Influence of varistor effect and contact phenomena on the characteristics of solid-state lithium-ion batteries with semiconductor electrodes

The results of measuring the charge-discharge characteristics of solid-state thin-film lithium-ion batteries with a nanocomposite anode based on $a$-Si(Al) solid solution are presented. The charging characteristics of batteries have a feature in the form of a step on the smooth branch of the charge curve. It is shown that the appearance of the step is associated with the compensation of $a$-Si(Al) and the change from hole to electron conductivity due to lithiation of the electrode during charging. As a result of lithiation, the electron over-barrier current becomes the main component of the charging current. To maintain a galvanostatic charge mode, the potentiostat increases the voltage by the height of the potential barrier, which leads to the appearance of a step on the charging curve. The impedance of a solid-state thin-film lithium-ion battery of the LiCoO$_2$–LiPON–Si@O@Al electrochemical system was measured in the temperature range from -20 to 50$^\circ$C. A structural model of the accumulator is proposed and the parameters of the structural elements of the model are calculated which provide the best fit for experimental Nyquist diagrams. The obtained values of the electrodes' resistivity are orders of magnitude higher than the results of direct measurements and data from literary sources. According to the IV-characteristics obtained by cyclic voltammetry the high resistance of the electrodes is due to the metal-semiconductor contact and the varistor effect of the electrode material. The results obtained make significant adjustments to the interpretation of the impedance spectra and structural models of solid-state lithium-ion batteries based on semiconductor materials.