Design,Synthesis And Study Of Electrochemical Properties Of Lithium Titanate And Lithium Titanate/Graphene Nanocomposites

As a anode material for a new generation secondary energy lithium ion battery,spinel lithium titanate(Li₄Ti₅O₁₂)has become a competitive material for social and industrial production.Li₄Ti₅O₁₂ material has many advantages such as reliable safety and reasonable production cost.Although Li₄Ti₅O₁₂ material has almost no volume change in the process of lithium ion intercalation/de-intercalation?ie,"zero-strain"property?,its poor electrical conductivity are severely limit and restrain the promotion for social production applications,especially in high-rate discharge conditions.Therefore,it is particularly important to further improve the electrochemical properties of the material by rationally designing the nanostructure of Li₄Ti₅O₁₂ and related modification studies.Firstly,PVP was introduced during the hydrothermal synthesis process of Li₄Ti₅O₁₂,tetrabutyl titanate as the source of titanium.Then the precursor was obtained under heat treatment.The novel nanosphere/nanosheet structure material with a three-dimensional porous structure was obtained.By studying different amount of PVP as additive,we know the effect factors on material morphology controlling.At the same time,the synthesis of Li₄Ti₅O₁₂ synthesized without PVP is for comparison.Compared with Li₄Ti₅O₁₂ without PVP,the obtained Li₄Ti₅O₁₂nanospheres/nanosheets exhibit excellent electrochemical performance,high specific reversible discharge capacity,and good cycle stability,its capacity can reach up to163.8 mA h g^-1 at a rate of 0.1 C.The capacity of Li₄Ti₅O₁₂ nanospheres/nanosheets also can maintain 115.2 mA h g^-1 at a rate of 5 C after 200 cycles,which keeps92.4%capacity retention.Secondly,we introduce reduced graphene oxide nanosheets?exhibit an excellent conductivity?during the hydrothermal synthesis process of Li₄Ti₅O₁₂ precursor,isopropyl titanate as the source of titanium.Subsequently,Li₄Ti₅O₁₂/reduced graphene oxide was obtained by heat-treating the precursor under inert gas atmosphere.The obtained material contains a three-dimensional porous structure with an average pore size of 2.43 nm,a pore volume of 0.26 cm³ g^-1,and a high specific surface area.At the same time,an excellent electrochemical performance is demonstrated in the subsequent testing process.This can be attributed to the pore structure present in the material not only provides buffer conditions for potential volume changes in the electrode and electrolyte during charge and discharge,but also enables the fully contact between electrolyte and active material.The pore structure can provide an effective path for lithium ion transmission and diffusion.The synergistic effect between Li₄Ti₅O₁₂ and reduced graphene oxide also plays an important role in improving the electrochemical performance of the material.Therefore,the LTO/RGO composite has a high reversible specific capacity(discharge capacity up to 182.2 mA h g^-1 at 0.1 C rate)and stable cycle performance(discharge capacity remains 160.6 mA h g^-1 at the rate of 5 C after 500 cycles).