High Li-ion Transference Number Research Articles

Porous activated carbon integrated carbon nitride nanosheets as functionalized separators for the efficient polysulfide entrapment in Li[sbnd]S batteries

Electrification of vehicles, hybrid aircraft and the advancement of portable electronics are exacting the deployment of high energy-dense batteries. The high theoretical capacity of sulfur (1675 mAh g−1), cost-effectiveness and environmental benignity of the lithium‑sulfur batteries (LSBs) are propitious for electrochemical energy storage beyond Li-ion battery technology. In this work, we described a simple, scalable preparation and electrochemical performance of porous activated carbon (PC)-infused graphitic carbon nitride (GCN) nanosheets with various ratios (PC@GCN 11, PC@GCN 12 and PC@GCN 21) as a polysulfide anchoring functionalized separator for LSBs. The high specific area (822 m2/g), hetero porosity, conductive carbon framework, surface functionalities and enriched N-doping of the PC@GCN synergistically induce mitigation of polysulfides via chemical and physical adsorption pathways in LSBs. The PC@GCN 21 modified separator demonstrates a high initial discharge capacity of 1389 mAh g−1 at a 0.1C rate and exhibits better capacity retention over 500 cycles at a 1C rate (655 mAh g−1) with sulfur loading of 3.8 mg/cm2 accompanied by high coulombic efficiency (94 %). The assembled cell with high S-loading (5.12 mg/cm2) shows a high initial discharge capacity of 712 mAh g−1 at 0.1C rate conditions. High Li-ion transference number (0.714), stable shuttle current, minimal coulombic efficiency loss (0.84 %), low shuttle factor and negligible self-discharge behaviour support the superior performance of the PC@GCN 21 coated cells. This report demonstrates that combining the high surface area, non-polar porous carbon with polar graphitic carbon nitride is a practical approach for designing metal-free functionalized separators for energy-dense LSBs.

Solid-State Lithium Batteries with in-Situ Polymerized Acrylate-Based Electrolytes Capable of Electrochemically Stable Operation at 100 ℃

In-situ polymerized acrylate-based polymers are very appealing as solid polymer electrolytes (SPEs) in lithium (Li) batteries due to the drop-in compatibility of such in-situ polymerization with conventional battery production, the ease of acrylate polymerization and their inexpensive, facile SPE chemistry. We identified, however, that such SPEs suffer from either a low cationic transference number with dual ion conducting salts (0.12-0.2) or a low ionic conductivity with single Li-ion conducting (SLIC) salts (6·10-6 S cm-1). In this project we overcame these limitations and developed significantly improved SPE with ionic conductivity of up to 2·10-4 Scm-1 and a relatively high Li-ion transference number of 0.4. With a significantly reduced fraction of mobile anions in the hybrid SPE, in-situ polymerized SPE cells with an LiFePO4 (LFP) cathode achieve a stable performance for over 100 cycles at temperatures as high as 100 °C, which is unattainable with conventional Li salts or electrolytes. Furthermore, the motional narrowing observed in the line-shapes of solid-state nuclear magnetic resonance (SS-NMR) spectra provided additional insights of the differences in Li nucleus environments and revealed a reduced activation energy for the hybrid salt SPEs due to their more open structure. This study opens the path for the fabrication of high-performance solid polymer lithium batteries capable of operating at high temperatures using commercial battery fabrication equipment. We expect that further tuning of the acrylate based SPE composition may allow further increases in its conductivity without sacrifices in its electrochemical stability or mechanical properties.

Highly Ionic Conductive, Self-Healing, Li10GeP2S12-Filled Composite Solid Electrolytes Based on Reversibly Interlocked Macromolecule Networks for Lithium Metal Batteries with Improved Cycling Stability.

Ceramic-polymer composite solid electrolytes (CSEs) have attracted great attention by combining the advantages of polymer electrolytes and inorganic ceramic electrolytes. Herein, Li10GeP2S12 (LGPS) particles are incorporated into poly(ethylene oxide) (PEO)-based reversibly interlocked polymer networks (RILNs) derived from the topological rearrangement of two PEO networks cross-linked by reversible imine bonds and disulfide linkages. A series of highly ionic conductive, self-healing CSEs are obtained accordingly. The interlocking architecture successfully inhibits PEO crystallization, increasing the amorphous phase for Li ion transportation, and stabilizes the conductive pathways of LGPS particles by its unique confinement effect. Meanwhile, the LGPS particles cooperate with the RILN matrix, forming a filler-polymer interfacial phase for additional Li ion transportation and strengthening and toughening the resultant CSEs via the strong intermolecular Li+-O2- interactions. Furthermore, the dynamic characteristics of the included reversible bonds ensure a multiple intrinsic self-healing capability. Consequently, the CSEs containing 15 wt % LGPS deliver a high ionic conductivity (1.06 × 10-3 S cm-1) and high Li ion transference number (∼0.6) at 25 °C, a wide electrochemical stability window (>4.9 V), good mechanical properties (0.63 MPa, 377%), and a stable CSE/Li anode interface. The integrated Li/CSE/LiFePO4 battery exhibits a specific discharge capacity of 110.8 mAh g-1 at 1 C (25 °C) and a capacity retention of 76.9% after 200 cycles. Thanks to the healability, the damaged CSEs can regain the structural integrity, ion conductive capability, and cycling performance of the assembled cells. The present work provides an effective strategy to fabricate CSEs for lithium metal batteries that are workable at ambient temperature.

Inorganic fillers tailored Li+ solvation sheath for stable lithium metal batteries

Ionogel electrolytes based on gel scaffolds and ionic liquids (ILs) have garnered widespread attention for their processing compatibility, non-flammability, and exceptional thermal/electrochemical properties. While there have been many studies demonstrating the effectiveness of the bisalt approach in stabilizing lithium metal anode, the precise impact of skeleton-constrained dual-anion ionogels on interface modulation remains somewhat obscured and deserves further attention. Herein, we formulate a Li6.4La3Zr1.4Ta0.6O12 (LLZTO)-incorporated dual-anion ionogel to reveal the solvation chemistry in the presence of LLZTO and detail the Li+ transport mechanism and effect on the interfacial chemistries of Li-metal. The impact of inorganic substances on the solvation structure in IL-based solid electrolytes and their role in forming the SEI layer on lithium metal was unveiled. To be specific, the introduction of fillers exert a selective modulating influence on the anions species in the Li+-solvated shell and fine-tunes the local Li+ environment, thereby fostering a more robust interfacial layer. Modified ion environment in ionogels enables a preferable shift from vehicular to structural Li+ transport, whereby a high Li ion conductivity (1.24×10−3 S/cm) and high Li ion transference number of 0.42 is achieved. The synergistic solvent coordination and adjustment of the electrode-electrolyte interface enable the LiFePO4|PIL-10|Li cells to cycle steadily with capacity retention of 95.4 % after 500 cycles at 1C and 25 °C. The strategy of promoting transport mechanisms holds promise for designing the next-generation solid-state lithium metal batteries with high energy density.

Design a polymer-based composite electrolyte with high ionic conductivity for high-performance lithium-metal batteries

Constructing a stable and robust solid polymer electrolyte (SPE) is crucial for achieving dendrite-free lithium-metal anodes and high-performance lithium batteries. However, realizing the integrity of solid electrolytes with high ion conductivity during long-life cycling under high current density remains a significant challenge. In this study, we propose a multifunctional SPE with a polyvinylidene fluoride (PVDF)/co-polyphenol coordination polymer (EACo2) hybrid composite to improve the durability of Li metal anode during repeat plating/stripping cycles by using a facile solution-casting method. The PVDF as a substrate with high mechanical strength and improved lithiophilicity exhibits high ionic conduction and excellent dendrite inhibition ability; meanwhile, the EACo2 fillers with a high density of Lewis-acidic sites contribute to the dissociation of lithium salts and decrystallization of the PVDF, resulting in a high Li-ion transference number and ion conductivity (2.66 × 10−3 S cm−1 at 30 ℃). The symmetrical cells with PVDF/EACo2 SPE can stabilize cycling over 1200 hours at a deposition capacity of 0.1 mAh cm−2. Moreover, the assembled full cells Li|LiFePO4 demonstrate long-term stability (1000 cycles at 1 C) with impressive capacity retention of 75 %, offering a promising approach towards high-performance lithium metal batteries.

Lithium Salt Combining Fluoroethylene Carbonate Initiates Methyl Methacrylate Polymerization Enabling Dendrite‐Free Solid‐State Lithium Metal Battery

This work demonstrates a novel polymerization‐derived polymer electrolyte consisting of methyl methacrylate, lithium bis(trifluoromethanesulfonyl)imide and fluoroethylene carbonate. The polymerization of MMA was initiated by the amino compounds following an anionic catalytic mechanism. LiTFSI plays both roles including the initiator and Li ion source in the polymer electrolyte. Normally, lithium bis(trifluoromethanesulfonyl)imide has difficulty in initiating the polymerization reaction of methyl methacrylate monomer, a very high concentration of lithium bis(trifluoromethanesulfonyl)imide is needed for initiating the polymerization. However, the fluoroethylene carbonate additive can work as a supporter to facilitate the degree of dissociation of lithium bis(trifluoromethanesulfonyl)imide and increase its initiator capacity due to the high dielectric constant. The as‐prepared poly‐methyl methacrylate‐based polymer electrolyte has a high ionic conductivity (1.19 × 10−3 S cm−1), a wide electrochemical stability window (5 V vs Li+/Li), and a high Li ion transference number () of 0.74 at room temperature (RT). Moreover, this polymerization‐derived polymer electrolyte can effectively work as an artificial protective layer on Li metal anode, which enabled the Li symmetric cell to achieve a long‐term cycling performance at 0.2 mAh cm−2 for 2800 h. The LiFePO4 battery with polymerization‐derived polymer electrolyte‐modified Li metal anode shows a capacity retention of 91.17% after 800 cycles at 0.5 C. This work provides a facile and accessible approach to manufacturing poly‐methyl methacrylate‐based polymerization‐derived polymer electrolyte and shows great potential as an interphase in Li metal batteries.

Aliphatic Hyperbranched Polycarbonates Solid Polymer Electrolytes with High Li-Ion Transference Number for Lithium Metal Batteries.

In this work, hyperbranched polycarbonate-poly(ethylene oxide) (PEO)-based solid polymer electrolytes (HBPC-SEs) are successfully synthesized via a straightforward organo-catalyzed "A1"+"B2"-ring-opening polymerization approach. The temperature-dependent ionic conductivity of HBPC-SEs, composed of different polycarbonate linkages and various LiTFSI concentrations, is investigated. The results demonstrate that HBPC-SE with an ether-carbonate alternating structure exhibits superior ionic conductivity, attributed to the solubility of Li salts in the polymer matrix and the mobility of the polymer segments. The HBPC1-SE with 30 wt% LiTFSI presents the highest ionic conductivities of 2.15 × 10-5, 1.78 × 10-4, and 6.07 × 10-4 Scm-1 at 30, 60, and 80 °C, respectively. Compared to traditional PEO-based electrolytes, the incorporation of polycarbonate segments significantly enhances the electrochemical stability window (5V) and Li+ transference number (0.53) of HBPC-SEs. Furthermore, the LiFePO4/HBPC1-SE-3/Li cell exhibits exceptional rate capability and long-cycling performance, maintaining a discharge capacity of 130 mAh g-1 at 0.5C with a capacity retention of 95% after 300 cycles.

Accelerated Single Li-Ion Transport in Solid Electrolytes for Lithium-Sulfur Batteries: Poly(Arylene Ether Sulfone) Grafted with Pyrrolidinium-Terminated Poly(Ethylene Glycol).

Polymeric solid electrolytes have attracted tremendous interest in high-safety and high-energy capacity lithium-sulfur (Li─S) batteries. There is, however, still a dilemma to concurrently attain high Li-ion conductivity and high mechanical strength that effectively suppress the Li-dendrite growth. Accordingly, a rapidly Li-ion conducting solid electrolyte is prepared by grafting pyrrolidinium cation (PYR+)-functionalized poly(ethylene glycol) onto the poly(arylene ether sulfone) backbone (PAES-g-2PEGPYR). The PYR+ groups effectively immobilize anions of Li-salts in Li-conductive PEGPYR domains phase-separated from PAES matrix to enhance the single-ion conduction. The tailored PAES-g-2PEGPYR membrane shows a high Li-ion transference number of 0.601 and superior ionic conductivity of 1.38mScm-1 in the flexible solid state with the tensile strength of 1.0MPa and Young's modulus of 1.5MPa. Moreover, this PAES-g-2PEGPYR membrane exhibits a high oxidation potential (5.5V) and high thermal stability up to 200(C. The Li/PAES-g-2PEGPYR/Li cell stably operates for 1000h without any short circuit, and the rechargeable Li/PAES-g-2PEGPYR/S cell discharges a capacity of 1004.7mAhg-1 at C/5 with the excellent rate capability and the prominent cycling performance of 95.3% retention after 200 cycles.

Ultra-thin SiO2 nanoparticle layered separators by a surface multi-functionalization strategy for Li-metal batteries: Highly enhanced Li-dendrite resistance and thermal properties

Mechanical and thermal failure of a polyolefin separator often causes the internal short-circuit of batteries, which leads to abrupt heat generation in a short time, so-called thermal runaway. For this, we introduce grafting polymer layers with cross-linking to make a superior, thin, and uniform SiO2 layer with strong chemical binding to the surface of a polypropylene separator (PPS). The surface of the PPS was modified with i) coating of double bond-contained PVDF, ii) grafting with poly(ethylene glycol) methacrylate, 3-(trimethoxysilyl)propyl methacrylate, and ethylene glycol dimethacrylate, and iii) coating with SiO2 nanoparticles via immersing (GDPS-SNPI) or casting (GDPS-SNPC) methods. The pore structure and distribution, electrolyte affinity, thermal stability, and mechanical properties were progressively improved after respective modification steps. The GDPS-SNPC cell shows excellent capacity retention of 100% at 1 C after 100 cycles and the lowest increase in the cell impedance, whereas the LFP half-cell with PPS exhibited capacity retention of 88.32%. Furthermore, it is found that the coating method for SiO2 nanoparticles substantially influences the long-term cycling stability of Li-symmetric cells. The GDPS-SNPC cell survived after cycling over 1,000 h at a current density of 1 mA cm−2, whereas the GDPS-SNPI cell died before 500 h. Post-mortem analysis of the cycled Li-metal surface shows that smooth Li-plating occurred at the GDPS-SNPC cell, presumably due to a high Li-ion transference number. This work provides a solid methodology for producing a novel and robust separator and advances the understanding of separators' impact on electrochemical and physical phenomena within the cell.

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.

Interfacially-enhanced quasi-solid electrolyte using ionic liquid for lithium-ion battery

Solid-state electrolytes (SEs), promising alternatives to liquid electrolytes (LEs), have their own pros and cons, necessitating exploring combined systems to achieve optimal performance. However, several issues occur due to the poor interface between combined SEs. Herein, Li7La3Zr2O12 (LLZO) inorganic SE and PVDF-HFP (poly(vinylidene fluoride-co-hexafluoropropylene)) solid polymer electrolyte are combined with the ionic liquid BMIM-TFSI (1-Butyl-3-methylimidazoliumbis-(trifluoromethylsulfonyl)imide) to obtain quasi-solid electrolyte (QSE) via a facile method. This study reveals that BMIM-TFSI in PVDF-HFP acts as a plasticizer and has an important role in covering LLZO particles for the properly formed interface between inorganic SE particles and solid polymer electrolyte. Thanks to the well-built interface, the QSE exhibits a high Li-ion transference number (tLi+), good ionic conductivity, and outstanding cycling performance, including a high capacity of 140 mAh g− 1 and stable Coulombic efficiency. Therefore, QSE has high potential as a next-generation SE for lithium batteries with its good electrochemical properties and simple fabrication process.

Single-Ion Conductive Polymer-Based Composite Electrolytes for High-Performance Solid-State Lithium Metal Batteries.

Flexible composite polymer electrolytes (CPEs) with inorganic electrolyte fillers dispersed in polymer electrolytes integrate the merits of the polymer and inorganic electrolytes and have attracted much attention in recent years. In order to increase the electrochemical performance, especially the low lithium (Li)-ion transference number in traditional dual-ion Li salt-containing CPEs, single-ion conductive CPEs are synthesized with a single-ion polymer conductor (SIPC) as the matrix and Li6.4 La3 Zr1.4 Ta0.6 O12 (LLZTO) particles as the active fillers. The single-ion conductive CPEs show a high Li-ion transference number (up to 0.96), high room-temperature (RT) ionic conductivity (>1.0 × 10-4 S cm-1 ), wide electrochemical stability window (>5.0V, vs Li/Li+ ), and excellent long-term cycling stability with Li metal at RT (3200h). Based on the SIPC-LLZTO CPE, the solid-state lithium metal batteries with LiFePO4 - and LiCoO2 -based cathodes deliver average discharge capacities of 159 mAh g-1 for 600 cycles and 119 mAh g-1 for 200 cycles at RT, respectively. This study sheds light on the design of high-performance CPEs for next-generation solid-state lithium metal batteries.

Highly conductive and mechanically robust single-ion conducting polymer electrolyte membranes with a high concentration of charge carriers for dendrite-proof lithium metal batteries

Single-ion polymer electrolytes (SIPEs) with high Li-ion transference number (tLi+≈1) are promising candidates for inhibiting the growth of lithium dendrites in lithium metal batteries (LMBs). However, it remains challenging to develop SIPEs applicable to high-performance LMBs due to their relatively low ionic conductivity and poor mechanical strength. Herein, an aromatic single-ion conductor (LiPSBI) with high Li-ion concentration is elaborately designed, yielding porous and mechanically robust SIPE membranes (NSIPM) when mixed with aliphatic poly (vinylidene fluoride-hexafluoropropylene) P(VDF-HFP) binder via “structural self-assembly” method. As expected, the as-prepared NSIPM porous membranes can simultaneously exhibit a high porosity of 41.4%, a considerable organic solvent uptake of 181.0%, and excellent mechanical strength of 20.5 MPa. Notably, the LiPSBI-based gel NSIPM demonstrates an ionic conductivity of 8.15 × 10−5 S cm−1 at 25 °C, which is almost twice that of the single-ion electrolyte with low Li-ion concentration (4.74 × 10−5 S cm−1). Consequently, the Li||LiFePO4 cells using the gel NSIPM display remarkable cycling durability for several hundred cycles while delivering high discharge specific capacities of 148.4 mA h g−1 and 122.9 mA h g−1 at 0.2C and 1 C, respectively. In addition, the Li/Li symmetric cells assembling the gel NSIPM can effectively alleviate concentration polarization and inhibit the lithium dendrites growth, which is responsible for an exceptionally steady striping/plating process with a low overpotential over 1300 h at 2.5 mA cm−1 at 25 °C. This work provides a new strategy to prepare high-performance SIPEs by increasing the concentration of charge carriers.

In-Situ Plasticized LLZTO-PVDF Composite Electrolytes for High-Performance Solid-State Lithium Metal Batteries

Solid polymer electrolytes (SPEs) are seen as the key component in the development of solid-state lithium batteries (SSLBs) by virtue of their good processability and flexibility. However, poor mechanical strength, low room-temperature lithium-ion (Li-ion) conductivity and unsatisfactory interfacial compatibility with electrodes limit their practical application. In this work, a composite electrolyte consisting of polyvinylidene fluoride and polyvinylidene carbonate with a Li6.4La3Zr1.4Ta0.6O12(LLZTO) active filler (PFPC: LLZTO-SPE) is reported to achieve excellent ionic conductivity (4.25 × 10−4 S cm−1 at 30 °C), a wide electrochemical window (>4.6 V), a high Li-ion transference number (tLi+ = 0.49) and good interfacial compatibility with the electrode. Incorporating LLZTO as an active filler not only increases the ionic conductivity of the electrolyte, but also homogenizes Li-ion flux and stabilizes the electrode/electrolyte interface, thereby preventing lithium dendrites from piercing the electrolyte. As a result, Li/Li symmetrical cells using PFPC: LLZTO-SPEs deliver more than 800 h of cyclability at 0.1 mA cm−2 and a high critical current density (CCD) of 2.6 mA cm−2. The assembled Li/PFPC: LLZTO/LFP SSLBs achieve 87% capacity retention after 150 cycles at 0.2 C and 89% capacity retention for 100 cycles at 0.5 C. This work inspires new insights into designing high-performance SPEs.

Organoboron- and Cyano-Grafted Solid Polymer Electrolytes Boost the Cyclability and Safety of High-Voltage Lithium Metal Batteries.

Solid-state polymer electrolytes (SPEs) are deemed as a class of sought-after candidates for high-safety and high-energy-density solid-state lithium metal batteries, but their low ionic conductivity, narrow electrochemical windows, and severe interfacial deterioration limit their practical implementations. Herein, an organoboron- and cyano-grafted polymer electrolyte (PVNB) was designed using vinylene carbonate as the polymer backbone and organoboron-modified poly(ethylene glycol) methacrylate and acrylonitrile as the grafted phases, which may facilitate Li-ion transport, immobilize the anions, and enlarge the oxidation voltage window; therefore, the well-tailored PVNB exhibits a high Li-ion transference number (tLi+ = 0.86), a wide electrochemical window (>5 V), and a high ionic conductivity (σ = 9.24 × 10-4 S cm-1) at room temperature (RT). As a result, the electrochemical cyclability and safety of the Li|LiFePO4 and Li|LiNi0.8Co0.1Mn0.1O2 cells with in situ polymerization of PVNB are substantially improved by forming the stable organic-inorganic composite cathode electrolyte interphase (CEI) and the Li3N-LiF-rich solid electrolyte interphase (SEI).

Chloride-Reinforced Solid Polymer Electrolyte for High-Performance Lithium Metal Batteries.

Flexible solid-state polymer electrolytes (SPEs) enable intimate contact with the electrode and reduce the interfacial impedance for all-solid-state lithium batteries (ASSLBs). However, the low ionic conductivity and poor mechanical strength restrict the development of SPEs. In this work, the chloride superionic conductor Li2ZrCl6 (LZC) is innovatively introduced into the poly(ethylene oxide) (PEO)-based SPE to address these issues since LZC is crucial for improving the ionic conductivity and enhancing the mechanical strength. The as-prepared electrolyte provides a high ionic conductivity of 5.98 × 10-4 S cm-1 at 60 °C and a high Li-ion transference number of 0.44. More importantly, the interaction between LZC and PEO is investigated using FT-IR and Raman spectroscopy, which is conducive to inhibiting the decomposition of PEO and beneficial to the uniform deposition of Li ions. Therefore, a minor polarization voltage of 30 mV is exhibited for the Li||Li cell after cycling for 1000 h. The LiFePO4||Li ASSLB with 1% LZC-added composite electrolyte (CPE-1% LZC) demonstrates excellent cycling performance with a capacity of 145.4 mA h g-1 after 400 cycles at 0.5 C. This work combines the advantages of chloride and polymer electrolytes, exhibiting great potential in the next generation of all-solid-state lithium metal batteries.

Poly(Ether-Ester)-Based Solid Polymer Electrolytes with High Li-Ion Transference Number for High Voltage All-Solid-State Lithium Metal Batteries

Considering the lower room temperature ionic conductivity, Li-ion transference number, and narrow electrochemical stability window in all-solid-state polymer electrolytes (ASSPEs)-based lithium metal batteries (LMBs), it is of particular necessity to find plausible strategies to accomplish these issues. In this paper, poly(ε-caprolactone-co-1,5-dioxepan-2-one) (PDCL)-based poly(ether-ester) ASSPEs have been successfully fabricated by the random ring-opening polymerization of cyclic CL and DXO. The PDCL-SPE exhibits a high ion conductivity of 3.54 × 10–5 S cm–1 at 30 °C with a high Li-ion transference number (0.62) and a superior electrochemical stability (5.1 V). FT-IR spectra confirm the synergistic effect of ether and carbonyl of ester from the main chain of PDCL, which is superior to the dissociation of lithium salts and facilitation the motivation of lithium ions. Furthermore, the assembled LiFePO4/PDCL-SPE/Li batteries displayed low interfacial resistance, Li dendrite suppression, high specific capacity, and excellent cyclic performance (capacity retention of 85% after 200 cycles at 0.1 C). The high-voltage LiNi0.5Co0.2Mn0.3O2/PDCL-SPE/Li batteries also exhibits good cycling performance and durability.

Regulating Lithium Plating/Stripping Behavior by a Composite Polymer Electrolyte Endowed with Designated Ion Channels.

The urgent demand for high energy and safety storage devices is pushing the development of lithium metal batteries. However, unstable solid electrolyte interface (SEI) formation and uncontrollable lithium dendrite growth are still huge challenges for the practical use of lithium metal batteries. Herein, a composite polymer electrolyte (CPE) endowed with designated ion channels is fabricated by constructing nanoscale Uio66-NH2 layer, which has uniformly distributed pore structure to regulate reversible Li plating/stripping in lithium metal batteries. The regular channels within the Uio66-NH2 layer work as an ion sieve to restrict larger TFSI- anions inside its channels and extract Li+ across selectively, which result in a high Li-ion transference number ( ) of 0.6. Moreover, CPE provides high ion conductivity (0.245 mS cm-1 at room temperature) and expanded oxidation window (5.1V) and forms a stable SEI layer. As a result, the assembled lithium metal batteries with CPE exhibit outstanding cyclic stability and capacity retention. The Li/CPE/Li symmetric cell continues plating/stripping over 500h without short-circuiting. The Li/CPE/LFP cell delivers a reversible capacity of 149.3 mAh g-1 with a capacity retention of 99% after 100 cycles.

Bicontinuous-Structured Elastomeric Electrolytes for High-Energy Solid-State Lithium-Metal Batteries

The use of lithium (Li) metal anodes in solid-state batteries is a strong strategy as a next-generation battery technology for surpassing the energy density and safety of conventional Li-ion batteries. However, in practice, current solid-state electrolytes have been limited to realize Li metal batteries due to their insufficient electrochemical and mechanical properties. Here, we design a new class of elastomeric electrolytes having a 3D interconnected plastic-crystal phase within the elastomer matrix—plastic crystal-embedded elastomer electrolytes (PCEEs).1 To elucidate the effects of structural changes in PCEEs on Li-ion transport property, mechanical elasticity, and electrochemical performance, we investigate various phase-separated structures of PCEEs by adjusting each phase’s volume ratio. Among these structures, we reveal that bicontinuous-structured PCEE, consisting of an equal volume ratio of elastomer to plastic-crystal phase, is well-balanced to develop the efficient ion-conducting, plastic-crystal pathways within a mechanically robust, cross-linked elastomer matrix. Hence, this optimal PCEE shows a combination of high ionic conductivity (>10-3 S cm-1) at ambient temperature, high Li-ion transference number (>0.70), and good mechanical resilience (elongation at break ≈ 300%). A full cell configured with the optimized PCEE, a limited Li source, and a high loading LiNi0.83Mn0.6Co1.1O2 cathode delivers a high energy density exceeding 430 Wh kganode+cathode+electrolyte -1. Understanding the structure-property-electrochemical performance relationship of PCEE through structural control can form the basis of structure-controlled elastomeric electrolytes, holding substantial promise in various electrochemical energy storage systems.

A high power density solid electrolyte based on polycaprolactone for high-performance all-solid-state flexible lithium batteries

All-solid-state lithium batteries (ASSLBs) have been regarded as the next-generation battery technology owing to the superiority of safety, potentially high enetgy density and long cycling life. However, the slow charging limitations of ASSLBs hinder their practical applications. To tackle this issue, composite polymer electrolytes (CPEs) based on polycaprolactone (PCL) are developed to achieve satisfactroy enhancements for charging/discharging performances of ASSLBs. The addition of ceramic powder in PCL-based CPEs suppresses the crystallization of PCL and at the same time enhances the Li-ion transport behaivor. The present ASSLBs within PCL-based CPEs display excellent cycling performance with the initial discharge specific capacity of 108.2 mAh g-1, as well as good capacity retention of 75% after 500 cycles at a current density of 2 C at 55 °C. The high performance of ASSLBs is attributed to the high Li-ion transference number of 0.8 and excellent interfacial stability and wettability originated from the addition of ceramic components. It is demonstated that the PCL-based CPEs exhibit high Young's Modulus (2.8 GPa) and to the long-term cycling stability of ASSLBs. This study opens up new possibilities for the development of fast-charging batteries with an emphasis on the design of new polymer electrolytes.