Chemical Buffer Layer Enabled Highly Reversible Zn Anode for Deeply Discharging and Long-Life Zn-Air Battery.

Rechargeable alkaline Zn-air batteries (ZABs) are attracting extensive attention owing to their high energy density and environmental friendliness. However, the dilemma of Zn anode, composed of ineluctable passivation and dissolution problems, severely hinders the discharge and cycling performance of the battery. Herein, the authors propose a chemical buffer layer coated on Zn metal (CBL@Zn) anode, in which ZnO nanorods are uniformly dispersed in graphene oxide (GO), to improve the reversibility of Zn↔ZnO electrochemical conversion process. Benefiting from the cooperative effect of ZnO nanorods' nuclei role and GO's adsorption affinity, the electrochemical precipitation-dissolution behavior of insulated ZnO is chemically regulated and the Zn(OH)4 2- ions are effectively confined in the chemical buffer layer. Therefore, the symmetrical CBL@Zn-CBL@Zn coin cell achieves a superior stability of 100 cycles with quite low overpotential (30 mv). When paired with commercial catalysts to assemble alkaline ZABs for practical use, an ultra high depth of discharge (DODZn ) >98% and excellent 450-h long-term cycling performance are realized. This chemical buffer strategy can potentially provide a new insight for developing other highly reversible alkaline Zn-metal batteries.

Synergistic Catalysis by Single-Atom Catalysts and Redox Mediator to Improve Lithium-Oxygen Batteries Performance.

Lithium-oxygen (Li-O2 ) batteries with ultrahigh theoretical energy density have attracted widespread attention while there are still problems with high overpotential and poor cycle stability. Rational design and application of efficient catalysts to improve the performance of Li-O2 batteries is of significant importance. In this work, Co single atoms catalysts are successfully combined with redox mediator (lithium bromide [LiBr]) to synergistically catalyze electrochemical reactions in Li-O2 batteries. Single-atom cobalt anchored in porous N-doped hollow carbon spheres (CoSAs-NHCS) with high specific surface area and high catalytic activity are utilized as cathode material. However, the potential performances of batteries are difficult to adequately achieve with only CoSAs-NHCS, owing to the blocked electrochemical active sites covered by insulating solid-state discharge product Li2 O2 . Combined with LiBr as redox mediator, the enhanced OER catalytic effect extends throughout all formed Li2 O2 during discharge. Meantime, the certain adsorption effect of CoSAs-NHCS on Br2 and Br3 - can reduce the shuttle of RMox . The synergistic effect of Co single atoms and LiBr can not only promote more Li2 O2 decomposition but also reduce the shuttle effect by absorbing the oxidized redox mediator. Li-O2 batteries with Co single atoms and LiBr achieve ultralow overpotential of 0.69 V and longtime stable cyclability.

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.

Guiding Smooth Li Plating and Stripping by a Spherical Island Model for Lithium Metal Anodes.

Lithium metal anodes are considered as promising candidates for next-generation high-energy-density batteries. However, the dendrite formation of Li metal anodes during charge-discharge results in some serious issues. Herein, we show a simple way to flatten the Li metal deposition surface on Ag-modified Cu foil using a spherical island model. In this model, Ag nuclei induce the deposition of Li atoms with low nucleation potentials at the initial heterogeneous nucleation stage. Then, Li homogeneously grows around the spherical islands and these regular islands overlap each other and form a flat Li surface. On the bare Cu foil surface, the Li growth behavior is random, and the deposition surface is porous and covered with dendrites. Stable long-term plating/stripping of a symmetric battery over 800 h at 1 mA cm-2 was achieved. Moreover, the super flat Li structure can be achieved by constructing islands into a three-dimensional (3D) current collector using the spherical island model. Benefiting from the spherical island model, Li||LiFePO4 and Li||O2 batteries with this 3D anode structure can obtain a stable performance.