S-Encapsulated Micropore Carbon Cathode

This chapter describes sulfur (S)-encapsulated micropore carbon as a cathode material for lithium (Li) S batteries. Although S cathodes have an extremely large theoretical capacity of 1672 mAh g−1, there have been critical issues preventing practical use: elution of polysulfide intermediates, irreversible reactions of them with an electrolyte, and so on. To solve these problems, extensive studies have been conducted for limiting the elution of Li polysulfides from S cathodes. For instance, various nanocarbon materials, polymers, and their precursors, etc., have been tested to confine S stably. This chapter focuses mainly on activated carbons especially microporous carbons, whose pores have a diameter less than 2 nm. Such microporous carbons can effectively confine S to prevent the intermediate elution and undesirable side reactions with electrolytes. In that case, charge and discharge curves exhibit a single plateau with a gentle slope, which are very similar to the curves observed in an all-solid-state Li–S battery. There are some critical factors to govern the cycle performance of S cathodes based on microporous carbons: pore distribution, pore volume, loadable S content, particle size, and fine structure of applied microporous carbons. The chapter also introduces a relatively simple and easy procedure to obtain microporous carbons from polysaccharides with heat treatment and alkali activation.