Preparation method and application of moso bamboo-based silicon-titanium composite carbon electrode material

Abstract

The invention relates to the field of electrode materials, in particular to a preparation method and application of a moso bamboo-based silicon-titanium composite carbon electrode material. The method comprises the steps that moso bamboo is crushed into particles with the particle size smaller than 2 mm, the particles are soaked in a mixed salt solution containing copper ions and zinc ions for 8-12 h, cleaning and drying are conducted, and pretreated bamboo powder is obtained; the pretreated bamboo powder and a titanium source are mixed according to the mass ratio of (1-2): 1, the mixture is heated to the target temperature at the speed of 10-50 DEG C / min in the inert atmosphere, the constant temperature is kept for 30-60 min, and a composite carbon material containing core-shell structure silicon-titanium oxide is obtained; and (2) preparing the composite carbon material containing the core-shell structure silicon-titanium oxide obtained in the step (2), a conductive agent and a binder into slurry according to the mass ratio of (6-8): (1-3): (0.5-1.5), coating the activated carbon cloth with the slurry, and performing freeze drying or liquid nitrogen directional freeze molding. According to the preparation method, the defects of the traditional technology in the aspects of environmental protection, pore regulation and control accuracy and functional compounding are effectively overcome, and the electrochemical performance of the agricultural residue-based electrode material is remarkably improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of electrode materials, and more particularly to a preparation method and application of a bamboo-based silicon-titanium composite carbon electrode material. BACKGROUND

[0002] Super capacitors have become key components for grid peak shaving due to their ultra-high power density and long cycle life, but their commercial application is limited by their low energy density. Biomass-derived carbon materials have become an important research direction due to their sustainability and structural designability. Bamboo, as an agricultural waste with an annual output of over 500 million tons in southern China, has a unique three-dimensional porous skeleton composed of cellulose, hemicellulose, and lignin. It has mechanical stability provided by high cellulose content, inhibition of pyrolysis side reactions due to low oxygen content, and enhancement of carrier mobility by silicon elements in the ash. Existing technologies mainly modify through pyrolysis carbonization combined with activation processes: staged temperature control pyrolysis can realize component directional conversion, in which steam activation can make the specific surface area reach 1182 m 2 / g, while KOH chemical activation can expand the mesopore volume to 1.044 cm 3 / g, but requires a high consumption of KOH / carbon mass ratio > 3:1 and generates alkaline waste liquid; in terms of functional modification, nitrogen-doped bamboo charcoal can achieve a specific capacitance of 475 F / g, but high-temperature doping leads to an imbalance of sp 2 / sp 3 hybrid carbon, and metal oxide composite strategies can increase the specific capacitance to 872 F / g, but there is significant capacity decay after 5000 cycles.

[0003] However, the existing technology still has the following core limitations: first, the energy density bottleneck is prominent, and the optimal bamboo-based electrode has an energy density of only 380 mAh / g in an asymmetric system, which is difficult to meet the needs of high-energy consumption scenarios; second, the cycle stability is insufficient, and the metal oxide and carbon substrate are mainly combined through physical adsorption, which leads to the shedding of active materials during the cycle process due to the weakening of the interface combination; third, the preparation process has high pollution and high cost defects, and the strong alkaline waste liquid generated by KOH activation increases the environmental protection treatment cost, and the noble metal catalyst accounts for more than 40% of the total cost of the electrode; in addition, the structure design has a high micropore ratio, which leads to ion diffusion resistance at high rates, and functional modification is also limited by the poor thermal stability of the doped elements. The current technology is trapped in the "impossible triangle" contradiction of energy density, power density, and cycle life, and it is urgent to develop innovative solutions with efficient interface engineering and green preparation processes. SUMMARY

[0004] To solve the above technical problems in the prior art, the present application provides a preparation method of a bamboo-based silicon-titanium composite carbon electrode material, comprising the following steps:

[0005] (1) raw material pretreatment: the bamboo is broken into particles with a particle size of <2 mm, soaked in a mixed salt solution containing copper ions and zinc ions for 8-12 h, washed, dried, and bamboo powder is obtained;

[0006] (2) simultaneous pyrolysis and functionalization: the pretreated bamboo powder and titanium source are mixed in a mass ratio of (1-2):1, heated to the target temperature at a rate of 10-50 ℃ / min under an inert atmosphere, and kept at the target temperature for 30-60 min to obtain a composite carbon material containing a core-shell structure silicon-titanium oxide;

[0007] (3) electrode preparation: the composite carbon material containing a core-shell structure silicon-titanium oxide obtained in step (2), a conductive agent, and a binder are prepared into a slurry in a mass ratio of (6-8):(1-3):(0.5-1.5), coated on an activated carbon cloth, and freeze-dried or directionally frozen in liquid nitrogen.

[0008] In the step (1), the concentrations of CuSO4 and ZnSO4 in the mixed salt solution are both 0.10-0.20 mol / L.

[0009] In the step (2), the target temperature includes: first pyrolysis at 200-300 ℃ to make the titanium source decompose into titanium dioxide nanoparticles embedded in the carbon skeleton; and second pyrolysis at 700-900 ℃ to make the silicon dioxide in the bamboo ash react with the titanium dioxide to form a core-shell structure silicon-titanium oxide.

[0010] In the step (2), the titanium source is tetraethyl titanate, and the mass ratio of bamboo powder to titanium source is 3:2; the second pyrolysis temperature is 800 ℃, the heating rate is 20-40 ℃ / min, and the constant temperature time is 45 min.

[0011] In the step (2), the shell thickness of the core-shell structure silicon-titanium oxide is 1-3 nm; and the mesoporous rate of the composite carbon material is 70-80%.

[0012] In the step (3), the freeze-drying is pre-frozen at -40 to -60 ℃ for 24 h.

[0013] In the step (3), the liquid nitrogen directional freezing step is to vertically immerse the carbon cloth coated with the slurry in liquid nitrogen at -196 ℃ to freeze and induce the formation of a vertical pore array.

[0014] In another aspect, the application provides a supercapacitor electrode, which uses the composite carbon material containing a core-shell structure silicon-titanium oxide prepared by the method as the active material, and the specific capacitance is ≥400 F / g, the capacity retention rate after 10,000 cycles at a current density of 10 A / g is ≥100%, and the energy density is ≥15 Wh / kg in a 0.5 mol / L sulfuric acid electrolyte.

[0015] The application has the following beneficial effects over the prior art:

[0016] The application breaks through the energy density bottleneck of traditional biomass electrodes by constructing a SiO / TiO core-shell structure in situ and synergizing with carbon-based folded sheets, realizes an energy density level much higher than that of commercial supercapacitors in a typical electrolytic system, and effectively meets the needs of high-energy consumption scenarios.

[0017] On the other hand, based on the strong chemical bonding mechanism of SiO / TiO and the carbon substrate and the stable mesoporous framework formed by self-growth of the melt, the electrode exhibits excellent structural integrity in large current cycling, completely solves the capacity attenuation problem caused by metal oxide shedding, and has a significantly longer cycle life than existing metal composite electrode systems.

[0018] Finally, self-activation and pore expansion are achieved using the inherent components of biomass, completely avoiding the dependence on corrosive chemicals and noble metal catalysts in traditional processes, eliminating pollution from alkali-containing waste liquid from the source; the synchronous pyrolysis-composite design greatly shortens the process flow, significantly reduces energy consumption and environmental protection treatment cost. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 is the cyclic voltammetry characteristic curve of Example 1 and Comparative Example 1;

[0020] Figure 2 is the cyclic voltammetry characteristic curve of Example 2 and Comparative Example 2;

[0021] Figure 3 is the cyclic voltammetry characteristic curve of Example 3 and Comparative Example 3;

[0022] Figure 4 is the constant current charge-discharge curve of Example 1 and Comparative Example 1 and Example 2 and Comparative Example 2;

[0023] Figure 5 is the constant current charge-discharge curve of Example 3 and Comparative Example 3;

[0024] Figure 6 is the constant current charge-discharge curve of Example 3 and Comparative Example 3;

[0025] Figure 7 is the constant current charge-discharge curve of Example 3 and Comparative Example 3;

[0026] Figure 8 is the alternating current impedance curve of Example 1 and Comparative Example 1, Example 2 and Comparative Example 2, Example 3 and Comparative Example 3;

[0027] Figure 9 is the electron microscope graph of Comparative Example 3;

[0028] Figure 10 is the energy spectrum graph of Comparative Example 3;

[0029] Figure 11 Electron micrograph of Example 3;

[0030] Figure 12 Energy spectrum of Example 3. DETAILED DESCRIPTION

[0031] In order to make the objects, technical solutions and advantages of the present application clearer, the present application will be described below by specific embodiments shown in the drawings. However, it should be understood that these descriptions are only exemplary and are not intended to limit the scope of the present application. In addition, in the following description, the description of well-known structures and techniques is omitted to avoid unnecessary confusion of the concept of the present application.

[0032] The present application provides a preparation method and application of a bamboo-based silicon-titanium composite carbon electrode material. The method comprises the following steps:

[0033] (1) Raw material pretreatment: crush the bamboo into particles with a particle size of <2 mm, soak in a mixed salt solution containing copper ions and zinc ions for 8-12 h, wash and dry to obtain pretreated bamboo powder;

[0034] (2) Simultaneous pyrolysis and functionalization: mix the pretreated bamboo powder with a titanium source at a mass ratio of (1-2):1, heat to the target temperature at a rate of 10-50 ℃ / min under an inert atmosphere, and keep the temperature constant for 30-60 min to obtain a composite carbon material containing a core-shell structure silicon-titanium oxide;

[0035] (3) Electrode preparation: prepare a slurry by mixing the composite carbon material containing a core-shell structure silicon-titanium oxide obtained in step (2), a conductive agent, and a binder at a mass ratio of (6-8):(1-3):(0.5-1.5), coat the slurry on an activated carbon cloth, and freeze-dry or directional freeze-form the slurry in liquid nitrogen.

[0036] In step (1), the concentrations of CuSO4 and ZnSO4 in the mixed salt solution are both 0.10-0.20 mol / L. In step (2), the target temperature includes: first-stage pyrolysis: 200-300 ℃ to make the titanium source decompose into titanium dioxide nanoparticles embedded in the carbon skeleton; second-stage pyrolysis: 700-900 ℃ to make the silicon dioxide in the bamboo ash react with the titanium dioxide to form a core-shell structure silicon-titanium oxide. In step (2), the titanium source is tetraethyl titanate or phosphoric acid, and the mass ratio of bamboo powder to titanium source is 3:2; the second-stage pyrolysis temperature is 800 ℃, the heating rate is 20-40 ℃ / min, and the constant temperature time is 45 min. In step (2), the shell thickness of the core-shell structure silicon-titanium oxide is 1-3 nm; the mesoporous rate of the composite carbon material is 70-80%. In step (3), the pre-freezing in freeze-drying is performed at -40 to -60 ℃ for 24 h. In step (3), the directional freezing in liquid nitrogen is performed by vertically immersing the carbon cloth coated with the slurry in -196 ℃ liquid nitrogen to induce the formation of a vertical pore array.

[0037] A supercapacitor electrode, which uses the core-shell structure silicon-titanium oxide composite carbon material prepared by the method as an active material, meets the following conditions in a 0.5 mol / L sulfuric acid electrolyte: specific capacitance ≥ 400 F / g; capacity retention rate ≥ 100% after 10,000 cycles at a current density of 10 A / g; and energy density ≥ 15 Wh / kg.

[0038] Example 1

[0039] 1. Raw material pretreatment

[0040] Phyllostachys edulis raw materials were selected, crushed, washed to remove impurities, dried in an oven at 110°C to a constant weight, and crushed to a particle size of <2 mm. The bamboo powder was soaked in a mixed solution of 0.15 mol / L CuSO4 and ZnSO4 for 12 h to enhance the porosity of the bamboo by ion exchange, then washed with distilled water for 3 times and dried to obtain pretreated bamboo powder. The metal impurities in lignin were removed, while the natural silicon elements (ash content SiO2 about 2.5wt%) of bamboo were retained, providing a silicon source for the subsequent in-situ formation of SiO2.

[0041] 2. Simultaneous pyrolysis and functionalization

[0042] (1) The pretreated bamboo powder was mixed with tetraethyl titanate at a mass ratio of 3:2.

[0043] (2) Placed in a tube furnace quartz boat, and nitrogen was introduced (flow rate 50 mL / min).

[0044] (3) The temperature was raised to 200°C at a rate of 30°C / min, and kept constant for 45 min to obtain a core-shell structure silicon-titanium oxide composite carbon material (SiO / TiO@C-1 active material).

[0045] Low temperature section (200-300°C): Tetraethyl titanate decomposes into TiO nanoparticles (size 5-10 nm), which are embedded in the bamboo carbon microporous structure to form a TiO@C primary composite. High temperature section (800°C): SiO2 in bamboo ash reacts with TiO2 through a solid phase reaction to form a core-shell structure SiO / TiO (XPS verifies Ti-O-Si bonding), while KOH (inherent potassium element in bamboo) is activated to produce mesopores (pore size 2-50 nm) with a mesopore rate of 75.5%.

[0046] 3. Electrode preparation

[0047] (1) The SiO / TiO@C active material, conductive carbon black, and PVDF binder were mixed at a mass ratio of 7:2:1. The active material was first dispersed in NMP solvent at 60°C for 30 min, and the PVDF was dissolved in NMP at 60°C for 1 h. The mixture was homogenized.

[0048] (2) carbon cloth immersed in 17% HNO3 solution for 1.5h; deionized water rinsing for 5 times, anhydrous ethanol ultrasonic for 20min, 60℃ drying for 12h;

[0049] (3) slurry coated on carbon cloth (loading capacity 0.003g / cm 2 ); microstructure fixed by freeze drying at-50℃ for 24h.

[0050] In the application, K2O in bamboo ash reacts with carbon (6KOH+2C→2K2CO3+3H2) to form autogenous K2CO3 melt (891℃), which expands the hole while avoiding external KOH pollution, and the mesopore volume reaches 1.172cm 3 / g (verified by BET), so that the application can replace traditional KOH activation. In the high-temperature section (800℃), SiO2 and TiO2 generate Ti-O-Si bond through solid-phase reaction (verified by XPS), solving the problem of interface peeling.

[0051] Example 2

[0052] In step 2, the temperature was raised to 300℃ at 30℃ / min, and kept constant for 45min to obtain a composite carbon material containing core-shell structure silicon-titanium oxide (SiO / TiO@C-3 active material). The other steps were the same as in example 1.

[0053] Example 3

[0054] In step 2, the temperature was raised to 800℃ at 30℃ / min, and kept constant for 45min to obtain a composite carbon material containing core-shell structure silicon-titanium oxide (SiO / TiO@C-13 active material). In step 3, the loading capacity was 0.045g / cm2, and the other steps were the same as in example 1.

[0055] Example 4

[0056] The mass ratio of bamboo powder to tetraethyl titanate was 1:1; the heating rate was 10℃ / min (800℃ constant temperature); the constant temperature time was 60min, and the other steps were the same as in example 1.

[0057] Example 5

[0058] The mass ratio of bamboo powder to tetraethyl titanate was 2:1; the heating rate was 50℃ / min (800℃ constant temperature); the constant temperature time was 30min, and the other steps were the same as in example 1.

[0059] Example 6

[0060] In step (1), the concentration of CuSO4 and ZnSO4 in the mixed salt solution was 0.10mol / L, and the other steps were the same as in example 1.

[0061] Example 7

[0062] The concentration of CuSO4 and ZnSO4 in the mixed salt solution in step (1) is 0.15 mol / L, and other steps are the same as those in Example 1.

[0063] Example 8

[0064] The concentration of CuSO4 and ZnSO4 in the mixed salt solution in step (1) is 0.20 mol / L, and other steps are the same as those in Example 1.

[0065] Example 9

[0066] The titanium source is phosphoric acid, and the mass ratio of bamboo powder to titanium source is 3:2; the second-stage pyrolysis temperature is 800℃, the heating rate is 30℃ / min, the constant temperature time is 45min, and other steps are the same as those in Example 1.

[0067] Example 10

[0068] In this example, the mass ratio of SiO / TiO@C active material: conductive carbon black: PVDF is 8:1.5:0.5, and other steps are the same as those in Example 1.

[0069] Example 9

[0070] In this example, the mass ratio of SiO / TiO@C active material: conductive carbon black: PVDF is 6:1:0.5, and other steps are the same as those in Example 1.

[0071] Example 11

[0072] In this example, the mass ratio of SiO / TiO@C active material: conductive carbon black: PVDF is 8:3:1.5, and other steps are the same as those in Example 1.

[0073] Example 12

[0074] The same process is applicable to corn straw (cellulose ≥38%), sugarcane residue (hemicellulose 28%) and rice husk ash (SiO2 20wt%)

[0075] Comparative Example 1

[0076] 1. The pretreated bamboo powder is mixed with KOH at a mass ratio of 1:3;

[0077] 2. Under nitrogen, the temperature is raised to 200℃ at a rate of 30℃ / min, and the constant temperature is obtained for 45min to obtain a composite carbon material (SiO@C active material).

[0078] 3. Electrode preparation

[0079] (1) SiO@C active material, conductive carbon black and PVDF binder are mixed at a mass ratio of 7:2:1; first, the active material is dispersed in NMP solvent at 60℃ for 30min; then, PVDF is dissolved in NMP at 60℃ for 1h; and finally, the mixture is homogenized.

[0080] (2) Carbon cloth immersed in 17% HNO3 solution for 1.5 h; rinsed with deionized water for 5 times, ultrasonic in anhydrous ethanol for 20 min, and dried at 60℃ for 12 h;

[0081] (3) The slurry was coated on the carbon cloth (loading capacity 0.003 g / cm 2 ); the microstructure was fixed by freeze-drying at -50℃ for 24 h.

[0082] Performance verification of supercapacitor electrodes of the examples and comparative examples

[0083] Test conditions:

[0084] Electrolyte: 0.5 mol / L H2SO4;

[0085] Voltage window: -0.3~0.4 V;

[0086] Active material loading capacity: 0.003 g / cm 2 .

[0087] Comparative Example 2

[0088] In step 2, the temperature was raised to 300℃ at 30℃ / min and kept constant for 45 min to obtain the composite carbon material (SiO@C active material), and in step 3, the loading capacity was 0.003 g / cm 2 , and the other steps were the same as those in Comparative Example 1.

[0089] Comparative Example 3

[0090] In step 2, the temperature was raised to 800℃ at 30℃ / min and kept constant for 45 min to obtain the composite carbon material (SiO@C active material), and in step 3, the loading capacity was 0.045 g / cm 2 , and the other steps were the same as those in Comparative Example 1.

[0091] Results comparison (1A / g):

[0092]

[0093]

[0094] The present patent technology significantly improves the comprehensive performance of the electrode material through an innovative preparation method, and the specific technical effects are as follows:

[0095] 1. Energy density breakthrough: the energy density of Example 3 under pyrolysis conditions at 800℃ reaches 15.94 Wh / kg, which is increased by 21.3% compared with Comparative Example 3 (10.23 Wh / kg), breaking through the energy density bottleneck of traditional biomass electrodes and meeting the needs of high-energy consumption scenarios.

[0096] 2. Power density improvement: The power density of Example 3 is 1.61 W / kg, which is improved by 32.2% compared to Comparative Example 3 (1.03 W / kg). The mesoporous rate of 75.5% of the stable framework structure accelerates ion diffusion, solving the problem of ion transmission obstruction at high rate.

[0097] 3. Cycle stability enhancement: The capacity retention rate is ≥100% after multiple cycles at a current density of 1 A / g. The cycle retention rate of Example 3 is 108%. The core-shell structure (SiO / TiO) enhances the interface stability through Ti-O-Si chemical bonding, completely solving the capacity decay caused by metal oxide shedding.

[0098] 4. Charge transfer efficiency optimization: The charge transfer resistance of Example 3 is as low as 0.15 Ω, which is reduced by 20.5% compared to Comparative Example 3 (0.59 Ω). The synergistic effect of SiO / TiO core-shell structure and carbon substrate improves the electron conduction rate.

[0099] 5. Green preparation process: The inherent potassium element of bamboo is used for self-life, avoiding corrosive chemicals such as KOH. The consumption of KOH is reduced by 0.5 tons per ton of bamboo, there is no alkali-containing waste liquid discharge, and the preparation period is shortened to 45 minutes through the simultaneous pyrolysis process, significantly reducing energy consumption and environmental protection cost.

[0100] 6. Raw material universality expansion: The process can be extended to corn stalks, sugarcane residues and other cellulose-rich agricultural wastes. The specific surface area is increased by more than 15% after replacing titanium source with phosphoric acid, providing a new path for high-value utilization of biomass resources.

[0101] Figure 1 is the cyclic voltammetry characteristic curve of Example 1 and Comparative Example 1; wherein Figure 1 (1) indicates the cyclic voltammetry characteristic curve of SiO / TiO@C-1 at a scan rate of 0.005 V / s, 0.01 V / s, 0.02 V / s at 200°C, (2) indicates the cyclic voltammetry characteristic curve of SiO / TiO@C-1 at a scan rate of 0.04 V / s, 0.06 V / s, 0.08 V / s at 200°C, (3) indicates the cyclic voltammetry characteristic curve of the blank experiment Blank Control-2 at a scan rate of 0.005 V / s, 0.01 V / s, 0.02 V / s at 200°C, and (4) indicates the cyclic voltammetry characteristic curve of the blank experiment Blank Control-2 at a scan rate of 0.06 V / s, 0.08 V / s at 200°C.

[0102] Figure 2 is the cyclic voltammetry characteristic curve of Example 2 and Comparative Example 2; wherein Figure 1(1) represents cyclic voltammetry curves of SiO / TiO@C-3 at 300 °C with scan rates of 0.005 V / s, 0.01 V / s, 0.02 V / s, (2) represents cyclic voltammetry curves of SiO / TiO@C-3 at 300 °C with scan rates of 0.04 V / s, 0.06 V / s, 0.08 V / s, (3) represents cyclic voltammetry curves of Blank Control-4 at 300 °C with scan rates of 0.005 V / s, 0.01 V / s, 0.02 V / s, (4) represents cyclic voltammetry curves of Blank Control-4 at 300 °C with scan rates of 0.04 V / s, 0.06 V / s, 0.08 V / s.

[0103] Figure 3 is the cyclic voltammetry curves of Example 1 and Comparative Example 1 and Example 2 and Comparative Example 2; wherein Figure 1 (1) represents cyclic voltammetry curves of SiO / TiO@C-13 at 800 °C with scan rates of 0.005 V / s, 0.01 V / s, 0.02 V / s, (2) represents cyclic voltammetry curves of SiO / TiO@C-13 at 800 °C with scan rates of 0.04 V / s, 0.06 V / s, 0.08 V / s, 0.1 V / s, (3) represents cyclic voltammetry curves of Blank Control-14 at 800 °C with scan rates of 0.005 V / s, 0.01 V / s, 0.02 V / s, (4) represents cyclic voltammetry curves of Blank Control-14 at 800 °C with scan rates of 0.04 V / s, 0.06 V / s, 0.08 V / s, 0.1 V / s.

[0104] Figure 4 is the constant current charge-discharge curves of Example 3 and Comparative Example 3; wherein Figure 1 (1) represents constant current charge-discharge curves of SiO / TiO@C-1 at 200 °C with current density of 1 A / g, (2) represents constant current charge-discharge curves of Blank Control-2 at 200 °C with current density of 1 A / g, (3) represents constant current charge-discharge curves of SiO / TiO@C-3 at 300 °C with current density of 1 A / g, (4) represents constant current charge-discharge curves of Blank Control-4 at 300 °C with current density of 1 A / g.

[0105] Figure 5 is the constant current charge-discharge curves of Example 3 and Comparative Example 3; wherein Figure 1(1) represents the constant current charge-discharge curve of SiO / TiO@C-13 at 800℃ with a current density of 1 A / g, (2) represents the constant current charge-discharge curve of the blank experiment Blank Control-14 at 800℃ with a current density of 1 A / g, (3) represents the constant current charge-discharge curve of SiO / TiO@C-13 at 800℃ with a current density of 2 A / g, and (4) represents the constant current charge-discharge curve of the blank experiment Blank Control-14 at 800℃ with a current density of 2 A / g.

[0106] Figure 6 are the constant current charge-discharge curves of Example 3 and Comparative Example 3; wherein Figure 1 (1) represents the constant current charge-discharge curve of SiO / TiO@C-13 at 800℃ with a current density of 3 A / g, (2) represents the constant current charge-discharge curve of the blank experiment Blank Control-14 at 800℃ with a current density of 3 A / g, (3) represents the constant current charge-discharge curve of SiO / TiO@C-13 at 800℃ with a current density of 4 A / g, and (4) represents the constant current charge-discharge curve of the blank experiment Blank Control-14 at 800℃ with a current density of 4 A / g.

[0107] Figure 7 are the constant current charge-discharge curves of Example 3 and Comparative Example 3; wherein Figure 1 (1) represents the constant current charge-discharge curve of SiO / TiO@C-13 at 800℃ with a current density of 5 A / g, and (2) represents the constant current charge-discharge curve of the blank experiment Blank Control-14 at 800℃ with a current density of 5 A / g.

[0108] The present application solves the problems of low energy density, poor cycle stability and high pollution in the preparation of biomass electrode materials by the integrated design of "raw material pretreatment-in-situ composite-green activation", realizes the synergistic breakthrough of high performance and sustainability, and provides a reliable technical path for the large-scale application of supercapacitors.

[0109] The present application selects bamboo waste as raw material, pretreats by soaking in metal salt solution, removes impurities while retaining the inherent silicon source of bamboo, provides a basis for subsequent in-situ composite, and makes the method have the characteristics of resource recycling and low cost.

[0110] The pretreated bamboo powder is mixed with tetraethyl titanate, and gradient pyrolysis is carried out under a nitrogen atmosphere, so that: the SiO / TiO core-shell structure is formed in situ: the TiO2 nanoparticles are embedded in the carbon skeleton in the low-temperature section; and the SiO2 and TiO2 in the bamboo ash are bonded through the solid-phase reaction Ti-O-Si to build the core-shell interface in the high-temperature section (800 DEG C), so that the ion diffusion efficiency is significantly enhanced. The potassium element inherent in the bamboo is used to react to generate a potassium carbonate melt at high temperature, so that the mesopores are amplified, and the pollution of external KOH is completely avoided.

[0111] On the other hand, the composite carbon material containing the core-shell structure silicon-titanium oxide (SiO / TiO@C active substance) is mixed with a conductive agent and a binder at a ratio of 7:2:1 to form a slurry, the microstructure is fixed by freeze-drying, the wrinkled graphene sheet layer is formed, and the conductivity is synergistically improved. The vertical pore array can be further constructed by directional freezing using an ice template, and the ion diffusion time is shortened.

[0112] The electrochemical performance of the electrode prepared by the method is significantly improved, and the method of the application discards the high-pollution activator, realizes no chemical waste liquid discharge by using the self-generated potassium carbonate of the bamboo, and saves 0.5 tons of KOH consumption per ton of bamboo. The process cycle is shortened to single-step pyrolysis (45 min), and the energy consumption and cost are significantly reduced. The charge transfer resistance is reduced, and the ion diffusion coefficient is significantly improved.

[0113] Finally, the method has raw material universality, and can be extended to corn stalks, sugarcane residues and other cellulose-rich agricultural wastes. Tetraethyl titanate can be replaced by green phosphoric acid, and the specific surface area is increased by >15%. The electrode prepared by the method has high energy density, super-long cycle life and environmental protection characteristics, and is suitable for high-demand energy storage scenes such as electric vehicles and smart grids, and promotes the high-value utilization of biomass resources.

Claims

1. A method for preparing a bamboo-based silicon-titanium composite carbon electrode material, characterized in that, Includes the following steps: (1) Raw material pretreatment: crush the bamboo into particles with a diameter of <2mm, soak it in a mixed salt solution containing copper ions and zinc ions for 8-12 hours, wash and dry it to obtain pretreated bamboo powder. (2) Synchronous pyrolysis and functionalization composite: Pretreated bamboo powder and titanium source are mixed at a mass ratio of (1-2):1, heated to the target temperature at 10-50℃ / min under an inert atmosphere, and kept at the temperature for 30-60min to obtain a composite carbon material containing silicon titanium oxide with core-shell structure. (3) Electrode preparation: The composite carbon material containing core-shell silicon titanium oxide obtained in step (2), conductive agent and binder are prepared into a slurry in a mass ratio of (6-8):(1-3):(0.5-1.5), coated on activated carbon cloth, and then freeze-dried or directionally frozen in liquid nitrogen.

2. The method for preparing bamboo-based silicon-titanium composite carbon electrode material according to claim 1, characterized in that, In step (1), the concentrations of CuSO4 and ZnSO4 in the mixed salt solution are both 0.10-0.20 mol / L.

3. The method for preparing bamboo-based silicon-titanium composite carbon electrode material according to claim 1, characterized in that, The target temperature in step (2) includes: first stage pyrolysis: 200-300℃ to decompose the titanium source into titanium dioxide nanoparticles embedded in the carbon skeleton; second stage pyrolysis: 700-900℃ to react the silicon dioxide in the bamboo ash with the titanium dioxide to generate core-shell structured silicon titanium oxide.

4. The method for preparing bamboo-based silicon-titanium composite carbon electrode material according to claim 3, characterized in that, In step (2), the titanium source is tetraethyl titanate, and the mass ratio of bamboo powder to titanium source is 3:2; the second stage pyrolysis temperature is 800℃, the heating rate is 20-40℃ / min, and the isothermal time is 45min.

5. The method for preparing bamboo-based silicon-titanium composite carbon electrode material according to claim 1, characterized in that, In step (2), the shell thickness of the core-shell structured silicon titanium oxide is 1-3 nm; the mesoporosity of the composite carbon material is 70-80%.

6. The method for preparing bamboo-based silicon-titanium composite carbon electrode material according to claim 1, characterized in that, In step (3), the freeze-drying process involves pre-freezing at -40 to -60°C for 24 hours.

7. The method for preparing bamboo-based silicon-titanium composite carbon electrode material according to claim 1, characterized in that, The step (3) of liquid nitrogen directional freezing involves vertically immersing the carbon cloth coated with slurry into liquid nitrogen at -196°C to freeze it, thereby inducing the formation of a vertical pore array.

8. A supercapacitor electrode, characterized in that, The composite carbon material containing core-shell structured silicon titanium oxide prepared by the method described in any one of claims 1-7 is used as the active material, and it meets the following requirements in 0.5 mol / L sulfuric acid electrolyte: specific capacitance ≥ 400 F / g; capacity retention ≥ 100% after 10,000 cycles at a current density of 10 A / g. Energy density ≥15Wh / kg.

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