First of all, it is product of intercalation of lithium into graphite. Structure is same as graphite have (hexagonal), but with different (bigger) parameters. Li6C is thermodinamically metastable under normal condition. Therefore, data about this compound should vary depend on parameters and method of synthesis. Direct synthesis and electrochemical one gave little bit different products. You can read lot of papers about this topic, see, for example, literature listed in appropriate chapters of basic for LIB books: "Advances in lithium-Ion batteries" (Schalkwijk and Scrossati), Lithium batteries: Science and Technology (Nazri and Pistoia). Also I can recommend relatively fresh article: Structural Diversity in Lithium Carbides (https://arxiv.org/pdf/1607.03170.pdf) for better understanding of problem.

First of all, it is product of intercalation of lithium into graphite. Structure is same as graphite have (hexagonal), but with different (bigger) parameters. Li6C is thermodinamically metastable under normal condition. Therefore, data about this compound should vary depend on parameters and method of synthesis. Direct synthesis and electrochemical one gave little bit different products. You can read lot of papers about this topic, see, for example, literature listed in appropriate chapters of basic for LIB books: "Advances in lithium-Ion batteries" (Schalkwijk and Scrossati), Lithium batteries: Science and Technology (Nazri and Pistoia). Also I can recommend relatively fresh article: Structural Diversity in Lithium Carbides (https://arxiv.org/pdf/1607.03170.pdf) for better understanding of problem.

They are all graphite intercalation compounds with graphite structure as the framework, and Li+, Na+ and K+ ions sit in between adjacent graphene layers. The illustrations of the crystal structures of LiC6 and KC8 are attached.

Tianyu Liu Thanks for the explanation