Ni-rich cathode materials have drawn lots of attention owing to its high discharge specific capacity and low cost. Nevertheless, there are still some inherent problems that desiderate to be settled, such as cycling stability and rate properties as well as thermal stability. In this article, the conductive polymers that integrate the excellent electronic conductivity of polyaniline (PANI) and the high ionic conductivity of poly(ethylene glycol) (PEG) are designed for the surface modification of LiNiCoMnO cathode materials. Besides, the PANI-PEG polymers with elasticity and flexibility play a significant role in alleviating the volume contraction or expansion of the host materials during cycling. A diversity of characterization methods including scanning electron microscopy, energy-dispersive X-ray spectrometer, transmission electron microscopy, thermogravimetric analysis, Fourier transform infrared have demonstrated that LiNiCoMnO cathode materials is covered with a homogeneous and thorough PANI-PEG polymers. As a result, the surface-modified LiNiCoMnO delivers high discharge specific capacity, excellent rate properties, and outstanding cycling performance.

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Sodium is first introduced to modify Ni-rich LiNi0.8Co0.15Al0.05O2 cathode material in this work, and Li1–x Na x Ni0.8Co0.15Al0.05O2 (x = 0, 0.01, 0.02, 0.05) is successfully synthesized by using Na2CO3 as sodium resource through coprecipitation and solid state calcination route. The morphology of the samples analyzed with SEM, EDS. and TEM show that all the samples maintain sphere-like morphology and the main elements are uniformly distributed. X-ray diffraction (XRD) results show that all the synthesized materials have typical hexagonal structure without impurities. The lattice parameters calculated from the XRD data are also refined by Rietveld refinement methods, confirming that the position of Na in the NCA is occupying the Li slab as designed. Despite a slight decrease in the initial discharge capacities, the sodium doped materials display improved capacity retention as well as superior performance at high rates. The Li0.99Na0.01Ni0.8Co0.15Al0.05O2 exhibits an initial discharge specific capacity of 184.6 mAh g–1 at 0.1 C and a capacity retention of 90.71% after 200 cycles when cycled at 1 C between 2.8 and 4.3 V, which is greatly superior to the pristine one, owing to the enlarged Li layer spacing, decreased Li+ migration activation energy, the low cation mixing, and enhanced structural stability brought by sodium treatment.

The electrochemical performance of Ni-rich cathode material at high temperature (>50 °C) and upper voltage operation (>4.3 V) is a challenge for next-generation lithium-ion batteries (LIBs) because of the rapid capacity degradation over cycling. Here we report improved performance of LiNi0.8Co0.15Al0.05O2 materials via a LiAlO2 coating, which was prepared from a Ni0.80Co0.15Al0.05(OH)2 precursor by spray-drying coating with nano-Al2O3. Investigations by X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and transmission electron microscopy revealed that an Al2O3 layer is uniformly distributed on the precursor and a LiAlO2 layer on the as-prepared cathode material. Such a coating shell acts as a scavenger to protect the cathode material from attack by HF and serious side reactions, which remarkably enhances the cycle performance at 55 °C and upper operating voltage (4.4 and 4.5 V). In particular, the sample with a 2% Al2O3 coating shows capacity retentions of 90.40%, 85.14%, 87.85%, and 81.1% after 150 cycles at a rate of 1.0C at room temperature, 55 °C, 4.4 V, and 4.5 V, respectively, which are significantly higher than those of the pristine one. This is mainly due to the significant improvement of the structural stability led by the effective coating technique, which could be extended to other cathode materials to obtain LIBs with enhanced safety and excellent cycling stability.