Sn–Ni Alloy Anode Pre-Doped in Vinylene Carbonate Containing Electrolyte for Lithium-Ion Capacitor

Lithium–ion capacitor (LIC), which is composed of non–Faraday reaction cathode used in electric double layer capacitor (EDLC), and Faraday reaction anode used in lithium–ion battery (LIB), is a promising energy storage device for electric vehicles, because LICs are ranked between LIBs and EDLCs for energy density and power density.¹ LIC with Sn–Ni alloy anode is superior to that with a graphite anode in energy and power density. ² For the purpose to improve its cycle durability to a practical level, the effect of vinylene carbonate (VC) which affects positively for LIBs, was investigated.

Sn–Ni alloy anode was electrodeposited according to the previous report.³ The Sn–Ni alloy anode was pre-doped (pre-lithiated) by several charge–discharge cycles in an electrolyte with or without vinylene carbonate (VC). The LICs composed of an activated carbon cathode and the pre-doped Sn–Ni alloy anode were evaluated.

The VC additive was revealed to affect positively during a pre-doping process and to affect negatively during charge–discharge cycling to the cycle performance of LIC. The difference for the additive effect was discussed by the potential changes and the morphology changes of the anode, revealing that VC formed a polymer-like SEI during the pre-doping process, suppressing deactivation of Sn caused by cracking growth and peeling-off during charge–discharge cycling. In contrast, VC was decomposed continuously during charge–discharge cycling with consuming pre-doped lithium. Thus, a strategy to use additives for alloying anode system was established. Finally, the excellent cycle durability (more than 10000 cycles with the capacity retention of 72.3%) of the LIC with high volumetric energy density of 38.9 Wh/L at 120 W/L was firstly demonstrated (Fig. 1).

Acknowledgement

This work is partially supported by Advanced Low Carbon Technology Research and Development Program of the Japan Science and Technology Agency (JST-ALCA, JPMJAL1008).

References

1. K. Naoi, S. Ishimoto, J. I. Miyamoto, and W. Naoi, Energy Environ. Sci., 5, 9363–9373 (2012).

2. S. Ahn, Y. Nakamura, H. Nara, T. Momma, W. Sugimoto, and T. Osaka, J. Electrochem. Soc., 166, A3615–A3619 (2019).

3. H. Mukaibo, T. Sumi, T. Yokoshima, T. Momma, and T. Osaka, Electrochem. Solid-State Lett., 6, A218 (2003).

Figure 1