Lithium-rich manganese-based positive electrode material precursor with gradient pore core-shell structure and preparation method of lithium-rich manganese-based positive electrode material precursor

Abstract

The invention discloses a lithium-rich manganese-based positive electrode material precursor with a gradient pore core-shell structure and a preparation method of the lithium-rich manganese-based positive electrode material precursor, and belongs to the technical field of lithium batteries. Through the combination of the gradient pore core technology, the compact shell technology and the fused salt sintering technology, the lithium ion transmission path is optimized from the structural design, the rate capability is improved, the side reaction and metal dissolution are inhibited by constructing the protective layer, the intrinsic structure of the material is improved through the advanced sintering technology, and the first effect is improved. Through the combined action of a series of innovations, a powerful technical support is provided for overcoming the traditional problems of the lithium-rich manganese-based positive electrode material and enabling the lithium-rich manganese-based positive electrode material to be applied to high performance.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium batteries, and in particular to a lithium-rich manganese-based positive electrode material precursor with a gradient pore core-shell structure and a preparation method thereof. Background Art

[0002] In the field of lithium-ion batteries, lithium-rich manganese-based layered oxides are considered promising candidates for next-generation high-energy-density cathode materials. However, bringing these promising materials to large-scale commercial application still faces numerous technical bottlenecks. One key challenge lies in the microstructural design of their precursors—pre-lithiation transition metal oxides.

[0003] Currently, the mainstream method for preparing lithium-rich manganese precursors, as disclosed in Chinese invention patent CN113247966A - Lithium-rich manganese-based precursors, cathode materials, and their preparation methods, tends to produce solid spherical particles. While this structure can improve the material's packing density, thereby enhancing the battery's volumetric energy density, its inherent physical properties significantly negatively impact electrochemical performance. Imagine lithium ions navigating a maze within such a dense "solid sphere," requiring them to painstakingly penetrate from the outer surface of the material to the deepest depths of the particle before participating in the charge and discharge reactions. This tortuous and lengthy diffusion path significantly limits the lithium ion transport rate. The direct consequence is a sharp decline in battery performance at high charge and discharge rates—so-called "poor rate performance." When rapid device charging is required or higher instantaneous power output is sought in power batteries, this solid structure becomes a significant bottleneck, limiting improvements in battery response speed and power density, making it difficult to meet growing application demands.

[0004] At the same time, the traditional co-precipitation method, as a common process for preparing such precursors, is relatively mature in controlling the macroscopic size of the particles and the agglomeration morphology of the primary particles, but it seems to be unable to precisely control the microscopic pore structure inside the particles. The co-precipitation process is essentially a rapid and complex chemical reaction and physical precipitation process. It is limited by the precise coordinated control of many parameters such as reactant concentration, pH value, temperature, stirring rate, etc. It is difficult to "carve" a uniform and controllable pore network inside the particles according to a preset blueprint like building blocks. This results in the internal structure of the solid spheres obtained being often relatively random and dense, lacking effective ion rapid transport channels and buffer space. This structural "congenital deficiency" further exacerbates the problem of lithium ion diffusion difficulties, and also limits the infiltration and contact area of ​​the electrolyte inside the particles, thereby affecting the overall electrochemical reaction kinetics.

[0005] In summary, the solid sphere structure commonly found in existing lithium-rich manganese precursors not only limits rate performance due to the long internal lithium ion diffusion path, but also the traditional co-precipitation method has limited ability to accurately construct an internal pore structure that is conducive to ion transport and buffering. These two constraints have jointly hindered the full realization of the performance potential of lithium-rich manganese-based positive electrode materials and posed a severe challenge to their application prospects in the next generation of high-performance batteries. Therefore, exploring new synthetic strategies to prepare lithium-rich manganese precursors with controllable porous structures has become a key issue that needs to be urgently addressed in this field. Summary of the Invention

[0006] The technical problem to be solved by this invention is to overcome the shortcomings of the existing technology and provide a lithium-rich manganese-based cathode material precursor with a gradient porosity core-shell structure and its preparation method. By combining the three technologies of gradient porosity core, dense shell and molten salt sintering, not only the lithium ion transmission path is optimized from the structural design and the rate performance is improved, but also the side reactions and metal dissolution are suppressed by constructing a protective layer. The material's intrinsic structure is improved through an advanced sintering process, thereby enhancing the initial efficiency. This series of innovations work together to provide strong technical support for lithium-rich manganese-based cathode materials to overcome traditional difficulties and move towards high-performance applications.

[0007] The technical solution of the present invention is: In one aspect, the present invention provides a method for preparing a lithium-rich manganese-based cathode material precursor having a gradient pore core-shell structure, comprising the following steps: S1 Core Layer Co-precipitation: Prepare a mixed salt solution of manganese, nickel, and cobalt, and introduce it into the reactor in parallel with CO2 bubbles while controlling the pH to 8-10. The reaction is carried out at 30-50°C for 3-8 hours to generate a porous core layer. The introduction of CO2 bubbles can construct a hierarchical porous structure through in-situ chemical reaction, while the pH value is precisely controlled to optimize crystal growth. S2 shell coating: add sodium tungstate, nickel cobalt manganese salt, and oxalic acid to the reactor, control the pH to 10-11, and react at 55-65 ° C for 6-10 hours to form a shell to obtain a core-shell structure precursor; S3 molten salt assisted sintering: The precursor is mixed with LiOH·H2O and NaCl-KCl molten salts and sintered in two stages in an oxygen flow: first sintering at 400-600℃ for 4-6h, and then sintering at 850-950℃ for 8-16h; the molten salt is removed by water washing to obtain a lithium-rich manganese-based positive electrode material precursor with a gradient pore core-shell structure.

[0008] Preferably, in step S1, the molar concentration of Mn in the mixed salt solution is 0.5-2 mol / L; the molar ratio of Mn, Ni, and Co is 0.7:(0.2-0.4):(0.1-0.3).

[0009] Preferably, in step S1, the flow rate of CO2 bubbles is 0.2-1 L / min.

[0010] Preferably, in step S1, 5-10 g / L of aqueous ammonia is added to the reactor to control the pH.

[0011] Preferably, in step S1 , the D50 of the porous core layer is 4-8 μm, and the porosity is 20-40%.

[0012] Preferably, in step S2, in the reactor, the concentration of sodium tungstate is 0.01-0.1 mol / L; the molar ratio of Ni:Co:Mn in the nickel-cobalt-manganese salt is 0.3:(0.2-0.4):(0.4-0.6), the concentration of Mn in the nickel-cobalt-manganese salt is 0.4-2 mol / L; and the concentration of oxalic acid is 0.1-1 mol / L.

[0013] Preferably, in step S2, the shell has a thickness of 0.1-1 μm.

[0014] Preferably, in step S3, the mass ratio of the precursor, LiOH·H2O, and NaCl-KCl molten salt is 100:(45-50):(15-20).

[0015] Preferably, in step S3, the mass ratio of NaCl to KCl in the NaCl-KCl molten salt is 1:(0.2-0.4).

[0016] On the other hand, the present invention provides a lithium-rich manganese-based positive electrode material precursor with a gradient pore core-shell structure, which is prepared by the above-mentioned method for preparing a lithium-rich manganese-based positive electrode material precursor with a gradient pore core-shell structure.

[0017] Compared with the prior art, the present invention has the following beneficial effects: 1. In order to overcome the inherent defects of traditional solid sphere precursors, the present invention innovatively prepared a lithium-rich manganese-based cathode material precursor with a "gradient porosity core-shell" structure. The core concept is to construct a hierarchical structure with gradually decreasing porosity from the inside to the outside of the particle. That is, the core of the particle is designed to have a high porosity area. This core is like a "sponge" full of microchannels. Its high porosity greatly shortens the lithium ion (Li + ) is the average distance that Li migrates from the interior of the particle to the surface. +Instead of having to traverse a thick solid matrix, they can quickly shuttle along these pre-set, short, and numerous pathways. This structural optimization directly leads to a leap in ion transport dynamics—experimental data show that this gradient pore core-shell structure increases the diffusion coefficient of lithium ions within the material by a full three times. This means that during the charge and discharge process, lithium ions can be embedded and extracted more quickly, significantly improving the material's rate performance, allowing the battery to maintain good capacity at high current densities, meeting the needs of fast charging and power-type applications.

[0018] 2. The present invention coats the precursor core particles with a dense outer shell. First, it effectively inhibits excessive electrolyte attack. Although the electrolyte participates in the electrochemical reaction, excessive contact or penetration into the particle interior, especially under high-voltage operating conditions, can trigger side reactions and damage the material structure. The dense outer shell acts as a physical barrier, limiting the deep penetration of the electrolyte into the particle interior, protecting the internal structure, particularly the highly porous core, from unwanted chemical attack. Second, and more critically, this outer shell significantly reduces the dissolution of transition metals (such as manganese and nickel). During charge-discharge cycles, especially at high voltages, some transition metal ions tend to dissolve into the electrolyte and deposit on the negative electrode. This can lead to a series of problems, including capacity decay of the positive electrode material and structural damage to the negative electrode—a phenomenon known as "transition metal dissolution." The presence of the dense outer shell restricts the pathways for metal ions to migrate from the particle interior to the outside, minimizing this dissolution loss and thus helping to maintain battery capacity stability and cycle life.

[0019] 3. To stably transform the gradient pore structure of the present invention into a high-performance cathode material, the present invention incorporates molten salt sintering technology during the lithiation sintering process. Lithium-rich manganese-based materials are prone to severe lattice distortion during high-temperature sintering. This is typically due to differences in ionic radius between different elements and stress during the formation of the layered structure. Lattice distortion not only reduces the material's ionic and electronic conductivity but also leads to structural instability, impacting cycle life. However, the present invention, through the efficient heat transfer and possible template / buffering effects of the molten salt, promotes orderly crystal growth at lower temperatures, effectively mitigating the severe lattice distortion associated with high-temperature sintering. Materials with more regular structures and reduced distortion have smoother ion channels and more efficient electron transport. A significant improvement in the initial coulombic efficiency (ICE) is a direct and important indicator of improvement. A high ICE means that a higher proportion of lithium ions embedded in the cathode are effectively released during the battery's first charge-discharge cycle, resulting in reduced losses. This is crucial for simplifying pre-cycling processing steps in the battery production process, reducing costs, and ensuring the initial capacity of the battery upon shipment.

[0020] 4. This invention combines a gradient-porous core, a dense shell, and molten salt sintering to optimize the lithium-ion transport pathway and enhance rate performance. It also inhibits side reactions and metal dissolution through the construction of a protective layer, and improves the material's intrinsic structure and initial efficiency through an advanced sintering process. This series of innovations collectively provides strong technical support for lithium-rich manganese-based cathode materials to overcome traditional challenges and advance towards high-performance applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is an SEM image of the lithium-rich manganese-based positive electrode material precursor with a gradient pore core-shell structure prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0022] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0023] Example 1 The method for preparing a lithium-rich manganese-based cathode material precursor having a gradient pore core-shell structure of this embodiment comprises the following steps: S1 core layer coprecipitation: A mixed salt solution of manganese, nickel, and cobalt was prepared using manganese sulfate, nickel sulfate, and cobalt sulfate, where the concentrations of Mn, Ni, and Co were 0.7 mol / L, 0.2 mol / L, and 0.1 mol / L, respectively. The mixed salt solution was introduced into a reactor in parallel with CO2 bubbles at a flow rate of 0.5 L / min. 8 g / L of ammonia water was added to control the pH to 9. The mixture was reacted at 40°C for 5 h to form a porous core layer (D50 = 6 μm, porosity 35%). S2 shell coating: 0.01 mol / L sodium tungstate, 0.5 mol / L manganese sulfate, 0.3 mol / L nickel sulfate, 0.2 mol / L cobalt sulfate, and 0.1 mol / L oxalic acid were added to the reactor, the pH was controlled at 10.5, and the reaction was carried out at 60°C for 8 h to form a shell (1 μm thick) to obtain a core-shell structure precursor; S3 molten salt-assisted sintering: A precursor with a mass ratio of 100:48.4:17.8 is mixed with LiOH·H2O and NaCl-KCl molten salt, where the mass ratio of NaCl to KCl in the NaCl-KCl molten salt is 1:0.3; two-stage sintering is performed in an oxygen flow: first sintering at 500°C for 4 hours and then sintering at 900°C for 10 hours; the molten salt is removed by water washing to obtain a lithium-rich manganese-based positive electrode material precursor with a gradient pore core-shell structure.

[0024] The SEM photo of the lithium-rich manganese-based cathode material precursor with a gradient pore core-shell structure prepared in this embodiment is shown in FIG. Figure 1 As shown in the figure, it can be seen that this embodiment successfully prepared a lithium-rich manganese-based positive electrode material precursor with a core-shell structure.

[0025] Example 2 The method for preparing a lithium-rich manganese-based cathode material precursor having a gradient pore core-shell structure of this embodiment comprises the following steps: S1 core layer coprecipitation: A mixed salt solution of manganese, nickel, and cobalt was prepared using manganese sulfate, nickel sulfate, and cobalt sulfate, where the concentrations of Mn, Ni, and Co were 0.7 mol / L, 0.3 mol / L, and 0.2 mol / L, respectively. The mixed salt solution was introduced into a reactor in parallel with CO2 bubbles at a flow rate of 1 L / min. 10 g / L ammonia water was added to control the pH to 10. The mixture was reacted at 50°C for 3 h to form a porous core layer (D50 = 5 μm, porosity 40%). S2 shell coating: 0.05 mol / L sodium tungstate, 0.6 mol / L manganese sulfate, 0.3 mol / L nickel sulfate, 0.3 mol / L cobalt sulfate, and 0.5 mol / L oxalic acid were added to the reactor, the pH was controlled at 11, and the reaction was carried out at 65°C for 6 h to form a shell (thickness of 0.8 μm) to obtain a core-shell structure precursor; S3 molten salt assisted sintering: The precursor with a mass ratio of 100:50:20 is mixed with LiOH·H2O and NaCl-KCl molten salt, where the mass ratio of NaCl to KCl in the NaCl-KCl molten salt is 1:0.4; two-stage sintering is carried out in an oxygen flow: first sintering at 600°C for 4 hours and then sintering at 950°C for 8 hours; the molten salt is removed by water washing to obtain a lithium-rich manganese-based positive electrode material precursor with a gradient pore core-shell structure.

[0026] Example 3 The method for preparing a lithium-rich manganese-based cathode material precursor having a gradient pore core-shell structure of this embodiment comprises the following steps: S1 core layer coprecipitation: A mixed salt solution of manganese, nickel, and cobalt was prepared using manganese oxalate, nickel oxalate, and cobalt oxalate, with concentrations of Mn, Ni, and Co, respectively, of 0.7 mol / L, 0.4 mol / L, and 0.3 mol / L. The mixed salt solution was introduced into a reactor concurrently with CO2 bubbles at a flow rate of 0.2 L / min. 5 g / L ammonia was added to control the pH to 8. The mixture was reacted at 30°C for 8 h to form a porous core layer (D50 = 4 μm, porosity 23%). S2 shell coating: 0.1 mol / L sodium tungstate, 0.4 mol / L manganese oxalate, 0.3 mol / L nickel oxalate, 0.4 mol / L cobalt oxalate, and 1 mol / L oxalic acid were added to the reactor, the pH was controlled at 10, and the reaction was carried out at 65°C for 6 h to form a shell (thickness of 0.7 μm) to obtain a core-shell structure precursor; S3 molten salt assisted sintering: The precursor with a mass ratio of 100:45:15 is mixed with LiOH·H2O and NaCl-KCl molten salt, where the mass ratio of NaCl to KCl in the NaCl-KCl molten salt is 1:0.2; two-stage sintering is carried out in an oxygen flow: first sintering at 400°C for 6 hours and then sintering at 850°C for 16 hours; the molten salt is removed by water washing to obtain a lithium-rich manganese-based positive electrode material precursor with a gradient pore core-shell structure.

[0027] Comparative Example 1 The difference from Example 1 is that in step S1, CO2 bubbles are not introduced.

[0028] Comparative Example 2 The difference from Example 1 is that step S2 is not performed.

[0029] Comparative Example 3 The difference from Example 1 is that in step S2, sodium tungstate is not added.

[0030] Comparative Example 4 The difference from Example 1 is that in step S2, nickel-cobalt-manganese salt is not added.

[0031] Comparative Example 5 The difference from Example 1 is that in step S2, oxalic acid is not added.

[0032] Comparative Example 6 The difference from Example 1 is that in step S3, NaCl-KCl molten salt is not added.

[0033] Comparative Example 7 The difference from Example 1 is that in step S3, one-stage sintering is adopted: sintering at 900° C. for 12 hours.

[0034] The lithium-rich manganese-based cathode material precursors prepared in Examples 1-3 and Comparative Examples 1-7 were assembled into batteries: 1) Electrode preparation Cathode slurry: Precursor: Super P:PVDF = 92:5:3 (NMP solvent); Coating: 150 μm wet film, vacuum drying at 120 ° C for 12 hours; Pole parameters: surface density 15±0.3mg / cm 2 , compacted density 3.2±0.1g / cm 3.

[0035] 2) Battery assembly (CR2032 button battery) Negative electrode: lithium foil (200 μm, 99.9%); Electrolyte: 1M LiPF6 in EC / DMC / EMC (1:1:1) + 2% LiDFOB; Separator: Celgard 2325 (25 μm); Assembly pressure: 8 MPa (argon glove box).

[0036] 3) Institutionalization 0.2C constant current charge to 4.8V → constant voltage until current ≤ 0.01C → 0.1C discharge to 2V (2 cycles).

[0037] The assembled battery was subjected to performance testing, and the test results are shown in Table 1: Table 1 Performance test results of the batteries assembled in Examples 1-3 and Comparative Examples 1-7

[0038] As can be seen from Table 1, compared with Example 1, the ion diffusion coefficient, first coulomb efficiency, and rate performance of Comparative Example 1 are all significantly reduced. This is because CO2 bubbles were not introduced into the core when preparing the core of Comparative Example 1, resulting in a decrease in porosity, making it impossible for lithium ions to quickly embed and de-embed in the material, thereby reducing the ion diffusion coefficient, first coulomb efficiency, and rate performance of the material. The first coulomb efficiency of Comparative Example 2 is reduced, and the amount of Mn dissolution increases. This is because Comparative Example 2 does not form a dense shell around the core, exposing the lithium-rich core layer directly to the electrolyte. The electrolyte penetrates into the interior of the particles, destroying their internal structure, and more Mn will dissolve in the electrolyte, resulting in a decrease in the performance of the assembled battery of Comparative Example 2. Comparative Example 3 does not add sodium tungstate, lacks the W-doped Li2WO4 grain boundary strengthening phase, and the grain boundary crack growth rate increases, resulting in a decrease in 5C / 0.1C rate performance and accelerated cycle capacity decay. In Comparative Example 4, nickel-cobalt-manganese salt was not added, the shell composition deviated, and a Li2MnO3 shell was formed, which reduced the electronic conductivity and thus the performance of the battery. In Comparative Example 5, oxalic acid was not added, which resulted in the inability to complex Mn 2+ , generating flaky rather than spherical particles, and the out-of-control morphology of the precursor leads to a decline in battery performance. Comparative Example 6 does not use molten salt sintering technology, the temperature required for the reaction is high, and the product crystallinity is poor, resulting in a decline in battery performance. Comparative Example 7 only uses one-stage sintering, and directly performs high-temperature sintering without low-temperature sintering, resulting in serious phase separation of Li2MnO3 and LiMO2. The layered-spinel phase transition occurs after 100 cycles, which reduces the ionic and electronic conductivity of the material, resulting in structural instability and affecting the cycle life.

[0039] Although the present invention has been described in detail by way of preferred embodiments, the present invention is not limited thereto. Without departing from the spirit and essence of the present invention, a person of ordinary skill in the art may make various equivalent modifications or substitutions to the embodiments of the present invention, and such modifications or substitutions shall be within the scope of the present invention. Any changes or substitutions that can be easily conceived by a person of ordinary skill in the art within the technical scope disclosed in the present invention shall be within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be based on the scope of protection of the claims.

Claims

1. A method for preparing a lithium-rich manganese-based cathode material precursor having a gradient pore core-shell structure, characterized in that: The following steps are involved: S1 Core layer co-precipitation: Prepare a mixed salt solution of manganese, nickel and cobalt, flow it into the reactor in parallel with CO2 bubbles, control the pH to 8-10, and react at 30-50℃ for 3-8h to form a porous core layer; S2 shell coating: add sodium tungstate, nickel cobalt manganese salt, and oxalic acid to the reactor, control the pH to 10-11, and react at 55-65 ° C for 6-10 hours to form a shell to obtain a core-shell structure precursor; S3 molten salt assisted sintering: the precursor is mixed with LiOH·H2O and NaCl-KCl molten salt and sintered in two stages in an oxygen flow: first sintering at 400-600℃ for 4-6h, and then sintering at 850-950℃ for 8-16h; The molten salt is removed by water washing to obtain a lithium-rich manganese-based cathode material precursor with a gradient pore core-shell structure.

2. The method for preparing a lithium-rich manganese-based cathode material precursor having a gradient pore core-shell structure according to claim 1, wherein: In step S1, the molar concentration of Mn in the mixed salt solution is 0.5-2 mol / L; the molar ratio of Mn, Ni, and Co is 0.7:(0.2-0.4):(0.1-0.3).

3. The method for preparing a lithium-rich manganese-based cathode material precursor having a gradient pore core-shell structure according to claim 1, wherein: In step S1, the flow rate of CO2 bubbles is 0.2-1 L / min.

4. The method for preparing a lithium-rich manganese-based cathode material precursor having a gradient pore core-shell structure according to claim 1, wherein: In step S1, 5-10 g / L of ammonia water is added to the reactor to control the pH.

5. The method for preparing a lithium-rich manganese-based cathode material precursor having a gradient pore core-shell structure according to claim 1, wherein: In step S1 , the D50 of the porous core layer is 4-8 μm, and the porosity is 20-40%.

6. The method for preparing a lithium-rich manganese-based cathode material precursor having a gradient pore core-shell structure according to claim 1, wherein: In step S2, in the reactor, the concentration of sodium tungstate is 0.01-0.1 mol / L; the molar ratio of Ni:Co:Mn in the nickel-cobalt-manganese salt is 0.3:(0.2-0.4):(0.4-0.6), the concentration of Mn in the nickel-cobalt-manganese salt is 0.4-2 mol / L; and the concentration of oxalic acid is 0.1-1 mol / L.

7. The method for preparing a lithium-rich manganese-based cathode material precursor having a gradient pore core-shell structure according to claim 1, wherein: In step S2, the shell thickness is 0.1-1 μm.

8. The method for preparing a lithium-rich manganese-based cathode material precursor having a gradient pore core-shell structure according to claim 1, wherein: In step S3, the mass ratio of the precursor, LiOH·H2O, and NaCl-KCl molten salt is 100:(45-50):(15-20).

9. The method for preparing a lithium-rich manganese-based cathode material precursor having a gradient pore core-shell structure according to claim 1, wherein: In step S3, the mass ratio of NaCl to KCl in the NaCl-KCl molten salt is 1:(0.2-0.4).

10. A lithium-rich manganese-based cathode material precursor having a gradient pore core-shell structure, characterized in that: The material is prepared by the method for preparing a lithium-rich manganese-based positive electrode material precursor having a gradient pore core-shell structure as described in any one of claims 1 to 9.

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