Lithium ion battery separator with improved performance via side-by-side bicomponent electrospinning of PVDF-HFP/PI followed by 3D thermal crosslinking

Here, a novel PVDF-HFP/PI side-by-side bicomponent electrospun separator with cross-linked structure is successfully fabricated for lithium-ion batteries (LIBs). The bicomponent composite fiber not only integrates the excellent characteristics of PVDF-HFP and PI, but also improves the mechanical strength of the electrospun nonwoven and maintains a high level of porosity, up to 85.9 %. Moreover, the PVDF-HFP/PI(T) fibrous separator emerges outstanding performance, including the thermal dimensional stability (up to 200 °C), self-extinguishment, high electrolyte uptake (483.5 %), good ionic conductivity (1.78 × 10−3 S/cm), wide electrochemical stability window (up to 4.94 V vs. Li+/Li) and favorable interface structure. It is further confirmed by the 3D simulation that the PVDF-HFP/PI(T) nonwoven using as the LIBs separator is beneficial to the homogeneous transmission of lithium ions. As a result, the coin cells with PVDF-HFP/PI(T) separator possess the best first discharge capacity (120.41 mAh g−1) and coulombic efficiency (99.36 %) with respect to that of Celgard2320 separator and cross-electrospun PVDF-HFP + PI(T) separator. After 50 cycles, the discharge capacity of Li/PVDF-HFP/PI(T)/LiFePO4 is found to be retained around 98.13 %, which is higher than 94.91 % of Celgard2320 separator and 96.09 % of cross-electrospun PVDF-HFP + PI(T) separator. Moreover, the coin cell using the PVDF-HFP/PI (T) separator exhibited good discharge capacity under different discharge C-rate at 45 °C, indicating its potential for the high-temperature safety of LIBs. In sum, the PVDF-HFP/PI(T) nonwoven with excellent property has an application prospect in the field of LIBs separator, which also provides a reliable strategy for designing the electrospun separator with improved performance.