As the most widely used energy storage device in consumer electronic and electric vehicle fields, lithium ion battery (LIB) is closely related to our daily lives, on which its safety is of paramount importance. LIB is a typical multidisciplinary product. A tiny single cell is composed of both organic and inorganic materials in multi scale. In addition, its relatively closure property made it difficult to be studied on line, let alone in the battery pack or system level. Safety, often manifested by stability on abuse, including mechanical, electrical, and thermal abuses, is a quite complicated issue of LIB. Safety has to be guaranteed in large scale application. Here, safety issues related to key materials and cell design techniques will be reviewed. Key materials, including cathode, anode, electrolyte, and separator, are the fundamental of the battery. Cell design and fabrication techniques also have significant influence on the cell's electrochemical and safety performances. Here, we will summarize the thermal runaway process in single cell level, and some recent advances on battery materials and cell design.

As an indispensable part of the lithium-ion battery (LIB), a binder takes a small share of less than 3% (by weight) in the cell; however, it plays multiple roles. The binder is decisive in the slurry rheology, thus influencing the coating process and the resultant porous structures of electrodes. Usually, binders are considered to be inert in conventional LIBs. In the pursuit of higher energy density, many new binders are being developed for specific targets, such as the high-voltage (typically, $$\geqslant$$⩾ 4.5 V) cathodes, conversion/alloy-type cathodes/anodes with large volume effect, and solid-state batteries (SSBs), in which these binders demonstrate their various functions. They may influence the solid electrolyte interface component, ensure the electrode/electrolyte interfacial stability, transport ions/electrons in the electrodes, provide adhesion and flexibility to solid-state electrolyte (SSE) films, etc. Here in this review, we try to summarize the advances on binders, among which the ones for high-voltage cathode materials, thick electrodes, micro-sized silicon particles, SSEs and SSBs are highlighted. We believe that the advanced functional binders would play decisive roles in the future development of high-energy–density LIBs and SSBs. Graphical Abstract Binder usually takes a small part in batteries, while recent studies prove that it has multi-functions more than just adhesive.