Structural and Electrochemical Characterization of Glassy Carbon Prepared from Silicon‐Doped Polymethacrylonitrile/Divinylbenzene Copolymer

Abstract

Recently, the formation of lithium graphite intercalation compounds (GICs) using turbostratic (random stacking) carbon has attracted considerable attention because significantly higher intercalation levels (compared to ordered graphite compounds) have been claimed, ranging up to the composition LiC 2 . 1 Furthermore, intercalation into these materials is associated with virtually no change in layer spacing, resulting in better reversibility. Because of these favorable properties, turbostratic and disordered carbon-based GICs have been of increased interest as a substitute for metallic lithium or lithium alloys as anode materials in rechargeable organic electrolyte batteries. Li anodes, while having a high specific energy and capacity, suffer from dendrite formation on repeated cycling, resulting in short-circuiting and reduced lifetimes. Li-ion carbon electrodes do not suffer these effects. The Li ϩ is shuttled back and forth between the intercalation cathode and the carbon anode during charge and discharge. The excellent cycling behavior of disordered carbonbased LiC n anodes is frequently associated with their topological stability during insertion/extraction of lithium.A very promising polymer precursor system has been emulsion-derived polymethacrylonitrile/divinylbenzene copolymers (PMAN/DVB). 2 Amorphous or turbostratic carbons derived from these materials are being studied for gas separation, catalysis, and battery-anode applications. Their preparation is carried out in a three-step process: (i) the comonomers are polymerized as the continuous phase in a surfactant stabilized micelle emulsion, (ii) the highly cross-linked networks are dried and further oxidatively stabilized by thermal treatment in air at temperatures near 220ЊC, and (iii) the final carbonized materials are prepared by pyrolysis within the temperature range 400-1100ЊC under an inert 95/5 Ar/H 2 atmosphere. The resulting samples are treated by sieving, followed by characterization of their physical and chemical properties and electrochemical testing.Work by Wilson and Dahn has suggested that the introduction of silicon-containing species into a carbon microstructure can improve electrochemical intercalation characteristics, especially by enhancing the reversible capacity of the lithium-intercalated material. Silicon-doped carbons were prepared by either of two methods: chemical vapor deposition of benzene and silicon-containing precursors, 3 or thermal pyrolysis of siloxane polymers (polymethylphenylsiloxane and polyphenylsesquisiloxane). 4 Reversible capacity for the CVD carbons was reported to be near 500 mAh/g, and reversible capacities for the pyrolyzed siloxane polymers were reported to be near 600 mAh/g at a level of 11 atom % Si. These capacities exceed the maximum theoretical capacity for lithium-intercalated graphite, LiC 6 , which is 372 mAh/g, making these materials interesting for further study.More recently, Dahn and co-workers have examined pyrolyzed pitch-polysilane blends and various polysiloxanes as anode materials for Li-io...

Nano- and bulk-silicon-based insertion anodes for lithium-ion secondary cells

“…Similarly, Hayes et al [70] reported formation of Si/C composites from polymethacrylonitrile/divinylbenzene (PMAN/DVB) copolymer as a carbon precursor and tetramethylsilane (TMS) or tetravinylsilane (TVS) as Si precursor. These were mixed to form an emulsion which was polymerized at 65 • C, thermally stabilized in air at 240 • C, and finally pyrolyzed at 700 • C. The resulting material was found to have large oxygen content (22.5 wt%), negligible nitrogen content (2.99 wt%), and 10 wt% Si.…”

Nanostructured Si-Based Anodes for Lithium-Ion Batteries

“…The improved performance is attributed to the coated amorphous carbon which enhanced high electrical conductivity and can buffer volume change and the agglomeration of Si nanoparticles. Hayes et al 85 86 prepared Si/C composite by ball milling graphite and crystalline Si in different atomic ratios for 150 h, then mixed the powder with colloidal polytetrafluoroethylene (PTFE) in anhydrous alcohol to prepare the anodes. The Si nanoparticles together with the graphite were encapsulated in amorphous carbon.…”