Electrochemical Fabrication and Characterization of Silicon Microwire Anodes for Li Ion Batteries

Abstract

With a technique allowing for large-scale production, which is based on electrochemical etching, silicon microwire anodes for Li ion batteries anodes are produced. The wires exhibit high areal capacity due to their diameters in the micron-range, and high cycling stability due to the formation of a homogeneous solid electrolyte interface around each of them. This study summarizes the importance of the (exact) battery work parameters and their dependence on the wire dimensions. Furthermore, it compares two anode concepts in which the wires can be incorporated. FFT-impedance analysis shows the characteristic resistance changes under specific conditions, which relate directly to the processes in the wires 6 can be used to structure Si. Nevertheless, in the most of the works with these techniques, wires randomly distributed are presented. A random distribution of sizes and spacings of the wires limits the battery performance because the diffusion of Li into the wires is not homogeneous.Due to progress in the electrochemical pore formation in n-and p-doped Si by different groups around the world, homogeneous, nano-and micro-structured Si can be produced. With the anodic etching of Si in various electrolytes, different pore structures have been developed. [7][8][9][10][11] In this study electrochemical pore etching and chemical over-etching processes for the production of wire arrays for battery anodes were optimized in order to obtain a silicon wire array with intergrown stabilizing planes. The wire arrays, when used as anodes of batteries, withstand large stresses, and present a stable capacity of 3150 mAh/g for over 100 cycles with an areal capacity of 4.25 mAh/cm 2 , 1 a record among Si anode concepts. It is well known that graphite anodes suffer from a continuously growing solid electrolyte interphase (SEI) which forms due to the decomposition of the electrolyte, thus hindering further intercalation of Li in the graphite. Astonishingly for the silicon microwire anodes discussed in this paper, we found that the SEI stops to grow after the first three charge/discharge cycles, which is one reason for the good cycling stability.This paper deals with the fabrication and electrochemical characterization of the Si microwire anodes, emphasizing the importance of the wire dimensions, which determine the optimum charging/discharging conditions of the anodes. Depending on the size of the wires, the characteristic potentials and impedances are given. For this study, besides the Si microwire array anodes, also paste electrodes have been produced with the same microwires; this allowed a simpler electrochemical characterization of Si microwires of different sizes without the need of optimizing Cu deposition on the wires (a needed step for the array anodes). Cyclic voltammetry and FFT impedance spectroscopy (FFT-IS) have been used for the electrochemical characterization. * Electrochemical Society Student Member.* * Electrochemical Society Active Member. z E-mail: sn@tf.uni-kiel.de Processing of Si MicrowiresThe basic fabrication...

Single CuO/Cu2O/Cu Microwire Covered by a Nanowire Network as a Gas Sensor for the Detection of Battery Hazards

“…Since the sensor is also sensitive to CO 2 and H 2 (and other VOCs) at lower temperatures, it has an early and fast gas response in case the battery starts to degrade, without further decomposition and spreading of the thermal event. Figure S12 in the Supporting Information shows an example of a Si microwire anode exposed to high temperatures during discharge of the battery. , This anode consists of many, individual Si microwires (∼130 μm long) without the need for additional conducting materials as is common in battery anode fabrication. More details on the fabrication of these wires can be found in the literature. , Compared to classical lithium-ion batteries, silicon has the advantage of being a noncritical material with increasing temperature, and it can thus be operated at higher temperatures …”

“…Figure S12 in the Supporting Information shows an example of a Si microwire anode exposed to high temperatures during discharge of the battery. , This anode consists of many, individual Si microwires (∼130 μm long) without the need for additional conducting materials as is common in battery anode fabrication. More details on the fabrication of these wires can be found in the literature. , Compared to classical lithium-ion batteries, silicon has the advantage of being a noncritical material with increasing temperature, and it can thus be operated at higher temperatures Figure S12 shows a typical voltammogram of such a Si anode cycled in a half-cell vs metallic lithium at 65 °C.…”

Effects of Lithium Polysulfides on the Formation of Solid Electrolyte Interfaces in Silicon Anodes

“…For the first cycle, independent of the degree of oxidation, the same trends can be observed. For the samples tested in the E1 electrolyte, the potential during the initial constant current discharge-cycling is decreasing more rapidly toward the lower potential limitation of 0.1 V. This behavior can be attributed to the initial alloying of silicon with lithium. ,,,,,− The differential capacity analysis (Figure S1a,b) indicates a minor peak around 1.1 V, attributed to the reduction of electrolyte components and therefore SEI formation. ,,, The samples cycled in the presence of lithium PS show a dominant plateau at about 1.8 V (Figure c,d and Figure S1a–d), which is even more pronounced for increasing PS concentration and can be related to the reaction of lithium-ions with the added PS, resulting in a more pronounced stepwise reduction of the mixed polysulfide species . With increasing cycle number, the charge and discharge behavior for the low and high surface oxide content differs, especially with respect to the added PS.…”

Отрицательные Электроды Для Литий-Ионных Аккумуляторов, Полученные Фотоанодированием Кремния Солнечной Градации

“…Кремниевые структуры, полученные методом электрохимического травления, являются перспективным материалом для анодов литий-ионных аккумуляторов [1][2][3][4][5]. При использовании Si-структурных элементов (наностенок или нанопроволок) нужного размера, ограничении количества лития, внедряемого в электрод, и оптимальных токов заряда/разряда кремниевые аноды стабильно работают в составе полуячейки [6][7][8]. Разработанная нами ранее технология получения упорядоченных 3D-структур с тонкими монодисперсными стенками [8][9][10] позволила получать аноды, не проявляющие признаков деградации в течение более 1200 циклов при удельной емкости 1000 mA • h/g и демонстрирующие кулоновскую эффективность на уровне 98−100% (за исключением первых нескольких циклов).…”