Vinylene Carbonate and Li Salicylatoborate as Additives in LiPF[sub 3](CF[sub 2]CF[sub 3])[sub 3] Solutions for Rechargeable Li-Ion Batteries

Abstract

Merck KGaA developed LiPF 3 (CF 2 CF 3 ) 3 , ͑LiFAP͒ as a new electrolyte that can replace the commonly used LiPF 6 in Li-ion batteries. Vinylene carbonate and Li salicylato borate ͑Merck's AD25͒ were studied as additives for LiFAP solutions in mixtures of ethylene, dimethyl, and diethyl carbonates with composite graphite and LiMn 2 O 4 electrodes. The tools for this study included voltammetry ͑fast and slow scan rates͒, chronopotentiometry, impedance spectroscopy, electron microscopy, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. It was found that LiFAP solutions containing VC were superior for both graphite and LiMn 2 O 4 ͑spinel͒ electrodes. The effect of additives on the electrodes' performance can be clearly attributed to their impact on the surface chemistry of these electrodes.The increasing demand of power sources for portable equipment and electric vehicles has intensified efforts to develop rechargeable lithium batteries with high power density and rapid rechargeability. The most common Li-ion batteries comprise lithiated graphite anodes, LiCoO 2 ͑composite͒ cathodes, and electrolyte solutions based on LiPF 6 salt in organic carbonate solvents. 1 In general, both the solvent molecules and the PF 6 Ϫ anions are reduced on the Li-C electrodes to form surface films comprising ROCO 2 Li, ROLi, and Li 2 CO 3 , species containing Li-C bonds, polymeric species ͑e.g., polycarbonate, polyethylene͒, LiF, Li x PF y , and Li x POF y species. 2 These films passivate the Li-C electrode and lead to their apparent ͑kinetically controlled͒ stability in solutions. Also, surface films are formed on LiMO 2 cathodes in these solutions (M ϭ V, Co, Mn, etc͒. 3 The performance of the cathodes is also largely influenced by surface phenomena. 4 LiPF 6 was chosen to be the commercially used electrolyte for Li-ion batteries only because other available salts are worse ͑for example: LiClO 4 is explosive, and LiAsF 6 is excluded due to the arsenic͒. LiPF 6 itself always brings with it HF contamination, which is detrimental to the performance of both negative and positive electrodes. 5 There is a pronounced difference in the surface chemistry of the negative and the positive electrodes in Li-ion batteries. In the case of the Li-C electrodes there is a constant driving force for the reduction of solution species, and hence, their passivation phenomena are driven by electrochemical ͑cathodic͒ reactions. In the case of cathodes, there is no major electrochemical reactivity of the solutions at the usual maximal charging potential of the cathodes (E Ͻ 4.2-4.3 V vs. Li/Li ϩ ). The major possible surface reactions of the cathodes are driven by chemical properties. For instance, HF reacts with the LiMO 2 cathode materials to form surface LiF, and some of the cathode materials, e.g., LiNiO 2 , are nucleophilic and attack the electrolytic alkyl carbonate molecules, thus forming ϪOCO 2 Li surface groups and/or inducing polymeric species such as polycarbonates. 6 It should be noted that the capacity fading found...

Impact of tripropyl borate on life and impedance of lithium-ion cells

“…(b) developing of alternative non-aqueous electrolytes [9]; (c) surface coating to slow down the degradation of the electrode materials [10][11][12][13][14] and (d) applying functionalized electrolyte additives [15][16][17][18][19][20] to suppress the chemical reaction of electrode materials with the electrolyte components and hence to extend the life of the lithium-ion cell or battery. We have also shown that the chemical composition of the solid electrolyte interphase (SEI) is also critical and can be tuned in a certain degree to achieve better cycle life and power capability by the addition of anion receptors [1,21].…”

Vinylene Carbonate as Co-Solvent for Low-Temperature Mixed Electrolyte Based Supercapacitors

“…These studies indicate that the use of VC as an additive improves the performance of lithiated graphite anodes and has no adverse effect on the cathode side. 19 According to Aurbach and co-workers, 20 it was demonstrated that it is possible to considerably improve the performance of Li-ion battery systems with low concentrations (a few percent) of VC which reacts predominantly on the electrode surfaces and improves their surface passivation in electrolyte solutions. Some authors reported that, two major advantages can be realized with the addition of VC in LiPF 6 /EC + DEC electrolyte.…”

The function of vinylene carbonate as a thermal additive to electrolyte in lithium batteries

“…These results indicate that the major component of the VC-induced SEI is attributable to the reduction of VC to polymeric-type species, which is different from the conventional SEI species, (CH 2 OCO 2 Li) 2 , in EC-based electrolytes. Some papers [21,27,[30][31][32][33][34][35][36] The most noteworthy thing is that the F1s spectrum related to the electrolyte without VC (Figure 8a) shows a pronounced LiF peak at 685 eV, but that related to the electrolyte with VC (Figure 8b) has its main peak at 687 eV, which is assigned to the PVdF binder [27]. This clear difference reveals that large amounts of LiF are formed in LiPF 6 /EC + DEC via electrochemical cycles, but the addition of VC to the electrolyte can suppress its production.…”