Research Progress of in situ Generated Polymer Electrolyte for Rechargeable Batteries

Rechargeable batteries, which are among the most promising energy storage devices, have become a research hotspot related to energy-storage and energy-convert systems. While the rechargeable batteries based on liquid electrolytes commonly possess serious safety risks such as electrolyte leakage, volatilization, combustion, and explosion, polymer electrolytes display great potentials in ameliorating and addressing these problems. Conventional polymer electrolytes are generally prepared by the solution casting method, which is difficult to implement in actual production owing to its complicated operation and harsh conditions. In addition, the poor electrolyte/electrode interfacial contact in solid-state lithium batteries is also a common issue, mainly originating from the ex situ assembly technique of solid-state electrolyte. These drawbacks hinder their large-scale promotion and application. In this context have emerged the in situ generated polymer electrolytes, which aim at solving the above mentioned problems effectively. The general process of in situ preparation of the polymer electrolytes is as follows: a precursor solution consisting of monomers, lithium salts, and initiators is injected into the battery to fully wet the electrode channels and gaps, and the monomers are then polymerized in situ under certain external conditions to afford a gel/solid polymer rechargeable battery in one step. Compared to the traditional routes to polymer electrolytes, such in situ polymerization simplifies the preparation process, facilitates favorable solid electrolyte interface, and enables the electrode and electrolyte to form an integrated structure for better interfacial contact. These advantages are beneficial to an improved performance of rechargeable batteries and endow the technique with a promising application prospect. For more efficient development, it is an urgent task to review the existing process routes, reaction principles, types of polymer electrolytes, and the practical applications of in situ generated polymer electrolytes in rechargeable batteries (such as lithium, sodium, magnesium, etc.). Herein, we summarize the research progress of in situ polymerization in significantly stabilizing the electrode/electrolyte interface and inhibiting the diffusion of intermediates. Further, we discuss the challenges and development treads of in situ generated polymer electrolytes, including the prospects of quasi-solid polymer electrolytes. We believe this review paper will serve as a valuable reference and theoretical guidance for researchers engaged in polymer electrolytes.