Deciphering the Thermal Evolution in 0.5Li2MnO3- 0.5LiNi0.33Co0.33Mn0.33O2 Cathode Material for Lithium-Ion Batteries By in Situ X-Ray Diffraction Technique

Lithium-ion batteries were introduced in 1990 by Sony Corporation. Since its successful debut, various transition metal oxides have been synthesized and investigated as new lithium ion battery electrode materials to fulfill the ever demanding high capacity requirements. Recently, composite layered material between Li2MnO3 and LMO2 (where M= Mn, Co, Ni), also known as the lithium rich cathode material, has received pronounced attention and has been considered as promising cathode materials due to their high discharge capacity of ~250 mAh g-1 [1].  

However, there are several intrinsic problems associated with this material family that need to be solved; e.g., the voltage as well as the capacity decay during cycling, the high irreversible capacity loss in the first cycle, poor rate capability, and oxygen release during cycling, in order to adopt these materials in practical cells [2–4]. Thermal stability is another challenge which could greatly impact the safety of lithium-ion batteries, however it has received little attention unlike the widely studied electrochemical performance and reaction mechanism of this material.

In this study, we use in situ X-ray diffraction technique to elucidate the thermal degradation mechanism of 0.5Li2MnO3-0.5LiNi0.33Co0.33Mn0.33O2 lithium rich cathode material in the absence and presence of electrolyte to simulate the real life battery conditions and compared its thermal behavior with the commercial LiNi0.33Co0.33Mn0.33O2 cathode material. We show that the thermal induced phase transformations in delithiated lithium rich cathode material are much more intense compared to similar single phase layered cathode material in the presence of electrolyte. The structural changes in both cathode materials with the temperature rise follow different trends in the absence and presence of electrolyte between 25-600 °C. Phase transitions are comparatively simple in the absence of electrolyte, the fully charged lithium rich cathode material demonstrates better thermal stability by maintaining its phase till 379 °C, and afterwards spinel structure is formed. Whereas in the presence of electrolyte, the spinel structure appears at 207 °C, subsequently it transforms to rock salt type cubic phase at 425 °C with additional metallic, metal fluoride, and metal carbonate phases. More detailed discussion will be presented at the time of meeting.

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