The LiBH₄-LiI Solid Solution as an Electrolyte in an All-Solid-State Battery

The charge and discharge performance of an all-solid-state lithium battery with the LiBH4-LiI solid solution as an electrolyte is reported. Lithium titanate (Li4Ti5O12) was used as the positive electrode and lithium metal as the negative electrode. The performance of the all-solid-state cell is compared with a cell with an identical electrode setup but a liquid electrolyte (1 M LiPF6 in EC:DMC).

All measurements were carried out at a temperature of 60°C. For the all-solid-state cells, 81% of the theoretical discharge capacity is reached for a discharge rate of 10 μA, but a capacity fade of 1.6% per charge-discharge cycle is observed. The electrochemical stability of the LiBH4-LiI solid solution was investigated using cyclic voltammetry and is found to be limited to 3 V.

The impedance of the battery cells was measured using impedance spectroscopy. A strong correlation is found between the change in the discharge capacity of the cells and changes in the cell impedance over 200 charge-discharge cycles. This is expectedly due to the possible formation of passivating areas in the cell and/or loss of contact area between the electrolyte and the electrodes.