High-performance Cathode Materials Research Articles

Hexagonal Carbon Nanoplates Decorated with Layer-Engineered MoS2: High-Performance Cathode Materials for Zinc-Ion Batteries.

Hexagonal carbon nanoplates bearing MoS2 (HCN@MoS2) were synthesized using two-dimensional (2D) microporous organic polymers as templating materials. The layer number of MoS2 in HCN@MoS2 and the 2D morphology of composites were critical factors to achieve high-performance cathode materials for aqueous zinc-ion batteries. The best cathode performance was obtained with HCN@MoS2 bearing 2-3 layered MoS2 (HCN@MoS2-2), showing excellent discharge capacities of 602 mAh/g (@50 mA/g), 498 mAh/g (@0.1 A/g), and 328 mAh/g (@1 A/g). The promising electrochemical performance of HCN@MoS2-2 is attributable to the facilitated insertion of zinc ions into 2-3 layered MoS2 due to the reduced lattice energy and the efficient electrochemical utilization of composite materials.

Unraveling the relationship between Sr stoichiometry in Sr Fe1.5Mo0.5O6− and its catalytic performance for high-temperature CO2 electrolysis

The solid oxide electrolytic cell (SOEC) is one of the most promising energy conversion and storage devices, which could convert CO2 to CO with high Faradaic efficiency and production rate. However, the lack of active and stable cathode materials impedes their practical applications. Here we focus on the promising perovskite oxide cathode material Sr2Fe1.5Mo0.5O6−σ, with the aim of understanding how A-atom stoichiometry and catalytic performance are linked. We find that increasing the strontium content in the perovskite improves the chemisorption of CO2 on its surface, forming a SrCO3 phase. This hinders the charge transfer and oxygen exchange processes. Simultaneously, strontoium segregation to the cathode surface facilitates coking of the surface during CO2 electrolysis, which poisons the electrode. Consequently, a small number of Sr deficiencies are optimal for both electrochemical performance and long-term stability. Our results provide new insights for designing high-performance CO2 electrolysis cathode materials.

High-Performance Layered Ni-Rich Cathode Materials Enabled by Stress-Resistant Nanosheets.

Layered O3-type transition metal oxides are promising cathode candidates for high-energy-density Li-ion batteries. However, the structural instability at the highly delithiated state and low kinetics at the fully lithiated state are arduous challenges to overcome. Here, a facile approach is developed to make secondary particles of Ni-rich materials with nanosheet primary grains. Because the alignment of the primary grains reduces internal stress buildup within the particle during charge-discharge and provides straightforward paths for Li transport, the as-synthesized Ni-rich materials do not undergo cracking upon cycling with higher overall Li+ ion diffusion rates. Specifically, a LiNi0.75Co0.14Mn0.11O2 cathode with nanosheet grains delivers a high reversible capacity of 206 mAh g-1 and shows ultrahigh cycling stability, e.g., 98% capacity retention over 500 cycles in a full cell with a graphite anode.

LiFePO4@C/graphene composite and in situ prepared NaFePO4@C/graphene composite as high-performance cathode materials for electrochemical energy storage

LiFePO4@C/graphene composite and in situ prepared NaFePO4@C/graphene composite as high-performance cathode materials for electrochemical energy storage

Effective chemisorption of polysulfides through organic molecules for high-performance lithium–sulfur batteries

Lithium–sulfur (Li–S) batteries with high theoretical energy density have been regarded as promising energy storage devices. However, the sluggish redox kinetics and shuttle effect of lithium polysulfides of sulfur cathodes remain obstacles to their development, especially with high sulfur content. Herein, we introduce the organic molecule of 3-amino-1,2,4-triazole (AT) on graphene (G) through π–π interactions as a sulfur host material to address the shuttle effect of lithium polysulfides. The molecular fragment of = N–CN– in AT as the active site can effectively anchor polysulfides existing as neutral molecules and free radicals in the electrolyte via “Li···N” interaction. Combined with the fast electron transport facilitated by the graphene, the redox kinetics of polysulfides is promoted. Thus, the electrochemical performance of Li–S batteries can be remarkably improved. The S/G-AT electrode displays excellent electrochemical performance in terms of a high initial capacity (1411 mAh/g at 0.2C), long-term cycling stability (799 mAh/g after 450 cycles at 1C), and superior rate performance (817 mAh/g at 10C). This study helps to utilize functional organic molecules for fabricating high-performance cathode materials for Li–S batteries.

Investigating the effect of pH on the growth of coprecipitated Ni0.8Co0.1Mn0.1(OH)2 agglomerates as precursors of cathode materials for Li-ion batteries

Understanding how the morphology and microstructure of secondary particles are affected by pH is essential to design spherical and dense hydroxide aggregates as precursors of high-performance cathode materials for lithium-ion batteries. To investigate the interplay between thermodynamic reaction conditions and the physicochemical properties of precursors, a chemical equilibrium model is used to describe the evolution of metal ammonia complexes. Furthermore, the formation and growth of aggregates are studied by monitoring the changes in surface morphologies and crystal structures of precursors at different reaction times. As the pH value varied, two notable phenomena occurred during crystal growth: the fast growth of grains in the early stage as the pH decreased and the layered growth of grains in the later stage with increased pH values. Such findings could be explained from the following two perspectives. First, the decrease in pH causes a significant increase in the complex ion concentration, thereby facilitating the growth of crystals along the [010] direction. Second, an increase in pH generally accelerates deprotonation of the crystal surface, thus strengthening the adsorption of complex ions on the crystal surface and promoting layer-by-layer growth of primary grains along the [001] direction.

Layered Oxide Cathodes for Sodium-Ion Batteries: Storage Mechanism, Electrochemistry, and Techno-economics.

ConspectusLithium-ion batteries (LIBs) are ubiquitous in all modern portable electronic devices such as mobile phones and laptops as well as for powering hybrid electric vehicles and other large-scale devices. Sodium-ion batteries (NIBs), which possess a similar cell configuration and working mechanism, have already been proven as ideal alternatives for large-scale energy storage systems. The advantages of NIBs are as follows. First, sodium resources are abundantly distributed in the earth's crust. Second, high-performance NIB cathode materials can be fabricated by using solely inexpensive and noncritical transition metals such as manganese and iron, which further reduces the cost of the required raw materials. Recently, the unprecedented demand for lithium and other critical minerals has driven the cost of these primary raw materials (which are utilized in LIBs) to a historic high and thus triggered the commercialization of NIBs.Sodium layered transition metal oxides (NaxTMO2, TM = transition metal/s), such as Mn-based sodium layered oxides, represent an important family of cathode materials with the potential to reduce costs, increase energy density and cycling stability, and improve the safety of NIBs for large-scale energy storage. However, these layered oxides face several key challenges, including irreversible phase transformations during cycling, poor air stability, complex charge-compensation mechanisms, and relatively high cost of the full cell compared to LiFePO4-based LIBs. Our work has focused on the techno-economic analysis, the degradation mechanism of NaxTMO2 upon cycling and air exposure, and the development of effective strategies to improve their electrochemical performances and air stability. Correlating structure-performance relationships and establishing general design strategies of NaxTMO2 must be considered for the commercialization of NIBs.In this Account, we discuss the recent progress in the development of air-stable, electrochemically stable, and cost-effective NaxTMO2. The favorable redox-active cations for NaxTMO2 are emphasized in terms of abundance, cost, supply, and energy density. Different working mechanisms related to NaxTMO2 are summarized, including the electrochemical reversibility, the main structural transformations during the charge and discharge processes, and the charge-compensation mechanisms that accompany the (de)intercalation of Na+ ions, followed by discussions to improve the stability toward ambient air and upon cycling. Then the techno-economics are presented, with an emphasis on cathodes with different chemical compositions, cost breakdown of battery packs, and Na deficiency, factors that are critical to the large-scale implementation. Finally, this Account concludes with an overview of the remaining challenges and new opportunities concerning the practical applications of NaxTMO2, with an emphasis on the cost, large-scale fabrication capability, and electrochemical performance.

Quantitative Regulation of Interlayer Space of NH4 V4 O10 for Fast and Durable Zn2+ and NH4 + Storage.

Layered vanadium-based oxides are the promising cathode materials for aqueous zinc-ion batteries (AZIBs). Herein, an in situ electrochemical strategy that can effectively regulate the interlayer distance of layered NH4 V4 O10 quantitatively is proposed and a close relationship between the optimal performances with interlayer space is revealed. Specifically, via increasing the cutoff voltage from 1.4, 1.6 to 1.8V, the interlayer space of NH4 V4 O10 can be well-controlled and enlarged to 10.21, 11.86, and 12.08 Å, respectively, much larger than the pristine one (9.5 Å). Among them, the cathode being charging to 1.6V (NH4 V4 O10 -C1.6), demonstrates the best Zn2+ storage performances including high capacity of 223mA h g-1 at 10 A g-1 and long-term stability with capacity retention of 97.5% over 1000 cycles. Such superior performances can be attributed to a good balance among active redox sites, charge transfer kinetics, and crystal structure stability, enabled by careful control of the interlayer space. Moreover, NH4 V4 O10 -C1.6 delivers NH4 + storage performances whose capacity reaches 296mA h g-1 at 0.1 A g-1 and lifespan lasts over 3000 cycles at 5 A g-1 . This study provides new insights into understand the limitation of interlayer space for ion storage in aqueous media and guides exploration of high-performance cathode materials.

Tremella-like Vanadium Tetrasulfide as a High-Performance Cathode Material for Rechargeable Aluminum Batteries

Rechargeable aluminum batteries (RABs) are gaining widespread attention for large-scale energy storage applications as a result of their high energy densities, high security, and abundance. The key to sustain the progress of RABs lies in the quest for the proper cathode materials with prominent capacity and reversible cycle life. Herein, we propose a tremella-like VS4 as a cathode material aiming to tackle this problem. Obtained from a morphology modification process, VS4 with a unique nanosheet structure provides sufficient active sites for intercalation and conversion reactions, shortens the transport paths for charge carrier ions, and facilitates the infiltration process for electrolyte. The RAB with the VS4 cathode exhibits excellent electrochemical performance, including outstanding specific capacity (407.9 mAh g-1) and stable cycling performance (∼300 cycles at a high current density). The energy storage mechanism has been comprehensively investigated and is confirmed to be a combination of the intercalation/deintercalation of Al3+ and AlCl4- ions and conversion reaction by various techniques and DFT calculation. Our study not only provides a peculiar and simple strategy for the rational design of metal sulfide cathode materials with high capacity and long-term stability but also proposes a specific energy storage mechanism that guides the development of cathode materials of RABs in the future.

Plasma-enhanced fluorination of layered carbon precursors for high-performance CFx cathode materials

Lithium/fluorinated carbon (Li/CFx) primary batteries employed in commercial, medical, and military fields, are still hindered by the poor rate performance, which is closely related to the fluorination process and precursor carbon materials. Herein, we reported an eco-friendly, simple and efficient fluorination strategy, namely, plasma-enhanced fluorination (PEF), to manufacture plasma fluorinated expanded graphite (PFEG) and plasma fluorinated graphene (PFG). Chemically similar PFEG and PFG materials were also constructed to study the effect of morphology and microstructure of the carbon precursors on the PEF process and the resulting CFx materials’ electrochemical performance. The Li/PFG coin cell exhibits excellent rate performance with a high specific capacity of 838.3 mAh/g at a high current density of 10 A/g. The pouch cell based on the PEF pilot reactor delivers a specific capacity 771.4 mAh/g at 0.1 A/g, confirming the potential of PEF for scalable production of high-quality (high energy density and high-power density) CFx cathode materials. These findings will greatly contribute to the research and development of Li/CFx primary batteries in the way of optimizing carbon precursors and developing new fluorination strategies.

FeOCl Nanoparticle-Embedded Mesocellular Carbon Foam as a Cathode Material with Improve d Electrochemical Performance for Chloride-Ion Batteries.

Chloride-ion batteries (CIBs) have been regarded as a promising alternative battery technology to lithium-ion batteries because of their abundant resources, high theoretical volumetric energy density, and high safety. However, the research on chloride-ion batteries is still in its infancy. Exploring appropriate cathode materials with desirable electrochemical performance is in high demand for CIBs. Herein, the FeOCl nanocrystal embedded in a mesocellular carbon foam (MCF) has been prepared and developed as a high-performance cathode material for CIBs. The MCF with uniform and large mesocells (15.7-31.2 nm) interconnected through uniform windows (15.2-21.5 nm) can provide high-speed pathways for electron and chloride-ion transport and accommodate the strain caused by the volume change of FeOCl during cycling. As a result, the optimized FeOCl@MCF cathode exhibits the highest discharge capacity of 235 mAh g-1 (94% of the theoretical capacity) among those of the previously reported metal (oxy)chloride cathodes for CIBs. A reversible capacity of 140 mAh g-1 after 100 cycles is retained. In contrast, only 18 mAh g-1 was kept for the FeOCl cathode.

One-Pot Synthesis of NiSe2 with Layered Structure for Nickel-Zinc Battery.

Transition metal organic framework materials and their selenides are considered to be one of the most promising cathode materials for nickel-zinc (denoted as Ni-Zn) batteries due to their low cost, environmental friendliness, and controllable microstructure. Yet, their low capacity and poor cycling performance severely restricts their further development. Herein, we developed a simple one-pot hydrothermal process to directly synthesize NiSe2 (denotes as NiSe2-X based on the molar amount of SeO2 added) stacked layered sheets. Benefiting from the peculiar architectures, the fabricated NiSe2-1//Zn battery based on NiSe2 and the Zn plate exhibits a high specific capacity of 231.6 mAh g-1 at 1 A g-1, and excellent rate performance (162.8 mAh g-1 at 10 A g-1). In addition, the NiSe2//Zn battery also presents a satisfactory cycle life at the high current density of 8 A g-1 (almost no decay compared to the initial specific capacity after 1000 cycles). Additionally, the battery device also exhibits a satisfactory energy density of 343.2 Wh kg-1 and a peak power density of 11.7 kW kg-1. This work provides a simple attempt to design a high-performance layered cathode material for aqueous Ni-Zn batteries.

Double sites doping local chemistry Adjustment: A Multiple-Layer oriented P2-Type cathode with Long-life and Water/Air stability for sodium ion batteries

P2-type Ni/Mn layered oxides have attracted intensive interest as a kind of promising cathode materials because of their high specific capacities and unique 2D Na+ diffusion path. However, the poor stability and irreversible phase transition at high voltage during charge and discharge process greatly hinders its practical applications. Herein, a novel double site substitution strategy is reported that large-sized K+ is riveted in the prismatic Na+ sites and Cu2+ is occupies in the transition metal sites. The K+ doping lead to the lattice expansion along c-axis, which facilitating sodium ions transport. In addition, the double sites substitution improves the stability of the materials exposed in air and water environments. A combined analysis of first-principles calculation simulation and experimental verification determining that larger interlayer spacing decreases the diffusion barrier of sodium ions. The as-prepared multiple-layer oriented P2-K0.05Na0.67Mn0.6Ni0.3Cu0.1O2 shows excellent rate performance, fast sodium ion transport ability and superior cycling performance with a high-capacity retention of 91.2 % at a high current density of 1 A g−1 after 1800th cycles. Therefore, this work provides a new insight for the design of stable and high-performance cathode materials for sodium ion batteries.

2D V10O24·nH2O sheets as a high-performance cathode material for aqueous zinc-ion batteries

In this work, 2D V10O24·nH2O sheets are synthesized via a facile solvothermal method. When used as a cathode material for aqueous rechargeable zinc ion batteries (ZIBs), the as-prepared V10O24·nH2O sheets show high reversible capacity (408 mA h g−1 at 0.1 A g−1), superior long-term cyclability (with a stable capacity of 314 mA h g−1 over 1000 cycles at 2.0 A g−1), as well as excellent rate performance. The impressive electrochemical performance can be attributed to the 2D morphology composed of staked nanosheets and the existence of V4+, which enhances the structural stability, promotes the electrochemical activity and improves the reaction kinetics as demonstrated by electrochemical tests and ex-situ characterizations. This study provides a viable and promising cathode material for practical ZIBs.

Analysis of the growth mechanism of hierarchical structure Ni0.8Co0.1Mn0.1(OH)2 agglomerates as precursors of LiNi0.8Co0.1Mn0.1O2 in the presence of aqueous ammonia

Hierarchical structure Ni0.8Co0.1Mn0.1(OH)2 agglomerates were formed by coprecipitation method in the presence of aqueous ammonia in a continuous stirred tank reactor (CSTR). The resultant spherical secondary particles are comprised of highly anisotropic primary grains as building blocks, which retain a distinct hexagonal flake morphology with six {010} equivalent crystal facets and two other {001} facets. The formation of hierarchical agglomerates typically undergoes three steps: (i) the formation of grain nuclei (homogeneous nucleation), (ii) anisotropic growth of grains and formation of hexagonal nanosheets, (iii) agglomeration of single crystal grains and formation and growth of spherical agglomerates. This unique hierarchical structures of Ni0.8Co0.1Mn0.1(OH)2 point to its promising applications in preparation of high-performance cathode materials for lithium-ion batteries.

Synthesis of a carbon-wrapped microsphere MoO2/Mo2C heterojunction as an efficient electrocatalyst for the oxygen reduction reaction and the hydrogen evolution reaction.

The development of non-noble metal catalysts for the optimization of conversion and storage devices is an important research topic. Hence, the microsphere MoO2/Mo2C/C heterojunction composites, which play an important role in the oxygen reduction reaction (ORR) and the hydrogen evolution reaction (HER), were synthesized using the solvothermal-sintering method. The results revealed that the as-prepared composite exhibited better ORR and HER catalytic performances than those of MoO2/Mo2C and Vulcan XC-72R (carbon black), and approaching that of commercial Pt/C. At the same time, it has a superior methanol tolerance and electrochemical stability than that of the commercial Pt/C. The excellent performance may be attributed to the synergistic effect of the MoO2/Mo2C heterostructure, highly conductive Vulcan XC-72R, and oxygen vacancies (Ov). This research offers new insights into the design and synthesis of cost-effective, environmentally friendly heterojunction composite catalysts used as a high-performance cathode material in fuel cells and water splitting.

Magnesium doping improved characteristics of high voltage cycle of layered cathode of sodium ion battery

Driven by global demand for new energy, Li-ion batteries (LIBs) have developed rapidly due to their competitive performance. Although LIBs show the advantages of high capacity and good cycling stability, their disadvantages such as uneven distribution of lithium resources are gradually exposed. Therefore, with abundant reserves, Na-ion batteries (NIB) have become one of the most promising solutions to make up for the deficiency of Li-ion battery. The NIBs layered oxide cathodes have the most potential applications of cathode material due to their high specific capacity (167 mAh·g<sup>–1</sup> in 2.4–4.3 V) and simple synthesis method. However, improving the cycling stability of layered cathode materials is one of the keys to their large-scale industrialization. To develop high capacity and cycling stability cathode materials, the Mg<sup>2+</sup> is substituted for Ni<sup>2+</sup> in NaNi<sub>0.4</sub>Cu<sub>0.1</sub>Mn<sub>0.4</sub>Ti<sub>0.1</sub>O<sub>2</sub> (NCMT), thereby obtaining a NaNi<sub>0.35</sub>Mg<sub>0.05</sub>Cu<sub>0.1</sub>Mn<sub>0.4</sub>Ti<sub>0.1</sub>O<sub>2</sub> (NCMT-Mg) cathode material. The NCMT-Mg has a high reversible specific capacity of 165 mAh·g<sup>–1</sup> in a voltage window of 2.4–4.3 V. The reversible specific capacity of about 110 mAh·g<sup>–1</sup> at 0.1 C after 350 cycles with a capacity retention of 67.3% is about 13% higher than the counterpart of NCMT. The irreversible reaction is suppressed from P'3 phase to X phase for NCMT. The ex-XRD spectrometers further prove that the NCMT-Mg shows a P3 and X mixed phase after being initially charged to 4.3 V, but the NCMT shows an X phase. The irreversible phase transition is suppressed to increase the cycling stability. The inactive Mg<sup>2+</sup> replaces Ni<sup>2+</sup>, reducing the charge compensation and stabilizing the structure, the inactive Mg<sup>2+</sup> can activate the charge compensation of Ni<sup>2+</sup>/Cu<sup>2+</sup>. The electrochemical activity increases from 77% to 86%. The high capacity and excellent cycling stability prove that the NCMT-Mg structure remains intact after various current rates have been tested. The long cycling stability mechanism is further systematically studied by using various technologies. The present work will provide an important reference for developing high-performance Na-ion cathode materials.

Research advance of lithium-rich cathode materials in all-solid-state lithium batteries

The development of all-solid-state lithium batteries with high energy density, long cycle life, low cost and high safety is one of the important directions for the developing next-generation lithium-ion batteries. Lithium-rich cathode materials have been widely used in liquid lithium batteries for their higher discharge specific capacity (> 250 mAh/g) and energy density (> 900 Wh/kg), high thermal stability and low raw material cost. With the rapid development of high-performance lithium-rich cathode materials and solid-state electrolytes in all-solid-state lithium batteries, the application of lithium-rich cathode materials in all-solid-state lithium batteries is expected to make a breakthrough toward the target of 500 Wh/kg energy density of lithium-ion batteries. In this review, first, we elaborate the failure mechanism of lithium-rich cathode materials in all-solid-state lithium batteries. The poor electronic conductivity, irreversible redox reaction of anionic oxygen and structute transformation during the electrochemical cycling of lithium-rich cathode materials result in the low initial coulomb efficiency, poor cycling stability and voltage decay. In addition, the high operating voltage of lithium-rich cathode materials (> 4.5 V <i>vs</i>. Li/Li<sup>+</sup>) triggers off not only the conventional interfacial chemical reactions between anode and electrolyte, but also the release of oxygen, aggravating the interfacial electrochemical reactions, which reduces the stability of the cathode/electrolyte interface. Therefore, the intrinsic characteristics of lithium-rich cathode materials and the severe interfacial reaction of lithium-rich cathode/electrolyte greatly limit the application of lithium-rich cathode materials in all-solid-state lithium batteries. Then, we review the research progress of lithium-rich cathode materials in various solid-state electrolyte systems in recent years. The higher room temperature ionic conductivity and wider voltage window of inorganic solid-state electrolytes provide opportunities for the application of lithium-rich cathode materials in all-solid-state lithium batteries. At present, the application of lithium-rich cathode materials in all-solid-state lithium batteries is explored on the basis of sulfide, halide and oxide solid-state electrolyte systems, and important progress has been made in the studies of composite cathode preparation methods, interfacial reaction mechanisms and activation mechanisms. Finally, we summarize the current research hotspot of lithium-rich cathode all-solid-state lithium batteries and propose several strategies for their future studies, such as the regulation of cathode material components, the construction of lithium ion and electron transport pathways within the composite cathode, and the interfacial modification of cathode materials that have been shown to have significant effects in solving the failure problem.

Advancing structural batteries: cost-efficient high-performance carbon fiber-coated LiFePO4 cathodes.

Structural batteries (SBs) have gained attention due to their ability to provide energy storage and structural support in vehicles and airplanes, using carbon fibers (CFs) as their main component. However, the development of high-performance carbon fiber-based cathode materials for structural batteries is currently limited. To address this issue, this study proposes a cost-efficient and straightforward method for creating a high-performance structural lithium iron phosphate (LiFePO4) positive electrode by coating carbon fibers at mild temperatures and pressures. The resulting cathode demonstrated a high LiFePO4 loading (at least 74%) and a smooth coating, as confirmed by X-ray spectroscopy, scanning electron microscopy, and Raman spectroscopy. This structural cathode exhibited a capacity of 144 mA h g-1 and 108 mA h g-1 at 0.1 C and 1.0 C, respectively. Additionally, the LiFePO4 cathode displayed excellent electrochemical properties, with a capacity retention of 96.4% at 0.33 C and 81.2% at 1.0 C after 300 cycles. Overall, this study presents a promising approach for fabricating high-performance structural batteries with enhanced energy storage and structural capabilities.

Improved strategies for ammonium vanadate-based zinc ion batteries.

Aqueous zinc ion batteries (ZIBs) are becoming increasingly popular as a new form of resource for electrochemical energy storage due to their high safety, affordability, availability of natural zinc resources, and high gravimetric energy density. However, the development of high-performance ZIB cathode materials remains a great challenge because current ZIB cathode materials tend to have low conductivity and relatively complex energy storage mechanisms. Compared with other cathode materials, ammonium vanadate-based materials have been extensively investigated as cathode materials for ZIBs due to their plentiful availability and high potential capacity. In this review, we highlight the mechanisms and challenges of ammonium vanadate-based materials and summarize the progress in improved strategies including the design of different morphologies, doping with different impurities, the introduction of different intercalators, and combination with other materials for high-performance ZIBs. Finally, the paper also provides an outlook on the future challenges and development prospects of ammonium vanadate-based cathode materials in ZIBs.