Earlier, various attempts to develop graphene structures using chemical and nonchemical routes were reported. Being efficient, scalable, and repeatable, 3D printing of graphene-based polymer inks and aerogels seems attractive; however, the produced structures highly rely on a binder or an ice support to stay intact. The presence of a binder or graphene oxide hinders the translation of the excellent graphene properties to the 3D structure. In this communication, we report our efforts to synthesize a 3D-shaped 3D graphene (3D 2 G) with good quality, desirable shape, and structure control by combining 3D printing with the atmospheric pressure chemical vapor deposition (CVD) process. Direct ink writing has been used in this work as a 3D-printing technique to print nickel powder−PLGA slurry into various shapes. The latter has been employed as a catalyst for graphene growth via CVD. Porous 3D 2 G with high purity was obtained after etching out the nickel substrate. The conducted micro CT and 2D Raman study of pristine 3D 2 G revealed important features of this new material. The interconnected porous nature of the obtained 3D 2 G combined with its good electrical conductivity (about 17 S/cm) and promising electrochemical properties invites applications for energy storage electrodes, where fast electron transfer and intimate contact with the active material and with the electrolyte are critically important. By changing the printing design, one can manipulate the electrical, electrochemical, and mechanical properties, including the structural porosity, without any requirement for additional doping or chemical postprocessing. The obtained binderfree 3D 2 G showed a very good thermal stability, tested by thermo-gravimetric analysis in air up to 500 °C. This work brings together two advanced manufacturing approaches, CVD and 3D printing, thus enabling the synthesis of high-quality, binder-free 3D 2 G structures with a tailored design that appeared to be suitable for multiple applications.

In order for lithium ion batteries to be successfully deployed into many emerging applications, such as transportation and advanced portable electronics, these batteries must have higher volumetric and gravimetric energy densities, as well as the ability to quickly charge and store energy. Alloy-based anode materials, such as silicon and tin, are promising candidates for increasing capacity, energy and power density because they possess maximum gravimetric capacities up to ten times that of graphite, the current standard for commercial lithium-ion cells. However, these materials suffer from dramatic volume changes during (de)lithiation (up to 300%), which can severely limit their lifetime. One effective route towards reversibly accommodating these large volume changes, improving capacity retention and at the same time increasing power density is to take advantage of lower stress and strain values and gradients at smaller length scales using nanostructures such as the inverse opal structure. While many different nanostructures and morphologies have been explored, the rational design and optimization of these structures has been hindered by a dearth of experimentally measured, quantitative strain data for nanostructured NiSn and Si anodes. The amorphous nature of lithiation in nanostructured Si anodes and the unclear lithiation mechanism(s) in nanostructured NiSn anodes has greatly hindered in operando strain measurement to date, especially on microscale and larger format cells. Additionally, transient effects or mechanistic changes that may occur when cycling these anodes at higher rates have not been very well explored in the literature. Using synchrotron-based X-ray diffraction techniques at the Advanced Photon Source, lattice strains in Si and NiSn coated Ni nanostructured inverse opal scaffolds were measured in operando at a variety of rates in order to deduce mismatch stresses and strain evolution during (dis)charging in the active anode material thin film and the nickel scaffold. Since both the active anode materials form strong bonds with the inverse opal nickel scaffold, the elastic strains measured in the nickel are similar to those present in the anode material, allowing stress and strain states present in the Si or NiSn to be indirectly measured. These inverse opal anodes were cycled at rates between 1C and 20C, and 1C and 500C for Si and NiSn based anodes respectively, with charge and discharge current densities held constant and equivalent at each cycling rate. Additionally, asymmetric cycling parameters were utilized to explore, in operando, a fast charge, slow discharge behavior that may be more representative of current and emerging applications, where lithiation rates of up to 115C for NiSn and 60C for Si and fixed delithiation current densities corresponding to a symmetric 1C rate were utilized. Strains measured in the Ni scaffold were directly correlated with the electrochemical cycling of the anode. These strains are discussed in terms of elasto-plastic deformation mechanisms in the scaffold, cracking of the active materials and other potential stress relief mechanisms. As observed through in operando strain measurements, potential changes in lithiation mechanisms and possible mechanical failure modes at various (dis)charge rates are also discussed.

Historically, porous metals have focused on structural applications where specific stiffness and strength were optimized, using conventional casting, sintering, cutting, machining and joining techniques to create ductile and strong porous metallic structure. For such load-bearing applications, porous metals are studied and used in many sectors, e.g., transportation, architecture, and medicine (for bone-replacement implants). This special issue of the Journal of Materials Research contains articles that were accepted in response to an invitation for manuscripts.

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