Lithium–air batteries are promising devices for electrochemical energy storage because of their ultrahigh energy density. However, it is still challenging to achieve practical Li–air batteries ...because of their severe capacity fading and poor rate capability. Electrolytes are the prime suspects for cell failure. In this Review, we focus on the opportunities and challenges of electrolytes for rechargeable Li–air batteries. A detailed summary of the reaction mechanisms, internal compositions, instability factors, selection criteria, and design ideas of the considered electrolytes is provided to obtain appropriate strategies to meet the battery requirements. In particular, ionic liquid (IL) electrolytes and solid‐state electrolytes show exciting opportunities to control both the high energy density and safety.
Performance enhancers: Electrolytes for Li–air batteries include non‐aqueous liquid electrolytes, solid‐state electrolytes, aqueous electrolytes, and hybrid electrolytes. This Review shows the importance of electrolytes to the mechanisms and performance of lithium–air batteries and provides a basis for selecting suitable electrolytes. The existing challenges, solutions, as well as guidance for the future direction of this field are also considered.
Aqueous batteries are promising devices for electrochemical energy storage because of their high ionic conductivity, safety, low cost, and environmental friendliness. However, their voltage output ...and energy density are limited by the failure to form a solid‐electrolyte interphase (SEI) that can expand the inherently narrow electrochemical window of water (1.23 V) imposed by hydrogen and oxygen evolution. Here, a novel (Li4(TEGDME)(H2O)7) is proposed as a solvation electrolyte with stable interfacial chemistry. By introducing tetraethylene glycol dimethyl ether (TEGDME) into a concentrated aqueous electrolyte, a new carbonaceous component for both cathode−electrolyte interface and SEI formation is generated. In situ characterizations and ab initio molecular dynamics (AIMD) calculations reveal a bilayer hybrid interface composed of inorganic LiF and organic carbonaceous species reduced from Li+2(TFSI−) and Li+4(TEGDME). Consequently, the interfacial films kinetically broaden the electrochemical stability window to 4.2 V, thus realizing a 2.5 V LiMn2O4−Li4Ti5O12 full battery with an excellent energy density of 120 W h kg−1 for 500 cycles. The results provide an in‐depth, mechanistic understanding of a potential design of more effective interphases for next‐generation aqueous lithium‐ion batteries.
A novel “ether‐in‐water” electrolyte is demonstrated by introducing the non‐aqueous co‐solvent TEGDME into an aqueous electrolyte. The designed Li4(TEGDME)(H2O)7 solvation sheath structure with stable interfacial chemistry dynamically expands the electrochemical stability window to 4.2 V. Meanwhile, the high‐quality solid electrolyte interphase (SEI) and cathode–electrolyte interface (CEI) derived from the reduction of Li+2(TFSI−) and Li+4(TEGDME) effectively suppress hydrogen/oxygen evolution and electrode dissolution.
Abstract
Li‐O
2
batteries are promising energy storage devices with ultra‐high theoretical energy density. However, in practice they show severe capacity fading and limited cycle life, meaning that ...more suitable electrolytes are urgently needed. Here, solvents are combined with high donor number and low donor number, and a Li salt to produce a new local strong solvation effect electrolyte. High discharge capacity and good cycling performance are achieved when the optimized electrolyte is used in a Li‐O
2
battery. The optimized electrolyte inhibits side reactions within the battery and facilitates stable solid electrolyte interphase film formation on the surfaces of Li anode. This work opens a new route for the design of high‐performance electrolytes to increase both capacity and cycle life of Li‐O
2
batteries.
The results obtained herein demonstrate that the oxygen electrode plays a critical role in determining the morphology and chemical composition of discharge products in Na–O2 batteries. ...Micrometer‐sized cubic NaO2, film‐like NaO2, and nano‐sized amorphous spherical Na2‐xO2 are characterized as the main discharge products on the surface of reduced graphite oxide (rGO), boron‐doped rGO (B‐rGO), and micrometer‐sized RuO2 catalyst‐coated B‐rGO (m‐RuO2‐B‐rGO) cathodes, respectively. The Na–O2 battery with m‐RuO2‐B‐rGO as the cathode exhibits a much longer cycle life than those with the other cathodes, maintaining an unchanged capacity (0.5 mAh cm‐2) after 100 cycles at a current density of 0.05 mA cm‐2. A good rate capability and deep discharge–charge energy efficiency are also obtained. The excellent electrochemical performance of the battery is attributed to the effect of the micrometer‐sized RuO2 catalyst. Owing to the high affinity of RuO2 for oxygen, the amorphous phase Na2‐xO2 discharge product, which has good electrical contact with the RuO2 particles, can decompose completely under 3.1 V without a sudden voltage jump. Meanwhile, the micrometer‐sized RuO2 catalysts also provide enough active sites and space for the reactions, and effectively minimize the occurrence of side reactions between discharge products and carbon defects.
The oxygen electrode determines the morphology and composition of the discharge product in the Na–O2 battery, which simultaneously influences the cycling performance. Attributing to the effect of micrometer‐sized RuO2 catalyst, the Na2‐xO2 with amorphous phase is identified as discharge products, and the occurrence of the side reactions is effectively minimized. Notably, the Na–O2 battery with m‐RuO2‐B‐rGO as cathode achieves a long cycle life.
A biomimetic functionalized separator has been developed for Li-O2 batteries. (1) The reduced LiOH accumulation and I3− reduction both demonstrate a significant inhibition of the side reactions ...involving iodine species. (2) The electronegative separator has dual function of suppressing the shuttle effect and facilitating Li+ transport.
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•An electronegative biomimetic separator has been developed for Li-O2 batteries.•The separator suppresses the shuttle effect and promotes Li+ transport.•The reduced LiOH yield demonstrates an inhibition of iodine-related side reactions.
LiI in Li-O2 batteries has shown promise in reducing charge overpotential. However, the shuttle effect of oxidated iodine species (OISs) can lead to lithium metal corrosion and loss of OISs. During the discharging process, these iodine species can undergo side reactions, resulting in the accumulation of LiOH and other parasitic products, which in turn accelerates battery failure. In this work, we have drawn inspiration from mussel protein and utilized a simple co-deposition method to form a robust biomimetic functionalized coating on the surface of the glass fiber separator. This was achieved by grafting catechol/polyamine (CA/PA) with 11-mercaptoundecanoic acid (MUA). This separator exhibits strong electrostatic repulsion towards negatively charged OISs and, conversely, electrostatic attraction towards Li+, this dual action effectively suppresses the shuttle effect and facilitates Li+ transport. When equipped with this modified separator, the Li-O2 battery effectively reduces the accumulation of LiOH and demonstrates significantly enhanced rate performance and cycle stability. Our findings provide a versatile approach for the design of modified separators for Li-O2 batteries with redox mediators (RMs).
Li‐O2 batteries are promising energy storage devices with ultra‐high theoretical energy density. However, in practice they show severe capacity fading and limited cycle life, meaning that more ...suitable electrolytes are urgently needed. Here, solvents are combined with high donor number and low donor number, and a Li salt to produce a new local strong solvation effect electrolyte. High discharge capacity and good cycling performance are achieved when the optimized electrolyte is used in a Li‐O2 battery. The optimized electrolyte inhibits side reactions within the battery and facilitates stable solid electrolyte interphase film formation on the surfaces of Li anode. This work opens a new route for the design of high‐performance electrolytes to increase both capacity and cycle life of Li‐O2 batteries.
Dimethylsulfoxide as a strong solvent and tetraethylene glycol dimethyl ether as a weak solvent are used to form a local strong solvation effect electrolyte (LSSE). The LSSE combines the benefit of dilute electrolyte and strong solvation effect electrolyte, allowing to produce Li‐O2 batteries with an appropriate balance of capacity and cycle life.
Lithium-oxygen battery has high energy density which is considered as promising candidate for next-generation energy storage system. One of the major challenges for Li–O2 battery is exploring ...efficient catalysts for the decomposition of Li2O2 and by-products. In this work, a robust cathode employing RuO2·nH2O clusters anchored on the carbon nanofibers (RNCs@CNFs) is fabricated for Li–O2 battery. RNCs demonstrate an excellent oxidation activity towards both Li2O2 and Li2CO3 during the oxygen evolution reaction (OER). The unique structure of RuO2·nH2O clusters also alleviate the deactivation caused by the coverage of active sites. As a result, the as-built battery exhibits a high specific capacity, a superior rate capability and an excellent cycling stability with low overpotentials. After 200 cycles, new Li anode is replaced and the battery continues 100 cycles without attenuation at a limited capacity of 1000 mAh g−1 and a current of 200 mA g−1. These results provide necessary information for the development of efficient cathode catalysts for the decomposition of Li2O2 and Li2CO3 in Li-air batteries.
•A robust cathode employing RNCs@CNFs is fabricated.•RNCs@CNFs accelerate the decomposition of both Li2O2 and Li2CO3.•The unique structure of RNCs alleviates the deactivation of the carbon-based cathode.•The cathode exhibits extremely long cycle life.
Lithium‐oxygen batteries (LOBs) are well known for their high energy density. However, their reversibility and rate performance are challenged due to the sluggish oxygen reduction/evolution reactions ...(ORR/OER) kinetics, serious side reactions and uncontrollable Li dendrite growth. The electrolyte plays a key role in transport of Li+ and reactive oxygen species in LOBs. Here, we tailored a dilute electrolyte by screening suitable crown ether additives to promote lithium salt dissociation and Li+ solvation through electrostatic interaction. The electrolyte containing 100 mM 18‐crown‐6 ether (100‐18C6) exhibits enhanced electrochemical stability and triggers a solution‐mediated Li2O2 growth pathway in LOBs, showing high discharge capacity of 10 828.8 mAh gcarbon−1. Moreover, optimized electrode/electrolyte interfaces promote ORR/OER kinetics on cathode and achieve dendrite‐free Li anode, which enhances the cycle life. This work casts new lights on the design of low‐cost dilute electrolytes for high performance LOBs.
The introduction of 18‐crown‐6 ether additive regulates the solvation structure of electrolyte, prevents nucleophilic attack of reactive oxygen species on the solvent, and reduces the release of harmful gases. The solution‐mediated mechanism is triggered to enhance the discharge capacity, and the anion‐derived SEI protects Li anode to improve the cycling stability of lithium‐oxygen batteries.
Solid electrolyte interphase (SEI) makes the electrochemical window of aqueous electrolytes beyond the thermodynamics limitation of water. However, achieving the energetic and robust SEI is more ...challenging in aqueous electrolytes because the low SEI formation efficiency (SFE) only contributed from anion-reduced products, and the low SEI formation quality (SFQ) negatively impacted by the hydrogen evolution, resulting in a high Li loss to compensate for SEI formation. Herein, we propose a highly efficient strategy to construct Spatially-Temporally Synchronized (STS) robust SEI by the involvement of synergistic chemical precipitation-electrochemical reduction. In this case, a robust Li
PO
-rich SEI enables intelligent inherent growth at the active site of the hydrogen by the chemical capture of the OH
stemmed from the HER to trigger the ionization balance of dihydrogen phosphate (H
PO
) shift to insoluble solid Li
PO
. It is worth highlighting that the Li
PO
formation does not extra-consume lithium derived from the cathode but makes good use of the product of HER (OH
), prompting the SEI to achieve 100 % SFE and pushing the HER potential into -1.8 V vs. Ag/AgCl. This energetic and robust SEI offers a new way to achieve anion/concentration-independent interfacial chemistry for the aqueous batteries.
Solid electrolyte interphase (SEI) makes the electrochemical window of aqueous electrolytes beyond the thermodynamics limitation of water. However, achieving the energetic and robust SEI is more ...challenging in aqueous electrolytes because the low SEI formation efficiency (SFE) only contributed from anion‐reduced products, and the low SEI formation quality (SFQ) negatively impacted by the hydrogen evolution, resulting in a high Li loss to compensate for SEI formation. Herein, we propose a highly efficient strategy to construct Spatially‐Temporally Synchronized (STS) robust SEI by the involvement of synergistic chemical precipitation‐electrochemical reduction. In this case, a robust Li3PO4‐rich SEI enables intelligent inherent growth at the active site of the hydrogen by the chemical capture of the OH− stemmed from the HER to trigger the ionization balance of dihydrogen phosphate (H2PO4−) shift to insoluble solid Li3PO4. It is worth highlighting that the Li3PO4 formation does not extra‐consume lithium derived from the cathode but makes good use of the product of HER (OH−), prompting the SEI to achieve 100 % SFE and pushing the HER potential into −1.8 V vs. Ag/AgCl. This energetic and robust SEI offers a new way to achieve anion/concentration‐independent interfacial chemistry for the aqueous batteries.
A novel strategy of constructing spatially–temporally synchronized (STS) robust solid–slectrolyte interphases (SEI) in aqueous Li‐ion batteries through synergistic chemical precipitation‐electrochemical reduction was proposed. In this case, a robust Li3PO4‐rich SEI protective layer enables intelligent inherent growth at the active site of the hydrogen by the chemical capture of the OH− stemming from the HER to trigger the ionization balance of dihydrogen phosphate (H2PO4−) shift to insoluble solid Li3PO4. It offers a new way to achieve anion/concentration‐independent interfacial chemistry for the aqueous batteries.
