Suppression Of Void Formation Research Articles

Li Stripping Behavior of Anode‐Free Solid‐State Batteries Under Intermittent‐Current Discharge Conditions

AbstractAnode‐free manufacturing holds promise to enable high energy densities and lower Lithium (Li)‐metal solid‐state batteries (LMSSBs). Nevertheless, in contrast to thick Li foil (>50 µm), the stripping capacity of in situ‐formed Li (10–30 µm) is limited due to diminished creep flow, resulting in reduced accessible capacity. This study explores the correlation between stripping capacity and surface roughness of garnet Li7La3Zr2O12 (LLZO) solid electrolyte. The results reveal that stripping capacity can be enhanced through the surface modification of solid electrolytes. Additionally, this study scrutinizes the stripping behavior of in situ Li under intermittent‐current discharge conditions, which are more relevant to the operational conditions of electric vehicles (EVs). It is demonstrated that, when compared to constant‐current stripping, intermittent‐current stripping effectively suppresses void formation and enhances the stripping capacity of in situ Li by 40%. It is considered that the intermittent current inhibits the accumulation of Li vacancies, thereby delaying the void formation. These findings provide valuable insights into the development of high‐performance anode‐free LMSSBs for EVs.

Exploring mechanism of suppressing void formation at Interface of Sn–9Zn and Cu

Exploring mechanism of suppressing void formation at Interface of Sn–9Zn and Cu

Minimizing the diffusivity difference between vacancies and interstitials in multi-principal element alloys

Interstitial atoms usually diffuse much faster than vacancies, which is often the root cause for the ineffective recombination of point defects in metals under irradiation. Here, via ab initio modeling of single-defect diffusion behavior in the equiatomic NiCoCrFe(Pd) alloy, we demonstrate an alloy design strategy that can reduce the diffusivity difference between the two types of point defects. The two diffusivities become almost equal after substituting the NiCoCrFe base alloy with Pd. The underlying mechanism is that Pd, with a much larger atomic size (hence larger compressibility) than the rest of the constituents, not only heightens the activation energy barrier (Ea) for interstitial motion by narrowing the diffusion channels but simultaneously also reduces Ea for vacancies due to less energy penalty required for bond length change between the initial and the saddle states. Our findings have a broad implication that the dynamics of point defects can be manipulated by taking advantage of the atomic size disparity, to facilitate point-defect annihilation that suppresses void formation and swelling, thereby improving radiation tolerance.

A Comprehensive Study on Chemical Bonding and Open Spaces with Silicon Carbon Nitride Films for Direct Bonding

Wafer-to-wafer (W2W) direct bonding has been extensively developed as a key unit process for BS-PDN, CFET and advanced chiplet. As a bonding dielectric layer, CVD-SiO2 has been comprehensively studied for direct/hybrid bonding. SiCN is emerging dielectric bonding layer due to its unique properties such as high bonding strength at low annealing temperatures, suppressing void formation after Post Bond Annealing (PBA) and barrier properties against Cu diffusion [1][2]. However, the bonding mechanism for SiCN has not yet been clearly described. In this study, we investigated the mechanism from several kinds of perspectives by analyzing the properties of different films under various conditions. From those results, SiCN is characterized and compared to SiO2.SiO2 and SiCN films were deposited on 300mm Si wafers using plasma-enhanced chemical vapor deposition (PECVD). Subsequently, the wafers were polished and bonded.Atomic level open spaces in dielectric films were analyzed by positron annihilation spectroscopy (PAS). For the SiO2 samples after plasma activation, the S parameter did not show significant changes. This indicates the open spaces in SiO2 were not significantly influenced by plasma. On the contrary, the S parameter of SiCN samples increased after post deposition annealing (PDA) and decreased after plasma activation. This atomic level open spaces might be contributed the unique properties of SiCN for direct bonding.Since the analysis by PAS is one of the examples, we will report the overall results of the analysis on SiCN, e.g. TDS, XPS, AFM, and so on, then discuss the bonding mechanism for SiCN-SiCN.[1] F. Inoue, et. al., ECS Journal of Solid State Science and Technology 8(6), P346(2019)[2] F. Nagano, et. al., ECS Journal of Solid State Science and Technology 9 123011(2020) Figure 1

Understanding and Engineering Interfacial Adhesion in Solid-State Batteries with Metallic Anodes.

High performance alkali metal anode solid-state batteries require solid/solid interfaces with fast ion transfer that are morphologically and chemically stable upon electrochemical cycling. Void formation at the alkali metal/solid-state electrolyte interface during alkali metal stripping is responsible for constriction resistances and hotspots that can facilitate dendrite propagation and failure. Both externally applied pressures (35-400 MPa) and temperatures above the melting point of the alkali metal have been shown to improve the interfacial contact with the solid electrolyte, preventing the formation of voids. However, the extreme pressure and temperature conditions required can be difficult to meet for commercial solid-state battery applications. In this review, we highlight the importance of interfacial adhesion or 'wetting' at alkali metal/solid electrolyte interfaces for achieving solid-state batteries that can withstand high current densities without cell failure. The intrinsically poor adhesion at metal/ceramic interfaces poses fundamental limitations on many inorganics solid-state electrolyte systems in the absence of applied pressure. Suppression of alkali metal voids can only be achieved for systems with high interfacial adhesion (i. e. 'perfect wetting') where the contact angle between the alkali metal and the solid-state electrolyte surface goes to θ=0°. We identify key strategies to improve interfacial adhesion and suppress void formation including the adoption of interlayers, alloy anodes and 3D scaffolds. Computational modeling techniques have been invaluable for understanding the structure, stability and adhesion of solid-state battery interfaces and we provide an overview of key techniques. Although focused on alkali metal solid-state batteries, the fundamental understanding of interfacial adhesion discussed in this review has broader applications across the field of chemistry and material science from corrosion to biomaterials development.

Nondestructive observation of the surrounding powder in the vicinity of polymer laser-sintered specimens for understanding orange peel formation

PurposeOrange peel formation remains to be understood clearly because it is difficult to directly observe a laser-sintered process in a partcake. Therefore, this study aims to provide insight into the orange peel formation mechanism through the nondestructive observation of laser-sintered specimens and their surrounding powders.Design/methodology/approachThis study observed polyamide 12 powder in the vicinity of a laser-sintered specimen via X-ray computed tomography (CT) scanning. The specimen for nondestructive observation was 3D modeled in a hollow box using 3D CAD software. The boxes built using a laser-sintering system contained unsintered surrounding powder and sintered specimens. The box contents were preserved even after the boxes were removed from the partcake. After X-ray CT scanning, the authors broke the boxes and evaluated the unevenness formed on the specimen surface (i.e. the orange peel evaluation).FindingsVoids (not those in sintered parts) generated in the powder in the vicinity of the specimen triggered the orange peel formation. Voids were less likely to form in the build with a 178.5° powder bed than in the build with a 173.5° powder bed. Similarly, the increment in laser energy density effectively suppressed void formation, although there was a tradeoff with overmelting. Thin-walled parts avoided void growth and made the orange peel less noticeable.Originality/valueTo the best of the authors’ knowledge, this study is the first to observe and understand the relationship between voids generated in the powder in the vicinity of sintered parts and orange peel formation.

Homogenizing Silicon Domains in SiOx Anode during Cycling and Enhancing Battery Performance via Magnesium Doping.

SiOx (x ≈ 1) is one of the most promising anode materials for application in secondary lithium-ion batteries because of its high theoretical capacity. Despite this merit, SiOx has a poor initial Coulombic efficiency, which impedes its widespread use. To overcome this limitation, in this work, we successfully demonstrate a novel synthesis of Mg-doped SiOx via a mass-producible physical vapor deposition method. The solid-state reaction between Mg and SiOx produces Si and electrochemically inert magnesium silicate, thus increasing the initial Coulombic efficiency. The Mg doping concentration determines the phase of the magnesium silicate domains, the size of the Si domains, and the heterogeneity of these two domains. Detailed electron microscopy and synchrotron-based analysis revealed that the nanoscale homogeneity of magnesium silicates driven by cycling significantly affected the lifetime. We found that 8 wt % Mg is the most optimized concentration for enhanced cyclability because MgSiO3, which is the dominant magnesium silicate composition, can be homogeneously mixed with silicon clusters, preventing their aggregation during cycling and suppressing void formation.

Pressure-Driven and Creep-Enabled Interface Evolution in Sodium Metal Batteries.

All-solid-state batteries (ASSBs) using an alkali metal anode and a solid-state electrolyte (SE) face several problems due to poor physical and electrical contact. Recent experiments have shown that applying a stack pressure can improve the interface contact and suppress void formation. The mechanical properties of Na metal are different from those of Li metal, leading to differences in the mechanisms of the pressure-dependent interface evolution. Herein, we report a three-dimensional time-dependent model for tracking the evolution of interfaces formed between Na metal and Na-β″-alumina SE. Our results show that Na metal contacts more conformally with the SE, providing a lower interfacial resistance, compared with Li metal, assuming equal resistance due to contamination. The differences due to contact elastoplasticity are larger than the differences in metal creep effects. In fact, we show that increased stack pressure can lead to lower creep because the contact is more conformal at high pressures. Our excellent agreement with recent experiments determines an effective hardness of Na in the Na-SE batteries to be 15 MPa. The results further reveal that the pressure dependence of void suppression is dominated by contact elastoplasticity.

Computational evaluation of optimal reservoir and sink lengths for threshold current density of electromigration damage considering void and hillock formation

Reservoirs, extensions at the cathode-end, are constructed to extend the lifetime of integrated circuit (IC) lines in terms of electromigration (EM) damage. The threshold current density jth is the maximum current density that can be supported without causing EM damage due to the matching of the EM driving force and the back flow force, which is related to the atomic density gradient. In a previous study, we reported that reservoirs can affect jth. In this present study, the jth of straight Al polycrystalline lines covered with passivation was evaluated using a numerical simulation technique focusing not only on the formation of voids but also hillocks. The optimum reservoir/sink length based on ease of formation of voids and hillocks was discussed. The reservoir suppressed void formation but promoted hillock formation. Conversely, the sink suppressed hillock formation but promoted void formation. Therefore, when void and hillock formation occurred with equal case, it was considered that either no extension, or reservoir and sink of identical length were preferable for optimal threshold current density jth. Additionally, when considering the diffusivity of atoms depending on grain boundary direction, the absence of the extension represented the optimum condition because longer reservoirs/sinks produced smaller jth. When the ease of void and hillock formation changed, the critical atomic density of void and hillock formation shifted in response, causing the optimal extension length to change. It was found that the optimum extension length changed almost linearly based on the ease of void and hillock formation.

Suppressing void formation in all-solid-state batteries: the role of interfacial adhesion on alkali metal vacancy transport

The segregation of alkali metal vacancies to the alkali metal/solid electrolyte interface is linked to the interfacial work of adhesion.

Preparation and evaluation of Pd membrane on supports activated by PEG embedded Pd nanoparticles for ATR membrane reactor

Stresses and formation of voids are the main origins of pinholes in palladium (Pd) composite membranes at high temperatures. The stresses are associated with the Pd layer-substrate interaction and the formation of the voids is due to the gas bubble trapped inside the deposits. Pd embedded polyethylene glycol (PEG) was used during the activation step of the electroless plating (ELP) method. Also, multiple plating and annealing steps were employed to suppress void formation. Three plating and annealing steps rendered the prepared Pd membrane quite dense and defect-free. The surface roughness of modified support was found to play a crucial role in the stability of the Pd membrane. The resulting membrane showed an infinite selectivity for H2/Ar with H2 flux of 1-6.6 m3 m-2 h-1. Besides, H2 permeate flux kept constant and the separation factor of H2/Ar over infinite for 240 h at different temperatures, indicating the high potential of the prepared membrane for H2 purification. Furthermore, membrane reactor experiments showed the CH4 conversion is about 15 % higher than that in the traditional reactor at the same condition.

Effect of Zn addition and Ti doping position on the diffusion reaction of internal tin Nb3Sn conductors

Addition of Zn to a Cu matrix during Cu–Zn/Sn interdiffusion reactions at 400 °C leads to the formation of a solid ternary Cu–Zn–Sn phase, β-CuZn, at the outermost reaction layer next to the porous ε phase. The use of a brass matrix considerably suppresses void formation and promotes homogeneous outward Sn diffusion in pre-annealing, prior to Nb3Sn formation. There are exactly three paths for Ti doping in the internal tin process, i.e. doping to Sn cores, Nb filaments, and Cu matrix. Ti doping to Sn cores causes a Ti-rich layer formation at the boundary of the Nb filament pack; however, no Ti-rich layers are formed as a result of small Ti doping to the matrix and to Nb filaments. The absence of Ti-rich layers is believed to contribute to a smooth Sn diffusion and suppression of void growth. Atom probe tomography measurements reveal that Ti doping to Sn cores leads to a more inhomogeneous Ti distribution near the grain boundary and a larger variation of the grain boundary thickness than doping to Nb filaments, which may contribute to a better Sn grain boundary diffusion. It is concluded that Ti doping to the matrix, instead of doping to Sn cores, might be more effective in maintaining better growth kinetics of Nb3Sn.

Suppression of Void Formation at Sn/Cu Joint Due to Twin Formation in Cu Electrodeposit

The use of organic additives is crucial for Cu electrodeposition. However, specific impure species originating from the additives are incorporated in the Cu electroplated layer, causing serious reliability problems such as void formation at the solder/Cu joints. In this study, three Cu substrates were electroplated using various additive formulas. The use of organic additives results in an incorporation of a higher level of impurity in the Cu-electroplated layers and also affects the atomic deposition behavior of Cu which alters the grain microstructures. By using a specific additive formula, the grain growth of Cu evolves into a slender structure with a high density of twins. Thermal aging experiments of the Sn/Cu joints show that the void formation is successfully suppressed at the joint using a slender-grained Cu substrate, and that the suppression effect is attributed to the high microstructural stability of the twinning structure.

Flash Lamp Annealed Polycrystalline Silicon TFT Dependence on Surface Morphology and the Back-Channel Material Interface

This work studies the operation of polycrystalline silicon p-channel TFTs prepared via Flash Lamp Annealing (FLA). Silicon nitride was investigated as a back-channel interface layer to suppress void formation via dewetting of molten silicon. Predefined polygons of amorphous silicon were crystallized on display glass using single-pulse FLA exposure. Two distinct surface morphologies were realized within the same exposed region as a result of the underlying silicon nitride film and localized variation in the substrate thermal contact during PECVD deposition of amorphous silicon. While both resulting morphologies have polysilicon grains on micron scale, differences in TFT electrical behavior appear to coincide with differences in grain structure and boundary regions. The electrical results also indicate inferior electrical performance in response to the back-channel silicon nitride in comparison to results demonstrated on SiO2. Extracted parameters provide a quantitative assessment of the device operation as related to surface morphology and the back-channel material interface.

Electromigration reliability of Sn–3.0Ag–0.5Cu/Cu–Zn solder joints

The electromigration reliability and failure modes of Sn–3.0Ag–0.5Cu (SAC)/Cu–Zn solder joints were investigated at 146 °C and a current density of 1.1 × 104 A/cm2. After aging at 146 °C for 150 h without electric current, typical bi-layers of Cu6Sn5 and Cu3Sn intermetallic compounds (IMCs) were formed in the SAC/Cu joints, whereas a single Cu6(Sn, Zn)5 phase was observed in the SAC/Cu–Zn joint. The total thickness of the IMC layer in the SAC/Cu–Zn specimen was thinner than that in the SAC/Cu specimen. After current stressing for 150 h on the anode side, the total thickness of the IMC layers of both types of solder joints was thicker than that without electric current. On the cathode side, the IMCs, Cu6Sn5 of SAC/Cu and Cu6(Sn, Zn)5 of SAC/Cu–Zn joints dissolved, and voids induced by electromigration propagated along the solder/IMC interfaces. Suppressed void formation was observed at the SAC/Cu–Zn interface when compared to the SAC/Cu interface. Further, electric current was applied to the solder joints until failure and the electromigration lifetime was plotted as a function of the Weibull cumulative distribution to examine the electromigration reliability of the solder joints. The mean time-to-failure of the SAC/Cu–Zn joint was two times longer than that of the SAC/Cu joint. Owing to the anisotropic behavior of Sn, two failure modes, the dissolution of the Cu pad (mode 1) and void propagation at the solder/IMC interface (mode 2) were observed in the SAC/Cu and SAC/Cu–Zn joints. In both specimens, the failure time of mode 2 was longer than that of mode 1. However, the main failure type was mode 1 in SAC/Cu joints and mode 2 in SAC/Cu–Zn joints. For both failure modes, the lifetime of Cu–Zn specimens was longer than that of Cu specimens. The electromigration reliability of the SAC/Cu–Zn joint was found to be superior to that of the SAC/Cu joint because the occurrence of failure mode 1 was suppressed and the lifetime of the SAC/Cu joint in both failure modes was longer.

Vacancy formation enthalpies of high-entropy FeCoCrNi alloy via first-principles calculations and possible implications to its superior radiation tolerance

Because atoms in high-entropy alloys (HEAs) coordinate in very different and distorted local environments in the lattice sites, even for the same type of constituent, their point defects could highly vary. Therefore, theoretical determination of the thermodynamic quantities (i.e., defect formation enthalpies) of various point defects is rather challenging because each corresponding thermodynamic quantity of all involve constituents is not unique. The knowledge of these thermodynamic quantities is prerequisite for designing novel HEAs and understanding the mechanical and physical behaviors of HEAs. However, to date there has not been a good method to theoretically derive the defect formation enthalpies of HEAs. Here, using first-principles calculations within the density functional theory (DFT) in combination of special quasi-random structure models (SQSs), we have developed a general method to derive corresponding formation enthalpies of point defects in HEAs, using vacancy formation enthalpies of a four-component equiatomic fcc-type FeCoCrNi HEA as prototypical and benchmark examples. In difference from traditional ordered alloys, the vacancy formation enthalpies of FeCoCrNi HEA vary in a highly wide range from 0.72 to 2.89eV for Fe, 0.88–2.90eV for Co, 0.78–3.09eV for Cr, and 0.91–2.95eV for Ni due to high-level site-to-site lattice distortions and compositional complexities. On average, the vacancy formation enthalpies of 1.58eV for Fe, 1.61eV for Cr, 1.70eV for Co and 1.89eV for Ni are all larger than that (1.41eV) of pure fcc nickel. This fact implies that the vacancies are much more difficult to be created than in nickel, indicating a reasonable agreement with the recent experimental observation that FeCoCrNi exhibits two orders of amplitudes enhancement of radiation tolerance with the suppression of void formation at elevated temperatures than in pure nickel.

Modification of PEG/PMMA binder by PVP for titanium metal injection moulding

Polyethylene glycol (PEG), with polymethyl methacrylate (PMMA) as the backbone binder component, is a common primary binder component in the design of water soluble binder systems for metal injection moulding (MIM). However, PEG crystallises upon cooling, producing voids in the injection moulded parts. These voids ultimately lead to porosity and degraded mechanical properties in the sintered bodies. We have previously reported on the use of polyvinylpyrrolidone (PVP) as a crystallisation inhibitor in the PEG/PMMA binder system to suppress void formation. In this paper, PEG/PMMA/PVP binder-based feedstocks were prepared with a 67vol% solid loading in order to evaluate the effects of PVP incorporation on the PEG/PMMA binder for titanium MIM. The homogeneity and rheological behaviours of the feedstocks with varying amounts of PVP were compared with the base PEG/PMMA binder-based feedstock. Microstructural observation, impurity measurement and mechanical testing were carried out. It was found that incorporation of 20wt% PVP into the PEG produced a void-free, high quality Ti-MIM component, with an average final density of 98% and a tensile elongation of 9.5%.

High-Throughput Screening of Extrinsic Point Defect Properties in Si and Ge: Database and Applications

Increased computational resources now make it possible to generate large data sets solely from first principles. Such “high-throughput” screening is employed to create a database of embedding enthalpies for extrinsic point defects and their vacancy complexes in Si and Ge for 73 impurities from H to Rn. Calculations are performed both at the PBE and HSE06 levels of theory. The data set is verified by comparison of the predicted lowest-enthalpy positions with experimental observations. The effect of temperature on the relative occupation of defect sites is estimated through configurational entropy. Potential applications are demonstrated by selecting optimal vacancy traps, directly relevant to industrial processes such as Czochralski growth as a means to suppress void formation.

Enhancing radiation tolerance by controlling defect mobility and migration pathways in multicomponent single-phase alloys.

A grand challenge in material science is to understand the correlation between intrinsic properties and defect dynamics. Radiation tolerant materials are in great demand for safe operation and advancement of nuclear and aerospace systems. Unlike traditional approaches that rely on microstructural and nanoscale features to mitigate radiation damage, this study demonstrates enhancement of radiation tolerance with the suppression of void formation by two orders magnitude at elevated temperatures in equiatomic single-phase concentrated solid solution alloys, and more importantly, reveals its controlling mechanism through a detailed analysis of the depth distribution of defect clusters and an atomistic computer simulation. The enhanced swelling resistance is attributed to the tailored interstitial defect cluster motion in the alloys from a long-range one-dimensional mode to a short-range three-dimensional mode, which leads to enhanced point defect recombination. The results suggest design criteria for next generation radiation tolerant structural alloys.

Enhancement of a cyclic endurance of phase change memory by application of a high-density C15(Ge21Sb36Te43) film

The lower cyclic endurance of Phase Change Memory (PCM) devices limits the spread of its applications for reliable memory. The findings reported here show that micro-voids and excess vacancies that are produced during the deposition process and the subsequent growth in sputtered carbon-doped GeSbTe films is one of the major causes of device failure in PCM with cycling. We found that the size of voids in C15(Ge21Sb36Te43) films increased with increasing annealing temperature and the activation energy for the growth rate of voids was determined to be 2.22 eV. The film density, which is closely related to voids, varies with the deposition temperature and sputtering power used. The lower heat of vaporization of elemental Sb and Te compared to that for elemental Ge and C is a major cause of the low density of the film. It was possible to suppress void formation to a considerable extent by optimizing the deposition conditions, which leads to a dramatic enhancement in cyclic endurance by 2 orders of magnitude in PCM devices prepared at 300oC-300W compared to one prepared at 240oC-500W without change of compositions.