Surface Modification of Li-Rich Mn-Based Layered Oxide Cathodes: Challenges, Materials, Methods, and Characterization

Rechargeable lithium-ion batteries have become the dominant power sources for portable electronic devices, and are regarded as the battery technology of choice for electric vehicles and as potential candidates for grid-scale storage. Commercial lithium-ion batteries, after three decades of cell engineering, are approaching their energy density limits. Toward continually improving the energy density and reducing cost, Li-rich Mn-based layered oxide (LMLO) cathodes are receiving more and more attention due to their high discharge capacity and low cost. However, commercialization has been hampered by severe capacity and voltage decay, sluggish rate capability, and poor safety performance during charge/discharge cycles. Surface modification has effectively adopted to improve the electrochemical performance of LMLO cathodes. In this review, the main problems and recent progress in the field are summarized, focusing on challenges, materials, methods, and characterization techniques. More effective surface modification can be accomplished by strengthening nondestructive in situ measurements, expanding atomic/molecular layer (ALD/MLD) deposition techniques, and adopting fluorinated cosolvents.