(351c) Revealing the Dynamics of Electrochemical Interfaces in Lithium Batteries

Electrochemical interfaces, spanning across a few nanometers, are the place active species meet, multiple physics impinge, and lots of uncertainties hide. Exploring such uncertainties will facilitate the rational design of high-performance energy conversion and storage materials and systems. This presentation summarizes the candidateâ??s original contributions in three different areas. (i) In porous electrodes of carbon-coated LiFePO₄ nanoparticles, the dynamic process consists of lithium ion insertion from the liquid electrolyte to the interstitial vacancies in the solid particles and electron transfer from the carbon coating to the Fe site of the solid particle. Besides the usual factors like concentration and temperature, the kinetics is largely affected by the phase transformation process inside the solid particles, which results in a particle-by-particle reaction pathway throughout the porous electrode. Modeling the dynamics at both the single-particle [1] and many-particle [2] scales enables the extraction of local reaction rates, which can be accurately explained by the Marcus theory [3]. (ii) In lithium metal anodes, whisker-like electrodeposits always develop by mechanisms that still remain elusive. Experimental results in novel capillary cells reveal that the insulating solid-electrolyte interphase (SEI) layer on lithium metal is the reason of the root-growing whiskers, which interweave with each other to form a mossy structure and can be blocked by nanoporous ceramic separators [4]. Only at the diffusion limitation, would tip-growing dendritic lithium start to grow and penetrate the nanopores to short the cell [5]. The safety of rechargeable lithium metal batteries can therefore be increase by using concentrated liquid electrolyte and nanoprous ceramic separators. (iii)Prototypes of energy-dense lithium-bromine/oxygen fuel cell using a liquid-solid-liquid hybrid electrolyte [6], and the degradation of the key component, the glass ceramic solid electrolyte, will also be discussed [7].

References

1. Peng Bai, Daniel A. Cogswell, Martin Z. Bazant. Suppression of phase separation in LiFePO4 nanoparticles during battery discharge. Nano Letters, 11(11): 4890-4896 (2011).
2. Peng Bai, Guangyu Tian. Statistical kinetics of phase-transforming nanoparticles in LiFePO4 porous electrodes. Electrochimica Acta, 89: 644-651 (2013).
3. Peng Bai, Martin Z. Bazant. Charge transfer kinetics at the solid-solid interface of porous electrodes. Nature Communications, 5:3585 (2014).
4. Peng Bai, Ju Li, Fikile Brushett and Martin Z. Bazant. Lithium growth mechanisms in liquid electrolytes. In revision.
5. Peng Bai, Miao Wang, Fikile Brushett and Martin Z. Bazant. Interactions between lithium growths and nanoporous ceramic separators: blockage versus penetration. To be submitted.
6. Peng Bai, Venkat Viswanathan and Martin Z. Bazant. A dual-mode rechargeable lithium-bromine/oxygen fuel cell. Journal of Materials Chemistry A, 3: 14165-14172 (2015)
7. Peng Bai and Martin Z. Bazant. Performance and degradation of a lithium-bromine rechargeable fuel cell using highly concentrated catholytes. Electrochimica Acta, 202: 216-223 (2016).