Investigation of PF₆⁻ and TFSI⁻ anion intercalation into graphitized carbon blacks and its influence on high voltage lithium ion batteries

Abstract

Graphitized carbon blacks have shown a more promising electrochemical performance than the non-treated ones when being applied in small amounts as conductive additives in composite cathode electrodes for lithium ion batteries, due to the absence of surface functional groups which contribute to detrimental side-reactions with the electrolyte. Here, we report that at high potentials of >4.5 V vs. Li/Li(+), graphitic structures in carbon black can provide host sites for the partially reversible intercalation of electrolyte salt anions. This process is in analogy to the charge reaction of graphite positive electrodes in dual-ion cells. A standard furnace carbon black with small graphitic structural units, as well as slightly and highly graphitized carbon blacks, were characterized and analyzed with regard to anion intercalation. A LiPF6 containing organic solvent based electrolyte as well as a state-of-the-art ionic liquid based electrolyte composed of LiTFSI in PYR14TFSI were applied. The intercalation of both PF6(-) and TFSI(-) could be confirmed by cyclic voltammetry in electrodes made of carbon blacks. When exposed to high potentials, carbon blacks experienced strong activation in the 1st cycle, which promotes the perception for anion intercalation, and thus increases the anion intercalation capacity in the following cycles. The specific capacity from anion intercalation was evaluated by constant current charge-discharge cycling. The obtained capacity was proportional to the graphitization degree. As anion intercalation might be accompanied by decomposition reactions of the electrolyte, e.g., by co-intercalation of solvent molecules, it could induce the decomposition of the electrolyte inside the carbon and thus degradation of the carbon black graphitic structure. In order to avoid side reactions from surface groups and from anion intercalation, the thermal treatment of carbon blacks must be optimized.

Analysis of the Interphase on Carbon Black Formed in High Voltage Batteries

“…Winter et al have shown that the nature and properties of CBs such as presence of functional groups and graphitic structure influence irreversible capacities at high voltage. [16][17][18] They have shown that thermal treatment of CB results in graphitization of CB as well as removal of functional groups, which consequently can decrease Q irr of CB.…”

“…The latter could be intercalation/deintercalation of PF 6 − or ClO 4 − anions to/from the positive electrode, as this can provide a small reversible capacity. 8,[15][16][17][18][19] The large irreversible capacity (defined as the difference between the charge and the discharge capacity) can be explained by i) formation of a AlF 3 passivation layer on the aluminum current collector via decomposition of LiPF 6, , 26,27 and ii) reactions between the electrolyte and the surface functional groups on the carbon surface. In order to clarify the contribution of Al current collector corrosion to the total irreversible capacities observed for CB cathodes, identical cells were assembled using only an Al disk (as it is without any carbon black or active material on it) as cathode.…”

“…[10][11][12][13][14][15][16][17][18] This charge capacity is attributed to oxidation reactions, anodic degradation of aprotic electrolytes on the surface of CBs, side reactions involving binder and salt, and intercalation of anions such as PF 6 − (partly reversible) and solvent molecules into graphitic layers. [10][11][12][13][14][15][16][17][18][19] The oxidation voltage, decomposition products, and possible formation of a surface layer are dependent on the chemistry of electrolyte and the surface area and the surface functional groups of CBs. [10][11][12][13][14] This is similar, but not identical, to the concept of formation of solid electrolyte interphase (SEI) on anodes.…”

Graphene-Coated Activated Carbon Fiber Cloth Positive Electrodes for Aluminum Rechargeable Batteries with a Chloroaluminate Room-Temperature Ionic Liquid

“…31 The intercalation is facilitated by the graphitic host showing a higher crystallinity and larger crystallite domain. [31][32][33][34][35][36] This is in contrast to the alkali metal cation intercalation. Based on Raman and SEM results, low-growth graphene-coated ACFC possesses both lower graphitization degree and smaller lateral size than the high-growth one.…”

Correlation among physical and electrochemical behaviour of nanostructured electrolytic manganese dioxide from leach liquor and synthetic for aqueous asymmetric capacitor

“…It is quite common to use carbon black as an additive 35,36 in the EMD cathode, to reduce interparticle contact resistance and enhance the electrical percolation network with improved electronic conductivity. To avoid any discrepancy (like irreversible cell capacitance) arises from the carbon black, only the active material has been taken into an account for calculating specific capacitance.…”