Multivalent‐ion batteries are emerging as low‐cost, high energy density, and safe alternatives to Li‐ion batteries but are challenged by slow cation diffusion in electrode materials due to the high polarization strength of Mg‐ and Al‐ions. In contrast, Ca‐ion has a low polarization strength similar to that of Li‐ion, therefore a Ca‐ion battery will share the advantages while avoiding the kinetics issues related to multivalent batteries. However, there is no battery known that utilizes the Ca‐ion chemistry due to the limited success in Ca‐ion storage materials. Here, a safe and low‐cost aqueous Ca‐ion battery based on a highly reversible polyimide anode and a high‐potential open framework copper hexacyanoferrate cathode is demonstrated. The prototype cell shows a stable capacity and high efficiency at both high and low current rates, with an 88% capacity retention and an average 99% coloumbic efficiency after cycling at 10C for 1000 cycles. The Ca‐ion storage mechanism for both electrodes as well as the origin of the fast kinetics have been investigated. Additional comparison with a Mg‐ion cell with identical electrodes reveals clear kinetics advantages for the Ca‐ion system, which is explained by the smaller ionic radii and more facile desolvation of hydrated Ca‐ions.

Abstract. Discerning mechanisms of sulfate formation during fine-particle pollution (referred to as haze hereafter) in Beijing is important for understanding the rapid evolution of haze and for developing cost-effective air pollution mitigation strategies. Here we present observations of the oxygen-17 excess of PM 2.5 sulfate ( 17 O(SO 2− 4 )) collected in Beijing haze from October 2014 to January 2015 to constrain possible sulfate formation pathways. Throughout the sampling campaign, the 12-hourly averaged PM 2.5 concentrations ranged from 16 to 323 µg m −3 with a mean of (141 ± 88 (1σ )) µg m −3 , with SO Our estimate suggested that in-cloud reactions dominated sulfate production on polluted days (PDs, PM 2.5 ≥ 75 µg m −3 ) of Case II in October 2014 due to the relatively high cloud liquid water content, with a fractional contribution of up to 68 %. During PDs of Cases I and III-V, heterogeneous sulfate production (P het ) was estimated to contribute 41-54 % to total sulfate formation with a mean of (48 ± 5) %. For the specific mechanisms of heterogeneous oxidation of SO 2 , chemical reaction kinetics calculations suggested S(IV) (= SO 2 q H 2 O + HSO − 3 + SO 2− 3 ) oxidation by H 2 O 2 in aerosol water accounted for 5-13 % of P het . The relative importance of heterogeneous sulfate production by other mechanisms was constrained by our observed 17 O(SO 2− 4 ). Heterogeneous sulfate production via S(IV) oxidation by O 3 was estimated to contribute 21-22 % of P het on average. Heterogeneous sulfate production pathways that result in zero-17 O(SO 2− 4 ), such as S(IV) oxidation by NO 2 in aerosol water and/or by O 2 via a radical chain mechanism, contributed the remaining 66-73 % of P het . The assumption about the thermodynamic state of aerosols (stable or metastable) was found to significantly influence the calculated aerosol pH (7.6 ± 0.1 or 4.7 ± 1.1, respectively), and thus influence the relative importance of heterogeneous sulfate production via S(IV) oxidation by NO 2 and by O 2 . Our local atmospheric conditions-based calculations suggest sulfate formation via NO 2 oxidation can be the dominant pathway in aerosols at high-pH conditions calculated assuming stable state while S(IV) oxidation by O 2 can be the dominant pathway providing that highly acidic aerosols (pH ≤ 3) exist. Our local atmospheric-conditions-based calculations illustrate the utility of 17 O(SO 2− 4 ) for quantifying sulfate forPublished by Copernicus Publications on behalf of the European Geosciences Union. 5516 P. He et al.: Isotopic constraints on heterogeneous sulfate production in Beijing haze mation pathways, but this estimate may be further improved with future regional modeling work.

Aqueous batteries are facing big challenges in the context of low working voltages and energy density, which are dictated by the narrow electrochemical window of aqueous electrolytes and low specific capacities of traditional intercalation‐type electrodes, even though they usually represent high safety, low cost, and simple maintenance. For the first time, this work demonstrates a record high‐energy‐density (1503 Wh kg−1 calculated from the cathode active material) aqueous battery system that derives from a novel electrolyte design to expand the electrochemical window of electrolyte to 3 V and two high‐specific‐capacity electrode reactions. An acid‐alkaline dual electrolyte separated by an ion‐selective membrane enables two dissolution/deposition electrode redox reactions of MnO2/Mn2+ and Zn/Zn(OH)42− with theoretical specific capacities of 616 and 820 mAh g−1, respectively. The newly proposed Zn–Mn2+ aqueous battery shows a high Coulombic efficiency of 98.4% and cycling stability of 97.5% of discharge capacity retention for 1500 cycles. Furthermore, in the flow battery based on Zn–Mn2+ pairs, more excellent stability of 99.5% of discharge capacity retention for 6000 cycles is achieved due to greatly improved reversibility of the Zn anode. This work provides a new path for the development of novel aqueous batteries with high voltage and energy density.

All-solid-state sodium batteries (ASSSBs) with nonflammable electrolytes and ubiquitous sodium resource are a promising solution to the safety and cost concerns for lithium-ion batteries. However, the intrinsic mismatch between low anodic decomposition potential of superionic sulfide electrolytes and high operating potentials of sodium-ion cathodes leads to a volatile cathode-electrolyte interface and undesirable cell performance. Here we report a high-capacity organic cathode, Na C O , that is chemically and electrochemically compatible with sulfide electrolytes. A bulk-type ASSSB shows high specific capacity (184 mAh g ) and one of the highest specific energies (395 Wh kg ) among intercalation compound-based ASSSBs. The capacity retentions of 76 % after 100 cycles at 0.1 C and 70 % after 400 cycles at 0.2 C represent the record stability for ASSSBs. Additionally, Na C O functions as a capable anode material, enabling a symmetric all-organic ASSSB with Na C O as both cathode and anode materials.

Abstract. The rapid mass increase of atmospheric nitrate is a critical driving force for the occurrence of fine-particle pollution (referred to as haze hereafter) in Beijing. However, the exact mechanisms for this rapid increase of nitrate mass have not been well constrained from field observations. Here we present the first observations of the oxygen-17 excess of atmospheric nitrate (Δ17O(NO3-)) collected in Beijing haze to reveal the relative importance of different nitrate formation pathways, and we also present the simultaneously observed δ15N(NO3-). During our sampling period, 12 h averaged mass concentrations of PM2.5 varied from 16 to 323 µg m−3 with a mean of (141±88(1SD)) µg m−3, with nitrate ranging from 0.3 to 106.7 µg m−3. The observed Δ17O(NO3-) ranged from 27.5 ‰ to 33.9 ‰ with a mean of (30.6±1.8) ‰, while δ15N(NO3-) ranged from −2.5 ‰ to 19.2 ‰ with a mean of (7.4±6.8) ‰. Δ17O(NO3-)-constrained calculations suggest nocturnal pathways (N2O5+H2O/Cl- and NO3+HC) dominated nitrate production during polluted days (PM2.5≥75 µg m−3), with a mean possible fraction of 56–97 %. Our results illustrate the potentiality of Δ17O in tracing nitrate formation pathways; future modeling work with the constraint of isotope data reported here may further improve our understanding of the nitrogen cycle during haze.

Forming compatible interfaces between cathode active materials and solid electrolytes is important for high-performance all-solid-state batteries. The organic cathode demonstrated here is (electro)chemically and mechanically compatible with a sulfide electrolyte. Its moderate redox potential enables the reversible formation of a resistive active material-electrolyte interface. It also maintains intimate contact with the electrolyte during cycling because of favorable mechanical properties. These features have contributed to the record cycling stability for all-solid-state sodium batteries.

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The boom of flexible and wearable electronic devices boosts the development of flexible batteries with high safety and stability.