Recently, lithium oxygen battery has become a promising candidate to satisfy the current large-energy-storage devices demand because of its amazing theoretical energy density. However, it still faces problems such as poor reversibility and short cycle life. Here, citrus maxima peel (CMP) was used as a precursor to prepare activated and Fe-loading carbon (CMPACs and CMPACs-Fe, respectively) via pyrolysis in nitrogen atmosphere at 900 °C, in which KOH was added as an activator. Electrochemical measurements show that CMPAC-based Li-O battery possesses high specific capacity of 7800 mA h/g, steady cycling performance of 466 cycles with a corresponding Coulombic efficiency of 92.5%, good rate capability, and reversibility. Besides, CMPACs-Fe-based O electrode delivers even lower overpotential in both charge and discharge processes. We conclude that these excellent electrochemical performances of CMPACs and CMPACs-Fe-based O electrode benefit from their cellular porous structure, plenty of active sites, and large specific surface area (900 and 768 m/g), which suggest that these biomass-derived porous carbons might become promising candidates to achieve efficient lithium oxygen battery.

Large energy-storage systems and electric vehicles require energy devices with high power and high energy density. Lithium oxygen (Li-O) batteries could achieve high energy density, but they are still facing problems such as low practical capacity and poor cyclability. Here, we prepare activated carbons (MGACs) based on the natural plant Miscanthus × giganteus (MG) through slow pyrolysis. It possesses a large surface area, plenty of active sites, and high porosity, which are beneficial to the utilization of oxygen electrode in Li-O batteries. The MGACs-based oxygen electrode delivers a high specific capacity of 9400 mAh/g at 0.02 mA/cm, and long cycle life of 601 cycles (with a cutoff capacity of 500 mAh/g) and 295 cycles (with a cutoff capacity of 1000 mAh/g) at 0.2 mA/cm, respectively. Additionally, the material exhibits high rate capability and high reversibility, which is a promising candidate for the application in Li-O batteries.

The pore-throat radius of the shale oil reservoir is extremely small, and it is difficult to accurately obtain the absolute permeability and oil–water two-phase relative permeability of the actual oil reservoir through conventional core experiments. However, these parameters are very important for reservoir numerical simulation. In this paper, a method for characterizing flow parameters based on a pore network model that considers differential pressure flow and diffusion flow is proposed. Firstly, a digital core was reconstructed using focused ion beam scanning electron microscopy (FIB-SEM) from the Gulong shale reservoir in the Songliao Basin, China, and a pore network model was extracted. Secondly, quasi-static single-phase flow and two-phase flow equations considering diffusion were established in the pore network model. Finally, pore-throat parameters, absolute permeability, and oil–water two-phase permeability curves were calculated, respectively. The results show that the pore-throat distribution of the Gulong shale reservoir is mainly concentrated in the nanometer scale; the mean pore radius is 87 nm, the mean throat radius is 41 nm, and the mean coordination number is 3.97. The calculated permeability considering diffusion is 0.000124 mD, which is approximately twice the permeability calculated without considering diffusion. The irreducible water saturation of the Gulong shale reservoir is approximately 0.4, and the residual oil saturation is approximately 0.35. The method proposed in this paper can provide an important approach for characterizing the flow parameters of similar shale oil reservoirs.

The pore-throat radius of shale oil reservoir is extremely small, and it is difficult to accurately obtain the absolute permeability and oil-water two-phase relative permeability of actual oil reservoir through conventional core experiments. However, these parameters are very important for reservoir numerical simulation. In this paper, a method for characterizing flow parameters based on pore network model that considers differential pressure flow and diffusion flow is proposed. Firstly, a digital core was reconstructed using focused ion beam scanning electron microscopy (FIB-SEM) from the Gulong shale reservoir in the Songliao Basin, China, and a pore network model was extracted. Secondly, quasi-static single-phase flow and two-phase flow equations considering diffusion were established in the pore network model. Finally, pore throat parameters, absolute permeability, and oil-water two-phase permeability curves were calculated, respectively. The results show that the pore throat distribution of Gulong shale reservoir is mainly concentrated in the nanometer scale, the mean pore radius is 87 nm, the mean throat radius is 41 nm, and the mean coordination number is 3.97; The calculated permeability considering diffusion is 0.000124mD, which is approximately twice the permeability calculated without considering diffusion; The irreducible water saturation of the Gulong shale reservoir is approximately 0.26, and the residual oil saturation is approximately 0.73. The method proposed in this paper can provide an important approach for characterizing the flow parameters of similar shale oil reservoirs.