Rechargeable Li metal batteries have attracted lots of attention because they can achieve high energy densities. However, the commercialization of rechargeable Li metal batteries is delayed because Li dendrites may be generated during the batteries’ electrochemical cycles, which may cause severe safety issues. In this research, a Li-B alloy is investigated as an anode for rechargeable batteries instead of Li metal. Results show that the Li-B alloy has better effects in suppressing the formation of dendritic lithium, reducing the interface impedance and improving the cycle performance. These effects may result from the unique structure of Li-B alloy, in which free lithium is embedded in the Li7B6 framework. These results suggest that Li-B alloy may be a promising anode material applicable in rechargeable lithium batteries.