Multipod Bi(Cu2‑xS)n nanocrystals formed by dynamic cation−ligand complexation and their use as anodes for potassium-ion batteries

We report the formation of an intermediate lamellar Cu–thiolate complex, and tuning its relative stability using alkylphosphonic acids are crucial to enabling controlled heteronucleation to form Bi(Cu2-xS)n heterostructures with a tunable number of Cu2-xS stems on a Bi core. The denticity of the phosphonic acid group, concentration, and chain length of alkylphosphonic acids are critical factors determining the stability of the Cu–thiolate complex. Increasing the stability of the Cu–thiolate results in single Cu2-xS stem formation, and decreased stability of the Cu–thiolate complex increases the degree of heteronucleation to form multiple Cu2-xS stems on the Bi core. Spatially separated multiple Cu2-xS stems transform into a support network to hold a fragmented Bi core when used as an anode in a K-ion battery, leading to a more stable cycling performance showing a specific capacity of ∼170 mAh·g–1 after 200 cycles compared to ∼111 mAh·g–1 for Bi–Cu2-xS single-stem heterostructures.