(307a) Understanding and Controlling Pseudocapacitance in Electrochemical Energy Storage: Design of Fast Charging and Low-Temperature Hybrid Battery Systems

Today’s energy storage technologies for electromobility and consumer electronics require batteries beyond lithium-ion that demonstrate faster charging times, wider operating temperature windows, inherent safety, and sustainable materials, which comply with the “Zeitgeist” of a circular economy. Fast-charging batteries that operate reliably and safely over wide temperature windows can be realized by designing materials and architectures that combine battery- and supercapacitor-like properties. These hybrid electrochemical energy storage technologies¹ push the limits of current storage capabilities by allowing high specific energy and fast charging rates, coupled with long cycle life. Recent examples include rechargeable aluminum-graphite^2,3, conducting polymer⁴ and niobium oxide-based⁵ batteries. To merge battery- and supercapacitor-like properties into one system, researchers must understand and control the underlying charge storage mechanisms, which in hybrid systems can be faradaic, capacitive, or pseudocapacitive in different relative contributions. However, to develop design principles aimed at realizing next-generation hybrid energy storage systems, the charge storage mechanisms must be understood and quantitatively disentangled.

Here, I present a rigorous and a physically intuitive framework for pseudocapacitance¹ in terms of competing rates of ion mass transport and heterogeneous electrochemical kinetics. In doing so, I explain why it is a critical ingredient for fast charging and low-temperature batteries. Using this framework, I show how different electrochemical techniques and analysis tools can be used to distinguish and quantify faradaic, capacitive and pseudocapacitive charge storage mechanisms in hybrid systems. Subsequently, I discuss rechargeable aluminum-graphite batteries, leveraging pseudocapacitance, as pioneering technology designed specifically for fast-charging and low-temperature electromobility and space applications. I shed light on the relationships between graphite structure, ion mass transport, and the overall rate of electrochemical aluminum deposition and ion intercalation. This understanding was used to develop design principles for graphite electrode structures and ionic liquid electrolytes that enhance ion mass transport, realizing aluminum-graphite batteries with superior capacity retention and favorable electrochemical kinetics at temperatures down to -40 °C.

Understanding how to quantify and control the relative rates of ion mass transport and heterogeneous electrochemical reactions will open a new design space for emerging hybrid electrochemical energy storage systems. Moreover, this framework can also be applied to other electrochemical technologies including electroplating (e.g., anti-corrosion coatings), energy conversion (e.g., fuel cells), photoelectronics (e.g., integrated solar cell-capacitors), AI hardware (e.g., memristors), and bioelectronics (e.g., bio-FETs and neurointerfaces).

References

[1] T. Schoetz, L.W. Gordon, S. Ivanov, A. Bund, D. Mandler, R.J. Messinger, Disentangling faradaic, pseudocapacitive, and capacitive charge storage: A tutorial for the characterization of batteries, supercapacitors, and hybrid systems, Electrochim. Acta 412 (2022) 140072.

[2] J.H. Xu, T. Schoetz, J.R. McManus, V.R. Subramanian, P.W. Fields, R.J. Messinger, Tunable pseudocapacitive intercalation of chloroaluminate anions into graphite electrodes for rechargeable aluminum batteries, J. Electrochem. Soc. 168 (2021) 060514.

[3] M.C Lin, M. Gong, B. Lu, Y. Wu, D.-Y. Wang, M. Guan, M. Angell, C. Chen, J. Yang, B.J. Hwang, H. Dai, An ultrafast rechargeable aluminium-ion battery, Nature 520 (2015) 324–328.

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