Controlling Na diffusion by rational design of Si-based layered architectures

Abstract

By means of density functional theory, we systematically investigate the insertion and diffusion of Na and Li in layered Si materials (polysilane and H-passivated silicene), in comparison with bulk Si. It is found that Na binding and mobility can be significantly facilitated in layered Si structures. In contrast to the Si bulk, where Na insertion is energetically unfavorable, Na storage can be achieved in polysilane and silicene. The energy barrier for Na diffusion is reduced from 1.06 eV in the Si bulk to 0.41 eV in polysilane. The improvements in binding energetics and in the activation energy for Na diffusion are attributed to the large surface area and available free volume for the large Na cation. Based on these results, we suggest that polysilane may be a promising anode material for Na-ion and Li-ion batteries with high charge-discharge rates.

Feasibility of Reversible Electrochemical Na-Storage and Cyclic Stability of Amorphous Silicon and Silicon-Graphene Film Electrodes

“…11 Such predicted Na-capacity, even though significantly lesser compared to the Li-capacity, would still be considerably superior to those of most other potential anode materials. [3][4][5][6]15,16 Furthermore, lower Na-intake in Si would result in lower volume expansion compared to the case of Li-intake (viz., ∼114% for Na vs. ∼400% for Li), 11 which might just lead to lesser problems related to stress induced degradation and capacity fade in the case of Na.Due to the earlier belief concerning electrochemical Na-insertion being difficult in Si, [6][7][8][9][10]13 only very recently few experimental works 12,17,18 have explored the possibilities of electrochemical sodiation/de-sodiation in crystalline (c-Si) 6,17 and amorphous Si (a-Si) 12,18 in the form of nanoparticles. Indeed, both Ellis et al 7 and Komaba et al, 6 in their studies with Si particle sizes of 325 mesh * Electrochemical Society Student Member.…”

“…Accordingly, reversible Na-capacities recorded with the 250 and 50 nm a-Si films at the end of 100 cycles were ∼120 and ∼240 mAh g −1 ; which are possibly the best reported to-date for Si-based electrode materials. Due to limited lithium reserves in the world as compared to the more widespread and abundant reserves of sodium, there has been recent surge of interests toward the development of Na-ion batteries (SIBs), possibly in lieu of the Li-ion technology.1,2 However, one of the major issues associated with the Na-ion system is that graphitic carbon, the commonly used anode material for Li-ion batteries (LIBs), possesses reversible Na-capacity of just ∼35 mAh g −1 .1, [3][4][5][6][7][8][9] This is an order of magnitude lower compared to the corresponding Li-capacity; 3,10-12 and is caused by the larger size of the Na-ion. Accordingly, metallic anode materials, such as Ge, Sb and Sn, have been investigated for SIBs, but without much success in terms of cyclic stabilities due to dimensional changes (and detrimental stress developments) upon Na-alloying/dealloying.…”

Insertion of Mono- vs. Bi- vs. Trivalent Atoms in Prospective Active Electrode Materials for Electrochemical Batteries: An ab Initio Perspective

“…The Mg and Al diffusion in NiS 2 is expected to be particularly facile. The activation energy for Mg diffusion in NiS 2 (0.46 eV) is comparable to Li diffusion barriers in the state-of-the-art electrode materials, such as LiTi 2 O 4 (0.56 eV) [155] and bulk silicon (0.61 eV) [19].…”

“…It is known that fast kinetics and high capacity can be achieved in battery materials by introducing porosity and large void spaces, as demonstrated in nanotubes and porous nanostructures [19,[157][158][159][160][161][162][163]. Improvements in charge-discharge rates can be achieved in layered materials and ultra-thin nanosheets, where Li/Na/K/Mg/Al storage mainly takes place on the surfaces (in a pseudocapacitive manner), maintaining rapid surface diffusion [11,[164][165][166][167].…”

“…Here, we only introduce key computed quantities which are important for a material's performance as an active electrode material and which are discussed in Sections 2 and 3. To analyze the thermodynamics of interaction of a potential electrode material with Li, Na, K, Mg, or Al, we use the binding energy E b (n) of n of these atoms to the active material, which is effectively the defect formation energy (E f , which is the term used in many studies [11][12][13]15,16,[19][20][21][22][23][24][25]). It is computed as:…”