Anionic Polymers, Electrolytes Comprising the Same, and Methods of Manufacture Thereof

Abstract

The invention provides a novel anionic polymer useful as a solid electrolyte in a lithium battery. The electrolyte matrix provides directional, flexible, polymeric ion channels with 100% lithium conduction with low-to-no affinity of the matrix for the lithium ion, in part due to the low concentration or absence of lone pair electrons in the anionic polymer.

Claims

1. An anionic polymer comprising a Lewis adduct.

2. The anionic polymer of claim 1, wherein the polymer is the copolymer of a Lewis acid and a Lewis base.

3. The anionic polymer of claim 1, wherein the polymeric backbone lacks lone pair electrons.

4. The anionic polymer of claim 1, wherein the polymer lacks lone pair electrons.

5. The anionic polymer of claim 1, wherein the polymer is represented by Formula I: ##STR00005## wherein: L.sup.1 and L.sup.2 are each independently a divalent residue of an organic molecule, X is selected from the group consisting of CR.sup.1R.sup.2, NR.sup.1, SiR.sup.1R.sup.2, PR.sup.1, O, S, Y is selected from the group consisting of BR.sup.1R.sup.2, and R.sup.1 and R.sup.2 are each independently selected from the group consisting of H, and optionally substituted alkyl, haloalkyl, alkenyl, alkynyl, aryl, cycloalkyl, heteroaryl, heterocycloalkyl, arylalkyl, heteroarylalkyl, cycloalkylalkyl, and heterocycloalkylalkyl, and can optionally be joined to form a ring.

6. The anionic polymer of claim 5, wherein the polymer is represented by Formula II: ##STR00006##

7. The anionic polymer of claim 5, wherein the polymer is represented by Formula III: ##STR00007##

8. The anionic polymer of claim 5, wherein the polymer is represented by Formula IV: ##STR00008##

9. A composition comprising the anionic polymer of claim 1, wherein a polymer molecule is adjacent to an ion channel.

10. A composition comprising the anionic polymer of claim 1 and a counterion.

11. The composition of claim 10, wherein the counterion is selected from the group consisting of Li.sup.+, Na.sup.+, and Me.sup.+.

12. A film comprising the anionic polymer of claim 1.

13. A crystal comprising the anionic polymer of claim 1.

14. A solid electrolyte comprising the anionic polymer of claim 1.

15. A battery comprising the electrolyte of claim 14.

16. A method of preparing the anionic polymer of claim 1, comprising mixing a Lewis acid and a Lewis base.

17. The method of claim 16, wherein the Lewis acid is an organoborane and the Lewis base is an organometallic compound.

18. A method of growing the anionic polymer of claim 1 on a substrate, comprising dipping the substrate in a precursor, rinsing the substrate, and dipping the substrate in a different precursor.

19. The method of claim 18, wherein the precursors are selected from the group consisting of an organoborane and an organometallic compound.

20. The method of claim 18 wherein the substrate is a conductive electrode.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The following detailed description of preferred embodiments of the invention will be better understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, there are shown in the drawings embodiments which are presently preferred. It should be understood, however, that the invention is not limited to the precise arrangements and instrumentalities of the embodiments shown in the drawings.

[0018] FIG. 1 depicts the design of an exemplary embodiment of an anionic polymer and methods of growing thereof on a substrate, for example on an electrode. The sequential, alternating attachment of organodilithium salts with diboranes generates a 2-D directional polymer with 1-D ion channels with almost no affinity for the Li counterion.

[0019] FIG. 2, comprising FIGS. 2A and 2B, depicts examples of lone-pair free anionic polymers. FIG. 2A depicts how traditional PEO polymers chelate Li.sup.+ through multiple lone pairs, generating a barrier to migration, wherein the motion of mobile counteranions lowers ion selectivity. FIG. 2B depicts borate-based polymers lacking lone pairs, wherein anion atoms are located in the polymer backbone, permitting facile, selective ion migration.

[0020] FIG. 3 depicts polymer building blocks used in synthesizing the anionic polymers of the invention.

[0021] FIG. 4 depicts the delocalization of nitrogen lone pair for decreased Li.sup.+ affinity in a polymeric backbone comprising nitrogen, versus a polymeric backbone without nitrogen wherein there are no lone pairs for attachment to Li.sup.+.

[0022] FIG. 5 depicts the sequential dip approach for controlled step-growth polymerization, also known as the dip-rinse-dip approach.

[0023] FIG. 6 depicts SEM showing SiO.sub.2 coated LISICON functionalized with surface organosilane interface.

DETAILED DESCRIPTION

[0024] It is to be understood that the figures and descriptions of the present invention have been simplified to illustrate elements that are relevant for a clear understanding of the present invention, while eliminating, for the purpose of clarity, many other elements found in the art related to polymer compositions, battery technology, electrolytes useful for batteries or other electrochemical devices, and the like. Those of ordinary skill in the art may recognize that other elements and/or steps are desirable and/or required in implementing the present invention. However, because such elements and steps are well known in the art, and because they do not facilitate a better understanding of the present invention, a discussion of such elements and steps is not provided herein. The disclosure herein is directed to all such variations and modifications to such elements and methods known to those skilled in the art.

[0025] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although any methods, materials and components similar or equivalent to those described herein can be used in the practice or testing of the present invention, the preferred methods and materials are described.

[0026] As used herein, each of the following terms has the meaning associated with it in this section.

[0027] The articles a and an are used herein to refer to one or to more than one (i.e., to at least one) of the grammatical object of the article. By way of example, an element means one element or more than one element.

[0028] About as used herein when referring to a measurable value such as an amount, a temporal duration, and the like, is meant to encompass variations of 20%, 10%, 5%, 1%, or 0.1% from the specified value, as such variations are appropriate.

[0029] Throughout this disclosure, various aspects of the invention can be presented in a range format. It should be understood that the description in range format is merely for convenience and brevity and should not be construed as an inflexible limitation on the scope of the invention. Accordingly, the description of a range should be considered to have specifically disclosed all the possible subranges as well as individual numerical values within that range. For example, description of a range such as from 1 to 6 should be considered to have specifically disclosed subranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6 etc., as well as individual numbers within that range, for example, 1, 2, 2.7, 3, 4, 5, 5.3, 6 and any whole and partial increments therebetween. This applies regardless of the breadth of the range.

Description

[0030] In one aspect, the invention relates to an entirely new type of conductive polymer with excellent thermal and mechanical properties, at the same time solving the conduction directionality, lithium affinity, and ion selectivity problems generally associated with solid electrolytes. According to the current invention, electrolyte components are generated by the step-growth of linear polymers of alternating diborane and organodilithium functionality with a sequential dip-rinse method. As illustrated in FIG. 1, each subsequent addition binds the anion of the lithium salt to a boron atom, converting all lone pairs into bond pairs; the formerly bound lithium ion, having no remaining lone pairs to bind it, is displaced into the ionic channel, and is fixed by coulombic charge balance forces (ionic bonding) but with no lone electron pairs in the polymer for direct attachment.

[0031] In another aspect, the invention relates to a single ion conductor (SIC) polymer and polymer/ceramic composites with the potential to form high ionic conductivity, dendrite inhibiting, processable solid electrolytes with good power performance for use with lithium metal anodes.

[0032] The major challenge with polymer electrolytes is that the lone-pair electrons (needed to solubilize Li.sup.+) also bind to Li.sup.+ through coordinate covalent bonds. The approach of the invention takes advantage of concomitant generation of negatively charged polymers that also solubilize Li.sup.+, but lack coordinating lone pairs to bind the ions tightly to the electrolyte matrix, as illustrated in FIG. 2. While borate salts have been used as lithium ion sources due to this low-affinity property, the invention extends this utility to embedding the low-affinity borate anion into the polymer itself. Another challenge with polymer electrolytes is that they are not conductive through the bulk crystalline phase, but rather, along grain boundaries or through amorphous phases, so that the conduction path is tortuous. The invention provides directional, flexible, polymeric ion channels with 100% lithium conduction (since the anions are fixed as part of the polymer backbone) with low-to-no affinity of the matrix for the lithium ion. The polymers of the invention are prepared using relatively inexpensive, scalable ingredients, and with no need for doping molecules, nanostructures, or liquids into the separator. Materials such as these lead to improved and unprecedented ionic conductivity for polymers. The thermal and mechanical properties are comparable to other organic polymers, and are ideal for device fabrication, with the added benefits of inherent directionality, and controllable thickness, achieving the goal of realistically sized electrolyte components thinner than 20 m.

Compositions of the Invention

[0033] In one aspect, the invention relates to an anionic polymer comprising a Lewis adduct, In one embodiment, the polymer is the copolymer of a Lewis acid and a Lewis base. A Lewis acid is a molecule, ion, or chemical species in general, which is capable of accepting an electron pair from another molecule, ion, or chemical species in general, by means of coordination, and/or bond formation. A Lewis base is similarly a molecule, ion, or chemical species in general, which is capable of donating an electron pair to another molecule, ion, or chemical species in general, by means of coordination, and/or bond formation. A Lewis adduct is a molecule, ion, or chemical species in general, which results from the reaction between a Lewis acid and a Lewis base.

[0034] In one embodiment, a Lewis acid used in the compositions and methods of the invention is a chemical species comprising at least one atom with an empty orbital, such as for example an empty p orbital. In another embodiment, the Lewis acid is an organoborane comprising a boron atom and an organic residue. Exemplary organoboranes include, but are not limited to, 1,4-bis(diarylboryl)benzenes, 1,4-histdiarylboryl)naphthalenes, 9,10-bis(diarylboryl)anthracenes, 1,4-bis(dialkylboryl)benzenes, 1,4-bis(dialkylboryl)naphthalenes, and 9,10-bis(dialkylboryl)anthracenes. In one embodiment, the organoborane is selected from the group comprising benzenediborane and bis(dimethylboryl)benzene. The organoborane compounds may be synthesized according to any method known in the art.

[0035] In one embodiment, a Lewis base used in the compositions and methods of the invention is a chemical species comprising at least one atom with a pair of electrons available to occupy an empty orbital of a Lewis acid. In another embodiment, the Lewis base is the anion of a metallic salt of an organic compound. In another embodiment, the Lewis base is a lithium salt. In another embodiment, the lithium salt is selected from the group comprising the dilithium salts of 1,4-bis(methylamino)benzene and p-xylene. The pair of electrons conferring Lewis base character to the molecule, reacts with an empty orbital of a Lewis acid and creates a new bond in a Lewis adduct.

[0036] In one aspect, the invention relates to an anionic polymer having a polymeric backbone which lacks lone pair electrons. In one embodiment, the entire polymer lacks lone pair electrons. An anionic polymer is typically part of a composition further comprising a positive counterion such as a metallic cation. If the anionic polymer contains lone pairs of electrons, the counterion can coordinate to these lone pairs of electrons and therefore exhibit low mobility. A composition comprising an anionic polymer having no lone pair of electrons, either just in its polymeric backbone, or preferably in the entirety of the polymer, will therefore exhibit low counterion affinity and high degree of counterion mobility.

[0037] In one aspect, the invention relates to an anionic polymer represented by Formula I:

##STR00003##

In one embodiment, L.sup.1 and L.sup.2 are each independently a divalent residue of an organic molecule. In another embodiment, X is selected from the group consisting of CR.sup.1R.sup.2, NR.sup.1, SiR.sup.1R.sup.2, PR.sup.1, O, S. In another embodiment, Y is selected from the group consisting of BR.sup.1R.sup.2. In another embodiment, R.sup.1 and R.sup.2 are each independently selected from the group consisting of H, and optionally substituted alkyl, haloalkyl, alkenyl, alkynyl, aryl, cycloalkyl, heteroalyl, heterocycloalkyl, arylalkyl, heteroarylalkyl, cycloalkylalkyl, and heterocycloalkylalkyl, and can optionally be joined to form a ring.

[0038] In another aspect, the invention relates to an anionic polymer represented by Formula II. In one embodiment, the polymer is represented by Formula III. In another embodiment, the polymer is represented by Formula V.

##STR00004##

[0039] In one aspect, the invention relates to a composition comprising an anionic polymer of the invention further comprising an ion channel adjacent to a polymer molecule. An ion channel refers generally to a space in a composition wherein an ion, more specifically a cation, and even more specifically a metallic cation, can move through with a certain degree of mobility. Given the polymerization methods described herein and the inherent morphological characteristics of the resulting polymers, the ionic channels comprised by the compositions of the invention are directional, flexible, and have a high degree of counterion conduction. In particular the lack of lone pair of electrons in the polymeric backbone, or the entirety of the polymer, results in ion channels with low-to-no affinity of the polymeric matrix to the lithium ions which are the typical counterions used. In one embodiment, the counterion is selected from the group consisting of Li.sup.+, Na.sup.+, and Mg.sup.2+.

[0040] In one aspect, the invention relates to a film comprising an anionic polymer of the invention. In one embodiment, the film is flexible, while in other embodiments the film is rigid or semi-rigid. In another aspect, the invention relates to a crystal comprising the anionic polymer of the invention. In one embodiment, the film can be prepared by solution-phase mixing of 1:1 solutions of diborane and organodilithium reagents, wherein the resulting mixture is dried into a film by solvent evaporation.

[0041] In one aspect, the invention relates to a solid electrolyte comprising an anionic polymer of the invention. In one embodiment, the solid electrolyte can be grown on a substrate such as for example a conductive electrode. In one embodiment, the electrolyte is used in a battery. In one embodiment, the battery is rechargeable, One popular type of rechargeable battery is the lithium ion battery. Compared to other types of rechargeable batteries, lithium ion batteries provide high energy densities, lose a minimal amount of charge when not in use, and do not exhibit memory effects. Due to these beneficial properties, lithium ion batteries have found use in various portable electronic devices such as cell phones, transportation, back-up storage, defense, and aerospace applications.

Methods of the Invention

[0042] In one aspect, the invention relates to a method of preparing an anionic polymer comprising a Lewis adduct, the method comprising mixing a Lewis acid and a Lewis base. In one embodiment, the Lewis acid is an organoborane and the Lewis base is an organometallic compound. In one embodiment, the method can be employed to prepare a film comprising an anionic polymer of the invention, wherein the film can be flexible, rigid, or semi-rigid. In one embodiment, the method comprises solution-phase mixing of 1:1 solutions of diborane and organodilithium reagents, wherein the resulting mixture is dried into a film by solvent evaporation. In another aspect, the method can be used to grow a crystal comprising an anionic polymer of the invention.

[0043] In another aspect, the invention relates to a method of growing an anionic polymer on a substrate, comprising dipping the substrate in a precursor, rinsing the substrate, and dipping the substrate in a different precursor. In one embodiment, the precursors are selected from the group consisting of an organoborane and an organometallic compound. In another embodiment, the substrate is a conductive electrode. In another embodiment, the substrate is first coated by a self-assembled monolayer (SAM), constructed for example using p-hydroxythiophenol. In another embodiment, the SAM is constructed on a gold layer. In some embodiments, the substrate comprises SiO.sub.2 surfaces or silicon substrates that have been oxidized on one side to form SiO.sub.2, and further functionalized with organo or chlorosilanes as the initial monomer. In another embodiment, the substrate comprises nanoporous SiO.sub.2 on Li ceramics. In another embodiment, nm nanoporous SiO.sub.2 coatings are used on Li ceramic conductors to provide covalent attachment to the single ion conductor (SIC) polymers, and thus form hybrid SIC solid electrolytes.

EXPERIMENTAL EXAMPLES

[0044] The invention is further described in detail by reference to the following experimental examples. These examples are provided for purposes of illustration only, and are not intended to be limiting unless otherwise specified. Thus, the invention should in no way be construed as being limited to the following examples, but rather, should be construed to encompass any and all variations which become evident as a result of the teaching provided herein.

[0045] Without further description, it is believed that one of ordinary skill in the art can, using the preceding description and the following illustrative examples, make and utilize the compositions of the present invention and practice the claimed methods. The following working examples therefore, specifically point out the preferred embodiments of the present invention, and are not to be construed as limiting in any way the remainder of the disclosure.

Example 1: Precursors

[0046] The precursors used to synthesize the polymers of the invention can be employed in both solution phase approaches as well as controlled growth on a substrate. Diboranes and organodilithium compounds are both used to synthesize the anionic polymers of the invention by the methods described herein. Example of dihoranes include benzenediborane and bis(dimethylboryl)benzene, while organolithium compounds include lithium salts such as the dilithium salts of 1,4-bis(methylamino)benzene and p-xylene, both obtainable by lithiation from alkylithium reagents.

Example 2: Solution Phase Polymer Synthesis

[0047] Solution-phase preparation of borate heteropolymers can be achieved by the mixing of 1:1 solutions of diborane and organodilithium reagents to generate short polymers. Step growth polymerization in solution generally results in short oligomeric segments due to polymer termination by the excess reagent. For this reason, reagents are measured with high analytical precision to obtain a 1:1 ratio of reagents as accurately as possible. The product is a solid, amorphous mixture of oligomers or short polymers, which are dried into a film by solvent evaporation and examined for conductivity properties using electrochemical impedance spectroscopy (EIS). Physical property characterization include thermal analysis , differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA), molecular weight and molecular weight distribution by size exclusion chromatography (SEC), and mechanical properties by dynamic mechanical analysis (DMA). The materials are structurally characterized using mass spectrometry, X-ray diffraction, and .sup.1H NMR spectroscopy. The absence of Lewis basic lone pair electrons results in excellent conductivity. While the amidoborane polymers technically have one lone pair, it is delocalized into the phenyl ring, making it less available for binding to lithium. The xyleneborane polymers typically exhibit superior conductivity due to the complete absence of lone pair electrons (FIG. 4).

Example 3: Growth of Oriented Polymers on Substrate

[0048] Controlled growth of oriented, low-affinity polymers can be achieved directly onto a fabricated electrode. While electrode-electrolyte interface issues are typically a challenge, for purposes of measurement of ionic conductivities, the polymers can be grown onto a conductive gold electrode by attachment to a self-assembled monolayer (SAM). The initial SAM can be constructed at the gold surface using a p-hydroxythiophenol, and the step growth begins with attachment of diborane to the SAM. The polymers can be grown to exact chain lengths by a sequential, alternating dip-rinse-dip cycle, where the SAM-coated substrate is dipped in the following sequence: diborane: rinse: organolithium precursor: rinse, then repeat. With each dip into a reagent, the polymer grows by one unit (FIG. 5). These films can be characterized using EIS, TGA, DSC, AFM and quartz crystal microbalance. As these polymers grow with high fidelity onto a crystalline gold surface, a crystalline material can be obtained, in which case the polymers can be structurally characterized using X-ray diffraction to obtain precise information on the 3D structure and constellation of the polymers and, optionally, the resting location of the lithium ions.

Example 4: Attachment to Composite Ceramics or Electrodes

[0049] Directional borane polymers are also grown on SiO.sub.2 surfaces or onto silicon substrates that have been oxidized on one side (to form SiO.sub.2, and functionalized with organo or chlorosilanes as the initial monomer. Hybrid ceramic/organic separators can be fabricated in this manner, since it has been already demonstrated that a SiO.sub.2 layer (200 nm) functionalized with polyethylene glycol silanes and lithium salts on a LISCION membrane has little interfacial resistance, with similar conductivity for LISCION with or without SiO.sub.2 between stainless steel electrodes. Interfaces to Li/Si alloys can also fabricated, where a thin Si layer on top of a Li/Si anode can be oxidized (to form SiO.sub.2), followed by functionalization using alkyl silanes.

[0050] The disclosures of each and every patent, patent application, and publication cited herein are hereby incorporated herein by reference in their entirety. While this invention has been disclosed with reference to specific embodiments, it is apparent that other embodiments and variations of this invention may be devised by others skilled in the art without departing from the true spirit and scope of the invention, The appended claims are intended to be construed to include all such embodiments and equivalent variations.