Lawrence G. Scanlon

Polymer–ceramic composite electrolytes: conductivity and thermal history effects

Abstract This paper reports the conductivity and DSC measurements of composite electrolytes containing the PEO:LiBF 4 complex, and TiO 2 and ZrO 2 nanosized particles. Below the melting temperature of PEO, conductivity is strongly dependent upon thermal history. The roles of the ceramic phase are to depress the melting temperature and retard the kinetics of crystallization of PEO. This results in a conductivity relaxation below the melting temperature of PEO which appears to be a characteristic of these composite electrolytes.

Structural evolution and conductivity of PEO:LiBF4–MgO composite electrolytes

This paper explores and proposes a structure–conductivity correlation in the PEO:LiBF4–MgO composite electrolyte system. The proposed correlation is derived from interpretations of DSC and conductivity measurements. Thermal cycling in the 0–100°C range yields an amorphous polymer structure believed to be beneficial for enhanced conductivity. The proposed roles of MgO are to depress the PEO melting temperature and retard the kinetics of its crystallization. A resistivity relaxation or conductivity enhancement below the melting temperature of PEO (68°C) occurs, which appears to be a characteristic of these electrolytes and related to an interaction of dipoles associated with polymer chains and MgO. A higher concentration (≃30%) of MgO leads to its segregation and reduction in conductivity resulting from crystallization of PEO.

Composite Electrolytes for Lithium Rechargeable Batteries

The paper reviews and presents attributes of emerging polymer-ceramic composite electrolytes for lithium rechargeable batteries. The electrochemical data of a diverse range of composite electrolytes reveal that the incorporation of a ceramic component in a polymer matrix leads to enhanced conductivity, increased lithium transport number, and improved electrode-electrolyte interfacial stability. The conductivity enhancement depends upon the weight fraction of the ceramic phase, annealing parameters, nature of polymer-ceramic system, and temperature. The ceramic additive also increases the effective glass transition temperature and thus decouples structural and electrical relaxation modes which in turn increases the lithium transport number. The ceramic additives also provide a range of free energy of reactions with lithium. A few of the ceramic materials (MgO, CaO, Si3N4) have positive free energy of reaction and they should not passivate lithium electrodes.

Layered carbon lattices and their influence on the nature of lithium bonding in lithium intercalated carbon anodes

Abstract Ab initio molecular orbital calculations have been used to investigate the nature of lithium bonding in stage 1 lithium intercalated carbon anodes. This has been approximated by using layered carbon lattices such as coronene, (C 24 H 12 ), anthracene, and anthracene substituted with boron. With two coronene carbon lattices forming a sandwich structure and intercalated with either two, three, four or six lithiums, it has been found that the predominant mode of bonding for the lithium is at the carbon edge sites as opposed to bonding at interior carbon hexagon sites. With a single planar coronene molecule approximating a graphene sheet, the bonding of four lithiums with this molecule is near the interior carbon hexagon sites. For anthracene and boron substituted anthracene, lithium bonding takes place within the carbon hexagon sites. The separation between lithiums in a sandwich type structure with two anthracenes in the eclipsed conformation is 5.36 A. The effect of boron substitution is to increases lattice flexibility by allowing the lattice to twist and lithium to bond at adjacent hexagon sites.

Composite Cathode with Li2Pc

Computational chemistry calculations performed with Gaussian 98 were used to develop an experimental method that facilitates ionic connection between the solid-state electrolyte dilithium phthalocyanine (Li 2 Pc) and manganese dioxide (MnO 2 ). The planar configuration of the phthalocyanine ring and the fact that the lithium ions are very close to the ring may sterically hinder effective ionic coupling between Li 2 Pc and any potential cathode. This same argument has been used for understanding the insertion and removal of magnesium from water solutions of deuteroporphyrins. Calculated results show that lithium ions are drawn closer to the phthalocyanine ring upon formation of (Li 2 Pc) 2 via molecular self-assembly when compared to the single-molecule Li 2 Pc. However, extension of lithium ions above the planar phthalocyanine ring in (Li 2 Pc) 2 can be enhanced through formation of a complex at the axial position above lithium. Calculations show that corannulene at the axial position above lithium forms an asymmetric structure with (Li 2 Pc) 2 and extends lithium further above the ring. To test the theoretical results, an electrically conducting carbon with a curved lattice was used in the fabrication of an all solid-state electrochemical cell with a lithium metal foil anode, Li 2 Pc electrolyte, and a MnO 2 cathode. Slow-scan-rate cyclic voltammograms of a Li x MnO 2 cathode demonstrate the charging and discharging of cells.

Chapter 6 Hydrogen adsorption in corannulene-based materials

Publisher Summary This chapter discusses the H adsorption in corannulene-based materials and describes the molecular structure of corannulene and doping of Li atoms on the corannulene molecule. Corannulene has potential advantages as H storage material over planar graphite and even C nanotubes. Such advantages are derived from the specific geometric and electronic characteristics of corannulene, which enhances the interaction with H molecules. Li atoms are more stably doped over the six-member rings than over the five-member ring of corannulene, with the concave side more favorable for doping than the convex side of corannulene. Li-doped corannulene complexes have higher dipole moment because of charge transfer from Li to C atoms of corannulene and thus enhance the induced dipole–dipole interaction with H molecules. Also, the interaction between the Li atom and H is stronger than the interaction between C atom and H. Besides, the doping of Li atoms provides more space in the doping complexes for H adsorption.

Preparation and characterization of a hybrid solid polymer electrolyte consisting of poly(ethyleneoxide) and poly(acrylonitrile) for polymer-battery application

For application in an ambient temperature solid state lithium battery a highly dimensionally-stable polymer electrolyte based on polyethyleneoxide (PEO) suffers from low ionic conductivity, whereas a highly conducting gel electrolyte based on polyacrylonitrile (PAN) suffers from low dimensional stability. In order to overcome these problems, a hybrid solid polymer electrolyte (HSPE) was prepared using PEO, PAN, propylene carbonate (PC), ethylene carbonate (EC) and lithium perchlorate. The HSPE films were highly conducting as well as dry, free-standing and dimensionally-stable. The films were characterized by constructing symmetrical cells containing nonblocking lithium electrodes and also blocking stainless steel electrodes. Investigations were carried out on ionic conductivity, electrochemical reaction, interfacial stability and morphology of the films. The properties of HSPE were compared with the films prepared using (i) PEO and LiClO/sub 4/ and (ii) PAN, PC, EC and LiClO/sub 4/. The results suggest that the HSPE is a potential electrolyte material for application in a polymer-battery.