Jie Lu,Shu Zhang,Jianhua Yao,Ziyang Guo,Markus Osenberg,André Hilger,Henning Markötter,Fabian Wilde,Ingo Manke,Xiao Zhang,Fu Sun,Guanglei Cui
Rechargeable alkali metal–CO2 batteries, which combine high theoretical energy density and environmentally friendly CO2 fixation ability, have attracted worldwide attention. Unfortunately, their electrochemical performances are usually inferior for practical applications. Aiming to reveal the underlying causes, a combinatorial usage of advanced nondestructive and postmortem characterization tools is used to intensively study the failure mechanisms of Li/Na–CO2 batteries. It is found that a porous interphase layer is formed between the separator and the Li/Na anode during the overvoltage rising and battery performance decaying process. A series of control experiments are designed to identify the underlying mechanisms dictating the observed morphological evolution of Li/Na anodes, and it is found that the CO2 synergist facilitates Li/Na chemical corrosion, the process of which is further promoted by the unwanted galvanic corrosion and the electrochemical cycling conditions. A detailed compositional analysis reveals that the as-formed interphase layers under different conditions are similar in species, with the main differences being their inconsistent quantity. Theoretical calculation results not only suggest an inherent intermolecular affinity between the CO2 and the electrolyte solvent but also provide the most thermodynamically favored CO2 reaction pathways. Based on these results, important implications for the further development of rechargeable alkali metal–CO2 batteries are discussed. The current discoveries not only fundamentally enrich our knowledge of the failure mechanisms of rechargeable alkali metal–CO2 batteries but also provide mechanistic directions for protecting metal anodes to build high-reversible alkali metal–CO2 batteries.
Rechargeable sodium-oxygen (Na–O2) battery is deemed as a promising high-energy storage device due to the abundant sodium resources and high theoretical energy density (1,108 Wh kg–1). A series of quasisolid electrolytes are constantly being designed to restrain the dendrites growth, the volatile and leaking risks of liquid electrolytes due to the open system of Na–O2 batteries. However, the ticklish problem about low operating current density for quasisolid electrolytes still hasn’t been conquered. Herein, we report a rechargeable Na–O2 battery with polyvinylidene fluoride-hexafluoropropylene recombination Nafion (PVDF–HFP@Nafion) based quasisolid polymer electrolyte (QPE) and MXene-based Na anode with gradient sodiophilic structure (M-GSS/Na). QPE displays good flame resistance, locking liquid and hydrophobic properties. The introduction of Nafion can lead to a high Na+ migration number (tNa+ = 0.68) by blocking the motion of anion and promote the formation of NaF-rich solid electrolyte interphase, resulting in excellent cycling stability at relatively high current density under quasisolid environment. In the meantime, the M-GSS/Na anode exhibits excellent dendrite inhibition ability and cycling stability. Therefore, with the synergistic effect of QPE and M-GSS/Na, constructed Na–O2 batteries run more stably and exhibit a low potential gap (0.166 V) after an initial 80 cycles at 1,000 mA g–1 and 1,000 mAh g–1. This work provides the reference basis for building quasisolid state Na–O2 batteries with long-term cycling stability.
Direct metal anodes are plating/stripping processes without a supporting framework and bulk ion conductivity; they are the electrodes susceptible to collapse and limiting the electrochemical reaction to the two-dimensional surface. The focus of this era is mostly on building a solid electrolyte interface (SEI). However, simply building protective layers cannot address essential issues; a thorough transformation of the metal electrode bulk is critical. We propose a reconstructed sodium metal anode (RSMA) by implanting an activatable ion-conductive network to the bulk. NaPF 6 will be activated with an electrolyte to conduct ions and form an anion-derived SEI. Conductive polymers become the supporting skeleton; thus, the RSMA has a metal-bulk storage matrix and an expanded three-dimensional plating/stripping mechanism and permits the homogeneous deposition/dissolution of Na + in high dimensions. Last, RSMA symmetric cells were stably cycled for 2700 hours and achieved a 100% depth of discharge. RSMA||PB cells can achieve 10-coulomb cycling and a proof-of-concept pouch cell energy density of 367 watt-hours per kilogram.
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