David G. Kwabi

Bio: David G. Kwabi is an academic researcher from Massachusetts Institute of Technology. The author has contributed to research in topics: Electrolyte & Lithium. The author has an hindex of 25, co-authored 45 publications receiving 3780 citations. Previous affiliations of David G. Kwabi include University of Michigan & Harvard University.

Lithium–oxygen batteries: bridging mechanistic understanding and battery performance

Abstract: Rechargeable energy storage systems with high energy density and round-trip efficiency are urgently needed to capture and deliver renewable energy for applications such as electric transportation Lithium–air/lithium–oxygen (Li–O2) batteries have received extraordinary research attention recently owing to their potential to provide positive electrode gravimetric energies considerably higher (∼3 to 5×) than Li-ion positive electrodes, although the packaged device energy density advantage will be lower (∼2×) In light of the major technological challenges of Li–O2 batteries, we discuss current understanding developed in non-carbonate electrolytes of Li–O2 redox chemistry upon discharge and charge, oxygen reduction reaction product characteristics upon discharge, and the chemical instability of electrolytes and carbon commonly used in the oxygen electrode We show that the kinetics of oxygen reduction reaction are influenced by catalysts at small discharge capacities (Li2O2 thickness less than ∼1 nm), but not at large Li2O2 thicknesses, yielding insights into the governing processes during discharge In addition, we discuss the characteristics of discharge products (mainly Li2O2) including morphological, electronic and surface features and parasitic reactivity with carbon On charge, we examine the reaction mechanism of the oxygen evolution reaction from Li2O2 and the influence of catalysts on bulk Li2O2 decomposition These analyses provide insights into major discrepancies regarding Li–O2 charge kinetics and the role of catalyst In light of these findings, we highlight open questions and challenges in the Li–O2 field relevant to developing practical, reversible batteries that achieve the anticipated energy density advantage with a long cycle life

The discharge rate capability of rechargeable Li–O2 batteries

Abstract: The O2electrode in Li–O2cells was shown to exhibit gravimetric energy densities (considering the total weight of oxygen electrode in the discharged state) four times that of LiCoO2 with comparable gravimetric power. The discharge rate capability of Au-catalyzed Vulcan carbon and pure Vulcan carbon (VC) as the O2electrode was studied in the range of 100 to 2000 mA gcarbon−1. The discharge voltage and capacity of the Li−O2 cells were shown to decrease with increasing rates. Unlike propylene carbonate based electrolytes, the rate capability of Li−O2 cells tested with 1,2-dimethoxyethane was found not to be limited by oxygen transport in the electrolyte. X-Ray diffraction (XRD) showed lithium peroxide as the discharge product and no evidence of Li2CO3 and LiOH was found. It is hypothesized that higher discharge voltages of cells with Au/C than VC at low rates could have originated from higher oxygen reduction activity of Au/C. At high rates, higher discharge voltages with Au/C than VC could be attributed to faster lithium transport in nonstoichiometric and defective lithium peroxide formed upon discharge, which is supported by XRD and X-ray absorption near edge structure O and Li K edge data.

Influence of Li2O2 morphology on oxygen reduction and evolution kinetics in Li–O2 batteries

Abstract: Understanding the origins of high overpotentials required for Li2O2 oxidation in Li–O2 batteries is critical for developing practical devices with improved round-trip efficiency. While a number of studies have reported different Li2O2 morphologies formed during discharge, the influence of the morphology and structure of Li2O2 on the oxygen evolution reaction (OER) kinetics and pathways is not known. Here, we show that two characteristic Li2O2 morphologies are formed in carbon nanotube (CNT) electrodes in a 1,2-dimethoxyethane (DME) electrolyte: discs/toroids (50–200 nm) at low rates/overpotentials (10 mA gC−1 or E > 2.7 V vs. Li), or small particles (<20 nm) at higher rates/overpotentials. Upon galvanostatic charging, small particles exhibit a sloping profile with low overpotential (<4 V) while discs exhibit a two-stage process involving an initially sloping region followed by a voltage plateau. Potentiostatic intermittent titration technique (PITT) measurements reveal that charging in the sloping region corresponds to solid solution-like delithiation, whereas the voltage plateau (E = 3.4 V vs. Li) corresponds to two-phase oxidation. The marked differences in charging profiles are attributed to differences in surface structure, as supported by X-ray absorption near edge structure (XANES) data showing that oxygen anions on disc surfaces have LiO2-like electronic features while those on the particle surfaces are more bulk Li2O2-like with modified electronic structure compared to commercial Li2O2. Such an integrated structural, chemical, and morphological approach to understanding the OER kinetics provides new insights into the desirable discharge product structure for charging at lower overpotentials.

Chemical and Morphological Changes of Li–O2 Battery Electrodes upon Cycling

Abstract: We report considerable chemical and morphological changes of reaction products in binder-free, vertically aligned carbon nanotube (VACNT) electrodes during Li–O2 battery cycling with a 1,2-dimethoxyethane (DME)-based electrolyte. X-ray absorption near edge structure (XANES) of discharged oxygen electrodes shows direct evidence for the formation of Li2CO3-like species at the interface between VACNTs and Li2O2 but not significantly on the Li2O2 surfaces exposed to the electrolyte. Although Li2O2 and Li2CO3-like species were largely removed upon first charge, the oxidation kinetics became increasingly difficult during Li–O2 cycling, which is accompanied by the accumulation of Li2CO3 in the discharged and charged electrodes as evidenced by selected area electron diffraction (SAED) and transmission electron microscopy (TEM). Together, these results indicate that the irreversibility during Li–O2 cycling in DME can be attributed largely to the growth of Li2CO3-like species associated with the reactivity between ...

Electrolyte Lifetime in Aqueous Organic Redox Flow Batteries: A Critical Review

Abstract: Aqueous organic redox flow batteries (RFBs) could enable widespread integration of renewable energy, but only if costs are sufficiently low. Because the levelized cost of storage for an RFB is a function of electrolyte lifetime, understanding and improving the chemical stability of active reactants in RFBs is a critical research challenge. We review known or hypothesized molecular decomposition mechanisms for all five classes of aqueous redox-active organics and organometallics for which cycling lifetime results have been reported: quinones, viologens, aza-aromatics, iron coordination complexes, and nitroxide radicals. We collect, analyze, and compare capacity fade rates from all aqueous organic electrolytes that have been utilized in the capacity-limiting side of flow or hybrid flow/nonflow cells, noting also their redox potentials and demonstrated concentrations of transferrable electrons. We categorize capacity fade rates as being "high" (>1%/day), "moderate" (0.1-1%/day), "low" (0.02-0.1%/day), and "extremely low" (≤0.02%/day) and discuss the degree to which the fade rates have been linked to decomposition mechanisms. Capacity fade is observed to be time-denominated rather than cycle-denominated, with a temporal rate that can depend on molecular concentrations and electrolyte state of charge through, e.g., bimolecular decomposition mechanisms. We then review measurement methods for capacity fade rate and find that simple galvanostatic charge-discharge cycling is inadequate for assessing capacity fade when fade rates are low or extremely low and recommend refining methods to include potential holds for accurately assessing molecular lifetimes under such circumstances. We consider separately symmetric cell cycling results, the interpretation of which is simplified by the absence of a different counter-electrolyte. We point out the chemistries with low or extremely low established fade rates that also exhibit open circuit potentials of 1.0 V or higher and transferrable electron concentrations of 1.0 M or higher, which are promising performance characteristics for RFB commercialization. We point out important directions for future research.

Li-O2 and Li-S batteries with high energy storage.

Abstract: Li-ion batteries have transformed portable electronics and will play a key role in the electrification of transport. However, the highest energy storage possible for Li-ion batteries is insufficient for the long-term needs of society, for example, extended-range electric vehicles. To go beyond the horizon of Li-ion batteries is a formidable challenge; there are few options. Here we consider two: Li-air (O(2)) and Li-S. The energy that can be stored in Li-air (based on aqueous or non-aqueous electrolytes) and Li-S cells is compared with Li-ion; the operation of the cells is discussed, as are the significant hurdles that will have to be overcome if such batteries are to succeed. Fundamental scientific advances in understanding the reactions occurring in the cells as well as new materials are key to overcoming these obstacles. The potential benefits of Li-air and Li-S justify the continued research effort that will be needed.

Challenges Facing Lithium Batteries and Electrical Double‐Layer Capacitors

Abstract: Energy-storage technologies, including electrical double-layer capacitors and rechargeable batteries, have attracted significant attention for applications in portable electronic devices, electric vehicles, bulk electricity storage at power stations, and “load leveling” of renewable sources, such as solar energy and wind power. Transforming lithium batteries and electric double-layer capacitors requires a step change in the science underpinning these devices, including the discovery of new materials, new electrochemistry, and an increased understanding of the processes on which the devices depend. The Review will consider some of the current scientific issues underpinning lithium batteries and electric double-layer capacitors.

High-power all-solid-state batteries using sulfide superionic conductors

Abstract: Compared with lithium-ion batteries with liquid electrolytes, all-solid-state batteries offer an attractive option owing to their potential in improving the safety and achieving both high power and high energy densities. Despite extensive research efforts, the development of all-solid-state batteries still falls short of expectation largely because of the lack of suitable candidate materials for the electrolyte required for practical applications. Here we report lithium superionic conductors with an exceptionally high conductivity (25 mS cm−1 for Li9.54Si1.74P1.44S11.7Cl0.3), as well as high stability ( ∼0 V versus Li metal for Li9.6P3S12). A fabricated all-solid-state cell based on this lithium conductor is found to have very small internal resistance, especially at 100 ∘C. The cell possesses high specific power that is superior to that of conventional cells with liquid electrolytes. Stable cycling with a high current density of 18 C (charging/discharging in just three minutes; where C is the C-rate) is also demonstrated. The development of all-solid-state batteries requires fast lithium conductors. Here, the authors report a lithium compound, Li9.54Si1.74P1.44S11.7Cl0.3, with an exceptionally high conductivity and demonstrate that all-solid-state batteries based on the compound have high power densities.

Metal-free catalysts for oxygen reduction reaction.

Abstract: Liming Dai,*,†,‡ Yuhua Xue,†,‡ Liangti Qu,* Hyun-Jung Choi, and Jong-Beom Baek* †Center of Advanced Science and Engineering for Carbon (Case4Carbon), Department of Macromolecular Science and Engineering, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, Ohio 44106, United States Key Laboratory of Cluster Science, Ministry of Education of China, Beijing Key Laboratory of Photoelectronic/Electrophotonic Conversion Materials, Department of Chemistry, School of Science, Beijing Institute of Technology, Beijing 100081, People’s Republic of China School of Energy and Chemical Engineering/Center for Dimension-Controllable Covalent Organic Frameworks, Ulsan National Institute of Science and Technology (UNIST), 100 Banyeon, Ulsan, 689-798, South Korea

A reversible and higher-rate Li-O2 battery.

Abstract: The rechargeable nonaqueous lithium-air (Li-O(2)) battery is receiving a great deal of interest because, theoretically, its specific energy far exceeds the best that can be achieved with lithium-ion cells. Operation of the rechargeable Li-O(2) battery depends critically on repeated and highly reversible formation/decomposition of lithium peroxide (Li(2)O(2)) at the cathode upon cycling. Here, we show that this process is possible with the use of a dimethyl sulfoxide electrolyte and a porous gold electrode (95% capacity retention from cycles 1 to 100), whereas previously only partial Li(2)O(2) formation/decomposition and limited cycling could occur. Furthermore, we present data indicating that the kinetics of Li(2)O(2) oxidation on charge is approximately 10 times faster than on carbon electrodes.