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Recently, lithium–sulfur batteries have attracted considerable attention due to their high theoretical specific capacity (1673 mA h g−1) and high energy density (2800 W h kg−1), which is regarded as the most promising next-generation energy used for portable electronic devices, vehicles, and energy storage systems. However, there are still some problems that persist for the practical applications of lithium–sulfur batteries; in particular, the problems caused by lithium dendrite growth can seriously hinder the real-world applications and development of lithium–sulfur batteries. In this paper, we summarize the strategies of lithium anode improvement formulated in recent years, and we introduce them in sufficient progressive order on the basis of three aspects: anode surface modification, anode modification, and anode structure design. Nevertheless, the growth of lithium dendrites is still a formidable problem, and we have to continue devoting time and energy toward addressing this issue.

In this work, we demonstrate a “three birds one stone” strategy for preparing 1D N-doped porous carbon nanotubes embedded with core–shell Co@CoOx nanoparticles (Co@CoOx/NCNTs) from bimetallic ZnO@Zn/Co-ZIF nanowires. The ZnO nanowires played three roles: (i) ZnO acted as a template for 1D metal–organic framework (MOF) growth, (ii) in situ evaporation of Zn during pyrolysis prevented the aggregation of the carbon framework and benefited the formation of hierarchical pores, and (iii) the excess oxygen species released from ZnO in situ reacted with metallic cobalt nanoparticles during pyrolysis, leading to the configuration of a Co@CoOx core–shell structure. The as-prepared 1D Co@CoOx/NCNTs exhibited excellent oxygen reduction reaction performance, including a high kinetic current (4.6 times better compared to 20 wt% Pt/C at 0.7 V), a low Tafel slope of 80 mV dec−1, outstanding stability, and strong tolerance to CH3OH crossover. The assembled Zn–air batteries with Co@CoOx/NCNTs yielded high open-circuit voltage (1.52 V), superior stability (over 100 h of operation), and unprecedented rate performance that ranged from 1 to 500 mA cm−2, while existing batteries have never achieved a galvanostatic discharge current density larger than 300 mA cm−2. Such exceptional rate capability was ascribed to the formation of a uniform interconnected nanotube network, facilitated electron transport, and an enlarged electrochemically accessible surface area in the unique 1D porous tubular structure.

A novel strategy for the fabrication of hollow Co and N-codoped carbon nanopolyhedra (H-CoNC) from metal-organic framework (MOF) using in situ evaporation of ZnO nanosphere templates is proposed. The excess Zn supply during the pyrolysis process is found beneficial in terms of high nitrogen (≈9.75 at%), relatively homogenous CoN bonding, and the electrochemically accessible hierarchical porous system. Compared with other reported "solid" CoNC of identical surface areas, the newly developed H-CoNC shows enhanced kinetic current in 0.1 m KOH electrolyte and elevated oxygen reduction reaction (ORR) performance in 6 m KOH. The latter exceeds results obtained with the benchmark 20 wt% Pt/C, which is related to the strong confinement of O2 molecules in the H-CoNC hierarchical porous system. Furthermore, the H-CoNC displays great tolerance toward the methanol crossover and KSCN poisoning. Finally, the assembled Zn-air batteries with H-CoNC yield a record open circuit potential (1.59 V vs Zn, stabilized at 1.52 V), high power density (331.0 mW cm-2 ), and promising rate performance. This work provides a new guideline for the design of MOF-derived carbon materials, as well as novel insights into spatial confinement effect toward the ORR activity.