Method for preparing high-entropy doped nickel-rich cobalt-free positive electrode material based on salt lake brine lithium source

Abstract

The invention discloses a high-entropy doped nickel-rich cobalt-free positive electrode material and a preparation method and application thereof based on a salt lake brine lithium source, and the method comprises the following steps: extracting salt lake brine to obtain a lithium chloride solution; then adding a nucleation inducer into the solution, and preparing lithium carbonate with a precipitator sodium carbonate; the preparation method comprises the following steps: preparing a high-entropy doped precursor: taking metal salts of Ni, Mn, Al, Ti, Mg and Mo doped elements as raw materials, and dissolving all transition metals in pure water; preparing an alkaline solution; the alkali solution is injected into the transition metal solution at the same time, magnetic stirring is conducted, and synthesis is conducted under the protection of argon at the temperature of 60-80 DEG C; centrifugally cleaning the precipitate, and carrying out vacuum drying at 110-120 DEG C to obtain a transition metal hydroxide precursor; fully mixing dried transition metal hydroxide precursor powder with the obtained lithium carbonate powder through ball milling; and calcining the precursor in a tubular furnace. The high-entropy doped nickel-rich cobalt-free positive electrode material has the advantages of high capacity, long cycle life and excellent thermal stability.

Description

Technical Field

[0001] This application relates to a method for preparing high-entropy doped nickel-rich cobalt-free cathode materials based on lithium sources from salt lake brine, which belongs to the field of battery material recycling. Background Technology

[0002] Nickel-rich layered oxides (such as LiNi) 0.8 Co 0.1 Mn 0.1 O2 (cobalt oxide) has become the preferred cathode material for high-energy-density batteries due to its high specific capacity. However, cobalt (Co) is expensive and toxic, making the development of cobalt-free cathodes an urgent need for industry. Pure LiNiO2 and its binary nickel-manganese (NMA) system suffer from a series of intrinsic defects: 1. Cation mixing: Ni 2+ (0.69Å) and Li + (0.76Å) Ions with similar radii are prone to positional interchange during sintering and cycling, blocking lithium-ion channels and leading to capacity reduction. 2. Poor cycling stability: Under deep delithiation (high voltage), Ni... 4+ It has strong oxidizing properties, which can catalyze the decomposition of the electrolyte and trigger the precipitation of lattice oxygen, causing the particle surface to reconstruct from a layered structure to a rock salt phase, increasing interfacial impedance. 3. Poor thermal stability: The charged material is prone to phase transition and oxygen release at high temperatures, which can lead to a violent exothermic reaction with the electrolyte, posing a safety hazard.

[0003] High-entropy stabilization strategies represent a cutting-edge approach to addressing the aforementioned problems. Its core scientific principle lies in dissolving four or more cations with similar molar ratios into the crystal lattice, utilizing extremely high configurational entropy to significantly reduce the system's Gibbs free energy (ΔG = ΔH - TΔS). During high-temperature sintering, the high configurational entropy effect can suppress the precipitation of specific impurity phases and promote uniform elemental distribution. During electrochemical cycling, it can "pin" the crystal lattice, effectively suppressing phase transitions, hindering oxygen loss and transition metal migration, thereby simultaneously improving the material's structural reversibility and thermal stability. However, the primary prerequisite for achieving high-entropy stabilization is the presence of multiple and uniformly distributed heterogeneous elements at the active sites (transition metal sites). Traditional doping modifications typically introduce only one or two small amounts of dopant elements, making it difficult to achieve a strong entropy effect. Furthermore, the synthesis of high-entropy materials requires extremely high uniformity and purity of the precursor. On the other hand, the performance of cathode materials is extremely sensitive to the purity of the lithium source. Lithium extraction from salt lake brines, especially those with a high magnesium-to-lithium ratio, is complex, leaving trace amounts of Mg, Ca, B, and SO4. 2- If impurities are introduced into the cathode material: Mg 2+ / Ca 2+ It may occupy lithium sites, exacerbate ion mixing, or agglomerate at grain boundaries, thus damaging particle integrity.

[0004] SO4 2- Decomposes at high temperatures to produce SO2 x Gases can cause pores to form inside the particles and may generate low-melting-point impurities such as Li2SO4, which can deteriorate the interfacial properties.

[0005] Currently, there are no systematic technical reports on combining specially purified brine lithium sources with high-entropy doping strategies to construct intrinsically stable nickel-rich cobalt-free cathode materials. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing ultra-high purity lithium salts suitable for high-end cathode materials from salt lake brine. The core objective of this invention is to utilize this lithium source, design specific high-entropy doping formulations, and synthesize precursors using a co-precipitation method to ultimately prepare a high-entropy doped nickel-rich, cobalt-free cathode material that possesses high capacity, long cycle life, and excellent thermal stability.

[0007] (1) The brine from the salt lake is extracted to obtain a lithium chloride solution; subsequently, a nucleation inducing agent is added to the obtained pure lithium chloride solution, followed by reaction with a specific precipitant (such as 1-1.5M sodium carbonate); after precipitation, aging, filtration, washing, and drying, ultra-high purity lithium carbonate is obtained. The key scientific measure is that, during the precipitation process, this application introduces a nucleation inducing agent (such as sodium citrate) at a molar ratio of 0.5% to 2% of lithium. Its mechanism of action is: citrate ions can react with Ca... 2+ The residual trace impurities form more stable water-soluble complexes, thereby "shielding" these impurities outside the crystal lattice during the growth of lithium carbonate crystal nuclei, achieving in-situ deep purification.

[0008] (2) Preparation of transition metal salt solutions: In the laboratory, NiSO4·6H2O (Aladdin, 99.9%), MnSO4·H2O (Aladdin, 99%), Al(NO3)3·9H2O (Macklin, 99.0%), TiOSO4 (Sigma, 99.9%), MgSO4·7H2O (Aladdin, 99.0%) and H2O were prepared using these solutions. 24 Mo7N6O 24 ·4H2O (Aladdin, 81-83%) is used as the transition metal source. According to the stoichiometric ratio of the products, all transition metals are dissolved in pure water and a homogeneous mixed solution is obtained by magnetic stirring. The total concentration of transition metals in the mixed solution is 0.8-1.5 M.

[0009] (3) Prepare an alkaline solution.

[0010] (4) The alkaline solution is simultaneously injected into the transition metal solution, magnetically stirred, and the precipitate is synthesized under argon protection at 60-80℃.

[0011] (5) The precipitate was centrifuged, washed, and vacuum dried at 110-120℃ to obtain the transition metal hydroxide precursor.

[0012] (6) The dry transition metal hydroxide precursor powder and the obtained lithium carbonate powder are thoroughly mixed by ball milling at a molar ratio of Li / (total transition metal) = 1.03-1.08; (7) The precursor was heated to 450-500℃ in a tube furnace at 2℃ / min and held for 4 hours, then heated to 730-750℃ at 2℃ / min and held for 15 hours, and then cooled in the furnace to obtain LiNi. 0.81 Mn 0.12 Al 0.04 Ti 0.01 Mg 0.01 Mo 0.01 O2 cathode material.

[0013] Furthermore, in the above technical solution, in step (1), the nucleation inducing agent is sodium citrate, and its molar amount is 0.5% to 2.0% of the lithium molar content. Furthermore, in the above technical solution, in step (1), the precipitation reaction temperature is 50-70℃, and the content of Mg and Ca in the obtained ultra-high purity lithium carbonate is less than 1 ppm.

[0014] Furthermore, in the above technical solution, in step (3), the alkaline solution is 2-3 M NaOH and 1.6-1.8 M NH4OH.

[0015] Furthermore, in the above technical solution, in step (2), the total concentration of transition metals in the mixed solution is 1-1.2 mol / L. Furthermore, in the above technical solution, in step (6), the molar ratio of lithium to total transition metal is 1.03. Furthermore, in the above technical solution, the method of extracting the brine from the salt lake to obtain a lithium chloride solution in step (1) is existing technology. For example, see CN119976895A, CN222846461U, etc.

[0016] Furthermore, in the above technical solution, in step (1), the drying conditions are vacuum drying at 110-120℃ for 9-12 hours.

[0017] This invention provides a high-entropy doped nickel-rich cobalt-free cathode material, which is prepared by the method described above.

[0018] The present invention provides a lithium-ion battery, including a positive electrode material, wherein the positive electrode material of the lithium-ion battery is the above-mentioned high-entropy doped nickel-rich cobalt-free positive electrode material.

[0019] Beneficial effects of the invention This invention utilizes lithium extraction technology from salt lakes, using the product from the extraction as a lithium source and regenerating it into a high-entropy doped nickel-rich, cobalt-free layered cathode material. This design strategy paves the way for the development of cobalt-free, high-energy-density lithium-ion battery cathodes and achieves sustainable and efficient utilization of lithium resources extracted from salt lakes while protecting the ecological environment. It has great potential for practical application in advanced energy storage systems, and the prepared high-entropy doped nickel-rich, cobalt-free cathode material exhibits electrochemical performance superior to commercial NCMs.

[0020] This invention combines innovative materials science theory with comprehensive consideration of the life cycle analysis of the new energy industry, providing theoretical guidance for lithium resource extraction and battery-grade lithium resource conversion. Attached Figure Description

[0021] Figure 1 The image shows the XRD pattern of the regenerated high-entropy doped nickel-rich cobalt-free cathode material obtained in Example 1 of this application.

[0022] Figure 2 This is a comparison chart of the electrochemical performance of the regenerated high-entropy doped nickel-rich cobalt-free cathode material obtained in Example 1 of this application and commercial materials.

[0023] Figure 3 The image shows a comparison of the electrochemical performance of regenerated doped nickel-rich cobalt-free cathode materials obtained in Comparative Example 2 of this application without the addition of doping elements such as Al, Ti, Mg, or Mo. Detailed Implementation

[0024] The present application is described in detail below with reference to the embodiments, but the present application is not limited to these embodiments.

[0025] Unless otherwise specified, all raw materials used in the embodiments of this application were purchased through commercial channels.

[0026] This application, through in-depth research on the optimization of electrochemical lithium extraction processes from salt lake brine and the preparation technology of battery-grade lithium-ion cathode materials, contributes to expanding the theoretical system of lithium resource chemistry, electrochemical engineering, and materials science, proposes new academic viewpoints, and promotes the development of related disciplines. This application improves the preparation efficiency and quality of battery-grade lithium-rich manganese cathode materials, providing technical support for the efficient utilization of lithium resources and the development of the battery industry.

[0027] Commercial NCM procurement from Shenzhen Kejing NCM811.

[0028] Example 1 A method for preparing high-entropy doped nickel-rich cobalt-free cathode materials based on lithium sources from salt lake brine, the method comprising the following steps: (1) Prepare a pure LiCl solution from old brine from a salt lake (see CN119976895A for the method). Add 0.8% mol of sodium citrate (calculated as lithium molar content) to the solution, then slowly add saturated Na2CO3 solution at 60℃, stir vigorously, and after the reaction is complete, age, filter, wash, and vacuum dry at 110℃ for 10 h to obtain lithium carbonate. ICP-MS analysis showed that the product contained Mg=0.6 ppm, Ca=0.3 ppm, and B=0.2 ppm.

[0029] (2) Using NiSO4·6H2O (Aladdin, 99.9%), MnSO4·H2O (Aladdin, 99%), Al(NO3)3·9H2O (Macklin, 99.0%), TiOSO4 (Sigma, 99.9%), MgSO4·7H2O (Aladdin, 99.0%) and H 24 Mo7N6O 24 ·4H₂O (Aladdin, 81-83%) is a transition metal source. Based on the stoichiometric ratio of the products, all transition metals were dissolved in pure water with a total concentration of 1 M, and a homogeneous mixed solution was obtained by magnetic stirring.

[0030] (3) An alkaline solution of 2 M NaOH and 1.6 M NH4OH was prepared.

[0031] (4) The alkaline solution was simultaneously injected into the transition metal solution, magnetically stirred, and the precipitate was synthesized under argon protection at 60°C.

[0032] (5) The precipitate was centrifuged, washed, and vacuum dried at 110°C to obtain the transition metal hydroxide precursor.

[0033] (6) The dry transition metal hydroxide precursor powder and the obtained lithium carbonate were mixed by ball milling at a molar ratio of Li / (total transition metal) = 1.03.

[0034] (7) Under an oxygen atmosphere, the temperature was increased to 500℃ at 2℃ / min and held for 4 hours, then increased to 750℃ at 2℃ / min and held for 15 hours, and then cooled in the furnace to obtain LiNi. 0.81 Mn 0.12 Al 0.04 Ti 0.01 Mg 0.01 Mo 0.01 O2 cathode material.

[0035] See Figure 1XRD analysis showed that the high-entropy doped sample maintained a pure layered structure. These results collectively confirm that multiple dopants have successfully entered the lattice of nickel-rich materials and stabilized the crystal structure.

[0036] Example 2 A method for preparing high-entropy doped nickel-rich cobalt-free cathode materials based on lithium sources from salt lake brine, the method comprising the following steps: (1) Prepare a pure LiCl solution from old brine from a salt lake (see CN119976895A for the method). Add 0.8% mol of sodium citrate (calculated as lithium molar content) to the solution, then slowly add saturated Na2CO3 solution at 60℃, stir vigorously, and after the reaction is complete, age, filter, wash, and vacuum dry at 115℃ for 10 h to obtain lithium carbonate. ICP-MS analysis showed that the product contained Mg=0.6 ppm, Ca=0.3 ppm, and B=0.2 ppm.

[0037] (2) Using NiSO4·6H2O (Aladdin, 99.9%), MnSO4·H2O (Aladdin, 99%), Al(NO3)3·9H2O (Macklin, 99.0%), TiOSO4 (Sigma, 99.9%), MgSO4·7H2O (Aladdin, 99.0%) and H 24 Mo7N6O 24 ·4H2O (Aladdin, 81-83%) is a transition metal source.

[0038] According to the stoichiometric ratio, all transition metals were dissolved in pure water with a total concentration of 1.2 M, and a homogeneous mixed solution was obtained by magnetic stirring.

[0039] (3) An alkaline solution of 2.5 M NaOH and 1.7 M NH4OH was prepared.

[0040] (4) The alkaline solution was simultaneously injected into the transition metal solution, magnetically stirred, and the precipitate was synthesized under argon protection at 70°C.

[0041] (5) Centrifuge and wash the precipitate and vacuum dry it at 115°C.

[0042] (6) The dry transition metal hydroxide precursor powder and the obtained lithium carbonate were mixed by ball milling at a molar ratio of Li / (total transition metal) = 1.05.

[0043] (7) Under an oxygen atmosphere, the temperature was increased to 450℃ at 2℃ / min and held for 4 hours, then increased to 730℃ at 2℃ / min and held for 15 hours, and then cooled in the furnace to obtain LiNi. 0.81 Mn 0.12 Al0.04 Ti 0.01 Mg 0.01 Mo 0.01 O2 cathode material.

[0044] Comparative Example 1 A method for preparing high-entropy doped nickel-rich cobalt-free cathode materials based on lithium sources from salt lake brine, the method comprising the following steps: (1) Prepare a pure LiCl solution from old brine in a salt lake (see CN119976895A for the method). Add 0.8% mol of sodium citrate (calculated as lithium molar content) to the solution, then slowly add saturated Na2CO3 solution at 60℃, stir vigorously, and after the reaction is complete, age, filter, wash, and vacuum dry at 120℃ for 10 h to obtain lithium carbonate. ICP-MS analysis showed that the product contained Mg=0.6 ppm, Ca=0.3 ppm, and B=0.2 ppm.

[0045] (2) Synthesis of high-entropy doped nickel-rich cobalt-free cathode material.

[0046] With NiSO4·6H2O (Aladdin, 99.9%), MnSO4·H2O (Aladdin, 99%), Al(NO3)3·9H2O (Macklin, 99.0%), TiOSO4 (Sigma, 99.9%), MgSO4·7H2O (Aladdin, 99.0%) and H 24 Mo7N6O 24 High-energy doped cathode material LiNi was synthesized in deionized aqueous solution via co-precipitation using 4H₂O (Aladdin, 81-83%) as the transition metal source. 0.81 Mn 0.12 Al 0.04 Ti 0.01 Mg 0.01 Mo 0.01 O2.

[0047] (3) According to the stoichiometric ratio, all transition metals are dissolved in pure water with a total concentration of 1.5 M, and a homogeneous mixed solution is obtained by magnetic stirring.

[0048] (4) An alkaline solution of 3 M NaOH and 1.8 M NH4OH was prepared.

[0049] (5) The alkaline solution was simultaneously injected into the transition metal solution, magnetically stirred, and the precipitate was synthesized under argon protection at 80°C.

[0050] (6) Centrifuge and wash the precipitate and vacuum dry it at 120°C.

[0051] (7) The dry transition metal hydroxide precursor powder and the obtained lithium carbonate were mixed by ball milling at a molar ratio of Li / (total transition metal) = 1.08. Under an oxygen atmosphere, the temperature was increased to 455°C at 2°C / min and held for 4 hours, then increased to 740°C at 1°C / min and held for 15 hours, and then cooled in the furnace.

[0052] In this comparative example, the temperature was increased at a rate of 1 °C / min. Due to this slow heating rate, the excessively long heating time would cause more lithium to volatilize at high temperatures, especially as Li₂O. This would result in insufficient actual lithium content in the final material, failing to yield the target product of this application.

[0053] Comparative Example 2 The difference from Example 1 is that no doping elements such as Al, Ti, Mg, or Mo are added. All other conditions are exactly the same as in Example 1; see [link to example]. Figure 3 In the high-entropy doping modification study of nickel-rich lithium-ion battery materials, the absence of any single element leads to a significant decrease in the overall performance of the material. This result strongly demonstrates that the advantage of high-entropy doping in this application does not stem from the independent effect of a specific element, but rather from the powerful "synergistic effect" generated between multiple elements.

[0054] The electrochemical performance testing conditions in this application are as follows: Let stand: After assembling the CR2032 button battery and removing it from the glove box, let it stand at room temperature for several hours to allow the electrolyte to fully soak in.

[0055] Long-cycle stability test: Test mode: Constant current charge and discharge.

[0056] Voltage window: set to 2.5 V - 4.4 V (vs. Li + / Li). This window is for the high-voltage range commonly used for nickel-rich materials.

[0057] Test magnification: Figure 2 It involves continuous charge-discharge cycles at a rate of C / 3. Figure 3 It performs continuous charge-discharge cycles at a 1C rate. Capacity retention calculation: Record the discharge capacity for each cycle. The formula for calculating capacity retention is: Capacity retention rate (%) = (Discharge capacity in round N / Discharge capacity in round 1) × 100% Continue testing until the predetermined number of cycles is reached, and record the final capacity retention rate.

[0058] See also, Figure 2A successful patent application demonstrated the modification of nickel-rich layered oxide cathode materials for lithium-ion batteries using a high-entropy doping strategy, and a systematic evaluation of their electrochemical performance was conducted. Experimental results show that high-entropy doping significantly improves the cycling stability of the material. Under specific test conditions (e.g., C / 3 rate, 2.5-4.4V voltage window), the unmodified commercial material retained only 47.37% capacity after 400 cycles, while the high-entropy-doped material exhibited a significantly improved capacity retention of 82.77%. This is attributed to the introduction of various heterogeneous metal cations with different ionic radii and bond energies through high-entropy doping. These ions form robust "pinning points" in the crystal lattice, effectively suppressing the inherent harmful phase transitions (e.g., the transformation from layered structure to rock salt phase) during deep lithium insertion / extraction in nickel-rich materials. Simultaneously, the localized lattice distortions of multiple elements can absorb and release internal stresses generated during cycling, reducing irreversible changes in lattice parameters and the generation and propagation of microcracks, thereby significantly improving the cycling stability of the material.

[0059] The above description is merely a few embodiments of this application and is not intended to limit this application in any way. Although this application discloses preferred embodiments as described above, it is not intended to limit this application. Any changes or modifications made by those skilled in the art without departing from the scope of the technical solution of this application using the disclosed technical content are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A method for preparing high-entropy doped nickel-rich cobalt-free cathode materials based on lithium sources from salt lake brine, characterized in that, Includes the following steps: (1) Extraction treatment of salt lake brine to obtain lithium chloride solution; Subsequently, a nucleation inducing agent was added to the solution, and then it was reacted with a sodium carbonate precipitant solution. After precipitation, aging, filtration, washing and drying, lithium carbonate was obtained. (2) Preparation of high-entropy doped precursors: Using metal salts of Ni, Mn, Al, Ti, Mg and Mo doped elements as raw materials, according to the stoichiometric ratio, all transition metals are dissolved in pure water and a uniform mixed solution is obtained by magnetic stirring. The total concentration of transition metals in the mixed solution is 0.8-1.5M. (3) Prepare an alkaline solution; (4) The alkaline solution was simultaneously injected into the transition metal solution, magnetically stirred, and the precipitate was synthesized under argon protection at 60-80℃. (5) The precipitate was centrifuged and washed, and then vacuum dried at 110℃-120℃ to obtain the transition metal hydroxide precursor; (6) The dry transition metal hydroxide precursor powder and the obtained lithium carbonate powder are thoroughly mixed by ball milling at a molar ratio of Li / (total transition metal) = 1.03-1.08; (7) The precursor was heated to 450-500℃ in a tube furnace at 2℃ / min and held for 4 hours, then heated to 730-750℃ at 2℃ / min and held for 15 hours, and then cooled in the furnace to obtain LiNi. 0.81 Mn 0.12 Al 0.04 Ti 0.01 Mg 0.01 Mo 0.01 O2 cathode material.

2. The method according to claim 1, characterized in that, In step (1), the nucleation inducing agent is sodium citrate, and its addition amount is 0.5% to 2.0% of the lithium molar content.

3. The method according to claim 1, characterized in that, In step (1), the precipitation reaction temperature is 50-70℃, and the content of Mg and Ca in the obtained lithium carbonate is less than 1 ppm.

4. The method according to claim 1, characterized in that, In step (3), the alkaline solution is 2-3 M NaOH and 1.6-1.8 M NH4OH.

5. The method according to claim 1, characterized in that, In step (2), the total concentration of transition metals in the mixed solution is 1-1.2 mol / L.

6. The method according to claim 1, characterized in that, In step (6), the molar ratio of lithium to total transition metals is 1.

03.

7. A high-entropy doped nickel-rich cobalt-free cathode material, characterized in that, The high-entropy doped nickel-rich cobalt-free cathode material is prepared by the method described in any one of claims 1-6.

8. A lithium-ion battery, comprising a positive electrode material, characterized in that, The cathode material of the lithium-ion battery is the high-entropy doped nickel-rich cobalt-free cathode material as described in claim 7.

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