Operando Raman analysis of electrolyte changes in Li-ion batteries with hollow-core optical fibre sensors

Abstract

New methods are urgently required to identify degradation and failure mechanisms in high energy density energy storage materials such as Ni-rich LiNi0.8Mn0.1Co0.1O2 cathodes (NMC811) for Li-ion batteries. Understanding and ultimately avoiding these mechanisms requires in-situ tracking of the complex electrochemical processes that occur in different parts of battery cells. Here we demonstrate a new operando spectroscopy method that enables the tracking of electrolyte chemistry, applied here for high energy density Li-ion batteries with a NMC811 cathode, during electrochemical cycling. This is achieved by embedding a novel hollow-core optical fibre probe inside the battery to monitor the evolution of electrolyte species by background-free Raman spectroscopy. Our data reveals changes in the ratio of carbonate solvents and electrolyte additives as a function of the cell voltage, as well as changes in the lithium-ion solvation dynamics. This advanced operando methodology delivers a new way to study battery degradation mechanisms, and the understanding it develops should contribute to extending the lifetime of next-generation batteries.

Monitoring battery electrolyte chemistry via in-operando tilted fiber Bragg grating sensors

“…On the contrary, the Bragg resonance remains invariant with RI in Fig. 2b and thus can be used as a stable power and wavelength reference 19 . Therefore, we use the wavelength separation (Fig.…”

“…However, in such a configuration, the fiber acts as a true waveguide with the traveling light being fully transparent to the fiber-surrounding environment. Nonetheless, this limitation can be bypassed by modifying the structure of the fibers to obtain either claddingetched fibers for optic evanescent wave spectroscopy 18 or hollow-core fibers with pumped electrolyte for Raman spectroscopy 19 . Besides, increasing the grating period (~500 nm to ~500 µm) and tilting the grating plane of FBGs leads to two other types of sensors called LPG for long-period grating sensing and TFBG for tilted fiber Bragg grating, respectively.…”

“…Unlike the solely peak pertaining to FBG and LPG detection, the rich features in TFBG's spectra facilitate the decoupling of multiple parameters such as T and RI. In addition, inscribed in commercial SMFs, TFBG gets rid of the intricate processes of hydrofluoric acid etching 18,26 or microstructural fiber fabrication 19 .…”