Diffusion Limited Current Density: A Watershed in Electrodeposition of Lithium Metal Anode

Liu Y., Xu X., Kapitanova O.O., Evdokimov P.V., Song Z., Matic A., Xiong S.

Nonuniform electrodeposition of lithium during charging processes is the key issue hindering development of rechargeable Li metal batteries. This deposition process is largely controlled by the solid electrolyte interphase (SEI) on the metal surface and the design of artificial SEIs is an essential pathway to regulate electrodeposition of Li. In this work, an electro-chemo-mechanical model is built and implemented in a phase-field modelling to understand the correlation between the physical properties of artificial SEIs and deposition of Li. The results show that improving ionic conductivity of the SEI above a critical level can mitigate stress concentration and preferred deposition of Li. In addition, the mechanical strength of the SEI is found to also mitigate non-uniform deposition and influence electrochemical kinetics, with a Young's modulus around 4.0 GPa being a threshold value for even deposition of Li. By comparison of the results to experimental results for artificial SEIs it is clear that the most important direction for future work is to improve the ionic conductivity without compromising mechanical strength. In addition, the findings and methodology presented here not only provide detailed guidelines for design of artificial SEI on Li-metal anodes but also pave the way to explore strategies for regulating deposition of other metal anodes.

Fedorov R.G., Maletti S., Heubner C., Michaelis A., Ein‐Eli Y.

An intrinsic challenge of Li-ion batteries is the instability of electrolytes against anode materials. For anodes with a favorably low operating potential, a solid-electrolyte interphase (SEI) formed during initial cycles provides stability, traded off for capacity consumption. The SEI is mainly determined by the anode material, electrolyte composition, and formation conditions. Its properties are typically adjusted by changing the liquid electrolyte's composition. Artificial SEIs (Art-SEIs) offer much more freedom to address and tune specific properties, such as chemical composition, impedance, thickness, and elasticity. Art-SEIs for intercalation, alloying, conversion and Li metal anodes have to fulfil varying requirements. In all cases, sufficient transport properties for Li-ions and (electro-)chemical stability must be guaranteed. Several approaches for Art-SEIs preparation have been reported: from simple casting and coating techniques to elaborated Phys-Chem modifications and deposition processes. This review critically reports on the promising approaches for Art-SEIs formation on different type of anode materials, focusing on methodological aspects. The specific requirements for each approach and material class, as well as the most effective strategies for Art-SEI coating, are discussed and a roadmap for further developments towards next-generation stable anodes are provided.

Vu T.T., Eom G.H., Lee J., Park M., Moon J.

Lithium metal (Li) is an ideal anode for designing high-energy Li metal batteries (LMBs) due to its high specific capacity (3860 mAh g −1 ) and lowest electrochemical potential. However, the practical use of Li is currently impeded by uncontrollable dendritic growth during repeated Li plating and stripping, causing serious safety hazards such as electrical short circuits. To regulate Li growth behavior, various solid electrolyte interfaces (SEIs) have been explored. Despite intensive efforts, further understanding of the dendritic growth mechanism is still required. In this respect, herein, we clarify the origin and growth mechanism of Li dendrites by evaluating the critical role of an artificial SEI using a finite element method. Based on our theoretical study, we suggest that the relatively low ionic conductivity of the SEI layer is responsible for facilitating the growth of Li dendrites and the growth can be effectively suppressed by employing an artificial SEI with a higher ionic conductivity. The high-conductivity artificial SEI regulates local current distributions, directly affecting the growth of Li dendrites as determined by measuring the current density, exchange current density, and geometry. Our findings provide new insight into the design of artificial SEIs for improving the cycling performance of advanced LMBs. • Li dendrite growth in Li-metal batteries was probed using a finite element method. • The effects of natural and artificial SEIs on Li growth morphology were studied. • Nonuniform current density at electrolyte-electrode interface caused dendrite growth. • Dendrite growth was suppressed by a high-ionic-conductivity artificial SEI. • The results help secure the stable cycling of Li-metal anodes in Li-metal batteries.

Zou P., Sui Y., Zhan H., Wang C., Xin H.L., Cheng H., Kang F., Yang C.

Lithium (Li) metal, a typical alkaline metal, has been hailed as the "holy grail" anode material for next generation batteries owing to its high theoretical capacity and low redox reaction potential. However, the uncontrolled Li plating/stripping issue of Li metal anodes, associated with polymorphous Li formation, "dead Li" accumulation, poor Coulombic efficiency, inferior cyclic stability, and hazardous safety risks (such as explosion), remains as one major roadblock for their practical applications. In principle, polymorphous Li deposits on Li metal anodes includes smooth Li (film-like Li) and a group of irregularly patterned Li (e.g., whisker-like Li (Li whiskers), moss-like Li (Li mosses), tree-like Li (Li dendrites), and their combinations). The nucleation and growth of these Li polymorphs are dominantly dependent on multiphysical fields, involving the ionic concentration field, electric field, stress field, and temperature field, etc. This review provides a clear picture and in-depth discussion on the classification and initiation/growth mechanisms of polymorphous Li from the new perspective of multiphysical fields, particularly for irregular Li patterns. Specifically, we discuss the impact of multiphysical fields' distribution and intensity on Li plating behavior as well as their connection with the electrochemical and metallurgical properties of Li metal and some other factors (e.g., electrolyte composition, solid electrolyte interphase (SEI) layer, and initial nuclei states). Accordingly, the studies on the progress for delaying/suppressing/redirecting irregular Li evolution to enhance the stability and safety performance of Li metal batteries are reviewed, which are also categorized based on the multiphysical fields. Finally, an overview of the existing challenges and the future development directions of metal anodes are summarized and prospected.

Yang C., Qi Y.

Electroplating has been the main focus in mitigating the dendrite growth on the Li-metal electrode; however, the stripping process is equally critical, since the nonsmooth Li surface during strippi...

Mistry A., Franco A.A., Cooper S.J., Roberts S.A., Viswanathan V.

Electrochemical systems function via interconversion of electric charge and chemical species and represent promising technologies for our cleaner, more sustainable future. However, their development time is fundamentally limited by our ability to identify new materials and understand their electrochemical response. To shorten this time frame, we need to switch from the trial-and-error approach of finding useful materials to a more selective process by leveraging model predictions. Machine learning (ML) offers data-driven predictions and can be helpful. Herein we ask if ML can revolutionize the development cycle from decades to a few years. We outline the necessary characteristics of such ML implementations. Instead of enumerating various ML algorithms, we discuss scientific questions about the electrochemical systems to which ML can contribute.

Wang Y., Liu F., Fan G., Qiu X., Liu J., Yan Z., Zhang K., Cheng F., Chen J.

Engineering a stable solid electrolyte interphase (SEI) is one of the critical maneuvers in improving the performance of a lithium anode for high-energy-density rechargeable lithium batteries. Herein, we build a fluorinated lithium/sodium hybrid interphase via a facile electroless electrolyte-soaking approach to stabilize the repeated plating/stripping of lithium metal. Jointed experimental and computational characterizations reveal that the fluorinated hybrid SEI mainly consisting of NaF, LiF, LixPOyFz, and organic components features a mosaic polycrystalline structure with enriched grain boundaries and superior interfacial properties toward Li. This LiF/NaF hybrid SEI exhibits improved ionic conductivity and mechanical strength in comparison to the SEI without NaF. Remarkably, the fluorinated hybrid SEI enables an extended dendrite-free cycling of metallic Li over 1300 h at a high areal capacity of 10 mAh cm-2 in symmetrical cells. Furthermore, full cells based on the LiFePO4 cathode and hybrid SEI-protected Li anode sustain long-term stability and good capacity retention (96.70% after 200 cycles) at 0.5 C. This work could provide a new avenue for designing robust multifunctional SEI to upgrade the metallic lithium anode.

Wang H., Kim S.C., Rojas T., Zhu Y., Li Y., Ma L., Xu K., Ngo A.T., Cui Y.

Temperature coefficients (TCs) for either electrochemical cell voltages or potentials of individual electrodes have been widely utilized to study the thermal safety and cathode/anode phase changes of lithium (Li)-ion batteries. However, the fundamental significance of single electrode potential TCs is little known. In this work, we discover that the Li-ion desolvation process during Li deposition/intercalation is accompanied by considerable entropy change, which significantly contributes to the measured Li/Li+ electrode potential TCs. To explore this phenomenon, we compare the Li/Li+ electrode potential TCs in a series of electrolyte formulations, where the interaction between Li-ion and solvent molecules occurs at varying strength as a function of both solvent and anion species as well as salt concentrations. As a result, we establish correlations between electrode potential TCs and Li-ion solvation structures and further verify them by ab initio molecular dynamics simulations. We show that measurements of Li/Li+ electrode potential TCs provide valuable knowledge regarding the Li-ion solvation environments and could serve as a screening tool when designing future electrolytes for Li-ion/Li metal batteries.

Liu Y., Xu X., Sadd M., Kapitanova O.O., Krivchenko V.A., Ban J., Wang J., Jiao X., Song Z., Song J., Xiong S., Matic A.

Due to an ultrahigh theoretical specific capacity of 3860 mAh g-1, lithium (Li) is regarded as the ultimate anode for high-energy-density batteries. However, the practical application of Li metal anode is hindered by safety concerns and low Coulombic efficiency both of which are resulted fromunavoidable dendrite growth during electrodeposition. This study focuses on a critical parameter for electrodeposition, the exchange current density, which has attracted only little attention in research on Li metal batteries. A phase-field model is presented to show the effect of exchange current density on electrodeposition behavior of Li. The results show that a uniform distribution of cathodic current density, hence uniform electrodeposition, on electrode is obtained with lower exchange current density. Furthermore, it is demonstrated that lower exchange current density contributes to form a larger critical radius of nucleation in the initial electrocrystallization that results in a dense deposition of Li, which is a foundation for improved Coulombic efficiency and dendrite-free morphology. The findings not only pave the way to practical rechargeable Li metal batteries but can also be translated to the design of stable metal anodes, e.g., for sodium (Na), magnesium (Mg), and zinc (Zn) batteries.

Clarance Mary L.

The mathematical model for mass transfer with reversible homogeneous reactions is discussed. Estimation of mass transfer to and from electrodes for this reaction needs the analytical solution of nonlinear reaction-diffusion equations. Taylor's series method and hyperbolic function method are used to solve the system of nonlinear reaction-diffusion equations. Approximate closed-form of analytical expression of the concentration of substrate, reactant and product are derived for all values parameters. The empirical results are compared with the simulation results, and there is noticeable agreement. The effect of various parameter on aqueous carbonate-species concentration are also discussed. The current density and homogeneous equilibrium constant are also obtained.

Hagopian A., Doublet M., Filhol J.

The whiskers/dendrites-growth phenomenon observed on metal anode-surfaces in batteries is shown to have a thermodynamic origin taking its root from negative surface tensions associated with a symmetry breaking of the crystal shape.

Wang Q., Zhang G., Li Y., Hong Z., Wang D., Shi S.

Rechargeable batteries have a profound impact on our daily life so that it is urgent to capture the physical and chemical fundamentals affecting the operation and lifetime. The phase-field method is a powerful computational approach to describe and predict the evolution of mesoscale microstructures, which can help to understand the dynamic behavior of the material systems. In this review, we briefly introduce the theoretical framework of the phase-field model and its application in electrochemical systems, summarize the existing phase-field simulations in rechargeable batteries, and provide improvement, development, and problems to be considered of the future phase-field simulation in rechargeable batteries.

Gao S., Sun F., Liu N., Yang H., Cao P.

Lithium (Li) metal has been considered as the ultimate anode material for next-generation rechargeable batteries due to its ultra-high theoretical specific capacity (3860 mAh g −1 ) and the lowest reduction voltage (−3.04 V vs the standard hydrogen electrode). However, the dendritic Li formation, uncontrolled interfacial reactions, and huge volume variations lead to unstable solid electrolyte interphase (SEI) layer, low Coulombic efficiency and hence short cycling lifetime. Designing artificial solid electrolyte interphase (artificial SEI) films on the Li metal electrode exhibits great potential to solve the aforementioned problems and enable Li–metal batteries with prolonged lifetime. Polymer materials with good ionic conductivity, superior processability and high flexibility are considered as ideal artificial SEI film materials. In this review, according to the ionic conductive groups, recent advances in polymeric artificial SEI films are summarized to afford a deep understanding of Li ion plating/stripping behavior and present design principles of high-performance artificial SEI films in achieving stable Li metal electrodes. Perspectives regarding to the future research directions of polymeric artificial SEI films for Li–metal electrode are also discussed. The insights and design principles of polymeric artificial SEI films gained in the current review will be definitely useful in achieving the Li–metal batteries with improved energy density, high safety and long cycling lifetime toward next-generation energy storage devices.

Xu X., Liu Y., Hwang J., Kapitanova O.O., Song Z., Sun Y., Matic A., Xiong S.

Ye S., Wang L., Liu F., Shi P., Wang H., Wu X., Yu Y.

Ni W., Lu J., Yang Y., Chen W., Fu Y., Yuan Z., Han Y., Wang J.

Zhang H., Liu D., Xu K., Meng Y.S.

AbstractRechargeable aqueous batteries based on metallic anodes hold tremendous potential of high energy density enabled by the combination of relatively low working potential and large capacity while retaining the intrinsic safety nature and economical value of aqueous systems; However, the realization of these promised advantages relies on the identification of an ideal metal anode chemistry with all these merits. In this review, the emerging Sn metal anode chemistry is examined as such an anode candidate in both acidic and alkaline media, where the inertness of Sn toward hydrogen evolution, flat low voltage profile, and low polarization make it a unique metal anode for aqueous batteries. From a panoramic viewpoint, the key challenges and detrimental issues of Sn metal batteries are discussed, including dead Sn formation, self‐discharge, and electrolyte degradation, as well as strategies for mitigating these issues by constructing robust Sn anodes. New design approaches for more durable and reliable Sn metal batteries are also discussed, with the aim of fully realizing the potential of Sn anode chemistry.

Bu Y., Huang S., Zhu J., Cui Z., Gao M., Wang W., Zou R.

Synergistic interaction of spatially self-reconfiguring bilayer lithium–magnesium and lithium–zinc alloys through covered graphene oxide improves the performance of lithium metal anodes.

Li S., Zhong Y., Huang J., Lai G., Li L., Jiang L., Xu X., Lu B., Liu Y., Zhou J.

By regulating interfacial kinetics, TG4/H2O co-solvent electrolyte promotes dense, dendrite-free Zn electrodeposition, reduces H2O-derived side reactions, and enhances cathode stability, enabling high reversibility and durability for Ah-level ZIBs.

Yang S., Zhao Y., Zhi C.

Aqueous zinc-based batteries (ZIBs), characterized by their low cost, inherent safety, and environmental sustainability, represent a promising alternative for energy storage solutions in sustainable systems. Significant advancements have been made in developing high-performance cathode materials for aqueous ZIBs, which exhibit enhanced lifespan and energy density. However, challenges associated with zinc anodes, such as dendrite formation and side reactions, impede the practical application of ZIBs. This manuscript discusses the role of electrolyte additives in the Zn electrodeposition process and comprehensively describes strategies to enhance the anode stability through additive incorporation. It specifically focuses on the underlying mechanisms that regulate the solvation structure and the electrical double layer. Finally, the manuscript concludes with future perspectives on advancing Zn anode technology, aiming to provide guidelines for developing more robust Zn-based energy storage systems.

Gao L.T., Jiang B., Ma Q., Guo Z.

Wu Q., Zhang J., Yang S., Luo F., Yan Z., Liu X., Xie H., Huang J., Chen Y.

AbstractThe main bottleneck of rechargeable aqueous zinc batteries (AZBs) is their limited cycle lifespans stemming from the unhealthy electrolyte bulk and fragile interface, especially in the absence of dynamic protection mechanism between them. To overcome this limitation, benefitting from their synergistic physical and chemical properties, chitin nanocrystals (ChNCs) are employed as superior colloid electrolyte to bridge electrolyte bulk and interfacial chemistry for ultra‐long lifespan AZBs. This unique strategy not only enables continuous optimization of the electrolyte bulk and interfacial chemistry within the battery but also facilitates self‐repairing of mechanical damage both internally and externally, thereby achieving comprehensive, persistent, and dynamic protection. As a result, the modified zinc (Zn) cells present high Zn plating/stripping coulombic efficiencies of 97.71 % ~99.81 % from 5 to 100 mA cm−2, and remarkably service lifespan up to 8,200 h (more than 11 months). Additionally, the Zn//MnO2 full cell exhibits a high capacity retention of 70.1 % after 3,000 cycles at 5 A g−1. This dynamic protective strategy to challenge aqueous Zn chemistry may open up a new avenue for building better AZBs and beyond.

Wu Q., Zhang J., Yang S., Luo F., Yan Z., Liu X., Xie H., Huang J., Chen Y.

AbstractThe main bottleneck of rechargeable aqueous zinc batteries (AZBs) is their limited cycle lifespans stemming from the unhealthy electrolyte bulk and fragile interface, especially in the absence of dynamic protection mechanism between them. To overcome this limitation, benefitting from their synergistic physical and chemical properties, chitin nanocrystals (ChNCs) are employed as superior colloid electrolyte to bridge electrolyte bulk and interfacial chemistry for ultra‐long lifespan AZBs. This unique strategy not only enables continuous optimization of the electrolyte bulk and interfacial chemistry within the battery but also facilitates self‐repairing of mechanical damage both internally and externally, thereby achieving comprehensive, persistent, and dynamic protection. As a result, the modified zinc (Zn) cells present high Zn plating/stripping coulombic efficiencies of 97.71 % ~99.81 % from 5 to 100 mA cm−2, and remarkably service lifespan up to 8,200 h (more than 11 months). Additionally, the Zn//MnO2 full cell exhibits a high capacity retention of 70.1 % after 3,000 cycles at 5 A g−1. This dynamic protective strategy to challenge aqueous Zn chemistry may open up a new avenue for building better AZBs and beyond.

Mushtaq F., Xiang Y., Fahim M., Xie X., Zhao H., Daoud W.A.

Wang X., Wen Y., Wang Y., Chen Y., Yang L., Guo C., Nie H., Zhou X., Xie X.

Wang S., Liu C., Zhao M., Song R., Lu Y., Gou L., Gong F., Fan X., Li D.

Hao Z., Li G., Zheng C., Liu X., Wu S., Li H., Zhang K., Yan Z., Chen J.

AbstractThe continuous electrolyte decomposition and uncontrolled dendrite growth caused by the unstable solid electrolyte interphase (SEI) have largely hindered the development of Li metal batteries. Here, we demonstrate that tuning the facet of current collector can regulate the composition of SEI and the subsequent Li deposition behavior using single‐crystal Cu foils as an ideal platform. The theoretical and experimental studies reveal that the (100) facet of Cu possesses strong adsorption to anions, guiding more anions to participate preferentially in the inner Helmholtz plane and further promoting the formation of the stable inorganic‐rich SEI. Consequently, the single‐crystal Cu foils with a single [100] orientation (s‐Cu(100)) achieve the dendrite‐free Li deposition with enhanced Li plating/stripping reversibility. Moreover, the Li anode deposited on s‐Cu(100) can stabilize the operation of an Ah‐level pouch cell (350 Wh kg−1) with a low negative/positive capacity ratio (~2) and lean electrolyte (2.4 g Ah−1) for 150 cycles. Impressively, this strategy demonstrates universality in a series of electrolytes employed different anions. This work provides new insights into the correlation between the SEI and current collector, opening a universal avenue towards high‐performance Li metal batteries.

Hao Z., Li G., Zheng C., Liu X., Wu S., Li H., Zhang K., Yan Z., Chen J.

AbstractThe continuous electrolyte decomposition and uncontrolled dendrite growth caused by the unstable solid electrolyte interphase (SEI) have largely hindered the development of Li metal batteries. Here, we demonstrate that tuning the facet of current collector can regulate the composition of SEI and the subsequent Li deposition behavior using single‐crystal Cu foils as an ideal platform. The theoretical and experimental studies reveal that the (100) facet of Cu possesses strong adsorption to anions, guiding more anions to participate preferentially in the inner Helmholtz plane and further promoting the formation of the stable inorganic‐rich SEI. Consequently, the single‐crystal Cu foils with a single [100] orientation (s‐Cu(100)) achieve the dendrite‐free Li deposition with enhanced Li plating/stripping reversibility. Moreover, the Li anode deposited on s‐Cu(100) can stabilize the operation of an Ah‐level pouch cell (350 Wh kg−1) with a low negative/positive capacity ratio (~2) and lean electrolyte (2.4 g Ah−1) for 150 cycles. Impressively, this strategy demonstrates universality in a series of electrolytes employed different anions. This work provides new insights into the correlation between the SEI and current collector, opening a universal avenue towards high‐performance Li metal batteries.

Ahmed R.A., Carballo K.V., Koirala K.P., Zhao Q., Gao P., Kim J., Anderson C.S., Meng X., Wang C., Zhang J., Xu W.

The high energy density advantage of lithium (Li) metal batteries (LMBs) makes them increasingly desirable; however, problems such as strong reactivity and dendrite growth of Li metal anode limit their practical uses. In this work, a novel Li‐containing glycerol (LiGL) or lithicone protection layer on a 50 μm thick Li metal anode is employed for improving the performance of LMBs. This LiGL layer was accurately deposited via a molecular layer deposition (MLD) process at 150 °C, using lithium tert‐butoxide and glycerol as precursors. The as‐formed LiGL coating layer is highly tunable in its thickness by simply adjusting MLD cycles and shows a good stability and outstanding ionic transport properties. The LiGL layer is found to effectively mitigate side reactions and enhance cycling stability in both symmetric cells and full cells. Specifically, the LMBs with LiGL@Li anode of 400 MLD cycles and LiNi0.6Mn0.2Co0.2O2 cathode enable a capacity retention of ≈87%, much higher than ≈35% of the cells with bare Li after 200 cycles at a charge/discharge current density of 2.1 mA cm−2. This work paves a feasible way for practical LMBs with improved capacity and stability through applying an innovative protection layer on Li metal anodes.

Chen Y., Yu Z., Gong H., Zhang W., Rudnicki P.E., Huang Z., Yu W., Kim S.C., Boyle D.T., Sayavong P., Celik H., Xu R., Lin Y., Wang S., Qin J., et. al.