Alkali Ion Intercalation Research Articles

Spin-Glass States Generated in a van der Waals Magnet by Alkali-Ion Intercalation.

Tuning magnetic properties in layered van der Waals (vdW) materials has captured significant attention due to the efficient control of ground states by heterostructuring and external stimuli. Electron doping by electrostatic gating, interfacial charge transfer, and intercalation is particularly effective in manipulating the exchange and spin-orbit properties, resulting in a control of Curie temperature (TC) and magnetic anisotropy. Here, an uncharted role of intercalation is discovered to generate magnetic frustration. As a model study, Na atoms are intercalated into the vdW gaps of pristine Cr2Ge2Te6 (CGT) where generated magnetic frustration leads to emerging spin-glass states coexisting with a ferromagnetic order. A series of dynamic magnetic susceptibility measurements/analysis confirms the formation of magnetic clusters representing slow dynamics with a distribution of relaxation times. The intercalation also modifies other macroscopic physical parameters including the significant enhancement of TC from 66 to 240K and the switching of magnetic easy-hard axis direction. This study identifies intercalation as a unique route to generate emerging frustrated spin states in simple vdW crystals.

Alkali-Ion Intercalation Chemistry and Phase Evolution of Sn4P3.

Despite its high theoretical capacities, Sn4P3 anodes in alkali-ion batteries (AIBs) have been plagued by electrode damage and capacity decay during cycling, mainly rooted in the huge volume changes and irreversible phase segregation. However, few reports endeavor to ascertain whether these causes bear relevance to phase evolution upon cycling. Moreover, the phase evolution mechanism for alkali-ion intercalation remains imprecise. Herein, the structural transformations and detailed mechanisms upon various alkali-ion intercalation processes are systematically revealed, utilizing both experimental techniques and theoretical simulations. The results reveal that the energy storage of Sn4P3 occurs in a two-stage process, starting from an insertion process, followed by a transition process. As the cycle proceeds, the final delithiated/desodiated/depotassiated components gradually trap alkali ions (Li+, Na+, and K+), which is attributed to the incomplete electrochemical transition and difficulty in Sn4P3 regeneration due to the kinetic limitations in removing M (M = Li, Na, and K). Furthermore, Sn4P3 anode obeys the "shrinking core mechanism" in potassium-ion batteries (KIBs), wherein a minor fraction of Sn4P3 in the outer layer of the particles is initially involved in the potassiation/depotassiation processes, followed by a gradual participation of the inner parts until the entire particle is involved. It is worth mentioning that K-Sn alloys are not found to exist during the transition process of KIBs; instead, K-Sn-P phases are found, which makes it differ from that in lithium-ion batteries (LIBs) and sodium-ion batteries (NIBs). These findings are expected to deepen the understanding of the reaction mechanism of Sn4P3 and enlighten the material designs for improved performance.

Theoretical insights into surface-phase transition and ion competition during alkali ion intercalation on the Cu4Se4 nanosheet.

The development of stable and efficient electrode materials is imperative and also indispensable for further commercialization of sodium/potassium-ion batteries (SIBs/PIBs) and new detrimental issues such as proton intercalation arise when utilizing aqueous electrolytes. Herein the electrochemical performance of the Cu4Se4 nanosheet was determined for both organic and aqueous SIBs and PIBs. By means of density functional theory calculation, Na+, K+ and H+ intercalations onto both sides of the Cu4Se4 nanosheet were revealed. The Cu4Se4 nanosheet well maintains its metallic electronic conductivity and the changes in lateral lattice parameters are within 4.66% during the whole Na+/K+ intercalation process for both SIBS and PIBs. The theoretical maximum Na/K storage capacity of 188.07 mA h g-1 can be achieved by stabilized second-layer adsorption of Na+/K+. The migration barriers of Na and K atoms on the Cu4Se4 nanosheet are 0.270 and 0.173 eV, respectively. It was discovered that Na/K- intercalation in the first layer is accompanied by a first-order surface phase transition, resulting in an intercalation voltage plateau of 0.659/0.756 V, respectively. The region of the two-surface phase coexistence for PIBs, is shifted toward a lower coverage when compared with that for SIBs. The partially protonated Cu4Se4 nanosheet (HxCu4Se4, x ≤ 10/9) was revealed to be structurally and thermodynamically stable. While the partially protonated Cu4Se4 nanosheet is favorable in acidic electrolytes (pH = 0) when protons and Na/K ions compete, we showed that Na+/K+ intercalated products may be preferred over H+ at low coverages in alkali electrolyte (pH = 14). However, the proton intercalation substantially decreases the battery capacity in aqueous SIBs and PIBs. Our work not only identifies the promising performance of Cu4Se4 nanosheets as an electrode material of SIBs and PIBs, but also provides a computational method for aqueous metal-ion batteries.

Enhancing the lithium storage properties of molten salt-etched Ti3C2Tx through sequential intercalation of alkali ions

A sequential alkali ion intercalation strategy was proposed to control the interlayer structure of Lewis acid-molten salt-etched MXenes.

Galvanostatic Fast Charging of Alkali-Ion Battery Materials at the Single-Particle Level: A Map-Driven Diagnosis.

In this work, we develop a new tool to provide a diagnostic map for alkali-ion intercalation materials under galvanostatic conditions. These representations, stated in the form of capacity level diagrams, are built from hundreds of numerical simulations representing different experimental conditions, summarized in two dimensionless parameters: a kinetic parameter denominated Ξ and a finite diffusion parameter l. To lay the theoretical and methodological foundations, a general model is used here. This model can be adapted to the thermodynamic and kinetic framework of specific systems. We provide two representative examples.

DFT investigations of KTiOPO4Mx (M = K, Na, and Li) anodes for alkali-ion battery.

The properties of KTiOPO4Mx (M = K, Na, and Li; x = 0.000-1.000) as an anode for potassium-ion batteries (PIBs), sodium-ion batteries (SIBs), and lithium-ion batteries (LIBs) are investigated by density functional theory calculations. Our work reveals that the electrochemical performance of KTiOPO4 as an anode for PIBs is superior to that for SIBs and LIBs, in terms of average voltage and ion diffusion kinetics. The ab initio molecular dynamics simulations indicate that the KTiOPO4Mx anode exhibits high structural stability, and alkali ion intercalation contributes to accelerating ion diffusion during the charging process. Particularly, the low activation energy of 0.406eV of K migration on surface KTP(210), obtained by the climbing-image nudged elastic band method, suggests a high-rate capability. The systematical comparison of the performance of KTiOPO4 as an anode for PIBs, SIBs, and LIBs on the theoretical perspective clarifies that a large channel is not always promising for small radius ion intercalation and diffusion.

K x VPO4f (x~0): A Host Structure for Versatile Alkali Ion Intercalation

Alkali-ion intercalation compounds are commonly used cathode materials for rechargeable batteries, including Li-, Na-, and K-ion batteries. In our previous works, we developed KVPO4F as a high voltage cathode material for K-ion batteries.[1, 2] The KVPO4F framework has large void spaces that can accommodate facile K ion intercalation. In this present work, we investigated KVPO4F as a host structure for versatile alkali ion (Li, Na, and K) intercalation after fully removing the K ions.[3] Interestingly, our work finds that the voltage for Na insertion is even higher than that for Li insertion in K x VPO4F (x~0) host structure, in contrast to the common belief that Li intercalation voltage is always higher than Na intercalation. The lower Li intercalation voltage is likely attributed to unstable Li site in a large cavity in KxVPO4F (x~0), making less stable discharged product upon Li insertion vs. Na insertion. In addition, we discovered that Li intercalation is much more sluggish than Na and K intercalation in KxVPO4F (x~0). Since Li ion is too small compared to the cavity in the KxVPO4F (x~0) structure, Li ions are under-coordinated in the transition state. Therefore, Li ion migration barrier becomes much higher than Na and K migration. This finding indicates that large cavity size (or channel size) is not always good for fast alkali ion migration and we need to finely tune the cavity size suitable for each intercalating ion species.

Chemo-Mechanics of Alkali-Ion Intercalation into Iron Phosphate Composite Cathodes

Development of cathode structures suitable for Na-ion and K-ion batteries is still one of the major challenges on the way to the design of next-generation alkali metal-ion batteries. Although Li, Na and K belong to the same alkali metal group with a single charge in their cation form, intercalation of Na+ and K+ ions in electrodes is difficult since ionic radii of Na+ (0.98 Å) and K+ (1.38 Å) are larger than that of Li+ (0.69Å). Therefore, physical, and electrochemical behavior of the cathode materials in response to Na+ and K+ ion intercalation is expected to be fundamentally different than the response to Li+ ion. However, there is not much known about how electrochemical reactions and transport of ions take place in cathode materials with different alkali metal ions. There have been several studies focusing on electrochemical characterization and investigation of the structural changes in the electrode materials. Lack of insight into these reaction-transport mechanisms limits the design of novel cathode materials for Na-ion and K-ion batteries. Comparative studies between Li-ion, Na-ion and K-ion battery cathodes are critical to identify fundamental similarities and differences during intercalation. Even modest expansions in brittle cathodes can cause particle fracturing in a larger crystalline-size scale. Intercalation of larger ions can cause structural collapse and amorphization induced by continuous strains and distortions. Although the amorphization in the structure can be easily identified by conventional diffraction or electron microscopy techniques, quantitative analysis of the physical changes in the structure during and after amorphization while cycling the battery electrode is critical.In the first part of the talk, we will first report the utilization of in situ digital image correlation and in-operando X-ray diffraction (XRD) techniques to probe dynamic changes in the amorphous phase of iron phosphate during potassium intercalation. A new experimental approach allows to monitor dynamic physical and structural changes in the amorphous phase of the electrodes. In-operando XRD demonstrates amorphization in the electrode’s nanostructure during the first charge / discharge cycle. In situ strain analysis detects the reversible deformations associated with redox reactions in the amorphous phases. This method offers new insights to study mechanics of ion intercalation in the amorphous nanostructures.In the second part of the talk, we will compare the electrochemical and mechanical response of the iron phosphate cathodes upon Li, Na and K ion intercalation by using electrochemical techniques and in situ digital image correlation. Iron phosphate model electrodes were prepared by electrochemical displacement technique in order to ensure identical morphology, structure and chemistry in the pristine iron phosphate electrodes. Strain evolution during Li and Na intercalation results in more linear dependence on the state of charge / discharge except the first discharge of NaFePO4. However, strains generated in the electrode shows nonlinear behavior during insertion / extraction of K ions. Interestingly, when the same amount of K and Na ions are intercalated, similar chemomechanical expansions were observed. However, strain rate calculations showed that K ion intercalation results in a progressive increase in the strain rate, whereas Li and Na intercalation induce nearly constant strain rates. Potential-dependent behaviors also demonstrate more sluggish redox reactions during K intercalation, compared to the Li and Na intercalation. These observations provide a fundamental insight into the impact of alkali ions on the redox chemistry and associated chemomechanical deformations.

Oxygen-Storage Materials to Stabilize the Oxygen Redox Activity of Three-Layered Sodium Transition Metal Oxides.

To double the energy density of lithium- and sodium-ion batteries there is a need to activate simultaneously cationic and anionic redox reactions at the intercalation-type electrodes. In contrast to the cationic redox activity, the oxygen redox activity enforces an enhancement in the surface reactivity of the oxides leading to their poor reversibility and cycling stability. Herein, we propose a new concept to stabilize oxygen redox activity by using oxygen-storage materials as an efficient buffer supplying and receiving oxygen during alkali ion intercalation. As a proof-of-concept, the study is focused on CeO2 as a modifier of sodium nickel-manganese oxide with a three-layer sequence, P3-Na2/3Ni1/2Mn1/2O2. The CeO2-modified P3-Na2/3Ni1/2Mn1/2O2 displays a drastic increase in the reversible capacity following the order Na+ intercalation < Li+ intercalation < Li+,Na+ cointercalation.

(Invited) How Does Intercalation Ion Species Determine the Electrochemical Properties of Cathode Materials for Rechargeable Batteries?

Alkali-ion intercalation compounds are widely used as cathode materials for rechargeable batteries, including Li-, Na-, and K-ion batteries. For many years, researchers have developed layered oxide cathode materials for Na- and K-ion batteries given that the layered oxides show high reversible capacity and high working voltage in Li-ion technology. However, our works have demonstrated that the layered oxide compounds may not be good cathode candidates for Na and K systems. There are two main issues:[1-4] (i) Na and K transition metal oxide compounds form non-stoichiometric composition (x<1.0 in A x MO2, A= Na and K). It leads practical difficulty of realizing Na- and K-ion batteries because all the Na and K ions should come from the cathode in rocking-chair batteries. (ii) As the insertion ion size increases, the voltage curve becomes much sloped. The sloped voltage curves result in low specific capacity and average voltage. Both the problems are attributable to much stronger Na+-Na+ and K+-K+ interaction than Li+-Li+ in the layered oxide structure. In this respect, polyanion compounds that have 3 dimensional arrangements of Na and K ions, resulting in longer Na+-Na+ and K+-K+ distance, will be better candidates. We proposed KVPO4F[5] as an example of polyanion compounds and it has stoichiometric composition and provides high average voltage of ~4.3 V (vs. K/K+) with a reversible capacity of ~105 mAh/g.We further investigated the effect of intercalation ion species in K x VPO4F (x~0).[6] Our work demonstrates the voltage for Na intercalation is even higher than that for Li insertion unlike the common belief that Li insertion voltage is always higher than Na insertion. The lower Li intercalation voltage is likely attributed to unstable Li site in large cavity, making less stable discharged product upon Li insertion vs. Na insertion. In addition, we found that Li intercalation is more sluggish than Na and K intercalation in K x VPO4F (x~0). Since Li ion is too small compared to cavity in the cathode, Li ions are undercoordinated in the transition state, in which a Li ion is coordinated by two anions only. Therefore, Li ion migration barrier is much higher than Na and K migration. This finding teaches us that large cavity size (or channel size) is not always good for fast alkali ion migration and we need to finely tune the cavity size suitable for each intercalating ion species.

Na Superionic Conductor-Type TiNb(PO4)3 Anode with High Energy Density and Long Cycle Life Enables Aqueous Alkaline-Ion Batteries.

High energy density aqueous alkaline-ion batteries have drawn significant attention because of their intrinsic high security and low cost. As suitable anode materials with satisfying capacity and proper operating potential in an aqueous electrolyte are limited, it is of urgent need to find candidate materials to build aqueous alkaline-ion batteries for practical applications. For the first time, highly crystalline Na superionic conductor-type phase TiNb(PO4)3 (TNPO) was explored as an alkali-ion intercalation host in the aqueous battery technology. The TNPO material manifests a high specific capacity of 94 mA h g-1 at 5 C rate together with superior cyclic stability and remarkable rate capacity in aqueous electrolytes, which is assigned to its super stable three-dimensional tunnel structure. Furthermore, the aqueous lithium-ion battery based on the TNPO anode and LiMn2O4 (LMO) cathode delivers a high specific energy of 121 W h kg-1 and a specific power of 189 W kg-1 with a voltage output of 2.1 V, while it exhibits excellent cycling performance (82% capacity retention after 1000 times at 5 C rate). The remarkable overall electrochemical performances of the TNPO anode have clearly suggested that TNPO can be used as a promising electrode material of aqueous alkali-ion batteries with high energy density and long cycle life for energy storage in future.

Virtual screening of inorganic materials synthesis parameters with deep learning

Virtual materials screening approaches have proliferated in the past decade, driven by rapid advances in first-principles computational techniques, and machine-learning algorithms. By comparison, computationally driven materials synthesis screening is still in its infancy, and is mired by the challenges of data sparsity and data scarcity: Synthesis routes exist in a sparse, high-dimensional parameter space that is difficult to optimize over directly, and, for some materials of interest, only scarce volumes of literature-reported syntheses are available. In this article, we present a framework for suggesting quantitative synthesis parameters and potential driving factors for synthesis outcomes. We use a variational autoencoder to compress sparse synthesis representations into a lower dimensional space, which is found to improve the performance of machine-learning tasks. To realize this screening framework even in cases where there are few literature data, we devise a novel data augmentation methodology that incorporates literature synthesis data from related materials systems. We apply this variational autoencoder framework to generate potential SrTiO3 synthesis parameter sets, propose driving factors for brookite TiO2 formation, and identify correlations between alkali-ion intercalation and MnO2 polymorph selection.

Engineering the Transformation Strain in LiMnyFe1–yPO4 Olivines for Ultrahigh Rate Battery Cathodes

Alkali ion intercalation compounds used as battery electrodes often exhibit first-order phase transitions during electrochemical cycling, accompanied by significant transformation strains. Despite ∼30 years of research into the behavior of such compounds, the relationship between transformation strain and electrode performance, especially the rate at which working ions (e.g., Li) can be intercalated and deintercalated, is still absent. In this work, we use the LiMnyFe1-yPO4 system for a systematic study, and measure using operando synchrotron radiation powder X-ray diffraction (SR-PXD) the dynamic strain behavior as a function of the Mn content (y) in powders of ∼50 nm average diameter. The dynamically produced strain deviates significantly from what is expected from the equilibrium phase diagrams and demonstrates metastability but nonetheless spans a wide range from 0 to 8 vol % with y. For the first time, we show that the discharge capacity at high C-rates (20-50C rate) varies in inverse proportion to the transformation strain, implying that engineering electrode materials for reduced strain can be used to maximize the power capability of batteries.

Intercalation Pseudocapacitance in Ultrathin VOPO4 Nanosheets: Toward High-Rate Alkali-Ion-Based Electrochemical Energy Storage.

There is a growing need for energy storage devices in numerous applications where a large amount of energy needs to be either stored or delivered quickly. The present paper details the study of alkali-ion intercalation pseudocapacitance in ultrathin VOPO4 nanosheets, which hold promise in high-rate alkali-ion based electrochemical energy storage. Starting from bulk VOPO4·2H2O chunks, VOPO4 nanosheets were obtained through simple ultrasonication in 2-propanol. These nanosheets as the cathode exhibit a specific capacity of 154 and 136 mAh/g (close to theoretical value 166 mAh/g) for lithium and sodium storage devices at 0.1 C and 100 and ∼70 mAh/g at 5 C, demonstrating their high rate capability. Moreover, the capacity retention is maintained at 90% for lithium ion storage and 73% for sodium ion storage after 500 cycles, showing their reasonable stability. The demonstrated alkali-ion intercalation pseudocapacitance represents a promising direction for developing battery materials with promising high rate capability.

Understanding sodium versus lithium intercalation potentials of electrode materials for alkali-ion batteries

Differences in average voltages for the alkali ion intercalation ( Li , Na ) in a variety of electrode materials are investigated. The average Li and Na insertion potentials in the cavities of ◻ ReO 3-perovskite, ramsdellite-◻ Ti 2 O 4, layered-◻2 A 2 Ti 3 O 7 ( A = Li , Na ) and NASICON-◻ Na 3 Ti 2( PO 4)3 have been calculated by first principles calculations at the density functional theory level. The results identify the type of site occupied by the inserted ion as the relevant structural parameter. Occupation of large sites (c.n. = 12, 8) might yield Na insertion voltages higher than Li ones. On the other extreme, occupation of tetrahedral sites raises the Li insertion voltage as much as 0.8 V above the Na one. For octahedral sites the higher polarizing character of Li ions vs. Na ions acts as a key-factor to bring the Li intercalation voltage above that of Na intercalation.

Rationalization of Intercalation Potential and Redox Mechanism for A2Ti3O7 (A = Li, Na)

Na2Ti3O7 was recently reported to be highly promising as a negative electrode material for Na-ion batteries, thanks to its very low intercalation voltage (0.3 V vs Na+/Na0) and high capacity (200 mAh/g). The investigation of the redox mechanism in A2Ti3O7 (A = Li, Na) upon additional alkali ion intercalation concomitant to reduction of titanium is reported in this paper. Even if the low stability of the reduced phases (A2+xTi3O7) precluded a direct study, density functional theory (DFT) calculations allowed us to propose structural models for the reduced phases (A2+xTi3O7), which were further successfully confronted to the available experimental data. The alkali atoms are octahedrally coordinated in the reduced A2+xTi3O7 phase, so that the whole resulting structure can be considered rocksalt type. The very different potentials at which ion insertion is observed for A = Li or A = Na clearly prove that analogies between lithium and sodium systems cannot be taken for granted. In this case, such findings can be fully rationalized through DFT and arise from the differences in polarizing character between lithium and sodium ions that cause, respectively, contraction and expansion of the cell volume and the destabilization of the inserted materials derived from the larger size of sodium ions.

Color change of V 2O 5 thin films upon exposure to organic vapors

The reaction of amorphous V 2O 5 thin films with various organic vapors is investigated using in-situ optical transmission and in-situ Raman spectroscopic measurements. When V 2O 5 thin films are exposed to vapors of methanol, ethanol, acetone, and isopropanol, changes in the Raman spectrum are observed. These changes are similar to those due to alkali ion intercalation and most pronounced for methanol and ethanol. The optical transmission also increases when the thin films are exposed to methanol and ethanol vapors. Depositing a thin catalyst layer of palladium does not promote the reaction. This result has implications for using this material in hydrogen sensor applications, as extended exposure to organic vapors may not be differentiated from the presence of hydrogen.

Alkali ion intercalation in V2O5: preparation and laboratory characterization of thin films produced by ALD

AbstractThin films of V2O5 act as performant alkali ion storage material, with applications mostly in Li microbatteries or in electrochromic windows. Oxide films less than 100 nm thick have been obtained by the Atomic Layer Deposition (ALD) method. The alkali ion insertion has been performed either via an electrochemical cathodic reaction in a non‐aqueous solvent, or from the vapour phase in a vacuum chamber at RT. Both experimental procedures promoted the insertion of large amounts of the alkali ion with consequent reduction of the oxidation state of V, from 5+ to 4+ and even to 3+, measured with XPS‐UPS. The reversibility of this reaction was a function of the amount of ionic charge inserted, of the substrate used (FTO, Cr‐coated glass) and of the heat treatment adopted for the ALD film. Copyright © 2006 John Wiley &amp; Sons, Ltd.