Lithium Insertion/Removal Mechanism of LiCoVO[sub 4] in Lithium-Ion Cells

Abstract

The first charge and discharge reaction of LiCoVO 4 with a spinel structure as an anode material for a Li-ion battery was investigated. LiCoVO 4 showed a much larger reversible capacity, about 685 Ah kg Ϫ1 , compared with a commercially available graphite anode. From the X-ray diffraction measurement, the spinel structure of LiCoVO 4 where V ions reside in a tetrahedral site initially changed to an atacamite-type structure where V ions occupied an octahedral site and finally showed irreversible deformation to an amorphous structure during the first Li insertion/removal reaction. The results of X-ray absorption spectroscopy analysis revealed that the oxidation state and the coordination environmental structure of V ions varied reversibly in the first cycle process.Development of oxide anodes is vital for improving the performance of Li-ion secondary batteries due to their chemical stability and large capacity. 1-7 Recently, vanadium-based oxides 8-13 have received increasing attention, because vanadium is known to have a wide range of oxidation states that directly relate to large capacity. However, despite its large capacity, these anodes suffer from relatively large irreversible capacity during the first charge-discharge cycle. Therefore fundamental studies, especially on the changes of crystal structure and oxidation state during the first charge-discharge cycle, are necessary to overcome such a problem. Two techniques are useful for the investigation of crystal structure and oxidation state of solid-state materials. One is X-ray diffraction ͑XRD͒ analysis which provides long-range-order structural information. For example, it was revealed by XRD that vanadium-based crystalline compounds like RVO 4 (R ϭ In,Cr,Fe,Al,Y) 12 and MnV 2 O 6 8 irreversibly transformed to an amorphous structure during the first Li insertion. The other technique is X-ray absorption spectroscopy ͑XAS͒ analysis which provides oxidation state and short-rangeorder structure. Rossignol et al. reported the Li insertion/removal mechanism of LiNiVO 4 as an anode material investigated by XAS analysis. 14 In our previous papers, the charge-discharge properties of both MnV 2 O 6 15 with brannerite structure and Mo-doped brannerite, Mn 0.6 Mo 0.8 V 1.2 O 6 16 were discussed in view of the variation of oxidation state and local environmental structure of transition metal using XRD and XAS.In this paper, we focus on the spinel LiCoVO 4 with cation distribution ͓V͔ 8a ͓LiCo] 16d O 4 ͑subscripts 8a and 16d indicate the cation site of Fd3m symmetry͒ to clarify the reason for such behavior as irreversible capacity. The changes of long-range-order structure, short-range-order structure, and oxidation states of each metal were investigated by XRD and XAS techniques, respectively. One advantage of investigating this material is the relative ease of analyzing the structural information, because LiCoVO 4 belongs to high symmetry ͑cubic symmetry͒ and is expected to provide simple features of XRD patterns and/or XAS spectra.The sample LiCoVO 4 was synthesized b...

Metal Oxides and Oxysalts as Anode Materials for Li Ion Batteries

“…Subsequently, the group of Tarascon 1098,1099 studied both crystalline and amorphous (hydrated) phases of LiNiVO 4 and found that they show capacity fading from ∼1000 mA•h g −1 to ∼550 mA•h g −1 after 50 cycles. Similar capacity fading in LiNiVO 4 was also reported by Han et al 1100 Shirakawa et al 1101,1102 studied in detail the Li−LiCoVO 4 system to understand the reaction mechanism. They found that at 0.02C and at 5C rates (1C = 350 mA g −1 ), reversible capacities of 980 and 800 mA•h g −1 are obtained.…”

“…They found that at 0.02C and at 5C rates (1C = 350 mA g −1 ), reversible capacities of 980 and 800 mA•h g −1 are obtained. X-ray absorption spectral studies on LiCoVO 4 1101,1102 and on LiNiVO 4 1103 show that upon reaction with Li, the Co and Ni ions are reduced to metal nanoparticles, whereas V 5+ ion is reduced to only a bivalent state (V 2+ ), but not to the metal.…”

24 Conducting solids

“…Shirakawa et al have examined the first charge and discharge reaction of spinel type LiCoVO 4 in order to evaluate its potential as a possible anode material, observing a high reversible capacity of 685 mAh/g. 63 During the process, the structure was observed to change from spinel to atacamite-type, before becoming amorphous.…”

Micro- and Nanocrystalline Inverse Spinel LiCoVO4 for Intercalation Pseudocapacitive Li+ Storage with Ultrahigh Energy Density and Long-Term Cycling

“…LiCoVO 4 possess an inverse spinel structure in which Li + and Co 2+ ion evenly reside in octahedral sites, and V 5+ ions occupy the tetrahedral sites. The Li + ions present in the octahedral site take part in the intercalation process. − Despite these investigations, the application of LiCoVO 4 for Li + storage via intercalation pseudocapacitance has not been studied.…”