A lithium-rich manganese-based positive electrode material, a preparation method and application thereof

Abstract

This invention provides a lithium-rich manganese-based cathode material, its preparation method, and its applications, belonging to the field of lithium-ion battery technology. This invention controls the particle size distribution of large and small lithium salt particles and their respective Dg. 50 The difference in concentration results in a higher melting concentration of large lithium salt particles and a lower melting concentration of small lithium salt particles during the sintering of lithium salt mixed with manganese-M precursor and dopant. This creates a differentiated local lithium salt concentration field in the microscopic space, allowing for precise control of the microscopic distribution of the two phases in the material. Then, the lithium-rich manganese-based sintered powder is mixed with a coating agent and sintered again to build a uniform and dense modified layer on the material surface. This effectively isolates the electrolyte from direct contact with the material body, reduces electrolyte oxidation and decomposition and transition metal dissolution at high potentials, and enhances the overall structural stability. This, in turn, improves the initial charge-discharge efficiency, discharge specific capacity, and cycle performance of the lithium-rich manganese-based cathode material, while also improving voltage decay.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, specifically relating to a lithium-rich manganese-based cathode material, its preparation method, and its application. Background Technology

[0002] With the rapid development of new energy vehicles, energy storage systems, and portable electronic devices, the market has placed comprehensive demands on lithium-ion batteries, including higher energy density, longer cycle life, lower cost, and higher safety. Traditional cathode materials are limited by their theoretical capacity limits, making it difficult to meet the needs of next-generation high-energy-density batteries; materials such as spinel lithium manganese oxide and lithium iron phosphate have the drawback of low energy density. Against this backdrop, lithium-rich manganese-based cathode materials, which combine ultra-high theoretical capacity, high operating voltage, and low cost, have become a key candidate cathode system for breaking through the energy density bottleneck of existing batteries and realizing large-scale commercial applications. They are also the core research direction in the current field of lithium-ion battery cathode materials.

[0003] Lithium-rich manganese-based materials (aLi2MnO3·(1-a)LiMn) x M y O2 (where 0.2≤a≤0.8, 0<x<1, x+y=1, and M is one or two of Ni and Co) has become a core candidate material for next-generation lithium batteries due to its ultra-high energy density and low cost potential. However, it also has inherent defects: on the one hand, the Li2MnO3 phase needs to be activated and delithiated at a high potential. The delithiation process is accompanied by irreversible precipitation of lattice oxygen, which will cause irreversible capacity loss during the first charge and discharge process. On the other hand, highly active lattice oxygen will continue to participate in side reactions during cycling, accompanied by manganese ion dissolution and lattice collapse, which will eventually lead to continuous voltage decay and rapid capacity decline, seriously restricting its practical application.

[0004] To address the aforementioned inherent defects, existing technologies primarily focus on modification studies related to elemental doping, surface coating, and pre-activation to alleviate oxygen evolution, suppress structural phase transitions, and improve interfacial stability. Elemental doping, by introducing heteroatoms to regulate the crystal structure, can enhance structural stability to some extent, but it is difficult to precisely control the microscopic distribution of the Li₂MnO₃ phase and the ternary phase, failing to fundamentally suppress oxygen evolution and structural phase transitions. Surface coating, by constructing a physical isolation layer to prevent electrolyte corrosion, can improve interfacial compatibility, but the coating layer is prone to damage at high potentials and cannot control the two-phase distribution and ion transport characteristics within the bulk material. While pre-activation processes can release some active oxygen in advance and reduce irreversible losses in the first cycle, they sacrifice some reversible capacity and have limited effectiveness in suppressing voltage decay during cycling.

[0005] In summary, existing modification technologies all passively alleviate inherent material defects and cannot simultaneously solve the problems of low initial charge-discharge efficiency, low discharge specific capacity, and severe cycle voltage decay. Summary of the Invention

[0006] The purpose of this invention is to provide a lithium-rich manganese-based cathode material, its preparation method, and its applications. The preparation method provided by this invention can improve the initial charge-discharge efficiency, discharge specific capacity, and cycle performance of the lithium-rich manganese-based cathode material, while also improving voltage decay.

[0007] To achieve the above-mentioned objectives, the present invention provides the following technical solution: A method for preparing a lithium-rich manganese-based cathode material includes the following steps: (1) The manganese-M precursor, lithium salt and dopant are mixed and then subjected to a first sintering to obtain lithium-rich manganese-based sintered powder; the lithium salt includes large-particle lithium salt and small-particle lithium salt; the D of the large-particle lithium salt is... 50 The particle size is 13~20μm and the span is ≤0.80; the D of the small lithium salt particles 50 The particle size is 3~7μm and the span is ≤0.80; and the D of the large-particle lithium salt is... 50 D with small-particle lithium salts 50 The difference is 9~12μm; (2) The lithium-rich manganese-based sintered powder obtained in step (1) is mixed with a coating agent and then subjected to a second sintering to obtain a lithium-rich manganese-based cathode material.

[0008] Preferably, in step (1), the mass ratio of large-particle lithium salt to small-particle lithium salt is (7.5~9):(1~3).

[0009] Preferably, the molar ratio of manganese-M precursor to lithium salt in step (1) is 1:(1.2~1.6).

[0010] Preferably, the temperature of the first sintering in step (1) is 700~1100℃ and the time of the first sintering is 8~20h.

[0011] Preferably, the chemical formula of the manganese-M precursor in step (1) is Mn. x M y (OH)₂, wherein M is Ni and / or Co, and 0.5 <x<1,0<y<0.5,x+y=1。

[0012] Preferably, the dopant in step (1) is a compound of at least one element selected from Li, Zr, Ti, Al, Mg, Co, Mn, Sr, Mo, Nb, W, B, F, P, N, H, and O; and the mass of the dopant is 300 to 30,000 ppm of the total mass of the manganese-M precursor.

[0013] Preferably, the temperature of the second sintering in step (2) is 200~1000℃, and the time of the second sintering is 2~15h.

[0014] Preferably, the coating agent in step (2) is a compound of at least one element selected from Li, Zr, Ti, Al, Mg, Co, Mn, Sr, Mo, Nb, W, B, F, P, N, H, and O; the mass of the coating agent is 300-5000 ppm of the mass of the lithium-rich manganese-based calcined powder.

[0015] This invention provides a lithium-rich manganese-based cathode material prepared by the preparation method described above.

[0016] This invention also provides the application of the lithium-rich manganese-based cathode material prepared by the above-described preparation method in lithium batteries.

[0017] This invention controls the particle size distribution of large and small lithium salts, and controls their D... 50 The difference results in a higher lithium salt concentration after the melting of large lithium salt particles and a lower lithium salt concentration after the melting of small lithium salt particles during the sintering of lithium salt mixed with manganese-M precursor and dopant. This leads to a differentiated local lithium salt concentration field in the microscopic space. The region near the large particles has relatively sufficient lithium salt, which induces the formation of more Li2MnO3 phase; the region near the small particles has relatively insufficient lithium salt, which is conducive to the formation of more ternary phase. This allows for precise control of the microscopic distribution of the two phases, Li2MnO3 and ternary phase, inside the material. This heterogeneous structure, characterized by "local ternary phase enrichment and overall two-phase coexistence" guided by differences in raw material particle size, significantly improves the initial charge-discharge efficiency by constructing continuous lithium-ion fast transport channels through the ternary phase enrichment region, reducing charge transfer resistance, and suppressing oxygen evolution during the first cycle. Furthermore, by optimizing the spatial distribution of the two phases and mitigating the lattice strain accumulated from asynchronous evolution of the phase interface, it effectively suppresses structural phase transformation and manganese dissolution during cycling, alleviates voltage decay, and enhances cycle stability. Then, a secondary sintering process is performed by mixing lithium-rich manganese-based calcined powder with a coating agent, which constructs a uniform and dense modified layer on the material surface. This effectively isolates the electrolyte from direct contact with the material bulk, reducing electrolyte oxidation and decomposition and transition metal dissolution at high potentials. Simultaneously, it further stabilizes the material surface lattice, suppresses interfacial side reactions and oxygen evolution, and strengthens the overall structural stability. The results of the examples show that the lithium-ion battery prepared using the lithium-rich manganese-based cathode material of this application has an initial charge-discharge efficiency of 88.4%, an average voltage decay of 1.76~1.82mV after 50 cycles, and a capacity retention rate of more than 93% after 50 cycles. Attached Figure Description

[0018] Figure 1 This is a particle size distribution diagram of the mixed lithium carbonate in Example 1 of the present invention; Figure 2 This is a SEM image of the lithium-rich manganese-based cathode material in Example 1 of the present invention; Figure 3It is the particle size distribution diagram of conventional lithium carbonate particles in Comparative Example 1 of the present invention; Figure 4 It is the SEM image of lithium-rich manganese-based cathode material in Comparative Example 1 of the present invention; Figure 5 It is the charge-discharge curve diagram of lithium-ion batteries prepared from the lithium-rich manganese-based cathode material in Example 1 and Comparative Example 1; Figure 6 It is the change curve diagram of cycle capacity retention rate versus cycle number of lithium-ion batteries prepared from the lithium-rich manganese-based cathode material in Example 1 and Comparative Example 1; Figure 7 It is the cycle voltage drop curve diagram of lithium-ion batteries prepared from the lithium-rich manganese-based cathode material in Example 1; Figure 8 It is the cycle voltage drop curve diagram of lithium-ion batteries prepared from the lithium-rich manganese-based cathode material in Comparative Example 1. Detailed Description of the Embodiments

[0019] The present invention provides a preparation method of a lithium-rich manganese-based cathode material, comprising the following steps: (1) Mixing a manganese-M precursor, a lithium salt and a dopant, followed by a first sintering to obtain a once-sintered lithium-rich manganese-based powder; the lithium salt comprises a large-particle lithium salt and a small-particle lithium salt; D of the large-particle lithium salt 50 is 13-20 μm and span ≤ 0.80; D of the small-particle lithium salt 50 is 3-7 μm and span ≤ 0.80; and the difference between D of the large-particle lithium salt 50 and D of the small-particle lithium salt 50 is 9-12 μm; (2) Mixing the once-sintered lithium-rich manganese-based powder obtained in step (1) with a coating agent, followed by a second sintering to obtain the lithium-rich manganese-based cathode material.

[0020] In the present invention, the manganese-M precursor, the lithium salt and the dopant are mixed and then subjected to a first sintering to obtain a once-sintered lithium-rich manganese-based powder.

[0021] As an embodiment of the present invention, the chemical formula of the manganese-M precursor can be Mn x M y (OH)₂, wherein in the chemical formula, M can be Ni and / or Co, and 0.5 < x < 1, 0 < y < 0.5, x+y=1. In an embodiment of the present invention, the manganese-M precursor is Ni 0.167 Co 0.167 Mn 0.666 (OH)₂, and D of the manganese-M precursor 50 is 3.5 μm.

[0022] In one embodiment of the present invention, the lithium salt may be lithium carbonate or lithium hydroxide. In an embodiment of the present invention, the lithium salt is lithium carbonate.

[0023] In this invention, the lithium salt includes large-particle lithium salt and small-particle lithium salt.

[0024] In this invention, the D of the large-particle lithium salt 50 The particle size is 13~20μm and the span is ≤0.80; as one embodiment of the present invention, the D of the large-particle lithium salt is... 50 The particle size can be 10.2~17.5μm, or even 10.2μm; the span of the large lithium salt particles can be 0.4~0.7.

[0025] In this invention, the D of the small-particle lithium salt 50 The particle size is 3~7μm, and the span is ≤0.80; as one embodiment of the present invention, the D of the small-particle lithium salt is... 50 The particle size can be 4.2~6.3μm; the span of the small lithium salt particles can be 0.5~0.6.

[0026] In this invention, the D of the large-particle lithium salt 50 D with small-particle lithium salts 50 The difference is 9~12μm, preferably 10~11μm.

[0027] This invention controls the particle size distribution of large and small lithium salts, and controls their D... 50 The difference in lithium salt concentration results in a higher lithium salt concentration after melting of large-particle lithium salt and a lower lithium salt concentration after melting of small-particle lithium salt during sintering. This leads to a differentiated local lithium salt concentration field in the microscopic space. The region near the large particles has relatively abundant lithium salt, inducing the formation of more Li2MnO3 phase; the region near the small particles has relatively insufficient lithium salt, which is conducive to the formation of more ternary phase. This allows for precise control of the microscopic distribution of Li2MnO3 and ternary phases within the material. This heterogeneous structure, guided by the difference in raw material particle size, characterized by "local ternary phase enrichment and overall coexistence of two phases," significantly improves the first charge-discharge efficiency by constructing continuous lithium-ion fast transport channels and reducing charge transfer resistance and suppressing oxygen evolution in the first cycle through the ternary phase enrichment region. Furthermore, by optimizing the spatial distribution of the two phases and alleviating the lattice strain accumulated by the asynchronous evolution of the phase interface, it effectively suppresses structural phase transformation and manganese dissolution during cycling, alleviates voltage decay, and enhances cycling stability.

[0028] In one embodiment of the present invention, the large and small lithium salt particles can be obtained by crushing and sieving. The present invention does not have special requirements for the crushing and sieving operations; methods well-known to those skilled in the art can be used to obtain lithium salts of the desired particle size.

[0029] In this invention, the preferred mass ratio of large-particle lithium salt to small-particle lithium salt is (7.5~9):(1~3), more preferably (7~8):(2~3). By controlling the mass ratio of large-particle lithium salt to small-particle lithium salt, this invention can balance the formation ratio of the ternary phase and the Li2MnO3 phase without changing the overall lithium content. This ensures the stability of the overall phase composition while maintaining the microstructure of locally enriched ternary phases. It also reduces interfacial impedance and suppresses oxygen evolution in the first cycle by relying on continuous ion transport channels, while slowing down the cycle phase transition and voltage decay, thereby improving the overall electrochemical performance of the material.

[0030] In this invention, the molar ratio of the manganese-M precursor to the lithium salt is preferably 1:(1.2~1.6), more preferably 1:1.5. By controlling the molar ratio of the manganese-M precursor to the lithium salt, this invention can optimize the two-phase spatial distribution without changing the overall lithium content, thereby achieving a balance between high capacity, high initial efficiency, and excellent cycle stability.

[0031] In one embodiment of the present invention, the dopant is a compound of at least one element selected from Li, Zr, Ti, Al, Mg, Co, Mn, Sr, Mo, Nb, W, B, F, P, N, H, and O; in an embodiment of the present invention, the dopant is MoO3.

[0032] In this invention, the mass of the dopant is preferably 300-30000 ppm of the total mass of the manganese-M precursor, more preferably 1500 ppm. By controlling the amount of dopant added, this invention can moderately broaden the lithium-ion diffusion channels, and the synergistic two-phase structure regulated by the lithium salt can further suppress lattice oxygen escape and cycling phase transitions, thereby improving the material's first-efficiency and cycling stability.

[0033] This invention does not impose any particular limitations on the mixing method and apparatus for the manganese-M precursor, lithium salt, and dopant; any conventional mixing method and apparatus that achieves uniform mixing is acceptable. As one embodiment of this invention, the mixing apparatus can be a high-speed mixer.

[0034] In this invention, the temperature of the first sintering is preferably 700~1100℃, more preferably 850℃; the time of the first sintering is preferably 8~20h, more preferably 13h. This invention ensures that the differentiated local lithium salt concentration field formed by large and small lithium salt particles is fully transformed into a spatially differentiated distribution of the two phases by controlling the temperature and time of the first sintering, thereby obtaining a lithium-rich manganese-based cathode material with high capacity, high initial efficiency, and excellent cycle stability.

[0035] As one embodiment of the present invention, the first sintering can be segmented sintering; in an embodiment of the present invention, the first sintering can be first held at 500°C for 3 hours in an air atmosphere, and then heated to 850°C at a rate of 5°C / min and held for 10 hours.

[0036] After the first sintering is completed, the present invention preferably cools the product obtained from the first sintering to obtain lithium-rich manganese-based sintered powder.

[0037] The present invention does not have special requirements for the specific cooling operation; any cooling method well known to those skilled in the art can be used to cool the lithium-rich manganese-based calcined powder to room temperature. As one embodiment of the present invention, the preferred cooling method is furnace-in-furnace cooling.

[0038] After obtaining lithium-rich manganese-based monocalcined powder, the present invention mixes the lithium-rich manganese-based monocalcined powder with a coating agent and then performs a second sintering to obtain lithium-rich manganese-based cathode material.

[0039] In one embodiment of the present invention, the coating agent is a compound of at least one element selected from Li, Zr, Ti, Al, Mg, Co, Mn, Sr, Mo, Nb, W, B, F, P, N, H, and O; in an embodiment of the present invention, the coating agent may be Al2O3.

[0040] The present invention does not impose any special limitations on the mixing method of the lithium-rich manganese-based calcined powder and the coating agent; any conventional mixing method that can achieve uniform mixing is acceptable.

[0041] This invention does not impose any particular limitations on the mixing device for lithium-rich manganese-based calcined powder and coating agent; conventional mixing devices are sufficient. As one embodiment of this invention, the mixing device can be a high-speed mixer.

[0042] In this invention, the mass of the coating agent is preferably 300-5000 ppm of the mass of the lithium-rich manganese-based calcined powder, more preferably 1500 ppm. By controlling the amount of coating agent added, this invention can effectively suppress voltage decay and cycle capacity loss without sacrificing capacity. This, combined with the two-phase spatially regulated bulk structure of this invention, forms an "internal and external synergistic" effect, enabling the lithium-rich manganese-based cathode material to maintain high initial charge-discharge efficiency while achieving superior cycle stability and lower voltage drop over its entire life cycle.

[0043] In this invention, the second sintering temperature is preferably 200~1000℃, more preferably 500℃; the second sintering time is preferably 2~15h, more preferably 5h. This invention, by controlling the temperature and time of the second sintering, ensures both the integrity and density of the coating layer while maintaining ion conductivity. Combined with the optimized two-phase structure of the matrix obtained through lithium salt gradation, it isolates electrolyte corrosion, inhibits surface oxygen evolution and transition metal dissolution, further stabilizes the material surface structure, and synergistically reduces cycle voltage decay and improves cycle stability.

[0044] After the second sintering is completed, the present invention preferably cools the product obtained from the second sintering to obtain a lithium-rich manganese-based cathode material.

[0045] The present invention does not have special requirements for the specific cooling operation; any cooling method well known to those skilled in the art can be used to cool the lithium-rich manganese-based cathode material to room temperature. As one embodiment of the present invention, the preferred cooling method is furnace-in-process cooling.

[0046] This invention provides a lithium-rich manganese-based cathode material prepared by the preparation method described above.

[0047] This invention also provides the application of the lithium-rich manganese-based cathode material prepared by the above-described preparation method in lithium batteries.

[0048] As one embodiment of the present invention, the positive electrode sheet in the lithium battery may include a current collector and a positive electrode material coated on the current collector. The positive electrode material includes the lithium-rich manganese-based positive electrode material described in the above technical solution, a conductive agent, and a binder. The content of the lithium-rich manganese-based positive electrode material in the positive electrode sheet may be 80% to 90%.

[0049] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0050] Example 1 A method for preparing lithium-rich manganese-based cathode material: (1) Particle size D 50 Lithium carbonate particles with a diameter of 121.3 μm and a span of 1.3 were pulverized using an air jet mill. The pulverization parameters were as follows: classification frequency of 23 Hz, feed frequency of 50 Hz, air pressure of 0.7 MPa, and induced draft fan frequency of 50 Hz. After pulverization, the resulting lithium carbonate powder was sieved through an 1800-mesh sieve (10 μm aperture) to separate particles of different sizes. The material remaining on the sieve was lithium carbonate D. 50Large lithium carbonate particles with a diameter of 15.1 μm and a span of 0.4; Particle size D 50 Lithium carbonate with a diameter of 121.3 μm and a span of 1.3 was pulverized using an air jet mill. The pulverization parameters were as follows: classification frequency of 55 Hz, feed frequency of 50 Hz, air pressure of 0.7 MPa, and induced draft fan frequency of 10 Hz. After pulverization, the resulting lithium carbonate powder was sieved through a 1000-mesh sieve (15 μm aperture) to separate particles of different sizes. The undersize particles were small lithium carbonate particles with a D50 of 4.2 μm and a span of 0.6. Large-particle lithium carbonate and small-particle lithium carbonate were mixed at a mass ratio of 8:2 to obtain mixed lithium carbonate. The particle size distribution of the mixed lithium carbonate was obtained by laser particle size analyzer. Figure 1 ; (2) Particle size D 50 =3.5μm manganese-M precursor Ni 0.167 Co 0.167 Mn 0.666 (OH)2 was mixed with mixed lithium carbonate and MoO3 using a high-speed mixer. The mixture was first kept at 500°C in air for 3 hours, and then heated to 850°C at a rate of 5°C / min and kept at that temperature for 10 hours. The mixture was then cooled in the furnace to obtain lithium-rich manganese-based calcined powder. The molar ratio of manganese-M precursor to mixed lithium carbonate was 1:1.5, and the mass of MoO3 was 5000 ppm of the total mass of manganese-M precursor.

[0051] (3) After mixing lithium-rich manganese-based calcined powder with Al2O3 using a high-speed mixer, the mixture was sintered at 400℃ for 5 hours to obtain lithium-rich manganese-based cathode material. The mass of Al2O3 was 1500 ppm of the mass of lithium-rich manganese-based calcined powder. The lithium-rich manganese-based cathode material prepared in this embodiment was observed using a scanning electron microscope, and the microstructure of the lithium-rich manganese-based cathode material was obtained as follows: Figure 2 As shown.

[0052] Example 2 A method for preparing lithium-rich manganese-based cathode material: (1) Particle size D 50 Lithium carbonate particles with a diameter of 121.3 μm and a span of 1.3 were pulverized using an air jet mill. The pulverization parameters were as follows: classification frequency of 21 Hz, feed frequency of 50 Hz, air pressure of 0.7 MPa, and induced draft fan frequency of 50 Hz. After pulverization, the resulting lithium carbonate powder was sieved through an 1800-mesh sieve (10 μm aperture) to separate particles of different sizes. The material remaining on the sieve was lithium carbonate D. 50 Large lithium carbonate particles with a diameter of 17.5 μm and a span of 0.8; Particle size D 50Lithium carbonate with a diameter of 121.3 μm and a span of 1.3 was pulverized using an air jet mill. The pulverization parameters were as follows: classification frequency of 52 Hz, feed frequency of 50 Hz, air pressure of 0.7 MPa, and induced draft fan frequency of 10 Hz. After pulverization, the resulting lithium carbonate powder was sieved through a 1000-mesh sieve (15 μm aperture) to separate particles of different sizes. The undersize particles were small lithium carbonate particles with a D50 of 6.3 μm and a span of 0.8. Large-particle lithium carbonate and small-particle lithium carbonate are mixed at a mass ratio of 8:2 to obtain mixed lithium carbonate. The first sintering and the second sintering were carried out using the same methods as in Example 1 (2) and (3) to obtain lithium-rich manganese-based cathode material.

[0053] Comparative Example 1 A method for preparing lithium-rich manganese-based cathode material: (1) Particle size D 50 Lithium carbonate particles with a diameter of 121.3 μm and a span of 1.3 were pulverized using an air jet mill. The pulverization parameters were as follows: classification frequency of 35 Hz, feed frequency of 50 Hz, air pressure of 0.7 MPa, and induced draft fan frequency of 20 Hz. After pulverization, D... 50 The mixed lithium carbonate, consisting of standard lithium carbonate particles with a diameter of 6.5 μm and a span of 1.7, was analyzed using a laser particle size analyzer. The particle size distribution of the standard lithium carbonate particles is shown in the figure. Figure 3 ; (2) Particle size D 50 =3.5μm manganese-M precursor Ni 0.167 Co 0.167 Mn 0.666 (OH)2 was mixed with conventional particulate lithium carbonate and MoO3 using a high-speed mixer. The mixture was first kept at 500°C in air for 3 hours, and then heated to 850°C at a rate of 5°C / min and kept at 850°C for 10 hours. The mixture was then cooled in the furnace to obtain lithium-rich manganese-based calcined powder. The molar ratio of manganese-M precursor to conventional particulate lithium carbonate was 1:1.5, and the mass of MoO3 was 5000 ppm of the total mass of manganese-M precursor. (3) After mixing lithium-rich manganese-based calcined powder with Al2O3 using a high-speed mixer, the mixture was sintered at 400℃ for 5 hours to obtain lithium-rich manganese-based cathode material. The mass of Al2O3 was 1500 ppm of the mass of lithium-rich manganese-based calcined powder. The lithium-rich manganese-based cathode material prepared in this comparative example was observed using a scanning electron microscope, and the microstructure of the lithium-rich manganese-based cathode material was as follows: Figure 4 As shown.

[0054] Comparative Example 2 A method for preparing lithium-rich manganese-based cathode material: (1) The large-particle lithium salt and small-particle lithium carbonate prepared in Example 1 (1) are mixed at a mass ratio of 9:1 to obtain mixed lithium carbonate. The first and second sintering processes were carried out using the same methods as in Example 1 (2) and (3) to obtain lithium-rich manganese-based cathode materials.

[0055] Comparative Example 3 A method for preparing lithium-rich manganese-based cathode material: (1) The large-particle lithium salt and small-particle lithium carbonate prepared in Example 1 (1) are mixed at a mass ratio of 7:3 to obtain mixed lithium carbonate; The first and second sintering processes were carried out using the same methods as in Example 1 (2) and (3) to obtain lithium-rich manganese-based cathode materials.

[0056] Comparative Example 4 A method for preparing lithium-rich manganese-based cathode material: (1) Particle size D 50 Lithium carbonate particles with a diameter of 121.3 μm and a span of 1.3 were pulverized using an air jet mill. The pulverization parameters were as follows: classification frequency of 18 Hz, feed frequency of 50 Hz, air pressure of 0.7 MPa, and induced draft fan frequency of 50 Hz. After pulverization, the resulting lithium carbonate powder was sieved through an 1800-mesh sieve (10 μm aperture) to separate particles of different sizes. The material remaining on the sieve was lithium carbonate D. 50 Large lithium carbonate particles with a diameter of 20.4 μm and a span of 0.7; Particle size D 50 Lithium carbonate with a diameter of 121.3 μm and a span of 1.3 was pulverized using an air jet mill. The pulverization parameters were as follows: classification frequency of 55 Hz, feed frequency of 50 Hz, air pressure of 0.7 MPa, and induced draft fan frequency of 10 Hz. After pulverization, the resulting lithium carbonate powder was sieved through a 1000-mesh sieve (15 μm aperture) to separate particles of different sizes. The undersize particles were small lithium carbonate particles with a D50 of 4.2 μm and a span of 0.6. Large-particle lithium carbonate and small-particle lithium carbonate are mixed at a mass ratio of 8:2 to obtain mixed lithium carbonate. The first and second sintering processes were carried out using the same methods as in Example 1 (2) and (3) to obtain lithium-rich manganese-based cathode materials.

[0057] Comparative Example 5 A method for preparing lithium-rich manganese-based cathode material: (1) Large-particle lithium carbonate was prepared by the method for preparing large-particle lithium carbonate in Example (1); The conventional granular lithium carbonate obtained in Comparative Example (1) was sieved through an 1800-mesh sieve (pore size of 10 μm) to separate the particles of different sizes. The material remaining on the sieve was lithium carbonate with D50=10.2 μm and span=0.8. Large-particle lithium carbonate and lithium carbonate are mixed at a mass ratio of 8:2 to obtain mixed lithium carbonate; The first and second sintering processes were carried out using the same methods as in Example 1 (2) and (3) to obtain lithium-rich manganese-based cathode materials.

[0058] Comparative Example 6 A method for preparing lithium-rich manganese-based cathode material: (1) Particle size D 50 Lithium carbonate particles with a diameter of 121.3 μm and a span of 1.3 were agglomerated using an air jet mill. The milling parameters were as follows: classification frequency of 18 Hz, feed frequency of 50 Hz, air pressure of 0.7 MPa, and induced draft fan frequency of 50 Hz. D was obtained. 50 Large-particle pulverized lithium carbonate with a diameter of 18.2 μm and a span of 1.1; Particle size D 50 Lithium carbonate particles with a diameter of 121.3 μm and a span of 1.3 were agglomerated using an air jet mill. The milling parameters were as follows: classification frequency 55 Hz, feed frequency 50 Hz, air pressure 0.7 MPa, and induced draft fan frequency 10 Hz. D was obtained. 50 Lithium carbonate pulverized into small particles with a diameter of 6.9 μm and a span of 1.8 μm; Large-particle pulverized lithium carbonate and small-particle pulverized lithium carbonate are mixed at a mass ratio of 8:2 to obtain mixed lithium carbonate. The first and second sintering processes were carried out using the same methods as in Example 1 (2) and (3) to obtain lithium-rich manganese-based cathode materials.

[0059] Test case The lithium-rich manganese-based cathode materials obtained in Examples 1-2 and Comparative Examples 1-4 were used to fabricate lithium-ion batteries: (1) Preparation of positive electrode sheet: Lithium-rich manganese-based positive electrode material, conductive carbon black, and polyvinylidene fluoride were mixed and ground evenly in a mortar at a mass ratio of 8:1:1. During the grinding process, the mixture was stirred at a rate of 0.08 mL / min. -1 Add an appropriate amount of NMP dropwise to adjust the viscosity of the slurry. After thorough grinding, mix the slurry at a rate of 8.5 mg / cm³. 2 The coating density is uniformly coated on the current collector aluminum foil and dried at 80℃ for 2 days. After the electrode is dried, the electrode is cut into circular electrode sheets with a diameter of 15mm using a punching machine. The mass of a single electrode sheet is weighed using an electronic balance and placed in a glove box (H2O concentration <1ppm, oxygen concentration <0.2ppm) for later use.

[0060] (2) Assembly of button cells: Using lithium foil as the negative electrode, 1 mol / L LiPF6 is dissolved in EC-EMC-DMC (volume ratio 1:1:1) as the electrolyte. The button cells are assembled in a glove box filled with argon gas. From top to bottom, they are: positive electrode shell, positive electrode, electrolyte, separator, electrolyte, lithium foil, and negative electrode shell.

[0061] The cathode materials and corresponding lithium-ion batteries prepared in Examples 1-2 and Comparative Examples 1-4 were tested as follows, and the results are shown in Table 1: (1) Initial discharge specific capacity: The test voltage was 2.0~4.8V, and the test was conducted at a rate of 0.1C. The initial charge-discharge curves of Example 1 and Comparative Example 1 are shown below. Figure 5 As shown.

[0062] (2) Cycle capacity retention: The test voltage is 2.0~4.6V, and the ratio of the discharge specific capacity after each cycle to the discharge specific capacity at the first cycle is measured under the 1C rate test condition. The cycle capacity retention curves of Example 1 and Comparative Example 1 as a function of the number of cycles are shown below. Figure 6 As shown.

[0063] (3) Average voltage decay over 50th percentile: The test voltage is 2.0~4.6V, and the calculation formula is: (1st average voltage - 50th average voltage) / 50 1000, the cyclic voltage drop curves of Example 1 and Comparative Example 1 are respectively as follows: Figure 7 and Figure 8 As shown.

[0064] Table 1. Performance of lithium-ion batteries prepared using lithium-rich manganese-based electrode materials from Examples 1-2 and Comparative Examples 1-4

[0065] from Figure 1 and Figure 3 It can be seen that by using crushing and sieving processes, followed by mixing, the particle size distribution of lithium carbonate can be significantly changed, resulting in a mixed lithium carbonate with a suitable ratio of particle sizes. This allows the prepared cathode material to have both high capacity and excellent cycle performance.

[0066] from Figure 2 and Figure 4 It can be seen that the cathode material obtained by sintering lithium salts with mixed large and small particles exhibits uneven particle size on the surface compared to the cathode material obtained by sintering conventional lithium salts, while conventional lithium salts have uniform particles.

[0067] from Figure 5 It can be seen that the specific capacity of lithium carbonate with mixed large and small particles is the same as that of conventional lithium salts, and it is not reduced.

[0068] from Figures 6-8 As shown in Table 1, the cathode materials of Examples 1 and 2, prepared using mixed lithium carbonate with appropriate particle size ratio, exhibit high initial efficiency (88.4% in the first charge), low voltage drop (1.76mV average voltage drop after 50 cycles), and excellent cycle performance (≥93.8% capacity retention after 50 cycles). In contrast, the cathode materials of Comparative Example 1, prepared using conventional particle size lithium carbonate, Comparative Examples 2 and 3, prepared using mixed lithium carbonate with inappropriate particle size ratio, Comparative Examples 4 and 5, prepared using Span but with excessive particle size difference, and Comparative Example 6, prepared using particle size difference but without Span, failed to achieve high initial efficiency, low voltage drop, and excellent cycle performance.

[0069] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a lithium-rich manganese-based cathode material, characterized in that, Includes the following steps: (1) The manganese-M precursor, lithium salt, and dopant are mixed and then subjected to a first sintering to obtain lithium-rich manganese-based sintered powder; the lithium salt includes large-particle lithium salt and small-particle lithium salt; the D of the large-particle lithium salt is... 50 The particle size is 13~20μm and the span is ≤0.80; the D of the small lithium salt particles 50 The particle size is 3~7μm and the span is ≤0.80; and the D of the large-particle lithium salt is... 50 D with small-particle lithium salts 50 The difference is 9~12μm; (2) The lithium-rich manganese-based sintered powder obtained in step (1) is mixed with a coating agent and then subjected to a second sintering to obtain a lithium-rich manganese-based cathode material.

2. The preparation method according to claim 1, characterized in that, In step (1), the mass ratio of large-particle lithium salt to small-particle lithium salt is (7.5~9):(1~3).

3. The preparation method according to claim 1 or 2, characterized in that, In step (1), the molar ratio of manganese-M precursor to lithium salt is 1:(1.2~1.6).

4. The preparation method according to claim 1, characterized in that, The temperature of the first sintering in step (1) is 700~1100℃, and the time of the first sintering is 8~20h.

5. The preparation method according to claim 1, characterized in that, The chemical formula of the manganese-M precursor in step (1) is Mn x M y (OH)₂, wherein M is Ni and / or Co, and 0.5 <x<1,0<y<0.5,x+y=1。 6. The preparation method according to claim 1, characterized in that, In step (1), the dopant is a compound of at least one element selected from Li, Zr, Ti, Al, Mg, Co, Mn, Sr, Mo, Nb, W, B, F, P, N, H, and O; the mass of the dopant is 300 to 30,000 ppm of the total mass of the manganese-M precursor.

7. The preparation method according to claim 1, characterized in that, The temperature of the second sintering in step (2) is 200~1000℃, and the time of the second sintering is 2~15h.

8. The preparation method according to claim 1, characterized in that, In step (2), the coating agent is a compound of at least one element selected from Li, Zr, Ti, Al, Mg, Co, Mn, Sr, Mo, Nb, W, B, F, P, N, H, and O; the mass of the coating agent is 300-5000 ppm of the mass of the lithium-rich manganese-based calcined powder.

9. The lithium-rich manganese-based cathode material prepared by the preparation method according to any one of claims 1 to 8.

10. The application of the lithium-rich manganese-based cathode material according to claim 9 in lithium batteries.

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