We study rechargeable batteries as multi-functional energy conversation devices beyond chemical energy storage.

The reversible electrochemical reactions are used to enable electrical to mechanical and thermal to electrical conversions.

1. Electrochemical-mechanical conversion

Electrically operated actuators can have applications from robotics to morphing structures. Compared to state of the art actuators such as piezoelectrics, dielectric elastomers, shape memory materials, and ionomer polymer metal composites, electrochemical actuators possess a unique combination of low voltage actuation, “set and forget” capability, large strain (capable of > 100%), and large stress (capable of > 1 GPa). We have previously shown the feasibility of using a battery as an actuator. Initial work with graphite intercalation compounds generated actuators with energy densities on the order of 1 MJ/m3 that rival those of NiTi shape memory alloys. We then extended this concept to electroplating of metals as an actuation mechanism. Our current interest is to greatly expand the chemistry and device architecture choices of electrochemical actuation to achieve unprecedented energy density that can enable a broad range of applications.

A solid-state lithium battery can act as a high-energy density actuator.

Solid-state actuation based on reversible Li electroplating, William Barvosa-Carter, Cameron G. Massey, Geoffrey McKnight, Ping Liu, Smart Structures and Materials 2005: Active Materials: Behavior and Mechanics, edited by William D. Armstrong, Proceedings of SPIE Vol. 5761, p. 90

2. Thermal-Electrochemical conversion

The potential for reversible electrochemical reactions often responds to temperature changes. Such effect can be explored to build thermocells. In these cells, the same reversible reactions are operated at both electrodes but at different temperatures. The generated potential difference enables conversion of thermal to electrical energy. We have shown that the isopropanol-acetone couple shows a record high temperature coefficient of 9.9 mV/K with a great potential to enable high efficiency generation of electricity from low grade heat sources.

The reversible isopropanol-acetone reaction enables waste heat conversion to electricity.

High Seebeck Coefficient Electrochemical Thermocells for Efficient Waste Heat Recovery, Hongyao Zhou and Ping Liu, ACS Appl. Energy Mater., 2018, DOI: 10.1021/acsaem.8b00247