Introduction
Basic principles of energy storage
Fig.3 Schematic illustrations of the three typical D-E curves. The black line and the red line show the charge and discharge pathway, respectively. The blue area and grey area represent charging energy density and loss energy density, respectively. Eb is the breakdown field strength of dielectrics materials. |
Methods for increasing energy storage density in film capacitors
Increasing the dielectric constant
Polymer polarity enhancement
Tab.1 Structural formula of PVDF-based polymers, binary copolymers and ternary copolymers |
Material | ‒[X]m‒[Y]n‒[Z]p‒ | ||
---|---|---|---|
‒X‒ | ‒Y‒ | ‒Z‒ | |
PVDF | ‒CH2‒CF2‒ | ‒ | ‒ |
P(VDF-TrFE) | ‒CH2‒CF2‒ | ‒CH2‒CHF‒ | ‒ |
P(VDF-HFP) | ‒CH2‒CF2‒ | ‒CH2‒C(CH3)F‒ | ‒ |
P(VDF-BTFE) | ‒CH2‒CF2‒ | ‒CH2‒CFBr‒ | ‒ |
P(VDF-CTFE) | ‒CH2‒CF2‒ | ‒CH2‒CFCl‒ | ‒ |
P(VDF-TrFE-CTFE) | ‒CH2‒CF2‒ | ‒CH2‒CHF‒ | ‒CF2‒CFCl‒ |
P(VDF-TrFE-CFE) | ‒CH2‒CF2‒ | ‒CH2‒CHF‒ | ‒CH2‒CFCl‒ |
Organic-inorganic hybridization
Tab.2 Volume fractions of some typical ceramic fillers for improving the dielectric constant of composites, and the dielectric constants of the composites |
Ceramic fillers | Polymer | εa) | Filler/vol-% | εb) | Energy storage density/(J∙cm−3) | Ref. |
---|---|---|---|---|---|---|
BT | P(VDF-HFP) | ~5 | 30 | ~20 | 9.7 | [47] |
BaSrTiO3 | P(VDF-CTFE) | ~13 | 40 | ~38 | 7.5 | [50] |
SrTiO3 | PVDF | ~10 | 10 | ~18 | 9.1 | [51] |
Pb(Mg1/3Nb2/3)O3-PbTiO3 | P(VDF-TrFE) | ~18 | 40 | ~100 | ‒ | [55] |
NNBT | PVDF | ~10 | 10 | ~100 | ‒ | [56] |
a) Dielectric constant of polymer; b) Dielectric constant of filler. |
Enhancing dielectric strength
Fig.8 Breakdown strength and energy storage density of polymer-based dielectrics prepared via different methods. The grey icons indicate methods of improving breakdown field strength by adding filler without modification; the blue icons represent methods involving addition of modified filler; and, red icons indicate methods of constructing multi-layered structures. |
Blending and hybridization
Multi-layer structure design
Tab.3 Previous research results on improving breakdown strength through by layer-structure design |
Number of layers | Scheme | Materials | Eb/(MV∙m−1) | We/(J∙cm−3) | Ref. |
---|---|---|---|---|---|
Sandwich structure | 1:20 vol-% BT-PVDF 2:1 vol-% BT-PVDF | 470 | 18.8 | [84] | |
1:PVDF 2:PTCF | 408 | 8.7 | [40] | ||
1:1 vol-% NBT-PVDF 2:PVDF | 410 | 12.5 | [86] | ||
Multiple layers | 16-Layers | P(VDF-HFP) P(VDF-TrFE-CFE) | 637.5 | 22.6 | [89] |
32-Layers | PET P(VDF-TFE) | ~1000 | 16 | [87] |
Low dielectric loss media for high-power energy transmission
High working temperature dielectrics
Tab.4 Physical properties of polymers with high temperature stability |
Polymer | ε | tand | The highest working temperature/°C | Discharge efficiency |
---|---|---|---|---|
PC | 3.2 | 0.0013 | 125 | ~90% |
PI | 3.1 | ~0.017 | 200 | 94% |
PEI | 3.2 | 0.01 | 200 | 96% |
FPE | 3.5 | 0.0025 | 200 | ‒ |
PEEK | 3.2 | 0.004 | 150 | ~90% |
Frequency response for energy storage dielectrics
Conclusions and future prospects
Tab.5 Methods and future application areas of polymer-based energy storage materials (with particular emphasis on different performances and properties) |
Performance | Physical parameters | Methods | Application |
---|---|---|---|
High energy density | ε | High polar group High permittivity filler Conductive/semi-conductive filler Surface modified filler Multi-layer structure | HVDC project Distributed energy New energy vehicles High power pulse system |
Eb | |||
Low dielectric loss | tan d | Multi-layered structure Blending/hybridization. | HVDC project Distributed energy (photovoltaic power/wind power) |
High working temperature | Working T | Polymer chain design Inter-chain design (hydrogen bonding/crosslinking) | New energy vehicles |
Fast frequency response | Working frequency | Filler design and doping Introduction of high polar atoms and bonds | High power pulse system (inertial restraint, laser weapons, etc.) |