The review focuses on variable-conductivity materials used to protect lithium-ion batteries from ignition. Examples of emergency situations arising in the operation of such batteries are given and their causes are considered. Thermal runaway that results in ignition of a lithium-ion battery and the chemical reactions accompanying this process are discussed. Internal battery protection using variable-resistance temperature- or voltage-sensitive components is described. Various approaches to the prevention of thermal runaway by modifying a battery with thermo- and voltage-resistive materials are summarized and analyzed. The advantages and drawbacks of various types of materials of this kind are demonstrated. Particular attention is paid to the practical significance of the creation and application of protective variable-resistance materials and approaches to the design of this kind of materials. The bibliography includes 165 references.

Lithium iron phosphate (LFP) has found many applications in the field of electric vehicles and energy storage systems. However, the increasing volume of end‐of‐life LFP batteries poses an urgent challenge in terms of environmental sustainability and resource management. Therefore, the development and implementation of efficient LFP battery recycling methods are crucial to address these challenges. This article presents a novel, comprehensive evaluation framework for comparing different lithium iron phosphate relithiation techniques. The framework includes three main sets of criteria: direct production cost, electrochemical performance, and environmental impact. Each criterion is scored on a scale of 0–100, with higher scores indicating better performance. The direct production cost is rated based on material costs, energy consumption, key equipment costs, process duration and space requirements. Electrochemical performance is assessed by rate capability and cycle stability. Environmental impact is assessed based on CO₂ emissions. The framework provides a standardized technique for researchers and industry professionals to objectively compare relithiation methods, facilitating the identification of the most promising approaches for further development and scale‐up. The total average score across the three criterion groups for electrochemical, chemical, and hydrothermal relithiation methods was approximately 60 points, while sintering scored 39 points, making it the least attractive relithiation technique. Combining approaches outlined in publications with scores exceeding 60, a relithiation scheme was proposed to achieve optimal electrochemical performance with minimal resource consumption and environmental impact. The results demonstrate the framework's applicability and highlight areas for future research and optimization in lithium iron phosphate cathode recycling.

Materials with a positive temperature coefficient have many applications, including overcharge and over-temperature protection in lithium-ion (Li-ion) batteries. The thermoresistive properties of an electrically conductive polymer, based on a Ni(salen)-type backbone, known as polyNiMeOSalen, were evaluated by means of in situ resistivity measurements. It was found that the polymer was conductive at temperatures below 220 °C; however, the polymer increased in resistivity by three orders of magnitude upon reaching 250 °C. Thermogravimetric results combined with elemental analyses revealed that the switch from the insulation stage to the conductive stage resulted from thermally dedoping the polymer. Electrochemical studies demonstrated that a polymer retains its electroactivity when it is heated and can be recovered to a conductive state through oxidation via electrochemical doping in an electrolyte solution.

This study presents an effective plasma treatment method for doping technical carbon by nitrogen- and sulfur-containing functional groups. Nitrogen incorporation shifted the oxygen reduction reaction onset potential by 0.25 V and increased the limiting current by 1 mA cm⁻², while sulfuration showed a more pronounced effect, with a 0.31 V shift in onset potential and an increase in the limiting current to 6.23 mA cm⁻². These enhancements are attributed to the formation of additional active sites and improved surface properties. The proposed plasma-based approach is simple, scalable, and environmentally friendly, minimizing the use of hazardous reagents and eliminating the need for multistep processes. This method demonstrates the potential for industrial applications using commercially available raw materials such as technical carbon and to be extended to other carbon-based materials.