Theoretical study of cubic-Li 7 La 3 Zr 2 O 12 (001)/LiCoO 2 (10-14) interface
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Research Letter
Theoretical study of cubic-Li7La3Zr2O12(001)/LiCoO2(10–14) interface Sara Panahian Jand and Payam Kaghazchi, Institut für Chemie und Biochemie, Freie Universität Berlin, Takustr. 3, 14195 Berlin, Germany Address all correspondence to Payam Kaghazchi at [email protected] (Received 2 November 2017; accepted 23 February 2018)
Abstract In this work, using density functional theory we study electronic and atomic structure as well as redistribution of ions at the interface between cubic-Li7La3Zr2O12 (LLZO) (001) and LiCoO2 (LCO) (10–14). It is found that a large lattice-mismatch-induced compressive strain of ∼12% at the interface leads to disordering of LLZO (001). However, even a large tensile strain of ∼13.5% does not influence ordering of LCO (10–14). Li ions tend to move from the surface of LCO and bulk LLZO to occupy the interstitial sites at the topmost layers of the LLZO slab. Li ion transfer from LCO to LLZO accompanies with electron transfer from the former to the latter and the formation of gap states.
Introduction Solid electrolytes are promising candidates to replace conventional liquid electrolytes in energy storages. They can suppress formation of dendrite in Li- or Na-ion batteries[1,2] and hinder the shuttle effect (migration of soluble Li polysulfide from the cathode to anode) in Li–S batteries.[3,4] Over the past years, lithium garnet oxide conductors have attracted an increasing interest as solid electrolytes due to their high Li ion conductivities as well as stabilities.[5–7] Cubic-Li7La3Zr2O12 (hereafter called LLZO) which has been synthesized for the first time by Murugan et al.[8] has a lithium ionic conductivity of ∼10−4 Scm−1 at room temperature.[9–12] In addition, LLZO has a relatively high stability against metallic lithium.[13–15] Thus, LLZO is one of the most promising electrolyte materials in energy research. On the other hand, LiCoO2 (LCO) with a theoretical capacity of about 274 mA h g−1 is widely used as a cathode material in Li-based batteries.[16–19] LCO is an oxide-based lithium intercalation compound, and it has been the subject of extensive studies owing to its high-volume energy density and excellent cycle life.[16,20] Therefore, many experimental studies have been carried out to construct a Li-based battery with LLZO as the solid electrolyte, LCO as the cathode, and Li as the anode material. In spite of a relatively high Li conductivity of LLZO, batteries constructed from these garnet materials have not been commercialized yet. Many experimental studies have reported a high interfacial resistance between LLZO and electrode materials.[21,22] Using transmission electron microscopy (TEM) and energy dispersive x-ray spectroscopy, Kim et al.[23] have found a strong interaction at the interface between LLZO and LCO during the high-temperature process of LCO coating on LLZO. Cation interchange and/or formation of new phases such as La2CoO4 have been reported.[23] Furthermore, in x-ray diffraction patterns and TEM images, Park et al.[24] have observed
cation inte
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