Study On Improvement Of Specific Capacity And Rate Performance Of Li-MnO₂Battery

Li-MnO₂primary battery demonstrates high specific capacity and high specific power.It has been widely used in military and daily life such as portable electronic devices.However, there is a severe capacity loss when Li-MnO₂battery is used at high dischargerate. The high rate performance of the battery is limited by the positive electrode material ofelectrolytic manganese dioxide（EMD）. In this thesis, the effect of high energy ball-millingtreatment of EMD on its morphology, structure and discharge performance are stuided,aiming to improve the discharge specific capacity and high rate discharge performance ofEMD in Li-MnO₂battery.The influence of high energy ball-milling treatment on the structure and dischargeperformance of EMD is first investigated. SEM and TEM results show that the morphologyof EMD was obviously changed from irregular block to spherical particles with a significantdecrease in particle size fater ball-milling. The majoty of the particle have nanosizeddimesion and the largest particles have a diameter of less than around5m. The result ofXRD showed that the ball-milling did not alter the crystal structure of EMD, which has aγ-phase and γ/β mixed phase after heated at400℃for12h. The electrochemical testdemonstrated that the ball-milled EMD has better electrochemical performance thancommercial EMD. At the discharge rate of0.1C, the specific capacity of the ball-milledEMD is26%higher than that of the prinstin commercial EMD.The effects of thermal treatment temperature and quenching on the dischargeperformance of ball-milled EMD were stidued. The result of XRD indicated that MnO₂wasconverted from γ-MnO₂to β-MnO₂upon heating treatment, and only presents as β-MnO₂when the temperature reached450℃. The sample heated at400℃showed the bestdischarge performance. At the discharge rate of0.1C, the specific capacity of the EMD was242mAh·g^-1. Quenching treatment did not change the structure of EMD but make the edgeof particles smoother. The discharge platform voltage of the quenched EMD was higher thanthat of the unquenched EMD.The EMD electrode made by mechancial pulping was better than that made byball-milling pulping. At the discharge rate of0.1C,0.5C and1C, the specific capacity ofthe electrode using PVDF as binder was17%,19%and19%higher than that using LA^-132 binder, respectively. The specific capacity of the electrode made by adding CF_xin the EMDwas286,169and163mAh·g^-1at the discharge rate of0.1C,0.5C and1C respectively,which proved that the discharge performance of the electrode was improved obviously byadding CF_x.