Lithium-ion conductivity in Li6Y(BO3)3: a thermally and electrochemically robust solid electrolyte

The development of new frameworks for solid electrolytes exhibiting fast Li-ion diffusion is critical for enabling new energy storage technologies. Here, we present a combined experimental and computational investigation into the ionic conductivity of Li6Y(BO3)3, a new class of solid electrolytes with a pseudo-layered structure. Temperature-dependent impedance spectroscopy shows the pristine material exhibits an ionic conductivity of 2.2 × 10-3 S cm-1 around 400 °C, despite the fact that density functional theory calculations point to multiple remarkably low-energy diffusion pathways. Our calculations indicate small energy barriers for lithium interstitials to diffuse along one-dimensional channels oriented in the c-direction, and also for lithium vacancies diffusing within ac planes. This coexistence of diffusion mechanisms indicates that Li6Y(BO3)3 is an extremely versatile host for exploring and understanding mechanisms for lithium-ion conductivity. We also find no evidence for reactivity with moisture in the atmosphere and that the material appears electrochemically stable when in direct contact with metallic lithium. This robust stability, alongside ionic conductivity that can be manipulated through appropriate aliovalent substitution, make Li6Y(BO3)3 an exceptionally promising new class of solid electrolyte

Degradation mechanisms at the Li10GeP2S12/LiCoO2 cathode interface in an all-solid-state lithium-ion battery

All-solid-state batteries (ASSBs) show great potential for providing high power and energy density with enhanced battery safety. While new solid electrolytes (SEs) have been developed with high enough ionic conductivities, SSBs with long operational life are still rarely reported. Therefore, on the way to high performance and long-life ASSBs, a better understanding of the complex degradation mechanisms, occurring at the electrode / electrolyte interfaces is pivotal. While the lithium metal / solid electrolyte interface is receiving considerable attention due to the quest for high energy density, the interface between the active material and solid electrolyte particles within the composite cathode is arguably the most difficult to solve and to study. In this work, multiple characterization methods are combined to better understand the processes that occur at the LiCoO2 cathode and the Li10GeP2S12 solid electrolyte interface. Indium and Li4Ti5O12 are used as anode materials to avoid the instability problems associated with Li metal anodes. Capacity fading and increased impedances are observed during longterm cycling. Post-mortem analysis with scanning transmission electron microscopy (STEM), electron energy loss spectroscopy (EELS), x-ray diffraction (XRD) and x-ray photoelectron spectroscopy (XPS) show that electrochemically driven mechanical failure and degradation at the cathode / solid electrolyte interface contribute to the increase in internal resistance and the resulting capacity fading. These results suggest that the development of electrochemically more stable SEs and the engineering of cathode / SE interfaces are crucial for achieving reliable SSB performance