A Redox-Active Organic Cation for Safer Metallic Lithium-Based Batteries

Abstract Safety concerns have severely impeded the practical application of high-energy-density lithium-based batteries. Dendrite growth and overcharging can lead to particularly catastrophic thermal failure. Here we report an organic cation, trisaminocyclopropenium (TAC), as a bi-functional electrolyte additive to suppress dendrite growth and offer reversible overcharge protection for metallic lithium-based batteries. During the Li plating process, TAC cations with aliphatic chains can form a positively charged electrostatic shield around Li protrusions, repelling the approaching Li+ and thereby attaining a more uniform plating. A two times longer cycle life of 300 h at 1 mA cm−2 is achieved in a Li|Li symmetric cell in comparison with the control. During the overcharging process, the redox-active TAC can repeatedly shuttle between two electrodes, maintaining the cell voltage within a safe value. A solid protection of 117 cycles (∼1640 h) at 0.2 C with a 100% overcharge is achieved in a LiFePO4/Li4Ti5O12 cell. This study sheds fresh light on the ability of organic cations to build safer batteries. Trisaminocyclopropenium cation was applied as a bi-functional electrolyte additive to build safer metallic lithium-based batteries. The cation can have a electrostatic shielding effect on Li protrusions, facilitating a dendrite free Li plating process. Additionally, the cation can shuttle between two electrodes during overcharge, limiting the cell voltage to less than the molecule's redox potential.