Li + intercalation in isostructural Li 2 VO 3 and Li 2 VO 2 F with O 2À and mixed O 2À /F À anions (original) (raw)
Related papers
Advanced Energy Materials, 2015
rock-salt structures, with Li + /TM evenly sharing cation sites and close-packed anion arrays, may be a reasonable alternative for effi cient Li + storage. After Li + extraction, the TM may remain at the cation sublattice sites and uphold well the disordered rocksalt framework. A recent work based on ab initio computations revealed that Li + transport can be facile in a disordered cubic rock-salt oxide (Li 1.211 Mo 0.467 Cr 0.3 O 2 ) with Li-excess. [ 8 ] It was found that such framework is stable with a maximum of 45% of the cation sites vacant. Herein, we demonstrate that a new dilithium disordered rock-salt Li 2 VO 2 F intercalation material can deliver up to about 1.8 Li + capacity per TM (420 mAh g −1 ) at ≈2.5 V (1000 Wh kg −1 ) with only minor lattice volume change (≈3%). Such material with mixed O 2− /F − anion environment has been synthesized by a simple ball-milling method. The two Li + storage with V 3+ /V 5+ redox reactions (Li 2 VO 2 F ↔ 2 Li + + 2e − + VO 2 F) leads to an attractively high theoretical capacity of 462 mAh g −1 . Moreover, Li 2 VO 2 F shows good capacity retention and minor increase in polarization upon fast charging/discharging or upon low-temperature operation.
Disordered Lithium-Rich Oxyfluoride as a Stable Host for Enhanced Li + Intercalation Storage
Advanced Energy Materials, 2015
rock-salt structures, with Li + /TM evenly sharing cation sites and close-packed anion arrays, may be a reasonable alternative for effi cient Li + storage. After Li + extraction, the TM may remain at the cation sublattice sites and uphold well the disordered rocksalt framework. A recent work based on ab initio computations revealed that Li + transport can be facile in a disordered cubic rock-salt oxide (Li 1.211 Mo 0.467 Cr 0.3 O 2 ) with Li-excess. [ 8 ] It was found that such framework is stable with a maximum of 45% of the cation sites vacant. Herein, we demonstrate that a new dilithium disordered rock-salt Li 2 VO 2 F intercalation material can deliver up to about 1.8 Li + capacity per TM (420 mAh g −1 ) at ≈2.5 V (1000 Wh kg −1 ) with only minor lattice volume change (≈3%). Such material with mixed O 2− /F − anion environment has been synthesized by a simple ball-milling method. The two Li + storage with V 3+ /V 5+ redox reactions (Li 2 VO 2 F ↔ 2 Li + + 2e − + VO 2 F) leads to an attractively high theoretical capacity of 462 mAh g −1 . Moreover, Li 2 VO 2 F shows good capacity retention and minor increase in polarization upon fast charging/discharging or upon low-temperature operation.
Lithium-ion diffusion mechanisms in the battery anode material Li(1+x)V(1-x)O₂
Physical chemistry chemical physics : PCCP, 2014
Layered Li(1+x)V(1-x)O2 has attracted recent interest as a potential low voltage and high energy density anode material for lithium-ion batteries. A greater understanding of the lithium-ion transport mechanisms is important in optimising such oxide anodes. Here, stoichiometric LiVO2 and Li-rich Li1.07V0.93O2 are investigated using atomistic modelling techniques. Lithium-ion migration is not found in LiVO2, which has also previously shown to be resistant to lithium intercalation. Molecular dynamics simulations of lithiated non-stoichiometric Li(1.07+y)V0.93O2 suggest cooperative interstitial Li(+) diffusion with favourable migration barriers and diffusion coefficients (D(Li)), which are facilitated by the presence of lithium in the transition metal layers; such transport behaviour is important for high rate performance as a battery anode.
Lithiation-driven structural transition of VO 2 F into disordered rock-salt Li x VO 2 F
We synthesize a new vanadium oxyfluoride VO 2 F (rhombohedral, R 3c) through a simple one-step ballmilling route and demonstrate its promising lithium storage properties with a high theoretical capacity of 526 mA h g À1 . Similar to V 2 O 5 , VO 2 F transfers into an active disordered rock-salt (Fm 3m) phase after initial cycling against the lithium anode, as confirmed by diffraction and spectroscopic experiments. The newly formed nanosized Li x VO 2 F remains its crystal structure over further cycling between 4.1 and 1.3 V.
Conventional intercalation cathodes for lithium batteries store charge in redox reactions associated with the transition metal cations, e.g. Mn 3+/4+ in LiMn 2 O 4 , and this limits the energy storage of Li-ion batteries. Compounds such as Li[Li 0.2 Ni 0.2 Mn 0.6 ]O 2 exhibit a capacity to store charge in excess of the transition metal redox reactions. The additional capacity occurs at and above 4.5 V vs. Li + /Li. The capacity at 4.5 V is dominated by oxidation of the O 2anions accounting for ~0.43 e -/formula unit, with an additional 0.06 e -/formula unit being associated with O loss from the lattice. In contrast, the capacity above 4.5 V, is mainly O loss, ~ 0.08 e -/formula. The O redox reaction involves the formation of localized hole states on O during charge, which are located on O coordinated by (Mn 4+ /Li + ). The results have been obtained by combining operando electrochemical mass spec on 18 O labelled Li[Li 0.2 Ni 0.2 Mn 0.6 ]O 2 with XANES, soft X-ray spectroscopy, Resonant Inelastic X-ray spectroscopy and Raman spectroscopy. Finally the general features of O-redox are described with discussion about the role of comparatively ionic (less covalent) 3d metal-oxygen interaction on anion redox in lithium rich cathode materials. Li[Li 0.2 Ni 0.2 Mn 0.6 ]O 2 and Li[Li 0.2 Ni 0.13 Co 0.13 Mn 0.54 ]O 2 are the two archetypal examples of intercalation electrodes exhibiting excess capacity. 1a-c, 2a, 2b, 6 Initially, the excess capacity in both compounds was ascribed to oxygen loss from the lattice, in effect the loss of Li 2 O. 1, 7 Recent work on Li[Li 0.2 Ni 0.13 Co 0.13 Mn 0.54 ]O 2 has shown that ~0.5 eper formula unit are stored by redox reactions on O. 2c, 8 Here we investigate the nature of the excess capacity observed for the Co free Li[Li 0.2 Ni 0.2 Mn 0.6 ]O 2 to see how it compares with Li[Li 0.2 Ni 0.13 Co 0.13 Mn 0.54 ]O 2 ; using 18 O isotopically Li[Li 0.2 Ni 0.2 Mn 0.6 ]O 2 (which allows us to identify O loss form the lattice even in the absence of direct O 2 gas evolution) along with operando electrochemical mass spectrometry (OEMS), soft X-ray spectroscopy (SXAS), resonant inelastic X-ray scattering (RIXS), Raman and XANES. The excess capacity of Li[Li 0.2 Ni 0.2 Mn 0.6 ]O 2 occurs at and above 4.5 V with most occurring at 4.5 V. The capacity at 4.5 V is dominated by O redox, accounting for ~0.43 e -/formula unit, with only 0.06 e -/formula unit due to O loss. Above 4.5 V the excess capacity is mainly O loss, accounting for ~0.08 e -/ formula unit. Oxidation of O 2on charging is associated with the generation of localized electron holes on O coordinated by (Mn 4+ /Li + ). Co, although expensive, is often included in the layered oxide cathodes because it improves kinetics and cycling stability. 9 Understanding the origin of the excess capacity in Co free Li[Li 0.2 Ni 0.2 Mn 0.6 ]O 2 is valuable, because it shows that the O 2redox mechanism involving localized holes coordinated by (Mn 4+ /Li + ) is not unique to Co containing cathodes but is seen in other, Co-free, 3d transition metal oxides. The balance between O loss and O redox is also similar with and without Co, hence Co is not necessary in 3d transition metal oxides to obtain O redox as the dominant process at 4.5 V.
Microporous and Mesoporous Materials, 2019
Enhanced anode performance has been achieved with nutshell shaped Li 3 VO 4 having a cascading mesopore hierarchy in a hydrothermally synthesized nanocrystalline material. The remarkable enhancement in the capacity (357 mAh g −1 at 0.1C) as compared to its solid-state counterpart (102 mAh g −1 at 0.1C) is solely due to mesopore hierarchy comprising of three-dimensional interconnected channels that allows better electrolyte infiltration into the bulk of the active electrode material ensuing short Li-ion diffusion distances, increased charge-transfer reaction sites and fast Li-ion transport pathways in addition to three-dimensional ion diffusion.
The lithium intercalation process in the low-voltage lithium battery anode Li1+xV1−xO2
Nature Materials, 2011
Lithium can be reversibly intercalated into layered Li 1+x V 1−x O 2 (LiCoO 2 structure) at ∼0.1 V, but only if x > 0. The low voltage combined with a higher density than graphite results in a higher theoretical volumetric energy density; important for future applications in portable electronics and electric vehicles. Here we investigate the crucial question, why Li cannot intercalate into LiVO 2 but Li-rich compositions switch on intercalation at an unprecedented low voltage for an oxide? We show that Li + intercalated into tetrahedral sites are energetically more stable for Li-rich compositions, as they share a face with Li + on the V site in the transition metal layers. Li incorporation triggers shearing of the oxide layers from cubic to hexagonal packing because the Li 2 VO 2 structure can accommodate two Li per formula unit in tetrahedral sites without face sharing. Such understanding is important for the future design and optimization of low-voltage intercalation anodes for lithium batteries.
Advanced Science, 2020
To meet the growing demand for global electrical energy storage, high-energy-density electrode materials are required for Li-ion batteries. To overcome the limit of the theoretical energy density in conventional electrode materials based solely on the transition metal redox reaction, the oxygen redox reaction in electrode materials has become an essential component because it can further increase the energy density by providing additional available electrons. However, the increase in the contribution of the oxygen redox reaction in a material is still limited due to the lack of understanding its controlled parameters. Here, it is first proposed that Li-transition metals (TMs) inter-diffusion between the phases in Li-rich materials can be a key parameter for controlling the oxygen redox reaction in Li-rich materials. The resulting Li-rich materials can achieve fully exploited oxygen redox reaction and thereby can deliver the highest reversible capacity leading to the highest energy density, ≈1100 Wh kg −1 among Co-free Li-rich materials. The strategy of controlling Li/transition metals (TMs) inter-diffusion between the phases in Li-rich materials will provide feasible way for further achieving high-energy-density electrode materials via enhancing the oxygen redox reaction for high-performance Li-ion batteries.
Pure and Applied Chemistry, 2000
Results on the local cation ordering in layered lithium-nickel/cobalt oxides and metal-substituted lithium-manganese spinels are presented. It is shown that electron spin resonance of Ni 3+ and Mn 4+ and magnetic susceptibility measurements are powerful tools to monitor the short-range cation ordering in these compounds, which is not accessible by diffraction techniques. Thus, owing to the different strength of the 90°and 180°N i 3+ -O-Ni 3+/2+ exchange interactions, the distribution of Ni 3+ /Ni 2+ between the lithium and nickel layers in Li 1-x Ni 1+x O 2 with 0 < x < 0.4 can be determined. For layered LiNi 1-y Co y O 2 and spinel LiMn 2-x Co x O 4 solid solutions, analysis of the temperature-independent EPR line width in terms of dipole-dipole and exchange interactions has been used to examine the local Ni 3+ /Co 3+ and Mn 4+ /Co 3+ ordering. The results obtained are correlated with the electrochemical intercalation of lithium in these compounds. the effect of the synthesis conditions on the local cation distribution in LiNi/CoO 2 and LiMn 2-x M x O 4 (M = Co, Mg) are presented. Since magnetic properties are sensitive to the cation distribution, magnetic measurements (electron spin resonance and magnetic susceptibility measurements) were used to monitor the short-range cation ordering in these compounds, which is not possible by means of diffraction techniques.
Correlation between structural and electrochemical properties of Li metal vanadates
Journal of Power Sources, 2001
LiCo y Ni 1Ày VO 4 compounds (y 0, 0.2, 0.5, 0.8, 1) have been prepared for lithium-ion cell cathode applications by different chemical routes. The polycrystalline materials were characterized by X-ray powder diffraction (XRPD) and by solid state 7 Li and 51 V nuclear magnetic resonance (NMR) analysis. The results show an increase of the lattice parameter with increasing Co content and a varying distribution of Co, Ni, and V in the crystallographic sites. Moreover, both XRPD and NMR data reveal different degrees of crystallinity depending on the preparation method. The ®rst electrochemical tests show that the distribution of ions in the various crystallographic sites and the crystallinity degree are correlated to the electrochemical performances. #