Research On Preparation And Energy Storage Mechanism Of Nickel-based Phosphides Supercapacitor Materials

Energy storage has become one of the hottest topics in the energy related research field.Supercapacitors,a new type of energy storage equipment between traditional capacitor and battery,have been used in many areas,owing to their long cycle stabilities,fast charging-discharging and larger power densities.However,its energy density is relatively low.At present,an effective way to improve energy density is to develop new electrode materials with high specific capacitance.Transition metal phosphides?TMPs?have been promised to be desirable candidates as electrode materials for supercapacitors due to their superior electrical conductivity.Among them,nickel-based phosphides have been widely studied because of their superior theoretical specific capacity.But single nickel-based phosphides electrode materials have poor rate capability and stability.In order to further improve the energy storage performance of a single nickel-based phosphides electrode materials,bimetallic and hybrid electrode materials were constructed based on this.The phosphides can be used to enhance the performance of supercapacitors,so that the transition metal phosphides as electrode materials play a greater advantage.In this paper,nickel-cobalt bimetallic phosphides and nickel-based phosphides were prepared by hydrothermal-phosphorization method.The mechanism of the micro structure and synergetic effect on electrochemical performance of the electrode materials were studied.The following tasks were completed:1.Based on the excellent properties of nickel-cobalt bimetallic materials and phosphides,porous binary nickel-cobalt phosphides nanosheet arrays anchored on nickel foam?NiCoP@NF?were rationally designed and manufactured as self-supported binder-free electrodes with excellent properties supercapacitor.The crystal structure,morphology and electronic state of single electrode were characterized by XRD,SEM and XPS and so on.And then the properties of the electrode materials were investigated.The nickel foam supported NiCoP nanosheet array?NiCoP@NF?electrode possesses much higher electrochemical performance in comparison with NiCo LDH@NF and NiCoO₂@NF electrodes.The NiCoP@NF electrode shows ultrahigh specific capacitance of 2143 F/g at 1 A/g and remained 1615 F/g even at 20 A/g,indicating the excellent rate performance.Furthermore,a binder-free all-solid-state asymmetric supercapacitor device?NiCoP@NF//AC ACS?is also designed,which exhibits a high energy density of 27Wh/kg at a power density of 647 W/kg,and it is expected to be applied in practice.2.We introduced the Fe₂O₃ with the characteristics of low cost,natural abundance and high stability.Different Fe/Ni proportions of Ni₂P/Fe₂O₃ hybrid electrode materials were successfully synthesized by a simple two-step method.According to the results of electrochemical test,the performance of hybrid electrode is better than that of single electrode.And when the ratio of Fe/Ni is 1/9,the performance of Ni₂P/Fe₂O₃-1 hybrid electrode is the best.The specific capacity of Ni₂P/Fe₂O₃-1 material can reach 1491 F/g at1A/g,and the rate capability of hybrid electrode material?74%?is obviously improved?58%of Ni₂P?.3.In order to further improve the rate capability and stability of nickel-based phosphides,we introduce the Ni?OH?₂ with rich resources,high stability and high redox activity.Ni₂P@CC materials and Ni₂P@Ni?OH?₂@CC hydrid electrode materials were synthesized by hydrothermal method.The electrochemical properties of the materials were analyzed.The results showed that the specific capacitance of Ni₂P@Ni?OH?₂@CC hydrid electrode material is much larger than that of Ni₂P@CC electrode material.Noticeably,the optimized 3D Ni₂P@Ni?OH?₂@CC nanosheets possesses exceptionally high gravimetric capacitances and areal capacitances up to 632 C/g and 0.73 C/cm² at a current density of 1mA/cm²,respectively,and remarkable capacitance retention?81.4%at 2 mA/cm² over1000 cycles?.The stability has been greatly improved.The synergistic effect between high conductivity of Ni₂P and high specific capacitance of Ni?OH?₂ makes Ni₂P@Ni?OH?₂@CC as a hybrid electrode material with excellent performance.