High-energy-density supercapacitor electrode material and preparation method thereof

Abstract

The invention relates to the technical field of capacitors, and particularly discloses a high-energy-density supercapacitor electrode material and a preparation method thereof. A nitrogen-doped graphene oxide-lithium titanate integrated composite structure is constructed through in-situ growth of lithium titanate nanoparticles on a graphene oxide sheet layer and synchronization of a nitrogen doping process, the lithium titanate nanoparticles are uniformly bonded to the surface of graphene through Ti-O-C covalent bonds, the nitrogen content is accurately controlled to be 5%-10% (pyridine nitrogen and graphite nitrogen have a synergistic effect), and the nitrogen-doped graphene oxide-lithium titanate integrated composite structure is obtained. The specific capacity of the material under the current density of 100 mA / g can reach 215 mAh / g at most, the specific capacity is improved by 79% compared with that of a traditional porous carbon positive electrode (120 mAh / g), the capacity retention rate after 1000 hours of circulation reaches 92% at most, the supercapacitor electrode material has the advantages of high energy density, long cycle life and industrial production, and the double bottlenecks of performance and cost of an existing positive electrode material are broken through.

Description

Technical Field

[0001] This application relates to the field of capacitor technology, and in particular to a high-energy-density supercapacitor electrode material and its preparation method. Background Technology

[0002] With the continuous advancement of modern technology, the demand for high-performance energy storage devices in various portable electronic devices and new energy vehicles is growing rapidly. The widespread adoption of products such as smartphones, tablets, and electric vehicles has made high-performance energy storage devices related to lithium-ion supercapacitors increasingly attract attention. As a new type of energy storage device that combines the high energy density of lithium-ion batteries with the high power density of supercapacitors, lithium-ion supercapacitors have enormous application potential in the field of energy storage.

[0003] Currently, research on lithium-ion supercapacitors focuses on material selection, modification, and structural design. For example, several patents, including CN202410950001.6 and CN201710381210.3, utilize transition metal oxides (such as niobium nitride / reduced graphene oxide nanocomposites and graphene / polypyrrole / titanium dioxide ternary nanowire array composites) as electrode materials. The unique crystal structure and good redox activity of these materials create conditions for improving the performance of lithium-ion supercapacitors, enhancing the specific capacity and electrochemical activity of the cathode. However, existing technologies also face many challenges. The performance of electrode materials may not be fully realized due to poor compatibility with other components such as electrolytes, or the difficulty in precisely controlling key process parameters during preparation. Consequently, their potential performance advantages cannot be fully realized.

[0004] The performance of cathode materials is constrained by process and compatibility issues, preventing them from reaching their full potential and resulting in a significant gap between R&D investment and actual output. The complex and costly manufacturing process limits large-scale production, keeping lithium-ion supercapacitors containing these materials expensive and hindering their widespread market adoption. Furthermore, poor cycle stability is a major issue; repeated charge-discharge cycles can alter the crystal structure of the material and cause instability at the electrolyte interface, leading to decreased capacitance retention and reduced lifespan. After multiple charge-discharge cycles, the performance of lithium-ion supercapacitors degrades significantly, posing a serious problem that urgently needs to be addressed in applications requiring long-term stable operation. These shortcomings have significantly hampered the further development of lithium-ion supercapacitor technology.

[0005] From the perspective of energy storage mechanism, the energy storage mechanism of lithium-ion supercapacitors combines the double-layer capacitance of supercapacitors with the redox reaction of lithium-ion batteries. During charging, lithium ions are extracted from the positive electrode, pass through the electrolyte, and embed into the negative electrode, while a double-layer capacitance is formed at the electrode-electrolyte interface to store charge; the discharge process is the opposite, with lithium ions being extracted from the negative electrode and returning to the positive electrode.

[0006] However, existing lithium-ion supercapacitors suffer from low positive electrode material capacity and poor cycle stability. Traditional porous carbon materials have insufficient specific capacity, poor conductivity of metal oxides, and significant volume expansion. Furthermore, existing nitrogen-doped lithium titanate / graphene materials (such as CN107221647B) for negative electrode orientation have problems such as large particle size (100-200nm), uncontrolled nitrogen doping, and weak interfacial bonding, making them unsuitable for positive electrodes. Summary of the Invention

[0007] The purpose of this application is to overcome the shortcomings of the prior art and provide a high-energy-density supercapacitor electrode material and its preparation method. The raw material cost of the supercapacitor electrode material of this application is only 600 yuan / kg, and it has the advantages of high energy density, long cycle life and industrial production.

[0008] To achieve the above objectives, the technical solution adopted in this application is as follows:

[0009] This application provides a supercapacitor electrode material, which includes a nitrogen-doped graphene-lithium titanate nanocomposite material;

[0010] The lithium titanate nanoparticles in the composite material are covalently bonded to the graphene surface via Ti-OC bonds, with an average spacing of <50 nm, and the nitrogen doping amount is 5-10% of the total mass of the composite material.

[0011] Using the above technical solutions, the supercapacitor electrode material contains nitrogen-doped graphene and lithium titanate. Nitrogen-doped graphene provides good conductivity and pseudocapacitance, while lithium titanate contributes high capacity. The two work synergistically to optimize the lithium-ion insertion / extraction process and improve the overall energy storage performance.

[0012] This application constructs an integrated composite structure of nitrogen-doped graphene oxide and lithium titanate, in which lithium titanate nanoparticles (particle size 20-50 nm) are uniformly bonded to the graphene surface through Ti-OC covalent bonds, and the nitrogen content is precisely controlled at 5%-10% (synergistic effect of pyridine nitrogen and graphitic nitrogen), enabling the material to achieve a specific capacity of up to 215 mAh / g at a current density of 100 mA / g, which is 79% higher than that of traditional porous carbon cathode (120 mAh / g), and the capacity retention rate is up to 92% after 1000 h of cycling.

[0013] In the nitrogen-doped graphene-lithium titanate nanocomposite material of this application, the pseudocapacitive activity and conductivity are optimal when the nitrogen doping amount is 5% to 10%. When the nitrogen content is less than 5%, the specific capacitance will decrease to as low as 73.5% due to insufficient active sites. When it is higher than 10%, the resistance will increase by 2 times due to the distortion of the graphene conjugated structure, and the capacitance retention rate will drop to 81% after 1000 hours of cycling.

[0014] The design of lithium titanate nanoparticles with an average spacing of <50nm can shorten the lithium-ion diffusion path, reduce transport resistance, and form a highly efficient conductive network through synergy with Ti-OC covalent bonds. At the same time, it can suppress particle agglomeration and volume expansion during charge and discharge, thereby improving rate performance and cycle stability.

[0015] In some specific embodiments, urea is added as a nitrogen source, and the nitrogen content is controlled by adjusting the urea content in the system.

[0016] As a preferred embodiment of the supercapacitor electrode material described in this application, the lithium titanate nanoparticles have a particle size of 20 nm to 50 nm.

[0017] By adopting the above technical solutions, when the particle size of lithium titanate nanoparticles is within the above range, the rate performance can be significantly improved by shortening the lithium ion solid-phase diffusion path (diffusion time is proportional to the square of the particle size). At the same time, the high specific surface area of ​​the nanoparticles enhances the Ti-OC bonding density of graphene, forming a highly efficient conductive network, and the small size effect is used to suppress volume strain during the charging and discharging process.

[0018] The lithium titanate nanoparticles are precisely controlled to a particle size of 20–50 nm. By shortening the lithium-ion solid-phase diffusion path (diffusion time is proportional to the square of the particle size), the rate performance is significantly improved. At the same time, the nanoscale effect is used to suppress the lattice stress during the charge and discharge process. Combined with the high-density Ti-OC covalent network, the structure is stabilized. Thus, a high specific capacity of 215 mAh / g is achieved at a current density of 100 mA / g, and the capacity retention rate is maintained at 92% after 1000 hours of cycling. This breaks through the bottleneck of the traditional electrode material where capacity and lifespan cannot be achieved simultaneously.

[0019] Preferably, the electrode sheet is a positive electrode material.

[0020] The nitrogen-doped graphene-lithium titanate nanocomposite material of this application is prepared by in-situ growth of lithium titanate nanoparticles on graphene oxide sheets and simultaneous nitrogen doping.

[0021] The nanoscale structure generated in situ in this application effectively suppresses the volume expansion of lithium titanate, and the interfacial charge transport efficiency is improved by 40% compared with the physical mixing process.

[0022] This application also provides a method for preparing the above-mentioned supercapacitor electrode material, wherein the method for preparing the nitrogen-doped graphene-lithium titanate nanocomposite material includes the following steps:

[0023] S1. Add graphene to concentrated sulfuric acid and stir, then add potassium permanganate and carry out a water bath reaction to obtain a reaction solution. Then add hydrogen peroxide solution to the reaction solution until the reaction solution turns bright yellow. Let it stand, centrifuge, and obtain graphene oxide dispersion.

[0024] S2. Prepare titanium ion solution and lithium ion solution. Slowly add the lithium ion solution dropwise to the graphene oxide dispersion obtained in step S1 to obtain a mixed solution containing graphene oxide and lithium ions.

[0025] S3. Slowly add titanium ion solution to the mixed solution, then add urea and carry out a thermal reaction. After the reaction is completed, cool to room temperature, centrifuge, and take the precipitate to obtain nitrogen-doped graphene-lithium titanate nanocomposite material. Dry the nitrogen-doped graphene-lithium titanate nanocomposite material to obtain supercapacitor electrode material.

[0026] This application utilizes a titanium source (titanium ions) to in-situ generate lithium titanate nanoparticles with a particle size of 20-50 nm on the surface of graphene oxide sheets. These nanoparticles are then directly connected to graphene via Ti-OC covalent bonds to form an integrated "conductive network-lithium storage unit" structure. Urea is used as the nitrogen source to simultaneously achieve uniform nitrogen atom doping during the hydrothermal reaction. Pyridine nitrogen and graphitic nitrogen synergistically contribute pseudocapacitance, resulting in a specific capacity of 215 mAh / g (100 mA / g). The in-situ generated nanoscale composite structure effectively suppresses the volume expansion of lithium titanate, and the capacity retention rate reaches 92% after 1000 hours of cycling. This material combines the advantages of high energy density, long lifespan, and low cost, breaking through the industry bottleneck of "high capacity and long cycle life being difficult to achieve simultaneously" in cathode materials.

[0027] In a preferred embodiment of the method for preparing the supercapacitor electrode material described in this application, in step S1, the temperature of the water bath reaction is 35-40°C, and the reaction time is 1-2 hours.

[0028] In some specific embodiments, in step S1, graphene is added to concentrated sulfuric acid and stirred for 30-60 minutes under ice bath conditions. Then, potassium permanganate is slowly added, and the reaction temperature is controlled to not exceed 20°C. Stirring is continued for 2-4 hours. Then, a water bath reaction is carried out at a temperature of 35-40°C. The reaction is stirred for 1-2 hours, and then deionized water is added. Stirring is continued for 30-60 minutes to obtain the reaction solution.

[0029] In some specific embodiments, the settling time in step S1 is 12 to 24 hours.

[0030] In a preferred embodiment of the method for preparing the supercapacitor electrode material described in this application, the preparation method of the titanium ion solution in step S2 includes: dissolving tetrabutyl titanate in ethanol and stirring until homogeneous to obtain a titanium ion solution;

[0031] The preparation method of lithium ion solution includes: dissolving lithium hydroxide in deionized water, stirring evenly, to obtain lithium ion solution.

[0032] This application controls the ratio of lithium titanate to graphene oxide in the product by adding a titanium ion solution.

[0033] In a preferred embodiment of the method for preparing the supercapacitor electrode material described in this application, in step S2, the molar ratio of the titanium ion solution and the graphene oxide dispersion is (0.05-0.12):1.

[0034] In a preferred embodiment of the method for preparing the supercapacitor electrode material described in this application, in step S3, the molar ratio of the lithium ion solution and the mixed solution is (3.0~3.8):1.

[0035] In a preferred embodiment of the method for preparing the supercapacitor electrode material described in this application, the mass ratio of graphene oxide to urea in the graphene oxide dispersion is 1:(1-3.5).

[0036] Preferably, the mass ratio of graphene oxide to urea is 1:(2-3).

[0037] In a preferred embodiment of the method for preparing the supercapacitor electrode material described in this application, in step S3, the temperature of the thermal reaction is 180–220°C, and the time of the thermal reaction is 12–24 h.

[0038] The preparation method of this application adopts a combination of thermal reaction and annealing, which does not require complex crosslinking agents. Furthermore, the above-mentioned mass ratio of graphene oxide to urea can achieve uniform doping. The raw material cost is only 600 yuan / kg. It has the advantages of high energy density, long cycle life and industrial production, and breaks through the dual bottlenecks of performance and cost of existing cathode materials.

[0039] Compared with the prior art, this application has the following beneficial effects:

[0040] This application provides a high-energy-density supercapacitor electrode material and its preparation method. This application constructs an integrated "nitrogen-doped graphene oxide-lithium titanate" composite structure by in-situ growing lithium titanate nanoparticles on graphene oxide sheets and simultaneously performing nitrogen doping. The lithium titanate nanoparticles (20–50 nm in diameter) are uniformly bonded to the graphene surface via Ti-OC covalent bonds, and the nitrogen content is precisely controlled at 5%–10% (due to the synergistic effect of pyridine nitrogen and graphitic nitrogen). This allows the material to achieve a specific capacity of up to 215 mAh / g at a current density of 100 mA / g, which is significantly higher than traditional methods. The porous carbon cathode (120mAh / g) is improved by 79%, and the capacity retention rate reaches up to 92% after 1000h cycling. The in-situ generated nanoscale structure effectively suppresses the volume expansion of lithium titanate, and the interfacial charge transport efficiency is improved by 40% compared with the physical mixing process. The preparation method adopts a combination of hydrothermal reaction and annealing, which does not require complex crosslinking agents. The addition of graphene oxide and urea achieves uniform doping and improves activity. The raw material cost is only 600 yuan / kg. It has the advantages of high energy density, long cycle life and industrial production, breaking through the dual bottlenecks of performance and cost of existing cathode materials. Attached Figure Description

[0041] Figure 1 SEM image of the nitrogen-doped graphene-lithium titanate nanocomposite material prepared in Example 1;

[0042] Figure 2 The graph shows the positive electrode capacity versus cycle time obtained in Example 1. Detailed Implementation

[0043] To better illustrate the purpose, technical solution, and advantages of this application, the following description will be provided in conjunction with the accompanying drawings and specific embodiments.

[0044] In the following examples and comparative examples, unless otherwise specified, the experimental methods used are conventional methods, and the materials and reagents used are commercially available unless otherwise specified. Furthermore, the raw materials used in each parallel experiment are the same.

[0045] Example 1: A high-energy-density supercapacitor electrode material and its preparation method

[0046] This embodiment provides a high-energy-density supercapacitor electrode material, including the following steps:

[0047] 1) Add 2g of natural graphite powder to 100mL of concentrated sulfuric acid, stir for 45 minutes under ice bath conditions, then slowly add 6g of potassium permanganate, control the reaction temperature to not exceed 20℃, and continue stirring for 3 hours.

[0048] 2) Transfer the reaction system to a 35°C water bath, stir for 1.5 hours, then add 200 mL of deionized water and continue stirring for 45 minutes;

[0049] 3) Add 5 mL of hydrogen peroxide solution to the reaction system until the solution turns bright yellow, then stop stirring and let it stand for 18 hours;

[0050] 4) Wash with deionized water until neutral, then centrifuge to obtain a graphene oxide dispersion;

[0051] 5) Dissolve 10 mL of tetrabutyl titanate in 50 mL of ethanol and stir until homogeneous to obtain a titanium ion solution;

[0052] 6) Dissolve 2.5g of lithium hydroxide in 50mL of deionized water and stir until homogeneous to obtain a lithium ion solution;

[0053] 7) Under stirring conditions, the lithium ion solution was slowly added dropwise to the graphene oxide dispersion. After the addition was complete, stirring was continued for 1.5 hours to obtain the solution.

[0054] 8) Under stirring conditions, the titanium ion solution is slowly added dropwise to the solution prepared in step 7), and 1.5g of urea is added to the solution as a nitrogen source (the mass ratio of urea to graphene oxide is 1.2:1). The mixture is stirred until homogeneous to obtain a mixed solution.

[0055] 9) Transfer the mixed solution to a hydrothermal reactor and react at 200°C for 18 hours. After the reaction is complete, allow it to cool naturally to room temperature.

[0056] 10) Wash with deionized water, centrifuge, and collect the precipitate to obtain nitrogen-doped graphene oxide-lithium titanate composite material (the mass ratio of nitrogen-doped graphene oxide to lithium titanate is 1:2.8).

[0057] 11) The nitrogen-doped graphene oxide-lithium titanate composite material was dried in a vacuum drying oven at 70°C for 8 hours to obtain the positive electrode material of lithium-ion supercapacitor (high energy density supercapacitor electrode material).

[0058] The SEM image of the nitrogen-doped graphene oxide-lithium titanate composite material is shown below. Figure 1 ( Figure 1 -a and Figure 1 As shown in -b).

[0059] The capacitance versus cycle time curves of the aforementioned lithium-ion supercapacitor cathode material are shown below. Figure 2 As shown.

[0060] The nitrogen-doped graphene oxide-lithium titanate composite material, conductive agent (Super P), and binder (PVDF) prepared above were weighed in a mass ratio of 80:10:10, N-methylpyrrolidone was added and mixed evenly, and then coated on aluminum foil and vacuum dried to obtain a positive electrode sheet.

[0061] Commercial activated carbon, conductive agent (Super P), and binder (PVDF) were weighed in a mass ratio of 70:15:15, and N-methylpyrrolidone was added for further homogenization. The mixture was then coated onto copper foil and vacuum dried to obtain a negative electrode sheet. A button-type lithium-ion supercapacitor was assembled in an argon-atmospheric glove box.

[0062] Example 2: A high-energy-density supercapacitor electrode material and its preparation method

[0063] This embodiment provides a high-energy-density supercapacitor electrode material, including the following steps:

[0064] 1) Add 2g of natural graphite powder to 100mL of concentrated sulfuric acid, stir for 45 minutes under ice bath conditions, then slowly add 6g of potassium permanganate, control the reaction temperature to not exceed 20℃, and continue stirring for 3 hours.

[0065] 2) Transfer the reaction system to a 35°C water bath, stir for 1.5 hours, then add 200 mL of deionized water and continue stirring for 45 minutes;

[0066] 3) Add 5 mL of hydrogen peroxide solution to the reaction system until the solution turns bright yellow, then stop stirring and let it stand for 18 hours;

[0067] 4) Wash with deionized water until neutral, then centrifuge to obtain a graphene oxide dispersion;

[0068] 5) Dissolve 5 mL of tetrabutyl titanate in 50 mL of ethanol and stir until homogeneous to obtain a titanium ion solution;

[0069] 6) Dissolve 1.25g of lithium hydroxide in 50mL of deionized water and stir until homogeneous to obtain a lithium ion solution;

[0070] 7) Under stirring conditions, the lithium ion solution was slowly added dropwise to the graphene oxide dispersion. After the addition was complete, stirring was continued for 1.5 hours to obtain the solution.

[0071] 8) Under stirring conditions, the titanium ion solution is slowly added dropwise to the solution prepared in step 7), and 1.5g of urea is added to the solution as a nitrogen source (the mass ratio of urea to graphene oxide is 1.2:1). The mixture is stirred until homogeneous to obtain a mixed solution.

[0072] 9) Transfer the mixed solution to a hydrothermal reactor and react at 200°C for 18 hours. After the reaction is complete, allow it to cool naturally to room temperature.

[0073] 10) Wash with deionized water, centrifuge, and collect the precipitate to obtain nitrogen-doped graphene oxide-lithium titanate composite material (the mass ratio of nitrogen-doped graphene oxide to lithium titanate is 1:1.4).

[0074] 11) The nitrogen-doped graphene oxide-lithium titanate composite material was dried in a vacuum drying oven at 70°C for 8 hours to obtain the positive electrode material of lithium-ion supercapacitor (high energy density supercapacitor electrode material).

[0075] The nitrogen-doped graphene oxide-lithium titanate composite material, conductive agent (Super P), and binder (PVDF) prepared above were weighed in a mass ratio of 80:10:10, N-methylpyrrolidone was added and mixed evenly, and then coated on aluminum foil and vacuum dried to obtain a positive electrode sheet.

[0076] Commercial activated carbon, conductive agent (Super P), and binder (PVDF) were weighed in a mass ratio of 70:15:15, and N-methylpyrrolidone was added for further homogenization. The mixture was then coated onto copper foil and vacuum dried to obtain a negative electrode sheet. A button-type lithium-ion supercapacitor was assembled in an argon-atmospheric glove box.

[0077] Example 3: A high-energy-density supercapacitor electrode material and its preparation method

[0078] This embodiment provides a high-energy-density supercapacitor electrode material, including the following steps:

[0079] 1) Add 2g of natural graphite powder to 100mL of concentrated sulfuric acid, stir for 45 minutes under ice bath conditions, then slowly add 6g of potassium permanganate, control the reaction temperature to not exceed 20℃, and continue stirring for 3 hours.

[0080] 2) Transfer the reaction system to a 35°C water bath, stir for 1.5 hours, then add 200 mL of deionized water and continue stirring for 45 minutes;

[0081] 3) Add 5 mL of hydrogen peroxide solution to the reaction system until the solution turns bright yellow, then stop stirring and let it stand for 18 hours;

[0082] 4) Wash with deionized water until neutral, then centrifuge to obtain a graphene oxide dispersion;

[0083] 5) Dissolve 20 mL of tetrabutyl titanate in 50 mL of ethanol and stir until homogeneous to obtain a titanium ion solution;

[0084] 6) Dissolve 5g of lithium hydroxide in 50mL of deionized water and stir until homogeneous to obtain a lithium ion solution;

[0085] 7) Under stirring conditions, the lithium ion solution was slowly added dropwise to the graphene oxide dispersion. After the addition was complete, stirring was continued for 1.5 hours to obtain the solution.

[0086] 8) Under stirring conditions, the titanium ion solution is slowly added dropwise to the solution prepared in step 7), and 1.5g of urea is added to the solution as a nitrogen source (the mass ratio of urea to graphene oxide is 1.2:1). The mixture is stirred until homogeneous to obtain a mixed solution.

[0087] 9) Transfer the mixed solution to a hydrothermal reactor and react at 200°C for 18 hours. After the reaction is complete, allow it to cool naturally to room temperature.

[0088] 10) Wash with deionized water, centrifuge, and collect the precipitate to obtain nitrogen-doped graphene oxide-lithium titanate composite material (the mass ratio of nitrogen-doped graphene oxide to lithium titanate is 1:5.6).

[0089] 11) The nitrogen-doped graphene oxide-lithium titanate composite material was dried in a vacuum drying oven at 70°C for 8 hours to obtain the positive electrode material of lithium-ion supercapacitor (high energy density supercapacitor electrode material).

[0090] The nitrogen-doped graphene oxide-lithium titanate composite material, conductive agent (Super P), and binder (PVDF) prepared above were weighed in a mass ratio of 80:10:10, N-methylpyrrolidone was added and mixed evenly, and then coated on aluminum foil and vacuum dried to obtain a positive electrode sheet.

[0091] Commercial activated carbon, conductive agent (Super P), and binder (PVDF) were weighed in a mass ratio of 70:15:15, and N-methylpyrrolidone was added for further homogenization. The mixture was then coated onto copper foil and vacuum dried to obtain a negative electrode sheet. A button-type lithium-ion supercapacitor was assembled in an argon-atmospheric glove box.

[0092] Example 4

[0093] Compared with Example 1, the difference in Example 4 is that the amount of urea added is 2.0g, and a nitrogen-doped graphene oxide-lithium titanate composite material (nitrogen mass fraction of 8%) is obtained. The other parameters are the same as in Example 1, and a button-type lithium-ion supercapacitor is assembled according to the method of Example 1.

[0094] Comparative Example 1

[0095] Compared with Example 1, the difference in Comparative Example 1 is that the amount of urea added is 0.5g, and a nitrogen-doped graphene oxide-lithium titanate composite material (nitrogen mass fraction of 2%) is obtained. The other parameters are the same as in Example 1, and a button-type lithium-ion supercapacitor is assembled according to the method of Example 1.

[0096] Comparative Example 2

[0097] Compared with Example 1, Comparative Example 2 differs in that the amount of urea added is 1.0g, resulting in a nitrogen-doped graphene oxide-lithium titanate composite material (nitrogen mass fraction of 4%). The remaining parameters are the same as in Example 1, and a button-type lithium-ion supercapacitor is assembled according to the method of Example 1.

[0098] Comparative Example 3

[0099] Compared with Example 1, Comparative Example 3 differs in that the amount of urea added is 3.7g, resulting in a nitrogen-doped graphene oxide-lithium titanate composite material (nitrogen mass fraction of 14%). The remaining parameters are the same as in Example 1, and a button-type lithium-ion supercapacitor is assembled according to the method of Example 1.

[0100] Comparative Example 4

[0101] Compared with Example 1, Comparative Example 4 differs in that no titanium or lithium source is added, and only 1.5g of urea is used as a nitrogen source to dope graphene oxide to obtain nitrogen-doped graphene oxide material. The other parameters are the same as in Example 1, and a button-type lithium-ion supercapacitor is assembled according to the method of Example 1.

[0102] Comparative Example 5

[0103] Compared with Example 1, Comparative Example 5 differs in that a titanium source solution and a lithium source solution were prepared as in Example 1, and the two were mixed to prepare a pure lithium titanate solution. Urea and graphene oxide were not added, and only pure lithium titanate nanoparticles were used as electrode materials. The other parameters were the same as in Example 1, and a button-type lithium-ion supercapacitor was assembled according to the method of Example 1.

[0104] Comparative Example 6

[0105] Compared with Example 1, Comparative Example 6 differs in that a titanium source solution and a lithium source solution were prepared as in Example 1, and the two were mixed to prepare a pure lithium titanate solution; 1.5g of urea was used as a nitrogen source to dope graphene oxide to obtain nitrogen-doped graphene oxide; the nitrogen-doped graphene oxide and lithium titanate were mechanically mixed at a mass ratio of 4:1 for 2 hours, and the remaining parameters were the same as in Example 1; and a button-type lithium-ion supercapacitor was assembled according to the method of Example 1.

[0106] The capacity retention rates (capacity after 1000 hours of cycling / original capacity) of the button lithium-ion supercapacitors obtained in Examples 1-4 and Comparative Examples 1-6 are compared in Table 1.

[0107] Table 1

[0108] Group Capacity retention rate % Example 1 92 Example 2 85 Example 3 83 Example 4 89 Comparative Example 1 73.5 Comparative Example 2 78 Comparative Example 3 81 Comparative Example 4 48 Comparative Example 5 53 Comparative Example 6 50

[0109] This application utilizes a titanium source (titanium ions) to in-situ generate lithium titanate nanoparticles with a particle size of 20-50 nm on the surface of graphene oxide sheets. These nanoparticles are then directly connected to graphene via Ti-OC covalent bonds to form an integrated "conductive network-lithium storage unit" structure. Urea is used as the nitrogen source to simultaneously achieve uniform nitrogen atom doping during the hydrothermal reaction. Pyridine nitrogen and graphitic nitrogen synergistically contribute pseudocapacitance, resulting in a specific capacity of 215 mAh / g (100 mA / g). The in-situ generated nanoscale composite structure effectively suppresses the volume expansion of lithium titanate, and the capacity retention rate reaches 92% after 1000 hours of cycling. This material combines the advantages of high energy density, long lifespan, and low cost, breaking through the industry bottleneck of "high capacity and long cycle life being difficult to achieve simultaneously" in cathode materials.

[0110] In Comparative Examples 1-3, a nitrogen mass fraction below 5% results in a decrease in specific capacity to as low as 73.5% due to insufficient active sites, while a mass fraction above 10% causes a doubling of resistance due to the distortion of the graphene conjugated structure, and a decrease in capacitance retention to 81% after 1000 hours of cycling.

[0111] In Comparative Example 4, no titanium or lithium source was added during the preparation process, resulting in a coin-type lithium-ion supercapacitor with low capacity retention after 1000 hours of cycling. The lack of lithium titanate, which provides the bulk redox reaction for lithium-ion insertion / extraction, led to a decrease in the performance of the coin-type lithium-ion supercapacitor.

[0112] In Comparative Example 5, the pure lithium titanate nanoparticles lacked graphene / nitrogen doping. The absence of graphene increased the internal resistance of the conductive network and led to lithium titanate agglomeration, ultimately resulting in a decline in performance. In Comparative Example 6, the physical mixing of nitrogen-doped graphene oxide with lithium titanate increased contact resistance, negated the synergistic effect, and caused decoupling between the nitrogen-doped pseudocapacitance and the redox reaction kinetics of lithium titanate, leading to an increased lithium-ion migration barrier. The coin-type lithium-ion supercapacitors obtained in Comparative Examples 5 and 6 also exhibited low capacity retention after 1000 hours of cycling.

[0113] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application and are not intended to limit the scope of protection of this application. Although this application has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of this application without departing from the substance and scope of the technical solutions of this application.

Claims

1. A supercapacitor electrode material, characterized in that, The supercapacitor electrode material includes a nitrogen-doped graphene-lithium titanate nanocomposite material. The lithium titanate nanoparticles in the composite material are covalently bonded to the graphene surface via Ti-OC bonds, with an average spacing of <50 nm, and the nitrogen doping amount is 5-10% of the total mass of the composite material.

2. The supercapacitor electrode material as described in claim 1, characterized in that, The lithium titanate nanoparticles have a particle size of 20 nm to 50 nm.

3. The method for preparing the supercapacitor electrode material as described in claim 1 or 2, characterized in that, The method for preparing the supercapacitor electrode material includes the following steps: S1. Add graphene to concentrated sulfuric acid and stir, then add potassium permanganate and carry out a water bath reaction to obtain a reaction solution. Then add hydrogen peroxide solution to the reaction solution until the reaction solution turns bright yellow. Let it stand, centrifuge, and obtain graphene oxide dispersion. S2. Prepare titanium ion solution and lithium ion solution. Slowly add the lithium ion solution dropwise to the graphene oxide dispersion obtained in step S1 to obtain a mixed solution containing graphene oxide and lithium ions. S3. Slowly add titanium ion solution to the mixed solution, then add urea and carry out a thermal reaction. After the reaction is completed, cool to room temperature, centrifuge, and take the precipitate to obtain nitrogen-doped graphene-lithium titanate nanocomposite material. Dry the nitrogen-doped graphene-lithium titanate nanocomposite material to obtain supercapacitor electrode material.

4. The method for preparing the supercapacitor electrode material as described in claim 3, characterized in that, In step S1, the temperature of the water bath reaction is 35-40°C, and the reaction time is 1-2 hours.

5. The method for preparing the supercapacitor electrode material as described in claim 3, characterized in that, In step S2, the method for preparing the titanium ion solution includes: dissolving tetrabutyl titanate in ethanol and stirring until homogeneous to obtain the titanium ion solution; The preparation method of lithium ion solution includes: dissolving lithium hydroxide in deionized water, stirring evenly, to obtain lithium ion solution.

6. The method for preparing the supercapacitor electrode material as described in claim 3, characterized in that, In step S2, the molar ratio of titanium ion solution to graphene oxide dispersion is (0.05-0.12):

1.

7. The method for preparing the supercapacitor electrode material as described in claim 3, characterized in that, In step S3, the molar ratio of the lithium ion solution to the mixed solution is (3.0-3.8):

1.

8. The method for preparing the supercapacitor electrode material as described in claim 3, characterized in that, The mass ratio of graphene oxide to urea in the graphene oxide dispersion is 1:(1~3.5).

9. The method for preparing the supercapacitor electrode material as described in claim 3, characterized in that, In step S3, the temperature of the thermal reaction is 180–220°C, and the time of the thermal reaction is 12–24 hours.

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