High-performance Cathode Materials Research Articles

Pillar strategy enhanced ion transport and structural stability toward ultra-stable KVPO4F cathode for practical potassium-ion batteries

KVPO4F (KVPF) is a promising cathode material for potassium-ion batteries (PIBs) because of its high operating voltage, high energy density, and excellent thermal stability. Nevertheless, the low kinetics and large volume change have been the major hurdles causing irreversible structural damage, high inner resistance, and poor cycle stability. Herein, a pillar strategy of Cs+ doping in KVPO4F is introduced to reduce the energy barrier for ion diffusion and volume change during potassiation/depotassiation, which significantly enhances the K+ diffusion coefficient and stabilizes the crystal structure of the material. Consequently, the K0.95Cs0.05VPO4F (Cs-5-KVPF) cathode exhibits an excellent discharge capacity of 104.5 mAh g−1 at 20 mA g−1 and a capacity retention rate of 87.9% after 800 cycles at 500 mA g−1. Importantly, Cs-5-KVPF//graphite full cells attain an energy density of 220 Wh kg−1 (based on the cathode and anode weight) with a high operating voltage of 3.93 V and 79.1% capacity retention after 2000 cycles at 300 mA g−1. The Cs-doped KVPO4F cathode successfully innovates the ultra-durable and high-performance cathode materials for PIBs, demonstrating its considerable potential for practical applications.

Covalency modulation enables stable Na-rich layered oxide cathodes for Na-ion batteries

As the analogs of Li-rich materials, Na-rich transition metal layered oxides are promising cathode materials for Na-ion batteries owing to their high theoretical capacity and energy density through cumulative cationic and anionic redox. However, most of the reported Na-rich cathode materials are mainly Ru- and Ir-based layered oxides, which limits the practical application. Herein, we report a Na-rich and Ru-doped O3-type Na1.1Ni0.35Mn0.55O2 cathode to mitigate this issue. By partially substituting Mn4+ with high-electronegativity Ru4+, the structural stability and electrochemical performance of the cathode are both greatly improved. It is validated that the high covalency of Ru–O bonds could harden the structural integrity with rigid oxygen framework upon cycling, leading to enhanced O3-P3 phase transition reversibility. Ru doping also induces an enlarged interlayer spacing to boost the Na+ diffusion kinetics for improved rate capability. In addition, benefiting from the large energetic overlap between Ru 4d and O 2p states, the reinforced Ru–O covalency enables highly reversible Ru4+/Ru5+ redox accompanied with more stable oxygen redox, leading to improved specific capacity and stability over cycling. Our present study provides a promising strategy for designing high-performance Na-rich layered oxide cathode materials through covalency modulation toward practical applications.

π-Conjugated N-heterocyclic compound with redox-active quinone and pyrazine moieties as a high-capacity organic cathode for aqueous zinc-ion batteries

Organic cathode materials have been widely used for aqueous zinc-ion batteries (ZIBs) due to their designable molecular structures and diverse redox groups. However, there are still many challenges that need to be overcome, such as limited specific capacity and utilization, inadequate electrical conductivity, unsatisfactory cycle durability and unclear charge storage mechanism. Herein, we report a π-conjugated N-heterocyclic compound containing dual-redox active groups (i.e. quinone and pyrazine), benzo[b]phenazine-6,11-dione (BPD), which are employed as a cathode material in aqueous ZIBs. The BPD cathode shows a high capacity of up to 429 mAh g−1 at 0.05 A g−1, 100 % capacity utilization and excellent cycling performance upon 10,000 cycles. The aqueous ZIB full cell with the BPD cathode delivers an energy density of 276 Wh kg−1, higher than the most previously reported organic cathode materials. Moreover, ex-situ characterizations, electrochemical experiments, and theoretical calculations, clearly illustrate that H+ and Zn2+ are co-inserted during the charge/discharge process. The high utilization and stability of BPD cathode is due to the high insolubility of both BPD and its discharge products. This work provides a reasonable strategy and unique perspective for the design and synthesis of novel high-performance organic cathode materials for aqueous ZIBs.

High-Performance Aqueous Zinc-Ion Batteries Enabled by Superlattice Intercalation Zn3V2O7-C Cathodes

Aqueous Zn-ion batteries (AZIBs) have received widespread attention for their advantages of environmental friendliness and high-safety, yet the development of high-performance AZIBs faces some critical issues, including exploring high-performance cathode materials with high electrical conductivity, high capacity, and stable crystal structures that may greatly affect the cycling stability and rate performance. Herein, we report a superlattice Zn3V2O7-C, which shows promising properties with high capacity and long-term stability as a conversion-type cathode material of AZIBs. The Zn||Zn3V2O7-C half-cells deliver a capacity of ∼210 mAh/g over 10, 000 charging/discharging cycles. A comprehensive investigation elucidates that the superlattice Zn3V2O7-C can provide more reactive sites, more stable structure, and more enhanced electrical conductivity for Zn2+ storage, thus benefiting the promotion of Zn2+ electrochemical and diffusion kinetics. The favorable characteristics of the designed cathode will pave an avenue for the development of promising electrodes for practical AZIBs.

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.