are cheaper and safer especially when aqueous electrolytes are leveraged, and the battery can also deliver a considerable theoretical energy density, thus making them a promising alternative to LIBs. [2] Compared with the case in alkaline electrolytes, Zn metal anodes follow a more direct transition pathway from metallic Zn to Zn 2+ ions upon the electro-stripping process in mild (neutral and faintly acidic) electrolytes, thus minimizing the presence of non-conductive by-products (e.g., Zn-hydroxides and ZnO) that might passivate Zn metal anodes. Unfortunately, Zn metal electro-plating still suffers from a non-compact nucleation/growth pattern, which potentially leads to dendrite formation and anode pulverization ("dead" metal deposits), particularly upon harsh cycling conditions (e.g., high rates, high deposition capacities, and large depth of discharge). [2,3] This will further lower the Coulombic efficiency (CE) and shorten the cell lifespan. Therefore, manipulating the Zn electroplating process to achieve dendrite-free and compact morphology is vital for improving the electrochemical performance of ZIBs.Metallic dendrite-growth behavior is susceptible to a series of physical fields, such as ion flux, electric field, stress, and temperature. [4a,b,c] Any local intensity/distribution unevenness of these physical fields around nucleation substrates or freshly plated metal electrodeposits may trigger selective nucleation/ growth, accounting for the dendrite growth. [5a,b] Under low current densities, metal nucleation/growth is a reaction-controlled process, while under high current densities, metal plating will be a diffusion-controlled behavior. [6] This implies that ion flux homogeneity and ion replenishment rates from electrolyte to reaction interface will be two key factors that control the deposition morphology upon fast-charging circumstances-that is, at a high plating rate. Random ion diffusion and sluggish ion replenishment at the reaction interface will lead to rampant and non-planar metallic dendrite formation (Figure 1a). To mitigate dendritic formation and improve the high-rate stability of Zn metal anodes, considerable approaches have focused on compositing the Zn metal anode with 3D conductive hosts that can deliver sufficient ion transportation channels and massive electrochemical active sites, thus endowing a low effective current density (namely, a low local reaction rate) and delaying dendrite formation. [7a,b] However, for hosts to function properly, they need to be pre-composited with metal anodes (typically Aqueous zinc ion batteries are receiving unprecedented attention owing to their markedly high safety and sustainability, yet their lifespan particularly at high rates is largely limited by the poor reversibility of zinc metal anodes, due to the random ion diffusion and sluggish ion replenishment at the reaction interface. Here, a tunnel-rich and corona-poled ferroelectric polymer-inorganic-composite thin film coating for Zn metal anodes to tackle above problems, is proposed. It is demon...

Developing cost‐effective and high‐efficiency electrocatalysts toward alkaline oxygen evolution reaction (OER) is crucial for water splitting. Amorphous bimetallic NiFe‐based (oxy)hydroxides have excellent OER activity under alkaline media, but their poorly electrical conductivity impedes the further improvement of their catalytic performance. Herein, a bimetallic NiFe‐based heterostructure electrocatalyst that is composed of amorphous NiFe(OH)x and crystalline pyrite (Ni, Fe)Se2 nanosheet arrays is designed and constructed. The catalyst exhibits an outstanding OER performance, only requiring low overpotentials of 180, 220, and 230 mV at the current density of 10, 100, and 300 mA cm−2 and a low Tafel slope of 42 mV dec−1 in 1 m KOH, which is among the state‐of‐the‐art OER catalysts. Based on the experimental and theoretical results, the electronic coupling at the interface that leads to the increased electrical conductivity and the optimized adsorption free energies of the oxygen‐contained intermediates plays a crucial role in enhancing the OER activities. This work focusing on improving the OER performance via engineering amorphous‐crystalline bimetallic heterostructure may provide some inspiration for reasonably designing advanced electrocatalysts.

The rechargeability of aqueous zinc metal batteries is plagued by parasitic reactions of the zinc metal anode and detrimental morphologies such as dendritic or dead zinc. To improve the zinc metal reversibility, hereby we report a new solution structure of aqueous electrolyte with hydroxyl-ion scavengers and hydrophobicity localized in solvent clusters. We show that although hydrophobicity sounds counterintuitive for an aqueous system, hydrophilic pockets may be encapsulated inside a hydrophobic outer layer, and a hydrophobic anode–electrolyte interface can be generated through the addition of a cation-philic, strongly anion-phobic, and OH–-reactive diluent. The localized hydrophobicity enables less active water and less absorbed water on the Zn anode surface, which suppresses the parasitic water reduction; while the hydroxyl-ion-scavenging functionality further minimizes undesired passivation layer formation, thus leading to superior reversibility (an average Zn plating/stripping efficiency of 99.72% for 1000 cycles) and lifetime (80.6% capacity retention after 5000 cycles) of zinc batteries.

Layered transition metal oxides are appealing cathodes for sodium‐ion batteries due to their overall advantages in energy density and cost. But their stabilities are usually compromised by the complicated phase transition and the oxygen redox, particularly when operating at high voltages, leading to poor structural stability and substantial capacity loss. Here an integrated strategy combing the high‐entropy design with the superlattice‐stabilization to extend the cycle life and enhance the rate capability of layered cathodes is reported. It is shown that the as‐prepared high‐entropy Na2/3Li1/6Fe1/6Co1/6Ni1/6Mn1/3O2 cathode enables a superlattice structure with Li/transition metal ordering and delivers excellent electrochemical performance that is not affected by the presence of phase transition and oxygen redox. It achieves a high reversible capacity (171.2 mAh g−1 at 0.1 C), a high energy density (531 Wh kg−1), extended cycling stability (89.3% capacity retention at 1 C for 90 cycles and 63.7% capacity retention at 5 C after 300 cycles), and excellent fast‐charging capability (78 mAh g−1 at 10 C). This strategy would inspire more rational designs that can be leveraged to improve the reliability of layered cathodes for secondary‐ion batteries.

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The electrochemical conversion behavior of metal oxides as well as its influence on the lithium-storage performance remains unclear. In this paper, we studied the dynamic electrochemical conversion process of CuO/graphene as anode by in situ transmission electron microscopy. The microscopic conversion behavior of the electrode was further correlated with its macroscopic lithium-storage properties. During the first lithiation, the porous CuO nanoparticles transformed to numerous Cu nanograins (2-3 nm) embedded in Li2O matrix. The porous spaces were found to be favorable for accommodating the volume expansion during lithium insertion. Two types of irreversible processes were revealed during the lithiation-delithiation cycles. First, the nature of the charge-discharge process of CuO anode is a reversible phase conversion between Cu2O and Cu nanograins. The delithiation reaction cannot recover the electrode to its pristine structure (CuO), which is responsible for about ∼55% of the capacity fading in the first cycle. Second, there is a severe nanograin aggregation during the initial conversion cycles, which leads to low Coulombic efficiency. This finding could also account for the electrochemical behaviors of other transition metal oxide anodes that operate with similar electrochemical conversion mechanism.

A carbon nanotube/polyaniline/graphene composite has been prepared to enhance the electrochemical performance of lithium–sulfur batteries.

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