LiMn 1.5 Ni 0.5 O 4 (LMNO) has a huge potential for use as a cathode material in electric vehicular applications. However, it could face discharge capacity degradation with cycling at elevated temperatures due to attacks by hydrofluoric acid (HF) from the electrolyte, which could cause cationic dissolution. To overcome this barrier, we coated 3-5 micron sized LMNO particles with a ∼3 nm optimally thick and conductive CeO 2 film prepared by atomic layer deposition (ALD). This provided optimal thickness for mass transfer resistance, species protection, and mitigation of cationic dissolution at elevated temperatures. After 1,000 cycles of chargedischarge between 3.5 V-5 V (vs. Li + /Li) at 55 • C, the optimally coated sample, 50Ce (50 cycles of CeO 2 ALD coated) had a capacity retention of ∼97.4%, when tested at a 1C rate, and a capacity retention of ∼83% at a 2C rate. This was compared to uncoated LMNO particles that had a capacity retention of only ∼82.7% at a 1C rate, and a capacity retention of ∼40.8% at a 2C rate. Lithium ion batteries have emerged as potential candidates for replacement of Ni-Cd batteries in electric vehicles because of their high intrinsic energy densities combined with their ease of portability. This potential creates a need for the development of new or modified cathode and anode materials that possess high energy density, long cycle life, excellent capacity retention, and a large voltage window for operation. For electric vehicles, in particular, the upper voltage cutoff window on the cathode side should be ∼5 V vs. Li + /Li. Lithium manganese nickel oxide LiMn 1.5 Ni 0.5 O 4 (LMNO) has emerged in the research community as a potential cathode material for use in electric vehicles due to its large theoretical capacity of ∼148 mAhg −1 , a high working voltage of ∼4.7 V vs. Li + /Li, and a high energy density.
1,2However, LMNO suffers from high capacity fade during performance at elevated temperatures because Mn dissolves due to generation of hydrofluoric acid (HF) in the electrolyte.
3-5The coating of surface protective layers on pristine LMNO particles has been extensively studied in literature. [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] These layers provide a shield from the HF, and prevent rapid capacity fade, leading to improved cycling performance and capacity retention. Of the different surface coating techniques, atomic layer deposition (ALD) has inherent advantages that provide conformal, pin-hole free, size-tunable ultrathin films 21 and, thus, provide high capacity retention and a long life cycle. The ALD process involves a sequence of self-limiting reactions that result in a coating of one monolayer at a time. This enables size tunability at the sub-nanometer level and promotes conformity in the films. Materials like Al 2 O 3 , 17 MgF 2 , 22 TiO 2 , 18 and LiAlO 2 10 have been studied as coating materials prepared by ALD on LMNO. Even though, these materials have provided effective mitigation of cationic dissolution, the ionic conductivity of such protective layers ...
