Improving Interfacial Stability for All-Solid-State Secondary Batteries with Precursor-Based Gradient Doping.

Recently, sulfide solid-state electrolytes with excellent ionic conductivity and facile electrode integration have gained prominence in the field of all-solid-state batteries (ASSBs). However, owing to their inherently high reactivity, sulfide electrolytes interact with the cathode, forming interfacial layers that adversely affect the electrochemical performance of all-solid-state cells. Unlike conventional cathode-coating methods that involve the formation of surface coatings from high-cost source materials, the proposed strategy involves the doping of precursors with low-cost oxides (Nb2O5, Ta2O5, and La2O3) prior to cathode fabrication. This novel approach aims to improve the stability of the cathode-sulfide electrolyte interface. Notably, doping significantly improved the discharge capacity, rate capability, and cyclic performance of cathodes while reducing their impedance resistance. Scanning electron microscopy, transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS) indicated a gradient dopant-concentration profile (with a high level of dopant at the surface) in the doped cathodes. Cathode doping, particularly with Nb and Ta, caused a reduction in cation mixing owing to crystal-structure adjustments and ionic-conductivity enhancements. XPS and high-resolution TEM confirmed that gradient doping effectively minimized cathodic side reactions, possibly due to the formation of a coating-like protective layer in the cathode-electrolyte interface coupled with structural stabilization attributed to the doping process. The protective ability of the interfacial layer generated by gradient doping was confirmed to be comparable to that of conventional surface coatings. Therefore, this study could guide the future development of low-cost, high-performance ASSBs, opening new frontiers in sustainable energy storage.

Additive-Derived Surface Modification of Cathodes in All-Solid-State Batteries: The Effect of Lithium Difluorophosphate- and Lithium Difluoro(oxalato)borate-Derived Coating Layers.

Sulfide-based electrolytes, with their high conductivity and formability, enable the construction of high-performance, all-solid-state batteries (ASSBs). However, the instability of the cathode-sulfide electrolyte interface limits the commercialization of these ASSBs. Surface modification of cathodes using the coating technique has been explored as an efficient approach to stabilize these interfaces. In this study, the additives lithium difluorophosphate (LiDFP) and lithium difluoro(oxalato)borate (LiDFOB) are used to fabricate stable cathode coatings via heat treatment. The low melting points of LiDFP and LiDFOB enable the formation of thin and uniform coating layers by a low-temperature heat treatment. All-solid-state cells containing LiDFP- and LiDFOB-coated cathodes show electrochemical performances significantly better than those comprising uncoated cathodes. Among all of the as-prepared coated cathodes, LiDFP-coated cathodes fabricated using a slightly lower temperature than the phase-transition temperature of LiDFP (320 °C) show the best discharge capacity, rate capability, and cyclic performance. Furthermore, cells comprising LiDFP-coated cathodes showed significantly low impedance. X-ray photoelectron spectroscopy and high-resolution transmission electron microscopy confirm the effectiveness of the LiDFP coating. LiDFP-coated cathodes minimized side-reactions during cycling, resulting in a significantly low cathode-surface degradation. Hence, this study highlights the efficiency of the proposed coating method and its potential to facilitate the commercialization of ASSBs. Overall, this study reports an effective technique to stabilize the cathode-electrolyte interface in sulfide-based ASSBs, which could expedite the practical implementation of these advanced energy-storage devices.

Suppressing Unfavorable Interfacial Reactions Using Polyanionic Oxides as Efficient Buffer Layers: Low-Cost Li3PO4 Coatings for Sulfide-Electrolyte-Based All-Solid-State Batteries.

The poor electrochemical performance of all solid-state batteries (ASSBs) that use sulfide electrolytes can be attributed to undesirable side reactions at the cathode/sulfide-electrolyte interface; this issue can be addressed via surface coating. Ternary oxides such as LiNbO3 and Li2ZrO3 are generally used as coating materials because of their high chemical stabilities and ionic conductivities. However, their relative high cost discourages their use in mass production. In this study, Li3PO4 was introduced as a coating material for ASSBs, because phosphates possess good chemical stabilities and ionic conductivities. Phosphates also prevent the exchange of S2- and O2- in the electrolyte and cathode and, thus, inhibit interfacial side reactions caused by ionic exchange, because they contain the same anion (O2-) and cation (P5+) species as those present in the cathode and sulfide electrolyte, respectively. Furthermore, the Li3PO4 coatings can be prepared using low-cost source materials such as polyphosphoric acid and lithium acetate. We investigated the electrochemical performance of the Li3PO4-coated cathodes and found that the Li3PO4 coating significantly improved the discharge capacities, rate capabilities, and cyclic performances of the all-solid-state cell. While the discharge capacity of the pristine cathode was ∼181 mAh·g-1, that of 0.15 wt % Li3PO4-coated cathode was ∼194-195 mAh·g-1. And the capacity retention of the Li3PO4-coated cathode over 50 cycles was much superior (∼84-85%) to that of the pristine sample (∼72%). Simultaneously, the Li3PO4 coating reduced the side reactions and interdiffusion at the cathode/sulfide-electrolyte interfaces. The results of this study demonstrate the potential of low-cost polyanionic oxides, such as Li3PO4, as commercial coating materials for ASSBs.

Interfacial Stabilization of Li2O-Based Cathodes by Malonic-Acid-Functionalized Fullerenes as a Superoxo-Radical Scavenger for Suppressing Parasitic Reactions.

The utilization of an anionic redox reaction as an innovative strategy for overcoming the limitations of cathode capacity in lithium-ion batteries has recently been the focus of intensive research. Li2O-based materials using the anionic (oxygen) redox reaction have the potential to deliver a much higher capacity than commercial cathodes using cationic redox reactions based on transition-metal ions. However, parasitic reactions attributed to the superoxo species (such as LiO2), derived from the Li2O active material of the cathode, deteriorate the stability of the interface between the cathode and electrolyte, which has limited the commercialization of Li2O-based cathodes. To address this issue, malonic-acid-functionalized fullerenes (MC60) were applied in the electrolyte as an additive for scavenging the superoxo radicals (O21- in LiO2) that trigger parasitic reactions. MC60 can efficiently capture superoxo radicals using the π-conjugated surface and the malonate functionality on the surface. As a result, MC60 considerably enhanced the available capacity and cycling performance of the Li2O-based cathodes, decreased the interfacial layer formed on the cathode surface, and hindered the generation of byproducts, such as Li2CO3, CO2, and C-F3, derived from parasitic reactions. In addition, the loss of Li2O from the cathode surface during cycling was also suppressed, validating the ability of MC60 to capture superoxo radicals. This result confirms that the introduction of MC60 can effectively alleviate the parasitic reactions at the cathode/electrolyte interface and improve the electrochemical performance of Li2O-based cathodes by scavenging the superoxo species.

Interfacial reactions in lithia-based cathodes depending on the binder in the electrode and salt in the electrolyte.

Lithia (Li2O)-based cathodes, utilizing oxygen redox reactions for obtaining capacity, exhibit higher capacity than commercial cathodes. However, they are highly reactive owing to superoxides formed during charging, and they enable more active parasitic (side) reactions at the cathode/electrolyte and cathode/binder interfaces than conventional cathodes. This causes deterioration of the electrochemical performance limiting commercialization. To address these issues, the binder and salt for electrolyte were replaced in this study to reduce the side reaction of the cells containing lithia-based cathodes. The commercially used polyvinylidene fluoride (PVDF) binder and LiPF6 salt in the electrolyte easily generate such reactions, and the subsequent reaction between PVDF and LiOH (from decomposition of lithia) causes slurry gelation and agglomeration of particles in the electrode. Moreover, the fluoride ions from PVDF promote side reactions, and LiPF6 salt forms POF3 and HF, which cause side reactions owing to hydrolysis in organic solvents containing water. However, the polyacrylonitrile (PAN) binder and LiTFSI salt decrease these side reactions owing to their high stability with lithia-based cathode. Further, thickness of the interfacial layer was reduced, resulting in decreased impedance value of cells containing lithia-based cathodes. Consequently, for the same lithia-based cathodes, available capacity and cyclic performance were increased owing to the effects of PAN binder and LiTFSI salt in the electrolyte.

Comparison of LiTaO3 and LiNbO3 Surface Layers Prepared by Post- and Precursor-Based Coating Methods for Ni-Rich Cathodes of All-Solid-State Batteries.

Surface coating is essential for the cathode materials applied in all-solid-state batteries (ASSBs) based on sulfide electrolytes because of the instability of the cathode/sulfide interface. In contrast with those for general lithium ion batteries (LIBs) using a liquid electrolyte, the coating materials for ASSBs require different functional properties such as high ionic conductivity, low reactivity with sulfide electrolytes, and low electronic conductivity. In addition to LiNbO3, which is the most popular coating material for ASSBs, LiTaO3 is another highly promising coating material, and both materials mostly satisfy these requirements. In this work, LiTaO3 and LiNbO3 were used to coat the surface of LiNi0.82Co0.12Mn0.06O2 cathodes for ASSBs. Further, the effects of two different coating methods, postcoating and precursor-based (PB) coating, were characterized and compared. The postcoating method simply forms a coating layer, whereas the PB coating method offers an additional doping effect owing to the diffusion of coating ions into the cathode structure. Surface coating considerably increased the capacity of the ASSB cathodes under all experimental conditions. With the same coating amount and method, the effect of the LiTaO3 coating was similar or superior to that of the LiNbO3 coating. Compared with the postcoating method, however, the PB coating method resulted in a superior rate capability and cyclic performance, which was mostly attributed to the doping effect of Ta or Nb. An X-ray photoelectron spectroscopy analysis confirmed that both the LiTaO3 and LiNbO3 coatings suppressed side reactions. Among the coatings we examined, the LiTaO3 coating prepared by the PB method most effectively enhanced the electrochemical performance of the cathodes for sulfide electrolyte-based ASSBs.

Enhanced electrochemical performance of lithia/Li2RuO3 cathode by adding tris(trimethylsilyl)borate as electrolyte additive.

In this study, we used tris(trimethylsilyl)borate (TMSB) as an electrolyte additive and analysed its effect on the electrochemical performance of lithia-based (Lithia/Li2RuO3) cathodes. Our investigation revealed that the addition of TMSB modified the interfacial reactions between a lithia-based cathode and an electrolyte composed of the carbonate solvents and the LiPF6 salt. The decomposition of the LiPF6 salt and the formation of Li2CO3 and -CO2 was successfully reduced through the use of TMSB as an electrolyte additive. It is inferred that the protective layer derived from the TMSB suppressed the undesirable side reaction associated with the electrolyte and superoxides (O- or O0.5-) formed in the cathode structure during the charging process. This led to the reduction of superoxide loss through side reactions, which contributed to the increased available capacity of the Lithia/Li2RuO3 cathode with the addition of TMSB. The suppression of undesirable side reactions also decreased the thickness of the interfacial layer, reducing the impedance value of the cells and stabilising the cyclic performance of the lithia-based cathode. This confirmed that the addition of TMSB was an effective approach for the improvement of the electrochemical performance of cells containing lithia-based cathodes.

Precursor-based surface modification of cathodes using Ta and W for sulfide-based all-solid-state batteries.

Sulfide ionic conductors are promising candidates as solid electrolytes for all-solid-state batteries due to their high conductivity. However, interfacial instability between cathodes and sulfide electrolytes still remains a challenge because sulfides are highly reactive. To suppress undesirable side reactions at the cathode/sulfide electrolyte interface, the surface of the cathode has been modified using stable coating materials. Herein, a precursor based (PB) surface modification using Ta and W is introduced as an effective approach for the formation of a suitable cathode coating layer. Through heat-treatment of the PB surface modification, the source materials (Ta or W) coated on the precursors diffused into the cathode and acted as a dopant. Formation of the surface coating layer was confirmed by X-ray photoelectron spectroscopy (XPS) depth profiles and scanning transmission electron microscopy (STEM) images. The PB surface modified electrodes showed higher capacity, improved rate capability and enhanced cyclic performance compared to those of the pristine electrode. The impedance value of the cells dominantly decreased after cycling due to the modification effect. Moreover, considering the XPS analysis, undesirable reaction products that formed upon cycling were reduced by PB surface modification. These results indicate that PB surface modification using Ta and W effectively suppresses undesirable side reactions and stabilizes the cathode/sulfide electrolyte interface, which is a synergic effect of the doping and coating attributed to Ta and W.

Effect of Vinylethylene Carbonate and Fluoroethylene Carbonate Electrolyte Additives on the Performance of Lithia-Based Cathodes.

Nanolithia-based materials are promising lithium-ion battery cathodes owing to their high capacity, low overpotential, and stable cyclic performance. Their properties are highly dependent on the structure and composition of the catalysts, which play a role in activating the lithia to participate in the electrochemical redox reaction. However, the use of electrolyte additives can be an efficient approach to improve properties of the lithia-based cathodes. In this work, vinylethylene carbonate (VEC) and fluoroethylene carbonate (FEC) were introduced as electrolyte additives in cells containing lithia-based cathode (lithia/(Ir, Li2IrO3) nanocomposite). The use of additives enhanced the electrochemical performance of the lithia-based cathodes, including the rate capability and cyclic performance. Especially, their available capacity increased without modifying the cathodes. Results of X-ray photoelectron spectroscopy (XPS) analysis confirmed that the additives form interface layers at the cathode surface, which contain Li2CO3, more carbon reactants, and more LiF than the interface layer formed with the pristine electrolyte. The Li2CO3 and carbon reactants may improve rate capability by facilitating Li+ transport, and LiF may stabilize the Li2O2 (and/or LiO2) produced by the oxygen redox reaction with lithia. Therefore, the additive-enhanced electrochemical performance of the cell is attributed to the effects of the interface layer derived from additive decomposition during cycling.

Correlation between mercury content and leaching characteristics in waste phosphor powder from spent UV curing lamp after thermal treatment.

This study evaluated the correlation between the amount of mercury (Hg) compounds in waste phosphor powder from spent UV curing lamps and their leaching characteristics. The appropriate thermal treatment conditions and Hg content in the residue necessary to satisfy the leaching criteria for classification as non-hazardous waste were identified. The decomposition of Hg compounds by thermal treatment was also evaluated by comparing sequential extraction results based on thermal stability and leaching potential of Hg compounds. Before the thermal treatment, the Hg content in waste phosphor powder and concentration in the leaching extract were 108.7 mg-Hg/kg and 0.56 mg-Hg/L, respectively. Hg compounds with low thermal stability were removed rapidly during the initial stage of thermal treatment at temperatures between 400 °C and 600 °C. After thermal treatment, Hg in the form of an intermetallic compound, such as Sr-Hg, was expected to be remained mainly, and the Hg content was reduced to 13 mg-Hg/kg in the waste phosphor powder, at that point the residue satisfied the leaching standard limit (5 µg-Hg/L) for non-hazardous waste stipulated in the legislation of Republic of Korea.

Lithia-Based Nanocomposites Activated by Li2RuO3 for New Cathode Materials Rooted in the Oxygen Redox Reaction.

Lithia-based materials are promising cathodes based on an anionic (oxygen) redox reaction for lithium ion batteries due to their high capacity and stable cyclic performance. In this study, the properties of a lithia-based cathode activated by Li2RuO3 were characterized. Ru-based oxides are expected to act as good catalysts because they can play a role in stabilizing the anion redox reaction. Their high electronic conductivity is also attractive because it can compensate for the low conductivity of lithia. The lithia/Li2RuO3 nanocomposites show stable cyclic performance until a capacity limit of 500 mAh g-1 is reached, which is below the theoretical capacity (897 mAh g-1) but superior to other lithia-based cathodes. In the XPS analysis, while the Ru 3d peaks in the spectra barely changed, peroxo-like (O2)n- species reversibly formed and dissociated during cycling. This clearly confirms that the capacity of the lithia/Li2RuO3 nanocomposites can mostly be attributed to the anionic (oxygen) redox reaction.

Lithia/(Ir, Li2IrO3) nanocomposites for new cathode materials based on pure anionic redox reaction.

Anionic redox reactions attributed to oxygen have attracted much attention as a new approach to overcoming the energy-density limits of cathode materials. Several oxides have been suggested as new cathode materials with high capacities based on anionic (oxygen) redox reactions. Although most still have a large portion of their capacity based on the cationic redox reaction, lithia-based cathodes present high capacities that are purely dependent upon oxygen redox. Contrary to Li-air batteries, other systems using pure oxygen redox reactions, lithia-based cathodes charge and discharge without a phase transition between gas and condensed forms. This leads to a more stable cyclic performance and lower overpotential compared with those of Li-air systems. However, to activate nanolithia and stabilize reaction products such as Li2O2 during cycling, lithia-based cathodes demand efficient catalysts (dopants). In this study, Ir based materials (Ir and Li2IrO3) were introduced as catalysts (dopants) for nanolithia composites. Oxide types (Li2IrO3) were used as source materials of catalyst because ductile metal (Ir) can hardly be pulverized during the milling process. Two types of Li2IrO3 were prepared and used for catalyst-sources. They were named '1-step Li2IrO3' and '2-step Li2IrO3', respectively, since they were prepared by '1-step' or '2-step' heat treatment. The nanocomposites prepared using lithia & 2-step Li2IrO3 presented a higher capacity, more stable cyclic performance, and lower overpotential than those of the nanocomposites prepared using lithia & 1-step Li2IrO3. The voltage profiles of the nanocomposites prepared using lithia & 2-step Li2IrO3 were stable up to a limited capacity of 600 mAh·g-1, and the capacity was maintained during 100 cycles. XPS analysis confirmed that the capacity of our lithia-based compounds is attributable to the oxygen redox reaction, whereas the cationic redox related to the Ir barely contributes to their discharge capacity.

Cathode coating using LiInO2-LiI composite for stable sulfide-based all-solid-state batteries.

All-solid-state batteries with inorganic solid electrolytes are ideal to overcome the safety issues related to the flammable organic electrolyte in lithium ion batteries. Sulfide materials are promising inorganic electrolytes due to their high ionic conductivity and good elasticity. Nevertheless, their application is limited by their high reactivity and instability at the cathode/electrolyte (Li[Ni0.8Co0.15Al0.05]O2/75Li2S-22P2S5-3Li2SO4) interface. In this study, LiInO2 and LiInO2-LiI were introduced as new cathode coating materials to suppress such undesirable reactions. The LiInO2-LiI composite coating layer reduced the undesirable interfacial reactions and prevented the diffusion of S and P ions from the sulfide electrolyte to the oxide cathode. Moreover, the electrochemical properties of all-solid-state cells were improved by the cathode coating. The LiInO2-LiI-coated electrode presented better rate capability and lower impedance than the pristine and LiInO2-coated electrodes. Hence, the LiInO2-LiI composite coating was successful at improving the cathode stability while providing superior electrochemical properties.

Medication Event Monitoring System for Infectious Tuberculosis Treatment in Morocco: A Retrospective Cohort Study.

Non-adherence to tuberculosis (TB) treatment is a barrier to effective TB control. We investigated the effectiveness of a Medication Event Monitoring System (MEMS) as a tailored adherence-promoting intervention in Morocco. We compared patients who received a MEMS (n = 206) with patients who received standard TB care (n = 141) among new active TB patients with sputum smear-positive. The mean total medication days were 141.87 ± 29.5 in the control group and 140.85 ± 17.9 in the MEMS group (p = 0.7147), and the mean age and sex were not different between the two groups (p > 0.05). The treatment success rate was significantly higher in the MEMS group than in the control group (odds ratio (OR): 4.33, 95% confidence interval (CI): 2.13⁻8.81, p < 0.001), and the lost to follow-up rate was significantly lower in the MEMS group than in the control group (OR: 0.03, 95% CI: 0.05⁻0.24, p < 0.001) after adjusting for sex, age, and health centers. The mean drug adherence rate in the first month was significantly higher in the MEMS group than in the control group (p = 0.023). MEMS increased TB treatment success rate and decreased the lost to follow-up rate overall for infectious TB patients in a Moroccan rural area.

Characterization and Control of Irreversible Reaction in Li-Rich Cathode during the Initial Charge Process.

Li-rich layered oxide has been known to possess high specific capacity beyond the theoretical value from both charge compensation in transition metal and oxygen in the redox reaction. Although it could achieve higher reversible capacity due to the oxygen anion participating in electrochemical reaction, however, its use in energy storage systems has been limited. The reason is the irreversible oxygen reaction that occurs during the initial charge cycle, resulting in structural instability due to oxygen evolution and phase transition. To suppress the initial irreversible oxygen reaction, we introduced the surface-modified Li[Li0.2Ni0.16Mn0.56Co0.08]O2 prepared by carbon coating (carbonization process), which was verified to have reduced oxygen reaction during the initial charge cycle. The electrochemical performance is improved by the synergic effects of the oxygen-deficient layer and carbon coating layer formed on the surface of particles. The sample with suitable carbon coating exhibited the highest structural stability, resulting in reduced capacity fading and voltage decay, which are attributed to the mitigated layered-to-spinel-like phase transition during prolonged cycling. The control over the oxygen reaction of Li2MnO3 by surface modification affects the activation reaction above 4.4 V in the initial charge cycle and structure changes during prolonged cycling. X-ray diffraction, X-ray photoelectron spectroscopy, and X-ray absorption spectroscopy analyses as well as electrochemical performance measurement were used to identify the correlation between reduced oxygen activity and structural changes.

Carbon nanotube/Co3O4 nanocomposites selectively coated by polyaniline for high performance air electrodes.

We herein report the preparation of carbon nanotube (CNT)/Co3O4 nanocomposites selectively coated with polyaniline (PANI) via an electropolymerization method, for use as an effective electrode material for Li-air (Li-O2) batteries. The Co3O4 catalyst attached to the CNTs facilitated the dissociation of reaction products and reduced the overpotential of the cells. As the carbon surface activates the side reactions, the PANI coating on the carbon surface of the electrode suppressed the side reaction at the electrode/Li2O2 and electrode/electrolyte interfaces, thus enhancing the cycle performance of the electrode. In addition, the catalytic activity of Co3O4 on the CNT/Co3O4 nanocomposites remained unaffected, as the Co3O4 surface was not covered with a PANI layer due to the nature of the electropolymerization method. Overall, the synergic effect of the PANI layer and the Co3O4 catalyst leads to a superior cyclic performance and a low overpotential for the electrode based on selectively PANI-coated CNT/Co3O4 nanocomposites.

Polyimide-coated carbon electrodes combined with redox mediators for superior Li-O2 cells with excellent cycling performance and decreased overpotential.

We report an air electrode employing polyimide-coated carbon nanotubes (CNTs) combined with a redox mediator for Li-O2 cells with enhanced electrochemical performance. The polyimide coating on the carbon surface suppresses unwanted side reactions, which decreases the amount of accumulated reaction products on the surface of the air electrode during cycling. The redox mediators lower the overpotential of the Li-O2 cells because they can easily transfer electrons from the electrode to the reaction products. The low overpotential can also decrease the side reactions that activate at a high potential range. Specifically, the CsI redox mediator effectively interrupted dendrite growth on the Li anode during cycling due to the shielding effect of its Cs+ ions and acted as a redox mediator due to its I- ions. LiNO3 also facilitates the decrease in side reactions and the stabilization of the Li anode. The synergic effect of the polyimide coating and the electrolyte containing the LiNO3/CsI redox mediator leads to a low overpotential and excellent cycling performance (over 250 cycles with a capacity of 1,500 mAh·gelectrode-1).

Tailored Combination of Low Dimensional Catalysts for Efficient Oxygen Reduction and Evolution in Li-O2 Batteries.

The development of efficient bifunctional catalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is a key issue pertaining high performance Li-O2 batteries. Here, we propose a heterogeneous electrocatalyst consisting of LaMnO3 nanofibers (NFs) functionalized with RuO2 nanoparticles (NPs) and non-oxidized graphene nanoflakes (GNFs). The Li-O2 cell employing the tailored catalysts delivers an excellent electrochemical performance, affording significantly reduced discharge/charge voltage gaps (1.0 V at 400 mA g(-1) ), and superior cyclability for over 320 cycles. The outstanding performance arises from (1) the networked LaMnO3 NFs providing ORR/OER sites without severe aggregation, (2) the synergistic coupling of RuO2 NPs for further improving the OER activity and the electrical conductivity on the surface of the LaMnO3 NFs, and (3) the use of GNFs providing a fast electronic pathway as well as improved ORR kinetics.

Attachment of Li[Ni0.2Li0.2Mn0.6]O2 Nanoparticles to the Graphene Surface Using Electrostatic Interaction Without Deterioration of Phase Integrity.

In this article, we report a facile approach to enhance the electrochemical performance of Li-rich oxides with vulnerable phase stability. The Li-rich oxide nanoparticles were attached to the surface of graphene; the graphene surface acted as a matrix with high electronic conductivity that compensated for the low conductivity and enhanced the rate capability of the oxides. Our novel approach constitutes a direct assembly of two materials via electrostatic interaction, without a high-temperature heat treatment. The inevitable deterioration in phase integrity of previous composites between carbon and Li-rich oxides resulted from the reaction of oxygen in the structure with carbon during the heat-treatment process. However, our new method successfully attached Li-rich nanoparticles to the surface of graphene, without a phase change of the oxides. The resulting graphene/Li-rich oxide composites exhibited superior capacity and rate capability compared to their pristine Li-rich counterparts.

CsI as Multifunctional Redox Mediator for Enhanced Li-Air Batteries.

We introduce CsI as a multifunctional redox mediator to enhance the performance of Li-air batteries. CsI dissolved in the electrolyte is ionized into Cs(+) and I(-), which perform their roles in the Li anode and air electrode, respectively. The I(-) ions in the electrolyte facilitate the dissolution of Li2O2 in the air electrode as a redox mediator, which reduces the overpotential of the cell. The low overpotential also leads to the suppression of parasitic reactions occurring in the high-voltage range, such as the decomposition of the electrolyte and the reaction between Li2O2 and carbon. At the same time, the Cs(+) ions act as an electrostatic shield at the sharp points of the Li anode, hindering the growth of Li dendrite. The combined effects of reduced parasitic reactions and hindered Li-dendrite growth successfully improve the cyclic performance of Li-air cells.