Correlative Analysis of Ion-Concentration Profile and Surface Nanoscale Topography Changes Using Operando Scanning Ion Conductance Microscopy

Although various spectroscopic methods have been developed to capture ion-concentration profile changes, it is still difficult to visualize the ion-concentration profile and surface topographical changes simultaneously during the charging/discharging of lithium-ion batteries (LIBs). To tackle this issue, we have developed an operando scanning ion conductance microscopy (SICM) method that can directly visualize an ion-concentration profile and surface topography using a SICM nanopipette while controlling the sample potential or current with a potentiostat for characterizing the polarization state during charging/discharging. Using operando SICM on the negative electrode (anode) of LIBs, we have characterized ion-concentration profile changes and the reversible volume changes related to the phase transition during cyclic voltammetry (CV) and charge/discharge of the graphite anode. Operando SICM is a versatile technique that is likely to be of major value for evaluating the correlation between the electrolyte concentration profile and nanoscale surface topography changes.

Sb Nanoparticles Embedded in the N-Doped Carbon Fibers as Binder-Free Anode for Flexible Li-Ion Batteries

Antimony (Sb) is considered a promising anode for Li-ion batteries (LIBs) because of its high theoretical specific capacity and safe Li-ion insertion potential; however, the LIBs suffer from dramatic volume variation. The volume expansion results in unstable electrode/electrolyte interphase and active material exfoliation during lithiation and delithiation processes. Designing flexible free-standing electrodes can effectively inhibit the exfoliation of the electrode materials from the current collector. However, the generally adopted methods for preparing flexible free-standing electrodes are complex and high cost. To address these issues, we report the synthesis of a unique Sb nanoparticle@N-doped porous carbon fiber structure as a free-standing electrode via an electrospinning method and surface passivation. Such a hierarchical structure possesses a robust framework with rich voids and a stable solid electrolyte interphase (SEI) film, which can well accommodate the mechanical strain and avoid electrode cracks and pulverization during lithiation/delithiation processes. When evaluated as an anode for LIBs, the as-prepared nanoarchitectures exhibited a high initial reversible capacity (675 mAh g^-1) and good cyclability (480 mAh g^-1 after 300 cycles at a current density of 400 mA g^-1), along with a superior rate capability (420 mA h g^-1 at 1 A g^-1). This work could offer a simple, effective, and efficient approach to improve flexible and free-standing alloy-based anode materials for high performance Li-ion batteries.

Revealing the Phase-Transition Dynamics and Mechanism in a Spinel Li4Ti5O12 Anode Material through in Situ Electron Microscopy

Spinel Li₄Ti₅O₁₂ is considered as a promising anode material for long-life lithium-ion batteries because of the negligible volumetric variation during the insertion and extraction of Li ions. Phase transition is an inevitable process during the migration of Li ions, and the transition process and mechanism need detailed investigation down to the atomic scale. In this study, we investigated the behavior and mechanism on the phase transition of Li₄Ti₅O₁₂ through in situ transmission electron microscopy (TEM). It has been found that the spinel-structured Li₄Ti₅O₁₂ was gradually transformed to a rock salt structure under electron beam irradiation. A sharp interface with an epitaxial relationship was observed between the transformed rock salt phase and the parent spinel phase. Furthermore, the heterostructure with different crystal structures of Li₄Ti₅O₁₂ has been precisely tailored with electron beam irradiation. Our detailed in situ TEM results and theoretical calculations led to unprecedented level on the understanding of phase-transition mechanism in Li₄Ti₅O₁₂. This study demonstrates a possible approach to precisely engineer the crystal structure of materials and to realize a well-designed heterostructure in electrode materials.