Electrode Material Modification And Electrolyte Design For Electrochemical Lithium Storage Batteries

Electrochemical energy storage technologies,especially lithium-ion batteries?LIBs?,have been widely used in many aspects of our daily life and significantly improve our living quality.However,it is much difficult for the currently commercialized LIBs to meet the growing demands of energy storage devices with high safety and energy density,which is driving researchers to urgently develop advanced energy storage systems with high safety performance,high energy density,environmental friendliness and low cost.Among various anode materials,TiO₂-based materials have been considered as one of the most promising alternatives to transitional graphite anode in rechargeable LIBs due to its effective suppression of Li dendrites,high stability with small volume expansion,low cost,and nontoxicity.However,the low Li ion mobility and the poor electronic conductivity for TiO₂-based materials significantly hinder their Li storage performance,which needs to be addressed urgently.Furthermore,as a novel high-energy-density Li storage system,the Li-sulfur?Li-S?battery with low cost and environment-friendly property has incomparable advantages with tranditional LIBs and is expected to be next-generation high-performance Li storage technology.Unfortunately,there are still many huge challenges to achieve a satisfactory performance of Li-S battery caused by the bad electronic conductivity of S cathode,shuttle effect of polysulfides,and growth of Li dendrites.In this paper,nanostructure regulation of electrode materials and electrolyte design were employed to improve the electrochemical Li storage performance.The corresponding electrochemical Li storage mechanisms were deeply revealed by invesgating the influence of the electrode materials and electrolyte on the Li storage process to guide to solve the issues of low safety and low energy density for traditional LIBs.The main research contents are as follows:?1?An aluminum?Al?-reduction method was developed to prepare blue TiO₂ nanoparticles with abundant oxygendeficiency for LIBs.SEM and TEM results demonstrated that the morphology of TiO₂ nanosheets changed from rectangular shape into uniform round or oval nanoparticles and the particle size also decreases after Al reduction,which can aggressively short the Li ion diffusion path and accelerate its diffusion rate.Meanwhile,plentiful oxygen deficiencies were successfully created in the blue TiO₂,which can not only provide more void space in TiO₂ crystal structure and then facilitate the storage and migration of Li ions,but also effectively enhance the electron conductivity of TiO₂.As a result,the as-prepared blue TiO₂ with oxygen deficiency dilivered improved Li storage performance.?2?Blue oxygen deficient anatase TiO₂?H-TiO₂?were successfully synthesized using a facile hydrogenation process which avoided tedious post treatment in Al-reduction method.Further investigation of the size effect demonstrated that the smaller the size of starting TiO₂ nanosheets was,the more oxygen vacancies were created into the nanostructure,which is more beneficial to the transfer and storage of Li ions and electrons;meanwhile,the size of obtained H-TiO₂ was obviously decreased after hydrogenation process,which is propitious to accelerate the diffusion and transfer of Li ions through the active materials.Such a unique synergistic effect from oxygen vacancies and nanoscale sizes promises the optimized H-TiO₂ a high specific capacity of 266 mAh/g after 100 cyclesat 1C.?3?In order to solve the serve issues of shuttle effect,dendritic growth of Li and low safety in Li-S battery,a novel ether-based highly concentrated electrolyte was originally developed via dissolving high concentration of LiFSI salt in dimethoxyether?DME?solvent.In such an extremely high concentration?12 M?,the polysulfides dissolution and migration are significantly weakened,which guarantees effective suppression of shuttle effect of polysulfides;meanwhile,this electrolyte can also promote the formation of LiF-rich SEI layer which remarkably limited the irreversible reaction between Li metal and ether solvent and then effectively suppressesed the formation of Li dendrites to achieve a stable Li anode.As a result,the assembled Li-S battery with such an electrolyte delivered an obviously improved electrochemical performance.Furthermore,such a unique mechanism of highly concentrated electrolyte inspires us to develop a new highly concentrated electrolyte for potassium ion battery,which also exhibits excellent potassium storage performance.?4?In order to reduce the cost of the highly concentrated electrolyte to accelerate its commercial applications in Li-S battery,a novel and inexpensive localized high-concentration electrolyte was rationally designed via introducing an inert cosolvent diluent of fluoroalkyl ether of 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether?OFE?into LiFSI/DME electrolyte system.Experiment results displayed that such a unique electrolyte can maintain stable dendrite-free Li cycling with a high coulombic efficiency?CE?up to 99.3%and completely avoid the dissolution of polysulides via adhusting the content of OFE to efficiently suppress the shuttling effect.As a result,the assembled Li-S battery delivered an excellent electrochemical performance with a high specific capacity?for the S cathode?of 674 mAh/g at 200^thh cycle at 500 mA/g.Furthermore,the Li storage mechanism of the local high-concentration electrolyte is also universal.An excellent Li storage performance can be also obtained when the inert OFE is replaced with another rational inert solvent.