The Conductivity And Capacitive Property Of Lithium Titanate Nanoarray Electrode Materials

In recent years,supercapacitors,as electrochemical energy conversion and storage devices,have attracted significant attention mainly due to their high power density,long lifecycle.A supercapacitor is consisted of two electrodes,an electrolyte,and a separator.The electrode material is most important component in a supercapacitor.In general,the morphology,structure and electrochemical properties of electrode materials play a key role in the study of supercapacitors.Spinel Li₄Ti₅O₁₂ is regard as one of the most prospective materials for supercapacitors owing to its aero-strain,reversible lithium-ion insertion/extraction reaction,superior cycling stability,structural stability,the outstanding safety performance,low cost and environmentally friendly.Therefore,it has crucial applied research value.However,Low electronic conductivity only with 10^-13 S cm^-1 is the main obstacles for the development and application of Li₄Ti₅O₁₂.Doping,nanostructuring,and surface coating are the three most applied strategies for improving the conductivity of Li₄Ti₅O₁₂ electrodes materials.This paper is devoted to improve the conductivity of Li₄Ti₅O₁₂ electrode material and optimize the electrochemical performance of Li₄Ti₅O₁₂ electrode material.We successfully prepared Li₄Ti₅O₁₂ electrode material with nanotube array structure(Li₄Ti₅O₁₂ NTA).The titanium nitride-lithium titanate nanotube array(TiN-Li₄Ti₅O₁₂ NTA),graphene carbon coated lithium titanate(RGO/C-Li₄Ti₅O₁₂ NTA)and titanium nitride-magnesium doped lithium titanate(TiN-Li_4-xMg_xTi₅O₁₂ NTA)electrode materials were prepared through ion doping,graphene?RGO?,titanium nitride?TiN?surface modification.We investigated the morphology,structure characterization and electrochemical performance of three electrodes.In addition,we also investigated their practical applications in supercapacitors.The research work of this paper are listed as follows:?1?The preparation and electrochemical properties of TiN-Li₄Ti₅O₁₂ NTA electrode material.The TiN-Li₄Ti₅O₁₂ NTA electrode material was prepared through lithiation treatment of anodic TiO2 NTA,annealing treatment and then coating TiO2 sol nitridation treatment in ammonia.TiO2 NTA was formed through anodizing Ti foil and then annealing treatment.Li₄Ti₅O₁₂ NTA was formed through lithiation reaction of TiO2 NTA with LiOH and then annealing treatment.The TiN-L4Ti5O12 NTA electrode materials was formed by coating TiO2 sol on the surface of Li₄Ti₅O₁₂ NTA and then nitriding treatment.The morphology characterization shows that TiN-Li₄Ti₅O₁₂ NTA electrode materials exhibited much rougher surface than Li₄Ti₅O₁₂ NTA when TiN nanoparticles were coated on the top surface of Li₄Ti₅O₁₂.The electrical conductivity was determined to be approximately 39.06 S cm^-1 for TiN-Li₄Ti₅O₁₂ and 14.01 S cm^-1 for N-Li₄Ti₅O₁₂ NTA.So,TiN-Li₄Ti₅O₁₂ NTA with full coating of TiN exhibited higher conductivity than N-Li₄Ti₅O₁₂ NTA with partial incorporation of TiN.The TiN-Li₄Ti₅O₁₂ NTA electrode materials possessed a specific capacitance of 143.83 F g^-1 at a current density of 0.5 A g^-1,at the potential window of-0.4?0.8 V in 0.5 M Li2SO4 solution.It kept high capacitance retention of 82.41%after 1000 cycles at a current density of 3 A·g^-1.It indicates that TiN-Li₄Ti₅O₁₂ NTA could provide the larger specific surface area and ion diffusion,improving its capacitive performance.All-solid-state symmetric supercapacitor using two pairs of TiN-Li₄Ti₅O₁₂ NTA electrode materials and Polyvinyl Alcohol-lithium sulfate polymer?PVA-Li2SO4?solid-state gel electrolytes was conducted at voltage of 2.4 V.The energy density of TiN-Li₄Ti₅O₁₂ NTA supercapacitor was 32.36 Wh kg^-1 at a low current density of 0.5 A g^-1.A small supercapacitor with a size 10 mm×22 mm× 0.5 mm could operate a green LED with the working potential of 2 V,indicating TiN-Li₄Ti₅O₁₂ NTA electrode materials can can be used as an effective supercapacitor materials.?2?The preparation and electrochemical properties of RGO/C-Li₄Ti₅O₁₂ NTA electrode material.The RGO/C-Li₄Ti₅O₁₂ NTA electrode materials were synthesized through calcining under 600? in the argon atmosphere with RGO and PVA as carbon source.Using the high conductivity of RGO can improve the conductivity of Li₄Ti₅O₁₂ NTA,which can enhance capacitance of Li₄Ti₅O₁₂ NTA.The morphology structure and electrochemical performance of RGO/C-Li₄Ti₅O₁₂ NTA electrode materials have been investigated.The morphology characterization shows that the PVA containing RGO are uniformly distributed on the surface of Li₄Ti₅O₁₂ NTA.The RGO/C-Li₄Ti₅O₁₂ NTA electrode materials had a specific capacitance of 210.76 F·g^-1 at a current density of 0.5 A·g^-1,at the potential window of-0.6-0.6 V in 0.5 M Li2SO4 solution.The capacitance retention was 89.99%after 1000 cycles at a current density of 3 A·g^-1.This result indicates that the performance of RGO/C-Li₄Ti₅O₁₂ NTA electrode materials has been obviously enhanced by coating RGO on its surface.All-solid-state symmetric supercapacitor was constructed using two pairs of RGO/C-Li₄Ti₅O₁₂ NTA electrode materials and PVA-Li2SO4 solid-state gel electrolytes.The electrochemical performance was investigated at voltage of of 2.4 V.The power density of RGO/C-Li₄Ti₅O₁₂ NTA electrode materials was improved from 0.6 to 12 kW kg^-1,the energy density was reduced from 39.98 to 12.36 Wh kg^-1 as current density was improved from 0.5 to 10 A g-l.A small supercapacitor with a size 10 mm×20 mm× 0.5 mm could light a LED,presenting reasonable energy storage performance.?3?The preparation and electrochemical performance of TiN-Li_4-xMg_xTi₅O₁₂ NTA electrode materials.The Li_4-xMg_xTi₅O₁₂ NTA was prepared by magnesium doped Li₄Ti₅O₁₂ NTA using magnesium nitrateas as magnesium source.TiN-Li1-xMgxTi5O12 NTA electrode materials was synthesized through coating TiO2 sol on the surface of Li_4-xMg_xTi₅O₁₂ NTA and then nitridation treatment by calcining in the ammonia atmosphere.The SEM shows that the morphology of Li₄Ti₅O₁₂ NTA have no obvious change after Mg2+ doped and the particles coating on the surface of Li_4-xMg_xTi₅O₁₂ NTA after nitridation treatment.The EDS shows that the obvious energy peaks of Ti,O,Mg and N can be observed.The TiN-Li_4-xMg_xTi₅O₁₂ NTA electrode materials had a specific capacitance of 224.58 F·g^-1 at a current density of 0.5 A·g^-1,at the potential window of-0.4?0.8 V in 0.5 M Li2SO4 solution.The capacitance retention of TiN-Li_4-xMg_xTi₅O₁₂ NTA was 89.53%after 1000 cycles at a current density of 3 A·g^-1.This result indicates that electrochemical performancethe of TiN-Li_4-xMg_xTi₅O₁₂ NTA electrode materials has been obviously enhanced by doping of Mg2+ and TiN loading of on its surface.All-solid-state symmetric supercapacitor was constructed using two pairs of TiN-Li_4-xMg_xTi₅O₁₂ NTA electrode materials and PVA-Li2SO4 solid-state gel electrolytes.The electrochemical performance was investigated at voltage of of 2.4 V.The energy density of TiN-Li_4-xMg_xTi₅O₁₂ NTA electrode materials was 42.61 Wh kg^-1 at current density was 0.5 Ag^-1.A small supercapacitor with a size 30 mm×10 mm× 0.5 mm could light a LED,presenting reasonable energy storage performance.