Stabilized lithium metal formations coasted with a shell containing nitrogen, and a method for the production of same

Abstract

The invention relates to particulate lithium metal formations having a substantially spherical geometry and a core composed of metallic lithium, which are enclosed with an outer passivating but ionically conductive layer containing nitrogen. The invention further relates to a method for producing lithium metal formations by reacting lithium metal with one or more passivating agent(s) containing nitrogen, selected from the groups N.sub.2, N.sub.xH.sub.y with x=1 or 2 and y=3 or 4, or a compound containing only the elements C, H, and N, and optionally Li, at temperatures in the range between 60 and 300 C., preferably between 100 and 280 C., and particularly preferably above the melting temperature of lithium of 180.5 C., in an inert organic solvent under dispersion conditions or in an atmosphere that contains a gaseous coating agent containing nitrogen.

Claims

1. A method for producing a stabilized lithium metal form of granules, characterized in that lithium metal with a sodium content less than 200 ppm is brought into contact with one or more nitrogen-containing passivating agent(s) selected from the groups N.sub.2 N.sub.xH.sub.y with x=1 or 2 and y=3 or 4, or a compound containing only the elements C, H, and N, and optionally Li at temperatures in the range above the melting point of lithium of 180.5 C., wherein the contacting between lithium metal and the one or more nitrogen-containing passivating agent(s) first takes place in an inert organic solvent under dispersion conditions and a molar ratio of Li metal to passivating agent is in a range of 100:0.01 to 100:10.

2. The method according to claim 1, characterized in that said lithium metal has a sodium content less than 100 ppm.

3. The method according to claim 1, characterized in that said lithium metal has a sodium content less than 50 ppm.

4. The method according to claim 1, characterized in that gaseous sources of nitrogen, liquid compounds, or substances that are capable of releasing nitrogen are used as nitrogen-containing passivating agents.

5. The method according to claim 4, characterized in that gaseous sources of nitrogen are selected from elemental nitrogen or ammonia.

6. The method according to claim 4, characterized in that liquid nitrogen-containing passivating agent(s) is hydrazine.

7. The method according to claim 4, characterized in that substances that are capable of releasing nitrogen are selected from lithium azide (LiN3) or organic azides (RN3).

8. The method according to claim 1, characterized in that organic substances which contain no other chemical elements besides C, H, N, and optionally Li are used as nitrogen-containing coating agents selected from primary, secondary, or tertiary aliphatic amines NR.sup.1R.sup.2R.sup.3, where R.sup.1, R.sup.2 independently stand for H or an aliphatic group containing 1 to 12 C atoms or an aromatic group containing at least 6 C atoms, and R.sup.3 independently stands for an aliphatic group containing 1 to 12 C atoms or an aromatic group containing at least 6 C atoms; nitrogen-containing 3- to 6-membered heterocycles.

9. The method according to claim 8, characterized in that nitrogen-containing 3- to 6-membered heterocycles are selected from azirines, aziridines, pyrrolidines, pyrroles, N-methylpyrrole, pyridines, imidazole.

10. The method according to claim 8, characterized in that as organic substances which contain no other chemical elements besides C, H, N, and Li lithium salts are used of a primary or secondary aliphatic or aromatic amine, selected from lithium diisopropyl amide; lithium pyrrolidide.

11. The method according to claim 1, characterized in that the molar ratio of Li metal to passivating agent is in the range of 100:0.05 to 100:5.

12. The method according to claim 1, characterized in that hydrocarbons selected from the group comprising hexane, heptane, octane, decane, undecane, dodecane, toluene, ethylbenzene, and cumene, either in pure form or in a mixture as commercially available boiling fractions, are used as inert organic solvent.

13. A stabilized particulate lithium metal received by the method according to claim 1 characterized in that the stabilized particulate lithium metal has a granular form and a core composed of metallic lithium, and the core is enclosed by an outer passivating layer containing nitrogen wherein that outer passivating layer containing nitrogen has a thickness between 0.01 and 1 m and contains or is composed of at least one lithium nitrogen compound selected from the group Li.sub.3N, Li.sub.4NH, Li.sub.2NH, LiNH.sub.2.

14. The stabilized particulate lithium metal according to claim 13, characterized in that the stabilized particulate lithium metal contains in the range of 0.01 to 10% by weight nitrogen.

15. The stabilized particulate lithium metal according to claim 13, characterized in that the stabilized particulate lithium metal has an average particle size of 5000 m maximum.

16. The stabilized particulate lithium metal according to claim 15, characterized in that the stabilized particulate lithium metal has an average particle size of 1000 m maximum.

17. The stabilized particulate lithium metal according to claim 15, characterized in that the stabilized particulate lithium metal has an average particle size of 300 m maximum.

18. The stabilized particulate lithium metal according to claim 13, characterized in that the stabilized particulate lithium metal does not exhibit a runaway phenomenon, when in contact with N-methyl-2-pyrrolidone, with a water content of approximately 200 ppm, for at least 15 hours at 50 C.

19. The stabilized particulate lithium metal according to claim 18, characterized in that the stabilized particulate lithium metal does not exhibit a runaway phenomenon, when in contact with N-methyl-2-pyrrolidone, with a water content of approximately 200 ppm, for at least 15 hours at 80 C.

Description

EXAMPLE 1: Production of a Lithium Metal Powder Passivated With Elemental Nitrogen

(1) 499 g Shellsol D100 and 20.3 g lithium metal rod sections were placed in a dry 2-L stainless steel double-jacketed reactor equipped with a dispersion agitator mechanism and inerted with argon. The lithium had a sodium content of 40 ppm. Under gentle agitation (approximately 50 rpm), the internal temperature was raised to approximately 205 C. by jacket heating, and a metal emulsion was produced by means of the dispersant. Nitrogen was then introduced over a period of 10 minutes (approximately 0.1 L/60 s) under dispersion conditions. The dispersion agitator was then stopped, and the suspension was cooled to ambient temperature with gentle agitation. The suspension was poured onto a glass suction filter, and the filter residue was washed several times with hexane until free of oil and then vacuum dried.

(2) Yield: 19.2 g (95% of theoretical) of a fine gray powder

(3) Average particle size: 90 m (FBRM particle size analyzer from Mettler-Toledo)

(4) N content: 4.8% by weight

(5) Metal content: 86% (gas volumetric)

(6) Behavior in air: not pyrophoric

(7) Stability in NMP, water content 167 ppm: stable for 15 h at 80 C.

(8) Stability in LiPF.sub.6, 10% in EC/EMC (1:1); EC/EMC (1:1), and 10% LiBOB in EC/EMC

(9) (1:1): T.sub.onset=150 C.; 170 C.; 190 C.

(10) Surface analysis by XRD: phase components of Li.sub.3N and Li.sub.4NH

EXAMPLE 2: Production of a Combined Passivated Lithium Metal Powder (Coating With Elemental Nitrogen and a Silicone Oil)

(11) 501 g Shellsol D100 and 20.8 g lithium metal rod sections were placed in a dry 2-L stainless steel double-jacketed reactor equipped with a dispersion agitator mechanism and inerted with argon. The lithium had a sodium content of 40 ppm. Under gentle agitation (approximately 50 rpm), the jacket temperature was raised to 240 C. by jacket heating, and a metal emulsion was produced by means of the dispersant. 1.2 g polydimethylsiloxane (CAS No. 9016-00-6) dissolved in approximately 3 mL Shellsol D100 was then added with a syringe over a period of 3 minutes. During the addition, the suspension was agitated with a strong shearing action. The dispersion agitator was then stopped, and nitrogen was introduced for 1 h (approximately 0.1 L/60 s). The suspension was then cooled to room temperature.

(12) The suspension was poured onto a glass suction filter, and the filter residue was washed several times with hexane until free of oil and then vacuum dried.

(13) Yield: 21.8 g (105% of theoretical)

(14) Average particle size: D.sub.50=59 m (FBRM particle size analyzer from Mettler-Toledo)

(15) Metal content: 95% (gas volumetric)

(16) Stability in NMP, water content 167 ppm: stable for 15 h at 80 C.

(17) Si content: 0.056% by weight

(18) N content: 0.93% by weight

(19) Surface analysis by XRD: small phase components of Li.sub.3N and Li.sub.4NH

EXAMPLE 3: Production of a Low-Sodium Lithium Powder Coated With Pyrrole

(20) 501 g Shellsol D100 and 20.4 g lithium metal rod sections were placed in a dry 2-L stainless steel double-jacketed reactor equipped with a dispersion agitator mechanism and inerted with argon. The lithium had a sodium content of 40 ppm. Under gentle agitation (approximately 50 rpm), the internal temperature was raised to 204 C. by jacket heating, and a metal emulsion was produced by means of the dispersant. 1.0 g pyrrole was then added with a syringe over a period of 3 minutes. During the addition, the suspension was agitated with a strong shearing action. The suspension was gently agitated for an additional 60 minutes at a jacket temperature of approximately 210 C., then the agitator was stopped, and the suspension was cooled to room temperature. The suspension was poured onto a glass suction filter, and the filter residue was washed several times with hexane until free of oil and then vacuum dried.

(21) Yield: 20.9 g (102% of theoretical)

(22) Average particle size D.sub.50=57 m (FBRM particle size analyzer from Mettler-Toledo)

(23) Metal content: 92% (gas volumetric)

(24) Stability in NMP, water content 167 ppm: stable for 15 h at 60 C.;

(25) Stability in LiPF.sub.6, 10% in EC/EMC (1:1); EC/EMC (1:1), and 10% LiBOB in EC/EMC

(26) (1:1): T.sub.offset=135 C.; 145 C.; 185 C.

(27) N content: 0.71% by weight

(28) Surface analysis by XRD: small phase components of Li.sub.3N and an unknown phase

COMPARATIVE EXAMPLE 1: Reactivity of Commercial Lithium Metal Foil With Dry Air

(29) 38.072 g lithium metal foil, battery quality, was stored in an open glass dish in a drying chamber having a dew point of 40 C. and temperatures around 25 C. The shell was weighed after certain time intervals:

(30) TABLE-US-00002 Storage period Change in weight (hours) (%) 1 0.01 2 0.02 7 0.03 53 0.06 101 0.09

(31) It is apparent from the measurement data that lithium foil in dry air reacts extremely slowly with nitrogen. The increase in weight corresponds to the absorption of the reactive components in the air (i.e., the sum based on the reaction with oxygen, nitrogen, carbon dioxide, and residual water content). The increase in weight is markedly lower in a pure nitrogen atmosphere.