A quinone-based oligomeric lithium salt for superior Li–organic batteries

Abstract

Organic electrode materials are promising alternatives to transition-metal based intercalation compounds for the next generation of high-performance and sustainable batteries. Herein, a novel quinone-based organic, lithium salt of poly(2,5-dihydroxy-p-benzoquinonyl sulfide) (Li 2 PDHBQS), was successfully synthesized through a simple one-step polycondensation reaction, and applied as a cathode for Li-organic batteries. As an oligomeric lithium salt with average polymerization degree of 7, Li 2 PDHBQS combines the advantages of the O/Li/O coordination bond and increased molecular weight, thus solves absolutely the dissolution problem of active material in non-aqueous electrolytes, which has seriously hindered development of organic electrode materials. Benefiting from the high theoretical capacity, intrinsic insolubility, fast reaction kinetics of the quinone group, accelerated Li-ion transport and uniform blending with conductive carbon, as well as the stable amorphous structure, Li 2 PDHBQS shows superior comprehensive electrochemical performance including high reversible capacity (268 mA h g À1 ), high cycling stability (1500 cycles, 90%), high rate capability (5000 mA g À1 , 83%) andhigh Coulombic efficiency (99.9-100.1%). Investigation of the structure-property relationship of Li 2 PDHBQS and its analogues also gives new insights into developing novel quinone-based organic electrode materials, for building better Li-organic or Na-organic batteries beyond traditional Li-ion batteries. Broader contextAll electroactive organics or polymers involving reversible redox reactions have the potential to be applied as organic electrode materials for rechargeable batteries. Aer nearly half a century's exploration, conjugated carbonyl compounds are recognized as one of the most promising types among various electroactive materials, as only they have the potential to achieve simultaneously high energy density, high cycling stability and high power density. The conjugated carbonyl compounds can be divided into small organic molecules, organic polymers and organic salts according to the molecular structure, or quinones, dianhydrides, carboxylates, diketones and so on according to the electroactive group. Usually the redox potential of conjugated carbonyl compounds is between 1.5 and 3.0 V vs. Li + /Li, but carboxylates show relatively low redox potential below 1.0 V vs. Li + /Li, so they have the potential to be applied as either cathode or anode. As the theoretical specic capacity is up to 600 mA h g À1 , it is possible to achieve high energy density, although the redox potential is much lower than that of conventional inorganic cathodes. Research on this topic mainly focuses on solving the dissolution problem of active materials to improve the cycling stability, as well as developing new organic electrode materials with higher energy density.

Highly durable organic electrode for sodium-ion batteries via a stabilized α-C radical intermediate

“…According to molecular orbital theory, a lower lowest unoccupied molecular orbital (LUMO) energy means a larger electron affinity and higher reduction potential, while the LUMO–HOMO (highest occupied molecular orbital) gap, usually represented by E g , is related to the electronic conduction56. The electron affinity and E g values of the proceeding intermediate are depicted in Fig.…”

Polyanthraquinone‐Based Organic Cathode for High‐Performance Rechargeable Magnesium‐Ion Batteries

“…A similar chelating coordination bonding model has also been demonstrated to account for the enhanced cycling performance when a redox-active quinone-based organic polymer was used in Li-ion batteries. [17] In addition to the overall improved long-term cycling performance of 14PAQ, the rapid capacity loss in the first few cycles also deserves attention. We speculate that the two adjacent carbonyl groups (C=O) could only stably accommodate one inserted magnesium cation species due to the induced steric hindrance resulted from the chelating interaction.…”

A novel quinone-based polymer electrode for high performance lithium-ion batteries

“…It is widely known that the formation of the SEI film is a very common phenomenon for the anode materials during the initial discharge process [31,32]. Even though, the initial reversible capacity is much better than most of the thioether or thianthrene bond-containing compounds [20,[33][34][35][36], indicating a superiority of PDB over them. Additionally, the potential plateaus observed in the charge-discharge profiles show good consistent with the redox peaks in the CV curves.…”

“…Apart from the carbonyl bonds that provided the reactive centers for the redox reactions, the thioether bonds was found to greatly enhance the conductivity of the electrode and thus leaded to a high stability of the electrode. More recently, polyanthraquinone (PAQ) and lithium salt of poly(2,5-dihydroxy-p-benzoquinonyl sulfide) (Li 2 PDHBQS) were also discovered to have the ability to deliver excellent cycling stability after ultra-long charge-discharge cycles [18,20]. The extraordinary electrochemical results of these polymers indicated that quinone-based polymers with the thioether bond could effectively improve the redox reactivity as well as prevent the unwanted dissolution of the organic compounds.…”

“…Although many small molecules have been synthesized and investigated as the electrode materials for LIBs, the reported electrochemical performances in terms of both specific capacity and cycling stability were still far away from the practical applications due to the serious dissolution issue [10][11][12]. Therefore, it is urgent to design novel organic compounds that can overcome the LETTERS of organic electrode materials [12,18,20,21,23,24]. The redox mechanism of the electrochemically reactive carbonyl groups is well explained by the enolation process between the lithium ions and the carbonyl groups.…”