Development of a modular lithium-ion battery for a sub-compact electric vehicle Peter Burda , Peter Keil , Markus Lienkamp , Andreas Jossen 1
2
1
2
MAY 6-9, 2012 LOS ANGELES, CALIFORNIA
TU München, Institute for Automotive Technology, Boltzmannstr. 15, 85748 Garching, Germany,
[email protected] 2 TU München, Institute for Electrical Energy Storage Technology, Arcisstr. 21, 80333 Munich, Germany,
[email protected] 1
Introduction
Cell Selection
One of the biggest drawbacks of current electric vehicles is their very high purchase price.
The development process of the battery system started with the selection of appropriate cells. Therefore, more than 800 different cells were evaluated for a well-grounded decision.
Therefore, the Technical University of Munich is currently developing the electric vehicle MUTE.
Criteria for selection process
MUTE is a lightweight sub-compact car, which has been presented at the Frankfurt Motor Show (IAA) 2011 as a fully functional prototype. Focus of this project lies on safe mobility at reasonable costs, comparable to a conventional car. MUTE presentation at Frankfurt Motor Show 2011
Vehicle Concept
Studies like [1] show customers’ driving characteristics: • average daily driving range: 10 kWh
• Capacity and voltage level can be varied easily with the number of cells / modules connected in series / parallel • Available space can be used efficiently in the construction process of the vehicle • Module voltage cost reduction
usage of available space
impact of cell failure when 10 % of the cells are defective
Development of a modular lithium-ion battery for a sub-compact electric vehicle Peter Burda , Peter Keil , Markus Lienkamp , Andreas Jossen 1
2
1
2
MAY 6-9, 2012 LOS ANGELES, CALIFORNIA
TU München, Institute for Automotive Technology, Boltzmannstr. 15, 85748 Garching, Germany,
[email protected] 2 TU München, Institute for Electrical Energy Storage Technology, Arcisstr. 21, 80333 Munich, Germany,
[email protected] 1
Construction of MUTE battery • Placement of the battery in a crash-protected area behind the passenger cabin • Battery consists of 1232 cylindrical cells which are devided into 11 modules • Cells are embedded in a system of two supporting frames with spacing elements between the cells • Separation of cells prevents thermal interaction of neighboring cells in case of a cell failure • Cells are interconnected by hilumin connectors applied by spot welding • Clamped copper bars lead from hilumin connectors to the external terminals • Cells have an optimized orientation inside the car to minimize vibrational loads onto the welding spots during driving • Construction suitable for prototype as well as largescale production • A design FMEA on module and system level has been performed to identify and improve weak spots • Positioning all high voltage components (battery, engine, power electronics, charger) in the rear leads to an ideal weight distribution of 60 % on the powered axle
Thermal Management
position of MUTE battery behind passenger cabin
supporting frames and spacing elements
• Aging and charging / discharging behavior of lithium-ion batteries is strongly temperature-dependent • Decreased performance at low temperatures ( 30°C) • Homogeneous temperature distribution inside the battery module necessary for uniform aging of all cells => Counter current cooling system to reduce temperature gradients => Heating battery cells with bioethanol heating system in winter
Results
components of battery module
• • • • •
Battery Management System (BMS) • Monitoring of voltages, currents and temperatures • Versatile master-slave-topology • Decentralized cell-individual state determination (e.g. Kalman-Filters) and cell balancing performed by BMS slave • Master receives preprocessed information of arbitrary amount of slaves for monitoring battery safety and range estimation
BMS slave board
simulation of temperature distribution
Modular battery system with energy content of 12 kWh Weight below 100 kg Specific energy on cell level: 208 Wh/kg Specific energy on module level: 170 Wh/kg Specific energy on system level: 130 Wh/kg
Conclusion
battery module with BMS on top
counter current cooling principle
weight distribution
Within the MUTE project a modular battery system has been developed. Although cost and weight reduction played an important role in the development process, no compromises on safety and durability were accepted. This can be observed throughout the whole development process of the CAD image of MUTE battery system battery system: Reliable lithium-ion cells combined with a safe mechanical integration into the vehicle and an optimized heating / cooling system are the basis for a comfortable, robust and long-lasting operation of the entire battery system. This battery system demonstrates that affordable electric mobility is already possible today.
References [1] Mobility in Germany, infas, DLR, summary report, p.4, 2008 (http://tinyurl.com/88m316u) [2] Final report on MINI E 1.0 research project, BMW AG, p.39, 2011 (http://tinyurl.com/834mjzo)
