Battery capacity (energy): How high can we reach? Dr Denis YU.pdfDr. Denis Y.W. Yu Assistant Professor School of Energy and Environment Battery capacity (energy): How high can we reach?

Dr. Denis Y.W. Yu Assistant Professor

School of Energy and Environment

Battery capacity (energy):

How high can we reach?

Oct 16, 2014

1

School of Energy and Environment, City University of Hong Kong

How many batteries are you carrying with you?

CD Player

Remote control

Laptop

Cell phone

PDA

Camera

Cordless

phone

Hand

cleaner

Hearing

aid

Lead-acid

Zinc

air

Li coin cell

Ni-Cd

Ni-C

d

Ni-

MH

Ni-C

d

Ni-M

H

Alk

alin

e

Alk

alin

e

Mn d

ry cell

Alkaline

dry cell

Li-io

n N

i-MH

Alkaline

Li-io

n

http://www.baj.or.jp/knowledge/stage.html

Primary

• Alkaline battery

• Li battery

Secondary

• Lead-acid battery

• Ni-Cd battery

• Ni-mH battery

• Li-ion battery

2


What are the trends?

Gets bigger and bigger

Gets smaller and smaller

3


What are the trends?

Need efficient energy storage for sustainability

4


Life Power

Cost

Capacity

Safety

Depending on applications

What do consumers want?

5


Battery capacity (energy)

Definition

History

Current status

Where do you go from here?

6


e.g. Typical cell phone batteries has capacity = 1000 mAh

Means it contains a charge of 3600 Coulomb

Battery capacity (energy) – definition

The higher the capacity, the longer the battery will last for

same current

Ampere [A] = charge (Coulomb) per second

Battery capacity (ampere hour) amount of charge that is stored

Type of battery

V – Voltage

Q – Capacity (mAh)

E – Energy = VxQ

7


Type of battery

Battery energy (Wh/kg or Wh/L)

Capacity depends on size (mass or volume) of the battery

Better to compare specific energy density:

Gravimetric energy density (Wh/kg) = energy/mass

Volumetric energy density (Wh/L) = energy/volume

V – Voltage

Q – Capacity (mAh)

E – Energy = VxQ

8


History of batteries

1869 Dmitri Mendeleev, first periodic table

1880s Thomas Edison, carbon filaments for light bulb

1897 J.J. Thomson, discovery of electrons

1947 Bell Labs, invention of transitor

1820s Andre-Maria Ampere, papers on electrodynamics

1827 Georg Ohm, Ohm's law

1785 Coulomb, first report on Electricity and Magnetism

1865 John Newlands, only 62 elements discovered

1800 Volta: Voltaic pile (Zn/Cu/brine)

1836 Daniell cell (Zn/Zn2+ Cu/Cu2+)

1859 Lead-acid battery (Pb/PbO2/H2SO4)

1866 Zinc-carbon cell (Zn/MnO2/NH4Cl)

1899 Nickel-cadmium cell (Ni/Cd/KOH)

1967 Nickel-metal hydride (Ni/MH/KOH)

1991 Li-ion battery (LiCoO2/C)

1979 Apple II+ personal computer

1991 World Wide Web

http://en.wikipedia.org/wiki/File:Newlands_periodiska_system_1866.png

9


Lithium-ion battery highest energy density

How much energy can be stored?

Energy density comparison of various battery systems

Energy

density

Gravimetric energy density (Wh/kg) = energy/mass

Volumetric energy density (Wh/L) = energy/volume

Wants lowest

mass and volume

http://www.epectec.c

om/batteries/cell-

comparison.html

10


Cell phone development

Decrease in size of electronics

Decrease in size of battery

1991

Li-ion

200 Wh/L

2013

Li-ion

600-700 Wh/L

<1990

Ni-Cd

50-150Wh/L

Effect of energy density on battery size

11


Inside a lithium-ion battery

e-

Li+

Basic principle: store energy by moving Li+ back and forth between the electrodes

LiCoO2

Li1-x

CoO2 + xLi

+ + xe

- Typical cathode:

Typical anode: C + xLi+ + xe

- Li

xC

e-

V

Al Cu

Positive

electrode

Negative

electrode

Electrolyte

Li+

Cell voltage

3.7V

12


Limitations of battery capacity/energy

Chemistry vs. engineering

Capacity allowable # of e- transfer

LiCoO2

Li1-x

CoO2 + xLi

+ + xe

-

C + xLi+ + xe

- Li

xC

Theoretical energy density ~ 400 Wh/kg

(~160mAh/g)

(~370mAh/g)

Material only

cathode

anode

separator

Cap (+)

Can (-)

Inactive material – can, metal foil,

electrolyte

Practical energy density ~ 200 Wh/kg

Cell level

Need to develop new materials to further increase capacity

Voltage ~3.7-3.8V

13


Examples of material development (cathode)

LiCoO2

~160 mAh/g

~250 mAh/g

Li-rich material

Challenge:

• Voltage drop during cycling

• Poor rate capability

• Requires surface coating to prevent electrolyte decomposition

DY091116D_5 21E-6:Ab:L-B-90:5:5

1.5

2

2.5

3

3.5

4

4.5

5

0 50 100 150 200 250 300

Capacity (mAh/g)

Pote

ntial

(V

vs.

Li/

Li+

)

0.05C1C0.1C

0.2C0.5C2C

Capacity (mAh/g)

Pote

ntial (V

vs. Li/Li+

) LiMO2 – Li2MnO3

“composite”

Li layer Transition

metal layer

Yu et al. J. Electrochem. Soc. 157 (2010) A1177-A1182

14


0

100

200

300

400

500

600

700

800

900

0 10 20 30 40 50

Cap

acit

y (

mA

h g

-1)

Cycle number

Optimized binder + electrolyte

New binder +

conventional electrolyte

0-2.5V

250mA g-1

Example of material development (anode)

Graphite

370 mAh/g >700 mAh/g

Metal sulfide

Yu et al. Scientific Reports 4

(2014), doi:10.1038/srep04562

Commercial

graphite

e.g. Sb2S3

Technologies to

improves

structural and

chemical stability

15


Future outlook (Li-ion battery)

Alternative anode materials

Challenge – volume expansion

Capacity Volume

change

Graphite 372mAh/g (C6Li) 12%

Silicon 4200mAh/g (Li22Si5) 320%

Zhang, W.-J. J. Power Sources, 196, 13-24 (2011)

e.g. Si, Ge, Sn – alloy with Li

Expected increase in energy

Cathode: 160 250 mAh/g

Anode: 370 2000 mAh/g

Energy density ~50% UP

16


Future outlook (Li-Sulfur battery)

S + 2 Li+ + 2 e- → Li2S

http://www.vorbeck.com/energy.html

Challenges:

• Electrical conductivity of S

• Dissolution of polysulfide into electrolyte (self discharge)

• Reactivity of Li metal (Li plating)

Feature:

• Uses Li metal as anode

• Uses S as cathode

• Both Li and S are lightweight

Capacity = 1670 mAh/g

Potential = 2V vs. Li/Li+


Research:

Nano-composite; carbon-coating; etc.

Prototypes of about

500 Wh/kg made

17


Future outlook (Li-Oxygen battery)

O2 + 2 Li+ + 2 e- → Li2O2

Challenges:

• How to enable reversible oxygen reaction

• Electrolyte type

• Reactivity of Li metal (Li plating)

• Real applicability in air

Feature:

• Uses Li metal as anode

• Oxygen can be obtained from air

Capacity = 3850 mAh/g (Li only)

Potential = 2.6V vs. Li/Li+


Research:

Nano-structure; solid electrolyte; etc.

18


Battery capacity: how high can we reach?

Theoretical Practical

Li-ion (existing technology) ~400 Wh/kg ~200 Wh/kg

Li-ion (new materials) 600-700 Wh/kg 300-350 Wh/kg

Li-sulfur 2300 Wh/kg 500 Wh/kg

(prototype)

Li-oxygen 10000 Wh/kg ??

Must include supporting battery

structure (inactive material)

• Need new materials and technologies to increase battery energy

•Caution when comparing energy density values

Petrol: energy density = 13000 Wh/kg

19


Future outlook - applications

Spiderman: “With great power comes great responsibility”

Battery scientists: “With great energy comes great safety

responsibility”

Electric

vehicles

Nissan

Leaf

Size

24kWh

Weight

(Battery+module)

218kg

Tesla

Model S

Size

85kWh 544kg

Renew-

ables

e.g. 350kW PV for 12h = 4200kWh

Need 21ton LIB

Documents

Battery capacity (energy): How high can we reach? Dr Denis YU.pdfDr. Denis Y.W. Yu Assistant Professor School of Energy and Environment Battery capacity (energy): How high can we reach?