The Full-Cell Design of a Li-Ion Capacitor Using a Sn-Ni Alloy As an Anode

Abstract

Lithium-ion capacitors (LIC) is composed of a capacitors-type cathode and battery-type anode. Thus, LIC has been considered as a favorable electrochemical energy storage device to bridge the lithium-ion batteries (LIB) and supercapacitors.1 We have reported that the synthesis of Sn-Ni alloy by electrodeposition in aqueous solution and its electrochemical behaviors as an anode for LIB and LIC.2,3 Through the above reports, we confirmed that the LIC consisting of Sn-Ni anode shows higher energy and power density than graphite anode based LIC because of high theoretical capacity of Sn (997 mAh g-1). Herein, the material characterization of Sn-Ni alloy was carried out. Besides, full-cell performances of LIC were tested and compared depending on with/without cell optimization.The Sn-Ni alloy is synthesized by electrodeposition using aqueous electrolyte consisting of Tin(II) chloride dihydrate and Nickel(II) chloride. The material characteristics of Sn-Ni alloy were examined by field emission scanning electron microscopy, X-ray diffraction, glow discharge optical emission spectroscopy, and inductively coupled plasma analysis. The electrochemical performances of Sn-Ni anode and LIC full-cell were tested using alf- and full-cell.The Sn-Ni alloy synthesized by electrodeposition has Ni3Sn4 phase which affects the reversible reaction of Sn-Ni alloy as an anode during lithiation/de-lithiation.2 For that reason, Sn-Ni alloy shows a good discharge performance as an anode for LIC (Fig. 1(a)). The in-depth chemical properties of Sn-Ni alloy was examined by GDOES (Fig. 1(b)). The region from the surface to around 6.9 μm shows that the Sn and Ni are mixed. After that, Cu peak corresponding to the Cu substrate was increased, resulting in an intermediate layer consisting of Sn, Ni, and Cu. The Cu signal after 29.4 μm is relatively higher than Sn and Ni, implying that only Cu substrate was presented. This result indicates that the Sn and Ni are mixed from top of Sn-Ni alloy to middle of film with a thickness of approximately 29. 4 μm.Full-cell optimization of LIC was conducted by mass balancing between cathode and anode. It was confirmed that LIC with cell optimization shows improved energy density and power density compared to LIC without cell optimization. Also, LIC consisting of Sn-Ni anode have higher energy and power density than LIC assembled using graphite anode (Fig.1 (c)). Through the above discussion, we believe that this report provides a blueprint for high-performance LIC with Sn-Ni alloy anode.(Figure 1)Fig. 1 (a) XRD patterns, (b) GDOES curves of Sn-Ni alloy, and (c) Ragone plot of LIC. 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).