The transition to vehicle electrification has generated high demand for batteries with higher energy storage capacity per mass and volume than achieved by current Li-Ion batteries. The typical graphite||layered oxide battery used commercially today allows for approximately 150 Wh.kg-1 and 250 Wh.L-1 falling short of targets of 350 Wh.kg-1 and 750 Wh.L-1 cell level targets put forth by the United States Advanced Battery Consortium. Silicon (Si) has emerged as a promising high-capacity (3579 mAh.g-1 by formation of Li15Si4) which could realize 300 Wh.kg-1 and 800 Wh.L-1 Li-Ion cells and replace the usual graphite (372 mAh.g-1 by formation of LiC6). However, Si as anode is confronted with short cycle life which fundamental studies have attributed to an unstable solid electrolyte interphase (SEI) and large volume expansion/contraction (~300%) leading to pulverization and loss of electrical contact. To mitigate these challenges, strategies such as limited-capacity cycling and blending of Si with graphite have been gaining traction. Under the chemical potential and kinetics differences of graphite and Si, the (de)lithiation of each component in the blended electrode cannot be reliably accessed using traditional electrochemical techniques. We will present a novel approach utilizing operando energy dispersive X-ray diffraction as a direct probe for the state of charge of the graphite-component and coupling with couloumetric monitoring estimate the state of charge of the Si-component. Direct deconvolution of the individual state of charge of graphite and Si in a silicon-graphite blended electrode will be a valuable guide in limited-capacity cycling schemes and enable a targeted choice of the optimal relative concentration of Si and graphite for next-generation Si-based anodes.

Direct operando quantification of active components (de)lithiation ratios in silicon/graphite composite high-capacity anodes for Li-ion batteries

256th National Meeting (2018)

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