Most next-generation Li ion battery chemistries require a functioning lithium metal (Li) anode. However, its application in secondary batteries has been inhibited because of uncontrollable dendrite growth during cycling. Mechanical suppression of dendrite growth through solid polymer electrolytes (SPEs) or through robust separators has shown the most potential for alleviating this problem. Studies of the mechanical behavior of Li at any length scale and temperature are limited because of its extreme reactivity, which renders sample preparation, transfer, microstructure characterization, and mechanical testing extremely challenging. We conduct nanomechanical experiments in an in situ scanning electron microscope and show that micrometer-sized Li attains extremely high strengths of 105 MPa at room temperature and of 35 MPa at 90°C. We demonstrate that single-crystalline Li exhibits a power-law size effect at the micrometer and submicrometer length scales, with the strengthening exponent of −0.68 at room temperature and of −1.00 at 90°C. We also report the elastic and shear moduli as a function of crystallographic orientation gleaned from experiments and first-principles calculations, which show a high level of anisotropy up to the melting point, where the elastic and shear moduli vary by a factor of ∼4 between the stiffest and most compliant orientations. The emergence of such high strengths in small-scale Li and sensitivity of this metal's stiffness to crystallographic orientation help explain why the existing methods of dendrite suppression have been mainly unsuccessful and have significant implications for practical design of future-generation batteries.dendrite | size effect | elastic anisotropy | dislocation | elevated temperature I ncreased adoption of electric vehicles requires an improvement in the energy density of rechargeable Li ion batteries. Li metal anode is a common and necessary ingredient in commercialization pathways for next-generation Li ion batteries. In the near term, Li metal coupled with an advanced cathode could lead to a specific energy of 400 Wh/kg at the cell level, which represents 200% improvement over current state of the art (1). In the longer term, Li metal coupled with a S and O 2 cathode could lead to even higher specific energies of >500 Wh/kg. Despite over 40 y of research, overcoming the uncontrollable dendrite growth during cycling has remained an insurmountable obstacle for Li-based components (2). Among multiple attempted approaches to eliminate or even reduce the dendrite growth, mechanical suppression has emerged as one of the most promising routes. In their pioneering theoretical work, Monroe et al. (3) considered a solid polymer electrolyte (SPE) in contact with a Li metal electrode and performed a linear stability analysis of the deformation at the interface. They used linear elasticity to compute the stresses generated at the interface due to small deformations. They found that the dendrite growth decays with time if the shear modulus of the SPE is higher than about t...

Short-circuiting via dendrites compromises the reliability of Li-metal batteries. Dendrites ensue from instabilities inherent to electrodeposition that should be amenable to dynamic control. Here, we report that by charging a scaled coin-cell prototype with 1 ms pulses followed by 3 ms rest periods the average dendrite length is shortened ∼2.5 times relative to those grown under continuous charging. Monte Carlo simulations dealing with Li+ diffusion and electromigration reveal that experiments involving 20 ms pulses were ineffective because Li+ migration in the strong electric fields converging to dendrite tips generates extended depleted layers that cannot be replenished by diffusion during rest periods. Because the application of pulses much shorter than the characteristic time τc ∼ O(∼1 ms) for polarizing electric double layers in our system would approach DC charging, we suggest that dendrite propagation can be inhibited (albeit not suppressed) by pulse charging within appropriate frequency ranges.

We have investigated electrochemical treatment of real domestic wastewater coupled with simultaneous production of molecular H 2 as useful byproduct. The electrolysis cells employ multilayer semiconductor anodes with electroactive bismuth-doped TiO 2 functionalities and stainless steel cathodes. DC-powered laboratory-scale electrolysis experiments were performed under static anodic potentials (+2.2 or +3.0 V NHE) using domestic wastewater samples, with added chloride ion in variable concentrations. Greater than 95% reductions in chemical oxygen demand (COD) and ammonium ion were achieved within 6 h. In addition, we experimentally determined a decreasing overall reactivity of reactive chlorine species toward COD with an increasing chloride ion concentration under chlorine radicals (Cl•, Cl 2 − •) generation at +3.0 V NHE. The current efficiency for COD removal was 12% with the lowest specific energy consumption of 96 kWh kgCOD −1 at the cell voltage of near 4 V in 50 mM chloride. The current efficiency and energy efficiency for H 2 generation were calculated to range from 34 to 84% and 14 to 26%, respectively. The hydrogen comprised 35 to 60% by volume of evolved gases. The efficacy of our electrolysis cell was further demonstrated by a 20 L prototype reactor totally powered by a photovoltaic (PV) panel, which was shown to eliminate COD and total coliform bacteria in less than 4 h of treatment.

In principle, the electric potential field, , should be obtained by solving Gauss's law. However, since electroneutrality is a valid approximation throughout the electrolyte up to the thin depletion boundary, and ion-ion electrostatic interactions are screened out by counter ions because the Debye length under present conditions ( ) is = 0.27 smaller than the average interionic separation ( ), Gauss's equationapproximately reduces to Laplace's equation. Since temperature profile is also described by Laplace's equation, we define a generic parameter as follows:where and are coordinates parallel and normal to the cathode. Hence we have: