Composite modified lithium-rich manganese-based positive electrode material, preparation method thereof and lithium ion battery

Abstract

The invention provides a composite modified lithium-rich manganese-based positive electrode material, a preparation method of the composite modified lithium-rich manganese-based positive electrode material and a lithium ion battery, and a preparation method of the composite modified lithium-rich manganese-based positive electrode material. And depositing aluminide on the surface of the material by using an atomic layer deposition method. An aluminum oxide pre-coating layer obtained through liquid-phase coating provides basic protection, and transition metal dissolution and electrolyte side reaction are inhibited; atomic layer deposition fills pores of the aluminum oxide pre-coating layer in a precise regulation and control manner to form compact coverage, atomic layer level uniformity is realized, and the surface uniformity and coating integrity of the positive electrode material are ensured, so that the problem of non-uniformity of a coating layer formed by liquid-phase coating is solved through the synergistic effect of the two components, and the positive electrode material is prepared. And uniform and complete aluminum oxide coating of the lithium-rich manganese-based positive electrode material is realized on the premise of controlling the cost, so that the initial coulombic efficiency and the thermal stability of the lithium-rich manganese-based positive electrode material are improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of cathode materials for batteries, and relates to a composite modified lithium-rich manganese-based cathode material, a preparation method thereof, and a lithium-ion battery. Background Art

[0002] With the sharp increase in the demand for high-energy-density lithium-ion batteries in new energy vehicles and energy storage systems, the theoretical specific capacity of traditional layered oxide cathode materials (such as lithium cobalt oxide and nickel cobalt manganese ternary materials) has approached its limit value. The lithium-rich manganese-based cathode material ( x Li2MnO3·(1- x )LiMO2) exhibits a breakthrough specific capacity due to its unique anion / cation synergistic redox mechanism and is regarded as the core material for the next generation of high-energy-density batteries. However, the irreversible precipitation of lattice oxygen on the surface of this material leads to a serious loss of the first Coulombic efficiency, the structural reconstruction caused by the dissolution of surface transition metal ions accelerates the voltage decay, and the abnormal thickening of the cathode electrolyte interface film (CEI film) caused by the interfacial side reaction significantly reduces the cycle life of the battery.

[0003] In order to obtain a highly stable lithium-rich manganese-based cathode material, the Chinese patent application with the publication number CN119143198A uses a wet chemical method to synergistically modify the lithium-rich manganese-based cathode material with phosphate, metal salts (such as soluble salts of aluminum, zirconium, and magnesium), and tetrabutyl titanate to form a discontinuous island-like coating layer, improving the cycle stability and thermal stability of the material. However, there is a problem of uneven coating layer in liquid-phase coating, resulting in unstable performance of the cathode material. The Chinese patent application with the publication number CN106684358A uses the sol-gel method to form an alumina coating layer on the surface of the lithium-rich manganese-based cathode material, improving the first Coulombic efficiency and cycle stability of the material. However, the sol-gel method also has problems of low coating uniformity and poor consistency. The Chinese patent application with the publication number CN109755547A uses a wet chemical method to coat an aluminum layer on the surface of the lithium-rich manganese-based cathode material under the condition of controlling the alcohol aqueous solution to be alkaline. However, the relatively fast deposition rate of this method will greatly affect the morphology of the coating layer and thus the coating effect, so it is not conducive to subsequent production applications. Summary of the Invention

[0004] In order to solve the problem of poor stability of the lithium-rich manganese-based cathode material in the above-mentioned prior art, the present invention provides a composite modified lithium-rich manganese-based cathode material, a preparation method thereof, and a lithium-ion battery.

[0005] The present invention is achieved through the following technical solutions: In the first aspect, the present invention provides a preparation method of a composite modified lithium-rich manganese-based cathode material, including: S1, dispersing the lithium-rich manganese-based cathode material in water to obtain a slurry; S2. Add an aluminum source to the slurry, adjust the pH value to alkaline, conduct a first reaction, then adjust the pH value to 5 - 7, conduct a second reaction, perform solid - liquid separation, drying, and sintering to obtain a primary coating material; S3. Place the primary coating material in an atomic layer deposition reaction chamber, evacuate the air, and heat up to the reaction temperature; S4. Introduce a first reaction precursor for reaction, purge with an inert gas, introduce a second reaction precursor for reaction, purge with an inert gas, and repeat this step until a coating layer with a preset thickness is obtained; wherein, the first reaction precursor is an aluminum source, and the second reaction precursor is water; S5. Sinter the product obtained in S4 to obtain a composite - modified lithium - rich manganese - based cathode material.

[0006] Preferably, in S1, the molecular formula of the lithium - rich manganese - based cathode material is yLi2MnO3·(1 - y)LiMO2, where M is one or more of Ni, Co, and Mn, and 0 < y < 1.

[0007] Preferably, in S2, the addition amount of the aluminum source satisfies that the atomic number of aluminum elements accounts for 1% - 3% of the transition metal atomic number in the lithium - rich manganese - based cathode material.

[0008] Preferably, in S2, the sintering is carried out in an air atmosphere, the sintering temperature is 300 - 600 °C, and the sintering time is 2 - 10 h.

[0009] Preferably, in S4, the first reaction precursor is trimethylaluminum.

[0010] Preferably, S4 is specifically: introduce a first reaction precursor for reaction, purge with an inert gas, introduce a second reaction precursor for reaction, purge with an inert gas, introduce a third reaction precursor for reaction, purge with an inert gas, introduce a second reaction precursor for reaction, purge with an inert gas; repeat this step until a coating layer with a preset thickness is obtained; where the first reaction precursor is an aluminum source, the second reaction precursor is water, and the third reaction precursor is a phosphorus source.

[0011] Preferably, in S5, the sintering is carried out in an air atmosphere, the sintering temperature is 300 - 600 °C, and the sintering time is 2 - 8 h.

[0012] In a second aspect, the present invention provides a composite - modified lithium - rich manganese - based cathode material obtained by using the preparation method as described above. The composite - modified lithium - rich manganese - based cathode material sequentially includes a lithium - rich manganese - based cathode material, an alumina pre - coating layer, and an aluminum compound deposition layer from the inside out.

[0013] Preferably, in the composite - modified lithium - rich manganese - based cathode material, the thickness of the alumina pre - coating layer is 5 - 50 nm, and the thickness of the aluminum compound deposition layer is 0.5 - 2 nm.

[0014] In a third aspect, the present invention provides a lithium-ion battery, comprising the composite modified lithium-rich manganese-based cathode material as described above.

[0015] Compared with the prior art, the present invention has the following beneficial effects: Through a composite strategy of liquid-phase pre-coating and atomic layer deposition (ALD) nano-layer secondary modification, the present invention deposits aluminide on the surface of the lithium-rich manganese-based cathode material by atomic layer deposition on the premise of liquid-phase coating of alumina on the lithium-rich manganese-based cathode material. The alumina pre-coating layer obtained by liquid-phase coating provides basic protection, inhibits the dissolution of transition metals and side reactions of the electrolyte; atomic layer deposition precisely regulates and fills the pores of the alumina pre-coating layer to form a dense coverage, achieving atomic-level uniformity, ensuring the uniformity of the surface of the cathode material and the integrity of the coating, thereby overcoming the problem of uneven coating layer formed by liquid-phase coating through the synergistic effect of the two, realizing uniform and complete alumina coating of the lithium-rich manganese-based cathode material on the premise of controlling costs, and further improving the first Coulomb efficiency and thermal stability of the lithium-rich manganese-based cathode material. Compared with the traditional single coating technology, the method of the present invention is compatible with low-cost mass production and precise regulation, has both process flexibility and performance superiority, and provides a feasible solution for breaking through the bottleneck of high-voltage cycle attenuation of the lithium-rich manganese-based cathode material. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0017] Figure 1 It is a schematic structural diagram of the composite modified lithium-rich manganese-based cathode material of the present invention; Figure 2 It is a transmission electron microscope characterization image of the composite modified lithium-rich manganese-based cathode material prepared in Example 1 of the present invention; Figure 3 It is a flowchart of the preparation method of the composite modified lithium-rich manganese-based cathode material of the present invention; Figure 4 It is the first charge-discharge curve graph of the batteries corresponding to Examples 1-4 and Comparative Examples 1-3 of the present invention; Figure 5 It is the charge-discharge cycle curve graph of the batteries corresponding to Examples 1-4 and Comparative Examples 1-3 of the present invention; Figure 6 It is the high-temperature charge-discharge cycle curve graph of the batteries corresponding to Examples 1-4 and Comparative Examples 1-3 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0018] The embodiments of the present invention are described below through specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0019] It should be noted that the process equipment or devices not specifically specified in the following embodiments all adopt conventional equipment or devices in the art.

[0020] It should be noted that the terms "comprising" and "having" and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or device that includes a series of steps or units does not necessarily have to be limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or are inherent to these processes, methods, products, or devices. Moreover, unless otherwise specified, the numbers of the method steps are only convenient tools for identifying the method steps, rather than limiting the arrangement order of the method steps or the scope in which the present invention can be implemented. The change or adjustment of their relative relationships, without substantial change in the technical content, should also be regarded as the scope in which the present invention can be implemented.

[0021] The preparation method of the composite modified lithium-rich manganese-based cathode material of the present invention mainly includes the following steps: first, perform liquid-phase coating on the lithium-rich manganese-based cathode material, and then perform secondary coating by atomic layer deposition.

[0022] Specifically, referring to Figure 3 , the preparation method of the present invention includes the following steps: S1, Disperse the lithium-rich manganese-based cathode material in water to obtain a slurry. S2, Add an aluminum source to the slurry, adjust the pH value to alkaline, perform a first reaction, then adjust the pH value to 5 - 7, perform a second reaction, separate the solid and liquid, and dry and sinter to obtain a primary coated material. S3, Place the primary coated material in the atomic layer deposition reaction chamber, evacuate, and heat up to the reaction temperature. S4, Use an inert gas as the carrier gas to introduce the first reaction precursor for reaction, purge with the inert gas to remove the excess first reaction precursor and reaction by-products, introduce the second reaction precursor for reaction, purge with the inert gas to remove the excess second reaction precursor and reaction by-products, and repeat this step until a coating layer with a preset thickness is obtained; wherein, the first reaction precursor is an aluminum source, and the second reaction precursor is water.

[0023] S5, Sinter the product obtained in S4 to obtain the composite modified lithium-rich manganese-based cathode material.

[0024] The preparation method of the above-mentioned composite modified lithium-rich manganese-based cathode material of the present invention constructs a pre-coated alumina layer through liquid-phase coating to achieve basic interface protection, which can reduce costs compared to forming a coating layer of the same thickness by atomic layer deposition alone; subsequently, a dense aluminide deposition layer is deposited on the surface of the pre-coated alumina layer by atomic layer deposition for a short time to fill the pores of the pre-coated alumina layer and achieve atomic-level uniform coverage, forming a gradient coating structure. This double-layer coating structure greatly improves the uniformity and consistency of the coating layer while controlling costs, thereby improving the initial Coulomb efficiency and thermal stability of the cathode material. At the same time, sintering is carried out after liquid-phase coating to promote the crystallization of the pre-coated alumina layer and its chemical bonding with the surface of the lithium-rich manganese-based cathode material. After atomic layer deposition, a second sintering can further induce the diffusion of Al 3+ to form a LiAlO2 fast ion conductor interface layer and improve the interfacial lithium ion transport efficiency.

[0025] Moreover, the present invention adopts acidic liquid-phase coating (pH = 5-7), which can avoid the problem of increased residual alkali on the surface of the lithium-rich manganese-based cathode material caused by alkaline conditions and avoid the deterioration of the cycle performance of the cathode material due to residual alkali.

[0026] In some preferred embodiments of the present invention, the molecular formula of the lithium-rich manganese-based cathode material is yLi2MnO3·(1-y)LiMO2, where M is one or more of Ni, Co, and Mn, and 0 < y < 1.

[0027] In some preferred embodiments of the present invention, the addition amount of the aluminum source in S2 satisfies that the atomic number of aluminum element accounts for 1%-3% of the transition metal atomic number in the lithium-rich manganese-based cathode material.

[0028] In some preferred embodiments of the present invention, in S2, the sintering is carried out in an air atmosphere, the sintering temperature is 300-600 °C, and the sintering time is 2-10 h.

[0029] In some specific embodiments of the present invention, in S4, the first reaction precursor is trimethylaluminum (TMA).

[0030] In some preferred embodiments of the present invention, S4 is specifically: introducing the first reaction precursor for reaction, purging with an inert gas, introducing the second reaction precursor for reaction, purging with an inert gas, introducing the third reaction precursor for reaction, purging with an inert gas, introducing the second reaction precursor for reaction, purging with an inert gas; repeating this step until a coating layer with a preset thickness is obtained; where the first reaction precursor is an aluminum source, the second reaction precursor is water, and the third reaction precursor is a phosphorus source.

[0031] In the present invention, a phosphorus source is introduced to react with an aluminum source to deposit an aluminum phosphate deposition layer, thereby obtaining a coating layer composed of a composite of aluminum oxide and aluminum phosphate. Aluminum phosphate can form surface spinel, thereby inhibiting the degradation of the material structure and improving the stability of the cathode material.

[0032] In some preferred embodiments of the present invention, S4 is repeated 2 - 5 times to make the aluminum compound deposition layer reach a preset thickness of 0.5 - 2 nm.

[0033] In some preferred embodiments of the present invention, in the preparation method of the composite modified lithium-rich manganese-based cathode material, in S5, the sintering is carried out in an air atmosphere, the sintering temperature is 300 - 600 °C, and the sintering time is 2 - 8 h.

[0034] The composite modified lithium-rich manganese-based cathode material obtained by the preparation method as described above in the present invention has, from the inside out, a lithium-rich manganese-based cathode material, an aluminum oxide pre-coating layer, and an aluminum compound deposition layer ( Figure 1 ).

[0035] Among them, the thickness of the aluminum oxide pre-coating layer is 5 - 50 nm, and the thickness of the aluminum compound deposition layer is 0.5 - 2 nm.

[0036] For the lithium-ion battery assembled based on the composite modified lithium-rich manganese-based cathode material of the present invention, both the discharge capacity and the first-cycle Coulombic efficiency are improved, and the stability is improved.

[0037] Example 1 The preparation method of the composite modified lithium-rich manganese-based cathode material of the present invention specifically includes the following steps: (1) Weigh 5 g of Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2 lithium-rich manganese-based cathode material, vacuum dry it at 120 °C for 24 h, disperse the dried material in 100 g of deionized water at 80 °C, and stir it at a rotation speed of 1500 rpm to obtain a uniformly mixed slurry; (2) Maintain the temperature of the slurry at 80 °C, add a 1 mol / L aluminum nitrate solution to the slurry at a flow rate of 1 g / min until the atomic number of Al element is 2% of the atomic numbers of transition metal elements (Ni, Co, Mn), add ammonia water to the slurry at a flow rate of 0.5 g / min until the pH value is 9, after reacting for 2 h, add citric acid to the slurry at a flow rate of 1 g / min until the pH value is 6, after reacting for 5 h, dehydrate the product, dry it at 120 °C for 24 h, and sinter it at 500 °C for 3 h in an air atmosphere to obtain a primary coated material with an aluminum oxide coating; (3) Place the primary coated material in an atomic layer deposition reaction chamber, evacuate it to 0.1 mPa, and heat it to 200 °C and keep it for 2 hours; (4) Introduce trimethylaluminum into the atomic layer deposition reaction chamber for 1 s with nitrogen as the carrier gas, react for 1 min, then purge with nitrogen for 80 s. Subsequently, introduce water into the atomic layer deposition reaction chamber for 1 s with nitrogen as the carrier gas, react for 1 min and then purge with nitrogen for 80 s. Repeat step (4) twice. Heat the obtained product to 300 °C at a heating rate of 5 °C / min and hold for 2 h, and then naturally cool to obtain the composite modified lithium-rich manganese-based cathode material.

[0038] Example 2 The preparation method of the composite modified lithium-rich manganese-based cathode material of the present invention specifically comprises the following steps: (1) Weigh 5 g of Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2 lithium-rich manganese-based cathode material, vacuum dry at 120 °C for 24 h. Disperse the dried material in 100 g of deionized water at 80 °C, and stir at a rotation speed of 1500 rpm to obtain a uniformly mixed slurry; (2) Maintain the temperature of the slurry at 80 °C, add a 1 mol / L aluminum nitrate solution to the slurry at a flow rate of 1 g / min until the atomic number of Al element is 2% of the atomic numbers of transition metal elements (Ni, Co, Mn). Add ammonia water to the slurry at a flow rate of 0.5 g / min until the pH value is 9. After reacting for 2 h, add citric acid to the slurry at a flow rate of 1 g / min until the pH value is 6. After reacting for 5 h, dehydrate the product, dry at 120 °C for 24 h, and sinter at 500 °C for 3 h in an air atmosphere to obtain the primary coated material coated with alumina; (3) Place the primary coated material in the atomic layer deposition reaction chamber, evacuate to 0.1 mPa, and heat to 200 °C and hold for 2 h; (4) Introduce trimethylaluminum into the atomic layer deposition reaction chamber for 1 s with nitrogen as the carrier gas, react for 1 min, then purge with nitrogen for 80 s. Subsequently, introduce water into the atomic layer deposition reaction chamber for 1 s with nitrogen as the carrier gas, react for 1 min and then purge with nitrogen for 80 s. Repeat step (4) twice. Heat the obtained product to 500 °C at a heating rate of 5 °C / min and hold for 2 h, and then naturally cool to obtain the composite modified lithium-rich manganese-based cathode material.

[0039] Example 3 The preparation method of the composite modified lithium-rich manganese-based cathode material of the present invention specifically comprises the following steps: (1) Weigh 5 g of Li 1.2 Ni 0.13 Co 0.13 Mn 0.54O2-rich lithium manganese-based cathode material, vacuum-dry at 120 °C for 24 h, disperse the dried material in 100 g of deionized water at 80 °C, stir at a rotation speed of 1500 rpm to obtain a uniformly mixed slurry; (2) Maintain the slurry temperature at 80 °C, add 1 mol / L aluminum nitrate solution to the slurry at a flow rate of 1 g / min until the atomic number of Al element is 2% of the atomic number of transition metal elements (Ni, Co, Mn), add ammonia water to the slurry at a flow rate of 0.5 g / min until the pH value is 9, after reacting for 2 h, add citric acid to the slurry at a flow rate of 1 g / min until the pH value is 6, after reacting for 5 h, dehydrate the product, dry at 120 °C for 24 h, sinter at 500 °C for 3 h under air atmosphere to obtain a primary coated material coated with alumina; (3) Place the primary coated material in an atomic layer deposition reaction chamber, evacuate to 0.1 mPa, and heat up to 200 °C, and hold for 2 hours; (4)Introduce trimethylaluminum into the atomic layer deposition reaction chamber for 1 s with nitrogen as the carrier gas, react for 1 min, then purge with nitrogen for 80 s, then introduce water into the atomic layer deposition reaction chamber for 1 s with nitrogen as the carrier gas, react for 1 min and then purge with nitrogen for 80 s, then introduce trimethyl phosphate into the atomic layer deposition reaction chamber for 1 s with nitrogen as the carrier gas, react for 1 min and then purge with nitrogen for 80 s, then introduce water into the atomic layer deposition reaction chamber for 1 s with nitrogen as the carrier gas, react for 1 min and then purge with nitrogen for 80 s. Repeat step (4) five times, heat the obtained product to 300 °C at a heating rate of 5 °C / min and hold for 2 h, and obtain a composite modified lithium manganese-based cathode material after natural cooling.

[0040] Example 4 The preparation method of the composite modified lithium manganese-based cathode material of the present invention specifically includes the following steps: (1)Weigh 5 g of Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2-rich lithium manganese-based cathode material, vacuum-dry at 120 °C for 24 h, disperse the dried material in 100 g of deionized water at 80 °C, stir at a rotation speed of 1500 rpm to obtain a uniformly mixed slurry; (2)Maintain the slurry temperature at 80 °C, add 1 mol / L aluminum nitrate solution to the slurry at a flow rate of 1 g / min until the atomic number of Al element is 2% of the atomic number of transition metal elements (Ni, Co, Mn), add ammonia water to the slurry at a flow rate of 0.5 g / min until the pH value is 9, after reacting for 2 h, add citric acid to the slurry at a flow rate of 1 g / min until the pH value is 6, after reacting for 5 h, dehydrate the product, dry at 120 °C for 24 h, sinter at 500 °C for 3 h under air atmosphere to obtain a primary coated material coated with alumina; (3) Place the primary coating material in the atomic layer deposition reaction chamber, evacuate to 0.1 mPa, and heat up to 200 °C, and hold for 2 hours; (4) Introduce trimethylaluminum into the atomic layer deposition reaction chamber for 1 s with nitrogen as the carrier gas, react for 1 min, then purge with nitrogen for 80 s. Subsequently, introduce water into the atomic layer deposition reaction chamber for 1 s with nitrogen as the carrier gas, react for 1 min and then purge with nitrogen for 80 s. Subsequently, introduce trimethyl phosphate into the atomic layer deposition reaction chamber for 1 s with nitrogen as the carrier gas, react for 1 min and then purge with nitrogen for 80 s. Subsequently, introduce water into the atomic layer deposition reaction chamber for 1 s with nitrogen as the carrier gas, react for 1 min and then purge with nitrogen for 80 s. Repeat step (4) five times. Heat the obtained product to 500 °C at a heating rate of 5 °C / min and hold for 2 h, and then naturally cool to obtain the composite modified lithium-rich manganese-based cathode material.

[0041] Comparative Example 1 The preparation method of the modified lithium-rich manganese-based cathode material of the present invention specifically includes the following steps: (1) Weigh 5 g of Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2 lithium-rich manganese-based cathode material, vacuum dry at 120 °C for 24 h. Disperse the dried material in 100 g of deionized water at 80 °C, and stir at a rotation speed of 1500 rpm to obtain a uniformly mixed slurry; (2) Add 1 mol / L aluminum nitrate solution to the slurry at a flow rate of 1 g / min until the atomic number of Al element is 2% of the atomic numbers of transition metal elements (Ni, Co, Mn). Add ammonia water to the slurry at a flow rate of 0.5 g / min until the pH value is 9. After reacting for 2 h, add citric acid to the slurry at a flow rate of 1 g / min until the pH value is 6. After reacting for 5 h, dehydrate the product, dry at 120 °C for 24 h, and sinter at 500 °C for 3 h in an air atmosphere to obtain the alumina-coated lithium-rich manganese-based cathode material.

[0042] Comparative Example 2 The preparation method of the composite modified lithium-rich manganese-based cathode material of the present invention specifically includes the following steps: (1) Weigh 5 g of Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2 lithium-rich manganese-based cathode material, vacuum dry at 120 °C for 24 h. Disperse the dried material in 100 g of deionized water at 80 °C, and stir at a rotation speed of 1500 rpm to obtain a uniformly mixed slurry; (2) Maintain the slurry temperature at 80 °C, add a 1 mol / L aluminum nitrate solution to the slurry at a flow rate of 1 g / min until the atomic number of Al element is 2% of the atomic numbers of transition metal elements (Ni, Co, Mn), add ammonia water to the slurry at a flow rate of 0.5 g / min until the pH value reaches 9, after reacting for 2 h, add citric acid to the slurry at a flow rate of 1 g / min until the pH value reaches 6, after reacting for 5 h, dehydrate the product, dry it at 120 °C for 24 h, and sinter it at 500 °C for 3 h under an air atmosphere to obtain a primary coated material coated with alumina; (3) Place the primary coated material in an atomic layer deposition reaction chamber, evacuate to 0.1 mPa, and heat up to 200 °C, and hold for 2 hours; (4) Introduce trimethylaluminum into the atomic layer deposition reaction chamber for 1 s with nitrogen as the carrier gas, react for 1 min, then purge with nitrogen for 80 s, then introduce water into the atomic layer deposition reaction chamber for 1 s with nitrogen as the carrier gas, and after reacting for 1 min, purge with nitrogen for 80 s. Repeat step (4) twice, and obtain the composite modified lithium-rich manganese-based cathode material after natural cooling.

[0043] Comparative Example 3 The preparation method of the composite modified lithium-rich manganese-based cathode material of the present invention specifically includes the following steps: (1) Weigh 5 g of Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2 lithium-rich manganese-based cathode material, vacuum dry it at 120 °C for 24 h, disperse the dried material in 100 g of deionized water at 80 °C, and stir at a rotation speed of 1500 rpm to obtain a uniformly mixed slurry; (2) Maintain the slurry temperature at 80 °C, add a 1 mol / L aluminum nitrate solution to the slurry at a flow rate of 1 g / min until the atomic number of Al element is 2% of the atomic numbers of transition metal elements (Ni, Co, Mn), add ammonia water to the slurry at a flow rate of 0.5 g / min until the pH value reaches 9, after reacting for 2 h, add citric acid to the slurry at a flow rate of 1 g / min until the pH value reaches 6, after reacting for 5 h, dehydrate the product, dry it at 120 °C for 24 h, and sinter it at 500 °C for 3 h under an air atmosphere to obtain a primary coated material coated with alumina; (3) Place the primary coated material in an atomic layer deposition reaction chamber, evacuate to 0.1 mPa, and heat up to 200 °C, and hold for 2 hours; (4) Trimethylaluminum was introduced into the atomic layer deposition reaction chamber for 1 s with nitrogen as the carrier gas, reacted for 1 min, then purged with nitrogen for 80 s. Subsequently, water was introduced into the atomic layer deposition reaction chamber for 1 s with nitrogen as the carrier gas, reacted for 1 min and then purged with nitrogen for 80 s. Subsequently, trimethyl phosphate was introduced into the atomic layer deposition reaction chamber for 1 s with nitrogen as the carrier gas, reacted for 1 min and then purged with nitrogen for 80 s. Subsequently, water was introduced into the atomic layer deposition reaction chamber for 1 s with nitrogen as the carrier gas, reacted for 1 min and then purged with nitrogen for 80 s. Step (4) was repeated five times, and after natural cooling, the composite modified lithium-rich manganese-based cathode material was obtained.

[0044] Figure 2 It is the transmission electron microscope characterization image of the composite modified lithium-rich manganese-based cathode material prepared in Example 1 of the present invention. It can be seen from the figure that there is an obvious and uniform surface coating layer on the surface of the lithium-rich manganese-based cathode material particles after composite coating.

[0045] Preparation of the battery: According to the mass percentage, 80% of the lithium-rich manganese-based cathode material, 10% of conductive carbon black and 10% of PVDF were mixed and dispersed by NMP. The mass ratio of the lithium-rich manganese-based cathode material to NMP was 1:2.2 to obtain a black viscous slurry. The slurry was coated (coating thickness was 90 μm) on aluminum foil and dried at 120 °C for 4 h to prepare the positive electrode sheet of the lithium-ion battery; a lithium sheet was used as the counter electrode, 1 mol / L LiPF6 solution (the solvent included EC and DMC, volume ratio was 3:7) was used as the electrolyte, and the separator was Celgar2502 separator, and a 2032 coin cell was assembled for charge and discharge tests. The lithium-rich manganese-based cathode material was selected from the modified lithium-rich manganese-based cathode materials prepared in the above Examples 1-4 and Comparative Examples 1-3.

[0046] Figure 4 It is the first cycle charge and discharge curve graph of the batteries corresponding to Examples 1-4 and Comparative Examples 1-3 of the present invention, where the charge and discharge voltage range is 2-4.8 V and the charge and discharge rate is 0.1 C (nominal specific capacity is 250 mAh / g).

[0047] From Figure 4It can be seen that the capacity of the modified lithium-rich manganese-based cathode material obtained in Example 1 is significantly higher than that in Comparative Example 1, indicating that on the basis of liquid-phase coating, the precise regulation of atomic layer deposition in Example 1 improves the uniformity and consistency of the coating, thereby enhancing the electrochemical performance of the cathode material. Comparing Example 1 with Comparative Example 2, it can be seen that although atomic layer deposition was carried out in Comparative Example 2, but no secondary sintering was performed, resulting in a decrease in performance, indicating that secondary sintering, as an important process for surface coating, can greatly improve the capacity performance of the coating material. Comparing Example 3 and Comparative Example 3, it can also be seen that the capacity of the cathode material obtained after secondary sintering in Example 3 is higher. At the same time, comparing each example, it can be seen that the cathode material of Example 1 with fewer and thinner atomic layer deposition layers exhibits the highest discharge capacity (292.9 mAh / g) and first-cycle Coulombic efficiency (93.4%). This is attributed to the fact that on the basis of liquid-phase coating, the precise regulation of atomic layer deposition improves the uniformity and consistency of the coating, and secondary sintering promotes the diffusion of Al elements into the bulk phase to form a solid electrolyte layer that promotes ion transport.

[0048] Figure 5 Fig. is the charge-discharge cycle curve of the batteries corresponding to Examples 1-4 and Comparative Examples 1-3 of the present invention, where the charge-discharge voltage range is 2-4.6 V and the charge-discharge rate is 0.33 C (nominal specific capacity is 250 mAh / g). It can be seen that the cycle stability of the modified lithium-rich manganese-based cathode material obtained in Example 1 is significantly better than that in Comparative Example 1, indicating that on the basis of liquid-phase coating, further atomic layer deposition coating can significantly improve the cycle stability of the lithium-rich manganese-based cathode material. This is because atomic layer deposition can fill the voids in the pre-coated alumina layer of the liquid-phase coating and improve its coating uniformity. Comparing Example 1 with Comparative Example 2, it can be seen that although atomic layer deposition was carried out in Comparative Example 2, but no secondary sintering was performed, resulting in a decrease in stability, indicating that secondary sintering can provide the stability of the cathode material. At the same time, among each example, under the premise of the highest capacity retention rate, the capacity performance of Example 1 is also the best among the examples. Therefore, thinner atomic layer deposition layers are not only beneficial to reducing costs, but also beneficial to the capacity performance of the material.

[0049] Figure 6 Fig. is the charge-discharge cycle curve at 45 °C of the batteries corresponding to Examples 1-4 and Comparative Examples 1-3 of the present invention, where the charge-discharge voltage range is 2-4.6 V and the charge-discharge rate is 0.33 C (nominal specific capacity is 250 mAh / g). It can be seen that the capacity performance of the composite-modified lithium-rich manganese-based cathode material in each example is significantly better than that in Comparative Example 1, indicating that after atomic layer deposition coating, the high-temperature stability of the lithium-rich manganese-based cathode material can be improved; at the same time, the composite-modified lithium-rich manganese-based cathode materials of Example 1 and Example 3 after secondary sintering at 300 °C have more advantages in terms of capacity performance and stability.

Claims

1. A preparation method of a composite modified lithium-rich manganese-based cathode material, characterized in that, Including: S1, dispersing the lithium-rich manganese-based cathode material in water to obtain a slurry; S2, adding an aluminum source to the slurry, adjusting the pH value to alkaline, performing a first reaction, then adjusting the pH value to 5-7, performing a second reaction, separating the solid and liquid, drying and sintering to obtain a primary coating material; S3, placing the primary coating material in an atomic layer deposition reaction chamber, evacuating, and heating to the reaction temperature; S4, introducing a first reaction precursor for reaction, purging with an inert gas, introducing a second reaction precursor for reaction, purging with an inert gas, repeating this step until a coating layer with a preset thickness is obtained; wherein, the first reaction precursor is an aluminum source, and the second reaction precursor is water; S5, sintering the product obtained in S4 to obtain a composite modified lithium-rich manganese-based cathode material.

2. The preparation method of the composite modified lithium-rich manganese-based cathode material according to claim 1, wherein, In S1, the molecular formula of the lithium-rich manganese-based cathode material is yLi2MnO3·(1-y)LiMO2, where M is one or more of Ni, Co, and Mn, and 0 < y < 1.

3. The preparation method of the composite modified lithium-rich manganese-based cathode material according to claim 1, characterized in that, In S2, the addition amount of the aluminum source satisfies that the atomic number of aluminum elements accounts for 1%-3% of the transition metal atomic number in the lithium-rich manganese-based cathode material.

4. The preparation method of the composite modified lithium-rich manganese-based cathode material according to claim 1, characterized in that In S2, the sintering is carried out in an air atmosphere, the sintering temperature is 300-600 °C, and the sintering time is 2-10 h.

5. The preparation method of the composite modified lithium-rich manganese-based cathode material according to claim 1, characterized in that In S4, the first reaction precursor is trimethylaluminum.

6. The preparation method of the composite modified lithium-rich manganese-based cathode material according to claim 1, characterized in that, S4 specifically is: introducing a first reaction precursor for reaction, purging with an inert gas, introducing a second reaction precursor for reaction, purging with an inert gas, introducing a third reaction precursor for reaction, purging with an inert gas, introducing a second reaction precursor for reaction, purging with an inert gas; repeating this step until a coating layer with a preset thickness is obtained; wherein, the first reaction precursor is an aluminum source, the second reaction precursor is water, and the third reaction precursor is a phosphorus source.

7. The preparation method of the composite modified lithium-rich manganese-based cathode material according to claim 1, wherein, In S5, the sintering is carried out in an air atmosphere, the sintering temperature is 300-600 °C, and the sintering time is 2-8 h.

8. A composite modified lithium-rich manganese-based cathode material obtained by using the preparation method described in any one of claims 1-7, characterized in that, The composite modified lithium-rich manganese-based cathode material from the inside out is successively a lithium-rich manganese-based cathode material, an alumina pre-coating layer, and an aluminide deposition layer.

9. The composite modified lithium-rich manganese-based cathode material according to claim 8, wherein, The thickness of the alumina pre-coating layer is 5-50 nm, and the thickness of the aluminide deposition layer is 0.5-2 nm.

10. A lithium-ion battery, characterized in that, Including the composite modified lithium-rich manganese-based cathode material described in claim 8.

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