Titanium-doped lithium manganate self-supporting electrode and preparation method and application thereof

Abstract

The invention relates to a titanium-doped lithium manganate self-supporting electrode as well as a preparation method and application thereof. The self-supporting electrode comprises a porous titanium fiber matrix and a titanium-doped lithium manganate nanosheet active layer which grows on the surface and in pore channels of the porous titanium fiber matrix in situ, and an overall conductive self-supporting electrode structure is formed. Wherein lithium manganate is of a spinel structure, the titanium element is introduced into lithium manganate crystal lattices in a doping mode, and the doping molar ratio of the titanium element is 1%-10% of the molar weight of the manganese element. Compared with the prior art, the method has the advantages that an integral conductive structure without a binder can be formed, the method can be applied to a capacitive deionization system, and efficient and selective recovery of lithium ions in a lithium-containing solution is realized.

Description

Technical Field

[0001] This invention relates to the field of water treatment technology, and in particular to a titanium-doped lithium manganese oxide self-supporting electrode, its preparation method, and its application. Background Technology

[0002] Lithium resources, as a crucial foundational material for the new energy industry and strategic emerging industries, are widely used in lithium-ion batteries, energy storage systems, and novel electronic devices. With the rapid development of new energy vehicles and large-scale energy storage technologies, the demand for lithium resources continues to grow, and traditional lithium resource supply methods face challenges such as declining resource quality and rising development costs. Salt lake brines, due to their abundant reserves and concentrated distribution, are considered an important source of lithium resources. However, salt lake brines typically have low lithium-ion content and are often accompanied by high concentrations of coexisting ions such as magnesium, sodium, and calcium ions, resulting in a complex ion composition that poses a significant challenge to the efficient separation and recovery of lithium resources.

[0003] Currently, lithium extraction technologies from salt lake brine mainly include precipitation, solvent extraction, adsorption, and membrane separation. Among these, precipitation and solvent extraction are relatively complex, consume large amounts of reagents, and have a heavy environmental burden; membrane separation is prone to membrane fouling and performance degradation in high-salt systems. In contrast, electrochemical capacitive deionization technology has gradually attracted attention due to its advantages such as lower energy consumption, milder operating conditions, and good renewability, and is being explored for the selective separation and recovery of lithium ions in salt lake brine.

[0004] In capacitive deionization lithium extraction systems, electrode materials are key factors determining separation efficiency and operational stability. Lithium manganese oxide materials possess reversible lithium insertion / extraction sites in their crystal structure, enabling selective lithium-ion insertion and release under an applied electric field. Therefore, they have been widely studied as electrode materials for capacitive deionization lithium extraction. For example, CN120250082A discloses a lithium iron phosphate-composite lithium manganese oxide composite material for lithium extraction from high-altitude salt lakes. By combining spinel-type and layered lithium manganese oxides with lithium iron phosphate, a lithium iron phosphate-composite lithium manganese oxide material is formed, solving the problem of difficult lithium-ion migration in high-altitude salt lake lithium extraction. However, the above scheme still uses composite lithium manganese oxide powder material combined with conductive agents and binders, loaded onto the surface of the current collector. This method suffers from limited utilization of active materials, long ion transport paths, and insufficient structural stability during cycling, making it prone to capacity decay and performance degradation in complex salt lake brine systems. In addition, existing capacitive deionization devices mostly adopt the working mode of fluid flowing parallel along the electrode surface, which limits the contact between the electrolyte and the electrode active layer, making it difficult to fully utilize the active sites inside the electrode, further restricting the improvement of lithium-ion separation efficiency.

[0005] Therefore, how to improve the structural stability, active site utilization efficiency, and effective contact between the electrolyte and the electrode of lithium manganese oxide electrodes through electrode structure design and material modification remains a pressing technical problem to be solved in the field of deionization lithium extraction from salt lake brine capacitors. Summary of the Invention

[0006] The purpose of this invention is to overcome at least one of the defects of the prior art and provide a titanium-doped lithium manganese oxide self-supporting electrode, its preparation method and application.

[0007] The objective of this invention can be achieved through the following technical solutions: The present invention first provides a titanium-doped lithium manganese oxide self-supporting electrode, the self-supporting electrode comprising a porous titanium fiber matrix and a titanium-doped lithium manganese oxide nanosheet active layer grown in situ on the surface and pores of the porous titanium fiber matrix, forming an overall conductive self-supporting electrode structure. The lithium manganese oxide has a spinel structure, and titanium is introduced into the lithium manganese oxide lattice in the form of doping. The molar ratio of titanium doping is 1% to 10% of the molar amount of manganese.

[0008] Furthermore, the porous titanium fiber matrix is ​​a conductive titanium fiber felt. The pores of the titanium fiber felt are interconnected, exhibiting good electrical conductivity and mechanical stability.

[0009] Furthermore, the titanium-doped lithium manganese oxide nanosheet active layer grows continuously along the surface of the metal fiber.

[0010] Furthermore, the morphology of the titanium-doped lithium manganese oxide nanosheet active layer is sheet-like, plate-like, or layered.

[0011] Furthermore, the size of the lithium manganese oxide nanosheets is 100-300 nm.

[0012] This invention also provides a method for preparing a titanium-doped lithium manganese oxide self-supporting electrode, the method comprising the following steps: S1: Surface treatment of porous titanium fiber matrix using oxalic acid solution; S2: Manganese source, urea and ammonium fluoride are prepared into a precursor solution, and the porous titanium fiber matrix pretreated by S1 is placed in the precursor solution for hydrothermal reaction, so that the manganese-containing precursor and titanium elements are deposited and grown on the surface and inside the pores of the porous titanium fiber matrix. S3: Heat-treat the porous titanium fiber matrix obtained in S2 to form a titanium-doped manganese oxide layer; S4: The porous titanium fiber matrix treated in S3 is placed in a lithium source solution for hydrothermal reaction to finally obtain the titanium-doped lithium manganese oxide self-supporting electrode.

[0013] Furthermore, in step S1, the oxalic acid solution has a mass fraction of 5%-8%.

[0014] Furthermore, in step S1, the surface treatment temperature is 80-90 ℃.

[0015] Further, in step S2, the manganese source is any one or more of manganese nitrate tetrahydrate, manganese sulfate, and manganese chloride, preferably manganese nitrate tetrahydrate.

[0016] Further, in step S2, the mass ratio of the manganese source, urea and ammonium fluoride is (0.1-0.6): (0.1-0.6): (0.05-0.3).

[0017] Furthermore, in step S2, the temperature of the hydrothermal reaction is 100-150 ℃, preferably 120 ℃.

[0018] Furthermore, in step S2, the hydrothermal reaction time is 2-10 h, preferably 6 h.

[0019] Furthermore, in step S3, the heat treatment is carried out in a muffle furnace.

[0020] Furthermore, in step S3, the temperature of the heat treatment is 200-400 ℃, preferably 300 ℃.

[0021] Further, in step S4, the lithium source is any one or more of lithium hydroxide monohydrate, lithium carbonate, and lithium chloride, preferably lithium hydroxide monohydrate.

[0022] Further, in step S4, the concentration of the lithium source is 10-50 mmol / L.

[0023] Furthermore, in step S4, the temperature of the hydrothermal reaction is 180-220 °C.

[0024] Furthermore, in step S4, the hydrothermal reaction takes 15-24 hours.

[0025] The present invention also provides an application of a titanium-doped lithium manganese oxide self-supporting electrode in a capacitive deionization system. The titanium-doped lithium manganese oxide self-supporting electrode serves as a working electrode for capacitive deionization, and is used to selectively insert and release lithium ions in a lithium-containing solution under the action of an external electric field, thereby achieving the enrichment and recovery of lithium ions.

[0026] Furthermore, the capacitor deionization working electrode is prepared by the following method: A titanium-doped lithium manganese oxide self-supporting electrode, activated carbon black, and polytetrafluoroethylene are mixed in a mass ratio of (75-85): (5-15): (5-15). A solvent is added and the mixture is stirred evenly to form a slurry. The slurry is coated onto a titanium plate and dried to obtain a capacitor deionization electrode.

[0027] Furthermore, the lithium-containing solution includes, but is not limited to, salt lake brine.

[0028] Furthermore, the capacitor deionization system adopts a fluid-penetrating operation mode, allowing the lithium-containing solution to flow along the three-dimensional channel direction of the titanium-doped lithium manganese oxide self-supporting electrode.

[0029] Compared with the prior art, the present invention has the following technical advantages: (1) This invention innovatively uses a porous titanium fiber matrix as a carrier and loads a titanium-doped lithium manganese oxide active layer on the surface of its three-dimensional porous skeleton through in-situ growth, thereby forming an integral conductive structure without the need for binders. When applied to a capacitor deionization system, it achieves efficient and selective recovery of lithium ions, while also possessing structural stability and engineering adaptability. It is suitable for lithium resource recovery in complex systems such as salt lake brines and has good prospects for widespread application.

[0030] (2) This invention innovatively introduces a porous titanium fiber matrix with dual functions. First, as a self-supporting electrode matrix, the porous titanium fiber matrix enables in-situ growth and firm bonding of active materials, avoiding the use of binders and improving the overall conductivity of the electrode and the utilization rate of active sites. Furthermore, the three-dimensional interconnected pore structure of the porous titanium fiber matrix facilitates the flow of solution inside the electrode, shortens the ion transport path, and enhances the adsorption rate and capacity of lithium. In addition, the porous titanium fiber matrix can also release titanium ions in the hydrothermal reaction, stabilize the lithium manganese oxide lattice structure through titanium doping, reduce the performance degradation caused by structural changes, and improve the stability of recycling.

[0031] (3) The titanium-doped lithium manganese oxide self-supporting electrode constructed in situ in this invention can enable lithium-containing solutions to pass vertically through the internal channels of the electrode during operation through the synergistic regulation of structure and composition. This can effectively improve the lithium-ion transport efficiency, structural stability and overall electrode utilization. When applied to the capacitor deionization system, it can achieve efficient and selective recovery of lithium ions from lithium-containing solutions. In particular, it exhibits higher lithium-ion adsorption capacity, adsorption rate and cycle stability under the conditions of salt lake brine with high magnesium-to-lithium ratio. It is suitable for continuous, low-energy-consumption capacitor deionization lithium extraction application scenarios. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the titanium-doped lithium manganese oxide self-supporting electrode material of the present invention used for lithium extraction from lithium-containing solutions.

[0033] Figure 2 X-ray powder diffraction of the titanium-doped lithium manganese oxide self-supporting electrode materials prepared in Examples 1-3 of this invention.

[0034] Figure 3 This is a scanning electron microscope image of the titanium-doped lithium manganese oxide self-supporting electrode material prepared in Example 2 of the present invention.

[0035] Figure 4 The images shown are transmission electron microscope (TEM) and energy dispersive spectroscopy (EDS) images of the titanium-doped lithium manganese oxide self-supporting electrode material prepared in Example 2 of this invention.

[0036] Figure 5 The adsorption capacity of lithium ions in 10 mmol / L LiCl solution is shown for the titanium-doped lithium manganese oxide self-supporting electrode material prepared in Examples 1-3 of this invention and the non-self-supporting lithium manganese oxide electrode material prepared in the comparative example.

[0037] Figure 6 The GCD curves and capacitance retention rates of the titanium-doped lithium manganese oxide self-supporting electrode material prepared in Example 2 of this invention and the non-self-supporting lithium manganese oxide electrode material prepared in the comparative example after 1000 constant current charge-discharge cycles in 1 mol / L LiCl solution are shown.

[0038] Figure 7 The bar chart shows the lithium separation coefficient of the titanium-doped lithium manganese oxide self-supporting electrode material prepared in Example 2 of this invention under different magnesium-lithium ratios.

[0039] Figure 8 The separation coefficient of lithium ions from other metal ions in the brine of Dongtaijinaier Salt Lake in Qinghai Province is given by the titanium-doped lithium manganese oxide self-supporting electrode material prepared in Example 2 of this invention. Detailed Implementation

[0040] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0041] The first aspect of this invention provides a titanium-doped lithium manganese oxide self-supporting electrode. This self-supporting electrode comprises a porous titanium fiber matrix and a titanium-doped lithium manganese oxide nanosheet active layer grown in situ on the surface and within the pores of the porous titanium fiber matrix, forming an overall conductive self-supporting electrode structure. The lithium manganese oxide has a spinel structure, and titanium is introduced into the lithium manganese oxide lattice as a dopant, with the molar ratio of titanium being 1% to 10% of the molar amount of manganese.

[0042] This invention, through the synergistic regulation of the structure and composition of the titanium-doped lithium manganese oxide self-supporting electrode, can effectively improve the lithium-ion transport efficiency, structural stability, and overall electrode utilization. When applied to a capacitor deionization system, it can successfully achieve efficient and selective recovery of lithium ions from salt lake brine.

[0043] In some specific embodiments, the porous titanium fiber matrix is ​​a conductive titanium fiber felt. The pores of the titanium fiber felt are interconnected, exhibiting good electrical conductivity and mechanical stability.

[0044] In some specific embodiments, the titanium-doped lithium manganese oxide nanosheet active layer grows continuously along the surface of the metal fiber and is uniformly attached to the inner wall of the three-dimensional interconnected pores of the metal fiber felt, forming an overall conductive self-supporting structure.

[0045] In some specific embodiments, the morphology of the titanium-doped lithium manganese oxide nanosheet active layer is sheet-like, plate-like, or layered.

[0046] In some specific embodiments, the lithium manganese oxide nanosheets are 100-300 nm in size.

[0047] A second aspect of the present invention provides a method for preparing a titanium-doped lithium manganese oxide self-supporting electrode, the method comprising the following steps: S1: Surface treatment of porous titanium fiber matrix using oxalic acid solution; S2: Manganese source, urea and ammonium fluoride are prepared into a precursor solution, and the porous titanium fiber matrix pretreated by S1 is placed in the precursor solution for hydrothermal reaction, so that the manganese-containing precursor and titanium elements are deposited and grown on the surface and inside the pores of the porous titanium fiber matrix. S3: Heat-treat the porous titanium fiber matrix obtained in S2 to form a titanium-doped manganese oxide layer; S4: The porous titanium fiber matrix treated in S3 is placed in a lithium source solution for hydrothermal reaction to finally obtain the titanium-doped lithium manganese oxide self-supporting electrode.

[0048] In some specific embodiments, in step S1, the oxalic acid solution has a mass fraction of 5%-8%.

[0049] In some specific embodiments, in step S1, the surface treatment temperature is 80-90 ℃.

[0050] In some specific embodiments, in step S2, the manganese source is any one or more of manganese nitrate tetrahydrate, manganese sulfate, and manganese chloride, preferably manganese nitrate tetrahydrate.

[0051] In some specific embodiments, in step S2, the mass ratio of the manganese source, urea, and ammonium fluoride is (0.1-0.6): (0.1-0.6): (0.05-0.3).

[0052] The mass ranges of the manganese source, urea, and ammonium fluoride mentioned above have been optimized through numerous experiments to ensure that the manganese source is fully dissolved and to provide a suitable reaction environment for the subsequent hydrothermal reaction, which is beneficial for the synthesis of precursors of lamellar manganese oxides tightly wrapped on titanium fibers.

[0053] In some specific embodiments, in step S2, the temperature of the hydrothermal reaction is 100-150 ℃, preferably 120 ℃.

[0054] In some specific embodiments, in step S2, the hydrothermal reaction time is 2-10 h, preferably 6 h.

[0055] In some specific implementations, in step S3, the heat treatment is carried out in a muffle furnace.

[0056] In some specific embodiments, in step S3, the temperature of the heat treatment is 200-400 ℃, preferably 300 ℃.

[0057] In some specific embodiments, in step S4, the lithium source is any one or more of lithium hydroxide monohydrate, lithium carbonate, and lithium chloride, preferably lithium hydroxide monohydrate.

[0058] In some specific embodiments, in step S4, the concentration of the lithium source is 10-50 mmol / L.

[0059] In some specific embodiments, in step S4, the temperature of the hydrothermal reaction is 180-220 ℃, preferably 220 ℃.

[0060] In some specific embodiments, in step S4, the hydrothermal reaction time is 15-24 h, preferably 20 h.

[0061] Within the temperature and time range described above for the hydrothermal reaction, the lithiation reaction can proceed fully, and the resulting lithium manganese oxide exhibits good structural stability. If the temperature is too low or the time is too short, the reaction will be incomplete, resulting in poor crystallinity of the product; if the temperature is too high or the time is too long, the coated lithium manganese oxide may detach.

[0062] In the preparation process of this invention, titanium is derived from the porous titanium fiber matrix itself. After treatment with oxalic acid solution in step S1, the surface activity of the titanium fibers is improved, which is beneficial to the slow release of titanium in subsequent reactions. Under the hydrothermal reaction conditions in step S2, some titanium is dissolved from the surface of the titanium fiber matrix and deposited simultaneously with the generated manganese-containing precursor on the surface and inside the pores of the titanium fibers. Subsequently, after heat treatment in step S3, titanium participates in the rearrangement of the manganese oxide lattice and enters the manganese oxide structure in the form of doping. Finally, in the lithiation hydrothermal reaction process in step S4, a titanium-doped lithium manganese oxide active layer is formed, thereby realizing the construction of a self-supporting titanium-doped lithium manganese oxide electrode without the need for an additional titanium source.

[0063] A third aspect of this invention provides an application of a titanium-doped lithium manganese oxide self-supporting electrode in a capacitive deionization system. For example... Figure 1 As shown, the titanium-doped lithium manganese oxide self-supporting electrode of the present invention can be directly used as a capacitor deionization working electrode to selectively insert and release lithium ions in lithium-containing solutions under the action of an external electric field, thereby achieving the enrichment and recovery of lithium ions.

[0064] In some specific embodiments, the lithium-containing solution includes, but is not limited to, salt lake brine, such as pseudo-salt lake brine or complex lithium-containing aqueous phase systems containing multiple alkali metal and alkaline earth metal ions.

[0065] In some specific embodiments, the capacitor deionization system adopts a fluid-penetrating operation mode, which allows the lithium-containing solution to flow along the three-dimensional channel direction of the titanium-doped lithium manganese oxide self-supporting electrode.

[0066] Each of the above embodiments can be implemented individually, or in any combination of two or more. The following detailed description of specific examples will further illustrate these embodiments.

[0067] Unless otherwise specified, the reagents, methods, instruments, and equipment used in this invention are conventional in the art. Unless otherwise specified, the reagents and materials used in the following examples are all commercially available.

[0068] Example 1: This embodiment provides a titanium-doped lithium manganese oxide self-supporting electrode and its preparation method. The self-supporting electrode uses titanium fiber felt as a substrate, and titanium-doped lithium manganese oxide active material is loaded onto its surface and internal pores via an in-situ reaction.

[0069] The specific steps are as follows: (1) Pretreatment of titanium fiber felt A 0.8 mm thick titanium fiber felt was immersed in a 5% oxalic acid solution and sonicated for 30 minutes. It was then placed in an 80 °C oven and heated for 3 hours until the solution turned brownish-black, thus removing the oxide layer from the titanium felt surface. Finally, it was ultrasonically rinsed with deionized water. After this process, the individual fibers on the surface of the titanium fiber felt were clearly visible.

[0070] (2) Synthesis of titanium-doped manganese oxide precursor Weigh 0.3 g manganese nitrate tetrahydrate, 0.3 g urea, and 0.15 g ammonium fluoride, add to 90 mL deionized water, and stir for one hour until transparent. Completely immerse the titanium fiber felt treated in step (1) in the precursor solution, place it in a 150 mL polytetrafluoroethylene-lined high-pressure reactor, and react at 120 ℃ for 6 h. Titanium-doped lithium manganese oxide is generated and loaded in situ on the surface and inside the pores of the titanium fiber felt. After hydrothermal treatment, rinse thoroughly with deionized water; the surface appears light brownish-red. Dry in an 80 ℃ oven. Place the dried titanium felt in a muffle furnace and calcine at a heating rate of 5 ℃ / min to 300 ℃ for 4 h to obtain a blackish-gray titanium-doped manganese oxide precursor.

[0071] (3) Preparation of titanium-doped lithium manganese oxide Prepare 90 mL of 10 mmol / L LiOH solution and place it into the titanium fiber felt treated in step (2). React at 220℃ for 20 h. After the reaction is complete, take out the obtained electrode material, wash it repeatedly with deionized water to remove residual precursors, and then dry it to obtain a titanium-doped lithium manganese oxide self-supporting electrode.

[0072] Example 2: This embodiment provides an in-situ constructed titanium-doped lithium manganese oxide self-supporting electrode material. The difference from Example 1 is that the concentration of LiOH in step (3) is 20 mmol / L, while the amount of other reagents and reaction conditions remain unchanged.

[0073] Example 3: This embodiment provides an in-situ constructed titanium-doped lithium manganese oxide self-supporting electrode material. The difference from Example 1 is that the concentration of LiOH in step (3) is 30 mmol / L, while the amount of other reagents and reaction conditions remain unchanged.

[0074] Figure 2X-ray powder diffraction (XRD) of the titanium-doped lithium manganese oxide self-supporting electrode materials prepared in Examples 1-3 of this invention is shown. The figure illustrates the crystal structure characteristics of lithium manganese oxide with different degrees of lithiation, exhibiting a series of characteristic diffraction peaks at 18.6°, 36.1°, and 43.9°. These peaks can be well attributed to the (111), (311), and (400) crystal planes of the standard spinel-type LiMn₂O₄ phase (PDF#89-0117), and no obvious impurity phases were detected. The position and intensity of the characteristic peaks confirm the presence of lithium manganese oxide and the crystallinity of the material.

[0075] Figure 3 This is a scanning electron microscope (SEM) image of the titanium-doped lithium manganese oxide self-supporting electrode material prepared in Example 2 of this invention. The morphology of the material is clearly visible in the image, intuitively demonstrating the effect of the lithium manganese oxide active layer encapsulating the titanium fiber felt.

[0076] Figure 4 This is a transmission electron microscope (TEM) image of the titanium-doped lithium manganese oxide self-supporting electrode material prepared in Example 2 of this invention. The image further reveals the layered structure of the material, clearly showing that the lithium manganese oxide nanosheets are approximately 100-300 nm in size. The energy dispersive spectroscopy (EDS) elemental mapping results on the right further confirm that Mn, Ti, and O elements are uniformly distributed in the nanosheets, indicating that Ti is uniformly introduced into the lithium manganese oxide lattice as a dopant during hydrothermal growth, rather than forming an independent titanium-containing phase.

[0077] Comparative Example 1: This comparative example provides a lithium manganese oxide material. The difference from Example 1 is that titanium fiber felt is not included in this comparative example, thus eliminating the dual effects of Ti doping and the self-supporting matrix. The amounts of other reagents and reaction conditions remain unchanged, and the specific operation is as follows: Weigh 0.3 g of manganese nitrate tetrahydrate, 0.3 g of urea, and 0.15 g of ammonium fluoride, add them to 90 mL of deionized water, and stir for one hour until the solution becomes transparent. Place the precursor solution into a 150 mL high-pressure reactor lined with polytetrafluoroethylene (PTFE), and react at 120 °C for 6 h. After hydrothermal treatment, rinse thoroughly with deionized water and dry in an 80 °C oven. Place the dried product in a muffle furnace and calcine at 300 °C for 4 h at a heating rate of 5 °C / min to obtain a blackish-gray manganese oxide precursor.

[0078] The manganese oxide precursor was placed in 90 mL of a 10 mmol / L LiOH solution and hydrothermally reacted at 220 °C for 20 h. After the reaction was completed, the resulting electrode material was removed, repeatedly washed with deionized water, and then dried to obtain lithium manganese oxide material.

[0079] This invention employs a combination of in-situ growth and hydrothermal reaction methods to achieve precise synthesis of lithium manganese oxide by controlling the amount of lithium source, successfully preparing a series of in-situ constructed titanium-doped lithium manganese oxide self-supporting electrode materials. In this comparative example, powdered lithium manganese oxide material was ultimately obtained. Therefore, to prepare a working electrode with supporting properties, it needs to be coated onto a titanium fiber felt substrate with conductive carbon black and a binder. However, the addition of the binder limits the contact between the active component and the current collector, resulting in poor electron transport efficiency.

[0080] Based on the successful preparation of the above-mentioned in-situ constructed titanium-doped lithium manganese oxide self-supporting electrode / lithium manganese oxide material, this invention further explores its application as an electrode material in capacitive deionization lithium extraction. The specific test steps are as follows: (1) Preparation of capacitive deionization electrode: The self-supporting electrode materials constructed in situ in Examples 1-3 of this invention do not require further preparation and can be used directly as working electrodes.

[0081] The non-self-supporting lithium manganese oxide electrode material of Comparative Example 1 required mixing 16 mg of lithium manganese oxide powder, 2 mg of activated carbon black, and 2 mg of polytetrafluoroethylene binder (PTFE), grinding them evenly in ethanol to form a slurry. The slurry was then uniformly coated onto titanium fiber felt, and the coated titanium fiber felt was dried in an oven at 80 °C for 12 h to obtain a capacitive deionization electrode.

[0082] (2) Assemble the above-prepared capacitive deionization electrodes into a capacitive deionization device, using a dual-electrode structure with a distance of 0.2 cm between the two electrodes. Prepare a 10 mmol / L lithium chloride (LiCl) solution as a simulated lithium-containing solution. At a working voltage of 1.2 V, pass the simulated lithium-containing solution into the capacitive deionization device at a flow rate of 40 mL / min to conduct a lithium extraction experiment.

[0083] (3) Take a sample every 2-5 minutes and use inductively coupled plasma optical emission spectrometry (ICP-OES) to determine the concentration of lithium ions in the solution and calculate the adsorption capacity of the material for lithium ions.

[0084] The selectivity of materials is determined by the separation coefficient ( The quantitative expression is as follows: ; In the formula For different interfering ions (M=K) + Ca 2+ Na + Mg 2+ The adsorption capacity of ) (mol L) -1The initial concentration of lithium ions in the solution is denoted as . (mol L) -1 ) represents the initial concentration of interfering ion M.

[0085] Figure 5 The comparison curves of the capacitive deionization performance of the titanium-doped lithium manganese oxide self-supporting electrode materials prepared in Examples 1-3 and the non-self-supporting lithium manganese oxide electrode material prepared in Comparative Example 1 in 10 mmol / L LiCl solution show the effect of different degrees of lithiation on the lithium adsorption capacity of lithium manganese oxide materials. The curves clearly show that as the degree of lithiation increases, the lithium ion adsorption capacity first increases and then decreases. The lithium adsorption capacity of the titanium-doped lithium manganese oxide self-supporting electrode materials prepared in Examples 1-3 is significantly higher than that of the non-self-supporting lithium manganese oxide electrode material prepared in Comparative Example 1. Among them, the lithium manganese oxide material with a medium degree of lithiation (LiOH concentration of 20 mmol / L) in Example 2 achieved a lithium adsorption capacity of 5.43 mmol g within 30 minutes. -1 This demonstrates excellent lithium-ion adsorption capacity. In contrast, the capacitive deionization electrode prepared in Comparative Example 1 only adsorbed approximately 3 mmol g of lithium. -1 .

[0086] Figure 6 The capacitance retention of the titanium-doped lithium manganese oxide self-supporting electrode material prepared in Example 2 of this invention after 1000 cycles of constant current charge-discharge cycling (GCD) in a 1 mol / L LiCl solution is demonstrated. After 1000 cycles, it still retains 92.2% of its initial capacitance, indicating that the electrode material has good cycle stability. In contrast, under the same test conditions, the capacitance of Comparative Example 1 rapidly decayed to near zero, indicating severe structural collapse during cycling. The significantly improved cycle durability of Example 2 is mainly attributed to titanium doping, which effectively suppresses the interaction between titanium and Mn. 3+ The associated Jahn-Teller effect enhances the spinel framework in repeated Li + The structural stability during the insertion / extraction process ensures its long-term stable electrochemical performance.

[0087] Figure 7 This is a bar chart showing the lithium separation coefficient of the titanium-doped lithium manganese oxide self-supporting electrode material prepared in Example 2 of this invention under different magnesium-to-lithium ratios. Even with the magnesium-to-lithium molar ratio increased to 20:1, the adsorption capacity of the material pair remains as high as 3.38 mmol g. -1 The corresponding separation coefficient can reach 43.60, which fully demonstrates that the electrode material has excellent selective adsorption of lithium ions and can efficiently separate lithium in magnesium-lithium coexistence systems.

[0088] Figure 8This invention, in Example 2, describes the separation coefficient of lithium ions from other metal ions in the brine of the Dongtaijinaier Salt Lake in Qinghai Province for the titanium-doped lithium manganese oxide self-supporting electrode material. The study found that this material exhibits excellent selective extraction capability for lithium in the actual brine of the Dongtaijinaier Salt Lake in Qinghai, China, with a separation coefficient as high as 11.49, fully demonstrating its good potential for practical application.

[0089] In summary, this invention achieves efficient and selective lithium-ion recovery by constructing a titanium-doped lithium manganese oxide self-supporting electrode material and applying it to a capacitor deionization system. It combines structural stability with engineering adaptability and is suitable for lithium resource recovery in complex systems such as salt lake brines, showing promising prospects for widespread application.

[0090] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A titanium-doped lithium manganese oxide self-supporting electrode, characterized in that, The self-supporting electrode includes a porous titanium fiber matrix and a titanium-doped lithium manganese oxide nanosheet active layer grown in situ on the surface and pores of the porous titanium fiber matrix, forming an overall conductive self-supporting electrode structure. The lithium manganese oxide has a spinel structure, and titanium is introduced into the lithium manganese oxide lattice in the form of doping. The molar ratio of titanium doping is 1% to 10% of the molar amount of manganese.

2. The titanium-doped lithium manganese oxide self-supporting electrode according to claim 1, characterized in that, The porous titanium fiber matrix is ​​a conductive titanium fiber felt.

3. The titanium-doped lithium manganese oxide self-supporting electrode according to claim 1, characterized in that, The active layer of titanium-doped lithium manganese oxide nanosheets grows continuously along the surface of the metal fiber. The active layer of titanium-doped lithium manganese oxide nanosheets has a morphology of sheet-like, plate-like, or layered. The lithium manganese oxide nanosheets are 100-300 nm in size.

4. A method for preparing a titanium-doped lithium manganese oxide self-supporting electrode according to any one of claims 1-3, characterized in that, The preparation method includes the following steps: S1: Surface treatment of porous titanium fiber matrix using oxalic acid solution; S2: Manganese source, urea and ammonium fluoride are prepared into a precursor solution, and the porous titanium fiber matrix pretreated by S1 is placed in the precursor solution for hydrothermal reaction, so that the manganese-containing precursor and titanium elements are deposited and grown on the surface and inside the pores of the porous titanium fiber matrix. S3: Heat-treat the porous titanium fiber matrix obtained in S2 to form a titanium-doped manganese oxide layer; S4: The porous titanium fiber matrix treated in S3 is placed in a lithium source solution for hydrothermal reaction to finally obtain the titanium-doped lithium manganese oxide self-supporting electrode.

5. The method for preparing a titanium-doped lithium manganese oxide self-supporting electrode according to claim 1, characterized in that, In step S1, the oxalic acid solution has a mass fraction of 5%-8%; The surface treatment temperature is 80-90 ℃.

6. The method for preparing a titanium-doped lithium manganese oxide self-supporting electrode according to claim 1, characterized in that, In step S2, the manganese source is any one or more of manganese nitrate tetrahydrate, manganese sulfate, and manganese chloride; The mass ratio of the manganese source, urea, and ammonium fluoride is (0.1-0.6): (0.1-0.6): (0.05-0.3); The hydrothermal reaction temperature is 100-150 ℃, and the hydrothermal reaction time is 2-10 h.

7. The method for preparing a titanium-doped lithium manganese oxide self-supporting electrode according to claim 1, characterized in that, In step S3, the heat treatment is carried out in a muffle furnace; The heat treatment temperature is 200-400 ℃.

8. The method for preparing a titanium-doped lithium manganese oxide self-supporting electrode according to claim 1, characterized in that, In step S4, the lithium source is any one or more of lithium hydroxide monohydrate, lithium carbonate, and lithium chloride; The concentration of the lithium source is 10-50 mmol / L; The hydrothermal reaction temperature is 180-220 ℃, and the hydrothermal reaction time is 15-24 h.

9. The application of the titanium-doped lithium manganese oxide self-supporting electrode according to any one of claims 1-3 in a capacitive deionization system, characterized in that, The titanium-doped lithium manganese oxide self-supporting electrode serves as a capacitive deionization working electrode, used to selectively insert and release lithium ions in a lithium-containing solution under the action of an external electric field, thereby achieving the enrichment and recovery of lithium ions.

10. The application of the titanium-doped lithium manganese oxide self-supporting electrode according to claim 9 in a capacitive deionization system, characterized in that, The lithium-containing solution includes, but is not limited to, salt lake brine; The capacitor deionization system adopts a fluid-penetrating operation mode, which allows the lithium-containing solution to flow along the three-dimensional channel direction of the titanium-doped lithium manganese oxide self-supporting electrode.

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