Regulating the local electronic structure to design a reliable dual-active site organic anode compatible with high-performance lithium-ion batteries

Abstract

Organic coordination compounds are promising candidates for anode active materials in lithium-ion batteries (LIBs) owing to their unique designable structures, abundant active sites, and simple and mild synthesis routes. Unfortunately, most of these materials face great challenges in practical applications because they result in low reversible specific capacity, poor rate performance, and short cycle life. In this study, three different metal ions (Mn²⁺, Sn²⁺, and Fe³⁺) were coordinated with phthalic acid (PA). Three novel organic anode active materials were synthesized for LIBs, namely, manganese phthalate (MnPA), stannous phthalate (SnPA), and iron phthalate, and their lithium storage properties were studied systematically. Owing to the good coordination between carboxylic acid groups in PA and metal ions, the inherent microstructure and electron distribution of PA were adjusted, and the three anode active materials showed excellent structural stabilities and electrochemical performances. Compared with the same type of anode active materials, MnPA, SnPA, and Fe₂PA₃ showed superior cyclic stability and reversible capacity of 1100, 910, and 804 mA h g⁻¹ at 100 mA g⁻¹, respectively, and they exhibited a good capacity retention rate even after 3–4 months of cycle time. Interestingly, Fe₂PA₃ showed surprisingly fast charge and discharge ability (reversible capacity could reach 200–300 mA h g⁻¹ at a super current density of 5 A g⁻¹ while maintaining a stable cycle); SnPA showed good long cycle performance (stable cycling of more than 600 cycles at a current density of 500 mA g⁻¹ and a reversible capacity of 580 mA h g⁻¹); and MnPA showed better cycle stability than the Fe₂PA₃ and SnPA (stable cycle of up to 2100 cycles at 2 A g⁻¹ current density). More importantly, physical characterization, DFT calculation and kinetic analysis revealed the influence of three metal centers with different electronic structures on the lithium storage mechanism of the active material. In addition to demonstrating these three high performance organic anode active materials, we expect that this work would be an inspiration for the preparation of other organic active materials for advanced LIBs.