Search

LiNi0.8Co0.1Mn0.1O2 (NCM811) has a high potential for using as the cathode material for lithium–ion batteries (LIBs) for electric vehicles owing to its high energy density and low cost. However, its poor rate capability and cycling performance have significantly hindered its application. In this study, we successfully design a uniform magnesium oxide (MgO) coating on NCM811 via a wet-chemical coating followed by heat treatment using magnesium ethoxide [Mg (OEt)2] dissolved in ethanol as the Mg source. The effects of MgO coating on the surface states, crystal structure, and electrochemical performances of NCM811 cathode material are studied in detail. After 100 cycles, the capacity retention of MgO-coated NCM811 is 90.1% at room temperature at 1 C, whereas the pristine NCM811 is only 74.5%. Besides, the MgO-coated NCM811 delivers a better rate property than pristine NCM811. Prominent improvements in electrochemical performances are attributed to the fact that the formation of MgO coating layer helps to suppress deleterious side reactions, lower the overpotential on the surface, and facilitate lithium–ion diffusion. [ABSTRACT FROM AUTHOR]

Li- and Mn-rich materials have high capacities but serious voltage attenuation, whereas Ni-rich materials LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM) have good rate characteristics but poor stabilities, and they readily to oxidize organic electrolytes. The core–shell strategy with Ni-rich materials as the core and Li- and Mn-rich materials as the shell was expected to balance these merits and drawbacks. In this work, simple and concentration-gradient Li- and Mn-rich shell were successfully synthesized on NCM and critically compared. As expected, a distinct core–shell interface was observed for the simple core–shell cathode, which causes the shell to crack during cycling and exhibits worse electrochemical performance than the single Li- and Mn-rich cathodes and Ni-rich cathodes. In contrast, the fabricated concentration-gradient core–shell cathode shows the uniform fusion of the core and shell at the atomic level, and the overall electrochemical performance is far superior to that of the simple core–shell and pristine cathodes. In addition, it delivers an initial reversible capacity of 226.6 mAh g−1 at a C-rate of 0.1C and 120.2 mAh g−1 at 10.0C, and it retains 86.9% of its capacity after 100 cycles to 4.6 V at 1.0C. Differential capacity versus potential (d Q /d V versus V) and EIS analyses show that the concentration-gradient core–shell cathode has a stable impedance and very stable average voltage. Obviously, the concentration-gradient coating of the Li- and Mn-rich shell can maximize the merits of the core and shell. • Both simple and concentration gradient Li- and Mn-rich shell coated samples increase the capacity of LiNi 0.8 Mn 0.1 Co 0.1 O 2. • A distinct core-shell interface was observed in simple core-shell cathode. • Simple core-shell structure exhibits a negative effect on cycling stability, rate capability and Li-ion diffusivity. • The concentration gradient Li- and Mn-rich shell is able to relieve side reactions and largely improved cycling stability. [ABSTRACT FROM AUTHOR]