electrolyte. The SC cell using cPT-200 polymer electrolyte demonstrates areal capacitance of 291 mF cm-2 at a current density of 0.75 mA cm-2 and capacity retention of about 96.3% after 50000 cycles at 7.5 mA/cm2. Even after bending the SC cell, the capacity retention was 98.4% after 50000 cycles. The enhanced performance was attributed to the high ionic conductivity of polymer electrolyte (3.0 mS/cm) and high electrical conductivity of nanofiber cellulose incorporated nanomesh graphene-CNT hybrid buckypaper (540 S/cm). The SC cell exhibits gravimetric energy density: 33.6 Wh kg-1 and volumetric energy density: 6.68 mWh cm-3.
Recently Jin et al. [50] reported the fabrication of SC cell using novel quasi-solid-state polymer electrolyte (QPE) of porous acrylate rubber/tetraethylammonium tetrafluoroborate-acetonitrile (pACM/Et4NBF4-AN) and nitrogen-doped porous graphene (NPG) film-supported vertically aligned polyaniline nanocones (NPG@PANI). The specific capacitance for NPG@PANI-2C electrode cell was 259.5 mF cm-2 (330.2 F/g; 51.9Fcm-3) at 1mAcm-2 (Figure 3.12a). The anode NPG@PDAA-3C was chosen and demonstrates specific capacitance of about 254.5 mF cm-2 (294.4 F/g; 50.9 F cm-2) at 1mAcm-2 (Figure 3.12b). Then an asymmetric SC device was fabricated using NPG@ PANI cathode, NPG@PDAA anode and pACM/Et4NBF4-AN as polymer electrolyte (Figure 3.12c). The specific capacitance of asymmetric device was 6.2 F cm-3 (124.7mF cm-2; 72.1 F/g) at 0.5 mAcm-2 with 88.7% capacity retention after 10000 cycles. The energy density was 6.18mWh cm-3 (123.5 mWh cm-2; 71.4 Wh/kg) with power density of 0.033Wcm-3 (0.668mWcm-2; 0.386kW/kg).
Figure 3.12 (a) CV curves at 10 mV s-1 and (b) GCD curves at 1mA cm-2 of NPG@PANI-2C and NPG@ PDAA-3C in three-electrode mode. (c) Schematic diagram of as-assembled NPG@PANI//QPE//NPG@PDAA oAFSC. [Reproduced with permission from Ref. [50], © Elsevier 2019].
To increase the energy density of the SC, various efforts have been done to tune the voltage window of the electrolytes by the addition of IL and plasticizers [51]. In continuation of this, Kang et al. [52] reported the preparation of solid electrolyte comprising poly(ethylene glycol) behenyl ether methacrylate-gpoly((2-acetoacetoxy)ethyl methacrylate) (PEGBEM-g-PAEMA) graft copolymer by one-pot free-radical polymerization process for application in bendable SC. The ionic conductivity of the PE was 1.23 × 10-3 S/cm and the increase was attributed to high polarity and amorphous nature. Two SC cells were fabricated using PEGBEM-g-PAEMA (Cell-1) and PVA/H3PO4 (Cell-2) as a solid electrolyte and activated carbon as an electrode. The PEGBEM-g-PAEMA based SC demonstrated the specific capacitance of about 55.5 F/g at 1.0 A/g (for Cell-2: 40.8 F/g at 1.0 A/g) with a power density of 900 and corresponding energy density of 25 Wh/kg. It is important to note that even after bending with an angle of 135o, the performance was good. Table 3.4 summarizes some reported polymer electrolytes, their ionic conductivity and the electrochemical performance of the cell using them. Table 3.5 shows some patents on the supercapacitor device using different separators.
Table 3.4 Reported polymer electrolytes and fabricated supercapacitor performance.
| Polymer electrolyte | Conductivity | Specific capacitance | Capacity retention | Energy density | Power density | Ref. |
| Boron-containing GPE | 5.13 mS/cm | 34.35 F/g (at 1 A/g) (RT) 74 F/g (80 °C) | 91.2 % (after 5000 cy.) | 54.20 Wh/kg | 0.79 kW/kg | [36] |
| IL/PVA/H2SO4 | - | 86.81 F/g at 1 mA/cm2 | 71.61 % (after 1000 cy.) | 176.90 Wh/kg | 21.27 kW/kg | [37] |
| PIL/IL-GPE | - | 9.6 F/g | - | 8.8 Wh/kg and 4.6 Wh/kg | 268 W/kg and 3732 W/kg | [39] |
| (C3(Br) DMAEMA)-PEGMA | 66.8 S/cmat 25 °C | 64.92 F/g at 1 A/g and 67.47 F/g at 0.5 A/g | 84.74 % | 9.34 Wh/kg | 2.26 kW/kg | [41] |
| BMITFSI-NaI-(PVdF-HFP) | - | 351 F/g at 5 mV/s | 95 % (after 10000 cy.) | 26.1 Wh/kg | 15 kW/kg | [43] |
| PEO/NBR | 2.4 mS/cm | 150 F/g at 10 A/g | 93.7 % (after 10000 cy.) | 181 Wh/kg | 5.87 kW/kg | [45] |
| PVDF-HFP-EMIMBF4 | 1.68 × 10-2S/cm (nanofiller free) | 103.5 F/g | 100 % | - | - | [47] |
| PVDF-HFP-(EMIMBF4)-ZnO | 2.57 × 10-2S/cm (with ZnO) | 134.6 F/g | 100 % | - | - | |
| PVDF-HFP-(EMIMBF4)-TiO2 | 3.75 × 10-2S/cm (with TiO2) | 206.4 F/g | 100 % | 33.19 Wh/Kg | 1.17 kW/kg | |
| EMIMBF4-P(VdF-HFP) | 12.76 mS/cm | 63.47 F/g at 10 mV/s. | 74 % (after 4000 cy.) | 18 Wh/kg | 1.2 kW/kg | [48] |
| Nanofiber Cellulose-Incorporated Nanomesh Graphene | 3.0 mS/cm | 291 mF cm-2 at 0.75 mA cm-2 | 96.3 % (after 50000 cy.) |
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