WO2006027925A2

WO2006027925A2 - Positive electrode material for non-aqueous electrolyte lithium-ion secondary battery and method for production thereof

Info

Publication number: WO2006027925A2
Application number: PCT/JP2005/014613
Authority: WO
Inventors: Takanori Ito
Original assignee: Nissan Motor Co., Ltd.
Priority date: 2004-09-06
Filing date: 2005-08-03
Publication date: 2006-03-16
Also published as: JP2006073482A; WO2006027925A3; JP4923397B2

Abstract

A positive electrode material for use in a non-aqueous electrolyte lithium-ion secondary battery is configured by attaching a lithium compound to the surfaces of particles of a lithium nickel cobalt manganese oxide. This configuration results in imparting exalted durability to the non-aqueous electrolyte lithium-ion secondary battery.

Description

DESCRIPTION

POSITIVE ELECTRODE MATERIAL FOR

NON-AQUEOUS ELECTROLYTE LITHIUM-ION SECONDARY BATTERY AND METHOD FOR PRODUCTION THEREOF

Technical Field

This invention relates to a positive electrode material for a non-aqueous electrolyte lithium-ion secondary battery. ^" More particularly, this inventionrelates toimprovements inandconcerning a positive electrode material for a non-aqueous electrolyte lithium- ion secondary battery using a lithium nickel cobalt manganese oxide as a positive electrode active material. Background Art In recent years, the diminution of the carbon dioxide content of the atmosphere has been inciting infinite yearning with a view to coping with the air pollution and the global warming. In the automobile industry, the introduction of electric vehicles (EV) and hybrid electric vehicles (HEV) is expected to result in diminishing the amount of carbon dioxide to be discharged and the development of a motor driving grade secondary battery as the key to the service application of these vehicles has been promoted enthusiastically.

As a motor driving grade secondary battery, the lithium-ion secondary battery which possesses the highest theoretical energy in all the known batteries has been arresting attention and has been undergoing a rapid development now. The lithium-ion secondary battery is generally configuredby causinga positive electrode having a positive electrode active material applied with a binder to the opposite faces ofapositiveelectrode current collectorandanegative electrode having a negative electrode active material applied with abindertotheopposite faces ofanegativeelectrode current collector to be connected through the medium of an electrolytic material and containing the connected electrodes in a battery case.

As the positive electrode active material for the lithium-ion secondary battery, the lithium nickel cobalt manganese oxide (Li (Ni, Co, Mn ) O₂) hasbeenattractingattentioninrecentyears. This lithium nickel cobalt manganese oxide is at an advantage in producing a high output as compared with such conventional positive electrode active materials as lithium manganese oxide and lithium cobalt oxide and remaining stable even in an electrolyte at an elevated temperature.

When this lithium nickel cobalt manganese oxide is used as a positive electrode activematerial and is subjectedto repeated cycles of charge/discharge at a high output under the conditions using an elevated temperature, however, this service entails the problem that the output of the battery and the cycle durability thereof at the elevatedtemperature are finallydegraded. This problemis prominent particularly in the on-vehicle lithium-ion secondary battery which is mounted as a motor driving grade power source on a vehicle and is expected to supply electric power at a high output for a long time. The lithium manganese oxide (LiMn₂O₄) which is similarly a manganese-containing positive electrode material is also known to entail theproblemofdissolvingofmanganese ion intothe electrolyte. With the object of solving this problem encountered by the lithium manganese oxide, a method of forming a layer of lithium vanadium oxide (LiV₂O₄) on the surface of a positive electrode material formed of lithium manganese oxide thereby preventing the manganese ion from being dissolved into the electrolyte and repressing the degradation of the performance of the battery has been proposed (official gazette of JP-A 2000-3709) . Disclosure of the Invention

The positive electrode active material which is disclosed in the patent document mentioned above is, however, lithium manganese oxide possessed of a spinel structure. In the first place, the lithium-ionsecondarybatteryusingthis spineltype lithiummanganese oxide is deficient in capacity and cycle durability. Particularly when it is mounted on a vehicle as the power source for driving the motor of the vehicle which is required tomanifest a stable performance for a long time, it has the possibility of failing to manifest a fully satisfactory battery service.

This invention, therefore, is aimed at providing a positive electrode material which can be used perfectly advantageously in a non-aqueous electrolyte lithium-ion secondary battery capable of supplying electric power stably at a high output for a long time. This invention provides a positive electrode material for a non-aqueous electrolyte lithium-ion secondary battery, produced by attaching a lithium compound (hereinafter referred to occasionally as "Li compound") to the surfaces of particles formed of lithiumnickel cobalt manganese oxide (hereinafter referred to occasionally as "LiNiCoMn oxide") . This invention also provides a method for the production of the positive electrode material mentioned above.

The other objects, characteristics, and advantages of this inventionwill be clarifiedbytaking into consideration the following explanation and the preferred modes of embodiment illustrated in the drawings attached hereto.

Brief Description of the Drawings

Fig. lisa commentarydiagramforexplainingtheabsolutemaximum length to be used in determining diameters of particles.

Fig. 2 is a schematic cross-sectional diagram of the positive electrode material of this invention which is configured by forming a coating layer made of a Li compound on the surfaces of particles formed of LiNiCoMn oxide.

Fig. 3 is a schematic perspective-view diagram of the positive electrode material of this invention which is configured by causing particles formed of a Li compound to be attached in an interspersed pattern to the surfaces of particles formed of LiNiCoMn oxide.

Fig. 4 is schematic cross-sectional diagram of a lithium-ion secondary battery which is not a bipolar type (ordinary lithium-ion battery) . Fig. 5 is a schematic cross-sectional diagram of a bipolar lithium-ion secondary battery. Detailed Description of the Embodiment

The first aspect of this invention is a positive electrode material for a non-aqueous electrolyte lithium-ion secondary battery which is characterized by having a lithium compound attached to the surfaces of particles formed of LiNiCoMn oxide which functions as a positive electrode active material. In the positive electrode material ofthis invention, it ismadepossibletoprevent themanganese ion in the positive electrode active material from being dissolved into the electrolyte and repress the increase of the internal resistance and the decrease of the battery performance in consequence of the dissolving of manganese ion, by having the Li compound attached to the surfaces of the particles of the positive electrode active material. As one cause for this good outcome, the fact that the attachment of the Li compound enables the Li compound to function as a physical barrier and consequently repress the dissolving of manganese ionmaybe cited. Of course, the presence of othermechanism in the phenomenon is permissible.

Now, the mode of embodying this invention will be described in detail below. The scope of this invention ought to be fixed on the basis of the description of the scope of claim for patent and is not restricted exclusively to the following concrete mode of embodiment.

The LiNiCoMn oxide functions as a positive electrode active material. Thus, it does not need to have the form thereof such as, for example, the concrete composition particularly restricted but is only required to be such an oxide as contains lithium atom, nickel atom, cobalt atom, and manganese atom and possesses the ability to function as apositive electrode activematerial. The atomsmentioned above may be substituted by other metal atoms. For example, the composition represented by the following chemical formula (1) may be cited.

Li_aNi_bCo_cMn_dM_eO_fN_g (1) wherein, the relations 0 < a ≤ 1.2, 0.3 ≤ b ≤ 0.9, 0.25 ≤ c ≤ 0.6, 0.25 ≤ d ≤0.6, 0 ≤ e ≤ 0.3, 1.5 ≤ f ≤ 2.2, and 0 ≤ g ≤ 0.5 are satisfied, M denotes one or more atoms selected from the group consisting of Al, Mg, Ca, Ti, V, Cr, Fe, and Ga, N denotes one or more atoms selected from the group consisting of F, Cl, and S and, where M and/or N denotes two or more atoms, e and/or g denotes the total of the two or more atoms. The composition of the LiNiCoMn oxide can be determined, for example, by ICP (inductively coupled plasma) emission spectral analysis, atomic absorption spectrometry, fluorescence X-ray analysis, chelate titration, particle analysis, and the like. The other analysis may be adopted on the condition that it is capable of accurately determining the composition. This rule holds good for the determination of such other parameters as will be described herein below.

The average diameter of the particles formed of the LiNiCoMn oxide is preferably in the range of 0.1 - 20 μm from the viewpoint of the reactivity as a positive electrode active material and the cycle durability. The particles mentioned above may be secondary particles which result from subjecting primaryparticles to cohesion. In such embodiment, the average diameter of the primary particles which form the secondary particles is preferably in the range of 0.01 - 5 μm. These average diameters of the particles can be determined, for example, by visually observing given samples through the medium of a scanning electron microscope (SEM) , a transmission electron microscope (TEM), and the like.

The particles made of the LiNiCoMn oxide do not need to be shaped exclusively in a spherical form but may be shaped in any of such forms as plates, needles, columns, and angular pillars. The form of the particles can be properly selected in consideration of the battery properties tobewished for (suchas, forexample, the charge/discharge property and the cycle durability) . When the particles are in any form other than the spherical form, the "absolute maximum length" of the particles is regarded as the average particle diameter because they are not uniform in form. The term "absolute maximum length" as used herein means the largest distance (L in Fig.l) in all the distances between any two points on the borderline of a particle 1 as illustrated in Fig.1. In the determination of the absolutemaximum length, it is commendable to use the mean value of the absolute maximum lengths of individual particles which fall within a prescribed region of an electron micrograph. Otherwise, when the LiNiCoMn oxide to be used in this invention is selected by sifting, the mesh size of the screen used for the sifting (mesh through size or mesh pass size) may be used as the absolute maximum length.

The average valence number of the manganese atoms which exist in the neighborhood of the surfaces of the particles formed of the LiNiCoMn oxide which is the positive electrode active material of the positive electrode material of this invention is preferably not less than +3.5 and more preferably not less than +4. Here, it is known that when the manganese atoms have a valence number of +3, they are readily dissolved as manganese ions into the electrolyte. It is considered that when the manganese atoms in the neighborhood of the surfaces are made to assume an average valence number of not less than +3.5, the amount of manganese atoms having a valence number of not less than +4 will be sufficiently increased and the dissolving of the manganese ions in the positive electrode active material into the electrolyte will be repressed further. Incidentally, the reason for setting the limitation to the neighborhood of the surfaces is that when all the particles of the active material are given an average valence number of not less than +3.5, they possibly entail a decrease in capacity.

Then, the term "neighborhood of the surfaces" of the particles formed of the LiNiCoMn oxide means the region to the depth of 1/20 of the diameter of the particles from the surfaces of the particles. When the particles formed of the LiNiCoMn oxide have a diameter of 2 μm, for example, the term "neighborhood of the surfaces" of these particles refers to the region to a depth of 100 nm from the surfaces of the particles. The valence number of the manganese atoms which exist in the neighborhood of the surfaces of the particles formed of the LiNiCoMn oxide can be determined, for example, by electron energy loss spectroscopy (EELS) .

Theparticles which are formedof the LiNiCoMnoxide arepreferred to contain an oxygen excess LiNiCoMn oxide in the neighborhood of the surfaces thereof. This inclusion results in increasing the average valence number of the manganese atoms in the neighborhood of the surfaces of the particles of the active material and enabling the particles to acquire more readily an average valence number of not less than+3.5 describedabove. Evenbythis embodiment, therefore, it is made possible to attain further repression of the dissolving of the manganese ions in the positive electrode active material into the electrolyte. Incidentally, the definition of the term "neighborhood of the surfaces" is the same as given above. The term "oxygen excess LiNiCoMn oxide" refers to of a non-stoichiometric compound of the LiNiCoMn oxide which belongs to the oxygen excess type (metal depletion type) . The oxygen excess LiNiCoMn oxide, unlike the ordinaryLiNiCoMn oxide, reveals depletion of metal atoms and excess presence of oxygen atoms in the crystal lattice. It is also possessed of holes (plus holes) for maintaining electrical neutrality. The amount ofthe oxygenexcess LiNiCoMnoxide to exist in the neighborhood of the surfaces of the particles does not need to be particularly restricted but is only required to allow thepresenceofanoxygenexcess siteat leastpartlyintheneighborhood of the surfaces of the particles. For the purpose of enabling the aforementionedeffecttobemanifestedmore fully, however, preferably not less than one half and more preferably the whole of the LiNiCoMn oxide in the neighborhood of the surfaces of the particles is required to be an oxygen excess LiNiCoMn oxide. The Li compound to be attached to the surfaces of the particles formedoftheLiNiCoMnoxidedoesnotneedtobeparticularlyrestricted but maybe any of the heretofore known Li compounds . It is permissible to use a newly developed Li compound. As concrete examples of the Li compound, Li₂SO₄, Li₃PO₄, LiPON, Li₂O-B₂O₃, Li₂O-B₂O₃-LiI, Li₂O-SiS₂, Li₂S-SiS₂-Li₃PO₄, LiCoO₂, LiMn₂O₄, LiOH, Li₂CO₃, Li₂S-SiS₂, LiFePO₄, LiBr, LiI, lithium acetate, lithium acetylide ethylene diamine, lithium benzoate, lithium fluoride, lithium oxalate, lithium pyruvate, lithium stearate, and lithium tartrate may be cited. Among other Li compounds enumerated above, Li₂SO₄, Li₃PO₄, LiPON, Li₂O-B₂O₃, Li₂O-B₂O₃-LiI, Li₂O-SiS₂, Li₂S-SiS₂-Li₃PO₄, LiCoO₂, LiMn₂O₄, LiOH, and Li₂CO₃ can be advantageously used from the viewpoint of the diffusion constant of lithium ions. These Li compoundsmaybe used either singly or in the form of a combination of two ormore members. It is provided, however, that these Li compounds do not need to be regarded exclusively acceptable and that other Li compounds may be considered usable as a matter of course.

The compositionoftheLi compoundcanbedetermined, forexample, byICP (inductivelycoupledplasma) emissionspectralanalysis, atomic absorption spectrometry, fluorescence X-ray analysis, chelate titration, particle analysis, and the like.

The form of the Li compound does not need to be particularly restricted and the form described above with respect to the LiNiCoMn oxide may be adopted similarly. Though the average particle diameter of the Li compound does not need to be particularly restricted, it is preferably in the range of 20 - 500 nm and more preferably in the range of 50 - 400 nm from the viewpoint of the diffusing property of lithium ions.

The valence number of manganese ions in the neighborhood of the surfaces of the particles of the active material is preferred to be not less than +3.5 as described above. From this point of view, the Li compound to be attached is preferred to be a compound which is capable of exalting the valence number of manganese ions in the neighborhood of the surfaces of the particles of the active substance. The Li compounds enumerated above are invariably such that their attachment to the particles of the active material results in exalting thevalencenumber ofmanganese ions intheneighborhoodofthe surfaces of the particles of the active material.

TheLi compoundis preferredtohavetheabilitytoconduct lithium ions. The reason for this preference of conductivity is that when a Li compound having no ability to conduct lithium ions is attached, the portion of this attachment entails an increase of the internal resistance of the positive electrode material because of the absence of conduction of lithium ions and inevitably suffers the battery performance to degrade. The Li compounds enumerated above are invariably possessed of the ability to conduct lithium ions.

When the Li compound is possessed of the conductivity of lithium ions, the conductivity is preferably not less than 10^~15 S/m and more preferably not less than 10^~12 S/m. The lithium ion conductivity can be determined, for example, by alternating current impedance method, constant-potential step method, constant current step method, and the like.

The specific formof having a Li compound attached to the surfaces of the particles made of the LiNiCoMn oxide does not need to be particularly restricted. The form illustrated in Fig.2 may be cited for example. Fig. 2 is a schematic cross-sectional diagram of a positive electrode material of this invention which is configured by having a coating layer 3 made of a Li compound formed on the surface of a particle 2 made of a LiNiCoMn oxide. The form illustrated in Fig. 3 may be also cited for example. Fig. 3 is a schematic perspective-view diagram of a positive electrode material of this invention configured by having particles 4 made of a Li compound attached as interspersed to the surface of a particle 2 made of a LiNiCoMn oxide. The "surface" of the particle 2 made of the LiNiCoMn oxide and adapted to allow the attachment of the Li compound may be the surface of a primaryparticle or the surface of a secondaryparticle resulting from the cohesion of primaryparticles. When the particles 2 made of the LiNiCoMn oxide and illustrated in Fig. 2 and Fig. 3 are assumed to be secondary particles, Fig. 2 and Fig. 3 are drawings each depicting the form of having a Li compound attached to the surface of a secondary particle. The forms illustrated in Fig. 2 and Fig. 3 mentioned above are capable of preventing manganese ions from dissolving in the electrolyte and repressing the rise of the internal resistance of the positive electrode material, no matter which of the two kinds of particles may be adopted. The choice between these two kinds, therefore, may be properly made by taking into consideration the compositions of the LiNiCoMo oxide and the Li compound to be used, the battery performance to be requested, and the means of production tobeprocured. Whenthedissolvingofmanganese ions fromthepositive electrode active material must be effectively prevented, the configuration obtained by forming the coating layer 3 as illustrated in Fig. 2 may be favorably adopted. When the lithium ions must be made to reactwiththe electrolytebydirect contact, the configuration having the particles 4 of a Li compound interspersed as illustrated in Fig. 3 may be favorably adopted.

Now, the preferred examples of the forms illustrated in Fig. 2 and Fig. 3 will be explained below.

First, the form illustrated in Fig.2 will be described in detail below. In the form illustrated in Fig. 2, the coating layer 3 made of a Li compound is formed by attaching the Li compound to the surface of the particle 2 made of a LiNiCoMn oxide as described above.

The thickness of this coating layer 3 is preferably in the range of 3 - 1000 nm, more preferably in the range of 5 - 1000 nm, and still more preferably in the range of 5 - 700 nm. If the thickness of the coating layer 3 falls short of 3 nm, the shortage will possibly result in preventing the dissolving of manganese ions fromthe LiNiCoMn oxide which is a positive electrode active material from being repressed fully satisfactorily. Conversely, if the thickness of the coating layer exceeds 1000 nm, the overage will possibly result in increasing the internal resistance of the positive electrode material and decreasingthe batteryperformance evenwhen the Li compoundpossesses the ability to conduct lithium ions. The thickness of the coating layer 3 canbe determinedbyvisuallyobserving the electronmicrograph of the cross section of the positive electrode material. Subsequently, the form illustrated in Fig. 3 will be described in detail below. In the form illustrated in Fig. 3, particles 3 made of a Li compound are attached as interspersed to the surface of the particle 3 made of a LiNiCoMn oxide as described above.

In this form, the ratio of the volume of the particles 4 made of the Li compound and so attached to the volume of the particle 2 made of the LiNiCoMn oxide is preferred to be in the range of 0.5 - 250% and more preferably in the range of 0.7 - 150%. If the volume ratio of the particles made of the Li compound falls short of 0.5%, the shortage will possibly result in preventing the dissolving of manganese ions from the LiNiCoMn oxide which is a positive electrode material from being repressed fully satisfactory. Conversely, if the volume ratio of the particles exceeds 250%, the overage will possibly result in increasing the internal resistance of the positive electrode material and decreasing the battery performance even when the Li compound possesses the ability to conduct lithium ions. The volume ratio mentioned above can be determined, for example, by visually observing the electron micrograph of the positive electrode material.

Further, in the form illustrated in Fig. 3, the average diameter of the particles 4 which are made of the Li compound and attached as interspersed is preferably in the approximate range of 10 - 200 μm and more preferably in the range of 20 - 100 μm. If the average diameter of the particles 4 made of the Li compound falls short of 10 μm, the shortage will possibly result in preventing the effect of the attachment of the Li compound from being attained fully satisfactorily. Conversely, if the average diameter exceeds 200 μm, the overage will possibly result in reducing the effect of the attachment and further exalting the resistance by the Li compound.

The surface of the positive electrode material of this invention is preferred to have attached thereto a compound containing a divalent metal atom (hereinafter referred to occasionally as "divalent compound") . By attaching the divalent compound to the surface of the positive electrode material, it is made possible to increase the valence number of manganese ions in the neighborhood of the surface of the active material particle. In this form, therefore, the dissolving ofmanganese ions inthepositive electrode activematerial into the electrolyte can be repressed more satisfactorily. The form oftheattachmentofthedivalentcompoundtothesurfaceofthepositive electrode material does not need to be particularly restricted. The form having the Li compound attached to the surface of the particle made of the LiNiCoMn oxide, namely the form illustrated in Fig. 2 or Fig. 3 above, may be adopted.

When the attachment of the divalent compound results in the formation of the coating layer on the surface of the positive electrode material, for example, the thickness of the coating layer made of the divalent compound is preferably in- the range of 3 - 1000 nm and more preferably in the range of 5 - 500 nm. When the particles made of the divalent compound is attached as interspersed, the ratio of the volume of the attached particles made of the divalent compound to the volume of the positive electrode material (the LiNiCoMn oxide having the Li compound attached thereto) is preferably in the range of 0.5 - 30% and more preferably in the range of 0.6 - 20%.

According to circumstances, the form having the particle made of the Li compound and the particle made of the divalent compound both attached as interspersed to the surface of the particle made of the LiNiCoMn oxide may be adopted.

The divalent metal atom contained in the divalent compound does not need to be particularly restricted but may be required to be a metal atom having a valence number of +2. As concrete examples of the divalent metal atom, alkaline earth metal atoms such as Mg, Ca, Sr and Ba, and Zn, Cu, Fe, Ni, V, Nb, Co, Ge, Si, In, Pb, and Mn may be cited. The compounds which contain such divalent metal atoms as enumerated above are usable without any particular restriction. As concrete examples of the divalent compound, such compounds as MgO, BaO, SrO, CaO, CaCO₃, SrCO₃, BaCO₃, MgCO₃, CaSO₄, BaSO₄, MgSO₄, Ca (NO₃) ₂, Sr (NO₃) ₂, Ba (NO₃)2, and Mg (NO₃)₂ which contain alkaline earth metal atoms and such other compounds as ZnO, CuO, FeO, NiO, VO, NbO, CoO, GeO, SiO, InO, PbO, CoCO₃, PbCO₃, MnCO₃, FeCO₃, NiCO₃, CoSO₄, PbSO₄, FeSO₄, MnSO₄, CuSO₄, Co (NO₃) ₂, Fe (NO₃) ₂, Cu (NO₃) ₂, Pb(NO₃J₂, Ni (NO₃)₂, and Mn (NO₃) ₂ may be cited.

Subsequently, the method for producing the positive electrode material contemplated by this invention will be explained. The positive electrode material of this invention can be produced, for example, by firing the raw material of s LiNiCoMn oxide thereby preparing the LiNiCoMn oxide (firing step) and attaching a Li compound to the surface of the particles of the LiNiCoMn oxide (attaching step) .

Now, one preferred embodiment of the method of production described above will be explained in detail below. The scope of this invention is not limited to the following embodiment. First, the firing step will be described.

In the firing step, the raw material of the LiNiCoMn oxide is fired to prepare the LiNiCoMn oxide as described above.

In the firing step, the raw material for the LiNiCoMn oxide is prepared. The raw material mentioned above does not need to be particularlyrestrictedbut is onlyrequiredtobe capableofpreparing the LiNiCoMn oxide by firing. It may be a single compound or a mixture of two or more compounds. The composition of the components in the raw material does not need to be particularly restricted but may be properly adjusted to suit the composition of the LiNiCoMn oxide to be obtained. Whenthe rawmaterial is amixtureoftwoormore compounds, the means to be used for mixing the two or more compounds does not need to be particularly restricted. Any of the known mixing means may be adopted. For the purpose of obtaining the mixture in a homogeneous formulation in this case, it is preferable to use wet mixture. The raw material which has undergone the wet mixture is preferably coprecipitated by the coprecipitating technique, for example, and then fired as described below. According to circumstances, the raw material may be screened to select the raw material having a uniform particle diameter and put it to the production.

As one example of the raw material, the mixture consisting of a lithium compound, a nickel compound, a cobalt compound, and a manganese compound may be cited.

The second aspect of this invention is directed toward a method for the production of a positive electrode material for a non-aqueous electrolyte lithium-ion secondary battery, which comprises a firing stepof obtainingparticles formedofa lithiumnickel cobaltmanganese oxide by firing a mixture consisting of a lithium compound, a nickel compound, a cobalt compound, and a manganese compound and an attaching step for effecting attachment of a lithium compound to the surfaces of the particles formed of the lithium nickel cobalt manganese oxide mentioned above.

By firing the raw material mentioned above, it is made possible to prepare the LiNiCoMn oxide which excels in dispersibility of the component atoms, abounds in crystallinity, and exhibits high reactivity as a positive electrode active material. Though the specific forms of the lithium compound, nickel compound, cobalt compound, and manganese compound mentioned above do not need to be particularly restricted, such forms as oxides and carbonates may be cited as concrete examples.

The firing conditions do not need to be particularly restricted but are only required to be capable of obtaining a LiNiCoMn oxide. The firing temperature, for example, is in the approximate range of 600 - 900°C and preferably in the range of 700 - 88O⁰C. The firing time is in the approximate range 6 - 36 hours and preferably in the range of 12 - 30 hours. Though the condition for the atmosphere at the time of firing does not need to be particularly restricted, it is commendable to perform the firing in the atmosphere of oxygen. Byperformingthe firingintheatmosphereofoxygen, it ismadepossible to effect introduction of excess oxygen to the neighborhood of the surface of the LiNiCoMn oxide to be formed and attain preparation of an oxide containing the oxygen excess LiNiCoMn oxide in the neighborhood of the surface.

After the firing step mentioned above, the LiNiCoMn oxide consequently obtained is cooled to the vicinity of room temperature. In this case, it is commendable to effect the cooling quickly. By quickening this cooling, it is made possible to obtain particles of the LiNiCoMnoxidehavinga small averagediameterand furtherexalting the average valence number of manganese atoms existing in the neighborhood of the surfaces of the particles of the produced LiNiCoMn oxide. The specific cooling speed is preferably not less than 150°C/min and more preferably not less than 170°C/min. By quickening the cooling speed in this case,_, it is made possible to obtain oxide particles having a smaller average diameter. It is commendable to perform the quick coolingmentioned above in the atmosphere of oxygen. As a result, excess oxygen can be introduced in the neighborhood of the surface of the oxide.

For the purpose of ensuring the introduction of excess oxygen to the neighborhood of the produced oxide and realizing the presence of the oxygen excess LiNiCoMn oxide, an annealing step performed in the atmosphere of oxygen may be incorporated separately of the aforementioned firing step in the process of production. In this case, the annealing temperature is in the approximate range of 250

- 600°C and the annealing time is in the approximate range of 30 minutes - 12 hours. The oxygen pressure in the atmosphere of oxygen is preferably in the approximate range of 1 - 100 atm and more preferably in the range of 1 - 50 atm.

As occasion demands, after the firing step or the annealing step mentioned above, the particles of the produced LiNiCoMn oxide may be screened to select the only particles having an average diameter to be required.

The mode of automatically preparing the LiNiCoMn oxide by firing the raw material thereof has been described. This preparation nevertheless does not need to be restricted to this mode. The commerciallyavailable LiNiCoMn oxidemaybe procured and, as occasion demands, subjectedto an annealing step, andput touse in the following attaching step according to circumstances.

The attaching step will be explained now.

In the attaching step, the positive electrode material contemplated by this invention is obtained by attaching a Li compound to the surface of a particle of the LiNiCoMn oxide preparedas described above in the firing step mentioned above.

First, in the attaching step, the particle of the LiNiCoMn oxide produced above and the Li compound to be attached thereto are prepared. Since this preferred embodiment is as described above, it will be omitted from the explanation here.

The specific method of this attachment does not need to be particularly restricted. Any of the known techniques of attachment maybeproperlyadopted. Thechoicebetweenthe formhavingthecoating layer 3 made of the Li compound as illustrated in Fig. 2 and the form having the particles 4 made of the Li compound interspersed as illustrated in Fig. 3 is properly attained by adjusting the volume ratio of the LiNiCoMn oxide particle and the Li compound to be used and the average particle diameters thereof. For the attachment of the Li compound, the dry method may be preferably adopted. To be specific, by dry mixing the LiNiCoMn oxide prepared in the aforementioned firing step and the Li compound, it is made possible to effect the attachment of the Li compound to the surfaces of the particles of the oxide mentioned above. The specific method for the dry attachment is not particularly restricted. As concrete examples of the method of dry attachment, the chemical vapor deposition (CVD) method, the physical vapor deposition (PVD) method, the pulse laser deposition (PLD) method, andthe sputteringmethodmaybecited. Thesemethods areparticularly advantageous for the production of the positive electrode material of the form having the coating layer 3 illustrated in Fig. 2. Such techniques which utilize a hybridization system (made by Nara Kikai Seisakusho K.K.), Cosmos (made by Kawasaki Jukogyo K.K.), Mechanofusion (made by Hosokawa Micron K.K. ) , Surfusion System (made by Nippon Pneumatic Kogyo K.K.), Mechanomill, Speed Kneader, Speed Mill, andSpiHerCoater (madebyOkda SeikoK.K. ) maybealsoavailable. These techniques are particularly advantageous for the production of the positive electrode material of the interspersed form illustrated in Fig. 3. The techniques enumerated above are not exclusive examples. Of course, it is permissible to use other techniques.

The particles consequently obtained may be heated as occasion demands. By heating the particles, it is made possible to enable the attachedLi compoundto adhere fast to the surfaces of theparticles of the active material.

The dry attaching method has been described in detail. Occasionally, the wet attaching method may be used. In this case, the attaching stepmaybe carried out simultaneously during the firing step mentioned above. To be specific, by causing the Li compound to be simultaneously mixed, coprecipitated, and further fired while the raw material for the LiNiCoMn oxide is subjected to the wet mixing in the aforementioned firing step, it is made possible to obtain the particles of the LiNiCoMn oxide having attached to the surface thereof the Li compound (the positive electrode material contemplated by this invention) .

Thereafter, the attachment of a divalent compoundmaybe effected as occasion demands. The preferred form of the divalent compound is as described above. For the attachment of the divalent compound, the method for the attachment of the Li compound described above can be similarly used.

The positive electrode material of this invention can be advantageously used for the positive electrode of a non-aqueous electrolyte lithium-ion secondary battery. Thus, the third aspect of this invention is directed toward the positive electrode which uses the positive electrode material for the non-aqueous electrolyte lithium-ion secondary battery set forth in the first aspect of this invention. Byusingthepositive electrodematerial ofthis invention as described above, it is made possible to curb the increase of the internal resistance andthedecrease ofthebatteryperformance. Now, one preferred form of the positive electrode for a non-aqueous electrolyte lithium-ion secondary battery using the positive electrodematerial ofthis inventionwillbe describedindetailbelow. The scope of this invention is not restricted only to the following form. The positive electrode contemplated by this invention is furnished with a current collector and a positive active material layer disposed on the current collector and is characterized by containing the positive electrode material set forth in the first aspect of this invention in the positive active material layer mentioned above. In the positive electrode of this invention, the battery reaction proceeds in the active material layer and the electrons produced by this reaction perform an electrical work on the external load.

Now, the current collector and the active material layer which form the positive electrode of this invention will be explainedbelow.

The current collector is formed of such an electroconductive material as aluminum foil, copper foil, or stainless steel (SUS) foil.

The current collector generally has a thickness in the range of 10

- 50 μm. Of course, the current collector which has a thickness deviating fromthis range, however, is usable. The size of the current collector is decided, depending on the purpose for which the positive electrode of this invention is used. In the manufacture of a large positive electrode for use in a large battery, the current collector to be used has a large area. In the manufacture of a small positive electrode, the current collector to be used has a small area.

The activematerial layeris disposedonthe surfaceofthecurrent collector mentioned above and adapted to contain the positive electrode material contemplated by this invention. Since the preferred form of the positive electrode material of the first aspect of this invention which is contained in the active material layer is as explained in the first aspect of this invention, it will be omitted from the present detail description.

The activematerial layer, whennecessary, maycontainapositive electrode active material other than the positive electrode material contemplated by this invention. The positive electrode active material other than the positive electrode material of this invention does not need to be particularly restricted. Any of the compounds heretofore known as positive electrode material may properly used to suit the battery performance to be expected. Composite oxides formedbetween lithium and transitionmetals maybe cited for example. As concrete examples, Li-Mn composite oxides such as LiMn₂O₄, Li-Co compositeoxides suchasLi-CoO₂, Li-Crcompositeoxides suchasLi₃Cr₃O₇ and Li₂CrO₄, and Li-Fe composite oxides such as LiFeO₂ may be cited. Further, such compounds which have part of the transition metals contained in the composite oxides substituted for other elements may be used. Besides, lithiumphosphoric acid compounds such as LiFePO₄, lithium sulfuric acid compounds, oxides and sulfides of transition metals such as V₂O₅, MnO₂, TiS₂, MoS₂, and MoO₃, and PbO₂, AgO, and NiOOH may be contained in the active material layer. The activematerial layer, when necessary, may containmaterials

■ other than those materials enumerated above. For example, a binder, an electroconductive auxiliary, a lithium salt (supporting electrolyte) , and an ion conducting polymer may be contained.

According to conditions, the active material layer may contain a polymerization initiator which is intended to induce polymerization of an ion conducting polymer contained in the active material layer. As concrete examples of the binder, poly (vinylidene fluoride) (PvdF) and rubber binder may be cited.

The term "electroconductive auxiliary" refers to an additive tobe incorporated for the purpose of exalting the electroconductivity of the active material layer in the electrode. As concrete examples of the electroconductive auxiliary, carbon powders such as acetylene black and graphite, and carbon fibers such as mesophase carbon, difficultly graphitizable carbon, ketchen black, and vapor phase growth carbon fibers (VGCF) may be cited.

As concreteexamples ofthe lithiumsalt (supportingelectrolyte) , LiBETI (lithium bis (perfluoroethylene sulfonylimide) ; Li (C₂F₅SO₂) ₂N) , LiPF₆, LiBF₄, LiClO₄, LiAsF₆, LiCF₃SO₃, and LiBOB may be cited. As concrete examples of the ion conducting polymer, the polymers of the polyethylene oxide (PEO) type and the polypropylene oxide (PPO) type may be cited. The ion conducting polymer mentioned above may be identical or not identical with the ion conducting polymer which is used as the electrolyte in the electrolytic layer of the non-aqueous electrolyte lithium-ion secondary battery for which the positive electrode of this invention is adopted. Preferably, it is identical.

The polymerization initiator is incorporated with the object of acting on the cross-linking group of the ion conducting polymer andpromotingthe cross-linkingreactionofthepolymer. It is divided into a thermal polymerization initiator and an optical polymerization initiator, depending on the external factor necessary for the operationofan initiator. As concrete examples of thepolymerization initiator, azobisisobutyronitrile (AIBN) as a thermal polymerization initiator andbenzyl dimethyl ketal (BDK) as an optical polymerization initiator may be cited.

The compounding ratio of the components to be contained in the active material layer and the size (area) of the active material layer do not need to be particularly restricted. These factors can be adjusted by properly consulting the knowledge about the active material layer of the electrode which is known to the art. The method for the production of the positive electrode contemplated by this invention does not need to be particularly restricted. The production can be performed by properly consulting the knowledge about the production of the positive electrode of a batterywhich is knownto the art. For example, the positive electrode of this invention can be produced by preparing a slurry of a positive electrode material containing the positive electrode material contemplated by this invention, applying this positive electrode material slurry to the surface of a current collector, and drying the applied layer of the slurry.

Now, one preferred embodiment of the method of the production mentioned above will be described in detail below.

For a start, the step for preparing the positive electrode material slurry will be explained. In this step, the positive electrode material constituting the first aspect ofthis inventionisaddedtoapropersolvent foradjusting the viscosity of slurry and dispersed therein to form the positive electrode material slurry. The positive electrode material slurry, when necessary, may have added thereto other components such as other positive electrode active material, binder, electrocnductive auxiliary, lithium salt (supporting electrolyte) , ion conducting polymer, and polymerization initiator besides the positive electrode material contemplated by this invention. The preferred forms of the individual components which are contained in the positive electrode material slurry are as already explained above and will be omitted from the following explanation.

In the preparation of the positive electrode material slurry, the order in which the individual components are added does not need to be particularly restricted. The positive electrode material slurry may be produced, for example, by preparing a mixture of all the components to be contained in the slurry except the solvent, subsequently adding the solvent to the resultant mixture, and mixing them. Otherwise, the positive electrode material slurry may be obtainedbypreparingamixtureof someofthe components tobecontained in the slurry mentioned above except the solvent, adding the solvent to the resultant mixture, mixing them, further adding thereto the rest of the components, and mixing them. In this case, the device which is used for adding and mixing the individual components does not need to be particularly restricted. A homomixer, for example, may be adopted.

Then, the step of applying the positive electrodematerial slurry will be explained.

In this step, the positive electrode material slurry prepared in the step described above is applied to a proper current collector. The method for applying the positive electrode material slurry to the current collector does not need to be particularly restricted. Any of the known methods which resort to such means as a coater may be used for this application. Such printingmethods as sprayprinting and ink jet printing are also usable where circumstances permit. Subsequently, the current collector to which the positive electrode material slurryhasbeenappliedisdriedtoexpel the solvent contained in the slurry. During the course of this drying, a vacuum drier may be used. The drying conditions cannot be decided uniquely because they are variable with numerous properties of the slurry. Generally, the drying is performed at a temperature in the range of 60 - 13O⁰C for a period in the approximate range of 5 - 60 minutes.

When the polymerization initiator for polymerizing the ion conductingpolymer contained in the activematerial layer is contained in the active material layer in this case, the ion conducting polymer mentioned above is subsequently polymerized (cross-linked) by a varying method to complete a positive electrode. The method for performing the polymerization (cross-linkage) in this case does not need to be particularly restricted but may be properly selected in conformity with the kind of the polymerization initiator contained in the active material layer. As concrete examples of the method of polymerization, thermal polymerization, optical (ultraviolet) polymerization, radiation-induced polymerization, and electron beam polymerization may be cited. The device and the condition for effecting this polymerization (cross-linkage) do not need to be particularly restricted. Any of the devices and the conditions heretofore known to the art may be used.

The positive electrode which has been produced by the method described above, when necessary, may be subjected to a pressing work. By carrying out this pressing work, it is made possible to flatten the surface of the produced positive electrode to a greater extent. The device and the condition for performing the pressing work do not need to be particularly restricted. Any of the devices and the conditions heretofore known to the art may be used.

In the process for industrial production, a procedure of manufacturingapositive electrode largerthan the size ofthe finished battery and cutting this positive electrode to the prescribed size may be adopted with the object of exalting the productivity of the process.

The positive electrode of this invention is suitably used for the non-aqueous electrolyte lithium-ion secondary battery. Thus, the fourth aspect of this invention is directed toward a battery which uses the positive electrode for the non-aqueous electrolyte lithium-ion secondary battery which constitutes the third aspect of this invention. In the battery of this kind, the increase of the internal resistance and the decrease of the battery performance can be curbed as described above. Now, one preferred embodiment of the non-aqueous electrolyte lithium-ion secondary battery using the positive electrode of this inventionmentionedabovewillbe described in detail below. The scope of this invention is not restricted exclusively to the following embodiment.

The battery of this invention uses the positive electrode of the third aspect of this invention as its positive electrode. That is, the battery is characterized by containing in the positive electrode thereof the positive electrode material of the first aspect of this invention.

In the ordinary battery, a positive electrode, an electrolytic layer, and a negative electrode are disposed sequentially in the order mentioned and these components are sealed in an exterior coat such as of a laminate sheet. The concrete form of the negative electrode and the form of the electrolyte contained in the electrolyte layer do not needto be particularly restricted. The forms heretofore known to the art can be adopted. As a concrete example of the negative electrode mentioned above, the configuration which is obtained by forming an active material layer containing such a negative electrode activematerial as a carbonaceousmaterial like graphite orhardcarbon on the same current collector as used in the positive electrode contemplated by this invention may be cited. The electrolyte mentioned above may be a liquid electrolyte, a solid electrolyte, or a gel electrolyte. When it further embraces an electrolytic solution, this electrolytic solution ought to be in a non-aqueous form.

When the components of the battery are included in the external coat, these components are stored in the external coat in such a manner that a tab attached thereto may be drawn out of the external coat. The external coat in the region not including the components of the battery is sealed for the purpose of enabling the interior to secure necessary sealingperformance. As the external coatmentionedabove, a polymer-metal composite film is used. The term "polymer-metal composite film" means a film resulting from laminating at least a metal thin film and a resin film. By adopting the external coat of this kind, it is made possible to form a thin laminate battery.

The battery contemplated by this invention is a lithium-ion secondarybattery. Preferably, it is abipolar lithium-ion secondary battery (bipolar battery) . For the sake of reference, Fig. 4 illustrates a schematic cross-sectional diagram of a lithium-ion secondary battery which is not a bipolar type (ordinary lithium-ion battery) and Fig. 5 illustrates a schematic cross-sectional diagram of a bipolar lithium-ion secondary battery (bipolar battery) . It is clear from Fig. 4 and Fig. 5 that the ordinary lithium-ion battery and the bipolar battery are different only in the layout of electrodes. Generally, the ordinary lithium-ion batterypossesses a large battery capacity and a high energy level and excels in the ability to supply electric power for a long time. In contrast, the bipolar battery possesses a high output density and excels in the ability to supply a large electric power for a short period of time. The choice between these two battery types, therefore, is properly decided in conformity with the form of electric power to be required. The scope of this invention does not need to be restricted to the contents of these drawings. Aplurality of batteries of this invention or at least one battery of this invention plus a battery of other kindmaybe joined in parallel connection, series connection, parallel-series connection, or series-parallel connection and used as a joint battery. Thus, the fifth aspect of this invention is directed toward a joint battery usingthebatterycontemplatedbythis invention. The jointbatttery, therefore, can meet the demand for battery capacity and output which vary with the purpose of use comparatively inexpensively without requiring manufacture of new batteries. The concrete form of the production of the joint battery does not need to be particularly restricted. The knowledge currently in popular use with any of joint batteries can be adopted. It is also permissible to have a plurality of such joint batteries of this invention joined to form a complex joint battery.

The batteries and the joint batteries contemplated by this invention and the complex joint batteries containing them are preferably used in vehicles as a driving power source or an auxiliary power source. Thus, the sixth aspect of this invention is directed towardavehiclewhichhasmountedthereonthebatteryofthis invention or the joint battery of this invention. The vehicles on which the battery or the joint battery or the complex joint battery including it can be loaded do not need to be particularlyrestricted. Nevertheless, electricvehicles, fuel cell vehicles, and hybrid cars combining them are preferably used. EXAMPLES Now, this invention will be explained in further detail below with reference to working examples. The invention, however, is not limited to these working examples. <Example 1> Example 1-1 <Manufacture of positive electrode material>

As the raw materials for a positive electrode active material, lithiumcarbonate (averageparticle diameter: 3.2 μm) (1) andamixture (2) of nickel carbonate (average particle diameter: 3.0 μm) , cobalt carbonate (averageparticlediameter: 3.5μm) , andmanganesecarbonate (average particle diameter: 2.5 μm) were prepared. The three components forming the mixture (2) mentioned above were so mixed that the nickel atoms, cobalt atoms, and manganese atoms would amount to an equal mol.

Subsequently, the components (1) and (2) mentioned above were so mixed that the ratio of the mol of lithium atoms to the total mol number of nickel atoms, cobalt atoms, and manganese atom would be 1.2 : 1 and were further mixed in a planetary ball mill for 24 hours. The resultantmixturewas subsequently fired inanatmosphere of oxygen at 850⁰C for 24 hours. The firedmixture was cooledto roomtemperature at a rate of 170°C/min as kept swept with oxygen to complete preparation of LiNiCoMn oxide as a positive electrode active material. When the produced LiNiCoMo oxide was assayed for composition by ICP emission spectral analysis, it was identified to be Li1.₀₅Nio.35Coo.32Mno.33O2. When this LiNiCoMn oxide was tested for average particle diameter, the particle diameter was found to be 5 μm.

Subsequently, lithium sulfate (average particle diameter: 100 nm) was prepared as a lithium compound. The surfaces of the particles of the LiNiCoMn oxide prepared as described above were coated in a thickness of 3 nm with this lithium sulfate to prepare a positive electrode material of the form illustrated in Fig.2. To be specific, the surfaces of the active material particles are coated with the lithium sulfate by attaching the lithium sulfate to the surfaces of the active material particles by using the mechanofusion technique andsubsequentlyannealingthe applied layer inanatmosphere of oxygen at 300⁰C for five hours.

The positive electrode material (75 mass parts) prepared as described above, poly (vinylidene fluoride) (PVdF) (15 mass parts) asabinder, andacetyleneblack (10massparts) as anelectroconducting auxiliary were prepared. N-methyl-2-pyrrolidone (NMP) as a slurry viscosity adjusting solvent was added in a suitable amount thereto and thoroughly mixed therewith by stirring to manufacture a positive electrode material slurry.

The positive electrode material slurry prepared as described above was applied to an aluminum foil (thickness: 20 μm) as a positive electrode current collector by the use of an applicator and then dried by heating at about 80⁰C by means of a vacuum drier. A disk 15 mm in diameter was punched out of the resultant electrode and further driedunder a highvacuumcondition at 9O⁰C for six hours tomanufacture a positive electrode for use in a coin-cell. The positive electrode layer formed on the current collector had a thickness of 50 μm. <Manufacture of negative electrode>

Carbon (average particle diameter: 10 μm) (85 mass parts), a carbonaceousmaterial intendedas anegativeelectrodeactivematerial, poly (vinylidene fluoride) (PVdF) (5massparts) as abinder, acetylene black (8 mass parts) as an electroconducting auxiliary, and vapor phase growth carbon fibers (VGCF) (2 mass parts) were prepared. A suitable amount of N-methyl-2-pyrrolidone (NMP) as a slurryviscosity adjusting solvent was added thereto and thoroughly mixed therewith by stirring to manufacture a negative electrode material slurry.

The negative electrode material slurry prepared as described above was applied to a copper foil (thickness: 20 μm) as a negative current collector by the use of an applicator and dried by heating to about 8O⁰C by means of a vacuum drier. A disk 16 mm in diameter was punched out of the produced electrode and further dried under a high vacuum condition at 90⁰C for six hours to manufacture a negative electrode. The negative electrode layer formed on the current collector had a thickness of 80 μm.

Manufacture of electrolytic layer> A polypropylene (PP) type microporous separator (average diameter of micropores: 800 nm, porosity: 35%, thickness: 30 μm) was preparedas a separator. Separately, an equivoluminalmixed solution consisting of ethylene carbonate (EC) and diethyl carbonate (DEC) andcontaining 1.0 MofLiPF₆was preparedas a non-aqueous electrolyte. An electrolytic layer was manufactured by pouring the solution of the electrolyte mentioned above into the separator mentioned above.

Manufacture of coin-cell>

Acoin-shapedbipolar cellwasmanufacturedbyusingthepositive and negative electrode, and electrolytic layer produced as described above. determination of change of internal resistance due to storage>

Immediatelyafterthecoin-cellmentionedabovewasmanufactured, it was charged with an electric current of 0.2C as reduced to the positiveelectrodeuptoavoltageof 4.1Vtocarryout constant-voltage charging for 12 hours. Thereafter, the charging was stopped and the cell was retained at room temperature for one week. After the one week's retention, it was discharged once to 2.5V and again subjected to constant-current and constant-voltage charging with an electric current of 0.2C up to 3.6V for 12 hours. Then, the cell was tested with a direct current for initial internal resistance.

Subsequently, the cell was subjected to constant-current and constant-voltage charging with an electric current of 0.2C up to 4. IV for 12 hours, relieved of the charging, and retained at a voltage of 4.1 V at 60⁰C for one month. Thereafter, it was tested with a direct current for an internal resistance (internal resistance after preservation) . The ratio of increase of the internal resistance was calculated in accordance with the following formula (2) using the results of the test. The results are shown in Table 1 below. Ratio of increase of internal resistance (%) = [Internal resistance after preservation - Initial internal resistance] / [Initial internal resistance] * 100 (2) Examples 1-2 - 1-9

Positive electrode materials were prepared and coin- cells were manufactured and tested for changes of internal resistance due to preservation by following the procedure of Example 1 -1 except for changing the thickness of the lithium sulfate layer coating the surfaces of the particles of the LiNiCoMn oxide to the magnitudes shown in Table 1 below. The results are shown in Table 1 below. <Comparative Example> A coin-cell was manufactured by following the procedure of Example 1-1 except for omitting the step of coating the surfaces of theLiNiCoMnoxideparticleswith lithiumsulfate as a lithiumcompound andwastestedforchangeoftheinternal resistanceduetopreservation. The results are shown in Table 1 below. [Table 1]

<Example 2> Example 1-5 described above will be taken as Example 2-1 here. Examples 2-2 - 2-21

Positive electrode materials were prepared by following the procedure of Example 2-1 while using compounds shown in Table 2 below intheplaceoflithiumsulfate forcoatingthe surfacesoftheparticles of LiNiCoMn oxide. Coin-cells were manufactured from the positive electrode materials and tested for change of internal resistance due to preservation. The results are shown in Table 2 below.

[Table 2]

<Example 3> Example 3-1

A positive electrode material of the form shown in Fig. 3 was manufactured by following the procedure of Example 1-1 except for using themechanofusion technique inthe attachment of lithiumsulfate as a lithium compound to the surfaces of the particles of LiNiCoMn oxide as a positive electrode active material and having 0.5 vol% of lithiumsulfatetotheLiNiCoMnoxide. Acoin-cellwasmanufactured fromthispositive electrodematerial andtested forchange of internal resistance due to preservation. The results are shown in Table 3 below. Examples 3-2 - 3-11

Positive electrode materials were prepared by following the procedure of Example 3-1 except for changing the amount of lithium sulfate added to the magnitudes shown in Table 3 below. Coin-cells were manufactured from the positive electrode materials and tested for changes of internal resistance due to preservation. The results are shown in Table 3 below. [Table 3]

Example 3-6 Lithium sulfate 10.0 1.8

Example 3-7 Lithium sulfate 50.0 1.8

Example 3-8 Lithium sulfate 100.0 1.5

Example 3-9 Lithium sulfate 150.0 1.5

Example 3-10 Lithium sulfate 200.0 1.4

Example 3-11 Lithium sulfate 300.0 1.1

<Example 4> Example 4-1

Example 3-4 described above will be taken as Example 4-1 here. Examples 4-2 - 4-21

Positive electrode materials were prepared by following the procedure of Example 4-1 except for using the compounds shown in Table 4 below in the place of lithium sulfate as a lithium compound for attachment to the surfaces of the particles of LiNiCoMn oxide. Coin-cells were manufactured from these positive electrode materials and tested for changes of internal resistance due to preservation. The results are shown in Table 4 below.

[Table 4]

<Example 5> Example 5-1

A positive electrode material was prepared by following the procedure of Example 1-5 except for placing a produced LiNiCoMn oxide in an autoclave, annealing it therein under an oxygen pressure of

1 atm at 500⁰C for 12 hours thereby introducing excess oxygen to the surfaces oftheparticles oftheLiNiCoMnoxide, andthereaftercoating the surfaces oftheparticles oftheLiNiCoMnoxidewith lithiumsulfate as alithiumcompound. Acoin-cellwasmanufacturedfromthispositive electrode material and tested for change of the internal pressure due to preservation. The results of the test are shown in Table 5 below.

Examples 5-2 - 5-5 Positive electrode materials were prepared by following the procedure ofExample 5-1 except for changingthe oxygenpressureduring the course of annealing to the magnitudes shown in Table 5 below. Coin-cells were manufactured from these positive electrode materials and tested for change of internal resistance due to preservation. The results of the test are shown in Table 5 below. [Table 5]

<Example β> Example 6-1

A positive electrode material was prepared by following the procedureofExample 1-5 except forhavingthe surfaces oftheparticles of the produced positive electrode material further coated with zinc oxide (average particle diameter: 100 nm) , a divalent compound. A coin-cell was manufactured from the positive electrode material and tested for change of internal resistance due to preservation. The results of the test are shown in Table 6 below. The attachment of zinc oxide to the positive electrode material was effected by the methanofusion technique. After this attachment, the product of the attachment was annealed under an atmosphere of oxygen at 300⁰C for five hours to coat the surfaces of the positive electrode material with zinc oxide. The amount of zinc oxide spent for this coating was about 5 volume% based on the volume of the positive electrode material before the coating. Examples 6-2 - 6-45

Positive electrode materials were prepared by following the procedure of Example 6-1 except for using the compounds shown in Table 6 below in the place of zinc oxide as a divalent compound for further coating the surfaces of the particles of the positive electrode material. Coin-cellsweremanufacturedfromthesepositiveelectrode materials and tested for change of internal resistance due to preservation. The results are shown in Table 6 below. [Table 6]

The results givenabove showthat byhaving a Li compoundattached to the surfaces oftheparticles ofa LiNiCoMnoxide, it ismadepossible to curb the rise of the internal resistance of a positive electrode material. By using the positive electrode material thus produced, it canbe expected that the rise of the internal resistance of a battery can be curbed and consequently the decrease of the battery performance can be effectively prevented.

The comparison of Example 1 and Example 5 reveals that the impartation of excess oxygen to the neighborhood of the surfaces of the particles of the LiNiCoMn oxide which is a positive electrode active material results in further repressing the rise of the internal resistance.

Then, the comparison of Example 1 and Example 6 reveals that the further attachment of a compound possessing a divalent metal atom to the surface of the positive electrode material contemplated by this invention results in further repressing the rise of the internal resistance.

The preceding examples are intended to explain this invention more specifically. This invention, therefore, is not limitedtothese examples.

The subject patent application is based on Japanese Patent Application No. 2004-258966 filed on September 6, 2004 and has the contents of disclosure thereof referred to and incorporated as a whole in the present description.

Claims

1. A positive electrode material for use in a non-aqueous electrolyte lithium-ion secondary battery, having a lithium compound attached to the surfaces of particles of lithium nickel cobalt manganese oxide.

2. A positive electrode material for a non-aqueous electrolyte lithium-ion secondary battery according to claim 1, wherein said particles of lithium nickel cobalt manganese oxide have an average particle diameter in the range of 0.1 - 20 μm.

3. A positive electrode material for a non-aqueous electrolyte lithium-ion secondary battery according to claims 1 or 2, wherein said lithium compound attached forms a coating layer for coating the particles of said lithium nickel cobalt manganese oxide and said coating layer has a thickness in the range of 3 - 1000 μm.

4. A positive electrode material for a non-aqueous electrolyte lithium-ion secondary battery according to any one of claims 1 - 3, wherein the ratio of the volume of said attached lithium compound to the volume of the particles of said lithium nickel cobalt manganese oxide is in the range of 0.5 - 250%.

5. A positive electrode material for a non-aqueous electrolyte lithium-ion secondary battery according to any one of claims 1 - 4, wherein said attached lithium compound is a compound possessed of lithium ion conductivity.

6. A positive electrode material for a non-aqueous electrolyte lithium-ion secondary battery according to any one of claims 1 - 5, wherein said attached lithium compound is one or more compounds selected from the group consisting of Li₂SO₄, Li₃PO₄, LiPON, Li₂O-B₂O₃, Li₂O-B₂O₃-LiI, Li₂O-SiS₂, Li₂S-SiS₂-Li₃PO₄, LiCoO₂, LiMn₂O₄, LiOH, and Li₂CO₃.

7. A positive electrode material for a non-aqueous electrolyte lithium-ion secondary battery according to any one of claims 1 - 6, wherein the manganese atoms which exist in the neighborhood of the surfaces of the particles of said lithium nickel cobalt manganese oxide have an average valence number of not less than +3.5.

8. A positive electrode material for a non-aqueous electrolyte lithium-ion secondary battery according to any one of claims 1 - 7, wherein the particles of said lithium nickel cobalt manganese oxide contain an oxygen excess lithium nickel cobalt manganese oxide in the neighborhood of the surfaces thereof.

9. A positive electrode material for a non-aqueous electrolyte lithium-ion secondary battery according to any one of claims 1 - 8, wherein a compound containing divalent metal atoms is further attached.

10. A positive electrode for a non-aqueous electrolyte lithium-ion secondary battery, using the positive electrode material for a non-aqueous electrolyte lithium-ion secondarybattery set forth in any of claims 1 - 9.

11. A non-aqueous electrolyte lithium-ion secondary battery, usingthepositiveelectrode foranon-aqueouselectrolytelithium-ion secondary battery set forth in claim 10.

12. A joint battery, using the non-aqueous electrolyte lithium-ion secondary battery set forth in claim 11.

13. A vehicle mounting thereon the non-aqueous electrolyte lithium-ionsecondarybatteryset forthinclaim11 orthe jointbattery set forth in claim 12.

14. Amethod for the production of a positive electrode material for a non-aqueous electrolyte lithium-ion secondary battery, comprising: a firing step for firing a mixture of a lithium compound, a nickel compound, a cobalt compound, and a manganese compound thereby- obtaining particles of lithium nickel cobalt manganese oxide; and an attaching step forattachinga lithiumcompoundtothe surfaces of the particles of lithium nickel cobalt manganese oxide.

15. A method according to claim 14, which further comprises a cooling step for causing the particles of lithium nickel cobalt manganeseoxideobtainedat saidfiringsteptobecooledinanoxidizing atmosphere at a rate of not lower than 150°C/min.