Pyrolyzed Polysiloxanes for Use as Anode Materials in Lithium‐Ion Batteries

Abstract

More than sixty siloxane polymers containing various organofunctional siloxane units were synthesized. The synthesized siloxane polymers were pyrolyzed in inert gas at 1000°C. Chemical analysis showed that the products of pyrolysis were distributed over a well‐defined region in the Si‐C‐O Gibbs phase diagram. The electrochemical and structural properties of these materials were measured using coin‐type test cells and x‐ray powder diffraction, respectively. The most interesting materials are found near the line in the Si‐C‐O Gibbs triangle connecting carbon to Si0.13 . Materials with the largest reversible specific capacity for lithium (about 900 mAh/g) are on this line and were at about 43% carbon, 32% oxygen, and 25% silicon (atomic percent). Materials which were almost pure carbon showed diffraction patterns characteristic of disordered carbons. Along the line from carbon to SiO1.3 the sample structure can be described as a mixture of single or small groups of graphene sheets mixed with regions of Si‐C‐O amorphous glass. The amount and composition of the glass changed according to the overall sample composition. Moving from carbon to SiO1.3 , the reversible capacity first rises from about 340 mAh/g for pure carbon, to a maximum of 900 mAh/g near 50% carbon, and then falls to near zero mAh/g at 0% carbon. This suggests that the amorphous glass can reversibly react with lithium, provided the carbon is present to provide a path for electrons and Li ions. However, the hysteresis in the voltage profile (difference between charge and discharge voltages) and the irreversible capacity increase almost linearly along this line. There is a clear correlation between both the irreversible capacity and hysteresis in these materials with their oxygen content. Along the line connecting carbon to silicon, the reversible capacity rises from 340 mAh/g for pure carbon to about 600 mAh/g for samples with about 15 atomic percent Si. It then decreases to near zero as the composition nears SiC. Along the C‐SiC line, the irreversible capacities remain below about 200 mAh/g. We are quite convinced that optimized silicon‐containing carbons can be good alternatives to pure carbons as anode materials in lithium‐ion batteries.

Lithium-silicon alloys: Phase diagram, electrochemical studies, thermodynamic properties, application in chemical power cells

“…The same evidence can be found in a review by Skundin and co-authors, published in Uspekhi Khimii journal (Russian Chemical Review) (390 references) [93]. The fi rst experimental studies of the processes of lithium introduction into anodes containing silicon nanoparticles were reported in [98][99][100][101][102][103][104][105].…”

Electrochemical studies of carbon-rich polymer-derived SiCN ceramics as anode materials for lithium-ion batteries

“…Usually "soft" carbons consist of graphene layers which can develop graphitic structures with increasing temperature. 6 In numerous studies related to disordered carbons, Dahn et al [7][8][9][10][11][12][13][14]25,26 have demonstrated that in both cases, for soft and hard carbons, the reversible capacity reaches its minimum for heat-treatments of the materials at about 1700 • C. However the reversible capacity of hard carbons thermolyzed at T < 1700 • C should be higher than that observed for our SiCN samples 1, 2 and 3. This result indicates the presence of soft disordered carbons in our investigated materials.…”

“…7 Lithium intercalation in some disordered carbons derived from various precursors, e.g. sucrose, 8,9 petroleum coke, 10 pitch-polysilanes blends, 11,12 siloxanes, [13][14][15][16][17][18] and silazanes [19][20][21][22] has been studied in the presence of conductive additives such as acetylene black powder. 22 It was demonstrated that despite the quite high irreversible capacity observed during first intercalation/deintercalation, the disordered carbons are perspective materials for negative electrodes in lithium-ion batteries because of their relatively high reversible capacity, stability in cycling, low price and availability.…”

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

“…Undoubtedly, these performance differences reveal that the microstructures of our TVS- doped PMAN carbons are still somewhat different from those of of the pitch-polysiloxane blends studied in Ref. 6 which were prepared at a much higher temperature than our PMAN carbons. The precursor pyrolysis temperature can have profound effects on the resulting microstructure and chemistry of the resulting carbons.…”