Method for preparing F-doped Li2RuO3 positive electrode material by sol-gel method

Abstract

The invention relates to a method for preparing an F-doped Li2RuO3 positive electrode material through a sol-gel method, and belongs to the technical field of lithium ion battery positive electrode materials. The method comprises the following steps: taking lithium acetate, ruthenium trichloride and ammonium fluoride as raw materials, taking citric acid monohydrate as a chelating agent, taking ethylene glycol as a cross-linking agent, and dissolving in deionized water to prepare a precursor solution; heating and stirring at 70-80 DEG C to form gel; drying to obtain a xerogel precursor; pre-sintering for 4-8 hours at the temperature of 300-400 DEG C in an air atmosphere to remove organic matters; and finally, sintering for 12-24 hours at the high temperature of 900-1000 DEG C in an inert atmosphere or a vacuum environment to obtain a final product. Lattice oxygen evolution and irreversible phase change of Li2RuO3 under high voltage are effectively inhibited through F-ion doping, and the electronic structure and the ionic conductivity of the material are improved, so that the reversible capacity, the rate capability and the cycling stability of the material are remarkably improved. The prepared material is uniform in component and stable in structure, and an effective scheme is provided for solving the problem of capacity fading of the lithium-rich positive electrode material.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery cathode material technology, and in particular to a method for preparing F-doped Li2RuO3 cathode material by sol-gel method. Background Technology

[0002] While lithium-rich layered cathode materials possess high capacity potential, they commonly suffer from lattice oxygen evolution under high voltage, leading to irreversible structural phase transitions and safety risks, severely limiting their practical applications. Although materials like Li₂RuO₃ can achieve high capacity through synergistic redox reactions of anions and cations, the irreversible structural changes that occur after the initial charge-discharge cycle still result in capacity decay and reduced cycle performance.

[0003] Known technical defects: 1. Oxygen precipitation in the lattice during high-voltage periods leads to structural degradation and decreased thermal stability. 2. Irreversible phase transitions occur in materials during electrochemical cycling, limiting long-term cycle life. Summary of the Invention

[0004] The technical solution of this invention to solve the above-mentioned technical problems is to provide a method for preparing F-doped Li2RuO3 cathode material by sol-gel method, comprising the following steps: (1) Preparation of precursor solution: Lithium salt, ruthenium salt and ammonium fluoride are used as raw materials, citric acid monohydrate is used as chelating agent and ethylene glycol is used as crosslinking agent. They are dissolved in deionized water and stirred to form a homogeneous solution. (2) Sol-gel process: The solution obtained in step (1) is heated and stirred at 70-80°C to evaporate the water until a viscous gel is formed; (3) Drying: The gel obtained in step (2) is dried to obtain a fluffy and porous dry gel precursor; (4) Pre-calcination: The dry gel precursor obtained in step (3) is heat-treated at 300-400°C in air atmosphere for 4-8 hours to remove organic matter; (5) High-temperature sintering: After grinding the powder pre-calcined in step (4), sinter it at 900-1000°C in an inert atmosphere or vacuum environment, hold it at the temperature for 12-24 hours, and cool it with the furnace to obtain the fluorine-doped lithium ruthenium oxide cathode material.

[0005] Furthermore, in step (1): The lithium salt is lithium acetate; The ruthenium salt is ruthenium trichloride; The fluorine source is ammonium fluoride; The lithium element in the lithium salt is in 5%-20% excess relative to the stoichiometric ratio of Li₂RuO₃.

[0006] Furthermore, in step (1): Citric acid monohydrate and all metal ions (Li + + Ru 3+） The ratio of total moles is (1.5 ~ 2): 1; The molar ratio of citric acid monohydrate to ethylene glycol is 1: (1 ~ 2).

[0007] Furthermore, the heating rate of the preheating in step (4) is 2-5°C / min.

[0008] Furthermore, in step (5): The inert atmosphere is a high-purity argon or nitrogen atmosphere; The heating rate for sintering is 2-5°C / min. The sol-gel method for preparing F provided by this invention - The method of doping Li2RuO3 cathode material has the following significant advantages: Improved electrochemical performance: F-doping optimizes the electronic structure of the material and promotes charge transfer kinetics, thereby contributing to improved reversible capacity and rate performance. More importantly, the stable crystal structure significantly reduces irreversible phase transitions during cycling, resulting in excellent capacity retention and long cycle life.

[0009] The synthesized material exhibits excellent uniformity and precise doping: Employing the sol-gel method, components are mixed at the molecular level in the form of a precursor solution. A uniform network structure is formed through the interaction of chelating and cross-linking agents, ensuring the uniform distribution of metal ions and F- ions at the atomic scale. This method overcomes the component segregation and inhomogeneous doping problems that may exist in traditional solid-state methods, resulting in a final product with high consistency in chemical composition and crystal structure.

[0010] In summary, this invention, through the combination of F-doping and an optimized sol-gel process, successfully prepared a Li2RuO3-based cathode material with stable structure, excellent electrochemical performance, and high safety. Furthermore, it influences the oxygen ion arrangement, resulting in the appearance of the R-3 phase during the initial synthesis of the material. This provides an effective technical solution to address key issues in lithium-rich cathode materials such as capacity decay, structural degradation, and irreversible phase transitions during electrochemical cycling. Attached Figure Description

[0011] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0012] Figure 1 Synchrotron radiation data for the charging and discharging process of Li₂RuO₃; Figure 2 F-doped Li₂RuO₃ of the present invention - Synchrotron radiation data during charging and discharging processes; Figure 3 This is a schematic diagram comparing the cyclic stability of the present invention; Figure 4 This is a schematic diagram showing the test comparison of the open-circuit impedance of the present invention. Detailed Implementation

[0013] This invention proposes a sol-gel method for preparing F-doped Li₂RuO₃ cathode materials, aiming to provide a sol-gel method for preparing F-doped Li₂RuO₃ cathode materials. - Methods for doping Li2RuO3 cathode materials.

[0014] The preparation of F-doped Li2RuO3 cathode material using the sol-gel method proposed in this invention will be described below in specific embodiments: Example 1: A method for preparing F-doped Li2RuO3 cathode material by sol-gel method, comprising the following steps: (1) Preparation of precursor solution: Lithium salt, ruthenium salt and ammonium fluoride are used as raw materials, citric acid monohydrate is used as chelating agent and ethylene glycol is used as crosslinking agent. They are dissolved in deionized water and stirred to form a homogeneous solution. (2) Sol-gel process: The solution obtained in step (1) is heated and stirred at 70-80°C to evaporate the water until a viscous gel is formed; (3) Drying: The gel obtained in step (2) is dried to obtain a fluffy and porous dry gel precursor; (4) Pre-calcination: The dry gel precursor obtained in step (3) is heat-treated at 300-400°C in air atmosphere for 4-8 hours to remove organic matter; (5) High-temperature sintering: After grinding the powder pre-calcined in step (4), sinter it at 900-1000°C in an inert atmosphere or vacuum environment, hold it at the temperature for 12-24 hours, and cool it with the furnace to obtain the fluorine-doped lithium ruthenium oxide cathode material.

[0015] Furthermore, in step (1): The lithium salt is lithium acetate; The ruthenium salt is ruthenium trichloride; The fluorine source is ammonium fluoride; The lithium element in the lithium salt is in 5%-20% excess relative to the stoichiometric ratio of Li₂RuO₃.

[0016] Furthermore, in step (1): Citric acid monohydrate and all metal ions (Li + + Ru 3+） The ratio of total moles is (1.5 ~ 2): 1; The molar ratio of citric acid monohydrate to ethylene glycol is 1: (1 ~ 2).

[0017] Furthermore, the heating rate of the preheating in step (4) is 2-5°C / min.

[0018] Furthermore, in step (5): the inert atmosphere is a high-purity argon or nitrogen atmosphere; The heating rate for sintering is 2-5°C / min. Example 2: A method for preparing F-doped Li2RuO3 cathode material by sol-gel method, comprising the following steps: Step 1: Calculation and weighing; 1. Target product: Assume the synthesis of 1g of pure phase Li2RuO3.

[0019] 2. Calculation of stoichiometry; Molecular weight of Li2RuO3: (2*6.94) + 101.1 + (3*16) = 177.98 g / mol Required mass of LiNO3: (2 * 68.94 g / mol / 177.98 g / mol) * 1 g * (1 + excess coefficient) ≈ 0.89 g Required mass of RuCl3·xH2O: The exact water content (x) needs to be determined first. It can usually be estimated based on the molecular weight of RuCl3 (207.4 g / mol), approximately 1.17 g. Lithium excess is required; due to the high volatility of lithium at high temperatures, an additional 5-20% lithium is typically added. An initial addition of 10% excess lithium is used. Therefore, the actual amount of LiNO3 weighed is approximately 0.89 g * 1.10 ≈ 0.98 g.

[0020] F doping amount: Assuming the synthesis of Li₂RuO₂.₉F₀.₁ (i.e., x = 0.1), the molar amount of F required is 0.1 times that of Ru.

[0021] Required mass of NH4F: (0.1 * 19 g / mol / 101.1 g / mol) * (37 g / mol / 19 g / mol) * 1 g ≈ 0.037 g. (Calculation path: molar amount of F -> molar amount of NH4F -> mass of NH4F) 3. Citric acid and ethylene glycol: The molar ratio of total metal ions (Li⁺ + Ru³⁺) to citric acid (CA) is usually 1:1.5 to 1:2, and the molar ratio of CA to EG is usually 1:1 to 1:2. Calculations can be made based on CA:metal ions = 2:1 and CA:EG = 1:1.5.

[0022] Step 2: Prepare the solution and form the sol; 1. Dissolve the weighed citric acid in an appropriate amount of deionized water (about 50 mL) and place it on a magnetic stirrer.

[0023] 2. Dissolve the weighed RuCl3·xH2O separately in a small amount of water (about 10 mL) to obtain a dark brownish-red solution. Slowly add it dropwise to the citric acid solution. The solution color may become darker or change at this time; continue stirring.

[0024] 3. Dissolve the weighed LiNO3 and NH4F in a small amount of water and add it to the above mixture.

[0025] 4. Continue stirring for 30 minutes to ensure that all metal ions are fully complexed with citric acid.

[0026] 5. Slowly add the measured amount of ethylene glycol (EG) to the mixture.

[0027] 6. Set the water bath or heating plate to 70-80°C and stir continuously. The solution will gradually evaporate and concentrate.

[0028] Step 3: Gelification and Pretreatment; 1. As water evaporates, the viscosity of the solution gradually increases, the color turns dark brown or black, and eventually forms a viscous gel.

[0029] 2. Continue heating until the gel stops flowing and a large number of bubbles are generated (esterification reaction and decomposition), finally obtaining a fluffy and porous black precursor dry gel.

[0030] 3. Transfer the dried gel to a forced-air drying oven and dry at 120°C for 12 hours to completely remove residual moisture.

[0031] Step 4: Pre-burning (decomposing organic matter); 1. Carefully remove the dried precursor powder from the beaker and lightly grind it in an agate mortar.

[0032] 2. Place the powder in a corundum crucible and put it in a muffle furnace.

[0033] 3. Set the heating program: heat to 350°C at a rate of 5°C / min and hold for 6 hours.

[0034] 4. The purpose of this step is to fully decompose and carbonize organic substances such as citric acid and ethylene glycol.

[0035] Step 5: High-temperature sintering (crystallization); 1. Grind the pre-calcined powder thoroughly again to make it as fine and uniform as possible.

[0036] 2. Press the powder into tablets.

[0037] 3. Place the compressed sheets or powder into a crucible. Since Ru may be oxidized to volatile RuO4 at high temperatures, sintering must be performed under an inert atmosphere (such as Ar) or in a vacuum. A tube furnace is used.

[0038] 4. Place the crucible in the center of the tube furnace and seal the furnace tube.

[0039] 5. Rinse the furnace tubes several times with high-purity Ar gas (≥99.99%) to remove air.

[0040] 6. Under an Ar atmosphere (with a continuous small flow of Ar), set the heating program: Increase the temperature to 950°C at a rate of 5°C / min.

[0041] Keep warm at 950°C for 24 hours.

[0042] After the process is completed, the furnace is cooled to room temperature.

[0043] 7. Turn off the Ar gas and carefully remove the sample. At this point, a sintered block should be obtained.

[0044] Step 6: Grinding and Preservation; 1. Grind the sintered block into fine powder in a mortar or ball mill.

[0045] 2. The final obtained Li2RuO3₋ x F x The powder is sealed and stored in a sample bag or sample bottle, and placed in a desiccator for later use.

[0046] Synchrotron X-ray absorption spectroscopy (XAS) and X-ray diffraction (XRD) were used to analyze the local and long-range structural changes of the material, confirming that the F-doped sample retains structural reversibility after cycling.

[0047] The original Li₂RuO₃ material has a C₂ / c structure. Analysis of synchrotron radiation test results shows that during charging to 4.5V, the crystal structure changes from the 1st C₂ / c phase through the intermediate 2nd C₂ / c phase and finally to the R⁻³ phase. The initial discharge phase transition is the opposite of the initial charging, with the material structure transforming from R⁻³ to C₂ / c. However, at 2.0V, the structure does not undergo a completely reversible change, but rather remains in a three-phase mixed state (1st C₂ / c, 2nd C₂ / c, and R⁻³ phases). This irreversible structural change is the reason for the poor electrochemical cycling stability of the material. The F-ion-doped sample, after synchrotron radiation testing, as shown... Figure 1 , Figure 2 As shown, F- doping initially induces changes in the oxygen ion arrangement, resulting in the initial appearance of the R-3 phase. However, after discharging to 2.0V, the material structure undergoes a completely reversible change, rather than remaining in a three-phase blend state. This reversible structural change is a direct reason for the improved electrochemical stability of the material.

[0048] Improved cycle stability, such as Figure 3 As shown, after initial cycle activation, the specific capacity of the F-ion-doped material stabilized at 260 mAh / g, while the specific capacity of the undoped original material Li₂RuO₃ was only 240 mAh / g after stabilization. Both in terms of specific capacity and cycle stability, F-ion doping significantly improves the electrochemical properties of the material.

[0049] The test results of the open-circuit impedance are as follows: Figure 4 As shown: Electrochemical impedance spectroscopy of the material before cycling revealed that the electrochemical impedance of the F- ion-doped material was significantly lower than that of the original material Li2RuO3, indicating that F doping can improve the conductivity of the material and further explain why it improves the electrochemical performance of the material. The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for preparing F-doped Li2Ru03 cathode material by sol-gel method, characterized in that, The method comprises the following steps: (1) Preparation of precursor solution: lithium salt, ruthenium salt and ammonium fluoride are used as raw materials, citric acid monohydrate is used as a chelating agent, ethylene glycol is used as a crosslinking agent, and deionized water is used as a solvent to form a uniform solution after stirring and mixing; (2) Sol-gel process: the solution obtained in step (1) is heated and stirred at 70-80°C, and water is evaporated until a viscous gel is formed; (3) Drying: the gel obtained in step (2) is dried to obtain a fluffy and porous xerogel precursor; (4) Calcination: the xerogel precursor obtained in step (3) is heat treated at 300-400°C in an air atmosphere for 4-8 hours to remove organic matter; (5) High-temperature sintering: the calcined powder of step (4) is ground and sintered at 900-1000°C in an inert atmosphere or vacuum environment for 12-24 hours, and then cooled in the furnace to obtain the fluorine-doped lithium ruthenium oxide positive electrode material.

2. The method for preparing F-doped Li₂RuO₃ cathode material by sol-gel method according to claim 1, characterized in that, In step (1): The lithium salt is lithium acetate; The ruthenium salt is ruthenium trichloride; The fluorine source is ammonium fluoride; The lithium element in the lithium salt is 5%-20% in excess relative to the stoichiometric ratio Li2RuO3.

3. The method for preparing F-doped Li₂RuO₃ cathode material by sol-gel method according to claim 1 or 2, characterized in that, In step (1): The ratio of citric acid monohydrate to the total moles of all metal ions (Li⁺ + Ru³⁺) is (1.5 ~ 2) : 1; The molar ratio of citric acid monohydrate to ethylene glycol is 1: (1 ~ 2).

4. The method for preparing F-doped Li₂RuO₃ cathode material by sol-gel method according to claim 1, characterized in that, The heating rate of the precalcination in step (4) is 2-5°C / min.

5. The method for preparing F-doped Li2Ru03 cathode material by sol-gel process according to claim 1, characterized in that, In step (5): The inert atmosphere is high-purity argon or nitrogen atmosphere; The heating rate of the sintering is 2-5°C / min.

Images