Study on Microstructural Deformation of Working Sn-containing Anode Particles for Lithium-ion Batteries by In-situ Transmission X-ray Microscopy
Date Issued
2012
Date
2012
Author(s)
Chao, Sung-Chieh
Abstract
The performance of high-energy and/or high-power Li-ion batteries depends strongly on the architecture of the electrode over-layers. Devising a proper characterization technique that is capable of providing qualitative/quantitative information of the architecture of the active over-layer is essential for such research. The main purpose of this research is to establish the protocol of synchrotron transmission x-ray microscopy (TXM) for studying the electrode architecture, in conjunction with other electrochemical characterization techniques to understand the interplay between the electrode architecture and cyclic performance of the electrode. For the first time, the evolution of interior microstructures of three types of Sn-containing particles, including Sn, SnSb, and SnO, during initial cycles of electrochemical lithiation/de-lithation has been revealed by in-situ transmission x-ray microscopy, complemented by in-situ x-ray diffraction to provide phase information.
The microstructures and deformation rates are shown to depend on particle composition, size and alloy stoichiometry with Li. During first lithiation, both Sn and SnSb particles exhibit core (metal) -shell (lithiated compounds) interior structures. Initial formation of a dense surface layer containing LixSn phases of low Li-stoichiometry on the Sn particle hinders further lithiation kinetics, resulting in delayed expansion of large particles. In contrast, Sb in SnSb is readily lithiated to form a porous Li-rich (Li3Sb) surface layer at higher potential than Sn, which enables to accelerate lithiation and remove the size dependence of the lithiation process. Both lithiated particles only partially contract upon de-lithiation, and their interiors evolve into porous structures due to metal re-crystallization. Such porous structures allow for fast lithiation and mitigated dimensional variations upon subsequent cycles.
A SnO secondary particle consisting of plates of primary particles has been shown to homogeneously expand during the first lithiation in two stages, including the first producing Li2O matrix that bears most original particle morphology and the second involving full lithiation of the precipitated Sn nano-particles from the first stage. Only the second stage is reversible upon de-lithiation, and the particle undergoes the reversible second-stage deformation during subsequent cycles. The results indicate clear advantages of using such a porous secondary SnO as the anode material in comparison with dense Sn particle previously revealed, including fast lithiation/de-lithiation kinetics, reduced overall volume expansion and enhanced mechanical robustness of the particle, supported by the Li2O backbones.
Moreover, according to the observation of porous Sn resulting from the local re-crystallization of Sn after first cycle, research in fabricating porous Sn anode particles via solution lithiation/de-lithiation method has been studied. Porous Sn particles with a porosity of 41.4% displays improved charge capacity retention of ~480 mAh/g after 49 cycles.
Subjects
Li-ion battery
In-situ analysis
Transmission x-ray microscopy
Li-alloying anode
Porous structure
SDGs
Type
thesis
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