pH modulation for high capacity and long cycle life of aqueous zinc-ion batteries with β-MnO2 /3D graphene-carbon nanotube hybrids as cathode

Abstract

With the continuous development of new energy application technology, there is an increasingly urgent need for the safety and affordability of new energy storage products. In recent years, aqueous zinc-ion batteries based on mild aqueous electrolytes have garnered widespread attention as a potential replacement for traditional lithium-ion batteries. However, the limited capacity and low operating voltage of aqueous zinc-ion batteries restrict their widespread application. For this reason, sulfuric acid was added to the electrolyte, which effectively promotes the two-electron conversion of MnO₂/Mn²⁺ during the discharge process. This enhancement results in the high-voltage segment of the batteries' discharge phase offering a higher reversible specific capacity. The results showed that the batteries with 0.1 M H₂SO₄ added to the electrolyte had a reversible discharge specific capacity of up to 536.07 mAh·g^-1 at a current density of 100 mA·g^-1. The activated batteries exhibited a reversible specific capacity of 85.11 mAh·g^-1 even at a high current density of 1 A·g^-1. Furthermore, the capacity retention rate after 1,000 cycles was 88.3%. Moreover, the activation rate of the batteries was faster with the addition of H₂SO₄, and the average operating potential increased compared to the batteries without H₂SO₄ in the electrolyte. This provides an effective solution for the practical application of aqueous zinc-ion batteries in power grids.