Recent Progress of Advanced Functional Separators in Lithium Metal Batteries.

As a representative in the post-lithium-ion batteries (LIBs) landscape, lithium metal batteries (LMBs) exhibit high-energy densities but suffer from low coulombic efficiencies and short cycling lifetimes due to dendrite formation and complex side reactions. Separator modification holds the most promise in overcoming these challenges because it utilizes the original elements of LMBs. In this review, separators designed to address critical issues in LMBs that are fatal to their destiny according to the target electrodes are focused on. On the lithium anode side, functional separators reduce dendrite propagation with a conductive lithiophilic layer and a uniform Li-ion channel or form a stable solid electrolyte interphase layer through the continuous release of active agents. The classification of functional separators solving the degradation stemming from the cathodes, which has often been overlooked, is summarized. Structural deterioration and the resulting leakage from cathode materials are suppressed by acidic impurity scavenging, transition metal ion capture, and polysulfide shuttle effect inhibition from functional separators. Furthermore, flame-retardant separators for preventing LMB safety issues and multifunctional separators are discussed. Further expansion of functional separators can be effectively utilized in other types of batteries, indicating that intensive and extensive research on functional separators is expected to continue in LIBs.

Delamination-Free Multifunctional Separator for Long-Term Stability of Lithium-Ion Batteries.

Next-generation lithium-ion batteries (LIBs) that satisfy the requirements for an electric vehicle energy source should demonstrate high reliability and safety for long-term high-energy-density operation. This inevitably calls for a novel approach to advance major components such as the separator. Herein, a separator is designed and fabricated via application of multilayer functional coating on both sides of a polyethylene separator. The multilayer-coated separator (MCS) has a porous structure that does not interfere with lithium ion diffusion and exhibits superior heat resistance, high electrolyte uptake, and persistent adhesion with the electrode. More importantly, it enables high capacity retention and reduced impedance build up during cycling when used in a coin or pouch cell. These imply its promising application in energy sources requiring long-term stability. Fabrication of the MCS without the use of organic solvents is not only environmentally beneficial but also effective at cost reduction. This approach paves the way for the separator, which has long been considered an inactive major component of LIBs, to become an active contributor to the energy density toward achieving longer cycle stability.

Strategy to Simultaneously Manipulate Direct Zn Nucleation and Hydrogen Evolution via Surface Modifier Hydrolysis for High-Performance Zn-Ion Batteries.

The demand for safer batteries is growing rapidly due to fire incidents in electronic devices that use Li-ion batteries. Zn-ion batteries are among the most promising candidates to replace Li-ion batteries because they use a water-based electrolyte and are not explosive. However, Zn-ion batteries suffer from persistent corrosion and dendritic crystal formation during the charge-discharge process, which decrease their reversibility and hinder their commercial usage. Extensive research has been conducted to address these issues, but there are significant limitations due to high process and time costs. In this study, the modulation of the Zn-electrolyte interface to overcome these challenges is attempted using acetamide-derived thioacetamide (TAA), a surface modifier used in electroplating. TAA undergoes hydrolysis in an aqueous solution and produces weakly acidic byproducts and sulfide ions. These species are adsorbed onto the Zn metal surface, which induces uniform Zn2+ deposition, facilitates the formation of a stable interfacial layer, and inhibits side reactions due to the reduced water activity. Consequently, the symmetric cell with TAA achieves a low polarization of 50 mV and stable cycling for 700 h at 1 mA cm-2. Additionally, a Zn|V6O13 full cell exhibits electrochemical reversibility, maintaining a capacity retention of 64% over 300 cycles. Therefore, this study offers useful insights into the development of a simple manufacturing process to ensure the competitiveness of Zn-ion batteries for practical applications using functional electrolyte additives.

Microwave-solvothermal synthesis of various polymorphs of nanostructured TiO2 in different alcohol media and their lithium ion storage properties.

The various polymorphs (anatase, rutile, and brookite) of TiO(2) with different nanomorphologies have been synthesized by a facile microwave-assisted solvothermal process without surfactants, employing TiCl(4) or TiCl(3) as precursors in various alcohol (ethanol, propanol, butanol, and octanol) media. The samples have been characterized by X-ray diffraction (XRD), electron microscopy, and Brunauer-Emmett-Teller (BET) surface area analysis. The Ti/Cl ion concentration, reaction pH, and size of the alcohol molecule are found to control the morphology, crystal structure, and crystallite size of the TiO(2) particles. Among the various TiO(2) polymorphs synthesized, the rutile TiO(2) spheres built up of nanorods that were synthesized with TiCl(4) in octanol have an average pore size and surface area of, respectively, 5 nm and 404 m(2)/g and exhibit the best electrochemical performance with a capacity of >200 mAh/g after 100 cycles and high rate capability. The excellent electrochemical properties originate from the nanorod-building morphology and mesoporosity of TiO(2) spheres that provide good electrical contact, accommodates the strain smoothly, and facilitates facile lithium-ion diffusion.

Designing a Bimodal BaTiO3 Artificial Layer to Boost the Dielectric Effect toward Highly Reversible Dendrite-Free Zn Metal Anodes.

With the growing interest in suppressing greenhouse gas emissions from fossil fuel combustion, the implementation of electrical energy storage devices for efficiently utilizing renewable energy is expanding worldwide. Zn-ion batteries are attractive for energy storage because of their safety, eco-friendliness, high energy density, and low cost. However, their commercialization is hindered by the poor rechargeability of the zinc anode because of Zn dendrite growth and hydrogen evolution. Herein, we present the application of an artificial layer composed of bimodal BaTiO3 particles on Zn metal to boost the dielectric properties and thus enhance the reversibility of Zn anodes during long-term cycling. The BaTiO3 layer induces electric polarization under external electric fields, causing the Zn ions to move sequentially toward the Zn anode. Moreover, its mechanical characteristics alleviate the volume changes between the BaTiO3 layer and Zn metal. Consequently, Zn dendrite growth is effectively inhibited, and the electrochemical performance is significantly improved in Zn|Zn symmetric cells, resulting in a low overvoltage (39 mV) and stable cycling (800 h) at 1 mA cm-2. Moreover, the Zn-ion full cell using an α-MnO2 cathode exhibits consistent capacity retention up to 380 cycles. This study demonstrates a new strategy to economically and readily suppress dendrite formation by using bimodal dielectric particles as artificial layers to stabilize metal-based batteries.

P-Doped SiOx /Si/SiOx Sandwich Anode for Li-Ion Batteries to Achieve High Initial Coulombic Efficiency and Low Capacity Decay.

Initial reversibility and excellent capacity retention are the key requirements for the success of high-capacity electrode materials in high-performance Li-ion batteries and pose a number of challenges to development. Silicon has been regarded as a promising anode material because of its outstanding theoretical capacity. However, it suffers from colossal volume change and continuous formation of unstable solid electrolyte interphases during lithiation/delithiation processes, which eventually result in low initial Coulombic efficiency (ICE) and severe capacity decay. To circumvent these challenges, a new sandwich Si anode (SiOx /Si/SiOx ) free from prelithiation is designed and fabricated using a combination of P-doping and SiOx layers. This new anode exhibits high conductivity and specific capacity compared to other Si thin-film electrodes. Cells with SiOx /Si/SiOx anodes deliver the highest presently known ICE value among Si thin-film anodes of 90.4% with a charge capacity of 3534 mA h g-1 . In addition, the SiOx layer has sufficient mechanical stability to accommodate the large volume change of the intervening Si layer during charge-discharge cycling, exhibiting high potential for practical applications of Si thin-film anodes.

Si Nanoparticles Coated with Co-Containing N-Doped Carbon: Preparation and Characterization as Li-Ion Battery Anode Materials.

Si nanoparticles uniformly coated with Co-containing N-doped carbon were investigated as an anode material for Li-ion batteries. The Si nanoparticle surfaces were modified with conductive and matrix, N-doped carbon and cobalt element and prepared by a simple pyrolysis process using an ionic liquid that contained nitrogen with metal complex. After a simple annealing process, the N-doped carbon containing cobalt element was uniformly coated onto the Si nanoparticles. The smooth carbon layer connected the Si nanoparticles without any morphological changes. Si nanoparticles containing 34 wt% N-doped carbon and cobalt element exhibited a stable electrochemical performance with a capacity of ~1133 mAh g-1 and excellent capacity retention over 60 cycles. The high electrochemical performances was attributed to the synergistic effect by presence cobalt in N-doped carbon matrix, which alleviated the lithium-silicon alloying reaction-induced volume expansion and enhanced electrical conductivity during cycling.

Doped lanthanum nickelates with a layered perovskite structure as bifunctional cathode catalysts for rechargeable metal-air batteries.

Rechargeable metal-air batteries have attracted a great interest in recent years because of their high energy density. The critical challenges facing these technologies include the sluggish kinetics of the oxygen reduction-evolution reactions on a cathode (air electrode). Here, we report doped lanthanum nickelates (La2NiO4) with a layered perovskite structure that serve as efficient bifunctional electrocatalysts for oxygen reduction and evolution in an aqueous alkaline electrolyte. Rechargeable lithium-air and zinc-air batteries assembled with these catalysts exhibit remarkably reduced discharge-charge voltage gaps (improved round-trip efficiency) as well as high stability during cycling.

Carbon-free cobalt oxide cathodes with tunable nanoarchitectures for rechargeable lithium-oxygen batteries.

Carbon-free cobalt oxide cathodes for lithium-oxygen batteries are fabricated via an electrodeposition-conversion process. The Co3O4-only cathodes show a remarkably reduced voltage gap (by ca. 550 mV compared to the carbon-only cathode) as well as excellent long-term cyclability.

Promoting Li2O2 oxidation by an La(1.7)Ca(0.3)Ni(0.75)Cu(0.25)O4 layered perovskite in lithium-oxygen batteries.

We demonstrate for the first time that La(1.7)Ca(0.3)Ni(0.75)Cu(0.25)O(4) with a layered perovskite structure promotes electrochemical oxidation of Li(2)O(2) in lithium-oxygen batteries with a non-aqueous aprotic electrolyte.