Sb–Si Alloys and Multilayers for Sodium-Ion Battery Anodes

Abstract

Silicon has a theoretical sodium-storage capacity of 954 mAh/g, which even exceeds that of tin (847 mAh/g). However, this capacity has never been reached in practice. Antimony is one of the best-performing Na-storage materials in terms of both capacity and cycling stability. By combining silicon and antimony, either by cosputtering or depositing multilayers with bilayer thickness down to 2 nm, we can achieve capacities exceeding even the theoretical capacity of Sb (660 mAh/g). Minor addition of silicon, 7 at. % or 7 wt % (25 at. %), increases the measured reversible capacity from 625 mAh/g for pure Sb to 663 and 680 mAh/g, respectively. All Sb-rich (>50 at. %) compositions show improved cycling stability over elemental Sb. Si 0.07 Sb 0.93 reached a maximum capacity of 663 mAh/g after 140 cycles and showed negligible capacity degradation up to 200 cycles. The fully sodiated state in cosputtered films evolves from single-phase amorphous to a mixture of a Sb-rich and Si-rich sodiated phases as cycling progresses, when the Si content is between 75 and 50 at. %. The typical desodiation signature of c-Na 3 Sb is observed only after 100 cycles or more. Careful examination of the voltage profiles of multilayers shows that they initially tend toward intermixing between the Si and Sb layers, contrary to expectations based on the phase diagram. When the Si and Sb layer thickness is decreased to 2 nm, the multilayer and cosputtered film behave almost identically. A general direction for finding promising multicomponent sodium-ion battery (SIB) alloy anodes is proposed.

State-of-the-Art Electrode Materials for Sodium-Ion Batteries

“…However, by combining silicon and antimony amorphous films with bilayer thickness down to 2 nm, and an amount of Si of 7 at.%, the mesoporous Si 0.07 Sb 0.93 reached a capacity of 663 mA•h•g −1 after 140 cycles at a low rate of 20 mA•g −1 . This is more than the theoretical capacity for Sb (660 mA•h•g −1 ) and more than the highest experimental capacity for pure Si reported so far (∼600 mA•h•g −1 ) [366]. Additional results for metallic Sn-and Sb-anodes can be found in [367].…”

Challenges of today for Na-based batteries of the future: From materials to cell metrics

“…The alloy-forming materials are generally represented by individual elements and could be divided into two primary groups according to their position in the periodic tablerepresentatives of group 14 and group 15. In addition, a number of examples of binary and tertiary alloys have also been reported [132][133][134]. The majority of the materials studied for this purpose are represented by rather benign and abundant elements, while potentially promising lead and arsenic were eliminated due to their toxicity [135,136].…”

Silicon Anodes for High‐Performance Storage Devices: Structural Design, Material Compounding, Advances in Electrolytes and Binders

“…Antimony is one of the best‐performing Na‐storage materials in terms of both capacity and cycling stability . Code posited Si−Sb alloys show reversible capacity exceeding that of elemental Sb and reached a maximum capacity of 663 mAh g −1 after 140 cycles . The Sb embedded silicon oxycarbide (SiOC) composites exhibits an initial desodiation capacity of around 510 mAh g −1 and maintained an excellent capacity retention above 97% after 250 cycles .…”

“…Alloy‐type materials are the most promising anodes for high performance Na/K ion batteries due to their high theoretical capacity . According to theoretical calculations, the specific capacity of silicon and Na/K alloying is higher than that of other alloy type anodes, which are NaSi 954 mAh g −1 and KSi 955 mAh g −1 , respectively . However, crystalline silicon exhibits electrochemical inertness in Na/K ion batteries and cannot be alloyed with Na/K ions.…”