Properties of Li4Ti5O12 as an anode material in non-flammable electrolytes

Two non-flammable electrolytes 1 M LiPF₆ in sulfolane (TMS) + 5 wt% VC and 0.7 M lithium bis(trifluoromethanesulphonyl)imide (LiNTf₂) in N-methyl-N-propylpyrrolidinium bis(trifluoromethanesulphonyl)imide (MePrPyrNTf₂) + 10 wt% gamma-butyrolactone (GBL) were tested with Li₄Ti₅O₁₂ (LTO) as highly promising anode material for application in lithium-ion batteries. The results were compared for the titanium anode in the classic electrolyte: 1 M LiPF₆ in propylene carbonate + dimethyl carbonate (PC + DMC, 1:1). The performances of LTO/electrolyte/Li cell were tested using cyclic voltammetry, electrochemical impedance spectroscopy, and galvanostatic charge/discharge and scanning electron microscopy (SEM). SEM images of electrodes and those taken after electrochemical cycling showed changes which may be interpreted as a result of solid-state interface formation. Good charge/discharge capacities and low capacity loss at medium C rates preliminary cycling was obtained for the Li₄Ti₅O₁₂ anode. For LTO/1 M LiPF₆ in PC + DMC/Li system, the best capacity was obtained at C/10 and C/3 (145 and 154 mAh g^?1, respectively). In the case of a system working on the basis of a TMS solution (1 M LiPF₆ in TMS + 5 wt% VC) the best value was obtained at a C/5 current and an average of more than 150 mAh g^?1 (86 % of theoretical capacity). For the 0.7 M LiNTf₂ in MePrPyrNTf₂ + 10 wt% GBL electrolyte, the highest capacitance value (at C/20 current) of about 150 mAh g^?1 was observed. The 1 M LiPF₆ in TMS + 5 wt% VC and 0.7 M LiNTf₂ in MePrPyrNTf₂ + 10 wt% GBL electrolytes had a relatively broad thermal stability range and no decomposition peak was observed below 150 °C.     

High flash point electrolyte for use in lithium-ion batteries

The high flash point solvent adiponitrile (ADN) was investigated as co-solvent with ethylene carbonate (EC) for use as lithium-ion battery electrolyte. The flash point of this solvent mixture was more than 110 °C higher than that of conventional electrolyte solutions involving volatile linear carbonate components, such as diethyl carbonate (DEC) or dimethyl carbonate (DMC). The electrolyte based on EC:ADN (1:1 wt) with lithium tetrafluoroborate (LiBF₄) displayed a conductivity of 2.6 mS cm⁻¹ and no aluminum corrosion. In addition, it showed higher anodic stability on a Pt electrode than the standard electrolyte 1 M lithium hexafluorophosphate (LiPF₆) in EC:DEC (3:7 wt). Graphite/Li half cells using this electrolyte showed excellent rate capability up to 5C and good cycling stability (more than 98% capacity retention after 50 cycles at 1C). Additionally, the electrolyte was investigated in NCM/Li half cells. The cells were able to reach a capacity of 104 mAh g⁻¹ at 5C and capacity retention of more than 97% after 50 cycles. These results show that an electrolyte with a considerably increased flash point with respect to common electrolyte systems comprising linear carbonates, could be realized without any negative effects on the electrochemical performance in Li-half cells.     

Electrochemical characteristics of phase-separated polymer electrolyte based on poly(vinylidene fluoride-co-hexafluoropropane) and ethylene carbonate

A polymer electrolyte based on microporous poly(vinylidene fluoride-co-hexafluoropropane) (PVdF-HFP) film was studied for use in lithium ion batteries. The microporous PVdF-HFP (Kynar 2801) matrix was prepared from a cast of homogeneous mixture of PVdF-HFP and solvents such as ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC). After evaporation of DMC and EMC, a sold film of the PVdF-HFP and the EC mixture was obtained. EC-rich phase started its formation in the PVdF-HFP/EC film at EC content of about 60 wt.% based on the total weight of PVdF-HFP and EC. The formation of the new phase resulted in the abrupt increase of the porosity of the PVdF-HFP matrix from 32 to 62%. The ionic conductivity of the film soaked in 1 M LiPF₆-EC/DMC=1/1 was significantly increased from order of 10⁻⁴ S/cm to order of 10⁻³ S/cm at the EC content of 60 wt.%. Thermal and spectroscopic investigations showed that most of the EC interact with PVdF-HFP with the EC content being below 60 wt.%. MCMB/polymer electrolyte/LiCoO₂ cells employing the microporous PVdF-HFP polymer film showed stable charging/discharging characteristics at 1C rate and good rate capability.     

Effect of vinylene carbonate as additive to electrolyte for lithium metal anode

The cycling efficiencies and cycling performance of a lithium metal anode in a vinylene carbonate (VC)-containing electrolyte were evaluated using Li/Ni and LiCoO₂/Li coin type cells. The cycling efficiencies of deposited lithium on a nickel substrate in an EC + DMC (1:1) electrolyte containing LiPF₆, LiBF₄, LiN(SO₂CF₃)₂ (LiTFSI), or LiN(SO₂C₂F₅) (LiBETI) at 25 and 50 °C were improved by presence of VC. However, the lithium cycling efficiencies at low temperature (0 °C) decreased by adding VC to the EC+DMC (1:1) electrolyte. The deposited lithium at low temperature exhibited a dendritic morphology and a thicker surface film. The lithium ion conductivity of the VC derived surface film was lower than that of the VC-free surface film at low temperature. Therefore, we concluded that the cycling efficiency decreased with decreasing temperature. On the other hand, the cell containing VC additive has excellent performance at elevated temperature. The deposited lithium at 50 °C in the VC-containing electrolyte exhibited a particulate morphology and formed a thinner surface film. The VC derived surface film, which consists of polymeric species, suppressed the deleterious reaction between the deposited lithium and the electrolyte.     

A study of electrochemical kinetics of lithium ion in organic electrolytes

Limiting current densities equivalent to the transport-controlling step of lithium ions in organic electrolytes were measured by using a rotating disk electrode (RDE). The diffusion coefficients of lithium ion in the electrolyte of PC/LiClO₄, EC : DEC/LiPF₆ and EC : DMC/LiPF₆ were determined by the limiting current density data according to the Levich equation. The diffusion coefficients increased in the order of PC/LiClO₄<EC : DEC/LiPF₆<EC : DMC/ LiPF₆ with respect to molar concentration of lithium salt. The maximum value of diffusivity was 1.39x10-5cm²/s for 1M LiPF₆ in EC : DMC=1 : 1. Exchange current densities and transfer coefficients of each electrolyte were determined according to the Butler-Volmer equation.     

Performance of lithium tetrafluorooxalatophosphate in methyl butyrate electrolytes

Methyl butyrate (MB) has been investigated as a co-solvent for lithium-ion battery electrolytes to improve the performance at low temperature (?10 to ?30 °C). The cycling performance of graphite/LiNi_1/3Co_1/3Mn_1/3O₂ cells with 1.2 M lithium tetrafluorooxalatophosphate (LiFOP) in 2:2:6 EC/EMC/MB was compared to 1.2 M LiPF₆ in both 3:7 EC/EMC and 2:2:6 EC/EMC/MB. The LiFOP/MB electrolyte has a good operational temperature window and comparable cycling performance to the LiPF₆ electrolyte at both room temperature and low temperature (?10 °C). However, after accelerated aging the LiFOP/MB electrolyte has worse performance at very low temperature (?30 °C) compared to LiPF₆ electrolytes. Ex-situ surface analysis was conducted by scanning electron microscopy, X-ray photoelectron spectroscopy, and Fourier transfer infrared spectroscopy to provide insight into the performance differences.     

Interfacial structural stabilization on amorphous silicon anode for improved cycling performance in lithium-ion batteries

Interfacial structures of electrode-current collector and electrode-electrolyte have been designed to be stabilized for improved cycling performance of amorphous silicon (Si) that is considered as an alternative anode material to graphite for lithium-ion batteries. Interfacial structural stabilization involves the interdigitation of Si electrode-Cu current collector substrate by anodic Cu etching with thiol-induced self-assembly, and the formation of self-assembled siloxane on the surface of Si electrode using silane. The novel interfacial architecture possesses promoted interfacial contact area between Si and Cu, and a surface protective layer of siloxane that suppresses interfacial reactions with the electrolyte of 1 M LiPF₆/ethylene carbonate (EC):diethylene carbondate (DEC). FTIR spectroscopic analyses revealed that a stable solid electrolyte interphase (SEI) layer composed of lithium carbonate, organic compounds with carboxylate metal salt and ester functionalities, and PF-containing species formed when having siloxane on Si electrode. Interfacially stabilized Si electrode exhibited a high capacity retention 80% of the maximum discharge capacity after 200 cycles between 0.1 and 1.5 V vs. Li/Li⁺. The data contribute to a basic understanding of interfacial structural causes responsible for the cycling performance of Si-based alloy anodes in lithium-ion batteries.     

Electrochemical performances of electric double layer capacitor with UV-cured gel polymer electrolyte based on poly[(ethylene glycol)diacrylate]-poly(vinylidene fluoride) blend

Poly[(ethylene glycol)diacrylate]-poly(vinylidene fluoride), a gel polymer blend with ethylene carbonate:dimethyl carbonate:ethylmethyl carbonate (EC:DMC:EMC, 1:1:1 volume ratio) and containing 1.0 M of lithium hexafluoro phosphate (LiPF₆) as liquid components, is employed as a gel polymer electrolyte for an electric double layer capacitor (EDLC). Its electrochemical characteristics is compared with that of liquid organic electrolyte mixture of ethylene carbonate, dimethyl carbonate and ethylmethyl carbonate in a 1:1:1 volume ratio containing 1.0 M LiPF₆ salt. The specific surface area of the activated carbon powder as an active material is 1908 m²/g. Liquid poly[(ethylene glycol)diacrylate] (PEGDA) oligomer with a high retention capability of liquid electrolytes is cured by UV irradiation and poly(vinylidene fluoride)-hexafluoropropylene (PVdF-HFP) copolymer with a porous structure endows polymer matrix with high mechanical strength.The specific capacitance of EDLC using the gel polymer electrolyte (GPE-EDLC) shows 120 F/g, which is better than the liquid organic electrolyte. Good cycling efficiency is observed for a GPE-EDLC with high retention capability of liquid components. The high specific capacitance and good cycling efficiency are most likely due to the polarization resistance of EDLC with the gel polymer electrolyte, which is lower than the liquid organic electrolyte. This may result from the distinguished adhesion between the activated carbon electrode and the gel polymer electrolyte, as well as high retention capability of liquid components.Power densities of GPE-EDLC and LOE-EDLC shows 1.88 kW/kg and 1.21 kW/kg, respectively. However, the energy densities are low in both electrolytes.The GPE-EDLC exhibits rectangular cyclic voltammogram similar to an ideal EDLC within operating voltage range of 0 V-2.5 V. It should be noted that a region of electric double layer means a wide voltage and a rapid formation. Redox currents of both EDLCs are not observed in the sweep region and the cyclic voltammograms are unchanged on repeated runs. The observed leakage current shows 49 μA after 720 s at a constant voltage of 2.5 V, due to the high ionic conductivity of 1.5 × 10⁻³ S cm⁻¹ during storage time. Swelling and well-developed pore structures of the GPE blend films allow ions and solvents to move easily.     

Electrochemical impedance study of Li-ion insertion into the raw acid-oxidized carbon nanotubes

Electrochemical impedance spectroscopy (EIS) was applied for the raw acid-oxidized multiwall carbon nanotubes during Li-ion insertion with the electrolyte of 1M LiPF₆ in EC and DMC. Impedance spectroscopy consists of two separated arcs in the high and intermediate range frequency. The high frequency arc is attributed to Li migration within the surface films and the medium frequency arc is associated with the charge transfer. Obtained spectra were analyzed with an equivalent circuit model. Kinetic parameters such as the charge transfer resistance, film resistance, diffusion coefficient and exchange current were evaluated. The contribution of the film to the measured impedance response is discussed.     

Surface layer formation on Sn anode: ATR FTIR spectroscopic characterization

Surface layer formed on Sn thin film electrode in 1 M LiPF₆/EC:DMC electrolyte was characterized using ex situ FTIR spectroscopy with the attenuated total reflection technique. IR spectral analyses showed that the immersion of Sn film in the electrolyte resulted in a chemical interfacial reaction leading to the passivation of Sn surface with primarily PF-containing inorganic surface species and small amount of organics. When constant current cycling was conducted with lithium cells with Sn film electrode at 0.1-1.0 V vs. Li/Li⁺, the interfacial reaction between Sn and electrolyte appeared significantly intensified that the features of PF-containing species became enhanced and new IR features of organic species (e.g. alkyl carbonate/carboxylate metal salts and ester functionalities) were observed. The surface layer continued to form with cycling, partly due to non-effective surface passivation as well as particle pulverization accompanied by enlargement of active surface area. Comparative IR spectral analyses indicated that the interfacial reaction between Sn and PF₆⁻ anion played a leading role in forming the surface layer, which is different from lithiated graphite that had mainly organic surface species. The data contribute to a better understanding of the interfacial processes occurring on Sn-based anode materials in lithium-ion batteries.     

A microporous gel electrolyte based on poly(vinylidene fluoride-co-hexafluoropropylene)/fully cyanoethylated cellulose derivative blend for lithium-ion battery

A gel polymer electrolyte based on the blend of poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) and fully cyanoethylated cellulose derivative (DH-4-CN) was prepared and characterized. Thermal, mechanical, swelling, liquid electrolyte retention and electrochemical properties, as well as microstructures of the prepared polymer electrolytes, were investigated using thermogravimetric analysis, electrochemical impedance spectroscopy, linear sweep voltammetry, and scanning electron microscopy. The results showed that the addition of DH-4-CN could obviously improve the conductivity of PVDF-HFP based electrolyte. The maximum ionic conductivity of 4.36 mS cm⁻¹ at 20 °C can be obtained for PVDF-HFP/DH-4-CN 14:1 in the presence of 1 M LiPF₆ in EC and DMC (1:1, w/w). The dry blend membranes exhibit excellent thermal behavior. All the blend electrolytes are electrochemically stable up to about 4.8 V vs. Li/Li⁺ for all compositions. The results reveal that the composite polymer electrolyte qualifies as a potential application in lithium-ion battery.     

Effects of solvents and salts on the thermal stability of LiC6

Accelerating rate calorimetry (ARC) was used to study the thermal stability of Li_0.81C₆ in dimethyl carbonate (DMC), diethyl carbonate (DEC), ethylene carbonate (EC), and an EC/DEC mixture as well as in LiPF₆- and LiBOB-based electrolytes. ARC results show that linear carbonates like DMC or DEC react strongly with Li_0.81C₆ and that robust passivating layers do not form. By contrast, the cyclic carbonate, EC, creates a robust passivating film that limits the rate of reaction between Li_0.81C₆ and EC as the temperature increases. X-ray diffraction shows that the addition of LiPF₆ to EC/DEC changes the surface film that forms on Li_0.81C₆ at elevated temperature to one dominated by LiF instead of lithium-alkyl carbonate or lithium carbonate. This increases the thermal stability of Li_0.81C₆ in LiPF₆ electrolyte compared to pure EC/DEC solvent. By an apparently similar mechanism, the addition of only 0.2 M LiBOB to EC/DEC greatly improves the thermal stability of Li_0.81C₆. ARC results for Li_0.81C₆ in pure and mixed salt LiPF₆ and LiBOB EC/DEC electrolytes of various molarities shed light on the reasons for the beneficial effect of the salts.     

Properties of Li-graphite and LiFePO4 electrodes in LiPF6–sulfolane electrolyte

Sulfolane (also referred to as tetramethylene sulfone, TMS) containing LiPF₆ and vinylene carbonate (VC) was tested as a non-flammable electrolyte for a graphite |LiFePO₄ lithium-ion battery. Charging/discharging capacity of the LiFePO₄ electrode was ca. 150 mAh g⁻¹ (VC content 5 wt%). The capacity of the graphite electrode after 10 cycles establishes at the level of ca. 350 mAh g⁻¹ (C/10 rate). In the case of the full graphite |1 M LiPF₆ + TMS + VC 10 wt% |LiFePO₄ cell, both charging and discharging capacity (referred to cathode mass) stabilized at a value of ca. 120 mAh g⁻¹. Exchange current density for Li⁺ reduction on metallic lithium, estimated from electrochemical impedance spectroscopy (EIS) experiments, was j_o(Li/Li⁺) = 8.15 × 10⁻⁴ A cm⁻². Moreover, EIS suggests formation of the solid electrolyte interface (SEI) on lithium, lithiated graphite and LiFePO₄ electrodes, protecting them from further corrosion in contact with the liquid electrolyte. Scanning electron microscopy (SEM) images of pristine electrodes and those taken after electrochemical cycling showed changes which may be interpreted as a result of SEI formation. No graphite exfoliation was observed. The main decomposition peak of the LiPF₆ + TMS + VC electrolyte (TG/DTA experiment) was present at ca. 275 °C. The LiFePO₄(solid) + 1 M LiPF₆ + TMS + 10 wt% VC system shows a flash point of ca. 150 °C. This was much higher in comparison to that characteristic of a classical LiFePO₄ (solid) + 1 M LiPF₆ + 50 wt% EC + 50 wt% DMC system (T_f ≈ 37 °C).     

Thermal analysis of a cylindrical lithium-ion battery

This work investigates the heat generation characteristics of a cylindrical lithium-ion battery. The battery consists of the graphite, LiPF₆ of the propylene carbonate/ethylene carbonate/dimethyl carbonate (PC/EC/DMC) solution, and spinal as anode, electrolyte and cathode, respectively. The coupled electrochemical–thermal model is developed with full consideration of electrolyte transport properties as functions of temperature and Li ion concentration. A truly conservative finite volume numerical method is employed for the spatial discretization of the model equations. Three types of heat generation sources including the ohmic heat, the active polarization heat and the reaction heat are quantitatively analyzed for the battery discharge process. The ohmic heat is found to be the largest contribution with around 54% in the total heat generation. About 30% of the total heat generation in average is ascribed to the electrochemical reaction. The active polarization contributes the least comparing to the ohmic heat and reactions heat. The results also show that the Li ion concentration and its gradient in electrolyte are the main factors giving the effect on the heat generations of active polarization and electrolyte electric resistance. The raised temperature in the battery discharge is positive related with the thickness of both separator and electrodes.     

Preparation and performance study on P(St‐MMA)‐SiO2 doped P(VDF‐HFP) based composite polymer electrolyte

The organic–inorganic hybrid material poly(styrene‐methyl methacrylate)‐silica (P(St‐MMA )‐SiO₂) was successfully prepared by in situ polymerization confirmed by Fourier transform infrared spectroscopy and was employed to fabricate poly(vinylidene fluoride‐hexafluoropropylene) (P(VDF‐HFP )) based composite polymer electrolyte (CPE ) membrane. Desirable CPEs can be obtained by immersing the CPE membranes into 1.0 mol L^?1 LiPF₆‐EC /DMC /EMC (LiPF₆ ethylene carbonate + dimethyl carbonate + ethylmethyl carbonate) liquid electrolyte for about 0.5 h for activation. The corresponding physicochemical properties were characterized by SEM , XRD , electrochemical impedance spectroscopy and charge–discharge cycle testing measurements. The results indicate that the as‐prepared CPEs have excellent properties when the mass ratio of the hybrid P(St‐MMA )‐SiO ₂ particles to polymer matrix P(VDF‐HFP ) reaches 1:10, at which point the SEM analyses show that the as‐prepared P(St‐MMA )‐SiO ₂ particles are uniformly dispersed in the membrane and the CPE membrane presents a homogeneous surface with abundant interconnected micropores. The XRD results show that there may exist interaction forces between the P(St‐MMA )‐SiO ₂ particles and the polymer matrix, which can obviously decrease the crystallinity of the composite membrane. Moreover, the ionic conductivity at room temperature and the electrochemical working window of the CPE membrane can reach 3.146 mS cm^?1 and 4.7 V, respectively. The assembled LiCoO₂/CPE /Li coin cell with the CPE presents excellent charge–discharge and C ‐rate performance, which indicates that P(St‐MMA )‐SiO ₂ hybrid material is a promising additive for the P(VDF‐HFP ) based CPE of the lithium ion battery. © 2016 Society of Chemical Industry     

Separator grafted with siloxane by electron beam irradiation for lithium secondary batteries

Polyethylene (PE) separator grafted with 2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane (siloxane) was newly prepared by electron beam irradiation. The degree of grafting and morphology of the grafted separators were characterized by FT-IR and scanning electron microscopy (SEM). The polymer electrolytes based on the grafted separators were prepared by immersing the separators in the electrolyte containing 1 M LiPF₆ in EC/DMC (1:1 by volume). The ionic conductivity of the grafted separators was changed with the degree of grafting and showed the highest value of 7 × 10⁻⁴ S cm⁻¹ at the degree of grafting of 6%. The electrochemical stability limit of the grafted separator with the degree of grafting of 6% was increased to 5.2 V. The Li ion cell using the grafted separator also showed an improved performance, suggesting that the grafted separator is a good candidate for the separator of lithium batteries at high voltage operation.     

Ionic liquid-based gel polymer electrolyte for LiMn0.4Fe0.6PO4 cathode prepared by electrospinning technique

Two polymer electrolytes (PEs), one consisting of 1 M LiPF₆ in ethylene carbonate (EC)/dimethyl carbonate (DMC) (PE_EC/DMC) and the other consisting of LiTFSI in room temperature ionic liquid (RTIL), 1-ethyl-3-methyl imidazolium bis(trifluoromethane sulfonyl)imide (EMITFSI) (PE_IL), were prepared by using electrospun P(VdF-HFP) membranes. The PEs showed typical impedance spectroscopic responses with high conductivity and good anodic stability. The PEs were applied with carbon coated LiMn_0.4Fe_0.6PO₄ cathode material prepared by sol-gel method. The charge-discharge kinetics of LiMn_0.4Fe_0.6PO₄ cathode cells were studied by electrochemical impedance spectroscopy. The excellent performance with high capacity and good cycle stability was observed for both the cells. The cell comprising of PE_IL showed a better performance than the other cell. The cells having PE_EC/DMC and PE_IL delivered discharge capacities of 150 and 141 mAh g⁻¹, and 168 and 162 mAh g⁻¹, respectively, after cycle 1 and 50. The differences in the performance of the PEs originate from the differences in viscosity, ionic conductivity and also from the different levels of interactions of a RTIL and EC/DMC with the polymer. The evaluation of lithium ion diffusion coefficients shows its fast diffusion in both the cases, the trend of which changed with the increase in the number of cycles.     

Cold sintering process of Li1.5Al0.5Ge1.5(PO4)3 solid electrolyte

The recently developed technique of cold sintering process (CSP) enables densification of ceramics at low temperatures, i.e., <300°C. CSP employs a transient aqueous solvent to enable liquid phase‐assisted densification through mediating the dissolution‐precipitation process under a uniaxial applied pressure. Using CSP in this study, 80% dense Li_1.5Al_0.5Ge_1.5(PO₄)₃ (LAGP) electrolytes were obtained at 120°C in 20 minutes. After a 5 minute belt furnace treatment at 650°C, 50°C above the crystallization onset, Li‐ion conductivity was 5.4 × 10^?5 S/cm at 25°C. Another route to high ionic conductivities ~10^?4 S/cm at 25°C is through a composite LAGP ‐ (PVDF‐HFP) co‐sintered system that was soaked in a liquid electrolyte. After soaking 95, 90, 80, 70, and 60 vol% LAGP in 1 M LiPF₆ EC‐DMC (50:50 vol%) at 25°C, Li‐ion conductivities were 1.0 × 10^?4 S/cm at 25°C with 5 to 10 wt% liquid electrolyte. This paper focuses on the microstructural development and impedance contributions within solid electrolytes processed by (i) Crystallization of bulk glasses, (ii) CSP of ceramics, and (iii) CSP of ceramic‐polymer composites. CSP may offer a new route to enable multilayer battery technology by avoiding the detrimental effects of high temperature heat treatments.     

A novel intrinsically porous separator for self-standing lithium-ion batteries

γ-LiAlO₂, Al₂O₃ and MgO were used as fillers in a PVdF-HFP polymer matrix to form self-standing, intrinsically porous separators for lithium-ion batteries. These separators can be hot-laminated onto the electrodes without losing their ability to adsorb liquid electrolyte. The electrochemical stability of the separators was tested by constructing half-cells with the configuration: Li/fibre-glass/filler-based separator/electrode. MgO-based separators were found to work well with both positive and negative electrodes. An ionic conductivity of about 4×10⁻⁴ S cm⁻¹ was calculated for the MgO-based separator containing 40% 1 M solution of LiPF₆ in an EC/DMC 1:1 solvent. Self-standing, lithium-ion cells were constructed using the MgO-based separator and the resulting battery performance evaluated in terms of cyclability, power and energy density.     

Influence of tris(pentafluorophenyl) borane as an anion receptor on ionic conductivity of LiClO4-based electrolyte for lithium batteries

The effect of tris(pentafluorophenyl) borane (TPFPB) as an anion receptor on the ionic conductivities of the liquid electrolyte, EC/DMC (1/2.5, v/v)/1 M LiClO₄, was investigated. It is found that the dissociation degree of lithium salts, the viscosity of the conducting medium, and the mobility of anions were changed by introducing TPFPB into the liquid electrolyte. The transference number of the liquid electrolyte was enhanced with increasing the TPFPB content, but the total ionic conductivity was decreased due to the decreasing anionic conductivity as a result of the anion trapping effect of TPFPB. The ionic conductivities of the separators soaked in the liquid electrolyte were much lower than those of the liquid electrolytes. The electrolyte retention of the separator can be improved by the interaction between TPFPB and DMC. The electrochemical stability of the liquid electrolyte was also enhanced by addition of TPFPB.