Transition-Metal Interdiffusion in Solid-State Batteries Revealed By Cryo-TEM

Abstract

Solid-state lithium-ion batteries are being considered as a future energy-storage technology, with superior energy/power density and improved safety over conventional lithium-ion batteries. However, their commercial implementation is hampered by side reactions and electro-chemo-mechanical degradation occurring during cycling (mostly at the positive electrode side). Many efforts have been made to reveal the underlying mechanisms in order to alleviate such problems.In the current study, the Thermo Scientific IGST workflow solution was used to enable a DualBeam to TEM workflow by protecting both bulk sample and prepared lamella under argon atmosphere with a CleanConnect transfer module. Because of the beam and temperature sensitivity of the superionic lithium thiophosphate solid electrolyte and the cathode interphases formed during cycling, the lamella preparation process (incl. bulk milling, lift out, attachment to the TEM grid, and final thinning) was carried out at cryogenic temperature (−178 °C). The lamella was then transferred to a Talos F200X CFEG for TEM analysis using an inert gas sample transfer workflow.STEM and EELS investigations revealed Ni, Co, and Mn dissolution from a Ni-rich cathode and subsequent solid electrolyte poisoning. Transition-metal dissolution/migration during cycling operation has previously only been reported for conventional (liquid-electrolyte-based) batteries.