Rapid increases in global energy use and growing environmental concerns have prompted the development of clean and sustainable alternative energy technologies. Electrical energy storage (EES) is critical for efficiently utilizing electricity produced from intermittent, renewable sources such as solar and wind, as well as for electrifying the transportation sector. Rechargeable batteries are prime candidates for EES, but widespread adoption requires optimization of cost, cycle life, safety, energy density, power density, and environmental impact, all of which are directly linked to severe materials challenges. This article presents a brief overview of the electrode materials currently used in lithium-ion batteries, followed by the challenges and prospects of next-generation insertion-reaction electrodes and conversion-reaction electrodes with a Li+ working ion. Finally, we discuss future directions involving solid electrolytes, multi-electron transfer hosts, and other working ions.