Graphite intercalation compounds (GICs) have attracted tremendous attention due to their exceptional properties that can be finely tuned by controlling the intercalation species and concentrations. Here, we report for the first time that potassium (K) ions can electrochemically intercalate into graphitic materials, such as graphite and reduced graphene oxide (RGO) at ambient temperature and pressure. Our experiments reveal that graphite can deliver a reversible capacity of 207 mAh/g. Combining experiments with ab initio calculations, we propose a three-step staging process during the intercalation of K ions into graphite: C → KC24 (Stage III) → KC16 (Stage II) → KC8 (Stage I). Moreover, we find that K ions can also intercalate into RGO film with even higher reversible capacity (222 mAh/g). We also show that K ions intercalation can effectively increase the optical transparence of the RGO film from 29.0% to 84.3%. First-principles calculations suggest that this trend is attributed to a decreased absorbance produced by K ions intercalation. Our results open opportunities for novel nonaqueous K-ion based electrochemical battery technologies and optical applications.

All-component 3D-printed lithium-ion batteries are fabricated by printing graphene-oxide-based composite inks and solid-state gel polymer electrolyte. An entirely 3D-printed full cell features a high electrode mass loading of 18 mg cm(-2) , which is normalized to the overall area of the battery. This all-component printing can be extended to the fabrication of multidimensional/multiscale complex-structures of more energy-storage devices.

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mechanism. The large impedance associated with transport for ions and electrons limits the thickness of the electrode usually less than 100 µm. To overcome the issue of charge transport, 1D and 2D nanomaterials (i.e., carbon nanotubes and graphene) have been used to provide fast percolative pathways for electron transport. [16][17][18][19] It is also found that low-tortuosity electrodes can provide fast ion transport, which indeed lead to much-improved rate performance. [ 20,21 ] Wood has a unique anisotropic structure, where there are open channels along the growth direction to help pump water, ions, and other ingredients. Herein, we design a 3D carbon electrode through directly carbonizing wood that is cut perpendicularly to the growth direction. The carbonized wood has the perfect open channels, which lead to a low tortuosity for ion transport. The well-connected carbon also provides excellent path for electron transport with small impedance. In this work, we demonstrated for the fi rst time that ultra-thick, mesoporous carbon with a thickness up to 850 µm and an areal mass of 55 mg cm −2 . The mesoporous carbon not only shows a high specifi c capacity of 270 mA h g −1 but also a high areal capacity of 13.6 mA h cm −2 evaluated as anode for SIB in half cells. The thickness, areal mass, and areal capacity are signifi cantly higher than the values from the state-of-the-art batteries. The ultra-thick wood-derived carbon is also a binder-free, current collector-free electrode that also signifi cant increases the weight percentage of the active mass in SIBs. Excellent cycling performance was demonstrated in full cells based on Na 3 V 2 (PO 4 ) 3 cathode and wood carbon anode. The woodbased freestanding, mesoporous carbon with a unique anisotropic structure is a promising anode in the emerging SIB technology. Note that other biomass has been investigated as the precursors for high-performance SIB anodes, [22][23][24] but the biomass-derived carbons follow traditional battery design with binders coated on current collectors and the areal capacity is much smaller than the reported value in this study. The lowtortuosity wood with the open, ordered channels can also open a range of other energy and environmental-related applications, such as membrane for gas separation, water fi ltration, and fl ow batteries.Wood is one of the most abundant biomass on Earth and has a heterogeneous and anisotropic structure ( Figure 1 a). There are a large number of straight multichannels in the up-growing direction of the tree, leading to a lowest tortuosity, close to one, along the growth direction. Such a unique structure inspires us a new insight for fabricating low-tortuosity carbon based on wood, which can be dramatically different from any other types of macroscopic carbon. As shown in Figure 1 b, a 3D structured carbon electrode is Grid-scale energy storage is critical in the renewable energy landscape due to the intermittent nature of the renewable energy sources such as wind, solar, and others. Compared with many other grid-sca...

Solution processed, highly conductive films are extremely attractive for a range of electronic devices, especially for printed macroelectronics. For example, replacing heavy, metal-based current collectors with thin, light, flexible, and highly conductive films will further improve the energy density of such devices. Films with two-dimensional building blocks, such as graphene or reduced graphene oxide (RGO) nanosheets, are particularly promising due to their low percolation threshold with a high aspect ratio, excellent flexibility, and low cost. However, the electrical conductivity of these films is low, typically less than 1000 S/cm. In this work, we for the first time report a RGO film with an electrical conductivity of up to 3112 S/cm. We achieve high conductivity in RGO films through an electrical current-induced annealing process at high temperature of up to 2750 K in less than 1 min of anneal time. We studied in detail the unique Joule heating process at ultrahigh temperature. Through a combination of experimental and computational studies, we investigated the fundamental mechanism behind the formation of a highly conductive three-dimensional structure composed of well-connected RGO layers. The highly conductive RGO film with high direct current conductivity, low thickness (∼4 μm) and low sheet resistance (0.8 Ω/sq.) was used as a lightweight current collector in Li-ion batteries.

High temperature heaters are ubiquitously used in materials synthesis and device processing. In this work, we developed three-dimensional (3D) printed reduced graphene oxide (RGO)-based heaters to function as high-performance thermal supply with high temperature and ultrafast heating rate. Compared with other heating sources, such as furnace, laser, and infrared radiation, the 3D printed heaters demonstrated in this work have the following distinct advantages: (1) the RGO based heater can operate at high temperature up to 3000 K because of using the high temperature-sustainable carbon material; (2) the heater temperature can be ramped up and down with extremely fast rates, up to ∼20 000 K/second; (3) heaters with different shapes can be directly printed with small sizes and onto different substrates to enable heating anywhere. The 3D printable RGO heaters can be applied to a wide range of nanomanufacturing when precise temperature control in time, placement, and the ramping rate are important.

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Nanoparticles hosted in conductive matrices are ubiquitous in electrochemical energy storage, catalysis and energetic devices. However, agglomeration and surface oxidation remain as two major challenges towards their ultimate utility, especially for highly reactive materials. Here we report uniformly distributed nanoparticles with diameters around 10 nm can be self-assembled within a reduced graphene oxide matrix in 10 ms. Microsized particles in reduced graphene oxide are Joule heated to high temperature (∼1,700 K) and rapidly quenched to preserve the resultant nano-architecture. A possible formation mechanism is that microsized particles melt under high temperature, are separated by defects in reduced graphene oxide and self-assemble into nanoparticles on cooling. The ultra-fast manufacturing approach can be applied to a wide range of materials, including aluminium, silicon, tin and so on. One unique application of this technique is the stabilization of aluminium nanoparticles in reduced graphene oxide film, which we demonstrate to have excellent performance as a switchable energetic material.