Study On PPO/TiO 2 NT Membrane Electrode Of Three-dimensional Micro Lithium Ion Battery

Lithium ion battery(LIB)is well known as one of the promising energy storage and conversion technologies owing to high capacity,long cycle life span,environmental friendliness and no memory effect,compared with traditional batteries.Therefore,LIB has been widely applied in many fields.With the development of miniaturization and integration of portable electronic devices,micro LIB with high energy density are proposed.Three dimensional(3D)micro battery with high volume energy density and good integrated compatibility has been the optimal choice to realize the miniaturization and integration of lithium-ion batteries.As the key components in lithium ion battery,the performances and assembly of the anode and the memrbane play an important role in the electrochemical performances of LIB.3D ordered TiO2 nanotube arrays(TiO2NT),as anode active materials of lithium ion battery,possess a lot of advantages such as regular structure,large specific surface area,short paths for lithium ion,small volume change and high safety.However,the poor electronic conductivity of TiO2NT limited its application in lithium ion battery.Hence it is necessary to ameliorate the electrochemical performance of LIB by improving the electrical conductivity of TiO2NT.The commercial separator is usually placed between two electrodes by physical stack for the membrane/electrode,in which only the highest top of the electrode can contact the membrane separator and the resultant contact area between the membrane and electrode may not be large enough,especially for the uneven electrode with sags and crests such as TiO2NT.For this purpose,the electrochemical performances of LIB will be improved in terms of the electrode,the separator and assembly in this paper as follows:(1)The electrodeposition of poly(phenylene oxide)(PPO)film on Ti3+-doped TiO2NT(Ti3+/TiO2NT)was designed and achieved via self-doping of Ti3+ and the following electropolymerization of phenol monomers.The microstructure and morphology of the as-synthesized PPO/Ti3+/TiO2NT membrane/electrode was investigated in terms of SEM,EDX and XPS.Furthermore,the electrochemical performance was studied by galvanostatic charge/discharge,cyclic voltammograms and alternative current impedance spectroscope.The results showed the electrical conductivity was indeed enhanced after self-doping of Ti3+ and the resultant PPO/Ti3+/TiO2NT membrane/electrode delivered an initial discharge capacity of about 415 mAh/g.Especially,PPO/Ti3+/TiO2NT membrane/electrode displayed the satisfactory rate performances,cyclic stability and Li+ diffusion coefficient,mainly attributed to the joint contributions from the improved electrical conductivity of Ti3+/TiO2NT electrode and the synergy effects between Ti3+/TiO2NT electrode and loose PPO film,which can increase the contact area of electrode/separator and shorten the length of Li+ diffusion paths.(2)Sulfonated PPO film was electrodeposited on Ti3+/TiO2NT electrode via sulfonation of phenol in room temperature and the following electropolymerization.The microstructure and morphology of the as-synthesized SPPO/Ti3+/TiO2NT membrane/electrode was investigated in terms of SEM,FESEM,EDX,XPS and FTIR.Furthermore,the electrochemical performance was studied by galvanostatic charge/discharge and cyclic voltammograms.The results showed that the initial discharge capacity of the resultant sulfonated PPO/Ti3+/TiO2NT membrane/electrode further increased to about 538 mAh/g,and good rate performance and cyclic stability were also achieved.It was worth noting that sulfonated PPO as the anode material can show the electrochemical activity.The enhanced electrochemical performance of sulfonated PPO/Ti3+/TiO2NT membrane/electrode mainly attributed to the joint contributions from sulfonation-induced ionic conductivity.