Solid State Batteries and the Mechanical Properties of Lithium

Thursday, 5 October 2017: 16:00
National Harbor 8 (Gaylord National Resort and Convention Center)
A. Masias (University of Michigan, Ford Motor Company) and J. Sakamoto (University of Michigan)
The current revival of electrified vehicles seen in recent years has been enabled by significant advances in lithium ion batteries. This technology has progressed steadily at approximately 8% per year improvement in specific energy (Wh/kg). The achievement and maintenance of this specific energy growth rate is the result of massive, global progress in battery research, development and manufacturing. However, to promote the rapid displacement of petroleum fuels from the transportation sector, the current evolutionary growth in battery energy may be insufficient.

Amongst candidate next generation battery approaches, solid state (SS) is one of the most versatile and promising technologies. SS batteries can enable improvements in specific energy mainly by allowing for the use of high energy (due to its low electronegativity and high capacity) lithium metal anodes. A SS separator of comparable dimensions as a conventional polyolefin separator could lead to ~50% improvement in cell energy density by enabling metallic lithium anodes [1]. However, elemental lithium is pyrophoric & difficult to stabilize owing to its strongly reactive nature, and as a result its use as a reliable rechargeable battery electrode has proven challenging despite research efforts for more than 50 years. The development of a SS electrolyte material that could introduce lithium metal anodes would provide rechargeable batteries with a step change improvement in specific energy, leading to longer range EVs due to lighter/smaller batteries.

The research and selection of a solid state material requires balancing many different and often competing requirements simultaneously, which no one material can satisfy currently. Additionally, some SS electrolytes have shown a tendency to allow for lithium dendrites to penetrate their structure once a critical charge density (CCD) has been reached [2]. The role lithium's mechanical properties play in the dendrite growth mechanism is poorly understood and is the focus of this work. The literature features limited reports of lithium's elastic modulus, with tension values as low as 1.9, commonly referencing bending values of 5.0 and single crystal calculations as high as 11.5 GPa [3,4,5]. This work will explore further the mechanical properties of lithium in context of the actual SS battery environment where additional properties such as creep may dominate.

[1] McCloskey, B. et al. J Phys. Chem. Lett. 6 (2015) 4581-4588.
[2] Sharafi, A. et al. J. Power Sources, 302 (2016) 135-139.
[3] Schultz, R. Technical Report FERMILAB-TM-2191. (2002).
[4] Bridgeman, P. Proc Am Acad Arts Sci., 57 (1922) 41-66.
[5] Robertson, W. et al. Phys. Rev., 117 (1960) 440-442.