A flame retarding separator with improved thermal stability for safe lithium-ion batteries

Side Reactions/Changes in Lithium-Ion Batteries: Mechanisms and Strategies for Creating Safer and Better Batteries

Lithium-ion batteries (LIBs), in which lithium ions function as charge carriers, are considered the most competitive energy storage devices due to their high energy and power density. However, battery materials, especially with high capacity undergo side reactions and changes that result in capacity decay and safety issues. A deep understanding of the reactions that cause changes in the battery's internal components and the mechanisms of those reactions is needed to build safer and better batteries. This review focuses on the processes of battery failures, with voltage and temperature as the underlying factors. Voltage-induced failures result from anode interfacial reactions, current collector corrosion, cathode interfacial reactions, overcharge, and over-discharge, while temperature-induced failure mechanisms include SEI decomposition, separator damage, and interfacial reactions between electrodes and electrolytes. The review also presents protective strategies for controlling these reactions. As a result, the reader is offered a comprehensive overview of the safety features and failure mechanisms of various LIB components.

In Situ Armoring: A Robust, High-Wettability, and Fire-Resistant Hybrid Separator for Advanced and Safe Batteries

Development of nonflammable separators with excellent properties is in urgent need by next-generation advanced and safe energy storage devices. However, it has been extremely challenging to simultaneously achieve fire resistance, high mechanical strength, good thermomechanical stability, and low ion-transport resistance for polymeric separators. Herein, to address all these needs, we report an in situ formed silica@silica-imbedded polyimide (in situ SiO₂@(PI/SiO₂)) nanofabric as a new high-performance inorganic-organic hybrid separator. Different from conventional ceramics-modified separators, this in situ SiO₂@(PI/SiO₂) hybrid separator is realized for the first time via an inverse in situ hydrolysis process. Benefiting from the in situ formed silica nanoshell, the in situ SiO₂@(PI/SiO₂) hybrid separator shows the highest tensile strength of 42 MPa among all reported nanofiber-based separators, excellent wettability to the electrolyte, good thermomechanical stability at 300 °C, and fire resistance. The LiFePO₄ half-cell assembled with this hybrid separator showed a high capacity of 139 mAh·g^-1@5C, which is much higher than that of the battery with the pristine PI separator (126.2 mAh·g^-1@5C) and Celgard-2400 separator (95.1 mAh·g^-1@5C). More importantly, the battery showed excellent cycling stability with no capacity decay over 100 cycles at the high temperature of 120 °C. This study provides a novel method for the fabrication of high-performance and nonflammable polymeric-inorganic hybrid battery separators.

Intrinsically Safe Gel Polymer Electrolyte Comprising Flame-Retarding Polymer Matrix for Lithium Ion Battery Application

State-of-the-art (SOTA) liquid electrolyte/polyolefin separator setups used in lithium ion batteries (LIBs) suffer from the hazard of leakage and high flammability. To address these issues, phosphonate, a flame-retarding moiety, is chemically bonded to a polymer matrix to fabricate a nonflammable gel polymer electrolyte (GPE). The obtained phosphonate-based polymer matrix as well as its corresponding GPE (gelled with flammable SOTA nonaqueous liquid electrolyte) shows remarkable flame resistivity. Unlike poly(vinylidene fluoride- co-hexafluoropropylene)-based GPEs, the phosphonate-based GPE does not react with lithiated graphite at high temperatures. Both features indicate that the phosphonate-based GPE is superior to SOTA GPEs in the aspect of safety performance. As the flame-retarding moiety is chemically bonding to the polymer, the parasitic reactions between the flame-retarding moiety and the electrodes are avoided. Consequently, LIB cells comprising phosphonate-based GPE show good capacity retention comparable to cells comprising SOTA GPEs. Compared with SOTA GPEs, phosphonate-based polymer-based GPEs show improved intrinsic safety performance and comparable cycle life. Therefore, phosphonate-based polymers exhibit high potential to be used as a new class of polymer matrix for GPE used in LIBs.

Nanonet-structured poly(m-phenylene isophthalamide)–polyurethane membranes with enhanced thermostability and wettability for high power lithium ion batteries

Nanonet-structured PMIA–PU nanofibrous membranes for high power lithium ion batteries are fabricated via a one-step electrospinning technique, and show enhanced thermostability and nonflammability as well as good wettability.

Progress in polymeric separators for lithium ion batteries

This study reviews the recent developments and the characteristics of polymeric separators used for lithium ion batteries.

Preparation of high performance lithium-ion batteries with a separator–cathode assembly

Comparison of the lithium-ion batteries with conventional separator (A) and separator–cathode assembly (B).