Patent Application
20240088437
Salts are used to carry the charge in an electrolyte of an electrochemical cell when being charged or discharged. Small molecule solvents (<150 g/mol) are conventionally used in batteries to dissolve salts and transport the charge. These small molecule solvents can also take place in redox reactions at the electrode and lead to a reduction in efficiency of the electrochemical cell and a reduction in cycle life over time. Small molecule solvents also typically have a high vapor pressure and high flammability leading to safety issues. Large molecule solvents (>5000 g/mol) would address many of these concerns. For example, large molecule solvents would prevent a continuous reaction at the interface of the electrode because the larger molecular weight would diffuse much less, leading the improved cycle life and efficiency of the electrochemical cell. Because of the large molecular weight, the vapor pressure may also be significantly less, resulting in improved safety.
A high dielectric material is helpful to achieving 100% or approximately 100% dissociation of the salts present in an electrochemical cell. Polymer materials with high dielectric constant (>10) are hard to come by because the combination of properties (containing a high dipole component and having high molecular mobility) are sometimes directly contrasting.
A polymer electrolyte is disclosed that includes a polymer backbone that contains a high dipole moiety and a low Tg moiety. The polymer electrolyte also includes a salt combined with the polymer.
In some prior devices, high dipole molecules were added to low Tg polymers like PEO and PDMS via side chains and multi-block copolymers. However, unlike embodiments of the prior art, the presently disclosed polymer electrolyte combines a superionic conductivity mechanism, where the high dipole moiety is in the backbone of the polymer, along with high dielectric constant polymers. The disclosed polymers do not require the aid of solvents to dissociate salts (e.g., lithium salts) and do not require solvents for processing.
In the disclosed polymer electrolytes, the high dipole moiety may be selected from one or more of the following: an allyl carbonate, diallyl carbonate, poly(diallyldimethylammonium) bis(trifluoromethanesulfonyl)imide (PDADMA TFSI), a quaternary ammonium salt, an organocarbonate, dimethyl carbonate, ethylene carbonate, polypropylene carbonate, and combinations thereof. In some embodiments, the high dipole moiety is selected from one or more of the following polymers:
In these and other embodiments, the low Tg moiety may be selected from one or more of the following: a thiol, 1,4-butanedithiol, 2,2′(Ethylenedioxy)diethanethiol, and combinations thereof. In select embodiments, the low Tg moiety may be selected from one or more of the following polymers:
In some embodiments, the low Tg moiety may have a Tg of less than 120° C. In these and other embodiments, the polymer backbone may have a molar ratio of the high dipole moiety and the low Tg moiety of between 0.4 and 0.10. The polymer backbone may have a molecular weight of greater than 5000 g/mol. In select embodiments, the salt combined with the polymer may be a lithium salt, such as lithium hexafluorophosphate (LiPF6), LiClO4, LiBF4, LiAsF6, or combinations thereof. The dielectric constant of the polymer electrolyte may greater than 10 or 20 at 10 k Hz, in some embodiments.
Upon consideration of the subject disclosure, one skilled in the art will readily appreciate that electrochemical cells containing the polymer electrolytes described herein are also contemplated and intended to fall within the scope of the present disclosure.
A polymer electrolyte solvent with a high dipole moiety in the backbone alternating with a low glass transition temperature (Tg) moiety is disclosed. The disclosed polymer electrolyte may exhibit numerous advantageous properties. For example, including the high dipole component in the backbone may increase the likelihood of superionic conductivity. Also, the combination of a moiety with a high dipole moment with a moiety to impart low Tg may result in a high dielectric constant (>10).
The high dipole moiety of the polymer electrolyte may be any suitable material or combination of materials. In select embodiments, the high dipole moiety is an allyl carbonate, such as diallyl carbonate. In other embodiments, the high dipole moiety is poly(diallyldimethylammonium) bis(trifluoromethanesulfonyl)imide (PDADMA TFSI). In select embodiments, the high dipole moiety may be a quaternary ammonium salt, an organocarbonate (e.g., dimethyl carbonate, ethylene carbonate, or polypropylene carbonate), or combinations thereof. Sample high dipole moieties include one or more of the following polymers:
The low Tg moiety may be a thiol or another type of material having a relatively low Tg. In some embodiments, the low Tg moiety may have a Tg of less than 120° C., such as less than 100° C., 80° C., 60° C., 40° C., or 20° C. as measured by differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and/or thermomechanical analysis (TMA).
In some embodiments, the low Tg moiety is 1,4-butanedithiol or 2,2′(Ethylenedioxy)diethanethiol. Sample low Tg moieties include one or more of the following polymers:
The atomic (molar) ratio of the high dipole moiety and the low Tg moiety in the polymer backbone may be between 0.4 and 0.10. In some embodiments, the polymer backbone contains a molar ratio of 0.6 to 0.8 high dipole moiety to low Tg moiety.
The polymer backbone may be combined with a salt to form the polymer electrolyte. In some embodiments, the salt may be a lithium salt, such as lithium hexafluorophosphate (LiPF6), LiClO4, LiBF4, LiAsF6, or combinations thereof.
At 10 k Hz, the dielectric constant of the polymer electrolyte may be greater than 10. In select embodiments, the dielectric constant of the polymer electrolyte may be greater than 20 at 10 k Hz, and in some cases greater than 25 at 10 k Hz.
A few experimental examples are disclosed herein for illustrative purposes.
Diallyl Carbonate (a high dipole moeity) undergoes a thiol-ene polymerization with 1,4-butanedithiol (a low Tg moeity). The purified polymer is used to dissolve LiTFSI (a salt) to create a polymer electrolyte with an ionic conductivity of 7×10−5 S/cm.
DiallylDimethylammonium TFSI (a high dipole moeity) undergoes a thiol-ene polymerization with 2,2′-(Ethylenedioxy)diethanethiol (a low Tg moeity). The purified polymer is used to dissolve LiTFSI (a salt) to create a polymer electrolyte with ionic conductivity of 7×10−5 S/cm.
Any of the high dipole moieties and/or low Tg moieties shown in
This application claims priority to U.S. Provisional Patent Application No. 63/401,276, filed Aug. 26, 2022, the entire contents of which are incorporated by reference herein.
| Number | Date | Country | |
|---|---|---|---|
| 63401276 | Aug 2022 | US |
