Rechargeable batteries based on lithium (Li) metal chemistry are attractive for next-generation energy storage. Nevertheless, dendritic growth, infinite relative dimension change, severe side reactions and limited power output, greatly impede their practical applications. The presented work for the first time introduces an electrolyte-proof design of three-dimensional Li metal anode where most of the Li domains are embedded in a Li-ion conductive matrix. In the new architecture, the Li-ion conductive matrix isolate the embedded Li domains from liquid electrolyte and thus prevent severe initial side reactions, while the matrix can simultaneously transport Li-ion and maintain the electrochemical activity of the embedded Li. This composite electrode was obtained by reacting over-stoichiometry of Li with SiO above Li melting temperature. The unique reaction dynamics results in a structure of Li embedded in the LixSi-Li2O matrix with one-pot synthesis. Since uniform Li nucleation and deposition can be fulfilled owing to the high-density active Li domains, the as-obtained nanocomposite electrode exhibits low polarization, stable cycling and high-power output (up to 10 mA/cm2) even in carbonate electrolytes. The Li-S prototype cells further exhibited highly improved capacity retention under power-intersive operation (~600 mAh/g at 6.69 mA/cm2). The all-round improvement on electrochemical performance sheds light on the effectiveness of the new design principle for developing safe and stable Li metal anodes with high-power capability.