Engineered polycrystalline electrodes are critical to the cycling stability and safety of lithium-ion batteries, yet it is challenging to construct high-quality coatings at both the primary- and secondary-particle levels. Here we present a room-temperature synthesis route to achieve a full surface coverage of secondary particles and facile infusion into grain boundaries, and thus offer a complete ‘coating-plus-infusion’ strategy. Cobalt boride metallic glass was successfully applied to a Ni-rich layered cathode LiNi0.8Co0.1Mn0.1O2. It dramatically improved the rate capability and cycling stability, including under high-discharge-rate and elevated-temperature conditions and in pouch full-cells. The superior performance originates from a simultaneous suppression of the microstructural degradation of the intergranular cracking and of side reactions with the electrolyte. Atomistic simulations identified the critical role of strong selective interfacial bonding, which offers not only a large chemical driving force to ensure uniform reactive wetting and facile infusion, but also lowers the surface/interface oxygen activity, which contributes to the exceptional mechanical and electrochemical stabilities of the infused electrode.