Sodium-ion batteries (SIBs) have emerged as promising candidate for large-scale energy storage systems, owing to the abundant natural reserves of sodium, low production costs, and similar electrochemical properties to lithium-ion batteries. However, the graphite anodes used in commercial lithium-ion batteries cannot be directly applied to sodium-ion batteries. Among various reported anode materials, hard carbon has attracted extensive attention in SIBs because of its excellent sodium storage capability and cost-effectiveness. In this review, we focus on summarizing the recent advances of coal-based hard carbon anode materials for SIBs. We first introduce the common preparation methods of coal-based hard carbon anode materials. In addition, we overview the effective modification strategies (regulation of oxygen-containing groups, hierarchical pore structures engineering, and heteroatom doping) to boost the sodium storage performance of coal-based hard carbon anode materials. Further research directions of coal-based hard carbon anode materials for SIBs are also proposed. This review is expected to significantly promote the commercial application of coal-based hard carbon anodes.

O3-type layered transition metal oxide cathodes have attracted considerable attention due to their high sodium storage capacity and straightforward synthesis process. However, their practical applications are limited by irreversible phase transitions, transition metal dissolution, and sluggish Na⁺ diffusion kinetics. Herein, a unique high-entropy oxide (HEO), Na_0.88K_0.02Ni_0.24Li_0.06Mg_0.07Fe_0.1Mn_0.41Ti_0.1Sn_0.02O₂ is constructed by combining biphasic engineering and dual-site high-entropy doping for stable sodium storage. This synergistic effect significantly improves structural stability, enhances particle integrity, suppresses transition metal dissolution, accelerates electrochemical reaction kinetics, and mitigates electrolyte decomposition during the electrochemical cycling. Therefore, the HEO cathode demonstrates exceptional electrochemical performance, delivering a remarkable rate capability of 74.19 mAh·g^–1 at 10 C and outstanding cycling stability with 82.68% capacity retention after 1000 cycles. In addition, the practical viability of HEO is confirmed by its outstanding air stability and stable operation of full cells. These findings underscore the potential of synergistic effect of biphasic engineering and dual-site high-entropy doping in developing high-performance cathode materials for sodium-ion batteries.

Vanadium dioxide (VO₂) with the advantages of high theoretical capacity and tunnel structure has attracted considerable promising candidates for aqueous zinc-ion batteries. Nevertheless, the intrinsic low electronic conductivity of VO₂ results in an unsatisfactory electrochemical performance. Herein, a flower-like VO₂/carbon nanotubes (CNTs) composite was obtained by a facile hydrothermal method. The unique flower-like morphology shortens the ion transport length and facilitates electrolyte infiltration. Meanwhile, the CNT conductive networks is in favor of fast electron transfer. A highly reversible zinc storage mechanism was revealed by ex-situ X-ray diffraction and X-ray photoelectron spectroscopy. As a result, the VO₂/CNTs cathode exhibits a high reversible capacity (410 mAh·g⁻¹), superior rate performance (305 mAh·g⁻¹ at 5 A·g⁻¹), and excellent cycling stability (a reversible capacity of 221 mAh·g⁻¹ was maintained even after 2000 cycles). This work provides a guide for the design of high-performance cathode materials for aqueous zinc metal batteries.

Lithium-sulfur (Li-S) battery is one of the promising energy storage devices because of its high energy density. However, the sulfur cathode suffers from sluggish electrochemical reaction kinetics, slow charge transfer, large volume expansion and severe shuttle effect of lithium polysulfides inevitably resulting in low reversible capacity, poor rate performance and short cycle life, limiting its practical applications. Herein, the recent progress of cobalt/carbon composites, including cobalt nanoparticles and cobalt single atoms, as the sulfur host materials in Li-S batteries is overviewed. In general, cobalt plays the role of electrocatalyst, which inhibits the shuttle effect of lithium polysulfides, accelerates the electrochemical reaction kinetics, facilitates ion/electron transfer and alleviates volume expansion. Meanwhile, the prospects for the development of cobalt/carbon composites as sulfur hosts in Li-S batteries are proposed. It is expected to offer a whole blueprint and constructive suggestions for the cobalt/carbon composites as sulfur hosts for Li-S batteries, and these strategies can also be effective for other metal-sulfur batteries.