WO1999000329A1 - Method for producing lithium-manganese mixed oxides and their use - Google Patents

Abstract

The invention relates to a method for producing mixed oxides with slightly variable electrochemical properties and spinel-type structures of formula (I): LixMeyMn2-yO4, in which Me is a metal cation from the II, III, IV, V and VI main groups or from the I, II, IV, V, VII or VIII subgroups of the periodic table of the elements, in particular a cation from the group of elements Al, Co, Cr, Fe, Ge, Mg, Nb, Ni, Sn, Ta, Te, V, W, Zn, and 0</=x</=2 and 0</=y<2. The invention also relates to their use in producing manganese dioxide electrodes for galvanic cells, electrochemical cells, secondary batteries, in particular for prismatic and round cells.

Description

Process for the preparation of mixed lithium manganese oxides and their use

The present invention relates to a process for producing mixed oxides with easily variable electrochemical properties and spinel-like structures of the formula (I)

Li _x MeyMn ₂ .yθ ₄ , (I)

wherein

Me a metal cation from the II., III, IV., V. and VI. Main group or from the I., II., IV., V, VII., Or VIII. Subgroup of the Periodic Table of the Elements, in particular a cation from the group of the elements AI, Co, Cr, Fe, Ge, Mg, Nb, Ni Sn

Ta, Te, V, W, Zn and

0 <x <2 and

0 <y <2 mean, and their use for the production of manganese dioxide electrodes for galvanic elements, electrochemical cells, secondary batteries, in particular for prismatic and round cells.

Typical components of a lithium secondary cell are a cathode consisting of lithiated metal oxide, an anode, preferably made of carbon, an aprotic electrolyte and an electrolyte-permeable separator material.

The separator material located between the electrodes has the task of electronically isolating the two electrodes.

A lithium manganese spinel, which has a very high electrochemical activity, is often used as the cathode material. To increase the electrical conductivity, such manganese dioxide electrodes are usually made of carbon, soot or graphite particles

IS NOT CONSIDERED IN THE INTERNATIONAL PROCEDURE

The object of the invention was therefore to provide a simple, fast and energy-saving method for producing suitable lithium-manganese mixed oxides with spinel-like structure with improved properties for cathodes in rechargeable electrochemical cells, which offers the possibility of

Modify the properties of the powder to be produced depending on the intended use.

The object is achieved by a process for producing lithium manganese oxide with easily variable electrochemical properties, in particular with a large surface area and spinel-like structure of the general formula I.

Li _x MΘyMn ₂ -yθ4, (I)

wherein

Me metal from the II., III, IV., V. and VI. Main group or from the I., II., IV., V., VII. Or VIII. Subgroup of the Periodic Table of the Elements, in particular a cation from the group of the elements AI, Co, Cr, Fe, Ge, Mg, Nb, Ni, Sn, Ta, Te, V, W, Zn and

0 <x <2 and

0 <y <2, which is characterized in that a) nitrate salts of the various metals in the stoichiometric ratio of the desired powder composition in a water-alcohol mixture with a water content of up to 100% in an amount of 5 to 50%, preferably 30 - 50%, based on the total mixture, and then b) pyrolyzing in a nitrate pyrolysis plant, the reactor outlet temperature being 400-700 ° C.

According to the invention, the pulverulent material obtained by the nitrate pyrolysis process is subjected to additional tempering steps at temperatures of 500-750 ° C. This tempering can be carried out in an oxygen-containing gas atmosphere, preferably with an oxygen concentration of up to 100%.

The invention also relates to the use of the lithium manganese oxide produced by this process for the production of manganese dioxide electrodes for galvanic elements, for electrochemical cells.

In order to achieve good cycle stability with high capacity at the same time, a powder material is particularly sought which has a homogeneous and stoichiometric composition, so that possible dopants are homogeneously contained in the material, the material has a spinel structure immediately after production and a uniform, very small particle size , advantageously less than 10 μm.

Experiments have shown that, surprisingly, these high material requirements can be met if powdery lithium manganese oxide is produced in a spray pyrolysis process. To carry out this process, it is possible to use mixtures of different salt solutions or corresponding suspensions which oxidize in the hot reaction zone with immediate evaporation of the solvent to give the desired lithium manganese oxides of the formula (I).

To prepare the above-mentioned lithium-manganese mixed oxides ^"is suitable in particular a method which nitrate pyrolysis may be characterized in principle as well. This method can with the aid of aqueous solutions of metal nitrate salts, or of a suspension of a component in an aqueous nitrate salt solution of the other components Depending on the desired end product, aqueous solutions or suspensions of the nitrate salts or the components can advantageously be used in stoichiometric amounts by spraying the solution or suspension prepared directly in air or in another defined gas atmosphere at temperatures of 400-700 ° C, Especially at 475 - 650 ° C, the desired spinel-like product can be produced phase-pure directly without further after-treatment.

Salt solutions which react in an exothermic reaction to the desired mixed oxides are preferably used to carry out the process. This has the advantage that, in order to start the reaction, the reaction space must be brought to a certain temperature at the beginning, but in the best case the reaction is self-supporting and the temperature can be maintained. If necessary, the reaction can also be started by ignition.

Advantageously, nitrates salts of the metals which are desired in the product can be used as starting materials for the formation of the lithium manganese oxides of the formula (I). Suitable salts are also acetates, citrates, hydroxides or other organic metal salts soluble in water or water-alcohol mixtures.

It is also possible to use appropriate hydroxides in combination with nitrate salts for the reaction. For example, stoichiometric amounts of lithium hydroxide, manganese nitrate and another suitable salt of a metal from II., III, IV., V. and VI. Main group or from the I., II., IV., V., VII., Or VIII. Subgroup of the Periodic Table of the Elements, in particular from the group of the elements AI, Co, Cr, Fe, Ge, Mg, Nb, Ni, Sn, Ta, Te, V, W, Zn can be used in the process according to the invention. This further salt is also preferably a water-soluble nitrate.

Before the spray pyrolysis process according to the invention is carried out, the abovementioned salts are brought into solution in the stoichiometric ratio of the desired powder compositions. Solutions in which the salts are present in a total concentration of 5-50%, in particular 30-50%, have particularly good properties. Both salt water solutions are suitable as salt solutions as well as those which contain an organic solvent as the solvent in addition to water. Water-miscible solvents are particularly suitable as organic solvents. Alcohols such as ethanol, methanol or propanol can be used for this purpose. However, other solvents can also be used, which can also act as complexing agents at the same time, such as. B. diethylene glycol. However, alcohols are preferably used because of their good water solubility. It is particularly preferred to work with ethanol.

The organic solvents contribute in particular to maintaining the temperature during the spray pyrolysis reaction. When using organic solvents, however, their concentration and reaction temperature must be selected so that the carbon-containing compounds undergo a complete exothermic reaction, but no carbon residues remain in the mixed oxide formed, since otherwise the formation of a spinel structure is disturbed. As such, solutions can be used in which an organic solvent alone is used, that is to say the concentration of the organic solvent in relation to the total amount of solvent increases to 100%.

To produce the lithium manganese oxides of the formula (I) according to the invention, the salt solutions prepared are sprayed into the NPA reactor (NPA nitrate pyrolysis system) brought to operating temperature. This reactor is a specially developed reactor from the applicant. Spraying takes place through a two-component nozzle using a pump. The reaction solution sprayed into the reactor in this way is thermally pyrolyzed and is obtained as a finely divided, free-flowing powder.

Depending on the further use, it is possible to modify the properties of the powder by subsequent heat treatment. In this way, physical as well as electrochemical-physical properties can be changed in a targeted manner, and thus adapted to the application requirements. The properties relevant to the manufacture of batteries such as grain size, specific surface area, oxygen content and lattice constant can be varied very well by post-treatment in a defined gas atmosphere.

Another advantage of the method according to the invention is the possibility of being able to produce doped mixed oxides of the above general formula in a simple manner. Even when using the smallest amounts of doping precursor material, a homogeneous distribution in the precursor material for electrodes is guaranteed.

It is particularly advantageous that the method according to the invention can be carried out simply and quickly, even on a larger scale. This manufacturing process is also characterized by a low energy input due to the self-supporting reaction.

If the reaction is carried out in a suitable manner, the powder produced is directly in the desired phase, the spinel, if the reaction exit temperature of the nitrate pyrolysis plant is selected. It is a finely divided powder with a particle size of less than 10 μm with a high bulk density.

Subsequent annealing steps can be followed to modify the electrochemical as well as the physico-chemical properties.

This aftertreatment of the powders in particular affects the crystallinity, the lattice constants, the grain sizes, the specific surface and the capacity.

Of course, the defined temperature, the heating and cooling rate as well as the annealing time play a decisive role here. Furthermore, the gas atmosphere of the furnaces used and the bed height of the crucibles are important influencing factors. To produce the actual cathode material, the powdery product obtained is mixed intensively with the other constituents and optionally suspended. Such necessary components such. B. organic or inorganic binders and conductivity additives. As organic binders such. B. PTFE,

PVDF and others a. binders known to those skilled in the art for this purpose are added. PTFE is particularly suitable. Suitable conductivity additives are carbon black, graphite, steel wool and other conductive fibers. Particularly good results were achieved by adding carbon black and graphite in an amount of 5-50, in particular about 15% by weight, based on the total amount.

Then the powder mixed with all additives is made into electrodes in a manner known per se. This can be done by pressing with very high pressure between wire meshes, consisting of an inert material, such as. B. aluminum. If appropriate, this can be followed by treatment at elevated temperature, the product obtained drying.

Electrodes produced in this way can be used in a known manner for the production of secondary galvanic cells in which a carbon electrode usually serves as a counter electrode in the presence of an aprotic electrolyte. However, other configurations of corresponding galvanic cells are also possible. Various additives, such as gelling agents, silica gel or others, can be used to increase the viscosity of the electrolyte, which is aqueous per se. A suitable polymer fabric or fleece can be attached as a separating material between the electrodes and, if necessary, a spacer should be inserted. Materials consisting of PVA, polypropylene or other inert polymers can serve as the polymer fleece. Spacers, as they are known from commercially available batteries, can have a corrugated shape and, for example, consist of PVC.

For experimental purposes, electrodes were produced from the lithium-manganese dioxide mixtures according to the invention by homogenizing the components in a mixer, one in each case Conductivity additive and a binder was added. The mixture thus obtained was pressed into cathodes for button cell batteries and dried.

In the following, examples are given to illustrate and facilitate understanding of the present invention, which, however, are not in themselves intended to limit the actual invention.

B e i s p i e l e

Preparation of a stoichiometric Liι.o ₄ 5Mn θ _{4 ± δ} precursor:

Experiment description:

Weigh in stoichiometric amounts of lithium and manganese nitrate and dissolve in deionized water and stir.

Spray pyrolysis conditions:

Nozzle pressure: 2.5 bar

Burner temperature: 600 ° C Air-gas ratio: 2

Flow rate: 4.95 kg / h

A Schlick two-fluid nozzle, model 970/4, with a bore of 0.8 mm was used.

The reactor was cooled during the reaction.

Theoretical yield: 5244 g

Crude yield: 5155 g

This corresponds to a conversion of 98.3% of the raw material.

The analytical examination of the product showed the following contents:

Experimental: Theoretical:

Li: 3.928% 3.879%

Mn: 60.465% 60.72%

O: 35.607% 35.40%

Calcining under different conditions: 1. Carrying out the experiment: 750 ° C for 10 h at a heating rate of 3K / min in air

2. Carrying out the experiment: 750 ° C for 24 h at a heating rate of 3K / min in air

Table 1 :

Results of the two calcination tests and comparison with the

Precursor mixture

Claims

PATENT CLAIMS 1. Process for the production of lithium manganese oxide with easily variable electrochemical properties and spinel-like structure of the general formula I. Li _x MeyMn ₂ . _y θ4, (I) where Me metal from the II., III, IV, V. and VI. Main group or from the I., II., IV., V., VII. Or VIII. Subgroup of the Periodic Table of the Elements, in particular a cation from the group of the elements AI, Co, Cr, Fe, Ge, Mg, Nb, Ni, Sn, Ta, Te, V, W, Zn and 0 <x <2 and 0 <y <2, characterized in that a) nitrate salts of the various metals in the stoichiometric ratio of the desired powder composition in a water-alcohol mixture with a water content of 0-100% in an amount of 5-50%, preferably 30- 50%, based on the total mixture, and then b) pyrolyzing in a nitrate pyrolysis plant, the The reactor outlet temperature is 400 - 700 ° C. 2. The method according to claim 1, characterized in that powdery material obtained by the nitrate pyrolysis process is subjected to additional tempering steps at temperatures of 500-750 ° C. 3. The method according to claims 1 and 2, characterized in that the annealing is carried out in an oxygen-containing gas atmosphere with an oxygen concentration of up to 100%. 4. Use of the lithium manganese oxide produced by a process according to one or more of claims 1-3 for the production of manganese dioxide electrodes for galvanic elements. 5. Use of the lithium manganese oxide produced by a process according to one or more of claims 1-4 for the production of cathodes for electrochemical cells, in which manganese dioxide electrodes serve as cathodes in the presence of aprotic electrolytes, and carbon electrodes are preferably used as anodes 6. Use of the lithium manganese oxide produced by a process according to one or more of claims 1-4 for the production of manganese dioxide electrodes for prismatic and round cells. 7. Use of the lithium manganese oxide produced by a process according to one or more of claims 1-4 for the production of manganese dioxide electrodes for secondary batteries.