Potassium-ion batteries were first introduced to the world for energy storage in 2004, over two decades after the invention of lithium-ion batteries.  Potassium-ion (or “K-ion”) batteries have many advantages, including low cost, long cycle life, high energy density, safety, and reliability. Potassium-ion batteries are the potential alternative to lithium-ion batteries, fueling a new direction of energy storage research in many applications and across industries.