Bimetal synergistically doped iron oxide negative electrode material and preparation method and application thereof

Abstract

The invention relates to the technical field of preparation of a lithium ion battery negative electrode material, in particular to double-metal synergistic doping for improving the performance of an iron oxide negative electrode lithium ion battery and a preparation method of the double-metal synergistic doping. According to the double-metal synergistic doping, metal is doped into iron oxide mainly through a wet ball milling method. According to the invention, bimetal with a synergistic effect is innovatively doped into the iron oxide, and the conductivity of the iron oxide is effectively improved and the charge transfer resistance is reduced by virtue of the conductivity of the doped metal and enhancement of the structural stability of the iron oxide; the volume expansion and shrinkage of the iron oxide in the charging and discharging process are buffered. The high-rate discharge performance and the specific discharge capacity of the iron oxide negative electrode are improved by doping different bimetals and regulating and controlling the ratio of the doped metals to the iron oxide.

Description

Technical Field

[0001] The present invention relates to the technical field of preparation of negative electrode materials for lithium ion batteries, and in particular to a bimetallic synergistic doping method for improving the performance of lithium ion batteries with iron oxide negative electrodes and a preparation method thereof. Background Art

[0002] Traditional lithium / sodium-ion battery negative electrode materials (such as graphite and silicon-based materials) face significant technical bottlenecks in practical applications, and there is an urgent need to develop new alternative materials with high capacity, long cycle and low cost. Graphite, as the mainstream commercial negative electrode, has a theoretical capacity of only 372 mAh / g, and it is easy to cause lithium dendrite growth during fast charging, posing a safety hazard; although silicon-based materials have an ultra-high capacity of 4200 mAh / g, the volume expansion of more than 300% during charging and discharging will cause the electrode structure to collapse and the cycle performance to deteriorate sharply. In contrast, transition metal oxides (such as iron oxide Fe2O3) have become a research hotspot due to their high theoretical capacity (about 1007 mAh / g), abundant resources and environmental friendliness, but their defects such as poor intrinsic conductivity, significant volume expansion during lithiation and slow reaction kinetics have seriously restricted their practical applications. Specifically, the semiconductor properties of Fe2O3 result in extremely low electron mobility, large charge transfer resistance during charging and discharging, and poor rate performance; at the same time, iron ions undergo drastic lattice changes during the lithium insertion / delithiation process, causing particle pulverization and continuous deterioration of the electrode-electrolyte interface, and rapid capacity decay; in addition, its densely packed crystal structure limits the diffusion rate of lithium ions, further reducing the electrochemical performance.

[0003] To improve the above problems, researchers have tried to modify iron oxide by single metal doping (such as Mn, Co, Ni, etc.). This type of doping can regulate the electronic structure of the material to a certain extent. For example, Co²⁺ doping can increase the carrier concentration of Fe2O3, and Mn³⁺ doping can stabilize the lattice framework. However, the optimization dimension of single metal doping is limited: although excessive doping can improve conductivity, it will sacrifice specific capacity; and it is difficult to achieve a breakthrough in comprehensive performance by only regulating a single property (such as conductivity or structural stability). In addition, single metal doping has a weak effect on improving surface reaction kinetics and cannot simultaneously solve the problems of slow ion diffusion and many interface side reactions. Summary of the invention

[0004] In order to overcome the shortcomings of the prior art, a bimetallic synergistically doped iron oxide negative electrode material and a preparation method and application thereof are provided. By simultaneously doping a bimetallic with conductivity and stability, the conductivity of iron oxide can be effectively increased and the volume expansion of iron oxide during the charge and discharge process can be inhibited, thereby reducing the loss of irreversible capacity and improving the electrochemical performance of the iron oxide negative electrode.

[0005] The specific technical solutions of the present invention are as follows: A bimetal co-doped iron oxide anode material, which is composed of iron oxide nanoparticles and at least one of cobalt (Co), copper (Cu), molybdenum (Mo) and vanadium (V) for improving electron conductivity and at least one of zinc (Zn), manganese (Mn), titanium (Ti) and aluminum (Al) for enhancing stability. The mass ratio of iron oxide to doped metal is 1:0.05 - 0.1, and the bimetal is uniformly incorporated into the iron oxide to increase electron conductivity and enhance structural stability.

[0006] A preparation method of the bimetal co-doped iron oxide anode material as described above, comprising the following steps: (1) Leaching reaction is carried out between iron concentrate and acid, the leaching time is 60 - 300 min, the leaching temperature is 60 - 90 °C, and the leaching solution is obtained by filtration; (2) A precipitant is added to the leaching solution, the precipitant is at least one of sodium carbonate, sodium hydroxide and ammonia water, the reaction temperature is 60 - 90 °C, the reaction time is 2 h, the aging temperature is 60 °C, and the aging time is 4 h to obtain a ferric hydroxide precursor; (3) The ferric hydroxide precursor is sintered in an argon or nitrogen atmosphere, the sintering temperature is 350 - 500 °C, and the heat preservation time is 2 - 4 h to obtain iron oxide; (4) Iron oxide, metals for increasing conductivity and metals for increasing stability are mixed and ball-milled. One of water and absolute ethanol is selected as the solvent, the ball-milling speed is 200 - 400 rpm, and the ball-milling time is 2 - 8 h to obtain a bimetal-doped iron oxide composite material.

[0007] A lithium-ion battery, comprising the aforementioned bimetal-doped iron oxide anode material, a conductive agent, a binder and an electrolyte. The mass ratio of the anode material, the conductive agent and the binder is 7:2:1, and the electrolyte is 1M LiPF6 / EC:DMC:EMC (1:1:1).

[0008] The beneficial effects of the present invention: 1) The present invention first uses the iron concentrate leaching solution as an iron source to prepare a bimetal co-doped iron oxide anode material. This method has a short process flow, is simple and reliable, has good repeatability, strong operability and low cost, is suitable for industrial production, and the electrochemical performance of the coated iron oxide is significantly improved, having broad development prospects.

[0009] 2) By bimetal co-doping iron oxide in the present invention, the electron and lithium-ion transfer rates of the composite material can be improved, the rate performance of the material can be enhanced, and the electrochemical performance can be significantly improved.

[0010] 3) In the bimetal co-doped iron oxide material of the present invention, the bimetals are uniformly distributed in the iron oxide nanoparticles through ball milling, which can effectively increase the conductivity of iron oxide and buffer the volume expansion of iron oxide during charge and discharge, improve the interfacial stability between the material and the electrolyte, and greatly improve the structural stability of iron oxide. Description of the Drawings

[0011] Figure 1 SEM image of the bimetal co-doped iron oxide prepared in the present invention; Figure 2 Long cycle performance graph of the bimetal co-doped iron oxide prepared in the present invention as the anode material of a lithium-ion battery, showing the discharge specific capacity of the material after 500 cycles at a current density of 500 mA / g; Figure 3 Rate performance graph of the bimetal co-doped iron oxide prepared in the present invention as the anode material of a lithium-ion battery, showing the discharge specific capacity of the material at different current densities. Detailed Embodiments

[0012] The present invention will be further described below in conjunction with the drawings and embodiments, but the present invention is not limited in any way. Any transformation or replacement based on the teachings of the present invention falls within the protection scope of the present invention.

[0013] A bimetal co-doped iron oxide anode material, the material is composed of iron oxide nanoparticles and at least one of cobalt (Co), copper (Cu), molybdenum (Mo), and vanadium (V) that improve the electronic conductivity and at least one of zinc (Zn), manganese (Mn), titanium (Ti), and aluminum (Al) that enhance the stability. The mass ratio of iron oxide to the doped metal is 1:0.05 - 0.1, and the bimetals are uniformly incorporated into the iron oxide to increase the electronic conductivity and enhance the structural stability.

[0014] The preparation method of the bimetal co-doped iron oxide anode material includes the following steps: (1) Leaching reaction is carried out on iron concentrate with acid, the leaching time is 60 - 300 min, the leaching temperature is 60 - 90 °C, and the leaching solution is obtained by filtration; (2) A precipitant is added to the leaching solution, the precipitant is at least one of sodium carbonate, sodium hydroxide, and ammonia water, the reaction temperature is 60 - 90 °C, the reaction time is 2 h, the aging temperature is 60 °C, and the aging time is 4 h to obtain a ferric hydroxide precursor; (3) The ferric hydroxide precursor is sintered in an argon or nitrogen atmosphere, the sintering temperature is 350 - 500 °C, and the heat preservation time is 2 - 4 h to obtain iron oxide; (4) Mix and ball-mill iron oxide, a metal for increasing conductivity, and a metal for increasing stability. Select one of water and absolute ethanol as the solvent. The ball-milling speed is 200 - 400 rpm, and the ball-milling time is 2 - 8 h to obtain a composite material of bimetal-doped iron oxide.

[0015] In step (1), the acid is at least one of sulfuric acid, hydrochloric acid, and nitric acid, and the concentration of the acid is 1 - 3 mol / L.

[0016] In step (2), the precipitant is at least one of sodium carbonate, sodium hydroxide, and ammonia water, and the concentration of the precipitant is 1 - 2 mol / L.

[0017] In step (4), the metal for increasing conductivity is at least one of cobalt (Co), copper (Cu), molybdenum (Mo), and vanadium (V), and the metal for increasing stability is at least one of zinc (Zn), manganese (Mn), titanium (Ti), and aluminum (Al). The ratio of iron oxide to the metals for increasing conductivity and stability is 1:1:0.05 - 0.1:1:0.05 - 0.1.

[0018] The material is used as the anode material of a lithium-ion battery, and after 500 cycles at a current density of 500 mA / g, the discharge specific capacity is not less than 700 mAh / g.

[0019] A lithium-ion battery includes the bimetal synergistically doped iron oxide anode material, a conductive agent, a binder, and an electrolyte. The mass ratio of the anode material, the conductive agent, and the binder is 7:2:1, and the electrolyte is 1M LiPF6 / EC:DMC:EMC (1:1:1).

[0020] A lithium-ion battery, after 500 cycles at a current density of 500 mA / g in the voltage range of 0 - 3V, the discharge specific capacity is not less than 700 mAh / g.

[0021] The core of this application lies in achieving multi-dimensional optimization through the synergistic effect of two metal ions. For example, when Mn and Co are co-doped, Mn³⁺ can expand the lattice spacing of iron oxide to promote the diffusion of lithium ions, while Co²⁺ can enhance the overall conductivity by forming an electron percolation network; the double doping of Ni and Cu can construct a "rigid-flexible" composite structure, where Ni²⁺ maintains the stability of the main framework and Cu⁺ relieves stress concentration, thus inhibiting particle rupture. In addition, the bimetal synergistic doping will also introduce oxygen vacancies or construct heterointerfaces, further reducing the charge transfer impedance and increasing the density of active sites. Theoretical calculations show that certain bimetal combinations (such as Ti - Mo) can synergistically regulate the energy band structure of Fe2O3, reducing its band gap from 2.1 eV to 0.8 eV and significantly enhancing the intrinsic conductivity.

[0022] This application aims to solve the problems of low conductivity and volume expansion of Fe2O3 during charge and discharge by co-doping with bimetals with conductivity and stability, thereby improving its cycle stability and electrochemical performance. Specifically, doping with one metal among cobalt (Co), copper (Cu), molybdenum (Mo), and vanadium (V) can improve the conductivity of iron oxide, and doping with zinc (Zn), manganese (Mn), titanium (Ti), and aluminum (Al) can increase stability and effectively buffer the volume change of Fe2O3 during lithium ion insertion and extraction, reduce the damage of the electrode structure, and at the same time improve the conductivity of the electrode and the lithium ion diffusion rate, thereby achieving more stable cycle performance and higher energy density.

[0023] Example 1: Preparation of Co and Zn co-doped iron oxide anode material Step 1: Mix iron concentrate with 2 mol / L sulfuric acid solution at a solid-liquid ratio of 1:15, leach at 80 °C for 180 min, and filter to obtain the leachate. Step 2: Add 1.5 mol / L sodium hydroxide solution to the leachate, adjust the pH to 9, react at 80 °C for 2 h, and then age at 60 °C for 4 h to obtain the iron hydroxide precursor.

[0024] Step 3: Sinter the iron hydroxide precursor in an argon atmosphere at 400 °C for 3 h to obtain iron oxide nanoparticles. Step 4: Mix the iron oxide nanoparticles, cobalt powder (Co), and zinc powder (Zn) at a mass ratio of 1:0.05:0.05, add anhydrous ethanol as a solvent, and ball mill at 300 rpm for 5 h in a ball mill to obtain a Co and Zn co-doped iron oxide composite. Step 5: Mix the iron oxide composite, conductive agent Super P, and binder PVDF at a mass ratio of 7:2:1, coat it on a copper foil to make an anode, and assemble it into a coin cell (electrolyte: 1M LiPF6 / EC:DMC:EMC = 1:1:1).

[0025] In the voltage range of 0~3 V, cycle at a current density of 500 mA / g for 500 cycles, and test its discharge specific capacity to be 720 mAh / g.

[0026] Example 2: Preparation of Cu and Ti co-doped iron oxide anode material Step 1: Mix iron concentrate with 1.5 mol / L hydrochloric acid solution at a solid-liquid ratio of 1:15, leach at 70 °C for 240 min, and filter to obtain the leachate. Step 2: Add 1 mol / L sodium carbonate solution to the leachate, adjust the pH to 8, react at 70 °C for 2 h, and then age at 60 °C for 4 h to obtain the iron hydroxide precursor; Step 3: Sinter the iron hydroxide precursor at 450 °C for 2.5 h under a nitrogen atmosphere to obtain iron oxide nanoparticles; Step 4: Mix the iron oxide nanoparticles, copper powder (Cu), and titanium powder (Ti) at a mass ratio of 1:0.08:0.08, use water as a solvent, and ball-mill in a ball mill at 350 rpm for 6 h to obtain an iron oxide composite material doped with Cu and Ti bimetals; Step 5: Mix the iron oxide composite material, Super P, and PVDF at a mass ratio of 7:2:1 to prepare a negative electrode and assemble a battery (electrolyte: 1M LiPF6 / EC:DMC:EMC = 1:1:1).

[0027] After cycling 500 times at a current density of 500 mA / g, the discharge specific capacity is 710 mAh / g.

[0028] Example 3: Preparation of an iron oxide negative electrode material co-doped with Mo and Al bimetals Step 1: Mix iron concentrate with a 2 mol / L nitric acid solution at a solid-liquid ratio of 1:15, leach at 80 °C for 180 min, and filter to obtain the leachate; Step 2: Add a 1.2 mol / L ammonia water solution to the leachate, adjust the pH to 9, react at 90 °C for 2 h, and then age at 60 °C for 4 h to obtain an iron hydroxide precursor; Step 3: Sinter the iron hydroxide precursor at 500 °C for 2 h under an argon atmosphere to obtain iron oxide nanoparticles; Step 4: Mix the nano iron oxide, molybdenum powder (Mo), and aluminum powder (Al) at a mass ratio of 1:0.1:0.1, use absolute ethanol as a solvent, and ball-mill in a ball mill at 400 rpm for 8 h to obtain an iron oxide composite material doped with Mo and Al bimetals; Step 5: Mix the iron oxide composite material, Super P, and PVDF at a mass ratio of 7:2:1 to prepare a negative electrode and assemble a battery (the electrolyte is the same as above).

[0029] Step 6: After cycling 500 times at a current density of 500 mA / g, the discharge specific capacity is 730 mAh / g.

[0030] Example 4: Preparation of an iron oxide negative electrode material co-doped with V and Mn bimetals Step 1: Mix iron concentrate with a mixed acid of sulfuric acid and hydrochloric acid (total concentration 2 mol / L, volume ratio 1:1) at a solid-liquid ratio of 1:15, leach at 90 °C for 180 min, and filter to obtain the leachate; Step 2: Add a mixed solution of 1.8 mol / L sodium hydroxide and sodium carbonate to the leaching solution, adjust the pH to 8.5, react at 80 °C for 2 h, and then age at 60 °C for 4 h to obtain an iron hydroxide precursor; Step 3: Sinter the iron hydroxide precursor at 380 °C for 4 h in a nitrogen atmosphere to obtain iron oxide nanoparticles; Step 4: Mix the iron oxide nanoparticles, vanadium powder (V), and manganese powder (Mn) in a mass ratio of 1:0.07:0.07, use water as a solvent, and ball-mill at 250 rpm in a ball mill for 3 h to obtain a V and Mn dual-metal doped iron oxide composite material.

[0031] Step 5: Mix the iron oxide composite material, Super P, and PVDF in a mass ratio of 7:2:1 to prepare a negative electrode and assemble a battery (electrolyte: 1M LiPF6 / EC:DMC:EMC = 1:1:1).

[0032] After cycling 500 times at a current density of 500 mA / g, the discharge specific capacity is 705 mAh / g.

[0033] Example 5: Preparation of a Co and Mn dual-metal co-doped iron oxide negative electrode material Step 1: Mix iron concentrate with a 2 mol / L sulfuric acid solution at a solid-liquid ratio of 1:15, leach at 80 °C for 180 min, and filter to obtain a leaching solution; Step 2: Add a 1.5 mol / L sodium hydroxide solution to the leaching solution, adjust the pH to 9, react at 80 °C for 2 h, and then age at 60 °C for 4 h to obtain an iron hydroxide precursor; Step 3: Sinter the iron hydroxide precursor at 420 °C for 3 h in an argon atmosphere to obtain iron oxide nanoparticles; Step 4: Mix the iron oxide nanoparticles, cobalt powder (Co), and manganese powder (Mn) in a mass ratio of 1:0.06:0.06, use absolute ethanol as a solvent, and ball-mill at 300 rpm in a ball mill for 4 h to obtain a Co and Mn dual-metal doped iron oxide composite material; Step 5: Mix the iron oxide composite material, Super P, and PVDF in a mass ratio of 7:2:1 to prepare a negative electrode and assemble a battery (electrolyte: 1M LiPF6 / EC:DMC:EMC = 1:1:1).

[0034] After 500 cycles at a current density of 500 mA / g, the discharge specific capacity is 715 mAh / g. In the above examples, the uniform doping of different bimetals (Co-Zn, Cu-Ti, Mo-Al, V-Mn, Co-Mn) in iron oxide was achieved by wet ball milling. After 500 cycles at a current density of 500 mA / g, the discharge specific capacities of the prepared anode materials are all not less than 700 mAh / g, verifying the effectiveness of the present invention in improving the conductivity and structural stability of the iron oxide anode material.

Claims

1. A bimetal co-doped iron oxide negative electrode material, characterized in that, The material consists of iron oxide nanoparticles and at least one of cobalt, copper, molybdenum, and vanadium that improves electronic conductivity and at least one of zinc, manganese, titanium, and aluminum that enhances stability. The mass ratio of iron oxide to the doped metal is 1:0.05 - 0.1, and the bimetals are uniformly incorporated into the iron oxide to increase electronic conductivity and enhance structural stability.

2. The preparation method of the bimetal co-doped iron oxide negative electrode material according to claim 1, characterized in that, It includes the following steps: (1) Leach the iron concentrate with an acid. The leaching time is 60 - 300 min, and the leaching temperature is 60 - 90 °C. Filter to obtain the leachate. (2) Add a precipitant to the leachate. The reaction temperature is 60 - 90 °C, the reaction time is 2 h, the aging temperature is 60 °C, and the aging time is 4 h to obtain an iron hydroxide precursor. (3) Sinter the iron hydroxide precursor in an argon or nitrogen atmosphere. The sintering temperature is 350 - 500 °C, and the heat preservation time is 2 - 4 h to obtain iron oxide. (4) Mix and ball-mill the iron oxide, the metal that increases conductivity, and the metal that increases stability. The solvent is selected from water or anhydrous ethanol. The ball-milling speed is 200 - 400 rpm, and the ball-milling time is 2 - 8 h to obtain a composite material of bimetal-doped iron oxide.

3. The preparation method according to claim 2, characterized in that, In step (1), the acid is at least one of sulfuric acid, hydrochloric acid, and nitric acid, and the concentration of the acid is 1 - 3 mol / L.

4. The preparation method according to claim 2, characterized in that, In step (2), the precipitant is at least one of sodium carbonate, sodium hydroxide, and ammonia water, and the concentration of the precipitant is 1 - 2 mol / L.

5. The preparation method according to claim 2, wherein In step (4), the metal that increases conductivity is at least one of cobalt, copper, molybdenum, and vanadium, and the metal that increases stability is at least one of zinc, manganese, titanium, and aluminum. The ratio of iron oxide to the metal that increases conductivity and stability is 1:1:0.05 - 0.1, 1:0.05 - 0.

1.

6. A lithium-ion battery, characterized in that, It includes the bimetal synergistically doped iron oxide negative electrode material, conductive agent, binder, and electrolyte described in claim 1. The mass ratio of the negative electrode material, conductive agent, and binder is 7:2:1, and the electrolyte is 1M LiPF6 / EC:DMC:EMC (1:1:1).

Images