Polycationic Polymer Layer for Air-Stable and Dendrite-Free Li Metal Anodes in Carbonate Electrolytes.

The short cycle life and safety concerns caused by uncontrollable dendrite growth have severely hindered the commercialization of lithium metal batteries. Here, a polycationic and hydrophobic polymer protective layer fabricated by a scalable tape-casting method is developed to enable air-stable, dendrite-free, and highly efficient Li metal anodes. The polymeric cations of poly(diallyl dimethyl ammonium) (PDDA) provide an electrostatic shielding effect that unifies Li+ flux at the surface of the Li anode and promotes a homogeneous Li plating, while the bis(trifluoromethanesulfonyl)imide (TFSI) anions bring hydrophobic characteristics and improve moisture stability. The accumulated TFSI anions by the polycationic film also facilitate the formation of a stable solid electrolyte interphase (SEI). Steady Li plating/stripping in the carbonate electrolyte can be achieved under a high areal capacity of 10 mAh cm-2 for 700 h with Li utilization efficiency up to 51.6%. LiNi0.8 Mn0.1 Co0.1 O2 and LiFePO4 cells using the modified anode exhibit much improved electrochemical performance compared with the bare Li counterpart. Moreover, ultrasonic imaging shows no gas generation in the modified Li/LiFePO4 pouch cell. Mechanism investigation demonstrates the stable SEI and homogeneous Li deposition derived by the polycationic layer.