Multiscale and hierarchical reaction mechanism in a lithium-ion battery

Yuki Orikasa,Yoshiharu Uchimoto,Takeshi Shimizu,Kentaro Yamamoto

doi:10.1063/5.0062329

Yuki Orikasa, Yoshiharu Uchimoto + Show 2 more

Open Access

https://doi.org/10.1063/5.0062329

Copy DOI

Abstract

The key to improving the performance of lithium-ion batteries is to precisely elucidate the temporal and spatial hierarchical structure of the battery. Lithium-ion batteries consist of cathodes and anodes and a separator containing an electrolyte. The cathodes and anodes of lithium-ion batteries are made of a composite material consisting of an active material, a conductive material, and a binder to form a complex three-dimensional structure. The reaction proceeds as lithium ions are repeatedly inserted into and removed from the active material. Therefore, the lattice of the active material is restructured due to ion diffusion, which results in phase change. At the active material–electrolyte interface, the insertion and de-insertion of lithium ions proceed with the charge transfer reaction. The charge–discharge reaction of a lithium-ion battery is a nonequilibrium state due to the interplay of multiple phenomena. Analysis after disassembling a battery, which is performed in conventional battery research, does not provide an accurate understanding of the dominant factors of the reaction rate and the degradation mechanism, in some cases. This review introduces the results of research on the temporal and spatial hierarchical structure of lithium-ion batteries, focusing on operando measurements taken during charge–discharge reactions. Chapter 1 provides an overview of the hierarchical reaction mechanism of lithium-ion batteries. Chapter 2 introduces the operando measurement technique, which is useful for analysis. Chapter 3 describes the reaction at the electrode–electrolyte interface, which is the reaction field, and Chapter 4 discusses the nonequilibrium structural change caused by the two-phase reaction in the active material. Chapter 5 introduces the study of the unique reaction heterogeneity of a composite electrode, which enables practical energy storage. Understanding the hierarchical reaction mechanism will provide useful information for the design of lithium-ion batteries and next-generation batteries.

Highlights

A lithium-ion battery is an energy storage system in which lithium ions shuttle electrolytes between a cathode and an anode via a separator (Fig. 1)
This review introduces the results of research on the temporal and spatial hierarchical structure of lithium-ion batteries, focusing on operando measurements taken during charge–discharge reactions
The coating stabilizes the defective crystal structure by inserting the solid solution of Mg2þ in MgO into the Li2O layer of LiCoO2.88 According to the operando total reflection fluorescence x-ray absorption near edge structure (XANES) analysis of the model interface with a MgO surface coating on a LiCoO2 thin film electrode, the interfacial layer formed by contact with the electrolyte solution observed with bare LiCoO2 does not form at the interface of MgOcoated LiCoO2.89,90 To observe the local structure change at the LiCoO2 surface, depth-resolved x-ray absorption spectroscopy (XAS) was carried out, showing that the formation of a solid–solution layer stabilizes the LiCoO2 surface.[89]

Summary

METHOD FOR OPERANDO X-RAY MEASUREMENT DURING CHARGE–DISCHARGE

This section explains the operando XAS setup using a laminatedtype battery cell to obtain XAFS results during the operation of a lithium-ion battery. Cathode materials with a high capacity using anion redox have been devised, and interesting charge–discharge properties have been reported in which only valence changes of transition metals cannot be explained.[29,30,31,32,33] It is important to clarify the electronic structure changes of active materials, especially the electronic structure change of anions such as oxide ions, for the material design of nextgeneration high-capacity cathode materials.[34,35] Oishi et al performed an electronic structure analysis of Li2MnO3 and Li-excess layer oxides using XANES in the soft x-ray range, showing that an oxide ion contributes to charge compensation at high potential.[36,37,38] Yabuuchi et al used the O K-edge XANES to investigate the “superoxide states” of cathode materials Li1.3Nb0.3Mn0.4O2 and Li1.2Ti0.4Mn0.4O2, which differ from conventional materials in their charge process.[33,39] These XAS measurements were performed using samples after cell disassembly and washing without air exposure.

ELECTRODE–ELECTROLYTE INTERFACE

CRYSTAL AND ELECTRONIC STRUCTURE CHANGES OF ELECTRODE ACTIVE MATERIALS

REACTION INHOMOGENEITY WITHIN A COMPOSITE ELECTRODE

Findings

SUMMARY