Anion secondary batteries utilizing a reversible BF4 insertion/extraction two-dimensional Si material

The development of lightweight, long lasting Li-ion batteries is of great technological importance for hybrid and plug-in hybrid electric vehicles, as well as for power grid applications. Here we report an alternative approach to the use of Li cations, based on the fabrication of BF4 anion rocking-chair-type secondary batteries. For the anode material, we report a Si-based compound, [Si10H8(OCH2CH2NH(CH3)2)2](BF4)2, which is capable of reacting with two BF4 anions per formula unit at a potential of 1.8 V, giving a reversible capacity of 80mA h g−1. This anion battery also showed superior performance under thermal abuse compared with Li-ion batteries. Furthermore, the anion battery is operable at −30 °C, a temperature at which Li-ion batteries are generally not operable because Li-ions are solvated by coordination with basic organic molecules around this temperature.