Electrospinning Machine | Dose-effect of ZIF-67-derived Co, N sites in carbon fibers: Optimizing Lithium deposition uniformity and Lithium sulfide precipitation capacity

Lithium-sulfur batteries are regarded as the next-generation energy storage technology due to their ultra-high energy density (2600 Wh/kg) and low-cost sulfur cathode, but lithium dendrite growth and polysulfide shuttle effect severely restrict the practicalization process. Adding an interlayer can simultaneously suppress lithium dendrites and the shuttle effect. The abundant channels in metal-organic framework (MOFs) materials can promote uniform ion diffusion, and metal active sites can adsorb and promote the conversion of polysulfides to lithium sulfide. Combining MOFs with fibers as an interlayer can prevent particle agglomeration and improve conductivity, but the performance of MOFs/fiber-based interlayers is affected by the loading amount and the dispersion of metal active substances. Excessive MOF loading leads to particle agglomeration, blocking ion transport channels; while lower loading reduces the density of active sites. Therefore, establishing a quantitative relationship between MOF loading and the electrochemical performance of the composite is a key issue for optimizing the design of multifunctional interlayers.

Recently, Researcher Song Yan's team at the Shanxi Institute of Coal Chemistry, Chinese Academy of Sciences, published the latest research results "Dose-effect of ZIF-67-derived Co, N sites in carbon fibers: Optimizing Lithium deposition uniformity and Lithium sulfide precipitation capacity" in "Chemical Engineering Journal". They proposed using an electrospinning + carbonization strategy, by adjusting the ratio of ZIF-67 to PAN precursor (30%-90%), to prepare flexible nano carbon fiber (Co, N@CFs) nonwoven fabric containing cobalt nanoparticles and pyridinic nitrogen. Cobalt nanoparticles catalyze the conversion of polysulfides to Li2S; pyridinic nitrogen homogenizes the lithium ion flow through strong Li-N coordination; the three-dimensional conductive network accelerates electron transfer. The binder-free self-supporting structure of the nonwoven fabric avoids the interface resistance problem of traditional powder catalysts. Ph.D. student Gong Xiangjie from the Shanxi Institute of Coal Chemistry, Chinese Academy of Sciences, is the first author of the paper. This research was supported by projects such as the National Natural Science Foundation of China.

The preparation process of Co, N@CFs is shown in Figure 1a. ZIF-67 nanoparticles synthesized at room temperature were mixed with a dimethylformamide (DMF) solution of polyacrylonitrile (PAN) and then subjected to electrospinning, pre-oxidation, and carbonization to obtain Co, N@CFs. From Figures 1 (b-d), it can be seen that the density of metal particles embedded in the fiber substrate increases with the ZIF-67 content, reaching a maximum in the Co, N@CFs (1:0.9) sample, where each fiber is uniformly decorated with particles. This unique structure is conducive to the uniform deposition of lithium sulfide and can inhibit the formation of lithium dendrites.

Figure 1. Morphology analysis of Co, N@CFs.

Long-term cycling tests were conducted on lithium symmetric batteries. The results demonstrated that the Li/Li symmetric battery cycled for 2500 hours at 1 mA/cm² with Co, N@CFs (1:0.9) as the interlayer maintained a stable overpotential of 30 mV (Fig. 2d). In-situ optical microscopy confirmed the achievement of dendrite-free lithium deposition on the Co, N@CFs (1:0.9) sample (Fig. 3d).

Figure 2. Experimental results of lithium-lithium symmetric battery stability.

Figure 3. Results of in-situ microscopic observation of lithium dendrites.

The catalytic effect of cobalt-nitrogen co-doped carbon fibers (Co, N@CFs) on lithium sulfide nucleation during sulfur reduction was verified. The results show that the Co, N@CFs (1:0.9) sample had the highest catalytic performance for Li2S6. In the lithium sulfide deposition experiment, the Li2S nucleation capacity reached 171.85 mAh/g (Figure 4c), and in-situ XRD showed its highest Li2S characteristic peak intensity (Figure 4f). 

Figure 4. Characterization of Co, N@CFs catalyzing lithium sulfide nucleation.

The morphology of the Co, N@CFs interlayer after 1000 cycles at 2C is shown in Figures 5 (a-c). The results indicate that lithium sulfide was uniformly deposited on the Co, N@CFs (1:0.9) sample. This promotes the efficient regeneration of sulfur and enhances long-cycle stability. The morphology of the lithium electrode after 2500 hours of lithium plating/stripping is shown in Figures 5 (d-f). The results show that the lithium deposition surface in the Co, N@CFs (1:0.9) battery was the smoothest with the fewest cracks, indicating that this interlayer promotes the formation of small and dense lithium deposition particles and maintains stability during long-term cycling. The cycling performance of a battery with Co, N@CFs (1:0.9) as the interlayer under high loading (3.5 mg/cm²) and low-concentration electrolyte conditions is shown in Figure 5 (g), indicating that the sample has good cycling stability even under high sulfur load.

Figure 5. Morphology of the Co, N@CFs interlayer and lithium sheet after cycling, and high-load electrochemical performance.

DOI: https://doi.org/10.1016/j.cej.2025.166768