A core-enriched gradient in-situ doped gradient lithium-rich cathode material precursor and its preparation method
By employing a dual-tank gradient co-precipitation and variable pH control process, core-enriched gradient doping of lithium-rich manganese-based cathode materials was achieved, solving the problem of structural instability of the material under high voltage and improving the cycle stability and electrochemical performance of the battery.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- BEIJING UNIV OF TECH
- Filing Date
- 2026-02-03
- Publication Date
- 2026-06-02
AI Technical Summary
Existing lithium-rich manganese-based cathode materials have poor structural stability under high voltage, are prone to lattice oxygen precipitation and layered structure transformation, and are prone to cracking during lithium-ion insertion/extraction, resulting in voltage decay and capacity loss. Traditional doping methods are difficult to meet the different needs of the internal and surface.
By employing a dual-tank gradient co-precipitation process combined with variable pH control, the concentration gradients of Mn and Ni transition metals and dopant elements are achieved, forming a core-enriched gradient doping structure with particles growing radially, thus constructing a core-shell structure with continuously varying concentrations.
It significantly improves the structural stability and electrochemical performance of the material, suppresses lattice oxygen evolution, extends battery life, optimizes lithium-ion transport and particle mechanical strength, and enhances the cycle stability and rate performance of the battery.
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Abstract
Description
Technical Field
[0001] This invention belongs to the field of key material preparation technology for lithium-ion batteries, specifically relating to a lithium-rich manganese-based cathode material precursor with core enrichment gradient in-situ doping and related preparation methods. Background Technology
[0002] With the rapid development of new energy vehicles and large-scale energy storage systems, higher requirements are being placed on the energy density of lithium-ion batteries. Lithium-rich manganese-based oxides (LLOs) are considered one of the most promising candidate cathode materials for next-generation high-energy-density power batteries due to their high discharge specific capacity (over 250 mAh / g) and high operating voltage.
[0003] However, lithium-rich manganese-based materials still face many challenges in practical applications:
[0004] Poor structural stability: During high-voltage charging, the precipitation of lattice oxygen can lead to the migration of transition metal ions, inducing an irreversible transformation of the layered structure to the spinel phase, resulting in severe voltage decay and capacity loss.
[0005] Secondary particle cracking: During long-term cycling, the volume expansion / contraction caused by repeated lithium ion insertion / extraction can easily lead to microcracks inside the particles, which can damage electrical contacts and exacerbate side reactions.
[0006] To address these issues, researchers typically employ elemental doping (such as Al, Mg, and Ti) or surface coating techniques. Elemental doping can enhance the binding energy of metal-oxygen bonds and stabilize the crystal structure. However, traditional bulk homogeneous doping often struggles to simultaneously meet the different needs of the material's interior and surface: the interior requires high structural stability to suppress voltage decay, while the surface requires high ionic / electronic conductivity to improve rate performance. Furthermore, current mainstream concentration gradient materials primarily focus on the gradient distribution of transition metals (Ni and Mn), with limited research on controlling the spatial distribution of doping elements. Moreover, the fabrication processes are complex, making it difficult to precisely control the primary particle morphology of the precursor.
[0007] Therefore, developing a lithium-rich manganese-based precursor and cathode material that can simultaneously achieve transition metal concentration gradients and dopant element concentration gradients, and has a special microstructure, is of great significance for improving the overall electrochemical performance of lithium-ion batteries. Summary of the Invention
[0008] The purpose of this invention is to overcome the shortcomings of existing lithium-rich manganese-based cathode materials, such as poor cycle stability and rapid voltage decay, and to provide a positive gradient doped lithium-rich manganese-based cathode material precursor and its preparation method.
[0009] The present invention adopts a unique "dual-tank gradient coprecipitation" combined with a "variable pH value control" process to achieve a concentration gradient of Mn and Ni transition metals while constructing a "core-enriched gradient" distribution (i.e., positive gradient doping) in which the concentration of doping elements (such as Al, Mg, etc.) decreases from the core to the surface layer, and induces the primary particles to grow radially in a radial direction, thereby significantly improving the structural stability and electrochemical performance of the material.
[0010] To achieve the above object, the present invention adopts the following technical solutions:
[0011] In the first aspect, the present invention provides a precursor of a lithium-rich manganese-based cathode material with positive gradient doping. The precursor is spherical or quasi-spherical particles, and its chemical general formula is Ni x Mn y M k (OH)2 or Ni x Mn y M k CO3, where 0 < x < 1, 0 < y < 1, 0 < k ≤ 0.1, and x + y + k = 1; the elements inside the precursor show a continuous gradient distribution, and the specific characteristics are as follows: Transition metal gradient: The concentration of Mn decreases in a gradient from the center to the surface of the particle; the concentration of Ni increases in a gradient from the center to the surface of the particle. This design utilizes the Mn-rich core to provide high capacity and structural support, and utilizes the Ni-rich surface to improve conductivity and electrochemical activity.
[0012] Positive gradient of doping elements: The concentration of doping element M decreases in a positive gradient from the center to the surface of the particle. That is, the average molar concentration of doping element M in the core region (radius 0 - 30%) of the precursor is higher than the average molar concentration of doping element M in the surface layer region (radius 70 - 100%). Types of doping elements: The doping element M is selected from at least one of Al, Mg, Ti, Nb, Ta, Mo, W, Zr.
[0013] Preferably, the ratio of the molar content C core of the doping element M in the core region to the molar content C shell in the surface layer region satisfies 1.5 ≤ C core / C shell ≤ 10. This significant concentration difference ensures that the core region has extremely strong lattice stability (inhibiting oxygen evolution), and the surface layer region will not hinder the rapid transmission of lithium ions due to the low doping amount.
[0014] There is no obvious core-shell interface formed along the radial direction of the precursor particles, and the element concentration change curve is a continuous and smooth curve, which helps to relieve the stress concentration during the charge and discharge process and prevent particle cracking.
[0015] Microscopic morphological characteristics: The precursor is formed by the aggregation of primary particles, and the primary particles exhibit a radially growing morphology from the center outwards. In terms of physical indicators, the median particle size D50 of the precursor is 3 - 15 μm, the particle size distribution coefficient (D90 - D10) / D50 ≤ 1.2, and the tapped density ≥ 1.8 g / cm 3 , and the specific surface area is 5 - 15 m 2 / g.
[0016] Second, the present invention provides a method for preparing the above-mentioned precursor of the lithium-rich manganese-based cathode material with a positive gradient doping.
[0017] The method includes the following steps:
[0018] (1) Prepare a metal salt solution:
[0019] Solution A (manganese-rich core solution): containing a manganese salt, a nickel salt, and a salt of doping element M, where the molar ratio of Mn to Ni is a:b, a > b, and contains a predetermined amount of doping element M; this solution serves as the source of the "bottom solution" for the reaction and determines the high-Mn and high-doping characteristics of the particle core.
[0020] Solution B (nickel-rich shell solution): containing a manganese salt and a nickel salt, where the molar ratio of Mn to Ni is e:f, e > f, a > e, b < f, and does not contain doping element M or the content of M is significantly lower than that of solution A; this solution is used to construct the high-Ni and low-doping characteristics of the particle surface layer.
[0021] Selection of salts: The salt of doping element M is preferably at least one of aluminum sulfate, aluminum nitrate, magnesium sulfate, and magnesium nitrate. The total metal ion concentration of solution A and solution B is 1.5 - 2.5 mol / L.
[0022] (2) Dual-tank gradient co-precipitation, using a mode of linkage between two feeding tanks and a reaction kettle:
[0023] Add the bottom solution (a mixture of pure water, ammonia water, and alkali) to the reaction kettle. Under stirring, pump solution B into the container containing solution A at a constant flow rate v1 for mixing; simultaneously, pump the mixed solution AB in the solution A container into the reaction kettle at a flow rate v2; preferably, the flow rates v1 and v2 are equal. This operation ensures that the metal ion concentration entering the reaction kettle changes continuously with time, thereby forming a gradient structure without an interface.
[0024] Reaction control (key step): Basic parameters: Under the protection of an inert gas (such as nitrogen, argon), control the temperature in the reaction kettle to be 40 - 60 °C, the ammonia water concentration to be 0.3 - 0.8 mol / L, the stirring speed to be 500 - 1500 rpm, and the reaction time to be 5 - 30 h.
[0025] Variable pH control strategy: During the liquid reaction, the pH of the reaction system is not constant, but decreases linearly or stepwise as the reaction time progresses, with a total decrease of 0.2~0.5 (pH range from 8.0~11.5 to 7.5-11.3). The higher pH value in the early stage of the reaction is conducive to the formation of dense Mn-rich cores; as the reaction proceeds, the gradually decreasing pH value is conducive to the radial growth of primary particles, forming a loose and porous or radially oriented surface structure, thus obtaining a special morphology of "dense inside and loose outside" or "radial orientation".
[0026] Aging: After the reaction is completed, the resulting slurry is aged in the original solution at 50~70℃ for 2~10h to eliminate internal stress and improve the crystal structure.
[0027] Thirdly, the present invention provides a cathode material prepared from the above-mentioned precursor.
[0028] The obtained precursor material is mixed with lithium carbonate at a molar ratio of Li:(Ni+Mn+M)=(1.15~1.45):1, and the final product is obtained by high-temperature solid-state sintering (e.g., 800-950℃). One-step sintering or stepwise sintering can be used. This cathode material inherits the gradient structure characteristics of the precursor.
[0029] Beneficial effects
[0030] Compared with existing technologies, the present invention has the following significant advantages:
[0031] Significantly improves structural stability: By enriching the core region of the particles with dopants (such as Al and Mg), the strong chemical bonds formed by them (such as Al-O bonds) pin the lattice oxygen, effectively suppressing the precipitation of lattice oxygen and the transformation of the layered structure to the spinel phase in lithium-rich materials under high voltage, thus greatly improving cycle stability and voltage decay.
[0032] Optimized lithium-ion transport: The high Ni content and low doping element content on the particle surface, combined with the radially arranged primary particle structure, significantly reduces the interfacial charge transfer impedance and shortens the lithium-ion diffusion path, thereby improving the rate performance of the material.
[0033] Enhanced particle mechanical strength: The continuous concentration gradient distribution eliminates the interfacial stress common in core-shell structures, while the radial arrangement of primary particles can effectively buffer the anisotropic volume expansion during charging and discharging, suppress the pulverization and cracking of secondary particles, and extend battery life.
[0034] High process controllability: Through a unique variable pH co-precipitation process, the microstructure of the precursor can be precisely controlled, and the prepared material has high tap density and good processing performance. Attached Figure Description
[0035] Figure 1 This is a scanning electron microscope (SEM) image of the positive gradient doped lithium-rich manganese-based cathode material prepared in Example 1 of this invention; it shows that the secondary particles are spherical.
[0036] Figure 2 The image shows an energy dispersive X-ray spectroscopy (EDS) line scan of the precursor along a radial cross section in Embodiment 1 of the present invention; it shows that Mn and the dopant element Al decrease from the center to the surface. Detailed Implementation
[0037] The present invention will be further described in detail below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto.
[0038] Example 1: Preparation of positive gradient Al-doped lithium-rich cathode material precursor and material
[0039] (1) Solution preparation:
[0040] Solution A (rich in manganese and highly doped): Prepare a 2 mol / L metal salt solution containing nickel sulfate, manganese sulfate, and aluminum sulfate. The Ni:Mn molar ratio is 0.25:0.75. Add aluminum sulfate to make the Al:(Ni+Mn) molar ratio 1:1000 (i.e., 0.1 mol%). Place this solution in salt container A equipped with a stirrer.
[0041] Solution B (Nickel-rich + Undoped): Prepare a 2 mol / L metal salt solution with nickel sulfate and manganese sulfate as solutes. The Ni:Mn molar ratio is 0.45:0.55. This solution does not contain an aluminum source.
[0042] Bottom solution and precipitant: Prepare a 4 mol / L sodium hydroxide solution as the precipitant; prepare a 10 mol / L ammonia solution as the complexing agent. Add appropriate amounts of pure water and ammonia solution to the reactor beforehand. (2) Dual-tank gradient co-precipitation:
[0043] Turn on the agitator (1000 rpm) and heating system of the reactor, introduce nitrogen for protection, and control the temperature inside the reactor to 55℃. Turn on the pump for solution B and pump solution B into solution A at a flow rate (v1) of 10 mL / min. Keep solution A vigorously stirred to ensure instantaneous and uniform mixing.
[0044] Simultaneously turn on the pump for solution A and pump the mixed solution AB into the reaction vessel at a flow rate of 10 mL / min (v2). At the same time, pump in sodium carbonate solution and ammonia water.
[0045] (3) pH-variable reaction control:
[0046] At the beginning of the reaction, the salt solution, complexing agent, and precipitated gold were simultaneously pumped into the reactor, and the pH of the system was controlled at 8.0.
[0047] As the reaction time progressed, the pH value decreased linearly and slowly by fine-tuning the amount of sodium carbonate added. The reaction was stopped after 20 hours (at the end), and the system pH value decreased by 7.5 (total decrease of 0.5). The ammonia concentration was maintained at approximately 0.5 mol / L.
[0048] After the reaction is complete, stop stirring and let the slurry age in the original solution at 55°C for 1-5 hours.
[0049] (4) Post-treatment and sintering:
[0050] The aged precursor was filtered, washed, and dried to obtain a positive gradient Al-doped precursor. Tests showed that its D50 was 10.5 μm and its tap density was 2.0 g / cm³.
[0051] The precursor was mixed with lithium carbonate at a molar ratio of Li:(Ni+Mn+Al)=1.45:1.
[0052] Under an inert gas atmosphere, the material is first pre-fired at 500°C for 5 hours, then heated to 850°C for sintering for 12 hours, and then naturally cooled to obtain the final cathode material.
[0053] Example 2: Preparation of positive gradient Mg-doped lithium-rich cathode material precursor and material
[0054] The steps are basically the same as in Example 1, except that:
[0055] Doping elements: Magnesium nitrate is added to solution A instead of aluminum sulfate, and the Mg content is set at 0.5 mol% of the total metal (high core concentration); solution B does not contain magnesium.
[0056] pH control: The initial pH of the reaction was 8.0, and the final pH was 7.5 (total decrease of 0.5). Example 3: Preparation of positive gradient Co-doped lithium-rich cathode material precursor and material.
[0057] The steps are basically the same as in Example 1, except that:
[0058] Doping elements: Cobalt sulfate is added to solution A instead of aluminum sulfate, and the Co content is set at 0.5 mol% of the total metal (high core concentration); solution B does not contain cobalt.
[0059] pH control: The initial pH of the reaction was 8.0, and the final pH was 7.5 (total decrease of 0.5).
[0060] Comparative Example 1: Uniformly Doped Material
[0061] A traditional single-tank co-precipitation method was employed. A single metal salt solution was prepared with a Ni:Mn ratio of 0.3:0.7 (the average value from Example 1), and 0.1 mol% aluminum sulfate was added. The pH was maintained at a constant 8.0 throughout the reaction. The resulting precursor exhibited a uniform elemental distribution and no gradient structure.
[0062] Comparative Example 2: Traditional transition metal gradient (undoped element gradient)
[0063] The solution was prepared using a two-tank method. The Ni and Mn ratios in solutions A and B were the same as in Example 1, but no doping elements were added to either solution A or solution B. That is, there was only a Ni-Mn gradient, without any doping elements.
[0064] Comparative Example 3: Traditional transition metal gradient (undoped element gradient)
[0065] The solution was prepared using a two-tank method. The Ni and Mn ratios in solutions A and B were the same as in Example 1, but the same molar ratio of dopant elements was added to both solutions A and B. That is, there was only a Ni-Mn gradient, and no dopant element concentration gradient.
[0066] Performance Testing and Results Analysis
[0067] The cathode materials prepared in Examples 1-3 and Comparative Examples 1-3 were assembled into CR2032 coin cells for electrochemical performance testing. The test voltage range was 2.0-4.8V, and the test temperature was 25℃. Their electrochemical performance is shown in Table 1. The first-cycle discharge specific capacity was 208.28 mAh / g. Cyclic tests were conducted at 25℃ and a 1C rate. Comparative Example 1 had no transition metal salt concentration gradient and only added Al dopant; Comparative Example 2 had only a transition metal salt concentration gradient without elemental doping; and Comparative Example 3 had a transition metal salt concentration gradient and uniform elemental doping without a concentration gradient of doped elements.
[0068] Table 1 Comparison of battery performance of coin cells assembled from different modified samples
[0069] sample Sample composition 1C discharge specific capacity (mAh / g) First-lap coulomb efficiency (%) Capacity retention rate after 300 laps (%) Example 1 G-LLOs-Al-positive gradient 210.2 93.0 95.2 Example 2 G-LLOs-Mg-positive gradient 212.3 93.2 93.0 Example 3 G-LLOs-Co-positive gradient 213.1 94.1% 92.8 Comparative Example 1 LLOs-Al 208.3 90.3 60.2 Comparative Example 2 G-LLOs 207.8 89.6% 65.3 Comparative Example 3 G-LLOs-Al-uniform 206.4 89.1% 85.2
[0070] .
Claims
1. A core-enriched gradient in-situ doped gradient lithium-rich cathode material precursor, characterized in that, The precursor is spherical or quasi-spherical particles, and its chemical general formula is Ni x Mn y M k (OH)2 or Ni x Mn y M k CO3, where 0 < x < 1, 0 < y < 1, 0 < k ≤ 0.1, and x + y + k = 1; each element inside the precursor shows a continuous gradient distribution, and the specific characteristics are as follows: Transition metal gradient: The Mn concentration decreases in a gradient from the particle center to the surface; the Ni concentration increases in a gradient from the particle center to the surface; Positive gradient of doping element: The concentration of doping element M decreases in a positive gradient from the particle center to the surface; the doping element M is selected from at least one of Al, Mg, Ti, Nb, Ta, Mo, W, Zr.
2. A core-enriched gradient in-situ doped gradient lithium-rich cathode material precursor according to claim 1, characterized in that, The average molar concentration of doping element M in the core region of the precursor is higher than that in the surface layer region. The molar content C of the dopant element M in the core region core With the molar content C in the surface region shell The ratio satisfies 1.5 ≤ C core / C shell ≤10.
3. A core-enriched gradient in-situ doped gradient lithium-rich cathode material precursor according to claim 1, characterized in that, There is no obvious core-shell interface formed along the radial direction of the precursor particles, and the element concentration change curve is a continuous and smooth curve.
4. A core-enriched gradient in-situ doped gradient lithium-rich cathode material precursor according to claim 1, characterized in that, Microscopic morphology characteristics: The precursor is aggregated by primary particles, and the primary particles exhibit a radially growing morphology from the center outwards.
5. A core-enriched gradient in-situ doped gradient lithium-rich cathode material precursor according to claim 1, characterized in that, In terms of physical properties, the median particle size D50 of the precursor is 3~15 μm, the particle size distribution coefficient (D90-D10) / D50 ≤ 1.2, and the tap density ≥ 1.8 g / cm³. 3 Specific surface area is 5~15m² 2 / g.
6. A method for preparing a core-enriched gradient in-situ doped gradient lithium-rich cathode material precursor according to any one of claims 1-5, characterized in that, This method includes the following steps: (1) Prepare a metal salt solution: Solution A, rich manganese core solution: containing manganese salt, nickel salt and salt of doping element M, where the molar ratio of Mn to Ni is a:b, a>b, and contains a predetermined amount of doping element M. Solution B, rich nickel shell solution: containing manganese salt and nickel salt, where the molar ratio of Mn to Ni is e:f, e>f, a>e, b<f, and does not contain doping element M or the content of M is significantly lower than that in Solution A. (2) Dual-tank gradient coprecipitation, adopting a mode of linkage between a dual-feeding tank and a reaction kettle: Add the bottom liquid into the reaction kettle. Under stirring, pump Solution B into the container containing Solution A at a constant flow rate v1 for mixing; simultaneously pump the mixed solution AB in the Solution A container into the reaction kettle at a flow rate v2; the bottom liquid is a mixed solution of pure water, ammonia water and alkali. Basic parameters for reaction control: Under the protection of inert gas, control the temperature in the reaction kettle to be 40-60°C, the ammonia water concentration to be 0.3-0.8 mol / L, the stirring speed to be 500-1500 rpm, and the reaction time to be 5-30 h. Variable pH value control strategy: During the liquid feeding reaction process, the pH value of the reaction system is not constant, but decreases linearly or stepwise with the progress of the reaction time. The total decrease amplitude of the pH value is 0.2-0.5, and the pH range decreases from 8.0-11.5 to 7.5-11.3; a higher pH value at the initial stage of the reaction is beneficial to the formation of a dense Mn-rich core; as the reaction proceeds, gradually decreasing the pH value is beneficial to the radial growth of primary particles, forming a loose porous or large aspect ratio radial surface structure, so as to obtain a special morphology of "dense inside and sparse outside" or "radial orientation". Aging: After the liquid feeding reaction is completed, the obtained slurry is aged in the original solution at 50-70°C for 2-10 h to eliminate internal stress and perfect the crystal structure.
7. The method according to claim 6, characterized in that, The salt of doping element M is preferably at least one of aluminum sulfate, aluminum nitrate, magnesium sulfate, magnesium nitrate.
8. The method according to claim 6, characterized in that, The total metal ion concentration of Solution A and Solution B is 1.5-2.5 mol / L; the flow rates v1 and v2 are equal.
9. A positive electrode material, characterized in that, Mix the core-enriched type gradient in-situ doped gradient lithium-rich cathode material precursor described in any one of claims 1-5 with lithium carbonate according to the molar ratio of Li:(Ni+Mn+M)=(1.15-1.45):1, and the final product can be obtained through high-temperature solid-phase sintering, and one-step sintering or stepwise sintering can be adopted.