In Situ STEM-EELS Observation of Nanoscale Interfacial Phenomena in All-Solid-State Batteries

Abstract

Behaviors of functional interfaces are crucial factors in the performance and safety of energy storage and conversion devices. Indeed, solid electrode-solid electrolyte interfacial impedance is now considered the main limiting factor in all-solid-state batteries rather than low ionic conductivity of the solid electrolyte. Here, we present a new approach to conducting in situ scanning transmission electron microscopy (STEM) coupled with electron energy loss spectroscopy (EELS) in order to uncover the unique interfacial phenomena related to lithium ion transport and its corresponding charge transfer. Our approach allowed quantitative spectroscopic characterization of a galvanostatically biased electrochemical system under in situ conditions. Using a LiCoO2/LiPON/Si thin film battery, an unexpected structurally disordered interfacial layer between LiCoO2 cathode and LiPON electrolyte was discovered to be inherent to this interface without cycling. During in situ charging, spectroscopic characterization revealed that this interfacial layer evolved to form highly oxidized Co ions species along with lithium oxide and lithium peroxide species. These findings suggest that the mechanism of interfacial impedance at the LiCoO2/LiPON interface is caused by chemical changes rather than space charge effects. Insights gained from this technique will shed light on important challenges of interfaces in all-solid-state energy storage and conversion systems and facilitate improved engineering of devices operated far from equilibrium.

Review—Promises and Challenges of In Situ Transmission Electron Microscopy Electrochemical Techniques in the Studies of Lithium Ion Batteries

“…84,92,99,114 In general, this kind of device offers a platform for coupled imaging, diffraction, and spectroscopy for extensive microstructural and chemical analysis of nanobatteries in the same battery-operation situation, although it is hard to move the specimen to a suitable orientation for imaging the lattice because of the rigidness of this all solid-state battery. In recent years, most researchers mainly focus on the closed liquid-cell configuration because it creates an environment that is closer to real conditions of an electrode in a cell's electrolyte.…”

“…These observations suggest that the chemical changes rather than space-charge effects are responsible for the interfacial impedance mechanism at the LiCoO 2 /LiPON interface. 84 Li(Ni 0.8 Co 0.15 Al 0.05 )O 2 -based cathode materials show impressive rate performance for HEV applications but exhibit a capacity loss and a concomitant increase in impedance as a function of cycling. Miller, et al, found that a critical separation between primary grains developed, and electrolyte penetration into the interior of the particles occurred during the first oxide delithiation.…”

Insight Into the Formation of Lithium Alloys in All-Solid-State Thin Film Lithium Batteries

“…In situ and/or operando characterization of electrode materials operating in all-solid-state cells are rare. They mainly focus on chemical depth profiling by means of neutron techniques (Oudenhoven et al, 2011;Wang et al, 2017) or chemical analysis of solid-solid interfaces by means of scanning tunneling electron microscopy-electron energy loss spectroscopy (STEM-EELS, (Ma et al, 2016;Wang et al, 2016;Gong et al, 2017). To our knowledge, no in situ structural characterization has been carried out by X-ray diffraction on ceramic all-solid-state batteries so far.…”

Tuning the interlayer of transition metal oxides for electrochemical energy storage

“…In addition to the large application demand, the constantly evolving capability to understand phenomena at electrochemical interfaces is leading to significant improvements in the fundamental understanding of electrochemical processes. Electrochemical measurements have now been coupled with such advanced materials characterization techniques as transmission electron microscopy (TEM), [2][3][4] x-ray diffraction (XRD), [5][6][7] x-ray absorption (XAS), 8,9 atomic force microscopy (AFM), [10][11][12] and Raman microscopy, [13][14][15] to name just a few. This pairing has enabled in situ and in operando characterization of materials for electrochemical technologies leading to advancements in the mechanistic understanding of interfacial phenomena.…”