Tin phosphide (SnP_0.94) particles were synthesized by thermal decomposition of tin acetate in a mixed solution of trioctylphosphine and a high-boiling solvent. Teardrop-shaped SnP_0.94 particles with the size of about 500 nm were obtained by using trioctylphosphine oxide as a coordinating solvent. In the case using oleylamine as a solvent, the shape of SnP_0.94 particles was not uniform. Formation mechanism of teardrop-shaped SnP_0.94 was discussed. SnP_0.94 particles prepared by using the trioctylphosphine oxide as a coordinating solvent were applied as an active material to all-solid-state lithium cells. The cell Li–In/80Li₂S·19P₂S₅·1P₂O₅/SnP_0.94 exhibited the initial discharge capacity of 1000 mAh g⁻¹ at a current density of 1.3 mA cm⁻².