Elimination of Extraneous Irreversible Capacity in Mesoporous Tin Phosphate Anode by Amorphous Carbon Coating

Abstract

Mesoporous tin phosphate with a ∼10 nm pore size was synthesized using a sodium-dodecyl-sulfate surfactant as a new anode for a Li-ion cell. The tin phosphate with body centered cubic (bcc) mesostructure exhibited a initial charge capacity of 540 mAhg, and showed good capacity retention ratio, corresponding to 87% after 20 cycles. Relatively large irreversible capacity (571 mAhg) ratio of 51%, which impedes the practical application in Li-ion cell, is reduced by the amorphous carbon coating. The coating leads not only to reduced extraneous irreversible capacity ratio of 26% but also improved capacity retention by 11% without changing the first charge cpacity, compared with the uncoated sample. However, intrinsic irreversible capacity loss from the decomposition reaction to tin metal and lithium phosphate phase is unavoidable.