The large void space of organic electrodes endows themselves with the capability to store different counter ions without size concern. In this work, a small-molecule organic bipolar electrode called diquinoxalino[2,3-a:2’,3’-c]phenazine-2,6,10-tris(phenoxazine) (DQPZ-3PXZ) is designed. Based on its robust solid structure by the π conjugation of diquinoxalino[2,3-a:2’,3’-c]phenazine (DQPZ) and phenoxazine (PXZ), DQPZ-3PXZ can indiscriminately and stably host 5 counter ions with different charge and size (Li⁺, Na⁺, K⁺, PF₆⁻ and FSI⁻). In Li/Na/K-based half cells, DQPZ-3PXZ can deliver the peak discharge capacities of 257/243/253 mAh g⁻¹_cathode and peak energy densities of 609/530/572 Wh kg⁻¹_cathode, respectively. The Li/Na/K-based dual-ion symmetric batteries can be constructed, which can be activated through the 1st charge process and show the stable discharge capacities of 85/66/72 mAh g⁻¹_cathode and energy densities of 59/50/52 Wh kg⁻¹_{total mass}, all running for more than 15000 cycles with nearly 100% capacity retention.

Photocatalytic hydrogen evolution efficiency is limited due to unfavorable carrier dynamics and thermodynamic performance. Here, we propose to introduce electronegative molecules to build an electric double layer (EDL) to generate a polarization field instead of the traditional built-in electric field to improve carrier dynamics, and optimize the thermodynamics by regulating the chemical coordination of surface atoms. Based on theoretical simulation, we designed CuNi@EDL and applied it as the cocatalyst of semiconductor photocatalysts, finally achieved a hydrogen evolution rate of 249.6 mmol h⁻¹g⁻¹and remained stable after storing under environmental conditions for more than 300 days. The high H₂yield is mainly due to the perfect work function, Fermi level and Gibbs free energy of hydrogen adsorption, improved light absorption ability, enhanced electron transfer dynamics, decreased HER overpotential and effective carrier transfer channel arose by EDL. Here, our work opens up new perspectives for the design and optimization of photosystems.

Sodium-ion batteries have been one of the most promising alternatives for lithium-ion batteries (LIBs) for large-scale energy storage systems due to cost-efficiency and rich resources of sodium. However, graphite, a commercial anode material of LIBs, shows a very low reversible capacity for sodium-ion storage because of the weak binding between sodium and graphite. Herein, an activated graphite (AG) material with abundant defects including edges and vacancies with oxygenic functional groups is well-designed and fabricated by a facile and eco-friendly ball-milling method. The structural evolutions during the ball-milling process and their effects on electrochemical sodium-ion storage performance are investigated. A stable reversible capacity of 139.1 mA h g⁻¹ can be achieved at 1.0 A g⁻¹ even after 4500 cycles for the AG-50 electrode with the 50-hour ball-milling treatment, amounting to a very low decay ratio of 0.0034% per cycle. Based on physical characterizations and density functional theory calculations, the greatly improved specific capacity and cycling stability of the AG anode for sodium-ion storage can be attributed to the enlarged interlayer space, increased specific surface area, and introduced defects caused by ball-milling treatment, which provide vast active sites for reversible sodium-ion storage based on a adsorption/desorption mechanism, thus leading to great improvement in the specific capacity of the AG electrode. These results can provide a meaningful reference for the application of modified graphite for high-performance sodium storage.

High energy density lithium-ion batteries are urgently needed due to the rapid growth demands of electric vehicles, electronic devices, and grid energy storage devices. There is still significant opportunity to improve the energy density of existing state-of-the-art lithium-ion batteries by optimizing the separator thickness, which is usually ignored. Here, the dependence of battery gravimetric and volumetric energy densities on separator thickness has been quantitatively discussed in different type Li-ion batteries by calculations combined with experiments. With a decrease in separator thickness, the volumetric energy density is greatly improved. Meanwhile, the gravimetric energy densities are significantly improved as the electrolyte soaking in the separator is reduced. The gravimetric and volumetric energy densities of graphite (Gr) ∣ NCM523 cells enable to increase 11.5% and 29.7%, respectively, by reducing the thickness of separator from 25 μm to 7 μm. Furthermore, the Li ∣ S battery exhibits an extremely high energy density of 664.2 Wh Kg⁻¹ when the thickness of the separator is reduced to 1 μm. This work sheds fresh light on the rational design of high energy density lithium-ion batteries.