High tLi Research Articles

Metal-Organic Coordination Enhanced Metallopolymer Electrolytes for Wide-Temperature Solid-State Lithium Metal Batteries.

The practical application of polymer electrolytes is seriously hindered by the inferior Li+ ionic conductivity, low Li+ transference number (tLi+), and poor interfacial stability. Herein, a structurally novel metallopolymer is designed and synthesized by exploiting a molybdenum (Mo) paddle-wheel complex as a tetratopic linker to bridge organic and inorganic moieties at molecular level. The prepared metallopolymer possesses combined merits of outstanding mechanical and thermal stability, as well as a low glass transition temperature (Tg < -50 °C). Based on this metallopolymer, an advanced metal-organic coordination enhanced metallopolymer electrolyte (MPE) is developed for constructing high-performance solid-state lithium metal batteries (LMBs). Due to the unsaturated coordination of Mo atoms, the uniformly distributed Mo-polyoxometalates (Mo-POMs) in metallopolymer skeleton can effectively bis(fluorosulfonyl)imide anions (FSI-) and promote the dissociation of Li salts. Moreover, dynamic metal-organic coordination bonds endow the MPE with re-processability and self-healing, enabling it to accommodate electrode volume changes and maintain good interfacial contact. Consequently, the MPE achieves a competitive ionic conductivity of 0.712 mS cm-1 (25 °C), a high tLi+ (0.625), and a wide electrochemical stability window (> 5.0 V). This study presents a unique MPE design based on metal-organic coordination enhanced strategy, providing a promising solution for developing wide-temperature solid-state LMBs.

Three-chamber electrochemical reactor for selective lithium extraction from brine

Efficient lithium recovery from geothermal brines is crucial for the battery industry. Current electrochemical separation methods struggle with the simultaneous presence of Na+, K+, Mg2+, and Ca2+ because these cations are similar to Li+, making it challenging to separate effectively. We address these challenges with a three-chamber reactor featuring a polymer porous solid electrolyte in the middle layer. This design improves the transference number of Li+ (tLi+) by 2.1 times compared to the two-chamber reactor and also reduces the chlorine evolution reaction, a common side reaction in electrochemical lithium extraction, to only 6.4% in Faradaic Efficiency. Employing a lithium-ion conductive glass ceramic (LICGC) membrane, the reactor achieved high tLi+ of 97.5% in LiOH production from simulated brine, while the concentrations of Na+ K+, Mg2+, and Ca2+ are below the detection limit. Electrochemical experiments and surface analysis elucidated the cation transport mechanism, highlighting the impact of Na+ on Li+ migration at the LICGC interface.

High‐Voltage Single‐Ion Covalent Organic Framework Electrolytes Enabled by Nitrile Migration Ladders for Lithium Metal Batteries

AbstractThe poor electrochemical stability window and low ionic conductivity in solid‐state electrolytes hinder the development of safe, high‐voltage, and energy‐dense lithium metal batteries. Herein, taking advantage of the unique electronic effect of nitrile groups, we designed a novel azanide‐based single‐ion covalent organic framework (CN−iCOF) structure that possesses effective Li+ transport and high‐voltage stability in lithium metal batteries. Density functional theory (DFT) calculations and molecular dynamics (MD) revealed that electron‐withdrawing nitrile groups not only resulted in an ultralow HOMO energy orbital but also enhanced Li+ dissociation through charge delocalization, leading to a high tLi+ of 0.93 and remarkable oxidative stability up to 5.6 V (vs. Li+/Li) simultaneously. Moreover, cyanation leveraging Strecker reaction transformed reversible imine‐linkage to a stable sp3‐carbon‐containing azanide anion, which facilitated contorted alignment of transport “ladders” along the one‐dimensional anionic channels and the ionic conductivity could reach 1.33×10−5 S cm−1 at ambient temperature without any additives. As a result, CN−iCOF allowed operation of solid‐state lithium metal batteries with high‐voltage cathodes such as LiNi0.8Mn0.1Co0.1O2 (NCM811), demonstrating stable lithium deposition up to 1,100 h and reversible battery cycling at ambient temperature up to 4.5 V, shedding light on the importance of discovering new functionality for forthcoming high‐performance batteries.

Fabrication of Single-Ion Conductors Based on Liquid Crystal Polymer Network for Quasi-Solid-State Lithium Ion Batteries.

Single-ion conductive polymer electrolytes can improve the safety of lithium ion batteries (LIBs) by increasing the lithium transference number (tLi+) and avoiding the growth of lithium dendrites. Meanwhile, the self-assembled ordered structure of liquid crystal polymer networks (LCNs) can provide specific channels for the ordered transport of Li ions. Herein, single-ion conductive nematic and cholesteric LCN electrolyte membranes (denoted as NLCN-Li and CLCN-Li) were successfully prepared. NLCN-Li was then coated on commercial Celgard 2325 while CLCN-Li was coated on poly(vinylidene fluoride-hexafluoropropylene) film, coupled with plasticizer, to make NLCN-Li/Cel and CLCN-Li/Pv quasi-solid-state electrolyte membranes, respectively. Their electrochemical properties were evaluated, and it was found that they possessed benign thermal stability and electrolyte/electrode compatibility, high tLi+ up to 0.98 and high electrochemical stability window up to 5.2 V. A small amount (0.5M) of extra Li salt added to the plasticizer could improve the ion conductivity from 1.79 × 10-5 to 5.04 × 10-4 S cm-1, while the tLi+ remained 0.85. The assembled LFP|Li batteries also exhibited excellent cycling and rate performances. The orderliness of the LCN layer played an important role in the distribution and movement of Li ions, thereby affecting the Li deposition and growth of Li dendrites. As the first report of nematic and cholesteric LCN single-ion conductors, this work sheds light on the design and fabrication of ordered quasi-solid-state electrolytes for high-performance and safe LIBs.

High-Voltage Single-Ion Covalent Organic Framework Electrolytes Enabled by Nitrile Migration Ladders for Lithium Metal Batteries.

The poor electrochemical stability window and low ionic conductivity in solid-state electrolytes hinder the development of safe, high-voltage, and energy-dense lithium metal batteries. Herein, taking advantage of the unique electronic effect of nitrile groups, we designed a novel azanide-based single-ion covalent organic framework (CN-iCOF) structure that possesses effective Li+ transport and high-voltage stability in lithium metal batteries. Density functional theory (DFT) calculations and molecular dynamics (MD) revealed that electron-withdrawing nitrile groups not only resulted in an ultralow HOMO energy orbital but also enhanced Li+ dissociation through charge delocalization, leading to a high tLi+ of 0.93 and remarkable oxidative stability up to 5.6 V (vs. Li+/Li) simultaneously. Moreover, cyanation leveraging Strecker reaction transformed reversible imine-linkage to a stable sp3-carbon-containing azanide anion, which facilitated contorted alignment of transport "ladders" along the one-dimensional anionic channels and the ionic conductivity could reach 1.33×10-5 S cm-1 at ambient temperature without any additives. As a result, CN-iCOF allowed operation of solid-state lithium metal batteries with high-voltage cathodes such as LiNi0.8Mn0.1Co0.1O2 (NCM811), demonstrating stable lithium deposition up to 1,100 h and reversible battery cycling at ambient temperature up to 4.5 V, shedding light on the importance of discovering new functionality for forthcoming high-performance batteries.

A dual-network structured poly (m-phenylene isophthalamide) nanofiber separator with Li6.4La3Zr1.4Ta0.6O12 for dendrite-free and high-safety lithium-metal batteries

Separator plays an important role in improving the long-term cycle stability and safety performance of high-energy–density lithium-metal batteries (LMBs). Herein, a robust thermotolerant separator is prepared by one-step electrospinning technique, combing fluorinated poly (m-phenylene isophthalamide) nanofibers with Li6.4La3Zr1.4Ta0.6O12 (LLZTO), a fast ionic conductor. The synergistically incorporated poly (vinylidene fluoride-co-hexafluoropropylene) and LLZTO trigger off the formation of a fancy dual-network structure with high porosity and well-distributed nanopores, in which ultrafine secondary nanonets are tightly bound with three-dimensional nanofiber scaffold. LLZTO can not only provide sufficient Li+ migration channels, but also immobilize free anions to strengthen ionic transmission. Moreover, this nanofiber separator possesses high mechanical strength, excellent thermal stability and desirable electrolyte affinity. It can gel liquid electrolyte well, leading to high tLi+, homogenized Li+ flux and uniform Li deposition. Consequently, LMBs with this dual-network structured nanofiber separator deliver satisfactory cycle stability and high C-rate capability. This contribution provides new insights into the design and development of high-quality nanofiber separators for dendrite-free and high-safety LMBs.

Borate-containing triblock copolymer electrolytes for improved lithium-ion transference number and interface stability

The electrolytes with high lithium-ion transference number (tLi+) can reduce the formation of concentration polarization during charge/discharge process and improve the electrochemical performance of lithium-ion batteries (LIBs). Herein, we report triblock copolymer electrolytes (PBOEE) containing borate. The sp2 hybridized boron atoms acting as Lewis acids can anchor the anions of lithium salts, enabling PBOEE to achieve high tLi+ of up to 0.53. Also, the borate groups can promote the formation of stable organic-rich solid electrolyte interphase (SEI) film, which enables the Li symmetric cell to cycle stably at 0.1 mA cm−2/0.1 mAh cm−2 for more than 3100 h with a low overpotential of 0.08 V under 50 °C. The optimized PBOEE_24 has an ionic conductivity of 1.41 × 10−4 S cm−1 and electrochemical stability window of 4.8 V vs. Li+/Li at 50 °C. Combining these advantages, the LiFePO4/PBOEE_24/Li cell exhibits an initial discharge specific capacity of 157.3 mA h g−1 at 0.5C with a capacity retention of 85 % after 600 cycles under 50 °C. At a higher current density of 1C, the discharge capacity maintains at 128.0 mA h g−1 after 400 cycles with a capacity retention of 84.88 %. These results suggest that block copolymer containing sp2 hybridized boron atoms is a promising all-solid-state polymer electrolyte.

Highly conductive and nonflammable boron-based gel type single ion conducting electrolyte membranes toward high-safety and dendrite-free lithium metal batteries

Single-ion conducting polymer electrolytes (SIPEs), having a high Li-ion transference number (tLi+) close to unity, hold great promise for circumventing the lithium dendrite growth of lithium metal batteries (LMBs). However, SIPEs synthesized by a simple method that also simultaneously fulfill the requirements of high ionic conductivity, good thermal stability, and remarkable fire resistance are still quite rare. Herein, a novel single-ion conducting fibrous membrane (es-DDBSB-Li) based on borate anions of single-ion conductors (denoted as DDBSB-Li) and poly(vinylidene fluoride-hexafluoropropylene) P(VDF-HFP) as a binder was prepared via facile electrospinning technology. The introduction of borate anions promotes the homogeneous distribution of highly concentrated Li-ions and accelerates the ionic migration, leading to an enhanced ionic conductivity of 3.75 × 10−4 S cm−1 at 25 °C for DDBSB-Li saturated with organic solvents. Additionally, the thermally stable and nonflammable DDBSB-Li endows the resultant fibrous membranes to possess good high-temperature stability and fire-resistance properties. The Li||Li cell using this electrolyte displays a high tLi+ of 0.91 and effectively mitigates concentration polarization, thereby enabling a remarkably stable cyclic performance over 2000 h at 2.5 mA cm−2 at 25 °C. Also, this gel SIPE-based Li||LiFePO4 battery demonstrates superior rate performances up to 3C and delivers long-term cycling durability over 600 cycles under 1C at 25 °C. We believe this novel gel SIPE-based fibrous membrane has great potential for practical application in high-safety and dendrite-proof LMBs.

One‐Step Polymerizations Enable Facile Construction and Structural Optimization of Graft Copolymer Electrolytes

AbstractThe development of poly(ethylene oxide) (PEO)‐based solid polymer electrolytes (SPEs) is limited by the semi‐crystalline nature of PEO and the extremely strong EO‐Li+ interactions. To promote the rapid migration of Li+, a one‐step method combining radical polymerization and ring‐opening polymerization catalyzed simultaneously by lithium carboxylate is proposed to construct multi‐component graft copolymer electrolytes (GCPEs) in this study. Tailored macroinitiator with catalytic and initiated sites (PAALi(OH‐Br)) realizes one‐step polymerizations of vinyl monomers and cyclic monomers, and provides GCPEs with poly(ethylene glycol) (PEG) and poly(ε‐caprolactone) (PCL) side chains. The grafted structure of GCPE greatly facilitates the intra‐chain hopping of Li+, resulting in excellent ionic conductivity. The introduction of PCL further improves the tLi+ of GCPE. The three‐component graft copolymer electrolyte constructed by polystyrene (PS), PEO, and PCL exhibits high tensile stress (1.62 MPa), a high ionic conductivity (2.4 × 10−5 S cm−1, 30 °C), and a high tLi+ of 0.47 and high electrochemical stability.

Fluorinated boron nitride nanosheet enhanced ultrathin and conductive polymer electrolyte for high‐rate solid‐state lithium metal batteries

AbstractPolyethylene oxide (PEO)‐based polymer solid electrolytes (PSE) have been pursued for the next‐generation extremely safe and high‐energy‐density lithium metal batteries due to their exceptional flexibility, manufacturability, and lightweight nature. However, the practical application of PEO‐PSE has been hindered by low ionic conductivity, limited lithium‐ion transfer number (tLi+), and inferior stability with lithium metal. Herein, an ultrathin composite solid‐state electrolyte (CSSE) film with a thickness of 20 μm, incorporating uniformly dispersed two‐dimensional fluorinated boron nitride (F‐BN) nanosheet fillers (F‐BN CSSE) is fabricated via a solution‐casting process. The integration of F‐BN effectively reduces the crystallinity of the PEO polymer matrix, creating additional channels that facilitate lithium‐ion transport. Moreover, the presence of F‐BN promotes an inorganic phase‐dominated electrolyte interface film dominated by LiF, Li2O, and Li3N on the lithium anode surface, greatly enhancing the stability of the electrode‐electrolyte interface. Consequently, the F‐BN CSSE exhibits a high ionic conductivity of 0.11 mS cm−1 at 30°C, high tLi+ of 0.56, and large electrochemical window of 4.78 V, and demonstrates stable lithium plating/striping behavior with a voltage of 20 mV for 640 h, effectively mitigating the formation of lithium dendrites. When coupled with LiFePO4, the as‐assembled LiFePO4|F‐BN CSSE|Li solid‐state battery achieves a high capacity of 142 mAh g−1 with an impressive retention rate of 82.4% after 500 cycles at 5 C. Furthermore, even at an ultrahigh rate of 50 C, a capacity of 37 mAh g−1 is achieved. This study provides a novel and reliable strategy for the design of advanced solid‐state electrolytes for high‐rate and long‐life lithium metal batteries.

In-Situ Crosslinked Single-Ion Conducting Gel Polymer Electrolyte for Lithium Metal Batteries

Lithium metal batteries (LMBs) have been considered as promising candidates for energy storage device due to their high energy density. However, high reactivity of lithium metal with liquid electrolyte and continuous growth of dendrite lead to degradation of cycle performance and cell failure. To overcome these problems, the strategy of employing gel polymer electrolytes (GPE) was investigated. GPE can effectively encapsulate organic solvents and facilitate uniform contact with electrodes. Both cations and anions migrate in conventional GPE, which gives rise to low Li+ ion transference number (tLi+). Low tLi+ causes inhomogeneous Li+ ion flux and continuous dendrite growth. Compared to conventional GPE, single-ion conducting gel polymer electrolytes (SIC-GPE) have superior tLi+ value close to unity, since the movement of anions is suppressed. In this work, we synthesized a novel sulfonamide based single-ion conductor and prepared the chemically crosslinked SIC-GPE. The electrolyte was obtained by a facile in-situ crosslinking that further improves interfacial contact with electrodes. The resulting SIC-GPE exhibited high tLi+, which led to homogeneous deposition of Li+ ion and enhanced electrochemical stability. The LMB cell employing SIC-GPE exhibited stable cycle performance, proving ability to suppress the growth of lithium dendrite.

Achieving multi-dimensional Li+ transport nanochannels via spatial-partitioning in crystalline ionic covalent organic frameworks for highly stable lithium metal anode

The fragile solid electrolyte interphase (SEI) and anisotropic dendrite growth during Li plating/stripping have posed as intractable handicaps to the practical implementation of lithium metal batteries (LMBs). The Li+ uniform distribution and unimpeded transfer play significant roles to enable protuberance-free Li textures. Herein, the highly-crystalline TFSI− ionic-covalent organic framework (I-COF) endowed with designated mixed-dimensional channels was constructed as an artificial SEI layer via anionic post-modification. Benefiting from the desirable spatial-partitioning effect triggered by nanochannels reconfiguration, the I-COF with expanded multi-dimensional Li+ transport channels and scaled-down pore volume could effectively disperse the local concentration gradient of Li+ flux and inhibit growth of Li dendrites. Besides, the coordinated TFSI− anions with a high tLi+ of 0.76 can selectively restrict the delivery and decomposition of homogeneous ions. To understand the interfacial charge transfer mechanisms, the lithophilic properties and the energy barriers for Li+ migration were also calculated. Correspondingly, the I-COF(TI−) modified Li|Li symmetric cell showed superb durability over 5500 h at 4 mA cm−2 with extraordinary overpotential. The Li|S full cell also displayed prolonged lifespan and excellent rate performance. The comprehension of the mixed-dimensional interfacial strategy via spatial-partitioning provides new insights into the fabrication of solid–solid interfaces, which can aid in the improved design and development of advanced lithium-metal batteries (LMBs).

A nano fiber–gel composite electrolyte with high Li+ transference number for application in quasi-solid batteries

As their Li+ transference number (tLi+), ionic conductivity, and safety are all high, polymer electrolytes play a vital role in overcoming uncontrollable lithium dendrites and low energy density in Li metal batteries (LMBs). We therefore synthesized a three-dimensional (3D) semi-interpenetrating network-based single-ion-conducting fiber–gel composite polymer electrolyte (FGCPE) via an electrospinning, initiation, and in situ polymerization method. The FGCPE provides high ionic conductivity (1.36 ​mS ​cm−1), high tLi+ (0.92), and a high electrochemical stability window (up to 4.84 ​V). More importantly, the aromatic heterocyclic structure of the biphenyl in the nanofiber membrane promotes the carbonization of the system (the limiting oxygen index value of the nanofiber membrane reaches 41%), giving it certain flame-retardant properties and solving the source-material safety issue. Due to the in situ method, the observable physical interface between electrodes and electrolytes is virtually eliminated, yielding a compact whole that facilitates rapid kinetic reactions in the cell. More excitingly, the LFP/FGCPE/Li cell displays outstanding cycling stability, with a capacity retention of 91.6% for 500 cycles even at 10C. We also test the FGCPE in high-voltage NMC532/FGCPE/Li cells and pouch cells. This newly designed FGCPE exhibits superior potential and feasibility for promoting the development of LMBs with high energy density and safety.

Single-Ion Conducting Polymeric Protective Interlayer for Stable Solid Lithium-Metal Batteries

With many reported attempts on fabricating single-ion conducting polymer electrolytes, they still suffer from low ionic conductivity, narrow voltage window, and high cost. Herein, we report an unprecedented approach on improving the cationic transport number (tLi+) of the polymer electrolyte, i.e., single-ion conducting polymeric protective interlayer (SIPPI), which is designed between the conventional polymer electrolyte (PVEC) and Li-metal electrode. Satisfied ionic conductivity (1 mS cm-1, 30 °C), high tLi+ (0.79), and wide-area voltage stability are realized by coupling the SIPPI with the PVEC electrolyte. Benefiting from this unique design, the Li symmetrical cell with the SIPPI shows stable cycling over 6000 h at 3 mA cm-2, and the full cell with the SIPPI exhibits stable cycling performance with a capacity retention of 86% over 1000 cycles at 1 C and 25 °C. This incorporated SIPPI on the Li anode presents an alternative strategy for enabling high-energy density, long cycling lifetime, and safe and cost-effective solid-state batteries.

Polysiloxane-based Electrolytes: Influence of Salt Type and Polymer Chain Length on the Physical and Electrochemical Properties.

An oligo/poly(methyl(2-(tris(2-H methoxyethoxy)silyl)ethyl)siloxane)), 390EO, and 2550EO, were synthesized. Dilute electrolyte solutions of 390EO and 2550EO were prepared using LiTFSI, LiFSI, and LiPF6 . The influence of the length of the siloxane polymer chain, salt type, and Si-tripodand centers at the side chain on ionic conductivity, tLi + , and physical properties were examined. Both electrolyte systems showed high values of tLi + (0.35 for 2550EO/LiTFSI and 0.64 for 390EO/LiTFSI). Alternatively 390EO/LiPF6 and 2550EO/LiPF6 displayed high tLi + values of 0.61 and 0.44, respectively, while 390EO/LiFSI displayed the smallest tLi+ (0.25). To clarify the role played by the Li+ environment in Li+ transport, the solvation states of electrolytes were examined. It was observed that anion solvation can be achieved using siloxane-based solvent in all systems. Walden plot analysis demonstrates that ionic diffusion was not controlled by either macroviscosity/microviscosity in the siloxane-based polymer electrolytes. Ions instead move along a relatively smooth ion-pathway without complete full segmental reorientation in 2550EO as a result of decoupling and high ion solvation behavior. Conversely, in 390EO, ions might move to available sites by a jumping after decoupling with low ion solvation behavior. Consequently, a high t Li + was achieved, and the oxidative stability of the salt was ensured.

Electronegativity‐Induced Single‐Ion Conducting Polymer Electrolyte for Solid‐State Lithium Batteries

The application of solid polymer electrolytes (SPEs) is severely impeded by the insufficient ionic conductivity and low Li+ transference numbers (tLi+). Here, we report an iodine‐driven strategy to address both the two long‐standing issues of SPEs simultaneously. Electronegative iodine‐containing groups introduced on polymer chains effectively attract Li+ ions, facilitate Li+ transport, and promote the dissociation of Li salts. Meanwhile, iodine is also favorable to alleviate the strong O−Li+ coordination through a Lewis acid–base interaction, further improving the ionic conductivity and tLi+. As a proof of concept, an iodinated single‐ion conducting polymer electrolyte (IPE) demonstrates a high ionic conductivity of 0.93 mS cm−1 and a high tLi+ of 0.86 at 25 °C, which is among the best results ever reported for SPEs. Moreover, symmetric Li/Li cells with IPE achieve a long‐term stability over 2600 h through the in‐situ formed LiF‐rich interphase. As a result, Li−S battery with IPE maintains a high capacity of 623.7 mAh g−1 over 300 cycles with an average Coulombic efficiency of 99%. When matched with intercalation cathode chemistries, Li/IPE/LiFePO4 and Li/IPE/LiNi0.8Mn0.1Co0.1O2 solid‐state batteries also deliver high‐capacity retentions of 95% and 97% at 0.2 C after 120 cycles, respectively.

Achieving High Performance of Lithium Metal Batteries by Improving the Interfacial Compatibility between Organic and Inorganic Electrolytes Using a Lithium Single-Ion Polymer

Composite solid electrolytes (CSEs) containing polymer electrolytes and inorganic particulate fillers have the potential to attain excellent electrochemical performance and good interfacial contact with Li metal. Nevertheless, the performance of CSEs is still constrained by the low Li+ transference number (tLi+) and problems at the polymer–ceramic interface. In this study, we present a CSE with high tLi+ and promising comprehensive performance, in which the surface of LLZTO micron particles was grafted by lithium (4-styrenesulfonyl) (trifluoromethanesulfonyl) imide (LiSTFSI). The existence of LiSTFSI on the surface of modified particles was confirmed by FTIR spectroscopy and X-ray photoelectron spectroscopy measurements. These surface-modified particles were uniformly dispersed in the poly(vinylidenefluoride-hexafluoropropylene) (PVDF-HFP) matrix for the improved interfacial compatibility, by which CSEs (PFL@LCSE) were formed. Li@LLZTO particles were found by X-ray diffraction spectra to decrease the crystallinity of PFL@LCSE and to increase the ionic conductivity. Simultaneously, LiSTFSI on the surface of Li@LLZTO was able to restrict the migration of anions and improve the concentration polarization phenomenon inside the battery. PFL@LCSE exhibits high ionic conductivity (1.40 × 10–4 S·cm–1 at 30 °C), high tLi+ (0.59 at 60 °C), good mechanical strength, and remarkable ability to inhibit Li dendrite growth. Li/Li symmetrical and LFP/Li full batteries were assembled and demonstrated good cycling performance. It indicates that improving the interfacial compatibility between organic and inorganic electrolytes is a promising strategy for enhancing the performance of CSEs.

Transference Number Reinforced-Based Gel Copolymer Electrolyte for Dendrite-Free Lithium Metal Batteries.

The progress of electric vehicles is highly inhibited by the limited energy density and growth of dendrite Li in current power batteries. Breakthroughs and improvements in electrolyte chemistry are highlighted to directly address the above issues, namely, the development of electrolytes with a high lithium-ion transference number (tLi+), enabling one to effectively restrict the concentration polarization during repetitious cycling. Herein, we propose a novel ether-based copolymer-based gel polymer electrolyte (ECP-based GPE) by in situ copolymerization as an intriguing strategy to achieve a high tLi+ of ∼0.64. Molecular dynamics simulations and finite element method analyses illustrate the enhanced Li+ diffusion process (DLi+, ∼1.76 × 10-10 m2 s-1) in ECP-based GPE with a homogeneous electric potential accommodated around the lithium metal anode. Therefore, such a high-tLi+-based electrolyte renders a high reversibility of dendrite-free lithium plating/stripping at a high areal capacity (5 mA cm-2/5 mA h cm-2) in an Li||Li symmetric cell and facilitates superior cycling performances (over 1000 cycles) at a high rate (5 C) with a capacity retention of ∼91.1% in Li||LiFePO4 batteries, promoting the practical application of solid-state lithium metal batteries.

Composite solid electrolytes containing single-ion lithium polymer grafted garnet for dendrite-free, long-life all-solid-state lithium metal batteries

Compared with traditional liquid electrolytes, the composite solid electrolytes (CSE) composed of polymer and inorganic particle fillers show better electrochemical stability and safety in lithium-ion batteries. However, the low lithium ion transference number (tLi+) and filler agglomeration still threat CSE performance. In response to these threats, we proposed a flexible anion-immobilized modified ceramic-polymer composite solid electrolyte, which significantly increased the lithium ion transference number and showed promising performance after assembled in an all-solid-state battery. Primarily, the surface of Ta-doped garnet Li6.4La3Zr1.4Ta0.6O12 (@LLZTO) was modified by a silane coupling agent bearing C = C bonds, then the lithium single-ion polymer (lithium (4-styrenesulfonyl) (trifluoromethanesulfonyl) imide (LiSTFSI)) was chemically grafted onto the above particles resulting in the ceramic-polymer composite particles (Li@LLZTO). These particles can be uniformly distributed in the polyethylene oxide (PEO) matrix to form composite solid electrolyte (PL@LCSE). It is found that the PL@LCSE promotes the dissociation of lithium salt and reduces the crystallinity of PEO, and shows a relatively high restriction on the migration of anions. Therefore, PL@LCSE shows a high ionic conductivity (1.5 mS·cm−1), a wide electrochemical window (∼5.3 V vs. Li/ Li+) and a high tLi+ (0.77). The Li/PL@LCSE/Li battery exhibits long cycle stability (cycling more than 1000 h). Excellent cycling stability and high rate capability are demonstrated in the all-solid-state batteries with LiFePO4 and LiNi0.8Co0.1Mn0.1O2 (NCM811) cathode. Consequently, the synthesized garnet-lithium single-ion polymer composite micron particles have great potential in the next generation of all-solid-state lithium metal batteries.

Li-Ion Transport and Solvation of a Li Salt of Weakly Coordinating Polyanions in Ethylene Carbonate/Dimethyl Carbonate Mixtures.

Electrolytes with a high Li-ion transference number (tLi) have attracted significant attention for the improvement of the rapid charge-discharge performance of Li-ion batteries (LIBs). Nonaqueous polyelectrolyte solutions exhibit high tLi upon immobilization of the anion on a polymer backbone. However, the transport properties and Li-ion solvation in these media are not fully understood. Here, we investigated the Li salt of a weakly coordinating polyanion, poly[(4-styrenesulfonyl)(trifluoromethanesulfonyl)amide] (poly(LiSTFSA)), in various ethylene carbonate and dimethyl carbonate mixtures. The highest ionic conductivity was unexpectedly observed for the lowest polar mixture at the highest salt concentration despite the low dissociation degree of poly(LiSTFSA). This was attributed to a unique conduction phenomenon resulting from the faster diffusion of transiently solvated Li ions along the interconnected aggregates of polyanion chains. A Li/LiFePO4 cell using such an electrolyte demonstrated improved rate capability. These results provide insights into a design strategy of nonaqueous liquid electrolytes for LIBs.