Method for preparing high-capacity lithium-ion battery negative electrode material from alkali metal-doped iron oxide

Abstract

The application provides a method for preparing high-capacity lithium ion battery negative electrode material from alkali metal doped iron oxide, and belongs to the technical field of lithium ion battery negative electrode material, and comprises the following steps: S1, placing a trivalent iron compound and an alkali metal ion compound in water, uniformly stirring, ultrasonic dispersion, and completely dissolving to obtain a mixed solution A; S2, slowly dropping a sodium hydroxide aqueous solution into the mixed solution A under stirring at room temperature, adjusting the pH of the mixed solution A to 4.0-4.5, and aging after reaction to obtain a colloidal precursor B; S3, sequentially performing suction filtration, washing and drying on the obtained colloidal precursor B; and S4, performing high-temperature calcination and decomposition on the dried powder to obtain the material. The application overcomes the shortcomings of poor conductivity and unstable structure of the iron oxide material, the doped alkali metal ions support the iron oxide particles, the structure of the iron oxide does not collapse in the charging and discharging cycle, the expansion and shrinkage of the volume is avoided, and the electrochemical performance of the lithium ion battery is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium ion battery negative electrode materials, and in particular relates to a method for preparing a high-capacity lithium ion battery negative electrode material by doping alkali metal with iron oxide. Background Art

[0002] Energy and environmental issues have always been a global concern and crucial factors influencing the energy strategies and technological development of various countries around the world. With the continuous improvement of human productivity, the demand for energy and sustainable development has become increasingly urgent. Against this backdrop, the search for a reusable, green, pollution-free, and stable energy storage device has become a pressing goal in the development of new energy. As a low-carbon, green energy storage medium, lithium-ion batteries (LIBs) have attracted significant attention and widespread favor from researchers and industry due to their outstanding advantages, including high energy density, no memory effect, long cycle life, and environmental friendliness. They have become a key research area that countries around the world are competing to develop.

[0003] Traditional commercial lithium-ion battery anode materials primarily use graphite and silicon. However, graphite has a relatively low theoretical capacity, while silicon anodes have a high expansion coefficient during charge and discharge, making them insufficient to meet the high energy density, high cycle capacity, and high stability requirements of modern devices. Consequently, researchers are seeking alternative materials with higher capacity, lower cost, non-toxicity, and excellent safety performance. Iron oxide (Fe2O3), a transition metal oxide, boasts a high theoretical specific capacity (1007 mAh / g), low cost, natural abundance, non-toxicity, and excellent safety performance. These properties have made Fe2O3 a recent research hotspot, and it is widely recognized as a promising anode material that could replace carbon materials in commercial applications in the future.

[0004] However, the large volume effect generated during the charge and discharge process can cause the Fe2O3 material to pulverize and fall off, thereby deteriorating the electrical contact between the active materials, leading to poor cycle stability and poor rate performance, which also hinder the application of Fe2O3 negative electrode materials. To overcome these problems, researchers have adopted a series of strategies, mainly including nanostructure optimization, composite material optimization, and carbon coating optimization.

[0005] Currently, there are various studies on the structural and material engineering modification of iron oxide as a negative electrode material. Chinese patent CN113346056 A discloses a silicon oxide @ iron oxide / carbon composite lithium ion battery negative electrode material and preparation method. Iron oxide microspheres agglomerate on the surface of silicon oxide particles and form a whole with the outermost carbon coating layer, overcoming the defects of poor conductivity and structural instability of iron oxide itself, and improving the conductivity and stability of the negative electrode material. However, the hydrothermal reactor synthesis method used in the process has many steps, high temperatures, dangerous operation, and complex process. Patent CN112047384 B discloses a method for preparing nano iron oxide negative electrode materials for lithium ion batteries using sulfuric acid leachate of tin ore tailings. The iron oxide is modified by nanostructure and improved cycle stability. However, the use of tailings to synthesize the negative electrode material has a high impurity content and poor conductivity of the iron oxide. Patented technology CN113735178B discloses a method for preparing a lithium-ion battery negative electrode material embedded with iron oxide particles in a carbon-nitrogen sheet. The method embeds nanoparticles of iron oxide into a carbon-nitrogen sheet with a lamellar structure, thereby improving the defects of pure iron oxide particles, such as weak conductivity and unstable structure. However, it is synthesized using organic substances such as melamine and formaldehyde, which is highly toxic and dangerous. Patent US2021083283A1 proposes adding iron oxide to the surface of the positive electrode, using its large specific surface area and porous structure to adsorb lithium polysulfide produced by the positive electrode, thereby improving the cycle performance and capacity. However, the method uses ferric nitrate to synthesize iron oxide, which has a long process flow and high requirements on the particle size of iron oxide. In addition, the coating and addition are prone to unevenness, making the operation difficult. Summary of the Invention

[0006] The present invention aims to overcome the defects of the prior art and provide a method for preparing an iron oxide negative electrode material for lithium-ion batteries with low cost, simple process, high capacity and long cycle life. The alkali metal ion-doped α-Fe2O3 negative electrode material prepared by this method exhibits excellent electrochemical properties.

[0007] In order to solve the above problems, the present invention provides the following technical solutions:

[0008] The present invention provides a method for preparing a high-capacity lithium-ion battery negative electrode material by doping alkali metal with iron oxide, the method comprising the following steps:

[0009] S1. placing a trivalent iron compound and an alkali metal ion compound in water, stirring them evenly, and then ultrasonically dispersing them until they are completely dissolved to obtain a mixed solution A;

[0010] S2. Slowly dropwise adding a sodium hydroxide aqueous solution into the mixed solution A under stirring at room temperature to adjust the pH of the mixed solution A to 4.0-4.5, and then ageing the solution after the reaction to obtain a colloidal precursor B;

[0011] S3, filtering, washing and drying the obtained colloidal precursor B in sequence to obtain a dried powder;

[0012] S4, calcining and decomposing the dried powder at high temperature to obtain the material.

[0013] Optionally, in step S1, the ferric iron compound is selected from at least one of ferric sulfate, ferric chloride, and ferric nitrate, and the alkali metal ion compound is selected from at least one of a water-soluble sodium salt, a potassium salt, a rubidium salt, and a cesium salt. Specifically, the water-soluble sodium salt is selected from at least one of sodium chloride, carbonate, and nitrate, the water-soluble potassium salt is selected from at least one of potassium chloride, carbonate, and nitrate, the water-soluble rubidium salt is selected from at least one of rubidium chloride, carbonate, and nitrate, and the water-soluble cesium salt is selected from at least one of cesium chloride, carbonate, and nitrate.

[0014] Optionally, in step S1, the concentration of iron ions in the mixed solution A is 25-40 g / L, and the concentration of alkali metal ions is 0.2-0.6 g / L; the pH of the mixed solution A is 1.35-1.92.

[0015] Optionally, in step S2, the concentration of the sodium hydroxide aqueous solution is 0.5-1.5 mol / L, the reaction time is 3-5h, and the aging time is 10-15h. The purpose of adding sodium hydroxide is to make the iron ions form iron hydroxide precipitation. During the precipitation process, a small amount of alkali metal ions are embedded in the iron hydroxide, and the main chemical reactions that occur are: Fe 3+ +OH - → Fe(OH)3. Iron hydroxide precipitate can exist stably in the pH range of 4.0~4.5.

[0016] Optionally, in step S3, the colloidal precursor B is washed with deionized water and alcohol, and dried in a vacuum at a drying temperature of 70-90° C. for 10-15 hours.

[0017] Optionally, in step S4, the high-temperature calcination and decomposition can be carried out under vacuum, inert gas, or atmospheric conditions, with a calcination temperature of 400-800°C and a calcination time of 1-3 hours. If the calcination is performed in a vacuum environment, the vacuum degree is ≤ 200 Pa. The chemical reaction that occurs is Fe(OH)3→Fe2O3+H2O, and the reaction produces nano-α-Fe2O3.

[0018] The present invention also provides a high-capacity lithium-ion battery negative electrode material prepared by the method.

[0019] Optionally, the alkali metal doping level in the high-capacity lithium-ion battery negative electrode material is 0.75%-2.5% of the mass of the nano-α-Fe2O3. The applicant's research has found that within this doping range, the overall material performance is optimal. Too little alkali metal doping has no effect, while too much increases both cost and material performance.

[0020] Optionally, the high-capacity lithium-ion battery negative electrode material is porous spherical or quasi-spherical particles, the undoped α-Fe2O3 is nano-scale with a particle size of 80-200nm; and the doped α-Fe2O3 nanoparticles have a particle size of 50-80nm.

[0021] Compared with the prior art, the present invention has the following positive effects:

[0022] The present invention adopts a chemical precipitation method to mix trivalent iron ions with alkali metal ions, embed alkali metal ions during the precipitation process of iron hydroxide, and obtain alkali metal ion-doped α-Fe2O3 lithium ion battery negative electrode material after high-temperature roasting. The method has a simple process flow, convenient operation, high safety, and low cost. The alkali metal ion-doped α-Fe2O3 lithium ion battery negative electrode material prepared by the present invention through the above method overcomes the shortcomings of poor conductivity and unstable structure of the iron oxide material itself. The porous spherical iron oxide becomes a lithium-embedded conductive channel, and the doped alkali metal ions support the iron oxide particles, so that the iron oxide structure will not collapse during the charge and discharge cycle, avoiding volume expansion and contraction, ensuring stability and conductivity, and improving the electrochemical performance of the lithium ion battery.

[0023] Taking cesium ion doping as an example, the prepared cesium-doped α-Fe2O3 lithium-ion battery anode material was applied to lithium-ion batteries, and electrochemical performance testing showed that the cesium-doped α-Fe2O3 lithium-ion anode material exhibited an initial discharge capacity of 1899 mAh / g during charge and discharge at a current density of 200 mAh / g. After 100 cycles at a current density of 200 mAh / g, the discharge capacity reached 1070 mAh / g, and after 300 cycles, the discharge capacity reached 970 mAh / g. This is significantly higher than that of undoped α-Fe2O3.

[0024] Therefore, the present invention has the advantages of simple process, low cost and convenient operation, and the prepared alkali metal-doped α-Fe2O3 lithium ion battery negative electrode material has good electrochemical performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0026] Figure 1 are scanning electron microscope images of the products, wherein (a) is a scanning electron microscope image of undoped α-Fe2O3 in comparative example 1, and (b) is a scanning electron microscope image of cesium-doped α-Fe2O3 in example 2;

[0027] Figure 2 2 is the XRD pattern of pure α-Fe2O3 in comparative example 1 and cesium-doped α-Fe2O3 in example 2;

[0028] Figure 3 This is a performance diagram of long-cycle lithium-ion batteries of pure α-Fe2O3 in Comparative Example 1 and cesium-doped α-Fe2O3 in Example 2. DETAILED DESCRIPTION

[0029] In order to make the technical problems, technical solutions and advantages to be solved by the present invention clearer, a detailed description will be given below with reference to the accompanying drawings and specific embodiments.

[0030] Comparative Example 1

[0031] 10 g of ferric sulfate powder was added to 200 mL of deionized water and magnetically stirred at room temperature for 1 hour to obtain an ferric sulfate solution. 1 mol / L sodium hydroxide solution was then added to adjust the pH to 4. The mixture was stirred at room temperature for 4 hours and allowed to solidify for 12 hours to obtain a colloidal precursor. The colloidal precursor was filtered and washed twice, then dried in an oven at 80°C and a vacuum of ≤200 Pa for 12 hours to obtain a precursor powder. 2 g of the precursor powder was calcined at 700°C and a vacuum of ≤200 Pa for 3 hours to obtain the α-Fe2O3 lithium-ion battery anode material.

[0032] The ferric sulfate is anhydrous ferric sulfate powder with a purity of ≥99%; the particle size of the prepared α-Fe2O3 lithium ion battery negative electrode material is 80-200nm.

[0033] The α-Fe2O3 lithium ion battery negative electrode material prepared in this comparative example was applied to a lithium ion battery to conduct an electrochemical performance test: α-Fe2O3, superphosphorus carbon powder, and 5% PVDF were uniformly mixed in NMP at a mass ratio of 8:1:1 to prepare a working electrode, metallic lithium was used as a counter electrode, and 1 mol / L LiPF6 / EC-DEC-DMC (volume ratio 1:1:1) was used as the electrolyte. A simulated battery was assembled in a glove box and the simulated battery was subjected to charge and discharge tests in the voltage range of 0.01~3V (vs. Li + / Li), with a current density of 100-4000 mAh / g. Test results show that the α-Fe2O3 anode material for lithium-ion batteries has an initial discharge capacity of 1480 mAh / g at 200 mAh / g. After 100 cycles, the discharge capacity is 780 mAh / g. After 300 cycles, the discharge capacity is 500 mAh / g.

[0034] Example 1

[0035] 10 g of ferric sulfate powder, 100 mL of a 0.6 g / L potassium ion solution, and 100 mL of deionized water were mixed and magnetically stirred at room temperature for 1 hour to obtain a mixed solution. 1 mol / L sodium hydroxide solution was then added to adjust the pH to 4. The mixture was stirred at room temperature for 4 hours and allowed to cure for 12 hours to obtain a colloidal precursor. The colloidal precursor was filtered and washed twice, then dried in an oven at 80°C and a vacuum of ≤200 Pa for 12 hours to obtain a precursor powder. 2 g of the precursor powder was calcined at 700°C and a vacuum of ≤200 Pa for 3 hours to obtain a potassium-doped α-Fe2O3 lithium-ion battery anode material.

[0036] The ferric sulfate is anhydrous ferric sulfate powder with a purity of ≥99%; the particle size of the prepared α-Fe2O3 lithium ion battery negative electrode material is 80-150nm; and the potassium doping amount is 0.69%.

[0037] The potassium-doped α-Fe2O3 lithium-ion battery negative electrode material prepared in this embodiment was applied to a lithium-ion battery, and electrochemical performance tests were performed: potassium-doped α-Fe2O3, superphosphorus carbon powder, and 5% PVDF were uniformly mixed in NMP at a mass ratio of 8:1:1 to prepare a working electrode, metallic lithium was used as a counter electrode, and 1 mol / L LiPF6 / EC-DEC-DMC (volume ratio 1:1:1) was used as the electrolyte. A simulated battery was assembled in a glove box, and charge and discharge tests were performed on the simulated battery. The voltage range was 0.01~3V (vs. Li + / Li), with current densities ranging from 100 to 4000 mAh / g. Test results show that the potassium-doped α-Fe2O3 anode material for lithium-ion batteries has an initial discharge capacity of 1570 mAh / g at 200 mAh / g. After 100 cycles, the discharge capacity is 810 mAh / g. After 300 cycles, the discharge capacity is 550 mAh / g.

[0038] Example 2

[0039] 10 g of ferric sulfate powder, 100 mL of a 0.6 g / L cesium ion solution, and 100 mL of deionized water were mixed and magnetically stirred at room temperature for 1 hour to obtain a mixed solution. 1 mol / L sodium hydroxide solution was added to the mixed solution to adjust the pH to 4. The mixture was stirred at room temperature for 4 hours and cured for 12 hours to obtain a colloidal precursor. The resulting colloidal precursor was filtered and washed twice, then dried at 60-70°C and a vacuum of <150 Pa for 12 hours to obtain a precursor powder. The precursor powder was calcined at 600-700°C and a vacuum of <100 Pa for 2-3 hours to obtain a cesium-doped α-Fe2O3 lithium-ion battery anode material.

[0040] The ferric sulfate is anhydrous ferric sulfate powder with a purity of ≥99%. The particle size of the prepared (α-Fe2O3):Cs lithium ion battery negative electrode material is 50-80 nm. The cesium doping amount is 0.74%.

[0041] The cesium-doped α-Fe2O3 lithium-ion battery negative electrode material prepared in this embodiment was applied to a lithium-ion battery, and electrochemical performance tests were performed: cesium-doped α-Fe2O3, superphosphorus carbon powder, and 5% PVDF were uniformly mixed in NMP at a mass ratio of 8:1:1 to prepare a working electrode, metallic lithium was used as a counter electrode, and 1 mol / L LiPF6 / EC-DEC-DMC (volume ratio 1:1:1) was used as the electrolyte. A simulated battery was assembled in a glove box, and charge and discharge tests were performed on the simulated battery. The voltage range was 0.01~3V (vs. Li + / Li), with a current density of 100-4000 mAh / g. Test results show that the cesium-doped α-Fe2O3 anode material for lithium-ion batteries has an initial discharge capacity of 1899 mAh / g at 200 mAh / g. After 100 cycles, the discharge capacity is 1070 mAh / g. After 300 cycles, the discharge capacity is 930 mAh / g.

[0042] Example 3

[0043] 10 g of ferric sulfate powder, 100 mL of a 0.45 g / L rubidium ion solution, and 100 mL of deionized water were mixed and magnetically stirred at room temperature for 1.5 hours, followed by sonication for 30 minutes to obtain a homogeneous mixed solution. 1 mol / L sodium hydroxide solution was slowly added to the mixed solution under magnetic stirring at room temperature to adjust the pH to 4. The mixture was then reacted for 4 hours and cured for 12 hours to obtain a colloidal precursor. The resulting colloidal precursor was filtered and washed twice, then dried at 60-80°C under a vacuum of <100 Pa for 12 hours to obtain a precursor powder. The precursor powder was calcined at 600-700°C under a vacuum of <60 Pa for 2-3 hours to obtain the rubidium-doped α-Fe2O3 lithium-ion battery anode material.

[0044] The ferric sulfate is anhydrous ferric sulfate powder with a purity of ≥99%; the particle size of the prepared (α-Fe2O3):Rb lithium ion battery negative electrode material is 40-70nm; and the mass ratio of rubidium to iron is 0.5%.

[0045] The rubidium-doped α-Fe2O3 lithium-ion battery negative electrode material prepared in this embodiment was applied to a lithium-ion battery, and electrochemical performance tests were performed: rubidium-doped α-Fe2O3, superphosphorus carbon powder, and 5% PVDF were uniformly mixed in NMP at a mass ratio of 8:1:1 to prepare a working electrode, metallic lithium was used as a counter electrode, and 1 mol / L LiPF6 / EC-DEC-DMC (volume ratio 1:1:1) was used as the electrolyte. A simulated battery was assembled in a glove box, and the simulated battery was subjected to charge and discharge tests, with a voltage range of 0.01~3V (vs. Li + / Li), with a current density of 100-4000 mAh / g. Test results show that the rubidium-doped α-Fe2O3 anode material for lithium-ion batteries has an initial discharge capacity of 2459 mAh / g at 100 mAh / g. After 100 cycles, the discharge capacity is 1470 mAh / g; and after 300 cycles, the discharge capacity is 980 mAh / g.

[0046] Figure 1 (a) is a scanning electron microscope image of undoped α-Fe2O3 in comparative example 1, Figure 1 (b) is a scanning electron microscope image of cesium-doped α-Fe2O3 in Example 2. Comparing the two, it can be seen that the doping of alkali metal element cesium reduces the particle size of α-Fe2O3.

[0047] Figure 2 The XRD patterns of pure α-Fe2O3 in comparative example 1 and cesium-doped α-Fe2O3 in example 2 indicate that cesium doping does not change the original crystal structure of α-Fe2O3 and only plays a structural supporting role.

[0048] Figure 3 This is a performance diagram of long-cycle lithium-ion batteries of pure α-Fe2O3 in Comparative Example 1 and cesium-doped α-Fe2O3 in Example 2, indicating that the prepared cesium-doped α-Fe2O3 exhibits good electrochemical performance, with an initial discharge capacity of up to 1899 mAh / g; it has excellent cycle performance, with a discharge capacity of 970 mAh / g after 300 cycles, and a small capacity decay, which is better than the performance of most iron oxide batteries on the market.

[0049] Therefore, this specific embodiment has the advantages of short process, easy operation, low cost and other preparation and synthesis advantages. At the same time, the battery prepared with the prepared alkali metal-doped α-Fe2O3 lithium-ion battery negative electrode material has excellent electrochemical performance, high capacity and good cycle performance.

[0050] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A method for preparing a high-capacity lithium-ion battery negative electrode material by doping alkali metal with iron oxide, characterized in that: The method comprises the following steps: S1. Place a trivalent iron compound and an alkali metal ion compound in water, stir them evenly, and then disperse them by ultrasonication to completely dissolve them to obtain a mixed solution A, wherein the alkali metal ion compound is selected from at least one of a water-soluble potassium salt, a rubidium salt, and a cesium salt; S2. Slowly dropwise adding a sodium hydroxide aqueous solution into the mixed solution A under stirring at room temperature to adjust the pH of the mixed solution A to 4.0-4.5, and then ageing the mixed solution after the reaction to obtain a colloidal precursor B; S3, filtering, washing and drying the obtained colloidal precursor B in sequence to obtain a dried powder; S4, calcining and decomposing the dried powder at high temperature to obtain the material; The particle size of the doped α-Fe2O3 nanoparticles is 50-80nm.

2. The method for preparing a high-capacity lithium-ion battery negative electrode material by using alkali metal-doped iron oxide according to claim 1, characterized in that: In step S1, the trivalent iron compound is selected from at least one of ferric sulfate, ferric chloride, and ferric nitrate.

3. The method for preparing a high-capacity lithium-ion battery negative electrode material by using alkali metal-doped iron oxide according to claim 2, characterized in that: The water-soluble potassium salt is selected from at least one of potassium chloride, carbonate, and nitrate; the water-soluble rubidium salt is selected from at least one of rubidium chloride, carbonate, and nitrate; and the water-soluble cesium salt is selected from at least one of cesium chloride, carbonate, and nitrate.

4. The method for preparing a high-capacity lithium-ion battery negative electrode material by using alkali metal-doped iron oxide according to claim 1, characterized in that: In step S1, the concentration of iron ions in the mixed solution A is 25-40 g / L, and the concentration of alkali metal ions is 0.2-0.6 g / L.

5. The method for preparing a high-capacity lithium-ion battery negative electrode material by using alkali metal-doped iron oxide according to claim 1, characterized in that: In step S2, the concentration of the sodium hydroxide aqueous solution is 0.5-1.5 mol / L, the reaction time is 3-5 h, and the aging time is 10-15 h.

6. The method for preparing a high-capacity lithium-ion battery negative electrode material by using alkali metal-doped iron oxide according to claim 1, characterized in that: In step S3, the colloidal precursor B is washed with deionized water and alcohol, and dried in a vacuum at a drying temperature of 70-90° C. for 10-15 hours.

7. The method for preparing a high-capacity lithium-ion battery negative electrode material by using alkali metal-doped iron oxide according to claim 1, characterized in that: In step S4, high-temperature calcination and decomposition are carried out under vacuum, inert gas or atmospheric conditions, with a calcination temperature of 400-800° C. and a calcination time of 1-3 hours. If the environment is vacuum, the vacuum degree is ≤200 Pa.

8. A high-capacity lithium-ion battery negative electrode material prepared by the method according to any one of claims 1 to 7.

9. The negative electrode material for lithium-ion batteries according to claim 8, characterized in that: In the material, the doping amount of the alkali metal element is 0.75%-2.5% of the mass of the nano-α-Fe2O3.

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