| Nickel hydroxide acts as positive material for the secondary batteries, which is used in Ni-MH, Ni-Cd, Ni-Fe batteries. Due to the good safety, high cost performances and better ability to overcharge/overdiacharge, Ni-MH battery is widely used in electrical appliances and new energy vehicles. But current commercial Ni-MH battery is limited by the positive material β-Ni(OH)2, which has lower specific capacity (289mAh·g-1) and comparatively little rise space. However,α-Ni(OH)2, another crystal shape for nickel hydroxide, can exhibit higher specific capacity (482mAh·g-1) and has larger interlayer spacing, which plays an important role on enhancing high-rate charging/discharging performance. But due to the low density and unstability in alkali solution, it can not be used in commercial batteries up to now. Furthermore, relatively low electrochemical conductivity of nickel hydroxide limit its electrochemical performance. Hence, how to improve the stability and enhance the electrochemical conductivity and its density has an important impact on improving market competitiveness and application prospect of Ni-MH battery.In this article, we prepare the samples by multi-doping other metal ions to overcome the technical bottleneck of unstability in alkali solution, and systematically study the relationship among the physicochemical performance, the doping ions species and doping ratio, the synergistic effect among doping metal ions, anions in the interlayer spacing, particle size and crystal structure. Meanwhile, we prepare the Sn-doped α-Ni(OH)2 and Ca-doped α/β-Ni(OH)2 by doping Sn2+ and codoping Ca2+ and PO43-, respectively, and study the relationship among the physicochemical performance, the the doping ions, anions in the interlayer spacing, particle size and crystal structure. This work is divided into three sections listed as follows:Firstly, Single, binary, ternary and undoped samples were synthesized by supersonic co-precipitation method. The results show that undoped sample is beta phase nickel hydroxide, and the doped samples are alpha phase nickel hydroxide. Meanwhile, with the increase of the doping elements and doping ratio, the structural stability and the electrochemical performance are improved gradually.Al-Mn-Yb a-Ni(OH)2 (tenary doped sample) can keep alpha phase after being soaked in alkali solution for 30 days. Moreover, the electrode made by Al-Mn-Yb α-Ni(OH)2 shows higher proton diffusion coefficient, lower electrochemical polarization and biggest discharge specific capacity (309.0mAh/g). This illustrates that suitable doping elements and doping ratio can make the prepared sample enhancing electrochemical performance, which is because of the synergistic effect among the doping ions, the effect of changing crystal field and the content of anions between the inter layers.Secondly, Sn-sunstituted α-Ni(OH)2 doped with different proportion was prepared by the same method as above. The doped ratio has important effects on morphology, crystallinity, particle size and electrochemical performance of the prepared sample. The results demonstrates that the interlayer spacing becomes larger with the increasing doping ion ratio, the secondary particle size decreases firstly and increase subsequently, and sample with 15mol% doping ion exhibits the best crystal crystallinity. the electrode made by 15mol% Sn-substituted α-Ni(OH)2 exhibits the best electrochemical performance(e.g. lowest charge transfer resistance, best proton diffusion coefficient and charge-discharge cycle performance, highest discharge specific capacity:306.2 mAh/g, etc) from CV, EIS and charging/discharging test. This indicates that the content of doping ion plays an important effect on changing crystal crystallinity and structure, and then change its electrochemical performance.Thirdly, we prepared Ca2+-PO43- codoped samples by the same method as above. The results demonstrate that it can not synthesis a phase Ni(OH)2 without Na3PO4, while Ca2+-PO43- (molar ratio of Ca2+ to PO43- is 1:0.066) codoped sample is alpha/beta mixed phase from XRD and FT-IR measurement. And undoped sample is pure β-Ni(OH)2 structure. Compared the pure β-Ni(OH)2, α/β-Ni(OH)2 shows higher electrochemical reaction activation, better electrochemical reversibility and charging efficient, higher discharge plateau and cyclic stability from CV and charging/discharging test. The specific capacity of the electrode made by Ca2+-PO43- codoped sample shows 302.8 mAh/g at 0.2 C and 285.2 mAh/g at 0.5 C, and still retain 271.7 mAh/g at 0.2 C and 238 mAh/g at 0.5 C after 80 cycles, which indicates that Ca2+-PO43- codoped sample exhibits excellent electrochemical performance. |
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