Performance of a Lithium Metal Anode in Poly(vinylidene fluoride)-Type Gel Electrolyte

Abstract

The performance of a lithium metal anode was studied in a poly(vinylidene fluoride-hexafluoropropylene) (PVdF-HFP) gel electrolyte. By using the PVdF-HFP gel electrolyte, we obtained a higher coulombic efficiency (ca. 85%) and a more uniform morphology of the lithium metal anode than those obtained with the propylene carbonate liquid or the poly(ethylene oxide) gel system. Additionally, the CO 2 addition to the PVdF-HFP gel system improved both the the uniformity in morphology of the lithium anode and the coulombic efficiency further to ca. 95%.The gel electrolyte, which consists of polymer matrix, organic solvent, and supporting electrolyte, was introduced as a novel material in the field of rechargeable battery applications as early as 1975. 1-3 Two advantages of the gel electrolyte applied to batteries include the fact that the electrolyte solution does not leak out from the cell, and that the electrolyte can be prepared as a thin film, which allows construction of a solid-state and high energy density battery. In particular, the gel electrolyte demonstrates a high ionic conductivity of about 10 -3 S cm -1 at room temperature and has a sufficient mechanical strength. Examples of the host polymer of the gel electrolyte are poly(acrylonitrile), 4,5 poly(methylmethacrylate), 3,4 and a new copolymer of vinylidene fluoride with hexafluoropropylene (PVdF-HFP). 6-9 The first reliable and practical rechargeable Li-ion plastic battery, which contained the carbon material as the anode, was developed in 1996 using the PVdF-HFP copolymer-type gel electrolyte. 10 For the next generation of rechargeable batteries, the lithium secondary battery using lithium metal as the anode is the most attractive candidate for higher energy power sources for portable electronic devices, electric vehicles, and load-leveling systems. Lithium metal demonstrates a remarkably low electrochemical equivalent and the most negative redox potential of all the metallic elements. There are, however, some disadvantages of the lithium metal anode compared to the carbon anode. The charge-discharge cycle life of the lithium metal anode is degraded by the formation of dendritic deposits, which causes the isolation of active lithium metal and also leads to short circuit with the cathode. Another reason for the poor cycle life of the lithium anode may be the formation of an interfacial layer between lithium metal and electrolyte with a low ionic or electronic conductivity as discussed in Ref. 9 and 10.In order to improve the lithium anode properties, the effect of additives to the liquid electrolyte was studied, e.g., CO 2 11-15 and HF. 16,17 Recently, we confirmed that a poly(ethylene oxide) (PEO) -based gel electrolyte effectively suppressed the dendritic deposition of lithium. 18 In the present study, the excellent charge-discharge performance of the lithium metal anode obtained with the PVdF-HFP gel electrolyte system is demonstrated. Furthermore, the effect of CO 2 addition to the PVdF-HFP gel electrolyte was investigated.Experimental The details of th...

Recent progress and remaining challenges in sulfur-based lithium secondary batteries – a review

“…Gel-type polymers are promising electrolytes for Li-S batteries due to their ability to be prepared as thin films. 41 Although the conduction mechanism is comparable to liquid ones, gel polymer electrolytes (GPEs) are preferably safer and mechanically more stable, while at the same time shape-conforming. 36a,42 To form GPEs, plasticizers are added to the polymer host.…”

Blends of POSS−PEO(n=4)8 and High Molecular Weight Poly(ethylene oxide) as Solid Polymer Electrolytes for Lithium Batteries

“…However, the decreased ionic conductivity compared with solvent or gel-based systems has motivated interest in developing methods to increase the ionic conductivity in all solid electrolytes. The most common solid polymer electrolyte is based on derivatives of poly(ethylene oxide) (PEO) and a lithium salt, LiX. , PEO/LiX complexes, formed by the dissolution of a LiX salt in a PEO matrix, with or with out the addition of inorganic components, have been extensively investigated for this purpose. PEO solvates the Li cations, whose motions are coupled to the free volume/local segmental mobility of the PEO chains.…”

Fluorinated Ethylene Carbonate as Electrolyte Additive for Rechargeable Na Batteries

“…However, a limited number of successful reports are found in the field of sodium insertion for layered Na x MeO 2 (Me = transition element) materials compared to Li x MeO 2 , for example, NaFeO 2 , Na x CoO 2 , Na 2/3 [Ni 1/3 Mn 2/3 ]O 2 , and NaNi 1/2 Mn 1/2 O 2 . − To the best of our knowledge, there are a few reports on challenges to rechargeable sodium-ion cells. − Recently, we demonstrated the rechargeable Na-ion cell consisting of hard-carbon (nongraphitizable carbon) and NaNi 0.5 Mn 0.5 O 2 electrodes, which are operable at the room temperature, and we fairly succeeded in the passivation of hard-carbon as electrode . It is generally known that the electrolyte additives are required for the practical Li-ion batteries. − In this study, we examine and compare electrochemical performance of Na cells with several additives, such as fluoroethylene carbonate (FEC), − trans -difluoroetyhene carbonate (DFEC), ethylene sulfite (ES), and vinylene carbonate (VC) (their molecular structures are shown in the Supporting Information, Figure S1) which are well-known to be the efficient electrolyte additives for Li-ion batteries. Because there have been no reports on acceptable electrolyte additives for Na or Na-ion cells according to our knowledge, herein we demonstrate for the first time the unique and promising electrolyte additive, FEC, to improve the reversible capacity and its retention for the Na insertion electrodes.…”