Additives For Li Metal Anode And The Researcn On Li-O₂ Battery

Li metal battery(LMB)has proved to be the most promising candidates for the next-generation batteries,owing to the nature advantage of Li metal such as its low potential comparted to the standard hydrogen electrode and low density and mass.Li-metal battery has the highest thereotical energy density among all the chemical systems,which can satisfy the demand for higher energy density of electronic storage devices.However,the drawbacks of Li metal anode are distinct,mainly on the formation of lithium dendrite.The formation of lithium dendrite may induce safety issues.Additives can somewhat improve the deposition of Li metal through surface-formation mode,and form a SEI film between Li metal and electrolyte.The SEI film is ionic conductive and electronic insulative,which can prevent Li metal react with electrolyte directly.Additives with a low amount will be depleted during cycling,and then will expose Li metal to electrolyte companying with side reactions.Additives as solvents can continuously form SEI during cycling,leading to higher coulombic efficency and cycleability of Li-Cu batteries.1M LiTFSI-VEC has the best Li-Cu performance,which can work at a current density of 1 mA/cm2 with a fixed area capacity of 1 mAh/cm2 and the cycle numbers achieve 600 cycles.SEM images show that morphology of Li-metal are low long-diameter-ratio grains,with little dendrite or whiskers.1M LiTFSI-VEC has a good performance when LCO、NCA and LFP as cathode even using 20um Li metal anode.PFPN is not only a fire retardant but also a bifunctional additives that can improve the performance of high-voltage cathode.When using with VC or FEC additives,PFPN can enhance the ionic conductivity of SEI formed by reduction of VC or FEC additives.With the synergistic effect of PFPN and VC,the Li-Cu batteries have better coulombic efficiency and cycle performance.According to calculations,Li-O2 battery is the highest energy density battery that has a therotical value of 3505 Wh/kg.A novel transparent and soft quasi-solid-state electrolyte(QSSE)was proposed and fabricated,which consists of ionic liquid(PYR14TFSI)and nano-fumed silica.The QSSE demonstrates high ionic conductivity of 4.6×10-4 S/cm at room temperature and wide electrochemical stability window of over 5V.The Li-O2 battery using such quasi-solid-state electrolyte exhibits a low charge-discharge overpotential at the first cycle and excellent long-term cyclability over 500 cycles.LiI is reported to be a redox mediator for Li-O2 batteries with good catalyzing capability,which can reduce the charge overvoltage below 3.5V and increase the round-trip efficiency.Compared to LiI,KI has better discharge capacity,and the same catalyzing functions of LiI.KI may be a better redox mediator for Li-O2 batteries.However,the cycling of Li-O2 battery with redox mediator is less than 30 cycles.After adding a protective layer of QSSE between Li metal anode and electrolyte,the Li-O2 battery can successfully discharge and charge more than 100 cycles.Because the QSSE prohibit the corrosion of Li metal anode from electrolyte and prevent the oxygen and water permeation.