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Abstract: Electrolytic manganese dioxide is one of the promising cathode candidates for electrochemical energy storage devices due to its high redox capacity and ease of synthesis. Yet, high‐loading MnO2 often suffers from sluggish reaction kinetics, especially in non‐aqueous electrolytes. The non‐uniform deposition of MnO2 on a porous current collectors also makes it difficult to fully utilize the active materials at high mass loading. Here, a 3D printed graded graphene aerogel (3D GA) that contains sparsely separated exterior ligaments is developed to create large open channels for mass transport as well as densely arranged interior ligaments providing large ion‐accessible active surface. The unique structural design homogenizes the thickness of electro deposited MnO2 even at an ultrahigh mass loading of ≈70 mg cm−2. The electrode achieves a remarkable volumetric capacity of 29.1 mA h cm−3 in the non‐aqueous electrolyte. A Li‐ion hybrid capacitor device assembled with a graded 3D GA/MnO2 cathode and graded 3D GA/VOx anode exhibits a wide voltage window of 0–4 V and a superior volumetric energy density of 20.2 W h L−1. The findings offer guidance on 3D printed electrode design for supporting ultrahigh loading of active materials and developments of high energy density energy storage devices.

Additively manufactured (AM) metallic materials commonly possess substantial microscale internal stresses that manifest as intergranular and intragranular residual stresses. However, the impact of these residual stresses on the mechanical behaviour of AM materials remains unexplored. Here we combine in situ synchrotron X-ray diffraction experiments and computational modelling to quantify the lattice strains in different families of grains with specific orientations and associated intergranular residual stresses in an AM 316L stainless steel under uniaxial tension. We measure pronounced tension-compression asymmetries in yield strength and work hardening for as-printed stainless steel, and show they are associated with back stresses originating from heterogeneous dislocation distributions and resultant intragranular residual stresses. We further report that heat treatment relieves microscale residual stresses, thereby reducing the tension-compression asymmetries and altering work-hardening behaviour. This work establishes the mechanistic connections between the microscale residual stresses and mechanical behaviour of AM stainless steel.

A limited understanding regarding the underlying dynamics and mechanisms of material removal during continuous wave laser drilling has presented significant challenges in achieving precision and process control. To address this, we employed high-fidelity, in situ synchrotron x-ray imaging to reveal previously unknown material behaviors during continuous wave laser drilling with power modulation. Our findings highlight that high-aspect ratio drill holes are achieved when the laser modulation frequency falls within the range of 8–12 kHz, provided that the laser average power and modulation amplitude levels meet the specified limits. Under these conditions, we identified a material removal mechanism driven by incremental accumulation of recoil pressure that gradually pushes material upward from deep within the substrate to the surface. This mechanism manifested as a low-frequency fluctuation in the vapor depression depth, resulting in periodic instances of material ejection. Furthermore, our study underscores that rapid expansion of the melt pool and the widening of the drill hole opening can impede effective material removal by redirecting energy from material ejection to increasing the melt pool size. This investigation contributes essential insights into the subsurface dynamics involved in the drilling of high-aspect ratio holes, furthering our fundamental understanding of this intricate process. [ABSTRACT FROM AUTHOR]

Various nondestructive diagnostic techniques have been proposed for in situ process monitoring of laser powder bed fusion (LPBF), including melt pool pyrometry, whole-layer optical imaging, acoustic emission, atomic emission spectroscopy, high speed melt pool imaging, and thermionic emission. Correlations between these in situ monitoring signals and defect formation have been demonstrated with acoustic signals having been shown to predict pore formation with especially high confidence in recent machine learning studies. In this work, time-resolved acoustic data are collected in both the conduction and keyhole welding regimes of LPBF-processed Ti-6Al-4V alloy. A non-dimensionalized Strouhal number analysis, used in whistle aeroacoustics, is applied to demonstrate that the acoustic signals recorded in the keyhole regimes can be directly associated with the vapor depression morphology. This mechanistic understanding developed from whistle aeroacoustics shows that acoustic monitoring during the LPBF process can provide a direct probe into the vapor depression dynamics and defect occurrence, especially in the keyhole regimes relevant to printing and defect formation. [ABSTRACT FROM AUTHOR]

Electrolytic manganese dioxide is one of the promising cathode candidates for electrochemical energy storage devices due to its high redox capacity and ease of synthesis. Yet, high‐loading MnO2 often suffers from sluggish reaction kinetics, especially in non‐aqueous electrolytes. The non‐uniform deposition of MnO2 on a porous current collectors also makes it difficult to fully utilize the active materials at high mass loading. Here, a 3D printed graded graphene aerogel (3D GA) that contains sparsely separated exterior ligaments is developed to create large open channels for mass transport as well as densely arranged interior ligaments providing large ion‐accessible active surface. The unique structural design homogenizes the thickness of electro deposited MnO2 even at an ultrahigh mass loading of ≈70 mg cm−2. The electrode achieves a remarkable volumetric capacity of 29.1 mA h cm−3 in the non‐aqueous electrolyte. A Li‐ion hybrid capacitor device assembled with a graded 3D GA/MnO2 cathode and graded 3D GA/VOx anode exhibits a wide voltage window of 0–4 V and a superior volumetric energy density of 20.2 W h L−1. The findings offer guidance on 3D printed electrode design for supporting ultrahigh loading of active materials and developments of high energy density energy storage devices. [ABSTRACT FROM AUTHOR]