Stabilizing Tin Anodes in Sodium-Ion Batteries by Alloying with Silicon

Abstract

Group(IV) of the periodic table is a promising column with respect to high capacity anode materials for sodium-ion batteries (SIBs). Unlike carbon that relies on interlayer defects, pores, and intercalation to store sodium, its heavier cousins, silicon, germanium, and tin, form binary alloys with sodium. Alloying does lead to the formation of high capacity compounds but they are, however, susceptible to large volumetric changes upon expansion that results in pulverization of the electrodes and poor cycling stability. Silicon and tin are particularly intriguing due to their high theoretical reversible capacities of 954 mAh/g (NaSi) and 847 mAh/g (Na15Sn4), respectively, but suffer from poor practical capacity and very short lifetimes, respectively. In order to buffer the detrimental effects of volume expansion and contraction, nanoscale multilayer anodes comprising silicon and tin films were prepared and compared with uniform films composed of atomically mixed silicon and tin, as well as elemental silicon and tin films. The results reveal that the high capacity fade for elemental Sn is associated with detrimental anodic (desodiation) reactions at a high cutoff voltage with a threshold defined as 0.8 VNa. Binary mixtures of Si and Sn were tested in a number of different architectures, including multilayer films and co-sputtered films with varying volume ratios of both elements. All mixed films showed improved capacity retention compared to the performance of anodes comprising only elemental Sn. A multilayer structure composed of 3 nm-thick silicon and tin layers showed the highest Coulombic efficiency and retained 97% of its initial capacity after 100 cycles, which is vastly improved compared to 7% retention observed for the elemental Sn film. The role of the Si interlayers appears to be one of acting as a buffer during cycling to help preserve Sn particles within the thin Sn interlayers. The alloying element, Si, plays two roles -it stabilizes grain growth/pulverization and also alters the surface chemistry of the anodes, thus affecting the formation of solid electrolyte interphase (SEI). File list (2) download file view on ChemRxiv SiSn_NaIBs_july10_PDF.pdf (10.62 MiB) download file view on ChemRxiv SiSn_NaIBs SI_july10_PDF.pdf (1.16 MiB)

Amorphization driven Na-alloying in SixGe1−x alloy nanowires for Na-ion batteries

“…The capacity share calculated for each element is based on the assumption that binary phases of sodiated NaxSi, NaxGe and NaySn will form at the fully sodiated state as previously reported. 34 Therefore, the maximum capacity share can be estimated based on the weight ratios of the elements present in the a-Si0.5Ge0.5 alloy. After 100 cycles, the a-Si sodiation capacity dropped to a mere 10.1 mAh g -1 , with a capacity retention of just 3.93 %.…”

“…25,31,32 Another strategy to overcome the Na ion diffusion barrier is through alloying of different Na active materials to mitigate the poor activation of parent Si and Ge. Various binary and ternary alloy compositions containing either Si or Ge such as Sb-Si, 33 Sn-Si, 34 Sn-Ge 35 and Sn-Ge-Sb 36 have been tested in NIBs. However, to the best of our knowledge, there have been no reports where the behaviour of Si and Ge as binary Si-Ge alloys have been explored in NIBs, despite their highly impressive performance in LIBs and potential for compositional tuneability.…”

Revealing Na-segregation at the Si/Graphene Interface and Its Implications toward the Na-storage Behavior of Si-Based Electrodes

“…However, earlier computational − and experimental studies , with crystalline Si disappointed the community by predicting/indicating that Si might be “inactive” toward hosting Na under the relevant electrochemical conditions. In fact, Kulish et al predicted a fairly large diffusion barrier (1.06 eV) and a positive binding energy (of 0.6 eV) for Na alloying with Si using first-principles calculations, although this conclusion was busted by the more recent studies, including ours, which indicated that it is primarily the limitation of Na transport in the coarser-sized Si particles/films ,,− and crystalline/defect-free nature of Si ,− ,− ,− that cause significant hindrance in Na uptake. In fact, our previously reported studies established that amorphous Si, unlike crystalline Si, does exhibit reversible Na alloying under the electrochemical conditions pertaining to being the anode of Na-ion cells. , Nevertheless, sodiation/desodiation was found to be kinetically more hindered, as compared to Li insertion/removal kinetics, since finer Si dimensions (preferably <∼50 nm) are needed for obtaining practically any useful performance as an anode material.…”

Carbon Encapsulated and rGO Wrapped Mo2C: an Anode Material with Enhanced Sodium Storage Capacity

“…Graphite anode is not suitable anode for SIB due to unfavourable thermodynamic stability of sodiated graphite [11] . There are numerous reports of anode materials storing sodium‐ ion via an alloy reaction mechanism and/or conversion reaction mechanism [12–14] . However, repeated intercalation/deintercalation process causes severe strain on the anode material which results in sever limitation in their cycle stability especially in large‐format cells.…”

“…[11] There are numerous reports of anode materials storing sodiumion via an alloy reaction mechanism and/or conversion reaction mechanism. [12][13][14] However, repeated intercalation/deintercalation process causes severe strain on the anode material which results in sever limitation in their cycle stability especially in large-format cells. This is a major technical challenge for battery researchers which need to be overcome by a cost-effective approach.…”