A metal-free all-organic ammonium-ion battery with low-temperature applications

Abstract

Current commercial batteries are mainly metal based, with metal elements in charge carriers and/or electrode materials, which poses potential economic and environmental concerns due to the heavy use of nonrenewable metals. Thus, metal-free batteries present a unique opportunity as sustainable energy storage devices, though the relevant research is still in its infancy. Herein, we present an all-organic metal-free NH₄⁺ ion full battery that can operate at a low temperature of 0 °C, by using polypyrrole (PPy) as the cathode, polyaniline (PANI) as the anode, and 19 m ammonium acetate aqueous solution as electrolyte. For the first time, PPy is demonstrated as a high-capacity host material for both NH₄⁺ and K⁺ storage, when cycled in water in salt electrolytes (WiSEs). When tested in a three-electrode cell containing 25 m NH₄CH₃COO electrolyte, PPy exhibits an impressive capacity of 125 mA h g⁻¹ at a specific current of 1 A g⁻¹ and retains 43.61 mA h g⁻¹ at 25 A g⁻¹. Additionally, a full battery is assembled using the PPy cathode and PANI anode coupled with 19 m NH₄CH₃COO WiSE. This battery is found to deliver a capacity of 78.405 mA h g⁻¹ at 25 °C and 49.083 mA h g⁻¹ at 0 °C with a capacity retention of 71.83% after 200 cycles, demonstrating its potential for operations at low temperatures. Additionally, the physiochemical properties of NH₄⁺-based WiSEs are examined by Raman and nuclear magnetic resonance (NMR) spectroscopies, to explore their electrochemical behaviors and the fundamental effect of salt concentration on the electrolyte characteristics. This study presents the first non-metal battery with potential for low-temperature applications and opens the door to future metal-free electronics that would generate long-term benefits to the environment.