Polymer Silica Nanocomposite Gel Electrolytes for Lithium-Ion Batteries

Akhila Das, Anjumole P. Thomas, Neethu T. M. Balakrishnan, Nikhil Medhavi, Jou-Hyeon Ahn, Jabeen Fatima M. J., and Prasanth Raghavan

Lithium-Ion Batteries (LIB): A Brief Introduction

Lithium-ion batteries (LIB) were commercialized in 1990 by the Sony Corporation. The development of LIBs for the fabrication of portable energy storage devices resulted in the award of the 2019 Nobel Prize in Chemistry to three eminent scientists, namely Prof. John. B. Goodenough, Prof. Michael Stanley Whittingham and Prof Akira Yoshino (Figure 10.1). Prof. Goodenough laid the foundation for a cathode based on lithium cobalt oxide (LCO) by studying the intercalation property of these inorganic materials [1]. The chemistry of intercalation was explained by Prof. Stanley Wittingham during his investigation of the intercalation behavior of transition metal ions in certain chalcogenides, like TiS2 [2]. Prof. Akira Yoshino was the person who created a prototype lithium-ion battery [3].

Images of Nobel laureates in Chemistry, 2019, from left to right

FIGURE 10.1 Images of Nobel laureates in Chemistry, 2019, from left to right: Prof. John B. Goodenough, Prof. M. Stanley Whittingham and Prof. Akira Yoshino. Adapted and reproduced with permission from The Royal Swedish Academy of Science [4]. Copyright © Nobel Media 2019. Illustration: Niklas Elmehed.

A typical lithium-ion battery consists of a cathode, an anode and an electrolyte (Figure 10.2). The material of the cathode employed in LIBs can include lithium cobalt oxide (LiCo02, LCO) or lithium iron phosphate (LiFeP04, simply LFP). The anode mainly found in commercial lithium-ion batteries is graphite, which has the capability to intercalate lithium ions into the interstitial sites, which is first proposed by Prof. Rachid Yazami. The electrolyte is considered to be the heart of the battery. During the early stages of LIB development, liquid electrolytes containing lithium salts were used. These liquid electrolytes caused many serious safety issues, such as leakage and fires.

The most vital issues limiting the use of these energy storage devices are the safety issues. Even after decades of commercialization, safe portable energy storage devices are still a nightmare, owing to the incidence of safety issues generated and reported over the past few years. Several reports, regarding fires and explosions of lithium-ion batteries, have been reported all over the world, hence, the risk of explosion is the most worrying issue. The US Federal Aviation Administration (FAA) announced new aviation standards, published by the U.S. Department of Transportation (DOT) in July 2014 [5], in order to reinforce the safety conditions to facilitate the safe and reliable transport of the lithium-ion batteries, as these could cause fires, if not appropriately packaged, shipped and transported. Several news reports were published on the recall of the batteries owing to the risk of fires. One of the largest recalls occurred when the famous laptop provider, Dell, recalled about

4.1 million batteries of notebook computers in 2006 [6]. On 26 February 2013, the Ryobi lithium battery pack (18 V 4 Ah) was recalled due to some batteries overheating and catching fire during charging [7]. During 2016, Samsung was forced to

Schematic illustration of the structure and operating principles of lithium- ion batteries, including the movement of ions between electrodes during charge

FIGURE 10.2 Schematic illustration of the structure and operating principles of lithium- ion batteries, including the movement of ions between electrodes during charge (forward arrow) and discharge (backward arrow) states.

recall the Dream mobile series Galaxy Note 7 as the batteries were reported to catch fire. These facts indicate that the batteries that we carried along with us were not at all safe. In addition to these portable devices, LIBs are being widely explored for use in electric vehicles (EVs) for a sustainable eco-friendly transportation system. Chevrolet's Volt EV was about to launch, but, during the crash test, the batteries was seriously affected, leading to them catching fire [8]. Many suggestions were put forward by scientists to overcome these issues, such as the use of safer electrolytes, like polymer electrolytes, and the inclusion of active flame-retardant agents in the electrolytes. Both these methods are being widely investigated by the researchers for commercialising safer and more efficient energy storage devices particularly for portable systems like mobile phones, laptops, tablets and EVs.

Gel Polymer Electrolytes for Lithium-Ion Batteries

Gel polymer electrolytes are the most active topic of battery research, owing to the risk factors encountered in portable energy storage devices. These gel polymer electrolytes are synthesized by immobilizing liquid electrolytes, containing the active metal ion, in a polymer membrane. Such liquids act as a medium for active conduction of ions, whereas the polymers form a mechanical support for these active liquids and as a separator in LIBs. Among polymers, polyethylene oxide (PEO), polypropylene oxide (PPO), polymethyl methacrylate (PMMA), polyvinyl pyrrolidone (PVP), polyacrylonitrile (PAN), polyvinylidene difluoride (PVdF), polyvinylidene difluo- ride-co-hexafluoropropylene (PVdF-co-HFP) and polyethylene terephthalate (PET) are some of the polymer matrices used as electrolytes in LIBs. The major disadvantage of these polymer electrolytes is their lower ionic conductivity compared with conventional liquid electrolytes. Various methods have been adopted to increase the ionic conductivity of these electrolytes materials. The most effective strategy, and the one most widely adopted, is to increase the amorphous nature of these polymers by the incorporation of fillers. Several organic and inorganic fillers, such as cellulose [9-12], cellulose derivatives [13], chitin [14], chitosan [15], kraft lignin [16], carbon nanotubes (CNTs) [17], graphene oxide (GO) [18], aluminum oxide (A1,0,) [19-23], nickel oxide (NiO) [24], titania (TiO,) [25-29] and silica (SiO,) [30-34], have been studied. The present chapter investigates the role of silica as a ceramic filler in the performance of gel polymer electrolytes for lithium-ion batteries. The different forms of silica, such as nano-silica, fumed silica, ш-л/Гм-generated silica, functionalized silica, etc., have been evaluated. A detailed investigation will be carried out in this chapter on the synthesis and the properties (thermal, mechanical, ion transport and electrochemical) of silica incorporated into gel polymer electrolytes for LIBs.

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