Research On Synthesis,modification And Electrochemical Performance Of Spinel Li₄Ti₅O₁₂

The spinel lithium titanium oxide(Li₄Ti₅O₁₂,LTO)is regarded as a most promising candidate due to its“zero-strain”characteristic,excellent cycle stability and high safety property.Nevertheless,the Li₄Ti₅O₁₂2 has poor electrical conductivity which greatly limits its ptactical application.In this paper,we use the hydrothermal route to fabricate the pure spinel LTO.Meanwhile,in order to improve the electrical conductivity of LTO,the reduced graphene oxide?rGO?and glucose were chose as the carbon sources to modify and coat the LTO in aim to promote the rate performance of spinel LTO.Firtly,we utilized the hydrothermal route to fabricate the pure spinel LTO and explored the influences of the hydrothermal time,calcination temperature and calcination time on the morphology characteristics and electrochemical properties of LTO.The results show that the sample was first hydrothermal treatment for 36h at180°C and then calcinated for 6h at 600°C which exhibited best electrochemical performance.The experiment results show the LTO sample has irregular nanosheets varied in the size of 100–500nm,uniform spatial distribution and good crystallinity.The discharge capacity can reach 129.2mAh g^-1 at 10C and remiain 95%even after200 cycles at 1C.Considering the spinel LTO and reduced graphene oxide both have own unique natural performance advantages separately,so we utilized a facile hydrothermal route to fabricate a composite which the spinel LTO grown on the rGO layers.The study reflects that the small ratio of rGO?about 6.2wt%?plays a key role in the improvement to the original morphology structure and rate performance of LTO.The discharge capacity of LTO/rGO-6.2wt%composite at 20C can reach 160.1mAh g^-1and remain 154.5mAh g^-1 even after 500 long cycles with the 96.5%capacity retention,showing a good rate performance and fine cycle stability.Owing to the complex synthesized process and the exorbitant price of some carbon materias,we use more commonplace,less-expensive glucose as carbon source to build well conductive LTO/C composite via a hydrothermal approach.The amorphous carbon layer encapsulated firmly in LTO precursor during the process of preparation which is not only to enhance the electronic conductivity of LTO,but also to hinder the growth of LTO particles to get relatively smaller size,thus reducing the Li⁺diffusion pathway.The experiment results show the 3.74wt%corbon-coated composite has the ideal morphology characteristics and the best electrochemical performance.The capacity retention of LTO/C-3.74wt%composite was 93.4%at 1C after 500 cycles and 74.2%even after 3000 ultralong cycles at 5C,exhibiting fine cycle stability.What is more,the discharge capacity of composite can reach 131.7mAh g^-1 even at the high rate of 50C,which is apparently superior than pristine LTO(58.9mAh g^-1),showing a good rate performance.