CBE Seminar - Snehashis Choudhury

Rational Design of Nanoporous Polymer Electrolytes and Solid-Liquid Interphases for Lithium Metal Batteries

Abstract

      Advances in the basic science and engineering principles of electrochemical energy storage is imperative for significant progress in portable electronic devices. In this regard, metal based batteries comprising of a reactive metal (like Li, Na, Al) as anode have attracted remarkable attention due to their promise of improving the anode-specific capacity by as much as 10-fold, compared to the current state-of-art Li-ion battery that uses a graphitic anode. However, a persistent challenge with batteries based on metallic anodes, concerns their propensity to fail due to short-circuits produced by dendrite growth during battery recharge, as well as by runaway of the cell resistance due to internal side reactions with liquid electrolytes. In this talk, I will discuss my PhD research that utilizes multiscale transport modeling and experiments to fundamentally understand and to thereby develop rational designs for polymer electrolytes and electrode-electrolyte interphases that overcome these challenges.

There have been several studies in literature dedicated to the prevention of dendrite growth by means of a high modulus physical barrier. However, electrolytes/separators with high mechanical strength tend to have low ionic conductivity, thus limiting their practical use. On the basis of a linear stability analysis of dendrite growth during metal electrodeposition, we have showed that the length-scale on which transport occurs near the electrodes can be as important as electrolyte modulus in stabilizing metals against dendrite formation. In a nutshell, this study concluded that dendrites can be prevented from crossing over to the counter electrode using battery separators with pore-diameter lower than critical (smallest) size of the dendritic nucleate. To evaluate this proposal, we designed cross-linked nanoparticle-polymer composite electrolytes with tunable pore size and quantified the stability of metal electrodeposition in these systems. Direct visualization of electrodeposition using these electrolytes showed remarkable agreement with the theoretical predictions. Furthermore, when operated in a battery, the crosslinked membrane demonstrated stable galvanostatic cycling of lithium metal anodes for several hundreds of hours.

Importantly, these studies showed that while the tendency for battery failure by dendrite-induced short-circuits can be reduced in polymer electrolytes, the issue of capacity-fading as a result of continuous reactions of the metal with liquid electrolyte persists. An additional striking fact in the electrodeposition literature not addressed by the linear stability analysis is that certain metals, including Magnesium, do not form dendrites. In the second part of my talk, I will show how multiscale analysis of transport at electrochemical interfaces enables design of stable solid-liquid interphases for reactive metal batteries. Complementing these studies with analysis of dendrite nucleate formation using Classical Nucleation Theory (CNT), I will explain the observed stability of Mg deposition and will show that solid-liquid interphases enriched with halide salts can stabilize electrodeposition at conventionally unstable metal anodes. The predictions from the coupled DFT-CNT analysis will be validated using both in-situ visualization by means of optical microscopy and ex-situ analysis by impedance spectroscopy. On basis of these studies, solid electrolyte interphase (SEI) designs will be proposed for alkali metal batteries to enable reversible recharging and low overpotentials even with highly reactive liquid electrolytes.

Bio

Snehashis Choudhury is a Ph.D. candidate in the School of Chemical and Biomolecular Engineering at Cornell University. He graduated with a B.Tech degree in Chemical Engineering from National Institute of Technology, India in 2013 and a M.Eng. degree in Chemical Engineering from Cornell University in 2014. His research focuses on the design of nanostructured polymer electrolytes and solid-liquid interphases for rechargeable metal batteries. His thesis, to date, has led to over 25 publications in leading journals of the field as well as three patents. Several of his works have generated significant attention in popular media; featuring in many outlets like Science Daily, Materials Today and Boss Magazine. His recent work on Lithium-Oxygen Battery was regarded to be among the “5 Green Energy Innovations Slated to Shake Up the Energy Industry”.