LiNi0.6Co0.2Mn0.2O2 cathode materials were surface-modified by coating with a dual conductive poly(3,4-ethylenedioxythiophene)-co-poly(ethylene glycol) (PEDOT-co-PEG) copolymer, and their resulting electrochemical properties were investigated. The surface-modified LiNi0.6Co0.2Mn0.2O2 cathode material exhibited a high discharge capacity and good high rate performance due to enhanced transport of Li(+) ions as well as electrons. The presence of a protective conducting polymer layer formed on the cathode also suppressed the growth of a resistive layer and inhibited the dissolution of transition metals from the active cathode materials, which resulted in more stable cycling characteristics than the pristine LiNi0.6Co0.2Mn0.2O2 cathode material at 55 (o)C.

As high‐energy‐density lithium‐ion batteries (LIBs) are being developed, their thermal stability problems become more apparent. In spite of elaborate precautions, exothermic reactions between electrolytes and electrode materials at elevated temperatures can lead to battery explosion. In this study, we introduce a novel flame‐retardant additive with a fluorinated hyperbranched cyclotriphosphazene structure for high‐voltage LIBs. Along with the effective reduction of flammability, it enhances the electrochemical performance by generating a thermally and electrochemically stable solid electrolyte interphase on both the cathode and the anode, which is rare for conventional additives. In full cells composed of a 5 V‐class spinel cathode and a graphite anode with practical‐level mass loading, this new additive demonstrates significant improvements in discharge capacity retention and coulombic efficiency during cycle testing.

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The roles of a partially fluorinated ether (PFE) based on a mixture of 1,1,1,2,2,3,3,4,4-nonafluoro-4-methoxybutane and 2-(difluoro(methoxy)methyl)-1,1,1,2,3,3,3-heptafluoropropane on the oxidative durability of an electrolyte under high-voltage conditions, the rate capability of the graphite and 5 V-class LiNiMnO (LNMO) electrodes, and the cycling performance of graphite/LNMO full cells are examined. Our findings indicate that the use of PFE as a cosolvent in the electrolyte yields thermally stable electrolytes with self-extinguishing ability. Electrochemical tests confirm that the PFE combined with fluoroethylene carbonate (FEC) effectively alleviates the oxidative decomposition of the electrolyte at the high-voltage LNMO cathode and enables reversible electrochemical reactions of the graphite anodes and LNMO cathodes at high rates. Moreover, the combination of PFE, which mitigates electrolyte decomposition at high voltages, and FEC, which stabilizes the anode-electrolyte interface, enables the reversible cycling of high-voltage full cells (graphite/LNMO) with a capacity retention of 70.3% and a high Coulombic efficiency of 99.7% after 100 cycles at 1C rate at 30 °C.

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