Understanding the Stabilizing Effects of Nanoscale Metal Oxide and Li-Metal Oxide Coatings on Lithium-Ion Battery Positive Electrode Materials.

Zahra Ahaliabadeh,Hua Jiang,Jouko Lahtinen,Timo Kankaanpää,Miia Mäntymäki,Kenichiro Mizohata,Tanja Kallio,Ville Miikkulainen,Yao Lide,Seyedabolfazl Mousavihashemi

doi:10.1021/acsami.1c11165

Abstract

Nickel-rich layered oxides, such as LiNi0.6Co0.2Mn0.2O2 (NMC622), are high-capacity electrode materials for lithium-ion batteries. However, this material faces issues, such as poor durability at high cut-off voltages (>4.4 V vs Li/Li+), which mainly originate from an unstable electrode-electrolyte interface. To reduce the side reactions at the interfacial zone and increase the structural stability of the NMC622 materials, nanoscale (<5 nm) coatings of TiOx (TO) and LixTiyOz (LTO) were deposited over NMC622 composite electrodes using atomic layer deposition. It was found that these coatings provided a protective surface and also reinforced the electrode structure. Under high-voltage range (3.0-4.6 V) cycling, the coatings enhance the NMC electrochemical behavior, enabling longer cycle life and higher capacity. Cyclic voltammetry, X-ray photoelectron spectroscopy, and X-ray diffraction analyses of the coated NMC electrodes suggest that the enhanced electrochemical performance originates from reduced side reactions. In situ dilatometry analysis shows reversible volume change for NMC-LTO during the cycling. It revealed that the dilation behavior of the electrode, resulting in crack formation and consequent particle degradation, is significantly suppressed for the coated sample. The ability of the coatings to mitigate the electrode degradation mechanisms, illustrated in this report, provides insight into a method to enhance the performance of Ni-rich positive electrode materials under high-voltage ranges.

Highlights

Today, lithium-ion batteries (LIBs) play an important role in the mobile energy sectors such as transportation and portable electronics
To confirm the successful coating on the electrodes, Transmission electron microscopy (TEM) images were taken from nickel manganese cobalt oxides [LiNixCoyMnzO2 (NMC)-TO and NMC-LTO
An approximately 2−3 nm layer of LTO was deposited on the NMC electrode, which is in agreement with the preliminary X-ray reflectivity (XRR) analysis of coatings on Si wafers (Figure S1a), showing a thickness below 5 nm

Summary

INTRODUCTION

Lithium-ion batteries (LIBs) play an important role in the mobile energy sectors such as transportation and portable electronics. The ALD technique can provide highly conformal and uniform nanoscale coatings at the entire surface of the underlying substrate and can be used as an effective method for electrode modification.[22] As a surface-reactionlimited method, the ALD coating can result in covering all electrode material surfaces leading to fewer issues with the electrode interface and improving battery performance.[11] Different coating materials including metal oxides, metal fluorides, metal phosphates, and metal hydroxides have been studied as coating materials by ALD.[11,21,23] these coatings frequently provide poor ionic and electronic conductivities, which can lead to capacity fading and increase cell polarization and resistance during cycling.[23] Introducing lithium-containing coating materials, with ideally a high Li-ion conductivity, can mitigate these issues.[19] For example, Li2ZrO3,24 LiAlO2,21 and LiAlF423 have been used as coatings on Ni-rich electrode materials. In addition to electrochemical analyses, post-mortem and volume change analyses were done to elucidate the reasons for the enhancement of the NMC cycling stability caused by the surface coating

EXPERIMENTAL SECTION

RESULTS AND DISCUSSION

CONCLUSIONS

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