Enhanced High‐Temperature Electrochemical Performance of Layered Nickel‐Rich Cathodes for Lithium‐Ion Batteries after LiF Surface Modification

Abstract

Layered nickel (Ni)-rich materials have been widely studied as attractive cathode materials for lithium-ion batteries, owing to their high theoretical specific capacity and low cost; however, most Ni-rich materials have poor cycle performance, especially at high temperatures. This study reports a simple sol-gel method for developing lithium fluoride (LiF)-coated Li-Ni 0.90 Co 0.08 Al 0.02 O 2 (NCA@LiF) by immersing NCA powder in a 1butyl-2,3-dimethylimidazolium tetrafluoroborate (BdmimBF 4 ) solution. The residual Li compound on the surface of NCA can be converted into a uniform LiF coating layer through the in situ hydrolysis of BdmimBF 4 . The Li-conducting LiF coating layer inhibits side reactions (LiPF 6 !PF 5 + LiF, PF 5 + H 2 O!POF 3 + HF, POF 3 + Li 2 O!Li x POF y + LiF, Li 2 O/LiOH + HF!H 2 O + 2LiF) with the electrolyte and protects the electrode from HF corrosion. The NCA@LiF sample shows a high capacity retention rate of 79.9 % after 200 cycles at 1 C and an excellent capacity of 155.7 mAh g À 1 at 10 C at room temperature. Additionally, the capacity retention rate of the NCA@LiF sample at high temperatures exhibited a significant improvement in comparison with the NCA sample, reaching 75.7 % after 100 cycles at 60°C at 1 C. This simple and effective method can be used for improving the electrochemistry stability and high-temperature performance of other Ni-based cathode materials.

Enhanced Electrochemical and Thermal Stabilities of Li[Ni0.88Co0.09Al0.03]O2 Cathode Material by La4NiLiO8 Coating for Li–Ion Batteries

“…Since most chemical degradation initially occurs at the electrode/electrolyte interface, surface modification plays an important role to reduce potential side reactions including irreversible phase transformation from layered structure to spinel and NiO‐type rock‐salt structures. Coating with LiF 3 , NiF 2 , TiO 2 , Li 3 PO 4 , and ZrP 2 O 7 has been applied to improve the capacity retention, which shows positive effects . Especially, Ni‐rich layered oxides have serious surface instability defects, making surface modification an essential role in improving the stability of cathode.…”

Nickel‐Rich Layered Cathode Materials for Lithium‐Ion Batteries

“…Considering the disadvantages of coating oxides with poor diffusion of lithium ions, lithium ion conductors can be used as coating materials in succession, such as LiF, LiVPO 4 F, Li 2 WO 4 , Li 2 SiO 3 , Li 2 ZrO 3 , LiNbO 3 , Li x S y O z , LiBO 2 , LiGeO 3 , LiFePO 4 , LiTi 2 (PO 4 ) 3 , Li 3 PO 4 , Li 2 O‐2B 2 O 3 , etc [87–99] . Zhao et al.…”

The Formation, Detriment and Solution of Residual Lithium Compounds on Ni-Rich Layered Oxides in Lithium-Ion Batteries

“…reactions with electrolyte at high potential. Up to now, various surface coating agents have been adopted to reduce the residual lithium impurities and to enhance the air storage stability of Ni-rich cathode materials, including phosphates (Jo et al, 2014a;Chen et al, 2017a;Min et al, 2018;Fan et al, 2019;Zou et al, 2020), fluoride (Dai et al, 2019;Huang et al, 2019b), conducting polymers (Sun et al, 2018;Gan et al, 2019;Yang et al, 2019b), and metallic oxides (Min et al, 2018;Zhao et al, 2018;Becker et al, 2019;Ho et al, 2020;Mo et al, 2020;Zhao et al, 2020). However, the formation mechanisms and functions of these coating layers are quite different, and need to be further investigated.…”