Two-Dimensional Layered Materials with Expanded Interlayer Distance for Rechargeable Magnesium Batteries

Introduction Rechargeable battery systems with different transporting ions are an alternative choice to Li batteries that can expand and diversify the existing energy storage market. Magnesium batteries are the most promising technology to achieve substantially greater energy density than Li-ion batteries, due to their divalent nature (two electron redox couple). Furthermore, because of its “green” character Mg is environmentally friendly, with high natural abundance in the Earth’s crust (13.9% as compared to 0.0007 % for Li), and atmospheric stability.The current quest for new cathode materials for rechargeable Mg batteries is focused on intercalation compounds exhibiting high working potential and capacity1. When transporting ions have much larger diameter or charge than the host metal ion, segregation of transporting and host metal ions in the crystalline structure is forseable. In this case deintercalation will lead to the collapse of the crystalline structure and breaking of electric conductance. Therefore, our approach to achieving magnesium intercalation is to use nanoscale material that have adjustable d spacing and two-dimensional layered structure that can to control polarizability of Mg2+ions and accommodate large charge/volume changes.Nanostructured electrode materials represent one of the most attractive strategies to dramatically enhance battery performance. Short diffusion length associated with the nanosized dimensions effectively reduces the distance that ions and electrons must travel during cycling. Their large surface area increases the contact area between electrode and electrolyte and hence the number of active sites for electrode reactions, which in turn reduces electrode polarization loss and improves power density, energy efficiency, and usable energy.Nanostructured bilayered V2O5 is highly efficient 3 V cathode material for ambient temperature sodium ion batteries2. It shows superb performance: theoretical reversible capacity for Na2V2O5 stochiometry of 250 mAh/g, excellent rate capability and cycle life, as well as high energy and power densities. Preliminary results show that it is possible to extend the reversible ion-insertion chemistry of nanostructured layered V2O5 beyond lithium and larger in size Na+ ions to those with higher charge: Mg2+ions. Results and Discussion As–prepared nanostructured bilayered V2O5 cathode is synthesized in the charged state. To provide source enrichment, prior to assembling into full Mg-ion cell, it was necessary to pre-condition V2O5 cathode (intercalate with Mg2+ ions). Half-cells were discharged galvanostatically at 20mA down to and 0.01 V versus Mg/ Mg2+, respectively, using an automated Maccor battery tester at ambient temperature. As shown in Figure 1., upon electrochemical pre-condition (Mg-ion half cell) the X-ray edge energy for vanadium is shifted toward the lower energy as a consequence of a vanadium reduction due to Mg intercalation. Pre-edge peak is proportional to the octahedral symmetry of the vanadium sites and its decrease upon transporting ion intercalation is due to modification of vanadium local environment into more ordered, symmetric structure. Based on the main-edge peak position and comparison with Na-ion half cell we estimate 1 Mg is incorporated in the V2O5 structure (V5+ is reduced to V4+). It was previously shown that the V5+ was reduced to V4+ when discharged to 1.5V versus Na/ Na+ (Na-ion half cell)2. As a result of this electrochemical pre-condition we created Mg-rich V2O5 cathodes that were able to provide source of Mg-ions in full-cell. Furthermore, we employed HRTEM, X-Ray fluorescence (XRF) imaging and classical molecular dynamics simulations to understand the role of environment in the intercalation processes of Mg-ions into V2O5cathode. Conclusions We have developed high-voltage nanostructured V2O5 cathode for Mg-ion rechargeable batteries that can operate in commercial electrolytes. Our results emphasize the importance of tailoring nanoarchitecture of electrode materials and open up new opportunities for rechargeable Mg batteries. In the near future, we plan using the combined experimental and theoretical approach to guide our efforts to increase the Mg enrichment to reach the ultimate goal of inserting 2 Mg-ions/V2O5. Acknowledgement. This work was supported as part of the Joint Center for Energy Storage Research (JCESR), an Energy Innovation Hub funded by DOE, Office of Science, Basic Energy Science (BES). Use of the Center for Nanoscale Materials was supported by the U. S. Department of Energy, Office of Science, and Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357. References (1) On the Way to Rechargeable Mg Batteries: The Challenge of New Cathode Materials, E. Levi, Y. Gofer, and D. Aurbach, Chem. Mater. 2010, 22, 860–868.(2) Vanadium Oxide Electrodes for Rechargeable Sodium-Ion Batteries, Sanja Tepavcevic, Hui Xiong, Vojislav R. Stamenkovic, Xiaobing Zuo, Mahalingam Balasubramanian, Vitali B. Prakapenka, Christopher S. Johnson, and Tijana Rajh, Nanostructured Bilayered ACS Nano, 2012, 6 (1), 530–538.

A novel coal-derived graphene-intercalated MoS2 heterostructure was prepared with a facile in situ hydrothermal approach followed by high-temperature calcination. XRD, FE-SEM, HR-TEM, HR-Raman, and TOC analytical instruments, combined with first-principles simulations, were employed to explore the structural and electrochemical properties of this heterostructure for use as an electrode material. The XRD measurements and simulations confirmed the formation of the MoS2/graphene (MoS2-G) heterostructure. The microstructure analysis indicated that a well-defined 3D flower-like structure with tunable interlayer distances was created in the MoS2 layer. The novel MoS2-09% G anode exhibits a remarkable initial discharge capacity of ∼929 mAh/g due to its interlayer expansion from the intercalation of graphene between the MoS2 layers. This anode maintains a capacity of ∼813 mAh/g with a Coulombic efficiency (CE) of ∼99% after 150 cycles at a constant current density of 100 mA/g. This anode also delivers a high-rate capability of ∼579 mAh/g at a current density of 2000 mA/g, significantly higher than that of other comparable structures. The unique flower-like arrangement, sufficient interlayer spacing for Li-ion diffusion, and the increased conductive matrix created using coal-derived graphene enhance the electrode kinetics during electrochemical reactions. Our first-principles calculations revealed that the diffusion barriers are significantly lower in heterostructures compared to that of bare MoS2. This heterostructure design has significant potential as a new type of anode for Li-ion storage in next-generation batteries.

The rapid worldwide energy consumption is necessitating more energy generation from environmentally benign sources like solar, wind, or tide. However, the lack of efficient energy storage devices is the major limitation for the practical harvest of these clean energies. Rechargeable batteries are the promising solution for the efficient energy storage. We have witnessed the great success of secondary lithium-ion batteries (LIBs) in portable electronic devices in the last two decades. However, the cost and safety barriers make traditional LIBs not desirable to meet the requirements for large power applications, such as the electric or plug-in hybrid vehicles. In contrast, the multivalent ion rechargeable batteries such as Mg1-3 and Ca4 , 5 ion batteries are more promising as larger and safer energy storage devices due to their advantages in safety, cost and capacity. For instance, compared to lithium, magnesium metal is non-toxic, more air resistant and free from the dangerous dendrite formation. The higher natural abundance of magnesium makes it more than 20 times cheaper than lithium in cost. In addition, the divalent characteristic of magnesium ion (Mg2+) enables magnesium to have a nearly doubled volumetric capacity as an anode than the lithium (3832 mA cm-3 vs 2062 mA cm-3). All these merits have brought significant attention on magnesium-ion batteries as the new generation rechargeable energy storage device. Inspired by the pioneer work by Aurbach group for the development of the famous dichloro-complex magnesium electrolyte (2EtAlCl2-MgBu2),6 a lot of efforts have been devoted to the development of high voltage electrolytes for rechargeable magnesium-ion batteries. In contrast to the rapid development of effective magnesium electrolytes capable of reversibly plating/stripping magnesium with wide electrochemical windows, the design of high potential cathode material for magnesium ion batteries is far behind. To date, the Chevrel phase Mo6S8 is still the only cathode material with excellent cycling reversibility and reasonable rate capability in rechargeable magnesium-ion batteries. However, Mo6S8 could only operate at a relatively low voltage in magnesium-ion batteries (< 1.3 V) with a typical below 100 mAh g-1 capacity. Thus, development of high operating voltage cathode material deserves great attention in nowadays. Herein, we would like to present our recent progress on the development of high voltage and high performance rechargeable magnesium-ion batteries using redox active organic molecules as cathode material. As shown in Figure 1(a), when the 0.3M Mg(HMDS)2-4MgCl2 in THF solution was used as the electrolyte,7 excellent reversible redox processes have been observed in the cyclic voltammetry measurement when the redox active organic molecule was used as the cathode material. The redox potential was detected at around 1.7 V (vs Mg/Mg2+), which is much higher than the well-known Chevral phase Mo6S8. The compatibility and reversibility of the organic cathode material with the electrolyte and magnesium metal anode was further demonstrated in the batteries upon cycling. As shown in Figure 1(b), excellent cycling performance has been observed with around 120 mAh g-1 initial specific discharge capacity at the current rate of 0.5C, and still about 102 mAh g-1specific discharge capacity was obtained in 100 cycles (around 84% capacity retention). The results further suggest the great success of using redox active organic molecules as cathode material for secondary multivalent-ion batteries. (1) Muldoon, J.; Bucur, C. B.; Gregory, T. Chem Rev 2014, 114, 11683. (2) Saha, P.; Datta, M. K.; Velikokhatnyi, O. I.; Manivannan, A.; Alman, D.; Kumta, P. N. Prog Mater Sci 2014, 66, 1. (3) Yoo, H. D.; Shterenberg, I.; Gofer, Y.; Gershinsky, G.; Pour, N.; Aurbach, D. Energ Environ Sci 2013, 6, 2265. (4) Padigi, P.; Goncher, G.; Evans, D.; Solanki, R. J Power Sources 2015, 273, 460. (5) Lipson, A. L.; Pan, B.; Lapidus, S. H.; Liao, C.; Vaughey, J. T.; Ingram, B. J. Chem Mater 2015, ASAP. (6) Aurbach, D.; Lu, Z.; Schechter, A.; Gofer, Y.; Gizbar, H.; Turgeman, R.; Cohen, Y.; Moshkovich, M.; Levi, E. Nature 2000, 407, 724. (7) Liao, C.; Sa, N.; Key, B.; Burrell, A. K.; Cheng, L.; Curtiss, L. A.; Vaughey, J. T.; Woo, J. J.; Hu, L. B.; Pan, B. F.; Zhang, Z. C. Journal of Materials Chemistry A 2015, 3, 6082. Figure 1

Rechargeable batteries are critical components of portable electronics, electric vehicles and grid storage. Li-ion is the dominant technology because of its low weight, large voltage and high capacity, but the demand for raw materials is putting strain on the supply chain, and there are several safety, ethical and environmental concerns. Therefore, developing adequate alternatives to Li-ion batteries is an active research area around the world. Multivalent ion batteries (MVIBs), utilizing Mg, Ca, Zn and Al, are promising due to being based on earth-abundant materials, and their higher weight can be compensated by their multivalent nature, which allows their ions to carry multiple charges. We are particularly interested in Ca ion batteries, which have received relatively little attention compared to Mg and Al, yet they are predicted to provide the largest voltage for a multivalent ion. However, their development has been limited by challenges in identifying adequate electrolytes to reversibly plate and strip metal Ca anodes. While there have been some encouraging recent developments, a systematic understanding of the interactions between electrolytes and Ca is needed. For example, it is not clear how the electrolyte (e.g., ethylene carbonate) decomposes at a Ca metal surface, nor are the structure and composition known of the solid-electrolyte interphase (SEI) that forms between the metal anode and the electrolyte. Furthermore, the diffusion of Ca2+ ions through the SEI is not well understood.We aim to address some of these points with computational modeling that combines density functional theory (DFT) with ab initio molecular dynamics (AIMD). We investigated the electrolyte decomposition of ethylene carbonate, with and without salt, at the Ca metal interface. We then compare this process to those occurring at Li and Al metal surfaces. The DFT calculations reveal the mechanism and energy barriers associated with the possible electrolyte decomposition pathways, while the AIMD trajectories show how quickly molecules decompose and their location. Next, we investigate the electron conductivity of the anode-electrolyte interface region at various stages of SEI layer formation. We accomplish this with the non-equilibrium Green’s function technique combined with DFT (NEGF-DFT), which not only tells us the conductivity but also the electron pathway through the interface. Finally, we investigate the possibility of protecting the electrolyte from reacting with the anode by separating them with an artificial SEI that still allows Ca2+ ions to diffuse through it. We propose that this strategy can aid in the development of rechargeable Ca ion batteries by bypassing the formation of an ionically insulating SEI as a result of electrolyte decomposition.

Raman studies of MoS2 under strain at different uniaxial directions

Understanding of the thermodynamic and kinetic properties of electrode materials is of great importance to develop new materials for high performance rechargeable batteries. Compared with computational understanding of physical and chemical properties of electrode materials, experimental methods provide direct and convenient evaluation of these properties. Often, the information gained from experimental work can not only offer feedback for the computational methods but also provide useful insights for improving the performance of materials. However, accurate experimental quantification of some properties can still be challenging. Among them, chemical diffusion coefficient is one representative example. It is one of the most crucial parameters determining the kinetics of intercalation compounds, which are by far the dominant electrode type used in rechargeable batteries. Therefore, it is of significance to quantitatively evaluate this parameter. For this purpose, various electrochemical techniques have been invented, for example, galvanostatic intermittent titration technique (GITT), potentiostatic intermittent titration technique (PITT), electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV). One salient advantage of these electrochemical techniques over other characterization techniques is that some implicit thermodynamic and kinetic quantities can be linked with the readily measurable electrical signals, current, and voltage, with very high precision. Nevertheless, proper application of these techniques requires not just an understanding of the structure and chemistry of the studied materials but sufficient knowledge of the physical model for ion transport within solid host materials and the analysis method to solve for chemical diffusion coefficient. Our group has been focusing on using various electrochemical techniques to investigate battery materials, as well as developing models for studying some emerging materials. In this Account, the principles of the aforementioned four electrochemical techniques and the corresponding analytical equations for calculating the chemical diffusion coefficients are first briefly summarized, followed by a discussion of the hidden assumptions for deriving these analytical equations and the resulting limitations in their implementation. To address these limitations, various corrections have been made in the literature. Nevertheless, the phase transition behavior, which is the typical feature for many intercalation materials, is barely considered. Here we retrospect our previous work on developing a two-phase model for describing the phase transition behavior of some intercalation compounds and discuss how to obtain the chemical diffusion coefficients based on the model, using LiFePO4 as an example material. After that, we have a discussion on the methodology for using electrochemical techniques to investigate new material features. It is our hope that this Account can serve as a call for more endeavors into the development of novel electrochemical tools for battery research.

The kinetics of electrochemical intercalation and electrosorption processes are often limited by the solid-state diffusion of ions inside the lattice of the host material. While some of these limitations can be mitigated by nanostructuring of the electrode material, there is a large interest in the electrochemical energy storage community to find materials with structural motifs that allow for intrinsically fast ion diffusion, even in bulk-sized particles.In this presentation, it will be highlighted how interlayer properties, such as interlayer distance and interlayer chemistry, affect electrochemical ion intercalation and electrosorption processes in layered host materials. Using the examples of hydrogen titanates1 and Ti3C2Tx MXenes2, it is demonstrated that the presence of structural interlayer atoms or molecules can increase the accessibility of ions to the interlayer space. In the model layered host material TiS2, it is shown that increased interlayer spacing and reduced deformation during ion intercalation can lead to a change from diffusion-limited to non-diffusion limited (or pseudocapacitive) charge storage behavior,3 providing some of the most compelling experimental evidence of the intimate relationship between deformation, interlayer distance, and intercalation kinetics in layered host materials.This contribution will emphasize the importance of interlayer properties of layered and 2D materials for electrochemical ion intercalation and electrosorption processes and provide perspectives and design strategies for next generation ion insertion hosts with fast kinetics for high power energy storage. Fleischmann, S. et al. Interlayer separation in hydrogen titanates enables electrochemical proton intercalation. J. Mater. Chem. A 8, 412–421 (2020).Liang, K. et al. Engineering the Interlayer Spacing by Pre-Intercalation for High Performance Supercapacitor MXene Electrodes in Room Temperature Ionic Liquid. Adv. Funct. Mater. 31, 2104007 (2021).Fleischmann, S., Shao, H., Taberna, P.-L., Rozier, P. & Simon, P. Electrochemically Induced Deformation Determines the Rate of Lithium Intercalation in Bulk TiS2. ACS Energy Lett. 6, 4173–4178 (2021).

Recently, rechargeable aqueous Zn-ion batteries have attracted much attention and are potential candidates for grid storage applications because of their low cost and safety. However, to approach practical applications, suitable cathode materials must be developed. As a two-dimensional layered material, MoS2-based materials are very potential candidates. Herein, MoS2/rGO materials were synthesized by hydrothermal method and then the charge-discharge properties of the fabricated materials were investigated when they are used as cathode materials for rechargeable Zn-ion batteries. The MoS2/rGO has an expanded interlayer, which achieves a high initial capacity of about 170 mAh/g but does not have a high stability. In contrast, the MoS2-KOA has a low capacity but is very stable, even after 200 charge/discharge cycles. This study has shown the advantages and disadvantages of MoS2-based materials with expanded interlayer and suggests further work to find methods to stabilize the expanded interlayer to increase the charge/discharge stability.

The use of electricity generated from clean and renewable sources, such as water, wind, or sunlight, requires efficiently distributed electrical energy storage by high-power and high-energy secondary batteries using abundant, low-cost materials in sustainable processes. American Science Policy Reports state that the next-generation “beyond-lithium” battery chemistry is one feasible solution for such goals. Here we discover new “multivalent ion” battery chemistry beyond lithium battery chemistry. Through theoretic calculation and experiment confirmation, stable thermodynamics and fast kinetics are presented during the storage of multivalent ions (Ni2+, Zn2+, Mg2+, Ca2+, Ba2+, or La3+ ions) in alpha type manganese dioxide. Apart from zinc ion battery, we further use multivalent Ni2+ ion to invent another rechargeable battery, named as nickel ion battery for the first time. The nickel ion battery generally uses an alpha type manganese dioxide cathode, an electrolyte containing Ni2+ ions, and Ni anode. The nickel ion battery delivers a high energy density (340 Wh kg−1, close to lithium ion batteries), fast charge ability (1 minute), and long cycle life (over 2200 times).

Fluorine (F)-doped MoS2 was prepared by F-doping into layered MoS2 via chemical solution process with fluoroboric acid. X-ray photoelectron spectroscopy, field emission scanning electron microscopy, energy dispersive X-ray spectroscopy, and X-ray diffraction were applied to conform the effect of F on the structure. The electrochemical performance was investigated by using cyclic voltammetry, electrochemical impedance spectroscopy, and galvanostatic charge/discharge studies. The F-doped MoS2 as cathode material for rechargeable Mg battery exhibited a good discharge capacity of 55[Formula: see text]mAhg[Formula: see text], with a good rate capability and good cycling stability when compared to pristine B-MoS2. The effective performance of F-doped MoS2 are attributed to the unique structure and synergetic effect between layered MoS2.

Polyethylene oxide-intercalated nanoporous graphene membranes for ultrafast H2/CO2 separation: Role of graphene confinement effect on gas molecule binding

The newly emerging rechargeable batteries beyond lithium‐ion, including aqueous and nonaqueous Na‐/K‐/Zn‐/Mg‐/Ca‐/Al‐ion batteries, are rapidly developing toward large‐scale energy storage application. The properties of electrode materials are determinant for electrochemical performance of the batteries. By virtue of the prominent features of low cost, non‐toxicity, high voltage, and rich valence states, Mn‐based electrode materials have attracted increasing attention. The big family of Mn‐based materials with rich composition and polymorphs, provides great possibilities for exploring and designing advanced electrode materials for these emerging rechargeable batteries. In this review, three main categories of Mn‐based materials, including oxides, Prussian blue analogous, and polyanion type materials, are systematically introduced to offer a comprehensive overview about the development and applications of Mn‐based materials in various emerging rechargeable battery systems. Their crystal structure, electrochemical performance, and reaction mechanism are highlighted. In addition, the key issues encountered by many Mn‐based materials, including Jahn–Teller distortion, Mn dissolution, crystal water, impact of electrolyte, etc., are also discussed. Finally, challenges and perspectives on the future development of manganese‐based materials are provided as well. It is believed this review is timely and important to further promote exploration and applications of Mn‐based materials in both aqueous and nonaqueous rechargeable battery systems beyond lithium‐ion.

A range of vanadium oxide nanotubes consisting of scrolled layers of primary amine functionalized xerogel have been produced by a hydrothermal treatment of a xerogel/amine mixture. The nanotubes consist of a hollow core flanked by parallel layers of scrolled vanadium oxide layers. The interlayer spacing is varied on the sub-nm scale by intercalated amines templates of various molecular lengths. High resolution transmission electron microscopy and X-ray diffraction were used to characterize the resulting nanotubes. When the molar ratio of xerogel:amine is 1:2, a maximum yield of nanotubes is produced and the interlayer spacing can be controlled. For a molar ratio of xerogel:amine of 2:1, the product contains a low yield of nanotubes and the corresponding interlayer spacing is independent of the length of the amine template. A comparison of measured interlayer distances with the actual physical length of the primary amine chains shows that interdigitation of the amines occurs.

Nowadays, rechargeable batteries are widely used for many different purposes and they areamong the main clean energy storage systems that are readily available. Electrical energy isstored in the battery through oxidation and reduction and via a charge transfer agent that movesbetween the cathode and anode. Rechargeable batteries commonly use the alkali metal, lithium(Li) as the charge transfer agent. The capacity of the anode material and selection of a chargetransfer agent that is easily adsorbed by the anode material are two important factors whendesigning rechargeable batteries. In this PhD thesis, we propose several types of carbonaceousmaterials that could be potentially used as an anode in rechargeable batteries. These materialsare derivatives of graphene: graphdiyne (GDY), hydrogenated defective graphene (H-DG),edge-functionalised graphene nanoribbons (F-GNRs), and doped graphene. In addition, weselect the charge transfer agents, sodium (Na) and calcium (Ca) on several materials, and wealso consider the use of potassium (K).The first material, GDY, adsorbed Na atoms with a binding energy appropriate for batteryapplications. Adsorption occurs on the 6-membered ring and the pores, with an empiricalformula of NaC2.57, which is equivalent to an electrical capacity of 497 mA h g-1. If expansionis allowed for the bulk layered GDY, this loading will occur on each layer of bulk GDY, withan expansion of 28% of the interlayer spacing compared with the unloaded material.Furthermore, the bulk layered GDY in an AB-2 stacking has a barrier of energy against Namovement, parallel to the layers of 0.84 eV and as low as 0.12 eV for vertical movement withina slit pore. These values were even lower for the bulk material with AB-3 stacking.A hydrogenated mono-vacancy repeated four times within a graphene sheet supercell with 68carbon atoms, 4(H1-MVG), has been considered as another suitable material for the NIB andCIBs. It also provided a model hydrogenated graphene that could be compared with graphene.Compared with graphene, this material strengthened the binding of Na by an energy of 0.72eV. A similar strengthening occurred for Ca binding. This material can bind up to 16 Na and14 Ca atoms per 4(H1-MVG) supercell on a single layer. Although the bulk layered 4(H1-MVG) did not strongly bind Na within the layers, Ca effectively intercalated within the layers,with binding energies varying between -2.05 to -2.79 eV, which is strong in comparison withCa binding to graphene (-0.82 eV). Finally, we found that up to 16 Ca atoms could intercalate within the bulk layered material, which is equivalent to an electrical capacity of 591.2 m A hg-1 and results in 29.3% for the interlayer expansion.Edge-functionalised graphene nanoribbons have been proposed as the third material for NIBsand CIBs. Nanoribbons with zigzag and armchair edges are functionalised with the selectedoxygen-containing functional groups hydroxyl (HO-), carbonyl (O=), and carboxyl (HOOC-).These groups are found abundantly in reduced graphene oxide (r-GO), and we intended tosimulate the strength of Na and Ca adsorption over these groups. According to the results, thehydrogen passivated and edge-functionalised ribbons improved the binding of Na and Ca byabout 1.1 to 1.9 eV compared with the bindings over the graphene sheet, respectively. Thisimprovement is due to electronic structure of the nanoribbons as well as the direct interactionwith the oxygen functional groups. The improvement in binding compared with graphene wasmore significant over the edge of the ribbons with carbonyl and carboxyl groups. In addition,each carbonyl and carboxyl group could bind as many as five Na or Ca adatoms around it.DFT calculations for the binding of Na atoms to the nitrogen-doped graphene (graphitic N) andnitrogen-containing functional groups within the graphene sheet showed that pyridinic N,amine and amide groups bound Na more strongly than the Na cohesive energy. We also carriedout DFT calculations to determine the binding of Na, Ca and K over the oxygen groups foundin the basal plane of the r-GO sheet. When considering Ca adsorption over the hydroxyl group,the Ca bound to the OH group in all cases due to the high charge of Ca as a multivalent metal.However, K did not form KOH, except in one case. Therefore, K is a better choice than Na andCa in binding over the oxygen groups in the r-GO. Finally, we considered the binding of Kover HO-, O-, and HOOC- groups at the edge of GNRs. We found that HO- and O-GNRsbound K with energies that are suitable for use in rechargeable batteries. We completed thisstudy to investigate the effect of oxygen groups found in the cellulose derivative materialapplicable in potassium ion batteries.

Polymer–ceramic composite electrolytes are emerging as a promising solution to deliver high ionic conductivity, optimal mechanical properties, and good safety for developing high‐performance all‐solid‐state rechargeable batteries. Composite electrolytes have been prepared with cubic‐phase Li7La3Zr2O12 (LLZO) garnet and polyethylene oxide (PEO) and employed in symmetric lithium battery cells. By combining selective isotope labeling and high‐resolution solid‐state Li NMR, we are able to track Li ion pathways within LLZO‐PEO composite electrolytes by monitoring the replacement of 7Li in the composite electrolyte by 6Li from the 6Li metal electrodes during battery cycling. We have provided the first experimental evidence to show that Li ions favor the pathway through the LLZO ceramic phase instead of the PEO‐LLZO interface or PEO. This approach can be widely applied to study ion pathways in ionic conductors and to provide useful insights for developing composite materials for energy storage and harvesting.