(35b) Graphitic Material with Engineered Graphene Units for High-Power Li Ion Battery Electrodes

Li ion batteries capable of delivering a high current without sacrificing voltage or energy density are highly desirable, since they can be recharged faster and provide longer operation time when used in devices that demand high power.  In the current generation of batteries using graphite as the negative electrode material, the rate of Li ion insertion into and migration out of the graphite is a major factor that limits the power delivered by the battery.  We have found that by carefully engineering the graphene units, which are the primary building block of graphite, it is possible to increase the Li ion diffusivity in the material significantly, which results in greatly increased charge capacity during high current operation.  We report here a solution chemical method to produce the engineered structure that is readily scalable and add minimal costs to the manufacturing process.  Electrodes prepared with the graphite formed from such engineered graphene sheets maintained a charge capacity of 180 mAh/g even when discharged at a rate of 2 A/g.  Without the engineered structure, the charge capacity would be less than 70 mAh/g.  The electrode prepared with the engineered material exhibits excellent cycling stability with no detectable capacity loss after >100 cycles.  The nature of the engineered graphene sheets was investigated using high resolution electron microscopy, and the results show that there is an optimum size and density of the engineered structure.