Bifunctional coating layer on Ni-rich cathode materials to enhance electrochemical performance and thermal stability in lithium-ion batteries

In this study we use N,N′-bismaleimide-4,4′-diphenylmethane (BMI), trithiocyanuric acid (TCA), and Jeffamine®-M1000 (molar ratio: 2:1:1; BTJ211) as a novel hybrid oligomer additive and surface modifier for coating (at concentrations of ca. 0.5–2 wt.%) of the cathode material LiNi0.80Co0.15Al0.05O2 (NCA) for lithium-ion batteries (LIBs). Qualitative analysis (1H NMR spectroscopy) confirms the polymerization of the BTJ additive. Morphological analyses (scanning electron microscopy/energy dispersive spectroscopy and high-resolution transmission electron microscopy) reveal that the hybrid oligomer is coated uniformly on the surface of the NCA, forming a BTJ@NCA powder material. Coin-type cells incorporating the 1 wt% BTJ@NCA electrode exhibit a significantly improved capacity retention (CR%) of 80.3%, relative to that of the bare NCA electrode (62.1%), at 1 C for 100 cycles at an upper voltage of 4.5 V. Electrochemical impedance spectroscopy and cyclic voltammetry reveal that this superior electrochemical performance originated from a lower charge transfer resistance (678.3 Ω vs. 349.6 Ω), improving Li+ ion diffusivity, and a lower polarization potential (242.9 mV vs. 368.9 mV). Furthermore, operando microcalorimetry of the cells containing the BTJ@NCA electrodes reveals that the modified electrodes can effectively decrease heat release by 69.6% when charging.