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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.

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The solid-state reaction has been widely employed as the standard procedure to prepare oxide cathode materials for sodium-ion batteries. However, it involves multiple steps and consumes much energy. In this work, we report a facile method to synthesize a large-grained O3−NaCrO 2 cathode by directly reducing sodium dichromate dihydrate (Na 2 Cr 2 O 7 • 2H 2 O) under a hydrogen atmosphere. Owing to its unique large particle morphology, the as-prepared NaCrO 2 exhibits a high tap density of 2.55 g cm −3 . The compact NaCrO 2 shows excellent electrochemical performance with a high reversible capacity of 123 mAh g −1 at 0.1C, a high capacity retention of 88.2% after 500 cycles at 2C, and an outstanding rate capability of 68 mAh g −1 at 20C. The performance is attributed to a stable structure from the distinctive morphology with small specific surface area to suppress interfacial side reactions and rapid Na-ion diffusion channels with a highly (110)-oriented crystal structure. Ex situ X-ray diffraction and cyclic voltammetry tests demonstrate the consecutive and reversible phase transition mechanism with facile Na + migration. Importantly, the obtained cathode material exhibits an excellent performance in sodium-ion full cells with hard carbon as the anode.

A novel design concept and green synthesis strategy of the Hummers method for fabricating 3D graphene directly from the GO mixed liquor.

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