Phosphorus, particularly the red phosphorus (RP) allotrope, has been extensively studied as an anode material in both lithium-ion batteries (LIBs) and emerging sodium-ion batteries (SIBs). RP is featured with high theoretical capacity (2,596 mA h g⁻¹), suitable low redox potential (~0.7/0.4 V for LIBs/SIBs), abundant resources, and environmental friendliness. Despite its promises, the inherent poor electrical conductivity of RP (~10⁻¹⁴ S cm⁻¹) and significant volume changes during charge/discharge processes (>300%) compromise its cycling stability. In order to address these issues, various countermeasures have been proposed, focusing on the incorporation of materials that provide high conductivity and mechanical strength in composite-type anodes. In addition, the interfacial instability, oxidation, and safety concerns and the low mass ratio of active material in the electrode need to be addressed. Herein, this review summarizes the up-to-date development in RP materials, outlines the challenges, and presents corresponding countermeasures aimed to enhance the electrochemical performance. It covers aspects such as the structural design of RP, the choice of the additive materials and electrolytes, rational electrode construction, etc. The review also discusses the future prospects of RP for LIBs/SIBs and aims to provide a different perspective on the challenges that must be overcome to fully exploit the potential of RP and meet commercial application requirements.

To meet the demands of high-voltage lithium-ion batteries (LIBs), we develop a novel electrolyte through theoretical calculations and electrochemical characterization. Triphenylphosphine oxide (TPPO) is introduced as a film-forming additive into a sulfone-based electrolyte containing 1 mol L⁻¹ lithium difluoro(oxalate)borate. Density functional theory calculations show that TPPO has a lower reduction potential than the sulfone-based solvent. Hence, TPPO should be oxidized before the sulfone-based solvent and form a cathode electrolyte interphase layer on the Li-rich cathode. Our research findings demonstrate that adding 2 wt% TPPO to the sulfone-based electrolyte considerably enhances the ionic conductivity within a range of 20–60 ℃. In addition, it increases the discharge capacity of LIBs in a range of 2–4.8 V while maintaining excellent rate performance and cycling stability. Flammability tests and thermal gravimetric analysis results indicate excellent nonflammability and thermal stability of the electrolyte.

In view of the drawbacks of rechargeable batteries, such as low mass and volumetric energy densities, as well as slow charging rate, proton exchange membrane fuel cells (PEMFCs) are reckoned to be promising alternative devices for energy conversion. Currently, commercial PEMFCs mainly use H₂ as the fuel, but the challenges in generation, storage, and handling of H₂ limit their further development. Among the liquid fuels, formic acid possesses the merits of low flammability, low toxicity, slow crossover rate, faster reaction kinetics, and high volumetric H₂ storage capacity, thus being considered as the most promising energy carrier. It can be used as the energy source for direct formic acid fuel cells (DFAFCs) and formic acid-based H₂-PEMFCs, which are also called indirect formic acid fuel cells (IFAFCs). A common issue hindering their commercialization is lacking efficient electrocatalysts. In DFAFCs, the anodic electrocatalysts for formic acid oxidation are suffering from stability issue, whereas the cathodic electrocatalysts for oxygen reduction are prone to poisoning by the permeated formic acid. As for IFAFCs, CO and CO₂ impurities generated from formic acid dehydrogenation will cause rapid decay in the catalytic activity. High working temperature can improve the CO and CO₂ tolerance of catalysts but will accelerate catalyst degradation. This review will discuss the mitigation strategies and recent advances from the aspect of electrocatalysts to overcome the above challenges. Finally, some perspectives and future research directions to develop more efficient electrocatalysts will be provided for this promising field.

Sodium superionic conductor (NASICON) is a class of compounds with robust polyanionic frameworks and high thermal stability, which are regarded as prospective cathodes candidates for secondary batteries. However, NASICON cathodes typically have low discharge plateaus and low practical capacities in aqueous electrolytes. Here, Na₃V_1.75Fe_0.25(PO₄)₂F₃ is investigated as a cathode material for the aqueous zinc/sodium batteries. While the addition of F helps with the improvement of NASICON structural stability, the low-cost Fe substitution has a positive impact on the capacity increment, reaction voltage increases, and cycling stability improvement. Because the Fe³⁺ substitution could induce a change in the spin magnetic moments of the 3d orbitals of the VO₄F₂ and FeO₄F₂ octahedra, the 2-electron reaction of V is activated, which are V⁴⁺/V³⁺ and V⁵⁺/V⁴⁺ redox couples. As a result, the novel Na₃V_1.75Fe_0.25(PO₄)₂F₃ cathode delivers a high operating voltage of 1.7 V, a high energy density of 209 W·h·kg⁻¹ and stable lifespan (83.5% capacity retention after 6,000 cycles at 1 A·g⁻¹) in the aqueous zinc/sodium batteries. This research demonstrates the practicality of activating multielectron reactions to optimize the electrochemical properties of NASICON cathodes for aqueous secondary batteries.

The continuous development of the global energy structure transformation has put forward higher demands upon the development of batteries. The improvements of the energy density have become one of the important indicators and hot topic for novel secondary batteries. The energy density of existing lithium-ion battery has encountered a bottleneck due to the limitations of material and systems. Herein, this paper introduces the concept and development of multi-electron reaction materials over the past twenty years. Guided by the multi-electron reaction, light weight electrode and multi-ion effect, current development strategies and future trends of high-energy-density batteries are highlighted from the perspective of materials and structure system innovation. Typical cathode and anode materials with the multi-electron reactions are summarized from cation-redox to anion-redox, from intercalation-type to alloying-type, and from liquid systems to solid-state lithium batteries. The properties of the typical materials and their engineering prospects are comprehensively discussed, and additionally, the application potential and the main challenges currently encountered by solid-state batteries are also introduced. Finally, this paper gives a comprehensive outlook on the development of high-energy-density batteries.

Spindle-shaped anatase TiO₂ secondary particles were successfully fabricated via the oriented attachment of primary nanocrystals. By adjusting the concentration of tetrabutyl titanate, the size of the TiO₂ nanocrystals and particles could be controlled, resulting in pore evolution. Pores for the random aggregation of secondary particles gradually transformed to nanopores originating from the oriented attachment of the primary nanocrystals, resulting in an excellent micro/nanostructure that increased the performance of a sodium-ion battery. The mesoporous TiO₂ microparticle anode, with its unique combination of nanocrystals and uniform nanopores, displays super durability (95 mAh/g after 11, 000 cycles at 1 C), high initial efficiency (61.4%), and excellent rate performance (265 and 77 mAh/g at 0.1 and 20 C, respectively). In particular, at slow discharge (0.1 C) and fast charge (5, 50, and 100 C) rates, the anatase TiO₂ shows remarkable initial charge capacities of 200, 119, and 56 mAh/g, corresponding to 172, 127, and 56 mAh/g, after 150 cycles, respectively, thus meeting the requirements for fast energy storage. This excellent performance can be attributed to the stability of the material and its high ionic conductivity, resulting from the stable architecture with a mesoporous microstructure and without the random aggregation of secondary particles. A fundamental understanding of the pore structure and controllable pore construction has been proven to be effective in increasing the rate capability and durability of nanostructured electrode materials.