Waste eggshell as bio-template to synthesize high capacity δ-MnO₂ nanoplatelets anode for lithium ion battery

In this work, abandoned chicken eggshell was used as hard biological template to synthesize battery material for the first time. We developed a simple hydrothermal method to form flocculent batt-like δ-MnO₂ nanoplatelets balls inside the pores of eggshell. Herein, eggshell was ground and screened into different mesh to prepare MnO₂ using the same method for comparison. MnO₂ made by similar eggshell-free method served as a contrast. The MnO₂ prepared from eggshell between 200 and 400 mesh has a large specific surface area up to 320.9 m²/g and a nanoplatelets ball structure capable of storing large amount of lithium ions. Most importantly, it shows the best electrochemical performances. At a current density of 100 mA/g, it delivered a high initial specific discharge/charge capacity of 2156.6/1008.2 mA h/g. After a short descent, its capacity gradually increased after about 30th cycle, and reached 1024.8/1022.1 mA h/g at the 100th cycle, much higher than that of MnO₂ from eggshell-free method and reported by others. Our original preparation method of using eggshell as hard biological template has referential significance of reducing particle size and advancing electrochemical performances for other battery materials.