A Functionalized Co₂P Negative Electrode for Batteries Demanding High Li-Potential Reaction

Abstract

Co-P alloy films were electrodeposited on a titanium electrode. The controlled addition of phosphorous acid or sodium hypophosphite to a Co 2+ -containing solution leads to the formation of amorphous or crystalline CoP phases. Particularly, the orthorhombic Co 2 P phase is obtained at 80 • C with a current density of 37.5 mA cm −2 during 10 and 20 min as determined by XRD and XPS analysis. The morphology of Co 2 P can be controlled from leopard-like spots to hexagonal symmetric particles as confirmed by SEM. This phase is for first time used as a negative electrode in rechargeable batteries. The electrochemical results in a lithium test cell of this unique product differ significantly from other metal phosphides reported in the literature. A high potential reaction at 1.3 V is observed in the first discharge. Successive charge/discharge branches are quite different to those reported so far. The preliminary results suggest that the Co to P ratio may affect the redox properties of the materials. In view of the limited amount of reports dealing with performances of cobalt phosphides in Li-cells, the properties presented here justify further effort to be done to evaluate their real potential application in Li-ion batteries with a predefined voltage operation.The last thirty years have seen an enormous research effort in the field of electrode materials for Li-ion batteries. The results not only affect the chemical composition of the solids but also the search for alternative preparation routes that may improve substantially the performance of the active materials while reducing their cost. 1,2 New synthesis of well-known materials, such as LiFePO 4 or spinel oxides, are constantly reported in the literature showing novel properties or electrochemical responses. The interest of cobalt phosphides was highlighted in the past in the literature because of their enhanced properties as magnetic, catalytic, electronic, and anode-materials. 3-8 General stoichiometries of cobalt phosphides are CoP, Co 2 P, CoP 2 , and CoP 3 . 9-11 However, there are few reports on the electrochemical fabrication of transition metal phosphide-based materials with amorphous character since Djokic employed phosphorous acid as P source. 12 Among others, Brenner and Riddell prepared the first ferromagnetic amorphous material based on Co-P alloys by autocatalytic chemical deposition or electroless deposition. 13 Electrochemical fabrication methods present technical and economical advantages, such as a low temperature processing, in which the nano-architecture of the electrodes in the form of nanotubes, nanowires or nanocomposites can be controlled. 14-19 The electrochemical fabrication method allows, for instance, the preparation of CoP films with a varied stoichiometry, in which the amount of P content can be controlled by adjusting different experimental parameters such as the quantity of reagents (e.g. H 3 PO 3 ), time or current density. 20 However, to the best of our knowledge Co 2 P has not been fabricated by this procedure yet. It is known th...

Layered phosphorus-like GeP5: a promising anode candidate with high initial coulombic efficiency and large capacity for lithium ion batteries

“…The three extra peaks are thought also from the bonding between GeP 5 and carbon, since similar extra XPS peaks have been identified for the P-C bonds by Cui et al in the composite of black P and carbon. As shown in Figure 7a , the GeP 5 electrode after discharging to 0.005 V clearly exhibits the XRD peaks of Li 22 Ge 5 (Li 4.4 Ge) and Li 3 P phases, [27][28] which evidences the large capacity of GeP 5 comes from the contribution of both Ge and P. According to this, the electrode reaction of GeP 5 can be described by the following equations: 15 34,42 CV measurements on GeP 5 /C in comparison of Ge/C and P/C composites further comfirm the above Li storage mechanism. On the one hand, the carbon network provides directional electron-transport paths and tight electronic contact between the active nanoparticles, so that electrons can be quickly transferred from the active sites to the electrode current collector along the carbon superhighway.…”

Hollow Co2P nanoflowers assembled from nanorods for ultralong cycle-life supercapacitors

“…13 Cobalt phosphides, which have been extensively studied in many fields (e.g., as electro-catalysts in water splitting, as anode materials in lithium-ion batteries, and as catalysts in hydrodesulfurization reactions), exhibit metalloid properties and superior electronic conductivity. [14][15][16][17][18][19][20][21] Since both cobalt phosphates and nickel phosphides have delivered high specific capacitance for supercapacitors in previous demonstrations, 11,22,23 cobalt phosphides can be reasonably believed to produce rich redox reactions in alkaline solution. Moreover, considering the relationship between cobalt oxides and nickel oxides, 24,25 cobalt phosphides should have a higher theoretical capacity than nickel phosphides.…”

Magnetic metal phosphide nanorods as effective hydrogen-evolution electrocatalysts

“…As an important class of magnetic metal phosphides, cobalt phosphides have been investigated for their special magnetic [24,25] and catalytic properties [26,27]. Recently, studies on the electrochemical performance of cobalt phosphide nanomaterials have indicated that they can be used as anode materials for potential applications in lithium ion batteries [28,29]. In comparison, reports on the electrocatalytic HER performance of nanoscale cobalt phosphides are very rare.…”