Enhanced High-Rate Cycling Stability of LiMn[sub 2]O[sub 4] Cathode by ZrO[sub 2] Coating for Li-Ion Battery

Abstract

The effect of a sol-gel derived amorphous zirconium oxide surface coating on the high charge-discharge ͑CD͒ rate performance of LiMn 2 O 4 was studied. When cycled between 4.5 and 2.9 V ͑vs. Li/Li + ͒ at room temperature, the coated spinel electrode, containing 5 wt %-ZrO 2 , shows tremendous enhancement in cycling stability at CD rates up to 10 C. Concurrently, the coated spinel electrode exhibits a lower cubic-tetragonal transition potential, a smaller charge-transfer impedance by 4-5-fold, and it profoundly reduces, by 66%, lattice contraction upon charge ͑delithiation͒. The enhancement in the high-rate cycling stability has been attributed to the combination of these favorable effects.Cubic spinel LiMn 2 O 4 is of great interest for the replacement of LiCoO 2 in Li-ion batteries due to its high voltage, natural abundance, low cost, and environmental benignity. 1-3 Particular enthusiasm has been shown to use this material in electric vehicle application owing to its superior safety properties to LiCoO 2 . 4,5 For this application, however, high-rate cycling stability will be one major issue. The discharge ͑lithiation͒ potential signatures in Li x Mn 2 O 4 ͑x ഛ 1͒ include two large plateaus near 4.1 and 4.0 V ͑all the potentials referred to herein are referenced to Li/Li + ͒, 6 which have been suggested 7 to involve transitions among three cubic phases. Insertion of Li for x Ͼ 1 results in another plateau near 2.8 V, corresponding to the transition from cubic LiMn 2 O 4 to tetragonal Li 2 Mn 2 O 4 . The phase transition involves Jahn-Teller distortions, associated with Mn 3+ Jahn-Teller ions. 8 The spinel exhibits faster capacity fading upon charge-discharge ͑CD͒ cycling than LiCoO 2 , and the cubic-tetragonal ͑CT͒ transition, which involves a large ͑ϳ10%͒ unit cell volume variation, has been considered as one important cause to the fading at room temperature ͑RT͒. 9 When a LiMn 2 O 4 electrode is discharged in the practical full-cell operation, the Li concentration gradient is expected to develop throughout the particle, and the Li stoichiometry, x in Li x Mn 2 O 4 , at particle surface may be well above 1.0, even when the average stoichiometry is less than 1.0. This was evidenced by microscopy analysis, which showed the presence of the tetragonal surface layer. 10 The higher the discharge rate is, the more pronounced this surface transition effect is expected to be. Accordingly, the fading rate of the spinel is expected to increase appreciably with CD rate. Capacity fading of the spinel is also increasingly serious with increasing temperature, and it has in part been attributed to the degradation of the spinel by dissolution of Mn ions into the acidic electrolyte. 11,12 Some studies ͑e.g., Ref. 13 and 14͒ showed the substitution of Mn at the 16d sites with ions with a valence ഛ+3 to give doped spinels Li x M y Mn 2−y O 4 ͑M = Ti, Fe, Ni, Co, Zn, Al, and Mg͒, which could enhance the cycling stability at RT. Although this approach has improved the structural stability, it seriously reduces initial capacity. As ...

All-solid-state rechargeable thin film lithium batteries with LixMn2O4 and LixMn2O4–0.5ZrO2 cathodes

“…However, the crystal grain boundary of LMZO thin film is unclear, and smoother surface than LMO thin film is obtained. According to previous report [13], ZrO 2 exits mainly as an amorphous phase below 600 • C. During the annealing process of LMZO thin film, amorphous ZrO 2 is facilitated to enter into the interstitial space among LMO crystal grains by the diffusion with each other, and subsequently form the ZrO 2 coating towards LMO. So the ZrO 2 could be well mixed with the LiMn 2 O 4 in LMZO thin film.…”

“…Apparently, unlike as-deposited LMO, LMZO cathode can avoid the crystallization evolution, which should be attributed that the addition of ZrO 2 may substantially weaken the change of free energy in annealed LMZO thin film. In addition, some other groups [11][12][13] have reported that the electrochemical features of amorphous ZrO 2 coating towards LiMn 2 O 4 with tiny concentrations (about 0.04-0.05 wt%). In their works, the tiny addition of ZrO 2 is not enough for effectively changing the typical plateaus of LiMn 2 O 4 .…”

“…The maximum R ct values of LMO and LMZO are reflected at 4 and 3.5 V regions, respectively. Lin et al [13] reported the tiny coating of amorphous ZrO 2 reduced the charge-transfer impedance by 4-5-folds. They considered that this thin coating was expected to act as a Li + conducting solid-electrolyte interphase (SEI) layer, which reduced the oxy- gen activity of electrode surface at high potentials through the formation of strong Zr-O bonds at electrode surface.…”

“…An attempt was made to resolve the adverse influence of two apparent plateaus with 1 V step by the addition of ZrO 2 into LMO electrode. ZrO 2 as electrochemically inactive material has been employed to coat spinel LiMn 2 O 4 in battery systems with liquid electrolytes [11][12][13]. These works mainly focused on the improvement of high-rate and high-temperature electrochemical behavior in 4 V region by tiny ZrO 2 coating.…”

Surface engineering of electrospun fibers to optimize ion and electron transport in Li%2B battery cathodes.

“…4 . Also, the coating helped to reduce the cubic-tetragonal phase transition and improved the stability of the spinel structure 8 . Figure 1 shows the improved stability of the ZrO 2 coated LiMn 2 O 4 spinel cathode particles at elevated temperature.…”