1. Design of nanostructured polymer electrolytes;

2. The structure-property relationship of polymer electrolytes;

3. Application of polymer electrolytes in soft robots;

2023-present, School of Materials Science and Engineering, Xi'an Jiaotong University, Associate Professor

2021-2022 Department of Chemistry, Pohang University of Science and Technology, Research Assistant Professor

2018-2021 Department of Chemistry, Pohang University of Science and Technology, Postdoc.

2013-2018 Department of Polymer Science and Engineering, Zhejiang University, PhD

2009-2013 School of Materials Science and Engineering, Wuhan University of Technology, Bachelor's degree

1. What is polymer electrolyte?

Polymer electrolyte is a type of polymer material that can transport ions. It has intrinsic ion conductivity, good processability, and good structural designability, making it a promising functional polymer material that can be applied in fields such as soft robots, sensors, and batteries. There are two types of polymer electrolytes. Salt doped polymers with no chemical bonds between ions and polymers, and polyelectrolytes, where the cation or anion is fixed on the polymer.

2. The current dilemma of polymer electrolytes.

Since Wright et al. first discovered that salt doped poly(ethylene oxide) (PEO) show good ion conductivity in 1973, polymer electrolytes have received widespread attention. But until now, salt doped PEO remains as the landmark material in this field, and the ion conductivity of polymer electrolyte has always been unsatisfactory, which is still lower than that of liquid electrolyte for some reasons.

In many cases, there is an inversely proportional relationship between the conductivity and mechanical property of polymer electrolyte, and the improvement of conductivity often needs to sacrifice the modulus. The general explanation is that the movement of ions and polymer segments are coupled, that is, ions must move along with polymer segments. And one has to improve the mobility of polymer segments in order to enhance the mobility of ions. Lowering the glass transition temperature can enhance the polymer chain mobility and the carried ions, which leads to an increase in conductivity and a decrease in modulus.

3. Possible ways to decouple the motion of ions from polymer segments? Or, is it possible to simultaneously improve the conductivity and mechanical property of polymer electrolytes？

It is unknow yet. The coupling of the motion between ions and polymer segments, or that ions have to move with polymer segments, originates from the liquid transport mechanism of ions in polymer electrolytes. Polymer can be viewed as chemically connected small molecules (repeating units). The presence of chemical bonds limits the free movement of the repeating unit, so the mobility potential of polymer segments is inevitably more limited than that of small molecules. Therefore, it is difficult to make the polymer electrolytes show better conductivity than liquid electrolytes, under the similar liquid-like transport mechanism.

The development of polymer electrolytes is delayed compare to that of ceramic electrolytes. The answer to solving polymer problems may not necessarily come from polymers, but may also come from ceramics. The liquid channels can be formed between rigid crystal lattices in the amorphous phase by certain ions. The rigid lattice and amorphous ion channels endow the material with high modulus and conductivity, respectively. Different from the liquid-like transport mechanism in traditional polymers, the ions exhibit solid-like transport behavior in ceramics, where the rigid lattice participates in the ion transportation. Moreover, the Coulomb attraction and repulsion between ions in different spatial positions may induce the generation of multi-ion concerted migration, which further amplifies the conductivity. Therefore, it is expected to decouple the motion of ions from polymer segments, if one can achieve the solid-like ion transport in polymer electrolytes.  

4. What is the significance to decouple the motion of ions from polymer segments?

The most direct goal is to develop the benchmark polymer electrolyte that surpass salt doped PEO, which is extremely important for the soft robots, seniors, and batteries. For example, soft robots have good safety, adaptability, and stimulative responsibility, making them the important innovation direction for the intelligent manufacturing. The polymer electrolytes based soft actuators, as the main executing part of soft robots, can output forces under the electric stimulus. However, due to the inversely proportional relationship between the modulus and conductivity of polymers, ionic actuators suffer from low loading force and slow response, which limits their application in soft robots. Decouple the motion of ions from polymer segments can simultaneously enhance the modulus and conductivity of polymer electrolytes, improve the loading force and response of ionic actuators, which is of great significance for the development of soft robots.

In addition, including polymer electrolytes, many smart functional polymers, can exhibit significant nonlinear responses under small stimuli such as light, electricity, magnetism, heat, and chemicals due to the unique coexistence of solid and fluid characteristics as soft matter. However, there also exists the common inversely proportional relationship between modulus and strain. Decoupling the motion of ions from polymer segments in polymer electrolytes, achieving the balance between the solid and fluid properties of smart functional polymers in application, can provide examples for the functionalization regulation of multi-scale relaxations in soft matter.