Physico-Chemical Studies of Some Novel Lithium Salts Based Nanocomposite Polymer Electrolytes for Lithium Rechargeable Batterie

In the present work, lithium bis(oxalate)borate (LiBOB), lithium fluoroalkylphosphate (LiFAP) and lithium difluoro(oxalato)borate (LiDFOB) identified as suitable novel lithium salts which were synthesized by a solid-state reaction method. These synthesized salts (and chemically modified) were incorporated into polymer host and subjected to various physico-chemical studies to optimize the ionic conductivity of the prepared membrane by varying filler/plasticizer ratio for all the novel salts synthesized while keeping the polymer host content as constant without compromising the electrochemical, mechanical and thermal stabilities. These membranes were prepared by either conventional or phase inversion technique with and without fillers. The fillers used were nanosized TiO2, ZrO2, SiO2, Sb2O3 and AlO(OH)n pseudo-boehmite and nanoporous Al2O3. The cycling performances of membranes fabricated by later technique were studied as electrolytes in coin cell configurations with lithium as an anode and LiFePO4 as a cathode.

            The chapter 1 covers the general introduction of electrochemical power sources and the materials in search of synergic activity and their important features. The classification of battery systems, i.e., primary and secondary is briefly described. Rechargeable battery systems such as lead-acid, Ni-Cd, Ni-MH and lithium-ion batteries are compared with the slowly emerging chemistries based on magnesium as an anode. State-of-the-art battery active materials for the lithium-based rechargeable batteries included. The platforms for the possible application avenues for solid, gel and composite polymer electrolytes are also discussed.

   The chapter 2 focuses on the synthesis of environment-friendly and cost-effective LiBOB by a solid-state reaction method and subsequent use of it in polymer membranes with suitable nanofillers. TiO2 and ZrO2 were used nanofillers with the polyvinylidene difluoride / polyvinylchloride blend as a host. The membranes were subjected to a.c. impedance, X-ray diffraction and morphological studies.

      The chapter 3 elucidates the electrochemistry of LiFAP based polyvinylidene difluoride-hexafluoropropylene (PVdF-HFP) host with nanoporous Al2O­3 (activated, acidic) and nanoparticulate SiO2 fillers and ethylene carbonate / diethyl carbonate as plasticizers. The membranes were subjected to a.c. impedance, differential scanning calorimetry, Fourier transform infrared spectroscopy, photoluminescence and scanning electron microscopy.     

       The chapter 4 presents the synthesis of LiDFOB and discusses the various physico-chemical characterizations of membranes based on it. Nanoparticles of TiO2 and Sb2O3 were consumed for the selected host of PVdF-HFP. The high resolution FT-Raman confirmed the conformational change of a to b phase of VdF crystals of the said host.

      The chapter 5 commences with phase inversion technique, a novel way of preparing the nanocomposite polymer electrolytes. As such the synthesis of PVdF-HFP microporous membranes by phase inversion technique is presented in this chapter. The nanopartilces of AlO(OH)n was used as a filler. These prepared membranes were soaked in 0.5 M LiX (X=BOB, FAP and DFOB) in 1:1 v/v EC:DEC. The physico-chemical observation in the present work identifies that long-term storage led to surface crystallization of the salts with those membranes containing LiBOB and LiDFOB. Consequently, the freshly prepared membranes were only subjected to charge-discharge studies in Li/LiFePO4 coin cells. The membranes were also subjected to mechanical stability, a.c. impedance, differential scanning calorimetry and scanning electron microscopy. The physical properties like liquid uptake, porosity, surface area, percentage of crystallinity, etc of these membranes were also carried out.

     Chapter 6 summarizes salient futures of LiBOB, LiFAP and LiDFOB based nanocomposite polymer membranes. The perspectives of current status of research of lithium battery technology are also enlightened in this chapter.