Effect of anisotropic volume change in tin phosphate nanoparticle anode material with mesocellular foam structure on capacity retention

Tin phosphate nanoparticles within microcellular foams were prepared using a nonionic triblock copolymer surfactant P123. The annealed sample at 500 degrees C showed the particle size of 50-200 nm, and the size of the mesocelluar foam was ranged from 4 to 20 nm. Due to the irregular porewall thickness and pore size of the annealed sample, the pore wall structure had completely collapsed after first cycle. As the number of cycles increased, metallic tin clusters grew in the lithium phosphate matrix, and uniformly dispersed tetragonal tin nanoparticles with a particle size of 3 nm were observed after 100 cycles. This indicated that tin clusters decomposed from tin phosphate expanded and contracted reversibly in the matrix without particle aggregation. This was well supported by the electrochemical data, and the capacity increased to from 285 to 520 mAh/g with no capacity fading.