Preparation Of Nickel Hydroxide And Based-Poly(Vinyl Alcohol)Hydrogel Electrolyte For Flexible Batteries

The specific capacity,energy density,cycling performance,and cost of nickel-metal hydride batteries are all between lithium-ion batteries and lead-acid batteries.More importantly,nickel-metal hydride batteries have a high safety factor.In addition,supercapacitors are also a good energy storage system,which can be used at a higher power density than batteries.Nickel hydroxide can be used in both nickel-metal hydride batteries and super capacitors as a positive electrode material,so this material has great potential in the future.In addition,with the rapid development of various flexible and wearable electronic devices,the core of flexible energy storage devices become more and more important today.Although nickel-metal hydride batteries have the above advantages,there are still relatively few related fields of flexible nickel-metal hydride batteries,so it is of great significance to develop flexible nickel-metal hydride batteries.This thesis focuses on the preparation and improvement of nickel hydroxide for the flexible nickel-metal hydride battery,and the discussion on the preparation and application of the hydrogel electrolyte film in the flexible nickel-metal hydride battery,in order to realize the flexible application of nickel-metal hydride battery.The results of this study are as follows:?1?A flower-like aluminum-doped?-Ni?OH?2 was successfully prepared by a one-step hydrothermal method,and the effects of aluminum ion concentration and urea concentration on the structure and electrochemical performance of?-Ni?OH?2 were investigated.We found that a small amount of aluminum content can improve the electrochemical performance of?-Ni?OH?2,but in the case of excessive amounts,it causes severe performance degradation.For another,the higher the urea concentration,the more by-products are generated,but it has little effect on the electrochemical performance of the?-Ni?OH?2 electrode.In order to optimize the utilization rate and electrochemical performance,based on the above tests,we selected the best solution to synthesize?-Ni?OH?2.It has a capacity of 302.22 mAh g^-1 at a current density of 1 A g^-1,and a capacity retention rate of 71.22%even at 10 A g^-1.?2?The performance of?-Ni?OH?2 is improved by coating?-Ni?OH?2 nanosheets,and the better electrochemical performance of flower-like?@?-Ni?OH?2 is mainly due to its unique nanometer core-shell and mesoporous structure.The?-Ni?OH?2 nuclei with flower-like structure have good electrical conductivity and can make ions and electrons quickly transfer along the mesoporous structure.As a shell,?-Ni?OH?₂nanosheets are tightly coated on the surface of the?-Ni?OH?2 core to form a core-shell structure,so they have good chemical and mechanical stability.In addition,because the?-Ni?OH?₂ shell can physically isolate a strong alkaline solution,the structure stability of?-Ni?OH?2 is improved during the charge-discharge cycle.In addition,the flower-like?@?-Ni?OH?2 with a unique nanometer core-shell and mesoporous structure can provide more active contact points with the electrolyte,which is conducive to improving the utilization and reactivity of the electrode,thereby improving specific capacity of the electrode.The assembled nickel-metal hydride battery has a high energy density of 100.17 Wh kg^-1 at a power density of 424.75 W kg^-1.?3?In order to achieve the flexibility of nickel-hydrogen batteries,we have prepared a self-healing the borax-PVA/KOH/GO hydrogel film with a controlled thickness and tested its mechanical properties.The twisting and piercing performance meets the requirements of flexible energy storage device electrolytes.The borax-PVA/KOH/GO hydrogel film is also applied to flexible?@?-21//AC ASC and flexible?@?-21//MH batteries.It is found that small thickness is good for specific capacity but not good for cycle life.However,the larger thickness is beneficial to the cycle life.Because the liquid storage capacity of thick hydrogel is greater than that of a thin one,it does not dry out quickly,retaining its high ionic conductivity.Even after 3,300 cycles,the capacity retention rate is still 70%at current density of 5 A g^-1.In addition,the borax-PVA/KOH/GO hydrogel films were applied to flexible?@?-21//MH batteries.The results indicate that the ionic conductivity of the hydrogel electrolyte was slightly lower than the 6 mol/L KOH aqueous solution.Specific capacity of the flexible?@?-21//MH battery decreases,but the GO and some oxygen-containing functional groups on the PVA in the hydrogel film can quickly store ions compared to the hydrogen storage alloy.It implies that the hydrogel also acts as a buffer layer in the battery.Therefore,under the condition of large current,the hydrogen storage alloy does not react sufficiently,but the hydrogel film can still provide it with ions,thereby improving the rate performance,and the portable flexible Ni-MH battery successfully lit the red LED.