Bifunctional Surface Coating of LiNbO₃ on High-Ni Layered Cathode Materials for Lithium-Ion Batteries

Abstract

High-Ni cathode materials with a layered structure generally suffer from structural instability induced by a highly reactive Ni component, especially at the surface. Crystalline LiNbO 3 , with excellent thermal stability and ionic conductivity, has the potential to considerably enhance the interfacial stability of these cathode materials. By optimizing the crystalline coating of bifunctional LiNbO 3 on a high-Ni cathode material, we are able to improve cycle performance and rate capability by minimizing the direct exposure of Ni with electrolytes. Since a LiNbO 3 coating layer directly affects electrochemical performance, we also focus on the correlation of LiNbO 3 crystallinity with electrochemical behaviors of Li + in the cathode materials. We show that the Li + conducting behaviors are closely related to the crystallinity of LiNbO 3 . Highly crystalline LiNbO 3 effectively suppresses the structural changes of the cathode materials by facilitating strain relaxation induced by repeated Li + intercalation and deintercalation into and from the host structure. Moreover, it offers strong enhancement in mechanical and thermal stabilities at elevated temperatures above 60 °C. In this regard, this research provides a practical solution for successfully utilizing high-Ni layered cathode materials in commercial LIBs.

Enabling a High-Throughput Characterization of Microscale Interfaces within Coated Cathode Particles

“…The modifications of LNMO and other cathode materials [e.g., LiMn 2 O 4 , LiCoO 2 , LiNi 0.8 Mn 0.1 Co 0.1 O 2 (NMC811)] with a coating of LiNbO 3 can improve the cycle performance and enhance the overall charge capacity of these materials. ,, In principle, LiNbO 3 is an excellent solid electrolyte with a high thermal and chemical stability, as well as a low charge transfer resistance. , The degree of crystallinity of the LiNbO 3 determines whether the coating can successfully suppress the detrimental structural changes to the cathode materials that can result from the intercalation and deintercalation of Li ions during electrochemical cycling. , Although the neutralization of free radicals or adverse chemical species (e.g., HF and/or residual alkali compounds) does not require the coating to have a uniform coverage over the particle, the coatings that serve as a physically protective layer often do require complete coverage of the particles . Prior art has indicated that ultrathin, uniform LiNbO 3 coatings (e.g., <10 nm in thickness) exhibit a relatively low charge transfer impedance, a high Li diffusivity, and an improved protection from structural collapse .…”

“…These characteristics contribute to the lower discharge capacity observed for the LiNbO 3 -coated LNMO particles (122 mAh/g) than that of the as-prepared LNMO particles (130 mAh/g) after the 100 charge–discharge cycles at a rate of 1C (Figure S19). The crystallinity of the coating is also an important factor that dictates the performance of the coating in response to mechanical and thermal stresses . The presence of amorphous domains in the coatings could also contribute to the relatively lower performance of the coated LNMO particles.…”

“…57,58 The degree of crystallinity of the LiNbO 3 determines whether the coating can successfully suppress the detrimental structural changes to the cathode materials that can result from the intercalation and deintercalation of Li ions during electrochemical cycling. 59,60 Although the neutralization of free radicals or adverse chemical species (e.g., HF and/or residual alkali compounds) does not require the coating to have a uniform coverage over the particle, the coatings that serve as a physically protective layer often do require complete coverage of the particles. 14 Prior art has indicated that ultrathin, uniform LiNbO 3 coatings (e.g., <10 nm in thickness) exhibit a relatively low charge transfer impedance, a high Li diffusivity, and an improved protection from structural collapse.…”

“…The crystallinity of the coating is also an important factor that dictates the performance of the coating in response to mechanical and thermal stresses. 59 The presence of amorphous domains in the coatings could also contribute to the relatively lower performance of the coated LNMO particles. The ability to inspect the particle−coating interface via a high-throughput method could be extended to characterizing the cathode materials at end of life, as well as to other types of cathode materials and materials within LIBs.…”

Engineering a Robust Interface on Ni-Rich Cathodes via a Novel Dry Doping Process toward Advanced High-Voltage Performance

“…To date, secondary or primary particles of LiNi x Co y Mn 1– x – y O 2 cathodes have been coated or recombined with chemically stable compounds (Al 2 O 3 , WO 3 , Li 3 PO 4 , LiNbO 3 , and LiAlO 2 ) to prevent the bulk material from electrolyte erosion and prolong the life span. − Actually, it is trouble to generate an adequately uniform coating layer to serve as a firewall against corrosion from the organic electrolyte, and the sophisticated coating procedure also hampers its industrial application. Alternatively, bulk doping with Nb, Zr, Mg, W, Na, F, and so forth in a transition metal layer or an oxygen layer has also been extensively reported. − Taking Zr 4+ substitution for instance, lattice Zr 4+ shows a stronger oxygen binding capacity than Ni 2+/3+ , Co 3+ , and Mn 4+ , leading to a stable transition metal layer .…”