INFLUENCE OF PORE TEXTURE OF CARBON XEROGELS ON THEIR BEHAVIOR AS ANODES FOR LI-ION BATTERIES

摘要

Carbon materials are widely used as anodes for Li-ion batteries due to their low cost and availability.Among these,graphite is the most widespread,but increased energy density and lifetime are expected from hard carbons due to their 3D porous architecture.Such materials however generally suffer from high irreversible losses during the first charge-discharge cycle and the influence of porosity on the electrochemical behavior still remains an open debate.This study aims at determining which textural parameters of porous carbons can explain some observed electrochemical features.For that purpose,carbon xerogels are extremely interesting since their textural parameters can be independently controlled and tailored through the synthesis conditions.Carbon xerogels(CX),prepared from resorcinol-formaldehyde mixtures,can be described as microporous nodules linked together to form meso-or macroporous voids inside a 3D gel structure;the size of these voids can be tuned by changing the synthesis conditions without affecting other parameters such as the micropore volume.On the opposite,the microporous fraction of a given macroporous carbon xerogel can be independently increased upon activation(e.g.by physical CO2 treatment),or reduced upon coating the nodules with an additional carbon layer,by CVD for instance.