NOVEL NANOARRAY STRUCTURES FORMED BY TEMPLATE BASED APPROACHES:

TiO2 NANOTUBES ARRAYS FABRICATED BY ANODIZING PROCESS

COMPOSITE OF V2O5 AEROGEL NANOWIRES ON A CONDUCTIVE METALTUBE ARRAY SUBSTRATE AS A LITHIUM INTERCALATION HOST

Dr. Mansour Al Hoshan

Electrodes Based on Highly Surface Area Nanoarray Structure

Main focusPrepare an array of electroactive (host) at nano-scale with a highly ordered structure and good control of size and morphology using a template based approach

Host for hydrogen (fuel cell applications) and lithium (Li battery applications)

Improve the performance of a host material with respect to insertion capacity, reversible cycling, and rate capability

V

e-

Ion+/-

Hos

t

Ion+/-Since the rate of insertion of guest ions into a host is limited by diffusion into the solid phase, reducing the diffusion path length (L) will lead to a reduction of diffusion time (increased rate of insertion)

Dispersed arraysUniform size and shapeSmaller Particles

High surface to volume ratios Large surfaces and interfacial areas Small diffusion distance into solid phase

L L

Conventional Host (1-100 μm)

Main strategy: Template-based approach

We have used both electroless deposition and electrodeposition reactions with various templates, so that once the template is removed, the desired structures are revealed

Templates provide a predetermined configuration or cast to guide the formation ofnanomaterials with the desired morphology

After a material is formed, the template can be sacrificially removed, leaving behindthe final product that replicates the morphology of the original template

Overcome a weakness of many other synthesis methods by providingGood control of the final morphology of the produced nanomaterials

Very general with respect to the types of materials that may be prepared

Very versatile method to fabricate nanomaterials with a wide range of different morphologies and tunable sizes

Significance :

Template

Electro/electroless deposition

Dissolving the template

Arrays

voids and cavities within the template

Removal of the template

Template

Template: Track-Etched Polycarbonate Membrane

Pore Diameter: 2 µmThickness : 10 µmPores Density : 2x106 pore/cm2

1 µm 10 µm 2x107 pore/cm2

0.2 µm 10 µm 3x108 pore/cm2

Cylindrical pores with mostly uniform size and shapeFlexible and shows good durability during handling Mainly perpendicular to the membrane surface (some of the pores are tilted)Contain some defects such as di and tri pores (two and three pores merge into one pore)

Main characteristics

1 µm

Templates : Aluminum Oxide Membrane

0.2 µm 50 µm 12x108 pore/ cm2

Pore Diameter: Membrane thickness : Pores Density :

The pores are perpendicular with better parallel alignmentHigher porosity and smaller interpore separation

Rigid and very fragile

Main characteristics

Template (Membrane)

Array of metal tubes formed by electroless deposition-template based approach

Mask is removed

The membrane is removed

D: 2 µmH: 10 µmAspect ratio: 52x106 tube/cm2

Ni array of tubes obtained from polycarbonate membrane (2 µm)

1 µm

1 µm

1 µm

0

500

1000

1500

2000

0 2 4 6 8 10 12

Ni

Ni

Ni

P

Inte

nsity

KeV

100 nm

D: 1 µmH: 10 µmAspect ratio: 102x107 tube/cm2

D: 0.2 µm H: 10 µmAspect ratio: 503x108 tube/cm2

Ni array of tubes obtained from polycarbonate membrane (1 and .2µm)

10 µm

1 µm

10 µm

1 µm

100 nm

D: 0.2 µmH: 50 µmAspect ratio: 25012x108 tubes/ cm2

Ni array of tubes obtained from alumina membrane (0.2µm)

High density, well aligned, organized nanotubewith uniform diameter

Deposition time

2μm

1 µm

800 nm

1µm

1 µm 1 µm 1 µm

V

Li+

Li+

Li+ Li+

Li+

Li+

e-

e-

e-e-

e-

e-

e- e-

Li conducting electrolyteLi Intercalation

cathode

Carbon black

Intercalation host

Polymer binder

Anode Cathode

n Li n Li+ + n e-n Li+ + n e- + (host) Li n (host)

(oxidation) (reduction)

Active MaterialCarbon Additive

Curr

ent C

olle

ctor

A B

Li+ ion Intercalation/release process

Smaller, lighter weight, efficient rechargeable batteries

+ -

Particle A is in direct contact with current collector (continuous conductive path )

Utilization of particles B requires that the current be passed through another particles of the host rather than the conductive carbon particles

Conventional Cathode

Proposed electrode

Ni/V2O5 Composite ( a thin film coating of V2O5 directly onto the Ni tubes )

Ni substrate ( Ni tubes)

High electrode-electrolyte interfacial area (More active material exposed to electrolyte which enhances the utilization of the host materials) Continuous electronic path to active material through electronically conducting network.

Significance:

COMPOSITE OF V2O5 AEROGEL NANOWIRES ON A CONDUCTIVE METAL TUBE ARRAY SUBSTRATE

Continuous and highly conductive support matrix

D= 2 µm H= 10 µm 2 million tube/ cm2

Void volume in excess of 90%

Conducting network of Ni array of microtubes

1 µm

V2O5 Hydrogel

H+/ Na+

Ion Exchange

Bicontinuous structure of solid-phase and pores (filled with water)

XerogelV2O5

Evaporation

Aerogel V2O5

(Super critical drying)

H2O Acetone

(Acetone exchanged with liquid CO2 and the CO2 was removed above its critical point)

Exchange

Sol-Gel Process[Na+ VO-

3 ]

Metal tube array

Array +V2O5 Hydrogel

Metal +V2O5

V2O5 Hydrogel

H2O Acetone

Supercritical Drying

(Gel network preserved)

V2O5

V2O5 aerogel/ Ni

Compact

Highly porous with high surface area

V2O5 aerogel/ Ni

Side view Top view

V2O5 arogel

Ni

Very thin nano wires surrounding larger Ni tubes array

10 μm 10 μm

1 μm 1 μm

1 μm

The host composite was characterized by a highly porous structure that ensures electrolyteaccess throughout the composite and enhances the utilization of the host materials

The electrochemical response of the composite is dominated by the V2O5

aerogel nanowire (not by the substrate)

CV (Ni/V2O5 , lithium metal (counter and reference) 1 M lithium perchlorate in propylene carbonate, 2mv/s)

Li+ Insertion

Li+ Release

The composite showed an insertion capacity of more than 2.7 equivalents of lithium per mol of V2O5 (370 mAh/g)

-0.03

-0.02

-0.01

0

0.01

0.02

0.03

1.5 2 2.5 3 3.5 4 4.5

Cu

rre

nt

(mA

cm

-2)

Potential (V vs. Li )

The composite showed high specific capacity for Li+ ion insertion

Ni

Ni/V2O5

Galvanostatic measurements (Ni / V2O5 composite electrode)

Voltage vs. Specific Li+ insertion capacity of Ni/V2O5

composite electrode at different insertion rates

Specific Li+ insertion capacity vs. Cycle number

2.5

3

3.5

4

0 100 200 300 400

Po

ten

tia

l (V

vs.

Li )

Capacity (mAhrg-1)

0.07 A/g

0.7 A/g7 A/g

Specific

The composite showed good rate performance

The composite tolerates (Li+ insertion) over a large span of rates

Almost ~ 40 % of the initial capacity is retained when the insertion rate increasedby two orders of magnitude

The composite exhibited minimal capacity loss during insertion/release cycling

0

20

40

60

80

100

120

140

0 10 20 30 40 50

Sp

esif

ic C

ap

acit

y (m

Ah

rg-1

)

Number of Cycle

The extent of reduction in capacity (fading) decreases during cycling

Capacity fading( first 10 cycles) : 0.47% per cycle

Capacity fading( following 40 cycles) : 0.27% per cycle