Lithium Bis(trifluoromethylsulfonyl)imide Research Articles

Ion-Exchange Polymer Network Enhanced Interfacial Compatibility for Stable and Efficient Inverted Perovskite Solar Cells.

Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) as a low-cost and water-processable hole transport material has been widely used in various optoelectronic devices. Although the incorporation of anionic polyelectrolyte PSS in PEDOT contributes to superior water solubility, the trade-off between efficiency and stability remains a challenging issue, limiting its reliable application in perovskite solar cells (PSCs). Herein, we proposed an ion-exchange (IE) strategy to effectively control the doping degree, interfacial charge dynamics, and reliability of PEDOT:PSS in PSCs. This IE approach based on hard cation-soft anion rules enabled effective anion exchange between PEDOT:PSS and lithium bis(trifluoromethylsulfonyl)imide (LiTFSI), which favored enhancing the film conductivity, regulating the perovskite crystallization, and reducing the carrier losses at the interfaces. Consequently, a notable increase of the open-circuit voltage from 0.88 to 1.02 V was realized, resulting in a champion efficiency of 18.7% compared to the control (15.4%) in inverted PSCs. More encouragingly, this IE strategy significantly promoted the thermal and environmental stability of unsealed devices by maintaining over 80% of initial efficiencies after 2000 h. This work provides an effective way to regulate the doping state of the PEDOT-based hole transport material and guides the development of robust polymeric conducting materials for efficient perovskite photovoltaics.

Functionalization of Cathode–Electrolyte Interface with Ionic Liquids for High-Performance Quasi-Solid-State Lithium–Sulfur Batteries: A Low-Sulfur Loading Study

We introduce a quasi-solid-state electrolyte lithium-sulfur (Li–S) battery (QSSEB) based on a novel Li-argyrodite solid-state electrolyte (SSE), Super P–Sulfur cathode, and Li-anode. The cathode was prepared using a water-based carboxymethyl cellulose (CMC) solution and styrene butadiene rubber (SBR) as the binder while Li6PS5F0.5Cl0.5 SSE was synthesized using a solvent-based process, via the introduction of LiF into the argyrodite crystal structure, which enhances both the ionic conductivity and interface-stabilizing properties of the SSE. Ionic liquids (IL) were prepared using lithium bis(trifluoromethyl sulfonyl)imide (LiTFSI) as the salt, with pre-mixed pyrrolidinium bis(trifluoromethyl sulfonyl)imide (PYR) as solvent and 1,3-dioxolane (DOL) as diluent, and they were used to wet the SSE–electrode interfaces. The effect of IL dilution, the co-solvent amount, the LiTFSI concentration, the C rate at which the batteries are tested and the effect of the introduction of SSE in the cathode, were systematically studied and optimized to develop a QSSEB with higher capacity retention and cyclability. Interfacial reactions occurring at the cathode–SSE interface during cycling were also investigated using electrochemical impedance spectroscopy, cyclic voltammetry, and X-ray photoelectron spectroscopy supported by ab initio molecular dynamics simulations. This work offers a new insight into the intimate interfacial contacts between the SSE and carbon–sulfur cathodes, which are critical for improving the electrochemical performance of quasi-solid-state lithium–sulfur batteries.

High toughness, ultra-sensitive, and extreme environment resistant fabric temperature sensors based on supramolecular-polymer dual network ionic conductive elastomers

Liquid-free ionic conductive elastomers (ICEs) show great potential for next-gen wearable electronics, free from issues like solvent evaporation and freezing. However, crafting ICEs with both strength and temperature sensitivity remains a significant challenge. In this study, a supramolecular gel based on 1,3:2,4-bis (3,4-dimethylbenzene methylene) sorbitol (DMBS) is selected as the first network, and poly(ethylene glycol) methyl ether methacrylate (PEGMA) copolymerized with diallyl dimethyl bis (trifluoromethyl sulfonyl)imide (DADMATFSI) is added as the second network, with the addition of lithium bis(trifluoromethyl sulfonyl)imide (LiTFSI). The supramolecular-polymer dual network ion-conductive elastomer SP-DN-LiTFSI is created. The elastomer exhibits exceptional mechanical characteristics, including a maximum tensile stress of 1591.1 kPa and an impressive strain of 2361 %. Additionally, it demonstrates an extraordinarily high toughness of 33.121 MJ m−3. Moreover, this elastomer-based temperature sensor is responsive to external stimuli, such as blowing, and boasts an outstanding temperature sensing coefficient (S) of 0.114 °C−1 within the range of 30–60 °C. Remarkably, it can discern even the slightest temperature variations as low as 0.5 °C within the typical human body temperature range. This work represents an innovative integration of a dual network structure and two strategies for elastomer fabrication. It provides a novel approach for developing highly sensitive wearable temperature measurement devices that exhibit exceptional resistance to mechanical wear.

Correlation between lithium-ion diffusion and coordination environment in solid polymer electrolytes: a molecular dynamics study

Lithium-ion diffusion in solid polymer electrolytes (SPEs) is a pivotal characteristic that significantly influences overall lithium-ion battery performance. This characteristic can be affected by the coordination environment of lithium ions within the polymer matrix. However, the correlation between lithium-ion diffusion and its coordination environment in biopolymer-based SPEs such as carboxymethyl chitosan (CMCS) remains understudied. In this study, we used molecular dynamics (MD) simulations to investigate this correlation. Lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) was used as the lithium salt in the simulated systems. All MD simulations were conducted using the GROMACS package with the general AMBER force field (GAFF). The coordination structures around Li+ were successfully estimated using the radial distribution function obtained from the MD simulations. These results indicate a preference for Li+ coordination with oxygen atoms, both from the CMCS polymer chains (OCMCS) and TFSI− ions (OTFSI-). The coordination number between Li+ and OCMCS decreases as the concentration of LiTFSI increases. The diffusion coefficients of Li+ varied depending on the concentration of LiTFSI and demonstrated a sensitivity to the coordination structure of Li+. A high diffusion coefficient of Li+ ions was observed at low LiTFSI concentrations, where Li+ was primarily coordinated with oxygen atoms from the CMCS polymer chains.

Ab Initio Molecular Dynamics Simulations of Aqueous LiTFSI Solutions─Structure, Hydrogen Bonding, and IR Spectra.

Simulations of Density Functional Theory-based ab initio molecular dynamics (AIMD) have been performed for a series of aqueous lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) solutions with concentrations ranging from salt-in-water to water-in-salt systems. Analysis of the structure of electrolytes has revealed a preference of Li+ cations to interact with water molecules. In concentrated LiTFSI solutions, water molecules form small associates. The total number of hydrogen bonds (HBs) in the system decreases with salt concentrations, with bonds to water acceptors being only partially replaced by interactions with TFSI anions. Infrared (IR) spectra in the region of the O-H stretching frequency calculated from AIMD trajectories are in good agreement with experimental data. Statistics of oscillations of individual O-H bonds have shown correlations between vibrational frequencies and the structure of HBs formed by water. The changes in the IR spectrum have been related to the varying contributions of different local environments of the water molecules. The abundances of the three spectral components calculated from the simulations agree well with the decomposition of the experimental IR spectra reported in the literature.

Investigating the Molecular Orientation and Thermal Stability of Spiro-OMeTAD and Its Dopants By Near Edge X-Ray Absorption Fine Structure

This work describes the utilization of near edge X-ray absorption fine structure (NEXAFS) to investigate the hole transporting material (HTM) 2,2ʹ,7,7ʹ-tetrakis(N,N-di-p-methoxyphenylamine)- 9,9ʹ-spirobifluorene (Spiro-OMeTAD) and its most common dopants, lithium bis-(trifluoromethylsulfonyl) imide (LiTFSI), 4-tert-butylpiridine (tBP) and 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4-TCNQ). Utilizing angle resolved NEXAFS, the orientation of the molecules on the surface can be observed. The data suggests it is difficult to determine any orientational preference for Spiro-OMeTAD deposited on a surface due to the 3D propeller-like geometry of this molecule. Both doped and undoped samples show thermal stability beyond the glass transition temperature of the molecules. Significant changes to the Spiro-OMeTAD spectra were observed with the addition of the dopants, in particular the C K-edge. Differences are also observed in the valence band spectra when dopants are added. It is also demonstrated how the doping combination of LiFTSI with tBP and, F4-TCNQ act as p-type dopants by altering the position of the HOMO levels. The F4-TCNQ induces a larger change in the HOMO levels when compared to the LiTFSI and tBP. These results are important to increase our understanding of Spiro-OMeTAD and the effect dopants have on this material for next generation solar cells.

Nanostructure of Locally Concentrated Ionic Liquids in the Bulk and at Graphite and Gold Electrodes.

The physical properties of ionic liquids (ILs) have led to intense research interest, but for many applications, high viscosity is problematic. Mixing the IL with a diluent that lowers viscosity offers a solution if the favorable IL physical properties are not compromised. Here we show that mixing an IL or IL electrolyte (ILE, an IL with dissolved metal ions) with a nonsolvating fluorous diluent produces a low viscosity mixture in which the local ion arrangements, and therefore key physical properties, are retained or enhanced. The locally concentrated ionic liquids (LCILs) examined are 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (HMIM TFSI), 1-hexyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate (HMIM FAP), or 1-butyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate (BMIM FAP) mixed with 1,1,2,2-tetrafluoroethyl 2,2,2-trifluoroethyl ether (TFTFE) at 2:1, 1:1, and 1:2 (w/w) IL:TFTFE, as well as the locally concentrated ILEs (LCILEs) formed from 2:1 (w/w) HMIM TFSI-TFTFE with 0.25, 0.5, and 0.75 m lithium bis(trifluoromethylsulfonyl)imide (LiTFSI). Rheology and conductivity measurements reveal that the added TFTFE significantly reduces viscosity and increases ionic conductivity, and cyclic voltammetry (CV) reveals minimal reductions in electrochemical windows on gold and carbon electrodes. This is explained by the small- and wide-angle X-ray scattering (S/WAXS) and atomic force microscopy (AFM) data, which show that the local ion nanostructures are largely retained in LCILs and LCILEs in bulk and at gold and graphite electrodes for all potentials investigated.

Lithium Self-Diffusion in a Polymer Electrolyte for Solid-State Batteries: ToF-SIMS/ssNMR Correlative Characterization and Modeling Based on Lithium Isotopic Labeling.

Manufacturers aim to commercialize efficient and safe batteries by finding new strategies. Solid-state electrolytes can be seen as an opportunity to develop batteries with a high energy density. They allow the use of lithium foil as the anode, increasing the energy density. Also, they are composed of nonflammable materials making them safer than liquid electrolytes. However, to enhance the electrochemical performances of forthcoming solid-state lithium metal batteries, phenomena governing ionic conductivity have yet to be mastered in such devices. Lithium isotopic tracing was successfully used in previous works to further understand lithium ion transport mechanisms in batteries. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) and 6/7Li high-resolution solid-state nuclear magnetic resonance (ssNMR) spectroscopy are two complementary techniques probing local and global scale, respectively. Both techniques can distinguish lithium isotopes. Here, four polymer membranes were elaborated with the same lithium concentration, but with various isotopic enrichments from 7.6 to 95.4% of 6Li. The selected material was a poly(ethylene oxide) (PEO) membrane containing lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) as lithium salt. They are widely studied in the lithium battery field. First, reliable ToF-SIMS and ssNMR methodologies were validated in light of the converging results. They led to accurate determination of lithium isotopic abundance of polymer membranes with a 1 or a 2% uncertainty, respectively. Then, the developed methodologies were applied to characterize lithium self-diffusion in a polymer membrane. Furthermore, numerical simulations based on a two-dimensional diffusion model compared with ToF-SIMS analyses allowed us to extract a lithium self-diffusion coefficient of 1.6 × 10-12 m2·s-1 at 60 °C, which complements other published values. The robust methodologies described in this work can be extended to various applications and materials. They stand as powerful strategies to better understand lithium ionic transport, especially in multiphase materials, for example, in hybrid solid-state electrolytes.

Lithium nitrate mediated dynamic formation of solid electrolyte interphase revealed by in situ Fourier transform infrared spectroscopy

A stable solid electrolyte interphase (SEI) plays a vital role in the cyclic stability and Coulombic efficiency (CE) of high-performance lithium-sulfur (Li-S) batteries. It is recognized that the LiNO3 additive can stabilize the SEI of the lithium electrode. However, the exact mechanism of the LiNO3 additive on the SEI of the lithium electrode remains unclear. In this work, we first revealed the mediation mechanism of LiNO3 additive on the dynamic evolution of the SEI on a lithium anode surface through in situ Fourier transform infrared (FTIR) spectroscopy and ab initio molecular dynamics (AIMD) methods. The FTIR and AIMD results directly proved that LiNO3 can accelerate the reduction of lithium bis(trifluoromethyl sulfonyl)imide (LiTFSI) into small molecules rich in Li2O on lithium anode, thus forming a compact and stable SEI after immersing in the LiNO3-containing electrolyte. Moreover, the decomposition of LiTFSI and the solvent is hindered in the subsequent lithium deposition stripping process due to the stable SEI, thus leading to higher Coulombic efficiency and long-term cyclic stability. In addition, an ROSO2Li-like intermediate is also observed during the lithium deposition process while decomposing or diffusing away during the lithium stripping process, maintaining a dynamic formation/dissolution equilibrium of the SEI. This research provides a new insight into understanding the role of LiNO3 in stabilizing lithium electrode.

Enhanced LiMn2O4 Thin-Film Electrode Stability in Ionic Liquid Electrolyte: A Pathway to Suppress Mn Dissolution.

Spinel-type lithium manganese oxide (LiMn2O4) cathodes suffer from severe manganese dissolution in the electrolyte, compromising the cyclic stability of LMO-based Li-ion batteries (LIBs). In addition to causing structural and morphological deterioration to the cathode, dissolved Mn ions can migrate through the electrolyte to deposit on the anode, accelerating capacity fade. Here, we examine single-crystal epitaxial LiMn2O4 (111) thin-films using synchrotron in situ X-ray diffraction and reflectivity to study the structural and interfacial evolution during cycling. Cyclic voltammetry is performed in a wide range (2.5-4.3 V vs Li/Li+) to promote Mn3+ formation, which enhances dissolution, for two different electrolyte systems: an imidazolium ionic liquid containing lithium bis-(trifluoromethylsulfonyl)imide (LiTFSI) and a conventional carbonate liquid electrolyte containing lithium hexafluorophosphate (LiPF6). We find exceptional stability in this voltage range for the ionic liquid electrolyte compared to the conventional electrolyte, which is attributed to the absence of Mn dissolution in the ionic liquid. X-ray reflectivity shows a negligible loss of cathode material for the films cycled in the ionic liquid electrolyte, further confirmed by inductively coupled plasma mass spectrometry and transmission electron microscopy. Conversely, a substantial loss of Mn is found when the film is cycled in the conventional electrolyte. These findings show the significant advantages of ionic liquids in suppressing Mn dissolution in LiMn2O4 LIB cathodes.

Achieving Practical High-Energy-Density Lithium-Metal Batteries by a Dual-Anion Regulated Electrolyte.

Lithium-metal batteries (LMBs) using lithium-metal anodes and high-voltage cathodes have been deemed as one of the most promising high-energy-density battery technology. However, its practical application is largely hindered by the notorious dendrite growth of lithium-metal anodes, the fast structure degradation of the cathode, and insufficient electrode-electrolyte interphase kinetics. Here, a dual-anion regulated electrolyte is developed for LMBs using lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) and lithium difluoro(bisoxalato)phosphate (LiDFBOP) as anion regulators. The incorporation of TFSI- in the solvation sheath reduces the desolvation energy of Li+ , and DFBOP- promotes the formation of highly ion-conductive and sustainable inorganic-rich interphases on the electrodes. Significantly enhanced performance is demonstrated on Li||LiNi0.83 Co0.11 Mn0.06 O2 pouch cells, with 84.6% capacity retention after 150 cycles in 6.0 Ah pouch cells and an ultrahigh rate capability up to 5 C in 2.0 Ah pouch cells. Furthermore, a pouch cell with an ultralarge capacity of 39.0 Ah is fabricated and achieves an ultrahigh energy density of 521.3Wh kg-1 . The findings provide a facile electrolyte design strategy for promoting the practical utilization of high-energy-density LMBs.

Investigating the Molecular Orientation and Thermal Stability of Spiro‐OMeTAD and its Dopants by Near Edge X‐Ray Absorption Fine Structure

AbstractThis study describes the utilization of near edge X‐ray absorption fine structure (NEXAFS) to investigate the hole transporting material (HTM) 2,2ʹ,7,7ʹ‐tetrakis(N,N‐di‐p‐methoxyphenylamine)‐ 9,9ʹ‐spirobifluorene (Spiro‐OMeTAD) and its most common dopants, lithium bis‐(trifluoromethylsulfonyl) imide (LiTFSI), 4‐tert‐butylpiridine (tBP), and 2,3,5,6‐tetrafluoro‐7,7,8,8‐tetracyanoquinodimethane (F4‐TCNQ). By changing the angle of the sample with respect to the beam, the orientation of the molecules on the surface can be observed. The data suggest that it is difficult to determine any orientational preference for Spiro‐OMeTAD deposited on a surface due to the 3D propeller‐like geometry of this molecule. Both doped and undoped samples show thermal stability beyond the glass transition temperature of the molecules. Significant changes to the Spiro‐OMeTAD spectra are observed with the addition of the dopants, in particular the C K‐edge. Differences are also observed in the valence band spectra when dopants are added. It is also demonstrated how the doping combination of LiFTSI with tBP and, F4‐TCNQ act as p‐type dopants by altering the position of the HOMO levels. The F4‐TCNQ induces a larger change in the HOMO levels when compared to the LiTFSI and tBP. These results are important to increase the understanding of Spiro‐OMeTAD and the effect dopants have on this material for next generation solar cells.

Highly conductive polyacrylonitrile-based hybrid aqueous/ionic liquid solid polymer electrolytes with tunable passivation for Li-ion batteries

The rapid growth in demand for lithium-ion batteries that can deliver more energy and power has generated concerns over safety. Aqueous electrolytes are a strong candidate to alleviate this apprehension, however their ability to overcome the “cathodic challenge” is limited due to anion-dominated passivation at the anode. In this work, the recently developed “hybrid aqueous/nonaqueous” electrolyte (HANE) strategy was employed to tune the degree of passivation at the anode in solid polymer electrolytes (SPEs) by using various ionic liquids as the nonaqueous component. Whereas common HANE systems sacrifice ionic conductivity to create a more robust passivation layer at the cathodic limit, the “hybrid aqueous/ionic liquid” SPEs (HAILSPEs) investigated in this work do not. Two HAILSPE systems (H1, H2.5) were fabricated from a blend of polyacrylonitrile (PAN), water, lithium bis(trifluoromethylsulfonyl)imide (LiTFSI), and either triethylsulfonium-TFSI (S2,2,2) or N-methyl-N-propylpyrrolidinium-TFSI (Pyr1,3). These HAILSPE systems demonstrated a remarkable improvement in transport properties compared to their predecessors, achieving room temperature ionic conductivities of up to 5.39 mS/cm. A reduction in apparent activation energy and nearly complete decoupling of ionic transport from polymer chain mobility were found to contribute to this increase. Stable and complete growth of a passivating layer at 2 V vs. Li/Li+ was also observed, which was tuned by changing the ionic liquid. The work presented here provides a potential route for overcoming the “cathodic challenge” in aqueous SPEs.

Ionogel Electrolytes Supported by Zwitterionic Copolymers Featuring Lithium Ion-Mediated, Noncovalent Cross-Links

A series of ionogel electrolytes, composed of an ionic liquid/lithium salt solution supported by a linear zwitterionic (ZI) copolymer scaffold containing solely noncovalent cross-links, were created in order to study the effects of varying the ZI fraction within the copolymer as well as the lithium ion concentration on gel mechanical properties and ion transport. The copolymer scaffold was synthesized via in situ UV photopolymerization of the ZI monomer 2-methacryloyloxyethyl phosphorylcholine (MPC) together with the non-ZI comonomer 2,2,2-trifluoroethyl methacrylate (TFEMA) in varying ratios, using a fixed fraction of 25 mol % total monomers. Ionic liquid electrolyte (ILE) solutions of 0.1, 0.3, 0.5, or 1 M lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) dissolved in the ionic liquid 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide (BMP TFSI) were employed. For ionogels created using the 1 M LiTFSI ILE, varying the MPC content from 6.3 mol % to 17 mol % in the precursor solution resulted in a substantial increase in gel elastic modulus, from 20 kPa to 11 MPa. In contrast, room temperature ionic conductivity values for the same samples remained nearly constant, varying from 0.57–0.70 mS cm–1. While the in situ photopolymerization approach remains highly versatile for ionogel formation, an alternative method is introduced here for the first time that can produce ionogels “on-demand” using a pre-made ZI copolymer/ionic liquid solution to which a Li+ ILE is subsequently added.

An electrochemical compatibility investigation of RTIL-based electrolytes with Si-based anodes for advanced Li-ion batteries

Silicon is amongst the most attractive anode materials for Li-ion batteries because of its high gravimetric and volumetric capacities; importantly, it is also abundant and cheap, thus sustainable. For a widespread practical deployment of Si-based electrodes, research efforts must focus on significant breakthroughs to addressing the major challenges related to their poor cycling stability. In this work, we focus on the electrolyte-electrode relationships to support the scientific community with a systematic overview of Si-based cell design strategies reporting a thorough electrochemical study of different room temperature ionic liquid (RTIL)-based electrolytes, which contain either lithium bis(fluorosulfonyl)imide (LiFSI) or lithium bis(trifluoromethylsulfonyl)imide (LiTFSI). Their galvanostatic cycling performances with mixed silicon/graphite/few-layer graphene electrodes are evaluated, with first cycle Coulombic efficiency approaching 90% and areal capacity ≈2 mAh/cm2 in the limited cut-off range of 0.1–2 V vs. Li+/Li0. The investigation evidences the superior characteristics of the FSI-based RTILs with respect to the TFSI-based one, which is mostly associated with the superior SEI forming ability of FSI-based systems, even without the use of specific additives. In particular, the LiFSI-EMIFSI electrolyte composition shows the best performance in both Li-half cells and Li-ion cells in which the Si-based electrodes are coupled with 4V-class composite NMC-based cathodes.

Quasi-Solid-State Lithium-Sulfur Batteries Consist of Super P – Sulfur Composite Cathode

Lithium-Sulfur (Li-S) batteries stand out to be one of the most promising candidates to meet the current energy storage requirement, with its natural abundance of materials, high theoretical capacity of 1672 mAhg-1, high energy density of 2600 Whkg-1, and low cost and lower environmental impact. Sulfur itself (S8), Li2S2 and Li2S formed during the discharge process, are electrical insulators and hence reduce the active material utilization and the electronic conductivity of the cathode affecting the battery performance. Combining of Carbon Super P (SP) with sulfur in cathode formulation is used to overcome these issues. In Liquid electrolyte batteries, polysulfides formed while charging and discharging, easily dissolve in liquid electrolyte and the resulting polysulfide shuttling leads to poor coulombic efficiency and cyclability. Liquid electrolytes used in the conventional Li-S batteries are easy to flow and become flammable. Further, Lithium dendrites piercing through separator causing short circuit paths leads to safety concerns. Replacement of the liquid electrolyte by a solid-state electrolyte (SSE) proves to be a strategy to overcome above mentioned issues. Sulfide based solid electrolytes have received greater attention due to their higher ionic conductivity, compatible interface with sulfur-based cathodes, and lower grain boundary resistance. Novel Li6PS5F0.5Cl0.5 due to its remarkable ionic conductivity of 3.5 x 10-4 S cm-1 makes it an excellent candidate for use in a Li-S solid state battery. However, the interface between SSEs and cathodes has become a challenge to be addressed in all solid-state Li-S batteries due to the rigidity of the participating surfaces. A hybrid electrolyte containing of SSE coupled with a small amount of ionic liquid at the interface, has been employed to improve the interface contact of the SSE with the electrodes.Cathode formulation consisting of sulfur as the active material, Super P as the conductive carbon black, acetylene carbon black as conductive carbon additive, with water based carboxymethyl cellulose (CMC) solution and Styrene butadiene rubber (SBR) as the binder was successfully developed. Thermo gravimetric analysis (TGA) studies of the cathode were carried out by the thermo gravimetric analyzer TA 2050 under N2 gas flow of 100 ml/min. Cathode surface morphology was characterized using the Field emission gun scanning electron microscope (FEI), TESCAN scanning electron microscope with energy dispersive X-ray spectroscopy (EDAX). Using a solvent-based process, Li6PS5F0.5Cl0.5 and Li6PS5F0.5Cl2 SSE were synthesized via the introduction of LiF into the argyrodite crystal structure, which enhances both the ionic conductivity and interface-stabilizing properties of the SSE. Relevant Ionic Liquids (IL) were prepared using Lithium bis(trifluoromethyl sulfonyl)imide (LiTFSI) as salt, with premixed pyrrolidinium bis(trifluoromethyl sulfonyl)imide (PYR) as solvent and 1,3-dioxolane (DOL) as diluent.SP-S cathode with 0.70 mgcm-2 sulfur loading was punched into disks of 2.0 cm2. SSE was pressed into 150 mg pellets using a stainless-steel tank. During the assembly, SSE was wetted with total of 40 μl of IL (LiTFSI dissolved in PYR and DOL solution) from both ends using a micropipette. 2032 type coin cells of Quasi-solid-state Li-S batteries (QSSLSB) consisting of SP-S based composite cathodes, Li anodes and novel Li6PS5F0.5Cl0.5 SSE were tested with an ionic liquid wetting both electrode-SSE interfaces. All the QSSLSB were cycled at 30 °C between 1.0 V and 2.8 V using an 8 channel Arbin battery testing system.Effect of IL dilution, co-solvent amount, LiTFSI concentration and C rate at which the batteries are tested, were systematically studied and optimized to develop a QSSLSB with higher capacity retention and cyclability. Optimum batteries had initial discharge capacity >1100 mAh/g and discharge capacity >400 mAh/g after 100 cycles at the C rate of C/10 with a significant coulombic efficiency. 40 μl of LiTFSI (2M) dissolved in PYR:DOL(1:1) IL was found to be optimum for high performance QSSEBs with low sulfur loading of 0.7 mg/cm2. From the C rate performance study QSSEBs have shown improved stability with the higher current rates. Next, cathodes with higher sulfur loading were studied and for sulfur loading > 4 mgcm-2, initial discharge capacity >950 mAh/g and 400 mAh/g after 60 cycles at C/20 rate were achieved with 40 μl of IL consisting of LiTFSI (3M) dissolved in PYR:DOL(1:3) for the SSE Li6PS5F0.5Cl2. Further testing is underway to improve the performance at high C rate for higher loading by incorporating SSE in the cathode to realize QSSLSB with higher capacity with improved cycle retention.

Corrosion suppression of aluminium current collectors within Li-ion cells using 3-methoxypropionitrile-based electrolytes

Electrolytes containing lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) as the conductive salt generally possess the high moisture tolerance and innate HF-free generation in moisture environments in comparison with those containing lithium hexafluorophosphate (LiPF6). However, severe corrosion of the aluminium current collector presently hinders the use of LiTFSI within Li-ion cells. Here 3-methoxypropionitrile (MPN) is introduced as an alternative, non-toxic solvent into the electrolyte formulation to explore the effects on Al corrosion. The MPN-containing electrolytes can suppress Al corrosion via the generation of an aluminium nitride dominated protection layer during charge-discharge cycling, as confirmed by X-ray photoelectron spectroscopy. For the cycling performance of Li||LiNi0.6Mn0.2Co0.2O2 half cells, the increasing addition of MPN solvent improves capacity retention and suppresses the corrosion of Al current collectors in LiTFSI containing electrolytes.

Enhanced Efficiency and Stability of n‐i‐p Perovskite Solar Cells by Incorporation of Fluorinated Graphene in the Spiro‐OMeTAD Hole Transport Layer

AbstractSpiro‐OMeTAD is one of the most used hole transport layers (HTLs) in high efficiency n‐i‐p perovskite solar cells (PSCs). However, due to the unsatisfactory conductivity of pristine Spiro‐OMeTAD, additives such as tert‐butylpyridine (tBP) and lithium bis (trifluoromethylsulfonyl)‐imide (LiTFSI) are required to improve its hole transportation. The hygroscopic nature of these additives inevitably deteriorates the device's stability. Here, it is shown that by adding fluorinated graphene (FG) into the Li‐TFSI and tBP doped Spiro‐OMeTAD, both efficiency and stability of the PSCs are significantly enhanced. Using the FG incorporated Spiro‐OMeTAD HTL, the power conversion efficiency (PCE) of the PSC reaches 21.92%, which is 11.8% higher than the original device. The FG not only improves the hole mobility of Spiro‐OMeTAD but also effectively reduces the amount of lithium ions in the perovskite layer and improves the hydrophobicity of the HTL. The FG incorporating cell shows better stability, maintaining 90% of initial efficiency over a 2400 h test in ambient conditions with 25% humidity. Finally, it is further demonstrated that the valence band of FG incorporated Spiro‐OMeTAD HTL has a positive effect on PSCs with a 2D interfacial layer, achieving an impressive PCE of 23.14% and a Voc of 1.226 V.

Additive engineering on spiro-OMeTAD hole transport material for CsPbI3 all-inorganic perovskite solar cells with improved performance and stability

CsPbI3 all-inorganic perovskite has now drawn much attention due to its superior thermal stability compared with the organic-inorganic hybrid counterparts. Despite the great progress achieved recently in this field, CsPbI3 still suffers from low phase stability when exposed to moisture. We found the phase transition of CsPbI3 would be accelerated after depositing the conventional hole transport material (HTM) 2,2′,7,7′-Tetrakis[N,N-di(4-methoxyphenyl)amino]− 9,9′-spirobifluorene (spiro-OMeTAD). This is attributed to the negative effects of the additives in spiro-OMeTAD HTM: the hydrolysis of lithium bis(trifluoromethylsulfonyl)imide (LiTFSI), the corrosivity of 4-tert-butylpyridine (TBP), and the evaporation of TBP. By slightly modifying the additive content, full coordination between LiTFSI and TBP could be achieved and the negative effects mentioned above could be mitigated. Furthermore, tris(2-(1 H-pyrazol-1-yl)− 4-tert-butylpyridine)cobalt(III)-tris(bis(trifluoromethylsulfonyl)imide) (Co(III)TFSI) was added to promote oxidation of spiro-OMeTAD HTM in inert environment. With these approaches of additive engineering, HTMs with better interface contact and charge transport capability could be obtained. The device with optimized spiro-OMeTAD HTM achieved a champion power conversion efficiency (PCE) of 10.61% compared with 6.63% of the control one. Moreover, the optimal device maintained 81% of its initial PCE after storage for 30 days, exceeding that (68%) of the control one. Our results highlight the importance of spiro-OMeTAD HTM on the stability of CsPbI3 all-inorganic perovskite and provide a facile and feasible way to increase the stability and performance of corresponding solar cells.

Preliminary study of new electrolytes based on [MPPyr][TFSI] for lithium ion batteries

The application of ionic liquids in lithium ion batteries has increased in recent years in order to find new electrolytes that improve both performance and safety. The gathering of experimental data in order to understand the behaviour of these systems will help us design electrolytes that can be optimized for a specific objective.Data on electrolytes made up of a ternary mixture with an ionic liquid are missing in the literature. In this work, we provide new data on physical properties and refractive indexes for the ternary mixtures 1-methyl-1-propylpyrrolidinium bis(trifluoromethylsulfonyl)imide ([MPPyr][TFSI]) + acetonitrile (AN) or γ butyrolactone (GBL) or dimethyl sulfoxide (DMSO) + lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) with different concentrations of salt, specifically, 10%, 15%, 20%, 30%, 35%. The measured properties were density (ρ), viscosity (η) and ionic conductivity (κ) in the temperature range of 278.15 to 358.15 K except for the mixtures with acetonitrile whose temperature range was 278.15 K to 328.15 K and the refractive indexes (nD) that were measured at a single temperature of 298.15 K.In general, the addition of salt in the binary mixtures provokes an increase of density and viscosity and therefore a decrease of ionic conductivity. It is worth mentioning that some of the studied systems showed values of ionic conductivity even better than those obtained for electrolyte systems based on carbonate.