The coordinated development of new energy vehicles and the energy storage industry has become essential for reducing carbon emissions. The cathode material is the key material that determines the energy density and cost of a power battery, but currently developed and applied cathode materials cannot meet the requirements for high specific capacity, low cost, safety, and good stability. High-entropy materials (HEMs) are a new type of single-phase material composed of multiple principal elements in equimolar or near-equimolar ratios. The interaction between multiple elements can play an important role in improving the comprehensive properties of the material, which is expected to solve the limitations of battery materials in practical applications. Therefore, this review provides a comprehensive overview of the current development status and modification strategies of power batteries (lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs)), proposes a high-entropy design strategy, and analyses the structure–activity relationship between the high-entropy effects and battery performance. Finally, future research topics related to high-entropy cathode materials, including computational guide design, specific synthesis methods, high-entropy electrochemistry, and high-throughput databases, are proposed. This review aims to provide practical guidance for the development of high-entropy cathode materials for next-generation power batteries.