mixed with a conductive agent carbon black (SP) and a binder (PVDF) in a mass ratio of 8:1:1, and an appropriate amount of N-methylpyrrolidone (NMP) was added, and 5 mm and 3 mm ball milling zirconium beads were configured in a ratio of 3:1, and placed in a planetary ball mill for homogenization for 3 hours to prepare a mixed slurry;

[0073] After completing the above slurry step, the coating and preparation process of the electrode began: use a 150μm scraper to coat it on the aluminum foil, blow dry it at 55℃ for 3h, vacuum dry it at 105℃ for 12h, use an argon environment glove box, add 55μL of electrolyte to each battery, and make the positive electrode for button batteries.

[0074] After the button cell was assembled and packaged in the glove box, it was placed at room temperature for 12 hours and then activated by three cycles of constant current and constant voltage charging and constant current discharging at a rate of 0.1C and a voltage range of 2.0 to 4.8V.

[0075] After activation, the long cycle and rate performance test of the material was started. The test process was still in the voltage range of 2.0-4.8V, and 200 charge and discharge cycles were performed at a 1C rate (nominal capacity 1C = 230mAh / g). The results are shown in Table 1 and Table 2:

[0076] Table 1 Capacity, capacity retention rate and voltage decay results of lithium-ion batteries of Examples 1-6 after 200 cycles

[0077]

[0078] Table 2 Capacity, capacity retention rate and voltage decay results of lithium-ion batteries of Examples 7-9 and Comparative Examples 1-3 after 200 cycles

[0079]

[0080] As shown in Table 1 and Table 2, the present invention can effectively improve the first coulombic efficiency of lithium-rich manganese-based positive electrode materials.

[0081] The materials obtained in the above examples and comparative examples were also subjected to scanning electron microscope test and X-ray electron energy spectrum test using German Zeiss Sigma500 and American ThermoScientific K-Alpha, respectively. The results are as follows: Figures 1 to 7 As shown. Figure 1 It can be seen that the surface of the lithium-rich manganese-based positive electrode precursor material of Example 1 is dense and has a high sphericity; Figure 2 It can be seen that the lithium-rich manganese-based precursor material after surface sintering in Example 1 forms a better surface structure; Figure 3 , Figure 4 , Figure 5 , Figure 6 This indicates that the surface directional in-situ proton exchange of the present invention does not destroy the atomic ratio of transition metals, and the element content still conforms to the chemical formula Ni:Co:Mn=0.13:0.13:0.54; in addition, Figure 5 , Figure 6 The atomic content information of the C element is additionally supplemented, and the introduction of the thin carbon layer of the present invention is proved from the perspective of element ratio.

[0082] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A lithium-rich manganese-based positive electrode material with surface-oriented in-situ proton exchange, characterized in that: The general structural formula of the lithium-rich manganese-based positive electrode material before surface directional in-situ proton exchange is: αLi2MnO3·(1-α)LiTMO2, wherein TM=Ni, Co or Mn, 0<α<1; the general structural formula of the surface directional in-situ proton exchange is: αLi 2(1−β1) H 2β1 MnO3·(1−α)Li (1−β2) H β2 TMO2@C (θwt%), where TM = Ni, Co or Mn, C represents carbon element, 0<α<1, 0≤β1<1, 0≤β2<1, 0≤θ≤20.

2. The method for preparing the surface-oriented in-situ proton exchanged lithium-rich manganese-based positive electrode material according to claim 1, characterized in that: The steps include: (1) vacuum drying the lithium-rich manganese-based precursor to obtain a dry powder; (2) mixing the dry powder obtained in step (1) and a lithium source in a molar ratio of 1:(1.2-1.5) and sintering to obtain a lithium-rich manganese-based positive electrode material; (3) uniformly dispersing the lithium-rich manganese-based positive electrode material obtained in step (2) and dry ice or oxalic acid or carbonic acid in a constant temperature liquid phase at a mass ratio of 1:(0.001-0.200), controlling the constant temperature water bath temperature at 25-100° C., controlling the solution pH at 8.0-11.0, and then vacuum drying; After repeated sintering and natural cooling to room temperature, a lithium-rich manganese-based positive electrode material with surface-oriented in-situ proton exchange is obtained.

3. The method according to claim 2, characterized in that In step (1), the lithium-rich manganese-based precursor is Mn 0.54 Ni 0.13 Co 0.13 CO3、Ni x Co y Mn z CO3 or Ni x Co y Mn z (OH)2, where 0 <x<0.5,0<y<0.5,0.5<z<1。 4. The method according to claim 2, characterized in that: In step (1), the vacuum drying conditions are: temperature 70-90°C, vacuum degree 0-1 Bar.

5. The method according to claim 2, characterized in that: In step (2), the lithium source is lithium hydroxide or lithium carbonate.

6. The method according to claim 2, characterized in that In step (2), the sintering conditions are: pre-sintering at 400-500°C for 4-8h, heating to 800-950°C for sintering for 12-15h, and naturally cooling to room temperature.

7. The method according to claim 2, characterized in that In step (3), the re-sintering conditions are: sintering at 400-550°C for 2-6 hours and then naturally cooling to room temperature.

8. The method according to claim 2, characterized in that: In step (3), the lithium-rich manganese-based positive electrode material is evenly dispersed with oxalic acid, dry ice or carbonic acid.

9. The method according to claim 3, characterized in that: The constant temperature liquid phase is selected from ethanol, acetone or deionized water, the temperature of the constant temperature liquid phase is controlled at 25-100° C., and the pH value of the solution is controlled at 8.0-11.0.

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