Controlled Preparation Of Defective Nickel/Cobalt Molybdate Nanomaterials And Study On The Performance Of Zinc Ion Batteries

With the consuming fossil fuels and deteriorating environment,it is in urgent need to vigorously promote the utilization of clean energy.And its realization hinges on how to effectively store and release these energy.That is why so many researchers are committed to developing environmentally friendly and high-efficiency electrochemical energy storage devices.It is under such circumstances that aqueous zinc ion batteries attract people's attention by virtue of their superiorities such as low cost,good safety and high power density.However,due to the lack of high-performance cathode materials,their progress is hampered by the defects of inferior energy density and poor cycling stability.Because of the excellent physical and chemical properties,transition metal molybdates are widely used as the cathodes of various energy storage devices.Nevertheless,there is almost no relevant work about their application in the aqueous zinc ion batteries.Moreover,their electrochemical reaction activity also needs to be further improvement.Herein,nickel molybdate and cobalt molybdate are taken as the study objects,and doped by cobalt and phosphorus respectively to introduce oxygen defects,serving as the cathodes of aqueous zinc ion batteries to enhance their performance.The specific research contents and achievements of this thesis are as follows:(1)Through the simple hydrothermal reaction and calcination treatment,cobalt doped nickel molybdate nanosheet arrays(CNMO)are synthesized on the substrate of nickel foam.And the impacts of doping mass on electrochemical properties are further studied by controlling the amount of cobalt source in the precursor solution.According to the electrochemical test results,the optimal doping amount of cobalt is 15%(CNMO-15).At the current density of 3 A g^-1,the specific capacity of CNMO-15 is as high as 361.4 m A h g^-1,while that of pure nickel molybdate(NMO)is only 206.4 m A h g^-1.This can mainly be attributed to the contribution of strengthened oxygen defects benefiting from the incorporation of cobalt,thus boosting the electrical conductivity of nickel molybdate.On this basis,a zinc-nickel battery is assembled with CNMO-15 and commercial zinc plate as cathode and anode,respectively.Under the power density of 3.5 k W kg^-1,the energy density of whole device can reach up to 474.1 W h kg^-1.Besides,at the scan rate of 60 m V s^-1,there exists no capacity decay after 5000 cycles.(2)In this paper,the electrochemical activity of nickel foam-supported cobalt molybdate nanosheet arrays is accelerated by phosphating treatment with sodium hypophosphate as the phosphorus source(P-Co Mo O₄).The characterization data proves that abundant oxygen defects are generated in the phosphating process,which can regulate the electronic structure and weaken the resistance of charge transfer.Meanwhile,the modification of surface phosphate ions can reduce the required activation energy for redox reaction,when in-situ formed Co P nanoparticles can provide extra active sites.Furthermore,the electrochemical properties of P-Co Mo O₄ are optimized by adjusting the heating temperature and holding time of phosphating treatment.At the current density of 10 A g^-1,the best capacity of P-Co Mo O₄ is 431.4 m A h g^-1,almost three times that of Co Mo O₄ under the same condition.The zinc-cobalt battery constructed by P-Co Mo O₄ and zinc plate also demonstrates outstanding electrochemical performance,displaying the maximum energy density and power density of 679.4 W h kg^-1 and 33.4 k W kg^-1,respectively.More importantly,the device still remains over 80%of initial capacity after 12000cycles at the scan rate of 60 mVs^-1.