Rationally Designed 1D/2D Core/Shell Nanowires for Flexible Supercapacitors

Nitin Choudhary

Supervisor: Prof. Yeonwoong JungNanoScience Technology Center

University of Central Florida

March 22, 2017

Nat. Commun. 5, 5678 (2014)

Flexible Electronics: Grand Vision

Global revenue: USD 16.50 billion by 2021

Thin Light weight Rolled up, twisted, bent Good mechanical properties Health & Environment safe

Flexible Energy Storage ?

Medical devices

Wearables

Flexible RFID

expectationIncompatible

Li-ion Batteries Supercapacitors

Batteries vs Supercapacitors

10-60 minutes Charge Time 1-10 seconds

～1500 Cycle Life > 500,000

1,000-3,000W/Kg Power Density 10,000 W/Kg

100-200 Wh/Kg Energy Density 5-10 Wh/Kg

-20 to +65 ∘C Operating Temp. -40 to +85 ∘C

Storage War

Different mechanisms: Different properties

Curr

ent

Potential

Curr

ent

Potential

Challenges for Flexible Devices

Li-ion batteries:

• Could easily break when twisted/bended or pressed too far• Low operation temperature- concerns due to overheating• Safety issues due to toxic, flammable, and corrosive nature of Li metal

Supercapacitors:

• Low energy density

Supercapacitor Electrodes

A special issue on Electrochemical Capacitors, Electrochem. Soc. Interf., 2008, Spring.

CNTs- bundle formationAC-Non-uniform pore

Shrinking/SwellingPoor cycle stability

Poor conductivityLow power density

AC

CNTs

Polymer

Electrode for Flexible Technology

Ultra thin electrodes Variable oxidation states (+2 to +6) Environmental Benign

Scalable production ?

1. Graphene 2. Transition Metal Dichalcogenides (TMDs)

Stacking issues High-quality production/ scalable approach Low throughput/yield-Exfoliation Methods High cost for supercapacitor fabrication

MoS2, WS2, etc.

TMDs electrode designs

RSC Adv., 2016, 6, 48788Glassy carbon/use binders40% after 2000 cycles

Electrochem. Commun. (2013)Ni foam/use binders45% after 500 cycles

Hydrothermal MethodGlassy carbon substrateUse BindersCap. Ret. 89% after 1000

Dalton Trans., 2016, 45, 2637

Chemical ExfoliationGlass & polyimide93% after 5000 cycles

WS2 Nanoribbons WS2/CNT compositeMoS2/Graphene composite

1T MoS2

(Nat. Nanotechnol. 10, 313 (2015)

(1) Scalable(2) High surface area(3) High electric conductivity(4) Binder free integration

Rational electrode designs

RSC Adv., 2016, 6, 39159

Chemical bath depositionStainless steel subs.Moderate capacitanceCap. Ret.= 82% after 3000

MoS2 Nanoflakes

ACS Nano, 2016, 10 (12), pp 10726–10735

1D core: h-WO32D shell: WS2

(Tungsten foil)

Recipe for Core/Shell Nanowires

ACS Nano, 2016, 10 (12), pp 10726–10735

One-body evolutionMechanically/chemically robust

XRD analysis

Raman-Before Sulfurization

Raman-After Sulfurization

• Single crystalline h-WO3 core• Characteristic Raman bands from high

quality h-WO3 & WS2

XRD & Raman Analysis

High Resolution Transmission Electron Microscopy (HRTEM)

ACS Nano, 2016, 10 (12), pp 10726–10735

Elemental analysis

Highly symmetric CV, GCD curves High capacitance Low Equivalent Series Resistance (ESR)

Core/Shell Electrode @ 0.1M Na2SO4

Liquid-exfoliated MoS2 sheets = 2 mF/cm2

Edge oriented-MoS2 = 12 mF/cm2

3D porous MoS2 = 33 mF/cm2

Metallic (1T)-WS2 = 2813 μF/cm2

Semiconducting WS2 = 223 μF/cm2

MoS2-graphene composite = 11 mF/cm2

47.5 mF/cm2 @ 5mV/s

Dominant EDLC mechanism High areal capacitance = 18.3 mF/cm2

High bendability

Solid State Core/Shell Nanowire Supercapacitor

ACS Nano, 2016, 10 (12), pp 10726–10735

Materials Electrolyte Retention No. of(%) Cycles

Unprecedented cyclic stability

WO3

WS2

After 30,000 cycles

Ragone Plot

Conclusions

Novel electrode design – new paradigm in 2D flexible technology

Binder free construction of the electrodes

High mechanical stability & High energy density

Unprecedented cyclic stability (30,000 cycles)

Scalable method

ACS Nano Cover Page –Dec, 2016 issue

Jung Research group @ University of Central Florida