Specific Capacity Research Articles

Freestanding Phosphonium Covalent Organic Frameworks with Efficient Hydroxide Conduction for Zinc–Air Batteries

Owing to their well‐defined crystalline pore structures and ordered functional ionic groups along the skeleton, ionic covalent organic frameworks (iCOFs) exhibit excellent performance and have significant potential for use in energy storage and conversion devices. Herein, we for the first time developed cationic phosphonium COFs with high hydroxide conduction even with low ion exchange capacity (IEC). Specifically, we synthesized COFs containing quaternary phosphonium groups as excellent ion transport moieties. Then, we fabricated freestanding phosphonium membranes through a vapor‐assisted method, which exhibited high hydroxide conductivity of 126 mS cm–1 at 80 °C from a minimal IEC of 1.17 mmol g–1. The resulting film was successfully applied to zinc–air batteries, demonstrating energy density of 96.1 mW cm–2, specific capacity of 95.0 mAh cm–2, and stable operation over 2,300 min. Overall, in addition to investigating a novel cationic functional group, we demonstrated a freestanding film formation method of COF‐based materials. The findings can provide a solid foundation for advancing the field of iCOFs to ion transport and promoting electrochemical applications.

Enhancing Supercapacitor Performance of NiCoMn‐Layered Double Hydroxide with Ag–Citrate/Polyaniline Nanocomposites

Layered double hydroxide (LDH) has a layered structure, which makes it a strong candidate for supercapacitors (SC) due to its high surface area. However, they suffer from low conductivity due to insufficient charge transfer across their layers. This research aims to overcome this obstacle by introducing conductive channels among the layers by the addition of Ag–citrate and polyaniline (PANI). Consequently, five electrodes (S1–5) were made from NiCoMn LDH (referred to as LDH henceforth) and 2:1 Ag–citrate and PANI composite (Ag/PANI) in different ratios and made into electrodes. Electrochemical analysis revealed successful improvement in the performance of LDH as the fraction of Ag/PANI increased until it equaled Ag/PANI where the highest specific capacitance of 617 F g−1 was obtained, which is 12% greater than the value for solely LDH electrode (550 F g−1). A device was fabricated with the best electrode (S3) and activated carbon electrode, which demonstrated energy densities and power densities of 41 WhKg−1 and 412.5 W Kg−1 and 14 WhKg−1and 8250 W Kg−1 at 0.5 and 10 A g−1 current densities, respectively. It also exhibited a capacitive retention of about 75% at 3000 galvanostatic charge–discharge cycles. These results encourage the use in of NiCoMn LDH, in a 1:1 ratio with Ag/PANI in SCs due to its remarkable performance.

Algae‐Derived Precursors for Sustainable Electrochemical Energy Storage

The simple production and harvesting of algae, along with its lower environmental impact and fewer geopolitical issues, make it a viable precursor for electrochemical energy storage devices. Algae represent a promising biomaterial for electrode materials in electrochemical energy storage devices, including hard carbon, sol–gel‐based anode batteries, sodium batteries, oxygen reduction reaction catalysts in zinc–air batteries, and cathode materials in zinc‐ion and lithium‐ion batteries. Algae‐based batteries are fabricated using methods like pyrolysis, hydrothermal processes, agar‐aided dissolution, electrolysis, annealing, and sol–gel methods. Among these, the sol–gel method using agar to construct refillable hydrogel batteries stands out. Agar's compatibility with acetylene black enhances electrochemical properties and offers the advantage of refill ability, which is challenging in metal‐ion batteries. Algae carbons have demonstrated enhanced specific capacity and cyclic performance, paving the way for their use in both medical and industrial applications. The article reviews the utilization of algae‐based batteries in different industrial and medical pacemaker applications as well as examines the feasibility of the operation of algae‐based batteries synthesized through various parameters and precursors.

Na Ions Doped Fe2VO4 Cathode for High Performance Aqueous Zinc-ion Batteries.

Aqueous zinc ion batteries are thought to be a new generation of secondary batteries that will replace lithium-ion batteries due to their great safety and inexpensive cost. In the cathode materials of aqueous zinc ion batteries with long life and high capacity, abundant active sites and crystal structure stability play an important role. In the present work, the strategy of Na+ intercalation of Fe2VO4 (FVO) is proposed, aiming at the insertion of Na+, which not only enriches the active sites, but also sodium and iron ions act as guest species with the negatively charged VOx lattice to provide strong electrostatic attraction to stabilize the lamellar structure. In terms of electrochemical performance, the discharge specific capacity is 370 mAh g-1 at a current density of 0.1 A g-1, and when the current density is arising 5 A g-1, the specific capacity also reaches 200 mAh g-1 after cycling 2000 with a capacity retention of 99 %, which is better than the electrochemical performance of Fe2VO4 (FVO) alone at 50 mAh g-1. The superior electrochemical performance proves that FVO-Na is an ideal cathode material for zinc ion batteries.

Electrospun Mesoporous Ni0.5Zn0.5Fe2O4 - CNT - Hollow Carbon Ternary Composite Nanofibers as High Performance Electrodes for Advanced Symmetric Supercapacitors.

Spinel ferrites have attracted considerable interest in energy storage systems due to their unique magnetic, electrical and catalytic properties. However, they suffer from poor electronic conductivity and low specific capacity. We have addressed this limitation by synthesizing composite hollow carbon nanofibers (HCNF) embedded with nanostructured Nickel Zinc Ferrite (NZF) and Multiwalled carbon nanotubes (CNT), through coaxial electrospinning. These ternary composite nanofibers NZF-CNT-HCNF have a high specific capacity of 833 C g-1 at a current density of 1 A g-1 and have a capacity retention of 90 % after 3000 cycles. Their performance is much better than pure NZF fibers (180 C g-1) or hollow carbon nanofibers (96 C g-1), suggesting synergy between various constituents of the composite. A symmetric supercapacitor fabricated from NZF-CNT-HCNF composite nanofibers (30 % NZF) has a high specific capacity of 302 C g-1 (302 A g-1) at a current density of 1 A g-1 and has a capacity retention of 95 % after 5000 cycles. At the same current density, the device has a high energy density of 39 Whkg-1 and power density of 1000 Wkg-1 at a current density of 1 A g-1. This performance can be attributed to the high specific surface area (776 m2 g-1), mesoporosity (pore size ~4 nm), interconnectedness of the nanofibers and high electrical conductivity of CNTs. These fibers can be used as light-weight high performance electrode materials in advanced energy storage devices.

Metal Organic Framework‐Derived Anionic P‐Substitution toward CoNiSe‐P with Excellent Electrochemical Stability for Supercapacitor

AbstractThe regulation of nanostructures and composition can significantly enhance the electrochemical activity and accelerate electrochemical reaction kinetics of electrode material. Herein, metal organic framework(MOF) is used as self‐sacrificing templates to prepare CoNiSe‐P by hydrothermal with following selenylation and phosphorization treatment. Due to the hollow porous structure, rich electrochemical active sites and elements synergistic influence, the obtained CoNiSe‐P electrode shows a high capacity of 838 C g−1, which is much higher than CoNiSe (322 C g−1) and CoNiP (616 C g−1). Furthermore, CoNiSe‐P electrode shows excellent rate characteristic (685 C g−1 at 20 A g−1) and ultrahigh electrochemical stability with capacity retention of 99.6% after 10 000 cycles. More importantly, an asymmetric supercapacitor is assembled with CoNiSe‐P as the positive electrode and nitrogen‐doped porous carbon as the negative electrode delivers an energy density of 42.4 Wh kg−1 at 266.6 W kg−1 and maintains a specific capacitance of 96.8% after 10 000 cycles. Significantly, the asymmetric supercapacitor shows a high energy density up to 21.3 Wh kg−1 at a very high power density of 21.3 kW kg−1, higher than those of previously reported asymmetric supercapacitors.

Facile synthesis and characterization of zinc molybdate (ZnMoO4) nanosheets for electrochemical supercapacitor application

Abstract This study explores the synthesis and characterization of zinc molybdate (ZnMoO4) nanosheets with emphasis on their potential application for energy storage devices particularly supercapacitors. The synthesis of ZnMoO4 nanosheets was done through co-precipitation followed by examination of their structure, morphology, optical, thermal behaviour and electrochemical performance by various characterization techniques. X-ray diffraction (XRD) analysis confirmed that the formation of monoclinic ZnMoO4 phase with the average crystallite size 17.93 nm. Scanning electron microscopy (SEM) and Transmission electron microscopy (TEM) revealed that this material had nanosheets-like structure which helps to increase ion transport and surface area; these two factors are essential for enhancing the material’s supercapacitor efficacy. The semiconductor characteristics were determined using UV–Visible diffuse reflectance spectroscopy (UV-DRS) which indicated a band gap energy of 4.2 eV. Fourier transform infrared (FTIR) analysis confirmed that the presence of Zn–O and Mo–O bonds in their crystal lattice. Thermogravimetric analysis (TGA) showed that the ZnMoO4 nanosheets had thermal stability since they experienced only a slight mass loss of 2.57 % up to 800 °C. Cyclic voltammetry (CV) and galvanostatic charge-discharge (GCD) tests were undertaken to find out the specific capacitance and the value is 618 F g⁻1 at a current density of 1 A g⁻1.

A review of hydroxyapatite synthesis for heavy metal adsorption assisted by machine learning.

Heavy metals (HMs) represent a persistent and significant threat to aquatic ecosystems. Hydroxyapatite (HAp) has emerged as a utilized material in the remediation of environmental HMs, owing to its exceptionally high porosity, expansive surface area, and the presence of three-dimensional ordered channels. An in-depth study of the synthesis strategy of HAp and its adsorption properties can help reduce the cost of remediating HMs in aquatic environments and alleviate the water shortage. In this paper, we reviewed 466 works of literature on the adsorption of heavy metals by HAp based on the Web of Science database between 2013 and 2023 that focused on the adsorption of heavy metals by HAp. We meticulously synthesized the findings related to the synthesis conditions-namely precipitation, hydrothermal, and calcination-as well as the characterization parameters and the adsorption capacity of HAp for heavy metals such as Pb2+, Cd2+, Cu2+, Zn2+, and Ni2+. Synthesizing advanced materials by reducing the number of experiments is essential to accelerate material development. Machine learning (ML) holds significant promise in material discovery and performance enhancement. We have consolidated the qualitative and quantitative relationships between HAp synthesis conditions, characterization parameters, and heavy metal adsorption capacity across previous studies, utilizing both the Statistical Package for Social Sciences (SPSS) and ML techniques. Building on the most recognized heavy metal adsorption mechanisms, we have evaluated the influence of characterization parameters on adsorption performance. We have outlined the optimal synthetic conditions for enhancing the adsorption of Pb2+, Cd2+, Cu2+, Zn2+, and Ni2+ through precipitation, hydrothermal, and calcination methods, offering a practical guide for the targeted synthesis of HAp tailored to specific heavy metal adsorption capacities.

Investigating the Effect of Carbon Nanotubes Decorated SmVO4-MoS2 Nanocomposite for Energy Storage Enhancement via VARTM-Fabricated Solid-State Structural Supercapacitors Using Woven Carbon Fiber.

Traditional supercapacitors are cumbersome and need separate enclosures, which add weight and reduce space efficiency. In contrast, structural supercapacitors combine energy storage with load-bearing materials, optimizing space and weight for automotive and aerospace applications. This study investigates the synthesis of SmVO4-MoS2 and SmVO4-MoS2-CNT nanocomposites, focusing on optimizing CNT concentration in SmVO4-MoS2-CNT for high-performance supercapacitors. The optimal concentration of SmVO4-MoS2-CNT is identified and used to fabricate structural supercapacitor devices via the vacuum-assisted resin transfer molding (VARTM) technique. The results indicate that the specific capacitance of Sm-Mo-C5, using a three-electrode system, reached 1.01Fcm-2 at a current density of 2.187mAcm-2. The performance improvement is attributed to the synergistic interaction among SmVO4, MoS2, and CNTs, collectively enhancing conductivity and active site availability. The practical application of this study is demonstrated by synthesizing Sm-Mo-C5 on woven carbon fiber (WCF) and subsequently fabricating a structural supercapacitor device (SSD) using the VARTM. The SSD, produced via VARTM, exhibited a specific capacitance of 0.287Fcm- 2 at a current density of 2Acm-2. The device showcased exceptional cyclic stability, maintaining 72.5% of its initial capacitance after 50,000 charge-discharge cycles. Additionally, it achieved a maximum energy density of 79.86Whkg-1 at a power density of 1017.69Wkg-1.

Grid-Like Structured Sb@DNC Anode by Self-Sacrificial Etching for Fast and Durable Sodium Storage.

Alloying-type materials are promising anodes for sodium storage due to high specific capacities and appropriate redox potentials, but their practical application is impeded by rapid capacity decay from volume change during sodium ion insertion/extraction. Hence, a dual-type N-doped carbon-confined antimony (Sb) nanoparticle (Sb@DNC, where DNC contains an outer N-doped carbon armor and an inner N-doped grid-like carbon skeleton) anode material is fabricated via a self-sacrificial etching strategy to address this challenge. Specifically, the dual-type N-doped carbon matrix can prevent the agglomeration and precipitation of Sb particles, increase a large number of reactive active sites, alleviate severe volume expansion/contraction, and construct a highly interconnected electron/ion transport network. Benefiting from the exquisite structure, the Sb@DNC electrode exhibits excellent cycling stability (2400 cycles at 1.0 A g-1) and astonishing high-rate performance (331.0 mAh g-1 at 10.0 A g-1). Additionally, the state-of-the-art in/ex situ technologies reveals the sodium storage mechanism of the "battery-capacitance dual-mode" and the origin of the ability to withstand continuous volumetric strain for the Sb@DNC electrode. Finally, the derived sodium-ion full cell presents outstanding practical potential. This work emphasizes the great significance of rational structural engineering strategies in the field of alloy-type anode materials for high-performance sodium-ion batteries.

Organic cation‐supported layered vanadate cathode for high‐performance aqueous zinc‐ion batteries

AbstractLayered vanadates are ideal energy storage materials due to their multielectron redox reactions and excellent cation storage capacity. However, their practical application still faces challenges, such as slow reaction kinetics and poor structural stability. In this study, we synthesized [Me2NH2]V3O7 (MNVO), a layered vanadate with expended layer spacing and enhanced pH resistance, using a one‐step simple hydrothermal gram‐scale method. Experimental analyses and density functional theory (DFT) calculations revealed supportive ionic and hydrogen bonding interactions between the thin‐layered [Me2NH2]+ cation and [V3O7]− anion layers, clarifying the energy storage mechanism of the H+/Zn2+ co‐insertion. The synergistic effect of these bonds and oxygen vacancies increased the electronic conductivity and significantly reduced the diffusion energy barrier of the insertion ions, thereby improving the rate capability of the material. In an acidic electrolyte, aqueous zinc‐ion batteries employing MNVO as the cathode exhibited a high specific capacity of 433 mAh g−1 at 0.1 A g−1. The prepared electrodes exhibited a maximum specific capacity of 237 mAh g−1 at 5 A g−1 and maintained a capacity retention of 83.5% after 10,000 cycles. This work introduces a novel approach for advancing layered cathodes, paving the way for their practical application in energy storage devices.

Interface engineering enabling thin lithium metal electrodes down to 0.78 μm for garnet-type solid-state batteries.

Controllable engineering of thin lithium (Li) metal is essential for increasing the energy density of solid-state batteries and clarifying the interfacial evolution mechanisms of a lithium metal negative electrode. However, fabricating a thin lithium electrode faces significant challenges due to the fragility and high viscosity of Li metal. Herein, through facile treatment of Ta-doped Li7La3Zr2O12 (LLZTO) with trifluoromethanesulfonic acid, its surface Li2CO3 species is converted into a lithiophilic layer with LiCF3SO3 and LiF components. It enables the thickness control of Li metal negative electrodes, ranging from 0.78 μm to 30 μm. Quasi-solid-state lithium-metal battery with an optimized 7.54 μm-thick lithium metal negative electrode, a commercial LiNi0.83Co0.11Mn0.06O2 positive electrode, and a negative/positive electrode capacity ratio of 1.1 shows a 500 cycles lifespan with a final discharge specific capacity of 99 mAh g-1 at 2.35 mA cm-2 and 25 °C. Through multi-scale characterizations of the thin lithium negative electrode, we clarify the multi-dimensional compositional evolution and failure mechanisms of lithium-deficient and -rich regions (0.78 μm and 7.54 μm), on its surface, inside it, or at the Li/LLZTO interface.

Intercalation of Polyacrylonitrile Nanoparticles in Ti3C2Tx MXene Layers for Improved Supercapacitance.

We report the intercalation of polyacrylonitrile nanoparticles in Ti3C2Tx MXene layers through simple sonication. The use of polyacrylonitrile, which was synthesized via radical polymerization, offered dual benefits: (1) It increased the interlayer spacing of MXene, thereby exposing more surface area and enhancing ion transport channels during charge and discharge cycles, and (2) Integrating MXene with polyacrylonitrile enables the creation of a composite with conductive properties, following percolation principle. X-ray diffraction analysis showed an increase in the c-lattice parameter, indicative of the interlayer spacing, from 22.31 Å for the pristine MXene to 37.73 Å for the MXene-polyacrylonitrile composite. The intercalated polyacrylonitrile nanoparticles facilitated the delamination by weakening the interlayer interactions, especially during sonication. Electrochemical assessments revealed significant improvement in the properties of the MXene-polyacrylonitrile composite compared to the pristine MXene. The assembled asymmetric device achieved a good specific capacitance of 32.1 F/g, an energy density of 11.42 W h/kg, and 82.2% capacitance retention after 10,000 cycles, highlighting the practical potential of the MXene-polyacrylonitrile composite.

The Investigation of Fe─F Bond Chemistry on Structural Stability for Highly Durable Layered Na2FePO4F Cathode

AbstractLayered iron (Fe) ‐based fluorophosphates, Na2FePO4F (NFPF) stands for a cost‐effective and voltage‐advantageous cathode material for sodium‐ion batteries. Nevertheless, the lack of stability imposes constraints on its development and the decay mechanism remains shrouded in ambiguity. Herein, this work proposes the breakup of Fe─F bond in octahedral dimer accountable for the dissolution of redox centers and the formation of electrochemically inert phase, ultimately leading to the deterioration of electrochemical stability. To verify and address this, Boron (B) atoms situated in interstitial positions of PO4 tetrahedra appearing trigonal BO3 can be specifically targeted to enhance bond covalency and tailor electronic rearrangements at Fe─F bonds, thus stabilizing the octahedral dimer structure. This also facilitates rapid Na+ diffusion dynamics and accelerated electronic conductivity. As expected, NFPF‐B exhibits an ultra‐high discharge specific capacity (118.34 mAh g−1 at 0.1C) and excellent long‐term durability (capacity retention of 91.9% after 1000 cycles). The stability of the octahedra dimer is underscored by minimal volume change (2.9%) within the two‐stage biphase reaction of sodium storage mechanism. This work elucidates the enduring degradation mechanism of NFPF from octahedral dimers and offer theoretical guidance for Fe‐based cathode materials with prolonged stability.

Constructing High‐Performance Zn‐Iodine Batteries with CuI‐PVP Composite Layer Coated Zn Anodes

AbstractAqueous zinc‐iodine (Zn‐I2) batteries featuring abundant raw materials, inherent safety, excellent cost competitiveness and environmental benignity have been identified as one kind of important electrochemical energy storage devices. However, these batteries always suffer from inferior electrochemical performance, because of dendrite growth and corrosion/passivation of the anodes. Herein, a copper iodide‐polyvinylpyrrolidone (CuI‐PVP) composite layer is proposed to suppress the parasitic reactions and protect the Zn anodes. In this layer, the CuI can spontaneously react with metallic Zn and convert into Cu and Cu5Zn8 (2CuI+Zn→2Cu+ZnI2; 5Cu+8Zn→Cu5Zn8). The highly zincophilic Cu and Cu5Zn8, as heterogeneous seeds, can guide the uniform Zn nucleation and deposition, while alleviating corrosion of the Zn anodes. At the same time, the iodide species releasing from the composite layer can be oxidized and deposited on the cathodes, contributing additional capacity. As a result, the symmetric cell prepared with the CuI‐PVP@Zn anodes demonstrates a long cycling lifetime of 1400 hours at 1 mA cm−2 and 1 mAh cm−2. Under an even higher current density of 5 mA cm−2, the CuI‐PVP@Zn cell can still stably work for more than 660 hours. The practical application of this CuI‐PVP@Zn electrode has been further demonstrated in Zn‐I2 full batteries, which achieve 60 % higher specific capacity than the untreated ones (251.4 vs. 157.1 mAh g−1 after 2800 cycles).

Metal-Hydroxide Organic Frameworks for Aqueous Nickel-Zinc Batteries.

Hydroxides exhibit a high theoretical capacity for energy storage by ion release and are often intercalated with anions to enhance the ion migration kinetics. In this study, a series of metal-hydroxide organic frameworks (MHOFs) are synthesized by intercalating aromatic organic linkers into hydroxides using I-M/Ni(OH)2 (where M = Co2+, Cu2+, Mg2+, Fe2+). The coordination environment and layer spacing (1.09 nm) of I-M/Ni(OH)2 are explored by X-ray absorption fine structure and cryo-electron microscopy. The intercalation nanostructure improves the conductivity of the hydroxides and facilitates Zn2+ migration by increasing the interlayer spacing, while enhancing the rate capability and cycling stability. Consequently, the I-Co/Ni(OH)2 material exhibites a satisfactory specific capacity of 0.35 mAh cm-2 at 3 mA cm-2 and a high peak power density of 6.78 mW cm-2. This study offers a novel perspective on the design of intercalated hydroxide and provides new insights into high-performance nickel-zinc batteres.

Revealing the Dual Role of Ammonia in the Hydroxide Co-precipitation Synthesis of Cobalt-free Nickel-rich LiNi0.9Mn0.05Al0.05O2 (NMA955) Cathode Materials for Lithium-ion Batteries.

Nickel-rich cobalt-free LiNi0.9Mn0.05Al0.05O2 (NMA955) is considered a promising cathode material to address the scarcity and soaring cost of cobalt. Particle size and elemental composition significantly impact the electrochemical performance of NMA955 cathodes. However, differences in precipitation rates among metal ions coveys a challenge in obtaining cathode materials with the desired particle size and composition via hydroxide co-precipitation synthesis. Utilizing complexing agents like ammonia offers an effective strategy to tackle these issues. Here, we investigate the optimal ammonia concentration to achieve moderate particle size and precise material composition. Although ammonia only forms complex coordination with transition metals, its concentration also affects the final product's precipitation and composition, including aluminum. This study shows that ammonia serves a dual function in NMA synthesis via hydroxide co-precipitation, i.e., regulating particle size and adjusting elemental composition. It was found that an ammonia concentration of 1.2 M achieved optimal particle size and composition, resulting in superior electrochemical performance. NMA955 synthesized in 1.2 M ammonia demonstrated a high specific capacity of 188.12 mAh g-1 at 0.1C, retained 71.16% of its capacity after 200 cycles at 0.2C, and delivered 110.30 mAh g-1 at 5C. These results suggest tuning ammonia concentration is crucial for producing high-performance cathode materials.

Enhancing activated carbon supercapacitor electrodes using sputtered Cu-doped BiFeO3 thin films.

This work describes the fabrication of a composite supercapacitor electrode made of Cu-doped BiFeO (Cu-BFO) films on an activated carbon (AC) electrode using radio-frequency (RF) magnetron sputtering. To prevent exfoliation of Cu-BFO and AC upon immersion in an electrolyte, the nickel foam sandwiching electrode technique was introduced. The Cu-BFO films significantly enhanced electrochemical properties, increasing specific capacitance by up to 151% compared to that of an AC electrode. This was attributed to Faradaic reactions and specific surface area in the Cu-BFO/AC electrode. The highest specific capacitance achieved was 169 F at 0.5 A , and cycling stability retention was 93.12% after 500 cycles. However, the remaining percentage of the specific capacitance decreased differently with increasing thickness, which is also discussed. Furthermore, an asymmetric supercapacitor using Cu-BFO/AC and AC electrodes demonstrated a high energy density of 4.71 Wh , power density of 2.66 kW , and over 90% retention after 1000 cycles, highlighting its durability. The uniform RF magnetron sputtering deposition is vital for mass production. Combined with impressive retention in asymmetric supercapacitors, this scalability suggests a promising pathway for large-scale manufacturing. Consequently, this work could pave the way for the large-scale production of supercapacitors.

A Method of Efficiently Regenerating Waste LiFePO4 Cathode Material after Air Firing Treatment.

Waste LiFePO4 (LFP) batteries can be harmful to the environment and lead to waste of resources if not properly disposed of. In this study, an efficient and environmentally friendly method for solid-phase recycling waste LFP cathode material (W-LFP) is proposed. Most of the impurities in the W-LFP are removed by air firing. The regenerated LFP is then obtained by adding lithium carbonate and triethanolamine for repair during heat treatment. The addition of triethanolamine converts Fe3+ to Fe2+ and also allows the formation of an N-doped modified carbon layer on the surface of the LFP particles, which improves the electrochemical properties of the regenerated material. Physical characterization and electrochemical tests are used to investigate the attenuation and regeneration mechanism of LFP. The regenerated LFP possesses a high specific discharge capacity (152.87 mAh g-1 at 0.2 C), which is about 95.32% of the commercial LFP, and the capacity retention rate is 88.52% after 600 cycles at 1 C. It is worth noting that we do not use solvents such as acids and alkalis in the regeneration process, thus avoiding the generation of large quantities of acid and alkaline waste liquids, which is friendly to the environment. This solid-phase regeneration process offers a promising method for the future recycling of used LFP batteries because of its simplicity, environmental friendliness, and high efficiency.

Multiple Strategies to Build High-Performance Spherical Na-Ion Layered Oxide Cathodes.

The development prospect of layered transition metal oxides in sodium-ion batteries is excellent, but there are some problems, such as poor cycle stability and a complex phase transition. The spherical NaNi0.25Fe0.15Mn0.3Ti0.1Sn0.05Co0.05Li0.1O2 (SP-HEO) has been developed to address the challenges faced by O3-type layered oxide in sodium-ion batteries. The SP-HEO material is synthesized by piling and high entropy. The multiple strategies combine to enhance the electrochemical performance and air stability. The SP-HEO demonstrated a specific discharge capacity of 150.1 mA h g-1 at 0.1 C and 100.4 mA h g-1 at 7 C. Ex situ XRD analysis confirmed that the SP-HEO effectively retards complex phase transitions. This study not only introduces a high-entropy design for high tap density spherical storage materials but also dispels industry concerns regarding the performance of sodium ion layered oxide cathode materials.