title: Atomistic Conversion Reaction Mechanism of WO3 in Secondary Ion Batteries of Li, Na, and Ca.
abstract: Intercalation and conversion are two fundamental chemical processes for battery materials in response to ion insertion. The interplay between these two chemical processes has never been directly seen and understood at atomic scale. Here, using in situ HRTEM, we captured the atomistic conversion reaction processes during Li, Na, Ca insertion into a WO3 single crystal model electrode. An intercalation step prior to conversion is explicitly revealed at atomic scale for the first time for Li, Na, Ca. Nanoscale diffraction and ab initio molecular dynamic simulations revealed that after intercalation, the inserted ion-oxygen bond formation destabilizes the transition-metal framework which gradually shrinks, distorts and finally collapses to an amorphous W and Mx O (M=Li, Na, Ca) composite structure. This study provides a full atomistic picture of the transition from intercalation to conversion, which is of essential importance for both secondary ion batteries and electrochromic devices.
authors.affiliation: Department of Mechanical Engineering and Materials Science, University of Pittsburgh, Pittsburgh, PA, 15261, USA.
authors.forename: Yang
authors.initials: Y
authors.lastname: He
authors.affiliation: Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, WA, 99352, USA.
authors.forename: Meng
authors.initials: M
authors.lastname: Gu
authors.affiliation: School of Physical Electronics, University of Electronic Science and Technology of China, Chengdu, 610054, China.
authors.forename: Haiyan
authors.initials: H
authors.lastname: Xiao
authors.affiliation: Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, WA, 99352, USA.
authors.forename: Langli
authors.initials: L
authors.lastname: Luo
authors.affiliation: Energy and Environmental Directorate, Pacific Northwest National Laboratory, Richland, WA, 99352, USA.
authors.forename: Yuyan
authors.initials: Y
authors.lastname: Shao
authors.affiliation: Department of Nuclear Engineering and Radiological Sciences, University of Michigan, Ann Arbor, MI, 48109, USA. gaofeium@umich.edu.
authors.forename: Fei
authors.initials: F
authors.lastname: Gao
authors.affiliation: Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, WA, 99352, USA. yingge.du@pnnl.gov.
authors.forename: Yingge
authors.initials: Y
authors.lastname: Du
authors.affiliation: Department of Mechanical Engineering and Materials Science, University of Pittsburgh, Pittsburgh, PA, 15261, USA. sxm2@pitt.edu.
authors.forename: Scott X
authors.initials: SX
authors.lastname: Mao
authors.affiliation: Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, WA, 99352, USA. chongmin.wang@pnnl.gov.
authors.forename: Chongmin
authors.initials: C
authors.lastname: Wang
keywords: WO3; conversion; intercalation; in situ TEM; ion batteries