Nanoporous-Carbon Based Anode Materials for Increased Li-Ion Energy Specific Capacity*

Li-ion intercalation into graphite anodes has an optimized practical (theoretical) specific capacity ~ 330 (370) mAh/g. With both sides of each sheet accessible for lithiation, graphene has double the specific capacity, but experiences low coulombic efficiency and capacity fade from Li-loss to the solid-electrolyte interphase (SEI) with repeated cycling. Instead, we study nanoporous carbon (NPC). NPC self-assembles at room-temperature during pulsed-laser deposition. NPC mass density (and surface area) is controlled via deposition energetics from 2.25 g/cm³ (~ graphite) to below 0.1 g/cm³, consisting of randomly aligned graphene sheet fragments with interplanar spacings expanded compared to graphite. Controlling these NPC properties enables a binderless study of Li intercalation vs. nanostructure, correlating electrochemical results with charge/discharge rate, mass density, and film thickness.

Furthermore, NPC can host other species with larger capacity than carbon, such as silicon (theoretical capacity ~ 4200 mAh/g). However, with lithiated volumetric expansion > 300%, Si literally pulverizes upon repeated cycling. Despite progress via nanostructures and composites, reversible capacity over long term cycling remains below projections. The large NPC interplanar spacings enable co-depositing Si atoms to take advantage of both the large Li capacity of Si and the rapid intercalation into NPC to further improve Li-ion energy storage. Preliminary work incorporating Si into NPC is encouraging, allowing the correlation of Si-decorated NPC with Si-content and mass density vs. specific capacity.