JP3230893B2 - Non-aqueous electrolyte secondary battery - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lithium ion non-aqueous electrolyte secondary battery having improved discharge performance and cycle performance.

[0002]

2. Description of the Related Art Secondary batteries in which a light metal alloy containing lithium or a material that absorbs and releases lithium ions is used as a negative electrode active material are being actively studied because of their high energy density. LiMn ₂ O ₄ , Li ₂ MnO ₃ , LiCoO ₂ , L
iCo _0.5 Ni _0.5 O ₂ , LiNiO ₂ , MoS _{2 and the} like have been generally used. Among them, especially LiCo
O ₂ is useful in providing a high discharge potential, but requires improvement for stabilization of the potential and capacity as in other positive electrode materials in terms of cyclability. In order to improve the charge / discharge performance and cycle performance, a method using a composite oxide obtained by further adding a polyvalent transition metal to the above composition is disclosed in
-61760, JP-A-4-162357 , JP-A-4-2
67053. However although there are effective in improving and stabilizing cycles of the potential in these methods were difficult to gauge Rukoto improved simultaneously discharge capacity and the discharge potential. In addition, Co, M
Many attempts have been made to use polyvalent transition metals in place of n, Ni, etc., but little has been studied on the effect of using a monovalent alkali metal replacing Li with a polyvalent metal.

[0003]

SUMMARY OF THE INVENTION An object of the present invention is to provide a lithium ion secondary battery excellent in charge / discharge characteristics, discharge potential and cycle characteristics of a positive electrode active material.

[0004]

To solve this problem, the present invention relates to a secondary battery comprising a positive electrode, a negative electrode and a non-aqueous electrolyte, wherein the active material of the positive electrode has the chemical formula LixNayCoz
TimOp (0.8 ≦ x ≦ 1.3, 0.02 ≦ y ≦ 0.1,
0.8 ≦ z ≦ 1.0, 0.02 ≦ m ≦ 0.1, 0 ≦ p ≦ 2.
7 ) A non-aqueous electrolyte secondary battery characterized by containing the composite oxide shown in the above item is used.

The positive electrode active material used in the present invention is LiCoO.
₂ as a basic composition, to which is characterized in that the first as minor dopant is an alkali metal to substitute Li N a, is Ti is a transition metal that substitutes Co Second is added together. Among these first and second dopants, it is considered that Na mainly contributes to the enhancement of the potential and the capacity in the initial cycle of charge and discharge, and Ti contributes to the stabilization of the potential (improvement of the cyclability). The effect of Na is that an element having a larger ion radius than Li is
It is expected that an energetically favorable field is formed for the occlusion and release of ions.

The additive concentration effective as a dopant for improving battery performance is limited to the following range. That is, Lix N
In the structure represented by ay Coz Tim Op , Na is 0.1% .
01 ≦ y ≦ 0.2, and Ti is in the range of 0.01 ≦ m ≦ 0.2. In any case, an addition fraction exceeding 0.2 is not effective for battery performance due to a decrease in capacity. Of these ranges, the addition ranges more desirable for improving the cycleability are 0.02 ≦ y ≦ 0.1, 0.02 ≦ m ≦ 0.10,
It is.

The positive electrode active material of the present invention is mainly composed of secondary particles having an average particle diameter of 0.1 to 15 μm, which are composed of primary particles having an average particle diameter of 0.01 to 5.0 μm. More preferably, it is more preferably composed of primary particle aggregates having an average particle diameter of 1 micron or more and 9.5 microns or less, wherein primary particles having an average particle diameter of 0.1 microns or more and 2.5 microns or less are aggregated,
It is particularly preferable that the primary particles be composed of primary particle aggregates having an average particle size of 3.5 to 9.5 microns, in which primary particles having an average particle size of 0.1 to 2.5 microns are aggregated. Further, in the primary particle aggregate, 80% or more of the total volume preferably has a particle size of 1 micron to 15 microns, and more preferably 8% or less of the total volume.
It is at least 5%, more preferably at least 90% of the total volume. The average particle size referred to here is a mode diameter indicating the most frequent point, and is an average value of values visually observed from electron micrographs of primary particles, and a particle size distribution measuring device for primary particle aggregates. Is the value measured by

The specific surface area of the active material in the positive electrode is 0.1
It is preferably greater than m ² / g and not more than 25 m ² / g, more preferably more than 0.1 m ² / g and 5 m
² / g or less, particularly preferably more than 0.1 m ² / g and 3 m ² / g or less.

In the present invention, an active material capable of occluding and releasing lithium ions is used as the negative electrode. These are alkali metals or their alloys, or carbonaceous materials, or
Lip MOr (where M is at least one of T
a transition metal oxide containing i, V, Mn, Co, Fe, Nb, and Mo; and p = 0 to 3.1, and r = 1.6 to 4.1). Preferably, as the alkali metal or its alloy, Li metal, Li-
Al alloy, Li-Mg alloy, Li-Al-Ni alloy, L
i-Al-Mn alloy, among which Li metal, Li-A
It is effective to use 1 alloy. As the carbonaceous material, graphite, natural graphite, artificial graphite and the like can be used.

As a preferred lithium-containing transition metal oxide used as a negative electrode, Lip M ₁ q ₁ M ₂ q ₂ Mnqn Or
(Where M is at least one of Ti, V, Mn, Co,
The transition metal containing Ni and Fe p = 0 to 3.1, q ₁ +
q ₂ +... + q n = 1, n = 1 to 10, r = 1.6 to
4.1). The most preferred lithium-containing transition metal oxide used for the negative electrode is Lip Coq.
V1-q Or, Lip Niq V1-q Or (where p = 0.
3-2.2, q = 0.02-0.7, r = 1.5-2.
5). The most preferred lithium-containing transition metal oxides are Lip CoVO ₄ and Lip Ni.
VO ₄ (where p = 0.3 to 2.2).

In the present invention, it is preferable that the composition formulas of the positive electrode active material and the negative electrode active material are different. The positive electrode active material and the negative electrode active material used in the present invention can be achieved by combining compounds having different standard oxidation-reduction potentials. Therefore, the secondary battery is essentially different from a secondary battery described in JP-A-1-120,765 in which an active material that becomes "non-polar in which a positive electrode and a negative electrode cannot be distinguished" is used. The shape of the positive electrode active material of the present invention can be obtained by a method of synthesizing by mixing and firing a lithium compound and a transition metal compound, or a method of washing with water, methanol or the like after firing.

The positive electrode active substance used in the present invention, Li, N
Powders of oxides or carbonates of each of a, Co, and Ti are used as raw materials, and they are selected, uniformly mixed, and then melted and fired in the atmosphere to be synthesized. Typical raw material is Li
₂ CO ₃ , NaCO ₃ , CoCO ₃ and TiO ₂ .
The firing temperature is in the range of 400 ° C to 1500 ° C, preferably in the range of 700 ° C to 1000 ° C. More preferably, it is in the range of 750 ° C to 900 ° C.

The positive electrode active material and the negative electrode active material of the present invention can be synthesized by a method in which a lithium compound and a transition metal compound are mixed and fired, or a solution reaction, but the firing method is particularly preferable. The firing temperature is in the range of 400 ° C. to 1500 ° C., preferably 700 ° C. to 1000 ° C., and the firing time is preferably 4 to 48 hours, more preferably 6 to 20 hours, and particularly preferably. 6-15
Time. The firing gas atmosphere used in the present invention is:
Although not particularly limited, in the case of a positive electrode active material, air or a gas having a high oxygen ratio (for example, about 30% or more), and for the negative electrode active material, a gas having a low air or oxygen ratio (for example, about 10% or less) or It is preferably in an inert gas (nitrogen gas, argon gas). The shape of the positive electrode active material of the present invention can be obtained by a method of synthesizing by mixing and firing a lithium compound and a transition metal compound, or a method of washing with water, methanol or the like after firing.

The cathode active material and the anode active material of the present invention are preferably synthesized by firing a mixture of a lithium compound and a transition metal compound described below. For example, lithium compounds include oxygen compounds, oxyacid salts and halides. As the transition metal compound,
Monovalent to hexavalent transition metal oxides, transition metal salts, and transition metal complex salts are used.

Preferred lithium compounds used in the synthesis of the active material include lithium hydroxide, lithium oxide, lithium carbonate, lithium nitrate, lithium sulfate, lithium sulfite, lithium phosphate, lithium tetraborate, lithium chlorate, and lithium perchlorate. , Lithium thiocyanate, lithium formate, lithium acetate, lithium oxalate, lithium citrate, lithium lactate, lithium tartrate, lithium pyruvate, lithium trifluoromethanesulfonate, lithium tetraborate, lithium hexafluorophosphate, lithium fluoride, Lithium chloride, lithium bromide and lithium iodide are mentioned.

Preferred transition metal compounds include:
TiO_Two(Rutile or anatase type), lithium titanate
, Acetylacetonatotitanyl, titanium tetrachloride, tetra
Titanium iodide, titanyl ammonium oxalate, VOd (d =
2-2.5 The compound of d = 2.5 is vanadium pentoxide.
), Lithium compound of VOd, vanadium hydroxide,
Ammonium tabanadate, ammonium orthovanadate
, Ammonium pyrovanadate, vanadium oxosulfate
, Vanadium oxytrichloride, vanadium tetrachloride,
Lithium Romate, Ammonium Chromate, Coba Chromate
Chromium acetylacetonate, MnO_Two, Mn_Two
O_Three, Manganese hydroxide, manganese carbonate, manganese nitrate,
Manganese sulfate, manganese ammonium sulfate, manulfite
Cancer, manganese phosphate, manganese borate, manganese chlorate
Manganese perchlorate, manganese thiocyanate, formic acid
Ngan, manganese acetate, manganese oxalate, manganese citrate
Manganese lactate, manganese tartrate, man stearate
Cancer, manganese fluoride, manganese chloride, manganese bromide, iodine
Manganese oxide, manganese acetylacetonate, iron oxide
(Divalent, trivalent), iron trioxide, iron hydroxide (divalent, trivalent), salt
Iron iodide (2,3), iron bromide (2,3), iron iodide (2,3)
Trivalent), iron sulfate (divalent, trivalent), ammonium iron sulfate
(2,3), iron nitrate (2,3), iron phosphate (2,3)
(Valent), iron perchlorate, iron chlorate, iron acetate (divalent, trivalent),
Iron enoate (2,3), ammonium ammonium citrate (2,
Trivalent), iron oxalate (divalent, trivalent), iron ammonium oxalate
(2,3), CoO, Co _TwoO_Three, Co_ThreeO_Four, Li
CoO_Two, Cobalt carbonate, basic cobalt carbonate, hydroxide
Cobalt, cobalt sulfate, cobalt nitrate, cobalt sulphite
G, cobalt perchlorate, cobalt thiocyanate, oxalate
Baltic, cobalt acetate, cobalt fluoride, cobalt chloride,
Cobalt bromide, cobalt iodide, hexaamminecobalt
Complex salts (as salts, sulfuric acid, nitric acid, perchloric acid, thiocyanate
Acid, oxalic acid, acetic acid, fluorine, chlorine, bromine, iodine), nickel oxide
Kel, nickel hydroxide, nickel carbonate, basic nickel carbonate
Kel, nickel sulfate, nickel nitrate, nickel fluoride, salt
Nickel iodide, nickel bromide, nickel iodide, nickel formate
, Nickel acetate, nickel acetylacetonate, acid
Copper oxide (1,2), copper hydroxide, copper sulfate, copper nitrate, phosphoric acid
Copper, copper fluoride, copper chloride, copper ammonium chloride, copper bromide, iodine
Copper oxide, copper formate, copper acetate, copper oxalate, copper citrate, oxysalt
Niobium iodide, niobium pentachloride, niobium pentaiodide, nio monoxide
, Niobium dioxide, niobium trioxide, niobium pentoxide, oxalic acid
Niobium, niobium methoxide, niobium ethoxide, niobium
Propoxide, niobium butoxide, lithium niobate,
MoO_Three, MoO_Two, LiMo_TwoO_Four, Molybdenum pentachloride
, Ammonium molybdate, lithium molybdate
Ammonium molybdophosphate, molybdenum oxide acetylene
Ruacetonate, WO_Two, WO_Three, Tungstic acid, TA
Ammonium Nungsteate, Ammonium Tungstophosphate
Is raised.

Particularly preferred transition metal compounds used in the synthesis of the positive electrode active material in the present invention are TiO ₂ (preferably rutile type or anatase type), titanyl ammonium oxalate, MnO ₂ , Mn ₂ O ₃ , manganese hydroxide , Manganese carbonate, manganese nitrate, manganese ammonium sulfate, manganese acetate, manganese oxalate, manganese citrate,
CoO, Co ₂ O ₃ , Co ₃ O ₄ , LiCoO ₂ , cobalt carbonate, basic cobalt carbonate, cobalt hydroxide, cobalt oxalate, cobalt acetate, nickel oxide, nickel hydroxide, nickel carbonate, basic nickel carbonate, nickel sulfate , Nickel nitrate and nickel acetate.

Of these, particularly preferred combinations of lithium compounds and transition metal compounds include lithium hydroxide, lithium carbonate, lithium acetate, MnO ₂ , Mn ₂ O ₃ ,
Manganese hydroxide, manganese carbonate, manganese nitrate, Co
O, Co ₂ O ₃ , Co ₃ O ₄ , LiCoO ₂ , cobalt carbonate, basic cobalt carbonate, cobalt hydroxide, cobalt sulfate, cobalt nitrate, nickel oxide, nickel hydroxide,
Examples include nickel carbonate, basic nickel carbonate, nickel sulfate, nickel nitrate, nickel acetate, and combinations with titanium oxide (anatase or rutile type).

The alkali metal additives Na and K used in the positive electrode active material of the present invention are prepared from alkali metal compounds such as sodium carbonate, potassium carbonate, sodium hydroxide and potassium hydroxide as raw materials. It is added to a lithium compound and a transition metal compound, mixed, fired, and used for synthesis.

The negative electrode active material used in the present invention can be obtained by chemically inserting lithium ions into a negative electrode active material precursor of a transition metal oxide and / or a lithium-containing transition metal oxide. For example, it is preferable to insert lithium ions electrochemically or by a method of reacting with lithium metal, a lithium alloy, butyllithium, or the like. In the present invention, it is particularly preferable to electrochemically insert lithium ions into a transition metal oxide that is a negative electrode active material precursor. Among them, it is most preferable to electrochemically insert lithium ions into a lithium-containing transition metal oxide that is a negative electrode active material precursor. As a method of electrochemically inserting lithium ions, a lithium-containing transition metal oxide (referred to as a negative electrode active material precursor in the present invention) as a positive electrode active material,
It can be obtained by discharging an oxidation-reduction system (for example, an open system (electrolysis) or a closed system (battery)) composed of a nonaqueous electrolyte containing lithium metal and lithium salt as the negative electrode active material. Further, as another embodiment, a lithium-containing transition metal oxide as a positive electrode active material, a negative electrode active material precursor having a composition formula different from that of the positive electrode active material as a negative electrode active material, and an oxidation comprising a non-aqueous electrolyte containing a lithium salt are used. Most preferred is a method obtained by charging a reduction system (for example, an open system (electrolysis) or a closed system (battery)).

The amount of lithium ions inserted is not particularly limited, but is 27 to 1340 mA / g of the negative electrode active material precursor.
h (equivalent to 1 to 50 mmol) is preferred. In particular, 40-1
070 mAh (equivalent to 1.5 to 40 mmol) is preferred.
In addition, 54 to 938 mAh (corresponding to 2 to 35 mmol) is most preferable. The cut-off voltage of the charge-discharge cycle varies depending on the type and combination of the positive electrode active material and the negative electrode active material to be used, and thus cannot be uniquely determined. However, a voltage that can increase the discharge voltage and substantially maintain the cyclability. Is preferred.

The structure of the compound obtained by calcining according to the method of the present invention is analyzed on the basis of an X-ray crystal diffraction spectrum, and its chemical formula is inductively coupled plasma (ICP) emission spectroscopy. It was calculated based on the difference in weight of the powder before and after firing.

The oxide of the positive electrode active material used in the present invention may be crystalline or amorphous, but a crystalline compound is preferred.

As the negative electrode active material that can be used in conjunction with the present invention, lithium metal, lithium alloy (Al, A
1-Mn (U.S. Pat. No. 4,820,599), Al-
Mg (JP-A-57-98977), Al-Sn (JP-A-63-6742), Al-In, Al-Cd (JP-A-1-144,573), etc., and lithium ions or lithium metal Releasable calcined carbonaceous compounds (for example, JP-A-58-209, 864, JP-A-61-214,4)
17, 62-88, 269, 62-216, 17
0, 63-13, 282, 63-24, 555, 63-121, 247, 63-121, 257, 6
3-155,568, 63-276,873, 63
314,821, JP-A-1-204,361, 1-
221, 859, 1-274, and 360). The purpose of using the above lithium metal or lithium alloy together is
This is for inserting lithium ions into the battery, and does not use a dissolution / precipitation reaction of lithium metal or the like as a battery reaction.

A conductive agent, a binder, a filler and the like can be added to the electrode mixture. The conductive agent may be any electronic conductive material that does not cause a chemical change in the configured battery. Usually, natural graphite (scale graphite, flaky graphite, earthy graphite, etc.), artificial graphite, carbon black, acetylene black, Ketjen black, carbon fibers and metals (copper, nickel, aluminum, silver (JP-A-63-1))
48, 554)) One or a mixture of conductive materials such as powder, metal fiber and polyphenylene derivative (JP-A-59-20971) can be included. A combination of graphite and acetylene black is particularly preferred. Although the addition amount is not particularly limited, it is preferably 1 to 50% by weight, particularly preferably 2 to 30% by weight. For carbon and graphite, 2 to 15% by weight is particularly preferred.

Examples of the binder include starch, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, regenerated cellulose, diacetyl cellulose, polyvinyl chloride, polyvinyl pyrrolidone, and the like.
Tetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butadiene rubber, polybutadiene, fluoro rubber,
Polysaccharides such as polyethylene oxide, thermoplastic resins, polymers having rubber elasticity, and the like are used alone or as a mixture thereof. When a compound containing a functional group that reacts with lithium, such as a polysaccharide, is used, for example, it is preferable to add a compound such as an isocyanate group to deactivate the functional group. The amount of the binder added is not particularly limited, but is preferably 1 to 50% by weight, and particularly preferably 2 to 30% by weight. As the filler, any fibrous material that does not cause a chemical change in the configured battery can be used. Usually, fibers such as olefin-based polymers such as polypropylene and polyethylene, glass, and carbon are used. The amount of the filler added is not particularly limited, but is preferably 0 to 30% by weight.

As the electrolyte, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, , 3-dioxolane,
Formamide, dimethylformamide, dioxolan,
Acetonitrile, nitromethane, methyl formate, methyl acetate, phosphoric acid triester (JP-A-60-2397)
3), trimethoxymethane (JP-A-61-4,17)
0), dioxolane derivatives (JP-A-62-1577)
1, 62-22, 372, 62-108, 47
4), sulfolane (JP-A-62-31959), 3-
Methyl-2-oxazolidinone (Japanese Unexamined Patent Publication No.
61), a propylene carbonate derivative (Japanese Unexamined Patent Publication No.
290,069, 62-290,071), tetrahydrofuran derivatives (JP-A-63-32,872), diethyl ether (JP-A-63-62,166), 1,3-
A solvent obtained by mixing at least one or more aprotic organic solvents such as propane sultone (Japanese Patent Application Laid-Open No. 63-102,173) and a lithium salt soluble in the solvent, for example, LiC
10 ₄ , LiBF ₆ , LiPF ₆ , LiCF ₃ SO ₃ ,
_{LiCF 3 CO 2, LiAsF 6,} LiSbF 6, Li
B ₁₀ Cl ₁₀ (JP-A-57-74,974), lithium lower aliphatic carboxylate (JP-A-60-41773), L
It is composed of at least one kind of salt such as iAlCl ₄ , LiCl, LiBr, Li I, lithium chloroborane (JP-A-61-165957), lithium tetraphenylborate (JP-A-61-214376). . Among them, propylene carbonate or ethylene carbonate and 1,2
LiCF ₃ SO ₃ , LiClO ₄ , LiCl _{3 in} a mixture of dimethoxyethane and / or diethyl carbonate
An electrolyte containing BF ₄ and / or LiPF ₆ is preferred. The amount of these electrolytes to be added to the battery is not particularly limited, but can be used in a required amount depending on the amounts of the positive electrode active material and the negative electrode active material and the size of the battery. The volume ratio of the solvent is not particularly limited, but in the case of a mixture of propylene carbonate or ethylene carbonate and 1,2-dimethoxyethane and / or diethyl carbonate,
0.4 / 0.6 to 0.6 / 0.4 (the mixing ratio when both 1,2-dimethoxyethane and diethyl carbonate are used is 0.4 / 0.6 to 0.6 / 0.4). preferable. The concentration of the supporting electrolyte is not particularly limited, but is preferably 0.2 to 3 mol per liter of the electrolytic solution.

In addition to the electrolytic solution, the following solid electrolyte can be used. Solid electrolytes are classified into inorganic solid electrolytes and organic solid electrolytes. Well-known inorganic solid electrolytes include nitrides, halides, and oxyacid salts of Li. Among them, Li ₃ N, LiI, Li ₅ N
_{I 2, Li 3 N-LiI} -LiOH, LiSiO 4, L
iSiO ₄ -LiI-LiOH (JP-A-49-811.8)
_{99), xLi 3 PO 4 -} (1-x) Li 4 SiO
₄ (JP-A-59-60,866), Li ₂ SiS ₃ (JP-A-60-501,731), phosphorus sulfide compound (JP-A-62-82,665) and the like are effective. As organic solid electrolytes, polyethylene oxide derivatives or polymers containing the derivatives (JP-A-63-135,447), polypropylene oxide derivatives or polymers containing the derivatives, and polymers containing ion-dissociating groups (JP-A-62-163) 254, 30
2, 62-254, 303, 63-193, 95
4), a mixture of a polymer containing an ion-dissociating group and the above-mentioned aprotic electrolyte (U.S. Pat. Nos. 4,792,504 and 4,830,939; JP-A-62-222375;
2-22,376 , JP-A-1-95,117) and phosphoric ester polymers (JP-A-61-256,573) are effective. Furthermore, there is also a method of adding polyacrylonitrile to an electrolytic solution (Japanese Patent Laid-Open No. 62-278,774). Also, a method of using both inorganic and organic solid electrolytes (Japanese Patent Application Laid-Open No.
-1,768) are also known.

As the separator, an insulating thin film having a high ion permeability, a predetermined mechanical strength, and the like is used. Sheets or nonwoven fabrics made of olefin polymers such as polypropylene or glass fibers or polyethylene are used because of their resistance to organic solvents and hydrophobicity. The pore size of the separator is in a range generally used for batteries. For example, 0.01-10 μ
m is used. The thickness of the separator is generally used in the range for batteries. For example, a thickness of 5 to 300 μm is used.

It is known that the following compounds are added to an electrolyte for the purpose of improving discharge and charge / discharge characteristics. For example, pyridine (JP-A-49-10852)
5), triethyl phosphite (JP-A-47-4,387)
76), triethanolamine (JP-A-52-722.4)
25), cyclic ethers (JP-A-57-152,68)
4), ethylenediamine (JP-A-58-87,77)
7), n-glyme (JP-A-58-87,778), hexaphosphoric triamide (JP-A-58-87,779),
Nitrobenzene derivatives (JP-A-58-21428)
1), sulfur (JP-A-59-8,280), quinoneimine dye (JP-A-59-68,184), N-substituted oxazolidinone and N, N'-substituted imidazolidinone (JP-A-5
9-154,778), ethylene glycol dialkyl ether (JP-A-59-205,167), quaternary ammonium salt (JP-A-60-30,065), polyethylene glycol (JP-A-60-41,773). ), Pyrrole (JP-A-60-79,677), 2-methoxyethanol (JP-A-60-89,075), AlCl3 (JP-A-61-88,466), a monomer of a conductive polymer electrode active material ( JP-A-61-161,673), triethylene phosphoramide (JP-A-61-208,758), trialkylphosphine (JP-A-62-80,976), morpholine (JP-A-62-80, 977) and aryl compounds having a carbonyl group (JP-A-62-28667).
3), hexamethylphosphoric triamide and 4-alkylmorpholine (JP-A-62-217575), bicyclic tertiary amine (JP-A-62-217578), oil (JP-A-62-217578) -287,580), quaternary phosphonium salts (JP-A-63-121268), tertiary sulfonium salts (JP-A-63-121269) and the like.

Further, in order to make the electrolyte nonflammable, a halogen-containing solvent such as carbon tetrachloride or ethylene trifluoride chloride can be contained in the electrolyte. (Japanese Patent Laid-Open No. 48-36,
632) Carbon dioxide can be included in the electrolyte to make it suitable for high-temperature storage. (JP-A-59-1
34,567)

The mixture of the positive electrode and the negative electrode may contain an electrolytic solution or an electrolyte. For example, the ion conductive polymer and nitromethane (Japanese Patent Application Laid-Open No. 48-36,
33), and a method of incorporating an electrolytic solution (Japanese Patent Laid-Open No. 57-124,870) is known.

Further, the surface of the positive electrode active material can be modified. For example, the surface of a metal oxide is treated with an esterifying agent (JP-A-55-163,779) or treated with a chelating agent (JP-A-55-163,780), and a conductive polymer (JP-A-55-163,780) is used. 58-163,188, 59-14,
274), polyethylene oxide, etc.
97, 561). Further, the surface of the negative electrode active material can be modified. For example, an ion conductive polymer or a polyacetylene layer is provided (Japanese Patent Laid-Open No. 58-111,276), or LiCl
(JP-A-58-142,771).

As the current collector of the electrode active material, any electronic conductor that does not cause a chemical change in the battery constituted may be used. For example, for the positive electrode, in addition to materials such as stainless steel, nickel, aluminum, titanium, and calcined carbon, the surface of aluminum or stainless steel has carbon,
Nickel, titanium or silver treated, negative electrode, stainless steel, nickel, copper, titanium,
In addition to aluminum, calcined carbon, and the like, copper, stainless steel, whose surface is treated with carbon, nickel, titanium, or silver), an Al—Cd alloy, or the like is used. Oxidizing the surface of these materials is also used. The shape is
In addition to the foil, a film, a sheet, a net, a punched material, a lath body, a porous body, a foam, a molded body of a fiber group, and the like are used. The thickness is not particularly limited, but is 1 to 5
One having a thickness of 00 μm is used.

The shape of the battery can be applied to any of coins, buttons, sheets, cylinders, corners and the like. In coins and buttons, the mixture of the positive electrode active material and the negative electrode active material is used after being pressed into a pellet shape. The thickness and diameter of the pellet are determined by the size of the battery. In the sheet, cylinder, and corner, the mixture of the positive electrode active material and the negative electrode active material is
It is used after being coated, dried, dehydrated, and pressed on a current collector. The thickness, length and width of the coat are determined according to the size of the battery, and the thickness of the coat in a compressed state after drying is preferably 1 to 2000 μm. As a method for drying or dehydrating pellets and sheets, a commonly used method may be used, but in particular, vacuum, infrared, far infrared,
Electron beams, low-humidity air or the like can be used alone or in combination. The temperature is preferably from 80 to 350C.
Particularly, 100 to 250 ° C is preferable. The method of pressing pellets and sheets may be a commonly used method.
A mold press method and a calendar press method are preferred. The pressing pressure is not particularly limited, but is preferably 0.2 to 3 t / cm ² . Press speed of calender press method is 1-50m
/ Min is preferred. The pressing temperature is preferably from room temperature to 200 ° C. The mixture sheet is wound or folded and inserted into a can, the can and the sheet are electrically connected, an electrolytic solution is injected, and a battery can is formed using a sealing plate. At this time, the safety valve can be used as a sealing plate. A metal or alloy having electrical conductivity can be used for the can or the lead plate. For example, metals such as iron, nickel, titanium, chromium, molybdenum, copper, and aluminum or alloys thereof are used. A conventionally known compound or mixture such as asphalt can be used as the sealing agent for closing.

[0036]

The present invention will be described in more detail with reference to specific examples, but the present invention is not limited to the examples unless it exceeds the gist of the invention.

Example 1 (Preparation of electrode mixture and coin battery and charge / discharge test) As the positive electrode material, 82% by weight of a positive electrode active material, 12% by weight of flake graphite as a conductive agent, and The positive electrode mixture prepared by mixing fluoroethylene at a mixing ratio of 6% by weight was compression-molded to produce a positive electrode pellet (13 mmφ, 0.06 g), which was then dried in a dry box (dew point of −40 to −70 ° C.,
The sample was sufficiently dehydrated and dried for 2 hours or more on a far-infrared heater in dry air). For the negative electrode material, a lithium / aluminum alloy (thickness 0.7 mm, 15 mmΦ, 0.066
g) was used. A SUS316 net having a thickness of 80 μm was used as a current collector, and this was welded to positive and negative electrode cans for coin batteries. 1mol / liter Li as electrolyte
250 μl of PF ₆ (a mixed solution of equal volume of ethylene carbonate and diethylene carbonate) was used, and this was impregnated into a separator made of a microporous polypropylene sheet and a polypropylene nonwoven fabric. A positive electrode and a negative electrode material were set on the current collector, a separator was inserted between the positive electrode and the negative electrode, and the positive electrode and the negative electrode can were combined using a caulking machine in a dry box to produce a coin-type lithium-ion battery. . 0.75 mA / c using this lithium ion battery
A charge / discharge test was performed at a constant current density of m ² . All tests started with charging. The charge / discharge cycle performance was evaluated by setting the charge cutoff voltage to 4.5 V and the discharge cutoff voltage to 3.0 V, and cycling between 4.5 V and 3.0 V.

(Preparation of Active Material) Comparative Sample-1 Lithium carbonate and cobalt carbonate were mixed so that the atomic ratio of lithium to cobalt was 1.2: 1.0, and calcined in air at 900 ° C. for 6 hours. 3 ° C / mi
and cooled to obtain Li1.2 CoO2.1.

Comparative Sample-2 Lithium carbonate, sodium carbonate, and cobalt carbonate were mixed so that the atomic ratio of lithium, sodium, and cobalt was 1.1: 0.1: 1.0, and the mixture was heated at 900 ° C. in air. After firing for 6 hours, 3 ° C / mi
After cooling with n, Li1.1 Na0.1 CoO2.1 was obtained.

Comparative Sample-3 Lithium carbonate, cobalt carbonate and titanium oxide (anatase type) were mixed so that the atomic ratio of lithium, cobalt and titanium was 1.2: 1: 0.05, After firing at 900 ° C for 6 hours, 3 ° C
/ Min to obtain Li1.2Co0.95Ti0.05O2.1. The above comparative sample was assembled into a coin-type battery as a positive electrode pellet by the above method, and a charge / discharge test was performed.

As a sample of the present invention, lithium carbonate,
Sodium carbonate, cobalt carbonate, and titanium oxide (anatase type) are mixed in an automatic mortar so that the atomic ratio of the four elements of lithium: sodium: cobalt: titanium becomes the following composition ratio, and the air is heated at 900 ° C. for 6 hours. After firing, 3 ℃ /
Then, the mixture was cooled in a minimum time to synthesize a composite oxide containing four elements. The fact that sodium and titanium are incorporated as dopants in the structure of the composite oxide is that the X-ray diffraction spectrum shows that these metal oxides are present as impurities as oxides of sodium and titanium. No peak was observed, and at the same time, peaks indicating the presence of these metals were detected by atomic absorption analysis.

Positive electrode active material composition Comparative 1 Li1.2 Co1.0 O2.1 Comparative 2 Li1.1 Na0.1 Co1.0 O2.1 Comparative 3 Li1.2 Co0.95 Ti0.05O2 Invention 1 Li1.05 Na0.15 Co0 .92Ti0.08O2.1 Invention 2 Li1.1 Na0.1 Co0.95Ti0.05O2.1 Invention 3 Li1.12Na0.08Co0.95Ti0.05O2.1 Invention 4 Li1.12Na0.08Co0.97Ti0.03O2.1 Invention 5 Li1.16Na0.04Co0.97Ti0.03O2.1

The results of evaluating the charge / discharge characteristics and cycle performance of the above samples are summarized in Table 1. As is clear from the results, in the samples (Comparative Examples 2 and 3) in which Na was added as an alkali metal and Ti was used as a transition metal, respectively, to the active material having the composition of LiCoO ₂ (Comparative Examples 2 and 3), the capacity in the initial capacity or the cycle property was reduced. Although appearing as disadvantages, in the system containing both of these, the stabilization of the capacity in the cycling property and the stabilization of the discharge potential were observed, and it can be seen that the charge / discharge performance was remarkably improved.

Example 2 Instead of the negative electrode material (Li / Al) used in Example 1, 82% by weight of LiCoVO ₄ as a lithium-containing transition metal compound, 12% by weight of flaky graphite as a conductive agent, A negative electrode pellet (13 mmφ, 0.060 g) obtained by compression-molding a mixture obtained by mixing polyvinylidene fluoride at a mixing ratio of 6% by weight as a binder was sufficiently dried with a far-red heater in a dry box. Coin cells were prepared in the same manner as in Example 1 except that they were used as the negative electrode, and their charge / discharge performance and cycleability were evaluated.

As a result, although the cycle performance of the discharge capacity as a whole is inferior to the case where Li / Al is used for the negative electrode,
Regarding the effect of addition of Na and Na, the same tendency of improvement in cycleability (stabilization of potential and capacity) as in the results of Table 1 was obtained for the comparative sample, and the superiority of the positive electrode active material according to the composition of the present invention was confirmed. Was.

Reference Example-1 Manganese dioxide or nickel carbonate was used as a raw material for synthesis in place of the cobalt carbonate used in the synthesis in Example 1, and the temperature was 700 ° C to 900 ° C and 6 to 1 ° C.
Various kinds of composite oxides having the following compositions were prepared under the firing condition of 0 hour. Positive electrode active material composition reference 1 Li1.1 Na0.1 Mn1.92Ti0.08O4.1 reference 2 Li1.1 Na0.1 Mn1.95Ti0.05O4.1 reference 3 Li1.15Na0.05 Mn1.92Ti0.08O4.1 reference 4 Li1 .15Na0.05Mn1.95Ti0.05O4.1 Reference 5 Li1.06Na0.04Mn1.97Ti0.03O4.1 Reference 6 Li1.1 Na0.1 Ni0.92Ti0.08O2.1 Reference7 Li1.1 Na0.1 Ni0.95Ti0. 05O2.1 reference 8 Li1.15Na0.05Ni0.92Ti0.08O2.1 reference9 Li1.15Na0.05Ni0.95Ti0.05O2.1 reference10 Li1.08K0.02Co0.97Ti0.03O2.05 reference11 Li1.08K0.02Mn1. 97Ti0.03O4.05 Reference 12 Li1.08K0.02Ni0.97Ti0.03O2.05

Using the pellets of the active material as a positive electrode, the charge / discharge characteristics of a coin battery prepared using Li / Al for the negative electrode were evaluated in the same manner as in Example-1. As a result, with respect to the comparative samples to which the alkali metal (Na or K) or Ti was solely added, the improvement of the cyclability was confirmed particularly in the potential stability. In particular, the system in which the cycleability was remarkably improved was a system in which Na or K was added at 5% or less and Ti was added at 5% or less. When the effects of Co, Mn, and Ni, which are the central transition metals in the structural formula, were compared with each other, including the results in Table 1, the effect of the present invention was greatest when Co was used. there were.

The conclusion of the above test results, the particular greater effect of the present invention in improving cell performance and cycle properties is represented by the general formula Lix Nay Coz Tim Op smell <br/> Te, its amount of addition of these Are respectively 0.02 ≦ y ≦ 0.1,
This was the case where 0.02 ≦ m ≦ 0.10.

Table 1 Discharge capacity Discharge average voltage After 50 cycles After 50 cycles mAh V vs. potential maintenance rate (%) of capacity maintenance rate (%) of Li / Al Comparison 1 9.0 3.90 67.7 96. 0 Comparison 2 9.0 3.95 35.4 87.5 Comparison 3 8.9 3.90 67.5 99.8 Invention 1 8.9 3.92 68.8 98.5 Invention 2 9.1 3.95 75.5 99.5 Present invention 3 9.2 4.00 80.5 99.8 Present invention 4 9.2 3.98 80.3 99.7 Present invention 5 9.1 3.95 77. 7 99.5

[0050]

By using the positive electrode active material of the present invention, a lithium ion secondary battery having excellent charge / discharge characteristics, discharge potential and cycle characteristics was obtained.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-55-136131 (JP, A) JP-A-3-236173 (JP, A) JP-A-3-289049 (JP, A) JP-A-2- 139861 (JP, A) JP-A-5-74451 (JP, A) JP-A-5-67466 (JP, A) JP-A-5-54889 (JP, A) JP-A-4-267053 (JP, A) JP-A-3-201368 (JP, A) JP-A-5-67467 (JP, A) JP-A-56-147368 (JP, A) JP-A-1-120765 (JP, A) JP-A-62-90863 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01M 4/58 H01M 4/02 H01M 6/16 H01M 10/40

Claims (3)

(57) [Claims] 1. A secondary battery comprising a positive electrode, a negative electrode and a non-aqueous electrolyte, wherein the active material of the positive electrode has a chemical formula of LixNayCoz.
TimOp (0.8 ≦ x ≦ 1.3, 0.02 ≦ y ≦ 0.1,
0.8 ≦ z ≦ 1.0, 0.02 ≦ m ≦ 0.1, 0 ≦ p ≦ 2.
7 ) A non-aqueous electrolyte secondary battery comprising the composite oxide represented by the formula: 2. A composite acid containing Li, Co, and V as a negative electrode.
The compound is used as an active material,
The non-aqueous electrolyte secondary battery according to the above. 3. The non-aqueous electrolyte also comprises propylene carbonate.
Or mixed solvent containing ethylene carbonate and supporting salt?
2. The non-aqueous electrolyte according to claim 1,
Next battery.