Electrochemical Intercalation Method Research Articles

Utilizing Topological Insulator Two-Dimensional Bismuth for Ultrasensitive Acoustic Detection.

Topological insulators (TIs) are characterized by a full insulating gap in the bulk and gapless edge or surface states, which have attracted tremendous attention. 2D Bi (110), as a typical TI, is of particular interest due to its low symmetry structure and topologically protected and spin-momentum-locked Dirac surface states. However, the material's potential applications are hindered by difficulties in fabrication, due to its strong semi-metallic bonding and poor stability. In this study, a novel electrochemical intercalation method for the fabrication of ultrathin Bi (110) nanosheets with the highest yield ever reported is presented. These nanosheets are stabilized through cathodic exfoliation in a reductive environment and further modification with polymer ionic liquids. The versatility of these nanosheets is demonstrated by fabricating flexible acoustic sensors with ultrahigh sensitivity. These sensors can even detect sounds as quiet as 45dB. Furthermore, these sensors are utilized for acoustic-to-electric energy conversion and information transfer. This work offers a promising approach for scalable fabrication and preservation of ultrathin 2D TI Bi (110) nanosheets and paves the way for their integration into smart devices.

Flexible organic-intercalated WSe2 hybrid: electronic structure modification and thermoelectric performance optimization

Two-dimensional tungsten selenide (WSe2) has great potential in thermoelectric (TE) applications, but dimensionality reduction results in a dramatic increase in thermal conductivity, which is not beneficial for improving thermoelectric performance. In this work, an electrochemical intercalation method is utilized to fabricate an organic-inorganic hybrid superlattice structure by decoupling the WSe2 layers without damaging the original bulk structure and then intercalating tetrabutylammonium (TBA) cations into the inorganic layers. The few-layer mixed-staging TBA-WSe2 hybrid with alternating stacking organic TBA cations and WSe2 inorganic layers possesses an electronic structure similar to that of the few-layer WSe2, which is beneficial for an enhanced Seebeck coefficient. The electron injection results in a considerable increase in the carrier concentration while the disorder in the mixed-staging structure succeeds in improving phonon scattering, leading to an enhanced figure-of-merit ZT of 0.25 at 340 K, which is three orders of magnitude higher than that of the pristine WSe2 single crystal and one of the highest ZT values among WSe2-based thermoelectric materials in recent years. This work may guide future research on dimensionality reduction in the electronic structures of bulk materials and the fabrication of flexible superlattice hybrids with considerable TE performance.

(Invited) Lithium-Ion Battery Direct Recycling Through Effective Electrochemical Intercalation

The Nobel Prize winning technology lithium-ion battery (LIB) has seen an annual market growth rate of 24% over the last decade. This rapid market expansion brings a huge amount of hazardous battery waste from end-of-life (EOL) disposal and creates concerns over the long-term sustainability of critical elements for producing batteries. There is an urgent need to develop effective battery recycling infrastructure to address these challenges. The incumbent indirect pyrometallurgical and hydrometallurgical recycling methods lead to high energy consumption and process cost, water contamination and low-value elemental products. [1,2] In contrast, direct recycling process that extract and restore high-value cathode materials (2-10 times more valuable than their corresponding elemental constituents depending on the chemistries used [3]) to their virgin composition, structure, morphology and electrochemical performance with minimal energy and environmental impact. We have developed disassembly automation and materials regeneration processes for direct recycling of LIBs. [4,5] The pouch cell with discrete electrode sheets separated via continuous z-folding separator dominates the design of the commercially available LIBs and is used here to introduce our direct disassembly process. The customized automatic disassembly machinery safely dismantles the cell pouch, separating anode and cathode sheets, and sort cell components (i.e., cathode sheets, anode sheets and separators) into different waste streams. The EOL cathode materials are retrieved and separated for relithiation via an effective electrochemical intercalation method. The dried cathode materials are then heat-treated after which the regenerated cathode materials exhibit physical properties and electrochemical performance is comparable to virgin commercial materials.[5][1] L. Gaines, K. Richa, J. Spangenberger, Key issues for Li-ion battery recycling, MRS Energy Sustain. 5 (2018). https://doi.org/10.1557/mre.2018.13.[2] G. Harper, R. Sommerville, E. Kendrick, L. Driscoll, P. Slater, R. Stolkin, A. Walton, P. Christensen, O. Heidrich, S. Lambert, A. Abbott, K. Ryder, L. Gaines, P. Anderson, Recycling lithium-ion batteries from electric vehicles, Nature. 575 (2019) 75–86. https://doi.org/10.1038/s41586-019-1682-5.[3] J.B. Dunn, L. Gaines, J.C. Kelly, K.G. Gallagher, Life Cycle Analysis Summary for Automotive Lithiumion Battery Production and Recycling, in: R.E. Kirchain, B. Blanpain, C. Meskers, E. Olivetti, D. Apelian, J. Howarter, A. Kvithyld, B. Mishra, N.R. Neelameggham, J. Spangenberger (Eds.), Rewas 2016 Mater. Resour. Sustain., John Wiley & Sons, Inc., 2016: pp. 73–79. https://doi.org/10.1002/9781119275039.ch11.[4] L. Li, P. Zheng, T. Yang, R. Sturges, M.W. Ellis, Z. Li, Disassembly Automation for Recycling End-of-Life Lithium-Ion Pouch Cells, JOM. 71 (2019) 4457–4464. https://doi.org/10.1007/s11837-019-03778-0.[5] T. Yang, Y. Lu, L. Li, D. Ge, H. Yang, W. Leng, H. Zhou, X. Han, N. Schmidt, M. Ellis, Z. Li, An Effective Relithiation Process for Recycling Lithium-Ion Battery Cathode Materials, Adv. Sustain. Syst. n/a (n.d.) 1900088. https://doi.org/10.1002/adsu.201900088.

Fabrication of Graphene by Electrochemical Intercalation Method and Performance of Graphene/PVA Composites as Stretchable Strain Sensor

Strain sensors fabricated from polymer and graphene composites are gaining attention due to its peculiar electrical and mechanical properties. Here, we used electrochemical intercalation method to produce graphene. Graphene/PVA composite intended for use as stretchable strain sensor was fabricated using different amounts of graphene. In addition, the effect of the applied electrochemical bias method on the properties of exfoliated graphene was investigated. Results showed that use of applied bias produced thinner graphene with low defect and better thermal stability compared to 10 V applied voltage. Notably, the electrical conductivity of the graphene obtained at 5 V applied voltage (2.53 × 10−1 S/cm) is higher than that of 10 V applied bias (6.33 × 10−2 S/cm). Significantly, incorporation of graphene produced at 5 V into PVA results in five-order increase in electrical conductivity of the composite film from 0.1 to 0.5 wt% graphene. In addition, the hysteresis and sensitivity performance of the sensor produced by 0.5 wt% of graphene loading is better than that of sensors with lower amount of graphene loadings. Therefore, the sensor produced by 0.5 wt% of graphene loading has a potential to be used as wearable sensor.

Electrochemical intercalation of sodium in vertically aligned molybdenum disulfide for hydrogen evolution reaction

The intercalation of alkaline cations such as lithium and sodium into two-dimensional (2D) van der Waals materials effectively modifies their electronic structure. Here, we show an electrochemical intercalation process of an alkaline ion (Li+ or Na+), into vertically aligned molybdenum disulfide (MoS2) thin films by using a three-electrode flooded vessel cell, and its application as electrocatalyst for hydrogen evolution reaction. The electrochemical intercalation method is controlled by the applied current density. After electrochemical insertion, the vertically alligned MoS2 layers display an extended Wan der Waals gap. The Li and Na intercalated vertically alligned MoS2 layers demonstrate an overpotential of 0.29 V at 10 mA cm−2 towards hydrogen evolution reaction (HER) in 0.5 M H2SO4. The intercalation of Li+ or Na+ leads to the partial exfoliation of the 2D layered material. Nevertheless, the Na intercalated catalyst can sustain the HER for 1000 cycles while Li intercalated catalyst show an activity fading, possibly due to restacking of the MoS2 layers.

FeSe-based superconductors with a superconducting transition temperature of 50 K

Due to the strong reactivity of alkaline metals and the easy formation of the impurity phase, the superconducting transition temperature (Tc) of alkaline metals intercalated FeSe is usually limited to 45 K. To avoid the formation of impurity and improve the Tc, we intercalate a more chemically inert organic ion (rather than the chemically reactive alkaline metals) into FeSe single crystal in this report. A new FeSe-based superconductor, namely (TBA)0.3FeSe, with Tc of 50 K, is synthesized by intercalating FeSe single crystal with organic ion tetrabutyl ammonium (TBA+) via an electrochemical intercalation method, which has the highest Tc among FeSe-based bulk superconductors. The structure of the organic ion intercalated product consists of the alternate stacking of monolayer FeSe and the organic molecule. The superconductivity of (TBA)0.3FeSe is confirmed by both the magnetic susceptibility and the transport measurement. It is suggested that the chemically inert organic ion should play a key role in the enhancement of Tc by avoiding the formation of impurity and disorder in FeSe plane as possible. We also suggest that the TBA+ intercalated FeSe with well defined shape and higher Tc offer a good playground for further bulk measurement investigation.

Organic-ion-intercalated FeSe-based superconductors

Finding a new derivative structure of FeSe-based superconductors with a high superconducting transition temperature (${T}_{c}$) is of great significance. Here, in this work, an organic-ion-[cetyltrimethyl ammonium (${\mathrm{CTA}}^{+}$)]-intercalated FeSe-based superconductor ${(\mathrm{CTA})}_{0.3}\mathrm{FeSe}$ with ${T}_{c}$ as high as 45 K is synthesized by an electrochemical intercalation method. The as-prepared ${(\mathrm{CTA})}_{0.3}\mathrm{FeSe}$ has a hybrid crystal structure consisting of double layers of ${\mathrm{CTA}}^{+}$ and one layer of FeSe, which is consistent with a lateral-bilayer model. The superconductivity of ${(\mathrm{CTA})}_{0.3}\mathrm{FeSe}$ is confirmed by magnetic susceptibility. Furthermore, a negative pressure effect on superconductivity $d{T}_{c}/dP=\ensuremath{-}5$ K/GPa is observed. This is the first pure organic-ion-intercalated FeSe-based superconductor with a high ${T}_{c}$ and high crystallinity. Our work offers a new method to modify the interface interaction between the FeSe layer and the intercalator, and sheds new light on finding new FeSe-based superconductors with higher ${T}_{c}$.

Tunable superconductivity by electrochemical intercalation in TaS2

The controllable manipulation of materials properties has always attracted broad interests since there exists the possibility to identify the relationship between different electronic states, and even discover new states. Here we report the electrochemical intercalation of cetyltrimethylammonium (CTA+) into 2H–TaS2. The single layer TaS2 is intercalated with CTA+ cations and the direction of CTA+ is approximately perpendicular to the lamellar structure of TaS2. With this facile and efficient method, the superconducting transition temperature (Tc) of pristine TaS2 increases from 0.8 K to the maximum 3.7 K, showing a dome-like behavior. The Hall coefficient measurement indicates that the intercalated CTA+ cations introduce electrons to this system. The present results demonstrate that electrochemical intercalation method is effective in tuning the materials properties and may pave the way for exploring new superconductors.

Exploration and physical investigation of FeSe-based superconductors

Since the high-Tc superconductivity in iron-based superconductors was found in 2008, numerous new iron-based superconductors have been discovered. Of them, FeSe-based superconductors receive the most attention due to their unique properties. Here, we briefly introduce the structure and physical properties of two newly found FeSe-based superconductors, i.e. (Li, Fe) OHFeSe and (CTA)x FeSe. The former is synthesized by the hydrothermal method, while the latter is synthesized by electrochemical intercalation method. Moreover, we also introduce the tuning of electronic properties of FeSe by electric-double-layer and solid-ion-conductor based transistors.

Electrochemical Control of Copper Intercalation into Nanoscale Bi2Se3.

Intercalation of exotic atoms or molecules into the layered materials remains an extensively investigated subject in current physics and chemistry. However, traditionally melt-growth and chemical interaction strategies are either limited by insufficiency of intercalant concentrations or destitute of accurate controllability. Here, we have developed a general electrochemical intercalation method to efficaciously regulate the concentration of zerovalent copper atoms into layered Bi2Se3, followed by comprehensive experimental characterization and analyses. Up to 57% copper atoms (Cu6.7Bi2Se3) can be intercalated with no disruption to the host lattice. Meanwhile the unconventional resistance dip accompanied by a hysteresis loop below 40 K, as well as the emergence of new Raman peak in CuxBi2Se3, is a distinct manifestation of the interplay between intercalated Cu atoms with Bi2Se3 host. Our work demonstrates a new methodology to study fundamentally new and unexpected physical behaviors in intercalated metastable materials.

Electrochemical Na-intercalation-induced high-temperature superconductivity in FeSe

Iron-chalcogenide-based superconductors have attracted much attention due to their relatively high superconducting transition temperatures (Tc) and their simple layered crystal structures. We have performed electrochemical co-intercalation of Na and propylene carbonate (PC) into FeSe, and successfully synthesized a new superconductor, Nax(PC)yFe2Se2, with Tc = 43 K. The type and amount of intercalated metal, and the electrolyte used in the intercalation affected the superconductivity. Our electrochemical intercalation method should be a useful tool for discovering new superconductors by controlling the intercalation conditions.

Interconnecting Carbon Fibers with the In-situ Electrochemically Exfoliated Graphene as Advanced Binder-free Electrode Materials for Flexible Supercapacitor.

Flexible energy storage devices are highly demanded for various applications. Carbon cloth (CC) woven by carbon fibers (CFs) is typically used as electrode or current collector for flexible devices. The low surface area of CC and the presence of big gaps (ca. micro-size) between individual CFs lead to poor performance. Herein, we interconnect individual CFs through the in-situ exfoliated graphene with high surface area by the electrochemical intercalation method. The interconnected CFs are used as both current collector and electrode materials for flexible supercapacitors, in which the in-situ exfoliated graphene act as active materials and conductive “binders”. The in-situ electrochemical intercalation technique ensures the low contact resistance between electrode (graphene) and current collector (carbon cloth) with enhanced conductivity. The as-prepared electrode materials show significantly improved performance for flexible supercapacitors.

Flexible n-type thermoelectric materials by organic intercalation of layered transition metaldichalcogenide TiS2.

Organic semiconductors are attracting increasing interest as flexible thermoelectric materials owing to material abundance, easy processing and low thermal conductivity. Although progress in p-type polymers and composites has been reported, their n-type counterpart has fallen behind owing to difficulties in n-type doping of organic semiconductors. Here, we present an approach to synthesize n-type flexible thermoelectric materials through a facile electrochemical intercalation method, fabricating a hybrid superlattice of alternating inorganic TiS2 monolayers and organic cations. Electrons were externally injected into the inorganic layers and then stabilized by organic cations, providing n-type carriers for current and energy transport. An electrical conductivity of 790 S cm(-1) and a power factor of 0.45 mW m(-1) K(-2) were obtained for a hybrid superlattice of TiS2/[(hexylammonium)x(H2O)y(DMSO)z], with an in-plane lattice thermal conductivity of 0.12 ± 0.03 W m(-1) K(-1), which is two orders of magnitude smaller than the thermal conductivities of the single-layer and bulk TiS2. High power factor and low thermal conductivity contributed to a thermoelectric figure of merit, ZT, of 0.28 at 373 K, which might find application in wearable electronics.

Two-dimensional synthetic templates

The isolation of atomic-thin graphene sheets from bulk graphite has led to the discovery of a number of novel properties of graphene that have enormously benefited the development of nanotechnology [1], which has inspired the exploration of other 2D materials, such as transition metal dichalcogenides (TMDs), hexagonal boron nitride (hBN), etc. [2]. To exfoliate a layered bulk crystal, the van der Waals interaction between the adjacent layers should be overcome, which can be realized by techniques like mechanical exfoliation [1] and solvent-assisted ultrasound exfoliation [3]. These two methods are relatively non-destructive so that the intrinsic properties of 2D materials could be preserved. However, the former method is mostly applied for fundamental studies and the latter one is difficult to produce high-yield single-layer nanosheets. The intercalation-based methods, on the other hand, are more effective and reliable in mass production of single-layer nanosheets. It was demonstrated decades ago that many chemical species, like alkali metals, transition-metal halides and amine molecules, can be intercalated into various layered materials [4]. As one of the most intensively studied intercalates, lithium, for example, can be inserted into the interlayer spaces of a layered crystal by soaking the crystal in n-butyl lithium solution at an elevated temperature (e.g. 100◦C) for a long time (e.g. 3 days). Alternatively, the electrochemical intercalation method (Fig. 1a–c), which employs electric 50 nm 5 nm (111)Pd

Potential Graphite Materials for the Synthesis of GICs

The potential of various graphite materials including Chinese flake graphite, Madagascan flake graphite, natural vein graphite, recycled vein graphite, and synthetic graphite for the preparation of -bisulfate was investigated through electrochemical intercalation method. All the graphite materials were characterized using laser particle size analyzer, SEM analysis, XRD analysis, and X-ray EDS elemental analysis. Chinese flake and Madagascan flake graphite materials were found to be capable of synthesizing GIC-bisulfate through electrochemical intercalation. Natural vein, recycled vein, and synthetic graphite materials did not show any evidence of forming GIC-bisulfate. The formation of GIC-bisulfate was verified through XRD results. Thermal exfoliation volume was observed as an indicator of GIC-bisulfate when the electrochemically treated material was exposed to a sudden thermal shock at a temperature of 850 °C.

Environmentally friendly preparation of exfoliated graphite

Graphite intercalation compounds (GIC) have received global attention in the last decade because of the growing number of applications of these materials. Conventionally, bisulfate intercalated graphite is synthesized by chemical intercalation; which requires concentrated sulfuric acid (98%) and an oxidizing agent such as H2O2 and HNO3. In this study, bisulfate intercalated graphite was prepared by electrochemical intercalation using dilute sulfuric acid with the aim to reduce the sulfur content in the final product. The electrochemical intercalation method required sulfuric acid with half of the concentration of that required for chemical intercalation, and without the need for an oxidizing agent. Chinese natural large flake graphite was used as the raw material for the electrochemical process. The GIC was characterized by the exfoliation volume obtained by thermal shock at a temperature of 850°C. The effect of sulfuric acid concentration, electrochemical treatment time, particle size and temperature on the exfoliation volume was investigated. It was found that the exfoliation volume of the GIC-bisulfate, which is a function of degree of intercalation, can be controlled using the sulfuric acid concentration and treatment time. A sulfuric acid concentration of 50% and an electrochemical treatment time of 60min were found to produce a GIC with the maximum exfoliation volume for the range of conditions studied.

Electrochemical intercalation of organic molecules into layered oxides, MoO 3

Electrochemical intercalation of a variety of organic cations such as alkylammonium, anilinium and alkylpyridinium ions including rhodamine 6G into layered oxide, MoO 3 were examined. Cyclic voltarnmetry indicated that redox potentials of MoO 3 depends on the kinds of organic electrolytes. The electrochemical intercalation method could be applied to MoO 3 thin film deposited onto transparent electrode. Interlayer spacing of MoO 3 measured by XRD increased from an intial value of 6.9 Å to an intercalated value in the range of 10–19 Å, and reduction of MoO 3 was confirmed by XPS measurement.