A significant drawback for Li-rich layered materials is the low tap and compaction density in contrast to layered LiMO₂[1]. Thus, improving tap density is an important issue for Li-rich layered materials. In our work, some efforts are contributed to addressing the issue. On one hand, a new pre-heat treatment procedure of carbonate precursors firstly using N₂ and then O₂ is adopted to separate processes of CO₂ emission and O₂ absorption, which presumably can reduce porosity of materials and then result in an improved tap density. The remarkably improved tap density of metal oxide (2.20 g cm^–1) and cathode material (2.20 g cm^–1) is observed with the procedure. However, it is at a cost of capacity. On the other hand, the dual chelating agents, ammonia and oxalate, which have a synergistic action on chelating transition-metal ion, are successfully introduced to prepare high tap density hydroxide precursors (1.67 g cm^–3) and Li-rich cathode (2.28 g cm^–3) with atomic level uniformity of elemental distribution.

From Fig.1 (b) and (c), it is obviously found that the two-steps procedure is indeed beneficial for obtaining the dense morphology with less pores, resulting in a higher tap density. From Fig.2, with the function of the dual chelating agents, the spherical secondary particles with dense morphology, which are closely aggregated from nano-sized primary particles, are demonstrated to be obtained. 

References

[1] P.Oh, S. Myeong, W. Cho, M.-J. Lee, M. Ko, H.Y. Jeong, J. Cho, Nano Lett. 14 (2014) 5965−5972.