The development of high-capacity, Earth-abundant, and stable cathode materials for robust aqueous Zn-ion batteries is an ongoing challenge. Herein, ultrathin nickel cobaltite (NiCo O ) nanosheets with enriched oxygen vacancies and surface phosphate ions (P-NiCo O ) are reported as a new high-energy-density cathode material for rechargeable Zn-ion batteries. The oxygen-vacancy and surface phosphate-ion modulation are achieved by annealing the pristine NiCo O nanosheets using a simple phosphating process. Benefiting from the merits of substantially improved electrical conductivity and increased concentration of active sites, the optimized P-NiCo O nanosheet electrode delivers remarkable capacity (309.2 mAh g at 6.0 A g ) and extraordinary rate performance (64% capacity retention at 60.4 A g ). Moreover, based on the P-NiCo O cathode, our fabricated P-NiCo O //Zn battery presents an impressive specific capacity of 361.3 mAh g at the high current density of 3.0 A g in an alkaline electrolyte. Furthermore, extremely high energy density (616.5 Wh kg ) and power density (30.2 kW kg ) are also achieved, which outperforms most of the previously reported aqueous Zn-ion batteries. This ultrafast and high-energy aqueous Zn-ion battery is promising for widespread application to electric vehicles and intelligent devices.

the developing trend of modern electronic technologies, [6] and significant efforts have been devoted to transforming these energy storage systems to their light, flexible, small, and thin counterparts. [7] The flexible battery market is forecast to increase rapidly from $69.6 million in 2015 to $958.4 million in 2022. [8] Lithium-ion batteries (LIBs) historically and presently dominant the markets of rechargeablebattery for portable devices because of the lightness of lithium and high energy density of the battery systems. [9,10] Nonetheless, LIBs are marred by the high cost and the shortage of lithium resources. Moreover, the aprotic electrolytes used in LIBs are generally toxic and flammable. This fact causes great safety issues for LIBs, especially when they are used in wearable/implantable applications in close contact with human body. It is highly challenging to assemble flexible LIBs due to the requirement of a highly reliable protective packaging to avoid the electrolyte leakage and reconcile with the washing need of wearable devices in practical applications. [3] Moreover, due to the high barrier encapsulation, the volumetric performance would be severely restricted, especially when LIBs are miniaturized. In this context, it is highly desirable to prepare flexible "beyond Li-based" batteries with safe, low-cost, and eco-friendly aqueous electrolytes. [11] As alternatives for LIBs, multivalent ion battery technologies (Zn-ion battery, ZIB, Mg-ion battery, and Al-ion battery) are of high interest for electrochemical energy storage. In comparison with LIBs operating with single-electron transfer, multivalent ion batteries employ multielectron transfer during the charge/ discharge processes, thus delivering much higher volumetric energy densities. [12][13][14] Since the first utilization of Zn in batteries in 1799, [15] Zn metal has captured increasing attention as an ideal anode material. In earlier studies, Zn anodes were widely explored in many alkaline battery systems, such as alkaline zinc-MnO 2 batteries, [16] zinc-nickel batteries, [17][18][19][20] zinc-silver batteries, [21] and zinc-air batteries. [22][23][24] Zn metal is able to offering both high gravimetric and high volumetric capacities (820 and 5855 mAh cm −3 ). [25] Moreover, Zn has the merits of low cost, low-toxicity, abundance in earth crust (≈300 times higher than for lithium), environmental benignity, easily recyclable, and intrinsic safety. [14,26] These advantages directly drove the recent renaissance of Zn anode based batteries. [15] However, the use of corrosive alkaline electrolyte leads to the Zn-dendritic (sharp, needle-like metallic protrusions) growth [27,28] and soluble ZnO 2 2− formation on Zn anode, which poison the cathode and result in the rapid capacity To keep pace with the increasing pursuit of portable and wearable electronics, it is urgent to develop advanced flexible power supplies. In this context, Zn-ion batteries (ZIBs) have garnered increasing attention as favorable energy storage devices for flexible electronics, ...

The construction of advanced Zn‐ion hybrid supercapacitors (ZHSCs) with high energy density is promising but still challenging, especially at high current densities. In this work, a high‐energy and ultrastable aqueous ZHSC is demonstrated by introducing N dopants into a hierarchically porous carbon cathode for the purpose of enhancing its chemical adsorption of Zn ions. Experimental results and theoretical simulations reveal that N doping not only significantly facilitates the chemical adsorption process of Zn ions, but also greatly increases its conductivity, surface wettability, and active sites. Consequently, the as‐fabricated aqueous ZHSC based on this N‐doped porous carbon cathode displays an exceptionally high energy density of 107.3 Wh kg−1 at a high current density of 4.2 A g−1, a superb power density of 24.9 kW kg−1, and an ultralong‐term lifespan (99.7% retention after 20 000 cycles), substantially superior to state‐of‐the‐art ZHSCs. Particularly, such a cathode also leads to a quasi‐solid‐state device with satisfactory energy storage performance, delivering a remarkable energy density of 91.8 Wh kg−1. The boosted energy storage strategy by tuning the chemical adsorption capability is also applicable to other carbon materials.

Rechargeable aqueous Zn-ion energy storage devices are promising candidates for next-generation energy storage technologies. However, the lack of highly reversible Zn2+-storage anode materials with low potential windows remains a primary concern. Here, we report a two-dimensional polyarylimide covalent organic framework (PI-COF) anode with high-kinetics Zn2+-storage capability. The well-organized pore channels of PI-COF allow the high accessibility of the build-in redox-active carbonyl groups and efficient ion diffusion with a low energy barrier. The constructed PI-COF anode exhibits a specific capacity (332 C g–1 or 92 mAh g–1 at 0.7 A g–1), a high rate capability (79.8% at 7 A g–1), and a long cycle life (85% over 4000 cycles). In situ Raman investigation and first-principle calculations clarify the two-step Zn2+-storage mechanism, in which imide carbonyl groups reversibly form negatively charged enolates. Dendrite-free full Zn-ion devices are fabricated by coupling PI-COF anodes with MnO2 cathodes, delivering excellent energy densities (23.9 ∼ 66.5 Wh kg–1) and supercapacitor-level power densities (133 ∼ 4782 W kg–1). This study demonstrates the feasibility of covalent organic framework as Zn2+-storage anodes and shows a promising prospect for constructing reliable aqueous energy storage devices.

The performance of pseudocapacitive electrodes at fast charging rates are typically limited by the slow kinetics of Faradaic reactions and sluggish ion diffusion in the bulk structure. This is particularly problematic for thick electrodes and electrodes highly loaded with active materials. Here, a surface‐functionalized 3D‐printed graphene aerogel (SF‐3D GA) is presented that achieves not only a benchmark areal capacitance of 2195 mF cm−2 at a high current density of 100 mA cm−2 but also an ultrahigh intrinsic capacitance of 309.1 µF cm−2 even at a high mass loading of 12.8 mg cm−2. Importantly, the kinetic analysis reveals that the capacitance of SF‐3D GA electrode is primarily (93.3%) contributed from fast kinetic processes. This is because the 3D‐printed electrode has an open structure that ensures excellent coverage of functional groups on carbon surface and facilitates the ion accessibility of these surface functional groups even at high current densities and large mass loading/electrode thickness. An asymmetric device assembled with SF‐3D GA as anode and 3D‐printed GA decorated with MnO2 as cathode achieves a remarkable energy density of 0.65 mWh cm−2 at an ultrahigh power density of 164.5 mW cm−2, outperforming carbon‐based supercapacitors operated at the same power density.

No abstract

By learning the PM 2.5 readings and meteorological records from 2010–2015, the severity of PM 2.5 pollution in Beijing is quantified with a set of statistical measures. As PM 2.5 concentration is highly influenced by meteorological conditions, we propose a statistical approach to adjust PM 2.5 concentration with respect to meteorological conditions, which can be used to monitor PM 2.5 pollution in a location. The adjusted monthly averages and percentiles are employed to test if the PM 2.5 levels in Beijing have been lowered since China's State Council set up a pollution reduction target. The results of the testing reveal significant increases, rather than decreases, in the PM 2.5 concentrations in the years 2013 and 2014 as compared with those in year 2012. We conduct analyses on two quasi-experiments—the Asia-Pacific Economic Cooperation meeting in November 2014 and the annual winter heating—to gain insight into the impacts of emissions on PM 2.5 . The analyses lead to a conclusion that a fundamental shift from mainly coal-based energy consumption to much greener alternatives in Beijing and the surrounding North China Plain is the key to solving the PM 2.5 problem in Beijing.

Aqueous zinc batteries are promising in daily quick energy storage, but their commercialization is limited by the poor rate capability and low capacity of Zn-ion hosts, especially at practical-level mass...