A Flexible Aqueous Asymmetric Lithium‐Ion Supercapacitor with High Voltage and Superior Safety

Abstract

Achieving high voltage and safety simultaneously in energy storage devices can greatly advance the development of flexible and wearable electronics. Thus, flexible aqueous asymmetric lithium‐ion supercapacitors with a high voltage attract the interest of many researchers. Herein, a new flexible aqueous asymmetric lithium‐ion supercapacitor with a high voltage and superior safety is fabricated using manganese oxide and iron hydroxide, which are electrodeposited on carbon cloths as electrodes and a super‐concentrated gel polymer as the electrolyte. Impressively, the flexible asymmetric lithium‐ion supercapacitor delivers a high voltage of 3.2 V, which is a high value in aqueous asymmetric supercapacitors. Moreover, the asymmetric supercapacitor exhibits a specific capacitance of 227.6 F g−1, a maximum energy density of 49.3 Wh kg−1, and a maximum power density of 11.5 kW kg−1, together with a capacitance retention of 82% after 1000 cycles at a current density of 2 A g−1. Importantly, the supercapacitor can keep good electrochemical performance under extremely harsh conditions, such as compressing, hammering, punching, and tailoring, which demonstrates superior safety.

Freestanding 1T‐MnxMo1–xS2–ySey and MoFe2S4–zSez Ultrathin Nanosheet‐Structured Electrodes for Highly Efficient Flexible Solid‐State Asymmetric Supercapacitors

“…[ 21–26 ] However, the presence of such redox reaction could not be reflected in the CV curve due to the relatively low content of Mn in the host MoS 2 that resulted in masking of Mn 2+ /Mn 3+ redox peak by the dominant redox peak of the Mo 2+ /Mo 6+ redox couple present in the similar potential range. [ 21–33 ] The possible reactions taking place at the electrodes with the insertion of electrolytic solvated cations can be represented as: MoS 2 OH + OH − ↔ MoS 2 O + H 2 O + e − and MnS 2 + OH − ↔MnS 2 (OH − ); MnS 2 (OH − ) ↔ MnOS 2 + H 2 O + e − . [ 21–26 ] A sequential increment in the area enclosed by the CV profiles was observed as: MoS 2 < Se‐doped MoS 2 (Se‐MoS 2 ) < Mn‐intercalated MoS 2 (Mn‐MoS 2 ) < 1T‐Mn x Mo 1− x S 2− y Se y (1T‐Mn‐Se‐MoS 2 ) (Figure 4A).…”

“…[ 10,13–18 ] Further, the charge‐storage mechanism and capacitive contribution of the 1T‐Mn x Mo 1− x S 2− y Se y electrode was investigated according to the formula i = aν b , where i represents current, ν is the scan rate, and a and b are constants. [ 21–33 ] For electric double layer capacitance (EDLC), b = 1 and for diffusion‐controlled process, b = 1/2. [ 21–33 ] Based on this concept, we can represent the above equation as: i ( V ) = k 1 ν + k 2 ν 1/2 , where i is the peak current, k 1 and k 2 are constants and numerically equal to the slope ≈0.7 mA cm −2 /mV s −1 and intercept ≈4.9 mA cm −2 /(mV s −1 ) 1/2 of the plot ν 1/2 versus i ( V )/ν 1/2 (Figure S9A, Supporting Information).…”

“…[ 21–33 ] For electric double layer capacitance (EDLC), b = 1 and for diffusion‐controlled process, b = 1/2. [ 21–33 ] Based on this concept, we can represent the above equation as: i ( V ) = k 1 ν + k 2 ν 1/2 , where i is the peak current, k 1 and k 2 are constants and numerically equal to the slope ≈0.7 mA cm −2 /mV s −1 and intercept ≈4.9 mA cm −2 /(mV s −1 ) 1/2 of the plot ν 1/2 versus i ( V )/ν 1/2 (Figure S9A, Supporting Information). [ 21–33 ] Knowing k 1 and k 2 values, the capacitive contribution ( k 1 ν) and the diffusive contribution ( k 2 ν 1/2 ) are calculated at different scan rates, as shown in Figure S9B (Supporting Information).…”

“…[ 21–33 ] Based on this concept, we can represent the above equation as: i ( V ) = k 1 ν + k 2 ν 1/2 , where i is the peak current, k 1 and k 2 are constants and numerically equal to the slope ≈0.7 mA cm −2 /mV s −1 and intercept ≈4.9 mA cm −2 /(mV s −1 ) 1/2 of the plot ν 1/2 versus i ( V )/ν 1/2 (Figure S9A, Supporting Information). [ 21–33 ] Knowing k 1 and k 2 values, the capacitive contribution ( k 1 ν) and the diffusive contribution ( k 2 ν 1/2 ) are calculated at different scan rates, as shown in Figure S9B (Supporting Information). It is observed that in all the different scan rates, the capacitive contributions are significantly lower than the diffusive contributions (Figure S9B, Supporting Information).…”

“…This indicates that the charge storage mechanism of the 1T‐Mn x Mo 1− x S 2− y Se y electrode is dominated by diffusion controlled process. [ 21–33 ] The highly ordered linear relationship observed for both the redox peaks upon varying scan rates also indicated that the Faradaic redox reactions were diffusion controlled. [ 10,13–18 ] GCD curves for the 1T‐Mn x Mo 1− x S 2− y Se y at different current densities (1 to 50 mA cm −2 ) showed a near symmetric nature in charging and discharging time (Figure 4E) justifying the excellent coulombic efficiency of the electrode.…”