Lithium Salt Anion Research Articles

Liquid-liquid extraction separation of lithium isotopes by using room-temperature ionic liquids-chloroform mixed solvent system contained benzo-15-crown-5

A novel liquid–liquid extraction system was investigated for the selective separation of lithium isotopes using ionic liquids (ILs=[C6,8,10,12mim]+[PF6]－) as extraction solvent and benzo-15-crown-5 (B15C5) as extractant. The effects of the concentration of lithium salt, counter anion of lithium salt, initial pH of aqueous phase, and extraction temperature on the lithium isotopes separation were studied. The maximum single-stage separation factor α of 6Li/7Li obtained in the present study was 1.038 ± 0.002, indicating the lighter isotope 6Li was enriched in organic phase while the heavier isotope 7Li was concentrated in the aqueous phase. The formation of 2:1 complex Li(B15C5)2+ in the IL phase was determined on the basis of slope analysis method. The large value of the free energy change (−G0=77.87 J mol−1) indicated the high separation capability of the lithium isotopes by B15C5/30%CH3Cl-70% C6mimPF6 mixture extraction system. Lithium in Li(B15C5)2+ complex was stripped by 0.5mol·L−1 HCl solution. The extraction system offers high efficiency, simplicity application prospect to separation lithium isotope separation from LiCl solution.

LiTDI as electrolyte salt for Li-ion batteries: transport properties in EC/DMC

The 4,5-dicyano-2-trifluoromethyl-imidazolide (TDI−) anion is a potential lithium salt anion for lithium-ion batteries. In this paper the transport properties of LiTDI solutions in EC/DMC (50/50wt%) are compared to competing salts such as LiTFSI (lithium bis(trifluoromethylsulfonyl) imide), LiFAP (lithium tris(pentafluoroethane)-trifluorophosphate) and the most commonly used LiPF6 (lithium hexafluorophosphate). LiTDI in EC/DMC exhibits the lowest viscosity among the investigated electrolytes, but also the lowest conductivity: 6.84mScm−1 at 25°C (1molL−1). The self-diffusion coefficients (D(7Li) and D(19F)) determined by observing 7Li and 19F nuclei with the pulsed-gradient spin-echo (PGSE) NMR technique allowed access, through application of the Stokes-Einstein and Nernst-Einstein equations, to the lithium transference number (t+), the effective ionic radius and the ionic dissociation coefficient (αD) of LiTDI in EC/DMC. The ion-pair dissociation and t+ were also determined using conductivity and viscosity measurements and by following the Bruce-Vincent method respectively and were in good agreement with those obtained by PGSE-NMR. LiTDI displays in EC/DMC a cationic transference number t+=0.58, which is higher than that of LiPF6 in the same solvent mixture, meaning that the mobility of the PF6− anion is higher than the larger TDI− anion. Still, results from both methods indicate that, LiTDI, as many other lithium salts is only partially dissociated in EC/DMC. Only 31% of the ion pairs are dissociated at 25°C whereas for LiPF6, LiTFSI and LiFAP this number reaches at least 64% in 1molL−1 solutions.

Galvanostatic characteristics of natural pyrite in cycling for DMC-LiAn electrolytes

The specific characteristics of natural pyrite (FeS2) are investigated using a galvanostatic cycling method. The investigation is carried out for electrolytes consisting of dimethylcarbonate (DMC) and a lithium salt (LiBF4, LiClO4, or LiN(CF3SO2)2). It is shown that the specific capacitance of FeS2 and its stability during cycling depend on the concentration and the nature of a lithium salt anion. The greatest efficiency of the galvanostatic cycling of FeS2 is achieved for the DMC-LiClO4 and DMC-LiN(CF3SO2)2 electrolytes in salt concentrations in the range of 0.1–0.2 molar fractions.

Synthesis of Polymer Electrolytes Based on Poly(ethylene oxide) and an Anion-Stabilizing Hard Polymer for Enhancing Conductivity and Cation Transport

We have investigated a new methodology for improving the ionic conductivity and cation transport of polymer electrolytes by incorporating an anion-stabilizing hard polymer. A lamellar-forming poly(ethylene oxide-b-dithiooxamide) (PEO-b-PDTOA) block copolymer having enhanced ion conduction and mechanical strength, arising from PEO and PDTOA, respectively, was synthesized. Compared to a simple PEO/PDTOA blend, lithium salt-doped PEO-b-PDTOA exhibited significantly enhanced ionic conductivity, which is ascribed to efficient ion transport along the nanoscale PEO domains. Strikingly, by applying a dc polarization voltage, the inclusion of PDTOA afforded a high ratio of the steady state to the initial current flow of 0.67 for the PEO-b-PDTOA electrolytes, surpassing the value of 0.31 observed for conventional PEO-salt electrolytes. A key reason for achieving enhanced cation transport was the hydrogen bonding interactions between the thioamide moieties of PDTOA and the anions of lithium salts. This work provides fascinating experimental insights into the enhancement of cation transport of polymer electrolytes without chemically bonded negative charges and has implications for fast charging energy storage systems.

The solid–liquid extraction separation of lithium isotopes by porous composite materials doped with ionic liquids and 2,2′-binaphthyldiyl-17-crown-5

A green and efficient solid–liquid extraction method of lithium isotopes separation by porous composite materials doped with imidazolium ionic liquids and 2,2′-binaphthyldiyl-17-crown-5 has been reported in this paper. The composite materials of mesoporous silica and impregnated resin were synthesized by sol–gel and direct impregnation process, respectively. Various extraction parameters such as the concentration of lithium salt, anion of lithium salt, initial pH, time and temperature were investigated. Under optimized conditions, the maximum single-stage separation factor of 6Li/7Li was 1.048 ± 0.002, the maximum extraction efficiency was 15.86 %. The sorbents can be regenerated easily with HCl solution and reused repeatedly.

Liquid–liquid extraction to lithium isotope separation based on room-temperature ionic liquids containing 2,2′-binaphthyldiyl-17-crown-5

A novel liquid–liquid extraction system was investigated for the selective separation of lithium isotopes using ionic liquids (ILs = C8mim+PF6−, C8mim+BF4−, and C8mim+NTf2−) as extraction solvent and 2,2′-binaphthyldiyl-17-crown-5 (BN-17-5) as extractant. The effects of the concentration of lithium salt, counter anion of lithium salt, initial pH of aqueous phase, extraction temperature, and time on the lithium isotopes separation were discussed. Under optimized conditions, the maximum single-stage separation factor α of 6Li/7Li obtained in the present study was 1.046 ± 0.002, indicating the lighter isotope 6Li was enriched in IL phase while the heavier isotope 7Li was concentrated in the solution phase. The formation of 1:1 complex Li(BN-17-5)+ in the IL phase was determined on the basis of slope analysis method. The large value of the free energy change (−ΔG° = 92.89 J mol−1) indicated the high separation capability of the Li isotopes by BN-17-5/IL system. Lithium in Li(BN-17-5)+ complex was stripped by 1 mol L−1 HCl solution. The extraction system offers high efficiency, simplicity, and green application prospect to lithium isotope separation.

Lithium Dendrite Formation at the Interface Between Lithium Metal and PEO Complexed with Various Lithium Salts

A water-stable lithium electrode (WSLE) based on Li1 +x+y(Ti,Ge)1 -xAlxP3-ySiyO12(LTAP) requires a lithium conducting interlayer between lithium metal and LTAP. Polyethylene oxide (PEO) based polymer electrolytes are the best candidate as the interlayer, because they are stable in contact with lithium metal and large-sized sheets can be easily fabricated. The interface resistance between lithium metal and polymer electrolytes in the WSLE was found to exhibit a major part of the electrode resistance [1], which can be suppressed by addition of ionic liquids, nanofillers and oligomer ethers into PEO. Further, the passivation film may play an important role for the lithium dendrite formation [2], especially the anion of lithium salts is expected to participate in forming the surface sublayer adjacent to lithium metal, whose role for the lithium dendrite formation is yet unveiled. In this study, the polymer electrolytes of PEO18LiX with different lithium salts of LiN(FSO2)2 (LiFSI), LiN(CF3SO2)2 (LiTFSI), LiN(C2F5SO2)2 (LiBETI), and LiC(C2F5SO2)3 (LiTFSM) were prepared, and the effects of lithium salt in PEO on the interface resistance and the lithium dendrite formation have been examined. Electrochemical impedance spectroscopy measurements were performed in the symmetrical lithium pouch cells of Li/PEO18LiX/Li as a function of storage time at 60 oC. The passivation film resistances (Rp) for PEO18LiTFSM and PEO18LiTFSI increased from 75 to 135 Ω·cm2 and 92 to 204 Ω·cm2 after 148 h, respectively. On the other hand, Rp for PEO18LiBETI and PEO18LiFSI decreased from 181 to 143 Ω·cm2 and 372 to 278 Ω·cm2, respectively after 148 h. The capacitance of the passivation film was in a descending order of PEO18LiTFSM, PEO18LiTFSI, PEO18LiBETI and PEO18LiFSI. Activation energies for the total interfacial resistance were calculated as 84.4 kJ·mol-1 for PEO18LiFSI, 84.1 kJ·mol-1 for PEO18LiTFSI, 85.8 kJ·mol-1 for PEO18LiBETI, and 90.9 kJ·mol-1 for PEO18LiTFSM. These results imply that FSI-could take part in the generation of a dense resistive passivation film. The short-circuit time (ts) for the Li/PEO18LiX/Li cell was examined at 0.1 mA·cm-2 and 60 oC, where the thickness of PEO18LiX was ca. 100 μm. Figure 1 shows the potential change with the polarization period for the Li/PEO18LiX/Li cell at 60 oC. The longest ts of 145 h was observed for the Li/PEO18LiFSI/Li cell with over-potential of 55 mV. ts for the Li/PEO18LiTFSI/Li cell was 63.7 h and the over-potential 62 mV. However, cells of Li/PEO18LiTFSM/Li and Li/PEO18LiBETI/Li were shorted at 3.2 and 8.7 h and the over-potentials were 32 and 40 mV, respectively. The cycling performance measurements were carried out for the Li/PEO18LiTFSI/Li and Li/PEO18LiFSI/Li cells at 0.1 mA·cm-2 and 60 oC, where the current was passed for 5 h in each half cycle. The total charge passed before short-circuit was calculated as 19.8 C·cm-2 for PEO18LiTFSI and 70.2 C·cm-2 for PEO18LiFSI. These results suggest that FSI-is a promising anion for suppressing lithium dendrite formation and enhancing the flexibility of the passivation film. Detailed study of the composition of the passivation film on the lithium metal is under investigation by in-situ FTIR, ex-situ XPS and SEM. We attempt to correlate lithium dendrite formation with anions of novel lithium salts for the development of WSLEs.

A green strategy for lithium isotopes separation by using mesoporous silica materials doped with ionic liquids and benzo-15-crown-5

Three new mesoporous silica materials IL15SGs (HF15SG, TF15SG and DF15SG) doped with benzo-15-crown-5 and imidazolium based ionic liquids (C8mim+PF6 −, C8mim+BF4 − or C8mim+NTf 2 − ) have been prepared by a simple approach to separating lithium isotopes. The formed mesoporous structures of silica gels have been confirmed by transmission electron microscopy image and N2 gas adsorption–desorption isotherm. Imidazolium ionic liquids acted as templates to prepare mesoporous materials, additives to stabilize extractant within silica gel, and synergetic agents to separate the lithium isotopes. Factors such as lithium salt concentration, initial pH, counter anion of lithium salt, extraction time, and temperature on the lithium isotopes separation were examined. Under optimized conditions, the extraction efficiency of HF15SG, TF15SG and DF15SG were found to be 11.43, 10.59 and 13.07 %, respectively. The heavier isotope 7Li was concentrated in the solution phase while the lighter isotope 6Li was enriched in the gel phase. The solid–liquid extraction maximum single-stage isotopes separation factor of 6Li–7Li in the solid–liquid extraction was up to 1.046 ± 0.002. X-ray crystal structure analysis indicated that the lithium salt was extracted into the solid phase with crown ether forming [(Li0.5)2(B15)2(H2O)]+ complexes. IL15SGs were also easily regenerated by stripping with 20 mmol L−1 HCl and reused in the consecutive removal of lithium ion in five cycles.

How does lithium salt anion affect oxidation decomposition reaction of ethylene carbonate: A density functional theory study

The effect of anions, PF6− and ClO4−, on the oxidation decomposition mechanism of electrolyte solvent ethylene carbonate (EC) for lithium ion battery has been investigated by using density functional theory at B3LYP/6-311++G(d) level, in both gas phase (dielectric constant ɛ = 1) and solvent (dielectric constant ɛ = 20.5). It is found that the presence of PF6− and ClO4− anions significantly reduces EC oxidation stability and changes the order of the oxidation decomposition paths. The primary oxidation decomposition products of EC, EC–PF6− and EC–ClO4− are CO2 and acetaldehyde radical. The formation of CO is highly improbable in the decomposition reaction of EC with and without PF6− or ClO4−.

Effect of anion of lithium salt on the property of lithium salt-epoxidized natural rubber polymer electrolytes

Lithium salt, LiX (where X = BF4−, I−, CF3SO3−, COOCF3− or ClO4−), was incorporated into epoxidized natural rubber (ENR). Thin films of LiX-ENR polymer electrolytes (PEs) were obtained via solvent casting method. These electrolytes were characterized using SEM/X-mapping, FTIR, differential scanning calorimeter, thermogravimetry analysis, and impedance spectroscopy. The trend in thermal stability and ionic conductivity of LiX-ENR PEs follow LiBF4 > > LiCF3SO3 ~ LiCOOCF3 > LiI > > LiClO4. The LiClO4 hardly dissociates and formed LiClO4 aggregates within the polymer matrix that resulted in a PE with low thermal stability and low ionic conductivity. The LiCF3SO3, LiCOOCF3, and LiI, however, exert moderate interactions with the ENR, and their respective PEs exhibit moderate ionic conductivity and thermal property. The occurrence of epoxide ring opening and complexation or cross-linking reactions in and between the ENR chains that involve BF4− ions have produced a LiBF4-ENR PE with superior thermal property and ionic conductivity as compared to other PEs studied in this work.

Ionic Liquids with the Bis(fluorosulfonyl)imide Anion: Electrochemical Properties and Applications in Battery Technology

Room temperature ionic liquids (RTILs) with the bis(fluorosulfonyl)imide (FSI) anion exhibit higher conductivities than the corresponding bis(trifluoromethanesulfonyl)imide (TFSI) compounds, thereby generating interest as novel electrolytes for lithium batteries. The electrochemical properties of a series of FSI RTILs, at inert metal and lithium electrodes, have been investigated using cyclic voltammetry (CV) and electrochemical impedance spectroscopy. Addition of , , or LiTFSI extends cathodic limits to significantly more negative values and allows reversible lithium electrodeposition. Variable-current cycling of symmetrical coin cells reveals significant changes in electrode–electrolyte interphasial impedance, which depends on the identity of the lithium salt anion, the concentration of the salt, and the RTIL cation. For most cells, voltage–time curves become unsteady early in duty, which is consistent with the formation of dendrites on the lithium surface. A stable voltage behavior returns within around 20 cycles, at notably a lower current density presumably because detachment/reattachment of dendrites eventually re-establishes a contiguous lithium electrode with a higher surface area. Importantly, the combination of the kinetics of lithium deposition and morphology of the deposit in FSI anion-based RTIL media does not result in lithium penetration of the separator. Therefore, FSI-based electrolytes can play a key role in the development of a viable lithium-metal battery technology.

Advanced, high-performance composite polymer electrolytes for lithium batteries

Progress in lithium battery technology may be achieved by passing from a conventional liquid electrolyte structure to a solid-state, polymer configuration. In this prospect, great R&D effort has been devoted to the development of suitable lithium conducting polymer electrolytes. The most promising results have been obtained with systems based on blends between poly(ethylene oxide) and lithium salts. In this work we show that the transport and interfacial properties of these electrolytes may be greatly enhanced by the dispersion of a ceramic filler having an unique surface state condition. The results, in addition to their practical reflection in the lithium polymer electrolyte battery technology, also provide a valid support to the model which ascribes the enhancement of the transport properties of ceramic-added composites to the specific Lewis acid–base interactions between the ceramic surface states and both the lithium salt anion and the PEO-chains .

Superacid ZrO 2-added, composite polymer electrolytes with improved transport properties

In this paper we report the synthesis and the properties of a new composite polymer electrolyte formed by dispersing a sulphate-promoted superacid zirconia into a poly(ethylene oxide)–lithium tetrafluoroborate, PEO–LiBF 4, matrix. We show that the addition of the superacid ceramic greatly enhances the properties of the electrolyte in terms of improvement of its transport properties, and particularly, of the lithium transference number. The results, in addition to their practical reflection in the lithium polymer electrolyte battery technology, also provide a valid support to the model which ascribes the enhancement of the transport properties of ceramic-added composites to the specific Lewis acid–base interactions between the ceramic surface states and both the lithium salt anion and the PEO-chains.

Structural factors to improve physico-chemical properties of zwitterions as ion conductive matrices

Thermal properties and ion conductive characteristics of equimolar mixtures of zwitterion and lithium salts (Z/L mixtures) have been investigated. Through a systematic study of their structure–property relationship, we describe a zwitterion structure that produces high ionic conductivity when the zwitterion is mixed with lithium salt. We found that a pure zwitterion containing imide anion melted at 87 °C and the melting point of pure zwitterions was lowered in proportion to the alkyl spacer chain length between the anion and cation sites. In Z/L mixtures, ionic liquid-like domain formed between the cation sites of zwitterions and the anions of lithium salts regardless of the anion structure of the zwitterions. However, the anion structure affected the transference number of the lithium cation in the Z/L mixtures. To improve the thermal stability and the ionic conductivity of Z/L mixtures, suitable alkyl chain length between the cation and anion sites was determined to be 5 to 7 CH2 units.

Effect of surface states of layered double hydroxides on conductive and transport properties of nanocomposite polymer electrolytes

All solid-state poly(ethylene oxide) (PEO) nanocomposite electrolytes were made containing nanoscale fillers of layered double hydroxides (LDHs). Two kinds of LDHs with different surface states were prepared by aqueous co-precipitation method. The LDHs were added into PEO matrix to study the structures, conductivities and ionic transport properties of nanocomposite electrolytes. The structures of LDHs were characterized by infrared spectra, thermogravimetric analysis and wide-angle X-ray diffraction. With enhanced compatibility of LDH sheets by oligo(ethylene oxide) surface modification, the PEO/OMLDH nanocomposite electrolyte exhibits an amorphous morphology and an enhancement of conductivity by three orders of magnitude as compared to pure PEO electrolyte. The lithium ion transference number T Li + of PEO/LDH nanocomposite electrolyte measured with a value of 0.42 is two times higher than the one of pure PEO electrolyte, which can be attributed to the Lewis acid–base interaction between surface states of metal hydroxides and counter anions of lithium salts.

New lithium organic salts for promising polymer electrolytes

In the plasticized and gel-like polymer, electrolytes containing such aprotic solvents as plasticizers, cations and anions of lithium salts are mobile. As a rule the transport number of lithium ions in these systems is far less than 1 (usually 0.5). Such a situation can result from the possibility of cation binding by polymer matrix polar groups (e.g., -Oin polyethylene oxide, -CN in polyacrylonitrile, -NR in polyamide, etc). In this case, an anion can contribute more to the conductivity than a cation can. The problems of the undesirable participation of anions in ion transport and decreasing reactivity of polymer electrolytes relative to the electrode materials can be solved by using lithium organic salts with large anions. This is illustrated by the increased interest in the application of new organic and inorganic lithium salts in the composition of polymer electrolytes:

Electrochemical stability and conductivity enhancement of composite polymer electrolytes

The electrochemical stability behavior of the composite polymer electrolytes obtained by adding a fine Al 2O 3 powder (activated acidic, neutral, and basic) with a diameter of 5.8 nm to the poly(ethylene oxide) (PEO)–LiClO 4 is described. The strong hydrogen bond between the surface group of Al 2O 3 and lithium salt anion prevents the decomposition of lithium salt anion. An enhancement of the ionic conductivity for the composite polymer electrolytes prepared with Al 2O 3 and BaTiO 3 is described in terms of a reduction of crystallinity and an increase of charge carrier concentration.