Utilizing the Intrinsic Thermal Instability of Swedenborgite Structured YBaCo4O7+δ as an Opportunity for Material Engineering in Lithium-Ion Batteries by Er and Ga Co-Doping Processes.

Sanghyuk Park,Kwangho Park,Jun-Young Park,Gyeongbin Ko,Wooseok Kim,Ji-Seop Shin,Kyungjung Kwon

doi:10.3390/ma14164565

Abstract

We firstly introduce Er and Ga co-doped swedenborgite-structured YBaCo4O7+δ (YBC) as a cathode-active material in lithium-ion batteries (LIBs), aiming at converting the phase instability of YBC at high temperatures into a strategic way of enhancing the structural stability of layered cathode-active materials. Our recent publication reported that Y0.8Er0.2BaCo3.2Ga0.8O7+δ (YEBCG) showed excellent phase stability compared to YBC in a fuel cell operating condition. By contrast, the feasibility of the LiCoO2 (LCO) phase, which is derived from swedenborgite-structured YBC-based materials, as a LIB cathode-active material is investigated and the effects of co-doping with the Er and Ga ions on the structural and electrochemical properties of Li-intercalated YBC are systemically studied. The intrinsic swedenborgite structure of YBC-based materials with tetrahedrally coordinated Co2+/Co3+ are partially transformed into octahedrally coordinated Co3+, resulting in the formation of an LCO layered structure with a space group of R-3m that can work as a Li-ion migration path. Li-intercalated YEBCG (Li[YEBCG]) shows effective suppression of structural phase transition during cycling, leading to the enhancement of LIB performance in Coulombic efficiency, capacity retention, and rate capability. The galvanostatic intermittent titration technique, cyclic voltammetry and electrochemical impedance spectroscopy are performed to elucidate the enhanced phase stability of Li[YEBCG].

Highlights

Recent research for cathode-active materials in the field of lithium-ion batteries (LIBs) pursues high energy density with a long cycle life, which has been triggered by the worldwide growth of the electric vehicle (EV) market
We synthesized Er and Ga co-doped swedenborgite-structured YBC, which was utilized as a cathode-active material to investigate the potential enhancement of phase stability
The peak intensity of secondary phases in the X-ray diffraction (XRD) patterns was mitigated in the case of Li[YEBCG], indicating the better structural stability at the oxidative high temperature compared with Li[YBC]

Summary

Introduction

Recent research for cathode-active materials in the field of lithium-ion batteries (LIBs) pursues high energy density with a long cycle life, which has been triggered by the worldwide growth of the electric vehicle (EV) market. Many researchers have made a variety of efforts to find new dopants or surface coating compounds to suppress the severe structural degradation of Ni-rich layered cathode active materials during cycling, notwithstanding the role of Mn and Al species for structural stabilization in NMC and NCA, respectively [3,4,5,6,7,8,9,10,11,12,13,14] This is mainly due to a specific phase transition region from H2 to H3 at around 4.2 V vs Li/Li+, which leads to abrupt lattice contraction causing particle pulverization induced by microcracks [15,16]. The Li-intercalated YBC and YEBCG oxides are referred to as Li[YBC] and Li[YEBCG], respectively

Electrochemical Analysis

Results and Discussion

Conclusions