Teaching an old dog new tricks: Ti-doped ZnFe2O4 as active material in zinc ion batteries – a proof of concept†

In this work, the suitability of the spinel material ZnFe₂O₄, which has already been widely investigated in the context of its magnetic and photocatalytic properties, for use as active material for the cathode side in zinc ion batteries is presented. In addition to pure ZnFe₂O₄, part of the Fe³⁺ was doped with Ti⁴⁺ to achieve stabilization of Zn vacancies in the material and increase ionic conductivity as indicated by previous modelling results. Ceramic samples with the composition ZnFe_2−xTi_xO₄ (x = 0 to 0.25) were prepared via a Pechini synthesis route and investigated regarding their optical, structural and electrochemical characteristics. It has been successfully demonstrated that both pure and Ti doped ZnFe₂O₄ can be used as active material in the positive electrodes of zinc metal batteries or in an “anode-free” setup with Sn metal. Cells with calcined ZnFe_2xTi_xO₄ (x = 0.09)|0.5 M zinc triflate in acetonitrile|Zn showed a stable cycling behavior over 1000 cycles and an average initial specific capacity of 55 mA h g⁻¹.