Synthesis of Sn-substituted Li-rich/Mn-rich NMC via an aqueous carbonate co-precipitation method

The rocksalt-type layered lithium-rich/Mn-rich lithium nickel manganese cobalt oxide (NMC) is considered as a promising alternative for the commercialised cathode material for Li-ion batteries LiCoO2 due to its higher... [ view full abstract ]

The rocksalt-type layered lithium-rich/Mn-rich lithium nickel manganese cobalt oxide (NMC) is considered as a promising alternative for the commercialised cathode material for Li-ion batteries LiCoO₂ due to its higher capacities in the range of 250–300 mAh/g,¹ its lower cost and higher thermal stability. However, Li-rich/Mn-rich NMC suffers from large voltage decays, most probably related to structural changes ascribed to transition metal (TM) migration during cycling. Migration of the octahedrally coordinated TM to other octahedral sites is believed to occur via intermediate tetrahedral (T_h) sites. As Sn⁴⁺ does not tend to adopt T_h coordination, the substitution of Sn⁴⁺ for Mn⁴⁺ is under investigation as a way to decrease the voltage fade.

Co-precipitation by using carbonate-based precipitating agents is a well-established route to prepare NMC. Here, we evaluate the synthesis of Sn-substituted Li-rich/Mn-rich NMC with composition Li_1.2Ni_0.13Mn_0.54Co_0.13O₂ via aqueous carbonate co-precipitation followed by an anneal at elevated temperatures. Tin substitution degrees were varied from 5% till 100% of Mn⁴⁺ replaced by Sn⁴⁺. It is shown by XRD that the spherical micrometer-sized particles obtained after co-precipitation and before anneal contain for the whole investigated composition range a tin oxohydroxo phase. The role of the pH and the metal-to-precipitating agent ratio applied during co-precipitation synthesis on the formation of this tin non-carbonate phase has been investigated. The XRD patterns recorded after anneal show additional peaks not indexed to NMC. The structure and composition of the end product has been further investigated by STEM with emphasis on the correlation between the tin oxohydroxo phase and the end product.

References

1.        Deng, Z. Q., J. Phys. Chem. C 115, 7097–7103 (2011).

Acknowledgements

The author acknowledges Research Foundation Flanders (FWO) project number G040116N for funding.