Research On The Interfacial Reactivity Between Li₄Ti₅O₁₂ And Electrolyte

Spinel Li₄Ti₅O₁₂（LTO） exhibits excellent reversibility due to its zero volume changeduring charge/discharge cycles. LTO also demonstrates excellent thermal stability andcyclic performance, making it as a potential anode material for high power lithium ionbatteries. Extensive studies have hitherto been carried out and different materialmodifications have been proposed with varied success, including carbon coating, metaland non-metal ion doping, hybridization with carbon and metal powders, reduction inLTO particle size.These methods inhance the conductivity and high rate chargeperformance. However, Li₄Ti₅O₁₂power batteries have not been applied widely due totheir serious inflatable behavior, which attract great attentions from battery industry andscientists.It is previously misunderstood that an SEI film cannot be formed on the surface ofLTO electrodes when cycled above1V because the electrolyte solution can only bereduced below1V. As such, the formation of SEI films has been neglected with littleattention so far. However, we demonstrated in this study that an SEI film could also beformed on the surface of LTO electrodes when cycled at1-3V. The interfacial reactionbetween LTO and the electrolyte solution was responsible for the observation, greatlyaffected by the morphology of LTO powders. The formation mechanisms and the roleof the SEI films during the cyclic tests were successfully identified. Particular emphasiswas placed on evaluating the effects of SEI films on the rate and cyclic performance ofLTO electrodes.The reasons that initiate the gassing behavior are unclear. PF5, as a strong Lewis acidof decomposition product of LiPF₆, is easily regarded as a major reason for gassing inthe presence of trace amount of water. However, we found that the gassing reactions,which include decarboxylation, decarbonylation and dehydrogenation reactions ofsolvents, are initiated not by PF5, but by LTO, especially by the outmost surface of LTO（111） plane. The interfacial reactions between LTO and electrolyte generate H2, CO2and CO, which are the main components for the gassing behaviors. It is found that thegassing reactions involve the plane transformation of LTO from （111） to （222） andformation of （101） plane of anatase TiO₂. The outmost surface Li⁺and O^2-ions of LTO （111） plane are taken away from LTO by interfacial reactions.Constructing a barrier layer is believed as an effective strategy to restrain theinterfacial reaction of LTO and surrounding electrolyte, and carbon coating around LTOis proved as an ideal approach to depress the gassing of LTO based battery. The coatedcarbon, together with a formed stable SEI film around the coating can jointly separateLTO from the surrounding electrolyte and prevent the interfacial gassing reactions ofLTO with electrolyte. The modification of the surface termination of LTO is simple yetvery effective strategy，which can depress the gassing behaviors of LTO based battery,which would greatly promote the vast applications of LTO materials and batteries infuture.