Fe‐Doped CoP Flower‐Like Microstructure on Carbon Membrane as Integrated Electrode with Enhanced Sodium Ion Storage

Abstract

Poor cyclability and rate performance always impedet he development of transition metal phosphidebased anode materials. Many strategies have been used to addresst he above problems, such as the designing of hierarchicals tructures,c ombination with carbon materials, and doping with other metal elements. Considering thoses trategies, af lower-like Fe-doped CoP material is designed. The synthesis consists of microsheets grown on ac arbon membrane (CM, leaves as precursor) through ah ydrothermal methoda nd in situ phosphorization.T he Fe dopinga nd carbon membrane synergistically induce the formationo fa flower-like hierarchical microstructure duringt he crystalgrowingp rocess. The unique hierarchical microstructure in-creases thec ontact area between electrode and electrolyte, and accommodates the volume expansion duringc ycling. The hierarchicalF e-doped CoP grownd irectly on the carbon membrane increases the active sites for intercalation of sodiums pecies and furtherp romotes the internal electron conduction in the Fe-doped CoP/CM electrode. Thereby,t he Fe-doped CoP/CM as the anode electrode fors odium ion batteries exhibits ah igh specific capacityo f5 15 mA hg À1 at 100 mA g À1 after 100 cycles. Even if the current density rises to 500 mA g À1 ,t he specific capacity is stillm aintained at 324 mA hg À1 after 500 cycles, showings uperior rate performances and cyclability.

CoP Nanoparticles Intertwined with Graphene Nanosheets as a Superior Anode for Half/Full Sodium‐Ion Batteries

“…The peak at 133.5 eV can be attributed to the oxidized P species due to the surface oxidations produced by exposure to air. [25][26][27] Figure 2f displays the high-resolution spectrum of C 1s, the three peaks located at 283.7, 284.6, and 285.3 eV are assigned to the CÀ C, CÀ O and C=C bonds, respectively. [28][29][30] The cycling performance of CoP/RGO with different weight ratios of RGO (0 wt %, 4.4 wt %, 5.6 wt %, and 11.2 wt %, based on the results of elemental analysis) are investigated.…”

Advances in metal phosphides for sodium‐ion batteries

“…The cycling performance of CoP electrodes is yet to be improved to satisfy the requirement of commercial application. To rationally design CoP x ‐based compounds to optimize the electrochemical performance, researchers primarily focused on (i) fabricating a porous architecture with high specific surface area to provide abundant active sites and relieve the large volume variation caused by the conversion and alloying reactions 111,112 ; (ii) constructing micro‐nano sized CoP x ‐based composites with consecutive conductive matrix (e.g., carbon nanotubes, carbon paper, and graphene) to reduce the diffusion path of Na + and increase the charge transfer kinetics 113–118 ; and (iii) improving the electronic conductivity via elemental doping in the CoP x (e.g., Fe, Mo, N) or in the conductive supports (e.g., N/S‐doped carbon materials) 27,31,109,119–124 …”

“…Doping CoP x /C with other elements is another strategy to address the issues mentioned above regarding CoP‐based anodes. In Xu's work, a hierarchical flower‐like Fe‐doped CoP array was grown on the carbon membrane (CoP/CM) and used as anode for SIBs 31 . The elemental Fe played a role in assisting the formation of hierarchical flower‐like morphology during the synthesis process.…”

“…To rationally design CoP x -based compounds to optimize the electrochemical performance, researchers primarily focused on (i) fabricating a porous architecture with high specific surface area to provide abundant active sites and relieve the large volume variation caused by the conversion and alloying reactions 111,112 ; (ii) constructing micro-nano sized CoP xbased composites with consecutive conductive matrix (e.g., carbon nanotubes, carbon paper, and graphene) to reduce the diffusion path of Na + and increase the charge transfer kinetics [113][114][115][116][117][118] ; and (iii) improving the electronic conductivity via elemental doping in the CoP x (e.g., Fe, Mo, N) or in the conductive supports (e.g., N/S-doped carbon materials). 27,31,109,[119][120][121][122][123][124] For example, in Liu's study, a hierarchical hollow CoP@C composite was prepared by controlling the atmosphere and temperature during the heat treatment. 112 The hollow spherical structure of the CoP@C prepared at 600°C (CoP@C-600) was well retained even after hundreds of cycles, showing excellent structural stability.…”

“…To address these issues, a diversity of impressive modification strategies have been proposed and systematically investigated, including (i) designing ingenious nano‐micro structure (e.g., sandwich‐like Ni 2 P nanoarray, 20 3D hierarchical rose‐like Ni 2 P@rGO, 23 and ultrathin few‐layer GeP nanosheets 24 ), which possesses plenty of space for volume expansion and increases the contact area between electrolyte and electrode materials to promote the diffusion of Na + and improve the stability of electrodes during the sodiation/desodiation processes; (ii) mixing with conductive carbonaceous materials (e.g., CuP 2 /C composites, 25 Sn 4 P 3 /reduced graphene oxide nanohybrids, 17 and carbon‐coated CoP 3 nanocomposites 26 ) to buffer volume variations and increase electrical conductivity of the electrodes; (iii) doping elements to improve the electrical conductivity of the electrodes (e.g., sulfur‐doped CoP 27 ). At present, combining multiple strategies to synergistically improve the performance of SIBs, such as nanochain‐like structure composed of hollow yolk‐shell Sn 4 P 3 @C nanospheres, 28 P doped onion‐like carbon layers coated FeP, 29 core‐shell Ni 2 P@carbon, 30 flower‐like Fe‐doped CoP, 31 cross‐linking hollow carbon sheet encapsulated CuP 2 nanocomposites, 32 and so on, has become the mainstream. Except for structural engineering on electrode materials, constructing self‐supporting electrodes without binder and conductive agents is another attractive approach to decrease the resistance and “dead area,” and thus can improve the electrochemical performance of SIBs.…”