Microstructure Of LiNi0 Research Articles

Study of the Impact of Microstructure on the Effective Electrical Properties of Composite Electrodes for Lithium-Ion Batteries; Acquisition Andsimulations on Real Microstructures

Better understanding of how the microstructure of composite electrodes affect their electrochemical performance is still required to achieve Lithium ion batteries of higher energy and power densities [1]. Novel opportunity for progressing in this direction and explore relationships between composite electrode microstructure and electrochemical performance is implementation of X-ray computed tomography (XRCT) and focused ion beam in combination with scanning electron microscopy (FIB-SEM) techniques [2]. Sophisticated characterization techniques such as broadband dielectric spectroscopy (BDS) [3] and/or Pulsed Field Gradient Spin - Echo NMR (PFG-SE NMR) [4] can also be used to measure transport properties and relate them to the composite electrode microstructure. Finally, numerical simulations performed on 3D volumes acquired by XRCT or FIB/SEM is a powerful tool to calculate effective transport properties and finely analyze the impact of the composite electrode microstructure [5].In this work, the microstructure of LiNi0.5Mn0.3Co0.2O2 (hereafter called NMC532)-based positive composite electrodes designed for EV applications were deeply investigated in relationship with their electrical properties.The composite electrode microstructures were acquired numerically in 3D at different scales by X-ray tomography and FIB-SEM tomography. Image analysis tools were developed to extract specific textural parameters (e.g. distribution and percolation of the carbon/binder mixture, type and tortuosity of the porosity, contact area of the active material with these other phases) to assess the electronic and ionic conductivities at different locations and spatial scales. In complement, 3D-resolved simulations with the Fast Fourier Transform (FFT) method were carried out to calculate the effective electronic and ionic conductivities of the composite electrodes and characterize the local current density paths for both type of charges (electrons and ions).From our results, it becomes apparent that it is possible to find a good compromise between the electronic and ionic conductivities that results in improved electrochemical performance by optimizing the microstructure. Acknowledgments Financial funding from the ANR program no. ANR-15-CE05-0001-01 is acknowledged. We also acknowledge the CLYM (Consortium Lyon Saint-Etienne de Microscopie) for the access to the FIB/SEM device used in this study.

Effect of Lithium Silicate Addition on the Microstructure and Crack Formation of LiNi0.8Co0.1Mn0.1O2 Cathode Particles.

The microstructure of LiNi0.8Co0.1Mn0.1O2 cathode materials was controlled by the addition of lithium silicate, and the influence on the cycle performance and the rate capability was investigated. Si was not included within the lattice, but localized at the grain boundaries of the primary particles and the pores inside the secondary particles. The addition of the lithium silicate greatly decreased the density of the pores between the primary particles and improved the density of the secondary particles. The capacity retention was successfully improved for lithium silicate-added LiNi0.8Co0.1Mn0.1O2. When lithium silicate-free LiNi0.8Co0.1Mn0.1O2 was charged to 4.3 V, many cracks were formed along the grain boundaries even in the first cycle, while crack formation was remarkably inhibited for lithium silicate-added LiNi0.8Co0.1Mn0.1O2. Moreover, lithium silicate-added LiNi0.8Co0.1Mn0.1O2 particles were almost free from visible microcracks even after 100 cycles at the discharged state. These results suggest that the lithium silicate reinforces the grain-adhesion at the grain boundaries, inhibiting crack formation and electrolyte decomposition inside the cracks.

Electrochemical Behavior Associated with Microstructure of LiNi0.8Co0.15Al0.05O2 for Lithium-Ion Batteries

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Microstructural Changes in LiNi0.8Co0.15Al0.05O2 Positive Electrode Material during the First Cycle

The microstructure of LiNi0.8Co0.15Al0.05O2 positive electrode material before and after the first cycle was investigated by scanning transmission electron microscopy (STEM) and electron energy loss spectroscopy (EELS). STEM and EELS analysis shows that, before cycling, there are very thin layers of material at grain boundaries that contain a small amount of transition metal ions (particularly Ni) on Li sites. After the first cycle, the thickness of some grain boundary layers increases significantly, accompanied by formation of microcracks at grain boundaries. Also, from the grain interior to the grain boundary, the structure gradually changes from an ordered layer structure (α-NaFeO2-type) to a partially ordered structure and then to a disordered rock-salt structure. We posit that these microstructural changes are primarily responsible for the irreversible capacity during the first cycle.

Pulsed-laser deposited LiNi0.8Co0.15Al0.05O2 thin films for application in microbatteries

Li Ni 0.8 Co 0.15 Al 0.05 O 2 thin films were prepared by pulsed-laser deposition at varying growth conditions. It was found that the growth and microstructure of the films is highly dependent on the target composition, deposition temperature, and the reactive atmosphere during laser ablation. The x-ray diffraction and Raman spectroscopic measurements indicated the high-structural quality of the grown LiNi0.8Co0.15Al0.05O2 thin films. A phase diagram mapping the effect of temperature on the microstructure of LiNi0.8Co0.15Al0.05O2 thin films has been proposed. The measurements of charge-discharge profiles of Li microcells using the LiNi0.8Co0.15Al0.05O2 films grown at 450°C demonstrate their possible applications in microbatteries. A stable capacity of 98μAh∕cm2μm was obtained in the potential range of 4.2–2.5V for LiNi0.8Co0.15Al0.05O2 films grown at 450°C.