Influence of Pyrolysis Conditions on the Performance of Hard Carbons as Anodes for Lithium Batteries

Abstract

Electrochemical lithium insertion/deinsertion has been correlated with the pyrolysis parameters of a polymeric precursor, the microtexture and chemical composition of the obtained hard carbon. A specific reversible capacity of 450 mAh/g (i.e. composition LiC_4.5) has been estimated for the optimal carbons from the galvanostatic charge/discharge characteristics. Voltammetry experiments and galvanostatic relaxation curves demonstrated that lithium insertion/extraction process is not kinetically controlled by diffusion, for the current load (20 mA/g) and scan rate used for our experiments. The sites for lithium insertion and/or intercalation were estimated from ex-situ ⁷Li NMR experiments for differently lithiated samples. A Knight shift of 60 ppm characteristic of lithium clusters has been found for carbons obtained under strains.

Key Words:

• hard carbon
• two-step pyrolysis
• carbon anode
• lithium insertion
• ⁷Li NMR