A Stretchable Lithium-Ion Battery Using Liquid Metal Nano Particle

Abstract

Introduction Stretchable devices have been highly demanded because of wearable devices in the IoT society. Stretchable lithium ion batteries are crucial to growth of IoT society, since the current developed devices possesses only interface part. The batteries and devices require higher stretchability and robustness to deformation. Liquid metal (LM) is one of the prominent materials for stretchable sensors(1) and wiring circuit(2). In addition, LMs have self-healing characteristics(3) and high capacity (Ga:769 mAh/g, Sn:990 mAh/g) in lithium ion batteries. Here, we investigated the electrochemical characteristics and improvement of robustness using liquid metal nano particles (LMNP) anode in stretchable lithium ion batteries. In this study, stretchable 3D porous LMNP electrodes are fabricated and assembled into stretchable batteries. The stretchable batteries consist of stretchable LMNP and LiFePO4 (LFP) electrodes based on 3D porous polydimethylsiloxane (PDMS)/Ecoflex/Super P carbon composites, stretchable separator, [Li(G4)][TFSI] electrolyte and stretchable package. The batteries have high stretchability and robustness to deformation. Experiment 3D porous PDMS/Ecoflex/Super P carbon composites were used for stretchable electrode substrates. The porous structure was prepared by sacrifice-template method using sugar(4). 3D porous PDMS/Ecoflex/Super P carbon composites was composed of PDMS, Ecoflex with the weight ratio of 6:4 and coating Super P carbon on the surface. LMNP was prepared by ultra-sonication GaSn (Ga:Sn=88:12) alloy. The LMNP alloy was used as active materials of anode. The anode slurries were prepared by mixing the LMNP, Super P carbon, poly(vinylidene fluoride) (PVDF) in N-methyl-2-pyrrolidione (NMP) solvent. LFP was used as active materials of cathode. The cathode slurries consisted of LFP, Super P carbon, PVDF. Stretchable electrodes were fabricated by drop cast method with the electrode slurries on the 3D porous substrates. [Li(G4)][TFSI] was composed of LiTFTI and Tetraethylene glycol dimethyl ether (G4). Stretchable batteries were assembled using the PDMS/Ecoflex/Super P carbon/LMNP anode, PDMS/Ecoflex/Super P carbon/LFP cathode, stretchable separator and stretchable packaging. The nickel/aluminum tabs are attached to PDMS/Ecoflex/Super P carbon/LMNP and PDMS/Ecoflex/Super P carbon/LFP electrode by using small amount of epoxy resin adhesive(Fig. 1). Results and Discussion To investigate the electrochemical characteristics of the stretchable electrode on lithium ion batteries, we respectively conducted galvanostatic tests of the stretchable LMNP anode and the stretchable LFP cathode in half-cell configurations paired with lithium metal as counter and reference electrode. The results show the electrodes can charge/discharge on lithium ion batteries at 1 C. In addition, the electrochemical performance of the stretchable LMNP electrode was investigated. The charge/discharge curves were measured after 100% strain-release cycle 50 and 100 times. The results of the stretchable LMNP electrode showed the capacity retention was higher than the stretchable Si NP (silicone nano particle) electrode. The LMNP used as active materials improve robustness to stretching were confirmed. The full cells were tested using PDMS/Ecoflex/Super P carbon/LMNP and PDMS/Ecoflex/Super P carbon/LFP electrode with charge/discharge measurement. As a result, the full battery could work. Acknowledgement This work was supported by JST CREST Grant Number JPMJCR1905, Japan, by the Japan Science and Technology Agency, PRESTO Grant Number JPMJPR18J2, and by JSPS Grant-in-Aid for Challenging Exploratory Research. References (1) Yuji Gao et al, Advanced. Materials , 2017, 1701985(2) Guangyong Li et al, Sensors and Actuators B , 2015, 221, 1114-1119(3) Yingpeng Wui et al, Energy & Environmental Science , 2017, 10, 1854-1861(4) Hongsen Li et al, Advanced. Materials , 2017, 1700898 Image Figure 1 Self-healing behavior of LMNP (left). Schematic diagram of stretchable battery (right). Figure 1