Electrolytic Sn/Li 2O coatings for thin-film lithium ion battery anodes

Abstract

Sn/Li 2O composite coatings on stainless steel substrate, as anodes of thin-film lithium battery are carried out in SnCl 2 and LiNO 3 mixed solutions by using cathodic electrochemical synthesis and subsequently annealed at 200 °C. Through cathodic polarization tests, three major regions are verified: (I) O 2 + 4H + + 4e − → 2H 2O (∼0.25 to −0.5 V), (II) 2H + + 2e − → H 2, Sn 2+ + 2e − → Sn, and NO 3 − + H 2O + 2e − → NO 2 − + 2OH − (−0.5 to −1.34 V), and (III) 2H 2O + 2e − → H 2 + 2OH − (−1.34 to −2 V vs. Ag/AgCl). The coated specimens are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), cyclic voltammetry (CV), and charge/discharge tests. The nano-sized Sn particles embedded in Li 2O matrix are obtained at the lower part of region II such as −1.2 V, while the micro-sized Sn with little Li 2O at the upper part, such as −0.7 V. Charge/discharge cycle tests elucidated that Sn/Li 2O composite film showed better cycle performance than Sn or SnO 2 film, due to the retarding effects of amorphous Li 2O on the further aggregation of Sn particles. On the other hand, the one tested for cut-off voltage at 0.9 V (vs. Li/Li +) is better than those at 1.2 and 1.5 V since the incomplete de-alloy at lower cut-off voltage may inhibit the coarsening of Sn particles, revealing capacity 587 mAh g −1 after 50 cycle, and capacity retention ratio C50/C2 81.6%, higher than 63.5% and 49.1% at 1.2 and 1.5 V (vs. Li/Li +), respectively.