Insights into the Distinct Lithiation/Sodiation of Porous Cobalt Oxide by in Operando Synchrotron X-ray Techniques and Ab Initio Molecular Dynamics Simulations

Abstract

Sodium-ion batteries (SIBs) have been considered as one of the promising power source candidates for the stationary storage industries owing to the much lower cost of sodium than lithium. It is well-known that the electrode materials largely determine the energy density of the battery systems. However, recent discoveries on the electrode materials showed that most of them present distinct lithium and sodium storage performance, which is not yet well understood. In this work, we performed a comparative understanding on the structural changes of porous cobalt oxide during its electrochemical lithiation and sodiation process by in operando synchrotron small angel X-ray scattering, X-ray diffraction, and X-ray absorption spectroscopy. It was found that compared to the lithiation process, the porous cobalt oxide undergoes less pore structure changes, oxidation state, and local structure changes as well as crystal structure evolution during its sodiation process, which is attributed to the intrinsic low sodiation activity of cobalt oxide as evidenced by ab initio molecular dynamics simulations. Moreover, it was indicated that the sodiation activity of metal sulfides is higher than that of metal oxides, indicating a better candidate for SIBs. Such understanding is crucial for future design and improvement of high-performance electrode materials for SIBs.

Direct Visualization of Li Dendrite Effect on LiCoO2 Cathode by In Situ TEM

“…However, the crystallographic transformation from CoO to Co is not as well‐defined as the evolution from LCO to CoO, which is also reflected by the diffused diffraction pattern of Co shown in Figures e,f and a. It is most likely due to the lack of consistent structure in the mixed amorphous/polycrystalline environment upon initial lithiation . The transformation from LCO to heavier Co metal and much lighter Li 2 O in fully reacted region should result in periodic contrast, which is confirmed in the HRTEM image shown in Figure S4a (Supporting Information).…”

Synchrotron X‐Ray and Neutron Diffraction, Total Scattering, and Small‐Angle Scattering Techniques for Rechargeable Battery Research

“…Unlike ordered materials, amorphous materials do not exhibit diffraction peaks, instead, they may produce broad SAS signals if there are domain or void structures that have different scattering lengths from the surrounding matrix. The size and shape of the domains or voids in battery may change during charging and discharging processes, which can be monitored and used to investigate reactions happening in materials . Elia et al studied the aluminum graphite batteries, and found the roughness of graphite electrodes increases after charge–discharge cycle comparing to pristine graphite electrode due to AlCl 3 intercalation, indicated by the deceased Porod law index .…”

“…The pore size and total volume change in battery also reflect in SAS pattern. Xu et al monitored structural change during the charging–discharging process for porous Co 3 O 4 anode ( Figure a). The battery materials produce two SAXS features: one at q of 0.005–0.1 Å −1 corresponding to mean pore size of 20–30 nm, and the other one at 0.2–0.5 Å −1 , corresponding to mean size of 6–12 Å.…”

“…Cyan and green curves are the scattering contribution from two structures with different sizes. Figures and data were reproduced with permission . Copyright 2017, American Chemical Society.…”

Synchrotron‐Based X‐ray Absorption Fine Structures, X‐ray Diffraction, and X‐ray Microscopy Techniques Applied in the Study of Lithium Secondary Batteries

“…Based on the energy range, the XAFS spectra can be divided to two regions, XANES and EXAFS . XANES is sensitive to oxidation state and coordination environment of the element in question.…”