WO2025049319A1

WO2025049319A1 - Highly conductive boron-containing polymer electrolytes and methods and compositions thereof

Info

Publication number: WO2025049319A1
Application number: PCT/US2024/043663
Authority: WO
Inventors: Ishrat Khan
Original assignee: Clark Atlanta University Inc
Current assignee: Clark Atlanta University Inc
Priority date: 2023-08-25
Filing date: 2024-08-23
Publication date: 2025-03-06
Anticipated expiration: 2026-02-25

Abstract

Disclosed herein are highly conductive polymer-boron containing compounds of Formulae I and II and electrolytes and their use for lithium batteries.

Description

HIGHLY CONDUCTIVE BORON-CONTAINING POLYMER ELECTROLYTES AND METHODS AND COMPOSITIONS THEREOF

BACKGROUND

[0001] Clean and renewable energy sources utilized at a higher level than currently used would minimize the adverse impact of using fossil fuels by reducing overall carbon emissions. (1-5) Consequently, the need to decrease dependence on fossil fuels and mitigate CO2 emissions is of global interest and necessitates the development of effective and efficient high-energy-density power sources. (6-8). Promising energy storage devices are the lithium-ion battery (LIB) and the Li-air battery (LAB), both of which uses lithium ions as the main component of its electrochemistry. Li batteries are rechargeable batteries commonly employed in portable electronic devices, electric vehicles, and aerospace applications. (5,6, 9-13) The electrolyte is an essential component of Li- ion batteries which facilitates the movement of lithium ions between the cathode and the anode during charge and discharge cycles. Traditional electrolytes consist of lithium salts dissolved in organic solvents, however, these electrolytes have safety issues such as leakage, flammability, and dendrite formation. There is a need for new electrolytes with improved ionic conductance for use in Li batteries.

BRIEF DESCRIPTION OF FIGURES

[0002] Figure 1 depicts the three interactions within an electrolyte containing both acidic and basic atoms in the polymer structure.

[0003] Figure 2 depicts the dispersion mechanism of Li-TFSI into the polymer matrices with and without the boron centers. Insets: the ion coordination in conventional PEO and the Lewis-acidic polymer and the calculated charge density at HOMO and LUMO levels. Brown circles show the position of the boron center and the positions of charge complexes formation.

[0004] Figure 3 depicts a 500 MHz 'H NMR spectrum of TPB350 in CDCh.

[0005] Figure 4 depicts glass transition temperature of TB systems with different Li salt ratios. [0006] Figure 5 depicts the changes in C-B bond stretching in the Lewis-acidic (PEO with boron- centers) polymer matrices with (a) and without (b) the Li-TFSI. Pink, green, white, and blue represent boron, carbon, hydrogen, and nitrogen. [0007] Figure 6 depicts simulated IR spectra showing peaks of the C-B bond at 1040 cm'¹ in the (a) Pure triglyme boron and at 1052 cm'¹ in the (b) blended triglyme boron, and experimental FT- IR spectra showing peaks of CB at 1045 cm'¹ in the (c) pure TPB350 and 1054 cm'¹ in the (d) TPB350/LiTFSI.

[0008] Figure 7 depicts the synthesis of Tri-pegylated Boron (TPB35O).

[0009] Figure 8 show a schematic of the conceptual, computational, and experimental design of highly conductive boron containing electrolytes.

[0010] Figure 9 depicts the ionic conductivities of the TPB350/LiTFSI electrolytes at [EO]: [Li⁺] ratios of 5, 15, 25, and 35 as a function of temperature. PE0/P2VP/LiC104 data from reference 22.

[0011] Figure 10 depicts in (a) a top view molecular model and in (b) the structure of [3-CD molecule.

[0012] Figure 11 shows the IR spectra of allyl-[3-cyclodextrin (A-J3-CD) indicating the disappearance of OH group of [3-CD to form A-0-CD.

[0013] Figure 12 shows 'HNMR spectra of [3-CD starting material and the A-[3-CD the product.

[0014] Figure 13 shows the IR spectra indicating the differences between A-[3-CD and [3-CD-G- B-MPEG.

[0015] Figure 14 shows the 'HNMR spectra of A-[3-CD and [3-CD-G-B-MPEG.

[0016] Figure 15 shows Nyquist plots of GPEs showing the bulk resistance used to determine the ionic conductivity.

[0017] Figure 16 shows the lithium transference number (LTN) of (a) GPE-4 and (b) GPE-5.

[0018] Figure 17 shows the linear sweep voltammetry (LSV) results of the GPE samples.

[0019] Figure 18 shows thermal analysis of (a) thermal gravimetric analysis (TGA), and (b) differential scanning calorimetry (DSC) of GPE-4 and GPE-5.

DETAILED DESCRIPTION

[0020] To address the need for improved electrolytes for lithium batteries, a highly conducting polymer electrolyte has been developed. Computational modeling was used to assist in the selection of certain molecular elements (Figure 8). The electrolyte includes within the molecular structure both the acidic boron and the basic oxygen atoms. Because of the presence of the boron and the oxygen atoms within the structure, it interacts with both the anion and the cation of the dissolved salt and functions as an ion separator by increasing the bond length between the anion and the cation. The consequence of increasing the bond length is the weakening of the electrostatic interaction between the anion and the cation resulting in decreased aggregation within the electrolyte matrix leading to higher ionic conductance. The new electrolytes show ionic conductivity values of 10'³ S cm'¹ at 25 °C which is suitable values for use in lithium batteries. The approach described herein demonstrates the use of computational modeling in combination with experimental studies to design and develop promising electrolytes for lithium batteries.

[0021] The presently disclosed subject matter will now be described more fully hereinafter. However, many modifications and other embodiments of the presently disclosed subject matter set forth herein will come to mind to one skilled in the art to which the presently disclosed subject matter pertains having the benefit of the teachings presented in the foregoing descriptions. Therefore, it is to be understood that the presently disclosed subject matter is not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. In other words, the subject matter described herein covers all alternatives, modifications, and equivalents. In the event that one or more of the incorporated literature, patents, and similar materials differs from or contradicts this application, including but not limited to defined terms, term usage, described techniques, or the like, this application controls. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in this field. All publications, patent applications, patents and other references mentioned herein are incorporated by reference into their entirety.

Definitions

[0022] Unless otherwise defined, all terms (including 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. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the present application and relevant art and should not be interpreted in an idealized or overly formal sense unless expressly so defined herein. The terminology used in the description of the invention herein is for the purpose of describing particular aspects only and is not intended to be limiting of the invention. In case of a conflict in terminology, the present specification is controlling.

[0023] The term “alkyl” as used herein is a branched or unbranched saturated hydrocarbon group of 1 to 6 carbon atoms, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, t-butyl, pentyl, hexyl, and the like.

[0024] The term “alkoxy” as used herein is an alkyl group bound through a single, terminal ether linkage; that is, an “alkoxy” group may be defined as -OR where R is alkyl as defined above.

[0025] As used herein, the term “and/or” refers to and encompasses any and all possible combinations of one or more of the associated listed items, as well as the lack of combinations when interpreted in the alternative (“or”).

[0026] As used herein, the term “residue” or “residue of’ a chemical moiety or compound refers to a chemical moiety or compound that is bound to a molecule, whereby through the binding, at least one covalent bond has replaced at least one atom of the original chemical moiety or compound, resulting in a residue of the chemical moiety or compound in the molecule.

[0027] The term “or” refers to any one member of a particular list.

[0028] Unless otherwise apparent from the context, the term “about” encompasses values within a standard margin of error of measurement (e.g., SEM) of a stated value or variations ± 0.5%, 1%, 5%, or 10% from a specified value.

[0029] The singular forms of the articles “a,” “an,” and “the” include plural references unless the context clearly dictates otherwise. For example, the term “a protein” or “at least one protein” can include a plurality of proteins, including mixtures thereof.

[0030] Compositions or methods “comprising” or “including” one or more recited elements may include other elements not specifically recited. For example, a composition that “comprises” or “includes” a protein may contain the protein alone or in combination with other ingredients.

[0031]

PEG-based Compounds and Compositions

[0032] Polymer electrolytes used in lithium-ion polymer batteries show relatively low ionic conductivities for a number of reasons, including the aggregation of the salts within the polymer matrix. In liquid and solid solutions of the electrolytes, the majority of the dissolved salts are present as dimers, tetramers, and higher aggregates. The aggregates are non-polar compared with individually charged anions and cations and are present in higher concentrations within the electrolyte matrix (14-15). The formation of aggregates results in only a small fraction of the dissolved salts acting as mobile charge carriers. Furthermore, increasing salt content increases aggregation and does not necessarily contribute to additional charge carriers within the matrix. Within a polymeric electrolyte, there are multiple interactions. To simplify the complex set of interactions, one can consider the three interactions shown in Figure 1. The three interactions are the anion and the cation interacting with the polymer backbone and the electrostatic interaction between the anion and the cation. Optimizing the three interactions may contribute to designing and developing new electrolytes with higher conductivity. Conceptually, controlling the interaction of the anion and the cation with the polymer backbone may well weaken the electrostatic interaction between the anion and the cation.

[0033] Most polymer electrolytes are based on poly(ethylene oxide). Interest in ion-conducting polymer electrolytes started in 1973 when Wright et al. demonstrated ion transport within poly(ethylene oxide)/alkali metal salt blends. (16, 17) The publications of Wright led to the design and development of many innovative, highly conductive electrolytes in the 1980s. (18-24) The reported electrolytes contained oxygen atoms which interacts with the lithium cation and formed polymer salt complexes. It was determined in the 1980s that the segmental motion of the polymers facilitated ion transport within the electrolyte matrix. Thus, polymers with short oligo-oxy ethylene side chains and low glass transition temperatures were synthesized. Two such polymers were the comb polymers of oligo-oxy ethylene with polysiloxane and polyphosphazene backbones. (25, 26) Modified versions of the siloxane polymers have since been reported. (27-29) One significant issue with these electrolytes was that the transference number of the anions was high and anion movement was the major contributor to the overall ionic conductivity value. (30-32). Therefore, to minimize the anions' contribution to the observed ionic conductivity values, single ion (cation) conducting polymers where the anion was covalently bonded to the polymer backbone has been reported. (33-35)

[0034] Towards the development of newer electrolytes, a structure was prepared that allows for controlling the interactions illustrated in Figure 1. In ethylene oxide-based polymers, the basic oxygen atom coordinates with the lithium-ion. In these polymers, because the anion is not coordinated with the polymer backbone, the anion becomes the dominant species contributing to the overall ionic conductivity. Recent studies showed that cation diffusion could be increased by suppressing anion diffusion via the presence of Lewis acid sites. (36) The addition of different boron structures to electrolytes have been reported to anchor the anion and increase cation mobility. (37,38) An oligo(ethylene glycol) borate (OEGB) utilized as an anion trapping material led to the dissociation of LiC104 by Lewis acid-Lewis base interaction between the boron atom of the OEGB and the CIO4 anion. (39)

[0035] Disclosed herein are three design requirements to develop a new electrolyte: (i) iontransport is a function of the segmental motion of the polymers, and thus polymers with low glass transition temperatures are required, (ii) the polymer must have the ability to dissolve salts by acidbase interactions, and (iii) the polymer contains both acids and primary sites.

[0036] The approach described herein utilizes computational methods to aid in identifying electrolytes that have the desired properties described herein. As an initial step, the methods utilize a first-principles study on the effect of boron centers in polymer electrolytes using model molecules with three oligo-oxyethylene arms connected with a central boron or carbon atom (Figure 2). Energetic consequences of ion-pair dissociation and anion complexation at boron centers were calculated for Li-TFSI. Force-field-based molecular dynamics (MD) and first-principles densityfunctional calculations were used to understand interfacial chemistry and the dispersion mechanism. Calculations were performed to determine the 1 : 1 molecular ratio for the model complexes between the polymer and the salt. The initial search for stable structures was done through force-field-based MD to obtain the optimum geometry and characterize the electronic interaction between PEG and Li-TFSI. These energy minimizations were performed in a vacuum. The resultant structures were further optimized through first-principles calculations. The binding energies were extracted from first-principles analyses.

[0037] After introducing boron centers, the calculation results reveal a reduction in binding energy between Li⁺ and TFSI (~29 Kcal/mol per Li+) i.e. the ionic bond strength between Li⁺ and TFSI decreased from 133 kcal/mol to 104 kcal/mol. As seen in Figure 2, the bond length between Li⁺ and TFSI increased from 1.8 to 2.1 A after adding boron centers. In addition, the interaction between the nearest neighbor O to Li⁺ increased. The distance between O and the Li⁺ ions decreased from 2.5 A to 1.9 A after introducing boron-centers. The increase in the bond length between the anion and cation and the decrease in the electrostatic interaction suggest that a structure containing both basic and acidic sites may act as an ion separator. [0038] The charge density was calculated using the first-principles density functional theory. As seen in Figure 2, the dashed brown circles in LUMO and LUMO+1 highlight where the charge complexes are forming. The charge density distribution of LUMO+1 shows that a charged complex is formed between Li⁺, TFSI , and the nearest neighbor oxygen in the polymer matrix after introducing boron-center. Thus, the charge density of LUMO depicts the strengthening of interaction between the anion (TFSI) and the boron center. It is worth noting that the changes mentioned earlier in the charge density distribution are absent with the pure PEO polymer.

Cyclodextrin-based Compounds and Compositions

[0039] To overcome these issues polymers including polyethylene oxide (PEO) have been employed as liquid, gel and slid electrolytes due to their futures such as the ability of dissolving lithium salt. Another material that has been used to develop electrolytes is Beta-cyclodextrin (P- CD). This material is a natural cyclic oligosaccharide composed of seven glucose units, arranged in a toroidal structure as shown in Figure 10. Researchers have been exploring its potential application as an electrolyte additive in Li-ion batteries due to its unique properties. Beta- cyclodextrin molecules have a hydrophobic inner cavity and a hydrophilic outer surface, allowing them to form inclusion complexes with variety of guest molecules, including lithium salts.

[0040] As described herein, we are introducing a P-CD-grafted-boron-polyethylene glycol (P-CD- G-B-MPEG) polymer electrolytes where methoxy polyethylene glycol (Mw: 350) (MPEG 350) were grafted on the 21 arms of P-CD using boron atom via conjugated bonds. Then, P-CD-G-B- MPEG and lithium salt were blended using THF solvent to prepare the gel polymer electrolytes by the solution casting techniques. Finally, chemical, electrochemical, and thermal properties of these electrolytes were characterized.

[0041] The subject matter described herein includes but is not limited to the following embodiments:

1. A compound having a structure of Formula I:

wherein, a, b and c are each independently an integer from 1 to 15; x, y and z are each independently an integer from 1 to 6; and,

R^x, R^y and R^z are each independently a Ci-Ce alkyl.

2. The compound of embodiment 1, wherein a, b and c are each independently an integer from 5 to 10.

3. The compound of embodiment 2, wherein a, b and c are each 7.

4. The compound of any one of embodiments 1-3, wherein x, y and z are each independently an integer from 2 to 5.

5. The compound of embodiment 4, wherein x, y and z are each 3.

6. The compound of any one of embodiments 1-5, wherein R^x, R^y and R^z are each independently a C1-C3 alkyl.

7. The compound of embodiment 6, wherein R^x, R^y and R^z are each methyl.

8. An electrolyte composition comprising the compound of any one of embodiments 1-7 and a lithium salt.

9. The electrolyte composition of embodiment 8, wherein the lithium salt is a hydrophilic salt.

10. The electrolyte composition of embodiment 9, wherein the lithium salt is LiTFSI.

11. The electrolyte composition of any one of embodiments 8-10, wherein the ionic conductivity of the electrolyte composition is about l.Oxl^-3 or higher at about 25 °C. 12. A lithium battery comprising an anode, a cathode, a lithium salt and a compound of embodiment 1.

13. A lithium battery comprising an anode, a cathode, a lithium salt and an electrolyte composition of embodiment 8.

14. A method of preparing a compound of embodiment 1, comprising: contacting with stirring a Boron/solvent complex with an allyl-alkoxy PEG polymer containing an alkene bond.

15. The method of embodiment 14, wherein the Boron/solvent is Boron/THF.

16. The method of embodiment 14 or 15, wherein the allyl-alkoxy PEG polymer is an allylmethoxy PEG polymer.

17. The method of any one of embodiments 14-16, wherein the allyl-methoxy PEG polymer has a MW from about 100 to about 4000.

18. The method of any one of embodiments 14-17, wherein the allyl-methoxy PEG polymer has a MW of about 350.

19. The method of any one of embodiments 14-18, wherein the contacting is in the absence of a catalyst.

20. The method of any one of embodiments 14-19, wherein the contacting is at a temperature from about 22 °C to about 0 °C.

21. The compound of embodiment 1, having the structure:

22. A cyclodextrin-grafted-boron-polymer comprising a monomer having a structure Formula

II:

wherein, a is an integer from 6 to 8; and,

G^x, G^y and G^z are each independently selected from the group consisting of hydrogen and Q, wherein at least one of G^x, G^y and G^z is Q;

Q is

wherein, x, y and z are each independently an integer from 1 to 6; b and c are each independently an integer from 1 to 15; and,

R^x and R^y are each independently a Ci-Ce alkyl.

23. The cyclodextrin-grafted-boron-polymer of embodiment 22, wherein one or two of G^x, G^y and G^z is hydrogen.

24. The cyclodextrin-grafted-boron-polymer of embodiment 22 or 23, wherein b and c are each independently an integer from 5 to 10.

25. The cyclodextrin-grafted-boron-polymer of embodiment 24, wherein b and c are each 7.

26. The cyclodextrin-grafted-boron-polymer of any one of embodiments 22-25, wherein x, y and z are each independently an integer from 2 to 5. 27. The cyclodextrin-grafted-boron-polymer of embodiment 26, wherein x, y and z are each 3.

28. The cyclodextrin-grafted-boron-polymer of any one of embodiments 22-27, wherein R^x and R^y are each independently a C1-C3 alkyl.

29. The cyclodextrin-grafted-boron-polymer of any one of embodiments 22-28, wherein R^x and R^y are each methyl.

30. The cyclodextrin-grafted-boron-polymer of any one of embodiments 22-29, wherein a is 7 and the cyclodextrin is B-cyclodextrin.

31. The cyclodextrin-grafted-boron-polymer of any one of embodiments 22-30, wherein 50% or more of the total number of G^x, G^y and G^z in the cyclodextrin-grafted-boron-polymer is Q; or wherein 70% or more of the total number of G^x, G^y and G^z in the cyclodextrin-grafted-boron- polymer is Q; or wherein 90% or more of the total number of G^x, G^y and G^z in the cyclodextrin- grafted-boron-polymer is Q; or wherein 95% or more of the total number of G^x, G^y and G^z in the cyclodextrin-grafted-boron-polymer is Q.

32. The cyclodextrin-grafted-boron-polymer of any one of embodiments 22-31, wherein Q is

33. An electrolyte composition comprising the compound of any one of embodiments 22-32 and a lithium salt.

34. The electrolyte composition of embodiment 33, wherein the lithium salt is a hydrophilic salt.

35. The electrolyte composition of embodiment 34, wherein the lithium salt is LiTFSI.

36. The electrolyte composition of any one of embodiments 33-35, wherein the ionic conductivity of the electrolyte composition is about l.Oxl'⁴ or higher at about 25 °C.

37. A lithium battery comprising an anode, a cathode, a lithium salt and a cyclodextrin-grafted- boron-polymer of embodiment 22. 38. A lithium battery comprising an anode, a cathode, a lithium salt and an electrolyte composition of embodiment 33.

EXAMPLES

[0042] The present subject matter will be described in greater detail by way of specific examples. The following examples are offered for illustrative purposes only, and are not intended to limit the invention in any manner. Those of skill in the art will readily recognize a variety of noncritical parameters which can be changed or modified to yield essentially the same results. Efforts have been made to ensure accuracy with respect to numbers used (e.g., amounts, temperatures, etc.), but some experimental error and deviation may be present. The practice of the subject matter described herein will employ, unless otherwise indicated, conventional methods of chemistry within the skill of the art. Such techniques are explained fully in the literature.

Example 1: Synthesis of Tri-pegylated Boron (TPB350)

[0043] The tri-pegylated boron structure shown in Figure 7 was synthesized. Allyl-methoxy polyethylene glycol 350 (abbreviated AMPEG 350) was synthesized using the reaction shown in Figure 7. The tri-pegylated boron, abbreviated as TPB350, synthesis was carried out by a dropwise addition of an excess amount of Boron/THF complex into a mixture of THF solution and allylmethoxy poly-ethylene glycol 350 (AMPEG 350) at 0 °C. The reaction mixture was then stirred under N2 gas at RT overnight. After that, the reaction mixture was filtered, and the THF solvent removed by evaporated. These steps were repeated two more times to ensure each of the B-H bonds of the BH3 had reacted successfully with the alkene group of the AMPEG to form the TPB350, as shown in Figure 7. One of the advantages of this reaction was that it could be carried out in mild conduction without any catalyst. Results of FT-IR spectroscopy of the obtained product show band around 1045 cm'¹, corresponding to the stretching of the B-C bond.

[0044] 1H NMR spectrum of the synthesized product displays peaks around 1.35 ppm that corresponds to (B-CH2) and peaks around 1.57 ppm that correspond to (BCC-H2C). The singlet peak at 3.37 ppm corresponds to the methyl group (CH3-). The peaks around 3.55 ppm correspond to (BCCCH2O-), whereas those around 3.64 ppm correspond to ethylene oxide (CH2CH2O) repeating units, as shown in Figure 3.

Example 2: Preparation and testing of a boron-containing TPB350/LITFSI polymer electrolyte [0045] The preparation of polymer electrolyte was conducted by mixing TPB350 and LiTFSI salt in THF solvent for 4 hours. The THF solvent was evaporated under N2 atmosphere at room temperature. The blends were then dried in a vacuum oven for 48 hours at 50 °C. Four different electrolyte compositions were prepared with different ratios of Li⁺ to ethylene oxide (EO) repeat units were prepared.

[0046] Electrical resistivity measurements of a batch of all samples were performed using the two- probe technique to obtain their current (I)-voltage (V) characteristic curves (I-V curve). The model 6430 SMU from Keithley with Remote PreAmp is used and controlled by Lab Tracer software (Keithley Instruments, Inc.). A Lab Tracer is a powerful graphical software that runs on a PC and communicates with the instrument using the GPIB interface. A varying current is passed through the outer probes and induces a voltage in the internal voltage probes from -2.0 V to +2.0 V. A Keithley 6430 was used to measure the resistance of the samples. Resistance of the samples was determined using the two-probe method under nitrogen gas at 25 °C, 40 °C, 55 °C, and 70 °C. The measurements were carried out during both the heating and cooling cycles. Each resistance measurement was repeated eight times. Conductivity measurements were carried out with the samples sandwiched between using copper electrodes. Conductivity was calculated from the bulk resistance according to the following equation:

[0047] o = (D/ A) x R

[0048] Where o is conductivity, D is the thickness of the sample, A is the section area of the sample, and R is bulk resistance.

[0049] The ionic conductivity values of TPB350/LiTFSI complexes are listed in Table 1.

[0050] Table 1 : Ionic conductivity of TPB350/LiTFSI as a function of salt content and temperature

EO/Li⁺ G (S cm'¹) o (S cm'¹) a (S cm'¹) a (S cm'¹)

25 °C 40 °C 55 °C 70 °C

5: 1 LOxlO'³ 1.2xl0'³ 1.3xl0'³ 1.5xl0'³

15: 1 1.4xl0'³ 1.5xl0'³ 1.5xl0'³ 1.7xl0'³

25: 1 1.6xl0'³ 1.8xl0'³ 1.9xl0'³ 1.9xl0'³

35: 1 2.1xl0'³ 2.5xl0'³ 3.4xl0'³ 3.9xl0'³

[0051] Interestingly, over a wide range of salt content, the ionic conductivity was higher than 10'³ S cm'¹ at 25 °C. Furthermore, the ionic conductivity behavior of the TPB35O/LiTFSI system differs from other electrolytes in that the conductivity values are fairly independent of salt content. The TPB350/LiTFSI electrolytes are compared to a previous system as shown in Figure 9 (22). In the PE0/P2VP/LiC104 system, the initial increase in the ionic conductivity on increasing salt content has been attributed to the initial increase of charge carriers, and further increase in salt content results in the pseudo crosslinking of the polymer chains resulting in a reduction of the segmental motion which translates into higher glass transition (Tg) values. Higher Tg values lower ion mobilities within the matrix. The initial increase in ionic conductivities followed by a decrease has been observed for several electrolytes including the poly(siloxane) and the poly(phosphazene) electrolytes (25,26). In the TPB350/LiTFSI electrolytes the ionic conductivities were higher than 10'³ S cm'¹ at 25 C over a wide range of salt content making them extremely promising electrolytes for lithium batteries.

[0052] The behavior of the TPB35O/LiTFSI electrolytes may be attributed to the role the boron atom plays within the matrix. As shown in Figure 1, in the TPB350/LITFSI system both the anion and the cation interact with the polymer structure, effectively increasing the distance between the anion and the cation. The TPB350 thus, functions as an ion separator, and this, in turn, can decrease ionic aggregation. The modeling study shown in Figure 2 evinces that this may be the effect of incorporating a boron atom within the structure i.e., that the bond length between Li⁺ and TFSI would increase. The increased bond length would decrease the electrostatic interactions and thus decrease aggregation resulting in a larger fraction of the dissolved ions acting as charge carriers. The modeling study provided an approximate decrease in 29 Kcal/mol for the electrostatic interaction for the boron containing structure compared with the structure without the boron.

[0053] In Figure 4, the DSC thermograms of the TPB350/LiTFSI electrolytes are shown, and the glass transition temperature is listed in Table 2. The ion separator function is possible because both the anion and the cation interacts with the TPB350. The interaction of the TFSI to the TPB350 was predicted by the computational methods and validated by FT-IR experiments.

[0054] Table 2: Glass Transition temperature (Tg) as a Function of Salt Content for the TPB350/LiTFSI Electrolytes

[0055] The pure TPB350 shows a glass transition temperature of -71 °C. The Tg increases with in-creasing salt content. The increasing Tg can be attributed to the formation of pseudo crosslinked structure because of ion-dipole interaction (25,26). However, the effect of the increasing Tg in the TPB350/LiTFSI are relatively small when compared to the poly(siloxane) and the poly(phosphazene) electrolytes. (25,26)

[0056] The infrared spectra of the TPB350/LiTFSI was simulated using the first-principles density functional theory within the electric field linear response formalism in the CASTEP code. (40) Theoretically, infrared absorption intensities are described in terms of a dynamical matrix known as Hessian and Bom effective charges. The Born effective charge of an ion is the partial derivative of the macroscopic polarization concerning a periodic displacement of all the periodic images of that ion at zero macroscopic electric fields. The Bom effective charge tensor is calculated within the linear response formalism by applying a Gonze approximation. (41,42) Perdew-Burke- Emzerhof (PBE) parametrization of the generalized gradient approximation (GGA) was used in the calculations. A kinetic energy cutoff of 630 eV in the plane-wave basis and appropriate Monk-horst- Pack k-points 6 >< 6 x l were sufficient to converge the grid integration of the charge density and stable conformations. The classical molecular dynamics method carried out the initial search for stable structures. The obtained local energy-minimum structures were optimized through first-principles calculations with forces less than 0.001 eV/ A. For IR spectroscopy calculations, normconserving pseudopotentials were employed. Optimizing atomic positions proceeds until the change in energy is less than 1 * 10'⁶ eV per cell. The interaction between boron centers and the anion (TFSI) results in a strong electron supply and increases the B-C bond strength. Stretching frequency changes occur with the B-C bond's strength upon interaction with a donor. Our results show that the B-C bond stretched up to 1.59 A from its initial value of 1.46 A after interacting with the TFSI, while the B-C bond stretched up to 1.61A from its initial value of 1.46 A in the absence of TFSI as shown in Figure 5. The wavenumbers are proportional to energy, and angstrom is inversely proportional to the energy. In IR, a blue shift in a bond frequency corresponds to an increased frequency or shift to higher wavenumbers. A redshift indicates a decrease in frequency or shifts to lower wavenumbers. We observe a change in absorption to the blue part of the spectrum (a blue shift), indicating a population of higher frequency transitions (1040 cm'¹ to 1053 cm'¹) (Figure 6). The vibrational analysis was carried out by importing a Hessian matrix from the calculation. Vibrational mode frequencies and infrared intensities were displayed by requesting the electric field response calculation.

[0057] The experimental FT-IR spectrum of the pure TPB350 shows a band around 1045 cm'¹, corresponding to the stretching of the C-B bond. For the TPB350/LiTFSI electrolyte, on the other hand, the band corresponding to the C-B bond was detected around 1054 cm’¹ (Figure 6). These findings aligned with the simulated IR spectra which show a C-B stretching bond around 1040 cm for the polymer without LiTFSI salt and around 1052 cm’¹.

[0058] In conclusion, we have shown that computational modeling can be utilized to focus on specific design requirements to synthesize new structures for developing promising electrolytes for lithium batteries. The incorporation of the acidic boron and the basic oxygen atoms, as suggested by the computational results, within the design of the new TPB350 structure was particularly valuable. Within the TPB350/LiTFSI matrix, both the cations and the anions were interacting with the TPB structure and this result is the TPB350 acting as an ion separator i.e. increase the bond length between the anion and the cation and thus decreasing the electrostatic interaction. The interaction of the TFSI anion was predicted by computational modeling and was validated by experimental FT-IR studies. The observed ionic conductivities of the TPB/LiTFSI electrolytes were greater than 10’³ S cm’¹ at room temperatures over a large salt content making the system very promising as electrolytes for Lithium batteries. The findings suggests the tremendous potential of structures containing both acidic and basic sites as effective electrolytes for lithium batteries.

Example 3: Synthesis of allyl- -cyclodextrin (A-fi-CD)

[0059] The allylation of P-cyclodextrin (P-CD) was carried out based on published protocols with slight modifications. (44) In a vacuum oven, 10g (0.0088 mol) of p-CD was dried at 100 °C for 24 hours, and then it was dissolved by heating and stirring in 100 mL beaker containing 50 mL of DMSO. While dissolving the P-CD, 4.5 g (0. 18 mol) of NaH was added into 500 mL three-necked round bottom flask containing 150 mL of DMSO, and the solution mixture was stirred for half an hour. Then, the P-CD solution was added dropwise to the flask at RT using separatory funnel and allowed to stir overnight where highly viscous orange liquid was formed. After that, 16 mL (22.9 g, 0.18 mol) of allyl bromide was dissolved in 50 mL of DMSO and added dropwise to the flask causing vigorously evolving of H2 gas. The reaction was allowed to proceed for 24 hours where the orange liquid converted into golden liquid. The reaction mixture was quenched in 500 ml distilled water. After that, the desired product was extracted from the aqueous solution by 50 mb of chloroform three times. The separated organic portion was washed again with 500 mL of diwater three times, and then dried over calcium sulfate overnight. Then, the calcium sulfate was filtered, and the solvent was removed by rotary evaporator. After running a flush column and removing chloroform solvent, 8g (46%) of the desired product was obtained which showed the following results of spectra: FT-IR: 1648 cm'¹ (C=C), 3073 cm'¹ (=C-H) See Figure 11. 'H NMR (500 MHz, CDCh 8 ppm): a, b & c) 3.60-3.38 ppm (m); d) 3.79-3.62 ppm (m); e) 3.93-3.81 ppm (d); f) 4.20-4.10 ppm (d); g) 4.36-4.33 ppm (d); h) 6.02-6.00 ppm (m); h*) 5.88-5.83 ppm (m); j) 5.29-5.25 ppm (d); j*) 5.21-5.04 ppm (d) See Figure 12.

Example 4: Synthesis of a f-CD-grafted-boron-polyethylene glycol (f-CD-G-B-MPEG) electrolyte [0060] In a proper reactor containing 100 mL of dried THF, 8.25g (7.3mL, 0.004 mol) of A-P-CD and 11.3g (10.33mL, 0.02 mol) of AMPEG were stirred while purging with N2 gas for an hour. Then, 0.4g (28.8 mL, 0.028 mol) of BH3-THF was injected into the reaction mixture using a syringe, and the reaction mixture was allowed to stir overnight at RT. After that, the reaction was stopped, the mixture was filtered, and the solvent was removed using rotary evaporator yielding 30.63g (34mL, 21%) of the desired product which shows the following spectra: FT-IR: 1030 cm'¹ (B-C) See Figure 13. 'H NMR (500 MHz, CDCh 8 ppm): a, b & c) 3.85-3.71 ppm (m); d, e & f 3.69-3.59 ppm (m); j) 3.48-3.36 ppm (d); g) 1.60-1.55 ppm (d); h)1.49- 1.43 ppm (m), h*); i) 0.95-0.67 ppm (m) See Figure 14.

Example 5: Preparation and testing of f-CD-G-B-MPEG gel polymer electrolytes

[0061] The gel polymer electrolytes were prepared by blending the G-P-CD with Lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). Five systems were prepared where each system contains specific weight ratio of G-P-CD and LiTFSI as shown in Table 3.

[0062] Table 3: Blends of Polymer Electrolytes Systems (PESs) of GP-CD

Polymer Electrolyte Systems LiTFSI Salt (Wt %)

GPE-1 5

GPE-2 15

GPE-3 25 GPE-4 35

GPE-5 45

[0063] To characterize the electrolyte systems several analyses were conducted including electrochemical impedance spectroscopy (EIS), direct current polarization (DC), and linear Sweep Voltammetry (LSV) using Admiral instruments Squidstat Plus.

[0064] The ionic conductivity (G) was calculated using the following equation:

£>

(Eq 1) o = - Where D (cm) is the thickness of the polymer electrolytes, A (Ttr ) is the area of the electrolyte contacted with the electrodes, and Rb (o) is the bulk impedance of the polymer electrolytes obtained from the Nyquist plot.

[0065] The bulk impedance was measured using electrochemical impedance spectroscopy (EIS) technique. The Rb usually could be determined on the X-intercept (Z’) at Y (Z") = 0 at the low- frequency region of Nyquist plot as shown in Figure 15. To measure the Rb, each sample was placed in symmetrical swage lock coin-cell where stainless steel (sst) was used as both cathode and anode.

[0066] After measuring the bulk resistance of the samples, equation 1 was used to measure the ionic conductivity as shown in Table 4. Based on the ionic conductivity results, GPE-4 and GPE- 5 were used for further electrochemical characterization because of the high ionic conductivity they exhibited.

[0067] Table 4: Ionic Conductivity of Polymer Electrolyte Systems Contains Gp-CD and LiTFSI

System name LiTFSI o (S cm'¹) G (S cm'¹) o (S cm'¹) o (S cm'¹) G (S cm'¹)

(Wt %) at 25 °C at 40 °C at 55 °C at 70 °C at 85 °C

GPE-1 5 3.19 x lO-⁵ 9.27 x 10'⁵ 1.15 x lO'⁴ 1.64 x lO'⁴ 1.96 x lO'⁴

GPE-2 15 2.15 x IO'⁴ 2.27 x IO'⁴ 2.73 x IO'⁴ 3.71 x 10'⁴ 4.55 x IO'⁴

GPE-3 25 1.04 x lO'⁴ 2.28 x IO'⁴ 2.63 x IO'⁴ 3.13 x IO'⁴ 3.98 x IO'⁴ GPE-4 35 2.71 x 10’⁴ 4.34 x I O’⁴ 6.51 x IO’⁴ 6.60 x 1 O’⁴ 8.70 x 10’⁴

GPE-5 45 1.17 x 10'⁴ 2.97 x IO’⁴ 4.98 x IO’⁴ 4.98 x 1 O’⁴ 6.67 x 10'⁴

[0068] The lithium transference number (t^) is the number of moles of Li-ion transferred for one Faraday of charge transferred, and it can be calculated using the following equation:

Where AV is the polarization voltage of 20 mV, Ro and Rs are initial and steady state bulk resistances of the electrolyte obtained by EIS, and L and L are the initial and steady state currents respectively obtained via a chronopotentiometry direct current (DC) polarization (20 mV).

For the sample preparations, each polymer electrolyte was sandwiched between two lithium metal electrodes in the Swagelok cell which directly connected to the potentiostat instrument to run the following tests:

1) an open circuit of 30 second is applied.

2) Followed by potentiostatic EIS (from 0.1 Hz to 1MHz; 10 steps per decade; 0 DC bias potential; 10 mV AC excitation amplitude) to obtain R_o

3) A chronopotentiometry direct current (DC) polarization (20 mV) was applied to reach the steady state current (Is)

4) Finally, another potentiostatic EIS was run to obtain Rs

All these tests were conducted under one built experiment named Z Lithium transfer number. The LTN results are shown in Figure 16, and Table 5.

[0069] Table 5. shows the LTN of GPE-4 and GPE-5

Electrolyte system Lithium Transference Number

GPE-4 098

GPE-5 0.38

[0070] Linear sweep voltammetry was performed to determine the electrochemical stability range of polymer electrolytes. The LSV results of the GPE samples are shown in Figure 17. To determine the application voltage used in electrochemical devices, it is necessary to evaluate the potential window. For sample preparation, electrolytes were sandwiched between stainless steel (as working electrode) and lithium metal (as counter electrode). The experiment was conducted in the following conditions:

1) Apply a voltage from 0 V until the breakdown of the electrolyte (sharp increment of current)

2) The voltage sweep was at scan rate of 5 mV/s

3) The test will allow us to know the maximum voltage that could be applied when doing cyclic voltammetry test which is also the maximum voltage the electrolyte can handle.

[0071] Thermal analyses were conducted to investigate the thermal stability of the electrolyte systems. First, thermal gravimetric analysis (TGA) was conducted to investigate the stability of GPE-4 and GPE-5 which start degrading around 150 °C. Second, differential scanning calorimetry (DSC) was also used to investigate thermal properties of electrolyte systems as shown in Figure 18.

[0072] In conclusion, a [3-CD-grafted-boron-polyethylene glycol (P-CD-G-B-MPEG) was synthesized and characterized. Then, it was used to prepare several polymer electrolytes. The electrochemical and thermal properties of these electrolytes were investigated. As a result, it was found that among the five gel polymer electrolyte systems that were prepared, GPE-4 and GPE-5 have promising performance.

[0073] Many modifications and other embodiments of the inventions set forth herein will come to mind to one skilled in the art to which the inventions pertain having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the inventions are not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.

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Claims

THAT WHICH IS CLAIMED:

1. A compound having a structure of Formula I:

R^x, R^y and R^z are each independently a Ci-Ce alkyl.

2. The compound of claim 1, wherein a, b and c are each independently an integer from 5 to

10.

3. The compound of claim 1, wherein a, b and c are each 7.

4. The compound of claim 1, wherein x, y and z are each independently an integer from 2 to

5.

5. The compound of claim 4, wherein x, y and z are each 3.

6. The compound of any one of claims 1 -5, wherein R^x, R^y and R^z are each independently a C1-C3 alkyl.

7. The compound of claim 6, wherein R^x, R^y and R^z are each methyl.

8. An electrolyte composition comprising a compound of claim 1 and a lithium salt.

9. The electrolyte composition of claim 8, wherein the lithium salt is a hydrophilic salt.

10. The electrolyte composition of claim 9, wherein the lithium salt is LiTFSI.

11. The electrolyte composition of any one of claims 8-10, wherein the ionic conductivity of the electrolyte composition is about l.Oxl'³ or higher at about 25 °C.

12. A lithium battery comprising an anode, a cathode, a lithium salt and a compound of claim 1.

13. A lithium battery comprising an anode, a cathode, a lithium salt and an electrolyte composition of claim 8.

14. A method of preparing a compound of claim 1, comprising: contacting with stirring a Boron/solvent complex with an allyl-alkoxy PEG polymer containing an alkene bond.

15. The method of claim 14, wherein the Boron/solvent is Boron/THF.

16. The method of claim 14, wherein the allyl-alkoxy PEG polymer is an allyl-methoxy PEG polymer.

17. The method of any one of claims 14-16, wherein the allyl-methoxy PEG polymer has a MW from about 100 to about 4000.

18. The method of claim 17, wherein the allyl-methoxy PEG polymer has a MW of about 350.

19. The method of 14, wherein the contacting is in the absence of a catalyst.

20. The method of claim 14, wherein the contacting is at a temperature from about 22 °C to about 0 °C.

21. The compound of claim 1, having the structure:

II: II

wherein, a is an integer from 6 to 8; and,

Q is

R^x and R^y are each independently a Ci-Ce alkyl.

23. The cyclodextrin-grafted-boron-polymer of claim 22, wherein one or two of G^x, G^y and G^z is hydrogen.

24. The cyclodextrin-grafted-boron-polymer of claim 22, wherein b and c are each independently an integer from 5 to 10.

25. The cyclodextrin-grafted-boron-polymer of claim 24, wherein b and c are each 7.

26. The cyclodextrin-grafted-boron-polymer of claim 22, wherein x, y and z are each independently an integer from 2 to 5.

27. The cyclodextrin-grafted-boron-polymer of claim 26, wherein x, y and z are each 3.

28. The cyclodextrin-grafted-boron-polymer of claim 22, wherein R^x and R^y are each independently a C1-C3 alkyl.

29. The cyclodextrin-grafted-boron-polymer of claim 28, wherein R^x and R^y are each methyl.

30. The cyclodextrin-grafted-boron-polymer of claim 22, wherein a is 7 and the cyclodextrin is 13-cyclodextrin.

31. The cyclodextrin-grafted-boron-polymer of claim 22, wherein 50% or more of the total number of G^x, G^y and G^z in the cyclodextrin-grafted-boron-polymer is Q; or wherein 70% or more of the total number of G^x, G^y and G^z in the cyclodextrin-grafted-boron-polymer is Q; or wherein 90% or more of the total number of G^x, G^y and G^z in the cyclodextrin-grafted-boron-polymer is Q; or wherein 95% or more of the total number of G^x, G^y and G^z in the cyclodextrin-grafted-boron- polymer is Q.

32. The cyclodextrin-grafted-boron-polymer of any one of claims 22-31, wherein Q is

33. An electrolyte composition comprising a compound of claim 22 and a lithium salt.

34. The electrolyte composition of claim 33, wherein the lithium salt is a hydrophilic salt.

35. The electrolyte composition of claim 34, wherein the lithium salt is LiTFSI.

36. The electrolyte composition of claim 33, wherein the ionic conductivity of the electrolyte composition is about l.Oxl'⁴ or higher at about 25 °C.

37. A lithium battery comprising an anode, a cathode, a lithium salt and a cyclodextrin-grafted- boron-polymer of claim 22.

38. A lithium battery comprising an anode, a cathode, a lithium salt and an electrolyte composition of claim 33.