Journal
NANO LETTERS
Volume 15, Issue 3, Pages 2111-2119Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acs.nanolett.5b00045
Keywords
LiNi0.6Co0.2Mn0.2O2; cathode; high voltage; thermal stability; primary particles; microcrack; structural degradation
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Funding
- IT R&D program of MOTIE/KEIT [10046309]
- Korea Evaluation Institute of Industrial Technology (KEIT) [10046306] Funding Source: Korea Institute of Science & Technology Information (KISTI), National Science & Technology Information Service (NTIS)
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Structural degradation of Ni-rich cathode materials (LiNixM1-xO2; M = Mn, Co, and Al; x > 0.5) during cycling at both high voltage (>4.3 V) and high temperature (>50 degrees C) led to the continuous generation of microcracks in a secondary particle that consisted of aggregated micrometer-sized primary particles. These microcracks caused deterioration of the electrochemical properties by disconnecting the electrical pathway between the primary particles and creating thermal instability owing to oxygen evolution during phase transformation. Here, we report a new concept to overcome those problems of the Ni-rich cathode material via nanoscale surface treatment of the primary particles. The resultant primary particles surfaces had a higher cobalt content and a cation-mixing phase (Fm (3) over barm) with nanoscale thickness in the LiNi0.6Co0.2Mn0.2O2 cathode, leading to mitigation of the microcracks by suppressing the structural change from a layered to rock-salt phase. Furthermore, the higher oxidation state of Mn4+ at the surface minimized the oxygen evolution at high temperatures. This approach resulted in improved structural and thermal stability in the severe cycling-test environment at 60 degrees C between 3.0 and 4.45 V and at elevated temperatures, showing a rate capability that was comparable to that of the pristine sample.
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