Enhanced Energy Storage in Lithium-Metal Batteries via Polymer Electrolyte Polysulfide-Polyoxide Conetworks

The present article entails a novel concept of storingextra energyin a multifunctional polymer electrolyte membrane (PEM) beyond thestorage capacity of a cathode, which is achieved by so-called "prelithiation" upon simply deep discharging to alow potential range of a lithium-metal electrode (i.e., -0.5to 0.5 V). This unique extra energy-storage capacity has been realizedrecently in the PEM consisting of polysulfide-co-polyoxide conetworksin conjunction with succinonitrile and LiTFSI salt that facilitatecomplexation via ion-dipole interaction of dissociated lithiumions with thiols, disulfide, or ether oxygen of the conetwork. Althoughion-dipole complexation may increase the cell resistance, theprelithiated PEM provides excess lithium ions during oxidation (orLi(+) stripping) at the Li-metal electrode. Once the PEMnetwork is fully saturated with Li ions, the remaining excess ionscan move through the complexation sites at ease, thereby affordingnot only facile ion transport but also extra ion-storage capacitywithin the PEM conetwork. Of particular interest is that the lithiatedpolysulfide-co-polyoxide polymer network-based PEM exhibits a highconductivity of 1.18 x 10(-3) S/cm at ambient,which can also store extra energy with a specific capacity of about150 mAh/g at a 0.1C rate in the PEM voltage range of 0.01-3.5V in addition to 165 mAh/g at 0.2C of an NMC622 (nickel manganesecobalt oxide) cathode (i.e., 2.5-4.6 V) with a Coulombic efficiencyof approximate unity. Moreover, its Li-metal battery assembly withan NMC622 cathode exhibits a very high specific capacity of similar to 260mAh/g at 0.2C in the full battery range of 0.01-5 V, havinga higher Li+ transference number of 0.74, suggestive ofdomination by the lithium cation transport relative to those (0.22-0.35)of organic liquid electrolyte lithium-ion batteries.