Rechargeable batteries: challenges old and new

This Account provides perspective on the evolution of the rechargeable battery and summarizes innovations in the development of these devices. Initially, I describe the components of a conventional rechargeable battery along with the engineering parameters that define the figures of merit for a single cell. In 1967, researchers discovered fast Na(+) conduction at 300 K in Na β,β''-alumina. Since then battery technology has evolved from a strongly acidic or alkaline aqueous electrolyte with protons as the working ion to an organic liquid-carbonate electrolyte with Li(+) as the working ion in a Li-ion battery. The invention of the sodium-sulfur and Zebra batteries stimulated consideration of framework structures as crystalline hosts for mobile guest alkali ions, and the jump in oil prices in the early 1970s prompted researchers to consider alternative room-temperature batteries with aprotic liquid electrolytes. With the existence of Li primary cells and ongoing research on the chemistry of reversible Li intercalation into layered chalcogenides, industry invested in the production of a Li/TiS2 rechargeable cell. However, on repeated recharge, dendrites grew across the electrolyte from the anode to the cathode, leading to dangerous short-circuits in the cell in the presence of the flammable organic liquid electrolyte. Because lowering the voltage of the anode would prevent cells with layered-chalcogenide cathodes from competing with cells that had an aqueous electrolyte, researchers quickly abandoned this effort. However, once it was realized that an oxide cathode could offer a larger voltage versus lithium, researchers considered the extraction of Li from the layered LiMO2 oxides with M = Co or Ni. These oxide cathodes were fabricated in a discharged state, and battery manufacturers could not conceive of assembling a cell with a discharged cathode. Meanwhile, exploration of Li intercalation into graphite showed that reversible Li insertion into carbon occurred without dendrite formation. The SONY corporation used the LiCoO2/carbon battery to power their initial cellular telephone and launched the wireless revolution. As researchers developed 3D transition-metal hosts, manufacturers introduced spinel and olivine hosts in the Lix[Mn2]O4 and LiFe(PO4) cathodes. However, current Li-ion batteries fall short of the desired specifications for electric-powered automobiles and the storage of electrical energy generated by wind and solar power. These demands are stimulating new strategies for electrochemical cells that can safely and affordably meet those challenges.

The rapid worldwide energy consumption is necessitating more energy generation from environmentally benign sources like solar, wind, or tide. However, the lack of efficient energy storage devices is the major limitation for the practical harvest of these clean energies. Rechargeable batteries are the promising solution for the efficient energy storage. We have witnessed the great success of secondary lithium-ion batteries (LIBs) in portable electronic devices in the last two decades. However, the cost and safety barriers make traditional LIBs not desirable to meet the requirements for large power applications, such as the electric or plug-in hybrid vehicles. In contrast, the multivalent ion rechargeable batteries such as Mg1-3 and Ca4 , 5 ion batteries are more promising as larger and safer energy storage devices due to their advantages in safety, cost and capacity. For instance, compared to lithium, magnesium metal is non-toxic, more air resistant and free from the dangerous dendrite formation. The higher natural abundance of magnesium makes it more than 20 times cheaper than lithium in cost. In addition, the divalent characteristic of magnesium ion (Mg2+) enables magnesium to have a nearly doubled volumetric capacity as an anode than the lithium (3832 mA cm-3 vs 2062 mA cm-3). All these merits have brought significant attention on magnesium-ion batteries as the new generation rechargeable energy storage device. Inspired by the pioneer work by Aurbach group for the development of the famous dichloro-complex magnesium electrolyte (2EtAlCl2-MgBu2),6 a lot of efforts have been devoted to the development of high voltage electrolytes for rechargeable magnesium-ion batteries. In contrast to the rapid development of effective magnesium electrolytes capable of reversibly plating/stripping magnesium with wide electrochemical windows, the design of high potential cathode material for magnesium ion batteries is far behind. To date, the Chevrel phase Mo6S8 is still the only cathode material with excellent cycling reversibility and reasonable rate capability in rechargeable magnesium-ion batteries. However, Mo6S8 could only operate at a relatively low voltage in magnesium-ion batteries (< 1.3 V) with a typical below 100 mAh g-1 capacity. Thus, development of high operating voltage cathode material deserves great attention in nowadays. Herein, we would like to present our recent progress on the development of high voltage and high performance rechargeable magnesium-ion batteries using redox active organic molecules as cathode material. As shown in Figure 1(a), when the 0.3M Mg(HMDS)2-4MgCl2 in THF solution was used as the electrolyte,7 excellent reversible redox processes have been observed in the cyclic voltammetry measurement when the redox active organic molecule was used as the cathode material. The redox potential was detected at around 1.7 V (vs Mg/Mg2+), which is much higher than the well-known Chevral phase Mo6S8. The compatibility and reversibility of the organic cathode material with the electrolyte and magnesium metal anode was further demonstrated in the batteries upon cycling. As shown in Figure 1(b), excellent cycling performance has been observed with around 120 mAh g-1 initial specific discharge capacity at the current rate of 0.5C, and still about 102 mAh g-1specific discharge capacity was obtained in 100 cycles (around 84% capacity retention). The results further suggest the great success of using redox active organic molecules as cathode material for secondary multivalent-ion batteries. (1) Muldoon, J.; Bucur, C. B.; Gregory, T. Chem Rev 2014, 114, 11683. (2) Saha, P.; Datta, M. K.; Velikokhatnyi, O. I.; Manivannan, A.; Alman, D.; Kumta, P. N. Prog Mater Sci 2014, 66, 1. (3) Yoo, H. D.; Shterenberg, I.; Gofer, Y.; Gershinsky, G.; Pour, N.; Aurbach, D. Energ Environ Sci 2013, 6, 2265. (4) Padigi, P.; Goncher, G.; Evans, D.; Solanki, R. J Power Sources 2015, 273, 460. (5) Lipson, A. L.; Pan, B.; Lapidus, S. H.; Liao, C.; Vaughey, J. T.; Ingram, B. J. Chem Mater 2015, ASAP. (6) Aurbach, D.; Lu, Z.; Schechter, A.; Gofer, Y.; Gizbar, H.; Turgeman, R.; Cohen, Y.; Moshkovich, M.; Levi, E. Nature 2000, 407, 724. (7) Liao, C.; Sa, N.; Key, B.; Burrell, A. K.; Cheng, L.; Curtiss, L. A.; Vaughey, J. T.; Woo, J. J.; Hu, L. B.; Pan, B. F.; Zhang, Z. C. Journal of Materials Chemistry A 2015, 3, 6082. Figure 1

[Introduction] Rechargeable batteries for the storage of electrical energy are required for the introduction of renewable energy and compact electronic devices for the sustainable society.[1] Although lithium-ion batteries currently dominate the market, rechargeable metal–air batteries with very high energy densities have been attracting attention due to increasing power consumption and demand for low environmental burden. They are composed of oxygen from air as the cathode-active material, metal as the anode-active material and a strong alkaline solution as the electrolyte. They have the advantage of high energy density and low environmental burden due to the use of oxygen as the cathode-active material. While primary Zn–air batteries are commercialized, rechargeable metal–air batteries are under investigation due to their low cycle performance caused by dendrites and metal oxides formed on the metal anode, which leads to disposal of anode-active materials. In addition, strong basic electrolytes are used due to their high ionic conductivity, and the carbonate clogging by carbon dioxide in the air is also a problem. Therefore, rechargeable air batteries, which consist of acid or neutral electrolyte and anode-active materials which is recyclable and do not form dendrites or metal oxides, are required. Organic redox molecules, which are reversibly redox-active organic compounds, are composed of earth-abundant and relatively available building blocks (C, H, N, O, and S), and their functions can be tuned by molecular design, which has attracted attention as new electrode-active materials. We have previously reported that rechargeable polymer–air batteries using an organic redox polymer with organic redox molecules in the side chain of polymer as the anode-active material and acidic aqueous solution as the electrolyte charged and discharged without the formation of dendrites or carbonates.[2] However, organic materials suffer from low durability, and organic redox materials with structural stability in the electrolyte have been required. In the current work, we focused on UiO-66, a metal-organic framework with structural stability in acid and base electrolyte, and synthesized UiO-66-(OH2) with 1,4-dihydroxybenzene, an organic redox molecule as a linker, which undergoes a reversible redox reaction even in acid electrolytes. An anode-active material composed of UiO-66-(OH2) did not form dendrites or metal oxides in H2SO4 aqueous electrolyte (pH 1) and exhibited charge storage with high cycle stability. A rechargeable acidic MOF–air battery was demonstrated for the first time. After use, UiO-66-(OH2) electrode was facilely decomposed and separated to the original raw chemicals by NH4HCO3 aqueous solution.[Results and Discussion] We synthesized UiO-66-(OH2) from zirconium(IV) chloride and 2,5-dihydroxyterephthalic acid by microwave irradiation. UiO-66-(OH2) was coated on a glassy carbon plate in the presence of single-walled carbon nanotube as the conductive additive. The UiO-66-(OH2) electrode exhibited charging-discharging curves of a plateau voltage at 0.2 V, and the ratio of discharging vs. charging capacity (i.e. coulombic efficiency) were nearly 96%. The high capacity of the UiO-66-(OH2) electrode suggested that almost all of the -OH moieties contributed to charge storage. Even after 300 cycles, UiO-66-(OH2) electrode exhibited high cycle performance, which was relatively robust compared to other n-type redox materials for rechargeable aqueous air batteries. These results demonstrated that UiO-66-(OH2) has high cycle stability as an anode-active material for rechargeable acidic MOF-air batteries. A rechargeable acidic MOF-air battery was fabricated with a UiO-66-(OH2), Pt/C, and H2SO4 aqueous electrolyte (pH 1) as the anode material, cathode material, and electrolyte, respectively. The coulombic efficiencies of the battery were nearly 97%, demonstrating the reversible charge storage property of the cell. The high capacity for the anode suggested that almost all of the -OH moieties contributed to charge storage. Even after 100 charging-discharging cycles, the battery kept the high discharging capacity even at a rapid discharging. These results demonstrated the long-life ability of the rechargeable acidic MOF-air battery. UiO-66-(OH2) electrode in the battery was facilely decomposed and separated to the original raw chemicals by NH4HCO3 aqueous solution after charging and discharging.[Conclusions] We synthesized UiO-66-(OH2), which is stable in aqueous electrolyte, and applied it to an anode-active material. The rechargeable acidic MOF-air battery exhibited high cycle performance without the formation of dendrites or carbonates. In addition, we successfully recycled UiO-66-(OH2) electrode after charging and discharging. The current work presented a first step for developing electrode materials for the future energy storage.[References][1] J. Kim, Y. Kim, J. Yoo, G. Kwon, K. Kang et al., Nat. Rev. Mater. , 8, 54–70, 2023.[2] K. Oka, S. Furukawa, S. Murao, H. Nishide, K. Oyaizu et al., Chem. Commun. , 56, 4055–4058, 2020. Figure 1

In the last two decades, rechargeable Li-ion batteries have dominated the market. However, the increasing demand for energy storage creates new challenges for further use of lithium-ion batteries mainly due to the problems associated with limited energy density and high cost. To improve the specific energy of rechargeable batteries, a lithium-sulphur (Li-S) battery attracts particular interest in recent years as next-generation energy storage device due to its highest energy density (2600 Wh/kg) and theoretical capacity (1672 mAh/g) among all known systems. Furthermore, sulphur is cheap, abundant and environmentally benign. Despite this, due to its insulating nature, large volume changes during cycling of cell, and solubility of the polysulfides formed during these processes, the practical application of lithium-sulphur rechargeable batteries has not been successful yet [1]. To overcome these problems, we developed and investigated a free-standing and flexible carbon membrane as an interlayer between the sulfur/PANI composite cathode and the separator to prevent the shuttling of the intermediate polysulfides in Li-S batteries. Sulphur/PANI composites were prepared based on the as-prepared sulphur powder via a self-assembly process. 15 ml of aqueous suspension, containing 1 g sulphur was sonicated for 10min. 15 ml of aniline (An) monomer solution in water was dissolved into the suspension and stirred magnetically for 0.5 h at room temperature. pH of the suspension was adjusted to pH 2.0 with 1 M HCl solution then replaced into ice bath. A precooled FeCl3 aqueous solution was added into the resulting mixture together with diluted HCl. The mixture was reacted for 5 h at 0−5 °C. A black precipitate was separated by filtration and then thouroghly washed several times with deionized water, ethanol, acetone and 0.01 M HCl, and dried overnight under reduced pressure at room temperature to get the final composite product. Different molar ratio of aniline to sulphur were used to optimize the formation condition for preparation of the sulphur/PANI composites. Cathode electrodes were prepared by mixing 80 wt% sulphur/PANI, 10 wt% polyvinylidene fluoride (PVdF, Kynar, HSV900) as a binder and 10 wt% acetylene black as a conducting agent in 1-methyl-2-pyrrolidinone (NMP, Sigma-Aldrich). The resultant slurry was coated on aluminium foil as a current collector, and vacuum dried at 60 °C for 3 h. Free-standing and flexible carbon membranes have been prepared by mixing carbon source and a binder at different molar ratio, coated on aluminium foil and vacuum dried at 60 °C for 4 h. After drying the composite has been detached from aluminium foil, cuted and set between the sulphur/PANI cathode and separator (Celgard). Lihium metal used as anode. The coin cell type cells were assembled in an argon filled glove box (MBRAUN LABMASTER). 1 M LiPF6solution in EC:DMC:DEC (1:1:1) was used as electrolyte. In summary, we have successfully prepared flexible and free-standing carbon membrane for Li–S batteries. Carbon membrane adsorbed the intermediate polysulfides and prevented their shuttling, and a battery with the sulphur/PANI composite exhibited excellent lithium storage performance, enhanced cycle stability and high rate capacity. This publication has been made within the Sub-project #157-2013 which is funded under the Technology Commercialization Project, supported by the World Bank and the Government of the Republic of Kazakhstan Keywords: lithium-sulphur batteries, free-standing membrane, energy storage.

With the development of Chinese industrial technique, electronic products tend to be small sized and portable. So it required batteries to be miniature, light weight, with high energy capacity and long service life. China had achieved great progress in electrochemical power sources industry in the last ten years. Especially, there is an ceaseless developing trend in the rechargeable battery field. Chinese chemical power source investigators had done a great deal of work on lead-acid, nickel-iron, nickel-cadmium (Ni-Cd), nickel-metal hydride (Ni-MH) and lithium ion batteries, among which, lead-acid, nickel-iron, nickel-cadmium and nickel-metal hydride batteries are produced in commercial scale. And some hopeful results were also achieved on rechargeable lithium batteries and lithium ion batteries. In this article we concentrate on the introduction of the research, development and manufacture status of nickel-cadmium and nickel-metal hydride batteries, hoping that this paper will give a deeper understanding in the field of Chinese rechargeable batteries.

Issue and challenges facing rechargeable thin film lithium batteries

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.

Chapter 9 - Rechargeable Batteries and Their Management

Rechargeable lithium ion batteries are important energy storage devices; however, the specific energy of existing lithium ion batteries is still insufficient for many applications due to the limited specific charge capacity of the electrode materials. The recent development of sulfur/mesoporous carbon nanocomposite cathodes represents a particularly exciting advance, but in full battery cells, sulfur-based cathodes have to be paired with metallic lithium anodes as the lithium source, which can result in serious safety issues. Here we report a novel lithium metal-free battery consisting of a Li(2)S/mesoporous carbon composite cathode and a silicon nanowire anode. This new battery yields a theoretical specific energy of 1550 Wh kg(-1), which is four times that of the theoretical specific energy of existing lithium-ion batteries based on LiCoO(2) cathodes and graphite anodes (approximately 410 Wh kg(-1)). The nanostructured design of both electrodes assists in overcoming the issues associated with using sulfur compounds and silicon in lithium-ion batteries, including poor electrical conductivity, significant structural changes, and volume expansion. We have experimentally realized an initial discharge specific energy of 630 Wh kg(-1) based on the mass of the active electrode materials.

Lithium-ion batteries (LIBs) have attracted significant attention as high-energy-density rechargeable power sources for electric vehicles and large-scale energy storage applications. Although LIBs have been successfully commercialized in the world battery market, the expected shortage of lithium resources resulting from the ever-increasing demand for LIBs needs to be addressed. This issue has accelerated the search for alternative power sources such as sodium-ion batteries (SIBs), which are emerging as promising candidates to replace LIBs. Sodium is one of the most plentiful resources on earth; thus, SIBs have been extensively studied because of their low cost as well as their competitiveness in terms of energy density versus LIBs. However, the ionic size of Na+ (1.02 Å) is larger than that of Li+ (0.76 Å), which affects the phase stability, transport properties, and interphase formation. The low standard redox potential of sodium (−2.71 V vs. standard hydrogen electrode (SHE)) compared with that of lithium (−3.04 V vs. SHE) is another demerit of SIBs; hence, a high capacity is necessary to compensate for the low operation voltage to approximate the energy density levels of LIBs. Thus far, various types of electrode materials have been suggested as cathode materials for SIBs, including Na2/3MnO2, Na2/3[MxMn1 −x]O2 (M: transition metals), NaCrO2, α-MnO2, and Na3V2PO3. Vanadium oxides (VxOy) is of interest because of the wide range of oxidation states available from +2 (as in VO) to +5 (as in V2O5), which affects the structural, electrochemical, and magnetic properties. This property has led to the application of vanadium oxides in catalysts, chemical sensors, and energy storage devices such as rechargeable lithium batteries. Herein, we introduce new nanosized hollandite-type VO1.75(OH)0.5 as a novel cathode material for Na-ion batteries. Structural investigation based on X-ray diffraction (XRD), neutron diffraction (ND), and Rietveld refinement suggests the presence of numerous vacant sites for Na+ intercalation and structural information on hydrogen in the VO1.75(OH)0.5. All of the possible Na+ sites and tunnel-type Na+ diffusion pathways along the c-axis are confirmed by bond-valence-sum analyses. The nanosized hollandite-type VO1.75(OH)0.5 delivers an unexpectedly high specific capacity of approximately 351 mAh g−1 at 15.5 mA g-1 in the voltage range of 1.0–3.7 V (vs. Na+/Na), which agrees well with the results predicted by first-principles calculations. In addition, combined studies using first-principles calculations and several experimental techniques including in-situ operando X-ray diffraction and ex situ X-ray absorption spectroscopy confirm that the nanosized hollandite-type VO1.75(OH)0.5 undergoes a single-phase reaction with a capacity retention of 71% over 200 cycles. Furthermore, the open structure and nanosized particles of hollandite-type VO1.75(OH)0.5 contribute to its excellent power capability with 56% of the capacity measured at 0.05C being delivered at 7C. These results indicated the outstanding cyclability of Na x VO1.75(OH)0.5 as a promising cathode material for SIBs. We believe that our novel approach will provide insight for the discovery and understanding of novel electrode materials for not only SIBs but also other rechargeable batteries. Figure 1

Research on solid-state batteries began in the 1950s to address issues that stem from the liquid electrolyte, such as electrolyte leakage. Today, with implementation of batteries in larger systems like electric vehicles or the grid, the performance demands are greatly increased, which compounds the safety issues associated with electrolyte decomposition. In solid state batteries, a solid electrolyte is utilized, which eliminates the use of flammable, organic solvents in the cell. Solid state electrolytes transport ions with better selectivity than liquid electrolytes, which reduces unwanted side reactions. Liquid electrolyte decomposition can also accelerate passivation of the solid/electrolyte interface1. Solid-state batteries may be the key to the development of safe lithium batteries. Lithium batteries are exciting next generation energy storage as lithium anodes have the most negative potential of any known material, which enables lithium anodes to have a high energy density and high discharge voltage. However, lithium batteries suffer from many issues that have prevented their widespread commercialization as rechargeable cells. When lithium metal batteries are cycled, the anode is used non-uniformly which leads to the development of finger-like dendrites. Dendrite formation leads to cell short circuits, higher rates of adverse reactions, and large volume changes. These problems are major safety issues but also account for the low Coulombic efficiency and poor cycling performance2. The utilization of all-solid-state cells for lithium batteries can reduce the growth of dendrites3, which greatly improves safety2. However, solid-state batteries suffer from high resistances at ambient temperatures. Wu et al.4 studied an all-solid-state battery composed of a lithium foil anode and a cathode made of lithium ferric phosphate (LFP) particles in a block copolymer matrix. In the cathode, the electronic conduction is facilitated by a conducting polymer, poly(3-hexylthiophene) (P3HT). The conductivity of this semiconductor polymer depends on the electrode potential because the conducting polymer is oxidized and reduced when transporting the electrons. The electronic conductivity of the cathode polymer matrix without the LFP active particles was measured as a function of the voltage, and this experimental fit was used with a macro-homogeneous continuum model developed by Newman and associates5,6. The model output was relatively independent of the rate and failed to capture the trend of the experimental data. The authors then reduced the electronic conductivity until the best agreement between the experimental data and the model was achieved4. This talk explores the possibility of obtaining better fits for the model predictions by performing detailed estimation of different parameters that affect the performance of the system by combining different/robust simulation and estimation methods. Acknowledgments The authors are thankful for the financial support from the Battery 500 Consortium and the Clean Energy Institute (CEI) at the University of Washington. References Takada, K., AIP Conf. Proc., 1765, (2016).Cheng, X. B., Zhang, R., Zhao, C. Z. & Zhang, Q., Chem. Rev., 117, 10403–10473 (2017).Kim, J. G. et al., J. Power Sources, 282, 299–322 (2015).Wu, S.-L., Javier, A. E., Devaux, D., Balsara, N. P. & Srinivasan, V. J., Electrochem. Soc., 161, A1836–A1843 (2014).Newman, J. S. & Tobias, C. W., J. Electrochem. Soc., 109, 1183 (1962).Doyle, M., Fuller, T. F. & Newman, J., J. Electrochem. Soc., 140, 1526 (1993).

A nanometer thick passivation layer will spontaneously form on Li-metal in battery applications due to electrolyte reduction reactions. This passivation layer in rechargeable batteries must have "selective" transport properties: blocking electrons from attacking the electrolytes, while allowing Li+ ion to pass through so the electrochemical reactions can continue. The classical description of the electrochemical reaction, Li+ + e → Li0, occurring at the Li-metal|electrolyte interface is now complicated by the passivation layer and will reply on the coupling of electronic and ionic degrees of freedom in the layer. This passivation layer is called "solid electrolyte interphase (SEI)" and is considered as "the most important but the least understood in rechargeable Li-ion batteries," partly due to the lack of understanding of its structure-property relationship. Predictive modeling, starting from the ab initio level, becomes an important tool to understand the nanoscale processes and materials properties governing the interfacial charge transfer reaction at the Li-metal|SEI|electrolyte interface. Here, we demonstrate pristine Li-metal surfaces indeed dissolve in organic carbonate electrolytes without the SEI layer. Based on joint modeling and experimental results, we point out that the well-known two-layer structure of SEI also exhibits two different Li+ ion transport mechanisms. The SEI has a porous (organic) outer layer permeable to both Li+ and anions (dissolved in electrolyte), and a dense (inorganic) inner layer facilitate only Li+ transport. This two-layer/two-mechanism diffusion model suggests only the dense inorganic layer is effective at protecting Li-metal in electrolytes. This model suggests a strategy to deconvolute the structure-property relationships of the SEI by analyzing an idealized SEI composed of major components, such as Li2CO3, LiF, Li2O, and their mixtures. After sorting out the Li+ ion diffusion carriers and their diffusion pathways, we design methods to accelerate the Li+ ion conductivity by doping and by using heterogonous structure designs. We will predict the electron tunneling barriers and connect them with measurable first cycle irreversible capacity loss. Finally, we note that the SEI not only affects Li+ and e- transport, but it can also impose a potential drop near the Li-metal|SEI interface. Our challenge is to fully describe the electrochemical reactions at the Li-metal|SEI|electrolyte interface. This will be the subject of ongoing efforts.

The charge/discharge microstructural conditions that lead to mechanical failure, salt precipitation, and lithium dendrite formation in rechargeable lithium-ion batteries are explored. By starting from high resolution X-ray tomography, three-dimensional representations of porous microstructures from commercially batteries are used to simulate its local electrochemical and chemo-mechanical behavior and identify those microstructural features that will favor failure and heterogeneous lithium nucleation. The analysis demonstrates that spatial variation in porosity, particle roughness and morphology significantly alter the local intercalation kinetics, state of charge, mechanical stability, and dendrite formation. Based on this analysis, the thermodynamic conditions that will enable current density-controlled failure, its macroscopic Weibull statistics, and a overpotential-controlled critical lithium electrodeposit to become energetically favorable are identified. We define several regimes of growth behavior and directly compare them against experimental data to propose: nucleation and growth regimes, where after a short incubation time nuclei will grow as a result of favored morphological instabilities and localized fields directly impacting the macroscopic response and long term useful life of the device.

Organic Ionic Plastic Crystals (OIPCs) are increasingly drawing attention as a new type of solid-state electrolyte for lithium rechargeable batteries, because they can essentially relieve the safety concerns of the present commercial lithium batteries based on organic and flammable solvents and thus pave the way towards more robust energy storage solutions for electric vehicles and power grids. However, although significant progress has been made towards the realisation of practical OIPC-based solid electrolytes, the lack of thorough fundamental understanding of their properties, especially the nature of their ionic motion and transport and the effects of Li salt addition, has limited the development of prototype lithium cells using OIPC-based electrolytes. This PhD thesis therefore has three goals: 1) to obtain more insights into the fundamentals of the materials, especially their phase-dependent plastic crystal behaviour; 2) to under- stand the effects of the addition of Li ions on the structure and dynamics of OIPC matrices; 3) to demonstrate prototype Li cells with OIPC-based electrolytes operating at ambient temperature. For Goal 1, two recently synthesised phosphonium cation-based OIPCs, i. e. diethyl(methyl)(isobutyl)phosphonium hexafluorophosphate ([P1224][PF6]) and triethyl(methyl)phosphonium bis(fluorosulfonyl)imide ([P1222][FSI]) were investigated by a combination of analytical methods and theoretical simulations/calculations. The evolution of the motions of the cations and the anions in different phases of both plastic crystals was examined, and models proposed to explain the strongly phase-dependent ionic conductivities of these OIPCs. Cooperative motion of cations and anions was proposed for [P1222][FSI] at a particular temperature range, in which some unusual phase behaviour was observed. For Goal 2, molecular dynamics simulations of the effects of lithium salt addition to a model plastic crystal, tetramethylammonium dicyanamide ([N1111][DCA]) were performed. Cluster formation between Li ions and anions was found: Li-DCA clusters enhance the mobility of the ions that are not in the clusters. This is a somewhat surprising atomic-level explanation of how doped Li ions in the OIPC enhance its ion transport properties. For Goal 3, the electrochemical properties of triisobutyl(methyl) phosphonium bis(fluorosulfonyl) imide ([P1444][FSI]) were examined, and this plastic crystal was used to build prototypical Li metal cells. These cells showed, for the first time, practical cell performance (ca. 160 mA h g-1 discharge capacity achieved at 0.1 C) at ambient temperature. The main contributions of this thesis to the field are 1) proposing new models of the ionic motions of OIPCs with respect to their phase behaviour 2) showing the value of the combined analytical and theoretical methodology in studying OIPCs; 3) demonstrating promising Li cell performance with an OIPC-based electrolyte at ambient temperature.

Biomass carbon micro/nano-structures derived from ramie fibers and corncobs as anode materials for lithium-ion and sodium-ion batteries