Operando Investigations toward Changeover of Phase Assemblage and Associated Electrochemical Behavior during Lithiation/Delithiation Cycles of Sn-Based Intermetallic Electrodes

Abstract

Moving toward the next-generation alkali metal-ion battery systems, poor cyclic stability of "alloying-reaction"-based anode materials, such as Sn, is still an unresolved issue of immense significance. There is some interest/ promise with Cu−Sn intermetallic-based anodes (viz., primarily Cu 6 Sn 5 -based), but with the stability still lagging behind the desired level and lithiation/ delithiation mechanisms not being understood. Against this backdrop, starting with a less explored Cu−Sn intermetallic (viz., ε-Cu 3 Sn), operando synchrotron X-ray diffraction scans obtained during galvanostatic lithiation/delithiation cycles have indicated that changes in phase assemblage/evolution take place not only during an individual Li-alloying/dealloying cycle but also across different cycles. In this context, by the end of just one full lithiation/delithiation cycle, Cu 3 Sn gives way to a Sn-deficient Cu 41 Sn 11 phase and some (ejected) β-Sn. Cu 41 Sn 11 behaves fairly similar to Cu 3 Sn during lithiation, forming primarily Li 7 Sn 2 toward the end, but with itself getting reformed upon delithiation (unlike Cu 3 Sn). With continued cycling, Cu 41 Sn 11 gives way to ternary LiCu 2 Sn as the primary phase, which becomes dominant by ∼25 cycles. Upon lithiation, LiCu 2 Sn forms Li 3 CuSn (via Li 2 CuSn), which reverts back to LiCu 2 Sn upon delithiation. This process does not involve dissociation to first form Sn during lithiation; which, otherwise, is the norm with Cu−Sn binary intermetallics. Such changes in phase assemblage and associated lithiation/delithiation pathways resulted in reduction of potential hysteresis and progressive increase of Li-storage capacity upon cycling beyond 25 cycles. Accordingly, a reversible capacity of ∼400 mA h/g could be obtained after 100 cycles, with the increasing trend promising further increment upon continued cycling. On a practical front, such excellent cyclic stability and "safe" operating potential of Cu 3 Sn-based electrodes are very encouraging and ultimate proofs toward their "activity", with the insights into various changes in phase assemblage/evolution and associated lithiation/delithiation mechanisms being expected to lead to the development of stable-cum-"safe" intermetallic anodes for Li-ion batteries and beyond.

Si Nanowires Grown on Cu Substrates via the Hot-Wire-Assisted Vapor–Liquid–Solid Method for Use as Anodes for Li-Ion Batteries

“…As per the Cu-Sn phase diagram, at our processing temperature of 400 °C, ∼13.8 wt % Sn is soluble in Cu. There are lots of reports available in the literature concerning the formation of Sn-Cu intermetallic compounds due to interdiffusion of the elements at even relatively lower temperatures ( viz ., even from room temperature to 250 °C). − In light of this information and our SEM observations, we believe that the Sn template does not remain on the surface at our processing temperature due to alloying between Sn and Cu in the case of the acetic acid-treated copper foils, which have negligible surface oxide. Now, since there are no Sn nanoparticles on the substrate to grow SiNWs, only deposition of the amorphous silicon film takes place, and this is perhaps the reason that the growth of SiNW on copper foil via the VLS route has never been reported before.…”

Cation–Oxygen Bond Covalency: A Common Thread and a Major Influence toward Air/Water‐Stability and Electrochemical Behavior of “Layered” Na–Transition‐Metal‐Oxide‐Based Cathode Materials

“…Similar setup and conditions were used for operando synchrotron X-ray diffraction studies also in the previously reported works with different electrode materials. [52][53][54][55][56]…”

Understanding the Effects of Tetrahedral Site Occupancy by the Zn Dopant in Li-NMCs toward High-Voltage Compositional–Structural–Mechanical Stability via Operando and 3D Atom Probe Tomography Studies

“…The electrochemical behavior and performances of the as-developed Li-NMCs (i.e., undoped and Zn-doped Li-NMC111) as cathode materials for Li-ion cells were reported in our previously published work . Here, in order to perform the operando synchrotron diffraction experiments (as further detailed in the following sub-section, i.e., Section ), the working electrodes were prepared in the same way as for the electrochemical studies performed in Li “half” cells using CR2032-type coin cells, − with the coin cells being slightly modified to enable the operando measurements during galvanostatic cycling. For the operando stress measurements as well (as detailed in a subsequent sub-section, i.e., Section ), the overall electrochemical conditions (including the potential window, electrolyte, separator, Li foil, etc.)…”

“…The diffraction patterns were recorded using MAR 345 imaging plates, which were calibrated with the NIST standard CeO 2 powder. Similar setup/conditions were used for some of our previously published works that involve operando synchrotron XRD studies. − …”