Nano Aspects of Advanced Positive Electrodes for Lithium-Ion Batteries
In the last two decades, demand for rechargeable batteries with high specific energy or high energy density has been increasing for applications in portable electronic devices such as mobile phones (feature phones and smartphones), notebook personal compu
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Nano Aspects of Advanced Positive Electrodes for Lithium-Ion Batteries Kuniaki Tatsumi
3.1
Introduction
In the last two decades, demand for rechargeable batteries with high specific energy or high energy density has been increasing for applications in portable electronic devices such as mobile phones (feature phones and smartphones), notebook personal computers (PCs), and tablet PCs. Since these electronic devices possess relatively large and bright display panels (liquid-crystal or organic electroluminescence), smaller and lighter rechargeable batteries are required to lengthen the devices’ battery life. Furthermore, the need is rapidly increasing for electrochemical power sources applied to electric vehicles (EVs), hybrid electric vehicles (HEVs), and plugin HEVs (PHEVs). In particular, the European Union (EU) CO2 emission regulation proposed for 2020 has made a strong impact on future automotive power trains, and EVs and PHEVs are thought to be indispensable for meeting this regulation. Concerning applications to vehicles, required specifications are often much more stringent than those for portable electronic devices. In particular, the calendar life favorable to vehicle application A calendar life of more than 10 years, which favors vehicles, is much longer than the calendar life of electronic devices. Hence, much effort has been devoted to understanding the degradation mechanisms that limit the calendar life of lithium-ion cells [1–18]. In recent years, it has been shown that changes at the nano-surface region of positive electrode materials play important roles in the power fading of lithium-ion batteries. From the viewpoint of lithium insertion/deinsertion of positive electrode materials, nano-surface effects on power fading are not surprising but rather reasonable. However, the nano-surface region of a material is generally too thin to be examined; conventional analysis methods are often insufficient to highlight such a shallow area.
K. Tatsumi (*) Research Institute for Ubiquitous Energy Devices, National Institute of Advanced Industrial Science and Technology (AIST), 1-8-31 Midorigaoka, 563-8577 Ikeda, Osaka, Japan e-mail: [email protected] T. Osaka and Z. Ogumi (eds.), Nanoscale Technology for Advanced Lithium Batteries, Nanostructure Science and Technology 182, DOI 10.1007/978-1-4614-8675-6_3, © Springer Science+Business Media New York 2014
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K. Tatsumi
This chapter focuses on the nano-surface area of positive electrode materials as a typical feature of the nano aspect of positive electrodes, and research results on the nano surface of positive electrode materials are reviewed. Moreover, nano-surface modification methods of positive electrode materials are summarized.
3.2
Interphase Between Positive Electrode Materials and Electrolytes
Solid-electrolyte interphase (SEI) [19] is a very important and fundamental model to explain how metallic lithium and lithiated negative electrodes, for example graphite and carbon, work as electrochemical electrodes in nonaqueous liquid electrol
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