Advances and Prospects of Surface Modification on Nickel‐Rich Materials for Lithium‐Ion Batteries^†

Abstract

Although layered Ni-rich cathode materials have attracted lots of attention for their high capacity and power density, several significant issues, such as poor thermal stability and moderate cyclability, limit their practical applications. Most of these undesired problems of Ni-rich materials are caused by the unstable surface or the parasitic reactions at cathode-electrolyte interface. Surface coating is the most common method to suppress such interfacial problems for Ni-rich materials. This review focuses on the surface engineering of the Ni-rich materials in recent years, including the species used in coating, synthetic strategies of uniform coating layer, and the positive effects of coating species on the active materials. Detailed discussions are also taken to describe the formation mechanism of the surface coating layer with design philosophy. Finally, the prospects for further developments and challenges in surface coating are also summarized. Yuefeng Su (left) is a professor in the School of Materials Science and Engineering at Beijing Institute of Technology (BIT). In 2013, he was awarded New Century Excellent Talents in University from the Chinese Ministry of Education. His research group mainly engaged in the research of green secondary batteries and advanced energy materials, including lithium-rich cathode materials, nickel-rich cathode materials and other high-power energy storage devices. As the principal investigator, Prof. Su successfully hosted the National Key Research and National Natural Science Foundation of China, etc. Gang Chen (middle) is currently a Ph.D. candidate under the supervision of Prof. Yuefeng Su in the School of Materials Science and Engineering at Beijing Institute of Technology. His major research includes the design and synthesis of Ni-rich cathode materials for high performance lithium ion batteries, especially for the interfacial design and its mechanism research of Ni-rich materials. Lai Chen (right) obtained his Ph.D. majoring in Environmental Engineering from Beijing Institute of Technology (BIT) in 2017, and is currently an associate professor at the school of Materials Science and Engineering at BIT. As the principal investigator, he has successfully hosted the

Roles of Fast‐Ion Conductor LiTaO3 Modifying Ni‐rich Cathode Material for Li‐Ion Batteries

“…The positive impacts originate from the synergistic effects of suitable LiTaO 3 coating and Ta 5+ doping as long as the fast ion‐conductor coating layer and the enlarged inter‐planar spacings could not only modify the interfaces and accelerate the transfer of Li‐ions, but also prevent the direct contact between electrolyte and electrode, decreasing the parasitic reactions and thus improving the cycling stabilities and rate performances of Ni‐rich materials [18] . However, the electrochemical performances of LTO‐3 and LTO‐4 at 10 C rate are abnormal and unexpected because the coating of fast ion‐conductor layer is always beneficial to the electrochemical performances of Ni‐rich materials [5d,19] . Herein, combined with the scanning electron microscopy (SEM) and TEM results, we can conclude that even though the LiTaO 3 is one kind of faster lithium‐ion conductor, and the self‐agglomeration and scattering of over‐added of LiTaO 3 will prolong the transfer length of Li ions, worsening the electrochemical kinetics and deteriorating the electrochemical performances of Ni‐rich materials.…”

Thermal Expansion Neutralization Enhancing the Cycling Stability of Ni-Rich LiNi0.6Co0.2Mn0.2O2 Cathode Material

“…The selected area electron diffraction (SAED) image (Figure b) indicates the characteristic layered structure mixed with a secondary phase detected in the as-prepared 622@LZPO particle. According to fast Fourier transform combined with the inverse fast Fourier transform analysis (Figure S3a,b), the interior region I (red rectangular) exhibits the layered phase ( R -3 m space group) of LiTMO 2 (lithium transition metal oxides); meanwhile, the near surface region II (yellow rectangular) presents the Fm -3 m space group which often appeared in various surface doping cases. ,− Element mapping images (Figure S3c) and line-scan profile (Figure c) based on EDS demonstrate that the signal of the Zr element can be distinctly detected, and its intensity is decreased from the surface to the interior of one 622@LZPO particle. Herein, it is suggested that the Zr doping might have occurred during LZPO modification, which usually facilitates the formation of Fm -3 m phases in the near surface region II.…”

Review of the Scalable Core–Shell Synthesis Methods: The Improvements of Li‐Ion Battery Electrochemistry and Cycling Stability

“…The scavenger of acidic HF leads to the dissolution of transition metal ions out of the surface of the active material, causing lattice damage and continuous loss of active material. [ 55c,e,80 ] During (de)lithiation, the coating layer could help to suppress the phase transition of cathodes from a layered structure to a rock‐salt phase because the presence of the physical layer can prevent the loss of oxygen from the lattice by preventing the reaction between reactive Ni 4+ and electrolyte. [ 81 ] Although core–shell materials cannot directly suppress the intergranular and intragranular cracking, it reduces effects of lattice expansion along the c ‐axis and shrinkage along the a‐axis and b‐axis.…”