Lithium Storage Mechanism: A Review of Perylene Diimide N-Substituted with a 1,2,4-Triazol-3-yl Ring for Organic Cathode Materials.

The demand for lithium-ion batteries (LIBs) has increased rapidly. However, commercial inorganic-based cathode materials have a low theoretical capacity and inherent disadvantages, such as high cost and toxicity. Redox-active organic cathodes with a high theoretical capacity, eco-friendly properties, and sustainability have been developed to overcome these limitations. Herein, perylene diimide derivatives N-substituted with 1,2,4-triazol-3-yl rings (PDI-3AT) were developed to apply as a cathode material for LIBs. The PDI-3AT cathode exhibited discharge capacities of 85.2 mAh g-1 (50 mA g-1 over 100 cycles) and 64.5 mAh g-1 (500 mA g-1 over 1000 cycles) with ratios to the theoretical capacities of 84 and 64%, respectively. Electrochemical kinetics analysis showed capacitive behaviors of the PDI-3AT cathode with efficient pathways for lithium-ion transport. Also, the activation step of the PDI-3AT cathode was demonstrated by improving the charge transfer resistance and lithium-ion diffusion coefficient during the initial few charge-discharge cycles. Furthermore, DFT calculations at the B3LYP/6-311+G** level and ex situ analysis of various charge states of the PDI-3AT electrode using attenuated total reflection Fourier transform infrared (ATR FT-IR) analysis, X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) were conducted for the further study of the lithium-ion storage mechanism. The results showed that the lithiation process formed the lithium enolate (═C-O-Li) coordinated with the N atoms of the 1,2,4-triazole ring. It is expected that our study results will encourage the production and use of redox-active perylene diimide derivatives as next-generation cathode materials.

Hybrid Nano Flake-like Vanadium Diselenide Combined on Multi-Walled Carbon Nanotube as a Binder-Free Electrode for Sodium-Ion Batteries.

As the market for electric vehicles and portable electronic devices continues to grow rapidly, sodium-ion batteries (SIBs) have emerged as energy storage systems to replace lithium-ion batteries (LIBs). However, sodium-ion is heavier and larger than lithium-ion, resulting in volume expansion and slower ion transfer. It is necessary to find suitable anode materials with high capacity and stability. In addition, wearable electronics are starting to be commercialized, requiring a binder-free electrode used in flexible batteries. In this work, we synthesized nano flake-like VSe2 using organic precursor and combined it with MWCNT as carbonaceous material. VSe2@MWCNT was mixed homogenously using sonication and fabricated film electrodes without a binder and substrate via vacuum filter. The hybrid electrode exhibited high-rate capability and stable cycling performance with a discharge capacity of 469.1 mAhg-1 after 200 cycles. Furthermore, VSe2@MWCNT exhibited coulombic efficiency of ~99.7%, indicating good cycle stability. Additionally, VSe2@MWCNT showed a predominant 85.5% of capacitive contribution at a scan rate of 1 mVs-1 in sodiation/desodiation process. These results showed that VSe2@MWCNT is a suitable anode material for flexible SIBs.

Revisiting Lithium- and Sodium-Ion Storage in Hard Carbon Anodes.

The galvanostatic lithiation/sodiation voltage profiles of hard carbon anodes are simple, with a sloping drop followed by a plateau. However, a precise understanding of the corresponding redox sites and storage mechanisms is still elusive, which hinders further development in commercial applications. Here, a comprehensive comparison of the lithium- and sodium-ion storage behaviors of hard carbon is conducted, yielding the following key findings: 1) the sloping voltage section is presented by the lithium-ion intercalation in the graphitic lattices of hard carbons, whereas it mainly arises from the chemisorption of sodium ions on their inner surfaces constituting closed pores, even if the graphitic lattices are unoccupied; 2) the redox sites for the plateau capacities are the same as those for the closed pores regardless of the alkali ions; 3) the sodiation plateau capacities are mostly determined by the volume of the available closed pore, whereas the lithiation plateau capacities are primarily affected by the intercalation propensity; and 4) the intercalation preference and the plateau capacity have an inverse correlation. These findings from extensive characterizations and theoretical investigations provide a relatively clear elucidation of the electrochemical footprint of hard carbon anodes in relation to the redox mechanisms and storage sites for lithium and sodium ions, thereby providing a more rational design strategy for constructing better hard carbon anodes.

Amino-Acid-Substituted Perylene Diimide as the Organic Cathode Materials for Lithium-Ion Batteries.

One of the most effective cost reduction and green engineering projects is to introduce organic compounds to electrode materials instead of expensive inorganic-based materials. In this work, derivatives of perylene diimide substituted with amino acids (PDI_AAs) showed the characteristics of redox-active organic compounds and were, therefore, used as cathode materials of lithium-ion batteries (LIBs). Among the as-synthesized PDI_AAs, the L-alanine-substituted PDI (PDI_A) showed the most improved cycling performances of 86 mAhg-1 over 150 cycles with retention of 95% at 50 mAg-1. Furthermore, at a high current density of 500 mAg-1, PDI_A exhibited a long-term cycling performance of 47 mAhg-1 (retention to 98%) over 5000 cycles. In addition, ex situ attenuated total reflection Fourier-transform infrared spectroscopy (ATR FT-IR) analysis of electrodes at various charging states showed the mechanism of the charge-discharge process of PDI_A.

Synthesis of Sb2S3 NRs@rGO Composite as High-Performance Anode Material for Sodium-Ion Batteries.

Sodium ion batteries (SIBs) have drawn interest as a lithium ion battery (LIB) alternative owing to their low price and low deposits. To commercialize SIBs similar to how LIBs already have been, it is necessary to develop improved anode materials that have high stability and capacity to operate over many and long cycles. This paper reports the development of homogeneous Sb2S3 nanorods (Sb2S3 NRs) on reduced graphene oxide (Sb2S3 NRs @rGO) as anode materials for SIBs. Based on this work, Sb2S3 NRs show a discharge capacity of 564.42 mAh/g at 100 mA/g current density after 100 cycles. In developing a composite with reduced graphene oxide, Sb2S3 NRs@rGO present better cycling performance with a discharge capacity of 769.05 mAh/g at the same condition. This achievement justifies the importance of developing Sb2S3 NRs and Sb2S3 NRs@rGO for SIBs.