Titanium dioxide composite negative electrode material and preparation method thereof, negative electrode sheet and lithium battery

Abstract

The application relates to the field of lithium ion batteries, and discloses a titanium dioxide composite negative electrode material, a preparation method of the titanium dioxide composite negative electrode material, a negative electrode sheet and a lithium battery. The negative electrode material comprises nanometer titanium dioxide, a vanadium ion doped titanium dioxide ultrathin layer and a carbon nanotube layer; the nanometer titanium dioxide is a core, is coated by the vanadium ion doped titanium dioxide ultrathin layer, and the carbon nanotube layer coats the vanadium ion doped titanium dioxide ultrathin layer. The application thins the thickness of a contact potential barrier by constructing a vanadium doped ultrathin tunneling layer between nanometer titanium dioxide and a carbon nanotube, the vanadium doped ultrathin tunneling layer matches an interface crystal lattice of the nanometer titanium dioxide layer, and the unique tunneling effect of the vanadium doped ultrathin tunneling layer can accelerate the transfer rate of electrons from the nanometer titanium dioxide to the carbon nanotube, thereby improving the various electrochemical performances of the composite material.

Description

Technical Field

[0001] This application relates to the field of lithium-ion batteries, and in particular to a titanium dioxide composite negative electrode material, its preparation method, negative electrode sheet, and lithium battery. Background Technology

[0002] Lithium-ion batteries have been widely used due to their high energy density and good cycle performance. As a crucial component of lithium-ion batteries, the performance of the anode material directly impacts the overall battery performance. Research on lithium-ion battery anode materials mainly focuses on improving the material's energy density and conductivity, effectively reducing irreversible capacity loss during the first charge-discharge cycle, enhancing cycle stability, and lowering production costs.

[0003] Currently, carbon materials remain the primary source of anode materials for commercial lithium-ion batteries. However, carbon materials still have several drawbacks in terms of cycle stability and safety: the potential of carbon anode materials after lithium insertion is very close to that of metallic lithium, easily leading to the formation of lithium dendrites and causing short circuits; many electrolytes are unstable at this potential, decomposing and producing flammable gases during battery charging. Compared to carbon-based materials, titanium dioxide exhibits minimal structural and volume changes during charge and discharge, resulting in higher safety and stable cycle performance. Furthermore, due to the low price and easy availability of titanium resources, it is considered a promising electrode material.

[0004] Carbon nanotubes (CNTs) are hollow tubes formed by coaxial winding of a single layer of graphite atoms. The outermost electrons of a carbon atom form stable bonds with three adjacent carbon atoms through sp² hybridization, while the remaining electron forms a delocalized large π bond. Therefore, the carbon nanotube wall contains a large number of free electrons, exhibiting excellent electrical conductivity and acting as a good conductive agent. It can form a three-dimensional conductive network structure within composite materials, acting as an electron transport channel, reducing the internal resistance of the battery, alleviating battery polarization, and thus further improving the electrochemical performance of the composite material.

[0005] Currently, carbon nanotube-titanium dioxide composite anode materials generally improve conductivity by bonding the carbon nanotubes and titanium dioxide more tightly. According to semiconductor physics, titanium dioxide has a low work function, while carbon nanotubes have a high work function. A higher work function means a stronger ability to gain electrons. Therefore, when titanium dioxide and carbon nanotubes come into contact, electrons from the titanium dioxide readily migrate to the carbon nanotube surface, making the carbon nanotube surface negatively charged and the titanium dioxide surface positively charged. This creates a positive space charge region on the semiconductor surface. This space charge region causes electrons on the semiconductor surface to have higher energy than those in the bulk, causing the energy bands to bend upwards. A contact barrier forms at the interface, preventing electrons from smoothly transferring from the titanium dioxide to the carbon nanotubes, thus hindering the carbon nanotubes from fully utilizing their high conductivity. Summary of the Invention

[0006] In view of this, the purpose of this application is to provide a titanium dioxide composite anode material and its preparation method, so that the anode material can improve the conductivity;

[0007] Another objective of this application is to provide a titanium dioxide composite anode material and its preparation method, which enables the anode material to improve the first discharge capacity and first efficiency of the battery.

[0008] Another objective of this application is to provide a titanium dioxide composite anode material and its preparation method, so that the anode material can improve the rate performance of the battery.

[0009] Another objective of this application is to provide a titanium dioxide composite anode material and its preparation method, which enables the anode material to improve the cycle performance of the battery.

[0010] Another objective of this application is to provide a negative electrode sheet and a lithium battery based on the aforementioned negative electrode material.

[0011] In order to solve the above-mentioned technical problems / achieve the above-mentioned objectives, or at least partially solve the above-mentioned technical problems / achieve the above-mentioned objectives, as a first aspect of this application, a titanium dioxide composite anode material is provided, comprising nano-titanium dioxide, a vanadium-doped titanium dioxide ultrathin layer, and a carbon nanotube layer; wherein the nano-titanium dioxide is the core, covered by the vanadium-doped titanium dioxide ultrathin layer, and the carbon nanotube layer covers the vanadium-doped titanium dioxide ultrathin layer.

[0012] Optionally, the mass ratio of the nano-titanium dioxide, the vanadium-doped titanium dioxide ultrathin layer, and the carbon nanotube layer is (1000-2000):(20-100):(50-100).

[0013] Optionally, the molar ratio of vanadium ions to titanium ions in the vanadium-doped titanium dioxide ultrathin layer is (1-3):20.

[0014] As a second aspect of this application, a method for preparing the negative electrode material is provided, comprising:

[0015] Nano-titanium dioxide is synthesized by hydrothermal reaction of titanium source material and water in acidic or alkaline environments.

[0016] In an acidic or alkaline environment, the nano-titanium dioxide, titanium source material, water, and vanadium source material are added to carry out a hydrothermal reaction to synthesize nano-titanium dioxide with a vanadium-doped titanium dioxide thin layer.

[0017] The nano-titanium dioxide loaded with vanadium-doped titanium dioxide thin layer is carbonized at high temperature in a carbon source gas atmosphere to form a carbon nanotube layer, thereby obtaining the negative electrode material.

[0018] Optionally, the vanadium source material includes ammonium metavanadate and / or vanadium trichloride.

[0019] Optionally, the acidic or alkaline environment is achieved by adding acidic or alkaline substances; further optionally, the acidic substances include organic acids and inorganic acids, and the alkaline substances include organic bases or inorganic bases.

[0020] Optionally, the titanium source material may include one or more of tetrabutyl titanate, isopropyl titanate, and titanium tetrachloride.

[0021] As a third aspect of this application, a negative electrode sheet is provided, using the negative electrode material described in this application or the negative electrode material prepared by the preparation method described in this application as the active material.

[0022] As a fourth aspect of this application, a lithium battery is provided, comprising a positive electrode, a separator, an electrolyte, and a negative electrode as described in the third aspect.

[0023] Compared with existing carbon nanotube and titanium dioxide composite anode materials, this application reduces the thickness of the contact barrier by constructing an ultrathin tunneling layer doped with metallic vanadium between nano-titanium dioxide and carbon nanotubes. The lattice of the tunneling layer matches the interface of the nano-titanium dioxide layer, and its unique tunneling effect can accelerate the transfer rate of electrons from nano-titanium dioxide to carbon nanotubes, thereby improving the various electrochemical properties of the composite material. Attached Figure Description

[0024] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments of this application and their descriptions are used to explain this application and do not constitute an undue limitation of this application.

[0025] Figure 1 The image shown is a SEM image of the titanium dioxide composite anode material described in this application.

[0026] Figure 2 The image shown is a TEM image of the titanium dioxide composite anode material described in this application; where CNTs represent carbon nanotube layers, V-TiO2(t) represents a vanadium-doped titanium dioxide ultrathin layer, and TiO2 represents nano-titanium dioxide.

[0027] Figure 3 The results of the electrochemical impedance spectroscopy test are shown. Detailed Implementation

[0028] This application discloses a titanium dioxide composite anode material and its preparation method, as well as the anode sheet and lithium battery. Those skilled in the art can refer to the content of this application and appropriately modify the process parameters to achieve the desired result. It should be particularly noted that all similar substitutions and modifications are obvious to those skilled in the art and are considered to be included in this application. The products, processes, and applications described in this application have been described through preferred embodiments. Those skilled in the art can obviously modify or appropriately change and combine the methods described herein without departing from the content, spirit, and scope of this application to realize and apply the technology of this application. Obviously, the described embodiments are only some, not all, of the embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0029] It should be noted that, in this document, relational terms such as "first" and "second," "step 1" and "step 2," and "(1)" and "(2)" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element. Moreover, the embodiments and features described in this application can be combined with each other without conflict.

[0030] To improve the conductivity of carbon nanotube-titanium dioxide composite anode materials while taking into account various electrochemical properties, this application synthesizes titanium dioxide nanomaterials with an ultrathin layer of titanium dioxide doped with vanadium ions on its surface using a hydrothermal method, and then deposits carbon nanotubes on its surface using a vapor deposition method, thereby improving the conductivity and various electrochemical properties of the material.

[0031] In the first aspect of this application, a titanium dioxide composite anode material V-TiO2(t)|TiO2 is provided, comprising nano-titanium dioxide, a vanadium-doped titanium dioxide ultrathin layer, and a carbon nanotube layer; the nano-titanium dioxide forms the core, which is covered by the vanadium-doped titanium dioxide ultrathin layer, and the carbon nanotube layer covers the vanadium-doped titanium dioxide ultrathin layer. Its SEM image is shown below. Figure 1 TEM image Figure 2According to the SEM and TEM results, the titanium dioxide composite anode material V-TiO2(t)|TiO2 of this application is generally granular with a particle size between 100-150nm. It exhibits a distinct three-layer structure: the outermost layer is a carbon nanotube layer, the middle layer is a vanadium-doped titanium dioxide ultrathin layer, and the innermost layer is a pure nano-titanium dioxide layer.

[0032] In some embodiments of this application, the mass ratio of the nano-titanium dioxide, the vanadium-doped titanium dioxide ultrathin layer, and the carbon nanotube layer is (1000-2000):(20-100):(50-100); in other embodiments of this application, the mass ratio of the nano-titanium dioxide, the vanadium-doped titanium dioxide ultrathin layer, and the carbon nanotube layer is 1500:50:75, 1000:20:100, or 2000:100:50.

[0033] In some embodiments of this application, the molar ratio of vanadium ions to titanium ions in the vanadium-doped titanium dioxide ultrathin layer is (1-3):20; in other embodiments of this application, the molar ratio of vanadium ions to titanium ions in the vanadium-doped titanium dioxide ultrathin layer is 1:20, 2:20, or 3:20.

[0034] In a second aspect of this application, a method for preparing the titanium dioxide composite anode material is provided, comprising:

[0035] Nano-titanium dioxide is synthesized by hydrothermal reaction of titanium source material and water in acidic or alkaline environments.

[0036] In an acidic or alkaline environment, the nano-titanium dioxide, titanium source material, water, and vanadium source material are added to carry out a hydrothermal reaction to synthesize nano-titanium dioxide with a vanadium-doped titanium dioxide thin layer.

[0037] The nano-titanium dioxide loaded with vanadium-doped titanium dioxide thin layer is carbonized at high temperature in a carbon source gas atmosphere to form a carbon nanotube layer, thereby obtaining the negative electrode material.

[0038] In some embodiments of this application, the hydrothermal reaction is carried out in a homogeneous reactor.

[0039] Titanium dioxide nanoparticles prepared by homogeneous hydrothermal method are smaller and more uniform, which can provide more specific surface area and more contact area with subsequent ultrathin doped layer V-TiO2(t) and carbon nanotubes, thereby enhancing their charge transport performance and the conductivity of composite materials, and improving rate performance. Moreover, the thickness of ultrathin doped layer V-TiO2(t) constructed by homogeneous hydrothermal method is controllable and uniform, and the doped metal has good dispersion.

[0040] In some embodiments of this application, the acidic or alkaline environment is achieved by adding acidic or alkaline substances; in other embodiments of this application, the acidic substances include organic and inorganic acids, such as hydrochloric acid and acetic acid, and the alkaline substances include organic or inorganic bases, such as triethylamine and sodium hydroxide.

[0041] In some embodiments of this application, the titanium source material may include one or more of tetrabutyl titanate, isopropyl titanate, and titanium tetrachloride.

[0042] In some embodiments of this application, the temperature of the hydrothermal reaction is between 180-220°C, for example, 180°C, 200°C or 220°C; and the reaction time is between 12-24h, for example, 12h, 18h or 24h.

[0043] In some embodiments of this application, the ratio of the alkaline / acidic substance, titanium source material, and water is 1-5 mL: 5-10 mL: 40-60 mL or 1-5 mL: 0.1-0.5 mL: 40-60 mL; in other embodiments of this application, the ratio of the alkaline / acidic substance, titanium source material, and water is 2 mL: 10 mL: 60 mL, 1 mL: 5 mL: 40 mL, 2 mL: 8 mL: 50 mL, 2 mL: 0.5 mL: 60 mL, 1 mL: 0.5 mL: 40 mL, or 2 mL: 0.1 mL: 50 mL. In some embodiments of this application, the amount of nano-titanium dioxide used is 0.02-2 g, for example, 20 mg, 50 mg, 100 mg, 1.5 g, 1 g, or 2 g.

[0044] In some embodiments of this application, the molar ratio of vanadium ions to thin-layer titanium dioxide in the vanadium source material is (1-3):20, such as 1:20, 2:20, or 3:20. In other embodiments of this application, the vanadium source material includes ammonium metavanadate and / or vanadium trichloride.

[0045] In some embodiments of this application, the carbon source gas includes C1-C4 alkanes, C2-C4 alkenes, C2-C4 alkynes, and gaseous aromatic hydrocarbons, such as methane, ethane, ethylene, acetylene, and toluene.

[0046] In some embodiments of this application, the high-temperature carbonization is carried out at a constant temperature of 900-1200℃ for 12-24 hours; the temperature can be selected as 900℃, 1000℃ or 1200℃, and the time can be selected as 12 hours, 18 hours or 24 hours; in other embodiments of this application, the high-temperature carbonization is carried out at a heating rate of 1-10℃ / min to reach the target temperature.

[0047] In some embodiments of this application, the preparation method of the titanium dioxide composite anode material includes:

[0048] Mix 1-5 mL of triethylamine, 5-10 mL of tetrabutyl titanate and 40-60 mL of deionized water, and hydrothermally react in a homogeneous reactor at 180-220 °C for 12-24 h. After the reaction, wash the product and dry it to obtain nano-titanium dioxide material.

[0049] The amount of raw materials was determined according to the mass ratio of nano-titanium dioxide material to vanadium-doped thin titanium dioxide layer (1000-2000): (20-100). 1-5 mL of triethylamine, 0.1-0.5 mL of tetrabutyl titanate, and 40-60 mL of deionized water were mixed. Then, vanadium ions, a transition metal that can provide electrons, were added. The molar ratio of vanadium ions to the thin titanium dioxide layer was (1-3):20. The mixture was hydrothermally reacted in a homogeneous reactor at 180-220℃ for 12-24 h. After the reaction, the product was washed and dried to obtain nano-titanium dioxide V-TiO2(t)|TiO2 loaded with vanadium-doped titanium dioxide thin layers.

[0050] A carbon source gas was introduced into V-TiO2(t)|TiO2 at 900-1200℃ and kept at a constant temperature for 12-24h. The mixture was then cooled to room temperature under protective gas to obtain a composite anode material of V-TiO2(t)|TiO2 supported on a carbon nanotube layer.

[0051] In a third aspect of this application, a negative electrode sheet is provided, using the titanium dioxide composite negative electrode material described in this application as the active material or the titanium dioxide negative electrode material prepared by the preparation method described in this application as the active material.

[0052] In some embodiments of this application, the negative electrode sheet includes a current collector and an active material coated on the current collector; wherein, the current collector may be selected from a metal foil with good conductivity, such as copper foil; the active material includes the negative electrode material described in this application, as well as a binder, a conductive agent, and a solvent. The binder, conductive agent, and solvent, and their amounts, are selected in accordance with conventional methods, and this application does not impose specific limitations. For example, the binder may be polyvinylidene fluoride (PVDF), styrene-butadiene rubber (SBR), LA132 binder, and sodium carboxymethyl cellulose (CMC), etc.; the conductive agent may be conductive carbon black (SP), acetylene black, etc.; and the solvent may be N-methylpyrrolidone (NMP), deionized water, etc. The ratio of negative electrode material: conductive agent: binder: solvent is 95g:1g:4g:200mL.

[0053] In a fourth aspect of this application, a lithium battery is provided, including a positive electrode, a separator, an electrolyte, and the negative electrode described in this application; in some embodiments of this application, the lithium-ion battery is a full cell, a pouch cell, or a button cell.

[0054] In some embodiments of this application, the positive electrode is a lithium metal sheet or lithium iron phosphate, high-nickel ternary, lithium-rich manganese-based material, etc.; the separator is a Celegard series separator, polyethylene (PE), polypropylene (PP), or polyethylene propylene (PEP) composite membrane; the electrolyte is a 1.0-1.5 mol / L LiPF6 solution, for example, a LiPF6 electrolyte with a volume ratio of ethylene carbonate (EC) and diethyl carbonate (DEC) as solvents of 1:1.

[0055] In the comparative experiments provided in this application, unless otherwise specified, all experimental conditions and materials remain consistent to ensure comparability. Furthermore, all materials used in this application are commercially available.

[0056] The following provides a further description of the titanium dioxide composite anode material, its preparation method, anode sheet, and lithium battery provided in this application.

[0057] Example 1:

[0058] S1: Take 10 mL of tetrabutyl titanate, 2 mL of triethylamine, and 60 mL of deionized water, mix and sonicate for 30 min to ensure uniform mixing. Pour the mixture into a 100 mL polytetrafluoroethylene reactor and hydrothermally react at 220 °C and 1500 r / h for 24 h in a homogeneous reactor. After the reaction, cool to room temperature, discard the supernatant, and wash the remaining reactants three times with ethanol and water respectively. Dry in an oven at 60 °C overnight to obtain titanium dioxide nanomaterials. Pour the dried powder into a mortar and grind manually for 30 min to obtain titanium dioxide nanopowder materials.

[0059] S2: Add 1.5g of titanium dioxide nanomaterial synthesized in S1 to the reactor, then add 0.5mL of tetrabutyl titanate, 2mL of triethylamine and 60mL of deionized water respectively, mix and stir for 30min, and finally add 0.02mg of ammonium metavanadate. The ratio of vanadium ions to titanium ions in the thin layer is 1:10. The mixture is hydrothermally reacted in a homogeneous reactor at 220℃ and 1500r / h for 24h. After the reaction is completed, cool to room temperature, discard the supernatant, wash and dry, pour into a mortar and grind manually for 40min to obtain V-TiO2(t)|TiO2 powder.

[0060] S3: Take 1.5g of V-TiO2(t)|TiO2 powder and transfer it to a tube furnace. Inert argon gas is introduced to remove air from the tube, followed by methane gas. The temperature is increased to 1200℃ at a rate of 5℃ / min and held at that temperature for 18h. The material is then cooled to room temperature under argon protection to obtain a negative electrode material with V-TiO2(t)|TiO2 loaded on the surface of carbon nanotubes. The mass ratio of nano-titanium dioxide, vanadium-doped titanium dioxide ultrathin layer and carbon nanotube layer is 1500:50:75.

[0061] Example 2:

[0062] S1: Mix 5 mL of tetrabutyl titanate, 1 mL of triethylamine, and 40 mL of deionized water, and ultrasonically stir for 30 min to ensure homogeneity. Pour the mixture into a 100 mL polytetrafluoroethylene reactor and hydrothermally react at 1500 r / h in a homogeneous reactor at 180 °C for 12 h. After the reaction, cool to room temperature, discard the supernatant, and wash the remaining reactants three times with ethanol and water respectively. Dry the mixture overnight in an oven at 60 °C to obtain titanium dioxide nanomaterials. Manually grind the dried powder in a mortar for 30 min to obtain titanium dioxide nanopowder materials.

[0063] S2: Add 1g of the titanium dioxide nanomaterial synthesized in S1 to the reactor, then add 0.5mL of tetrabutyl titanate, 1mL of triethylamine and 40mL of deionized water respectively, mix and stir for 30min, and finally add 0.012mg of vanadium trichloride. The amount of vanadium ions: the amount of titanium ions in the thin layer = 1:20. The mixture is hydrothermally reacted in a homogeneous reactor at 180℃ and 1500r / h for 12h. After the reaction is completed, cool to room temperature, discard the supernatant, wash and dry, pour into a mortar and grind manually for 30min to obtain V-TiO2(t)|TiO2 powder.

[0064] S3: Take 1g of V-TiO2(t)|TiO2 powder and transfer it to a tube furnace. Inert argon gas is introduced to remove air from the tube. Ethane gas is introduced and the temperature is raised to 900℃ at a rate of 5℃ / min. The temperature is held for 24h and then cooled to room temperature under argon protection to obtain a negative electrode material with V-TiO2(t)|TiO2 loaded on the surface of carbon nanotubes. The mass ratio of nano-titanium dioxide, vanadium-doped titanium dioxide ultrathin layer and carbon nanotube layer is 1000:20:100.

[0065] Example 3:

[0066] S1: Take 8 mL of tetrabutyl titanate, 2 mL of triethylamine, and 50 mL of deionized water, mix and sonicate for 30 min to ensure homogeneity. Pour the mixture into a 100 mL polytetrafluoroethylene reactor and hydrothermally react at 1500 r / h in a homogeneous reactor at 200 °C for 18 h. After the reaction, cool to room temperature, discard the supernatant, and wash the remaining reactants three times with ethanol and water respectively. Dry in an oven at 60 °C overnight to obtain titanium dioxide nanomaterials. Powder the dried material in a mortar and grind manually for 30 min to obtain titanium dioxide nanopowder.

[0067] S2: Add 2g of the titanium dioxide nanomaterial synthesized in S1 to the reactor, then add 0.1mL of tetrabutyl titanate, 2mL of triethylamine and 50mL of deionized water respectively, mix and stir for 60min, and finally add 0.007mg of vanadium trichloride. The amount of vanadium ions: the amount of titanium ions in the thin layer = 3:20. The mixture is hydrothermally reacted in a homogeneous reactor at 200℃ and 1500r / h for 18h. After the reaction is completed, cool to room temperature, discard the supernatant, wash and dry, pour into a mortar and grind manually for 30min to obtain V-TiO2(t)|TiO2 powder.

[0068] S3: Take 2g of V-TiO2(t)|TiO2 powder and transfer it to a tube furnace. Inert gas argon is introduced to remove air from the tube, and acetylene gas is introduced. The temperature is increased to 1000℃ at a rate of 5℃ / min and held at that temperature for 12h. The material is then cooled to room temperature under argon protection to obtain a negative electrode material with V-TiO2(t)|TiO2 loaded on the surface of carbon nanotubes. The mass ratio of nano-titanium dioxide, vanadium-doped titanium dioxide ultrathin layer and carbon nanotube layer is 2000:100:50.

[0069] Comparative Example 1:

[0070] The titanium dioxide nanomaterial prepared in step S1 of Example 1 was used. 1.5g was taken and transferred to a tube furnace. Inert argon gas was introduced to remove the air in the tube. Then methane gas was introduced and the temperature was raised to 1200℃ at a heating rate of 5℃ / min and kept at the temperature for 18h. After cooling to room temperature under argon protection, the material was washed, dried and poured into a mortar and manually ground for 30min to obtain the negative electrode material with TiO2 loaded on the surface of carbon nanotubes.

[0071] Comparative Example 2:

[0072] Based on Example 1, the only difference is that the homogeneous reactor for the hydrothermal reaction is replaced with a conventional oven.

[0073] Comparative Example 3:

[0074] The only difference from Example 1 is the amount of vanadium ions doped in the titanium dioxide ultrathin interlayer in S2, specifically:

[0075] 1.5 g of titanium dioxide nanomaterial synthesized in S1 of Example 1 was added to the reactor, followed by 0.5 mL of tetrabutyl titanate, 2 mL of triethylamine and 60 mL of deionized water. The mixture was stirred for 30 min, and finally 0.034 mg of ammonium metavanadate was added. The ratio of vanadium ions to titanium ions in the thin layer was 1:5. The mixture was hydrothermally reacted in a homogeneous reactor at 220 °C and 1500 r / h for 18 h. After the reaction was completed, the mixture was cooled to room temperature, the supernatant was discarded, and the mixture was washed, dried and then manually ground in a mortar for 30 min to obtain V-TiO2(t)|TiO2 powder.

[0076] Comparative Example 4:

[0077] The only difference from Example 1 is that the titanium dioxide ultrathin interlayer is not doped with metallic vanadium ions.

[0078] Comparative Example 5:

[0079] The only difference from Example 1 is that the metal ions doped in the titanium dioxide ultrathin interlayer are molybdenum ions, the amount of ammonium molybdate added is 0.03 mg, and the ratio of molybdenum ions to titanium ions in the thin layer is 1:10.

[0080] Experimental Example 1:

[0081] 1. SEM morphology characterization

[0082] The titanium dioxide composite anode material prepared in Example 1 was subjected to SEM and TEM tests, and the test results are as follows: Figure 1 and Figure 2 As shown. By Figure 1 It can be seen that the titanium dioxide composite anode material prepared in Example 1 has a uniform overall distribution, with a particle size between 100-150 nm. Furthermore, TEM analysis was performed on the titanium dioxide composite anode material after it was damaged. Figure 2 TEM images showed a distinct three-layer structure: the outermost layer was a carbon nanotube layer, the middle layer was a vanadium-doped TiO2 ultrathin layer, and the innermost layer was pure TiO2 nanomaterial. The SEM and TEM results of other embodiments were essentially the same as in Example 1, and will not be repeated here.

[0083] 2. Electrochemical impedance spectroscopy

[0084] Electrochemical impedance spectroscopy (EIS) is a method for measuring the charge diffusion resistance of a battery, reflecting the magnitude of the resistance experienced by the battery. EIS is performed at room temperature with an input voltage of 1V and a high-frequency range of 10 Hz. 5HZ, the working electrode is the electrode sheet of the materials in each embodiment and comparative example, and the counter electrode and reference electrode are metallic lithium. Electrochemical impedance spectroscopy results are as follows: Figure 3 As shown.

[0085] from Figure 3 It can be seen that the electrochemical impedance of the titanium dioxide composite anode materials in Examples 1-3 is significantly lower than that in the comparative examples. The reason for this is that a contact barrier forms between TiO2 and carbon nanotubes. Electrons transferring from titanium dioxide to carbon nanotubes need to overcome this high barrier, thus affecting the electron transfer efficiency. Therefore, this application reduces the thickness of the contact barrier by constructing an ultrathin tunneling layer between the carbon nanotubes and titanium dioxide, allowing electrons to transfer to the carbon nanotubes by penetrating the ultrathin tunneling layer, reducing charge diffusion resistance and shortening the electron transfer time. A lower electrochemical impedance indicates a shorter charge transfer time.

[0086] 3. Powder conductivity test

[0087] The titanium dioxide composite anode materials prepared in Examples 1-3 and Comparative Examples 1-5 were pressed into block structures, and then the conductivity of the powder was tested using a four-probe tester. The test results are shown in Table 1.

[0088] Table 1

[0089]

[0090] As shown in Table 1, the powder conductivity of the titanium dioxide composite anode materials in Examples 1-3 is significantly higher than that of the comparative examples. The reason for this is that a thin layer of TiO2 doped with metal V ions is sandwiched between TiO2 and carbon nanotubes. This allows electrons to transfer to the carbon nanotubes by penetrating the thin tunneling layer, accelerating the charge transfer rate, reducing the resistivity of the anode material, and improving its conductivity. Excessive vanadium ions, no vanadium ions, and doping with other transition metal ions all fail to achieve high conductivity.

[0091] 4. Button cell battery test

[0092] The TiO2 composite anode materials obtained in Examples 1-3 and Comparative Examples 1-5 were assembled into coin cells A1, A2, A3, B1, B2, B3, B4, and B5, respectively. The preparation method was as follows: binder, conductive agent, and solvent were added to the anode material, stirred and slurryed, coated on copper foil, and dried and rolled. The binder used was LA132 binder, the conductive agent was SP, and the negative electrode material was the TiO2 composite negative electrode material prepared in Examples 1-3 and Comparative Examples 1-5, respectively. The solvent was double-distilled water, and the ratio was: negative electrode material: SP: LA132: double-distilled water = 95g: 1g: 4g: 200mL, and a negative electrode sheet was prepared. The electrolyte was LiPF6 / EC+DEC (volume ratio 1:1, concentration 1.2mol / L), the counter electrode was lithium metal sheet, and the separator was polyethylene (PE), polypropylene (PP), or polyethylene propylene (PEP) composite membrane. The simulated battery was assembled in an argon-filled glove box, and the electrochemical performance was tested on a Wuhan Landian CT2001A battery tester. The charge / discharge voltage range was 0.005V to 2.0V, and the charge / discharge rate was 0.1C. The rate capability (2C / 0.1C) and cycle performance (0.2C / 0.2C, 400 cycles) of the coin cell were also tested. The test results are shown in Table 2 below.

[0093] Table 2

[0094]

[0095]

[0096] As shown in Table 2, compared with Comparative Examples 1-5, the TiO2 composite anode materials prepared in Examples 1-3 have higher initial discharge capacity, initial efficiency, rate performance, and cycle performance. The reason for this is that the TiO2 nanoparticles prepared by the homogeneous hydrothermal method are smaller and more uniform, which can provide more specific surface area, resulting in a larger contact area with the thin TiO2(t) and carbon nanotubes, thus enhancing their charge transport performance and the conductivity of the composite material, and improving the rate performance. The ultrathin doped V-TiO2(t) constructed by the homogeneous hydrothermal method has a controllable and uniform thickness, and good impurity metal dispersion. The constructed ultrathin metal-doped V-TiO2(t) has a lattice match with the inner TiO2 interface, and its unique tunneling effect can accelerate the transfer rate of electrons from TiO2 to carbon nanotubes, thereby improving the conductivity and cycle performance of the composite material.

[0097] 5. Soft-pack battery test

[0098] Using the TiO2 composite anode materials prepared in Examples 1-3 and Comparative Examples 1-5 as the anode active materials, anode sheets were prepared. Ternary materials (LiNi) were also used. 1 / 3 Co 1 / 3 Mn 1 / 3Using O2 as the positive electrode, a LiPF6 solution (solvent: EC+DEC, volume ratio 1:1, LiPF6 concentration 1.2 mol / L) as the electrolyte, and a Celegard 2400 membrane as the separator, 2Ah pouch cells A-1, A-2, A-3 and B-1, B-2, B-3, B-4, B-5 ​​were prepared. The cycle performance and rate performance of the pouch cells were then tested.

[0099] Rate performance test conditions: charging rate: 1C / 2C / 3C / 5C, discharging rate: 1C; voltage range: 2.65-4.2V, temperature: 25±3℃. The constant current ratio of the battery was tested, and the test results are shown in Table 3.

[0100] The cyclic test conditions were: charge / discharge rate 2C / 2C, voltage range: 2.65-4.2V; temperature: 25±3℃, number of cycles: 1000; the test results are shown in Table 3.

[0101] Table 3

[0102]

[0103]

[0104] As shown in Table 3, the pouch cell prepared with the TiO2 composite anode material of this application exhibits a better constant current ratio. This is attributed to the lattice matching between the constructed ultrathin metal-doped V-TiO2(t) and the inner TiO2 interface. Furthermore, its tunneling effect accelerates the electron transfer rate from TiO2 to carbon nanotubes, thereby improving the conductivity of the composite material, which in turn enhances the constant current ratio and improves the long-cycle performance of the material.

[0105] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A titanium dioxide composite negative electrode material, characterized by, The nanometer titanium dioxide, the vanadium ion doped titanium dioxide ultra-thin layer and the carbon nanotube layer; the nanometer titanium dioxide is the core, which is coated by the vanadium ion doped titanium dioxide ultra-thin layer, and the carbon nanotube layer is coated on the vanadium ion doped titanium dioxide ultra-thin layer; The mass ratio of the nanometer titanium dioxide, the vanadium ion doped titanium dioxide ultra-thin layer and the carbon nanotube layer is (1000-2000):(20-100):(50-100); the molar ratio of vanadium ion and titanium ion in the vanadium ion doped titanium dioxide ultra-thin layer is (1-3):

20.

2. The method for preparing the negative electrode material according to claim 1, characterized in that, The preparation method comprises the following steps: In an acidic or alkaline environment, a nanometer titanium dioxide is synthesized by a hydrothermal reaction of a titanium source raw material and water; In an acidic or alkaline environment, a nanometer titanium dioxide loaded with a vanadium ion doped titanium dioxide thin layer is synthesized by a hydrothermal reaction of the nanometer titanium dioxide, the titanium source raw material, water and a vanadium source raw material; The nanometer titanium dioxide loaded with the vanadium ion doped titanium dioxide thin layer is carbonized at high temperature in an atmosphere of a carbon source gas to form a carbon nanotube layer, thereby obtaining the negative electrode material.

3. The preparation method according to claim 2, characterized in that, The vanadium source raw material comprises ammonium metavanadate and / or vanadium trichloride.

4. The preparation method according to claim 2, characterized in that, The acidic or alkaline environment is realized by adding an acidic substance or an alkaline substance.

5. The preparation method according to claim 4, characterized in that, The acidic substance comprises an organic acid and an inorganic acid; and the alkaline substance comprises an organic base and an inorganic base.

6. The preparation method according to claim 2, characterized in that, The titanium source raw material comprises one or more than two of tetrabutyl titanate, isopropyl titanate and titanium tetrachloride.

7. A negative electrode sheet characterized by comprising: The negative electrode material of claim 1 or the negative electrode material prepared by the preparation method of any one of claims 2-6 is used as an active material.

8. A lithium battery, characterized by The negative electrode material of claim 1 or the negative electrode material prepared by the preparation method of any one of claims 2-6 is used as an active material. The battery comprises a positive electrode sheet, a diaphragm, an electrolyte and the negative electrode sheet of claim 7.

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