High-performance Cathode Materials Research Articles

Regulating d0 transition metals and facilitating high-performance Li-excess cation-disordered rock salt cathode materials

A systematic study was performed on Ti-doped Li1.2Mn0.43+TixMn0.4−x4+O2, which revealed the fast kinetics of Li diffusion with an improvement in the electrochemical property of MT0−1, thus providing a guideline for DRXs cathode materials design.

Improved structure stability and performance of a LiFeSO4F cathode material for lithium-ion batteries by magnesium substitution.

Tavorite LiFeSO4F with high Li-ion conductivity has been considered a promising alternative to LiFePO4. However, its poor cycle stability and low electronic conductivity limit the practical application of Tavorite LiFeSO4F. In the present study, we employ a solvothermal method to produce magnesium-substitution LiMgxFe1-xSO4F (x = 0, 0.02, 0.04) cathode materials in which the Mg substitutes the Fe(2) sites. The first-principles calculations demonstrate that Mg-substitution could reduce the bandgap of LiFeSO4F and increase its electronic conductivity to 2.5 × 10-11 S cm-1. Meanwhile, CI-NEB and BV calculations reveal that the diffusion energy barrier of lithium along the (100) direction after Mg substitution is lower than the pristine sample, and the electrochemical inactive Mg2+ could improve the structure stability. The results show that the Mg-substituted LiFeSO4F exhibits enhanced cycle stability and rate performance compared with the pristine LiFeSO4F, suggesting that the use of electrochemically inactive ion substitution may be critical for the development of high-performance LiFeSO4F cathode materials for lithium-ion batteries.

Layered BaV6O16·3H2O@GO as a high performance cathode material for calcium ion batteries.

The lack of suitable cathode materials has hampered the further development of calcium-ion batteries (CIBs). A novel composite cathode material, namely BaV6O16·3H2O@GO, was fabricated, which delivers a high specific capacity of 285.72 mA h g-1 at 50 mA g-1 after 50 cycles and a long cycle life, benefiting from a large layer spacing and robust structure. This study provides guidance for the development of vanadium-based cathode materials for CIBs.

Porous layered ZnV2O4@C synthesized based on a bimetallic MOF as a stable cathode material for aqueous zinc ion batteries.

Vanadium-based oxides are considered potential cathode materials for aqueous zinc ion batteries (AZIBs) due to their distinctive layered (or tunnel) structure suitable for zinc ion storage. However, the structural instability and sluggish kinetics of vanadium-based oxides have limited their capacity and cycling stability for large-scale applications. To overcome these shortcomings, here a porous vanadium-based oxide doped with zinc ions and carbon with the molecular formula ZnV2O4@C (ZVO@C) as the cathode material is synthesized by the pyrolysis of a bimetallic MOF precursor containing Zn/V. This electrode demonstrates a remarkable specific capacity of 425 mA h g-1 at 0.5 A g-1 and excellent cycling stability with about 97% capacity retention after 1000 cycles at 10 A g-1. The excellent electrochemical performance of ZVO@C can be attributed to more reaction active sites and the faster reaction kinetics for zinc ion diffusion and storage brought about by the porous layered spinel-type tunnel structure with high surface area and massive mesoporosity, as well as the enhanced electron transport efficiency and more stable channel structure achieved from the doped conductive carbon. The reaction mechanism and structural evolution of the ZVO@C electrode are analyzed using X-ray diffraction and X-ray photoelectron spectroscopy, revealing the formation of a new phase of ZnxV2O5·nH2O during the first charge, which participates in reversible cycling together with ZVO@C during the charging and discharging processes. Moreover, the energy storage mechanism is revealed, in which zinc ions and hydrogen ions jointly participate in intercalation and extraction. The present study demonstrates that constructing composite vanadium-based oxides based on bimetallic organic frameworks as precursor templates is an effective strategy for the development of high-performance cathode materials for AZIBs.

First-row transition metal carbide nanosheets as high-performance cathode materials for lithium-sulfur batteries.

Despite the prodigious potential of lithium-sulfur (Li-S) batteries as future rechargeable electrochemical systems, their commercial implementation is hindered by several vital issues, including the shuttle effect and sluggish migration of lithium-polysulfides leading to rapid capacity fading. Here, we systematically investigate the potential of first-row two-dimensional transition metal carbides (TMCs) as sulfur cathodes for Li-S batteries. The adsorption strength of lithium-polysulfides on TMCs is induced by the amount of charge transfer from the former to the latter and the proposed periodic relationship between sulfur in Li2S and 3d-transition metals. Our findings show that the VC nanosheet possesses immense anchoring potential and exhibits a comparatively low migration energy barrier for lithium-ion and Li2S molecules. Additionally, we report ab initio molecular dynamics simulations for lithiated polysulfide species anchored on a TMC-based model with a liquid-electrolyte medium. The microscopic reaction mechanism, revealed by the evolution of the reaction voltage during lithiation, demonstrates that the dissolution of high-order lithium-polysulfides in the electrolytes can be prevented due to their robust interaction with TMC-based cathode materials. These appealing features suggest that TMCs present colossal performance improvements for anchoring lithium-polysulfides, stimulating the active design of sulfur cathodes for practical Li-S batteries.

Chitosan-induced NH4V4O10 hierarchical hybrids as high-capacity cathode for aqueous zinc ion batteries.

Aqueous zinc ion batteries (AZIBs) have been widely investigated due to their characteristics of convenient operation and intrinsic safety. However, there are several issues to be addressed in AZIBs, such as slow diffusion kinetics of Zn2+, cathode material dissolution and the dendrite formation of zinc anodes. Thus, it is challenging to prepare a high-performance cathode material. In this work, we prepare NH4V4O10 flower-like structures by a facile hydrothermal route. The introduction of chitosan significantly enlarges the layer spacing of the (001) crystal plane. The assembled Zn//NVO-0.15C batteries deliver a specific capacity of 520.54 mA h g-1 at a current density of 0.2 A g-1. Furthermore, they maintain 91% of the retention rate at 5.0 A g-1 after 1000 times cycling. It demonstrates the excellent zinc ion storage behavior of ammonium vanadate electrode materials for AZIBs.

A mass-producible polyoxovanadate cathode for ultrafast-kinetics zinc-ion batteries

The mass-producible KZnV5O14·2.5H2O cathode featuring rich open Zn2+-ion migration channels has demonstrated excellent rate capability and superb cycling stability, thus paving the way for advancing the development of cathode materials for ZIBs.

A silver and manganese dioxide composite with oxygen vacancies as a high-performance cathode material for aqueous zinc-ion batteries.

Aqueous zinc ion batteries (AZIBs) are regarded as a promising alternative for energy storage due to their safety, cost-effectiveness and environmental friendliness. Manganese dioxide is considered a promising cathode material for energy storage because of its abundant reserves and high energy density. However, its inherent low electronic conductivity and limited cycling performance due to structural instability hinder its further development. Herein, a silver and manganese dioxide composite (Ag@MnO2) enriched with oxygen vacancies was prepared by a simple liquid-phase reduction method. The introduction of silver particles facilitates the improvement of electrical conductivity, and the incorporation of oxygen vacancies helps change the surface properties of manganese dioxide, providing additional active sites for ion transport, enhancing the overall electrochemical kinetics, and further improving the battery performance. As a result, the Ag@MnO2 cathode exhibits an astonishingly high capacity of 353 mAh g-1 at a current density of 0.1 A g-1 and a capacity retention of 78% after 1500 cycles. Additionally, electrochemical and structural analyses have revealed that the Ag@MnO2 cathode undergoes a reversible and stable process of H+ and Zn2+ insertion/extraction.

Two p-type ester-linked dihydrophenazine-based polymers as high-performance cathode materials for lithium-ion batteries

Two novel redox-active ester-linked polymers were effectively achieved from an industrial waste product, phenazine, and exploited as sustainable superior organic cathode materials of lithium-ion batteries.

Sustainable regeneration of high-performance cathode materials from spent lithium-ion batteries through magnetic separation and coprecipitation

Extensive research and application of recycling methods for spent lithium-ion batteries (LIBs) have been undertaken in recent years with great success. However, the separation of valuable metals from the lixivium of spent LIBs, which contains Al, Cu, Ni, Co, Mn, and Li, is complicated, burdensome, and unsustainable. Therefore, there is a need to establish a more sustainable and energy-efficient method for recycling spent LIBs. The study introduced an innovative methodology for replacing the impurity ion removal process in the lixivium with magnetic separation pretreatment. Then, the co-precipitation method was used to directly resynthesize LiNi0.5Co0.2Mn0.3O2 (LNCM523) with recovered metals as raw materials. The results demonstrate that, with a magnetic field intensity of 3000 Oe and feed particle size of −0.074 mm, the magnetic separation concentrates the following grades: Ni-26.34%, Co-14.26%, Mn-28.30%, Al-0.23%, and Cu-0.41%. The corresponding recovery rates were also determined as follows: Ni-92.57%, Co-94.16%, Mn-85.68%, Al-1.62%, and Cu-2.14%. The total impurities (Al, Cu, and Fe) in the lixivium obtained by magnetic separation concentrate under conventional acid leaching conditions were below 0.05 wt%, while the contents of Ni, Co, and Mn were measured at 13.08 g/L, 7.10 g/L, and 14.06 g/L, respectively. Spherical LNCM523 was successfully regenerated from the lixivium through co-precipitation and sintering. The LNCM523 demonstrated exceptional electrochemical performance, exhibiting a notable initial discharge capacity of 173.9 mAh/g at 0.2 C and remarkable cycling stability with 91.9% retention over 100 cycles at 0.5 C. In comparison to the conventional approach, this method circumvented the intricate procedure of separating metal ions, thereby realizing the resource regeneration of cathode materials and enabling a closed-circuit recycling process. These advancements contributed to fostering sustainable low-carbon development of the spent LIBs.

Influence of oxygen vacancies enhances structural, optical, and electrochemical properties of P2 type NaxMnO2-δ for high-performance Na-ion cathode materials

Due to the accessibility of raw materials and good cost-effectiveness, Sodium-ion batteries (SIB) are a possible replacement for lithium-ion batteries. The subject of this paper is the layered P2-type NaxMnO2-δ nanostructure which was synthesized by a solid-state process and annealed in an Ar–H2 atmosphere at various calcination temperatures. X-ray diffraction, Raman spectroscopy, Scanning electron microscopy, Ultraviolet–visible spectroscopy, and X-ray photoelectron spectroscopy were used to describe the cathode material's crystalline structure, vibrational analysis, surface morphology, elemental composition, optical properties, and electrochemistry performance. The calcination temperature significantly affects the structural, optical, and electrochemical characteristics of layered P2-type NaxMnO2-δ material. After 20 cycles, the reduction annealing of 400 °C has the highest specific discharge capacity of 130 mAhg−1 at C/10 where capacity retention is 98.84 % and average coulombic efficiency of 98.37 % in between 2.0 and 4.2 V range (Na+/Na).

Anionic Additive-Integrated Electrolyte Therapy: Enhancing High-Voltage Stability and Performance in Lithium-Ion Batteries

Significant endeavours have been undertaken to advance the development of eco-friendly, abundant, cost-effective, and high-performance cathode materials for lithium-ion batteries. Among the various contenders for next-generation energy storage systems, spinel LiNi0.5Mn1.5O4 has emerged as a leading high-voltage cathode candidate, owing to its aforementioned benefits. Nonetheless, the widespread adoption of LNMO-based lithium-ion batteries is substantially impeded by the electrochemical instability of conventional carbonate electrolytes above 4.5 V. High-voltage cycling of such batteries results in rapid capacity degradation and metal-ion dissolution from the LNMO electrode into the electrolyte, particularly at elevated temperatures, further causing deposition of metal-ions on anode electrode. Therefore, stabilizing the electrode/electrolyte interface is crucial to achieve improved electrochemical performance of the Li-ion cell at high voltages. The utilization of sacrificial electrolyte additives is regarded as a straightforward and efficacious method to accomplish this objective. These additives form a protective layer on the cathode surface, mitigating electrolyte decomposition and transition metal-ion dissolution and deposition on anode’s surface. Various additives facilitating high-voltage cathode materials have been documented, encompassing fluorides and sulfonates. However, borate salt-containing additives are particularly promising within this context.In the present study, we endeavour to elucidate the surface modifications transpiring on the electrode’s surface when minute quantities of borate-based salt are employed as an additive in the conventional EC:EMC electrolyte for high-voltage operation. We explored the impact of the additive salt in a standard LiPF6-EC/EMC base electrolyte on the discharge capacity and rate performance of the LiNi0.5Mn1.5O4/Graphite based Li-ion cell. The electrochemical behaviour, morphological behaviour, and electrode-electrolyte interphase layer stability on the electrode were meticulously examined using high-resolution transmission electron microscopy (HR-TEM), electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). These characterisations conformed the presence of an electrode-electrolyte interface forming a thin-layer via the sacrificial decomposition of the utilised additive. The introduction of this salt exhibits favourable effects on enhancing the electrochemical performance of the LiNi0.5Mn1.5O4/Graphite in high-voltage lithium-ion batteries. Notably, the utilised additive excels in mitigating irreversible capacity loss and reducing cycling fade, as it preferentially decomposes and forms a conductive, protective film that impedes subsequent electrolyte decomposition, thereby substantially enhancing cell performance.

Stabilizing Cobalt-Free Li-Rich Layered Oxide Cathodes By Site-Specific Doping

The limited theoretical capacity of traditional cathode materials solely based on transition metal (TM) redox has been a primary factor for the ceiling placed on the energy density of LIBs. In this regard, Li-rich layered oxides (LLOs) have received a great deal of attention, due to their high reversible capacity (> 250 mAh g-1) and high energy density (900 Wh kg-1), courtesy of the TM redox and the additional high-voltage O2- redox.1, 2 Although the electrochemical performance of Co-free LLOs is significantly less satisfactory, developing Co-free cathodes is inevitably a holy grail owing to cobalt’s economic, ethical, and political issues caused by high-cost toxicity. Therefore, studies on Co-free LLOs are necessary for creating long-term benefits for the cathode industry.Unfortunately, Co-free LLOs suffer from capacity and voltage decay on cycling, which for now obviously limits the materials use outside the academics laboratory. It is well accepted that that performance decay is primarily attributed to the irreversible anionic redox and structural degradation in LLOs. The doping strategy has been widely used to address the voltage decay of LLOs.3 While the dopant is typically introduced to the layered R m component, the lithium-rich component (C2/c) in the LLOs, which is the source of anionic redox, has always been ignored.Our team comprehensively investigates the structural involution of LLOs based on a Co-free Li-rich Mn-based Li1.2Ni0.2Mn0.6O2 (LNMO) cathode using in-operando and ex-situ synchrotron-based characterizations. We learned through mechanistic characterization that the transition from the monoclinic (C2/c) to the hexagonal (R-3m) behaviour is an intrinsic behaviour of LLOs for the first time. According to this structure-function relationship, we introduced a small quantity of one electrochemically active metal, ruthenium, into both R-3m and C2/c components in LNMO and found that the oxygen lattice and structural stability can be significantly improved by the site-specific doping against lithiation and delithiation processes.4 Additionally, reducing the irreversible TM migration is key to advancing the performance of layered oxide cathode materials. Contrary to many previous studies that emphasize suppressing cation migration, our team proposed that reversible tetrahedral-octahedral TM migration helps inhibit the formation of undesirable structural changes and phase transformation. The oxidation state of TM, such as Ni, Mn, and Co, are easily trapped into the octahedral sites in the Li layer due to their high octahedral-site splitting energy when a large amount of Li has extracted from the structure. By introducing Cr into LNMO, we found that Cr can migrate reversibly between the tetrahedral and octahedral sites, which makes Cr-doped LNMO possess significantly enhanced structural stability and thus achieve higher electrochemical performance than LNMO.In all, our research focuses on the site-specific doping of the Co-free LLOs and understanding the structure- and chemistry-function relationship of the LLOs. The findings in our work might provide possible pathways for the future design of high-performance cathode materials for lithium-ion batteries and may also apply to developing cathode materials for other energy storage systems.Reference S. Hu, A. S. Pillai, G. Liang, W. K. Pang, H. Wang, Q. Li and Z. Guo, Electrochem. Energy Rev., 2019, 2, 277-311.M. Han, J. Jiao, Z. Liu, X. Shen, Q. Zhang, H.-J. Lin, C.-T. Chen, Q. Kong, W. K. Pang, Z. Guo, R. Yu, L. Gu, Z. Hu, Z. Wang and L. Chen, Adv. Energy Mater., 2020, 10, 1903634.Y. Fan, W. Zhang, Y. Zhao, Z. Guo and Q. Cai, Energy Stor. Mater., 2021, 40, 51-71.Y. Fan, E. Olsson, G. Liang, Z. Wang, A. M. D'Angelo, B. Johannessen, L. Thomsen, B. Cowie, J. Li, F. Zhang, Y. Zhao, W. K. Pang, Q. Cai and Z. Guo, Angew. Chem. Int. Ed., 2022, DOI: 10.1002/anie.202213806.

On Synthesis and Electrochemical Performance of Na4Fe3(PO4)2(P2O7) Cathode for Sodium-Ion Batteries

Developing cost-effective and large-scale energy storage systems (ESSs) has been an important topic over the past years in order to implement efficient utilization of renewable electricity generated from sources like solar, wind, geothermal and tidal energy (1). Since the commercialization in 1991, lithium-ion batteries (LIBs) have been widely used in portable electronics, electric vehicles (EVs), and energy storage devices (2). However, there is an increase in demand for alternative energy sources based on abundant and low-cost materials due to the limited reserves and high costs of lithium compounds. In this context, sodium-ion batteries (SIBs) have received great attention because of their similarities to LIBs and the large abundance (2.3%) on earth, and low cost of sodium compounds (3). However, the energy density of most SIBs are lower that of LIBs, primarily due to the larger ionic radius and higher mass of Na+ ion compared to Li+ ions, as well as the lower electrochemical potential of sodium cells relative to lithium cells (4). Many efforts have been devoted to the development of high-performance cathode materials, including layered transition metal oxides, Prussian blue analogues (PBAs), sulfates, phosphates and pyrophosphates. Polyanionic compounds, in particular, are considered as promising cathode materials with regard to their high working voltage, structural stability, thermal stability and small volume change upon cycling (5). For example, iron phosphate-based materials have gained attention inspired by LiFePO4 for LIBs. However, the olivine NaFePO4 is predominantly produced through an ion exchange process (6). The maricite NaFePO4 is electrochemically inactive due to the lack of Na migration channels within its structure. On the other hand, Na2FeP2O7 shows long cycle life and structural stability with a low capacity because of its single electron diffusion process. Na4Fe3(PO4)2(P2O7) (NFPP) combines the benefits of both phosphate and pyrophosphate, offering potential advantages such as low-cost, environmental friendliness, high average working voltage (~ 3.1 V vs. Na+/Na), favorable theoretical capacity (129 mAh g-1), low volume change (< 4%) due to its open framework composed of [Fe3P2O13] layers connected by (P2O7)4- groups with 3D ion channels and low activation barriers for Na+ transport as well as structural and thermal stability. However, NFPP is susceptible to the formation of impurities such as NaFePO4 and Na2FeP2O7, which can arise from the synthesis temperature and adopted reaction materials, potentially restricting the electrochemical performance of NFPP. Additionally, the inherent insulating characteristics of the (PO4)3- group in NFPP may result in reduced electronic conductivity and slow ion diffusion, which hinders its practical application (7, 8). Therefore, various strategies have been developed to enhance conductivity such as nanosizing, carbon coating and metal ion doping.NFPP can be synthesized by various methods like solid-state, sol-gel, spray drying and combustion. In this study, we present our results on employing both sol–gel and combustion methods with distinct synthesis parameters. The structure, morphology and particle size of NFPP are characterized by X-ray powder diffraction (XRPD) and scanning electron microscopy (SEM) techniques. The electrochemical performance of NFPP cathodes is investigated in both half- and full-cells via galvanostatic charge-discharge cycling tests. Keywords: sodium-ion batteries, cathode material, iron-based mixed phosphate, sol-gel synthesis, large scale M. Armand and J. M. Tarascon, Nature, 451, 652 (2008).J. B. Goodenough and K.-S. Park, Journal of the American Chemical Society, 135, 1167 (2013).B. Dunn, H. Kamath and J.-M. Tarascon, Science, 334, 928 (2011).M. H. Han, E. Gonzalo, G. Singh and T. Rojo, Energy & Environmental Science, 8, 81 (2015).P. Barpanda, L. Lander, S.-i. Nishimura and A. Yamada, Advanced Energy Materials, 8, 1703055 (2018).K. T. Lee, T. N. Ramesh, F. Nan, G. Botton and L. F. Nazar, Chemistry of Materials, 23, 3593 (2011).X. Wu, G. Zhong and Y. Yang, Journal of Power Sources, 327, 666 (2016).H. Kim, I. Park, S. Lee, H. Kim, K.-Y. Park, Y.-U. Park, H. Kim, J. Kim, H.-D. Lim, W.-S. Yoon and K. Kang, Chemistry of Materials, 25, 3614 (2013).

Effects of nickel content on the electrochemical performance of nanosized ternary nickel–zinc–cobalt oxide supercapacitors

To improve the electrochemical performance and structural durability of supercapacitors, herein, well-ordered, porous Ni–Zn–Co ternary oxide nanostructures were synthesized by doping Ni to Zn–Co oxide using ultrasonic electrodeposition. Our investigations revealed that Ni–Zn–Co ternary oxide exhibited superior capacity and rate performance when compared to Zn–Co oxide. In particular, the incorporation of 1 mol/L of Ni markedly improved the electrochemical capabilities of the cathode materials. Remarkably, under the influence of ultrasonic power at 500 W, Ni–Zn–Co oxide exhibited a superior mass loading of 6.2 mg/cm2, coupled with exceptional electron transfer efficiency. The growth mechanism and valence composition of Ni–Zn–Co oxides were studied by SEM and XPS analysis. Moreover, electrodes fabricated from Ni–Zn–Co oxide, synthesized via ultrasonic electrodeposition, demonstrated remarkable area capacitance and rate capabilities, achieving an impressive 1.779 F/cm2 at a current density of 3 mA/cm2. Additionally, the supercapacitor incorporating the Ni–Zn–Co oxide electrode exhibited exceptional long-term stability, maintaining a capacity retention rate of 125.2 % over 24,000 cycles in a mild alkaline electrolyte. This study not only contributes to advancing high-performance cathode materials but also offers valuable perspectives on novel techniques for their fabrication.

Exploring the Electrochemical Properties of Ultrathin LiMn1.5Ni0.5O4 Films at High and Low Current Rates for Lithium-Ion Micro Battery Applications

The development in the miniaturized - smart electric and electronic gadgets with the advancement in technologies has dramatically enhanced the demand for cobalt free-high energy density batteries. Among various choice of high-performance cathode materials Ni substituted LiMn2O4 spinel of composition LiMn1.5Ni0.5O4 (LMNO) has proved to be one of the solutions to yield a high-performance high-energy density battery which can operate at a higher potential window. Ultra - thin films of LMNO fabricated by Pulsed laser deposition method at 600 °C substrate temperature using 2000 pulses. LMNO films fabricated on SrTiO3 (STO) and stainless steel (SS) substrates are employed for a detailed structural and electrochemical performance analysis. Disordered phase corresponding to fd3m space group of LMNO thin film exhibits better electrochemical performance compared to the ordered phase. Phase formation of LMNO thin films are studied employing X-ray diffraction and Raman spectroscopy methods. The morphology obtained for the film of thickness 41.63 nm identified from the scanning electron microscopy (SEM) images clearly reveals the effect of growth conditions such as substrate temperature and base pressure on the growth behavior of these films. Since the electrochemical data obtained for the films are area limited, the capacity of the ultra-thin film is significantly low and can be ameliorate by controlling the area. Kinetic study of LMNO film reveals that the lithium diffusion during the charge storage mechanism resembles to a diffusion-limited process similar to a faradic process. The cycling stability and rate capability at different current densities of LMNO thin film electrodes are further investigated. Charge discharge profile for both higher (25, 50, 75, 100 and 125 mA) and lower (5, 10, 15, 20, and 25 mA) current densities are obtained and subjected for 500 cycles. The thin film electrode shows a stable profile for 500 cycles. Areal discharge capacity of 1.3 μAh/cm2 is observed at a higher current density while at lower current density an areal discharge capacity obtained is 2.13 μAh/cm2 with a coulombic efficiency of around 80% and 96% respectively. Electrochemical impedance spectroscopy studies carried out on LMNO films before and after cycle shows a strong contribution of charge-transfer resistance along with film resistance and solution resistance and the equivalent circuit model for the same is evolved. Present studies indicates that LMNO ultra-thin films can be employed as a cathode layer for fabricating the all-solid thin film micro-batteries for energy applications. Figure 1

Bimetallic sulfide CoNi2S4 hollow nanospheres as a high-performance cathode material for Mg-ion batteries

Mg-ion batteries (MIBs), as a next-generation battery, are drawing considerable attention due to abundant and well-distributed magnesium sources available. The construction of structurally ideal bimetallic sulfides can effectively alleviate the poor cycling stability of MIBs. Herein, we report for the first time, the synthesis of bimetallic sulfide CoNi2S4 hollow nanospheres (CoNi2S4 HSs) via a one-step solvothermal method and their application as a cathode material for MIBs. Compared with common unary transition metal sulfides, CoNi2S4 HSs have more electrochemically active sites and higher electronic conductivity. Meanwhile, the distinct morphology of CoNi2S4 HSs exhibits higher surface area, smaller charge-transfer resistance, and higher magnesium diffusion coefficient. Further, CoNi2S4 HSs deliver a considerable reversible capacity of 290.1 mAh g−1 at 50 mA g−1, and a high capacity of 97.8 mAh g−1 can be achieved at 1000 mA g−1, demonstrating excellent rate performance. The structural integrity, high specific capacity, good rate capability and cycling stability of CoNi2S4 HSs render it a promising cathode material for advanced MIBs.

A layered/spinel heterostructured cathode for Li-ion batteries prepared by ultrafast Joule heating

Spinel LiMn2O4 is one of the most promising cathode materials due to its low cost, high discharge voltage (∼4.0 V), and non-toxicity. However, it suffers from insufficient cycling performance caused by irreversible phase transition and Mn dissolution. In addition, the low synthesis efficiency caused by the long heating time also plagues its application and depletes the cost merits of raw materials. Herein, we report a heterostructured cathode material of electrochemically-inert layered Li2MnO3 and active spinel LiMn2O4 phases, which is synthesized in seconds by ultrafast Joule heating. The heterostructure is rapidly formed as a result of the non-equilibrium process produced by the ultrafast Joule heating rate. The inert layered phase serves as a structure stabilization agent to suppress the structure damage and Mn dissolution, thus promising an excellent electrochemical performance with a high capacity retention of 83 % after 800 cycles at 5C. Our findings provide an efficient design and synthesis strategy for developing high-performance and low-cost cathode materials.

Na3(VO)2(PO4)2F coated carbon nanotubes: A cathode material with high-specific capacity for aqueous zinc-ion batteries

Aqueous zinc-ion batteries (AZIBs) are one of the candidate technologies for large-scale energy storage systems due to their environmental friendliness, safety and resourcefulness. However, designing and synthesizing high-performance cathode materials with practical application value is currently a great challenge. Herein, we synthesize a carbon-nanotube-coated Na3(VO)2(PO4)2F (Na3(VO)2(PO4)2F@CNT) cathode material for AZIBs, which has a continuous and interconnected ion transport channel structure. A Zn2+/H+ co-intercalation mechanism is revealed by ex-situ X-ray diffraction (XRD) and ex-situ X-ray photoelectron spectroscopy (XPS) characterizations. The Na3(VO)2(PO4)2F@CNT cathode material exhibits a high specific capacity of 143 mAh‧g Wan et al. (2019). at 0.2 C in the electrolyte of 3 M Zn(OTf)2 aqueous solution. In addition, Na3(VO)2(PO4)2F@CNT shows a good low-temperature electrochemical performance in the electrolyte of 2 M Zn(OTf)2 deionized water/ethylene glycol (DIW/EG) mixed solution with a different ion storage mechanism. This study provides a new polyanionic cathode material for AZIBs and an idea to modulate the electrolyte polarity to enhance the zinc storage capacity of the cathode material.

V-MOFs derived Na3V2(PO4)3/C core-shell spheres toward ultrastable sodium-ion batteries

Due to the large ionic radius of sodium-ion, the transport of ions is hindered, leading to slow ion diffusion. This, in turn, results in significant structural stresses, causing rapid material deterioration and reduced cycle stability. Furthermore, the low electronic conductivity of Na3V2(PO4)3 further contributes to the unsatisfactory rate performance. To address these challenges, we have employed an adjustable V-MOFs as precursors to synthesize Na3V2(PO4)3/C core-shell spheres with tunable sizes. The incorporation of a carbon shell serves a dual purpose: it not only alleviates the structural stress experienced during charge and discharge processes but also facilitates rapid electron conduction. Moreover, the small-sized core-shell structure effectively shortens the ion and electron transport distances while providing more reactive sites, thus enhancing the kinetics. Consequently, the NVP-0.01M sample obtained exhibits exceptional rate performance, with a remarkable reversible capacity of 115.1 mAh g−1 at 0.1C and 92.2 mAh g−1 at 30C. Furthermore, this material demonstrates remarkable long-term stability, as evidenced by a specific discharge capacity of 99.3 mAh g−1 even after 500 cycles at 1C, corresponding to a capacity retention rate of 91.3 %. The NVP-0.01M∥HC full cell also display outstanding electrochemical performance. This research introduces a novel approach for synthesizing high-performance cathode materials specifically designed for sodium-ion batteries.