Proceedings of the National Power Systems Conference (NPSC) - 2018, December 14-16, NIT Tiruchirappalli, India Design, Fabrication and Electrochemical performance of Soluble Lead Redox-Flow Battery for Energy Storage Shivangi Kosta R Sneha Kuldeep Rana Electrical Appliances Technology Electrical Appliances Technology Electrical Appliances Technology Division Division Division Central Power Research Institute Central Power Research Institute Central Power Research Institute Bangalore, India Bangalore, India Bangalore, India [email protected] [email protected] [email protected] Single electrolyte, single pump and absence of membrane Abstract - Flow batteries are being considered as a potential reduces the cost of the system and makes it less candidate for large scale energy storage system, however, complicated as compared with other flow batteries. It can main issue with them is their higher cost due to the electrode also be operated without any separable membrane leading materials and membrane used in them. In this regards, current work is focused on the development of cost effective to decrease in the cost as well as the usage of cell flow batteries. In order to reduce the cost of flow batteries, equipment; overall simplifies the cell design. The low cost graphitic carbon was used for both positive and performance of the cell is completely based on the negative electrodes to fabricate the soluble lead redox flow fabrication and structure of the electrodes and the batteries (100 cm2) without using any separator. Lead electrolyte composition [8]. The reaction site and the methane sulfonate (1M) and methane sulfonic acid (1M) were current collector membrane determine battery power used as electrolytes, which plays an important role in whereas volume of the electrolyte tank gives battery reduction and oxidation process of redox flow batteries. The energy. The reason why soluble lead redox flow batteries charge/discharge behavior has been studied at constant are uniquely opted using single electrolyte is because a current of 500 mA, which showed an average efficiency of 79 % with an initial discharge capacity of 200 mAh. The cell single species lead (II) ion is both oxidized and reduced capacity decreases during the 14-15th cycles and becomes 110 upon charging and discharging of the cell. The electrolyte mAh, this loss in capacity has been studied after cut down consists of high concentrated lead methanesulfonate (LMS) analysis of cell. and methanesulfonic acid (MSA) circulated between the electrodes by pumping it [2]. During the charge Pb2+ is Keywords – Energy Storage, Electrode Fabrication, Membrane oxidized leading to deposition of lead-oxide on positive free SLRFB, electrochemical performance. electrode surface and metallic lead at negative electrode. I. INTRODUCTION During the discharge, the electrodeposits dissolve back into electrolyte [9]. With the growing energy demand worldwide for The following reversible reactions take place at the cleaner and cheaper energy, energy storage plays a crucial electrodes as described above- role to facilitate the penetration of renewables into Negative: Pb2+ + 2e- → Pb E0 = -0.125 V (1) 2+ + electricity network. Redox flow batteries (RFB) are Positive: Pb + 2H2O - 2e- → PbO2 + 4H (2) becoming popular choice for large scale energy storage E0 = 1.468 V 2+ + including load levelling and reserve electricity supplies as Overall: 2Pb + 2H2O → Pb + PbO2 + 4H (3) well as power sources for traction. RFBs are well- E0 = 1.593 V established energy storage technologies which is accessible RFBs are comparatively different from other lead acid worldwide, due to its flexibility in decoupling energy and batteries as they have different chemistry and performance power. Various chemistries of flow batteries such as characteristics, as well, used for different industrial vanadium, Fe-Cr, Fe-V, Zn-Br, Br-polysulphide are applications. The two major problems associated with existing today, however among all other technologies, SLRFBs are dendrite growth of Pb at the negative vanadium redox system is more matured and developed electrode and partial irreversibility of PbO2 at the positive system [1]. All the flow battery system employed an ion- electrode, as reported in earlier papers [10]. The SLRFB exchange membrane, which are expensive and increases has been developed in different size and configuration, as the complexity associated with unwanted ion transport reported previously [11]. through this membrane. Further different electrolytes being Here we report the electrochemical behaviour of a used for the anode and cathode as anolyte and catholyte, single cell without using any separable membrane and any leading to increase in the complexity of the system. additives. The graphite electrodes of 10 x 10 cm were Therefore, they require further modification to make it as fabricated and designed to form a single cell. The higher commercial application by lowering the cost. concentration of electrolyte has been reported [2,3], Further attempts are being made to improve the therefore, 0.5 M of lead methanesulfonate and 0.5 M of performance and cost reduction of flow batteries. The methanesulfonic acid has been considered to eventually soluble lead redox flow battery (SLRFB) system has know the behaviour of lead ions with different shown the much promise of reducing cost. It is based on configurations. 2+ 2+/ the two redox couples Pb/Pb and Pb PbO2, which can be fabricated without using any membrane/separator [2-7]. 978-1-5386-6159-8/18/$31.00 ©2018 IEEE Proceedings of the National Power Systems Conference (NPSC) - 2018, December 14-16, NIT Tiruchirappalli, India II. EXPERIMENT to the G-band, which arises from the in-plane vibrations of carbon atoms; the other peak, at which is around 1350 cm−1 Chemicals Used corresponds to the D-band, arises from the disorder in The electrolyte used in SLRFB has been synthesized graphitic structure. Thus the XRD and Raman spectrum using lead methane sulfonate (LMS, Pb(SO CH ) , 50% of 3 3 2 confirms that the electrode material used for cell H O) and methane sulfonic acid (MSA, HSO CH ). An 2 3 3 fabrication is well crystalline without having any aqueous solution of the electrolyte was prepared using de- impurities. ionised (DI) water and molarity concentration was kept at 0.5 M. The electrolyte was used as synthesized. TABLE I DIMENSIONS OF SOLUBLE LEAD REDOX FLOW BATTERY Flow cell Width Length (cm) Thickness (mm) parts (cm) Graphite 12 (depth of 2 mm 12 12 Electrodes for each cell) Circulation 10 10 4 area Current 12 12 2.5 Collectors Aluminum 20 20 12 End Plate Designing of Redox flow single cell A single flow cell of soluble lead redox flow battery (SLRFB) was designed and fabricated, which consists of graphite plates (electrodes), copper current collectors, insulating end plates insulated with current collector by Fig. 1. Optical image of (a) Al end plate (b) Cu current collector (c) Graphite plate (d) FRG gasket (e) Redox flow battery single cell (100 cm2 FRG sheets. The detail dimensions of the SLRFB are listed area) (f) Graphical Side view of Redox flow battery in Table 1. The A rotor pump (Ravel-Peristalic Pump) at a flow rate of 90 ml min-1 was operated for the circulation of electrolyte. The electrolyte was pumped inside the single cell assembly to check the electrochemical behaviour of the cell. The designing and fabrication details of the single cell have been demonstrated in Fig. 1. It consists of two graphite electrodes (Fig. 1c) which are assembled without using any separator. Both the graphite plates have been fabricated in such a way to provide the space for the flow of electrolyte. In this design two graphite plates are stacked with a FRG gasket in between and the active area for the 2 electrode is 100 cm . These graphite plates are provided with inlet and outlet connections for the flow of electrolyte. Fig. 2. (a) XRD pattern of Graphite (b) Raman spectra of The two graphite plates are attached with copper current Graphite. collectors as shown in Fig. 1 (f). Finally the fabricated cell has been connected with electrolyte tank through the Electrochemical Performance of SLRFB single cell peristatic pump. The battery was connected to a Battery The SLRFB single cell was assembled and tested with Life Cycle Tester (LCV16-100-12) and charge/discharge constant current mode. Each electrode had an exposed studies were carried out at electrolyte flow rate of 90 ml surface area of 10 cm x 10 cm. The galvanostatic cycling min-1. tests were performed using Bitrode battery testing system. The electrodes were consistently subjected to a constant III. RESULTS AND DISCUSSIONS current of 500 mA in voltage range of 1.0 to 1.98 V at the flow rate of 90 ml min-1. Before assembling the cell the electrode material used Initially in formation cycles the charge/discharge in cell has been characterized by XRD and Raman capacity was low as shown in Fig. 3 (b), which increases spectrum in order to confirm the crystal structure and and stabilized in next few cycles. The fourth quality of carbon materials used respectively. Carbon based charge/discharge behaviour of the cell is demonstrated in materials are already being used as the material of choice Fig. 3 (a). From the charging profile of cell two different for various energy storage devices [12,13,14]. The XRD charging plateau can be seen clearly, at constant current pattern of electrode materials is shown in Fig 2 (a), which voltage initially increases and then became constant (~1.98 shows a sharp peak at 26.6o which is characteristic V). After reaching the voltage up to 1.98 V, cell has been diffraction peak of crystalline graphite corresponding to discharge at constant current of 500 mA till end voltage of 002 plane, no peaks other than graphite has been observed 1.0 V. The discharge plateau has been observed at around ~ in XRD pattern.