Polarization Behavior of Lithium Electrode in Solid Electrolytes Consisting of a Poly(Ethylene Oxide)‐Grafted Polymer

Abstract

A complex of poly(ethylene oxide)-grafted poly(methyl)-methacrylate (PEO-PMMA) with a lithium salt has been examined as a solid electrolyte of an ambient-temperature rechargeable lithium battery. The electrolyte film was prepared by radical polymerization of PEO-grafted methacrylate which contained a lithium salt dissolved in poly(ethylene glycol) dimethyl ether. The resulting composite had a high conductivity of 10 -4 S cm -~ at room temperature. The rate of charge transfer at the lithium electrode/polymeric electrolyte interface was high, and the ion transfer in the bulk electrolyte was rate-determining at high cathodic polarization. The coulombic efficiency of lithium during the charge-discharge cycle depended on the cycling current density. The average efficiency reached 88% at 50 ~A cm -2 cycling when an A1 plate was used as a substrate.Rechargeable lithium (Li) batteries using so-called polymeric solid electrolytes such as poly(ethylene oxide) (PEO)-based polymer complexes with Li salts have been fabricated by way of trial and error (1-4). This type of battery can have an ultra-thin form and high energy density. Also, the use of a polymeric solid electrolyte will give high reliability to the battery without leakage of the electrolyte during long-term storage. Therefore, much interest has been taken in the charge-discharge behavior of cells with polymeric solid electrolytes. On the other hand, some disadvantages are also anticipated (5), e.g., relatively low conductivity of the polymeric electrolyte at ambient temperature, and poor electrical contact at the electrode/ electrolyte interface due to the volumetric change of the electrode material, especially the positive electrode, during the charge-discharge cycle.The polymer matrices so far considered are mainly PEO, poly(propylene oxide) (PPO), and related polymers. There have been many publications regarding the compositions of polymers. There have been many publications regarding the compositions of the polymer matrix-electrolytic salt systems and the ionic conductance of the resulting complexes (6). However, only a few research groups have studied the electrochemical processes at the solid electrode(s)/polymeric electrolyte interface (7-13). Despite the technical difficulty of the experimental work, it is of much importance to understand the interfacial properties of the solid electrode/polymeric electrolyte system in order to develop a high-performance rechargeable battery for practical use.We have previously reported the synthesis of a new polymeric electrolyte (Fig. 1) composed of PEO-grafted poly-(methylmethacrylate) (PEO-PMMA) with a Li salt, and showed its high ionic conductivity at room temperature (~ = -10 -4 S cm -1 at 30~ (14). The polymer matrix was PMMA with flexible side chains of PEO groups, which are effective for the transport of Li + in the matrix. Analogous concepts for designing the polymer matrix have been presented by Bannister et al. (15), and Tada and Kawahara (16). At this point Scrosati and co-workers (12, 13) have demonstrated th...

Single Lithium‐Ion Conducting Polymer Electrolytes Based on a Super‐Delocalized Polyanion

“…However, conventional SPEs formed by dissolving Li salt with a small anion in a polymer host (usually high‐molecular‐weight PEO), are dual‐ion conductors, in which both cations and anions are mobile . This would generate the concentration gradients of the salt and cell polarization, which causes premature battery failure …”

“…[10][11][12][13][14] This would generate the concentration gradients of the salt and cell polarization, which causes premature battery failure. [15,16] One of the best solutions to the above-mentioned problem is to prepare single Li-ion conductors (SLICs), in which the anions are immobilized by anion trapping agents or by fixing the anions to the polymeric backbones, [17][18][19][20] so that the transference number (t Li + )ofLi + cations is close to one.Until now,m ost of SLICs have been synthesized by grafting common alkyl carboxylate (RCO 2 À ) [17] and/or sulfonate (RSO 3 À ) [18] anions to the polymeric backbones.H owever, the ion dissociation in polyether media is very limited, owing to the low degrees of negative charge distribution in these anions.…”

Enhanced electrochemical properties and interfacial stability of poly(ethylene oxide) solid electrolyte incorporating nanostructured Li 1. 3 Al 0 . 3 Ti 1 .7 ( PO 4

“…For improving the conductivity of PEO SPE, different methods have been adopted to modify PEO matrix, such as co‐polymerization, 22 grafting, 23 cross‐linking, 24 and combing 25 . Currently, introducing inorganic particles into the polymer matrix is a facile method to enhance ionic conductivity of PEO SPE.…”

“…However, the ion transfer in PEO SPEs mainly occurs in amorphous regions, the high crystallinity of PEO below its melting point leads to low ionic conductivity, which seriously affects the charge and discharge capacity at large current. For improving the conductivity of PEO SPE, different methods have been adopted to modify PEO matrix, such as co-polymerization, 22 grafting, 23 cross-linking, 24 and combing. 25 Currently, introducing inorganic particles into the polymer matrix is a facile method to enhance ionic conductivity of PEO SPE.…”

Single Lithium‐Ion Conducting Polymer Electrolytes Based on a Super‐Delocalized Polyanion

“…[9] However, conventional SPEs formed by dissolving Li salt with as mall anion in ap olymer host (usually high-molecular-weight PEO), are dual-ion conductors,i nw hich both cations and anions are mobile. [15,16] One of the best solutions to the above-mentioned problem is to prepare single Li-ion conductors (SLICs), in which the anions are immobilized by anion trapping agents or by fixing the anions to the polymeric backbones, [17][18][19][20] so that the transference number (t Li + )ofLi + cations is close to one.Until now,m ost of SLICs have been synthesized by grafting common alkyl carboxylate (RCO 2 À ) [17] and/or sulfonate (RSO 3 À ) [18] anions to the polymeric backbones.H owever, the ion dissociation in polyether media is very limited, owing to the low degrees of negative charge distribution in these anions. [15,16] One of the best solutions to the above-mentioned problem is to prepare single Li-ion conductors (SLICs), in which the anions are immobilized by anion trapping agents or by fixing the anions to the polymeric backbones, [17][18][19][20] so that the transference number (t Li + )ofLi + cations is close to one.Until now,m ost of SLICs have been synthesized by grafting common alkyl carboxylate (RCO 2 À ) [17] and/or sulfonate (RSO 3 À ) [18] anions to the polymeric backbones.H owever, the ion dissociation in polyether media is very limited, owing to the low degrees of negative charge distribution in these anions.…”