Graphitic and non-graphitic carbonaceous anodes in lithium-ion batteries

The Li+-ion accommodation into carbonaceous anodes in terms of potential profiles, specific charge and parasitic reactions depends in a complex manner on their crystallinity, texture, (micro-) structure and (micro-) morphology. In general, carbonaceous materials can be classified into graphitic (materials with a layered structure) and non-graphitic (disordered), whereas the latter can be further classified into graphitizing carbons (soft carbons) and non-graphitizing carbons (hard carbons) according to their ability to develop a graphite structure during heat treatment.

Graphitic carbons consist of stacked graphene layers in the stacking sequence AB (hexagonal graphite) or ABC (rhombohedral graphite), which are held together by weak van der Waal forces. During electrochemical lithiation a maximum content of one Li+-ion per six carbon host atoms can be stored which corresponds to a theoretical specific capacity of 372 mAh g−1. The process of Li+-ion intercalation is accompanied by a change in the graphite stacking sequence to AA. Thereby, Li+-ion intercalation proceeds via a staging mechanism in which the Li+-ion fully intercalates into very distant graphene layer gaps before occupying the space between neighboring layers. The staging process is characterized by well-defined potential plateaus in the potential region between 0.25 V and 0.05 V vs. Li/Li+ of the potential profile. Due to the low operation potential of graphite anodes close to the operating potential of lithium metal, all known electrolytes are thermodynamically unstable at the anode/electrolyte interface. However, the decomposition of the commonly used LiPF6/organic carbonate-based electrolyte in the initial charge/discharge cycles leads to the formation of a passivation layer and thus to kinetic stability at the interface.