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Lowest-energy lithium-vacancy arrangements in Li x NiO 2 at x values of 1/4, 1/3, 2/5, 1/2, 3/5, and 3/4. The big black circles denote the in-plane lithium orderings and the small black circles designate the positions of the Li ions in the adjacent plane. Dashed line indicates the 180 Li-O-Ni 3-O-Li configurations. Ni 3 ions are indicated by dark gray circles, Ni 3.5 ions by light gray circles, and Ni 4 ions by white circles.
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The phase diagram of LixNiO2 (0<x<1) is calculated using a combination of first-principles energy methods and Monte Carlo simulations. The energy dependence of the Li-vacancy configurational disorder is parametrized with a cluster expansion. At room temperature ordered LixNiO2 phases appear in the phase diagram at x=1/4, 1/3, 2/5, 1/2, and 3/4. The...
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... interplane inter- actions turn out to be crucial for stabilizing some of the ordered ground states in the phase diagram. Figure 6 shows the ground-state Li-vacancy arrange- ments. Two successive planes of lithium ions are shown, with large and small filled black circles, respectively. ...
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... these structures, the approximate charge around each Ni ion has been calculated by integrating the unpaired electron den- sity within a sphere of a radius 1.5 Å centered at the different Ni sites. 33 These charges have been rounded off to 3, 4, and 3.5, depending on which of the three formal valence states is closest to the integration result. In Fig. 6, Ni 3 ions are indicated by dark gray circles, Ni 3.5 ions by light gray circles, and Ni 4 ions by white circles. For clarity only the Ni ions in one unit cell are ...
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... in the case of Li x NiO 2 , where strong Jahn-Teller induced interplanar in- teractions have been documented, 33 particular stacking se- quences may be favored. Figure 6 shows for each structure the most stable stacking. As in Ref. 33, we find that at each composition the lowest-energy structure has Li-Li or - pairs along the O-Ni 3 -O extensions, but never a Li-pair. ...
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... been documented, 33 particular stacking se- quences may be favored. Figure 6 shows for each structure the most stable stacking. As in Ref. 33, we find that at each composition the lowest-energy structure has Li-Li or - pairs along the O-Ni 3 -O extensions, but never a Li-pair. These Li A -O-Ni 3 -O-Li B complexes are shown by the dotted lines in Fig. 6. This is consistent with the attractive interac- tions observed in the cluster expansion along this direction. The result of the charge integrations around Ni ions, shown in Fig. 6, indicates clearly that distinct valence states of the Ni ions exist in partially delithiated materials. This is unlike Li x CoO 2 where the effective ...
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... lowest-energy structure has Li-Li or - pairs along the O-Ni 3 -O extensions, but never a Li-pair. These Li A -O-Ni 3 -O-Li B complexes are shown by the dotted lines in Fig. 6. This is consistent with the attractive interac- tions observed in the cluster expansion along this direction. The result of the charge integrations around Ni ions, shown in Fig. 6, indicates clearly that distinct valence states of the Ni ions exist in partially delithiated materials. This is unlike Li x CoO 2 where the effective charge on the transition metal is delocalized over all Co ions and the material is metallic when enough Li is removed. 5,33 In the low-energy configu- rations the unit cell for Ni-charge ...
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... can be seen in Fig. 6 that for x0.4, Ni 4 ions occupy sites fully coordinated by lithium ions. This is a very sym- metrical environment favorable for a nonactive JT ion, such as Ni 4 . The effect of this can be seen in the nearest- neighbor triplet interaction 10.7 meV in Fig. 5c which is strongly attractive, weakening the effect of the nearest- neighbor ...
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The structural properties of the (Zn, Mg) (S, Se) solid solutions are determined by a combination of the computational alchemy and the cluster expansion methods with Monte Carlo simulations. We determine the phase diagram of the alloy and show that the homogeneous phase is characterized by a large amount of short-range order occurring among first-n...
Citations
... This is partly consistent with previously predicted ordering of 0.25, 0.33, 0.4, 0.5, 0.6, 0.75, and 0.83. [27] or 0.125, 0.25, 0.33, 0.5, 0.6, 0.625, 0.67, 0.75, 0.83, and 0.875. [28] Extend cell Delithiated Li ions and vacancies are denoted as green solid dots and black solid dots, respectively. ...
... [4] red solid line denoting our calculated voltage profile, blue line referring to Sicolo's calculated voltage profile [4] at 300 K, and yellow line being Ceder's calculated voltage profile. [27] The equilibrium voltage of an electrochemical lithium battery depends on the difference in Li chemical potential between the anode material and cathode material. [29] According to the ground state structures found, we can calculate the average chemical potential, i.e., the voltage of Li x NiO 2 at 0 K between different concentrations as given below: ...
Combining the first-principles calculations and structural enumeration with recognition, the delithiation process of LiNiO2 is investigated, where various supercell shapes are considered in order to obtain the formation energy of Li x NiO2. Meanwhile, the voltage profile is simulated and the ordered phases of lithium vacancies corresponding to concentrations of 1/4, 2/5, 3/7, 1/2, 2/3, 3/4, 5/6, and 6/7 are predicted. To understand the capacity decay in the experiment during the charge/discharge cycles, deoxygenation and Li/Ni antisite defects are calculated, revealing that the chains of oxygen vacancies will be energetically preferrable. It can be inferred that in the absence of oxygen atom in high delithiate state, the diffusion of Ni atoms is facilitated and the formation of Li/Ni antisite is induced.
... For the sake of illustration, during delithiation process in TLMO, the formation energy of a Li x Mn 2 O 4 phase is calculated from its total energy and the reference materials energies of LiMn 2 O 4 and Mn 2 O 4 . The formation energy for all Li x Mn 2 O 4 phases, which are stable in comparison to the reference phases, lie on the lower convex hull in a plot of E f versus composition x [36][37][38]. ...
... Ab initio calculations are not suitable for describing the stable intermediate phases that are formed during battery charging/discharging, due to the extensive number of possible lithium/vacancy orderings, preventing the energy evaluation of all configurations [37]. Generally, the intermediate phases are obtained by the cluster expansion technique [38][39][40] zoom of the convex hull can be observed in figure S4, where one can better perceive the formation of the intermediate phase. The TLMO follows the same pattern presented by the cubic and orthorhombic structures [41,42], that is, a single stable intermediate phase is observed for x = 0.5. ...
In the field of sustainable energy storage systems, zinc-ion batteries (ZIB) employing aqueous electrolytes have emerged as viable successors to the widely used lithium-ion batteries, attributed to their cost-effectiveness, environmental friendliness, and intrinsic safety features. Despite these advantages, the performance of ZIBs is significantly hindered by the scarcity of suitable cathode materials, positioning manganese zinc oxide (ZnMn2O4) as a potential solution. In this study, we describe the ZnMn2O4 (ZMO) compound focusing on its properties variations during Zn extraction and potential battery applications. For the sake of comparison, we also analyze the same properties of the LiMn2O4 in its tetragonal phase (TLMO), for the first time, motivated by a recent discovery that the substitution of Zn ions by Li in ZMO forms isostructural TLMO compound at room temperature. The study was conducted within the density functional theory (DFT) framework, where the structural, electronic, magnetic, electrochemical, and spectroscopic properties of ZMO and TLMO are investigated under various conditions. Although both systems crystallize in tetragonal structures, they demonstrate distinct electronic and magnetic properties due to different oxidation states of the Mn. Computationally optimized lattice parameters align closely with experimental values. The TLMO exhibits a narrower band gap compared to ZMO, indicating enhanced electrical conductivity. In addition, TLMO presented a lower diffusion energy barrier than ZMO, indicating better ionic conductivity. To evaluate the potential application of these materials in battery technologies, we further explored their volume changes during charging/discharging cycles, simulating Zn or Li ions extraction. TLMO underwent a significant volume contraction of 5.8% upon complete Li removal, while ZMO experienced a more pronounced contraction of 12.5% with full Zn removal. By adjusting ion extraction levels, it is possible to reduce these contractions, thereby approaching more viable battery applications. Voltage profiles, constructed from DFT-based simulation results, unveiled an average voltage of 4.05 V for TLMO, closely matching experimental values. Furthermore, spectroscopy results provide insights into the electronic transitions and validate the computational findings, consolidating our understanding of the intrinsic properties of ZMO and TLMO.
... According to above studies, we know that the valence of Mn ion changes from + 4 to + 3, and the sodium content has almost no effect on the transition metal layer of the material. [27][28][29] Therefore, we designed and calculated the total energy of P2 and O '3 phases when the Na/Mn ratio is 1 and Mn is in different valence states. The change in the reaction free energy of Mn ions in the P2 or O'3 phase when they change from + 4 to + 3 at different temperatures ( Fig. 4e and f). ...
Considering the non-stoichiometric feature of sodium layered oxides cathode, oxygen content in the calcination atmosphere would play a key role in the phase evolution, which is still unclear and deserves detailed investigation. In the present study, with the controlled oxygen content via under different atmospheres, structural oxygen release driven by heating was evidenced to be the phase transition trigger, which destroy the initial local Mn-O structure and results in rearranged Mn-O octahedral ordered structure. The varied oxygen content would change the star-up temperature of phase transition. These results can promote the materials phase design by adjusting the release of structural oxygen and provide guideline for the synthesis of layered oxides.
... Note that this conclusion should be only available in the full lithiation state under the ideal identical structure of LiMO 2 (M ¼ Co, Ni) with the same lattice parameters. In real cases, multiple-stages phase transformations accompanied by different extent of expansion and contraction of c-lattice parameters will proceed in Li x MO 2 (0 < x 1, M ¼ Co, Ni) with increasing x. [164][165][166] These processes can result in different phase-transformation-dependent diffusion properties (see Sec. III). In addition, Li x NiO 2 is more thermally favorable to form the antisite-defect structure referred by Li 1-x Ni 1þx O 2 with Ni randomly occupying the Li sites, 167 which can impede the migration of Li 168 and can lead to the weaker diffusion capability of Li in contrast with Li x CoO 2 as confirmed from the NMR measurements 169 and rate-dependence results. ...
Because of the increasing demand, high-power, high-rate energy storage devices based on electrode materials have attracted immense attention. However, challenges remain to be addressed to improve the concentration-dependent kinetics of ionic diffusion and understand phase transformation, interfacial reactions, and capacitive behaviors that vary with particle morphology and scanning rates. It is valuable to understand the microscopic origins of ion transport in electrode materials. In this review, we discuss the microscopic transport phenomena and their dependence on ion concentration in the cathode materials, by comparing dozens of well-studied transition metal oxides, sulfides, and phosphates, and in the anode materials, including several carbon species and carbides. We generalize the kinetic effects on the microscopic ionic transport processes from the phenomenological points of view based on the well-studied systems. The dominant kinetic effects on ion diffusion varied with ion concentration, and the pathway- and morphology-dependent diffusion and capacitive behaviors affected by the sizes and boundaries of particles are demonstrated. The important kinetic effects on ion transport by phase transformation, transferred electrons, and water molecules are discussed. The results are expected to shed light on the microscopic limiting factors of charging/discharging rates for developing new intercalation and conversion reaction systems.
... Moreover, the limited concentration and nature of antisite defects makes them difficult to probe with conventional characterisation techniques, for example X-ray scattering has low sensitivity for Li, or the relatively high electronic conductivity of LiNiO2 reduces its Raman scattering efficiency.25 Researchers have hence turned to more advanced methods, including neutron scattering, 12,26 X-ray absorption spectroscopy,27 and solid-state nuclear magnetic resonance (NMR) spectroscopy28,29 to more precisely resolve the crystallographic, electronic, and magnetic structure of LiNiO2. In tandem with experimental studies, several authors have also adopted computational modelling to predict possible structures of LiNiO2.[30][31][32][33] Yet, to date in most of the literature models of either antisite defects or off-stoichiometry are often chosen without a precise reasoning behind the choice of the models.Using a comprehensive suite of characterisation techniques, we aim to resolve the relationship between material stoichiometry and the presence of site defects over a wide range of compositions with nominal stoichiometry Li1-zNi1+zO2 where -0.05 ≤ z ≤ 0.35, and the resulting consequences for the physical properties of the materials. ...
As contemporary battery applications such as electric vehicles demand higher energy densities, layered LiNiO2 (LNO) could contribute as the end-member of the LiNi1-x-yCoxMnyO2 (NCM) family with the highest extractable specific capacity in a practical voltage window. Achieving high capacities requires among other things a defect free crystal structure, which is not easily achieved due to the natural occurrence of Ni excess on the Li site (NiLi) and/or antisite defects where Ni and Li switch crystallographic sites. Here, we present a study of the evolution of point defects in a series of LNO samples varying from underlithiated to fully lithiated stoichiometry in layered Li1-zNi1+zO2 with -0.05 ≤ z ≤ 0.35. Using the high angular resolution of synchrotron X-ray diffraction complemented with the different element contrast provided by neutron diffraction, we are able to identify two defect regimes. In the first regime at the underlithiathed end, both NiLi as well as Li on the Ni site (LiNi) defects are present. Inhibited crystal growth during synthesis is found to coincide with the presence of these LiNi defects for z ≥ 0.15. Upon decreasing z values and the vanishing of LiNi, the primary particle size distribution as well as average refined crystallite size increases. Investigation of the local structure by nuclear magnetic resonance reveals the presence of a Li environment not detected by diffraction methods at the low z, the Li-rich end of the sample series. Finally, magnetometry data suggest the onset of the ferrimagnetic-to-antiferromagnetic transition in LNO correlates with the elimination of LiNi defects in the structure. The present study thus not only highlights the correlation between defect chemistry and physical properties, but also shows the relationship to crystal growth, a field highly relevant for industrial battery cathode materials engineering.
... The nature, extent, and mechanism of this transformation are currently not well understood, due to differences in the pristine material properties, extent of delithiation, and charging protocols [66]. For example, the O3 to O1 transformation was reported to be suppressed or hindered in LiNiO 2 until full delithiation based on operando XRD [69] and first-principles calculations [70]. However, there is ample evidence for the presence of O1-type stacking in highly delithiated Li x NiO 2 [30,71,72]. ...
The desire to increase the energy density of stoichiometric layered LiTMO2 (TM = 3d transition metal) cathode materials has promoted investigation into their properties at high states of charge. Although there is increasing evidence for pronounced oxygen participation in the charge compensation mechanism, questions remain whether this is true O-redox, as observed in Li-excess cathodes. Through a high-resolution O K-edge resonant inelastic x-ray spectroscopy (RIXS) study of the Mn-free Ni-rich layered oxide LiNi0.98W0.02O2, we demonstrate that the same oxidized oxygen environment exists in both Li-excess and non-Li-excess systems. The observation of identical RIXS loss features in both classes of compounds is remarkable given the differences in their crystallographic structure and delithiation pathways. This lack of a specific structural motif reveals the importance of electron correlation in the charge compensation mechanism for these systems and indicates how a better description of charge compensation in layered oxides is required to understand anionic redox for energy storage.
... for studying the statistical mechanics of configurational disorder in solids [1,2,3,4]. The CE method has been used to calculate phase diagrams in alloys [5,6,7,8] and ionic solids [9,10,11,12], predict the short-range order related properties [13,14,15,16], find the ground-state ordering in alloys [17,18,19,20,21,22], and compute voltage profiles of battery electrode materials [23,24,25,26,27]. ...
... Some of them, however, are related by symmetry. The stable configurations are determined here from a convex hull construction [9,63]. Here, the formation ...
The electrochemical performance of potassium titanyl arsenate (KTiOAsO4, KTA) as the cathode and anode in K-ion batteries is calculated within density-functional theory. Cathodes and anodes are modeled using K-deficient K1−xTiOAsO4 (x=0.0–1.0) and K-doped KTiOAsO4Kx (x=0.0–0.5), respectively. For KTA cathodes/anodes a slightly larger/smaller open circuit voltage is found than predicted for potassium titanyl phosphate. The present results suggest that a solely KTA-based K-ion battery can reach an average working voltage of about 3.8V. The migration barriers of K vacancies and K dopants are found to be smaller than 750 meV. In addition, the present calculations show a very moderate volume expansion and shrinkage upon K intercalation and deintercalation. Our results suggest KTA to be a promising electrode material for K-ion batteries.
... Such a system with coupled disorder on multiple sublattices can be well studied using the coupled cluster-expansion approach. 71 The cluster-expansion model has been demonstrated to be an effective method to capture long-range order in intercalation cathodes 72,73 as well as short-range order in DRX systems. 30,32,56,74 In a cluster expansion, the configurational-energy dependence is captured by an expansion into different cluster functions, which can be formulated as 37 ...
The cycling of cathode materials for Li-ion batteries is often accompanied by a change in volume, posing a challenge to the integrity of cathode particles and electrolyte/cathode interface in solid-state batteries. To enhance capacity retention, it is thus crucial to design materials that remain structurally invariant during electrochemical cycling. Here, we use well-calibrated first-principles calculations to systematically investigate the effect of transition-metal chemistry, cation ordering, Li site occupancy, redox-inactive species, anion substitution, and cation migration on the volume change associated with the delithiation of cathode materials with an FCC anion framework. Suggested by an in-depth first-principles Monte Carlo simulation of the Li⁺–V³⁺–Nb⁵⁺–O²⁻–F⁻ system, we experimentally confirm Li1.3V0.4Nb0.3O2 and Li1.25V0.55Nb0.2O1.9F0.1 as nearly zero-strain cathodes. Our study establishes a fundamental understanding of the important physical descriptors that determine the dimensional change of materials during cycling and provides general guidelines for designing low- or zero-strain cathodes.
... A more sophisticated approach for estimating configurational entropy that accounts for short-range ordering involves cluster expansion and Monte Carlo simulations, which have been reviewed elsewhere [58]. In chemical spaces having partially or fully disordered materials, configurational entropy can play a significant role in defining the convex hull and decomposition energies of all phases in that space and becomes more significant as more species contribute to disorder [59,60]. ...
Improvements in the efficiency and availability of quantum chemistry codes, supercomputing centers, and open materials databases have transformed the accessibility of computational materials design approaches. Thermodynamic stability predictions play a central role in the efficacy of these approaches and should be considered carefully. This review covers the fundamentals of calculating thermodynamic stability using first-principles methods. Stability is delineated into two main topics—stability with respect to decomposition into competing phases and stability with respect to phase transition into alternative structures at fixed composition. For each topic, a summary of the state-of-the-art is provided along with a tutorial overview of practical considerations. The application of machine learning to both kinds of stability predictions is also covered. Finally, the limitations of thermodynamic stability predictions are discussed within the context of predicting the synthesizability of materials.
