Electrolytes For Lithium Metal Batteries Research Articles

Pseudo-concentrated electrolytes for lithium metal batteries

Lithium metal batteries suffer from short lifespans and low Coulombic efficiency (CE) due to the high reactivity of Li and the poor stability of the solid electrolyte interphase (SEI). Herein, we propose the concept of a pseudo-concentrated electrolyte (PCE) induced by an electron-deficient additive (4-pyridylboronic acid; 4-PBA) to form a robust, LiF-rich SEI, thus addressing the above issues. Molecular dynamics simulations confirm that 4-PBA can increase the coordination number of PF6- anions in the Li+ solvation sheath to achieve pseudo-concentrated LiPF6 in the electrolyte. Moreover, the 4-PBA can scavenge harmful PF5 decomposed from LiPF6 to stabilize the LiF-rich SEI. The resulting robust LiF-rich SEI promotes Li growth along the SEI/Li interface and represses the growth of Li dendrites. Thus, excellent performance is achieved, with a high CE of 97.1% for a Li||Cu cell at 1.0 ​mA ​cm−2, and over 950 cycles at 0.5 ​mA ​cm−2 for Li||Li symmetric cells with 1.0 ​wt% 4-PBA electrolyte. Meanwhile, the resulting stable boron-containing cathode electrolyte interphase enables Li||LiNi0·6Co0·2Mn0·2O2 (NCM622) cells to achieve excellent stability, with a capacity retention of 86.9% after 200 cycles.

Dual In Situ Polymerization Strategy Endowing Rapid Ion Transfer Capability of Polymer Electrolyte toward Ni‐Rich‐Based Lithium Metal Batteries

Poly(vinylidenefluoride-co-hexafluoropropylene) (PVDF-HFP) is one of the most promising candidate electrolyte matrices for high energy batteries. However, the spherical skeleton structure obtained through the conventional method fails to build continuous Li ion transmission channels due to the slow volatilization of high boiling solvent, leading to inferior cycling performance, especially in a Ni-rich system. Herein, a novel strategy is presented to enrich the Li ion transfer paths and improve the Li ion migration kinetics. The tactic is to prepare cross-linked segments through the PVDF-HFP matrix by adopting free radical polymerization and Li salt induced ring-opening polymerization. Most significantly, the visualization of the structure of as-prepared electrolyte is innovatively realized with the combination of polarization microscopy, transmission electron microscopy, scanning electron microscope-energy dispersive spectroscopy, PVDF-HFP, and cross-linked network form interconnected microstructures. Therefore, poly(glycidyl methacrylate and acrylonitrile)@poly(vinylidene fluoride-hexafluoropropylene) electrolyte presents a high ionic conductivity (1.04mScm-1 at 30°C) and a stable voltage profile for a Li/Li cell after 1200h. After assembly with a LiNi0.8 Co0.15 Al0.05 O2 cathode, a high discharge specific capacity of 190.3mAhg-1 is delivered, and the capacity retention reaches 88.2% after 100 cycles. This work provides a promising method for designing high-performance polymer electrolytes for lithium metal batteries.

In-situ construction of dual lithium-ion migration channels in polymer electrolytes for lithium metal batteries

Solid polymer electrolytes (SPEs) are expected to play an important role in high-energy lithium metal batteries (LMBs). Unfortunately, SPEs suffer from inadequate room-temperature ionic conductivity and sluggish interfacial charge transport, which severely limit their widespread applications in LMBs. Herein, we in-situ construct dual lithium-ion migration channels based SPEs by combining ring-opening polymerization of 1,3-dioxolane and solid-state organic ionic plastic crystals. “Coordination-dissociation” with the oxygen atoms in polymer chain segments and fast ion migration inside the organic ionic plastic crystal are two migration modes formed in-situ to synergistically enhance the ionic conductivity and interfacial charge transfer of SPEs. As a result, the in-situ formed poly(1,3-dioxolane)-based solid electrolytes (PDEs) not only afford an integrated battery structure with stabilized electrodes/electrolyte interface but also achieve outstanding oxidation stability, uniform lithium deposition (greater than1200 h under 0.5 mAh cm−2 in symmetric Li cells). Based on PDEs, the Li-LiFePO4 batteries demonstrate excellent cycle stability (almost no capacity decay after 500 cycles under 2C at 25 °C) and a wide operating temperature (-15 ∼ 45 °C). Also, applications of PDEs in Li-LiNi0.6Mn0.2Co0.2O2 batteries further demonstrate the compatibility of PDE with high voltage battery systems. Our study provides a facile and practical approach for creating solid electrolytes that meet both the ionic conductivity and interfacial charge transport requirements for practical solid-state batteries.

Protection of Cobalt-Free LiNiO2 from Degradation with Localized Saturated Electrolytes in Lithium-Metal Batteries

Protection of Cobalt-Free LiNiO₂ from Degradation with Localized Saturated Electrolytes in Lithium-Metal Batteries

Interface science in polymer‐based composite solid electrolytes in lithium metal batteries

AbstractSolid‐state lithium metal batteries (SSLMBs) have attracted considerable attention as one of the most promising energy storage systems owing to their high safety and energy density. Solid electrolytes, particularly polymer‐based composite solid electrolytes (CSEs), are considered promising electrolyte candidates for SSLMBs. However, their wide application is inhibited by various electrochemical issues, such as low ionic conductivity, the growth of lithium dendrites, and poor cycling stability, which are related to interface issues within SSLMBs. In this review, the parameters related to various interfaces in the CSE of SSLMBs, including the interfaces between the polymer matrix and inorganic fillers, between the CSEs and the cathode, and between the CSEs and the lithium metal anode, are examined. Relevant issues and corresponding remediation strategies are proposed. Finally, future perspectives based on interfacial engineering and the characterization of polymer/inorganic filler interactions are proposed for building high‐performance CSEs for use in SSLMBs.

Investigation of a Fluorine-Free Phosphonium-Based Ionic Liquid Electrolyte and Its Compatibility with Lithium Metal.

A novel fluorine-free ionic liquid electrolyte comprising lithium dicyanamide (LiDCA) and trimethyl(isobutyl)phosphonium tricyanomethanide (P111i4TCM) in a 1:9 molar ratio is studied as an electrolyte for lithium metal batteries. At room temperature, it demonstrates high ionic conductivity and viscosity of about 4.5 mS cm-1 and 64.9 mPa s, respectively, as well as a 4 V electrochemical stability window (ESW). Li stripping/plating tests prove the excellent electrolyte compatibility with Li metal, evidenced by the remarkable cycling stability over 800 cycles. The evolution of the Li-electrolyte interface upon cycling was investigated via electrochemical impedance spectroscopy, displaying a relatively low impedance increase after the initial formation cycles. Finally, the solid electrolyte interphase (SEI) formed on Li metal appeared to have a bilayer structure mostly consisting of DCA and TCM reduction products. Additionally, decomposition products of the phosphonium cation were also detected, despite prior studies reporting its stability against Li metal.

Revisiting the corrosion mechanism of LiFSI based electrolytes in lithium metal batteries

Lithium bis(fluorosulfonyl)imide (LiFSI), regarded as one of the most promising alternative of lithium hexafluorophosphate (LiPF6), seriously weakens the electrochemical performance of lithium metal batteries at high voltages, due to its extreme corrosion in nonaqueous electrolyte towards some components of the batteries. Though studies have shown that the aluminum (Al) collector will be corroded in LiFSI electrolytes, few attentions have been paid to the corrosion of steel components of lithium metal batteries, the corrosion intensity of which is much more severe than that of Al. Herein, by comparing the electrochemical corrosion behaviors of Al foil and stainless steel (SS) in LiFSI electrolytes, the corrosion products were characterized and analyzed, and the corrosion mechanism of SS was further proposed. Based on the corrosion mechanism, a strategy to inhibit the corrosion by using high concentration electrolyte (HCE) was also proposed. Moreover, introduction of 1,1,2,2-tetrafluoroethyl 2,2,2-trifluoroethyl ether into HCE, forming a localized high concentration electrolyte (LHCE), which not only addresses the viscosity and wettability issues of HCE but also inhibits the corrosion in conventional concentration electrolyte. As a result, Li||LiCoO2 coin cells using HCE and LHCE show excellent cycling stability with capacity fading rates of 0.53% and 0.26% per cycle, respectively, at 1 C (1 C = 180 mAh g − 1) between 3 – 4.45 V. The same corrosion inhibition regular also has been proved in pouch cells.

A highly ionic conductive succinonitrile-based composite solid electrolyte for lithium metal batteries

Solid-state Li metal batteries with solid electrolytes have built a potential way to solve the safety and low energy density problems of current commercial Li-ion batteries with liquid electrolyte. As a key component of solid-state Li metal batteries, solid electrolytes require high ionic conductivities and good mechanical properties. We have designed a composite solid electrolyte (CSE) consisting of poly(vinylidene fluoride-hexafluoropropylene) (PVDF-HFP)-Li6.5La3Zr1.5Ta0.5O12 (LLZTO)-succinonitrile (SN) and Li bis(trifluoromethylsulphonyl)imide (LiTFSI). The PVDF-HFP-based porous matrix made by electrospinning ensures good mechanical properties of the electrolyte membrane, and the large proportion of SN filling material makes the electrolyte membrane have an ionic conductivity of 1.11 mS·cm−1 without the addition of liquid electrolyte. The symmetric battery assembled with CSE can be cycled stably for more than 600 h, and the LiFePO4∣CSE∣Li full battery can also be cycled stably for more than 200 cycles. In addition to Li metal batteries, Li-O2 and Li-CO2 batteries that use CSE as electrolytes also have good performances, reflecting the universality of CSE. CSE does not only guarantee good mechanical properties but also obtain a high ionic conductivity. This design provides a new idea for the commercial application of polymer-based solid batteries.

Enabling Stable Interphases via In Situ Two-Step Synthetic Bilayer Polymer Electrolyte for Solid-State Lithium Metal Batteries

Poly(ethylene oxide) (PEO)-based electrolyte is considered to be one of the most promising polymer electrolytes for lithium metal batteries. However, a narrow electrochemical stability window and poor compatibility at electrode-electrolyte interfaces restrict the applications of PEO-based electrolyte. An in situ synthetic double-layer polymer electrolyte (DLPE) with polyacrylonitrile (PAN) layer and PEO layer was designed to achieve a stable interface and application in high-energy-density batteries. In this special design, the hydroxy group of PEO-SPE can form an O-H---N hydrogen bond with the cyano group in PAN-SPE, which connects the two layers of DLPE at a microscopic chemical level. A special Li+ conducting mechanism in DLPE provides a uniform Li+ flux and fast Li+ conduction, which achieves a stable electrolyte/electrode interface.LiFePO4/DLPE/Li battery shows superior cycling stability, and the coulombic efficiency remains 99.5% at 0.2 C. Meanwhile, LiNi0.6Co0.2Mn0.2O2/DLPE/Li battery shows high specific discharge capacity of 176.0 mAh g−1 at 0.1 C between 2.8 V to 4.3 V, and the coulombic efficiency remains 95% after 100 cycles. This in situ synthetic strategy represents a big step forward in addressing the interface issues and boosting the development of high-energy-density lithium-metal batteries.

Improving ionic conductivity of polymer-based solid electrolytes for lithium metal batteries

Because of its superior safety and excellent processability, solid polymer electrolytes (SPEs) have attracted widespread attention. In lithium based batteries, SPEs have great prospects in replacing leaky and flammable liquid electrolytes. However, the low ionic conductivity of SPEs cannot meet the requirements of high energy density systems, which is also an important obstacle to its practical application. In this respect, escalating charge carriers (i.e. Li+) and Li+ transport paths are two major aspects of improving the ionic conductivity of SPEs. This article reviews recent advances from the two perspectives, and the underlying mechanism of these proposed strategies is discussed, including increasing the Li+ number and optimizing the Li+ transport paths through increasing the types and shortening the distance of Li+ transport path. It is hoped that this article can enlighten profound thinking and open up new ways to improve the ionic conductivity of SPEs.

Design of networked solid-state polymer as artificial interlayer and solid polymer electrolyte for lithium metal batteries

• Using low energy polymer to completely cover Li anode and regulate Li + transport. • Using low energy polymer to form Li−F bonds facilitating uniform Li deposition. • Using high elasticity polymer to accommodate Li anode volume changes. • Being used as an artificial interlayer or solid electrolyte in lithium batteries. • Enabling solid batteries to retain 86% capacity after 750 cycles at 30 °C. Major challenges in the development of lithium metal batteries (LMBs) are nonuniform Li deposition and substantial variation in Li volume, resulting in Li dendrite growth and Li consumption. A networked solid-state polymer electrolyte (NSPE) that comprises poly(ethylene oxide- co -propylene oxide) (P(EO- co -PO)) and poly(dimethylsiloxane) diglycidyl ether (PDMSDGE) chains and a lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt is developed for resolving the Li deposition challenges. The methyl pendants on P(EO- co -PO) and PDMSDGE chains render the NSPE a low-surface-energy film for complete coverages on the high-energy Li electrode and regulating Li + transport. The low-surface-energy characteristics induces overspreading of the highly lithiophilic C-F ends of the TFSI − anion at the Li electrode–NSPE interface, forming Li−F bonds and facilitating uniform Li deposition. The elastic PDMS chains enable the NSPE to accommodate Li volume changes. Liquid-phase Li||LiFePO 4 and Cu||LiFePO 4 cells with the NSPE as an artificial interface or a solid-state Li||LiFePO 4 cell with the NSPE as solid electrolyte had uniform anodic Li deposition, resulting in long cycle life and high coulombic efficiency. Our study demonstrated that (a) low surface energy to completely cover the Li anode and (b) the presence of interfacial Li − F bonds are two essential requirements for uniform Li deposition in LMBs.

Mechanistic Insight into La2O3 Dopants with High Chemical Stability on Li3PS4 Sulfide Electrolyte for Lithium Metal Batteries

Unlike the unstable liquid-state organic electrolyte at high temperatures, the solid-state electrolytes with high safety have attracted a broad prospect for the development of all-solid-state lithium metal battery (ASSLMB). Among the solid electrolytes, the sulfide-based electrolyte with low grain boundary resistances is one of the most practical choices due to its high lithium-ionic conductivity. The introduction of non-conducting oxide fillers into sulfide matrix is an effective way to increase their ionic conductivities and interfacial stabilities with the electrodes of battery simultaneously. Unfortunately, the acting mechanism of non-conducting oxide dopants with high chemical stability on the sulfide electrolyte has not been elucidated clearly. In this work, the rare-earth oxide La2O3 with high chemical stability was selected as a doping component of Li3PS4 sulfide electrolyte for the first time. The experimental results show that a certain amount of La2O3 can not only increase the ionic conductivity of Li3PS4 electrolyte, but also enhance their interfacial stability with the electrodes effectively. The XPS analytical results reveal the enhanced stability of Li3PS4 electrolyte with La2O3 doping due to the formation of SEI film on the lithium anode. Both the static and dynamic simulations illustrate that La2O3 particles inside the Li3PS4 electrolyte could facilitate the migration of Li+ ion by way of the “space-charge effect.”

Hydrogenated borophene nanosheets based multifunctional quasi-solid-state electrolytes for lithium metal batteries

Despite the fact that solid-state electrolytes have attracted broad research interests, the limited ion transfer and high interface impedance restrain their application in high-performance batteries with high cyclic stability and power density. Here, a new quasi-solid-state polymer electrolyte containing lightweight semiconducting hydrogenated borophene (HB) nanosheets, ionic liquids, and poly (ethylene oxide) is reported. The cyclic overpotential of the Li-Li symmetrical battery is about 65 mV lower than that of HB-free quasi-solid-state electrolyte, demonstrating the lower interface impedance. The interaction between lithium-ion and ethylene-oxide chains decreases owing to the existence of HB nanosheets and ionic liquids, which facilitates lithium-ion diffusion. The lithium bis(trifluoromethanesulfonyl)imide molecule surface adsorption at the HB nanosheets enhances the dissociation of lithium ions, and thus the matched lithium iron phosphate/Li full cell delivers the acceptable rate performance up to 5C. This work provides a new filler candidate to enhance the ionic conductivity of quasi-solid-state electrolytes that may facilitate to construct the high-performance HB nanosheets and ionic liquids-based lithium metal batteries.

Safe and Stable Lithium Metal Batteries Enabled by an Amide-Based Electrolyte

HighlightsA novel amide-based nonflammable electrolyte is proposed. The formation mechanism and solvation chemistry are investigated by molecular dynamics simulations and density functional theory.An inorganic/organic-rich solid electrolyte interphase with an abundance of LiF, Li3N and Li–N–C is in situ formed, leading to spherical lithium deposition.The amide-based electrolyte can enable stable cycling performance at room temperature and 60 ℃.The formation of lithium dendrites and the safety hazards arising from flammable liquid electrolytes have seriously hindered the development of high-energy-density lithium metal batteries. Herein, an emerging amide-based electrolyte is proposed, containing LiTFSI and butyrolactam in different molar ratios. 1,1,2,2-Tetrafluoroethyl-2,2,3,3-tetrafluoropropylether and fluoroethylene carbonate are introduced into the amide-based electrolyte as counter solvent and additives. The well-designed amide-based electrolyte possesses nonflammability, high ionic conductivity, high thermal stability and electrochemical stability (> 4.7 V). Besides, an inorganic/organic-rich solid electrolyte interphase with an abundance of LiF, Li3N and Li–N–C is in situ formed, leading to spherical lithium deposition. The formation mechanism and solvation chemistry of amide-based electrolyte are further investigated by molecular dynamics simulations and density functional theory. When applied in Li metal batteries with LiFePO4 and LiMn2O4 cathode, the amide-based electrolyte can enable stable cycling performance at room temperature and 60 ℃. This study provides a new insight into the development of amide-based electrolytes for lithium metal batteries.

Designing Polyurethane Solid Polymer Electrolytes for High-Temperature Lithium Metal Batteries

Potentially high-performance lithium metal cells in extreme high-temperature electrochemical environments is a challenging but attractive battery concept that requires stable and robust electrolytes to avoid severely limiting lifetimes of the cells. Here, the properties of tailored polyester and polycarbonate diols as the soft segments in polyurethanes are investigated and electrochemically evaluated for use as solid polymer electrolytes in lithium metal batteries. The polyurethanes demonstrate high mechanical stability against deformation at low flow rates and moreover at temperatures up above 100 °C, enabled by the hard urethane segments. The results further indicate transferrable ion transport properties of the pure polymers when incorporated as the soft segments in the polyurethanes, offering designing opportunities of the polyurethane by tuning the soft segment ratio and composition. Long-term electrochemical cycling of polyurethane-containing cells in lithium metal batteries at 80 °C proves the stability at elevated temperatures as well as the compatibility with lithium metal with stable cycling maintained after 2000 cycles.

Mitigating Interfacial Mismatch between Lithium Metal and Garnet-Type Solid Electrolyte by Depositing Metal Nitride Lithiophilic Interlayer.

Solid-state lithium batteries are generally considered as the next-generation battery technology that benefits from inherent nonflammable solid electrolytes and safe harnessing of high-capacity lithium metal. Among various solid-electrolyte candidates, cubic garnet-type Li7La3Zr2O12 ceramics hold superiority due to their high ionic conductivity (10–3 to 10–4 S cm−1) and good chemical stability against lithium metal. However, practical deployment of solid-state batteries based on such garnet-type materials has been constrained by poor interfacing between lithium and garnet that displays high impedance and uneven current distribution. Herein, we propose a facile and effective strategy to significantly reduce this interfacial mismatch by modifying the surface of such garnet-type solid electrolyte with a thin layer of silicon nitride (Si3N4). This interfacial layer ensures an intimate contact with lithium due to its lithiophilic nature and formation of an intermediate lithium–metal alloy. The interfacial resistance experiences an exponential drop from 1197 to 84.5 Ω cm2. Lithium symmetrical cells with Si3N4-modified garnet exhibited low overpotential and long-term stable plating/stripping cycles at room temperature compared to bare garnet. Furthermore, a hybrid solid-state battery with Si3N4-modified garnet sandwiched between lithium metal anode and LiFePO4 cathode was demonstrated to operate with high cycling efficiency, excellent rate capability, and good electrochemical stability. This work represents a significant advancement toward use of garnet solid electrolytes in lithium metal batteries for the next-generation energy storage devices.

Highly Conductive Iodine and Fluorine Dual Doped Argyrodite Solid Electrolyte for Lithium Metal Batteries

Highly Conductive Iodine and Fluorine Dual Doped Argyrodite Solid Electrolyte for Lithium Metal Batteries

Deep Eutectic Solvent with Film-Forming Fluoroethylene Carbonate as a Nonflammable Electrolyte for Lithium Metal Batteries

Deep Eutectic Solvent with Film-Forming Fluoroethylene Carbonate as a Nonflammable Electrolyte for Lithium Metal Batteries

New nonflammable tributyl phosphate based localized high concentration electrolytes for lithium metal batteries

A new tributyl phosphate based nonflammable localized high concentration electrolyte exhibits good electrochemical performance.

Composite polymer electrolyte with high inorganic additive contents to enable metallic lithium anode

Composite polymer electrolytes (CPE) are a very promising strategy for using lithium metal anodes safely. These electrolytes are formed by polymeric matrices in which ceramic nanoparticles are incorporated to modify their mechanical and conduction properties. In this work a methacrylate-based polymer matrix containing 63 wt% of ZrO2 nanoparticles (NPs) was prepared and tested as electrolyte for lithium metal batteries. The prepared CPE shows a higher ionic conductivity than the polymer matrix without ZrO2 NPs and a higher lithium transport number than Celgard with liquid electrolyte and stabilizes the processes of deposition-dissolution of lithium with respect to the reference cell, thus prolonging the cycling time without short circuits. Finally, the compatibility of the CPE with a LiFePO4 cathode was verified, achieving a stable cycling at 1.0 C and at ambient temperature, with an impressive capacity of 140.18 mAh g−1 even after 250 cycles.