Polymer electrolytes
[4] The field has expanded since and is now primarily focused on the development of polymer electrolytes with applications in batteries, fuel cells, and membranes.
[1][2] The degree of crystallinity of a polymer electrolyte matrix impacts ion mobility and the transport rate.
Amorphous regions promote greater percolation of charge in gel and plasticized polymer electrolytes.
It is theorized that a polymer electrolyte with a shear modulus twice that of metallic lithium should be able to physically suppress dendrite formation.
[11] High elastic moduli or yield strengths can similarly decrease the uneven lithium deposition that leads to dendrite formation.
[12] The contrasting relationship between tensile strength and ionic conductivity inspires research into plasticized and composite polymer electrolytes.
As a result, ion conduction, which is primarily a diffusion-controlled process, is typically greater across regions of amorphous character than through crystalline domains.
An important aspect of gel electrolytes is the choice of solvent primarily based on their dielectric constants which is noted to impact ion conductivity.
[3] Gel polymer electrolytes using poly(ethylene oxide) (PEO) are the most studied due to its compatibility with lithium electrodes.
This type of electrolyte has also been shown to be able to be prepared from renewable and degradable polymers while remaining capable of mitigating current issues at the cathode-electrolyte interface.
[2] It has been demonstrated that the blending of polymer electrolytes with an inorganic filler affords a composite material with properties exceeding the sum of those of the individual components.
2D boron nitride is a potential filler material due to its high mechanical strength arising from modulation of the electrolyte membrane.
[20] Ion transport mechanisms will primarily focus on that for the transport of cations as the use of cation-conductive polymers is a greater area of academic focus due to the widespread use of lithium-ion batteries and other efforts aimed at developing multivalent metal ion batteries such as magnesium.
[3] In certain applications thin films of polymer electrolytes are needed, which necessitates careful control of morphology and properties due to deviations in the glass transition temperature and other mechanical properties associated with increasingly thin films of amorphous polymer electrolytes.
[21] Ion transport is impacted by concentration of the counterion and the ability of polymer chains to remain mobile.
[3][4] The adjacent image illustrates a possible mechanisms for ion transport through short range chain ordering and motions in amorphous regions of polymer electrolytes.
There are several factors to be optimized in the design of polymer electrolytes such as ion conductivity, mechanical strength, and being chemically inert.
[1][2] Several important characteristics can be measured including impedance, admittance, modulus, and permittivity (dielectric constant and loss).
[2][3] Additionally, the high processability of compatible polymers results in simpler design and construction of the chemical cell.
[1][9] The shear moduli of polymer electrolytes exceed those of lithium metal, which aid in preventing dendrite growth.
[10] Fuel cell applications of polymer electrolytes typically employ perfluorosulfonic acid membranes capable of selective proton conduction from the anode to the cathode.
[7] However, current conductive polymer membranes are limited by requiring humidification, and the face durability issues related to their mechanical properties.
