Solid-phase gradient doped lithium-rich manganese-based positive electrode material as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of lithium ion battery positive electrode materials, and particularly relates to a solid-phase gradient doped lithium-rich manganese-based positive electrode material as well as a preparation method and application thereof. The preparation method comprises the following steps: mixing a precursor and a surface dopant for the first time, carrying out heat treatment, mixing an obtained surface doped precursor and a subsurface dopant for the second time, carrying out medium-temperature reaction, mixing an obtained surface-subsurface doped precursor and a bulk phase dopant for the third time, carrying out high-temperature solid solution, mixing an obtained gradient doped precursor and a lithium source for the fourth time, and sintering. The solid-phase gradient doped lithium-rich manganese-based positive electrode material is obtained. According to the invention, the diffusion path of doped elements is controlled through step-by-step thermal decomposition, and a synergistic doped three-level structure of surface enrichment, subsurface layer gradient and bulk phase uniformity is formed, so that the prepared solid-phase gradient doped lithium-rich manganese-based positive electrode material has excellent first coulombic efficiency and cycling stability and low voltage attenuation.

Description

Technical Field

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

[0002] Lithium-rich manganese-based cathode materials (Li-rich layered oxides) are considered core materials for next-generation high-energy-density lithium-ion batteries due to their advantages such as high specific capacity (>250mAh / g), low cost (abundant manganese resources), and high compaction density. However, their industrialization still faces the following bottlenecks: low initial coulombic efficiency: irreversible oxygen release during the first charge and discharge process typically results in efficiency below 85%; poor cycle stability: transition metal (TM) dissolution and structural phase transitions cause capacity decay (capacity retention <80% after 200 cycles); voltage decay: layered-spinel phase transitions during cycling lead to a continuous decrease in average discharge voltage (>0.5mV / cycle).

[0003] To address the aforementioned issues, existing technologies primarily employ bulk doping or surface coating for modification, but both methods suffer from significant drawbacks: 1. Wet gradient doping: The process is complex, requiring multiple steps of impregnation, centrifugation, and drying, resulting in high energy consumption and difficulty in scaling up; liquid-phase reactions can easily lead to precursor particle breakage or excessive hydrolysis of surface hydroxyl groups; differences in solvent evaporation can cause elemental segregation, making it difficult to accurately control the gradient distribution.

[0004] 2. Solid-phase ball milling doping: High-energy ball milling destroys the lattice integrity of the precursor, introducing cracks and grain boundary defects; it can only achieve uniform element distribution, and cannot take into account both surface stability and bulk diffusion requirements; the ball milling media (such as zirconium balls) wears and contaminates the material, reducing electrochemical performance. Summary of the Invention

[0005] In view of this, the purpose of this invention is to provide a solid-phase gradient-doped lithium-rich manganese-based cathode material, its preparation method and application. The solid-phase gradient-doped lithium-rich manganese-based cathode material prepared by this invention has excellent first coulombic efficiency and cycle stability as well as low voltage decay.

[0006] To achieve the above objectives, the present invention provides the following technical solution: This invention provides a method for preparing a solid-phase gradient-doped lithium-rich manganese-based cathode material, comprising the following steps: The precursor and surface dopant are first mixed and then heat-treated to obtain a surface-doped precursor. The surface-doped precursor and the subsurface dopant are mixed and reacted at a medium temperature to obtain a surface-subsurface doped precursor. The surface-subsurface doped precursor and the bulk dopant are mixed and subjected to high-temperature solid solution to obtain a gradient doped precursor. The gradient-doped precursor and the fourth lithium source are mixed and sintered to obtain a solid-phase gradient-doped lithium-rich manganese-based cathode material.

[0007] Preferably, the surface dopant, subsurface dopant, and bulk dopant are independently any one of a metal oxide, a salt precursor, and an anion source, and the surface dopant, subsurface dopant, and bulk dopant are not the same; the metal oxide includes one or more of TiO2, La2O3, Ta2O5, ZrO2, Nb2O5, Al2O3, MgO, CeO2, MoO3, SnO2, Co3O4, and Y2O3; the salt precursor includes one or more of aluminum nitrate, ammonium niobate oxalate, magnesium carbonate, titanium oxysulfate, zirconium oxynitrate, lanthanum nitrate, ammonium cerium sulfate, yttrium acetate, ammonium fluorotantalate, ammonium metavanadate, and ammonium molybdate; the anion source includes one or more of ammonium hexafluorosilicate, lithium fluoride, ammonium pyrophosphate, ammonium sulfate, ammonium borate, and ethyl silicate.

[0008] Preferably, the particle size of the surface dopant is 1~20 μm; the particle size of the subsurface dopant is 1~10 μm, and the specific surface area is 2~10 m². 2 / g; the particle size of the bulk dopant is D 90 <2μm.

[0009] Preferably, the heat treatment temperature is 250~450℃, and the holding time is 3~5h.

[0010] Preferably, the intermediate temperature reaction is carried out in an air atmosphere; the temperature of the intermediate temperature reaction is 450~650℃, and the holding time is 5~8h.

[0011] Preferably, the high-temperature solution treatment is carried out in an air atmosphere; the temperature of the high-temperature solution treatment is 750~900℃, and the holding time is 8~12h.

[0012] Preferably, the lithium source is one or more of Li2CO3, LiOH, LiOH·H2O, Li2O, Li2O2, lithium acetate, lithium oxalate, and lithium nitrate.

[0013] Preferably, the sintering is carried out in an air atmosphere; the sintering includes sequential low-temperature sintering and high-temperature sintering; the low-temperature sintering temperature is 300~600℃, and the holding time is 3~6h; the high-temperature sintering temperature is 850~950℃, and the holding time is 8~15h.

[0014] The present invention also provides a solid-phase gradient-doped lithium-rich manganese-based cathode material prepared by the preparation method described above, comprising a precursor and doping elements doped on the surface of the precursor; the doping elements include surface doping elements, subsurface doping elements and bulk doping elements; the surface doping elements, subsurface doping elements and bulk doping elements are doped on the surface of the precursor from shallow to deep.

[0015] The present invention also provides the application of the solid-phase gradient doped lithium-rich manganese-based cathode material described above in lithium-ion batteries.

[0016] This invention provides a method for preparing a solid-phase gradient-doped lithium-rich manganese-based cathode material, comprising the following steps: mixing a precursor and a surface dopant in a first manner, and performing heat treatment to obtain a surface-doped precursor; mixing the surface-doped precursor and a subsurface dopant in a second manner, and performing a medium-temperature reaction to obtain a surface-subsurface doped precursor; mixing the surface-subsurface doped precursor and a bulk dopant in a third manner, and performing high-temperature solid solution treatment to obtain a gradient-doped precursor; and mixing the gradient-doped precursor and a lithium source in a fourth manner, and performing sintering to obtain a solid-phase gradient-doped lithium-rich manganese-based cathode material.

[0017] This invention controls the diffusion path of dopant elements through stepwise thermal decomposition, forming a synergistic three-level doped structure of "surface enrichment (e.g., Al, F) - subsurface gradient (e.g., Mo, P) - bulk homogeneity (e.g., Nb, Sn)". This results in complementary elemental functions, with surface elements inhibiting oxygen release, subsurface elements stabilizing the structure, and bulk elements expanding Li. + Through channel optimization, the prepared solid-phase gradient-doped lithium-rich manganese-based cathode material exhibits excellent initial coulombic efficiency, cycle stability, and low voltage decay, achieving comprehensive performance optimization. The results of the examples show that the Al-Mo-Nb solid-phase gradient-doped lithium-rich manganese-based cathode material prepared in Example 1 achieves a capacity of 221.92 mAh / g at 0.1C, a 14.5% improvement compared to Comparative Example 1 (undoped). The FP-Sn solid-phase gradient-doped lithium-rich manganese-based cathode material prepared in Example 5 retains 97.76% of its capacity after 100 cycles, with a voltage decay rate of only 0.08 mV / cycle, which is superior to traditional homogeneous doping (Comparative Example 3 has a retention rate of only 89.96%).

[0018] Furthermore, this invention simplifies the process, eliminating steps such as wet impregnation, centrifugation, and drying in the all-solid-phase process; it features low cost: the air atmosphere eliminates the need for inert gases, reducing energy consumption and making it compatible with existing cathode production lines; it is environmentally friendly and safe: there is no solvent emission, avoiding the wastewater treatment problems of wet processes. Attached Figure Description

[0019] Figure 1 The discharge specific capacity cycling curves of Example 1, Example 5, and Comparative Example 1 at 1C rate are shown. Figure 2 The above are charge-discharge curves of Example 1, Example 5, and Comparative Example 1 at a rate of 0.1C. Detailed Implementation

[0020] This invention provides a method for preparing a solid-phase gradient-doped lithium-rich manganese-based cathode material, comprising the following steps: The precursor and surface dopant are first mixed and then heat-treated to obtain a surface-doped precursor. The surface-doped precursor and the subsurface dopant are mixed and reacted at a medium temperature to obtain a surface-subsurface doped precursor. The surface-subsurface doped precursor and the bulk dopant are mixed and subjected to high-temperature solid solution to obtain a gradient doped precursor. The gradient-doped precursor and the fourth lithium source are mixed and sintered to obtain a solid-phase gradient-doped lithium-rich manganese-based cathode material.

[0021] Unless otherwise specified, the present invention does not have special requirements on the source of raw materials used, and commercially available products well known to those skilled in the art can be used.

[0022] The present invention first mixes the precursor and the surface dopant, and then performs heat treatment to obtain the surface-doped precursor.

[0023] In one implementation, the precursor is commercially available Ni. x Co y Mn z CO3 and Ni x Co y Mn z One or more of (OH)₂, wherein 0 < x ≤ 0.5, 0 ≤ y ≤ 0.3, 0.5 ≤ z < 1, and x + y + z = 1, and in a specific embodiment, Ni is used. 0.35 Mn 0.65 (OH)2; the particle size of the precursor is 5~15μm, and in a specific embodiment it is 6~10μm.

[0024] In one implementation, the surface dopant, subsurface dopant, and bulk dopant are independently any one of metal oxides, salt precursors, and anion sources, and the surface dopant, subsurface dopant, and bulk dopant are not the same; the metal oxide includes one or more of TiO2, La2O3, Ta2O5, ZrO2, Nb2O5, Al2O3, MgO, CeO2, MoO3, SnO2, Co3O4, and Y2O3, and in a specific embodiment, TiO2, La2O3, Ta2O5, and MnO2 are used. The salt precursors include one or more of aluminum nitrate, niobium ammonium oxalate, magnesium carbonate, titanium oxysulfate, zirconium oxynitrate, lanthanum nitrate, cerium ammonium sulfate, yttrium acetate, ammonium fluorotantalate, ammonium metavanadate, and ammonium molybdate, with aluminum nitrate, magnesium carbonate, lanthanum nitrate, or niobium ammonium oxalate being used in specific embodiments; the anion source includes one or more of ammonium hexafluorosilicate, lithium fluoride, ammonium pyrophosphate, ammonium sulfate, ammonium borate, and ethyl silicate, with lithium fluoride or ammonium pyrophosphate being used in specific embodiments.

[0025] In one embodiment, the particle size of the surface dopant is 1~20 μm, specifically 1 μm, 10 μm, 15 μm or 20 μm in some embodiments; the particle size of the subsurface dopant is 1~10 μm, specifically 1 μm, 2 μm or 10 μm in some embodiments, and the specific surface area is 2~10 m². 2 / g, specifically 2.5m in the embodiment. 2 / g, 2.8m 2 / g, 3.4m 2 / g, 3.5m 2 / g or 6.2m 2 / g; the particle size of the bulk dopant is D 90 <2μm, specifically 0.4μm, 0.5μm, or 1μm in the embodiments. The bulk dopant is made of ultrafine powder, which helps to achieve uniform solid solution.

[0026] In one implementation, the dopant element in the surface dopant accounts for 1-10 at.% of the transition metal element in the precursor, specifically 3 at.%, 4 at.%, or 5 at.% in this embodiment; the dopant element in the subsurface dopant accounts for 1-10 at.% of the transition metal element in the precursor, specifically 2-3 at.% in this embodiment; the dopant element in the bulk dopant accounts for 0.5-5 at.% of the transition metal element in the precursor, specifically 1 at.% in this embodiment; when the surface dopant, subsurface dopant, and bulk dopant are metal oxides, the dopant element is a metal element in the metal oxide; when the surface dopant, subsurface dopant, and bulk dopant are salt precursors, the dopant element is a metal element in the salt precursor; when the surface dopant, subsurface dopant, and bulk dopant are anion sources, the dopant element is a non-oxygen non-metallic element in the anion source.

[0027] In one implementation, the equipment used for the first mixing is a high-speed mixer; the rotation speed of the first mixing is 500~800 rpm, specifically 800 rpm in this embodiment, and the time is 10~30 min, specifically 20 min in this embodiment; the heat treatment is carried out in an air atmosphere; the temperature of the heat treatment is 250~450℃, specifically 250℃, 300℃, 350℃, 400℃ or 450℃ in this embodiment, and the holding time is 3~5 h, specifically 3 h in this embodiment.

[0028] After obtaining the surface-doped precursor, the present invention mixes the surface-doped precursor with a second subsurface dopant and performs a medium-temperature reaction to obtain a surface-subsurface doped precursor.

[0029] In one embodiment, the equipment used for the second mixing is a high-speed mixer; the rotation speed of the second mixing is 400~600 rpm, specifically 600 rpm in this embodiment, and the time is 10~25 min, specifically 15 min in this embodiment; the intermediate temperature reaction is carried out in an air atmosphere; the temperature of the intermediate temperature reaction is 450~650℃, specifically 450℃, 550℃, 600℃ or 650℃ in this embodiment, and the holding time is 5~8 h, specifically 5 h in this embodiment.

[0030] After obtaining the surface-subsurface doped precursor, the present invention mixes the surface-subsurface doped precursor with the bulk dopant and performs high-temperature solid solution to obtain the gradient doped precursor.

[0031] In one implementation, the equipment used for the third mixing is a high-speed mixer; the rotation speed of the third mixing is 200~400 rpm, specifically 400 rpm in this embodiment, and the time is 20~40 min, specifically 30 min in this embodiment; the high-temperature solid solution is carried out in an air atmosphere; the temperature of the high-temperature solid solution is 750~900℃, specifically 700℃, 750℃, 800℃ or 850℃ in this embodiment, and the holding time is 8~12 h, specifically 8 h in this embodiment.

[0032] After obtaining the gradient-doped precursor, the present invention mixes the gradient-doped precursor with a lithium source and sinters to obtain a solid-phase gradient-doped lithium-rich manganese-based cathode material.

[0033] In one embodiment, the lithium source is one or more of Li2CO3, LiOH, LiOH·H2O, Li2O, Li2O2, lithium acetate, lithium oxalate, and lithium nitrate, with Li2CO3 being a specific example; the particle size of the lithium source is 0.5~5μm, with 2~5μm being a specific example; the atomic ratio of the total transition metal elements in the precursor to the Li elements in the lithium source is 1:1.1~1.5, with 1:1.3 being a specific example.

[0034] In one implementation, the equipment used for the fourth mixing is a high-speed mixer; the rotation speed of the fourth mixing is 600~1000 rpm, specifically 1000 rpm in this embodiment, the time is 20~40 min, specifically 25 min in this embodiment, and the humidity is <10% RH; the sintering is carried out in an air atmosphere; the sintering includes sequential low-temperature sintering and high-temperature sintering; the temperature of the low-temperature sintering is 300~600℃, specifically 500℃ in this embodiment, and the holding time is 3~6 h, specifically 5 h in this embodiment; the temperature of the high-temperature sintering is 850~950℃, specifically 900℃ in this embodiment, and the holding time is 8~15 h, specifically 12 h in this embodiment; the heating rate to the low-temperature sintering temperature and the heating rate to the high-temperature sintering temperature are independently 0.5~10℃ / min, specifically 2~5℃ / min in this embodiment.

[0035] This invention provides a synergistic optimization method for achieving gradient doping and uniform mixing under all-solid-phase, ball-mill-free, air-atmosphere conditions, which can improve material properties while significantly reducing process costs. The method of this invention has the following technical advantages: 1. By stepwise mixing: surface → subsurface → bulk phase stepwise mixing (speed 200~1000rpm), the diffusion path of dopant elements is controlled by stepwise thermal decomposition, forming a synergistic doping structure of "surface enrichment - subsurface gradient - bulk uniformity", realizing gradient doping design; 2. Single atmosphere, all-process air atmosphere: The entire process from doping to sintering is completed in an air atmosphere, without the need for inert gas protection or gas switching. The process is extremely simple and safe, and equipment costs are reduced by 30%. 3. Dopant particle size classification: surface dopant (1~20μm), subsurface dopant (1~10μm), bulk dopant (D... 90 <2μm), suitable for gradient diffusion requirements.

[0036] 4. High-efficiency mixing technology: By optimizing the rotation speed, time and dispersant, a highly uniform combination of lithium source and precursor is achieved, avoiding ball milling damage and wet process contamination.

[0037] The present invention also provides a solid-phase gradient-doped lithium-rich manganese-based cathode material prepared by the preparation method described above, comprising a precursor and doping elements doped on the surface of the precursor; the doping elements include surface doping elements, subsurface doping elements and bulk doping elements; the surface doping elements, subsurface doping elements and bulk doping elements are doped on the surface of the precursor from shallow to deep.

[0038] The present invention also provides the application of the solid-phase gradient doped lithium-rich manganese-based cathode material described above in lithium-ion batteries.

[0039] The present invention does not impose any particular limitation on the application of the solid-phase gradient doped lithium-rich manganese-based cathode material in lithium-ion batteries; any application method known in the art can be used.

[0040] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention, but they should not be construed as limiting the scope of protection of the present invention.

[0041] Example 1 Commercial precursor Ni with a particle size of 6μm was used. 0.35 Mn 0.65 (OH)2 and Al(NO3)3·9H2O powder with a particle size of 10μm (Al:TM (transition metal element in the precursor) atomic ratio = 0.03:1) were added to a high-speed mixer and mixed at 800rpm for 20min. The resulting mixture was kept at 250℃ for 3h in air atmosphere to obtain Al-doped precursor. An Al-doped precursor was used with a particle size of 1 μm and a specific surface area of ​​2.5 μm. 2 / g of MoO3 (Mo:TM atomic ratio = 0.02:1) was mixed in a high-speed mixer at 600 rpm for 15 min, and the resulting mixture was kept at 450℃ for 5 h in air atmosphere to obtain the Mo-Al doped precursor. Mo-Al doped precursor and D 90Nb2O5 with a particle size of 1 μm (Nb:TM atomic ratio = 0.01:1) was mixed at 400 rpm for 30 min in a high-speed mixer, and the resulting mixture was kept at 750 °C for 8 h in air atmosphere to obtain a gradient doped precursor. Gradient-doped precursors were mixed with Li2CO3 with a particle size of 5 μm. (Atomic ratio = 1.3:1) was mixed in a high-speed mixer at 1000 rpm for 25 min under conditions of humidity <10% RH. The resulting mixture was first heated to 500℃ at 2℃ / min and held for 5 h, then heated to 900℃ at 5℃ / min and held for 12 h. After natural cooling, it was sieved through a 400-mesh sieve to obtain Al-Mo-Nb gradient-doped lithium-rich manganese-based cathode material.

[0042] Example 2 Commercial precursor Ni with a particle size of 6μm was used. 0.35 Mn 0.65 (OH)2 and titanium dioxide powder with a particle size of 1μm ( (Atomic ratio = 0.04:1) is added to a high-speed mixer and mixed at 800 rpm for 20 min. The resulting mixture is then kept at 300 °C for 3 h in an air atmosphere to obtain the Ti-doped precursor. Ti-doped precursors were combined with particles of 2 μm in size and 3.4 μm in specific surface area. 2 / g of MgCO3 (Mg:TM atomic ratio = 0.02:1) was mixed in a high-speed mixer at 600rpm for 15min, and the resulting mixture was kept at 600℃ for 5h in air atmosphere to obtain Ti-Mg doped precursor; Ti-Mg doped precursor and D 90 ZrO2 with a particle size of 0.5 μm (Zr:TM atomic ratio = 0.01:1) was mixed at 400 rpm for 30 min in a high-speed mixer. The resulting mixture was kept at 850 °C for 8 h in an air atmosphere to obtain a gradient doped precursor. Gradient-doped precursors were mixed with Li2CO3 with a particle size of 5 μm. (Atomic ratio = 1.3:1) was mixed in a high-speed mixer at 1000 rpm for 25 min under conditions of humidity <10% RH. The resulting mixture was first heated to 500℃ at 2℃ / min and held for 5 h, then heated to 900℃ at 5℃ / min and held for 12 h. After natural cooling, it was sieved through a 400-mesh sieve to obtain Ti-Mg-Zr gradient-doped lithium-rich manganese-based cathode material.

[0043] Example 3 Commercial precursor Ni with a particle size of 6μm was used. 0.35 Mn 0.65(OH)2 and La(NO3)3 with a particle size of 15μm (La:TM atomic ratio = 0.03:1) were added to a high-speed mixer and mixed at 800rpm for 20min. The resulting mixture was kept at 400℃ for 3h in air atmosphere to obtain the La-doped precursor. The La-doped precursor was combined with particles of 1 μm size and a specific surface area of ​​6.2 μm. 2 / g of CeO2 (Ce:TM atomic ratio = 0.02:1) was mixed in a high-speed mixer at 600 rpm for 15 min, and the resulting mixture was kept at 650℃ for 5 h in air atmosphere to obtain Ti-Mg doped precursor; Ti-Mg doped precursor and D 90 ZrO2 with a particle size of 0.5 μm (Zr:TM atomic ratio = 0.01:1) was mixed at 400 rpm for 30 min in a high-speed mixer. The resulting mixture was kept at 850 °C for 8 h in an air atmosphere to obtain a gradient doped precursor. Gradient-doped precursors were mixed with Li2CO3 with a particle size of 5 μm. (Atomic ratio = 1.3:1) was mixed in a high-speed mixer at 1000 rpm for 25 min under conditions of humidity <10% RH. The resulting mixture was first heated to 500℃ at 2℃ / min and held for 5 h, then heated to 900℃ at 5℃ / min and held for 12 h. After natural cooling, it was sieved through a 400-mesh sieve to obtain La-Ce-Zr gradient-doped lithium-rich manganese-based cathode material.

[0044] Example 4 Commercial precursor Ni with a particle size of 6μm was used. 0.35 Mn 0.65 (OH)2 and Ta2O5 with a particle size of 1 μm (Ta:TM atomic ratio = 0.03:1) were added to a high-speed mixer and mixed at 800 rpm for 20 min. The resulting mixture was kept at 350 °C for 3 h in an air atmosphere to obtain the Ta-doped precursor. The Ta-doped precursor was combined with a particle size of 1 μm and a specific surface area of ​​2.5 μm. 2 / g of MoO3 (Mo:TM atomic ratio = 0.02:1) was mixed in a high-speed mixer at 600rpm for 15min, and the resulting mixture was kept at 550℃ for 5h in air atmosphere to obtain the Ta-Mo doped precursor. Ta-Mo doped precursor and D 90 SnO2 with a particle size of 1 μm (Sn:TM atomic ratio = 0.01:1) was mixed at 400 rpm for 30 min in a high-speed mixer, and the resulting mixture was kept at 800 °C for 8 h in air atmosphere to obtain a gradient doped precursor. Gradient-doped precursors were mixed with Li2CO3 with a particle size of 5 μm. (Atomic ratio = 1.3:1) was mixed in a high-speed mixer at 1000 rpm for 25 min under conditions of humidity <10% RH. The resulting mixture was first heated to 500℃ at 2℃ / min and held for 5 h, then heated to 900℃ at 5℃ / min and held for 12 h. After natural cooling, it was sieved through a 400-mesh sieve to obtain Ta-Mo-Sn gradient doped lithium-rich manganese-based cathode material.

[0045] Example 5 Commercial precursor Ni with a particle size of 6μm was used. 0.35 Mn 0.65 (OH)2 and LiF with a particle size of 20 μm (F:TM atomic ratio = 0.05:1) were added to a high-speed mixer and mixed at 800 rpm for 20 min. The resulting mixture was kept at 300 °C for 3 h in an air atmosphere to obtain the F-doped precursor. The F-doped precursor was combined with particles of 10 μm size and 2.8 μm specific surface area. 2 / g of (NH4)4P2O7 (P:TM atomic ratio = 0.03:1) was mixed at 600rpm for 15min in a high-speed mixer, and the resulting mixture was kept at 600℃ for 5h in air atmosphere to obtain the FP-doped precursor. FP-doped precursor with D 90 SnO2 with a particle size of 1 μm (Sn:TM atomic ratio = 0.01:1) was mixed at 400 rpm for 30 min in a high-speed mixer, and the resulting mixture was kept at 800 °C for 8 h in air atmosphere to obtain a gradient doped precursor. Gradient-doped precursors were mixed with Li2CO3 with a particle size of 5 μm. (Atomic ratio = 1.3:1) was mixed in a high-speed mixer at 1000 rpm for 25 min under conditions of humidity <10% RH. The resulting mixture was first heated to 500℃ at 2℃ / min and held for 5 h, then heated to 900℃ at 5℃ / min and held for 12 h. After natural cooling, it was sieved through a 400-mesh sieve to obtain FP-Sn gradient doped lithium-rich manganese-based cathode material.

[0046] Example 6 Commercial precursor Ni with a particle size of 6μm was used. 0.35 Mn 0.65 (OH)2 and Co3O4 with a particle size of 1μm (Co:TM atomic ratio = 0.04:1) were added to a high-speed mixer and mixed at 800rpm for 20min. The resulting mixture was kept at 350℃ for 3h in air atmosphere to obtain the Co-doped precursor. The Co-doped precursor was combined with a particle size of 1 μm and a specific surface area of ​​3.5 μm. 2 / g of Ta2O5 (Ta:TM atomic ratio = 0.02:1) was mixed in a high-speed mixer at 600rpm for 15min, and the resulting mixture was kept at 550℃ for 5h in air atmosphere to obtain the Co-Ta doped precursor. Co-Ta doped precursor and D 90 Y2O3 with a particle size of 0.4 μm (Y:TM atomic ratio = 0.01:1) was mixed at 400 rpm for 30 min in a high-speed mixer. The resulting mixture was kept at 700 °C for 8 h in an air atmosphere to obtain a gradient-doped precursor. Gradient-doped precursors were mixed with Li2CO3 with a particle size of 5 μm. (Atomic ratio = 1.3:1) was mixed in a high-speed mixer at 1000 rpm for 25 min under conditions of humidity <10% RH. The resulting mixture was first heated to 500℃ at 2℃ / min and held for 5 h, then heated to 900℃ at 5℃ / min and held for 12 h. After natural cooling, it was sieved through a 400-mesh sieve to obtain Co-Ta-Y gradient-doped lithium-rich manganese-based cathode material.

[0047] Example 7 Commercial precursor Ni with a particle size of 6μm was used. 0.35 Mn 0.65 (OH)2 and MoO3 with a particle size of 1 μm (Mo:TM atomic ratio = 0.03:1) were added to a high-speed mixer and mixed at 800 rpm for 20 min. The resulting mixture was kept at 450 °C for 3 h in air atmosphere to obtain the Mo-doped precursor. Mo-doped precursors were combined with particles of 2 μm in size and 3.4 μm in specific surface area. 2 / g of MgCO3 (Mg:TM atomic ratio = 0.02:1) was mixed in a high-speed mixer at 600rpm for 15min, and the resulting mixture was kept at 600℃ for 5h in air atmosphere to obtain the Mo-Mg doped precursor. Mo-Mg doped precursor and D 90 La2O3 with a particle size of 0.5 μm (La:TM atomic ratio = 0.01:1) was mixed at 400 rpm for 30 min in a high-speed mixer, and the resulting mixture was kept at 750 °C for 8 h in an air atmosphere to obtain a gradient doped precursor. Gradient-doped precursors were mixed with Li2CO3 with a particle size of 5 μm. (Atomic ratio = 1.3:1) was mixed in a high-speed mixer at 1000 rpm for 25 min under conditions of humidity <10% RH. The resulting mixture was first heated to 500℃ at 2℃ / min and held for 5 h, then heated to 900℃ at 5℃ / min and held for 12 h. After natural cooling, it was sieved through a 400-mesh sieve to obtain Mo-Mg-La gradient-doped lithium-rich manganese-based cathode material.

[0048] Comparative Example 1 Commercial precursor Ni with a particle size of 6μm was used. 0.35 Mn 0.65 (OH)2 and Li2CO3 with a particle size of 5μm (Atomic ratio = 1.3:1) was mixed in a high-speed mixer at 1000 rpm for 25 min under conditions of humidity <10% RH. The resulting mixture was first heated to 500℃ at 2℃ / min and held for 5 h, then heated to 900℃ at 5℃ / min and held for 12 h. After natural cooling, it was sieved through a 400-mesh sieve to obtain undoped lithium-rich manganese-based cathode material.

[0049] Comparative Example 2 Commercial precursor Ni with a particle size of 6μm was used. 0.35 Mn 0.65 (OH)2, Al(NO3)3 powder with a particle size of 10 μm (Al:TM = 0.03:1) and Li2CO3 with a particle size of 5 μm (OH)2, Al(NO3)3 powder with a particle size of 10 μm (Al:TM = 0.03:1) (Atomic ratio = 1.3:1) was mixed at 1000 rpm for 25 min in a high-speed mixer under conditions of humidity <10% RH. The resulting mixture was first heated to 500℃ at 2℃ / min and held for 5 h, then heated to 900℃ at 5℃ / min and held for 12 h. After natural cooling, it was sieved through a 400-mesh sieve to obtain Al-doped lithium-rich manganese-based cathode material.

[0050] Comparative Example 3 Commercial precursor Ni with a particle size of 6μm was used. 0.35 Mn 0.65 (OH)2 with Al(NO3)3 powder with a particle size of 10 μm (Al:TM atomic ratio = 0.03:1), MoO3 with a particle size of 1 μm (Mo:TM atomic ratio = 0.02:1), Nb2O5 with a particle size of 1 μm (Nb:TM atomic ratio = 0.01:1) and Li2CO3 with a particle size of 5 μm (OH)2 with Al(NO3)3 powder with a particle size of 10 μm (Al:TM atomic ratio = 0.03:1), MoO3 with a particle size of 1 μm (Mo:TM atomic ratio = 0.02:1), Nb2O5 with a particle size of 1 μm (Nb:TM atomic ratio = 0.01:1) with Li2CO3 with a particle size of 5 μm (OH)2 with Al(NO3)3 powder with a particle size of 10 μm (Al:TM atomic ratio = 0.03:1), MoO (Atomic ratio = 1.3:1) was mixed in a high-speed mixer at 1000 rpm for 25 min under conditions of humidity <10% RH. The resulting mixture was first heated to 500℃ at 2℃ / min and held for 5 h, then heated to 900℃ at 5℃ / min and held for 12 h. After natural cooling, it was sieved through a 400-mesh sieve to obtain Al-Mo-Nb homogeneous doped lithium-rich manganese-based cathode material.

[0051] Comparative Example 4 Commercial precursor Ni with a particle size of 6μm was used. 0.35 Mn 0.65(OH)2 was mixed with La(NO3)3 with a particle size of 15 μm (La:TM atomic ratio = 0.03:1), CeO2 with a particle size of 1 μm (Ce:TM atomic ratio = 0.02:1), and ZrO2 with a particle size of 0.5 μm (Zr:TM atomic ratio = 0.01:1) in a high-speed mixer at 400 rpm for 30 min. The resulting mixture was then kept at 850 °C for 8 h in air to obtain a gradient-doped precursor. Gradient-doped precursors were mixed with Li2CO3 with a particle size of 5 μm. (Atomic ratio = 1.3:1) was mixed in a high-speed mixer at 1000 rpm for 25 min under conditions of humidity <10% RH. The resulting mixture was first heated to 500℃ at 2℃ / min and held for 5 h, then heated to 900℃ at 5℃ / min and held for 12 h. After natural cooling, it was sieved through a 400-mesh sieve to obtain La-Ce-Zr homogeneous doped lithium-rich manganese-based cathode material.

[0052] Comparative Example 5 The only difference between this comparative example and Example 1 is that the Nb bulk uniform doping step is omitted; all other conditions and parameters are exactly the same as in Example 1.

[0053] Comparative Example 6 The only difference between this comparative example and Example 1 is that there is no Mo subsurface doping and no Nb bulk uniform doping steps; all other conditions and parameters are exactly the same as in Example 1.

[0054] Performance testing The evaluation methods for the electrochemical performance of the lithium-rich manganese-based material samples prepared in Examples 1-7 and Comparative Examples 1-6 are as follows: A lithium-rich manganese-based material sample was weighed and mixed with conductive carbon black and polyvinylidene fluoride adhesive at a mass ratio of 90:5:5 to form a uniform slurry. The slurry was then evenly coated onto carbon-coated aluminum foil and transferred to a vacuum oven at 100°C. After complete drying, the aluminum foil was cut into positive electrode sheets for later use. Using lithium metal sheets as the negative electrode, a double-sided ceramic coating film (12μm dry-process base film + 2μm double-sided ceramic layer) as the separator, and a high-voltage electrolyte for lithium-ion batteries, a CR2032 type button cell was assembled in a glove box under argon atmosphere protection. Finally, cyclic charge-discharge tests were conducted within a voltage window of 2.5~4.55V. The results are shown in Table 1.

[0055] The electrical performance testing conditions were as follows: charge / discharge voltage range of 2.5~4.55V, and test temperature of 25℃. First, the cells were activated once at a rate of 0.1C within a voltage range of 2.5~4.55V. Then, the activated coin cells were tested at a rate of 1C within the same voltage range, followed by cycle testing at 1C. The results are shown in Table 2.

[0056] Table 1. Discharge capacity and initial coulombic efficiency of samples at different discharge rates.

[0057] As shown in Table 1, the initial coulombic efficiency of the samples prepared in Examples 1-7 was 88-93%, which was significantly higher than that of the comparative samples (82-87%), indicating that gradient doping can effectively suppress the initial irreversible oxygen release.

[0058] Table 2 Sample Cyclic Performance and Voltage Decay

[0059] As shown in Table 2, the cycle retention rates of all embodiments were 95-98%, which were better than those of the comparative examples (81-92%). The gradient structure alleviated the phase transition and TM dissolution. In Example 5, due to the synergistic effect of the anion gradient and bulk Sn, the voltage decay rate was the lowest at 0.07 mV / cycle.

[0060] The sample prepared in Comparative Example 1 had the worst capacity and cycle performance, proving that the unmodified lithium-rich material suffered from severe structural degradation. Although the capacity of the sample prepared in Comparative Example 3 was higher than that of the single-doped (Comparative Example 2), the cycle retention rate of 89.96% was still lower than that of the gradient-doped system (95~98%) due to the disordered element distribution.

[0061] The sample prepared in Comparative Example 5 retained the Mo subsurface gradient, resulting in a slightly better cycle retention rate than Comparative Example 5. Even with subsurface optimization (Mo), the lack of bulk Nb still led to Li... + The transmission capacity is limited, and its capacity is significantly insufficient compared to Example 1. The sample prepared in Comparative Example 6 lacked the subsurface conductive network of Mo and the bulk Li of Nb. + With channel expansion, the cycle retention rate was only 91% (compared to 96.72% in Example 1), and the voltage decay rate was 0.2mV / cycle (compared to 0.11mV / cycle in Example 1), demonstrating the synergistic necessity of Mo and Nb. In summary, the completeness of gradient doping is demonstrated in Example 1, which achieves comprehensive performance improvement through a three-level structure design of "surface Al-subsurface Mo-bulk Nb", thus verifying the effectiveness of the gradient strategy.

[0062] The high-speed mixing stepwise process (example) achieves precise element distribution while ensuring the integrity of the material structure. Simultaneous mixing and sintering (comparative examples 3-4) results in disordered element diffusion and limited performance improvement.

[0063] Figure 1 The discharge specific capacity cycling curves of Examples 1, 5, and Comparative Example 1 at 1C rate are shown.

[0064] from Figure 1As can be seen, Comparative Example 1 (undoped) exhibits rapid capacity decay, with a retention rate of only 81.1% after 100 weeks, reflecting the inherent structural instability of the unmodified material. In stark contrast, Example 1 (Al-Mo-Nb gradient doping) shows a healthy "activation followed by slow decline" characteristic, with a retention rate as high as 96.7% after 100 weeks, proving that its three-level gradient structure of "surface-subsurface-bulk phase" effectively suppresses structural degradation. Example 5 (FP-Sn gradient doping) has the flattest curve, with a retention rate of 97.8%, the best in the field, highlighting the unique advantages of anion doping in stabilizing the lattice oxygen framework and achieving ultra-long lifetime.

[0065] Figure 2 The above are charge-discharge curves of Example 1, Example 5, and Comparative Example 1 at a rate of 0.1C.

[0066] from Figure 2 It can be seen that Comparative Example 1 exhibits a long charging plateau above 4.4V, corresponding to severe irreversible oxygen release, resulting in a low first-cycle efficiency (81.9%). In both examples, this plateau is significantly shortened, and the first-cycle efficiency is improved to over 90%, demonstrating that doping effectively suppresses oxygen loss during the first charge and discharge process. Meanwhile, Example 5 exhibits the highest and flattest discharge voltage plateau, directly corresponding to its lowest voltage decay rate (0.08 mV / cycle), indicating that its layered structure is the most stable during cycling.

[0067] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention and not all embodiments. People can obtain other embodiments based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for preparing a solid-phase gradient-doped lithium-rich manganese-based cathode material, characterized in that, Includes the following steps: The precursor and surface dopant are first mixed and then heat-treated to obtain a surface-doped precursor. The surface-doped precursor and the subsurface dopant are mixed and reacted at a medium temperature to obtain a surface-subsurface doped precursor. The surface-subsurface doped precursor and the bulk dopant are mixed and subjected to high-temperature solid solution to obtain a gradient doped precursor. The gradient-doped precursor and the fourth lithium source are mixed and sintered to obtain a solid-phase gradient-doped lithium-rich manganese-based cathode material.

2. The preparation method according to claim 1, characterized in that, The surface dopant, subsurface dopant, and bulk dopant are each independently one of a metal oxide, a salt precursor, and an anion source, and the surface dopant, subsurface dopant, and bulk dopant are not the same; the metal oxide includes one or more of TiO2, La2O3, Ta2O5, ZrO2, Nb2O5, Al2O3, MgO, CeO2, MoO3, SnO2, Co3O4, and Y2O3; the salt precursor includes one or more of aluminum nitrate, ammonium niobate oxalate, magnesium carbonate, titanium oxysulfate, zirconium oxynitrate, lanthanum nitrate, ammonium cerium sulfate, yttrium acetate, ammonium fluorotantalate, ammonium metavanadate, and ammonium molybdate; the anion source includes one or more of ammonium hexafluorosilicate, lithium fluoride, ammonium pyrophosphate, ammonium sulfate, ammonium borate, and ethyl silicate.

3. The preparation method according to claim 1 or 2, characterized in that, The surface dopant has a particle size of 1~20 μm; the subsurface dopant has a particle size of 1~10 μm and a specific surface area of ​​2~10 m². 2 / g; the particle size of the bulk dopant is D 90 <2μm.

4. The preparation method according to claim 1, characterized in that, The heat treatment temperature is 250~450℃, and the holding time is 3~5h.

5. The preparation method according to claim 1, characterized in that, The intermediate-temperature reaction is carried out in an air atmosphere; the temperature of the intermediate-temperature reaction is 450~650℃, and the holding time is 5~8h.

6. The preparation method according to claim 1, characterized in that, The high-temperature solution treatment is carried out in an air atmosphere; the temperature of the high-temperature solution treatment is 750~900℃, and the holding time is 8~12h.

7. The preparation method according to claim 1, characterized in that, The lithium source is one or more of Li2CO3, LiOH, LiOH·H2O, Li2O, Li2O2, lithium acetate, lithium oxalate, and lithium nitrate.

8. The preparation method according to claim 1, characterized in that, The sintering is carried out in an air atmosphere; the sintering includes sequential low-temperature sintering and high-temperature sintering; the temperature of the low-temperature sintering is 300~600℃, and the holding time is 3~6h; the temperature of the high-temperature sintering is 850~950℃, and the holding time is 8~15h.

9. The solid-phase gradient-doped lithium-rich manganese-based cathode material prepared by the preparation method according to any one of claims 1 to 8, characterized in that, It includes a precursor and doping elements doped on the surface of the precursor; the doping elements include surface doping elements, subsurface doping elements and bulk doping elements; the surface doping elements, subsurface doping elements and bulk doping elements are doped on the surface of the precursor from shallow to deep.

10. The application of the solid-phase gradient-doped lithium-rich manganese-based cathode material of claim 9 in lithium-ion batteries.

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