In Situ Observation of the Insulator-To-Metal Transition and Nonequilibrium Phase Transition for Li1- xCoO2 Films with Preferred (003) Orientation Nanorods

Yue Chen; Qing Yu; Guigui Xu; Guiying Zhao; Jiaxin Li; Zhensheng Hong; Yingbin Lin; Chung-Li Dong; Zhigao Huang

doi:10.1021/acsami.9b11140

In Situ Observation of the Insulator-To-Metal Transition and Nonequilibrium Phase Transition for Li_{1- x}CoO₂ Films with Preferred (003) Orientation Nanorods

ACS Appl Mater Interfaces. 2019 Sep 11;11(36):33043-33053. doi: 10.1021/acsami.9b11140. Epub 2019 Aug 26.

Authors

Yue Chen^{1

2}, Qing Yu^{1

2}, Guigui Xu^{1

2}, Guiying Zhao^{1

3}, Jiaxin Li^{1

3}, Zhensheng Hong^{1

2}, Yingbin Lin^{1

2}, Chung-Li Dong⁴, Zhigao Huang^{1

3}

Affiliations

¹ College of Physics and Energy , Fujian Normal University, Fujian Provincial Key Laboratory of Quantum Manipulation and New Energy Materials , Fuzhou 350117 , China.
² Fujian Provincial Engineering Technical Research Centre of Solar-Energy Conversion and Stored Energy , Fuzhou 350117 , China.
³ Fujian Provincial Collaborative Innovation Center for Optoelectronic Semiconductors and Efficient Devices , Xiamen 361005 , China.
⁴ Department of Physics , Tamkang University , 151 Yingzhuan Road , Tamsui 25137 , Taiwan.

PMID: 31419106
DOI: 10.1021/acsami.9b11140

Abstract

It is notoriously difficult to distinguish the stoichiometric LiCoO₂ (LCO) with a O3-I structure from its lithium defective O3-II phase because of their similar crystal symmetry. Interestingly, moreover, the O3-II phase shows metallic conductivity, whereas the O3-I phase is an electronic insulator. How to effectively reveal the intrinsic mechanism of the conductivity difference and nonequilibrium phase transition induced by the lithium deintercalation is of vital importance for its practical application and development. Based on the developed technology of in situ peak force tunneling atomic force microscopy (PF-TUNA) in liquids, the phase transition from O3-I to O3-II and consequent insulator-to-metal transition of LCO thin-film electrodes with preferred (003) orientation nanorods designed and prepared via magnetron sputtering were observed under an organic electrolyte for the first time in this work. Then, studying the post-mortem LCO thin-film electrode by using ex situ time-dependent XRD and conductive atomic force microscopy, we find the phase relaxation of LCO electrodes after the nonequilibrium deintercalation, further proving the differences of the electronic conductivity and work function between the O3-I and O3-II phases. Moreover, X-ray absorption spectroscopy results indicate that the oxidation of Co ions and the increasing of O 2p-Co 3d hybridization in the O3-II phase lead to electrical conductivity improvement in Li_1-xCoO₂. Simultaneously, it is found that the nonequilibrium deintercalation at a high charging rate can result in phase-transition hysteresis and the O3-I/O3-II coexistence at the charging end, which is explained well by an ionic blockade model with an antiphase boundary. At last, this work strongly suggests that PF-TUNA can be used to reveal the unconventional phenomena on the solid/liquid interfaces.

Keywords: LiCoO thin-film electrode; X-ray absorption spectroscopy; in situ peak force tunneling AFM; lithium batteries; nonequilibrium phase transition.