Inlaying Bismuth Nanoparticles on Graphene Nanosheets by Chemical Bond for Ultralong-Lifespan Aqueous Sodium Storage

Pre-intercalated Sodium Ions Enhance Sodium Storage of MoS2 Anode by Mitigating Structural Dissociation

Molybdenum disulfide (MoS2) is a promising anode for sodium-ion batteries (SIBs) due to its high theoretical capacity and layered structure. However, a poor reversible conversion reaction and a low initial Coulombic efficiency (ICE) limit its practical application. This study systematically investigated the potential of pre-intercalated sodium ions molybdenum disulfide (Na-MoS2) as an anode material for SIBs. Because of the mitigation of MoS2 structural dissociation and effective replenishment of active sodium ions, Na-MoS2 delivered an outstanding capacity of 507.7 mAh g-1 after 2000 cycles at 5 A g-1, along with an ICE of 95.30%. Pre-intercalating sodium ions can expand interlayer spacing and modulate electronic structure, allowing Na-MoS2 to have greater tolerance to the electrochemical intercalation/extraction process. Furthermore, the conversion reaction of Na-MoS2 has a higher Gibbs free energy, implying its structural dissociation is thermodynamically unfavorable. This work provides a new perspective on the study of transition metal dichalcogenide electrode materials for SIBs.

High-Voltage Fe-Based Tunnel-Type Na0.66[Mn0.33Fe0.33Ti0.3Sn0.04]O2 Cathode for Aqueous Rechargeable Sodium-Ion Battery

Tunnel-type-structure Na0.44MnO2 has been extensively researched for cathode material in aqueous rechargeable sodium-ion battery owing to its high specific capacity (120 mA h g-1), large channels facilitating Na extraction/insertion, chemical and electrochemical stability in aqueous electrolytes, and low cost. However, the low average working potential (0.1 V versus standard hydrogen electrode, SHE) and no more than half of its available theoretical capacity within full batteries limit the practical application. Herein, we develop an Fe-based tunnel-type Na0.66[Mn0.33Fe0.33Ti0.3Sn0.04]O2 cathode, delivering a high reversible specific capacity (95 mA h g-1) under a high working voltage (0.75 V versus SHE). A full battery, assembled with a NaTi2(PO4)3@C anode, exhibits a high energy density of 80 W h kg-1 (total mass of cathode and anode active materials) and a long cycle life with 84% capacity retention after 1000 cycles at 1 C.

Bismuth nanoparticles embedded in carbon fibers as flexible and free-standing anodes for efficient sodium ion batteries

Metallic bismuth is a promising anode electrode material for sodium ion batteries due to its high theoretical specific capacity. However, the formation of Na3Bi during the reaction process brings about significant volume changes and structural collapse of the electrode, resulting in the destruction of structures and a decrease in the cycling stability of sodium ion batteries. In this study, bismuth nanoparticles embedded in carbon fibers (Bi/CF) through a facile approach of electrospinning and calcination. Bi nanoparticles with diameters of approximately 20 nm were homogeneously dispersed in the carbon fibers, as confirmed by relevant morphological and structural features. The carbon fiber substrate can serve as a flexible and free-standing electrode, forming a conductive network to accelerate electron transport and ion diffusion. In light of this, Bi/CF anodes exhibit a high reversible capacity (376.6 mA h g-1 at 0.1 A g-1) and long-term cycle stability (only attenuates 0.12% in each cycle after 2000 times). This work provides a convenient and effective strategy for the synthesis of flexible and free-standing anodes for high-performance sodium ion batteries.

On the remarkable resistance to oxidation by the Bi18- cluster

The reactivity of Bin- clusters (n = 2 to 30) with O2 is found to display even-odd alternations. The open-shell even-sized Bin- clusters are more reactive than the closed-shell odd-sized clusters, except Bi18-, which exhibits no observable reactivity toward O2. We have investigated the structure and bonding of Bi18- to understand its remarkable resistance to oxidation. We find that the most stable structure of Bi18- consists of two Bi8 cages linked by a Bi2 dimer, where each atom is bonded to three neighboring atoms. Chemical bonding analyses reveal that each Bi uses its three 6p electrons to form three covalent bonds with its neighbors, resulting in a Bi18- cluster without any dangling bonds. We find that the robust Bi18 framework along with the totally delocalized unpaired electron is responsible for the surprising inertness of Bi18- toward O2. The Bi18 framework is similar to that in Hittorf's phosphorus, suggesting the possibility to create bismuth nanoclusters with interesting structures and properties.

Ionic Competition between Na+ and H+ in Aqueous Sodium-Ion Battery Electrolytes

Aqueous electrolytes have become a research hotspot because of their high safety and low cost, while the inevitable ionization phenomenon of water in aqueous solution leads to the existence of competitive ions (H+) except the active ions. In this article, we take aqueous Na base electrolyte as an example to clear the ion competition behavior by modeling, simulating together with experimental verification. First, the reaction tendency of the two ions (Na+ and H+) is obtained by calculating the Gibbs energy change of the reaction. Furthermore, the properties of electrolytes with different concentrations including transportation are obtained by modeling. After that, relevant experiments are also proceeded to verify the simulation results. Then, the ion competition behavior is analyzed by in situ observation by controlling the constant concentration of Na+: the high concentration of Na+ can reduce the proportion of H+ and reduce the competitiveness of H+; a high concentration of Na+ causes the increased viscosity and reduces the ion diffusion. Based on this, the correlation between ion competitiveness and ion ratio is also confirmed by keeping the concentration of Na+ unchanged and adjusting the concentration of H+ (adjusting pH). The influence of the ion competition phenomenon (Na+ and H+) is the reaction characteristics of the substance itself and the ratio of ion concentration. Finally, the electrochemical performance is further verified in 3,4,9,10-perylene tetracarboxylic dianhydride (PTCDI) symmetric cells and in full-cells with vanadium phosphate sodium (NVP) as the cathode and PTCDI as the anode.

Advances in Electrochemical Energy Storage over Metallic Bismuth-Based Materials

Bismuth (Bi) has been prompted many investigations into the development of next-generation energy storage systems on account of its unique physicochemical properties. Although there are still some challenges, the application of metallic Bi-based materials in the field of energy storage still has good prospects. Herein, we systematically review the application and development of metallic Bi-based anode in lithium ion batteries and beyond-lithium ion batteries. The reaction mechanism, modification methodologies and their relationship with electrochemical performance are discussed in detail. Additionally, owing to the unique physicochemical properties of Bi and Bi-based alloys, some innovative investigations of metallic Bi-based materials in alkali metal anode modification and sulfur cathodes are systematically summarized for the first time. Following the obtained insights, the main unsolved challenges and research directions are pointed out on the research trend and potential applications of the Bi-based materials in various energy storage fields in the future.