Influence of Pore Architecture and Chemical Structure on the Sodium Storage in Nitrogen ‐Doped Hard Carbons

The impact of porosity and nitrogen content on the sodium storage mechanism in sodium ion battery anodes is studied using a series of nitrogen ‐doped, microporous hard carbons. It is found that nitrogen functionalities contribute to the sloping region, while the formation of quasimetallic sodium occurs during a voltage plateau. Further, important relations between gas physisorption and sodium storage are revealed. AbstractHard carbon is the material of choice for sodium ion battery anodes. Capacities comparable to those of lithium/graphite can be reached, but the understanding of the underlying sodium storage mechanisms remains fragmentary. A two ‐step process is commonly observed, where sodium first adsorbs to polar sites of the carbon (“sloping region”) and subsequently fills small voids in the material (“plateau region”). To study the impact of nitrogen functionalities and pore geometry on sodium storage, a systematic series of nitrogen‐doped hard carbons is synthesized. The nitrogen content is found to contribute to sloping capacity by binding sodium ions at edges and defects, whereas higher plateau capacities are found for materials with less nitrogen content and more extensive graphene layers, suggesting the formation of 2D sodium structures stabilized by graphene‐like pore walls. In fact, up to 84% of the plateau capacity is measured at potentials less than 0 V versus metallic Na, that is, quasimetallic sodium can be stabilized in such structure motifs...
Source: Small - Category: Nanotechnology Authors: Tags: Full Paper Source Type: research