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.      

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.     

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...     

Facile construction of a water-defendable Li anode protection enables rechargeable Li-O2 battery operating in humid atmosphere

The rechargeable Li-O₂ battery endowed with high theoretical specific energy density has sparked intense research interest as a promising energy storage system. However, the intrinsic high activity of Li anode, especially to moisture, usually leads to inferior electrochemical performance of Li-O₂ battery in humid environments, hindering its widespread application. To settle the trouble of poor moisture tolerance, fabricating a water-proof layer on the Li-metal anode could be an effective tactic. Herein, a facile strategy for constructing an ibuprofen-based protective layer on the Li anode has been proposed to realize highly rechargeable Li-O₂ battery in humid atmosphere. Due to the in-situ reaction between ibuprofen reagent and metallic Li, the protective layer with a thickness of ∼30 µm has been uniformly deposited on the surface of Li anode. Particularly, the protective layer, consisting of a large amount of hydrophobic alkyl group and benzene ring, can significantly resist water ingress and enhance the electrochemical stability of Li anode. As a result, the Li-O₂ battery based on the protected Li anode achieves a long cycle life of 210 h (21 cycles at 1000 mAh/g, 200 mA/g) in highly moist atmosphere with relative humidity (RH) of 68%. This convenient and efficient strategy offers novel design concept of water-resistant metal anode, and paves the way to the promising future prospect for the high-energy Li-O₂ battery implementing in the ambient atmosphere.     

Solvent autoxidation, electrolyte decomposition, and performance deterioration of the aprotic Li-O2 battery

The electrolyte decomposition is widely recognized as the greatest challenge to the successful development of the aprotic Li-O₂ battery. The decomposition of the organic ethers, which are the commonly used electrolyte solvents in the current studies, can be chemical or electrochemical during discharge or charge. In this paper, the influence of oxygen on the decomposition of the ether-based electrolyte is discussed. Ether solvents are found to be oxidized in contact with oxygen whether the cells operate or not. The solvent autoxidation significantly promotes the electrolyte decomposition during the discharge process of the ether-based Li-O₂ battery. As a result, the oxygen exposure time before battery operation significantly affects the electrochemical performance of the ether-based Li-O₂ battery. After the prolonged exposure to oxygen, both the discharge capacity and the working potential of the battery decrease to some extent. More importantly, the recharge potential of the battery greatly increases with extending the previous oxygen exposure time.     

Defective TiO2 hollow nanospheres as photo-electrocatalysts for photo-assisted Li-O2 batteries

The large overpotential for conventional Li-O₂ batteries is an enormous challenge, which impedes their practical application. Here, we prepare a defective TiO₂ (Ov-TiO₂) hollow nanosphere as photo-electrocatalyst for photo-assisted Li-O₂ batteries to reduce the overpotential. Under illumination, the oxygen vacancies as a charge separation center contribute to the separation of electrons and holes. The generated electrons could promote reducing O₂ to Li₂O₂ during oxygen reduction reaction (ORR) process, while the generated holes are beneficial to Li₂O₂ decomposition during oxygen evolution reaction (OER) process. Additionally, the proper concentration of oxygen vacancies will decrease the recombination rate between electrons and holes. The photo-assisted Li-O₂ batteries with Ov-TiO₂-650 exhibit advanced performances, such as the low overpotential (0.70 V), the fine rate capability, and the considerable reversibility accompanied with the formation/decomposition of Li₂O₂. We expect that these results could open a new mind to design of highly efficient photo-electrocatalysts for photo-assisted Li-O₂ battery.     

Recent Advances in the Research of Photo-Assisted Lithium-Based Rechargeable Batteries

The application of solar energy is crucial for alleviating the energy crisis and achieving sustainable development. In recent years, photo-assisted rechargeable batteries have attracted researchers because they can directly convert and store solar energy in the batteries. And it also can be used like a normal battery without light illumination. Photo-assisted lithium-based batteries have received more attention than other energy storage systems due to their higher energy density and relatively mature development. This Review focuses on the design of various photo-assisted lithium-based batteries including Li-ion, Li-S, Li-O₂, Li-CO₂ and Li-I batteries, as well as the working mechanism of photoelectrodes in these battery systems. The basic understanding and challenge of photo-assisted lithium-based batteries are also discussed. At last, perspectives for the photoelectrode development are provided in the summary to advance photo-assisted energy storage systems.     

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.     

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.     

Nanostructured Sn/TiO2/C composite as a high-performance anode for Li-ion batteries

A nanostructured Sn/TiO₂/C composite was prepared from SnO, Ti, and carbon powders using a mechanochemical reduction method and evaluated as an anode material in rechargeable Li-ion batteries. The Sn/TiO₂/C nanocomposite was composed of uniformly dispersed nanocrystalline Sn and rutile TiO₂ in amorphous carbon matrix. In addition, electrochemical Li insertion/extraction in rutile TiO₂ was examined by ex situ XRD and extended X-ray absorption fine structure. The Sn/TiO₂/C nanocomposite exhibited excellent electrochemical performance, which highlights its potential as a new alternative anode material in Li-ion batteries.     

Fabrication and evaluation of a polymer Li-ion battery with microporous gel electrolyte

This paper introduces an easy method for the fabrication of polymer Li-ion batteries with microporous gel electrolyte (MGE). The MGE is a multiphase electrolyte, which is composed of liquid electrolyte, gel electrolyte, and polymer matrix. The MGE not only has high ionic conductivity and good adhesion to the electrodes at low temperatures, but also retains good mechanical strength at elevated temperatures. Therefore, the MGE batteries are able to operate over a wide temperature range. During battery fabrication, the MGE is formed in situ by introducing liquid electrolyte into a swellable microporous polymer membrane and then heating or cycling the battery. In this work, the chemical compatibility of MGE with metal lithium during 60 °C storage and with LiMn₂O₄ cathode during cycling was studied. In addition, graphite/MGE/LiMn₂O₄ Li-ion batteries were made and evaluated.     

Temperature dependence of charging characteristic of C-free Li2O2 cathode in Li-O2 battery

Charging characteristics of lithium–oxygen (Li-O₂) batteries, using C-free lithium peroxide (Li₂O₂)-based electrodes, have been explored in this paper based on ether-based electrolytes. Charging overpotential can be lowered with the decrease of current density, and the most possible reason behind this may lie in the poor electrical conductivity of Li₂O₂. Meanwhile, high temperature seems beneficial for the charging process indicating Li-O₂ batteries may be promising high-temperature batteries. Charging voltage plateau is about 3.05 V at the test temperature of 343 K and current density of 4.2 mA g^?1, which is the lowest value among the Li-O₂ batteries reported to date.     

Hydrides compounds for electrochemical applications

Hydrides have been used since a long time for solid-state hydrogen storage and electrochemical nickel-metal hydride batteries. Besides these applications, growing attention has been devoted to their development as anode materials, as well as solid electrolytes for Li-ion and other ion batteries. Herein, we review and summarize the recent advances of hydrides as negative electrodes for Ni-MH and A-ion batteries (A = Li, Na), and as electrolyte for all solid-state batteries (ASSB). Metallic hydrides such as intergrowth compounds are highlighted as the best compromise up to now for Ni-MH. Regarding anodes of Li-ion batteries, MgH₂, especially its combination with TiH₂, provides very promising results. Complex hydrides such as Li-borohydride and related closo-borates and monovalent carborate boron clusters appear to be very attractive as solid electrolytes for Li-based ASSB, whereas closo-hydroborate sodium salts and closo-carboborates are investigated for Na- and Mg-ASSB. Finally, further research directions are foreseen for hydrides in electrochemical applications.     

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.     

Electrochemical Assessment of Indigo Carmine Dye in Lithium Metal Polymer Technology

Lithium metal batteries are inspiring renewed interest in the battery community because the most advanced designs of Li-ion batteries could be on the verge of reaching their theoretical specific energy density values. Among the investigated alternative technologies for electrochemical storage, the all-solid-state Li battery concept based on the implementation of dry solid polymer electrolytes appears as a mature technology not only to power full electric vehicles but also to provide solutions for stationary storage applications. With an effective marketing started in 2011, BlueSolutions keeps developing further the so-called lithium metal polymer batteries based on this technology. The present study reports the electrochemical performance of such Li metal batteries involving indigo carmine, a cheap and renewable electroactive non-soluble organic salt, at the positive electrode. Our results demonstrate that this active material was able to reversibly insert two Li at an average potential of ≈2.4 V vs. Li⁺/Li with however, a relatively poor stability upon cycling. Post-mortem analyses revealed the poisoning of the Li electrode by Na upon ion exchange reaction between the Na countercations of indigo carmine and the conducting salt. The use of thinner positive electrodes led to much better capacity retention while enabling the identification of two successive one-electron plateaus.     

Effect of oxygen-containing functional groups of carbon materials on the performance of Li–O2 batteries

In this communication, we present some new findings on surface oxidized carbon nanotubes (CNTs) when used as cathode of Li–O₂ batteries. It is found that the content of oxygen-containing functional groups has a significant influence on the electrochemical performance of Li–O₂ batteries, by altering the electrical conductivity and density of electrocatalytically active sites of the CNTs and promoting side reactions of the electrolyte. An optimal surface oxygen atomic content of 6.0 at.% on CNTs is found to reach a balance and give the best cycling stability of the Li–O₂ battery under constant capacity and constant current density tests.     

A Rechargeable Li‐CO2 Battery with a Gel Polymer Electrolyte

The utilization of CO₂ in Li‐CO₂ batteries is attracting extensive attention. However, the poor rechargeability and low applied current density have remained the Achilles’ heel of this energy device. The gel polymer electrolyte (GPE), which is composed of a polymer matrix filled with tetraglyme‐based liquid electrolyte, was used to fabricate a rechargeable Li‐CO₂ battery with a carbon nanotube‐based gas electrode. The discharge product of Li₂CO₃ formed in the GPE‐based Li‐CO₂ battery exhibits a particle‐shaped morphology with poor crystallinity, which is different from the contiguous polymer‐like and crystalline discharge product in conventional Li‐CO₂ battery using a liquid electrolyte. Accordingly, the GPE‐based battery shows much improved electrochemical performance. The achieved cycle life (60 cycles) and rate capability (maximum applied current density of 500 mA g⁻¹) are much higher than most of previous reports, which points a new way to develop high‐performance Li‐CO₂ batteries.     

Highly Rechargeable Lithium‐CO2 Batteries with a Boron‐ and Nitrogen‐Codoped Holey‐Graphene Cathode

Metal‐air batteries, especially Li‐air batteries, have attracted significant research attention in the past decade. However, the electrochemical reactions between CO₂ (0.04 % in ambient air) with Li anode may lead to the irreversible formation of insulating Li₂CO₃, making the battery less rechargeable. To make the Li‐CO₂ batteries usable under ambient conditions, it is critical to develop highly efficient catalysts for the CO₂ reduction and evolution reactions and investigate the electrochemical behavior of Li‐CO₂ batteries. Here, we demonstrate a rechargeable Li‐CO₂ battery with a high reversibility by using B,N‐codoped holey graphene as a highly efficient catalyst for CO₂ reduction and evolution reactions. Benefiting from the unique porous holey nanostructure and high catalytic activity of the cathode, the as‐prepared Li‐CO₂ batteries exhibit high reversibility, low polarization, excellent rate performance, and superior long‐term cycling stability over 200 cycles at a high current density of 1.0 A g⁻¹. Our results open up new possibilities for the development of long‐term Li‐air batteries reusable under ambient conditions, and the utilization and storage of CO₂.     

Sulfur-doped LaNiO3 perovskite oxides with enriched anionic vacancies and manipulated orbital occupancy facilitating oxygen electrode reactions in lithium-oxygen batteries

The rational design of effective bifunctional catalysts with enhanced activity toward oxygen reduction reaction and oxygen evolution reaction is of significance to develop high-performance lithium-oxygen (Li–O₂) batteries. Herein, sulfur-doped LaNiO₃ nanoparticles are elaborately synthesized, and their catalytic activity toward oxygen redox reactions in Li–O₂ batteries is comprehensively studied. As confirmed by the density functional theory calculations and experimental results, the substitution of oxygen atoms by sulfur atoms with lower Pauling electronegativity can enhance the covalent feature of bonds, thus increasing electrical conductivity of catalyst. In addition, abundant oxygen vacancies created after sulfur doping are capable of providing concentrated active sites. Simultaneously, sulfur dopants boost the hybridization between Ni 3d orbital and O 2p orbital and increase the covalency of Ni–O bonds due to the increase of Ni³⁺ with the near-unity occupancy of the e_g orbital, thereby increasing the adsorption strength of oxygen-containing intermediates on the surface. Eventually, lowered reaction energy barriers and accelerated reaction kinetics of oxygen electrode reactions are realized, contributing to the optimized electrochemical performance of Li–O₂ battery. The Li–O₂ battery based on sulfur-doped LaNiO₃ with the optimized S-doping level of 2.89 wt% (marked as S_2.89 wt%-LNO) delivers a high specific discharge capacity of 24067 mAh/g, an ultralow overpotential of 0.37 V and extended life of 347 cycles.     

Recent progress in liquid electrolytes for lithium metal batteries

Li metal batteries are revived as the next-generation batteries beyond Li-ion batteries. The Li metal anode can be paired with intercalation-type cathodes LiMO₂ and conversion-type cathodes such as sulfur and oxygen. Then, energy densities of Li/LiMO₂ and Li/S,O₂ batteries can reach 400 Whkg^?1 and more than 500 Whkg^?1, respectively, which surpass that of the state-of-the-art LIB (280 Whkg^?1). However, replacing the intercalation-type graphite anode with the Li metal anode suffers from low coulombic efficiency during repeated Li plating/stripping processes, which leads to short cycle lifetime and potential safety problems. The key solution is to construct a stable and uniform solid electrolyte interphase with high Li⁺ transport and high elastic strength on the Li metal anode. This review summarizes recent progress in improving the solid electrolyte interphase by tailoring liquid electrolytes, a classical but the most convenient and cost-effective strategy.