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.
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.
Here, we report the first electrochemical assessment of organophosphonate-based compound as a safe electrode material for lithium-ion batteries, which highlights the reversible redox activity and inherent flame retarding property. Dinickel 1,4-benzenediphosphonate delivers a high reversible capacity of 585 mA h g with stable cycle performance. It expands the scope of organic batteries, which have been mainly dominated by the organic carbonyl family to date. The redox chemistry is elucidated by X-ray absorption spectroscopy and solid-state P NMR investigations. Differential scanning calorimetry profiles of the lithiated electrode material exhibit suppressed heat release, delayed onset temperature, and endothermic behavior in the elevated temperature zone.
The Inside Cover Picture illustrates a new flame‐retarding compound, which stabilizes the electrode–electrolyte interface. This benefits high‐voltage Li–Ni–Mn–O composite cathodes that suffer from decomposition of electrolytes and are vulnerable to explosions under abuse conditions. More details can be found in the Full Paper by S. Y. Hong, N.‐S. Choi, and co‐workers on page 913 in Issue 6, 2016 (DOI: 10.1002/celc.201600025).
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