title: Phase evolution of tin nanocrystals in lithium ion batteries.
abstract: Sn-based nanostructures have emerged as promising alternative materials for commercial lithium-graphite anodes in lithium ion batteries (LIBs). However, there is limited information on their phase evolution during the discharge/charge cycles. In the present work, we comparatively investigated how the phases of Sn, tin sulfide (SnS), and tin oxide (SnO2) nanocrystals (NCs) changed during repeated lithiation/delithiation processes. All NCs were synthesized by a convenient gas-phase photolysis of tetramethyl tin. They showed excellent cycling performance with reversible capacities of 700 mAh/g for Sn, 880 mAh/g for SnS, and 540 mAh/g for SnO2 after 70 cycles. Tetragonal-phase Sn (β-Sn) was produced upon lithiation of SnS and SnO2 NCs. Remarkably, a cubic phase of diamond-type Sn (α-Sn) coexisting with β-Sn was produced by lithiation for all NCs. As the cycle number increased, α-Sn became the dominant phase. First-principles calculations of the Li intercalation energy of α-Sn (Sn8) and β-Sn (Sn4) indicate that Sn4Li(x) (x ≤ 3) is thermodynamically more stable than Sn8Li(x) (x ≤ 6) when both have the same composition. α-Sn maintains its crystalline form, while β-Sn becomes amorphous upon lithiation. Based on these results, we suggest that once α-Sn is produced, it can retain its crystallinity over the repeated cycles, contributing to the excellent cycling performance.
authors.affiliation: Department of Chemistry, Korea University , Jochiwon 339-700, Korea.
authors.forename: Hyung Soon
authors.initials: HS
authors.lastname: Im
authors.forename: Yong Jae
authors.initials: YJ
authors.lastname: Cho
authors.forename: Young Rok
authors.initials: YR
authors.lastname: Lim
authors.forename: Chan Su
authors.initials: CS
authors.lastname: Jung
authors.forename: Dong Myung
authors.initials: DM
authors.lastname: Jang
authors.forename: Jeunghee
authors.initials: J
authors.lastname: Park
authors.forename: Fazel
authors.initials: F
authors.lastname: Shojaei
authors.forename: Hong Seok
authors.initials: HS
authors.lastname: Kang