Electrolyte is very critical to the performance of the high-voltage lithium (Li) metal battery (LMB), which is one of the most attractive candidates for the next-generation high-density ...energy-storage systems. Electrolyte formulation and structure determine the physical properties of the electrolytes and their interfacial chemistries on the electrode surfaces. Localized high-concentration electrolytes (LHCEs) outperform state-of-the-art carbonate electrolytes in many aspects in LMBs due to their unique solvation structures. Types of fluorinated cosolvents used in LHCEs are investigated here in searching for the most suitable diluent for high-concentration electrolytes (HCEs). Nonsolvating solvents (including fluorinated ethers, fluorinated borate, and fluorinated orthoformate) added in HCEs enable the formation of LHCEs with high-concentration solvation structures. However, low-solvating fluorinated carbonate will coordinate with Li
ions and form a second solvation shell or a pseudo-LHCE which diminishes the benefits of LHCE. In addition, it is evident that the diluent has significant influence on the electrode/electrolyte interphases (EEIs) beyond retaining the high-concentration solvation structures. Diluent molecules surrounding the high-concentration clusters could accelerate or decelerate the anion decomposition through coparticipation of diluent decomposition in the EEI formation. The varied interphase features lead to significantly different battery performance. This study points out the importance of diluents and their synergetic effects with the conductive salt and the solvating solvent in designing LHCEs. These systematic comparisons and fundamental insights into LHCEs using different types of fluorinated solvents can guide further development of advanced electrolytes for high-voltage LMBs.
Functional electrolyte is the key to stabilize the highly reductive lithium (Li) metal anode and the high-voltage cathode for longlife, high-energy-density rechargeable Li metal batteries (LMBs). ...However, fundamental mechanisms on the interactions between reactive electrodes and electrolytes are still not well understood. Recently localized high-concentration electrolytes (LHCEs) are emerging as a promising electrolyte design strategy for LMBs. Here, we use LHCEs as an ideal platform to investigate the fundamental correlation between the reactive characteristics of the inner solvation sheath on electrode surfaces due to their unique solvation structures. The effects of a series of LHCEs with model electrolyte solvents (carbonate, sulfone, phosphate, and ether) on the stability of high-voltage LMBs are systematically studied. The stabilities of electrodes in different LHCEs indicate the intrinsic synergistic effects between the salt and the solvent when they coexist on electrode surfaces. Experimental and theoretical analyses reveal an intriguing general rule that the strong interactions between the salt and the solvent in the inner solvation sheath promote their intermolecular proton/charge transfer reactions, which dictates the properties of the electrode/electrolyte interphases and thus the battery performances.
It has been widely assumed that the flammability of the liquid electrolyte is one of the most influential factors that determine the safety of lithium‐ion batteries (LIBs). Following this ...consideration, a completely nonflammable electrolyte is designed and adopted for graphite||LiFePO4 (Gr||LFP) batteries. Contrary to the conventional understanding, the completely nonflammable electrolyte with phosphorus‐containing solvents exhibits inferior safety performance in commercial Gr||LFP batteries, in comparison to the flammable conventional LiPF6‐organocarbonate electrolyte. Mechanistic studies identify the exothermic reactions between the electrolyte (especially the salt LiFSI) and the charged electrodes as the “culprit” behind this counterintuitive phenomenon. The discovery emphasizes the importance of reducing the electrolyte reactivity when designing safe electrolytes, as well as the necessity of evaluating safety performance of electrolytes on a battery level.
Flammability of electrolyte has been considered to be the major safety hazard in lithium‐ion batteries (LIBs). To enhance the safety performance of LIBs, a completely nonflammable electrolyte is developed. Counterintuitively, its safety performance in graphite||LiFePO4 is inferior to a flammable, conventional electrolyte. Mechanistic studies reveal that the reactivity of the electrolyte overweighs the flammability in the battery safety performance.
LiNixMnyCo1−x−yO2 (NMC) cathode materials with Ni ≥ 0.8 have attracted great interest for high energy‐density lithium‐ion batteries (LIBs) but their practical applications under high charge voltages ...(e.g., 4.4 V and above) still face significant challenges due to severe capacity fading by the unstable cathode/electrolyte interface. Here, an advanced electrolyte is developed that has a high oxidation potential over 4.9 V and enables NMC811‐based LIBs to achieve excellent cycling stability in 2.5–4.4 V at room temperature and 60 °C, good rate capabilities under fast charging and discharging up to 3C rate (1C = 2.8 mA cm−2), and superior low‐temperature discharge performance down to −30 °C with a capacity retention of 85.6% at C/5 rate. It is also demonstrated that the electrode/electrolyte interfaces, not the electrolyte conductivity and viscosity, govern the LIB performance. This work sheds light on a very promising strategy to develop new electrolytes for fast‐charging high‐energy LIBs in a wide‐temperature range.
Advanced localized high‐concentration electrolytes are developed to inhibit Ni dissolution and particle cracking in high‐Ni (≥0.8) LiNixMnyCo1−x−yO2 cathode materials when cycling under 4.4 V through formation of uniform, robust, and conductive electrode/electrolyte interfaces, thus enabling excellent long‐term cycling stability in a wide‐temperature range, superior fast‐charging and fast‐discharging capabilities, and superior low‐temperture performance when compared to conventional electrolytes.
High‐energy‐density batteries with a LiCoO2 (LCO) cathode are of significant importance to the energy‐storage market, especially for portable electronics. However, their development is greatly ...limited by the inferior performance under high voltages and challenging temperatures. Here, highly stable lithium (Li) metal batteries with LCO cathode, through the design of in situ formed, stable electrode/electrolyte interphases on both the Li anode and the LCO cathode, with an advanced electrolyte, are reported. The LCO cathode can deliver a high specific capacity of ≈190 mAh g−1 and show greatly improved cell performances under a high charge voltage of 4.5 V (even up to 4.55 V) and a wide temperature range from −30 to 55 °C. This work points out a promising approach for developing Li||LCO batteries for practical applications. This approach can also be used to improve the high‐voltage performance of other batteries in a broad temperature range.
High‐voltage LiCoO2 cathodes are highly desirable for various energy‐storage applications, especially when coupled with lithium metal anodes. Fluorine‐rich electrode/electrolyte interphases in situ formed in an advanced ether electrolyte are found to enable highly stable cell cycling under elevated temperatures. Such interphases effectively suppress electrolyte side reactions and preserve the integrity of both cathode and anode materials.
Despite being an effective flame retardant, trimethyl phosphate (TMPa) is generally considered as an unqualified solvent for fabricating electrolytes used in graphite (Gr)‐based lithium‐ion batteries ...as it readily leads to Gr exfoliation and cell failure. In this work, by adopting the unique solvation structure of localized high‐concentration electrolyte (LHCE) to TMPa and tuning the composition of the solvation sheaths via electrolyte additives, excellent electrochemical performance can be achieved with TMPa‐based electrolytes in Gr∥LiNi0.8Mn0.1Co0.1O2 cells. After 500 charge/discharge cycles within the voltage range of 2.5–4.4 V, the batteries containing the TMPa‐based LHCE with a proper additive can achieve a capacity retention of 85.4 %, being significantly higher than cells using a LiPF6‐organocarbonates baseline electrolyte (75.2 %). Meanwhile, due to the flame retarding effect of TMPa, TMPa‐based LHCEs exhibit significantly reduced flammability compared with the conventional LiPF6‐organocarbonates electrolyte.
Advanced low‐flammable electrolytes are developed for high‐voltage lithium‐ion batteries (LIBs). With fluoroethylene carbonate as a proper electrolyte additive, the trimethyl phosphate‐based localized high‐concentration electrolyte achieves greatly extended cycle life over the conventional LiPF6‐organocarbonates electrolyte, due to the formation of enhanced surface protection layers, making it a promising candidate for high‐energy‐density LIBs.
Rechargeable lithium (Li)-metal batteries (LMBs) offer a great opportunity for applications needing high-energy-density battery systems. However, rare progress has been demonstrated so far under ...practical conditions, including high voltage, high-loading cathode, thin Li anode, and lean electrolyte. Here, in opposition to common wisdom, we report an ether-based localized high-concentration electrolyte that can greatly enhance the stability of a Ni-rich LiNi0.8Mn0.1Co0.1O2 (NMC811) cathode under 4.4 and 4.5 V with an effective protection interphase enriched in LiF. This effect, in combination with the superior Li stability in this electrolyte, enables dramatically improved cycling performances of Li||NMC811 batteries under highly challenging conditions. The LMBs can retain over 80% capacity in 150 stable cycles with extremely limited amounts of the Li anode and electrolyte. The findings in this work point out a very promising strategy to develop practical high-energy LMBs.
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•Ether-based LHCE enables high-voltage (4.5 V) cycling of Li||NMC811 cells•Ether-LHCE improves Coulombic efficiency and cycling stability of LMAs•Ether-LHCE greatly improves LMB performances under practical conditions
High-energy-density Li-metal batteries are promising next-generation energy-storage systems. However, their development is greatly restricted because of the lack of functional electrolytes that can work efficiently on both the reactive Li anode and the aggressive cathodes under practical conditions, where high-voltage, high-loading cathode, thin Li anode and lean electrolyte are all indispensable. Here, we chose ether as the base solvent, which has intrinsic good cathodic but poor anodic stabilities and redesigned the electrolyte in a localized high-concentration electrolyte (LHCE) formulation to build the protective interphases onto both the anode and the cathode, simultaneously. Ether-based LHCE can effectively suppress side reactions, resulting in stable cycling of Li||NMC811 cells under voltages up to 4.5 V and under practical conditions. This electrolyte design provides critical insights for future electrolyte development for practical high-energy-density Li-metal batteries.
Instability of electrolytes toward both highly reactive Li-metal anode and high-voltage cathodes has greatly impeded the development of Li-metal batteries. The authors designed an ether-based localized high-concentration electrolyte that can form stable interphases on both the Li anode and the Ni-rich NMC811 cathode to inhibit the undesired side reactions. This electrolyte enables a significantly enhanced battery performance under stringent practical conditions with a thin Li-metal anode or Li-free anode, a high-loading cathode, and lean electrolyte.
Localized high‐concentration electrolytes (LHCEs) based on five different types of solvents were systematically studied and compared in lithium (Li)‐ion batteries (LIBs). The unique solvation ...structure of LHCEs promotes the participation of Li salt in forming solid electrolyte interphase (SEI) on graphite (Gr) anode, which enables solvents previously considered incompatible with Gr to achieve reversible lithiation/delithiation. However, the long cyclability of LIBs is still subject to the intrinsic properties of the solvent species in LHCEs. Such issue can be readily resolved by introducing a small amount of additive into LHCEs. The synergetic decompositions of Li salt, solvating solvent and additive yield effective SEIs and cathode electrolyte interphases (CEIs) in most of the studied LHCEs. This study reveals that both the structure and the composition of solvation sheaths in LHCEs have significant effect on SEI and CEI, and consequently, the cycle life of energetically dense LIBs.
The effects of microscopic solvation structure, solvating solvent and additive of localized high‐concentration electrolytes (LHCEs) over the electrolyte properties, the electrode/electrolyte interphases and the cycling stability of lithium‐ion batteries (LIBs) were systematically studied. The synergetic decomposition of anion, proper solvent and additive in LHCEs is the key to forming effective interphases and achieving long cycle life of LIBs.
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Rechargeable lithium (Li) metal batteries (LMBs) with ultrahigh-nickel (Ni) layered oxide cathodes offer a great opportunity for applications in electrical vehicles. However, ...increasing Ni content inherently arouses a tradeoff between specific capacity and electrochemical cyclability due to the aggressive side reactions with electrolyte contributed by the highly reactive Ni species. Here, a protective and stable cathode/electrolyte interphase featuring enriched and evenly-distributed LiF is in situ formed on ultrahigh-Ni cathode LiNi0.94Co0.06O2 (NC) with an advanced ether-based localized high-concentration electrolyte (LHCE), which concurrently shows good compatibility with Li metal anode. Subsequently, the NC cathode can deliver high capacity retentions of 81.4% after 500 cycles at 25 °C and 91.6% after 100 cycles at 60 °C in the voltage range of 2.8–4.4 V in Li||NC cells at 1C cycling rate (1.5 mA cm−2). Meanwhile, the conductive electrode/electrolyte interphases formed in LHCE enable a high reversible capacity of about 209 mAh g−1 at 3C charging rate. This work provides an effective approach and important insight from the perspective of in situ ultrahigh-Ni cathode/electrolyte interphase protection for high energy–density, long-lasting LMBs.
Abstract
Automatic segmentation of key microstructural features in atomic-scale electron microscope images is critical to improved understanding of structure–property relationships in many important ...materials and chemical systems. However, the present paradigm involves time-intensive manual analysis that is inherently biased, error-prone, and unable to accommodate the large volumes of data produced by modern instrumentation. While more automated approaches have been proposed, many are not robust to a high variety of data, and do not generalize well to diverse microstructural features and material systems. Here, we present a flexible, semi-supervised few-shot machine learning approach for segmentation of scanning transmission electron microscopy images of three oxide material systems: (1) epitaxial heterostructures of SrTiO
3
/Ge, (2) La
0.8
Sr
0.2
FeO
3
thin films, and (3) MoO
3
nanoparticles. We demonstrate that the few-shot learning method is more robust against noise, more reconfigurable, and requires less data than conventional image analysis methods. This approach can enable rapid image classification and microstructural feature mapping needed for emerging high-throughput characterization and autonomous microscope platforms.
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