Andrew van Bommel

Investigation of the Irreversible Capacity Loss in the Lithium-Rich Oxide Li[Li1/5Ni1/5Mn3/5]O2

The lithium-rich transition metal oxides show a larger first charge capacity and larger cycling capacities than the non-lithium-rich transition metal oxides. The disadvantages of the lithium-rich transition metal oxides include relatively poor rate capabilities and relatively large irreversible capacities. In this report, the irreversible capacity loss of the lithium rich oxide Li[Li 1/5 Ni 1/5 Mn 3/5 ]O 2 was investigated. Stepwise traverse of the oxygen-release plateau increased the cycling capacity of Li/Li[Li 1/5 Ni 1/5 Mn 3/5 ]O 2 cells and gave evidence that lithium was removed from the transition metal layer at the start of the oxygen release plateau. The irreversible capacity loss was attributed to the diffusion of transition metals into the lithium vacancies in the transition metal layer and the subsequent inability for lithium reinsertion into the transition metal layer. Isothermal calorimetry of Li/Li[Li 1/5 Ni 1/5 Mn 3/5 ]O 2 cells cycled from 2.5 to 4.4 V (no oxygen loss) supported the view that lithium is not deintercalated from the transition metal layer at the start of charge.

Synthesis of Spherical and Dense Particles of the Pure Hydroxide Phase Ni1 ∕ 3Mn1 ∕ 3Co1 ∕ 3 ( OH ) 2

The structure of the coprecipitated precursor to the positive electrode material, Li[Ni 1/3 Mn 1/3 Co 1/3 ]O 2 (NMC), is typically synthesized via a coprecipitation reaction and assumed to be Ni 1/3 Mn 1/3 Co 1/3 (OH) 2 or Ni 1/3 Mn 1/3 Co 1/3 OOH. The coprecipitation reaction and its products are not thoroughly understood. Here, pure phase Ni 1/3 Mn 1/3 Co 1/3 (OH) 2 is synthesized in the presence of aqueous ammonia, yielding dense and spherical particles. Ni 1/3 Mn 1/3 Co 1/3 (OH) 2 was found to readily oxidize in air, especially during heating. The obtained product was analyzed with powder X-ray diffraction and thermogravimetric analysis. The results indicate that Ni 1/3 Mn 1/3 Co 1/3 (OH) 2 undergoes oxidation to the oxyhydroxide phase, Ni 1/3 Mn 1/3 Co 1/3 OOH. Heating also resulted in an increase in tap density of the oxyhydroxide; the final tap density of the material was found to be 2.0 g cm -3 .