Taeho Yoon

Continuous activation of Li2MnO3 component upon cycling in Li1.167Ni0.233Co0.100Mn0.467Mo0.033O2 cathode material for lithium ion batteries

Li-rich layered cathode materials are very promising candidates for next generation high energy lithium ion batteries. One of the Li-rich layered cathode materials, Li1.167Ni0.233Co0.100Mn0.467Mo0.033O2 is prepared by a co-precipitation method. In this report, we focus on anomalous changes upon cycling in Li1.167Ni0.233Co0.100Mn0.467Mo0.033O2 cathode material in a voltage range of 2.0–4.55 V at room temperature. The structural transitions upon cycling are analyzed by ex situ X-ray diffraction. In addition, the changes in local structure during cycling are studied by X-ray absorption near edge structure. With differential capacity plots by controlling the cut-off voltage, the voltage decay during cycling is intensively studied. The continuous activation process of the residual Li2MnO3 component during cycling is correlated with voltage decay during cycling, and increasing capacity during the initial several cycles. Also, the electrochemical performance in Li1.167Ni0.233Co0.100Mn0.467Mo0.033O2 cathode material below 4.4 V is discussed. Furthermore, cycle performance is improved by reassembling Li1.167Ni0.233Co0.100Mn0.467Mo0.033O2 into another cell after washing.

Effective passivation of a high-voltage positive electrode by 5-hydroxy-1H-indazole additives

5-Hydroxy-1H-indazole (HI) is investigated as an effective film-forming additive for an over-lithiated layered oxide (OLO) positive electrode. The protective film that is generated by oxidative decomposition of the additive (HI) prior to the carbonate electrolyte is thin and less resistive. As a result, a full cell comprised of OLO/graphite in the HI-added electrolyte gives a better cycling performance.

A first-cycle coulombic efficiency higher than 100% observed for a Li2MO3 (M = Mo or Ru) electrode.

The lithiation/de-lithiation behavior of a ternary oxide (Li2MO3, where M = Mo or Ru) is examined. In the first lithiation, the metal oxide (MO2) component in Li2MO3 is lithiated by a conversion reaction to generate nano-sized metal (M) particles and two equivalents of Li2O. As a result, one idling Li2O equivalent is generated from Li2MO3. In the de-lithiation period, three equivalents of Li2O react with M to generate MO3. The first-cycle Coulombic efficiency is theoretically 150% since the initial Li2MO3 takes four Li(+) ions and four electrons per formula unit, whereas the M component is oxidized to MO3 by releasing six Li(+) ions and six electrons. In practice, the first-cycle Coulombic efficiency is less than 150% owing to an irreversible charge consumption for electrolyte decomposition. The as-generated MO3 is lithiated/de-lithiated from the second cycle with excellent cycle performance and rate capability.