Cathode Host Research Articles

Porous 3D graphene-based biochar materials with high areal sulfur loading for lithium–sulfur batteries

A novel pomelo peel biochar integrated graphene composite was applied as a cathode host for Li–S batteries with high sulfur loading.

Revealing reaction mechanisms of nanoconfined Li2S: implications for lithium-sulfur batteries.

Using Li2S as an active material and designing nanostructured cathode hosts are considered as promising strategies to improve the performance of lithium-sulfur (Li-S) batteries. In this study, the reaction mechanisms during the delithiation of nanoconfined Li2S as an active material, represented by a Li20S10 cluster, are examined by first-principles based calculations and analysis. Local reduction and disproportionation reactions can be observed although the overall delithiation process is an oxidation reaction. Long-chain polysulfides can form as intermediate products; however they may bind to insoluble S2-via Li atoms as mediators. Activating the charging process only requires an overpotential of 0.37 V if using Li20S10 as the active material. Sulfur allotropes longer than cyclo-S8 are observed at the end of the charge process. Although the discharge voltage of Li20S10 is only 1.27 V, it can still deliver an appreciable theoretical energy density of 1480 W h kg-1. This study also suggests that hole polarons, in Li20S10 and intermediate products, can serve as carriers to facilitate charge transport. This work provides new insights toward revealing the detailed reaction mechanisms of nanoconfined Li2S as an active material in the Li-S battery cathode.

Experimental and first-principles study of a metal–organic framework with sulfur embedding cathode for enhanced performance lithium–sulfur battery

A cobalt metal–organic framework, CoMOF–S, as host cathode material to immobilize sulfur for Li–S batteries was prepared in this study.

Hierarchically Porous Carbon Derived from Peanut Shells for High-performance Lithium-sulfur Batteries

Lithium-sulfur (Li-S) batteries are considered to be a promising energy storage device because of their high theoretical energy density and relatively low cost. But low rate performance and poor cycle stability arising from the poor electronic conductivity and the shuttling of polysulfide intermediates hamper its practical application. In order to address these shortcomings, hierarchically porous carbon (HPC) derived from peanut shells is employed as a host to accommodate sulfur for the first time. As-prepared HPC possesses a hierarchically porous structure with a relatively high specific surface area of 1775.7 m2 g−1 and a large pore volume of 1.457 cm3 g−1. When as-prepared HPC was employed as cathode hosts for lithium-sulfur batteries, it was found that S/HPC composite displayed an excellent electrochemical performance. The initial discharge capacity of 1659.8 mA h g−1 is reached at 0.5 C and a reversible capacity of 815.7 mA h g−1 can be maintained after 100 cycles. Even if the current density increas...

Yolk–Shell Structured Assembly of Bamboo‐Like Nitrogen‐Doped Carbon Nanotubes Embedded with Co Nanocrystals and Their Application as Cathode Material for Li–S Batteries

AbstractDespite their high theoretical specific capacity (1675 mA h g−1), the practical application of Li–S batteries remains limited because the capacity rapidly degrades through severe dissolution of lithium polysulfide and the rate capability is low because of the low electronic conductivity of sulfur. This paper describes novel hierarchical yolk–shell microspheres comprising 1D bamboo‐like N‐doped carbon nanotubes (CNTs) encapsulating Co nanoparticles (Co@BNCNTs YS microspheres) as efficient cathode hosts for Li–S batteries. The microspheres are produced via a two‐step process that involves generation of the microsphere followed by N‐doped CNTs growth. The hierarchical yolk–shell structure enables efficient sulfur loading and mitigates the dissolution of lithium polysulfides, and metallic Co and N doping improves the chemical affinity of the microspheres with sulfur species. Accordingly, a Co@BNCNTs YS microsphere‐based cathode containing 64 wt% sulfur exhibits a high discharge capacity of 700.2 mA h g−1 after 400 cycles at a current density of 1 C (based on the mass of sulfur); this corresponds to a good capacity retention of 76% and capacity fading rate of 0.06% per cycle with an excellent rate performance (752 mA h g−1 at 2.0 C) when applied as cathode hosts for Li–S batteries.

Li-Rich Layered Cathode Materials: Transition Metals in Transit

In the most recent issue of Nature Communications , William Gent, William Chueh, and co-authors examine in depth the electronic structure and redox processes that occur during cycling of Li 1.17 Ni 0.21 Co 0.08 Mn 0.54 O 2 and reveal an important new insight that suggests oxygen redox is coupled with local transition metal migration. Aided by a suite of cutting-edge characterization methods, the authors formulate a clear and unprecedented view of both local and averaged structure evolution during cycling.

Manganese Dioxide As Rechargeable Magnesium Battery Cathode

Rechargeable magnesium battery (rMBs) has received increased attention as a promising alternative to current Li-ion technology. However, the lack of appropriate cathode that provides high energy density and good sustainability greatly hinders the development of practical rMBs. To date, the successful Mg2+-intercalation was only achieved in only a few cathode hosts, one of which is manganese dioxide. This Review summarizes the research activity of studying MnO2 in magnesium cells. In recent years the cathodic performance of MnO2 was impressively improved to the capacity of >150-200 mAh g-1 at voltage of 2.6-2.8 V with cyclability to hundreds or more cycles. In addition to reviewing electrochemical performance, we sketch a mechanistic picture to show how the fundamental understanding about MnO2 cathode has been changed and how it paved the road to the improvement of cathode performance.

A Sodium-Aluminum Hybrid Battery

To effectively harvest the energy from renewable sources such as solar and wind, cheap and long-lasting electric energy storage (EES) devices are essential.1 Among various EES technologies, lithium ion batteries (LIBs) are the most mature technologies with high energy density, high coulombic efficiency and long cycle life. Unfortunately, their high cost and the unevenly distributed global lithium source are major concerns. 2 Thus, beyond lithium technologies based on cheap and naturally abundant elements such as sodium (Na), magnesium (Mg), and aluminum (Al) ion batteries 3, 4 have been intensively studied during the last few years. Among different metals, Al is one of the most earth abundant elements, only second to silicon, resulting in its low price of $0.52/kg, 100 times lower than Li. In addition, Al with three electrons redox couple has distinct advantage over one electron redox couple such as Li and Na and two electrons redox couple such as Mg and Ca, providing a high theoretical specific capacity of 2980 mAh g-1 and a high volumetric capacity of 8040 mAh cm-3. The development of rechargeable Al ion batteries has been hampered by the electrolyte and cathode materials. Due to the low reduction potential of Al (-1.68 V vs. SHE), aqueous electrolytes cannot be used when Al is being used as the anode, since hydrogen will be released before Al can be plated during the reduction process. As an alternative, ambient room temperature ionic liquids with high ionic conductivity and wide electrochemical windows are good candidates for rechargeable Al batteries. Currently, the ionic liquids used for Al deposition are still based on mixtures of anhydrous AlCl3 and organic halide salts.5 It is well-known that only the acidic mixtures show reversible Al deposition/stripping, which poses stringent requirement for the hardwares of the Al batteries.6 To avoid the corrosion issue, pouch cell and special cell configuration have been used.7 Besides electrolytes, Al batteries also face challenges from the cathodes due to the high charge density of the Al3+ ion, making its insertion/extraction into/from the cathode host very difficult. An alternative way to take advantage of metallic Al anode but bypasses the need for efficient Al insertion cathodes is hybrid Al battery.7 It was demonstrated that high voltage and high capacity were possible in a hybrid Al battery with LiFePO4 as the cathode in an acidic ionic liquid electrolyte.7 However, a switch to the more earth-abundant sodium chemistry is more desirable due to the limited Li resources. In this presentation, we report a new hybrid battery using earth-abundant Na and Al chemistry, that is, Al as the anode, Na3V2(PO4)3 (NVP) as the cathode and NaAlCl4 dissolved in acidic ionic liquid as the electrolyte.8 The hybrid battery exhibits a discharge voltage of 1.25 V and a cathodic capacity of 99 mAh g-1 under a current rate of C/10. In addition, the hybrid battery exhibits good rate performance and long cycling stability while maintaining a high coulombic efficiency of 98 %. It is also demonstrated that increasing salt concentration can further enhance the cycling performance of the hybrid battery. X-ray diffraction analysis of the NVP electrodes under different conditions confirms that the main cathode reaction is indeed the Na extraction/insertion. 1. B. Dunn, H. Kamath and J. M. Tarascon, Science, 2011, 334, 928-935. 2. H. L. Pan, Y. S. Hu and L. Q. Chen, Energy Environ. Sci. , 2013, 6, 2338-2360. 3. G. A. Elia, K. Marquardt, K. Hoeppner, S. Fantini, R. Y. Lin, E. Knipping, W. Peters, J. F. Drillet, S. Passerini and R. Hahn, Adv. Mater. , 2016, 28, 7564-7579. 4. T. Gao, X. G. Li, X. W. Wang, J. K. Hu, F. D. Han, X. L. Fan, L. M. Suo, A. J. Pearse, S. B. Lee, G. W. Rubloff, K. J. Gaskell, M. Noked and C. S. Wang, Angew. Chem. Int. Ed. , 2016, 55, 9898-9901. 5. J. S. Wilkes, J. A. Levisky, R. A. Wilson and C. L. Hussey, Inorg. Chem. , 1982, 21, 1263-1264. 6. L. D. Reed and E. Menke, J. Electrochem. Soc., 2013, 160, A915−A917. 7. X. G. Sun, Z. H. Bi, H. S. Liu, Y. X. Fang, C. A. Bridges, M. P. Paranthaman, S. Dai and G. M. Brown, Chem. Commun., 2016, 52, 1713-1716. 8. X. G. Sun, Z. Z. Zhang, H. Y. Guan, C. A. Bridges, Y. X. Fang, Y.-S. Hu, G. M. Veith and S. Dai, J. Mater. Chem. A, 2017, 5, 6589-6596. Figure 1

Polyoxometalate Heterogeneous Nanostructures As Cathodes for Mg2+ Ion Storage

As global energy demands continue to rise each year, current state-of-the-art Li-ion battery (LIB) systems are predicted to reach the limit in the amount of energy that they can supply. In addition to this, LIBs are also limited by the low resource availability of Li metal. One proposed solution is to move away from LIBs to multivalent ion systems; of these alternatives, magnesium (Mg) is considered a promising material for the next generation of rechargeable batteries. Unlike Li, Mg metal does not form dendritic structures during cycling which would allow it to be employed as an anode which has a specific capacity of 2205 mAh/g compared to 777 mAh/g of the graphite anode that is currently used in LIBs. Mg also has a very high elemental abundance in the earth’s crust (2.44x104 ppm) which would drive down the production cost while simultaneously ensuring the longevity of these batteries in terms resource availability. Most importantly, the divalent nature of the Mg-ion means that it can carry twice the amount of charge per ion compared to Li. This is largely related to the high volumetric capacity (3833 mAh/ml) of Mg which is superior to even that of Li metal. While there is potential for Mg to replace LIBs, commercialization of these batteries has been hindered by sluggish insertion kinetics into cathode host materials as a direct result of the strong coulombic interactions experienced by the divalent Mg-ion. Due to this drawback, conventional metal oxide or sulfide insertion cathodes for Mg batteries tend to exhibit low capacities and operating voltages. In response to this, a large portion of Mg battery research is currently focused on the development of novel materials capable of functioning as cathodes for fast and efficient Mg-ion insertion. The idea proposed in this work is to depart from the conventional intercalation mechanism of LIBs and move towards a molecular cluster battery (MCB) based on polyoxometalate (POM) metal oxygen cluster molecules of early transition metals (Mo, W, V, or Nb). The unique redox activity of POMs are due to their intrinsic ability to form highly stable reduced and oxidized species allowing them to partake in fast reversible electron transfer reactions. Although POMs are also able to function as electron reservoirs, POMs themselves have negligible electronic conductivity as well as high solubility in both aqueous and organic media. Therefore, in order for these materials to be used as electrodes for electrochemical energy storage, they must first undergo hybridization with highly conductive insoluble substrates such as conductive organic polymers (COPs) or multi-walled carbon nanotubes (MWCNTs). The fabrication of heterogenous cathodes provide a “wiring” effect by electrically connecting the POM molecules allowing them all to take part in the redox chemistry while simultaneously anchoring them to a substrate, thus preventing any loss of active material to electrolyte dissolution during cycling. By taking advantage of the synergistic effect of pairing the ionically conductive POM molecule with the electrically conductive substrate; the resulting cathode material will thus be capable of fast electron transfer reactions with high ionic mobility. In this work, hybrid nanostructured electrodes of poly-3,4-ethylenedioxythiophene (PEDOT) and a phosphomolybdic acid (H3PMo12O40) POM have been fabricated electrochemically and applied as cathodes for Mg-ion storage. Preliminary cyclic voltammetry and galvanostatic cycling data have demonstrated an enhancement in the capacity of the PEDOT cathode after integration of the POM molecules throughout the polymer matrix. The initial cycling studies have also shown that the PEDOT-POM redox peaks are still present after 7 days of soaking in the organic electrolyte which suggests that the POM molecules do not readily dissolve out of the PEDOT matrix. This work highlights the potential of redox active POM inorganic clusters to function as cathodes with the capability of advancing the current state of Mg batteries.

Confined Sulfur in 3 D MXene/Reduced Graphene Oxide Hybrid Nanosheets for Lithium-Sulfur Battery.

Three-dimensional metal carbide MXene/reduced graphene oxide hybrid nanosheets are prepared and applied as a cathode host material for lithium-sulfur batteries. The composite cathodes are obtained through a facile and effective two-step liquid-phase impregnation method. Owing to the unique 3 D layer structure and functional 2 D surfaces of MXene and reduced graphene oxide nanosheets for effective trapping of sulfur and lithium polysulfides, the MXene/reduced graphene oxide/sulfur composite cathodes deliver a high initial capacity of 1144.2 mAh g-1 at 0.5 C and a high level of capacity retention of 878.4 mAh g-1 after 300 cycles. It is demonstrated that hybrid metal carbide MXene/reduced graphene oxide nanosheets could be a promising cathode host material for lithium-sulfur batteries.

Thermal Exfoliation of Layered Metal-Organic Frameworks into Ultrahydrophilic Graphene Stacks and Their Applications in Li-S Batteries.

2D nanocarbon-based materials with controllable pore structures and hydrophilic surface show great potential in electrochemical energy storage systems including lithium sulfur (Li-S) batteries. This paper reports a thermal exfoliation of metal-organic framework crystals with intrinsic 2D structure into multilayer graphene stacks. This family of nanocarbon stacks is composed of well-preserved 2D sheets with highly accessible interlayer macropores, narrowly distributed 7 Å micropores, and ever most polar pore walls. The surface polarity is quantified both by its ultrahigh water vapor uptake of 14.3 mmol g-1 at low relative pressure of P/P0 = 0.4 and ultrafast water wetting capability in less than 10.0 s. Based on the structural merits, this series hydrophilic multilayer graphene stack is showcased as suitable model cathode host for unveiling the challenging surface chemistry issue in Li-S batteries.

Three-dimensional hierarchical C-Co-N/Se derived from metal-organic framework as superior cathode for Li-Se batteries

Three-dimensional, porous graphitic carbon co-doped with cobalt and nitrogen (C-Co-N) is prepared with metal-organic framework (MOF) and employed as Lewis base matrix to host selenium. Owing to the unique structure with abundant micro/meso-pores, the highly-conductive C-Co-N matrix provides highly-efficient channels for electron transfer and ionic diffusion, and sufficient surface area for loading of selenium nanoparticles while mitigating dissolution of polyselenides and suppressing volume expansion. The homogenous distribution of cobalt nanoparticles and nitrogen-group in C-Co-N composite immobilize polyselenides through strong chemical interaction in the operation of Li-Se batteries. With a very high Se loading of 76.5 wt%, the C-Co-N/Se cathode delivers superior electrochemical performance with an ultrahigh reversible capacity of 672.3 mAh g−1 (99.6% of the theoretical value) and a capacity of 574.2 mAh g−1 after 200 cycles, giving a capacity fading of only 0.07% per cycle and a nearly 100% Columbic efficiency. In-situ Raman spectroscopy and density functional theory simulations are employed to investigate the Se (de)lithiation mechanism at the electrolyte/cathode interface, and confirm that the structure and composition of C-Co-N scaffold give rise to efficient cathode host for high-performance Se-based cathodes with dramatically reduced capacity fading.

Fabrication Methods of Porous Carbon Materials and Separator Membranes for Lithium–Sulfur Batteries: Development and Future Perspectives

Lithium–sulfur batteries (Li–S batteries) have a five times higher energy density than state-of-the-art lithium-ion batteries and have attracted world-wide attention. However, many inherent problems limit the practical application of Li–S batteries. Among them, the dissolution of polysulfides, which is called the “shuttle effect”, is rather severe and usually causes irreversible capacity decay. Many methods have been developed to overcome this problem, including the rational design of porous cathode hosts, modification of separators to prevent the migration of polysulfides, and the addition of transition-metal oxides for polysulfide adsorption. Here, the various preparation methods for the development of high performance Li–S batteries are reviewed. The advantages and disadvantages of each method are discussed in detail, shedding light on directions for further research and development in the future.

Mesoscale Evaluation of Titanium Silicide Monolayer as a Cathode Host Material in Lithium–Sulfur Batteries

Two-dimensional materials are competitive candidates as cathode materials in lithium–sulfur batteries for immobilizing soluble polysulfides and mitigating the shuttle effect. In this study, a mesoscale modeling approach, which combines first-principles simulation and kinetic Monte Carlo simulation, is employed to evaluate titanium silicide (Ti2Si and TiSi2) monolayers as potential host materials in lithium–sulfur batteries. It is found that the Ti2Si monolayer has much stronger affinities to Li2S x (x = 1, 2, 4) molecules than does the TiSi2 monolayer. Also, Ti2Si can facilitate the dissociation of long-chain Li2S4 to LiS2. On the other hand, TiSi2 can only provide a weak chemical interaction for trapping soluble Li2S4. Therefore, the Ti2Si monolayer can be considered to be the next-generation cathode material for lithium–sulfur batteries. Nevertheless, the strong interaction between Ti2Si and Li2S also causes fast surface passivation. How to control the Li2S precipitation on Ti2Si should be answered by future studies.

Mechanism of Zn Insertion into Nanostructured δ-MnO2: A Nonaqueous Rechargeable Zn Metal Battery

Unlike the more established lithium-ion based energy storage chemistries, the complex intercalation chemistry of multivalent cations in a host lattice is not well understood, especially the relationship between the intercalating species solution chemistry and the prevalence and type of side reactions. Among multivalent metals, a promising model system can be based on nonaqueous Zn2+ ion chemistry. Several examples of these systems support the use of a Zn metal anode, and reversible intercalation cathodes have been reported. This study utilizes a combination of analytical tools to probe the chemistry of a nanostructured δ-MnO2 cathode in association with a nonaqueous acetonitrile–Zn(TFSI)2 electrolyte and a Zn metal anode. As many of the issues related to understanding a multivalent battery relate to the electrolyte–electrode interface, the high surface area of a nanostructured cathode provides a significant interface between the electrolyte and cathode host that maximizes the spectroscopic signal of any s...

Recent progress and challenges in the development of Prussian blue analogues as new intercalation cathode materials

As a large family of the lattices with open framework structure, abundant redox-active sites and chemically stable structures, Prussian blue and its analogues (PBAs) can serve in principle as promising insertion cathode materials for a variety of metal ions. This paper reviews the recent progress in the development of PBAs compounds as Li+, Na+ and other multivalent ions (Mg2+, Al3+, Zn2+, Ca2+ and etc.) insertion cathodes, discusses the relationship between the crystal structure of PBAs and their ion insertion behaviors and briefly analyzes the possible strategies for the problems present in the battery applications of PBAs, aiming at promoting the development of a new type of cathode host materials for next generation advanced batteries.

Strings of Porous Carbon Polyhedrons as Self‐Standing Cathode Host for High‐Energy‐Density Lithium–Sulfur Batteries

AbstractRational design of cathode hosts with high electrical conductivity and strong sulfur confinement is a great need for high‐performance lithium–sulfur batteries. Herein, we report a self‐standing, hybrid‐nanostructured cathode host comprised of metal–organic framework (MOF)‐derived porous carbon polyhedrons and carbon nanotubes (CNTs) for the significant improvement of both the electrode cyclability and energy density. The strong coupling of the intertwined CNTs and strung porous carbon polyhedrons as a binder‐free thin film significantly enhances the long‐range electronic conductivity and provides abundant active interfaces as well as robust electrode integrity for sulfur electrochemistry. Attributed to the synergistic combination of the CNTs and carbon polyhedrons, the obtained sulfur electrodes exhibit outstanding cyclability, an excellent high‐rate response up to 10 C, and an ultra‐high volumetric capacity of 960 Ah L−1.

Strings of Porous Carbon Polyhedrons as Self-Standing Cathode Host for High-Energy-Density Lithium-Sulfur Batteries.

Rational design of cathode hosts with high electrical conductivity and strong sulfur confinement is a great need for high-performance lithium-sulfur batteries. Herein, we report a self-standing, hybrid-nanostructured cathode host comprised of metal-organic framework (MOF)-derived porous carbon polyhedrons and carbon nanotubes (CNTs) for the significant improvement of both the electrode cyclability and energy density. The strong coupling of the intertwined CNTs and strung porous carbon polyhedrons as a binder-free thin film significantly enhances the long-range electronic conductivity and provides abundant active interfaces as well as robust electrode integrity for sulfur electrochemistry. Attributed to the synergistic combination of the CNTs and carbon polyhedrons, the obtained sulfur electrodes exhibit outstanding cyclability, an excellent high-rate response up to 10 C, and an ultra-high volumetric capacity of 960 Ah L-1 .

Low-Cost High-Energy Potassium Cathode.

Potassium has as rich an abundance as sodium in the earth, but the development of a K-ion battery is lagging behind because of the higher mass and larger ionic size of K+ than that of Li+ and Na+, which makes it difficult to identify a high-voltage and high-capacity intercalation cathode host. Here we propose a cyanoperovskite KxMnFe(CN)6 (0 ≤ x ≤ 2) as a potassium cathode: high-spin MnIII/MnII and low-spin FeIII/FeII couples have similar energies and exhibit two close plateaus centered at 3.6 V; two active K+ per formula unit enable a theoretical specific capacity of 156 mAh g-1; Mn and Fe are the two most-desired transition metals for electrodes because they are cheap and environmental friendly. As a powder prepared by an inexpensive precipitation method, the cathode delivers a specific capacity of 142 mAh g-1. The observed voltage, capacity, and its low cost make it competitive in large-scale electricity storage applications.

Ordered SnO nanoparticles in MWCNT as a functional host material for high-rate lithium-sulfur battery cathode

Lithium-sulfur battery has become one of the most promising candidates for next generation batteries, and it is still restricted due to the low sulfur conductivity, large volume expansion and severe polysulfide shuttling. Herein, we present a novel hybrid electrode with a ternary nanomaterial based on sulfur-impregnated multiwalled carbon nanotubes filled with ordered tin-monoxide nanoparticles (MWCNT-SnO/S). Using a dry plasma reduction method, a mechanically robust material is prepared as a cathode host material for lithium-sulfur batteries. The MWCNT-SnO/S electrode exhibits high conductivity, good ability to capture polysulfides, and small volume change during a repeated charge–discharge process. In situ transmission electron microscopy and ultraviolet–visible absorption results indicate that the MWCNT-SnO host efficiently suppresses volume expansion during lithiation and reduces polysulfide dissolution into the electrolyte. Furthermore, the ordered SnO nanoparticles in the MWCNTs facilitate fast ion/electron transfer during the redox reactions by acting as connective links between the walls of the MWCNTs. The MWCNT-SnO/S cathode with a high sulfur content of 70 wt.% exhibits an initial discharge capacity of 1,682.4 mAh·g–1 at 167.5 mA·g–1 (0.1 C rate) and retains a capacity of 530.1 mAh·g–1 at 0.5 C after 1,000 cycles with nearly 100% Coulombic efficiency. Furthermore, the electrode exhibits the high capacity even at a high current rate of 20 C.