EP1188196A1

EP1188196A1 - Lithium-mixed oxide particles coated with metal-oxides

Info

Publication number: EP1188196A1
Application number: EP00929419A
Authority: EP
Inventors: Rüdiger OESTEN; Udo Heider; Andreas Kühner; Natascha Lotz; Anja Amann; Marlies Niemann
Original assignee: Merck Patent GmbH
Current assignee: Merck Patent GmbH
Priority date: 1999-05-15
Filing date: 2000-04-25
Publication date: 2002-03-20
Also published as: CN1350706A; AU4751200A; JP2003500318A; RU2001132863A; KR20020013887A; WO2000070694A1; CA2373756A1; BR0010566A; DE19922522A1

Abstract

The invention relates to lithium-mixed oxide particles coated with metal-oxide. Said particles are used to improve the characteristics of electrochemical cells. The invention relates to undoped and doped mixed oxides which are selected from the group Li(MnMez)2O4, Li(CoMez)O2, Li(Ni1-x-yCoxMey)O2 as cathode material. Me means at least one metal cation from the groups IIa, IIIa, IVa, IIb, IIIb, IVb, VIb, VIIb, VIII of the periodic table. Copper, silver, nickel, magnesium, zinc, aluminium, iron, cobalt, chromium, titanium and zircon are especially useful cations. Lithium is especially useful for the spinel compositions. The present invention also relates to lithium intercalations and insertion compounds that can be used for 4V-cathodes and have improved high temperature characteristics, especially at temperatures above room temperature. The invention further relates to the production and utilisation thereof, especially as cathode material in electrochemical cells. Various metal-oxides, especially oxides or mixed oxides of Zr, Al, Zn, Y, Ce, Sn, Ca, Si, Sr, Mg and Ti and the mixtures thereof, such as ZnO, CaO, SrO, SiO2, CaTiO3, MgAl2O4, ZrO2, Al2O3, Ce2O3, Y2O3, SnO2, TiO2 and MgO for instance, can be used as coating materials. It has been found that the undesired reactions of the electrolyte with the electrode materials can be significantly hindered by means of the coating with said metal-oxides.

Description

LITHIUM-MI CHOXIDE PARTICLES COATED WITH METAL OXIDS

The invention relates to coated lithium mixed oxide particles for improving the high-temperature properties of electrochemical cells.

The need for rechargeable lithium batteries is high and will increase much more in the future. The reasons for this are the high achievable energy density and the low weight of these batteries. These batteries are used in mobile phones, portable video cameras, laptops etc.

The use of metallic lithium as the anode material is known to lead to insufficient cycle stability of the battery and to a considerable safety risk (internal short circuit) because of the dent formation during dissolution and deposition of the lithium (J. Power Sources, 54 (1995) 151).

These problems were solved by replacing the lithium metal anode with other compounds which can reversibly intercalate lithium ions. The principle of operation of the lithium-ion battery is based on the fact that both the cathode and the anode materials can reversibly intercalate lithium ions. I.e. during charging, the lithium ions migrate out of the cathode, diffuse through the electrolyte and are intercalated in the anode. The same process takes place in the opposite direction when unloading. Because of this mode of operation, these batteries are also called “rocking chairs” or lithium-ion batteries.

The resulting voltage of such a cell is determined by the lithium intercalation potentials of the electrodes. In order to achieve the highest possible voltage, one must use cathode materials that intercalate lithium ions at very high potentials and anode materials that intercalate lithium ions at very low potentials (vs. Li / Li ⁺ ). Cathode materials that meet these requirements are LiCo0 ₂ and LiNi0 ₂ , which have a layer structure, and LiMn ₂ 0 ₄ , which has a cubic spatial network structure. These compounds deintercalate lithium ions at potentials around 4V (vs Li / Li ⁺ ). In the anode connections certain carbon compounds such as. B. Graphite the requirement of low potential and high capacity.

In the early 1990s, Sony launched a lithium-ion battery, which consists of a lithium cobalt oxide cathode, a non-aqueous liquid electrolyte and a carbon anode (Progr. Batteries Solar Cells, 9 (1990) 20) .

LiCo0 ₂ , LiNi0 ₂ and LiMn ₂ 0 _{4 are} discussed and used for 4V cathodes. Mixtures are used as the electrolyte which, in addition to a conductive salt, also contain aprotic solvents. The most commonly used solvents are ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC) and ethyl methyl carbonate (EMC). Although a whole series of conductive salts are discussed, LiPF _{6 is} used almost without exception. Graphite is usually used as the anode.

A disadvantage of the state-of-art batteries is that

High temperature storage and cyclability is bad. The

In addition to the electrolyte, the reasons for this are the ones used

Cathode materials, especially the lithium manganese spinel

LiMn ₂ 0 ₄ .

However, the lithium manganese spinel is for the cathode

Device batteries are a promising material. The advantage over LiNi0 ₂ and LiCo0 ₂ based cathodes is the improved one

Loaded safety, non-toxicity and lower raw material costs.

A disadvantage of the spinel is its lower capacity and its insufficient high-temperature storage capacity and the associated poor cycle stability at high temperatures. The reason for this is considered to be the solubility of the divalent manganese in the electrolyte (Solid State Ionics 69 (1994) 59; J. Power Sources 66 (1997) 129; J. Electrochem. Soc. 144 (1997) 2178). In the spinel LiMn ₂ 0 ₄ , the manganese is present in two oxidation states, namely trivalent and tetravalent. The LiPF ₆ -containing electrolyte always contains water impurities. This water reacts with the conductive salt LiPF ₆ to form LiF and acidic components, eg HF. These acidic components react with the trivalent manganese in the spinel to form Mn ²⁺ and Mn ⁴⁺ (disproportionation: 2Mn ³⁺ → Mn ²⁺ + Mn ⁴⁺ ). This degradation also takes place at room temperature, but accelerates with increasing temperature.

One way to increase the stability of the spinel at high temperatures is to dope it. For example, part of the manganese ions can be replaced by other, for example trivalent, metal cations. Antonini et al. report that spinels doped with gallium and chromium (e.g.

Li _1.02 Gao _. o ₂₅ C-ro _. o ₂₅ Mn _1.95 θ ₄ ) at 55 ° C show satisfactory storage and cycle stability (J. Electrochem. Soc, 145 (1998) 2726).

The researchers at Bellcore Inc. are following a similar path. They replace some of the manganese with aluminum and some of the oxygen ions with fluoride ions ((Li _{1 + x} Al _y Mn ₂ .χ. _Y ) 0 ₄ - _z F _z ). This doping also leads to an improvement in the cycle stability at 55 ° C. (WO 9856057).

Another approach is to modify the surface of the cathode material. In US 5695887

Spinel cathodes have been proposed which have a reduced surface area and whose catalytic centers by treatment with chelating agents, e.g. Acetylacetone to be saturated. Such cathode materials show significantly reduced self-discharge and improved shelf life at 55 ° C. The cycle stability at 55 ° C is only slightly improved (Solid State Ionics 104 (1997) 13).

Another possibility is to coat the cathode particles with a layer, for example a lithium borate glass (Solid State Ionics 104 (1997) 13). For this, a spinel is placed in a methanolic solution of H ₃ B0 ₃ , LiBO ₂ ^* 8H ₂ 0 and LiOH ^* H ₂ 0 given and stirred at 50-80 ° C until the solvent has completely evaporated. The powder is then heated to 600-800 ° C to ensure the conversion into the borate. This improves the shelf life at high temperatures. However, no improved cycle stability was found.

In WO 98/02930 undoped spinels are treated with alkali metal hydroxide solutions. The treated spinel is then heated in a CO ₂ atmosphere in order to convert the adhering hydroxides into the corresponding carbonates. The spinels modified in this way show improved high-temperature shelf life as well as improved cycle stability at high temperatures.

The coating of electrodes to improve various properties of lithium ion batteries has been described many times.

For example, the cathode and / or anode is coated in such a way that the active material is pasted onto the current conductor together with binder and a conductive material. Then a paste consisting of the

Coating material, binder and / or solvent applied to the electrode. Inorganic and / or organic materials which can be conductive are named as coating materials, e.g. B. Al ₂ 0 ₃ , nickel, graphite, LiF, PVDF etc. Lithium-ion batteries that contain electrodes coated in this way show high voltages and capacities as well as improved safety characteristics (EP 836238).

A very similar procedure is also followed in US 5869208. Here too, the electrode paste (cathode material: lithium manganese spinel) is first produced and applied to the current conductor. Then the protective layer, consisting of a metal oxide and binder, is pasted onto the electrode. Metal oxides used are, for example, aluminum oxide, titanium oxide and zirconium oxide.

JP 08236114 likewise first produces the electrode, preferably LiNi _{0 5} C0 _0.5 O ₂ as the active material, and then one Oxide layer applied by sputtering, vacuum evaporation or CVD.

In JP 09147916 a protective layer consisting of solid oxide particles, for example MgO, CaO, SrO, Zr0 ₂ , Al ₂ 0 ₃ Si0 ₂ , and a polymer is applied to the side of the current collector that contains the electrode. As a result, high voltages and high cycle stability are achieved.

Another way is described in JP 09165984. The lithium manganese spinel, which is coated with boron oxide, serves as the cathode material. This coating is created during the spinel synthesis. For this purpose, a lithium, manganese and boron compound are calcined in an oxidizing atmosphere. The boron oxide-coated spinels obtained in this way show no manganese dissolution at high voltages.

However, it is not only coated with oxidic materials, but also with polymers as described in JP 07296847 to improve the safety characteristics. JP 08250120 is used for coating with sulfides, selenides and tellurides

Improvement of the cycle performance and in JP 08264183 with fluorides to improve the cycle life.

The object of the present invention is to provide electrode materials which do not have the disadvantages of the prior art and which have improved storage stability and cycle stability at high temperatures, in particular at temperatures above room temperature.

The object according to the invention is achieved by lithium mixed oxide particles which are coated with one or more metal oxides.

The invention also relates to a method for coating the lithium mixed oxide particles and the use in electrochemical cells, batteries and secondary lithium batteries. The present invention relates to undoped and doped mixed oxides as cathode materials selected from the group Li (MnMe _z ) ₂ 0 ₄ , Li (CoMe _z ) 0 ₂ , Li (Ni ₁ - _x - _y Co _x Me _y ) 0 ₂ , where Me is at least is a metal cation from the groups Ila, lila, IVa, Ilb, Illb, IVb, VIb, Vllb, VIII of the periodic table. Particularly suitable metal cations are copper, silver, nickel, magnesium, zinc, aluminum, iron, cobalt, chromium, titanium and zircon, and also lithium for the spinel compounds. The present invention also relates to other lithium intercalation and insertion compounds which are suitable for 4V cathodes with improved high-temperature properties, in particular at temperatures above room temperature, their production and use, in particular as cathode material in electrochemical cells.

In the present invention, the lithium mixed oxide particles are coated with metal oxides in order to obtain improved storage stability and cyclability at high temperatures (above room temperature).

Various metal oxides, in particular oxides or mixed oxides of Zr, Al, Zn, Y, Ce, Sn, Ca, Si, Sr, Mg and Ti and mixtures thereof, for example ZnO, CaO, SrO, Si0 ₂ , CaTi0 ₃ , are suitable as coating materials. MgAI ₂ 0 ₄ , Zr0 ₂ , Al ₂ 0 ₃ , Ce ₂ 0 ₃ , Y ₂ 0 ₃ , Sn0 ₂ , Ti0 ₂ and MgO.

It has been found that the undesired reactions of the electrolyte with the electrode materials can be strongly inhibited by coating with the said metal oxides.

Surprisingly, it was found that the coating of the lithium mixed oxide particles significantly improves the

High temperature cycle stability of the cathodes made from it comes. This almost halves the loss of capacity per cycle of the coated cathode material compared to uncoated cathode materials. In addition, an improved shelf life above room temperature was found. Spinels coated with metal oxides have a significantly reduced manganese dissolution.

Furthermore, it was found that the coating of the individual

Particle has some advantages over the coating of the electrode strips. If the electrode material is damaged, a large part of the active material can attack the coated tapes, while these undesired reactions remain highly localized when the individual particles are coated.

The coating process achieves layer thicknesses between 0.03 μm and 5 μm. Preferred layer thicknesses are between 0.05 μm and 3 μm. The lithium mixed oxide particles can be coated one or more times.

The coated lithium mixed oxide particles can be processed with the usual carriers and auxiliaries to 4V cathodes for lithium-ion batteries.

In addition, the coating is carried out at the supplier so that the battery manufacturer does not have to make the process changes necessary for the coating.

Due to the coating of the materials, the safety aspects can also be improved.

By coating the cathode material with inorganic materials, the undesirable reactions of the electrode material with the electrolyte are strongly inhibited, and thus an improvement in the shelf life and cycle stability at higher temperatures is achieved.

The cathode material according to the invention can be used in secondary lithium-ion batteries with common electrolytes. For example, electrolytes with conductive salts selected from the group LiPF ₆ , LiBF ₄ , LiCI0 ₄ , LiAsF ₆ , LiCF ₃ S0 ₃ , LiN (CF ₃ S0 ₂ ) ₂ or LiC (CF ₃ S0 ₂ ) ₃ and mixtures thereof are suitable. The electrolytes can too contain organic isocyanates (DE 199 44 603) to reduce the water content. The electrolytes can also contain organic alkali salts (DE 199 10 968) as an additive. Alkali borates of the general formula are suitable

Li ⁺ B- (OR ¹ ) _m (OR ² ) _p where, m and p 0, 1, 2, 3 or 4 with m + p = 4 and

R ¹ and R ^{2 are the} same or different,

optionally connected directly to one another by a single or double bond, each individually or jointly having the meaning of an aromatic or aliphatic carbon, dicarbon or sulfonic acid radical, or in each case individually or jointly meaning an aromatic ring from the group consisting of phenyl, naphthyl and anthracenyl or phenanthrenyl, which can be unsubstituted or substituted one to four times by A or shark, or in each case individually or jointly the meaning of a heterocyclic aromatic ring from the group pyridyl, pyrazyl or bipyridyl, which is unsubstituted or mono- to triple by A or shark may be substituted, or in each case individually or jointly, have the meaning of an aromatic hydroxy acid from the group of aromatic hydroxy-carboxylic acids or aromatic hydroxy-sulfonic acids, which may be unsubstituted or substituted one to four times by A or shark, and

Shark F, Cl or Br and

A is alkyl with 1 to 6 carbon atoms, which can be halogenated one to three times. Alkaline alcoholates of the general formula are also suitable Li ⁺ OR ^" , in which R has the meaning of an aromatic or aliphatic carbon, dicarbon or sulfonic acid residue, or

has the meaning of an aromatic ring from the group phenyl, naphthyl, anthracenyl or phenanthrenyl, which may be unsubstituted or substituted one to four times by A or shark, or

has the meaning of a heterocyclic aromatic ring from the group Py dyl, pyrazyl or bipyhdyl, which may be unsubstituted or mono- to trisubstituted by A or shark, or

the meaning of an aromatic hydroxy acid from the group of aromatic hydroxy-carboxylic acids or aromatic hydroxy-sulfonic acids, which can be unsubstituted or substituted one to four times by A or shark,

has and

Shark F, Cl, or Br,

and

A alkyl with 1 to 6 carbon atoms, which can be halogenated one to three times.

Also lithium complex salts of the formula

in which

R ¹ and R ^{2 are the} same or different, optionally connected directly to one another by a single or double formation, each individually or jointly the meaning of an aromatic Rings from the group phenyl, naphthyl, anthracenyl or

Phenanthrenyl, which is unsubstituted or one to six times by alkyl

(Ci to C ₆ ), alkoxy groups (d to C ₆ ) or halogen (F, Cl, Br) can be substituted,

or in each case individually or jointly the meaning of an aromatic heterocyclic ring from the group pyridyl,

Pyrazyl or pyrimidyl, which is unsubstituted or one to four times by

Alkyl (Ci to C ₆ ), alkoxy groups (d to C ₆ ) or halogen (F, Cl, Br) can be substituted,

or in each case individually or jointly the meaning of an aromatic ring from the group hydroxylbenzoecarboxyl, hydroxylnaphthalenecarboxyl, hydroxylbenzenesulfonyl and hydroxylnaphthalenesulfonyl, which is unsubstituted or one to four times by alkyl (Ci to C ₆ ), alkoxy groups (d to C ₆ ) or halogen (F, Cl , Br) may have substituted,

R ³ -R ⁶ can each have the following meaning individually or in pairs, optionally directly linked to one another by a single or double bond:

1. alkyl (d to C ₆ ), alkyloxy (d to C ₆ ) or halogen (F, Cl, Br)

2. an aromatic ring from the groups

Phenyl, naphthyl, anthracenyl or phenanthrenyl, which can be unsubstituted or monosubstituted to sixfold substituted by alkyl (d to C ₆ ), alkoxy groups (d to C ₆ ) or halogen (F, Cl, Br),

Pyridyl, pyrazyl or pyrimidyl, which can be unsubstituted or mono- to tetrasubstituted by alkyl (d to C ₆ ), alkoxy groups (d to C ₆ ) or halogen (F, Cl, Br),

which are shown using the following method (DE 199 32 317)

a) 3-, 4-, 5-, 6-substituted phenol is mixed with chlorosulfonic acid in a suitable solvent, b) the intermediate from a) is reacted with chlorotrimethylsilane, filtered and fractionally distilled,

c) the intermediate from b) with lithium tetramethanolate borate (l-), reacted in a suitable solvent and from it the

The end product is isolated can be contained in the electrolyte.

Likewise, the electrolytes can be compounds of the following formula (DE 199 41 566)

[([R ¹ (CR ² R ³ ) _k ], A _x ) _y Kt] ⁺ -N (CF ₃ ) ₂

in which

Kt = N, P, As, Sb, S, Se

A = N, P, P (O), O, S, S (O), S0 ₂ , As, As (O), Sb, Sb (O)

R ¹ , R ² and R ³

the same or different

H, halogen, substituted and / or unsubstituted alkyl C _n H _{2n +} ι, substituted and / or unsubstituted alkenyl with 1-18 carbon atoms and one or more double bonds, substituted and / or unsubstituted alkynyl with 1-18 carbon atoms and one or more triple bonds, substituted and / or unsubstituted cycloalkyl C _m H _2m -ι, mono- or polysubstituted and / or unsubstituted phenyl, substituted and / or unsubstituted heteroaryl,

A can be enclosed in different positions in R ¹ , R ² and / or R ³ ,

Kt can be enclosed in a cyclic or heterocyclic ring,

the groups bound to Kt can be the same or different

With n = 1-18

m = 3-7

k = 0.1-6

l = 1 or 2 in the case of x = 1 and 1 in the case of x = 0

x = 0.1

y = 1-4

mean contain. The process for the preparation of these compounds is characterized in that an alkali salt of the general formula

D ^{+ "} N (CF ₃ ) ₂ (II)

with D ⁺ selected from the group of alkali metals in a polar organic solvent with a salt of the general formula

[([R ¹ (CR ² R ³ ) _k ], A _x ) _y Kt] ⁺ Ε (III)

in which

Kt, A, R ¹ , R ² , R ³ , k, I, x and y have the meaning given above and

^~ EF, Cl ^" , Br ^" , r, BF ₄ ^" , CI0 ₄ ^" , AsF ₆ ^" , SbF ₆ ^' or PF ₆ ^"

means is implemented.

But also electrolytes containing compounds of the general formula (DE 199 53 638)

X- (CYZ) _m -S0 ₂ N (CR R ² R ³ ) ₂

With

XH, F, Cl, C _n F _{2n + 1} , dF ^, (S0 ₂ ) _k N (CR ¹ R ² R ³ ) ₂

YH, F, Cl ZH, F, Cl

R ¹ , R ² , R ³ H and / or alkyl, fluoroalkyl, cycloalkyl

m 0-9 and if X = H, m ≠ O

n 1-9

k 0 if m = 0 and k = 1 if m = 1-9,

prepared by the reaction of partially or perfluorinated alkysulfonyl fluorides with dimethylamine in organic solvents and complex salts of the general formula (DE 199 51 804)

MHEZ] :;

in which mean:

x, y 1, 2, 3, 4, 5, 6

M ^{x +} a metal ion

E of a Lewis acid selected from the group

BR ¹ R ² R ³ , AIR ¹ R ² R ³ , PR ¹ R ² R ³ R ⁴ R ⁵ , AsR ¹ R ² R ³ R ⁴ R ⁵ , VR ¹ R ² R ³ R ⁴ R ⁵ ,

R ¹ to R ^{5 are the} same or different, optionally connected directly to one another by a single or double formation, each individually or jointly the meaning

a halogen (F, Cl, Br),

an alkyl or alkoxy radical (d to C ₈ ) which can be partially or completely substituted by F, Cl, Br,

an aromatic ring from the group phenyl, naphthyl, anthracenyl or phenanthrenyl, optionally bonded via oxygen, which may be unsubstituted or monosubstituted to sixfold substituted by alkyl (d to C ₈ ) or F, Cl, Br an aromatic heterocyclic ring, optionally bonded via oxygen, from the group pyridyl, pyrazyl or pyrimidyl, which may be unsubstituted or substituted one to four times by alkyl (d to C ₈ ) or F, Cl, Br and

Z OR ⁶ , NR ⁶ R ⁷ , CR ⁶ R ⁷ R ⁸ , OS0 ₂ R ⁶ , N (S0 ₂ R ⁶ ) (S0 ₂ R ⁷ ), C (S0 ₂ R ⁵ ) (S0 ₂ R ⁷ ) (S0 ₂ R ⁸ ), OCOR ⁶ , where

R ⁶ to R ^{8 are the} same or different, optionally connected directly to one another by a single or double bond, each individually or jointly the meaning

a hydrogen or the meaning as R ¹ to R ⁵ , prepared by reacting a corresponding boron or phosphorus-Lewis acid solvency adduct with a lithium or tetraalkylammonium imide, methanide or triflate can be used.

Also borate salts (DE 199 59 722) of the general formula

in which mean:

M is a metal ion or tetraalkylammonium ion

x, y 1, 2, 3, 4, 5 or 6

R ¹ to R ^{4 may be the} same or different, optionally by means of a single or double bond directly bonded alkoxy or carboxy radicals (CC ₈ ). These borate salts are prepared by reacting lithium tetraalcoholate borate or a 1: 1 mixture of lithium alcoholate with a boric acid ester in an aprotic solvent with a suitable hydroxyl or carboxyl compound in a ratio of 2: 1 or 4: 1. A general example of the invention is explained below.

Process for coating cathode materials

4 V cathode materials, in particular materials with a layer structure (for example Li (CoMe _z ) 0 ₂ or Li (Ni _1. _X - _y Co _x Me _y ) 0 ₂ ) and spinels (for example Li (MnMe _z ) ₂ 0 ₄ ) suspended in polar organic solvents such as alcohols, aldehydes, halides or ketones, spinels also in water and placed in a reaction vessel. The materials can also be suspended in non-polar organic solvents, such as cycloalkanes or aromatics. The reaction vessel can be heated and is equipped with a stirrer. The reaction solution is heated to temperatures between 10 and 100 ° C, depending on the boiling point of the solvent.

Soluble metal salts selected from the group of zirconium, aluminum, zinc, yttrium, cerium, tin, calcium, silicon, strontium, titanium and magnesium salts and their mixtures, which are in organic solvents, are used as the coating solution , or water are soluble. Acids, bases or water are suitable as the hydrolysis solution, depending on the solvent used for the coating solution.

The coating solution and the hydrolysis solution are slowly metered in. The dosing quantities and speeds depend on the desired layer thicknesses and the metal salts used. In order to ensure that the hydrolysis reaction proceeds quantitatively, the hydrolysis solution is added in excess.

After the end of the reaction, the solution is filtered off and the powder obtained is dried. In order to ensure complete conversion into the metal oxide, the dried powder must still be calcined. The powder is heated to 400 ° C. to 1000 ° C., preferably 700 to 850 ° C., and kept at this temperature for 10 minutes to 5 hours, preferably 20 to 60 minutes. The particles can be coated one or more times. If desired, the first coating can be carried out with a metal oxide and the next coatings with the oxides of other metals.

The following examples are intended to explain the invention in more detail, but without restricting it.

Examples

example 1

Process for coating cathode materials with Zr0 ₂

100 g of lithium manganese spinel, SP30 Selectipur ^® from Merck, and 500 ml of ethanol, which serves as a solvent, are placed in a 2 liter flask. This flask is immersed in a water bath and is equipped with a stirring tool. The water bath is heated to 40 ° C.

Tetrapropyl orthozirconate (26.58 g), which is dissolved in ethanol (521.8 ml), serves as the coating solution. Water (14.66 g) is used as the hydrolysis solution. Both solutions are slowly added. The addition of zirconium propylate is complete after approx. 6.5 hours. To ensure that the hydrolysis reaction also takes place quantitatively, water (36.4 g) is added for the further hydrolysis for a further 16.2 hours.

After the end of the reaction, the ethanolic solution is filtered off and the powder obtained is dried at about 100.degree. To ensure complete conversion into the Zr0 ₂ , the dried powder must still be calcined. After drying, the powder is therefore heated to 800 ° C. and kept at this temperature for 30 minutes.

Example 2:

Storage test at elevated temperatures

Commercially available spinel cathode powders, SP30 and SP35 Selectipur ^® from Merck, are used. The samples, SP30, untreated and with Zr0 ₂ -coated SP30, are each placed in a 1 liter aluminum bottle (approx. 3g sample) and with 30ml

Electrolyte mixed (LP600 Selectipur ^® from Merck, EC: DEC: PC 2: 1: 3 1M LiPF ₆ ). The aluminum bottles are then sealed gas-tight. These preparations are all carried out in an argon-flushed glove box. The bottles prepared in this way are then removed from the glove box and stored in a drying cabinet at 80 ° C. for 6 or 13 days. After the end of the storage test, the aluminum bottles cooled to room temperature are reinserted into the glove box and opened there. The electrolyte is filtered off and the amount of manganese dissolved in the electrolyte is determined quantitatively by means of ICP-OES.

Table 1 compares the analytical results of the uncoated and coated lithium manganese spinels.

Table 1: Results of the manganese determination

The manganese dissolution in the uncoated spinels is very strong and increases with time. In the case of the coated spinels, however, the manganese dissolution is significantly reduced both in absolute numbers and as a function of the storage time. The significant improvement in high-temperature shelf life due to the metal oxide coating for these cathode materials is clearly demonstrable. Example 3:

Cyclize at high temperatures

The cathode powder prepared according to Example 1, coated, and as a comparison, an uncoated material SP30 Selectipur ^® from Merck be cycled at 60 ° C.

To produce the electrodes, the cathode powder is mixed well with 15% conductive carbon black and 5% PVDF (binder material). The paste thus produced is applied to an aluminum mesh, which serves as a current conductor, and dried overnight at 175 ° C. under an argon atmosphere and under reduced pressure. The dried electrode is introduced into the glove box flushed with argon and the measuring cell is installed. Lithium metal serves as the counter and reference electrode. LP 50 Selectipur ^® from Merck is used as the electrolyte (1 M LiPF ₆ in EC: EMC 50: 50% by weight). The measuring cell with the electrodes and the electrolyte is placed in a steel container, which is sealed gas-tight. The cell produced in this way is removed from the glove box and placed in a climatic cabinet which is set to 60 ° C. After connecting the measuring cell to one

Potentiostats / galvanostats, the electrode is cycled (charging: 5 hours, discharging: 5 hours).

The result is that the cycle stability of the uncoated spinel is less than that of the coated one.

In the first 5 cycles there are irreversible reactions such as film formation on the cathode and anode, so that they are not used for the calculation. The capacity loss per cycle of the uncoated spinel is then 0.78 mAh / g, while the Zr0 ₂ -coated spinel loses only 0.45 mAh / g per cycle. This is almost a halving of the loss of capacity per cycle. This shows that the high temperature cycle stability of the cathode powder is significantly improved by coating with oxides.

Claims

claims

1. Mixed lithium oxide particles, characterized in that they are coated with one or more metal oxides.

2. Lithium mixed oxide particles according to claim 1, characterized in that the particles from the group Li (MnMe _z ) ₂ 0 ₄ , Li (CoMe _z ) 0 ₂ , Li (Ni ₁ _ _x . _Y Co _x Me _z ) 0 ₂ and other lithium intercalation and insertion compounds are selected.

3. lithium mixed oxide particles according to claim 1 or 2, characterized in that the metal oxides from the group ZnO, CaO, SrO, Si0 ₂ , CaTi0 ₃ , MgAI ₂ 0 ₄ , Zr0 ₂ , Al ₂ 0 ₃ , Ce ₂ 0 ₃ , Y ₂ 0 ₃ , Sn0 ₂ , Ti0 ₂ and MgO are selected.

4. Lithium mixed oxide particles according to one of claims 1 to 3, characterized in that the layer thicknesses of the metal oxides are 0.05-3 microns.

5. Cathodes, essentially containing lithium mixed oxide particles according to one of claims 1 to 4 and conventional carriers and auxiliaries.

Process for the production of lithium mixed oxide particles coated with one or more metal oxides, characterized in that the particles are suspended in an organic solvent, the suspension is mixed with a solution of a hydrolyzable metal compound and a hydrolysis solution and the filtered particles are then filtered off, dried and optionally calcined.

7. Method of making with one or more

Metal oxide-coated lithium mixed oxide particles according to claim 6, characterized in that the metal oxides from the Group ZnO, CaO SrO, Si0 ₂ , CaTi0 ₃ , MgAI ₂ 0 ₄ , Zr0 ₂ , Al ₂ 0 ₃ , Ce 0 ₃ , Y ₂ 0 ₃ , Sn0 ₂ , Ti0 ₂ and MgO are selected.

8. A method for producing lithium mixed oxide particles coated with one or more metal oxides according to claim 6, characterized in that the hydrolysis solution are acids, bases or water.

9. Use of coated lithium mixed oxide particles according to one of claims 1 to 4 for the production of cathodes with improved shelf life and cycle stability at temperatures above room temperature.

10. Use of coated lithium mixed oxide particles according to one of claims 1 to 4 for the production of 4V cathodes.

11. Use of coated lithium mixed oxide particles according to one of claims 1 to 4 in electrodes for electrochemical cells, batteries and secondary lithium batteries.