Li-ion Battery Technology Research Articles

Degradation of Li-Oxide Garnets in Humidity, Air and Aqueous Solutions: A Study Using a Large Li6.4La3ZrTaO12 Single Crystal

Lithium-ion batteries are indispensable in our mobile electronic devices. Although considered as promising next-generation storage systems for green energy, safety aspects are of top priority of current research. The root of these safety issues associated with lithium-ion batteries lies in the electrolyte materials used at present. Those are based on flammable non-aqueous liquid electrolytes. Irrespective of these risks they could not been replaced so far because of the lack of inherently safe inorganic solids which should show both very high ionic diffusivities1,2 and a practicable electro­chemical stability. Garnet-type metal oxides,3 such as Li7La3Zr2O12 (LLZO), are being considered as suitable candidates as they fulfil many of the requirements to realize “beyond” Li-ion battery technologies. As an example, to be applicable as a water-protective layer for Li- metal electrodes, the solid electrolyte must be stable in aqueous solutions. In general, the majority of different LLZO types show a high stability in humid environments compared to other solid electrolytes. Upon exposure to aqueous solutions, a Li+/H+ exchange reaction is reported to occur in this class of materials. In certain compounds this exchange is believed to lead to structural changes and degradation of the Li+ conductivity.4 The present work is aimed at investigating degradation phenomena on single crystalline Li6.4La3ZrTaO12 samples in aqueous solutions (distilled water, 0.1 M HCl, saturated LiCl, and 1 M LiOH) as well as the degradation in both humidity and air. While grazing-incidence XRD and SEM helped identify degradation products, broadband conductivity spectroscopy was used to characterize ionic transport parameters of the bulk electrical responses. Albeit the ionic conductivities stay nearly constant the activation energies show drastic changes. As an example, for Li6.4La3ZrTaO12 immersed in distilled water we obtained an activation energy of 0.75 eV in contrast to 0.59 eV of the pristine sample at ambient conditions. This observation can be attributed to the change in the Arrhenius pre-factor caused by the reduction of the number density of Li-ion charge carriers in the garnet. Financial support by the Austrian Federal Ministry of Science, Research and Economy, as well as the Austrian National Foundation for Research, Technology and Development is highly appreciated. 1 V. Epp, O. Gün, H.-J. Deiseroth, M. Wilkening, J. Phys. Chem. Lett. 4 (2013) 2118. 2 M. Uitz, V. Epp, P. Bottke, M. Wilkening, J. Electroceram. 38 (2017), 142. 3 Thangadurai et al., Chem. Soc. Rev. 43 (2014) 4714. 4 C. Ma, E. Rangasamy, C. Liang, J. Sakamoto, K. L. More, M. Chi, Angew. Chem. Int. 54(1) (2015), 129-133.

Going Green By Going Blue: Recycling Li-Ion Batteries By Extracting Cobalt and Nickel Using Deep Eutectic Solvents

With the ever-imminent electrification of the transportation sector, the growth of renewable energy systems requiring better storage units, and the desire for smaller, faster, and smarter consumer electronics, the demand for Li-ion batteries (LIBs) to power the needs of the world is higher than ever. Over the past ten years, while battery prices have plummeted by a factor of four going from about $800/kWh to now $200/kWh for current chemistries1,2, costs of valuable metals within the batteries themselves have surged—notably in the most expensive part of the battery, the cathode, commonly made of cobalt-rich compounds. Cobalt in particular poses not only an economical burden, but a social and environmental one as well, instigating efforts to reduce the reliance on the conflict mineral while still maintaining high performance. Such efforts have led to the development of chemistries using other metals such as manganese and nickel, and has also pushed researchers to pursue more battery recycling options. In this work, a process to extract and reuse cobalt from LIBs containing lithium cobalt (III) oxide (LCO) has been developed using deep eutectic solvents (DESs), a “green” alternative to traditionally toxic solvents. DESs are solutions of two or more Lewis or Brønsted acids and bases that exhibit a deeply depressed freezing point; they can additionally made from cheap and potentially renewable materials3. Nickel metal was also tested in these eutectics, as the nickel manganese cobalt oxide (NMC) and lithium nickel cobalt aluminum oxide (NCA) batteries are projected to play a more prominent role in the future of Li-ion battery technology. The objective is to sustainably recycle these metals from LIBs and then repurpose it in other energy applications. In dissolution experiments simulating the extraction of cobalt from the traditional LIBs, LCO powder was mixed directly with the DES under heat, resulting in a vibrant aqua-blue solution indicating the presence of Co2+ ions. The solubilized metal was filtered and subsequently electrodeposited. Inductively coupled plasma optical emission spectrometry results showed record solubility values for a metal oxide in the presence of a DES. Similarly, experiments done using the nickel-based compounds showed promise for further development, leading to the eventual testing on spent Li-ion cathodes as well. Usage of the recovered metal in a supercapacitor and a new LIB cell demonstrates that such recycling can indeed apply sustainable means to a sustainable end—or rather a new beginning. References Opitz, A. et al., Can Li-Ion batteries be the panacea for automotive applications? Renewable and Sustainable Energy Reviews 2017, 68 (1), 685-692.“After electric cars, what more will it take for batteries to change the face of energy?” The Economist [London] 12 Aug. 2017. Electronic.Smith, E., et al. Deep Eutectic Solvents (DESs) and Their Applications. Rev. 2014, 114, 11060-11082.

(Invited) Organic Molecules for Redox Flow Batteries

The need for grid-scale electricity storage demands cost-effectiveness and durability beyond the reach of current Li-ion battery technologies. Redox flow batteries (RFB) decouple energy from power that promise low cost for long discharge duration as required for load shifting, and they offer long cycle lives as no phase change occurs in the electrodes. However, the most mature RFB technology relies on vanadium salts, whose high and volatile cost threatens its practicality. Among alternative redox couples, organic molecules are emerging with a high promise for their projected low cost and versatility in terms of providing various properties desired in a RFB. In this talk, I will focus the attention on the use of quinone molecules for aqueous RFBs. I will start with molecular selection and design strategies that have been successfully applied to tune the redox potential, the solubility, and the stability of quinones. I will then discuss the engineering aspects of delivering the promise of quinone molecules in stable, high-performance RFBs. I hope that the talk will provide a comprehensive overview of the application of organic molecules in RFBs and stimulate new ideas for exploiting organic materials for energy storage.

Nanoscale electrochemical response of lithium-ion cathodes: a combined study using C-AFM and SIMS.

The continuous demand for improved performance in energy storage is driving the evolution of Li-ion battery technology toward emerging battery architectures such as 3D all-solid-state microbatteries (ASB). Being based on solid-state ionic processes in thin films, these new energy storage devices require adequate materials analysis techniques to study ionic and electronic phenomena. This is key to facilitate their commercial introduction. For example, in the case of cathode materials, structural, electrical and chemical information must be probed at the nanoscale and in the same area, to identify the ionic processes occurring inside each individual layer and understand the impact on the entire battery cell. In this work, we pursue this objective by using two well established nanoscale analysis techniques namely conductive atomic force microscopy (C-AFM) and secondary ion mass spectrometry (SIMS). We present a platform to study Li-ion composites with nanometer resolution that allows one to sense a multitude of key characteristics including structural, electrical and chemical information. First, we demonstrate the capability of a biased AFM tip to perform field-induced ionic migration in thin (cathode) films and its diagnosis through the observation of the local resistance change. The latter is ascribed to the internal rearrangement of Li-ions under the effect of a strong and localized electric field. Second, the combination of C-AFM and SIMS is used to correlate electrical conductivity and local chemistry in different cathodes for application in ASB. Finally, a promising starting point towards quantitative electrochemical information starting from C-AFM is indicated.

Mechanisms of Degradation and Strategies for the Stabilization of Cathode-Electrolyte Interfaces in Li-Ion Batteries.

Undesired reactions at the interface between a transition metal oxide cathode and a nonaqueous electrolyte bring about challenges to the performance of Li-ion batteries in the form of compromised durability. These challenges are especially severe in extreme conditions, such as above room temperature or at high potentials. The ongoing push to increase the energy density of Li-ion batteries to break through the existing barriers of application in electric vehicles creates a compelling need to address these inefficiencies. This goal requires a combination of deep knowledge of the mechanisms underpinning reactivity, and the ability to assemble multifunctional electrode systems where different components synergistically extend cycle life by imparting interfacial stability, while maintaining, or even increasing, capacity and potential of operation. The barriers toward energy storage at high density apply equally in Li-ion, the leading technology in the battery market, and in related, emerging concepts for high energy density, such as Na-ion and Mg-ion, because they also conceptually rely on electroactive transition metal oxides. Therefore, their relevance is broad and the quest for solutions inevitable. In this Account, we describe mechanisms of reaction that can degrade the interface between a Li-ion battery electrolyte and the cathode, based on an oxide with transition metals that can reach high formal oxidation states. The focus is placed on cathodes that deliver high capacity and operate at high potential because their development would enable Li-ion battery technologies with high capacity for energy storage. Electrode-electrolyte instabilities will be identified beyond the intrinsic potential windows of stability, by linking them to the electroactive transition metals present at the surface of the electrode. These instabilities result in irreversible transformations at these interfaces, with formation of insulating layers that impede transport or material loss due to corrosion. As a result, strategies that screen the reactive surface of the oxide, while reducing the transition metal content by introducing inactive ions emerge as a logical means toward interfacial stability. Yet they must be implemented in the form of thin passivating barriers to avoid unacceptable losses in storage capacity. This Account subsequently describes our current ability to build composite structures that include the active material and phases designed to address deleterious reactions. We will discuss emerging strategies that move beyond the application of such barriers on premade agglomerated powders of the material of interest. The need for these strategies will be rationalized by the goal to effectively passivate all interfaces while fully controlling the chemistry that results at the surface and its homogeneity. Such outcomes would successfully minimize interfacial losses, thereby leading to materials that exceed the charge storage and life capabilities possible today. Practically speaking, it would create opportunities to design batteries that break the existing barriers of energy density.

Pioneering Li-ion batteries on an offshore platform

Woodside is an Australian oil and gas company and a leading global operator of offshore gas platforms and onshore LNG processing facilities. It is a public company listed on the Australian Securities Exchange headquartered in Perth, Western Australia. Woodside operates the Goodwyn A gas platform on behalf of the North West Shelf (NWS) Project. Woodside assessed Li-ion battery technology and considered the technology mature and ready to be utilised on offshore and onshore operating assets. Woodside operates dedicated islanded gas turbine power generation at each of its onshore and offshore facilities. It was concluded that a large battery energy storage solution (BESS) can deliver several advantages if connected to such an islanded power generation system. The most significant benefit materialises by using a BESS as backup (or spinning reserve) for the gas turbine generators (GTGs). Woodside decided to pioneer the Li-ion BESS technology in a first of its kind application on the NWS Project offshore Goodwyn A gas platform. The Goodwyn A BESS is designed for a 1 MW power and 1 MWh energy capacity, which is considered sufficient to provide the spinning reserve for the Goodwyn A platform. Currently, Goodwyn A operates four 3.2 MW GTGs to provide a typical load of 7–8 MW, with one GTG providing the N+1 spinning reserve. When the BESS is connected to the power generation system, Goodwyn A will operate three GTGs, with the BESS proving the backup in case one of the GTGs trip. The BESS will provide the full 1 MW for a minimum of 1 h, which will give the operators enough time to start the standby GTG or adjust the facility loads (load shedding). The result will be a decrease in overall fuel gas consumption (due to better efficiencies on the remaining GTGs in operation) and a related reduction in CO2 emissions. The project supports the overall objective of the North West Shelf Project to improve the energy intensity of its facilities by 5% by 2020. Woodside believes that developing capability and experience on the installation of BESSs, using Goodwyn A as an early adopter, will facilitate similar and larger installations on other Woodside operated offshore and onshore assets. This is one of the technologies Woodside believes will play an important role to ensure a lower carbon future globally.

State-of-the-Art and Energy Management System of Lithium-Ion Batteries in Electric Vehicle Applications: Issues and Recommendations

A variety of rechargeable batteries are now available in world markets for powering electric vehicles (EVs). The lithium-ion (Li-ion) battery is considered the best among all battery types and cells because of its superior characteristics and performance. The positive environmental impacts and recycling potential of lithium batteries have influenced the development of new research for improving Li-ion battery technologies. However, the cost reduction, safe operation, and mitigation of negative ecological impacts are now a common concern for advancement. This paper provides a comprehensive study on the state of the art of Li-ion batteries including the fundamentals, structures, and overall performance evaluations of different types of lithium batteries. A study on a battery management system for Li-ion battery storage in EV applications is demonstrated, which includes a cell condition monitoring, charge, and discharge control, states estimation, protection and equalization, temperature control and heat management, battery fault diagnosis, and assessment aimed at enhancing the overall performance of the system. It is observed that the Li-ion batteries are becoming very popular in vehicle applications due to price reductions and lightweight with high power density. However, the management of the charging and discharging processes, CO2 and greenhouse gases emissions, health effects, and recycling and refurbishing processes have still not been resolved satisfactorily. Consequently, this review focuses on the many factors, challenges, and problems and provides recommendations for sustainable battery manufacturing for future EVs. This review will hopefully lead to increasing efforts toward the development of an advanced Li-ion battery in terms of economics, longevity, specific power, energy density, safety, and performance in vehicle applications.

Slurry-Based Processing of Solid Electrolytes: A Comparative Binder Study

Limited energy density of today's Li-ion battery technologies demands for novel cell technologies, such as the all-solid-state battery (ASSB). In order to achieve high energy densities and enable large-scale processing, thin and flexible solid electrolyte (SE) layers have to be implemented. This study focuses on slurry-based processing of the sulfidic solid electrolyte Li10SnP2S12 (LSPS). Various polymers were investigated concerning their suitability as binders for thin and freestanding SE sheets. We conducted a parameter study in order to optimize e.g. LSPS-to-binder ratio, solids content and porosity. Significant differences were found with regard to the minimum amount of binder required for mechanically stable sheets as well as the homogeneity, density and flexibility of the resulting SE layers. The impacts of binder type and weight fraction on ionic conductivity were examined through lithium diffusion measurements. Impedance analysis was conducted in comparison, proving sufficiently high ionic conductivity for potential application of the SE sheets in ASSB. This work highlights the important role of the polymeric binder in slurry-based processing of SEs and gives an impression how important a well-considered selection of parameters is to achieve good processing properties as well as desirable features for the final SE sheet.

Li-Rich Layered Cathode Materials: Transition Metals in Transit

In the most recent issue of Nature Communications , William Gent, William Chueh, and co-authors examine in depth the electronic structure and redox processes that occur during cycling of Li 1.17 Ni 0.21 Co 0.08 Mn 0.54 O 2 and reveal an important new insight that suggests oxygen redox is coupled with local transition metal migration. Aided by a suite of cutting-edge characterization methods, the authors formulate a clear and unprecedented view of both local and averaged structure evolution during cycling.

Anionic Redox Chemistry in Polysulfide Electrode Materials for Rechargeable Batteries.

Classical Li-ion battery technology is based on the insertion of lithium ions into cathode materials involving metal (cationic) redox reactions. However, this vision is now being reconsidered, as many new-generation electrode materials with enhanced reversible capacities operate through combined cationic and anionic (non-metal) reversible redox processes or even exclusively through anionic redox transformations. Anionic participation in the redox reactions is observed in materials with more pronounced covalency, which is less typical for oxides, but quite common for phosphides or chalcogenides. In this Concept, we would like to draw the reader's attention to this new idea, especially, as it applies to transition-metal polychalcogenides, such as FeS2 , VS4 , TiS3 , NbS3 , TiS4 , MoS3 , etc., in which the key role is played by the (S-S)2- /2 S2- redox reaction. The exploration and better understanding of the anion-driven chemistry is important for designing advanced materials for battery and other energy-related applications.

Aqueous Li-Ion Batteries: Now in Striking Distance

In the inaugural issue of Joule , Chunsheng Wang, Kang Xu, and colleagues demonstrate a groundbreaking advance in Li-ion battery electrolytes with their design and demonstration of 4 V aqueous Li-ion batteries, which in theory could eliminate several environmental, safety, and manufacturing restrictions and concerns raised by non-aqueous electrolytes.

On Cell Variability and Fade Mechanisms in High Energy Density Lithium Batteries

Li-ion battery technology is approaching its limits in terms of capacity density and energy density based on current anode and cathode materials, which poses a technical challenge for increasing the range of electric vehicles and minimizing overall battery pack size. An alternative lithium battery technology utilizing a high capacity cathode such as a Ni-rich layered oxide can theoretically deliver an energy density upwards of 500 Wh/kg [1]. Combined with a lithium anode and a suitable liquid electrolyte, one such Nickel–rich layered oxide, LiNi0.6Mn0.2Co0.2O2 (NMC 622), has the theoretical potential to deliver batteries with an energy density of at least 500 Wh/kg [2, 3]. Here we have studied the performance of such high energy density full cells comprised of a Li metal anode, NMC622 cathode, and 1.2 M in LiPF6 (3:7) EC:EMC electrolyte. In order to better understand and compare the performance of different systems, a deep understanding of cell variability and its impact on fade mechanisms is necessary [4]. Hence, challenges in identifying true fade mechanisms due to cell variability will be discussed The presentation will cover the different fade mechanisms and their gradual progression as observed during cycling of these cells. Differential capacity analysis was applied to identify different fade mechanisms and to quantify degradation modes. The different fade mechanisms are related to variations in cells. Statistical analyses will be presented to characterize and quantify cell variability based on the different fade mechanisms observed.

(Invited) Data-Driven Materials Design for Compounds with Improved Mg Intercalation Mobility

The increasing demand of solid-state energy storage requires improved technologies, such as Mg-ion batteries, to address safety and cost concers as well as the energy density limitations of state-of-the-art Li-ion battery technology, however, the realization of Mg-ion batteries hinges on the discovery of host materials that possess sufficiently high voltage, large energy capacity, and, most importantly, adequate mobility of the Mg2+ to ensure the viable intercalation cycling. To date, there has only been a limited number of examples demonstrating the feasibility of rechargeable Mg-ion batteries, motivating the current investigation to search over more broad chemical spaces for attainable multivalent (Mg2+, Ca2+, Zn2+) intercalation cathode candidates. In this presentation, we show our detailed work, based on the robust automated high-throughput density functional calculations and the high-quality theoretical data from Materials Project, to systematically evaluate the electrochemical performance as well as the intercalating mobility of multivalent cation over several hundreds of host compounds. We also demonstrate our in-house theoretical approaches (e.g., diffusion path topology analysis) that have been designed and practiced to quantitatively estimate the multivalent cation mobility. Our study suggests that the matching between the intercalant site preference to the diffusion path topology of the host structure plays a decisive role to control mobility more than any other factor.[1] Our “in silico” design and evaluation have found several promising Mg-ion cathode materials that possess improved Mg mobility (migration activation energy lower than 600meV) [2,3], and some of them have been confirmed by experimental research teams recently [4]. The results demonstrate that the data-driven computational materials design is a realistic tool to the successful discover and optimize new materials for energy-dense multivalent batteries. The work is entirely supported by the Department of Energy as part of the Joint Center for Energy Storage Research (JCESR). [1] Z. Rong, R. Malik, P. Canepa, G. Gautam, M. Liu, A. Jain, K. Persson and G. Ceder, Materials Design Rules for Multi-Valent Ion Mobility in Intercalation Structures, Chem. Mat. 2015, 27, 6016. [2] M. Liu, Z. Rong, R. Malik, P. Canepa, A. Jain, G. Ceder and K. Persson, Spinel compounds as multivalent battery cathodes: a systematic evaluation based on ab initiocalculations, Energy Environ. Sci. 2015, 8, 964. [3] M. Liu, A. Jain, Z. Rong, X. Qu, P. Canepa, M. Ralik, G. Ceder and K. Persson, Evaluation of sulfur spinel compounds for multivalent battery cathode applications, Energy Environmental Science, Energy Environ. Sci. 2016, 9, 3201. [4] X. Sun, P. Bonnick, V. Duffort, M. Liu, Z. Rong, K. Persson, G. Ceder and L.F. Nazar, A High Capacity Thiospinel Cathode for Mg Batteries, Energy Environmental Science, Energy Environ. Sci. 2016, 9, 2273.

Advances in Understanding Oxygen Reduction in the Metal-O2 Battery

Li-ion and related battery technologies will be important for years to come. However, we must explore alternatives if we are to have any hope of meeting the long-term needs for energy storage. One such alternative is the metal-O2 battery; the theoretical specific energy of typical aprotic metal-O2batteries exceeds that of Li-ion, but many obstacles hinder realization of this technology.[1-4] Overcoming these hurdles will require an understanding of the fundamental electrochemistry at the positive electrode within aprotic metal-air batteries.[5-12] Recently interest in the Na-O2 battery has grown due to the relatively low polarization during cycling and the high rates.[13, 14] This is despite the lower specific energy of this battery chemistry.[15] A number of groups have shown promising results with this system.[16-18] An important area of contention is the nature of the discharge product, which, unlike the lithium system that forms Li2O2, may form the superoxide, peroxide or oxide. The discharge product in the metal-O2 battery directly influences the specific capacity and ease of charge. Therefore, it is important to understand the mechanism such that this can be controlled. We have combined a range of electrochemical, spectroscopic and microscopy methods to investigate the mechanism of electrochemical O2 reduction. The results of these studies will be presented, along with the implications for the future of rechargeable metal-O2 batteries.

Simulation Protocol for Prediction of a Solid-Electrolyte Interphase on the Silicon-based Anodes of a Lithium-Ion Battery: ReaxFF Reactive Force Field.

We propose the ReaxFF reactive force field as a simulation protocol for predicting the evolution of solid-electrolyte interphase (SEI) components such as gases (C2H4, CO, CO2, CH4, and C2H6), and inorganic (Li2CO3, Li2O, and LiF) and organic (ROLi and ROCO2Li: R = -CH3 or -C2H5) products that are generated by the chemical reactions between the anodes and liquid electrolytes. ReaxFF was developed from ab initio results, and a molecular dynamics simulation with ReaxFF realized the prediction of SEI formation under real experimental conditions and with a reasonable computational cost. We report the effects on SEI formation of different kinds of Si anodes (pristine Si and SiOx), of the different types and compositions of various carbonate electrolytes, and of the additives. From the results, we expect that ReaxFF will be very useful for the development of novel electrolytes or additives and for further advances in Li-ion battery technology.

Boosting the adsorption performance of BN nanosheet as an anode of Na-ion batteries: DFT studies

Despite the high advance in the Li-ion battery technology, there exist great concerns about its lifetime, safety, cost, and low-temperature performance. It is expected that the Li-ion batteries may be replaced by Na-ion batteries (NIB) because of the low cost, nontoxicity, and wide availability of sodium. Here, we investigated the potential application of BN nanosheets in anode of NIBs by means of density functional theory calculation and introduced a strategy to increase their performance. It was shown that the Na and Na+ are mainly adsorbed on the center of a hexagonal ring of BN sheet with adsorption energies of −0.08 and −33.7 kcal/mol, respectively. Replacing three N atoms of the hexagonal ring with larger P atoms significantly increases the performance of the sheet as an anode of a NIB but the replacement of B by Al decreases the performance. The initial cell voltage of LIB is increased by about 0.67 V after the P-doping which causes a high storage performance with long discharge time. The results are discussed based on the energetic, structural, orbital, charge transfer and electronic properties and provide guidelines to build better high-capacity anode materials for NIBs.

Investigating the Three-Dimensional Microstructural Characteristics of Lithium-Sulfur Electrodes with X-Ray Micro-Tomography

Lithium sulfur (Li-S) batteries offer a theoretical specific capacity of 1675 mAh g-1, an order of magnitude greater than current Li-ion battery technology, along with lower cost and improved safety. However, their commercialization has been hindered by poor cycle life and low coulombic efficiency. As opposed to the relatively simple ‘rocking chair’ intercalation-based mechanism underpinning Li-ion battery technology, the reaction mechanism within Li-S conversion-type cathodes involves multiple stages and phase changes. During the charge process, solid lithium sulfide is delithiated by a series of electrochemical reactions involving soluble polysulfide intermediates before being converted into elemental sulfur, and during the discharge process, the reverse occurs. The development of Li-S batteries has been hindered by complex phenomenon including large volume change (ca. 80%) between elemental sulfur (S) and lithium sulfide (Li2S), active material loss resulting from polysulfide dissolution, poor electrical conductivity of both S and Li2S, significant self-discharge, and the polysulfide shuttle mechanism causing poor coulombic efficiency and anode corrosion.Whilst recent advances have been made in contained cathode materials for Li-S batteries to prevent polysulfide dissolution into the bulk electrolyte phase and suppress active material loss and the polysulfide shuttle effect, a more comprehensive understanding of the underlying mechanisms contributing to active material loss to the electrolyte phase is essential for further optimization of cycle life and capacity, particularly so for high mass loading sulfur cathodes. However, the roles that the electrode morphology and the microstructure of the carbon binder domain (CBD) play in contributing to these failure mechanisms during cycling remain poorly understood. Lab-scale micro- and nano-tomography was performed on a Li-S battery with the ZEISS Xradia Versa 520 and Ultra 810 X-ray microscopes, achieving voxel dimensions of ca. 126 nm and 30 nm respectively. These instruments enabled a multi length-scale, three-dimensional X-ray tomography study to be carried out, with the extraction of various metrics as a function of cycle life and state of charge on the sulfur cathode. The metrics included morphological parameters, such as sulfur mass loading and particle size distribution, and microstructural characteristics, such as electrode porosity, tortuosity and contact area between phases. Nano-tomography of the CBD revealed the resolution dependent nature of certain parameters (i.e. contact area between phases), and highlighted the significance of multi length-scale characterization. Digital volume correlation (DVC) was applied to track the evolution of sulfur particles as a function of cycle number. The 3D visualization of Li-S electrodes with this technique provides a wealth of information, improving understanding of the evolution of morphological and microstructural parameters of the different phases; as X-ray imaging is inherently non-destructive, it enables these parameters to be observed in-situ as a function of cycle life and state of charge (SoC). The inherently anisotropic nature of active material dissolution, recrystallization and other degradation processes within the electrode necessitates a three-dimensional approach to enable their quantification, and X-ray tomography is a useful tool in informing the development of more optimal electrode designs. Figure 1

Strategy for Metal Anode Protection in Advanced Energy Storage Systems

To meet the demand for higher capacity longer life batteries in a “next-generation batteries” technology, anodes with substantially higher energy density than current graphite are needed. One class - metal anodes (particularly Li, Na) - offers far higher energy density, but to date their utilization has been impeded by their high surface reactivity (especially to the organic electrolyte) and tendency to form dendrites (a shorting and safety hazard). We have used atomic layer deposition (ALD) to create highly controlled, thin ceramic type coatings as an artificial solid electrolyte interphases (SEIs) to protect these anode surfaces by preventing dendrite formation and electrolyte decomposition. The ultrathin Al2O3 protective coating on Na stabilizes the Na-electrolyte interface and extends its cycle life under high current density (i.e., high power) cycling conditions. We have also developed a hybrid (elastomer + ceramic-type) protective coating on Li metal by combining ALD ceramic (LiPON) and electrochemical deposition of a polymeric elastomer. The hybrid layer achieves high Li conductivity while suppressing corrosion and due to electrolyte breakdown. The elastomer component provides mechanical flexibility to accommodate volume change both may play roles in the observed mitigation of dendrite growth at high current density. These results demonstrate promise for achieving high energy density anodes with significantly enhanced chemical stability, electrochemical cyclability, and dendrite protection as needed for a viable beyond Li or Na ion battery technology.

Lithium-Sulfur Batteries with an Ultrahigh-Sulfur-Loading Carbon-Cotton Cathode

Going beyond lithium-ion chemistry, the lithium-sulfur (Li-S) chemistry could offer 2 – 3 times higher energy density than the current Li-ion battery technology.1,2 However, as reported in recent publications, the progress is far from adequate with respect to the high-loading capability of the active material in building high-energy-density Li-S batteries.1-3 Although the sulfur cathode has a high theoretical capacity (1,675 mA h g-1), a high-loading cathode fabricated by conventional electrode coating method has, unfortunately, proved it to be difficult to attain the necessary electrochemical conversion/utilization of sulfur. Given that a traditional cathode configuration is not ideal for a Li-S battery, advanced electrode structures have been extensively studied for increasing sulfur loading and achieving a high areal capacity.2,3 However, new challenges arise with respect to how to simultaneously improve the sulfur loading and maintain the dynamic and static cell stability.2,4 We present here a carbon-cotton cathode that possesses hierarchical macro-/micro-porous architecture for establishing the high-loading capacity of Li-S cells and simultaneously enhancing their dynamic and static stability.4 Fig. 1 shows the microstructure of the carbon cotton and carbon-cotton cathode. The carbon cotton is fabricated by carbonizing the cotton at 900 °C for 6 h with a heating rate of 2 °C min-1 under argon atmosphere. The carbon-cotton electrode (Fig. 1a) has a cross-linked spiral carbon-fiber network that is armored with microporous reaction sites, forming a hierarchical macro-/micro-porous architecture. The macroporous channels allow the carbon-cotton cathode to encapsulate a high amount of catholyte (Fig. 1b). The high-sulfur-loading carbon-cotton cathode is fabricated by impregnating the carbon cotton with a high amount of Li2S6 catholyte (80 µL). The cells have a fixed electrolyte-to-sulfur ratio of 6.8. The high tortuosity of the carbon-cotton cathode benefits the catholyte infiltration and the ensuing active-material retention. As a result, the carbon-cotton cathodes with the highest values of both sulfur loading (61.4 mg cm-2) and sulfur content (80 wt.%) demonstrate enhanced electrochemical utilization with the highest areal capacity (56 mA h cm-2), volumetric capacity (1,121 mA h cm-3), and gravimetric capacity (724 mA h g-1) simultaneously (Fig. 2a). On the other hand, the abundant microporous reaction sites (micropore surface area: 557 m2 g-1) spread throughout the carbon cotton enlarge the accessible reaction area among electrons, catholyte, and active material, facilitating the redox chemistry and guaranteeing the smooth operation of the high-loading/content Li-S system. Therefore, in Fig. 2, the high-loading carbon-cotton cathode exhibits (i) enhanced cycle stability with a good dynamic capacity retention of 70% after 100 cycles and (ii) improved cell-storage stability with a high static capacity retention of above 93% and a low time-dependent self-discharge rate of 0.12% per day after storing for a long period of 60 days. In conclusion, the electrochemical enhancements and engineering designs of the carbon-cotton cathodes make them advanced cathode architectures for the development of high-loading/content sulfur cathodes in high-energy-density Li–S batteries. REFERENCES 1. S. Urbonaite, T. Poux and P. Novák, Adv. Energy Mater., 5, 1500118 (2015). 2. A. Manthiram, S.-H. Chung and C. Zu, Adv. Mater., 27, 1980 (2015). 3. M. Hagen, D. Hanselmann, K. Ahlbrecht, R. Maça, D. Gerber, J. Tübke, J. Adv. Energy Mater., 5, 1401986 (2015). 4. S.-H. Chung, C.-H. Chang and A. Manthiram, ACS Nano, 10, 10462 (2016). Figure 1

Generic Model Control for Lithium-Ion Batteries - II

Battery Management Systems (BMS) are critical to safe and efficient operation of lithium-ion batteries and accurate prediction of the internal states [1]. Smarter BMS that can estimate and implement optimal charging profiles in real-time are important for advancement of the Li-ion battery technology. Estimating optimal profiles using physics-based models is computationally expensive because of the non-linear and stiff nature of the model equations, involving the need for constrained non-linear optimization [2-12]. In this work, we present an alternative approach to control batteries applying the concept of differential geometry. This approach is known as Generic Model Control (GMC), or Reference System Synthesis [13,14]. This work enables robust stabilization and control of battery models to set-point as an alternative approach, eliminating the need to perform optimization of nonlinear models. This work builds on our previous work of implementation of GMC for differential variables occurring in a model consisting of differential algebraic equations (DAEs), and extends it to set point based control for algebraic variables. Conventional GMC is applicable for cases in which the output is typically independent of control [13]. We also extend it for cases for which the measured variable can be an explicit function of the manipulated variable. As compared to the generic model control approaches implemented by previous researchers, we have implemented the same concept using direct DAE numerical solvers [15]. The results are presented for single input single objective, and for constrained problems. The proposed approach is compared with standard control approaches and is found to be equally robust if not better. Acknowledgements The work presented herein was funded in part by the Advanced Research Projects Agency – Energy (ARPA-E), U.S. Department of Energy, under Award Number DE-AR0000275 and the Clean Energy Institute at the University of Washington, Seattle.