METHOD FOR ALKALIATING ELECTRODES

Abstract

The present invention relates to a method for lithiation of an intercalation-based anode or a non-reactive plating-capable foil or a reactive alloy capable anode, whereby utilization of said lithiated intercalation-based anode or a plating-capable foil or reactive alloy capable anode in a rechargeable battery or electrochemical cell results in an increased amount of lithium available for cycling, and an improved reversible capacity during charge and discharge.

Claims

1. A method for lithiation of a material, preferably, in a continuous process, comprising the steps of: (a) providing a material; (b) providing a bath comprising a non-aqueous solvent and at least one dissolved lithium halide salt, wherein said bath contacts the material, preferably in a continuous process, and wherein a dry gas blanket covers said bath; (c) providing an electrolytic field plate comprising an inert conductive material wherein said field plate establishes a field between the material and the field plate; and (d) applying a reducing current to the material and an oxidizing current to the field plate, wherein lithium ions from the bath lithiate into the material.

2. The method of claim 1, wherein the material is an anode active material selected from carbon, coke, graphite, tin, tin oxide, silicon, silicon oxide, aluminum, lithium active metals, alloying metal materials, composites and mixtures thereof.

3. The method of claim 1, wherein the non-aqueous solvent is selected from butylene carbonate, propylene carbonate vinylene carbonate, vinyl ethylene carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl ethyl carbonate, acetonitrile, gamma -butyrolactone, room temperature ionic liquids, and mixtures thereof.

4. The method of claim 3, wherein the non-aqueous solvent is gamma -butyrolactone.

5. The method of claim 1, wherein the halogen of the dissolved lithium halide salt is selected from ionic F.sup.-, Cl.sup.-, Br.sup.-, I.sup.- and mixtures thereof.

6. The method of claim 1, wherein the dissolved lithium halide salt is LiCl.

7. The method of claim 1, wherein the dissolved lithium halide salt is LiBr.

8. The method of claim 1, wherein the dissolved lithium halide salt is LiF.

9. The method of claim 1, wherein the electrolytic field plate is selected from platinum, gold, glassy carbon, and graphite.

10. The method of claim 1, wherein the lithiated material and foil are used in the final assembly of a rechargeable battery.

11. The method of claim 1, wherein the lithiated material is used in the assembly of an electrochemical cell to provide the lithium needed for cycling when paired with a cathode not initially containing lithium.

12. The method of claim 1, comprising the step of performing a pre-charging cycle upon the anode externally prior to the assembly of an electrochemical cell.

13. The method of claim 1, wherein the evolving gas generated at the field plate is captured by a reflux unit, a membrane contactor, a gas scrubber, and combinations thereof.

14. The method of claim 1, comprising one or more reflux units, membrane contactors, gas scrubbers, baths, inline heaters, filters, salt dosing units, pumps, valves, and combinations thereof, connected in a loop comprising series and parallel connections.

15. The method of claim 14, wherein said inline heaters heat a non-aqueous solvent and dissolved alkali metal halide salt to a temperature of between 30° C. and 65° C.

16. The method of claim 15, wherein said temperature is about 40° C.

17. The method as in claim 1, wherein a separate immersion bath is used to rinse the material in a solvent while holding the electrode in a reducing current mode.

18. A method as in claim 1, wherein the salt is recovered periodically by distillation of the used non-aqueous solvent and subsequent rinsing of the salt in a light non -solvating fluid.

19. The method of claim 14, wherein the rate of said continuous process can be increased and decreased.

20. The method of claim 17, wherein the rate of continuous lithiation of the anode and foil can be increased and decreased.

21. The method of claim 17, wherein the rate of loop circulation can be increased and decreased.

22. The method of claim 3, wherein the non-aqueous solvent contains an additive to facilitate high quality SEI formation.

23. The method of claim 22, wherein the additive is vinylene carbonate.

24. The method of claim 1, wherein a dissolved gas is added.

25. The method of claim 24, in which the dissolved gas is carbon dioxide.

26. A method for alkaliation of a material, preferably, in a continuous process, comprising the steps of: (a) providing a material; (b) providing a bath comprising a non-aqueous solvent, dissolved CO2 or SO2 gas and at least one dissolved alkali metal salt, wherein said bath contacts the material, preferably in a continuous process, and wherein a dry gas blanket covers said bath; (c) providing an electrolytic field plate comprising an inert conductive material wherein said field plate establishes a field between the material and the field plate; and (d) applying a reducing current to the material and an oxidizing current to the field plate, wherein metal ions from the bath alkaliate into the material.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0031] FIG. 1: Characterization of the SEI layer on carbon negative electrode (anode).

[0032] FIG. 2: Lithiation tank layout.

[0033] FIG. 3: Lithiation system layout with a solvent conditioning system and salt replenishment system.

[0034] FIG. 4: Multi-tank lithiation layout.

[0035] FIG. 5: First charge and discharge of a standard anode versus LiFePO.sub.4 cathode.

[0036] FIG. 6: First charge and discharge of a pre-lithiated anode versus LiFePO.sub.4 cathode.

[0037] FIG. 7: Lithiation system layout with a solvent conditioning system, solvent distillation system, and salt replenishment system.

[0038] FIG. 8: Cell capacity comparison of LiCoO.sub.2/graphite control versus pre-lithiated button cell.

[0039] FIG. 9: Lithium intercalation efficiency with CO.sub.2 and without CO.sub.2.

[0040] FIG. 10: Coulombic efficiency of pre-lithiated and control sample cells.

[0041] FIG. 11: Comparative heat test results of pre-lithiated and control sample cells.

[0042] The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0043] Anodes comprised of metal oxides or metal alloys or graphite or carbon or silicon or silicon/carbon blends, such as anodes comprised of graphite or carbon, are lithiated during the first charging step in the battery operation after assembly, with lithium coming from the cathode material. In these cases, the cathode is the heaviest and most expensive component in the battery. It would therefore be desirable and of commercial importance to reduce the weight of the cathode, with minimal loss to the battery efficiency and output. If the dead weight that results from SEI and cathode passivation layer formation could be eliminated by sourcing the metal ions in such a way that alleviated the effects of the irreversible losses of the metal ions, then the specific capacity and volumetric capacity density of the battery could be increased, and cost of the battery could be reduced. In some cases, it may be beneficial to place an amount of lithium into the cathode that is slightly above the as produced stoichiometric value. The present invention relates to a method for lithiation of an intercalation-based material, such as an anode or cathode, a non-reactive plating-capable foil, or an alloying capable film or foil whereby utilization of said lithiated material e.g., an anode or cathode, in a rechargeable battery or electrochemical cell results in an increased amount of lithium available for cycling, and an improved reversible capacity during charge and discharge. The additional lithium available may also support the cycling of an initially non-lithium-containing cathode material. Alternately, an initially non lithium containing cathode material such as sulfur can be lithiated directly prior to assembly. As mentioned above, anodes comprised of graphite or carbon or silicon or silicon-carbon blends have been lithiated during the first charging step in the battery operation after assembly, with lithium coming from the cathode material. In these cases, the cathode is the heaviest and most expensive component in the battery. One of the desired features in lithium battery technology is to reduce the weight of the battery coming from the excess cathode material, without compromising battery efficiency and output.

[0044] A method for fabricating a lithiated material, e.g., an anode or cathode, which provides increased amounts of lithium available for cycling, improved reversible capacity during charge and discharge of a rechargeable battery and a consequent lighter battery is disclosed in FIG. 2. Electrolytic field plates are held at a voltage necessary to establish a field between the anode or cathode and the field plate, and to lithiate the anode, such as to plate or intercalate lithium onto a foil, or into an anode or cathode substrate or sheet, or to form an SEI layer upon the anode or cathode. A typical operating voltage for this is 4.1 V. An appropriate reference electrode, such as Ag/AgNO.sub.3 non-aqueous reference from Bioanalytical Systems, Inc., located close to the targeted negative electrode may be preferred to monitor the anode or cathode conditions. It is possible to operate the field plates in either voltage or current control mode. With current control, the full operating potential may not be immediately obtained. This operation under current control may result in lower initial operating voltages. This lower voltage may prefer secondary side reactions instead of the dissociation of the lithium halide salt (e.g. LiCl) and the resulting intercalation of the anode material. Operating under voltage control can ensure that the field plate potential is immediately set to a sufficient potential to favor the dissociation of the lithium halide salt (e.g. 4.1 Volt for LiCl) and to minimize secondary side reactions. Current control can alternatively be used if the subsequent operating voltage remains above the lithium halide salt dissociation threshold. This can be done by setting a sufficiently high initial current density (e.g. 2 mA/cm.sup.2) that will favor the dissociation rather than secondary side reactions. An oxidizing current is applied at the field plate, so there is a need to use an inert material or a conductive oxide. In one embodiment, the inert material comprising the field plate is selected from glassy carbon, tantalum, gold, platinum, silver, and rhodium. In a preferred embodiment, the inert material comprising the field plate is selected from platinum, gold or carbon. In a more preferred embodiment, the inert material comprising the field plate is carbon or glassy carbon. The field plates may also be comprised of a base material such as stainless steel that is plated with an inert conductive material such as gold, platinum, or glassy carbon. The field plates are immersed within the bath, with the anode passing between the field plates as illustrated in FIGS. 2 and 4. The field plates can be operated as a single entity at a single controlled voltage or current density, or multiple plates can be implemented that allow for independent control of voltage or current density over multiple zones. This is illustrated in FIGS. 2 and 4.

[0045] The anode typically comprises a compatible anodic material which is any material which functions as an anode in an electrolytic cell. As herein disclosed, the term anode is equivalent to the terms negative electrode, conductive foil, anode sheet, anode substrate, or non-reactive plating-capable foil. In one embodiment, anodes are lithium-intercalating anodes. Examples of materials that comprise lithium-intercalating anodes include but are not limited to carbon, graphite, tin oxide, silicon, silicon oxide, polyvinylidene difluoride (PVDF) binder, and mixtures thereof. In a further embodiment, lithium-intercalating anode materials are selected from graphite, cokes, mesocarbons, carbon nanowires, carbon fibers, silicon nanoparticles or other metal nanomaterials and mixtures thereof. In another embodiment, alloying metals such as tin or aluminum may be used to host the lithium metal as a result of the lithiation. A cathode is a substance typically coated on a current collector that gives up lithium ions and electrons during the charging step of an electrochemical cell. Examples of these cathode materials include but are not limited to LiFePO.sub.4, LiMn.sub.2O.sub.4 etc. A reducing current is applied to the electrode in such a way as to intercalate the lithium. The anode or cathode is bathed in a solution comprising a non-aqueous solvent and at least one dissolved lithium salt. The term non-aqueous solvent is a low molecular weight organic solvent added to an electrolyte which serves the purpose of solvating the inorganic ion salt. Typical examples of a non-aqueous solvents are butylene carbonate, propylene carbonate, ethylene carbonate, vinylene carbonate, vinyl ethylene carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl ethyl carbonate, acetonitrile, gamma-butyrolactone, triglyme, tetraglyme, dimethylsulfoxide, dioxolane, sulfolane, room temperature ionic liquids (RTIL) and mixtures thereof. In one embodiment, a non-aqueous solvent is selected from ethylene carbonate, vinylene carbonate, vinyl ethylene carbonate, gamma-butyrolactone, and mixtures thereof. In a second embodiment, a non-aqueous solvent is gamma-butyrolactone. In a third embodiment, an additive can be introduced to support high quality SEI formation. The additive could be vinylene carbonate, ethylene carbonate or maleic anhydride. In a fourth embodiment, a gas such as CO.sub.2 or SO.sub.2 is sparged into the non-aqueous solution in order to: increase salt solubility; increase the ionic conductivity; support the formation of a Li.sub.2CO.sub.3 or Li.sub.2SO.sub.3 SEI layer; and increase the lithiation efficiency. FIG. 9 describes the efficiency of reversible lithium intercalation from an initial amount of lithium sourcing measured in mAhr. The lost amount can be described as side reactions such as but not limited to SEI formation.

[0046] The term alkali metal salt refers to an inorganic salt which is suitable for use in a non-aqueous solvent. Examples of suitable alkali metal cations comprising an alkali metal salt are those selected from Li.sup.+, Na.sup.+, K.sup.+, Rb.sup.+, Cs.sup.+, Fr.sup.+, and mixtures thereof. Examples of suitable halogen anions comprising an alkali metal salt are those selected from F.sup.-, Cl.sup.-, Br.sup.-, I.sup.-, and mixtures thereof. In one embodiment, the alkali metal salt is selected from LiF, LiCl, LiBr, NaF, NaCl, NaBr, KF, KCl, KBr, and mixtures thereof. Other salts such as LiNO.sub.3 may be used, but in the preferred embodiment, the alkali metal salt is the halide LiCl.

[0047] Inexpensive salts with gaseous decomposition products can be halides such as LiCl, LiBr, and LiF. LiCl and other simple salts can be difficult to dissolve or ionize in non-aqueous solvents. Solvents such as propylene carbonate (PC), dimethyl carbonate (DMC), and acetonitrile support only trace amounts of LiCl in solution without the use of a complexing agent such as AlCl.sub.3. AlCl.sub.3 and other complexing agents can be difficult to handle in regard to moisture management and high corrosivity. In addition, some solvents that can dissolve halide salts, such DMSO or tetrahydrofuran (THF), do not allow complete ionization of the salt, and/or attack the binding polymers in the anode composites. Gamma-butyrolactone has been found to facilitate the dissolution and ionization of the desirable alkali metal halide salts. It combines good solubility of the alkali metal halide salts with compatibility with TFE Teflon.sub.c, PVDF, butadiene rubber and other binders. The use of halide salts with gaseous decomposition products such as LiCl prevents the production of solid precipitates during the lithiation process. Since the lithiation process products are primarily lithium ions and gas, there are few solid precipitates or intermediate compounds that can accumulate in the non-aqueous solvent solution. Removal of dissolved gas from the non-aqueous solvent solution is preferred over solid precipitates during long term continuous operation of a production system.

[0048] Gamma-butyrolactone also has a capable electrochemical window, including the lithium potential near —3 volts vs. a standard hydrogen electrode (SHE). It is a capable electrolyte with high permittivity and low freezing point, and can dissolve and ionize up to a 1 M concentration of LiCl. A modest amount of heat can be used to reach this value. In one embodiment, the heat to dissolve and ionize up to a 1 M concentration of LiCl is between about 30° C. and 65° C. In a more preferred embodiment, the heat is between about 38° C. and 55° C. In a most preferred embodiment, the heat is about 45° C. The lithiation tank can also have an internal circulating pump and distribution manifold to prevent localized salt concentration deprivation.

[0049] It has been discovered here that a dissolved gas such as CO.sub.2 or SO.sub.2 can enhance the lithiation process. It increases the solubility of the salt, the ionic conductivity of the non-aqueous solvent, and doubles the efficiency of lithiation. Since CO.sub.2 is inexpensive, easily dried, chemically safe, and a potential building block gas for a high quality SEI layer, it has been selected as the preferred dissolved gas. CO.sub.2 preferentially reacts with trace H.sub.2O and Li.sup.+ during the lithiation process to form a stable, insoluble SEI material (Li.sub.2O, Li.sub.2CO.sub.3 etc.). FIGS. 8 and 10 exemplify the operating efficiency of the LiCoO.sub.2/graphite cells with and without pre-lithiation. The moisture level in the lithiation tank is driven down by the consumption of CO.sub.2 and H.sub.2O according to this process, and care is given to control the moisture level in the tank to between about 5 to 20 ppm (see FIG. 2). In this way, anode lithiation with a quality SEI material is produced continuously.

[0050] The intercalation or plating process for lithium ions (or generally lithiation) from 1 M LiCl salt in gamma-butyrolactone solvent will occur at about 4.1 volts measured between the anode sheet and the reference electrode up to a reducing current density of 2 mA/cm.sup.2 or more. As intercalation rates are increased too far beyond this current density, dendrites or lithium plating may begin to take place which harm the final battery or electrochemical cell performance. This will vary depending on the graphite porosity etc. In order to control both the currents and dependant voltages accurately, it may be necessary to divide the field plate into zones as shown in the FIGS. 2 and 4. Other metals can also be plated or intercalated with this method including sodium as an example. As mentioned above, the byproduct of the intercalation process when using a halide alkali metal salt is an evolving gas at the counter electrode (field plate). In a preferred embodiment, the evolving gas is selected from F.sub.2, Cl.sub.2, Br.sub.2, and mixtures thereof. In a more preferred embodiment, the evolving gas is Cl.sub.2.

[0051] Prior to entering the lithiation bath, the anode or cathode material can be pre-soaked in an electrolyte solution as shown in FIG. 4. The pre-soaking of the material will ensure full wetting of the material prior to the start of the lithiation process. This pre-soak bath can contain a non-aqueous solvent with or without a lithium salt, with or without a sparge gas, and with or without an SEI promoting additive.

[0052] The evolution of gas at the field plate or counter electrode can result in evolving gas entering into, and/or being released from, the bath solution. As a result, controlling the buildup of dissolved and released gas is desired to avoid corrosion, as for example, in the hypothetical case of trace water contamination reacting with chlorine gas, to form HCl during chlorine gas evolution. The tank assembly can be configured to control the introduction of moisture into the system by using a dry gas blanket on top of the liquid. In one embodiment, the dry gas (1-10 ppm moisture) is selected from helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), sulfur hexafluoride (SF.sub.6), nitrogen (N.sub.2), dry air, carbon dioxide (CO.sub.2) and mixtures thereof. In a preferred embodiment, the dry gas is selected from nitrogen, argon, carbon dioxide, dry air and mixtures thereof. Moisture ingress can also be controlled by having a long narrow gap entry and exit tunnel for the anode film where a counter flowing dry gas is used to mitigate air entry into the system.

[0053] FIGS. 2, 3, 4 and 7 illustrate a process and apparatus that continuously controls moisture, gas, and small quantities of lithiated organic compounds during a continuous lithiation process. Liquid is drawn from a bath through a series of valves. The liquid can be delivered in a batch mode to a refluxing unit, or it can be continuously circulated through a conditioning loop including distillation or reverse osmosis. The reflux unit can take batches of material through a vacuum refluxing process that will remove both accumulated gas as well as moisture from the liquid. In one embodiment, the accumulated gas is selected from F.sub.2, Cl.sub.2, Br.sub.2, and mixtures thereof. In a more preferred embodiment, the accumulated gas is Cl.sub.2. The use of reflux conditioning instead of a distillation process can prevent a change in the salt concentration of the working fluid which would result in a loss of salt content through precipitation. Once the batch liquid has been refluxed for a designated period of time, the liquid can be returned to the bath with a lower moisture and gas content. The size and rate of the reflux unit can be matched to the moisture ingress rate and to the gas production rate in order keep the bath liquid at optimum conditions. The reflux rate can be increased through use of multiple simultaneous batches and through the use of high rate reflux equipment such as a rotary evaporator and high vacuum conditions. The reflux batch moisture content typically decays in an exponential fashion and the turnover rate can be tuned for optimal moisture control with minimal energy input and equipment cost.

[0054] The refluxing unit can be placed after a salt dosing unit. The salt dosing unit can be used to add and mix the desired salt into the non-aqueous solvent solution. The temperature of the dosing unit can be held to maximize the solubility of the salt in the electrolyte and the elevated temperature can also be used as a pre-heating step for the refluxing unit. In one embodiment, the dosing unit maintains an elevated process temperature of between about 30° C. and 65° C. In a more preferred embodiment, the dosing unit maintains an elevated process temperature of between about 38° C. and 55° C. In a most preferred embodiment, the dosing unit maintains an elevated process temperature of about 45° C. The benefit of dosing in the salt in a dosing unit before the refluxing unit is that the salt does not have to be in a completely dry state. Removing the moisture from a solid phase salt can be very difficult. Once a salt is dissolved into solution, however, the water content of the salt can be removed through the refluxing process. Maintaining the dosing unit at an elevated temperature increases the solubility of the lithium salt in the non-aqueous solvent and ensures full dissolution of the salt prior to the refluxing unit.

[0055] The conditioning/replenishment loop operates in a continuous mode and can also be used to remove dissolved gases from the bath liquid through use of a membrane contactor. The gas output from the membrane contactor and the reflux unit can be passed through a scrubber to capture any effluent, such as chlorine gas, produced by the process. In one embodiment, the dissolved gases are selected from F.sub.2, Cl.sub.2, Br.sub.2, and mixtures thereof. In a more preferred embodiment, the dissolved gas is Cl.sub.2. The bath liquid can also be paired against either vacuum or a dry gas within the membrane contactor in order to remove unwanted gases. In one embodiment, the dry gas is selected from helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), sulfur hexafluoride (SF.sub.6) nitrogen (N.sub.2), carbon dioxide (CO.sub.2), dry air and mixtures thereof. In a preferred embodiment, the dry gas is selected from nitrogen, argon, carbon dioxide, dry air and mixtures thereof.

[0056] An inline heater can be used to maintain an elevated tank temperature to maintain consistent bath operating conditions, even with variations in facility temperature. Elevated lithiation tank temperatures can aid in the formation of a high quality SEI layer. In one embodiment, the inline heater maintains an elevated tank temperature of between about 30° C. and 55° C. In a more preferred embodiment, the inline heater maintains an elevated tank temperature of between about 30° C. and 45° C. In a most preferred embodiment, the inline heater maintains an elevated tank temperature of about 40° C.

[0057] A filter unit can be used to remove any accumulated particulate contamination. The filter unit can be located at various points in the loop including prior to the pump and after the salt dosing unit. The filter unit can be used to remove particulates from the non-aqueous solvent in cases where a non-halide lithium salt such as LiNO.sub.3 is used such that a precipitate is formed at the field plates.

[0058] Lithium halide salt can be added to the non-aqueous solvent using the salt dosing unit. An excess of solid lithium salt can be maintained within the dosing unit to keep the lithium salt concentration within the loop and within the bath at the desired level (i.e., a saturated solution of about 0.5 M to 1.0 M) over long periods of time. The dosing unit can be configured to keep the solid salt from entering the bath or refluxing unit. By dosing salt prior to the refluxing unit, there is no need to separately dry the salt with its high water binding energy in its granular state. In one embodiment, the lithium salt within the salt dosing unit is selected from LiF, LiCl, LiBr, and mixtures thereof. In a preferred embodiment, the lithium halide salt within the salt dosing unit is LiCl. Dissolved lithium salts can be carried through the rest of the loop. The fluid circulation loop pump rate can be matched to maintain a constant lithium salt concentration in the tank. For a given anode or cathode substrate process rate, a matching loop circulation rate will dose the same amount of lithium salt as the lithiation process consumes. As the anode or cathode process rate is increased or decreased, the loop circulation rate can be modified to maintain an equilibrium state within the bath.

[0059] Depending on the specific tank conditions, the bath fluid can be treated using a circulating loop, a refluxing unit or a distillation unit as shown in FIGS. 2 and 4. A circulating loop can dose in salt, remove dissolved gases, control the bath temperature and removed particulate contaminants. A refluxing unit is effective at removing dissolved gases and for removing moisture content without reducing the salt content of the solution. A distillation unit is effective at removing dissolved gases, removing moisture content, removing all salt content and removing lithiated organic compounds. The output from the distillation unit can be fed back into a dosing and refluxing unit to reestablish the salt content if required. The effluent from the distillation unit can be collected and treated to recover used salt for reuse in the lithiation process. For example, DMC solvent will rinse away all but the insoluble salt so that the salt may be re-introduced into the dosing unit. Recirculating loops, refluxing unit and distillation units can be shared across multiple tanks that have different input and output requirements as a means of minimizing equipment size and cost.

[0060] When the anode is lithiated to the extent of the irreversible and extended cyclic loss amount, it can be assembled into a rechargeable battery or electrochemical cell with a smaller amount of lithium-bearing cathode material than would otherwise be required, thereby improving the specific capacity, specific energy, volumetric capacity density and volumetric energy density of the cell while reducing its cost. Alternately, a cathode can be pre-lithiated to or above the normal stoichiometric value to supply excess lithium to the forming cell.

[0061] When the anode is lithiated to the extent of the irreversible and extended cyclic loss amount, as well as the intended cycling amount, it can be assembled into a battery or electrochemical cell with a cathode material that does not initially contain lithium. This type of cathode material can be much less expensive than lithium containing cathode materials, and examples include, but are not limited to, MnO.sub.2, V.sub.2O.sub.5 and polyaniline. Alternatively, the cathode itself may be pre-lithiated prior to assembly. The cost of the battery or cell produced with this method will be lower due to the lower cost of the feedstock lithium salt.

[0062] Therefore, previous limitations to the low cost production of more efficient lithium ion batteries and electrochemical cells are overcome by the novel processes described here. The materials and processes of the present invention will be better understood in connection with the following examples, which are intended as an illustration only and not limiting of the scope of the invention.

EXAMPLES

[0063] The following is a detailed example of an anode preparation and processing. 25 micron thick copper foil was cleaned with isopropyl alcohol and Kimberly-Clark Kimwipes to remove oil and debris and then dried in air. A solution was prepared by adding 2.1 grams of 1,000,000 weight PVDF powder from Arkema Fluoropolymers Div. to 95 ml of dry NMP solvent from Aldrich Chemical. The solution was mixed with a stir bar overnight to fully dissolve the PVDF material. The solution was kept in the dark to prevent the light sensitive solvent from reacting. 33.9 ml of this PVDF solution was then added to 15 grams of Conoco Philips CPreme G5 graphite and 0.33 grams of acetylene black and stirred for 2 hours in a ball mill at 600 RPM without any mixing balls. The resulting slurry was cast onto the copper foil using a vacuum hold down plate with heating capability. The finished graphite thickness after casting and drying at 120° C. was about 100 microns or 14 mg/cm.sub.2. The anode sheet was then die punched into 15 mm diameter discs and then pressed at about 3000 psi and 120° C. for use in a 2032 button cell assembly. The copper/graphite anode discs were then vacuum baked at 125° C. and about 1 mTorr in a National Appliance Company model 5851 vacuum oven for at least 12 hours.

[0064] The anode discs were then transferred into a Terra Universal dry air glove box with -65° C. dew point air supplied by compressed dry air passed through a Kaeser two stage regenerative drier. The anode discs were then vacuum infiltrated with a GBL solvent with a 0.5 M concentration of LiCl salt solution. This electrolyte solution had been prepared by heating to 90° C. and then vacuum refluxing at about 1 mTorr for 6 hours to remove moisture down to about 10 ppm. The anode discs were allowed to soak for a half hour at vacuum conditions, a half hour in atmospheric pressure conditions and a half hour in the lithiation vessel itself prior to any currents being passed. The lithiation vessel included a constant bubbling of CO.sub.2 gas to achieve a saturation level and a temperature of 30° C. Test leads from a Maccor 4300 battery tester were connected to the anode sample (red working) and glassy carbon (black counter) electrode. Voltage at the working electrode is monitored via a Ag/AgNO.sub.3 non-aqueous electrode. A reducing current of 2 mA/cm.sup.2 was applied to the graphite anode until a total of 1 mAhr/cm.sup.2 was achieved. The pre-lithiated anode disc was then rinsed in pure distilled GBL and vacuum dried. The anode discs were then assembled against either LiFePO.sub.4 or LiCoO2 12 mm diameter cathode discs. The separator used was Celguard 2400, and about 0.2 ml of electrolyte was used in the assembly. The electrolyte was 1:1:1 EC:DMC:DEC with 1M LiPF.sub.6 salt and 1% VC with moisture levels at about 10 ppm. A vacuum was applied to the assembled cell to remove bubbles before crimping in an MTI model MT-160D crimping tool. Subsequent electrical tests were then performed on the battery tester unit using a 12 hour delay, two about C/12 formation cycles to at least 3.7 volts, about C/3 charge/discharge cycles, and 20 minute rest steps between them. All the battery tests were carried out in a home-made environmental chamber controlled to 26° C.

[0065] A Maccor model 4300 battery tester was used to test the CR2032 size button cells assembled with a CPreme graphite anodes, LiFePO.sub.4 or LiCoO.sub.2 cathodes, and Celguard 2400 separators. Electrolyte solutions containing a 1:1:1 mixture of EC:DMC:DEC with 1 molar concentration of LiPF6 salt and 1% VC were used. Both anodes and cathodes were cast with PVDF binders. First charge and discharge cycles, often called the formation cycles, were performed at a current rate of approximately C/12. FIGS. 5 and 6 illustrate the first cycle irreversible loss using pre-lithiated and non-pre-lithiated graphite anodes mounted against LiFePO.sub.4 cathodes. The initial absolute charge capacity of the two samples is different due to extraneous packaging variation. The irreversible losses are representative of the methods described, however. In FIG. 5, the reversible capacity of the button cell is 56%. In FIG. 6, the reversible capacity of the button cell when matched to a pre-lithiated anode is 98%. FIG. 8 shows a typical LiCoO.sub.2/graphite vs. a LiCoO.sub.2/pre-lithiated graphite, but otherwise identical sample, tested over an extended range of charges and discharge cycles at approximately a C/3 rate. The results indicate that there is a long lasting benefit to the battery cell due to pre-lithiation using the methods described. FIG. 11 shows the effectiveness of the SEI layer formed during the prelithiation process, by comparing capacity retention of the cell with prelithiated anode to a control cell, with both cells being subjected to 48 hours of 50° C. heat as a form of accelerated aging test.

Example 2

[0066] An NMC cathode is mounted in a half cell containing lithium metal as the negative electrode. The NMC cathode is “charged” to liberate most of its lithium content. This cell is disassembled and the cathode taken out to use as an electrode in the pre-lithiation apparatus that includes the above mentioned GBL and LiCL salt solution including CO2 gas. The NMC cathode is subjected to a reducing current of 1 mA/cm2 with a total dosage of 1 mAhr/cm2. The cathode is then rinsed while held in a small reducing current (0.1 mA/cm2) to inhibit chemical oxidation and then vacuum dried. The cathode is then mounted into a half cell as described earlier and cycled starting with the “charge” step to measure the amount of cycleable lithium that is present. The amount of cycleable lithium can be measured. After the charge step is completed, normal cycling can be performed at a rate of C/3 between 4.2 volts and 3.0 volts. The half cell capacity can be determined.

[0067] An example of a salt other than LiCl that has been used by the inventor to achieve lithiation is LiNO.sub.3. Reasonable rates of lithiation have been achieved with LiNO.sub.3. When the anodes pre-lithiated using LiNO.sub.3 were paired with LiFePO.sub.4 cathodes, however, poor cycling resulted, possibly due to an unidentified byproduct. This problem can be solved by a slightly more complicated removal process such as an additional anode rinse.

[0068] While there has been illustrated and described what is at present considered to be the preferred embodiment of the present invention, it will be understood by those skilled in the art that various changes and modifications may be made and equivalents may be substituted for elements thereof without departing from the true scope of the invention. Therefore, it is intended that this invention not be limited to the particular embodiment disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.