Organic light emitting diodes (OLED) have been greatly investigated for application in flat panel display and light source. A different type of OLED is light emitting electrochemical cell (LEC), which consists of luminescent chromophore films with solid electrolyte such as ionic ruthenium complex film. Driving process of LEC is different from that of OLED. That is, upon applied voltage, the electric double layer is formed at the interface between the anode or cathode and ionic luminescent film and hole and electron are injected from both electrodes into the luminescent film and then light is emitted by charge recombination. Thus, LEC has attractive features which are single-layer device and no requirement to use low work function metal as a cathode. However, LEC has some drawback which is ill charge-injection balance between hole and electron caused by the difference in ion size between large ruthenium complex cation and small counter anion. To improve the charge-injection balance, incorporation of small cation into ionic luminescent layer will be expected. In this study, current efficiency for LEC was improved by introduction of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) as additive electrolyte into the ruthenium complex film of LEC. LEC was prepared by spin-coating tris(2,2’-bipyridyl) ruthenium(II) complex TFSI₂ (Ru(bpy)₃(TFSI)₂) and poly(methyl methacrylate) (PMMA) matrix in acetonitrile solution with LiTFSI solid electrolyte on ITO anodes. And then silver was vacuum-deposited onto the resulting ruthenium complex film with solid electrolyte on ITO anodes. The luminescent property of LEC was performed by applying constant current. The standard LEC without LiTFSI was not emitted and the lower voltage than 1 V was observed in the constant current of smaller than 1.5 mA whereas it was emitted and the voltage of around 2.5 V was observed in the constant current of larger than 1.5 mA. These results indicate that the only hole injection occurs and the electron injection does not occur until the applied current over 1.5 mA. It’s due to the thicker electric double layer of ruthenium complex at the cathode of LEC. As introduction of LiTFSI into the ionic luminescent layer, the emission starts at the smaller applied current with increasing amount of LiTFSI. The maximum current efficiency becomes 3.0 cd/A in the LEC containing 3 wt% LiTFSI. However, the addition of more than 3 wt% LiTFSI into LEC makes LEC performance worse because the distance between ruthenium complex become wide and the electron hopping rate becomes slow. Finally, addition of 10 wt% LiTFSI makes crystalize ionic luminescent layer and it does not function as LEC. Therefore, we found that the introduction of 3 wt% LiTFSI to LEC was the optimum condition.