Fig. 1: Performance of a twisted SWCNT rope and other viable energy carriers.

a, Energy-storage and power-density ranges of common energy storage media. Hatched areas (LIB, TNT explosive and fossil fuel) identify potentially unsafe carriers of electrochemical or chemical energy that may catch on fire or explode in hostile environments. Unlike in other energy carriers, release of record energy amounts stored in chemical bonds of fossil fuels and explosives is irreversible. ★, Power density of TNT explosive, ∼6.2 × 10¹¹ W kg⁻¹. We graphically distinguished non-cyclable from cyclable storage media and identified potential safety risks. b, Schematic morphology of a twisted SWCNT rope (left) and a single constituent strand (right), reproduced from ref. ¹⁶, © American Physical Society. c, SEM micrograph of a twisted SWCNT rope. d, Temperature dependence of the maximum GED of a twisted SWCNT rope at torsional strain ε ≈ 0.6. The maximum GED has been normalized with respect to the GED at 25 °C. Individual data points are depicted as black solid squares; data are presented as the mean ± s.d. for n = 3 y-rope (TPU) samples. During a continuous measurement, each rope sample was first heated from 298 K to high temperature and subsequently cooled to low temperature. At each temperature, three consecutive twist/release cycles were performed. The dashed orange line suggests that, within error bars, the GED is rather independent of temperature. e, Cycling stability of a y-rope (TPU) during 100 consecutive twist/release cycles. The normalized GED is measured up to a maximum torsional strain ε = 0.6 at a rotational frequency of 110 rpm. The time dependence of the GED during the first few cycles is shown in the inset. Individual data points are depicted as red solid squares; data are presented as the mean ± s.d. for n = 3 y-rope (TPU) samples. Insets: SEM micrographs of y-rope (TPU) after initial preconditioning cycles and after 100 twist/release cycles.