From O2− to HO2−: Reducing By‐Products and Overpotential in Li‐O2 Batteries by Water Addition

The development of aprotic Li‐O₂ batteries, which are promising candidates for high gravimetric energy storage devices, is severely limited by superoxide‐related parasitic reactions and large voltage hysteresis. The fundamental reaction pathway of the aprotic Li‐O₂ battery can be altered by the addition of water, which changes the discharge intermediate from superoxide (O₂⁻) to hydroperoxide (HO₂⁻). The new mechanism involving HO₂⁻ intermediate realizes the two‐electron transfer through a single step, which significantly suppresses the superoxide‐related side reactions. Moreover, addition of water also triggers a solution‐based pathway that effectively reduces the voltage hysteresis. These discoveries offer a possible solution for desirable Li‐O₂ batteries free of aggressive superoxide species, highlighting the design strategy of modifying the reaction pathway for Li‐O₂ electrochemistry.     

Recent advances in charge mechanism of noble metal-based cathodes for Li-O2 batteries

Lithium-oxygen(Li-O₂ ) batteries are considered as the next generation for energy storages systems due to the higher theoretical energy density than that of Li-ion batteries. However, the high charge overpotential caused by the insulated Li₂O₂ results in low energy efficiency, side reaction from electrolyte and cathode, and therefore poor battery performance. Designing noble metal-based catalysts can be an effective strategy to develop high-performance Li-O_2...     

A soluble phenolic mediator contributing to enhanced discharge capacity and low charge overpotential for lithium-oxygen batteries

In this study, a phenolic antioxidant of 2,6-di-tert-butyl-hydroxytoluene (BHT) is applied in Li-O₂ batteries to simultaneously improve discharge capacity and reduce charge overpotential. BHT exhibits a redox couple at ~ 3.0 V (vs. Li⁺/Li), which is extremely close to the thermodynamic potential of a Li-O₂ battery (2.96 V). The unique chemical and electrochemical behaviors of BHT contribute to the improvement on both oxygen reduction reaction and oxygen evolution reaction performances. These factors lead to the notable enhancement of discharge capacity (capacity increases by 72%) and the reduction of charge plateau (the plateau is 3.2 V and 4.2 V, respectively, with and without BHT) for Li-O₂ batteries. Furthermore, in-situ X-ray diffraction results confirm that the BHT-mediated formation and decomposition of Li₂O₂, rather than parasitic reactions, dominate the discharge and charge processes. The results provide a new approach for exploiting appropriate soluble mediators for rechargeable Li-O₂ batteries.     

High-Capacity and Stable Li-O2 Batteries Enabled by a Trifunctional Soluble Redox Mediator

Li-O₂ batteries with ultrahigh theoretical energy densities usually suffer from low practical discharge capacities and inferior cycling stability owing to the cathode passivation caused by insulating discharge products and by-products. Here, a trifunctional ether-based redox mediator, 2,5-di-tert-butyl-1,4-dimethoxybenzene (DBDMB), is introduced into the electrolyte to capture reactive O₂⁻ and alleviate the rigorous oxidative environment of Li-O₂ batteries. Thanks to the strong solvation effect of DBDMB towards Li⁺ and O₂⁻, it not only reduces the formation of by-products (a high Li₂O₂ yield of 96.6 %), but also promotes the solution growth of large-sized Li₂O₂ particles, avoiding the passivation of cathode as well as enabling a large discharge capacity. Moreover, DBDMB makes the oxidization of Li₂O₂ and the decomposition of main by-products (Li₂CO₃ and LiOH) proceed in a highly effective manner, prolonging the stability of Li-O₂ batteries (243 cycles at 1000 mAh g⁻¹ and 1000 mA g⁻¹).     

Enzyme-Inspired Room-Temperature Lithium–Oxygen Chemistry via Reversible Cleavage and Formation of Dioxygen Bonds

Li-O₂ batteries are promising energy storage systems due to their ultra-high theoretical capacity. However, most Li-O₂ batteries are based on the reduction/oxidation of Li₂O₂ and involve highly reactive superoxide and peroxide species that would cause serious degradation of cathodes, especially carbon-based materials. It is important to explore lithium-oxygen reactions and find new Li-O₂ chemistry which can restrict or even avoid the negative influence of superoxide/peroxide species. Here, inspired by enzyme-catalyzed oxygen reduction/oxidation reactions, we introduce a copper(I) complex 3 N-Cu^I (3 N=1,4,7-trimethyl-1,4,7-triazacyclononane) to Li-O₂ batteries and successfully modulate the reaction pathway to a moderate one on reversible cleavage/formation of O−O bonds. This work demonstrates that the reaction pathways of Li-O₂ batteries could be modulated by introducing an appropriate soluble catalyst, which is another powerful choice to construct better Li-O₂ batteries.     

Sabatier Relations in Electrocatalysts Based on High-entropy Alloys with Wide-distributed d-band Centers for Li-O2 Batteries

Li-O₂ battery (LOB) is a promising “beyond Li-ion” technology with ultrahigh theoretical energy density (3457 Wh kg⁻¹), while currently impeded by the sluggish cathodic kinetics of the reversible gas-solid reaction between O₂ and Li₂O₂. Despite many catalysts are developed for accelerating the conversion process, the lack of design guidance for achieving high performance makes catalysts exploring aleatory. The Sabatier principle is an acknowledged theory connecting the scaling relationship with heterogeneous catalytic activity, providing a tradeoff strategy for the topmost performance. Herein, a series of catalysts with wide-distributed d-band centers (i.e., wide range of adsorption strength) are elaborately constructed via high-entropy strategy, enabling an in-depth study of the Sabatier relations in electrocatalysts for LOBs. A volcano-type correlation of d-band center and catalytic activity emerges. Both theoretical and experimental results indicate that a moderate d-band center with appropriate adsorption strength propels the catalysts up to the top. As a demonstration of concept, the LOB using FeCoNiMnPtIr as catalyst provides an exceptional energy conversion efficiency of over 80 %, and works steadily for 2000 h with a high fixed specific capacity of 4000 mAh g⁻¹. This work certifies the applicability of Sabatier principle as a guidance for designing advanced heterogeneous catalysts assembled in LOBs.     

Intermittent operation of the aprotic Li-O2 battery: the mass recovery process upon discharge interval

The intermittent operation of the aprotic Li-O₂ battery is systematically studied in this paper. A combined study of the battery charge retention and the electrolyte stability to O₂ suggests a low self-discharge rate of the Li-O₂ battery, which is a prerequisite to achieve desirable intermittent discharge performance. The battery under intermittent operation exhibits significantly improved discharge performance as compared to the continuously discharged one. It is found that the capacity output is directly associated with the time interval between two discharge steps and with the capacity limit for each discharge step. The open-circuit potential and linear scan voltammetry analyses confirm that a “mass recovery” process, corresponding to the concentration relaxation of the oxygen which is available at the cathode, proceed during the discharge intervals. In the “mass recovery” process, an increased amount of O₂ homogeneously redistributes at the electrolyte/carbon interface at both sides of the electrode, which relieves the O₂ transport limit, enhances the availability of O₂ and the utilization of carbon material for the cathode, and thus significantly improves the discharge performance of the aprotic Li-O₂ battery.     

Rechargeable Aluminium–Sulfur Battery with Improved Electrochemical Performance by Cobalt-Containing Electrocatalyst

The rechargeable aluminium–sulfur (Al–S) battery is regarded as a potential alternative beyond lithium-ion battery system owing to its safety, promising energy density, and the high earth abundance of the constituent electrode materials, however, sluggish kinetic response and short life-span are the major issues that limit the battery development towards applications. In this article, we report Co^II,III as an electrochemical catalyst in the sulfur cathode that renders a reduced discharge–charge voltage hysteresis and improved capacity retention and rate capability for Al–S batteries. The structural and electrochemical analysis suggest that the catalytic effect of Co^II,III is closely associated with the formation of cobalt sulfides and the changes in the valence states of the Co^II,III during the electrochemical reactions of the sulfur species, which lead to improved reaction kinetics and sulfur utilization in the cathode. The Al–S battery, assembled with the cathode consisting of Co^II,III decorated carbon matrix, demonstrates a considerably reduced voltage hysteresis of 0.8 V, a reversible specific capacity of ≈500 mAh g⁻¹ at 1 A g⁻¹ after 200 discharge–charge cycles and of ≈300 mAh g⁻¹ at 3 A g⁻¹.     

Superoxide Anion Disproportionation Induced by Li+ and H+: Pathways to 1O2 Release in Li−O2 Batteries

We explore the disproportionation reaction of superoxide anions in the presence of H⁺ and Li⁺ cations with high quality multiconfigurational ab-initio methods. This reaction is of paramount importance in Li−O₂ battery chemistry as it represents the source of a major degrading impurity, singlet molecular oxygen. For the first time, the thermodynamic and kinetic data of the reaction are drawn from an accurate theoretical model where the electronic structure of the reactant and products is treated at the necessary level of theory. Overall, the H⁺ catalyzed O₂⁻+O₂⁻ disproportionation follows a very efficient thermodynamic and kinetic reaction path leading to neutral ³O₂, ¹O₂ and peroxide anions. On the contrary, we have found that the Li⁺ catalysis promotes only the release of ³O₂ whereas the ¹O₂ formation is energetically unfeasible at room temperature.     

Catalytic Disproportionation of the Superoxide Intermediate from Electrochemical O2 Reduction in Nonaqueous Electrolytes

Tris(pentafluorophenyl)borane (TPFPB) was found to be an efficient catalyst for rapid superoxide (O₂^?) disproportionation. The kinetics for the catalytic disproportionation reaction is much faster than the reaction between O₂^? and propylene carbonate. Therefore, the negative impact of the reaction between the electrolyte and O₂^? produced by the O₂ reduction is minimized. The cathodic current for O₂ reduction can be doubled in the presence of TPFPB. The high reduction current resulted from the pseudo two‐electron O₂‐reduction reaction due to the replenishment of O₂ at the electrode surface. This discovery could lead to a new avenue for the development of high‐capacity, high‐rate, rechargeable Li–air batteries.     

Facile synthesis of Fe@Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> core-shell nanowires as O<Subscript>2</Subscript> electrode for high-energy Li-O<Subscript>2</Subscript> batteries

Fe@Fe₂O₃ core-shell nanowires were synthesized via the reduction of Fe³⁺ ions by sodium borohydride in an aqueous solution with a subsequent heat treatment to form Fe₂O₃ shell and employed as a cathode catalyst for non aqueous Li-air batteries. The synthesized core-shell nanowires with an average diameter of 50–100 nm manifest superior catalytic activity for oxygen evolution reaction (OER) in Li-O₂ batteries with the charge voltage plateau reduced to ～3.8 V. An outstanding performance of cycling stability was also achieved with a cutoff specific capacity of 1000 milliampere hour per gram over 40 cycles at a current density of 100 mA g^?1. The excellent electrochemical properties of Fe@Fe₂O₃ as an O₂ electrode are ascribed to the high surface area of the nanowires’ structure and high electron conductivity. This study indicates that the resulting iron-containing nanostructures are promising catalyst in Li-O₂ batteries.     

Filling the Charge–Discharge Voltage Gap in Flexible Hybrid Zinc-Based Batteries by Utilizing a Pseudocapacitive Material

The high charge–discharge voltage gap is one of the main bottlenecks of zinc–air batteries (ZABs) because of the kinetically sluggish oxygen reduction/evolution reactions (ORR/OER) on the oxygen electrode side. Thus, an efficient bifunctional catalyst for ORR and OER is highly desired. Herein, honeycomb-like MnCo₂O_4.5 spheres were used as an efficient bifunctional electrocatalyst. It was demonstrated that both ORR and OER catalytic activity are promoted by Mn^IV-induced oxygen vacancy defects and multiple active sites. Importantly, the multivalent ions present in the material and its defect structure endow stable pseudocapacitance within the inactive region of ORR and OER; as a result, a low charge–discharge voltage gap (0.43 V at 10 mA cm⁻²) was achieved when it was employed in a flexible hybrid Zn-based battery. This mechanism provides unprecedented and valuable insights for the development of next-generation metal–air batteries.     

Realizing Stable Carbonate Electrolytes in Li–O2/CO2 Batteries†

The increasing demand for high-energy storage systems has propelled the development of Li-air batteries and Li-O₂/CO₂ batteries to elucidate the mechanism and extend battery life. However, the high charge voltage of Li₂CO₃ accelerates the decomposition of traditional sulfone and ether electrolytes, thus adopting high-voltage electrolytes in Li-O₂/CO₂ batteries is vital to achieve a stable battery system. Herein, we adopt a commercial carbonate electrolyte to prove its excellent suitability in Li-O₂/CO₂ batteries. The generated superoxide can be captured by CO₂ to form less aggressive intermediates, stabilizing the carbonate electrolyte without reactive oxygen species induced decomposition. In addition, this electrolyte permits the Li metal plating/stripping with a significantly improved reversibility, enabling the possibility of using ultra-thin Li anode. Benefiting from the good rechargeability of Li₂CO₃, less cathode passivation, and stabilized Li anode in carbonate electrolyte, the Li-O₂/CO₂ battery demonstrates a long cycling lifetime of 167 cycles at 0.1 mA·cm^–2 and 0.25 mAh·cm^–2. This work paves a new avenue for optimizing carbonate-based electrolytes for Li-O₂ and Li-O₂/CO₂ batteries.      

High-Voltage Rechargeable Alkali–Acid Zn–PbO2 Hybrid Battery

Aqueous rechargeable batteries have attracted attention owning to their advantages of safety, low cost, and sustainability, while the limited electrochemical stability window (1.23 V) of water leads to their failure in competition with organic-based lithium-ion batteries. Herein, we report an alkali–acid Zn–PbO₂ hybrid aqueous battery obtained by coupling an alkaline Zn anode with an acidic PbO₂ cathode. It shows the capability to deliver an impressively high open-circuit voltage (V_oc) of 3.09 V and an operate voltage of 2.95 V at 5 mA cm⁻², thanks to the contribution of expanding the voltage window and the electrochemical neutralization energy from the alkali–acid asymmetric-electrolyte hybrid cell. The hybrid battery can potentially deliver a large area capacity over 2 mAh cm⁻² or a high energy density of 252.39 Wh kg⁻¹ and shows almost no fading in area capacity over 250 charge–discharge cycles.     

The Stabilization Effect of CO2 in Lithium–Oxygen/CO2 Batteries

The lithium (Li)–air battery has an ultrahigh theoretical specific energy, however, even in pure oxygen (O₂), the vulnerability of conventional organic electrolytes and carbon cathodes towards reaction intermediates, especially O₂⁻, and corrosive oxidation and crack/pulverization of Li metal anode lead to poor cycling stability of the Li-air battery. Even worse, the water and/or CO₂ in air bring parasitic reactions and safety issues. Therefore, applying such systems in open-air environment is challenging. Herein, contrary to previous assertions, we have found that CO₂ can improve the stability of both anode and electrolyte, and a high-performance rechargeable Li–O₂/CO₂ battery is developed. The CO₂ not only facilitates the in situ formation of a passivated protective Li₂CO₃ film on the Li anode, but also restrains side reactions involving electrolyte and cathode by capturing O₂⁻. Moreover, the Pd/CNT catalyst in the cathode can extend the battery lifespan by effectively tuning the product morphology and catalyzing the decomposition of Li₂CO₃. The Li–O₂/CO₂ battery achieves a full discharge capacity of 6628 mAh g⁻¹ and a long life of 715 cycles, which is even better than those of pure Li–O₂ batteries.     

An Organic Coordination Manganese Complex as Cathode for High-Voltage Aqueous Zinc-metal Battery

Aqueous Zn−Mn battery has been considered as the most promising scalable energy-storage system due to its intrinsic safety and especially ultralow cost. However, the traditional Zn−Mn battery mainly using manganese oxides as cathode shows low voltage and suffers from dissolution/disproportionation of the cathode during cycling. Herein, for the first time, a high-voltage and long-cycle Zn−Mn battery based on a highly reversible organic coordination manganese complex cathode (Manganese polyacrylate, PAL−Mn) was constructed. Benefiting from the insoluble carboxylate ligand of PAL−Mn that can suppress shuttle effect and disproportionationation reaction of Mn³⁺ in a mild electrolyte, Mn³⁺/Mn²⁺ reaction in coordination state is realized, which not only offers a high discharge voltage of 1.67 V but also exhibits excellent cyclability (100 % capacity retention, after 4000 cycles). High voltage reaction endows the Zn−Mn battery high specific energy (600 Wh kg⁻¹ at 0.2 A g⁻¹), indicating a bright application prospect. The strategy of introducing carboxylate ligands in Zn−Mn battery to harness high-voltage reaction of Mn³⁺/Mn²⁺ well broadens the research of high-voltage Zn−Mn batteries under mild electrolyte conditions.     

Solvation Structure with Enhanced Anionic Coordination for Stable Anodes in Lithium-Oxygen Batteries

Li-O₂ batteries have garnered much attention due to their high theoretical energy density. However, the irreversible lithium plating/stripping on the anode limits their performance, which has been paid little attention. Herein, a solvation-regulated strategy for stable lithium anodes in tetraethylene glycol dimethyl ether (G4) based electrolyte is attempted in Li-O₂ batteries. Trifluoroacetate anions (TFA⁻) with strong Li⁺ affinity are incorporated into the lithium bis(fluorosulfonyl)imide (LiTFSI)/G4 electrolyte to attenuate the Li⁺-G4 interaction and form anion-dominant solvates. The bisalt electrolyte with 0.5 M LiTFA and 0.5 M LiTFSI mitigates G4 decomposition and induces an inorganic-rich solid electrolyte interphase (SEI). This contributes to decreased desolvation energy barrier from 58.20 to 46.31 kJ mol⁻¹, compared with 1.0 M LiTFSI/G4, for facile interfacial Li⁺ diffusion and high efficiency. It yields extended lifespan of 120 cycles in Li-O₂ battery with a limited Li anode (7 mAh cm⁻²). This work gains comprehensive insights into rational electrolyte design for Li-O₂ batteries.     

An Adjustable-Porosity Plastic Crystal Electrolyte Enables High-Performance All-Solid-State Lithium-Oxygen Batteries

The limited triple-phase boundaries (TPBs) in solid-state cathodes (SSCs) and high resistance imposed by solid electrolytes (SEs) make the achievement of high-performance all-solid-state lithium-oxygen (ASS Li-O₂) batteries a challenge. Herein, an adjustable-porosity plastic crystal electrolyte (PCE) has been fabricated by employing a thermally induced phase separation (TIPS) technique to overcome the above tricky issues. The SSC produced through the in-situ introduction of the porous PCE on the surface of the active material, facilitates the simultaneous transfer of Li⁺/e⁻, as well as ensures fast flow of O₂, forming continuous and abundant TPBs. The high Li⁺ conductivity, softness, and adhesion of the dense PCE significantly reduce the battery resistance to 115 Ω. As a result, the ASS Li-O₂ battery based on this adjustable-porosity PCE exhibits superior performances with high specific capacity (5963 mAh g⁻¹), good rate capability, and stable cycling life up to 130 cycles at 32 °C. This novel design and exciting results could open a new avenue for ASS Li-O₂ batteries.     

Coupling Magnetic Single-Crystal Co2Mo3O8 with Ultrathin Nitrogen-Rich Carbon Layer for Oxygen Evolution Reaction

Transition-metal oxides as electrocatalysts for the oxygen evolution reaction (OER) provide a promising route to face the energy and environmental crisis issues. Although palmeirite oxide A₂Mo₃O₈ as OER catalyst has been explored, the correlation between its active sites (tetrahedral or octahedral) and OER performance has been elusive. Now, magnetic Co₂Mo₃O₈@NC-800 composed of highly crystallized Co₂Mo₃O₈ nanosheets and ultrathin N-rich carbon layer is shown to be an efficient OER catalyst. The catalyst exhibits favorable performance with an overpotential of 331 mV@10 mA cm⁻² and 422 mV@40 mA cm⁻², and a full water-splitting electrolyzer with it as anode catalyst shows a cell voltage of 1.67 V@10 mA cm⁻² in alkaline. Combined HAADFSTEM, magnetic, and computational results show that factors influencing the OER performance can be attributed to the tetrahedral Co sites (high spin, t₂³e⁴), which improve the OER kinetics of rate-determining step to form *OOH.     

Photoinduced Oxygen Reduction Reaction Boosts the Output Voltage of a Zinc–Air Battery

Utilization of solar energy is of great interest for a sustainable society, and its conversion into electricity in a compact battery is challenging. Herein, a zinc–air battery with the polymer semiconductor polytrithiophene (pTTh) as the cathode is reported for direct conversion of photoenergy into electric energy. Upon irradiation, photoelectrons are generated in the conduction band (CB) of pTTh and then injected into the π_2p* orbitals of O₂ for its reduction to HO₂^?, which is disproportionated to OH^? and drives the oxidation of Zn to ZnO at the anode. The discharge voltage was significantly increased to 1.78 V without decay during discharge–charge cycles over 64 h, which corresponds to an energy density increase of 29.0 % as compared to 1.38 V for a zinc–air battery with state‐of‐the‐art Pt/C. The zinc–air battery with an intrinsically different reaction scheme for simultaneous conversion of chemical and photoenergy into electric energy opens a new pathway for utilization of solar energy.