Low-Temperature Cation Ordering in High Voltage Spinel Cathode Material

• The spinel cathode LiNi0.5Mn1.5O4 (LNMO) is a promising material for battery applications; however, issues regarding its cycling stability need to be addressed to fully utilize its potential. Specifically, LNMO suffers from rapid capacity loss following prolonged electrochemical cycling where the capacity drop occurs at an earlier stage for its transition metal ordered form. Further, the disordered form has been found to partially order during cycling, leading to the question if the failing of the disordered form is driven by Ni and Mn ordering in the structure. However, ordering is usually initiated at temperatures above 700 degrees C in the fully lithiated state, sparking the question if the energy barrier for the ordering process is lowered at the reduced Li content. In the work presented here, in situ neutron diffraction was used to further elucidate the ordering temperature and thermal stability of LixNi0.5Mn1.5O4 (0.000 (10) < x < 0.675 (10)). The temperature for Ni and Mn ordering was found to be dramatically lowered to 310-320 degrees C for LixNi0.5Mn1.5O4 compositions of 0.222 (8) < x < 0.675 (10), explained by a lower energy barrier for formation of intermediate Frenkel defect states. Li ordering and a lowering of symmetry to P213, together with formation of both a NiMn2O4-type spinel phase and a NiMnO3-type phase, could also be observed. The formation of NiMn2O4- and NiMnO3-type phases could be linked to reorganization of transition metals (TM) within the spinel structure and were found to be in competition with Ni and Mn ordering. At higher Li contents, transition metal diffusion tended to favor Ni and Mn ordering, while NiMn2O4- and NiMnO3-type phases were formed to a greater extent at lower Li contents. These results highlight the importance of suppressing transition metal reorganization in LiNi0.5Mn1.5O4, via increased TM diffusion energy barriers, as a key strategy for minimizing structural rearrangements and ultimately improving its electrochemical cyclability.

Ämnesord

NATURVETENSKAP  -- Kemi -- Materialkemi (hsv//swe)

NATURAL SCIENCES  -- Chemical Sciences -- Materials Chemistry (hsv//eng)

Nyckelord

Li-ion batteries

spinel

high voltage

in situ

neutron diffraction

Publikations- och innehållstyp

ref (ämneskategori)

art (ämneskategori)