Lithium Bis(trifluoromethanesulfonyl)imide Research Articles

Application of GO anchored mediator in a polymer electrolyte membrane for high-rate solid-state supercapacitors

We synthesized a novel polymer electrolyte membrane by combining poly (vinylidene fluoride) (PVDF) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) with graphene oxide (GO) nanosheets and a lithium salt of tungstosilicic acid (Li4SiW12O40, hereafter, referred to SiWLi). The impact of the addition of GO/SiWLi on the microstructure and morphology of the membrane were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). We found that adding the GO/SiWLi to the PVDF/LiTFSI polymer electrolyte membrane significantly reduced the pore size. Furthermore, the addition of the GO/SiWLi resulted in not only an increase of the ionic conductivity from 0.87 × 10−2 to 3.12 × 10−2 S cm−1 but also an increase in the lithium-ion transference number from 0.52 to 0.87. The polymer electrolyte membranes with and without GO/SiWLi were utilized to fabricate solid-state supercapacitors. The supercapacitors fabricated with the membrane containing GO/SiWLi displayed 37.2% lower equivalent series resistance and 88.2% greater specific capacitance than those fabricated using the membrane without GO/SiWLi at 200 mV s−1.

Lithium trifluorosulfonimide salt containing siloxane-based electrolytes for lithium-ion batteries: Aluminum corrosion behaviors and electrochemical properties

Recently, our group verified an oligomer 390EO and a polymer 2550EO with the same chemical structure (siloxane) by characterizing their electrochemical and physical properties. A dilute electrolyte solution of 390EO and 2550EO was prepared using lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) as the Li source. LiTFSI has high ionic and thermal conductivity and high voltage stability but corrodes the aluminum (Al) current collectors. Therefore, its potential use in Li-ion batteries is limited. The present study investigates the half-cell battery performance of a LiFePO4 composite electrode with 390EO/LiTFSI and 2550EO/LiTFSI electrolytes. The Li stabilities of the electrolytes and the corrosion of an Al current collector exposed to the electrolytes are examined. The siloxane structure reduces the corrosive behavior of LiTFSI by forming a uniform stable-protective-layer on the Al foil spontaneously. Moreover, the carbon coating on Al improves the adhesion behavior of the siloxane-based electrolyte. The time-dependent plating/stripping profiles of cells with 2550EO/LiTFSI and 390EO/LiTFSI electrolytes confirm the promising Li stability of both the electrolytes at low current density and 25 °C. The 2550EO/LiTFSI cell showed especially promising cycling stability at 25 °C, which is attributed to the critical roles of siloxane polymer (2550EO). Specifically, 2550EO inhibits corrosion of the Al current collector and improves Li stability.

D 6 h Symmetric Radical Donor–Acceptor Nanographene Modulated Interfacial Carrier Transfer for High-Performance Perovskite Solar Cells

<i>D</i> ^{6 <i>h</i>} Symmetric Radical Donor–Acceptor Nanographene Modulated Interfacial Carrier Transfer for High-Performance Perovskite Solar Cells

Relationship between Ion Transport and Phase Behavior in Acetal-Based Polymer Blend Electrolytes Studied by Electrochemical Characterization and Neutron Scattering

We have studied ion transport in electrolytes created by blending two different polymers and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). The polymers covered in this study are poly(ethylene oxide) (PEO), poly(1,3,6-trioxocane) (P(2EO-MO)), and poly(1,3-dioxolane) (P(EO-MO)). Ion transport is quantified by the product κρ+ which is defined as the efficacy of the electrolytes, where κ is conductivity and ρ+ is the current fraction determined by the Bruce–Vincent method. Polymer blends can be either one-phase or macrophase-separated. We used small-angle neutron scattering (SANS) to distinguish between these two possibilities. The random phase approximation (RPA) was used to interpret SANS data from one-phase blends. The effect of added salt on polymer blend thermodynamics is quantified by an effective Flory–Huggins interaction parameter. All polymer blends were one-phase in the absence of salt. Adding salt in small concentrations results in macrophase separation in all cases. One-phase systems were observed in the PEO/P(EO-MO)/LiTFSI blends at high salt concentrations. In most of the polymer blend electrolytes, the measured κρ+ was either lower than or comparable to that of the homopolymer electrolytes. An exception to this was one-phase PEO/P(EO-MO)/LiTFSI blends electrolytes at high salt concentrations.

Solvent-free design of argyrodite sulfide composite solid electrolyte with superb interface and moisture stability in anode-free lithium metal batteries

Anode-free lithium metal batteries (AFLMBs) reveal as future potential high-energy devices. Solidifying the electrolyte enables safer and more reliable battery operation. However, the commercial pristine sulfide and slurry-based preparation of sulfide composite solid electrolytes induce numerous pores on the pellet and membrane surfaces, respectively, which cause severe interface reactions and internal short circuits during cell performance. To overcome these challenges, we propose a solvent-free approach by fabricating deformable sulfide composite solid electrolyte (SCSE-4) via incorporating lithium argyrodite (Li6PS5Cl, LPSC) into a eutectic solution (succinonitrile (SN) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI)) together with polyvinylidene fluoride (PVDF) binder and LiF salt additive, then shearing the composite for an hour. As a result, the Li|SCSE-4|Li cell achieves a high critical current density of 8 mA cm−2, suggesting its high Li-dendrite inhibition capability. Furthermore, the new SCSE-4 electrolyte with surface-modify Li and silver modify copper (Cu@Ag) at 0.2 mA cm−2 delivers ultra-stable cycling above 3000 h with high coulombic efficiency of 97.34% after 150 cycles with no sign of short circuit issue in comparison with the LPSC cycles only for 200 h. A promising anode-free full cell demonstrates successfully by inserting the SCSE-4 electrolyte between Cu@Ag current collector and high voltage NMC811 cathode.

Ion Transport in 2D Nanostructured π-Conjugated Thieno[3,2-b]thiophene-Based Liquid Crystal.

Leveraging the self-assembling behavior of liquid crystals designed for controlling ion transport is of both fundamental and technological significance. Here, we have designed and prepared a liquid crystal that contains 2,5-bis(thien-2-yl)thieno[3,2-b]thiophene (BTTT) as mesogenic core and conjugated segment and symmetric tetra(ethylene oxide) (EO4) as polar side chains for ion-conducting regions. Driven by the crystallization of the BTTT cores, BTTT/dEO4 exhibits well-ordered smectic phases below 71.5 °C as confirmed by differential scanning calorimetry, polarized optical microscopy, temperature-dependent wide-angle X-ray scattering, and grazing incidence wide-angle X-ray scattering (GIWAXS). We adopted a combination of experimental GIWAXS and molecular dynamics (MD) simulations to better understand the molecular packing of BTTT/dEO4 films, particularly when loaded with the ion-conducting salt lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). Ionic conduction of BTTT/dEO4 is realized by the addition of LiTFSI, with the material able to maintain smectic phases up to r = [Li+]/[EO] = 0.1. The highest ionic conductivity of 8 × 10-3 S/cm was attained at an intermedium salt concentration of r = 0.05. It was also found that ion conduction in BTTT/dEO4 is enhanced by forming a smectic layered structure with irregular interfaces between the BTTT and EO4 layers and by the lateral film expansion upon salt addition. This can be explained by the enhancement of the misalignment and configurational entropy of the side chains, which increase their local mobility and that of the solvated ions. Our molecular design thus illustrates how, beyond the favorable energetic interactions that drive the assembly of ion solvating domains, modulation of entropic effects can also be favorably harnessed to improve ion conduction.

Molecular-Resolution Imaging of Interfacial Solvation of Electrolytes for Lithium-Ion Batteries by Frequency Modulation Atomic Force Microscopy.

Solvation structures formed by ions and solvent molecules at solid/electrolyte interfaces affect the energy storage performance of electrochemical devices, such as lithium-ion batteries. In this study, the molecular-scale solvation structures of an electrolyte, a solution of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) in propylene carbonate (PC) at the electrolyte-mica interface, were measured using frequency-modulation atomic force microscopy (FM-AFM). The spacing of the characteristic force oscillation in the force versus distance curves increased with increasing ion concentration, suggesting an increase in the effective size of molecules at the interface. Molecular dynamics simulations showed that the effective size of molecular assemblies, namely, solvated ions formed at the interface, increased with increasing ion concentrations, which was consistent with the experimental results. Knowledge of molecular-scale structures of solid/electrolyte interfaces obtained by a combination of FM-AFM and molecular dynamics simulations is important in the design of electrolytes for future energy devices and in improving their properties.

The Effect of Annealing on the Grain Structure and Ionic Conductivity of Block Copolymer Electrolytes

Block copolymer electrolytes that microphase-separate into rigid non-conducting domains and soft ion-conducting domains are known to exhibit stability against lithium metal anodes. In these systems, order is confined to grains with concomitant defects. When these electrolytes are annealed, the grain size typically increases, which is assumed in the literature to lead to a decrease in the ionic conductivity. In this work, we study the interplay between grain size and ionic conductivity using a block polymer electrolyte composed of a polystyrene (PS) block with a molecular weight of 19 kg/mol and a poly(ethylene oxide) (PEO) block with a molecular weight 20 kg/mol mixed with lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt at a variety of salt concentrations. The electrolytes have lamellar morphologies at all salt concentrations. At low salt concentrations, the average grain size before annealing is large and ionic conductivity decreases upon annealing. At high salt concentrations, however, the average grain size before annealing is small and ionic conductivity increases upon annealing.

Improved ionic conductivity and enhancedinterfacial stability of solid polymer electrolytes with porous ferroelectric ceramic nanofibers

Solid polymer electrolyte has aroused widespread research interest due to the potential to achieve high-safety and high-energy density lithium metal batteries. However, its practical application has been hampered by low ion conductivity. In this work, we innovatively prepare porous ferroelectric ceramic Bi4Ti3O12 nanofibers (BIT NFs) to construct fast conductive networks of Li+ ions in the poly(ethylene oxide) (PEO)/lithium bis(trifluoromethanesulfonyl) imide (LiTFSI) system to achieve the great improvement of lithium ion conductivity (6.25 × 10−4 S cm−1 at 50 °C). Various electrochemical characterizations and density functional theory (DFT) calculations reveal that the abundant oxygen vacancies possessed by the ferroelectric ceramic nanofibers help the accelerated dissociation of LiTFSI and promote the rapid transfer of free Li+ ions. Notably, thanks to the piezoelectric properties of BIT NFs, the dynamic regulation of the electrolyte/lithium interface is realized. The assembled lithium symmetric cells with the composite electrolyte exhibit excellent cycle stability (without short circuiting after 3000 h at 50 °C), and the all-solid-state LiFePO4||Li cells present a superior cycling performance (remained 118.2 mA h g − 1 after 1000 cycles at 0.2 mA cm−2).

Effects of the Electrolyte Concentration on the Nature of the Solid Electrolyte Interphase of a Lithium Metal Electrode

The need of more powerful systems with higher energy density raises a lot of interest in lithium metal batteries (LMBs). As LMBs suffer from safety concerns due to the dendrite growth, several strategies have been studied to limit this growth. Using a highly concentrated electrolyte allows a homogeneous lithium plating that delays the formation of dendrites. Herein, different techniques are used in order to better understand the beneficial role of the salt concentration in the lithium plating/stripping. Operando Fourier transform infrared spectroscopy highlights the better reversibility of the Li+ solvation in the 5 M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) in 1,2‐dioxolane/1,3‐dimethoxyethane electrolyte in comparison with the 1 M electrolyte. This obviously leads to different electrolyte decompositions during the lithium plating/stripping and changes the nature of the electrode solid electrolyte interphase (SEI) depending on the salt concentration. Gas chromatography coupled with mass spectrometry as well as X‐ray photoelectron spectroscopy confirms that with the 5 M LiTFSI electrolyte the salt is preferentially reduced during the plating/stripping, leading to a more inorganic SEI on the lithium metal electrode.

Rational design of sustainable diblock copolymers toward strong adhesives and stretchable ionic conductive materials

Sustainable diblock copolymers of poly (isobornyl acrylate)-block-poly (methyl acrylate) (PIBOA-b-PMA) were rationally designed and synthesized with terpenoid-derived monomer IBOA as the rigid segment. These PIBOA-b-PMA diblock copolymers show excellent mechanical performance comparable to traditional triblock copolymer elastomers. They can be successfully utilized as strong sustainable adhesives with good adhesion performance and high adhesive strength. Moreover, stretchable liquid-free ionic conductive materials can be successfully fabricated by incorporating lithium bis(trifluoromethane sulfonyl) imide (LiTFSI) into PIBOA-b-PMA diblock copolymers without leakage or evaporation risks. Intriguingly, these ionic conductive materials show decreased tensile strength compared to that of pristine PIBOA-b-PMA diblock copolymer due to the plasticizing effect while still maintaining excellent extensibility. The resultant stretchable ionic conductive materials show accurate and dramatic resistance change in response to intermittent stretching-retraction deformations, finger joint bending/straightening curvatures, and elbow joint bending/straightening movements, demonstrating exceptional performance. This convenient and facile strategy can offer new opportunities for the development of novel bio-based diblock copolymers toward strong adhesives and stretchable ionic conductive materials.

Introducing KI as a functional electrolyte additive to stabilize Li metal anode

A lithium metal battery (LMBs) is an excellent battery system for advanced electrochemical energy storage. However, the growth of lithium dendrites, the accumulation of inactive lithium, and the side reactions between lithium metal and electrolytes limit the cycling stability of LMBs. Herein, we introduce KI additive into lithium bis(trifluoromethanesulfonyl)imide (LiTFSI)/ether-based electrolyte and lithium hexafluorophosphate (LiPF6)/ester-based electrolyte for cycling stability improvement of LMBs. Cu-mesh@Ag||Li half-cell with 0.01 M KI additive exhibits a Coulombic efficiency as high as 98.8 % over 200 cycles. The improved performance due to the electrostatic shielding effect formed by K+ at low concentration and the rapid recovery of inactive lithium by iodine redox. The corresponding Li||Li symmetrical cell shows an outstanding lifespan of 1400 h at 1.0 mA cm−2 with 1.0 mAh cm−2. Meanwhile, in the 1 M LiTFSI + 0.01 M KI electrolyte, the Cu-mesh@Ag-Li||LiFePO4 (LFP) full cell holds capacity retention of 91.7 % over 800cycles at 2.0 C, the Li||LiNi0.8Co0.1Mn0.1O2 (NCM811) full cell possesses much better capacity retention of 54 % after 500 cycles at 1.0 C. This work offers a cost-effective proposal to improve application potential with the electrolyte engineering of rechargeable Li metal batteries.

Hydrofluoroether Diluted Dual-Salts-Based Electrolytes for Lithium-Sulfur Batteries with Enhanced Lithium Anode Protection.

With a high energy density, lithium-sulfur batteries (LSB) are regarded as one of the promising next-generation energy storage systems. However, many challenges hinder the practical applications of LSB, such as the dendrite formations/parasitic reactions on the Li metal anode and the "shuttle effect" of lithium polysulfides of the LSB cathode. Herein, a novel diluted medium-concentrated electrolyte (DMCE) is developed by adding 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether (TTE) into a dual salt medium-concentrated electrolyte (MCE) consisting of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI)-lithium bis(fluorosulfonyl)imide (LiFSI)/tetrahydrofuran (THF)-dipropyl ether (DPE). The optimized DMCE electrolyte is capable of protecting the Li metal anode and suppresses the dissolution of polysulfides and the "shuttle effect", delivering a high coulombic efficiency (CE) of Li plating-stripping up to 99.6% even at a low concentration of Li salt (1.0-2.0m). Impressively, compared with the cells cycled in the MCE electrolyte, the LiS cells with the DMCE-2.0m electrolyte have delivered an enhanced initial capacity of 682 mAh g-1 with an excellent capacity retention of 92% for 500 cycles. This strategy of using fluorinated ether as diluent solvent in a medium-concentrated electrolyte can accelerate the commercialization of LSB.

A Nonflammable High-Voltage 4.7 V Anode-Free Lithium Battery.

Anode-free lithium-metal batteries employ in situ lithium-plated current collectors as negative electrodes to afford optimal mass and volumetric energy densities. The main challenges to such batteries include their poor cycling stability and the safety issues of the flammable organic electrolytes. Here, a high-voltage 4.7V anode-free lithium-metal battery is reported,which usesa Cu foil coated with a layer (≈950nm) of silicon-polyacrylonitrile (Si-PAN, 25.5µg cm-2 ) as the negative electrode, a high-voltage cobalt-free LiNi0.5 Mn1.5 O4 (LNMO) as the positive electrode and a safe, nonflammable ionic liquid electrolyte composed of 4.5m lithium bis(fluorosulfonyl)imide (LiFSI) salt in N-methyl-N-propyl pyrrolidiniumbis(fluorosulfonyl)imide (Py13 FSI) with 1 wt% lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) as additive. The Si-PAN coating is found to seed the growth of lithium during charging, and reversibly expand/shrink during lithium plating/stripping over battery cycling. The wide-voltage-window electrolyte containing a high concentration of FSI- and TFSI- facilitates the formation of stable solid-electrolyte interphase, affording a 4.7V anode-free Cu@Si-PAN/LiNi0.5 Mn1.5 O4 battery with a reversible specific capacity of ≈120 mAh g-1 and high cycling stability (80% capacity retention after 120 cycles). These results represent the first anode-free Li battery with a high 4.7V discharge voltage and high safety.

Realizing compatibility of high voltage cathode and poly (ethylene oxide) electrolyte in all-solid-state lithium batteries by bilayer electrolyte design

Poly (ethylene oxide) (PEO) is easily oxidized at the cathode interface when coupled with high voltage cathodes (such as LiCoO2), leading to rapid capacity fade, limiting its application in high energy density all-solid-state battery. In this work, a bilayer concept is applied to design two PEO electrolyte layers composited with lithium difluoro (oxalato) borate (LiDFOB) and lithium bis(trifluoromethane sulfonyl) imide (LiTFSI), respectively. The thin PEO/LiDFOB layer is introduced by directly dropping the PEO/LiDFOB solution on the LiCoO2 cathode surface to construct a closely contact interphase. Meanwhile, a stable cathode electrolyte interphase (CEI) containing LixBxOy and LiF formed during electrochemical cycling realizes the LiCoO2/PEO interfacial compatibility. The self-generated PEO/LiTFSI layer towards the anode side provides high ionic conductivity and stabilizes the Li/electrolyte interface. As a result, the assembled cell using the bilayer PEO electrolyte achieves good cycling stability, the capacity retention increases from 15% to 75% after 100 cycles at 0.2C. The enhanced electrochemical performance is also achieved in LiNi0.6Co0.2Mn0.2O2/Li cell using this bilayer PEO electrolyte architecture. This work provides a simple strategy to make high-voltage cathode compatible with PEO electrolyte.

A Sulfolane-Based Electrolyte Optimized for Microporous Activated Carbon-Sulfur Composites for Lithium Sulfur Batteries

The dissolution of lithium polysulfide into electrolytes is a major limitation of Li-S batteries that hinders their practical applications. Lithium polysulfide dissolution is suppressed by using sulfur-complexed microporous-carbon cathodes in lithium–sulfur batteries. This study reports the use of a localized high-concentration electrolyte (LHCE), in which a sulfolane (SL) high-concentration electrolyte is diluted with hydrofluoroether (HFE), for the strong suppression of lithium polysulfide elution. A previously reported sulfolane electrolyte in the solvated state exhibits a short cycle life of eight cycles, whereas the sulfur-containing microporous-carbon cathode with a sulfolane-based electrolyte prepared in the ratio of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) : SL : HFE = (0.572–0.953) : 2.00 : 1.26 (mol) exhibits a discharge capacity of more than 550 mAh g−1, even after 50 charge–discharge cycles. Increasing the LiTFSI ratio decreases the response current during discharge, as indicated by cyclic voltammetry. A sulfur cathode with microporous carbon (AZC) shows equivalent performance on decreasing the amount of solvated LiTFSI. This study could guide the design and development of electrolytes for sulfur-containing microporous-carbon cathodes.

A room-temperature high performance all-solid-state lithium-sulfur battery enabled by a cross-linked copolymer@ceramic hybrid solid electrolyte

The use of solid electrolytes (SEs) is a key strategy for enabling the intrinsically safe operation of batteries comprising lithium metal anodes as they suppress the growth of lithium dendrites. Among the different types of SEs, polymer-based hybrid electrolytes (HEs) are highly promising due to their synergetic properties from the constituent polymer matrix and inorganic filler particles. However, the lithium-ion diffusion pathway in HEs is still dominated by the polymer, especially for polyethylene oxide (PEO)-based HEs. The main limitation of PEO is the strong temperature dependence of its ionic conductivity, preventing its use at room temperature (RT). Herein, a cross-linked polymer-based HE with a high ionic conductivity of 1.1 × 10-3 S cm-1 at RT is presented. The novel cross-linked copolymer, composed of pentaerythritol tetraacrylate (PETEA), tri(ethylene glycol) divinyl ether (TEG), and lithium bis(trifluoromethanesulfonyl)-imide (LiTFSI), serves as a matrix to achieve satisfactory mechanical strength. Integrated Li7La3Zr2O12 (LLZO) particles are covalently bound to the copolymer by a prior surface modification step. To demonstrate the suitability of the developed HE for RT application in advanced battery systems, a solid-state lithium-sulfur cell is built which exhibits an initial specific capacity of 688 mA h g-1. The ability of this HE to operate at RT can be expected to boost the development of safe all-solid-state batteries for many applications.

A Practical Polymer Electrolyte for Lithium and Sodium Batteries: Poly(pentyl malonate)

The rate at which rechargeable batteries can be charged and discharged depends primarily on ion transport between the electrodes. This is governed by the limiting current and electrochemical stability of the electrolyte. To our knowledge, the limiting current values of all dry polymer electrolytes in the literature are either not reported or lower than that of the benchmark polymer electrolyte comprising poly(ethylene oxide) (PEO) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). We describe the synthesis and characterization of a new polymer electrolyte, poly(pentyl malonate) (PPM). The length-normalized limiting current of PPM/LiTFSI in lithium-polymer-lithium symmetric cells is about a factor of 2.8 higher than that of PEO/LiTFSI at the same salt concentration and temperature. This polymer also exhibits increased electrochemical stability at high potentials (up to 5 V against Li+/Li) relative to PEO. Promising preliminary data obtained in sodium-polymer-sodium symmetric cells is also presented.

Effect of Lithium Salt Concentration on Materials Characteristics and Electrochemical Performance of Hybrid Inorganic/Polymer Solid Electrolyte for Solid-State Lithium-Ion Batteries

Lithium-ion batteries are popular energy storage devices due to their high energy density. Solid electrolytes appear to be a potential replacement for flammable liquid electrolytes in lithium batteries. This inorganic/hybrid solid electrolyte is a composite of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt, (poly(vinylidene fluoride-hexafluoro propylene) (PVDF-HFP) polymer and sodium superionic conductor (NASICON)-type Li1+xAlxTi2−x(PO4)3 (LATP) ceramic powder. The structure, morphology, mechanical behavior, and electrochemical performance of this composite solid electrolyte, based on various amounts of LiTFSI, were investigated. The lithium-ion transfer and conductivity increased as the LiTFSI lithium salt concentration increased. However, the mechanical strength apparently decreased once the percentage of LITFSI was over 60%. The hybrid electrolyte with 60% LiTFSI content showed high ionic conductivity of 2.14 × 10−4 S cm−1, a wide electrochemical stability window (3–6 V) and good electrochemical stability. The capacity of the Li|60% LiTFSI/PVDF-HFP/LATP| LiFePO4 solid-state lithium-metal battery was 103.8 mA h g−1 at 0.1 C, with a high-capacity retention of 98% after 50 cycles.

Highly Ion-Conductive, Elastic, and Adhesive Zwitterionic Polymer Electrolyte for All-Solid-State Lithium Batteries

Currently, lithium-ion batteries (LIBs) are considered to be one of the most popular energy storage systems for electronic devices supported by high energy density, high operating voltage, and favorable cycling performance. However, commercial LIBs with the organic liquid electrolyte and lithium (Li) salts are associated with critical safety issues such as uncontrollable side reactions, toxic liquid electrolyte leakage, flammability of electrolytes, and poor thermal stability. Therefore, replacing the liquid electrolyte with solid electrolytes is quite necessary. Among several solid ion conductors, solid polymer electrolytes (SPEs) can offer excellent flexibility, interfacial compatibility with electrodes, good processibility, low cost, and light weights that can overcome the limitations of ceramic ion conductors. However, current SPEs often encounter limitations such as poor mechanical strength and dimensional thermal stability, inferior electrochemical stability, and low Li+ ion conductivity at room temperature (~10-5 S cm-1 at 25 ℃).Here we present a multifunctional solid polymer electrolyte based on zwitterionic polyurethanes (zPU-SPE) for all-solid-state LIBs (SLBs). Our zPU-SPE exhibits a great potential to overcome current technical limitations of conventional SPE materials in SLB applications (e.g., low Li+ ion conductivity, inferior electrochemical/mechanical stabilities, unsatisfactory suppression of Li dendrite growth). We designed and synthesized a series of zPU [i.e., poly ((diethanolamine ethyl acetate)-co-poly(tetrahydrofuran)-co-(1,6-diisocyanatohexane))]. Our zPU-SPE can host an equal amount of lithium bis(trifluoromethanesulfonyl) imide (LiTFSI) without phase separation (up to 90 wt% of LiTFSI loading). The Li-ion conductivity value of zPU exponentially increases with the addition of LiTFSI and reaches 7.4 × 10-4 S/cm at 25° C, almost 14 times higher than that of poly(ethylene oxide) (PEO) SPE with ethylene oxide/Li+ ratio = 16. In addition, its superior adhesion energy (487.5 J/m2 of zPU-SPE vs. 150 J/m2 of commercial 3M Scotch Tape) can minimize interfacial resistance between electrode and SPE, and thus cell resistance of 100-µm-thick zPU SPE is as low as 280 W/cm2 compared to 1230 W/cm2 of the cell with a similar thickness of PEO SPE. Our zPU-SPE also showed an excellent elastic property with a tensile break of 1700% owing to its high density of inter- and intra-molecular hydrogen bonding in polymer matrix. The SLB battery performance of PEO and zPU-SPEs was evaluated using a solid-state Li/SPE/LiFePO4 cell; the assembled SLB cell was cycled at a constant current rate of 1 C at 25 °C. After a discharge capacity of the cell with zPU-SPE stabilized at 100 mAh g-1 after 15 cycles, there was a negligible capacity decrease (only 3% capacity decrease after 500 cycles), delivering a discharge capacity of 97 mAh g-1 with stable Coulombic efficiency (100%) over entire cycles. However, the discharge capacity of Li/PEO/LiFePO4 cells drops rapidly to 3 mAh g-1 after 100 cycles. These results demonstrate that the SLB cell assembled with PCB-PTHFU shows high discharge/charge capacity and excellent capacity retention with stable Coulombic efficiency. The good electrochemical performance of the zPU SPE can be attributed to good compatibility with electrodes, low charge transfer resistance at the interface of electrode/electrolyte, and high Li-ion conductivity, strongly suggesting that zPU SPEs are potential candidates for development of high performance of SLBs. Figure 1