Li₃VP₃O₉N as a Multielectron Redox Cathode for Li-Ion Battery

Li₃VP₃O₉N was for the first time synthesized from its sodium analogue Na₃VP₃O₉N using a solid–solid Li⁺/Na⁺ ion-exchange method. This lithium variant of nitridophosphate is found to possess similar crystal structure (space group <i>P</i>2₁3) as its sodium analogue Na₃VP₃O₉N (<i>a</i> = 9.4507(1) Å) but with much smaller lattice parameter (<i>a</i> = 9.1237(1) Å). The crystal structure of Li₃VP₃O₉N was solved and refined using combined synchrotron X-ray and time-of-flight neutron powder diffraction data, allowing the three distinct lithium-ion sites to be identified. A lithium bond valence sum difference map calculation suggests the existence of isotropic three-dimensional lithium-ion-conducting pathways with a minimum valence threshold |ΔV| of 0.02. Li₃VP₃O₉N behaves as a promising reversible cathode material for rechargeable lithium-ion batteries with an average V³⁺/V⁴⁺ redox potential of 3.8 V (vs Li⁺/Li). Both cyclic voltammetry tests and chemical delithiation (using NO₂BF₄) indicate it is possible to partially remove the second lithium from the structure, though only at very high potentials (>4.9 V vs Li⁺/Li). It is also found that the unit cell volume of this compound expands instead of shrinking upon lithium removal, a rare phenomenon for polyanion-based cathodes. This abnormal volume expansion is found to be associated with the drastic expansion of the Li1­(O1)₃N tetrahedral site after removing lithium from this site

Li₃VP₃O₉N as a Multielectron Redox Cathode for Li-Ion Battery

Li₃VP₃O₉N was for the first time synthesized from its sodium analogue Na₃VP₃O₉N using a solid–solid Li⁺/Na⁺ ion-exchange method. This lithium variant of nitridophosphate is found to possess similar crystal structure (space group <i>P</i>2₁3) as its sodium analogue Na₃VP₃O₉N (<i>a</i> = 9.4507(1) Å) but with much smaller lattice parameter (<i>a</i> = 9.1237(1) Å). The crystal structure of Li₃VP₃O₉N was solved and refined using combined synchrotron X-ray and time-of-flight neutron powder diffraction data, allowing the three distinct lithium-ion sites to be identified. A lithium bond valence sum difference map calculation suggests the existence of isotropic three-dimensional lithium-ion-conducting pathways with a minimum valence threshold |ΔV| of 0.02. Li₃VP₃O₉N behaves as a promising reversible cathode material for rechargeable lithium-ion batteries with an average V³⁺/V⁴⁺ redox potential of 3.8 V (vs Li⁺/Li). Both cyclic voltammetry tests and chemical delithiation (using NO₂BF₄) indicate it is possible to partially remove the second lithium from the structure, though only at very high potentials (>4.9 V vs Li⁺/Li). It is also found that the unit cell volume of this compound expands instead of shrinking upon lithium removal, a rare phenomenon for polyanion-based cathodes. This abnormal volume expansion is found to be associated with the drastic expansion of the Li1­(O1)₃N tetrahedral site after removing lithium from this site

Li₃VP₃O₉N as a Multielectron Redox Cathode for Li-Ion Battery

Li₃VP₃O₉N was for the first time synthesized from its sodium analogue Na₃VP₃O₉N using a solid–solid Li⁺/Na⁺ ion-exchange method. This lithium variant of nitridophosphate is found to possess similar crystal structure (space group <i>P</i>2₁3) as its sodium analogue Na₃VP₃O₉N (<i>a</i> = 9.4507(1) Å) but with much smaller lattice parameter (<i>a</i> = 9.1237(1) Å). The crystal structure of Li₃VP₃O₉N was solved and refined using combined synchrotron X-ray and time-of-flight neutron powder diffraction data, allowing the three distinct lithium-ion sites to be identified. A lithium bond valence sum difference map calculation suggests the existence of isotropic three-dimensional lithium-ion-conducting pathways with a minimum valence threshold |ΔV| of 0.02. Li₃VP₃O₉N behaves as a promising reversible cathode material for rechargeable lithium-ion batteries with an average V³⁺/V⁴⁺ redox potential of 3.8 V (vs Li⁺/Li). Both cyclic voltammetry tests and chemical delithiation (using NO₂BF₄) indicate it is possible to partially remove the second lithium from the structure, though only at very high potentials (>4.9 V vs Li⁺/Li). It is also found that the unit cell volume of this compound expands instead of shrinking upon lithium removal, a rare phenomenon for polyanion-based cathodes. This abnormal volume expansion is found to be associated with the drastic expansion of the Li1­(O1)₃N tetrahedral site after removing lithium from this site

Li₃VP₃O₉N as a Multielectron Redox Cathode for Li-Ion Battery

Li₃VP₃O₉N was for the first time synthesized from its sodium analogue Na₃VP₃O₉N using a solid–solid Li⁺/Na⁺ ion-exchange method. This lithium variant of nitridophosphate is found to possess similar crystal structure (space group <i>P</i>2₁3) as its sodium analogue Na₃VP₃O₉N (<i>a</i> = 9.4507(1) Å) but with much smaller lattice parameter (<i>a</i> = 9.1237(1) Å). The crystal structure of Li₃VP₃O₉N was solved and refined using combined synchrotron X-ray and time-of-flight neutron powder diffraction data, allowing the three distinct lithium-ion sites to be identified. A lithium bond valence sum difference map calculation suggests the existence of isotropic three-dimensional lithium-ion-conducting pathways with a minimum valence threshold |ΔV| of 0.02. Li₃VP₃O₉N behaves as a promising reversible cathode material for rechargeable lithium-ion batteries with an average V³⁺/V⁴⁺ redox potential of 3.8 V (vs Li⁺/Li). Both cyclic voltammetry tests and chemical delithiation (using NO₂BF₄) indicate it is possible to partially remove the second lithium from the structure, though only at very high potentials (>4.9 V vs Li⁺/Li). It is also found that the unit cell volume of this compound expands instead of shrinking upon lithium removal, a rare phenomenon for polyanion-based cathodes. This abnormal volume expansion is found to be associated with the drastic expansion of the Li1­(O1)₃N tetrahedral site after removing lithium from this site

Asymmetric Lithium Extraction and Insertion in High Voltage Spinel at Fast Rate

Spinel-structured ordered-LiNi0.5Mn1.5O4 (o-LNMO) has experienced a resurgence of interest in the context of reducing scarce elements such as cobalt from the lithium-ion batteries. O-LNMO undergoes two two-phase reactions at slow rates. However, it is not known if such phenomenon also applies at fast rates. Herein, we investigate the rate-dependent phase transition behavior of o-LNMO through in operando time-resolved X-ray diffraction. The results indicate that a narrow region of the solid solution reaction exists for charge and discharge at both slow and fast rates. The overall phase transition is highly asymmetric at fast rates. During fast charge, it is a particle-by-particle mechanism resulting from an asynchronized reaction among the particles. During fast discharge, it is likely a core–shell mechanism involving transition from Li0+xNi0.5Mn1.5O4 to Li1+xNi0.5Mn1.5O4 in the outer layer of particles. The Li0.5Ni0.5Mn1.5O4 phase is suppressed during fast discharge and appears only through Li redistribution upon relaxation

Large-Scale Synthesis and Comprehensive Structure Study of δ‑MnO₂

Layered δ-MnO₂ (birnessites) are ubiquitous in nature and have also been reported to work as promising water oxidation catalysts or rechargeable alkali-ion battery cathodes when fabricated under appropriate conditions. Although tremendous effort has been spent on resolving the structure of natural/synthetic layered δ-MnO₂ in the last few decades, no conclusive result has been reached. In this Article, we report an environmentally friendly route to synthesizing homogeneous Cu-rich layered δ-MnO₂ nanoflowers in large scale. The local and average structure of synthetic Cu-rich layered δ-MnO₂ has been successfully resolved from combined Mn/Cu K-edge extended X-ray fine structure spectroscopy and X-ray and neutron total scattering analysis. It is found that appreciable amounts (∼8%) of Mn vacancies are present in the MnO₂ layer and Cu²⁺ occupies the interlayer sites above/below the vacant Mn sites. Effective hydrogen bonding among the interlayer water molecules and adjacent layer O ions has also been observed for the first time. These hydrogen bonds are found to play the key role in maintaining the intermediate and long-range stacking coherence of MnO₂ layers. Quantitative analysis of the turbostratic stacking disorder in this compound was achieved using a supercell approach coupled with anisotropic particle-size-effect modeling. The present method is expected to be generally applicable to the structural study of other technologically important nanomaterials

Probing Reversible Multielectron Transfer and Structure Evolution of Li_1.2Cr_0.4Mn_0.4O₂ Cathode Material for Li-Ion Batteries in a Voltage Range of 1.0–4.8 V

Li_1.2Cr_0.4Mn_0.4O₂ (0.4LiCrO₂·0.4Li₂MnO₃) is an interesting intercalation-type cathode material with high theoretical capacity of 387 mAh g^–1 based on multiple-electron transfer of Cr³⁺/Cr⁶⁺. In this work, it has been demonstrated that the reversible Cr³⁺/Cr⁶⁺ redox reaction can only be realized in a wide voltage range between 1.0 and 4.8 V. This is mainly due to large polarization during the discharge. The reversible migration of the Cr ions between octahedral and tetrahedral sites leads to large extent of cation mixing between lithium and transition metal layers, which does not affect the lithium storage capacity and stabilize the structure. In addition, a distorted spinel phase (Li₃M₂O₄) is identified in the deeply discharged sample (1.0 V, Li_1.5Cr_0.4Mn_0.4O₂). The above results can explain the high reversible capacity and high structural stability achieved on Li_1.2Cr_0.4Mn_0.4O₂. These new findings will provide further in depth understanding on multielectron transfer and local structure stabilization mechanisms in intercalation chemistry, which are essential for understanding and developing a high capacity intercalation-type cathode for next generation high energy density Li-ion batteries

Divalent Iron Nitridophosphates: A New Class of Cathode Materials for Li-Ion Batteries

Divalent Iron Nitridophosphates: A New Class of Cathode Materials for Li-Ion Batterie

Nanoscale Lamellar Monoclinic Li₂MnO₃ Phase with Stacking Disordering in Lithium-Rich and Oxygen-Deficient Li_1.07Mn_1.93O_4−δ Cathode Materials

The powdered crystalline samples of nominal composition Li_1.07Mn_1.93O_4−δ have been investigated by transmission electron microscopy (TEM) combined with X-ray powder diffraction (XRD) at room temperature. As suggested by the TEM observation, the dominant phase of the particles is a cubic spinel Li_1+αMn_2−αO_4−δ with space group <i>Fd</i>3̅<i>m</i>. A monoclinic Li₂MnO₃ phase with <i>C</i>2/<i>m</i> space group was also identified. Furthermore, the occurrence of nanoscale rotational twinning domains in Li₂MnO₃ with 120° rotation angles, stacked along the [103]_m/[111]_c (“m” and “c” represent the monoclinic and cubic descriptions, respectively) axis was also observed. These nanoscale rotational twining domains are responsible for the pseudo-3-fold axis and their formation is supported by the superstructure reflections in selected-area electron-diffraction (SAED) patterns. Similar patterns were reported in the literature but may have been misinterpreted without the consideration of such domains. Consistent with the TEM observation, the XRD results reveal the increasing percentage of monoclinic Li₂MnO₃ with increasing annealing time, associated with more oxygen vacancies. In addition, the electron beam irradiation during TEM studies may cause the nucleation of nanoscale cubic spinel Li–Mn–O crystallites on the monoclinic Li₂MnO₃ grains. These results provide the detailed structural information about the Li_1.07Mn_1.93O_4−δ samples and advance the understanding of corresponding electrochemical properties of this material as well as other layer structured cathode materials for lithium-ion batteries

Oxygen-Release-Related Thermal Stability and Decomposition Pathways of Li_<i>x</i>Ni_0.5Mn_1.5O₄ Cathode Materials

The thermal stability of charged cathode materials is one of the critical properties affecting the safety characteristics of lithium-ion batteries. New findings on the thermal-stability and thermal-decomposition pathways related to the oxygen release are discovered for the high-voltage spinel Li_<i>x</i>Ni_0.5Mn_1.5O₄ (LNMO) with ordered (<i>o</i>-) and disordered (<i>d</i>-) structures at the fully delithiated (charged) state using a combination of in situ time-resolved X-ray diffraction (TR-XRD) coupled with mass spectroscopy (MS) and X-ray absorption spectroscopy (XAS) during heating. Both <i>o</i>- and <i>d</i>- Li_<i>x</i>Ni_0.5Mn_1.5O₄, at their fully charged states, start oxygen-releasing structural changes at temperatures below 300 °C, which is in sharp contrast to the good thermal stability of the 4V-spinel Li_<i>x</i>Mn₂O₄ with no oxygen being released up to 375 °C. This is mainly caused by the presence of Ni⁴⁺ in LNMO, which undergoes dramatic reduction during the thermal decomposition. In addition, charged <i>o</i>-LNMO shows better thermal stability than the <i>d</i>-LNMO counterpart, due to the Ni/Mn ordering and smaller amount of the rock-salt impurity phase in <i>o</i>-LNMO. Two newly identified thermal-decomposition pathways from the initial Li_<i>x</i>Ni_0.5Mn_1.5O₄ spinel to the final NiMn₂O₄-type spinel structure with and without the intermediate phases (NiMnO₃ and α-Mn₂O₃) are found to play key roles in thermal stability and oxygen release of LNMO during thermal decomposition