Ni-rich layered cathode materials LiNi x Co y Mn (1-x–y) O 2 (x ≥ 0.8) suffer from capacity decay due to structural deterioration during electrochemical cycling. To overcome these problems, the fast-ion conductor Li 0.33 La 0.56 TiO 3 (LLTO) is coated on the surface of LiNi 0.83 Co 0.12 Mn 0.05 O 2 (NCM83) cathodes through the sol–gel method, which can stabilize the electrode/electrolyte interface of cathode materials and facilitate Li + transport and charge transfer. As a result, the LLTO-coated NCM83 exhibits better cycle stability and higher rate performance. The NCM83 modified by 5 wt% LLTO has the discharge capacity of 185.9 mAh g −1 at 1C rate after 100 cycles and with higher capacity retention of 92.9% than the pristine NCM83 of 86.2%, and as well as the 5 wt% LLTO-coated NCM83 has a higher Li + -insert diffusion coefficient of 1.143 × 10 −11 cm 2 s −1 than the pristine NCM83 of 8.757 × 10 −12 cm 2 s −1 . Therefore, the fast-ion conductor LLTO coating strategy shows great potential in improving the performance of Ni-rich layered cathode materials.
Ni-rich layered structure materials are appealing cathodes for high-energy-density lithium-ion batteries developed for electric vehicles, drones, power tools, etc. However, poor interfacial stability between a Ni-rich cathode and carbonate electrolyte, especially at high temperatures, and fast capacity fading still hinder their mass market penetration. Here, we investigate cyclopentyl isocyanate (CPI) with a single isocyanate (−NCO) functional group as a bifunctional electrolyte additive for the first time to improve the interfacial stability of Ni-rich cathode LiNi0.83Co0.12Mn0.05O2 (NCM83). With an electrolyte containing 2 wt % CPI, the NCM83 cathode shows capacity retention of up to 92.3% after 200 cycles at 1C and 30 °C, much higher than that with the standard electrolyte (78.6%). It is demonstrated that the −NCO of CPI could largely inhibit the thermal decomposition of LiPF6 salt and scavenge water and hydrogen fluoride (HF) species, improving electrolyte stability. More importantly, the additive CPI could be preferentially oxidized, forming a stabilized and protective cathode electrolyte interphase (CEI) layer on the surface of NCM83, which effectively suppresses the parasitic side reactions and maintains the superior interfacial charge-transfer and lithium-ion diffusion kinetics. Both functions enable a significant improvement in electrochemical performance at both 30 and 60 °C.
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