Snsb Film As a Long Cycle Life Binder Free Anode Material for Sodium-Ion Batteries Facilitated By High Concentration Electrolyte

Abstract

With demand for battery devices projected to grow substantially over the coming decades the cost of lithium is expected to increase proportionally[1]. Li mining is an unsustainable process and developing post lithium-ion battery technology will be a critical step in accommodating the increasing demand for energy storage.[2] At the forefront of post-Li battery technology are sodium ion batteries (SIBs). SIBs are not only inherently more sustainable due to avoiding the use of Li but can potentially be more cost efficient. Sodium precursors, such as Na2CO3 and NaCl, are low cost and can be sourced globally. Furthermore, aluminium can be used as the anode current collector instead of copper, significantly reducing costs[1]. However, LIBs are still superior in terms of energy density, and SIB will require much progress to be competitive in that respect. To date, the most widely used anode material in SIBs is hard carbon. Although there are many advantages to using this carbonaceous anode material, it has several limitations, such as limited capacity and some uncertainty surrounding the sodiation mechanism.[3,4] Na-alloying metals are an interesting alternative to hard carbon with some key advantages. Group 14 and 15 metals such as Sn, Sb, and Bi have received much attention recently as potential anode materials because of their high theoretical capacities. However, application of these materials has been limited due to pulverization caused by large volume change during cycling. Nano-structuring alloying materials has been established as a key step in mitigating this issue as the nano-dimensions can accommodate the volume change without pulverization.[5][6]Forming composites of Na-alloying metals is another method that has been successful in extending anode cycle life. One such material is SnSb, which is a promising anode material for sodium-ion batteries due its high theoretical capacity of 751 mAh g-1 while a buffering effect between Sn and Sb during sodiation reduces pulverization.[7] Depositing SnSb directly onto the current collector via physical vapor deposition yields a conductive additive and binder free anode. The resulting layer, being both a composite and nanosized, benefits from the aforementioned advantages. The absence of conductive additives, binders and the need for solvents results in an increased energy density and reduced cost. When tested with a bespoke high concentration electrolyte consisting of NaClO4 in dimethoxyethane and fluoroethylene carbonate additive this anode can achieve capacities exceeding 390 mAh/g after 1500 cycles. The material was tested versus Na foil in a half-cell configuration using 2032 coin-cells.