Sulfonimide Lithium Salt Research Articles

PEO kaolinite intercalation interface accelerates lithium-ion transfer for all-solid-state lithium metal batteries

The improvement of ionic conductivity and Li dendrite inhibition capability of poly(ethylene oxide)(PEO)-based solid polymer electrolytes(SPEs) is urgent for the development of all-solid-state lithium metal batteries (ASSLMBs). Here, intercalated composite consisted with PEO polymer chains inserted into the clay gallery of the formamide intercalated kaolinite (KM) is formed. Due to this alternating organic-inorganic layered structure, the crystallinity of PEO decreases to 26.2% and the ion conductivity of SPE with 3% KM of PEO mass added(PEO+KM-3) increased to 1.43 × 10−3 S cm−1 at 60 °C. Besides, bis (trifluoromethane) sulfonimide lithium salt (LiTFSI) interacts with formamide to form a complex, making the local solvated Li+ transports close to a quasi-solid model. PEO+KM-3 SPE exhibits a good inhibition effect on lithium dendrites due to the formation of organic silicon at lithium anode side, and Li/ PEO+KM-3/Li cell works steadily for more than 1600 h at 60 °C with 0.1 mA cm−2. The assembled Li//LiFePO4 cell provides a capacity of 118 mAh g−1 after 500 cycles at 0.5 C at 60 °C.

(2-Furanylmethyl)spiro(N/N)cyclotriphosphazenes and some quaternized derivatives: syntheses, structural elucidation and free radical scavenging activity studies

In the present study, the reaction of hexachlorocyclotriphosphazene (N3P3CI6, HCCP) and N1,N2-bis(2-furanylmethyl)-1,2-diaminoethane (1) yielded the tetrachloro-spiro(ethane-1,2-diamino)-N,N-bis(2-furanylmethyl)cyclotriphosphazene (2). Tetrachlorocyclotriphosphazene (2) was then converted to fully substituted cyclotriphosphazenes (2a-2e) using secondary amines and sodium dimethylaminoethoxide. Compound 2e with dimethylaminoethoxy chains was quaternized in substituted nitrogen by reacting with methyl iodide (CH3I) to give polyiodo salt (2f). Subsequent metathesis with bis(trifluoromethane)sulfonimide lithium salt (LiNTf2) gave the corresponding ionic salt (2g). This phosphazene-based amide salt (2g) arose as a viscous liquid at room temperature. The structures of 2–2g were confirmed by elemental analysis, HRMS, FT-IR, 1H, 13C, and 31P NMR data. The crystal structures of 2 and 2b were also elucidated by X-ray crystallography. Additionally, the antioxidant activities of the phosphazene derivatives were investigated using free radical scavenging assays. The highest radical scavenging activity values (%) were detected for compounds 2e (53.4 ± 0.4) and 2f (56.1 ± 0.2).

Two-step strategy to optimize interfacial compatibility of polyether sulfone-Li6.75La3Zr1.75Ta0.25O12 composite polymer electrolytes with Li anode for solid lithium battery with a wide working temperature range

Although composite polymer electrolytes (CPEs) are currently regarded as one of the most promising solid electrolyte systems closing to commercial application, some basic problems, including low conductivity at low temperature, serious interfacial compatibility with Li metal anode, inhibit the development of CPEs for solid state lithium batteries (SSLBs). Herein, a “polymer-in-ceramic” CPEs consisting of polyether sulfone (PESF), Li6·75La3Zr1·75Ta0·25O12 (LLZTO) and bis(trifluoromethane) sulfonimide lithium salt (LiTFSI) is reported, and a two-step strategy is proposed to optimize its conductivity and interfacial compatibility with Li metal anode. Benefitting from both the continuous porous structure to provide additional Li+ conducting pathways on internal porous interfaces and the typical heterogeneous bilayer structure to enhance compatibility with Li metal anode, the optimized CPEs delivers promising Li+ conductivities in a wide operating temperature range (>2.0 × 10−4 S cm−1 at −10 °C, >1.4 × 10−3 S cm−1 at 60 °C), improved tolerance against Li dendrites and/or pulverization. Moreover, commercial LiFePO4 cathode based SSLBs show acceptable discharge specific capacities of >160 mA h g−1 and excellent cycling stabilities of over 200 cycles at both room temperature and 60 °C at 0.2C.

Electrothermal model of all‐solid‐state lithium battery with composite solid‐state electrolyte

AbstractFor secondary batteries, thermal runaway has become the main issue, and how to solve it is full of challenges. In this work, a universal thermal model for lithium ion batteries (LIBs) was proposed, which was validated by using commercially available 18650 batteries as well as testing the electrochemical parameters of a Poly(ethylene oxide)(PEO)–bis(trifluoromethane)sulfonimide lithium salt(LiTFSI)–Li2MnO3(LMO) (PLL) composite solid‐state electrolyte (CSSE), while a computational model was developed for all‐solid‐state LIBs (ASSLIBs) based on PLL CSSE. The simulation results show that the maximum temperature of ASSLIBs based on PLL CSSE and commercial standards are both significantly lower than the thermal runaway temperature of solid‐state electrolyte. However, as the temperature of the battery varies greatly under different operating conditions, it will cause great difficulties in the control of other ancillary components and even finally lead to certain safety issues. Therefore, from the perspective of performance and practical application, the CSSE should be improved toward improving the ionic conductivity at low temperatures to have more commercial prospects, and lower interfacial impedance and a higher lithium ion migration number would also be beneficial for optimizing the thermal behavior of ASSLIBs to achieve better commercial prospects.

Fluorinated Carbonate‐aided Ionic‐liquid Electrolyte Enables High‐capacity Lithium‐metal Batteries

AbstractIonic liquids (ILs) are promising electrolyte candidates for high‐safety and stability lithium metal batteries. However, their practical application is hindered by high viscosity resulting in a poor wettability of separator and sluggish Li+ transport at room temperature. Herein, a weakly‐solvating solvent of methyl (2,2,2‐trifluoroethyl) carbonate (FEMC) is employed as a co‐solvent in non‐flammable ionic‐liquid electrolyte (ILE) which composed with N‐butyl‐N‐methylpyrrolidinium bis (fluorsulfonyl) imide (Pyr14FSI) and bis (trifluoromethanesulfonyl) sulfonimide lithium salt (LiTFSI), effectively ameliorates the shortcomings of ILs mentioned above without sacrificing its safety character. Compared with pure ILE, the addition of FEMC can distinctly decrease the polarization voltage and electrode‐electrolyte interface resistance. With the assistance of FEMC solvent, the discharge specific capacity of Li||LiFePO4 (LFP) and Li||LiNi0.6Co0.2Mn0.2O2 (NCM622) cells are significantly improved. The origin of this great improvement is contributed to the exceptionally stable and LiF‐rich cathode electrolyte interphase (CEI) layer formed in this electrolyte. Additionally, Li||LiNi0.8Co0.1Mn0.1O2 (NCM811) cells exhibit a remarkable rate capability (105 mAh g−1 at 2 C rate), achieve an initial specific capacity of 202.8 mAh g−1 and outstanding capacity retention of 88.2 % over 100 cycles.

Thermally Stable Ceramic-Salt Electrolytes for Li Metal Batteries Produced from Cold Sintering Using DMF/Water Mixture Solvents.

The cold sintering process (CSP) for synthesizing oxide-based electrolytes, which uses water transient solvents and uniaxial pressure, is a promising alternative to the conventional high temperature sintering process due to its low temperature (<200 °C) and short processing time (<2 h). However, the formation of amorphous secondary phases in the intergranular regions, which results in poor ionic conductivity (σ), remains a challenge. In this study, we introduced high-boiling solvents of dimethylformamide (DMF, b.p.: 153 °C) and dimethyl sulfoxide (DMSO, b.p.: 189 °C) as transient solvents to develop composite electrolytes of Li1.5Al0.5Ge1.5(PO4)3 (LAGP) with bis(trifluoromethane)sulfonimide lithium salt (LiTFSI). Our results show that composite electrolytes processed with the DMF/water mixture (CSP LAGP-LiTFSI DMF/H2O) yield a high σ of 10-4 S cm-1 at room temperature and high relative densities of >87%. Furthermore, the composite electrolytes exhibit good thermal stability; the σ maintains its initial value after heat treatment. In contrast, the composite electrolytes processed with the DMSO/water mixture and water alone show thermal degradation. The CSP LAGP-LiTFSI DMF/H2O composite electrolytes exhibit long-term stability, showing no signs of short circuiting after 350 h at 0.1 mAh cm-2 in Li symmetric cells. Our work highlights the importance of selecting appropriate transient solvents for producing efficient and stable composite electrolytes using CSP.

Direct interface engineering using dopant of hole transport layer for efficient inorganic perovskite solar cells

With respect to the aim of achieving a suitable optical band gap and high thermal and chemical stability in next-generation perovskite solar cells (PSCs), inorganic CsPbI3 perovskite has gained significant attention. However, when it absorbs light, it quickly transforms into an undesired nonperovskite yellow phase at 25 °C. Therefore, it is crucial to stabilize the phase by reducing the defect density, which acts as a nonradiative recombination center at the interface of each layer. In this paper, we present an efficient interface treatment method that does not require any additional surface treatment such as annealing or coating, and the dopant Mn(TFSI)2 is directly mixed with the hole transporting material instead of bis(trifluoromethane)sulfonimide lithium salt (Li-TFSI). The use of Mn(TFSI)2 as a dopant diminishes the interfacial defects between the perovskite and hole transporting layer, reducing nonradiative recombination, increasing the lifetime of the carrier, and improving the power conversion efficiency from 16.5% for the control device using conventional Li-TFSI as a dopant to 17.6%. Moreover, the Mn(TFSI)2-doped device demonstrates superior long-term stability for 1000 h under ambient conditions without encapsulation, demonstrating 95% efficiency when compared with the initial performance. Therefore, Mn(TFSI)2 is a more powerful dopant of HTL and can increase the power conversion efficiency of PSCs by passivating the interface between the perovskite and HTL. Using Mn(TFSI)2, it is possible to quickly and effectively manufacture a stable inorganic perovskite device.

Constructing fast-ion-diffusion cathode-electrolyte-interphase to improve LiNi0.8Co0.1Mn0.1O2 cathode cyclic stability with composite polymer conductors

As one of the mainstream cathode materials used in power battery, it’s necessary for the LiNixCoyMn1-x-yO2 (NCM) to perform fast charge and discharge capabilities. However, the unstable cathode-electrolyte-interphase (CEI) at high charging/discharging rates causes cycling performance to degrade rapidly. Modified polyaniline (PANI) and polyethylene glycol (PEG) are adsorbed on layer-structured Ni-rich cathode, forming cathode-electrolyte-interphase CEI film with high electro-chemical stability and mechanical strength layer by coordinating interaction of hydrogen bonds with transition metals. When the carbon nanotubes (CNTs) or the -SO2F functional group in bis(trifluoromethane)sulfonimide lithium salt (LiTFSI) enters PANI skeleton, the composition, morphology and thickness of CEI film would be influenced by the CNTs or -SO2F groups. The improved interface would enhance the cathode-electrolyte interface stability by providing a steady channel for Li+ transport. Hence, the optimized CEI film effectively inhibit the occurrence of side reactions, and the capacity retention of NCM@PANIPEG/LiTFSI||Li cells has been improved from ∼ 55% to ∼ 77% at 45 °C and 2.7–4.3 V (vs. Li+/Li) in 100 cycles at 1 C. This low cost and straightforward preparation process exhibit great application prospects in future industrial applications.

High Ion Conducting Dobule Network Crosslinked Gel Polymer Electrolytes for High‐Performance Supercapacitors

AbstractAs the demand for electrical energy storage devices increases, various electrolytes are being studied. In particular, gel polymer electrolytes (GPEs) with excellent physical properties can improve safety and cycle life, so attempts are underway to replace organic liquid electrolytes facing fire or explosion issues. However, the intrinsic poor electrochemical properties of GPEs limit their commercialization in all‐solid‐state energy storage devices. In an attempt to solve this problem, epoxy/poly(ethylene glycol) (PEG)‐based double network electrolytes (DNEs) containing a mixture of bis(trifluoromethane)sulfonimide lithium salt (LiTFSI) and 1‐ethyl‐3‐methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIMTFSI) are designed to enhance the electrochemical properties of traditional single network electrolytes (SNEs). The synthesized epoxy/PEG‐based DNE has higher mechanical strength (G′ = 1.7 MPa) with outstanding ionic conductivity (σDC ≈ 5.8 × 10−4 S cm−1) at room temperature, compared to the epoxy‐based SNE. Then, an all‐solid‐state supercapacitor based on the DNE and activated carbon electrodes exhibits higher specific capacitance (≈153 F g−1) and power density (833 W kg−1), compared to the SNE‐based supercapacitor.

Application of salts of chaotropic anions in the development of hplc methods for the determination of meldonium in dosage forms

The aim of the work was to create an approach for the development of HPLC methods for the determination of meldonium in dosage forms with the usage of salts of chaotropic anions in mobile phases.&#x0D; Material and methods. Analytical equipment: Shimadzu UPLC system LC-40 PDA; Shimadzu Nexera-i LC-2040C 3D-Plus, controlled by software Lab Solution version 5.97, electronic laboratory balance RAD WAG AS 200/C, pH-meter I-160MI. Meldonium dihydrate (purity 99.3 %) was purchased from Sigma-Aldrich (Switzerland), and Vasopro capsules 500 mg were purchased from a local pharmacy. Chromatographic conditions: Agilent Zorbax C-18 SB 150 mm x 4.6 mm 3.5 μm column was used (Agilent Technologies, USA). Mobile phases: 1) 0.25 % KPF6 w/v – 0.1 % v/v 85 %H3PO4 95 % – 5 % ACN, 2) 0.3 % bis-(trifluoromethane)sulfonimide lithium salt 97 % w/v – 0.1 %v/v 85 % H3PO4 80 % – 20 % acetonitrile. Flow rate - 1mL/min, T=32 °C, detection UV=at 4 channels - 190 nm, 195 nm, 200 nm, 205 nm.&#x0D; Results and discussion. We have proposed two approaches using two different salts of chaotropic anions - potassium hexafluorophosphate and bis-(trifluoromethane)sulfonimide lithium salt – for the HPLC method development. The chaotropic effects of these anions toward meldonium strongly influenced the analyte migratory behaviour. Both mobile phases involved, in addition to the use of a chaotrope, also the use of acetonitrile and pH adjustment with 0.1 % v/v 85 % H3PO4 solution. The detection wavelength (190 nm, 195 nm, 200 nm, 205 nm) was selected experimentally. The results were obtained for 8 concepts. Parameters of the chromatographic system confirm the conclusions and results of this investigation for the influence of chaotropic salts on N-containing molecules in an acidic pH medium, by increasing their retentivity and improving peak shape and uniformity homogeneity, even on the column without end-capping and base-deactivating. Validation of the analytical method was carried out following the requirements of SPhU. Conclusions. HPLC methods for the determination of meldonium in dosage forms have been developed, using positive impacts of chaotropic salts on the molecules containing N-atoms in their molecule on their retentions and peak symmetries on the chromatogram. The validation of the analytical methods showed their suitability for pharmaceutical analysis

Effect of Li-salt additives on the optical features and solar cell performance of Cs0.05FA0.85MA0.10Pb(I0.90Br0.10)3 perovskite solar cells

Glass substrate/FTO/Compact TiO2/Mesoporous TiO2 layers/x mg LiTFSI/Cs0.05FA0.85MA0.10Pb(I0.90Br0.10)3 films were prepared. The effect of bis(trifluoromethane)sulfonimide lithium (LiTFSI) salt on the phases formation, crystal structure and crystallinity of pervoskite Cs0.05FA0.85MA0.10Pb(I0.90Br0.10)3 layer was investigated using X-ray diffraction technique. The influence of the LiTFSI additives with different ratios on the optical features of Glass substrate/FTO/Compact TiO2/Mesoporous TiO2 layers/x mg LiTFSI/Cs0.05FA0.85MA0.10Pb(I0.90Br0.10)3 films was studied using UV spectrophotometric technique. The optical bandgap energies for all films were found to be 1.58 eV. The maximum value of refractive index (n = 2.6) for the film without LiTFSI was observed in the IR range, while in the visible range, the film with 21 mg of LiTFSI has a maximum n value (∼2.3). In the UV and visible regions, the film with 21 mg LiTFSI has the highest nonlinear optical parameters (NLO) values, while in the IR range, the film without LiTFSI salt has the highest NLO values. The effect of LiTFSI salt on the photoluminescence emitted spectra was also examined. The power conversion efficiency (PCE) and fill factor (FF) were enhanced to 18.85 and 76.6%, respectively, as the amount of LiTFSI additive became 21 mg.

Achieving fast and stable Li+ transport in lithium-sulfur battery via a high ionic conduction and high adhesion solid polymer electrolyte

Solid-state lithium (Li)-sulfur (S) batteries are promising secondary batteries because of their high energy density and high safety, but their practical application is severely hindered by poor Li-ions (Li+) transport in batteries due to low ionic conduction of the electrolyte and unstable electrode/electrolyte interface. Here, we address the issue by using a polyurethane (PU)-based electrolyte. The polar urethane/urea groups of PU reduce the hopping energy barrier of Li+, which results in high ionic conductivity of 1.8 × 10-4 S cm-1 (25 °C), high ion transference number of 0.54, and low activation energy of 0.39 eV. In addition, the polar urethane/urea groups endow the electrolyte with high adhesion, which allows the electrode/electrolyte interfaces to self-heal timely after being damaged during cycling. Benefiting from these merits, a symmetric Li||Li cell using the polyolefin-PU-bis(trifluoromethane)sulfonimide lithium salt electrolyte can cycle for approximately 800 h with a stable overpotential (approximately 40 mV), and a solid-state Li-S battery using the electrolyte delivers a specific capacity of approximately 610 mAh g-1 after testing for 125 cycles at a S loading of about 4 mg cm-2. Self-healing of the electrode/electrolyte interfaces during cycling was observed in situ by a laser confocal microscope. This study demonstrates the importance of polar groups in electrolytes in maintaining a fast and stable Li+ transport, which can be applied to other solid-state batteries.

Solid state fiber-dye sensitized solar cells (SS-FDSSC): A mini review

Fiber-shaped dye-sensitized solar cells (FDSSC) can fulfill the energy demand of portable electronic devices, specifically in remote applications; however, the stability of such systems is a bottleneck, due to the use of liquid electrolytes. Liquid electrolytes pose evaporation problem, leakage issue, and possibility of short circuit, hence solid electrolytes are the ultimate solution for long-lasting FDSSCs. Considering this, recent advances in solid electrolytes, photoanode materials, and counter electrode materials are summarized for all solid-FDSSCs. A special focus has been given to the types of solid electrolytes, their synthesis, and associated photovoltaic performance. The performance parameters of solid electrolytes, such as ionic conductivity, light transmittance, and photovoltaic performance are summarized in this review. Furthermore, the works related to novel photoanode and counter electrode materials employing solid electrolytes are also included in the review. A comparison table of power conversion efficiencies and lifetime of solid-state-FDSSCs is provided, which shows that the highest efficiency is possible for Li-TFSI (bis(trifluoromethane)sulfonimide lithium salt) soaked Iodide electrolytes. Better transparency and conductivity of such electrolytes are key parameters in imparting high efficiency of such electrolytes, i.e. 6.5%.

Probing hydrogen-bond networks in plastic crystals with terahertz and infrared spectroscopy

A molecular-level understanding of phase changes in hydrogen-bonded solid-state systems is of great importance in fields spanning thermal science to medical therapeutics. Polyols have recently emerged as prime targets for deployment, given their versatility in phase-induced changes, and occupy a deep space in eutectic solvents. Here, we explore the hydrogen-bond network of neopentyl glycol (NPG) with terahertz time-domain spectroscopy, attenuated total reflection spectroscopy in the far- and mid-infrared regions augmented by electronic structure calculations. A picture emerges where vibrational spectroscopy can exquisitely probe a crystalline to amorphous solid-solid phase transition while spectroscopy in the mid-infrared region provides a molecular picture of the phase transition. These methods are then applied to understand the thermal properties and phase changes in NPG upon incorporation of bis(trifluoromethane)-sulfonimide lithium salt, to demonstrate that vibrational spectroscopy can directly probe the disruption of hydrogen-bond networks in plastic crystals.

Passerini polymerization as a novel route for high ionic conductivity solid polymer electrolyte

Polyethylene glycol (PEG) used as solid polymer electrolyte has shown disadvantages of low ionic conductivity and lithium ion transference number due to its high crystallinity. In this study, we propose Passerini three-component polymerization (P-3CP) to modify PEGs for solid polymer electrolytes (SPEs). Thus, a series of PEG-based polyesters (PGPEs) with molar masses between 14,400 and 30,200 gmol−1 are synthesized by P-3CP. The crystallinity of obtained PGPEs is successfully suppressed by the introduction of side groups via P-3CP. SPEs consisting of PGPEs as matrix and bis(trifluoromethane)sulfonimide lithium salt (LiTFSI) with different concentrations were investigated in detail. The SPE composed of PGPE-4000 with 30 wt% LiTFSI presented the best ionic conductivities of 5.85 × 10-5 Scm−1 and 1.94 × 10-3 Scm−1 at room temperature and 80 °C, respectively, which are significantly higher than the commonly used PEG-based SPE. The LiFePO4/Li solid-state lithium-ion battery assembled with PGPE-based SPE showed excellent cycle stability. After 100 cycles at 0.5C at 60 °C, the discharge specific capacity remains 133 mAhg−1. Furthermore, due to the addition of amide side groups, the flame retardant property of PGPE-based SPEs is improved. Compared to PEG, the limiting oxygen index (LOI) values increase from 21.0 to 25.5 after modification by P-3CP. Therefore, the P-3CP is an attractive method to obtain polyesters from dicarboxylic acid or diol monomers for the application in the lithium battery field.

Amorphous-conjugated polymer-additive approach to prepare quality Spiro-OMeTAD-based hole transporting material for efficient Sb2S3 solar cells

2,2′,7,7′-Tetrakis-(N,N-di-p-methoxyphenylamine)-9,9′-spirobifluorene (Spiro-OMeTAD) is a common hole transport material (HTM) for efficient solar cells. However, the conventional Spiro-OMeTAD-based HTM contains the bis(trifluoromethane)sulfonimide lithium salt (Li-TFSI) additive that often introduces pinholes into the HTM layer to deteriorate device performance. Here, we use amorphous polymer poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) as an additive into the Spiro-OMeTAD-based HTM for efficient Sb2S3 solar cells. It is showed that MEH-PPV remarkably improves the quality of the HTM layer, suppresses the charge recombination and enhances the charge collection efficiency in the Sb2S3 solar cells. With the MEH-PPV additive, the power conversion efficiency of the solar cells is boosted up to 6.02% from the original 5.51% without the additive.

Flexible and Foldable Films of SWCNT Thermoelectric Composites and an S-Shape Thermoelectric Generator with a Vertical Temperature Gradient.

Organic thermoelectric (TE) composites and flexible devices have gained a rapid development in recent decade. Herein, a flexible and foldable film of poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate)/single-walled carbon nanotube (PEDOT:PSS/SWCNT) composite is fabricated by post-treatment with an ionic liquid (IL), and an S-shape TE generator (TEG) is designed to harvest heat from human body via a vertical temperature gradient. After being post-treated with IL of bis(trifluoromethane)sulfonimide lithium salt (LiTFSI), the PEDOT:PSS/SWNCT composite displays an improved electrical conductivity from 1063 ± 80 to 1562 ± 170 S cm-1, with an almost constant Seebeck coefficient of ∼21.9 μV K-1 with a 30 wt % content of SWCNT. The TE properties exhibit excellent stability against repeated bending or folding cycles. Furthermore, an S-shape architecture is designed for TEG assembling, which enables effective utilization of a vertical temperature gradient between the human body and surroundings. The present study proposes a universal strategy for harvesting heat using a wearable TEG via a vertical temperature gradient, which represents great prospects for application in self-powered wearable electronics.

3D cellulose fiber networks modified by PEDOT:PSS/graphene nanoplatelets for thermoelectric applications

Organic materials have attracted considerable attention for thermoelectric (TE) applications. Given their potential as wearable power generators, there is an urgent need to develop organic TE materials that possess superior electronic properties as well as excellent mechanical and environmental stability. Here, we develop paper-based TE materials using the poly(3,4-ethylenedioxythiophene): polystyrenesulfonate (PEDOT:PSS), graphene nanoplatelets (GNPs), and a starch-based biopolymer as a binder for GNPs. The device fabrication consists of spraying the biopolymer/GNP ink onto the cellulose paper followed by spraying the PEDOT:PSS solution. Further enhancement of TE properties was obtained by adding an ionic liquid (IL), bis(trifluoromethane)sulfonimide lithium salt to the PEDOT:PSS solution. Upon addition of the IL, the electrical conductivity of as-fabricated PEDOT:PSS films increased nearly two orders of magnitude. The electrical conductivity increases with GNPs' content due to formation of an effective electrical percolation network. Interestingly, incorporating GNPs simultaneously improves the Seebeck coefficient. Raman measurements suggest that the concurrent enhancement of the Seebeck coefficient and electrical conductivity might be related to the chemical bonding between the conducting polymer chains and the filler. In addition, these composites display remarkable flexibility at various bending angles and environmental stability without losing their original conductivity after three months of exposure to ambient conditions.

High performance of polyethylene composite separators modified by carbon nanotube, lithium salt and SiO2 nanoparticles for lithium ion batteries

In this work, the polyethylene (PE) separator is firstly modified with bis(trifluoromethane)sulfonimide lithium salt (LiTFSI) solution, and then coated with a solution of hydroxyl functionalized carbon nanotube (CNT), nano-SiO2 and polyvinyl alcohol (PVA) on its one side. The obtained composite separator (PE@LiSiO2CNT) is with a thermal shrinkage of 14% at 150 °C for 0.5 h, and the ionic conductivity can be as high as 1.69 × 10-3 S cm-1. Furthermore, the specific discharge capacity of the assembled lithium ion batteries (LIBs) reaches 164 mAh g-1 at 0.2 C, and the coulomb efficiency remains above 99% after 250 cycles. This can be attributed to the network structure of SiO2 and CNT which increases the porosity of the separator and improves the electrolyte uptake. Besides, the CNT effectively alleviates the self-aggregation of SiO2, and promotes the rapid electrochemical reactions between the separator and the cathode. And it can also allow the free diffusion of lithium ions through its walls and channels with high efficiency, thus reducing the charge transfer resistance and improving the battery performance. Therefore, the modified separator with excellent dimensional thermal stability and electrochemical performance are successfully obtained, which are helpful to the development of LIBs.

Mechanistic insight into the chemical treatments of monolayer transition metal disulfides for photoluminescence enhancement

There is a growing interest in obtaining high quality monolayer transition metal disulfides for optoelectronic applications. Surface treatments using a range of chemicals have proven effective to improve the photoluminescence yield of these materials. However, the underlying mechanism for the photoluminescence enhancement is not clear, which prevents a rational design of passivation strategies. Here, a simple and effective approach to significantly enhance the photoluminescence is demonstrated by using a family of cation donors, which we show to be much more effective than commonly used p-dopants. We develop a detailed mechanistic picture for the action of these cation donors and demonstrate that one of them, bis(trifluoromethane)sulfonimide lithium salt (Li-TFSI), enhances the photoluminescence of both MoS2 and WS2 to a level double that of the currently best performing super-acid trifluoromethanesulfonimide (H-TFSI) treatment. In addition, the ionic salts used in our treatments are compatible with greener solvents and are easier to handle than super-acids, providing the possibility of performing treatments during device fabrication. This work sets up rational selection rules for ionic chemicals to passivate transition metal disulfides and increases their potential in practical optoelectronic applications.