New organic cathodes to replace inorganic materials for the capacity enhancement of sodium-ion batteries (SIBs) are highly desirable. In this research, we described the investigation of pillar[5]quinone (P5Q), which we determined to have a theoretical capacity of 446 mAh g -1 , a value that makes it a very promising candidate as a cathode in rechargeable batteries. Inspired by this value, P5Q was encapsulated into CMK-3 to form a composite, and then integrated with singlewalled carbon nanotubes (SWCNTs) to generate a film that was used as the cathode in SIBs. The as-assembled SIBs showed an initial capacity up to 418 mAh g -1 and maintained 290 mAh g -1 after 300 cycles at 0.1 C. Even at 1 C, the capacity could still reach 201 mAh g -1 .

SWCNTs formed a three-dimensional conductive network between C4Q/CMK-3 nanocomposites, significantly improving the electrochemical performance of C4Q-SIBs.

Conjugated carbonyl electrode materials have attracted much attention because of their ability to store various cations, relatively high theoretical capacity, designability, and sustainability. In this Minireview, pyrene-4,5,9,10-tetraone (PTO) with four carbonyl functional groups served as the electrode material in secondary batteries. It exhibits excellent electrochemical performance, such as high theoretical specific capacity, high redox potential, and the high utility of active sites. Currently, there are many kinds of optimizations to address the high solubility of PTO in organic electrolytes and improve cycle stability. Forming polymers, immobilizing with carbon materials, changing polarity to form salts, and optimizing electrolytes, such as all-solid-state electrolytes, are mainly summarized. We hope this Minireview can provide a guideline for the development of high-performance secondary batteries using PTO.

Organic electrode materials have become a hot research field in lithium-ion batteries. However, the dissolution issue of organic materials (especially small molecules) in traditional electrolytes has become one of the important reasons to limit their application. The usage of highly concentrated electrolyte (HCE, >3 M) has been demonstrated to solve this problem, where the electrochemical performance of Pillar[5]quinone (P5Q) in 4.2 M LiTFSA/AN electrolyte was investigated. The HCE can avoid the reaction between acetonitrile molecules and lithium metal anode, reduce the dissolution of organic materials, and display excellent battery performance. At a current density of 0.2 C, a high specific capacity of 310 mAh g À1 (C theo = 446 mAh g À1 ) was maintained after 900 cycles, and the reversible capacity is higher than 113 mAh g À1 even at 10 C, indicating a good rate capability. This research would expand the new application of acetonitrile-based electrolyte in organic secondary battery.

Organic cathode materials have potential applications in rechargeable batteries due to their several advantages such as high specific capacity, flexible designability, plentiful raw materials, environmental friendliness, and renewability. However, their high solubility in organic electrolytes strongly impedes the further research progress. Thus, it is highly desirable to develop some new strategies to address this issue. Herein, we report one method to address this dissolution issue by increasing molecular weight without reducing theoretical capacity, where a novel Calix[8]quinone (C8Q) with 8 p-benzoquinone units connected by methylene groups was designed and prepared in a good yield (total: 23%). C8Q exhibits higher cycle stability (268 mAh g À1 ) in lithium-ion batteries (LIBs) compared to the same series of substances Calix[4]quinone (C4Q, 30 mAh g À1 ) and Calix[6]quinone (C6Q, 207 mAh g À1 ) after 100 cycles at 0.2 C. Moreover, C8Q shows better electrochemical performance in 4.2 M LiTFSI-AN highly-concentrated electrolyte with special aggregate structure configured with high-dissociation salt LiTFSI and low-viscosity solvent acetonitrile (AN), namely, C8Q possesses high capacity (340 mAh g À1 after 100 cycles at 0.2 C), superior rate ability (440 mAh g À1 at 0.1 C and 167 mAh g À1 at 5 C), and ultra-long cycle life (220 mAh g À1 after 1000 cycles at 0.5 C). This work could provide a promising strategy to address the dissolution issue of organic electrode materials in organic electrolyte.