Unsatisfying reversibility of zinc (Zn) metal anode seriously hinders its further practical applications. It corresponds to two major issues including the notorious dendrite growth and the exacerbated hydrogen evolution, resulting...
Rechargeable calcium-ion batteries are intriguing alternatives for use as post-lithium-ion batteries. However, the high charge density of divalent Ca2+ establishes a strong electrostatic interaction with the hosting lattice, which results in low-capacity Ca-ion storage. The ionic radius of Ca2+ further leads to sluggish ionic diffusion, hindering high-rate capability performances. Here, we report 5,7,12,14-pentacenetetrone (PT) as an organic crystal electrode active material for aqueous Ca-ion storage. The weak π-π stacked layers of the PT molecules render a flexible and robust structure suitable for Ca-ion storage. In addition, the channels within the PT crystal provide efficient pathways for fast ionic diffusion. The PT anode exhibits large specific capacity (150.5 mAh g-1 at 5 A g-1), high-rate capability (86.1 mAh g-1 at 100 A g-1) and favorable low-temperature performances. A mechanistic study identifies proton-assisted uptake/removal of Ca2+ in PT during cycling. First principle calculations suggest that the Ca ions tend to stay in the interstitial space of the PT channels and are stabilized by carbonyls from adjacent PT molecules. Finally, pairing with a high-voltage positive electrode, a full aqueous Ca-ion cell is assembled and tested.
Cathodes of rechargeable Zn batteries typically face the issues of irreversible phase transformation, structure collapse, and volume expansion during repeated charge/discharge cycles, which result in an increased transfer resistance and poor long‐term cycling stability. Herein, a facile F doping strategy is developed to boost the cycling stability of nickel cobalt carbonate hydroxide (NiCo–CH) cathode. Benefiting from the extremely high electronegativity, the phase and morphology stabilities as well as the electrical conductivity of NiCo–CH are remarkably enhanced by F incorporation (NiCo–CH–F). Phase interface and amorphous microdomains are also introduced, which are favorable for the electrochemical performance of cathode. Benefiting from these features, NiCo–CH–F delivers a high capacity (245 mA h g−1), excellent rate capability (64% retention at 8 A g−1), and outstanding cycling stability (maintains 90% after 10 000 cycles). Moreover, the quasi‐solid‐state battery also manifests superior cycling stability (maintains 90% after 7200 cycles) and desirable flexibility. This work offers a general strategy to boost the cycling stability of cathode materials for aqueous Zn batteries.
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