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Silicon 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 × 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 2 mg cm−2) delivers a charge capacity of ∼588 mAh g−1electrode (∼393 mAh cm−3electrode) 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., Most high-loading silicon-based anodes for lithium-ion batteries suffer from low efficiency and volumetric capacity. Here, the authors show that a paper-like electrode of silicon oxycarbide glass and graphene at mass loading of >2 mg cm−2 can efficiently deliver high energy density for over 1,000 cycles.

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%.

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, co...

We study the laser irradiance behavior and resulting structural evolution of polymer-derived silicon-boron-carbonitride (Si(B)CN) functionalized multiwall carbon nanotube (MWCNT) composite spray coatings on copper substrate. We report a damage threshold value of 15 kWcm(-2) and an optical absorbance of 0.97 after irradiation. This is an order of magnitude improvement over MWCNT (1.4 kWcm(-2), 0.76), SWCNT (0.8 kWcm(-2), 0.65) and carbon paint (0.1 kWcm(-2), 0.87) coatings previously tested at 10.6 μm (2.5 kW CO2 laser) exposure. Electron microscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy suggests partial oxidation of Si(B)CN forming a stable protective SiO2 phase upon irradiation.

Lithium ion batteries (LIB) is currently the most promising of all battery technologies for efficient storage of electrical energy and powering of electric vehicles. However, the ongoing LIB research faces multiple issues pertaining to materials, cost and safety. One of the major factors that dictate the performance of LIB is its electrode’s Li-storage (anode/cathode) capacity, cycleability and efficiency. In this article, the authors evaluate the recent experimental progress made in LIB anode materials prepared from polymer-derived ceramics (PDC). PDCs have several unique characteristics that differentiate them from other conventional carbon or silicon-based anodes. Most notably PDCs exhibit high chemical and thermodynamic stability under adverse operational conditions. Learnings from the analysis of experimental observations can be carried forward to design advanced PDCs, thereby improving overall performance of the battery, particularly for automotive applications.

Separation of bulk tungsten disulfide (or WS2) into few-layer two-dimensional (2-D) crystals is of interest because of their high surface area for certain chemical processes and size-dependent optical and electronic characteristics. Herein, we demonstrate a process that involves the physical separation of weakly bonded WS2 layers by use of a strong acid treatment (chlorosulfonic acid) at 2 mg/mL, followed by quenching in deionized (DI) water. X-ray photoelectron spectroscopy of the superacid-treated WS2 suggests the formation of W-O type bonds, signifying oxidation of tungsten and reduction of the sulfur phase. Thermogravimetric analysis showed a three-phase weight-loss pattern, suggesting acid functionalization of WS2 surfaces. We also studied the electrochemical behavior of an acid-treated WS2 anode in a lithium half-cell configuration that showed a three-step charge-discharge behavior, characteristic of a conversion reaction. The electrochemical capacity was 118 mAh/g after 50 cycles.

Carbon nanotubes (CNT) and polymer-derived ceramics (PDCs) are of interest due to their unique multifunctional properties. CNTs, however, tend to lose their well-defined structure and geometry at about 400°C in air. PDCs on the other hand are structureless in X-ray diffraction but show high chemical and thermal stability in air (up to ~1400°C). Herein, we demonstrate synthesis of a composite nanowire structure consisting of polymer-derived silicon boron-carbonitride (Si–B–C–N) shell with a multiwalled carbon nanotube core. This was achieved through a novel process involving preparation of a boron-modified liquid polymeric precursor through a reaction of trimethyl borate and poly (ureamethylvinyl) silazane under normal conditions; followed by conversion of polymer to ceramic on carbon nanotube surfaces through controlled heating. Chemical structure of the polymer was studied by liquid-Nuclear Magnetic Resonance (NMR) while evolution of various ceramic phases was studied by solid-NMR, Fourier transform infrared and X-ray photoelectron spectroscopy. Electron microscopy and X-ray diffraction confirm presence of amorphous Si(B)CN coating on individual nanotubes for all specimens processed below 1400°C. Thermogravimetric analysis, followed by Raman spectroscopy and transmission electron microscopy revealed high temperature stability of the carbon nanotube core in flowing air up to 1000°C.

The authors demonstrate the synthesis of a freestanding composite paper consisting of polymer-derived ceramic Silicon oxycarbide (SiOC) functionalized carbon nanotube (CNT) network. The paper is prepared by vacuum filtration of CNT followed by drop coating of tetramethyl tetravinylcyclotertrasiloxane polymer on its surface. The polymer coating on the CNT paper is then transformed to silicon oxycarbide ceramic by controlled heating. Scanning electron microscopy reveals a uniform and compact CNT paper surface with thickness of ∼225 μm. An X-ray diffraction spectrum of the composite paper highlight the amorphous nature of ceramic coating surrounding the CNTs. The authors further demonstrate the use of this paper as an independent anode material in rechargeable lithium-ion batteries and thereby, simplifying the anode design by eliminating the binder, conductive additives and current collector metal. The composite paper anode weighs ∼37% less than those made by using conventional copper substrates. Electrochemical performance of the SiOC–CNT composite anode studied by initial galvanostatic cycles shows a high discharge capacity of 1168 mAh/g and 13 mAh/cm2 with first cycle loss of 53·8%.

A 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.

We study the process of graphene growth on Cu and Ni substrates subjected to rapid heating (approximately 8 °C/s) and cooling cycles (approximately 10 °C/s) in a modified atmospheric pressure chemical vapor deposition furnace. Electron microscopy followed by Raman spectroscopy demonstrated successful synthesis of large-area few-layer graphene (FLG) films on both Cu and Ni substrates. The overall synthesis time was less than 30 min. Further, the as-synthesized films were directly utilized as anode material and their electrochemical behavior was studied in a lithium half-cell configuration. FLG on Cu (Cu-G) showed reduced lithium-intercalation capacity when compared with SLG, BLG and Bare-Cu suggesting its substrate protective nature (barrier to Li-ions). Although graphene films on Ni (Ni-G) showed better Li-cycling ability similar to that of other carbons suggesting that the presence of graphene edge planes (typical of Ni-G) is important in effective uptake and release of Li-ions in these materials.

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.

We demonstrate synthesis of a polymer-derived ceramic (PDC)-multiwall carbon nanotube (MWCNT) composite using microwave irradiation at 2.45 GHz. The process takes about 10 min of microwave irradiation for the polymer-to-ceramic conversion. The successful conversion of polymer coated carbon nanotubes to ceramic composite is chemically ascertained by Fourier transform-infrared and X-ray photoelectron spectroscopy and physically by thermogravimetric analysis and transmission electron microscopy characterization. Frequency dependent dielectric measurements in the S-Band (300 MHz to 3 GHz) were studied to quantify the extent of microwave–CNT interaction and the degree of selective heating available at the MWCNT-polymer interface. Experimentally obtained return loss of the incident microwaves in the specimen explains the reason for heat generation. The temperature-dependent permittivity of polar molecules further strengthens the argument of internal heat generation.