Lithium Metal Polymer Research Articles

Cycling performance and thermal stability of lithium polymer cells assembled with ionic liquid-containing gel polymer electrolytes

Gel polymer electrolytes containing 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide and a small amount of additive (vinylene carbonate, fluoroethylene carbonate, and ethylene carbonate) are prepared, and their electrochemical properties are investigated. The cathodic limit of the gel polymer electrolytes can be extended to 0 V vs. Li by the formation of a protective solid electrolyte interphase on the electrode surface. Using these gel polymer electrolytes, lithium metal polymer cells composed of a lithium anode and a LiNi 1/3Co 1/3Mn 1/3O 2 cathode are assembled, and their cycling performances are evaluated at room temperature. The cells show good cycling performance, comparable to that of a cell assembled with gel polymer electrolyte containing standard liquid electrolyte (1.0 M LiPF 6 in ethylene carbonate/diethylene carbonate). Flammability tests and differential scanning calorimetry studies show that the presence of the ionic liquid in the gel polymer electrolyte considerably improves the safety and thermal stability of the cells.

Lithium metal polymer cells assembled with gel polymer electrolytes containing ionic liquid

Gel polymer electrolytes containing a mixture of organic solvent and ionic liquid were prepared and their electrochemical properties were investigated. The gel polymer electrolytes exhibited good electrochemical stability and stable interfacial properties toward lithium metal. Using these gel polymer electrolytes, lithium metal polymer cells composed of a lithium anode and a LiFePO 4 cathode were assembled, and their cycling performances were evaluated. The cells showed good cycling performance comparable to that of a cell assembled with gel polymer electrolyte containing only organic liquid electrolyte. The Li/LiFePO 4 cells assembled with a gel polymer electrolyte containing ionic liquid are expected to be one of the promising candidates for high energy density lithium batteries with improved safety.

Effect of organic additives on the cycling performances of lithium metal polymer cells

Gel polymer electrolytes were prepared by immersing a porous poly(vinylidene fluoride- co-hexafluoropropylene) membrane in an electrolyte solution containing small amounts of organic additive. Three kinds of organic compounds, thiophene, 3,4-ethylenedioxythiophene and biphenyl, were used as a polymerizable monomeric additive. The organic additives were found to be electrochemically oxidized to form conductive polymer films on the electrode at high potential. By using the gel polymer electrolytes containing different organic additive, lithium metal polymer cells, composed of lithium anode and LiCoO 2 cathode, were assembled and their cycling performance evaluated. Adding small amounts of a suitable polymerizable additive to the gel polymer electrolyte was found to reduce the interfacial resistance in the cell during cycling, and it thus exhibited less capacity fade and better high rate performance. Differential scanning calorimetric studies showed that the thermal stability of the fully charged LiCoO 2 cathode was improved in the cell containing an organic additive.

Ionic Liquid-Based Rechargeable Lithium Metal-Polymer Cells Assembled with Polyaniline/Carbon Nanotube Composite Cathode

A polyaniline (PANI)/multiwalled carbon nanotube (CNT) composite was synthesized by in situ chemical polymerization. The PANI/CNT composite was used as an active cathode material in lithium metal-polymer cells assembled with ionic liquid (IL) electrolyte. The IL-based electrolyte was composed of 1-ethyl-3-methylimidazolium tetrafluoroborate and vinylene carbonate (VC) as an additive, together with . Porous poly(vinylidene-co-hexafluoropropylene) [P(VdF-co-HFP)] film was used as a polymer membrane for assembling the cell. Electrochemical performance of the Li/IL/PANI-CNT cells was evaluated by cyclic voltammetry, ac impedance measurements, and constant-current charge/discharge cycling. Lithium metal-polymer cells assembled with the IL electrolyte showed good cyclability with a maximum discharge capacity of and good high-rate performance.

Electrochemical characterization of blend polymer electrolytes based on poly(oligo[oxyethylene]oxyterephthaloyl) for rechargeable lithium metal polymer batteries

Solid polymer electrolytes composed of poly(ethylene oxide)(PEO), poly(oligo[oxyethylene]oxyterephthaloyl) and lithium perchlorate have been prepared and characterized. Addition of poly(oligo[oxyethylene]oxyterephthaloyl) to PEO/LiClO 4 reduced the degree of crystallinity and improved the ambient temperature ionic conductivity. The blend polymer electrolyte containing 40 wt.% of poly(oligo[oxyethylene]oxyterephthaloyl) showed an ionic conductivity of 2.0 × 10 −5 S cm −1 at room temperature and a sufficient electrochemical stability to allow application in the lithium batteries. By using the blend polymer electrolytes, the lithium metal polymer cells composed of lithium anode and LiCoO 2 cathode were assembled and their cycling performances were evaluated at 40 °C.

Electrochemical characteristics of multi-functional polymer electrolyte based on dual-layer membrane for lithium metal polymer battery

A novel dual-layer type polymer electrolyte was prepared by impregnating the interconnected pores with an ethylene carbonate(EC)/dimethyl carbonate(DMC)/lithium hexafluorophosphate(LiPF 6) solution. An incompatible layer is based on a micro-porous polyethylene(PE) and a compatible layer, based on a poly(vinylidenefluoride-co-hexafluoropropylene)(P(VdF-co-HFP)), is submicro-porous and compatible with an electrolyte solution. To enhance the ionic conductivity in the compatible layer, inorganic type Li + single ion conductor particle based on hydrophilic silica has been synthesized. The maximum apparent ionic conductivity of the dual-layer polymer electrolyte is 7.7 × 10 −3 S/cm at the ambient temperature. High rate capability of the Li/the dual-layer polymer electrolytes/Li[Ni 0.15Li 0.23M n0.62]O 2 cell was significantly improved as the incompatible layer thickness decreases.

Solid-state Li/LiFePO 4 polymer electrolyte batteries incorporating an ionic liquid cycled at 40 °C

The cycle behaviour and rate performance of solid-state Li/LiFePO 4 polymer electrolyte batteries incorporating the N-methyl- N-propylpyrrolidinium bis(trifluoromethanesulfonyl)imide (PYR 13TFSI) room temperature ionic liquid (IL) into the P(EO) 20LiTFSI electrolyte and the cathode have been investigated at 40 °C. The ionic conductivity of the P(EO) 20LiTFSI + PYR 13TFSI polymer electrolyte was about 6 × 10 −4 S cm −1 at 40 °C for a PYR 13 +/Li + mole ratio of 1.73. Li/LiFePO 4 batteries retained about 86% of their initial discharge capacity (127 mAh g −1) after 240 continuous cycles and showed excellent reversible cyclability with a capacity fade lower than 0.06% per cycle over about 500 cycles at various current densities. In addition, the Li/LiFePO 4 batteries exhibited some discharge capability at high currents up to 1.52 mA cm −2 (2 C) at 40 °C which is very significant for a lithium metal-polymer electrolyte (solvent-free) battery systems. The addition of the IL to lithium metal-polymer electrolyte batteries has resulted in a very promising improvement in performance at moderate temperatures.

Effect of an inorganic additive on cycling performance of Li/V 2O 5 polymer cells prepared with gel polymer electrolyte

A gel polymer electrolyte is prepared by soaking a polymer-coated separator in electrolyte solution that contains an inorganic additive. The porous polymer coated on the separator is gelled by soaking in an electrolyte solution to encapsulate a larger amount of electrolyte solution. By using the gel polymer electrolyte, lithium-metal–polymer cells composed of a lithium anode and V 2O 5 cathode are assembled and their cycling performances are evaluated. The effect of an inorganic additive (AlI 3) on the cycling performance of Li/V 2O 5 polymer cells is investigated. The addition of AlI 3 to the gel polymer electrolyte reduces the interfacial resistance and thus the cells exhibit a less capacity fading and better high rate performance.

Recent developments in the ENEA lithium metal battery project

Solvent-free P(EO) 20LiTFSI + PYR 14TFSI polymer electrolyte films with PYR 14 +/Li + mole ratios ranging from 0.96 to 3.22 were prepared by hot-pressing mixtures composed of PEO, LiTFSI and PYR 14TFSI of selected stoichiometries. The PYR 14TFSI room temperature ionic liquid (RTIL) is homogeneously incorporated into the P(EO) 20LiTFSI membrane without phase separation. For a PYR 14 +/Li + mole ratio of 3.22, the ionic conductivity was about 2 × 10 −4 S/cm at 20 °C, i.e., more than one order of magnitude higher than that of the RTIL-free electrolyte. The electrochemical stability window of the polymer electrolyte containing the RTIL was about 6 V (versus Ag/Ag +). Li/V 2O 5 cells with the polymer electrolyte (PYR 14 +/Li + = 1.92) showed a 60% capacity retention after 80 cycles at 40 °C (the initial capacity was 210 mA h/g). Li/V 2O 5 cells (PYR 14 +/Li + = 1.28) held at 30 °C delivered about 93 mA h/g (at 0.057 mA/cm 2), which corresponds to approximately 34% utilization of the active material. These results suggest that the incorporation of the RTILs into PEO-based polymer electrolytes is very promising for the future realization of solid-state lithium metal polymer batteries operating near ambient temperatures.

PEO-Based Polymer Electrolytes with Ionic Liquids and Their Use in Lithium Metal-Polymer Electrolyte Batteries

The influence of adding the room-temperature ionic liquid (RTIL) -methyl--propylpyrrolidinium bis(trifluoromethanesulfonyl)imide to polymer electrolytes and the use of these electrolytes in solid-state batteries has been investigated. polymer electrolytes with various mole fractions (, 1.08, 1.73, 1.94, 2.15, and 3.24) were prepared. The addition of up to a 3.24 mole fraction of the RTIL to electrolytes, corresponding to a RTIL/PEO weight fraction of up to 1.5, resulted in freestanding and highly conductive electrolyte films reaching at . The electrochemical stability of was significantly improved by the addition of LiTFSI. cells using the polymer electrolyte with showed excellent reversible cyclability with a capacity fading of 0.04% per cycle over several hundreds cycles at . The incorporation of the RTIL into lithium metal-polymer electrolyte batteries has resulted in a promising improvement in performance at moderate to low temperatures.

What's new with hybrid electric vehicles

This article has two main parts. The first part provides examples of recent advancements with advanced battery technologies: nickel metal hydride (NiMH), lithium ion (Li ion), lithium metal polymer (Li MP), sodium metal chloride (Zebra) and nickel zinc (NiZn). The next part addresses, in overview form, a selection of significant hybrid electric vehicle (HEV) designs, concepts, and prototypes from Japan, France, and the United States.

Cycling performances of Li/LiCoO 2 cell with polymer-coated separator

Gel polymer electrolyte (GPE) was prepared with the porous polymer-coated separator by soaking in an electrolyte solution. The porous polymer coated on both sides of polyethylene separator was gelled in contact with the electrolyte solution and encapsulated a larger amount of electrolyte solution. The gel polymer electrolyte exhibited high ionic conductivity in order of 10 −3 S/cm and was electrochemically stable up to 4.9 versus Li. With the gel polymer electrolyte, lithium metal polymer cell composed of a lithium anode and LiCoO 2 cathode was assembled and its cycling performances were evaluated.

Preparation and characterization of gel polymer electrolytes for solid state magnesium batteries

Magnesium-ion conducting gel polymer electrolytes (GPE) were prepared and their electrochemical properties were characterized. The composition of GPE containing P(VdF- co-HFP), Mg(ClO 4) 2–EC/PC and SiO 2 was optimized in consideration of ionic conductivity and mechanical stability. Solid state magnesium cell employing magnesium anode, GPE, and vanadium oxide cathode was assembled and its cycling characteristics were investigated. The Mg/GPE/V 2O 5 cell showed low initial discharge capacity of 58 mAh/g based on active V 2O 5 material and poor cycling characteristics. At present, the results show that the Mg/GPE/V 2O 5 cell has an inferior cycling performance in comparison with that of well-developed, lithium metal polymer cells.

The role of an adhesive gel-forming polymer coated on separator for rechargeable lithium metal polymer cells

The gel-forming polymer of different thicknesses was coated on both sides of polyethylene separator. The porous polymer coated on the separator was gelled by soaking in an electrolyte solution and encapsulated a larger amount of electrolyte solution. Adhesive gel formed on both sides of PE separator provided an efficient transport of lithium ion through the solid electrolyte interphase, and the electrolyte solution absorbed in the separator gave an acceptable ionic conductivity. By using the separators with adhesive gel layer, lithium metal polymer cells composed of a lithium anode and LiCoO 2 cathode were assembled and their cycling performances were evaluated. The effect of thickness of gel polymer layer on cycling performances of the rechargeable lithium-metal polymer cells was investigated.

Preparation and Characterization of Asymmetric Composite Polymer Electrolytes for Lithium Metal Polymer Batteries

An asymmetric composite polymer electrolyte composed of porous polymer matrix which micro-porous layer based on the polyethylene acts as a support and submicro-porous layer is introduced on one side of the micro-porous layer through a coating process and ethylene carbonate/dimethyl carbonate/LiPF6 liquid solution occupying the pores has been prepared. The maximum ionic conductivity of this system was 7.0 × 10-3 S/cm at the ambient temperature. The conductivity seems to be significantly affected by the uptake amount of liquid electrolyte within the matrix.

Ionic liquids to the rescue? Overcoming the ionic conductivity limitations of polymer electrolytes

Polymer electrolytes – solid polymeric membranes with dissolved salts – are being intensively studied for use in all-solid-state lithium-metal-polymer (LMP) batteries to power consumer electronic devices. The low ionic conductivity at room temperature of existing polymer electrolytes, however, has seriously hindered the development of such batteries for many applications. The incorporation of salts molten at room temperature (room temperature ionic liquids or RTILs) into polymer electrolytes may be the necessary solution to overcoming the inherent ionic conductivity limitations of ‘dry’ polymer electrolytes.

Towards room-temperature performance for lithium–polymer batteries

Recent work on molecular simulations of the mechanisms of lithium ion conductance has pointed towards two types of limiting process. One has involved the commonly cited segmental motion while the other is related to energy barriers in the solvation shell of polymeric ether oxygens around the lithium ions. Calculations of the barriers to lithium ion migration have provided important indicators as to the best design of the polymer. The theoretical work has coincided with and guided some recent developments on polymer synthesis for lithium batteries. Structural change of the polymer solvation shell has been pursued by the introduction of trimethylene oxide (TMO) units into the polymer. The conductivity measurements on polymers containing TMO unit are encouraging. The architecture of the polymer networks has been varied upon which the solvating groups are attached and significant improvements in sub-ambient performance are observed as a result. However, the above-ambient temperature performance appears controlled by an Arrhenius process that is not completely consistent with the theoretical calculations described here and may indicate the operation of a different mechanism. The new polymers possess significantly lower T g values in the presence of lithium salts, which indicates weaker binding of the lithium ions by the polymers. These properties provide considerable improvement in the transport properties close to the electrode surfaces resulting in decreased impedances at the surfaces both at lithium metal and in composite electrodes. The greater flexibility of the solvation groups combined with appropriate architecture not only has applications in lithium metal–polymer batteries but also in lithium ion liquid and gel systems as well as in fuel cell electrodes.

Performance and capacity fade of V 2O 5–lithium polymer batteries at a moderate–low temperature

Lithium metal–polymer electrolyte batteries with improved utilization of the active material at a moderate–low temperature (65°C) were realized. Low molecular weight poly(ethylene glycol) (PEG, MW=2000) was used as the lithium-ion conductive matrix in the composite cathode. The cathode active material was crystalline V 2O 5. A blend of poly(ethylene oxide) (PEO, MW=4×10 6) and PEG was used as a solid polymer electrolyte (SPE). The transport properties of the SPE were evaluated at various temperatures. A specific conductivity as high as 1.0×10 −4 S cm −1 was calculated at 45°C. The temperature dependence of the interfacial resistances between lithium/SPE and cathode material/PEG was evaluated. The lithium/SPE interfacial resistance decreases linearly with the temperature. The charge transfer resistance between the cathode material and PEG reaches a minimum at 60°C and it does not decrease with a further temperature increase. The data clearly show that the battery is able to work at a temperature as low as 60°C. The operating temperature was set at 65°C and the battery performance was evaluated at different discharge rates. An energy density of about 500 W h kg −1 and a power density of about 150 W kg −1 were achieved cycling the cell in about 3.3 h at 0.20 mA cm −2. Prolonged cycling showed a capacity fading of about 0.45% per cycle. This value does not differ very much from the value found cycling the cell in liquid electrolyte. The fade in capacity was associated with an increase of cell resistance. The evolution of the lithium/SPE and cathode material/PEG interfaces resistances was monitored. The interfacial resistance increases with time, but its value is not so high as to explain the increase of the total resistance of the cell. Anyhow, this additional resistance could be responsible for the difference in the capacity fading when cycling the cell in polymer electrolyte instead of in liquid electrolyte.

Improved composite materials for rechargeable lithium metal polymer batteries

Abstract The performance of several polymer electrolytes for lithium metal batteries for electric vehicle applications are reported. The best performing electrolyte is the composite PEO 20 LiCF 3 SO 3 –γLiAlO 2 , which was prepared by a solvent-free procedure. It showed coulombic efficiency values of the lithium deposition–stripping process of 94%–96%. Electrochemical tests of lithium polymer battery (LPB) prototypes based on a 3 V LiMn 2 O 4 composite cathode material laminated together with the PEO 20 LiCF 3 SO 3 –γLiAlO 2 electrolyte gave promising results for electric vehicle applications. Even under non-optimized battery design, the prototypes delivered, at the C/3 rate and at 94°C, 40%–30% of theoretical capacity over 100 charge–discharge cycles.

An Improved Composite Polymer Electrolyte for Lithium Metal Batteries

ABSTRACTWe have demonstrated that PEO-based polymer electrolytes prepared by solvent-free procedures and with the addition of particle-size ceramic powder have very stable lithium interface properties—a very important feature for the development of successful lithium metal polymer batteries (LPBs). The results of cyclability tests at different charge-discharge rates carried out on prototypes of LPBs assembled with the dry prepared PEO20-LiCF3SO3-20%w/w λLiAlO2 composite electrolyte and with a composite cathode based on LiMn204 spinel operating at 3V are reported and discussed.