Local Current Density Research Articles

Electrochemistry-Based Diagnosis of Li Plating for Fast-Charging Li-Ion Batteries

Recent innovations in battery technologies have facilitated the development and widespread use of electric vehicles (EVs), by increasing the energy density of batteries while lowering their cost. Despite the rapid growth of the EV market, the long charging time of lithium-ion batteries (LIBs) remains as a major obstacle for expanding customer acceptance of EVs. Typically, graphite-based anodes in the state-of-the-art LIBs suffer from Li plating under fast-charging conditions, which causes severe performance degradations and early cell failure of batteries. To prevent the Li plating-induced failure, extensive research efforts have been devoted to developing diagnostic methods capable of detecting Li plating. The electrochemical analysis of Li plating enables non-destructive, in operando detection without complicated experimental procedures or special equipment.Herein, we present a non-destructive method for detecting Li plating during fast-charge cycling by analyzing current transients during the constant-voltage charging step, based on electrochemical battery models. Three-dimensional (3D) and pseudo-two-dimensional (P2D) battery models are employed to predict the electrochemical behavior of full cells under fast-charging conditions. 3D model enables the evaluation of local electrochemical properties, such as local reaction current densities and electrode potentials, which are largely affected by the microstructure of the electrode. Furthermore, P2D models are employed to investigate the effect of changes in microstructural properties (e.g., porosity and fraction of active surface of the graphite anode) on electrochemical behavior of full cells.For 3D modeling, the 3D Voronoi tessellation and Catmull-Clark algorithm are employed to construct the model geometry of graphite anodes. 3D modeling results predict that upon fast-charging, the charge-transfer potential on the top surface of graphite anode rapidly drops below 0 V vs. Li/Li+, triggering Li plating. To extract the electrochemical signals of Li plating, the fast-charging behaviors of full cells are investigated by using the P2D model with a partially reversible Li plating–stripping reaction. In specific, the constant-current and constant-voltage (CC-CV) charging process of the full cells with graphite anodes is simulated with Li plating-induced degradation modes; reduction of (i) interparticle pores, (ii) active surface area for Li intercalation reaction, and (iii) cyclable Li amount. Modeling results demonstrate that an inflection point appears in the current transient curve, and it shows a positive shift when the Li plating-induced degradation occurs. Electrochemical tests and microstructural analyses further confirm the validity of proposed electrochemical detection of Li plating. This study provides an effective strategy to design electrochemical methods for Li plating detection during fast-charging batteries based on electrochemistry-based models.

Using Magnetic Field Analysis for Localizing Defects of Fuel Cell & Electrolyzer Components

Production capacities of electrolysis and fuel cell technologies are expected to increase significantly in the upcoming years, reducing costs of stack components through numbering-up. To ensure reliability and durability and reduce costs along the manufacturing process, developing suitable in-line non-destructive diagnostic methods for quality control becomes essential for their industrialization.In both fuel cell and electrolyzer stacks, the main components' electrical resistance and current density distribution greatly influence stack efficiency and longevity. Here, the flowing electric current generates a magnetic field depending on its strength and direction. Potential defects caused by the manufacturing process, including cracks, defective welding spots, coating adhesion issues, delamination, and contamination, influence the components' electric conductivity and current density distribution and hence the magnetic field distribution.This work investigates non-destructive diagnostic methods using magnetic field analysis (MFA) to identify changes in the magnetic field distribution and, thus, local electrical resistance and current density distributions of fuel cell and electrolyzer components. The methods used are magnetic field imaging (MFI) and Eddy Current Testing (ECT). MFI analyzes the magnetic field distribution in all three spatial directions to trace electrical currents and identify electrical defects, creating a magnetic field signature that can potentially distinguish between functional and non-functional components along the manufacturing process. ECT measures variations in local conductivity by inducing eddy currents in the sample through an alternating magnetic field generated by a sender coil. These eddy currents create a detectable magnetic field in a receiver and are affected by defects and changes in electrical conductivity. Therefore, the method can characterize sheet resistance and material homogeneity through electrical anisotropy in electrically conductive components.In initial experiments, ECT measurements on coated and uncoated hollow embossed stainless steel bipolar half plates showed systematic differences depending on quality characteristics resulting in unique patterns and inhomogeneities which require further investigation. Furthermore, experiments with both methods on other stack components will be presented and discussed. In addition, their in-line capability will be assessed and evaluated. However, these first promising results imply that MFA is potentially useful as an in-line, non-destructive diagnostic method for quality control.

Fault Detection and Identification for Polymer Electrolyte Membrane Fuel Cell Stack by External Magnetic Field

Many technological locks prevent the deployment of Proton Exchange Membrane Fuel Cell (PEMFC). Particularly for vehicle applications, cost and durability represent two of the most significant challenges to achieve clean, reliable, and cost-effective PEMFC systems. Solving these shortcomings will be a great opportunity for a decisive breakthrough towards mass-diffusion of the current PEMFC technology. The long-term electrical performance losses are associated to either the degradation of the MEA constitutive materials or due to specific operating conditions (flooding, drying, etc.). In perspective, local current density distribution may support stack-level degradation analyzes as well as effective stack control to mitigate the consequences of degradation due to load cycles (electrochemical, thermal, mechanical and humidity effects) or faults.External magnetic field measurement (MFM) shows a high potential in PEMFC non-invasive diagnosis. Thus, 2D and 3D current distributions and their anomalies in the fuel cell can be identified independent of the size of the causing fault.To perform this local characterization, the external magnetic field measurement will enable to model the current density in stationary conditions over the cell surface and for the different cells of the stack. This methodology requires the complementary development of magnetic field techniques and inverse models.In this work, this challenge is tackled by using tailored defective MEAs and specific operating conditions (flooding, drying, ...) to characterize, how local and overall performances of the MEA are affected and to identify the signatures of the various anomalies. Figure 1

Lithiophilic Nanowire Architectures as Hosts for Lithium Metal Anodes

Lithium (Li) metal is considered the ‘holy grail’ of battery anodes and has attracted enormous interest due to its low density (0.59 g cm-3), high theoretical capacity (3860 mAh g-1) and lowest electrochemical potential (-3.07 V vs. standard hydrogen electrode - SHE) [1-2]. However, several issues during its cycling in a Li-metal battery (LMB) have hindered its commercialization. Some notable problems include the formation of an unstable solid electrolyte interphase (SEI), excessive dendrite growth and subsequent short-circuiting during the Li stripping/plating process [3-4].In our poster presentation, we will detail the design of a hierarchical nanowire (NW) – Carbon paper (CP) host for dendrite-free and stable cycling in LMBs. These NWs were grown on high surface area carbon paper substrate via a modified Vapour-Liquid-Solid (VLS) approach. The lithiophilic NWs enabled quick Li infusion (< 10 sec) in the NW-CP substrate whereas no Li infusion was possible in lithiophobic bare CP substrate (without the presence of NWs). Additionally, the NW morphology helped in reducing the localized current density on the surface of the NW-CP host, thereby promoting uniform Li deposition during plating/stripping process. With careful design of the NW-CP host, symmetric cell performance with high current density (3 mA cm-2) and areal capacity (3 mAh cm-2) was achieved for up to 500 h while a typical Li metal anode failed within 200 h. High loading NMC811 and high specific capacity Sulfur (S) cathodes demonstrated superior performance using NW-CP host as compared to pristine Li anodes.In addition, we will also present some new concepts of NW decorated lithiophilic interlayers, which can be integrated with pristine Li metal anodes for uniform Li deposition. These lithiophilic interlayers can promote ‘bottom-up’ Li infilling between the Li-interlayer interface such that dendrite formation near the separator and eventual short-circuit is avoided. Detailed electrochemical as well as density functional theory (DFT) analysis shedding light on the improved lithiophilic properties of NW use in stabilizing Li metal anodes will also be presented. Overall, our work is aimed to develop high energy density (ED) Li metal anodes to meet the rising ED demands of electric vehicle (EV) industry.

Nanotwinned Structure in Copper Affects Lithium Deposition Behavior at Electrolyte-Electrode Interface in Anode-Free Lithium Metal Battery

Anode-free lithium metal battery (AFLMB) is one of new promising energy storage systems. In contrast to lithium-ion battery, the negative electrode of AFLMB does not contain any active materials, resulting in a two-fold increase in energy density. As a result, the charging mechanism on the negative electrode in AFLMB is based on electrodeposition of lithium, rather than intercalation of lithium ions. Unfortunately, that causes a series of problems, such as lithium dendrite formation, volume expansion, broken SEI and dead lithium accumulation, leading to the low cycling stability of AFLMB. Consequently, interfacial characteristics of the negative electrode (usually copper) play a critical role in determining the morphology of lithium deposits which largely affects the issues mentioned above. Understanding the mechanism of lithium electrodeposition across the electrode-electrolyte interface is crucial to design a better copper electrode for long-cyclability AFLMB.The interfacial characteristics of copper are mainly influenced by crystal phase, surface roughness and defects. While the effects of crystal phase and surface roughness on lithium electrodeposition have been extensively studied, the role of micro-scale defects has been seldom discussed, despite their potential to strongly influence the surface properties of copper. Therefore, this work focuses on elucidating the elementary process about how the defects on copper affect the lithium nucleation and subsequent growth. Specifically, we use (111)-nanotwinned and (111)-preferred orientation copper foils with the same surface roughness to conduct a series of electrochemical measurements. The presence of nanotwin structure can reduce the grain boundary and atomic step density, a type of the defects with high surface energy, on the copper. Before lithium electrodeposition, solvents and anions in an electrolyte adsorb on the electrode-electrolyte interface to form the electric double layer. During this process, the atomic steps with high surface energy on copper can establish strong adsorption with the substance in the electrolyte. The solvents adsorbed on the defects may hinder the reduction of anion. Accordingly, the (111)-nanotwinned Cu foil with fewer defects induces the formation of LiF-rich solid electrolyte interphase (SEI), which is beneficial to the transportation of lithium ions. In cyclic voltammetry test, the (111)-nanotwinned Cu foil exhibits higher reduction current density of the precipitation of LiF (Fig. 1).For lithium electrodeposition, during the initial stage, lithium adatoms tend to adsorb on the defects with high surface energy on the copper surface, where other adatoms accumulate to form stable nucleus. Subsequently, the nucleus on each nucleation sites might have different growth direction and crystal phase, resulting in a lot of independent lithium grains. In other words, compared to the (111)-preferred orientation substrate, the (111)-nanotwinned Cu foil with less nucleation sites provides more space for the nucleus to grow in 2-D direction, which leads to the lower nucleation overpotential (Fig. 2 a). That result also facilitates the formation of larger lithium grains with smaller surface area exposed to the electrolyte (Fig. 3). As shown in Figure 2 (b), quasi-steady state over-potential of Li plating on the (111)-nanotwinned Cu is generally larger than that on the (111)-preferred orientation Cu foil, which has been ascribed to the high local current density on larger lithium grains. The quasi-steady state overpotential of Li plating on the (111)-preferred orientation Cu foil gradually increased with the cycle number, which might be attributable to the relatively unstable SEI and the accumulation of dead lithium with the GCD cycling. Furthermore, the (111)-nanotwinned Cu foil always exhibits a lower quasi-steady state overpotential of lithium stripping in comparison with the (111)-preferred orientation substrate at each cycle, probably resulting from the uniform Li deposit and the special LiF-rich SEI formation due to the nanotwinned structure. In the cycling stability test (Figure 2 c), for the Cu//Li cell using the (111)-nanotwinned Cu foil, the coulombic efficiency was kept being around 90% in this 160-cycle test. However, for the Cu//Li cell using the (111)-preferred orientation Cu foil, the coulombic efficiency is generally lower than that of the cell using the (111)-nanotwinned Cu foil at the cycle number > 15. In addition, the coulombic efficiency starts to obviously decay at the 135th cycle and becomes lower than 5% at the 160th cycle.To sum up, we proposed a mechanism about how the defects affect the reaction at electrode-electrolyte interface. The nanotwinned columnar grains reduces the atomic density on the copper surface, which effectively reduces the formation of lithium dendrite, the accumulation of dead lithium and broken SEI. The (111)-nanotwinned Cu foil is proved to be a superior substrate for lithium deposition and stripping, significantly improving the Li+/Li redox reversibility and cycling stability. Figure 1

Contribution of Oxygen Reduction to Mg Corrosion: Experimental Evidence By Electrochemical Microprobes

Unravelling the mechanisms of magnesium corrosion is vital for establishing reliable research methodologies, developing new alloys and predicting magnesium degradation behaviour. Hydrogen evolution reaction is widely regarded as by far the main cathodic process during corrosion of magnesium. Hence, tracing the amount of released hydrogen was thought to be a reliable measure of magnesium degradation rate. Recently, experimental evidences obtained by different methods have been presented by several groups that oxygen reduction (ORR) is important secondary cathodic reaction during Mg corrosion [1-8]. For model galvanic couple Al-Cu-Mg, oxygen consumption on the surface of Mg along with that on Cu was observed by using oxygen sensing microoptode [1]. A simultaneous measurement of local current density by scanning vibrating electrode technique (SVET) and local oxygen concentration by oxygen sensing microoptode found a strong oxygen consumption at the active corrosion sites on the surface of commercially pure Mg in NaCl electrolyte [2]. Then, the evidence for the varying contributions of ORR to the total cathodic process on Mg alloys during atmospheric and aqueous corrosion was presented based on newly developed respirometric methods [3-5]. While around 10% of the total cathodic current was ascribed to ORR during aqueous corrosion, up to 60% of the total corrosion process was shown to be due to the ORR contribution during simulated atmospheric corrosion with wet-dry cycles. Nanoparticle-based O2 imaging was used to map decreased O2 concentration at the interface of several Mg alloys exposed to simulated body fluids [6].High ORR rate on a slowly corroding ultra-high-purity Mg (UHP-Mg) in NaCl electrolyte was shown in our recent work [7]. Comparing that with lower ORR rate for faster corroding commercial purity Mg (CP-Mg), the rate of ORR was found to depend on the growth rate of Mg(OH)2 , which is the main corrosion product of Mg in the simple saline solution. The formation of Mg(OH)2 impeded the diffusion of oxygen from bulk electrolyte to metal interface, preventing metallic Mg substrate from the interaction with oxygen. The distribution of local concentration of dissolved gaseous H2 and O2 assessed by amperometric Clark-type micorprobes at the interface of UHP-Mg and CP-Mg demonstrated the inverse relationship between HER and ORR, and supports the finding that diffusion-controlled ORR highly depends on the barrier property of corrosion products on the surface [8]. The contribution of ORR current to total cathodic current reached 29.1% for UHP-Mg, while only 0.9% for CP-Mg after 1 hour of immersion in NaCl solution. The contribution of ORR decreases with immersion time, due to the impeded access of dissolved O2 to Mg interface caused by thickening of Mg(OH)2 layer. A numerical model was developed considering the mixed potential diagram and measured local oxygen concentration. REFERENCES: [1] D. Snihirova, M. Taryba, S.V. Lamaka, M.F. Montemor, Corrosion inhibition synergies on a model Al-Cu-Mg sample studied by localized scanning electrochemical techniques, Corrosion Science, 112 (2016) 408-417.[2] E.L. Silva, S.V. Lamaka, D. Mei, M.L. Zheludkevich, The Reduction of Dissolved Oxygen During Magnesium Corrosion, ChemistryOpen, 7 (2018) 664-668.[3] M. Strebl, S. Virtanen, Real-Time Monitoring of Atmospheric Magnesium Alloy Corrosion, Journal of The Electrochemical Society, 166 (2019) C3001-C3009.[4] M. Strebl, M. Bruns, S. Virtanen, Editors’ Choice—Respirometric in Situ Methods for Real-Time Monitoring of Corrosion Rates: Part I. Atmospheric Corrosion, Journal of The Electrochemical Society, 167 (2020) 021510.[5] M. Strebl, M.P. Bruns, G. Schulze, S. Virtanen, Respirometric In Situ Methods for Real-Time Monitoring of Corrosion Rates: Part II. Immersion, Journal of the Electrochemical Society, (2021).[6] B. Zeller-Plumhoff, A.R. Akkineni, H. Helmholz, D. Orlov, M. Mosshammer, M. Kühl, R. Willumeit-Römer, M. Gelinsky, Oxygen-sensitive nanoparticles reveal the spatiotemporal dynamics of oxygen reduction during magnesium implant biodegradation, NPJ Materials Degradation, 6 (2022) 95.[7] C. Wang, D. Mei, G. Wiese, L.Q. Wang, M. Deng, S.V. Lamaka, M.L. Zheludkevich, High rate oxygen reduction reaction during corrosion of ultra-high-purity magnesium, NPJ Materials Degradation, 4 (2020) 42.[8] C. Wang, W. Xu, D. Höche, M.L. Zheludkevich, S.V. Lamaka, Exploring the contribution of oxygen reduction reaction to Mg corrosion by modeling assisted local analysis, Journal of Magnesium and Alloys, 11 (2023) 100-109. ACKNOWLEDGEMENTS: C. Wang, Wen Xu, thank China Scholarship Council for the funding, grants no. 201806310128 and 201908510177

A comprehensive investigation on performance heterogeneity of commercial-size fuel cell stacks during dynamics operation

The performance heterogeneity of commercial-size proton exchange membrane (PEM) fuel cells comprises both inter-cell consistency and intra-cell uniformity, which can lead to the generation of degrading stressors, such as harmful variations in local cell voltage and current density. However, there is a notable absence of a thorough investigation of the potential correlation between inter-cell consistency and intra-cell uniformity. To address this knowledge gap, a comprehensive experimental study was conducted via the current distribution model to assess the impact of several operating variables, including loading rate, cathode stoichiometry ratio, and cathode pressure, on the performance heterogeneity of commercial-size fuel cell stacks. The results indicate that cells situated on both end sides of the stack are more susceptible to non-equipotential phenomena owing to liquid water accumulation and the inhomogeneity of oxygen distribution, which in turn lead to the redistribution of the in-plane current as well as the deviation of the bipolar plate potential. Moreover, a significant correlation exists between inter-cell consistency and intra-cell uniformity of cells placed at both ends of the stack with a correlation coefficient > 0.85. The enhancement of fuel cell stack output performance and reduction of performance heterogeneity may be achieved by optimizing pressure and stoichiometric ratio. However, it should be noted that there exists a discrepancy in the operating conditions necessary to achieve optimal performance and minimal performance heterogeneity. Finally, the recommendations given for the implementation of cell voltage monitors (CVMs) were summarized. This study provides a comprehensive reference for analyzing complex heterogeneity issues within fuel cells, revealing significant potential in their application.

Thermal Transients to Accelerate Cyclic Aging of Lithium‐Ion Batteries

AbstractCyclic aging tests of lithium‐ion batteries are very time‐consuming. Therefore, it is necessary to reduce the testing time by tightening the testing conditions. However, the acceleration with this approach is limited without altering the aging mechanisms. In this paper, we investigate whether and how thermal transients accelerate the aging. The tests are performed on NMC/graphite pouch cells by applying temperatures in a range of 5 °C to 45 °C to the cell surface. The results show, that an accelerated capacity loss can be achieved in comparison to the reference cell at a steady‐state temperature of 25 °C. However, capacity difference analysis (CDA) prognoses a covering layer for the transient cells, which is confirmed upon post‐mortem analysis. We suspect the origin to lie in the dynamics of temperature fields and current distribution during temperature changes when charging. More specifically, areas of higher temperature in the cell lead to high local current densities and plating. Subsequently, high temperatures promote the reaction of the plated lithium with electrolyte. The results show that thermal transients are a critical condition for lifetime and safety and should be treated with caution as they can occur during real life operation.

Combining Electrical Resistivity, Induced Polarization, and Self-Potential for a Better Detection of Ore Bodies

Electrical resistivity (ER), induced polarization (IP), and self-potential (SP) are three geophysical methods that have been broadly used in the realm of mineral exploration. These geophysical methods provide complementary information, each exhibiting a distinct sensitivity to various types of mineral deposits. Considering the relationship among these three methods, we propose an integrated approach that merges their respective information to offer an improved localization technique for ore bodies. First, we invert the electrical conductivity distribution through electrical resistance tomography (ERT). Then, we use the inverted conductivity distribution to invert the IP and SP data in terms of chargeability and source current density distributions. Then, we normalize the inverted chargeability and source current density distributions and we combine them to obtain an ore body index (ORI) χ used to delineate the potential locations of ore deposits. We design this index to be sensitive to the presence of ore bodies, which are reflected by either strong and localized source current density (SP) and/or strong chargeability values (IP). The proposed method is first validated using a synthetic model with two distinct anomalies characterized by different properties. The results show the limitation of individual inversion, as each method exclusively detects one of these anomalies. The combined approach allows a better characterization of the target. Then, the approach is applied to a sandbox experiment in which two metallic bodies are buried in water-saturated sand used as the background. Again, the proposed methodology is successfully applied to the detection of the metallic targets, improving their localization compared with individual methods.

Full-scale three-dimensional simulation of air cooling metal bipolar plate proton exchange membrane fuel cell stack considering a non-isothermal multiphase model

Addressing issues such as the mass transfer characteristics and internal performance consistency of the air cooling (AC) proton exchange membrane fuel cell (PEMFC) stack. A full-scale AC metal bipolar plate (BP) stack is proposed in this study, comprising inlet and outlet manifolds, membrane electrode assembly (MEA), reaction flow field (FF) and cooling FF. The coupling of electrochemical reactions and heat and mass transfer processes in the stack is simulated using a non-isothermal multiphase numerical model. The characterization of the mass spatial distribution in the stack is explored by varying the stoichiometric ratio of the cathode gas, the thermal boundary conditions, the flow direction of the reaction gas and the air inlet flow configuration. According to the simulation results, it is found that, initially, the simulation errors in the one-dimensional (1D) AC stack are large and mainly concentrated in the concentration loss region. Subsequently, the increased stoichiometric ratio enhances the proton exchange membrane (PEM) water content, improves the local current density by 1.6% and facilitates the discharge of waste heat from the stack. Furthermore, thermal boundary conditions significantly affect the distribution of temperature uniformity in the stack, with high local temperatures causing significant water vapor generation and resulting in oxygen dilution. The counter-flow of hydrogen and air enhances the electrochemical reaction rates in the cathode catalyst layer (CCL) by 0.353%, with the lowest liquid water content in the seventh cell, influenced by the uneven distribution of manifold flow. Finally, changing the position of the cathode manifold gas inlet indicates that the positive flow of the cathode and AC inlets from the Z axis reduces the maximum stack temperature and water vapor by 1.04% and 0.38% respectively. The CCLs in Case 4 have optimal oxygen distribution and output voltages of approximately 0.66 V per fuel cell (FC).

3D lithiophilic framework with bimetallic phosphates to improve lithium deposition

Bimetallic phosphides, Cu3P and Ni2P, were decorated on nickel foam to fabricate 3D lithiophilic framework by electrodeposition method and subsequent phosphating reaction. The electrodeposition time affected the uniformity of the Cu coating, then influenced the distribution of bimetallic phosphides. The half cell using the Cu3P-Ni2P@Ni (CNPNF-300) framework as an anode achieved 98.6 % Coulombic efficiency and 270 cycles under cycle capacity of 1 mAh cm−2 and current density of 1 mA cm−2. The performance of half cell confirmed that the optimal plating time was 300 s. The symmetrical cell fabricated with Li/LCNPNF (Li-Cu3P-Ni2P@Ni foam) showed remarkable cycling stability for 1800 h at 5 mA cm−2 with Li amount of 5 mAh cm−2. The excellent performance was attributed to favourable lithiophilic property, uniform local current density, and inhibition volume expansion of the LCNPNF hybrid framework electrode. Finally, a full battery combined with LiFePO4 as cathode and LCNPNF as anode exhibited the potential for practical applications with superior cycling stability (400 cycles at 0.5 C) and good rate performance.

Soft Carbon-Thiourea with Fast Bulk Diffusion Kinetics for Solid-State Lithium Metal Batteries.

The development of all-solid-state lithium-metal batteries (ASSLMBs) is impeded by low coulomb efficiency, short lifetime, poor rate performance, and other problems caused by the rapid growth of lithium (Li) dendrites. Herein, a multiple-diffusion-channel N,S-doped soft carbon with expanded layer spacing is designed/developed by thiourea calcination for dendrite-free anodes. Since the enlarged layer spacing can improve Li+ transportation rate within the layers and N,S-doping can facilitate Li+ transport between the layers, the bulk phase diffusion (not just surface diffusion) kinetics can be improved, which in turn reduces the local current density, inhibits the growth of Li dendrites, and improves the rate performance. The resulting ASSLMB achieves record-high current density (15mA cm-2 ), areal capacity (20 mAh cm-2 ), energy density (403Wh kg-1 ), and ultra-long cycle life (13000 cycles). >305Wh kg-1 pouch cells are realized, representing one of the most critical breakthroughs for real-world application of ASSLMBs.

Synergizing 3D-printed structure and sodiophilic interface enables highly efficient sodium metal anodes

Sodium (Na) metal batteries have gained increasing attention more recently, owing to their high energy densities and cost efficiencies, but are severely handicapped by the unsatisfactory Coulombic efficiency (CE) and cycling stability stemming from dendrite growth on Na anodes. In this study, we developed a strategy of direct ink writing (DIW) 3D printing combined with electroless deposition to construct a hierarchical Cu grid coated with a dense nanoscale Ag interfacial layer as the host material for Na plating. The sodiophilic Ag interface contributes to a fall in the Na nucleation energy, hence enabling uniform Na deposition on each 3D-printed filament. The constructed 3D-printed structure can effectively moderate the electric-field distribution and lower the local current density for relieving Na inhomogeneous growth, as confirmed by finite element simulation and Na plating/stripping morphology evolution results. In particular, the unique 3D structure also promotes the lateral growth of Na, thus the volume change of Na metal was accommodated to stabilize the solid electrolyte interphase (SEI). As a result, the CE of the half-cell can reach 99.9 % at the current density of 1 mA/cm2 after 300 cycles and the full-cell exhibits outstanding electrochemical performance (capacity retention of 91.0 % after 500 cycles at 2 C).

Integration of Porous High‐Loading Electrode and Gel Polymer Electrolyte for High‐Performance Quasi‐Solid‐State Battery

AbstractThe practical applications of lithium‐ion batteries (LIBs) are challenged by safety concerns using liquid electrolytes (LEs). The gel polymer electrolytes (GPEs) are considered as a promising candidate to solve this safety issue. In addition, using high‐mass loading electrodes is essential to achieve high energy density. However, poor interfacial contact between electrode and electrolyte remains a challenging issue, particularly for the high‐mass‐loading electrode. Here, porous channels are constructed in electrodes with high active material loading using the melamine formaldehyde sponge, and then the GPE is penetrated into porous channels of electrodes through an in‐situ thermal induced polymerization. The porous electrode structure with sufficient surface area improves electrolyte percolation and fast ion diffusion kinetics, which enables a uniform distribution of Li‐ion flux and effectively homogenizes the local current density to realize uniform Li deposition. The half cells and anode‐free full cells using the integration of porous electrodes and in‐situ polymerized GPEs exhibit excellent discharge capacity and cycle stability. This integration method is applicable for fabricating batteries with high energy density and safety.

Dynamic evolutions of local current density and water–gas distribution of proton exchange membrane fuel cell with dead-ended anode

Dynamic evolutions of local current density and water–gas distribution of proton exchange membrane fuel cell with dead-ended anode

Functional lithiophilic skeleton/evolving lithium sulfide artificial protective layer for dendrite-free Li metal anode

The intrinsic high activity and skeletonless development of lithium (Li) metal have resulted in gruesome security issues, limiting the widespread use of Li metal anodes. Herein, a three-dimensional (3D) nanosheet skeleton with CuO/CuS (3D CuO/CuS-NS skeleton) is designed as the functional Li metal anode current collector. The functional skeleton’s 3D structure features a large specific surface area to reduce the local current density and inhibit dendrite growth. CuO/CuS loaded by the skeleton can be employed as lithiophilic sites to direct the uniform deposition of Li metal, according to density functional theory (DFT). Furthermore, during the first deposition, CuO/CuS can interact with Li metal to produce Li2O/Li2S, in which Li2S can act as an artificial protective layer to effectively improve the cycle stability of the cells. The dendrite-free deposition in the depositional process demonstrates that the 3D CuO/CuS-NS skeleton can achieve excellent Li metal anode stability. The Li metal anodes with 3D CuO/CuS-NS skeletons also exhibit outstanding electrochemical stability over 1000 h of long-term cycling. In full cells assembled with commercial LiCoO2 cathodes, the 3D CuO/CuS-NS skeletons exhibit good rate performance and capacity retention performance.

Two-pronged approach to achieving high-capacity and long stable-life aqueous Zn-ion batteries

Rechargeable Zn-ion batteries (ZIBs) have attracted much attention due to their high energy density, high safety, and low cost. Nevertheless, the practical implementation of ZIBs has been dreadfully hindered by the lack of stable high-capacity cathode candidate and serious dendritic growth in Zn anode. Superior device-level performance can only be achieved by simultaneously addressing the fatal shortcomings of both electrodes. Herein, we explore a two-pronged approach to achieving high-capacity, long-life stable ZIBs via synergistic design in both anodes and cathodes. Specifically, hierarchical accordion-like ZnV2O4@C (A-ZVO@C) framework derived from multi-layered V2CTx is fabricated and endowed with high electronic/ionic conductivities and structural/chemical stability, exhibiting striking high-rate capacities/stability when utilized as a cathode. Meanwhile, a dendrite-free Zn with an artificial protective layer of zincophilic ZnO/C hollow spheres affords outstanding Zn plating-stripping stability with a prolonged lifespan, which reduces local current density, homogenizes Zn2+ ion diffusion/deposition, and suppresses volume changes during long-term plating/stripping. As a result, the assembled full ZIBs deliver a high-rate capacity of 232.2 mAh g−1 at 8 A g−1, and superb stability with capacity degradation of 7.8 % over 3000 consecutive cycles at 15.0 A g−1. More meaningfully, the contribution here provides an essential guidance for rationally designing next-generation ZIBs.

Double-layered skeleton of Li alloy anchored on 3D metal foam enabling ultralong lifespan of Li anode under high rate

The high specific capacity and low negative electrochemical potential of lithium metal anodes (LMAs), may allow the energy density threshold of Li metal batteries (LMBs) to be pushed higher. However, the existing detrimental issues, such as dendritic growth and volume expansion, have hindered the practical implementation of LMBs. Introducing three-dimensional frameworks (e.g., copper and nickel foam), have been regarded as one of the fundamental strategies to reduce the local current density, aiming to extend the Sand’ time. Nevertheless, the local environment far from the skeleton is almost the same as the typical plane Li, due to macroporous space of metal foam. Herein, we built a double-layered 3D current collector of Li alloy anchored on the metal foam, with micropores interconnected macropores, via a viable thermal infiltration and cooling strategy. Due to the excellent electronic and ionic conductivity coupled with favorable lithiophilicity, the Li alloy can effectively reduce the nucleation barrier and enhance the Li+ transportation rate, while the metal foam can role as the primary promotor to enlarge the surface area and buffer the dimensional variation. Synergistically, the Li composite anode with hierarchical structure of primary and secondary scaffolds realized the even deposition behavior and minimum volume expansion, outputting preeminent prolonged cycling performances under high rate.

3D hierarchically fractal structure stabilized anode for achieving long-term cycle life of aqueous Zn-ion batteries

The cycling stability of aqueous Zn-ion battery (AZIB) is a serious issue for their successful application, mainly due to the considerable growth of Zn dendrites and the existence of side effects during operation. Herein, the hierarchically three-dimensional (3D) fractal structure of the ZnO/Zn/CuxO@Cu (ZZCC) anode is prepared by a two-step process, where CuxO nanowires are prepared on Cu foam by thermal oxidation method and Zn layer and ZnO surface are formed by plating. This fractal structure increases the electrodynamic surfaces and reduces the local current density, which can regulate Zn plating and inhibit dendritic growth and side effects. Apparently, the symmetric ZZCC-based cell shows a long-term operation time of 3000 h at 1 mA cm−2 with 1 mAh cm−2, and an operation time of more than 1000 h with a discharge depth of 15.94%. Compared with the bare Zn foil anode, the AZIB assembled with the composite of Mn-doped vanadium oxide and reduced graphene oxide cathode and ZZCC anode (MnVO@rGO//ZZCC) exhibits significantly improved cyclability (i.e. with 88.5% capacity retention) and achieves a Coulomb efficiency of 99.4% at 2 A g-1. This hierarchically 3D structure strategy to design anodes with superior cyclic stability contributes to the next generation of secure energy.

Designing Janus separators reinforced by hydrogen/ionic bonds for stable lithium metal anodes

Lithium metal batteries (LMBs), with their ultra-high theoretical energy density, are considered the most promising high-density energy storage devices. However, uncontrolled lithium dendrites and safety issues have seriously hindered the widespread application of LMBs. Separators are a vital component in ensuring the safety of batteries, preventing direct electrical contact between the cathode and anode while allowing ion transport. Here we report a Janus separator with an electrically and thermally conductive layer of carbon nanotubes on one side and a solid–solid phase change layer on the other side. Meanwhile, hydrogen/ionic bonds are introduced to enhance the internal structural connectivity of the separator, leading to a significant improvement in mechanical strength. The electrically and thermally conductive layer of the Janus separator regulates lithium deposition by eliminating local current density and hot spots, to mitigate the growth of lithium dendrites. When lithium dendrites inevitably pierce the separator and cause short circuit, the solid–solid phase change layer can serve as safety compensation, absorbing heat through the solid–solid phase change and alleviating the temperature rise caused by the short circuit. Experimental results and theoretical simulations show that the Janus separator can effectively suppress lithium dendrites and alleviate the temperature rise of the battery during short circuit. More importantly, the Janus separators exhibit superior electrochemical performance to commercial polyolefin separators. The as-designed Janus separator with the functions of lithium dendrite suppression and solid–solid phase change thermoregulation provides an effective strategy for enhancing the safety of LMBs.