Development of a rechargeable lithium cell power source

As microelectronic systems become increasing smaller and more complex, the need for non-traditional micro-energy sources grows. In particular, mechanical energy harvesters, which convert mechanical to electrical energy, are volumetrically energy dense potential micro-energy sources. Recent literature[1-4] has demonstrated a new mechanical energy harvesting class of materials called piezoelectrochemical (PEC) materials, where mechanical energy is coupled to electrochemical energy through the potential of mobile ions. PEC materials have orders of magnitude higher theoretical energy density than conventional mechanical harvesters, such as piezoelectrics. Studies have experimentally demonstrated this PEC effect in many systems, including lithium-cobalt-oxide[1], lithium-silicon[2], sodium-phosphorus[3], lithium-carbon[4] and others. Commercially available lithium-ion pouch cells have been used to understand this effect as they are a convenient system of standardized quality that exhibits PEC coupling. Previous work[1] has suggested that there exists a coupling factor, k, which relates the conversion of applied mechanical stress to electrochemical potential. From this coupling factor, an equation for theoretical single-cycle energy density was derived as a function of k and dU0/dQ , where dU0/dQ is the slope of the charge curve. As the expansion of lithium electrodes is nonlinear with capacity, the theoretical single-cycle energy density is dependent on the state-of-charge (SOC) of the cell. In this work, we focus on the relationship between coupling factor and theoretical single-cycle energy density in commercial lithium-cobalt-oxide (LCO) pouch cells. We find that the theoretical energy density, which is characterized by measuring differential expansion and differential voltage of a pouch cell, can vary significantly between different commercial cells of the same manufacturing batch. In addition, we compare the theoretical energy density to energy harvesting experimental results from the LCO pouch cells at different SOCs. We find that there is a difference between theoretical and actual harvested energy and the efficiency loss is related to the state-of-charge. We speculate that the efficiency loss is due to kinetic transfer being too slow to fully extract all possible charge.

Lithium (Li) metal is an ideal anode material for rechargeable batteries due to its extremely high theoretical specific capacity (3860 mAh/g), low density (0.59 g/cm3) and the lowest negative electrochemical potential (-3.04 V vs. the standard hydrogen electrode, SHE). Li battery based on Li metal anode is expected to have an order of magnitude higher energy density than today's Li-ion battery. This will enhance energy and power capability of battery devices used in portable electronics, hybrid electric cars, aerospace, telecommunication, military, etc.). The Li metal battery will fulfill the high energy demand that cannot be met through the current Li-ion batteries (e.g. all electric transportation or many other applications which require light weight, high energy density, high power density batteries with small battery footprint and safest). But, to date, uncontrolled dendritic Li growth and limited Coulombic efficiency (CE) during Li deposition/stripping of a bulk Li anode, are the main reason behind low cycle life, which has limited their practical applications. Furthermore, the rate of dendrite growth gets amplified when the cell is cycled at high charge-discharge current density, high charge voltage, and high areal discharge. Increasing anode surface area would reduce the effective charge/discharge current. Additionally, thin films and high surface area Li anodes exhibit high ionic and electronic conductivity contributing to the high efficiency of the current collection required for high capacity battery. Although low CE can be partially compensated by an excess amount of Li (at the expense of lower useable Li energy), fire and other hazards associated with the dendrite growth have limited the development of rechargeable Li metal batteries. Most approaches to dendrite prevention focus on improving the stability and uniformity of the solid-electrolyte interface (SEI) on the bulk Li surface by adjusting electrolyte components and optimizing SEI formation additives. It is very difficult to achieve sufficient passivation on Li electrode due to the thermodynamic instability of Li with electrolytes [1,2]. As an alternative, various mechanical barriers have been proposed to block dendrite penetration [3]. These approaches rely on a strong mechanical barrier provided by an SEI film or a separator to suppress Li dendrite penetration but do not change the fundamental, self-amplifying behavior of the dendrite growth. Also, it is hard to find a mechanical barrier material with required shear modulus (required > 109 Pa) with desired conductivity. In other words, these methods did not prevent Li dendrites from growing during long-term cycling at high charge-discharge current density, high charge voltage, and high areal discharge, or hardly improved the CE and safety in Li deposition/stripping which is not suitable for practical rechargeable Li batteries [1]. We have developed a novel ionic-electronic-mechanical membrane (an artificial SEI), which allows long-term Li cycleability and improved safety by reducing dendrite formation. The new artificial SEI is comprised of three different materials to fulfill the desired SEI criteria such as: (a) facilitate uniform Li ion dispersion and deposition on entire Li surface, (b) desired SEI conductivity (c) mechanical separation of Li and electrolyte and flexibility to contain anode volume change during Li stripping and deposition. The combined effect of the invented SEI result into more than 300% increase in number of cycles and 3-4 times increase in usable Li energy density (i.e. high Coulombic efficiency (CE)) of a wet battery composed of protected Li metal anode, liquid electrolyte (e.g. lithium hexafluoro arsenate, LiAsF6) and Li-ion cathode (e.g. lithium cobalt oxide, LCO) for the advancement of a battery beyond the state-of-the-art Li-ion battery. The added advantage of the invented SEI is improved safety due to suppression of dendrite growth by mechanically strong/flexible SEI and controlled, uniform deposition/stripping of Li from Li anode surface. The protected Li anode may be incorporated into wet cell batteries or solid state batteries having transition metal oxide cathodes (more specifically the state-of-the-art Li-ion cathodes) or Sulfur cathode (Li-S battery) or Oxygen cathode (Li-O2 battery). Moreover, similar methodologies can be applied to other rechargeable metal anodes (Na, Al, Mg, etc.) used in batteries.

The low gravimetric and volumetric energy densities of energy storage technologies are principal limitations for realizing the full potential of modern robotics technologies[1]. In many cases, the size and weight of energy storage technologies required to power robotic systems are too large or massive for a robot to carry untethered. Therefore, most robotic systems are tethered, or constrained to limited operational times and long-recharging times over which they remain unused. Energy storage technologies are particularly limiting for micrometer to centimeter scale robots, vehicles, and sensors, as microbatteries dominate the size and mass of the corresponding devices [2,3]. One approach to overcome the energy limitations of batteries is to use battery chemistries with increased energy density. Metal-air batteries are particularly appealing due to their high energy densities. Iron-air, zinc-air, and aluminum-air batteries have 1229, 1535, and 8076 Wh/kg theoretical energy densities [4], which is 5 – 32 X larger than commercial lithium ion batteries. Practical metal-air batteries, however, only achieve a fraction of the theoretical energy density (350 – 500 Wh/kg for Zn-air, for example) and suffer from poor and inefficient rechargeability. Although promising, realizing rechargeable metal-air batteries with near theoretical energy densities is likely several years or decades away. New approaches for powering robots that take advantage of specific environments or use-cases are required to realize untethered robotic systems in the near future. In a conventional battery, active materials are stored in a rigid package so that the maximum volumetric energy density is the energy available in the lowest capacity electrode divided by the total battery volume or mass. A robot, therefore, is required to carry both the active material mass as well as the packaging and electrolyte required for the battery to work. In metal-air batteries, the pertinent electrode is the solid metal anode which oxidizes to produce electrons and, typically, a metal hydroxide or metal oxide. An electrolyte connects the metal anode to a thin porous cathode that reduces oxygen in the air. Metal-air batteries have high energy densities because oxygen for the cathode reaction can be extracted from the air and therefore does not contribute to the battery mass or volume. Electrons from the anode are transferred to the cathode through the robot electronics, powering the robot. In this work, we present a metal-air scavenger (MAS), which is a device that extracts electrical energy from external metal surfaces to power centimeter scale or smaller robots, vehicles, and electronics. The MAS undergoes the same chemical reactions as a metal-air battery, but is only composed of a polymer electrolyte and cathode current collector so that both the anode and cathode active materials are external to the device. The powered devices, therefore, only need to carry the mass of the electrolyte and cathode current collector. We show that, when stationary, a MAS extracts near the theoretical capacity of aluminum and zinc surfaces, as well as extracts up to 1,450 mAh/g from iron surfaces. The maximum power densities of a MAS on aluminum, zinc, and iron surfaces are 130, 80, and 25 mW/cm2. A principal advantage of the MAS is that it can continue to power a device as it moves across a metal surface, so that the total mass and volume of metal oxidized are many multiples of the mass and volume of the device. We demonstrate the utility of a MAS by powering a 5 x 4 x 2 cm electric vehicle on aluminum and zinc surfaces with a 2 x 2 x 0.3 cm MAS. The MAS powered the vehicle over many square feet of metal surface and at up to 8 mm/s velocity. The MAS concept presented here takes advantage of the prolific variety of external metal energy sources available in modern urban environments. We believe the MAS will find utility in many applications, lead to further unconventional methods for powering robotic systems, and open new materials development opportunities. Yang, Guang-Zhong, et al. "The grand challenges of Science Robotics." Science Robotics3.14 (2018): eaar7650.St. Pierre, Ryan, and Sarah Bergbreiter. "Toward Autonomy in Sub-Gram Terrestrial Robots." Annual Review of Control, Robotics, and Autonomous Systems(2019).Oudenhoven, Jos FM, Loïc Baggetto, and Peter HL Notten. "All‐solid‐state lithium‐ion microbatteries: a review of various three‐dimensional concepts." Advanced Energy Materials1.1 (2011): 10-33.Li, Yanguang, and Jun Lu. "Metal–air batteries: will they be the future electrochemical energy storage device of choice?." ACS Energy Letters2.6 (2017): 1370-1377. Figure 1

The hydrogen-bromate flow battery represents one of the promising variants for hybrid power sources. Its membrane-electrode assembly (MEA) combines a hydrogen gas diffusion anode and a porous flow-through cathode where bromate reduction takes place from its acidized aqueous solution: BrO3- + 6 H+ + 6 e- = Br- + 3 H2O (*). The process of electric current generation occurs on the basis of the overall reaction: 3 H2 + BrO3- = Br- + 3 H2O (**), which has been studied in previous publications. Until this work, it has been unknown whether this device is able to function as a rechargeable power source. This means that the bromide anion, Br-, should be electrooxidized into the bromate anion, BrO3-, in the course of the charging stage inside the same cell under strongly acidic conditions, while until now this process has only been carried out in neutral or alkaline solutions with specially designed anode materials. In this study, we have demonstrated that processes (*) and (**) can be performed in a cyclic manner, i.e., as a series of charge and discharge stages with the use of MEA: H2, Freidenberg H23C8 Pt-C/GP-IEM 103/Sigracet 39AA, HBr + H2SO4; square cross-section of 4 cm2 surface area, under an alternating galvanostatic mode at a current density of 75 mA/cm2. The coulombic, voltaic and energy efficiencies of the flow battery under a cyclic regime, as well as the absorption spectra of the catholyte, were measured during its operation. The total amount of Br-containing compounds penetrating through the membrane into the anode space was also determined.

Introduction Rechargeable battery systems with different transporting ions are an alternative choice to Li batteries that can expand and diversify the existing energy storage market. Magnesium batteries are the most promising technology to achieve substantially greater energy density than Li-ion batteries, due to their divalent nature (two electron redox couple). Furthermore, because of its “green” character Mg is environmentally friendly, with high natural abundance in the Earth’s crust (13.9% as compared to 0.0007 % for Li), and atmospheric stability.The current quest for new cathode materials for rechargeable Mg batteries is focused on intercalation compounds exhibiting high working potential and capacity1. When transporting ions have much larger diameter or charge than the host metal ion, segregation of transporting and host metal ions in the crystalline structure is forseable. In this case deintercalation will lead to the collapse of the crystalline structure and breaking of electric conductance. Therefore, our approach to achieving magnesium intercalation is to use nanoscale material that have adjustable d spacing and two-dimensional layered structure that can to control polarizability of Mg2+ions and accommodate large charge/volume changes.Nanostructured electrode materials represent one of the most attractive strategies to dramatically enhance battery performance. Short diffusion length associated with the nanosized dimensions effectively reduces the distance that ions and electrons must travel during cycling. Their large surface area increases the contact area between electrode and electrolyte and hence the number of active sites for electrode reactions, which in turn reduces electrode polarization loss and improves power density, energy efficiency, and usable energy.Nanostructured bilayered V2O5 is highly efficient 3 V cathode material for ambient temperature sodium ion batteries2. It shows superb performance: theoretical reversible capacity for Na2V2O5 stochiometry of 250 mAh/g, excellent rate capability and cycle life, as well as high energy and power densities. Preliminary results show that it is possible to extend the reversible ion-insertion chemistry of nanostructured layered V2O5 beyond lithium and larger in size Na+ ions to those with higher charge: Mg2+ions. Results and Discussion As–prepared nanostructured bilayered V2O5 cathode is synthesized in the charged state. To provide source enrichment, prior to assembling into full Mg-ion cell, it was necessary to pre-condition V2O5 cathode (intercalate with Mg2+ ions). Half-cells were discharged galvanostatically at 20mA down to and 0.01 V versus Mg/ Mg2+, respectively, using an automated Maccor battery tester at ambient temperature. As shown in Figure 1., upon electrochemical pre-condition (Mg-ion half cell) the X-ray edge energy for vanadium is shifted toward the lower energy as a consequence of a vanadium reduction due to Mg intercalation. Pre-edge peak is proportional to the octahedral symmetry of the vanadium sites and its decrease upon transporting ion intercalation is due to modification of vanadium local environment into more ordered, symmetric structure. Based on the main-edge peak position and comparison with Na-ion half cell we estimate 1 Mg is incorporated in the V2O5 structure (V5+ is reduced to V4+). It was previously shown that the V5+ was reduced to V4+ when discharged to 1.5V versus Na/ Na+ (Na-ion half cell)2. As a result of this electrochemical pre-condition we created Mg-rich V2O5 cathodes that were able to provide source of Mg-ions in full-cell. Furthermore, we employed HRTEM, X-Ray fluorescence (XRF) imaging and classical molecular dynamics simulations to understand the role of environment in the intercalation processes of Mg-ions into V2O5cathode. Conclusions We have developed high-voltage nanostructured V2O5 cathode for Mg-ion rechargeable batteries that can operate in commercial electrolytes. Our results emphasize the importance of tailoring nanoarchitecture of electrode materials and open up new opportunities for rechargeable Mg batteries. In the near future, we plan using the combined experimental and theoretical approach to guide our efforts to increase the Mg enrichment to reach the ultimate goal of inserting 2 Mg-ions/V2O5. Acknowledgement. This work was supported as part of the Joint Center for Energy Storage Research (JCESR), an Energy Innovation Hub funded by DOE, Office of Science, Basic Energy Science (BES). Use of the Center for Nanoscale Materials was supported by the U. S. Department of Energy, Office of Science, and Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357. References (1) On the Way to Rechargeable Mg Batteries: The Challenge of New Cathode Materials, E. Levi, Y. Gofer, and D. Aurbach, Chem. Mater. 2010, 22, 860–868.(2) Vanadium Oxide Electrodes for Rechargeable Sodium-Ion Batteries, Sanja Tepavcevic, Hui Xiong, Vojislav R. Stamenkovic, Xiaobing Zuo, Mahalingam Balasubramanian, Vitali B. Prakapenka, Christopher S. Johnson, and Tijana Rajh, Nanostructured Bilayered ACS Nano, 2012, 6 (1), 530–538.

Recent research in electrification of transportation, particularly road and air transportation, has led to increased interest in high-energy-density rechargeable batteries. In particular, the metal-air battery group is attractive, thanks to high theoretical energy density, both gravimetric and volumetric. At present, the Li-O2 battery, one of the most promising members of the class, exhibiting the highest energy density of any known battery chemistry, suffers from electrolyte and electrode instability, as well as limited rechargeability and discharge capacity. Hartmann et al. have demonstrated a rechargeable Na-O2 battery, with the primary observed discharge product reported to be sodium superoxide (NaO2).[1] Their battery shows superior cycle life and Coulombic efficiency to state-of-the-art Li-O2 batteries. Rigorous description of the Na-O2 battery reaction mechanism requires detailed understanding of the electronic structure throughout the phase space of sodium oxides. The roles of nucleation, nanoscale stabilization, and surface energetics of various sodium-oxygen compounds have been examined through a combination of Density Functional Theory (DFT) calculations and electrochemical measurements.[2] This research has led to improved understanding of Na-O2 battery reactions, which, as proposed, constitute a combination of surface and solution mechanisms involving the NaO2 discharge product. As a group, alkali superoxides are known to be highly disordered materials, both in internal geometry and magnetic ordering.[3] Presently, there is limited understanding of geometric and magnetic disorder in bulk NaO2. It is crucial to map out disorder in room-temperature NaO2, considering its importance in determining electronic structure, surface energetics, and growth properties relevant to Na-O2 battery cycling. In this work, we aim to fill gaps in the current understanding of the electronic structure of bulk NaO2. We perform a series of DFT calculations, incorporating the Hubbard U correction applied to oxygen, to describe geometric and magnetic disorder in bulk NaO2. DFT-calculated energies are used to construct an Ising Model of interactions between oxygen dimer units within the bulk NaO2. We find that both 2-body and 3-body nearest-neighbor interactions, which take into account both the geometric and magnetic disorder of the structure, are critical to accurately describe bulk NaO2. Further, we extend the study to examine the role of next-nearest-neighbor interactions within the bulk; although these interactions are lower in energy, they influence long-range ordering within the bulk material. The constructed Ising Model is used within the framework of a Metropolis Monte Carlo simulation to calculate bulk properties for supercells of increased dimension; these simulations demonstrate phase transitions within the bulk material, which are most clearly seen within the largest simulated supercells, as is demonstrated in the accompanying figure.[5] Further, we observe that the calculated bandgap of bulk NaO2 is strongly affected by the degree of internal disorder of the material.

The field of advanced batteries faces today two main challenges: development of power sources for electro-mobility (i.e., electrochemical propulsion) and development of storage technologies for load-leveling applications (i.e., large scale batteries). Our starting point in this presentation is state-of-the-art Li-ion batteries. Using carbonaceous anodes and lithiated transition metal cathodes with selected combinations of transition metals may offer very suitable batteries for full EVs. Ni rich Li[NiCoMn]O2, Mn and Li rich Li1+x[NiMnCo]1-xO2 cathode materials operating in the right potential windows can provide Li-ion batteries high enough energy density as needed for full electrochemical propulsion. Also, by combining Li-Ti-O anodes with LiMPO4 olivine cathodes it is possible to demonstrate very suitable battery systems for stationary large energy storage applications. We will review briefly the updated frontier of Li-ion battery technology. Despite the high capability of this battery technology, there are so many applications for power sources in modern life, what promote very strongly a search for more new battery systems. The use of sulfur cathodes in Li batteries can increase considerably their gravimetric energy density, however, the volumetric energy density of Li-sulfur battery systems is not advantageous compared to advanced Li ion batteries. The good news are that in recent years, we see a nice progress in developing durable composite sulfur cathodes. It seems that there are 3 main approaches: encapsulating sulfur in activated carbon matrices, the use of substrates to which the LiSn species formed by sulfur reduction adsorb very strongly and the use of composite cathodes with high loading of sulfur and semi-permeable membranes that avoid transport of LiSn species to the negative electrodes. There is intensive work on Li-oxygen systems. We see progress in development of electro-catalysis for these systems. We will demonstrate electro-catalytic electrodes in Li-oxygen cells, which anodic reactions (Li-peroxide oxidation and molecular oxygen evolution) occur at very low over-potential, that does not endanger the stability of the electrolyte solutions. We demonstrate also red-ox mediators in solutions that facilitate both ORR and OER. Despite the frustration from the slow progress made towards practical directions, it is important to continue investing efforts in Li-oxygen systems. The community should understand that a long-term research is still required in order to see practical horizons to Li-air battery systems. A main problem is the reactivity of all kinds of polar-aprotic solvents towards superoxide and peroxide species formed by oxygen reduction, in the presence of the super-electrophilic Li ions. The intensive work on both Li-S and Li-oxygen systems is connected to a renaissance in efforts to develop practical Li metal anodes for rechargeable batteries. However, intensive studies that were carried out during more than 3 decades, concluded more than 15 years ago that there is no way to cycle Li metal anodes in practical rechargeable Li battery systems. Even if dendrites formation is avoided, continuous detrimental reactions between the active metal and any type of relevant electrolyte solution is inevitable. We will examine briefly what are the chances to overcome the intrinsic problems in using Li metal anodes in practical rechargeable batteries. We may be able to suggest practical alternative anodes for non-aqueous batteries based on sulfur or oxygen cathodes. Discussing other options for “beyond Li-ion batteries” usually includes Na-ion and magnesium batteries. In fact, the plethora of relevant Na-ion insertion cathodes available today is a good surprise, especially since many of them demonstrate excellent kinetics. However, there is no way that Na-ion systems can rival Li-ion battery systems in terms of energy density. Hence, Na-ion systems may be relevant for large energy storage applications, that can benefit from the high abundance of Na in earth crust. However for such uses, demonstrating high stability during prolonged cycling is mandatory. Consequently, a major challenge in R&D of Na-ion batteries is to exhibit the durability required for load-leveling applications. Finally, we will mention the status of R&D of rechargeable Mg battery systems: excellent work was done so far on the anode-solutions part. Several families of electrolyte solutions with wide electrochemical windows, in which Mg anodes are fully reversible were demonstrated. We have not seen yet cathodes materials that function well in the solutions in which Mg anodes are fully reversible, except the low voltage/low capacity Chevrel phase cathode materials. Hence, these systems still require long term research work, especially towards high voltage/high capacity cathode materials. A main incentive to develop rechargeable Mg batteries may relate to advantages in safety and high volumetric energy density.

Magnesium (Mg) batteries have been considered one of the most promising “post-lithium-ion” energy storage technologies owing to their high theoretical energy density, earth abundance, and intrinsic safety with air and moisture. However, the cell performance of Mg batteries has been limited to cathode materials leading to sluggish kinetics, low reversible energy density, and poor cycling stability. The development of Mg intercalation cathode materials[1–3] has been impeded by slow Mg2+ solid diffusion due to high charge density, sluggish charge redistribution, and strong electrostatic interaction with host and anions.[4] Many of the Li+-intercalation cathodes are not suitable for Mg2+ insertion.[5] Organic materials with high tunability have attracted significant attention,[6] but it has been challenging to achieve organic Mg batteries with a satisfactory energy density as the commercial lithium-ion battery (100-170 Wh kg-1 [7]) with high power and long cycle life. Here, a new organic cathode for rechargeable Mg batteries is reported based on ethyl viologen (EV), which not only has a fast redox couple EV2+/EV0 but also is capable of coupling with redox-active anions, such as iodide (I-), achieving a total four-electron storage. The EV2+/EV0 redox couple demonstrates a stable cycle life (500 cycles) with a superior rate performance (10 C) owing to intrinsic fast electrode kinetics, and a high material utilization (>80%) was achieved at 1.0 C under a high areal loading of 5 mg cm−2. When coupling with iodide I-, a reversible four-electron storage is achieved with a high energy density (304.2 Wh kg-1) and a stable cycle life (>100 cycles). This study provides effective strategies for designing reversible multielectron storage for high-rate and high-energy rechargeable Mg batteries.[8] Reference s : [1] X. Sun, P. Bonnick, V. Duffort, M. Liu, Z. Rong, K. A. Persson, G. Ceder, L. F. Nazar, Energy Environ. Sci. 9 (2016) 2273-2277.[2] X. Sun, P. Bonnick, L. F. Nazar, ACS Energy Lett. 1 (2016) 297-301.[3] B. Liu, T. Luo, G. Mu, X. Wang, D. Chen, G. Shen, ACS nano 7 (2013) 8051-8058.[4] E. Levi, M. D. Levi, O. Chasid, D. Aurbach, J Electroceram. 22 (2009) 13-19.[5] M. Bouroushian, Electrochemistry of metal chalcogenides, Springer Science & Business Media, Heidelberg, Berlin, 2010.[6] M. Mao, T. Gao, S. Hou, C. Wang, Chem. Soc. Rev. 47 (2018) 8804-8841.[7] J.-M. Tarascon, M. Armand, in: V. Dusastre (Ed.), Materials for Sustainable Energy: A Collection of Peer-Reviewed Research and Review Articles from Nature Publishing Group, World Scientific, Singapore, 2011, pp. 171–179.[8] Y. Sun, Q. Zou, Y. Lu, Adv. Energy Mater. 9 (2019) 1903002. Acknowledgements : This work was supported by a grant from the Research Grants Council (RGC) of the Hong Kong Administrative Region, China, under an RGC project No. T23-601/17-R.

A key aspect of any future battery technology development is safety. Although lithium-based batteries are ubiquitous, there are still challenges related to their energy density, cycle life, cost and safety. In regard to safety, compared with organic electrolyte, aqueous rechargeable batteries may provide a safer alternative for reliable, low-cost and large-scale energy storage systems. As seen from the penetration test in Fig. 1a-1b, the battery with organic electrolyte catches fire, yet the battery with aqueous electrolyte is relatively safe. Moreover, aqueous batteries have high ion conductivity and cost effectiveness. Generally, the cell voltage and energy density of aqueous batteries are lower than those of organic-based batteries (e.g. Li-ion) because of the relatively smaller electrochemical stability window of water. Among all the metals that are stable in water, zinc is the most active and has the lowest possible operating potential. This means using Zn anode can increase overall cell voltage of aqueous batteries. Moreover, zinc is globally available, inexpensive (3.19 USD kg-1), and has high capacity (820 Ah kg-1 and 5854 Ah L-1). Zinc-based aqueous batteries also possess the stability to be operated in ambient air. Accordingly, Zn aqueous rechargeable batteries are promising to become a safer energy storage system. Among zinc-based aqueous batteries, Zn-air batteries have high theoretical volumetric energy density, which is around three times that of conventional Li-ion batteries (LIB). Zn anodes have been investigated in neutral/mild acidic aqueous electrolytes. Yet in order to pair them with oxygen cathode to reach the highest energy density, alkaline aqueous electrolyte is ideal, in which the oxygen electrode has low polarization. In alkaline aqueous electrolyte, Zn anode undergoes a Zn (s) ↔ Zn(OH)4 2- (aq) ↔ ZnO (s) conversion. This solid-solute-solid transformation and insulating discharge product ZnO lead to three vital challenges: 1) ZnO passivates Zn surface and prevents further discharging, leading to low Zn utilization; 2) ZnO is insulating and can hardly be charged back to Zn; 3) diffusion of Zn(OH)4 2- causes the loss of active material and change of electrode morphology. Thus, anode modification and protection are needed to alleviate the passivation and dissolution. We firstly designed a Zn mesh@GO anode (Fig 1c). Graphene oxide (GO) layers on the Zn mesh surface deliver electrons across insulating ZnO and can slow down the Zn dissolution. However, the utilization of zinc is still low because passivation problem is not completely solved. Through SEM investigation, critical passivation size was found to be ~ 2 µm. Thus, we further designed a lasagna-inspired ZnO@GO anode (Fig 1d). ZnO nanoparticles are encapsulated by GO. ZnO lasagna structure has three features: 1) the size of ZnO nanoparticles is smaller than the critical size of passivation; 2) the fabrication of ZnO lasagna anode starts with commercially available ZnO nanoparticles (~100 nm), and is compatible with the roll-to-roll process, which is ideal for large-scale manufacturing; 3) GO allows permeation of OH- and water, and prevents loss of Zn active material through blocking bigger Zn(OH)4 2-. As a result, such lasagna anode achieves a high volumetric capacity of 2308 Ah/L and a remarkable capacity retention of 86% after 150 cycles. In contrast, the open-structured ZnO nanoparticle anode, without the protection of GO, completely died after 90 cycles. Figure 1

4 - Nickel batteries

Li-ion batteries are commonly used in portable electronic devices due to their outstanding energy and power density. However, in order to reach the requirements of the automotive industry for next-generation electric vehicles regarding safety, life-time, energy density, and fast charging further developments are inevitable. Additionally, a reduction of material and production costs is needed to improve the price competitiveness. In this contribution we will present a study of different electrode design concepts with the goal to optimize energy and power density of Li-Ion battery electrodes and cells by microstructure resolved electrochemical simulations [1]. State-of-the-art NMC positive electrodes with different thickness and density were prepared and characterized electrochemically in collaboration with our partners [2]. In a next step reconstructions of the electrodes were created with the help of synchrotron tomography and a 3D stochastic microstructure generator [3], [4]. The resulting microstructures are then input to electrochemical simulations within our software BEST and good qualitative agreement between the simulations and experimental data can be reported. Especially, the pivotal role of inactive materials for battery performance could be demonstrated through microstructure-resolved impedance simulations. Based on these results different design concepts were evaluated regarding their energy and power density. An attractive strategy to decrease the share of inactive materials is to increase the mass loading of the electrodes [5], [6]. This concept provides a high theoretical capacity and energy density. However, it also shifts the transport limitations of shuttling lithium ions in the electrolyte to lower C-rates and reduces the rate capability and practical capacity of the cell [6], [7]. In order to enable a fast charging of the batteries structuring techniques are investigated. A promising concept is the laser perforation of the electrodes which creates a hierarchical pore network with macroscopic transport pathways between anode and cathode. Our simulations confirm the beneficial effects which are found in the experiments and we perform an extensive simulation study in order to investigate the effect of different hole geometries and configurations on battery performance and life time. Our study shows that this simulation-based approach is a powerful and efficient tool for the analysis and design of porous electrodes for Li-ion batteries. Acknowledgement This work has been funded by the ‘Bundesministerium für Bildung und Forschung’ within the project HighEnergy under the reference numbers 03XP0073D.

There are many design tradeoffs in lithium-ion batteries, the most notable being the loss of energy density at high power densities. New design requirements, such as low battery cost, further exacerbate these classic tradeoffs because they require thick electrodes with high loading. The power density in these dense electrodes is typically limited by Li+ depletion in the cathode electrolyte, which shuts off the cell before the full capacity can be extracted. In most industrial processes, concentration depletion can be overcome by introducing advection, but the small-scale pores and solid current collectors in batteries prevent the electrolyte from sustaining any form of bulk motion. Strategies to improve power density in thick electrodes, therefore, include increasing the electrode porosity (which reduces energy density) or increasing the electrolyte transference number (which is a difficult materials challenge).This work uses finite-element simulations to understand how battery performance would be influenced by internal advection of liquid electrolyte. We also propose a mechanism to achieve this through electro-osmotic flow of the electrolyte through charged separators. Our simulations demonstrate that the addition of a channel that circulates the electrolyte between the two ends of the cell can improve the battery’s volumetric energy density by 69% when discharged at a 4 C rate. Performance gains can be further amplified to 104% if an advective current can be maintained at 1 um/s.Figures 1(a) and 1(b) depict the simulation layout, which includes a standard lithium-ion battery with an 80-um thick lithium cobalt oxide (LCO) cathode, 50 um separator region, and 152 um LiC6 anode with 1 M LiPF6 in 1:1 EC/DEC. A modification introduces a thin channel, 1.2X the width of the cell (~340 um), that allows for electrolyte flow between the current collector ends of the cathode and anode. The multiphysics model follows a Newman approach and captures Li+ diffusion, migration, and advection in the electrolyte. Lithium diffusion and electron conduction are modeled in the electrodes, and Butler-Volmer kinetics govern the reaction kinetics. In both geometries, the LCO cathode is discharged from 4.3 V to 2.5 V.We perform simulations of the following geometries to understand the isolated effects of electrolyte continuity and advection: (1) a standard cell with no channel, (2) a cell with a channel but no flow, and (3) a cell with bulk motion of electrolyte through a channel. Figure 1(c) shows the electrolyte salt concentration within each battery at the end of discharge. The standard cell geometry notably features depletion of lithium ions ~15 um into the cathode, rationalizing the sharp drop in the cell’s discharge curve at 2.85 V (Figure 2). The addition of a channel results in migration and diffusion of lithium ions along the concentration gradient between the two current collector ends, significantly delaying ion depletion in the cathode during discharge. Introducing bulk motion further minimizes the depletion of electrolyte in the cathode and, in the extreme case of 100 um/s flow, completely eliminates ion depletion limitations.Figure 2 shows the voltage vs. energy density graph of each design, demonstrating a 104% increase in energy density for a channel-added geometry with 1 um/s of continuous bulk motion. Higher flow rates have marginal performance benefits, as a two order of magnitude increase in velocity leads to a <1% increase in energy density. Figure 2 further illustrates that, without bulk motion, the introduction of a channel results in an energy density increase of 69% relative to a normal, channel-less cell. Because the channel’s contribution to the battery size varies depending on the design of the modified cell, the discharge curves in Figure 2 do not account for volumetric changes and thus represent the maximum performance benefit that can be realized. Taking into account the channel’s volume in this particular design, however, only drops the performance gains to 82% for 1 um/s flow and 52% without any flow, demonstrating significant improvements despite the lack of robust design optimization.This simulation shows that advective flow of liquid electrolyte can improve the high rate performance of classic lithium-ion battery designs, as well as future designs with thick and dense electrodes. We believe that this can be rationally done by using porous current collectors and allowing flow through individual cell layers until the electrolyte is recirculated at cylindrical cell walls. To drive the flow internally, a charged membrane can function as an electro-osmotic pump that harnesses the inherent electric field of the electrolyte, allowing for massive gains in energy density within compact energy storage systems. Figure 1

The challenges for rechargeable batteries are cost, safety, energy, density, life, and rate. Traditional rechargeable batteries based on aqueous electrolytes have good rate capabilities but limited energy density because the voltage for a long shelf-life is restricted to 1.5 V. The discovery of fast Na ion conductivity in β-alumina in 1967 introduced the novel concept of a solid oxide electrolyte and molten electrodes: the sodium–sulfur battery operates at 350 °C. Interest in rechargeable batteries with aprotic electrolytes was further stimulated by the first energy crisis in the early 1970s. Since protons are not mobile in aprotic electrolytes, the Li+ ion was the logical choice for the working ion, and on-going work on reversible Li intercalation into layered sulfides suggested the TiS2//Li cell, which was shown in 1976 to have a voltage of V ≃ 2.2 V and good rate capability. However, the organic liquid carbonates used as electrolytes are flammable, and dendrites growing across the electrolyte from the lithium anode on repeated charge/discharge cycles short-circuited the cells with disastrous consequences. Safety concerns caused this effort to be dropped. However, substitution of the layered oxides LiMO2 for the layered sulfides MS2 and reversible intercalation of Li into graphitic carbon without dendrite formation at slow charging rates gave a safe rechargeable lithium ion battery (LIB) of large-enough energy density to enable the wireless revolution. Although carbon-buffered alloys now provide anodes that allow a fast charge and have a higher capacity, nevertheless a passivation layer permeable to Li+ forms on the anode surface, and the Li+ in the passivation layer is taken irreversibly from the cathode on the initial charge. Since the specific capacity of a cell with an insertion-compound cathode is limited by the latter, strategies to increase the specific capacity for a LIB powering an electric vehicle or storing electricity from wind or solar farms include a return to consideration of a solid electrolyte.

Lithium‐ion rechargeable batteries are widely used not only for mobile devices but also for electric vehicles and energy‐storage systems because of their high voltage, high energy density, high power density, long cycle life, no memory effect, and other excellent characteristics. Sony was the first company in the world which mass‐produced lithium‐ion rechargeable batteries using lithium cobalt oxide (LiCoO 2 )/carbon system. Unlike the previous batteries, it was completed not only by electrochemical knowledge but also by the integration of physics, chemistry, metallurgy, electronics, and almost all other sciences and technologies. Sony had fortunately almost all of the technologies within the group even in the year 1991. The success of Sony will be described in this article.

Li-S batteries are among the most promising candidates for the next generation rechargeable batteries due to their high energy density, low raw material cost and environmental friendliness [1]. Despite this great potential, the complicated electrochemical process introduces many challenges for Li-S batteries, including low conductivity of both elemental sulfur and end discharge product Li2S, large volume expansion of 80% upon discharge, and unfavorable redox shuttle effect due to soluble nature of intermediate lithium polysulfide LiPS [2,3]. Although Li-S batteries possess a high theoretical cathode specific capacity of 1,672 mAh g-1, the energy density of practical Li-S batteries is much smaller and depends on electrolyte/sulfur (E/S in mL g-1) ratio. From previous works, successful operation of Li-S batteries under lean electrolyte conditions can be challenging, especially in the case when the solubility of LiPS sets an upper bound for polysulfide dissolution. Very recently, we have demonstrated that the E/S ratio of Li-S cells has a significant effect on both performance and theoretical energy density of Li-S batteries. Since the lower-bound for E/S ratio is restricted by the solubility of LiPS in the organic electrolyte, the theoretical energy density of Li-S batteries is significantly reduced. Experimentally, it was approved that when the LiPS concentration reached to the solubility limitation in the electrolyte, the reaction rate of reducing sulfur to LiPS in the cathode will reduce significantly [4]. In this talk, we will discuss the relationship between theoretical specific energy and the solubility of LiPS in the electrolyte. The theoretical specific energy of a Li-S battery can be expressed as: e=CLVcell/(MC+MA+Mele) (1) where, CL is the lower capacity in amount of cathode and anode, Vcell is the cell voltage (e.g. 2.1 V), MC, MA, Mele are weights of sulfur (cathode), lithium (anode), and electrolyte, respectively. In an ideal case, capacities of cathode and anode are equal and to be MA=2×6.94MC/32.065, the atomic weights of lithium and sulfur are 6.94 and 32.065 g/mol, respectively, the capacity is CL=cSMC where cS=1,672 mAh/g is the theoretical specific capacity of sulfur. The minimum weight ratio of electrolyte to sulfur is: Mele/MC=rele/32.065S (2) where, rele is the mass density of electrolyte (e.g. 1.2 g/cm3) and S is the solubility of LiPS in unit of M[S]/L; therefore, the theoretical specific energy for a Li-S battery is: e=3511/(1.4327+37.42/S[M/L])[Wh/kg] (3) Fig. 1 shows the theoretical specific energy of Li-S batteries when the LiPS solubility is considered as an intrinsic limitation for Li-S battery capacity. Here only the weight of active electrode material, such as sulfur and lithium, as well as electrolyte weight is included in calculation. From Fig. 1, it can be seen that for commonly used electrolytes with LiPS solubility less than 8 M[S]/L, the theoretical energy is less than 575 Wh/g. Fig. 2 further presents a series of specific energy calculation for Li-S battery with different E/S ratios. From Fig. 2(a), it can be seen that the electrolyte weight would dominate in a Li-S battery even in relatively low E/S conditions. Fig. 2(b) plots the effective theoretical specific capacity of a Li-S battery. Fig. 2(c) that the reduced effective specific capacity introduced by LiPS solubility limit would offset electrolyte weight loss under low E/S conditions, making the theoretical specific energy curve relatively flat under low E/S region, while without considering LiPS solubility the specific energy will increase sharply when E/S ratio is decreased. The above results imply that reducing E/S ratio would become pointless when LiPS solubility is reached. For further boosting capacity of Li-S batteries, electrolyte with even higher LiPS solubility is favorable. Fig. 2(d) plots the specific energy of an ideal Li-S cell under different LiPS solubility. Reference: [1] A. Manthiram, Y. Fu, S. Chung, C. Zu, Y. Su, Rechargeable Lithium–Sulfur Batteries, Chem. Rev. 114 (2014) 11751–11787. [2] Z.W. Seh, Y. Sun, Q. Zhang, Y. Cui, Designing high-energy lithium–sulfur batteries, Chem. Soc. Rev. (2016). [3] W. Kang, N. Deng, J. Ju, Q. Li, D. Wu, X. Ma, et al., A review of recent developments in rechargeable lithium-sulfur batteries, Nanoscale. 1 (2016) 16541–16588. [4] C. Shen, J. Xie, M. Zhang, J.P. Zheng, M. Hendrickson, and E.J. Plichta, J. Electrochem. Soc., 164 (2017) A1220-A1222. Figure 1