SnO2 / TiO2 composite self-supporting lithium ion battery negative electrode and micro-arc oxidation in-situ preparation method and application thereof

Abstract

The application provides a SnO2 / TiO2 composite self-supporting lithium ion battery negative electrode and an in-situ micro-arc oxidation preparation method and application thereof, and belongs to the technical field of lithium ion battery negative electrodes. The micro-arc oxidation method is adopted, sodium stannate is added in an electrolyte, a porous SnO2 / TiO2 film layer which is combined firmly with a titanium substrate can be directly generated on the titanium substrate in one step, an active substance is in-situ grown on a current collector, and no additional binder and conductive agent are needed. The self-supporting structure not only maximizes the loading capacity of the active substance, but also provides a continuous and fast channel for the transmission of ions and electrons, and the porous morphology is helpful for the full infiltration of the electrolyte, so that the comprehensive electrochemical performance of the TiO2 negative electrode, such as conductivity, specific capacity and cycle stability, is improved.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery anode technology, specifically to a SnO2 / TiO2 composite self-supporting lithium-ion battery anode and its micro-arc oxidation in-situ preparation method and application. Background Technology

[0002] Graphite anodes in lithium-ion batteries are widely used due to their high conductivity and relatively mature technology. However, graphite electrodes have a relatively low theoretical capacity and are prone to significant volume changes during charge and discharge, leading to structural instability and affecting battery cycle life. Furthermore, graphite may undergo over-lithiation and lithium dendrite growth during repeated charge and discharge cycles. Uncontrolled lithium dendrite growth can penetrate the separator, causing internal short circuits or even explosions. Therefore, finding structurally stable lithium-ion battery anode materials with low expansion characteristics has become a current research hotspot.

[0003] Titanium dioxide (TiO2) possesses excellent structural stability, resulting in a long cycle life as a negative electrode in lithium-ion batteries and maintaining good performance through multiple charge-discharge cycles. Furthermore, TiO2's low expansion rate helps maintain the structural integrity of the electrode, exhibiting good high-rate charge-discharge capabilities in high-power applications. However, TiO2's poor conductivity limits electron conduction efficiency, leading to a reduction in the actual battery capacity. Additionally, TiO2's slow ion diffusion rate restricts ion movement within the electrode, thus affecting the efficiency of the charge-discharge process. Therefore, the actual specific capacity of TiO2 often falls short of its theoretical value, requiring material modification or composite techniques to improve its performance and enhance its competitiveness in the lithium-ion battery field.

[0004] Traditional TiO2 anode fabrication typically employs a coating method, requiring multiple steps including mixing (active material + conductive agent + binder), coating, drying, and slicing. During this process, inactive binders (such as polyvinylidene fluoride, PVDF) and conductive agents (such as acetylene black) occupy a portion of the limited space within the electrode, reducing the active material loading (typically only 60-90% of the total electrode mass) and thus sacrificing the overall energy density of the device. Simultaneously, the insulating properties of the binder hinder the rapid diffusion of lithium ions, increasing the ion transport impedance within the electrode. While the introduction of conductive agents improves electron conduction, their point contact with the active material still cannot achieve optimal charge transfer efficiency, prolonging the electron and ion transport paths. Furthermore, the presence of binders not only increases the complexity and cost of electrode fabrication but also poses environmental pressures on the recycling and disposal of spent batteries due to their non-degradable nature.

[0005] Therefore, developing a self-supporting TiO2 electrode that does not require binders and conductive agents has become the key to breaking through the bottlenecks of traditional processes. Summary of the Invention

[0006] In view of this, the purpose of this invention is to provide a SnO2 / TiO2 composite self-supporting lithium-ion battery anode and its in-situ preparation method using micro-arc oxidation, as well as its application. This invention employs a micro-arc oxidation method to prepare a SnO2 / TiO2 composite self-supporting anode in one step in situ, which can effectively improve the specific capacity, conductivity, and rate capability of lithium-ion batteries.

[0007] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a method for in-situ preparation of SnO2 / TiO2 composite self-supporting lithium-ion battery anodes via micro-arc oxidation, comprising the following steps: Provide an electrolyte containing Na3PO4, Na2SnO3 and an inorganic base; The titanium substrate was subjected to micro-arc oxidation in the electrolyte to obtain a SnO2 / TiO2 composite self-supporting lithium-ion battery anode.

[0008] Preferably, in the electrolyte, the concentration of Na3PO4 is 5~10 g / L, the concentration of Na2SnO3 is 3~5 g / L, and the concentration of inorganic base is 1~1.5 g / L.

[0009] Preferably, the positive voltage of the micro-arc oxidation is +370~400 V, the negative voltage is -10~-20 V, the pulse frequency is 100~150 Hz, the duty cycle is ±45%, and the oxidation time is 300~360 s.

[0010] Preferably, before the micro-arc oxidation, the titanium substrate is further subjected to pretreatment, which includes polishing, cleaning and drying in sequence.

[0011] The present invention provides a SnO2 / TiO2 composite self-supporting lithium-ion battery anode prepared by the above method, comprising a titanium substrate and a SnO2 / TiO2 composite film layer grown in situ on the surface of the titanium substrate.

[0012] Preferably, the thickness of the SnO2 / TiO2 composite film is 10~20 μm; the SnO2 content in the SnO2 / TiO2 composite film is 5~10 wt%.

[0013] Preferably, the SnO2 / TiO2 composite film has a porous structure, with a pore size of 1.5~2.5 μm and a porosity of 5~10%.

[0014] Preferably, the TiO2 in the SnO2 / TiO2 composite film comprises anatase and rutile phases.

[0015] This invention provides the application of the above-mentioned SnO2 / TiO2 composite self-supporting lithium-ion battery anode in lithium-ion batteries.

[0016] The present invention provides a lithium-ion battery, comprising a positive electrode, a separator, an electrolyte, and a negative electrode, wherein the negative electrode is the aforementioned SnO2 / TiO2 composite self-supporting lithium-ion battery negative electrode.

[0017] This invention provides a method for in-situ preparation of a SnO2 / TiO2 composite self-supporting lithium-ion battery anode using micro-arc oxidation, comprising the following steps: providing an electrolyte containing Na3PO4, Na2SnO3, and an inorganic alkali; and performing micro-arc oxidation on a titanium substrate in the electrolyte to obtain the SnO2 / TiO2 composite self-supporting lithium-ion battery anode. This invention employs a micro-arc oxidation method, adding sodium stannate to the electrolyte, which enables the direct one-step generation of a porous SnO2 / TiO2 film layer firmly bonded to the titanium substrate. The active material grows in situ on the current collector, eliminating the need for additional binders and conductive agents. This self-supporting structure not only maximizes the loading of active material but also provides continuous and rapid channels for ion and electron transport. Simultaneously, the porous morphology facilitates thorough wetting of the electrolyte, thereby improving the overall electrochemical performance of the TiO2 anode, such as conductivity, specific capacity, and cycle stability.

[0018] This invention adds sodium stannate (Na2SnO3) to the electrolyte. Sn can introduce additional redox reactions during lithium-ion insertion / extraction, thereby contributing additional reversible capacity; simultaneously, Sn 4+ The ionic radius is 0.69 Å, similar to that of Ti. 4+ (Ionic radius 0.605 Å) makes it easier to substitute Ti sites into the TiO2 lattice. Furthermore, during charge and discharge, the titanium dioxide matrix undergoes reversible Li... + The insertion / extraction reaction (with minimal volume change) provides rigid support for the overall structure, while the dispersed tin atoms undergo a high-capacity alloying reaction (forming Li). x The tight bonding of SnO2 and TiO2 at the atomic scale effectively disperses and constrains the volume expansion strain of tin within the surrounding titanium dioxide lattice, thereby improving capacity while suppressing particle breakage and failure. The results of the embodiments show that the SnO2 / TiO2 composite self-supporting lithium-ion battery anode prepared by the micro-arc oxidation method of this invention exhibits good conductivity and structural stability, and the doping of SnO2 in the film can reduce Li... + Impedance transfer and diffusion improve battery specific capacity and cycle stability.

[0019] Furthermore, the preparation method provided by this invention is simple to operate, low in cost, and easy to achieve industrial-scale mass production. Attached Figure Description

[0020] Figure 1 XRD patterns of the negative electrodes of PS0 and PS5; Figure 2 XRD patterns of the negative electrodes of SS5 and AS5; Figure 3 SEM images and mapping images of PS0 and PS5 negative electrodes at different magnifications; Figure 4 SEM images and mapping images of the AS5 and SS5 negative electrodes at different magnifications; Figure 5 Cross-sectional mapping diagrams of the negative electrodes of PS0 and PS5; Figure 6 XPS graphs for the negative electrodes of PS0 and PS5; Figure 7 CV diagrams for the negative electrodes of PS0 and PS5; Figure 8 EIS diagrams of the negative electrodes of PS0 and PS5; Figure 9 Rate performance curves for PS0 and PS5 anodes after 10 cycles at 0.1C, 0.2C, 0.5C, 1C, and 2C; Figure 10 Rate performance curves of SS5 and AS5 anodes after 10 cycles at 0.1C, 0.2C, 0.5C, 1C and 2C respectively; Figure 11 The diagram shows the coulomb efficiency of the PS0 and PS5 anodes after 300 long cycles at 0.5C. Detailed Implementation

[0021] This invention provides a method for in-situ preparation of SnO2 / TiO2 composite self-supporting lithium-ion battery anodes via micro-arc oxidation, comprising the following steps: Provide an electrolyte containing Na3PO4, Na2SnO3 and an inorganic base; The titanium substrate was subjected to micro-arc oxidation in the electrolyte to obtain a SnO2 / TiO2 composite self-supporting lithium-ion battery anode.

[0022] This invention first provides an electrolyte containing Na3PO4, Na2SnO3, and an inorganic base. In this invention, the inorganic base is preferably KOH and / or NaOH. In this invention, the concentration of Na3PO4 in the electrolyte is preferably 5-10 g / L, more preferably 6-8 g / L; the concentration of Na2SnO3 is preferably 3-5 g / L, more preferably 4 g / L; and the concentration of the inorganic base is preferably 1-1.5 g / L, more preferably 1-1.2 g / L. In this invention, the pH value of the electrolyte is preferably 12. This invention controls the concentration and pH value of the raw materials in the electrolyte, thereby controlling the OH- ions in the solution.- and SnO3 -2 The concentration is used to control the concentration of ions induced for oxidation and doping on the anode (titanium sheet) surface during the micro-arc oxidation process, thereby controlling the oxide layer thickness, doping amount, and pore structure.

[0023] This invention involves micro-arc oxidation of a titanium substrate in an electrolyte to obtain a SnO2 / TiO2 composite self-supporting lithium-ion battery anode. In this invention, the titanium substrate is preferably a high-purity titanium sheet with a purity preferably of 99.9%. Prior to micro-arc oxidation, the titanium substrate is preferably pretreated, including sequential polishing, cleaning, and drying. The polishing is preferably performed by polishing the titanium foil surface with 600-mesh and 1000-mesh SiC sandpaper to remove the oxide film layer present on the original titanium substrate; followed by polishing with 1200-mesh SiC sandpaper to make the titanium substrate surface scratch-free and smooth, with a certain degree of mirror reflectivity and a surface roughness Ra ≤ 0.1 μm. The cleaning reagents are preferably ethanol and water. The drying temperature is preferably 60°C.

[0024] In this invention, the titanium substrate is connected to the positive terminal of the power supply, and the electrolyte is connected to the negative terminal of the power supply. In this invention, the positive voltage of the micro-arc oxidation is preferably +370~400 V, more preferably +380~390 V, and the negative voltage is preferably -10~-20 V, more preferably -10~-15 V. Because the addition of Na2SnO3 increases the ion concentration of the electrolyte and improves the electrolyte conductivity, the required breakdown voltage potential of the titanium sheet decreases. In this invention, the pulse frequency of the micro-arc oxidation is preferably 100~150 Hz, more preferably 120~150 Hz, the duty cycle is preferably ±45%, and the oxidation time is preferably 300~360 s, more preferably 300~330 s. By controlling the conditions of micro-arc oxidation, this invention can control the thickness and pore structure of the oxide film.

[0025] Following the micro-arc oxidation reaction, the titanium substrate is preferably removed, cleaned, and dried. In this invention, the cleaning reagent is preferably water and ethanol, and the drying temperature is preferably 60°C.

[0026] The present invention provides a SnO2 / TiO2 composite self-supporting lithium-ion battery anode prepared by the above method, comprising a titanium substrate and a SnO2 / TiO2 composite film layer grown in situ on the surface of the titanium substrate.

[0027] In this invention, the thickness of the SnO2 / TiO2 composite film is 10-20 μm, more preferably 15 μm; the SnO2 content in the SnO2 / TiO2 composite film is preferably 5-10 wt%, more preferably 6 wt%. In this invention, the SnO2 / TiO2 composite film has a porous structure, the pore size of the SnO2 / TiO2 composite film is preferably 1.5-2.5 μm, and the porosity is preferably 5-10%, more preferably 5.9%. In this invention, the TiO2 in the SnO2 / TiO2 composite film preferably includes anatase and rutile phases.

[0028] This invention provides the application of the above-mentioned SnO2 / TiO2 composite self-supporting lithium-ion battery anode in lithium-ion batteries.

[0029] This invention provides a lithium-ion battery, comprising a positive electrode, a separator, an electrolyte, and a negative electrode, wherein the negative electrode is the aforementioned SnO2 / TiO2 composite self-supporting lithium-ion battery negative electrode. This invention does not impose any special requirements on the specific types of the positive electrode, separator, and electrolyte; conventional lithium-ion battery positive electrodes (such as lithium iron phosphate and ternary cathodes), separators (such as PP separators), and electrolytes (such as lithium hexafluorophosphate LB-008 electrolyte) can be used.

[0030] The following detailed description, in conjunction with embodiments, illustrates the SnO2 / TiO2 composite self-supporting lithium-ion battery anode and its in-situ micro-arc oxidation preparation method and applications provided by the present invention. However, these descriptions should not be construed as limiting the scope of protection of the present invention.

[0031] Example 1 The preparation method of SnO2 / TiO2 composite self-supporting lithium-ion battery anode adopts the following steps: (1) The high-purity titanium sheet (0.1×100×100 mm) was polished and cleaned. Specifically, the surface of the titanium sheet was polished with 600-grit and 1000-grit SiC sandpaper respectively, and then polished with 1200-grit SiC sandpaper to make the surface of the titanium sheet free of scratches and flat, with a certain mirror reflectivity and a surface roughness ≤0.1 μm. After that, it was cleaned with anhydrous ethanol and deionized water in sequence, and then dried in a 60℃ oven.

[0032] (2) The polished and cleaned titanium sheet was connected to the positive terminal of the micro-arc oxidation power supply, and the negative terminal of the power supply was connected to a stainless steel electrolytic cell containing electrolyte. The electrolytic cell contained 2L of electrolyte with the following composition: 10 g / L Na3PO4·12H2O, 1 g / L KOH, and 5 g / L Na2SnO3·4H2O. Positive and negative voltages of +370 V and -10 V were applied, the pulse frequency was 150 Hz, the duty cycle was ±45%, and the oxidation time was 300 s. After micro-arc oxidation, the power supply was turned off, the reacted titanium sheet was removed, and the surface was cleaned with deionized water and anhydrous ethanol. After drying, the SnO2 / TiO2 composite self-supporting lithium-ion battery negative electrode was obtained, denoted as PS5. PS5 was cut into small squares of 10 mm × 10 mm and used as lithium battery negative electrodes. After polishing one side, its weight was measured to be 1.5 mg using a high-precision electronic balance.

[0033] Comparative Example 1 Compared to Example 1, Na2SnO3·4H2O was not added to the electrolyte. All other operations were the same, and the resulting negative electrode material was denoted as PSO. PSO was cut into small squares of 10 mm × 10 mm and used as the negative electrode of the lithium battery. After polishing one side, its weight was measured to be 1.2 mg using a high-precision electronic balance.

[0034] Comparative Example 2 Compared to Example 1, Na3PO4 in the electrolyte was replaced with Na2SiO3. All other operations were the same, and the resulting negative electrode material was designated SS5. SS5 was cut into 10 mm × 10 mm square pieces for use as lithium battery negative electrodes. After polishing one side, its weight was measured to be 1.3 mg using a high-precision electronic balance.

[0035] Comparative Example 3 Compared to Example 1, Na3PO4 in the electrolyte was replaced with NaAlO2. All other operations were the same, and the resulting negative electrode material was designated AS5. AS5 was cut into 10 mm × 10 mm square pieces for use as lithium battery negative electrodes. After polishing one side, its weight was measured to be 1.2 mg using a high-precision electronic balance.

[0036] Structural characterization (1) XRD patterns of the negative electrodes of PS0 and PS5 are shown below. Figure 1 As shown, the XRD patterns of SS5 and AS5 anode materials are as follows: Figure 2 As shown. From Figure 1It can be seen that the PSO and PS5 anodes prepared in phosphate electrolyte are mainly composed of anatase and rutile. The PSO anode has a large proportion of anatase, and the eight diffraction peaks of anatase TiO2 (PDF#21–1272) can be clearly seen. The PS5 anode has a larger proportion of rutile, and the diffraction peaks of rutile TiO2 (PDF#76–1941) can be observed. Compared with the standard card, the diffraction peak positions are all shifted to the left, with the strongest diffraction peaks at 27.12° and 35.6°, corresponding to the (110) and (101) crystal planes. The interplanar spacing of these two diffraction peaks is calculated to be 0.3297 nm and 0.2522 nm, respectively, by Bragg equation. The lattice constants a and c are 0.446 nm and 0.2998 nm, respectively. Compared with the standard card, they are all increased. This is because Sn 4+ The ionic radius (71 ppm) is greater than that of Ti. 4+ The ionic radius (68 ppm) indicates that SnO2 is doped into TiO2 via substitution. Therefore, when Sn... 4+ Replace Ti 4+ When SnO2 is doped, the lattice constant of the TiO2 crystal increases, which explains why no Sn or Sn oxide diffraction peaks were found. After doping with SnO2, a transformation from the anatase phase to the rutile phase can be observed, indicating that the introduction of SnO2 promotes the phase transition of TiO2. This is due to the increased electrolyte concentration, which leads to increased conductivity in the solution, increased spark discharge energy, and increased electrolyte temperature.

[0037] from Figure 2 It can be seen that the TiO2 content in the oxide layers SS5 and AS5 prepared by the silicate and aluminate systems is very low, especially in the aluminate system, where only weak diffraction peaks of rutile TiO2 are observed, and a large amount of Al2TiO5 without lithium storage activity is generated. The silicate system generates a small amount of anatase TiO2, along with a small amount of SiO2, indicating that different electrolyte systems have a significant impact on the phase structure of the oxide film.

[0038] (2) SEM images and mapping images of PS0 and PS5 negative electrodes at different magnifications are as follows: Figure 3 As shown. Figure 3 In the image, (a) is a SEM image of the PSO anode surface, (b) is a magnified view of (a), (c) is a mapping image of the PSO anode, (d) is a SEM image of the PS5 anode surface, (e) is a magnified view of (d), and (f) is a mapping image of the PS5 anode. Figure 3In (a), the surface morphology of the micro-arc oxidation film clearly shows a porous structure with large pores surrounding smaller pores. This is because the film surface is repeatedly broken down by plasma discharge during the micro-arc oxidation stage, resulting in localized melting. Residual gas is ejected from these channels, and the molten material cools and solidifies upon contact with the electrolyte, forming discharge channels. ImageJ software calculations show a high surface porosity of approximately 5.6%, with thin and smooth pore walls. The macropore diameter is approximately 2.9–5.7 μm, and the micropore diameter is approximately 0.31–1.25 μm. Figure 3 In (c), we can see that Ti elements are uniformly distributed on the negative electrode surface, while O and P elements are distributed near the pores.

[0039] contrast Figure 3 In (d) and (a), it is evident that the porosity of the PS5 anode surface is significantly increased, approximately 5.9%. The pore wall thickness of the membrane layer is increased, with almost every macropore being isolated by a thick pore wall, forming a "honeycomb" structure. This "honeycomb" structure allows for better uniform contact between the membrane layer and the pores with the electrolyte, reducing electrochemical impedance. Measurements revealed that the macropore diameter is approximately 1.5–2.5 μm, a reduction of approximately 1.4–3.2 μm compared to the PSO anode. This reduction in pore size is due to the decrease in the reaction potential between the substrate and the electrolyte after the addition of Na2SnO3. This allows for micro-arc oxidation reactions to occur at lower voltages, and the lower voltage leads to a decrease in the spark discharge intensity, weakening the energy required to break down the membrane layer, thus resulting in a decrease in the pore size. Figure 3 As shown in (f), the PS5 anode composite film contains four elements: Ti, O, P, and Sn, which are uniformly distributed on the surface. Close observation reveals fine cracks on both the PS0 and PS5 films. This is mainly due to the high energy of the spark discharge during the micro-arc oxidation stage, causing thermal stress from the solidification and contraction of the molten oxide upon contact with the cold electrolyte, leading to the appearance of microcracks. The presence of microcracks and porous morphology reduces the film's density, but when used as a lithium-ion battery anode material, it can enhance the Li... + Diffusion during charging and discharging provides more transport channels, which is beneficial to improving electrochemical performance. The porous structure can also promote lithium-ion movement and suppress mechanical stress caused by the large volume change of SnO2 during cycling.

[0040] SEM images and mapping diagrams of AS5 and SS5 negative electrodes at different magnifications are as follows: Figure 4 As shown. Figure 4 In the image, (a) is a SEM image of the AS5 anode surface, (b) is a SEM image of the SS5 anode surface, (c) is a mapping image of the AS5 anode, and (d) is a mapping image of the AS5 anode. Figure 4It can be seen that the oxide film prepared under the aluminate electrolyte has certain porosity, but the porosity is not high and the pore size is uneven. In contrast, the oxide film prepared under the silicate electrolyte system has almost no porosity and is granular. The higher the porosity of the oxide layer, the larger the specific surface area and the more micron-sized pores there are, making it easier for the electrolyte to wet the membrane electrode. Therefore, the morphology of the membrane electrode in Example 1 of this invention is significantly better than that of the electrodes in Comparative Examples 2 and 3, indicating that the phosphate electrolyte system has unique advantages for preparing porous electrodes.

[0041] (3) Cross-sectional mapping diagrams of PS0 and PS5 negative electrodes are shown below. Figure 5 As shown, Figure 5 (a) is the cross-sectional mapping diagram of the PS0 negative electrode, and (b) is the cross-sectional mapping diagram of the PS5 negative electrode. From... Figure 5 The boundary between the film and the substrate is clearly visible. The portion with a higher Ti content originates from the pure Ti substrate, while the portion with a higher P content is the film formed by micro-arc oxidation, originating from the electrolyte. Measurements showed that the thickness of the PSO anode was approximately 11 μm, and the thickness of the P5 anode was approximately 15 μm. The film thickness increased after the addition of Na₂SnO₃. This phenomenon occurs due to the decomposition of SnO₃ in the electrolyte. 2- Ions react with the film layer to form tin-containing oxides that adhere to the film surface, increasing the film thickness. The addition of Na₂SnO₃ thickens the film, increasing the loading of active materials, while the addition of tin oxides also improves the specific capacity of the anode material.

[0042] (4) XPS diagrams of PS0 and PS5 negative electrodes are shown below Figure 6 As shown, Figure 6 In the diagram, (a) is the O 1s spectrum, (b) is the Ti 2p spectrum, (c) is the P 2p spectrum, and (d) is the Sn 3d spectrum. Figure 6 As shown in (a), the O1s spectra of both PSO and PS5 anodes consist of multiple peaks. Both anodes contain C-OH, PO, and Ti-O bonds. The small amount of (-OH) hydroxyl groups is due to electrolyte hydrolysis. The PS5 anode, due to the addition of Na2SnO3 to the electrolyte, has an additional Sn-O bond at 530.6 eV, originating from SnO2. Calculations show that the Sn-O bond content in the sample is approximately 13.5% based on the ratio of the Sn-O peak area to the total O1s peak area. This is because the concentration of Na2SnO3 added to the electrolyte is relatively low, and the film contains a higher concentration of Ti and P elements. Figure 6 (b) shows the P 2p diagrams for the two negative electrodes. Peaks of P 2p3 / 2 were found at 133.42 eV and 133.61 eV, respectively. The p element comes from the phosphate in the electrolyte. Figure 6(c) shows the spectrum of Ti2p, with two peaks at 464.50 eV and 458.75 eV for both films, and 464.14 eV and 458.70 eV for the other film. This is attributed to the Ti in TiO2. 4+ The high binding energies of Ti 2p1 / 2 and Ti 2p3 / 2, along with the high peak intensity, indicate a high TiO2 content in the film. Figure 6 (d) in the image shows the Sn 3d spectrum of the PS5 anode. It exhibits two peaks at binding energies of 495.47 eV and 488.99 eV, corresponding to the Sn 3d3 / 2 and Sn 3d5 / 2 energy levels, respectively. The calculated area ratio of the two peaks is 0.76, and the binding energy distance is 8.48 eV, indicating that Sn possesses... +4 The SnO2 valence state exists primarily as SnO2 in the film. Therefore, this invention successfully prepared a SnO2 / TiO2 composite anode on a titanium substrate using a micro-arc oxidation method, thereby improving the conductivity and stability of the anode material and enhancing its electrochemical performance.

[0043] Performance testing The battery assembly process is as follows: Batteries are assembled in an argon-filled glove box. Before entering the glove box, the system undergoes three vacuuming and three venting processes. The water and oxygen content in the glove box must be below 0.1 ppm. The button cell uses lithium metal as the counter electrode, and the electrolyte is a solution prepared from lithium salt (LiPF6) and a mixed organic solvent. The battery assembly is performed in the following order: negative electrode shell - spring contact - steel sheet - lithium sheet - electrolyte - separator - electrolyte - negative electrode material - positive electrode shell. The battery is then sealed using a battery packaging machine (sealing pressure is 50 MPa). After standing in the glove box for 12 hours, the battery is removed and electrochemical tests are performed.

[0044] (1) The CV diagrams of the negative electrodes of PS0 and PS5 are shown below. Figure 7 As shown, Figure 7 (a) shows the cyclic voltammetry curves of the PSO anode at a scan rate of 0.5 mV / s for three cycles. A reduction peak can be clearly observed near 1.3 V, which corresponds to the lithium-ion intercalation reaction, where Ti⁴⁺ is reduced to Ti. 3+ When scanning at the anode, there is an oxidation peak at 2.1V, which corresponds to the lithium ion desorption reaction, where Ti3+ is oxidized to Ti4+. Figure 7(b) shows the CV curve of the PS5 anode. The weak redox peaks near 2.1V and 1.4V correspond to the redox reaction between TiO2 and Li+, with the peak at 1.4V indicating the decomposition of SnO2 into Sn. The reduction peak at 0.1V and the oxidation peak at 0.6V represent the alloying process of Sn and the dealloying process of LiXSn. Comparing the two curves, it can be seen that the overlap of the PS5 anode is better than that of the PSO anode, indicating that it has higher reversibility and a more stable lithium insertion / extraction process. Comparing the current magnitude on the vertical axis, it is found that the PS5 anode is larger than that of the PSO anode, indicating that the doping of SnO2 improves the conductivity of the TiO2 anode.

[0045] (2) EIS diagrams of the negative electrodes of PS0 and PS5 are shown below Figure 8 As shown, Figure 8 The illustration in the middle shows the equivalent circuit, R e For Li + The resistances migrating in the electrolyte, CPE and Rct, represent the ionic capacitance and charge transfer resistance at the negative electrode surface. The Rct values ​​for PS0 and PS5 negative electrodes are 52.88 Ω and 23.31 Ω, respectively. It is evident that the impedance of the PS5 negative electrode is lower than that of the PS0 negative electrode. This is because the doping of SnO2 increases the conductivity of the TiO2 negative electrode, thereby effectively reducing the resistance of Li. + The impedance of transfer and diffusion also explains why the PS5 anode has a higher initial specific capacity and a larger current in CV.

[0046] (3) The rate performance curves of PS0 and PS5 negative electrodes after 10 cycles at 0.1C, 0.2C, 0.5C, 1C and 2C are shown in the figure. Figure 9 As shown. By Figure 9 It can be seen that under the test conditions of transitioning from low to high rate, both negative electrodes exhibit good specific capacity with minimal capacity decay. When transitioning from 2C to 0.1C, the average capacity of the two negative electrodes recovers to 85% and 79% of the initial average specific capacity after 10 cycles, respectively. The porous morphology of the negative electrodes can, to a certain extent, suppress the stress generated when the active material undergoes volume expansion, resulting in good battery performance even at high rates. The PS5 negative electrode exhibits higher specific capacity at all rates, with specific capacities of approximately 658 mAh / g, 602 mAh / g, 510 mAh / g, 442 mAh / g, and 367 mAh / g at 0.1C, 0.2C, 0.5C, 1C, and 2C, respectively.

[0047] The rate performance curves of SS5 and AS5 anodes after 10 cycles at 0.1C, 0.2C, 0.5C, 1C, and 2C are shown below. Figure 10 As shown. By Figure 10It can be seen that the capacity of the oxide film anode prepared in the silicate and aluminate electrolyte system is significantly lower than that of the titanium dioxide anode prepared in the phosphate electrolyte system at different rate limits. This is mainly because the amount of titanium dioxide that can play a role in lithium storage in the oxide film prepared in the silicate and aluminate system is too small, and the porosity of the film is also low, the specific surface area is small, and there are few effective reaction sites that can contact and react with the electrolyte.

[0048] (4) The coulomb efficiency of PS0 and PS5 negative electrodes after 300 cycles at 0.5C is shown in the figure. Figure 11 As shown. By Figure 11 It can be seen that the initial coulombic efficiencies of the PS0 and PS5 anodes were 68.11% and 70.04%, respectively, which is an irreversible reaction caused by the formation of the SEI layer. After one cycle, they recovered to 98.87% and 102.37%, respectively, and remained above 99% for a long period. Due to the higher specific capacity provided by SnO2 doping and the better promotion of contact between the active material and the electrolyte by the porous morphology, the SnO2 / TiO2 composite film exhibited a higher capacity. After 300 cycles, the specific capacity remained at 236.52 mAh / g. The undoped PS0 anode had a lower specific capacity, maintaining a capacity of 131.82 mAh / g after 300 cycles.

[0049] In summary, the PS5 anode, due to its ideal porous structure, achieves better composite of SnO2 and TiO2, exhibiting superior electrochemical performance in multiple tests.

[0050] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for in-situ preparation of SnO2 / TiO2 composite self-supporting lithium-ion battery anode using micro-arc oxidation, characterized in that, Includes the following steps: Provide an electrolyte containing Na3PO4, Na2SnO3 and an inorganic base; The titanium substrate was subjected to micro-arc oxidation in the electrolyte to obtain a SnO2 / TiO2 composite self-supporting lithium-ion battery anode.

2. The method according to claim 1, characterized in that, The electrolyte contains 5-10 g / L Na3PO4, 3-5 g / L Na2SnO3, and 1-1.5 g / L inorganic base.

3. The method according to claim 1 or 2, characterized in that, The positive voltage of the micro-arc oxidation is +370~400 V, the negative voltage is -10~-20 V, the pulse frequency is 100~150 Hz, the duty cycle is ±45%, and the oxidation time is 300~360 s.

4. The method according to claim 1, characterized in that, Before the micro-arc oxidation, the titanium substrate is pretreated, which includes grinding, cleaning and drying in sequence.

5. The SnO2 / TiO2 composite self-supporting lithium-ion battery anode prepared by the method according to any one of claims 1 to 4, characterized in that, It includes a titanium substrate and a SnO2 / TiO2 composite film layer grown in situ on the surface of the titanium substrate.

6. The SnO2 / TiO2 composite self-supporting lithium-ion battery anode according to claim 5, characterized in that, The thickness of the SnO2 / TiO2 composite film is 10~20 μm; the SnO2 content in the SnO2 / TiO2 composite film is 5~10 wt%.

7. The SnO2 / TiO2 composite self-supporting lithium-ion battery anode according to claim 5 or 6, characterized in that, The SnO2 / TiO2 composite film has a porous structure with a pore size of 1.5~2.5 μm and a porosity of 5~10%.

8. The SnO2 / TiO2 composite self-supporting lithium-ion battery anode according to claim 5, characterized in that, The TiO2 in the SnO2 / TiO2 composite film includes anatase and rutile phases.

9. The application of the SnO2 / TiO2 composite self-supporting lithium-ion battery anode as described in any one of claims 5 to 8 in lithium-ion batteries.

10. A lithium-ion battery, comprising a positive electrode, a separator, an electrolyte, and a negative electrode, characterized in that, The negative electrode is the SnO2 / TiO2 composite self-supporting lithium-ion battery negative electrode according to any one of claims 5 to 8.

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