Enhanced Electrochemical Energy Stoarge Of Tin-based Electrode Material

Supercapacitor is the most powerful candidates to satisfy the requirement,ascribing to its ultralong cycling stability and fast charging-discharging process when compared to conventional batteries.Therefore,investigation of the high-performance supercapacitor electrode material is particularly important.Tin dioxide(SnO₂)is a promising anode for SCs due to its high theoretical capacity(?780 m Ah g-1),cost-effectiveness and environmental friendliness.However,the band gap of SnO₂ is 3.6 e V,leading weak electronic conductivity.Improving the electronic conductivity,electrochemical activity and electrochemical energy storage of SnO₂-based electrode material is still of great significance.Here,SnO₂-based electrode material was used as the basic unit of research,and the porous carbon fiber(PCF)or activated carbon fiber(ACF)was used as substrate to support SnO₂-based nanomaterial.The PCF or ACF substrate can improve the wettability between SnO₂-based electrode material and electrolyte.On this basis,SnO₂-based electrode was modified by single doping and double doping,reasonably regulating the conductivity and electrochemical activity of SnO₂ based electrode materials and enhance their electrochemical energy storage.Here,nitrogen(N)was used in single-doping modification,while the sulfur and nitrogen,cobalt and nitrogen were used in S,N co-doping and Co,N co-doping modification,respectively.Based on this,the effects of single-doping and double-doping,metal-doping and nonmetal-doping on the electronic structure and electrochemical activity of SnO₂ were studied.Furthermore,the energy storage behavior and potential application of SnO₂-based electrode in linear micro-supercapacitor and wearable brace-type supercapacitor were also studied.The specific works of this paper are as follows:(1)The enhanced electrochemical energy storage of nitrogen doped tin dioxide in wire-shaped supercapacitor.N-SnO₂ nanoflower array was prepared on the porous carbon fiber(PCF)substrate by solvothermal method and nitriding under an ammonia atmosphere.Density functional theory and electrochemical experiments show that:(i)N doping can effectively enhance the valence band edge of SnO₂ in one-direction and reduce its band gap energy to 1.9 e V.The conductivity of SnO₂-based electrode was enhanced.The specific capacitance of N-SnO₂/PCF electrode is 185.2 F g^-1 at 1 A g^-1,which is higher than 75.5 F g^-1 of SnO₂/PCF electrode;(ii)N doping can introduce Sn-N and O-N bonds in the supercell,reducing the potential energy of SnO₂ to-4988.6 e V.The electrochemical stability of SnO₂-based electrode was enhanced.The capacitance retention of N-SnO₂/PCF electrode is 104.1%at 5 A g^-1 after 5000 cycles,which is higher than 74.3%of SnO₂/PCF;(iii)N doping can control the distribution of charge density in SnO₂ and improve its rate capability.The capacitance retention of N-SnO₂/PCF electrode is 47.9%from 1 A g^-1 to 10 A g^-1,which is higher than 36.5%of SnO₂/PCF.Thus,N-SnO₂/PCF electrode exhibits enhanced electrochemical energy storage than SnO₂/PCF.In addition,a linear micro-supercapacitor N-SnO₂/PCF//Ti N was constructed using N-SnO₂/PCF as positive electrode,Ti N as negative electrode and protonic acid as gel-electrolyte.The linear micro-supercapacitor can achieve output voltage of 1.6 V and energy density of 0.31 m W h cm^-3 at power density of 8 m W cm^-3.The specific capacitance retention of this supercapacitor is 90.2%at 5 A g^-1 after1000 cycles.(2)The enhanced electrochemical energy storage of sulfur and nitrogen co-doped tin dioxide nanoarray in wire-shaped supercapacitor.S,N-SnO₂ nanoflower array was prepared on PCF substrate by solvothermal and one-step co-doping methods.Density functional theory and electrochemical experiments show that:(i)S and N co-doping can cooperatively enhance the valence band edge of SnO₂ in one-direction and reduce its band gap energy to 1.2 e V.The conductivity of SnO₂-based electrode was effectively enhanced.Therefore,the specific capacitance of S,N-SnO₂/PCF electrode is 349.2 F g^-1 at 1 A g^-1,which is much higher than that of N-SnO₂/PCF(185.2 F g^-1)and S-SnO₂/PCF(127.2 F g^-1);(ii)S and N co-doping can cooperatively introduce Sn-N,O-N and Sn-S,O-S bonds in the supercell,reducing the potential energy of SnO₂ to-5230.4 e V.The electrochemical stability of SnO₂-based electrode was enhanced.Therefore,the specific capacitance retention of S,N-SnO₂/PCF electrode is 107.7%after 5000 cycles at 5 A g^-1,which is higher than that of S-SnO₂/PCF(98.6%)and N-SnO₂/PCF(104.1%);(iii)S and N co-doping exhibits a synergistic effect on the regulation of the charge density distribution in SnO₂ and improve its rate capability.Therefore,the capacitance retention of S,N-SnO₂/PCF electrode is 64.8%from 1 A g^-1 to 10 A g^-1,which is higher than that of S-SnO₂/PCF(61.6%)and N-SnO₂/PCF(47.9%).Thus,S,N-SnO₂/PCF electrode exhibits enhanced electrochemical energy storage than S-SnO₂/PCF and N-SnO₂/PCF.In addition,the linear micro-supercapacitor S,N-SnO₂/PCF//Ti N was constructed using S,N-SnO₂/PCF as positive electrode,Ti N as negative electrode and protonic acid as gel-electrolyte.The linear micro-supercapacitor could achieve output voltage of 1.6 V,energy density of 0.43 m W h cm^-3 at power density of 8 m W cm^-3.The specific capacitance retention of this supercapacitor is 98.7%after 2000 cycles at the current density of 5 A g^-1.(3)The enhanced electrochemical energy storage of cobalt and nitrogen co-doped tin dioxide in brace-type supercapacitor.Co,N-SnO₂ nanoflower array was prepared on activated carbon fiber(ACF)substrate by co-hydrothermal and ammonia nitriding methods.Density functional theory and electrochemical experiments show that:(i)Co and N co-doping plays the respective roles in adjusting the bandgap.Co-doping makes the conduction band edge decrease and N-doping makes valence band edge increase in SnO₂.The conduction band and valence band approach each other and the band gap energy of SnO₂ was greatly narrowed to 0.7 e V.The conductivity of SnO₂-based electrode material was enhanced effectively.Additionally,the protonation energy of SnO₂ cells decreased from 4.97 e V to 3.08 e V,which was more favorable to the enhancement of the capacitance.Therefore,the specific capacitance of Co,N-SnO₂/ACF electrode is 361.2F g^-1 at 1 A g^-1,which is much higher than that of N-SnO₂/ACF(185.2 F g^-1)and Co-SnO₂/ACF(295.5 F g^-1);(ii)Co and N co-doping can introduce Sn-N,Co-N and Sn-O,Co-O bonds in the supercell,reducing the potential energy of SnO₂ cell from-2309.2e V to-2452.8 e V,and greatly improves its electrochemical stability.Therefore,the specific capacitance retention of Co,N-SnO₂/ACF electrode is 103.3%after 10,000cycles at 5A g^-1,which is much higher than that of N-SnO₂/ACF(99.8%)and Co-SnO₂/ACF(71.9%);(iii)Co and N co-doping exhibits more synergistic effect on the regulation of the charge density distribution of SnO₂,which can improve its rate performance more effectively.Therefore,the capacitance retention of Co,N-SnO₂/ACF electrode is 61.1%from 1 A g^-1 to 10 A g^-1,which is higher than that of N-SnO₂/ACF(56.2%)and Co-SnO₂/ACF(50.7%).Thus,Co,N-SnO₂/ACF electrode exhibits enhanced electrochemical energy storage than Co-SnO₂/ACF and N-SnO₂/ACF.The wearable brace-type supercapacitor Co,N-SnO₂/ACF//Ti N was constructed using Co,N-SnO₂/ACF as positive electrode,PANI/ACF as negative electrode and protonic acid as gel-electrolyte.The wearable supercapacitor could achieve output voltage of 2.0 V,energy density of 70.7 Wh kg^-1 at power density of 500 W Kg^-1.The specific capacitance retention is 90.8%after 1000 cycles at the current density of 5 A g^-1.