Synthesis and electrochemical properties of nanosized polyoxovanadate K7[NiV13O38] hybridised with carbon conductive additives

Improvement in the electrochemical property of polyoxovanadate K7[NiV13O38] (KNV) was attempted by downsizing to nanometre order by simple re-crystallisation and mixing or hybridising it with Ketjen black (KB) that has higher electric conductivity and surface area than acetylene black (AB). By mixing nanosize KNV with KB, the discharge capacity was improved up to 500 mAh/g, whereas capacity for micro-size KNV mixed with AB was limited to ∼120 mAh/g. The cycle performance and rate performance of KNV were also improved by downsizing and mixing with KB. On the other hand, KNV hybridised with KNV by in situ re-crystallisation showed lower cycle performance. This low cycle stability may be concerning with the surface sub-reaction such as surface film formation produced by the reaction with the electrolyte solution and/or dissolution of KNV, those are enhanced by increase with contacting surface area with the electrolyte.