• Mičušík, Matej
• Güneren, Alper
• Hudec, Boris
• Siffalovic, Peter
• Sahoo, Prangya P.
• Lenčéš, Zoltán

Abstract

<jats:p>Surface modification using thin layers grown by atomic layer deposition (ALD) is an effective strategy for performance improvement of Li-ion batteries. Ultrathin Al<jats:sub>2</jats:sub>O<jats:sub>3</jats:sub> layers are the most studied coating material. In our contribution we compare properties of Al<jats:sub>2</jats:sub>O<jats:sub>3</jats:sub> and ZnO ultrathin layers prepared by ALD on lithium-iron-phosphate (LFP) cathodes and Si-graphite anodes.</jats:p><jats:p>Ultrathin Al<jats:sub>2</jats:sub>O<jats:sub>3</jats:sub> and ZnO films were grown at 100 °C using trimethylaluminum (TMA) and diethylzinc (DEZ) precursors, respectively, with water vapors as reactant. The growth rates of the Al<jats:sub>2</jats:sub>O<jats:sub>3</jats:sub> and ZnO films were about 0.1 nm/cycle on control flat Si substrates. ALD layers thickness in this study ranged from 5 to 20 cycles. A modified deposition recipe utilizing a prolonged precursor dwell time in the reactor chamber for coverage of the highly porous battery electrodes has been utilized. As TMA, DEZ and H<jats:sub>2</jats:sub>O all have rather high vapor pressures, we assume that significant part of the electrodes were coated.</jats:p><jats:p>Porous LFP cathodes (NANOMYTE BE-60E, NEI Corp.) with the thickness of 70 μm were used as a substrate. The average particle size of the LFP substrate was ~ 2 μm with the specific surface area of 15 m2/g and active material loading of 7.3 mg/cm2. Experimental capacity C of the LFP electrode is 170 mAh/g in the voltage range 2.5 - 4.1 V using 0.1 charging/discharging c-rate.</jats:p><jats:p>As an anode material porous silicon-graphite composite electrode sheets NANOMYTE BE-150E (NEI Corp) with the thickness of 65 μm and composition of active material 20% Si and 65 % graphite were used. The nominal capacity C of the silicon-graphite anode is 750mAh/g in the voltage range 0.05 - 1V using 0.05 charging/discharging c-rate.</jats:p><jats:p>In our contribution we present specific discharge capacity of the electrodes as a function of charging/discharging cycles. For both pristine and Al<jats:sub>2</jats:sub>O<jats:sub>3</jats:sub> protected LFP cathode sheets specific discharge capacity of 160 mAh/g was achieved at the c-rate of 0.2. The specific capacity of the pristine LFP electrode dropped from 160 mAh/g at the c-rate 0.2 to about 90 mAh/g for the c-rate 1, while the electrode protected by 0.5 nm of Al<jats:sub>2</jats:sub>O<jats:sub>3</jats:sub> saturated at 120 mAh/g. Properties of ZnO- protected LFP cathodes are compared to that covered by Al<jats:sub>2</jats:sub>O<jats:sub>3</jats:sub>.</jats:p><jats:p>Electrochemical properties of the silicon-graphite anode were studied using low c-rate of 0.05. During the first cycles the specific capacity is relatively low due to the formation of the solid-electrolyte interface layer at the surface. After several cycles the capacity increased to the nominal value of 750 mAh/g. In our study we compare the charging/discharging capability of the pristine silicon-graphite anode and that of the electrodes covered by 5 -20 ALD cycles of Al<jats:sub>2</jats:sub>O<jats:sub>3</jats:sub> and ZnO films during the first charging/discharging cycles. We discuss the effect of ALD protecting layers on the rate capability of the silicon-graphite anode. Finally, the results of the electrochemical measurements are compared to those obtained by X-ray photoelectron spectroscopy.</jats:p>

Topics

• porous
• impedance spectroscopy
• surface
• x-ray photoelectron spectroscopy
• composite
• Silicon
• Lithium
• iron
• atomic layer deposition