Lithium anodes (13, 15, 17, and 20 wt% Li) were fabricated by mixing molten lithium and iron powder, which was used as a binder to hold the molten lithium, at about 500℃ (discharge temp.). In this study, the effect of applied pressure and lithium content on the discharge properties of a thermal battery’s single cell was investigated. A single cell using a Li anode with a lithium content of less than 15 wt% presented reliable performance without any abrupt voltage drop resulting from molten lithium leakage under an applied pressure of less than 6 kgf/㎠. Furthermore, it was confirmed that even when the solid electrolyte is thinner, the Li anode of the single cell normally discharges well without a deterioration in performance. The Li anode of the single cell presented a significantly improved open-circuit voltage of 2.06 V, compared to that of a Li-Si anode (1.93 V). The cut-off voltage and specific capacity were 1.83 V and 1,380 As g^-1 (Li anode), and 1.72 V and 1,364 As g^-1 (Li-Si anode). Additionally, the Li anode exhibited a stable and flat discharge curve until 1.83 V because of the absence of phase change phenomena of Li metal and a subsequent rapid voltage drop below 1.83 V due to the complete depletion of Li at the end state of discharge. On the other hand, the voltage of the Li-Si anode cell decreased in steps, 1.93 V → 1.72 V (Li₁₃Si₄ → Li₇Si₃) → 1.65 V (Li₇Si₃→ Li₁₂Si₇), according to the Li-Si phase changes during the discharge reaction. The energy density of the Li anode cell was 807.1 Wh l^-1, which was about 50% higher than that of the Li-Si cell (522.2 Wh l^-1).