Ion Storage Capacity Research Articles

(Invited) Chloride-Ion Concentration Flow Cells for Efficient Salinitygradient Energy Recovery

Salinity gradient (SG) is a natural and renewable energy source, which naturally exists between river water and seawater and can also be created by engineering processes. Here, a novel chloride-ion (Cl−) concentration flow cell based on two symmetrical electrodes (BiCl3, CoCl2, VCl3 or BiOCl) separately by a cation-exchange membrane (CEM) was used as an efficient method to recover SG energy. Analysis from X-ray diffraction and X-ray photoelectron spectroscopy indicated that the concentration flow cell with metal chloride electrode (BiCl3, CoCl2 or VCl3) was based on Cl− extraction and insertion, and that of the BiOCl electrode was depended on Cl– intercalation and deintercalation. Besides, the Donna potential across the CEM was also employed for the SG energy harvest. The cell with BiOCl electrodes had the highest power density of 4.36 W m-2 with synthetic river water (1 g L-1 NaCl) and seawater (30 g L-1 NaCl), which was higher than those of most previous technologies for SG energy recovery. The higher power output could be attributed to the faster kinetics of Cl− intercalation/deintercalation on BiOCl electrodes with a layered structure compared to that of Cl- extraction/insertion on metal chloride electrodes. In addition, the results from cyclic voltammetry, electrochemical impedance spectroscopy and galvanostatic charge/discharge suggested that low charge transfer and ion diffusion resistances, and the high ion storage capacities of the BiOCl electrode also benefit its the higher power output.

High-performance nanohybrid anode based on FeS2 nanocubes and nitrogen-rich graphene oxide nanoribbons for sodium ion batteries

Sodium ion batteries (SIBs) have attracted considerable attention as an alternative to Li ion batteries (LIBs) because of the sustainable sodium resources and similar chemistry to LIBs. On the other hand, the larger and heavier sodium results in unfavorable sodium ion storage capacity. In this study, an inexpensive precursor-based conversion material, FeS2, was synthesized as a nanostructured pyrite crystal, <100 nm in size, which has a carbon coating layer, a few nanometers in thickness. The deficient electrical conductivity of the synthesized FeS2 nanocubes (FeS2-NCs) was strengthened by forming a nanohybrid structure with high-aspect ratio graphene oxide nanoribbons containing nitrogen dopants (N-GONRs). N-GONRs bind tightly the FeS2-NCs well-dispersed in the N-GONRs matrix, inducing highly improved electrochemical performance as an anode for SIBs. The FeS2-NCs/N-GONRs nanohybrid anode delivered a high reversible capacity of ∼800 mA h g−1 at 0.2 A g−1, of which approximately 60% was maintained at a 50 times higher current rate, indicating high rate capability. In addition, stable cycling performance over 200 cycles was achieved with an average capacity of ∼670 mA h g−1. The hybrid anode demonstrated its feasibility in a full cell test using an O3-type cathode material.

Nitrogen and Sulfur Co-doped Mesoporous Carbon for Sodium Ion Batteries

Enhanced sodium ion storage capacity of carbon anodes can be realized by heteroatom doping. Designing doped carbons with superior rate performance, high initial Coulombic efficiency (ICE), and exce...

Chloride-ion concentration flow cells for efficient salinity gradient energy recovery with bismuth oxychloride electrodes

Salinity gradient (SG) energy is a large, renewable, and clean energy source, which naturally exists between river water and seawater and can also be created by engineering processes. Here, bismuth oxychloride (BiOCl) electrodes was used for efficient SG energy recovery in a chloride-ion concentration flow cell (Cl-CFC) based on a new mechanism, that is, chloride ion (Cl−) intercalation/deintercalation. Compared to previous Cl-CFC with BiCl3 electrodes based on Cl− extraction/insertion (3.17 W m−2), the peak power density of the cell with BiOCl electrodes (4.36 W m−2) was higher under the same testing conditions when using synthetic river water (1 g L−1 NaCl) and seawater (30 g L−1 NaCl). Further investigations demonstrated that the relatively higher power density was attribute to the faster kinetics of Cl− intercalation/deintercalation at BiOCl electrodes than that of Cl− extraction/insertion at BiCl3 electrodes. In addition, three BiOCl electrodes with different carbon black ratios (CB, 10%, 20% and 30%) were also prepared and examined in this study. Compared to BiOCl/10%CB and BiOCl/30%CB electrodes, the lower charge transfer and ion diffusion resistances, larger ion storage capacities and higher cell open circuit voltages of the BiOCl/20%CB electrodes were all beneficial to its higher power output.

Investigation of the Effect of Electrolyte Composition on the Performance of Pre-Structured Porous Silicon Anode Materials

Crystalline silicon is an ideal anode candidate for lithium ion batteries as it offers a high Li+ ion storage capacity, direct current pathway and is a stable and earth abundant element. One of the limitations of silicon as electrode material is its mechanical instability during repeated cycling of the battery. The incorporation of lithium ions into the silicon crystal structure causes extreme volume expansion (400 %) of the anode material. The high volume expansion during cycling can lead to crack formation and pulverization of the silicon anode. Consequently, the silicon can react further with the electrolyte, resulting in a build-up of the solid electrolyte interphase (SEI) layer, eventually hindering Li+ ion diffusion. Porous silicon, characterized by bulk silicon crystallites separated by pores, can compensate to some extent for the volume expansion without unwanted mass increase of the electrode (as with paste electrodes), while still maintaining lower costs than with silicon microwires due to the scalability of the porous silicon etching process[1]. In addition, porous silicon offers shorter diffusion pathways for Li+ due to the incorporation of the electrolyte into the pore structure. Porous silicon still possesses some limitations regarding the amount of volume expansion it can undergo, as well as the diffusion of the electrolyte into the pore structure. To further compensate for the mechanical stress during cycling, by creating pre-defined breakage points in the silicon surface, and open up the pore structure to improve the electrolyte diffusion, pre-structuring of the porous silicon was performed via reactive ion etching (RIE) techniques using a flow ratio of 2 SF6/6 Ar (sccm/sccm), power level of 200 W and etch times varying from 30 seconds to 8 minutes. The resulting textured surface possessed microstructures with trench depths ranging from 1-2 µm and widths of around 1 µm. Improved cycling stability was seen for samples subjected to lower etch times (30 seconds to 2 minutes). In order to have long term cycling stability, it is required to have an SEI layer that is thin enough to allow faster uptake of Li+ into the Si structure, and stable enough that it will not continuously react with active silicon. The composition of this SEI layer can be tailored by modifying the electrolyte composition. The type and concentration of lithium salt (LiTFSA, LiPF6, LiBOB etc.) and solvent molecule (ethylene carbonate, dimethyl ether, doluene, propylene carbonate etc.) can be altered in order to improve the SEI layer. In this work, we investigate the effect of varying electrolyte compositions on the performance of porous silicon anodes in a half-cell as well as on the SEI layer. The change in composition of the SEI layer is investigated via ex situ Raman and X-ray photoelectron spectroscopy techniques. Electrolytes with high viscosity (such as LiPF6 containing electrolytes) experience limited infiltration into the silicon pore structure of the anode. The viscosity of the electrolyte can be tailored by modifying the salt concentration to ensure easy infiltration into the pores to allow maximum charging of the porous silicon anode. Improved electrolyte infiltration into the pores was seen with the RIE treated porous silicon samples for all electrolytes, including those with high viscosity. Reduction of the organic solvent molecules after repeated cycling lead to higher carbon content in the SEI after repeated cycling. Electrolytes with flourine containing lithium salts lead to the formation of LiF compounds, reducing the amount of active lithium. [1] Hansen, S., Schütt, A., Carstensen, J. and Adelung, R., J. Electrochem. Soc., 2016, 163(14), A3036-A3045.

A Brief Overview on the Anticorrosion Performances of Sol-Gel Zeolite Coatings

Research activity concerning nanoporous zeolites has grown considerably in recent decades. The structural porosity of zeolites provides versatile functional properties such as molecular selectivity, ion and molecule storage capacity, high surface area, and pore volume which combined with excellent thermal and chemical stability can extend its application fields in several industrial sectors. In such a context, anti-corrosion zeolite coatings are an emerging technology able to offer a reliable high performing and environmental friendly alternative to conventional chromate-based protective coatings. In this article, a focused overview on anti-corrosion performances of sol-gel composite zeolite coatings is provided. The topic of this review is addressed to assess the barrier and self-healing properties of composite zeolite coating. Based on results available in the literature, a property–structure relationship of this class of composites is proposed summarizing, furthermore, the competing anti-corrosion active and passive protective mechanisms involved during coating degradation. Eventually, a brief summary and a future trend evaluation is also reported.

Porous MXenes enable high performance potassium ion capacitors

High power K+ ion capacitors have great potential in various large-scale applications because of the cost advantages and the low redox potential of K/K+. However, the large ionic radius of potassium brings huge challenges for the development of suitable electrode materials. Here we demonstrate a general strategy for preparing porous MXene electrodes that can significantly enhance K+ storage performance. Using V2C MXene as a model system, we show that the K+ ion storage capacity can be greatly boosted by a simple sequential acid/alkali treatment. The resulting product, K–V2C, not only delivers a capacity of 195 mAh g−1 (in contrast to 98 mAh g−1 of pristine V2C) at 50 mA g−1, but also good rate performance. The charge storage mechanism was carefully studied and is shown to involve a solvent co-intercalation process. In addition, full cells were fabricated by coupling the K–V2C anode and Prussian blue analogous (KxMnFe(CN)6) cathode, which can work at a high average operating voltage of ~3.3 V within a wide range (0.01 V–4.6 V). Moreover, the devices can achieve a high energy density of 145 Wh kg−1 at a power density of 112.6 W kg−1, suggesting that K–V2C, and other porous MXenes prepared by our approach, are promising electrodes in mobile ion capacitors.

High performance all-solid-state electrochromic device based on LixNiOy layer with gradient Li distribution

In the complementary electrochromic devices (ECDs), nickel oxide (NiOx) is the mostly studied material as counter electrode for its neutral brown color and relatively large coloration efficiency. However, there exist some obstacles that limit the utilization of NiOx counter electrode in ECDs due to the poor transparency in the bleached state and inadequate ion storage capacity. Here, a new type of counter electrode LixNiOy layers has been investigated, and LixNiOy-based all-solid-state inorganic ECD has been successfully fabricated by magnetron sputtering. The prepared ECD exhibits excellent electrochromic performance with an optical contrast of 72.8% at 550 nm, and desirable response time with 13 s and 3.5 s for coloring and bleaching process, respectively. Furthermore, the advantages of LixNiOy-based ECDs have been demonstrated due to the gradient distribution of Li element in the LixNiOy layer. The LixNiOy layer in the proposed ECD shows a Li-rich surface, which can provide more Li ions for the coloration process. Meanwhile, the bottom of LixNiOy layer is Li-poor, which can accommodate more ions during the bleaching reaction. This structure shows superiority over the traditional NiOx-based structure, as well as some other structures. Hence, our work guided a promising new structure for the electrochromic practical application and commercial mass production.

Graphene and diglyme assisted improved Al3+ ion storage in MoO3 nanorod: steps for high-performance aqueous aluminum-ion battery

An approach to improve the Al3+ ion storage capacity of MoO3 in aqueous electrolyte is illustrated here. Graphene as conductive additive and diglyme as electrolyte additive play a pivotal and synergistic role in the improvement. Graphene-MoO3 composite exhibits stable capacity of 160 mAh g−1 over 100 cycles in diglyme mixed aqueous electrolyte with v/v mixing ratio of 50:50, whereas it delivers a capacity of only 75 mAh g−1 at the 100th cycle in pristine aqueous electrolyte. Besides, pristine MoO3 also demonstrates improved stability in diglyme mixed aqueous electrolyte.

Understanding Sodium Ion Storage and Diffusivity into CNT-TiO2 Hybrid Electrodes

Sodium ion batteries (NIBs) have attracted much attention of researchers worldwide due to its competence to be used in stationary applications, where cost plays a major role than the size and weight of the battery. Till date, a large variety of materials have been investigated as anodes for sodium ion battery.1 Graphite, the state-of-art of the lithium ion battery anode, can host a negligible amount of sodium during electrochemical intercalation/deintercalation processes.2 Considerable efforts have been made to develop alternative anodes for NIBs such as tin and antimony based alloys3, metal phosphides/oxides/sulphides4, spinel oxides5, and hard carbons6. Hard carbons show a promising sodium ion storage capacity of about 200-400 mAh g-1, but low operating potential of the hard carbon may rise to severe safety issues of dendrite formation and metal plating. Alloy based anodes have very high theoretical capacity between 600 (Na3Sb) to 2600 mAhg-1 (Na3P). Unfortunately, very poor electrochemical performance has been observed for alloy based anodes because of volume changes during sodiation/desodiation which leads to pulverisation. Consequently, an appropriate anode material for NIB is desired which is free from both metal plating and pulverisation. Titanium dioxide (TiO2)7, which is extensively used as multifunctional material because of its stability, non-toxicity, robustness and physio-chemical properties with the advantage of its moderate cost have also been investigated as anodes for NIBs. Titanium based compounds are very stable and safe, delivers long cycle life of over 1000s of cycles. The 3-dimensional open structure of anatase TiO2 offers possible pathways for Na ion insertion and deinsertion. TiO2 offer capacities close to 335 mAh g-1 due to redox reaction of Ti4+/Ti3+. But, electrochemical performance in terms of capacity and rate capability of TiO2 is limited due to its poor conductivity. Therefore, most of the research in this material is focussed on to improve sluggish kinetics of Na+ ion in TiO2 to gain high capacity and good C rate performance. To improve the charge storage and kinetics of TiO2 anodes for NIBs, in this work we present a hybrid material of TiO2 nanoparticles (NPs) is incorporated onto multiwall carbon nanotube (CNTs) (Figure 1a). The cycling stability and C-rate performance of CNT-TiO2 hybrid as anodes for NIBs demonstrate two and half times enhancement in electrochemical performance in the presence of CNT. CNT - TiO2 hybrid shows discharge capacity of about 100 mAh g-1 at current density of 1 A g-1 and cycles for 1000 cycles with little loss in capacity. The overall charge storage properties of pristine TiO2 and CNT-TiO2 hybrid is quantified into pseudo capacitive and diffusion-control Na+ intercalation (Figure 1b). Two times increase in Na+ diffusivity in CNT-TiO2 hybrid is achieved in relation to pristine TiO2. Sodium ion full cell based on CNT-TiO2 hybrid and phosphate based cathode delivers capacity of 184 mAh g-1 and cycles very well. The outstanding electrochemical performance is due to the synergetic effect of TiO2 nanoparticles and conducting CNT network which provides efficient charge storage as well Na+ diffusivity. This work not only develops the fundamental understanding of Na+ storage and kinetics of TiO2 electrode but also its practical realisation in sodium ion full cells. Acknowledgements SG acknowledges MHRD, VKK acknowledges UGC-NET, Govt. of India, and SKM acknowledges Research Center Imarat (DRDO), Hyderabad under grant no. RCI/CAAT/8151/CARS-358 for the financial support. References N. Yabuuchi, K. Kubota, M. Dahbi, and S. Komaba, Chem. Rev., 114, 11636 (2014).B. Jache, and P. Adelhelm, Angew. Chem. Int. Ed., 53, 10169 (2014).D. Ellis, T. D. Hatchard, and M. N. Obrovac, J. Electrochem. Soc., 159 , A1801 (2012).Z.-J. Zhang, Y.-X. Wang, S.-L. Chou, H.-J. Li, H.-K. Liu, and J.-Z. Wang, J. Power Sources, 280, 107 (2015).R. Alcántara, M. Jaraba, P. Lavela, and J. L. Tirado, Chem. Mater., 14, 2847 (2002).E. Irisarri, A. Ponrouch, and M. R. Palacina, J. Electrochem. Soc., 162, A2476 (2015).S. Guo, J. Yi, Y. Sun, and H. Zhou, Energy Environ. Sci., 9 , 2978 (2016). Figure 1

3D nitrogen-doped framework carbon for high-performance potassium ion hybrid capacitor

Post-lithium ion hybrid capacitors have great potential to serve as mid-to large-scale energy storage applications because of their high energy/power densities, abundant resources and low cost. Here we report a high-performance dual-carbon potassium ion hybrid capacitor (PIHC) based on two carbon electrode materials derived from a single precursor–ethylene diamine tetraacetic acid tetrasodium (EDTA-4Na). By means of a simple calcination, the EDTA-4Na can be directly converted to a three-dimensional (3D) nitrogen-doped framework carbon (3DNFC) that exhibits high reversible capacity and good electrochemical kinetic property for potassium ion storage. Such 3DNFC can be further converted to a 3D nitrogen-doped framework activated carbon (3DNFAC) that shows ultrahigh specific surface area (3839 m2 g−1) and excellent capacitance performance. Using the 3DNFC as battery-type anode and the 3DNFAC as capacitor-type cathode, a dual-carbon PIHC is fabricated, and it is able to normally work at 0–4.2 V, delivers high energy and power densities (163.5 Wh kg−1 at 210 W kg−1, and 76.4 Wh kg−1 at 21 000 W kg−1), and exhibits outstanding cycling stability (91.7% capacity retention after 10 000 cycles at 2.0 A g−1), which are all the best values for the state-of-the-art PIHCs.

Aqueous Zinc-Ion Storage in MoS2 by Tuning the Intercalation Energy.

Aqueous Zn-ion batteries present low-cost, safe, and high-energy battery technology but suffer from the lack of suitable cathode materials because of the sluggish intercalation kinetics associated with the large size of hydrated zinc ions. Herein we report an effective and general strategy to transform inactive intercalation hosts into efficient Zn2+ storage materials through intercalation energy tuning. Using MoS2 as a model system, we show both experimentally and theoretically that even hosts with an originally poor Zn2+ diffusivity can allow fast Zn2+ diffusion. Through simple interlayer spacing and hydrophilicity engineering that can be experimentally achieved by oxygen incorporation, the Zn2+ diffusivity is boosted by 3 orders of magnitude, effectively enabling the otherwise barely active MoS2 to achieve a high capacity of 232 mAh g-1, which is 10 times that of its pristine form. The strategy developed in our work can be generally applied for enhancing the ion storage capacity of metal chalcogenides and other layered materials, making them promising cathodes for challenging multivalent ion batteries.

Nanopore confined anthraquinone in MOF-derived N-doped microporous carbon as stable organic cathode for lithium-ion battery

Anthraquinone (AQ), as organic cathode material, has provided an excellent opportunity to update the preexisting energy storage technologies owing to its facile and desirable fabrication at molecular level, higher theoretical gravimetric capacities and remarkable sustainability. However, some of its pristine properties like insulation and dissolution into electrolyte of organic active materials during cycling, have been inevitable obstacles to boost its electrochemical performance. Herein, we report a rational strategy to improve lithium ion storage performance of AQ by confining nanosized amorphous AQ into zeolitic imidazolate framework-8 (ZIF-8)-derived nitrogen-doped microporous carbon scaffold (AQ@N-ZIF-8). The AQ@N-ZIF-8 cathode delivers a high reversible specific capacity of 240 mAh g−1 at current rate of 0.1 C and retains ~216 mAh g−1 after 300 cycles (remarkably low capacity fading rate of 0.08% per cycle) with coulombic efficiency up to 99%. The exceptional lithium ion storage capacity of AQ@N-ZIF-8 is mainly ascribed to the synergistic effect of high loading capacity of AQ encapsulation and nanopore confinement of AQ dissolution in carbon scaffolds, and the enhanced conductivity of the encapsulated AQ by higher contents of nitrogen dopant. Moreover, the N-ZIF-8 with micropores facilitates the fast diffusion of organic electrolyte ions.

New Insights in the Prolonged Cycle Life of Si Electrodes Prepared in Aqueous Buffered Media at Low pH

Silicon as an anode material in lithium-ion batteries (LIB) has the 10-fold storage capacity of lithium ions than graphite and is thus an interesting candidate for next generation LIB.[1] However, due to the sever volume expansion during the alloying reaction of Si with Li, the physical inter-particle connections mediated by the electrode binder are broken. As a result the electrode disintegrates and its capacity fades rapidly. The mechanical and interfacial properties can be enhanced when the Si electrodes are prepared in an aqueous solution of a citric acid buffer at pH=3, instead of neutral pH, such as water.[2] This behavior was previously ascribed to the acid-catalyzed formation of a silyl ester between binder and the native silicon oxide surface.[3] However, many questions still remain unanswered, e.g. what is the impact of the pH or how does the type of acid affect the surface functionalization? Additionally, recent results suggest that citric acid itself interacts strongly with the Si surface, thus forming an artificial SEI layer.[3] In our study we are providing a deeper insight in the role of the carboxylic acids by examining a series of different carboxylic acids, namely glycolic acid (GlyAc), malic acid (MalAc) and citric acid (CitAc) (Figure 1). The carboxylic acids carry a different number of functional groups, which helps to interpret the rather complex FTIR spectra (Fig. 1a) of these silicon:acid:binder composites. The impact of the carboxylic acid on other cell components (e.g. electrolyte salt or current collectors) was investigated by on-line mass spectroscopy, electron microscopy and electrochemical techniques (e.g. Fig. 1b). Our aim is to evaluate how the capacity retention of acid-treated Si electrodes could be further improved by rational choice of the buffer chemistry and to identify the key control parameters in the functionalization process and during slurry preparation (e.g. pH and acid strength) in order to advance the slurry fabrication process and the performance of Si-containing electrodes.

Sparsely Pillared Graphene Materials for High-Performance Supercapacitors: Improving Ion Transport and Storage Capacity.

Graphene-based materials are extensively studied as promising candidates for supercapacitors (SCs) owing to the high surface area, electrical conductivity, and mechanical flexibility of graphene. Reduced graphene oxide (RGO), a close graphene-like material studied for SCs, offers limited specific capacitances (100 F·g–1) as the reduced graphene sheets partially restack through π–π interactions. This paper presents pillared graphene materials designed to minimize such graphitic restacking by cross-linking the graphene sheets with a bifunctional pillar molecule. Solid-state NMR, X-ray diffraction, and electrochemical analyses reveal that the synthesized materials possess covalently cross-linked graphene galleries that offer additional sites for ion sorption in SCs. Indeed, high specific capacitances in SCs are observed for the graphene materials synthesized with an optimized number of pillars. Specifically, the straightforward synthesis of a graphene hydrogel containing pillared structures and an interconnected porous network delivered a material with gravimetric capacitances two times greater than that of RGO (200 F·g–1vs 107 F·g–1) and volumetric capacitances that are nearly four times larger (210 F·cm–3vs 54 F·cm–3). Additionally, despite the presence of pillars inside the graphene galleries, the optimized materials show efficient ion transport characteristics. This work therefore brings perspectives for the next generation of high-performance SCs.

Silver vanadium oxide@water-pillared vanadium oxide coaxial nanocables for superior zinc ion storage properties

The Ag0.333V2O5@V2O5·nH2O coaxial nanocables with optimal ion/electron conductivity enable synergistic enhancement of zinc ion storage properties.

Order-disorder transition in nano-rutile TiO2 anodes: a high capacity low-volume change Li-ion battery material.

Nano-sized particles of rutile TiO2 is a promising material for cheap high-capacity anodes for Li-ion batteries. It is well-known that rutile undergoes an irreversible order-disorder transition upon deep discharge. However, in the disordered state, the LixTiO2 material retains a high reversible ion-storage capacity of >200 mA h g-1. Despite the promising properties of the material, the structural transition and evolution during the repeated battery operation has so far been studied only by diffraction-based methods, which only provide insight into the part that retains some long-range order. Here, we utilize a combination of ex situ and operando total scattering with pair distribution function analysis and transmission electron microscopy to investigate the atomic-scale structures of the disordered LixTiO2 forming upon the discharge of nano-rutile TiO2 as well as to elucidate the phase behavior in the material during the repeated charge-discharge process. Our investigation reveals that nano-rutile upon Li-intercalation transforms into a composite of ∼5 nm domains of a layered LixTiO2α-NaFeO2-type structure with ∼1 nm LixTiO2 grain boundaries with a columbite-like structural motif. During repeated charge-discharge cycling, the structure of this composite is retained and stores Li through a complete solid-solution transition with a remarkably small volume change of only 1 vol%.

Al3+ ion intercalation in MoO3 for aqueous aluminum-ion battery

While addressing the question of Al3+ ion intercalation/deintercalation in MoO3, we unravel that Al3+ ion preferentially intercalates in MoO3 in certain aqueous electrolytes. The Al3+ ion electrochemistry in MoO3 shows stark contrasting characteristics in different aqueous electrolytes. Although very high initial Al3+ ion storage capacity of 680 mAhg−1 is observed, a stable discharge capacity of approximately 170 mAhg−1 is attained after 20th cycle over the measured time (350th cycle) at a specific current of 2.5 Ag-1 (5 mA cm−2) in AlCl3 aqueous electrolyte. AlCl3 aqueous electrolyte exhibits superior benefits than Al2(SO4)3 and Al(NO3)3 aqueous electrolytes in terms of offering higher Al3+ ion storage capacity, long-term stability, capacity retention and minimized polarization.

High-throughput first-principles-calculations based estimation of lithium ion storage in monolayer rhenium disulfide

Two-dimensional materials are promising candidates for lithium ion battery anodes due to their large surface to volume ratio. The distorted T′ phase of the rhenium disulfide crystal makes the study of lithium binding more complex than for other two-dimensional materials with symmetric crystal structures. Here we explore the lithium ion storage capacity of monolayer rhenium disulfide by first-principles based calculations. We employ hardware-accelerator-assisted high-throughput calculations, using a van der Waals density-functional-theory based ‘structure search’ technique, to emulate the lithiation process. Exploring 2000 structures, each containing 49 to 98 atoms, we find the most stable lithiated structures for various lithium concentrations. We then design a delithiation algorithm and apply it to those lithiated structures for the estimation of the reversible specific capacity. Despite possessing high molar mass, a reasonably high specific capacity (214.13 mAh/g) and open-circuit voltage (0.8 V), in agreement with experimental results, make rhenium disulfide a promising alternative anode material.

Densely pillared holey-graphene block with high-level nitrogen doping enabling ultra-high volumetric capacity for lithium ion storage

Developing high volumetric capacity and long cycle-life anode materials for high-performance lithium-ion batteries (LIBs) still remains a great challenge. Herein, densely pillared holey-graphene block with high N-doping (P-NHG) has been successfully synthesized through thermal decomposition of (NH4)6Mo7O24 in-between stacked GO sheets. The dense graphene building block processes a high packing density of 2.53 g cm−3, high nitrogen doping (19.2 at%), numerous holes on the graphene sheet, and ∼5 nm Mo2C nanoparticles as the pillars in-between the graphene sheets, facilitating rapid ion diffusion and storage and ensuring structural stability during Li ion storage. As a result, the P-NHG electrode can deliver high gravimetric capacity of 1221 mAh g−1 and ultrahigh volumetric capacity of 3089 mAh cm−3 at 0.1 A g−1, as well as excellent cyclability (713 mAh g−1/1803 mAh cm−3 after 300 cycles at 0.5 A g−1). The novel design of densely pillared holey-structure materials represents greatly improved properties such as superior cyclability, and high volumetric capacity for LIBs.