Improvement of Charge-Discharge Characteristics of the Mg-Ni Powder Electrodes at 55°C

Magnesium-nickel (Mg-Ni) powders are used as the anode materials for secondary lithium (Li) ion batteries. Mg-Ni powders with ratios of 1？:？1 (Mg？:？Ni) are prepared and their structure and electrochemical behavior at room temperature and 55°C are investigated. The results show that adding Ni powders to Mg powders can reduce the charge-discharge capacities and improve cycling life. In charge-discharge cycle testing at 55°C, the Li ion concentration gradually increased with increasing the duration of electrochemical reactions, indicating that the charge-discharge capacities increase with increment of cycling number. The formation of a solid electrolyte interface (SEI) layer restrains Mg ions from dissolving into the electrolyte and thus improves the charge-discharge capacities at high temperature. 1. Introduction Magnesium (Mg) was used as a negative electrode in lithium (Li) ion secondary batteries due to its high theoretic capacity [1]. However, pure metal electrodes have a serious problem of volume expansion during cycling that resulted in poor cycling life. Adding poor-activity elements into a pure metal matrix reduces the volume expansion of an electrode. Studies on alloy electrode materials have focused on Sn- [2], Si- [3], and Mg-based alloys [4, 5]. Of the electrodes based on these alloys, Mg-based ones are one of the potential material in Li-ion battery applications. Many studies have indicated that Mg-based alloy electrode, such as Mg-Li, Mg-C, and Mg-Ni alloys, can enhance battery performance via various electrochemical mechanisms [4, 6–8]. Adding Li into Mg can enhance the efficiency of lithiation and delithiation [9] and Mg-C alloys can restrain the growth of the solid electrolyte interface (SEI) layer [4]. In the present study, Mg-Ni powder electrodes were fabricated to suppress the volume change of the electrode and increase oxidation resistance. Mg-Ni material is a typical active/nonactive alloy system that can effectively suppress the volume expansion and improve battery cycling life. Many researchers have prepared Mg-Ni alloys using the mechanical grinding method [10, 11]. However, the proportion of Mg to Ni is not easy to control, and Mg-Ni alloys with excessive Ni have reduced charge-discharge capacity [12]. In addition, Mg easily oxidized to form MgO phases during mechanical milling [13]. The formation of MgO phases may degrade the cycling performance of batteries. In this study, Mg powder was directly mixed with Ni powder in a glove box. Because the particle size of Mg powder and that of Ni powder is very different, alloying effect