Electrochemical Intercalation Behaviors of Lithium Ions into Graphene-Like Graphite

Abstract

Electrochemical intercalation behaviors of lithium ions into graphene-like graphite (GLG) were investigated at high cell voltages. The interlayer spacing of GLG started to increase at much higher cell voltages than that needed for graphite. It stepwisely increased at a decrease in the cell voltages, indicating the staging phenomenon. The thermodynamic considerations suggested that the strong interaction between oxygen atoms introduced in GLG and lithium ions is responsible for the formation of intercalation compounds of desolvated lithium ions. The interlayer distance of GLG was more important than the content of oxygen in it for the decreased separation energy of carbon layers and, accordingly, for the onset voltage of the intercalation of lithium ions into it. The intercalation of desolvated lithium ions into GLG was achieved even in an electrolyte solution containing dimethoxyethane in which solvents are co-intercalated into graphite. Graphite has been widely used as an anode for lithium ion batteries for portable devices such as laptop computers, cell phones, etc. However, its limited theoretical capacity of 372 mAh/g and relatively poor rate performance are not suitable for use in electric vehicles, etc. In this context, graphene-based carbon materials showing high capacity and rate performance have been introduced and widely studied. [1][2][3][4] However, because of the intrinsically high surface area of graphenebased carbons, they suffer from low columbic efficiency. We have recently introduced graphene-like graphite (GLG) as a superior anode material for lithium ion batteries, showing a high capacity of 608 mAh/g with a cut off voltage of 2 V, high rate performance (the ratio of the capacity at 6 C and 0.1 C rates of 79%), and good cycling properties.5 This material is prepared from the thermal reduction of graphite oxide at 800• C, carefully avoiding the exfoliation of the carbon layers. The regularity of the stacking of carbon layers of GLG is also quite high and the surface area is low. Moreover, the morphology and interlayer spacing of it are similar to those of graphite, though it contains considerable amounts of oxygen and pores with the size of 1-5 nm within carbon layers mainly in the state of C-O-C. The lithium storage capacity of GLG is strongly related to the oxygen content and the large expansion of interlayer spacing during the intercalation of lithium ions was ascribed to the high capacity, reaching 673 mAh/g of discharge capacity. 6,7 The coulombic efficiency of GLG was higher than those reported for graphene-based carbons, however, was still not enough high (50-56% with a cutoff voltage of 2 V). In the case of a graphite anode operated in an ethylene carbonate based electrolyte solution, solvated lithium ions are first intercalated into it and then the solvent molecules are reduced to form a lithium ion conducting passivation layer so called solid electrolyte interphase (SEI) at higher potential regions of around 0.8 V vs Li/Li + . This SEI layer effectively prevents the further decomposi...

Effects of Pre-Lithiation on the Electrochemical Properties of Graphene-Like Graphite

“…Figure 7 shows the variations of OCP of GLG pre-lithiated with lithium metal, together with that of GLG during the 1st charge reported in our previous paper. 10 The OCP of GLG decreased monotonically during electrochemical lithiation. When GLG was pre-lithiated with a small amount of lithium metal, the OCP values were only slightly lower than those observed during electrochemical lithiation of GLG.…”

“…80% of SOC) estimated from our previous report. 10 From these results, it was clarified that excessive amount of lithium naphthalenide solution was required to accomplish the pre-lithiation of GLG. However, after the pre-lithiation with excessive amount of the solution (145% and 193%), exfoliation of the composite electrode proceeded.…”

“…For the non-doped GLG, SEI is formed on its surface from the early stage of charge. However, since the gradual expansion of GLG proceeds during charging, 10 the once formed SEI cannot stand up to the expansion, leading to repeated exfoliation and re-formation of SEI. As a result, the reductive decomposition of electrolyte solution continuously occurs, resulting in large irreversible capacity at the initial cycle.…”

“…In this regard, we have recently introduced graphene-like graphite (GLG) as a new candidate for an anode material of LIBs, which can overcome these intrinsic difficulties of the carbon-based materials. [7][8][9][10] The capacity of GLG reaches 608 mAh g ¹1 with a cutoff voltage of 2 V, and it shows good cycle performance. In addition, the rate capability of GLG is superior to that of graphite; the capacity of GLG at 6 C remains 79% of the capacity at 0.1 C. GLG is synthesized via thermal reduction of graphite oxide (GO) under vacuum with quite small increasing-rate of temperature to avoid exfoliation of graphene sheets.…”

Hierarchical Nanostructured Benzoic Naphthalene Tetracarboxylic Di‐imide Organic Cathode for Lithium Ion Battery

“…Additionally, it is also known by calculating the average voltage of two lithium ion intercalation with experimental voltage. [45][46][47] Hence the chargedischarge within the potential window 0 V to 3.5 V is not possible. Thus, charge-discharge performance of as prepared benzoic NTCDI should be performed at 1.5 V to 3.5 V only.…”