Paper SA-ThP3
In situ Probing of the Potential Distribution in a Thin Film All-solid-state Li-ion Battery

Thursday, October 25, 2018, 6:00 pm, Room Hall B

The next generation of portable electronic devices, electric vehicles, power grids, and robots require safer, smaller, lighter, cheaper, and more stable batteries. Of special importance are all-solid-state power sources that do not use conventional, flammable electrolytes and are intrinsically safer. Rational design of such batteries is challenging without in-depth understanding of the chemical and physical processes in electrochemical cells at the microscopic, nanoscopic, and eventually, atomic levels. Particularly important structural elements of solid-state Li-ion batteries (SSLIBs) that control the overall device performance are the interfaces that form between the electrodes and the cathode/anode materials and solid electrolyte. Despite decades of studies with classical electrochemical techniques, spectroscopic and microscopic tools, the interfacial characteristics of batteries, including the origins of high impedance often observed at solid state interfaces, are still poorly understood. Here, we employ in situ Kelvin Probe Force Microscopy (KPFM) to probe the potential distribution in a SSLIB as a function of its charge state. The battery was fabricated by sequentially depositing thin layers of Pt (110-130 nm), LiCoO₂ (280-420 nm), LIPON (1100-1200 nm), Si (50-240 nm) Cu or Pt (150-200 nm) onto a Si/SiO₂ wafer (oxide thickness 100 nm). The fabricated battery was cleaved in an Ar atmosphere to expose the stacked layers, mounted on a holder, wired, and safely transferred without exposing to air into a dual-beam instrument that combines a scanning electron microscope (SEM), a Ga-ion focused ion beam (FIB) and an atomic force microscope (AFM) in one vacuum chamber (residual pressure of 10^-4 Pa). The stacked battery was milled to expose a cross-section of the layers, and imaged using SEM and KPFM, while cycling the battery. The acquired potential maps reveal a highly non-uniform interelectrode potential distribution, with most of the potential drop occurring at the electrolyte-Si anode interface in the pristine battery. During the first charge, the potential distribution gradually changes, revealing complex polarization within the LIPON layer due to Li-ion redistribution. The acquired data shed light onto the interfacial Li-ion transport in SSLIBs and its reversibility.

ES acknowledges support under the Cooperative Research Agreement between the University of Maryland and the National Institute of Standards and Technology Center for Nanoscale Science and Technology, Award 70NANB14H209, through the University of Maryland.