Review—Surface Coatings for Cathodes in Lithium Ion Batteries: From Crystal Structures to Electrochemical Performance

Lithium ion batteries (LIBs) have dominated the energy industry due to their unmatchable properties that include a high energy density, a compact design, and an ability to meet a number of required performance characteristics in comparison to other rechargeable systems. Both government agencies and industries are performing intensive research on Li-ion batteries for building an energy-sustainable economy. LIBs are single entities that consist of both organic and inorganic materials with features covering multiple length scales. Two vital parameters for LIBs are their stable and safe operation. Critical insights should be made for understanding the structure to property relationships and the behavior of components under the working condition of LIBs. Since, the cathode serves as a central component of LIBs, the overall cell performance is significantly affected by the chemical and physical properties of the cathode. Cathodes tend to react with the electrolytes and, hence, to undergo surface modifications accompanied by degradation. These side-reactions result in an erosion of battery performance, thereby causing a reduced battery life and power capacity. Recently, techniques for preparing surface coatings on cathode materials have been widely implemented as a measure to improve their stability, to enhance their electrochemical performance, and to prevent detrimental surface reactions between the electrode materials and electrolyte. This review will cover different types of surface coatings for cathode materials, as well as a comparison of the changes in electrochemical performance between those materials with and without an applied coating. In addition, a brief outlook is included for different cathode materials and their coatings.