Preparation And Lithium/Sodium Storage Performance Studies Of Lithium Titanate And Cobalt Sulfide Anode Materials

Lithium-ion battery?LIB?has been applied to electronic products,electric vehicles,aerospace,military defense and large-scale power storage,due to the features of light weight,high specific capacity/energy,long cycle life,safety and environmental benignity.Sodium ion battery?SIB?,which is similar to LIB,can greatly alleviate the contradiction between the limited lithium resources and high costs of LIB and growing market demand.Anode material plays a decisive role in enhancing the electrochemical lithium/sodium storage capacities of LIB and SIB.The low operating voltage of graphite anode is liable to cause a safety hazard and it is not suitable for graphite to transport Na+ with a larger radius?1.02 ??.It is important to develope new anode materials with betterer comprehensive performance and allowing reversible insertion/extraction of Li+/Na+.With unique advantages of safely operation,"zero stress" and so on,cubic spinel phase lithium titanate(Li₄Ti₅O₁₂)have been favored by the researchers.Owing to higher theoretical capacity,hexagonal cobalt sulfide?Co S?has gradually catched the sights of people as well.In this paper,dual properties of lithium/sodium storage of Li₄Ti₅O₁₂ and Co S as anodes were studied by approaches of doping,carbon coating and graphene integrating,and the major jobs are as follows.???Highly-crystalline lanthanide?Ln3+=Gd3+,Y3+and La3+?doped and carbon encapsulated Li₄Ti₅O₁₂?designated as C-Ln-LTO?nanosheets as an anode material for SIB are synthesized on large scale via a facile hydrothermal reaction followed by annealing treatment.Benefiting from synergistic effect of Ln3+doping and carbon encapsulation,sheet-like morphology and spinel-crystal structure of LTO are maintained,while electrode reaction kinetics and structural stability during Na+insertion/extraction are promoted.When evaluated as an anode material for SIB,the C-Ln-LTO nanosheets exhibit initial discharge specific capacity of 198 m Ahg^-1 at0.1C,enhanced rate capability of 141 m A h g^-1 at 2C and superior cyclic performance of 122 m A h g^-1at 2C after 150 cycles.???A composite consisted of highly-crystalline Li₄Ti₅O₁₂ nanosheets and rGO as anode materials for both LIB and SIB is prepared via electrostatic screening interaction in aqueous solution containing NH4+/HCO3-followed by annealing.The well-assembled composites exhibit pseudocapacitance behavior due to synergistic effect between r GO layers and LTO nanosheets,leading to interface ion storage and rapid charge transportation.Meanwhile,increased conductivity and diffusivity greatly promotes the electrode kinetics during redox reaction.Benefited from these properties,the prepared composites exhibit excellent discharge specific capacity(²10/185 m A h g^-1 for LIB/SIB at 1C/0.1C),improved rate capability(¹60/99 m A h g^-1 for LIB/SIB at 30C/10C)and comparable cyclic performance(¹75/134 m A h g^-1for LIB/SIB at10C/2C after 200/300 cycles).???Unique microsphere of carbon encapsulated highly-crystalline Co S nanosheets?designated as C-Co S NSs?as anode materials for LIB/SIB are prepared via a hydrothermal reaction followed by annealing.SEM images show that smaller Co S nanosheets covered by carbon layer cross each other to form larger microspheres,building-up a unique and stable high conductive structure.Thanks to the improvement in electron and ion transport during electrochemical reactions,the prepared sample exhibits outstanding Li/Na dual storage performances.As regard of LIB,reversible capacities of 548.7 and 442.7 m A h g^-1after 300 and 200 cycles at 1 and 5 A g^-1respectively,are delivered for C-Co S anodes;as SIB anode materials,C-Co S has a reversible capacity of 462.2 m A h g^-1 after 300 cycles at 1 A g^-1 and a reversible capacity of 342.8 m A h g^-1after 200 cycles at 5 A g^-1.