Combined Neutron Diffraction, NMR, and Electrochemical Investigation of the Layered-to-Spinel Transformation in LiMnO₂

Abstract

The conversion that occurs from layered LiMnO2 to spinel on electrochemical cycling has been studied by neutron diffraction and NMR. Neutron diffraction results indicate that the tetrahedral sites in the Li layers that share faces with octahedral sites in the transition metal layers are occupied even following the first charge to 4.6 V. NMR results are consistent with the conversion from the monoclinic, Jahn−Teller distorted, to the rhombohedral, layered phase on charging. On subsequent discharging, clear evidence for the monoclinic phase is seen by NMR indicating the presence of Jahn−Teller distorted domains in the material at 3.5 V and below. The fraction of monoclinic phase decreases gradually as a function of cycle number and disappears by 35 charge−discharge cycles. Diffraction patterns obtained as a function of cycle number were refined with a structural model that included both a layered phase (with octahedral and tetrahedral site occupancy) and a spinel phase, with the fraction of spinel increasing from 0.12 (5 cycles) to 0.93 following 92 cycles. Both diffraction and NMR results indicate that the spinel phase that nucleates from the layered material is stoichiometric and does not contain Li occupancy on the Mn sites. An additional site is seen by NMR which reaches a maximum in cycles 25−50, which is assigned to tetrahedrally coordinated Li in a local environment intermediate between that of the spinel and the layered phase. The observation of this site by NMR is associated with two characteristic peaks in the incremental capacity plot at 3.75 and 3.9 V on charge and discharge. The data indicate that the mechanism for Li insertion and removal into these local environments is complex and involves simultaneous structural rearrangements. The intermediate environment decreases in concentration on subsequent cycling as the concentration of the spinel phase continues to grow.

High-rate, high capacity ZrO2 coated Li[Li1/6Mn1/2Co1/6Ni1/6]O2 for lithium secondary batteries

“…Figure 4 also shows the remarkable cyclability of the ZrO 2 -coated powder at a rate of 6 C, indicating that a very high discharge capacity of 115 mAh g -1 is maintained under a high current density for 50 cycles owing to the ZrO 2 coating. An increase in the discharge capacity at a rate of 6 C during the initial cycles is seen; similar trends have been observed in other works on cathode materials with high rate capability [10,11].…”

Review—Recent Advances and Remaining Challenges for Lithium Ion Battery Cathodes

“…15,16,22,64 Moreover, as further transition metals occupy Li-slab sites, Li + intercalation into the transition metal layer sites becomes more difficult, resulting in a preference for Li-layer intercalation, at the lowest voltage redox couple (Figure 2). 15,16,22,64 We present in Figure 3, the individual typical dq/dV plots over prolonged cycling, the discharge capacity calculated from integrating each of the three peaks, and the voltage contribution V Contr of each specific peak. Integration ranges were chosen from local minima between peaks and three different cells were averaged to generate standard deviation values.…”

Study of Cathode Materials for Lithium-Ion Batteries: Recent Progress and New Challenges

“…Important materials for cathodes (or positive electrodes) of LIBs are lithium and manganese-rich layered composites from the xLi 2 MnO 3 ·(1 − x)Li[Ni a Co b Mn c ]O 2 (a + b + c = 1) family that are normally described as comprising two layered structure phases, Li 2 MnO 3 (C/2m space group) and Li[Ni a Co b Mn c ]O 2 (a + b + c = 1) (R3m space group), integrated on the atomic level [5][6][7][8]. These two The TM migration to the Li-layer during later stages of charging, that causes the large charge/discharge voltage hysteresis, is also the main reason for the large capacity fades during the cycling of the Li-and Mn-rich materials [37][38][39][40].…”

“…It is the highest capacity reported until now among the known Li-Mn-O electrode materials. The TM migration to the Li-layer during later stages of charging, that causes the large charge/discharge voltage hysteresis, is also the main reason for the large capacity fades during the cycling of the Li-and Mn-rich materials [37][38][39][40].…”