Melt-Formable Block Copolymer Electrolytes for Lithium Rechargeable Batteries

Abstract

Microphase separated block copolymers consisting of an amorphous poly͑ethylene oxide͒ ͑PEO͒-based polymer covalently bound to a second polymer offer a highly attractive avenue to achieving both dimensional stability and high ionic conductivity in polymer electrolytes for solid-state rechargeable lithium batteries. However, due to the strong thermodynamic incompatibility typically found for most polymer pairs, the disordered, liquid state of the copolymer can rarely be achieved without the incorporation of a solvent, which complicates processing. Herein, we report the design of new block copolymer electrolytes based on poly͑methyl methacrylate͒, PMMA, and poly͑oligo oxyethylene methacrylate͒, POEM, which are segmentally mixed at elevated temperatures appropriate for melt processing, while exhibiting a microphase separated ͑ordered͒ morphology at ambient temperature. Although pure PMMA-b-POEM is segmentally mixed at all temperatures, it is shown that microphase separation in these materials can be induced in a controlled manner by the incorporation of even limited amounts of lithium trifluoromethane sulfonate (LiCF 3 SO 3 ), a salt commonly employed to render PEO ionically conductive. Such ''salt-induced'' microphase separation suggests a simple method for designing new solid polymer electrolytes combining high ionic conductivities with excellent dimensional stability and improved processing flexibility.

Thermodynamics of Ion-Containing Polymer Blends and Block Copolymers

“…The lithium ions are complexed with EO groups [5], and together with their counterions, provide the charge carriers [6]. The nonconducting block can be tuned to confer other functions, such as mechanical robustness [3,4,6].Experimentally, the addition of lithium salts has been shown to have significant effects on the order-order and order-disorder transitions in block copolymers [3,7,8]. Among other effects, it is found that the effective parameter characterizing the immiscibility of the two blocks increases linearly with salt concentration [9,10],…”

Transport and Electro‐Optical Properties in Polymeric Self‐Assembled Systems

“…using plasticizers or using short PEO chains that have increased mobility and suppressed crystallization where the graft and branched architectures have been useful [237][238][239][240]. Also, self-assembly is used where amorphous ethylene oxide-containing domains are incorporated within block copolymeric structures, leading to synergistic properties [225,[241][242][243]. There were early efforts to combine PEO within block copolymer structures, for example by grafting short PEO grafts to the middle block of polystyrene-bpolybutadiene-b-polystyrene triblock copolymer [244,245].…”

“…Reducing the length of the lauryl sidechain to be only methyl, i.e. using poly(methyl methacrylate)-b-poly[oligo(oxyethylene) methacrylate], reduces the repulsion between the blocks and self-assembly does not occur [242]. However, adding CF 3 SO 3 Li leads to self-assembly and conductivity.…”

“…Due to the comb-shaped architecture consisting of the backbone and Fig. 3.11 Examples of self-assembled Li-conducting polymer electrolytes [242,251].…”

AC Analysis of PEO₁₀LiCF₃SO₃ Polymeric Material for Memory Storage Application

“…The CF 3 SO 3 -anion forms another ionic bond with the methylene group outside the helical structure when the ring structured monomers. It is suggested (Hehmeyer et al, 2007;Curtright et al, 2004;Moore and Schneider, 2001;Turcu et al, 2006;Anne-Valerie Ruzette et al, 2001;Mui et al, 2002) that ionic conduction in PEO x LiCF 3 SO 3 occurs by the cation (Li+) hopping between sites in either the single or double helix structures. Other studies showed the ionic conductivity occurs mainly in the amphorous phase rather than in the crystalline phase.…”