Finding a Needle in the Haystack: Identification of Functionally Important Minority Phases in an Operating Battery

Abstract

The in-depth understanding of the minority phases' roles in functional materials, e.g., batteries, is critical for optimizing the system performance and the operational efficiency. Although the visualization of battery electrode under operating conditions has been demonstrated, the development of advanced data-mining approaches is still needed in order to identify minority phases and to understand their functionalities. The present study uses nanoscale X-ray spectromicroscopy to study a functional LiCoO/Li battery pouch cell. The data-mining approaches developed herein were used to search through over 10 million X-ray absorption spectra that cover more than 100 active cathode particles. Two particles with unanticipated chemical fingerprints were identified and further analyzed, providing direct evidence and valuable insight into the undesired side reactions involving the cation dissolution and precipitation as well as the local overlithiation-caused subparticle domain deactivation. The data-mining approach described in this work is widely applicable to many other structurally complex and chemically heterogeneous systems, in which the secondary/minority phases could critically affect the overall performance of the system, well beyond battery research.

Quantifying redox heterogeneity in single-crystalline LiCoO2 cathode particles

“…voxels at tens of nanometres) (Meirer et al, 2011). Successful applications of this technique can be found in studies of many different cathode materials including many of those that play major roles in today's market, like LiCoO 2 (LCO; Xu et al, 2017;Zhang et al, 2017), LiFePO 4 (Boesenberg et al, 2013;Wang et al, 2016;Hong et al, 2017) and LiNi x Mn y Co (1-x-y) O 2 (Lin et al, 2016;Gent et al, 2016). Meanwhile, in situ/operando spectro X-ray imaging experiments are also carried out to elucidate the cathode materials' response to different reaction driving forces (Xu et al, 2017;Nelson Weker et al, 2017), highlighting the structural and chemical complexity under non-equilibrium conditions.…”

Thermally driven mesoscale chemomechanical interplay in Li0.5Ni0.6Mn0.2Co0.2O2 cathode materials

“…The real-world battery operating conditions could introduce complex local chemical events that are undesired for sustaining battery cycle and safety. Commonly observed local chemical events include but are not limited to local overcharge/overdischarge, 14,15 oxygen release, 16 local structural transformation, 8,17 domain deactivation, 18 transition metal dissolution/precipitation, 6,8,19,20 and dendrite/whisker/protrusion growth. 21,22 The local regions that undergo these undesired chemical reactions may not account for much of the total mass or volume of the battery materials, but they can significantly impact the deliverable energy through impedance growth as well as undermine the safety characteristics of the battery cells through thermal runaway.…”

Probing the reversibility and kinetics of Li+ during SEI formation and (de)intercalation on edge plane graphite using ion-sensitive scanning electrochemical microscopy

“…2,[4][5][6][7] Materials characterization methods have led to improved understanding of the components and precursors involved in the SEI, 1,2,8,9 on the observation of its reactivity and morphological changes during formation, 10,11 and tracking of the intercalation process. [12][13][14] On the other hand, there are few in situ methods capable of tracking interfacial alkali ions (e.g. Li + ) 15 and the impact of SEI progressive growth on their response.…”

“…Thus, structural heterogeneity may lead to reactive heterogeneity, ultimately affecting local ionic uxes and cycling performance at differentiated sites. 16,17 Several groups have successfully relied on tracking atomic states or phase change to infer Li + movement throughout bulk electrode materials, 13,14,18,19 but the extension of this analysis to the SEI is not easily attainable due to its thickness (typically <100 nm), variable molecular content, and amorphous nature. 1 Ultimately, direct and localized quantication of Li + is desirable to provide key insight into ion intercalation kinetics, the ion diffusion mechanism through the SEI, localized heterogeneities, and SEI dynamics during charge/discharge.…”