The effect of CO2 contamination in rechargeable non-aqueous sodium–air batteries

Fundamental Understanding of Nonaqueous and Hybrid Na-CO2 Batteries: Challenges and Perspectives

Alkali metal-CO₂ batteries, which combine CO₂ recycling with energy conversion and storage, are a promising way to address the energy crisis and global warming. Unfortunately, the limited cycle life, poor reversibility, and low energy efficiency of these batteries have hindered their commercialization. Li-CO₂ battery systems have been intensively researched in these aspects over the past few years, however, the exploration of Na-CO₂ batteries is still in its infancy. To improve the development of Na-CO₂ batteries, one must have a full picture of the chemistry and electrochemistry controlling the operation of Na-CO₂ batteries and a full understanding of the correlation between cell configurations and functionality therein. Here, recent advances in CO₂ chemical and electrochemical mechanisms on nonaqueous Na-CO₂ batteries and hybrid Na-CO₂ batteries (including O₂ -involved Na-O₂ /CO₂ batteries) are reviewed in-depth and comprehensively. Following this, the primary issues and challenges in various battery components are identified, and the design strategies for the interfacial structure of Na anodes, electrolyte properties, and cathode materials are explored, along with the correlations between cell configurations, functional materials, and comprehensive performances are established. Finally, the prospects and directions for rationally constructing Na-CO₂ battery materials are foreseen.

Kinetic-enhanced carbon fiber for rechargeable zinc-air batteries

Metal-free catalysts are made by the elements with infinite reserve in nature and, therefore, show the potential for large-scale applications in energy devices including metal-air batteries. The construction of metal-air batteries prefers using self-supporting catalysts with favorable activity as well as fast kinetics. However, it is challenging due to the limited electropositivity of metal-free catalysts for O-O bond formation in oxygen evolution reaction (OER), scaling relationship restrictions between OER and oxygen reduction reaction, and difficulty in porosity construction on the monolith electrode surface. In this contribution, through developing a facile methodology of quenching high-temperature carbon clothes in liquid nitrogen, a self-supported carbon cloth with bifunctional active graphene skin and fast kinetics is well constructed to serve as the air cathode in metal-air batteries. Regulated oxygen species and three-dimensionally hierarchical porosity are well constructed on the carbon fiber surfaces, contributing high intrinsic activity and prominently enhanced kinetics, which leads to favorable performances in aqueous as well as flexible rechargeable zinc-air batteries. The work proposed a promising strategy in the rational design and smart synthesis of fast-kinetic monolith electrodes, which refreshes concepts and strategies of advanced material fabrication, and also bridges material science and practical energy devices.

Designing a Novel Electrolyte Na3.2 Hf2 Si2.2 P0.8 O11.85 F0.3 for All-Solid-State Na-O2 Batteries

Sodium-air battery has great development potential due to its high energy density and high safety. However, most previous works are based on liquid electrolyte or polymer electrolyte, which will inevitably result in safety hazards such as electrolyte leakage and sodium dendrite growth. Herein, an all-solid-state Na-O₂ battery based on a well-designed NASICON-type electrolyte Na_3.2 Hf₂ Si_2.2 P_0.8 O_11.85 F_0.3 , which has high ionic conductivity (2.39 × 10^-3 S cm^-1 ) and excellent chemical stability, is developed. Collaborating with the reasonable humidity of the atmosphere, the battery shows good cycle stability. This research demonstrates that NASICON-type electrolyte Na_3.2 Hf₂ Si_2.2 P_0.8 O_11.85 F_0.3 has good application potential for all-solid-state Na-O₂ batteries and lays a solid foundation on the material preparation and optimization for developing high-energy sodium-air batteries.

Fast 3D-lithium-ion diffusion and high electronic conductivity of Li2MnSiO4 surfaces for rechargeable lithium-ion batteries

High theoretical capacity, high thermal stability, the low cost of production, abundance, and environmental friendliness are among the potential attractiveness of Li2MnSiO4 as a positive electrode (cathode) material for rechargeable lithium-ion batteries. However, the experimental results indicated poor electrochemical performance in its bulk phase due to high intrinsic charge transfer resistance and capacity fading during cycling, which limit its large-scale commercial applications. Herein, we explore the surface stability and various lithium-ion diffusion pathways of Li2MnSiO4 surfaces using the density functional theory (DFT) framework. Results revealed that the stability of selected surfaces is in the following order: (210) > (001) > (010) > (100). Moreover, the Wulff-constructed equilibrium shape revealed that the Li2MnSiO4 (001) surface is the most predominant facet, and thus, preferentially exposed to electrochemical activities. The Hubbard-corrected DFT (DFT + U, with U = 3 eV) results indicated that the bulk insulator with a wide band gap (E g = 3.42 eV) changed into narrow electronic (E g = 0.6 eV) when it comes to the Li2MnSiO4 (001) surface. Moreover, the nudged elastic band analysis shows that surface diffusion along the (001) channel was found to be unlimited and fast in all three dimensions with more than 12-order-of-magnitude enhancements compared with the bulk system. These findings suggest that the capacity limitation and poor electrochemical performance that arise from limited electronic and ionic conductivity in the bulk system could be remarkably improved on the surfaces of the Li2MnSiO4 cathode material for rechargeable lithium-ion batteries.

Boron and pyridinic nitrogen-doped graphene as potential catalysts for rechargeable non-aqueous sodium–air batteries

In this work, we performed density functional theory (DFT) analysis of nitrogen (N)- and boron (B)-doped graphene, and N,B-co-doped graphene as potential catalysts for rechargeable non-aqueous sodium–air batteries. Four steps of an NaO₂ growth and depletion mechanism model were implemented to study the effects of B- and N-doped and co-doped graphene on the reaction pathways, overpotentials, and equilibrium potentials. The DFT results revealed that two-boron- and three-nitrogen (pyridinic)-doped graphene exhibited plausible reaction pathways at the lowest overpotentials, especially during the charging process (approximately 200 mV), thus, significantly improving the oxygen reduction and oxidation reactions of pristine graphene. In addition, pyridinic nitrogen-doped graphene meaningfully increased the equilibrium potential by approximately 0.30 eV compared to the other graphene-based materials considered in this study. This detailed DFT study provides valuable data that can be used for the successful development of low-cost and efficient graphene-based catalysts for sodium–air battery systems operating with non-aqueous electrolyte.

We performed density functional theory analysis of heteroatom doped graphene as potential catalysts for rechargeable non-aqueous sodium–air batteries. Pyridinic nitrogen and boron doped graphene exhibited too low overpotential reaction pathways.