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Li–O2 batteries are considered as one of the promising beyond Li-ion battery technologies owing to their high energy density. But, their poor cycle life due to sluggish oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) hinder the commercialization of this technology. Hence, fabrication of highly efficient ORR and OER catalysts is of paramount importance in order to improve the cyclic stability and longevity of this device. Herein, we discuss systematically the synthesis and electrochemical analysis of such bifunctional perovskite catalysts, namely, pristine CaMnO3 and its defect induced counterpart. When evaluated as a cathode catalyst in a Li–O2 battery along with a redox mediator LiI, the oxygen deficient CaMnO3 gives an improved cycle life reported at a high current rate of 500 mA g–1 with a capacity of 500 mA h g–1 in comparison with similar catalysts reported in the literature. Introduction of defects in the pristine framework predominantly improves the catalytic activity by lowering the overpotential. The presence of oxygen vacancies creates mixed-valence states of Mn3+/Mn4+ which modify the electronic structure, resulting in the improved catalytic activity. Comprehensive phase and compositional analysis confirm the formation of the desired defect-induced structure with improved catalytic activity toward ORR and OER which is elaborated with electrochemical analysis.

Graphite has been the conventional lithium-ion anode for the negative electrode for the past three decades. One of the major challenges for graphite anodes is the exfoliation of graphite framework on deep cycling at a fast current rate, leading to a gradual capacity fade. In this regard, poly­(vinylidene fluoride) (PVDF) has been the conventional binder widely used for stabilizing the graphite framework. Unfortunately, its nonconducting nature, slow dissolution in the electrolyte, and poor adherence to the current collector limit its utility as a robust binder for lithium-ion batteries with a long cycle life. Here, we report an n-type conjugated copolymer bis-imino-acenaphthenequinone-paraphenylene (BP) as an alternate binder material for the graphite anode. The BP binder-based anodic half-cells outperformed the PVDF-based counterpart, showing an excellent performance with a reversible capacity of 260 mA h g–1, cyclability up to 1735 long cycles at 1 C rate, and 95% capacity retention. The superior performance of the BP binder was attributed to its ability to provide mechanical robustness to the electrode laminate, maintain electronic conductivity within the electrode, and undergo n-doping in the anodic environment, influencing the formation of a thin solid electrolyte interface with low interfacial impedance.

An allylimidazolium-based poly(ionic liquid), poly-[vinylbenzylallylimidazolium bis(trifluoromethane)sulfonylimide] (PVBCAImTFSI) was used as a binder for graphite anodes in lithium-ion batteries. The anodes with the synthesized binder exhibited lesser electrolyte degradation and higher lithium-ion diffusion. Electrochemical impedance spectroscopy (EIS) results showed decreased interfacial and diffusion resistance for PVBCAImTFSI-based electrodes after cycling compared to PVDF-based anodes. Dynamic electrochemical impedance spectroscopy (DEIS) results indicated the interfacial resistance of the interface formed for the PVBCAImTFSI-based anodes to be 3 times lesser than the PVDF-based anodes. Suppression of electrolyte degradation and decrease in the intercalation− deintercalation potential and improved Li-ion diffusion coefficient for PVBCAImTFSI-based half-cells were observed from cyclic voltammetry measurements. DFT-based theoretical studies also speculated the suppression in the electrolyte degradation in the case of PVBCAImTFSI binder due to the positioning of its HOMO−LUMO levels. A reversible discharge capacity of 210 mAh/g was obtained for PVBCAImTFSI-based half-cells at 1C rate as compared to the 140 mAh/g obtained for PVDF-based anodic half-cells. After 500 cycles, 95% retention in the discharge capacity was observed. Also, PVBCAImTFSI-based anodes exhibited better charge− discharge stability than the PVDF-based anodes. Suppression of electrolyte degradation, reduction in the interfacial resistance, enhanced wettability, and an optimal SEI layer formed in the case of PVBCAImTFSI-based anodes cumulatively led to an enhanced stability and cyclability during the charge−discharge studies as compared to the commercially employed PVDF-based anodes. Thus, the tuning of the interfacial properties leads to the improvement in the performance of the lithium-ion batteries with PVBCAImTFSI as a binder.