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Batteries for electric commercial
vehicles and mobile machinery
Tekes EVE annual seminar, Dipoli 6.11.2012
Dr. Mikko Pihlatie
VTT Technical Research Centre of Finland
2 07/11/2012
Outline
1. Battery technology for electric vehicles and mobile machinery
Current state-of-the-art
Challenges and limitations
Beyond state-of-the-art
2. From battery cells to applications
Application-specific requirements
Battery use and operation window
Cost analysis factors
3 07/11/2012
What is a battery?
A battery contains one or more electrochemical cells
for storage of electric energy; these may be
connected in series or parallel to provide the desired
voltage and power
The anode is the negative electrode from which
electrons are generated to do external work
The cathode is the positive electrode to which positive
ions migrate inside the cell and electrons migrate
through the external electrical circuit
The electrolyte allows the flow of positive ions from
one electrode to another. The electrolyte is commonly
a liquid solution containing a salt dissolved in a
solvent. The electrolyte must be stable in the
presence of both electrodes. Typically lithium salt
(LiPF6) + mixed organic solvent (ethylene carbonate-
dimethyl carbonate EC-DMC).
The current collectors allow the transport of electrons
to and from the electrodes.
B. Scrosati, Journal of Power Sources 195 (2010) 2419–2430
4 07/11/2012
Basic principle of Li-ion battery charging - discharging
Source: auto.howstaffworks.com
5 07/11/2012
Operation principle of SEI formation in a C/LiCoO2 battery
The C/LiMO2 system with current
electrolytes is thermodynamically
unstable (low kinetics!)
Reaction with the electrolyte
creates a passive Solid
Electrolyte Interface (SEI) on the
anode side
Normally the SEI stabilises the
cell (normal operation limits)
Abnormal conditions can lead to
oxidative processes on the
cathode cell failure risk
B. Scrosati, Journal of Power Sources 195 (2010) 2419–2430
6 07/11/2012
Li-ion batteries – a large range of possible materials combinations
Positive electrodes
Electrode material Average potential
difference Specific capacity Specific energy
LiCoO2 3.7 V 140 mA·h/g 0.518 kW·h/kg
LiMn2O4 4.0 V 100 mA·h/g 0.400 kW·h/kg
LiNiO2 3.5 V 180 mA·h/g 0.630 kW·h/kg
LiFePO4 3.3 V 150 mA·h/g 0.495 kW·h/kg
Li2FePO4F 3.6 V 115 mA·h/g 0.414 kW·h/kg
LiCo1/3Ni1/3Mn1/3O2 3.6 V 160 mA·h/g 0.576 kW·h/kg
Li(LiaNixMnyCoz)O2 4.2 V 220 mA·h/g 0.920 kW·h/kg
Negative electrodes
Electrode material Average potential
difference Specific capacity Specific energy
Graphite (LiC6) 0.1-0.2 V 372 mA·h/g 0.0372-0.0744 kW·h/kg
Hard Carbon (LiC6) ? V 450 mA·h/g ? kW·h/kg
Titanate (Li4Ti5O12) 1-2 V 160 mA·h/g 0.16-0.32 kW·h/kg
Si (Li4.4Si)[38] 0.5-1 V 4212 mA·h/g 2.106-4.212 kW·h/kg
Ge (Li4.4Ge)[39] 0.7-1.2 V 1624 mA·h/g 1.137-1.949 kW·h/kg
9 07/11/2012
The safe operability window for Lithium-ion battery
The battery should
be strictly kept in the
proper operating
window
Safety concerns
from improper use
or conditions
Durability and
performance suffer
greatly when
misoperated
Requirements for pack
design and battery
management
FTA, US Department of Transportation, Report No. FTA-MA-26-7125-2011.1
10 07/11/2012
Li-ion and beyond – status and outlook
Energy density insufficient for full EV operation
New electrode materials for higher capacity / lower cost
Lithium-metal alloys for anode, e.g. Li-Si (4000 mAh/g) and Li-Sn (990 mAh/g) anodes
instead of graphite (370 mAh/g)
Higher voltage cathodes, such as LMO ( stability of electrolytes!)
Challenges with safety of operation
Replacement of the organic carbonate lquid electrolyte solutions with more reliable and
safer electrolytes
E.g., solid polymer or ionic liquid electrolytes
Inherently safe electrode materials, such as LTO anodes ( improved cycle life)
Power capability – when quick charging becomes imprative, both
electrodes have to be optimised for this
Completely new systems will take several years to come to
demonstrations, but clear performance improvements are expected
Metal-air (Li-air) batteries bring potentially high electrode capacity (1200 mAh/g)
Li-S Lithium-suphur batteries offer potentially great capacity (2500 Wh/kg)
11 07/11/2012
Battery pack engineering towards application – case by case
Nissan Leaf battery
pack
Exact designs highly
dependent on vehicle /
application
Geometries and the
available space vary
drastically depending
on vehicle / application
Source: Wikipedia
12 07/11/2012
Relative performance of electrochemical storage devices
Different types of
power sources
have each their
optimal
application areas
Li-ion batteries
are struggling to
fulfil
requirements for
all-electric
vehicles
Venkat Srinivasan, Almaden Conf. 2009: “The Batteries for
Advanced Transportation Technologies (BATT) Program.”)
13 07/11/2012
Battery management system vs. vehicle energy balance
The tasks of the BMS
Protect the cells or the
battery from damage
Prolong the life of the
battery
Maintain the battery in a
state in which it can fulfil
the functional requirements
of the application for which
it was specified
Communication interfaces
BMS – vehicle control
BMS – charger
Charger – power/energy
grid
Source: Electropaedia, http://www.mpoweruk.com/bms.htm
15 07/11/2012
Comparison of different current Li-ion battery types
(power/energy)
Work cycle analysis
and end-user view
are central in
designing the
driveline and energy
storages
Right choice of
battery type and
battery design are
the key to succesful
EV design
Source: Al-Hallaj, EV Li-ion Battery forum, Barcelona 2012
19 07/11/2012
Battery lifetime has a crucial impact on the total system cost
Calendar life or cycle life
may be limiting
Different fading modes
Capacity loss
Impedance rise
Increase in self
discharge
Strong effect from how
the battery is used
Load cycles (C-rate)
Temperature
Depth of discharge