A Highly Flexible Yet >300 mAh cm⁻³ Energy Density Lithium‐Ion Battery Assembled with the Cathode of a Redox‐Active Polyether Binder

Abstract

A highly flexible yet high‐energy‐density cathode for lithium‐ion batteries is fabricated with a novel redox‐active binder polymer composed of 2,2,6,6‐tetramethylpiperidine 1‐oxyl (TEMPO) with vinyl ether main chain, lithium cobalt oxide, and single‐walled carbon nanotube. The cathode itself and its battery display excellent durability against repeated bending over 104 times. The highest volumetric capacity beyond 300 mAh cm−3 as a flexible electrode is achieved based on the highly adhesive and redox‐active, robust radical polyether binder. A highly flexible, only 0.5 mm‐thick, lithium‐ion battery charge/discharges repeatedly with constant output around 3.8 V even under rapid bending. Herein, the operation of flexible electronic devices with well‐balanced energy density and power‐supplying purposes is discussed.

Tuning Morphology and Properties of Epoxy-Based Solid-State Polymer Electrolytes by Molecular Interaction for Flexible All-Solid-State Supercapacitors

“…We further investigated the capacitance retention of the device under the rolling deformation and observed a remarkable capacitive retention of ∼80% even after the supercapacitor was continuously operated under the harsh rolling condition for 2000 cycles (Figure d). Like the electrical reliability of the epoxy-based SSPE (Figure e), the electrochemical reliability of the supercapacitor device was also performed under the continuous bending operation (with 1.5 cm of bending radius, 75 °/s of bending rate, and 100 cycles of bending number), and then the specific capacitance after the n th bending ( C n th ) was compared with the initial capacitance before the bending ( C 0 ) (Figure S15). Although the C n th values slightly decrease as the bending number increases to the 10th, beyond the 20th the normalized specific capacitance, C n th / C 0 remains constant up to the 100th bending.…”

Redox: Organic Robust Radicals and Their Polymers for Energy Conversion/Storage Devices

“…14,94,106,107 The polymers can also function as binders in carbon composite electrodes, maintaining close contact with electrodes. 108,109 1.2.4. Persistency for Charge Storage.…”

“…270,271 For mobile devices, the volumetric energy density of batteries is critical. 109 The organic/inorganic hybrid electrodes can increase the energy density and electrochemical kinetics. The inorganic metal oxides offer much slower electrode reactions than radical polymers because of the insufficient interface contact with current collectors and other kinetic reasons (e.g., k 0 = 10 −9 cm/s for LiFePO 4 ).…”

“…Similar mediation was achieved with other active materials with different redox potentials. 50,109,142,270,271 Adding less than 1 wt % redox polymer to metal oxides could improve the electrode performance. 58,60 Solid-state batteries have also been fabricated with organic/inorganic hybrid electrodes.…”

“…9,10,108,225 In contrast, a smaller amount of carbon is sufficient to form conductive pathways of semiconducting and compact inorganic metal oxides (>3 g/cm 3 ). 50,58,109,137,142 Continuous percolating networks of carbon additives are critical to achieving the maximum performance from radical polymers. Highly crystalline carbon nanotubes only require a content of 1 wt % to form conductive pathways and achieve rapid charge/discharge.…”