Abstract It is important to understand the growth mechanism of Li dendrites for the protection of Li metal anodes. Herein, joule heat as another inducing mechanism for Li dendrites is proposed and demonstrated by experiments and theoretical simulations. A nonuniform interface structure can lead to disordered surface thermal distribution based on joule heat theory, which may induce chaotic nucleation and growth of dendrites. Based on this concept, a new strategy of liquid metal welding is explored to overcome such joule heat distribution issue. This strategy is universally compatible with other traditional protection routes such as solid electrode interphase films, charging protocols, and electrolytes. Multistrategy synergetic protection strategies result in remarkable performance.