High Voltage Stability of Interfacial Reaction at the LiMn[sub 2]O[sub 4] Thin-Film Electrodes/Liquid Electrolytes with Boroxine Compounds

Abstract

Liquid electrolytes with boroxine compounds were prepared, and interfacial reactions at the liquid electrolytes/LiMn 2 O 4 thin-film electrodes were investigated. Boroxine compounds, B 3 O 3 ͑OR͒ 3 , with different kinds of substituents ͓R = CH 3 , CH 2 CH 3 , ͑CH 2 ͒ 2 CH 3 , and CH͑CH 3 ͒ 2 ͔ were dissolved in 1 mol kg −1 LiCF 3 SO 3 /ethylene carbonate + EMC ͑1:1 by volume͒. Both cyclic voltammetry and electrical impedance spectroscopy measurements revealed that interfacial resistance depended on the chain length in the substituent of the boroxine compounds, and the resistance decreased with the increase in the chain length. Moreover, the anodic stability of the electrolytes was improved up to 5.0 V ͑vs Li/Li + ͒ on the film electrodes by the addition of tri-isopropoxy boroxine ͓R = CH͑CH 3 ͒ 2 ͔ with a steric structure ͑branched chain substituent͒. These results indicate that mixing boroxine compounds with both appropriate chain length and steric structure can be an effective way to develop advanced liquid electrolytes for high voltage rechargeable lithium ion batteries. © 2010 The Electrochemical Society. ͓DOI: 10.1149/1.3374638͔ All rights reserved. Rechargeable lithium ion batteries have been expected as power sources for hybrid and electric vehicles, and some of them have been commercialized. However, further improvements in the current battery system are strongly demanded at the social end, and one of the most expected properties is the enhancement of energy density to prolong the cruising distance of electric vehicles. In this prospect, increase in battery operating voltage must be a possible way because there are several kinds of 5 V class positive electrode materials such as LiNi 0.5 Mn 1.5 O 4 , 1 LiCoPO 4 , 2 and LiCoMnO 4 . 3One of the drawbacks to realize 5 V class rechargeable lithium ion batteries is to develop advanced electrolytes with a wide potential window, high ionic conductivity, sufficient safety, low cost, etc. Although new kinds of electrolytes, typically ionic liquids 4 and solid electrolytes, 5 have been proposed, several problems such as cost, power density, and large resistance at the interface still remained to put them in practical use.In addition to the developments of the above electrolytes, various boron-based compounds have been studied as a new class of electrolytes. Zhang and Angell discovered the electrolytes with boronbased cosolvent. They showed that the electrolyte obtains an approximately 5 V stability on platinum electrodes and that the electrolyte can work well in both Li/LiMnO 2 and carbon/LiMnO 2 cells at 2.0-4.4 V.6 Barthel et al. proposed new lithium salts with a cherate-type anion of boron. 7,8 Sasaki et al. prepared their derivatives and applied them to a practical lithium ion battery system. 9,10Although the anodic stability of these lithium salts was ca. 4.2 V vs Li/Li + , Xu and Angell discovered lithium bis͑oxalate͒ borate ͑Li-BOB͒, which obtained superior anodic stability up to 4.5 V vs Li/Li + on platinum electrode. 11 The LiBOB obtained other interactiv...

Electrolytes and Interphases in Li-Ion Batteries and Beyond

“…250 (Table 22) and found that, when the substituent was iso-propyl, the anodic stability of carbonate electrolytes improved up to 5.0 V on Li 2 Mn 2 O 4 surface over the baseline electrolyte ( Figure 26a). 250 Of course, as a 4.0 V class cathode, Li 2 Mn 2 O 4 does not have any redox activity in the vicinity of 5.0 V, and it was only used here as a more reliable working electrode than nonporous electrodes such as Pt or glassy carbon. Ping et al investigated the effect of TMOBX (Tables 18 and 22) on various cathode surfaces such as LiNi 0.8 Co 0.15 Al 0.05 O 2 , LiNi 0.33 Mn 0.33 Co 0.33 O 2 , and LiCoO 2 , 251 and concluded that, while there is no obvious oxidation of TMOBX, the cell impedance was decreased when its concentration was below 1%.…”

“…Finally, besides their interphasial properties on graphitic anode, , boroxine compounds were also explored as cathode additives. − Horino et al studied a series of trialkoxy boroxines (Table ) and found that, when the substituent was iso-propyl, the anodic stability of carbonate electrolytes improved up to 5.0 V on Li 2 Mn 2 O 4 surface over the baseline electrolyte (Figure a) . Of course, as a 4.0 V class cathode, Li 2 Mn 2 O 4 does not have any redox activity in the vicinity of 5.0 V, and it was only used here as a more reliable working electrode than nonporous electrodes such as Pt or glassy carbon.…”

“…Effect of boroxines as cathode additives: (a) Cyclic voltammetry of LiMn 2 O 4 thin films in baseline electrolyte 1.0 m LiCF 3 SO 3 /EC/EMC (50:50) (solid lines) or electrolytes with TMBX (trimethyl boroxine, thin dash line), TEBX (triethyl boroxine, medium line), TnPBX (tri-n-propyl boroxine, medium broken line) and TiPBX (tri-iso-propyl boroxine, bold line). Reprinted with permission from ref . Copyright 2010 Electrochemical Society.…”

Impact of the Range of Voltage Change on the Electrode/Electrolyte Interface of Layered Rock-Salt Positive Electrode Materials

“…For example, introducing additives to the electrolyte is a widely used technique to prevent such direct contacts, by forming surface films on the electrodes with decomposition products of the additives. 16,[19][20][21]46,47 Although this study uses a conventional electrolyte (LiPF 6 and EC+DEC) without any additive, a surface film can nevertheless be formed by the decomposition of the electrolyte itself, particularly during high-voltage charging. However, while the surface film formed in the charging can be considered stable in the highvoltage region, it may become unstable in the low-voltage region.…”

Electrochemical Behavior of Graphite Negative Electrode in Electrolyte Solutions Containing Anion Receptors

“…So it is necessary to develop the electrolytes with wide potential window to use high potential positive electrodes. It has been reported that the electrolyte solutions containing boron-based compounds show high oxidation stability [1]. Lee et al, also reported that the electrolyte solutions containing anion receptor, tris(pentafluorophenyl)borane (TPFPB), showed high oxidation stability [2].…”