As the demand grows for lithium-ion (Li-ion) batteries, their performance requirements and environmental impact increase. Battery performance strongly depends on the composition of the cathode materials, requiring precise elemental ratios. Meanwhile, disposing spent batteries can have a negative environmental impact, which can be greatly reduced through recycling. Inductively coupled plasma–optical emission spectroscopy (ICP-OES) provides solutions in both of these areas. By using high-precision ICP-OES, precise measurements can be made to accurately determine compositions of a variety of different cathode materials. In battery recycling, ICP-OES meets the requirements of being a multielement technique with a wide dynamic range and the ability to handle complex matrices. Therefore, it can measure both high-concentration and impurity elements resulting from the incineration of spent batteries, providing recycling facilities information about the elements present and their levels so that recoveries can be optimized.