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.
Redox from the holes at the O2p orbitals is a well‐known phenomenon in Li‐rich Mn‐based batteries. However, such an anionic redox process results in the formation of O2, leading to structural instability owing to unstable O2p holes. Herein, a swing‐like non‐isothermal sintering technique is used to stabilize the lattice oxygen by suppressing the formation of O2 during charging. It reduces both the number of intrinsic oxygen vacancies of the Li‐rich Mn‐based oxides and the formation of O2 during charging as compared with traditional constant high‐temperature sintering. Consequently, the number of holes generated during charging in the O2p orbitals increases, whereas the number of unstable O2p holes forming O2 decreases. Therefore, the sample prepared via swing‐like non‐isothermal sintering exhibited considerably slower voltage fading and better cycling stability. This study provides valuable guidelines for stabilizing the lattice oxygen and improving the structural stability of the oxide cathodes for electrochemical energy storage.
Li-rich layered oxide (LLO) cathode materials with high specific capacities could significantly enhance the energy density of all-solid-state lithium batteries (ASSLBs). However, the specific practical capacities of LLO materials in ASSLBs are extremely low due to poor initial activation. Here, scanning transmission electron microscopy with in situ differential phase contrast imaging was first used to study the initial activation mechanism of Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O 2 . Li-ion transport heterogeneity was observed in LLO grains and across the LLO/Li 6 PS 5 Cl interface, due to the coexistence of the nanoscale Li 2 MnO 3 and LiNi 1/3 Co 1/3 Mn 1/3 O 2 phases. Consequently, the severely constrained activation of Li 2 MnO 3 during the first charging could be attributed to a nanoscale phase separation in LLO, hindering Li-ion transport through its particles, and causing high impedance in the Li 2 MnO 3 domain/Li 6 PS 5 Cl interface. This study could facilitate interface design of high-performance LLO-based ASSLBs.
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