Pre-heat treatment of carbonate precursor firstly in nitrogen and then oxygen atmospheres: A new procedure to improve tap density of high-performance cathode material Li1.167(Ni0.139Co0.139Mn0.556)O2 for lithium ion batteries

• A new two-steps pre-heat treatment procedure of carbonate precursors is proposed.
• The two-steps sintering procedure is carried out using N2 firstly and then O2.
• CO2 emission and O2 absorption during decomposed process of carbonate are separated.
• An improved tap density with dense particle is obtained, but at a cost of capacity.

In order to increase the tap density of Li-rich layered materials, a new pre-heat treatment procedure of (Ni1/6Co1/6Mn4/6)CO3 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. In contrast to one-step pre-heat treatment procedure only in O2, two-steps procedure causes differences in morphology, tap density, particle distribution as well as structure for resultant metal oxides. A remarkably improved tap density of metal oxide with dense particles is observed with two-steps procedure. Consequently, Li1.167(Ni0.139Co0.139Mn0.556)O2 obtained through two-steps procedure (LM-N) presents dense particle, much improved tap density, small BET specific surface area and additional existence of Ni3+ in comparison with that obtained through one-step procedure (LM-O), although both samples exhibit similar well-defined layered structure. However, the results of cyclic voltammograms and charge–discharge test demonstrate the inferior electrochemical performances of LM-N with a discharge capacity of 76.7 mAh g−1 for LM-N, which is in stark contrast with 267.9 mAh g−1 of LM-O. This is possibly associated with the dense morphology, lattice defect as well as large Rct for LM-N.