KR20020013887A - Lithium-mixed oxide particles coated with metal-oxides - Google Patents

Abstract

The present invention relates to lithium mixed oxide particles coated with a metal oxide. The particles are used to improve the properties of the electrochemical cell. The present invention relates to undoped mixed oxides selected from the group of Li (MnMe _z ) ₂ O ₄ Li (CoMe _z ) O ₂ and Li (Ni _1-xy Co _x Me _y ) O ₂ as cathode materials and To doped mixed oxides. Me means one or more metal cations from groups IIa, IIIa, IVa, IIb, IIIb, IVb, VIb, VIIb, VIII of the periodic table. Copper, silver, nickel, magnesium, zinc, aluminum, iron, cobalt, chromium, titanium and zircon are particularly useful cations. Lithium is particularly useful for spinel compositions. The invention also relates to lithium intercalation and insertion compositions which can be used for 4V-cathodes and have improved high temperature properties, especially at temperatures above room temperature. In addition, the present invention relates to the production and use of these materials, in particular as cathode materials, in electrochemical cells. Oxides or mixed oxides of various metal oxides, in particular Zr, Al, Zn, Y, Ce, Sn, Ca, Si, Sr, Mg and Ti, and mixtures thereof, such as ZnO, CaO, SrO, SiO ₂ , CaTiO ₃ , MgAl ₂ O ₄ , ZrO ₂ , Al ₂ O ₃ , Ce ₂ O ₃ , Y ₂ O ₃ , SnO ₂ , TiO ₂ and MgO can be used as the coating material. It has been found that undesirable reactions between electrolyte and electrode material can be significantly inhibited by coating with the metal oxide.

Description

Lithium mixed oxide particles coated with metal oxides {LITHIUM-MIXED OXIDE PARTICLES COATED WITH METAL-OXIDES}

As is known, when metal lithium is used as the anode material, dendritic crystals form during melting and deposition of lithium, resulting in improper circulation stability and significant safety risk of lithium (inner short) (J. Power Sources, 54 (1995) 151).

The problems can be solved by replacing the lithium-metal anode with another compound that can reversibly intercalate lithium ions. The principle of operation of a lithium ion battery is based on the fact that both cathode and anode materials can intercalate lithium ions, i.e., lithium ions come out of the cathode during charging, diffuse through the electrolyte and are interposed on the anode. . During discharge, the same process is reversed. Also, by this mechanism of action, such batteries are referred to as "swing chairs" or lithium ion batteries.

The voltage produced by this type of cell is measured by the lithium interposition potential of the electrode. In order to obtain the highest possible voltage, a cathode material which intercalates with lithium at a very high potential and an anode material which intercalates with lithium at a very low potential (vs. Li / Li ⁺ ) should be used. Cathode materials satisfying the above requirements include LiCoO ₂ having a layered structure, LiNiO ₂ , and LiMn ₂ O ₄ having a cubic three-dimensional network structure. These compounds deintercalate lithium ions at a potential (vs. Li / Li ⁺ ) of about 4V. In the case of anode compounds, certain carbon compounds, for example graphite, meet the requirements of low potential and high capacity.

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

LiCoO ₂ , LiNiO ₂ and LiMn ₂ O ₄ are under discussion and being used for 4V cathodes. The electrolyte used is a mixture containing an aprotic solvent in addition to the conductive salt. The most frequently used solvents are ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC) and ethyl methyl carbonate (EMC). Although all kinds of conductive salts are discussed, LiPF ₆ is used in practice without exception. The anode used is generally graphite.

A disadvantage of conventional batteries is their poor shelf life and cycling stability at high temperatures. This drawback is due to the cathode materials used in addition to the electrolyte, in particular lithium manganese spinel LiMn ₂ O ₄ .

However, lithium manganese spinels are very promising materials as cathodes of portable batteries. These materials have the advantages of improved safety, low toxicity, and low cost of raw materials compared to LiNiO ₂ and LiCoO ₂ based cathodes.

The disadvantages of spinel are low capacity and inadequate high temperature shelf life and hence poor circulation stability at high temperatures. The reason for this disadvantage is believed to be due to the dissolution of divalent manganese in the electrolyte (Solid State Ionics 69 (1994) 59), J. Power Sources 66 (1997) 129 and J. Electrochem. Soc. 144 (1997) 2178). Manganese in spinel LiMn ₂ O ₄ exists in two oxidation states, trivalent and tetravalent. In addition, LiPF ₆ -containing electrolytes always contain water impurities. This water reacts with the LiPF ₆ conductive salts to form LiF and acidic components such as HF. This acid component reacts with trivalent manganese in the spinel to form Mn ²⁺ and Mn ⁴⁺ (disproportionation: 2Mn ^{3 +} → Mn ²⁺ + Mn ⁴⁺ ). This decomposition occurs even at room temperature but is accelerated at elevated temperatures.

One way to increase the stability of the spinel at high temperatures is to dope the spinel. For example, some manganese ions may be substituted with other ions, for example trivalent metal ions. Antonini et al. Reported that spinels doped with gallium and chromium (eg, Li _1.02 Ga _0.025 Cr _0.025 Mn _1.95 O ₄ ) showed satisfactory shelf life and cycling stability at 55 ° C. (J. Electrochem. Soc., 145 (1998) 2726].

Researchers at Bellcore Inc. have studied similar pathways. They replace some manganese with aluminum and further some oxygen ions with fluoride ions ((Li _{1 + x} Al _y Mn _2-xy ) O _4-z F _z ). This doping also improves circulating stability at 55 ° C. (WO 98156057).

Another possible solution is to modify the surface of the cathode material. U. S. Patent No. 5695887 proposes a spinel cathode having a reduced surface area and saturating its catalyst center by treatment with a chelating agent such as acetylacetone. Cathode materials of this type exhibit markedly reduced self-discharge and improved shelf life at 55 ° C. Cycling stability at 55 ° C. is only slightly improved (Solid State Ionics 104 (1997) 13).

Another possibility is to cover the cathode particles with a coating, for example lithium borate glass (Solid State Ionics 104 (1997) 13). For this purpose, stir the spinel in H ₃ BO _3, LiBO ₂ and 8H ₂ O and 50 to 80 ℃ the introduced and the resulting mixture on a methanolic solution of LiOH and H ₂ O until the solvent is completely evaporated. The powder is then heated to 600-800 ° C. to ensure conversion to borate. Thus, the shelf life at high temperatures is improved. However, there is no known improvement in circulation stability.

In WO 98/02930, undoped spinels are treated with alkali metal hydroxide solution. The treated spinel is then heated in a CO ₂ atmosphere to convert the adhesive hydroxide to the corresponding carbonate. Spinels modified in this manner exhibit improved hot shelf life and improved circulation stability at high temperatures.

Coating the electrodes to improve various properties of lithium ion batteries has already been described several times.

For example, the cathode and / or anode are coated by pasting the active material into the collector together with the binder and the conductive material. Thereafter, a paste consisting of the coating material, the binder and / or the solvent is applied to the electrode. The coating material may be a conductive material such as Al ₂ O ₃ , nickel, graphite, LiF, PVDF, or the like as an inorganic and / or organic material. Lithium ion batteries containing electrodes coated in this way exhibit high voltage, high capacity and improved safety properties (European Patent 836238).

In addition, US Pat. No. 5869208 describes a very similar procedure. Also here, first, an electrode paste (cathode material: lithium manganese spinel) is prepared and applied to the collector. The protective coating consisting of the metal oxide and the binder is then pasted onto the electrode. Examples of metal oxides used are aluminum oxide, titanium oxide and zirconium oxide.

In Japanese Patent No. 08236114, the electrode is also made preferentially, preferably LiNi _0.5 Co _0.5 O ₂ is prepared as the active material, and then an oxide layer is applied by sputtering, vacuum deposition or CVD.

In Japanese Patent No. 09147916, a protective layer composed of solid oxide particles such as MgO, CaO, SrO, ZrO ₂ , Al ₂ O ₃ or SiO ₂ , and a polymer is applied to the side of the collector containing the electrode. Thus, high voltage and high circulation stability are achieved.

Japanese Patent No. 09165984 describes another route. The cathode material used is lithium manganese spinel coated with boron oxide. The coating is produced during spinel synthesis. Finally, lithium, manganese and boron compounds are calcined in an oxidizing atmosphere. The boron oxide-coated spinel obtained by this method shows no melting of manganese at high voltage.

However, in order to improve safety as described in Japanese Patent No. 07296847, the coating is made using a polymer as well as an oxidizing material.

In Japanese Patent No. 08250120, coating is performed using sulfide, selenide and telluride to improve circulation performance, and in Japanese Patent No. 08264183, coating is performed using fluoride to improve circulation life.

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

The demand for rechargeable lithium batteries is high and will increase very rapidly in the future. This is because of the achievable high energy density and light weight of the battery. The battery is used in mobile phones, portable video cameras, laptop computers and the like.

It is an object of the present invention to provide an electrode material which does not have the disadvantages of the prior art and has improved shelf life and circulation stability at high temperatures, in particular at temperatures above room temperature.

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

The present invention also relates to a method of coating lithium mixed oxide particles and their use in electrochemical cells, batteries and secondary lithium batteries.

The invention relates to Li (MnMe _z ) ₂ O ₄ , Li (CoMe _z ) O ₂ and Li (Ni _1-xy Co _x Me _y ) O ₂ , wherein Me is IIa, IIIa, IVa, IIb, IIIb of the Periodic Table of Elements. , At least one metal cation from Groups IVb, VIb, VIIb, and VIII], as a cathode material and undoped and doped mixed oxides. Particularly suitable metal cations are copper, silver, nickel, magnesium, zinc, aluminum, iron, cobalt, chromium, titanium and zirconium, and lithium is also suitable for spinel compounds. The present invention also relates to other lithium intercalating and intercalating compounds suitable for 4V cathodes, having improved high temperature properties, especially at temperatures above room temperature, and in particular their preparation and use as cathode materials in electrochemical cells.

In the present invention, the lithium mixed oxide particles are coated with metal oxide to improve the shelf life and circulation stability at high temperature (temperature higher than room temperature).

Suitable coating materials include oxides or mixed oxides of various metal oxides, in particular Zr, Al, Zn, Y, Ce, Sn, Ca, Si, Sr, Mg and Ti, and mixtures thereof, such as ZnO, CaO, SrO, SiO ₂ , CaTiO ₃ , MgAl ₂ O ₄ , ZrO ₂ , Al ₂ O ₃ , Ce ₂ O ₃ , Y ₂ O ₃ , SnO ₂ , TiO ₂ and MgO.

It has been found that coating with the metal oxide can greatly inhibit undesirable reactions between the electrolyte and the electrode material.

Surprisingly, it has been found that coating lithium mixed oxide particles significantly improves the high temperature cycling stability of the cathodes prepared from them. This substantially reduces the capacity loss per cycle of the coated cathode material in half compared to the uncoated cathode material.

In addition, it has been found that the shelf life is improved at temperatures above room temperature. Spinels coated with metal oxides significantly reduced manganese fusion.

In addition, the coating of each particle has several advantages over the coating of electrode bands. When the electrode material is damaged, the electrolyte can attack most of the active material in the case of the coated band, whereas the undesirable reaction occurs very locally when the individual particles are coated.

The coating process is such that the layer thickness is 0.03 to 5 mu m. Preferred layer thicknesses are from 0.05 to 3 μm. The lithium mixed oxide particles may have one or more coatings.

The coated lithium mixed oxide particles can be converted to 4V cathodes for lithium ion batteries using conventional support materials and auxiliaries.

In addition, the coating is performed by the supplier, which means that the battery manufacturer does not need to carry out the process modifications required for the coating.

By coating the material, improvements in safety can also be expected.

The coating of the cathode material with the inorganic material can greatly suppress undesirable reactions between the electrode material and the electrolyte, thereby improving the shelf life and circulation stability at elevated temperatures.

The cathode material according to the invention can be used in secondary lithium ion batteries with conventional electrolytes. Examples of suitable electrolytes include conductivity selected from the group consisting of LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ and LiC (CF ₃ SO ₂ ) ₃ , and mixtures thereof Those with salts. In addition, the electrolyte may comprise organic isocyanates to reduce the water content (German Patent No. 199 44 603). The electrolyte may also contain organic alkali metal salts as additives (German Patent No. 199 10 968). Suitable alkali metal salts are alkali metal borate of the formula:

^{Li + B - (OR 1)} m (OR 2) p

Where

m and p are 0, 1, 2, 3 or 4 when m + p is 4

R ¹ and R ² are the same or different and are optionally bonded to each other by a single or double bond,

Each alone or together is an aromatic or aliphatic carboxyl, dicarbosil or sulfonic acid radical;

Each is alone or together an aromatic ring from the group consisting of phenyl, naphthyl, anthracenyl or phenanthrenyl, which aromatic ring may be unsubstituted or mono- to tetra-substituted by A or halogen;

Each independently or together represents a heterocyclic ring from the group consisting of pyridyl, pyrazyl or bipyridyl, said heterocyclic ring being unsubstituted or mono- to tri-substituted by A or halogen;

Each is an aromatic hydroxy acid from the group consisting of aromatic hydroxycarboxylic acids or aromatic hydroxysulfonic acids, alone or in combination, which aromatic hydroxy acids may be unsubstituted or mono- to tetra-substituted by A or halogen. There is,

Hal is F, Cl or Br,

A is an alkyl group having 1 to 6 carbon atoms and may be 1- to 3-halogenated.

Also suitable are alkali metal alkoxides of the formula:

Li ⁺ OR ^-

Where

R is an aromatic or aliphatic carboxyl, dicarboxyl or sulfonic acid radical, or

An aromatic ring from the group consisting of phenyl, naphthyl, anthracenyl or phenanthrenyl, which aromatic ring may be unsubstituted or mono- to tetra-substituted by A or halogen;

A heterocyclic ring from the group consisting of pyridyl, pyrazyl or bipyridyl, which heterocyclic ring may be unsubstituted or mono- to tri-substituted by A or halogen;

Aromatic hydroxy acids from the group consisting of aromatic hydroxycarboxylic acids or aromatic hydroxysulfonic acids, said aromatic hydroxy acids can be unsubstituted or mono- to tetra-substituted by A or halogen,

Hal is F, Cl or Br,

A is an alkyl group having 1 to 6 carbon atoms, and may be 1- to 3-halogenated.

The lithium complex salt of the formula

a) adding chlorosulfonic acid to 3-, 4-, 5- or 6-substituted phenols in a suitable solvent,

b) reacting the intermediate from step a) with chlorotrimethylsilane, filtering and fractionally distilling the product, and

c) reacting the intermediate from step b) with lithium tetramethoxy borate in a suitable solvent and isolating the final product therefrom (German Patent No. 199 32 317) and also in the electrolyte May include:

Where

R ¹ and R ² are the same or different and are optionally bonded to each other by a single or double bond, each of which is an aromatic ring from the group consisting of phenyl, naphthyl, anthracenyl or phenanthrenyl, alone or together; The ring may be unsubstituted or mono- to _six- substituted by an alkyl group (C ₁ -C ₆ ), an alkoxy group (C ₁ -C ₆ ) or a halogen (F, Cl or Br);

Each is an aromatic heterocyclic ring from the group consisting of pyridyl, pyrazyl or pyrimidyl, alone or together, said aromatic heterocyclic ring being unsubstituted or substituted with an alkyl group (C ₁ -C ₆ ), an alkoxy group (C ₁ -C ₆ ) or mono- to tetra-substituted by halogen (F, Cl or Br);

Each independently or together is an aromatic ring from the group consisting of hydroxybenzocarboxyl, hydroxynaphthalenecarboxyl, hydroxybenzosulfonyl and hydroxynaphthalenesulfonyl, said aromatic ring being unsubstituted or substituted with an alkyl group (C _1- ). C ₆ ), an alkoxy group (C ₁ -C ₆ ) or halogen (F, Cl or Br) can be mono- to 4-substituted,

R ³ to R ⁶ , each alone or in pairs, are optionally bonded to each other by a single or double bond, and can be represented as follows:

1. alkyl (C ₁ -C ₆ ), alkoxy (C ₁ -C ₆ ) or halogen (F, Cl or Br), and

2. Phenyl, naphthyl, anthracenyl, which may be unsubstituted or mono- to six-substituted by alkyl groups (C ₁ -C ₆ ), alkoxy groups (C ₁ -C ₆ ) or halogens (F, Cl or Br) Or aromatic rings from the group consisting of phenanthrenyl, and unsubstituted or substituted by alkyl groups (C ₁ -C ₆ ), alkoxy groups (C ₁ -C ₆ ) or halogens (F, Cl or Br); Pyridyl, pyrazyl or pyrimidyl which may be substituted.

The electrolyte may also comprise a compound of the formula (German Patent No. 199 41 566).

^{[([R 1 (CR 2} R 3) k] l A x) y Kt] + - N (CF 3) 2

Where

Kt is N, P, As, Sb, S or Se,

A is N, P, P (O), O, S, S (O), SO ₂ , As, As (O), Sb or Sb (O),

R ¹ , R ² and R ³ are the same or different and are H, halogen, substituted and / or unsubstituted alkyl C _n H _{2n + 1} ; Substituted and / or unsubstituted alkenyl of 1 to 18 carbon atoms having one or more double bonds; Substituted and / or unsubstituted alkynyl having 1 to 18 carbon atoms having one or more triple bonds; Substituted and / or unsubstituted cycloalkylC _m H _2m-1 ; Mono- or polysubstituted and / or unsubstituted phenyl; Or substituted and / or unsubstituted heteroaryl,

A may be included in other positions of R ¹ , R ² and / or R ³ ,

Kt may be included in a cyclic or heterocyclic ring; Groups bound to Kt may be the same or different,

n is 1 to 18,

m is 3 to 7,

k is 0, 1 to 6,

l is 1 or 2 when x is 1 and 1 when x is 0,

x is 0 or 1,

y is 1 to 4.

The process for the preparation of the compound is characterized in that an alkali metal salt of D ⁺ -N (DF ₃ ) ₂ , wherein D ⁺ is selected from the group consisting of alkali metals, is reacted with a salt of the formula: in a polar organic solvent:

^{[([R 1 (CR 2} R 3) k] l A x) y Kt] + - E

Where

Kt, A, R ¹ , R ² , R ³ , k, l, x and y are as defined above,

^- E is ^{F -, Cl -, Br -} , I -, BF 4 -, ClO 4 -, AsF 6 -, SbF 6 - or PF ₆ ^- shows.

However, a compound of formula (1) prepared by reacting a partially fluorinated or perfluorinated alkylsulfonyl fluoride with dimethylamine in an organic solvent (German Patent No. 199 53 638) and the corresponding boron or phosphorus Lewis acid / solvent addition An electrolyte comprising a complex salt of formula (2) (German Patent No. 199 51 804) prepared by reacting water with lithium or tetraalkylammonium imide, metaide or triflate can be used.

X- (CYZ) _m -SO ₂ N (CR ¹ R ² R ³ ) ₂

Where

X is H, F, Cl, C _n F _{2n + 1} , C _n F _2n-1 or (SO ₂ ) _k N (CR ¹ R ² R ³ ) ₂ ,

Y is H, F or Cl,

Z is H, F or Cl,

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

m is 0 to 9 and is not 0 when x is H,

n is 1 to 9,

k is 0 when m is 0 and 1 when m is 1-9.

M ^{x +} [EZ] _{x / y} ^y-

Where

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

M ^{x +} is a metal ion,

E is a group of BR ¹ R ² R ³ , AlR 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 and VR ¹ R ² R ³ R ⁴ R ⁵ Lewis acid selected from

R ¹ to R ⁵ are the same or different and are optionally bonded directly to each other by a single or double bond, each alone or in combination:

Halogen (F, Cl or Br);

Alkyl or alkoxy radicals (C ₁ -C ₈ ) which may be partially or fully substituted by F, Cl or Br;

Group consisting of phenyl, naphthyl, anthracenyl or phenanthrenyl, which may be unsubstituted or may be _one- to six-substituted by alkyl (C ₁ -C ₈ ) or F, Cl or Br and optionally bonded via oxygen Aromatic rings from; And

Aromatic from the group consisting of pyridyl, pyrazyl or pyrimidyl which may be unsubstituted or may be mono- to tetra-substituted by alkyl (C ₁ -C ₈ ) or F, Cl or Br and optionally bonded via oxygen May represent a heterocyclic ring,

Z is OR ⁶ , NR ⁶ R ⁷ , CR ⁶ R ⁷ R ⁸ , OSO ₂ R ⁶ , N (SO ₂ R ⁶ ) (SO ₂ R ⁷ ), C (SO ₂ R ⁶ ) (SO ₂ R ⁷ ) ( SO ₂ R ⁸ ) or OCOR ⁶ ,

R ⁶ to R ⁸ are the same or different and are directly bonded to each other, optionally by a single or double bond, each being hydrogen alone or together or as defined for R ¹ to R ⁵ .

In addition, a borate salt of the formula (German Patent No. 199 59 722) may be present.

Where

M is a metal ion or tetraalkylammonium ion,

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

R ¹ to R ⁴ are the same or different and are alkoxy or carboxy radicals (C ₁ -C ₈ ) optionally bonded directly to each other by a single bond or a double bond.

The borate salts are prepared by reacting lithium tetraalkoxy borate, or 1: 1 mixture of lithium alkoxide and borate, in a ratio of 2: 1 or 4: 1 with a suitable hydroxy or carboxyl compound in an aprotic solvent.

General embodiments of the invention are described below.

Coating method of cathode material

4V cathode material, in particular a material with a layered structure (eg Li (CoMe _z ) O ₂ or Li (Ni _1-xy Co _x Me _y ) O ₂ ) and spinel (Li (MnMe _z ) ₂ O ₄ ) Is suspended in a polar organic solvent such as alcohol, aldehyde, halide or ketone, and the spinel is suspended in water and introduced into the reaction vessel. The material may also be suspended in nonpolar organic solvents such as cycloalkanes or aromatics. The reaction vessel can be heated and equipped with a stirrer. The reaction solution is warmed to a temperature of 10 ° C. to 100 ° C. depending on the boiling point of the solvent.

Suitable coating solutions are soluble metal oxides selected from the group consisting of zirconium, aluminum, zinc, yttrium, cerium, tin, calcium, silicon, strontium, titanium and magnesium salts, and mixtures thereof, and are soluble in organic solvents or water. Suitable hydrolysis solutions are acids, bases or water corresponding to the solvents used in the coating liquid.

The coating solution and the hydrolysis solution are slowly injected. The dosage and rate depends on the desired layer thickness and the metal salt used. To ensure that the hydrolysis reaction proceeds quantitatively, excess hydrolysis solution is added.

When the reaction is complete, the solution is filtered and the powder obtained is dried. In order to ensure full ring conversion to the metal salt, the dried powder must then be calcined. The powder is heated to 400 to 1000 ° C., preferably 700 to 850 ° C., at this temperature for 10 minutes to 5 hours, preferably Is maintained for 20 to 60 minutes.

The particles may be subjected to one or more coating processes. If desired, the first coating process is carried out with a specific metal oxide, followed by the next coating process with another metal oxide.

The following examples illustrate the invention in more detail, but are not intended to be limiting.

Example 1

Method of coating cathode material with ZrO ₂

100 g of lithium manganese spinel, a commercially available SP30 selector (Selectipur®) from Merck and 500 ml of ethanol used as solvent are introduced into a 2-liter flask. The flask is immersed in a water bath and a stirrer is provided. The water bath is heated to 40 ° C.

The coating solution used was tetrapropyl orthozirconate (26.58 g) dissolved in ethanol (521.8 g). The hydrolysis solution used was water (14.66 g). Inject the two solutions slowly. After about 6.5 hours the addition of zirconium propylate is complete. In addition, to ensure that the hydrolysis reaction proceeds quantitatively, water (36.4 g) is added for an additional 16.2 hours for post-hydrolysis.

When the reaction is complete, the ethanol solution is filtered and the resulting powder is dried at about 100 ° C. To ensure complete conversion to ZrO ₂ , the dried powder must then be calcined. After drying, the powder is heated to 800 ° C. and held at this temperature for 30 minutes.

Example 2

Storage test at elevated temperature

Commercially available spinel cathode powders, SP30 and SP 35 selectors® from Merck, are used. Sample, untreated SP30 and ZrO ₂ -coated SP35 were each introduced into a 1 liter aluminum container (approximately 3 g of sample) and 30 ml of electrolyte (LP600 Selector® from Merck, EC: DEC: PC). = 2: 1: 3 1M LiPE ₆ ) is added. Thereafter, the aluminum container is sealed to prevent leakage of gas. All of the above preparations are carried out in an argon-flushed glovebox. The vessel prepared by the above method is then removed from the glovebox via lock and stored in a drying cabinet at 80 ° C. for 6 or 13 days. When the storage test is complete, the aluminum container is cooled to room temperature and then introduced into the glovebox through the lock and opened. The electrolyte is filtered and the amount of manganese dissolved in the electrolyte is quantitatively determined by ICP-OES.

Table 1 compares the analytical results for the uncoated lithium manganese spinel and the coated lithium manganese spinel.

Manganese measurement result Uncovered SP30 SP30 coated with Zr0 ₂ Room temperature, 15 days 5 ppm 3 ppm 80 ° C, 6 days 220 ppm 100 ppm 80 ℃, 13 days 460 ppm 140 ppm

In the case of uncoated spinels, the melting of manganese is very significant and increases with time. In the case of coated spinels, on the other hand, the melting of manganese is significantly reduced both in absolute value and also as a function of storage time. Significant improvements in high temperature shelf life by metal oxide coatings are very evident for the cathode materials.

Example 3

Circulation at high temperature

The coated cathode material powder prepared as described in Example 1, and the uncoated material SP30 selector® from Merck for comparison are circulated at 60 ° C.

To prepare the electrolyte, the cathode powder is mixed well with 15% conductive black and 5% PVDF (binder material). The paste prepared in this way is applied to an aluminum mesh acting as a collector and dried overnight at 175 ° C. under argon atmosphere and reduced pressure. The dried electrode is introduced through the lock into an argon-flushed glovebox and placed in the measuring cell. The counter electrode and reference electrode are lithium metal. The electrolyte used was LP 50 Selectif® (EC: EMC = 50 wt%: 50 wt% 1M LiPF ₆ ) from Merck. The measuring cell with electrodes and electrolyte is placed in a steel container and sealed to prevent gas leakage. The cells produced in this manner are withdrawn from the glovebox via locks and placed in an atmosphere-controlled cabinet set set at 60 ° C. After the measuring cell is connected to a constant potentiometer / regulator, the electrode is circulated (charged for 5 hours and discharged for 5 hours).

The result is that the circulation stability of the uncoated spinel is lower than that of the coated spinel.

In the first five cycles, irreversible reactions such as film formation at the cathode and anode occur, which means that they cannot be used for measurement. The loss of capacity per cycle of uncoated spinel is then 0.78 mAh / g and the ZrO ₂ -coated spinel is 0.45 mAh / g per cycle. This is substantially the loss of capacity per cycle is halved. This indicates that the high temperature cycling stability of the cathode powder is significantly improved by coating with oxide.

Claims (11)

Lithium mixed oxide particles, characterized in that they are coated with one or more metal oxides. The method of claim 1, Lithium mixed oxides selected from the group consisting of Li (MnMe _z ) ₂ O ₄ , Li (CoMe _z ) O ₂ , Li (Ni _1-xy Co _x Me _y ) O ₂ and other lithium intercalation and insertion compounds particle. The method according to claim 1 or 2, Metal oxide is selected from the group consisting of ZnO, CaO, SrO, SiO ₂ , CaTiO ₃ , MgAl ₂ O ₄ , ZrO ₂ , Al ₂ O ₃ , Ce ₂ O ₃ , Y ₂ O ₃ , SnO ₂ , TiO ₂ and MgO Lithium mixed oxide particles. The method according to any one of claims 1 to 3, Lithium mixed oxide particles having a layer thickness of metal oxide of 0.05 to 3 μm. Cathode consisting essentially of the lithium mixed oxide particles according to claim 1, and conventional support materials and auxiliaries. Suspending the particles in an organic solvent; Mixing the resulting suspension with a hydrolyzable metal compound solution and a hydrolysis solution; And And then filtering and drying the coated particles and optionally calcining the lithium mixed oxide particles coated with at least one metal oxide. The method of claim 6, Metal oxide is selected from the group consisting of ZnO, CaO, SrO, SiO ₂ , CaTiO ₃ , MgAl ₂ O ₄ , ZrO ₂ , Al ₂ O ₃ , Ce ₂ O ₃ , Y ₂ O ₃ , SnO ₂ , TiO ₂ and MgO A method of making lithium mixed oxide particles coated with one or more metal oxides. The method of claim 6, A process for preparing lithium mixed oxide particles coated with one or more metal oxides, wherein the hydrolysis solution is acid, base or water. Use of the coated lithium mixed oxide particles according to any one of claims 1 to 4 for producing cathodes having improved shelf life and circulation stability at temperatures above room temperature. Use of the coated lithium mixed oxide particles according to any one of claims 1 to 4 for the production of 4V cathodes. Use of the coated lithium mixed oxide particles according to any one of claims 1 to 4 in electrodes for electrochemical cells, batteries and secondary lithium batteries.