In situ formed uniform and elastic SEI for high-performance batteries

The solid electrolyte interphase (SEI) is one of the most important components of a battery, and plays a crucial role in the battery performance. Here, a uniform and elastic SEI was constructed by in situ electro-polymerization (ISEP-SEI) of ionic liquid electrolytes. The excellent uniformity of ISEP-SEI and its excellent contact with the substrate could passivate the electrode surface effectively. At the same time, the superior elasticity of ISEP-SEI could enable the electrode to sustain a large number of volume changes during cycling and maintain its structural integrity. Both these features are essential for building high-performance batteries. With ISEP-SEI, the potassium metal symmetric batteries stably cycled for 5000 h with only a piece of separator and no special treatment of the potassium metal surface. Moreover, a Prussian Blue (PB) cathode matched with potassium metal operated for more than 3000 cycles at 1000 mA g−1. The graphite anode, which does not cycle stably in traditional electrolytes, can be operated for more than 1000 cycles after an ISEP-SEI formed on its surface. Importantly, the flame-retardant ionic liquid guaranteed the batteries' safety. The electrochemical performance of full batteries, PB||K batteries at high temperatures, and lithium batteries with ISEP-SEI have also been explored.