EP0950023A1

EP0950023A1 - Process for preparing lithium and manganese oxides

Info

Publication number: EP0950023A1
Application number: EP97953902A
Authority: EP
Inventors: Horst Krampitz; Gerhard Wöhner
Original assignee: Riedel de Haen AG
Current assignee: Honeywell Riedel de Haen AG
Priority date: 1996-12-30
Filing date: 1997-12-22
Publication date: 1999-10-20
Also published as: AU5762898A; CA2276301A1; WO1998029342A1; TW446685B; US6706443B1; KR20000062340A; JP2001508391A

Abstract

A process is disclosed for preparing a lithium manganese oxide by reacting at least one lithium compound and at least one manganese compound in hydrothermic conditions, i.e. in heated aqueous solutions at sub-atmospheric pressures. Also disclosed is such a lithium and manganese oxide and its use as cathode material for electrochemical cells.

Description

Process for the production of lithium manganese oxides

The present invention relates to a process for producing a lithium manganese oxide by reacting at least one lithium and at least one manganese compound under hydrothermal conditions, i.e. from heated aqueous solutions at subatmospheric pressures, such a lithium manganese oxide per se and its use as a cathode material for electrochemical cells.

Processes for producing lithium manganese oxides of the approximate composition LiMn ₂ O ₄ are known per se.

No. 4,980,251 describes a process for producing a lithium manganese oxide of the formula Li ₁ . _x Mn ₂ O, with 0 <x <1 by means of a solid-state reaction in which, by mixing the corresponding oxides and / or carbonates together and heating the resulting mixtures in an oxidizing atmosphere to a temperature in the range from 200 to 600 ° C., the corresponding lithium Manganese oxide is obtained. As stated in US Pat. No. 4,980,251, spinels with exceptionally high BET surface areas of, for example, more than 30 m ² / g with poor crystallinity are obtained. According to the publication, such spinels are particularly well suited for use in electrochemical cells.

DE-A-43 27 760 relates to a method for producing a positive

Electrode for lithium secondary batteries, the active material of one

Lithium-manganese oxide with spinel structure, which is obtained by mixing manganese dioxide with lithium formate and / or lithium acetate and then heating the mixture at a temperature of 550 to 800 ° C and subsequent grinding is obtained.

Another method for producing such oxides with a spinel structure is claimed in US Pat. No. 5,135,732. There, a gel-like precipitate is initially formed by mixing stoichiometric amounts of an aqueous solution of lithium hydroxide and manganese acetate in the presence of a base at a pH of approximately 7. This is then dried at 60 to 150 ° C to form a xerogel. Finally, the xerogel is heated to a temperature of 200 to 600 ° C, whereby a lithium-manganese spinel is obtained.

DE-A 195 19 044 describes spinels containing lithium and manganese (HI / TV) with a specific surface area of 0.1 to 4 m ² / g and their use as cathode material for electrochemical cells. The reaction of the starting compounds at elevated temperature is specified as a process for the preparation of the spinels claimed there.

However, the above-mentioned processes have disadvantages with regard to the homogeneity of the products obtained. Furthermore, in the course of these processes, by-products which cannot be used or are difficult to use, such as Salts and exhaust gases.

Although the prior art documents discussed above also state the use of the oxides produced there as cathode material in electrochemical cells, the oxides with spinel structure produced according to the prior art processes have a comparatively poor, often inadequate, cycle stability during use as cathode material in electrochemical cells. State of the art is the use of LiCoO ₂ and LiNiO ₂ as cathode materials for electrochemical cells. Due to the relatively high material costs, the limited availability with regard to cobalt, its environmental concerns and the potential for overloading associated with the use of these compounds, there is great interest in replacing the above-mentioned compounds with, for example, lithium-manganese oxides with a spinel structure, as also in the publications cited above is proposed according to the prior art. For example, D. Fouchard et al. in a scientific article in "The Electrochemical Society Proceedings", Vol. 94-28, p. 348, the use of lithium manganese oxides with spinel structure in electrochemical cells.

In view of the above prior art, the object of the present invention is to provide a method which, on the one hand, makes it possible to use lithium-manganese oxides, in particular i.a. to produce phase-pure lithium manganese oxides with a spinel structure, and furthermore can be carried out on a large industrial scale without any problems and by avoiding unusable or even harmful by-products and leads to lithium manganese oxides with very good electrochemical properties.

This object is achieved by a process for producing a lithium manganese oxide of the formula Li _{1; 5} . _x Mn ₂ O ₄ , where the value for x corresponds to the relation 0 <x <1, 5, which comprises the following level:

Reaction of at least one lithium and at least one manganese compound, characterized in that the reaction is carried out in an aqueous medium at a temperature in the range from 80 to 500 ° C and a pressure of 1 · 10 ⁵ Pa to 5 • 10 ⁷ Pa. As can be seen from the above, it is possible within the scope of the method according to the invention to obtain not only lithium-manganese oxides with spinel structure of the approximate composition LiMn ₂ O ₄ but also oxides with a very low proportion of lithium, including λ-MnO ₂ . However, an oxide with a spinel structure is preferably obtained.

Although in principle all lithium compounds can be used in the process according to the invention, Li ₂ O, LiOH, LiCl, LiNO ₃ , Li ₂ CO ₃ , Li carboxylates, such as Li formate or lithium acetate, or a mixture of two, are preferably used or more of them.

In principle, there are also no restrictions with regard to the manganese compounds which can be used in the process of the invention. However, MnO ₂ , MnO, MnOOH, Mn ₂ O ₃ , Mn ₃ O ₄ , MnCO ₃ , Mn (NO ₃ ) ₂ , Mn carboxylates, such as, for example, Mn formate or Mn acetate or a mixture of two or more, are preferred thereof used as a manganese compound, in particular oxidic manganese raw materials and mixed manganese oxides, such as MnO, MnOOH, Mn ₂ O ₃ , Mn ₃ O ₄ , and MnCO ₃ , and mixtures of two or more thereof being used.

In addition, the lithium-manganese oxides produced according to the invention can additionally contain a further metal M or a mixture of two or more further metals, preferably a metal from the group Ha, lilac, IVa, Ilb, Illb, IVb, VIb, Vllb or VIII des Periodic table or a mixture of two or more thereof, and in particular iron, cobalt, nickel, titanium, boron, aluminum or a mixture of two or more thereof, wherein oxides of the general formula

^Li l, 5-x ^M z ^Mn 2-z ° 4> where x is as defined above and the value for z corresponds to the relation 0.01 <z <1.

To produce such metal-doped Li-Mn oxides, a salt of a metal or a mixture of two or more thereof, as defined above, is preferably made of an Fe, Co, Ni or a mixture of in the reaction according to the invention two or more of them, each used in the desired amount.

Accordingly, the present invention also relates to a method for producing a lithium manganese oxide of Formula Li _{1. 5} _x M _z Mn ₂ . _z O ₄ , where the value for x corresponds to the relation 0 <x <1.5, M is a metal from the group Ha, lilac, IVa, Ilb, Illb, IVb, VIb, Vllb, or VIII of the periodic table or a mixture of two or more thereof and the value for z corresponds to the relation 0.01 <z <1, preferably the relation 0.1 <z <0.4, which comprises the following step: reaction of at least one lithium, at least one manganese and at least one compound of a metal as defined above, characterized in that the reaction is carried out in an aqueous medium at a temperature in the range from 80 to 500 ° C and a pressure of 1 • 10 ⁵ Pa to 5 • 10 ⁷ Pa.

The lithium and manganese compound are preferably used in an amount such that the molar ratio of manganese: lithium is 2: approximately 1, but also molar ratios Mn: Li of 2: approximately 1.5 to approximately 2.5, preferably second : about 1.3 to about 0.6.

The peculiarity of the process according to the invention can be seen in the fact that the lithium and manganese compounds are reacted under hydrothermal conditions. This means that the implementation in one aqueous medium. The reaction is carried out at a temperature in the range of about 80 to about 500 ° C, preferably about 100 to about 350 ° C and especially about 150 to about 250 ° C.

The reaction is carried out at a pressure of about 1 • 10 ⁵ Pa to about 5 • 10 ⁷ Pa, preferably about 1 • 10 ⁶ Pa to about 5 • 10 ⁶ Pa and in particular at about 1.5 ^• 10 ⁶ Pa to about 2, 5 • 10 ⁶ Pa.

Depending on the components used, the actual implementation can be followed by a washing process for removing dissolved impurities that are present in the metal salts used, e.g. Sulfates, Na and K salts, and other components that are not part of the spinel according to the invention, connect.

In the context of the present process, the product obtained in the reaction can additionally be dried, with temperatures here preferably in a range from approximately 60 to approximately 200 ° C., more preferably approximately 100 to approximately 150 ° C. and in particular approximately 120 to approximately 135 ° C. , be applied.

Furthermore, after the reaction or also after the reaction and drying, the product obtained afterwards can be additionally annealed, here preferably at a temperature in the range from approximately 200 to approximately 900 ° C., more preferably approximately 300 to approximately 850 ° C. and in particular at about 800 ° C.

The duration of the annealing is preferably at least about one hour, more preferably more than about 15 hours, and in particular approximately 24 hours, the maximum duration of the annealing being approximately 30 hours, particularly for economic reasons.

An annealing stage is particularly useful if the manganese valence level e.g. is above about 3.5. In the course of this tempering process, which influences the oxygen content and the Mn valence level, the valence level of the manganese is optimized in the direction of 3.5. The valence level indicates the mean value of the oxidation level of the manganese contained in the oxide.

A reduction of the Li content with increased use of Li or a general reduction of this content is possible after the actual implementation by means of an acid leaching process, which can preferably be done before the optional drying or tempering. It should be noted that the aqueous phase can be separated off before drying, but in general, e.g. spray drying can be dispensed with.

The crystallinity and the specific surface area of the lithium manganese oxide obtained according to the process according to the invention can be influenced by a specific temperature, pressure and reaction time control during the reaction and / or the subsequent tempering.

The particle size of the lithium-manganese oxide obtained according to the invention can be influenced by taking the grain fineness of the manganese raw materials used into account by preceding wet or dry grinding processes. It is also possible to grind the wet or dried lithium manganese oxide to refine the grain. The spinel obtained according to the invention preferably has an average particle size, measured by means of a Cilas granulometer, in the range from approximately 0.5 to approximately 100 μm, more preferably from approximately 1 to approximately 50 μm.

The BET surface area of the lithium manganese oxide produced according to the invention is preferably below approximately 10 m ² / g, more preferably below approximately 8 m ² / g and in particular approximately 5 m ² / g, the lower limit being approximately 0. 1 m ² / g.

The following reaction variants in particular can be carried out successfully in the context of the present process:

4 MnO ₂ + 2LiOH 2LiMn ₂ O ₄ + H ₂ O + V4O ₂ 3MnO ₉ + MnO + 2LiOH 2LiMn ₂ O ₄ + H ₂ O

MnO-, + MnOOH + LiOH LiMn ₂ O ₄ + H ₂ O 2MnO ₂ + Mn ₂ O ₃ + 2LiOH 2LiMn ₂ O ₄ + H ₂ O 10MnO ₂ + 2Mn ₃ O ₄ + 8LiOH 8LiMn ₂ O ₄ + H ₂ O 3MnO ₂ + MnCO ₃ + 2LiOH 2LiMn ₂ O ₄ + H ₂ O + CO ₂

In addition, the present invention also relates to a lithium manganese oxide of the formula L ^ ₅ _ _x Mn ₂ O ₄ or a lithium manganese oxide of the formula L ^ ₅ _ _x M _z Mn ₇ _ _z O ₄ , obtainable by reaction at least one lithium and at least one manganese or at least one lithium, at least one manganese and at least one compound of a metal M, characterized in that the reaction in an aqueous medium at a temperature in the range from 80 to 500 ° C and a Pressure of 1 • 10 ⁵ Pa to 5 • 10 ⁷ Pa is carried out.

This oxide naturally has the same properties with regard to the BET surface area, the Li and Mn content and the particle size, as stated in the description of the method according to the invention. The lithium-manganese oxide described above is preferably one with a spinel structure, in particular a phase-pure Li-Mn oxide with a spinel structure.

The lithium manganese oxide according to the invention or produced according to the invention, preferably with a spinel structure, is a so-called intercalation compound. Such compounds can store active Li ⁺ ions in a host lattice, the lithium being stored in interstitial sites of the host material. Accordingly, such intercalation compounds can be used in particular for electrochemical cells. The storage and removal can be carried out electrochemically using a lithium ion-conducting electrolyte with high reversibility, preferably LiClO ₄ , LiBF ₄ , LiPF ₆ , LiSO ₃ CH ₃ , LiAsF ₆ . Combining two different intercalation compounds with very different electrochemical potentials results in an accumulator in which lithium ions move back and forth between the host materials during the charging and discharging process. Electrochemical cells of this type are known as lithium-ion cells. When using a lithium-manganese oxide, preferably with a spinel structure, a carbon-containing substance, such as graphite or coke, is particularly suitable as the host material for the anode. Such a cell could correspond to a short designation Li _x C ₆ / Li _y.χ Mn ₂ O ₄ .

Accordingly, the present invention also relates to the use of the lithium manganese oxide according to the invention or produced according to the invention, preferably with a spinel structure, as cathode material or as part thereof for an electrochemical cell. The lithium-manganese oxide represents the cathode, optionally in conjunction with a binder such as PTFE and acetylene black, while the anode acts as the host material preferably a carbonaceous substance as defined above or metallic lithium.

In principle, there are no particular restrictions when choosing the anode when using the lithium manganese oxide described here as the cathode. The compounds that can be used only have to be intercallable for lithium ions and have a higher electrochemical activity than the cathode.

The preparation of the lithium manganese oxide according to the invention or produced according to the invention, preferably with a spinel structure, as the battery cathode material takes place in a manner known per se. In an electrochemical cell, this cathode material can be used in a manner known per se against an anode which absorbs lithium cations. The electrodes of such cells, when fully assembled and closed, are usually uncharged, i.e. all available lithium is stored in the positive electrode, while the host structure of the negative electrode is in a non-lithium-loaded state. During the first charge, the lithium is removed from the positive host lattice (cathode) and embedded in the negative host lattice (anode), preferably a carbon matrix. A part of the lithium ions which is irreversibly attached to the carbon matrix and which is removed from the further intercalation mechanism can be compensated for by an over-stoichiometric amount of lithium in the lithium-manganese oxide, which preferably has a spinel structure.

The basic structure of such electrochemical cells is known and is described, inter alia, by JM Tarascon in J. Electrochem. Soc. 140, p. 3071 ff. When used as a battery cathode material, the lithium manganese oxides according to the invention or produced according to the invention, preferably with a spinel structure, have good capacitive properties and cycle stability, as is demonstrated by the examples.

Accordingly, the present invention also relates to an electrochemical cell which has at least one cathode which contains the lithium manganese oxide according to the invention or produced according to the invention, preferably with a spinel structure.

The present invention will now be explained in more detail with reference to some exemplary embodiments.

EXAMPLES

example 1

4 liters of water were placed in a 10 liter autoclave, 1,010 g of lithium hydroxide and 4,000 g of manganese dioxide were introduced. With stirring, the mixture was brought to an internal temperature of

Approach a): 110 ° C,

Approach b): 165 ° C and

Approach c): 195 ° C

heated and held at this temperature for 24 hours. The following pressure ratios were established:

Approach a): 4 ^• 10 ⁵ Pa (4 bar), Approach b): 10 ^• 10 ⁵ Pa (10 bar) and approach c): 16 • 10 ⁵ Pa (16 bar).

The solid was then separated from the aqueous phase by filtration, dried and heated at 800 ° C. for 24 hours.

The solid obtained had the following analytical data:

Table 1

Example 2

4 l of water and 1,010 g of lithium hydroxide were placed in a 10 l autoclave, and 4,000 g of manganese dioxide raw material with different grain sizes, as defined below, were used in each case.

According to experiment d), a commercially available manganese dioxide raw material with an average particle size of 30 μm was used.

In experiment e), a commercially available manganese dioxide raw material was used, which after dry grinding had an average particle size of 10 μm.

In experiment f), a commercially available manganese dioxide raw material was used which, after wet grinding, had an average particle size of 1 μm.

The reaction temperature in the autoclave was kept at 195 ° C. for 24 hours in all three experiments, an internal pressure of 16 ^· 10 ⁵ Pa (16 bar) being established.

After this reaction, the solid was separated from the aqueous phase, dried and heated at 800 ° C. for 24 hours. Phase-pure lithium-manganese spinels with the following particle sizes were obtained as temper products:

Test d): 15 μm, test e): 8 μm and test f): 2 μm.

Claims

PATENT CLAIMS

Process for the preparation of a lithium manganese oxide of the formula Li _{1 5} . _x Mn ₂ O ₄ , where the value for x corresponds to the relation 0 <x <1, 5, which comprises the following level:

Reaction of at least one lithium and at least one manganese compound, characterized in that the reaction is carried out in an aqueous medium at a temperature in the range from 80 to 500 ° C and a pressure of 1 ^• 10 ⁵ Pa to 5 ^• 10 ⁷ Pa.

A method according to claim 1, characterized in that the at least one lithium compound is Li ₂ O, LiOH, LiCl, LiNO ₃ , Li ₂ CO ₃ , a Li carboxylate or a mixture of two or more thereof.

A method according to claim 1 or 2, characterized in that the at least one manganese compound MnO ₂ , MnO, MnOOH, Mn ₂ O ₃ , Mn ₃ O ₄ , MnCO ₃ , Mn (NO ₃ ) ₂ , a Mn carboxylate or Is a mixture of two or more of them.

4. A process for producing a lithium manganese oxide of the formula L ^ ₅ _ _x M _z Mn ₂ _ _z O, where x is as defined in claim 1, M is a metal from the group Ha, lilac, IVa, Ilb, Illb, IVb, VIb, Vllb, or VIII of the periodic table or a mixture of two or more thereof and the value for z corresponds to the relation 0.01 <z <1, which comprises the following stages:

Reaction of at least one lithium, at least one manganese and at least one compound of the metal M, characterized in that the reaction in an aqueous medium at a temperature in the range of 80 to 500 ° C and a pressure of 1 • 10 ⁵ Pa to 5 ^• 10 ⁷ Pa.

5. The method according to any one of the preceding claims, characterized in that it additionally comprises the following step:

Drying a product obtained from the reaction.

6. The method according to any one of the preceding claims, characterized in that it additionally comprises the following step: annealing a product obtained from reaction or from a product obtained from reaction and drying.

7. Lithium-manganese oxide of the formula Li _{j 5} _ _x Mn ₂ O ₄ or lithium manganese oxide of the formula Li, ₅ _ _χ M _z Mn ₂ _ _z O ₄ , where x is as defined in claim 1 and z and M are each as defined in claim 4, obtainable by reacting at least one lithium and at least one manganese or at least one lithium, at least one manganese and at least one compound of a metal M, characterized in that the reaction in one aqueous medium at a temperature in the range of 80 to 500 ° C and a pressure of 1 ^• 10 ⁵ Pa to

5 ^• 10 ⁷ Pa is carried out.

8. Use of a lithium manganese oxide as defined in claim 7 or a lithium manganese oxide, produced as defined in one of claims 1 to 6, as cathode material or part thereof for an electrochemical cell.

9. Use according to claim 8, characterized in that the electrochemical cell comprises an anode which contains a carbon-containing compound as the host material.

10. Electrochemical cell, characterized in that it has at least one cathode containing a lithium manganese oxide according to claim 7 or a lithium manganese oxide, as defined in any one of claims 1 to 6, contains.