Silicon oxycarbide glass-graphene composite paper electrode for long-cycle lithium-ion batteries

Citation: David, L., Bhandavat, R., Barrera, U., & Singh, G. (2016). Silicon oxycarbide glass-graphene composite paper electrode for long-cycle lithium-ion batteries. Nature Communications, 7, 10. doi:10.1038/ncomms10998Silicon and graphene are promising anode materials for lithium-ion batteries because of their high theoretical capacity; however, low volumetric energy density, poor efficiency and instability in high loading electrodes limit their practical application. Here we report a large area (approximately 15 cm x 2.5 cm) self-standing anode material consisting of molecular precursor-derived silicon oxycarbide glass particles embedded in a chemically-modified reduced graphene oxide matrix. The porous reduced graphene oxide matrix serves as an effective electron conductor and current collector with a stable mechanical structure, and the amorphous silicon oxycarbide particles cycle lithium-ions with high Coulombic efficiency. The paper electrode (mass loading of 2mg cm(-2)) delivers a charge capacity of similar to 588mAhg(-1) (electrode) (similar to 393mAhcm(-3) (electrode)) at 1,020th cycle and shows no evidence of mechanical failure. Elimination of inactive ingredients such as metal current collector and polymeric binder reduces the total electrode weight and may provide the means to produce efficient lightweight batteries

Polymer-Derived Ceramic Functionalized MoS2 Composite Paper as a Stable Lithium-Ion Battery Electrode

Citation: David, L., Bhandavat, R., Barrera, U., & Singh, G. (2015). Polymer-Derived Ceramic Functionalized MoS2 Composite Paper as a Stable Lithium-Ion Battery Electrode. Scientific Reports, 5, 7. doi:10.1038/srep09792A facile process is demonstrated for the synthesis of layered SiCN-MoS2 structure via pyrolysis of polysilazane functionalized MoS2 flakes. The layered morphology and polymer to ceramic transformation on MoS2 surfaces was confirmed by use of electron microscopy and spectroscopic techniques. Tested as thick film electrode in a Li-ion battery half-cell, SiCN-MoS2 showed the classical three-stage reaction with improved cycling stability and capacity retention than neat MoS2. Contribution of conversion reaction of Li/MoS2 system on overall capacity was marginally affected by the presence of SiCN while Li-irreversibility arising from electrolyte decomposition was greatly suppressed. This is understood as one of the reasons for decreased first cycle loss and increased capacity retention. SiCN-MoS2 in the form of self-supporting paper electrode (at 6 mg.cm(-2)) exhibited even better performance, regaining initial charge capacity of approximately 530 mAh.g(-1) when the current density returned to 100 mA.g(-1) after continuous cycling at 2400 mA.g(-1) (192 mAh.g(-1)). MoS2 cycled electrode showed mud-cracks and film delamination whereas SiCN-MoS2 electrodes were intact and covered with a uniform solid electrolyte interphase coating. Taken together, our results suggest that molecular level interfacing with precursor-derived SiCN is an effective strategy for suppressing the metal-sulfide/electrolyte degradation reaction at low discharge potentials

Freeze-dried WS2 composites with low content of graphene as high-rate lithium storage materials

Few layered WS2-graphene nanosheet composites are prepared by a simple and scalable hydrothermal reaction and a subsequent freeze-drying method. The freeze-dried WS2-graphene composite exhibits good cycling stability and outstanding high-rate capability of lithium storage. The reversible capacity remains 647 mA h g-1 after 80 cycles at a current density of 0.35 A g-1. Comparable capacities of 541 and 296 mA h g-1 can still be maintained when cycling at even higher current densities of 7 and 14 A g-1 (7 and 14 mA cm-2) respectively.close10

MoS2/graphene composite paper for sodium-ion battery electrodes.

We study the synthesis and electrochemical and mechanical performance of layered freestanding papers composed of acid-exfoliated few-layer molybdenum disulfide (MoS₂) and reduced graphene oxide (rGO) flakes for use as a self-standing flexible electrode in sodium-ion batteries. Synthesis was achieved through vacuum filtration of homogeneous dispersions consisting of varying weight percent of acid-treated MoS₂ flakes in GO in DI water, followed by thermal reduction at elevated temperatures. The electrochemical performance of the crumpled composite paper (at 4 mg cm⁻²) was evaluated as counter electrode against pure Na foil in a half-cell configuration. The electrode showed good Na cycling ability with a stable charge capacity of approximately 230 mAh g⁻¹ with respect to total weight of the electrode with Coulombic efficiency reaching approximately 99%. In addition, static uniaxial tensile tests performed on crumpled composite papers showed high average strain to failure reaching approximately 2%

Molecular precursor derived SiBCN/CNT and SiOC/CNT composite nanowires for energy based applications

Doctor of PhilosophyDepartment of Mechanical and Nuclear EngineeringGurpreet SinghMolecular precursor derived ceramics (also known as polymer-derived ceramics or PDCs) are high temperature glasses that have been studied for applications involving operation at elevated temperatures. Prepared from controlled thermal degradation of liquid-phase organosilicon precursors, these ceramics offer remarkable engineering properties such as resistance to crystallization up to 1400 °C, semiconductor behavior at high temperatures and intense photoluminescence. These properties are a direct result of their covalent bonded amorphous network and free (-sp2) carbon along with mixed Si/B/C/N/O bonds, which otherwise can not be obtained through conventional ceramic processing techniques. This thesis demonstrates synthesis of a unique core/shell type nanowire structure involving either siliconboroncarbonitride (SiBCN) or siliconoxycarbide (SiOC) as the shell with carbon nanotube (CNT) acting as the core. This was made possible by liquid phase functionalization of CNT surfaces with respective polymeric precursor (e.g., home-made boron-modified polyureamethylvinylsilazane for SiBCN/CNT and commercially obtained polysiloxane for SiOC/CNT), followed by controlled pyrolysis in inert conditions. This unique architecture has several benefits such as high temperature oxidation resistance (provided by the ceramic shell), improved electrical conductivity and mechanical toughness (attributed to the CNT core) that allowed us to explore its use in energy conversion and storage devices. The first application involved use of SiBCN/CNT composite as a high temperature radiation absorbant material for laser thermal calorimeter. SiBCN/CNT spray coatings on copper substrate were exposed to high energy laser beams (continuous wave at 10.6 μm, 2.5 kW CO2 laser, 10 seconds) and resulting change in its microstructure was studied ex-situ. With the aid of multiple techniques we ascertained the thermal damage resistance to be 15 kW/cm2 with optical absorbance exceeding 97 %. This represents one order of magnitude improvement over bare CNTs (1.4 kW/cm2) coatings and two orders of magnitude over the conventional carbon paint (0.1 kW/cm2) currently in use. The second application involved use of SiBCN/CNT and SiOC/CNT composite coatings as energy storage (anode) material in a Li-ion rechargeable battery. Anode coatings (~1mg/cm2) prepared using SiBCN/CNT synthesized at 1100 °C exhibited high reversible (useable) capacity of 412 mAh/g even after 30 cycles. Further improvement in reversible capacity was obtained for SiOC/CNT coatings with 686 mAh/g at 40 cycles and approximately 99.6 % cyclic efficiency. Further, post cycling imaging of dissembled cells indicated good mechanical stability of these anodes and formation of a stable passivating layer necessary for long term cycling of the cell. This improved performance was collectively attributed to the amorphous ceramic shell that offered Li storage sites and the CNT core that provided the required mechanical strength against volume changes associated with repeated Li-cycling. This novel approach for synthesis of PDC nanocomposites and its application based testing offers a starting point to carry out further research with a variety of PDC chemistries at both fundamental and applied levels

Stable and efficient Li-ion battery anodes prepared from polymer-derived silicon oxycarbide-carbon nanotube shell/core composites

We demonstrate synthesis and electrochemical performance of polymer-derived silicon oxycarbide-carbon nanotube (SiOC-CNT) composites as a stable lithium intercalation material for secondary battery applications. Composite synthesis was achieved through controlled thermal decomposition of 1,3,5,7-tetramethyl 1,3,5,7-tetravinyl cyclotetrasiloxane (TTCS) precursor on carbon nanotubes surfaces that resulted in formation of shell/core type ceramic SiOC-CNT architecture. Li-ion battery anode (prepared at a loading of~ 1.0 mg cmˉ²) showed stable charge capacity of 686 mAh gˉ¹ even after 40 cycles. The average coulombic efficiency (excluding the first cycle loss) was 99.6 %. Further, the post electrochemical imaging of the dissembled cells showed no apparent damage to the anode surface, highlighting improved chemical and mechanical stability of these composites. Similar trend was observed in the rate capability tests, where the SiOC-CNT anode (with 5 wt.% loading in TTCS) again showed stable performance, completely recovering the first cycle capacity of ~ 750 mAh gˉ¹ when the current density was brought back to 50 mA gˉ¹ after cycling at higher current densities

Stable and Efficient Li-Ion Battery Anodes Prepared from Polymer-Derived Silicon Oxycarbide–Carbon Nanotube Shell/Core Composites

We demonstrate the synthesis and electrochemical performance of polymer-derived silicon oxycarbide–carbon nanotube (SiOC–CNT) composites as a stable lithium intercalation material for secondary battery applications. Composite synthesis was achieved through controlled thermal decomposition of 1,3,5,7-tetramethyl 1,3,5,7-tetravinyl cyclotetrasiloxane (TTCS) precursor on carbon nanotubes surfaces that resulted in formation of shell/core type ceramic SiOC–CNT architecture. Li-ion battery anode (prepared at a loading of ∼1.0 mg cm^–2) showed stable charge capacity of 686 mA h g^–1 even after 40 cycles. The average Coulombic efficiency (excluding the first cycle loss) was 99.6%. Further, the post electrochemical imaging of the dissembled cells showed no apparent damage to the anode surface, highlighting improved chemical and mechanical stability of these composites. A similar trend was observed in the rate capability tests, where the SiOC–CNT anode (with 5 wt % loading in TTCS) again showed stable performance, completely recovering the first cycle capacity of ∼750 mA h g^–1 when the current density was brought back to 50 mA g^–1 after cycling at higher current densities

Improved Electrochemical Capacity of Precursor-Derived Si(B)CN-Carbon Nanotube Composite as Li-Ion Battery Anode

We study the electrochemical behavior of precursor-derived siliconboron carbonitride (Si­(B)­CN) ceramic and Si­(B)­CN coated-multiwalled carbon nanotube (CNT) composite as a lithium-ion battery anode. Reversible capacity of Si­(B)­CN was observed to be 138 mA h/g after 30 cycles, which is four times that of SiCN (∼25 mA h/g) processed under similar conditions, while the Si­(B)­CN-CNT composite showed further enhancement demonstrating 412 mA h/g after 30 cycles. Improved performance of Si­(B)­CN is attributed to the presence of boron that is known to modify SiCN’s nanodomain structure resulting in improved chemical stability and electronic conductivity. Post-cycling microscopy and chemical analysis of the anode revealed formation of a stable passivating layer, which resulted in stable cycling

MoS₂/Graphene Composite Paper for Sodium-Ion Battery Electrodes

We study the synthesis and electrochemical and mechanical performance of layered free-standing papers composed of acid-exfoliated few-layer molybdenum disulfide (MoS₂) and reduced graphene oxide (rGO) flakes for use as a self-standing flexible electrode in sodium-ion batteries. Synthesis was achieved through vacuum filtration of homogeneous dispersions consisting of varying weight percent of acid-treated MoS₂ flakes in GO in DI water, followed by thermal reduction at elevated temperatures. The electrochemical performance of the crumpled composite paper (at 4 mg cm^–2) was evaluated as counter electrode against pure Na foil in a half-cell configuration. The electrode showed good Na cycling ability with a stable charge capacity of approximately 230 mAh g^–1 with respect to total weight of the electrode with Coulombic efficiency reaching approximately 99%. In addition, static uniaxial tensile tests performed on crumpled composite papers showed high average strain to failure reaching approximately 2%