WO2011031401A2

WO2011031401A2 - Lithium non-fluorinated and fluorinated phenyl trifluoro borate salts for non-aqueous battery electrolytes

Info

Publication number: WO2011031401A2
Application number: PCT/US2010/044947
Authority: WO
Inventors: Hung Sui Lee; Xiao-qing YANG; James Mcbreen
Original assignee: Brookhaven Science Associates Llc
Priority date: 2009-08-28
Filing date: 2010-08-10
Publication date: 2011-03-17
Also published as: WO2011031401A3

Abstract

Novel non-fluorinated and fluorinated phenyltrifluoroborate compounds which act as ionic conducting agents in non-aqueous batteries have been developed through this invention. When used as non-aqueous battery electrolytes, the lithium non-fluorinated and fluorinated phenyltrifluoroborate salts enhance conductivity, lithium ion transference number, and Solid Electrolyte Interphase (SEI) formation capability during the formation cycling.

Description

TITLE OF THE INVENTION

Lithium Non-Fluorinated and Fluorinated Phenyl Trifluoro Borate Salts for Non- Aqueous Battery Electrolytes

CROSS-REFERENCE TO A RELATED APPLICATION

[0001] This application claims the benefit under 35 U.S.C. 119(e) of U.S. Provisional

Application no. 61/237,756 filed on August 28, 2009, the content of which is incorporated herein in its entirety.

STATEMENT OF GOVERNMENT LICENSE RIGHTS

[0002] This invention was made with Government support under contract number

DE-AC02-98CH10886, awarded by the U.S. Department of Energy. The Government has certain rights in the invention.

BACKGROUND OF THE INVENTION

I. FIELD OF THE INVENTION

[0003] The present invention relates generally to electrochemical storage devices containing a non-aqueous lithium-based electrolyte with high ionic conductivity, low impedance, and high thermal stability. More particularly, this invention relates to the design, synthesis, and application of novel lithium phenyl trifluoro borate based compounds which act as ionic conducting agents in non-aqueous battery electrolytes.

II. BACKGROUND OF THE RELATED ART

[0004] The demand for lithium secondary batteries to meet high power and high- energy system applications has resulted in substantial research and development activities to improve their safety, as well as performance. [0005] At present, lithium and lithium ion batteries normally operate in a voltage range from 3.0 to 4.2 V vs. Li/Li⁺. In liquid or gel-polymer lithium-ion batteries, it is common to use an electrolyte containing alkyl carbonates, such as ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethylmethyl carbonate (EMC), and propylene carbonate (PC). However, these non-aqueous electrolytes are not thermodynamically stable in the operational voltage range of the batteries and it is possible that electrolyte reduction and oxidation could occur at the anode and cathode, respectively. In order to prevent such an occurrence, a complete and stable solid electrolyte interphase (SEI) needs to be formed. Indeed, electrolyte solvents that are capable of good performance in lithium-ion batteries are those which possess an ability to stabilize the graphite anode by forming a protective SEI which inhibits further reactions of the electrolyte while permitting Li⁺ charge transfer between the anode and the electrolyte. (E. Peled, J. Electrochem Soc, 126, 2047, (1979); incorporated herein by reference). Thus, the development of electrolytic salts which can enhance performance through better SEI formation and increased thermal stability and conductivity are quite important and desirable.

[0006] While performance is critical in choosing the electrolyte for commercial applications, the performance is only one factor and must be considered together with other key factors such as cost and safety. In recent years, extensive world-wide efforts have been undertaken to develop systems that meet such criteria. Nonetheless, all lithium salts including commercially available salts, such as lithium hexafluorophosphate (LiPF₆), lithium tetrafluoroborate (LiBF₄), lithium trifluoromethane-sulfonyloxide (L1OSO2CF3), lithium bis(trifluoromethanesulfonyl)imide (LiN(S0₂CF₃)₂), lithium bis(trifluoroethanesulfonyl)- imide (LiN(S0₂CF₂CF₃)₂), and salts under development, such as lithium bis(trifluoro- methanesulfonyl)carbonade LiC(S0₂CF₃)₂, lithium bis(oxalate)borate (LiBOB), lithium tris(trifluoromethanesulfonyl)triphosphate (LiPF₃(S0₂CF₃)3) do not fully meet the above three requirements of cost, performance, and safety.

[0007] By way of example, most commercial lithium-ion batteries use electrolytes containing lithium hexafluorophosphate (LiPF₆). This salt has the necessary prerequisites for use in high-energy cells, i.e. it is easily soluble in aprotic solvents, it leads to electrolytes having high conductivities, and it has a high level of electrochemical stability. (Sloop, SE, et al. Electrochem. and Solid State Lett., 4, A42; (2001); incorporated herein by reference). LiPF₆, however, also has serious disadvantages, which are mainly to be attributed to its lack of thermal stability (Krause, LJ., et al., Power Sources 68:320, (1997); incorporated herein by reference). In solution, LiPF₆ dissolves over time into LiF and PF₅, which can lead to a cationic polymerization of the solvent, caused by the Lewis acid PF₅. Upon contact with moisture, the caustic hydrofluoric acid (HF) is released, which not only makes handling more difficult, because of its toxicity and corrosiveness, but also can lead to the (partial) dissolution of the transition-metal oxides (for example LiMn₂0 ) used as cathode material that can cause the capacity fading and the impedance increase during charge-discharge cycling.

[0008] Other commercially available salts are also problematic. For example, L1BF4 exhibits poor solubility and may be contaminated with hydrofluoric acid. Both L1OSO2CF3 and LiN(S0₂CF₃)₂ are highly corrosive to aluminum substrates at potentials above 2.79 V and 3.67 V, respectively. Lithium methide, LiC(S0₂CF₃)₂, (U.S. Pat. No. 5,273,840; incorporated herein by reference) is presently under development, but the price of its production may be an obstacle for consumer applications. [0009] One solution that has been considered is to use organic lithium salts, which in general are believed to be safer than inorganic lithium salts and may produce higher conductivity. Typical examples include lithium borates and phosphates, which are well known thermally stable salts, however, with equally well known disadvantages. For example, lithium tetrkis(haloacyloxy) borates, Li[B(OCORX)₄] (Yamaguchi, et al., J. Electrochem. Soc, 150, A312 (2003); incorporated herein by reference), are less conductive and thermally less stable as compared with LiPF₆. Lithium bis(polyfluorodiolato) borates, represented by LiB[OCPh(CF₃)₂]₄ (Strauss, et al, J. Electrochem. Soc , 150, A1726 (2003); incorporated herein by reference), have poor solubility in common carbonate solvents. Lithium tris(polyfluorodiolato) phosphates (Nanbu et al., Electrochem. Solid-State Letters, 5(9), A202 (2002) and Eberwein, et al., J. Electrochem. Soc , 150, A994 (2003); incorporated herein by reference) are difficult to prepare and have low oxidative decomposition potential. Lithium bis(oxalato) borate, LiBOB (German Pat. DE19829030 CI (1999); incorporated herein by reference) shows unsatisfactory performance in battery systems containing L1C0O₂, poor solubility in common carbonate solvents, and hydrolytic instability. (Xu et al, Electrochemical and Solid State Letters, 4(1) E1-E4 (2001); incorporated herein by reference).

SUMMARY OF THE INVENTION

[0010] Having recognized the above and other considerations, the inventors determined that there is a need to design and synthesize lithium salt(s) which act as ionic conducting salts in non-aqueous battery electrolytes with better conductivity, higher lithium ion transference number, and superior SEI formation capability during the formation cycling while maintaining chemical stability and reduced moisture sensitivity. Thus, certain embodiments of the present invention provide a non-aqueous electrolyte salt for use in electrochemical systems with better conductivity, higher lithium ion transference number, and superior SEI formation capability during the formation cycling than the electrolytes containing LiPF₄, while maintaining chemical stability and reduced moisture sensitivity compared to electrolytes containing LiPF₆.

[0011] In one embodiment, this is accomplished by a non-aqueous electrolyte that contains a lithium phenyltrifluoroborate salt (LiPTFB), represented by the formula (1)

where R can be H, one or more fluorine bearing moieties, or a combination thereof, dissolved in a non-aqueous solvent. A non-limiting example of the fluorine-bearing moiety is a fluorine, fluoromethyl, difluoromethyl, trifluoromethyl, 1-fluoroethyl, 1,1-difluoroethyl, 1,1 ,2-trifluoroethyl, 1 , 1 ,2,2-tetrafluoroethyl, pentafluoroethyl, or any other fluorinated/ nonfluorinated alkyl having from 1 to 6 carbon atoms, which may be linear or branched.

[0012] In another embodiment, the LiPTFB is lithium non-fluorinated phenyltrifluoro-borate, lithium 2-fluorophenyltrifluoroborate, lithium 3,5-difluorophenyl- trifluoroborate, lithium 2,5,6-trifluorophenyltrifluoroborate, lithium 2,3,5,6-tetrafluoro- phenyltrifluoroborate, lithium pentafluorophenyltrifluoroborate, lithium 2-trifluoromethyl- phenyltrifluoroborate, lithium 2,5-bis(trifluoromethylphenyl)trifluoroborate, or lithium 3,5- bis(trifluoromethylphenyl)trifluoro-borate.

[0013] In yet another embodiment, the non-aqueous electrolyte may contain in addition to LiPTFB, other organic and/or inorganic salts, such as lithium orthoborates, lithium orthophosphates, and lithium salts that are perhalogenated or peroxidated. A non- limiting example of the non-aqueous electrolyte that contains two or more salts is LiPTFB/LiPF₆ or LiPTFB/LiBOB.

[0014] In yet another embodiment, the non-aqueous electrolyte may contain in addition to salt(s) and solvent(s), other additives/anion receptors that may be used to prevent or to reduce gas generation of the electrolytic solution as the battery is charged and discharged at temperatures higher than ambient temperature, and/or to prevent overcharge or overdischarge of the battery. The additives may be further used to improve SEI formation capabilities, cathode protection, salt stabilization, safety protection, Li deposition improvement, solvation enhancement, corrosion inhibition, and wetting.

[0015] In one embodiment, the invention is directed to electrochemical cells and batteries, particularly lithium rechargeable batteries, which include an anode, a cathode and non-aqueous electrolytes containing the organic lithium salts of the present invention that exhibit one or more of the improved properties such as better conductivity, higher lithium ion transference, superior SEI formation capability, electrochemical stability, reduced moisture sensitivity, and enhanced thermal stability.

[0016] In a preferred embodiment, the electrochemical cell includes a graphite anode, a lithium mixed metal oxide (LiMMO) cathode, and a non-aqueous electrolyte that contains LiPTFB in non-aqueous solvent. In a preferred embodiment, the solvent is a binary mixed ethylene carbonate (EC) or propylene carbonate (PC) and dimethyl carbonate (DMC), i.e., EC/DMC or PC/DMC. However, the compositions of the cathode, the anode, and the electrolyte are not limited to compositions of the preferred embodiment and may comprise any compositions made apparent from the following detailed description, which is to be read in conjunction with the accompanying drawings. The scope of the invention will be limited only by the claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] FIG. 1 illustrates the chemical structure for several examples of lithium fluorinated or nonfluorinated phenyl trifluoroborate salts of the present invention.

[0018] FIG. 2 illustrates a first and second cycle voltammograms (Current (A) vs.

Potential (V vs. Li/Li⁺)) of aluminum electrode in 0.5M lithium pentafluoro- phenyltrifluoroborate solution dissolved in 1 : 1 volume ratio of PC/DMC. The electrochemical stability after the first formation cycle is > 4.5 V.

[0019] FIG. 3 illustrates charge/discharge curves of the first three cycles of (A)

Li/LiMn₂0₄ cathode and (B) Li/MCMB anode in 0.5 M lithium pentafluorophenyltrifluoroborate (LiPFPTFB) salt dissolved in 1 : 1 volume ratio of PC/DMC at 25 °C at 0.25C and 0.06C rate, respectively. FIG. 3A shows the charge/discharge of Li/LiMn₂0₄ cells in voltage range of 3.2-4.3 V. The data shows that the cell achieved an initial efficiency of 97.2% and a reversible capacity of 103 mAh/g. The Coulomb efficiency of LiMn₂0₄ cathode further increased to 99.4% and then to 99.6% during the second and third formation cycles, respectively. FIG. 3B shows the charge/discharge of Li/MCMB cells in voltage range of 0-2.5 V. The data shows that the cell cycled well and achieved an initial efficiency of 80% and a reversible capacity of 325 mAh g. This data demonstrates that a stable SEI film formation occurs on the MCMB anode in the first cycle. The Coulomb efficiency of MCMB anode further increased to 95% and then to 97% during the second and third formation cycles, respectively, indicating a stable SEI layer formation.

[0020] FIG. 4 illustrates voltage profile (V vs. hour) of an electrochemical cell with electrode Li/MCMB in two other boron-based lithium salts as references: (A) 0.5 M LiBF₄ and (B) 0.5 M LiBF₃C₃F₇ dissolved in 1: 1 volume ratio of PC/DMC. This data shows the reference salts can not form stable SEI film on the MCMB anode in PC based electrolytes, while the LiPFPTFB salt of the instant invention can form stable SEI film on the MCMB anode.

[0021] FIG. 5 shows the TGA results of lithium pentafluorophenyltrifluoroborate salts (LiPFPTFB) in comparison with two reference salts: LiBF₄ and L1BF3C3F7. This data shows that although the thermal stability of the LiPFPTFB salts is lower than the two reference salts, the LiPFPTFB still maintains the stability at temperatures of up to 180 °C, which is sufficient for the conventional use of the electrolytic salts.

[0022] FIG. 6 illustrates the conductivities of 0.5 M lithium pentafluorophenyltrifluoroborate salt (LiPFPTFB) dissolved in 1 : 1 volume ratio of PC/DMC at different temperatures, in comparison with two reference salts: L1BF4 and L1BF3C3F7. This data shows that the conductivity of the inventive LiPFPTFB salt is better than L1BF4.

DETAILED DESCRIPTION OF THE INVENTION

[0023] The above and other aspects of the invention will become more apparent from the following description and illustrative embodiments which are described in detail with reference to the accompanying drawings.

[0024] The present invention is based on the discovery of novel lithium salts of general formula (1):

where R may be hydrogen (H), a fluorine-bearing moiety, a combination of hydrogen and a fluorine-bearing moiety, or a combination of two or more fluorine bearing moieties. The lithium salt of the present invention may be used in the electrolytic solution of lithium based non-aqueous electrochemical cells (batteries) that have an anode, a cathode and an electro lytic solution. The major components, electrolytic salts, solvents, anode and cathode are each described below in turn.

I. ELECTROLYTIC SALT

[0025] The electrolytic salts are ionic salts containing at least one metal ion.

Typically this metal ion is lithium (Li⁺). The electrolytic salts function to transfer charge between the anode and the cathode of a battery. The organic lithium salts of the present invention are lithium phenyl trifluoroborate (LiPTFB) salts of formula (1):

where R may be hydrogen (H), a fluorine-bearing moiety, a combination of hydrogen and a fluorine-bearing moiety or a combination of two or more fluorine bearing moieties. The fluorine bearing moiety may be, for example, a fluorine, fluoromethyl, difluoromethyl, trifluoromethyl, 1-fluoroethyl, 1 , 1 -difluoroethyl, 1 , 1 ,2-trifluoroethyl, 1 , 1 ,2,2-tetrafluoroethyl, pentafluoroethyl, or any other fluorinated/nonfluorinated alkyl having from 1 to 6 carbon atoms, which may be linear or branched.

[0026] The non-limiting example of LiPTFB is lithium non-fluorinated phenyltrifluoroborate (2), lithium 2-fluorophenyltrifluoroborate (3), lithium 3,5-difluoro- phenyltrifluoroborate (4), lithium 2,5,6-trifluorophenyltrifluoroborate (5), lithium 2,3,5,6- tetrafluorophenyltrifluoro-borate (6), lithium pentafluorophenyltrifluoroborate (7), lithium 2- trifluoromethylphenyltrifluoroborate (8), lithium 2,5-bis(trifluoromethylphenyl)- trifluoroborate (9), and lithium 3,5-bis(trifluoromethylphenyl)trifluoroborate (10). The structures of these compounds are summarized in Table 1. Other examples of the LiPTFB are shown in FIG. 1. [0027] Table 1. Representative non-limiting examples of LiPTFB structures

[0028] The preparation of the LiPTFB salts of the present invention may be conveniently co ducted m three relatively simple synthesis steps:

(B) (C)

Step (2)

Step (3) where R may be hydrogen (H), a fluorine bearing moiety, a combination of hydrogen and a fluorine-bearing moiety, or a combination of two or more fluorine bearing moieties. [0029] Synthesis Step (1): The potassium fluorinatedphenyltrifluoroborate

(Compound (A)) can be prepared following the procedure described in Vedejs, E.R. et al., J. Org. Chem., 60, 3020 (1995) and Frohn, H.J. et al, J. Organomet. Chem., 598, 127 (2000) incorporated herein by reference in its entirety.

[0030] Synthesis Step (2): The fluorinatedphenyl difluoroborane (Compounds (B)) can be prepared following the procedure described in Frohn, H.J. et al., J. Organomet. Chem. , 598, 127 (2000) incorporated herein by reference in its entirely. Specifically, 0.05 M-0.1 M of potassium fluorinated phenyltrifluoroborate is suspended in 150 ml of fluorotrichloromethane liquid mixture. Boron trifluoride is bubbled through the mixture for one to one and a half hours until no more boron trifluoroborate is adsorbed, while the mixture is cooled by acetone-dry ice and stirred. Then the mixture is warmed to room temperature and continuously stirred for an additional two hours. The precipitates are then separated by centrifugation. The solution is distilled to obtain the pure borane compounds. lUUJ ij ayninesis

or Compound of Formula (1)) can be prepared by suspending 0.05 M of lithium fluoride in 15-20 ml of anhydrous 1 ,2-dimethoxyethane (DME). The mixture is cooled in an ice bath. Fluorinated phenyldifluoroborane is added slowly through a syringe. The mixture is then stirred at room temperature for 2-3 hours. The unreacted lithium fluoride is filtered off and the solvent is then evaporated. The liquid residue is dried at 60°C under 0.2 mm vacuum until it becomes solid. The final products are obtained through recrystallization in ether or ether-pentane solvents. Examples 1 through 9 demonstrate synthesis step (3) for the LiPTFB salt production of the present invention.

[0032] It is to be understood that the method of synthesizing LiPTFB as described above is merely exemplary. Any of a plurality of alternative methods which are well-known in the art and which are capable of forming LiPTFB with the desired purity may be employed.

[0033] The LiPTFB salt may be used alone or in combination with other electrolytic salts that include salts of chelated orthoborates, chelated orthophosphates, perhalogenated and peroxidated lithium salts. The ortho-salts salts may be used in the instant invention, for example, are lithium bis(oxalo)borate (LiBOB), lithium bis(malonato) borate (LiBMB), lithium bis(difluoromalonato) borate (LiBDFMB), lithium (malonato oxalato) borate (LiMOB), lithium (difluoromalonato oxalato) borate (LiDFMOB), lithium tris(oxalato)phosphate (LiTOP), and lithium tris (difluoromalonato) phosphate (LiTDFMP). The lithium salts that are perhalogenated, or peroxidated, for example, are LiF, Li₂0, Li₂0₂, LiPF₆, LiBF₄, LiC10₄, LiAsF₆, LiTaF₆, L1AICI₄, Li₂BioClio, and L1CF₃SO₃. Any combination of two or more of the aforementioned salts may also be used.

[0034] The concentration of LiPTFB optionally with other electrolytic salt(s) in the electrolytic solution can be in the range of about 0.01-2.5 Ivl (moles per liter). Preferably the concentration is 0.05-2.0 M.

II. SOLVENT

[0035] A solvent useful in the present invention is a non-aqueous, aprotic, polar organic substance which dissolves the solute. Blends of more than one solvent may be used. Generally, solvents may be carbonates, carboxylates, lactones, phosphates, five- or six- member heterocyclic ring compounds, and organic compounds having at least one C1-C4 group connected through an oxygen atom to a carbon. Lactones may be methylated, ethylated and/or propylated. Generally, the electrolytic solution comprises at least one solute dissolved in at least one solvent. Useful solvents that can be made for the present invention include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), dibutyl carbonate (DBC), ethyl methyl carbonate (EMC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), tetrahydrofuran, 2methyl tetrahydrofuran, 1,3-dioxolane, 1,4-dioxane, 1,2- dimethoxyethane, 1 ,2-diethoxyethane, 1,2-dibutoxyethane, acetonitrile, dimethylformamide, methyl formate, ethyl formate, propyl formate, butyl formate, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate, butyl butyrate, γ-butyrolactone, 2-methyl-Y-butyrolactone, 3-methyl-y-butyrolactone, 4-methyl-y-butyrolactone, β- propiolactone, δ-valerolactone, tnmethyl phosphate, triethyl phosphate, tris(2-chloroethyl) phosphate, tris(2,2,2-trifluoroethyl) phosphate, tripropyl phosphate, triisopropyl phosphate, tributyl phosphate, trihexyl phosphate, triphenyl phosphate, tritolyl phosphate, and combinations thereof. Other solvents may be used so long as they are non-aqueous and aprotic. and are capable of dissolving the solute salts.

[0036] In a preferred embodiment, the solvent is made from one or more carbonates selected from ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), dibutyl carbonate (DBC), ethyl methyl carbonate (EMC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC). Preferably, the solvent is a binary mixture of two carbonates, however, other mixtures are also envisioned such as between carbonates and non-carbonates, ternary mixtures and other combinations so long as they are non-aqueous and aprotic, and are capable of dissolving the solute salts.

[0037] Preferably, the solvent comprises a binary mixed organic solvent containing a

1: 1 volume ratio of EC/DMC, PC/DMC, EC/PC, EC/DMC, PC/DMC, and PC/DME or a teraary mixed organic solvent containing a 1 : 1 :1 volume ratio of EC/DMC/DEC. More preferably, the organic solvent is a binary mixed EC/DMC or PC/DMC at 1: 1 volume ratio.

III. ANODE

[0038] The anode may comprise carbon or lithium based alloy. The carbon may be in the form of graphite such as, for example, mesophase carbon microbeads (MCMB). Lithium metal anodes may be lithium mixed metal oxide (MMOs) such as LiMn0₂ and Li₄Ti₅0i₂. Alloys of lithium with transition or other metals (including metalloids) may be used, including LiAl, LiZn, Li₃Bi, Li₃Cd, Li₃Sd, LLiSi, Li₄₄Pb, LL^Sn, LiC₆, Li₃FeN₂, Li₂.₆Coo.₄N, Li₂,6Cuo.₄N, and combinations thereof. The anode may further comprise an additional material such as a metal oxide including SnO, Sn0₂, GeO, Ge0₂, ln₂0, ln₂0₃, PbO, Pb0₂, Pb₂0₃, Pb₃0₄, Ag₂0, AgO, Ag₂0₃, Sb₂0₃, Sb₂0₄, Sb₂0₅, SiO, ZnO, CoO, NiO, FeO, and combinations thereof.

[0039] The anode may further comprise a polymeric binder. In a preferred embodiment, the binder may be polyvinylidene fluoride, styrene-butadiene rubber, polyamide or melamine resin, and combinations thereof.

IV. CATHODE

[0040] The cathode may comprise a lithium metal oxide compound. In particular, the cathode may comprise at least one lithium mixed metal oxide (Li-MMO). Lithium mixed metal oxides contain at least one other metal selected from the group consisting of Mn, Co, Cr, Fe, Ni, V, and combinations thereof. For example the following lithium MMOs may be used in the cathode: LiMn0₂, LiMn₂0 , LiCo0₂, Li₂Cr₂0₇, Li₂Cr0₄, LiNi0₂, LiFe0₂, LiNi_xCoi_-x0₂ (0<x<l), LiFeP0₄, LiMn_zNii_-z0₂ (0<z<l), LiMno.5Nio.5O2, LiMno.3₃Coo_.33Ni_0.330₂, LiMc₀.5Mni.₅O , where Mc is a divalent metal; and LiNi_xCo_yMe_z0₂ where Me may be one or more of Al, Mg, Ti, B, Ga, or Si and 0<x,y,z<l . Furthermore, transition metal oxides such as Mn0₂ and V₂0₅; transition metal sulfides such as FeS₂, MoS₂ and TiS₂; and conducting polymers such as polyaniline and polypyrrole may be present. The preferred positive electrode material is the lithium transition metal oxide, including, especially, LiCo0 , LiMn₂0₄, LiNio.sCoo.isAIo_.osO^ LiFeP0₄, and LiNio.33-vIno.33Coo.330₂. Mixtures of such oxides may also be used.

[0041] The cathode may further comprise a polymeric binder. In a preferred embodiment, the binder may be polyvinylidene fluoride, styrene-butadiene rubber, polyamide or melamine resin, and combinations thereof.

V. ANION RECEPTOR/ADDITIVE

[0042] Optionally, the electrolytic solution of the present invention may comprise one or more anion receptors and/or additives at concentrations at about 0.01-1.0 M, and preferably at about 0.05-0.5 M. Use of electrolyte additives is one of the most economic and effective methods for the improvement of Li-ion battery performance. Usually, the amount of an additive in the electrolyte is no more than 5% either by weight or by volume while its presence significantly improves the cycleability and cycle life of Li-ion batteries. For better battery performance, the additives are able to: facilitate formation of solid electrolyte ίηί6φη38ε/ϊηΐει 1ΐ38β (SEI) on the surface of graphite, reduce irreversible capacity and gas generation for the SEI formation and long-term cycling, enhance thermal stability of LiPF₆ against the organic electrolyte solvents, protect cathode material from dissolution and overcharge, and improve physical properties of the electrolyte such as ionic conductivity, viscosity, wettability to the polyolefine separator, and so forth. For better battery safety, the additives are able to: lower flammability of organic electrolytes, provide overcharge protection or increase overcharge tolerance, and terminate battery operation in abuse conditions.

[0043] The additives useful for the present invention may be selected from (1) reduction-type additives, (2) reaction-type additives, (3) SEI morphology modifiers, (4) cathode protection agents, (5) LiPF₆ salt stabilizers, (6) overcharge protectors, (7) fire- retardant additives, (8) Li deposition improvers, (9) ionic salvation enhancers, (10) Al corrosion inhibitors, (11) wetting agents, and (12) viscosity diluters. A review on electrolyte additives for lithium-ion batteries may be found in Zhang, S-S. Journal of Power Sources 162 (2006) 1379-1394, the content of which is incorporated herein by reference in its entirety.

[0044] An example of additives useful in the present invention alone or in combination is vinylene carbonate (VC), vinyl ethylene carbonate, allyl ethyl carbonate, vinyl acetate, divinyl adipate, acrylic acid nitrile, 2-vinyl pyridine, maleic anhydride, methyl cinnamate, phosphonate, vinyl-containing silane-based compounds, furan derivatives that contain two double bonds in each molecule, S0₂, CS₂, polysulfide (S_x ² ), cyclic alkyl sulfites such as ethylene sulfite and propylene sulfite, aryl sulfites, N₂0, nitrate, nitrite, halogenated ethylene carbonate, halogenated lactone such as a-bromo-y-butyrolactone, methyl chloroformate, the A series of carboxyl phenol, aromatic esters, anhydride, tris(2,2,2- trifluoroethyl) phosphite (TTFP), l-methyl-2-pyrrolidinone, fluorinated carbamate, hexamethyl-phosphoramide, monomethoxy benzene class compounds, hexaethyl benzene, bipyridyl or biphenyl carbonates, difluoroanisoles, thianthrene, 2,7-diacetyl thianthrene, phenothiazine based compounds, xylene, cyclohexylbenzene, biphenyl, 2,2-diphenylpropane, phenyl-tert-butyl carbonate, phenyl-R-phenyl compounds (R = aliphatic hydrocarbon, fluorine substituted), 3-thiopheneacetonitrile, tetraalkylammonium chlorides with a long alkyl chain, cetyltrimethylammonium chlorides, lithium and tetraethylammomum salts of perfluorooctanesulfonate, perfluoropolyethers, borate, borane, borole and other compounds so long as they provide one or more benefits (1)-(12) listed above.

VI. ELECTROCHEMICAL CELL

[0045] As with most batteries, the lithium based non-aqueous electrochemical cell has an outer case made of metal or other material(s) or composite(s). This case holds a long spiral comprising three thin sheets pressed together:

[0046] (1) A positive electrode (cathode);

[0047] (2) A negative electrode (anode); and

[0048] (3) A separator.

[0049] The separator is a very thin sheet of plastic with micro pores, however, other materials may used in the present invention to separate the positive and negative electrodes while allowing ions to pass through. The cathode is generally made of metal oxide, such as lithium cobalt oxide. The anode is generally made of carbon. Both the anode and cathode are materials into which and from which lithium can migrate. When the battery charges, ions of lithium move through the electrolyte from the positive electrode to the negative electrode and attach to the carbon. During discharge, the lithium ions move back to the cathode from the anode. Inside the case these sheets are submerged in an organic solvent that acts as the electrolyte. The electrolyte is composed of one or more lithium salts, one or more solvents and optionally one or more additives.

[0050] An important aspect of the present invention is that the lithium salt consists at least of one LiPTFB that has the ability to facilitate the formation of a stable Solid Electrolyte Interphase (SEI) layer on the graphite surface of the anode during the formation cycling. [0051] It has been proposed that the main components of SEI are the decomposed products of electrolyte solvents and salts. These components include, for example, Li₂C0₃, lithium alkyl carbonate, lithium alkyloxide, and other salt moieties (Ein-Eli, Y et al. J. Electrochem. Soc. 144 (1997) LI 80; Aurbach, D. et al. Electrochem. Soc. 142 (1995) 1746; both of which are incorporated herein by reference in their entireties.) Based on this fact, two mechanisms have been proposed for the electrochemically induced reduction of carbonate- based solvents, for example ethylene carbonate (EC):

where RA is an abbreviation for "radical anion". Both of these two mechanisms are present in the process of SEI formation and compete with each other. When mechanism (I) is predominate, the reduction of solvents generates more gaseous products, and the resulting SEI is Li₂C0₃-abundant and less stable. On the other hand, mechanism (II) leads to less gaseous products and the resulting products are substantially insoluble in the electrolyte and the formed SEI is more compact and stable. It has been suggested that these two mechanisms are affected by the morphology and chemistry of graphite surface, and are associated with the catalytic activity of the fresh graphite surface. The catalytic effect has been confirmed by the strong location-dependence of SEI composition (Bar-Tow, D. et al., Electrochem. Soc. 146 (1999) 824; Peled, E. et al., J. Power Sources 97-98 (2001) 52; both of which are incorporated herein by reference in their entireties.) That is, the SEI formed in prismatic (edge) areas of a highly oriented pyrolytic graphite is enriched with inorganic compounds, while that in basal planes is enriched with organic compounds. Id.

[0052] A dynamic study using an electrochemical impedance spectroscopy (EIS) further revealed that the SEI formation takes place in two major voltage stages (Zhang, S.S. et al. Electrochem. Solid-State Lett. 4 (2001) A206; Zhang, S.S. et al, Electrochim. Acta 51 (2006) 1636; both of which are incorporated herein by reference in their entireties.) The first stage takes place before the intercalation of Li⁺ ions into graphite and the SEI formed in this stage is structurally porous, highly resistive, and dimensionally unstable. The second stage occurs simultaneously with the intercalation of Li⁺ ions and the resulting SEI is more compact and highly conductive. In the view of chemical composition, the better stability of the SEI formed in the second stage is attributed to the formation of a network between organic compounds through the coordination of Li⁺ ions and organic carbonate anions (Matsuta, S. et al, J. Electrochem. Soc. 147 (2000) 1695; incorporated herein by reference.)

[UU3JJ wiuioui Deing ouuiiu uy uue uieory, ii is aiiuuipaieu uiai urirD sans facilitate the formation of a stable SEI layer on the graphite surface during the formation cycling (1) by forcing the electrochemically induced reduction of carbonate-based solvents via mechanism (II), (2) by inducing a favorable electrochemical reduction of LiPTFB, (3) by inducing the SEI formation during the second major voltage stage that occurs simultaneously with the intercalation of Li⁺ ions, or (4) by a combination of these mechanisms. Hence, the resulting SEI is more compact and highly conductive, which is advantageous for the electrochemical performance of the lithium-ion batteries, especially for long-cycling and shelf life, as well as good safety characteristics.

[0054] It is envisioned that the electrochemical cells (batteries) that include the electrolyte solution(s) of the present invention and in particular the electrolytic salts of the present invention have a wide range of applications, including, but not limited to, calculators, wrist watches, hearing aids, electronics such as computers, cell phones, games etc, and transportation applications such as battery powered and/or hybrid vehicles.

[0055] While the lithium-based electrochemical cell of the present invention has been described in connection with what is presently considered to be the most practical and preferred embodiments, it is to be understood that the invention is not to be limited to the disclosed embodiments, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

EXAMPLES

[0056] The examples set forth below also serve to provide further appreciation of the invention but are not meant in any way to restrict the scope of the invention.

Example 1

[0057] This example illustrates the synthesis of LiPTFB salts summarized in Table 1.

The boronic acid employed as starting material was purchased from Sigma-Aldrich (St. Louis, MO) except for the 2,5-bis(trifluoromethyl)phenyboronic acid, which was synthesized following the procedure outlined in U.S. Patent No. 6,022,643, incorporated herein by reference in its entirety. All moisture sensitive reactions were carried out under argon. All products contain crystalline ether and DME. The crystalline ether can be removed by heating at 50-60 °C under 0.2 mm vacuum. In order to remove the crystalline DME, higher temperature heating can be applied except for the mono- or difluorinatedphenyl trifluoroborate salts.

Lithium phenyltrifluoroborate (2)

[0058] Five grams (0.04M) of phenyldifluoroborane (Compound (B)) was synthesized as follows. 0.05 M-0.1 M of potassium fluorinated phenyltrifluoroborate is suspended in 150 ml of fluorotrichloromethane liquid mixture. Boron trifluoride is bubbled through the mixture for one to one and a half hours until no more boron trifluoroborate is adsorbed, while the mixture is cooled by acetone-dry ice and stirred. Then the mixture is warmed to room temperature and continuously stirred for an additional two hours. The precipitates are then separated by centrifugation. The solution is distilled to obtain the pure borane compounds. Then, compound (B) was reacted with 1.04g lithium fluoride in 10 ml of DME at room temperature for 24 hours under argon and then at 60 °C for 3 hours. 4.8 g of pure salt in needle crystal shape was obtained through recrystallizing the crude product in ether. The salt (Compound (C)) was dried at 50 °C under 0.3 mm vacuum for 3 hours. NMR revealed that the product contains ½ mole of crystalline DME. The NMR chemical shifts of the product are reported in parts per million (δ), couplings are reported as a singlet (s) or a multiplet (m), and integrations are reported as number of protons. The product has the following chemical shift profile in the aceton-d6 solvent: 3.3 (s, 3H), 3.6 (s, 2H), 7-7.3 (m, 3H), 7.3-7.7 (m, 2H). (NMR (Aceton-d₆ ppm) δ 3.3 (s, 3H), 3.6 (s, 2H), 7-7.3 (m, 3H), 7.3- 7.7 (m, 2H)).

Lithium 2-fluorophenyl trifluoroborate (3)

[0059] 3.3g of 2-fluorophenyldifluoroborane (Compound (B)), synthesized using procedures described above for lithium phenyltrifluoroborate, was reacted with 0.6g lithium fluoride in 10 ml of DME at room temperature for 48 hours. The pure salt in needle crystal shape was obtained through recrystallizing the crude product in a mixed solvent of ether and pentane. The salt (Compound (C)) was dried at 50 °C under 0.1 mm vacuum for 3 hours with a yield of 3.7g. NMR revealed that the product contains ½ mole of crystalline DME. (NMR (Aceton-d₆ ppm) δ 3.3 (s, 3H), 3.6 (s, 2H), 6.25-7.35 (m, 3H), 7.35-8.2(m, 1H)). Lithium 3,5-difluorophenyltrifluoroborate (4)

[0060] 6.5g of 3,5-difluorophenyldifluoroborane (Compound (B)), synthesized using procedures described above for lithium phenyltrifluoroborate, was reacted with 1.04g lithium fluoride in 10 ml of DME at room temperature for 2 hours. The pure salt in needle crystal shape was obtained through recrystallizing the crude product in a mixed solvent of ether and pentane. The salt (Compound (C)) was dried at 65 °C under 0.15 mm vacuum for one hour with a yield of 5g. NMR revealed that the product contains 1/2 mole of crystalline DME. (NMR (Aceton-d₆ ppm) δ 3.3 (s, 3H), 3.6 (s, 2H), 6.35-6.9 (m, 1H), 6.9-7.25 (m, 2H)).

Lithium 2,5,6-trifluorophenyltrifluoroborate (5)

[0061] 8g of 2,5,6-trifiuorophenyldifluoroborane (Compound (B)), synthesized using procedures described above for lithium phenyltrifluoroborate, was reacted with 1.17g lithium fluoride in 10 ml of DME at room temperature for 3 hours. The pure salt in needle crystal shape was obtained through recrystallizing the crude product in a mixed solvent of ether and pentane. The salt (Compound (C)) was dried at 100 °C under 0.2 mm vacuum for 8 hours with a yield of 6.4g. NMR revealed that no crystalline DME was present. (NMR (Aceton-d6 ppm) δ 6.5-7.5 (m)).

Lithium 2,3,5,6-tetrafluorophenyltrifluoroborate (6)

[0062] 5.54g of 2,3,5,6-tetrafluorophenyldifluoroborane (Compound (B)), synthesized using procedures described above for lithium phenyltrifluoroborate, was reacted with 0.73g lithium fluoride in 10 ml of DME at room temperature for 3 hours. The pure salt in needle crystal shape was obtained through recrystallizing the crude product in a mixed solvent of ether and pentane. The salt (Compound (C)) was dried at 100 °C under 0.15 mm vacuum for 7 hours with a yield of 4.5 g. NMR revealed that no crystalline DME was present. The melting point of the salt is > 350 °C. (NMR (Aceton-de ppm) δ 6.5-7.5 (m)).

Lithium pentafluorophenyltrifluoroborate (7)

[0063] 13g pentafluorophenyldifluoroborane (Compound (B)), synthesized using procedures described above for lithium phenyltrifluoroborate, was reacted with 1.56g lithium fluoride in 10 ml of DME at room temperature for 3 hours. The pure salt in needle crystal shape was obtained through recrystallizing the crude product in a mixed solvent of ether and pentane. The salt (Compound (C)) was dried at 100 °C under 0.15 mm vacuum for 7 hours with a yield of 7.8g. NMR revealed that no crystalline DME was present. The melting point of the salt is > 350 °C. No proton NMR data is available.

Lithium 2-trifluoromethylphenyltrifluoroborate (8)

[0064] 9.7g (0.05M) of 2-trifluoromethylphenyldifluoroborane (Compound (B)), synthesized using procedures described above for lithium phenyltrifluoroborate was reacted with 1.3g lithium fluoride in 10 ml of DME at room temperature for 15 hours. The pure salt in needle crystal shape was obtained through recrystallizing the crude product in a mixed solvent of ether and pentane. The salt (Compound (C)) was dried at 50 °C under 0.15 mm vacuum for 1 hours with a yield of 12.5g. NMR revealed that the product contains 1 mole of crystalline DME. (NMR (Aceton-d₆ ppm) δ 3.3 (s, 6H), 3.6 (s, 4H), 7.2-7.7 (m, 3H), 7.7-8 (m, 1H)).

Lithium 2,5-bis(trifluoromethyl phenyltrifluoroborate (9)

[0065] 11.5g of 2,5-bis(trifluoromethyl)phenyldifluoroborane (Compound (B)), synthesized using procedures described above for lithium phenyltrifluoroborate, was reacted with 1.14g lithium fluoride in 10 ml of DME at room temperature for 2 hours. The pure salt in needle crystal shape was obtained through recrystallizing the crude product in a mixed solvent of ether and pentane. The salt (Compound (C)) was dried at 50 °C under 0.3 mm vacuum for 2 hours with a yield of 1 Og. NMR revealed that the product contains 1 mole of crystalline DME. (NMR (Aceton-d₆ ppm) δ 3.3 (s, 6H), 3.6 (s, 4H), 7.6-7.8 (m, 2H), 8-8.3 (m, 1H)).

Lithium 3,5-bis(trifluoromethyl)phenyl-trifluoroborate (10)

[0066] 8.12g 3,5-bis(trifluoromethyl)phenyldifluoroborane (Compound (B)), synthesized using procedures described above for lithium phenyltrifluoroborate, was reacted with 0.8g lithium fluoride in 10 ml of DME at room temperature for 2 hours. The pure salt in needle crystal shape was obtained through recrystallizing the crude product in a mixed solvent of ether and pentane. The salt (Compound (C)) was dried at 50 °C under 0.3 mm vacuum for 2 hours with a yield of 8g. NMR revealed that the product contains 1/2 mole of crystalline DME. (NMR (Aceton-d₆ ppm) δ 3.3 (s, 3H), 3.6 (s, 2H), 7.85 (s, 1H), 8.05 (s, 2H)).

Table 2: Yields of compound (B)

Compound Boiling Point (°C) Yield (%) phenyldifluoroborane (2) 95-97 68

2-fluorophenyldifluoroborane (3) 110-112 41

3,5-difluorophenyldifluoroborane (4) 95-97 52

2-trifluoromethylphenyldifluoroborane (8) 124-126 95

2,5-bis(trifluoromethyl)phenyldifluoroborane (9) 130-132 84

3,5-bis(trifluoromethyl)phenyldifluoroborane (10) 120-122 80

2,5,6-trifluorophenyldifluoroborane (5) 118-120 57

2,3,5,7-tetrafluorophenyldifluoroborane (6) 113-115 48 pentafluorophenyldifluoroborane (7) 108-1 10 57 Example 2

[0067] This example illustrates the preparation of electrolytic solutions of lithium fluorinateoVnonfluorinated phenyltrifluoroborate salts, for example, salts summarized in Table 1 and prepared in Example 1, in non-aqueous solvents. In a dry glove box, a certain amount of lithium fluorinated/nonfluorinated phenyltrifluoroborate salt was placed into a volumetric flask and the non-aqueous solvents or solvent mixtures were added. The mixture was shaken occasionally to allow all salt to dissolve and the solution mixing well.

Example 3

[0068] The conductivity data of 0.5 M lithium pentafluorophenyltrifluoroborate

(LiBF₃(C6F5)) (7) in the 1 : 1 mixture of PC/DMC is summarized in Table 3 and compared to the conductivity of LiBF₄ and LiBF₃C₃F7, salts in the same solvent mixture. The data indicates that the conductivity of 0.5M lithium pentafluorophenyltrifluoroborate (LiBF₃(C₆F₅)) (7) salt (LiPFPTFB) salt in PC/DMC is better than 0.5M of LiBF₄ salt, but smaller than 1.0 M LiBF₄ salt. However, the lithium ion transference number of LiPFPTFB salt is double that of LiBF₄ salt, making the effective conductivity for the lithium ion of LiPFPTFB better than that of the 1.0 M LiBF₄ salt.

Table 3, Conductivity data for lithium pentafluorophenyltrifluoroborate salt in 1 : 1 volumetric ratio of PC/DMC.

Electrolyte Conductivity (mS/cm)

(PC/DMC, 1 : 1) -30 0 30 60

0.5M LiBF₄ 0.6 2.1 3.7 5.5 0.31

0.5 M LiBF₃(C₆F₅) (7) 0.7 2.2 4.0 6.2 0.71

0.5M L1BF3C3F7 1.1 3.5 6.1 8.8 0.43

1.0M LiBF₄ 1.2 3.2 5.6 7.9 0.29 Example 4

[0069] This example illustrates the results of cyclic voltammetry recorded for a reversible single electrode transfer reaction using Al electrode of a first and second cycle in 0.5M lithium pentafluorophenyltrifluoroborate solution dissolved in 1 : 1 volume ratio of PC/DMC. The voltammogram shows that the electrochemical stability of this electrolyte after the first formation cycle is > 4.5 V. The voltammogram is shown in Fig. 2.

Example 5

[0070] This example illustrates the charge/discharge of Li/LiMn₂0₄ cells using 0.5 M lithium pentafluorophenyltrifluoroborate salt dissolved in 1 : 1 volume ratio of PC/DMC in voltage range of 3.2-4.3 V. The data shows that the cell cycled well and achieved an initial efficiency of 97.2% and a reversible capacity of 103 mAh g, which is similar to the published values of LiMn₂0₄ using conventional LiPF₆ based electrolytes. The Coulomb efficiency of the LiMn₂0₄ cathode further increased to 99.4%> and then to 99.6% during the second and third formation cycles, respectively.

Example 6

[0071] This example illustrates the charge/discharge of Li/MCMB cells using 0.5 M lithium pentafluorophenyltrifluoroborate salt dissolved in 1 : 1 volume ratio of PC/DMC in voltage range of 0-2.5V. The data shows that the cell cycled well and achieved an initial efficiency of 80% and a reversible capacity of 325 mAh/g. This is clear evidence for the formation of a stable SEI film on the MCMB anode in the first cycle. The Coulomb efficiency of the MCMB anode further increased to 95% and then to 97% during the second and third formation cycles, respectively, indicating stable SEI layer formation. [0072] In contrast, for the reference electrolyte using L1BF4 as the conducting salt in

PC/DMC (1 : 1 volume ratio), the Coulomb efficiency was almost zero during the formation cycling, caused by the lack of stable SEI layer formation.

Example 7

[00731 This example in FIG. 4 illustrates a voltage profile of an electrochemical cell with Li/MCMB electrodes in (A) 0.5 M L1BF4 and (B) 0.5 M L1BF3C3F7 dissolved in 1 : 1 volume ratio of PC/DMC. This data shows that no stable SEI film was formed on these two reference salts during the formation in PC/DMC solutions.

Example 8

[0074] This example in FIG. 5 illustrates the TGA results of lithium pentafluoro- phenyltrifluoroborate salts (LiPFPTFB) in comparison with two reference salts: L1BF4 and L1BF3C3F7. This data shows that although the thermal stability of our LiPFPTFB salts is lower than that of the two reference salts, but is stable to temperatures of up to 180 °C, which is sufficient for most electrolytic systems.

Example 9

[0075] FIG. 6 illustrates the conductivities of 0.5 M lithium pentafluorophenyl- trifluoroborate salt (LiPFPTFB) dissolved in 1 : 1 volume ratio of PC/DMC at different temperatures, in comparison with two reference salts: L1BF4 and L1BF3C3F7. This data shows that the conductivity of 0.5 M LiPFPTFB salt is better than 0.5M L1BF4 in PC/DMC solution.

[0076] It will be appreciated by persons skilled in the art that the present invention is not limited to what has been particularly shown and described hereinabove. Rather, the scope of the present invention is defined by the claims which follow. It should further be understood that the above description is only representative of illustrative examples of embodiments. For the reader's convenience, the above description has focused on a representative sample of possible embodiments, a sample that teaches the principles of the present invention. Other embodiments may result from a different combination of portions of different embodiments.

[0077] The description has not attempted to exhaustively enumerate all possible variations. The alternate embodiments may not have been presented for a specific portion of the invention, and may result from a different combination of described portions, or that other undescribed alternate embodiments may be available for a portion, is not to be considered a disclaimer of those alternate embodiments. It will be appreciated that many of those undescribed embodiments are within the literal scope of the following claims, and others are equivalent. Furthermore, all references, publications, U.S. Patents, and U.S. Patent Application Publications cited throughout this specification are hereby incorporated by reference as if fully set forth in this specification.

Claims

CLAIMS:

1. An electrolyte for a lithium ion electrochemical system comprising a lithium phenyltrifluoroborate salt, having the formula

wherein R is H, a fluorine -bearing moiety, or a combination thereof.

2. The electrolyte for the lithium ion electrochemical system, as recited in claim 1, wherein the lithium phenyltrifluoroborate salt is selected from the group consisting of lithium non-fluorinated phenyltrifluoroborate, lithium 2-fluorophenyltrifluoroborate, lithium 3,5-difluorophenyltrifluoroborate, lithium 2,5,6-trifluorophenyltrifluoroborate, lithium 2,3,5,6-tetrafluorophenyltrifluoroborate, lithium pentafluorophenyltrifluoroborate, lithium 2- trifluoromethylphenyltrifiuoroborate, lithium 2,5-bis(trifluoromethylphenyl)trifluoroborate, lithium 3,5-bis(trifluoromethylphenyl)trifluoroborate, and a mixture thereof.

3. The electrolyte for the lithium ion electrochemical system, as recited in claim 1, wherein the lithium phenyltrifluoroborate salt is lithium pentafluorophenyltrifluoroborate.

4. The electrolyte for the lithium ion electrochemical system, as recited in claim 1 , wherein the electrolyte is dissolved in an organic solvent selected from ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), methylethyl carbonate (MC), γ-butyrolactone (GBL),methyl butyrate (MB), propyl acetate (PA), trimethyl phosphate (TMP), triphenyl phosphate (TPP), and combinations thereof.

5. The electrolyte for the lithium ion electrochemical system, as recited in claim 4, wherein the electrolyte is dissolved in a binary mixed organic solvent containing a 1 : 1 volume ratio of EC/DMC.

6. The electrolyte for the lithium ion electrochemical system, as recited in claim 4, wherein the electrolyte is dissolved in a binary mixed organic solvent containing a 1 : 1 volume ratio of PC/DMC.

7. The electrolyte for the lithium ion electrochemical system, as recited in claim 4, wherein the electrolyte is dissolved in a ternary mixed organic solvent containing a 1 :1: 1 volume ratio of EC/DMC/MC.

8. The electrolyte for the lithium ion electrochemical system, as recited in claim 1, wherein the electrolyte is able to form a stable Solid Electrolyte Interphase layer on a graphite surface.

9. The electrolyte for the lithium ion electrochemical system, as recited in claim 1, wherein the electrolyte further comprises one or more anion receptors and/or additives.

10. A lithium ion electrochemical system, comprising: an anode, a cathode, an electrolyte composed of a lithium phenyltrifluoroborate salt, having the formula

wherein R is H, a fluorine -bearing moiety, or a combination thereof.

11. The lithium ion electrochemical system, as recited in claim 10, wherein the lithium phenyltrifluoroborate salt is selected from the group consisting of lithium non- fluorinated phenyltrifluoroborate, lithium 2-fiuorophenyltrifluoroborate, lithium 3,5- difluorophenyltrifluoroborate, lithium 2,5,6-trifluorophenyltrifiuoroborate, lithium 2,3,5,6- tetrafluorophenyltrifluoroborate, lithium pentafluorophenyltrifluoroborate, lithium 2- trifluoromethylphenyltrifluoroborate, lithium 2,5-bis(trifluoromethylphenyl)trifluoroborate, lithium 3,5-bis(trifluoromethylphenyl)trifluoroborate, and a mixture thereof.

12. The lithium ion electrochemical system, as recited in claim 11 , wherein the lithium phenyltrifluoroborate salt is lithium pentafluorophenyltrifluoroborate.

13. The lithium ion electrochemical system, as recited in claim 10, wherein the electrolyte is dissolved in an organic solvent selected from ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), methylethyl carbonate (MC), γ-butyrolactone (GBL), methyl butyrate (MB), propyl acetate (PA), trimethyl phosphate (TMP), triphenyl phosphate (TPP), or combinations thereof.

14. The lithium ion electrochemical system, as recited in claim 13, wherein the electrolyte is dissolved in a binary mixed organic solvent containing a 1 : 1 volume ratio of

EC/DMC.

15. The lithium ion electrochemical system, as recited in claim 13, wherein the electrolyte is dissolved in a binary mixed organic solvent containing a 1 : 1 volume ratio of

PC/DMC.

16. The lithium ion electrochemical system, as recited in claim 13, wherein the electrolyte is dissolved in a ternary mixed organic solvent containing a 1 : 1 : 1 volume ratio of EC/DMC/EMC

17. The lithium ion electrochemical system, as recited in claim 10, wherein the electrolyte is able to form a stable Solid Electrolyte Interphase layer on a graphite surface.

18. The lithium ion electrochemical system, as recited in claim 10, wherein the electrolyte further comprises one or more anion receptors and/or additives.

19. A rechargeable lithium ion battexy cell, comprising: an anode; a cathode, an electrolyte composed of a lithium phenyltrifluoroborate salt, having the formula

wherein R is H, a fluorine bearing moiety, or a combination thereof.

20. The rechargeable lithium ion battery cell, as recited in claim 19, wherein the lithium phenyltrifluoroborate salt is selected from the group consisting of lithium non- fluorinated phenyltrifluoroborate, lithium 2-fluorophenyltrifluoroborate, lithium 3,5- difluorophenyltrifluoroborate, lithium 2,5,6-trifluorophenyltrifluoroborate, lithium 2,3,5,6- tetrafluorophenyltrifluoroborate, lithium pentafluorophenyltrifluoroborate, lithium 2- trifluoromethylphenyltrifluoroborate, lithium 2,5-bis(trifluoromethylphenyl)trifluoroborate, lithium 3,5-bis(trifluoromethylphenyl)trifluoroborate, and a mixture thereof.

21. The rechargeable lithium ion battery cell, as recited in claim 20, wherein the lithium phenyltrifluoroborate salt is lithium pentafluorophenyltrifluoroborate.

22. The rechargeable lithium ion battery cell, as recited in claim 19, wherein the electrolyte is dissolved in an organic solvent selected from ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethylmethyl carbonate (EMC), γ-butyrolactone (GBL), methyl butyrate (MB), propyl acetate (PA), trimethyl phosphate (TMP), triphenyl phosphate (TPP), or combinations thereof.

23. The rechargeable lithium ion battery cell, as recited in claim 22, wherein the electrolyte is dissolved in a binary mixed organic solvent containing a 1 : 1 volume ratio of EC/DMC.

24. The rechargeable lithium ion battery cell, as recited in claim 22, wherein the electrolyte is dissolved in a binary mixed organic solvent containing a 1 : 1 volume ratio of PC/DMC.

25. The rechargeable lithium ion battery cell, as recited in claim 22, wherein the electrolyte is dissolved in a ternary mixed organic solvent containing a 1 : 1 : 1 volume ratio of EC/DMC/MC.

26. The rechargeable lithium ion battery cell, as recited in claim 19, wherein the electrolyte is able to form a stable Solid Electrolyte Interphase layer on a graphite surface.

27. The rechargeable lithium ion battery cell, as recited in claim 19, wherein the electrolyte further comprises one or more anion receptors and/or additives.

28. An electrolyte for a lithium ion electrochemical system comprising a lithium phenyltrifluoroborate salt selected from the group consisting of lithium non-fluorinated phenyltrifiuoroborate, lithium 2-fluorophenyltrifluoroborate, lithium 3,5- difluorophenyltrifluoroborate, lithium 2,5,6-trifluorophenyltrifluoroborate, lithium 2,3,5,6- tetrafluorophenyltrifluoroborate, lithium pentafluorophenyltrifluoroborate, lithium 2- trifluoromethylphenyltrifluoroborate, lithium 2,5-bis(trifluoromethylphenyl)trifluoroborate, lithium 3,5-bis(trifluoromethylphenyl)trifluoroborate, and a mixture thereof; the salts dissolved at a molar concentration of 0.05 M to 1.0 M in a binary mixed organic solvent containing a 1: 1 volume ratio of PC/DMC or EC/DMC; the electrolyte able to form a stable Solid Electrolyte Interphase layer on a graphite surface; and having a stable oxidation potential and a reversible cycle life behavior.

29. A lithium ion electrochemical system, comprising: an anode, a cathode, and an electrolyte as recited in claim 28.

30. A rechargeable lithium ion battery cell, comprising: an anode; a cathode, and an electrolyte as recited in claim 28.