MXenes, as a new type of two-dimensional layered structure material, have attracted much attention. MXenes have high electronic conductivity, a large specific area, excellent mechanical properties ...and a unique layered structure and have been extensively used in energy storage, adsorption, catalysis and other fields. In recent years, Mxenes and their composite materials have been widely used in the field of secondary batteries. Although oxides, sulfides and other materials have high capacity, there are problems such as low conductivity, volume expansion in the reaction process, poor cycling stability,
etc
. Therefore, building composite materials with MXenes can not only improve the capacity but also enhance the electronic conductivity of the materials, effectively alleviate volume expansion in the reaction process, and achieve better electrochemical performance. This article reviews the latest research status of MXenes, the synthesis methods, properties and application of MXenes and their composite materials in sodium-ion batteries (SIBs) and potassium-ion batteries (PIBs), briefly introduces the research background of SIBs, PIBs and MXenes, and focuses on the application research of MXene composite materials in SIBs and PIBs, including classification according to sulfide, oxide and carbon materials. Finally, the development and application prospects of MXenes and their composite materials are summarized.
This paper reviews the latest research progress of MXenes and their composite materials in sodium and potassium ion batteries, briefly introduces the research background of SIBs, PIBs and MXenes, and focuses on the application of MXene composite materials in SIBs and PIBs.
Sodium-ion batteries (SIBs) have been considered as an attractive and promising alternative for energy storage applications due to their advantages of abundant resources, low cost and relatively high ...safety. However, the low electrochemical kinetics of sodium-ion batteries is a major issue limiting their large-scale application. One of the main strategies to address this shortcoming is to find or develop novel cathode materials, which has encouraged a large number of materials chemists to design and develop a variety of polyanionic compounds. Herein, the latest research progress of pyrophosphates as cathode materials for SIBs is reviewed. It is pointed out that pyrophosphate-based cathode materials have abundant crystal chemistry, are easy to synthesize and have a stable structure. The remaining challenges and opportunities of these systems are also discussed and provided. This review will provide better guidance on pyrophosphate electrode materials used in advanced rechargeable batteries.
Recent advances in various pyrophosphates and their diverse modification strategies as well as further horizons have been summarized.
Abstract
The practical application of room-temperature Na-S batteries is hindered by the low sulfur utilization, inadequate rate capability and poor cycling performance. To circumvent these issues, ...here, we propose an electrocatalyst composite material comprising of N-doped nanocarbon and Fe
3
N. The multilayered porous network of the carbon accommodates large amounts of sulfur, decreases the detrimental effect of volume expansion, and stabilizes the electrodes structure during cycling. Experimental and theoretical results testify the Fe
3
N affinity to sodium polysulfides via Na-N and Fe-S bonds, leading to strong adsorption and fast dissociation of sodium polysulfides. With a sulfur content of 85 wt.%, the positive electrode tested at room-temperature in non-aqueous Na metal coin cell configuration delivers a reversible capacity of about 1165 mA h g
−1
at 167.5 mA g
−1
, satisfactory rate capability and stable capacity of about 696 mA h g
−1
for 2800 cycles at 8375 mA g
−1
.
Transition‐metal phosphides (TMPs) have emerged as promising catalyst candidates for the hydrogen evolution reaction (HER). Although numerous methods have been investigated to obtain TMPs, most rely ...on traditional synthetic methods that produce materials that are inherently deficient with respect to electrical conductivity. An electrospinning‐based reduction approach is presented, which generates nickel phosphide nanoparticles in N‐doped porous carbon nanofibers (Ni2P@NPCNFs) in situ. Ni2P nanoparticles are protected from irreversible fusion and aggregation in subsequent high‐temperature pyrolysis. The resistivity of Ni2P@NPCNFs (5.34 Ω cm) is greatly decreased by 104 times compared to Ni2P (>104 Ω cm) because N‐doped carbon NFs are incorporated. As an electrocatalyst for HER, Ni2P@NPCNFs reveal remarkable performance compared to other previously reported catalysts in acidic media. Additionally, it offers excellent catalytic ability and durability in both neutral and basic media. Encouraged by the excellent electrocatalytic performance of Ni2P@NPCNFs, a series of pea‐like MxP@NPCNFs, including Fe2P@NPCNFs, Co2P@NPCNFs, and Cu3P@NPCNFs, were synthesized by the same method. Detailed characterization suggests that the newly developed method could render combinations of ultrafine metal phosphides with porous carbon accessible; thereby, extending opportunities in electrocatalytic applications.
Like peas in a pod: An electrospinning‐based reduction approach was used to embed metal phosphide nanoparticles in nitrogen‐doped porous carbon nanofibers (NPCNFs). A series of pea‐like MxP@NPCNFs structures were fabricated (MxP=Ni2P, Fe2P, Co2P, and Cu3P). Ni2P@NPCNFs is a highly active catalyst for the hydrogen evolution reaction at all pH values.
Double‐shelled NiO‐NiCo2O4 heterostructure@carbon hollow nanocages as efficient sulfur hosts are synthesized to overcome the barriers of lithium–sulfur (Li–S) batteries simultaneously. The ...double‐shelled nanocages can prevent the diffusion of lithium polysulfides (LiPSs) effectively. NiO‐NiCo2O4 heterostructure is able to promote polysulfide conversion reactions. Furthermore, the thin carbon layer outside can improve the electrical conductivity during cycling. Besides, such unique double‐shelled hollow nanocage architecture can also accommodate the volumetric effect of sulfur upon cycling. As a result, the prepared S/NiO‐NiCo2O4@carbon (C) electrode exhibits good rate capacities and stable cycling life up to 500 cycles at 0.5 C with a very low capacity decay rate of only ≈0.059% per cycle.
An efficient double‐shelled hollow sulfur host in which hollow NiO‐NiCo2O4 heterostructure nanocages constructed from building blocks of NiO‐NiCo2O4 nanoparticles are sealed by a thin carbon layer is proposed and designed. Benefiting from the structural and compositional advantages, the S/NiO‐NiCo2O4@C composite cathode shows excellent electrochemical performance.
Sodium manganese hexacyanoferrates (NMHFCs) synthesized in aqueous solution at room temperature show high reversible capacity and outstanding rate capability as cathodes for a rechargeable sodium‐ion ...battery (SIB). Earth‐abundant elements and a low‐cost synthesis route make these NMHFCs promising cathodes for SIBs, independent of natural lithium sources.
Cobalt phosphides electrocatalysts have great potential for water splitting, but the unclear active sides hinder the further development of cobalt phosphides. Wherein, three different cobalt ...phosphides with the same hollow structure morphology (CoP‐HS, CoP2‐HS, CoP3‐HS) based on the same sacrificial template of ZIF‐67 are prepared. Surprisingly, these cobalt phosphides exhibit similar OER performances but quite different HER performances. The identical OER performance of these CoPx‐HS in alkaline solution is attributed to the similar surface reconstruction to CoOOH. CoP‐HS exhibits the best catalytic activity for HER among these CoPx‐HS in both acidic and alkaline media, originating from the adjusted electronic density of phosphorus to affect absorption–desorption process on H. Moreover, the calculated ΔGH* based on P‐sites of CoP‐HS follows a quite similar trend with the normalized overpotential and Tafel slope, indicating the important role of P‐sites for the HER process. Moreover, CoP‐HS displays good performance (cell voltage of 1.67 V at a current density of 50 mA cm−2) and high stability in 1 M KOH. For the first time, this work detailly presents the critical role of phosphorus in cobalt‐based phosphides for water splitting, which provides the guidance for future investigations on transition metal phosphides from material design to mechanism understanding.
This work firstly reveals the critical role of phosphorus in cobalt‐based phosphides for both oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). The phenomenon that cobalt‐based phosphides exhibit similar OER performances but quite different HER performances has been in‐depth analyzed. This work provides the guidance for the future investigations on transition metal phosphides for water splitting.
Novel K3V2(PO4)3 and three-dimensional conductive network K3V2(PO4)3/C nanocomposites are successfully fabricated and further evaluated as cathode materials for potassium-ion batteries for the first ...time. The K3V2(PO4)3/C nanocomposite exhibits a high-potential platform of 3.6-3.9 V and a good capacity retention of at least 100 cycles. This work may provide new insight into developing cathode materials for potassium-ion batteries.
SnS nanoparticle-modified Ti3C2Tx MXene composites were synthesized via hydrothermal and annealing methods and used as anode for sodium-ion batteries. The SnS nanoparticles are homogeneously ...dispersed between the MXene sheets, forming a unique sandwich structure. SnS/Ti3C2Tx nanocomposites electrode delivers a high reversible capacity of 412.8 mAh g−1 at 100 mA g−1. In addition, the prepared SnS/Ti3C2Tx composites possess good rate performance with a capacity of 255.9 mAh g−1 at 1000 mA g1.
•SnS/Ti3C2Tx composites were synthesized by facile method.•It's the first time used as anode for sodium -ion batteries.•It exhibits enhanced reversible capacity and good rate performance.•The enhanced performance is ascribed to unique structure of SnS/Ti3C2Tx.
Novel K2Ti8O17 is successfully fabricated via a facile hydrothermal method combined with a subsequent annealing treatment and further evaluated as an anode material for potassium-ion batteries for ...the first time. This study may provide a broader vision into developing anode materials for potassium-ion batteries.
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