Despite the high theoretical capacity, the deposition of solid alkali metals can trigger dendrites growth, causing safety risk, capacity and life decay. While liquid NaK alloy is dendrite-free, their fluidity may cause leakage or even short circuit. In this work, a novel controllable phase transformation strategy was proposed enabled NaK anode to be processed in near-solid and work in liquid, effectively overcoming the challenges of dendrite formation and leakage. Specifically, a near-solid anode was fabricated by liquid metal (LM)-assisted mechanochemistry reaction, which can be easily shaped and integrated into batteries without leakage risk. Then self-accelerated phase transformation continues within the battery, driven by an LM-mediated in-situ replacement reaction, converts the near-solid electrode into liquid state and enabling dendrite-free operation. For the first time, a cylindrical cell with liquid NaK alloy anode was successfully matched and demonstrated excellent electrochemical performances. This innovation not only enhances safety but also advancing the practical application of liquid metal electrodes in energy storage systems.