Research On The Interface Performance Of High-voltage And High-area-density Lithium Metal Batteries

Recently,high-energy density lithium ion batteries have become the focus in academic and industrial circles.The basic way of achieving high energy density lithium metal batteries is combining the high-specific capacity anode material?i.e.lithium metal?with high voltage cathode material?i.e.lithium cobalt oxide?with increased active mass loading.However,the interfacial instability between the electrodes and the conventional electrolyte causes continuous electrochemical decomposition of electrolyte,dissolution of transition metal ions and uncontrolled growth of Li dendrites,especially at high voltage.Above-mentioned issues correspondingly lead to a severe deterioration of long-term cyclability.Therefore,an essential mode to enhance cycle performance of battery is stabilizing the electrodes/electrolyte interface,for instance,lithium metal anode's surface modification lithium metal anode or using additives.Firstly,a polyethylene oxide?PEO?coating was modified on the surface of lithium metal to stabilize the lithium metal/electrolyte interface and extend the cycle life of 4.55V-class LiCoO₂/Li battery?12 mg/cm²?.The results showed that the PEO coating enabled the battery enhanced cycle stability?76%capacity retention after 90 cycles?.More thorough characterizations?SEM,XPS?unveiled that the PEO coating can effectively avoid direct contact between the electrolyte and the lithium metal anode,which inhibiting the reductive decomposition of the electrolyte on the surface of lithium metal anode and the growth of lithium dendrites,thereby improving the stability of the lithium metal anode.A multi-functional electrolyte was prepared by adding 0.05 M lithium hexafluorophosphate?LiPF₆?to 1 M lithium difluoro?oxalate?borate?LiODFB?/ethylene carbonate?EC?-ethyl methyl carbonate?EMC?electrolyte for 4.55 V-class LiCoO₂/Li battery?12 mg/cm²?.The battery applying this multi-functional electrolyte exhibited excellent long cycle performance?86%capacity retention after 150 cycles?and rate performance at room temperature.More intriguingly,compared with LiPF₆/EC-EMC electrolyte and LiODFB/EC-EMC electrolyte,this electrolyte also dramatically improved long-term cycling stability of batteries at 60 ^oC?80%capacity retention after 150 cycles?and-20 ^oC?100%capacity retention after 15 cycles?.Further investigations unveiled that it is the synergistic effect between LiPF₆ and LiODFB that promoted the generation of a stable CEI,thereby inhibiting cobalt ion dissolution and maintaining integrity of LiCoO₂cathode.Meanwhile,a favorable SEI could be formed on the surface of lithium metal anode,suppressing uncontrolled growth of lithium dendrites.