JPH11307094A - Lithium secondary battery positive electrode active material and lithium secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a positive electrode active material for a lithium secondary battery, high in capacity, long in life, low in price, and excellent in heat stability at the time of delithiuming. SOLUTION: A positive electrode active material for a lithium secondary battery is used having a composition expressed by Li1-a Ni1-b-c-d Mnb Coc Md O2 (M: an additional minor element), where -0.15<=a<=0.10, 0.02<=b<=0.45, 0<=c<=0.50, and 0<=d<=0.20, and having a calorific value (y) of 0<=y<=30% relative to Lix NiO2 at heating temperatures ranging from 175 to 300 deg.C when the quantity (x) of lithium remaining after extraction is assumed to be 0.20<=x<=0.30. In the formula, M is one or more kinds of elements selected from among the group Ia excluding hydrogen and lithium, group IIa, group IIb, group IIIb, and group IVb in the periodic table of elements, and a group comprising transition elements excluding Ni, Co, and Mn.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a positive electrode active material for a lithium secondary battery and a lithium secondary battery which have excellent thermal stability and are used as a power source for portable electronic devices and electric vehicles.

[0002]

2. Description of the Related Art In recent years, with the expansion of the market in the field of portable electronic devices and personal computers, the size and weight of drive power supplies have been rapidly reduced, and further reductions in size, weight and density have been demanded. . On the other hand, not only the development of conventional small batteries, but also the movement toward the practical use of electric vehicles that require a large power supply is becoming active. These are linked to the improvement of the global environment centered on the reduction of harmful exhaust gas, and the safety is particularly important in addition to the small size, light weight and high density as the power supply function.

At present, non-aqueous lithium-ion batteries are widely used as power sources for portable electronic devices in addition to aqueous solutions such as nickel-cadmium batteries and nickel-metal hydride batteries. However, these aqueous batteries are excellent in cycle characteristics and cost, but cannot be said to be sufficiently satisfactory in terms of battery weight and energy density. On the other hand, demand for non-aqueous lithium-ion batteries has increased rapidly in recent years, but since expensive cobalt is used as the main component, they are more expensive than aqueous solutions, and have a higher volumetric energy density and safety. There is much room for improvement in this respect.

On the other hand, large batteries for electric vehicles include:
Nickel-metal hydride batteries are still being selected at the stage of development and trial production, especially from the viewpoint of safety. However, they cannot be said to be satisfactory in terms of battery weight and energy density like small batteries.

[0005] In addition, the installation of lithium ion batteries for electric vehicles has been studied, but the biggest issues are safety and cost. In particular, cobalt-based (Li
_1-x CoO ₂ ), nickel (Li _1-x NiO ₂ ), manganese (Li
_1-x Mn ₂ O ₄ ) All positive electrode active materials have thermally unstable crystal structures due to delithiation during charging. That is, overcharge
(De Li ≧ 0.6) When the battery is heated to 200 to 270 ° C., a rapid structural change and a subsequent oxygen release reaction proceed (J.
R. Dahn et al., Solid State Ionics , 69, 265 (1994)).
The heat generation behavior differs depending on the material system. For example, the heat generation start temperature shifts to a low temperature region in the order of nickel system <cobalt system <manganese system.

In the lithium-ion batteries that have attracted attention, cobalt-based cathode materials are often used for small batteries, but are difficult to apply as large batteries for electric vehicles in terms of price and resources.

It is said that nickel-based cathode materials have a high capacity but are most unstable in terms of cycle life and heat, and are difficult to apply in terms of safety. In order to improve this, trials such as slightly shifting the exothermic onset temperature and broadening the exothermic peak by replacing a part of nickel with other elements (for example, T. Ohzuku et al., J. Ele
ctrochem. Soc., 142, 4033 (1995), Japanese Patent Application Laid-Open No. 9-237631), but satisfactory results have not yet been obtained. Manganese-based positive electrode materials are promising in terms of price, but have many problems in terms of capacity and cycle characteristics.

[0008] As described above, the nickel system is expected to have the highest capacity among the three systems, but has a problem from the viewpoint of cycle life and thermal stability. However,
This problem is caused by the fact that in small consumer batteries, which use a relatively small amount of positive electrode active material, are inexpensive compared to cobalt-based batteries. System (for example, JP-A-9-259884), a nickel-manganese composite system (for example, JP-A-6-203829, JP-A-6-
No. 96768) and cobalt-manganese (for example, JP-A-3-201368 and JP-A-4-28162), and a dry-synthesis method is being studied as a production method.

As the wet complexing method from the raw material synthesis stage, a nickel-cobalt composite system (for example, JP-A-9-270257 and JP-A-8-236117), a nickel-manganese composite system (for example, JP-A-8-171910), a nickel-cobalt-manganese composite system (for example,
JP-A-9-222220 and JP-A-9-251854) have been proposed.

[0010]

[Problems to be Solved by the Invention] Nickel (LiNiO ₂ )
Is expected to have a higher energy density at a lower price than the cobalt-based (LiCoO ₂ ), but the above-mentioned attempts to compound the composition in which part of the nickel element is replaced with cobalt and / or manganese mainly improve cycle life and capacity. It was thought that it was not possible to expect a significant improvement in thermal stability during charge delithiation.

Therefore, in order to solve such a problem, it has been proposed to consider a raw material production method and to replace a part of the nickel element with aluminum which is an element other than manganese and cobalt.

[0012] As an examination of the raw material production method, for example, p.101 of the 38th Symposium on Battery Symposium states that ammonia / (nickel + cobalt) is added to a mixed aqueous solution of nickel nitrate and cobalt nitrate.
Add ammonia water so that the ratio becomes 3 and stir at 80 ° C for 3 hours. Drop 1 mol / l sodium hydroxide solution dropwise so as to maintain pH = 6.5 to 7.5, boil to remove ammonia, and wash with water , Filtered, dried and the resulting composite hydroxide Ni _0.85 Co
_0.15 (OH) ₂ and lithium hydroxide mixed, oxygen at 750 ° C
Bake for 0 minutes. LiNi _0.85 Co obtained in this way
_By increasing the particle size of _0.15 O ₂ to 2 μm or more, DTA (Differential Thermal Analysis:
(Differential thermal analysis) It is described that the exothermic peak shifts to a higher temperature side by about 7 ° C. as compared with fine particles of 1 μm or less.

Japanese Patent Application Laid-Open No. 9-237631 discloses that LiNi
_{1-xyz Co x Mn y Al} z when the O ₂ in the y = 0 0.15 ≦ x
≦ 0.25, 0 <z ≦ 0.15, or 0 <y ≦ 0.3, 0
≦ x ≦ 0.25,0 <z ≦ 0.15 , x + y ≦ 0.4 when producing a positive active material for a lithium secondary battery, characterized by a coprecipitation synthesized _{β-Ni 1-xy Co x} Mn y (OH ) _2, or _{β-Ni 1-xy Co x} Mn y OOH (0 ≦ x ≦ 0.25,0 ≦ y ≦ 0.
3) and Li sources such as LiOH, Li ₂ CO ₃ , LiNO ₃ and Al (OH) ₃ , Al ₂ O
₃・ Al ・ Ni ・ Co
-Mn-Al composite oxide is obtained.

The present invention proposes the effect of suppressing the displacement between the crystal layers of the positive electrode active material at the time of delithiation by adding cobalt and manganese, and improving the thermal stability by introducing inert points into the crystal lattice by adding aluminum. doing. The effect of suppressing heat generation during lithium removal by the presence or absence of the addition of aluminum is as follows: DSC (Differential Scanning Car
(Lorimetry: Differential scanning calorimeter) A figure is described in the specification as evidence that the exothermic peak is broad in the data.

However, although a sharp peak due to the compounding of aluminum becomes broad in data, it is hard to recognize that the total calorific value has been improved at the same level. Certainly, the broadening of the sharp exothermic peak slightly improves the risk of ignition, but it is not enough to control the exothermic peak behavior and the total calorific value required for the battery.

As another example, JP-A-4-22066 and JP-A-9-232002 disclose a composite oxide of a transition metal such as nickel or cobalt and a non-transition metal such as aluminum for a lithium secondary battery. It is shown to be used as a positive electrode active material. However, the relationship between the elements is not defined only by the provision of the total amount of transition metal, and in any invention, the quantitative relationship between the amount of transition metal and the added replacement element is the thermal stability, and the safety related thereto, and The important issue of affecting the cycle life has not been recognized.

SUMMARY OF THE INVENTION The present invention has been made to solve such problems, and has a high capacity, a long life, a low price, and an extremely excellent thermal stability during lithium removal from a lithium secondary battery. It is intended to provide a material and a lithium secondary battery.

From still another aspect, the present invention provides a positive electrode active material for a lithium secondary battery and a lithium secondary battery which are excellent in capacity, life and thermal stability as a large battery for driving an electric vehicle or the like. The purpose is to:

[0019]

Means for Solving the Problems As a result of intensive studies conducted by the present inventors to achieve such an object, a predetermined amount of a plurality of elements are uniformly mixed in a predetermined amount from the step of synthesizing a nickel-manganese-cobalt-based raw material. By skillfully combining a novel manufacturing method including a synthesis step with a method of mixing and firing with lithium salts, the groundbreaking positive electrode active material for lithium secondary batteries and lithium secondary battery with excellent capacity, life and thermal stability. The inventors have found that a secondary battery can be obtained, and have completed the present invention.

In addition, an electrochemical method and an acid treatment method using a disproportionation reaction are known for lithium removal. The former determines the amount of lithium removal by the charge capacity and the latter by the chemical analysis. be able to. In particular, in the case of a nickel-based material, since the heat generation amount greatly changes even if the exothermic peak position does not change due to the amount of lithium removal, it is meaningless unless the amount of heat generation is compared with a fixed amount of lithium removal, but as described above. Prepared composition formula: Li _1-a Ni _1-bcd Mn _b Co _c M _d O ₂
(M: trace addition element), -0.15 ≦ a ≦ 0.10, 0.02
In the case of a nickel-manganese-based material having a composition of ≦ b ≦ 0.45, 0 ≦ c ≦ 0.50, and 0 ≦ d ≦ 0.20, the residual lithium amount x
However, it has been clarified by the study of the present inventors that they show a substantially constant calorific value in the range of 0.20 ≦ x ≦ 0.30.
The inventor has found that the calorific value is less than 30% of the calorific value of Li _x NiO ₂ in the heating range of 175 to 300 ° C, and the present invention has been accomplished.

Here, the present invention relates to Li _1-a Ni _1-bcd Mn _b
In Co _c M _d O ₂ (M: trace addition element), -0.15 ≦ a ≦
It has a composition of 0.10, 0.02 ≦ b ≦ 0.45, 0 ≦ c ≦ 0.50, 0 ≦ d ≦ 0.20, and has a residual lithium content x in the range of 0.20 ≦ x ≦ 0.30 and a heating value y in the heating range of 175 to 300 ° C. y Is Li _x NiO ₂
Is a positive electrode active material for a lithium secondary battery, wherein 0 ≦ y ≦ 30% of the calorific value of the positive electrode.

According to a preferred embodiment of the present invention, M in the above general formula is Ia of the periodic table other than hydrogen and lithium.
, IIa, IIb, IIIb, and IVb,
And one or more elements selected from the group consisting of transition elements other than Ni, Co, and Mn. Further, from another aspect, the present invention is a lithium secondary battery using the positive electrode active material.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below in detail. However, the present invention is not limited to the following embodiments, and the present invention can be implemented by appropriately changing the gist of the present invention. can do.

First, the reason for limiting the composition in the present invention as described above will be described. FIG. 1 shows the composition formula: Li _1-a Ni
_The positive electrode active material having _1-bcd Mn _b Co _c M _d O ₂ is _{subjected to delithiation} by charging, and the composition formula is: Li _x Ni _1-bcd Mn
₆ is a graph showing the relationship between the residual lithium amount x and the heat generation / endotherm amount when _b Co _c M _d O ₂ is used.

As can be seen from FIG. 1, (i) the calorific value (structural change) shows a constant value in the range of the residual lithium amount x = 0.2 to 0.3, and (ii) the calorific value when the residual lithium amount x> 0.3. Appears small (small part subject to structural change), (iii) On the other hand, when the residual lithium content x <0.2, the calorific value is apparently smaller due to the endothermic decomposition to NiO accompanied by oxygen release (calorific value-endothermic amount) For the balance).

The unit of the chemical calorific value is generally ca
1 / g is used, and in the present invention, as shown in FIG. 2 described later, it can be easily obtained from the exothermic peak area in DTA. For example, the calorific value of lithium nickelate (LiNiO ₂ ) is 170 to 200 cal / g, though slightly different depending on the production method and the like.

FIG. 2 shows the composition formula: Li _1-a Ni _1-bcd Mn _b Co
The relationship between the amount of lithium (1-a) in _c M _d O ₂ and the discharge capacity is
It is a graph shown by setting a to the horizontal axis. The following points can be seen from FIG.

(1) If the amount of lithium a in the composition formula is larger than 0.10, that is, if Li <0.90, the formation of an oxide single phase other than Li (inhibiting charge / discharge, high reaction / Li transfer diffusion resistance) due to insufficient Li. Reduces the discharge capacity (≦ 15
0 mAh / g).

Here, 150 mAh / g is the theoretical capacity of LiCoO ₂
Calculated by charging / discharging up to 4.2 V for 4 mAh / g
The capacity is equivalent to Li 1.0 to 0.45, and is an index for practical use in the present invention. However, this discharge capacity varies depending on the charging / discharging conditions, and can be used even if it is less than 150 mAh / g if an application such as a space is selected. However, in the present invention, the output energy density (Wh / kg, Wh / l 15)
0 mAh / g or more is preferable.

(2) If a is smaller than -0.15, that is,
When Li> 1.15, the Li oxide phase is precipitated by excessive Li, which inhibits the battery reaction and reduces the discharge capacity (≦ 15
0 mAh / g).

FIG. 3 shows the composition formula: Li _1-a Ni _1-bcd Mn _b Co
_{In c} M _d O ₂ , a = −0.05, 0.02 ≦ b ≦ 0.45, c =
0.20, d = 0, ie composition example: Li _1.05 Ni
4 is a graph showing the relationship between the Mn composition molar ratio, the discharge capacity, and the calorific value ratio in (0.08 to _0.20 ) Mn (0 to 0.60) Co _0.20 O ₂ .

The following points can be seen from FIG. (1) When the amount of Mn b in the composition formula is larger than 0.45, 4
Spinel LiNi _0.5 Mn _1.5 O ₄ that does not contribute to charge and discharge in the V region
Is rapidly increased and the discharge capacity is reduced.

(2) On the other hand, in the LiNiO ₂ skeleton composite of the present invention, the effect of the Mn composite on the suppression of heat generation is extremely large.
When the amount b ≧ 0.02, the calorific value ratio is suppressed to 30% or less, which is the target index, and the calorific value approaches zero as the composite amount increases to 0.45.

It is considered that this is due to the layer structure and the skeleton stabilizing action of Mn ^{3+ having} a smaller ionic radius and stronger oxygen affinity than the skeleton Ni ³⁺ . In this specification, the calorific value ratio is LixNiO ₂ x = 0.
The calorific value ratio when the calorific value in the range of 175 to 300 ° C of 2 to 0.3 is set to 100.

FIG. 4 shows the composition formula: Li _1-a Ni _1-bcd Mn _b Co
_{In c} M _d O ₂ , a = −0.05, b = 0.30, 0 ≦ c ≦ 0.5
0, d = 0, that is, a composition example: Li _1.05 Ni (0.72
4 is a graph showing a relationship between a Co composition molar ratio, a discharge capacity, and a calorific value ratio in (.about.0.20) Mn _0.30 Co (0 to 0.60) O ₂ .

The following points can be seen from FIG. (1) When the amount c of Co in the composition formula is larger than 0.50, Li
A single phase of CoO ₂ precipitates, and the capacity due to the nickel skeleton structure decreases. In addition, since Co is a resource-poor and expensive material, it is not preferable to increase the Co content.

(2) On the other hand, although the exothermic peak slightly shifts to the high temperature side due to the Co composite in the LiNiO ₂ skeleton composite of the present invention, the effect of suppressing the exothermic is relatively small, and the value of the Co composite amount is substantially constant. Is shown. This is also because the Co ³⁺ ion is smaller than the Ni ³⁺ ion and thus easily forms a solid solution, and the oxygen affinity is Mn ³⁺ > Co ³⁺ > Ni ³⁺ .

FIG. 5 shows the composition formula: Li _1-a Ni _1-bcd Mn _b Co
In _{c M d O 2, a =} -0.05, b = 0.20, c = 0.1,
When 0 ≦ d ≦ 0.20, ie, composition example: Li _1.05 Ni
(0.70 ~ _0.20 ) Mn _0.20 Co _0.1 M (0 ~ 0.30) M = A in O ₂
1 is a graph showing a relationship between a composition molar ratio, a discharge capacity, and a calorific value ratio.

The following points can be seen from FIG. (1) When M = Al amount d in the composition formula is larger than 0.20, a by-product phase that does not contribute to charge and discharge is precipitated (Al → Al ₂ O ₃ , Li
AlO ₂ ) reduces the discharge capacity (≦ 150 mAh / g).

(2) The effect of suppressing the calorific value is greater by the Mn compound, but is extremely effective as a suppressing effect element at a low Mn content. The calorific value is further improved by the small amount of compound (d ≦ 0.2). You.

In the present invention, Li _x used for comparison of the calorific value is used.
NiO ₂ is a commercially available reagent such as lithium hydroxide (LiOH, H ₂ O)
And nickel hydroxide (Ni (OH) ₂ ) mixed at a Li / Ni ratio of 1.01 and molded to a diameter of 20 mm were placed in a tube furnace, and oxygen-aerated at 150 ° C. for 4 to 6 hours. 15 ° C
Temperature rise at 0 ° C / hour, and then up to 750 ° C at 50 ° C / hour
A material obtained by pulverizing and classifying a material cooled to 100 to 200 ° C./hour to room temperature at a temperature of 100 to 200 ° C./hour (250 mesh or less) and delithiating LiNiO ₂ to a residual lithium amount x, 0.20 ≦ x ≦ 0.30. As such, it can be used with good reproducibility.

As a general thermal behavior and reaction calorie measurement method, a precise heat capacity measurement method using adiabatic calorie is used in addition to DTA and DSC, but each has advantages and disadvantages. As a method for confirming the effect of the present invention, DSC (Differential Sc
nning Calorimetry: It is not necessary to use a differential scanning calorimeter, and a normal thermal analyzer (TG / DTA: Thermogravimetry-D)
(ifferential ThermalAnalysis, thermogravimetric / differential thermal analysis)
Is enough.

FIG. 8 is a diagram showing the charged state of DTA reported by the Battery Society of Japan (IBA Battery Technology Study Group, Taiwan, 1997).
This is the exothermic behavior of LiNiO ₂ , LiCoO ₂ , and LiMn ₂ O ₄ after delithium removal. LiNiO ₂ shows much greater exothermicity than other materials.

It should be noted that in the present invention, when adding a trace amount of the additive element M, the raw material is uniformly mixed and crystallized from the raw material stage at the atomic level together with the nickel, manganese, and cobalt elements, and the amount of the additive is defined within a predetermined range. It is to be.

As a method of compounding from the raw material stage, a precipitation method in which the pH is controlled to an alkaline side, which is used as a basic technology such as wastewater treatment, is well known, but the precipitation generation pH for each element differs greatly. Therefore, the final precipitate becomes a physical mixed state of hydroxides of the respective elements, and it is difficult to homogenize the elements at the atomic level. Especially high alkali like aluminum (pH ≧ 10.0
From the raw material stage, it is difficult to combine elements dissolved as complex ions on the (near) side, for example, as described in JP-A-9-237631, after synthesizing a Ni / Mn / Co composite hydroxide. Alternatively, a method of obtaining a composite oxide by mixing and firing aluminum oxide or aluminum hydroxide as a separate raw material together with a lithium source has been adopted.

To solve these problems, the inventors of the present invention have conducted intensive studies, and as a result, a synthesis method which has been found is that a sulfate aqueous solution of various elements and an ammonium bicarbonate aqueous solution to which a trace amount of ammonia is added are mixed at a predetermined temperature and pH. This is a method of adding simultaneously or alternately under conditions (neutral region) to grow crystals substantially concentrically and uniformly. According to this method, it is possible to easily perform the complexing of various elements at the raw material stage, which has been considered difficult so far.

On the other hand, in the present synthesis method, a dense amorphous composite can be obtained by setting the pH to the alkali side and adding an alkali such as lithium hydroxide instead of ammonium bicarbonate. It has been found that the same effect can be obtained by mixing and firing this with a lithium source and removing lithium as in the previous synthesis method. The composite raw material composition obtained in this case is not a so-called pure carbonate, for example, 2NiCO ₃・ 3Ni (OH) ₂・
It seems that a double salt having a complex composition such as 4H ₂ O was formed.

Therefore, by increasing the pH range as in the latter case,
In the present invention, the method of increasing the hydroxide generation ratio of the double salt is referred to as a hydroxide method (abbreviated as a water method), and the former method mainly using carbonate is referred to as a carbonate method (abbreviated as a charcoal method). Distinguish.

The charcoal method is characterized by the fact that the crystal growth is of a fixed shape and the water method is of an indefinite shape. In any case, the stabilization of the structure by uniform mixing at the raw material stage is a feature of the present invention. This is considered to be the main cause of the effect.

In the prior art relating to this point, there is a method disclosed in JP-A-1-294364 other than the above-mentioned precipitation method. This publication discloses Li _x (Co _1-y Ni _y ) O ₂ , x = 0 to 1,
y = 0.5 to 0.9 nickel and cobalt chloride as a method to obtain a composite material having the composition _{(NiCl 2 · 6H 2 O +} CoCl 2 · 6H 2 O) saturated with carbon dioxide gas in the aqueous solution, left for both the addition of sodium bicarbonate solution It describes a method in which the precipitate is precipitated, washed with water, dried in argon gas at 140 ° C., and calcined with lithium carbonate. The present invention is to dissolve Ni in LiCoO ₂ to lower the open circuit voltage to obtain a large charge / discharge capacity at a low voltage of 4 V or less. The crystallization process is quite different.

The present inventors have attempted to combine various elements and evaluate characteristics using the above-described new compounding method. As a result, in the composition of Li _1-a Ni _1-bcd Mn _b Co _c M _d O ₂ (M: trace addition element), −0.15 ≦ a ≦ 0.10, 0.02 ≦ b ≦ 0.
45, 0 ≦ c ≦ 0.50, 0 ≦ d ≦ 0.20, preferably,
M is hydrogen, group Ia of the periodic table other than the lithium element,
By defining at least one member selected from the group consisting of Group IIa, Group IIb, Group IIIb, and Group IVb, and transition elements other than Ni, Mn, and Co, the residual lithium content is 0.20%.
It was found that the calorific value y in the heating range of 175 to 300 ° C. when ≦ x ≦ 0.30 was 0 ≦ y ≦ 30% with respect to Li _x NiO ₂ . In other words, such a heat generation characteristic and a stable structure are equivalent.

Although the effect manifestation mechanism of the present invention is not clear, as already described, a dense crystal growth process and structural stabilization in combination with atomic level mixing at the raw material stage greatly contribute to improvement in thermal stability. Think that you are. Therefore, in producing the positive electrode active material according to the present invention, there is no particular limitation as long as the production method can satisfy the mechanism of exhibiting the effects of the present invention.

The lithium secondary battery according to the present invention comprises Li
_1-ax Ni _1-bcd Mn _b Co _c M _d O ₂ (However, -0.15 ≦ a ≦
0.10, 0.02 ≤ b ≤ 0.45, 0 ≤ c ≤ 0.50, 0 ≤ d ≤ 0.20, composed of a positive electrode composed of a positive electrode active material mainly composed of a composition, a negative electrode composed of lithium metal or a carbon material, and a non-aqueous electrolyte. You.

According to a preferred embodiment of the present invention, M is hydrogen,
Other than lithium element, other than Ia group,
One or more elements selected from the group consisting of Group IIa, Group IIb, Group IIIb, and Group IVb, and transition elements other than nickel, manganese, and cobalt. Examples of these elements are as follows.

Group Ia: Na, K, Rb, Cs, Fr Group IIa: Be, Mg, Ca, Sr, Ba, Ra Group IIb: Zn, Cd, Hg, Cf Group IIIb: B, Al, Ga, In, Tl Group IVb: C, Si, Ge, Sn, PbThe negative electrode used in the lithium secondary battery according to the present invention uses lithium metal in the examples,
Such a negative electrode active material may be any as long as it can dope and undope lithium.
Pyrolyzed carbons, cokes (pitch coke, needle coke, petroleum coke, etc.), graphites, glassy carbons, organic polymer compound fired bodies (phenolic resin, furan resin, etc.) And carbonaceous materials such as carbon fibers and activated carbon, and polymers such as polyacetylene and polypyrrole in addition to metallic lithium and lithium alloys (for example, lithium-aluminum).

As the electrolyte, a non-aqueous electrolyte in which a lithium salt is used as an electrolyte and dissolved in an organic solvent at a concentration of 0.5 to 1.5 mol / liter is used. Here, the organic solvent is not particularly limited, for example, propylene carbonate, ethylene carbonate, butylene carbonate, γ-butyrolactone, dimethyl carbonate, ethyl methyl carbonate, an acetate compound, a propionate compound, a diacetate ester There are compounds, dimethoxyethane, diethoxyethane, dimethoxypropane, diethoxypropane, tetrahydrofuran, dioxolane and the like, alone or in combination of two or more.

Examples of the electrolyte include lithium perchlorate, lithium trifluoromethanesulfonate, lithium tetrafluoroborate, lithium hexafluorophosphate, lithium hexafluoroarsenate and the like.

The shape of the non-aqueous lithium secondary battery according to the present invention is not particularly limited, and may be any of a coin battery, a cylindrical spiral battery, a flat rectangular battery, an inside-out cylindrical battery, and the like. It is also applicable to batteries. Although the present invention refers to a small battery, it is particularly suitable for a large battery from the viewpoint of safety by suppressing heat generation.

[0059]

[Example 1] Production of raw material composite material First, 26.9 kg of nickel sulfate, 5.0 kg of manganese sulfate, and 6.6 kg of cobalt sulfate were added to pure water so that the molar ratio of Ni-Mn-Co was 0.65-0.20-0.15. To 100 liters (A
Liquid). On the other hand, 14.7 kg of ammonium bicarbonate was dissolved in pure water, and 11.8 liters of concentrated ammonia water was dissolved and diluted in pure water.
100 liters (solution B).

Next, 15 liters of preliminary water was placed in a stirring reaction vessel of about 300 liters, and the temperature was raised by heating, and the above-mentioned reaction solutions A and B were reacted at a flow rate of several liters / minute for about 12 hours by a quantitative pump. It was added alternately into the tank. After the completion of the addition of the reaction solution, the mixture was kept stirred for about 1 hour to promote further crystal growth.
Thereafter, the reaction product was filtered and washed with water, and then dried overnight to obtain 18.6.
kg of complex carbonate was obtained.

Production of lithium composite oxide 13.4 kg of the composite carbonate obtained above and 2.85 of lithium hydroxide
kg was crushed and mixed, further molded, and fired at 840 ° C. for 24 hours in an electric furnace through which oxygen gas was passed. After the fired product was cooled to room temperature, it was pulverized and classified to obtain about 10 kg of a product having a predetermined particle size or less (a positive electrode active material for a lithium secondary battery). The pulverization classification was performed in a dry atmosphere.

The battery characteristics and thermal stability of the obtained lithium composite oxide were measured by the methods described below, and the obtained results are shown in Table 1.

Preparation and Test of Battery To 100 parts by weight of the positive electrode active material obtained as described above, 15 parts by weight of acetylene black as a conductive material and 10 parts by weight of a fluororesin powder as a binder were added, and mixed well. And rolled to about 400 μm with a roll, dried at 150 ° C., and punched out to a predetermined diameter to produce a positive electrode.

On the other hand, a metal lithium foil punched to a predetermined size was rolled into a current collector mesh to form a negative electrode, and a 6-foil solution of a mixed solution of ethylene carbonate (EC) and dimethyl carbonate (DMC) (volume ratio 1: 2) was prepared. Lithium phosphide (LiPF ₆ )
Was used as an electrolyte, and a secondary battery shown in FIG. 6 was assembled.

In FIG. 6, reference numeral 1 denotes a positive electrode, 2 denotes a positive electrode current collector made of stainless steel, and the positive electrode 1 and the current collector 2 are integrated with each other. Spot welded. 4 is a negative electrode made of metallic lithium,
Reference numeral 7 denotes a separator made of a polypropylene nonwoven fabric, which is impregnated with the electrolytic solution. Reference numeral 8 denotes an insulating packing. The battery dimensions are 20.0 mm in diameter and 1.6 mm in depth.

Using the batteries prepared as described above, charge / discharge was repeated at a charge / discharge current of 1 mA / cm ^{2 at} a charge end voltage of 4.2 V and a discharge end voltage of 3.0 V, and charge / discharge characteristics up to 50 cycles were confirmed.

The results are shown only with the initial discharge capacity.
This was expressed in terms of unit weight-equivalent discharge capacity (mAn / g) of the active material in the first cycle. A discharge capacity of 150 mAn / g or more was judged to be acceptable.

Thermal stability test Using the battery having the above configuration, 4.2 V at a current density of 1 mA / cm ²
Charge up to constant current up to 4.2V constant voltage
The battery was charged by a constant current + constant voltage method for charging for 15 hours, and lithium was extracted from the positive electrode active material. The amount of lithium extracted is the theoretical capacity calculated from the molecular weight of the active material
[(1g active material / molecular weight) × (96500 coulomb / 3600) × 10
[00 mAh / g] or the number of moles of lithium analyzed for the active material after charging.

After charging the battery with a constant current and a constant voltage, the dew point of the battery is approximately 50 ° C.
The positive electrode sheet was taken out by disassembly in a glove box adjusted to a humidity, and washed three times in 100 ml of an acetone solvent to remove an attached electrolyte, and then left standing on a filter paper and dried. After drying, the positive electrode was peeled off from the stainless steel mesh constituting the current collector, and a platinum container (capacity 0.05
ml, dimensions 5φ × 2.5 mm) are filled with 40 mg in terms of the positive electrode active material. The thermal analysis measurement was performed from room temperature to 600 ° C. at a heating rate of 5 ° C./min using a TAS200 differential thermal balance made by Rigaku. The measurement was carried out by differential thermal analysis (DTA: Differ
TG: Thermal Thermal Analysis)
rmogaravimetry).

Processing of Thermal Stability Data Standard sample LiNiO ₂ from which the exothermic peak area appearing between 175 ° C. and 300 ° C. of the DTA data of the positive electrode active material from which lithium was extracted from 0.20 to 0.30 of residual lithium was delithiated in the same amount. Was compared with the exothermic peak area. For the area at this time, for example, as shown in FIGS. 7 (a) and 7 (b), the portion above the baseline before and after the heat generation (heat generation side) in the enlarged copy at the same ratio as the standard sample was cut out, and four digits after the decimal point The weight was determined by the integral method on the figure and compared with the heat generation data of the standard sample.

FIG. 7 (a) is TG • DTA data of the standard sample LixNiO _{2 with} the remaining lithium amount x = 0.05, and shows the decomposition (weight loss) to NiO accompanied by the endothermic oxygen release immediately after heat generation. . FIG. 7 (b) shows the residual lithium content of the same material x = 0.25
This is an example of TG / DTA data in the above.

Preparation of Thermal Stability Standard Sample 48.09 g of a nickel hydroxide reagent Ni (OH) ₂ (Ni61.0%) having a chemical purity of 96.4% manufactured by Wako Pure Chemical Industries, Ltd. and a Li / Ni ratio = 1.01 equivalent of reagent-grade dehydrated lithium hydroxide (at 120 ° C
After dewatering for 16 hours, keep tightly closed) After mixing 12.09 g in a mortar for 10 minutes, crush the vessel vessel (SUS304, inner diameter 140 φmm depth 49)
(mm, space volume: 340 ml) and mixed and crushed by a vibration vessel for 3 minutes. After crushing, immediately transfer the whole amount to a mortar and mix and disintegrate for 1 minute.
Four pellets were prototyped at 1 ton / cm ² in a SUS mold.

Four prototype pellets were placed in the center of a SUS310S boat and fired using a tubular electric furnace (60φ × 600 mm) while flowing oxygen gas (linear velocity ≧ 1 cm / sec). Initially, purge with oxygen at 150 ° C for 6 hours, then speed up to 600 ° C
The temperature rises at 150 ° C / hour, and then rises to 750 ° C at 50 ° C / hour.
After holding at 750 ° C. for 24 hours, the temperature was lowered to room temperature at 200 ° C./hour, and the sample was stored in a desiccator.

The baked sample was pulverized and classified using a mortar and a sieve net (250 mesh, all passed through 74 μm or less) and in a glove box filled with argon gas. All the samples were placed in a plastic container protected from moisture and placed in a desiccator. Saved. The thermal stability measurement after delithiation of the obtained standard sample LiNiO ₂
The test was performed by the above-mentioned method (thermal stability test method).

[Example 2] Nickel sulfate 2 was used in the same manner as in Example 1 so that the molar ratio of Ni-Mn-Co was 0.65-0.20-0.15.
8.5 kg, manganese sulfate 5.3 kg and cobalt sulfate 7.0 kg were dissolved in pure water to make 100 liter. 12.5 liters of concentrated ammonia water was added thereto, and the mixture was stirred while controlling the temperature.
Next, an aqueous solution of lithium hydroxide and a mixed solution of ammonium bicarbonate having a predetermined concentration were added little by little so that the pH was 8.0 to 10.0, and the mixture was reacted for about 8 hours. Filtration of the resulting solid
After washing with water, drying was carried out all day and night to obtain 14.9 kg of a composite hydroxide (including a double salt).

10.4 kg of the composite hydroxide obtained above and 2.85 kg of sodium hydroxide were pulverized and mixed, and further molded,
It was calcined at 800 ° C. for 24 hours in an electric furnace through which oxygen gas was passed. After cooling the fired product to room temperature, it is pulverized and classified and the product is smaller than a specified particle size (Positive electrode active material for lithium secondary battery) Approx. 10 kg
I got The pulverization classification was performed in a dry atmosphere.

The battery characteristics and thermal stability of the obtained lithium composite oxide were measured by the above-mentioned method, and the obtained results are also shown in Table 1.

Example 3 In accordance with Examples 1 and 2, various cathode materials having a composition of Li _1-a Ni _1-bcd Mn _b Co _c M _d O ₂ (M: trace addition element) were prepared. Then, a similar characteristic test was performed. The results are summarized in Tables 2 to 4.

In the table, the term “charcoal method” in the item “classification” refers to the case where a composite carbonate was produced in accordance with Example 1, and the term “water method” refers to the method in the example. 2 shows a case where a composite hydroxide was produced according to 2.

[0080]

[Table 1]

[0081]

[Table 2]

[0082]

[Table 3]

[0083]

[Table 4]

[0084]

As described above, according to the present invention, a positive electrode active material for a lithium secondary battery having a high capacity, a long life, a low price, and extremely excellent thermal stability at the time of lithium removal can be obtained. However, it can also be used for large batteries for electric vehicles, and is of great practical significance in terms of expanding applications of lithium ion secondary batteries.

[Brief description of the drawings]

FIG. 1 is a graph showing a relationship between a residual lithium amount x and a heat generation / endotherm amount.

FIG. 2 is a graph showing the relationship between the lithium content and the discharge capacity in the composition formula.

FIG. 3 is a graph showing a relationship between a composition molar ratio of Mn, a discharge capacity, and a calorific value ratio.

FIG. 4 is a graph showing a relationship between a Co composition molar ratio, a discharge capacity, and a calorific value ratio.

FIG. 5 is a graph showing the relationship between M = Al composition molar ratio, discharge capacity, and calorific value ratio.

FIG. 6 is a cross-sectional view showing a configuration of a coin-type lithium secondary battery to which the present invention is applied.

FIG. 7 is a graph showing an example of TG / DTA data in the thermal stability measurement. FIG. 7 (a) is TG / DTA data of the standard sample LixNiO _{2 with} the remaining lithium amount x = 0.05.
(b) is the TG · DT when the remaining lithium amount of the same material x = 0.25
This is an example of A data.

FIG. 8 LiNiO ₂ and Li after charging (elimination of lithium) by DTA
₄ is a graph showing a known measurement example of CoO ₂ and LiMn ₂ O ₄ .

Continuing on the front page (72) Inventor Kimifumi Yamato 272 Taguchi, Myokokogen-cho, Nakakubijo-gun, Niigata Chuo Denki Kogyo Co., Ltd. Inside the corporation

Claims (3)

[Claims] (1) In Li _1-a Ni _1-bcd Mn _b Co _c M _d O ₂ (M: trace addition element), -0.15 ≦ a ≦ 0.10, 0.02 ≦ b ≦
0.45, 0 ≦ c ≦ 0.50, 0 ≦ d ≦ 0.20, and when the residual lithium amount x after drawing is 0.20 ≦ x ≦ 0.30, the heat value y in the heating temperature range of 175 to 300 ° C. A positive electrode active material for a lithium secondary battery, wherein 0 ≦ y ≦ 30% with respect to Li _x NiO ₂ . 2. In the general formula, M is hydrogen, an element other than lithium element, Periodic Table Group Ia, Group IIa, Group IIb, Group IIIb.
The positive electrode active material according to claim 1, wherein the positive electrode active material is one or more elements selected from the group consisting of Group IVb, Group IVb, and transition elements other than Ni, Co, and Mn. 3. A lithium secondary battery using the positive electrode active material for a non-aqueous electrolyte according to claim 1.