High Lithium Ion Transference Number Research Articles

Synergistic Dual Electrolyte System of LATP and In‐ Situ Solod‐State PDOL System and its Improvement on the Performance of NCM811 Batteries

Abstract1,3‐Dioxolane (DOL) can undergo in‐situ polymerization in batteries to form solid‐state organic electrolyte PDOL. When applied to NCM811||Li battery system, PDOL electrolyte helps optimize the contact and interface stability between electrolyte and electrodes. This study explores the effects of PDOL with PE separators coated with Li1.3Al0.3Ti1.7(PO4)3(LATP) on the performance of NCM811||Li batteries. 2,2,2‐trifluoroethyl phosphite (DETFPi), was mixed with DOL at a 1 : 35 mass ratio. Then, LiBF4 was used to initiate in‐situ polymerization and thereby obtained DETFPi‐PDOL electrolyte after 24 h at room temperature. The composite electrolyte exhibits enhanced ion conductivity (1.59×10−4 S cm−1), high lithium ion transference number (0.78), wide electrochemical stability window (4.53 V), and high critical current density (2.2 mA cm−2). Li||PDOL@LATP||Li battery shows extremely low overpotential (35 mV) after a constant current stable cycle of 500 h at 1.0 mA cm−2. After 500 cycles at 1 C, the remaining capacity is 153.9 mAh g−1 with a capacity retention of 82.1 % in NCM811||PDOL@LATP||Li batteries. This indicates that the LATP coating on the surface of the PE separator plays an important role in optimizing the performance of DETFPI‐PDOL electrolyte batteries. LATP and DETFPI‐PDOL are effective in improving the cycling stability, rate performance, and interface state of NCM811 batteries.

Organic-Inorganic Dual-Network Composite Separators for Lithium Metal Batteries.

The suboptimal ionic conductivity of commercial polyolefin separators exacerbates uncontrolled lithium dendrite formation, deteriorating lithium metal battery performance and posing safety hazards. To address this challenge, a novel organic-inorganic composite separator designed is prepared to enhance ion transport and effectively suppress dendrite growth. This separator features a thermally stable, highly porous poly(m-phenylene isophthalamide) (PMIA) electrospun membrane, coated with ultralong hydroxyapatite (HAP) nanowires that promote "ion flow redistribution." The synergistic effects of the nitrogen atoms in PMIA and the hydroxyl groups in HAP hinder anion transport while facilitating efficient Li+ conduction. Meanwhile, the optimized unilateral pore structure ensures uniform ion transport. These results show that the 19µm-thick HAP/PMIA composite separator achieves remarkable ionic conductivity (0.68mS cm-1) and a high lithium-ion transference number (0.51). Lithium symmetric cells using HAP/PMIA separators exhibit a lifespan exceeding 1000h with low polarization, significantly outperforming commercial polypropylene separators. Furthermore, this separator enables LiFePO4||Li cells to achieve an enhanced retention of 97.3% after 200 cycles at 1C and demonstrates impressive rate capability with a discharge capacity of 72.7mAh g-1 at 15C.

In Situ Fabrication of Solvent-Free Solid Polymer Electrolytes for Wide-Temperature All-Solid-State Lithium Metal Batteries.

All-solid-state lithium metal batteries (ASSLMBs) have been regarded as promising candidates to settle the safety issues of liquid electrolytes for rechargeable lithium batteries. However, the currently reported gel polymer electrolytes still have flammable liquid solvents, thus leading to the potential safety hazard. Here, solvent-free deep eutectic solid polymer electrolytes (SPEs) are designed and fabricated via an in situ polymerization, which are composed of a poly(vinylidene fluoride-hexafluoropropylene) (PVDF-HFP) electrospun membrane, succinonitrile (SN), poly(ethylene glycol) diacrylate (PEGDA200, Mn = 200 g mol-1), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and lithium difluoro(oxalato)borate (LiDFOB). The deep eutectic solvent (DES) with SN/LiTFSI provides a superior room-temperature ionic conductivity, while the PEGDA200 precursor acts as cross-linking network to form SPEs under thermal initiation for free radical polymerization, and LiDFOB can form a stable solid electrolyte interface (SEI) layer. The PVDF-HFP electrospun membrane with a three-dimensional nanofibrous network structure for SN/PEGDA200/LiTFSI/LiDFOB SPEs exhibits a wide electrochemical stability window, high lithium-ion transference number, and good compatibility with the lithium metal anode. Furthermore, the obtained SPEs assembled with Li//LiMn0.6Fe0.4PO4, Li//LiFePO4, and Li//LiNi0.8Co0.1Mn0.1O2 asymmetric cells show excellent cycling performance and rate capability at a wide temperature. This strategy provides a promising path in designing high-energy-density ASSLMBs for practical application.

In situ construction of 3D crossing-linked gel polymer electrolyte toward high performance and safety lithium metal batteries

Our study focuses on developing high-performance gel polymer electrolytes (GPEs) tailored for lithium metal batteries (LMBs), harnessing the combined benefits of high conductivity of liquid electrolytes and the enhanced safety of solid electrolytes. To this end, we engineered an in situ polymerized GPE (PMIA- TP) that integrates trifluoroethyl methacrylate (TFMA) and pentaerythritol triacrylate (PETA) monomers within an electrospun poly (m-phthaloyl-m-phenylenediamine) (PMIA) supporting membrane. In addition to high ionic conductivity, high lithium ion transference number, enhanced tensile strength and good thermal stability, the resulting PMIA-TP GPE exhibits satisfactory electrochemical stability against lithium electrodes, enabling long-term and stable lithium plating/stripping in symmetric Li//Li cells, and good rate capability and prolonged cycle life for LiFePO4//Li cells. Further X-ray photoelectron spectroscopy analysis and density functional theory calculations revealed that the electrochemical stability of the PMIA-TP GPE towards lithium metal electrode is due to the formation of a fluorine-rich solid electrolyte interphase (SEI) layer facilitated by reactions involving the –CF3 groups in TFMA, which is beneficial for the effective Li+ transport and lithium dendrite suppression. In summary, our study offers a promising approach to fabricating GPEs that offer high safety and high performance for LMBs.

(Digital Presentation) Physical and Chemical Properties of Lithium Tetrachloroaluminate Monosolvate with Sulfur Dioxide

In connection with the expansion of the areas of application of lithium-ion batteries and the increase in their energy characteristics, researchers are increasingly paying attention to the problems of battery safety. The use of non-flammable electrolyte systems will significantly improve the safety of lithium-ion batteries.Electrolyte systems based on solvate complexes of sulfur dioxide have high electrical conductivity and are non-flammable [1]. The most studied composition is LiAlCl4 × 1.6 SO2 [1] and LiAlCl4 × 3 SO2 [2]. The properties of LiAlCl4 x SO2 monosolvate have not been described in the literature.The presented work summarizes the results of studies of the physicochemical properties (electrical conductivity, viscosity, density) of lithium tetrachloroaluminate monosolvate with sulfur dioxide (table). The temperature dependences of viscosity, density and electrical conductivity are presented in the figure.This work was performed as part of the Ministry of Science and Higher Education of the Russian Federation [Government Order Theme No. 121111900148-3]. References Hartl, R., Fleischmann, M., Gschwind, R., Winter, M., & Gores, H. (2013). A Liquid Inorganic Electrolyte Showing an Unusually High Lithium-Ion Transference Number: A Concentrated Solution of LiAlCl4 in Sulfur Dioxide. Energies, 6(9), 4448–4464. DOI:10.3390/en6094448Chul Wan Park, & Oh, S. M. (1997). Performances of Li/LixCoO2 cells in LiAlCl4 · 3SO2 electrolyte. Journal of Power Sources, 68(2), 338–343. DOI:10.1016/s0378-7753(97)02518-4 Figure 1

Regulating the Solvation Structure in Polymer Electrolytes for High‐Voltage Lithium Metal Batteries

AbstractSolid polymer electrolytes are promising electrolytes for safe and high‐energy‐density lithium metal batteries. However, traditional ether‐based polymer electrolytes are limited by their low lithium‐ion conductivity and narrow electrochemical window because of the well‐defined and intimated Li+‐oxygen binding topologies in the solvation structure. Herein, we proposed a new strategy to reduce the Li+‐polymer interaction and strengthen the anion‐polymer interaction by combining strong Li+‐O (ether) interactions, weak Li+‐O (ester) interactions with steric hindrance in polymer electrolytes. In this way, a polymer electrolyte with a high lithium ion transference number (0.80) and anion‐rich solvation structure is obtained. This polymer electrolyte possesses a wide electrochemical window (5.5 V versus Li/Li+) and compatibility with both Li metal anode and high‐voltage NCM cathode. Li||LiNi0.5Co0.2Mn0.3O2 full cells with middle‐high active material areal loading (~7.5 mg cm−2) can stably cycle at 4.5 V. This work provides new insight into the design of polymer electrolytes for high‐energy‐density lithium metal batteries through the regulation of ion‐dipole interactions.

Regulating the Solvation Structure in Polymer Electrolytes for High-Voltage Lithium Metal Batteries.

Solid polymer electrolytes are promising electrolytes for safe and high-energy-density lithium metal batteries. However, traditional ether-based polymer electrolytes are limited by their low lithium-ion conductivity and narrow electrochemical window because of the well-defined and intimated Li+-oxygen binding topologies in the solvation structure. Herein, we proposed a new strategy to reduce the Li+-polymer interaction and strengthen the anion-polymer interaction by combining strong Li+-O (ether) interactions, weak Li+-O (ester) interactions with steric hindrance in polymer electrolytes. In this way, a polymer electrolyte with a high lithium ion transference number (0.80) and anion-rich solvation structure is obtained. This polymer electrolyte possesses a wide electrochemical window (5.5 V versus Li/Li+) and compatibility with both Li metal anode and high-voltage NCM cathode. Li||LiNi0.5Co0.2Mn0.3O2 full cells with middle-high active material areal loading (~7.5 mg cm-2) can stably cycle at 4.5 V. This work provides new insight into the design of polymer electrolytes for high-energy-density lithium metal batteries through the regulation of ion-dipole interactions.

Highly Tough Slide-Crosslinked Gel Polymer Electrolyte for Stable Lithium Metal Batteries.

Gel polymer electrolytes (GPEs) hold great promise for the practical application of lithium metal batteries. However, conventional GPEs hardly resists lithium dendrites growth and maintains long-term cycling stability of the battery due to its poor mechanical performance. Inspired by the slide-ring structure of polyrotaxanes (PRs), herein we developed a dynamic slide-crosslinked gel polymer electrolyte (SCGPE) with extraordinary stretchability of 970.93 % and mechanical strength of 1.15 MPa, which is helpful to buffer the volume change of electrodes and maintain mechanical integrity of the battery structure during cycling. Notably, the PRs structures can provide fast ion transport channels to obtain high ionic conductivity of 1.73×10-3 S cm-1 at 30 °C. Additionally, the strong polar groups in SCGPE restrict the free movement of anions to achieve high lithium-ion transference number of 0.71, which is favorable to enhance Li+ transport dynamics and induce uniform Li+ deposition. Benefiting from these features, the constructed Li|SCGPE-3|LFP cells exhibit ultra-long and stable cycle life over 1000 cycles and high-capacity retention (89.6 % after 1000 cycles). Even at a high rate of 16 C, the cells deliver a high capacity of 79.2 mAh g-1. The slide-crosslinking strategy in this work provides a new perspective on the design of advanced GPEs for LMBs.

Amorphous Boron Nitride Nanosheet‐Based Solid State Electrolytes with High Ionic Conductivity

AbstractAmorphous boron nitride nanosheets, with natural electrical insulation, outstanding chemical stability and mechanical properties, are introduced as a matrix to be incorporated with lithium bis (trifluoromethanesulfonyl) imide (LiTFSI) and polymer polyvinylidene fluoride‐hexafluoropropylene copolymer (PVDF‐HFP), for constructing a novel composite solid‐state electrolyte by a simple solution‐casting method. Amorphous boron nitride nanosheets are produced via a combination method of ball milling and pure water exfoliation. The obtained composite solid‐state electrolyte containing 40 % (mass fraction) PVDF‐HFP shows a high lithium ion conductivity (1.936×10−3 S cm−1) and lithium ion transference number (0.47), and a wide electrochemical stability window (5 V) at room temperature. The LiFePO4/Li based all solid‐state battery, consisting of the composite solid electrolyte (40 % PVDF‐HFP), delivers a capacity of 128.1 mAh g−1, a Coulombic efficiency of 99.79 % after 500 cycles and a capacity retention rate of 94.5 % at 1.0 C and 25 °C. The composite solid electrolyte (40 % PVDF‐HFP) can maintain flat and stable stripping/plating plateaus for over 800 hours in symmetrical cells. The amorphous boron nitride nanosheets with high lithium ion conductivity are employed to construct solid‐state electrolytes, which is important significant for the development of high energy density, high safety, and long cycle life all‐solid‐state lithium‐ion batteries.

Across Interfacial Li+ Conduction Accelerated by a Single-Ion Conducting Polymer in Ceramic-Rich Composite Electrolytes for Solid-State Batteries.

Composite electrolytes have been accepted as the most promising species for solid-state batteries, exhibiting the synergistic advantages of solid polymer electrolytes (SPEs) and solid ceramic electrolytes (SCEs). Unfortunately, the interrupted Li+ conduction across the SPE and SCE interface hinders the ionic conductivity improvement of composite electrolytes. In our study on a ceramic-rich composite electrolyte (CRCE) membrane composed of borate polyanion-based lithiated poly(vinyl formal) (LiPVFM) and Li1.3Al0.3Ti1.7(PO4)3 (LATP) particles, it is found that the strong interaction between the polyanions in LiPVFM and LATP particles results in a uniform distribution of ceramic particles at a high proportion of 50 wt % and good robustness of the electrolyte membrane with a Young's modulus of 9.20 GPa. More importantly, ab initio molecular dynamics simulation and experimental results demonstrate that Li+ conduction across the SPE and SCE interface is induced by the polyanion-based polymer due to its high lithium-ion transference number and similar Li+ diffusion coefficient with the SCE. Therefore, the unblocked Li+ conduction among ceramic particles dominates in the CRCE membrane with a high ionic conductivity of 6.60 × 10-4 S cm-1 at 25 °C, a lithium-ion transference number of 0.84, and a wide electrochemical stable window of 5.0 V (vs Li/Li+). Consequently, the high nickel ternary cathode LiNi0.8Mn0.1Co0.1O2-based batteries with CRCE deliver a high-rate capability of 135.08 mAh g-1 at 1.0 C and a prolonged cycle life of 100 cycles at 0.2 C between 3.0 and 4.3 V. The polyanion-induced Li+ conduction across the interface sheds new light on solving composite electrolyte problems for solid-state batteries.

Solid polymer electrolytes regulated by ion-dipole interactions for high voltage lithium batteries

Solid polymer electrolytes (SPEs) with wide electrochemically stable window and high lithium-ion transference number (tLi+) are a requirement for high energy density lithium batteries. Here, we construct a copolymer electrolyte (PDA) with ether-ester bifunctional groups that exhibits a low highest occupied molecular orbital (HOMO) energy level by in situ polymerization. Compared to the poly(1,3-dioxolane) (PDOL) pure polyether electrolyte, the weakening of the ion-dipole interaction between lithium salt and polymer in the PDA electrolyte promotes the formation of a “weak solvation” structure. Therefore, the electrolyte achieves high oxidative stability (4.6 V vs. Li+/ Li with a standard leakage current of 10 μA), high Li+ transference number (0.60), and importantly, derives a stable LiF-rich composition on high voltage cathode surface. Which ultimately enables stable cycling of Li||LiNi0.5Co0.2Mn0.3O2 (NCM523) batteries at a range of 3.0–4.3 V. This work provides a fundamental understanding of the design of antioxidant SPEs to achieve high energy density lithium batteries.

Resolving electrochemical incompatibility between LATP and Li-metal using tri-layer composite solid electrolyte approaches for solid-state Li-metal batteries

Due to its excellent air stability, low cost, and high ionic conductivity, Li1.3Al0.3Ti1.7(PO4)3 (LATP) has emerged as a viable option for solid-state lithium batteries (SSLBs). However, the irreversible reactivity between LATP and the Li-metal anode severely restrict its electrochemical performances. Herein, a tri-layer composite solid electrolyte (t-CSE1) comprised of LATP, PVDF-HFP, SN, and LiTFSI as the middle layer and Al-LLZO, PVDF-HFP, SN, and LiTFSI as the top and bottom layers is prepared to solve these prominent limitations since Al-LLZO is stable towards Li metal anode. As a result, the lithium plating-stripping lifetimes for the Li||Li symmetry cell is prolonged from 550 to 1950 h at 0.1 mA cm−2 without any residual redox products. In addition, the as-prepared t-CSE1 exhibited excellent ionic conductivity (ca. 6.46 × 10−4 S cm−1 at room temperature), high lithium-ion transference number (ca. 0.69) and remarkable mechanical strength (ca. 12.82 MPa). Furthermore, the Li||LiFePO4 (Li||LFP) full cell achieved significantly improved long cycle performances of 500 cycles with 80.31 % capacity retention and 99.93 % average coulombic efficiency at 0.2C. Moreover, the Li||LFP full cell showed 85.53 % capacity retention and 99.95 % coulombic efficiency after 200 cycles at 0.5C at room temperature. Thus, this study gives an insight into how to prevent the electrochemical incompatibility between LATP and Li metal for SSLBs.

Fluorine-Doped Li7La3Zr2O12 Fiber-Based Composite Electrolyte for Solid-State Lithium Batteries with Enhanced Electrochemical Performance.

Garnet-based electrolytes with high ionic conductivity and excellent stability against lithium metal anodes are promising for commercial applications in solid-state lithium batteries (SSLBs). However, the further development of SSLBs is inhibited by issues such as low ionic conductivity and uncontrolled lithium dendrite growth. Herein, we report the synthesis of fluorine-doped Li7La3Zr2O12 (LLZO-F0.2) fibers by electrospinning and the subsequent calcination at high temperatures. The solid composite electrolyte with LLZO-F0.2 exhibits an ionic conductivity of 5.37 × 10-4 S cm-1 and a high lithium-ion transference number of 0.61 at room temperature. Meanwhile, it exhibits lower resistance and more uniform lithium metal stripping and deposition in symmetric cells. The full cell with LiFePO4 cathode exhibits excellent rate capability and cycling stability for 800 cycles at 0.5 C with a discharge specific capacity retention of 97.7%. This fluorine-doped fibrous garnet-type electrolyte provides a viable option for preparing high-performance SSLBs.

Halloysite nanotubes enhanced polyimide/oxidized-lignin nanofiber separators for long-cycling lithium metal batteries

The high energy density and robust cycle properties of lithium-ion batteries contribute to their extensive range of applications. Polyolefin separators are often used for the purpose of storing electrolytes, hence ensuring the efficient internal ion transport. Nevertheless, the electrochemical performance of lithium-ion batteries is constrained by its limited interaction with electrolytes and poor capacity for cation transport. This work presents the preparation of a new bio-based nanofiber separator by combining oxidized lignin (OL) and halloysite nanotubes (HNTs) with polyimide (PI) using an electrospinning technique. Analysis was conducted to examine and compare the structure, morphology, thermal characteristics, and EIS of the separator with those of commercially available polypropylene separator (PP). The results indicate that the PI@OL and PI-OL@ 10 % HNTs separators exhibit higher lithium ion transference number and ionic conductivity. Moreover, the use of HNTs successfully impeded the proliferation of lithium dendrites, hence exerting a beneficial impact on both the cycle performance and multiplier performance of the battery. Consequently, after undergoing 300 iterations, the battery capacity of LiFePO4|PI-OL@ 10 % HNTs|Li stays at 92.1 %, surpassing that of PP (86.8 %) and PI@OL (89.6 %). These findings indicate that this new bio-based battery separator (PI-OL@HNTs) has the great potential to serve as a substitute for the commonly used PP separator in lithium metal batteries.

Functionalized polypropylene separator coated with polyether/polyester blend for high-performance lithium metal batteries

Commercial polyolefin separators used in lithium metal batteries (LMBs) have the disadvantages of insufficient thermal stability and poor wettability with electrolytes, which causes bad safety and battery performance. Poly(ε-caprolactone) (PCL)-based electrolytes have drawn widespread attention in the field of polymer electrolytes owing to their electrochemical stability and high lithium-ion transference number. This work proposes a strategy of functionalizing commercial polypropylene (PP) separator coated by blending PCL (M w ~ 50,000) and poly(ethylene oxide) (PEO, M V ~ 600,000). Compared to commercial PP separators, PP-blended PEO60w/PCL5w separators possess better wettability with electrolytes and electrochemical performances. The initial discharge specific capacity of LiFePO4-based LMBs assembled with PP-blended PEO60w/PCL5w separators reaches 144 mAh g-1 (1C) and 103 mAh g-1 (5C) at room temperature, respectively. Notably, Li/PP-blended PEO60w/PCL5w/LiFePO4 shows an improved capacity retention rate of 77% after 800 cycles, confirming that the functionalized separator with coated PEO/PCL blend has great potential for application in the field of LMBs.

Coconstruction of Supramolecular Lithium-Conducting Cross-Linked Networks Based on PVDF and Triblock Polymer Nanomicrosphere Solid-State Polymer Electrolytes for Lithium-Metal Batteries.

Uneven lithium plating and low ionic conductivity currently impede the realization of high-capacity rechargeable lithium metal batteries. And the conventional poly(ethylene oxide) (PEO) solid-state electrolytes are unsuitable for high-energy-density Li anode applications due to their low lithium-ion transference number and high reactivity with Li metal, leading to detrimental dendrite formation and potentially hazardous exothermic reactions with the electrolyte. In this study, we employ a supramolecular approach to develop a novel polymer solid-state electrolyte based on poly(vinylidene fluoride) (PVDF) and a novel triblock polymer nanomicrosphere, (poly(ε-caprolactone)-poly(ethylene glycol)-poly(ε-caprolactone), (PCL-PEG-PCL). The abundance of carbonyl and ether-oxygen functional groups in PCL-PEG-PCL enhances the lithium coordination environment within the polymer solid-state electrolyte. Additionally, the original C-F moieties of PVDF form hydrogen bonds with C-H and terminal hydroxyl groups in PCL-PEG-PCL, collectively creating a multichannel fast Li+-conducting supramolecular cross-linked network. The resulting electrolyte demonstrates a high ionic conductivity of 1.4 × 10-3 S cm-1 and an extended electrochemical window of 5.2 V. Moreover, the electrolyte exhibits a high lithium-ion transference number (tLi+ = 0.63) at room temperature and exhibits excellent interfacial compatibility with the lithium metal anode. For the resulting electrolyte utilized in LiFePO4 batteries, the capacity retention of the cells assembled with this electrolyte exceeds 91.3% after 1000 cycles at 25 °C and 2 C (0.281 mA cm-2).

Polymer solid electrolytes with ultra-stable cycles and high-capacity retention for all-solid-state Li-metal battery

Polymer electrolytes have become widely popular on account of their low expenses, reduced weight, simple processing, and excellent safety features. However, polymer electrolytes have yet to find use in commercial batteries because of their limited mechanical durability and poor ionic conductivity. In this paper, an ultra-stable cycles and interfaces blending polymer electrolyte (BPE) suitable for all solid-state Li metal batteries was prepared by blending three polymers: polymethyl methacrylate (PMMA), polyvinylidene fluoride hexafluoropropylene (PVDF-HFP), and polyethylene oxide (PEO). Microstructure characterization showed numerous amorphous areas with strong interfacial strength of the BPE. The BPE3 exhibited a maximum of 15.65 MPa in tensile strength. BPE2 have excellent electrochemical performance, such as wide electrochemical windows (up to 4.7 V vs Li/Li+), high lithium ion transference numbers (up to 0.75), high ion conductivity (up to 1.87 × 10-4 S cm−1 at 60 °C), and excellent interface stability. By assembling all state-solid LiFePO4/BPE2/Li batteries for electrochemical testing, BPE2 exhibit high electrochemical characteristics. BPE2 discharge specific capacity is as high as 154.7 mAh g−1 at 1C. The BPE2 underwent 200 cycles at 0.5C and 400 cycles at 1C, with capacity retention rates of 95.7 % and 96.6 %, respectively. BPE is a promising electrolyte candidate for flexible lithium metal batteries.

Excellent Stable Cycle Performance of Polyethylene Oxide‐Based 3D Solid Dual‐Salt Composite Electrolyte with Porous Polyimide Thin Films Host

AbstractPolyethylene oxide composite electrolytes are widely used in lithium‐ion batteries because of their excellent moldability, good flexibility, and favorable chemical compatibility. However, they still suffer from low ionic conductivity and weak mechanical strength. Herein, a 3D nanofiber‐reinforced dual‐salt composite solid electrolyte (PI@PCB) is synthesized. Benefiting from the support of the porous polyimide films and the addition of lithium bis(oxalate)borate, the obtained PI@PCB electrolyte exhibits high mechanical strength, good thermal stability, excellent electrochemical stability, and a high lithium ion transference number (0.70). In addition, the assembled Li/PI@PCB/Li cell shows the lowest overpotential of 200 mV at the initial cycling stage and increases to 246 mV slightly after 1500 h. The capacity retention rate of Li/PI@PCB/LFP battery is about 88.3% after 500 cycles at 60 °C.

Covalent Organic Framework Enhanced Solid Polymer Electrolyte for Lithium Metal Batteries.

High ionic conductivity, outstanding mechanical stability, and a wide electrochemical window are the keys to the application of solid-state lithium metal batteries (LMBs). Due to their regular channels for ion transport and tailored functional groups, covalent organic frameworks (COFs) have been applied to solid electrolytes to improve their performance. Herein, we report a flexible polyethylene oxide-COF-LZU1 (abbreviated as PEO-COF) electrolyte membrane with a high lithium ion transference number and satisfactory mechanical strength, allowing for dendrite-free and long-time cycling for LMBs. Benefiting from the interaction between bis(triflfluoromethanesulonyl)imide anions (TFSI-) and aldehyde groups in COF-LZU1, the Li+ transference number of the PEO-5% COF-LZU1 electrolyte reached up to 0.43, much higher than that of neat PEO electrolyte (0.18). Orderly channels are conducive to the homogenous Li-+ deposition, thereby inhibiting the lithium dendrites. The assembled LiFePO4|PEO-5% COF-LZU1/Li cells delivered a discharge specific capacity of 146 mAh g-1 and displayed a capacity retention of 80% after 200 cycles at 0.1 C (60 °C). The Li/Li symmetrical cells of the PEO-5% COF-LZU1 electrolyte presented a longer working stability at different current densities compared to that of the PEO electrolyte. Therefore, the enhanced comprehensive performance of the solid electrolyte shows potential application prospects for use in LMBs.

Enhancement mechanism of the comprehensive performance of all-solid-state polymer electrolytes by halloysite nanotubes: Construction of efficient lithium-ion conduction channels

Considering the current issues with poly(ethylene oxide)-based all-solid-state polymer electrolytes (PEO-ASSPEs) employed in lithium-ion batteries (LIBs), such as low ionic conductivity, low lithium-ion transference number, narrow electrochemical stability window, and poor cyclic stability. This study introduces oxygen-vacancy-rich halloysite nanotubes (HNTs) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) into the PEO matrix to fabricate a flexible composite polymer electrolyte (CPEs) via a solvent-free method. The interaction between HNTs and LiTFSI in the PEO matrix serves to mitigate the ionic solvation effect, increase the number of free lithium-ion, and reduce the lithium-ion migration energy barrier. Additionally, the internal framework formed by the mutual stacking of HNTs reduces the number of entanglements in polymer molecular chains, enhances the mobility of the chains, and generates a continuous interface effect, forming fast lithium-ion transport channels. The CPEs prepared in this study are in conformity with the Vogel-Tammann-Fulcher (VTF) empirical equation. The CPE containing 10 wt% HNTs exhibits a high ionic conductivity (7.15 × 10−4 S cm−1) at 25 °C, a high lithium-ion transference number (0.600), a wide electrochemical stability window (5.5 V), and excellent cyclic performance (capacity retention of 82.02 % after 100 cycles at 0.1C), satisfying the electrochemical performance requirements for ASSPEs in LIBs.