A surface modification method of a lithium-rich manganese-based positive electrode material

Abstract

This invention provides a method for surface modification of lithium-rich manganese-based cathode materials, comprising: (1) dissolving a polymer with multiple carboxyl functional groups in deionized water to obtain a coating agent aqueous solution of 0.1–10 mg / mL; (2) dissolving a soluble inorganic salt containing a modified metal element in deionized water to obtain a metal precursor solution; (3) uniformly dispersing the lithium-rich manganese-based cathode material in the coating agent aqueous solution, and then adding the metal precursor solution, or mixing the coating agent aqueous solution and the metal precursor solution before uniformly dispersing the lithium-rich manganese-based cathode material therein; (4) washing and filtering the reactants obtained in step (3), and then heat-treating them under an oxygen-free atmosphere to form a metal ion gradient doping in the lithium-rich manganese-based cathode material, and forming a metal oxide layer, a spinel phase, and a carbon layer sequentially from the inside to the outside on the surface of the lithium-rich manganese-based cathode material. This invention improves the comprehensive electrochemical performance of the modified lithium-rich manganese-based cathode material.

Description

Technical Field

[0001] This invention relates to the field of secondary battery technology, and in particular to a method for surface modification of lithium-rich manganese-based cathode materials. Background Technology

[0002] With the expanding application scope and increasing market demand of lithium-ion batteries, the development of lithium-ion batteries with higher energy density, greater safety, and lower cost is imperative. Among the factors determining the energy density, safety, and cost of lithium-ion batteries, the cathode material plays a crucial role. Therefore, developing high-capacity, safe, and inexpensive cathode materials is currently a key research focus in the lithium-ion battery field. Currently common commercial cathode materials, including lithium cobalt oxide (~140 mAh / g), lithium iron phosphate (~160 mAh / g), ternary materials (~150-160 mAh / g), and lithium manganese oxide (~120 mAh / g), generally have a discharge specific capacity of less than 200 mAh / g, which is insufficient to meet the further development and application needs of lithium-ion batteries. In recent years, lithium-rich manganese oxide (LMO) cathode materials have been considered ideal cathode materials for next-generation lithium-ion batteries due to their advantages such as high capacity (>300 mAh / g), high operating voltage (>3.5V), good safety, and low cost.

[0003] However, lithium-rich manganese-based cathode materials still have some defects and face a series of bottlenecks in practical applications. These mainly include poor electronic conductivity, which limits the rapid insertion and extraction of lithium ions, resulting in poor rate performance; irreversible phase transitions during high-voltage charge and discharge, causing voltage decay; side reactions between the material and the electrolyte under high voltage, forming an unstable interfacial film, leading to reduced initial efficiency and shortened cycle life; and the surface active sites are prone to releasing lattice oxygen, causing material structure collapse and electrolyte decomposition, posing safety hazards.

[0004] The electrochemical stability of lithium-rich manganese-based cathode materials is largely influenced by their surface properties. Currently, the main modification strategies for lithium-rich manganese-based cathode materials include near-surface bulk doping, surface coating, and crystal structure and morphology control. Given the complexity of the electrochemical performance degradation of lithium-rich manganese-based cathode materials, the improvement effect of a single modification method on the electrochemical performance of LMO is limited. Therefore, in order to comprehensively improve the cycle stability and rate performance of LMO materials, multi-synergistic modification strategies combining the advantages of multiple modification methods have attracted much attention in recent years.

[0005] Currently, the most widely used multi-strategy synergistic modification research mainly includes methods such as ion co-doping, multiple coating modification, bulk doping and surface coating synergistic modification, crystal structure regulation and surface coating, and elemental doping and crystal structure regulation. Although these synergistic modification strategies are more effective than single modification strategies for LMO surface modification, the interaction mechanisms between different modification strategies still need in-depth exploration of the atomic-scale crystal structure, local fine structure, and their relationship with electrochemical performance of LMO materials after interface modification. In addition, the synergistic modification of multiple strategies usually involves complex experimental steps, which increases the time and economic cost of material preparation, prolongs the processing time, and limits practical applications. Moreover, pre-activated LMO materials usually use chemically active acidic substances, which can easily damage the surface structure, causing capacity loss and decreased cycling stability. Therefore, it is still necessary to explore suitable surface modification methods.

[0006] It should be noted that the information disclosed in the background section above is only for understanding the background of this application, and therefore may include information that does not constitute prior art known to those skilled in the art. Summary of the Invention

[0007] To overcome the shortcomings of existing technologies, this invention provides a surface modification method for lithium-rich manganese-based cathode materials.

[0008] The present invention adopts the following technical solution:

[0009] In a first aspect, a method for surface modification of lithium-rich manganese-based cathode materials is provided, comprising the following steps:

[0010] (1) Dissolve the coating agent in deionized water to obtain a coating agent aqueous solution with a coating agent concentration of 0.1 to 10 mg / mL, wherein the coating agent is a polymer with multiple carboxyl functional groups;

[0011] (2) Dissolve the soluble inorganic salt containing the modified metal element in deionized water to obtain a metal precursor solution;

[0012] (3) The lithium-rich manganese-based cathode material to be modified is uniformly dispersed in the coating agent aqueous solution of step (1), and then the metal precursor solution of step (2) is added. Alternatively, the coating agent aqueous solution of step (1) and the metal precursor solution of step (2) are mixed and then the lithium-rich manganese-based cathode material to be modified is uniformly dispersed therein, so that the modified metal element in the metal precursor solution undergoes a complexation adsorption reaction with the carboxyl functional group in the coating agent to form a preliminary coating layer and ion adsorption.

[0013] (4) After washing and filtering the reactants obtained in step (3), heat treatment is carried out in an oxygen-free atmosphere to form a metal ion gradient doping in the lithium-rich manganese-based cathode material, and a metal oxide layer, spinel phase and carbon layer are formed sequentially from the inside to the outside on the surface of the lithium-rich manganese-based cathode material.

[0014] Preferably, the polymer having multiple carboxyl functional groups is at least one of polyacrylic acid, polymethacrylic acid, and polymaleic acid.

[0015] Preferably, the modified metal element in step (2) is at least one of Al, Mg, Zr, Ti, Mo, W, V, Zn, Na, and La.

[0016] Preferably, in the metal precursor solution of step (2), the content of modified metal elements is positively correlated with the thickness of the metal oxide layer formed in step (4).

[0017] Preferably, the heat treatment temperature in step (4) is 300-700℃ and the heat treatment time is 1-6h.

[0018] Preferably, in step (3), the chemical formula of the lithium-rich manganese-based cathode material to be modified is xLi2MnO3·(1-x)LiTMO2, where TM is at least one of Mn, Co, and Ni, and 0 <x<1。

[0019] Preferably, in step (3), the uniform dispersion is carried out under magnetic stirring and / or ultrasonic vibration, and the amount of lithium-rich manganese-based cathode material to be modified is sufficient to make it uniformly dispersed without agglomeration.

[0020] Preferably, the oxygen content in the oxygen-free atmosphere in step (4) is less than 10 ppm; the oxygen-free atmosphere is one of argon, helium, and nitrogen.

[0021] In a second aspect, a lithium-rich manganese-based cathode modified material is provided, which is prepared by the surface modification method described in the first aspect, comprising a lithium-rich manganese-based cathode material, a metal ion gradient doping formed in the lithium-rich manganese-based cathode material, and a metal oxide layer, a spinel phase, and a carbon layer sequentially formed from the inside to the outside on the surface of the lithium-rich manganese-based cathode material.

[0022] Thirdly, a lithium-ion battery is provided, wherein the positive electrode of the lithium-ion battery comprises the lithium-rich manganese-based positive electrode modified material described in the second aspect.

[0023] This invention has the following beneficial effects: It utilizes a weakly acidic aqueous solution of a polycarboxyl functional group polymer to pre-activate LMO materials. Through the adsorption of metal ions by the polycarboxyl functional group polymer, a complex is formed. Combined with oxygen-free atmosphere heat treatment, this achieves gradient doping modification of metal ions and the formation of a metal oxide layer and a spinel fast ion conductor (spinele phase Li4Mn5O). 12 The coating modification with a carbon layer electronic conductor results in a metal ion gradient doping in the LMO material, with a metal oxide layer, spinel phase, and carbon layer forming sequentially from the inside out on the LMO material surface. The multi-carboxyl functional group polymer used in this invention does not cause significant damage to the surface structure, and the modification of the LMO material through "metal ion gradient doping - metal oxide layer - fast ion conductor - carbon layer" is achieved simultaneously in a single heat treatment. This achieves stress buffering at the interface, suppresses side reactions, and improves the overall electrochemical performance of the lithium-rich manganese-based cathode modified material, such as cycle stability and rate performance. Attached Figure Description

[0024] Figure 1a This is the SEM-EDS image of C&Al-1 in Example 1 of the present invention.

[0025] Figure 1b This is a TOF-SIMS diagram of C&Al-1 in Embodiment 1 of the present invention.

[0026] Figure 2 yes Figure 1a A magnified schematic diagram of the EDS spectrum.

[0027] Figure 3 These are SEM images of base, PAA-Al pre-coating material, C&Al-1, C&Al-2, and C&Al-3 in the embodiments of the present invention.

[0028] Figure 4 These are the XRD patterns of base, C&Al-1, C&Al-2, and C&Al-3 in the embodiments of this invention.

[0029] Figure 5 These are the Raman spectra of base, C&Al-1, C&Al-2, and C&Al-3 in the embodiments of this invention.

[0030] Figure 6a , 6b 6c and 6d are the HR-TEM images of base, C&Al-1, C&Al-2, and C&Al-3 in the embodiments of the present invention, respectively.

[0031] Figure 7a and 7bThe figures are the first charge-discharge curves and the first capacity increment curves of base and C&Al-1 at 0.1C in Example 1, respectively.

[0032] Figure 7c yes Figure 7b The diagram showing the complete display at box A.

[0033] Figure 8a These are the CV curves of base and C&Al-1 in the first loop of Embodiment 1 of the present invention.

[0034] Figure 8b These are the CV curves of base and C&Al-1 in the second loop of Embodiment 1 of the present invention.

[0035] Figure 9 This is a graph showing the cyclic performance of base and C&Al-1 in 1C in Embodiment 1 of the present invention.

[0036] Figure 10a and 10b This is a comparison chart of the cycling performance of C&Al-1 in Example 1 and C&Al-1-air in Comparative Example 1 of the present invention.

[0037] Figure 10c and 10d This is a comparison chart of the cycling performance of C&Al-1 in Example 1 of the present invention and "C" material in Comparative Example 1. Detailed Implementation

[0038] The embodiments of the present invention will be described in detail below. It should be emphasized that the following description is merely exemplary and not intended to limit the scope and application of the present invention. Unless otherwise specified, the embodiments and features in the embodiments of this application can be combined with each other.

[0039] This invention provides a surface modification method for lithium-rich manganese-based cathode materials, comprising the following steps:

[0040] (1) Dissolve the coating agent in deionized water to obtain a coating agent aqueous solution with a coating agent concentration of 0.1 to 10 mg / mL, wherein the coating agent is a polymer with multiple carboxyl functional groups;

[0041] (2) Dissolve the soluble inorganic salt containing the modified metal element in deionized water to obtain a metal precursor solution;

[0042] (3) The lithium-rich manganese-based cathode material to be modified is uniformly dispersed in the coating agent aqueous solution of step (1), and then the metal precursor solution of step (2) is added. Alternatively, the coating agent aqueous solution of step (1) and the metal precursor solution of step (2) are mixed and then the lithium-rich manganese-based cathode material to be modified is uniformly dispersed therein, so that the modified metal element in the metal precursor solution undergoes a complexation adsorption reaction with the carboxyl functional group in the coating agent to form a preliminary coating layer and ion adsorption.

[0043] (4) After washing and filtering the reactants obtained in step (3), heat treatment is carried out in an oxygen-free atmosphere to form a metal ion gradient doping in the lithium-rich manganese-based cathode material, and a metal oxide layer, spinel phase and carbon layer are formed sequentially from the inside to the outside on the surface of the lithium-rich manganese-based cathode material.

[0044] Among them, metal ion gradient doping refers to the gradual decrease of metal ion content from the surface of lithium-rich manganese-based cathode material particles to a predetermined depth.

[0045] In some embodiments, in step (1), the polymer having multiple carboxyl functional groups is a polymer capable of forming metal complexes with modified metal elements, preferably at least one of polyacrylic acid, polymethacrylic acid, and polymaleic acid.

[0046] In some embodiments, the modified metal element in step (2) is at least one selected from Al, Mg, Zr, Ti, Mo, W, V, Zn, Na, and La. The soluble inorganic salt in step (2) is, for example, a nitrate.

[0047] In some embodiments, the content of modified metal elements in the metal precursor solution of step (2) is positively correlated with the thickness of the metal oxide layer formed in step (4).

[0048] In some embodiments, the heat treatment temperature in step (4) is 300-700°C and the heat treatment time is 1-6 hours.

[0049] In some embodiments, the chemical formula of the lithium-rich manganese-based cathode material to be modified is xLi₂MnO₃·(1-x)LiTMO₂, where TM is at least one of Mn, Co, and Ni, and 0 <x<1。

[0050] In some embodiments, the uniform dispersion is carried out under magnetic stirring and / or ultrasonic vibration, and the amount of the lithium-rich manganese-based cathode material to be modified is sufficient to achieve uniform dispersion without agglomeration. More preferably, the mass ratio of the metal oxide of the metal oxide layer to the lithium-rich manganese-based cathode material to be modified is 1% to 5%.

[0051] In some embodiments, the oxygen content in the oxygen-free atmosphere in step (4) is less than 10 ppm; the oxygen-free atmosphere is one of argon, helium, and nitrogen.

[0052] The present invention also provides a lithium-rich manganese-based cathode modified material, which is prepared by the surface modification method described above, including a lithium-rich manganese-based cathode material and having a metal oxide layer, a spinel phase and a carbon layer sequentially from the inside to the outside on the surface of the lithium-rich manganese-based cathode material.

[0053] A specific embodiment of the present invention also provides a lithium-ion battery, wherein the positive electrode of the lithium-ion battery comprises the aforementioned lithium-rich manganese-based positive electrode modified material.

[0054] The following describes specific embodiments of the present invention.

[0055] Example 1

[0056] The surface modification method for a lithium-rich manganese-based cathode material in this embodiment uses a lithium-rich manganese-based cathode material with the chemical formula 0.5Li₂MnO₃·0.5LiMn. 1 / 3 Co 1 / 3 Ni 1 / 3 O2 (purchased), sample number base, the method includes the following steps:

[0057] 1. Dissolve polyacrylic acid (PAA) in deionized water to prepare a PAA aqueous solution with a concentration of 1 mg / mL;

[0058] 2. Dissolve Al(NO3)3·9H2O in deionized water to prepare a 0.1 mg / mL aluminum nitrate aqueous solution;

[0059] 3. Disperse 1g of base material in 10mL of PAA aqueous solution and stir continuously to obtain a suspension;

[0060] 4. Measure an aqueous solution of aluminum nitrate at a mass ratio of 1% for Al2O3 / base material, and add it dropwise to the suspension containing the base material in step (3);

[0061] 5. After repeated washing and filtration using deionized water and a vacuum filter (to remove unreacted impurities, etc.), PAA-Al pre-coated material is obtained. This PAA-Al pre-coated material is then heat-treated in a muffle furnace with an argon atmosphere at 500°C for 4 hours. After natural cooling to room temperature (20-30°C), lithium-rich manganese-based cathode modified material is obtained. During the heat treatment, a metal ion gradient doping is formed in the lithium-rich manganese-based cathode material. The initial coating layer carbonizes to form a carbon layer, and the modified metal elements form a metal oxide layer (Al2O3). A spinel phase is formed between the carbon layer and the metal oxide layer. In other words, during the heat treatment, a metal ion gradient doping is formed in the lithium-rich manganese-based cathode material, and the surface of the lithium-rich manganese-based cathode material sequentially forms a metal oxide layer, a spinel phase, and a carbon layer from the inside out.

[0062] The lithium-rich manganese-based cathode modified material prepared in Example 1 includes a lithium-rich manganese-based cathode material, an aluminum ion gradient doping formed in the lithium-rich manganese-based cathode material (the content of aluminum ions gradually decreases from the particle surface of the lithium-rich manganese-based cathode material to a depth of about 100 nm), and a metal oxide layer, a spinel phase, and a carbon layer sequentially formed from the inside to the outside on the surface of the lithium-rich manganese-based cathode material. This sample is named C&Al-1. Figure 1a and Figure 2 The image shown is the SEM-EDS spectrum of C&Al-1; as shown... Figure 1b The image shown is a time-of-flight secondary ion mass spectrometry (TOF-SIMS) image of C&Al-1.

[0063] Example 2

[0064] The difference from Example 1 is that in step 4, the aluminum nitrate aqueous solution was measured at a mass ratio of 3% for the Al2O3 / base material. The lithium-rich manganese-based cathode modified material sample obtained in Example 2 was named C&Al-2.

[0065] Example 3

[0066] The difference from Example 1 is that in step 4, the aluminum nitrate aqueous solution was measured at a mass ratio of 5% for the Al2O3 / base material. The lithium-rich manganese-based cathode modified material sample obtained in Example 3 was named C&Al-3.

[0067] Comparative Example 1

[0068] 1. Dissolve Al(NO3)3·9H2O in deionized water to prepare a 0.1 mg / mL solution. -1 Aqueous solution of aluminum nitrate;

[0069] 2. Measure aluminum nitrate aqueous solution according to the mass ratio of Al2O3 / base material of 1%, disperse 1g of base material in aluminum nitrate aqueous solution, and stir continuously to obtain a suspension;

[0070] 3. After repeated washing and filtration using deionized water and a vacuum filter (to remove unreacted impurities, etc.), the material is processed in a muffle furnace with an air atmosphere. After heat treatment at 500℃ for 4 hours, it is naturally cooled to room temperature (20-30℃) to obtain a lithium-rich manganese-based cathode modified material. This material includes a lithium-rich manganese-based cathode material, an aluminum ion gradient doping layer formed in the lithium-rich manganese-based cathode material, and a metal oxide (Al2O3) layer coated on the outer surface of the lithium-rich manganese-based cathode material, named C&Al-1-air.

[0071] Comparative Example 2

[0072] 1. Dissolve polyacrylic acid (PAA) in deionized water to prepare a PAA aqueous solution with a concentration of 1 mg / mL;

[0073] 2. Disperse 1g of base material in 10mL of PAA aqueous solution and stir continuously to obtain a suspension;

[0074] 3. After repeated washing and filtration using deionized water and a vacuum filter (to remove unreacted impurities, etc.), the material is processed in a muffle furnace with an argon atmosphere. After heat treatment at 500°C for 4 hours, it is naturally cooled to room temperature (20-30°C) to obtain a lithium-rich manganese-based cathode modified material, which includes a lithium-rich manganese-based cathode material and a carbon layer coated on the outer surface of the lithium-rich manganese-based cathode material, named C.

[0075] The materials prepared in each embodiment and comparative example were tested as follows.

[0076] The changes in elemental composition of the material before and after modification were analyzed by ICP and STEM-EDS, as shown in Table 1 and Figure 1-2, indicating the successful introduction of Al. 3+ The sample contains doped elements, with carbon uniformly coated on the sample surface and aluminum uniformly distributed throughout the material.

[0077] Table 1: Atom number ratio of sample materials, with the remainder being O atoms.

[0078] sample Mn Ni Co Li Al base 0.540％ 0.135％ 0.155％ 1.176％ 0 C&Al-1 0.540％ 0.139％ 0.160％ 1.090％ 0.005％ C&Al-2 0.540％ 0.133％ 0.154％ 1.097％ 0.023％ C&Al-3 0.540％ 0.139％ 0.163％ 1.098％ 0.022％

[0079] Using SEM to analyze the base ( Figure 3 Figures (a) and (b) in the text), PAA-Al pre-coated material (i.e., the material before C&Al-1 heat treatment), Figure 3 (c) in the figure) and the heat-treated material ( Figure 3The morphology of (d) C&Al-1, (e) C&Al-2, and (f) C&Al-3 is analyzed, as follows: Figure 3 As shown; XRD patterning and Raman spectroscopy were used for testing, such as... Figure 4 , 5 As shown, this indicates a transformation from layered to spinel phase through structural modulation; high-resolution HR-TEM measurements, such as... Figure 6a , 6b As shown in 6c and 6d, this indicates successful carbon layer coating. Figure 6b , 6c In 6d, the area defined by the two dashed lines is the carbon layer.

[0080] Electrochemical tests were conducted by assembling coin cells (hereinafter referred to as "cells"). The assembly process of the cells is as follows:

[0081] 1) Preparation of positive electrode coating: Weigh the positive electrode material (base material, materials prepared in each example and comparative example), acetylene black conductive agent and PVDF binder in a mass ratio of 8:1:1, put them in an agate mortar and dry mix them evenly. Then add an appropriate amount of N-methylpyrrolidone (NMP) and wet mix and grind to obtain a stable positive electrode slurry for later use.

[0082] 2) Coating, drying, and slicing: 16-micron thick aluminum foil is selected as the positive electrode current collector. Both sides are wiped with anhydrous ethanol, and the smooth side is placed face down on a flat glass plate with the rough side facing up. The parameters of the doctor blade are adjusted to achieve a coating thickness of approximately 15 microns. The positive electrode slurry is then evenly coated onto the aluminum foil surface. The coated sheet is placed in a forced-air drying oven and dried at 110℃ for 12 hours. Afterward, the sheet is cut into 10mm diameter round pieces using a stamping machine, ready for use as the positive electrode sheet for the battery.

[0083] 3) Battery Assembly: 11-micron diameter lithium metal discs are used as the negative electrode, matched with high voltage, electrolyte, and a 16mm diameter glass fiber separator. The battery model is 2032. Assembly includes positive and negative electrode shells, spring plates, gaskets, etc., all of which are cleaned with anhydrous ethanol and dried for 12 hours. Assembly is performed in a low-oxygen glove box, controlling the water and oxygen content to be below 0.1ppm. The assembly steps are as follows: first, place the negative electrode shell, then add the spring plate, gasket, and lithium sheet in sequence, add the electrolyte dropwise, place the separator, ensure the separator is moistened, then place the positive electrode sheet, close the positive electrode shell, and finally seal with a hydraulic sealing machine. After sealing, let it stand for 24 hours for later use.

[0084] During electrochemical performance testing, all assembled cells were first activated at a low rate of 0.1C after the initial resting period. Initial voltage curves and corresponding dQ and dV values ​​for base and C&Al-1 cells were plotted. -1 Curves, such as Figure 7a , 7bThe figures shown are the first-cycle charge-discharge curves and the first-cycle capacity increment curves for base and C&Al-1 at 0.1C, respectively. Figure 7c yes Figure 7b The diagram shown in box A, after completion, illustrates that C&Al-1 exhibits a stronger redox peak near 4.5V. The redox reaction of the cathode material was further analyzed using cyclic voltammetry (CV), and the CV curves of different materials in the first and second cycles are presented, as shown below. Figure 8a and 8b As shown; the cycling performance of the base material and the C&Al-1 material is compared, as follows. Figure 9 As shown in Table 2, the corresponding cyclic data indicate that the reversibility of the redox reaction of the treated material is significantly enhanced compared to the base material, and the interfacial side reactions are effectively suppressed.

[0085] Table 2

[0086]

[0087] In the table, 0.1C represents the battery's initial discharge capacity at a 0.1C rate; ICE (Initial Coulombic Efficiency) represents the battery's initial charge-discharge efficiency; First 1C represents the battery's initial discharge capacity at a 1C rate; 300th cycle represents the battery's discharge capacity after 300 charge-discharge cycles; Capacity retention rate refers to the degree to which the battery's capacity is maintained relative to its initial discharge capacity after 300 charge-discharge cycles (200 cycles for batteries based on the same material); Capacity decay refers to the rate at which the battery's capacity decreases after each charge-discharge cycle; Voltage decay refers to the rate at which the battery's voltage decreases after each charge-discharge cycle.

[0088] The cycling performance of C&Al-1 from Example 1 was compared with that of carbon coating alone (Comparative Example 2), aluminum doping modification (Comparative Example 1), and Example 1. Figures 10a-10d As shown, aluminum doping significantly enhances the cycling stability of the base material, indirectly confirming that aluminum doping enhances surface structure stability, effectively promotes the transformation of the layered structure to the spinel phase, and alleviates voltage decay.

[0089] In this embodiment of the invention, a weakly acidic aqueous solution of polyacrylic acid (PAA) is used to pre-activate the LMO material. Then, a complex is formed through the adsorption of metal ions by PAA. This, combined with subsequent heat treatment in an oxygen-free atmosphere, achieves metal ion gradient doping modification of the LMO cathode material and coating modification of the metal oxide layer, spinel fast ion conductor, and carbon layer electronic conductor. Specifically, this method has the following advantages:

[0090] 1. Pre-activating the surface of lithium-rich manganese-based materials with weakly acidic polycarboxyl functional group polymers can effectively reduce the capacity loss caused by the damage to the surface structure caused by traditional acid activation. In addition, since such acids are rich in a large number of carboxyl functional groups, they have a strong coordination effect with low-valence metal ions, which is conducive to the formation of long-chain complexes on the surface, such as PAA-M (M is a metal element). The complexes adhere tightly to the surface of the material particles, which is beneficial to enhancing the stability of lattice oxygen.

[0091] 2. Through heat treatment in an oxygen-free atmosphere, a gradient doping of metal ions is formed in the lithium-rich manganese-based cathode material, and a metal oxide layer is formed on the surface. A carbon layer and a spinel phase (Li4Mn5O4) connecting the metal oxide layer and the carbon layer are formed outside the metal oxide layer. 12 This invention solves the problem of low intrinsic conductivity of LMO materials and suppresses interfacial side reactions. Compared with other methods of carbon coating, the method of this invention uses inexpensive raw materials, is environmentally friendly, produces pure pyrolysis products, and does not release toxic gases, making it suitable for large-scale industrial applications.

[0092] 3. Traditional surface modification methods, such as achieving metal doping, surface reconstruction, and carbon coating, require multiple steps and various reagents. However, the method of this invention uses polycarboxylic acid functional group polymers such as PAA and aqueous solutions of metal salts, which is green and safe. It also avoids traditional precipitation and coating steps. Multiple modifications of LMO can be achieved in one step of solution treatment and heat treatment, reducing experimental costs and shortening processing time.

[0093] The above description provides a further detailed explanation of the present invention in conjunction with specific / preferred embodiments, and it should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various substitutions or modifications can be made to these described embodiments without departing from the concept of the present invention, and all such substitutions or modifications should be considered within the scope of protection of the present invention. In the description of this specification, the reference to terms such as "an embodiment," "some embodiments," "preferred embodiment," "example," "specific example," or "some examples," etc., indicates that the specific features, structures, materials, or characteristics described in connection with that embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in any suitable manner in one or more embodiments or examples. Without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification and the features of different embodiments or examples. Although the embodiments of the present invention and their advantages have been described in detail, it should be understood that various changes, substitutions, and modifications can be made herein without departing from the scope of protection of the patent application.

Claims

1. A method for surface modification of a lithium-rich manganese-based positive electrode material, characterized in that, Includes the following steps: (1) Dissolve the coating agent in deionized water to obtain a coating agent aqueous solution with a coating agent concentration of 0.1 to 10 mg / mL, wherein the coating agent is a polymer with multiple carboxyl functional groups; (2) Dissolve the soluble inorganic salt containing the modified metal element in deionized water to obtain a metal precursor solution; (3) The lithium-rich manganese-based cathode material to be modified is uniformly dispersed in the coating agent aqueous solution of step (1), and then the metal precursor solution of step (2) is added. Alternatively, the coating agent aqueous solution of step (1) and the metal precursor solution of step (2) are mixed and then the lithium-rich manganese-based cathode material to be modified is uniformly dispersed therein, so that the modified metal element in the metal precursor solution undergoes a complexation adsorption reaction with the carboxyl functional group in the coating agent to form a preliminary coating layer and ion adsorption. (4) After washing and filtering the reactants obtained in step (3), heat treatment is carried out in an oxygen-free atmosphere to form a metal ion gradient doping in the lithium-rich manganese-based cathode material, and a metal oxide layer, spinel phase and carbon layer are formed sequentially from the inside to the outside on the surface of the lithium-rich manganese-based cathode material.

2. The surface modification method of claim 1, wherein: In step (1), the polymer with multiple carboxyl functional groups is at least one of polyacrylic acid, polymethacrylic acid and polymaleic acid.

3. The surface modification method of claim 1, wherein: In step (2), the modified metal element is at least one of Al, Mg, Zr, Ti, Mo, W, V, Zn, Na, and La.

4. The surface modification method of claim 1, wherein: In the metal precursor solution of step (2), the content of modified metal elements is positively correlated with the thickness of the metal oxide layer formed in step (4).

5. The surface modification method of claim 1, wherein: In step (4), the heat treatment temperature is 300-700℃ and the heat treatment time is 1-6h.

6. The surface modification method of claim 1, wherein: In step (3), the chemical formula of the lithium-rich manganese-based cathode material to be modified is xLi2MnO3·(1-x)LiTMO2, where TM is at least one of Mn, Co, and Ni, and 0 <x<1。 7. The surface modification method of claim 1, wherein: In step (3), the uniform dispersion is carried out under magnetic stirring and / or ultrasonic vibration, and the amount of lithium-rich manganese-based cathode material to be modified is sufficient to make it uniformly dispersed without agglomeration.

8. The surface modification method of claim 1, wherein: The oxygen content in the oxygen-free atmosphere described in step (4) is less than 10 ppm; the oxygen-free atmosphere is one of argon, helium, and nitrogen.

9. A lithium-rich manganese-based positive electrode modifying material, characterized in that, The cathode material is prepared by the surface modification method according to any one of claims 1-8, and includes a lithium-rich manganese-based cathode material, a metal ion gradient doping formed in the lithium-rich manganese-based cathode material, and a metal oxide layer, a spinel phase and a carbon layer sequentially formed from the inside to the outside on the surface of the lithium-rich manganese-based cathode material.

10. A lithium-ion battery, characterized by, The positive electrode of the lithium-ion battery comprises the lithium-rich manganese-based positive electrode modified material as described in claim 9.

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