Electrochemical Lithiation and Delithiation Properties of FeSi₂/Si Composite Electrodes in Ionic-Liquid Electrolytes

Abstract

We investigated the applicability of ionic-liquid electrolytes to FeSi 2 / Si composite electrode for lithium-ion batteries. In conventional organic-liquid electrolytes, a discharge capacity of the electrode rapidly faded. In contrast, the electrode exhibited a superior cycle life with a reversible capacity of 1000 mA h g(Si) −1 over 850 cycles in a certain ionic-liquid electrolyte. The difference in the cycle life was explained by surface film properties. In addition, the rate performance of the FeSi 2 /Si electrode improved in another ionic-liquid electrolyte. Remarkably, lithiation of only Si in FeSi 2 /Si composite electrode occurred whereas each FeSi 2 -and Si-alone electrode alloyed with Li in the ionic-liquid electrolyte. FeSi 2 certainly covered the shortcomings of Si and the FeSi 2 /Si composite electrode exhibited improved cycle life and rate capability compared to Sialone electrode.

Anode Properties of CrxV1–xSi2/Si Composite Electrodes for Lithium-Ion Batteries

“…We considered that the silicide phase in the silicide/Si composite electrodes did not react with the Li-ion because we have confirmed that only lithiation of Si in the FeSi 2 /Si electrode should occur while both FeSi 2 -and Si-alone electrodes reacted with Li. 27 The initial charge and discharge capacity of the electrodes were almost the same. Additionally, there is little difference in the initial charge−discharge behavior among each silicide/Si composite electrode.…”

“…We considered that the silicide phase in the silicide/Si composite electrodes did not react with the Li-ion because we have confirmed that only lithiation of Si in the FeSi 2 /Si electrode should occur while both FeSi 2 - and Si-alone electrodes reacted with Li. 27 …”

Impact of Low Temperatures on the Lithiation and Delithiation Properties of Si-Based Electrodes in Ionic Liquid Electrolytes

“…We demonstrated that the cycle life of Si-based electrodes in FSA-based ionic liquid electrolytes was superior to that in conventional organic liquid electrolytes at room temperature. 17 , 20 , 21 , 50 In organic liquid electrolytes, a surface film with an inhomogeneous thickness forms on the electrode surface, and preferential Li + storage into Si occurs through thinner parts of the film. Inhomogeneous Li + storage prompts the local formation of a Li-rich Li–Si alloy phase, which causes local changes in the Si volume and electrode disintegration.…”

“… 3 − 5 Nevertheless, the poor cycling performance of Si-based electrodes is an obstacle to their practical use, which can be attributed to following: the significant volume change during lithiation and delithiation which generates considerable stress and high strain in active materials; high electrical resistivity; and a low Li + diffusion coefficient. 5 − 9 Various attempts have been made to address such issues, for example, synthesizing nanosized Si materials to prevent the occurrence of surface cracking and fracture; 7 , 10 , 11 reducing the electrical resistivity of Si by coating it with carbon materials; 12 , 13 fabricating composite electrodes to cover the shortcomings of Si; 14 − 17 doping Si with impurities, such as phosphorus (P), boron, antimony, or arsenic, to adjust its properties, including its electrical resistivity, Li distribution, crystallinity, and morphology; 18 − 24 preparing silicides to give ductility and electronic conductivity specific to metals; 25 − 27 and the prelithiation of Si to increase the initial Coulombic efficiency. 28 − 31 …”

Si/FeSi2 Nanoparticles Prepared by Thermal Plasma with Stress‐releasing Effect for Li‐ion Storage

“…compounds are electrochemically inactive with Li + and they also have high electronic conductivity, which can be utilized as conductive Li‐inactive components to buffer the volume expansions and improve the structural stability during charge/discharge process of Si‐based materials [28–30] . Especially, iron‐silicide have been researched intensively due to its high abundance, low price, environment friendly, and high electronic conductivity [31–34] . Thus, the iron‐silicide can be utilized as a suitable conductive Li‐inactive material for commercialization of Si‐based anodes to maintain structural integrity.…”