Study On The Preparation, Modification And Electrochemical Properties Of Mg-based And AB₅-type Hydrogen Storage Alloys

The present researches focus on the exploitation of hydrogen storage alloys used for Ni/MH hybrid electric vehicles is. In order to obtain negative electrode materials with excellent overall performance, several hydrogen storage alloys were prepared, the effects of element substitution, surface treatment and formation composite alloy on the phase structure, surface morphology and electrochemical properties of the alloys were studied. This thesis is composed of three parts. The first part is study on the element substitution and modification of Mg-based alloy. The second part is concerned with the modification of AB5-type alloy. The third part is related to the preparation, structure and electrochemical properties of AB3-AB5 composite alloys.Firstly, we performed the element substitution and modification to improve the cycle stability of Mg-based alloy.Mg1-xTixNi (x= 0,0.1,0.2, and 0.3) alloys were prepared. With the increase of Ti content, the alloy electrodes exhibited the better cycle stability. Furthermore, Mg0.9Ti0.1Ni1-xMx(M= Co, Mn; x= 0,0.1,0.2) alloys were prepared, and the cycle performance was improved with Co or Mn substitution. The discharge capacity and cycle stability of Mg0.9Ti0.1Ni0.9Mn0.1 alloy electrode was much higher the literature data.Adopting surface coating and heat treatment to improve the cycle performance of Mg-based alloy. With the addition of CoB, the alloy electrode exhibited the better cycle stability and the maximum discharge capacity reached 425.8 mAh/g. Moreover, Mgo.9Tio.1Ni alloy was prepared by being treated at 873 K for 5 h and then ball milling. After being pre-heat treated, the discharge capacity increased from 229.9 mAh/g to 331.9 mAh/g, and the discharge capacity retention (S30) raised from 17.2% to 59.4%.The MgNi-x wt% TiNi0.56Co0.44 (x= 0,10,30,50) alloys were prepared. The electrochemical results confirmed that the cycle stability of the alloy was noticeably improved due to intensive corrosion resistance of TiNi0.56Co0.44 alloy. A high discharge capacity and good cycle stability had been observed for the x= 10 (10 h) composite electrode with a maximum discharge capacity of 397.3 mAh/g and capacity retaining rate S50 of 62.4%.Secondly, F-treatment, catalytic modification with metal oxides and formation composites were conducted to enhance the discharge capacity of AB5 type alloy.Fluorination treatment of the MlNi3.5Co0.6Mn0.4Al0.5 alloy was carried out by using different fluorine-containing solution. The discharge capacity and cycle property were improved after fluorination treatment. The maximum discharge capacity increased from 314.8 mAh/g to 325.7 mAh/g (NH4F),326.5 mAh/g (LiF) and 316.4 mAh/g (LiF+KBH)4, respectively. After 40 cycles, the capacity retention rate enhanced from 93.6% to 96.5% (NH4F),96.9% (LiF), and 97.1% (LiF+KBH4).MlNi3.5Co0.6Mn0.4Al0.5 alloy was modified by ball-milling the pristine alloy with different contents of ZnO and MnO2. The activation property of the electrode was enhanced with the addition of metal oxides. The maximum discharge capacity of MlNi3.5Co0.6Mn0.4Al0.5-x wt% ZnO (x= 0,5,10) alloy electrode increased from 314.8 mAh/g to 333.5 mAh/g (x= 5) and 341.1 mAh/g (x= 10).MlNi3.5Co0.6Mn0.4Al0.5-x wt% Mm0.89Mg0.11Ni2.97Mn0.14Al0.20Co0.54 (x= 0,5,10) alloys were prepared. The maximum capacity increased from 314.8 mAh/g for MlNi3.5Co0.6Mn0.4Al0.5 electrode to 324.1 mAh/g (x= 5) and 324.6 mAh/g (x= 10). After 50 cycles, the capacity retention rate of the electrodes increased from 92.3% (x= 0) to 95.2%(x= 10).Though the documents consultation, it is found that little is related to the incorporation of AB5-type alloy with La-Mg-Ni system alloy. In the third part, AB3-AB5 composite alloys were prepared to improve the cycle stability of AB3 type alloy.The alloys Ml0.80Mg0.20Ni2.56Co0.50Mn0.14Al0.12-x wt% AB5 (x= 0,10, 20,30) were prepared. It showed that the capacity retention rate S60 increased from 70.0%(x= 0) to 79.5%(x= 10), and then decreased to 74.4%(x= 30). The high-rate dischargeability (HRD600) of the alloy electrodes increased from 78.8%(x= 0) to 88.4%(x= 20), and then dropped to 82.4%(x= 30).The properties of the La0.78Mg0.22Ni2.67Mn0.11Al0.11Co0.52-x wt% AB5 (x=0,10,20,30)alloys were investigated.With the increase of x,the capacity retention rate S50 increased from 55.4%(x=0)to 76.5%(x=20), and then dropped to 73.1%(x=30).The HRD600 of the alloy electrodes increased from 94.2%(x=0)to 95.8%(x=10),and then decreased to 88.8%(x=30).