A Rational Design for a High‐Safety Lithium‐Ion Battery Assembled with a Heatproof–Fireproof Bifunctional Separator

Abstract

High‐Ni‐content LiNixCoyMn1−x−yO2 is regarded as a feasible cathode material to meet the urgent requirement for high energy density batteries. However, such cathode has a poor safety performance because of reactive oxygen releasing at elevated temperatures. In pursuit of high‐safety lithium‐ion batteries, a heatproof–fireproof bifunctional separator is designed in this study by coating ammonium polyphosphate (APP) particles on a ceramic‐coated separator modified with phenol‐formaldehyde resin (CCS@PFR). The CCS@PFR separator acts as a thermal‐supporting layer to inhibit the shrinkage of the separator at elevated temperatures, whereas the APP‐coated layer functions as a fireproof layer, forming a dense polyphosphoric acid (PPA) layer above 300 °C. The PPA layer not only isolates the combustibles from the highly reactive oxygen released from the cathodes but also converts violent combustion reactions into mild stepwise exothermic reactions by carbonizing the combustibles in the batteries. Enabled with such a heatproof–fireproof bifunctional separator, LiNi0.8Co0.1Mn0.1O2|SiOx−Gr full cells are constructed and these exhibit an excellent safety performance by not catching fire during a 30 s combustion test and surviving the 10 min high‐temperature test above 300 °C. Additionally, an adiabatic rate calorimeter and nail penetration test are conducted with 3 Ah LiNi0.8Co0.1Mn0.1O2|SiOx−Gr pouch cells to further verify the safety performance.

Sandwich-like solid composite electrolytes employed as bifunctional separators for safe lithium metal batteries with excellent cycling performance

“…S10†), the LiFePO 4 |PVDF–DBDPO/PP|Li cell demonstrates nonetheless an especially excellent performance with the specific capacity (113 mA h g −1 initially) and cycling stability (capacity retention of 100% after 1000 cycles) overwhelmingly superior to those of the LiFePO 4 |PP|Li cell (initial capacity of 98 mA h g −1 with the retention of 64.2%). Therefore, even when compared with the separators which are positively reported in the literature, 20,22,38,41,42,44,53,61–63 the LiFePO 4 /Li cell with the PVDF–DBDPO/PP separator still exhibits considerable competitive advantages (Fig. 7d), in not only the highly stable long-term cycling performance, but also the real demand of the lower-content liquid electrolyte (10 μL cm −2 ) for higher cell safety.…”

“…The PVDF-based composite layers attached to PP membranes are not only employed as a protective armor away from the combustion, but also play a critical role here to realize homogeneous redistribution of ions across the porous PP separators, which is supposed to promote uniform lithium deposition for dendrite-free lithium anodes. Moreover, different from most of the reported functional separators that require a large amount of liquid electrolyte, 41,42 the sandwich-like composite separators only need to be wetted with about 10 μL cm −2 of the electrolyte enabling low-liquid-content LMBs without sacrificing the electrochemical performance, which thus naturally reduces the flammability substantially. As a result, compared with the PP separators loaded with liquid electrolyte, such PVDF-based SCE-facilitated separators under the same conditions can exhibit prominent safety of fire prevention, and much improved electrochemical properties such as larger ionic conductivity, higher stability against lithium metal and more excellent cycling performance.…”

High‐Voltage and High‐Safety Practical Lithium Batteries with Ethylene Carbonate‐Free Electrolyte

“…The severe safety concern, generally presented as thermal runaway (TR), is triggered by the poor thermal tolerance of aggressive Ni‐rich cathodes at charged state, especially when it encounters highly reductive ethylene carbonate (EC). [ 12,13 ] Tremendous efforts are made to address safety concerns, including optimization of separator, [ 14,15 ] cathode, [ 8,16 ] current collector, [ 17 ] and the use of non‐flammable electrolyte. [ 18–21 ] Although such efforts can somewhat reduce the risk of TR, more efforts are urgently required to obtain intrinsically safe LIBs for practical applications.…”

A non‐Newtonian fluidic cellulose‐modified glass microfiber separator for flexible lithium‐ion batteries

“…Due to the increasing demand for portable communication devices, 1,2 flexible electronic equipment, 3–6 and electric vehicles, 7–9 there is an urgent need to develop flexible rechargeable energy storage and conversion devices such as supercapacitors, 10–12 lithium‐ion batteries (LIBs), 13–15 metal‐air batteries, and so on 16–18 . The separator is a part of these electrochemical energy devices that ensures ion transmission and maintains electrode stability and device safety 19–21 …”