Tailoring Disordered/Ordered Phases to Revisit the Degradation Mechanism of High‐Voltage LiNi_0.5Mn_1.5O₄ Spinel Cathode Materials

Abstract

In the spinel oxide cathode family, LiNi 0.5 Mn 1.5 O 4 (LNMO) shows a high operating voltage (≈4.7 V vs Li/Li + ) and excellent Li-ion mobility with stable 3D conducting channels. Ni/Mn cation disordered and ordered phases usually coexist in LNMO materials, and they have distinct structural and electrochemical properties, resulting in different battery performances for LNMO materials with different phase compositions. Identifying the correlation between phase compositions and electrochemical properties is of significance to the improvement of battery performance and understanding of degradation mechanisms. Herein, the disordered/ordered phase compositions in LNMO materials are tailored by post-annealing strategies and their impacts on electrochemical performance and degradation mechanisms from the surface to the bulk are systematically investigated. The ordered phase increases rapidly as Mn 3+ is oxidized to Mn 4+ through a post-annealing process. LNMO with an intermediate fraction of disordered and ordered phases gives rise to improved cycling stability. This article further reports that a high ordered phase fraction can preferentially protect Ni from dissolution during cycling. However, these results suggest that the transition metal dissolution and surface structural change of LNMO do not exhibit a direct correlation with cycling stability. These results indicate the capacity fading mainly correlates with the bulk structural distortion, leading to decreased Li-ion kinetics.

Truncated Octahedral Shape of Spinel LiNi0.5Mn1.5O4 via a Solid-State Method for Li-Ion Batteries

“…Where the separation >50 mV corresponds to predominantly disordered (Fd3̅ m phase) and a separation <30 mV is considered to the ordered (P4 3 32 phase) structure of LNMO. 3,39 For both samples, the separation of the route 1 and route 2 samples are 57.21 and 57.32 mV, respectively.…”

“…LNMO can crystallize into two different crystal forms, ordered cation (Ni/ Mn) with space group P4 3 32 phase or disordered cation (Ni/ Mn) space group Fd3̅ m, while a single phase formation belongs to other cathode materials (i.e., LCO, NMC, NCA, or LFP). 3 The P4 3 32 phase has a characteristic ordering structure as the octahedral 4a and 12d sites are occupied by Ni 2+ and Mn 4+ , respectively. For the electrochemical behavior of the ordered phase, the merge of Ni 2+ /Ni 3+ and Ni 3+ /Ni 4+ redox reaction led to Li-ion extraction from the host lattice, whereas the Mn 4+ remains electrochemically inactive.…”

Study on annealing treatment of spinel LiNi 0 . 5 Mn 1 . 5 O 4 as cathode materials for high‐voltage lithium‐ion batteries

“…Based on the previous studies on the lattice parameters related to the two space groups of LiNi 0.5 Mn 1.5 O 4 , the typical ranges of the lattice parameters for the two space groups are basically given. Among them, [68][69][70] the disordered structure Fd3m corresponds to 8.172-8.183 Å (upper limit can be adjusted) and the ordered structure P4 3 32 corresponds to 8.166-8.173 Å(lower limit can be adjusted). We noticed that lattice parameters of LNMO-UN prepared under high temperature and hypoxia environment corresponds to typical Fd3m structure, and the annealing process promotes partial transformation between the two phases.…”

Dynamic Structure Evolution of Extensively Delithiated High Voltage Spinel Li1+xNi0.5Mn1.5O4 x < 1.5

“…It must be noted, that disordered spinel reacts slightly different and forms a solid solution in the compositional range of approximately 0.5 < x < 1 in Li x Ni 0.5 Mn 1.5 O 4 . Furthermore, it shows a voltage step at 4 V during charge and discharge, associated with the redox activity of Mn 3+/4+ . − Both, ordered and disordered spinel are investigated intensively regarding their electrochemical performance and structural evolution in the high voltage region. − …”