Lithium Ion Transference Number Research Articles

Polybenzimidazole-reinforced polyethylene oxide-based polymer-in-salt electrolytes enabling excellent structural stability and superior electrochemical performance for lithium metal batteries

Polyethylene oxide (PEO)-based solid polymer electrolyte (SPEs) is full of attraction due to its exceptional lithium ion dissolubility and strong resistance toward lithium metal reduction. Nevertheless, it still suffers from the unfulfilling room temperature ionic conductivity and poor mechanical properties. Herein, a flexible and robust polymer-in-salt electrolyte based on composite of polybenzimidazole (PBI) and PEO via a facile preparation approach has been developed for room-temperature lithium metal batteries (LMBs). The rigid framework structure of PBI and dense hydrogen bonds formed between PBI and PEO jointly reinforce the structural stability of SPEs at high lithium salt concentration, which makes the SPEs possess sufficient mechanical properties to resist the lithium dendrites growth. The thermal stability and fire resistance of SPEs have also been improved relying on the distinctive flame retardancy and incombustibility of PBI. Besides, PBI is prone to forming hydrogen bonds with lithium salt anions to limit their mobility, while the rich N atoms on PBI chains can promote the dissociation of lithium salt through electrostatic attraction interaction. Their synergistic effects make the PEO-based polymer-in-salt electrolytes achieve the high room temperature ionic conductivity of 5.7 × 10−4 S cm−1, wide electrochemical window of 4.45 V, and large lithium transference number of 0.639. When applied to LMBs with LiFePO4 or LiNi0.88Co0.06Mn0.06O2 cathode, both coin cells exhibit improved cycling performance and rate capability. Furthermore, the LiNi0.88Co0.06Mn0.06O2/SiOx-C pouch cells using the SPEs demonstrate remarkable flexibility and safety, clarifying that the PEO-based polymer-in-salt electrolytes possess a promising application prospect for safe and high-performance LMBs.

Sandwich-Structured Quasi-Solid Polymer Electrolyte Enables High-Capacity, Long-Cycling, and Dendrite-Free Lithium Metal Battery at Room Temperature.

The insufficient ionic conductivity, limited lithium-ion transference number (tLi +), and high interfacial impedance severely hinder the practical application of quasi-solid polymer electrolytes (QSPEs). Here, a sandwich-structured polyacrylonitrile (PAN) based QSPE is constructedin which MXene-SiO2 nanosheets act as a functional filler to facilitate the rapid transfer of lithium-ion in the QSPE, and a polymer and plastic crystalline electrolyte (PPCE) interface modification layer is coated on the surface of the PAN-based QSPE of 3wt.% MXene-SiO2 (SS-PPCE/PAN-3%) to reduce interfacial impedance. Consequently, the synthesized SS-PPCE/PAN-3% QSPE delivers a promising ionic conductivity of ≈1.7mScm-1 at 30°C, a satisfactory tLi + of 0.51, and a low interfacial impedance. As expected, the assembled Li symmetric battery with SS-PPCE/PAN-3% QSPE can stably cycle more than 1550h at 0.2 mA cm-2 . The Li||LiFePO4 quasi-solid-state lithium metal battery (QSSLMB) of this QSPE exhibits a high capacity retention of 81.5% after 300 cycles at 1.0C and at RT. Even under the high-loading cathode (LiFePO4 ≈10.0mgcm-2 ) and RT, the QSSLMB achieves a superior area capacity and good cycling performance. Besides, the assembled high voltage Li||NMC811(loading≈7.1 mgcm-2 ) QSSLMB has potential applications in high-energy fields.

The effects of functionalization of imidazolium-based ionic liquid electrolytes on the lithium-ion transport

The application of salt-in-ionic liquid electrolytes (SILEs) in lithium-ion batteries is restricted by the negative transference number of lithium ion (tLi+) from strong ion-ion correlations. In this study, we applied molecular dynamics (MD) simulations on three imidazolium-based functionalized SILEs, composed of 1-hexyl-3-methylimidazolium (HMIM+), 1-(2-methoxyethoxy)methyl-3-methylimidazolium (MOEOMMIM+), or 1-[2-(methoxycarbonyloxy)ethyl]-3-methylimidazolium (EMCMIM+), and bis(trifluoromethanesulfonyl)imide (TFSI−), doped with 0.25 molar fraction of LiTFSI. MD simulations show that tLi+ is improved in the SILE composed of [EMCMIMTFSI]0.75[LiTFSI]0.25. Detailed analyses show that Li+ can coordinate with the carbonyl oxygen on the side chain of EMCMIM+, which competes with TFSI−, and thus weakens Li+–TFSI− coordination. On the other hand, one of ether oxygens on the side chain of MOEOMMIM+ tends to form intra-ionic hydrogen bonds (HBs) with the hydrogen atoms on the imidazolium ring, which even hinders the coordination between MOEOMMIM+ and TFSI−, and thus reinforces Li+–TFSI− coordination. The net result is that tLi+ increases in the order [MOEOMMIM] < [HMIM] < [EMCMIM]. These findings may help on the further design of functionalized SILEs toward a desired tLi+.

A Highly Salt-Soluble Ketone-Based All-Solid-State Polymer Electrolyte with Superior Performances for Lithium-Ion Batteries

Solid polymer electrolytes (SPEs) have great potential to be used in high-safety lithium-ion batteries (LIBs). However, it is still a significant challenge for SPEs to develop high ionic conductivity, high mechanical strength, and good interior interfacial compatibility. In this work, a ketone-based all-solid-state electrolyte (PAD) resulting from allyl acetoacetate (AAA), diacetone acrylamide (DAAM), and poly(ethylene glycol) diacrylate (PEGDA) was prepared by UV-inducing photopolymerization. The abundant ketone groups endow the prepared PAD all-solid-state electrolyte with strong dissociation of lithium salts and weak coordination interactions between ketone groups and Li+. Depending on the unique properties of the ketone groups in the electrolyte system, the prepared polymer electrolytes show a high lithium-ion transference number of 0.87 and a wide electrochemical window of 4.95 V. Furthermore, the PAD electrolyte also exhibits superior viscoelasticity, which is beneficial for good contact with electrodes. As a result, the assembled LFP/PAD/Li cells with PAD electrolytes show good cycle performance and rate performance. Concretely, the all-solid-state symmetric lithium cells with the PAD electrolyte can achieve stable lithium plating and stripping at 0.05 mA cm-2 for over 1000 h at 60 °C. This work highlights the advantages of ketone-based electrolyte as a polymer electrolyte and provides a design method for advanced polymer electrolytes applied in high-performance solid lithium batteries.

Ultrathin and Robust Composite Electrolyte for Stable Solid-State Lithium Metal Batteries

Solid-state polymer electrolytes (SPEs) are considered as one of the most promising candidates for the next-generation lithium metal batteries (LMBs). However, the large thickness and severe interfacial side reactions with electrodes seriously restrict the application of SPEs. Herein, we developed an ultrathin and robust poly(vinylidene fluoride) (PVDF)-based composite polymer electrolyte (PPSE) by introducing polyethylene (PE) separators and SiO2 nanoparticles with rich silicon hydroxyl (Si-OH) groups (nano-SiO2). The thickness of the PPSE is only 20 μm but possesses a quite high mechanical strength of 64 MPa. The introduction of nano-SiO2 fillers can tightly anchor the essential N,N-dimethylformamide (DMF) to reinforce the ion-transport ability of PVDF and suppress the side reactions of DMF with Li metal, which can significantly enhance the electrochemical stability of the PPSE. Meanwhile, the Si-OH groups on the surface of nano-SiO2 as a Lewis acid promote the dissociation of the lithium bis(fluorosulfonyl)imide (LiFSI) and immobilize the FSI- anions, achieving a high lithium transference number (0.59) and an ideal ionic conductivity (4.81 × 10-4 S cm-1) for the PPSE. The assembled Li/PPSE/Li battery can stably cycle for a record of 11,000 h, and the LiNi0.8Co0.1Mn0.1O2/PPSE/Li battery presents an initial specific capacity of 173.3 mA h g-1 at 0.5 C, which can stably cycle 300 times. This work provides a new strategy for designing composite solid-state electrolytes with high mechanical strength and ionic conductivity by modulating their framework.

UV-photopolymerized cellulose acetate-acrylate membranes for lithium-ion battery separator

Cellulose acetate (CA) is attractive for use as a separator in lithium-ion batteries (LIBs). However, the dissolubility in the liquid electrolyte limits its applications. Herein, we would report a cellulose acetate (CA) cross-linked film for the separator of lithium-ion battery. First, methacrylate modified cellulose acetate (M-CA) was prepared by esterification between CA and methylacryloyl chloride. Subsequently, an insoluble polymer membrane was obtained through the UV-induced polymerization of M-CA, poly(ethylene glycol) methyl ether methacrylate (PEGMEMA) and trihydroxymethylpropyl trimethylacrylaye (TMPTMA). The results show that these polymer membranes have good thermal and chemical stability due to the cross-linked polymer matrix. When the amount of TMPTMA is 20% of the molar amount of PEGMEMA, not only has the obtained gel polymer electrolyte (GPE) a suitable ionic conductivity of 4.17 mS cm−1 and an excellent lithium ion transfer number of 0.80, but also it has discharge capacity of the half battery composed of LiFePO4/GPE/Li 120 mAh g−1 at 2 C. This study demonstrated a great possibility that the high-performance and biodegradable GPE could be applied in LIBs. In addition, there are many other methacrylate monomers that can be polymerized with M-CA to prepare various GPEs, which will open a new avenue for the application of CA in GPEs.

Ultrathin poly(cyclocarbonate-ether)-based composite electrolyte reinforced with high-strength functional skeleton

Composite polymer electrolytes (CPEs) are considered to be the most promising to break through the performance and safety limitations of traditional lithium-ion batteries because of their excellent electrochemical and mechanical properties. Aiming at the performance limitations of the most common polyether matrix such as poly(ethylene oxide) (PEO), a novel poly(cyclocarbonate-ether) polymer matrix was prepared by in-situ thermal curing, the weaker interaction between its C = O bond and Li+ can promote the rapid transport of Li+. Adding ionic liquid and active filler LLZTO to the matrix can synergistically reduce the crystallinity of matrix and promote the dissociation of lithium salts. In addition, a 3D functional skeleton made of polyacrylonitrile (PAN) and lithium fluoride (LiF) can greatly improve the mechanical strength of polymer matrix after cold pressing, and LiF is also conducive to interface stability. The thickness of the optimal sample (VP6L/CPL) was only 25 μm, and its ionic conductivity, lithium ion transference number, and electrochemical stability window were as high as 7.17 × 10−4 S cm−1 (25 °C), 0.54 and 5.4 V, respectively, while the mechanical strength reaches 6.1 MPa, which can fully inhibit the growth of lithium dendrites. The excellent electrochemical performance and mechanical strength enable the assembled Li|VP6L/CPL|Li battery to be continuously charged for over 200 h and cycled stably for more than 2300 h, and Li|VP6L/CPL|LFP battery can be stably cycled for more than 400 and 550 cycles at 1 C (40 °C) and 0.5 C (25 °C), respectively.

Effect of LiTFSI Electrolyte Salt Composition on Characteristics of PVDF-PEO-LiTFSI-Based Solid Polymer Electrolyte (SPE) for Lithium-Ion Battery

A lithium-ion battery with PVDF-PEO synthetic polymer sheet added by LiTFSI electrolyte salt has been made by assembling method. This study aims to determine the effect of LiTFSI salt concentration on the performance of lithium-ion batteries. The composition of LiTFSI electrolyte salts was varied into 5%; 10%; 15%; and 20%. Several characterizations were carried out to determine battery performance, including Electrochemical Impedance Spectrometry (ElS), Cyclic Voltammetry (CV), Charge/Discharge (CD), and Lithium Transference Number (LTN). The results showed that the synthesized separator sheet with a LiTFSI salt composition of 20% producing voltage, ionic conductivity, and lithium-ion transfer number of 0.72 V; 3.94 x 10-8 SCm-1; and 0.895, respectively is potential for lithium-ion batteries application. These results indicate the use of LiTFSI electrolyte salts with a concentration of 20% shows the best performance for PVDF-PEO-LiTFSI-based lithium-ion batteries.

A dielectric electrolyte composite with high lithium-ion conductivity for high-voltage solid-state lithium metal batteries.

The ionic conductivity of composite solid-state electrolytes does not meet the application requirements of solid-state lithium (Li) metal batteries owing to the harsh space charge layer of different phases and low concentration of movable Li+. Herein, we propose a robust strategy for creating high-throughput Li+ transport pathways by coupling the ceramic dielectric and electrolyte to overcome the low ionic conductivity challenge of composite solid-state electrolytes. A highly conductive and dielectric composite solid-state electrolyte is constructed by compositing the poly(vinylidene difluoride) matrix and the BaTiO3-Li0.33La0.56TiO3-x nanowires with a side-by-side heterojunction structure (PVBL). The polarized dielectric BaTiO3 greatly promotes the dissociation of Li salt to produce more movable Li+, which locally and spontaneously transfers across the interface to coupled Li0.33La0.56TiO3-x for highly efficient transport. The BaTiO3-Li0.33La0.56TiO3-x effectively restrains the formation of the space charge layer with poly(vinylidene difluoride). These coupling effects contribute to a quite high ionic conductivity (8.2 × 10-4 S cm-1) and lithium transference number (0.57) of the PVBL at 25 °C. The PVBL also homogenizes the interfacial electric field with electrodes. The LiNi0.8Co0.1Mn0.1O2/PVBL/Li solid-state batteries stably cycle 1,500 times at a current density of 180 mA g-1, and pouch batteries also exhibit an excellent electrochemical and safety performance.

Ion Transport Regulated Lithium Metal Batteries Achieved by Electrospun ZIF/PAN Composite Separator with Suitable Electrolyte Wettability

Lithium metal battery (LMB) is a topic receiving growing attention due to the high theoretical capacity, while its practical application is seriously hindered by the lithium dendrites issue. As the physical barrier between two electrodes, the separator can achieve dendrite suppression by means of providing higher mechanical strength, regulating ion transport and facilitating homogeneous lithium deposition. Based on this, a composite separator is fabricated with zeolitic imidazolate framework (ZIF-8) and polyacrylonitrile (PAN) via electrospinning techniques, and its physical properties and electrochemical performances, together with its dendrite suppression mechanism, are investigated. The ZIF8-PAN separator possesses a unique 3D interconnected porous skeleton, displaying higher electrolyte uptake, preferable electrolyte wettability, and lower thermal shrinkage compared with the commercial polypropylene separator. In addition, a battery assembled with the ZIF8-PAN separator can effectively regulate ion transport and suppress dendrites growth, which exhibits an enhanced ionic conductivity (1.176 mS/cm), an increased lithium-ion transference number (0.306), a wider electrochemical stability window (5.04 V), and superior cycling stability (over 600 h with voltage hysteresis of 30 mV). This work offers a promising strategy to realize safe separator for dendrite suppression in LMB.

Click chemistry-initiated highly uniform semi-interpenetrating polymer electrolyte with dual salts for high-performance lithium metal batteries

Solid-state lithium metal batteries built with polymer electrolytes are attractive owing to their high energy density, easy manufacturing, and high safety. However, polymer electrolytes' low ionic conductivity and poor interfacial stability seriously restrict their practical application. Herein, we designed a highly uniform semi-interpenetrating polymer network electrolyte (SIPE) based on thiol–ene click chemistry. This SIPE embedded with linear poly(ethylene glycol) dimethyl (PEGDME) short chains achieves good ionic conductivity (1.78 × 10−4 S cm−1 at 30 °C), low activation energy (0.21 eV), and high lithium-ion transference number (0.53). The thiol–ene click reaction-initiated network effectively promotes homogenous distribution of PEGDME nanodomain in polymer matrix. Therefore, short PEG chains can activate the segmental motion of polymer matrix, provide strong Li+-coordination for fast diffusion, and thus facilitate the dissociation of more lithium salts. We demonstrate a dual-salt of LiTFSI and LiDFOB salt in SIPE (D-SIPE), which contributes to a rigid and stable LiF-rich solid electrolyte interphase towards electrodes. The D-SIPE-based cell achieves improved specific capacity and cyclability when tested in solid-state Li metal batteries with LiFePO4 cathode. This work provides a strategy for rationally designing polymer electrolytes and broadening the application of click chemistry in solid-state lithium metal batteries.

Polymers with Cyanoethyl Ether and Propanesulfonate Ether Side Chains for Solid-State Li-Ion Battery Applications

Two key challenges of solid-state polymer electrolytes (SPEs) are low ionic conductivity and low lithium transference number, which must be resolved in order to achieve satisfactory cycling performance for solid-state lithium batteries. Herein, we successfully substituted β-cyanoethyl ether [−O–(CH2)2–CN] and propanesulfonate ether [−O–(CH2)3–SO3–] groups for the −OH group in polyvinyl alcohol. SPEs were then prepared by mixing the resultant graft-polymer with various levels of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). The SPE with an optimal concentration of LiTFSI (50 wt %) showed a maximum ionic conductivity of 5.4 × 10–4 S cm–1 with an activation energy of 31.6 kJ mol–1, an electrochemical stability window of 5.3 V (vs Li/Li+), and a lithium-ion transference number of 0.48 at room temperature (∼25 °C). The plating/stripping tests for a Li|SPE|Li cell demonstrated a steady voltage profile without short-circuiting issues for 500 cycles (i.e., 500 h). Furthermore, a solid-state Li|SPE|LiFePO4 battery was assembled with exceptional cycling stability at 25 °C. A discharge (DC) capacity of 159.1 mA h g–1 was attained at a 0.1 C-rate. In addition, the DC capacity at a 0.5 C-rate and capacity retention after 576 cycles are 138.0 mA h g–1 and 70%, respectively.

A single-ion conducting quasi-solid polymer electrolyte made from synthetic rubber for lithium metal batteries

A lithium-ion conducting triblock copolymer bearing pendant lithium sulfonates, termed as SSEBS-Li, is derived from commercial synthetic rubber poly(styrene-block-(ethylene-ran-butylene)-block-styrene); and free-standing quasi-solid polymer electrolyte (QSPE) membranes made of demonstrate high efficiency and high safety in the application for lithium metal batteries (LMBs). SSEBS-Li possesses a hybrid molecular structure containing “soft” segments that enable seamless contact with the lithium metal; and “hard” segments possessing anchored anions that offer continuous pathways to benefit lithium ion conduction and homogeneous lithium deposition. The unique molecular architecture features the QSPE membranes interpenetrated network microstructures to provide good mechanical strengths and ductility at a thickness of 25 µm. A high lithium ion conductivity of up to 5 × 10-4 S cm−1 at ∼ 35 wt% liquid electrolyte uptake is achieved, along with a high lithium transference number of 0.92 at room temperature. Galvanostatic cycling studies prove the excellent capability of SSEBS-Li QSPE in suppressing lithium dendrite growth. The Li//QSPE//LFP cell exhibits a high discharge capacity and excellent long-term stability after 300 cycles at 0.5C and room temperature without deleterious decay, elucidating a feasible and economical approach to improve the stability and safety of LMBs.

Single and multilayer composite electrolytes for enhanced Li-ion conductivity with restricted polysulfide diffusion for lithium–sulfur battery

Lithium–sulfur battery is a promising energy source to achieve high energy density at low cost, but its commercialization has been being impeded by a few huddles associated with Li dendrite growth, polysulfide shuttle, and flammability, due to the utilization of liquid electrolytes. In this study, the single- and multi layered flexible composite electrolytes comprising organic poly(arylene ether sulfone)-g-poly(ethylene glycol) and inorganic Li6PS5Br nanoparticles are designed. Both composite electrolyte membranes exhibit excellent mechanical flexibility and thermal stability up to 200 °C. The single-layer composite electrolyte illustrates high ionic conductivity of 2.4 ⅹ 10−3 S/cm because of the self-assembled poly(ethylene glycol) domains accommodating large amount of free charge carriers. Even though the multilayer electrolyte membrane shows slightly lower conductivity of 8.7 ⅹ 10−4 S/cm, it provides quite high lithium-ion transference number of 0.81 with self-extinguishing ability and effective suppression of Li dendrite growth and polysulfide diffusion because of the highly selective Li6PS5Br layer. Accordingly, the Li/S cell assembled with multilayer composite electrolyte shows outstanding cyclic stability retaining 99.2% after 100 cycles at 0.1 C-rate. Those results demonstrate the application possibility of the prepared solid electrolytes for high safety and high performance lithium–sulfur battery.

Effects of a high-performance, solution-cast composite electrolyte on the host electrospun polymer membrane for solid-state lithium metal batteries

Dispersed nano-silica fillers in poly (ethylene oxide) were solution cast on a host electrospun polyacrylonitrile membrane. The host electrospun polyacrylonitrile membrane enhanced the overall elasticity and ionic conductivity of the composite polymer electrolyte membrane for solid-state lithium metal batteries. Three different concentrations of silica fillers were added (1%, 3%, and 5%) called CSE 1, CSE 3, and CSE 5. The composite electrolyte membranes were compared with the 0% concentration of silica fillers and named SE. Among them, the CSE 3 membrane outperformed and delivered an ionic conductivity of 7.1 × 10 −4 S cm−1, lithium-ion transference number of 0.62, and the ultimate tensile strength of 27.3 MPa with 110.9% strain, revealing the elasticity of the CSE 3 membrane. The thermal stability of up to 354 °C and the wide range of electrochemical stabilities of up to 5.1 V were achieved. The symmetric cell Li|CSE 3|Li showed satisfactory long operation of lithium plating/stripping for 500 h without a significant voltage drop or short circuit. Furthermore, the electrode surface showed the homogeneous deposition of lithium on the plated electrode and a relatively smooth surface on the stripped electrode. The LCO|CSE 3|Li exhibits better rate capability and excellent cycling performance with 91.1% capacity retention and maintains 131.9 mAh g−1at 0.5C after 200 cycles.

Cross-Linking of Sugar-Derived Polyethers and Boronic Acids for Renewable, Self-Healing, and Single-Ion Conducting Organogel Polymer Electrolytes.

This report describes the synthesis and characterization of organogels by reaction of a diol-containing polyether, derived from the sugar d-xylose, with 1,4-phenylenediboronic acid (PDBA). The cross-linked materials were analyzed by infrared spectroscopy (FT-IR), thermal gravimetric analysis (TGA), scanning electron microscopy (FE-SEM), and rheology. The rheological material properties could be tuned: gel or viscoelastic behavior depended on the concentration of polymer, and mechanical stiffness increased with the amount of PDBA cross-linker. Organogels demonstrated self-healing capabilities and recovered their storage and loss moduli instantaneously after application and subsequent strain release. Lithiated organogels were synthesized through incorporation of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) into the cross-linked matrix. These lithium-borate polymer gels showed a high ionic conductivity value of up to 3.71 × 10-3 S cm-1 at 25 °C, high lithium transference numbers (t + = 0.88-0.92), and electrochemical stability (4.51 V). The gels were compatible with lithium-metal electrodes, showing stable polarization profiles in plating/stripping tests. This system provides a promising platform for the production of self-healing gel polymer electrolytes (GPEs) derived from renewable feedstocks for battery applications.

In-situ construction of tetraethylene glycol diacrylate based gel polymer electrolyte for long lifespan lithium metal batteries

Replacing the liquid electrolytes with polymer electrolytes is an irresistible trend to meet the application requirement of lithium metal batteries. However, for obtaining a better cycling performance, traditional polymer electrolytes typically need to be operated at high temperature, which limits the commercialization of next-generation lithium metal batteries. Here, a flexible gel polymer electrolyte (TGD-TCGG-PAN) is constructed in polyacrylonitrile (PAN) porous spinning membrane via the in-situ free radical polymerization. At 30 °C, the lithium-ion conductivity and lithium-ion transference number of TGD-TCGG-PAN are 1.57 × 10−4 S cm−1 and 0.72, respectively. The LFP|TGD-TCGG-PAN|Li battery can cycle at 3C for more than 700 cycles with a capacity retention rate of 95.02%. Compared with commercial PE membrane, application of PAN makes the TGD-TCGG-PAN perform a better thermal stability. This new process is a viable way for lithium metal batteries using gel polymer electrolyte.

Flexible PVDF-HFP based hybrid composite solid electrolyte membrane co-filled with hydroxypropyl methyl cellulose and Li6.4La3Zr1.4Ta0.6O12 for high-performance solid-state lithium batteries

Solid polymer electrolytes (SPEs) have sparked attention due to their superior mechanical robustness and excellent security in solid-state lithium batteries. However, intrinsic limitations, such as poor ionic transport properties and large interface impedance, severely hinder their practical applications. Herein, a novel composite solid electrolyte (PLHL-CSE) membrane, which consists of poly (vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), hydroxypropyl methyl cellulose (HPMC), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and Li6.4La3Zr1.4Ta0.6O12 (LLZTO), was prepared by solution-casting technique. The incorporation of HPMC into PVDF-HFP-based electrolyte played crucial roles in reducing the crystallinity of PVDF-HFP, promoting the dissociation of lithium salt, and increasing the amount of mobile Li+. With synergistic effects of HPMC and LLZTO, the mechanical and electrochemical performance of PVDF-HFP-based electrolytes were greatly enhanced. The obtained PLHL-CSE membrane showed better mechanical strength (3.0 MPa), enhanced ionic conductivity (0.25 mS/cm at 25 °C), greater lithium-ion transference number (0.7), and broadened electrochemical window of 5.0 V (vs. Li+/Li) than the PVDF-HFP/LiTFSI solid polymer electrolyte (PL-SPE) membrane. After 300 cycles at 1 C, the assembled LiFePO4/PLHL-CSE/Li cell with PLHL-CSE membrane as the hybrid composite solid electrolyte displayed a high capacity retention (95.6%). In addition, the positive effects of HPMC and LLZTO on promoting the generation of stable SEI and the uniform lithium deposition were also confirmed by the SEM results of cycled lithium metals. These findings point to the good potential of PLHL-CSE membrane as a hybrid composite solid electrolyte for practical application in lithium batteries.

Polycaprolactone-poly(vinylidene fluoride) blended composite polymer electrolyte with enhanced high power performance and interfacial stability for all-solid-state Li metal batteries

Polycaprolactone (PCL) based composite polymer electrolytes (CPEs) is a promising candidate applied in all-solid-state Li metal batteries (LMBs). However, vexing issues such as poor power performances and unstable interface layers are frequently observed. To address these issues, poly(vinylidene fluoride) (PVDF) with high dissociation of Li salts and good compatibility against Li metal are introduced into PCL to prepare blended CPEs. The PCL-PVDF blended CPEs obtain a high ionic conductivity of 1.38 × 10-4 S·cm−1 and a high lithium ion transference number of 0.89 at 60 °C, owing to the high dissociation coming from the PVDF. Particularly, the Li//P5-CPEs-40 %//Li symmetrical battery can work steadily over 800 h at a high current density of 0.25 mA·cm−2. Furthermore, the LiFePO4//P5-CPEs-40 %//Li batteries exhibit high capacity retention of 84.9 % for 500cycles at 3.0 C. The excellent cycling stability for the LMBs is considered to be originated from the LiF containg SEI layer that formed during cycling. This study provides new perspectives to develop new CPEs with high power performances and stable interface for LMBs.

Sandwich Structured Metal oxide/Reduced Graphene Oxide/Metal Oxide-Based Polymer Electrolyte Enables Continuous Inorganic-Organic Interphase for Fast Lithium-Ion Transportation.

Introducing inorganic fillers into organic poly(ethylene oxide)(PEO)-based electrolyte has attracted substantial attention to enhance its ionic conductivity and mechanical strength, but limited inorganic-organic interphasesare always caused by isolated particles agglomeration. Herein, a variety of sandwich structured metal oxide/reduced graphene oxide(rGO)/metal oxide nanocomposites to optimize lithium-ion conduction by interconnected amorphous organic-inorganic interphases in lithium metal batteries, are proposed. With the support of high surface area rGO, the agglomeration of metal oxide particles is precluded, forming continuous amorphous organic-inorganic interphases with stacked layer-by-layer structure, thus creating 3D interconnected lithium-ion transportation channels vertically and laterally. Besides, metal oxide nanoparticles with hydroxyls possess high affinity toward bis(tri-fluoromethanesulfonyl)imideanionsby hydrogen bindings between hydroxyls and fluorine and metal-oxygen bonds, releasing more free lithium ions. Consequently, PEO-ZnO/rGO/ZnO electrolyte delivers superior ionic conductivity of 1.02 × 10-4 S cm-1 at 25°C and lithium-ion transference number of 0.38 at 60°C. Furthermore, ZnO/rGO/ZnO insertion promotes the formation of LiF-rich stable solid electrolyte interface, endowing Li symmetric cells with long-term cycling stability over 900 hours. The corresponding LiFePO4 cathode possesses a high reversible specific capacity of 130 mAh g-1 at 0.5C after cycling 300 cycles with a poor capacity fading of 0.05% per cycle.