Abstract
We report synchrotron-based operando soft X-ray microscopic photoelectron spectroscopy under charge-discharge control of single crystalline LiCoO2 (LCO) particles as an active electrode material for an all solid-state lithium-ion battery (LIB). Photoelectron mapping and the photoelectron spectrum of a selected microscopic region are obtained by a customized operando cell for LIBs. During the charge process, a more effective Li extraction from a side facet of the single crystalline LCO particle than from the central part is observed, which ensures the reliability of the system as an operando microscopic photoelectron analyzer that can track changes in the electronic structure of a selected part of the active particle. Based on these assessments, the no drastic change in the Co 2p XPS spectra during charge-discharge of LCO supports that the charge-polarization may occur at the oxygen side by strong hybridization between Co 3d and O 2p orbitals. The success of tracking the electronic-structure change at each facet of a single crystalline electrode material during charge-discharge is a major step toward the fabrication of innovative active electrode materials for LIBs.
Highlights
Development of high-performance lithium-ion batteries (LIBs) with large energy density, high power performance, high charge-discharge cycle stability, and high safety is strongly demanded to promote the use of clean energy devices, such as electric vehicles, to build a sustainable low-carbon society[1]
LCO is suitable as a model material for the novel analysis method because LCO is a typical material for use at the positive electrode of LIBs
A photoelectron map could be obtained by scanning a soft X-ray beam focused on a sample using a Fresnel zone plate (FZP) and detecting the photoelectrons at each beam spot
Summary
Development of high-performance lithium-ion batteries (LIBs) with large energy density, high power performance, high charge-discharge cycle stability, and high safety is strongly demanded to promote the use of clean energy devices, such as electric vehicles, to build a sustainable low-carbon society[1]. In the development of negative electrode materials for LIBs, strategies for the materials design have been established and metal lithium or silicon-lithium alloys have attracted much attention as high capacity materials[2,3] Strategies for such innovative materials to be used at the positive electrode have not been established because there are a lot of unknown charge-discharge mechanisms that occur at the positive electrode[4,5,6,7,8]. To understand the above-mentioned complex phenomena, analytical techniques using synchrotron radiation X-rays have enabled a major advance: hard X-rays having a short wavelength can be used to clarify the crystal structure[21,22] and soft X-ray spectroscopies, which cover the 3d transition-metal L and oxygen K edges, are advantageous to obtain element-specific electronic-structure information on the host material[23,24,25,26,27,28]. We achieved lithium insertion and extraction of LCO and obtained the mapping image of photoelectrons for selected energy regions at each area under potential control
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