Laser-assisted surface engineering of thin film electrode materials for lithium-ion batteries
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Laser-assisted surface engineering of thin film electrode materials for lithium-ion batteries Wilhelm Pfleging 1, Robert Kohler 1, Steffen Scholz 2, Carlos Ziebert 1, Johannes Proell 1 1 2
Institute for Applied Materials, Karlsruhe Institute of Technology, Karlsruhe, Germany Manufacturing Engineering Centre, School of Engineering, Cardiff University, CF24 3AA, UK
ABSTRACT Electrode thin films made of LiCoO2, Li-Mn-O and SnO2 were synthesized by rf magnetron sputtering on silicon and stainless steel substrates. In order to increase the active surface direct laser structuring methods using ns- and ps-laser sources were applied. A laser system operating at a wavelength of 248 nm with a pulse length of 4-6 ns and repetition rates up to 500 Hz enabled the formation of high aspect ratio micro- and sub-micron structures with feature sizes down to less than 400 nm. Subsequent to the laser structuring process, laser annealing of LiCoO2 and Li-Mn-O was performed in order to achieve an appropriate crystalline phase which shows improved electrochemical cycling performance. Laser annealing was applied via a high power diode laser system operating at a wavelength of 940 nm. In case of LiCoO2 the high temperature phase was obtained through laser-annealing while for Li-Mn-O the spinel phase was formed. For both LiCoO2 and Li-Mn-O thin films appropriate annealing parameters were temperatures of up to 680 °C and an annealing time of 100 s. INTRODUCTION There is an increasing demand for powerful rechargeable battery systems suitable for automotive applications as well as for temporary storage of electrical energy provided by wind generators or solar power plants. The demand for further miniaturization has also opened the research field for micro-batteries which can be integrated into nearly any mobile device [1-3]. With respect to the type of application different challenges and requirements concerning the type and architecture of battery materials will arise. Energy density, power density and battery lifetime (cycle stability) strongly depend on the scenario of application. Nowadays, research and development of those specialized battery systems is mainly focused on powerful rechargeable lithium-ion batteries (LIB) due to their high reversible capacity [4]. Hereby, the development of cathode and anode materials plays an important role in battery technology [5]. Three dimensional battery systems have been proposed to enhance the power density while maintaining high energy densities for micro-battery systems [6]. To create thin film electrodes applicable for this purpose, different manufacturing methods have been investigated, e.g. chemical vapor deposition [7-9], pulsed laser deposition [10,11] or rf magnetron sputtering [12-15]. Investigations have been carried out to create 3D micro-batteries, yet most efforts have been focused on structuring the substrate which was silicon in most cases [16,17]. The deposition of such thin films on structured substrates is still a difficult task [18].
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Current studies are focused on nano-comp
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