KR20010006797A - Phosphonate additives for nonaqueous electrolyte in rechargeable cells - Google Patents

Abstract

PURPOSE: A lithium ion electrochemical cell is provided to exhibit a reduced first cycle irreversible capacity with high charge/discharge capacity and long cycle life. CONSTITUTION: A lithium ion electrochemical cell with high charge/discharge capacity and long cycle life adds at least one phosphonate additive to an electrolyte comprising an alkali metal salt dissolved in a solvent mixture that includes ethylene carbonate, dimethyl carbonate, ethylmethyl carbonate and diethyl carbonate. The preferred additive is an alkyl phosphonate compound.

Description

Phosphonate additives for nonaqueous electrolyte in rechargeable cells

The present invention relates generally to alkali metal electrochemical cells, more particularly to rechargeable alkali metal cells. More particularly, the present invention relates to a lithium ion electrochemical cell activated with an electrolyte having an additive provided to achieve high charge / discharge capacity and long cycle life and to minimize first cycle irreversible capacity. According to the invention, preferred additives for the activated electrolyte are phosphonate compounds. Phosphite compounds are also preferred in the present invention by another name for phosphonate compounds.

Alkali metal rechargeable cells typically include carbonaceous anode electrodes and lithiated cathode electrodes. At the high potential of the negative electrode material (4.3 V or less for Li / Li ⁺ of Li _1-x CoO ₂ ) and the low potential of the carbonic anode material (0.01 V for Li / Li ⁺ of graphite) in a fully charged lithium ion battery Due to this, the choice of electrolyte solvent system is limited. Since carbonate solvents typically have high oxidative stability to the lithiated anode materials used and good dynamic stability to carbon anode materials, they are generally used in lithium ion battery electrolytes. In order to achieve optimal cell performance (high speed and long cycle life), solvent systems comprising a mixture of cyclic carbonates (high dielectric constant solvents) and linear carbonates (low viscosity solvents) are typically used in conventional secondary cells. do. Cells with carbonate based electrolytes are known to carry more than 1000 charge / discharge cycles at room temperature.

U.S. Patent Application Serial No. 09 / 133,799, assigned to the assignee of the present invention and incorporated herein by reference, discloses organic in activating electrolytes for lithium ion batteries capable of discharging at temperatures below -20 ° C and as low as -40 ° C while exhibiting excellent cycling characteristics A quaternary mixture of carbonate solvents. Quaternary solvent systems include ethylene carbonate (EC), dimethyl carbonate (DMC), ethylmethyl carbonate (EMC) and diethyl carbonate (DEC).

Lithium ion cell designs generally exchange one area for another, requiring improvement, depending on the target cell application. Low cycle performance may be achieved by using the above mentioned four solvent solvents instead of the typically used two solvent solvents (e.g., 1.0M LiPF ₆ / EC: DMC = 30: 70, v / v frozen at -11 ° C). Lithium ion cells are achieved at the expense of increased first cycle irreversible capacity during initial charging (about 65 mAh vs. 1.0 per g of graphite for 1.0 M LiPF ₆ /EC:DMC:EMC:DEC=45:22:24.8:8.2) 35 mAh per 1 g of graphite against M LiPF ₆ / EC: DMC = 30: 70). Due to the presence of the first cycle irreversible capacity described above, lithium ion batteries are generally limited cathodes. Since all the lithium ions reciprocating the positive and negative electrodes during charge and discharge are originally derived from the lithiated negative electrode, the larger the first cycle irreversible capacity, the lower the battery capacity in subsequent cycles and the lower the battery efficiency. Therefore, it is desirable to minimize or even eliminate the first cycle irreversible capacity in lithium ion cells while maintaining the low temperature cycling capability of such cells.

According to the invention, the above object is achieved by providing an organic phosphonate or phosphite in a quaternary solvent electrolyte. Lithium ion cells activated with the above electrolytes exhibit lower first cycle irreversible capacity compared to cells activated with the same quaternary solvent electrolyte without the phosphonate additive. As a result, cells comprising phosphonate additives exhibit higher subsequent cycling capacity than control cells. At room temperature as well as at low temperatures, ie below about −40 ° C., the cycleability of the cells of the present invention is as good as those activated with quaternary electrolytes without phosphonate additives.

When the potential is first applied to a lithium ion battery assembled with a carbon anode in a discharged state to charge the cell, some permanent capacity loss occurs due to the formation of a positive electrode surface passivation film. This permanent capacity loss is called the first cycle irreversible capacity. However, the film formation method is very dependent on the reactivity of the electrolyte component at the cell charging potential. The electrochemical properties of the passivation film also depend on the chemical composition of the surface film.

Formation of the surface film is inevitable in alkali metal systems, in particular lithium metal anodes, and lithium intercalated carbon anodes, due to their relatively low potential and the high reactivity of lithium to organic electrolytes. Ideal surface films known as solid-electrolyte intermediate phases (SEIs) should be electrically insulating and ion conductive. Most alkali metals, in particular lithium electrochemical systems, meet the first requirement, but the second requirement is difficult to achieve. The resistance of such films is not negligible and consequently the impedance builds up inside the cell due to the formation of the surface layer described above which causes unacceptable polarization during charging and discharging of the lithium ion battery. On the other hand, when the SEI film is electrically conductive, the electrolyte decomposition reaction at the anode surface does not stop due to the low potential of the lithiated carbon electrode.

Thus, the composition of the electrolyte has a significant effect on the discharge efficiency of the alkali metal system, in particular the permanent capacity loss in the secondary cell. For example, when 1.0 M LiPF ₆ / EC: DMC = 30: 70 is used to activate the secondary cell, the first cycle irreversible capacity is about 35 mAh per gram of graphite. However, under the same cycling conditions, when 1.0 M LiPF ₆ /EC:DMC:EMC:DEC=45:22:24.8:8.2 was used as the electrolyte, the first cycle irreversible capacity was found to be about 65 mAh per gram of graphite. In addition, lithium ion batteries activated with binary solvent electrolytes of ethylene carbonate and dimethyl carbonate cannot be cycled at temperatures below about -11 ° C. The quaternary solvent electrolytes of the above-referenced patents, which can cycle lithium ion cells at much lower temperatures, are a compromise for providing a wider temperature with acceptable cycling efficiency. It would be highly desirable to maintain the benefits of lithium ion batteries that can operate at temperatures as low as about -40 ° C. and can minimize the first cycle irreversible capacity.

According to the present invention, the above object is achieved by adding a phosphonate additive to the aforementioned four-way solvent electrolyte. The invention may also be generalized to electrolyte systems containing solvents other than mixtures of linear or cyclic carbonates, as well as other non-aqueous organic electrolyte systems such as binary and ternary solvent systems. For example, linear or cyclic ethers or esters may also be included as electrolyte components. Although the exact reason for the observed improvement is not clear, it is assumed that the phosphonate additive competes with existing electrolyte components that react at the carbon anode surface during initial lithiation to form a beneficial SEI film. The SEI film thus formed is more electrically insulating than the film formed without the phosphonate additive, and consequently the lithiated carbon electrode is more protected from reaction with other electrolyte components. Thus, less first cycle irreversible capacity is obtained.

Phosphonate or phosphite additives are defined herein as organic mono-alkyl alkyl or dialkyl alkyl phosphonate compounds or phosphorous acid (phosphonic acid) provided as cosolvents with other non-aqueous electrolyte solvents. Organic phosphonate additives are condensed phases that make them easy to handle in the preparation of electrolytes.

These and other objects of the present invention will become more and more apparent to those skilled in the art with reference to the following description and attached drawings.

1 shows the average discharge capacity for 20 cycles for two groups of lithium-ion cells, a group assembled similarly with a phosphonate electrolyte additive and a group activated with a ternary carbonate solvent mixture without phosphonate additives. It is a graph showing the.

Secondary electrochemical cells assembled according to the present invention comprise a positive electrode active material selected from Group IA, Group IIA or Group IIIB elements of the periodic table, including alkali metal lithium, sodium, potassium and the like. Preferred positive electrode active materials include lithium.

In secondary electrochemical cells, the positive electrode comprises a material capable of inserting and deinserting alkali metals, in particular lithium. Carbonaceous anodes comprising various forms of carbon capable of reversibly retaining lithium species (eg, coke, graphite, acetylene black, carbon black, glassy carbon, etc.) are preferred. Graphite is particularly preferred because of its relatively high lithium holding capacity. Regardless of the form of carbon, fibers of carbonaceous materials are particularly advantageous because they have excellent mechanical properties that allow them to be assembled into hard electrodes that can withstand degradation during repeated charge / discharge cycling. In addition, the high surface area of the carbon fibers enables fast charge / discharge rates. Preferred carbonaceous materials for the positive electrode of secondary electrochemical cells are described in US Pat. No. 5,443,928 to Takeuchi et al., Assigned to the assignee of the present invention and incorporated herein by reference.

Typical secondary battery cathodes comprise about 90-97 wt% graphite and preferably polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyethylenetetrafluoroethylene (ETFE), polyamide and polyimide , And about 3 to 10% by weight of the binder material, which is a fluoro-resin powder, such as a mixture thereof. Such electrode active mixtures are provided to current collectors such as nickel, stainless steel, or copper foil or screens by casting, compressing, rolling or otherwise contacting the active mixture.

The positive electrode constituent material is integrally molded with it by welding and is contacted by a weld to the battery case of conductive metal in a case-negative electrical arrangement with an expanded tab of the same material, preferably nickel, of the same material. It further has a tab or a lead. In addition, carbonaceous anodes may be formed in several different geometries such as bobbin form, cylinders or pellets to enable alternating low surface cell designs.

The negative electrode of the secondary battery preferably comprises a lithiated material that is air stable and easy to handle. Examples of such air stable lithiated anode materials include oxides, sulfides, selenides and tellurides of metals such as vanadium, titanium, chromium, copper, molybdenum, niobium, iron, nickel, cobalt and manganese. More preferred oxides include LiNiO ₂ , LiMn ₂ O ₄ , LiCoO ₂ , LiCo _0.92 Sn _0.08 O ₂ and LiCo _1-x Ni _x O ₂ .

Prior to assembly into an electrode for introduction into an electrochemical cell, the lithiated active material is preferably mixed with a conductive additive. Suitable conductive additives include acetylene black, carbon black and / or graphite. Metals such as nickel, aluminum, titanium and stainless steel in powder form are also useful as conductive diluents when mixed with the active materials described above. The electrode preferably further comprises a fluoro-resin binder such as PTFE, PVDF, ETFE, polyamide and polyimide, and mixtures thereof in powder form.

In order to discharge the secondary battery described above, lithium ions constituting the negative electrode are inserted into the carbonaceous anode by applying an externally generated potential to recharge the battery. The applied recharge potential draws alkali metal ions from the cathode material by the electrolyte and saturates the carbon constituting the anode at the carbonaceous anode. The resulting Li _x C ₆ electrode may have x in the range of 0.1 to 1.0. The cell is then supplied with a potential and discharged in a standard manner.

AC secondary cell assembly involves inserting carbonaceous material with active alkaline material into the cell prior to inserting the positive electrode into the cell. In such a case, the negative electrode body may be a solid and includes, but is not limited to, materials such as manganese dioxide, silver vanadium oxide, copper silver vanadium oxide, titanium disulfide, copper oxide, copper sulfide, iron sulfide, iron disulfide and carbon fluoride It is not. However, this approach is a compromise of the problems associated with the handling of lithiated carbon outside the cell. Lithiated carbon tends to react upon contact with air.

The secondary battery of the present invention includes a separator that physically separates between the positive electrode and the negative electrode active electrode. The separator is an electrically insulating material to prevent internal electrical shorts between the electrodes, and the separator material is also chemically non-reactive with the positive and negative electrode active materials, both chemically non-reactive and insoluble in the electrolyte. In addition, the separator material has sufficient porosity to flow through the electrolyte during the electrochemical reaction of the cell. The shape of the separator is typically a sheet placed on the anode and cathode electrodes. This can occur when the anode is placed in the middle of the anode layer and overlaps a serpentine-like structure with a plurality of negative electrode plates housed in the cell casing or the electrode combination is rolled or otherwise formed in a cylindrical “jellyroll” arrangement. If so.

Exemplary separator materials include knitted fabrics from fluoropolymeric fibers of polyethylenetetrafluoroethylene and polyethylenechlorotrifluoroethylene that are used alone or in combination with fluoropolymeric microporous films. Other suitable separator materials include nonwoven glass, polypropylene, polyethylene, glass fiber materials, ceramics, ZITEX; Manufacturer: Polytetrafluoroethylene membrane, Celgard, sold under the tradename Chaplast Inc .; CELGARD; Manufacturer: Polypropylene Membrane and DEXIGLAS sold under the trade name Celanese Plastic Company, Inc .; Manufacturer: C.H. Dexter, Div., Dexter Corp.].

The choice of an electrolyte solvent system for activating alkali metal electrochemical cells, especially fully charged lithium ion cells, is characterized by the high potential of the negative electrode material (4.3 V or less for Li / Li ⁺ of Li _1-x CoO ₂ ) and the positive electrode material. It is very limited due to the low potential (0.01V for Li / Li ⁺ of graphite). According to the invention, suitable non-aqueous electrolytes are inorganic salts dissolved in non-aqueous solvents, more preferably dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), ethylmethyl carbonate (EMC), Dialkyl (bicyclic) carbonates selected from methylpropyl carbonate (MPC) and ethylpropyl carbonate (EPC), and mixtures thereof, and propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate (BC) and vinylene And alkali metal salts dissolved in a quaternary mixture of an organic carbonate solvent comprising at least one cyclic carbonate selected from carbonate (VC), and mixtures thereof. Organic carbonates are generally used in the electrolyte solvent systems for battery chemistry described above because they exhibit high oxidative stability for the negative electrode material and good dynamic stability for the positive electrode material.

Preferred electrolytes according to the invention comprise a solvent mixture of EC: DMC: EMC: DEC. The most preferred volume percent range for various carbonate solvents is in the range of about 10 to about 50% EC, in the range of about 5 to about 75% DMC, in the range of about 5 to about 50% EMC, and about DEC 3 to about 45%. The electrolyte containing the quaternary carbonate mixture described above exhibits a freezing point of -50 ° C or lower, and the lithium ion battery activated with this mixture has very good cycling behavior at room temperature as well as very good discharge and charge / Discharge cycling behavior.

Known lithium salts useful as a vehicle for transporting alkali metal ions from anode to cathode and vice versa are LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiSbF ₆ , LiClO ₄ , LiAlCl ₄ , LiGaCl ₄ , LiC (SO ₂ CF ₃ ) ₃ , LiNO ₃ , LiN (SO ₂ CF ₃ ) ₂ , LiSCN, LiO ₃ SCF ₂ CF ₃ , LiC ₆ F ₅ SO ₃ , LiO ₂ CCF ₃ , LiSO ₃ F, LiB (C ₆ H ₅ ) ₄ and LiCF ₃ SO ₃ , and mixtures thereof. Suitable salt concentrations typically range from about 0.8 to 1.5 mol.

According to the invention, one or more organic phosphonate additives, preferably mono-alkyl alkyl or dialkyl alkyl phosphonate compounds, are provided as cosolvents in the electrolyte solution of the above-mentioned alkali metal ions or rechargeable electrochemical cells. The phosphonate additive is preferably an alkyl phosphonate compound of formula (1).

(R ¹ O) P (= O) (OR ² ) (R ³ )

In Chemical Formula 1,

R ¹ , R ² and R ³ are the same or different and may be hydrogen atoms or saturated or unsaturated organic groups having 1 to 13 carbon atoms. The biggest effects are dimethyl phosphonate, diethyl phosphonate, dipropyl phosphonate, dibutyl phosphonate, diphenyl phosphonate, dibenzyl phosphonate, dimethyl methyl phosphonate, diethyl methyl phospho , Dipropyl methylphosphonate, dibutyl methylphosphonate, diphenyl methylphosphonate, dibenzyl methylphosphonate, dimethyl benzylphosphonate, ethyl methylphosphonate, dimethyl diphenylmethylphosphonate and Phosphorous or phosphonic acid, and mixtures thereof, appear when used as an additive in an electrolyte.

The foregoing compounds are merely considered as examples of compounds useful in the present invention and are not to be construed as being limited thereto. Those skilled in the art are within the scope of the compound of formula 1 above and are useful according to the invention as phosphonate compounds useful as additives for electrolytes to achieve high charge / discharge capacity and long cycle life and to minimize first cycle irreversible capacity. Will be easily recognized.

While not wishing to be bound to a particular mechanism, due to the presence of P═O bonds in the —OP (═O) (R) O— functional group, the bond between oxygen and at least one of groups R ¹ and R ² is strictly In addition, the phosphonate intermediate can effectively compete with other electrolyte solvents or solutes that react with lithium to form phosphonate salts, ie lithium salts of lithium phosphonate, or phosphonate reduction products, on the surface of the carbonaceous anode Is considered. The resulting SEI layer is more ionically conductive than the SEI layer that can be formed in the absence of organic phosphonate additives. As a result, the chemical composition and possibly the morphology of the carbonaceous anode surface protective layer is considered to change the benefits that coexist in cell cycling characteristics.

The assembly of cells described herein is preferably in the form of a winding element cell. That is, the assembled negative electrode, positive electrode, and separator are together in a "jelly roll" type arrangement or "winding element cell stack" such that the positive electrode is in electrical contact with the battery case in the case-negative arrangement on the outer surface of the roll. It is wound up. The wound cell stack is inserted into a metal case of suitable size dimensions using suitable top and bottom insulators. The metallic case may include materials such as stainless steel, mild steel, nickel plated mild steel, titanium or aluminum, but is not limited to this as long as the metallic material is compatible for use as a component of the cell.

The battery header includes a metallic disk-shaped body having a first hole for adjusting the glass-to-metal seal / end pin feedthrough and a second hole for filling the electrolyte. The glass used is in a corrosion resistant form having up to about 50% by weight of silicon, such as CABAL 12, TA 23 or FUSITE 425 or Fused 435. Molybdenum, aluminum, nickel alloys or stainless steel may also be used, but the anode end pin feedthrough preferably comprises titanium. The battery header includes elements that are compatible with other constituent materials of the electrochemical cell and are corrosion resistant. The cathode lead is welded to the anode end pin in the glass to metal seal and the header is welded to the case containing the electrode stack. The cell is then filled with an electrolyte solution comprising one or more of the phosphonates described above, but not limited thereto, and hermetically sealed by hermetically welding stainless steel balls to the fill holes.

The above assembly describes a case-negative cell, which is the preferred structure of a typical cell of the present invention. As is well known to those skilled in the art, typical electrochemical systems of the present invention can also be assembled in a case-positive arrangement.

The following examples describe the manner and method of the electrochemical cell according to the present invention and represent, but are not limited to, the best mode expected by the inventors of the present invention.

Example I

Six lithium ion cells are assembled as test vehicles. The cells are divided into two groups of three cells. One group of cells is activated with a quaternary carbonate solvent system electrolyte free of phosphonate additives, while the other cells have the same electrolyte but contain phosphonate additives. Except for the electrolyte, the cell is the same. In particular, the negative electrode is prepared by casting a LiCoO ₂ negative electrode mixture on aluminum foil. The negative electrode mixture contains 91% by weight of LiCoO ₂ , 6% by weight graphite additive and 3% by weight PVDF binder. The positive electrode is made by casting on a copper foil a positive electrode mixture containing 91.7 weight% graphite and 8.3 weight% PVDF binder. The electrode assembly puts a layer of polyethylene separator between the cathode and the anode, spirally wound the electrode and assembled to an AA size cylindrical stainless steel can. The cell is activated with an electrolyte of EC: DMC: EMC: DEC = 45: 22: 24.8: 8.2 in which 1.0 M LiPF ₆ is dissolved (Group 1). Group 2 cells assembled according to the present invention further contain 0.05M dibenzyl phosphonate (DBPI) dissolved therein. Finally, the cell is hermetically sealed.

Then all six cells are cycled at 4.1-2.75V. The charge cycle is performed until the battery reaches 4.1V under a rated current of 100mA. The charge cycle then continues at 4.1V until the current drops to 20mA. After 5 minutes of rest, the battery is discharged to 2.75V under a rated current of 100mA. Allow the cell to rest for 5 minutes before the next cycle.

The initial average charge and discharge capacities of the two groups of cells are summarized in Table 1. The first cycle irreversible capacity is calculated as the difference between the first charge capacity and the first discharge capacity.

First cycle capacity and irreversible capacity group First charge (mAh) First discharge (mAh) Irreversible (mAh) One 641.4 ± 1.5 520.2 ± 9.5 121.2 ± 10.7 2 635.1 ± 13.9 541.7 ± 4.3 93.4 ± 18.2

The data in Table 1 clearly demonstrates that both groups of cells have similar first cycle charge capacity. However, the first cycle discharge capacity is very different. Group 2 cells activated with an electrolyte containing a dibenzyl phosphonate additive have a first cycle discharge capacity that is significantly higher (about 4.1% higher) than Group 1 cells. As a result, the Group 2 cells also have a first cycle irreversible capacity about 23% lower than the Group 1 cells.

Example II

After the initial cycle, the cycling of the six cells continued a total of ten times under the same cycling conditions as described in Example I. The discharge capacity and capacity residual of each cycle are summarized in Table 2. The capacity residual rate is defined as the capacity% of each discharge cycle with respect to the first cycle discharge capacity.

Cycling Discharge Capacity and Capacity Residual Group 1 Group 2 Cycle number Capacity (mAh) % Remaining Capacity (mAh) % Remaining One 520.2 100.0 541.7 100.0 2 510.2 98.1 534.1 98.6 3 503.4 96.8 528.0 97.5 4 497.6 95.7 522.7 96.5 5 493.0 94.8 519.0 95.8 6 489.4 94.1 515.3 95.1 7 486.1 93.4 512.4 94.6 8 483.2 92.9 509.8 94.1 9 480.2 92.3 507.4 93.7 10 478.2 91.9 505.5 93.3

The data in Table 2 demonstrates that Group 2 cells containing dibenzyl phosphonate additives consistently provide higher discharge capacity in all cycles. In addition, this higher capacity is not achieved at the expense of lower cycle life. Group 1 and 2 cells have essentially the same cycling capacity residual throughout the various cycles.

Example III

After the cycle test described in Example II, the cell is charged according to the procedure described in Example I. Then, the battery was discharged to 2.75V under a rated current of 1000 mA, followed by a 5-minute open circuit, followed by a discharge of 2.75 V under a 500 mA rated current, followed by a 5-minute open circuit, followed by a 250 mA After the discharge at 2.75V under the rated current, the circuit is stopped for 5 minutes, and finally after the discharge at 2.75V under the rated current of 100 mA, the circuit is stopped for 5 minutes. The average total capacity under each discharge rate is summarized in Table 3, and a comparison of the average discharge efficiency (defined as percent capacity of 100 mA rated current discharge) under various rated currents is summarized in Table 4. In Table 3, the discharge capacity is accumulated next in one discharge current.

Discharge Capacity Under Various Currents (mAh) group 1000 mA 500 mA 250 mA 100 mA One 277.8 439.8 459.8 465.9 2 231.6 460.9 484.2 492.3

Discharge Efficiency Under Various Currents (%) group 1000 mA 500 mA 250 mA 100 mA One 59.7 94.4 98.7 100.0 2 47.0 93.6 98.3 100.0

The data in Table 3 shows that Group 2 cells containing phosphonate additives deliver increased discharge capacity compared to Group 1 control cells under discharge rates of 500 mA (about 1 C rate) or less. However, under the higher discharge rate (1000 mA, about 2 C rate), the Group 1 control cell delivers higher capacity than the Group 2 cell. The same trend is also shown in Table 4. Under a discharge current of 500 mA or less, Group 2 cells provide similar discharge efficiencies as Group 1 cells. Under the higher discharge current (ie 1000 mA), the Group 1 control cell provides higher discharge efficiency than the Group 2 cell.

Example IV

After the discharge rate capability test, all cells were fully charged according to the procedure described in Example I. Six test cells are then stored on open circuit voltage (OCV) at 37 ° C. for 2 weeks. Finally, the battery is discharged and cycled eight more times. The percentages of self-discharge and capacity residuals were calculated and shown in Table 5.

Self-discharge rate and remaining capacity after storage group Self-discharge (%) Capacity Remaining Rate (%) One 12.6 93.4 2 15.0 93.6

The data in Table 5 demonstrates that both groups of cells showed similar self-discharge rates and similar capacity retention rates after storage. However, because Group 2 cells have a higher discharge capacity than Group 1 cells, the capacity of Group 2 cells is much higher than Group 1 cells, even though they provide similar self-discharge and capacity retention rates. A total of 20 cycles were obtained and the results are summarized in FIG. 1. In particular, curve 10 is plotted from the average cycling data of group 1 cells without phosphonate additives, while curve 12 is plotted from averaged group 2 cells with dibenzyl phosphonate additives. Increased discharge capacity is clearly demonstrated through 20 cycles.

In order to generate an electrically nonconductive SEI layer containing the reduction product of the phosphonate additive according to the invention, the reduction reaction of the phosphonate additive must effectively compete with the reaction with other electrolyte components at the anode surface. In this regard, at least one of the RO bonds in the phosphonate additive of formula 1 should be weak or reactive. If one of R is H, the compound will acidically react with lithium metal or lithiated carbon to readily form a lithium salt. However, when both the R ¹ and R ² groups are organic groups, the reactivity of the CO bond depends on the bond strength and the structure of the R group.

This has been demonstrated in US patent application Ser. No. 08 / 964,492, assigned to the assignee of the present invention and incorporated herein by reference. In this patent application, when phosphonate additives such as tribenzyl phosphonate and dibenzyl phosphonate (both have reactive OH bonds and active CO bonds) have relatively weak CO bonds, the voltage delay is reduced and reduced. Advantageous effects are observed for primary lithium / silver vanadium oxide cells in terms of Rdc growth.

For similar reasons, the same type of phosphonate additive, which benefits the discharge performance of primary lithium electrochemical cells, is due to the formation of a good SEI film on the carbon anode surface and the first cycle irreversible capacity and cycling of lithium ion cells. It is also considered to benefit from efficiency. Thus, in lithium ion batteries, at least one of the R groups in the phosphonate additive of formula 1 must be hydrogen (acidic protons) or a saturated or unsaturated organic group having 1 to 13 carbon atoms.

While not wishing to be bound by any theory, the reductive cleavage of one or more of the OR ¹ and OR ² bonds in the phosphonate additive of the present invention is positive due to the presence of the -OP (= O) (R) O- functional group. Lithium phosphonates deposited on the surface or lithium salts of phosphonate reduction products of the formula O = P (O-Li) _n (OR) _m , wherein n is 1 or 2; m is 0 or 1 Can be generated. Such positive electrode surface films are more ionically conductive than films formed in the absence of additives and are believed to be involved in the improved performance of lithium ion batteries.

The concentration limit of the phosphonate additive is preferably from about 0.001 to about 0.40 M. The beneficial effect of the phosphonate additive is not apparent when the additive concentration is less than about 0.001 M. On the other hand, if the additive concentration is greater than about 0.40 M, the beneficial effects of the additive will be offset by the adverse effects of higher internal cell resistance due to thicker anode surface film formation and lower electrolyte conductivity.

It is recognized that various modifications will be apparent to those skilled in the art without departing from the spirit and scope of the invention as defined by the appended claims.

The present invention provides high charge / discharge capacity and cycle life by adding one or more phosphonate additives to an electrolyte comprising an alkali metal salt dissolved in a solvent mixture comprising ethylene carbonate, dimethyl carbonate, ethylmethyl carbonate and diethyl carbonate. Provided is a lithium ion electrochemical cell that exhibits a long, reduced first cycle irreversible capacity.

Claims (39)

a) a negative electrode inserting an alkali metal; b) an anode comprising an electrode active material inserting an alkali metal; c) a non-aqueous electrolyte activating a cathode and an anode; And d) an electrochemical cell comprising a phosphonate additive provided in an electrolyte. The electrochemical cell of claim 1, wherein the phosphonate additive has the following formula (1). Formula 1 (R ¹ O) P (= O) (OR ² ) (R ³ ) In Chemical Formula 1, R ¹ , R ² and R ³ are the same or different and may be hydrogen atoms or saturated or unsaturated organic groups having 1 to 13 carbon atoms. The method of claim 1, wherein the phosphonate additive is dimethyl phosphonate, diethyl phosphonate, dipropyl phosphonate, dibutyl phosphonate, diphenyl phosphonate, dibenzyl phosphonate, dimethyl methylphospho Diethyl methylphosphonate, dipropyl methylphosphonate, dibutyl methylphosphonate, diphenyl methylphosphonate, dibenzyl methylphosphonate, dimethyl benzylphosphonate, ethyl methylphosphonate, dimethyl An electrochemical cell selected from the group consisting of diphenylmethylphosphonate and phosphorous acid or phosphonic acid, and mixtures thereof. The electrochemical cell of claim 1, wherein the phosphonate additive is present in the electrolyte at a concentration of about 0.001 to about 0.40M. The electrochemical cell of claim 1 wherein the phosphonate additive is dibenzyl phosphonate present in the electrolyte at a concentration of about 0.05 M or less. The electrochemical cell of claim 1, wherein the electrolyte comprises a quaternary non-aqueous carbonate solvent mixture. The electrochemical cell of claim 1 wherein the electrolyte comprises at least one linear carbonate selected from the group consisting of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethylmethyl carbonate, methylpropyl carbonate and ethylpropyl carbonate, and mixtures thereof. 8. The electrochemical cell of claim 7, wherein the electrolyte comprises at least three linear carbonates. The electrochemical cell of claim 1 wherein the electrolyte comprises at least one cyclic carbonate selected from the group consisting of ethylene carbonate, propylene carbonate, butylene carbonate and vinylene carbonate, and mixtures thereof. The electrochemical cell of claim 1 wherein the electrolyte comprises ethylene carbonate, dimethyl carbonate, ethylmethyl carbonate and diethyl carbonate. The method of claim 10 wherein ethylene carbonate is in the range of about 10 to about 50 volume percent, dimethyl carbonate is in the range of about 5 to about 75 volume percent, ethylmethyl carbonate is in the range of about 5 to about 50 volume percent, di An electrochemical cell with ethyl carbonate in the range of about 3 to about 45 vol%. The method of claim 1, wherein the electrolyte is LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiSbF ₆ , LiClO ₄ , LiAlCl ₄ , LiGaCl ₄ , LiNO ₃ , LiC (SO ₂ CF ₃ ) ₃ , LiN (SO ₂ CF ₃ ) ₂ , Alkali metal salts selected from the group consisting of LiSCN, LiO ₃ SCF ₂ CF ₃ , LiC ₆ F ₅ SO ₃ , LiO ₂ CCF ₃ , LiSO ₃ F, LiB (C ₆ H ₅ ) ₄ and LiCF ₃ SO ₃ , and mixtures thereof Electrochemical cell comprising a. The electrochemical cell of claim 12 wherein the alkali metal is lithium. The electrochemical cell of claim 1, wherein the negative electrode comprises a negative electrode active material selected from the group consisting of coke, carbon black, graphite, acetylene black, carbon fiber and glassy carbon, and mixtures thereof. The electrochemical cell of claim 1 wherein the negative electrode active material is mixed with a fluoro-resin binder. The lithium oxide of the group selected from vanadium, titanium, chromium, copper, molybdenum, niobium, iron, nickel, cobalt and manganese, and mixtures thereof, lithiated sulfides, lithiated selenides and lithiations. An electrochemical cell comprising a positive electrode active material selected from the group consisting of telluride. The electrochemical cell of claim 16, wherein the positive electrode active material is mixed with a fluoro-resin binder. The electrochemical cell of claim 16 wherein the positive electrode active material is mixed with a conductive additive selected from the group consisting of acetylene black, carbon black, graphite, nickel powder, aluminum powder, titanium powder and stainless steel powder, and mixtures thereof. a) a negative electrode inserting lithium; b) a positive electrode comprising an electrode active material inserting lithium; c) an electrolyte solution comprising an alkali metal salt dissolved in a quaternary non-aqueous solvent mixture of ethylene carbonate, dimethyl carbonate, ethylmethyl carbonate and diethyl carbonate and activating the positive and negative electrodes; And d) an electrochemical cell comprising a phosphonate additive provided in an electrolyte. 20. The electrochemical cell of claim 19, wherein the phosphonate additive has the formula Formula 1 (R ¹ O) P (= O) (OR ² ) (R ³ ) In Chemical Formula 1, R ¹ , R ² and R ³ are the same or different and may be hydrogen atoms or saturated or unsaturated organic groups having 1 to 13 carbon atoms. The compound of claim 19, wherein dimethyl phosphonate, diethyl phosphonate, dipropyl phosphonate, dibutyl phosphonate, diphenyl phosphonate, dibenzyl phosphonate, dimethyl methylphosphonate, diethyl methyl Phosphonate, dipropyl methylphosphonate, dibutyl methylphosphonate, diphenyl methylphosphonate, dibenzyl methylphosphonate, dimethyl benzylphosphonate, ethyl methylphosphonate, dimethyl diphenylmethylphospho An electrochemical cell wherein a phosphonate additive selected from the group consisting of nate and phosphorous acid or phosphonic acid, and mixtures thereof, is used as an additive in an electrolyte. The process of claim 19 wherein ethylene carbonate is in the range of about 10 to about 50 volume percent, dimethyl carbonate is in the range of about 5 to about 75 volume percent, ethylmethyl carbonate is in the range of about 5 to about 50 volume percent, An electrochemical cell with ethyl carbonate in the range of about 3 to about 45 vol%. The method of claim 19, wherein the electrolyte is LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiSbF ₆ , LiClO ₄ , LiAlCl ₄ , LiGaCl ₄ , LiNO ₃ , LiC (SO ₂ CF ₃ ) ₃ , LiN (SO ₂ CF ₃ ) ₂ , Alkali metal salts selected from the group consisting of LiSCN, LiO ₃ SCF ₂ CF ₃ , LiC ₆ F ₅ SO ₃ , LiO ₂ CCF ₃ , LiSO ₃ F, LiB (C ₆ H ₅ ) ₄ and LiCF ₃ SO ₃ , and mixtures thereof Electrochemical cell comprising a. a) an anode of carbonaceous material capable of inserting lithium; b) a negative electrode comprising lithium cobalt oxide; And c) an electrochemical comprising a phosphonate additive for providing a lithium salt of a lithium phosphonate or phosphonate reduction product on the surface of a lithium intercalated positive electrode in contact with the electrolyte and comprising a non-aqueous electrolyte activating the positive and negative electrodes battery. a) providing a cathode for inserting an alkali metal; b) providing a positive electrode comprising an electrode active material inserting an alkali metal; c) activating the cathode and anode with a non-aqueous electrolyte; And d) providing a phosphonate additive in the electrolyte. The method of claim 25, wherein the phosphonate additive has the formula Formula 1 (R ¹ O) P (= O) (OR ² ) (R ³ ) In Chemical Formula 1, R ¹ , R ² and R ³ are the same or different and may be hydrogen atoms or saturated or unsaturated organic groups having 1 to 13 carbon atoms. The method of claim 25, wherein the dimethyl phosphonate, diethyl phosphonate, dipropyl phosphonate, dibutyl phosphonate, diphenyl phosphonate, dibenzyl phosphonate, dimethyl methylphosphonate, diethyl methyl Phosphonate, dipropyl methylphosphonate, dibutyl methylphosphonate, diphenyl methylphosphonate, dibenzyl methylphosphonate, dimethyl benzylphosphonate, ethyl methylphosphonate, dimethyl diphenylmethylphospho A phosphonate additive selected from the group consisting of nates and phosphorous acid or phosphonic acid, and mixtures thereof, is used as an additive in an electrolyte. The method of claim 25, wherein the phosphonate additive is present in the electrolyte at a concentration of about 0.001 to about 0.40M. The method of claim 25, wherein the phosphonate additive is dibenzyl phosphonate present in the electrolyte at a concentration of about 0.05 M or less. The method of claim 25 comprising providing an electrolyte comprising a quaternary non-aqueous carbonate solvent mixture. The method of claim 25, wherein the electrolyte comprises one or more linear carbonates selected from the group consisting of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethylmethyl carbonate, methylpropyl carbonate and ethylpropyl carbonate, and mixtures thereof. The method of claim 31, wherein the electrolyte comprises three or more linear carbonates. The method of claim 25, wherein the electrolyte comprises one or more cyclic carbonates selected from the group consisting of ethylene carbonate, propylene carbonate, butylene carbonate and vinylene carbonate, and mixtures thereof. The method of claim 25, wherein the electrolyte comprises ethylene carbonate, dimethyl carbonate, ethylmethyl carbonate and diethyl carbonate. 35. The method of claim 34 wherein ethylene carbonate is in the range of about 10 to about 50 volume percent, dimethyl carbonate is in the range of about 5 to about 75 volume percent, ethylmethyl carbonate is in the range of about 5 to about 50 volume percent, The ethyl carbonate is in the range of about 3 to about 45 vol%. The method of claim 25, wherein the electrolyte is LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiSbF ₆ , LiClO ₄ , LiAlCl ₄ , LiGaCl ₄ , LiNO ₃ , LiC (SO ₂ CF ₃ ) ₃ , LiN (SO ₂ CF ₃ ) ₂ , Alkali metal salts selected from the group consisting of LiSCN, LiO ₃ SCF ₂ CF ₃ , LiC ₆ F ₅ SO ₃ , LiO ₂ CCF ₃ , LiSO ₃ F, LiB (C ₆ H ₅ ) ₄ and LiCF ₃ SO ₃ , and mixtures thereof How to include. The method of claim 25 comprising providing the alkali metal as lithium. The lithiated oxide, lithiated sulfide, lithiated selenide and lithiated telluride of the group according to claim 25 selected from vanadium, titanium, chromium, copper, molybdenum, niobium, iron, nickel, cobalt and manganese, and mixtures thereof. Providing a positive electrode comprising a positive electrode active material selected from the group consisting of: The method of claim 25 comprising providing a negative electrode comprising a negative electrode active material selected from the group consisting of coke, carbon black, graphite, acetylene black, carbon fiber and glassy carbon, and mixtures thereof.