In situ X-ray diffraction studies on nominal composition of C2Li under high pressure and temperature

Abstract

Abstract Superdense phase between graphite and Li metal, $$\hbox {C}_{2}$$ C 2 Li, has been significant in the research on both lithium-ion batteries (LIBs) and graphite intercalated compounds (GICs). However, a detailed method for synthesizing $$\hbox {C}_{2}$$ C 2 Li remains unknown owing to the limited information regarding $$\hbox {C}_{2}$$ C 2 Li and difficulties in distinguishing $$\hbox {C}_{2}$$ C 2 Li from $$\hbox {C}_{6}$$ C 6 Li. Thus, we performed in situ X-ray diffraction measurements on samples with the nominal composition of $$\hbox {C}_{2}$$ C 2 Li under high pressures and temperatures of up to 10 GPa and 400 $$^{\circ }\hbox {C}$$ ∘ C , respectively. We employed two types of $$\hbox {C}_{2}$$ C 2 Li samples; one was a mixture of $$\hbox {C}_{6}$$ C 6 graphite powder and Li metal (C $$_{6}+3$$ 6 + 3 Li), and the other was a mixture of $$\hbox {C}_{6}$$ C 6 Li and Li metal in which the $$\hbox {C}_{6}$$ C 6 Li was prepared by the electrochemical discharge (reduction) reaction that occurs in LIBs. Considering changes in the d-value based on the 001 diffraction peak from $$\hbox {C}_{6}$$ C 6 Li or $$\hbox {C}_{2}$$ C 2 Li, C $$_{6}$$ 6 Li + 2Li is suitable for synthesizing $$\hbox {C}_{2}$$ C 2 Li, although the nonaqueous electrolyte used for the electrochemical reaction should be removed to avoid structural transformations to lower-stage compounds such as $$\hbox {C}_{12}$$ C 12 Li and $$\hbox {C}_{18}$$ C 18 Li during the heating. These findings pave the way toward a method for synthesizing C $$_{2}$$ 2 Li, which could increase the energy density of LIBs and establish GICs with novel physical and electronic properties.