TiN Nanoparticles As The Cathode Catalyst For Lithium-Oxygen Batteries

Lithium-oxygen battery is a clean energy source,which has high energy density(11430Wh·kg^-1)and is friendly to environment.It is considered to be an alternative to lithium-ion battery as the next generation of new energy storage system.So far,the research on lithium-oxygen batteries has made initial progress,but there is still a lot of work to be done from the goal of commercialization.There are some key problems that need to be solved urgently,such as developing stable electrolytes,finding suitable double-effect catalysts.The problem that the electrolyte is unstable and easily decomposed is caused by an excessive over-potential during charging and discharging.The double-effect catalyst can effectively reduce the charge/discharge over-potential,and then reduce the decomposition of the electrolyte.In this paper,cubic TiN nanoparticles are synthesized and used as a catalyst for lithium-oxygen batteries to reduce the charge over-potential and improve the capacity and cycle performance of the lithium-oxygen battery.TiN,which has similar catalytic activity to noble metal Pt,has good electrical conductivity and high chemical stability,and widely used in the field of batteries as a catalyst or catalyst carrier.In addition,TiN has the advantages of simple preparation and low production cost.In this paper,TiN nanoparticles were prepared by DC arc-discharge method in a mixed atmosphere of hydrogen and nitrogen.Various analytical methods,including X-ray diffraction,Transmission Electron Microscopy,are used to characterize the microstructure and morphology of the TiN nanoparticles.The results show that the TiN nanoparticles are single crystal and have a cubic structure.Its grain size varies from 30.00 to 70.00 nm.The crystallinity is great,and the preparation purity is high.In addition,XPS was used to analyze the surface elements and bonding states of the samples.It was found that there were traces of O elements in addition to Ti and N on the surface of TiN.The Ti-N bonds,Ti-N-O bonds and Ti-O bonds were formed on the surface,that is,the surface of TiN nanoparticles contains a small amount of titanium oxynitride?TiO_xN_y?and low-valent titanium oxide(Ti_nO_2n-1).These oxides are caused by air passivation of nanoparticles,which have very little content and are amorphous phases.They can enhance the conductivity and catalytic activity of TiN.The catalytic activity of TiN nanoparticles was tested by the Rotating Disk Electrode?RDE?test.The results show that the TiN nanoparticles have dual catalytic properties of both oxygen reduction reaction?ORR?and oxygen evolution reaction?OER?.According to the calculation results,the oxygen reduction reaction under TiN catalysis is regarded as two-electron reaction.As the cathode catalyst for the lithium-oxygen batteries,the TiN electrode delivers 3037 mAh·g^-11 discharge specific capacity at a current density of 50 mA·g^-1,and the charging platform is 4.2 V,which is lower than the decomposition voltage of the electrolyte?4.3 V?.When the capacity is limited to 300 mAh·g^-1 and the current density is 75mA·g^-1,the battery can be stably cycled for 25 cycles,which means good reversibility and low capacity attenuation.The battery has a stable cycle of 13 cycles and the energy efficiency of the battery can maintain in 62%at a limited capacity 500 mAh·g^-1 and a current density of 75mA·g^-1.After the charge and discharge of the battery,XRD,TEM and FT-IR were used to detect the substance of the electrode sheet.It was found that a disk-shaped lithium peroxide was formed on the surface of electrode during the discharge,which disappeared during the subsequent charging process.It was verified that the generation and decomposition of lithium peroxide was the main reaction of lithium-oxygen battery.At the same time,it was found that the diffraction peak of TiN did not change before and after cycling,which proved that TiN has good stability under high voltage.