Preparation Investigation of Stable Negative Electrode for Lithium-Sulfur Battery
Authors: Machida Kazuki , Ushioda Yusuke , Miyauchi Hibiki , Takahashi Keitaro , Seki Shiro 
Published: July 2021

Rechargeable batteries have been desired improvement of energy density and cost performance owing to increase utilization of renewable energies. Lithium-Sulfur (Li-S) battery is expected as a next-generation rechargeable battery. This battery has consisted by elemental sulfur (S8) as the positive electrode and lithium metal as the negative electrode. Li-S batteries have advantage in terms of capacity, S8 has high theoretical capacity (1,672 mAhg-1) as positive active material. And, S8 obtained from by- products of petroleum. However, some problems exist for practical application of Li-S batteries. As problem of the S8 positive electrode, Li-S batteries were caused greatly capacity degradation by dissolution of lithium polysulfide (Li2S
x
(x=2~8)) which is reaction intermediate into electrolyte during charge process. Also, as problem of the negative electrode, short-circuit occur owing to the growth of Li dendrites on the electrode surface during charging process. Therefore, we propose electrochemically stable positive and negative electrodes. Li4Ti5O12 (LTO) is known as non-degradation negative electrode material. LTO electrode, is called “strain-free intercalation material”, don't change in lattice size during Li insertion/desorption. The LTO negative electrode is expected to high reversible characteristics and long battery life. On the other hand, positive electrode was applied sulfurized polyacrylonitrile (SPAN) for sulfur positive electrode. SPAN has theoretical capacity of 545 mAhg-1. The SPAN prevent dissolution of Li2S
x
into the electrolyte owing to chemical bonding with S. Application of SPAN to Li-S battery is not limited to electrolyte materials such as carbonate-based electrolyte. However, both LTO and SPAN electrode don't have reactive lithium ion. Therefore, We proposed the method to install Li ion into electrode without cell disassembling. In this study, possibility of proposed method was evaluated by charge/discharge tests.

We propose installing method of Li metal on negative electrode during charge/discharge processes. In this method, Li metal is installed on the LTO negative electrode, and were doped gradually into electrode during early charge/discharge reactions. The weight of the positive electrode, negative electrode and Li foil were controlled, so that each capacity would be LTO > Li > SPAN and fabricated cell was evaluated by constant current charge/discharge tests at 303K.

Fig. 1 shows the charge/discharge profiles of fabricated cell by proposed method which was installed Li metal on LTO negative electrode. Prepared cell exhibited the capacity of approximately 450 mAhg-1 at 1st cycle. Therefore, reversible charge/discharge reactions without cell reassembling were achieved. However, considering long term use, electrolyte choice is also important for high thermal stability. Therefore, we focused ionic liquid and polymer electrolyte owing to their high thermal stability. In this presentation, we will report the result of battery evaluation using ionic liquid and polymer electrolyte.

Figure 1