Rational Design Of Electrolytes Research Articles

Manipulating Electrolyte Interface Chemistry Enables High-Performance TiO2 Anode for Sodium-Ion Batteries

Titanium dioxide (TiO2) has emerged as a candidate anode material for sodium-ion batteries (SIBs). However, their applications still face challenges of poor rate performance and low initial coulomb efficiency (ICE), which are induced by the unstable solid-electrolyte interface (SEI) and sluggish Na+ diffusion kinetics in conventional ester-based electrolytes. Herein, inspired by the electrode/electrolyte interfacial chemistry, tetrahydrofuran (THF) is exploited to construct an advanced electrolyte and reveal the relationship between the improved electrochemical performance and the derived SEI film on TiO2 anode. The robust and homogeneously distributed F-rich SEI film formed in THF electrolyte favors fast interfacial charge transfer dynamics and excellent interfacial stability. As a result, the THF electrolyte endows the TiO2 anode with greatly improved ICE (64.5%), exceptional rate capabilities (186 mAh g−1 at 5.0 A g−1), and remarkable cycling stability. This study elucidates the control of interfacial chemistry by rational electrolyte design and offers insights into the development of high-performance and long-lifetime TiO2 anode.

Electrolyte Engineering via Fluorinated Siloxane Solvent for Achieving High-Performance Lithium-Metal Batteries.

Advanced solvent is of important significance to develop an excellent electrolyte that simultaneously maintains a high ionic conductivity, wide electrochemical window, and good compatibility with electrodes for high-performance lithium-metal batteries (LMBs). To realize a stable electrode/electrolyte interface and a uniform lithium (Li) deposition process, an optimal fluorinated siloxane (3,3,3-trifluoropropyltrimethoxysilane, TFTMS) is proposed as a cosolvent with 1,2-dimethoxyethane (DME) and highly antioxidative fluoroethylene carbonate (FEC) to formulate a Li-metal compatibility electrolyte. The TFTMS-based electrolyte presents high oxidization stability, high Li+ conductivity, and high Li+ transfer number, contributing to the accelerated reaction kinetics, homogeneous Li deposition behavior, and stable interfacial chemistry. Therefore, high Li stripping/plating reversibility (∼99%) and stable cycling (1400 h) are achieved in the TFTMS-based electrolyte, giving rise to the excellent electrochemical performance of practical Li-metal full cells. Moreover, an industrial 4 Ah NCM811|Gr pouch cell with the TFTMS-based electrolyte is demonstrated to display similar cycling performance with the commercial carbonate electrolyte in 120 cycles at 1 C. This work offers an approach toward high-performance LMBs through rational electrolyte design with fluorinated siloxane solvent.

High ionic conducting lithium fluoride rich solid electrolyte interphase induced by polysulfide for carbon-based dual ion batteries

Carbon-based dual ion batteries (DIBs) promise a high working voltage, ease of production, low cost and low environmental impact, yet they suffer from poor electrochemical performances ascribed predominantly to electrolyte decomposition, consequently impacting the stability of solid electrolyte interphase (SEI) formation in the negative electrode. Herein, we report a facile pre-formation of lithium fluoride (LiF)-rich SEI derived from lithium polysulfide (LiPS) added lithium bis(trifluoromethane)sulfonimide (LiTFSI)-based electrolyte. A pre-formed lithium sulfide (Li2S) as the inner passivation layer effectively facilitates the growth of LiF on carbon anode, which greatly enhances the ionic conductivity of SEI and prevents the formation of Li dendrites. The designed electrolyte consisting of 3.4 M LiTFSI in the mixture of ethyl methyl carbonate (EMC) and dimethyl carbonate (DMC) (1:1 by vol.) with the addition of 0.1 M LiPS achieves excellent compatibility with activated carbon, delivered an initial specific capacity of 408 mAh g−1 with coulombic efficiency ∼100% at 1 A g−1 over 150 cycles. With an in-depth analysis of compositions and the distribution of decomposition products at the interface, the critical impact of Li2S on SEI formation is revealed. DIB full cells assembled using the carbon anodes with a pre-formed SEI layer delivered an initial discharge capacity of 57.2 mAh g−1 and average voltage of 4.35 V. The above-mentioned findings shed new light on SEI pre-forming technique for high-performance DIB based on the rational design of electrolytes.

Nanotechnologies in ceramic electrochemical cells.

Although they are emerging technologies for achieving high-efficiency and green and eco-friendly energy conversion, ceramic electrochemical cells (CECs), i.e. solid oxide electrolysis cells (SOECs) and fuel cells (SOFCs), are still fundamentally limited by their inferior catalytic activities at low temperature, poor thermo-mechanical stability, high material cost, etc. The materials used in electrolytes and electrodes, which are the most important components in CECs, are highly associated with the cell performances. Therefore, rational design of electrolytes and electrodes with excellent catalytic activities and high stabilities at relatively low cost is a meaningful and valuable approach for the development of CECs. Nanotechnology is a powerful tool for improving the material performances in CECs owing to the favourable effects induced by the nanocrystallization of electrolytes and electrodes. Herein, a relatively comprehensive review on the nanotechnologies implemented in CECs is conducted. The working principles of CECs and the corresponding challenges were first presented, followed by the comprehensive insights into the working mechanisms of nanocrystalline materials in CECs. Then, systematic summarization and analyses of the commonly used nano-engineering strategies in the fabrication of CEC materials, including physical and chemical methods, were provided. In addition, the frontiers in the research of advanced electrolyte and electrode materials were discussed with a special emphasis on the modified electrochemical properties derived from nanotechnologies. Finally, the bottlenecks and the promising breakthroughs in nanotechnologies were highlighted in the direction of providing useful references for rational design of nanomaterials for CECs.

Rational electrolyte design and electrode regulation for boosting high-capacity Zn-iodine fiber-shaped batteries with four-electron redox reactions.

Aqueous Zn ion-based fiber-shaped batteries (AZFBs) with the merits of high flexibility and safety have received much attention for powering wearable electronic devices. However, the relatively low specific capacity provided by cathode materials limits their practical application. Herein, we first propose a simple strategy for fabricating high-capacity Zn-iodine fiber-shaped batteries with a high concentration electrolyte and a reduced graphene oxide fiber (GF) cathode. It was found that oxygen functional groups in the graphene sheet demonstrate strong interaction with polyiodides but hinder electron conductivity; thus, the optimal balance between the specific capacity and coulombic efficiency of the GF electrode can be a function of the surface properties at different hydrothermal temperatures. Besides, the regulated high concentration electrolyte effectively suppresses the diffusion of polyiodides, which is attributed to the constrained freedom of water. More importantly, a four-electron redox mechanism was experimentally revealed through in situ Raman spectra. As a result, this fiber-shaped battery delivers a superior high reversible capacity of 390 mA h cm-3 at 1 A cm-3, an excellent rate performance of 125.7 mA h cm-3 at a high current density of 8 A cm-3 and outstanding cycling life with 82% capacitance retention after 2500 cycles.

Multifunctional Electrolyte Additives for Better Metal Batteries

AbstractThe high energy density of rechargeable metal (Li, Na, and Zn) batteries has garnered a lot of interest. However, the poor cycle stability and low Coulomb efficiency(CE), which are mostly brought on by side reactions and dendrite development on the metal anode, place a cap on commercialization. The rational design of electrolytes via incorporating a small dose of additives is a simple, yet effect strategy to address the above issues. The majority of additives govern uniform metal deposition and significantly improve the cycling performance of metal anodes. However, the battery is a complex system and the electrolyte affects both the anode and cathode. Complex reactions during discharge/charge process put forward higher requirements for the functionality of electrolytes, such as improving the stability of the cathode and flame retardant. Thus, multifunctional additives are necessary and have more advantages in building high‐performance metal batteries. The recent developments in multifunctional additives for stable and dendrite‐free Li/Na/Zn anodes are the major focus of this review. Breakthrough research on multifunctional additives toward the durable cathode and high‐compatible electrolytes is also highlighted. Finally, the critical challenges and new perspectives on the optimization of electrolyte formulation via multifunctional additives are emphasized. This review will provide important insight to develop more effective electrolytes for high‐performance rechargeable metal batteries.

Heterogeneous Nitride Interface Enabled by Stepwise‐Reduction Electrolyte Design for Dense Li Deposition in Carbonate Electrolytes

AbstractStable solid electrolyte interphase (SEI) with high Li+‐ion conductivity is desperately desired for lithium (Li) metal anodes. However, it remains challenging to build a robust SEI rationally for the Li‐metal anodes in carbonate electrolytes. Herein, a heterogeneous nitride‐rich SEI that consists of organic nitrides on the surface and inorganic nitrides inside by stepwise‐reduction electrolyte design is constructed. The heterogeneous structure endows SEI with the capability to capture and distribute Li+ on the surface and facilitate internal Li+ transportation, leading to the redistributed Li+ flux and uniform Li electrodeposition. With the newly‐formulated carbonate electrolyte, Li||Cu cells deliver a high Coulombic efficiency of 98.0% after 300 cycles at 0.5 mA cm‐2 and 0.5 mAh cm‐2. Meanwhile, superb cycling stability is also determined with full Li‐metal cells using LiNi1/3Mn1/3Co1/3O2 and high‐loading LiFePO4 (12.0 mg cm−2) cathodes. This study provides a promising strategy to regulate the SEI components and stabilize the Li anodes by rational electrolyte design.

Designing Anion-Derived Solid Electrolyte Interphase in a Siloxane-Based Electrolyte for Lithium-Metal Batteries.

The rational electrolyte design with weak solvation is regarded as an effective way to regulate the electrolyte/electrode interface (SEI) that profoundly affects the performance of Li-metal batteries. Herein, we propose a newly developed siloxane-based weakly solvating electrolyte (SiBE) with contact ion pairs (CIPs) or aggregates (AGGs) dominating the solution structure, which enables the dendrite-free Li deposition and long cycle stability of Li-metal batteries. By altering the combination of Li salts, the SiBE leads to the formation of an inorganic anion-derived solid electrolyte interphase, which is highly stable and Li+-conductive. Based on SiBE, the Li||LiFePO4 (LFP) full cell can stably cycle for 1000 cycles at a 2C rate with a capacity retention of 76.9%. Even with a limited Li-metal anode, it can maintain a capacity retention of 80% after 110 cycles with a high average Coulombic efficiency of 99.8%. This work reveals that siloxane can be a promising solvent to obtain weakly solvating electrolytes, which opens a new avenue for SEI composition regulation of Li-metal batteries.

Rational Electrolyte Design toward Cyclability Remedy for Room‐Temperature Sodium–Sulfur Batteries

AbstractRechargeable room‐temperature sodium–sulfur (RT Na–S) batteries are a promising energy storage technology, owing to the merits of high energy density and low cost. However, their electrochemical performance has been severely hindered by the poor compatibility between the existing electrolytes and the electrodes. Here, we demonstrate that an all‐fluorinated electrolyte, containing 2,2,2‐trifluoro‐N,N‐dimethylacetamide (FDMA) solvent, 1,1,2,2‐tetrafluoroethyl methyl ether (MTFE) anti‐solvent and fluoroethylene carbonate (FEC) additive, can greatly enhance the reversibility and cyclability of RT Na–S batteries. A NaF‐ and Na3N‐rich cathode electrolyte interphase derived from FDMA and FEC enables a “quasi‐solid‐phase” Na–S conversion, eliminating the shuttle of polysulfides. The MTFE not only reduces polysulfide dissolution, but also further stabilizes the Na anode via a tailored solvation structure. The as‐developed RT Na–S batteries deliver a high capacity, long lifespan, and enhanced safety.

Rational Electrolyte Design toward Cyclability Remedy for Room-Temperature Sodium-Sulfur Batteries.

Rechargeable room-temperature sodium-sulfur (RT Na-S) batteries are a promising energy storage technology, owing to the merits of high energy density and low cost. However, their electrochemical performance has been severely hindered by the poor compatibility between the existing electrolytes and the electrodes. Here, we demonstrate that an all-fluorinated electrolyte, containing 2,2,2-trifluoro-N,N-dimethylacetamide (FDMA) solvent, 1,1,2,2-tetrafluoroethyl methyl ether (MTFE) anti-solvent and fluoroethylene carbonate (FEC) additive, can greatly enhance the reversibility and cyclability of RT Na-S batteries. A NaF- and Na3 N-rich cathode electrolyte interphase derived from FDMA and FEC enables a "quasi-solid-phase" Na-S conversion, eliminating the shuttle of polysulfides. The MTFE not only reduces polysulfide dissolution, but also further stabilizes the Na anode via a tailored solvation structure. The as-developed RT Na-S batteries deliver a high capacity, long lifespan, and enhanced safety.

Modification of Nitrate Ion Enables Stable Solid Electrolyte Interphase in Lithium Metal Batteries.

The lifespan of high-energy-density lithium metal batteries (LMBs) is hindered by heterogeneous solid electrolyte interphase (SEI). The rational design of electrolytes is strongly considered to obtain uniform SEI in working batteries. Herein, a modification of nitrate ion (NO3 - ) is proposed and validated to improve the homogeneity of the SEI in practical LMBs. NO3 - is connected to an ether-based moiety to form isosorbide dinitrate (ISDN) to break the resonance structure of NO3 - and improve the reducibility. The decomposition of non-resonant -NO3 in ISDN enriches SEI with abundant LiNx Oy and induces uniform lithium deposition. Lithium-sulfur batteries with ISDN additives deliver a capacity retention of 83.7 % for 100 cycles compared with rapid decay with LiNO3 after 55 cycles. Moreover, lithium-sulfur pouch cells with ISDN additives provide a specific energy of 319 Wh kg-1 and undergo 20 cycles. This work provides a realistic reference in designing additives to modify the SEI for stabilizing LMBs.

Modification of Nitrate Ion Enables Stable Solid Electrolyte Interphase in Lithium Metal Batteries

AbstractThe lifespan of high‐energy‐density lithium metal batteries (LMBs) is hindered by heterogeneous solid electrolyte interphase (SEI). The rational design of electrolytes is strongly considered to obtain uniform SEI in working batteries. Herein, a modification of nitrate ion (NO3−) is proposed and validated to improve the homogeneity of the SEI in practical LMBs. NO3−is connected to an ether‐based moiety to form isosorbide dinitrate (ISDN) to break the resonance structure of NO3−and improve the reducibility. The decomposition of non‐resonant −NO3in ISDN enriches SEI with abundant LiNxOyand induces uniform lithium deposition. Lithium–sulfur batteries with ISDN additives deliver a capacity retention of 83.7 % for 100 cycles compared with rapid decay with LiNO3after 55 cycles. Moreover, lithium–sulfur pouch cells with ISDN additives provide a specific energy of 319 Wh kg−1and undergo 20 cycles. This work provides a realistic reference in designing additives to modify the SEI for stabilizing LMBs.

Conversion-type fluoride cathodes: Current state of the art

Conversion-type transition metal fluoride cathodes offer a 200%–300% higher theoretical energy density limit than state-of-the-art intercalation cathodes. Recent publications have reshaped our understanding of the reaction mechanism in these materials. Herein, we review recent reports highlighting how active material dissolution, particle fusing, electrolyte consumption, and the resultant capacity fade can be mitigated by rational electrolyte design. Recent work has established the possibility of high discharge rate in transition metal fluorides at significant active material mass fraction; we examine the relationship between rate capability and active material fraction. Tuning transition metal fluoride chemistry via cation and anion substitution has demonstrated the potential to improve its electrochemical properties. A brief technoeconomic analysis is presented to highlight the practical advantages of different transition metal chemistries.

Electrolyte Structure of Lithium Polysulfides with Anti-Reductive Solvent Shells for Practical Lithium-Sulfur Batteries.

The lithium-sulfur (Li-S) battery is regarded as a promising secondary battery. However, constant parasitic reactions between the Li anode and soluble polysulfide (PS) intermediates significantly deteriorate the working Li anode. The rational design to inhibit the parasitic reactions is plagued by the inability to understand and regulate the electrolyte structure of PSs. Herein, the electrolyte structure of PSs with anti-reductive solvent shells was unveiled by molecular dynamics simulations and nuclear magnetic resonance. The reduction resistance of the solvent shell is proven to be a key reason for the decreased reactivity of PSs towards Li. With isopropyl ether (DIPE) as a cosolvent, DIPE molecules tend to distribute in the outer solvent shell due to poor solvating power. Furthermore, DIPE is more stable than conventional ether solvents against Li metal. The reactivity of PSs is suppressed by encapsulating PSs into anti-reductive solvent shells. Consequently, the cycling performance of working Li-S batteries was significantly improved and a pouch cell of 300 Wh kg-1 was demonstrated. The fundamental understanding in this work provides an unprecedented ground to understand the electrolyte structure of PSs and the rational electrolyte design in Li-S batteries.

Electrolyte Structure of Lithium Polysulfides with Anti‐Reductive Solvent Shells for Practical Lithium–Sulfur Batteries

AbstractThe lithium–sulfur (Li–S) battery is regarded as a promising secondary battery. However, constant parasitic reactions between the Li anode and soluble polysulfide (PS) intermediates significantly deteriorate the working Li anode. The rational design to inhibit the parasitic reactions is plagued by the inability to understand and regulate the electrolyte structure of PSs. Herein, the electrolyte structure of PSs with anti‐reductive solvent shells was unveiled by molecular dynamics simulations and nuclear magnetic resonance. The reduction resistance of the solvent shell is proven to be a key reason for the decreased reactivity of PSs towards Li. With isopropyl ether (DIPE) as a cosolvent, DIPE molecules tend to distribute in the outer solvent shell due to poor solvating power. Furthermore, DIPE is more stable than conventional ether solvents against Li metal. The reactivity of PSs is suppressed by encapsulating PSs into anti‐reductive solvent shells. Consequently, the cycling performance of working Li–S batteries was significantly improved and a pouch cell of 300 Wh kg−1 was demonstrated. The fundamental understanding in this work provides an unprecedented ground to understand the electrolyte structure of PSs and the rational electrolyte design in Li–S batteries.

Effects of High and Low Salt Concentrations in Electrolytes at Lithium-Metal Anode Surfaces Using DFT-ReaxFF Hybrid Molecular Dynamics Method.

Due to creating a passivated solid electrolyte interphase (SEI), high concentration (HC) electrolytes demonstrate peculiar physicochemical properties and outstanding electrochemical performance. However, the structures of such SEI remains far from clear. In this work, a hybrid ab initio and reactive molecular dynamics (HAIR) scheme is employed to investigate the concentration effect of SEI formation by simulating the reductive degradation reactions of lithium bis(fluorosulfonyl)imide (LiFSI) in 1,3 dioxalane (DOL) electrolytes at concentrations of 1 M, 4 M, and 10 M. The efficient HAIR scheme allows the simulations to reach 1 ns to predict electrolytes' deep products at different concentrations. The simulation findings show that the most critical distinction between HC and its low concentration (LC) analogue is that anion decomposition in HC is much more incomplete when only S-F breaking is observed. These insights are important for the future development of advanced electrolytes by rational design of electrolytes.

Crucial Challenges and Recent Optimization Progress of Metal–Sulfur Battery Electrolytes

By virtue of environmental friendliness, low cost, and the high theoretical capacity of sulfur (1675 mAh/g), metal–sulfur batteries (MSBs), as promising next-generation rechargeable cells, have attracted ever-increasing attention from both academic and industrial fields. Despite good progress, however, thus far MSBs have been rarely able to bring their energy storage performance up to the needed levels of reliability due to challenging issues such as the shuttle effect of polysulfides, low utilization efficiency of the S, inferior cycling performance, and safety hazards. To tackle this, the rational optimization of the electrolyte, which tremendously affects the cycling stability, rate capability, lifespan, and safety of the investigated batteries, is considered to be one of the crucial directions to improve the performance of MSBs. Herein we outline the challenges and recent optimization progress on electrolytes in MSBs with Li, Na, Mg, Ca, K, and Al as metal anodes. The topics regarding the fundamentals of electrolyte optimization strategies and the possible solution to further performance improvement are highlighted. Finally, a perspective on further electrolyte development is presented. This discussion aims at gaining good insight into the rational design of electrolytes so as to boost the commercial process of MSB development.

Modification and regulation of electrode/electrolyte interface for high specific energy and long life lithium ion batteries

<p indent="0mm">In recent years, with the rapid developments of high-technology industries such as information technology and electric vehicles, there are urgent need to develop new generations of lithium-ion batteries with higher energy density, longer cycle life and improved safety. In addition to the development of high specific energy cathode and high specific capacity anode materials, regulating the stability of the electrode/electrolyte interface is critical to achieve and balance various performances of the batteries and finally realize their commercial application widely. However, the traditional carbonate electrolytes not only suffer from severe oxidation decomposition when the charging voltage is higher than 4.3 V (vs. Li/Li⁺), but also show poor compatibility with high-capacity silicon or silicon-carbon (Si-C) composite anodes and lithium metal anodes. Moreover, the traditional carbonate electrolytes are flammable, which is still a big safety concern to address for lithium ion battery. Therefore, rational design of electrolytes that match the high voltage cathode, high specific capacity Si-C abode or lithium metal anode, and has better safety property and especially under harsh conditions, has become a decisive factor for the rapid developments of high specific energy lithium-ion batteries. The present work reviews different kinds of liquid electrolytes with functional additives and utilization of solid state electrolytes which are explored by our group in the past 15 years. The design strategies and systematic investigations of the electrolytes recipes include: (1) Developing anti-oxidation solvent systems, for example, applications of new high-voltage nitriles or fluorinated solvents for high-voltage cathodes, such as suberonitrile (SUN), fluoroethylene carbonate (FEC) and ethyl-(2,2,2-trifluoroethyl) carbonate (ETFEC); (2) exploiting some novel multifunctional solvents or additives which contain flame retardant groups or can be used as film-forming agents for high-voltage cathodes. For example, some P-containing compounds such as <italic>N</italic>,<italic>N</italic>-diallyl-diethoxy phosphoramide (DADEPA), phenoxy cyclophosphazene (PFPN), and ionic liquid such as N-methyl-N-butylpyrrolidinium bis(trifluoromethylsulfonyl)imide (Py14TFSI), etc. In addition, we have also investigated a series of solid electrolytes such as Garnet-type electrolytes, gel polymer or composite polymer electrolyte with inorganic additives, which could greatly reduce the safety risk of batteries. These works include measurements of the activation energy and ion transport mechanism of oxide solid electrolyte with solid NMR techniques, interface modification of sulfide-type solid state battery with ionic liquids, and interface passivation mechanism of PEO-based polymer electrolyte, etc. Finally, some discussions and future perspectives in developing high-voltage and highly-safe liquid electrolyte and flexible solid-state electrolytes for all solid state batteries are presented. Although the commonly used high-voltage electrolytes are mainly composed of lithium salts, anti-oxidation solvents and functional additives such as nitriles, sulfones, fluoro-ethers or fluoro-carbonates, However, the acting mechanisms of those high-voltage electrolytes, especially solvents, salts and additives, are still not clear, especially the composition, structure and evolution of the electrochemical interfaces are lack of quantitative understanding. Therefore, combining theoretical calculation and advanced in-/ex-situ interface characterization techniques, fully understanding the working mechanism of the additives in high-voltage systems and the effective components of interface film, and designing novel functional electrolyte additives are crucial for the development of a new generation of high-specific energy lithium batteries. In addition, applications of flame-retardant solvents or additives to develop flame-retardant liquid-type electrolytes and developing new solid state electrolytes are both important strategies to reduce the potential safety hazards of lithium ion batteries. The future research should focus on how to improve the compatibility between flame-retardant solvents/additives and the cathode/anode interfaces in liquid electrolytes, minimize the negative impact on battery performance (cycle performance, rate performance, etc.), enhance the ionic conductivity and mechanical flexibilities of the solid electrolytes, optimize the electrolyte phase structure/mechanical properties, and regulate the stability of interfaces to ensure the long-term cycling stability of lithium metal anodes and metal oxide cathodes.

Non-concentrated aqueous electrolytes with organic solvent additives for stable zinc batteries.

Rechargeable aqueous zinc batteries (RAZBs) are promising for large-scale energy storage because of their superiority in addressing cost and safety concerns. However, their practical realization is hampered by issues including dendrite growth, poor reversibility and low coulombic efficiency (CE) of Zn anodes due to parasitic reactions. Here, we report a non-concentrated aqueous electrolyte composed of 2 m zinc trifluoromethanesulfonate (Zn(OTf)2) and the organic dimethyl carbonate (DMC) additive to stabilize the Zn electrochemistry. Unlike the case in conventional aqueous electrolytes featuring typical Zn[H2O]62+ solvation, a solvation sheath of Zn2+ with the co-participation of the DMC solvent and OTf− anion is found in the formulated H2O + DMC electrolyte, which contributes to the formation of a robust ZnF2 and ZnCO3-rich interphase on Zn. The resultant Zn anode exhibits a high average CE of Zn plating/stripping (99.8% at an areal capacity of 2.5 mA h cm−2) and dendrite-free cycling over 1000 cycles. Furthermore, the H2O + DMC electrolytes sustain stable operation of RAZBs pairing Zn anodes with diverse cathode materials such as vanadium pentoxide, manganese dioxide, and zinc hexacyanoferrate. Rational electrolyte design with organic solvent additives would promote building better aqueous batteries.

Moderate-Concentration Fluorinated Electrolyte for High-Energy-Density Si//LiNi0.8Co0.1Mn0.1O2 Batteries

Highly concentrated electrolytes, although promising, are of high cost and show high viscosity and unsatisfactory wettability toward electrodes and separators, making them unfavorable for practical applications. A more rational electrolyte design is thus needed. Here, we investigate moderately concentrated electrolytes and find that the lithium bis(fluorosulfonyl)imide (LiFSI) concentration effects on the capacity, rate capability, and cycling stability of Si anodes in an ethylene carbonate (EC)/diethyl carbonate (DEC) mixed electrolyte are opposite to those in a fluoroethylene carbonate (FEC) electrolyte. The reasons for these results are systematically examined using Raman spectroscopy, transmission electron microscopy, electrochemical impedance spectroscopy, and the galvanostatic intermittent titration technique. A detailed X-ray photoelectron spectroscopy analysis is performed to study the solid electrolyte interphase chemistry. Al corrosion that occurs with the EC/DEC-based electrolyte can be effectively suppressed with the FEC-based electrolyte if an adequate LiFSI concentration is used. In the proposed 2 mLiFSI/FEC electrolyte, the Si anode has reversible capacities of 2630 and 855 mA h g–¹ at 0.2 and 5 A g–¹, respectively, and ∼75% capacity retention after 200 cycles (remarkably higher than that obtained with the EC/DEC-based electrolyte). This electrolyte also shows great compatibility with the high-energy-density LiNi₀.₈Co₀.₁Mn₀.₁O₂ (NMC-811) cathode, allowing a stable charge–discharge of a Si//NMC-811 full cell.