Carbonized Polymer Dots with Controllable N,O Functional Groups as Electrolyte Additives to Achieve Stable Li Metal Batteries

Electrolyte additive is an effective strategy to inhibit the uncontrolled growth of Li dendrites for lithium metal batteries (LMBs). However, most of the additives are complex synthesis and prone to decompose in cycling. Herein, in order to guide the homogeneous deposition of Li⁺, carbonized polymer dots (CPDs) as electrolyte additives are successfully designed and synthesized by microwave (M-CPDs) and hydrothermal (H-CPDs) approaches. The controllable functional groups containing N or O (especially pyridinic-N, pyrrolic-N, and carboxyl group) enable CPDs to keep stable in electrolytes for at least 3 months. Meanwhile, the clusters formed between CPDs and Li⁺ through electrostatic interaction effectively guide the uniform Li dispersion and limit the “tip effect” and dendrite formation. Moreover, as lithiophilic groups increase, the strong electrostatic interference for the solvation effect of Li⁺ in the electrolyte is formed, which induces faster Li⁺ diffusion/transfer. As expected, H-CPDs achieve the ultra-even Li⁺ transfer. The corresponding Li//LiFePO₄ full cell delivers a high capacity retention rate of 93.8% after 200 cycles, which is much higher than that of the cells without additives (61.2%) and with M-CPDs (83.7%) as additives. The strategy in this work provides a theoretical direction for CPDs as electrolyte additives used in energy storage devices.     

A Novel Approach to Open “Dead Space” and Modify Interfacial Features of Carbon Nanotube Assemblies by a Microwave Shock

Despite 30-year development of carbon nanotube (CNT) based materials, harnessing the outstanding nanoscale properties of individual CNT for macroscale applications remains challenging. High specific surface area, a crucial feature of CNTs, often suffers from the formation of tightly packed bundles with inaccessible “dead space”. Herein, a novel “microwave shock” approach to open the “dead space” trapped within bundles is reported. Employing N₂ ambient during microwave irradiation, CNT bundles undergo an efficient structural alteration and interfacial modification simultaneously due to the strong radiative coupling, while the graphitic structure remains undamaged. In this way, a 15-fold increase (from 42 to 648 m² g⁻¹) in the interstitial surface area as well as the lithiophilic functionalization (≈1 atom% nitrogen doping) are achieved without the degradation of other properties. Furthermore, to highlight the merits of this microwave shock process, the treated CNT films are applied as a host material for the anode in a lithium metal battery and demonstrate the suppression of dendritic lithium growth and improve cycling stability. This microwave shock approach provides an efficient avenue to modify nanocarbon-based materials for further applications.     

Dendrite-Free Lithium Metal Battery Enabled by Dendritic Mesoporous Silica Coated Separator

Concentration polarization-induced lithium dendrites seriously impede the practical application of high-energy-density lithium metal batteries. Porous materials that aim to inhibit lithium dendrites are extensively explored. However, their effects are still limited by the intrinsic features of the pores, especially channel geometry and surface properties. Herein, a separator modification strategy of blocking “dendritic deposition” via “dendritic channels” is proposed. A porous shield-like film is formed on the polypropylene separator through the close packing of ultra-small (≈100 nm) silica nanospheres with unique dendritic mesopores (DMS). Besides the hierarchical pores homogenizing the ion flux, the DMS film also provides abundant Si(OH)_x groups, preferentially adsorbing the TFSI⁻ in the electrolyte and accelerating the transport of Li⁺. Most notably, the dendritic mesochannels with high complexity can diversify the growth directions of lithium and contribute to a more substantial homogenizing process of Li⁺. Consequently, a dendrite-free deposition with 1000 stable cycles in Li|Li symmetric cells even at 10 mA cm⁻² is achieved. This study provides a scalable approach for the fabrication of mesoporous separators and offers a fresh perspective on the future design of advanced separators utilized for dendrite suppression.     

Multiscale Structural Gel Polymer Electrolytes with Fast Li+ Transport for Long-Life Li Metal Batteries

Li metal batteries (LMBs) are considered as promising candidates for future rechargeable batteries with high energy density. However, Li metal anode (LMA) is extensively sensitive to general liquid electrolytes, leading to unstable interphase and dendrites growth. Herein, a novel gel polymer electrolyte consisting of a micro-nanostructured poly(vinylidene fluoride-co-hexafluoropropylene) matrix and inorganic fillers of Zeolite Socony Mobil-5 (ZSM-5) and SiO₂ nanoparticles, is fabricated to expedite Li⁺ ions transport and suppress Li dendrite growth. Due to the Lewis acid interaction, SiO₂ can absorb amounts of PF₆⁻ and promote the dissociation of LiPF₆. The specific sub-nanometer pore structure of ZSM-5 greatly enhances the Li⁺ ion transference number. These structures can restrain the decomposition of electrolytes and build stable interphase on LMA. Therefore, the Li||Ni_0.8Co_0.1Mn_0.1O₂ full cell maintains 92% capacity retention after 300 cycles at 1 C (1 C ≈190 mAh g⁻¹) in carbonate electrolyte. This multiscale design provides an effective strategy for electrolyte exploration in high-performance LMBs.     

Integration Plasma Strategy Controlled Interfacial Chemistry Regulation Enabling Planar Lithium Growth in Solid-State Lithium Metal Batteries

Solid-state lithium metal batteries (SSLMBs) are identified as a highly promising candidate for next-generation energy storage devices, yet they still face uncontrollable dendritic lithium (Li) growth originating from interfacial incompatibility. To address this issue, an “integration plasma (IP)” strategy for interlayer construction is proposed that integrates metal reduction and vapor deposition functions, featuring the ability to give a manipulable and quantifiable chemical regulation for controlling the surface concentration (C_surface) and the atomic ratio of the introduced metal element and electronegative element (AR_E/M) on solid-state electrolyte (SSE). This IP-formed interlayer can in situ react with Li anode to synchronously produce metal-Li alloy, Li salt and amorphous carbon, thus offering an “integrated function” to promote a spherical and hexagonal Li growth, preventing the dendrite propagation from SSE. When C_surface of metal elements and corresponding AR_E/M is regulated as ≈1.13 nmol cm^-2 and ≈2.6, the IP-modified SSE prolongs the lifespan of SSLMBs with LiNi_0.8Co_0.1Mn_0.1O₂ cathode to over 1000 cycles with a low-capacity attenuation of 0.03% per cycle, highlighting the multiply functions of IP to accelerate the practical application of SSLMBs.     

Amino-Functionalized Interfacial Layer Enables an Ultra-Uniform Amorphous Solid Electrolyte Interphase for High-Performance Aqueous Zinc-Based Batteries

Aqueous rechargeable zinc-based batteries (ZBBs) are emerging as desirable energy storage systems because of their high capacity, low cost, and inherent safety. However, the further application of ZBBs still faces many challenges, such as the issues of uncontrolled dendrite growth and severe parasitic reactions occurring at the Zn anode. Herein, an amino-grafted bacterial cellulose (NBC) film is prepared as artificial solid electrolyte interphase (SEI) for the Zn metal anodes, which can significantly reduce zinc nucleation overpotential and lead to the dendrite-free deposition of Zn metal along the (002) crystal plane more easily without any external stimulus. More importantly, the chelation between the modified amino groups and zinc ions can promote the formation of an ultra-even amorphous SEI upon cycling, reducing the activity of hydrate ions, and inhibiting the water-induced side reactions. As a result, the Zn||Zn symmetric cell with NBC film exhibits lower overpotential and higher cyclic stability. When coupled with the V₂O₅ cathode, the practical pouch cell achieves superior electrochemical performance over 1000 cycles.     

Unraveling the Solvation Structure and Electrolyte Interface through Carbonyl Chemistry for Durable and Dendrite-Free Zn Anode

Aqueous Zn ion batteries are appealing systems owing to their safety, low cost, and environmental friendliness; however, their practical applicability is impeded by the growth of Zn dendrites and side reactions. Herein, a dual-functional electrolyte additive, namely acetylacetone (AT) is utilized for the simultaneous regulation of the solventized structure and anode–electrolyte interface (AEI) to achieve a durable, dendrite-free Zn anode. Theoretical calculations and experimental characterizations reveal that the AT molecule can be adsorbed onto Zn metal surface to reconstruct the AEI and allow for the primordial desolvation of [Zn(H₂O)₆]²⁺ at locations away from the surface of the Zn anode during deposition, which is attributed to the strong polarity of the carbonyl functional group. In addition, the two carbonyls of AT can replace two H₂O molecules in the primary solventized structure of Zn²⁺ to reduce the number of active H₂O molecules, efficiently suppressing Zn dendrite growth and detrimental reactions. As a proof of concept, a Zn//Cu cell is constructed in ZnSO₄ containing 3 vol.% AT electrolyte, delivering stable cycling over 1800 cycles while maintaining a high Coulombic efficiency of 99.74%. This study provides a practical approach for inhibiting dendrite growth and side reactions by harnessing carbonyl chemistry.     

A Forceful “Dendrite-Killer” of Polyoxomolybdate with Reusability Effectively Dominating Dendrite‑Free Lithium Metal Anode

In this work, a series of Mo-containing polyoxometalates (POMs) modified separators to inhibit the growth of lithium dendrites, and thus improving the lifespan and safety of the cells is proposed. When the deposited lithium forms dendrites and touches the separator, the optimized Dawson-type POM of (NH₄)₆[P₂Mo₁₈O₆₂]·11H₂O (P₂Mo₁₈) with the stronger oxidizability, acts like a “killer”, is more inclined to oxidize Li⁰ into Li⁺, thus weakening the lethality of lithium dendrites. The above process is accompanied by the formation of Li_x[P₂Mo₁₈O₆₂] (x = 6–10) in its reduced state. Converting to the stripping process, the reduced state Li_x[P₂Mo₁₈O₆₂] (x = 6–10) can be reoxidized to P₂Mo₁₈, which achieves the reusability of P₂Mo₁₈ functional material. Meanwhile, lithium ions are released into the cell system to participate in the subsequent electrochemical cycles, thus the undesired lithium dendrites are converted into usable lithium ions to prevent the generation of “dead lithium”. As a result, the Li//Li symmetrical cell with P₂Mo₁₈ modified separator delivers exceptional cyclic stability for over 1000 h at 3 mA cm⁻² and 5 mAh cm⁻², and the assembled Li–S full cell maintains superior reversible capacity of 600 mAh g⁻¹ after 200 cycles at 2 C.     

The Inducement and “Rejuvenation” of Li Dendrites by Space Confinement and Positive Fe/Co-Sites

The high reactivity of Li metal and the inhomogeneous Li deposition leads to the formation of Li dendrites and “dead” Li, which impedes the performance of Li metal batteries (LMBs) with high energy density. The regulating and guiding the Li dendrite nucleation is a desirable tactic to realize concentrated distribution of Li dendrites instead of completely inhibiting dendrite formation. Here, a Fe-Co-based Prussian blue analog with hollow and open framework (H-PBA) is employed to modify the commercial polypropylene separator (PP@H-PBA). This functional PP@H-PBA can guide the lithium dendrite growth to form uniform lithium deposition and activate the inactive Li. In details, the H-PBA with macroporous structure and open framework can induce the growth of lithium dendrites via space confinement, while the positive Fe/Co-sites lowered by polar cyanide (−CN) of PBA can reactivate the inactive Li. Thus, the Li|PP@H-PBA|Li symmetric cells exhibit long-term stability at 1 mA cm⁻² for 1 mAh cm⁻² over 500 h. And the Li-S batteries with PP@H-PBA deliver favorable cycling performance at 500 mA g⁻¹ for 200 cycles.     

Recent research progress of alloy-containing lithium anodes in lithium-metal batteries

Lithium metal is regarded as one of the most ideal anode materials for next-generation batteries, due to its high theoretical capacity of 3860 mAh g⁻¹ and low redox potential (−3.04 V vs standard hydrogen electrode). However, practical applications of lithium anodes are impeded by the uncontrollable growth of lithium dendrite and continuous reactions between lithium and electrolyte during cycling processes. According to reports for decades, artificial solid electrolyte interface (SEI), electrolyte additives, and construction of three-dimensional (3D) structures are demonstrated essential strategies. Among numerous approaches, metals that can alloy with lithium have been employed to homogenize lithium deposition and accelerate Li ion transportation, which attract more and more attention. This review aims to summarize the lithium alloying applied in lithium anodes including the fabricating approaches of alloy-containing lithium anodes, and the action mechanism and challenges of fabricated lithium anodes. Based on summarizing the literature, shortcomings and challenges as well as the prospects are also analyzed, to impel further research of lithium anodes and lithium-based batteries.