“Anode-free” Zn/LiFePO4 aqueous batteries boosted by hybrid electrolyte

Abstract

Aqueous rechargeable batteries with Zn as anode directly have become prospective alternatives to conventional lithium-ion batteries. However, the growth of zinc dendrites restricts the practical application of Zn anode greatly. In addition, the use of thick zinc foil as anode also increases the total weight of the battery and impacts the whole energy density. Herein, a kind of “anode-free” Zn/LiFePO4 battery (zero-excess Zn) is designed to solve such problems, and corresponding electrolyte is optimized to ensure the electrochemical performance. As a result, ethylene glycol (EG) is added to the aqueous electrolyte with 1.5 M Zn(CF3SO3)2 and 1.5 M LiCF3SO3 as solutes, which not only improves the stability of the electrolyte, but also inhibits the growth of zinc dendrites. And the Zn/Cu batteries with 70 vol% EG/H2O hybrid electrolyte show highly reversible Zn plating/stripping process, in which the average coulombic efficiency (ACE) is as high as 99.77 % at a current density of 1 mA cm−2. In order to better adapt to the “anode-free” Zn/LiFePO4 battery system, the ratio of Zn2+ to Li+ ions in this electrolyte is further optimized, and it’s found that the battery with 2 M Zn(CF3SO3)2 + 1 M LiCF3SO3-70 vol% EG/H2O electrolyte shows the most excellent electrochemical stability, in which the capacity retention rate is 75.2 % after 100 cycles at a current density of 1 mA cm−2. Our work makes it possible for the application of aqueous “anode-free” batteries.