Side‐Chain Engineering for High‐Performance Conjugated Polymer Batteries

Abstract

Conjugated polymers are attractive for energy storage but typically require significant amounts of conductive additives to successfully operate with thin electrodes. Here, side-chain engineering is used to improve the electrochemical performance of conjugated polymer electrodes. Naphthalene dicarboximide (NDI)-based conjugated polymers with ion-conducting ethylene glycol (EG) side chains (PNDI-T2EG) and non-ion-conducting 2-octyldodecyl side chains (PNDI-T2) are synthesized, tested, and compared. For thick (20 µm, 1.28 mg cm −2) electrodes with a 60 wt% polymer, the PNDI-T2EG electrodes exhibit 66% of the theoretical capacity at an ultrafast charge-discharge rate of 100C (72 s per cycle), while the PNDI-T2 electrodes exhibit only 23% of the theoretical capacity. Electrochemical impedance spectroscopy measurements on thin (5 µm, 0.32 mg cm −2), high-polymer-content (80 wt%) electrodes reveal that PNDI-T2EG exhibits much higher lithium-ion diffusivity (D Li+ = 7.01 × 10 −12 cm 2 s −1) than PNDI-T2 (D Li+ = 3.96 × 10 −12 cm 2 s −1). PNDI-T2EG outperforms most previously reported materials in thick, high-polymer-content electrodes in terms of rate performance. The results demonstrate that the rate performance and capacity are significantly improved through the incorporation of EG side chains, and this work demonstrates a route for increasing the rate of ion transport in conjugated polymers and improving the performance and capacity of conjugated-polymer-based electrodes.

Integrated Covalent Organic Framework/Carbon Nanotube Composite as Li‐Ion Positive Electrode with Ultra‐High Rate Performance

“…Comparable current densities have previously been reported for a non‐COF organic electrode material, wherein a linear polymer (PNDI‐T2) was reportedly measured up to 500 C, corresponding to the absolute current density of 27 100 mA g −1 , but for comparison, this material only exhibited a capacity of 23 mAh g −1 . [ 44 ] In our case, we tested the DAPQ‐COF50 based cathode up to 50 000 mA g −1 and it delivered a capacity of 94 mAh g −1 , corresponding to a high power density of ≈110 kW kg −1 . This magnitude of power density, and the rapid charge/discharge times, would be competitive with electrochemical capacitors.…”

Conjugated Polyelectrolytes: Underexplored Materials for Pseudocapacitive Energy Storage

“…[27,28] In the interest of completeness, it is worth pointing out that CP structures containing nonionic polar side chains (e.g., oligo(ethylene glycol)) can exhibit some of the physico-electrochemical properties that characterize CPEs. [29,30] Nevertheless, they typically lack self-doping effects, adjustable solubility through pH modulation/ion-exchange, Coulombic interactions for inter-chain crosslinking, and the multiple structural handles for molecular design conferred by the ionic pendant groups, and associated counterions, of CPEs. We also refer the reader to other organic electronic materials that are of interest for electrochemical energy storage, such as nonconjugated polymers with redox-active sites embedded in-chain [31,32] or in their pendant groups, [33][34][35] covalent organic frameworks, [36,37] and graphene derivatives.…”

Macromolecular Engineering of Poly(catechol) Cathodes towards High-Performance Aqueous Zinc-Polymer Batteries

“…It is important to note that this lack of sufficient ion mobility is often a limiting factor to get practical high mass loading electrodes (of high areal capacity) with good performance at high currents. Lately, such synthetic strategies have been extended to design dual redox-active and ion conducting RAPs for organic electrochemical energy storage systems [ 33 , 34 , 35 , 36 , 37 ].…”