Monalisa Patel

Utilizing an ionic liquid for synthesizing a soft matter polymer “gel” electrolyte for high rate capability lithium-ion batteries

A cross-linked polymer “gel” electrolyte obtained from free radical polymerization of a vinyl monomer (acrylonitrile; AN) in a room temperature ionic liquid electrolyte (N,N-methyl butyl pyrrolidinium-bis(trifluoromethanesulphonyl)imide-lithium bis(trifluoromethanesulphonyl)imide; LiTFSI-[Py1,4-TFSI]) for application in high rate capability rechargeable lithium-ion batteries is discussed here. This is a novel alternative compared to the often employed approach of using a molecular liquid as the medium for performing the polymerization reaction. The polymer “gel” electrolytes (AN:Py1,4-TFSI = 0.16–0.18, w/w) showed remarkable compliable mechanical strength and higher thermal stability compared to LiTFSI-[Py1,4-TFSI]. Despite two orders increase in magnitude of viscosity of polymer “gels”, the room temperature ionic conductivity of the “gels” (1.1 × 10−3–1.7 × 10−3 Ω−1 cm−1) were nearly identical to that of the ionic liquid (1.8 × 10−3 Ω−1 cm−1). The present “gel” electrolytes did not exhibit any ageing effects on ionic conductivity similar to the conventional polymer gel electrolytes (e.g. high molecular weight polymer + salt + high dielectric constant molecular solvent). The disorder (ionic liquid) to a relative order (cross-linked polymer electrolyte) transformation does not at all influence the concentration of conducting species. The polymer framework is still able to provide efficient pathways for fast ion transport. Unlike the ionic liquid which is impossible to assemble without a conventional separator in a cell, the polymer “gel” electrolyte could be conveniently assembled without a separator in a Li|lithium iron phosphate (LiFePO4) cell. Compared to the ionic liquid, the “gel” electrolyte showed exceptional cyclability and rate capability (current density: 35–760 mA g−1 with LiFePO4 electronically wired with carbon (amorphous or multiwalled nanotube [MWCNT]).

A crosslinked “polymer–gel” rechargeable lithium-ion battery electrolyte from free radical polymerization using nonionic plastic crystalline electrolyte medium

A cross-linked polymer–gel soft matter electrolyte with superior electrochemical, thermal and mechanical properties obtained from free radical polymerization of vinyl monomers in a semi-solid organic nonionic plastic crystalline electrolyte for application in rechargeable lithium-ion batteries is discussed here.

Ion Transport in a Polymer-Plastic Solid Soft Matter Electrolyte in the Light of Solvent Dynamics and Ion Association

Ion transport in a recently demonstrated promising soft matter solid plastic-polymer electrolyte is discussed here in the context of solvent dynamics and ion association. The plastic-polymer composite electrolytes display liquid-like ionic conductivity in the solid state, compliable mechanical strength (approximately 1 MPa), and wide electrochemical voltage stability (> or = 5 V). Polyacrylonitrile (PAN) dispersed in lithium perchlorate (LiClO(4))-succinonitrile (SN) was chosen as the model system for the study (abbreviated LiClO(4)-SN:PAN). Systematic observation of various mid-infrared isomer and ion association bands as a function of temperature and polymer concentration shows an effective increase in trans conformer concentration along with free Li(+) ion concentration. This strongly supports the view that enhancement in LiClO(4)-SN:PAN ionic conductivity over the neat plastic electrolyte (LiClO(4)-SN) is due to both increase in charge mobility and concentration. The ionic conductivity and infrared spectroscopy studies are supported by Brillouin light scattering. For the LiClO(4)-SN:PAN composites, a peak at 17 GHz was observed in addition to the normal trans-gauche isomerism (as in neat SN) at 12 GHz. The fast process is attributed to increased dynamics of those SN molecules whose energy barrier of transition from gauche to trans has reduced under influences induced by the changes in temperature and polymer concentration. The observations from ionic conductivity, spectroscopy, and light scattering studies were further supplemented by temperature dependent nuclear magnetic resonance (1)H and (7)Li line width measurements.

A Cross-Linked Soft Matter Polymer Electrolyte for Rechargeable Lithium-Ion Batteries

Over the last few decades, there has been an upsurge in research activity to develop alternatives for conventional liquid electrolytes (e.g. , lithium hexafluorophosphate (LiPF6) in 1:1 volume ratio of ethylene carbonate (EC) and dimethyl carbonate (DMC)). One such direction has been to synthesize soft matter electrolytes based on polymers, 4] ionic liquids, 6] and plastic crystalline materials. 8] This has facilitated the idea of development of an all solid-state lithium ion battery. Solid polymer electrolytes (SPEs) are the most widely studied soft matter electrolyte comprising essentially of a salt (say lithium) solvated in a polyether matrix. The major drawback of SPE is low ambient temperature ionic conductivity (ca. 10 6 W 1 cm ). Several attempts have been made to overcome this drawback. Notable among them are the gel electrolytes (non-aqueous liquid solvent + polymer electrolyte) and composite polymer electrolytes (heterogeneous doping with oxide filler). However, both approaches have failed to generate materials with optimized ionic conductivity, mechanical, and electrochemical properties simultaneously. It has been proposed that special polymer architecture, copolymerization may additionally aid in optimization of physical properties such as ionic conductivity and mechanical strength of polymer and hence generate superior polymer electrolytes. We demonstrate here for the first time, a soft matter electrolyte obtained from free-radical polymerization of vinyl monomers in a liquid solution matrix comprising of dinitrile adiponitrile (N C (CH2 CH2)2 C N, ADPN) and lithium salt [bis(trifluoromethanesulfonimide), LiTFSI] . ADPN was chosen as it is a colorless, moderately viscous (ca. 10 2 Pa) liquid with a dielectric constant (e) of 30. It readily dissolves a wide variety of ionic lithium salts and demonstrated to be non-corrosive towards metallic current collector in Ref. [16] We present here the electrical, thermal, mechanical, and electrochemical properties of the cross-linked polymer electrolytes obtained from the new methodology. For acrylonitrile (AN)/ADPN >0.20 (w/w), free radical polymerization in LiTFSI-ADPN solution resulted in gel-like solid electrolytes (Figure 1D,E). For all concentration regimes, no phase separation was observed and electrolyte samples were homogeneous and mechanically stable. Figure 2 shows the thermogravimetric analysis (TGA) for ADPN and AN/ADPN (0.25 and 0.31). The TGA trace for ADPN showed a 100% weight loss in a single step between 120 8C (onset) and 230 8C. The gel electrolytes on the other hand showed a two step weight loss of total 83% in the temperature range between 100 8C to 450 8C. The initial loss of approximately 65% (2–4% below 100 8C and 61% within 100-200 8C) corresponds to the decomposition of unpolymerized monomers and adiponitrile present in the polymer-gel electrolyte and the final step of 18% (200– 450 8C) correspond to the cross-linked polymer network. Thus, formation of a polymer network in the LiTFSI–ADPN leads to an electrolyte with higher thermal stability. Mechanical properties of the neat and polymer-gel electrolytes were studied using static and dynamic rheology (Figure 3a,b). Figure 3a shows the variation of viscosity (h) as a function of shear rate (ġ) for LiTFSI–ADPN and AN/ADPN >0.20. For the liquid electrolyte (i.e. , 0 wt% AN), the viscosity is nearly independent of the shear rate, indicating a Newtonian behavior. On the other hand, the viscosity decreases with an increase in shear rate for

Soft matter electrolytes for Li-ion batteries

Demand for safe lithium-ion batteries (LiBs) for varied applications such as portable electronics, transportation, space technologies have lead to significant emphasis on development of new materials and concepts. This talk will focus on prospective soft matter electrolytes which have been synthesized from liquids (e.g. molecular solvents, ionic liquids) as the starting medium. Although conversion from liquid to the soft matter state constrains intrinsic spatial and temporal disorder of the liquid solvent, the materials properties in the soft matter state however, are far more interesting and beneficial than the liquid state. Assembly of various soft matter electrolytes in cells containing in-house synthesized nanostructured (nanotubes/sheets, mesoporous) non-carbonaceous anode and cathode materials show improved battery performance compared to the liquid electrolytes. The talk will also discuss mechanistics of ion transport in the electrolytes.