Li Yujin, Mei Yu, Huang Yujie, Zhong Xue, Geng Zhenglei, He Zidong, Ding Hanrui, Deng Wentao, Zou Guoqiang, Liu Tongchao, Ji Xiaobo, Amine Khalil, Hou Hongshuai
State Key Laboratory of Powder Metallurgy, College of Chemistry and Chemical Engineering, Central South University, Changsha 410083, China.
Chemical Sciences and Engineering Division, Argonne National Laboratory, Lemont 60439, Illinois, United States.
ACS Nano. 2024 Sep 10;18(36):25053-25068. doi: 10.1021/acsnano.4c06571. Epub 2024 Aug 23.
The carbon coating strategy has emerged as an indispensable approach to improve the conductivity of polyanionic cathodes. However, owing to the complex reaction process between precursors of carbon and cathode, establishing a unified screening principle for carbonaceous precursors remains a technical challenge. Herein, we reveal that carbonaceous precursor pyrolysis chemistry undeniably influences the formation process and performance of NaV(PO) (NVP) cathodes from in situ insights. By investigating three types of carbonaceous precursors, it is found that O/H-containing functional groups can provide more bonding sites for cathode precursors and generate a reducing atmosphere by pyrolysis, which is beneficial to the formation of polyanionic materials and a uniform carbon coating layer. Conversely, excessive pyrolysis of functional groups leads to a significant amount of gas, which is detrimental to the compactness of the carbon layer. Furthermore, the substantial presence of residual heteroatoms diminishes graphitization. In this case, it is demonstrated that carbon dots (CDs) precursors with suitable functional groups can comprehensively enhance the Na migration rate, reversibility, and interface stability of the cathode material. As a result, the NVP/CDs cathode displays outstanding capacity retention, maintaining 92% after 10,000 cycles at a high rate of 50 C. Altogether, these findings provide a valuable benchmark for carbon source selection for polyanionic cathodes.
碳包覆策略已成为提高聚阴离子阴极导电性不可或缺的方法。然而，由于碳前驱体与阴极之间反应过程复杂，建立统一的含碳前驱体筛选原则仍是一项技术挑战。在此，我们通过原位研究揭示，含碳前驱体的热解化学不可否认地影响了NaV(PO)（NVP）阴极的形成过程和性能。通过研究三种类型的含碳前驱体发现，含O/H的官能团可为阴极前驱体提供更多键合位点，并通过热解产生还原气氛，这有利于聚阴离子材料和均匀碳包覆层的形成。相反，官能团过度热解会导致大量气体产生，这对碳层的致密性不利。此外，大量残留杂原子的存在会降低石墨化程度。在这种情况下，已证明具有合适官能团的碳点（CDs）前驱体可全面提高阴极材料的Na迁移速率、可逆性和界面稳定性。结果，NVP/CDs阴极表现出出色的容量保持率，在50 C的高倍率下循环10000次后仍保持92%。总之，这些发现为聚阴离子阴极的碳源选择提供了有价值的参考标准。
