Aluminum ion chemistry of Na4Fe3(PO4)2(P2O7) for all-climate full Na-ion battery.

Na4Fe3(PO4)2(P2O7) (NFPP) is currently drawing increased attention as a sodium-ion batteries (SIBs) cathode due to the cost-effective and NASICON-type structure features. Owing to the sluggish electron and Na+ conductivities, however, its real implementation is impeded by the grievous capacity decay and inferior rate capability. Herein, multivalent cation substituted microporous Na3.9Fe2.9Al0.1(PO4)2(P2O7) (NFAPP) with wide operation-temperature is elaborately designed through regulating structure/interface coupled electron/ion transport. Greatly, the derived Na vacancy and charge rearrangement induced by trivalent Al3+ substitution lower the ions diffusion barriers, thereby endowing faster electron transport and Na+ mobility. More importantly, the existing Al-O-P bonds strengthen the local environment and alleviate the volume vibration during (de)sodiation, enabling highly reversible valence variation and structural evolution. As a result, remarkable cyclability (over 10,000 loops), ultrafast rate capability (200 C), and exceptional all-climate stability (-40-60 °C) in half/full cells are demonstrated. Given this, the rational work might provide an actionable strategy to promote the electrochemical property of NFPP, thus unveiling the great application prospect of sodium iron mixed phosphate materials.

Electrochemically Engineering a Single-Crystal Nickel-Rich Layered Cathode.

Nickel-rich layered electrode material has been attracting significant attention owing to its high specific capacity as a cathode for lithium-ion batteries. Generally, the high-nickel ternary precursors obtained by traditional coprecipitation methods are micron-scale. In this work, the submicrometer single-crystal LiNi0.8Co0.1Mn0.1O2 (NCM) cathode is efficiently prepared by electrochemically anodic oxidation followed by a molten-salt-assisted reaction without the need of extreme alkaline environments and complex processes. More importantly, when prepared under optimal voltage (10 V), single-crystal NCM exhibits a moderate particle size (∼250 nm) and strong metal-oxygen bonds due to reasonable and balanced crystal nucleation/growth rate, which are conducive to greatly enhancing the Li+ diffusion kinetics and structure stability. Given that a good discharge capacity of 205.7 mAh g-1 at 0.1 C (1 C = 200 mAh g-1) and a superior capacity retention of 87.7% after 180 cycles at 1 C are obtained based on the NCM electrode, this strategy is effective and flexible for developing a submicrometer single-crystal nickel-rich layered cathode. Besides, it can be adopted to elevate the performance and utilization of nickel-rich cathode materials.

Trace tea polyphenols enabling reversible dendrite-free zinc anode.

Zinc ion batteries (ZIBs) suffer from severe corrosion effects and dendrite growth on the unstable anode/electrolyte interface (AEI) during the plating/stripping process. Therefore, it is of great significance to build a stable AEI enabling a long lifetime for ZIBs. Herein, trace tea polyphenols (TP) were introduced firstly as additive of zinc acetate electrolyte to protect zinc anode from corrosion invasion and boost uniform zinc deposition, thus achieving reversible dendrite-free zinc anode. In situ synchrotron radiation X-ray imaging was conducted to illustrate the positive role of TP molecules in the uniform plating process of zinc. The stable AEI induced by the specific adsorption of TP molecules reduced hydrogen and oxygen evolution side reactions and increased the coulombic efficiency. The TP additive with an ultralow dosage of 0.028 g L-1 delivered favorable cycling stability of 720 h at 0.5 mA cm-2 and 0.5 mAh cm-2. The Zn-Na3V2(PO4)3 full cell assembled with the hybrid Zn(Ac)2-TP electrolyte contributed an energy density of 130 mAh g-1 at the current density of 0.2C and enhanced cycling stability of 78% retention after 300 cycles. These results will provide new insights into additive engineering for aqueous electrolytes and the fundamental understanding of AEI phenomena for high performance ZIBs.

Graphitic Carbon Quantum Dots Modified Nickel Cobalt Sulfide as Cathode Materials for Alkaline Aqueous Batteries.

Carbon quantum dots (CQDs) as a new class of emerging materials have gradually drawn researchers' concern in recent years. In this work, the graphitic CQDs are prepared through a scalable approach, achieving a high yield with more than 50%. The obtained CQDs are further used as structure-directing and conductive agents to synthesize novel N,S-CQDs/NiCo2S4 composite cathode materials, manifesting the enhanced electrochemical properties resulted from the synergistic effect of highly conductive N,S-codoped CQDs offering fast electronic transport and unique micro-/nanostructured NiCo2S4 microspheres with Faradaic redox characteristic contributing large capacity. Moreover, the nitrogen-doped reduced graphene oxide (N-rGO)/Fe2O3 composite anode materials exhibit ultrahigh specific capacity as well as significantly improved rate property and cycle performance originating from the high-capacity prism-like Fe2O3 hexahedrons tightly wrapped by highly conductive N-rGO. A novel alkaline aqueous battery assembled by these materials displays a specific energy (50.2 Wh kg-1), ultrahigh specific power (9.7 kW kg-1) and excellent cycling performance with 91.5% of capacity retention at 3 A g-1 for 5000 cycles. The present research offers a valuable guidance for the exploitation of advanced energy storage devices by the rational design and selection of battery/capacitive composite materials.

Yolk-Shell-Structured Bismuth@N-Doped Carbon Anode for Lithium-Ion Battery with High Volumetric Capacity.

As an anode for lithium-ion batteries, metallic bismuth (Bi) can provide a superb volumetric capacity of 3800 mA h cm-3, showing perspective value for application. It is a pity that the severe volume swelling during the lithiation process leads to the dramatic deterioration of the cycling performances. To overcome this issue, Bi nanorods encapsulated in N-doped carbon nanotubes (yolk-shell Bi@C-N) are elaborately designed through in situ thermal reduction of Bi2S3@polypyrrole nanorods. In comparison with the commercial Bi, the lithium storage capacities of Bi@C-N are significantly enhanced, and it presents a stable volumetric capacity of 1700 mA h cm-3 over 500 cycles at a high current density of 1.0 A g-1, nearly 2.2 times that of graphite. The N-doped carbon nanotube and the cavity between the carbon wall and Bi jointly contribute to this superior performance. Especially, the failure mechanism of Bi nanorods and the protective effect of the carbon shell are revealed by ex situ TEM, which illuminates the decreasing tendency in the initial 10-20 cycles and the subsequent stable trend of cyclic performance.