Author Contributions
Conceptualization, C.-T.P. and B.-H.L.; methodology, M.-S.W.; software, M.-S.W.; validation, J.C.C., Y.-L.S. and C.-F.L.; formal analysis, C.-F.L.; investigation, C.-F.L.; resources, R.-Y.Y.; data curation, M.D.F.; writing—original draft preparation, M.D.F.; writing—review and editing, M.D.F.; visualization, Z.-H.W.; supervision, Z.-H.W.; project administration, C.-T.P.; funding acquisition, Z.-H.W. All authors have read and agreed to the published version of the manuscript.
Figure 1.
Near-field electrospinning (NFES) equipment. (a) experimental set up (b) schematic experimental illustration.
Figure 1.
Near-field electrospinning (NFES) equipment. (a) experimental set up (b) schematic experimental illustration.
Figure 2.
Fabrication of PVDF fiber-membrane separators; (A) membrane with pore size of 220 nm, (B) membrane with pore size of 450 nm, and (C) sandwich technique for preparing monolayer and bilayer fiber-membrane separators.
Figure 2.
Fabrication of PVDF fiber-membrane separators; (A) membrane with pore size of 220 nm, (B) membrane with pore size of 450 nm, and (C) sandwich technique for preparing monolayer and bilayer fiber-membrane separators.
Figure 3.
Assembly process of the button battery for ion conductivity determination.
Figure 3.
Assembly process of the button battery for ion conductivity determination.
Figure 4.
(A) Schematic figure, (B) assembly process of the coin battery for thermal stability determination.
Figure 4.
(A) Schematic figure, (B) assembly process of the coin battery for thermal stability determination.
Figure 5.
SEM images of PP separators and PVDF fiber-membranes; (a) PP separators at 5000× magnification, (b) PVDF membrane with 220 nm pore size at 5000× magnification, (c) PVDF membrane with 220 nm pore size sandwiched between a monolayer of electrospun PVDF fibers at 1000× magnification, (d) PVDF membrane with 220 nm pore size, sandwiched between a bilayer of electrospun PVDF fibers at 500× magnification, (e) PVDF membrane with 450 nm pore size at 2000× magnification, (f) PVDF membrane with 450 nm pore size, sandwiched between a monolayer of electrospun fibers, at 500× magnification, and (g) PVDF membrane with 450 nm pore size, sandwiched between a bilayer of electrospun fibers, at 500× magnification.
Figure 5.
SEM images of PP separators and PVDF fiber-membranes; (a) PP separators at 5000× magnification, (b) PVDF membrane with 220 nm pore size at 5000× magnification, (c) PVDF membrane with 220 nm pore size sandwiched between a monolayer of electrospun PVDF fibers at 1000× magnification, (d) PVDF membrane with 220 nm pore size, sandwiched between a bilayer of electrospun PVDF fibers at 500× magnification, (e) PVDF membrane with 450 nm pore size at 2000× magnification, (f) PVDF membrane with 450 nm pore size, sandwiched between a monolayer of electrospun fibers, at 500× magnification, and (g) PVDF membrane with 450 nm pore size, sandwiched between a bilayer of electrospun fibers, at 500× magnification.
Figure 6.
SEM images of nano-ceramic solutions coated on the four substrates; (a) BX900 coated on A4 paper, (b) BX900 coated on rice paper, at 70× magnification, (c) BX100 coated on the nonwoven fabric, (d) BX900 coated on nonwoven fabric, at 27× magnification, (e) BX100 coated on the carbon synthetic fabric at 20× magnification, and (f) BX900 coated on the carbon synthetic fabric at 20× magnification.
Figure 6.
SEM images of nano-ceramic solutions coated on the four substrates; (a) BX900 coated on A4 paper, (b) BX900 coated on rice paper, at 70× magnification, (c) BX100 coated on the nonwoven fabric, (d) BX900 coated on nonwoven fabric, at 27× magnification, (e) BX100 coated on the carbon synthetic fabric at 20× magnification, and (f) BX900 coated on the carbon synthetic fabric at 20× magnification.
Figure 7.
Comparison of exothermic peaks of PP separator and PVDF fiber-membranes.
Figure 7.
Comparison of exothermic peaks of PP separator and PVDF fiber-membranes.
Figure 8.
SEM images showing the effect of heating on the pore size of the PP separator and PVDF fiber-membranes; (a) pore size of PP separator when heated to 165 °C for 1 h, at 5000× magnification, (b) pore size of the 220 nm PVDF membrane when heated to 173 °C for 1 h, at 5000× magnification, (c) pore size of the 220 nm PVDF membrane sandwiched between a monolayer of electrospun fibers when heated to 173 °C for 1 h, at 1000× magnification, (d) pore size of the 220 nm PVDF membrane sandwiched between a bilayer of electrospun fibers when heated to 173 °C for 1 h, at 500× magnification, (e) pore size of the 450 nm PVDF membrane heated to 173 °C for 1 h, at 2000× magnification, (f) pore size of the 450 nm PVDF membrane sandwiched between a monolayer of electrospun fibers when heated to 173 °C for 1 h, at 500× magnification, and (g) pore size of the 450 nm PVDF membrane sandwiched by a bilayer of electrospun fibers when heated to 173 °C for 1 h, at 500× magnification.
Figure 8.
SEM images showing the effect of heating on the pore size of the PP separator and PVDF fiber-membranes; (a) pore size of PP separator when heated to 165 °C for 1 h, at 5000× magnification, (b) pore size of the 220 nm PVDF membrane when heated to 173 °C for 1 h, at 5000× magnification, (c) pore size of the 220 nm PVDF membrane sandwiched between a monolayer of electrospun fibers when heated to 173 °C for 1 h, at 1000× magnification, (d) pore size of the 220 nm PVDF membrane sandwiched between a bilayer of electrospun fibers when heated to 173 °C for 1 h, at 500× magnification, (e) pore size of the 450 nm PVDF membrane heated to 173 °C for 1 h, at 2000× magnification, (f) pore size of the 450 nm PVDF membrane sandwiched between a monolayer of electrospun fibers when heated to 173 °C for 1 h, at 500× magnification, and (g) pore size of the 450 nm PVDF membrane sandwiched by a bilayer of electrospun fibers when heated to 173 °C for 1 h, at 500× magnification.
Figure 9.
(A). Comparison of CV graphs of the separators: (a) PP separator versus 220 nm PVDF fiber-membranes sandwiched between mono- and bi-layers of electrospun fibers; (b) PP separator versus 450 nm PVDF fiber- membranes sandwiched between mono- and bi-layers of electrospun fibers; (B). Comparison of CV graphs: (a) CV graphs of substrate with best conductivities after coating with sol-gel; (b) CV graphs of the substrate after sol-gel coating showing that the ion conductivity is similar to the PP separator.
Figure 9.
(A). Comparison of CV graphs of the separators: (a) PP separator versus 220 nm PVDF fiber-membranes sandwiched between mono- and bi-layers of electrospun fibers; (b) PP separator versus 450 nm PVDF fiber- membranes sandwiched between mono- and bi-layers of electrospun fibers; (B). Comparison of CV graphs: (a) CV graphs of substrate with best conductivities after coating with sol-gel; (b) CV graphs of the substrate after sol-gel coating showing that the ion conductivity is similar to the PP separator.
Figure 10.
(A) Comparison of charge-discharge curves; (a) PP separator, (b) 220 nm PVDF membrane, (c) 220 nm PVDF membrane sandwiched in fiber monolayer, (d) 220 nm PVDF membrane sandwiched in fiber bilayer, (e) 450 nm PVDF membrane, (f) 450 nm PVDF membrane sandwiched in fiber monolayer, and (g) 450 nm PVDF membrane sandwiched in fiber bilayer, (B) Comparison of charge and discharge curves; (a) A4 paper with BX900 coating, (b) rice paper with BX900 coating, (c) nonwoven fabric with BX900 coating, (d) carbon synthetic fabric with BX900 coating, (e) nonwoven fabric with BX100 coating, and (f) carbon synthetic fabric with BX100 coating.
Figure 10.
(A) Comparison of charge-discharge curves; (a) PP separator, (b) 220 nm PVDF membrane, (c) 220 nm PVDF membrane sandwiched in fiber monolayer, (d) 220 nm PVDF membrane sandwiched in fiber bilayer, (e) 450 nm PVDF membrane, (f) 450 nm PVDF membrane sandwiched in fiber monolayer, and (g) 450 nm PVDF membrane sandwiched in fiber bilayer, (B) Comparison of charge and discharge curves; (a) A4 paper with BX900 coating, (b) rice paper with BX900 coating, (c) nonwoven fabric with BX900 coating, (d) carbon synthetic fabric with BX900 coating, (e) nonwoven fabric with BX100 coating, and (f) carbon synthetic fabric with BX100 coating.
Table 1.
Details of chemicals used in the preparation of PVDF solution.
Table 1.
Details of chemicals used in the preparation of PVDF solution.
Chemical | Formula | Molecular Weight (g/mol) |
---|
PVDF | (C12H13NO3)n | 534,000 |
DMSO | C2H6OS | 78.13 |
Acetone | C3H6O | 58.08 |
Surfactant | C12H25NaSO4 | 288.378 |
Table 2.
PVDF solution configuration.
Table 2.
PVDF solution configuration.
Solution A | Solution B |
---|
PVDF powder (g) | Acetone (g) | DMSO (g) | Surfactant (g) |
0.90 | 2.50 | 2.50 | 0.20 |
Table 3.
NFES parameters for the fabrication of PVDF fibers.
Table 3.
NFES parameters for the fabrication of PVDF fibers.
Equipment Part/Aspect | Parameter |
---|
Needle size | Length, 12.7 mm; inside diameter, 0.25 mm |
Collecting distance | 1 mm |
Tangential speed | 2618.10 mm/s |
Pump feed rate | 0.15 mL/h |
Voltage field | 1.40 × 107 V/m |
Table 4.
Comparison of the Crystallinity of PP Separator and PVDF Fiber-membranes.
Table 4.
Comparison of the Crystallinity of PP Separator and PVDF Fiber-membranes.
Separator | Tm (°C) | | Crystallinity (%) |
---|
PP | 164.8 | 33.33 | 16.1 |
PVDF (220 nm) membrane only | 171.1 | 23.84 | 22.77 |
PVDF (220 nm) with a monolayer of fibers | 170.7 | 22.18 | 21.18 |
PVDF (220 nm) with a bilayer of fibers | 170.8 | 21.23 | 20.28 |
PVDF (450 nm) membrane only | 171.0 | 21.16 | 20.21 |
PVDF (450 nm) with a monolayer of fibers | 170.3 | 19.32 | 18.45 |
PVDF (450 nm) with a bilayer of fibers | 171.1 | 23.1 | 22.06 |
Table 5.
Comparison of ion conductivity of PP separator and PVDF fiber membranes.
Table 5.
Comparison of ion conductivity of PP separator and PVDF fiber membranes.
Separator | Thickness (μm) | Resistance (Ω) | Ionic Conductivity mS/cm (Error) |
---|
PP | 28 | 3.79 | 0.29 (−0.01–0.01) |
PVDF (220 nm) membrane only | 128 | 7.62 | 0.66 (−0.02–0.02) |
PVDF (220 nm) with monolayer of fibers | 144 | 12.88 | 0.44 (−0.04–0.02) |
PVDF (220 nm) with bilayer of fibers | 161 | 11.06 | 0.57 (−0.01–0.01) |
PVDF (450 nm) membrane only | 120 | 7.24 | 0.65 (−0.03–0.01) |
PVDF (450 nm) with monolayer of fibers | 142 | 11.98 | 0.46 (−0.01–0.01) |
PVDF (450 nm) with bilayer of fibers | 164 | 12.64 | 0.51 (−0.01–0.02) |
Table 6.
The ion conductivity of A4 paper, rice paper, nonwoven fabric, and carbon synthetic fabric.
Table 6.
The ion conductivity of A4 paper, rice paper, nonwoven fabric, and carbon synthetic fabric.
Sample | Thickness (μm) | Resistance (Ω) | Ionic Conductivity (mS/cm) |
---|
A4 paper only | 105 | 26.78 | 0.15 |
A4 (with BX100) | 142 | 208.75 | 0.026 |
A4 (with BX300) | 120 | 139.49 | 0.034 |
A4 (with BX900) | 117 | 92.99 | 0.049 |
Rice paper only | 86 | 7.10 | 0.48 |
Rice paper (with BX100) | 102 | 32.39 | 0.12 |
Rice paper (with BX300) | 105 | 59.33 | 0.072 |
Rice paper (with BX900) | 89 | 22.13 | 0.16 |
Nonwoven fabric only | 211 | 21.42 | 0.39 |
Nonwoven fabric (with BX100) | 365 | 47.70 | 0.30 |
Nonwoven fabric (with BX300) | 349 | 26.20 | 0.52 |
Nonwoven fabric (with BX900) | 347 | 14.30 | 0.96 |
Carbon Synthetic fabric only | 327 | 57.93 | 0.22 |
Carbon synthetic fabric (with BX100) | 452 | 48.36 | 0.36 |
Carbon synthetic fabric (with BX300) | 445 | 47.07 | 0.37 |
Carbon synthetic fabric (with BX900) | 430 | 36.26 | 0.47 |