Center for Advanced Life
Cycle Engineering

calce address

CALCE  Battery  Research  Group

Synopsis

CALCE is focused on the development of state of the art battery management systems (BMS) for single and multi-cell systems to provide the most accurate state of charge (SOC) and state of health (SOH) metrics. CALCE is working towards this goal through studies on fundamental process that degrade battery cells, battery testing methods, techniques for battery failure analysis, and advanced data processing techniques for implementation of battery prognostics and health management (PHM) solutions. PHM is an enabling discipline consisting of technologies and methods to assess the reliability of a product in its actual life cycle conditions to determine the advent of failure and mitigate system risk. By applying these methods, CALCE hopes to develop a BMS that not only assures safe usage, but also provides the best reliability and operational health information to the user.

 
Fig. 1 PHM-based Advanced BMS
 

Introduction

Lithium-ion batteries represent a major and expanding energy storage solution. Lithium ion batteries present more advantages, including high energy densities, cycling durability, no memory effect and low self-discharge over other available battery chemistries. At present, lithium-ion batteries are used in virtually all portable electronic devices including cell phones, laptops, and cameras. Demand for these batteries will continue to increase as the market for hybrid and electric vehicles takes over pure gasoline-powered cars. Other markets that require portable power supplies are also taking significant interest in lithium-ion batteries. These markets have begun utilizing lithium-ion batteries in military applications such as unmanned ground vehicles, aerospace applications for unmanned aerial vehicles and satellite hardware, medical applications such as implantable devices and portable health monitoring equipment, and in conjunction with renewable energy technologies such as solar panels and wind turbines.

 
Fig. 2 Specific Power & Energy of Different Battery Types
 

Although lithium-ion batteries are reliable and popular as energy storage devices, the thermal and electrochemical instability of the electrodes and the flammability of the electrolyte make lithium-ion batteries prone to catastrophic failures. Failures involving fires and explosions have resulted in numerous accidents in the consumer electronics, automotive and airplane industry involving millions of batteries. Fig. 3 shows a damaged United Parcel Service (UPS) cargo plan fire in 2006, a failed battery pack in a Boeing 787 in 2013 and a Chevy Volt battery fire after side-impact collision test in 2012.

 
Fig. 3 Battery Failure (a) UPS cargo plane fire (b) lithium-ion battery pack in Boeing 787 (c) Chevy Volt battery fire three weeks after side-impact collision test.
 

The strides made over the past two decades of lithium ion battery commercialization have opened the door to many future opportunities. However, the technology surrounding lithium-ion batteries is still in its infancy and has room for improvement. This improvement can be realized through two major avenues:

  • The first is through the development of new battery materials. For example, it has been known for decades that the theoretical capacity of silicon to store lithium polymer batteries in today’s market. However, lithium insertion into silicon is accompanied by a large volume expansion resulting in large stresses and structural damage to the anode.
  • The second avenue for improvement is the optimization of battery performance and reliability. Apart from the battery materials, the research can be directly applied to battery management systems (BMSs), which are electronic systems that monitor battery parameters and govern current and voltage to assure safe and reliable operation.
CALCE are looking at different research directions as follows:
  • With respect to material science, CALCE’s degradation analysis identifies dominate mechanisms of failure and how these are influenced by usage conditions. This information can be used to help optimize cell design based on the expected field conditions.
  • Taking into account the significance of BMSs, CALCE has been generating data to test and validate algorithms that can be used in advanced battery management systems, particularly in the area of state of charge and state of health estimation.

CALCE proposed an advanced BMS with prognostic components. The novel features in the new BMS include SOC prediction, SOH prediction, PHM-based decision making: Fig. 4 illustrates a decision making example based on PHM, the SOH of the battery can be evaluated. We not only can know the SOH at the current cycle, but also can predict the SOH in a future cycle. This allows for better mission plan and maintenance arrangement. Since we know the maximum capacity of the battery, we can predict whether the battery will run out of power during the mission. Second, PHM provides state-of-life prediction, or the remaining useful cycles of the battery. In this example, the remaining useful cycle is 18 cycles. Based on this information, the maintenance arrangement and action can be scheduled in advance to ensure the availability of the system and save cost.

 
Fig. 4 Decision making based on battery PHM.