Limiting Interfacial Free Water and Proton Concentration by Hydrogel Electrolytes for Stable MoO3 Anode in a Proton Battery.

Aqueous rechargeable proton batteries are attractive due to the small ionic radius, light mass, and ultrafast diffusion kinetics of proton as charge carriers. However, the commonly used acidic electrolyte is usually very corrosive to the electrode material, which seriously affects the cycle life of the battery. Here, it is proposed that decreasing water activity and limiting proton concentration can effectively prevent side reactions of the MoO3 anode such as corrosion and hydrogen precipitation by using a lean-water hydrogel electrolyte. The as-prepared polyacrylamide (PAAM)-poly2-acrylamide-2-methylpropanesulfonic acid (PAMPS)/MnSO4 (PPM) hydrogel electrolyte not only has abundant hydrophilic groups that can form hydrogen bonds with free water and inhibit solvent-electrode interaction, but also has fixed anions that can maintain a certain interaction with protons. The assembled MoO3||MnO2 full battery can stably cycle over 500 times for ≈350 h with an unprecedented capacity retention of 100% even at a low current density of 0.5 A g-1. This work gives a hint that limiting free water as well as proton concentration is important for the design of electrolytes or interfaces in aqueous proton batteries.

Low-Electronegativity Cationic High-Entropy Doping to Trigger Stable Anion Redox Activity for High-Ni Co-Free Layered Cathodes in Li-Ion Batteries.

LiNi0.8 Co0.1 Mn0.1 O2 (NCM-811) exhibits the highest capacity in commercial lithium-ion batteries (LIBs), and the high Ni content (80 %) provides the only route for high energy density. However, the cationic structure instability arisen from the increase of Ni content (>80 %) limits the further increase of the capacity, and inevitable O2 release related to anionic structure instability hinders the utilization of anion redox activity. Here, by comparing various combinations of high-entropy dopants substituted Co element, we propose a low-electronegativity cationic high-entropy doping strategy to fabricate the high-Ni Co-free layered cathode (LiNi0.8 Mn0.12 Al0.02 Ti0.02 Cr0.02 Fe0.02 O2 ) that exhibits much higher capacity and cycling stability. Configurational disorder originated from cationic high-entropy doping in transition metal (TM) layer, anchors the oxidized lattice oxygen ((O2 )n- ) to preserve high (O2 )n- content, triggering the anion redox activity. Electron transfer induced by applying TM dopants with lower electronegativity than that of Co element, increases the electron density of O in TM-O octahedron (TM-O6 ) configuration to reach higher (O2 )n- content, resulting in the higher anion redox activity. With exploring the stabilization effect on both cations and anions of high-entropy doping and low-electronegativity cationic modified anion redox activity, we propose an innovative and variable pathway for rationally tuning the properties of commercial cathodes.

A mesoporous Al2O3 zincophilic sieve enables ultra-long lifespan of Zn-ion batteries.

The Zn dendrite growth and side reactions hinder the practical application of aqueous Zn-ion batteries. Here, a lactic acid-induced mesoporous Al2O3 (LA-MA) zincophilic sieve was constructed on a Zn anode to resolve these issues. The LA-MA layer with abundant mesoporous ion channels of 3.0 nm can regulate the solvation structure from [Zn2+(H2O)6]SO42- to more highly coordinated [Zn2+(H2O)5OSO32-] and restrain water-induced side reactions. Furthermore, the electrostatic attraction with zincophilic groups (CO, C-O) in the LA-MA layer has a positive effect on reducing the Zn2+ desolvation barrier and accelerating the Zn2+ diffusion. Under the synergism, the LA-MA@Zn symmetric cell exhibits over 5100 h at 0.25 mA cm-2. Impressively, an excellent capacity retention of 94.2% is achieved after 3500 cycles for the CNT/MnO2 cathode.

Stable Plating and Stripping of Lithium Metal Anodes through Space Confinement and Stress Regulation.

Lithium metal anodes suffer from enormous mechanical stress derived from volume changes during electrochemical plating and stripping. The utilization of derived stress has the potential for the dendrite-free deposition and electrochemical reversibility of lithium metal. Here, we investigated the plating and stripping process of lithium metal held within a cellular three-dimensional graphene skeleton decorated with homogeneous Ag nanoparticles. Owing to appropriate reduction-splitting and electrostatic interaction of nitrogen dopants, the cellular skeletons show micron-level pores and superior elastic property. As lithium hosts, the cellular skeletons can physically confine the metal deposition and provide continuous volume-derived stress between Li and collectors, thus meliorating the stress-regulated Li morphology and improving the reversibility of Li metal anodes. Consequently, the symmetrical batteries exhibit a stable cycling performance with a span life of more than 1900 h. Full batteries (NCM811 as cathodes) achieve a reversible capacity of 181 mA h g-1 at 0.5 C and a stable cycling performance of 300 cycles with a capacity retention of 83.5%. The meliorative behavior of lithium metal within the cellular skeletons suggests the advantage of a stress-regulating strategy, which could also be meaningful for other conversion electrodes with volume fluctuation.

An Ion-Sieving Janus Separator toward Planar Electrodeposition for Deeply Rechargeable Zn-Metal Anodes.

The irregular and random electrodeposition of zinc has emerged as a non-negligible barrier for deeply rechargeable aqueous zinc (Zn)-ion batteries (AZIBs), yet traditional texture regulation of the Zn substrate cannot continuously induce uniform Zn deposition. Here, a Janus separator is constructed via parallelly grown graphene sheets modified with sulfonic cellulose on one side of the commercial glass fiber separator through the spin-coating technique. The Janus separator can consistently regulate Zn growth toward a locked crystallographic orientation of Zn(002) texture to intercept dendrites. Furthermore, the separator can spontaneously repel SO4 2- and anchor H+ while allowing effective transport of Zn2+ to alleviate side reactions. Accordingly, the Zn symmetric cell harvests a long-term lifespan over 1400 h at 10 mA cm-2 /10 mAh cm-2 and endures stable cycling over 220 h even at a high depth of discharge (DOD) of 56%. The Zn/carbon nanotube (CNT)-MnO2 cell achieves an outstanding capacity retention of 95% at 1 A g-1 after 1900 cycles. Furthermore, the Zn/NH4 V4 O10 pouch cell with a Janus separator delivers an initial capacity of 178 mAh g-1 and a high capacity retention of 87.4% after 260 cycles. This work provides a continuous regulation approach to achieve crystallographic homogeneity of the Zn anode, which can be suitable for other metal batteries.

Crystal Plane Reconstruction and Thin Protective Coatings Formation for Superior Stable Zn Anodes Cycling 1300 h.

Some new insights into traditional metal pretreatment of anticorrosion for high stable Zn metal anodes are provided. A developed pretreatment methodology is employed to prefer the crystal plane of polycrystalline Zn and create 3.26 µm protective coatings mainly consisting of organic polymers and zinc salts on Zn foils (ROZ@Zn). In this process, Zn metal exhibits a surface-preferred (001) crystal plane proved by electron backscattered diffraction. Preferred (001) crystal planes and ROZ coatings can regulate Zn2+ diffusion, promote flat growth of Zn, and prevent side reactions. As a result, ROZ@Zn symmetrical cells exhibit superior plating/stripping performance over 1300 h. Impressively, it is significantly prolonged over 40 times in comparison to the bare Zn symmetric cell at 5 mA cm-2 . Moreover, Zn//MnO2  button cells have a high capacity retention of 96.3% after 1600 cycles and pouch cells have a high capacity 122 mAh g-1  after 200 cycle at 5 C. This work provides inspiration for high stable aqueous Zn metal batteries using the developed metal pretreatment of anticorrosion, which will be a viable, low-cost, and efficient technology. More interesting, it demonstrates the availability of reconstructing crystal planes by the largely heterogeneous reaction activation of the different crystal planes to H+ .

Enamel-like Layer of Nanohydroxyapatite Stabilizes Zn Metal Anodes by Ion Exchange Adsorption and Electrolyte pH Regulation.

The instability of Zn anode caused by severe dendrite growth and side reactions has restricted the practical applications of aqueous zinc-ion batteries (AZIBs). Herein, an enamel-like layer of nanohydroxyapatite (Ca5(PO4)3(OH), nano-HAP) is constructed on Zn anode to enhance its stability. Benefiting from the ion exchange between Zn2+ and Ca2+, the adsorption for Zn2+ in enamel-like nano-HAP (E-nHAP) layer can effectively guide Zn deposition, ensuring homogeneous Zn2+ flux and even nucleation sites to suppress Zn dendrites. Meanwhile, the low pH of acidic electrolyte can be regulated by slightly soluble nano-HAP, restraining electrolyte corrosion and hydrogen evolution. Moreover, the E-nHAP layer features high mechanical flexibility due to its enamel-like organic-inorganic composite nanostructure. Hence, symmetric cells assembled by E-nHAP@Zn show superior stability of long-term cycling at different current densities (0.1, 0.5, 1, 5, and 10 mA cm-2). The E-nHAP@Zn∥E-nHAP@Cu cell exhibits an outstanding cycling life with high Coulombic efficiency of 99.8% over 1000 cycles. Notably, the reversibility of full cell based on CNT/MnO2 cathode can be effectively enhanced. This work shows the potential of drawing inspiration from biological nanostructure in nature to develop stable metal electrodes.