Tin(ii) amide/alkoxide coordination compounds for production of Sn-based nanowires for lithium ion battery anode materials

摘要

A series of tin(ii) amide alkoxides ([(OR)Sn(NMe _2)] _n) and tin(ii) alkoxides ([Sn(OR) _2] _n) were investigated as precursors for the production of tin oxide (SnO x) nanowires. The precursors were synthesized from the metathesis of tin dimethylamide ([Sn(NMe _2) _2] _2) and a series of aryl alcohols {H-OAr = H-OC _6H _4(R)-2: R = CH _3 (H-oMP), CH(CH _3) _2 (H-oPP), C(CH _3) _3 (H-oBP)] or [H-OC _6H _3(R) _2-2,6: R = CH _3 (H-DMP), CH(CH _3) _2 (H-DIP), C(CH _3) _3 (H-DBP)]}. The 1:1 products were all identified as the dinuclear species [(OAr)Sn(μ-NMe _2)] _2 where OAr = oMP (1), oPP (2), oBP (3), DMP (4), DIP (5), DBP (6). The 1:2 products were identified as either a polymer ([Sn(μ-OAr) _2] ∞ (where OAr = oMP (7), oPP (8)), dinuclear [(OAr)Sn(μ-OAr)] _2 (where OAr = oBP (9), DMP (10) or DIP/HNMe _2 (11)), or mononuclear [Sn(DBP) _2] (12) complexes. These novel families of compounds (heteroleptic 1-6, and homoleptic 7-12) were evaluated for the production of SnO _x nanowires using solution precipitation (SPPT; oleylamine/octadecene solvent system) or electrospinning (ES; THF solvent) processing conditions. The SPPT route that employed the heteroleptic precursors yielded mixed phases of Sn ~o:romarchite [1 (100:0); 2 (80:20); 3 (68:32); 4 (86:14); 5 (66:35); 6 (88:12)], with a variety of spherical sized particles [1 (350-900 nm); 2 (150-1200 nm); 3 (250-950 nm); 4 (20-180 nm); 5 (80-400 nm); 6 (40-200 nm)]. For the homoleptic precursors, similar phased [7 (80:20); 8 (23:77); 9 (15:85); 10 (34:66); 11 (77:23); 12 (77:23)] spherical nanodots were isolated [7 (50-300 nm); 8: (irregular); 10 (200-800 nm); 11 (50-150 nm); 12 (50-450 nm)], except for 9 which formed polycrystalline rods [Sn ~o:romarchite (15:85)] with aspect ratios >100. From ES routes, the heteroleptic species were found to form 'tadpole-shaped' materials whereas the homoleptic species formed electrosprayed nanodots. The one exception noted was for 7, where, without use of a polymer matrix, nanowires of Sn ~o, decorated with micron sized 'balls' were observed. Due to the small amount of material generated, PXRD patterns were inconclusive to the identity of the generated material; however, cyclic voltammetry on select samples was used to tentatively identify the final Sn ~o (from 7) with the other sample identified as SnO _x (from 1).