Process for producing a lithium dispersion

Abstract

A process for forming a lithium dispersion comprising the steps of: a) contacting lithium metal with a hydrocarbon oil; b) heating the lithium metal and the hydrocarbon oil to a temperature higher than the melting point of the lithium metal; c) subjecting the heated lithium metal and the hydrocarbon oil to conditions sufficient to disperse the lithium metal in the oil, wherein subjecting means vigorously agitating or stirring and contacting the lithium metal powder with a polymer at a temperature between that temperature and at or above the melting point of the lithium; and d) contacting the lithium metal with a polymer selected from the group consisting of polyurethanes, polytetrafluoroethylene, polyvinyl fluoride, polyvinyl chloride, polystyrenes, polypropylenes, polyformaldehyde, styrene-butadiene-styrene block polymers, ethylene-vinyl acetate, ethylene-acrylic acid copolymers, polyethylene oxide, polyimides, polythiophenes, poly(para-phenylene), polyaniline, poly(p-phenylenevinylene), copolymers based on silicon dioxide, titanium dioxide, unsaturated polycarboxylic acids and polysiloxanes at a temperature between the melting point of the lithium metal and the melting point of the polymer to provide a continuous layer of polymer on the lithium metal.

Description

FIELD AND BACKGROUND OF THE INVENTION

[0001] The present invention relates to a process for forming a lithium dispersion.

[0002] Lithium and lithium-ion batteries, or rechargeable lithium and lithium-ion batteries, have recently found widespread use in certain applications, such as mobile phones, camcorders, and laptop computers, and even more recently in high-energy applications, such as electric vehicles and hybrid electric vehicles. In these applications, it is preferred that the batteries have the highest possible specific capacity while still maintaining safe operating conditions and good cycling stability so that the high specific capacity is maintained during subsequent recharge and discharge cycles.

[0003] Although there are various designs for secondary batteries, each includes a positive electrode (or cathode), a negative electrode (or anode), a separator separating the cathode and anode, and an electrolyte in electrochemical communication with the cathode and anode. In lithium secondary batteries, lithium ions are transported from the anode to the cathode by the electrolyte when the battery is discharged, i.e., used for its specific application. During this process, electrons are collected from the anode and carried to the cathode by an external circuit. When the secondary battery is charged or recharged, the lithium ions are transported from the cathode to the anode by the electrolyte.

[0004] In the past, lithium batteries were manufactured using non-lithiated compounds with high specific capacities, such as TiS2, MoS2, MnO2, and V2O5, as active cathode materials. These active cathode materials were often combined with a lithium metal anode. When the battery was discharged, lithium ions were transported from the lithium metal anode to the cathode through the electrolyte. Unfortunately, the lithium metal developed dendrites during cycling, ultimately leading to unsafe conditions within the battery. As a result, production of these types of batteries was discontinued in the early 1990s in favor of lithium-ion batteries.

[0005] Lithium-ion batteries typically use lithium metal oxides such as LiCoO2 and LiNiO2 as active cathode materials, bonded to a carbon-based anode. In these batteries, the formation of lithium dendrites on the anode is avoided, making the battery safer. However, the lithium, the amount of which determines the battery capacity, is supplied entirely by the cathode. This limits the choice of active cathode materials, as the active materials must contain removable lithium. In addition, the delithiated products corresponding to LiCoO2 and LiNiO2, which are formed during charging (e.g., LixCoO2 and LixNiO2, where 0.4 < x < 1.0) and overcharging (i.e., Li x CoO2 and Li x NiO2, where x < 0.4) are not stable. In particular, these delithiated products tend to react with the electrolyte and generate heat, raising safety concerns.

[0006] Another option is lithium metal. However, lithium metal, particularly lithium metal powder, can be deterrent for use in a variety of applications due to its high surface area due to its pyrophoric nature. It is known to stabilize lithium metal powder by passivating the surface of the metal powder with CO2, as described in U.S. Pat. Nos. 5,567,474, 5,776,369, and 5,976,403, the disclosures of which are incorporated herein by reference in their entirety. However, the CO2-passivated lithium metal powder can only be used in low-humidity air for a limited period of time before the lithium metal content decreases due to the reaction of lithium metal and air.

[0007] US 5 643 665 A discloses substrates made of lithium and lithium alloys.

[0008] US 2005 0 244 715 A1 discloses a lithium secondary battery.

[0009] US 2005 / 0 239 917 A1 discloses lithium metal powder based inks.

[0010] US 2004 / 0 018 430 A1 discloses electrodes for use in electrochemical devices.

[0011] US 2004 / 0 002 005 A1 discloses a secondary battery with a high specific capacity.

[0012] DE 11 2007 002 375 T5 discloses a process for producing a lithium dispersion.

[0013] Therefore, there is still a need for stabilized lithium metal powder that has improved stability and storage stability. SUMMARY OF THE INVENTION

[0014] The process of the present invention provides a lithium metal powder protected by a continuous layer of a polymer. Such a continuous polymer layer provides improved protection compared to typical CO2 passivation. The resulting lithium metal powder exhibits improved air and solvent stability and improved storage stability. Furthermore, the polymer-protected lithium metal powder exhibits significantly better stability in N-methyl-2-pyrrolidone (NMP), which is commonly used as a slurry solvent in the electrode manufacturing process and reacts with unprotected lithium.

[0015] Objects and advantages of the present invention will become more apparent by describing various embodiments of the present invention with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig.Figure 1 is an ARSST stability test of CO2 coated SLMP (Comparative Example 2) with NMP as supplied (< 100 ppm moisture) and with NMP doped with 0.6% water. Fig. Figure 2 is an ARSST stability test of PEO-coated SLMP (Example 2) with NMP doped with 0.6% water. Fig. Figure 3 is an ARSST stability test of EVA coated SLMP with NMP doped with 0.6% water, Example 10. Fig. Figure 4 is an ARSST stability test of SBR-coated SLMP with NMP doped with 0.6% water, Example 7. Fig. Figure 5 is an ARSST stability test of SLMP coated with BYK P 104 (low molecular weight polycarboxylic acid polymer) with NMP added with 0.6% water, Example 3. Fig. Figure 6 shows the effect of polymer coated lithium on the electrochemical behavior Fig.Figure 7 is an ARSST stability test of CO2 coated SLMP and Example 11. Fig. 8A, Fig. 8B and Fig. 8C are SEM images of samples prepared using different process parameters. Fig. Figure 9A is a comparison of lithium metal concentration in anhydrous NMP as a function of time. Fig. Figure 9B is a comparison of the lithium metal concentration in NMP spiked with 0.6% water as a function of time. DETAILED DESCRIPTION OF THE INVENTION

[0016] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the term "and / or" includes any and all combinations of one or more of the listed associated terms. As used herein, the singular forms "a" and "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It is further understood that the terms "comprises" and / or "comprising," when used in this specification, specify the presence of the recited features, integers, steps, actions, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, actions, elements, components, and / or groups thereof.Furthermore, the term "about", as used herein, when referring to a measurable value such as an amount of a compound or agent of the invention, a dose, time, temperature, etc., is intended to include variations of 20%, 10%, 5%, 1%, 0.5%, or even 0.1% of the stated amount.

[0017] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as would commonly be understood by one of ordinary skill in the art to which the invention belongs. It is further understood that terms such as those defined in commonly used dictionaries should be interpreted to have a meaning consistent with their meaning in the context of the relevant art and should not be interpreted in an idealized or overly formal sense, unless expressly so defined herein.

[0018] According to the present invention, lithium dispersions are prepared by heating the lithium metal powder in a hydrocarbon oil to a temperature above its melting point, subjecting it to conditions sufficient to disperse the molten lithium, vigorously agitating or stirring it, and contacting the lithium metal powder with a polymer at a temperature between that temperature and at or above the melting point of the lithium to provide a continuous layer of the polymer. The continuous layer of polymer has a thickness of 25 to 200 nm and frequently has a thickness of 80 to 120 nm. Other alkali metals, such as sodium and potassium, can be coated according to the present invention.

[0019] The invention allows the use of polymers that are water-resistant and lithium-ion conductive or non-lithium-ion conductive, e.g., if they are soluble in conventional electrolyte solvents. The polymers may be lithium-reactive or lithium-nonreactive. The following polymer compounds are according to the invention: polyurethanes, polytetrafluoroethylene, polyvinyl fluoride, polyvinyl chloride, polystyrenes, polypropylene, polyformaldehyde (Delrin), styrene-butadiene-styrene block polymers, ethylene-vinyl acetate, ethylene-acrylic acid copolymers, polyethylene oxide, polyimides, polythiophenes, poly(para-phenylene), polyanilines, poly(p-phenylenevinylene), silicon dioxide-titanium dioxide copolymers, unsaturated polycarboxylic acid polymers, and polysiloxane copolymers, among others.

[0020] The polymer can be added to contact the lithium droplets during dispersion or at a lower temperature after the lithium dispersion has cooled. It is understood that combinations of different types of polymers with different chemical compositions, molecular weights, melting points, and hardnesses can be used to achieve specific coating properties for specific applications. For example, the degree of tack can be controlled to enable the incorporation of the SLMP using the "transfer release paper" concept, where a specific degree of tack is required. It is also understood that the monomers can be used to create an in-situ polymer coating on the surface of the lithium particles.

[0021] It is further advantageous to combine polymer or polymer blends with any inorganic coating, e.g., Li2CO3, LiF, Li3PO4, SiO2, Li4SiO4, LiAlO2, Li2TiO3, LiNbO3, Al2O3, SiO2, SnO2, ZrO2, and the like, to improve both air stability and stability against polar solvents, which would allow safer handling and also the possibility of using commonly used polar solvents that dissolve commonly employed polymer binders. It is recognized that most polymers are soluble in nonpolar solvents at elevated temperatures and that solubility at room temperature can be considerable (see Table 2), and that washing solvents used to remove oil from the particles should be appropriately selected. Sometimes, dry unstabilized or stabilized powders can be converted to nonpolar solvents.are compatible with lithium, and the polymer coatings can be deposited, e.g., using rotary evaporation techniques, thus avoiding the solubility problem.

[0022] Suitable polymers described above can produce two types of coatings on lithium particles: a first type representing a physical or adhesive type, and a second type representing chemically bonded coatings, which uses polymers with functional groups. For example, polypropylene (PP) and polystyrene (PS) contain carbon-hydrogen groups that do not react with Li. This type of polymer is useful as a coating reagent for lithium particles because the physical van der Waals interaction allows carbon-hydrogen molecules to adhere to the surface of lithium particles. On the other hand, polymers such as poly(acrylic acid) and ethylene-vinyl acetate react with lithium because they contain acid functional groups, thus forming a chemically bonded coating.

[0023] Changing the procedures and process parameters and the order of reagent addition for polymer-coated lithium particles can lead to different surface properties. Different process parameters can lead to samples with different surface properties (see Fig. 7). Polymers or polymer blends can be added above the melting point of lithium before or after other dispersants (e.g., wax) and coating reagents to improve chemical bonding and the uniformity of the protective layer by altering the reaction interfaces. The cooling profile, the temperature at which the polymer is added during the dispersion process, can be used to control the degree of crystallinity and obtain samples with a predetermined degree of stickiness.

[0024] The following examples are merely illustrative of the invention and are not limitative thereof. EXAMPLESComparison example 1

[0025] Battery-grade lithium metal (405 g) was cut into 2 × 2-inch pieces and placed under a constant dry argon flow at room temperature in a 3-liter stainless steel flask reactor with a 4-inch head and a stirrer shaft connected to a fixed high-speed stirrer motor. The reactor was fitted with upper and lower heating mantles. The reactor was then assembled and 1,041.4 g of Penetek ®-Oil (Penreco, a division of Penzoil Products Company) was added. The reactor was then heated to approximately 200°C, and gentle stirring was maintained between 250 rpm and 800 rpm to ensure that all of the metal was melted, with argon flow maintained throughout the heating step. The mixture was then stirred at high speed (up to 10,000 rpm) for 2 minutes. 8.1 g of oleic acid was added to the reactor, and high-speed stirring was continued for another 3 minutes, followed by the addition of 5.1 g of CO2. High-speed stirring was then stopped, the heating mantles were removed, and the dispersion was allowed to cool to approximately 50°C and transferred to storage bottles. The lithium dispersion was further filtered and washed three times with hexane and once with n-pentane in an enclosed sintered glass filter funnel to remove the hydrocarbon oil medium under argon flow.The funnel was heated with a heat gun to remove traces of solvents, and the resulting free-flowing powder was transferred into tightly sealed storage bottles. Comparison example 2

[0026] Penetek ®Mineral oil (4,449 g) and 1,724 g of battery-grade lithium metal were added to a 15-liter jacketed dispersion reactor at room temperature under an argon atmosphere. The reactor was then heated from room temperature to 200°C by pumping hot heat transfer fluid through the jacket. While the dispersion was heating, the stirrer was kept at low speed to facilitate heat exchange. After the temperature inside the reactor reached 200°C, the speed of the dispersing stirrer was increased to 5,000 rpm. After 3.5 min of high-speed stirring, 36 g of oleic acid were added to the reactor, and high-speed stirring was continued for another 4.5 min, followed by the addition of 22 g of CO2 gas. After an additional 4 min of high-speed stirring, the high-speed stirrer was turned off, and the reactor contents were allowed to cool to room temperature.During the cooling process, the dispersion was kept in suspension by low-speed stirring. The lithium dispersion was transferred to a discontinuous filter under argon pressure, and the mineral oil was allowed to drain off. The dispersion in the filter was washed four times with hexane; then, dry argon was bubbled through the filter to remove any remaining volatile organic compounds. The dry, stabilized, polymer-coated lithium dispersion was removed from the filter as the final product. Example 1

[0027] A lithium dispersion (47.30 g) passivated with CO2 gas in oil (27.5%), containing 13.01 g of lithium with an average particle size of 45 microns, was placed in a 120 mL Hastelloy can equipped with a 1-inch Teflon-coated stir bar. 1.3 g of dry PEO (Polyox WSR N80) powder was also added to the can. The solution was heated from ambient temperature to 75°C at a rate of 5°C / min and held for 10 min. The sample was further heated from 75°C to 175°C at 5°C / min and held for 1 h. This mixture was stirred continuously at 200 rpm during the heating phase. The sample was allowed to cool to room temperature and transferred to the storage bottle. The lithium dispersion was further filtered and washed three times with hexane in an enclosed sintered glass filter funnel and twice with n-pentane to remove the hydrocarbon oil medium.The funnel was heated with a heat gun to remove traces of solvents, and the resulting free-flowing powder was transferred into tightly sealed storage bottles. Example 2

[0028] A lithium dispersion (45.00 g) passivated with CO2 gas in oil (27.5%), containing 12.37 g of lithium with an average particle size of 45 microns, was placed in a 120 mL Hastelloy can equipped with a 1-inch Teflon-coated stir bar. 1.2 g of dry PEO (Polyox WSR N80) powder was also added to the can. The solution was heated from ambient temperature to 75°C at a rate of 5°C / min and held for 10 min. The sample was further heated from 75°C to 175°C at 5°C / min and held for 1 h. Finally, the sample was heated from 175°C to 200°C at 20°C / min. This mixture was stirred continuously at 200 rpm during the heating phase. The sample was allowed to cool to room temperature and transferred to a storage bottle. The lithium dispersion was further filtered and washed three times with hexane and twice with n-pentane in an enclosed sintered glass filter funnel to remove the hydrocarbon oil medium.The funnel was heated with a heat gun to remove traces of solvents, and the resulting free-flowing powder was transferred into tightly sealed storage bottles. Example 3

[0029] A lithium dispersion (44.00 g) passivated with CO2 gas in oil (27.5%), containing 12.10 g of lithium with an average particle size of 45 microns, was placed in a 120 mL Hastelloy can equipped with a 1-inch Teflon-coated stir bar. The solution was heated to 75°C, and 1.2 mL of BYK-P 104 S (BYK Chemie) was added to the lithium dispersion. This mixture was stirred continuously at 200 rpm for 1 h. The sample was allowed to cool to room temperature and transferred to a storage bottle. The lithium dispersion was further filtered and washed three times with hexane and twice with n-pentane in an enclosed sintered glass filter funnel to remove the hydrocarbon oil medium. The funnel was heated with a heat gun to remove traces of solvents, and the resulting free-flowing powder was transferred into tightly sealed storage bottles. Example 4

[0030] A stabilized lithium dispersion (54.99 g) in oil (11.275%) containing 6.20 g of lithium with an average particle size of 58 microns was placed in a 120 mL Hastelloy can equipped with a 1-inch Teflon-coated stir bar. At ambient temperature, 0.62 g of SBR as a 10% solution in p-xylene (Aldrich) was added to the lithium dispersion. This mixture was stirred continuously at 200 rpm for 19 h. The sample was transferred to a storage bottle. The lithium dispersion was further filtered and washed three times with hexane and twice with n-pentane in an enclosed sintered glass filter funnel to remove the hydrocarbon oil medium. The funnel was heated with a heat gun to remove traces of the solvents, and the resulting free-flowing powder was transferred to tightly sealed storage bottles. Example 5

[0031] A stabilized lithium dispersion (54.68 g) in oil (11.275%) containing 6.17 g of lithium with an average particle size of 58 microns was placed in a 120 mL Hastelloy can equipped with a 1-inch Teflon-coated stir bar. At ambient temperature, 0.62 g of EVA (Aldrich) as a 5% solution pre-dissolved in p-xylene (Aldrich) was added to the lithium dispersion. This mixture was stirred continuously at 200 rpm for 2.5 h. The sample was transferred to a storage bottle. The lithium dispersion was further filtered and washed three times with hexane and twice with n-pentane in an enclosed sintered glass filter funnel to remove the hydrocarbon oil medium. The funnel was heated with a heat gun to remove traces of solvents, and the resulting free-flowing powder was transferred into tightly sealed storage bottles. Example 6

[0032] A stabilized lithium dispersion (54.00 g) in oil (11.275%) containing 6.09 g of lithium with an average particle size of 58 microns was placed in a 120 mL Hastelloy can equipped with a 1-inch Teflon-coated stir bar. At ambient temperature, 0.5 mL of butadiene (Aldrich) and 0.5 mL of styrene (Aldrich) were added to the lithium dispersion. This mixture was stirred continuously at 200 rpm for 1 h. The sample was transferred to a storage bottle. The lithium dispersion was further filtered and washed three times with hexane and twice with n-pentane in an enclosed sintered glass filter funnel to remove the hydrocarbon oil medium. The funnel was heated with a heat gun to remove traces of solvents, and the resulting free-flowing powder was transferred to tightly sealed storage bottles. Example 7

[0033] 10.0 g of SLMP (stabilized lithium metal powder) was weighed into a 1 L round-bottomed flask. 32.1 g of p-xylene (Aldrich) and 0.28 g of SBR as a 10% solution pre-dissolved in p-xylene (Aldrich) were added to the flask. The flask containing the mixture was attached to a rotary vacuum evaporator extractor and heated to 70°C while rotating. After holding the temperature at 70°C for 15 minutes, vacuum was applied to evaporate the solvent. The sample was then transferred to a storage bottle. Example 8

[0034] 4.0 g of unstabilized lithium powder with an average particle size of 58 microns and 36 g of p-xylene (Aldrich) were placed in a 120 mL Hastelloy can equipped with a 1-inch Teflon-coated stir bar. The mixture was heated to 40°C while mixing at 200 rpm. At 40°C, 0.40 g of EVA, pre-dissolved in p-xylene (Aldrich) as a 10% solution, was added to the lithium and p-xylene mixture. This mixture was stirred continuously at 200 rpm for 20 h. The sample was transferred to a 200 mL round-bottom flask. Furthermore, p-xylene was evaporated by bubbling dry argon over the sample. The resulting free-flowing powder was transferred to a tightly sealed storage bottle. Example 9

[0035] A stabilized lithium dispersion (2,149.8 g) in oil (11.0%) containing 236.5 g of lithium with an average particle size of 58 microns was added to a 3 L round-bottom flask equipped with a variable-speed propeller stirrer. At ambient temperature, 23.8 g of EVA (Aldrich) as a 10% solution in p-xylene (Aldrich) was added to the lithium dispersion. This mixture was stirred continuously at 500 rpm for 4 h. The sample was transferred to a storage bottle. The lithium dispersion was further filtered and washed three times with hexane and twice with n-pentane in an enclosed sintered glass filter funnel to remove the hydrocarbon oil medium. The funnel was heated with a heat gun to remove traces of the solvents, and the resulting free-flowing powder was transferred to tightly sealed storage bottles. Example 10

[0036] A stabilized lithium dispersion (1,127.0 g) in oil (11.2%) containing 126.6 g of lithium with an average particle size of 63 microns was added to a 5 L round-bottom flask equipped with a variable-speed propeller stirrer. The temperature was raised to 41.3°C, and 12.5 g of EVA (Aldrich) as a 5% solution in p-xylene (Aldrich) was added to the lithium dispersion. This mixture was stirred continuously at 500 rpm for approximately 6 h at 40°C and then for another ~18 h at ambient temperature. The sample was transferred to a storage bottle. The lithium dispersion was further filtered and washed three times with hexane and twice with n-pentane in an enclosed sintered glass filter funnel to remove the hydrocarbon oil medium. The funnel was heated with a heat gun to remove traces of solvents, and the resulting free-flowing powder was transferred into tightly sealed storage bottles. Example 11

[0037] Penetek ®Mineral oil, 15,390 g, and 4,415 g of battery-grade lithium metal were added to a 57-liter jacketed dispersion reactor at room temperature under an argon atmosphere. The reactor was then heated from room temperature to 190°C by pumping hot heat transfer fluid through the jacket. During heating, the dispersion impeller was maintained at low speed to facilitate heat transfer to the reactor contents. After the temperature inside the reactor reached 190°C, the dispersion impeller speed was increased to 4,800 rpm. After 3 min of high-speed stirring, 90 g of oleic acid was added to the reactor, and high-speed stirring was continued for another 4 min, followed by the addition of 56 g of CO2 gas. After an additional 6 min of high-speed stirring, 154 g of polyethylene oxide (PEO) granules were added to the reactor and high-speed stirring was continued for another 3 minutes.The high-speed stirrer was then turned off, and the reactor contents were cooled to room temperature. During the cooling process, the dispersion was kept in suspension by low-speed stirring. The lithium dispersion was transferred to a discontinuous filter under argon pressure, and the mineral oil was drained off under argon pressure. The dispersion in the filter was washed four times with hexane; then, dry argon was bubbled through the filter to remove any remaining volatile organic compounds. The dry, stabilized, polymer-coated lithium dispersion was removed from the filter as the final product.

[0038] The following Fig. 1 to Fig. 5 and Fig.Figure 7 shows the stability of polymer-coated samples in NMP, which is widely used as a solvent in the electrode manufacturing process for rechargeable lithium-ion batteries. The following procedure was used to conduct this test: SLMP and solvent were filled into the test cell under argon. The test cell was then heated to 25°C and kept isothermal for 72 hours. The temperature was then raised to 55°C and kept isothermal for 48 hours; the mixture was continuously stirred. The lithium metal content of the samples was measured after the test: the higher the content, the better the protective properties of the coating. As can be seen from Table 1 below, the lithium concentration was 17.3% and higher for the samples in the examples shown. No adverse effects on the electrochemical properties of the polymer additive for the graphite electrode were observed. (See Fig. 6.) The Fig. 8A, Fig. 8B and Fig. 8C show the different surface properties of Examples 5, 8, and 9 due to changes in process parameters. A separate test was performed to determine the lithium content as a function of time for water-added NMP, and a significant improvement was observed. (See Fig. 9A and Fig. 9B.) Table 1. Examples of residual lithium metal concentration measured using the ARSST standard test with NMP spiked with 0.6% water Coating agents Example Residual lithium metal concentration EVA Example 10 (785-106) 24,3% SBR Example 7 (767-200) 17,3% PEO Example 1 (PEOR043007) 38,2% PEO Example 2 (PEOR050807) 30,9% Table 2. Examples of the solubility of the polymers in selected solvents LuWax A SBR EVA PEO Hexane 0,46% 3,92% 1,21% 0,03% Pentane 0,48% 4,1% 0,46% 0,03% xylene 0,81% > 10% > 10% > 10%

Claims

[1] A process for forming a lithium dispersion comprising the steps of: a) contacting lithium metal with a hydrocarbon oil; b) heating the lithium metal and the hydrocarbon oil to a temperature higher than the melting point of the lithium metal; c) subjecting the heated lithium metal and the hydrocarbon oil to conditions sufficient to disperse the lithium metal in the oil, wherein subjecting means vigorously agitating or stirring and contacting the lithium metal powder with a polymer at a temperature between that temperature and at or above the melting point of the lithium; and d) contacting the lithium metal with a polymer selected from the group consisting of polyurethanes, polytetrafluoroethylene, polyvinyl fluoride, polyvinyl chloride, polystyrenes, polypropylenes, polyformaldehyde, styrene-butadiene-styrene block polymers, ethylene-vinyl acetate, ethylene-acrylic acid copolymers, polyethylene oxide, polyimides, polythiophenes, poly(para-phenylene), polyaniline, poly(p-phenylenevinylene), copolymers based on silicon dioxide, titanium dioxide, unsaturated polycarboxylic acids and polysiloxanes at a temperature between the melting point of the lithium metal and the melting point of the polymer to provide a continuous layer of polymer on the lithium metal.

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