次世代電池用Si負極の創製へ向けたLi-ナフタレニド溶液によるLiプレドープ技術の開発

Abstract

In recent years, new-generation batteries such as Li-S and Li-O_2 systems, have been strongly demanded for the power source of electric vehicles (EVs). These systems possess excellent potentials for higher energy densities beyond the conventional Li-ion batteries. However, Li metal was basically used as the negative electrode (NE) because of not only the achievement of high energy density but also non-containing of Li in the positive electrodes. However, this causes to the risk of short-circuit by Li dendrite growth during charge/discharge cycling. On the contrary, Si is a good alternative to Li metal NE because of the high theoretical energy capacity (3580 mAh g^<-1>) and difficulty of Li dendrite growth. To apply the Si NEs to next-generation batteries, it is necessary to Li pre-dope, i.e. Li-Si alloying, in advance to practical use. In this study, two different approaches: (1) direct pre-doping (DP) method by contacting Li metal foil in electrolyte solutions and (2) solution pre-doping (SP) method using Li-naphthalenide (Li-NTL) solutions were introduced especially for the effects on the homogeneity and depth of Li alloying of Si NE and the following charge/discharge properties. The DP method using fluoroethylene carbonate (FEC) additive clarified the importance of the interphase stabilization of Si NE to improve the cycle performance. For the practical use, the SP method using 2-methyltetrahydrofulan (MeTHF) solvent also found to achieve an excellent homogeneity and depth owing the lowest equilibrium potential relating the solution structure.