Preparation And Electrochemical Properties Of High Density Micro-sized Lithium Titanate Anode Materials

As a zero strain anode material,lithium titanate(Li₄Ti₅O₁₂)has a high charging and discharging platform of 1.55 V,which is safer than the traditional graphite anode material.Li₄Ti₅O₁₂ has three-dimensional lithium ion diffusion channels,stable cycling performance,excellent rate performance and superior cycle performance.The Li₄Ti₅O₁₂can achieve rapid charge-discharge,which has been widely used in batteries for the portable equipment,electric vehicle power and large-scale rapid energy storage.However,its disadvantages are also very obvious,such as lower theoretical capacity and intrinsic conductivity and serious gassing behavior.It is the breakthrough to achieve a large-scale application of Li₄Ti₅O₁₂ with high tap density,small specific surface area.Nanosized Li₄Ti₅O₁₂?LTO?materials enabling high rate performance suffer from a large specific surface area and low tap density lowering the cycle life and practical energy density.Microsized LTO materials have high density which generally compromises their rate capability.Aiming at combining the favourable nano and micro size properties,we present a facile method to synthesize LTO microbars with micropore created by ammonium bicarbonate?NH₄HCO₃?as a template.The compact LTO microbars are in-situ grown by spinel LTO nanocrystals.The as-prepared LTO microbars have a very small specific surface area(6.11 m² g^-1)combined with large tap densities(1.20 g cm^-3)and a high ionic conductivity(5.53×10^-12 cm^-2 s^-1),responsible for their exceptionally stable long-term cyclic performance and superior rate properties.The specific capacity reaches 141.0 and 129.3 mAh g^-1 at the current rate of 10 and 30 C,respectively.The capacity retention is as high as 94%and 83.3%after 500 cycles and 1000 cycles at 10 C.This work demonstrates that,in-situ creating micropore in microsized LTO using NH₄HCO₃ not only facilitate a high LTO tap density,to enhance the volumetric energy density,but also provides abundant Li-ion transportation channels enabling high rate performance.At the same time,this paper also provides a method for preparing micron spindle like lithium titanate by hydrothermal method.The titanium nitride was used as the titanium source.The original spherical precursor was changed into a micron spindle shape under the condition of the hydrothermal treatment and without the help of ethanol.Moreover,the type of lithium sources affects the size of precursor.The spindle shape of the precursor is composed of nanosheets,and the special structure can not maintain the morphology after high temperature treatment.Polyvinylpyrrolidone?PVP?has a positive effect on maintance of the precursor morphology for LTO.By adjusting the different lithium source and PVP content,uniform micron spindle like LTO can be obtained after calcination the precursor in 750 ^oC for 10 h.The charge specific capacities of the materials at 10 C and 30 C are 129.3 and 99.6 mAh g^-1,respectly.The capacity retention at 10 C rate is 72.2%after 500 charge-discharge cycles.