As technology becomes smaller and smaller, the need for micro-energy sources becomes increasingly imperative. One promising technology to address this need is piezoelectrochemical harvesting, a recently identified mechanism to directly convert mechanical energy to electrochemical potential^[1-4]. In piezoelectrochemical (PEC) materials, the chemical potential of ions is affected by an applied stress, and under such circumstances these materials can be used in a thermodynamic cycle to harvest energy, at a relatively slow rate commensurate with the kinetic transport in electrochemical systems. Previous work^[1] has demonstrated that commercial lithium cobalt oxide (LCO) batteries exhibit the PEC effect, as both the lithium cobalt oxide cathode and lithium-intercalated graphite anode are PEC materials. The coupling factor between the change in equilibrium potential and applied mechanical stress has been found to be linear.

In this presentation, we will discuss our research to use piezoelectrochemical energy harvesting to increase the voltage generated from commercial lithium ion batteries. We measured the differential expansion and differential voltage of a lithium ion battery, and used this data to estimate the coupling factor as a function of state-of-charge (SOC). We analyzed the coupling factor for commercial LCO batteries, and found the SOC where the coupling factor was maximized. At this SOC, batteries were placed under a mechanical load to harvest energy. The voltage generated was quantified by measuring the voltage drop across a resistor. To understand how the PEC effect operates in multiple batteries, we wired cells in series and parallel, and performed similar mechanical load experiments. As expected, the PEC voltage can be increased by compressing batteries in series. Increasing the PEC voltage generated would allow the effect to be used in practical applications such as micro-energy devices.

References:

[1] J. Cannarella and C. B. Arnold, “Toward Low-Frequency Mechanical Energy Harvesting Using Energy-Dense Piezoelectrochemical Materials," Advanced Materials, 27, 7440 (2015).

[2] S. Kim, S. J. Choi, K. Zhao, H. Yang, G. Gobbi, S. Zhang, and J. Li, “Electrochemically driven mechanical energy harvesting," Nature Communications, 7, 10146 (2016).

[3] N. Muralidharan, M. Li, R. E. Carter, N. Galioto, and C. L. Pint, “Ultralow Frequency Electrochemical−Mechanical Strain Energy Harvester Using 2D Black Phosphorus Nanosheets,”
ACS Energy Lett., 2, 1797 (2017).

[4] E. Jacques, G. Lindbergh, D. Zenkert, S. Leijonmarck, and M. H. Kjell, “Piezo-Electrochemical Energy Harvesting with Lithium-Intercalating Carbon Fibers,” ACS Appl. Mater. Interfaces, 7, 13898 (2015).