A battery management system (BMS) controls charging and discharging of the battery while guaranteeing reliable and safe operation. The conventional method for preventing premature aging and catastrophic “thermal runaway” events involves expensive, heavy overdesign of the battery and a BMS that underutilizes the available battery capacity. This work aims to alleviate two major impediments to faster adoption of electric vehicles: high cost and slow charging rates of Li-ion batteries.
In this talk, we will show how an advanced BMS can potentially increase usable capacity and enhance charging rates by using model-based approaches. Rather than relying upon conventional current, voltage, and temperature measurements, our approach is radically different in that it uses estimations of immeasurable internal states to impose more appropriate constraints on battery operation, thus pushing the envelope on charging rates and battery utilization while maintaining battery safety and longevity. In particular, we achieve our objectives via four key innovations: (i) identifying states of physics-based Li-ion cell models that are relevant to aging and performance degradation; (ii) developing real-time estimation strategies for accurate estimation of battery state-of-charge and state-of-health; (iii) developing aging models that predict the impact of duty cycles on state-of-health; and (iv) developing optimal control techniques to modulate charge and discharge current to maximize performance while minimizing degradation. If successful, this technology is expected to reduce the overall system cost for batteries by 25%, and improving the charge-rate of batteries by a factor of two.

We have developed a battery state estimator based on a finite impulse response (FIR) filter. Simulation results indicate that the estimator gives accurate prediction and numerically-stable performance in the regression of filter coefficients and the open-circuit potential, which yields the battery state of charge. The estimator is also able to predict battery power capabilities. Comparison of the measured and predicted state of charge (SOC) and the charge and discharge power capabilities (state of power, SOP) of a Li-ion battery are provided. This new approach appears to be more flexible than previous battery state estimation approaches; we show that the FIR filter can capture the behavior of batteries governed by various physicochemical phenomena.

We envision that future battery systems for vehicle and grid energy storage resemble today&’s internal combustion engines with elaborative sensing, diagnostics, and control capabilities. In this talk we describe a novel concept to substantially boost battery power and energy without increasing its size or cost: active control of batteries (ACB). To meet power and energy demands without over-sizing the battery, ACB employs a combination of sensors, actuators and controllers. We shall show an ACB system enabled by internal actuators built in Li-ion cells during battery manufacturing as well as multi-terminals on the outside for controllers and control algorithm implementation. We have successfully demonstrated 600 W/kg and 140 Wh/kg at the ambient temperature of -30oC, which is a 10-fold improvement over conventional Li-ion batteries. Extensive performance data from both a lab-scale cell of 2.4Ah and a prototype battery of 26Ah will be shown and discussed.

Direct and fast sensory perceptions are critical to the survival of many species. Lithium-ion (Li-ion) batteries that have been plagued by catastrophic events that occur within milliseconds are no exception. For their survival, Li-ion cells need fast tracking, small, noninvasive and cost effective sensors. We will discuss a suite of noninvasive sensors that tracks the Li-ion cells&’ internal states in milliseconds and enables near real-time feedback control and optimization of battery health. We envision an intelligent Power Routing Device (iProud) that is designed to manage the battery in seconds and provide unique battery utilization and safety. We will provide a contextual perspective in the development of a battery management system (BMS) for satellites. Today, satellites use Li-ion batteries with safety and reliability as major goals, with two adverse outcomes: i) Poor energy density and ii) False sense of security. Direct sensory perception enabled by our sensors has the potential to improve energy density and safety.
Li-ion cells are complex “energy storage” and “power delivery” systems; however, they are not too complicated for today&’s technological tools to decipher and manage their intricacies. Surface-mounted temperature sensing has proven to be incongruent with the dynamics of the quickly changing and quirkily unpredictable internal thermal states. They provide, at best, a false sense of security; their unreliability in preventing fire is a familiar outcome. More recent advances, such as the fiber optics based internal temperature sensor that is being developed under the sponsorship of Department of Energy, Advanced Research Projects Agency-Energy (ARPA-E), are efforts in the right direction.1 This sensor is invasive, with restricted dimension. Its veracity will be measured by its ability to measure global changes within the cell while measuring a local temperature and its longevity in the harsh chemical environment of a Li-ion cell.
Our two noninvasive miniature sensors2 have quick response times and provide favorable implications on managing the battery. Among the first set of findings on them have been: i) the existence of multiple modes of heat sources inside a Li-ion cell; and ii) the capability of the sensors to track each mode separately and in near real time.3 Adapting these sensors into the iPROUD controls has the potential to improve reliability of the BMS and the safety of the battery.
References
1. Peter Kiesel and Ajay Raghavan, “SENSOR: Embedded Fiber-optic Sensing Systems for Advanced Battery Management,” Advanced Energy Technology Congress, November 12-15, 2013, San Diego, CA, USA.
2. R. Srinivasan, “Monitoring Dynamic Thermal Behavior of the Carbon Anode in a Lithium-ion Cell” J. Power Sources, 198 (2012) 351; US Patent Publication, 2012/0155507 A1; Patent No. US 7,554,294, June 30, 2009.
3. R. Srinivasan, “Improving lithium battery safety” SPIE Newsletter, http://spie.org/x93839.xml.

It is very important to estimate health/degradation of lithium ion batteries (LIBs) utilized in vehicles, airplanes, emergency power sources and so on. We have investigated a method to evaluate states of rechargeable cells such as the LIBs at any time in situ. We report a novel and fundamental method to judge the states of the LIBs using the capacitance and the voltage of the cells that were estimated from the real-time currents and voltage characteristics of the cells. It is well known that the degradation is mainly caused by some undesirable composite materials built on the electrode surfaces due to severe conditions such as over-charge/over-discharge and charge/discharge at high temperature, and that the cell with such a failure cannot play the initial performance. It is thought that the effective area of the electrodes decreases in the damaged cell and the capacitance, that is, induced charge (Q) per voltage (V), should decrease with the degradation. As the battery is one of active devices, we measured the differential capacitance (dQ/dV or delta Q/ delta V) that is equal to currents (I) divided by differential voltages (dV/dt) calculated from the current and the voltage characteristics of the cell during the charging/discharging. Degradation for commercial LIBs with different capabilities has been investigated using this novel method. The differential capacitance in some specific voltage range for the LIBs was approximately proportional to the state of the degradation of the cell. Therefore, it is concluded that the novel method is very useful to judge the state of the LIBs.

Internal faults in batteries occur infrequently, but have major safety and reliability consequences. These faults are often local in behavior and difficult to detect with global measurements such as voltage, current and temperature. Battelle, together with the University of Akron, is developing a novel technique to monitor batteries continuously during operation. An optical sensor will detect changes in light propagating through each cell, well before local shorts occur, providing early warning to the battery management system.
One mechanism for the initiation of these faults is the growth of metal dendrites from one electrode to another, resulting in an internal short circuit. Other mechanisms include stray metal inclusions within the cell, breakdown of materials, and other side reactions.
In Battelle&’s system, the space between the electrodes is converted to an optical waveguide that transmits light throughout the space. The waveguide can be formed from a modified battery separator or a gel electrolyte. Thus, standard cell components and geometry are expected to be used, and light sources and detectors are added to the system. Changes in light scattering as dendrites grow or shorting currents develop are measured by an optical detector in real time without interrupting normal operation. The operating battery can be monitored continuously for impending faults, providing early warning to the control system before hazardous conditions occur. The method is expected to be applicable to a wide class of battery chemistries. To control costs, the design leverages cost reductions that have already occurred in the telecommunications and medical device industries. The fault sensor is designed to provide essential information to the battery management system for diagnosing and controlling thermal runaway and faults. Conditions are monitored locally at the cell level, and with adequate warning, the BMS has sufficient time to act.
Current work has focused on selecting waveguide materials that meet battery and optical requirements, designing devices for sufficient light transmission, detecting artificial dendrites in a fixture and real dendrites in operating batteries. A simple mechanical fixture is used to demonstrate the principle and will show sufficient scattering to detect dendrites with characteristic dimensions of the order of mm. Dendrites have been grown in single cells, which serve as the platform for sensor evaluation in operating batteries. Implications for design in operating commercial scale batteries will be discussed.

Rational nanostructure design has been a promising route to address critical materials issues for enabling next-generation high capacity lithium ion batteries for portable electronics, vehicle electrification and grid-scale storage. However, synthesis of functional nanostructures often involves expensive starting materials and elaborate processing, which present a challenge for successful implementation in low-cost applications. In seeking a sustainable and cost-effective route to prepare nanostructured battery electrode materials, we are inspired by the diversity of natural materials. Here, we show that crab shells with the unique Bouligand structure consisting of highly mineralized chitin-protein fibers can be used as biotemplates to fabricate hollow carbon nanofibers; these fibers can then be used to encapsulate sulfur and silicon to form cathodes and anodes for Li-ion batteries. The resulting nanostructured electrodes show high specific capacities (1230 mAh/g for sulfur and 3060 mAh/g for silicon) and excellent cycling performance (up to 200 cycles with 60% and 95% capacity retention, respectively). Since crab shells are readily available due to the 0.5 million tons produced annually as a by-product of crab consumption, their use as a sustainable and low-cost nanotemplate represents an exciting direction for nanostructured battery materials.

With the goal of obtaining metallic metals with elongated pores and a high specific surface area for energy or functional applications, we developed a new freeze-casting method using metal oxide precrusor particles which are reduced and sintered to metal in a subsequent step. During directional freezing of a slurry of nanometric copper oxide or nickel oxide suspended in water, the particles accumulate between the ice dendrites. Upon removal of the ice by freeze drying, the dendrites become elongated pores surrounded by a green scaffold of the oxide particles. When sintering in a reducing atmosphere, the oxide particles are reduced to metal (Cu or Ni) and sintered to form a metallic scaffold surrounding the elongated pores created by the ice dendrites. Here, we report on the microstructure of these freeze-cast, reduced and sintered Cu and Ni foams and discuss their potential for use as electrodes in lithium battery and dye-sensitized solar cell.

Lithium-ion batteries are characterized by their high-energy storage density and competitive cost. However, their applications are limited because of strong self-heating effects. The battery packs utilize multiple Li-ion cells, which are positioned close together to provide high electric power. This arrangement leads to increased temperatures that degrade the battery life. Prior work on thermal issues in high-power density battery packs has demonstrated that a passive thermal management system, which uses phase-change materials (PCM), is a promising approach. The PCM thermal management uses the latent heat stored in the material as its phase changes over a small temperature range. However, PCMs typically have low thermal conductivity. They store heat from the batteries rather than transfer it outside. In this talk we describe a possibility of using graphene and few-layer graphene (FLG) as fillers for PCM for increasing PCM&’s thermal conductivity while preserving its ability for the latent heat storage. Graphene is known to have extremely high thermal conductivity [1]. Graphene flakes couple well with the variety of matrix materials [2] thus providing an opportunity for synthesis of composites with improved thermal properties. I this work we demonstrated experimentally that incorporation of graphene to the hydrocarbon-based PCM allows one to increase its thermal conductivity while preserving its latent heat storage ability [3]. As a matrix we used IGI-1260 paraffin with the high latent heat of fusion (200 - 250 kJ/kg) and melting point of ~70 oC. It consists of C34-C35 hydrocarbons, which are mainly composed of n-alkanes. Graphene fillers were produced using the inexpensive liquid phase exfoliation technique. Raman spectroscopy and microscopy studies indicated that graphene flakes attach well to hydrocarbons in the resulting composites. The thermal measurements were conducted with the “laser flash” system. It was found that the thermal conductivity of pristine paraffin was ~0.25 W/mK. The thermal conductivity of the hybrid graphene-PCM reached ~15 W/mK at room temperature with the small 1 wt. % loading fraction of graphene. This is a significant increase by a factor of 60. The highest value achieved at 20 wt. % loading was ~45 W/mK, which is more than a two order magnitude of enhancement. In addition to thermal measurements we conducted the temperature rise tests with the Li-ion batteries proving that the temperature rise in the battery packs with graphene enhanced PCM is substantially less than in the conventionally cooled batteries [3]. The described combined heat storage - heat conduction approach can lead to a transformative change in thermal management of high-power density battery packs. [1] A.A. Balandin, Nature Materials, 10, 569 (2011); [2] K.M.F. Shahil and A.A. Balandin, Nano Letters, 12, 861 (2012); [3] P. Goli, S. Legedza, A. Dhar, R. Salgado, J. Renteria and A.A. Balandin, Journal of Power Sources, 248, 37 (2014).

Differential Scanning Calorimetry (DSC) and Thermogravimetric Analysis (TGA) are commonly used thermal analysis techniques to study the battery materials (i.e., cathode, anode, electrolyte, and separator) individually and in some cases in combination with each other. These methods typically required a lengthy sample preparation step. A coin cell must be made and then cycled as appropriate for the testing requirements. The cells must then be opened inside a glove box and the battery material harvested, loaded into a DSC crucible, crimp-all in a repeatable manner.
A new method for characterizing coin cells directly has been developed based on the principal of DSC for both scanning and isothermal calorimetry. The NETZSCH&’s modular MMC Nexus 274 instrument platform was expanded to include a calorimeter capable of running commonly used coin cells resulting in a method which is inherently easier and more reproducible than the traditional DSC approach. The calorimeter can also be used to measure the heats associated with charging and discharging of the sample with a simple connection to an external battery analyzer.

Polyethylene (PE) membranes having various porosities are required for use as microfilters and separators in lithium ion batteries. Phthalates, whose mixtures with PE exhibit upper critical solution temperature (UCST)-type phase behavior, are used as diluents for the fabrication of PE membranes. However, the use of phthalates as diluents is limited because of their toxicity. Triethylolpropane tris(2-ethylhexanoate) (TEPTEH) was synthesized for use as a new nontoxic diluent for the fabrication of the PE membranes. The PE/TEPTEH blends showed UCST-type phase behavior and their phase separation temperatures decreased with increasing PE content. TEPTEH and paraffin oil (PO) mixtures were also examined as diluents to control the porosity of PE separators. PE//(TEPTEH/PO) blends also exhibited UCST-type phase behavior when TEPTEH/PO diluent mixtures contained greater than or equal to 70 wt% of TEPTEH, and their phase separation temperatures decreased with increasing PO content in the diluent mixture with a fixed PE content. The average size of pores and the porosity of the membrane increased with increasing TEPTEH content in the diluent mixture. The porosity of the PE separator fabricated using a lab-scale twin extruder equipped with biaxial stretching machines also increased with increasing TEPTEH content in the diluent mixture. As a result, when the air permeability of the separator prepared from the PE/PO blend was compared with that prepared from PE/TEPTEH blend, the latter was about 2.5 times higher than the former.

Cationic transference number and ionic conductivity of an electrolyte are among the key parameters which regulate battery performance significantly. In the present work, we introduce a noval concept of using porous organic frameworks as an electrolyte for lithium ion batteries. As an expected outcome of this work, the conductivity is improved significantly due to the inherent porosity of the frameworks, which provides a smooth passage for the solvent to flow. The rigid three dimensional frameworks, function as an anionic part of the electrolyte, reduce anionic transference number almost to zero; consequently, cationic transference number increases and approaches to unity. In addition, by virtue of its synthesis procedure, the electrolyte displays excellent sustainability at high temperatures, which is vital for battery safety as well as for enhancing the performance and longevity of the battery.

In order for energy storage to play a key role in the world's transition to a more reliable and sustainable energy infrastructure, the scientific community must succeed in n higher performing and lower cost battery systems. Materials research has driven significant advances in cell chemistries and architectures of late, but these efforts alone will not suffice. Fundamental design, management, and control challenges can have an equal or greater impact as chemistry on system-level performance and cost, and present a critical barrier to rapid technology improvement. This talk will address the scientific and technological grand challenges of battery management, and will highlight opportunities for breakthrough research and development in this field.

The primary task of a vehicle power management strategy (PMS) is determining the power flow between hybrid powertrain components to minimize fuel consumption and emissions.
This work describes the idea of incorporating mechanical information, bulk mechanical stress, into the design of a PMS, since high mechanical stress can cause capacity fade and power loss. The bulk stress on the battery cell corresponds to the composite swelling and contraction of the anode and cathode layers during charging due to the Lithium intercalation. Repeated expansion and contraction causes particle cracking or becoming electrically disconnected from the current collector leading to power capability loss.
To characterize the relationship among bulk stress, battery state-of-charge (SOC) and operating temperature, carefully designed experiments were conducted for Lithium-Nickel-Manganese-Cobalt-Oxide/Graphite prismatic cells. Specifically, the volumetric change or bulk mechanical stress as a function of SOC is first measured by using load sensors. A nonlinear map between SOC and stress is then constructed and used as a penalty function to indirectly account for battery performance degradation in the optimal power management problem.
The optimal power management problem is then solved by using Dynamic Programming (DP), which a powerful numerical tool to determine optimal control policies or trajectories explicitly using the Bellman&’s optimality principle. By varying the penalty between fuel economy and battery degradation, indirectly indicated by the cumulative bulk mechanical stress and Ah-processed, DP results show that the battery cumulative bulk mechanical stress can be significantly reduced at a small expense of fuel economy.

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.

The swelling of a prismatic 5Ah lithium-ion cell with a nickel/manganese/cobalt-oxide cathode was investigated. The swelling is due to lithium intercalation and thermal expansion. The swelling was measured as a function of the state of charge, the C-rate, and temperature using high-precision displacement sensors. The cell is enclosed in an aluminum casing. The location of the electrodes in the casing is known. The results show that the deformation of the casing can be correlated to electrochemical and mechanical transformations at cell level. Thermal expansion and lithium intercalation were both found to cause significant swelling. At low C-rates, the thermal expansion is negligible, and the dilation of the electrode sandwich is the main reason for the swelling. At high C-rates, the thermal expansion is dominant. The analysis of the derivative of the swelling with respect to the cell capacity showed that the swelling is highly correlated with the phase transition induced by lithium intercalation. The results also show that the swelling and the phase transitions have a strong dependence on the C-rate even though the potential changes minimally with the C-rate. Thus, the swelling provides a more sensitive gauge for characterizing the dynamic behavior than its potential, and thus swelling measurements can be quite useful in the design of battery packs to improve their stability and to predict their lifespan.

It is well known that degradation due to intercalation of ions in the electrode material is a key consideration in the design and operation of a Lithium Ion battery. Intercalation effects during charge and discharge of a battery cause periodic stress and strain of the electrode materials that can ultimately lead to fatigue resulting in capacity loss and potential battery failure. This process is not monitored directly based on measurements performed on cells today and few studies to date have quantified these effects and their relationship with cell performance. This work will focus on several techniques to quantify battery swelling with the ultimate goals of physical understanding of swelling behavior and development of in-situ monitoring techniques for onboard vehicle applications. Leveraging a 5 Ah cell with a nickel/manganese/cobalt-oxide cathode (Sanyo, Japan) used by Ford in their Fusion HEV battery pack, testing has been performed to spatially characterize cell expansion using Moire interferometry. Moire interferometry is a technique commonly used to monitor strain or displacement where two patterns of fine lines (gratings) are overlaid on the surface and one of the patterns is displaced or rotated relative to the fixed grating. This technique allows for measurement of swelling across the surface of the cell throughout the entire charge and discharge process. This information will be used to understand the effects of cell construction, pack layout, SOC and other operational factors on the expansion. Previous work by ourselves and our collaborators from the University of Michigan have characterized the free expansion of these cells to be approximately 100-125 microns (1% of the total thickness) at the center point of the cell but little is understood to date on how that measurement varies across the face of the cell and how cell packaging as part of the pack affects this value. Mapping of the cell swelling during cycling is an important step in the development of expansion sensors for the monitoring of cell swelling during battery operation. GE is developing ultra-thin expansion and temperature sensors capable of being integrated into the pack with a small form factor. Key outcomes of this work will lead to understanding of sensor placement, sensor requirement development and data to validate physics based models of cell expansion.

As mobile phones, laptops, and other devices become more universally prevalent, high capacity lithium ion batteries with even better cycling efficiency will be in greater demand. It is well established in the scientific community that intermetallic anodes show increased capacity while maintaining a high coulombic efficiency, however they suffer from large volumetric changes during charge cycling, causing degradation of the anode through cracking and delamination from the current collector. Being able to detect this evolved stress in-situ would greatly aid researchers in understanding how changing material composition affects anode life and utility. Piezoresistive materials are substances that change in electrical resistance in response to applied pressure. They are commonly used as pressure sensors in microelectronic systems. Our goal is to develop an in-situ piezoresistive sensor for detecting the stress from anodic volumetric expansion by a measureable resistance change.
In this presentation, we will demonstrate that by distributing nickel microparticles within a mixture of carboxymethylcellulose (CMC) and styrene-butadiene-rubber (SBR), a piezoresistive material can be made that drops in resistance when strain is induced by an external force. Furthermore we will show how we can take advantage of the ferromagnetic nature of the nickel particles, to tune the sensitivity of the sensor.
The resistance drop through a sample as a function of applied strain is demonstrated with an in-house testing apparatus. This data is directly correlated to the stress vs. strain curve generated for the respective samples using a material testing system (MTS). Therefore this allows us to relate the stress to a measurable resistance change. As a proof of concept, this methodology will be applied to an in-situ electrochemical half-cell setup. Using various compositions of nickel/tin planar anodes, the evolved stress with lithiation can be detected with the abovementioned piezoresistive material.
We will also exhibit that anisotropic alignment of the nickel microparticles induced by a magnetic field leads to a larger change in the resistance with applied stress, and a faster response time in resistance change; that is, a piezoresistive sensor with higher sensitivity and a lower detection limit can be obtained. Our results demonstrate the feasibility of using nickel microparticle based piezoresistive sensors for accurately and quickly determining the in-situ stress generated in intermetallic anodes.

Lithium (Li)-ion batteries today present attractive options for high-performance energy storage in a number of cutting-edge applications. 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 presently significantly limited by the use of available externally monitored parameters such as voltage, current, and temperature. Consequently, battery packs are often designed with multiple, redundant protection layers and used conservatively by the BMS to ensure safety and reasonable battery life. 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, electromagnetic interference, and can measure multiple parameters with high sensitivity, such as strain, temperature, pressure, and chemical composition in multiplexed configurations. With regard to chemical composition, FO sensors have been demonstrated to accurately and specifically resolve a number of liquid 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 tested FO chemical sensing schemes will be presented and compared, both during normal cycling conditions and under simulated abuse cycles/aged conditions. These results will be bench-marked with other published data in the literature from controlled lab studies on side reactions in Li-ion cells. The potential of such side-reaction monitoring capabilities for significantly improved SOH estimation algorithms will be highlighted. Finally, the use of such embedded side-reaction FO chemical sensors in commercial battery packs to improve safe, optimal utilization of true battery capacity by the BMS will be discussed.

Applications such as plug-in hybrid vehicles, hybrid vehicles, and electricity grid have need for sustained fast charge of batteries without degradation over thousands of cycles. This need introduces challenges both for the design of the batteries and for their control while in use. A123 has developed battery designs and battery control strategies that have demonstrated fast charge at recharge rates up to 5C (corresponding to recharge times less than 10 minutes) with less than 10% capacity fade after 2000 cycles.
There are several mechanisms that contribute to capacity fade in lithium-ion batteries. They can be grouped generally into three categories, loss of cyclable lithium, loss of accessible active material, and increase in resistance (which causes loss of accessible lithium). The extent to which a particular mechanism dominates the degradation can depend on chemistry, cell construction, and cycling conditions. In this presentation we will discuss graphical voltage-based techniques for state of health monitoring developed at A123 to quantify the extent to which each category has contributed to capacity fade in a particular battery. These techniques have been very useful in quantifying, for example, disconnection of anode active material.
Understanding of the failure mechanism yields insight into control strategies to mitigate the failure mechanism. In addition, control algorithms must be robust, protecting the battery over a wide range of possible usage conditions in the field. In this presentation, we will discuss robust control strategies for fast charge of lithium-ion batteries.