Lithium-sulfur batteries (LSBs) are among the most promising candidates for next-generation energy storage technologies, thanks to their exceptionally high theoretical capacity (1675 mAh g -1 ), ultrahigh energy density (2600 Wh kg -1 ), low cost, and environmental friendliness. However, the practical implementation of LSBs has long been hindered by fundamental challenges: the dissolution and diffusion of intermediate lithium polysulfides (LPSs) give rise to the notorious “shuttle effect”, causing active material loss and electrode passivation; the insulating nature of sulfur and its lithiation products, combined with the complex multi-electron, multi-phase conversion mechanism, leads to sluggish sulfur redox kinetics. These issues collectively result in low reaction efficiency, poor cycling stability, and limited rate capability. In this context, single-atom catalysts (SACs) have emerged as a powerful approach to address these bottlenecks, particularly when their coordination structures are carefully engineered.
In a recent study, a research team led by Prof. Gaoran Li from Nanjing University of Science and Technology reported the development of an undercoordinated chromium SAC (CrN 3 ) that enables highly efficient sulfur electrocatalysis. The unique undercoordination design rationally regulates the electronic states, leading to significant enhancement in sulfur electrocatalytic activity and LSB performance.
The team published their work in Nano Research on December 31, 2025.
“LSBs are attractive for future energy storage yet limited by the shuttle effect and sluggish kinetics inherent in their chemistry.” Said Prof. Li, from the School of Materials Science and Engineering at Nanjing University of Science and Technology. “In this work, we prepared the undercoordinated CrN 3 by using a Cr-impregnated layered zeolitic imidazolate framework (Cr@ZIF-L) as a precursor, which yielded atomically dispersed Cr sites anchored on a nitrogen-rich, porous, and two-dimensional carbon matrix. A series of electron microscopy and X-ray adsorption characterizations confirmed the successful synthesis of CrN 3 and revealed its undercoordinated structure in comparison with conventional CrN 4 derived from a polyhedral precursor (Cr@ZIF-8).”
SACs, as compelling candidates for sulfur electrocatalysis, are characterized by atomically dispersed active sites that maximize metal utilization and catalytic efficiency. In addition, their well-defined local structure provides an ideal platform for tuning the electronic environment to achieve superior catalytic performance. Conventional SACs often adopt a symmetric MN 4 configuration, in which the metal center is surrounded by four nitrogen atoms (coordination number, CN=4). While this configuration offers favorable thermodynamic stability, it does not necessarily deliver optimal catalytic performance. Coordination regulation, either through overcoordination (CN>4) or undercoordination (CN<4), can alter the electronic structure and optimize SAC-LPS interactions, thereby enhancing catalytic activity.
The research team tuned the lattice extension pattern of the MOF-based precursor to construct undercoordination in the resulting SACs. The correlation between coordination structure and catalytic behavior was systematically investigated and consistently validated through combined theoretical calculations, physicochemical characterizations, and electrochemical evaluations. “Compared to conventional CrN 4 , our undercoordination design increases Cr 3d electron density and activates the Cr d xy and d x2-y2 orbitals upon hybridization with S 3p orbitals, leading to moderately weakened LPS adsorption but significantly reduced energy barriers for bidirectional sulfur conversions.” Prof. Li explained.
“Benefiting from these electronic regulations, the CrN 3 catalyst enabled fast and reversible sulfur electrochemistry,” Prof. Li said, “LBSs based on CrN 3 achieved outstanding cycling stability over 1000 cycles and an excellent rate capability of up to 5 C, not only outperforming their CrN 4 counterparts but also ranking highly competitive among recent reports. A high areal capacity of 5.53 mAh cm -2 can be maintained even under demanding conditions, such as high sulfur loading (5.5 mg cm -2 ) and lean electrolyte (5.0 mL g -1 )” The research team expects this work to stimulate further exploration of coordination engineering in SACs and other nanocatalysts, paving the way for the rational design of advanced sulfur electrocatalyst and accelerating the practical implementation of LSBs.
Other contributors include Hongyang Li, Jianjun Zhang, Yingrui Ding, Zhanpeng Huang, Pengsen Qian, Fanyang Sun from Nanjing University of Science and Technology, and Huimin Wang from The Hong Kong Polytechnic University, respectively.
This work was supported by the National Natural Science Foundation of China (22379069) and Fundamental Research Funds for the Central Universities (30922010304).
About Nano Research
Nano Research is a peer-reviewed, open access, international and interdisciplinary research journal, sponsored by Tsinghua University and the Chinese Chemical Society, published by Tsinghua University Press on the platform SciOpen. It publishes original high-quality research and significant review articles on all aspects of nanoscience and nanotechnology, ranging from basic aspects of the science of nanoscale materials to practical applications of such materials. After 18 years of development, it has become one of the most influential academic journals in the nano field. Nano Research has published more than 1,000 papers every year from 2022, with its cumulative count surpassing 7,000 articles. In 2024 InCites Journal Citation Reports, its 2024 IF is 9.0 (8.7, 5 years), and it continues to be the Q1 area among the four subject classifications. Nano Research Award, established by Nano Research together with TUP and Springer Nature in 2013, and Nano Research Young Innovators (NR45) Awards, established by Nano Research in 2018, have become international academic awards with global influence.
Nano Research
Undercoordination engineering of chromium single-atom catalyst with optimized d-p hybridization for lithium-sulfur batteries
31-Dec-2025