Fluorinated carbon as high-performance cathode for aqueous zinc primary batteries.

Fluorinated carbon (CFx) has been extensively served as promising positive electrode material for lithium primary batteries due to its high energy density. However, there are comparatively far less reports about the use of CFx on other battery systems, let alone on the research of aqueous batteries. Herein in this study, we employed CFx as the cathode active for aqueous zinc batteries for the first time and systematically investigated its electrochemical behavior under a series of aqueous zinc-ion electrolytes. As is discovered that the F/C ratio (the x value in CFx) of CFx have significant effects on the electrochemical performance of aqueous Zn/CFx batteries. Specifically, CF0.85 exhibits excellent electrochemical property with delivering a remarkable discharge capacity of 503 mA h g-1 and energy density of 388 W h kg-1 (at a current rate of 30 mA g-1 under temperature of 25 °C), much better than several other CFx electrode with F/C ratio of 0.70, 0.95, and 1.10, respectively. Besides, it also exhibits decent temperature performance with discharge capacities of 550 mA h g-1 at 50 °C and 460 mA h g-1 at 0 °C under current density of 30 mA g-1. Furthermore, the electrochemical discharge mechanism based on conversion reaction was further uncovered by applying XPS, XRD, SEM and EDS elemental analysis characterization techniques. In conclusion, these results demonstrate the potential application value of CFx in aqueous zinc primary batteries.

Safe, Low-Cost, Fast-Kinetics and Low-Strain Inorganic-Open-Framework Anode for Potassium-Ion Batteries.

A key challenge for potassium-ion batteries is to explore low-cost electrode materials that allow fast and reversible insertion of large-ionic-size K+ . Here, we report an inorganic-open-framework anode (KTiOPO4 ), which achieves a reversible capacity of up to 102 mAh g-1 (307 mAh cm-3 ), flat voltage plateaus at a safe average potential of 0.82 V (vs. K/K+ ), a long lifespan of over 200 cycles, and K+ -transport kinetics ≈10 times faster than those of Na-superionic conductors. Combined experimental analysis and first-principles calculations reveal a charge storage mechanism involving biphasic and solid solution reactions and a cell volume change (9.5 %) even smaller than that for Li+ -insertion into graphite (≈10 %). KTiOPO4 exhibits quasi-3D lattice expansion on K+ intercalation, enabling the disintegration of small lattice strain and thus high structural stability. The inorganic open-frameworks may open a new avenue for exploring low-cost, stable and fast-kinetic battery chemistry.

Highly reversible potassium-ion intercalation in tungsten disulfide.

Rechargeable potassium-ion batteries (PIBs) show promise beyond Li-ion technology in large-scale electrical-energy storage due to the abundance and low cost of potassium resources. However, the intercalation of large-size K+ generally results in irreversible structural degradation and short lifespan to the hosts, representing a major obstacle. Here, we report a new electrochemical K+-intercalation host, tungsten disulfide (WS2), which can store 0.62 K+ per formula unit with a reversible capacity of 67 mA h g-1 and well-defined voltage plateaus at an intrinsically safe average operation potential of 0.72 V versus K/K+. In situ X-ray diffraction and ex situ electron microscopy revealed the underlying intercalation mechanism, a relatively small cell volume change (37.81%), and high reversibility of this new battery chemistry. Such characteristics impart WS2 with ultrahigh structural stability and a long lifespan, regardless of deep or fast charging. WS2 achieved record-high cyclability among chalcogenides up to 600 cycles with 89.2% capacity retention at 0.3C, and over 1000 cycles with 96.3% capacity retention and an extraordinary average Coulombic efficiency of 99.90% at 2.2C. This intercalation electrochemistry may open up new opportunities for the design of long-cycle-life and high-safety PIBs.

Concentrated electrolytes stabilize bismuth-potassium batteries.

Storing as many as three K-ions per atom, bismuth is a promising anode material for rechargeable potassium-ion batteries that may replace lithium-ion batteries for large-scale electrical energy storage. However, Bi suffers from poor electrochemical cyclability in conventional electrolytes. Here, we demonstrate that a 5 molar (M) ether-based electrolyte, versus the typical 1 M electrolyte, can effectively passivate the bismuth surface due to elevated reduction resistance. This protection allows a bismuth-carbon anode to simultaneously achieve high specific capacity, electrochemical cyclability and Coulombic efficiency, as well as small potential hysteresis and improved rate capability. We show that at a high electrolyte concentration, the bismuth anode demonstrates excellent cyclability over 600 cycles with 85% capacity retention and an average Coulombic efficiency of 99.35% at 200 mA g-1. This "concentrated electrolyte" approach provides unexpected new insights to guide the development of long-cycle-life and high-safety potassium-ion batteries.

Aggregation-based abrupt crystallization from amorphous Ag2S to Ag2S nanocrystals.

Abrupt crystallization from ∼2-5 nm (amorphous) to ∼12-15 nm (crystalline) was observed in hydrothermal coarsening of Ag2S. The desorption behavior of capping ligands could be associated with the aggregation and fusion of amorphous particles into crystals.