On the structure and electrochemical reactions with lithium of tin(II) phosphate chloride

A crystalline solid of Sn2PO4Cl stoichiometry and orthorhombic structure wa s characterized and used as electrode material vs. a lithium metal anode. T he structure of the solid resembles that of SnO; tin atoms protrude from la yers of PO4 tetrahedra, while chlorine atoms are located between Sn layers. Two-electrode electrochemical cells of the type Li/LiClO4(PC:EC)/Sn2PO4Cl (PC, propylene carbonate; EC, ethylene carbonate) were mounted and discharg ed to a maximum capacity close to 6.4 faradays per Sn atom. This correspond s to the complete reduction of Sn(II) to Sn(0) followed by the formation of noncrystalline Li-Sn alloys up to a limiting composition of Li22Sn5. The s econd step of the discharge shows an interesting reversibility. After a dec rease in capacity during the first ten cycles, ascribable to the increase i n the size of tin domains, the charge and discharge capacities remain close to 300 Ah/kg (Sn) up to ra. 40 cycles. (C) 2000 The Electrochemical Societ y, S0013-4651(99)10-086-7. Al rights reserved.