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XPS depth profile analysis of a Li electrode after the 50th cycle at 0.5 mA/cm 2 current density in carbonate (D/E-0) and mixed carbonate−ether (D/E-30) electrolytes. Surface element contents of Li electrodes cycled in (a) D/E-0 and (b) D/E-30 electrolytes. (c) Fitted C 1s and O 1s XPS spectra of Li electrodes cycled in D/E-0 and D/E-30 electrolytes. 

XPS depth profile analysis of a Li electrode after the 50th cycle at 0.5 mA/cm 2 current density in carbonate (D/E-0) and mixed carbonate−ether (D/E-30) electrolytes. Surface element contents of Li electrodes cycled in (a) D/E-0 and (b) D/E-30 electrolytes. (c) Fitted C 1s and O 1s XPS spectra of Li electrodes cycled in D/E-0 and D/E-30 electrolytes. 

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Article
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Batteries with lithium (Li) metal anodes are promising because of lithium’s high energy density. However, the growth of Li dendrites on the surface of the Li electrode in a liquid electrolyte during cycling reduces the safety and cycle performance of batteries, hindering their commercial application. In this work, we observe for the first time a sm...

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... the case of the DME-30 electrolyte, the Li deposits exhibit a flat outer surface and an average diameter of ∼10 μm (Figure 1d 1−3 ). In addition, the cross-sectional SEM image ( Figure S3) shows that the deposited Li exhibits a columnlike structure. Note that the Li electrode cycled in D/E-30 shows Li deposits that are even denser than those of the electrode cycled in the electrolyte with 100% DME ( Figure S4). ...
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... electrodes after the 50th cycle in D/E-0 and D/E-30 were investigated by XPS depth profile analysis. The results of the elemental analysis and the fitted C and O spectra are shown in Figure 3. Compared to the D/E-0 electrolyte, for each etch time period, the F content substantially increased; by contrast, the O content substantially decreased for D/E-30 (Figure 3a,b). ...
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... electrodes after the 50th cycle in D/E-0 and D/E-30 were investigated by XPS depth profile analysis. The results of the elemental analysis and the fitted C and O spectra are shown in Figure 3. Compared to the D/E-0 electrolyte, for each etch time period, the F content substantially increased; by contrast, the O content substantially decreased for D/E-30 (Figure 3a,b). The fitted XPS spectra of elemental F, as shown in Figure S8, show that the majority of elemental F is associated with LiF in both electrodes. ...
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... fitted C XPS spectrum for D/E-0 ( Figure 3c (Figure 3c) shows peaks related to Li 2 O (528.4 eV), LiOH (531.2 eV), Li 2 CO 3 (531.8 eV), ROCO 2 Li (532 eV), and −(CH 2 CH 2 O) n − (533.4 eV). ...
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... fitted C XPS spectrum for D/E-0 ( Figure 3c (Figure 3c) shows peaks related to Li 2 O (528.4 eV), LiOH (531.2 eV), Li 2 CO 3 (531.8 eV), ROCO 2 Li (532 eV), and −(CH 2 CH 2 O) n − (533.4 eV). ...

Citations

... [5][6][7][8][9][10][11][12] Different strategies have been applied to ameliorate the above-mentioned issues, such as doping and coating of electrode materials, modification of separators, optimization of binders, and electrolyte engineering. [13][14][15][16][17] Compared with other measures, electrolyte engineering has attracted increasing interest from academia and industry due to the unchanged procedure of battery fabrication. Ideal electrolytes should have higher safety, lower cost, wider working temperature range, and stronger anti-oxidative stability. ...
Article
Full-text available
The performance of Li batteries is influenced by the Li+ solvation structure, which can be precisely adjusted by the components of the electrolytes. In this review, we overview the strategies for optimizing electrolyte solvation structures from three different perspectives, including anion regulation, binding energy regulation, and additive regulation. These strategies can optimize the composition of the electrode‐electrolyte interface, enhance the anti‐oxidative stability of electrolytes as well as regulate the behaviors of anions, solvents, and Li+ during the cycling process. Moreover, we also provide our insights into these aspects as well as present perspectives on high‐performance Li batteries. In this review, we discuss about the structural regulation chemistry of lithium ion solvation for lithium batteries, from the strategies for optimizing electrolyte solvation structures to perspectives on high‐performance Li batteries.
... The fitted detailed C and F XPS spectra of the cycled Li metal were consistent with the results of those contacting the pure and composite electrolytes. As demonstrated in Fig. 5c, the intensity of the -CF 3 in LiTFSI and PEO peaks significantly decreased, which was consistent with the results for Li 1s [49]. In contrast, the signals of C 1s in Li metal contacting the PEO/ LiTFSI electrolyte without AlF 3 exhibited a sharp decline, which was consistent with the surface of the PEO/LiTFSI electrolyte. ...
Article
The development of high-performance solid polymer electrolytes is crucial for producing all-solid-state lithium metal batteries with high safety and high energy density. However, the low ionic conductivity of solid polymer electrolytes and their unstable electrolyte/electrode interfaces have hindered their widespread utilization. To address these critical challenges, a strong Lewis acid (aluminum fluoride (AlF3)) with dual functionality is introduced into polyethylene oxide) (PEO)-based polymer electrolyte. The AlF3 facilitates the dissociation of lithium salt, increasing the iontransfer efficiency due to the Lewis acid-base interaction; further the in-situ formation of lithium fluoride-rich interfacial layer is promoted, which suppresses the uneven lithium deposition and continuous undesired reactions between the Li metal and PEO matrix. Benefiting from our rational design, the symmetric Li/Li battery with the modified electrolyte exhibits much longer cycling stability (over 3600 h) than that of the pure PEO/lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) electrolyte (550 h). Furthermore, the all-solid-state LiFePO4 full cell with the composite electrolyte displays a much higher Coulombic efficiency (98.4% after 150 cycles) than that of the electrolyte without the AlF3 additive (63.3% after 150 cycles) at a large voltage window of 2.4–4.2 V, demonstrating the improved interface and cycling stability of solid polymer lithium metal batteries.
... Furthermore, using the mixture of ester and ether solvents also can suppress dendritic formation and improve the CE of Li metal anode. Huang et al. reported an interesting phenomenon that Li dendrites can be self-inhibited in esterether mixed electrolyte [108]. As shown in Fig. 4c, when adding different concentrations 1,2-Dimethoxyethane (DME) into ester-based electrolyte, the surface morphology of Li electrode after 50 cycles changed drastically. ...
Article
Li metal anode is among the most promising anode materials for next generation of lithium batteries (Li–O2, Li–S batteries). However, the commercial applications of Li metal batteries have been seriously hindered due to safety and lifetime concerns caused by the formation of Li dendrites. In this review, we focus on the electrolyte designs in handling Li dendritic growth and improving electrochemical performance of Li metal anode, and outline the trend of electrolyte designs from traditional composition adjustment of the liquid electrolyte to molecular design of the solid polymer electrolyte. We aim to provide strategic guidance for the rational design and fabrication of safety electrolytes, and to explore the possibility of these designs in practical application. We critically evaluate the existing challenges and future opportunities associated with this burgeoning field.
... Therefore, mixing carbonate solvents with ether solvents is able to effectively optimize the organic composition of SEI film. With a certain amount of DME adding into EC solvents, flexible Li organic species (− (CH 2 CH 2 O)n− ) could be generated to protect the metallic Li from continuous reactions with the electrolyte, leading to better stability of the Li electrode and inhibiting the growth of Li dendrites [92]. However, current ether solvents possess a low oxidative stability (<4 V), which cannot support cells with high-voltage cathode. ...
Article
Rechargeable Li metal batteries once had a glory moment in 1980s, but its development was sooner suspended for safety concerns from dendrite formation. After falling into oblivion for several decades, Li metal anode is reviving in recent years with the ever-growing demands for high energy devices. Despite great progresses have been achieved, current Li metal anode still lacks of efficiency and safety. Essentially, Li deposition is a process involving the transport and reduction of Li ions on different interfaces. Therefore, deeply understanding the interfacial chemistry and kinetics of metallic Li is of vital significance towards practical Li metal anodes. In this review, key interfacial challenges faced in Li metal anode and their initiation mechanisms are comprehensively summarized. Furthermore, the prospective developments and alternative approaches towards these challenges are presented to better regulate the interfaces and improve the performance of Li metal anode.
... With regards to the electrolyte, increasing the concentrations of lithium salts and adding inorganic or organic additives into the electrolyte not only helps to stabilize the spontaneous solid electrolyte interphase (SEI) films, which reduce side reactions, but could also control the nucleation and growth of metallic lithium thus enhancing the stability of lithium anodes during the stripping and plating processes. 15,[18][19][20][21] Recently, our group employed octaphenyl polyoxyethylene as an electrolyte additive to enable a stable complex layer on the surface of the lithium anode. This surface layer not only promoted uniform lithium deposition, but also facilitated the formation of a robust SEI film. ...
Article
Full-text available
Due to the soaring growth of electric vehicles and grid‐scale energy storage, high‐safety and high‐energy density battery storage systems are urgently needed. Lithium metal anodes, which possess the highest theoretical specific capacity (3860 mA h g⁻¹) and the lowest electrochemical potential (−3.04 V vs standard hydrogen electrode) among anode materials, are regarded as the ultimate choice for high‐energy density batteries. However, its safety problems as well as the low Coulombic efficiency during the Li plating and stripping process significantly limit the commercialization of lithium metal batteries. Recently, Li‐containing alloys have demonstrated vital roles in inhibiting lithium dendrite growth, controlling interfacial reactions and enhancing the Coulombic efficiency (CE) as well as cycle life. Accordingly, in this perspective, the progresses of lithium alloys for robust, stable, and dendrite free anodes for rechargeable lithium metal batteries are summarized. The challenges and future research focus of lithium‐containing alloys in lithium metal batteries are also discussed.
... 6−8 However, the notorious soluble polysulfide ion (PS) shuttle effect, subsequent lithium dendrite formation, lower Coulombic efficiency, and severe safety hazards are still the most critical challenges in the widespread application and practical implementations of Li−S batteries. 9−11 Aiming to target these issues, tremendous efforts have been devoted to developing novel sulfur-host electrodes, 12,13 electrolyte modification, 14,15 structural confinement design interlayer configurations, 16,17 and stabilizing Li metal anodes. 18,19 The majority of current investigations is just for either the cathode or anode, which can suppress both dendrite growth and polysulfide shuttling to a certain extent. ...
Article
Lithium-sulfur (Li-S) batteries are considered as one of the most prospective candidates for electric vehicles, due to their superior theoretical energy density and low cost. However, the issues of polysulfide ion (PS) shuttling and uncontrollable Li dendrite growth hindered their further application. Herein, a multifunctional nanoporous polybenzimidazole (PBI) membrane with well-controllable morphology was successfully designed and fabricated to address the aforementioned obstacles. In this design, the PBI membrane could offer strong chemical binding interaction with PS, thus applying dynamic adsorption toward PS as well as stable sulfur electrochemistry, which is further verified by experiments and density functional theory (DFT) simulation. Moreover, PBI membranes with high porosity and high electrolyte uptake capability can provide ample lithium storage space and abundant Li+ supplements to facilitate Li deposition and improve Li metal batteries' cyclic stability. Besides that, the PBI membrane has excellent mechanical and thermal stability and exclusive flame resistance, which guarantees the safety of the Li-S battery as well. As a result, Li-S batteries assembled with an as-developed PBI membrane demonstrated a remarkable rate capability of 780 mAh g-1 at 2C and an impressive reversible capacity of 523 mAh g-1 at 0.5C after 400 cycles, which is much higher than the commercial separators. More importantly, even with a lofty sulfur loading of 3 mg cm-2, a high discharge capacity of 744 mAh g-1 (capacity retention 93.96%, at 0.1C after 100 cycles) can also be achieved. Overall, the current study highlighted a robust material platform for stable, safe, and efficient multifunctional separators for high-performance Li-S batteries.
... In the literature, multiple reports have demonstrated that a stable SEI layer can suppress dendrite formation and promote stable cycling. 45 Therefore, it is expected that the dendrite-free Li morphology observed at 20 mA cm −2 is also due to the formation of a more stable SEI layer, compared to that formed at 1 mA cm −2 , and these samples were subjected to further surface analysis by EIS, XPS, and ToF-SIMS. ...
Article
High-energy-density systems with fast charging rates and suppressed dendrite growth are critical for the implementation of efficient and safe next-generation advanced battery technologies such as those based on Li metal. However, there are few studies that investigate reliable cycling of Li metal electrodes under highrate conditions. Here, by employing a superconcentrated ionic liquid (IL) electrolyte, we highlight the effect of Li salt concentration and applied current density on the resulting Li deposit morphology and solid electrolyte interphase (SEI) characteristics, demonstrating exceptional deposition/dissolution rates and efficiency in these systems. Operation at higher current densities enhanced the cycling efficiency, e.g., from 64 ± 3% at 1 mA cm−2 up to 96 ± 1% at 20 mA cm−2 (overpotential <±0.2 V), while resulting in lower electrode resistance and dendrite-free Li morphology. A maximum current density of 50 mA cm−2 resulted in 88 ± 3% cycling efficiency, displaying tolerance for high overpotentials at the Ni working electrode (0.5 V). X-ray photoelectron microscopy (XPS), time-of-flight secondary-ion mass spectroscopy (ToF-SIMS), and scanning electron microscopy (SEM) surface measurements revealed that the formation of a stable SEI, rich in LiF and deficient in organic carbon species, coupled with nondendritic and compact Li morphologies enabled enhanced cycling efficiency at higher currents. Reduced dendrite formation at high current is further highlighted by the use of a highly porous separator in coin cell cycling (1 mAh cm−2 at 50 °C), sustaining 500 cycles at 10 mA cm−2 .
... Tremendous efforts have been devoted to solving the notorious lithium dendrite problem by employing advanced electrolytes, separators, and novel electrode materials/structures. In the aspect of electrolyte, increasing the concentrations of lithium salts and adding inorganic or organic additives in electrolyte could not only benefit to stabilize the spontaneous solid electrolyte interphase (SEI) films to reduce the side reactions happening, but also control the nucleation and growth of metallic lithium, thus enhancing the stabilities of lithium anodes during the stripping and plating processes [18][19][20][21][22]. Recently, our group employed octaphenyl polyoxyethylene as an electrolyte additive to enable a stable complex layer on the surface of the lithium anode. ...
... Another advantage of the process used for Ce doping is the spontaneous generation of LiF by the in-situ chemical reduction of CeF 3 with Li metal. The protective effects of LiF to improve the SEI and cycling of Li metal are well known [56][57][58][59][60]. Following previous reports, a control sample of LiF-coated Li metal (see details in EXPERI-MENTAL SECTION) was fabricated, which showed improved cycle life compared with bare Li metal (Fig. S3). ...
Article
Lithium (Li) metal is regarded as the holy grail anode material for high-energy-density batteries owing to its ultrahigh theoretical specific capacity. However, its practical application is severely hindered by the high reactivity of metallic Li against the commonly used electrolytes and uncontrolled growth of mossy/dendritic Li. Different from widely-used approaches of optimization of the electrolyte and/ or interfacial engineering, here, we report a strategy of in-situ cerium (Ce) doping of Li metal to promote the preferential plating along the [200] direction and remarkably decreased surface energy of metallic Li. The in-situ Ce-doped Li shows a significantly reduced reactivity towards a standard electrolyte and, uniform and dendrite-free morphology after plating/ stripping, as demonstrated by spectroscopic, morphological and electrochemical characterizations. In symmetric half cells, the in-situ Ce-doped Li shows a low corrosion current density against the electrolyte and drastically improved cycling even at a lean electrolyte condition. Furthermore, we show that the stable Li LiCoO2 full cells with improved coulombic efficiency and cycle life are also achieved using the Ce-doped Li metal anode. This work provides an inspiring approach to bring Li metal towards practical application in high energy-density batteries.
... The native SEI layers are generally an inhomogeneous mixture of inorganic species such as LiF or Li2O, and organic species such as ROLi and ROCO2Li, exhibiting poor uniformity for Li + conduction, Li nucleation and deposition 6 . Interfacial engineering to regulate the SEI layers has been devoted as a main roadmap to stabilize the Li/electrolyte interfaces, including the SEI modification by electrolyte formulations [7][8][9][10][11][12][13] and construction of artificial SEI layers and host structures [14][15][16][17][18][19][20] . In particular, fluorine (F) has recently been revealed as a critical element to affect the interfacial stability of Li metal anodes. ...
Article
In past decades, lithium-ion batteries (LIBs) were the dominant energy storage systems for powering portable electronic devices because of their reliable cyclability. However, further increase in the energy density of LIBs was met by a bottleneck when low-specificcapacity graphite was used at the anode. Li metal has long been regarded as the ideal anode material for building the next high-energy-density batteries due to its ultrahigh capacity of 3860 mAh·g⁻¹, which is ten times higher than that of graphite. However, using Li metal as an anode in rechargeable batteries is challenging due to its high uncontrolled volume expansion and aggressive side reactions with liquid electrolytes. In this study, we demonstrate the effect of a three-dimensional (3D) framework with enriched fluorinated sites for Li metal protection. This framework is obtained via a facile integration of down-sized fluorinated graphite (CFx) particles into Li⁺ conducting channels. Thermogravimetry, energy dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy results show that Li⁺ conducting channels rich in lithium fluoride (LiF) are formed in situ across the embedded CFx particles during the initial lithiation process, leading to fast Li⁺ transfer. Scanning electron microscopy results show that residual CFx particles could act as high-quality nucleation sites for uniform Li deposition inside the framework. These features could not be achieved with a 2D structure consisting of large CFx flakes, due to the limited Li⁺ transfer paths and low utilization ratio of CFx for conversion into LiF-based solid electrolyte interphase (SEI) layers. Consequently, better performance of Li metal anodes in a 3D framework with enriched fluorinated sites is demonstrated. Stable Li plating/stripping over 240 cycles is obtained at a current density of 0.5 mA·cm⁻² for a fixed capacity of 1 mAh·cm⁻² by maintaining a voltage hysteresis below 80 mV. Improved Li-LiFePO4 full cell performance with a practical negative/positive capacity ratio of 3 is also demonstrated. These results show the rational combination of well-developed 3D Li⁺ transfer channels and enriched fluorinated sites as an optimized interfacial design beyond the single use of a 2D fluorinated interface, giving new insight into the protection of Li metal anodes in high-energy-density batteries.