TiO₂-coated LiCoO₂ electrodes fabricated by a sputtering deposition method for lithium-ion batteries with enhanced electrochemical performance

Abstract

We fabricated lithium cobalt oxide (LiCoO 2 , LCO) electrodes in the absence and presence of TiO 2 layers as cathodes for lithium-ion batteries (LIBs) using a sputtering deposition method under an Ar atmosphere. In particular, TiO 2 coating layers on sputtered LCO electrodes were directly deposited in a layer-by-layer form with varying TiO 2 sputtering times from 60 to 120 s. These sputtered electrodes were heated at 600 C in an air atmosphere for 3 h. The thicknesses of TiO 2 layers in TiO 2 -coated LCO electrodes were controlled from $2 to $10 nm. These TiO 2 -coated LCO electrodes exhibited superior electrochemical performance, i.e. high capacities (93-107 mA h g À1 @0.5C), improved retention of >60% after 100 cycles, and high-rate cycling properties (64 mA h g À1 @1C after 100 cycles). Such an improved performance of TiO 2 -coated LCO electrodes was found to be attributed to relieved volumetric expansion of LCO and protection of LCO electrodes against HF generated during cycling.

Enhanced Cycling and Rate Capability by Epitaxially Matched Conductive Cubic TiO Coating on LiCoO2 Cathode Films

“… 50 − 52 In comparison, the commonly used metal oxide coatings (e.g., TiO 2 , Al 2 O 3 ) do not provide such high rate capability due to the close-packed nature of the crystal structures with lower lithium diffusivity. 19 , 48 , 68 , 69 Therefore, the improved electrochemical performance is attributed to the combination of effective stabilization of the Co 3+ state at the LiCoO 2 surface with the optimized pathway through the TiO layer for lithium diffusion, as schematically shown in Figure 7 b. The effect of the TiO coating on the electrochemical performance was investigated by EIS analysis for (104)-oriented LiCoO 2 (LCO) thin-film electrodes with and without a TiO coating in the discharge state after the 1st and 50th charge–discharge cycle at 5 C in 3.5–4.2 V range; see Figure 7 c. The noncoated LCO film exhibits a much higher initial resistance after the 1st cycle as compared to the TiO-coated LCO film, which suggests a reaction between the liquid electrolyte and LiCoO 2 surface leading to the formation of a CEI layer.…”

“…In contrast, the TiO-coated LiCoO 2 films show remarkable enhanced cycling and rate performance (5 C = 2.33 μA h/cm 2 , 10 C = 2.25 μA h/cm 2 , 20 C = 2.10 μA h/cm 2 , and 40 C = 1.95 μA h cm 2 ) as compared to noncoated LiCoO 2 . Although the capacity also decreases with increasing C rate, the overall reduction is rather limited as compared to that in noncoated LiCoO 2 and a significant amount of initial capacity is recovered by final cycling at 2 C. Furthermore, the cubic (100)-oriented TiO layer clearly exhibits good lithium-ion transport behavior, as was expected for the open cubic structure providing a large number of interstitial sites for lithium diffusion. − In comparison, the commonly used metal oxide coatings (e.g., TiO 2 , Al 2 O 3 ) do not provide such high rate capability due to the close-packed nature of the crystal structures with lower lithium diffusivity. ,,, Therefore, the improved electrochemical performance is attributed to the combination of effective stabilization of the Co 3+ state at the LiCoO 2 surface with the optimized pathway through the TiO layer for lithium diffusion, as schematically shown in Figure b. The effect of the TiO coating on the electrochemical performance was investigated by EIS analysis for (104)-oriented LiCoO 2 (LCO) thin-film electrodes with and without a TiO coating in the discharge state after the 1st and 50th charge–discharge cycle at 5 C in 3.5–4.2 V range; see Figure c.…”

Advancing to 4.6 V Review and Prospect in Developing High‐Energy‐Density LiCoO2 Cathode for Lithium‐Ion Batteries

“…Accordingly, a large variety of coating materials which are electrochemically inactive have been used, which typically includes but not limited to metal oxides, metal fluorides, and metal phosphates. For example, Al 2 O 3 has been widely used as coating materials for the surface protection of LCO, [ 97,136–139 ] which was able to improve the cycling performance of the cathode material with much‐reduced electrolyte decomposition as well as the irreversible side reactions. Recently, Zhou et al.…”

Enhanced Interfacial Kinetics and High Rate Performance of LiCoO2 Thin-Film Electrodes by Al Doping and In Situ Al2O3 Coating

“…(4) The crystallographic orientation of the film is controlled to optimize the transport path of lithium ions and electrons. , Dai prepared LiCoO 2 films with different selective orientations using magnetron sputtering, investigated the electrochemical properties of films with different crystalline orientations and found that it is difficult to jointly optimize the capacity and cycling performance of single-phase LiCoO 2 films. (5) Electrode surface interface treatment. − The electrode–electrolyte interface is stabilized by depositing a coating layer on the electrode surface to reduce the interface impedance . It was reported that Al 2 O 3 coating can significantly improve the electrochemical performance of LCO films. , Woo et al coated Al 2 O 3 on the surface of a LiCoO 2 positive electrode and found that the Al 2 O 3 coating layer can effectively inhibit the interdiffusion between LiCoO 2 and the solid electrolyte and reduce the increase in interfacial impedance during cycling.…”