Enabling Effective Thiocyanogen/Thiocyanate Couple for the Zinc─Pseudohalogen Battery
Kun Gao, Shuning Li, Jiajia Liu, Tian Yang, Wenjing Yu, Shidi Ju, Shaohua Zhang, Zhipan Zhang
Abstract
Abstract Pseudohalogens are neutral molecules with similar chemical properties to halogens that can be utilized in zinc batteries. For instance, thiocyanogen, (SCN) 2 , features a fairly positive standard redox potential when coupled with SCN − (0.77 V vs SHE, standard hydrogen electrode) and serves as a feasible cathode to pair zinc anode. However, the severe hydrolysis of (SCN) 2 and generation of trithiocyanate ion, (SCN) 3 − , and parathiocyanogen, (SCN) x , seriously undermine the couple reversibility, leading to a poor electrochemical performance. Herein, by selecting a water‐in‐salt ZnCl 2 electrolyte and an oxygen‐enriched carbon electrode, an effective (SCN) 2 /SCN − electrochemistry is activated. On the one hand, intensive ion coordination decreases free H 2 O and SCN − contents to suppress detrimental hydrolysis of (SCN) 2 and generation of (SCN) 3 − and (SCN) x . On the other hand, high electronegativity of oxygen‐containing functional groups facilitates the adsorption of in situ generated (SCN) 2 and reduces side reactions. As a result, Zn─(SCN) 2 battery can be charged–discharged for 500 cycles and exhibits high capacities (479 mAh g −1 based on the mass of (SCN) 2 or 1.73 mAh cm −2 based on device area) and remarkable energy densities (644 Wh kg −1 or 2.216 mWh cm −2 ). This first reported Zn─(SCN) 2 battery pioneers the zinc─pseudohalogen battery and raises it to a higher level among aqueous batteries.