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.

The lithium-ion battery is the currently leading energy storage technology for these applications, but will face severe challenges in meeting the increasing energy density demand as the implementation of new chemistries based on high energy density cathodes [2] will require new anode materials in order to overcome the limited energy density of graphite with a low specific capacity of 372 mAh g −1. [3] Lithium metal has an ultra-high theoretical specific capacity (3860 mAh g −1), and the lowest reduction potential (−3.04 V vs standard hydrogen electrode) and is thus considered as a "holy grail" for anode materials for high energy-density battery systems. [2,4] However, the practical application of Li metal batteries (LMBs) has been held back by a low Coulombic efficiency and safety concerns related to use of Limetal anodes. [4a, 5] In general, the problematic issues of Li-metal anodes can be attributed to two main factors, the preferred electrodeposition resulting in a mossy/dendritic morphology and the high reactivity of Li metal toward common liquid electrolytes generating a solid electrolyte interphase (SEI). [6] The mossy/dendritic morphology of Li inevitably results in a structural collapse of the electrode with The application of lithium metal as an anode material for next generation high energy-density batteries has to overcome the major bottleneck that is the seemingly unavoidable growth of Li dendrites caused by non-uniform electrodeposition on the electrode surface. This problem must be addressed by clarifying the detailed mechanism. In this work the mass-transfer of Li-ions is investigated, a key process controlling the electrochemical reaction. By a phase field modeling approach, the Li-ion concentration and the electric fields are visualized to reveal the role of three key experimental parameters, operating temperature, Li-salt concentration in electrolyte, and applied current density, on the microstructure of deposited Li. It is shown that a rapid depletion of Li-ions on electrode surface, induced by, e.g., low operating temperature, diluted electrolyte and a high applied current density, is the underlying driving force for non-uniform electrodeposition of Li. Thus, a viable route to realize a dendrite-free Li plating process would be to mitigate the depletion of Li-ions on the electrode surface. The methodology and results in this work may boost the practical applicability of Li anodes in Li metal batteries and other battery systems using metal anodes.

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.

Porous anodic aluminium oxide has a long history of practical application for corrosion protection and coloring. In the last few decades a lot of hi-tech applications of this material have been found owing to the discovery of anodization conditions leading to the formation of highly ordered porous structures with a narrow pore size distribution. Here we show that in-plane orientation of the porous system in anodic films on aluminium is fully determined by the intrinsic crystallographic orientation of the Al substrate. The anisotropy of aluminium oxidation rates on a scalloped metal-oxide interface leads to reorientation of Al spikes in certain directions, which builds up an in-plane orientational order on a macroscopic scale restricted by a crystallite size. This is a unique example of the inheritance of the substrate crystal structure by an amorphous film through a size difference of three orders of magnitude.

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vehicles, consumer electronics, and smart grid. [1] The pathway for gaining these targets is to build new battery chemistry by exploration of high-capacity anode and cathode materials as well as nonflammable electrolytes. [2,3] Metallic anodes, represented by lithium (Li), were the promising anode materials owing to their high theoretical capacity and it is, for instance, as high as 3860 mAh g −1 for Li-metal anodes. [4,5] Nevertheless, the non-uniform electrodeposition of Li metal during the charging process invariably leads to low Coulombic efficiency and growth of Li dendrites, hindering its commercialization in rechargeable batteries. [6][7][8] Utilization of solid electrolytes with high shear modulus was known as the most promising approach to suppress the formation of Li dendrites and to guarantee high safety of the battery at the same time. [9] Despite the significant advances aiming for high ionic conductivity of solid electrolytes, operation of solid-state batteries under the practical industry conditions, particularly for high-power systems, is not achieved yet. [10] A cell failure induced by the propagation of Li filaments (or Li dendrites) through solid electrolytes will be triggered once the applied current density is over a certain value which is defined as critical current density. [11] The growth of Li filaments leads to the failure of physical contact at interface, mechanical degradation of solid electrolyte, and even the short circuit of cell when the filaments connect the anode with cathode. [12] These failure processes have been reported for various solid electrolytes, including garnet Li 7 La 3 Zr 2 O 12 (LLZO), [13] amorphous 70Li 2 S-30P 2 S 5 glass, [14] argyrodite (Li 6 PS 5 Cl), [15] and sodium superionic conductor type (NASICON, such as Li 1+x Al x Ge 2−x (PO 4 ) 3 ). [16] Capturing the formation and the propagation of Li filaments in solid electrolyte to understand the failure mechanism of solid-state batteries is a great challenge since the microstructure evolution of interest is buried inside the solid electrolyte. [10] State of the art characterization techniques including operando synchrotron X-ray tomographic microscopy, [17] in situ transmission electron microscopy, [18] and operando neutron depth profiling [13] have been employed to track the internal evolution of solid electrolyte in real time by the combination of electrochemical methodologies. It is found that origin of Li filaments Growth of lithium (Li) filaments within solid electrolytes, leading to mechanical degradation of the electrolyte and even short circuit of the cell under high current density, is a great barrier to commercialization of solid-state Li-metal batteries. Understanding of this electro-chemo-mechanical phenomenon is hindered by the challenge of tracking local fields inside the solid electrolyte. Here, a multiphysics simulation aiming to investigate evolution of the mechanical failure of the solid electrolyte induced by the internal growth of Li is reported. Visualization of local stress, damage, and cra...

Lithium metal is considered to be a promising anode material for high‐energy‐density rechargeable batteries because of its high theoretical capacity and low reduction potential. Nevertheless, the practical application of Li anodes is challenged by poor cyclic performance and potential safety hazards, which are attributed to non‐uniform electrodeposition of Li metal during charging. Herein, diffusion limited current density (DLCD), one of the critical fundamental parameters that govern the electrochemical reaction process, is investigated as the threshold of current density for electrodeposition of Li. The visualization of the concentration field and distribution of Faradic current density reveal how uniform electrodeposition of Li metal anodes can be obtained when the applied current density is below the DLCD of the related electrochemical system. Moreover, the electrodeposition of Li metal within broken solid electrolyte interphases preferentially occurs at the crack spots that are caused by the non‐uniform electrodeposition of Li metal. This post‐electrodeposition leads to more consumption of active Li when the applied current density is greater than the DLCD. Therefore, lowering the applied current density or increasing the DLCD are proposed as directions for developing advanced strategies to realize uniform electrodeposition of Li metal and stable interfaces, aiming to accelerate the practical application of state‐of‐the‐art Li metal batteries.

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