Mechanistic insight of Li cluster formation and dendrite deposition in sulfide all-solid-state battery with hard-carbon electrode analyzed using 7Li operando nuclear magnetic resonance

Because lithium dendrite deposition during charging and discharging of all solid-state batteries (ASSLBs) is an important difficulty leading to deactivation, precise analysis of the lithium state is indispensable. We explored the potential use of hard-carbon (HC) for an ASSLB anode using operando 7 Li NMR to investigate lithium behavior. Cells using circular electrodes capable of applying constraint pressure to the electrode material were fabricated to achieve precise operando NMR measurements for sulfur-based ASSLBs. Adsorption and desorption behaviors of lithium in HC were found to be nearly identical to those of HC in liquid LIBs. However, short circuits occurred after several hours of constant current overlithiation or potential holding at −5.5 mV although no clear amplification of Li dendrite signal was observed. Signal components attributable to quasimetallic clusters were observed in both cases, which suggests that lithium can form clusters in open pores or on the HC surface during overlithiation. Clusters in the open pores or surface can conduct electricity and may serve as nucleation sites for dendrite growth. Although the use of HC anodes can suppress dendrite formation in ASSLBs, more precise voltage control is required than that used for liquid LIBs. • The potential use of hard-carbon for an ASSLB anode was explored using operando NMR. • Operando 7 Li NMR reveals lithium cluster and dendrite behaviors in ASSLBs. • Quasimetallic Li in open pores or surfaces can induce short-circuits. • More precise control than liquid LIBs is required to prevent short-circuit.