With lithium-ion (li-ion) batteries as energy storage devices, operational safety from thermal runaway remains a major obstacle especially for applications in harsh environments such as in the oil industry. In this approach, a facile method via microwave irradiation technique (MWI) was followed to prepare co 3 o 4 /reduced graphene oxide (RGO)/hexagonal boron nitride (h-BN) nanocomposites as anodes for high temperature li-ion batteries. Results showed that the addition of h-BN not only enhanced the thermal stability of Co 3 o 4 /RGO nanocomposites but also enhanced the specific surface area. co 3 o 4 /RGO/h-BN nanocomposites displayed the highest specific surface area of 191 m 2 /g evidencing the synergistic effects between RGO and h-BN. Moreover, Co 3 o 4 /RGO/h-BN also displayed the highest specific capacity with stable reversibility on the high performance after 100 cycles and lower internal resistance. Interestingly, this novel nanocomposite exhibits outstanding high temperature performances with excellent cycling stability (100% capacity retention) and a decreased internal resistance at 150 °C. Li-ion batteries energy storage devices are used as a power source for almost all electronic devices due to the superior benefits over other types of batteries 1-4. However, the safety feature and the narrow temperature operating range of li-ion batteries remain a major obstacle for more complex applications of li-ion batteries such as in the oil industry, defense, automotive applications and aerospace that demand safe operation at wide temperature range (up to 150 °C). Li-ion batteries are known to operate effectively between −20 °C and 60 °C 5. With the increasing demand for li-ion batteries, many research has been made on increasing its thermal stability and the upper operating temperature range. When considering safety issues of li-ion batteries it is mainly related to thermal runaway. Conditions such as elevated temperature and high charge levels or overcharging abuses one or more of the battery components that results in what is called a short circuit leading to heat, fire or explosion. A process referred to as thermal runaway 6. Thermal runaway mechanisms occur mainly at the electrodes and electrolytes. Thermal decomposition of the electrodes or electrolytes and reduction or oxidation of the electrolyte is the main cause of thermal runaways. To solve this issue, many preventative measures have been investigated. Preventative measures can be the use of safety devices, that is, design devices that release high pressure and heat before thermal runaway but this is for engineers to set up new safe li-ion battery devices. However, what concerns scientists more is the inherent safety from electrodes, to electrolytes 7. Compromising between the electrochemical performances and thermal stability is a challenge.

We report a microwave irradiation method for the preparation of reduced graphene oxide (RGO) based Co3O4 nanocomposites as anodes for lithium-ion (li-ion) batteries. The Co3O4/RGO nanocomposites displayed good electrochemical behavior as anodic materials for li-ion batteries when compared to pure Co3O4. The Co3O4/RGO nanocomposites with low RGO content resulted in stable electrochemical performance with 100% coulombic efficiency at a high current density of 500 mA/g for 50 cycles. The enhanced capacity of the Co3O4/RGO nanocomposites is due to the incorporation of RGO, which resulted in a four times larger surface area than that of Co3O4. This increased surface area could facilitate the absorption of more lithium ions, resulting in excellent electrochemical performance. Interestingly, the novelty of this work is that the designed li-ion batteries showed stable electrochemical performance even at a high temperature of 100 °C, which might be useful for rechargeable battery applications in a wide temperature range.

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The high theoretical energy density and low cost of lithium–sulfur (Li–S) batteries make them promising candidates for future energy storage devices. Here, we developed Co3O4/CoO/graphene nanosheets (GNS)/hexagonal boron nitride (h-BN) nanocomposite-based sulfur as cathodes for Li–S batteries. Due to the synergistic effects of GNS/h-BN and Co3O4/CoO, the reported Co3O4/CoO/GNS/h-BN nanocomposites not only effectively trap lithium polysulfides but also can accelerate the redox kinetics for the conversion of polysulfides. The enhanced electrochemical activity of Co3O4/CoO/GNS/h-BN is due to the (111) exposed surface of Co3O4 and the formation of CoO on Co3O4, which is the catalytically active phase of Co3O4-based catalysts. GNS/h-BN provides a large surface area for the high exposure of the Co3O4/CoO catalyst and can also influence the catalytic activity due to enhanced charge transfer. Co3O4/CoO/GNS/h-BN/S nanocomposites showed superior electrochemical performances and high sulfur utilization compared to GNS/h-BN/S and Co3O4/CoO/S. More significantly, a very high capacity retention of 89% was obtained with a reversible capacity of 356.29 mA h/g after 250 cycles at a current rate of 1 C. Also, enhanced redox conversion of lithium polysulfides was observed when the cell was operated at higher temperatures. Besides cobalt oxide, other metal oxides such as Fe2O3 and SnO2 on GNS/h-BN could also be potential candidates for high-performance Li–S batteries.

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