Lei Zhong

Solid-state batteries have become a critical growth area for next-generation energy storage systems, driven by their inherent benefits of superior operational safety, exceptional theoretical energy density, and extended cycle life. This work provides a systematic overview of recent progress in solid-state battery research, organized around three core components: electrode materials, electrolytes, and interphase engineering. In terms of electrode design, commercially dominant cathode systems primarily include lithium iron phosphate (LiFePO4) and high-nickel nickel-cobalt-manganese (NCM) oxides, while anode development is heavily concentrated on lithium metal and carbon-based architectures. Each material class offers unique technical advantages but also suffers from intrinsic drawbacks, requiring tailored modification approaches to overcome their respective performance limitations. Electrolyte platforms are broadly categorized into three main families: polymer, oxide, and sulfide-based systems. For polymer electrolytes in particular, this review analyzes both free-standing electrolyte membranes and cathode-integrated coating layers, two configurations that exhibit distinct suitability for diverse application requirements. Interphase regulation represents the most significant barrier to the practical deployment of solid-state batteries. Longstanding challenges including poor solid-solid interfacial contact, elevated interfacial resistance, and undesired parasitic reactions severely degrade cell performance. These issues can be effectively alleviated through monolithic manufacturing techniques and targeted interphase modification strategies.

Over the past decades, biodegradable polymer films have gained significant attention owing to their environmental friendliness and abundant raw material availability. However, the barrier properties of biodegradable polymers as packaging materials remain inferior to those of traditional petroleum-based plastic films, limiting their suitability for applications sensitive to oxygen or moisture such as food preservation, pharmaceutical packaging, and electronic device protection. In this paper, we summarize effective strategies to enhance the barrier properties of biodegradable polymer packaging films, such as surface coating, polymer blending, multilayer compounding, copolymerization and modification, nanocomposite technology, and filler reinforcement. Subsequently, we discuss the application of these strategies to biodegradable polymers, including both natural and synthetic varieties. A central focus is elucidating the relationship between the modification approaches, molecular structure, and oxygen/water barrier properties in high-barrier biodegradable polymer materials, aiming to provide valuable guidance for the development of advanced biodegradable polymer packaging materials. Finally, we present the existing challenges and future prospects for the development of high-barrier biodegradable polymer packaging materials.

Polymer binders for the cathodes of lithium-ion batteries play a pivotal role in enhancing the battery energy density, cycle life and interfacial stability. Conventional polyvinylidene fluoride (PVDF) binders have difficulty meeting the multiple requirements of high specific energy electrodes due to their inherent drawbacks including electrical insulation, mechanical rigidity and interfacial inertness. In recent years, function-oriented binders have emerged as a research hotspot, which are endowed with properties such as electrical conductivity, mechanical adaptability, self-healing capability and high voltage tolerance via rational molecular structure design. This review systematically reviews the molecular design strategies of polymer-based cathode binders, including the introduction of polar groups (e.g., hydroxyl and carboxyl groups) to strengthen hydrogen bonding and electrostatic interactions, the construction of conjugated polymers or ion-conductive networks to improve electrical conductivity, and the utilization of dynamic chemical bonds to achieve self-healing function. In addition, high voltage-tolerant binders can significantly suppress capacity fading of high-voltage cathodes via chelating transition metal ions, optimizing electrode dispersibility and forming a stable interfacial layer. By integrating molecular dynamics simulations with experimental characterizations, the correlation between the molecular structure of binders and the electrochemical performance of electrodes is elucidated, which provides a theoretical framework for the design of next-generation high-performance binders.

High ionic conductivity, outstanding mechanical stability, and a wide electrochemical window are the keys to the application of solid-state lithium metal batteries (LMBs). Due to their regular channels for ion transport and tailored functional groups, covalent organic frameworks (COFs) have been applied to solid electrolytes to improve their performance. Herein, we report a flexible polyethylene oxide-COF-LZU1 (abbreviated as PEO-COF) electrolyte membrane with a high lithium ion transference number and satisfactory mechanical strength, allowing for dendrite-free and long-time cycling for LMBs. Benefiting from the interaction between bis(triflfluoromethanesulonyl)imide anions (TFSI⁻) and aldehyde groups in COF-LZU1, the Li⁺ transference number of the PEO-5% COF-LZU1 electrolyte reached up to 0.43, much higher than that of neat PEO electrolyte (0.18). Orderly channels are conducive to the homogenous Li-⁺ deposition, thereby inhibiting the lithium dendrites. The assembled LiFePO₄|PEO-5% COF-LZU1/Li cells delivered a discharge specific capacity of 146 mAh g⁻¹ and displayed a capacity retention of 80% after 200 cycles at 0.1 C (60 °C). The Li/Li symmetrical cells of the PEO-5% COF-LZU1 electrolyte presented a longer working stability at different current densities compared to that of the PEO electrolyte. Therefore, the enhanced comprehensive performance of the solid electrolyte shows potential application prospects for use in LMBs.