Here we propose the use of a carbon material called graphene-like-graphite (GLG) as anode material of lithium ion batteries that delivers a high capacity of 608 mAh/g and provides superior rate capability. The morphology and crystal structure of GLG are quite similar to those of graphite, which is currently used as the anode material of lithium ion batteries. Therefore, it is expected to be used in the same manner of conventional graphite materials to fabricate the cells. Based on the data obtained from various spectroscopic techniques, we propose a structural GLG model in which nanopores and pairs of C-O-C units are introduced within the carbon layers stacked with three-dimensional regularity. Three types of highly ionic lithium ions are found in fully charged GLG and stored between its layers. The oxygen atoms introduced within the carbon layers seem to play an important role in accommodating a large amount of lithium ions in GLG. Moreover, the large increase in the interlayer spacing observed for fully charged GLG is ascribed to the migration of oxygen atoms within the carbon layer introduced in the state of C-O-C to the interlayer space maintaining one of the C-O bonds.

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...

Pre-lithiation of graphene-like graphite (GLG) was conducted and its effects on structural and electrochemical properties of GLG were investigated. When lithium naphthalenide was used for the pre-lithiation, a large amount of the solution was required for the intercalation of lithium ions into GLG. Moreover, binder in the composite electrode was degraded by the pre-lithiation and the discharge capacity considerably decreased. On the other hand, prelithiation of GLG with lithium metal resulted in the increase of interlayer distance to similar value to that of electrochemically full-charged GLG, even though the amount of the added lithium metal was equivalent to only 28% or 38% of SOC of the GLG. In addition, the decreases in the charge capacity were more than those expected from the amounts of lithium metal. The full and immediate interlayer expansion by the pre-lithiation of GLG suppressed the repeated exfoliation and reformation of SEI unlike electrochemically charged GLG. Since the discharge capacities were almost identical to that of the pristine GLG, the coulombic efficiency was greatly improved. The issue of low coulombic efficiency of GLG at the initial cycle can be conquered by this method, and it would increase the probability of the practical application of GLG.

Nitrogen-doped carbons were prepared by the thermal reduction of furfurylamine-intercalated graphite oxide. The nitrogen atom content in the resulting samples was around 6 wt% and was almost constant, independent of the thermal reduction temperature. The nitrogen atoms were introduced in the forms of pyridinic, pyrrolic and graphitic, and the amount of graphitic nitrogen greatly increased for the sample prepared at 800 °C. The discharge capacity above 1.0 V greatly decreased for nitrogen-doped carbon samples when used as anodes of a lithium ion battery. It reached a maximum value of 334 mA h/g for the sample prepared at 500 °C. X-ray diffraction measurements during a charge-discharge cycle indicated that lithium ions were stored between and extracted from the layers in the material and the increase in the interlayer spacing after lithium storage was similar to that observed for graphite. This result has been well reproduced by theoretical calculations and nitrogen atoms stayed at almost the same position even after the intercalation of lithium ions. This would prevent the intercalation of a large amount of lithium and accordingly lower the capacity.

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