Bottom-Up Magnesium Deposition Induced by Paper-Based Triple-Gradient Scaffolds toward Flexible Magnesium Metal Batteries

An integrated dual-gradient host facilitates oriented bottom-up lithium growth in lithium metal anodes

Integrated gradient hosts, composed of poorly conductive frameworks on copper current collectors, have been extensively explored for the development of Li metal anodes (LMAs). Despite their potential, high Li nucleation overpotentials and slow interface kinetics often lead to inferior performance. Herein, we combine electrospinning and electrodeposition to create an integrated gradient host, namely OPAN/rGO-Cu2O/Cu. This involves electrodeposition of graphene oxide onto copper foil, reacting in situ to form a lithiophilic rGO-Cu2O layer, which is then covered with an oxidized polyacrylonitrile (OPAN) nanofiber layer, establishing conductivity and lithiophilicity dual gradients. The insulating OPAN top layer blocks electron transmission to the surface and prevents Li deposition, while the lithiophilic rGO-Cu2O layer facilitates Li ion transport to the bottom and reduces the nucleation barrier, both of which promote uniform Li deposition from bottom to top. As a result, the battery achieves an average coulombic efficiency of 98.4% over 500 cycles at 1 mA cm-2, and the symmetric cell sustains an ultra-long cycle life of 1600 h with a minimal polarization voltage of 12 mV. When paired with a LiFePO4 cathode, the full cell demonstrates a capacity retention of 92.6% after 300 cycles at 1 C, with an average capacity decay rate of just 0.025% per cycle. This innovative approach offers a promising pathway for developing high-performance LMAs.

Enhancing Reversibility and Stability of Mg Metal Anodes: High-Exposure (002) Facets and Nanosheet Arrays for Superior Mg Plating/Stripping

Magnesium metal batteries (MMBs), recognized as promising contenders for post-lithium battery technologies, face challenges such as uneven magnesium (Mg) plating and stripping behaviors, leading to uncontrollable dendrite growth and irreversible structural damage. Herein, we have developed a Mg foil featuring prominently exposed (002) facets and an architecture of nanosheet arrays (termed (002)-Mg), created through a one-step acid etching method. Specifically, the prominent exposure of Mg (002) facets, known for their inherently low surface and adsorption energies with Mg atoms, not only facilitates smooth nucleation and dense deposition but also significantly mitigates side reactions on the Mg anode. Moreover, the nanosheet arrays on the surface evenly distribute the electric field and Mg ion flux, enhancing Mg ion transfer kinetics. As a result, the fabricated (002)-Mg electrodes exhibit unprecedented long-cycle performance, lasting over 6000 h (>8 months) at a current density of 3 mA cm-2 for a capacity of 3 mAh cm-2. Furthermore, the corresponding pouch cells equipped with various electrolytes and cathodes demonstrate remarkable capacity and cycling stability, highlighting the superior electrochemical compatibility of the (002)-Mg electrode. This study provides new insights into the advancement of durable MMBs by modifying the crystal structure and morphology of Mg.

Enhancing Interfacial Lithiophilicity and Stability with PVDF/In(NO3)3 Composite Separators for Durable Lithium Metal Anodes

Separator modification is a promising method for advancing lithium metal anodes; however, achieving homogeneous lithium-ion flux and uniform plating/stripping processes remains challenging. In this work, we introduce a novel approach by developing a composite separator, termed PVDF-INO, which integrates In(NO3)3 (INO) into polyvinylidene fluoride (PVDF) to create a 12 μm thick layer. This addition significantly enhances the interaction between the separator and the electrolyte, creating a lithophilic matrix that ensures an even distribution of lithium ions. This uniform ion distribution promotes consistent lithium deposition and dissolution, resulting in a durable, dendrite-free lithium metal anode. Moreover, the PVDF-INO separator not only enhances the affinity with electrolytes but also maintains stable lithium-ion flux, which is essential for reliable and safe battery operation. Consequently, it sustains operation over 750 h in a Li||Li symmetric battery configuration, with a low overpotential of just 28 mV. Additionally, full cells equipped with LiFePO4 cathodes and the PVDF-INO separator exhibit superior cycling performance, maintaining a capacity retention of 92.9% after 800 cycles at 1 C. This work paves the way for significant advancements in the field of lithium metal batteries, offering a promising solution to longstanding energy storage challenges.

Sustainable release of LiNO3 in carbonate electrolytes for stable lithium metal anodes

LiNO3 is recognized as an effective additive, forming a dense, nitrogen-rich solid electrolyte interphase (SEI) on lithium's surface, which safeguards it from parasitic reactions. However, its use is limited due to the poor solubility in carbonate electrolytes. Herein, we introduce a bilayer separator designed to release LiNO3 sustainably. This continual release not only alters the chemistry of the SEI but also replenishes the additives that are depleted during battery cycling, thereby enhancing the durability of the modified interphase. This strategy effectively curtails Li dendrite formation, significantly enhancing the longevity of Li|LiFePO4 batteries, evidenced by an impressive 85% capacity retention after 800 cycles. This research offers a compelling remedy to the longstanding challenge of incorporating LiNO3 in carbonate electrolytes.

Stabilizing Lithium-Metal Host Anodes by Covalently Binding MgF2 Nanodots to Honeycomb Carbon Nanofibers

Constructing lithiophilic carbon hosts has been regarded as an effective strategy for inhibiting Li dendrite formation and mitigating the volume expansion of Li metal anodes. However, the limitation of lithiophilic carbon hosts by conventional surface decoration methods over long-term cycling hinders their practical application. In this work, a robust host composed of ultrafine MgF2 nanodots covalently bonded to honeycomb carbon nanofibers (MgF2/HCNFs) is created through an in situ solid-state reaction. The composite exhibits ultralight weight, excellent lithiophilicity, and structural stability, contributing to a significantly enhanced energy efficiency and lifespan of the battery. Specifically, the strong covalent bond not only prevents MgF2 nanodots from migrating and aggregating but also enhances the binding energy between Mg and Li during the molten Li infusion process. This allows for the effective and stable regulation of repeated Li plating/stripping. As a result, the MgF2/HCNF-Li electrode delivers a high Coulombic efficiency of 97% after 200 cycles, cycling stably for more than 2000 h. Furthermore, the full cells with a LiFePO4 cathode achieve a capacity retention of 85% after 500 cycles at 0.5C. This work provides a strategy to guide dendrite-free Li deposition patterns toward the development of high-performance Li metal batteries.