Despite the importance of the electron correlation in the first-principles description of the Li-ion cathode materials, the Coulomb interaction parameter, U is often treated as an ad hoc value. In practice, one usually relies on empirical ways of parametric treatment of U to optimally match the experimentally observed physical properties such as band gap or reaction energy. Here, using constrained random phase approximation (cRPA) method, we self-consistently evaluate the Coulomb U and Hund J values for representative layered cathode materials including not only Li compounds but also Na compounds; LiCoO2, LiNiO2, LiMnO2, NaCoO2, NaNiO2, and NaMnO2. We found that the Coulomb interaction parameters for Li and Na compounds and their polymorphs with different layer stackings do not deviate much, which shows the dominant role of local environment rather than of global structural features. We have analyzed the origin of variable Coulomb parameters, which is mainly due to the competition between the localization and screening. We provided cRPA Coulomb parameters for battery cathode materials and validate the values by observing systematic improvement in describing the experimentally observed average intercalation voltage and lattice parameters. These results can be applied for the first-principles calculations as well as model-based simulations for the theoretical investigation of cathode systems.
Natural abundance of sodium and its similar behavior to lithium triggered recent extensive studies of cost-effective sodium-ion batteries (SIBs) for large-scale energy storage systems. A challenge is to develop electrode materials with a high electrode potential, specific capacity and a good rate capability. In this work we propose mixed eldfellite compounds \ce{Na_x(Fe_{1/2}M_{1/2})(SO4)2} (M = Mn, Co, Ni) as a new family of high electrode potential cathodes of SIBs and present their material properties predicted by first-principles calculations. The structural optimizations show that these m…
This article reviews the development of cathode materials for secondary lithium ion batteries since its inception with the introduction of lithium cobalt oxide in early 1980s. The time has passed and numerous cathode materials are designed and developed to realize not only the enhanced capacity but also the power density simultaneously. However, there are numerous challenges such as the cyclic stability of cathode materials, their structural and thermal stability, higher operating voltage together with high ionic and electronic conductivity for efficient ion and charge transport during chargin…
We have studied low-temperature magnetic properties as well as high-temperature lithium ion diffusion in the battery cathode materials LixNi1/3Co1/3Mn1/3O2 by the use of muon spin rotation/relaxation. Our data reveal that the samples enter into a 2D spin-glass state below TSG=12 K. We further show that lithium diffusion channels become active for T>Tdiff=125 K where the Li-ion hopping-rate [nu(T)] starts to increase exponentially. Further, nu(T) is found to fit very well to an Arrhenius type equation and the activation energy for the diffusion process is extracted as Ea=100 meV.
We report the synthesis of a graphene-sulfur composite material by wrapping polyethyleneglycol (PEG) coated submicron sulfur particles with mildly oxidized graphene oxide sheets decorated by carbon black nanoparticles. The PEG and graphene coating layers are important to accommodating volume expansion of the coated sulfur particles during discharge, trapping soluble polysulfide intermediates and rendering the sulfur particles electrically conducting. The resulting graphene-sulfur composite showed high and stable specific capacities up to ~600mAh/g over more than 100 cycles, representing a prom…
Li-ion rechargeable batteries have enabled the wireless revolution transforming global communication. Future challenges, however, demands distributed energy supply at a level that is not feasible with the current energy-storage technology. New materials, capable of providing higher energy density are needed. Here we report a new class of lithium-ion batteries based on a graphene ink anode and a lithium iron phosphate cathode. By carefully balancing the cell composition and suppressing the initial irreversible capacity of the anode, we demonstrate an optimal battery performance in terms of spec…
Using density functional theory the ground state structural, electronic, and magnetic properties of monatomic lithium and sodium chains with low average density are investigated. A metallic, zigzag ground state structure is predicted but, most interestingly, stable equilibria for chains under tension are predicted to be {\it ferromagnetic}, which can be traced to exchange effects arising from occupation of the second subband as a function of the interatomic distance.
The biggest challenge for the commercialization of layered structured nickel rich lithium transition metal oxide cathode is the capacity and voltage fading. Resolving this problem over the years follows an incremental progress. In this work, we report our finding of totally a new approach to revolutionize the cycle stability of aggregated cathode particles for lithium ion battery at both room and elevated temperatures. We discover that infusion of a solid electrolyte into the grain boundaries of the cathode secondary particles can dramatically enhance the capacity retention and voltage stabili…
Electronic structure calculations carried out to estimate the free energies of Na(aq)+ exchange for lithium in LiM2(PO4)3 (LMP, M=Si4+,Ge4+,Ti4+,Sn4+,Zr4+) and Li1+xAlxM2-x(PO4)3 (LAMP; M=Ge4+,Ti4+, between 0 and 0.5) compounds in seawater. The calculations show that resistance to sodium-ion exchange increases with decreasing cell volume. For the pure LMP compounds, only the hypothetical LiSi2(PO4)3 is predicted to be stable against sodium ion exchange in aqueous solution. The calculations indicate that increasing the extent of Al3+ substitution for M4+ in the LAMP compounds increases the resi…
The surface coating of cathodes using insulator films has proven to be a promising method for high-voltage cathode stabilization in Li-ion batteries. However, there is still substantial uncertainty about how these films function, specifically with regard to important coating design principles such as lithium solubility and transport through the films. This study uses Density Functional Theory to examine the diffusivity of interstitial lithium in crystalline α-$AlF_3$, α-$Al_2O_3$, m-$ZrO_2$, c-MgO, and α-quartz $SiO_2$, which provide benchmark cases for further understanding of insulator coati…
We study how the Mott metal-insulator transition (MIT) is influenced when we deal with electrons with different angular momenta. For lithium we found an essential effect when we include $p$-orbitals in the description of the Hilbert space. We apply quantum-chemical methods to sodium rings and chains in order to investigate the analogue of a MIT, and how it is influenced by periodic and open boundaries. By changing the interatomic distance we analyse the character of the many-body wavefunction and the charge gap. In the second part we mimic a behaviour found in the ionic Hubbard model, where a …
Composite cathode coatings made of a high energy density layered oxide (Li1.2Ni0.15Mn0.55Co0.1O2, theoretical capacity ~377 mAh/g), polyvinylidene fluoride (PVdF) binder, and electron-conduction additives, were bonded to an elastic substrate. An electrochemical cell, built by pairing the cathode with a capacity-matched graphite anode, was electrochemically cycled and the real-time average stress evolution in the cathode coating was measured using a substrate-curvature technique. Features in the stress evolution profile showed correlations with phase changes in the oxide, thus yielding data com…
In layered LiNixMnyCozO2 cathode material for lithium-ion batteries, the spins of transition metal (TM) ions construct a two-dimensional triangular networks, which can be considered as a simple case of geometrical frustration. By performing neutron powder diffraction experiments and magnetization measurements, we find that long-range magnetic order cannot be established in LiNixMnyCozO2 even at low temperature of 3 K. Remarkably, the frustration parameters of these compounds are estimated to be larger than 30, indicating the existence of strongly frustrated magnetic interactions between spins …
Layered LiMnO$_2$ and Li$_2$MnO$_3$ are of great interest for lithium-ion battery cathodes because of their high theoretical capacities. The practical application of these materials is, however, limited due to poor electrochemical performance. We herein report a comprehensive first-principles study of defect physics in LiMnO$_2$ and Li$_2$MnO$_3$ using hybrid-density functional calculations. We find that manganese antisites have low formation energies in LiMnO$_2$ and may act as nucleation sites for the formation of impurity phases. The antisites can also occur with high concentrations in Li$_…
Solid state lithium- and sodium-ion batteries utilize solid ionicly conducting compounds as electrolytes. However, the ionic conductivity of such materials tends to be lower than their liquid counterparts, necessitating research efforts into finding suitable alternatives. The process of electrolyte screening is often based on a mixture of domain expertise and trial-and-error, both of which are time and resource-intensive. Data-driven and machine learning approaches have recently come to the fore to accelerate learnings towards discovery. In this work, we present a simple machine-learning based…
Defects and their interactions in crystalline solids often underpin material properties and functionality as they are decisive for stability, result in enhanced diffusion, and act as a reservoir of vacancies. Recently, lithium-rich layered oxides have emerged among the leading candidates for the next-generation energy storage cathode material, delivering 50 % excess capacity over commercially used compounds. Oxygen-redox reactions are believed to be responsible for the excess capacity, however, voltage fading has prevented commercialization of these new materials. Despite extensive research th…
Phosphorus has received recent attention in the context of high-capacity and high-rate anodes for lithium and sodium-ion batteries. Here, we present a first principles structure prediction study combined with NMR calculations which gives us insights into its lithiation/sodiation process. We report a variety of new phases phases found by AIRSS and the atomic species swapping methods. Of particular interest, a stable Na$_5$P$_4$-C2/m structure and locally stable structures found less than 10 meV/f.u. from the convex hull, such as Li$_4$P$_3$-P2$_1$2$_1$2$_1$, NaP$_5$-Pnma and Na$_4$P$_3$-Cmcm. T…
Vacancy-induced Modification of Electronic Band Structure of LiBO$_{2}$ Material as Cathode Surface Coating of Lithium-ion Batteries
University of Missouri（密苏里大学）；University of Missouri Research Reactor (MURR)（密苏里大学研究反应堆中心）；Escuela de Física, Universidad Pedagógica y Tecnológica de Colombia（哥伦比亚教育技术大学物理学院）
Improved Electrochemical Performance and Diffusion kinetics by Boron-doping in Na$_{0.66}$Mn$_{0.8}$Fe$_{0.2}$O$_{2}$ Layered Cathodes for Sodium-Ion Batteries
Indian Institute of Technology Delhi（印度德里理工学院）；Hindu College, University of Delhi（德里大学印度教学院）；Indian Institute of Technology Delhi-Abu Dhabi（印度德里理工学院阿布扎比分校）
Cathode materials undergo various phase transitions during the charge/discharge process, and the structural transitions significantly affect the battery performance. Although phonon properties can provide a direct clue for structural stability and transitions, it has been less explored in sodium cathode materials. Here, using the first-principles calculations, we investigate phonon and electronic properties of various layered NaMnO$_2$ materials, especially focusing on the dependency of the Jahn-Teller distortion of Mn$^{3+}$. The phonon dispersion curves show that the O$'$3 and P$'$2 structur…
Discovering new electrodes for sodium-ion battery requires clear understanding of the material process during battery operation. Using first-principles calculations, we identify mechanisms of ionic diffusion and electronic transfer in newly developed cathode material, eldfellite Na$_x$Fe(SO$_4$)$_2$, reproducing the electrochemical properties in good agreement with experiment. The inserted sodium atom is suggested to diffuse along the two-dimensional pathway with preceding movement of the host sodium atom, and the activation energy is calculated to be reasonable for fast insertion. We calculat…
Structural and Optical properties of the (Na0.5 K0.5)y Li 1-y NbO3 (y = 0.934 & 0.936) ceramics have been explored in terms of the X-Ray diffraction patters, Rietveld analysis, UV-Vis spectroscopy, and Kubelka-Munk functions. Rietveld analysis of both these structures reveals them to be tetragonal with space group P4mm. It is found that increase in Li doping increases the optical band gap. Presence of additional hardening dopant MnO2 is found to have a uniform behavior for both these composition. With increasing MnO2 concentration, the band gap decreases indicative of increase in B-site cation…
While Si is an effective insertion type anode for Li-ion batteries, crystalline Si has been shown to be unsuitable for Na and Mg storage due, in particular, to insufficient binding strength. It has recently been reported that Si nanowires could be synthesized with high-concentration (several atomic %) and dispersed Al doping. Here we show based on density functional theory calculations that Al doping significantly improves the energetics for Na and Mg insertion, specifically, making it thermodynamically favored versus vacuum reference states. For high Al concentrations, the energy of Mg in Al-…
The search for an alternative high-voltage polyanionic cathode material for Li-ion batteries is vital to improve the energy densities beyond the state-of-the-art, where sulfate frameworks form an important class of high-voltage cathode materials due to the strong inductive effect of the S$^{6+}$ ion. Here, we have investigated the mechanism of cationic and/or anionic redox in Li$_x$M(SO$_4$)$_2$ frameworks (M = Mn, Fe, Co, and Ni and 0 $\leq$ x $\leq$ 2) using density functional calculations. Specifically, we have used a combination of Hubbard $U$ corrected strongly constrained and appropriate…
We present first-principles calculations for quasiparticle excitations in sodium and lithium including the effects of charge and spin fluctuations. We employ the Overhauser-Kukkonen form for the electron self energy arising from spin fluctuations and demonstrate that the coupling of electrons to spin fluctuations gives an important contribution to the quasiparticle lifetime, but does not significantly reduce the occupied bandwidth. Including correlation effects beyond the random-phase approximation in the screening from charge fluctuations yields good agreement with experiment.
We present a comparative ab initio study of Li and Na insertion in molecular (van der Waals) crystals of TCNE (tetracyanoethylene) as well as in covalent Li/Na-TCNE crystals. We confirm the structure of previously synthesized (covalent) Li-TCNE crystal as well as predict the existence of its Na-TCNE analogue. In the molecular/covalent TCNE crystals, insertion sites are identified with the binding energy of Li and Na up to 2.7/1.8 and 2.6/1.8 eV stronger than Li and Na cohesive energy, respectively, in dilute concentrations. Up to 5.5/2.5 and 3/2 Li and Na atoms per TCNE unit can be inserted in…
It is well known that the spatial distribution of the carbon-binder domain (CBD) offers a large potential to further optimize lithium-ion batteries. However, it is challenging to reconstruct the CBD from tomographic image data obtained by synchrotron tomography. In the present paper, we consider several approaches to segment 3D image data of two different cathodes into three phases, namely active material, CBD and pores. More precisely, we focus on global thresholding, a local closing approach based on EDX data, a k-means clustering method, and a procedure based on a neural network that has be…
Following the successful utilization of LiFePO4 as a novel cathode material for rechargeable lithium batteries, interest and efforts have grown in the research of another olivine structured material LiMnPO4 due to its higher operating potential voltage and energy density. However, high rate performance for LiMnPO4-based cathode materials has been challenging due to its extremely low electrical and ionic conductivities. Here, we develop a synthesis of Fe-doped LiMnPO4 (LiMn0.75Fe0.25PO4) nanorods directly bonded on graphene sheets (reduced from graphene oxide) to render LiMn0.75Fe0.25PO4 nanoro…
Li and Na attachment to free tetracyanoethylene (TCNE) molecules and TCNE adsorbed on doped graphene is studied using density functional theory. While TCNE is adsorbed only weakly on ideal graphene, we identified a configuration in which TCNE is chemisorbed on Al-doped graphene via molecule C atom and a surface oxygen atom. Up to four (five) Li and Na atoms can be stored on both free (adsorbed) TCNE with binding energies stronger than cohesive energies of the Li and Na metals. When storing up to three atoms per molecule, it should be possible to avoid reduction of common battery electrolytes. …
Sodium orthosilicates Na2MSiO4 (M denotes transition metals) have attracted much attention due to the possibility of exchanging two electrons per formula unit. In this work, we report a group of sodium iron orthosilicates Na2FeSiO4, the crystal structures of which are characterized by a diamond-like Fe-Si network. The Fe-Si network is quite robust against the charge/discharge process, which explains the high structural stability observed in experiment. Using the density functional theory within the GGA+U framework and X-ray diffraction studies, the crystal structures and structural stabilities…
A LiFe0.6Mn0.4PO4 (LFMP) cathode exploiting the olivine structure is herein synthesized and characterized in terms of structure, morphology, and electrochemical features in a lithium cell. The material shows reversibility of the electrochemical process which evolves at 3.5 and 4 V versus Li+/Li due to the Fe+2/Fe+3 and Mn+2/Mn+3 redox couples, respectively, as determined by cyclic voltammetry. The LFMP has a well-defined olivine structure revealed by X-ray diffraction, a morphology consisting of submicron particle aggregated into micrometric clusters as indicated by scanning and transmission e…
Lithium-metal batteries employing concentrated glyme-based electrolytes and different cathode chemistries are herein evaluated in view of a safe use of the highly energetic alkali-metal anode. Indeed, diethylene-glycol dimethyl-ether (DEGDME) and triethylene-glycol dimethyl-ether (TREGDME) dissolving lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and lithium nitrate (LiNO3) in concentration approaching the solvents saturation limit are used in lithium batteries employing either a conversion sulfur-tin composite (S:Sn 80:20 w/w) or a Li+ (de-)insertion LiFePO4 cathode. Cyclic voltammetry (…
Electrochemical performance and diffusion kinetics of a NASICON type Na$_{3.3}$Mn$_{1.2}$Ti$_{0.75}$Mo$_{0.05}$(PO$_4$)$_3$/C cathode for low-cost sodium-ion batteries
Crystal structures play a vital role in determining materials properties. In Li-ion cathodes, the crystal structure defines the dimensionality and connectivity of interstitial sites, thus determining Li-ion diffusion kinetics. While a perfect crystal has infinite structural coherence, a class of recently discovered high-capacity cathodes, Li-excess cation-disordered rocksalts, falls on the other end of the spectrum: Their cation sublattices are assumed to be randomly populated by Li and transition metal ions with zero configurational coherence based on conventional X-ray diffraction, such that…
Here we report fabrication of flexible and stretchable battery composed of strain free LiFePO4 cathode, Li4Ti5O10 anode and a solid poly ethylene oxide (PEO) electrolyte as a separator layer. The battery is developed in a view of smart textile applications. Featuring solid thermoplastic electrolyte as a key enabling element this battery is potentially extrudable or drawable into fibers or thin stripes which are directly compatible with the weaving process used in smart textile fabrication. The paper first details the choice of materials, fabrication and characterisation of electrodes and a sep…
Composite materials achieved by including transition-metal oxides with different structures and morphologies in sulfur are suggested as scalable cathodes for high-energy lithium-sulfur (Li-S) batteries. The composites contain 80 wt.% sulfur and 20 wt.% of either MnO2 or TiO2, leading to a sulfur content in the electrode of 64 wt.% and revealing a reversible, fast, and lowly polarized conversion process in the cell with limited interphase resistance. The S-TiO2 composite exhibits an excellent rate capability between C/10 and 2C, and a cycle life extended over 400 cycles at 2C, owing to the effe…
Unraveling the storage mechanism of Na$_{3}$V$_{2-x}$Ni$_x$(PO$_4$)$_2$F$_3$/C cathodes for sodium-ion batteries through electrochemical, {\it operando} X-ray diffraction and microscopy studies
本研究结合 EIS、GITT、CV、operando XRD 与原位同步辐射 TXM，揭示 Ni 掺杂 Na₃V₂(PO₄)₂F₃/C 正极的储钠机制、扩散动力学及长循环稳定性。
Using a solid electrolyte to tune the carrier density in thin-film materials is an emerging technique that has potential applications in both basic and applied research. Until now, only materials containing small ions, such as protons and lithium ions, have been used to demonstrate the gating effect. Here, we report the study of a lab-synthesised sodium-ion-based solid electrolyte, which shows a much stronger capability to tune the carrier density in graphene than previously reported lithium-ion-based solid electrolyte. Our findings may stimulate the search for solid electrolytes better suited…
The performance of lithium and sodium ion batteries relies notably on the accessibility to carbon electrodes of controllable porous structure and chemical composition. This work reports a facile synthesis of well-defined porous N-doped carbons (NPCs) using a poly(ionic liquid) (PIL) as precursor, and graphene oxide (GO)-stabilized poly(methyl methacrylate) (PMMA) nanoparticles as sacrificial template. The GO-stabilized PMMA nanoparticles were first prepared and then decorated by a thin PIL coating before carbonization. The resulting NPCs reached a satisfactory specific surface area of up to 56…
