Ion Transport In Electrolytes Research Articles

Three dimensional hierarchical porous nickel cobalt layered double hydroxides (LDHs) and nitrogen doped activated biocarbon composites for high-performance asymmetric supercapacitor

Nitrogen-doped activated biocarbon (AC) and nickel-cobalt layered double hydroxides (LDHs) composites (NixCo1−x LDH/AC) are prepared by solvothermal method at various Ni/Co molar ratios. 3D nanoflowers composed of LDH nanosheets are spontaneously grown on the surface of AC from bio-waste, providing a suitable structure for the diffusion and transport of electrolyte ions. Ni0.5Co0.5LDH/AC composite electrode has high specific capacitance of 947 F g−1 at the current density of 1 A g−1, which could be explained by the synergistic effect of LDHs and AC. Furthermore, symmetric coin-cell AC//Ni0.5Co0.5 LDH/AC supercapacitor is assembled using Ni0.5Co0.5 LDH/AC composite as the cathode, and the pristine AC as the anode. Within 1.6 V voltage range, the supercapacitor device shows a maximum capacitance values (Csc) of 112 F g−1 at 1 A g−1. The developed asymmetric supercapacitor exhibits excellent rate performance and good cycle stability reflected through the maintenance of 80% of the initial Csc after 5000 consecutive cycles. Moreover, high energy density (39.7 Wh kg−1) is observed at low power density of 0.8 kW kg−1, and maintained at relatively high value (22.2 Wh kg−1) at high power density (16 kW kg−1). All these data indicate the potential applicability of AC//Ni0.5Co0.5 LDH/AC asymmetric supercapacitor for energy storage.

Maximizing ion accessibility in MXene-knotted carbon nanotube composite electrodes for high-rate electrochemical energy storage

Improving the accessibility of ions in the electrodes of electrochemical energy storage devices is vital for charge storage and rate performance. In particular, the kinetics of ion transport in organic electrolytes is slow, especially at low operating temperatures. Herein, we report a new type of MXene-carbon nanotube (CNT) composite electrode that maximizes ion accessibility resulting in exceptional rate performance at low temperatures. The improved ion transport at low temperatures is made possible by breaking the conventional horizontal alignment of the two-dimensional layers of the MXene Ti3C2 by using specially designed knotted CNTs. The large, knot-like structures in the knotted CNTs prevent the usual restacking of the Ti3C2 flakes and create fast ion transport pathways. The MXene-knotted CNT composite electrodes achieve high capacitance (up to 130 F g−1 (276 F cm−3)) in organic electrolytes with high capacitance retention over a wide scan rate range of 10 mV s−1 to 10 V s−1. This study is also the first report utilizing MXene-based supercapacitors at low temperatures (down to −60 °C).

Free-standing nitrogen doped graphene/Co(OH)2 composite films with superior catalytic activity for aprotic lithium-oxygen batteries

The recent boom in large-scale energy storage system promotes the development of lithium-oxygen batteries because of their high theoretical energy density. However, their applications are still limited by the sluggish kinetic, insoluble discharge product deposition and the undesired parasitic reaction. Herein, the free-standing nitrogen doped reduced graphene oxide/Co(OH)2 (NRGO/Co(OH)2) composite films were prepared by a facile hydrothermal method. The NRGO/Co(OH)2 composite films display interconnected three-dimensional conductive network, which can not only promote the diffusion of O2 and the transport of electrolyte ions, but also provide abundant storage space for discharge products. Moreover, the introduction of nitrogen-containing functional groups results in improved conductivity and electron adsorption ability, which can facilitate electron transport and enhance the surface catalytic activity. Combining with excellent catalytic performance, the lithium-oxygen batteries with NRGO/Co(OH)2 composite film cathodes deliver low charge overpotential and excellent cycling performance.

Effect of salt concentration profiles on protrusion growth in lithium-polymer‑lithium cells

The formation of dendrites and other protrusions on lithium metal anodes is a subject of continued interest due to the potential to incorporate these anodes in next-generation rechargeable batteries with increased energy densities. Solid polymer electrolytes show improved stability against lithium metal compared to liquid carbonate electrolytes. We have studied the effect of salt concentration on the formation of protrusions formed on electrodeposited lithium through a rigid block copolymer electrolyte, polystyrene-block-poly(ethylene oxide) (PS-b-PEO or SEO), in a lithium‑lithium symmetric cell. The cell lifetime decreases by a factor of 100 when salt concentration is increased by a factor of 5. Our main objective is to understand the reason for this observation. We show that this decrease is not due to a salt-induced change of the morphology of the block-copolymer electrolyte, nor is it due to a salt-induced change of mechanical properties. We use an approach based on Newman's concentrated solution theory to fully characterize ion transport in the block-copolymer electrolyte, and report the conductivity, salt diffusion coefficient, cation transference number, and thermodynamic factor. Neither cell lifetime nor protrusion density in failed cells correlate with any of these electrochemical parameters. However, the electrochemical parameters can be used to predict salt concentration profiles in our symmetric cells. We posit that an important parameter in protrusion growth is the magnitude of the salt concentration gradient, ∆. We observe a direct correlation between ∆ and lithium protrusion growth.

Fabrication of Co3O4/polyaniline-based carbon electrode for high-performance supercapacitor

Novel hierarchical porous Co3O4/polyaniline-based carbon has been successfully designed and synthesized by a simple drop coating/carbonization method for supercapacitor electrodes. The Co3O4/polyaniline-based carbon electrodes exhibit improved conductivity, large specific surface area (1688.2 m2 g−1), high specific capacitance (2122.5 F g−1, 0.5 A g−1), along with high rate capability (73.2% after increasing the current densities 40-fold) and stable energy-storage performance (specific capacitance retention of 95.3% after 10,000 cycles). The hierarchical porous structure can facilitate the transportation of electrolyte ions, and buffer the volume changes during charge/discharge process. The results demonstrate the potential of the electrodes for the future generation supercapacitors.

Visualization of Ion Transport and Electrode/Electrolyte Interaction in Electrolytes for Lithium Metal Batteries

Visualization of ion transport in electrolyte provides fundamental understandings of electrolyte dynamics and electrolyte-electrode interaction, shedding light on material designs to enhance device performance, such as batteries and fuel cells. However, this task is challenging for existing techniques, since it is difficult to capture the low ionic concentration (<1 M) and the fast dynamics (1-10 s) of the electrolyte. Here we show that an emerging Stimulated Raman Scattering (SRS) microscopy offers the required spatial (sub-micrometer optical resolution), temporal (faster than 1 s per frame) and chemical (around mM) sensitivities to address this challenge.The SRS microscopy has been used to study ion depletion and lithium dendrite growth in both liquid and polymer electrolyte, and distinct behaviors are observed. In liquid electrolyte, we observe a three-stage lithium deposition process, each corresponding to no-depletion, partial-depletion and full-depletion regime of Li+, respectively. A positive feedback mechanism between the inhomogeneous growth of lithium and the local ionic concentration or flux. In polymer electrolyte, we clearly see phase separation due to ion depletion and observe the accompanying transport of plasticizer inside, which was not observed in the past. The new phase has significantly higher modulus than the bulk electrolyte. These new understanding also leads to new strategies to suppress lithium dendrites. This study shows that SRS microscopy is a powerful technique for imaging ion transport and will open various applications in materials and energy fields.

Molecular Analysis of Li Ion Transport Characteristics in Polymer Electrolytes of All Solid-State Lithium Ion Battery

These days, the demands for a new technology for producing energy without consuming fossil fuels are increasing. One of the reasons is strict regulations of emitting CO2 and NO on cars like Euro 6 in European countries. It is predicted these regulations will be much stricter in many countries in the future. Also, the demands for a new battery that is smaller and has higher energy outputs for smartphones and computers are increasing in the twenty first century. So, one of the solutions for the problems in the twenty first century is inventing new battery without emitting CO2 and NO. Above all, lithium ion battery is given attention as one of the new batteries because it has high energy density and can be stored for a long time.Lithium ion battery has some merits such as rechargeable battery, high energy density and large range of operating temperatures. With these benefits, lithium ion battery is used for electronic vehicles (EV), cellphones and computers. However, lithium ion battery has some demerits. Because its electrolyte is liquid, liquid leak and automatic firing occurs and it has low degree of design freedom. One of the solutions for these problems is all solid-state lithium ion battery whose electrolyte is solid. Now, electrolyte materials that have high Li ion transport property are required.In this study, we focus on polymer electrolyte for its high brittleness. In polymer electrolyte, it is known that Li ion transports by four diffusion mechanisms, inter-segmental hopping, intra-segmental hopping, inter-chain hopping and co-diffusion. We focus on polyethylene oxiside (PEO) and P(2EO-MO) as the electrolyte materials for this study. PEO is known for the most common polymer electrolyte material that has high Li ion transport property. P(2EO-MO) was reported in 2018 [1] that it has higher transference number than PEO but lower ionic conductivity than PEO. However, the reason why P(2EO-MO) has different Li ion transport property from PEO have not been investigated. To reveal the reason in molecular level is required because the knowledge will help to produce a new polymer that has better Li ion transport property in the future. For that, Li ion transport mechanisms in PEO and P(2EO-MO) need to be revealed.The objective of this study is to reveal the Li ion transport mechanism in PEO and P(2EO-MO). In particular, the ratio of each four types of Li ion transport mechanisms was investigated using molecular dynamics (MD) simulation because the Li ion diffusion is nano scale dynamics. The simulation systems are constructed with 30 LiTFSI molecules as Lithium salts for r = 0.01 and either 30 PEO chains or 30 P(2EO-MO) chains. The salt concentration ratio r is set 0.01, 0.04, 0.08, 1.2 and 1.6. The r is defined by the equation r = [Li]/[O]. Here, [O] means all O atoms concentration in the polymer. TraPPE-UA forcefield is used for all calculations with LAMMPS and the motion equations are integrated with timestep of 1 fs by Velocity Verlet method. Pressure and temperature are controlled by Nose-Hoover barostat and thermostat and 3-dimensional boundary conditions are applied. After equilibrating the system, NVT simulation was applied 300 ns for production. The temperature and pressure were set as 400 K and 1 bar, respectively.As the analysis of structural property, radial distribution function (RDF) was calculated. As the analysis of transport property, self-diffusion coefficient of Li ion was calculated by mean square displacement (MSD) and each Li ion displacements were also calculated. Additionally, with calculating oxygen index, Li ion transport mechanism was identified. With LiTFSI cluster analysis, the relationship between the Li or TFSI diffusion and the salt concentration ratio was explained.Reference[1] Zheng, Q. et al. Optimizing Ion Transport in Polyether-Based Electrolytes for Lithium Batteries. Macromolecules 51, 2847–2858 (2018)

Concentration and Velocity Profiles in a Polymeric Lithium-Ion Battery Electrolyte

Predictive and quantitative understanding of ion and mass transport in liquid and polymeric electrolytes is at the heart of electrochemistry. Here, the goal is to accurately simulate the performance of an electrochemical cell, for which the temperature- and concentration-dependent transport coefficients of a given electrolyte, as well as the thermodynamic mean salt molal activity coefficient, must be known. These are the conductivity, σ, the salt diffusion coefficient, D, and the cation transference number, t+. The transport coefficients must hence be extracted with high accuracy from experimental measurements. The transference number is defined as the ratio of current carried by the cation to the total electric current. Its importance with regards to energy density and power density was recognized in the early 1990s by Doyle, Fuller and Newman (1). Nevertheless, researchers still argue about transference number values, even in baseline systems such as lithium bistrifluoromethanesulfonimidate (LiTFSI) in Poly(ethylene oxide) (PEO) (2). The transference number can be measured via the steady-state Bruce-Vincent polarization method (3, 4), the Balsara-Newman method (5), as well as pulsed field gradients NMR (pfg-NMR) (6) and pulsed field gradients electrophoretic NMR (e-NMR) (2). Despite extensive efforts towards unified results of these approaches, in particular as a function of ion concentration, a clear picture has not yet emerged.Towards this end, we developed an alternative approach towards determining the ion transport properties. Specifically, we directly and operando measured precise microscopic and macroscopic physical properties of the electrolyte upon cell polarization in a Li/electrolyte/Li cell, combined this with calculations via concentrated solution theory continuum modelling (CM), and rationalized our findings with microscopic insight from molecular dynamics (MD) simulations. We utilized a well-studied benchmark model system electrolyte consisting of PEO and LiTFSI at Li+ to EO molar ratio of r = 0.1. Under constant voltage polarization, we directly measured the velocity associated with electrolyte and ions via heterodyne synchrotron X-ray photon correlation spectroscopy (XPCS), and the TFSI- concentration gradient from electrode to electrode via X-ray absorption microscopy (XAM). The significance of our results lies in the unification of microscopic and macroscopic predictions from simulation with experimental measurements as well as the self-consistent determination of a concentration-independent transference numbers of approximately 0.2. Our study paves the way for further length- and time-scale bridging understanding of ion transport.1. M. Doyle, T. F. Fuller, J. Newman, The Importance of the Lithium Ion Transference Number in Lithium Polymer Cells. Electrochimica Acta 39, 2073-2081 (1994).2. M. P. Rosenwinkel, M. Schönhoff, Lithium Transference Numbers in PEO/LiTFSA Electrolytes Determined by Electrophoretic NMR. Journal of The Electrochemical Society 166, A1977-A1983 (2019).3. J. Evans, C. A. Vincent, P. G. Bruce, Electrochemical Measurement of Transference Numbers in Polymer Electrolytes. Polymer 28, 2324-2328 (1987).4. P. G. BRUCE, C. A. VINCENT, STEADY STATE CURRENT FLOW IN SOLID BINARY ELECTROLYTE CELLS. J. Electroanal. Chem. 225, 1-17 (1987).5. D. M. Pesko, S. Sawhney, J. Newman, N. P. Balsara, Comparing Two Electrochemical Approaches for Measuring Transference Numbers in Concentrated Electrolytes. Journal of The Electrochemical Society 165, A3014-A3021 (2018).6. D. M. Pesko et al., Negative transference numbers in poly(ethylene oxide)-based electrolytes. Journal of the Electrochemical Society 164, E3569-E3575 (2017).

Effects of Ion Size and Dielectric Constant on Ion Transport and Transference Number in Polymer Electrolytes

Salt-doped polymers without added solvents have the potential to be nonflammable, robust electrolytes for batteries but suffer from low ion conductivity. Using bulky anions with delocalized charge may reduce ion agglomeration and increase conduction. However, size asymmetry between ions may increase preferential solvation of cations versus the larger anions, lowering the transference number t+ (fraction of conductivity contributed by the cation, relevant to battery performance). We use coarse-grained molecular dynamics simulations, including a 1/r4 potential to capture size-dependent solvation effects, to relate polymer and ion chemistry to t+ and overall conductivity. At low ion size disparity, increasing dielectric constant improves cation conduction due to the mitigation of ion aggregation and correlated cation–anion motion. However, at high ion size disparity, high dielectric medium results in strong preferential solvation of cations, reducing cation mobility and t+. The trade-off between better cation–anion separation and cation preferential solvation suggests that the strategy of developing high dielectric polymers may enhance performance only at low ion size disparity.

Synthesis of mesoporous hollow carbon microcages by combining hard and soft template method for high performance supercapacitors

Carbon materials have been widely used in electrochemistry filed such as supercapacitors because of the good conductivity, abundant sources and low prices. Further improving the electrochemical performance of carbon materials still attracts the interest of researchers. In this work, nitrogen-doped mesoporous hollow carbon microcages (N-MHCC) are successfully prepared by combining hard and soft template method. This hierarchically porous structure (meso- & micro-pore) of N-MHCC provides a large number of active centers, sufficient space and reaction interface, promoting the rapid diffusion of electron and electrolyte ions transport. By comparing the electrochemical performance of nitrogen-doped hollow carbon microcages (N-HCC) and N-MHCC, it can be calculated that N-MHCC shows high specific capacitance of 210.66 F g−1 at 0.5 A g−1 while N-HCC only shows 132.6 F g−1. The cycle retention rate of N-MHCC is as high as 96.92 % at 5 A g−1 after 4000 cycles. Furthermore, the simple preparation method and attractive performance make N-MHCC a promising candidate for high performance supercapacitors.

Nanostructured tin oxide layer as a porous template for the growth of manganese oxide nanobouquets and a conductive support network for supercapacitors

As-prepared SnO2 layer with poor conductivity acted as a porous template for deposition of discrete γ-MnO2 with primary nanosheets and secondary nanobouquets along the pore channels inside the SnO2 barrier layer. The MnO2 tended to form aggregate nanosheets on the bare SSM (stainless steel mesh) substrate and CNT (carbon nanotube)-wrapped SSM without the SnO2 template. Porous SnO2 layer could prevent the nanosheets from aggregating effectively. After heat treatment, the SnO2 became electrically conductive and thus acted as a conductive and stable support for MnO2 nanobouquets. After the introduction of CNT layer between porous SnO2 layer and SSM substrate, the supporting CNT/SnO2 could provide large contact area, multiple pore channels, and conductive networks for transport of electrons and electrolyte ions. The tri-layered structure of CNT/SnO2/MnO2 realized larger capacitive current than bare, CNT-, and SnO2-supported MnO2 materials. The specific capacitance of CNT/SnO2/MnO2 could reach 427 F g−1 under a discharge current density of 1 A g−1, far greater than that of MnO2 (254 F g−1), CNT/MnO2 (325 F g−1), and SnO2/MnO2 (375 F g−1). An improved supercapacitive performance of the CNT/SnO2/MnO2 came from its lower internal resistance than the bare MnO2 electrode.

Reduced graphene oxide decorated CoSnO3@ZnSnO3 with multi-component double-layered hollow nanoboxes for high energy storage and capacity retention asymmetric supercapacitors

Double-layered hollow nanostructure composed of CoSn(OH)6@ZnSn(OH)6 which are derived from CoSn(OH)6 nanoboxes wrapped by ZnSn(OH)6 cover layers is prepared by a controlled alkali etching method, followed by heating treatment to prepare reduced graphene oxide (rGO) decorated CoSnO3@ZnSnO3 nanoboxes. The results revealed that the specific surface area of CoSnO3@ZnSnO3 reached 70.29 m2 g−1, which is much higher than that of CoSnO3 (44.25 m2 g−1). The enlargement in specific surface area of the double-layered hollow structure can responsible to provide sufficient buffer space for the dramatic volume change during the cycle. Moreover, rGO can effectively promote the transmission of ions or electrons and can provides a large reaction interface for electrochemical reaction. In addition, it can avoid CoSnO3@ZnSnO3 agglomeration and further improve storage capacity and stability. When the current density is 0.5 A g−1, the capacitance of material is 400.2 F g−1, which is higher than CoSnO3 and CoSnO3@ZnSnO3. Besides, the capacity retention rate of CoSnO3@ZnSnO3/rGO reaches 85% after 1100 cycles at a current density of 3 A g−1. This work demonstrates the interaction between the modification of the rGO network and the multi-layered hollow structure with the high specific surface areas can provide large spaces to effectively buffer volume changes and facilitate electron and electrolyte ion transport.

Construction of nitrogen‑sulfur co-doped porous carbon to boost, integrate Li/Na/K ion storage

Heteroatom-doped carbon materials with expanded interlayer distance show attractive charm as anodes for lithium/sodium/potassium-ion batteries, making the easier Na/K ions insertion/extraction and more Li-ions insertion/extraction during the charge-discharge process. Herein, the N/S co-doped hierarchically porous carbon (NSPC) with rational interlayer distance is successfully synthesized by heteroatom doping and metal salt strategy. As a consequence, NSPC achieves the expanded interlayer spacing, excellent electronic conductivity, and short electrolyte diffusion and ion transport pathways. For Li/Na/K-ions batteries, the developed NSPC delivers a high discharge capacity of 364 mAh g−1 for sodium-ion storage, 1220 mAh g−1 for lithium-ion storage and 278 mAh g−1 for potassium-ion storage at the current density of 0.1 A g−1, respectively. And, the NSPC maintains excellent cyclic stability over long charge/discharge cycles at large current density. The NSPC shows remarkable Li+/Na+/K+ storage performance, proving the effectiveness of the material doped design.

Ion transport in small-molecule and polymer electrolytes.

Solid-state polymer electrolytes and high-concentration liquid electrolytes, such as water-in-salt electrolytes and ionic liquids, are emerging materials to replace the flammable organic electrolytes widely used in industrial lithium-ion batteries. Extensive efforts have been made to understand the ion transport mechanisms and optimize the ion transport properties. This perspective reviews the current understanding of the ion transport and polymer dynamics in liquid and polymer electrolytes, comparing the similarities and differences in the two types of electrolytes. Combining recent experimental and theoretical findings, we attempt to connect and explain ion transport mechanisms in different types of small-molecule and polymer electrolytes from a theoretical perspective, linking the macroscopic transport coefficients to the microscopic, molecular properties such as the solvation environment of the ions, salt concentration, solvent/polymer molecular weight, ion pairing, and correlated ion motion. We emphasize universal features in the ion transport and polymer dynamics by highlighting the relevant time and length scales. Several outstanding questions and anticipated developments for electrolyte design are discussed, including the negative transference number, control of ion transport through precision synthesis, and development of predictive multiscale modeling approaches.

Mechanisms of Ion Transport in Lithium Salt-Doped Polymeric Ionic Liquid Electrolytes

Recent experimental results have demonstrated that polymeric ionic liquids doped with Li salts exhibit enhanced ionic mobilities and lithium ion transference numbers with increasing salt concentrat...

Proton-Conducting Polyoxometalates as Redox Electrolytes Synergistically Boosting the Performance of Self-Healing Solid-State Supercapacitors with Polyaniline

Energy storage devices with high volumetric and gravimetric capacitance are in urgent demand due to the booming market of portable and wearable electronics. Using redox-active molecules as electrol...

CoO@CoS/Ni3S2 hierarchical nanostructure arrays for high performance asymmetric supercapacitor

CoO@CoS/Ni3S2 (CoO@Ni-Co-S) hierarchical nanostructure electrode materials are synthesized on nickel foam (NF) through hydrothermal process and electrodeposition. The three dimensional porous CoO@Ni-Co-S hierarchical nanostructure is formed through the interconnection between the CoO nanoneedles and the Ni-Co-S nanosheets. This structure is beneficial for the transport of electrolyte ions and electrons. The CoO@Ni-Co-S nanocomposite exhibits a specific capacitance of 2507 F g−1 at 1 A g−1 (which is superior to CoO@CoS electrode, 1855 F g−1 at 1 A g−1) and possesses a capacitance retention of 84.2% at 10 A g−1. Furthermore, an asymmetric supercapacitor with CoO@Ni-Co-S//activated carbon is assembled, and the energy density reaches 110.7 W h kg−1 when the power density is 880 W kg−1. The asymmetric supercapacitor also exhibits an excellent cyclic stability (84.3% capacitance retention over 10,000 cycles). Preliminary results demonstrate that CoO@Ni-Co-S is a promising material for energy storage.

High-Performance Anti-freezing Flexible Zn-MnO2 Battery Based on Polyacrylamide/Graphene Oxide/Ethylene Glycol Gel Electrolyte.

It remains a great challenge for aqueous zinc-ion batteries to work at subzero temperatures, since the water in aqueous electrolytes would freeze and inhibit the transportation of electrolyte ions, inevitably leading to performance deterioration. In this work, we propose an anti-freezing gel electrolyte that contains polyacrylamide, graphene oxide, and ethylene glycol. The graphene oxide can not only enhance the mechanical properties of gel electrolyte but also help construct a three-dimensional macroporous network that facilitates ionic transport, while the ethylene glycol can improve freezing resistance. Due to the synergistic effect, the gel electrolyte exhibits high ionic conductivity (e.g., 14.9 mS cm−1 at −20 °C) and good mechanical properties in comparison with neat polyacrylamide gel electrolyte. Benefiting from that, the assembled flexible quasi-solid-state Zn-MnO2 battery exhibits good electrochemical durability and superior tolerance to extreme working conditions. This work provides new perspectives to develop flexible electrochemical energy storage devices with great environmental adaptability.

Peapod-like MnO@Hollow carbon nanofibers film as self-standing electrode for Li-Ion capacitors with enhanced rate capacity

Lithium ion capacitors (LICs), combining with the advantages of supercapacitors and batteries, are considered as one of the most attractive energy storage devices. The key point of constructing high-performance LICs is to address the sluggish kinetics behavior of battery-type anode. Herein, we demonstrate that nano-MnO with low Li-ion insertion voltage and fast kinetics can be favorably used for LICs. Self-standing hollow carbon-encapsulated MnO nanofibers film (MnO@HCF) is synthesized through a morphology-inheritance route, exhibiting high electrical conductivity, good structural stability, and continuous open channels to facilitate electrolyte ion transportation. Such a synergistic structure endows MnO@HCF with excellent electrochemical properties including a considerably enhanced capacity of 586.8 mAh g−1 at a current density of 0.1 A g−1. The LIC based on the MnO@HCF anode and activated carbon cathode deliver a high energy density of 87.4 Wh kg−1 at 215 W kg−1, under a high mass loading of 7.1 mg cm−2. Even at an ultrahigh power density of 10750 W kg−1, the energy density can still reach 50.6 Wh kg−1. Additionally, the LIC exhibits a remarkable capacity retention of 98.6% after 3000 cycles at 1075 W kg−1.

Electrochemically capacitive deionization of copper (II) using 3D hierarchically reduced graphene oxide architectures

Herein, we have developed the simple and novel 3-dimensional reduced graphene oxide (3D rGO) with large specific surface and superior electrochemical performance for capacitive deionization (CDI) of Cu2+ ions. The graphene oxides, produced from graphite powder by the modified Hummers method at pH 5, can be directly reduced into 3D rGO structures through the hydrothermal process at 150 °C for 12 h. The SEM/TEM images clearly indicate that 10–50 μm rGO can constitute the ordered structures with continuously inter-connected in-plane nanopores and micropores in 3D architecture, which can not only increase the surface area to 662 m2 g−1 but also facilitate the rapid transport of electrons and electrolyte ions. The 3D rGO exhibits an excellent electrochemical performance and the specific capacitance of 3D rGO is 508F g−1 at a scan rate of 5 mV s−1. Moreover, the applicability of 3D rGO was examined by CDI for the removal of Cu2+ ions. The electrosorption capacity of 3D rGO toward Cu2+ adsorption is 18.1 mg g−1 at 1.0 V. In addition, the electrosorption of Cu2+ ion follows the pseudo-second-order kinetics. Results of this study clearly demonstrate the excellence of 3D rGO to serve as a superior electrode material for Cu2+ ions removal, which can open a new way to design 3D rGO based composites for a wide variety of applications including water purification, catalysis and energy conversion and storage.