Preparation And Electrochemical Properties Of Quasi-solid-state Nickel-zinc Batteries

To efficiently use clean energy such as solar and wind energy,it is urgent to develop energy storage and conversion device.Chemical energy storage has attracted wide attentions due to low cost,high energy storage and conversion efficiency.In chemical energy storage devices,nickel-zinc battery has been payed attentions to by researchers because of the high theoretical energy density,excellent low-temperature performance,high power density,safety and eco-friendly etc.The study and development for its relevant material has become focus.In this thesis,we first study the impact of various kinds of electrolytes on the performance of nickel-zinc batteries in order to obtain the optimal electrolyte formula;Then,nano-ZnO/carbon composites are prepared by adopting sol-gel method,the assembled nickel-zinc battery displays long cycle life and high energy density;Third,the intermediate phaseα-β-Ni_1-xAl_x（OH）₂ is synthesized by doping Al³⁺in Ni（OH）₂ lattices,the effect of reaction conditions on product performance is investigated;Finally,nickel-zinc battery is assembled by usingα-β-Ni_1-xAl_x（OH）₂（x=0.05）cathode,nano-ZnO/C anode and polyacrylic acid sodium（PAAS）gel electrolyte in an aluminum-plastic film package,and its electrochemical performance is studied.Compare with commercial nickel-zinc batteries,the batteries prepared by us exhibite relatively high energy density and long cycle life.The specific research contents are as follows:（1）By adding different polymers into KOH aqueous solution,PAAS-KOH quasi-solid electrolyte,polyvinyl alcohol（PVA）-KOH solid electrolyte and PVA-glutaraldehyde（GA）-KOH solid electrolyte were obtained.The electrochemical performances of batteries by adopting different electrolytes were compared.The cycle stability testing results showed PAAS-KOH quasi-solid electrolyte>PVA-GA-KOH solid electrolyte>PVA-KOH solid electrolyte>KOH aqueous electrolyte.The NiZn battery adopting PAAS-KOH quasi-solid electrolyte was charged for 3 min at a charge-discharge current density of 20 m A·cm^-2.After 800 cycles,the battery still maintained the energy density of 169.41 Wh·kg^-1 and Coulombic efficiency of above 96%,showing good cycle stability and long cycle life.（2）we designed a novel and facil sol-gel method to prepare nano-ZnO/carbon composite,including the formation of Zn（NO₃）₂-polyvinylalcohol（PVA）-glutaraldehyde（GA）gel and transformation into nano-ZnO/carbon composite at high temperature.Transmission electron microscopy（TEM）,elemental mapping measurement evidence the formation of nano-ZnO/C particles with 20-50 nm.Cyclic voltammetry（CV）and electrochemical impedance spectroscopy（EIS）measurement demonstrated an optimal mass ratio of C to ZnO being 1:8 for the high electrochemical performances,outperforming commercial ZnO and pure ZnO.Nickel-zinc battery fabricated by nano-ZnO/C composite could maintain an energy density of 172.33Wh·kg^-1 and coulombic efficiencies of above 95%for 2000 cycles.This was greatly attributed to the synergistic effect of the conductivity carbon layer and nanoscale of the composites.The influence of carbon content on the electrochemical performances of nano-ZnO/carbon composite was systematically investigated,and a detailed formation mechanism was proposed.This facile and easily scaled-up synthesis method could further extend to the preparation of other metal-oxide/carbon nanocomposites for energy storage devices.（3）Using urea as precipitant,the intermediate phaseα-β-Ni（OH）₂ was prepared by using Al³⁺to replace part of Ni²⁺of Ni（OH）₂ crystalline lattices under hydrothermal condition.The effect of Al³⁺contents on the phase structure of the product was investigated in the detail.The possible reasons were proposed.The field emission scanning electron microscope images illustrated that when the aluminum content is 5%,the morphology of the particles was honeycomb-like structures formed by intersecting sheets.The CV,EIS and the charge-discharge properties of the single electrode had also been tested.The optimal synthesis conditions were obtained.When the molar content of Al³⁺was 5%,the CV test showed that the specific capacity ofα-β-Ni_1-xAl_x（OH）₂（x=0.05）was 444.44 m Ah·g^-1 at a scan speed of 2 m V·s^-1,which was close to theoretical specific capacity ofα-Ni（OH）₂.The NiZn battery assembled withα-β-Ni_1-xAl_x（OH）₂ as the cathode exhibited significant rate performance.After cycling 300 times at 20m A·cm^-2,the nickel-zinc battery still retained the energy density of 165.86 Wh·kg^-1 and Coulomb efficiency of more than 97%,showing better cycle stability.（4）The NiZn battery was assembled usingα-β-Ni_1-xAl_x（OH）₂（x=0.05）cathode,nano-ZnO/C composite anode instead of zinc flakes,and PAAS gel electrolyte.When the cycle numbers were more than 1100 times at the charge-discharge current density of 20 m A·cm^-2,the NiZn battery still maintained 143.21 Wh·kg^-1 of the energy density,which was 96%of the original energy density,and Coulomb efficiency was more than 97%.It showed that the battery has better cycle stability and performance was better than commercial nickel-zinc batteries.