PEO gel electrolytes

Generally, the cross-linked PEO gel electrolytes have good mechanical strength, thermal behavior, and electrochemical performance. For example, their exothermic peak (340°C) is higher than that of common organic electrolytes (266°C), and their ionic conductivity at 20°C can be as high as 2.4 x 10-3 S/cm. 

Nanofillers can also be added to cross-linked PEO gel electrolyte. For example, when PEO oligomeric units are incorporated in the main chain of polysiloxane to prepare an intermolecular cross-linking network polymer, nano-Si02 filler and, after, plasticizer are added. The obtained gel polymer... 

It was possible to improve the interfacial properties of Li metal anodes in liquid electrolyte solutions using additives that modify the Li-surface chemistry, such as C02 [23-27] and HF [28,29], Using PEO-based gel electrolyte systems effectively suppressed dendritic deposition of lithium [30], In Section C we report on a very good charge-discharge performance of lithium metal anodes in PVdF-HFP gel electrolyte systems. Furthermore, addition of C02 to the PVdF-HFP gel electrolyte system considerably improves the charge/discharge characteristics [31]. 

As shown in Figure 7a, the lithium anode tested in the EC/PC-based liquid solution shows relatively high efficiency only at the first cycle. In subsequent cycles, the cycling efficiency drops to around 75%. The Li cycling efficiencies measured in EC/PC are similar to those measured in the PEO gel. It is obvious that lithium anodes in the PVdF-HFP gel electrolyte system show higher cycling efficiency. 

In addition, various gel electrolytes were investigated for EDLC as well. Polyethylene oxide) (PEO)-, poly(acrylonitrile) (PAN)-, polymethylmethacrylate) (PMMA)- and poly(vinylidene flouride) (PVdF)-based gel electrolytes, which have been applied for secondary lithium batteries [5-7,50,51,64], were also studied as electrolyte systems for EDLC with carbon electrodes [65-68],... 

The performance of EDLCs with the above gel electrolytes was investigated using isotropic HDG electrodes and is described in Table 3. The ionic conductivities of the various gel electrolytes were around 10-4—10 3 S cnr2, and they decrease in the order PAN > PEO > PMMA at ambient temperature. Capac-... 

Recent 7Li-NMR studies on gel electrolytes based on PAN/EC/PC/LiC104 confirms that the onset of the narrowing of linewidth of the 7Li-NMR signal is closely correlated with the Tg of the material [Fig. 22] as is found for PEO-LiX electrolytes [266]. Further from the similarity of the 7Li-NMR linewidths ( 300 Hz at 300 K) observed in gel electrolytes with that of PEO-LiX electrolytes in comparison with liquid electrolytes containing EC-PC and LiX (15 Hz at 295K), it is concluded that the interpretation of the high conductivity of gel electrolytes in terms of microscopic packets of liquid electrolyte separated by regions of inert PAN matrix may be erroneous [266]. 

Compared with PEO electrolytes, PDVF, and PMMA electrolytes exhibited higher ionic conductivities. In particular, PMMA has attracted increasing attentions due to its low cost, high solvent retention ability, high transparency, and processibility. The first allpolymer electrochromic device was obtained based on a gel electrolyte and PEDOT-PSS [poly(styrene sulfonate)] electrochromic material (Argun et al., 2003). The fabricated device exhibited a maximum transmittance change of 51% at 540 nm. In addition, this device was fairly stable and only 5% contrast loss was observed after 32,000 cycles. 

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