| The development of new negative electrode materials with high capacity, long cycle life and environmental friendliness is of great importance for nickel/metal-hydride battery(Ni/MH). In comparison with traditional AB5-type rare-earth negative electrode materials, the amorphous Mg-Ni alloy exhibits great potential because of high discharge capacity, short activation period, low cost and environmental friendliness. However, the poor cyclic stability restricts its practical application due to the extremely readily oxidation of active Mg element in the strong alkaline electrolyte. To improve the cyclic performance of amorphous Mg Ni alloy electrode, in this thesis, red phosphorus P and graphene G were used for structural modification of amorphous Mg Ni alloys by mechanical milling method. The effects of ball-milling process, the fraction of additives, and the doping process on the structure and electrochemical properties were investigated. In addition, the electrochemical performances of amorphous Mg Ni films and Mg Ni/Pd/PTFE film electrodes with various layers prepared by magnetron sputtering were also investigated. Important conclusions have been drawn as following:The amorphous Mg Ni alloys doped with red phosphorus P were prepared by two different methods.(1) Two-step method, namely the amorphous Mg Ni-P alloys were prepared by mechanical milling, then further milled with red phosphorus.(2) One-step method, namely, the amorphous Mg-Ni-P alloys were prepared by ball-milling the original Mg, Ni and P powders. The electrochemical results showed that P could promote the amorphization of Mg Ni alloys and enhance their corrosion resistance, thus improved the cycle stability of the amorphous Mg Ni alloys. The Mg Ni-5wt%P electrode showed the best electrochemical properties among Mg Ni-P alloys by Two-step method, and its discharge capacity and capacity retention at the 30 th cycle were 108.5 m Ah/g and 34.4%, respectively, higher than those(51 m Ah/g, 9.9%) of amorphous Mg Ni alloys. While the Mg-Ni-5wt%P electrode showed the best electrochemical properties among the Mg-Ni-P alloys by One-step method, and its discharge capacity and capacity retention at the 30 th cycle were 118.8 m Ah/g and 43.4%, respectively.The amorphous Mg Ni alloys were also doped with graphene G by mechanical milling. The results showed that graphene could form a coating layer on the surface of Mg Ni alloy particles, and thus inhibiting the corrosion of the alloys in the alkaline solution. Therefore, the cyclic stability of the composite alloys was improved. The Mg Ni-5wt%G electrode showed the best electrochemical properties. Its discharge capacity and capacity retention at the 30 th cycle was 115.7m Ah/g and 24% respectively, however, the maximum discharge capacity decreased from 516.3 m Ah/g of Mg Ni to 481.6m Ah/g. Further, the Mg-Ni-P alloys by One-step method were ball-milled with 5wt% graphene, the obtained Mg-Ni- xwt%P-G(x=2, 5) alloys showed the best electrochemical properties. Its discharge capacity and capacity retention at the 30 th cycle was 431.7m Ah/g and 136 m Ah/g respectively, much higher than those of alloys without G-coating layers.In addition, four different amorphous films, namely Mg Ni, Mg Ni/Pd, Mg Ni/PTFE, Mg Ni/Pd/PTFE film, were prepared by magnetron sputtering method. The results showed that Pd could catalyze the dissociation and recombination of H2 and provide a hydrogen diffusion channel, while the PTFE films could provide an overall protection of Mg Ni films and improve its corrosion resistance. Under the synergetic effects of Pd and PTFE films, the Mg Ni/Pd/PTFE three-layer film exhibited the best electrochemical performances. Its maximum discharge capacity, discharge capacity and capacity retention at the 100 th cycle were 263.2m Ah/g, 104.5m Ah/g and 39.7% respectively, higher than 248.0m Ah/g, 19.6m Ah/g and 7.9% of Mg Ni film electrode. |
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