Silicon (Si) is one of the most promising anode materials for high-energy lithium-ion batteries. However, the widespread application of Si-based anodes is inhibited by large volume change, unstable solid electrolyte interphase, and poor electrical conductivity. During the past decade, significant efforts have been made to overcome these major challenges toward industrial applications. This review summarizes the recent development of microscale Si-based electrodes fabricated by Si microparticles or other industrial bulk materials from the perspective of industrialization. First, the challenges for microscale Si anodes are clarified. Second, structural design strategies of stable micro-sized Si materials are discussed. Third, other critical practical metrics, such as robust binder construction and electrolyte design, are also highlighted. Finally, future trends and perspectives on the commercialization of Si-based anodes are provided. KEYWORDSsilicon, micro-sized particles, lithium-ion batteries, porous structures, polymer binder, electrolyte design Figure 1 Overview of Si-based anodes for LIBs: (a) merits and (b) fundamental challenges. Reproduced with permission from Ref. [16], © Wiley-VCH GmbH 2021.
efforts have been made to design unique Si nanostructures or construct elaborate SEIs to address the reversibility issues of Si-based anodes. [4] Despite these advances, ensuring the safe operation of Si anodes is still challenging, which impedes commercialization. In addition, the uncontrolled breakdown of the SEI will accelerate capacity fading, resulting in safety hazards, especially under harsh conditions. [5] As a low-cost alternative, low-grade microsized Si particles promise practical industrial-scale applications, but they may be more prone to failure. [6] Therefore, exploring the comprehensive thermochemical/electrochemical/mechanical behaviors of microsized Si anodes is essential for guiding the design strategies for safe, high-energy LIBs.In general, the thermal runaway process in LIBs includes three main stages: the pre-stage, heat accumulation stage, and thermal runaway stage. [7] Reversible heat (Q r ), polarization heat (Q p ), and side reaction heat (Q s ) are generated as a result of a series of reversible and irreversible electrochemical/chemical reactions. [8] Owing to the positive feedback loop from the heat-temperature-reaction, heat generated in the cells will increase the temperature and accelerate the exothermic reactions. Furthermore, the intrinsic nature of the SEI has shown to be closely related to cell performance (e.g., reversible capacity, rate capability, low/high-temperature performance, self-discharging, and safety). [9] The initial breakdown of the SEI occurs at the onset temperature of the self-heating stage, which usually depends on the SEI component/structure, and causes the cell to continue heating up. [1c] Regulating SEI formation on the anode surface has proven to be effective in postponing or preventing the thermal failure of batteries. [10] Nevertheless, microsized Si particles pose a much more significant challenge owing to the high mechanical stress during cycling. An investigation into the interplay between SEI and the thermal safety of microsized Si anodes is still lacking, especially one that combines thermal runaway analysis.In this work, we demonstrate reversibly cycled, thermally stable microsized Si anodes boosted by the construction of a robust SEI, where a moderate-concentration ionic-liquid (IL) electrolyte of lithium bis(fluorosulfonyl)amide (LiFSI, 2 m) in N-butyl-N-methyl pyrrolidinium bis(fluorosulfonyl)imide (Pyr 14 FSI) is utilized. The synergistic effects of SEI on the Battery safety is vital to the application of lithium-ion batteries (LIBs), especially for high energy density cells applied in electric vehicles. As an anode material with high theoretical capacity and natural abundance, Si has received extensive attention for LIBs. However, it suffers from severe electrode pulverization during cycling due to large volume changes and an unstable solid electrolyte interphase (SEI), resulting in accelerated capacity fading and even safety hazards. Therefore, safe and long-term cycling of Si-based anodes, especially under high-temperature cycling, is...
Incidents in the use of lithium-ion batteries are usually caused by the malfunction of flammable organic liquid electrolytes with poor thermal stability. Therefore, the development of noncombustible electrolytes is regarded as one of the most effective means to prevent the safety hazards of lithium-ion batteries. Ionic liquids have attracted much interest recently, mainly due to their high ionic conductivity, low volatility, and incombustibility. The application of ionic liquids to the preparation of quasi-solid-state gel electrolytes combines the advantages of ionic liquids and avoids the risks of organic liquid electrolytes. Therefore, the solid-state ionogels have been considered as a promising alternative electrolyte system, especially for the much-desired energy storage devices with higher energy density and flexibility. This review focuses on the recent progress of ionogel electrolytes for lithium-ion batteries. The preparation strategies for ionogel electrolytes based on different frameworks, namely inorganic matrix, organic matrix, and organicinorganic hybrid matrix, are discussed. Subsequently, efforts to improve the properties of the ionogel electrolytes, including the ionic conductivity, mechanical properties, and lithium-ion transfer number, are summarized. Besides, the applications of ionogel electrolytes in high-voltage lithiumion batteries and lithium metal batteries as well as the batteries under extreme environments are outlined. Finally, the perspectives on studying and improving the performances of ionogel electrolytes for advanced lithium-ion batteries are provided.
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