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.