A layered lithium titanate film electrode and a method for preparing the same

Abstract

The application discloses a layered lithium titanate film electrode and a preparation method thereof. The preparation method comprises the following steps: S100, placing a lithium source, a titanium source and a carbon source in water to obtain a mixed electrolyte through dispersion; S200, constructing a three-electrode system, taking a current collector as a working electrode, taking a graphite rod as a counter electrode, taking Ag / AgCl as a reference electrode, and stirring in the mixed electrolyte; S300, applying a constant voltage for treatment, distributing the layered lithium titanate on the surface of the current collector to obtain a layered lithium titanate film electrode precursor; and S400, cleaning and drying the layered lithium titanate film electrode precursor, then placing the layered lithium titanate film electrode precursor in acid liquid for treatment to obtain the layered lithium titanate film electrode. The electrochemical codeposition method used in the application can form a close contact between the lithium titanate and the current collector, improve the structural stability and mechanical stability, increase the selective adsorption performance and adsorption capacity of lithium ions, reduce the generation of agglomeration phenomenon, reduce the production cost, and increase the economic benefit.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electrochemical lithium extraction, and in particular to a layered lithium titanate film electrode and a preparation method thereof. BACKGROUND

[0002] In recent years, with the wide application of lithium ion batteries in new energy vehicles, energy storage systems and portable electronic devices, the global demand for lithium resources has grown rapidly. At present, lithium resources are mainly derived from ore extraction and extraction from salt lake brine. Among them, salt lake brine has become one of the most promising lithium resources due to its large lithium reserves and low cost. However, traditional salt lake lithium extraction technologies, such as evaporation crystallization method, adsorption method, solvent extraction method, etc., generally have long process flow, high energy consumption and environmental pollution, etc., which are difficult to meet the needs of efficient and green lithium extraction in production.

[0003] It is worth mentioning that electrochemical lithium extraction technology has become a research hotspot in the industry due to its high lithium selectivity, low energy consumption and environmental friendliness. This technology can realize the selective extraction of lithium by reversible adsorption and desorption of lithium ions on the electrode material under the action of an external electric field, avoiding the use of chemical reagents to cause consumption and secondary pollution. Among many electrode materials, layered lithium titanate (Li2Ti3O7) has attracted much attention due to its unique crystal structure and stable electrochemical performance. Its ion channels can realize efficient intercalation and extraction of lithium ions, and the environmental friendliness and low cost of titanium element are conducive to large-scale application. However, the intrinsic conductivity of traditional lithium titanate materials is low, which leads to slow lithium ion diffusion kinetics, further limiting the rate of lithium extraction. On the other hand, the active sites of traditional lithium titanate materials are insufficient, especially in halide systems with multiple metal ions, such as in halide with high sodium ion / lithium ion ratio. The selective adsorption capacity of lithium ions is insufficient, the cycle stability is poor, and the lattice structure is prone to collapse after multiple charge and discharge, resulting in significant capacity decay. Although the lithium titanate is modified by carbon coating and element doping in the prior art, the preparation process is complex, and the modified product cannot balance the conductivity and selectivity. SUMMARY

[0004] One object of the present application is to provide a layered lithium titanate film electrode and a preparation method thereof, which is conducive to improving the selective adsorption performance of lithium ions, reducing the interference of other ions, and reducing the risk of agglomeration.

[0005] Another object of the present application is a layered lithium titanate film electrode and a preparation method thereof, which is conducive to improving the structural stability and mechanical stability of the electrode, enhancing the contact performance between the deposited layered lithium titanate and the current collector, and further improving the electron transport efficiency.

[0006] Another object of the present application is to provide a layered lithium titanate film electrode and a preparation method thereof, which is conducive to simplifying the production process and further reducing the production cost consumed during preparation.

[0007] To achieve the above object, the technical scheme adopted by the present application is as follows: a preparation method of a layered lithium titanate film electrode, comprising the steps of:

[0008] S100, placing a lithium source, a titanium source and a carbon source in water to obtain a mixed electrolyte by dispersion;

[0009] S200, constructing a three-electrode system, taking a current collector as a working electrode, taking a graphite rod as a counter electrode, taking Ag / AgCl as a reference electrode, and placing them in the mixed electrolyte for stirring;

[0010] S300, applying a constant voltage for treatment, and distributing the layered lithium titanate on the surface of the current collector to obtain a layered lithium titanate film electrode precursor;

[0011] S400, after washing and drying the layered lithium titanate film electrode precursor, placing it in an acid solution for treatment to obtain a layered lithium titanate film electrode.

[0012] In some embodiments, the number of moles of lithium in the mixed electrolyte is n1, and the number of moles of titanium is n2, wherein the ratio between n1 / n2 is (1.90~2.10):3.

[0013] In some embodiments, the mass of the carbon source is m1, and the mass of the layered lithium titanate prepared in step S200 is m2, wherein 0.005≤m1 / m2≤0.03.

[0014] In some embodiments, the concentration of lithium ions in the mixed electrolyte is 0.05mol / L~0.2mol / L, and the lithium source is one or more of lithium carbonate, lithium chloride and lithium hydroxide.

[0015] In some embodiments, the titanium source is one or more of titanium dioxide, titanium chloride and metatitanic acid.

[0016] In some embodiments, the carbon source is one or more of glucose, acetylene black and graphene oxide.

[0017] In some embodiments, in step S300, the constant voltage is -1V~-0.5V, and the time for applying the constant voltage is 10min~60min.

[0018] In some embodiments, in the step S400, the acid liquid is one or more of dilute sulfuric acid, dilute hydrochloric acid, dilute nitric acid, acetic acid, and citric acid; the acid liquid treatment time is t1, wherein 0s≤t1≤30s, and the concentration of the acid liquid is 0.05mol / L-0.2mol / L.

[0019] In some embodiments, in the step S200, the current collector is one or more of aluminum foil, foamed nickel, titanium mesh, and carbon paper.

[0020] To achieve the above object, the technical scheme adopted by the present application is as follows: a layered lithium titanate film electrode is prepared by the preparation method described in any of the above.

[0021] Compared with the prior art, the present application has the beneficial effects that:

[0022] (1) The present application directly grows a layered lithium titanate film on a current collector by an electrochemical co-deposition method, forms a close physical and electrochemical contact between the deposited layered lithium titanate and the current collector, further improves the structural stability and mechanical stability of the electrode. After acid etching treatment, oxygen vacancies are formed as active sites, which increase the selective adsorption performance and adsorption capacity of lithium ions, reduce the interference risk of other ions, especially sodium ions, and reduce the occurrence of agglomeration.

[0023] (2) The layered lithium titanate film electrode and the preparation method thereof provided by the present application use an electrochemical co-deposition method instead of high-temperature sintering and subsequent coating steps, which is beneficial to reduce energy consumption in the production process, further reduce production cost, and increase economic benefit.

[0024] (3) The layered lithium titanate film electrode and the preparation method thereof provided by the present application have the advantages of simple preparation process, easy operation, environmental friendliness, and potential for large-scale production. DETAILED DESCRIPTION

[0025] In the following, the present application will be further described in conjunction with specific embodiments, and it should be noted that the embodiments described below or the technical features thereof can be combined in any manner to form new embodiments without conflict.

[0026] As used herein, the term "prepared from" is synonymous with "comprising". As used herein, the terms "comprise", "comprises", "comprising", "include", "includes", "including", "have", "has", "having", or any other variation thereof, are intended to cover a non-exclusive inclusion. For example, a composition, a step, a method, an article, or an apparatus that comprises a list of elements is not necessarily limited to only those elements but can include other elements not expressly listed or inherent to such composition, step, method, article, or apparatus.

[0027] When a range, preferably a range, or a series of upper preferred values and lower preferred values, is used to define an equivalent, concentration, or parameter, it should be understood that the use of the range formed by any pairings of an upper range limit or preferred value with a lower range limit or preferred value, regardless of whether the range is explicitly disclosed, is specifically disclosed. For example, when a range is disclosed as "1-5," the described range should be interpreted to include ranges of "1-4," "1-3," "1-2 and 4-5," "1-3 and 5," etc. When numerical ranges are described herein, unless otherwise stated, the range includes its end values and all integers and fractions within the range.

[0028] Approximating language is used herein to convey the approximate but not exact dimensions of an implementation intended to provide a practical recommendation. The use of "about" or "approximately" in connection with a recited quantity means that the amount in question can vary from the recited quantity by a reasonable amount. In some examples, the approximation can correspond to the precision of an instrument used to measure the quantity. In the description and claims of the application, ranges are used as endpoints to provide embodiments that include the same precise figure where that figure is an exact value. Suitable values within each range are explicitly included in the description and claims. These are only examples of what is provided by the present application. Other examples can be derived from the description, experiments and claims by one of ordinary skill in the art without departing from the scope of the present application.

[0029] To achieve the above object, the technical scheme adopted by the present application is as follows: A preparation method of a layered lithium titanate film electrode, comprising the steps of:

[0030] S100, placing a lithium source, a titanium source and a carbon source in water to obtain a mixed electrolyte by dispersion;

[0031] S200, constructing a three-electrode system, taking a current collector as a working electrode, a graphite rod as a counter electrode, and Ag / AgCl as a reference electrode, and stirring them in the mixed electrolyte;

[0032] S300, applying a constant voltage for treatment, so that the layered lithium titanate is distributed on the surface of the current collector to obtain a layered lithium titanate film electrode precursor;

[0033] S400, after washing and drying the layered lithium titanate film electrode precursor, treating it in an acid solution to obtain a layered lithium titanate film electrode.

[0034] The present application directly grows a layered lithium titanate film on a current collector by an electrochemical co-deposition method, forms a close physical and electrochemical contact between the deposited layered lithium titanate and the current collector, and further improves the structural stability and mechanical stability of the electrode. After acid etching treatment, oxygen vacancies are formed as active sites, which increase the selective adsorption performance and adsorption capacity of lithium ions, reduce the interference risk of other ions, and reduce the generation of agglomeration.

[0035] In some embodiments, the number of moles of lithium element in the mixed electrolyte is n1, and the number of moles of titanium element is n2, wherein the ratio between n1 / n2 is (1.90-2.10):3, specifically, the ratio between n1 / n2 is 1.90, 1.91, 1.92, 1.93, 1.94, 1.95, 1.96, 1.97, 1.98, 1.99, 2.00, 2.01, 2.02, 2.03, 2.04, 2.05, further preferably, the ratio between n1 / n2 is (1.90-2.05):3, more preferably, the ratio between n1 / n2 is (1.95-2.00):3, more preferably, the ratio between n1 / n2 is 1.95:3. It is worth mentioning that since the layer-shaped lithium titanate (Li2Ti3O7) is directly grown on the current collector by using the electrochemical co-deposition method, the molar ratio of Li element to Ti in the target product is 2:3, therefore, by setting the ratio between n1 / n2 as (1.90-2.10):3, it is beneficial to ensure that the main component of the compound formed in the electrochemical co-deposition process is layer-shaped lithium titanate, it is worth mentioning that the layer-shaped lithium titanate is beneficial to the rapid intercalation or deintercalation of lithium ions, since lithium ions can rapidly diffuse in the two-dimensional channel between the layers of the layer-shaped lithium titanate, thereby improving the adsorption and desorption performance of the electrode. Further, since the Ti-O bond in the layer-shaped lithium titanate can form negatively charged adsorption sites, thereby specific capture of lithium ions can be achieved through electrostatic interaction, further enhancing the selective adsorption of lithium ions, thereby being suitable for extracting lithium ions in salt lake brine with various impurity ions. On the other hand, the Ti-O bond in the layer-shaped lithium titanate has high strength, therefore, in various use environments, especially in acidic and neutral environments, it has excellent structural stability, further enhancing the use stability of the layer-shaped lithium titanate film electrode.

[0036] In some embodiments, the mass of the carbon source is m1, and the mass of the layered lithium titanate prepared in step S200 is m2, wherein 0.005≤m1 / m2≤0.03, specifically, the ratio of m1 to m2 ranges from 0.005, 0.007, 0.009, 0.01, 0.012, 0.014, 0.016, 0.018, 0.02, 0.025, 0.03, further preferably, the ratio of m1 to m2 ranges from 0.005≤m1 / m2≤0.02, more preferably, the ratio of m1 to m2 ranges from 0.02. It can be understood that by introducing the carbon source to be compounded with the layered lithium titanate in the electrochemical deposition process, a continuous conductive network is formed throughout the layered lithium titanate film electrode, which is conducive to enhancing the electrical conductivity to increase the charge conduction. On the other hand, the carbon source can act as a physical isolation layer inserted between the layers of the layered lithium titanate, preventing the face-to-face stacking phenomenon of the two-dimensional sheets generated during the deposition process, which is conducive to enhancing the diffusion phenomenon of lithium ions, further reducing the risk of agglomeration of lithium titanate particles, and increasing the use stability of the layered lithium titanate film electrode.

[0037] In some embodiments, the concentration of lithium ions in the mixed electrolyte is 0.05 mol / L-0.2 mol / L, specifically, the concentration of lithium ions in the mixed electrolyte is 0.05 mol / L, 0.07 mol / L, 0.09 mol / L, 0.1 mol / L, 0.12 mol / L, 0.14 mol / L, 0.16 mol / L, 0.18 mol / L, 0.2 mol / L, further preferably, the concentration of lithium ions in the mixed electrolyte is 0.1 mol / L-0.2 mol / L, more preferably, the concentration of lithium ions in the mixed electrolyte is 0.1 mol / L. It can be understood that in the preparation of the layered lithium titanate film electrode, the selection of an appropriate concentration of lithium ions is conducive to forming a uniform layered lithium titanate structure, optimizing the electrical conductivity of the layered lithium titanate film electrode, and further enhancing the use performance and use stability of the prepared layered lithium titanate film electrode. On the other hand, the selection of an appropriate concentration of lithium ions is conducive to improving the dispersion uniformity of the lithium source, the titanium source, and the carbon source in water, thereby forming a uniform mixed electrolyte, which is also conducive to forming a uniform layered lithium titanate in the subsequent steps.

[0038] In some embodiments, the lithium source is one or more of lithium carbonate, lithium chloride, and lithium hydroxide. Among them, lithium carbonate is a commonly used lithium source, which has high purity and good chemical stability. Therefore, in the preparation process of the layered lithium titanate film electrode, lithium carbonate can stably provide lithium ions, which helps to form a uniform layered lithium titanate structure in subsequent reactions, thereby improving the electrochemical performance of the electrode. Lithium chloride has high solubility in water, which allows lithium ions to be uniformly dispersed into the mixed electrolyte, further improving the uniformity of the mixed electrolyte, thereby improving the uniformity and consistency of the prepared layered lithium titanate film electrode. On the other hand, lithium hydroxide has high alkalinity, which can provide a good pH environment during preparation, further promoting the formation of layered lithium titanate, and the high solubility of lithium hydroxide also helps to form a uniformly distributed mixed electrolyte.

[0039] In some embodiments, the titanium source is one or more of titanium dioxide, titanium chloride, and metatitanic acid. By using appropriate titanium sources in the preparation, the stability of the generated layered lithium titanate is improved. It is worth mentioning that titanium dioxide can act as a heterogeneous nucleation site, which is conducive to guiding the ordered epitaxial growth of layered lithium titanate and reducing the standard deviation of the interlayer spacing. Titanium chloride can quickly release active titanium, improving the reaction rate of subsequent preparation reactions. The hydroxyl groups and layered structure contained in metatitanic acid can induce lithium titanate crystal face orientation growth, which is conducive to the preparation of uniformly distributed layered lithium titanate.

[0040] In some embodiments, the carbon source is one or more of glucose, acetylene black, and graphene oxide. It can be understood that by introducing a carbon source to composite with the layered lithium titanate during electrochemical deposition, a continuous conductive network is formed throughout the layered lithium titanate film electrode, which is conducive to enhancing the electrical conductivity to increase the charge conduction rate. On the other hand, the carbon source can act as a physical isolation layer, inserted between the layers of the layered lithium titanate, preventing the face-to-face stacking phenomenon of two-dimensional sheets during the deposition process, which is conducive to the diffusion of lithium ions, further reducing the risk of lithium titanate particles agglomeration, and improving the use stability of the layered lithium titanate film electrode.

[0041] In some embodiments, in step S300, the constant voltage is -1V~ -0.5V, specifically, the constant voltage is -1V, -0.9V, -0.8V, -0.7V, -0.6V, -0.5V, further preferably, the constant voltage is -1V~ -0.8V, more preferably, the constant voltage is -1V. The time for applying the constant voltage is 10min~60min, specifically, the time for applying the constant voltage is 10min, 15min, 20min, 25min, 30min, 35min, 40min, 45min, 50min, 55min, 60min, further preferably, the time for applying the constant voltage is 10min~30min, more preferably, the time for applying the constant voltage is 30min. It can be understood that by setting the voltage of the current collector at (-1.2~ -0.8V) vs. Ag / AgCl, it is beneficial to drive the reduction reaction of cations such as lithium ions and titanium ions on the surface of the working electrode, and further form a lithium titanate deposition layer. Among them, while selecting a suitable potential window for depositing layered lithium titanate, the constant voltage is beneficial to accurately maintain the window and drive the titanium titanate crystal nucleus to arrange along the lowest surface energy crystal face, thereby stably generating layered lithium titanate.

[0042] It is worth mentioning that when the constant voltage is over negative, it may trigger the water reduction hydrogen evolution reaction, and the generated bubbles will destroy the deposition of layered lithium titanate on the surface of the current collector, reducing the continuity of the film during production. When the constant voltage is over positive, the deposition driving force of lithium titanate is insufficient, resulting in a loose and porous film.

[0043] Among them, using electrochemical co-deposition method instead of high-temperature sintering and subsequent coating steps is beneficial to reduce energy consumption in the production process, further reduce production cost, increase economic benefit, and is easy to operate, environmentally friendly, and has the potential for large-scale production.

[0044] In some embodiments, in step S400, the acid solution is one or more of dilute sulfuric acid, dilute hydrochloric acid, dilute nitric acid, acetic acid, and citric acid; the acid solution treatment time is t1, wherein 0s≤t1≤30s, specifically, the acid solution treatment time is 0s, 0.5s, 1s, 2s, 3s, 4s, 5s, 10s, 15s, 20s, 25s, 30s, further preferably, the acid solution treatment time is 10s~20s, more preferably, the acid solution treatment time is 10s. It can be understood that the etching effect generated by the acid solution treatment is beneficial to form oxygen vacancy active sites on the surface of the layered lithium titanate, increase the selective adsorption performance and adsorption capacity of lithium ions, and reduce the interference risk of other ions, especially sodium ions, and reduce the generation of agglomeration phenomenon. Therefore, the layered lithium titanate film electrode driven by defect engineering has good use performance and use stability.

[0045] In some embodiments, the concentration of the acid solution is 0.05 mol / L to 0.2 mol / L, specifically, the concentration of the acid solution is 0.05 mol / L, 0.1 mol / L, 0.15 mol / L, or 0.2 mol / L, and further preferably, the concentration of the acid solution is 0.1 mol / L. Selecting appropriate acid solution treatment conditions is conducive to forming oxygen vacancy active sites on the surface of the layered lithium titanate, increasing the adsorption performance of lithium ions, and reducing the interference of impurity ions, especially sodium ions.

[0046] In some embodiments, in step S200, the current collector is one or more of an aluminum foil, a foamed nickel, a titanium mesh, and a carbon paper. It is worth mentioning that the (111) crystal plane in the aluminum foil forms a semi-coherent interface with the (001) plane of lithium titanate, which promotes the vertical arrangement of the layered lithium titanate. On the other hand, the aluminum foil has a low cost, which is conducive to large-scale production. The foamed nickel has a high porosity and a large specific surface area, thereby increasing the deposition amount of the layered lithium titanate. The titanium mesh has corrosion resistance, with a corrosion rate < 0.01 mm / year in an acidic deposition solution with a pH value of 2 to 4, and good high-temperature stability. The carbon paper has a low density, which is conducive to reducing the mass of the electrode and further reducing energy consumption.

[0047] To achieve the above purposes, the application also provides a layered lithium titanate film electrode prepared by the above preparation method.

[0048] The application directly grows the layered lithium titanate film on the current collector by the electrochemical co-deposition method, so that the deposited lithium titanate forms a close physical and electrochemical contact with the current collector, further improving the structural stability and mechanical stability of the electrode. After acid etching treatment, oxygen vacancies are formed as active sites, increasing the selective adsorption performance and adsorption capacity of lithium ions, reducing the interference risk of other ions, and reducing the generation of agglomeration, thereby obtaining a layered lithium titanate film electrode with good lithium ion adsorption performance and convenient preparation.

[0049] Embodiment 1

[0050] A preparation method of a layered lithium titanate film electrode, comprising the steps of:

[0051] S100, dissolving 8 g of lithium chloride, 46.3 g of titanium trichloride, and 0.08 g of graphene oxide in 3.8 L of water, ultrasonic dispersion for 10 min to obtain a mixed electrolyte, wherein the molar ratio of lithium ions to titanium ions in the mixed electrolyte is 1.90:3, the concentration of lithium ions is 0.05 mol / L, and the mass ratio of graphene oxide to the prepared layered lithium titanate is 0.005;

[0052] S200, constructing a three-electrode system, carbon paper as a working electrode, a graphite rod as a counter electrode, and Ag / AgCl as a reference electrode, which are placed in the mixed electrolyte and stirred;

[0053] S300, after applying a constant voltage of -0.5V for 30min, the layered lithium titanate is distributed on the surface of the current collector to obtain a layered lithium titanate film electrode precursor;

[0054] S400, after washing and drying the lithium titanate film electrode at 60°C, the lithium titanate film electrode is obtained by treating in 0.05mol / L citric acid for 20s.

[0055] Example 2

[0056] Example 2 differs from Example 1 in that the molar ratio of lithium ions to titanium ions in the mixed electrolyte in step S100 is 1.95:3, and the mass of lithium chloride is 8.3g.

[0057] Example 3

[0058] Example 3 differs from Example 1 in that the molar ratio of lithium ions to titanium ions in the mixed electrolyte in step S100 is 2.05:3, and the mass of lithium chloride is 8.7g.

[0059] Example 4

[0060] Example 4 differs from Example 1 in that the molar ratio of lithium ions to titanium ions in the mixed electrolyte in step S100 is 1.95:3, the concentration of lithium ions is 0.1mol / L, and the amount of water used is 1.95L.

[0061] Example 5

[0062] Example 5 differs from Example 1 in that the molar ratio of lithium ions to titanium ions in the mixed electrolyte in step S100 is 1.95:3, the concentration of lithium ions is 0.1mol / L, the mass ratio of graphene oxide to the prepared layered lithium titanate is 0.02, and the mass of graphene oxide is 0.54g.

[0063] Example 6

[0064] Example 6 differs from Example 1 in that the molar ratio of lithium ions to titanium ions in the mixed electrolyte in step S100 is 1.95:3, the concentration of lithium ions is 0.1mol / L, the mass ratio of graphene oxide to the prepared layered lithium titanate is 0.02, and the constant voltage in step S300 is -0.8V.

[0065] Example 7

[0066] Example 7 differs from Example 1 in that the molar ratio of lithium ions to titanium ions in the mixed electrolyte in step S100 is 1.95:3, the concentration of lithium ions is 0.1mol / L, the mass ratio of graphene oxide to the prepared layered lithium titanate is 0.02, and the constant voltage in step S300 is -1V.

[0067] Example 8

[0068] Example 8 differs from Example 1 in that the molar ratio of lithium ions to titanium ions in the mixed electrolyte in step S100 is 1.95:3, the concentration of lithium ions is 0.1 mol / L, and the mass ratio of graphene oxide to the prepared layered lithium titanate is 0.02. The etching time of the acid solution treatment in step S400 is 10 s.

[0069] Comparative Example 1

[0070] Comparative Example 1 differs from Example 1 in that the molar ratio of lithium ions to titanium ions in the mixed electrolyte in step S100 is 1.95:3, the concentration of lithium ions is 0.1 mol / L, and no graphene oxide is used.

[0071] Comparative Example 2

[0072] Comparative Example 2 differs from Example 1 in that the molar ratio of lithium ions to titanium ions in the mixed electrolyte in step S100 is 1.95:3, the concentration of lithium ions is 0.1 mol / L, the mass ratio of graphene oxide to the prepared layered lithium titanate is 0.02, and no citric acid etching is used.

[0073] Performance Evaluation

[0074] The layered lithium titanate film electrodes in Examples 1-8 and Comparative Examples 1-2 were used to construct an electrochemical lithium extraction system for performance testing. The construction and testing method steps were as follows: the layered lithium titanate film electrode and the counter electrode were placed in parallel with a distance of 1 cm, with the reference electrode close to the layered lithium titanate film electrode. A mixed simulated brine with a pH of 6 and a concentration of 0.1 mol / L LiCl and 1 mol / L NaCl was injected until the electrodes were immersed. The constant voltage was set to -0.5 V (vs. Ag / AgCl) and run for 30 min, and magnetic stirring was started at a speed of 200 rpm to promote mass transfer. After the electrochemical desorption of lithium ions was completed, the working electrode was removed and quickly transferred to an enrichment tank containing 0.1 mol / L LiCl solution. The counter electrode was replaced with a platinum sheet to reduce side reactions. After applying a constant voltage of +0.9 V (vs. Ag / AgCl) for 20 min, the lithium ion concentration was measured using inductively coupled plasma mass spectrometry, and 100 cycles of cyclic testing were performed to detect the capacity retention rate of the layered lithium titanate film electrode. The test results are shown in Table 1.

[0075] Table 1: Performance test of layered lithium titanate film electrode

[0076]

[0077] It can be known from Example 1, Example 2 and Example 3 that the adsorption capacity of lithium ions is the highest when the molar ratio of lithium ions to titanium ions in the mixed electrolyte is 1.95:3, and therefore, it is beneficial to select an appropriate molar ratio of lithium ions to titanium ions to improve the adsorption capacity of lithium ions of the layered lithium titanate film electrode.

[0078] It can be known from Example 2 and Example 4 that the adsorption capacity of lithium ions of the layered lithium titanate film electrode increases as the concentration of lithium ions increases. On the other hand, it can be known from Example 4 and Example 5 that the cycle stability of the layered lithium titanate film electrode can be significantly improved as the amount of carbon source added increases.

[0079] It can be known from the analysis of Example 5, Example 6 and Example 7 that increasing the constant voltage is beneficial to increase the thickness of the layered lithium titanate film deposited on the current collector, and further improve the adsorption capacity and cycle stability of the layered lithium titanate film electrode.

[0080] It can be found from the analysis of Example 5, Example 7 and Comparative Example 1 that the stability of the layered lithium titanate film electrode after multiple cycles is significantly reduced when graphene oxide is not added. This is because the carbon source can act as a physical isolation layer, inserted between the layers of the layered lithium titanate, preventing the face-to-face stacking phenomenon of two-dimensional sheets generated during the deposition process, facilitating the diffusion of lithium ions, further reducing the risk of agglomeration of lithium titanate particles, and increasing the use stability of the layered lithium titanate film electrode.

[0081] It can be found from the analysis of Example 7, Example 8 and Comparative Example 2 that the lithium ion selective adsorption of the lithium titanate film electrode without citric acid etching is poor, and a shorter etching time will also damage the crystal lattice structure, which is not conducive to enhancing the selective adsorption of lithium ions.

[0082] The above describes the basic principles, main features and advantages of the present application. It should be understood by those skilled in the art that the present application is not limited by the above examples, and the above examples and descriptions in the specification are only the principles of the present application. Without departing from the spirit and scope of the present application, various changes and improvements can be made to the present application, and these changes and improvements all fall within the scope of the claimed present application. The scope of protection claimed by the present application is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a layered lithium titanate film electrode, characterized by, The method comprises the steps of: S100, placing a lithium source, a titanium source and a carbon source in water to obtain a mixed electrolyte, wherein the number of moles of lithium in the mixed electrolyte is n1, the number of moles of titanium is n2, and the ratio of n1 / n2 is (1.90-2.10):3; S200, constructing a three-electrode system, wherein a current collector is used as a working electrode, a graphite rod is used as a counter electrode, and Ag / AgCl is used as a reference electrode, and the three electrodes are placed in the mixed electrolyte and stirred; S300, applying a constant voltage for treatment, and distributing layered lithium titanate on the surface of the current collector to obtain a layered lithium titanate film electrode precursor, wherein the constant voltage is-1V to-0.5V, and the time for applying the constant voltage is 10min to 60min; S400, washing and drying the layered lithium titanate film electrode precursor, and then placing it in an acid solution for treatment to obtain a layered lithium titanate film electrode, and the chemical formula of the layered lithium titanate is Li2Ti3O7.

2. The production method according to claim 1, characterized by, The mass of the carbon source is m1, and the mass of the layered lithium titanate obtained in step S200 is m2, wherein 0.005≤m1 / m2≤0.

03.

3. The preparation method according to claim 1, characterized in that, The concentration of lithium ions in the mixed electrolyte is 0.05mol / L to 0.2mol / L, and the lithium source is one or more of lithium carbonate, lithium chloride and lithium hydroxide.

4. The method of claim 1, wherein, The titanium source is one or more of titanium dioxide, titanium chloride and metatitanic acid.

5. The preparation method according to claim 1, characterized in that, The carbon source is one or more of glucose, acetylene black and graphene oxide.

6. The method of claim 1, wherein, In step S400, the acid solution is one or more of dilute sulfuric acid, dilute hydrochloric acid, dilute nitric acid, acetic acid and citric acid; the treatment time of the acid solution is t1, wherein 0s 7. The preparation method according to claim 1, characterized in that, In step S200, the current collector is one or more of aluminum foil, foamed nickel, titanium mesh and carbon paper.

8. A layered lithium titanate film electrode, characterized by, Prepared by the preparation method of any one of claims 1-7.

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