DE19727611A1 - Process for the preparation of 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

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

Li _x Me _y Mn _2-y O 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 Al, Co, Cr, Fe, Ge, Mg, Nb, Ni, Sn, Ta, Te, V, W, Zn
and
0 ≦ x ≦ 2
and
0 ≦ y <2,
and their use for the production of Mangandioxidelektro the for galvanic elements, electrochemical cells, secondary batteries, in particular for prismatic and round cells.

Typical components of a lithium secondary cell are one of lithiated metal oxide existing cathode, an anode, preferably of carbon, an aprotic electrolyte and an electrolyte pass through sige separator material.

The separator material located between the electrodes has the Task to electronically isolate the two electrodes.

As the cathode material is often a lithium manganese spinel ver which has a very high electrochemical activity. To increase the electrical conductivity such Man gandioxidelektroden usually carbon, soot or graphite particles  added. As binders come organic or inorganic Additives for use.

The LiMn ₂ O ₄ and Li ₄ Mn ₅ O ₁₂ mentioned in DE-A1-41 19 944 are stoichiometric spinels. The cathode material is prepared by reacting a lithium salt, particularly lithium hydroxide, with a manganese oxide at temperatures above 750 ° C.

From DE-A1-43 28 755 a corresponding cathode material be known with a variable stoichiometry of the form Li _{1 + x} Mn _2-x O _{4 + δ} with 0 ≦ x <0.33 and 0 ≦ δ <0.5. The variable parameters x and δ are chosen so that the material in the discharged state in which it is used, just a cubic symmetry (spinel lattice) and the average degree of oxidation of Mn is not less than 3.5.

By MN Richard et al. (Solid State Ionics 73 (1994) 81-91), however, an "oxygen-deficient" spinel of the formula Li (Li _1/3 Mn _5/3 ) O _4-δ , described. As the δ increases, an average degree of oxidation of the Mn decreasing from 4 to 3.5 is achieved. Lithium can be deintercalated by simultaneous oxidation of the Mn ³ ⁺, making such an "oxygen-deficient" spinel usable as a reversible cathode material.

The achievable with these cathode materials capacity swan between 10 mAhg and 120 mAhg. Depending on stoichiometric access Composition and crystalline nature are the materials more or less sensitive to moisture and unstable in air. A improved high-temperature storage ability while satisfying Gender cycle stability can only be achieved in most cases in the capacity of lower capacities.  

From the publications known method for the preparation of However, lithium mandel oxides with spinel structure usually have the disadvantage that the powder materials only batch-wise can be prepared and subjected to very long temperature treatments which requires a very high energy input becomes.

The object of the invention was therefore a simple, fast and energy-saving process for the production of suitable lithium Manganese mixed oxides with spinel-like structure with improved egg properties for cathodes in rechargeable electrochemical To provide cells which offers the possibility that Properties of the powder to be produced depending on the intended Use to modify specifically.

The object is achieved by a method for the production of lithium manganese oxide with slightly variable electrochemical egg properties, in particular with a high surface area and spinellartiger structure of the general formula I.

Li _x Me _y Mn _2-y O ₄ , (I)

wherein
Me 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 Ele ments Al, 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 various metals in the stoichiometric Ratio of the desired powder composition in one Water-alcohol mixture with a water content of up to 100% in in an amount of 5 to 50%, preferably 30-50%, based on  the total mixture are dissolved and then
• b) are pyrolyzed in a nitrate pyrolysis plant, wherein the Reactor exit temperature is 400-700 ° C.

According to the invention erhal by the nitrate pyrolysis process tene powdery material at temperatures of 500-750 ° C. subjected to additional Temperschritten.

This tempering can take place in an oxygen-containing gas atmosphere be carried out, preferably with an oxygen concentration until 100%.

The invention is also the use of the after Lithium manganese oxide produced by this method for the production of Manganese dioxide electrodes for galvanic elements, for electrochemicals mix cells.

To achieve a good cycle stability with high Ka In particular, a powder material is sought, which egg has a homogeneous and stoichiometric composition, so that possible dopants are homogeneously contained in the material, the Material directly after production already on a spinel structure has and a uniform, very small particle size, vorteilhaf terweise less than 10 microns, has.

Experiments have shown that, surprisingly, this high Ma Material requirements can be met if powdered Lithi ummanganoxid is produced in a spray pyrolysis. to Implementation of this process can mixtures of various Salt solutions or corresponding suspensions are used, which in the hot reaction zone with immediate evaporation of the solvent to the desired lithium manganese oxides of Oxidize formula (I).

For the preparation of the above lithium-manganese mixed oxides is In particular, a method is suitable, which in principle is used as nitrate Pyrolysis can be characterized. This procedure can with Help of aqueous solutions of metal nitrate salts or of a  Suspension of a component in an aqueous nitrate salt solution of other components are performed. Advantageously Kings depending on the desired end product aqueous solutions or Sus pensions of nitrate salts or components in stoichiometry quantities are used. By direct spraying the prepared solution or suspension in air or in another defined gas atmosphere at temperatures of 400-700 ° C, ins special at 475-650 ° C, the desired spinel-like Pro phase-directly produced without further treatment become.

Preferably, for carrying out the method such salt solutions used in an exothermic reaction to the ge wanted to react mixed oxides. This has the advantage that, although to start the reaction at the beginning of the reaction space on a certain temperature must be brought, then the reaction itself but in the best case, carry yourself and keep the temperature can be. The start of the reaction may optionally also done by ignition.

Advantageously, as educts for the formation of Lithiumman ganoxide of the formula (I) Nitrate salts of metals, which in the product are desired to be used. However, suitable salts are also Acetates, citrates, hydroxides or others in water or water Alcohol mixtures soluble organic metal salts.

It is also possible to use corresponding hydroxides in combination with Use nitrate salts for the reaction. For example, you can ever because 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. Ne Bengruppe of the Periodic Table of the Elements, in particular from the group of elements Al, Co, Cr, Fe, Ge, Mg, Nb, Ni, Sn, Ta, Te, V, W, Zn can be used in the process according to the invention. Also in this further salt is preferably a in water-soluble nitrate.  

Before carrying out the spray pyrolysis process according to the invention The above salts are in the stoichiometric ratio the desired powder compositions dissolved. Particularly good properties have such solutions in which the salts in a total concentration of 5-50%, in particular from 30-50%.

As salt solutions, both purely aqueous solutions are suitable as also those, which except water as solvent an organic Solvent included. As organic solvents are esp especially water-miscible solvents suitable. To this Purpose can alcohols such. As ethanol, methanol or propanol be used. Can be used but also other Lö agents, which at the same time function as complexing agents can such. B. diethylene glycol. Preferably, however, we will gen of good water solubility alcohols used. In particular it is preferable to work with ethanol.

The organic solvents carry during the spray pyrolysis Reaction in particular with to maintain the temperature at. at However, use of organic solvents is their Kon to choose concentration and reaction temperature so that a full stan dige exothermic reaction of the carbonaceous compounds he follows, but no more carbon residues in the formed mixed oxide remain, otherwise the formation of a spinel structure is disturbed. On solutions can be used in which alone an organi solvent is used, ie the concentration of or ganic solvent with respect to the total solvents amount goes up to 100%.

For the preparation of the lithium manganese oxides according to the invention Formula (I), the salt solutions prepared in the operation temperature brought NPA reactor (NPA nitrate pyrolysis plant) sprayed. This reactor is a special one developed reactor of the Applicant. The spraying is done by a jet nozzle by means of a pump. The so in the reactor ver  sprayed reaction solution is thermally pyrolyzed and falls here as a finely divided, free-flowing powder.

It is possible, depending on further use, the properties of the Powder by a subsequent temperature treatment modify. This allows physical, but also electro chemico-physical properties are selectively changed, and thus be adapted to the application requirements.

The properties relevant for the production of batteries such as Grain size, specific surface, oxygen content and Gifterkon Stants can be cured by a temperature aftertreatment in a de Finished gas atmosphere can be varied very well.

Another advantage of the method according to the invention consists in the possibility of easily doped mixed oxides of the above to be able to produce said general formula. Also at Ver Use of very small amounts of dopant precursor material is homo gene distribution in the prepared precursor material for electro guaranteed.

It is particularly advantageous that the inventive method easy and fast is feasible, even in one size ren scale. Also, this manufacturing process is characterized reason of self-sustaining reaction by a low Energy input.

By suitable reaction, the powder produced is directly in the desired phase, the spinel before, when the reaction Occurrence temperature of the nitrate pyrolysis plant ge suitably is chosen. It is a finely divided, powder with a Particle size smaller than 10 μm with high bulk density.

Subsequent annealing steps can be used to modify the electrochromes mix as well as physico-chemical properties nachgeschal be.  

By this aftertreatment of the powder in particular the Crystallinity, the lattice constants, the grain sizes, the specific Surface and capacity affected.

Here, of course, the defined temperature, the heating and Ab plays Cooling rate, as well as the annealing time a crucial role. more There are the gas atmosphere of the ovens used and the Schütthö the crucible important influencing factors.

To produce the actual cathode material is obtained ne powdered product intensively with the other ingredients mixed and optionally suspended. Such necessary Be components for. As organic or inorganic binders and Leit ability additives. As organic binders can be added be PTFE, PVDF u. a. known to the skilled person for this purpose Binder. Particularly suitable is PTFE. 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, especially about 15 Wt .-% based on the total amount.

Subsequently, the mixed with all additives powder in Known way to formulate electrodes. This can by pressing with very high pressure between wire meshes, consisting of an inert material, such as. As aluminum, done. Optionally, this may be a treatment at elevated Tem followed by drying the resulting product. ,

Thus produced electrodes can be prepared in a known manner use of secondary galvanic cells in which Presence of an aprotic electrolyte usually a Koh lenstoffelektrode serves as a counter electrode. But there are others too Embodiments of corresponding galvanic cells possible. So  can by various additives, such as Gelierungsmit tel, silica gel or others, the viscosity of the per se aqueous Elek be increased. Between the electrodes can be a suitable Polymer fabric or nonwoven be attached as a release material and if necessary, a spacer should be inserted. As polymer fleece materials can be used, consisting of PVA, Polypropy len or other inert polymers serve. Spacers, like them are known from commercially available batteries, a ge corrugated form and consist for example of PVC.

For experimental purposes, starting from the lithium Manganese dioxide blanks made by adding in a Mi xer the components have been homogenized, wherein each one Conductivity additive and a binder was added. That so The mixture obtained was converted into cathodes for coin-cell batteries presses and dried.

The following are examples for illustration and for easier understanding of the present invention given to but not serve to limit the actual invention.

Examples Preparation of a stoichiometric Li _1.045 Mn ₂ O _{4 ± δ} precursor test description

Weigh in stoichiometric amounts of lithium and manganese nitrate and dissolve in deionised water and stirring.
Spray pyrolysis conditions:
Nozzle pressure: 2.5 bar
Burner temperature: 600 ° C
Air to gas ratio: 2
Flow rate: 4.95 kg / h.

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

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 gave the following contents:

experimental Theoretically Li: 3.928% 3.879% Mn: 60.465% 60.72% O: 35.607% 53.40% ⇒ Li _1.029 Mn ₂ O _4.044

Calcining under different conditions:

• 1. Experimental procedure: 750 ° C for 10 h at a heating rate of 3 K / min in air
• 2. Experimental procedure: 750 ° C for 24 h at a heating rate of 3 K / min in air.

Table 1

Results of the two calcination experiments and comparison with the precursor mixture

Claims (7)

1. A process for the preparation of lithium manganese oxide with easily variable electrochemical properties and spinel-like structure of the general formula I.
Li _x Me _y Mn _2-y O ₄ , (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 Al, 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 having a water content of 0-100% in an amount of 5-50%, preferably 30-50%, based on the total mixture are dissolved and then
• b) are pyrolyzed in a nitrate pyrolysis plant, wherein the reactor exit temperature is 400-700 ° C.

2. The method according to claim 1, characterized in that the nitrate pyrolysis method obtained powdery material at temperatures of 500-750 ° C additional Temperschritten is subjected. 3. Method according to claims 1 and 2, characterized in that that the annealing in an oxygen-containing gas atmosphere is carried out with an oxygen concentration of up to 100%.   4. Use of the according to a method according to one or more Ranks of claims 1-3 prepared lithium manganese oxide Production of manganese dioxide electrodes for galvanic elemen te. 5. Use of the according to a method according to one or more Ranks of claims 1-4 prepared lithium manganese oxide Production of cathodes for electrochemical cells, in which Manganese dioxide electrodes in the presence of aprotic electrolytes th serve as cathodes, and as anodes preferably carbons Substance electrodes are used. 6. Use of the method according to one or more Ranks of claims 1-4 prepared lithium manganese oxide Production of manganese dioxide electrodes for prismatic and Round cells. 7. Use of the method according to one or more Ranks of claims 1-4 prepared lithium manganese oxide Production of manganese dioxide electrodes for secondary batteries.