Carbonaceous materials are the most promising anodes for alkali metal-ion batteries (AMIBs); however, it is still a great challenge to construct carbonaceous materials with elaborate microstructures to achieve superior electrochemical performance. Herein, a space-confined chemical vapor deposition (SC-CVD) method is developed for the first time to fill graphitic-like carbon domains into the micropores of commercial activated carbon (AC) to form hard carbon materials with tunable microstructures. The interlayer spacing of graphitic carbon, the size of graphitic carbon domains, and the micropores of the filling carbon (FC) materials can be facilely adjusted by changing the SC-CVD residence time and the adoption of post-heat treatment. The as-prepared FC demonstrates an excellent sodium storage capacity of 435.5 mA h g⁻¹ at 20 mA g⁻¹ and excellent cycling stability with a capacity retention of 80% over 1000 cycles. Besides, the FC also delivers outstanding electrochemical performance for lithium- and potassium-ion batteries. Impressively, record-level potassium storage performance is achieved by the FC. Moreover, the effect of carbon substrates and carbon sources on the microstructures and electrochemical properties of as-obtained FC is systematically investigated. This work provides a practical strategy to engineer commercial carbon materials to construct advanced hard carbon materials for high-performance AMIBs.

Exceptional performance reported for battery materials and devices in the scientific literature is often measured under conditions that are not aligned with practical applications. Aiming to bridge the gap between academia and industry, this Comment advocates the best practices for gauging performance and proposes guidelines on measurements with respect to a list of key metrics such as capacity, cyclability, Coulombic efficiency and electrolyte consumption.

Covalent organic frameworks (COFs) represent an emerging class of porous crystalline materials and have recently shown interesting applications in energy storage. Herein, we report the construction of a cycle-stable sulfur electrode by embedding sulfur into a 2D COF. The designed porphyrin-based COF (Por-COF), featuring a relatively large pore volume and narrow pore size distribution, has been employed as a host material for sulfur storage in Li–S batteries. With a 55% sulfur loading in the composite, the thus-prepared cathode delivers a capacity of 633 mA h g⁻¹ after 200 cycles at 0.5C charge/discharge rates. Therefore, embedding sulfur in the nanopores of the Por-COF significantly improves the performance of the sulfur cathode. Considering the flexible design of COFs, we believe that it is possible to synthesize a 2D COF host with a suitable pore environment to produce more stable Li–S batteries, which may help in exploration of the structure–property relationship between the host material and cell performance.

Commercial development of lithium–sulfur (Li–S) batteries is severely hindered by their insufficient cyclability, which is due to the loss of soluble lithium polysulfide intermediates generated during the discharge processes. To overcome this problem, considerable efforts have been devoted to designing novel micro- or nano-structured host materials, aiming to trap soluble polysulfide within the network. Herein, we report a new approach to construct a sulfur electrode by impregnating sulfur into the nanopores of covalent-organic frameworks (COFs). Our results clearly demonstrate that by using a 2D COF as a host material, e.g. CTF-1 (CTF: covalent triazine-based framework), the thus-prepared cathode can show a remarkable positive effect on the capacity retention of Li–S batteries. Considering the unique features of COFs, such as highly flexible molecular design and a controllable pore size, this proof-of-principle study provides new opportunities for materials scientists for tailoring cathode materials in Li–S batteries.