Electrochemical Properties of Polymer‐Derived SiCN Materials as the Anode in Lithium Ion Batteries

Abstract

Polymer‐derived SiCN materials, pyrolyzed from polysilylethylenediamine at temperatures between 600° and 1500°C, are used as the anode in lithium batteries, and their electrochemical performance is studied. The SiCN materials, having composition ranging from organic to inorganic and phase structures from amorphous to crystalline, are obtained from pyrolysis at different temperatures. Electrochemical measurements show that the 1000°–1300°C derived SiCN materials exhibit a first‐cycle discharge capacity of 608–754 mAh/g at a current density of 40 mA/g, which is higher than that of a graphite anode. The discharge capacity reduces to 170–230 mAh/g after seven charge–discharge cycles and stays in this range over 30 cycles. Compositional and structural analyses show that the 1000°–1300°C derived SiCN materials have an amorphous phase and contain free carbon in the SiCN network. In contrast, the 600°–800°C derived SiCN, which contains organic groups, and the 1400°–1500°C derived SiCN, which contains SiC crystallites, show a much lower charge and discharge capacity compared with that of the amorphous SiCN anode. This suggests that free carbon in SiCN and the amorphous structure of the SiCN materials contribute to the electrochemical performance of the SiCN materials. It seems that the free carbon phase acts as an active site for the insertion of Li ions while the amorphous SiCN network provides a path for Li‐ion transfer. The strong dependence of the electrochemical capacities of the polymer‐derived SiCN materials on their compositions and structures suggests the potential to enhance the electrochemical performance of the materials through molecular design and/or the control of material structure.

Determination of the Diffusion Coefficient of Lithium ions in Graphite Coated with Polymer‐Derived SiCN Ceramic

“…Depending on the scan rate the intercalation/extraction mechanism may be controlled by electron transfer (slow scan rate) or diffusion transport (high scan rate). If the redox process is controlled by diffusion, then the diffusion coefficient can be calculated from the modified Randles-Sevcik equation: /, = 2.69xl0 5 ■ n vi ■ S ■ D' /2 ■ c" · v ,/2 (4) where ¡ p is the peak current, n is the number of electrons per species reaction, S is the apparent surface area of the electrode (geometric area), D is the diffusion coefficient of Li + in the solid state and c* is the change in Li concentration in the material due to the specific step to which the peak is related. The Li concentration in graphite/SiCN composites was calculated using elemental analysis data of the C, N, O contents combined with electrochemical measurements according to equation (5) where xu = molar ratio of Li atoms in the host, Q rev = reversible capacity in mAh/g (galvanostatic charge/discharge with i = 18 mA/g), M mo \ -molecular mass of the host (100 g/mol), F = Faraday constant (96485 C/mol).…”

“…Recently, there has been a growing interest in SiCN polymer-derived ceramics (PDCs) as anode materials for lithium ion batteries [3,4]. We showed that polyvinylsilazane (PVS)-derived SiCN ceramics exhibit low discharge capacity (about 44 mAh/g) while the reversible capacity of graphite/polymer-derived SiCN composite is 10 times higher [3].…”

“…Li et al studied SiCN materials derived from polysilylethylenediamine (PSEDA). The authors showed that the capacity of such anode material is between 170 and 230 mAh/g after 30 cycles [4].…”

“…The free carbon in the SiCN materials is an active site for lithium intercalation while the amorphous structure of SiCN provides a pathway for lithium ion transfer [4,7].…”

Lithium intercalation into SiCN/disordered carbon composite. Part 1: influence of initial carbon porosity on cycling performance/capacity

“…In spite of those promising results, the research on lithium storing in Si-based ceramics has been mostly dedicated to silicon oxycarbide (SiOC) materials while the lithium intercalation into SiCN-based ceramics has been Breviewed^first about 20 years later by Kolb et al [7], who studied lithium insertion into SiCN/graphite composites. Pure polymer-derived SiCN materials obtained from polysilylethylendiamine have been investigated by Su et al [8] and Feng [9]. The work of Su et al showed a first discharge cycle capacity of 456 mAh g −1 but the material suffered from strong fading with cycling.…”