Basic performance requirements of polymer electrolytes

Basic performance requirements of polymer electrolytes

The polymer electrolyte is sandwiched between the positive and negative electrodes of the battery, which plays a dual role of preventing short circuit of the battery and conducting lithium ions. Therefore, the performance of polymer electrolytes has an important impact on the performance of lithium batteries. Polymer electrolytes with good performance generally need to meet the following requirements:

(1) Ionic conductivity. The polymer electrolyte needs to have the highest possible ionic conductivity at room temperature to ensure that the lithium battery has an ideal large-rate charge and discharge capability and shorten the charging time.

(2) The number of lithium ion migration. Represents the electrolyte’s ability to transport lithium ions. A high lithium ion migration number can effectively reduce the ohmic polarization during battery charging and discharging and inhibit the formation of lithium dendrites, which is one of the important factors that determine the charging and discharging performance of lithium batteries.

(3) Electronic insulation. The polymer electrolyte must have the function of isolating the positive and negative electrodes and preventing the battery from short-circuiting. Therefore, the polymer electrolyte must have excellent electronic insulation.

(4) Compatibility with lithium negative electrode. Lithium metal anode is a potential choice for the development of high-energy density metal lithium batteries. It is required that the polymer electrolyte and lithium metal anode have good interface stability, so as to achieve uniform and stable deposition and dissolution of lithium ions.

(5) Mechanical properties. The polymer electrolyte must have good mechanical properties: high tensile strength, high Young’s modulus, and excellent flexibility. The high tensile strength will be beneficial to the processing of the polymer electrolyte, the high polar modulus will effectively prevent the lithium dendrites from penetrating the polymer electrolyte during the charging and discharging process, and excellent flexibility can extend the polymer electrolyte to the field of flexible and wearable batteries. At the same time, high mechanical properties are also the material basis for large-scale roll-to-roll manufacturing processes.

(6) Thermal stability. Including chemical thermal stability and dimensional thermal stability. Chemical thermal stability means that the material remains stable under high temperature conditions and cannot be decomposed or degraded; dimensional thermal stability means that when the polymer electrolyte membrane material hopper is stored at high temperature, the dimensional shrinkage rate should be as small as possible (generally less than 1% at 150°C). High dimensional thermal stability will greatly improve the safety of lithium batteries during high temperature operation or storage.

(7) Chemical stability. Polymer electrolyte can not or as little as possible chemical reaction with electrolyte, positive and negative materials, including electrode coupling chemical reaction.

(8) Electrochemical stability. That is, the polymer electrolyte does not undergo side reactions within a certain charge and discharge voltage range, nor does it undergo oxidation-reduction reactions with the positive and negative electrodes.

(9) The price is low, the preparation process is simple, and it is easy to form and prepare in a large area, thereby realizing commercial promotion.