Re-evaluating critical current density in solid-state batteries: Challenges and proposing an alternative.

The critical current density (CCD) test protocols are widely adopted to examine the quality of solid electrolyte (SE), the stability of lithium (Li)/SE interfaces, and solid-solid interfacial kinetics in all solid-state lithium batteries (SSLBs). This work systematically investigated the impact of major experimental parameters on CCD values of Li symmetric cells using argyrodite Li 6 PS 5 Cl SE. Four categories of experimental parameters were investigated: (i) SE parameters, (ii) Li metal parameters, (iii) cell die parameters, and (iv) CCD testing protocols. Each parameter uniquely influences the density of the SE or the SE/Li interface, thereby affecting the resulting CCD values. Notably, CCD values are highly dependent on the cell operating histories, particularly the operating period (h) and the applied current density (mA/cm2). Consequently, without standardizing and unifying CCD testing protocols, obtaining reliable and repeatable CCD values remain challenging. To overcome this limitation, we propose the cumulative areal capacity (CAC) test protocol – the total capacity (mAh/cm2) delivered by a cell before its failure – as a more accurate measure of cell performance. CAC analysis of over 30 Li symmetric cells demonstrated statistical convergence in CAC values, highlighting its potential as a supplementary or even alternative testing protocol to conventional CCD methods. [Display omitted] • Impact of experimental parameters on CCD of Li symmetric cells with sulfide SE. • CCD values are highly dependent on the cell's operating histories. • Propose and statistically validated CAC as an alternative testing protocols. • Cell with higher-density SE demonstrated a wider CAC convergence window. • CAC window as useful metric for designing and estimating rate capability of SSLBs. [ABSTRACT FROM AUTHOR]