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Materials Research Society Spring 2014
Conferences & Talks

 

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1.  SENSOR: embedded fiber optic sensing for accurate state estimation in advanced battery management systems - April 21, 2014  (Dr. Ajay Raghavan, Dr. Peter Kiesel, and Dr. Bhaskar Saha)

Under the ARPA-E AMPED program for advanced battery management systems (BMS), PARC and LG Chem Power are developing SENSOR (Smart Embedded Network of Sensors with an Optical Readout), an optically based smart monitoring system prototype targeting batteries for hybrid and electric vehicles (EVs). The system will use fiber optic (FO) sensors embedded within Lithium (Li)-ion batteries to measure parameters indicative of cell state in conjunction with PARC's low-cost, compact wavelength-shift detection technology and intelligent algorithms to enable effective real-time performance management and optimized battery design. FO sensors are lightweight and thin, immune to electrostatic discharge, electromagnetic interference, can be protected with suitable coatings to withstand harsh environments, and can measure multiple parameters with high sensitivity, such as strain, temperature, pressure, and chemical composition in multiplexed configurations. All of these characteristics make them very attractive candidates for embedding as sensors in batteries. This paper will give an overview of the project, the underlying enabling technologies, and then cover some promising initial experimental results. Towards the end project goal of automotive-grade cell modules that incorporate this technology, the team has fabricated initial functional prototypes of small format FO-embedded Li-ion pouch cells. Preliminary data indicates comparable performance and seal integrity of these cells to un-instrumented cells. Analysis of sensor data from these cells recorded over charge-discharge cycles have shown a number of interesting features that hold promise to aid accurate cell state estimation algorithms. In parallel, experiments to explore the potential of high sensitivity skin strain and temperature monitoring with FO sensors mounted externally on the cell are also ongoing. These experiments have also yielded notable results in terms of detecting cell state features that can be monitored with PARC’s sensitive FO readout and are not detectable with the voltage and current signals monitored during typical usage by present-day BMS. The paper will examine these results and compare internal versus external cell sensing with FO sensors. Finally, the use of these monitored internal cell state features for state estimation algorithms and suitable BMS control strategies for safe, optimal utilization of true battery capacity will be discussed, which can reduce conservative design and use practices of batteries for various applications.

 

2.   Embedded Fiber Optic Chemical Sensing for Internal Cell Side-Reaction Monitoring in Advanced Battery Management Systems - April 21  (Dr. Ajay Raghavan, Dr. Peter Kiesel, and Dr. Bhaskar Saha)

Advanced Lithium (Li)-ion batteries today present attractive options for high-performance energy storage in a number of applications ranging from portable electronics to aerospace vehicles. Battery management systems (BMS) play a crucial role in the safe, efficient utilization of capacity and power from these high-density energy storage devices and ensuring that battery state of health (SOH) is not compromised. In this respect, BMS SOH estimation functions are significantly limited by the use of externally monitored parameters such as voltage, current, and temperature. Consequently, battery packs are often designed and used very conservatively by the BMS to ensure safety and reasonable lifecycles. Present-day commercial Li-ion battery electrolytes, typically consisting of cyclic alkyl carbonate and chain alkyl carbonate solutions with Li-hexafluorophosphate as salt, are known to generate gases and other adverse chemical species when subjected to aggressive cycling or with aging. However, the conditions that cause such adverse side-reactions are not fully understood and can change with different use scenarios. These can accelerate cell aging and in the worst case, lead to safety hazards. Internal sensing within the cell to monitor chemical side reactions to detect such adverse side-reactions at an early stage would be highly desirable to support BMS functions. However, the harsh chemical environment within the cells and tight constraints on acceptable cost and size overheads for BMS sensors have historically challenged viable embedded sensor solutions for cell monitoring. In this respect, fiber optic (FO) sensors present an appealing potential solution. They are lightweight and thin, immune to electrostatic discharge, EMI, and can measure multiple parameters with high sensitivity, such as strain, temperature, pressure, and chemical composition in multiplexed configurations. FO sensors have been demonstrated to accurately and specifically resolve a number of chemical and gas species in various applications. This paper focuses on in situ FO chemical sensing methods tailored for accurate cell side-reaction monitoring. Studies on sensitivity, response time and other characteristics of in situ chemical measurements during different charge cycles in Li-ion cells will be summarized. Some experimentally tested chemical sensing schemes are presented and compared, both during normal cycling conditions and under simulated abuse cycles/aged conditions. These results will be benchmarked with other published data in the literature from controlled lab studies on chemical side reactions in Li-ion cells. The potential of such chemical side-reaction monitoring capabilities for significantly improved SOH estimation algorithms will be highlighted. Finally, the practical use of such embedded side-reaction FO chemical sensors in commercial battery packs to improve safe and optimal utilization of true battery capacity by the BMS will be discussed.                                    

3.  Radiation induced defects in poly (3-alkylthiophene) - April 24, 2014  (Dr. John E. Northrup and Dr. Bob Street)

Defect formation arising from radiation induced hydrogen rearrangement in polythiophenes has been investigated experimentally and theoretically.[1] Defect formation by irradiation of BHJ solar cells has been proposed to be a source of recombination centers in organic solar cells.[1] Formation of the defects is reversible by annealing. Calculations show that hydrogen related defects indeed give rise to electronic states in the gap, and that such defects can migrate with an activation energy that is in agreement with annealing studies. To fully understand the process of radiation induced hydrogen rearrangement we must determine the minimum energy required to form such defects. We therefore will discuss density functional calculations of the energy barriers that must be surmounted to form hydrogen related defects in polymers such as poly(3-alkylthiophene).[2] Pathways for defect production corresponding to interpolymer and intrapolymer H rearrangement were identified. The calculations indicate that radiation induced gap state production in poly(3-alkylthiophene), via removal of H from the alkyl chain, becomes possible when the energy of the radiation exceeds a threshold value in the range from 2.7 to 3.2 eV. [2] This energy is less than the nominal value for C-H bond breaking (~4.4eV), because bond breaking and bond forming occur concurrently. This work was supported in part by the AFOSR under Grant No. FA9550-13-1-0106. [1] R. A. Street, J. E. Northrup, and B. S. Krusor, Phys. Rev. B 85 (2012) 205211. [2] J. E. Northrup, Radiation induced hydrogen rearrangement in poly(3-alkylthiophene), Applied Physics Express 6, 121601 (2013)                                     

4. Design and Fabrication of Damange Tolerant Hierarchical Materials - April 25, 2014  (Dr. Corie Cobb and David M. Johnson)

Hierarchical, architected materials have the potential to be transformational for a variety of applications, providing components which simultaneously offer the best performance attributes of ceramics, metals, and plastics. Hierarchical materials are materials which concurrently realize functional features on multiple length scales (sub-micron up to a millimeter level). This allows large void space in a material structure to be filled with load bearing members, adding compliance to the material without significantly increasing the density. Researchers have pursued hierarchical material structures for almost 20 years, leveraging inspiration from both nature and architecture, but few have shown success in synthetically re-creating these structures at multiple length scales. Prior attempts to experimentally fabricate hierarchical structures using 3D printing have only produced structures at large (mm) scales while micro-fabrication techniques using expensive custom equipment to produce sub-micron structures do not translate well to high-volume, low-cost production. Palo Alto Research Center (PARC) has invented a novel approach for manufacturing large area hierarchical materials based on electrohydrodynamic film patterning (EHD-FP) that mitigates both of the aforementioned shortcomings. EHD-FP enables the fabrication of hierarchical, architected materials with features at multiple length scales while creating a process which can easily scale up to quickly create large area patterned films at low cost. This talk focuses on evaluating a series of two-dimensional (2D) EHD-FP kagome and triangular truss structures made with ultraviolet (UV) curable polymers. Using the EHD-FP process, films with hierarchical spatial features can be easily and rapidly created with low viscosity UV cross-linked polymers. The EHD-FP process also has the unique ability to infuse these hierarchical features with aligned nanoparticles during the curing phase, providing nanoscale structure. Estimations of mechanical toughness and strength will be presented based on experimental tensile testing results. Experimental results will be compared with modeling expectations of improvements in material properties. A finite element model (FEM) in COMSOL®, a commercial simulation package, is used to further explore the impact of varying geometrical parameters and levels of hierarchy in the EHD-FP films in order to recommend an optimal subset of damage tolerant hierarchical materials structures. Our results provide confirmation of some of the underlying mechanics for hierarchical materials, allowing for a path towards transformative, large area hierarchical materials with superior functionality over bulk constituents.

 
 
 

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