Origin of Degradation in Si‐Based All‐Solid‐State Li‐Ion Microbatteries

Abstract

Like all rechargeable battery systems, conventional Li-ion batteries (LIB) inevitably suffer from capacity losses during operation. This also holds for all-solid-state LIB. In this contribution an in operando Neutron Depth Profiling (NDP) method is developed to investigate the degradation mechanism of all-solid-state, thin film Si-Li 3 PO 4 -LiCoO 2 batteries. Important aspects of the long-term degradation mechanisms are elucidated. It is found that the capacity losses in these thin film batteries are mainly related to lithium immobilization in the solid-state electrolyte, starting to grow at the anode/electrolyte interface during initial charging. The Li-immobilization layer in the electrolyte is induced by silicon penetration from the anode into the solid-state electrolyte and continues to grow at a lower rate during subsequent cycling. X-ray Photoelectron Spectroscopy (XPS) depth profiling and Transmission Electron Microscopy (TEM) analyses confirm the formation of such immobilization layer, which favorably functions as an ionic conductor for lithium ions. As a result of the immobilization process, the amount of free moveable lithium ions is reduced, leading to the pronounced storage capacity decay. Insights gained from this research shed interesting light on the degradation mechanisms of thin film, all-solid-state LIB and facilitate potential interfacial modifications which finally will lead to substantially improved battery performance.

The Road Towards Planar Microbatteries and Micro‐Supercapacitors: From 2D to 3D Device Geometries

“…On the other hand, directly forming bonds, introducing intermediate layers, and direct growth of electrodes on current collectors are useful strategies for producing strongly coupled interfaces between microelectrodes and current collectors. As demonstrated in Si–Li 3 PO 4 –LiCoO 2 MBs, the formation of lithium immobilization layer at the interface between electrode and solid electrolyte has a remarkable influence on the cycling performance . Therefore, more studies should be devoted to the interfacial engineering, including the composition, modification, evolution, and dynamics of the interfaces.…”

A new neutron depth profiling spectrometer at the JCNS for a focused neutron beam

“…The NDP technique was first reported by J. Ziegler, G. W. Cole and J. E. E. Baglin in 1972 as a non-destructive tool to study 10 B impurities inside silicon substrates (1). Around the same time and independently similar experimental approach was used by J. P. Biersack and D. Fink (2).…”

“…Only in this case, an Li profile through the entire battery cell can be derived with high resolution by analysis of α-particle signal. Examples of NDP being applied to operando study solid-state thin-film LIB can be found in (9,10). The moderate neutron flux and single charged particle detector available at the NDP facility (9, 10) made 10 min measurement time for a single NDP spectrum possible.…”

Spatiotemporal Quantification of Lithium both in Electrode and in Electrolyte with Atomic Precision via Operando Neutron Absorption

“…42 Besides this, the ability to measure the 6 Li isotope independent of oxidation state allows for the simultaneous detection of lithium in both electrode and electrolyte, which makes NDP a unique diagnostic tool capable of unraveling the space- and time-dependent lithium density resulting from the complex electrochemical processes taking place across battery electrodes. 37,44,45…”