High-Performance Cr₈O₂₁ Cathode Materials with MnO₂ as an Activator for High-Energy-Density Lithium Primary Batteries

Chromium oxides (Cr₈O₂₁) have attracted wide application due to their high theoretical capacity and high voltage for lithium primary batteries. However, Cr₈O₂₁ is usually prepared by pyrolysis of a CrO₃ precursor and suffers from low capacity and poor rate capability due to the fusion of CrO₃ during the high-temperature reaction process. Herein, MnO₂ was investigated as an activator to study its impact on the electrochemical properties of Cr₈O₂₁, which significantly changed with the addition of MnO₂ during the calcination process. With the addition of MnO₂, the discharge capacity and rate capability of the reaction products (Cr₈O₂₁-M) were dramatically improved compared with those of pure Cr₈O₂₁. This improvement is attributed to the superior lithium-ion diffusion kinetics caused by the uniform surface structure and porous features, which reduce the charge transfer resistance. As a result, Cr₈O₂₁-M10 exhibited an excellent discharge specific capacity of 388 mAh g^-1 at 0.1C with discharge voltage plateaus of about 3.0 V (vs Li⁺/Li), reaching an energy density of 1223 Wh kg^-1 based on the cathode material. In addition, Cr₈O₂₁-M showed remarkable rate performance, enabling a high-capacity retention of about 70% at 5C. Therefore, it is essential to add an activator agent during the preparation of Cr₈O₂₁, which offers a promising avenue for the development of high-energy-density and high-rate-capability Li/Cr₈O₂₁ primary batteries.