Synthesis of AlCl 3 -Graphite Intercalation Compounds for Lithium-Ion Capacitor Anode

Lithium-ion capacitors (LIC) are hybrid energy storage devices combining electric double layer capacitors (EDLC) and lithium-ion batteries (LIB). In typical LIC systems, faradaic reaction on anode restricts high power performance because of slow reaction rate than that of non-faradaic reaction on cathode. The conventional graphite anode suffers from low rate capability for LIC and shows low theoretical capacity which is not suitable for high energy density. To achieve high rate performance and high capacity, ferric chloride-graphite intercalation compounds (FeCl 3 -GICs) are reported as LIB anodes[1]. Intercalated FeCl 3 enlarges interlayer spacing of graphite and reacts like following reaction (FeCl 3 +3Li + +3e - ↔ Fe+3LiCl). We focused on aluminum chloride-GICs (AlCl 3 -GICs), lighter than FeCl 3 -GICs, as new anode materials for LIB and LIC. AlCl 3 -GICs have possibility of high rate performance and higher capacity at low potential by following reaction (AlCl 3 +3Li + +3e - ↔Al+3LiCl, Al+2.25Li + +2.25e - ↔Li 2.25 Al). In this paper, AlCl 3 -GICs were synthesized and evaluated their material characteristics and electrochemical properties. AlCl 3 -GICs was synthesized via vapor phase intercalation mehod[2]. First, graphite, AlCl 3 and N-chlorosuccinimide as chlorinating agent were mixed under Ar atomosphere. Then, mixed powder was heated under vacuum at various temperatures (115, 135, 150, 200 ℃), forming AlCl 3 -GICs (named as 115, 135, 150, 200, respectively). Electrochemical properties were evaluated by galvanostatic charge/discharge test at various current densities with assembled Li//AlCl 3 -GIC cells. As experimental condition, electrolyte was 1M LiPF 6 in EC/DEC (1/1 vol.), voltage range was 0.01–3.0 V and current density values were 0.1–2.0 A g -1 . Fig. 1 shows XRD patterns of obtained AlCl 3 -GICs. Peaks derived from GICs were confirmed for all AlCl 3 -GICs. The different intensity ratio of pristine(002)/GIC(00x) of the AlCl 3 -GICs synthesized with different heating temperature indicated various intercalated structures. Fig. 2 shows rate performance of the Li//AlCl 3 -GIC cells. From this result, it was confirmed that AlCl 3 -GICs could react with Li + and showed over 70 mAh g -1 even at high current density such as 2.0 A g -1 (over 4 C-rate). The results demonstrated high rate performance of AlCl 3 -GICs as anode for LIB and LIC. We have considered that the high rate capability can be due to improvement of Li + diffusibility caused by enlarg