Tamio Oguchi

Discharge Reaction Mechanisms in Na/FeS2 Batteries: First-Principles Calculations

We have studied microscopic discharge reaction mechanisms in Na/FeS2 batteries by first-principles calculations. The calculated Na–Fe–S phase diagram shows that the discharge reactions can proceed by converting 4Na and FeS2 into 2Na2S and Fe as a fully discharged state. As an intermediate discharge reaction, we find that NaxFeS2 (x ∼ 1.5) intermediate products can be generated in the cathode, giving two major plateaus in voltage–capacity curves. The calculated voltage–capacity characteristics and X-ray absorption spectra at S and Fe K-edges of Na-discharged FeS2 cathode materials are compared with experimental results, showing that theoretically determined reaction formulas can account for the experimental discharge reactions.