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AABC 2012: Challenges and solutions for cost-effective integration of batteries into EVs

13 February 2012

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At the Advanced Automotive Battery Conference (AABC) last week in Orlando, Florida, Michael Keller, Leader Energy Storage, Volkswagen AG, chaired a session on challenges and solutions for cost-effective integration of batteries into EVs. As official media partner, cars21.com provides a summary of the presentations in this last update from the AABC 2012.

Modularity is the first key topic related to cost-effectiveness in the EV battery industry. Indeed, as mentioned by all speakers but more specifically by Michael Keller: “Costs are reduced thanks to modularization which allows components to be used more than once and the various modules to be detached from vehicle development cycles”. Modularity also allows for time savings, which directly impact on the battery costs as well.

The modularisation of the battery covers a wide range of functions:

  • Cooling the cells
  • Balancing the cells
  • Monitoring the status
  • Communicating with the vehicle
  • Exchanging status parameters
  • Providing a mount for the individual cell stacks
  • Connecting to and disconnecting from the high-voltage vehicle electrical system

Thermal management of Li-ion Batteries

Thermal management is part of the battery management, having a great impact on the lifetime and the performance of the battery, especially because Li-ion batteries degrade dramatically over 55°C. What makes thermal management difficult is that many factors have an impact on battery temperature, stating with the environment. As shown by Dr.-Ing. Christian Pankiewitz, SB LiMotive, high temperatures can greatly affect the lifetime of the battery: in Berlin, Germany, tests have shown that the battery has over 90% capacity retention after ten years, where in Athens, Greece, the capacity drops below 90% after seven years.

Air cooling, liquid cooling of the pack or inter-cell liquid cooling is currently done, depending on applications (HEV/PHEV/EV). You can see below the specificities in design and thermal management of each solution:

 

Liquid cooling – Bottom

Liquid Cooling – Inter-cell

Air cooling – Inter-cell

Design

- Compact

- Focus point: thermal contact

- Compact

- Complex piping design

- Focus point: tightness

- Less compact

- Focus point: air distribution

Thermal

- Uniform temperature spread

- Limited heat transfer area

- Uniform temperature spread

- Large heat transfer area

- Inhomogeneous temperature distribution

- Limited heat capacity

On the cost perspective, Dr.-Ing. Christian Pankiewitz has shown that the cost of liquid cooling – bottom only had by 2011, drop to 70% of the 2009 cost level. It is expected that costs will continue to drop by 2015 to 40-50% 2009 cost levels. Key elements for cost reduction are the use of standard automotive technologies, materials and parts for cooling applications. Further important are the avoiding of over-design and less complexe solutions to meet thermal requirements.

Battery Management System (BMS)

Dr. Uwe Wiedermann, Product Manager Battery Systems Engineering and Technology, Powertrain Systems from AVL List GmbH also thinks that affordable batteries are achievable through smart module and pack design. He emphasised the importance of the BMS, which are developed for multiple applications, such as:

  • Battery core functionalities (State of Charge (SOC), State of Health (SOH) and State of Functionality (SOF) calculation).
  • Active and passive cell balancing
  • Cell failure detection
  • Start-up / shutdown procedures
  • Signal processing / actuator control
  • Main contactor and pre-charge circuit control
  • Isolation detection
  • Thermal management
  • Safety monitoring
  • Diagnostics
  • Service access and testing
BMS allows the battery to have longer lifetime and higher performance through a specific control strategy, linked to the thermal management of the battery. Is also improves the reliability of the battery and increases its safety level.


Comments

George Brilmyer

We are building cells for HEV\'s that approximate the size and shape of a bagel. The cells have short grids for high power and we stack and interconnect the cells like a package of bagels. High voltage packs are easy to construct. We then manage the temperature by circulating air in and around the cell stacks. Our cells are low cost and fully recycled because they are VRLA. Our goal is to keep the temperature of all cells equal and in the proper temperature range for long life and high performance. Battery pack weight is not a problem for packs below 2kWh. See what we are doing at HighWater Innovations.
added 2012-02-21 15:58:54

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