Battery in the Form of a Soil-Matrix Composite

This work has shown the feasibility of a soil-based battery, in which the electrolyte (soil) was continuous throughout the anode, cathode, and electrolyte. The soil contained 49 wt.% water. The battery was in the shape of a soil-based monolithic slab and involved an anode (zinc, particle size 7 μm, acetic acid washed), a cathode (MnO2, particle size 40 μm), and an electrically conductive additive (carbon black, particle size 30 nm). A battery was composed of three successive layers: a cathode layer (a soil-matrix MnO2 particle composite, 12 wt.% MnO2, 15 mm thick), an electrolyte layer (soil, 2 mm thick), and an anode layer (a soil-matrix zinc particle composite, 9 wt.% Zn, 5 mm thick). After assembly, it was compacted at a pressure of 1.67 MPa. The soil electrolyte exhibited resistivity of 220 Ω·cm and a relative dielectric constant of 29 (1 kHz). The soil-based battery discharged at 10 mA (0.25 mA/cm2) and exhibited open-circuit voltage up to 0.24 V, initial running voltage up to 0.17 V, power output up to 43 μW/cm2, capacity up to 179 mAh, and fraction of zinc consumed up to 0.06. The running voltage decreased continuously during discharge. The soil-based battery was much superior to a previously reported cement-based battery.