Spontaneous Proton Chemistry Enables Ultralow-temperature and Long-life Aqueous Copper Metal Batteries.

Aqueous copper metal batteries with acidic electrolytes are regarded as promising candidates for low-temperature energy storage, benefiting from fast kinetics of protons and acid resistance of copper. Here, a Cu(BF4 )2 electrolyte that spontaneously generates protons is developed for ultralow-temperature copper metal batteries. Systematic studies demonstrate that the hydrolysis of BF4 - generates more protons, rendering the Cu(BF4 )2 among the most effective aqueous electrolyte capable of breaking hydrogen bonds in water molecules. This electrolyte endows a polyaniline/Cu battery to deliver a short charging time of 21 s and a charge/discharge capability of up to 10 A g-1 at -30 °C, along with a high discharge specific capacity of 70 mAh g-1 and a supercapacitor-comparable power density of 3000 W kg-1 . Furthermore, it can exhibit a long and stable cycling lifespan over 10 000 cycles at -50 °C and works well at -70 °C. This work provides an opportunity for intrinsically acidic electrolytes.

Cooperative Chloride Hydrogel Electrolytes Enabling Ultralow-Temperature Aqueous Zinc Ion Batteries by the Hofmeister Effect.

Aqueous zinc ion batteries have high potential applicability for energy storage due to their reliable safety, environmental friendliness, and low cost. However, the freezing of aqueous electrolytes limits the normal operation of batteries at low temperatures. Herein, a series of high-performance and low-cost chloride hydrogel electrolytes with high concentrations and low freezing points are developed. The electrochemical windows of the chloride hydrogel electrolytes are enlarged by > 1 V under cryogenic conditions due to the obvious evolution of hydrogen bonds, which highly facilitates the operation of electrolytes at ultralow temperatures, as evidenced by the low-temperature Raman spectroscopy and linear scanning voltammetry. Based on the Hofmeister effect, the hydrogen-bond network of the cooperative chloride hydrogel electrolyte comprising 3 M ZnCl2 and 6 M LiCl can be strongly interrupted, thus exhibiting a sufficient ionic conductivity of 1.14 mS cm-1 and a low activation energy of 0.21 eV at -50 °C. This superior electrolyte endows a polyaniline/Zn battery with a remarkable discharge specific capacity of 96.5 mAh g-1 at -50 °C, while the capacity retention remains ~ 100% after 2000 cycles. These results will broaden the basic understanding of chloride hydrogel electrolytes and provide new insights into the development of ultralow-temperature aqueous batteries.