High-capacity Electrode Materials Research Articles

High Energy Density in Combination with High Cycling Stability in Hybrid Supercapacitors.

Hybrid supercapacitors are considered the next-generation energy storage equipment due to their superior performance. In hybrid supercapacitors, battery electrodes need to have large absolute capacities while displaying high cycling stability. However, enhancing areal capacity via decreasing the size of electrode materials results in reductions in cycling stability. To balance the capacity-stability trade-off, rationally designed proper electrode structures are in urgent need and still of great challenge. Here we report a high-capacity and high cycling stability electrode material by developing a nickel phosphate lamination structure with ultrathin nanosheets as building blocks. The nickel phosphate lamination electrode material exhibits a large specific capacity of 473.9 C g-1 (131.6 mAh g-1, 1053 F g-1) at 2.0 A g-1 and only about 21% capacity loss at 15 A g-1 (375 C g-1, 104.2 mAh g-1, 833.3 F g-1) in 6.0 M KOH. Furthermore, hybrid supercapacitors are constructed with nickel phosphate lamination and activated carbon (AC), possessing high energy density (42.1 Wh kg-1 at 160 W kg-1) as well as long cycle life (almost 100% capacity retention after 1000 cycles and 94% retention after 8000 cycles). The electrochemical performance of the nickel phosphate lamination structure not only is commensurate with the nanostructure or ultrathin materials carefully designed in supercapacitors but also has a longer cycling lifespan than them. The encouraging results show the great potential of this material for energy storage device applications.

Modeling of the Lithium Calendering Process for Direct Contact Prelithiation of Lithium-Ion Batteries

The automotive industry’s rapid advancement and complex demands concerning energy storage capacities and service life require lithium-ion batteries with improved energy density and cycle life. There are several ways to improve these two performance indicators for battery cells, such as using innovative, high-capacity electrode materials or novel and improved processes within battery production. One approach is prelithiation, a method to compensate for the initial capacity losses occurring either during the cell formation or during battery operation through the addition of lithium during cell production. In the case of direct contact prelithiation, thin lithium foils with a thickness below 10 µm are necessary to ensure the safe and accurate execution of the prelithiation process. However, the commercial availability of free-standing lithium foils is limited to minimum thicknesses of down to only 20 µm. For this reason, the present work examines in detail the calendering process of lithium. As part of a comprehensive parameter study, the influences of lithium foil geometries, line load, and roller temperature on the deformation behavior of lithium during calendering are investigated. A suitable process model is developed to understand the processing and thickness reduction of lithium and the calendering of lithium foils for direct contact prelithiation. For this purpose, a model based on empirical and semi-analytical approaches using fundamental physical interactions during calendering and material properties is developed and is parameterized based on experimental investigations on a laboratory scale. The combination of empirical and analytical modeling allows predictions about lithium processing and their validity ranges. The modeling intends to enable upscaling of the process and a transferability of direct contact prelithiation to the production of lithium-ion batteries on an industrial scale. Finally, the developed model contributes to understanding metallic lithium processing and its use for direct contact prelithiation in a roll-to-roll process and enables transferability of direct contact prelithiation to the production of lithium-ion batteries.

Halogenated Ti3C2 MXene as High Capacity Electrode Material for Li-ion Batteries

Halogenated Ti₃C₂ MXene as High Capacity Electrode Material for Li-ion Batteries

Unlocking the potential of a novel hierarchical hybrid (Ni–Co)Se2@NiMoO4@rGO–NF core–shell electrode for high-performance hybrid supercapacitors

Nano-hybridization of a core–shell structure integrating a transition metal selenide with oxides results high-capacity electrode materials for energy storage devices thanks to the ample electroactive sites and relatively high electronic conductivity.

Magnesium/Lithium Hybrid Batteries Based on SnS 2 -MoS 2 with Reversible Conversion Reactions

The magnesium/lithium hybrid batteries (MLHBs) featuring dendrite-less deposition with Mg anode and Li-storage cathode are a promising alternative to Li-ion batteries for large-scale energy storage. However, their limited energy density limits their practical implementation. To improve this, beyond the commonly proposed intercalation compounds, high-capacity conversion-type cathodes based on heterostructures of tin sulphide-molybdenum disulphide (SnS 2 -MoS 2 ) are proposed in this work. Individual SnS 2 is already a promising high-capacity electrode material for multivalent batteries and undergoes conversion reactions during the ion storage process. The introduction of S-deficient MoS 2 enhances the reversibility of SnS 2 in the conversion reaction via strong polysulfide anchoring and catalytic effect. Our results show that the SnS 2 -MoS 2 electrode achieves a high charge capacity of ~600 mAh g -1 at 50 mA g -1 and an excellent rate capability of 240 mAh g -1 at 1000 mAh g -1 with a negligible capacity fading rate of 0.063% per cycle across 1000 cycles. The results highlight a new direction toward designing 2D heterostructures as high-capacity cathodes beyond intercalation-type cathodes for multivalent-ion batteries.

Fundamentals of metal oxide/oxyfluoride electrodes for Li-/Na-ion batteries

Lithium-ion batteries provide the development of a clean and sustainable society based on renewable energy resources. To further enhance energy density and reduce the cost of batteries, innovations on electrode materials and high-performance nickel-/cobalt-free materials are necessary. In this review, lithium-excess manganese-based electrode materials with layered/rock salt oxides/oxyfluorides are emphasized because of their potential ability to be utilized as advanced and low-cost lithium-ion batteries in the near future. For these emerging electrode materials, higher energy density is realized, compared with traditional layered materials based on nickel/cobalt ions, relying on anionic and/or cationic redox as multi-electron reactions. Although, currently, anionic redox suffers from degradation of reversibility on continuous cycles, significant progress on theoretical understanding and material design concepts has been made in the past several years. Recently, as alternatives to traditional layered materials, many disordered rock salt oxides, including metastable and nanosized oxyfluorides, have been also found as a new class of high-capacity electrode materials with anionic/cationic redox. In the later part, these new trends for the material design are also extended to the development of electrode materials for sodium-ion batteries. By reviewing the fundamental and recent research progress in metal oxide/oxyfluoride electrodes, a valuable guide for materials scientists in the field of batteries is provided to accelerate the industrial development of high-performance nickel-/cobalt-free electrode materials.

La2Ni0.5Li0.5O4 Modified Single Polycrystalline Particles of NMC622 for Improved Capacity Retention in High-Voltage Lithium-Ion Batteries

Ni-rich lithium nickel manganese cobalt oxides have been extensively studied as high capacity and low cost positive electrode materials for lithium-ion batteries. In order to improve their electrochemical properties, especially cycle capability, we develop a surface modification on single polycrystalline particles of LiNi0.6Mn0.2Co0.2O2 (NMC622) powder with a lanthanum-based oxide. A wet-chemical process and following heat-treatment at 750 °C produce K2NiF4-type La2Ni0.5Li0.5O4 nanoparticles on the surface of NMC622 particles. The La2Ni0.5Li0.5O4-modification improves capacity retention of NMC622 during long-term charge-discharge cycling in the wide voltage range of 3.0–4.5 V at room temperature. The capacity retention at the 150th cycle is about 86% (from 182 to 157 mAh g−1) which is higher than 78% (from 176 to 135 mAh g−1) obtained for the unmodified NMC622 electrode. Further improvements by the La2Ni0.5Li0.5O4 modification are confirmed in the capacity retention cycled at 60 °C and in the discharging rate capability. The La2Ni0.5Li0.5O4-modification is highly effective on the single polycrystalline particles of Ni-rich NMC for long cycle-life and high-rate lithium-ion batteries.

Facile Material Design Concept for Co-Free Lithium Excess Nickel-Manganese Oxide as High-Capacity Positive Electrode Material

High-capacity Li1+x(Ni0.3Mn0.7)1-xO2, (0 < x < 1/3) samples were synthesized by the coprecipitation–calcination method. Both electrochemical cycle and high-rate performances were drastically improved by selecting an N2 atmosphere as final calcination. Scanning transmission electron microscopy—energy dispersive X-ray spectroscopy analysis showed that the sample calcined in an N2 atmosphere had a more homogeneous transition metal distribution into primary particles than that calcined in air. The solid-state 7Li nuclear magnetic resonance data showed that electrochemically inactive domains were only diminished for the sample calcined in an N2 atmosphere after electrochemical activation. X-ray Rietveld analysis revealed that the suitable transition metal distribution and content of the samples were different from those of typical layered rock-salt materials. Only that calcined in an N2 atmosphere had no spinel formation during charging and no oxide ion insertion reaction during discharging. No positive Co substitution effect was observed under the optimized preparation conditions. At the 100th cycle, the discharge capacity was 216 mAh g−1, which corresponds to 87% of the initial capacity (251 mAh g−1) at optimizing synthetic condition.

The synthesis of the conjugated polymers based on phenanthroline-5,6-dione and thiophene derivatives, their composites with carbon and the lithium storage performances as anode materials

• Linear polymer@AC composites are prepared, used as anode materials in lithium ion batteries. • Thiophene derivatives and 1,10-phenanthroline-5,6-dione are used as the alternating monomers. • The polymers have a donor–acceptor structure, low redox potentials, be suitable as anode materials. • PBTPD@AC composite has a capacity of 410 mAh g −1 at a current density of 100 mA g −1 . • PBTPD has the most extended conjugation length, give rise to the highest capacity for the PBTPD@AC composite. Three linear conjugated polymers, including poly[(thiophene-2,5-yl)-((1,10-phenanthroline-5,6-dione)-2,7-yl)] (PTPD), poly[((2,3-dihydrothieno[3,4-b][1,4]dioxine)-5,7-yl)-((1,10-phenanthroline-5,6-dione)-2,7-yl)] (POTPD) and poly[(thieno[3,2‐ b ]thiophene-2,5-yl)-((1,10-phenanthroline-5,6-dione)-2,7-yl)] (PBTPD) have been synthesized. Three composites (PTPD@AC, POTPD@AC and PBTPD@AC) are made by introducing active carbon (AC) in the polymerization reaction. The composites are adopted as anode materials, and evaluated their electrochemical parameters in lithium-ion batteries (LIBs). After 300 cycles of running, the specific discharge capacities (at 100 mA g −1 ) of PTPD@AC, POTPD@AC and PBTPD@AC are 318.7 mAh g −1 , 319.5 mAh g −1 and 410 mAh g −1 , respectively. Subtracting the capacity of AC to that of the composites, the actual capacities of pure polymers are 726.3, 729 and 1030.7 mAh g −1 for PTPD, POTPD and PBTPD at 100 mA g −1 , respectively. The structure–activity relationships of the composites are discussed in detail in terms of the electron donating properties of the donor units. This work may pave a way to the exploration of high-capacity electrode materials based on conjugated polymers for LIBs.

Three-dimensional, heteroatom-enriched, porous carbon nanofiber flexible paper for free-standing supercapacitor electrode materials derived from microalgae oil

Polyacrylonitrile (PAN) based carbon nanofiber (CNF) papers have unique physicochemical properties including flexibility, good electrical conductivities, and excellent mechanical properties for supercapacitor electrodes. However, their surface-to-weight ratios and density of active sites on the surface are much poorer than those of other active carbons. Herein, a simple, renewable, multifunctional, and effective way is described to fabricate three-dimensional (3D) heteroatom-enriched porous PAN-based CNF papers by adding a moderate amount of microalgae-derived oil that has a large fraction of light compounds and nitrogen- and oxygen-containing functional components. CNF papers with enhanced porosity and large specific surface area, unique pore structure, and 3D heteroatom-enriched surfaces were successfully fabricated by stabilization and carbonization of PAN nanofibers with the algae oil. The as-fabricated algal-30% CNF paper is scalable and highly flexible as a free-standing supercapacitor electrode material and can deliver a specific capacitance of 272 F/g under a scan rate of 10 mV/s with noticeably high charge-discharge cycling stability, with 94% retained even after 10,000 cycles. The fabrication mechanism and the enhancement of the electrochemical behaviors of three-dimensional, heteroatom-enriched, porous CNF papers are proposed. Our work underlines the promise of algae oil-modified PAN-based CNF papers for high-capacity supercapacitor electrode materials.

Multifunctional Conformal Polymer Coating by Oxidative Chemical Vapor Deposition for High Specific Energy Ni-Rich Cathode

The successful commercialization of lithium-ion batteries (LIBs) leads to wide utilization in portable electronic devices such as cellphones and laptops because of their excellent cycle performance and moderate rate capability [1]. Technical challenges still remain to enhance specific energy of LIBs to be implemented in large-scale devices including hybrid electric vehicles (HEVs) and electric vehicles (EVs) [2]. Adopting high specific capacity electrode materials and decreasing the weight ratio of non-capacity materials in batteries are considered as two main methods for improving the overall specific energy for LIBs.Ni-rich layer oxides as one of the mainstream cathode materials have drawn much attention due to their high theoretical specific capacity. However, the surface and bulk degradation of Ni-rich materials during circulation may trigger capacity loss and generate serious safety issues, which limits its application in LIBs [3]. Coating inert inorganic compounds has been suggested to enhance the stability of Ni-rich materials. However, it is also reported that the coating layer was delaminated from the cathode bulk particles due to the anisotropic volume change during lithiation and delithiation as well as the stiff nature of inorganic coating materials [4].On the other hand, reducing non-capacity materials such as conductive carbon led to the lower electronic conductivity, which may cause polarization and increase the resistance of the battery. Meanwhile, a traditional binder is electronically insulating, limiting electron transportation. In addition, less binder in electrodes could result in separation of the active materials from the electrode, causing battery capacity loss [5].In order to accommodate the volume variation during circulation, polymers with resilience possibly protect the Ni-rich particles during cycle life. Further, binders and conductive carbonaceous are preferred to construct conductive networks for electrodes for enhancing the overall conductivity of the battery. As thus the polymer with electronic conductivity is supposed to be uniformly coated on Ni-rich particles and sufficiently distributed in the electrode.Poly(3,4-ethylenedioxythiophene) (PEDOT) is a promising polymer due to its high electrical conductivity and the demonstrated protection ability for Ni-rich materials in LIBs [6]. Meanwhile, as an emerging technique, oxidative chemical vapor deposition (oCVD) is a deposition process that generates uniform and conformal polymers via gas phase reaction with a vaporized source monomer (in this case EDOT) and an oxidizer (in this case FeCl3). PEDOT deposited on the electrode through the oCVD method is homogeneous on the surface of Ni-rich particles. And the high electronic conductivity of the polymer would enhance the battery performance as well as the adhesive ability of the polymer own.In this study, Ni-rich cathode with 99% active materials weight ratio was prepared from as-synthesized LiNi0.8Co0.1Mn0.1O2 (NCM811) particles and oxidative chemical vapor deposition method was employed to generate a controllable PEDOT layer with 55 nm thickness. Moreover, the PEDOT layer was found between the secondary particles, indicating excellent conformal coating capability of the oCVD technique. Further characterization X-ray photoelectron spectroscopy (XPS) and Density functional theory calculation (DFT) revealed that sulfide in PEDOT is preferentially bonded with transition metal (Ni, Co and Mn) in NCM811, which prolonged the service life of the PEDOT layer. Time-of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS) and XPS was employed which unveiled the formed PEDOT layer restricted the parasite reaction during the charge/discharge process and diminished the transition metal dissolving, and endowed the battery with improved stability (81.6% after 300 cycles under 1C, 1C = 200 mA g-1) Cyclic voltammetry (CV) showed less difference value for modification sample (△E=0.14 V) compared with pristine sample (△E=0.25 V). Furthermore, the battery even showed 171.5 mAh g-1 under 7C and high reversibility after a high rate, which provides a potential for the fast-charge. The trifunctional PEDOT layer is verified to serve as the protection layer, binder and electronic conductivity network for the cathode materials. The results of this study demonstrate significant promises of employing the high active material weight ratio with high cycle life and a pathway for various kinds of cathode materials for reaching higher specific energy as well.Reference:[1]. Goodenough, J. B.; Park, K. S., J Am Chem Soc 2013, 135 (4), 1167-76.[2]. Lee, W.; Yoon, W.-S., Advanced Energy Materials 2018, 8 (4), 1701788.[3]. Sun, Y. K.; Myung, S. T.; Park, B. C.; Prakash, J.; Belharouak, I.; Amine, K., Nat Mater 2009, 8 (4), 320-4.[4]. Liu, J.; Manthiram, A., Journal of The Electrochemical Society 2009, 156 (1).[5]. Jeong S.S., Journal of Power Source 2012, 199 (1).[6]. Xu G.-L.; Chen G., Nature Energy 2019, 4. Figure 1

(Invited) Nanostructured High-Capacity Positive Electrode Materials for Li-Ion Batteries

In the past decade, lithium-enriched compounds, Li2 MO3 (M = Mn4+, Ru4+ etc.), have been extensively studied for high-capacity positive electrode materials of Li-ion batteries. Large reversible capacities originate from charge compensation by anions species (anionic redox) coupled with partial cationic redox of transition metal ions. Recently, many cation-disordered rocksalt oxides have been proposed as a new series of electrode materials, which utilize reversible anionic redox. Nevertheless, insufficient electrode kinetics for the cation-disordered rocksalt system limits its use for practical applications. One simple strategy is synthesizing nanosized materials to overcome a problem of electrode kinetics (for electrons, holes and ions), and electrode kinetics are significantly improved through nanosizing even for a non-lithium-excess and stoichiometric system.1) Moreover, Nanosized Li/Na-excess oxides also deliver large reversible capacities at room temperature,2-4) which shows much better electrode kinetics compared with as-prepared samples.From these findings, we discuss the advantages/disadvantages of “nanostructured” electrode materialsto develop high energy advanced Li-ion batteries.References1) Sato et al., and N. Yabuuchi., Journal of Materials Chemistry A, 6, 13943 (2018).2) Kobayashi et al., and N. Yabuuchi, Small, 15, 1902462 (2019).3) Kobayashi et al., and N. Yabuuchi, Materials Today, 37, 43 (2020).4) Sawamura et al., and N. Yabuuchi, ACS Central Science, 6, 2326 (2020).

Charge/Discharge Reaction Mechanisms of Nanosized Li-Excess Li2TiO3–LiVO2 System

The demand of high-energy Li-ion batteries (LIBs) is rapidly growing for electric vehicles (EVs) to reduce dependence on fossil fuel. Although currently, Ni-rich layered oxides are mainly used as positive electrode materials for LIBs, the cost of Ni is raising because of increase demand of EVs. Therefore, the development of alternative materials without Co/Ni ions is necessary. In this study, vanadium ions with double electron redox reaction (V3+/V5+) are targeted as potential high capacity electrode materials. Stoichiometric LiVO2 is electrochemical inactive due to the phase transition from a layered to rocksalt-type structure.[1] Nevertheless, a Li-excess V-based oxide, Li1.25Nb0.25V0.5O2, with the rocksalt-type structure delivers a large reversible capacity of 250 mA h g-1 with percolative Li migration in the structure. [2] In this study, Li-excess Li2TiO3–LiVO2 binary system is synthesized and tested as potential high-capacity electrode materials. Among the tested samples, Li8/7Ti2/7V4/7O2 (x = 0.33 in x Li2TiO3–(1–x) LiVO2 binary system delivers the largest reversible capacity of approximately 300 mA h g-1 with no capacity degradation for over 100 cycles (Fig. 1). To clarify detailed reaction mechanisms, synchrotron X-ray total scattering was utilized and obtained pair distribution function (PDF) data are shown in Fig. 2. It is revealed that the crystallinity of the sample is lowered and V migration from original octahedral to tetrahedral sites on charging, which is consistent with the finding by X-ray absorption spectroscopy. Small V5+ ions are energetically stabilized at tetrahedral sites. Nevertheless, this process is highly reversible, and the high crystallinity phase with V ions at octahedral sites is obtained after discharging. From these data together with operando XRD data, the origin of the long cycle life for Li8/7Ti2/7V4/7O2 will be discussed in more details.[1] J. B. Goodenough, et al, Mater. Res. Bull., 15, 783-789 (1980)[2] N. Nakajima and N. Yabuuchi, Chem. Mater., 29, 6927 (2017). Figure 1

(Invited) The Challenge of High Energy Density in Li/Na-Ion Batteries

Anionic redox in Li-rich and Na-rich transition metal oxides (A-rich-TMOs) has emerged as a new paradigm to increase the energy density of rechargeable batteries. [1,2] However, most A-rich-TMOs reported so far with high energy density due to anionic redox are prone to structural instabilities that prevent their use in practical applications. [3] Several alternatives have been proposed to limit or suppress these instabilities, among them the increase of M–O bond covalency, [4] the chemical substitution of M for d 0 metals, [5] the control of cationic migration, [6] or the use of cation-disordered rocksalt structures. [7] The unified picture developed in this introduces the number of holes per oxygen (h O) as another critical parameter to sustain a reversible anionic capacity. From a representative set of materials reported in the literature, h O = 1/3 seems to be the critical value to avoid O2 release and achieve fully reversible anionic redox. [8] Measurable quantities such as ΔCT, x stoichiometry and disorder are therefore sufficient to determine h O and to infer the electrochemical behaviour of A[AxM1−x]O2 electrodes. Within this general framework, the best candidates for high energy density are those exhibiting the an homogeneous O-network (no cation disorder), a (1-x)e- cationic capacity and an anionic capacity limited to h O ≤ 1/3 on each individual O-sublattice. Tridimensional structures should be preferred over layered structures to prevent structural instability at low A content and take advantage of the full theoretical capacity. Ordered structures should favour homogeneous O networks and prevent one O sublattice to uptake a critical h O > x. Very few TMOs should satisfy these requirements, in particular when they also have to meet industrial specifications such as cost, toxicity and natural abundance. Overall, strategies devoted to the activation of anionic redox as a lever to improve the energy density of electrode materials are risky, as they implicitly question the general chemical rules to guarantee structural stability of oxide-materials. The triptych of high potential, high capacity and high structural stability still appears out of our current reach and calls for trade-offs. Reference s : [1] Koga, H. et al. Reversible oxygen participation to the redox processes revealed for Li1.20Mn0.54Co0.13Ni0.13O2. J. Electrochem. Soc. 160, A786–A792 (2013).[2] Sathiya, M. et al. Reversible anionic redox chemistry in high-capacity layered-oxide electrodes. Nat. Mater. 12, 827–835 (2013).[3] Assat, G. et al. Fundamental interplay between anionic/cationic redox governing the kinetics and thermodynamics of lithium-rich cathodes. Nat. Commun. 8, 2219 (2017).[4] Pearce, P. E. et al. Evidence for anionic redox activity in a tridimensional- ordered Li-rich positive electrode β-Li2IrO3. Nat. Mater. 16, 580–587 (2017).[5] Yabuuchi, N. et al. High-capacity electrode materials for rechargeable lithium batteries: Li3NbO4-based system with cation-disordered rocksalt structure. Proc. Natl Acad. Sci. USA 112, 7650–7655 (2015).[6] Gent, W. E. et al. Coupling between oxygen redox and cation migration explains unusual electrochemistry in lithium-rich layered oxides. Nat. Commun. 8, 2091-1–12 (2017).[7] Urban, A., Matts, I., Abdellahi, A. & Ceder, G. Computation design and preparation of cation-disordered oxides for high-energy-density Li-ion batteries. Adv. Energy Mater. 6, 1600488-1–1600488-8 (2016).[8] Ben Yahia, M.; Vergnet, J., Saubanère, M., Doublet, M.-L., Unified picture of anionic redox in Li/Na-ion batteries. Nat. Mat. 18, 496-502 (2019).

New phases of MBenes M2B (M = Sc, Ti, and V) as high-capacity electrode materials for rechargeable magnesium ion batteries

Rechargeable magnesium ion batteries (MIBs) have attracted great interests as a prospective candidate for next generation large-scale energy storage systems owing to the low cost and high abundance of Mg resources. However, MIBs have been restricted by the lack of suitable electrode materials for a long term. Therefore, three new phases of two-dimensional transition metal borides (MBenes) including Sc2B, Ti2B and V2B are explored as electrode candidates for MIBs. All the three M2B (M = Sc, Ti, and V) with ground states of ferromagnetic configurations are proved dynamically and thermally stable by using phonon dispersions and molecular dynamics simulations. The results show that all M2B phases have ultra-high specific capacity of 3192.813 mA h/g, 3018.414 mA h/g and 2853.953 mA h/g for Mg on Sc2B, Ti2B and V2B, respectively. In addition, the M2B monolayer only undergoes a small change in lattice constant with adsorption of single layer or multilayer ions. This work not only reports three new phases of M2B with layered structure but also further provides useful information of MBenes as promising electrode candidates for high-performance metal ion batteries.

Understanding the Stabilizing Effects of Nanoscale Metal Oxide and Li-Metal Oxide Coatings on Lithium-Ion Battery Positive Electrode Materials.

Nickel-rich layered oxides, such as LiNi0.6Co0.2Mn0.2O2 (NMC622), are high-capacity electrode materials for lithium-ion batteries. However, this material faces issues, such as poor durability at high cut-off voltages (>4.4 V vs Li/Li+), which mainly originate from an unstable electrode-electrolyte interface. To reduce the side reactions at the interfacial zone and increase the structural stability of the NMC622 materials, nanoscale (<5 nm) coatings of TiOx (TO) and LixTiyOz (LTO) were deposited over NMC622 composite electrodes using atomic layer deposition. It was found that these coatings provided a protective surface and also reinforced the electrode structure. Under high-voltage range (3.0-4.6 V) cycling, the coatings enhance the NMC electrochemical behavior, enabling longer cycle life and higher capacity. Cyclic voltammetry, X-ray photoelectron spectroscopy, and X-ray diffraction analyses of the coated NMC electrodes suggest that the enhanced electrochemical performance originates from reduced side reactions. In situ dilatometry analysis shows reversible volume change for NMC-LTO during the cycling. It revealed that the dilation behavior of the electrode, resulting in crack formation and consequent particle degradation, is significantly suppressed for the coated sample. The ability of the coatings to mitigate the electrode degradation mechanisms, illustrated in this report, provides insight into a method to enhance the performance of Ni-rich positive electrode materials under high-voltage ranges.

Unraveling the role of ion-solvent chemistry in stabilizing small-molecule organic cathode for potassium-ion batteries

Redox-active organic cathodes are promising high-capacity and low-cost electrode materials for potassium-ion batteries (KIBs), but usually suffer from poor cyclability due to the severe dissolution and notorious K dendrites. Herein, the effects of salt concentrations and solvents on the performance of potassium-organic batteries based on a typical phenothiazine derivative, methylene blue (MB), are explored, and the high-concentration potassium bis(fluorosulfonyl)amide-based ether electrolyte is versatile to achieve long lifespan. The high donor number and strong solvation ability of ether solvent endow MB cathode with high voltage plateaus and reversible capacity as compared to the carbonate counterpart. Moreover, the enhanced interactions of K+-ether and anion-participated ion-ether complexes in concentrated electrolyte not only decrease the amount of free solvent, but also contribute to forming highly ionic-conducting and thin anion-derived interphase layers, which effectively mitigate the shuttle effect and inhibit K dendrite growth. Consequently, MB cathode exhibits a high capacity of 139.5 mAh g−1 after 500 cycles at 0.1 A g−1, and long-term cycling stability for 4500 cycles. The good performance of full cells matched with graphite anode further demonstrates the feasibility of MB as KIB cathode. This work highlights the roles of ion-solvent chemistry in stabilizing small-molecule organic cathodes, which may bring new insights in the electrolyte design for wide organic electrode-based battery systems.

Screening MXenes for novel anode material of lithium-ion batteries with high capacity and stability: A DFT calculation

As an advanced battery technology, lithium-ion batteries have attracted extensive attention, especially in electric vehicles. However, low capacity and poor stability are two factors hindering more extensive application of lithium-ion batteries. Herein, we performed a screening study on MXenes including M2C, MC2, M2N, MN2 (M = Sc, Ti, V, Cr), in the search for promising lithium-ion battery anode materials by using density functional theory (DFT) calculations and ab initio molecular dynamic (AIMD) simulations. The theoretical capacities of Ti2N and V2N are 975 mAh/g and 924 mAh/g, respectively. Based on low deformation rate, and small energy variation, Ti2N and V2N have higher stability than that of graphite electrodes. The lower diffusion barrier accelerates the charging and discharging process of the battery. Considering their low diffusion barrier, excellent conductivity, high theoretical capacity, low deformation rate and high thermal stability, Ti2N and V2N are proposed as promising anode materials for lithium-ion batteries. The adsorption of lithium-ion belongs in the category of weak adsorption where the d-band center is negative. However, it is strong adsorption when the d-band center is positive. A linear relationship between the lithium-ion concentration and adsorption energy is developed for strong adsorption, which can be used to guide the design of high-capacity electrode materials.

Plasma phosphorization of self-adaptive electrode Cu3P@RGO for lithium ion storage

High-capacity electrode material is of great significance to further improve the energy density of lithium-ion batteries (LIB). Phosphorus (P) is a promising candidate for anode material due to its high theoretical capacity and low cost. However, the large volume expansion and poor conductivity restrict the practical application. Transition-metal phosphides hybrid with lamellar graphene oxide are recognized as an ideal structure to resolve these issues. Preparation of phosphides is always of great challenge with severe reaction conditions. Herein, a mild phosphorization process in low temperature plasma has been developed to synthesize lamellar Cu3P@RGO nanostructures at only 200 °C for 40 min. The in situ phosphatized Cu foam is a self-adaptive electrode without any conductive additives. Attributed to the unique architecture, the Cu3P@RGO electrode reveal a high initial coulombic efficiency of >80% and excellent long-cycling performance at a high current density of 500 mA/g (2330 mAh/g after 183 cycles).

Ordered assembly of MXene based composite films and their applications in energy storage and electromagnetic interference shielding

The increasing popularity of 5G electronic consumer products has brought convenience to people’s life, while there are some problems, such as high risk of electromagnetic interference (EMI) and high power consuming of 5G networks. To solve these problems, it is necessary to develop novel materials with high EMI shielding performance and high-capacity electrode materials. As a new two-dimensional (2D) material, transition metal carbides/nitrides (MXene) have excellent conductivity, low density, hydrophilic surface, 2D layer morphology and tunable surface chemistry, etc. MXene shows promising application prospects in EMI shielding and energy storage due to the facile operation for fabricating films. A lot of MXene-based composite films have been reported recently. Thus in this article, we introduced the preparation methods of MXene nanosheets and MXene-based composite films including their advantages and disadvantages. Secondly, we summarized the research progress of MXene in lithium battery, supercapacitor and EMI shielding fields, and concluded the current mainstream composite materials and the characteristics of MXene composite film in structure and performance. Finally, we proposed critical insights on these scientific challenges and potential solutions. Besides, a future perspective on this technology including other challenges was also described.