Rechargeable aqueous zinc-ion batteries (RZIBs) provide a promising complementarity to the existing lithium-ion batteries due to their low cost, non-toxicity and intrinsic safety. However, Zn anodes suffer from zinc dendrite growth and electrolyte corrosion, resulting in poor reversibility. Here, we develop an ultrathin, fluorinated two-dimensional porous covalent organic framework (FCOF) film as a protective layer on the Zn surface. The strong interaction between fluorine (F) in FCOF and Zn reduces the surface energy of the Zn (002) crystal plane, enabling the preferred growth of (002) planes during the electrodeposition process. As a result, Zn deposits show horizontally arranged platelet morphology with (002) orientations preferred. Furthermore, F-containing nanochannels facilitate ion transport and prevent electrolyte penetration for improving corrosion resistance. The FCOF@Zn symmetric cells achieve stability for over 750 h at an ultrahigh current density of 40 mA cm−2. The high-areal-capacity full cells demonstrate hundreds of cycles under high Zn utilization conditions.

3D thick electrode design is a promising strategy to increase the energy density of lithium-ion batteries but faces challenges such as poor rate and limited cycle life. Herein, a coassembly method is employed to construct low-tortuosity, mechanically robust 3D thick electrodes. LiFe 0.7 Mn 0.3 PO 4 nanoplates (LFMP NPs) and graphene are aligned along the growth direction of ice crystals during freezing and assembled into sandwich frameworks with vertical channels, which prompts fast ion transfer within the entire electrode and reveals a 2.5-fold increase in ion transfer performance as opposed to that of random structured electrodes. In the sandwich framework, LFMP NPs are entrapped in the graphene wall in a "plate-on-sheet" contact mode, which avoids the detachment of NPs during cycling and also constitutes electron transfer highways for the thick electrode. Such vertical-channel sandwich electrodes with mass loading of 21.2 mg cm −2 exhibit a superior rate capability (0.2C-20C) and ultralong cycle life (1000 cycles). Even under an ultrahigh mass loading of 72 mg cm −2 , the electrode still delivers an areal capacity up to 9.4 mAh cm −2 , ≈2.4 times higher than that of conventional electrodes. This study provides a novel strategy for designing thick electrodes toward high performance batteries.

In situ formed LiF grains are confined and evenly distributed throughout a covalent organic framework (COF) film, which exhibits cooperative effectiveness to greatly stabilize the lithium metal.

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Rechargeable aqueous zinc-ion batteries (RZIBs) provide a promising complementarity to the existing lithium-ion batteries due to their low cost, non-toxicity and intrinsic safety. However, Zn anodes suffer from zinc dendrite growth and continuous unfavorable side reactions, resulting in low Coulombic efficiency (CE) and severe capacity decay. Here, we develop an ultrathin, fluorinated two-dimensional porous covalent organic framework (FCOF) film as a protective layer on the Zn surface to address these issues. The strong interaction between fluorine (F) in FCOF and Zn reduces the surface energy of the Zn (002) crystal plane and regulates planar growth of zinc anode materials. As a result, Zn deposits underneath FCOF films show parallel platelet morphology with (002) planar orientations preferred. Furthermore, F-containing nanochannels facilitate the de-solvation of hydrated Zn ions and prevent electrolyte penetration, thus retarding corrosion of Zn. Such unique FCOF films prolonged the Zn symmetric cell lifespan to over 1700 h, which is 13 times longer than the cells without protection (125 h). The assembled full cells demonstrate a cycle life of over 250 cycles at 3 mAcm-2 under practical conditions, including lean electrolyte (12 μLmAh-1), limited Zn excess (only 1×excess), and a high mass loading of MnO2 cathode (16 mgcm-2). This work provides a new perspective for the realization of planar deposition of zinc metal anodes for developing high performance Zn-based batteries.

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