Mobility and Ionic Association of Lithium Salts in a Propylene Carbonate‐Ethyl Methyl Carbonate Mixed Solvent

Abstract

Electrolytic conductivities of lithium salts have been measured in equimolar mixtures of pr_o~vlene carbonate and either ethyl methyl carbonate or 1,2-dimethoxyethane at 25~ over a salt concentration range of 10 -~ to 10 3 mol dm 3. The limiting molar eonduetivities and association constants were calculated from the expanded Fuoss-Hsia equation. The Walden product of lithium ion was not enhanced by the addition of ethyl methyl carbonate as observed in the ease of 1,2-dimethoxyethane, due to the lack of specific solvation. LiPF6 and Li(CF3SO2),N in the propylene carbonate-ethyl methyl carbonate mixed solvent formed solvent-separated ion pairs, which resulted in decreased ion association. This work is a part of our systematic study ~-6 on the transport properties of nonaqueous electrolytes. Our previous study 5 on the conductometric analysis of lithium salts including LiC10~, LiBF4, LiPF6, LiAsF6, LiCF~SO3, Li(CF3SO~_)2N, and LiC~FgSO3 in propylene carbonate (PC) and ~-butyrolactone (GBL) is extended into mixtures of PC and either ethyl methyl carbonate (EMC) or 1,2-dimethoxyethane (DME).Mixed solvent systems such as LiC]O4/PC + DME and LiBF4/GBL + DME have a long history of use as nonaqueous electrolytes in primary Li/MnO2 and Li/(CF~)~ batteries because the addition of the ether increases the electrolytic conductivity due to its low viscosity. ;'8 However, ether solvents are often replaced with linear esters and carbonates, e.g., methyl formate (MF), methyl acetate (MA), dimethyl carbonate (DMC), and diethyl carbonate (DEC), because 4 V rechargeable lithium (ion) batteries using an Li~CoO2 cathode require solvents much more stable toward oxidation. 9-u Properties of ethylene carbonate (EC)-based electrolytes ~2-1~ and PC-based electrolytes ~'t~ containing these linear esters and carbonates have been investigated.Conduetometrie analysis on lithium salts in MF, ~;.,8 MA, ~9 and DMC 20 in the dilute range has been reported by by Salomon et aI., however, there is no report on mixed ABSTRACT We report studies of lithium insertion in a variety of organic precursors pyrolyzed below 1000~ These include two types of petroleum pitch, polyvinyl chloride (PVC), polyvinylidene fluoride (PVDF), polypheny]ene sulfide (PPS), and epoxy novolac resin (ENR). Each of these materials shows reversible specific capacities for lithium of between 550 and 900 mAh/g when treated near 700~ The majority of this high capacity shows large hysteresis; that is the lithium is inserted near 0 V (vs. lithium metal) and removed near 1 V. Furthermore, the amount of capacity showing large hysteresis is well correlated to the hydrogen to carbon atomic ratio of the samples. As the pitch, PVC and PVDF samples are heated above 700~ the H/C ratio and the specific capacity decrease proportionally, suggesting that the hydrogen in these samples plays an important role. The PPS and ENR samples behave differently; as they are heated above 700~ the high capacity is maintained as H/C is reduced, although the voltage profile changes dramatically to one without sig...

Safer Electrolytes for Lithium‐Ion Batteries: State of the Art and Perspectives

“…According to reports in the literature, the onset temperature for the decomposition of dry, + [20] o [59] + [61] + [62] + [63] electrochemicalstability + [23,64,98] o [60] o [52] + [23,65] + [23] + [33] thermal stability À [43,[66][67][68][69] o [70] o [71] + [72] À [62] + [42,43] stability towardsm oisture À [38,39,[73][74][75] o [60] o [71] o [65] o [76] + [77] Al current collectorp assivation + [36,44,47] ++ [71,78] + [79] o [62] À [46][47][48][49]80] nontoxicity solid LiPF 6 is about 100 8C. [43,[66]…”

“…[59] Considering performance metrics only,l ithium hexafluoroarsenate (LiAsF 6 )w ould certainly be an ideal candidate for LIB electrolytes. LiAsF 6 provides very good ionic conductivitya nd superior cycling performance.…”

Bio-Derivative Galactomannan Gum Binders for Li4Ti5O12Negative Electrodes in Lithium-Ion Batteries

“…Such different surface coverages by binder significantly affected lithium-ion transports because the lithium-ion conductivity through the polymer layer was approximately 10 −8 S cm −1 , 10,20 which is much smaller than that in a normal electrolyte solution (10 −2 -10 −3 S cm −1 ). [21][22][23] Thus, a narrow and homogeneous surface coverage is preferable in the viewpoint of lithium-ion transport. To investigate the surface coverage of LTO by the binders, XPS analysis was conducted, and the results, C 1s and Ti 2p spectra with Ti/C atomic ratios, are shown in Fig.…”

Influence of Temperature on Supercapacitor Performance

“…The nanoscale particles offer higher surface area compared to an electrode composed of microscale particles and therefore display better kinetics at low temperatures [52]. Many other techniques such as adding co-solvents with low freezing points to the electrolytes have been adopted to increase their liquidus range and thus improve their low-temperature performance [55][56][57].…”