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Designing and controlling the anode-electrolyte interfacial chemistry of a micron Sn-Ni/graphite composite battery anode led to the formation of a stable solid electrolyte interphase (SEI) layer. We utilized fluoroethylene carbonate (FEC)-based electrolyte that is more interfacially compatible than an EC-based electrolyte, trimethyl phosphite electrolyte additive that reduces the attack of LiPF 6 -derived acidic species in the electrolyte, and the addition of a low fraction of SnF 2 to anode for capturing the F anions of HF present in the electrolyte. Mechanistic surface chemistry studies using ATR FTIR and X-ray photoelectron spectroscopy revealed that the SnF 2 transforms to SnF 4 by capturing F anions, while FEC and phosphite provide a surface protective and robust SEI. The interfacially controlled composite anode with a tuned content of graphite exhibits good cycling stability (90% retention at the 50 th cycle) with high discharge capacity of ∼800 mAhg −1 of tin, in contrast to a rapid capacity fade in the conventional electrolyte.

that enable to form a stable solid electrolyte interphase (SEI) layer at the surface of the alternative anode for reliable battery performance. Tin (Sn)-based anode material based on alloy formation with Li has been one of the promising candidates because of the large theoretical capacity (≈992 mAhg −1 ) of Sn compared to that of graphite (372 mAhg −1 ). Sn also holds its merits of appropriate operating voltage above Li, which prevents dendrite formation, and high electronic conductivity as metallic, and improved Li + -transport kinetics. [1][2][3][4] The Sn, however, suffers from a rapid performance fade due to large volume change (≈300%) upon repeated charge (lithiation)-discharge (delithiation) cycling, which results in mechanical and electrical disintegration (i.e., particle cracking) between Sn particles and between the particles and current collector. [1][2][3][4] Several strategies were explored to reduce or accommodate the volume change by mostly adding various carbon (e.g., graphite) and inactive matrix, [2,5,6] and by using nanostructured Sn-carbon composites [7][8][9][10] or functional binder. [11] Since the particle cracking causes the enlarged interfacial area of Sn particles to electrolyte and continuous electrolyte decomposition at the new surface, the volume change event is closely linked to anode-electrolyte interfacial reactivity and stability. Our earlier reported results showed that interfacial irreversible reaction on Sn and destabilization of SEI layer with cycling are additional origins of a rapid performance fade in the ethylene carbonate (EC)-based conventional electrolyte. [12][13][14] Electrophilic attack of LiPF 6 salt-derived acids of PF 5 and PF 3 O (LiPF 6 → PF 5 + LiF, PF 5 + H 2 O PF 3 O + 2HF) [15,16] to the anode surface were determined to be the cause for interfacial reactivity. Surface degradation can also occur by the dissolution of surface oxide by HF. The most explored approaches to improve the interfacial (SEI) stability have been the use of electrolyte additives, such as phosphite [12,13] and fluoroethylene carbonate (FEC) [17][18][19] but just few studies have focused on investigating the SEI formation on Sn-based anode. [12,13,[19][20][21][22] Despite some improvement, challenges in the improvement of performance and SEI stability still remain. Thus, a fundamental understanding of electrode-electrolyte interfacial phenomena Tin-based anode materials are promising candidates for high-energy density Li-ion batteries. Unstable anode-electrolyte interface is a critical problem that needs to be resolved for these materials. The improvement of solid electrolyte interphase (SEI) stability and cycling stability of fluorine-doped Sn-Ni film electrode is observed by the use of fluoroethylene carbonate (FEC)based electrolyte with respect to ethylene carbonate (EC)-based conventional electrolyte. Mechanisms of FEC-derived SEI formation and stabilization are investigated using state of charge-dependent ex situ attenuated total reflection FTIR combined with X-ray photoelectron spectr...

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Lithium diffusivity of fluorine-free and -doped tin-nickel (Sn-Ni) film model electrodes with improved interfacial (solid electrolyte interphase (SEI)) stability has been determined, utilizing variable rate cyclic voltammetry (CV). The method for interfacial stabilization comprises fluorine-doping on the electrode together with the use of electrolyte including fluorinated ethylene carbonate (FEC) solvent and trimethyl phosphite additive. It is found that lithium diffusivity of Sn is largely dependent on the fluorine-doping on the Sn-Ni electrode and interfacial stability. Lithium diffusivity of fluorinedoped electrode is one order higher than that of fluorine-free electrode, which is ascribed to the enhanced electrical conductivity and interfacial stabilization effect.

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