Biomimetic Superoxide Disproportionation Catalyst for Anti-Aging

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A Biomimetic Superoxide Disproportionation Catalyst for Anti-Aging Lithium-Oxygen Batteries Chihyun Hwang, JongTae Yoo, Gwan Yeong Jung, Se Hun Joo, Jonghak Kim, Aming Cha, JungGu Han, Nam-Soon Choi, Seok Ju Kang, Sang-Young Lee, Sang Kyu Kwak, and Hyun-Kon Song ACS Nano, Just Accepted Manuscript • DOI: 10.1021/acsnano.9b03525 • Publication Date (Web): 18 Jul 2019 Downloaded from pubs.acs.org on July 19, 2019

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A Biomimetic Superoxide Disproportionation Catalyst for Anti-Aging Lithium-Oxygen Batteries Chihyun Hwang,†,§ JongTae Yoo,‡,§ Gwan Yeong Jung,†,§ Se Hun Joo,† Jonghak Kim,† Aming Cha,† Jung-Gu Han,† Nam-Soon Choi,† Seok Ju Kang,† Sang-Young Lee,† Sang Kyu Kwak,*,† and Hyun-Kon Song*,† †

School of Energy and Chemical Engineering, Ulsan National Institute of Science and

Technology (UNIST), 50 UNIST-gil, Ulsan 44919, Republic of Korea ‡R&D

Investment Planning Team, Korea Institute of Science & Technology Evaluation and

Planning (KISTEP), Seoul 06775, Republic of Korea

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ABSTRACT Reactive oxygen species or superoxide (O2-) to damage or age biological cells is generated during metabolic pathways using oxygen as an electron acceptor in biological systems. Superoxide dismutase (SOD) protects cells from the superoxide-triggered apoptosis by converting superoxide to oxygen and peroxide. Lithium-oxygen battery (LOB) cells have the same aging problems caused by superoxide-triggered side reactions. We transplanted the function of SOD of biological systems into LOB cells. Malonic acid-decorated fullerene (MAC60) was used as a superoxide disproportionation chemo-catalyst mimicking the function of SOD. As expected, MA-C60 as the superoxide scavenger improved capacity retention along charge/discharge cycles successfully. A LOB cell that failed to provide a meaningful capacity just after several cycles at high current (0.5 mA cm-2) with 0.5 mAh cm-2 cut-off survived up to 50 cycles after MA-C60 was introduced to electrolyte. Moreover, the SOD-mimetic catalyst increased capacity: e.g., more than six-fold increase at 0.2 mA cm-2. Experimentally observed toroidal morphology of the final discharge product of oxygen reduction (Li2O2) and density functional theory calculation confirmed that the solution mechanism of Li2O2 formation, more beneficial than the surface mechanism from the capacity-gain standpoint, was preferred in the presence of MA-C60.

KEYWORDS: superoxide dismutase, superoxide disproportionation, lithium-oxygen batteries, catalyst, biomimetic


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In living organisms, energy is stored in a form of adenosine triphosphate (ATP) by mitochondria. The ATP is generated through an electron transport chain where the final electron acceptor is an oxygen molecule. The most of oxygen molecules are completely reduced to water during the process. However, reactive oxygen species including superoxide radical (O2•-) are often generated as a result of incomplete reduction of oxygen. The superoxide radical makes damages to mitochondria and resultantly triggers an apoptosis process of cells. 1-3

Superoxide dismutase (SOD) is the most important actor in the defence mechanism of

organisms against the superoxide-triggered apoptosis. The enzyme catalyzes dismutation or disproportionation of superoxide radicals into less reactive species, oxygen or hydrogen peroxide in biological systems: O2•- + O2•- D O2 + O22-

(1)

In artificial energy storage devices using oxygen as electron acceptors, also, harmful effects of chemically reactive superoxide are found. Lithium-oxygen batteries (LOBs) have received considerable attentions due to their high theoretical energy densities (3505 Wh kg-1 for LOBs versus 387 Wh kg-1 for lithium ion batteries).4-10 During the discharge process of LOBs, O2 is initially reduced to superoxide intermediate (O2•-). Unstable and reactive superoxide species (O2•- or LiO2) is converted to lithium peroxide (Li2O2) via two different routes (Figure 1a).11-13 Superoxide radical is combined with Li+ to be insoluble LiO2 on electrode surface immediately after its formation, followed by electrochemical conversion to Li2O2 (surface mechanism). A dense layer of Li2O2 is formed on the surface of electrode via the surface mechanism. Alternatively, superoxide radicals dissolved in electrolyte forms toroidal Li2O2 particles on cathode without transient formation of insoluble LiO2 (solution mechanism). Superoxide disproportionation reaction (equation 1) plays an important role of producing peroxide in the solution mechanism.14 In addition to the superoxide-to-peroxide 3 ACS Paragon Plus Environment

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conversion for discharge, superoxide triggers side reactions like in organisms, which are serious hurdles limiting LOB performances. Superoxide as a strong nucleophile attacks organic solvent molecules and carbon cathodes to form by-product deposits including Li2CO3 and LiOH (Figure 1b).11,

13, 15

The by-products are accumulated on cathode to hinder oxygen

evolution reaction during the following charge process and to develop large polarization. Four categories of strategies to improve performances of LOBs should be mentioned: (1) strong solvation by high-donor-number (DN) molecules, (2) redox-active mediation for discharge (DRM for discharge redox mediator), (3) superoxide scavenging and (4) redox-active mediation for charge (CRM for charge redox mediator).5, 16-19 First, high DN solvent molecules (e.g., dimethyl sulfoxide and water) stabilized superoxide by strong solvation and encouraged the solution mechanism for Li2O2 formation.20-22 Solution mechanism is preferred for achieving higher capacity since the insulating film of Li2O2 generated in surface mechanism hindered electron transfer to reactants. Therefore, the use of high-DN solvents improved capacity from 0.7 mAh cm-2 with dimethyl ether at DN = 20 to 2.1 mAh cm-2 with dimethyl sulfoxide at DN = 29.8. In the second strategy of DRM, redox-active molecules mediated electrons between cathode and oxygen in a kinetically fast way, decreasing discharge overpotential.23, 24 Abundant superoxide radicals generated by the mediation encouraged the solution mechanism and therefore capacities were improved by the DRM: 0.1 mAh cm-2 to 3.1 mAh cm-2 by introducing 2,5-Di-tert-butyl-1,4-benzoquinone (DBBQ). Even if the strategies (high DN and DRM) worked successfully in terms of capacity and overpotential, it should be notified that the previous works did not mention or emphasize durable operation of LOBs guaranteeing capacity retention of extensive cycles.


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Cyclability or stability could be improved if an excess of superoxide triggering side reactions were removed. Polydopamine as a sacrificial superoxide radical scavenger successfully improved the cyclability even if capacity gains and overpotential benefits were not expected.25 A slight decrease in capacity (~10 %) was observed probably due to the excessive removal of superoxide. In the fourth strategy of CRM, another redox mediator were used for boosting up the electron transfer kinetics between electrode and Li2O2.26-28 In addition to overpotential benefit as shown in DRM, Li2O2 formed on electrodes as a result of discharge processes was fully utilized without leaving dead deposits. High coulombic efficiencies led to good cyclability. As a summary, the first two strategies (high DN and DRM) encourage capacity to increase while the latter two strategies (scavenger and CRM) support improved cyclability. Superoxide disproportionation is a part of solution mechanism of Li2O2 formation during discharge. From the lesson of SOD in biological systems, the superoxide-triggered side reaction pathways could be detoured by adopting the SOD. The catalyzed disproportionation would bring additional merits in LOBs in addition to the side-reaction suppression resulting in more durable operation. By accelerating one of the constituent steps, disproportionation, the solution mechanism could be favored rather than the surface mechanism in the presence of SOD, guaranteeing higher capacity with smaller overpotential during discharge. However, it looks difficult to use SOD in LOB systems because natural enzymes work in an aqueous (not organic) environment and their stability is not guaranteed for a long-term operation. Fortunately, various organic and inorganic compounds, the function of which is that of SOD or superoxide dismutation (equivalent to disproportionation), have been reported in the field of anti-aging.29, 30


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Herein, we used a SOD-mimetic compound (SODm) to scavenge superoxide and then convert superoxide to peroxide chemically during Li-O2 battery operation. Malonic-aciddecorated fullerene (MA-C60), one of the SODm showing the superior chemical stability, captured or stabilized superoxide radicals on their L

=

surface and the malonate

functionality (Figure 1b).31 Disproportionation of two superoxide molecules adsorbed on MAC60 (equation 1) was catalyzed to form Li2O2 by the help of Li+ electrostatically combined with carboxylates of malonic acid groups. Therefore, the electrolyte decomposition and the side reactions with carbon, which are triggered by superoxide species, were detoured. Li2O2 formation via solution mechanism, rather than via surface mechanism, was encouraged in the presence of MA-C60. It should be notified that the solution route is more beneficial than the surface route because electrode surface can be used in a more efficient way without the formation of insoluble Li2O2 films blocking the access of O2 to electrically conductive surface.

RESULTS AND DISCUSSION The stabilization of the short-lived superoxide radicals by MA-C60 was confirmed by the spin trapping technique detecting superoxide radicals.32, 33 Superoxide radical generated from KO2 dissolved in dimethyl sulfoxide was reacted with 5-diethoxyphosphoryl-5-methyl-1-pyrroline N-oxide (DMPO as the spin trap) to form the adduct having the unpaired electrons responsible for paramagnetism. It should be notified that dimethyl sulfoxide was used as the solvent of the radical experiments even if ether was used in electrolytes of LOBs (e.g., 1 M LiTFSI in DEGDME). The reasons are (1) KO2 is sparingly soluble in the ether electrolytes and (2) dimethyl sulfoxide is more stable against superoxide radical than ether. Therefore, the dimethyl-sulfoxide environment is appropriate to investigate the interaction between MA-C60 6 ACS Paragon Plus Environment

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and superoxide radical, excluding the possible consumption of superoxide radical through electrolyte decomposition. The stable paramagnetic radical of the DMPO-superoxide adduct in dimethyl sulfoxide was evidently detected by the electron paramagnetic resonance (EPR) spectroscopy (Figure 2a). However, the singlet signal relevant to superoxide radical, instead of the multiplet signal of the unpaired-electron DMPO-superoxide adduct, was found in the presence of MA-C60. It supports that superoxide radical was stabilized by MA-C60 and the reaction between superoxide and DMPO was inhibited. The extended life of superoxide in the presence of MA-C60 probably increases the chance of the collision between superoxides and consequently promotes the subsequent disproportionation reaction in LOB cells. The solubility of MA-C60 was estimated between 30 mM and 100 mM in the ether electrolyte used in LOB cells (1 M LiTFSI in DEGDME). MA-C60 was completely dissolved in the electrolyte up to 30 mM while a precipitate was found on the bottom of the vial containing 100 mM MA-C60 solution (Figure S1). Therefore, we used MA-C60 less than the solubility limit in electrolytes for LOB cells. The ionic conductivity of the ether electrolyte containing MA-C60 changed insignificantly up to 2 mM: 3.89 mS cm-1 at 1 mM to 3.31 mS cm-1 at 2 mM (Figure S2). However, it decreased abruptly from 4 mM MA-C60: 1.83 mS cm1

at 4 mM to 0.97 mS cm-1 at 10 mM. As a best practice, therefore, the highest concentration

of MA-C60 guaranteeing acceptable ionic conductivity (i.e., 2 mM MA-C60) was used for LOB cells. The MA-C60 was electrochemically stable in anaerobic LOB cells (electrolyte = 1 M LiTFSI in DEGDME) within the operating voltage window (MA-C60/Ar in Figure 2b). In the presence of oxygen, the cathodic current of oxygen reduction reaction (ORR) in the cyclic voltammogram was significantly amplified by the MA-C60 while the onset potential of the cathodic current was shifted to the more positive value (from 2.68 V to 2.76 V; less overpotential) in the presence of MA-C60 (MA-C60/O2 versus None/O2 in Figure 2b). The 7 ACS Paragon Plus Environment

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increase in ORR current as well as less overpotential supports that the solution mechanism of Li2O2 formation was more preferred rather than the surface mechanism by MA-C60. More amount of Li2O2 deposited on the surface of electrode via the surface mechanism is responsible for the increase in charges relevant to the ORR reaction (i.e., the peak area of current). Porous morphology resulting from the accumulation of Li2O2 toroids, as the characteristics of the solution mechanism, provides a facile access of species in electrolyte to electrode (i.e., less overpotential for MA-C60/O2 in Figure 2b). On the other hand, the surface mechanism favors formation of a dense Li2O2 film that hinders the access of electrolyte species to electrode (i.e., higher overpotential for None/O2 in Figure 2b). In the galvanostatic operation of LOB cells, the MA-C60 significantly improved discharge capacities based on cathodic ORR and anodic lithium metal stripping (Figure 2c). Capacities in the presence of MA-C60 was more than doubled in three different ethers when compared with capacities of the MA-C60-absent controls at 0.1 mA cm-2. As current densities increased, the superiorities of MA-C60-present cells to their controls were more emphasized (Figure 2c). The control cells hardly worked at 0.5 mA cm-2 while capacity of MA-C60-present cells at the same current was comparable to the value obtained at 0.1 mA cm-2. The capacities of MA-C60present cells at 0.5 mA cm-2 were ~ 50 fold higher than those of MA-C60-absent controls. Such high capacities obtained in the presence of MA-C60 are considered due to the reduction of superoxide-triggered side reactions. Solvent dependency of capacity was observed in the presence of MA-C60 (Figure 2c): discharge capacity in diethylene glycol dimethyl ether (DEGDME) was larger than that in tetraethylene glycol dimethyl ether (TEGDME) and 1,2-Dimethoxyethane (DME). The interaction between superoxide and MA-C60 was considered to be independent of solvent molecules because the DNs of ethers tested in this work were too small to make differences in 8 ACS Paragon Plus Environment

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solvation/desolvation of superoxide.20, 21 On the other hand, the solvent dependency of Li+ solvation should be considered. Weaker binding strength between Li+ and solvent molecules (solvation energy, PEbind by density function theory (DFT) calculation in Figure S3a) allowed MA-C60 to capture more number of Li+ in solvent environments (nLi by molecular dynamics calculation in Figure S3b to d): PEbind = Q3.97 eV for Li(DEGDME)+ weaker than Q5.02 eV for Li(TEGDME)+ while nLi = 1 for Li(DEGDME)+ higher than 0.6 for Li(TEGDME)+). Weak solvation indicated by less negative PEbind encourages desolvation that is required for adsorption of Li+ on MA-C60. Higher effective Li+ concentration or higher values of nLi to participate in Li2O2 formation on MA-C60 possibly facilitates disproportionation reaction on MA-C60 in a faster way. Therefore, disproportionation is more accelerated by MA-C60 in DEGDME rather than in TEGDME and DME. The roles of MA-C60 to encourage solution mechanism over surface mechanism were confirmed by microscopic morphologies of discharged cathodes. Toroidal Li2O2 were grown on carbon cathode of MA-C60-present cells, which indicates that solution mechanism dominates Li2O2 formation (Figure 3a). On the contrary, any toroidal features were not found from the control cell without MA-C60 (Figure 3a). Only Li2O2 was found on discharged cathode in the presence of MA-C60 without any by-product formation in X-ray diffraction patterns (Figure 3b).34-36 In the absence of MA-C60, however, peaks assigned to Li2CO3 were identified.37 The carbonate compound is the evidence of superoxide-triggered side reactions with solvent molecules and/or carbon substrates.38 The preference to solution mechanism over surface mechanism in the presence of the SODmimic compound was confirmed by DFT calculation. First, adsorption configuration of superoxide on MA-C60 was determined by adsorption energies ( Eads) of superoxide radical or


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soluble lithium superoxide on MA-C60 (Figure S4 and S5).

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Eads was maximized when a

superoxide radical as well as lithium superoxide was attached to –OH of a carboxylic acid group of MA-C60. Hydrogen bonding is responsible for the thermodynamically favoured interaction. Second, the superoxide radical adsorption on MA-C60 was compared with the adsorption on Li2O2. Superoxide radical was adsorbed much more preferentially on MA-C60 than Li2O2: Eads(O2-) = Q1.43 eV for MA-C60 versus +0.12 eV for Li2O2 (100) surface (Figure 3c).39 Since Li2O2 is the deposits on electrode surface, the Eads(O2-) comparison indicates that superoxide radicals generated on electrode surface is diffused into electrolyte and then captured by MA-C60 rather than staying on the electrode surface. That is to say, the solution mechanism is expected to be preferred to the surface mechanism when MA-C60 is present. This calculation result is consistent with the formation of Li2O2 toroids in the presence of MA-C60 (Figure 3a).21, 40 We tested the possibility that the malonic acid (MA) without C60 moiety plays the same role of MA-C60 since the MA moiety of the MA-C60 was revealed to be the thermodynamically most favoured adsorption sites for superoxide (Figure S6). Very different from the EPR spectra of MA-C60 (Figure 2a), there were no EPR peaks of the superoxide radical observed in the presence of MA (Figure S7), indicating that the MA converted the superoxide radical to a nonradical species. Although we are not yet sure what the reaction promoted by MA is, the reaction is not supposed to be the superoxide disproportionation, given the inferior contribution of MA to the LOB capacity. When the MA was used as the additive instead of MA-C60, there was an insignificant improvement in LOB performances observed (Figure S6). The effects of 6 mM MA, equivalent to 2 mM MA-C60 in terms of the number of MA (3 MA functionality in 1 MAC60), on LOB capacity was totally negligible. A small improvement was observed when 50 mM MA, ~10 times more MA than 2 mM MA-C60, was introduced. Moreover, the adsorption 10 ACS Paragon Plus Environment

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of superoxide to the MA in solution was estimated to be much weaker than that to the MA-C60 (Figure S8). The hydrogen-bond-based 5-mer cluster of MAs was thermodynamically favoured in an aprotic environment.41 The inter-MA hydrogen bonds made the superoxide-MA interaction weaker than the superoxide-MA-C60 interaction: the adsorption energy of four superoxide molecules: +0.55 eV to HO- of MA > Q0.38 eV to -C60 of MA-C60 > Q0.92 eV to C60 > Q2.68 eV to HO- of MA-C60. Therefore, both MA moiety and C60 moiety are required for facilitating the superoxide disproportionation. Benefit of the use of superoxide disproportionation catalyst was more clearly understood from a mechanistic standpoint by sketching free energy diagram along reaction pathways of the solution mechanism (Figure 3d and Figure S9 and 10). The thermodynamic barrier of the disproportionation step of (LiO2)2

Li2O2 + O2 (

G] = G(Li2O2 + O2) Q G((LiO2)2))

was +0.78 eV for MA-C60-free situation. The barrier decreased significantly to +0.28 eV when MA-C60 was adopted. Consequently, the solution-phase reaction is considered more favored in the presence of MA-C60 by lowering the endothermicity of the disproportionation barrier. The expected increase in discharge capacity was not always achieved but dependent on concentration of MA-C60. Capacity was improved by MA-C60 up to 2 mM MA-C60 (Figure S11a and b). The capacity increased with increasing amounts of MA-C60 in this hypoconcentration range (2 mM) as more superoxide ions were scavenged by MA-C60. Too low MA-C60 concentration would not suppress parasitic side reactions by the reactive superoxide. In a hyper-concentration situation such as 4 mM in this case, however, the discharge capacity dropped unexpectedly and dramatically to less than the capacity of cells without MA-C60. Sufficient Li+ required for producing Li2O2 (the final product of ORR in LOB cells) would not be provided onto electrode surface because too much Li+ is captured by the carboxylates of


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hyper-concentrated MA-C60. The transition from the hypo to hyper-concentration was already expected from the above-mentioned abrupt drop of ionic conductivity observed from 4 mM MA-C60. The serious decrease of ionic conductivity is possibly caused by the immobilization of lithium ions onto MA-C60 leading to the decrease in the amount of charge carriers in electrolyte. There were no toroidal Li2O2 found in the hyper-concentrated situation (4 mM). It was clearly contrasted to the lower concentration cases (1 mM and 2 mM) (Figure S11c). The lack of lithium ions discouraged the solvent mechanism leading to toroidal Li2O2 particles and encouraged the surface mechanism for making dense film of Li2O2 on electrodes.21 In addition to the investigation on discharge products, gases released during charge were analyzed by using in situ differential electrochemical mass spectroscopy (DEMS) (Figure 4a and b).42, 43 O2 was dominantly generated in the presence of MA-C60 while the amount of CO2 was much smaller than that of MA-C60-absent cells. The DEMS profiles supported that carbonate formation was suppressed in the presence of MA-C60 during discharge prior to charge. The OER efficiency of MA-C60-present LOB cells during charge, calculated from the consumption and evolution of oxygen, was 25 % higher than that of the MA-C60-absent one (Figure S12c and d). Both the significant CO2 evolution during charge and the low efficiency of MA-C60-absent cell are the evidences indicating the parasitic side reaction triggered by superoxide during the previous discharge process. Chemical reactions of reactive superoxide with carbon electrodes and organic solvent molecules result in carbonate formation.44 By contrast, in LOB cells containing MA-C60, the opportunities of the side reactions are eliminated by disproportionating the superoxide ions to oxygen and peroxide ions. Smaller overpotentials developed during charge as well as discharge in the presence of MA-C60 also indicated the suppressed side reactions (Figure S12a and b). The soluble O22- precipitates in the presence of Li+ to form insoluble toroidal Li2O2 on electrodes. 12 ACS Paragon Plus Environment

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The dominant formation of Li2O2 with minimal carbonate formation during discharge guaranteed an improved cyclability as well as high discharge capacity (Figure S12c). Successful repeated discharge/charge operations up to 58 cycles were confirmed in the presence of MA-C60 when LOB cells were discharged up to the capacity of 0.5 mAh cm-2 by 0.5 mA cm-2. The MA-C60-present cell exhibited well-defined potential plateaus up to the charging capacity even at latter cycles (Figure S13). In contrast to the MA-C60-present cells, the MA-C60-absent LOB cells did not work successfully even from the first cycle. The solution mechanism could be preferred by the protic nature of MA-C60 to protonate the insoluble Li2O2 (LiOOLi) into a soluble HOOLi.45 However, the suppressed side reactions resulting in the prolonged cycles suggested that the dominant role of MA-C60 was to manage superoxide even if the possibility of the weak acid effects of MA-C60 cannot be totally rejected.

CONCLUSIONS MA-C60, a SOD mimic, catalyzed disproportionation reaction of reactive superoxide to molecular oxygen and peroxide. Superoxide-triggered side reactions were suppressed while lithium peroxide as a final product of ORR in LOBs was dominantly produced via solution mechanism in a toroidal form on electrode surface. Resultantly, discharge capacities of LOB cells containing MA-C60 were tremendously improved especially at high rates. This MA-C60 strategy should be distinguished from previously reported superoxide-controlling strategies. Both high donor number solvent molecules and discharge mediators help superoxide electrochemically converted to peroxide without side reactions or in a fast manner. However, MA-C60 drives chemical disproportionation of superoxide. Peroxide is generated without electron gain from electrode while generated oxygen is recycled for electrochemical ORR. It 13 ACS Paragon Plus Environment

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should be notified that a comprehensive library of SOD mimics is ready for improving performances of LOBs and sodium-oxygen batteries (SOBs). Research societies would find more opportunities on extending the use of SOD mimics for superoxide management in energy storage and generation systems.

EXPERIMENTAL SECTION Electro paramagnetic resonance. Electro paramagnetic resonance (EPR) was carried out to examine the superoxide scavenging effect of MA-C60. A reference sample is produced that 3 mM potassium oxide (KO2, Sigma-Aldrich), used as a superoxide radical equivalent, and 60 mM 5,5-Dimethyl-1-pyrroline N-oxide (DMPO, Sigma-Aldrich), used as a spin trapping agent to stabilize the superoxide radical, are dissolved in anhydrous dimethyl sulfoxide (DMSO) solvent. The MA-C60 added-electrolytes were produced by introducing 1 mM MA-C60 to the reference sample. The EPR parameters were : frequency, 9.6 GHz, modulation frequency, 100 kHz, microwave power 9.2 mW, modulation amplitude, 1.5 G; time constant, 81.92 ms; conversion time, 100 ms, sweep time, 290 s; Electrochemical measurements. The carbon paper (P50) was prepared and dried at 110 oC

in vacuum oven for 12 hr. The well dried air cathode was punched into disc with a diameter

of 12.5 mm. Customized Swagelok-type cell was used to investigate the electrochemical performance. The Li-O2 cells were assembled in a glove box (Mbraun, Ar-filled with water and oxygen contents less than 0.1 PPM). A lithium foil was used as the anode and was separated by glass microfiber filter (GF/D from Whatman) in electrolyte (1 M LiTFSI in TEGDME (Tetraethylene glycol dimethyl ether) with or without MA-C60). All measurements were conducted in a 770 Torr dry oxygen atmosphere. The cyclic voltammogram and


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electrochemical impedance spectroscopy was examined by potentiostat (VMP3, Bio-Logic). The galvanostatic discharge and charge was tested by a battery cycler (WBCS3000, WonATech). DFT calculations. DFT calculations have been performed to compare the adsorption energies ( Eads’s) of superoxide radicals or lithium superoxide on the MA-C60 or Li2O2 surface (Figure 3a), and to investigate the reaction pathway of Li2O2 formation via solution mechanism (Figure 3b). First, the MA-C60 with three MA groups, which was used in the experiments, was modeled by following the previous work.46 Also, we representatively constructed the Li2O2 (100) stepped surface, which was found to be the most stable and thus expected to be the most abundant surface on the Li2O2 particles, previously reported by Hummelshøj et al.47 The model surface consisted of 72 Li and 72 O atoms with sufficient vacuum regions in both x- and z-directions (i.e., 50.0×7.7×40.0 Å3). Note that a single Li+ ion was introduced in vacuum to maintain the charge neutrality of the periodic cell. For solution mechanism calculation, we followed the elementary steps for reaction path recently proposed by Zhang et al.’s work.48 The implicit solvent environment was applied using conductor-like screening model (COSMO) scheme with a dielectric constant for experimental condition (i.e., = 5.8 for DEGDME).49 All DFT calculations were carried out using the DMol3 program, with the generalized gradient approximation (GGA) with the Perdew-Burke-Ernzerhof (PBE) functional.50

- 52

The semi-empirical Grimme scheme was applied for the dispersion

correction.53 Spin-polarized calculations were carried out with DNP 4.4 level. All electron relativistic effect was included for core treatment with a smearing value of 0.005 Ha. The Brillouin zone was sampled with 1×2×1 k-point by Monkhorst-Pack mesh for all surface systems.54 The convergence criterion of self-consistent field (SCF) was set to 1.0×10-6 Ha, and


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the geometry optimization was performed until satisfying the criteria (i.e., 1.0×10-5 Ha for energy, 0.002 Ha/Å for force, and 0.005 Å for displacement, respectively). MD simulations. Molecular dynamics (MD) simulations were performed to investigate the capturing ability of Li+ ion of MA-C60 in each solvent system (i.e., DEGDME and TEGDME). Since the solvent molecules were known to form the complex structures in the presence of Li+ ions, the stable geometries of complex structures for [Li(DEGDME)]+ and [Li(TEGDME)]+ were initially identified by DFT calculations. The mole ratios between solvents and LiTFSI used in our simulations were taken from the experimental condition of 1 M LiTFSI in solvents. Five MA-C60’s were initially placed in a periodic box with LiTFSI and solvents (i.e., 200 LiTFSI with 1098 DEGDME or 712 TEGDME, respectively). Subsequently, MD simulations with NPT (i.e., isobaric-isothermal) ensemble were conducted at room temperature and 1 atm for 2 ns with the time step of 1 fs. Configurations of the last 1 ns were analyzed for the results. All MD simulations were performed using the COMPASSII forcefield. 55, 56

The temperature was controlled by Nosé-Hoover Langevin (NHL) thermostat,57 and the

pressure was controlled by Berendsen barostat.58 Ewald scheme and atom-based cutoff method (i.e., a length of 15.5 Å) were used to treat the electrostatic and van der Waals (vdW) forces, respectively.

ASSOCIATED CONTENT Supporting Information is available free of charge on the ACS Publications website at http://pubs.acs.org. Solubility of MA-C60 in the electrolyte, coin cell configuration for ionic conductivity measurement, DFT and MD simulation results, experimental data of malonic acids for 16 ACS Paragon Plus Environment

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LOB cells (i.e., voltage profiles and EPR spectra), MA-C60 concentration dependency of discharge capacity, potential profiles during DEMS measurement, and cycle data. The authors declare no competing financial interest.

AUTHOR INFORMATION Corresponding Author *E-mail: [email protected] (S.K.K.), [email protected] (H.-K.S) Author Contributions §These

authors contributed equally to this work.

ORCID Chihyun Hwang: 0000-0001-7469-3119 Gwan Yeong Jung: 0000-0001-5867-4575 Se Hun Joo: 0000-0003-4507-150X Sang Kyu Kwak: 0000-0002-0332-1534 Hyun-Kon Song: 0000-0001-7914-4186

ACKNOWLEDGEMENTS This work was supported by Samsung Research Funding & Incubation Center of Samsung Electronics under Project Number SRFC-MA-1802-04. S.K.K. acknowledges the computational resources from Korea Institute of Science and Technology Information (KISTIHPC).


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REFERENCES 1.

Turrens, J. F., Mitochondrial Formation of Reactive Oxygen Species. J. Physiol-London 2003, 552, 335-344.

2.

Han, D.; Williams, E.; Cadenas, E., Mitochondrial Respiratory Chain-Dependent Generation of Superoxide Anion and Its Release into the Intermembrane Space. Biochem. J. 2001, 353, 411-416.

3.

Li, X. Y.; Fang, P.; Mai, J. T.; Choi, E. T.; Wang, H.; Yang, X. F., Targeting Mitochondrial Reactive Oxygen Species as Novel Therapy for Inflammatory Diseases and Cancers. J. Hematol. Oncol. 2013, 6, 19.

4.

Bruce, P. G.; Freunberger, S. A.; Hardwick, L. J.; Tarascon, J. M., Li-O2 and Li-S Batteries with High Energy Storage. Nat. Mater. 2012, 11, 19-29.

5.

Aurbach, D.; McCloskey, B. D.; Nazar, L. F.; Bruce, P. G., Advances in Understanding Mechanisms Underpinning Lithium-Air Batteries. Nat. Energy 2016, 1, 16128.

6.

Choi, J. W.; Aurbach, D., Promise and Reality of Post-Lithium-Ion Batteries with High Energy Densities. Nat. Rev. Mater. 2016, 1, 16013.

7.

Lim, H. D.; Lee, B.; Bae, Y.; Park, H.; Ko, Y.; Kim, H.; Kim, J.; Kang, K., Reaction Chemistry in Rechargeable Li-O2 Batteries. Chem. Soc. Rev. 2017, 46, 2873-2888.

8.

Chen, Z.; Yu, A.; Higgins, D.; Li, H.; Wang, H.; Chen, Z. Highly Active and Durable Core-Corona Structured Bifunctional Catalyst for Rechargeable Metal-Air Battery Application. Nano Lett. 2012, 12, 1946-1952.

9.

Kim, J. G.; Noh, Y.; Kim, Y.; Lee, S.; Kim, W. B. Fabrication of Three-Dimensional Ordered Macroporous Spinel CoFe2O4 as Efficient Bifunctional Catalysts for the Positive Electrode of Lithium-Oxygen Batteries. Nanoscale 2017, 9, 5119-5128.


Page 19 of 29 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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10. Kim, J. G.; Kim, Y.; Noh, Y.; Lee, S.; Kim, W. B. Bifunctional Hybrid Catalysts with Perovskite LaCo0.8Fe0.2O3 Nanowires and Reduced Graphene Oxide Sheets for an Efficient Li-O2 Battery Cathode. ACS Appl. Mater. Interfaces 2018, 10, 5429-5439. 11. Freunberger, S. A.; Chen, Y. H.; Drewett, N. E.; Hardwick, L. J.; Barde, F.; Bruce, P. G., The Lithium-Oxygen Battery with Ether-Based Electrolytes. Angew. Chem. Int. Edit. 2011, 50, 8609-8613. 12. Bryantsev, V. S.; Giordani, V.; Walker, W.; Blanco, M.; Zecevic, S.; Sasaki, K.; Uddin, J.; Addison, D.; Chase, G. V., Predicting Solvent Stability in Aprotic Electrolyte Li-Air Batteries: Nucleophilic Substitution by the Superoxide Anion Radical (O2•-). J. Phys. Chem. A 2011, 115, 12399-12409. 13. Thotiyl, M. M. O.; Freunberger, S. A.; Peng, Z. Q.; Chen, Y. H.; Liu, Z.; Bruce, P. G., A Stable Cathode for the Aprotic Li-O2 Battery. Nat. Mater. 2013, 12, 1049-1055. 14. Lu, Y. C.; Gallant, B. M.; Kwabi, D. G.; Harding, J. R.; Mitchell, R. R.; Whittingham, M. S.; Shao-Horn, Y., Lithium-Oxygen Batteries: Bridging Mechanistic Understanding and Battery Performance. Energ. Environ. Sci. 2013, 6, 750-768. 15. Black, R.; Oh, S. H.; Lee, J. H.; Yim, T.; Adams, B.; Nazar, L. F., Screening for Superoxide Reactivity in Li-O2 Batteries: Effect on Li2O2/LiOH Crystallization. J. Am. Chem. Soc. 2012, 134, 2902-2905. 16. Mahne, N.; Fontaine, O.; Thotiyl, M. O.; Wilkening, M.; Freunberger, S. A., Mechanism and Performance of Lithium-Oxygen Batteries - A Perspective. Chem. Sci. 2017, 8, 67166729. 17. Ryu, W. H.; Gittleson, F. S.; Thomsen, J. M.; Li, J. Y.; Schwab, M. J.; Brudvig, G. W.; Taylor, A. D., Heme Biomolecule as Redox Mediator and Oxygen Shuttle for Efficient Charging of Lithium-Oxygen Batteries. Nat. Commun. 2016, 7, 12195.


ACS Nano 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 20 of 29

18. Park, J. B.; Lee, S. H.; Jung, H. G.; Aurbach, D.; Sun, Y. K., Redox Mediators for Li-O2 Batteries: Status and Perspectives. Adv. Mater. 2018, 30, 1704162. 19. Dilimon, V. S.; Hwang, C.; Cho, Y. G.; Yang, J.; Lim, H. D.; Kang, K.; Kang, S. J.; Song, H. K., Superoxide Stability for Reversible Na-O2 Electrochemistry. Sci. Rep. 2017, 7, 17635. 20. Burke, C. M.; Pande, V.; Khetan, A.; Viswanathan, V.; McCloskey, B. D., Enhancing Electrochemical Intermediate Solvation through Electrolyte Anion Selection to Increase Nonaqueous Li-O2 Battery Capacity. Proc. Natl. Acad. Sci. U.S.A. 2015, 112, 9293-9298. 21. Aetukuri, N. B.; McCloskey, B. D.; Garcia, J. M.; Krupp, L. E.; Viswanathan, V.; Luntz, A. C., Solvating Additives Drive Solution-Mediated Electrochemistry and Enhance Toroid Growth in Non-Aqueous Li-O2 Batteries. Nat. Chem. 2015, 7, 50-56. 22. Johnson, L.; Li, C. M.; Liu, Z.; Chen, Y. H.; Freunberger, S. A.; Ashok, P. C.; Praveen, B. B.; Dholakia, K.; Tarascon, J. M.; Bruce, P. G., The Role of LiO2 Solubility in O2 Reduction in Aprotic Solvents and Its Consequences for Li-O2 Batteries. Nat. Chem. 2014, 6, 1091-1099. 23. Gao, X. W.; Chen, Y. H.; Johnson, L.; Bruce, P. G., Promoting Solution Phase Discharge in Li-O2 Batteries Containing Weakly Solvating Electrolyte Solutions. Nat. Mater. 2016, 15, 882-888. 24. Zhang, Y. T.; Wang, L.; Zhang, X. Z.; Guo, L. M.; Wang, Y.; Peng, Z. Q., High-Capacity and High-Rate Discharging of a Coenzyme Q10-Catalyzed Li-O2 Battery. Adv. Mater. 2018, 30, 1705571. 25. Kim, B. G.; Kim, S.; Lee, H.; Choi, J. W., Wisdom from the Human Eye: A Synthetic Melanin Radical Scavenger for Improved Cycle Life of Li-O2 Battery. Chem. Mater. 2014, 26, 4757-4764.


Page 21 of 29 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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26. Lim, H. D.; Lee, B.; Zheng, Y.; Hong, J.; Kim, J.; Gwon, H.; Ko, Y.; Lee, M.; Cho, K.; Kang, K., Rational Design of Redox Mediators for Advanced Li-O2 Batteries. Nat. Energy 2016, 1, 16066. 27. Chen, Y. H.; Freunberger, S. A.; Peng, Z. Q.; Fontaine, O.; Bruce, P. G., Charging A LiO2 Battery using A Redox Mediator. Nat. Chem. 2013, 5, 489-494. 28. Liang, Z. J.; Lu, Y. C., Critical Role of Redox Mediator in Suppressing Charging Instabilities of Lithium-Oxygen Batteries. J. Am. Chem. Soc. 2016, 138, 7574-7583. 29. Melov, S.; Ravenscroft, J.; Malik, S.; Gill, M. S.; Walker, D. W.; Clayton, P. E.; Wallace, D. C.; Malfroy, B.; Doctrow, S. R.; Lithgow, G. J., Extension of Life-Span with Superoxide Dismutase/Catalase Mimetics. Science 2000, 289, 1567-1569. 30. Ogata, T.; Senoo, T.; Kawano, S.; Ikeda, S., Mitochondrial Superoxide Dismutase Deficiency Accelerates Chronological Aging in the Fission Yeast Schizosaccharomyces Pombe. Cell. Biol. Int. 2016, 40, 100-106. 31. Ali, S. S.; Hardt, J. I.; Quick, K. L.; Kim-Han, J. S.; Erlanger, B. F.; Huang, T. T.; Epstein, C. J.; Dugan, L. L., A Biologically Effective Fullerene (C60) Derivative with Superoxide Dismutase Mimetic Properties. Free Radical Bio. Med. 2004, 37, 1191-1202. 32. Bolojan, L.; Takacs, I. M.; Miclaus, V.; Damian, G., An EPR Study of Superoxide Radicals from Potassium Superoxide Solutions. Appl. Magn. Reson. 2012, 42, 333-341. 33. Kishioka, S.; Takekawa, T.; Yamada, A., Electrochemical Determination of the Superoxide Ion Concentration from KO2 Dissolved in Dimethyl Sulfoxide. Anal. Sci. 2004, 20, 1465-1466. 34. Ganapathy, S.; Adams, B. D.; Stenou, G.; Anastasaki, M. S.; Goubitz, K.; Miao, X. F.; Nazar, L. F.; Wagemaker, M., Nature of Li2O2 Oxidation in a Li-O2 Battery Revealed by Operando X-ray Diffraction. J. Am. Chem. Soc. 2014, 136, 16335-16344.


ACS Nano 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 22 of 29

35. Lim, H.; Yilmaz, E.; Byon, H. R., Real-Time XRD Studies of Li-O2 Electrochemical Reaction in Nonaqueous Lithium-Oxygen Battery. J. Phys. Chem. Lett. 2012, 3, 32103215. 36. Xu, D.; Wang, Z. L.; Xu, J. J.; Zhang, L. L.; Zhang, X. B., Novel DMSO-Based Electrolyte for High Performance Rechargeable Li-O2 Batteries. Chem. Commun. 2012, 48, 69486950. 37. Chen, Y.; Freunberger, S. A.; Peng, Z.; Barde, F.; Bruce, P. G., Li-O2 Battery with a Dimethylformamide Electrolyte. J. Am. Chem. Soc. 2012, 134, 7952-7957. 38. McCloskey, B. D.; Speidel, A.; Scheffler, R.; Miller, D. C.; Viswanathan, V.; Hummelshoj, J. S.; Norskov, J. K.; Luntz, A. C., Twin Problems of Interfacial Carbonate Formation in Nonaqueous Li-O2 Batteries. J. Phys. Chem. Lett. 2012, 3, 997-1001. 39. Yang, Y.; Liu, W.; Wu, N. A.; Wang, X. C.; Zhang, T.; Chen, L. F.; Zeng, R.; Wang, Y. M.; Lu, J. T.; Fu, L.; Xiao, L.; Zhuang, L., Tuning the Morphology of Li2O2 by Noble and 3d Metals: A Planar Model Electrode Study for Li-O2 Battery. ACS Appl. Mater. Inter. 2017, 9, 19800-19806. 40. Xu, J. J.; Wang, Z. L.; Xu, D.; Zhang, L. L.; Zhang, X. B., Tailoring Deposition and Morphology of Discharge Products Towards High-Rate and Long-Life Lithium-Oxygen Batteries. Nat. Commun. 2013, 4, 2438. 41. Dick-Perez, M.; Windus, T. L., Computational Study of the Malonic Acid Tautomerization Products in Highly Concentrated Particles. J. Phys. Chem. A 2017, 121, 2259-2264. 42. McCloskey, B. D.; Bethune, D. S.; Shelby, R. M.; Girishkumar, G.; Luntz, A. C., Solvents' Critical Role in Nonaqueous Lithium-Oxygen Battery Electrochemistry. J. Phys. Chem. Lett. 2011, 2, 1161-1166.


Page 23 of 29 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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43. Kang, S. J.; Mori, T.; Narizuka, S.; Wilcke, W.; Kim, H. C., Deactivation of Carbon Electrode for Elimination of Carbon Dioxide Evolution from Rechargeable LithiumOxygen Cells. Nat. Commun. 2014, 5, 3937. 44. Wang, Z. L.; Xu, D.; Xu, J. J.; Zhang, X. B., Oxygen Electrocatalysts in Metal-Air Batteries: From Aqueous to Nonaqueous Electrolytes. Chem. Soc. Rev. 2014, 43, 77467786. 45. Gao, X. W.; Jovanov, Z. P.; Chen, Y. H.; Johnson, L. R.; Bruce, P. G., Phenol-Catalyzed Discharge in the Aprotic Lithium-Oxygen Battery. Angew. Chem. Int. Edit. 2017, 56, 6539-6543. 46. Yan, W. B.; Seifermann, S. M.; Pierrat, P.; Brase, S., Synthesis of Highly Functionalized C60 Fullerene Derivatives and Their Applications in Material and Life Sciences. Org. Biomol. Chem. 2015, 13, 25-54. 47. Hummelshoj, J. S.; Blomqvist, J.; Datta, S.; Vegge, T.; Rossmeisl, J.; Thygesen, K. S.; Luntz, A. C.; Jacobsen, K. W.; Norskov, J. K., Communications: Elementary Oxygen Electrode Reactions in the Aprotic Li-Air Battery. J. Chem. Phys. 2010, 132, 071101. 48. Zhang, Y. L.; Zhang, X. M.; Wang, J. W.; McKee, W. C.; Xu, Y.; Peng, Z. Q., PotentialDependent Generation of O2- and LiO2 and Their Critical Roles in O2 Reduction to Li2O2 in Aprotic Li-O2 Batteries. J. Phys. Chem. C 2016, 120, 3690-3698. 49. Klamt, A.; Schuurmann, G., COSMO - A New Approach to Dielectric Screening in Solvents with Explicit Expressions for the Screening Energy and Its Gradient. J. Chem. Soc. Perk. T. 2 1993, 799-805. 50. Delley, B., An All-Electron Numerical-Method for Solving the Local Density Functional for Polyatomic-Molecules. J. Chem. Phys. 1990, 92, 508-517.


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51. Delley, B., From Molecules to Solids with the DMol3 Approach. J. Chem. Phys. 2000, 113, 7756-7764. 52. Perdew, J. P.; Burke, K.; Ernzerhof, M., Generalized Gradient Approximation Made Simple. Phys. Rev. Lett. 1996, 77, 3865-3868. 53. Grimme, S., Semiempirical GGA-Type Density Functional Constructed with a Long-range Dispersion Correction. J. Comput. Chem. 2006, 27, 1787-1799. 54. Monkhorst, H. J.; Pack, J. D., Special Points for Brillouin-Zone Integrations. Phys. Rev. B 1976, 13, 5188-5192. 55. Sun, H.; Ren, P.; Fried, J. R., The COMPASS Force Field: Parameterization and Validation for Phosphazenes. Comput. Theor. Polym. S. 1998, 8, 229-246. 56. Sun, H., COMPASS: An Ab Initio Force-Field Optimized for Condensed-Phase Applications - Overview with Details on Alkane and Benzene Compounds. J. Phys. Chem. B 1998, 102, 7338-7364. 57. Samoletov, A. A.; Dettmann, C. P.; Chaplain, M. A. J., Thermostats for "Slow" Configurational Modes. J. Stat. Phys. 2007, 128, 1321-1336. 58. Berendsen, H. J. C.; Postma, J. P. M.; Vangunsteren, W. F.; Dinola, A.; Haak, J. R., Molecular-Dynamics with Coupling to an External Bath. J. Chem. Phys. 1984, 81, 36843690.


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a n’ ( mol min-1 )

0.06

b 0.06

CO2

O2

O2

0.04

0.04

0.02

0.02

None 0.00

CO2

MA-C60

0.00 0.0

0.2

0.4

0.6

0.8

1.0

0.0

0.2

0.4

0.6

0.8

1.0

Q (mAh) 1.0

c 0.5 mA cm-2

Q (mAh cm-2)

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0.8

MA-C60

0.6 0.4 0.2 0.0 0

None 10

20

30

40

50

60

70

Cycle Figure 4. Superoxide-triggered side reactions. The same cell configuration and electrolyte of Figure 2 was used. (a and b) Gases produced at 0.2 mA cm-2 during charging by oxidizing discharge products generated by ORR during a precedent charging at 1 mAh cm-2. O2 (cyan) and CO2 (blue) were detected by differential electrochemical mass spectrometry (DEMS). (c) Capacity retention of LOB cells along repeated discharge/charge cycles at 0.5 mA cm-2. Capacity was cut off at 0.5 mAh cm-2.


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