Silica from diatom frustules as anode material for Li-ion batteries

In spite of its insulating nature, SiO2 may be utilized as active anode material for Li-ion batteries. Synthetic SiO2 will typically require sophisticated synthesis and/or activation procedures in order to obtain a satisfactory performance. Here, we report on diatom frustules as active anode material without the need for extensive activation procedures. These are composed primarily of silica, exhibiting sophisticated porous structures. Various means of optimizing the performance were investigated. These included carbon coating, the addition of fluoroethylene carbonate (FEC) and vinylene carbonate (VC) to the carbonate-based electrolyte, as well as activation by an initial potentiostatic hold step. The highest capacity (723 mA h g-1) was obtained with composite electrodes with pristine diatom frustules and conventional carbon black as additive, with the capacity still increasing after 50 cycles. The capacity was around 624 mA h g-1 after subtraction of the contributions from the carbon black. Carbon coated diatom frustules showed a slightly lower but stable capacity after 50 cycles (600 mA h g-1 after subtraction of contributions from the carbon coating and the carbon black). By the use of electrochemical characterization methods, as well as post-mortem studies, differences in reaction mechanisms could be identified and attributed to the operating and processing parameters.