Cross-linked Polymer Electrolyte Research Articles

Gel Polymer Electrolytes Based on Polymerizable Lithium Salt and Poly(ethylene glycol) for Lithium Battery Applications.

Here, a polymerizable lithium salt, lithium (trifluoromethanesulfonyl)(vinylsulfonyl)imide, was synthesized and used to prepare cross-linked gel polymer electrolyte systems with poly(ethylene glycol) methyl ether methacrylate as an ion-conducting moiety, poly(ethylene glycol) dimethacrylate as a cross-linker, and propylene carbonate as a liquid electrolyte without adding any conventional inorganic lithium salt. The gel polymer electrolytes prepared in this study exhibited a reasonably high ionic conductivity (6.7 × 10-4 S cm-1 at 25 °C and 1.8 × 10-3 S cm-1 at 60 °C) and lithium-ion transference number (0.52), and the lithium battery prepared using the gel polymer electrolyte showed a stable cycling performance over 50 cycles.

Bicontinuously crosslinked polymer electrolyte membranes with high ion conductivity and mechanical strength

Recently, safety has become an important issue for energy storage devices due to explosion and leakage of conventional liquid electrolytes. Traditional polymer electrolytes also have a strong dependence on the tradeoff relationship and do not exhibit sufficient ionic conductivity as a solid; thus, they are often used as a gel. We report the preparation of a highly ion-conductive, mechanically strong solid electrolyte membranes based on bicontinuously crosslinked polymer electrolytes for solid-state supercapacitors. The solid electrolyte membranes are synthesized in situ via facile ring-opening polymerization in the presence of a conductive ionic liquid without any solvents. The crosslinking structure is based on the reaction of the amines of the polyethylenimine oligomer with the epoxy groups of hydrophilic poly(ethylene glycol) diglycidyl ether and hydrophobic bisphenol A diglycidyl ether at 50 °C for 3 h. This unique structure endows the solid electrolyte membranes with high tensile strength as well as high ion conductivity (2.41 × 10−3 S cm−1 at 25 °C). All the membranes have good thermal stability and an amorphous phase in which the ionic species are uniformly distributed in the matrix. Upon application to solid-state supercapacitors based on carbon electrodes, a capacitance of 19.8 F g−1 at 2 mV s−1 is obtained, with an excellent capacitance retention and a coulombic efficiency close to 100% for 10,000 cycles. The solid electrolyte membrane has potential applications in structural supercapacitors and batteries, which require high mechanical strength.

Enabling high-areal-capacity all-solid-state lithium-metal batteries by tri-layer electrolyte architectures

All-solid-state lithium-ion batteries (ASSLiBs) with metallic lithium (Li) anode, ceramic-type solid-state electrolyte (SSE) and nickel (Ni)-rich cathode offer great promise to deliver high energy density and high safety. However, the low cathode material loading and poor metallic Li/SSE interface are two major challenges. Herein, we design a new tri-layer SSE structure to address the challenges. A porous three-dimensional (3D) Li1·5Al0.5Ge1.5(PO4)3 (LAGP) layer acts as a host for LiNi0·8Mn0·1Co0·1O2 (NCM811) cathode, a thin but dense LAGP layer is employed to conduct ions and block dendrite, and a cross-linked solid-state polymer electrolyte (SPE) of polyethylene glycol bis(amine)-triglycidyl isocyanurate is introduced to the NCM811/LAGP/metallic Li interfaces to ameliorate contact issues. Enabled by such structure, the cathode loading in 3D porous LAGP layer reaches 13 mg cm−2, and delivers a reversible areal capacity of 2.01 mAh cm−2 at 0.1 C and a capacity retention of 70% over 50 cycles, whereas the conventional two-dimensional (2D) electrode only gives a low areal capacity of 0.11 mAh cm−2 and undergoes a rapid capacity fading. The significantly enhanced performance is ascribed to the continuous SSE structure and SSE/electrode interfacial compatibility. Our methodology on SSE construction design can provide a new strategy to develop the ASSLiBs with high energy density.

Understanding the Effect of UV-Induced Cross-Linking on the Physicochemical Properties of Highly Performing PEO/LiTFSI-Based Polymer Electrolytes.

We report a thorough, multitechnique investigation of the structure and transport properties of a UV-cross-linked polymer electrolyte based on poly(ethylene oxide), tetra(ethylene glycol)dimethyl ether (G4), and lithium bis(trifluoromethane)sulfonimide. The properties of the cross-linked polymer electrolyte are compared to those of a non-cross-linked sample of same composition. The effect of UV-induced cross-linking on the physico/chemical characteristics is evaluated by X-ray diffraction, differential scanning calorimetry, shear rheology, 1H and 7Li magic angle spinning nuclear magnetic resonance (NMR) spectroscopy, 19F and 7Li pulsed field gradient stimulated echo NMR analyses, electrochemical impedance spectroscopy, and Fourier transform Raman spectroscopy. Comprehensive analysis confirms that UV-induced cross-linking is an effective technique to suppress the crystallinity of the polymer matrix and reduce ion aggregation, yielding improved Li+ transport number (>0.5) and ionic conductivity (>0.1 mS cm?1) at ambient temperature, by tailoring the structural/morphological characteristics of the polymer matrix. Finally, the polymer electrolyte allows reversible operation with stable profile for hundreds of cycles upon galvanostatic test at ambient temperature of LiFePO4-based lithium-metal cells, which deliver full capacity at 0.05 or 0.1C current rate and keep high rate capabilities up to 1C. This enforces the role of UV-induced cross-linking in achieving excellent electrochemical characteristics, exploiting a practical, easy up-scalable process.

One-pot synthesis of crosslinked polymer electrolyte beyond 5V oxidation potential for all-solid-state lithium battery

A new crosslinked copolymer electrolyte is prepared with a simply method. The optimal electrolyte presents a maximum conductivity of 1.15 × 10−4 S cm−1 at 60 °C. Especially, this new electrolyte presents an outstanding electrochemical stability not only for a wide electrochemical window (0–5.1 V) but also for a long–term compatibility with the Li metal. Due to electrochemical stability, LiMn0.2Fe0.8PO4 is selected as cathode material cycling between 3 V and 4.25 V. Moreover, a convenient integration method is used in this work to enhance the interfacial contact between cathode and electrolyte. Finally, the all-solid-state battery LiMn0.2Fe0.8PO4/Li shows a maximum capacity of 161.1 mAh g−1 and an excellent capacity retention ratio of 94.5% after 100 cycles. This new crosslinked polymer electrolyte may provide useful insights for introducing high voltage cathode material rather than LiFePO4 only into solid polymer electrolytes system.

Synthesis of Single Lithium-Ion Conducting Polymer Electrolyte Membrane for Solid-State Lithium Metal Batteries

Synthesis of single lithium-ion conducting polymer electrolyte membrane (SLIC-PEM) composed of polymerized lithium 4-styrenesulfonyl(trifluoromethylsulfonyl)imide (PLiSTFSI), poly(ethylene glycol) methyl ether methacrylate (PEGM), poly(ethylene glycol) dimethacrylate (PEGDMA), and ethylene carbonate (EC) is reported. SLIC-PEM combines the advantages of single lithium-ion conducting polymer electrolytes, cross-linked flexible polymer electrolytes, and the liquid electrolyte of carbonate. The synthesized SLIC-PEMs have superior thermostability, high ionic conductivity, a wide electrochemical window, and high lithium-ion transference number. The corresponding LiFePO4|SLIC-PEM|Li cell delivers high Coulombic efficiency and excellent discharge capacity and cycling performance, demonstrating that SLIC-PEMs will have promising application in next-generation safe lithium metal batteries.

Free-standing polydimethylsiloxane-based cross-linked network solid polymer electrolytes for future lithium ion battery applications

A series of cross-linked network solid polymer electrolytes based on dual end-functionalized polydimethylsiloxane bearing reactive thiol terminal groups with poly(ethylene glycol) diglycidyl ether and pentaerythritol tetrakis(3-mercaptopropionate) have been synthesized and characterized. The obtained results can be briefed as: ionic conductivity in the range of 1.5 × 10−6 S cm−1 at room temperature to 1.6 × 10−4 S cm−1 at 90 °C, lithium ion transference number ranged from 0.15 to 0.20, electrochemical window up to 5.3 V (vs. Li+/Li), thermal resistance (Td5ca. 254.5 °C), and tensile strength (ca. 1.6 MPa at max.). The interplay taking place between structure and physico-electrochemical properties of in these systems based on merits of poly(ethylene glycol) moieties as high solvation matrix for Li+ ions flexible along with smooth solid support from polydimethylsiloxane allow the tailoring of the design of polymer electrolytes for future all-solid-state lithium batteries.

UV-Cross-Linked Composite Polymer Electrolyte for High-Rate, Ambient Temperature Lithium Batteries

We report an innovative cross-linked composite polymer electrolyte (CPE) based on the garnet-type ceramic super Li+ ion conductor, Li7La3Zr2O12 (LLZO), that is encompassed in a supersoft poly(ethylene oxide)/tetraglyme matrix. UV-induced, facile and solvent-free cross-linking process ensures flexible and self-standing CPEs, which are nonflammable and perfectly shape-retaining under thermal/mechanical stress. The CPEs exhibit high ionic conductivity, exceeding 0.1 mS cm–1 at 20 °C, suitable for ambient and subambient temperature operation. Lab-scale lithium metal polymer cells assembled with LiFePO4-based composite cathode and the optimized CPE deliver full capacity at low current rates and outstanding specific discharge capacity of 115 mAh g–1 at 1C rate and ambient temperature. Remarkably, the lithium metal cell can run for hundreds of galvanostatic cycles (>400) with low overpotential, limited fading, and excellent Coulombic efficiency (>99%), which postulates the practical application of the newly deve...

UV-curable boron nitride nanosheet/ionic liquid-based crosslinked composite polymer electrolyte in lithium metal batteries

Crosslinked polymer electrolyte (CPE) and composite polymer electrolyte are two of the most promising polymer electrolyte (PE) systems for improving the resistance to Li dendrite growth, but the trade-off and agglomerated effects of these PEs hinder the development of safe Li metal battery (LMB). Herein, a new class of crosslinked composite polymer electrolyte (CCPE) with the combination of confined ionic liquid (IL) polymer network and homogeneously dispersed boron nitride nanosheet (BNNS) for LMB is reported. This UV-curable CCPE is formed on electrode via in-situ crosslinking of a precursor solution in a rapid and solvent-free step, and the assembly process of LMBs and interfacial contact/adhesion are maximum optimized. The critical point of this CCPE is that a facile channel for Li+ transfer and a robust skeleton for confining IL and strengthening interface are simultaneously achieved via the introduction of network structure and 2D BNNS in PE. Consequently, the LiFePO4ǀLi batteries involving CCPE show a great improvement in the charge-discharge cycling stability and rate performance compared with those of the cells with pure CPE. This study offers an effective and facile strategy for fabricating dendrite-resistant CCPE with potential applicability in next-generation energy storage systems.

High-performance binary cross-linked alkaline anion polymer electrolyte membranes for all-solid-state supercapacitors and flexible rechargeable zinc–air batteries

A high-performance binary cross-linked alkaline anion polymer electrolyte membrane was fabricated for energy storage and conversion devices.

Investigation of Mechanical and Electrochemical Performance of Multifunctional Carbon-Fiber Reinforced Polymer Composites for Electrical Energy Storage Applications

Concept of structural supercapacitors, based on carbon fiber reinforced polymer composites, has been introduced that can act as a structural load bearing component as well as an electrical energy storing device simultaneously. This multifunctional carbon fiber reinforced structural supercapacitors are fabricated by using carbon fiber and glass fiber/filter paper as reinforcements and cross-linked polymer electrolyte as a matrix. Carbon fiber mats also simultaneously serve the role of electrodes in addition to reinforcements whereas the glass fiber mat/filter paper also acts as an insulator to avoid the short-circuiting of the carbon fiber electrodes. A polymer epoxy matrix is modified by introducing ions within the cross-linked structure in order to develop an optimized polymer electrolyte. Flexural tests of structural supercapacitor are conducted to evaluate the structural performance while charge/discharge tests are conducted to evaluate the electrochemical performance. Multifunctional structural supercapacitors are tested mechanically as well as electrochemically. A structural supercapacitor is fabricated showing simultaneously an energy density of 0.11 mWh m-3, a specific capacitance of 0.8 mF.cm-3 and a flexural modulus of 26.6 GPa simultaneously.

A borate-rich, cross-linked gel polymer electrolyte with near-single ion conduction for lithium metal batteries

A borate-rich polymer electrolyte with near-single ion conduction and a stable solid electrolyte interphase for high performance lithium metal batteries.

Influence of Al2O3 Nanowires on Ion Transport in Nanocomposite Solid Polymer Electrolytes

Understanding the ion transport mechanism in nanocomposite solid polymer electrolytes is necessary to develop next-generation electrochemical devices. We investigate the role of inorganic nanoparticle on ion conduction and segmental dynamics in cross-linked epoxy-based nanocomposite solid polymer electrolytes, complexed with Li+F3CSO2NSO2CF3– (LiTFSI) salt and Al2O3 nanowire, using dielectric relaxation spectroscopy. The addition of Al2O3 not only increases the ionic conductivity σDC by up to ∼10 times but also accelerates the segmental α motion compared to the host electrolyte. Increasing Al2O3 content leads to a reduction in segmental α relaxation temperature Tα (fast dynamics), resulting in increased ion mobility as well as an enhancement in segmental α relaxation strength Δeα, lowering ion dissociation energy, as revealed by density functional theory calculations, thereby providing more mobile ions for conduction. This ion transport investigation provides insights into the design of high-conductivity ...

Cross-linked polymer electrolyte and its application to lithium polymer battery

Cross-linked solid polymer electrolytes (cross-linked SPEs) composed of poly(ethylene glycol) dimethyl ethers (PEGDMEs) with various molecular weights and high molecular weight poly(ethylene oxide) (PEO), Acryl-HBP having various ethylene oxide (EO) units (3EO (n = 3), 4EO (n = 4), 6EO (n = 6), 11EO (n = 11)), and LiN(SO2CF3)2 salt were prepared by using radical initiator and electron beam (EB) irradiation. The effects of molecular weights of PEGDMEs and PEO, EO units in the Acryl-HBP, crosslinking methods, and EB irradiation intensity on the ionic conductivity and mechanical property for the cross-linked SPEs were investigated. Ionic conductivities of the cross-linked SPEs composed of Acryl-HBP having 4EO (n = 4) units and PEGDME with molecular weight of 500 were found to be 1.24 × 10−4 S/cm at 20 °C and 1.97 × 10−3 S/cm at 80 °C for benzoyl peroxide radical initiator and to be 2.44 × 10−4 S/cm at 20 °C and 3.22 × 10−3 S/cm at 80 °C for EB irradiation, respectively. Further addition of a copolymer (EO-AGE) of ethylene oxide with allyl glycidyl ether improved mechanical properties of the cross-linked SPE, and provided mechanical strength suitable for practical lithium battery application. The Li4Ti5O12/cross-linked SPE/LiFePO4–C cell was assembled by using the cross-linked SPE modified with EO-AGE, and the battery performance was evaluated. The battery showed reversible charge-discharge capacity of 42 mAh at 25 °C and C/10 rate.

A porous cross-linked gel polymer electrolyte separator for lithium-ion batteries prepared by using zinc oxide nanoparticle as a foaming agent and filler

In this work, a new porous cross-linked membrane is prepared and used as the separator for rechargeable lithium-ion batteries. The inorganic zinc oxide nanoparticle (nano-ZnO) was added as a pore-forming agent and filler to the preparation process of membranes composed of poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP) and a cross-linked polymer by the copolymerization from poly(ethylene glycol methyl ether methacrylate) (PEGMEMA), methyl methacrylate (MMA) and octavinyl-T8-silsesquioxane (OVPOSS). The prepared membrane was firstly swollen by propylene carbonate (PC) and nano-ZnO was then eluted by hydrochloric acid to form the microporous structure. The effects of particle size and additive amount of nano-ZnO on the mechanical and electrochemical properties of microporous membranes were studied. SEM analysis showed that 30 nm nano-ZnO was the most suitable diameter for forming microporous structure. It is generally considered that the ionic conductivity is inversely correlated with the mechanical strength of separator. In our research, we have found that 18% addition of nano-ZnO was the most appropriate amount for the preparation of a microporous membrane (CRZ18) with an ionic conductivity of 1.4 mS cm−1 and a tensile strength of 10.7 MPa. Meanwhile, the LiFePO4/Li half-cell assembled with the CRZ18 membrane as a separator exhibited the best C-rate capacity and cycle charge-discharge performance, indicating that the CRZ18 membrane would be a kind of promising separator for the high-performance lithium-ion batteries.

High-Performance All-Solid-State Polymer Electrolyte with Controllable Conductivity Pathway Formed by Self-Assembly of Reactive Discogen and Immobilized via a Facile Photopolymerization for a Lithium-Ion Battery.

All-solid-state polymer electrolytes (SPEs) have aroused great interests as one of the most promising alternatives for liquid electrolyte in the next-generation high-safety, and flexible lithium-ion batteries. However, some disadvantages of SPEs such as inefficient ion transmission capacity and poor interface stability result in unsatisfactory cyclic performance of the assembled batteries. Especially, the solid cell is hard to be run at room temperature. Herein, a novel and flexible discotic liquid-crystal (DLC)-based cross-linked solid polymer electrolyte (DLCCSPE) with controlled ion-conducting channels is fabricated via a one-pot photopolymerization of oriented reactive discogen, poly(ethylene glycol)diacrylate, and lithium salt. The experimental results indicate that the macroscopic alignment of self-assembled columns in the DLCCSPEs is successfully obtained under annealing and effectively immobilized via the UV photopolymerization. Because of the existence of unique oriented structure in the electrolytes, the prepared DLCCSPE films exhibit higher ionic conductivities and better comprehensive electrochemical properties than the DLCCSPEs without controlled ion-conductive pathways. Especially, the assembled LiFePO4/Li cells with oriented electrolyte show an initial discharge capacity of 164 mA h g-1 at 0.1 C and average specific discharge capacities of 143, 135, and 149 mA h g-1 at the C-rates of 0.5, 1, and 0.2 C, respectively. In addition, the solid cell also shows the first discharge capacity of 124 mA h g-1 (0.2 C) at room temperature. The outstanding cell performance of the oriented DLCCSPE should be originated from the macroscopically oriented and self-assembled DLC, which can form ion-conducting channels. Thus, combining the excellent performance of DLCCSPE and the simple one-pot fabricating process of the DLC-based all-solid-state electrolyte, it is believed that the DLC-based electrolyte can be one of the most promising electrolyte materials for the next-generation high-safety solid lithium-ion batteries.

Cross-Linked Nanohybrid Polymer Electrolytes With POSS Cross-Linker for Solid-State Lithium Ion Batteries.

A new class of freestanding cross-linked hybrid polymer electrolytes (HPEs) with POSS as the cross-linker was prepared by a one-step free radical polymerization reaction. Octavinyl octasilsesquioxane (OV-POSS) with eight functional corner groups was used to provide cross-linking sites for the connection of polymer segments and the required mechanical strength to separate the cathode and anode. The unique cross-linked structure offers additional free volume for the motion of EO chains and provides fast and continuously interconnected ion-conducting channels along the nanoparticles/polymer matrix interface. The HPE exhibits the highest ionic conductivity of 1.39 × 10−3 S cm−1, as well as excellent interfacial compatibility with the Li electrode at 80°C. In particular, LiFePO4/Li cells based on the HPE deliver good rate capability and long-term cycling performance with an initial discharge capacity of 152.1 mAh g−1 and a capacity retention ratio of 88% after 150 cycles with a current density of 0.5 C at 80°C, demonstrating great potential application in high-performance LIBs at elevated temperatures.

Multifunctional structural lithium ion batteries for electrical energy storage applications

Multifunctional structural batteries based on carbon fiber-reinforced polymer composites are fabricated that can bear mechanical loads and act as electrochemical energy storage devices simultaneously. Structural batteries, containing woven carbon fabric anode; lithium cobalt oxide/graphene nanoplatelets coated aluminum cathode; filter paper separator and cross-linked polymer electrolyte, were fabricated through resin infusion under flexible tooling (RIFT) technique. Compression tests, dynamic mechanical thermal analysis, thermogravimetric analysis and impedance spectroscopy were done on the cross-linked polymer electrolytes while cyclic voltammetry, impedance spectroscopy, dynamic mechanical thermal analysis and in-plane shear tests were conducted on the fabricated structural batteries. A range of solid polymer electrolytes with increasing concentrations of lithium perchlorate salt in crosslinked polymer epoxies were formulated. Increased concentrations of electrolyte salt in cross-linked epoxy increased the ionic conductivity, although the compressive properties were compromised. A structural battery, exhibiting simultaneously a capacity of 0.16 mAh L−1, an energy density of 0.32 Wh L−1 and a shear modulus of 0.75 GPa have been reported.

Improving the multifunctional behaviour of structural supercapacitors by incorporating chemically activated carbon fibres and mesoporous silica particles as reinforcement

Novel structural supercapacitors have been fabricated which can simultaneously carry mechanical loads as well as store electrochemical energy. Structural supercapacitors are fabricated by impregnating activated carbon fibre mat electrodes and glass fibre mat separator with crosslinked polymer electrolytes using the resin infusion under flexible tooling method. Mesoporous silica particles are also used as reinforcements to further improve the electrochemical and mechanical performance of structural supercapacitors. The fabricated structural supercapacitors have been characterised through chronoamperometry method and impedance spectroscopy to evaluate the electrochemical performance and in-plane shear properties to evaluate the mechanical performance. A multifunctional structural supercapacitor, exhibiting simultaneously a power density of 34 W kg−1, an energy density of 0.12 Wh kg−1 and a shear modulus of 1.75 GPa, has been fabricated.

Ion Conduction, Dielectric and Mechanical Properties of Epoxy-Based Solid Polymer Electrolytes Containing Succinonitrile

We use impedance spectroscopy to investigate ionic conduction and dielectric response and mechanical tests to study mechanical properties of cross-linked epoxy-based solid polymer electrolytes (SPEs) containing a mixture of succinonitrile (SN) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) with different ratio of mechanically robust epoxy and ionic conducting SN/LiTFSI mixture content. Increasing SN/LiTFSI mixture content results in a proportional increase in ionic conductivity σ DC , and its maximum conductivity approaches σ DC ∼10-4 S/cm at room temperature. This is consistent with accelerating the observed relaxation processes such as ion rearrangement and segmental motion, upon adding further SN/LiTFSI content. The combination of epoxy and SN/LiTFSI also leads to a large increase in static dielectric constant e s ∼75, which is higher than the prediction from the Landau and Lifshitz mixing rule, compared to the host epoxy (e s ∼4) and pure SN/LiTFSI mixture (e s ∼53). On the other hand, the addition of SN/LiTFSI decreases Young’s modulus (E), compared to the neat epoxy, and approaches E∼10 MPa at room temperature, reflecting a trade-off relationship between E and σ DC .