gcheng Chen

Pyrite FeS2 for high-rate and long-life rechargeable sodium batteries

It is desirable to develop electrode materials for advanced rechargeable batteries with low cost, long life, and high-rate capability. Pyrite FeS2, as an easily obtained natural mineral, has been already commercialized in primary lithium batteries, but encountered problems in rechargeable batteries with carbonate-based electrolytes due to the limited cycle life caused by the conversion-type reaction (FeS2 + 4M → Fe + 2M2S (M = Li or Na)). Herein, we demonstrate that FeS2 microspheres can be applied in room-temperature rechargeable sodium batteries with only the intercalation reaction by simultaneously selecting a compatible NaSO3CF3/diglyme electrolyte and tuning the cut-off voltage to 0.8 V. A surprisingly high-rate capability (170 mA h g−1 at 20 A g−1) and unprecedented long-term cyclability (∼90% capacity retention for 20 000 cycles) has been obtained. We suggest that a stable electrically conductive layer-structured NaxFeS2 was formed during cycling, which enables the highly reversible sodium intercalation and deintercalation. Moreover, 18650-type sodium batteries were constructed exhibiting a high capacity of ∼4200 mA h (corresponding to 126 W h kg−1 and 382 W h L−1) and a capacity retention of 97% after an initial 200 cycles at 4 A during charge–discharge. This shows that the production of rechargeable sodium batteries with FeS2 microspheres is viable for commercial utilization.

Phase and composition controllable synthesis of cobalt manganese spinel nanoparticles towards efficient oxygen electrocatalysis

Spinel-type oxides are technologically important in many fields, including electronics, magnetism, catalysis and electrochemical energy storage and conversion. Typically, these materials are prepared by conventional ceramic routes that are energy consuming and offer limited control over shape and size. Moreover, for mixed-metal oxide spinels (for example, CoxMn3−xO4), the crystallographic phase sensitively correlates with the metal ratio, posing great challenges to synthesize active product with simultaneously tuned phase and composition. Here we report a general synthesis of ultrasmall cobalt manganese spinels with tailored structural symmetry and composition through facile solution-based oxidation–precipitation and insertion–crystallization process at modest condition. As an example application, the nanocrystalline spinels catalyse the oxygen reduction/evolution reactions, showing phase and composition co-dependent performance. Furthermore, the mild synthetic strategy allows the formation of homogeneous and strongly coupled spinel/carbon nanocomposites, which exhibit comparable activity but superior durability to Pt/C and serve as efficient catalysts to build rechargeable Zn–air and Li–air batteries.

Spinels: Controlled Preparation, Oxygen Reduction/Evolution Reaction Application, and Beyond

Spinels with the formula of AB2O4 (where A and B are metal ions) and the properties of magnetism, optics, electricity, and catalysis have taken significant roles in applications of data storage, biotechnology, electronics, laser, sensor, conversion reaction, and energy storage/conversion, which largely depend on their precise structures and compositions. In this review, various spinels with controlled preparations and their applications in oxygen reduction/evolution reaction (ORR/OER) and beyond are summarized. First, the composition and structure of spinels are introduced. Then, recent advances in the preparation of spinels with solid-, solution-, and vapor-phase methods are summarized, and new methods are particularly highlighted. The physicochemical characteristics of spinels such as their compositions, structures, morphologies, defects, and substrates have been rationally regulated through various approaches. This regulation can yield spinels with improved ORR/OER catalytic activities, which can further accelerate the speed, prolong the life, and narrow the polarization of fuel cells, metal-air batteries, and water splitting devices. Finally, the magnetic, optical, electrical, and catalytic applications beyond the OER/ORR are also discussed. The future applications of spinels are considered to be closely related to environmental and energy issues, which will be aided by the development of new species with precise preparations and advanced characterizations.

High K-storage performance based on the synergy of dipotassium terephthalate and ether-based electrolytes

Potassium-ion batteries (KIBs) are strongly dependent on the development of anodes with high safety and good electrochemical performance. Here, we achieved excellent anode performance of KIBs based on the synergy of dipotassium terephthalate (K2TP) and a 1,2-dimethoxyethane (DME)-based electrolyte for the first time. The K2TP is featured as a typical layered structure with K+ transport channels. It delivers a large capacity of 249 mA h g−1 at 200 mA g−1 and a high capacity retention of 94.6% after 500 cycles of discharge and charge at 1000 mA g−1 with a Coulombic efficiency of 100%. This is attributed to the active carboxylate groups and the flexible molecular structure of K2TP, and the stable solid electrolyte interphase (SEI) formed in the DME-based electrolyte. Furthermore, the redox voltage around 0.6 V of K2TP favors K+ insertion rather than deposition during discharge. These make K2TP a promising anode material for KIBs, and encourage more investigations into the new system of KIBs.

Rapid Synthesis and Efficient Electrocatalytic Oxygen Reduction/Evolution Reaction of CoMn2O4 Nanodots Supported on Graphene

Transition-metal oxides have attracted extensive interest as oxygen-reduction/evolution reaction (ORR/OER) catalyst alternatives to precious Pt-based materials but generally exhibit limited electrocatalytic performance due to their large overpotential and low specific activity. We here report a rapid synthesis of spinel-type CoMn2O4 nanodots (NDs, below 3 nm) monodispersed on graphene for highly efficient electrocatalytic ORR/OER in 0.1 M KOH solution. The preparation of the composite involves the reaction of manganese and cobalt salts in mixed surfactant-solvent-water solution at mild temperature (120 °C) and air. CoMn2O4 NDs homogeneously distributed on carbonaceous substrates show strong coupling and facile charge transfer. Remarkably, graphene-supported CoMn2O4 NDs showed 20 mV higher ORR half-wave potential, twice the kinetic current, and better catalytic durability compared to the benchmark carbon-supported Pt nanoparticles (Pt/C). Moreover, CoMn2O4/reduced graphene oxide afforded electrocatalytic OER with a current density of 10 mA cm(-2) at a low potential of 1.54 V and a small Tafel slope of ∼56 mV/dec. This indicates that the composite of CoMn2O4 nanodots monodispersed on graphene is promising as highly efficient bifunctional electrocatalysts of ORR and OER that can be used in the areas of fuel cells and rechargeable metal-air batteries.

Rechargeable Room-Temperature Na-CO2 Batteries.

Developing rechargeable Na-CO2 batteries is significant for energy conversion and utilization of CO2 . However, the reported batteries in pure CO2 atmosphere are non-rechargeable with limited discharge capacity of 200 mAh g(-1) . Herein, we realized the rechargeability of a Na-CO2 battery, with the proposed and demonstrated reversible reaction of 3 CO2 +4 Na↔2 Na2 CO3 +C. The battery consists of a Na anode, an ether-based electrolyte, and a designed cathode with electrolyte-treated multi-wall carbon nanotubes, and shows reversible capacity of 60000 mAh g(-1) at 1 A g(-1) (≈1000 Wh kg(-1) ) and runs for 200 cycles with controlled capacity of 2000 mAh g(-1) at charge voltage <3.7 V. The porous structure, high electro-conductivity, and good wettability of electrolyte to cathode lead to reduced electrochemical polarization of the battery and further result in high performance. Our work provides an alternative approach towards clean recycling and utilization of CO2 .

Uniform MnO2 nanostructures supported on hierarchically porous carbon as efficient electrocatalysts for rechargeable Li-O2 batteries

AbstractThrough in situ redox deposition and growth of MnO2 nanostructures on hierarchically porous carbon (HPC), a MnO2/HPC hybrid has been synthesized and employed as cathode catalyst for non-aqueous Li-O2 batteries. Owing to the mild synthetic conditions, MnO2 was uniformly distributed on the surface of the carbon support, without destroying the hierarchical porous nanostructure. As a result, the as-prepared MnO2/HPC nanocomposite exhibits excellent Li-O2 battery performance, including low charge overpotential, good rate capacity and long cycle stability up to 300 cycles with controlling capacity of 1,000 mAh·g−1. A combination of the multi-scale porous network of the shell-connected carbon support and the highly dispersed MnO2 nanostructure benefits the transportation of ions, oxygen and electrons and contributes to the excellent electrode performance.

A Co3O4@MnO2/Ni nanocomposite as a carbon- and binder-free cathode for rechargeable Li–O2 batteries

Rational design and synthesis of cathode catalysts are crucial for enhancing the performance of rechargeable Li–O2 batteries. Here, we report a controlled synthesis of the nanocomposite, Co3O4 nanohorns coated with MnO2 nanosheets on a Ni foam (Co3O4@MnO2/Ni). It integrates the catalytic activities of oxygen reduction and oxygen evolution reactions and functions as a carbon- and binder-free cathode catalyst for rechargeable Li–O2 batteries. This nanocomposite catalyst presents a small discharge/charge voltage gap of 0.76 V (a low polarization) and a long cycle life of 170 cycles at 300 mA g−1, coupled with an ionic liquid-based electrolyte, 0.5 M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) in 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (EMITFSI), which are much better than those based on the individual Co3O4 and MnO2 cathodes. The enhanced electrochemical performance is ascribed to the integrated bifunctional catalytic activities and the porous micro/nanostructure of the Co3O4@MnO2/Ni nanocomposite, as well as the ionic liquid-based electrolyte, indicating its promising application in rechargeable Li–O2 batteries.

Stable layered Ni-rich LiNi0.9Co0.07Al0.03O2 microspheres assembled with nanoparticles as high-performance cathode materials for lithium-ion batteries

The layered LiNi1−x−yCoxAlyO2 family with advantages of high capacity and low cost is considered as a promising cathode material for lithium-ion batteries (LIBs) for powering electric vehicles. However, such layered oxides still suffer from poor cycle stability and thermal instability during cycling. Herein, we report an easy coprecipitation synthesis of an Ni-rich microspherical Ni0.9Co0.07Al0.03(OH)2 precursor with uniform particle size and large BET specific surface area via employing AlO2− as the Al source. The uniform and dense LiNi0.9Co0.07Al0.03O2 microspheres with well-assembled nanoparticles and low degree of Ni2+/Li+ mixing are synthesized by optimizing the calcination conditions. As a cathode material for LIBs, LiNi0.9Co0.07Al0.03O2 delivers an appealing initial reversible capacity (236 mA h g−1 at 0.1C), good cyclic stability at various temperatures (e.g. capacity retention of 93.2% at 25 °C and 83.8% at 55 °C after 100 cycles at 1C), high rate capability (140 mA h g−1 at 10C), and excellent thermal stability (heat generation of 517.5 J g−1 at 4.3 V). Such superior electrochemical performance is mainly attributed to the combination of the high Ni component, layered structure with low degree of Ni2+/Li+ mixing, and uniform microspheres with homogeneous distribution of Ni, Co, and Al. Moreover, the full cell of LiNi0.9Co0.07Al0.03O2/KS6 has been assembled, delivering a high capacity of 210 mA h g−1 at 0.1C and excellent cycle stability.

Nanostructured organic electrode materials grown on graphene with covalent-bond interaction for high-rate and ultra-long-life lithium-ion batteries

Nanostructured organic tetralithium salts of 2,5-dihydroxyterephthalic acid (Li4C8H2O6) supported on graphene were prepared via a facile recrystallization method. The optimized composite with 75 wt.% Li4C8H2O6 was evaluated as an anode with redox couples of Li4C8H2O6/Li6C8H2O6 and as a cathode with redox couples of Li4C8H2O6/Li2C8H2O6 for Li-ion batteries, exhibiting a high-rate capability (10 C) and long cycling life (1,000 cycles). Moreover, in an all-organic symmetric Li-ion battery, this dual-function electrode retained capacities of 191 and 121 mA·h·g–1 after 100 and 500 cycles, respectively. Density functional theory calculations indicated the presence of covalent bonds between Li4C8H2O6 and graphene, which affected both the morphology and electronic structure of the composite. The special nanostructures, high electronic conductivity of graphene, and covalent-bond interaction between Li4C8H2O6 and graphene contributed to the superior electrochemical properties. Our results indicate that the combination of organic salt molecules with graphene is useful for obtaining high-performance organic batteries.