Solid-state Polymer Electrolytes Research Articles

Effect of oligo(ethylene glycol) length on properties of poly(oligoethylene glycol terephthalate)s and their cyclic oligomers

We present here the effect of oligo(ethylene glycol) (OEG) segmental length on properties of cyclic oligo(oligoethylene glycol terephthalate)s (COEGTs) and their corresponding polymer counterparts, poly(oligoethylene glycol terephthalate)s (POEGTs). COEGT monomers were synthesized from terephthaloyl chloride with corresponding diethylene glycol, triethylene glycol, and tetraethylene glycol under pseudo-high-dilution conditions. As those large ring cyclic monomers are hard to be polymerized via traditional ring-opening polymerization, a cascade polycondensation-coupling ring-opening polymerization method is utilized to obtain high molecular weight POEGTs. The cascade polymerization mechanism is confirmed by the kinetics study. The structures of COEGTs and POEGTs were well characterized and their properties were studied to reveal the structure-property relationship. With the increment of OEG length in repeating units, the chain flexibility of POEGT and COEGTs is enhanced. As a result, the melting temperatures of COEGTs and glass transition temperatures of POEGTs decrease. On the other hand, the thermal degradation temperature of POEGTs and COEGTs increases due to the enhanced ether fraction and reduced ring strain. Solid-state polymer electrolytes based on POEGTs was prepared by blending with lithium bis(trifluoromethanesulfonyl)imide. The measured ionic conductivity increased with the OEG length in POEGT repeating units. Our results revealed the effect of OEG length on the structure-property relationship in cyclic oligo(ether ester)s and copoly(ether ester)s, providing a facile way to tune their properties.

Enthalpic and Entropic Contributions to Fast Lithium Ion Conduction in Solid-State Aqueous Polymer Electrolytes

Solid-state aqueous polymer electrolytes (SAPEs), a mixture of hydrophilic polymers and an appropriate amount of water, can produce high Li-ion conductivity while maintaining a solid state. Also, they can overcome the limitations of normal solid electrolytes. This study reports that the very high SAPE ionic conductivity (∼10 mS/cm at T = 298.15 K) originates from a low energy barrier (∼0.28 eV) closely correlated with water-filled ion passages in the medium. The low energy barrier is ascribed to a considerable reduction of the enthalpic barrier due to water addition despite a growth of the entropic barrier incurred by the negative nature of entropy change across water tubes. The extremely high ionic conductivity, coupled with an exceptionally low energy barrier, provides a unique advantage to SAPEs over conventional solid electrolytes.

Double-Network Polymer Electrolytes with Ionic Liquids for Lithium Metal Batteries.

Solid-state polymer electrolytes have become promising candidates for high-energy-density lithium metal batteries (LMBs). However, they suffer from low ionic conductivities at room temperature. In this work, two types of composite polymer electrolytes based on a double-network polymer, an ionic liquid (IL) of 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl) imide (Pyr14TFSI) or 1-ethyl-3-methylimidazolium bis((trifluoromethyl)sulfonyl) imide (EmimTFSI), and bis(trifluoromethane)sulfonamide lithium salt (LiTFSI) were prepared by a facile one-pot method. The two types of CPEs possess good mechanical properties, excellent thermal stability, and high ionic conductivities greater than 10−4 S cm−1 at 20 C with 26 wt% IL. The performance diversity of the CPEs was also carefully investigated through a series of electrochemical measurements. Although the CPEs containing EmimTFSI show higher ionic conductivities than those of CPEs with Pyr14TFSI, the latter ones have wider electrochemical stability windows and better resistance to the growth of lithium dendrites. Moreover, CPE with 34 wt% Pyr14TFSI leads to Li/LiFePO4 batteries with favorable rate capability and cycling stability and a columbic efficiency of 98.8% at 20 °C, which suggests that CPEs are promising for practical application in solid-state LMBs.

Superionic Bifunctional Polymer Electrolytes for Solid-State Energy Storage and Conversion.

Achieving superionic conductivity from solid-state polymer electrolytes is an important task in the development of future energy storage and conversion technologies. Herein, a platform for innovative electrolyte technologies based on a bifunctional polymer, poly(3-hydroxy-4-sulfonated styrene) (PS-3H4S), is presented. By incorporating OH and SO3 H functional groups at adjacent positions in the styrene repeating unit, "intra-monomer" hydrogen bonds are formed to effectively weaken the electrostatic interactions of the SO3 - moieties in the polymer matrix with embedded ions, promoting rich structural and dynamic heterogeneity in the PS-3H4S electrolyte. Upon the incorporation of an ionic liquid, interconnected rod-like ion channels, which allow the decoupling of ion relaxation from polymer relaxation, are formed in the stiff motif of the polymeric domains passivated by interfacial ionic layers. This results in accelerated proton hopping through the glassy polymer matrix, and proton hopping becomes more pronounced at cryogenic temperatures down to -35 °C. The PS-3H4S/ionic liquid composite electrolytes exhibit a high ionic conductivity of 10-3 S cm-1 and high storage modulus of ≈100MPa at 25 °C, and can be successfully applied in soft actuators and lithium-metal batteries.

Structure and Evolution of Quasi-Solid-State Hybrid Electrolytes Formed Inside Electrochemical Cells.

Solid-state electrolytes (SSEs) formed inside an electrochemical cell by polymerization of a liquid precursor provide a promising strategy for overcoming problems with electrolyte wetting in solid-state batteries. Hybrid solid-state polymer electrolytes (HSPEs) created by in situ polymerization of a conventional liquid precursor containing electrochemically inert nanostructures are of particular interest because they offer a mechanism for selectively reinforcing or addingnewfunctionalitiesto the electrolyte-removing the need for high degrees of polymerization. The synthesis, structure, chemical kinetics,ion-transportpropertiesand electrochemical characteristics of HSPEs created by Al(OTf)3 -initiated polymerization of 1,3-dioxolane (DOL) containing hairy, nano-sized SiO2 particles are reported. Small-angle X-ray scattering reveals the particles are well-dispersed inliquidDOL. Strong interaction between poly(ethylene glycol) molecules tethered to the SiO2 particles and poly(DOL) lead to co-crystallization-anchoring the nanoparticles in their host It also enables polymerization-depolymerization processes in DOL to be studied and controlled. The utility of the in-situ-formed HSPE, is demonstrated first in Li|HSPE|Cu half cells, which manifest Coulombic efficiencies (CE) values approaching 99%. HSPEs are also demonstrated in solid-state lithium-sulfur-polyacrylonitrile (SPAN) composite full-cell batteries. The in-situ-formed Li|HSPE|SPAN cells show good cycling stability and thus provide a promising path toward all-solid-state batteries.

PEGDA with Metal-Organic Frameworks As Composite Electrolyte for All-Solid-State Lithium Batteries

The widely use of volatile and flammable traditional organic carbonate-based electrolytes in high-performance lithium-ion batteries (LIBs) is prone to cause safety hazards. Solid-state polymer electrolytes (SPE) have been developed to address the safety issues due to their numerous advantages, such as solvent-free, low flammability, wide electrochemical stability window, and good thermal and mechanical stability. However, the polymer tends to recrystallize at room temperature leading to insufficient ionic conductivity. Organic-matter-based fillers (e.g., metal-organic frameworks, covalent−organic frameworks, and lithiophilic polymers) have been found to increase the ionic conductivity of SPEs effectively by decreasing the crystallinity of polymer, synchronously to improve the mechanical property, thermal stability, and interfacial compatibility. Porous zeolitic imidazolate framework-8 (ZIF-8) has been used as fillers in this study. The ZIF-8 are integrated with the PEGDA matrix in this study, showing enhanced electrochemical and mechanical properties. Such performance enhancement is due to the composite solid-state electrolyte inherited the advantages of both polymer and fillers. The fillers not only inhibited the recrystallization of the polymer but also prevent the dendrite growth of the Li. The polymeric PEGDA enhanced the contact interface between the electrolyte and electrodes. Therefore, PEGDA-based SPEs with ZIF-8 is of great promise for all-solid-state lithium metal batteries.

Role of Agent Molecules for Low-Temperature Activation of Lithium-Ion Transport for Solid-State Polymer Electrolytes

The realization of all-solid-state lithium-ion batteries (LIBs) is often considered as the final challenge in the development of LIBs. Replacing Li-ion conductive liquid electrolytes with high-performance solid-state electrolytes is indispensable for the development of all-solid-state LIBs. Solid-state electrolytes under development fall into three classes: polymers, oxides, and sulfides. Polymer-based electrolytes have advantages over oxides and sulfides, such as formation of low-resistance electrolyte/electrode interfaces, good processability, and high energy-density owing to low density. Therefore, polymer-based solid-state electrolytes are being developed in both industry and academia as a practical route for realizing high-capacity LIBs.[1]For application in commercial LIBs, the electrolyte should have an ionic conductivity higher than 10-4 S/cm at room temperature. Conventional solid polymer electrolytes, such as polyethylene oxide (PEO)-based electrolytes, do not meet the performance requirements due to insufficient ionic conductivity in the range of 10-6 to 10-5 S/cm. Recently, polyphenylene sulfide (PPS)-based polymer electrolytes have been reported to yield ion conductivities as high as those of liquid electrolytes over a wide temperature range (> 1.0 × 10-4 S/cm at 25 °C, > 1.0 × 10-3 S/cm at 80 °C, and > 1.0 × 10-3 S/cm at −40 °C).[2] These electrolytes consist of base polymer chains containing PPS, Li salts that can dissociate into cations and anions, and neutral agent molecules. However, the detailed Li-ion transport mechanism in terms of the respective roles of the molecular components of PPS electrolytes is yet to be determined. This limited understanding hinders the further improvement of PPS-based electrolytes.In this study, we perform a series of first-principle calculations and demonstrate that certain types of neutral molecules (so-called agent molecules) accelerate solid-state lithium-ion migration when mixed with lithium salts.[3] We find that the intermolecular interaction in a selected agent-molecule/lithium-salt binary system is governed by the strong coupling between lithium and oxygen atoms. Upon the addition of agent molecules, the anionic species surrounding the lithium of lithium salts is replaced by the agent molecules. The resulting weakened Coulomb energy coupling between lithium and oxygen atoms is determined to be a key factor in enabling fast lithium-ion migration via facile dissociation of lithium salts and subsequent formation of ion-hopping sites in the form of lithium-free oxygen-cages. The structure-based interpretation of agent molecules suggests that neutral molecules with functional groups which enhance chemical resonance can be selected as potential agent molecules. We believe that the results obtained in this study serve as a theoretical basis for the future development of solid-state polymer electrolytes, particularly toward mitigating the dependence of lithium-ion transport on the movement of polymer chains.

Novel Acrylonitrile-Based Polymers for Solid–State Polymer Electrolyte and Solid-State Lithium Ion Battery

Rechargeable lithium-ion batteries (LIBs) involving lithium metal oxides, liquid electrolyte and graphite have been widely used in portable electronic devices due to their relatively high energy density and long cycle life. These desirable features make LIBs very attractive as the power source for electronic devices, hybrid electric vehicles (HEVs) and electric vehicles (EVs) applications [1, 2]. For future EV applications, higher energy density of LIBs up to 360 Wh kg-1 is required. Currently, the energy density of the state-of-the-art LIBs using conventional graphite anode, LiFePO4 (denoted as LFP) or LiNi0.5Co0.2Mn0.3O2 (NCM523) cathodes and 1-1.2 M LiPF6 in organic carbonate electrolytes provide practically achievable energy densities of up to around 200-260 Wh kg−1 [3]. When commercial graphite anodes are used, LiNi0.8Co0.15Al0.05O2 (NCA), LiNi0.8Co0.1Mn0.1O2 (NCM811), LiNi0.5Mn1.5O4 (LNMO) and LiNiPO4 (LNP) cathode based batteries with high-voltage provide energy densities of 354, 338, 351 and 414 Wh kg-1, respectively. However, LIBs using these high-voltage cathode materials and the organic carbonate electrolytes exhibit quite low thermal stability and tend to catch fire or even explode when abnormal charge/discharge cycling or accidental penetration of cells occurs, which greatly limits the automotive applications. When replacing graphite with a Li metal anode, the energy densities of all battery systems can be enhanced significantly due to the highest theoretical specific energy density (3860 mAh g-1) among all anode materials for rechargeable LIBs. Nevertheless, commercial LIBs are prone to cause safety problems due to the safety concern arising from Li dendrite growth in liquid organic electrolytes [4-6].The promising solid-state LIBs offer high thermal stability (i.e., low risk in catching fire), high energy density, wide electrochemical stability window and less environmental impact. A competent electrolyte is the key component of solid-state LIBs. The solid-state electrolyte materials are mainly classified as solid polymer electrolytes (SPEs), inorganic solid electrolytes (ISEs), and organic/inorganic composite electrolytes. ISEs include oxide-based and sulfide-based materials [7, 8], which show very high ionic conductivity (10-2 – 10-3 S cm-1). Furthermore, the lithium ion transference number is close to 1. However, the major limitation factors of practical solid-state LIB applications are the large interfacial impedance between electrode and ISE and the difficulty of processing [9]. Considering processability, mechanical flexibility, interfacial compatibility and electrochemical stability, one prefers SPEs to the inorganic ceramic electrolytes. Nevertheless, SPEs have low ion conductivities (10−7 − 10−5 S cm−1 near room temperature) and most of the Li+ transference numbers are lower than 0.5 [10, 11]. The major requirements for SPEs include high ionic conductivity and transference number at room temperature, wide electrochemical potential window, high mechanical strength and excellent thermal stability. However, the ion conductivity is the most important (> 10-4 S cm-1 at room temperature desired) and should be considered first. The coordinating groups of a good polymeric host are expected to interact with Li+ and facilitate dissociation.In this study, we prepared various novel acrylonitrile-based polymers (e.g., acrylonitrile/acrylate copolymer and polymer with two pendant groups b-cyano ethyl ether (-O-CH2CH2-CN) sulfonate alkyl ether (-O-(CH2)3SO3Li). The corresponding SPEs comprising acrylonitrile-based polymer and ca. 50 wt.% lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) with high ionic conductivity (up to 10-3 S cm-1) at room temperature, high ion transfer number (up to 0.45) and large electrochemical potential window (oxidation stability > 5 V vs. Li+/Li) achieved. The selected SPEs were used as the separator in solid-state batteries with LiFePO4 as the cathode and Li foil as the anode; and long-term cycle stability of solid-state LIB was achieved. The polymers and corresponding SPEs were characterized by using DSC, SEM, XRD and FTIR measurements. Ionic conductivities of SPEs were determined from electrochemical impedance spectroscopy results. The linear sweep voltammetry technique was adopted to measure the oxidation stability window of SPE, and the Evans-Vincent-Bruce method was used to determined ion transfer number.

Nanoarchitecture of Novel 3D Ion Transferring Channel Containing Composite Solid Polymer Electrolyte Membrane Based on Holey Graphene Oxide and Chitosan Biopolymer

In three-dimensional (3D) nanoarchitecture arena, two-dimensional (2D) nanostructured graphene oxide (GO) and its derivatives have been emerged as a promising choice of advanced additive materials due to their outstanding properties: high specific surface area (2630 m2g-1), flexibility, light weight, diverse functionality, super mechanical and thermal stability. Particularly, holey graphene oxide (HGO)—single atom thick unique 2D porous nanosheet is obtained from exfoliation of functional GO—a class of graphene sheet with abundant nanopore in their plane; can potentially be used for designing, fabricating and evaluating advanced 3D nanocomposite materials for the development of demandable renewable energy technologies including next generation of solid-state Li+ and Na+ rechargeable batteries. Having been the most significant, momentous, and effectual commercial energy storage devices over the past decade, however, lithium-ion batteries (LIBs) have some key limitations: flammability, poor thermal, and mechanical stability. To overcome these existing limitations, incorporation of ceramic or polymer-based solid-state electrolytes into the LIBs are being explosively focused by the energy storage research community because of their full solid-state condition and tunable molecular level engineering scope.In this research work, a novel 3D nanocomposite solid polymer electrolyte membrane (SPEM) has been successfully developed based on 2D-HGO and chitosan (CH) biopolymer—naturally occurring only alkaline polysaccharide obtained from industrial shrimp shells, super cheap, nanostructured, non-toxic, completely biodegradable, also abundant in nature. In addition, a facial and cost-effective solution-casting technique has been utilized to fabricate SPEM and applied as a solid-state polymer electrolyte for next generation of flexible and wearable rechargeable LIB technology. To investigate the structural, morphological, thermal, mechanical, and electrochemical performance of as prepared SPEM, so far, a comprehensive characterization has been done with the help of SEM, TEM, XRD, TGA, DSC, FTIR, Raman, elemental analysis, tensile strength test, and electrochemical impedance spectroscopy techniques. The SEM analysis of as-prepared flexible, wearable, free-standing, and super thin (~0.08 mm) SPEM depicts the coherently aligned 2D-HGO nanosheets formed a uniform and strong interconnecting 3D ion transfer channels with the host CH biopolymer. Moreover, 1wt% HGO, almost evenly distributed nanofiller SiO2 particles along with polyvinylpyrrolidone (PVP) polymer binder played an important role to generate better mechanical and electrochemical properties in SPEM. Thus, SPEM exhibited impressive ionic conductivity (6.44 x 10-3 Scm-1 at 23.1 oC and 1.02×10-2 Scm-1 at 70oC), a high level of tensile strength (5.87 MPa) as well as 672% and 93.7% increase of tensile strength than that of without HGO additive and GO based nanocomposite membranes respectively. In fact, very low activation energy (Ea = 0.08 eV) value shows the approval of easy lithium-ion diffusion capability in the SPEM system. In addition, fast ion transfer mechanism in SPEM has been investigated with an in-depth dielectric study that tells us the mainly hopping mechanism is dominating in the novel 3D architecture of SPEM. Besides, the obtained impressive electrochemical and mechanical properties of as-prepared SPEM could assist to understand the further fundamental aspects and impacts of SPEM in the application of LIB technology.

Automated Design of Li+ -Conducting Polymer by Quantum-Inspired Annealing.

Automated molecule design by computers is an essential topic in materials informatics. Still, generating practical structures is not easy because of the difficulty in treating material stability, synthetic difficulty, mechanical properties, and other miscellaneous parameters, often leading to the generation of junk molecules. The problem is tackled by introducing supervised/unsupervised machine learning and quantum-inspired annealing. This autonomous molecular design system can help experimental researchers discover practical materials more efficiently. Like the human design process, new molecules are explored based on knowledge of existing compounds. A new solid-state polymer electrolyte for lithium-ion batteries is designed and synthesized, giving a promising room temperature conductivity of 10-5 S cm-1 with reasonable thermal, chemical, and mechanical properties.

Bifunctional Solid-State Copolymer Electrolyte with Stabilized Interphase for High-Performance Lithium Metal Battery in a Wide Temperature Range.

Solid-state polymer electrolytes (SPEs) are expected to guarantee safe and durable operations of lithium metal batteries (LMBs). Herein, inspired by the salutary poly(vinyl ethylene carbonate) (PVEC) component in the solid electrolyte interphase, cross-linking vinyl ethylene carbonate and ionic liquid copolymers were synthesized by in-situ polymerization to serve as polymer electrolyte for LMBs. On one hand, due to rich ester bonds of PVEC, Li+ could transfer by coupling/decoupling with oxygen atoms. On the other hand, the imidazole ring of ionic liquid could facilitate the dissociation of lithium salt to promote the free movement of Li+ . The bifunctional component synergistically increased the ionic conductivity of the SPE to 1.97×10-4 S cm-1 at 25 °C. Meanwhile, it also showed a wide electrochemical window, superior mechanical properties, outstanding non-combustibility, and excellent interfacial compatibility. The bifunctional copolymer-based LiFePO4 batteries could normally operate at 0 to 60 °C, making them a promising candidate for wide-temperature-rang LMBs.

Integrating a three-dimensional Cu2MoS4 electrode and solid-state polymer electrolyte for sodium-ion batteries

The improvement of solid-state batteries (SSBs) in terms of safety performance and energy density has an unusual significance for it to apply to power batteries, and the interface matching of solid-state electrolytes and adapted electrode materials has become the key. Due to poor electrode-electrolyte interface contact in SSBs which could result in low ionic conductivity, we designed a 3D integrated electrode constructed from a Cu2MoS4 electrode grown in situ on the surface of copper foam with a polymer-in-salt solid electrolyte based on PVDF-HFP. The ion clusters formed by NaPF6 near the PVDF-HFP network structure can effectively shorten the Na+ transport path, and then adding 1-(4-cyanophenyl)-guanidine can also provide more ion transport routes by forming coordination bonds. The polymer electrolyte exhibited excellent ionic conductivity (1.67×10−5 S cm−1 at room temperature) and electrochemical stability (5.6 V vs Na|Na+). At the same time, it showed excellent stability during the cycle performance test of the symmetrical batteries, compared with the liquid electrolytes, the polymer-in-salt solid electrolytes were not short circuit under the same test conditions, indicating that the polymer-in-salt solid electrolytes can effectively inhibit the growth of Na dendrites. This 3D integrated electrode exhibited excellent interface-contact compatibility, mechanical stability, and electrochemical performance closed to that of liquid electrolytes and even outperformed liquid electrolytes at a high rate cycle.

In-situ formation of quasi-solid polymer electrolyte for improved lithium metal battery performances at low temperatures

Solid-state polymer electrolytes, featuring excellent processability and flexibility, have received considerable attentions. However, the inherent low ionic conductivity, especially at subzero temperatures, limits their widespread application. Herein, quasi-solid polymer electrolyte (QSPE) with high low-temperature ionic conduction ability is prepared by in-situ ring-opening polymerization of 1,3-Dioxlane with fluoroethylene carbonate (FEC) as plasticizer. The in-situ polymerization imparts good interface contact between QSPE and electrode. The addition of FEC improves the chain mobility and facilitates the dissociation of LiTFSI, giving QSPE a remarkable ionic conductivity and Li+ transference number (2.4 × 10−5 S cm−1 at −60 °C and 0.55 at −20 ° C), two orders of magnitude and 2.3 times higher than those of liquid electrolyte, respectively. As a result, the Li/QSPE/Li cell without significant polarization is obtained, which can operate at 0.2 mA cm−2 and 0 °C for 850 h. Moreover, the LiFePO4/Li cell exhibits excellent cycling stability at 0.2 C and 0 °C: its capacity remains 125.2 mAh g−1 at 400th cycle, exceeding most polymer electrolytes. Even at −20 °C, a discharge capacity of 73.3 mAh g−1 is obtained at 100th cycle under 0.2 C.

The interphasial degradation of 4.2 V-class poly(ethylene oxide)-based solid batteries beyond electrochemical voltage limit

Solid-state polymer electrolytes (SPEs) have attracted increasing attention due to good interfacial contact, light weight, and easy manufacturing. However, the practical application of SPEs such as the most widely studied poly(ethylene oxide) (PEO) in high-energy solid polymer batteries is still challenging, and the reasons are yet elusive. Here, it is found that the mismatch between PEO and 4.2 V-class cathodes is beyond the limited electrochemical window of PEO in the solid LiNi1/3Mn1/3Co1/3O2 (NMC)-PEO batteries. The initial oxidation of PEO initiates remarkable surface reconstruction of NMC grains in solid batteries that are different from the situation in liquid electrolytes. Well-aligned nanovoids are observed in NMC grains during the diffusion of surface reconstruction layers towards the bulk in solid batteries. The substantial interphasial degradation, therefore, blocks smooth Li+ transport across the NMC-PEO interface and causes performance degradation. A thin yet effective LiF-containing protection layer on NMC can effectively stabilize the NMC-PEO interface with a greatly improved lifespan of NMC|PEO|Li batteries. This work deepens the understanding of degradations in high-voltage solid-state polymer batteries.

Gas‐Permeable Organic Electrochemical Transistor Embedded with a Porous Solid‐State Polymer Electrolyte as an on‐Skin Active Electrode for Electrophysiological Signal Acquisition

AbstractFibrous nanomesh organic electrochemical transistors (OECTs) embedded with porous solid‐state polymer electrolytes (SPE) are developed for use as on‐skin active electrodes. The OECTs exhibit a microporous structure, which makes them gas permeable, allowing for the evaporation of sweat vapor when they are in conformable contact with the skin. The non‐volatility of the SPE allows for the long‐term functionality of organic electrochemical transistors. The superior electrical characteristics of the OECT can be utilized to locally amplify on‐skin bio‐potential signals. The acquisition of high‐quality electrocardiogram signals is demonstrated in this study. This porous transistor‐type on‐skin active electrode enables the long‐term acquisition of high‐quality electrophysiological signals.

Quasi-Solid-State Polymer Electrolyte Based on Highly Concentrated LiTFSI Complexing DMF for Ambient-Temperature Rechargeable Lithium Batteries

Solid-state polymer electrolytes (SPEs) complexing a plasticizer is a valid strategy to improve the poor ionic conductivity of SPEs at ambient temperature. In this study, a quasi-SPE based on a polyurethane matrix (QSPE-PU) is constructed by regulating the contents of bis(trifluoromethanesulfonyl) imide (LiTFSI) salt and N,N-dimethylformamide (DMF) and shows high performance in ambient-temperature rechargeable lithium batteries. Highly concentrated LiTFSI is designed to anchor DMF, decreasing the free solvent molecules in the QSPE to improve the stability with lithium metal. Meanwhile, DMF can fully dissociate the highly concentrated LiTFSI, providing more carriers. The prepared QSPE-PU40 shows a high ionic conductivity of 1.12 × 10–4 S cm–1 at ambient temperature since DMF not only provides more carriers but also enhances the movement of the polymer segments and lowers the energy barrier of lithium ion migration. Density functional theory calculations further prove that DMF facilitates the conduction of lithium ions in the QSPE system. QSPE-PU40 shows good compatibility with the lithium metal electrode by forming a stable solid electrolyte interphase during lithium plating/stripping processes. The lithium ferrophosphate (LFP)/QSPE-PU40/Li battery exhibits a high specific capacity of 138 mA h g–1 with remarkable cycling stability at 0.5 C and 30 °C (94% capacity retention after 800 cycles). More impressively, the pouch cell based on QSPE-PU40 delivers good flexibility and high safety. Such a QSPE is expected to provide an effective strategy where SPEs are applied in solid-state lithium batteries at ambient temperature and even flexible batteries for next-generation wearable devices.

Incorporation of Poly(Ionic Liquid) with PVDF-HFP-Based Polymer Electrolyte for All-Solid-State Lithium-Ion Batteries

A solid-state polymer electrolyte membrane is formed by blending poly(vinylidene fluoride-co-hexafluoropropylene) with the synthesized copolymer of poly(methyl methacrylate-co-1-vinyl-3-butyl-imidazolium bis(trifluoromethanesulfonyl)imide, in which lithium bis(trifluoromethane)sulfonimide molecules are applied as the source of lithium ions. The accordingly formed membrane that contains 14 wt.% of P(MMA-co-VBIm-TFSI), 56 wt.% of PVDF-HFP, and 30 wt.% of LiTFSI manifests the best electrochemical properties, achieving an ionic conductivity of 1.11 × 10−4 S·cm−1 at 30 °C and 4.26 × 10−4 S·cm−1 at 80 °C, a Li-ion transference number of 0.36, and a wide electrochemical stability window of 4.7 V (vs. Li/Li+). The thus-assembled all-solid-state lithium-ion battery of LiFePO4/SPE/Li delivers a discharge specific capacity of 148 mAh·g−1 in the initial charge–discharge cycle at 0.1 C under 60 °C. The capacity retention of the cell is 95.2% after 50 cycles at 0.1 C and the Coulombic efficiency remains close to 100% during the cycling process.

High-performance solid-state supercapacitors integrated with thermal management systems based on phase change materials: All in one

Electrochemical energy storage (EES) devices such as batteries and supercapacitors (SCs) have been widely used in electric vehicles and portable electronics. However, safety issues and performance degradation of these devices, particularly when working at elevated temperatures, limit their further applications. Here, we propose a new all-in-one design of high-performance solid-state SCs integrated with thermal management systems by developing a multifunctional solid-state polymer electrolyte (SPE) with encapsulated phase change materials (PCMs). The PCM-containing SPEs exhibited a homogenously dispersed core–shell-like structure. The paraffin wax (PW) core ─ a typical organic PCM ─ could store a large amount of thermal energy upon phase transitions. The shell, polyvinyl alcohol (PVA)/H2SO4 frameworks, could provide interconnected ion-conducting pathways, keep the encapsulated PW in the form of micro-sized particles and prevent it from leaking during the melting, and serve as separators. Consequently, the temperature rise of the all-in-one, solid-state SCs integrated with PCMs can be effectively suppressed under thermal abuse conditions. Moreover, the all-in-one devices can retain high capacitance, outstanding rate capability, and excellent stability upon charge/discharge and heating/cooling cycles. Therefore, the rationally designed multifunctional SPEs may open a new pathway to design novel high-performance and safe all-in-one devices with integrated EES and thermal management systems.

A Polymer-in-Salt Electrolyte Enables Room Temperature Lithium Metal Batteries

The lithium metal battery with solid-state polymer electrolyte (SPE) is a promising candidate for solid-state batteries with high safety and high energy density. However, the low room temperature ionic conductivity and poor electrolyte/electrode interfacial stability of the SPEs seriously hinder the practical application. Herein, we adopt a polymer-in-salt electrolyte (PISE) strategy on the comb-like polycaprolactone (PCL) to circumvent the low ionic conductivity and poor interfacial stability of the conventional SPE, thus enabling the full function of room temperature lithium metal batteries. The all-solid-state PISE exhibits a high ionic conductivity of 3.9 × 10−4 S cm−1 at 30 °C, a superior lithium-ion transference number of 0.61 and an improved oxidative stability of ∼4.8 V vs Li/Li+. Due to the ultra-stable interface generated by the superconcentrated lithium salt, the all-solid-state LiFePO4∣∣Li cells exhibit prominent high cycling stability, with high capacity retention (92%) after 300 cycles at ambient temperature. The full function of the ambient temperature PISE offers a promising pathway towards high energy density and high safety room temperature LMBs.

Reducing the crystallinity of PEO-based composite electrolyte for high performance lithium batteries

Poly(ethylene oxide) (PEO) based polymer electrolytes show great potential as the high energy density, mass-producible, low cost and high safety in the application of all-solid-state lithium (Li)-ion batteries. However, the unsatisfied ionic conductivity due to the high crystallinity of the intrinsic PEO limits its application. In this paper, the composite PEO-based electrolytes with sandwich-like structure have been designed, and the maneuverable heat-assisted process and multi-phase composite in order to suppress the crystallinity of PEO matrix are researched systematically. It's confirmed that the ionic conductivity of composite solid-state polymer electrolytes (CSPEs) after a hot-press process (90 °C, 15 min) reaches 4.9 × 10−4 S cm−1 at 25 °C. The sandwich structure of CSPEs not only enhances the ionic conductivity over the PEO electrolyte by decreasing the degree of crystallinity, but also enhances the mechanical strength and electrochemical window. Solid-state Li-ion cells fabricated with the CSPEs exhibit excellent and stable cycle performance. The specific capacity of cells is 160 mA h g−1 at 0.2C, and the capacity retention rate is almost 100% after 110 cycles. The Li|CSPE|Li cells could survive steadily for over 1,800 h. In this work, the multi-phase sandwich structure and practical manufacturing heat-assisted methods for CSPEs result in the excellent ionic conductivity, high mechanic strength and low cost of mass production, which offer a guidance on the commercialization of high-performance PEO-based electrolytes.