Titanium dioxide negative pole piece, preparation method thereof and aqueous lithium ion battery

Abstract

The invention relates to a titanium dioxide negative pole piece, a preparation method thereof and an aqueous lithium ion battery, and belongs to the field of electrochemical materials. And at least one of the problems of low conductivity, easy agglomeration of nano-particles, poor rate capability caused by serious hydrogen evolution in an aqueous battery, fast cycle capacity fading and the like of the negative plate in the aqueous lithium ion battery in the prior art is solved. The preparation method of the titanium dioxide negative pole piece comprises the following steps: performing electrochemical expansion treatment on graphite paper to obtain expanded graphite paper; carrying out fluorination treatment on the expanded graphite paper; loading titanium dioxide on the fluorinated expanded graphite paper to obtain an active precursor; and combining the active precursor with a current collector to obtain the titanium dioxide negative pole piece. By improving the conductivity of the negative plate, the phenomena of nanoparticle aggregation and hydrogen evolution are reduced, and the rate capability and the cycle capacity retention ratio of the aqueous lithium ion battery are improved.

Description

Technical Field

[0001] This invention relates to the field of electrochemical materials technology, and in particular to a titanium dioxide negative electrode sheet and its preparation method, and an aqueous lithium-ion battery. Background Technology

[0002] Traditional lithium-ion batteries pose safety risks due to the flammability and explosiveness of their organic electrolytes, and require stringent assembly conditions, strict moisture control, and high production costs. To overcome these drawbacks, aqueous lithium-ion batteries utilize aqueous electrolytes, fundamentally solving safety issues and reducing production costs, demonstrating promising application prospects.

[0003] Among known candidate materials for aqueous battery anodes, titanium-based oxides (such as TiO2) are highly favored due to their high stability and abundant resources. However, the performance of anode sheets made from them is still unsatisfactory, mainly due to the following three problems: Low conductivity: TiO2 itself is a wide bandgap semiconductor with extremely low intrinsic electronic conductivity. Simultaneously, the diffusion rate of lithium ions in its lattice is also slow, resulting in high internal resistance and poor rate performance. Nanoparticle agglomeration: Nanoparticles used to improve conductivity, due to their extremely high surface energy, thermodynamically tend to aggregate to reduce surface energy, leading to a decrease in active area and blockage of ion transport channels. Severe hydrogen evolution in aqueous batteries: Although the operating potential of TiO2 is higher than the theoretical decomposition potential of water, during actual charge and discharge processes, due to electrode polarization and interfacial catalysis, local potentials may trigger the reduction reaction of water, generating hydrogen gas, causing capacity decay and safety hazards.

[0004] Therefore, developing novel electrode materials and preparation processes to improve the electrochemical performance of aqueous systems while maintaining their safety has become a critical technological bottleneck that urgently needs to be overcome in this field. Summary of the Invention

[0005] Based on the above analysis, the present invention aims to provide a titanium dioxide negative electrode sheet and its preparation method, as well as an aqueous lithium-ion battery, to solve at least one of the following problems existing in the negative electrode sheet of aqueous lithium-ion batteries: low conductivity, easy agglomeration of nanoparticles, and poor rate performance and rapid cycle capacity decay caused by severe hydrogen evolution in aqueous batteries.

[0006] The objective of this invention is achieved through the following technical solution: This invention provides a method for preparing a titanium dioxide negative electrode sheet, comprising the following steps: S1: Electrochemical expansion treatment of graphite paper to obtain expanded graphite paper; S2: Fluoride treatment is performed on the expanded graphite paper; S3: Titanium dioxide is loaded onto the fluorinated expanded graphite paper to obtain an active precursor; S4: Combine the active precursor with the current collector to obtain the titanium dioxide negative electrode sheet.

[0007] Further, the fluorination treatment in step S2 includes: reacting the dried expanded graphite paper with a gaseous fluorine source at 350~440℃ for 2~10h to form a CFx component on the surface of the expanded graphite paper, wherein 0 < X ​​< 1.25.

[0008] Furthermore, the electrochemical expansion treatment in step S1 is carried out in an acidic electrolyte at a voltage of 1.5~1.9V for 0.5~2 minutes.

[0009] Furthermore, after the electrochemical expansion treatment, a post-treatment step is also included: the electrochemically treated graphite paper is first placed in a solution containing hydrogen peroxide and left to stand at room temperature for 0.5 to 3 minutes, and then transferred to a water bath at 45 to 75°C and kept for 0.5 to 4 hours.

[0010] Further, step S3 includes: using fluorinated expanded graphite paper as the cathode, depositing it at a constant voltage of 2.8~3.3V for 8~12 minutes in an acidic electrolyte containing TiOSO4.

[0011] Further, the concentration of TiOSO4 in the acidic electrolyte is 0.015~0.03M; and / or, The acidic electrolyte further comprises potassium nitrate at a concentration of 0.05~0.2M and / or hydrogen peroxide at a concentration of 0.005~0.02M; and / or, The pH value of the acidic electrolyte is 1.5~2.0.

[0012] Furthermore, the gaseous fluorine source is one or more of F2, NF3, or XeF2.

[0013] Furthermore, in step S4, the bonding method is compression, and the compression pressure is 7~10MPa.

[0014] This invention provides a titanium dioxide negative electrode sheet, which is prepared by the aforementioned method.

[0015] The present invention provides an aqueous lithium-ion battery, including the aforementioned titanium dioxide negative electrode sheet.

[0016] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects: (1) An expanded graphite paper substrate with a three-dimensional conductive network is formed by electrochemical expansion treatment of graphite paper, and then fluorination treatment is used to introduce CF with good conductivity onto the surface of the expanded graphite paper. XThe layer constructs a dual conductive channel of "bulk phase-interface", thereby improving the electronic conduction capability of the negative electrode, effectively reducing the internal resistance, and enabling the negative electrode material to exhibit excellent rate performance.

[0017] (2) Expanded graphite paper is used as a load substrate. Its rich pore structure and huge specific surface area provide a guarantee for the uniform loading of titanium dioxide. This structure can provide sufficient active sites and prevent direct contact of nanoparticles through physical barrier, thereby achieving uniform dispersion of titanium dioxide nanoparticles, ensuring full contact between active material and electrolyte, improving material utilization, and thus improving rate performance.

[0018] (3) By constructing CF on the surface of expanded graphite paper X As an additive for SEI formation, the CF layer plays a crucial role during the first charge and discharge process of the battery. X Reacts with lithium ions In situ, a uniform and dense LiF passivation layer is generated. As a wide bandgap insulator, this passivation layer can block the transfer of electrons to water molecules in the electrolyte through physical barrier effect, and increase the difficulty of hydrogen evolution reaction by raising the interfacial energy barrier. Thus, it can effectively suppress hydrogen evolution side reaction from both thermodynamic and kinetic perspectives, significantly improve rate performance and cycle capacity retention, and enhance interfacial compatibility and reduce battery polarization.

[0019] (4) In some preferred embodiments, by controlling key process parameters and material selection, the conductivity, uniform dispersion of active materials and hydrogen evolution suppression of titanium dioxide negative electrode sheet are further improved in a synergistic manner from multiple aspects such as structural regulation, interface engineering and process optimization, thereby improving rate performance and cycle capacity retention. By controlling the electrochemical expansion process parameters, a three-dimensional conductive network with ideal interlayer spacing and porosity can be constructed in graphite paper. This structure can effectively improve electrode conductivity and promote the uniform dispersion of titanium dioxide nanoparticles, providing a better foundation for the subsequent construction of a complete LiF passivation layer. By controlling the temperature, time, and CFx composition range of the fluorination treatment, a conductive interface layer with a moderate degree of fluorination is formed on the surface of the expanded graphite paper substrate, providing a better foundation for the subsequent in-situ generation of a uniform LiF passivation layer and suppression of hydrogen evolution reaction. By introducing a stepwise oxidation post-treatment step after fluorination, the expanded graphite paper structure is further stabilized and an appropriate amount of oxygen-containing functional groups are introduced, thereby enhancing the integrity of the expanded graphite paper substrate structure and promoting the uniform formation of the fluorinated layer. By controlling the voltage, time, and electrolyte composition of titanium dioxide electrochemical deposition, a better uniform loading and tight adhesion of titanium dioxide active materials can be achieved, effectively preventing the aggregation of titanium dioxide nanoparticles.

[0020] (5) In some specific embodiments, the present invention improves the rate performance and cycle capacity retention of aqueous lithium-ion batteries by increasing the conductivity of the negative electrode sheet, reducing the agglomeration of nanoparticles and hydrogen evolution, which is reflected in: 2C / 0.5C capacity retention ≥70%, and 0.5C capacity retention ≥70% after 100 cycles; for example, 2C / 0.5C capacity retention is 70%~77%, and 0.5C capacity retention is 70%~80% after 100 cycles.

[0021] In this invention, the above-described technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of this invention will be set forth in the following description, and some advantages may become apparent from the description or be learned by practicing the invention. The objects and other advantages of this invention can be realized and obtained from what is particularly pointed out in the description and drawings. Attached Figure Description

[0022] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts. Figure 1 The cycling performance graphs for Example 1 and Comparative Example 1 are shown. Figure 2 The graphs show the cyclic performance of Example 2 and Comparative Example 2. Detailed Implementation

[0023] Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which form part of this application and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not intended to limit the scope of the present invention.

[0024] In a first aspect, the present invention provides a method for preparing a titanium dioxide negative electrode sheet, comprising the following steps: S1: Electrochemical expansion treatment of graphite paper to obtain expanded graphite paper; S2: Fluoride treatment is performed on the expanded graphite paper; S3: Titanium dioxide is loaded onto the fluorinated expanded graphite paper to obtain an active precursor; S4: Combine the active precursor with the current collector to obtain the titanium dioxide negative electrode sheet.

[0025] Specifically, the electrochemical expansion treatment in step S1 is carried out in an acidic electrolyte at a voltage of 1.5~1.9V for 0.5~2 minutes.

[0026] Specifically, in the electrochemical expansion process, graphite paper is used as the working electrode and a platinum electrode is used as the counter electrode. The distance between the graphite paper and the counter electrode during the electrochemical expansion treatment is 1.5–3 cm.

[0027] Specifically, the acidic electrolyte is a sulfuric acid solution. The mass concentration of the sulfuric acid solution is 95 wt.%~98 wt.%.

[0028] Preferably, the graphite paper undergoes vacuum drying before electrochemical expansion, and the vacuum drying process is carried out at a temperature of 60~80℃ for a time of ≥10h. For example, the vacuum drying process is carried out for 10h~16h.

[0029] For example, in the electrochemical expansion treatment of step S1, the voltage is 1.5V, 1.6V, 1.7V, 1.8V, or 1.9V; preferably 1.6V to 1.8V. The holding time is 0.5min, 0.75min, 1.0min, 1.25min, 1.5min, 1.75min, or 2.0min; preferably 1 to 1.5min.

[0030] Specifically, the electrochemical expansion treatment temperature is 20-40℃.

[0031] Specifically, the thickness of the graphite paper is 100~300µm; preferably 150~200µm.

[0032] Specifically, the graphite paper used in the electrochemical expansion is dried graphite paper; for example, before the electrochemical expansion, the graphite paper is placed at 60~80℃ and vacuum dried to obtain dried graphite paper; the vacuum drying time is ≥10h.

[0033] It should be noted that by precisely controlling the process parameters of electrochemical expansion, graphite paper can form a three-dimensional conductive network with ideal interlayer spacing and porosity. This structure effectively improves electrode conductivity by constructing continuous electronic conduction channels, achieves uniform dispersion of titanium dioxide nanoparticles through interlayer confinement, and lays the foundation for the subsequent construction of a complete LiF passivation layer through uniform current distribution. Conversely, insufficient expansion will result in an incomplete three-dimensional network structure, failing to effectively improve conductivity and dispersion; excessive expansion will cause graphite lattice collapse, not only reducing intrinsic conductivity, but the resulting structural defects will also lead to uneven titanium dioxide deposition and CF2 corrosion. X Problems such as incomplete protective layer formation, and the fact that defective sites, as catalytic centers for hydrogen evolution reaction, can significantly exacerbate side reactions and affect electrochemical performance.

[0034] Specifically, after the electrochemical expansion treatment, a post-treatment step is also included: the electrochemically treated graphite paper is first placed in a solution containing hydrogen peroxide and left to stand at room temperature for 0.5 to 3 minutes, and then transferred to a water bath at 45 to 75°C and kept for 0.5 to 4 hours.

[0035] It should be noted that the post-processing steps, through "structural stabilization" and "fluorination precursor preparation" of the electrochemically expanded graphite paper, provide a better foundation for subsequent fluorination. First, hydrogen peroxide effectively removes residual sulfate and other intercalating agents between graphite layers, providing a clean reaction interface for the fluorinating agent. Second, the stepwise oxidation process permanently fixes the interlayer spacing of the graphite sheets, preventing structural shrinkage during subsequent high-temperature fluorination and ensuring the stability of the three-dimensional porous structure. Furthermore, the introduced oxygen-containing functional groups alter the electron cloud distribution of the carbon skeleton, providing uniform active initiation sites for the fluorination reaction and promoting CF425. X The uniform formation of the protective layer is beneficial for the subsequent construction of a high-quality LiF passivation layer, thereby preventing hydrogen evolution.

[0036] Specifically, in the post-treatment steps, the room temperature standing period (0.5~3 min) aims to ensure that the hydrogen peroxide solution fully and uniformly penetrates into the internal structure of the expanded graphite paper, establishing a uniform pretreatment foundation for the subsequent heating reaction and avoiding the violent surface reaction caused by direct water bath, which hinders internal penetration. The heated water bath (45~75℃, 0.5~4 h) achieves efficient introduction of oxygen-containing functional groups while maintaining the integrity of the graphite skeleton structure. The temperature and time range balance reaction efficiency and material stability. If the temperature is too low or the time is too short, the functional group formation will be insufficient; if the temperature is too high or the time is too long, it will cause rapid decomposition of hydrogen peroxide and excessive oxidation of the carbon skeleton and an increase in defects, affecting conductivity and the continuity and stability of the CFx layer in the subsequent fluorination treatment.

[0037] Specifically, in the post-processing step, the concentration of the hydrogen peroxide solution is 0.01~0.05M; for example, 0.01M, 0.02M, 0.03M, 0.04M, 0.05M. Preferably, it is 0.01~0.02M.

[0038] For example, in the post-processing step, the temperature is allowed to stand for 0.5 min, 1.0 min, 1.5 min, 2.0 min, 2.5 min, or 3.0 min; preferably 0.5 to 1.5 min.

[0039] For example, in the post-processing step, the water bath temperature is 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, or 75°C; preferably 50~65°C. The water bath is maintained for 0.5h, 1.0h, 1.5h, 2.0h, 2.5h, 3.0h, 3.5h, or 4.0h; preferably 2.5~4h.

[0040] Preferably, after being placed in a water bath at 45-75°C for 0.5-4 hours, the graphite paper is removed and cleaned and dried. For example, the graphite paper is placed at 95-120°C and vacuum dried for ≥12 hours.

[0041] Specifically, the fluorination treatment in step S2 includes: reacting dried expanded graphite paper with a gaseous fluorine source at 350~440℃ for 2~10h to form CFx component on the surface of expanded graphite paper, where 0 < X ​​< 1.25.

[0042] It should be noted that by precisely controlling the temperature and time of the fluorination treatment, the degree of fluorination (i.e., CF) on the surface of expanded graphite paper can be controlled. X Control of the x-value and fluorinated layer structure: Within the above temperature and time range, it is possible to ensure that the gaseous fluorine source has sufficient activity to react with graphite carbon, while avoiding excessively high temperatures that could damage the graphite sp. 2 The structure leads to decreased conductivity; the reaction time and temperature work together to determine the depth and amount of fluorine doping. Too short a time will result in an incomplete fluorinated layer and insufficient protection, while too long a time may cause over-fluorination, forming an overly insulating CF layer. X This layer, in turn, affects the overall conductivity of the electrode.

[0043] Specifically, the gaseous fluorine source is one or more of F2, NF3, or XeF2.

[0044] Specifically, the fluorination process is carried out in a sealed container, and the vacuum level in the sealed container is maintained at <-0.01 Pa; the aim is to eliminate interfering gases, ensure sufficient diffusion of the fluorine source and optimize reaction kinetics, thereby forming a CFx layer with controllable composition and structure on the surface of expanded graphite paper.

[0045] For example, the fluorination treatment temperature is 350℃, 360℃, 370℃, 380℃, 390℃, 400℃, 410℃, 420℃, 430℃, or 440℃; preferably 380~415℃. The fluorination treatment time is 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h, or 10h; preferably 7~10h.

[0046] Specifically, step S3 includes: using fluorinated expanded graphite paper as the cathode, depositing it at a constant voltage of 2.8~3.3V for 8~12 minutes in an acidic electrolyte containing TiOSO4.

[0047] Specifically, the concentration of TiOSO4 in the acidic electrolyte is 0.015~0.03M.

[0048] For example, the concentration of TiOSO4 in the acidic electrolyte is 0.015M, 0.018M, 0.02M, 0.022M, 0.025M, 0.028M, or 0.03M; preferably 0.018~0.022M.

[0049] Specifically, when preparing the acidic electrolyte of TiOSO4, TiOSO4 is dissolved in a 0.15~0.3M (e.g. 0.2M) sulfuric acid aqueous solution and stirred until homogeneous.

[0050] Specifically, the acidic electrolyte also contains potassium nitrate at a concentration of 0.05~0.2M and / or hydrogen peroxide at a concentration of 0.005~0.02M.

[0051] For example, the concentration of potassium nitrate in the acidic electrolyte is 0.05M, 0.08M, 0.1M, 0.12M, 0.15M, 0.18M, ​​or 0.2M, preferably 0.08~0.12M.

[0052] For example, the concentration of hydrogen peroxide in the acidic electrolyte is 0.005M, 0.008M, 0.01M, 0.012M, 0.015M, 0.018M, or 0.02M, preferably 0.008~0.012M.

[0053] Specifically, the pH value of the acidic electrolyte is 1.5 to 2.0. Preferably, the pH value is 1.7 to 1.9. For example, ammonia is added to adjust the pH value.

[0054] Specifically, in step S3, Pt is used as the anode. Exemplarily, the deposition voltage is 2.8V, 2.9V, 3.0V, 3.1V, 3.2V, or 3.3V, preferably 3.0~3.2V. The deposition time is 8min, 9min, 10min, 11min, or 12min, preferably 10~12min.

[0055] Specifically, after deposition, the active precursor is washed and dried at low temperature. The low-temperature drying temperature is 50~80℃, and the time is 4~8 hours.

[0056] Specifically, in step S4, the bonding method is compression, and the compression pressure is 7~10MPa.

[0057] For example, the pressing pressure is 7 MPa, 8 MPa, 9 MPa, 9.5 MPa, or 10 MPa. Preferably, it is 9 to 10 MPa.

[0058] Specifically, the current collector is a titanium mesh.

[0059] In a second aspect, the present invention provides a titanium dioxide negative electrode sheet, which is prepared by the preparation method described in the first aspect.

[0060] Thirdly, the present invention provides an aqueous lithium-ion battery, comprising the titanium dioxide negative electrode sheet described in the second aspect.

[0061] Specifically, the aqueous lithium-ion battery includes an aqueous electrolyte, a positive electrode, a titanium dioxide negative electrode sheet, and a separator.

[0062] For example, the positive electrode uses lithium manganese oxide (LMO), a conductive agent, and a binder as raw materials, which are mixed with a solvent in a certain mass ratio to obtain an active layer with a thickness of 100-200µm. After drying, the active layer is pressed together with a current collector (for example, the pressing pressure is 8-10MPa). In the active layer, the mass percentage of LMO is 80%-90%, the mass percentage of the conductive agent (such as conductive carbon black) is 5%-15%, and the mass percentage of the binder (such as PTFE) is 3%-8%.

[0063] For example, the aqueous electrolyte is an aqueous solution containing lithium salt, wherein the lithium salt is lithium trifluoromethanesulfonate with a concentration of 1.5 M to 3.0 M; the solvent of the electrolyte is a ternary mixed solvent of isopropanol, trimethyl phosphate and water, wherein the volume percentage of isopropanol is 30% to 50%, the volume percentage of trimethyl phosphate is 30% to 50%, and the volume percentage of water is 10% to 30%.

[0064] The aqueous lithium-ion battery assembled using the titanium dioxide negative electrode sheet described in this invention exhibits excellent rate performance and cycle stability. For example, the discharge capacity at 2C rate remains above 70% relative to that at 0.5C rate, and the capacity retention rate reaches above 70% after 100 cycles at 0.5C rate. Under the same conditions of positive electrode, separator, and electrolyte, the rate performance and cycle stability of the aqueous lithium-ion battery assembled using the titanium dioxide negative electrode sheet described in this invention are significantly better than those of the aqueous lithium-ion battery assembled using a conventional negative electrode sheet.

[0065] The technical solution of the present invention will be further described in detail below with reference to specific embodiments and comparative examples.

[0066] Example 1 This embodiment provides a method for preparing a titanium dioxide negative electrode sheet, including the following steps: S1: Electrochemical expansion treatment of graphite paper to obtain expanded graphite paper; S11. Take a piece of graphite paper with a thickness of 200µm and dry it under vacuum at 70℃ for 10h to obtain dried graphite paper. S12. Using dried graphite paper as the working electrode and a platinum electrode as the counter electrode, with a distance of 2 cm between the two electrodes, a constant voltage of 1.7 V is applied in a sulfuric acid electrolyte with a mass concentration of 98 wt.% at 25 °C and maintained for 1.5 min to perform electrochemical expansion treatment to obtain expanded graphite paper. S13. Immerse the electrochemically expanded graphite paper in a 0.01M hydrogen peroxide solution and let it stand at room temperature (25℃) for 1.0 min to allow it to be fully wetted; then transfer it to a 60℃ water bath and keep it warm for 3.5 h. S14. After removal, wash three times with deionized water, and then place in a vacuum dryer at 110℃ for 12 hours to obtain expanded graphite paper.

[0067] S2: Fluoride treatment is performed on the expanded graphite paper; The expanded graphite paper treated with S1 was placed in a vacuum fluorination reactor and evacuated to -0.02 Pa. Fluorine gas (F2) was introduced as a gaseous fluorine source, and the reaction was carried out at 400℃ for 8 hours. After the reaction was completed and the sample was allowed to cool naturally to room temperature, it was removed, and CF was formed on the surface. X Fluorinated expanded graphite paper.

[0068] S3: Titanium dioxide is loaded onto the fluorinated expanded graphite paper to obtain an active precursor; Fluorinated expanded graphite paper was used as the cathode and platinum sheet as the anode. A constant voltage of 3.1V was applied in an acidic electrolyte, and deposition was carried out for 11 minutes. In the preparation of the acidic electrolyte, TiOSO4 is dissolved in a 0.20M sulfuric acid aqueous solution and stirred evenly; in the acidic electrolyte, the concentration of TiOSO4 is 0.020M, the concentration of KNO3 is 0.10M, the concentration of H2O2 is 0.010M, and the pH value of the electrolyte is adjusted to 1.8 with ammonia water. After deposition, the sample was removed, washed with deionized water, and then vacuum dried at 65°C for 6 hours to obtain the active precursor. S4: Combine the active precursor with the current collector to obtain the titanium dioxide negative electrode sheet; The active precursor and titanium mesh are aligned and stacked; a pressure of 9 MPa is applied in a tablet press and held for 30 seconds to compress the mixture, thus obtaining the final titanium dioxide negative electrode sheet.

[0069] Example 2 The steps in this embodiment are the same as in embodiment 1, except that: S2: The expanded graphite paper treated in S1 was placed in a vacuum fluorination reactor and evacuated to -0.015 Pa; nitrogen tetrafluoride (NF3) was introduced as a gaseous fluorine source, and the reaction was carried out at 420℃ for 5 h; after the reaction was completed, the sample was naturally cooled to room temperature and taken out, resulting in CF formed on the surface. X Fluorinated expanded graphite paper.

[0070] Example 3 The steps in this embodiment are the same as in embodiment 1, except that: S2: The expanded graphite paper treated in S1 was placed in a vacuum fluorination reactor and evacuated to -0.015 Pa; nitrogen tetrafluoride (NF3) was introduced as a gaseous fluorine source, and the reaction was carried out at 340℃ for 12 h; after the reaction was completed, the sample was naturally cooled to room temperature and taken out, resulting in CF formed on the surface. X Fluorinated expanded graphite paper.

[0071] Example 4 The steps in this embodiment are the same as those in Embodiment 1, except that in the electrochemical expansion treatment in step S1, the applied constant voltage is 1.5 V and the holding time is 2.0 min.

[0072] Example 5 The steps in this embodiment are the same as those in Embodiment 1, except that in the electrochemical expansion treatment in step S1, the applied constant voltage is 2.0 V and the holding time is 0.3 min.

[0073] Example 6 The steps in this embodiment are the same as those in Embodiment 1, except that in the post-processing step, the electrochemically treated graphite paper is placed in a solution containing hydrogen peroxide (0.03M), left to stand at room temperature (25℃) for 2.5 min, and then transferred to a 70℃ water bath for 1.0 h.

[0074] Example 7 The steps in this embodiment are the same as those in Embodiment 1, except that in the post-processing step, the electrochemically treated graphite paper is placed in a solution containing hydrogen peroxide (0.07M), left to stand at room temperature (25℃) for 0.3 min, and then transferred to an 80℃ water bath for 0.3 h.

[0075] Example 8 The steps in this embodiment are the same as those in Embodiment 1, except that in step S3, fluorinated expanded graphite paper is used as the cathode, and a constant voltage of 2.9 V is applied for deposition for 8.5 min in an acidic electrolyte containing TiOSO4.

[0076] Example 9 The steps in this embodiment are the same as those in Embodiment 1, except that in step S3, fluorinated expanded graphite paper is used as the cathode, and a constant voltage of 3.5V is applied for deposition for 6 minutes in an acidic electrolyte containing TiOSO4.

[0077] Example 10 The steps in this embodiment are the same as those in Embodiment 1, except that in step S3, the concentration of TiOSO4 in the acidic electrolyte is 0.028M; the concentration of potassium nitrate is 0.18M; the concentration of hydrogen peroxide is 0.018M; and the pH value is 1.6.

[0078] Example 11 The steps in this embodiment are the same as those in Embodiment 1, except that in step S3, the concentration of TiOSO4 in the acidic electrolyte is 0.012M; the concentration of potassium nitrate is 0.03M; the concentration of hydrogen peroxide is 0.025M; and the pH value is 2.5.

[0079] Example 12 This embodiment provides a method for preparing a titanium dioxide negative electrode sheet, including the following steps: S1: Electrochemical expansion treatment of graphite paper to obtain expanded graphite paper; S11. Take a piece of graphite paper with a thickness of 100µm and dry it under vacuum at 60℃ for 10h to obtain dried graphite paper. S12. Using dried graphite paper as the working electrode and a platinum electrode as the counter electrode, with a distance of 1.5 cm between the two electrodes, a constant voltage of 1.5 V is applied in a sulfuric acid electrolyte with a mass concentration of 95 wt.% at 20 °C and maintained for 0.5 min to perform electrochemical expansion treatment, thereby obtaining expanded graphite paper. S13. Immerse the electrochemically expanded graphite paper in a 0.01M hydrogen peroxide solution and let it stand at room temperature (25℃) for 0.5 min; then transfer it to a 45℃ water bath and keep it warm for 0.5 h. S14. After removal, wash three times with deionized water, and then place in a vacuum dryer at 95℃ for 12 hours to obtain expanded graphite paper.

[0080] S2: Fluoride treatment is performed on the expanded graphite paper; The expanded graphite paper treated with S1 was placed in a vacuum fluorination reactor and evacuated to -0.02 Pa. XeF2 was introduced as a gaseous fluorine source, and the reaction was carried out at 350°C for 2 hours. After the reaction was completed and the sample was allowed to cool naturally to room temperature, it was removed, and CF was formed on the surface. X Fluorinated expanded graphite paper.

[0081] S3: Titanium dioxide is loaded onto the fluorinated expanded graphite paper to obtain an active precursor; Fluorinated expanded graphite paper was used as the cathode and platinum sheet as the anode. A constant voltage of 2.8V was applied in an acidic electrolyte, and deposition was carried out for 8 minutes. In the preparation of the acidic electrolyte, TiOSO4 is dissolved in a 0.15M sulfuric acid aqueous solution and stirred evenly; in the acidic electrolyte, the concentration of TiOSO4 is 0.015M, the concentration of KNO3 is 0.05M, the concentration of H2O2 is 0.005M, and the pH is adjusted to 1.5 with ammonia. After deposition, the sample was removed, washed with deionized water, and then vacuum dried at 50°C for 8 hours to obtain the active precursor. S4: Combine the active precursor with the current collector to obtain the titanium dioxide negative electrode sheet; The active precursor and titanium mesh are aligned and stacked; a pressure of 7 MPa is applied in a tablet press and held for 30 seconds to compress the mixture, thus obtaining the final titanium dioxide negative electrode sheet.

[0082] Example 13 This embodiment provides a method for preparing a titanium dioxide negative electrode sheet, including the following steps: S1: Electrochemical expansion treatment of graphite paper to obtain expanded graphite paper; S11. Take a graphite paper with a thickness of 300µm and place it in a vacuum dryer at 80℃ for 16h to obtain dried graphite paper. S12. Using dried graphite paper as the working electrode and a platinum electrode as the counter electrode, with a distance of 3.0 m between the two electrodes, a constant voltage of 1.9 V is applied in a sulfuric acid electrolyte with a mass concentration of 95 wt.% at 40 °C for 2 min to perform electrochemical expansion treatment, thereby obtaining expanded graphite paper. S13. Immerse the electrochemically expanded graphite paper in a 0.05M hydrogen peroxide solution and let it stand at room temperature (25℃) for 3 minutes; then transfer it to a 75℃ water bath and keep it warm for 4 hours. S14. After removal, wash three times with deionized water, and then place in a vacuum dryer at 120℃ for 16 hours to obtain expanded graphite paper.

[0083] S2: Fluoride treatment is performed on the expanded graphite paper; The expanded graphite paper treated with S1 was placed in a vacuum fluorination reactor and evacuated to -0.02 Pa. F2 was introduced as a gaseous fluorine source, and the reaction was carried out at 440℃ for 10 hours; After the reaction was completed and the sample was allowed to cool naturally to room temperature, it was removed, and CF was formed on the surface. X Fluorinated expanded graphite paper.

[0084] S3: Titanium dioxide is loaded onto the fluorinated expanded graphite paper to obtain an active precursor; Fluorinated expanded graphite paper was used as the cathode and a platinum sheet as the anode. A constant voltage of 3.3V was applied in an acidic electrolyte, and deposition was carried out for 12 minutes. In the preparation of the acidic electrolyte, TiOSO4 is dissolved in a 0.30M sulfuric acid aqueous solution and stirred evenly; in the acidic electrolyte, the concentration of TiOSO4 is 0.03M, the concentration of KNO3 is 0.2M, the concentration of H2O2 is 0.02M, and the pH is adjusted to 2.0 with ammonia. After deposition, the sample was removed, washed with deionized water, and then vacuum dried at 80°C for 4 hours to obtain the active precursor. S4: Combine the active precursor with the current collector to obtain the titanium dioxide negative electrode sheet; The active precursor and titanium mesh are aligned and stacked; a pressure of 10 MPa is applied in a tablet press and held for 30 seconds to compress the mixture, thus obtaining the final titanium dioxide negative electrode sheet.

[0085] Comparative Example 1 This comparative example provides a method for preparing a titanium dioxide negative electrode sheet, including the following steps: Preparation of expanded graphite paper: Same as step S1 in Example 1.

[0086] Slurry preparation: Titanium dioxide nanoparticles (P25) and fluorinated carbon compound CF X The powder (x≈0.8), conductive carbon black (Super P), and polyvinylidene fluoride (PVDF) binder were mixed in a mass ratio of 70:20:5:5.

[0087] Slurry preparation and coating: N-methylpyrrolidone (NMP) solvent was added, and the mixture was ball-milled for 6 h to obtain a uniform slurry, which was then coated onto the expanded graphite paper obtained in step 1.

[0088] Drying and pressing: Vacuum drying at 80℃ for 12 h, followed by pressing with titanium mesh current collector at 9 MPa.

[0089] Comparative Example 2 Titanium dioxide nanoparticles (P25), conductive carbon black (Super P), and polyvinylidene fluoride (PVDF) binder were mixed at a mass ratio of 70:20:10, and NMP was used as a solvent. The mixture was ball-milled for 6 hours to obtain a uniform slurry, which was then coated onto graphite paper. After drying, the slurry was pressed together with a titanium mesh current collector at 7-9 MPa.

[0090] Comparative Example 3 Titanium dioxide nanoparticles (P25), conductive carbon black (Super P), and polytetrafluoroethylene (PTFE) binder were mixed at a mass ratio of 85:10:5, with water and anhydrous ethanol as solvents. The mixture was thoroughly mixed, rolled into a thickness of 50-100µm, dried, and then pressed together with a titanium mesh current collector under a pressure of 7-9MPa.

[0091] The electrodes from the above embodiments and comparative examples are used to assemble an aqueous battery: The positive electrode uses lithium manganese oxide (LMO): LMO, conductive carbon black (Super P), and polytetrafluoroethylene (PTFE) binder are mixed at a mass ratio of 85:10:5, using water and anhydrous ethanol as solvents. The mixture is thoroughly mixed, rolled into a thickness of 100-200µm, dried, and then pressed with a titanium mesh current collector under 8-10MPa. Lithium trifluoromethanesulfonate is dissolved in isopropanol:trimethyl phosphate:water at a volume ratio of 4:4:2 to prepare a 2M lithium trifluoromethanesulfonate solution as the electrolyte.

[0092] 1. Activation: 12mA / g, 2 cycles; 2. Cycle: 60mA / g for 100 cycles.

[0093] Table 1 Test results of the examples and comparative examples

[0094] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a titanium dioxide negative electrode sheet, characterized in that, Includes the following steps: S1: Electrochemical expansion treatment of graphite paper to obtain expanded graphite paper; S2: Fluoride treatment is performed on the expanded graphite paper; S3: Titanium dioxide is loaded onto the fluorinated expanded graphite paper to obtain an active precursor; S4: Combine the active precursor with the current collector to obtain the titanium dioxide negative electrode sheet.

2. The preparation method according to claim 1, characterized in that, The fluorination treatment in step S2 includes reacting dried expanded graphite paper with a gaseous fluorine source at 350~440℃ for 2~10h to form CFx component on the surface of expanded graphite paper, where 0 < X ​​< 1.

25.

3. The preparation method according to claim 1, characterized in that, The electrochemical expansion treatment in step S1 is carried out in an acidic electrolyte at a voltage of 1.5~1.9V for 0.5~2 minutes.

4. The preparation method according to claim 3, characterized in that, The electrochemical expansion treatment is followed by a post-treatment step: the electrochemically treated graphite paper is first placed in a solution containing hydrogen peroxide and left to stand at room temperature for 0.5 to 3 minutes, and then transferred to a water bath at 45 to 75°C and kept for 0.5 to 4 hours.

5. The preparation method according to claim 1, characterized in that, Step S3 includes: using fluorinated expanded graphite paper as the cathode, depositing it at a constant voltage of 2.8~3.3V for 8~12 minutes in an acidic electrolyte containing TiOSO4.

6. The preparation method according to claim 5, characterized in that, The concentration of TiOSO4 in the acidic electrolyte is 0.015~0.03M; and / or, The acidic electrolyte further comprises potassium nitrate at a concentration of 0.05~0.2M and / or hydrogen peroxide at a concentration of 0.005~0.02M; and / or, The pH value of the acidic electrolyte is 1.5~2.

0.

7. The preparation method according to claim 2, characterized in that, The gaseous fluorine source is one or more of F2, NF3, or XeF2.

8. The preparation method according to claim 1, characterized in that, In step S4, the bonding method is compression, and the compression pressure is 7~10MPa.

9. A titanium dioxide negative electrode sheet, characterized in that, It is prepared by the preparation method described in any one of claims 1 to 8.

10. An aqueous lithium-ion battery, characterized in that, Includes the titanium dioxide negative electrode sheet as described in claim 9.

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