| Summary: | Ammonium vanadium oxide (NH<sub>4</sub>V<sub>4</sub>O<sub>10</sub>) is a promising layered cathode for aqueous zinc-ion batteries owing to its high specific capacity (>300 mA h g<sup>−1</sup>). However, the structural instability causes serious cycling degradation through irreversible insertion/extraction of NH<sub>4</sub><sup>+</sup>. Herein, a new potassium ammonium vanadate K<i><sub>x</sub></i>(NH<sub>4</sub>)<sub>1−<i>x</i></sub>V<sub>4</sub>O<sub>10</sub> (named KNVO) is successfully synthesized by a one-step hydrothermal method. The inserted of K<sup>+</sup> can act as structural pillars, connect the adjacent layers closer and partially reduce the de-insertion of NH<sub>4</sub><sup>+</sup>. Due to the multi-functional of K<sup>+</sup>, the prepared KNVO presents a high specific discharge capacity of 432 mA h g<sup>−1</sup> at a current density of 0.4 A g<sup>−1</sup>, long cycle stability (2000 cycles, 94.2%) as well as impressive rate performance (200 mA h g<sup>−1</sup> at 8 A g<sup>−1</sup>).
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