Hard carbon for sodium batteries: Wood precursors and activation with first group hydroxide

Abstract This manuscript contains a survey of composite anodes for sodium ion batteries based on hard carbon obtained from different wood precursors. The hard carbon was activated with various metal hydroxide (MeOH with Me = Na, K, Rb, Cs). A commercially available carbon was also tested to compare the performance of the hard carbon so prepared. Electrochemical tests have shown that anodes prepared with different hard carbons have different specific capacities. The different capacity was related both to the type of wood used as the precursor and to the metal hydroxide used as the activation agent. The cycling tests indicated that KOH activated hard carbons show the best performance in terms of specific capacity and rate capability. The effect of the cation size on the carbon activation process can be explained considering that the alkali metal acts through a mechanism combined which on the one hand determines an increase in the porosity of the carbon and on the other one, an increase in the inter-atomic distance of the carbon structure.