Rechargeable lithium-ion cell

Abstract

A rechargeable lithium-ion cell has a cell capacity and includes a positive electrode having a recharged potential and a negative electrode. The rechargeable lithium-ion cell also includes a charge-carrying electrolyte. The charge-carrying electrolyte includes a charge-carrying medium and a lithium salt. The rechargeable lithium-ion cell also includes a redox shuttle having the following structure.

##STR00001##

Description

RELATED APPLICATIONS

This application

To obtain a large redox shuttle current, the charge-carrying electrolyte can promote a large diffusion constant D to the redox shuttle and/or support a high redox shuttle concentration C. Thus the charge-carrying electrolyte can initially or eventually include a dissolved quantity of the substituted phenothiazine, substituted carbazole, substituted phenazine, and/or the redox shuttle. The redox shuttle diffusion constant D typically increases as the viscosity of the charge-carrying electrolyte decreases. Non-limiting concentrations of the substituted phenothiazine, substituted carbazole, substituted phenazine, and/or the redox shuttle in the charge-carrying electrolyte are about 0.05 M up to a limit of solubility, more than 0.1 M up to a limit of solubility, about 0.2 M up to a limit of solubility or about 0.3 M up to a limit of solubility. The concentration of the substituted phenothiazine, substituted carbazole, substituted phenazine, and/or the redox shuttle may be increased by incorporating a suitable cosolvent in the charge-carrying electrolyte. Non-limiting co-solvents include acetonitrile, benzene, ethers (e.g. dimethyl ether), esters (e.g. ethyl acetate or methyl acetate), lactones (e.g. gamma-butyrolactone), pyridine, tetrahydrofuran, toluene and combinations thereof. In other embodiments, the co-solvent is chosen from ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethylmethyl carbonate, butylene carbonate, vinylene carbonate, fluoroethylene carbonate, fluoropropylene carbonate, γ-butyrolactone, methyl difluoroacetate, ethyl difluoroacetate, dimethoxyethane, diglyme (bis(2-methoxyethyl)ether), and combinations thereof. In still other embodiments, the co-solvent is chosen from ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethylmethyl carbonate, or combinations thereof.

The redox shuttle may alternatively be described as including one or more sterically bulky groups at sites adjacent to the nitrogen atom(s). Typically, the inclusion of electron-donating groups would be expected to shift the oxidation potential of the redox shuttle to a less positive number. However, in the instant disclosure, it is surprisingly discovered that sterically bulky groups, even if they are electron-donating groups, do precisely the opposite and shift the oxidation potential of the redox shuttle to a more positive number.

In various embodiments, the redox-shuttle may be 1-CF₃-3,6-bis(t-Bu)carbazole; 1-acetyl-3,6-bis(t-Bu)carbazole; 1-acetyl-8-CF₃-3,6-bis(t-Bu)carbazole; 1,8-bis(CF₃)-3,6-bis(t-Bu)carbazole; the phenothiazines analogous to the aforementioned compounds; 1,4,6,9-tetra(t-Bu)phenazine; 1,6-bis(t-Bu)-4,9-bis(CF₃)phenazine; 1,6-bis(t-Bu)-3,8-bis(CF₃)phenazine; and/or any analogs having substitution at N such as C₁-C₂₀ alkyl, alkyl ether or oligoether, trialkylammonium alkyl, or other solubilizing groups. In other embodiments, the solubilizing group may be any known in the art.

For example, the solubilizing groups may be as described in U.S. Pat. No. 6,445,486, which is expressly incorporated herein by reference in various non-limiting embodiments. Moreover, it is also contemplated that any compounds described in the Examples below may be utilized in any embodiments described herein in various non-limiting embodiments.

Referring back to the cell itself, the cell may also include a porous cell separator disposed between the positive and negative electrodes and through which charge-carrying species (including the oxidized or reduced substituted phenothiazine, substituted carbazole, or substituted phenazine, and/or redox shuttle) may pass.

In various embodiments, the redox shuttle provides overcharge protection to the cell after at least 30, 40, 50, 60, 70, 80, 90, 100, 200, 300, 400, 500, 600, 700, 800, 900, 1,000, 1,500, 2,000, 2,500, 3,000, 3,500, 4,000, 4,500, 5,000, 5,500, 6,000, 6,500, 7,000, 7,500, 8,000, 8,500, 9,000, 9,500, 10,000, or even greater, charge-discharge cycles at a charging voltage sufficient to oxidize the redox shuttle and at an overcharge charge flow equivalent to 100% of the cell capacity during each charge-discharge cycle. Alternatively, all values and ranges of values within those values described above are hereby expressly contemplated in various non-limiting embodiments.

This disclosure also provides an article including the cell and an array of cells. The article may be any known in the art that utilizes cells (or batteries), e.g. hand-held devices, flashlights, power tools, or any of those described above. The array of cells may also be any known in the art.

Examples

Various substituted phenothiazines, substituted carbazoles, substituted phenazines, and redox-shuttles are synthesized and evaluated to determine oxidation potential. Additional theoretical calculations of oxidation potential are also performed on compounds not actually synthesized. The calculation of oxidation potential is based on the work of R. L. Wang et al., as set forth in Wang, R. L.; Buhrmester, C.; Dahn, J. R. J. Electrochem. Soc. 2006, 153, A445-A449, which is expressly incorporated by reference herein in various non-limiting embodiments.

The oxidation potential E⁰ of a redox shuttle candidate relative to a lithium-ion cell can be determined by comparing the difference in standard free energies between the B3LYP energy G⁰ (in electronvolts) between the shuttle S and its radical cation S⁺:

$E^0\left(S\right)=-\frac{\left[G^0\left(S\right)-G^0\left(S^{+}\right)\right]}{e}-1.46V$

All electrochemical measurements were performed in propylene carbonate including 0.2M tetraethylammonium tetrafluoroborate as a supporting electrolyte. Oxidation potentials were determined by averaging the anodic and cathodic peak potentials obtained via cyclic voltammetry (100 mV/s) or from differential pulse voltammetry. Ferrocene was used as an internal standard having E_0X=3.25 V vs. Li/Li⁺.

The calculations, both theoretical and actual, of various substituted phenothiazines, carbazoles, and phenazines, are set forth in the tables below.

Substituted Phenothiazine Calculations:

##STR00007##
R1 = R2	R3 = R4	R5	E calc (Li/Li+)	E exp (Li/Li+)
H	H	H	3.25	3.49
				(Commercially
				Available)
H	H	CH3	3.36	3.60
				(Commercially
				Available)
CH3	H	CH3	3.22	3.55
H	CH3	CH3	3.49	—
H	t-Bu	CH3	3.87	—
CH3	CH3	CH3	3.38	—
t-Bu	t-Bu	CH3	3.79	—
CN	H	CH3	3.84	4.01
CN	CH3	CH3	3.96	—
CN	t-Bu	CH3	4.29	—
CF3	CH3	CH3	3.89	—
CF3	t-Bu	CH3	4.15	—
CH3	CF3	CH3	3.80	—
H	H	CH(CH3)2	3.37	—
H	CH3	CH(CH3)2	3.68	—
H	H	(CH2)3N(CH2CH3)3	3.56	—
CH3	CH3	(CH2)3N(CH2CH3)3	3.67	—
CH3	t-Bu	(CH2)3N(CH2CH3)3	3.75	—
CF3	t-Bu	(CH2)3N(CH2CH3)3	4.46	—
CN	t-Bu	(CH2)3N(CH2CH3)3	4.31	—
H	H	(CH2)2N(CH3CH2)3	3.64	—
CH3	CH3	(CH2)2N(CH3CH2)3	3.71	—
CH3	t-Bu	(CH2)2N(CH3CH2)3	4.06	—
CF3	t-Bu	(CH2)2N(CH3CH2)3	4.30	—
CN	t-Bu	(CH2)2N(CH3CH2)3	4.40	—
t-Bu	CF3	CH3	3.75	—
R1 = R2	R3	R4	R5	E calc (Li/Li+)	E exp (Li/Li+)
t-Bu	CF3	H	CH3	3.49	—
t-Bu	C2H3O	H	CH3	3.42	—

Preparation of 3,7-dibromo-10-methylphenothiazine (A)

1.0 g (4.69 mmol) of 10-methylphenothiazine was dissolved in 50 mL dichloromethane and placed in a round bottom flask which was covered in foil to prevent light exposure. 3.0 g of silica gel and 1.75 g of N-bromosuccinimide (9.85 mmol) were added, and the reaction was allowed to stir overnight. The mixture was filtered to remove silica and washed with 100 mL of deionized water. The organic layer was isolated, dried over MgSO₄, filtered to remove the drying agent, and concentrated using rotary evaporation. The white crystal product was then recrystallized from ethanol.

Preparation of 3,7,10-trimethylphenothiazine (B)

1.0 g (2.7 mmol) of (A) was dissolved in 20 mL of anhydrous tetrahydrofuran (THF) under a dry N₂ atmosphere in a round bottom flask, and the reaction mixture was cooled using an ice/acetone bath. 2.2 mL (5.5 mmol) of n-butyl lithium (2.5 M solution in hexanes) was added via syringe, and the reaction was allowed to stir for 1 hour. 0.48 mL of methyl iodide (11 mmol) was added via syringe, and the solution was stirred in the cold bath for 2 hours, then removed and stirred at room temperature overnight. deionized water (100 mL) was added to the reaction and the product was extracted with diethyl ether (100 mL). The organic layer was dried over MgSO₄, filtered to remove the drying agent, and concentrated using rotary evaporation. The product was purified by column chromatography on silica using a dichloromethane/hexanes gradient.

Preparation of 3,7-dicyano-10-methylphenothiazine (C)

1.0 g (2.7 mmol) of (A) was dissolved in 20 mL of anhydrous dimethylformamide (DMF) in a round bottom under dry N₂ pressure, along with 1.0 g (11.2 mmol) of copper cyanide. The solution was heated to 150° C. and stirred overnight. Ethyl acetate (100 mL) and deionized water (100 mL) were added to the cooled solution. The organic layer was dried over MgSO₄, filtered to remove the drying agent, and concentrated using rotary evaporation. The product was purified by column chromatography on silica using acetonitrile as eluent.

Carbazole Calculations:

##STR00008##
R1 = R2	R3 = R4	R5	E calc (Li/Li+)	E exp (Li/Li+)
H	H	CH3	3.86	—
H	H	Et	3.86	4.09(irr)
				(Commercially Available)
H	CH3	CH3	3.69	—
H	t-Bu	CH3	3.89	—
H	t-Bu	t-Bu	3.94	—
t-Bu	t-Bu	CH3	3.71	4.02
CH3	CH3	CH3	3.50	3.80
Br	CH3	CH3	3.86	—
CF3	CH3	CH3	4.13	—
CN	CH3	CH3	4.28	—
Br	t-Bu	CH3	4.04	—
CF3	t-Bu	CH3	4.30	—
CN	t-Bu	CH3	4.43	—
t-Bu	CF3	CH3	4.13	4.53*
R1 = R2	R3	R4	R5	E calc (Li/Li+)	E exp (Li/Li+)
t-Bu	CF3	H	CH3	3.91	4.19*
t-Bu	C2H3O	H	CH3	3.81	4.12*
t-Bu	C2H3O	CF3	CH3	4.06
*The experimental data (E exp) was obtained using diethyleneglycol monomethylether at R5 while the calculated data (E calc) was obtained using N-methyl groups at R5. The diethyleneglycolmonomethylether is used for greater solubility in electrolytes. However, and without intending to be bound by any particular theory, it is believed that there is little or no difference in the redox potential between the compounds having the diethyleneglycolmonomethylether and those having the N-methyl groups.

Preparation of 1,3,6,8-tetra(t-butyl)carbazole (I)

16.7 g (10.0 mmol) of carbazole was suspended in 70 mL of t-butylchloride and stirred at room temperature for 20 minutes. 13.5 g of AlCl₃ was added, which resulted in the formation of a viscous reddish purple sludge. 80 mL of t-butylchloride was added to facilitate stirring, and the mixture was allowed to stir under a N₂ atmosphere for 7 days. The reaction mixture was quenched with 150 mL of DI water and the crude product was extracted with 150 mL of diethyl ether, dried over MgSO₄, filtered to remove the drying agent, and concentrated using rotary evaporation. The crude product was purified by column chromatography on silica using a dichloromethane/hexanes gradient.

Preparation of 1,3,6,8-tetra(t-butyl)-9-methylcarbazole (II)

1.06 g (2.71 mmol) of I was dissolved in 50 mL of dry tetrahydrofuran (THF). 0.56 g (16.24 mmol) of NaH was added, and the mixture was allowed to stir for 20 minutes at room temperature under a dry N₂ atmosphere. 1.03 mL (10.8 mmol) of (CH₃)₂SO₄ was added via syringe, and the mixture was allowed to stir at room temperature for 1 week. Additional portions of both NaH (0.56 g) and (CH₃)₂SO₄ (1.03 mL) were introduced at the 24 hour and 72 hour marks in order to drive the reaction to completion. The crude product was obtained by quenching the reaction with DI water, extracting with dichloromethane, drying over MgSO₄, filtering to remove the drying agent, and concentrating using rotary evaporation. The product was purified by column chromatography on silica using a dichloromethane/hexanes gradient.

Preparation of 1,3,6,8-tetramethylcarbazole (III)

1.36 mL (10.0 mmol) of 1-bromo-2,4-dimethylbenzene, 2.405 g (12.0 mmol) of 2-bromo-4,6-dimethylaniline, 0.115 g (0.05 mmol) of palladium diacetate, 1.61 mL (1.0 mmol) of tricyclohexylphosphine (1.0 mmol), 6.365 g (3.0 mmol) of K₃PO₄, and 0.5 g (0.30 mmol) of KI were added to a 200 mL 3-necked round bottom flask including 125 mL of N-methyl-2-pyrrolidone (NMP) as solvent. The flask was equipped with a condenser and stir bar, and the reaction was heated to 130° C. for 72 hours. Diethyl ether (200 mL) and DI water (200 mL) were added to the reaction after cooling to room temperature. The organic layer was washed with brine (100 mL), dried over MgSO₄, filtered to remove the drying agent and any reduced palladium, and concentrated using rotary evaporation. The product was purified by column chromatography on silica using a dichloromethane/hexanes gradient.

Preparation of 1,3,6,8,9-pentamethylcarbazole (IV)

0.239 g (1.07 mmol) of III was dissolved in 50 mL of dry THF. 0.221 g (6.42 mmol) of NaH was added, and the mixture was allowed to stir for 20 minutes. 0.406 mL (4.28 mmol) of (CH₃)₂SO₄ was then added via syringe, and the reaction was allowed to stir at room temperature under a dry N₂ atmosphere for 72 hours. The crude product was obtained by quenching the reaction with DI water, extracting with dichloromethane, drying over MgSO₄, filtering to remove the drying agent, and concentrating using rotary evaporation. The product was purified by column chromatography on silica using a dichloromethane/hexanes gradient.

Preparation of 3,6-di-t-butylcarbazole (V)

##STR00009##

5.02 g (30.0 mmol) of carbazole was dissolved in 50 mL of dichloromethane. 4.00 g (30.0 mmol) of AlCl₃ was added, and the mixture was cooled to 0° C. 5.55 g (60.0 mmol) of t-butylchloride in 20 mL dichloromethane was added slowly. After addition, the ice bath was removed and the reaction was stirred at room temperature under N₂ for 24 hours. The reaction mixture was quenched with 150 mL of deionized water and the crude product was extracted with 150 mL of dichloromethane, dried over MgSO₄, filtered to remove the drying agent, and concentrated using rotary evaporation. The crude product was purified by column chromatography on silica using a dichloromethane/hexanes gradient.

Preparation of Bis(ethylene glycol) monomethylether monotosylate (VI)

##STR00010##

A 3-neck round bottom flask was charged with 4.70 mL (40 mmol) diethylene glycol methyl ether & 40 mL pyridine. The solution was chilled in an ice bath, under N₂. To this mixture, tosyl chloride dissolved in dichloromethane was added dropwise. Once the addition was complete, the reaction temperature was allowed to rise to room temperature and stirred under N₂ for 3 hours. The crude product was added to 100 mL of deionized water, extracted with 100 mL of dichloromethane, dried over MgSO₄, filtered to remove the drying agent, and concentrated using rotary evaporation. The crude product was purified by column chromatography on silica using a dichloromethane/hexanes gradient.

Preparation of 3,6-di-t-butyl-9-diethyleneglycolmonomethylether-carbazole (VII)

##STR00011##

0.500 g (1.79 mmol) of V dissolved in a minimal amount of DMF was slowly dropped into a solution of 0.09 g (3.57 mmol) of NaH in 20 mL DMF. 0.978 g (3.57 mmol) of VI was then added dropwise. The mixture was heated to 65° C. and stirred for 24 hours under N₂. The reaction was cooled to room temperature, filtered through filter paper, poured into 100 mL of deionized water, extracted with 100 mL ethyl acetate, dried over MgSO₄, filtered to remove the drying agent, and concentrated using rotary evaporation. The crude product was purified by column chromatography on silica using a dichloromethane/hexanes gradient.

Preparation of 1-acetyl-3,6-di-t-butyl-9-(diethyleneglycolmonomethylether)carbazole (VIII)

##STR00012##

4.29 (11.25 mmol) of VII was dissolved in 50 mL of dichloromethane. 1.50 g (11.25 mmol) of AlCl₃ was added, and the mixture was cooled to 0° C. 1.77 g (62.50 mmol) of acetylchloride in 20 mL of dichloromethane was added slowly. After addition, the ice bath was removed and the reaction was stirred at room temperature under N₂ for 24 hours. Additional equivalents of AlCl₃ and acetylchloride were added after 24 h to push reaction to completion. The mixture was stirred overnight, quenched with 150 mL of deionized water, and the crude product was extracted with 150 mL of dichloromethane, dried over MgSO₄, filtered to remove the drying agent, and concentrated using rotary evaporation. The crude product was purified by column chromatography on silica using a dichloromethane/hexanes gradient.

Preparation of 3,6-di-t-butyl-1,8-diiodo-9-(diethyleneglycolmonomethylether)-carbazole (IX)

##STR00013##

1.00 g (3.26 mmol) of VII was dissolved in 10 mL dichloromethane and 10 mL acetic acid in a round bottom flask. The flask was covered with aluminum foil to shield its contents from light, then 1.51 g (6.72 mmol) of N-iodosuccinimide was added and the flask was fitted with a rubber stopper. After 24 hours, the crude product was added to 150 mL of deionized water, extracted with 150 mL of dichloromethane, dried over MgSO₄, filtered to remove the drying agent, and concentrated using rotary evaporation. The crude product was purified by column chromatography on silica using a dichloromethane/hexanes gradient.

Preparation of 3,6-di-t-butyl-1,8-ditrifluoromethyl-9-(diethyleneglycol monomethylether)carbazole (X)

##STR00014##

In a dry nitrogen glove box, a round bottom flask was charged with 0.1254 g (1.267 mmol) of CuCl, 0.1439 g (1.282 mmol) of KOt-Bu, 0.2063 g (1.1448 mmol) of 1,10-phenanthroline and 2.5 mL of anhydrous deaerated DMF. The reaction mixture was stirred at room temperature for 30 minutes in the glovebox. 185 μL (1.252 mmol) of TMSCF₃ (trifluoromethyltrimethylsilane) was added by micro-syringe to the flask and stirred at room temperature for an additional 60 minutes. Stirring was stopped, and 0.1703 g (0.2690 mmol) of (5) was added, then the flask was capped with a septum and removed from the glove box. The mixture was stirred in an oil bath for 44 hours at 50° C. The reaction mixture was cooled to room temperature. Diluted with 10 mL of diethyl ether, filtered through a pad of Celite (three times). The filtrate was washed in a separatory funnel w/sat. aq. NaHCO₃, draining the aqueous layer after each wash. The solution was then dried with Na₂SO₄, gravity filtered to remove the Na₂SO₄, and concentrated using rotary evaporation.

Preparation of 3,6-di-t-butyl-1,8-dibromo-9-(diethyleneglycol monomethylether)carbazole (XI)

##STR00015##

0.545 g (1.43 mmol) of VII was dissolved in 20 mL dichloromethane, along with 2.83 g (47.19 mmol) silica in a round bottom flask. The flask was covered with aluminum foil to shield its contents from light, then 0.561 g (3.15 mmol) N-bromosuccinimide was added and the flask was fitted with a rubber stopper. After 24 hours, the crude product was added to 150 mL of deionized water, extracted with 150 mL of dichloromethane, dried over MgSO₄, filtered to remove the drying agent, and concentrated using rotary evaporation. The crude product was purified by column chromatography on silica using a dichloromethane/hexanes gradient.

Preparation of 1-Acetyl-8-bromo-3,6-di-t-butyl-9-(diethyleneglycol monomethylether)carbazole (XII)

##STR00016##

0.99 g (2.60 mmol) of VIII was dissolved in 20 mL dichloromethane, along with 5.15 g (85.8 mmol) silica in a round bottom flask. The flask was covered with aluminum foil to shield its contents from light, then 0.905 g (5.20 mmol) N-bromosuccinimide was added and the flask was fitted with a rubber stopper. After 24 hours, the crude product was added to 150 mL of deionized water, extracted with 150 mL of dichloromethane, dried over MgSO₄, filtered to remove the drying agent, and concentrated using rotary evaporation. The crude product was purified by column chromatography on silica using a dichloromethane/hexanes gradient.

Phenazine Calculations:

##STR00017##
							E calc	E exp
R3 = R4	R9	R1	R2	R10	R7 = R8	R5 = R6	(Li/Li+)	(Li/Li+)
H	H	H	H	H	H	CH3	2.71	—
CH3	H	H	H	H	CH3	CH3	2.91	—
t-Bu	H	H	H	H	H	CH3	3.28	—
t-Bu	H	H	H	H	t-Bu	CH3	3.54	—
t-Bu	CF3	H	H	CF3	t-Bu	CH3	3.56	—
t-Bu	CF3	H	CF3	H	t-Bu	CH3	4.08	—

As set forth above, the phenazine data shows an unexpected a shift from a low oxidation potential (2.71) for a compound with no extra substituents to 2.91 for a compound with methyl substituents to 3.54 for a compound with 4 t-butyl substituents. The potential can be further increased by adding electron-withdrawing substituents at the sites not adjacent to the N atoms.

In addition, the phenothiazine data shows the unexpected effects of substituents R³ and R⁴, especially relevant for methyl and t-butyl, and also shows that the oxidation potential can be further customized by adding electron-withdrawing groups R¹ and R² (non-adjacent to nitrogen).

The carbazole data shows that methyl groups have a smaller steric effect (potentially due to the molecular structure of the ring system, i.e., that is, more “splayed”). However, the oxidation potential of compound II is unexpectedly over 4V, even after addition of four strongly electron-donating groups, and the oxidation is reversible, which is also unexpected.

Some examples focus on t-butyl substituents para to the N for ease of synthesis while still allowing for substitution at the 1,8 carbons (carbazole) or 1,9 carbons (phenothiazine). The observed effect is typically greater with larger groups at 1,8 (or 1,9) positions. However, substitution with trifluoromethyl or acetyl still shows a significant effect. For example, the calculated value for 3,6-di-CF₃-1,8-di-t-Bu-9-methylcarbazole is 4.30 V as compared to 4.13 V for 1,8-di-CF₃-3,6-di-t-Bu-9-methylcarbazole.

One or more of the values described above may vary by ±5%, ±10%, ±15%, ±20%, ±25%, etc. so long as the variance remains within the scope of the disclosure. Unexpected results may be obtained from each member of a Markush group independent from all other members. Each member may be relied upon individually and or in combination and provides adequate support for specific embodiments within the scope of the appended claims. The subject matter of all combinations of independent and dependent claims, both singly and multiply dependent, is herein expressly contemplated. It is contemplated that any and all values or ranges of values between those described above may also be utilized. Moreover, all combinations of all chemistries, compounds, and concepts described above, and all values of subscripts and superscripts described above, are expressly contemplated in various non-limiting embodiments. The disclosure is illustrative including words of description rather than of limitation. Many modifications and variations of the present disclosure are possible in light of the above teachings, and the disclosure may be practiced otherwise than as specifically described herein.

Claims

1. A rechargeable lithium-ion cell having a cell capacity and comprising:

A. a positive electrode having a recharged potential;

B. a negative electrode;

C. a charge-carrying electrolyte comprising a charge-carrying medium and a lithium salt; and

D. a redox shuttle having the following structure:

2. A rechargeable lithium-ion cell having a cell capacity and comprising:

A. a positive electrode having a recharged potential;

B. a negative electrode;

C. a charge-carrying electrolyte comprising a charge-carrying medium and a lithium salt; and

D. a redox shuttle having the following structure:

3. The rechargeable lithium-ion cell of claim 2 wherein each of R¹ and R² is independently an alkyl group having 1-12 carbon atoms or a haloalkyl group having 1-12 carbon atoms.

4. The rechargeable lithium-ion cell of claim 2 wherein each of R¹ and R² is independently an alkyl group having 1-6 carbon atoms.

5. The rechargeable lithium-ion cell of claim 2 wherein each of R³ and R⁴ is independently an alkyl group having 1-12 carbon atoms, a haloalkyl group having 1-12 carbon atoms, a acetyl group, a haloacetyl group, or a hydrogen atom.

6. The rechargeable lithium-ion cell of claim 2 wherein each of R³ and R⁴ is independently an alkyl group having 1-6 carbon atoms.

7. The rechargeable lithium-ion cell of claim 2 wherein one of R³ and R⁴ is a hydrogen atom and the other of R³ and R⁴ is not a hydrogen atom.

8. The rechargeable lithium-ion cell of claim 2 wherein R⁵ is an alkyl group having 1-12 carbon atoms, an alkylether group having 1-12 carbon atoms, or a trialkylammoniumalkyl group having 1-12 carbon atoms.

9. The rechargeable lithium-ion cell of claim 2 wherein R⁵ is an alkyl group having 1-6 carbon atoms.

10. The rechargeable lithium-ion cell of claim 2 wherein said redox shuttle is dissolved in the charge-carrying electrolyte.

11. The rechargeable lithium-ion cell of claim 2 wherein said redox shuttle has an oxidation potential from 3.5 to 5 V as compared to Li/Li⁺.

12. The rechargeable lithium-ion cell of claim 2 wherein said redox shuttle provides overcharge protection to said rechargeable lithium-ion cell after at least 10 charge-discharge cycles at a charging voltage sufficient to oxidize said redox shuttle and at an overcharge charge flow equivalent to 100% of cell capacity during each charge-discharge cycle.

13. The rechargeable lithium-ion cell of claim 2 wherein said redox shuttle provides overcharge protection to said rechargeable lithium-ion cell after at least 500 charge-discharge cycles at a charging voltage sufficient to oxidize said redox shuttle and at an overcharge charge flow equivalent to 100% of cell capacity during each charge-discharge cycle.

14. The rechargeable lithium-ion cell of claim 2 wherein said redox shuttle is present in an amount from 1 to 10 percent by weight based on a total weight of said charge-carrying electrolyte.

15. The rechargeable lithium-ion cell of claim 2 wherein said positive electrode comprises LiFePO₄, Li₂FeSiO₄, MnO₂, Li_xMnO₂, LiNiMnCoO₂, and/or LiNiCoAlO₂, wherein x is 0.3 to 0.4.

16. The rechargeable lithium-ion cell of claim 2 wherein said negative electrode comprises graphitic carbon, lithium metal or a lithium alloy.

17. The rechargeable lithium-ion cell of claim 2 wherein said charge carrying medium comprises ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethylmethyl carbonate or combinations thereof.

18. A rechargeable lithium-ion cell having a cell capacity and comprising:

A. a positive electrode having a recharged potential;

B. a negative electrode;

C. a charge-carrying electrolyte comprising a charge-carrying medium and a lithium salt; and

D. a redox shuttle having the following structure:

19. An article comprising the rechargeable lithium-ion cell of claim 2.

20. An array comprising two or more of said rechargeable lithium-ion cells of claim 2.

21. The rechargeable lithium-ion cell of claim 18 wherein each of R¹ and R² is independently an alkyl group having 1-12 carbon atoms.

22. The rechargeable lithium-ion cell of claim 18 wherein each of R³ and R⁴ is independently an alkyl group having 1-6 carbon atoms or a haloalkyl group having 1-12 carbon atoms.

23. The rechargeable lithium-ion cell of claim 18 wherein said redox shuttle has an oxidation potential from 3.5 to 5 V as compared to Li/Li⁺.

24. An article comprising the rechargeable lithium-ion cell of claim 18.

25. An array comprising two or more of said rechargeable lithium-ion cells of claim 18.