Exploration Of Anode Electrode Materials For Ni-MH Battery With Complex Environment Application

Ni/MH battery is an energy storage device that can realize the mutual conversion of chemical energy into electric energy by the storage and release of hydrogen.It has been commercialized because of excellent electrochemical performance and safety at room temperature.However,the low capacity and poor cycle stability of anode electrode material for Ni-MH battery are still the technical challenges with complex working environment.In this work,the key problems of the anode electrode,such as low discharge capacity at low temperature,poor overcharge resistance and cycle stability at wide temperature and high temperature,low capacity of AB₅alloy and poor rate capability of superlattice alloy,were investigated.The anode electrode materials,with excellent electrochemical performances in complex environments,were designed and developed from the regulation of thermodynamics and kinetics,the improvement of the corrosion resistance and pulverization resistance,and overpotential regulation.The main study contents are as follows:Firstly,based on the problem of low discharge capacity of anode electrode for Ni-MH battery at low temperature,the first principle calculation showed that the hydride stability of Ce Ni₅ was lower than that of LaNi₅ alloy.Therefore,a dual regulation strategy by La/Ce ratio to regulate the thermodynamics and kinetics of alloy electrode at low temperature was proposed,and its effect on the performance of alloy electrode was systematically studied.The optimized La/Ce ratio reduced the thermodynamic stability,and the decrease of the charge transfer resistance and the increase of the hydrogen diffusion coefficient improved the kinetic performance of the alloy electrode.The low temperature discharge performance of the alloy electrode significantly improved by optimizing the La/Ce ratio.The maximum discharge capacity of La_0.55Ce_0.37M electrode at 0.2C reached 317.3 m Ah g^-1,and the rate capability at 1C and discharge capacity were 8.38%and 27.2 m Ah g^-1 at-40°C,respectively.The discharge capacity of commercial AAA battery reached 71 m Ah at a large current of 1000 m A at-40°C.Then,in view of the poor cycle stability and overcharge resistance of the alloy electrode at high temperature and wide temperature,Nb element with large bulk modulus,high standard potential and high hydrogen adsorption energy was introduced.The first principle calculation showed that that Nb preferentially occupied the position of Ni in LaNi₅ alloy.The calculation results of Gibbs free energy of reaction on the alloy electrode surface showed that Nb-doped alloy electrode promoted Volmore reaction and inhibited Hhelovsky and Tafel reaction,which promoted the overpotential of alloy electrode.Based on the above theoretical analysis,the La_0.68Ce_0.30-xZr_0.02Nb_xNi_4.16Co_0.36Mn_0.30Al_0.38（x=0,0.025,0.05）and La_0.46Ce_0.42-xPr_0.03Nd_0.08Zr_0.02Nb_xNi_4.41Mn_0.36Al_0.28（x=0,0.05,0.1）alloy electrodes with high temperature and wide temperature overcharge resistance were prepared,respectively.The mechanism of Nb-doped on improving the high temperature and wide temperature performance of the electrodes was analyzed by the tests of corrosion,pulverization and overpotential.It is clarified that Nb-doped increased the corrosion resistance,and the increase of overpotential improved the pulverization resistance of the alloy electrodes.Therefore,the alloy electrodes are expected to be used in overcharge resistant at wide temperature and high temperature for Ni-MH batteries.Finally,in order to solve the problems of low capacity of AB₅ and poor rate capability of superlattice alloy electrode,high capacity A₂B₇ second phase was introduced in AB₅ alloy and element doped was used to improve the electrochemical performance of the alloy electrode.The Sm-doped and Y-doped Pr/Nd/Mg-free low-cobalt La_3.0xCe_xSm_0.98-4.0xZr_0.02Ni_3.91Co_0.14Mn_0.25Al_0.30（x=0.08,0.12,0.16,0.20,0.245）and La_0.90-xCe_0.08Y_xZr_0.02Ni_3.91Co_0.14Mn_0.25Al_0.30（x=0,0.3,0.5,and 0.7）alloy electrodes were prepared,respectively.The introduction of the second phase promoted the hydrogen diffusion capability and the Ca Cu₅ phase had excellent catalytic performance,which made the AB_4.6 alloy electrode exhibiting excellent rate capability.Y tended to form[A₂B₄]subunit and promoted the formation of stable Ce₂Ni₇ phase,which increased the discharge capacity.The increase of the anti-corrosion resistance improved the cycle stability for Sm-and Y-doped alloy electrodes.Moreover,the formation of Sm（OH）₃ and Y（OH）₃ films on the alloy electrode surface were conducive to the improvement of cycle stability.