Antimony-carbon nanocomposites are known anode materials for lithium- and sodium-ion batteries that can display an attractively stable cyclic behaviour in half-cells. They can also be used for potassium-ion batteries but a similar stability is not achieved, and electrode failure (abrupt capacity decay) is noted. Here, we probe the failure mechanism in potassium cells using samples with varied Sb particle sizes and weight fractions. A smaller particle size and extra carbon result in a failure in a later cycle. Mechanical degradation is the main reason for capacity drop; the phenomena associated with unstable solid electrolyte interphase are less critical. A number of strategies (an electrolyte additive, the type of a binder and adding an extra alloying element to composites) are explored. The choice of a binder affects the nature of decay and may lead to longer cycling. The inclusion of phosphorus in the nanocomposite coupled with an alternative binder appears to be more effective in improving the cyclic stability; a capacity of above 400 mAh g−1 is achieved in the first 50 cycles. The results demonstrate that the stability of alloying-dealloying anode materials in potassium-ion batteries can be influenced by optimising the composition of these materials and altering a binder.