Interfacial stability is one of the crucial factors for long-term cyclability of lithium (Li) metal batteries (LMBs). While cross-contamination phenomena have been well-studied in Li-ion batteries (LIBs), similar phenomena have rarely been reported in LMBs. Here, we investigated cathode failure triggered by chemical crossover from the anode in LMBs. In contrast to LIBs, the cathode in LMBs suffers more significant capacity fading, and its capacity cannot be fully recovered by replacing the Li anode. In-depth surface characterization reveals severe deterioration related to the accumulation of highly resistive polymeric components in the cathode–electrolyte interphase. The soluble byproducts generated by extensive electrolyte decomposition at the Li metal surface can diffuse toward the cathode side, resulting in severe deterioration of the cathode and separator surfaces. A selective Li-ion permeable separator with a polydopamine coating has been developed to mitigate the detrimental chemical crossover and enhance the cathode stability.

the energy density of LIBs because Si has ten times higher theoretical capacity (3579 mAh g −1 ) comparing with those of conventional graphite (372 mAh g −1 ). [9][10][11] However, large-scale applications of Si anodes still face several significant challenges, including pulverization of Si particles, continuous growth of a solid electrolyte interface (SEI) layer during the charge/discharge processes, and large swelling of the Si-based anode. [12,13] Without successfully overcoming those challenges, Si can be used only as a limited additive in graphite-based anodes to incrementally increase the energy density of LIBs.Several approaches have been developed in recent years to address those challenges. [14][15][16][17] In this regard, Si nanocomposites stabilized by heterogeneous elements has been used as one of most effective approaches to accommodate large volume changes and prevent side reactions between the electrolyte and Si. [15,16,[18][19][20] Moreover, practical issues associated with the use of nanoengineered Si anodes [21] (e.g., high surface area, low density, and high interparticle resistance) have been addressed by building the nanostructure in a local scale within micrometersized particles. [14,[22][23][24] Representative design of nanostructured Si includes the pomegranate-inspired Si/C anode [23] and Si nanolayer embedded graphite. [24] These nanostructure materials form micrometer (µm) size particles that can be used in practical applications and that are compatible with conventional battery manufacturing process. However, as the primary particle size decreases to nanometer-scale, it is increasingly difficult to assemble nanostructured Si into micrometer-sized material. [25][26][27][28] In this work, we demonstrate a facile method for preparing a Si/C composite containing micrometer-sized nanoporous Si (denoted Np-Si) that is protected by pitch-derived carbon (denoted PC). The resulting PC/Np-Si not only successfully retains its single nanometer-sized Si primary particle without sintering in micrometer-scale, but also exhibits favorable powder properties for conventional battery manufacturing process such as narrow particle size distribution, high density, strong mechanical strength, and small surface area. It also exhibits low swelling upon lithiation at both particle-and Porous silicon (Si)/carbon nanocomposites have been extensively explored as a promising anode material for high-energy lithium (Li)-ion batteries (LIBs). However, shrinking of the pores and sintering of Si in the nanoporous structure during fabrication often diminishes the full benefits of nanoporous Si. Herein, a scalable method is reported to preserve the porous Si nano structure by impregnating petroleum pitch inside of porous Si before high-temperature treatment. The resulting micrometer-sized Si/C composite maintains a desired porosity to accommodate large volume change and high conductivity to facilitate charge transfer. It also forms a stable surface coating that limits the penetration of electrolyte into nanoporous Si and ...

No abstract

Although Li–O2 batteries are promising next‐generation energy storage systems with superior theoretical capacities, they have a serious limitation regarding the large overpotential upon charging that results from the low conductivity of the discharge product. Thus, various redox mediators (RMs) have been widely studied to reduce the overpotential in the charging process, which should promote the oxidation of Li2O2. However, RMs degrade the Li metal anode through a parasitic reaction between the RM and the Li metal, and a solution for this phenomenon is necessary. In this study, an effective method is proposed to prevent the migration of the RM toward the anode side of the lithium using a separator that is modified with a negatively charged polymer. When DMPZ (5,10‐dihydro‐5,10‐dimethylphenazine) is used as an RM, it is found that the modified separator suppresses the migration of DMPZ toward the counter electrode of the Li metal anode. This is investigated by a visual redox couple diffusion test, a morphological investigation, and an X‐ray diffraction study. This advanced separator effectively maximizes the catalytic activity of the redox mediator. Li–O2 batteries using both a highly concentrated DMPZ and the modified separator exhibit improved performance and maintained 90% round‐trip efficiency up to the 20th cycle.