Application of 7Li NMR to characterize the evolution of intercalated and non-intercalated lithium in LiFePO4-based materials for Li-ion batteries

What Can We Learn from Solid State NMR on the Electrode-Electrolyte Interface?

Rechargeable battery cells are composed of two electrodes separated by an ion-conducting electrolyte. While the energy density of the cell is mostly determined by the redox potential of the electrodes and amount of charge they can store, the processes at the electrode-electrolyte interface govern the battery's lifetime and performance. Viable battery cells rely on unimpeded ion transport across this interface, which depends on its composition and structure. These properties are challenging to determine as interfacial phases are thin, disordered, heterogeneous, and can be very reactive. The recent developments and applications of solid state NMR spectroscopy in the study of interfacial phenomena in rechargeable batteries based on lithium and sodium chemistries are reviewed. The different NMR interactions are surveyed and how these are used to shed light on the chemical composition and architecture of interfacial phases as well as directly probe ion transport across them is described. By combining new methods in solid state NMR spectroscopy with other analytical tools, a holistic description of the electrode-electrolyte interface can be obtained. This will enable the design of improved interfaces for developing battery cells with high energy, high power, and longer lifetime.

Electrochemical lithiation/delithiation of SnP2O7 observed by in situ XRD and ex situ7Li/31P NMR, and 119Sn Mössbauer spectroscopy

The lithiation of the SnP₂O₇ anode material leads to tin extrusion and formation of Li_xSn alloys with stable capacity during the subsequent cycles.