1

Design and Develop Dielectric PolymersWith High Energy Density and Low Losses

Q. M. ZhangShan Wu, Quinn Burlingame, Minren Lin

The Pennsylvania State University, PA

Shihai Zhang, Chen Zhou, Douglas Ian Kushner, Xin Zhou,Raymond J. Orchard Jr., Nanyan Zhang

StategicPolymers, Inc. PA

2

Outline

• Introduction and background• Ferroelectric polymers (strongly coupled dipoles)

with defects modifications can have high energydensity (> 30 J/cm3)

-- P(VDF-CTFE) and P(VDF-HFP) copolymers• How to reduce the losses of high energy density

polymers-- P(VDF-HFP-TFE) terpolymers-- P(VDF-CTFE)/ECTFE blends

Nanocomposites to reduce the dielectric loss• Summary

3

Dielectrics for High Energy Density Capacitors

Ragone Plot of Energy Storage Devices Battery: High energy density(> 500 J/cm3) and very lowpower density (charge/discharge ~ hrs)

Supercaps: Moderate energydensity (~ 50 J/cm3) andpower density(charge/discharge ~ seconds)

Dielectric capacitor: lowenergy density (< 1 J/cm3)and high power density( < 1 ms charge/discharge)

How to significantly raise the energy density of dielectric capacitors?

Energy Density of Film Capacitors

•The future miniaturizationof electronics and powersystems will dependcritically on the markedreduction in capacitorvolumes, which oftenoccupy more than 50% ofthe device volume

Plastic Film DielectricConstant

BreakdownField(MV/m)

Energydensity

(J/cc)

Polypropylene(PP)

2.2 640 1-2

Polyester(PET)

3.3 570 1-1.5

Polycarbonate(PC)

2.8 528 0.5-1

Polyvinylidenefluoride(PVDF)

12 590 2.4

Polyethylene-naphlate

(PEN)

3.2 550 1-1.5

Polyphenylene-sulfide(PPS)

3.0550 1-1.5

(M. Lanagan, DOE Report, 2003)

Dielectric Film Fabrication:Biaxial Orientation: Simultaneous Process

• CapacitanceC=e e0 A/t

e: dielectric const.A: areat: thickness

• Many polymerfilms can be producedin thicknessdown to 0.5 mm

• Requires large amountof polymer resins(> 100 kgs)

Roll-To-Roll Solvent Film Casting

• Less resin needed (< 1 kg)• Films in thickness down to 3 mm have been produced

7

Dielectric CapacitorApplications

Power Factor Correction, Filters

Pulse Power(defibrillators, camera flash, laser, motor

run, military)

Appliances/Electronics(LCD, microwave oven, X-Ray, lighting,

telecommunications)

HEV Electric Energy Storage and Regulation

Supercapacitors

Raise battery voltage to drive motor

Reduce the magnitude of ripple current

> 1000 mF Film Capacitors

Ford Fusion

Dielectric Background

D

E E E

Linear FE AFE

EsatEsat

PsatPsat

D DD

E E E

Linear FE AFE

EsatEsat

PsatPsat

D D

Low Dielectric ConstantHigh Breakdown Strength

Low Energy DensityPP, PC, PET, Polyimide

Stored Energy (Shaded Area)

High Dielectric ConstantHigh Breakdown Strength

High Remnant PolarizationLow Energy Density

PVDF

High energy densityPolymers?

10

Develop Dielectrics withHigh Energy Density And Low Losses

I. Working with ferroelectrics of ultrahigh dielectric energy density— Copolymers, blends, crosslinking tosignificantly reduce the loss.

II. Working with dielectrics of highdipole moments and low loss toachieve high energy density, whilemaintaining low losses at high fields.

III. Tailoring nano/micro structuremorphologies to enhancepolarization response, reduce losses,and achieve high breakdown andreliability.

Ferroelectricpolymers

Intrinsicallylow losspolymers

Dielectric polymerwith high energydensity and low losses

11

•In PVDF based polar-polymers,large polarization (D >0.1 C/m2)can be reached with highbreakdown field (>600 MV/m)-- Ue = ½ D E

=1/2*0.1*600= 30 J/cm3

•The remnant polarization of thenormal ferroelectric polymerscauses low energy density

•Defects modifications to breakupthe large polar-domains, reducingor eliminating polar-hysteresis

-100 0 100

-100

0

100

Po

lari

za

tio

n(m

C/m

2)

E le c tr ic F ie ld (M V /m )

Ferroelectric Polymers -- Strongly Coupled Dipoles

12

Modified Polar-FluoropolymersWith Ultra-High Energy Density

Discharged energy density

Charge/discharge curves

•Discharged energy density> 25 J/cm3

•How to reduce the losses athigh electric fields is achallenge.

VF2

P(VDF-CTFE) and P(VDF-HFP) Random Copolymer

High Field Efficiency and Loss

13

• High field dielectric loss can be deduced from the D-E loops:Loss = area II/(area I + area II) = energy loss/stored energy,Efficiency = 1- loss

• In the impedance analyzer, loss tangent = area I/area II• When the loss is small <10%), the two are nearly the same

14

The Role of CTFE (or HFP)In Reducing the Ferroelectric Hysteresis Loss•In the defects modified PVDF

polymers, the defects (bulky CTFEor HFP) introduced break up theferroelectric domains (regular all-trans-conformations)

•As the domain size becomes smallerthan some critical size, theferroelectric phase becomesunstable, leading to the formation ofnon-polar phase and much reducedferroelectric hysteresis

15

Main Losses In P(VDF-CTFE)and P(VDF-HFP) at High Electric Field

• Ferroelectric hysteresis loss: experimental results indicatethat the “defects”CTFE or HFP are not strong enough toagainst the poling of high electric field –large polardomains form at high electric field

• Conduction loss, which exists in all dielectrics and, ingeneral, increases exponentially with applied fields

• Need stronger and more defects while not causing reduction ofthe elastic modulus (too much CTFE and HFP cause significantloss of elastic modulus in P(VDF-CTFE) and P(VDF-HFP),-- looking for other “defects”… …

• Polymer blends and crosslinking,…

16

Molecular Design of High TemperatureHigh Energy Density Dielectrics with Low Losses

P(TFE-VDF-HFP)

17

Improved Temperature Stability

DSC Data

C76/13/11

18

P(VDF-HFP-TFE)11/13/76 wt% (THV-C):dielectric const. ~ 4 andLoss < 1 % to 150 oC

19

P(VDF-HFP-TFE)11/13/76 wt% (THV-C)

Double the energydensity while the highfield loss is the same asthat of BOPP

20

Polar Fluoropolymer Nanocomposites• By blending the high energy density P(VDF-CTFE) with

a low dielectric loss polymer, both the polarcorrelation (dielectric loss) and conduction loss at highfields can be reduced

• P(VDF-CTFE)/ECTFE blends:ECTFE (ethylene-chlorotrifluoroethylene):

K = 2.6 Dielectric loss = 0.18% Tm=240 C

• CTFE: common co-monomer improves miscibility

• Crosslinking further reduces loss and improve thebreakdown

Blends of P(VDF-CTFE) with P(ECTFE)

Extruded Films

30% ECTFE

40% 50%

Charge/DischargeCharacteristics of Extruded Blend Films

•Losses are reducedP(VDF-CTFE): Loss >30%, Ue= 8J/cc (at 300 MV/m)

with 30% ECTFE: ~15%, Ue=4 J/ccwith 50% ECTFE: ~6%, Ue=2.9 J/cc

P(VDF-CTFE)

30%

30%

50%

50%

23

Crosslinking in P(VDF-CTFE)/ECTFE blends

+TAICBC

24

Polymer NanocompositesP(VDF-CTFE)/ECTFE Blends

Comparison of charging/discharging curves

Pure P(VDF-CTFE) P(VDF-CTFE)/0.33ECTFE P(VDF-CTFE)/0.33CTFEwith crosslinking

• The high field loss of the crosslinked P(VDF-CTFE)/ECTFEis nearly the same as that of BOPP, the state-of-the-art low lossdielectric polymer

• Crosslinking provides additional and stronger “defects”to prevent theformation of large polar-regions in the polymer under high electric fields

Blends Film with Crosslinking

Better mixingwith crosslinkinglead higher UeBetter mixing

with crosslinking

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

-10 0 10 20 30 40 50 60% of ECTFE

2

3

4

5

6

7

8

9

-10 0 10 20 30 40 50 60% of ECTFE

•Film microstructures have marked effect on the dielectricresponse of blend films, especially on the losses

loss is reducedfrom 15% (extru)to 4.8%

26

Summary

• In polymers with strong dipoles, a high energy density (> 30 J/cm3)can be achieved

• Making use of low dielectric loss and high temperature stability ofTFE and high dielectric constant of VDF/HFP, the terpolymer ofP(TFE/HFP/VDF) shows a higher energy density while maintaininglow loss compared with BOPP

• In modified P(VDF-CTFE) ferroelectric polymers, blending withlow loss dielectrics plus crosslinking can lead to marked reduction inlosses

27

Acknowledgement

This work was supported by ONR, Grant No.N00014-11-1-0324(Program manager: Dr. P. Armistead )

Thank you !