23 may 2019 - uib

D epa r tm en t o f P hy s i c s a nd Tech no l og y

Lars Egil Helseth

Department of Physics and Technology

23 May 2019

Nanotechnology


Outline of this talk

❖What is nanotechnology? Benefits and challenges

❖Nanotechnology for harvesting electrical energy

❖Nanotechnology for storing electrical energy❖ Batteries

❖ Supercapacitors


0.1 nm

1 nm

10 nm

100 nm

1000 nm

10000 nm

100000 nm

Water

molecule

Red

blood

cell

DNA

Hair

strand

What is nanotechnology?

Study and construct technology based on

structures with at least one dimension

between 1 nm and 100 nm


We are self-assembled nanotechnology!

• DNA and other biopolymers in the

body

• Motorproteins for cleaning

(kinesin) or actuation (myosin)


Why nanotechnology?

• Quantum effects become

important at small scales.

Examples: New light sources

(lasers,labels, etc), data storage and

communication technology.

By changing the dimension of the quantum well you may change

the energy levels and therefore also the colors of the emitted light!

n=1

n=2

n=3

electron

http://en.wikipedia.org/wiki/Image:Fluorescence_in_various_sized_CdSe_quantum_dots.png


Why nanotechnology?

• Surface features become more important

Examples: self-cleaning surfaces

1 mm

Nature Made by reactiveion etching at UiB


Why nanotechnology?

• Fluctuations and cluster formation becomes more important.

Example: Gluing soft tissue (for example wounds)

Glue tissue using nanoparticlesGlue tissue using pH-

controlled chitosan


Solution: Everyone should drive

a nanocar.

(only 0.014 mm/hour)

Why nanotechnology?

• New and unexpected solutions to current problems

Example: Bompengesituasjonen


http://wumo.no/2012/06/08/

• We do not know enough about how the nanoparticles

influence the environment and our health

Challenges: Environmental threats


Challenges: Environmental threats

NaClO

+

Carbon nanotubes

CO2

CSIRO

❖ > 100 companies and hundreds of tons produced annually.

How to deal with the waste?

❖ Carbon nanotubes are known to influence cell growth and may

produce asbestos-like pulmonary response.


How can nanotechnology contribute to renewable electrical energy sources?


All activity requires energy

• Deleting 1 bit on a computer harddisc leads to a heat loss of kBT ≈10-20 J

• One search using Google is estimated to require about 1 kJ (1/4

Wh). Google report more than 40 000 searches per second.

Unit: Joule (J) or Wh (=1 W x 3600 s = 3600 J)

Power = Energy/time (unit: Watt = Joule/second)

•Minimum power needed to run all searchs: 40 MW


How much electrical energy do humans use?

• A normal heating oven may consume 1 kW electrical power. In one hour the energy used would

be 1 kWh = 1000 W·3600 s=3.6 MJ. In one year this becomes 365·24·1kWh ≈ 9 MWh

• If a household consumes 16 MWh electrical energy per year it will cost 9120 kr if the price per

kWh is 0.57 kr (16000 kWh * 0.57 kr/kWh = 9120 kr)

• One could use this electricity to heat the home, or do 16 MWh / (0.25 Wh per search) = 64

million Google searches


Use of electrical power Power = Energy/time

(unit: Watt)


Energy demand

Renewable energy sources Why

Large scale(>> 1 kW)

Sun farms(photovoltaic or photothermal), windfarmshydro power plants, geothermal power plants, etc

Reducedependency onoil

Small scale

(< 10 W)

Use sunlight, vibrations, rain, temperature differences, etc

Run smallcomputers, sensors and actuators; democraticdistribution ofelectrical energy?

The distribution of

electrical energy is not

democratic!

Can a better

distribution give rise to

less conflict?

Large versus small units


Small units needed to power IoT

Node

Sensor1

Sensor2

Aktuator1

Aktuator2

• Internet of Things (IoT).

• If each node uses 1 W, one needs

at least 20 GW (175 TWh over

one year) to power IoT…today

mostly with batteries…

• In 50-100 years we may have

20·1012 nodes, demanding 20 TW.

Where should all this energy come

from?

• Today there are > 20·109 nodes (mobile

phones, smartwatches, traffic and

environmental stations, etc)


How to develop future energy sources?

Need to consider:

1) Democratic and easy distribution

2) Life cycle analysis (no net waste)

http://www.dilbert.com/


Nanotechnology for harvesting electrical energy

❖Solar cells

❖Triboelectrical nanogenerators (contact electrification)


Solar cells based on nanotechnology

- Increased ‘capture’ of sunlight

using nanostructures as

compared to flat surfaces

- There is a great hope of

cheaper production

- Increased thermal management

(heat lead away more efficiently)

-Self-cleaning surfaces that reduce

absorbtion of sunlight


Contact electrification for energy harvesting

Electrostatic charging occurs when two materials are contacted or rubbed

and then separated

Contact

+ + + + + + + - - - - - - -

No contact No contact

+ + + + + + +

- - - - - - -

For an insulator, the charge may remain at the surface for a very long time (many decades), whereas for a metal the charge may quickly move away ifit has somewhere to go (e.g. an external wire).


RL

I

Metal

- - - - - - - - - -Dielectric

RL

+ + + + + + + + + +

- - - - - - - - - -

+ +

I

+ + + + + + + + + +

- - - - - - - - -

RLRL

+ + + + + + + + + +

- - - - - - - - - -

+ + + + + + + + +

- - - - - - - - - -

+ +

- -

Metal

+ + + + + + + + + +

Triboelectrical nanogenerators: principle


Triboelectric nanogenerators powered by humans

Mechanical energy is

transformed into

electrical energy


Examples of systems benefitting from nanotechType Principle Power density Advantages Disadvantages

Solar cell Photovoltaic effect 10-100 mW/cm2 Long lifetime, high power

density, continuous

current, mature

technology

Does not work at night,

needs cleaning, low

voltage

Rain cell Contact charging 10-100 mW/cm2 Made of flexible

materials, can be mounted

on any infrastructure, can

be combined with solar

cells

Only works when there

is rain, low power

density, discontinuous

current, immature

technology.

Thermoelectric cell Thermoelectric

effect

10-100 mW/cm2 Long lifetime, continous

current

Needs temperature

differences, low power

density, immature

technology

Vibration cell Piezoelectric or

triboelectric

nanogenerators

(contact charging)

1-100 mW/cm2 Small, flexible, high

power density

Needs vibrations,

discontinuous current,

immature technology


Nanotechnology for storing electrical energy

❖Li-ion rechargeable batteries

❖Supercapacitors


Working principle of modern Li-ion batteries

Convert chemical energy to electrical energy.

Polymer Reviews 51(3):239-264 · July 2011

https://www.youtube.com/watch?v=VxMM4g2Sk8U

D epa r tm en t o f P hy s i c s a nd Tech no l og yT

emp

eratu

re(°

C)

Safe operation

2 4 6 Voltage (V)

100

Danger: LiFePO4 breaks

down and releases oxygen

200

300

Warning: electrolyte

decomposition;

destruction of electrode

protection layers

Danger: Overcharge;

formation of dendrites,

short circuit

Limits of modern Li-ion batteries


Example: An AA battery has charge capacity 2500 mAh (=2.5A x 3600s =9000 C).

How long time does it take to discharge it using a current of 100 mA?

How much charge can a battery store?

𝐐 = 𝐈𝐭 • Q=charge, I=charging/discharging current, and t is the

time needed to discharge/charge the battery.

Answer: 𝑡 =2500𝑚𝐴ℎ

100𝑚𝐴= 25 h


How much energy can you expect from a battery?


Batteries versus gasoline

• Gasoline has an energy density of 12.5 kWh/kg.

• A car using 1 liter bensin per 10 km, consumes 3.6 MJ per km =

1kWh/km.

• 400 km therefore requires 400 kWh. If the

the car is to drive 400 km it has to use 40

liter bensin (=40 liter · 0.8 kg/liter = 32 kg).

• Li-ion batteries have specific energy density of about 1 kWh/kg.

http://www.tu.no/industri/2014/03/27/denne-bussen-har-fire-tonn-batterier

• This requires Li-ion batteries of mass 400

kWh/(1 kWh/kg)= 400 kg. More work is

needed to reduce weight of batteries!!

http://www.tu.no/incoming/2014/03/27/1200026717.jpg/alternates/h1080/1200026717.jpg


Can we make lighter Li-ion batteries?

•Can we find another easily accessible

element with large ability to store

charge? Yes: Si

•Li4.4Si has the largest charge capacity of

4212 mAh/g (15 163 Coulomb/gram) and

gives 8.5 kWh/kg.

Possible anode materials


•Si has the largest capacity of the easy

available materials.

•Si films or bulk cracks in use due to large

internal stress. Solution: nanostructured anode!

Nanostructuring increases the battery charge capacity

•Problem: Si- nanostructures detach from

the metal electrode.


Electrical energy can be stored in capacitors

http://hyperphysics.phy-astr.gsu.edu/hbase/electric/capac.html#c1

𝐄 =𝟏

𝟐𝐂𝐕𝟐


Ordinary capacitors versus supercapacitors

+ + + + + +

- - - - - -

d

Solid state capacitor (d>1mm)

+ + + + + +- - - - - -

+ + + + + +- - - - - -

d

Electrolyte capacitor (d<10 nm)

++++++++++++++--------------------

++++++++++++++--------------------

Supercapacitor (d<10 nm and A large)

d-Uses nanocarbon to create

large A (> 1000 m2/g) and small

d (< 1 nm). This gives >10F/g.

-Capacitances up to about 5000

F available

C<1 mF C<1 F


Appearance of a supercapacitor

L. Zhang et al., Renewable and sustainable energy reviews (2017)


How much charge can a supercapacitor store?

𝐐 = 𝐂𝐕 • Q=charge, V is the largest available voltage

determined by the electrolyte and C is the capacitance.

Example: A supercapacitor a rated capacitance of 5000 F and maximum voltage 2.7 V.

What is the charge that this supercapacitor can store?

Answer: Q = 5000F × 2.7V = 13 500 C


How much energy can a supercapacitor store?

Example: A supercapacitor a rated capacitance of 5000 F and maximum voltage 2.7 V.

What is the energy that this supercapacitor can store in Wh ?

𝐄 =𝟏

𝟐𝐂𝐕𝟐

• Q=charge, V is the largest available voltage and

C is the capacitance.

Answer: E =1

2× 5000 × (2.7V)2= 18 225 J ≈ 5 Wh


Charge-discharge of 400F supercap

Time (s)10 0005 0000

Vo

lta

ge

(V

) 2

1

0

-Ideal supercapacitors should charge at constant current with voltage V=It/C and

remain at the same voltage when the current becomes zero.

-Real supercapacitors show self-discharge due to unwanted leakage currents and

redistribution of charge

-Real supercapacitors cannot be used to rectify ac currents at frequencies > 10 Hz

Limits of modern supercapacitors

D epa r tm en t o f P hy s i c s a nd Tech no l og yT

emp

eratu

re(°

C)

Safe operation

2 4 6 Voltage (V)

100

200

300

Warning: increased

leakage currentand and

possible electrolyte

decomposition

Danger: Overcharge;

gas formation

Limits of modern supercapacitors


Battery vs capacitor107

101

104

Capacitor106

105

103

102

1

0.01 0.1 1 10 100 1000

Supercapacitor

Battery

Fuel cell

Sp

ecif

icp

ow

er(W

/kg)

Specific energy (Wh/kg)


Applications of supercapacitors


Thank you for not falling asleep!

23 may 2019 - uib

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