Zhaojun Xie

The First Introduction of Graphene to Rechargeable Li–CO2 Batteries

The utilization of the greenhouse gas CO2 in energy-storage systems is highly desirable. It is now shown that the introduction of graphene as a cathode material significantly improves the performance of Li-CO2 batteries. Such batteries display a superior discharge capacity and enhanced cycle stability. Therefore, graphene can act as an efficient cathode in Li-CO2 batteries, and it provides a novel approach for simultaneously capturing CO2 and storing energy.

Metal–CO2 Batteries on the Road: CO2 from Contamination Gas to Energy Source

Rechargeable nonaqueous metal-air batteries attract much attention for their high theoretical energy density, especially in the last decade. However, most reported metal-air batteries are actually operated in a pure O2 atmosphere, while CO2 and moisture in ambient air can significantly impact the electrochemical performance of metal-O2 batteries. In the study of CO2 contamination on metal-O2 batteries, it has been gradually found that CO2 can be utilized as the reactant gas alone; namely, metal-CO2 batteries can work. On the other hand, investigations on CO2 fixation are in focus due to the potential threat of CO2 on global climate change, especially for its steadily increasing concentration in the atmosphere. The exploitation of CO2 in energy storage systems represents an alternative approach towards clean recycling and utilization of CO2 . Here, the aim is to provide a timely summary of recent achievements in metal-CO2 batteries, and inspire new ideas for new energy storage systems. Moreover, critical issues associated with reaction mechanisms and potential directions for future studies are discussed.

Two better than one: cobalt–copper bimetallic yolk–shell nanoparticles supported on graphene as excellent cathode catalysts for Li–O2 batteries

Despite the extremely high energy density of Li–O2 batteries, the sluggish kinetics severely hinder their practical applications. Here, we report the preparation and electrochemical performance of cost-effective cobalt–copper bimetallic nanoparticles supported on graphene (CoCu/graphene) as the cathode material for Li–O2 batteries. The batteries delivered a high initial discharge capacity of 14 821 mA h g−1 and a low average charge voltage of ∼4.0 V at 200 mA g−1. In addition, the batteries exhibited superior rate capability (7955 mA h g−1 at 800 mA g−1), long cyclability (122 cycles at 200 mA g−1 with a cutoff capacity of 1000 mA h g−1), and outstanding coulombic efficiency (92% at 200 mA g−1). These superior performances resulted from the synergistic effect of non-noble metal Co and Cu supported on graphene, which could simultaneously enhance the oxygen reduction and evolution reaction kinetics. The favorable composite ensures uniform coverage of nanowall-shaped Li2O2 on CoCu/graphene instead of typical toroidal Li2O2 aggregation, thus promoting the reversible formation and decomposition of discharge product Li2O2. The excellent catalytic performance is expected to provide new insights into designing low-cost and high-efficiency cathode materials for Li–O2 batteries and promote their practical applications.

Designing high-voltage carbonyl-containing polycyclic aromatic hydrocarbon cathode materials for Li-ion batteries guided by Clar's theory

Increasing the voltage of organic electrodes is critical in improving their energy density. Here, we examined the correlation between the electron delocalization (aromaticity) and the lithiation voltage of carbonyl-containing polycyclic aromatic hydrocarbons by means of density functional theory computations. Our analyses revealed that the correlation can be well explained by Clars aromatic sextet theory. An index denoted as ΔC2Li is introduced to characterize the aromaticity change during lithiation. Several molecules with high ΔC2Li and high voltage were designed, and we also experimentally investigated a molecule with positive ΔC2Li as the cathode material. Our results demonstrated the importance and the feasibility of Clars theory in screening and developing high-voltage organic electrode materials.

NiFe2O4–CNT composite: an efficient electrocatalyst for oxygen evolution reactions in Li–O2 batteries guided by computations

Lithium–oxygen batteries are regarded as the most promising candidate for future energy storage systems. However, their poor rechargeability and low efficiency remain critical barriers for practical applications. By using first-principles computations, we disclosed that NiFe2O4 has superior oxygen evolution reaction (OER) activity for the decomposition of Li2O2. Guided by computations, we prepared a composite of NiFe2O4 and carbon nanotubes (CNTs) through a hydrothermal route and applied it to Li–O2 batteries. The batteries with NiFe2O4–CNT air cathodes displayed lower charging overpotential and better cycling performance than those with CNT air cathodes. The improved electrochemical performance was attributed to the high OER activity of NiFe2O4 for the decomposition of Li2O2.

Verifying the Rechargeability of Li‐CO2 Batteries on Working Cathodes of Ni Nanoparticles Highly Dispersed on N‐Doped Graphene

Abstract Li‐CO2 batteries could skillfully combine the reduction of “greenhouse effect” with energy storage systems. However, Li‐CO2 batteries still suffer from unsatisfactory electrochemical performances and their rechargeability is challenged. Here, it is reported that a composite of Ni nanoparticles highly dispersed on N‐doped graphene (Ni‐NG) with 3D porous structure, exhibits a superior discharge capacity of 17 625 mA h g−1, as the air cathode for Li‐CO2 batteries. The batteries with these highly efficient cathodes could sustain 100 cycles at a cutoff capacity of 1000 mA h g−1 with low overpotentials at the current density of 100 mA g−1. Particularly, the Ni‐NG cathodes allow to observe the appearance/disappearance of agglomerated Li2CO3 particles and carbon thin films directly upon discharge/charge processes. In addition, the recycle of CO2 is detected through in situ differential electrochemical mass spectrometry. This is a critical step to verify the electrochemical rechargeability of Li‐CO2 batteries. Also, first‐principles computations further prove that Ni nanoparticles are active sites for the reaction of Li and CO2, which could guide to design more advantageous catalysts for rechargeable Li‐CO2 batteries.

High performance Li–CO2 batteries with NiO–CNT cathodes

Rechargeable Li–CO2 batteries are promising energy storage systems for reducing fossil fuel consumption and mitigating the “greenhouse effect” due to the use of a reversible reaction between lithium and CO2. However, current Li–CO2 batteries still suffer from several unresolved problems such as high charge potential and low coulombic efficiency, and hence more efforts are required to optimize their electrochemical performance. In this work, a composite of sheet-like NiO dispersed on carbon nanotubes was prepared via a solvothermal method. The composite was employed as an efficient air cathode for Li–CO2 batteries, with very high coulombic efficiency (97.8%) and good cycling stability (40 cycles). This study provides new strategies to develop cheap and abundant catalysts to improve the performance of Li–CO2 batteries.

The First Example of Hetero-Triple-Walled Metal–Organic Frameworks with High Chemical Stability Constructed via Flexible Integration of Mixed Molecular Building Blocks

An unprecedented 3D hetero‐triple‐walled metal‐organic framework is obtained by straightforward elaboration of the mixed molecular building block (MBB) strategy. In this approach, multiple individual flexible and rigid MBBs are integrated into one composite building block as separate layers, which are of the same shape but different sizes. This MOF shows exceptional water stability and the application of Li‐ion battery electrodes.

Bifunctional electrocatalysts of MOF-derived Co–N/C on bamboo-like MnO nanowires for high-performance liquid- and solid-state Zn–air batteries

Exploration of cost-effective electrocatalysts that could replace noble metals to promote the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) holds great potential for large-scale applications in energy storage devices such as metal–air batteries. Metal–organic frameworks (MOFs) provide a new route to design highly active catalysts owing to their adjustable composition, morphology and surface area. Herein, a highly efficient bifunctional catalyst was fabricated by forming an interconnected and conducting Co–N/C framework on bamboo-like hollow MnO nanowires. The hybrid demonstrates prominent ORR/OER activity and promising potential in rechargeable Zn–air batteries. Especially, when assembled into solid-state Zn–air batteries, high open-circuit potential and stable discharge–charge cycling platforms were achieved. The outstanding performances stem from the synergistic effect of the two composites in one-dimensional nanowires, facilitating the convenient and sustainable diffusion of electrolytes to active sites. This work provides a new guideline to optimize MOF-derived materials as substitutes for Pt/C and RuO2 noble-metal catalysts for air cathodes in both liquid- and solid-state Zn–air batteries.

Fabricating Ir/C Nanofiber Networks as Free-Standing Air Cathodes for Rechargeable Li-CO2 Batteries

Li-CO2 batteries are promising energy storage systems by utilizing CO2 at the same time, though there are still some critical barriers before its practical applications such as high charging overpotential and poor cycling stability. In this work, iridium/carbon nanofibers (Ir/CNFs) are prepared via electrospinning and subsequent heat treatment, and are used as cathode catalysts for rechargeable Li-CO2 batteries. Benefitting from the unique porous network structure and the high activity of ultrasmall Ir nanoparticles, Ir/CNFs exhibit excellent CO2 reduction and evolution activities. The Li-CO2 batteries present extremely large discharge capacity, high coulombic efficiency, and long cycling life. Moreover, free-standing Ir/CNF films are used directly as air cathodes to assemble Li-CO2 batteries, which show high energy density and ultralong operation time, demonstrating great potential for practical applications.