Evolution of Phase Transformation Behavior in Li(Mn1.5Ni0.5)O4 Cathodes Studied By In Situ XRD

Abstract

In situ X-ray diffraction of Li(Mn 1.5 Ni 0.5 )O 4 was performed using a novel electrochemical cell based on coin cell hardware. The pristine material had a cubic spinel structure with a Ni 2þ oxidation state. As the cell was charged through its 4.75V plateau, a transition between spinels with Ni 2þ , Ni 3þ , and Ni 4þ oxidation was observed. As the oxidation of the nickel increased, the lattice parameter of the corresponding spinel diminished. During discharge, the spinel reversed its phase changes until only the Ni 2þ spinel was observed. As the discharge potential reached a plateau at 2.75V a tetragonal spinel phase was formed, which upon subsequent cell charging was completely converted back to a cubic spinel phase. Lattice parameter changes of each phase were calculated and showed a characteristic strain release during phase changes. After 15 full cycles the transition between cubic spinels was no longer complete and the formation of the tetragonal spinel phase was no longer detected. This suggests a gradual change from an ordered to disordered MNO structure and lithium trapping in the active material. These cycle-induced changes to phase transition behavior can be related to capacity fade and overall cell performance.A global demand for portable, high power energy storage systems has made the development of improved lithium ion batteries (LIBs) an important research priority. 1 Consumer electronics, electrical vehicles, power grid regulation, and remote sensing applications all stand to benefit from LIBs with higher power, greater capacity, and longer life. To achieve this goal the structural behavior of the active electrode materials must be well understood at multiple levels from lattice, to particle, to composite. How the structure changes as the material is reversibly intercalated or alloyed with lithium as well as how the structure evolves over the course of many lithiation/delithiation cycles are important considerations in the design, development, and selection of active materials.Among current cathode materials for lithium ion batteries those based on the LiMn 2 O 4 spinel structure are advantageous in their nontoxicity, low cost, and ease of preparation. 2-7 The spinel structure of this material offers a 3D diffusion pathway for lithium intercalation/ deintercalation. Lithiation occurs reversibly as per the following reactionHowever, use of this material faces several challenges including somewhat limited rate capabilities, 8 dissolution of Mn 2þ ions into the electrolyte, 9,10 and a strong Jahn-Teller distortion at low potentials. 10-12 At low potentials the Mn 3þ /Mn 4þ redox couple produces Mn 3þ ions which may participate in the following disproportion reaction at the interface between the particle and the electrolyte 2Mn 3þ solid ! Mn 4þ solid þMn 2þ electrolyte At high degrees of lithiation, LiMn 2 O 4 will undergo a Jahn-Teller distortion that forces it from a cubic to tetragonal spinel structure as Li 2 Mn 2 O 4 is formed. 10-12 Any regions of material in this tetragonal phase, most likely ...

In Situ XRD of Thin Film Tin Electrodes for Lithium Ion Batteries

“…In situ XRD cells were prepared as previously described 17,18 with some modifications. The in situ XRD cell is shown in Figure 1 at various stages of fabrication.…”

High Voltage Cathode Materials

“…However, a different phase diagram has been reported for this same disordered LMN, with a solid solution for large values of x, followed with a two-phase region at x * 0.6, due to the onset of a second cubic phase, phase II, then another two-phase region is observed at x < 0.4, in which phase II coexists with another cubic phase, phase III [42]. Rhodes et al [35] have found that the three phases coexist in a finite range of concentrations. However, the authors did not specify if their measurements were made on ordered or disordered LMN.…”

“…32) from dc-susceptibility measurements [30]. As an alternative approach, the off-stoichiometric material LiNi 0.5 Mn 1.5 O 4−δ has been synthesized in the disordered structure [9,[31][32][33][34][35]. The small voltage plateau at ca.…”

“…4 V for LiNi 0.5 Mn 1.5 O 4−δ is attributed to the Mn 3+ /Mn 4+ couple due to the existence of a small amount of Mn 3+ ions resulting from the charge compensation of oxygen loss. The crystal structure of LiMn 1.5 Ni 0.5 O 4 has been determined by various techniques including XRD [35,36], neutron diffraction [36,37], XAFS [38], XANES [39], ex situ electron diffraction [36], in situ synchrotron X-ray absorption (XAS) [40], Raman scattering spectroscopy [19,25,41], ex situ Fourier transform infrared (FTIR) spectroscopy [25,[41][42][43] and in situ FTIR [44]. Raman and FTIR spectroscopy have been proven to be effective tools in differentiating the ordered versus disordered LNM structures; the sample with cationic ordering is known to exhibit characteristic infrared bands at 650, 465 and 430 cm −1 [43].…”

“…Lithium insertion in The phase evolution during lithium de-intercalation/intercalation within the LNM spinel phase has been studied using both ex situ [69,[102][103][104] and in situ [35,39,42, 105] X-ray diffraction techniques. Conflicting results have been reported.…”