Tailoring π-Conjugated Systems: From π-π Stacking to High-Rate-Performance Organic Cathodes

Abstract

Organic sodium-ion batteries (OSIBs) have numerous promising advantages for foreseeable large-scale applications, particularly including the convenience of performance optimization through molecular design. However, the reported organic cathodes still suffer from limited capacity, low cyclability, and poor rate performance. The tailoring of the p-conjugated system reported here can enhance the p-p intermolecular interactions, leading to insolubility, long-range layer-by-layer p-p stacking, fast-charge transport, and extraordinary stability and ionic conductivity (10 À9 cm 2 s À1 ). Consequently, the obtained cathodes delivered high electrochemical performance with high capacity ($290 mAh g À1 ), superior fast-chargedischarge ability ($160 and 100 mAh g À1 at 10 and 50 A g À1 , respectively), and ultra-long cycle life (capacity as high as 97 mAh g À1 after 10,000 cycles at 50 A g À1 ).

In Situ Coating Graphdiyne for High‐Energy‐Density and Stable Organic Cathodes

“…Except for mixing high amount of conductive additives, the polymerization strategies are usually applied but cause the undesired decrease in the molecular stacking density and electroactive components (Figure 1a). [ 15–17 ] However, the active mass ratio of organic cathodes in the electrode is hard to exceed 60% (Figure 1b), [ 4,18–21 ] much lower than the inorganic materials (more than 90%). This seriously sacrifices the advantages of organic cathodes in energy density, resulting in an energy density much less than those of inorganic batteries.…”

Natural Compounds Gallic Acid Derivatives for Long‐Life Li/Na Organic Batteries

“…The stable discharge/charge plateaus around 1.0 V are observed, which refers the insertions and withdrawing of Li into/from aromatic rings (equation 2, Figure 3) and contribute more to the discharge capacity of LIBs. [33,35] At 0.1 A g À 1 , the first discharge capacity is 540 mAh g À 1 which is higher than corresponded charge capacity (284 mAh g À 1 ) because of the formation of SEI film. And the second discharge capacity was 297 mAh g À 1 with the coulombic efficiency of 89.9 %.…”

“…The charge plateau around 1.9 and 2.5 V in Figure A shows the delithiation process, and the oxidation reactions occur on the electrode (equation 1, Figure ). The stable discharge/charge plateaus around 1.0 V are observed, which refers the insertions and withdrawing of Li into/from aromatic rings (equation 2, Figure ) and contribute more to the discharge capacity of LIBs . At 0.1 A g −1 , the first discharge capacity is 540 mAh g −1 which is higher than corresponded charge capacity (284 mAh g −1 ) because of the formation of SEI film.…”

“…The capacity retention was maintained for 95 % for LIBs after 50 cycles at 24.1 mA g −1 and 84 % for SIBs after 100 cycles at 19 mA g −1 . By improving π‐π inter‐molecular conjugated interactions and long‐range layer‐by‐layer π‐π stacking of benzoquinone‐based polymers and Li and Na salts of azobenzene compounds, the insolubility, stability, charge transport, ion diffusion, charging‐discharging rates were enhanced remarkably …”

“…By improving π-π inter-molecular conjugated interactions and long-range layerby-layer π-π stacking of benzoquinone-based polymers and Li and Na salts of azobenzene compounds, the insolubility, stability, charge transport, ion diffusion, charging-discharging rates were enhanced remarkably. [32][33][34][35] However, most of these organic electrode materials would cause environmental pollutions and undergo the complex and rigorous synthetic procedures, which are expensive and hard to be applied in the commercial LIBs and SIBs. In the other hand, the low specific capacity and unsatisfied cycling stability are still big problems for developing organic LIBs and SIBs.…”