Deformation and Stresses During Alkali Metal Alloying/Dealloying of Sn-Based Electrodes

Abstract

Enhancement of energy density and safety aspects of Li-ion cells necessitate the usage of 'alloying reaction' based anode materials in lieu of the presently used intercalation-based graphitic carbon. This becomes even more important for the upcoming Na-ion battery system since graphitic carbon does not intercalate sufficient Na-ions to qualify as an anode material. Among the potential 'alloying reaction' based anode materials for Li-ion batteries and beyond (viz., Na-ion, K-ion battery systems), Si and Sn have received the major focus; with the inherently ductile nature of Sn (as against the brittleness of Si) and the considerably better performance in the context of electrochemical Na-/K-storage, of late, tilting the balance somewhat in favor of Sn. Nevertheless, similar to Si and most other 'alloying reaction' based anode materials, Sn also undergoes volume expansion/contraction and phase transformations during alkali metal-ion insertion/removal. These cause stress-induced cracking, pulverization, delamination from current collector, accrued polarization and, thus, rapid capacity fade upon electrochemical cycling. Unlike Si, the aforementioned loss in mechanical integrity is believed to be primarily caused by some of the deleterious 1st order phase transformations and concomitant formation of brittle intermetallic phases during the alloying/de-alloying process. Against this backdrop, this review article focuses on aspects related to deformation, stress development and associated failure mechanisms of Sn-based electrodes for alkali-metal ion batteries; eventually establishing correlations between phase assemblage/transformation, stress development, mechanical integrity, electrode composition/architecture and electrochemical behavior.

Facile and Scalable Development of High-Performance Carbon-Free Tin-Based Anodes for Sodium-Ion Batteries

“…This is because ultrafine/nanoscaled electrode-active particles, due to the very high specific surface area, suffer from excessive irreversible surface reactions with the electrolyte and also inferior tap densities. However, on the other hand, such relatively coarse “alloying-reaction”-based electrode-active particles are known to suffer from stress-induced degradations, ,, as well as relatively inferior rate capability. Hence, it needs to be seen whether the incorporation of Bi can alleviate these problems for Sn, that too in the absence of nanoscaled carbon as a buffer material, which will be the focus of the following sections of this paper.…”

“…“Alloying-reaction”-based anodes suffer from stress development due to volume expansion during the electrochemical alkali-metal-alloying process, ,, with the theoretical volume expansion of Sn upon complete sodiation being >400% and thus being the major cause of instability of Sn-based anodes. Despite this, while operando stress measurements have been previously reported for electrochemical Li alloying and K alloying in Sn, the same has not been reported for Na alloying in Sn and also in Bi.…”

“…Electrochemical Na alloying in Sn takes place via a series of intermetallic phases (Na x Sn), with the volume expansion upon complete sodiation reaching up to ∼400%. 1,2 Such structural and dimensional changes cause a loss in mechanical integrity and concomitant electrochemical cyclic instability during electrochemical sodiation/desodiation of Sn, which forms the major bottleneck toward the usage of such otherwise promising "alloying-reaction"-based anode materials.…”

“…Tin (Sn) has been recognized as a promising “alloying-reaction”-based anode material for sodium (Na)-ion batteries due to its higher theoretical Na-storage capacity and improved safety aspects compared to the presently used insertion-based hard carbon. Electrochemical Na alloying in Sn takes place via a series of intermetallic phases (Na x Sn), with the volume expansion upon complete sodiation reaching up to ∼400%. , Such structural and dimensional changes cause a loss in mechanical integrity and concomitant electrochemical cyclic instability during electrochemical sodiation/desodiation of Sn, which forms the major bottleneck toward the usage of such otherwise promising “alloying-reaction”-based anode materials.…”

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

“…A 100 nm-thick Pt film (as the current collector) was pre-deposited on the quartz substrate via DC magnetron sputtering, having a 20 nm-thick Ti film as an intermediate adhesive layer between the Pt and quartz (as shown in Figure S1 in the Supporting Information). The isotropic, stiff, and Li-inert quartz substrate aids the in-plane stress measurements via the substrate curvature methodology; the procedure and mechanistic aspects of which have been detailed in our previous publications. ,− …”