Nickel and nickel oxide nanoparticle-embedded functional carbon nanofibers for lithium sulfur batteries

Lithium-sulfur (Li-S) batteries are attracting tremendous attention owing to their critical advantages, such as high theoretical capacity of sulfur, cost-effectiveness, and environment-friendliness. Nevertheless, the vast commercialisation of Li-S batteries is severely hindered by sharp capacity decay upon operation and shortened cycle life because of the insulating nature of sulfur along with the solubility of intermediate redox products, lithium polysulfides (LiPSs), in electrolytes. This work proposes the use of multifunctional Ni/NiO-embedded carbon nanofibers (Ni/NiO@CNFs) synthesized by an electrospinning technique with the corresponding heat treatment as promising free-standing current collectors to enhance the kinetics of LiPS redox reactions and to provide prolonged cyclability by utilizing more efficient active materials. The electrochemical performance of the Li-S batteries with Ni/NiO@CNFs with ∼2.0 mg cm-2 sulfur loading at 0.5 and 1.0C current densities delivered initial specific capacities of 1335.1 mA h g-1 and 1190.4 mA h g-1, retrieving high-capacity retention of 77% and 70% after 100 and 200 cycles, respectively. The outcomes of this work disclose the beneficial auxiliary effect of metal and metal oxide nanoparticle embedment onto carbon nanofiber mats as being attractively suited up to achieve high-performance Li-S batteries.

Exploiting High-Voltage Stability of Dual-Ion Aqueous Electrolyte Reinforced by Incorporation of Fiberglass into Zwitterionic Hydrogel Electrolyte

Rechargeable zinc aqueous batteries are key alternatives for replacing toxic, flammable, and expensive lithium-ion batteries in grid energy storage systems. However, these systems possess critical weaknesses, including the short electrochemical stability window of water and intrinsic fast zinc dendrite growth. Hydrogel electrolytes provide a possible solution, especially cross-linked zwitterionic polymers that possess strong water retention ability and high ionic conductivity. Herein, an in situ prepared fiberglass-incorporated dual-ion zwitterionic hydrogel electrolyte with an ionic conductivity of 24.32 mS cm-1 , electrochemical stability window up to 2.56 V, and high thermal stability is presented. By incorporating this hydrogel electrolyte of zinc and lithium triflate salts, a zinc//LiMn0.6 Fe0.4 PO4 pouch cell delivers a reversible capacity of 130 mAh g-1 in the range of 1.0-2.2 V at 0.1C, and the test at 2C provides an initial capacity of 82.4 mAh g-1 with 71.8% capacity retention after 1000 cycles with a coulombic efficiency of 97%. Additionally, the pouch cell is fire resistant and remains safe after cutting and piercing.

Catalytic effects of Ni nanoparticles encapsulated in few-layer N-doped graphene and supported by N-doped graphitic carbon in Li–S batteries†

Although lithium–sulfur batteries possess the highest theoretical capacity and lowest cost among all known rechargeable batteries, their commercialization is still hampered by the intrinsic disadvantages of low conductivity of sulfur and polysulfide shuttle effect, which is most critical. Considerable research efforts have been dedicated to solving these difficulties for every part of Li–S batteries. Separator modification with metal electrocatalysts is a promising approach to overcome the major part of these disadvantages. This work focuses on the development of Ni nanoparticles encapsulated in a few-layer nitrogen-doped graphene supported by nitrogen-doped graphitic carbon (Ni@NGC) with different metal loadings as separator modifications. The effect of metal loading on the Li–S electrochemical reaction kinetics and performance of Li–S batteries was investigated. Controlling the Ni loading allowed for the modulation of the surface area-to-metal content ratio, which influenced the reaction kinetics and cycling performance of Li–S cells. Among the separators with different Ni loadings, the one with 9 wt% Ni exhibited the most efficient acceleration of the polysulfide redox reaction and minimized the polysulfide shuttling effect. Batteries with this separator retained 77.2% capacity after 200 cycles at 0.5C, with a high sulfur loading of ∼4.0 mg cm⁻², while a bare separator showed 51.3% capacity retention after 200 cycles under the same conditions. This work reveals that there is a vast utility space for carbon-encapsulated Ni nanoparticles in electrochemical energy storage devices with optimal selection and rational design.

Ni@NGC with different contents of Ni coated onto the surface of commercial separators effectively suppresses the polysulfide shuttle effect and enhances the electrochemical reaction kinetics and overall performance of a Li–S battery.

KTi2 (PO4 )3 Electrode with a Long Cycling Stability for Potassium-Ion Batteries

In this work, rhombohedral KTi₂ (PO₄ )₃ is introduced to investigate the related theoretical, structural, and electrochemical properties in K cells. The suggested KTi₂ (PO₄ )₃ modified by electro-conducting carbon brings about a flat voltage profile at ≈1.6 V, providing a large capacity of 126 mAh (g-phosphate)^-1 , corresponding to 98.5% of the theoretical capacity, with 89% capacity retention for 500 cycles. Structural analyses using electrochemical performance measurements, first-principles calculations, ex situ X-ray absorption spectroscopy, and operando X-ray diffraction provide new insights into the reaction mechanism controlling the (de)intercalation of potassium ions into the host KTi₂ (PO₄ )₃ structure. It is observed that a biphasic redox process by Ti^4+/3+ occurs upon discharge, whereas a single-phase reaction followed by a biphasic process occurs upon charge. Along with the structural refinement of the electrochemically reduced K₃ Ti₂ (PO₄ )₃ phase, these new findings provide insight into the reaction mechanism in Na superionic conductor (NASICON)-type KTi₂ (PO₄ )₃ . The present approach can also be extended to the investigation of other NASICON-type materials for potassium-ion batteries.

P2-Na2/3MnO2 by Co Incorporation: As a Cathode Material of High Capacity and Long Cycle Life for Sodium-Ion Batteries

The P2-Na_2/3MnO₂ compound is one of the attractive cathodes for sodium-ion batteries due to its high initial capacity and abundance of Na and Mn elements in nature. The existence of Mn³⁺ Jahn-Teller ion, however, impedes electrode performance for long term. Here, we challenge to minimize the effect of the Jahn-Teller distortion caused by Mn³⁺ in the structure, via substitution of Mn³⁺ by Co³⁺ in P2-Na_2/3[Mn_1-xCo_x]O₂ (x = 0-0.3). The P2-Na_2/3[Mn_0.8Co_0.2]O₂ compound substantializes the electrochemical performance with a capacity of about 175 mAh g^-1 (26 mA g^-1) and retained over 90% of its initial capacity for 300 cycles at 0.1 C (26 mA g^-1) and 10 C (2.6 A g^-1). The operando X-ray diffraction study indicates that a single-phase reaction is associated with the insertion of sodium ions into the structure, accompanied by a small volume change of approximately 3%. Furthermore, ex situ X-ray diffraction and high-resolution transmission electron microscopy results show that the crystal structure remained after 300 continuous cycles. It is believed that such good electrode performances attribute to the structural stabilization assisted by the presence of Co³⁺ in the crystal structure. Our finding provides a way to take advantage of low-cost Mn-rich cathode materials for sodium-ion batteries.