A lithium-rich manganese-based precursor, a preparation method thereof, a cathode material and a lithium ion battery

Abstract

This invention relates to a lithium-rich manganese-based precursor and its preparation method, a cathode material, and a lithium-ion battery. The lithium-rich manganese-based precursor comprises spherical or near-spherical secondary particles. Each secondary particle includes a first part and a second part, with the first part being closer to the center of the secondary particle than the second part. The secondary particles contain Mn and Ni elements. The molar percentage of Mn in the first part is greater than that in the second part; the molar percentage of Ni in the first part is less than that in the second part. This invention can improve the structural stability of the lithium-rich manganese-based cathode material.

Description

Technical Field

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

[0002] Lithium-rich manganese-based cathode material xLi2MnO3·(1-x)LiMO2 is considered an ideal cathode material for next-generation high-energy-density lithium-ion power batteries due to its ultra-high specific capacity exceeding 250 mAh / g. Currently, in industry, hydroxide or carbonate precursors are mainly prepared by co-precipitation, and then mixed with lithium source and sintered to obtain polycrystalline cathode materials.

[0003] However, traditional polycrystalline lithium-rich manganese-based cathode materials face three major challenges in application: low initial coulombic efficiency, poor rate performance, and short cycle life. Among these, short cycle life is the key bottleneck restricting its commercialization. The root cause lies in the fact that in polycrystalline materials sintered from traditional dense spherical precursors, the anisotropic volume changes of primary particles during long cycles lead to intergranular cracks within secondary particles, resulting in poor structural stability of lithium-rich manganese-based cathode materials. This, in turn, causes electrolyte infiltration, exacerbates side reactions, and leads to particle pulverization. Summary of the Invention

[0004] One objective of this invention is to provide a lithium-rich manganese-based precursor to solve the problem of poor structural stability of lithium-rich manganese-based cathode materials in the prior art; another objective is to provide a method for preparing a lithium manganese-based precursor; a third objective is to provide a cathode material; and a fourth objective is to provide a lithium-ion battery.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A lithium-rich manganese-based precursor, comprising spherical or near-spherical secondary particles; the secondary particles comprising a first part and a second part, wherein the first part is closer to the center of the secondary particles than the second part. The secondary particles contain Mn and Ni elements; the molar percentage of Mn in the first part is greater than that in the second part; the molar percentage of Ni in the first part is less than that in the second part.

[0006] According to the above-mentioned technical means, the first part is the core region close to the center of the secondary particles, and the second part is the shell region far away from the center of the secondary particles. The gradient setting of Mn element decreasing from the first part to the second part and Ni element increasing makes the cell parameters of the secondary particles transition smoothly from the center to the surface, effectively eliminating the lattice mismatch and interface stress caused by abrupt changes in composition in the traditional core-shell structure; at the same time, the first part with higher manganese content forms a structural anchor for the second part with higher nickel content on the surface through continuous lattice connection, suppressing the cation mixing that is prone to occur in the higher nickel region, thereby significantly improving the long-term cycle structural stability of the lithium-rich manganese-based precursor after subsequent sintering into a cathode material.

[0007] Furthermore, in the secondary particles, the molar percentage of Mn decreases linearly or stepwise from the interior of the first part to the surface of the second part away from the first part along the radial direction. The molar percentage of Ni increases linearly or stepwise.

[0008] Based on the above technical means, the cell parameters of the secondary particles transition smoothly and continuously from the center to the surface, effectively suppressing the cation mixing and phase transition that are prone to occur in the high nickel region during charging and discharging. In addition, the linear or stepwise change provides clear process controllability, allowing both continuous gradient growth and multi-layer stepwise deposition. While reducing internal stress, it significantly improves the cycle stability and structural integrity of the cathode material obtained after sintering the lithium-rich manganese-based precursor.

[0009] Furthermore, the change in the molar percentage of Mn decreasing linearly or stepwise is greater than or equal to 15 mol; and / or, the change in the molar percentage of Ni increasing linearly or stepwise is greater than or equal to 15 mol.

[0010] Based on the aforementioned technical means, the aforementioned change threshold ensures a sufficiently wide compositional transition range between the higher manganese first part (core region) and the higher nickel second part (shell region), thereby more effectively eliminating residual lattice mismatch stress caused by small changes or abrupt changes in traditional core-shell structures. At the same time, the second part (shell region) has a sufficiently high Ni content to improve capacity, while the first part (core region) maintains a sufficiently high Mn content to maintain the chemical stability of the structural framework, suppressing cation mixing and microcrack propagation in the higher nickel region during long cycles. Thus, based on the aforementioned stability improvement, the cycle life of the cathode material is significantly extended and the structural retention capability under high voltage is improved.

[0011] Furthermore, the secondary particles are composed of primary particles with plate-like structures stacked together; the thickness of the primary particles ranges from 20 nm to 100 nm; and / or, the diameter of the primary particles ranges from 200 nm to 800 nm.

[0012] Based on the aforementioned technical means, an "interlocking pinning" structure can be formed in the first part (core region). The thin, plate-like primary particles within this size range possess high bending stiffness and packing density. The mechanical interlocking effect generated by the cross-stacking significantly suppresses the radial cracking tendency of secondary particles during charge-discharge volume changes. Simultaneously, the interlocking pinning structure in the first part (core region) serves as a skeletal support point, effectively extending cycle life and reducing capacity decay caused by particle breakage while maintaining the integrity of the lithium-rich manganese-based precursor and subsequent cathode material particles. Furthermore, the primary particle thickness range of 20nm to 100nm provides ample and interconnected channels for lithium-ion diffusion and gas release during subsequent sintering, effectively avoiding uneven lithiation due to insufficient porosity and loose particle structure due to excessive porosity.

[0013] Furthermore, the porosity of the first part ranges from 20% to 40%.

[0014] According to the above technical means, the porosity of the first part is controlled between 20% and 40%, which provides sufficient and connected channels for lithium ion diffusion and gas release in the subsequent sintering process. This effectively avoids uneven lithiation caused by too few pores and loose particle structure caused by too many pores. Therefore, the cathode material obtained by sintering the lithium-rich manganese-based precursor can achieve a discharge specific capacity of more than 290 mAh / g at a 0.1C rate and an initial coulombic efficiency of more than 88%. This indicates that the high porosity brings good electrolyte wetting and lithium ion transport path. Combined with the aforementioned gradient composition and "interlocking pinning" structure, it achieves a synergistic improvement in high capacity and high initial efficiency.

[0015] Furthermore, the total porosity of the first part is greater than that of the second part.

[0016] According to the above technical means, the high and uniformly distributed porosity in the first part (core region) can effectively absorb and buffer the micro-strain caused by lattice expansion / contraction during charging and discharging, and avoid stress accumulation inside the particle leading to the initiation of microcracks; while the relatively dense structure of the second part (shell region) maintains the integrity of the particle surface while ensuring lithium ion transport.

[0017] Furthermore, the total porosity of the second part is 4% to 10%, and the ratio of the total porosity of the first part to the total porosity of the second part is approximately 3 to 7.

[0018] Based on the aforementioned technical means, the total porosity of the second part (outer shell region) is controlled at 4%-10%, forming a dense surface protective layer that effectively blocks excessive erosion of the high-nickel second part (outer shell region) by the electrolyte and suppresses surface side reactions. Simultaneously, the ratio of the total porosity of the first part to the second part ranges from 3 to 7, ensuring that the porosity difference between the inner and outer layers is not too large, thus preventing stress abrupt changes or delamination at the interface. The 20%-40% high-porosity region in the first part (core region) is uniformly distributed, fully absorbing and buffering the micro-strain caused by lattice expansion / contraction during charging and discharging. Meanwhile, the 4%-10% low porosity of the second part (outer shell region) maintains the integrity of the particle surface structure and mechanical strength while ensuring rapid lithium-ion transport, suppressing microcrack propagation and capacity decay during long-term cycling.

[0019] Furthermore, the ratio of the thickness of the second part to the radius of the secondary particles ranges from 0.5 to 0.6.

[0020] Based on the aforementioned technical means, the second part (outer shell region) with a higher nickel content can have sufficient structural thickness to support high-capacity output, while avoiding the first part (core region) from being exposed to the electrolyte during cycling due to an excessively thin second part (outer shell region). The thicker second part (outer shell region), combined with its low porosity of less than 10%, forms a robust surface protective layer, effectively suppressing side reactions and surface phase transitions between the high-nickel region and the electrolyte. Simultaneously, the first part (core region) can fully absorb and buffer the lattice expansion / contraction micro-strain during charge and discharge processes. With an inner-outer layer thickness ratio of 0.5~0.6, and combined with a linear or stepwise gradient change (≥15 mol%) of Mn and Ni along the radial direction from the first part (core region) to the second part (outer shell region), the cell parameters achieve a full and smooth continuous transition from the center to the surface, eliminating interfacial stress concentration and exhibiting excellent crack resistance and structural stability during long cycles.

[0021] Furthermore, the precursor has the chemical formula Ni x Mn M 1-x- (CO3) or Ni x Mn M 1-x- (OH)2, wherein M is at least one of Co, Al, Mg, and Ti.

[0022] Based on the above technical means, the synergistic effect of buffering micro-strain in the first part (core region), dense protection in the second part (outer shell region), and continuous lattice matching is achieved, further improving the long-cycle structural stability of lithium-rich manganese-based precursors.

[0023] A method for preparing a lithium-rich manganese-based precursor includes: preparing spherical or near-spherical secondary particles, and stacking multiple secondary particles to form a lithium-rich manganese-based precursor; wherein the secondary particles contain Mn and Ni elements; the molar percentage of Mn element in the first part is greater than the molar percentage of Mn element in the second part; and the molar percentage of Ni element in the first part is less than the molar percentage of Ni element in the second part.

[0024] Understandably, the embodiments of the present invention provide a method for preparing a lithium-rich manganese-based precursor, and the beneficial effects that can be achieved can be referred to the beneficial effects of the lithium-rich manganese-based precursor mentioned above, which will not be repeated here.

[0025] Further, the preparation of spherical or near-spherical secondary particles includes: providing an alkaline base solution, the base solution comprising a complexing agent and a precipitating agent; adding a nickel-manganese mixed salt solution to the base solution to perform a co-precipitation reaction to obtain a lithium-rich manganese-based precursor; wherein, during the addition of the nickel-manganese mixed salt solution to the base solution, the molar ratio of Mn to Ni in the nickel-manganese mixed salt solution is adjusted so that the molar ratio of Mn to Ni in the nickel-manganese mixed salt solution gradually decreases with the time of the co-precipitation reaction.

[0026] Based on the above technical means, by continuously reducing the molar ratio of Mn / Ni in the nickel-manganese mixed salt solution during the co-precipitation reaction, Mn and Ni form a linear or stepwise gradient distribution along the radial direction of the secondary particles. The resulting lithium-rich manganese-based precursor cathode material exhibits excellent structural stability during long-cycle operation.

[0027] Furthermore, the coprecipitation reaction includes at least a first stage reaction and a second stage reaction, wherein the stirring speed of the first stage reaction is greater than the stirring speed of the second stage reaction; wherein the first stage reaction is the first part of the growth stage, and the second stage reaction is the second part of the growth stage.

[0028] Based on the above technical means, a high-porosity core is grown by a first stage of high stirring speed and a low-porosity dense shell is grown by a second stage of low stirring speed. In combination with the gradual decrease of the Mn / Ni ratio in the salt solution to achieve a radially large change in composition gradient, and the plate-like primary particle interlocking pinning in the core region, the cathode material can suppress particle cracking during long-term cycling.

[0029] A cathode material comprising: a lithium-containing material and any one of the above-mentioned lithium-rich manganese-based precursors.

[0030] Understandably, the embodiments of the present invention provide a cathode material whose beneficial effects can be referred to the beneficial effects of the lithium-rich manganese-based precursor mentioned above, and will not be repeated here.

[0031] A lithium-ion battery, comprising: the positive electrode material as described above.

[0032] Understandably, the embodiments of the present invention provide a lithium-ion battery, the beneficial effects of which can be referred to the beneficial effects of the lithium-rich manganese-based precursor mentioned above, and will not be repeated here.

[0033] The beneficial effects of this invention are: (1) In the lithium-rich manganese-based precursor of the present invention, the lithium-rich manganese-based precursor includes spherical or near-spherical secondary particles; the secondary particles include a first part and a second part, the first part being closer to the center of the secondary particles than the second part. The first part is the core region close to the center of the secondary particles, and the second part is the shell region far from the center of the secondary particles. The gradient setting of Mn element decreasing from the first part to the second part and Ni element increasing makes the cell parameters of the secondary particles transition smoothly from the center to the surface, effectively eliminating the lattice mismatch and interface stress caused by the abrupt change in composition in the traditional core-shell structure; at the same time, the first part with higher manganese content forms a structural anchor to the second part with higher nickel content on the surface through continuous lattice connection, suppressing the cation mixing that is prone to occur in the higher nickel region, thereby significantly improving the long-term cycle structural stability of the lithium-rich manganese-based precursor after subsequent sintering into a cathode material.

[0034] (2) In the lithium-rich manganese-based precursor of the present invention, in the secondary particles, the molar percentage of Mn element decreases linearly or stepwise from the interior of the first part to the surface of the second part away from the first part in the radial direction, and the molar percentage of Ni element increases linearly or stepwise. This makes the cell parameters of the secondary particles transition continuously and smoothly from the center to the surface, avoiding the lattice mismatch and interface stress concentration caused by abrupt changes in composition in the traditional core-shell structure. At the same time, this gradient setting allows the first part with higher manganese to form a structural anchoring effect on the second part with higher nickel through continuous lattice connection, effectively suppressing the cation mixing and phase transition that are prone to occur in the higher nickel region during charging and discharging. In addition, the linear or stepwise change provides clear process controllability, allowing both continuous gradient growth and multi-layer stepwise deposition. While reducing internal stress, it significantly improves the cycle stability and structural integrity of the cathode material obtained after sintering the lithium-rich manganese-based precursor. After 100 cycles at 1C, the capacity retention rate can still reach more than 90%.

[0035] (3) In the lithium-rich manganese-based precursor of the present invention, the porosity of the first part is in the range of 20%~40%, which provides sufficient and connected channels for lithium ion diffusion and gas release in the subsequent sintering process. It effectively avoids uneven lithiation caused by too few pores and loose particle structure caused by too many pores. Therefore, the cathode material obtained by sintering the lithium-rich manganese-based precursor can achieve a discharge specific capacity of more than 290 mAh / g at a rate of 0.1C and an initial coulombic efficiency of more than 88%, indicating that the high porosity brings good electrolyte wetting and lithium ion transport path. Combined with the aforementioned gradient composition and "interlocking pinning" structure, it achieves a synergistic improvement of high capacity and high initial efficiency.

[0036] (4) The secondary particles of the lithium-rich manganese-based precursor of the present invention are composed of primary particles with plate-like morphology stacked together. The thickness of the primary particles ranges from 20 nm to 100 nm, and an "interlocking pinning" structure can be formed in the first part (core region). The thin plate-like primary particles in this size range have high bending stiffness and packing density. The mechanical interlocking effect generated by the cross-stacking significantly suppresses the radial cracking tendency of the secondary particles during charge and discharge volume changes. At the same time, the interlocking pinning structure in the first part (core region) serves as a skeleton support point, dispersing and transferring the volume expansion stress to the entire secondary particle, avoiding local stress concentration. Thus, while maintaining the integrity of the lithium-rich manganese-based precursor and subsequent cathode material particles, the cycle life is effectively extended and the capacity decay caused by particle breakage is reduced. Attached Figure Description

[0037] Figure 1 This is a flowchart of the method for preparing spherical or near-spherical secondary particles according to the present invention; Figure 2 A scanning electron microscope image of a cross-section of the lithium-rich manganese-based precursor of the present invention; Figure 3 This is a scanning electron microscope image of the cathode material of the present invention; Figure 4 This is a comparison chart of the first charge-discharge performance of the cathode materials of Example 1 and Comparative Examples 1 to 3 of the present invention at 0.1C. Figure 5 This is a comparison chart of the cycling performance of the cathode materials of Example 1 and Comparative Examples 1 to 3 of the present invention at 1C. Detailed Implementation

[0038] The embodiments of the present invention will be described below with reference to the accompanying drawings and preferred embodiments. 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. It should be understood that the preferred embodiments are only for illustrating the present invention and not for limiting the scope of protection of the present invention.

[0039] An embodiment of the present invention provides a lithium-ion battery, comprising: a positive electrode material.

[0040] The cathode material can be a lithium-rich manganese-based cathode material.

[0041] An embodiment of the present invention provides a cathode material, comprising: a lithium-containing material and a lithium-rich manganese-based precursor.

[0042] In some examples, the cathode material can be obtained by mixing a lithium-rich manganese-based precursor with a lithium source and then sintering it.

[0043] For example, the sintering temperature can be 700℃~950℃, the sintering heating rate can be 1℃ / min~3℃ / min, and the sintering time can be 8h~20h.

[0044] For example, sintering can be carried out in two steps: heating to 450℃~600℃ at 1℃ / min~3℃ / min and holding for 3h~6h; then continuing to heat to 700℃~950℃ at 1℃ / min~2℃ / min and holding for 8h~20h.

[0045] However, the structural stability of cathode materials in existing technologies is relatively poor.

[0046] In some implementations, doping is used to improve the structural stability of the cathode material and reduce electrolyte side reactions. However, these are mostly post-processing or local optimization of morphology, and fail to fundamentally solve the problem of poor internal structural stability of polycrystalline materials.

[0047] Based on this, embodiments of the present invention provide a lithium-rich manganese-based precursor, which includes spherical or near-spherical secondary particles; the secondary particles include a first part and a second part, wherein the first part is closer to the center of the secondary particles than the second part.

[0048] The secondary particles contain Mn and Ni elements; the molar percentage of Mn in the first part is greater than that in the second part; the molar percentage of Ni in the first part is less than that in the second part.

[0049] Here, the first part can be understood as the core region near the center of the secondary particle, and the second part can be understood as the outer shell region far from the center of the secondary particle.

[0050] Understandably, the gradient setting of decreasing Mn and increasing Ni from the first part to the second part allows for a smooth transition of cell parameters from the center to the surface of the secondary particles, effectively eliminating lattice mismatch and interfacial stress caused by abrupt changes in composition in traditional core-shell structures. At the same time, the first part with higher manganese content forms a structural anchor to the second part with higher nickel content on the surface through continuous lattice connections, suppressing the cation mixing that is prone to occur in the higher nickel region, thereby significantly improving the long-term cycle stability of the lithium-rich manganese-based precursor after subsequent sintering into a cathode material.

[0051] In some embodiments, in the secondary particles, the molar percentage of Mn decreases linearly or stepwise and the molar percentage of Ni increases linearly or stepwise from the interior of the first portion to the surface of the second portion away from the first portion in the radial direction.

[0052] Understandably, from the interior of the first part (core region) to the surface of the second part (shell region) radially, the Mn content decreases linearly or stepwise, while the Ni content increases linearly or stepwise. This means that the secondary particles exhibit a "full concentration gradient," resulting in a continuous and smooth transition of the cell parameters from the center to the surface. This avoids the lattice mismatch and interfacial stress concentration caused by abrupt changes in composition in traditional core-shell structures. Simultaneously, this gradient setting allows the higher-manganese first part to form a structural anchoring effect on the higher-nickel second part through continuous lattice connections, effectively suppressing cation mixing and phase transitions that are prone to occur in the higher-nickel region during charging and discharging. Furthermore, the linear or stepwise change provides clear process controllability, allowing both continuous gradient growth and multi-layer stepwise deposition. While reducing internal stress, this significantly improves the cycle stability and structural integrity of the cathode material obtained after sintering the lithium-rich manganese-based precursor.

[0053] In some embodiments, the change in the molar percentage of Mn decreasing linearly or stepwise is greater than or equal to 15 mol; and / or, the change in the molar percentage of Ni increasing linearly or stepwise is greater than or equal to 15 mol.

[0054] Understandably, the aforementioned change threshold ensures a sufficiently wide compositional transition range between the higher manganese first part (core region) and the higher nickel second part (shell region), allowing for a sufficient and gradual continuous change in cell parameters along the radial direction. This more effectively eliminates residual lattice mismatch stress caused by small changes or abrupt changes in traditional core-shell structures. Simultaneously, the second part (shell region) has a sufficiently high Ni content to improve capacity, while the first part (core region) maintains a sufficiently high Mn content to preserve the chemical stability of the structural framework. The two are strongly bonded through a wide gradient transition layer, suppressing cation mixing and microcrack propagation in the higher nickel region during long cycles. Thus, based on the aforementioned stability improvement, the cycle life of the cathode material is significantly extended and the structural retention capability under high voltage is improved.

[0055] In some embodiments, the secondary particles are composed of primary particles with a plate-like structure stacked together; the thickness of the primary particles ranges from 20 nm to 100 nm; and / or the diameter of the primary particles ranges from 200 nm to 800 nm.

[0056] For example, the thickness of a single particle can be 20nm, 40nm, 60nm, 80nm or 100nm, etc., and there is no limitation here.

[0057] For example, the diameter of a primary particle can be 200nm, 400nm, 600nm or 800nm, etc., and there is no limitation here.

[0058] Understandably, the secondary particles are formed by the cross-stacking of plate-shaped primary particles with a thickness of 20nm~100nm and / or a diameter of 200nm~800nm, and an "interlocking pinning" structure is formed in the first part (core region). The thin plate-shaped primary particles in this size range have high bending stiffness and packing density. The mechanical interlocking effect generated by the cross-stacking significantly suppresses the radial cracking tendency of the secondary particles during charge and discharge volume changes. At the same time, the interlocking pinning structure in the first part (core region) serves as a skeleton support point, dispersing and transferring the volume expansion stress to the entire secondary particle, avoiding local stress concentration. Thus, while maintaining the integrity of the lithium-rich manganese-based precursor and subsequent cathode material particles, it effectively extends the cycle life and reduces the capacity decay caused by particle breakage.

[0059] In addition, the thickness range of 20nm to 100nm of the primary particles provides sufficient and interconnected channels for lithium-ion diffusion and gas release during the subsequent sintering process, effectively avoiding the problems of uneven lithiation caused by too few pores and loose particle structure caused by too many pores.

[0060] In some embodiments, the total porosity of the first portion ranges from 20% to 40%.

[0061] For example, the total porosity of the first part can be 20%, 25%, 30%, 35% or 40%, etc., and there is no limitation here.

[0062] Understandably, the total porosity of the first part is controlled between 20% and 40%, providing sufficient and interconnected channels for lithium-ion diffusion and gas release during the subsequent sintering process. This effectively avoids uneven lithiation caused by too few pores and loose particle structure caused by too many pores. Therefore, the cathode material obtained by sintering this lithium-rich manganese-based precursor can achieve a discharge specific capacity of over 290 mAh / g at a 0.1C rate and an initial coulombic efficiency of over 88%. This indicates that the high porosity provides good electrolyte wetting and lithium-ion transport pathways. Combined with the aforementioned gradient composition and "interlocking pinning" structure, it achieves a synergistic improvement in high capacity and high initial efficiency.

[0063] Here, the total porosity can be obtained through BET testing, which is the open-pore porosity measured by gas adsorption-desorption method.

[0064] In some embodiments, the total porosity of the first portion is greater than the total porosity of the second portion.

[0065] Understandably, the first part has a larger total porosity, i.e., "porosity in the core". The high and uniformly distributed pores in the first part (core region) can effectively absorb and buffer the micro-strain caused by lattice expansion / contraction during charging and discharging, and avoid stress accumulation inside the particle leading to the initiation of microcracks. The relatively dense structure of the second part (shell region) ensures lithium-ion transport while maintaining the integrity of the particle surface.

[0066] In some embodiments, the total porosity of the second part is 4% to 10%, and the ratio of the total porosity of the first part to the total porosity of the second part is in the range of 3 to 7.

[0067] For example, the total porosity of the second part can be 4%, 5%, 6%, 7%, 8%, 9%, or 10%, etc., and there is no limitation here.

[0068] For example, the ratio of the total porosity of the first part to the total porosity of the second part can be 3, 4, 5, 6 or 7, etc., and there is no limitation here.

[0069] Understandably, the total porosity of the second part (outer shell region) is controlled at 4%-10%, forming a dense surface protective layer that effectively blocks excessive erosion of the high-nickel second part (outer shell region) by the electrolyte and suppresses surface side reactions. Simultaneously, the ratio of the total porosity of the first part to the second part is between 3 and 7, ensuring that the porosity difference between the inner and outer layers is not too large, thus preventing stress abrupt changes or delamination at the interface. The 20%-40% high-porosity region in the first part (core region) is uniformly distributed, fully absorbing and buffering the micro-strain caused by lattice expansion / contraction during charging and discharging. Meanwhile, the 4%-10% low porosity of the second part (outer shell region) maintains the integrity of the particle surface structure and mechanical strength while ensuring rapid lithium-ion transport, suppressing microcrack propagation and capacity decay during long-term cycling.

[0070] In some embodiments, the ratio of the thickness of the second portion to the radius of the secondary particles ranges from 0.5 to 0.6.

[0071] Understandably, the ratio of the thickness of the second part (outer shell region) to the radius of the secondary particle is controlled within the range of 0.5 to 0.6, meaning that the second part (outer shell region) occupies more than half of the particle radius. This allows the second part (outer shell region) with a higher nickel content to have sufficient structural thickness to support high capacity output, while avoiding the first part (core region) from being exposed to the electrolyte during cycling due to the second part (outer shell region) being too thin. The thicker second part (outer shell region), combined with its low porosity of 4% to 10%, forms a robust surface protective layer, effectively suppressing side reactions and surface phase transitions between the high nickel region and the electrolyte.

[0072] Meanwhile, although the first part (core region) accounts for a small proportion (radius proportion of about 0.4~0.5), its high porosity of 20%~40% is uniformly distributed. Combined with the interlocking pinning structure formed by the plate-like primary particles in the first part (core region), it can fully absorb and buffer the micro-strain of lattice expansion / contraction during the charging and discharging process. The thickness ratio of the inner and outer layers is 0.5~0.6. With the linear or stepwise gradient change of Mn and Ni from the first part (core region) to the second part (outer shell region) in the radial direction (change amount ≥15 mol%), the cell parameters achieve a full and smooth continuous transition from the center to the surface, eliminating the stress concentration at the interface, and exhibiting excellent crack resistance and structural stability in long cycles.

[0073] In some embodiments, the precursor has the chemical formula Ni x Mn M 1-x- (CO3) or Ni x Mn M 1-x- (OH)2, wherein M is at least one of Co, Al, Mg, and Ti.

[0074] Understandably, the above configuration, combined with the secondary particles having a higher porosity (20%~40%) in the first part (core region) and a lower porosity (4%~10%) in the second part (shell region) with a thickness ratio of 0.5~0.6, and the "interlocking pinning" structure of the plate-shaped primary particles and the gradient transition of large radial variation (≥15 mol%) of Mn and Ni, achieves the synergistic effect of buffering micro-strain in the first part (core region), dense protection in the second part (shell region), and continuous lattice matching, further improving the long-cycle structural stability of lithium-rich manganese-based precursors.

[0075] An embodiment of the present invention provides a method for preparing a lithium-rich manganese-based precursor, comprising: Spherical or near-spherical secondary particles are prepared, and multiple secondary particles are stacked to form a lithium-rich manganese-based precursor. Each secondary particle comprises a first part and a second part, with the first part being closer to the center of the secondary particle than the second part. The secondary particles contain Mn and Ni elements. The molar percentage of Mn in the first part is greater than the molar percentage of Mn in the second part; the molar percentage of Ni in the first part is less than the molar percentage of Ni in the second part.

[0076] Understandably, the embodiments of the present invention provide a method for preparing a lithium-rich manganese-based precursor, and the beneficial effects that can be achieved can be referred to the beneficial effects of the lithium-rich manganese-based precursor mentioned above, which will not be repeated here.

[0077] In some embodiments, spherical or near-spherical secondary particles are prepared, such as... Figure 1 As shown, it includes: S1~S2.

[0078] S1: Provides an alkaline base solution, which includes a complexing agent and a precipitating agent.

[0079] S2: Add a nickel-manganese mixed salt solution to the base liquid and carry out a coprecipitation reaction to obtain a lithium-rich manganese-based precursor; wherein, during the process of adding the nickel-manganese mixed salt solution to the base liquid, the molar ratio of Mn to Ni in the nickel-manganese mixed salt solution is adjusted so that the molar ratio of Mn to Ni in the nickel-manganese mixed salt solution gradually decreases with the time of the coprecipitation reaction.

[0080] For example, during the coprecipitation reaction, the molar ratio of Mn to Ni in the nickel-manganese mixed salt solution is gradually changed, so that it is continuously or stepwise reduced from a high Mn / Ni ratio (such as 7:3 or 8:2) to a low Mn / Ni ratio (such as 5:5 or 6:4).

[0081] For example, the temperature of the coprecipitation reaction can be 50℃~65℃, and the pH value can be controlled at 11.0-12.5.

[0082] In some examples, the process after S2 coprecipitation includes aging, washing, and drying the resulting lithium-rich manganese-based precursor.

[0083] Understandably, by continuously reducing the molar ratio of Mn / Ni in the nickel-manganese mixed salt solution during the co-precipitation reaction, Mn and Ni form a linear or stepwise gradient distribution along the radial direction of the secondary particles, resulting in a cathode material with excellent long-cycle structural stability after sintering the lithium-rich manganese-based precursor.

[0084] In some embodiments, the coprecipitation reaction includes at least: a first stage reaction and a second stage reaction, wherein the stirring speed of the first stage reaction is greater than the stirring speed of the second stage reaction; wherein the first stage reaction is a first part of the growth stage and the second stage reaction is a second part of the growth stage.

[0085] For example, high shear force stirring with a linear velocity of 8 m / s to 12 m / s can be used in the first stage of the reaction, while ultrasonic-assisted dispersion is activated at the same time.

[0086] For example, during the first stage of the reaction, the stirring linear velocity can be 8m / s to 12m / s, and ultrasonic assistance can be used. For example, the power of the ultrasonic wave can be 300W to 800W, and the frequency can be 20kHz to 60kHz.

[0087] For example, during the second stage of the reaction, the stirring linear velocity can be 4 m / s to 6 m / s, and the ultrasonic waves can be reduced or turned off.

[0088] Understandably, by growing a high-porosity core at a higher stirring speed in the first stage and a low-porosity dense shell at a lower stirring speed in the second stage, combined with the gradual decrease in the Mn / Ni ratio in the salt solution to achieve a radially large change in composition gradient, and combined with the plate-like primary particle interlocking pinning in the core region, the cathode material can suppress particle cracking during long-term cycling.

[0089] To more clearly illustrate the technical solution of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. The following embodiments are only for illustrating the present invention and should not be regarded as limiting the present invention.

[0090] Example 1 Example 1 provides a positive electrode material, the preparation method of which includes steps (1) to (2).

[0091] (1) Preparation of lithium-rich manganese-based precursor: Prepare a nickel-manganese mixed solution with a total metal ion concentration of 2 mol / L, wherein the initial molar ratio of Mn:Ni is 7:3. Prepare an ammonia solution and sodium carbonate solution in a 5L reactor to make the pH of the bottom solution 12.0 and control the temperature at 55℃.

[0092] During the first 8 hours of the reaction, stirring was started with a linear velocity of 10 m / s, and ultrasonic waves (500 W power, 40 kHz frequency) were simultaneously activated. Then, the nickel-manganese mixed solution was added to the reactor in parallel with the precipitant and complexing agent mixed solution.

[0093] Subsequently, two hours into the reaction, the stirring speed was reduced to 6 m / s and the ultrasonic waves were turned off.

[0094] The entire reaction process is automatically regulated by a mixed solution of precipitant and complexing agent to maintain a constant pH of 12.0 within the reactor. Through program control, the molar ratio of Mn to Ni in the nickel-manganese mixed solution is linearly reduced from the initial 7:3 to 5:5.

[0095] After the reaction was completed, the resulting slurry was aged for 4 hours, then washed, filtered and dried to obtain a lithium-rich manganese-based precursor.

[0096] (2) Preparation of cathode material: The above precursor and Li2CO3 were mixed evenly in a mixer at a Li / Me (Me=Ni+Mn) molar ratio of 1.5. The mixture was placed in an air atmosphere furnace and heated to 550℃ at 1.5℃ / min and held for 4h. Then, the temperature was increased to 900℃ at 1℃ / min and held for 12h. After natural cooling, the mixture was crushed and sieved to obtain a polycrystalline lithium-rich manganese-based cathode material.

[0097] Scanning electron microscopy (SEM) was performed on the cross-section of the lithium-rich manganese-based precursor and the cathode material of Example 1. The results are as follows: Figure 2 and Figure 3 As shown, the prepared lithium-rich manganese-based precursor has a porous core and a dense outer shell.

[0098] Comparative Example 1 Comparative Example 1 provides a cathode material, the preparation method of which includes steps (1) to (2).

[0099] (1) Preparation of lithium-rich manganese-based precursor: The only difference from step (1) of Example 1 is that the molar ratio of Mn:Ni in the nickel-manganese mixed solution is kept constant at 6:4, the stirring linear speed is kept constant at 4m / s, and the ultrasonic waves are not turned on.

[0100] (2) Preparation of cathode material: Same as step (2) in Example 1.

[0101] Comparative Example 2 Comparative Example 2 provides a cathode material, the preparation method of which includes steps (1) to (2). (1) Preparation of lithium-rich manganese-based precursor: The only difference from step (1) of Example 1 is that the molar ratio of Mn to Ni in the nickel-manganese mixed solution remains constant throughout the reaction process (Mn:Ni=6:4) and does not undergo gradient changes; at the same time, the stirring and ultrasonic parameters are maintained at a linear velocity of 10m / s, ultrasonic power of 500W, and frequency of 40kHz throughout the process.

[0102] (2) Preparation of cathode material: Same as step (2) in Example 1.

[0103] Comparative Example 3 Comparative Example 3 provides a cathode material, the preparation method of which includes steps (1) to (2).

[0104] (1) Preparation of lithium-rich manganese-based precursor: The only difference from step (1) of Example 1 is that during the first 8 hours of the reaction, a low stirring speed of 4 m / s is used and the ultrasonic waves are not turned on; during the last 2 hours of the reaction, the stirring speed is increased to 10 m / s and the ultrasonic waves are turned on with a power of 500 W and a frequency of 40 kHz.

[0105] (2) Preparation of cathode material: Same as step (2) in Example 1.

[0106] Performance testing The cathode materials from Example 1 and the comparative examples were assembled into CR2032 coin cells (voltage window 2.0-4.8V), and their electrochemical performance was tested. The structures are shown in Table 1, and the cycle performance comparisons are as follows. Figure 4 and Figure 5 As shown.

[0107] Table 1 Electrochemical performance data

[0108] From Table 1, Figure 4 and Figure 5 It is evident that the cathode material of Example 1 of this invention is comprehensively superior to the comparative examples in terms of capacity, initial efficiency, and cycle life. In particular, compared with the cathode material of Comparative Example 3, the cathode material of Example 1 of this invention exhibits unexpected technical effects in cycle stability, demonstrating the uniqueness and advancement of the technical concept of this invention.

[0109] The lithium-rich manganese-based precursor in Comparative Example 1, lacking porosity and gradient, was prone to developing numerous cracks after cycling, confirming the importance of the physical buffer layer. The lithium-rich manganese-based precursor in Comparative Example 2, although porous, lacked gradient, and its cycling stability, while improved, was still insufficient, indicating that physical buffer alone could not completely eliminate the internal stress caused by lattice mismatch. The lithium-rich manganese-based precursor in Comparative Example 3 was not conducive to stress release in the core, and its porous outer shell was easily corroded by the electrolyte.

[0110] In contrast, the lithium-rich manganese-based precursor of Example 1 achieves its ultra-long cycle life through the synergistic effect of "core porosity" and "full concentration gradient". It absorbs physical strain through pores and eliminates chemical stress through gradient transition. At the same time, the dense shell protects the particle as a whole. This stress management mechanism of force-electrochemical coupling is the fundamental reason for achieving its ultra-long cycle life.

[0111] The above embodiments are merely preferred embodiments provided to fully illustrate the present invention, and the scope of protection of the present invention is not limited thereto. Equivalent substitutions or modifications made by those skilled in the art based on the present invention are all within the scope of protection of the present invention.

Claims

1. A lithium-rich manganese-based precursor, characterized in that, The lithium-rich manganese-based precursor comprises spherical or near-spherical secondary particles; each secondary particle comprises a first part and a second part, wherein the first part is closer to the center of the secondary particle than the second part. The secondary particles contain Mn and Ni elements; the molar percentage of Mn in the first part is greater than the molar percentage of Mn in the second part; the molar percentage of Ni in the first part is less than the molar percentage of Ni in the second part.

2. The lithium-rich manganese-based precursor according to claim 1, characterized in that, In the secondary particles, the molar percentage of Mn decreases linearly or stepwise from the interior of the first part to the surface of the second part away from the first part in the radial direction. The molar percentage of Ni increases linearly or stepwise.

3. The lithium-rich manganese-based precursor according to claim 2, characterized in that, The linear or stepwise decrease in the molar percentage of Mn is greater than or equal to 15 mol%; and / or, The change in the molar percentage of Ni element that increases linearly or stepwise is greater than or equal to 15 mol.

4. The lithium-rich manganese-based precursor according to claim 1, characterized in that, The secondary particles are composed of primary particles with a plate-like structure stacked together; the thickness of the primary particles ranges from 20 nm to 100 nm; and / or, the diameter of the primary particles ranges from 200 nm to 800 nm.

5. The lithium-rich manganese-based precursor according to claim 1, characterized in that, The total porosity of the first part ranges from 20% to 40%.

6. The lithium-rich manganese-based precursor according to claim 5, characterized in that, The total porosity of the first part is greater than the total porosity of the second part.

7. The lithium-rich manganese-based precursor according to claim 6, characterized in that, The total porosity of the second part ranges from 4% to 10%, and the ratio of the total porosity of the first part to the total porosity of the second part ranges from 3 to 7.

8. The lithium-rich manganese-based precursor according to claim 1, characterized in that, The ratio of the thickness of the second part to the radius of the secondary particle ranges from 0.5 to 0.

6.

9. The lithium-rich manganese-based precursor according to any one of claims 1 to 8, characterized in that, The precursor has the chemical formula Ni x Mn M 1-x- (CO3) or Ni x Mn M 1-x- (OH)2, wherein M is at least one of Co, Al, Mg, and Ti.

10. A method for preparing a lithium-rich manganese-based precursor, characterized in that, include: Prepare spherical or near-spherical secondary particles, and stack multiple of the secondary particles to form the lithium-rich manganese-based precursor; The secondary particles contain Mn and Ni elements; the molar percentage of Mn in the first part is greater than the molar percentage of Mn in the second part; the molar percentage of Ni in the first part is less than the molar percentage of Ni in the second part.

11. The method for preparing the lithium-rich manganese-based precursor according to claim 10, characterized in that, Preparation of spherical or near-spherical secondary particles, including: An alkaline base solution is provided, the base solution comprising a complexing agent and a precipitating agent; A nickel-manganese mixed salt solution is added to the base solution to carry out a coprecipitation reaction, thereby obtaining the lithium-rich manganese-based precursor. During the addition of the nickel-manganese mixed salt solution to the base solution, the molar ratio of Mn to Ni in the nickel-manganese mixed salt solution is adjusted so that the molar ratio of Mn to Ni in the nickel-manganese mixed salt solution gradually decreases with the duration of the coprecipitation reaction.

12. The method for preparing the lithium-rich manganese-based precursor according to claim 11, characterized in that, The coprecipitation reaction includes at least a first stage reaction and a second stage reaction, wherein the stirring speed of the first stage reaction is greater than the stirring speed of the second stage reaction; The first reaction segment is the first growth stage, and the second reaction segment is the second growth stage.

13. A positive electrode material, characterized in that, include: Lithium-containing materials and lithium-rich manganese-based precursors as described in any one of claims 1 to 9.

14. A lithium-ion battery, characterized in that, include: The cathode material as described in claim 13.

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