The Role of Electrolyte Additives on the Interfacial Chemistry and Thermal Reactivity of Si-Anode-Based Li-Ion Battery

Abstract

Silicon (Si) has gained huge attention as an anode material for next-generation high-capacity lithium-ion batteries (LIBs). However, despite its overwhelming beneficial features, its large-scale commercialization is hampered due to unavoidable challenges such as colossal volume change during (de)­alloying, inherent low electronic and ionic conductivities, low Coulombic efficiency, unstable/dynamic solid electrolyte interphase (SEI), electrolyte drying and so forth. Among other strategies, the use of a fraction dose of chemical additives is hailed as the most effective, economic and scalable approach to realize Si-anode-based LIBs. Functional additives can modify the nature and chemical composition of the SEI, which in turn dictates the obtainable capacity, rate capability, Coulombic/energy efficiency, safety, and so forth of the battery system. Thus, we report a systematic and comparative investigation of various electrolyte additives, namely tetraethoxysilane (TEOS), (2-cyanoethyl)­triethoxysilane (TEOSCN), vinylene carbonate (VC), fluoroethylene carbonate (FEC), and a blend of TEOSCN, VC, and FEC (i.e., VC/FEC/TEOSCN) using electrochemical analysis, X-ray photoelectron spectroscopy, density functional theory calculation, and differential scanning calorimetry. The ternary mixture (FEC/VC/TEOSCN) results in a thinner SEI layer consisting of high shear modulus SEI-building species (mainly LiF). It also provides much improved thermal stability amid all tested additives, showing its potentiality to enable high capacity and safer Si-based anode LIBs. Thus, nitrile-functionalized silanes are highly promising electrolyte additives to boost the electrochemical performance and safety-induced risks of Si-based anode LIBs, emanating from the formation of a robust SEI layer.

Production of high-energy Li-ion batteries comprising silicon-containing anodes and insertion-type cathodes

“…Such additives possess electrochemically reducible and oxidisable functional moieties 53 . Designer additives used as precursors to build robust SEI/CEI should result in compounds with (1) a high shear modulus, which is essential for boosting the mechanical/chemical stabilities 54 56 . In general, electrolyte additives are depleted during each cycle; hence, their early effect (e.g.…”

“…Such additives possess electrochemically reducible and oxidisable functional moieties 53 . Designer additives used as precursors to build robust SEI/CEI should result in compounds with (1) a high shear modulus, which is essential for boosting the mechanical/chemical stabilities 54 ; (2) a low alkalinity/basicity (i.e. low acid-base reactivity), which is critical for suppressing the chemical and electrochemical degradations of electrolytes and electrodes 55 ; (3) high Li + transport and negligible diffusion of electrons and electrolyte; and (4) a low solubility in alkyl carbonate solvents, which is beneficial for reducing the reactivity of acidic species and other trace impurities (HF, POF 3 , H 2 O, PF 5 , among others) 56 .…”

“…Nitrile (−C≡N)-functionalized silane (e.g. 2-cyanoethyl triethoxysilane (TEOSCN)) forms highly conductive and mechanically stable SEI/CEI layers, leading to an improvement in performance at elevated temperatures (45 °C, starting temperature for the thermal decomposition of LiPF 6 ) compared to the electrolyte without TEOSCN (1 M LiPF 6 in EC/DEC (1/1, w/w)) 54 .…”

Enabling the thermal stability of solid electrolyte interphase in Li‐ion battery

“…Further addition of (2-cyanoethyl)triethoxysilane (TEOSCN, 5 wt.%) into EC/DEC/LiPF 6 (1 M)/VC/FEC could push T onset of the SEI breakdown further to as high as 267-275 C, which is the most effective electrolyte formula to enhance thermal stability of the Si anode. 67 DFT calculations revealed that C≡N functionalized TEOS had low LUMO energy values. The mechanism behind is the preferential decomposition of electrolyte additives on the anode surface changing compositions of the SEI.…”

Impact of single vs. blended functional electrolyte additives on interphase formation and overall lithium ion battery performance

“…Electronic supplementary material The online version of this article (https://doi.org/10.1007/s10008-020-04781-1) contains supplementary material, which is available to authorized users. formation at the anode|electrolyte interface, cathode elect r o l y t e i n t e r p h a s e ( C E I ) f o r m a t i o n a t t h e cathode|electrolyte surface, safety (overcharge protection and flammability issues) can be addressed [14][15][16][17][18][19], while the bulk physical properties of the SOTA electrolyte, which consists of LiPF 6 as a conducting salt and a mixture of cyclic and linear organic carbonate-based solvents, remain mostly unaffected. The rapid increase in demand of high-energy density cells [4,5] calls for increased cutoff cell voltage beyond 4.3 V [20,21], which can be enabled by addition of CEI functional additives [22].…”