A Polar and Ordered-Channel Composite Separator Enables Antidendrite and Long-Cycle Lithium Metal Batteries

Dead Lithium in Lithium Metal Batteries: Formation, Characterization and Strategies

Lithium (Li) metal anode (LMA) replacing graphite anode for developing Li metal batteries (LMB) with the higher energy density has attracted much attention. However, LMA faces many issues, e. g., Li dendrites, dead Li and the side reactions, which causes the safety hazards and low coulomb efficiency (CE) of battery, therefore, LMB still cannot replace the current Li ion battery for practical use. Among those issues, dead Li is one of the decisive factors affecting the CE of LMB. To better understand dead Li, we summarize the recent work about the generation of dead Li, its impact on batteries performance, and the strategies to reuse and eliminate dead Li. Finally, the prospect of the future LMA and resultant LMB is also put forward.

Stabilized and Almost Dendrite-Free Li Metal Anodes by In Situ Construction of a Composite Protective Layer for Li Metal Batteries

Li metal anodes (LMAs) are promising candidates for the anodes of high-energy-density batteries due to their lower reduction potential and high specific capacity. Unfortunately, LMAs usually suffer from uncontrollable Li plating and insecure solid electrolyte interphase layers, especially when used in conjunction with carbonate-based electrolytes. Herein, we proposed using metal alkoxides of titanium butyrate to react with hydroxyl groups on Li metal. A composite protective layer containing TiO₂ and ROLi was generated to modify Li (designated as treated Li), leading to dendrite-free LMAs and achieving significantly enhanced cycling stability. Notably, symmetric cells using treated Li electrodes can deliver over 1500 h of stable cycling under a current density of 2 mA cm^-2 in an ether-based electrolyte. Moreover, under extreme conditions of 5 mA cm^-2 using a carbonate-based electrolyte, symmetric cells employing a treated Li electrode demonstrated stable cycling for over 80 h, as compared to the fluctuating voltage seen after only 10 h of cycling when using a bare Li electrode. Furthermore, full cells using a treated Li anode coupled with a high loading of LiCoO₂ cathode (≈15 mg cm^-2) displayed excellent cycling stability at 0.2 C over 150 cycles with a high capacity retention of 98.1% and an enhanced average Coulombic efficiency above 99.6%. By comparison, full cells using the bare Li anode drop to 125.4 mA h g^-1 with a capacity retention of just 83.3%. The treated Li exhibited superior rate performance and delivered 132.7 mA h g^-1 even at 5 C. This strategy provided a facile and effective option for the construction of advanced LMAs.

Expounding the Initial Alloying Behavior of Na-K Liquid Alloy Electrodes

Primary electrodeposition is an accepted strategy to elucidate the nucleation and growth kinetics of metal electrodes. Nevertheless, when confronted with the phase transition process caused by bi-active metals such as NaK liquid alloys, the research process becomes complex and elusive. Herein, we have reduced the intricate issues to relatively simple initial alloying behaviors. Two exchange diffusion mechanisms of the Na atom embedded in K crystals and K atom embedded in Na crystals are investigated by first-principles density functional theory (DFT) calculation and mechanical simulation. As a result, the process of embedding the Na atom in K crystals shows a better thermodynamic stability and lower activation barrier and structural stress than those of the other. The abovementioned conclusions are further proved by stepwise Na and K electrodeposition experiments, and the prepared NaK alloy electrode displays excellent electrochemical performance. Our findings correlate the original alloying mechanism model specification with electrodeposition experimental verification and provide strategies to achieve controllable NaK electrode construction.