The sodium superionic conductor (NASICON)-type cathode, Na₃V₂(PO₄)₃ (NVP), is considered as a promising cathode material for sodium-ion batteries (SIBs), which offers stable sodium storage capability. However, hazardous and expensive vanadium (V) has limited its practical application. To reduce the V dependency in NASICON-type cathodes, two new NASICON-structured materials, Na₃VMg_0.5Ti_0.5(PO₄)₃ (N_3.0VMTP/C) and Na_3.5V_0.5MgTi_0.5(PO₄)₃ (N_3.5VMTP/C), were designed for cost-effectiveness as well as improvement of battery performance. N_3.0VMTP/C and N_3.5VMTP/C provided a sodium storage capacity of 155.84 mAh g⁻¹ and 105 mAh g⁻¹ at 12 mA g⁻¹ with 88 % and 84 % capacity retention after 500 cycles at 150 mA g⁻¹, respectively. In-situ XRD analysis revealed that both cathodes undergo a progressive solid solution reaction in the lower voltage region and two-phase reaction at higher voltages during (de)sodiation, with only minor difference in the degree of lattice displacement, confirming their high potential for the SIBs with sustainable and cheaper Mg for grid-scale utilization.

Cobalt sulfide catalysts (CoS and CoS₂) with different phases, electrical conductivities, porosities, and specific surface areas are synthesized and loaded on a carbon paper (CP) interlayer which has a role to support an electrically conductive network for maximizing the catalytic activity of cobalt sulfide. Based on the detailed diagnosis about electrochemical results, cobalt sulfides reveal their electrocatalytic activity to promote both polysulfide reduction and Li₂S nucleation during discharge. We propose a new interpretation about the capacity vs. voltage profiles of Li–S cells, which can elaborate on the reduction reaction of sulfur during the discharge reaction. Through the electrochemical examination, we determine the role of cobalt sulfide catalysts as well as CP interlayer and the critical factors of cobalt sulfides for the enhanced performances of Li–S batteries. Our work provides new insights for understanding about the catalytic activity of cobalt sulfides and designing advanced catalysts for the high utilization of sulfur in Li–S batteries.

Various redox-active organic molecules can serve as ideal electrode materials to realize sustainable energy storage systems. Yet, to be more appropriate for practical use, considerable architectural engineering of an ultrathick, high-loaded organic electrode with reliable electrochemical performance is of crucial importance. Here, by utilizing the synergetic effect of the non-covalent functionalization of highly conductive non-oxidized graphene flakes (NOGFs) and introduction of mechanically robust cellulose nanofiber (CNF)-intermingled structure, a very thick (≈ 1 mm), freestanding organic nanohybrid electrode which ensures the superiority in cycle stability and areal capacity is reported. The well-developed ion/electron pathways throughout the entire thickness and the enhanced kinetics of electrochemical reactions in the ultrathick 5,10-dihydro-5,10-dimethylphenazine/NOGF/CNF (DMPZ-NC) cathodes lead to the high areal energy of 9.4 mWh·cm^-2 (= 864 Wh·kg^-1 at 158 W·kg^-1). This novel ultrathick electrode architecture provides a general platform for the development of the high-performance organic battery electrodes.