Self-Chargeable Lithium Ion Batteries with Perovskite Solar Cells
Authors: Yeongbeom Kim , Na Dan , Lim Hyeonsu , Jeong Hyeonwoo , Baek Jiyeon , Seo Inseok 
Published: December 2020

The necessity of developing new types of energy conversion and storage systems is evident by the rapidly decreasing fossil fuels and the continuously growing environmental issues. Coupling of lithium ion secondary batteries and photovoltaic cells is a reasonable candidate of new types of energy transform and storage system to reduce environmental concerns. Solar cells can ensure sustainable access to electrical power for charging LIBs anywhere around the world with no air pollution, hazardous waste or noise. Accordingly, the solar cell technology that generates electricity from the sunlight [1], could offer a viable approach to ‘self-charging’ of LIBs. However, most current solar cells, especially polymer solar cells, generally show low current densities and power conversion efficiencies, and to improve this we used perovskite solar cell for power supply of self-chargeable batteries. The recent availability of high-performance perovskite solar cells (PSCs) could not only facilitate the development of highly efficient (up to ~ 20 %) [2] and low cost solar cells for practical applications but also allow for the integration of PSCs into various energy systems. One of the important problems of PSC-LIB coupling is that when charging, the voltage of the PSCs must be higher than the operating voltage of the LIBs. If the above conditions are not established, PSCs may cause discharge of the LIBs. The most structurally stable LiFePO4(LFP)-LTO(Li4Ti5O12) batteries were used for coupling. In the case of LFP-LTO batteries, the OCV(open circuit voltage) value has a low voltage of 1.85V. It was confirmed that stable self-charging is achieved by connecting it to a manufactured PSCs pack with a charging voltage of 2.1 V. This work clearly indicates that the PSC-LIB units developed in this study hold great promise for potential applications as self-chargeable batteries to various portable electronics.

In this study, we have fabricated lithium-ion pouch cell and coin cell based on LFP and (LTO) as a cathode and an anode, respectively. The cathode was fabricated by blending LFP powder with carbon black (Super P) and polyvinylidene difluoride (PVDF) at a weight ratio of 8:1:1. The anode was also prepared in the same way as the cathode using LTO powder and N-Methyl-2-pyrrolidone (NMP) was used as the solvent, respectively. The Electrolyte was used 1.2 M LiPF6 in a 1:1(v/v, %) mixture of ethylene carbonate and dimethyl carbonate. Pouch cell was fabricated with size of 3 cm x 5 cm. Ni and Al were used as cathode and anode lead tabs, respectively. The LIBs were assembled as the CR 2032 coin-type cells and pouch cells in an Ar-filled glove box. Structural properties and chemical compositions of LFP and LTO powders were investigated by x-ray diffraction (XRD) and x-ray photoelectron spectroscopy (XPS). The XRD pattern shows that the LiFePO4 cathode sheets are crystalline. The powder and surface morphologies of electrode sheet were characterized by FE-SEM. The primary particles size was identified as approximately 50 to 150 nm and the secondary particles size approximately 10mm. The electrochemical performance of LFP and LTO half cells and the LFP-LTO full cell were conducted by cyclic voltammetry and charge/discharge cycle tests at various current densities in the voltage ranges. Electrochemical impedance spectroscopy (EIS) was performed in frequency range from 0.1 Hz to 1 MHz, using 10 mV ac signals at room temperatures. LFP-LTO pouch cells showed good cycling stability a wide range of C-rates from 0.1 to 1.0 C with charge/discharge capacities of 142/138 mAhg-1 at 0.1 C and 152/144 mAhg-1 at 1.0 C. As a result, LiB-PSC coupling enabled the implementation of self-chargeable batteries. Finally, Perovskite solar cells and the Li-ion battery coupling were tested for a self-chargeable device.

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