The phase transition, charge compensation, and local chemical environment of Ni in LiNiO2 were investigated to understand the degradation mechanism. The electrode was subjected to a variety of bulk and surface-sensitive characterization techniques under different charge-discharge cycling conditions. We observed the phase transition from the original hexagonal H1 phase to another two hexagonal phases (H2 and H3) upon Li deintercalation. Moreover, the gradual loss of H3-phase features was revealed during the repeated charges. The reduction in Ni redox activity occurred at both the charge and the discharge states, and it appeared both in the bulk and at the surface over the extended cycles. The degradation of crystal structure significantly contributes to the reduction of Ni redox activity, which in turn causes the cycling performance decay of LiNiO2.

Understanding the Degradation Mechanism of Lithium Nickel Oxide Cathode for Li-Ion Batteries

The layered LiNi1∕3Co1∕3Mn1∕3O2 system has recently drawn considerable interest for use as a cathode material for rechargeable lithium batteries. In order to investigate the charge-compensation mechanism and structural perturbations occurring in the system during cycling, in situ x-ray absorption spectroscopy (XAS) measurements were performed utilizing a novel electrochemical in situ cell specifically designed for long term x-ray experiments. The cell was cycled at a moderate rate through a typical Li-ion battery operating voltage range (2.9–4.7 V). The electrode contained 2.025 mg of LiNi1∕3Co1∕3Mn1∕3O2 on a 25-μm Al foil and had an area of 0.79cm2. The x-ray absorption spectroscopy (XAS) measurements were performed at the Ni, Co, and the Mn edges at different states of charge (SOC) during cycling, revealing details about the response of the cathode to Li insertion and extraction processes. Changes of bond distance and coordination number of Ni, Co, and Mn absorbers as a function of the state of charge o...

In Situ x-ray absorption spectroscopic study of theLi[Ni1/3CO1/3Mn1/3]O2 cathode material

Funding Information: This work made use of the Aalto University Otanano and RAMI infrastructures. The authors also thank Dr. Hannu Revitzer for performing AAS measurements. Financial support from Business Finland BATCircle (Energy) (no. 2117574) is also greatly acknowledged. Publisher Copyright: © 2021 The Authors. Published by American Chemical Society.

Understanding the Stabilizing Effects of Nanoscale Metal Oxide and Li-Metal Oxide Coatings on Lithium-Ion Battery Positive Electrode Materials

LiNi₀.₆Mn₀.₂Co₀.₂O₂ (NMC622) is one of the most promising Li-ion battery cathodes as it delivers high capacity at high potentials. However, high potentials also lead to decreases in capacity retention where the disintegration of the secondary particles has been implicated as a major driving force of this capacity fade. This has been attributed to anisotropic lattice changes and increased microstrain during cycling. To probe how these factors affect capacity fade, Li/NMC622 batteries were cycled from 3 to 4.3 or 4.7 V and probed with operando X-ray diffraction (XRD) over the 1st, 2nd, and 101st cycles. Further characterization with scanning electron microscopy and inductively coupled plasma-optical emission spectroscopy was also performed. The use of operando XRD over many cycles allowed for the collection of detailed structural information in real time over a time frame in which fading can be observed. During the first two cycles, the cells charged to 4.7 V exhibit increased anisotropic lattice changes as compared to the cells charged to 4.3 V. Upon the 101st cycle, when significant fade has been observed, the cells charged to 4.3 and 4.7 V show identical lattice changes to one another, while the 4.7 V charge limit induces more microstrain. This shows that elevated microstrain at high charge limits is a major driver for particle disintegration in NMC622 cathodes. This study provides important insights into the mechanisms of particle disintegration and capacity fade in NMC/Li-ion batteries, which will enable the design of NMC electrodes that deliver both higher capacities and exhibit better capacity retention.

Probing Sources of Capacity Fade in LiNi₀.₆Mn₀.₂Co₀.₂O₂ (NMC622): An Operando XRD Study of Li/NMC622 Batteries during Extended Cycling

http://manuscript.elsevier.com/S240582972200201X/pdf/S240582972200201X.pdf

Synchrotron-based X-ray Diffraction and Absorption Spectroscopy Studies on Layered LiNixMnyCozO2 Cathode Materials: A Review

Ni-rich NMC materials are a particularly promising class of Li-ion cathodes for various applications. LiNi0.6Mn0.2Co0.2O2 (NMC622) offers a unique balance of thermal stability and energy density, t...

Nickel-rich Nickel Manganese Cobalt (NMC622) Cathode Lithiation Mechanism and Extended Cycling Effects Using Operando X-ray Absorption Spectroscopy

Electron transfer and ion transport occurs over multiple-length scales ranging from the atomic to mesoscale within battery materials and electrodes. Micro-X-ray fluorescence (µ-XRF) is an important characterization tool as it can resolve structural, compositional, and redox information while providing insight into the spatial distribution of an electroactive material. In this work, µ-XRF mapping is used to probe the distribution of iron within thin planar slurry-based and thick porous carbon nanotube (CNT)-based magnetite (Fe3O4) electrodes. Notably, the porous CNT-based electrode showed homogenous distribution of Fe within the electrode whereas the planar electrode demonstrated distinct Fe aggregates. This information was used to rationalize the electrochemistry observed by cyclic voltammetry and galvanostatic cycling. The thick porous electrode delivered 215% more capacity per gram of magnetite during the first discharge, consistent with increased electrode homogeneity enabling effective ion access and electron transfer.

Christopher J. Kern

Papers

Nickel-rich Nickel Manganese Cobalt (NMC622) Cathode Lithiation Mechanism and Extended Cycling Effects Using Operando X-ray Absorption Spectroscopy

X-ray fluorescence mapping: Insights into mesoscale structure impact on battery functional electrochemistry