Lithium metal-based batteries offer promising prospects as alternatives to today's lithium-ion batteries, due to their ultra-high energy density. Unfortunately, the application of lithium metal is full of challenges and has puzzled researchers for more than 40 years. In this feature article, we describe the history of the development of lithium metal batteries and their existing key challenges, which include non-uniform electrodeposition, volume expansion, high reactivity of the lithium metal/unstable solid electrolyte interphase (SEI), and the shuttling of active cathode materials. Then, we focus on the growth mechanisms of uneven lithium electrodeposition and extend the discussion to the approaches to inhibit lithium dendrites. Finally, we discuss future directions that are expected to drive progress in the development of lithium metal batteries.