Modification of Single-Walled Carbon Nanotube Networks Anodes for Application in Aqueous Lithium-Ion Batteries

The changes in global energy trends and the high demand for secondary power sources, have led to a renewed interest in aqueous lithium-ion batteries. The selection of a suitable anode for aqueous media is a difficult task because many anode materials have poor cycling performance due to side reactions with water or dissolved oxygen. An effective method for improving the characteristics of anodes in aqueous electrolyte solutions is adding carbon nanotubes (CNTs) to the electrode materials. For a better comprehension of the mechanism of energy accumulation and the reasons for the loss of capacity during the cycling of chemical current sources, it is necessary to understand the behaviour of the constituent components of the anodes. Although CNTs are well studied theoretically and experimentally, there is no information about their behaviour in aqueous solutions during the intercalation/deintercalation of lithium ions. This work reveals the mechanism of operation of untreated and annealed single-walled carbon nanotubes (SWCNT) anodes during the intercalation/deintercalation of Li⁺ from an aqueous 5 M LiNO₃ electrolyte. The presence of -COOH groups on the surface of untreated SWCNTs is the reason for the low discharge capacity of the SWCNT anode in 5 M LiNO₃ (3 mAh g⁻¹ after 100 cycles). Their performance was improved by annealing in a hydrogen atmosphere, which selectively removed the -COOH groups and increased the discharge capacity of SWCNT by a factor of 10 (33 mAh g⁻¹ after 100 cycles).