Prediction of Li intercalation voltages in rechargeable battery cathode materials: effects of exchange-correlation functional, van der Waals interactions, and Hubbard $U$
Quantitative predictions of the Li intercalation voltage and of the electronic properties of rechargeable battery cathode materials are a substantial challenge for first-principles theory due to the possibility of (1) strong correlations associated with localized transition metal $d$ electrons and (2) significant van der Waals (vdW) interactions in layered systems, both of which are not accurately captured by standard approximations to density functional theory (DFT). Here, we perform a systematic benchmark of electronic structure methods based on the widely-used generalized gradient approximation of Perdew, Burke, and Ernzerhof (PBE) and the new strongly constrained and appropriately normed (SCAN) meta-generalized gradient approximation for battery cathode materials. Studying layered Li$_x$TiS$_2$, Li$_x$NiO$_2$, and Li$_x$CoO$_2$, olivine Li$_x$FePO$_4$, and spinel Li$_x$Mn$_2$O$_4$, we compute the voltage, crystal structure, and electronic structure with and without extensions to incorporate on-site Hubbard interactions and vdW interactions. Within pure DFT (i.e., without corrections for on-site Hubbard interactions), SCAN is a significant improvement over PBE for describing cathode materials, decreasing the mean absolute voltage error by more than 50%. Although explicit vdW interactions are not critical and in cases even detrimental when applied in conjunction with SCAN, Hubbard $U$ corrections are still in general necessary to achieve reasonable agreement with experiment. We show that no single method considered here can accurately describe the voltage and overall structural, electronic, and magnetic properties (i.e., errors no more than 5% for voltage, volume, band gap, and magnetic moments) of battery cathode materials, motivating a strong need for improved electronic structure approaches for such systems.
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…
We present a thermodynamic analysis of the driving forces for intercalation and conversion reactions in battery cathodes across a range of possible working ion, transition metal, and anion chemistries. Using this body of results, we analyze the importance of polymorph selection as well as chemical composition on the ability of a host cathode to support intercalation reactions. We find that the accessibility of high energy charged polymorphs in oxides generally leads to larger intercalation voltages favoring intercalation reactions, whereas sulfides and selenides tend to favor conversion reacti…
Searching for efficient and high-performance cathode materials for rechargeable magnesium ion batteries (RMBs) is urgent for exploring sustainable energy technologies. However, the majority of cathode materials for RMBs usually suffer from low rate capacity and inferior cycle performance caused by structure collapse. Herein, ternary CuCo$_2$S$_4$/Cu$_7$S$_4$ composites with nano-sized are first synthesized by a facile solvothermal method in this work and the magnesium ion storage behavior is discussed when applied in the cathode for RMBs. Electrochemical results demonstrate that the nanosphere…
Study of In-plane and Interlayer Interactions During Aluminum Fluoride Intercalation in Graphite: Implications for the Development of Rechargeable Batteries
We present theoretical analysis on why and how rechargeable metal-air type batteries can be made significantly safer and more practical by utilizing CO2/oxalate conversions instead of O2/peroxide or O2/hydroxide ones, in the positive electrode. Metal-air batteries, such as the Li-air one, may have very large energy densities, comparable to that of gasoline, theoretically allowing for long range all-electric vehicles. There are, however, still significant challenges, especially related to the safety of their underlying chemistries, the robustness of their recharging and the need of supplying hi…
A new nanofibrous material, consisting of a conductive carbon core and an external layer made of vanadium oxide, has been studied as a cathode for aluminium-ion batteries. The material enables a mixed-ion intercalation mechanism, resulting in the alternating insertion of $\text{Al}^{3+}$ and $\text{AlCl}_4^-$ in the $\text{V}_2\text{O}_5$ and carbon layers, respectively. This is a highly desirable feature for cathode materials which may increase the energy density of future batteries by optimising the utilisation of the electrolyte.
We report the electrochemical performance of nanostructures of Na$_{0.66}$V$_4$O$_{10}$ as cathode material for rechargeable batteries. The Rietveld refinement of room temperature x-ray diffraction pattern shows the monoclinic phase with C2/m space group. The cyclic voltammetry curves of prepared half-cells exhibit redox peaks at ~3.1 and 2.6~V, which are due to two-phase transition reaction between V$^{5+/4+}$ and can be assigned to the single step deintercalation/intercalation of Na-ion. We observe a good cycling stability with specific discharge capacity (measured vs. Na$^+$/Na) between 80 …
Potassium-ion ($\rm K$-ion) rechargeable batteries; considered to be lucrative low-cost battery options for large-scale and capacious energy storage systems, have been garnering tremendous attention in recent years. However, due to the scarcity of cathode materials that can condone the reversible re-insertion of the large $\rm K$-ions at feasible capacities, the viability of $\rm K$-ion batteries has been greatly undercut. In this paper, we explore a potential cathode material in the $\rm K_2O$-$\rm Fe_2O_3$-$\rm MnO_2$ ternary phase system, that not only demonstrates reversible $\rm K$-ion re…
The structural stability and electrochemical performance of boron substituted fluorinated graphite as a Li ion batteries cathode material are studied by first principles calculations. The results show that boron substituted fluorinated graphite BC3F4 possesses excellent structural stability, good electrical and ionic conductivities. Unexpectedly, the average Li intercalation voltage of LiBC3F4 is up to 4.44 V, which is much larger than that of LiBCF2. The average voltage of LiBC3F4 is even larger than that of common commercial transition metal oxides cathodes, indicating that LiBC3F4 is a brea…
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…
Up to now, many guest atoms/molecules/ions have been successfully synthesized into graphite to form the various compounds. For example, alkali-atom graphite intercalation compounds are verified to reveal the stage-n structures, including LiC6n and LiM8n [M=K. Rb and Cs; n=1, 2, 3; 4]. On the other side, AlCl4-ion/molecule ones are examined to show stage-4 and stage-3 cases at room and lower temperatures, respectively. Stage-1 and stage-2 configurations, with the higher intercalant concentrations, are unable to synthesize in experimental laboratories. This might arise from the fact that it is q…
The design of novel cathode materials for Li-ion batteries would greatly benefit from accurate first-principles predictions of structural, electronic, and magnetic properties as well as intercalation voltages in compounds containing transition-metal elements. For such systems, density-functional theory (DFT) with standard (semi-)local exchange-correlation functionals is of limited use as it often fails due to strong self-interaction errors that are especially relevant in the partially filled $d$ shells. Here, we perform a detailed comparative study of the phospho-olivine cathode materials Li$_…
Cycle life is critically important in applications of rechargeable batteries, but lifetime prediction is mostly based on empirical trends, rather than mathematical models. In practical lithium-ion batteries, capacity fade occurs over thousands of cycles, limited by slow electrochemical processes, such as the formation of a solid-electrolyte interphase (SEI) in the negative electrode, which compete with reversible lithium intercalation. Focusing on SEI growth as the canonical degradation mechanism, we show that a simple single-particle model can accurately explain experimentally observed capaci…
Intercalation materials are promising candidates for reversible energy storage and are, for example, used as lithium-battery electrodes, hydrogen-storage compounds, and electrochromic materials. An important issue preventing the more widespread use of these materials is that they undergo structural transformations (of up to ~10% lattice strains) during intercalation, which expand the material, nucleate microcracks, and, ultimately, lead to material failure. Besides the structural transformation of lattices, the crystallographic texture of the intercalation material plays a key role in governin…
We present a refined Mn-Zn-H$_2$O Pourbaix diagram with the emphasis on parameters relevant for the Zn/MnO$_2$ rechargeable cells. It maps out boundaries of electrochemical stability for MnO$_2$, ZnMn$_2$O$_4$, ZnMn$_3$O$_7$, and MnOOH. The diagram helps to rationalize experimental observation on processes and phases occurring during charge/discharge, including the position of charge/discharge redox peaks and capacity fade observed in rechargeable aqueous Zn-ion batteries for stationary storage. The proposed Pourbaix diagram is validated by observing the pH-dependent transformation of electrol…
In Lithium ion batteries (LIBs), proper design of cathode materials influences its intercalation behavior, overall cost, structural stability, and its impact on environment. At present, the most common type of cathode materials, NCA , has very high cobalt concentration. Since cobalt is toxic and expensive, the existing design of cathode materials is not cost-effective, and environmentally benign. However, these immensely important issues have not yet been properly addressed. Therefore, we have performed density functional theory (DFT) calculations to investigate three types of NCA cathode mate…
Co-intercalation is a potential approach to influence the voltage and mobility with which cations insert in electrodes for energy storage devices. Combining a robust thermodynamic model with first-principles calculations, we present a detailed investigation revealing the important role of H$_2$O during ion intercalation in nano-materials. We examine the scenario of Mg$^{2+}$ and H$_2$O co-intercalation in nano-crystalline Xerogel-V$_2$O$_5$, a potential cathode material to achieve energy density greater than Li-ion batteries. Water co-intercalation in cathode materials could broadly impact an …
Rechargeable Zn batteries with aqueous electrolytes have been considered as promising alternative energy storage technology, with various advantages such as low cost, high volumetric capacity, environmentally friendly, and high safety. However, a lack of reliable cathode materials has largely pledged their applications. Herein, we developed a machine learning (ML) based approach to predict cathodes with high capacity (>150 mAh/g) and high voltage (>0.5V). We screened over ~130,000 inorganic materials from the Materials Project database and applied the crystal graph convolutional neural network…
Non-equilibrium defects often dictate macroscopic functional properties of materials. In intercalation hosts, widely used in rechargeable batteries, high-dimensional defects largely define reversibility and kinetics1,2,3,4. However, transient defects briefly appearing during ionic transport have been challenging to capture, limiting the understanding of their life cycle and impact. Here, we overcome this challenge and track operando the interaction and impact of metastable defects within NaxNi1-xMnyO2 intercalation hosts in a charging sodium-ion battery. Three-dimensional coherent X-ray imagin…
At present, the most common type of cathode materials, NCA [Li_(1-x)Ni_(0.80)Co_(0.15)Al_(0.05)O_(2), x = 0 to 1], have a very high concentration of cobalt. Since cobalt is toxic and expensive, the existing design of cathode materials is neither cost-effective nor environmentally benign. We have performed density functional theory (DFT) calculations to investigate electrochemical, electronic, and structural properties of four types of NCA cathode materials with the simultaneous decrease in Co content along with the increase in Ni content. Our results show that even if the cobalt concentration …
Interfaces are ubiquitous in Li-ion battery electrodes, occurring across compositional gradients, regions of multiphase intergrowths, and between electrodes and solid electrolyte interphases or protective coatings. However, the impact of these interfaces on Li energetics remains largely unknown. In this work, we calculated Li intercalation-site energetics across cathode interfaces and demonstrated the physics governing these energetics on both sides of the interface. We studied the olivine/olivine-structured LixFePO4/LixMPO4 (x=0 and 1, M=Co, Ti, Mn) and layered/layered-structured LiNiO2/TiO2 …
Layered lithium intercalating transition metal (TM) oxides are promising cathode materials for Li-ion batteries. Here we scrutinize the recently developed strongly constrained and appropriately normed (SCAN) density functional method to study structural, magnetic and electrochemical properties of prototype cathode materials LiNiO2, LiCoO2, and LiMnO2 at different Li-intercalation limits. We show that SCAN outperforms earlier popular functional combinations, providing results in considerably better agreement with experiment without use of Hubbard parameters, and dispersion corrections are found…
Conversion cathode materials are gaining interest for secondary batteries due to their high theoretical energy and power density. However, practical application as a secondary battery material is currently limited by practical issues such as poor cyclability. To better understand these materials, we have developed a pseudo-two-dimensional model for conversion cathodes. We apply this model to FeS2 - a material that undergoes intercalation followed by conversion during discharge. The model is derived from the half-cell Doyle-Fuller-Newman model with additional loss terms added to reflect the con…
We prepared Na$_x$TO$_2$ (T = Mn, Co) nanostructures to use as cathode material in Na-ion batteries. The Rietveld refinement of x-ray diffraction data confirms the hexagonal symmetry. Scanning and transmission electron microscopy measurements show hexagonal and rod-shape morphology for T = Co and Mn, respectively. The magnetic measurements indicate the presence of variable oxidation states of Mn/Co ions, but no long range ordering till 5~K. We find that the Na$_{0.6}$MnO$_2$ is highly insulating whereas Na$_{0.7}$CoO$_2$ is semiconducting in nature. The conduction in Na$_{0.7}$CoO$_2$ takes pl…
Covalent functionalization is a way to tune the electrochemical properties of hexagonal boron nitride (h-BN) monolayers. The wide band gap insulator h-BN may become metallic conductor upon functionalization with strong oxidants, such as fluorosulfonyl radicals ($\cdot$OSO$_2$F), as known since 1978 [N. Bartlett et al., J. Chem. Soc. Chem. Comm. {\bf 5}, 200 (1978)], with electrical conductivity of 1.5 S/cm [C. Shen et al., J. Solid State Chem. {\bf 147}, 74 (1999)] that greatly surpasses commercial cathode material Li$_{x}$CoO$_{2}$ while retaining excellent ionic conductivity. Functionalized …
Disordered rocksalt (DRX) Li3V2O5 is a promising candidate for anode in rechargeable lithium-ion batteries because of its ideal low voltage, high rate capability, and superior cycling stability. Herein, we presents a comprehensive study of intercalation chemistry of the DRX-Li3V2O5 anode using density functional theory calculations combined with machine learning cluster expansions and interatomic potentials. The predicted voltage profile of the disordered Li3V2O5 anode at room temperature based on Monte Carlo simulations with a fitted cluster expansion model is in excellent agreement with expe…
Natural abundance, impressive chemical characteristics and economic feasibility have rekindled the appeal for rechargeable sodium (Na) batteries as a practical solution for the growing energy demand, environmental sustainability and energy independence. However, the scarcity of viable positive electrode materials remains a huge impediment to the actualization of this technology. In this paper, we explore honeycomb layered oxides adopting the composition Na$_2$Ni$_{2-x}$Co$_x$TeO$_6$ ($x = 0, 0.25$ and $0.50$) as feasible positive electrode (cathode) materials for rechargeable sodium batteries …
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…
Accurate first-principles predictions of the structural, electronic, magnetic, and electrochemical properties of cathode materials can be key in the design of novel efficient Li-ion batteries. Spinel-type cathode materials Li$_x$Mn$_2$O$_4$ and Li$_x$Mn$_{1.5}$Ni$_{0.5}$O$_4$ are promising candidates for Li-ion battery technologies, but they present serious challenges when it comes to their first-principles modeling. Here, we use density-functional theory with extended Hubbard functionals - DFT+$U$+$V$ with on-site $U$ and inter-site $V$ Hubbard interactions - to study the properties of these …
First-principles calculation predict that olivine Li4MnFeCoNiP4O16 has ferrotoroidic characteristic and ferrimagnetic configuration with magnetic moment of 1.56 \muB per formula unit. The ferrotoroidicity of this material makes it a potential candidate for magnetoelectric materials . Based on the orbital-resolved density of states for the transtion-metal ions in Li4MnFeCoNiP4O16, the spin configuration for Mn2+,Fe3+,Co2+, and Ni2+ is t2g3eg2, t2g3eg2,t2g1t2g3eg1eg2, and t2g2t2g3eg1eg2, respectively. Density functional theory plus U (DFT+U) shows a indirect band gap of 1.25 eV in this predicted…
Graphite has been reported to have anion as well as cation intercalation capacities as both cathode and anode host materials for the dual ion battery. In this work, we study the intercalation of bis(trifluoromethanesulfonyl) imide (TFSI) anion from ionic liquid electrolyte into graphite with first-principles calculations. We build models for TFSI-C$_n$ compounds with systematically increasing unit cell sizes of graphene sheet and investigate their stabilities by calculating the formation energy, resulting in the linear decrease and arriving at the limit of stability. With identified unit cell …
Multivalent batteries are an energy storage technology with the potential to surpass lithium-ion batteries, however their performance has been limited by the low voltages and poor solid-state ionic mobility of available cathodes. A computational screening approach to identify high-performance multivalent intercalation cathodes among materials that do not contain the working ion of interest has been developed which greatly expands the search space that can be considered for materials discovery. This approach has been applied to magnesium cathodes as a proof of concept and four resulting candida…
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 compou…
Mg batteries utilizing a Mg metal anode with a high-voltage intercalation cathode define a potential pathway toward energy storage with high energy density. However, the realization of Mg batteries is plagued by the instability of existing electrolytes against the Mg-metal anode and high-voltage cathode materials. One viable solution to this problem is the identification of protective coating materials that could effectively separate the distinct chemistries of the metal-anode and the cathode materials from the electrolyte. Using first-principles calculations we map the electrochemical stabili…
Smoothed Boundary Method Framework for Electrochemical Simulation of Li-ion Battery Cathode with Complex Microstructure: Model, Formulation and Parameterization
Lithium-intercalated layered transition-metal oxides, LixTMO2, brought about a paradigm change in rechargeable batteries in recent decades and show promise for use in memristors, a type of device for future neural computing and on-chip storage. Thermal transport properties, although being a crucial element in limiting the charging/discharging rate, package density, energy efficiency, and safety of batteries as well as the controllability and energy consumption of memristors, are poorly managed or even understood yet. Here, for the first time, we employ quantum calculations including high-order…
A novel non-destructive methodology for operando observation of ion intercalation and the state of charge on battery electrodes is presented based on spectroscopic ellipsometry (SE). The potentiality of this technique for performing time-resolved measurements of (de-)lithiation processes on electrode materials has been demonstrated using thin film spinel LiMn$_2$O$_4$ as a cathode for Li-ion batteries. The chemical diffusivity of Li+ ions in this material has been determined by the time evolution of the Li insertion into the film, and in the light of these results, it has been possible to rela…
The identification of alternatives to the Lithium-ion battery architecture remains a crucial priority in the diversification of energy storage technologies. Accompanied by the low reduction potential of $\mathrm{Ca^{2+}/Ca}$, -2.87 V vs. SHE, metal-anode-based rechargeable Calcium (Ca) batteries appear competitive in terms of energy densities. However, the development of Ca-batteries lacks high-energy density intercalation cathode materials. Using first-principles methodologies, we screen a large chemical space for potential Ca-based cathode chemistries, with composition of $\mathrm{Ca_iTM_jZ_…
A lamellar lepidocrocite-type titanate structure with ~25% $\text{Ti}^{4+}$vacancies was recently synthesized, and it showed potential for use as an electrode in rechargeable lithium-ion batteries. In addition to lithium, we explore this material's ability to accommodate other monovalent ions with greater natural abundance (e.g. sodium and potassium) in order to develop lower-cost alternatives to lithium-ion batteries constructed from more widely available elements. Galvanostatic discharge/charge curves for the lepidocrocite material indicate that increasing the ionic radius of the monovalent …
The polyanionic compound Na2MnSiO4 is regarded as one of the promising cathode materials for Na-ion batteries due to good specific capacity with its attractive prospect of utilization of two electrons in the redox processes. So, in this study, we have performed the thermodynamic and electronic structure analysis of Na2MnSiO4 using first principles density functional theory calculations. The intermediate ground state configurations for Na2MnSiO4of Na de-intercalation were found using the cluster expansion method and are used to obtain the 0 K voltage profile as a function of Na concentration. T…
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…
