Highly Reversible and Rapid Sodium Storage in GeP3 with Synergistic Effect from Outside-In Optimization

Metal Phosphide Anodes in Sodium-Ion Batteries: Latest Applications and Progress

Sodium-ion batteries (SIBs), as the next-generation high-performance electrochemical energy storage devices, have attracted widespread attention due to their cost-effectiveness and wide geographical distribution of sodium. As a crucial component of the structure of SIBs, the anode material plays a crucial role in determining its electrochemical performance. Significantly, metal phosphide exhibits remarkable application prospects as an anode material for SIBs because of its low redox potential and high theoretical capacity. However, due to volume expansion limitations and other factors, the rate and cycling performance of metal phosphides have gradually declined. To address these challenges, various viable solutions have been explored. In this paper, the recent research progress of metal phosphide materials for SIBs is systematically reviewed, including the synthesis strategy of metal phosphide, the storage mechanism of sodium ions, and the application of metal phosphide in electrochemical aspects. In addition, future challenges and opportunities based on current developments are presented.

A High-Voltage Cathode Material with Ultralong Cycle Performance for Sodium-Ion Batteries

Vanadium-based polyanionic materials are promising electrode materials for sodium-ion batteries (SIBs) due to their outstanding advantages such as high voltage, acceptable specific capacity, excellent structural reversibility, good thermal stability, etc. Polyanionic compounds, moreover, can exhibit excellent multiplicity performance as well as good cycling stability after well-designed carbon covering and bulk-phase doping and thus have attracted the attention of multiple researchers in recent years. In this paper, after the modification of carbon capping and bulk-phase nitrogen doping, compared to pristine Na3 V2 (PO4 )3 , the well optimized Na3 V(PO3 )3 N/C possesses improved electromagnetic induction strength and structural stability, therefore exhibits exceptional cycling capability of 96.11% after 500 cycles at 2 C (1 C = 80 mA g-1 ) with an elevated voltage platform of 4 V (vs Na+ /Na). Meanwhile, the designed Na3 V(PO3 )3 N/C possesses an exceptionally low volume change of ≈0.12% during cycling, demonstrating its quasi-zero strain property, ensuring an impressive capacity retention of 70.26% after 10,000 cycles at 2 C. This work provides a facial and cost-effective synthesis method to obtain stable vanadium-based phosphate materials and highlights the enhanced electrochemical properties through the strategy of carbon rapping and bulk-phase nitrogen doping.

Molten salt synthesis of disordered spinel CoFe2O4 with improved electrochemical performance for sodium-ion batteries

Sodium-ion (Na-ion) batteries are currently being investigated as an attractive substitute for lithium-ion (Li-ion) batteries in large energy storage systems because of the more abundant and less expensive supply of Na than Li. However, the reversible capacity of Na-ions is limited because Na possesses a large ionic radius and has a higher standard electrode potential than that of Li, making it challenging to obtain electrode materials that are capable of storing large quantities of Na-ions. This study investigates the potential of CoFe2O4 synthesised via the molten salt method as an anode for Na-ion batteries. The obtained phase structure, morphology and charge and discharge properties of CoFe2O4 are thoroughly assessed. The synthesised CoFe2O4 has an octahedron morphology, with a particle size in the range of 1.1-3.6 μm and a crystallite size of ∼26 nm. Moreover, the CoFe2O4 (M800) electrodes can deliver a high discharge capacity of 839 mA h g-1 in the first cycle at a current density of 0.1 A g-1, reasonable cyclability of 98 mA h g-1 after 100 cycles and coulombic efficiency of ∼99%. The improved electrochemical performances of CoFe2O4 can be due to Na-ion-pathway shortening, wherein the homogeneity and small size of CoFe2O4 particles may enhance the Na-ion transportation. Therefore, this simple synthetic approach using molten salt favours the Na-ion diffusion and electron transport to a great extent and maximises the utilisation of CoFe2O4 as a potential anode material for Na-ion batteries.

Disclosing the Origin of Irreversible Sodiation-Desodiation of a Cu4SnP10 Nanowire Anode by Ex Situ Transmission Electron Microscopy

Cu₄SnP₁₀, a promising phosphide material for sodium-ion battery anode applications, suffers from poor cycling stability, and its mechanism remains unclear. This is largely due to the amorphous nature of the active materials upon cycling and its possible structural change at a small length scale (e.g., nanometers), making it difficult to access the phase/structural evolution of the electrode. In the present work, we show that the phase/structural change of the Cu₄SnP₁₀ nanowire electrode can be systematically investigated using a comprehensive set of ex situ transmission electron microscopy-based techniques, which are ideal for decay mechanism analysis of electrode materials of amorphous nature and with nanoscale structural evolution. The compositional elements of Cu₄SnP₁₀ nanowires are found to be spatially redistributed at a nanometer scale upon the initial sodiation, and this is partially reversible in the following desodiation process. Damage accumulates until a critical size of phase separation/segregation is reached, when the active material loss takes place, leading to fast deterioration of the entire Cu₄SnP₁₀ nanowire structure and thus its electrochemical performance. The phase segregation driven-active material loss is found to dominate the cycle-dependent capacity decay of the Cu₄SnP₁₀ nanowire electrode.

Bimetallic phosphide AlP/SiP2 composite as an anode material for lithium-ion batteries with long cycle life

AlP and SiP₂ are promising alloy-type anode materials for lithium-ion batteries (LIBs), owing to their good conductivity, high storage capacity and appropriate working potential. However, they still suffer from rapid capacity decay due to the huge volume expansion and the resultant pulverization. Carbon modification can not only relieve volume changes but also provide a conducting matrix for the active material. Moreover, the charge transfer of the multi-phase composite can be accelerated owing to its electric field at the heterointerface. Hence, a bimetallic phosphide AlP/SiP₂@C composite was synthesized for the first time via a facile and scalable high energy ball milling method and applied as an anode material for LIBs. Benefitting from the above combined advantages of the heterostructure and carbon layer protection, the AlP/SiP₂@C electrode delivered a high reversible capacity (1482 mA h g^-1 at the current density of 0.3 A g^-1) and durable lifespan (516 mA h g^-1 after 4000 cycles at a current density of 3 A g^-1), which are superior to those of the binary AlP@C and SiP₂@C composites.

Conversion-Alloying Anode Materials for Sodium Ion Batteries

The past decade has witnessed a rapidly growing interest toward sodium ion battery (SIB) for large-scale energy storage in view of the abundance and easy accessibility of sodium resources. Key to addressing the remaining challenges and setbacks and to translate lab science into commercializable products is the development of high-performance anode materials. Anode materials featuring combined conversion and alloying mechanisms are one of the most attractive candidates, due to their high theoretical capacities and relatively low working voltages. The current understanding of sodium-storage mechanisms in conversion-alloying anode materials is presented here. The challenges faced by these materials in SIBs, and the corresponding improvement strategies, are comprehensively discussed in correlation with the resulting electrochemical behavior. Finally, with the guidance and perspectives, a roadmap toward the development of advanced conversion-alloying materials for commercializable SIBs is created.

Two-Phase Transition Induced Amorphous Metal Phosphides Enabling Rapid, Reversible Alkali-Metal Ion Storage

Metal phosphides as anode materials for alkali-metal ion batteries have captured considerable interest due to their high theoretical capacities and electronic conductivity. However, they suffer from huge volume expansion and element segregation during repetitive insertion/extraction of guest ions, leading to structure deterioration and rapid capacity decay. Herein, an amorphous Sn_0.5Ge_0.5P₃ was constructed through a two-phase intermediate strategy based on the elemental composition modulation from two crystalline counterparts and applied in alkali-metal ion batteries. Differing from crystalline P-based compounds, the amorphous structure of Sn_0.5Ge_0.5P₃ effectively reduces the volume variation from above 300% to 225% during cycling. The ordered distribution of cations and anions in the short-range ensures the uniform distribution of each element during cycles and thus contributes to durable cycling stability. Moreover, the long-range disordered structure of amorphous material shortens the ion transport distance, which facilitates diffusion kinetics. Benefiting from the aforementioned effects, the amorphous Sn_0.5Ge_0.5P₃ delivers a high Na storage capacity of 1132 mAh g^-1 at 0.1 A g^-1 over 100 cycles. Even at high current densities of 2 and 10 A g^-1, its capacities still reach 666 and 321 mAh g^-1, respectively. As an anode for Li storage, the Sn_0.5Ge_0.5P₃ similarly also exhibits better cycling stability and rate performance compared to its crystalline counterparts. Significantly, the two-phase transition strategy is generally applicable to achieving other amorphous metal phosphides such as GeP₂. This work would be helpful for constructing high-performance amorphous anode materials for alkali-metal ion batteries.

Tailor-Made Gives the Best Fits: Superior Na/K-Ion Storage Performance in Exclusively Confined Red Phosphorus System

As the most promising anodic candidate for alkali ion batteries, red phosphorus (P) still faces big challenges, such as the poor rate and cycling performance, which are caused by the insulative nature and the large volume change throughout the alloy/dealloy process. To ameliorate above issues, the traditional way is confining P into the carbon host. However, investigations on maximizing P utilization are inadequate; in other words, how to achieve entire confinement with a high loading amount is still a problem. Additionally, the application of P in potassium-ion batteries (PIBs) is in its infant stage, and the corresponding potassiation product is controversial. Herein, a nitrogen-doped stripped-graphene CNT (N-SGCNT) as carbon framework is prepared to exclusively confine ultrafine P to construct P@N-SGCNT composites. Benefitting from the in situ cross-linked structure, N-SGCNT loaded with 41.2 wt % P (P₂@N-SGCNT) shows outstanding Na⁺/K⁺ storage performance. For instance, P₂@N-SGCNT exhibits high reversible capacities of 2480 mAh g^-1 for sodium-ion batteries (SIBs) and 762 mAh g^-1 for PIBs, excellent rate capabilities of 1770 mAh g^-1 for SIBs and 354 mAh g^-1 for PIBs at 2.0 A g^-1, and long cycling stability (a capacity of 1936 mAh g^-1 after 2000 cycles for SIBs and 319 mAh g^-1 after 1000 cycles for PIBs). Furthermore, due to this exclusively confined P structure, the K⁺ storage mechanism with the end product of K₄P₃ has been identified by experimental and theoretical results.