CN1350706A

CN1350706A - Lithium-mixed oxide particles coated with metal-oxides

Info

Publication number: CN1350706A
Application number: CN00807605A
Authority: CN
Inventors: R·奥斯顿; U·海德; A·库纳; N·罗兹; A·阿曼; M·尼曼
Original assignee: Merck Patent GmbH
Current assignee: Merck Patent GmbH
Priority date: 1999-05-15
Filing date: 2000-04-25
Publication date: 2002-05-22
Also published as: AU4751200A; RU2001132863A; KR20020013887A; WO2000070694A1; CA2373756A1; BR0010566A; JP2003500318A; DE19922522A1; EP1188196A1

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

Metal oxide coated lithium mixed oxide particles

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

Secondary lithium batteries are highly desirable and the demand will grow greatly in the future. This is because of the high achievable energy density and low weight of these batteries. These batteries are used in mobile phones, camcorders, laptops, etc.

It is known that the use of metallic lithium as anode material results in an insufficient number of cycles and a significant safety hazard (internal short circuit) for the cell due to dendrite formation upon dissolution and deposition of lithium (j. power Sources, 54(1995) 151).

The solution of these problems is achieved by replacing the lithium metal anode with other compounds capable of reversibly intercalating lithium ions. The functional principle of lithium ion batteries is based on the fact that cathode and anode materials are capable of reversibly intercalating lithium ions, i.e. lithium ions migrate from the cathode, diffuse through the electrolyte and then intercalate into the anode upon charging. Upon discharge, the same process is reversed. Because of this mode of operation, these batteries are also referred to as "rocking chair" batteries or lithium ion batteries.

The resulting voltage of such a cell is determined by the lithium intercalation potential of the electrodes. In order to obtain the highest available voltage, it is necessary to use a cathode material capable of intercalating lithium ions at a very high potential and an anode material capable of intercalating lithium ions at a very low potential (vs Li/Li)⁺). The cathode material satisfying these requirements is LiCoO having a layered structure₂And LiNiO₂And LiMn having a three-dimensional cubic structure₂O₄. These compounds are at about 4V (vs Li/Li)⁺) Deintercalate lithium ions at a potential of (3). In the case of anodic compounds, certain carbon compounds such as graphite meet the requirements of low potential and high capacity.

In the early 90 s of the 20 th century, Sony introduced into the market a lithium ion battery consisting of a lithium cobalt oxide cathode, a non-aqueous liquid electrolyte and a carbon anode (progr. batteries SolarCells, 9(1990) 20).

For the 4V anode, LiCoO has been discussed and used₂、LiNiO₂And LiMn₂O₄. The electrolyte used is a mixture containing an aprotic solvent in addition to the electrolyte salt. 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 full range of electrolyte salts has been discussed, LiPF is not used exceptionally in practice₆. The anode used is typically graphite.

One disadvantage of the prior art batteries is that the storage life and cycle characteristics at high temperatures are poor. The reason for this is that both the electrolyte and the cathode material used, in particular the lithium-manganese spinel LiMn₂O₄。

Lithium-manganese spinel is a very promising cathode material for portable batteries. Relative LiNiO₂-and LiCoO₂The advantages of-based cathodes are improved safety in the charged state, low toxicity and low raw material cost.

The lithium manganese spinel has disadvantages in that its capacity is low and its high-temperature storage life is not satisfactory and thus the cycle characteristics at high temperatures are not good. The reason for this is believed to be the solubility in electrolytes of divalent manganese (Solid State Ionics 69(1994) 59; J.Power Sources66(1997) 129; J.electrochem. Soc.144(1997) 2178). In spinel LiMn₂O₄Manganese is present in two oxidation states, trivalent and tetravalent. Containing LiPF₆Always contains some water contaminants. This water and conductive salt LiPF₆The reaction forms LiF and an acid component, such as HF. These acid components react with the trivalent manganese in the spinel to form Mn²⁺And Mn⁴⁺(disproportionation reaction: ). This degradation occurs even at room temperature, but is accelerated at high temperatures.

One way to increase the stability of spinel at high temperatures is to dope it. For example, certain manganese ions may be replaced with other, e.g., trivalent metal cations. Antonini et al describe gallium and chromium doped spinels (e.g., Li)_1.02Ga_0.025Cr_0.025Mn_1.95O₄) Has satisfactory shelf life and cycle characteristics at 55 ℃ (j. electrochem. soc.145(1998) 2726).

Researchers by Bellcore Inc subsequently proposed a similar protocol. They replace part of the manganese with aluminum and part of the oxygen ions with fluoride ions ((Li)_1+xAl_yMn_2-x-y)O_4-zF_z). This doping also improves the cycling characteristics at 55 ℃ (WO 9856057).

Another approach involves modifying the surface of the cathode material. Us patent 5695887 proposes a spinel cathode having a relatively low surface area and whose catalytic center is saturated by treatment with a chelating agent such as acetylacetone. This cathode material has a significantly lower self-discharge and an improved shelf life at 55 ℃. The cycling behavior at 55 ℃ is only slightly improved (Solid State Ionics104(1997) 13).

The cathode particles may also be coated, for example, with a layer of lithium borate glass (Solid State Ionics104(1997) 13). For this purpose, spinel is added to H₃BO₃、LiBO₂*8H₂O and LiOH H₂A solution of O in methanol, then stirred at 50-80 ℃ until the solvent is completely evaporated. The powder was then heated at 600-800 ℃ to complete conversion to borate. This improves the shelf life at high temperatures, but no improvement in cycle characteristics was found.

In WO98/02930, undoped spinels are treated with alkali metal hydroxide solutions. The treated spinel is then in CO₂Heating in an atmosphere to convert the adhered hydroxide into the corresponding carbonate. The spinel that has been so modified has improved high temperature storage life and improved cycle characteristics at high temperatures.

It has been described many times that coating the electrodes can improve various properties of lithium ion batteries.

For example, the cathode and/or anode are coated by applying the active material together with a binder and a conductive material as a paste onto a current collector. Subsequently, a paste consisting of coating material, binder and/or solvent is applied to the electrode. The coating material is an inorganic and/or organic material, which may be electrically conductive, such as Al₂O₃Nickel, graphite, LiF, PVDF, etc. Lithium ion batteries comprising such coated electrodes have high voltage and capacity as well as improved safety characteristics (EP 836238).

Us patent 5869208 also employs a very similar process. Here again, an electrode paste (cathode material: lithium-manganese spinel) is first produced and then applied to the current collector. A protective layer consisting of a metal oxide and a binder is subsequently applied as a paste to the electrode. The metal oxides used are, for example, aluminum oxide, titanium oxide and zirconium oxide.

In JP08236114, the electrodes are likewise used, above all, preferably LiNi_0.5Co_0.5O₂As active material and then the oxide layer is applied by sputtering, vacuum vapor deposition or CVD.

In JP09147916, the catalyst is made of solid oxide particles, e.g. MgO, CaO, SrO, ZrO₂、Al₂O₃Or SiO₂And a protective layer composed of a polymer is applied to the side of the current collector including the electrode. Thus, high voltage and high cycle characteristics can be realized.

Another approach was subsequently proposed in JP 09165984. The cathode material used was a lithium-manganese spinel coated with boron oxide. The coating is generated during the synthesis of the spinel. For this purpose, compounds of lithium, manganese and boron are calcined in an oxidizing atmosphere. The boron oxide-coated spinel obtained thereby does not dissolve manganese at high voltages.

However, as described for example in JP07296847, not only oxidized state materials but also polymers are used for the preparation of the coating to improve the safety properties. JP08250120 uses sulfides, selenides and tellurides in the coating to improve cycle performance, and JP08264183 uses fluorides in the coating to improve cycle life.

It is an object of the present invention to provide electrode materials having improved shelf life and cycling stability at high temperatures, in particular above room temperature, without the disadvantages of the prior art.

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

The present invention also provides a method of coating lithium mixed oxide particles and its use in electrochemical cells (cells), batteries (batteries), lithium secondary batteries.

The invention relates to undoped or doped mixed oxides selected from Li (MnMe) as cathode material_z)₂O₄、Li(CoMe_z)O₂And Li (Ni)_1-x-yCo_xMe_y)O₂Wherein Me is at least one metal cation from groups IIa, IIIa, IVa, IIb, IIIb, IVb, VIb, VIIb and VIII of the periodic Table of the elements. Particularly suitable metal cations are copper, silver, nickel, magnesium, zinc, aluminum, iron, cobalt, chromium, titanium and zirconium, and also lithium for spinel compounds. The invention likewise relates to other lithium intercalation and insertion compounds suitable for 4V cathodes, which have improved high-temperature properties, in particular above room temperature, to a process for their production and to their use, in particular as cathode materials in electrochemical cells.

In the present invention, the lithium mixed oxide particles are coated with a metal oxide to obtain improved high temperature (above room temperature) storage life and cycle stability.

Suitable coating materials are various metal oxides, in particular oxides or mixed oxides selected from the group consisting of Zr, Al, Zn, Y, Ce, Sn, Ca, Si, Sr, Mg and Ti, and mixtures thereof, for example ZnO, CaO, SrO, SiO₂、CaTiO₃、MgAl₂O₄、ZrO₂、Al₂O₃、Ce₂O₃、Y₂O₃、SnO₂、TiO₂And MgO.

It has been found that coating the metal oxide can greatly inhibit the undesirable reaction of the electrolyte with the electrode material.

It has surprisingly been found that the high temperature cycling stability of cathodes obtained therefrom can be significantly improved by coating the lithium mixed oxide particles. This essentially halves the capacity loss per cycle for the coated cathode material compared to the uncoated cathode material.

Furthermore, it has been found that there is an improved shelf life above room temperature. The manganese dissolution of the metal oxide coated spinel is significantly reduced.

Furthermore, it has been found that coating individual particles has many advantages over coating electrode strips. If the electrode material is damaged in the case of coated strips, the electrolyte can attack most of the active material, but if it is a coated individual particle, these undesirable reactions can be very localized.

The coating process can achieve coating thicknesses of 0.03 microns to 5 microns. The preferred thickness is between 0.05 microns and 3 microns. The lithium mixed oxide particles may be coated with one or more layers.

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

Furthermore, the coating process can be performed by the supplier, so that the battery manufacturer does not have to make the necessary process changes for the coating step.

Improved safety may also be desirable due to the coating of the material.

Coating the cathode material with an inorganic material greatly suppresses the undesired reaction of the electrode material with the electrolyte, and thus, improves the storage life and cycle stability at high temperatures.

The cathode material of the present invention can be used for a lithium ion secondary battery using a conventional electrolyte. Suitable electrolytes are, for example, those comprising a compound selected from LiPF₆、LiBF₄、LiClO₄、LiAsF₆、LiCF₃SO₃、LiN(CF₃SO₂)₂Or LiC (CF)₃SO₂)₃And conductive salts of mixtures thereof. The electrolyte may also contain organic isocyanates (DE19944603) to reduce the water content. Likewise, the electrolyte may comprise organic alkali metal salts (DE19910968) as additives. Suitable alkali metal salts are alkali metal borates having the general formula:

Li⁺B^-(OR¹)_m(OR²)_p

wherein

m and p are 0, 1, 2, 3 or 4 and m + p is 4, and R is¹And R²The same or different, and the same or different,

if desired, directly bonded to one another by single or double bonds,

in each case, individually or collectively, are aromatic or aliphatic carboxylic, dicarboxylic or sulfonic acid groups, or

In each case, individually or collectively, an aromatic ring selected from phenyl, naphthyl, anthryl or phenanthryl, which may be unsubstituted or mono-to tetrasubstituted by A or halogen, or

In each case, individually or together, a heteroaromatic ring selected from pyridyl, pyrazolyl or bipyridyl which may be unsubstituted or mono-to trisubstituted by A or halogen, or

In each case, individually or collectively, an aromatic hydroxy acid, selected from aromatic hydroxycarboxylic acids or aromatic hydroxysulfonic acids, which may be unsubstituted or mono-to tetrasubstituted by A or halogen,

and is

Halogen being F, Cl or Br

And A is an alkyl group having 1 to 6 carbon atoms, which may be mono-halogenated to tri-halogenated. Other suitable alkali metal salts are alkali metal alkoxides having the general formula:

Li⁺OR^-

wherein R is

Is an aromatic or aliphatic carboxylic, dicarboxylic or sulfonic acid group, or

Is an aromatic ring selected from phenyl, naphthyl, anthryl or phenanthryl, which may be unsubstituted or mono-to tetrasubstituted by A or halogen, or

Is a heteroaromatic ring selected from pyridyl, pyrazolyl or bipyridyl, which may be unsubstituted or mono-to trisubstituted by A or halogen, or

Is an aromatic hydroxy acid, selected from aromatic hydroxycarboxylic acids or aromatic hydroxysulfonic acids, which may be unsubstituted or mono-to tetrasubstituted by A or halogen,

and is

The halogen is F, Cl or Br,

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

Lithium complex salts having the following structural formula may also be present in the electrolyte:

wherein

R¹And R²Identical or different, if desired directly bonded to one another by single or double bonds, and in each case, individually or jointly, are aromatic rings, selected from the group consisting of phenyl, naphthyl, anthryl or phenanthryl, which may be unsubstituted or substituted by alkyl (C)₁-C₆) Alkoxy (C)₁-C₆) Or mono-to hexa-substitution of halogen (F, Cl or Br),

or in each case, individually or together, are an aromatic heterocycle from the group consisting of pyridyl, pyrazolyl or pyrimidinyl, which may be unsubstituted or substituted by alkyl (C)₁-C₆) Alkoxy (C)₁-C₆) Or mono-to tetrasubstituted with halogen (F, Cl or Br),

or in each case, individually or together, are aromatic rings selected from the group consisting of hydroxybenzenecarboxy, hydroxynaphthalenecarboxyl, hydroxybenzenesulfonyl and hydroxynaphthalenesulfonyl, which may be unsubstituted or substituted by alkyl (C)₁-C₆) Alkoxy (C)₁-C₆) Or mono-to tetrasubstituted with halogen (F, Cl or Br),

and R is³-R⁶In each case, independently or in pairs, if desired directly bonded to one another by single or double bonds, have the following meanings:

1. alkyl radical (C)₁-C₆) Alkoxy (C)₁-C₆) Or a halogen (F, Cl or Br),

2. an aromatic ring selected from:

phenyl, naphthyl, anthryl or phenanthryl, which may be unsubstituted or substituted by alkyl (C)₁-C₆) Alkoxy (C)₁-C₆) Or mono-to hexa-substitution of halogen (F, Cl or Br),

pyridyl, pyrazolyl or pyrimidinyl, which may be unsubstituted or substituted by alkyl (C)₁-C₆) Alkoxy (C)₁-C₆) Or mono-to tetrasubstituted with halogen (F, Cl or Br),

can be prepared by the following method (DE 19932317):

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

b) reacting the intermediate from a) with chlorotrimethylsilane, filtering and fractionating,

c) reacting the intermediate from b) with lithium tetramethoxyborate (1-) in a suitable solvent and isolating the final product therefrom.

The electrolyte may also comprise compounds having the following formula (DE 19941566):

[([R¹(CR²R³)_k]_lA_x)_yKt]⁺ ^-N(CF₃)₂

wherein

Kt ═ N, P, As, Sb, S, or Se

A＝N、P、P(O)、O、S、S(O)、SO₂As, As (O), Sb (O) or Sb (O)

R¹、R²And R³

The same or different, and are respectively:

H. halogen, substituted and/or unsubstituted alkyl C_nH_2n+1Substituted and/or unsubstituted alkenyl having 1 to 18 carbon atoms and one or more double bonds, substituted and/or unsubstituted alkynyl having 1 to 18 carbon atoms and one or more triple bonds, substituted and/or unsubstituted cycloalkyl C_mH_2m-1One or more substituted and/or unsubstituted phenyl groups, substituted and/or unsubstituted heteroaryl groups,

a may be included in R¹、R²And/or R³In a variety of positions in the (c),

kt may be included in a ring or a heterocycle,

the groups bonded to Kt may be the same or different,

wherein

n＝1-18，

m＝3-7，

k is 0 or 1 to 6,

1 ═ 1 or 2 (when x ═ 1) and 1 (when x ═ 0)

x is 0 or 1, and x is a linear or cyclic,

y＝1-4。

the process for preparing these compounds is characterized in that alkali metal salts having the following general formula:

D⁺ ^-N(CF₃)₂ (II)

wherein D⁺Selected from alkali metals, in a polar solvent with a salt having the general formula:

[([R¹)CR²R³)_k]_lA_x)_yKt]⁺ ^-E (III)

wherein

Kt、A、R¹、R²、R³K, l, x and y are as defined above, and

^-e is F^-、Cl^-、Br^-、I^-、BF₄ ^-、ClO₄ ^-、AsF₆ ^-、SbF₆ ^-Or PF₆ ^-。

Furthermore, electrolytes comprising compounds of the formula (DE19953638) can also be used:

X-(CYZ)_m-SO₂N(CR¹R²R³)₂

wherein

X is H, F, Cl, C_nF_2n+1、C_nF_2n-1、(SO₂)_kN(CR¹R²R³)₂，

Y is H, F or Cl,

z is H, F or Cl,

R¹、R²、R³is H and/or alkyl, fluoroalkyl, cycloalkyl,

m is 0 to 9, and if X ═ H, m does not equal 0,

n is a number of 1 to 9,

k is 0 (if m is equal to 0) and k is 1 (if m is equal to 1-9),

prepared by reaction of partially or perfluorinated alkylsulfonyl fluorides with dimethylamine in an organic solvent, and complex salts having the general formula (DE 19951804):

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

wherein

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

M^x+is a metal ion, and is a metal ion,

e is a Lewis acid selected from: BR (BR)¹R²R³、AlR¹R²R³、PR¹R²R³R⁴R⁵、AsR¹R²R³R⁴R⁵、VR¹R²R³R⁴R⁵，

R¹-R⁵Identical or different, if desired directly bonded to one another by single or double bonds, in each case individually or together have the following meanings:

a halogen (F, Cl or Br),

alkyl or alkoxy (C) which may be partially or fully substituted by F, Cl or Br₁-C₈)，

The aromatic rings, if desired bonded via an oxygen atom, selected from phenyl, naphthyl, anthryl and phenanthryl, may be unsubstituted or substituted by alkyl (C)₁-C₈) Or F, Cl or Br from mono-to hexa-substitution,

the aromatic heterocyclic ring, if desired bonded via an oxygen atom, selected from pyridyl, pyrazolyl or pyrimidinyl, may be unsubstituted or substituted by alkyl (C)₁-C₈) Or F, Cl or Br from mono-to tetrasubstituted, and

z is OR⁶、NR⁶R⁷、CR⁶R⁷R⁸、OSO₂R⁶、N(SO₂R⁶)(SO₂R⁷)、C(SO₂R⁶)(SO₂R⁷)(SO₂R⁸) Or OCOR⁶Wherein

R⁶-R⁸Identical or different, if desired directly bonded to one another by single or double bonds, and in each case individually or collectively:

hydrogen atom or according to the formula to R¹-R⁵In the definition of (a) is,

by reacting the appropriate boron or phosphorus Lewis acid/solvent adduct with an imide, methide or triflate of lithium or tetraalkylammonium.

Borates of the general formula (DE19959722) may also be present:

wherein:

m is a metal ion or a tetraalkylammonium ion,

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

R¹-R⁴are identical or different alkoxy or carboxyl (C)₁-C₈) They may be directly bonded to each other through a single bond or a double bond as required. These borates are prepared by reacting a 1: 1 mixture of lithium tetraalkoxyborate or lithium alkoxide and borate with the appropriate hydroxy or carboxy compound in a 2: 1 or 4: 1 ratio in an aprotic solvent.

One general example of the present invention is described below.

Process for coating cathode material

4V cathode material, especially material having a layered structure (e.g., Li (CoMe))_z)O₂Or Li (Ni)_1-x-yCo_xMe_y)O₂) And spinel (Li (MnMe)_z)₂O₄) Suspended in a polar organic solvent, such as an alcohol, aldehyde, halide or ketone, and the spinel may also be suspended in water and then introduced into the reaction vessel. These materials may also be suspended in non-polar organic solvents such as cycloalkanes or aromatics. The reaction vessel is heatable and equipped with a stirrer. The reaction solution is warmed to 10-100 ℃ depending on the boiling point of the solvent.

Suitable coating solutions are soluble metal salts soluble in organic solvents or water selected from the group consisting of the salts of Zr, Al, Zn, Y, Ce, Sn, Ca, Si, Sr, Ti and Mg and mixtures thereof. Suitable hydrolysis solutions are acids, bases or water corresponding to the solvents used in the coating solution.

The coating solution and the hydrolysis solution are slowly metered in. The amount and rate of metering depends on the desired coating thickness and the metal salt used. To ensure quantitative progress of the hydrolysis reaction, the hydrolysis solution is added in excess.

After the reaction was completed, the solution was filtered, and the resulting powder was dried. To ensure complete conversion to the metal oxide, the dry powder must be calcined. The resulting powder is heated to 400 ℃ and 1000 ℃, preferably 700 ℃ and 850 ℃, and then held at that temperature for 10 minutes to 5 hours, preferably 20 to 60 minutes.

The particles may have one or more coatings. If desired, the first coating may be one metal oxide and the subsequent coatings may be other metal oxides.

The following examples are intended to illustrate the invention without limiting it in any way.

Examples

Example 1

Process for coating cathode material with ZrO2

100 g of lithium-manganese spinel (SP 30 Selectipur. ex Merck) and 500 ml of ethanol as solvent were introduced into a 2 l flask. The flask was immersed in a water bath and equipped with a stirrer. The water bath was heated to 40 ℃.

The coating solution used was tetrapropyl ortho zirconate (26.58g) dissolved in ethanol (521.8 ml). The hydrolysis solution used was water (14.66 g). The two solutions are slowly metered in. The addition of zirconium propylate was complete after about 6.5 hours. To ensure that the hydrolysis reaction also proceeded quantitatively, an additional 16.2 hours of water (36.4g) was added for post hydrolysis.

After completion of the reaction, the ethanol-containing solution was filtered, and the resulting product was dried at about 100 ℃. To ensure complete conversion to ZrO₂The dried powder must be calcined. Thus, after drying, the powder was heated to 800 ℃ and held at this temperature for 30 minutes.

Example 2

High temperature storage test

Commercially available spinel cathode powders SP30 and SP35 (Selectipur @fromMerck) were made. The sample, untreated SP30 and ZrO₂Coated SP30 in each caseIn case of 1 liter aluminum bottles (about 3 g samples) and 30 ml of electrolyte (LP 600 Selectipur from Merck, EC: DEC: PC 2: 1: 31M LiPF₆). The aluminum bottle was then sealed in an airtight manner. These preparations were all carried out in an argon flushed glove box. The bottles prepared in this way were then removed from the glove box via a locking device and placed in a drying chamber at 80 ℃ for 6 or 13 days. At the end of the storage test, the aluminum bottles were cooled to room temperature and introduced into the glove box again via the locking device and opened there. The electrolyte was filtered off and the amount of manganese dissolved in the electrolyte was determined quantitatively by ICP-OES.Table 1 compares the results of the analysis of the uncoated and coated lithium manganese spinels.

	Uncoated SP30	ZrO₂Coated SP30
	Uncoated SP30	ZrO₂Coated SP30	Room temperature, 15 days	5ppm	3ppm
80 ℃ for 6 days	220ppm	100ppm	Room temperature, 15 days	5ppm	3ppm
80 ℃ for 6 days	220ppm	100ppm	80 ℃ for 13 days	460ppm	140ppm

Table 1: results of manganese determination

The manganese dissolution of the uncoated spinel is considerable and increases further with time. In contrast, the manganese dissolution of the coated spinel decreased significantly, both in absolute value and in the amount of change over storage time. It is apparent that for these cathode materials, the high temperature storage life is greatly improved due to the coating of the metal oxide.

Example 3

High temperature cycle

The coated cathode powder prepared as in example 1 and the uncoated material as a comparison (SP 30 Selectipur from Merck) were cycled at 60 ℃.

To prepare the electrode, the cathode powder was thoroughly mixed with 15% conductive black and 5% PVDF (binder). The paste thus prepared was coated on an aluminum mesh serving as a current collector and dried overnight at 175 ℃ under reduced pressure under an argon atmosphere. The dried electrode was introduced via a lock into an argon flushed glove box and installed in the test cell. The counter and reference electrodes are lithium metal. The electrolyte used was LP50 Selectipur from Merck (1 MLiPF6 in EC: EMC 50: 50 wt%). The test cell with the electrodes and electrolyte was placed in a steel container and sealed in a gas tight manner. The battery obtained in this way was taken out of the glove box via a locking device and placed in an atmosphere-controlled chamber set at 60 ℃. The cell was connected to a constant voltage/galvanostat and the cell was cycled (5 hours for charge and 5 hours for discharge).

The results show that the cycling stability of the uncoated spinel is lower than that of the coated spinel.

In the first 5 cycles, irreversible reactions occurred, e.g., films formed on the cathode and anode, indicating that they could not be used for calculations. The capacity loss per cycle of the uncoated spinel was 0.78mAh/g, while ZrO₂The coated spinel has only 0.45mAh @g loss per cycle. This is achieved byEssentially reducing the capacity loss per cycle by half. This demonstrates a significant improvement in the high temperature cycle stability of the cathode material by coating with the oxide.

Claims

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

2. Lithium mixed oxide particles according to claim 1, characterised in that the particles are selected from Li (MnMe)_z)₂O₄、Li(CoMe_z)O₂And Li (Ni)_1-x-yCo_xMe_y)O₂And other lithium intercalation and insertion compounds.

3. Lithium mixed oxide particles according to claim 1 or 2, characterised in that the metal oxide is selected from the group consisting of ZnO, CaO, SrO, SiO₂、CaTiO₃、MgAl₂O₄、ZrO₂、Al₂O₃、Ce₂O₃、Y₂O₃、SnO₂、TiO₂And MgO.

4. Lithium mixed oxide particles according to any one of claims 1 to 3, characterised in that the layer thickness of the metal oxide is 0.05 to 3 micrometres.

5. Cathode consisting essentially of lithium mixed oxide particles according to any one of claims 1 to 4 and conventional support materials and auxiliary materials.

6. A method for producing 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 hydrolysable metal compound and a hydrolysis solution, and then the coated particles are filtered off, dried and optionally calcined.

7. Process for producing lithium mixed oxide particles coated with one or more metal oxides according to claim 6, characterized in that the metal oxides are selected from ZnO, CaO, SrO, SiO₂、CaTiO₃、MgAl₂O₄、ZrO₂、Al₂O₃、Ce₂O₃、Y₂O₃、SnO₂、TiO₂And MgO.

8. The method according to claim 6 for producing lithium mixed oxide particles coated with one or more metal oxides, characterized in that the hydrolysis solution is an acid, a base or water.

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

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

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