Preparation method and application of lithium defect 3D porous lithium iron titanate positive electrode material

Abstract

The invention relates to the technical field of battery electrode materials, in particular to a lithium iron titanate positive electrode material with a lithium defect 3D porous structure and a preparation method and application of the lithium iron titanate positive electrode material. The preparation method of the lithium iron titanate positive electrode material comprises the following steps: dispersing Li2FeTiO4 powder into an alkali solution or an acid solution, stirring, filtering, washing and drying to obtain the lithium iron titanate positive electrode material with a lithium defect 3D porous structure; the alkali solution is an NH3.H2O solution; the acid solution is an HCl solution. Through organic combination of lithium defect engineering and a 3D porous structure, the intrinsic ion and electron transmission capability of the material is optimized, the high activity of lattice oxygen is inhibited, the electrochemical performance is remarkably improved, and a new technical path is provided for development of a high-performance lithium ion battery positive electrode material.

Description

Technical Field

[0001] The present invention relates to the technical field of battery electrode materials, and particularly relates to a lithium-deficient 3D porous lithium iron titanate cathode material with a cation-disordered rock salt structure, a preparation method thereof, and an application thereof. Background Art

[0002] In recent years, with the transformation of the global energy structure and the rapid development of the electric vehicle industry, higher requirements have been put forward for the energy density, cycle life, and safety of energy storage systems. As one of the most promising energy storage technologies at present, the performance improvement of lithium-ion batteries largely depends on the breakthrough of cathode materials. However, existing commercial cathode materials such as lithium iron phosphate and ternary materials generally have the problem of low specific capacity, making it difficult to meet the increasing demand for high energy density.

[0003] Among many new cathode material systems, the iron-based cation-disordered rock salt cathode material Li2FeTiO4 exhibits great application potential due to its unique crystal structure and multiple redox characteristics. This material not only has a theoretical specific capacity as high as 295 mAh·g -1 but also has abundant reserves and environmental friendliness of its constituent elements in the earth's crust, with significant cost advantages and environmental protection characteristics. However, studies have found that this material faces many challenges in practical applications: First, its inherent low electronic conductivity and ion diffusion coefficient lead to slow material reaction kinetics and poor rate performance; second, the reversibility of the oxygen redox reaction during charge and discharge of the material is poor, easily causing problems such as large voltage hysteresis, oxygen evolution, and poor cycle stability. These inherent defects seriously restrict the practical application and industrialization process of the Li2FeTiO4 material. Therefore, optimizing the ion and electron transport properties of Li2FeTiO4 through chemical structure regulation and microstructure design, while improving the stability of lattice oxygen and promoting the redox of active cations, is the key way to break through the performance bottleneck of this material.

[0004] In the prior art, the modification research on cation-disordered rock salt cathode materials mainly focuses on two aspects: anion doping and surface coating. Although these methods have improved the electrochemical performance of the materials to a certain extent, there are still limitations. Specifically, although anion doping can regulate the lithium ion transport path and stabilize the crystal structure, excessive doping easily causes phase separation phenomena, resulting in a decrease in the electrochemical activity of the material and a reduction in structural stability. On the other hand, although the surface coating technology can effectively inhibit the side reactions at the electrode / electrolyte interface, it is difficult to precisely control the thickness uniformity and interfacial bonding strength of the coating layer, and it is prone to peeling off during long-term cycling, losing the protective effect. Therefore, it is urgent to develop new modification strategies to optimize the intrinsic properties of the materials. Summary of the Invention

[0005] In view of the above problems, the present invention provides a lithium iron titanate cathode material with a lithium-deficient 3D porous structure to improve the intrinsic ion and electron conductivity and the redox activity of anions and cations.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] A preparation method of a lithium iron titanate cathode material with a lithium-deficient 3D porous structure, dispersing Li2FeTiO4 powder in an alkali solution or an acid solution, stirring, filtering, washing, and drying to obtain the lithium iron titanate cathode material with a lithium-deficient 3D porous structure; the alkali solution is an NH3·H2O solution; the acid solution is an HCl solution.

[0008] Preferably, the concentration of the alkali solution is 0.5 - 1.5 mol / L; the concentration of the acid solution is 0.1 - 0.5 mol / L.

[0009] Preferably, the concentration of the alkali solution is 1.0 mol / L; the concentration of the acid solution is 0.3 mol / L.

[0010] Preferably, dispersing Li2FeTiO4 powder in an NH3·H2O solution, the mass-volume ratio of Li2FeTiO4 powder to NH3·H2O solution is 10 mg:(3 - 5) mL; and placing it in a water bath at 40 - 50 °C and stirring for 1 - 2 h, filtering, washing with deionized water until neutral, and drying at 50 - 70 °C to obtain the lithium iron titanate cathode material with a lithium-deficient 3D porous structure.

[0011] Preferably, dispersing Li2FeTiO4 powder in an HCl solution, the mass-volume ratio of Li2FeTiO4 powder to HCl solution is 10 mg:(3 - 5) mL; stirring at room temperature for 0.5 - 1 h, filtering, washing with deionized water until neutral, and drying at 50 - 70 °C to obtain the lithium iron titanate cathode material with a lithium-deficient 3D porous structure.

[0012] Preferably, the preparation method of the Li2FeTiO4 powder is as follows:

[0013] (1) Dissolving tetrabutyl titanate and citric acid in absolute ethanol, and stirring at room temperature for 2 - 4 h to obtain solution A;

[0014] (2) Dissolving lithium acetate dihydrate and ferric nitrate nonahydrate in absolute ethanol, and stirring at room temperature for 2 - 4 h to obtain solution B;

[0015] (3) Slowly dripping solution B into solution A, stirring at room temperature for 4 - 6 h, and then transferring it to a water bath at 70 °C and stirring for 2 - 3 h to obtain a gel;

[0016] (4) Drying and grinding the gel to obtain a precursor;

[0017] (5) Place the precursor in a tubular furnace, and under an N2 atmosphere, heat it to 550 °C at a heating rate of 5 °C / min, and keep it at this temperature for 10 - 12 h to obtain Li2FeTiO4.

[0018] The technical key point of the present invention lies in significantly improving the electrochemical performance of the cation-disordered rock salt cathode material through the synergistic effect of lithium defect engineering and 3D porous structure design. Specifically, the present invention adopts the lithium defect engineering strategy and achieves the following technical effects: First, the introduction of lithium vacancies effectively reduces the number of Li-O-Li configurations, reduces the activity of lattice oxygen, and thus significantly improves the reversibility and stability of the anion redox reaction; Second, the existence of lithium vacancies optimizes the lithium ion transport path, reduces the lithium ion diffusion energy barrier, increases the migration rate and utilization rate of lithium ions, and enables the full play of the cation redox reaction.

[0019] The present invention realizes the optimized design of the material microstructure by constructing a 3D porous structure. This structure significantly increases the specific surface area of the material, provides more active sites for the electrode / electrolyte interface reaction, and promotes the rapid transfer of interfacial charge; Second, the 3D continuous channels formed by the porous structure provide efficient transport paths for lithium ions and electrons, effectively shortening the diffusion distance of lithium ions and significantly improving the rate performance of the material; In addition, the porous structure can relieve the volume change during charge and discharge, inhibit the pulverization and structural collapse of the electrode material, and thus improve the cycle stability.

[0020] In summary, through the organic combination of lithium defect engineering and 3D porous structure, the present invention not only optimizes the intrinsic ionic and electronic conductivity of the material, but also significantly improves its electrochemical performance, providing a new technical path for the development of high-performance lithium ion battery cathode materials. Description of the Drawings

[0021] Appendix Figure 1 XRD patterns (a) and TG curves (b) of LFT-0.5M, LFT-1.0M, and LFT-1.5M;

[0022] Appendix Figure 2 SEM images of LFT-0.5M (a, d), LFT-1.0M (b, e), and LFT-1.5M (c, f) at different magnifications;

[0023] Appendix Figure 3 Charge-discharge curves and CV curves of LFT-0.5M (a, d), LFT-1.0M (b, e), and LFT-1.5M (c, f) at 100 mA g –1 -1;

[0024] Appendix Figure 4Cycling performance (a) and rate performance (b) of LFT-0.5M, LFT-1.0M, and LFT-1.5M at 100 mA g –1 ;

[0025] Attached Figure 5 is the XRD pattern of H-LFT;

[0026] Attached Figure 6 is the TG curve of H-LFT;

[0027] Attached Figure 7 is the SEM image of H-LFT;

[0028] Attached Figure 8 is the charge-discharge curve of H-LFT;

[0029] Attached Figure 9 is the cycling performance of H-LFT at 100 mA g -1 ;

[0030] Attached Figure 10 is the rate performance of H-LFT;

[0031] Attached Figure 11 is the CV curve of H-LFT. Detailed implementation manners

[0032] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Apparently, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0033] Embodiment 1

[0034] A preparation method of a lithium-deficient 3D porous structure lithium iron titanate cathode material includes the following steps:

[0035] (1) Dissolve 0.8509 g of tetrabutyl titanate and 0.5254 g of citric acid in 5 mL of absolute ethanol, and stir at room temperature for 4 h to obtain solution A. Dissolve 0.5101 g of lithium acetate dihydrate and 1.0100 g of iron(III) nitrate nonahydrate in 5 mL of absolute ethanol, and stir at room temperature for 4 h to obtain solution B. Slowly add solution B dropwise to solution A, stir at room temperature for 6 h, and then transfer to a 70 °C water bath and stir for 2 h to obtain a gel. Place the gel in a 60 °C forced-air drying oven and dry for 24 h, and then grind to obtain a precursor. Finally, place it in a tube furnace, and under a N2 atmosphere, heat it to 550 °C at a heating rate of 5 °C min -1 and hold for 10 h to obtain Li2FeTiO4.

[0036] (2) 0.1000 g of Li2FeTiO4 powder was separately dispersed into 30 mL of NH3·H2O solutions with concentrations of 0.5 mol / L, 1.0 mol / L, and 1.5 mol / L, and placed in a 45 °C water bath and stirred for 1 h. After filtration and washing with deionized water until neutral, the samples LFT-0.5M, LFT-1.0M, and LFT-1.5M were obtained after drying at 60 °C.

[0037] Figure 1 XRD patterns (a) and TG curves (b) of LFT-0.5M, LFT-1.0M, and LFT-1.5M. The diffraction peaks of LFT-0.5M, LFT-1.0M, and LFT-1.5M all match the standard card of Li2FeTiO4 with a cation-disordered rock salt structure (PDF#97-018-3562, space group Fm-3m), indicating that the alkali treatment did not destroy the main structure of the material. In addition, no diffraction peaks of carbon were observed in the XRD pattern, suggesting that carbon exists in an amorphous structure ( Figure 1 a).

[0038] Combined with the TG curve, the carbon contents of the LFT-0.5M, LFT-1.0M, and LFT-1.5M samples are 15.8%, 15.6%, and 15.8% respectively. At the same time, all three samples showed obvious weight loss in the temperature range of 100 - 300 °C, which corresponds to the loss of H + in the lattice, further confirming that a proton exchange reaction occurred during the alkali treatment.

[0039] Table 1 Metal element ratios in LFT-0.5M, LFT-1.0M, and LFT-1.5M obtained by ICP-OES test

[0040]

[0041] The contents of Li, Fe, and Ti elements in the LFT-0.5M, LFT-1.0M, and LFT-1.5M samples were quantitatively analyzed using an inductively coupled plasma optical emission spectrometer (ICP), and the relative contents of other elements were calculated based on Fe. The specific results are shown in Table 1. The test results show that after treatment with NH3·H2O, the Li content in the samples decreased significantly, confirming the loss of lithium. This phenomenon is consistent with the occurrence of the proton exchange reaction, that is, H + in H2O replaced Li + on the surface of the material, resulting in the formation of Li vacancies.

[0042] Figure 2SEM images of LFT-0.5M, LFT-1.0M, and LFT-1.5M. When the concentration of NH3·H2O was 0.5 mol / L, a 3D porous network structure was only constructed on the surface of the LFT-0.5M material, while the interior still maintained a massive morphology( Figure 2 a, d). When the concentration of NH3·H2O increased to 1.0 mol / L, obvious changes occurred inside the LFT-1.0M material, the porosity increased significantly, the pore structures were interconnected and extended into the bulk( Figure 2 b, e), presenting a 3D network structure composed of mesopores and macropores. When the concentration of NH3·H2O increased to 1.5 mol / L, the pore size increased significantly, resulting in a decrease in the pore structure stability of LFT-1.5M, and collapse occurred in some areas( Figure 2 c, f). The 3D network structure can provide abundant active sites for electrochemical reactions and fast diffusion channels for ions.

[0043] Figure 3 a - c are the galvanostatic charge - discharge curves of the three samples at a current density of 100 mA g -1 −1. Among them, the initial charge / discharge specific capacities of LFT-1.0M were 74.5 / 104.6 mAh g -1 −1, which were better than those of LFT-0.5M (62.6 / 90.8 mAh g -1 −1) and LFT-1.5M (71.1 / 99.0 mAh g -1 −1). The excellent electrochemical performance of LFT-1.0M is mainly due to the good 3D porous structure composed of mesopores and macropores, which is beneficial to the diffusion of the electrolyte and the storage of ions. Since lithium deficiencies exist in all three samples, during the first - cycle discharge process, lithium in the negative electrode is replenished to the positive electrode, resulting in an initial Coulombic efficiency of over 100% for all of them.

[0044] Observation Figure 3 From d - f, it can be seen that the cyclic voltammograms of the three samples show similar shapes. Taking LFT-1.0M as an example, its redox mechanism was analyzed in detail. During the charging process, four obvious oxidation peaks were observed, corresponding to the following reactions respectively: Ti 3+ →Ti 4+ (1.8 V), Fe 2+ →Fe 3+ (2.6 V), Fe 3+ →Fe 4+ (4.3 V), and O 2- →O n- (4.5 V). During the discharge process, the reduction peaks at 3.1 V, 2.2 V, and 1.7 V corresponded to Fe 4+ →Fe 3+ , Fe 3+ →Fe2+ / O n- →O 2- and Ti 4+ →Ti 3+ reduction reaction.

[0045] Figure 4 a shows the cycling performance of the three samples. After 200 cycles, the discharge specific capacity of LFT-1.0M is 116.6 mAh g -1 , higher than that of LFT-0.5M (95.3 mAh g -1 ) and LFT-1.5M (107.9 mAh g -1 ). In addition, Figure 4 b compares the rate performance of all samples. The average discharge specific capacities of the LFT-1.0M electrode at current densities of 0.05, 0.2, 0.5, 0.8, and 1.0 A g -1 are 121.4, 104.0, 87.5, 80.1, and 77.5 mAh g -1 , respectively, all superior to those of LFT-0.5M (108.1, 93.8, 77.5, 69.7, and 66.6 mAh g -1 ) and LFT-1.5M (118.8, 102.3, 84.4, 76.4, and 73.9 mAh g -1 ). When the current density returns to 0.05 A g -1 , the LFT-1.0M electrode can still provide a reversible capacity of 134.6 mAh g -1 , fully demonstrating its excellent electrochemistry reaction kinetics performance and structural stability.

[0046] Example 2

[0047] Disperse the Li2FeTiO4 prepared in Example 1 in 30 mL of 0.3 mol / L HCl solution, stir at room temperature for 0.5 h, filter, wash with deionized water until neutral, and dry at 60 °C to obtain sample H-LFT.

[0048] Figure 5 is the XRD pattern of H-LFT. The sample matches the Li2FeTiO4 with a cation-disordered rock salt structure, and the corresponding space group is Fm-3m (PDF#97-018-3562), indicating the successful preparation of the target sample and that the acid treatment in the example does not damage the main structure of the material.

[0049] Figure 6 is the TG curve of H-LFT. The carbon content of H-LFT is 16.7%. In addition, an obvious weight loss of H-LFT in the temperature range of 100-300 °C is observed, which is related to H in the lattice +The loss of 3.3 N·m3 / cm2 corresponds to that of 2.5 N·m3 / cm2, indicating that proton exchange occurred during the treatment with HCl solution.

[0050] Table 2 Proportion of metal elements in H-LFT

[0051]

[0052] The contents of Li, Fe and Ti in H-LFT were determined by ICP-OES, and the relative contents of other elements were determined based on Fe. The results are shown in Table 2. The content of Li in H-LFT was significantly reduced, indicating that H + Replaces Li on the surface of the material + , a proton exchange reaction occurred, generating a Li vacancy.

[0053] The morphology and structure of H-LFT were further analyzed by SEM. Figure 7 It can be seen that the surface of H-LFT presents a 3D porous structure, which can provide abundant active sites for electrochemical reactions and fast diffusion channels for ions.

[0054] Figure 8 The charge and discharge curve of H-LFT. The first cycle charge / discharge specific capacity of H-LFT is 93.1 / 137.9 mAh g -1 , the corresponding first cycle coulombic efficiency is 148.0%. Since all samples have lithium defects, at the end of the first cycle of discharge, the lithium in the negative electrode is supplemented to the lithium-deficient positive electrode, so the ICE exceeds 100%.

[0055] Figure 9 For H-LFT at 100mA g -1 Cyclic performance of H-LFT at 100mA g -1 The capacity after 200 cycles is 121.9 mAh g -1 , showing excellent cycle stability. The discharge specific capacity of the electrode gradually increases during the initial cycle, which is attributed to the fact that more active substances are activated and participate in the electrochemical reaction as the electrolyte penetrates.

[0056] Figure 10 Rate performance of LFT-1.0M and (b) H-LFT. H-LFT at 0.1, 0.2, 0.5, 0.8 and 1.0 A g -1 The average discharge specific capacities at different current densities are 135.6, 120.8, 105.4, 99.1, and 96.2 mAh g -1 Even if it is restored to 0.1Ag -1 , H-LFT can still provide 134.6mAh g -1Capacity. The excellent rate performance of the above samples is mainly attributed to the lithium defect synergistic 3D porous structure, which improves the ion and electron transport kinetics of the material.

[0057] Figure 11 The CV curves of H-LFT are shown. The CV curves of LFT-1.0M and H-LFT are similar in shape. During the charging process, four distinct oxidation peaks are observed, corresponding to the oxidation reactions of Ti 3+ →Ti 4+ (1.8 V), Fe 2+ →Fe 3+ (2.5 V), Fe 3+ →Fe 4+ (4.1 V) and O 2- →O n- (4.5 V), respectively. During the discharging process, reduction peaks located at 3.1, 2.4, and 1.5 V are observed, corresponding to the reduction reactions of Fe 4+ →Fe 3+ , Fe 3+ →Fe 2+ / O 2- →O n- and Ti 4+ →Ti 3+ , respectively.

[0058] The above experimental results show that:

[0059] (1) Lithium-deficient 3D porous lithium iron titanate can be obtained by both alkali (NH3·H2O) and acid (HCl) treatment.

[0060] (2) The electronic structure of the material is adjusted through the proton exchange process to improve the intrinsic ion and electron conductivity of Li2FeTiO4 and inhibit the high activity of lattice oxygen.

[0061] (3) The 3D porous structure provides channels for the penetration of the electrolyte, increases the contact area between the electrolyte and the electrode, and also provides abundant active sites for the electrochemical reaction.

[0062] (4) The lithium defect synergistic 3D porous structure results in a cathode material with high capacity, excellent cycle stability, and rate performance.

[0063] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to these embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A preparation method of a lithium iron titanate cathode material with a lithium-deficient 3D porous structure, characterized in that, Disperse Li2FeTiO4 powder into an alkaline solution or an acidic solution, stir, filter, wash, and dry to obtain a lithium-deficient 3D porous structure lithium iron titanate cathode material; the alkaline solution is an NH3·H2O solution; the acidic solution is an HCl solution.

2. The preparation method of a lithium iron titanate cathode material with a lithium-deficient 3D porous structure according to claim 1, characterized in that, The concentration of the alkaline solution is 0.5 - 1.5 mol / L; the concentration of the acidic solution is 0.1 - 0.5 mol / L.

3. The preparation method of the lithium iron titanate cathode material with a lithium-deficient 3D porous structure according to claim 1, characterized in that, The concentration of the alkaline solution is 1.0 mol / L; the concentration of the acidic solution is 0.3 mol / L.

4. The preparation method of a lithium iron titanate cathode material with a lithium-deficient 3D porous structure as described in claim 1, characterized in that, Disperse Li2FeTiO4 powder into the NH3·H2O solution, and the mass-to-volume ratio of Li2FeTiO4 powder to the NH3·H2O solution is 10 mg:(3 - 5) mL; place it in a water bath at 40 - 50 °C and stir for 1 - 2 h, filter, wash with deionized water until neutral, and dry at 50 - 70 °C to obtain a lithium iron titanate cathode material with a lithium-deficient 3D porous structure.

5. The preparation method of a lithium iron titanate cathode material with a lithium-deficient 3D porous structure as described in claim 1, characterized in that, Disperse Li2FeTiO4 powder in the HCl solution, and the mass-to-volume ratio of Li2FeTiO4 powder to the HCl solution is 10 mg:(3 - 5) mL; stir at room temperature for 0.5 - 1 h, filter, wash with deionized water until neutral, and dry at 50 - 70 °C to obtain a lithium iron titanate cathode material with a lithium-deficient 3D porous structure.

6. The preparation method of a lithium iron titanate cathode material with a lithium-deficient 3D porous structure according to any one of claims 1-5, characterized in that, The preparation method of the Li2FeTiO4 powder is as follows: (1) Dissolve tetrabutyl titanate and citric acid in absolute ethanol, and stir at room temperature for 2 - 4 h to obtain solution A; (2) Dissolve lithium acetate dihydrate and iron(III) nitrate nonahydrate in absolute ethanol, and stir at room temperature for 2 - 4 h to obtain solution B; (3) Slowly add solution B to solution A, stir at room temperature for 4 - 6 h, and then transfer it to a water bath at 70 °C and stir for 2 - 3 h to obtain a gel; (4) Dry and grind the gel to obtain a precursor; (5) Place the precursor in a tubular furnace, under N2 atmosphere, heat it at a heating rate of 5 °C / min to 550 °C, and hold for 10 - 12 h to obtain Li2FeTiO4.

7. A lithium iron titanate cathode material with a lithium-deficient 3D porous structure prepared by the preparation method according to any one of claims 1 - 6.

8. The application of a lithium iron titanate cathode material with a lithium-deficient 3D porous structure according to claim 7 in the preparation of a lithium-ion battery cathode.

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