Lithium Bis(trifluoromethanesulfonyl)imide Research Articles

Poly(ethylene oxide)- and Polyzwitterion-Based Thermoplastic Elastomers for Solid Electrolytes.

In this article, ABA triblock copolymer (tri-BCP) thermoplastic elastomers with poly(ethylene oxide) (PEO) middle block and polyzwitterionic poly(4-vinylpyridine) propane-1-sulfonate (PVPS) outer blocks were synthesized. The PVPS-b-PEO-b-PVPS tri-BCPs were doped with lithium bis-(trifluoromethane-sulfonyl) imide (LiTFSI) and used as solid polyelectrolytes (SPEs). The thermal properties and microphase separation behavior of the tri-BCP/LiTFSI hybrids were studied. Small-angle X-ray scattering (SAXS) results revealed that all tri-BCPs formed asymmetric lamellar structures in the range of PVPS volume fractions from 12.9% to 26.1%. The microphase separation strength was enhanced with increasing the PVPS fraction (fPVPS) but was weakened as the doping ratio increased, which affected the thermal properties of the hybrids, such as melting temperature and glass transition temperature, to some extent. As compared with the PEO/LiTFSI hybrids, the PVPS-b-PEO-b-PVPS/LiTFSI hybrids could achieve both higher modulus and higher ionic conductivity, which were attributed to the physical crosslinking and the assistance in dissociation of Li+ ions by the PVPS blocks, respectively. On the basis of excellent electrical and mechanical performances, the PVPS-b-PEO-b-PVPS/LiTFSI hybrids can potentially be used as solid electrolytes in lithium-ion batteries.

Metal-Doped NASICON/Polymer Composite Solid Electrolyte for Lithium Titania Anode in Lithium-Ion Batteries.

This study reports five types of metal-doped (Co, Cu, Sn, V, and Zr) NASICON-type Li1.3Al0.3Ti1.7(PO4)3 (LATP)/polymer composite solid electrolytes (CSEs) enabling Li4Ti5O12 (LTO) anodes to have high rate capability and excellent cycling performance. The high Li+-conductivity LATP samples are successfully synthesized through a modified sol-gel method followed by thermal calcination. We find that the cation dopants clearly influence the substitution of Al for Ti, with the type of dopant serving as a crucial factor in determining the ionic conductivity and interfacial resistance of the solid electrolyte. The CSE containing poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and Sn-LATP shows an ionic conductivity of 1.88 × 10-4 S cm-1 at ambient temperature. The optimum conductivity can be attributed to alterations in the lattice parameters and Li+ transport pathways owing to Sn doping. The solid-state cell equipped with the LTO-supported CSE containing Sn-LATP fillers demonstrates both excellent high rate capability at 5 C (with a capacity retention of 86% compared to the value measured at 0.2 C) and superior cycling stability, maintaining high Coulombic efficiency (>99.0%) over 510 cycles. These findings indicate that the proposed CSE is highly promising for use in solid-state lithium batteries with desirable charge-discharge properties and high durability.

High‐Performance All‐Solid‐State Lithium Metal Batteries Enabled by Ionic Covalent Organic Framework Composites

AbstractIonic covalent organic frameworks (iCOFs) are crystalline materials with stable porous structures. They hold great potential for ion transport, particularly as solid‐state electrolytes (SSEs) for all‐solid‐state lithium metal batteries (ASSLMBs). However, achieving an ionic conductivity of over 10−3 S cm−1 at room temperature using pure‐iCOF‐based SSEs, even adding additives such as lithium salts, is challenging as the voids work as strong resistances. Thus, highly conductive iCOFs typically require quasi‐solid‐state configurations with organic solvents or plasticizers. In this study, composites comprising iCOFs and poly(ionic liquid) (PIL) are prepared to make all‐solid‐state iCOFs electrolytes with an exceptional ionic conductivity up to 1.50 × 10−3 S cm−1 and a high Li+ transference number of > 0.80 at room temperature. Combined experimental and computational studies show that the co‐coordination and competitive coordination mechanism established between the PIL, lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and iCOFs enabled rapid Li+ transport while restricting TFSI− movement. ASSLMB cells, made of composite SSEs and LiFePO4 composite cathode, demonstrate an initial discharge capacity of 141.5 mAh g−1 at 1C and r.t., with an impressive capacity retention of 87% up to 800 cycles. Overall, this work presents a breakthrough approach for developing advanced SSEs for next‐generation high‐energy‐density ASSLMBs.

Elucidating Interfacial Hole Extraction and Recombination Kinetics in Perovskite Thin Films

Hybrid organic–inorganic perovskite solar cells (PSCs) are receiving huge attention owing to their marvelous advantages, such as low cost, high efficiency, and superior optoelectronics characteristics. Despite their promising potential, charge-carrier dynamics at the interfaces are still ambiguous, causing carrier recombination and hindering carrier transport, thus lowering the open-circuit voltages (Voc) of PSCs. To unveil this ambiguous phenomenon, we intensively performed various optoelectronic measurements to investigate the impact of interfacial charge-carrier dynamics of PSCs under various light intensities. This is because the charge density can exhibit different mobility and charge transport properties depending on the characteristics of the charge transport layers. We explored the influence of the hole transport layer (HTL) by investigating charge transport properties using photoluminescence (PL) and time-resolved (TRPL) to unveil interfacial recombination phenomena and optoelectronic characteristics. We specifically investigated the impact of various thicknesses of HTLs, such as 2,2′,7,7′-tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9′-spirobifluorene (spiro-OMeTAD), and poly(triaryl)amine (PTAA), on FA0.83MA0.17Pb(Br0.05I0.95)3 perovskite films. The HTLs are coated on perovskite film by altering the HTL’s concentration and using F4-TCNQ and 4-tert-butylpyridine (tBP) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSi) as dopants both for spiro-OMeTAD and PTAA. These HTLs diversified the charge concentration gradients in the absorption layer, thus leading to different recombination rates based on the employed laser intensities. At the same time, the generated charge carriers are rapidly transferred to the interface of the HTL/absorption layer and accumulate holes at the interface because of inefficient capacitance and mobility differences caused by differently doped HTL thicknesses. Notably, the charge concentration gradient is low at lower light intensities and did not accumulate holes at the HTL/absorption layer interface, even though they have high charge mobility. Therefore, this study highlights the importance of interfacial charge recombination and charge transport phenomena to achieve highly efficient and stable PSCs.

Anion-mediated interphase construction enabling high-voltage solid-state lithium metal batteries

Enhancing the interphase stability of polymer electrolytes with high-voltage cathodes is crucial for the development of high-energy-density lithium metal batteries (LMBs), especially in wearable devices area. Herein, lithium difluorophosphate (LiDFP) is incorporated into the solid polymer electrolyte of poly(ethylene oxide) (PEO) to enhance the formation of a robust cathode-electrolyte interphase (CEI) in high-voltage LiCoO2 LMBs. Through combining electrochemical measurements, spectroscopic techniques and theoretical calculations, the underlying modification mechanism is revealed. Due to its stronger anionic coordination with both polymer electrolyte chain and proton, and more oxidation-active resultant anion-coordinated polymer compared with lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), LiDFP suppresses the formation of the strong acid HTFSI deriving from the deprotonated process of the terminal O-H group thus avoiding the further oxidative attack to the polymeric framework. Furthermore, under the synergetic decomposition of HDFP intermediate, the polymer-derived radical helps to reconstruct a chemo-mechanically stable and Li-conductive CEI layer, which consists of abundant LiF/Li3PO4/LixPOyFz inorganic species distributed in lithiated organic macromolecules. The in-situ constructed CEI effectively passivates catalytic sites on LiCoO2 directly against PEO, resulting in well-maintained layered structure during high-voltage cycling. The proposed interphasial chemistry that regulates CEI formation provides directive knowledge of electrolyte optimization for high-voltage solid-state batteries.

Effect of Salt Concentration in Water‐In‐Salt Electrolyte on Supercapacitor Applications

AbstractElectrical double‐layer supercapacitors offer numerous advantages in the context of energy storage; however, their widespread use is hindered by the high unit energy cost and low specific energy. Recently, water‐in‐salt (WIS) electrolytes have garnered interest for use in energy storage devices. Nevertheless, their direct application in high‐power devices is limited due to their high viscosity. In this study, we investigate the WIS Lithium bis(trifluoromethanesulfonyl)Imide (LiTFSI) electrolyte, revealing a high specific capacitance despite its elevated viscosity and restricted ionic conductivity. Our approach involves nuclear magnetic resonance (NMR) analysis alongside electrochemical analyses, highlighting the pronounced advantage of the WIS LiTFSI electrolyte over the WIS LiCl electrolyte at the molecular level. The NMR analysis shows that the LiTFSI electrolyte ions preferentially reside within the activated carbon pore network in the absence of an applied potential, in contrast to LiCl where the ions are more evenly distributed between the in‐pore and ex‐pore environments. This difference may contribute to the difference in capacitance between the two electrolytes observed during electrochemical cycling.

Understanding Sorption of Aqueous Electrolytes in Porous Carbon by NMR Spectroscopy.

Ion adsorption at solid-water interfaces is crucial for many electrochemical processes involving aqueous electrolytes including energy storage, electrochemical separations, and electrocatalysis. However, the impact of the hydronium (H3O+) and hydroxide (OH-) ions on the ion adsorption and surface charge distributions remains poorly understood. Many fundamental studies of supercapacitors focus on non-aqueous electrolytes to avoid addressing the role of functional groups and electrolyte pH in altering ion uptake. Achieving microscopic level characterization of interfacial mixed ion adsorption is particularly challenging due to the complex ion dynamics, disordered structures, and hierarchical porosity of the carbon electrodes. This work addresses these challenges starting with pH measurements to quantify the adsorbed H3O+ concentrations, which reveal the basic nature of the activated carbon YP-50F commonly used in supercapacitors. Solid-state NMR spectroscopy is used to study the uptake of lithium bis(trifluoromethanesulfonyl)-imide (LiTFSI) aqueous electrolyte in the YP-50F carbon across the full pH range. The NMR data analysis highlights the importance of including the fast ion-exchange processes for accurate quantification of the adsorbed ions. Under acidic conditions, more TFSI- ions are adsorbed in the carbon pores than Li+ ions, with charge compensation also occurring via H3O+ adsorption. Under neutral and basic conditions, when the carbon's surface charge is close to zero, the Li+ and TFSI- ions exhibit similar but lower affinities toward the carbon pores. Our experimental approach and evidence of H3O+ uptake in pores provide a methodology to relate the local structure to the function and performance in a wide range of materials for energy applications and beyond.

Multilayer hybrid solid-state electrolyte membrane for the high rate and long-life cycle performance of lithium-metal batteries

Hybrid solid-state electrolytes (HSEs) can be used to increase the electrochemical performance of lithium-metal batteries (LMBs), while also suppressing dendrite formation and preventing flammable behavior and electrolyte leakage, which are frequently present in conventional organic-liquid electrolytes. Notably, multilayer HSE membranes have received increasing emphasis since they can significantly ameliorate the interface contact toward electrodes and the mechanical strength. In this current work, we fabricated multilayer HSE membranes via a solution-casting technique that incorporated poly(vinylidene fluoride–co–hexafluoropropylene) (PVDF-HFP), polydopamine-modified Li6.28La3Zr2Al0.24O12 (PDA@LLZAO) filler, succinonitrile (SN) and lithium bis(trifluoromethane sulfonyl)imide (LiTFSI). The resulting HSE membrane exhibited a high ionic conductivity (2.49 ×10−4 S cm−1 at 30 ℃), transference number of 0.65, and excellent electrochemical window (4.80 V). The symmetrical cell featuring Li/HSE/Li was stable and cycled without short circuiting for 1000 h during the Li plating/stripping cycles. Furthermore, the coin-type cell assembled with LiFePO4/HSE/Li showed an initial discharge capacity of 134.7 mAh g1 and exhibited superior retained capacity and average coulombic efficiency of 93.45% and 99.39%, respectively, after 687 cycles at 2 C and 30 ℃. Therefore, the as-prepared multilayer HSE is a promising SSE for next-generation LMBs.

Enhancement mechanism of the comprehensive performance of all-solid-state polymer electrolytes by halloysite nanotubes: Construction of efficient lithium-ion conduction channels

Considering the current issues with poly(ethylene oxide)-based all-solid-state polymer electrolytes (PEO-ASSPEs) employed in lithium-ion batteries (LIBs), such as low ionic conductivity, low lithium-ion transference number, narrow electrochemical stability window, and poor cyclic stability. This study introduces oxygen-vacancy-rich halloysite nanotubes (HNTs) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) into the PEO matrix to fabricate a flexible composite polymer electrolyte (CPEs) via a solvent-free method. The interaction between HNTs and LiTFSI in the PEO matrix serves to mitigate the ionic solvation effect, increase the number of free lithium-ion, and reduce the lithium-ion migration energy barrier. Additionally, the internal framework formed by the mutual stacking of HNTs reduces the number of entanglements in polymer molecular chains, enhances the mobility of the chains, and generates a continuous interface effect, forming fast lithium-ion transport channels. The CPEs prepared in this study are in conformity with the Vogel-Tammann-Fulcher (VTF) empirical equation. The CPE containing 10 wt% HNTs exhibits a high ionic conductivity (7.15 × 10−4 S cm−1) at 25 °C, a high lithium-ion transference number (0.600), a wide electrochemical stability window (5.5 V), and excellent cyclic performance (capacity retention of 82.02 % after 100 cycles at 0.1C), satisfying the electrochemical performance requirements for ASSPEs in LIBs.

Easily accessible linear and hyperbranched polyesters as solid polymer electrolytes

Herein we report synthesis, characterization, thermal properties, ionic conductivity and oxidative stability of novel linear and hyperbranched polyesters. Tri-acrylate ester of commercially available 1,1,1-Tris(hydroxymethyl)propane (M1) was used as the primary building block for the synthesis of linear and hyperbranched polymers. A3 + B2 type polycondensation between M1 and dithiols of two different chain lengths (C3, C6) by 100 % atom efficient thiol-acrylate Michael addition reaction, followed by consumption of the unreacted acrylate esters (in the linear or terminal units) with 1-butane thiol produced two hyperbranched polymer namely HB-P1 and HB-P2. For synthesis of linear analogues, one of the equivalent acrylate esters was reacted first with 1-butane thiol and the resulting di-acrylate monomer was polymerized with the C3 and C6-dithiols, producing linear polymers L-P1 and L-P2. All the polymers showed molecular weight (Mn) in the range of 5000–6000 gmol−1 with low dispersity. TGA analysis revealed sufficient thermal stability of the polymers for the application as solid polymer electrolyte. All the polymers are amorphous, showing only a glass transition in the range of ∼ -45 °C (C3 spacer) to −50 °C (C6 spacer) and no crystallization peak. In presence of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt the Tg increased by ∼ 10 °C. Solid polymer electrolytes were prepared by incorporating LiTFSI at a molar ratio of polymer carbonyl units to lithium of C=O/Li of 10 and ionic conductivity (σ) was evaluated by electrochemical impedance spectroscopy (EIS). Moderate values in the range of 10-7 S cm−1 were obtained at 25 °C with slightly higher values for the linear polymers. The ionic conductivity increased up to ∼ 2 orders of magnitude at higher temperatures. The oxidative stability of the polymer electrolytes against lithium-metal electrodes revealed onset potential for the first degradation in the range of 3.8 V, indicating moderate stability that might be suitable for testing applications in all-solid-state lithium-metal batteries using sulfur or lithium iron phosphate cathodes.

Non‐Resonant Structure Induces N‐Rich Solid Electrolyte Interface toward Ultra‐Stable Solid‐State Lithium‐Metal Batteries

AbstractThe practical application of all‐solid‐state lithium metal batteries (ASSLMBs) is limited by lithium (Li) anode instability including Li dendrite formation and deteriorating interface with electrolytes. Here, a functional additive, isosorbide mononitrate (ISMN) with a non‐resonant structure (O2−N−O−) is reported, which improves its reactivity and is utilized to build a stable N‐rich solid electrolyte interface, effectively alleviating Li dendrite and side reactions for poly(vinylidene fluoride) (PVDF)‐lithium bis(trifluoromethane sulfonyl) imide (LiTFSI)‐based electrolyte (PLE‐ISMN). In addition, the ion‐dipole interaction between ISMN and Li ions facilitates the dissociation of LiTFSI to form carrier ions, improving the ionic conductivity (4.4 × 10−4 S cm−1) and transference number (0.50) of PLE‐ISMN. Consequently, the Li/Li symmetric cell delivers a high critical current density of 2.0 mA cm−2 and stable Li stripping/plating cycling over 5000 h with a capacity of 1.0 mAh cm−2. Moreover, the Li|LiFePO4 cell delivers an excellent initial discharge capacity of 154.0 mAh g−1 with an outstanding capacity retention of 88.9% after 500 cycles at 0.5 C. The Li|LiNi0.8Co0.1Mn0.1O2 cell also exhibits a good cycling performance at 4.4 V at 1 C.

Perfluorinated Zinc Porphyrin Sensitized Photoelectrosynthetic Cells for Enhanced TEMPO-Mediated Benzyl Alcohol Oxidation.

This research introduces a novel series of perfluorinated Zn(II) porphyrins with positive oxidation potentials designed as sensitizers for photoelectrosynthetic cells, with a focus on promoting the oxidation of benzyl alcohol (BzOH) mediated by the 2,2,6,6-tetramethyl-1-piperidine N-oxyl (TEMPO) organocatalyst. Three dyes, CLICK-3, CLICK-4, and BETA-4, are meticulously designed to explore the impact of substituents and their positions on the perfluorinated porphyrin ring in terms of redox potentials and energy level alignment when coupled with SnO2/TiO2-based photoanodes and TEMPO mediator. A comprehensive analysis utilizing spectroscopy, electrochemistry, photophysics, and computational techniques of the dyes in solution and sensitized thin films unveils an enhanced charge-separation character in the 4D-π-1A type BETA-4. Incorporating four dimethylamino donor groups at the periphery of the porphyrin ring and a BTD-accepting linker at the β-pyrrolic position equips the structure with a more efficient donor-acceptor system. This enhancement ensures improved light-harvesting capacity, resulting in a doubled incident photon-to-current conversion efficiency (IPCE% ≃30%) in the presence of LiI compared to meso-substituted dyes CLICK-3 and CLICK-4. Sensitizing SnO2/TiO2 thin films with BETA-4 successfully promotes the photooxidation of benzyl alcohol (BzOH) in the presence of the rapid TEMPO radical catalyst, yielding photocurrents of approximately 125 μA/cm2 in an optimized TBPy/LiClO4/ACN electrolyte. Notably, when lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) replaces TBPy as the base for TEMPO-catalyzed BzOH oxidation, a remarkable photocurrent of around 800 μA/cm2 is achieved, marking one of the highest values reported for this photoelectrochemical reaction to date. This study underscores that the proper functionalization of perfluorinated zinc porphyrins positions these dyes as ideal candidates for sensitizing SnO2/TiO2 in the photodriven oxidation of BzOH. It also highlights the crucial role of carefully tuning electrolyte composition based on the electronic properties of molecular sensitizers.

Tuning the FEC‐Related Electrolyte Solvation Structures in Ether Solvents Enables High‐Performance Lithium Metal Anode

AbstractLithium metal is the most promising high‐energy‐density anode. However, it is incompatible with high‐voltage cathodes in ether solvents due to their narrow electrochemical window. Herein, fluoroethylene carbonate (FEC) co‐solvent is introduced to regulate the Li+ solvation structures in ether solvents, including cyclic ether (1,3‐dioxolane [DOL]) and linear glymes with different chain lengths (1,2‐dimethoxyethane [DME], diglyme [G2] and triglyme [G3]). The apparently different effects of ether solvents on solvation ability and interaction strength with FEC are revealed. FEC plays a diverse role and function in 1 m lithium bis(trifluoromethanesulfonyl)imide (LiTFSI)‐ether/FEC electrolyte, thus relevant batteries perform distinct performances due to various ionic dynamics and solid‐electrolyte interphase. The Li+‐solvation structures are explored by Raman and nuclear magnetic resonance spectroscopies. Specifically, part of FEC molecules are inserted into the first solvation shell in 1 m LiTFSI‐DOL/FEC because of the weak solvation ability of DOL and strong interaction of DOL‐FEC, leading to few coordinated TFSI− and sluggish interfacial kinetics. In sharp contrast, FEC as a weak coordinated solvent almost exclusively occupies the second solvation sheath in 1 m LiTFSI‐glyme/FEC, favoring TFSI− coordination and rapid de‐solvation dynamics. Ultimately, the LiNi0.8Co0.1Mn0.1O2/Li battery in G2/FEC presents the most excellent performance, derived from abundant free‐FEC and rapid ionic kinetics.

Shear rheology senses the electrical room-temperature conductivity optimum in highly Li doped dinitrile electrolytes.

Glutaronitrile (GN) doped with lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) at concentrations below and above the room-temperature conductivity optimum near 1M of Li salt is investigated using dielectric spectroscopy and shear rheology. The experiments are carried out from ambient down to the glass transition temperature Tg, which increases considerably as LiTFSI is admixed to GN. As the temperature is lowered, the conductivity optimum shifts to lower salt concentrations, while the power-law exponents connecting resistivity and molecular reorientation time remain smallest for the 1M composition. By contrast, the rheologically detected time constants, as well as those obtained using dielectric spectroscopy, increase monotonically with increasing Li salt concentration for all temperatures. It is demonstrated that the shear mechanical measurements are, nevertheless, sensitive to the 1M conductivity optimum, thus elucidating the interplay of the dinitrile matrix with the mobile species. The data for the Li doped GN and other nitrile solvents all follow about the same Walden line, in harmony with their highly conductive character. The composition dependent relation between the ionic and the reorientational dynamics is also elucidated.

Highly Concentrated Electrolyte Superlubricants Enhanced by Interfacial Water Competition Around Chemically Active MgO Additives.

The low concentration of water-based lubricants and the high chemical inertness of the additives involved are often regarded as basic norms in the design of liquid lubricants. Herein, a novel liquid superlubricant of an aqueous solution containing a relatively high concentration of salt, lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), is reported for the first time, and the superlubricity stability and load-bearing capacity of the optimized system (MgO0.10/LiTFSI10) are effectively strengthened by the addition of only trace (0.10 wt %) water-chemically active MgO additives. It demonstrates higher applicable loads, lower COF (∼0.004), and stability relative to the base solution. Only a trace amount of MgO additive is needed for the superlubricity, which makes up for the cost and environmental deficiencies of LiTFSI10. The weak interaction region between free water and the outer-layer water of Li+ hydration shells becomes a possible ultralow shear resistance sliding interface; the Mg(OH)2 layer, generated by the reaction of MgO with water, further creates additional weakly interacting interfaces, leading to the formation of an asymmetric contact between the clusters/particles within the hydrodynamic film by moderating the competition between interfacial water and free water, thus achieving high load-bearing macroscopic superlubricity. This study deepens the contribution of electrolyte concentration to ionic hydration and superlubricity due to the low shear slip layer formed by interfacial water competition with water-activated solid additives, providing new insights into the next generation of high load-bearing water-based liquid superlubricity systems.

Succinonitrile-Lithium Salt Complexes as Solid Catholytes for LLZO-Based Solid-State Batteries

The thermal and electrochemical properties of several succinonitrile (SN)-based organic ionic plastic crystals (OIPCs) containing lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(oxalate) borate (LiBOB) or mixtures of the two salts, were investigated with the goal of determining which is most promising for use as a catholyte in solid-state lithium batteries. The best combination of properties for this use was found for the mixture containing 3 mol% LiTFSI and 2 mol% LiBOB in SN. Based on these observations, several solid-state cells containing Al-substituted Li7La3Zr2O12 separators with composite cathodes consisting of LiNi0.33Mn0.33Co0.33O2 (NMC111), carbon black, and the succinonitrile-salt mixtures were assembled and cycled at room temperature, without exogenous pressure, using a simple design.

Thermal stability of perovskite solar cells incorporated with spiro-OMeTAD and an ionic liquid dopant

Perovskite solar cells (PSCs) have garnered attention as novel photovoltaic devices due to their cost-effectiveness, lightweight nature, and high photoconversion efficiency. To facilitate their commercialization, developing PSCs with enhanced environmental stability with respect to thermal and light resilience, making them suitable for outdoor applications, is imperative. However, despite ongoing research and development efforts, PSCs exhibit stability issues, including thermal- and light-induced degradation. In conventional PSCs, lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) as a dopant is essential to enhance the conductivity of the hole transport layer (HTL), such as 2,2′,7,7′-tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9′-spirobifluorene (spiro-OMeTAD). However, LiTSFI incorporation into spiro-OMeTAD renders it unsuitable for applications requiring thermal stability owing to the Li+ diffusion within the PSCs. Since LiTFSI is a hydrophilic salt, we utilized organic TFSI salts to improve PSC thermal stability. By optimizing HTL using organic TFSI dopants, we achieved a remarkable two-fold enhancement in thermal stability compared to non-optimized PSCs.

Deshielding Anions Enable Solvation Chemistry Control of LiPF6-Based Electrolyte toward Low-Temperature Lithium-Ion Batteries.

Severe capacity decay under subzero temperatures remains a significant challenge for lithium-ion batteries (LIBs) due to the sluggish interfacial kinetics. Current efforts to mitigate this deteriorating interfacial behavior rely on high-solubility lithium salts (e.g., Lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), Lithium bis(fluorosulfonyl)imide (LiFSI))-based electrolytes to construct anion participated solvation structures. However, such electrolytes bring issues of corrosion on the current collector and increased costs. Herein, the most commonly used Lithium hexafluorophosphate (LiPF6) instead, to establish a peculiar solvation structure with a high ratio of ion pairs and aggregates by introducing a deshielding NO3 - additive for low-temperature LIBs is utilized. The deshielding anion significantly reduces the energy barrier for interfacial behavior at low temperatures. Benefiting from this, the graphite (Gr) anode retains a high capacity of ≈72.3% at -20°C, which is far superior to the 32.3% and 19.4% capacity retention of counterpart electrolytes. Moreover, the LiCoO2/Gr full cell exhibits a stable cycling performance of 100 cycles at -20°C due to the inhibited lithium plating. This work heralds a new paradigm in LiPF6-based electrolyte design for LIBs operating at subzero temperatures.

Lithium iron phosphate cathode supported solid lithium batteries with dual composite solid electrolytes enabling high energy density and stable cyclability

In this research, we present a report on the fabrication of a Lithium iron phosphate (LFP) cathode using hierarchically structured composite electrolytes. The fabrication steps are rationally designed to involve different coating sequences, considering the requirements for the electrode/electrolyte interfaces. Two layers of composite solid electrolyte, consisting of poly(propylene carbonate) (PPC) + lithium bis (trifluoromethanesulfonyl)imide (LiTFSI) salt and poly(ethylene oxide) (PEO) + LiTFSI + Li7La3Zr2O12 (LLZTO), are employed as hierarchical structured composite electrolytes on the LFP cathode. Experimental results indicate that the optimal combination consists of a thinner PPC + LITFSI layer on the LFP cathode and a thicker PEO + LiTFSI + LLZTO facing Li metal. The Li-metal batteries, equipped with LFP supported hierarchical electrolytes exhibited an ultra-high specific capacity (~155 mAh g−1). Additionally, they demonstrated electrode polarization in the reduced form of −0.15 V, and an excellent cyclic stability with the retention capacity of 87.6 % even in 200 cycles. The ionic conductivity of the dual-layer electrolytes is achieved as high as 1.63–2.60 × 10−4 S cm−1 at ambient temperature. The impressive cycling performance demonstrated in this study is primarily attributed to the significance of the coating sequence in the design of dual composite solid electrolytes. The PPC + LiTFSI composite layer appears to function as a flexible filler on the LFP side. On the other hand, the PEO + LiTFSI + LLZTO composite layer, which faces the Li metal anode, not only provides excellent ionic conductivity but also serves as a barrier against the mechanical stress by the formation of Li-dendrite. The dual-layer electrolyte configuration, as demonstrated in this work, can be engineered to enable high energy density and stable cyclability of Li-metal batteries.

Nanoscale Ion Transport Enhances Conductivity in Solid Polymer-Ceramic Lithium Electrolytes.

The predictive design of flexible and solvent-free polymer electrolytes for solid-state batteries requires an understanding of the fundamental principles governing the ion transport. In this work, we establish a correlation among the composite structures, polymer segmental dynamics, and lithium ion (Li+) transport in a ceramic-polymer composite. Elucidating this structure-property relationship will allow tailoring of the Li+ conductivity by optimizing the macroscopic electrochemical stability of the electrolyte. The ion dissociation from the slow polymer segmental dynamics was found to be enhanced by controlling the morphology and functionality of the polymer/ceramic interface. The chemical structure of the Li+ salt in the composite electrolyte was correlated with the size of the ionic cluster domains, the conductivity mechanism, and the electrochemical stability of the electrolyte. Polyethylene oxide (PEO) filled with lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) or lithium bis(fluorosulfonyl) imide (LiFSI) salts was used as a matrix. A garnet electrolyte, aluminum substituted lithium lanthanum zirconium oxide (Al-LLZO) with a planar geometry, was used for the ceramic nanoparticle moieties. The dynamics of the strongly bound and highly mobile Li+ were investigated using dielectric relaxation spectroscopy. The incorporation of the Al-LLZO platelets increased the number density of more mobile Li+. The structure of the nanoscale ion-agglomeration was investigated by small-angle X-ray scattering, while molecular dynamics (MD) simulation studies were conducted to obtain the fundamental mechanism of the decorrelation of the Li+ in the LiTFSI and LiFSI salts from the long PEO chain.