| Micro supercapacitor is used as the core energy storage device of electronic circuit due to its long life,fast charging and discharging characteristics.However the low energy storage density limits its development and application.Metal nitride(TiN)is expected to replace the traditional metal oxide and become the next generation of new micro supercapacitor electrode materials due to its excellent conductivity and good pseudo capacitance.Metal nitrides are usually synthesized by the hydrothermal method or sol gel method with nitrogen or ammonia gas at high temperature,and then the nitrides mixed with binder are coated on the collector to obtain the electrodes of micro supercapacitors.The introduction of binder will inevitably reduce the conductivity of the electrode.Magnetron sputtering equipment is simple,easy to control,large coating area and strong adhesion.It can directly deposit high-purity TiN films on electrode substrates.The specific surface area and surface activity of TiN films also affect the supercapacitor characteristics of the electrode.Therefore,in this paper,the structure of TiN films was controlled by controlling deposition parameters,so as to improve the specific surface area and surface activity of electrode materials.The effects of TiN film specific surface area and surface activity on electrode specific capacitance and cycle stability were systematically investigated.The effects of TiN film composition regulation(Cr doping/C doping/β-N(TiOxNy)on the energy storage characteristics of TiN film electrode were clarified,and the energy storage mechanisms of TiN film electrode were revealed.This paper have obtained the following innovative research results:(1)The effects of magnetron sputtering pressure,nitrogen flow rate and deposition time on the microstructure and electrochemical properties of TiN thin film electrodes were studied.Working air pressure from 0.98×10-3 torr increased to 1.5×10-3 torr,the crystal columns of TiN films gradually grew in a "feather like" structure,the porosity and surface roughness of the films increased,the conductivity of TiN films decreased from 1530 S/cm to 426 S/cm,and the areal capacitance increased from 10.42 mF/cm2 to 15.60 mF/cm2(10 mV/s);TiN films with different stoichiometric ratios can be obtained by adjusting the nitrogen flow rate.When the nitrogen flow rate was 6 sccm,the stoichiometric ratio of TiN films was 1:1,and the conductivity of TiN films was 1530 S/cm,which had the best electrochemical performance(b value was 0.83,after 10000 cycles,the capacitance retention rate was 91.4%(200 mV/s));There was a linear relationship of y=0.66x+6.22 between the specific surface area(x)of TiN film and the areal capacitance of electrode area(y).When the film thickness was greater than 930 nm,the volume capacitance of TiN film tended to a constant value of 175 F/cm3.(2)TiN was deposited on in-situ chemically etched Si substrate to obtain Si nanowires TiN thin film electrodes(Si NWs/TiN)with fine size and good continuity,which can effectively increase the specific capacitance of the thin film electrode.When the Si substrate was etched for 30 min,a continuous nanowire electrode(Si30 NWs/TiN).In 0.5 M H2SO4 electrolyte,the mass specific capacitance(41.63 F/g)of Si30 NWs/TiN electrode was 7.5 times that of non etched TiN electrode(5.53 F/g)at 100 mV/s.At the scanning rate of 200 mV/s,the attenuation rate of electrode mass specific capacitance was only 12.4%after 2000 cycles.The improved specific capacitance performance of the Si30 NWs/TiN electrode was due to its larger specific surface area.(3)The effects of Cr content on the microstructure and electrochemical properties of TiN films were analyzed.TiN films with different Cr contents(TiN/Cr)were prepared by magnetron co sputtering.The introduction of Cr into TiN films to form Cr-N bonds not only increased the quality of active substances on the electrode surface,but also inhibited the oxidation of the electrode surface.When Cr conten was 4.03 at.%(TiN film had the maximum conductivity of 2687 S/cm);In 0.5 M K2SO4 electrolyte,the areal capacitance(40 mF/cm2)of TiN film electrode was 4 times that of undoped Cr film electrode at a scanning rate of 10 mV/s;After 10000 cycles,the areal capacitance of the film electrode remained 94.28%of the initial capacitance(200 mV/s).(4)The effect of C doping on the electrochemical properties of TiN films was studied.TiN films with different C contents(TiN/C)were prepared by magnetron co sputtering.When C content was 5.33 at.%In 0.5 M H2SO4 electrolyte solution,the maximum areal capacitance of the film electrode was 45.81 mF/cm2 at a scanning speed of 10 mV/s,which was three times that of the pure TiN film electrode;At the scanning rate of 100 mV/s,the areal capacitance of the film electrode remained 96.28%of the initial capacitance after 5000 cycles.The first principle calculation showed that H in the electrolyte was mainly adsorbed on the Ti atom of the TiN electrode during the charge and discharge process,while H was more easily adsorbed on the C atom of the C-N bond in the TiN electrode,and the charge density distribution between the TiN/C film and H was higher and the bonding effect was stronger,which effectively improved the areal capacitance and cycle stability of the TiN/C film electrode.Therefore,doping a small amount of C in TiN film can enhance the adsorption of H on the electrode and effectively improved the charge discharge performance of the film electrode.(5)In order to explore the effect of and oxygen vacancies(Vo)on the energy storage mechanism of TiN thin film electrodes,the TiN films were subjected to vacuum thermal annealing experiments at 350℃,400℃ and 450℃,respectively.As the annealing temperature from room temperature(RT)increased to 450℃,the β-N on the film surface increased from 16.34%to 28.65%.When the annealing temperature was 450℃,the areal capacitance of TiN film was twice that of room temperature TiN at the scanning rate of 50 mV/s;After annealing,the N in the center of the electrode diffuses to the Vo formed on the surface,and the dynamic balance maintained during the charge and discharge process was the essence of improving the long cycle stability of TiN thin film electrode.The off-site XRD results show that the crystal plane spacing of TiN electrode increased and decreased with the insertion and removal of K+ions during the charge and discharge process,which proved that the type of charge stored in TiN film was the type of intercalated pseudocapacitance. |
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