Facile fabrication of Ni, Fe-doped δ-MnO2 derived from Prussian blue analogues as an efficient catalyst for stable Li-CO2 batteries.

Rechargeable Li-CO2 batteries are regarded as an ideal new-generation energy storage system, owing to their high energy density and extraordinary CO2 capture capability. Developing a suitable cathode to improve the electrochemical performance of Li-CO2 batteries has always been a research hotspot. Herein, Ni-Fe-δ-MnO2 nano-flower composites are designed and synthesized by in situ etching a Ni-Fe PBA precursor as the cathode for Li-CO2 batteries. Ni-Fe-δ-MnO2 nanoflowers composed of ultra-thin nanosheets possess considerable surface spaces, which can not only provide abundant catalytic active sites, but also facilitate the nucleation of discharge products and promote the CO2 reduction reaction. On the one hand, the introduction of Ni and Fe elements can improve the electrical conductivity of δ-MnO2. On the other hand, the synergistic catalytic effect between Ni, Fe elements and δ-MnO2 will greatly enhance the cycling performance and reduce the overpotential of Li-CO2 batteries. Consequently, the Li-CO2 battery based on the Ni-Fe-δ-MnO2 cathode shows a high discharge capacity of 8287 mA h g-1 and can stabilize over 100 cycles at a current density of 100 mA g-1. The work offers a promising guideline to design efficient manganese-based catalysts for Li-CO2 batteries.

Advanced Li/Na-CO2 Batteries Enabled by the γ-MnO2 Catalyst with Enhanced Carbonate Decomposition.

Metal-CO2 batteries, especially Li-CO2 and Na-CO2 batteries, are regarded as ideal new-generation energy storage systems owing to their high energy density and extraordinary CO2 capture capability. However, the advancement of metal-CO2 batteries is still at an early stage. The problems caused by accumulation of carbonates during charge-discharge cycles, such as large polarization and poor reversibility, restrict their practical application. Therefore, designing efficient catalysts is crucial for promoting the decomposition of carbonate to improve the electrochemical performance of metal-CO2 batteries. Herein, we first adopted sea urchin-like γ-MnO2 as the cathode material for Li/Na-CO2 batteries. Benefiting from the unique structure and excellent catalytic activity of γ-MnO2, the as-prepared Li-CO2 and Na-CO2 batteries can achieve low overpotentials of 1.28 and 1.36 V, respectively, at a current density of 100 mA g-1 with a cutoff capacity of 1000 mA h g-1. The overpotentials are lower than those of most of the state-of-the-art catalysts in previous reports. After 100 and 50 cycles of Li-CO2 and Na-CO2 batteries, respectively, their charging termination voltages remain at around 4.1 and 3.9 V, respectively; such a low charging platform indicates the excellent catalytic activity of the γ-MnO2 cathode on the discharge products. Our findings offer a promising guideline to design efficient electrocatalysts for high-performance metal-CO2 batteries.

Isostructural Synthesis of Iron-Based Prussian Blue Analogs for Sodium-Ion Batteries.

Rechargeable sodium ion batteries (SIBs) have promising applications in large-scale energy storage systems. Iron-based Prussian blue analogs (PBAs) are considered as potential cathodes owing to their rigid open framework, low-cost, and simple synthesis. However, it is still a challenge to increase the sodium content in the structure of PBAs and thus suppress the generation of defects in the structure. Herein, a series of isostructural PBAs samples are synthesized and the isostructural evolution of PBAs from cubic to monoclinic after modifying the conditions is witnessed. Accompanied by, the increased sodium content and crystallinity are discovered in PBAs structure. The as-obtained sodium iron hexacyanoferrate (Na1.75 Fe[Fe(CN)6 ]0.9743 ·2.76H2 O) exhibits high charge capacity of 150 mAh g-1 at 0.1 C (17 mA g-1 ) and excellent rate performance (74 mAh g-1 at 50 C (8500 mA g-1 )). Moreover, their highly reversible Na+ ions intercalation/de-intercalation mechanism is verified by in situ Raman and Powder X-ray diffraction (PXRD) techniques. More importantly, the Na1.75 Fe[Fe(CN)6 ]0.9743 ·2.76H2 O sample can be directly assembled in a full cell with hard carbon (HC) anode and shows excellent electrochemical performances. Finally, the relationship between PBAs structure and electrochemical performance is summarized and prospected.

CoS2 /N-Doped Hollow Spheres as an Anode Material for High-Performance Sodium-Ion Batteries.

In this work, we first synthesized polyacrylic acid (PAA) spheres and then used PAA as a template to load Co(OH)2 particles onto its surface. The product of CoS2 nanoparticles dispersed in N-doped hollow spheres (N-HCS) was prepared through sulfurization treatment (CoS2 /S@N-HCS). During the sulfuration process, sulfur penetrates into the PAA, embedding into the graphite layer along with the carbonization process. It was found that during the charging and discharging process, the sulfur in the carbon layer will gradually dissolve out, thereby forming new ion diffusion channels in the carbon spheres and exposing more CoS2 active sites. The CoS2 /S@N-HCS composite exhibits a specific capacity of 729.6 mAh g-1 after 500 cycles at a current density of 1 A g-1 . The sodium-storage mechanism and reaction kinetics of the materials were further measured by in-situ electrochemical impedance spectroscopy, ex-situ X-ray diffraction, capacitance performance evaluation, and galvanostatic intermittent titration technique. The excellent cycling performance and rate capability demonstrated that the CoS2 /S@N-HCS is a potential and prospective anode material for sodium-ion batteries.

Synthesis of Porous Ni-Doped CoSe2 /C Nanospheres towards High-Rate and Long-Term Sodium-Ion Half/Full Batteries.

Carbon-layer-coated porous Ni-doped CoSe2 (Ni-CoSe2 /C) nanospheres have been fabricated by a facile hydrothermal method followed by a new selenization strategy. The porous structure of Ni-CoSe2 /C is formed by the aggregation of many small particles (20-40 nm), which are not tightly packed together, but are interspersed with gaps. Moreover, the surfaces of these small particles are covered with a thin carbon layer. Ni-CoSe2 /C delivers superior rate performance (314.0 mA h g-1 at 20 A g-1 ), ultra-long cycle life (316.1 mA h g-1 at 10 A g-1 after 8000 cycles), and excellent full-cell performance (208.3 mA h g-1 at 0.5 A g-1 after 70 cycles) when used as an anode material for half/full sodium-ion batteries. The Na storage mechanism and kinetics have been confirmed by ex situ X-ray diffraction analysis, assessment of capacitance performance, and a galvanostatic intermittent titration technique (GITT). GITT shows that Na+ diffusion in the electrode material is a dynamic change process, which is associated with a phase transition during charge and discharge. The excellent electrochemical performance suggests that the porous Ni-CoSe2 /C nanospheres have great potential to serve as an electrode material for sodium-ion batteries.