G. Yang, Y. Zhang, Ethan Self, Teerth Brahmbhatt, Jean-Christophe Bilheux, Hassina Bilheux, Jagjit Nanda
Oak Ridge National Laboratory,
Keywords: solid-state battery, in situ neutron tomography, lithium metal anode, NMC cathode
Summary:A solid-state electrolyte (SSE) plays an irreplaceable role in enabling lithium metal batteries to reach specific energy >500 Wh/kg. Among different SSE types, the sulfide-based SSE has emerged as a prominent class of soft ionic conductors. Compared to their ceramic and oxide SSE counterparts, sulfide SSEs provide several favorable advantages, including a) high room temperature ionic conductivity up to 10 mS/cm that is comparable to liquid-based electrolytes; b) ductile and mechanically soft SSE that enables better processible and intimate contact with electrodes; and c) scalability with solution-based low-temperature synthesis route. However, when paring with a high voltage cathode (e.g. LiNi0.8Mn0.1Co0.1O2 (NMC811)), the (electro)chemical instability of the sulfide SSE at the cathode/SSE interfaces becomes a major challenge to tackle with. The interfacial instability can result in up to 50% initial capacity loss in a Li metal/sulfide SSE/NMC battery, thereby keeping the sulfide SSEs from commercialization. In this study, we trace in situ lithium displacement in an all-solid-state battery using neutron computed tomography. Such a solid-state battery is composed of a 7Li anode, natLi¬¬3PS4(LPS) electrolyte, and a natLiNi0.8Mn0.1Co0.1O2 (NMC811) cathode. We show that after the first galvanostatic charge/discharge cycle, lithium accumulates at the LPS/NMC811 interface and preferably fills in the pre-formed cracks in the cold-pressed LPS SSE pellet. Such irreversible lithium displacement contributes to the initial capacity loss of the Li/LPS/NMC battery. The oxidation decomposition by-products will be explored by in situ Raman mapping. Our findings suggest that to achieve high-capacity retention of an all-solid-state sulfide-based battery using an NMC cathode, the cathode/sulfide interface should be better engineered and the defects of the LPS pellet should be suppressed.