LAYERED TITANATE SODIUM-ION BATTERY NEGATIVE ELECTRODES

Abstract

Sodium-ion batteries could offer an economical and environmentally friendly alternative to lithium-ion batteries, however, many challenges must be overcome first. The need for innovative negative electrode materials for sodium-ion batteries is of paramount importance as graphite, the most highly used negative electrode material in lithium-ion batteries, intercalates sodium to an insignificant degree and other current negative electrode materials do not perform satisfactorily. This work focuses on the investigation of layered sodium titanate phase systems as electrode materials in Na-ion batteries, specifically NaxMxTi1-xO2 where M = Cr or V. The layered systems are of great importance for the development of not only traditional positive electrode materials, but novel negative electrode materials for sodium-ion batteries as well. The high capacity and ease of sodium intercalation of these layered systems make them prime candidates for implementation in sodium-ion batteries. The gravimetric capacity of these materials was found to directly relate to the number of vacancies within their layered structure. A vacancy limit of ~0.4 was determined for these sodium based layered oxides. To increase the capacity, the number of vacancies needs to be increased. Two methods were employed to increase vacancies in intercalation materials, namely the investigation of sulfide and potassium analogues, to varying degrees of success. The potassium analogues led to preliminary studies of materials for potassium-ion batteries, such as graphite and KxCoO2.