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Research Papers

# Innovating Safe Lithium-Ion Batteries Through Basic to Applied ResearchPUBLIC ACCESS

[+] Author and Article Information
Corey T. Love

Chemistry Division,
U.S. Naval Research Laboratory,
4555 Overlook Avenue, SW,
Washington, DC 20375
e-mail: corey.love@nrl.navy.mil

Christopher Buesser

EXCET, Inc.,
6225 Brandon Avenue #360,
Springfield, VA 22150
e-mail: Christopher.buesser.ctr@nrl.navy.mil

Michelle D. Johannes

Materials Science and Technology Division,
U.S. Naval Research Laboratory,
4555 Overlook Avenue, SW,
Washington, DC 20375
e-mail: michelle.johannes@nrl.navy.mil

Karen E. Swider-Lyons

Chemistry Division,
U.S. Naval Research Laboratory,
4555 Overlook Avenue, SW,
Washington, DC 20375
e-mail: karen.lyons@nrl.navy.mil

1Corresponding author.

Manuscript received June 2, 2017; final manuscript received August 21, 2017; published online October 25, 2017. Assoc. Editor: Partha P. Mukherjee.The United States Government retains, and by accepting the article for publication, the publisher acknowledges that the United States Government retains, a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this work, or allow others to do so, for United States government purposes.

J. Electrochem. En. Conv. Stor. 15(1), 011006 (Oct 25, 2017) (7 pages) Paper No: JEECS-17-1064; doi: 10.1115/1.4038075 History: Received June 02, 2017; Revised August 21, 2017

## Abstract

This paper for inclusion in the special issue provides a brief synopsis of lithium-ion battery safety research efforts at the Naval Research Laboratory (NRL) and presents the viewpoint that lithium-ion battery safety is a growing research area for both academic and applied researchers. We quantify how the number of lithium-ion battery research efforts worldwide has plateaued while publications associated with the safety aspect of lithium-ion batteries are on a rapid incline. The safety challenge creates a unique research opportunity to not only understand basic phenomena but also enhance existing fielded system through advanced controls and prognostics. As the number of lithium-ion battery safety research contributions climbs, significant advancements will come in the area of modeling across multiple time and length scales. Additionally, the utility of in situ and in operando techniques, several performed by the NRL and our collaborators, will feed the data necessary to validate these models. Lithium-ion battery innovations are no longer tied to performance metrics alone, but are increasingly dependent on safety research to unlock their full potential. There is much work to be done.

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## Introduction

As the research community pushes for battery technologies “beyond lithium-ion” [1,2] and the commercial sector anxiously awaits the “battery of tomorrow” [3], it is important to note that traditional lithium-ion battery chemistries are here, now! But, along with high performance offered by lithium-ion batteries come safety challenges. Safety concerns must be addressed and understood now to support safe implementation and use. The best approach to attack the safety issue is to combat the problem across the full spectrum of basic to applied research. Within the U.S. Navy for instance, the lithium-ion battery safety problem is confronted by coordinated research efforts across the two domains within the U.S. Naval Research Enterprise: early basic science and technology research and applied system-level research and development (R&D). Largely, this cross-domain coordination happens organically and is the result of dedicated individuals: department directors, program managers, technical agents, technical warrant holders, and front-end researchers, aligning their individual duties to achieve combined success. A goal of the U.S. Naval Research Laboratory (NRL) is to support the greater effort; fielding safe, reliable lithium battery systems through basic to early-applied research (science and technology) where the work products are often new insights and understanding of battery phenomena through novel characterization techniques which feed into larger-scale systems-level efforts (R&D). This paper for inclusion in the special issue “Emerging Investigators in Electrochemical Energy Conversion and Storage 2017” provides a brief synopsis of battery safety research efforts at NRL and presents the viewpoint, supported in part by data analytics, that lithium-ion battery safety research is a worthy and necessary pursuit for academic and applied researchers.

###### State of Lithium-Ion Battery Research.

Lithium-ion battery research has gained enough traction over the last two decades that most academic conferences will feature symposia dedicated to their discussion. Attendees to academic research conferences within the past few years have likely seen symposia dedicated to all areas of lithium-ion battery research. These conferences extend far beyond the expected venues, The Electrochemical Society and International Society of Electrochemistry, to include the American Chemical Society, the American Ceramic Society, American Institute of Chemical Engineers, American Society of Mechanical Engineers, ASM International, the Minerals, Metals and Materials Society, Gordon Research Conference, International Air Transport Association, the Institute of Electrical and Electronics Engineers, the Materials Research Society, the Society of Automotive Engineers, and even the American Crystallographic Association. From a purely subjective point of view, one would be hard-pressed to deny the massive growth of this field of research across multiple academic disciplines. Jain and co-workers describe the “scientific richness of underlying physical processes” of lithium-ion batteries as a driver for multidisciplinary research efforts across the globe [4]. Progress has been rapid in the 29 year history of lithium-ion batteries, from initial experimental discoveries by Goodenough, Thackerey, and Whittingham to the present operation of multiple Tier-1 lithium-ion battery manufacturers.

Although the field of lithium-ion battery research has enjoyed rapid growth over the past ten years, Oleg et al. suggest, it has recently entered into an era called the “plateau of productivity” [2]. Their analysis of published papers on lithium-ion and beyond lithium-ion technologies provides a “hype cycle” which progresses through five stages: (1) the innovation trigger, (2) the peak of inflated expectations, (3) the trough of disillusionment, (4) the slope of enlightenment and the current state of lithium-ion battery research, and (5) the plateau of productivity. The plateau signals a shift from basic science to applied R&D. With the ground-level research of understanding fundamental processes now behind us, we are no longer continuously on the edge of understanding.

Our own data analysis shows a similar trend. Figure 1 shows the total literature work product (published papers, meeting abstracts, etc.) according to data provided by Web of Knowledge™ spanning 2007 through 2016. Applying a simple exponential fit ($y=ea·x+b$), we see the exponential factor is approximately a = 0.29. Oleg et al. found the exponential factor to be a = 0.33 over the range 2009 to 2014 [2]. It is noted that in this data set one paper may be mapped to multiple countries, inflating overall numbers, but having a negligible effect on the overall trend. An examination of publications beyond 2014 supports the notion of the research plateau where a better fit is provided by a leveling fourth degree polynomial expression. This plateau of raw publication numbers supports Oleg’s hypothesis that the hype cycle of lithium-ion batteries is entering a period of incremental improvements where the focus is on materials scale-up and advanced manufacturing processes. Figure 1 also breaks down the country of origin of the published work products, where the top five volume contributing nations are China, U.S., South Korea, Germany, and Japan.

###### State of Lithium-Ion Battery Safety Research.

With manufacturers and scientists searching for performance gains, safety is becoming the barrier to mainstream acceptance. With new and more commercially relevant battery and material failures becoming hot topics in mainstream news (a list of such failures is contained in Ref. [5]), research into safety is sure to be encouraged by integrators and manufacturers who do not wish to garner negative publicity. To encourage implementation and large-scale operation of lithium-ion batteries, both regulators and consumers need to be convinced that safety has been taken into account. Figure 2 illustrates the increasing trend for total work product for lithium-ion battery research with “safety” used as an additional keyword search field. The volume of safety publications is a small fraction of the total papers which mostly report on performance and reliability concerns. The large safety growth factor is a = 0.33 compared to the overall lithium-ion research (a = 0.29) which is a positive sign toward continued adaptation of lithium-ion battery technology. The output observed between 2011 and 2012 appears to be rather stagnant, but this may be due to increased individual efforts by the U.S. and Japan in 2011, contributing to a large jump in cumulative papers that makes 2011 an outlier year. Inspection of that year’s publications shows overlap in U.S. and Japanese authors due to collaborations between Argonne National Lab and Japanese research institutions on the development of Li4Ti5O12 anode materials, known to improve safety based on their inherent non-SEI forming working voltage. A list of notable battery failures and fires is given in Ref. [5].

In 2012, Japanese and U.S. contributions in lithium-ion battery safety retreated to percentages consistent with previous years. The percentage of safety-related papers with global output in Fig. 3 shows 2011 is clearly an outlier, while the positive trends of lithium-ion safety research (especially in the U.S.) are evident. The leveling of total battery papers in the U.S. is seen, while the percentage related to safety increases from approximately 3% in 2012 and 2013 to 4% in 2014, 5% in 2015, and 6% in 2016, contributing to the increased exponential factor described previously. In 2012, a significant investment from the ARPA-E Advanced Management and Protection of Energy Storage Devices program could have been the catalyst for the increased safety productivity seen in 2014.

A projection for 2017 safety papers to reach 7% of total output is not unlikely, especially due to the recent breakthroughs and disclosures of potential safety-improving materials by Goodenough and co-workers [6].

## The Pursuit of Safe Batteries

At the NRL, we align battery safety research efforts to address the fundamental contributors to battery fires: oxygen, heat, and fuel. Lithium-ion cells contain combustible fuel in the form of carbon-containing electrodes, flammable electrolyte solvents, and packaging materials. Eliminating fuel from the equation requires a full paradigm shift to solid state electrolytes [6] or dendrite-free aqueous systems [7]. However, there are safety gains still to be made to mitigate the release of oxygen and minimize heat generation through new characterization and prediction techniques which can be used to inform novel design and control methodologies. To make existing batteries safer requires the alignment of theory with in situ and in operando techniques.

###### Oxygen Loss as the Origin of Instability.

Loss of oxygen gas from metal-oxide battery cathodes has been identified as a failure mechanism to batteries, particularly when they are overcharged or overheated. Figure 4 illustrates the large heat release due to oxygen removal from charged and overcharged Li1−xNi1/3Co1/3Mn1/3O2 cathode materials as measured by dynamic scanning calorimetry [8]. When the manganese component is substituted with the higher oxygen pinning metal, aluminum, there is a significant reduction in heat generation and oxygen loss.

We have utilized computational methods to better understand the oxygen liberation and developed a computational method to screen new battery materials for such instability toward O2 release. First, the electronic ground state of a material is calculated using density functional theory. Then, the partial density of states (PDOS), which shows the energy distribution of electrons with a breakdown of their site-localization, is studied to determine the propensity for electrons to be extracted from metal sites versus oxygen sites as the material loses lithium during charging. Figure 5 shows a comparison of the calculated PDOS in experimentally stable LiFePO4 and very unstable Li2CuO2 cathode materials [9,10]. In lithium iron phosphate, LiFePO4, the metal PDOS dominates the highest filled energy states at full discharge, signaling that electrons will be pulled from metal (stable) states. This indicates a typical, stable redox reaction, in this case Fe2+/3+. However, for lithium copper oxide, Li2CuO2, the oxygen PDOS states are dominant at the top of the filled spectrum at full discharge and in the empty states at partial delithiation. This higher PDOS for the oxygen signals a transition from stable O2− ions to peroxide (O22−) and then, generally, O2 gas via oxidation. The excellent correlation between calculated PDOS spectra and observed instabilities allows computational stability prediction as a function of state-of-charge (SOC).

###### Watching Dendrites Grow.

Heat generation results when a rush of current is passed across a small cross-sectional area, often the result of a lithium dendrite short in a cell. Dendrite-induced short-circuits have been identified as a factor in several notable lithium-ion battery failures listed in Ref. [5]. Model predictions have shown a temperature-dependence toward the formation and growth mechanisms of dendrites below about −10 °C, due to mass transport and kinetic limitations. Through the use of an in situ optical microscopy electrochemical cell, we have actually observed and compared not only the formation and growth of lithium electrodeposits at ambient temperature (20 °C, Fig. 6(a)) and below (5 °C, Fig. 6(b) and −10 °C, Fig. 6(c)) but also observed a strict temperature-dependence to the dendrite morphology [11]. We determined experimentally that the temperature most conducive to short circuits is approximately 5 °C, where rapid dendrite initiation, fast growth rate, and a morphology with robust mechanical properties all combine to produce the quickest cell failure (Fig. 6). At −10 °C, lithium metal deposits nonuniformly as mushroom-shaped growths are formed which are less favorable to forming shorts. Lithium was observed to deposit more uniformly at 20 °C, beginning as plating processes.

###### Electrothermomechanical Coupling.

Understanding the formation, growth, and morphology of lithium dendrites is important to the development of safer systems. However, one must also consider the effects of the component responsible for preventing short circuits, the polymer separator. As dendrite structure–property changes occur with temperature, so too do the viscoelastic properties of polymer separators which ultimately affect their physical modes of interaction. The electrothermomechanical coupling of dendrite/separator interactions is the focus of several advanced modeling efforts [13]. The thermomechanical nature of commercial polymer separators is shown in Fig. 7 where several mechanical transitions are induced by varying temperature under static mechanical load [14].

Knowledge of the local temperature-dependent mechanical properties of the separator can inform the battery designer of potential failure modes that lead to internal short circuit. An awareness of the potential lithium dendrite morphologies at various anticipated operating conditions, and the interplay between temperature-dependent dendrite morphologies and the temperature-dependent polymer physical properties should guide separator materials selection. Specifically, the ductile-to-brittle transition temperature plays a key role in the ability of the separator to withstand an imposing mechanical load from dense blunt-shaped dendrites, while ductility and resistance to puncture and penetration are critical at elevated temperatures where the polymers are prone to mechanical creep. Figure 6(e) shows notionally the anticipated temperature-dependent failure modes from dendrite/separator interactions. Only limited examples of dendrite morphologies have been shown where failure modes may exist: mixed penetration from lithium particulates, puncture from high aspect ratio needlelike dendrites, and brittle fracture at temperatures below the separator Tg where dense blunt dendrites impose a compressive load.

###### Diagnosing Damaged and Hazardous Cells.

Innovation and design of engineering controls are also effective paths toward battery safety. Our group has been working to develop diagnostics to monitor battery safety based upon impedance spectroscopy. While this characterization technique is not new to batteries, we have identified a novel methodology for targeted data collection to monitor battery state-of-health (SOH). A first paper in 2012 identified a single impedance frequency, nominally somewhere between 100 and 500 Hz, applied independently of battery state-of-charge to detect abuse due to cell overcharge [15]. The imaginary component of the complex impedance was found to be a very important measuring stick for battery stability. A single impedance frequency probes the efficiency of the electrochemical processes at the anode/SEI interface where abuse due to overcharge, lithium plating, and dendrite formation and growth are known to manifest. By consistently monitoring the processes at this interface, we can identify when the anode SEI has deteriorated or changed irreversibly, suggesting some degree of abuse or degradation. For overcharge abuse, the imaginary impedance increases (becomes less negative) due to the accumulation of lithium-ion in the anode SEI layer. This layer should not store charge and therefore should not have varying capacitive features. Figure 8 shows the means to identify the “SOH frequency range” by overlaying full impedance spectra from 0% to 100% SOC [16]. The SOH frequency range shows minimal changes in impedance response during normal battery operation. This approach, while empirical, proves meaningful state-of-health information for tracking irreversible changes in cell impedance. The impedance response can then be mapped to identify regions exhibiting normal or abnormal impedance responses. Figure 9 shows the SOH map produced from monitoring a commercial lithium-ion cell at 500 Hz. Operating within the normal upper voltage limit of 4.2 V yields an impedance value within the narrow “healthy” region. As the cell is overcharged to 4.6, 4.8, and 5.0 V, the impedance deviates from the healthy region, alerting the user that the battery is “damaged.” The impedance change occurs as the cathode loses oxygen and/or lithium dendrites are formed, changing the cell capacitance and resistance. As the cell is repeatedly overcharged, the impedance values increase to an unsafe level, making the cell susceptible to overheating and decomposition of the electrode and electrolyte materials. Cells which have been exposed to overcharge abuse fall outside of this safe region, identifying to the user of a detected fault. This methodology has proven useful in the diagnosis of overcharge abuse of a single cell in a 4S pack configuration [16]. Making use of the fact that impedance is additive in series, we demonstrated the ability of the single-point probe to root out overcharge abuse when the methodology was applied over the 4S pack and in the absence of single cell monitoring. The intrinsic link between impedance and temperature was further exploited by two follow-on efforts linking temperature changes within the cell to the imaginary impedance response at the identified single-point frequency for single cells under extended temperature regimes [17] and for the 4S1P pack configurations [18]. In fact, this approach performed well when tested against similar reported techniques by a third party research group [19].

## Conclusion

Naval Research Laboratory has made progress toward understanding the instabilities in lithium-ion batteries, which if uncontrolled, can lead to battery failures and fires. Our in situ optical cell successfully showed that common lithium-ion battery chemistries are vulnerable to lithium dendrite formation at the low temperature of 5 °C. We also have a theoretical tool to predict O2 loss and instability of battery cathode materials. These instabilities and other decomposition and degradation mechanisms are probed practically in a simple impedance method which can be used in real-time as part of a battery management system to monitor the state-of-health of lithium-ion batteries. Even though lithium-ion battery research efforts have plateaued, there are still sizable advancements to be made on the safety front. The safety challenge creates a unique research opportunity to not only understand basic phenomena but apply that knowledge directly to enable the safe implementation of existing fielded system through advanced controls and prognostics. As the number of lithium-ion battery safety research contributions climbs, no doubt significant advancements will come in the area of modeling across multiple time and length scales. Additionally, the utility of in situ and in operando techniques will feed the data necessary to validate these models. Lithium-ion battery innovations are not tied to performance metrics alone anymore. Safety research will unlock the full potential of lithium-ion batteries. There is much work to be done.

## Acknowledgements

C.T.L. acknowledges the support from many co-workers, co-authors, and collaborators. C.T.L. dedicates this paper to the memory of Dr. Barry Spargo for his mentorship and help navigating a federal career and Professor Dave Ramaker for his valuable insights and always positive attitude.

## Funding Data

• Office of Naval Research (ONR).

## References

Choi, J. W. , and Aurbach, D. , 2016, “ Promise and Reality of Post-Lithium-Ion Batteries With High Energy Densities,” Nat. Rev. Mater., 1, p. 16013.
Sapunkov, O., Pande, V., Khetan, A., Choomwattana, C., and Viswanathan, V., 2015, “ Quantifying the Promise of ‘Beyond’ Li–Ion Batteries,” Transl. Mater. Res., 2(4), p. 045002.
Urry, A. , 2017, “ Inside the Race to Build the Battery of Tomorrow,” WIRED, Boone, IA, accessed Feb. 22, 2017,
Shah, K. , Balsara, N. , Banerjee, S. , Chintapalli, M. , Cocco, A. P. , Chiu, W. K. S. , Lahiri, I. , Martha, S. , Mistry, A. , Mukherjee, P. P. , Ramadesigan, V. , Sharma, C. S. , Subramanian, V. R. , Mitra, S. , and Jain, A. , 2017, “ State of the Art and Future Research Needs for Multiscale Analysis of Li-Ion Cells,” ASME J. Electrochem. Energy Convers. Storage, 14(2), p. 020801.
Abada, S. , Marbair, G. , Lecocq, A. , Petit, M. , Sauvant-Moynot, V. , and Huet, F. , 2016, “ Safety Focused Modeling of Lithium-Ion Batteries: A Review,” J. Power Sources, 306, pp. 178–192.
Braga, M. H. , Grundish, N. S. , Murchison, A. J. , and Goodenough, J. B. , 2017, “ Alternative Strategy for a Safe Rechargeable Battery,” Energy Environ. Sci., 10(1), pp. 331–336.
Parker, J. F. , Chervin, C. N. , Pala, I. R. , Machler, M. , Burz, M. F. , Long, J. W. , and Rolison, D. R. , 2017, “ Rechargeable Nickel–3D Zinc Batteries: An Energy-Dense, Safer Alternative to Lithium-Ion,” Science, 356(6336), pp. 415–418. [PubMed]
Love, C. T. , Johannes, M. D. , and Swider-Lyons, K. , 2010, “ Thermal Stability of Delithiated Al-Substituted Li(Ni1/3Co1/3Mn1/3)O2 Cathodes,” ECS Trans., 25(36), pp. 231–240.
Johannes, M. D. , Swider-Lyons, K. , and Love, C. T. , 2016, “ Oxygen Character in the Density of States as an Indicator of the Stability of Li-Ion Battery Cathode Materials,” Solid State Ionics, 286, pp. 83–89.
Love, C. T. , Dmowski, W. , Johannes, M. D. , and Swider-Lyons, K. E. , 2011, “ Structural Originations of Irreversible Capacity Loss From Highly Lithiated Copper Oxides,” J. Solid State Chem., 184(9), pp. 2412–2419.
Love, C. T. , Baturina, O. A. , and Swider-Lyons, K. E. , 2015, “ Observation of Lithium Dendrites at Ambient Temperature and Below,” ECS Electrochem. Lett., 4(2), pp. A24–A27.
Love, C. T. , 2016, “ Perspective on the Mechanical Interaction Between Lithium Dendrites and Polymer Separators at Low Temperature,” ASME J. Electrochem. Energy Convers. Storage, 13(3), p. 031004.
Chen, C.-F. , Verma, A. , and Mukherjee, P. P. , 2017, “ Probing the Role of Electrode Microstructure in the Lithium-Ion Battery Thermal Behavior,” J. Electrochem. Soc., 164(11), pp. E3146–E3158.
Love, C. T. , 2011, “ Thermomechanical Analysis and Durability of Commercial Micro-Porous Polymer Li-Ion Battery Separators,” J. Power Sources, 196(5), pp. 2905–2912.
Love, C. T. , and Swider-Lyons, K. , 2012, “ Impedance Diagnostic for Overcharged Lithium-Ion Batteries,” Electrochem. Solid State Lett., 15(4), pp. A53–A56.
Love, C. T. , Virji, M. B. V. , Rocheleau, R. E. , and Swider-Lyons, K. E. , 2014, “ State-of-Health Monitoring of 18650 4S Packs With a Single-Point Impedance Diagnostic,” J. Power Sources, 266, pp. 512–519.
Spinner, N. S. , Love, C. T. , Rose-Pehrsson, S. L. , and Tuttle, S. G. , 2015, “ Expanding the Operational Limits of the Single-Point Impedance Diagnostic for Internal Temperature Monitoring of Lithium-Ion Batteries,” Electrochim. Acta, 174, pp. 488–493.
Huhman, B. M. , Heinzel, J. M. , Mili, L. , Love, C. T. , and Wetz, D. A. , 2017, “ Investigation Into State-of-Health Impedance Diagnostic for 26650 4P1S Battery Packs,” J. Electrochem. Soc., 164(1), pp. A6401–A6411.
Beelen, H. P. G. J. , Raijmakers, L. H. J. , Donkers, M. C. F. , Notten, P. H. L. , and Bergveld, H. J. , 2016, “ A Comparison and Accuracy Analysis of Impedance-Based Temperature Estimation Methods for Li-Ion Batteries,” Appl. Energy, 175, pp. 128–140.
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## References

Choi, J. W. , and Aurbach, D. , 2016, “ Promise and Reality of Post-Lithium-Ion Batteries With High Energy Densities,” Nat. Rev. Mater., 1, p. 16013.
Sapunkov, O., Pande, V., Khetan, A., Choomwattana, C., and Viswanathan, V., 2015, “ Quantifying the Promise of ‘Beyond’ Li–Ion Batteries,” Transl. Mater. Res., 2(4), p. 045002.
Urry, A. , 2017, “ Inside the Race to Build the Battery of Tomorrow,” WIRED, Boone, IA, accessed Feb. 22, 2017,
Shah, K. , Balsara, N. , Banerjee, S. , Chintapalli, M. , Cocco, A. P. , Chiu, W. K. S. , Lahiri, I. , Martha, S. , Mistry, A. , Mukherjee, P. P. , Ramadesigan, V. , Sharma, C. S. , Subramanian, V. R. , Mitra, S. , and Jain, A. , 2017, “ State of the Art and Future Research Needs for Multiscale Analysis of Li-Ion Cells,” ASME J. Electrochem. Energy Convers. Storage, 14(2), p. 020801.
Abada, S. , Marbair, G. , Lecocq, A. , Petit, M. , Sauvant-Moynot, V. , and Huet, F. , 2016, “ Safety Focused Modeling of Lithium-Ion Batteries: A Review,” J. Power Sources, 306, pp. 178–192.
Braga, M. H. , Grundish, N. S. , Murchison, A. J. , and Goodenough, J. B. , 2017, “ Alternative Strategy for a Safe Rechargeable Battery,” Energy Environ. Sci., 10(1), pp. 331–336.
Parker, J. F. , Chervin, C. N. , Pala, I. R. , Machler, M. , Burz, M. F. , Long, J. W. , and Rolison, D. R. , 2017, “ Rechargeable Nickel–3D Zinc Batteries: An Energy-Dense, Safer Alternative to Lithium-Ion,” Science, 356(6336), pp. 415–418. [PubMed]
Love, C. T. , Johannes, M. D. , and Swider-Lyons, K. , 2010, “ Thermal Stability of Delithiated Al-Substituted Li(Ni1/3Co1/3Mn1/3)O2 Cathodes,” ECS Trans., 25(36), pp. 231–240.
Johannes, M. D. , Swider-Lyons, K. , and Love, C. T. , 2016, “ Oxygen Character in the Density of States as an Indicator of the Stability of Li-Ion Battery Cathode Materials,” Solid State Ionics, 286, pp. 83–89.
Love, C. T. , Dmowski, W. , Johannes, M. D. , and Swider-Lyons, K. E. , 2011, “ Structural Originations of Irreversible Capacity Loss From Highly Lithiated Copper Oxides,” J. Solid State Chem., 184(9), pp. 2412–2419.
Love, C. T. , Baturina, O. A. , and Swider-Lyons, K. E. , 2015, “ Observation of Lithium Dendrites at Ambient Temperature and Below,” ECS Electrochem. Lett., 4(2), pp. A24–A27.
Love, C. T. , 2016, “ Perspective on the Mechanical Interaction Between Lithium Dendrites and Polymer Separators at Low Temperature,” ASME J. Electrochem. Energy Convers. Storage, 13(3), p. 031004.
Chen, C.-F. , Verma, A. , and Mukherjee, P. P. , 2017, “ Probing the Role of Electrode Microstructure in the Lithium-Ion Battery Thermal Behavior,” J. Electrochem. Soc., 164(11), pp. E3146–E3158.
Love, C. T. , 2011, “ Thermomechanical Analysis and Durability of Commercial Micro-Porous Polymer Li-Ion Battery Separators,” J. Power Sources, 196(5), pp. 2905–2912.
Love, C. T. , and Swider-Lyons, K. , 2012, “ Impedance Diagnostic for Overcharged Lithium-Ion Batteries,” Electrochem. Solid State Lett., 15(4), pp. A53–A56.
Love, C. T. , Virji, M. B. V. , Rocheleau, R. E. , and Swider-Lyons, K. E. , 2014, “ State-of-Health Monitoring of 18650 4S Packs With a Single-Point Impedance Diagnostic,” J. Power Sources, 266, pp. 512–519.
Spinner, N. S. , Love, C. T. , Rose-Pehrsson, S. L. , and Tuttle, S. G. , 2015, “ Expanding the Operational Limits of the Single-Point Impedance Diagnostic for Internal Temperature Monitoring of Lithium-Ion Batteries,” Electrochim. Acta, 174, pp. 488–493.
Huhman, B. M. , Heinzel, J. M. , Mili, L. , Love, C. T. , and Wetz, D. A. , 2017, “ Investigation Into State-of-Health Impedance Diagnostic for 26650 4P1S Battery Packs,” J. Electrochem. Soc., 164(1), pp. A6401–A6411.
Beelen, H. P. G. J. , Raijmakers, L. H. J. , Donkers, M. C. F. , Notten, P. H. L. , and Bergveld, H. J. , 2016, “ A Comparison and Accuracy Analysis of Impedance-Based Temperature Estimation Methods for Li-Ion Batteries,” Appl. Energy, 175, pp. 128–140.

## Figures

Fig. 1

Number of search results by country for publications about lithium-ion batteries between 2007 and 2016. The top five countries are listed and an “other” category which is the sum of all other country data. Keyword search criteria, TOPIC: (“lithium ion” OR “Li ion” OR “Li-ion” OR “Lithium-ion”).

Fig. 2

Number of search results by country for publications with a lithium-ion battery safety focus between 2007 and 2016. The top five countries are listed and an other category which is the sum of all other country data. The exponential growth factor (0.33) is higher than for lithium-ion battery publications without a safety focus. Keyword search criteria, TOPIC: (lithium ion OR Li ion OR Li-ion OR Lithium-ion) and TOPIC: (safety).

Fig. 3

Number of search results by country for publications with percentage of safety-related papers between 2007 and 2016. Keyword search criteria, TOPIC: (lithium ion OR Li ion OR Li-ion OR Lithium-ion) and TOPIC: (safety).

Fig. 4

Dynamic scanning calorimetry thermograms illustrating the heat of reaction for pristine and delithiated (a) Li1−xNi1/3Co1/3Mn1/3O2 and (b) Li1−xNi1/3Co1/3Al1/3O2 heated under argon at 10 °C/min. (Reproduced with permission from Love et al. [8]. Copyright 2010 by The Electrochemical Society.)

Fig. 5

PDOS for M (Fe or Cu) and O in LixFePO4/Li2CuO2 at full discharge (top) and full/partial charge (bottom). Arrows indicate states from which an electron was removed during delithiation. Filled states are to the left of the Fermi energy (set to zero) and empty states to the right. A close-up of the hole states left behind after withdrawal of an electron are shown adjacent to each DOS plot, where oxygen ions are shown as dark spheres. The removed charge is clearly centered around Fe for LiFePO4, but comes heavily from oxygen in Li2CuO2. (Reprinted with permission from Johannes et al. [9]. Copyright 2016 by Elsevier.)

Fig. 6

Morphology changes of lithium dendrites formed at (a) 20 °C, (b) 5 °C, and (c) −10 °C. Arrows highlight the distinct morphologies (mushroom, balloon-shaped at −10 °C; jagged, needlelike at 5 °C; and granular, microparticulates at 20 °C). (d) tan δ for polymer separators with temperature and (e) schematic interaction of anticipated mechanical interaction between temperature-dependent dendrite morphologies and polymer separators at three thermomechanical regimes [11,12].

Fig. 9

SOH map for a commercial lithium-ion battery cell identifying three regions of impedance response: healthy (normal operation), damaged (a fault has been detected), and unsafe (significant irreversible damage has occurred downgrading cell safety)

Fig. 8

(a) Phase angle and (b) magnitude of impedance as a function of frequency for data collected between 0% and 100% SOC during discharge and charge. The SOH frequency region is highlighted between the charge transfer, solid-state diffusion and inductance regions where the impedance originated from electrochemical processes is nearly independent of SOC. (Reprinted with permission from Love et al. [16]. Copyright 2014 by Elsevier.)

Fig. 7

Thermomechanical behavior of (a) Celgard 2320, an anisotropic battery separator (this behavior is also typical for polymer separators: Celgard 2400 and Celgard 2500) and (b) Entek Gold LP, a nearly isotropic biaxial battery separator, with static load applied in the axial and transverse-directions. (Reprinted with permission from Love [14]. Copyright 2011 by Elsevier.)

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