The poor performance of Zn electrode in aqueous electrolytes prevents the practical application of aqueous zinc-ion batteries (AZIBs). Here, 2-Pyrrolidinone (Pr) is introduced into conventional ZnSO4 electrolytes as additive and only 3 vol.% addition (Pr-to-H2O volume ratio) enables boosted performance. The Pr molecules are preferentially adsorbed on the surface of Zn electrodes to promote the uniform deposition of Zn ions and modulate the solvation structure of Zn2+ to inhibit the side reactions. As a result, the Zn electrode is boosted to run over 1200 h during charge/discharge cycling processes and delivers high average coulombic efficiency (CE) of 99.9 % under 1 mA cm-2, 1 mAh cm-2. Even under harsh testing conditions of 20 mA cm-2 and 20 mAh cm-2, Zn electrode still run over 100 h, which is much longer than that at pristine electrolyte (25 h). Moreover, the Zn||MnO2 full cells with the Pr additive exhibit a high capacity of 201 mAh g-1 and good capacity retention of 89 % after 550 cycles at 0.5 A g-1. Trace amount of 2-Pyrrolidinone (Pr) additive manipulates solvation structure and alters the Zn anode-electrolyte interface via absorbing Pr molecules on the Zn surface, reducing water activity, suppressing corrosion and dendrite formation, and resulting in a boosted Zn electrode running over 1200 h with average CE 99. 9 % under 1 mA cm-2 and 1 mAh cm-2.+image

The practical application of aqueous zinc-ion batteries (AZIBs) is limited by serious side reactions, such as the hydrogen evolution reaction and Zn dendrite growth. Here, the study proposes a novel adoption of a biodegradable electrolyte additive, γ-Valerolactone (GVL), with only 1 vol.% addition (GVL-to-H2O volume ratio) to enable a stable Zn metal anode. The combination of experimental characterizations and theoretical calculations verifies that the green GVL additive can competitively engage the solvated structure of Zn2+ via replacing a H2O molecule from [Zn(H2O)6]2+, which can efficiently reduce the reactivity of water and inhibit the subsequent side reactions. Additionally, GVL molecules are preferentially adsorbed on the surface of Zn to regulate the uniform Zn deposition and suppress the Zn dendrite growth. Consequently, the Zn anode exhibits boosted stability with ultralong cycle lifespan (over 3500 h) and high reversibility with 99.69% Coulombic efficiency. The Zn||MnO2 full batteries with ZnSO4-GVL electrolyte show a high capacity of 219 mAh g-1 at 0.5 A g-1 and improved capacity retention of 78% after 550 cycles. This work provides inspiration on bio-based electrolyte additives for aqueous battery chemistry and promotes the practical application of AZIBs.

Aqueous zinc-ion batteries (ZIBs) have gained significant attention owing to their high energy densities, low costs, and enhanced safety profiles. However, the development of suitable host materials (i.e., cathodes) with high capacity, structural stability, and rate performance remains challenging. Herein, a nanoflower-like Ca0.10MnO20.61H(2)O (CaMnO) is successfully synthesized as a high-performance cathode material for ZIBs using a simplified one-step hydrothermal method. The unique nanoflower-like 3D porous structure provides a continuous conductive path and abundant adsorption sites for Zn2+ ions and mitigates aggregation during long-term cycling processes. In addition, doping Ca2+ ions into the interlayer of MnO2 has a dual functional effect: 1) it acts as a pillar to broaden the interlayer spacing and enhance the crystal structure stability, and 2) it induces the formation of oxygen vacancies to enhance the reaction kinetics and increase the reversible capacity. Therefore, the CaMnO cathode exhibits a high specific capacity of 289 mAh g(-1), with excellent capacity retention (90%) over 750 cycles at a high current rate of 1.5 A g(-1). This study provides a new perspective on the development of advanced cathode materials for ZIBs.

Aqueous Zn-ion batteries (AZIBs) have attracted strong attention for widespread applications because of their safety, cheapness and ecological amiability. Nevertheless, challenges exist at the Zn anode such as the side reactions. Here, a small amount of sulfolane (SL) (1 vol%) was added into the typical ZnSO4 electrolyte as an additive. Detailed studies shown that SL adjusts the solvation structure of Zn2+, reduces the water activity and regulates the Zn deposition. Consequently, the side reactions are suppressed. Therefore, with only addition of 1% SL, the symmetric cells exhibit long cycling lifespan of more than 2000 h and high Coulombic efficiency of 99.7% at 1 mA cm-2 and 1 mAh cm-2. Even under harsh conditions of 5 mA cm-2 and 5 mAh cm-2, the Zn anode still displays long cycling performance of 1000 h. Furthermore, Zn||MnO2 full batteries with SL/ZnSO4 electrolyte shows a high capacity of about 120 mAh g-1 after 500 cycles at 0.5 A g-1.

The binder is an indispensable battery component that maintains the integrity of the electrode. Polyvinylidene fluoride (PVDF) is most commonly used as a binder in rechargeable batteries; however, it is associated with the toxic and expensive N-methyl-2-pyrrolidone organic solvent. Here, through the cross-linking of sodium alginate (SA) with metal cations, a high-performance hydrogel binder is developed that maintains the stability of MnO2 cathodes in an aqueous electrolyte. Owing to the strong adhesion, high hydrophilicity, and good mechanical stability resulting from the strong bonding of Ca2+ with SA, a commercial microsized MnO2 cathode with a Ca-SA binder delivered a capacity above 300 mAh/g at 1 C, which was larger than those of Mn-SA and Zn-SA (∼200 mAh/g) and PVDF (∼150 mAh/g) binders, and a capacity of 250 mAh/g at 3 C for over 200 cycles. These encouraging results could unlock the enormous potential of aqueous binders for practical applications in aqueous batteries.

The practical application of aqueous zinc‐ion batteries (AZIBs) is significantly limited by poor reversibility and stability of the Zn anode. Here, the first time addition of trace organic gamma butyrolactone (GBL) is reported to a typical ZnSO 4 electrolyte to controllably manipulate the electrolyte structure and interface. Judiciously combined experimental characterization and theoretical computation confirm that the GBL additive weakens the bonding strength between Zn 2+ ion and solvated H 2 O and rearranges the “Zn 2+ −H 2 O−SO 4 2– GBL” bonding network to reduce water activity and suppress corrosion and side products. The GBL molecules preferentially absorb on the surface of the Zn anode to give a uniform and compact Zn deposition. As a result, the Zn anode is boosted to run over 3105 cycles (6210 h) with average Coulombic efficiency of 99.93% under 1 mA cm –2 and 1 mAh cm –2 , and exhibit stable cycling for 1170 h under harsh testing conditions of 10 mA cm –2 and 10 mAh cm –2 . Additionally, the Zn–MnO 2 full cells using the ZnSO 4 –GBL electrolyte exhibit a high capacity of 287 mAh g –1 at 0.5 A g –1 and good capacity retention of 87% following 400 cycles. These findings will be of immediate benefit to design low cost AZIBs for clean energy storage.

Mn3O4 powders with nanometer size are successfully synthesized by a simple one-step method via flame spray pyrolysis. The precursor droplet is generated by heating under high temperature flame with fixed flow rate, and the exothermic reaction is induced to form nanosized Mn3O4 powders. When used as anode material for lithium-ion battery, the Mn3O4 exhibits good cycling capacity and rate performance. It delivers a specific capacity of 1,182 mA h g−1 over 110 cycles at a current density of 200 mA g−1, and has a high capacity of 140 mA h g−1 at 5,000 mA g−1.