Polyvinylene carbonate-based solid polymer electrolyte

Polyvinylene carbonate-based solid polymer electrolyte

Vinylene carbonate (VC) is often used as an electrolyte additive (SEI film former) to improve the performance of lithium batteries. Because of the special structure and properties of vinylene carbonate, its polymers can be used as solid polymer electrolytes. Lu et al. prepared a composite polymer electrolyte based on cross-linked poly(ethylene glycol)-vinylene carbonate/PVDF-HFP blends. The semi-interpenetrating network polymer electrolyte prepared by this preparation process has high ionic conductivity, wide electrochemical stability window, and good interfacial stability to the lithium negative electrode. Moreover, the LiFePO4/Li battery assembled with the semi-interpenetrating network polymer electrolyte showed excellent long-cycle performance and excellent rate performance.

To further improve the comprehensive properties of VC copolymer polymer electrolytes, Itoh et al. studied solid polymer electrolytes based on alternating copolymers of methoxyvinyl ether oligomers and vinylene carbonate (Figure 1). The test results show that the ionic conductivity of the solid polymer electrolyte increases with the increase of the side chain length. When the vinyl length of the side chain is 23.5, the ionic conductivity can reach up to 1.2×10-4S/cm (30℃), and the solid polymer electrolyte has good dimensional thermal stability and wide electrochemical stability window, showing excellent application prospects.

Polyvinylene carbonate-based solid polymer electrolyte
Figure 1 – Synthesis of vinylene carbonate and vinyl ether block copolymers

Excessive solid-solid contact resistance is also an urgent problem to be solved in solid-state batteries. The Qingdao Energy Storage Industry Technology Research Institute prepared a polyvinylene carbonate-based solid polymer electrolyte (PVCA-SPE) with vinylene carbonate (VC) as a monomer in situ polymerization (Figure 2). Due to the in-situ polymerization technique, PVCA-SPE has good interfacial compatibility and low interfacial impedance between the electrodes. In addition, the interaction between the ester groups in polycarbonate and lithium ions is beneficial to the transport of lithium ions in the electrolyte, which makes PVCA-SPE have high ionic conductivity (2.23×10-5S/cm) at room temperature. At 50℃, the ionic conductivity of PVCA-SPE can reach 9.85×10-5S/cm, which is higher than the solid polymer electrolyte of traditional PEO system; and PVCA-SPE has a wide electrochemical stability window (4.5V), which can meet the needs of high-voltage solid-state lithium batteries. Meanwhile, they assembled LiCoO2/Li half-cells with PVCA-SPE as electrolyte, and tested the charge-discharge performance of LiCoO,/PVCA-SPE/Li half-cells at 50℃. At 0.1C, the battery has a specific discharge capacity of 146 mA·h/g, and after 150 long-cycle tests, the capacity retention rate is 84.2%, indicating that PVCA has high application value in lithium batteries.

Polyvinylene carbonate-based solid polymer electrolyte
Figure 2 – In situ copolymerization of polyvinylene carbonate-based solid polymer electrolytes

PVC-based solid polymer electrolytes can be prepared by an in-situ polymerization process, which will greatly improve the compatibility between electrolytes and electrodes, and effectively solve the problem of interfacial compatibility between electrolytes and electrodes. At the same time, the in-situ polymerization method does not require other solvents to dissolve, which avoids the cumbersome preparation process of the solid-state electrolyte, does not change the current production process of lithium batteries, and reduces the production cost of solid-state lithium batteries.