Understanding the Rate Capability of High‐Energy‐Density Li‐Rich Layered Li_1.2Ni_0.15Co_0.1Mn_0.55O₂ Cathode Materials

Abstract

The high‐energy‐density, Li‐rich layered materials, i.e., xLiMO2(1‐x)Li2MnO3, are promising candidate cathode materials for electric energy storage in plug‐in hybrid electric vehicles (PHEVs) and electric vehicles (EVs). The relatively low rate capability is one of the major problems that need to be resolved for these materials. To gain insight into the key factors that limit the rate capability, in situ X‐ray absorption spectroscopy (XAS) and X‐ray diffraction (XRD) studies of the cathode material, Li1.2Ni0.15Co0.1Mn0.55O2 [0.5Li(Ni0.375Co0.25 Mn0.375)O2·0.5Li2MnO3], are carried out. The partial capacity contributed by different structural components and transition metal elements is elucidated and correlated with local structure changes. The characteristic reaction kinetics for each element are identified using a novel time‐resolved XAS technique. Direct experimental evidence is obtained showing that Mn sites have much poorer reaction kinetics both before and after the initial activation of Li2MnO3, compared to Ni and Co. These results indicate that Li2MnO3 may be the key component that limits the rate capability of Li‐rich layered materials and provide guidance for designing Li‐rich layered materials with the desired balance of energy density and rate capability for different applications.

Review—Recent Advances and Remaining Challenges for Lithium Ion Battery Cathodes

“…14,36 This model is supported by XRD, electron diffraction, high-angle annular dark-field (HAADF) STEM images and X-ray absorption spectroscopy (Figure 1). 14,36,37 The C2/m phase introduces a tilt to the R3m phase, lowering the crystal symmetry, with new peaks arising indicated in Figure 1A. For Figures 1-4, data from our groups is of 0.…”

“…1,2,6 Li-rich materials have a layered structure, described by some groups as either a single phase solid solution, [26][27][28][32][33][34] or a composite of two phases, the rhombohedral R3m phase Li(TM)O 2 and an additional monoclinic C2/m phase, Li 2 MnO 3 . 3,14,35 There is mounting evidence however for the composite phase, with the Li(TM)O 2 and Li 2 MnO 3 phases intimately integrated and interconnected on a nano-scale. 14,36 This model is supported by XRD, electron diffraction, high-angle annular dark-field (HAADF) STEM images and X-ray absorption spectroscopy (Figure 1).…”

“…3,14,35 There is mounting evidence however for the composite phase, with the Li(TM)O 2 and Li 2 MnO 3 phases intimately integrated and interconnected on a nano-scale. 14,36 This model is supported by XRD, electron diffraction, high-angle annular dark-field (HAADF) STEM images and X-ray absorption spectroscopy (Figure 1). 14,36,37 The C2/m phase introduces a tilt to the R3m phase, lowering the crystal symmetry, with new peaks arising indicated in Figure 1A.…”

“…250 mAh/g, and the lower cost of Mn than Co or even Ni, lithium and manganese rich, (Li-rich) xLi 2 MnO 3 ·(1-x)LiNi a Co b Mn c O 2 materials are considered as likely candidates for the next generation of cathodes following Ni-rich materials (discussed in the preceding review of this issue). [1][2][3][4][5][6][7] The mechanism behind such a high, reversible capacity is still under intense investigation, [8][9][10] as well as many other aspects such as the nature of the materials' activation, [11][12][13][14] the large voltage hysteresis after activation, [15][16][17][18] redox couple designations, 14,19,20 and the nature of fading mechanisms during cycling. 16,[21][22][23][24][25] Even something as basic as the structure of the pristine material remains the subject debate.…”

Ti-substituted tunnel-type Na0.44MnO2 oxide as a negative electrode for aqueous sodium-ion batteries

“…In situ and ex situ hard XAS experiments were performed at beamline X18A of the National Synchrotron Light Source in Brookhaven National Laboratory (NSLS, BNL) in transmission mode with a Si (111) double-crystal monochromator detuned to the 35-50% value of its original maximum intensity to eliminate the higher-order harmonics. Detailed in situ experimental configurations are reported in our previous paper 49 . The reference spectrum of each element was simultaneously collected with the corresponding spectrum of the in situ cells by using a reference metal foil.…”