Study On Cathode Material Ag-modified MnO₂of Li-MnO₂Primary Battery

Lithium-manganese dioxide battery（Li-MnO₂battery）is one of the most widely usedprimary batteries, which is the cheapest and safest battery among all lithium primarybatteries. It has high voltage and energy density, excellent discharge performance, superiorstorage characteristics, wide operating temperature range and low self-discharge. Theperformance of a Li-MnO₂battery is greatly influenced by the properties of the manganesedioxide cathode material. Electrolytic manganese dioxide （EMD） is generally used forLi-MnO₂battery cathode material. EMD has low electrical conductivity, which leads to thebattery with poor high rate discharge performance. This work aims to increasing theconductivity and improving the high-rate discharge performance of Li-MnO₂battery.Ag modified ball-milled commercial MnO₂（Ag-MnO₂） cathode materials weresynthesized by the formation of Ag metal on the surface of MnO₂via thermal decomposionand chemical reduction of Ag salts. The obtained materials were characterized byX-diffraction spectroscopy （XRD）, scanning electron microscopy （SEM）, transmissionelectron microscopy （TEM） and energy-dispersive spectrometry （EDS）. Li-MnO₂primarybatteries were fabricated using Ag-MnO₂material as positive electrode and lithium metalsheet as negative electrode. Their electrochemical performance was investigated byconstant current discharge measurements and electrochemical impedance spectroscopy.XRD results show that the as-prepared MnO₂has γ and β phase, and β phase is themajority. SEM and TEM images show that Ag-MnO₂has a spherical shape with differentdiameters. EDS analysis indicates that the content of Ag is close to the calculated value anduniformally dispersed on the surface of MnO₂.Ag-MnO₂was synthesized via the thermal decomposition of AgNO₃and AgAc,respectively. The optimal heat treatment temperature and loading of Ag were found to be400℃and5wt%, respectively. The discharge specific capacity of Ag-MnO₂preparedusing AgNO₃and AgAc is233.9and202.6mAh·g^-1at0.1C,172.0and164.5mAh·g^-1at0.5C,110.6and106.3mAh·g^-1at1C. The discharge plateau voltage is around2.75,2.60and2.50V, respectively.Ag-MnO₂was synthesized by chemical reduction of AgNO₃using NaBH4、C2H5OHand HCHO as reducing agent. The optimal Ag content is5wt%. The discharge specific capacity of the Ag-MnO₂prepared using NaBH4、C2H5OH and HCHO reducing agent is187.2,238.0and227.2mAh·g^-1at0.1C;144.1,128.9and160.6mAh·g^-1at0.5C;89.9,88.3and114.5mAh·g^-1at1C, respectively. The highest discharge plateau voltage reachedaround2.76,2.60and2.50V, respectively. Ag-MnO₂exhibited higher discharge specificcapacity and plateau voltage than EMD. It is believed that Ag particles formed an electricalconductivity network and increased the conductivity of EMD, resulting in improvedhigh-rate discharge performance of Li-MnO₂battery.