Abstract:

High-performance Cr₈O₂₁ materials were prepared using a high-temperature solid-phase method to pyrolyse a CrO₃ precursor. The effect of pyrolysis temperature on the properties of Cr₈O₂₁ was explored, and the first discharge mechanism of Cr₈O₂₁ was analyzed. Using X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy (XPS), and electrochemical techniques, the crystallization degree, morphology, and electrochemical performance of samples prepared at different pyrolysis temperatures were compared and analyzed, and the discharge mechanism was elucidated. The results showed that among the samples, the Cr₈O₂₁ sample prepared at 270 ℃ has the highest crystallinity and an excellent discharge performance. At 0.05 mA/cm², the discharge specific capacity reached 419 mAh/g with an average voltage of 2.99 V. At 1.0 mA/cm², the discharge specific capacity reached 315 mAh/g with an average voltage of 2.82 V. The capacity retention rate was 75.11%. Furthermore, the electrochemical performance of this sample is higher than that of Cr₈O₂₁ samples prepared at other temperatures. When the pyrolysis temperature is lower than 270 ℃, the reaction of the CrO₃ precursor is insufficient. When the pyrolysis temperature is higher than 270 ℃, the impurity phase will be formed. The XPS results showed that the Cr element in Cr₈O₂₁ only contains +3 and +6 valence, and no other valence states exist. The first discharge mechanism of Cr₈O₂₁ is as follows: from 3.5 V to 3.0 V, lithium ion intercalates inside Cr₈O₂₁, and from 3.0 V to the end, lithium ion reacts with Cr₈O₂₁ to generate LiCrO₂ and highly irreversible Li₂O. This study helps to promote the application of high-capacity Cr₈O₂₁ materials in lithium primary batteries and provides an experimental basis for the research and development of high specific energy primary battery techniques.

Key words: Cr₈O₂₁, lithium primary batteries, cathode material, heating temperature, LiCrO₂