(De)Lithiation Mechanism of Hierarchically Layered LiNi1/3Co1/3Mn1/3O2 Cathodes during High-Voltage Cycling

Weibo Hua,Alkesandr Missiul,Helmut Ehrenberg,Suning Wang,Sylvio Indris,Xiaoke Mu,Christian Kübel,Björn Schwarz,Michael Knapp,Anatoliy Senyshyn,Joachim R Binder

doi:10.1149/2.0051903jes

Abstract

In view of the requirements for high-energy lithium ion batteries (LIBs), hierarchically layered LiNi1/3Co1/3Mn1/3O2 (NCM111) cathode materials have been prepared using a hydroxide coprecipitation method and subsequent high-temperature solid-state reaction. The diffraction results show that the synthesized NCM111 has a well-defined layered hexagonal structure. The initial specific discharge capacity of a Li/NCM111 cell is 204.5 mAh g−1 at a current density of 28 mA g−1 between 2.7 and 4.8 V. However, the cell suffers from poor capacity retention over extended charge-discharge cycles. The structural evolution of NCM111 electrode during electrochemical cycling is carefully investigated by in situ high-resolution synchrotron radiation diffraction. It is found that the nanodomain formation of a layered hexagonal phase H3 and a cubic spinel phase after charging to voltages above 4.6 V is the main source for the structural collapse in c direction and the poor cycling performance. This process is accompanied by the removal of oxygen, the transition metal (TM) migration and the crack generation in the nanodomains of the primary particles. These results may help to better understand the structural degradation of layered cathodes in order to develop high energy density LIBs.

Highlights

Results and DiscussionThese secondary particles consist of many ultra-thin nano-plates to form a kind of rose flower hierarchical architecture
The SEM image of NCM111.—The synthesis procedure of LiNi1/3Co1/3Mn1/3O2 (NCM111) demonstrates that the as-prepared final product reveals secondary particles agglomerated from packed primary nanosheets or polyhedra, see Figure 2b
The co-refinements were performed by using a single α-NaFeO2 layered structure model where Li and transition metals (TMs) are mainly located on 3b site and 3a site, respectively, and oxygen is positioned on 6c site

Summary

Results and Discussion

These secondary particles consist of many ultra-thin nano-plates to form a kind of rose flower hierarchical architecture. The structure is refined simultaneously against both data sets, SRD and NPD diffraction data, with a single structural model with constrained structural parameters.[21] simultaneous analysis of SRD and NPD helps to obtain an accurate crystal structure of these Li insertion compounds.

Refinement parameters

Coulombic efficiency

Conclusions