Potential for energy storage applications with supercapacitor technology. Chris Stirling, Development Manager - Energy, Haydale Ltd.

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1 Potential for energy storage applications with supercapacitor technology. Chris Stirling, Development Manager - Energy, Haydale Ltd. Cambridge Graphene Technology Days rd CIR Graphene Business Conference, 6 November

2 EDLC s (Supercapacitors) C=(ε/δ)A E=(1/2)CV² P=V²/(4R) (1) Wikipedia High surface area High voltage Low internal resistance

3 Supercaps vs. batteries Ragone plot showing power density vs. energy density for different devices h:p://en.wikipedia.org/wiki/supercapacitor#/media/file:supercapacitors- vs- ba:eries- chart.png

4 Supercap applications From : PresentaNon of Paolo Bondavalli, Thales R&T, at EuroNanoForum, 2015.

Supercapacitor construction SchemaNc construcnon of a wound supercapacitor 1.Terminals, 2.Safety vent, 3.Sealing disc, 4.Aluminum can, 5.PosiNve pole, 6.Separator, 7.Carbon electrode, 8.Collector, 9.

0 via Wikimedia Commons - h:p://commons.wikimedia.org/wiki/file: Electric_double- layer_capacitor_(acnvated_carbon_electrode_- _Tube_type).

5 Supercapacitor construction SchemaNc construcnon of a wound supercapacitor 1.Terminals, 2.Safety vent, 3.Sealing disc, 4.Aluminum can, 5.PosiNve pole, 6.Separator, 7.Carbon electrode, 8.Collector, 9.Carbon electrode, 10.NegaNve pole "Electric double- layer capacitor (AcNvated carbon electrode - Tube type)" by Tosaka - Own work by uploader (ref:isbn ). Licensed under CC BY 3.0 via Wikimedia Commons - h:p://commons.wikimedia.org/wiki/file: Electric_double- layer_capacitor_(acnvated_carbon_electrode_- _Tube_type).PNG Typically, electrodes are made from porous activated carbon, with high surface area. 1g : area > 4 tennis courts, capacity > 100 F. Graphene also has high surface area. 1g : area of 10 tennis courts, theoretical capacitance of 550 F. High electrical conductivity of graphenes, combined with the engineering of accessible microstructures (e.g. combined with CNT s), offers better rate and frequency performance.

6 Some things that plasma processing offers Processing Better dispersion for creating electrodes (e.g. spraying). Improved interaction with binder, and wetting with electrolyte. Hydrophobicity: moisture issue in non-aqueous, e.g. ionic liquids Performance Surface groups for additional pseudocapacitance (probably limited). Compatibility with electrolyte system (wetting). Treatment to minimise the re-stacking of graphene sheets and improve accessibility. Treatment to remove/modify undesirable pre-existing surface functionalities. Functionalised hybrid materials (e.g. graphene plus CNT/CNF )

7 HAYDALE PLASMA TECHNOLOGY

8 Plasma processing

Data Measurement Method Bulk Density 200-400 kg/m 3 EN ISO 60 Amorphous

9 HDPlas FLG Plasma processed few layered graphene (FLG) nanoplatelets with exfolianon of graphene sheets. Data Measurement Method Bulk Density kg/m 3 EN ISO 60 Amorphous Carbon Not detected Specific Surface Area SEM/TEM > 650 m 2 /g BET Analysis FLG Planar Size μm SEM FLG Thickness < 10 nm SEM

10 Plasma Treatment FuncNonalisaNon : high energy electrons generated in the plasma can split or disassociate molecules into their component parts. These charged parncles readily bond with a surface. Cleaning : ReacNve electrons and ions bombard the material surface removing contaminanon Electrons - - Photons, glow discharge u- v. Excited Gas species : molecules, atoms, ions, free radicals, metastables Adsorbed Molecules Pre- exisnng oxygen- containing surface groups (carboxylic, hydroxyl, carbonyl ) Basal vs edges. Other surface contaminanon, amorphous materials.

11 Initial investigation Electrochemical testing Sandwich- type capacitor: two carbon pellets, comprising 90% (dried) FLG, 5% PTFE, 5% Super P carbon black. Electrode thickness was between 260 and 300 µm. Cyclic voltammetry at scan rates between 1 and 50 mv/s. The voltage ranged from 0 to 0.8 V. non- treated FLG FLG O 2 ( low ) 2M H 2 SO 4 2M H 2 SO 4 Voltammograms indicate near ideal capacinve behaviour. At highest rate the non- treated FLG is limited, whereas (unexpectedly) oxygen plasma- treated FLG performs be>er.

12 Effect of plasma treatment on capacitance retention Further work with the FLG showed that capacitance retention may also be reduced by more intensive plasma processing, with more extensive oxygen functionalisation Examples BULK oxygen content (wt% dry basis) % Oxygen FLG 6.4 FLG(Ar) 6.7 FLG(O) 7.5

13 XPS Analysis XPS : C1s peak fit XPS : O1s peak fit atomic % atomic % Major effect of oxygen plasma treat on this FLG is increase in carboxylic surface groups. In the literature the presence of this group has been shown to be associated with a reduction in capacitance retention.

14 Moisture adsorption of the FLG Hydrophilic: up to c. 10wt% adsorption in laboratory air over prolonged period. Essential for many applications that moisture is controlled. Example shown : Haydale HT60 fluorination plasma treatment increasing hydrophobicity.

15 Conclusions Plasma treatments with a scalable process demonstrated to have significant effects on performance of a commercial FLG in a supercap test. The benefit (for rate capability in this case) depends on several factors ; including plasma chemistry, extent of treatment and pre-existing surface chemistry. Plasma treatment to tailor nanomaterial surfaces for compatibility and improved performance in range of chemistries shows significant potential for supercapacitors and expected to translate to battery applications.

16 Thank You Acknowledgements : Haydale Ltd. for permission to a:end and present. Dr. Teresa A. Centeno, of InsNtuto Nacional Del Carbón (INCAR- CSIC), Oviedo, for valuable advice and suggesnons. Emily Smith (Haydale/Univ. Surrey) for XPS analysis.

Optimization of MnO2 Electrodeposits using Graphenated Carbon Nanotube Electrodes for Supercapacitors

Optimization of MnO2 Electrodeposits using Graphenated Carbon Nanotube Electrodes for Supercapacitors Waleed Nusrat, 100425398 PHY 3090U Material Science Thursday April 9 th 2015 Researchers optimize the