Research On Li₄Ti₅O₁₂ And Its Silicon Nanocomposite As Anodes For Lithium-ion Batteries

Lithium-ion batteries（LIBs）exhibite numerous advantages,including large capacity,long life,and small self-discharge,which have been widely applied in portable electronic devices,electric vehicles,and grid energy storage.However,the commercial lithium-ion batteries based on graphite as anode materials have the problems of small specific capacity,low rate and poor safety,which limit their further development in power and energy storage batteries.Therefore,the development of safe anode materials with large capacity,high rate and excellent recyclability is of great significance for the new generation of lithium-ion batteries.Previous studies have shown that lithium titanate(Li₄Ti₅O₁₂)is a safe material with high rate and good recyclability,but its capacity is too low;silicon（Si）material has large capacity,but its recyclability is too poor.If the two materials can be effectively compounded,it is expected to obtain high performance lithium-ion battery anode materials.The green and environmentally friendly liquid phase method is an effective process for uniform and controllable preparation and compounding of materials.Therefore,this paper focuses on the liquid-phase preparation and composite process,exploring the new formulation of Li₄Ti₅O₁₂ and its in-situ composite with Si to obtain the Si@Li₄Ti₅O₁₂ with both excellent electrochemical properties.The main contents and conclusions of the research are as follows.（1）Study on the preparation of lithium peroxotitanate complexs and precursors by a new formulation in liquid phase method.The lithium peroxotitanate complexs were successfully prepared by using low-cost and environment-friendly organic metatitanic acid and soluble lithium acetate.The effects of different bath temperature and concentration on the decomposition reaction and product morphology of the complex system were analyzed.The experimental results show that,the precursor was facilely prepared by decomposing reaction at 60℃and atmospheric evaporating concentration of the lithium peroxotitanate complex.And the powder is more uniform and delicate when the overall concentration is higher.（2）Self-assembly preparation and electrochemical properties of Li₄Ti₅O₁₂ nanomaterials.The effects of molar concentration of lithium-titanium,calcination time and dissolution of metatitanic acid on the product were studied.The ideal pure Li₄Ti₅O₁₂ nanomaterial was obtained by calcining precursor,with lithium-titanium molar concentration of 0.4mmol ml^-1-0.5 mmol ml^-1 at 600℃for 5 h,Based on this,the growth mechanism of Li₄Ti₅O₁₂ can be described as“dissolution–decomposition–self assembly–crystallization”.Moreover,the electrochemical properties of Li₄Ti₅O₁₂ nanomaterials showed a high rate performance(the specific capacity of 157 mAh g^-1 at 4000 mA g^-1),and an excellent cycling reversibility(still maintaining 95.2%of discharge capacity after 400 cycles at 500 mA g^-1).（3）In-situ composite and the electrochemical properties of Si@Li₄Ti₅O₁₂ core-shell nanomaterials.The synthesis of Si@Li₄Ti₅O₁₂core-shell nanocomposite was followed in-situ self-assembly reaction,subatmospheric evaporation fast concentration and calcination.The subatmospheric evaporation concentration is the key to obtain ideal Si@Li₄Ti₅O₁₂ core-shell nanocomposites.The rapid concentration avoids side effects,thus protecting the Si core and successfully obtaining the pure Li₄Ti₅O₁₂ coating.The as-prepared Si@Li₄Ti₅O₁₂ nanocomposite anode displayed a large specific capacity(1756 mAh g^-1 at 500 mA g^-1),a high rate capability(specific capacity of 620 mAh g^-1 at 4000 mA g^-1),and an outstanding cycling stability(reversible specific capacity of 883 mAh g^-1after 150 cycles)...