A cooperative biphasic MoOx–MoPx promoter enables a fast-charging lithium-ion battery

The realisation of fast-charging lithium-ion batteries with long cycle lifetimes is hindered by the uncontrollable plating of metallic Li on the graphite anode during high-rate charging. Here we report that surface engineering of graphite with a cooperative biphasic MoOx–MoPx promoter improves the charging rate and suppresses Li plating without compromising energy density. We design and synthesise MoOx–MoPx/graphite via controllable and scalable surface engineering, i.e., the deposition of a MoOx nanolayer on the graphite surface, followed by vapour-induced partial phase transformation of MoOx to MoPx. A variety of analytical studies combined with thermodynamic calculations demonstrate that MoOx effectively mitigates the formation of resistive films on the graphite surface, while MoPx hosts Li+ at relatively high potentials via a fast intercalation reaction and plays a dominant role in lowering the Li+ adsorption energy. The MoOx–MoPx/graphite anode exhibits a fast-charging capability (<10 min charging for 80% of the capacity) and stable cycling performance without any signs of Li plating over 300 cycles when coupled with a LiNi0.6Co0.2Mn0.2O2 cathode. Thus, the developed approach paves the way to the design of advanced anode materials for fast-charging Li-ion batteries. © 2021, The Author(s).1

Computational design of a mixed A-site cation halide solid electrolyte for all-solid-state lithium batteries

All-solid-state Li-ion batteries (ASSBs) are considered as ideal next-generation energy storage devices owing to their safe operation and high energy densities. Recently, halide-based solid electrolytes (SEs) have come under the spotlight because of their wide electrochemical stability windows and high ionic conductivities. However, their usage as coating materials for cathodes is limited. To examine the wide electrochemical stability window of SEs for lithium-metal anodes and their interfacial stability with high-voltage cathodes, a systematic first-principles investigation of A-site cation and anion exchange in Li3MX6 (M: Lu, Sc, Bi, In, Y, Tm, Dy, Ho, Er, Tm, Sm, Tb; X: Br, Cl, and I) was conducted. The systematic analysis showed that the electrochemical behavior of chloride SEs can be modulated by mixing M3+ cations. Furthermore, the replacement of M3+ by Zr4+ and the anionic blending of Br with Cl, which exhibits a relatively high ionic conductivity, was also computed for comparison with the A-site cation-mixed halide electrolyte. Our computational work provides an overview of the evolution of lithium halide SEs in high-voltage ASSBs

Defect mediated lithium adsorption on graphene-based silicon composite electrode for high capacity and high stability lithium-ion battery

Carbon-coated silicon materials are considered as promising anode materials in high-capacity lithium-ion batteries (LIBs). Theoretically, using graphene as the anode material in the LIB would afford high electrical conductivity, mechanical stability of Si, and suppression of the unstable solid–electrolyte interface. However, its usage is hindered by its electrochemical characteristic, which is not electrochemically active when combined with lithium. Therefore, research on graphene as the anode and coated material in LIBs has been conducted using defect engineering to enhance the storage capacity of graphene. Although the electrochemical characteristics of various defects in graphene have been studied experimentally and theoretically, graphene-based composite anode materials such as graphene–silicon composite electrodes have rarely been studied from the electrochemical and mechanical perspectives. In this study, lithium adsorptions are conducted on various defected graphene and graphene–silicon composites using density functional theory calculation. The formation energies of Li on the various defected graphene are assessed, and the mechanical strengths of the graphene–silicon composites are analyzed. Our calculations validate that the defects in graphene enhance the electrochemical adsorptions and interfacial mechanical strengths of the graphene and graphene–silicon composites. During lithiation, the defects mediate greater interfacial adhesion of the silicon–graphene composite. Hence, we elucidate that defected graphene increases the electro-chemo mechanical stabilities of silicon composites in high-capacity LIBs

Liquid electrolyte-free cathode for long-cycle life lithium–oxygen batteries

Ether-based organic liquid electrolytes (OLEs) have been commonly used in lithium–oxygen batteries (LOBs); however, they become unstable and cause rapid performance degradation during LOB operation. To address these problems, in this study we propose an OLE-free cathode architecture based on a Li+-selective solid membrane (LSSM). An LSSM with a seamless duplex (dense/porous) architecture is prepared by a tape casting process combined with co-sintering, and carbon nanotubes (CNTs) decorated with Au nanoparticles (CNT@Au) are directly formed on its porous framework. We show that the duplex-LSSM can effectively protect the metallic Li anode from parasitic reactions with impurity species and improve the cycling stability of Li. Furthermore, an LOB assembled with the duplex-LSSM and CNT@Au components exhibits a discharge capacity as high as 3650 mAh g−1 and improved cycling stability (>140 cycles) compared to a conventional OLE-based LOB; this can be explained in terms of the combined advantages provided by the OLE-free cathode and the LSSM-protected Li anode. © 2021 Elsevier B.V.1

High-performance bifunctional electrocatalyst for iron-chromium redox flow batteries

Despite a variety of advantages over the presently dominant vanadium redox flow batteries, the commercialization of iron-chromium redox flow batteries (ICRFBs) is hindered by sluggish Cr2+/Cr3+ redox reactions and vulnerability to the hydrogen evolution reaction (HER). To address these issues, here, we report a promising electrocatalyst comprising Ketjenblack (KB) carbon with embedded bismuth nanoparticles (Bi-C). The uniform incorporation of Bi nanoparticles into KB carbon via a simple reduction process excellently promotes the electrochemical activity of Cr2+/Cr3+ redox reactions while retarding the HER. A combination of experimental analysis and density functional theory (DFT) calculations indicates that these phenomena are attributable to the synergistic effect of Bi and KB, which inhibits hydrogen evolution and provides active sites to enhance the Cr2+/ Cr3+ redox reaction, respectively. An ICRFB cell containing the Bi-C catalyst as the negative electrode exhibits a high energy efficiency of 86.54% with excellent capacity retention during charge-discharge cycling at room temperature. This study offers an intelligent hybrid material as a useful design principle for electrocatalysts capable of addressing the critical problems in ICRFBs.

Tailoring grain boundary structures and chemistry of Li7La3Zr2O12 solid electrolytes for enhanced air stability

Solid-state batteries with inorganic solid electrolytes provide a fundamental solution for resolving safety concerns. Garnet-type Li7La3Zr2O12 (LLZO) is considered a promising candidate for solid electrolytes because of its high Li+ conductivity and superior chemical/electrochemical stability against metallic Li. However, when exposed to ambient air, LLZO electrolytes react with H2O and CO2 to form Li2CO3, resulting in significant degradation of Li+ conductivity. In this study, we propose a simple but effective approach to enhance air stability of LLZO via tailoring grain boundary structures and chemistry. The interfacial stability of the solid electrolytes is examined under accelerated durability test (ADT) conditions, where the concentrations of O2, H2O, and CO2 are precisely controlled to promote interfacial reactions. We show that Ga incorporation into Ta-doped LLZO (LLZTO) plays a crucial role in governing the grain growth behavior during the sintering process to modify the density, morphology, and composition of the grain boundaries. Furthermore, Ga-incorporated LLZTO (Ga-LLZTO) exhibits remarkably improved stability over LLZTO upon ADTs with high H2O and CO2 concentrations and enables stable cycling of metallic Li electrodes. The combined microstructural/compositional analyses and theoretical simulations suggest that the enhanced air stability of Ga-LLZTO can be attributed to the remarkably reduced grain boundary density with enlarged grains and segregation of H2O/CO2-tolerant lithium gallate (LiGaO2) in the grain boundaries. The findings of this study are critical for understanding the role of microstructural engineering in mitigating the degradation of Li+ conductivity and developing highly conductive and stable LLZO electrolytes. © 2022 Elsevier B.V.FALS

Ionic conductivity and mechanical properties of the solid electrolyte interphase in lithium metal batteries

With the fullness of time, metallic lithium (Li) as an anode could become highly promising for high-energy-density batteries. Theoretically, using Li metal as the negative electrode can result in higher theoretical capacity and lower oxidation voltage and density than in current commercially available batteries. During the charge/discharge process, however, metallic Li shows unavoidable drawbacks, such as dendritic growth, causing capacity degradation and a solid electrolyte interphase (SEI) layer derived from the side reactions between the Li metal anode and the electrolyte, resulting in depletion of the electrolyte. The formation of a suitable SEI is crucial to avoid the side reactions at the interface by circumventing direct contact. Unavoidable dendritic growth at the Li metal anode can be controlled by its ionic conductivity. Furthermore, the SEI is also required as a mechanical reinforcement for withstanding the volume change and suppressing dendritic growth in the Li metal anode. A limiting factor due to complex SEI formation must be considered from the perspectives of chemical and mechanical properties. To further enhance the cycling performance of Li metal batteries, an in-depth understanding of the SEI needs to be achieved to clarify these issues. In this mini review, we focus on the SEI, which consists of various deposited components, and discuss its ionic conductivity and mechanical strength for applications in electric vehicles