Abstract
In situ muon spin relaxation is demonstrated as an emerging technique that can provide a volume-averaged local probe of the ionic diffusion processes occurring within electrochemical energy storage devices as a function of state of charge. Herein, we present work on the conceptually interesting NASICON-type all-solid-state battery LiM2(PO4)3, using M = Ti in the cathode, M = Zr in the electrolyte, and a Li metal anode. The pristine materials are studied individually and found to possess low ionic hopping activation energies of ∼50−60 meV and competitive Li+ self-diffusion coefficients of ∼10–10–10–9 cm2 s–1 at 336 K. Lattice matching of the cathode and electrolyte crystal structures is employed for the all-solid-state battery to enhance Li+ diffusion between the components in an attempt to minimize interfacial resistance. The cell is examined by in situ muon spin relaxation, providing the first example of such ionic diffusion measurements. This technique presents an opportunity to the materials community to observe intrinsic ionic dynamics and electrochemical behavior simultaneously in a nondestructive manner.
Highlights
As the electric vehicle market expands rapidly, the social and economic importance of improved energy storage devices grows concurrently, proving vital the utilization of nextgeneration technologies such as solid-state-batteries (SSBs).[1]
A further challenge for solid electrolytes is that of ionic conductivity, a process generally governed by defect/vacancy concentration and distribution
Both materials exhibit low λ values; the flat regions at low temperatures indicate a static environment while the subsequent decrease is a consequence of dynamical field fluctuations above 300 K, indicating the onset of Li+ diffusion
Summary
As the electric vehicle market expands rapidly, the social and economic importance of improved energy storage devices grows concurrently, proving vital the utilization of nextgeneration technologies such as solid-state-batteries (SSBs).[1]. Both materials exhibit low λ values; the flat regions at low temperatures indicate a static environment while the subsequent decrease is a consequence of dynamical field fluctuations above 300 K, indicating the onset of Li+ diffusion. Both samples exhibit a relatively constant value or a slight decrease, before a sharper drop is seen at high temperatures This is a consequence of a motional narrowing effect: as Li+ ions begin to diffuse rapidly, their nuclear fields increasingly differ throughout the structure and their contribution to Δ is lowered.[46] The larger decrease observed for LZP may be explained by the phase change from triclinic to rhombohedral at around 320 K as the spatial arrangement of muon stopping sites is altered. Interfacial resistance growth is not expected to contribute toward the reduced self-diffusion observed within the bulk at low potential; over extended cycling, it will lead to an inhomogeneous current distribution and a short-circuit
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