JP2001351690A - Nonaqueous electrolyte cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively improve a safety at high temperature and to secure an excellent safety at charge and discharge. SOLUTION: A cathode contains lithium carbonate and lithium complex oxide shown by the formula LixM(1-y)AlyO2, (where; 0.05<=x<=1.10, 0.01<=y<0.10, M is an element chosen from transition metal), and the ratio of the content of lithium carbonate to the content of lithium complex oxide is 1 weight % or higher but less than 5 weight %.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-aqueous electrolyte battery.

[0002]

2. Description of the Related Art In recent years, remarkable progress in electronic technology has realized a reduction in size and weight of electronic devices one after another. Along with this, there is an increasing demand for batteries that are power sources to be further reduced in size, weight, and energy density. Conventionally, aqueous batteries such as lead batteries and nickel cadmium batteries have been the mainstream as batteries for general use. However, although these aqueous batteries have excellent cycle characteristics, they cannot be said to be sufficiently satisfactory in terms of battery weight and energy density.

Therefore, recently, non-aqueous electrolyte batteries having a high battery voltage, a high energy density and excellent cycle characteristics have begun to be used. A typical nonaqueous electrolyte battery is a lithium ion battery using a material capable of reversible lithium ion intercalation as an electrode material. Since such a lithium ion battery is excellent in energy density and charge / discharge cycle characteristics, it is expected to be used as a power supply for a portable device having relatively high power consumption.

However, in a lithium ion battery, an abnormal reaction such as decomposition of an electrolyte or an active material occurs at the time of overcharge, and the battery may generate heat or be damaged. For this reason,
In order to prevent thermal runaway at the time of overcharging, a lithium ion carbonate is added to the positive electrode mixture and a current interruption element mounted on the battery is operated by utilizing the generation of CO2 gas by an electrochemical decomposition reaction. Methods have been proposed (see, for example, JP-A-4-328278, JP-A-4-329268). In a battery in which lithium carbonate is added to the positive electrode, the safety valve can be easily operated by the generation of CO2 gas in the same manner as described above by using a safety valve, which is opened by increasing the internal pressure of the battery, instead of the current interrupting element.
Thermal runaway during overcharge can be prevented.

[0005]

However, when lithium carbonate is added to the positive electrode as described above, since the lithium carbonate and the electrolyte in the electrolyte cause an exothermic reaction, the safety of the battery at high temperatures is increased. It has been found that the battery may have an adverse effect such as a decrease in the battery capacity. It was also found that the addition of lithium carbonate does not always exert an effect on the improvement of safety at the time of overcharging, and that the addition varies depending on the amount added and the type of active material.

In view of the above, it is an object of the present invention to provide a battery using lithium carbonate, which effectively improves the safety at high temperatures and has excellent safety against overcharging. And

[0007]

According to the first invention of the present application, the general formula is Li _x M _(1-y) Al _y O ₂ (provided that 0.05 ≦ x ≦ 1.
10, 0.01 ≦ y <0.10, M is an element containing at least one element selected from transition metals. A non-aqueous electrolyte battery comprising a positive electrode containing a lithium composite oxide represented by the formula (1) and lithium carbonate.

As described above, by including a lithium composite oxide to which a specific amount of Al has been added and lithium carbonate in the positive electrode, the effect of preventing thermal runaway during overcharging due to the generation of CO 2 gas due to the addition of lithium carbonate is reduced. Without this, safety under high temperatures can be improved. Further, safety at the time of overcharging can be further improved, and the capacity of the battery is not reduced.

It is considered that such an effect is due to the following operation. In other words, in a battery in which lithium carbonate is added to the positive electrode, CO2 due to an electrochemical decomposition reaction during overcharge is reduced.
By using the generation of the two gases to activate the current cutoff element and the safety valve at an early stage, thermal runaway during overcharge can be prevented. However, since lithium carbonate and the electrolyte in the electrolyte cause an exothermic reaction, this destabilizes the lithium composite oxide and the like, and conversely reduces the safety of the battery when the battery is exposed to high temperatures. Cases arise. In contrast, the addition of aluminum to the lithium composite oxide improves the thermal stability of the lithium composite oxide, thereby offsetting the instability of the battery due to heat generation due to the addition of lithium carbonate. Can solve such a problem. Furthermore, when a lithium composite oxide to which aluminum is added is used, although the detailed mechanism is unknown, thermal runaway is less likely to occur than in the case of a combination with a conventional lithium composite oxide, and safety is improved. .

In the positive electrode active material Li _x M _(1-y) Al _y O ₂ , if the molar ratio of M to Al is too small, the thermal stability of the positive electrode active material itself does not improve, and If the amount is too large, the charge / discharge capacity of the positive electrode active material itself is greatly reduced, which is not preferable. M and Al in positive electrode active material
Thus, the molar ratio of 0.01 or more and 0.
Desirably less than 1.

The second invention of the present application is the non-aqueous electrolyte battery according to the first invention of the present application, wherein the ratio of the content of the lithium carbonate to the content of the lithium composite oxide is 1% by weight or more and 5% by weight or more. It is characterized by the following.

In the positive electrode to which lithium carbonate is added,
If the proportion of lithium carbonate contained in the positive electrode is too small,
Activating a current interrupting element or a safety valve utilizing the generation of CO2 gas due to an electrochemical decomposition reaction during overcharging cannot be sufficiently demonstrated. On the other hand, if the proportion of lithium carbonate is too large, the resistance of the positive electrode plate will increase and the discharge capacity will decrease, and the exothermic reaction between lithium carbonate and the electrolyte in the electrolyte will increase, and the thermal stability of the positive electrode active material itself will decrease. Even if improved, it becomes difficult to ensure safety at high temperatures.
For this reason, the added amount of each component is appropriately adjusted and used, but by setting the content in such a range, the effects of the present invention can be more reliably and remarkably exhibited.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be specifically described below.

According to the present invention, the general formula is Li _x M _(1-y) Al _y
O ₂ (however, 0.05 ≦ x ≦ 1.10, 0.01 ≦ y <
0.10 and M are elements containing at least one or more elements selected from transition metals. A non-aqueous electrolyte battery comprising a positive electrode containing a lithium composite oxide represented by the formula (1) and lithium carbonate, wherein the lithium composite oxide in the positive electrode acts as a positive electrode active material and lithium carbonate is CO 2 _It plays the role of generating gas.

In the general formula showing a lithium composite oxide, M is
Contains at least one element selected from transition metals
The elements are shown, but Co, Ni, and Mn are particularly desirable. example
A lithium composite that can be used in the present invention
As the oxide, Li_xCo_{( 1-y)}Al_yO_Two, Li_xNi
_(1-y)Al_yO_Two, Li_2xMn_{2 (1-y)}Al_2yO_Four, Li
_x(Co_1-ZNi_Z)_(1-y)Al_yO_TwoM of Co, Ni,
One composed of one type of transition metal element such as Mn, Co and N
i, two types of transition metal elements such as Ni and Mn, and Mn and Co
, Three types of transition metals such as Co, Ni and Mn
Those composed of elements, and also Li_xCo_{(1-y ー Z)}Al_y
Me_ZO_Two(Me is the element of at least one of the metal elements
And the same applies to the following), Li_xNi_{(1-y ー Z)}Al_yMe_Z
O_Two, Li_x(Co_1-aNi_a)_{(1-y ー Z)}Al_yMe_ZO_TwoEtc.
In addition to Co, Ni, and Mn transition metals, M
Metal elements such as Si, Ti, Sn, Mg, etc.
And at least one of them is added.
Also Li_xCo_(1-y)Al_yO_Two, Li_xNi_(1-y)Al
_yO_Two, Li_x(Co_1-ZNi_Z)_(1-y)Al_yO_Two, Li_xC
o_{(1-y ー Z)}Al_yMe_ZO_Two, Li_xNi_{(1-y ー Z)}Al_yMe_Z
O_Two, Li_x(Co_1-aNi_a)_{(1- y ー Z)}Al_yMe_ZO_TwoM
Are preferably those containing Co or Ni as
Those containing o are preferred.

For the preparation of the positive electrode, for example, a mixture obtained by mixing a lithium composite oxide powder, a lithium carbonate powder, and a conductive agent and a binder is formed into a paste, which is then put on a metal current collector such as aluminum. It is produced by coating and forming.

In this case, preferably, the mixing ratio is adjusted so that the ratio of the content of lithium carbonate in the positive electrode to the content of the lithium composite oxide in the positive electrode is 1% by weight or more and 5% by weight or less. .

As the conductive agent, for example, acetylene black, Ketjen black, furnace black or the like can be used alone or in combination.

As the binder, for example, polyvinylidene fluoride, polytetrafluoroethylene, a rubber-based polymer, a mixture of these with a cellulose-based polymer, a copolymer mainly containing polyvinylidene fluoride, or the like can be used. it can.

A negative electrode required for producing a nonaqueous electrolyte battery can be produced in the same manner as the above-mentioned positive electrode. The negative electrode active material used at this time is, for example, lithium metal, lithium aluminum alloy, or the like. It is possible to use carbon materials that occlude and release lithium, such as pyrolytic carbon, coke, graphite such as natural graphite and artificial graphite, fired organic polymer compounds, carbon fibers, and activated carbon, or polymer materials such as polypyrrole and polyacetylene. it can.

When a non-aqueous electrolyte is used as the non-aqueous electrolyte, examples of the electrolyte solvent include carbonates such as ethylene carbonate, propylene carbonate, diethyl carbonate, dimethyl carbonate and methyl ethyl carbonate, and γ-butyl lactone. , 1,2 dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, methyl propionate, and other organic solvents can be used alone or in combination of two or more.

As the solute of the non-aqueous electrolyte, for example, Li
ClO ₄ , LiAsF ₆ , LiPF ₆ , LiBF ₄ , LiC
F ₃ SO ₃ , LiN (CF ₃ SO ₂ ) _{2 and the} like can be used alone or in combination of two or more. Above all, LiP
F ₆ is the most desirable.

When the battery of the present invention is provided with a safety device such as a current interrupting element or a safety valve which operates by increasing the internal pressure of the battery, the operating pressure of the safety device is set to 3 to 2
The content is preferably set to be in a range of 5 kg / cm ² , and particularly, the ratio of the content of the lithium carbonate to the content of the lithium composite oxide is 1 wt% or more and 5 wt%.
The following case is more preferable. This is because the safety device can operate well.

[0024]

The present invention will be described in more detail with reference to the following examples.
However, it is limited by the following examples.
There is no
It goes without saying that it is possible to carry out the operation. <Example 1> [Positive electrode] A positive electrode having a different molar ratio of cobalt and aluminum.
5 kinds of polar active materials, LiAl _0.01Co_0.99O_Two, LiAl_0.03Co
_0.97O_Two, LiAl_0.05Co_0.95O_Two, LiAl_0.07Co_0.93O_Two, And Li
Al_0.10Co_0.90O_TwoTo 100% by weight of lithium carbonate
Are 0.5% by weight, 1.5% by weight and 3.5% by weight, respectively.
%, 5.0% by weight and 6.0% by weight, carbon-based conductive
Acetylene black, 100% by weight LiCo
3% by weight with respect to O2, and further as a binder
4% by weight of vinylidene fluoride (PVdF)
Add NMP (N-methylpyrrolidone) as a solvent
And kneaded to obtain a positive electrode paste. Next, this active material pace
Is applied to the electrode substrate made of aluminum foil and dried.
Then, a positive electrode for a lithium battery was obtained. Therefore made here
The type of positive electrode plate differs in the above molar ratio of cobalt and aluminum.
Five kinds of positive electrode active materials and five kinds with different amounts of lithium carbonate
And 25 types in total.

[Negative Electrode] Mesocarbon microbeads made of mesophase spheres generated during the carbonization process of pitch are used as lithium ion intercalation members,
A paste was prepared by kneading polyvinylidene fluoride (PVdF) as a binder, adding NMP as appropriate, and applying the paste to a copper foil substrate and drying the paste. The mesocarbon microbeads at this time had a particle size of 5 to 50 μm.
m, specific surface area is 1 to 10 m2 / g.

[Non-Aqueous Electrolyte] A mixed solvent of ethylene carbonate and diethyl carbonate at a volume ratio of 1: 1
Adjust what dissolved LiPF6 mol / 1L,
This was used.

[Separator] Thickness 25 μm, porosity 4
A 0% polyethylene microporous membrane was used as a separator. The separator is not particularly limited, and various types of conventionally used separators can be used.

[Lithium ion battery]
Separator, electrolyte solution, width 30mm height 48mm thickness 5
A non-aqueous electrolyte battery was prepared by storing the battery in a square-shaped battery container having a thickness of 2 mm. FIG. 1 shows a schematic configuration diagram of this battery. The main components of this battery are an electrode group 2 in which a positive electrode 3, a negative electrode 4, and a separator 5 are wound, a battery case 6, a safety valve 8, an electrolyte (not shown), and the like. In this example, 25 types of batteries differing only in the positive electrode plate were manufactured. The operating pressure of the safety valve was 10 kg / cm ² .

Comparative Example 1 A battery was manufactured in the same manner as in Example 1 except that lithium carbonate was not added. That is, five types of batteries were prepared which differed only in the molar ratio of cobalt and aluminum in the positive electrode active material.

Comparative Example 2 A battery was manufactured in the same manner as in Example 1, except that the molar ratio of cobalt and aluminum in the positive electrode active material was 100 to 0, that is, LiCoO 2 was used as the positive electrode active material. That is, five types of batteries differing only in the amount of lithium carbonate added to the positive electrode were manufactured.

Comparative Example 3 A battery was fabricated in the same manner as in Example 1 except that lithium carbonate was not added to the positive electrode and LiCoO 2 was used as the positive electrode active material.

[Initial Capacity Test] A charge and discharge test was performed on each of the ten batteries of the above Examples and Comparative Examples under the following conditions to measure the initial capacity of the batteries. Charge: 570 mA constant current 4.2 V constant voltage 5 h (25
C) Discharge: 570 mA constant current End voltage 3.0 V (25 ° C.) [Hot plate heating test] Five batteries each of the above Examples and Comparative Examples were charged under the following conditions.
The behavior of the battery was observed on a hot plate heated to 20 ° C. Charge: 570mA constant current 4.2V
Constant voltage 5 h (25 ° C.) [Overcharge test method]
Each was subjected to an overcharge test under the following conditions.

Continuous charging at 3 A constant current for 3 hours (25 ° C.) The results of the initial capacity test of the batteries in the examples and comparative examples are shown in Table 1 (Example), Table 2 (Comparative Example 1), and Table 3 (Comparative Example). It is shown in 2, 3). The test batteries were all 570 mA
h.

[0034]

[Table 1]

[0035]

[Table 2]

[0036]

[Table 3]

From Tables 1 and 2, there is no capacity degradation when the molar ratio of cobalt and aluminum in the positive electrode active material is up to 0.93: 0.07, but when the molar ratio of cobalt and aluminum becomes 0.9: 0.1. It can be seen that the capacity deterioration is large. This indicates that the molar ratio of cobalt to aluminum in the positive electrode active material is preferably such that aluminum is smaller than 0.1.

Next, in Examples and Comparative Examples,
Table 4 (Example) and Table 5 show the results of the hot plate heating test.
The results are shown in (Comparative Example 1) and Table 6 (Comparative Examples 2, 3). In the table,
In each case of "smoke or leak", the valve was operated, and in the case of "no abnormality", no valve was operated.

[0039]

[Table 4]

[0040]

[Table 5]

[0041]

[Table 6]

From Tables 4 and 6, it can be seen that the greater the amount of lithium carbonate added, the lower the safety. When the amount of lithium carbonate added is 6.5% by weight, the moles of cobalt and aluminum of the positive electrode active material are reduced. Regardless of the ratio, all batteries resulted in leakage or fuming. Further, the molar ratio of cobalt to aluminum of the positive electrode active material is 1: 0, that is, LiC
At the time of oO2, when the amount of lithium carbonate added to the positive electrode was 1.5% by weight or more, the battery leaked or smoked. This is presumably because the lithium carbonate and the electrolyte in the electrolyte caused an exothermic reaction, which led to thermal runaway of the battery.

However, from Tables 4 and 6, when the molar ratio of aluminum in the positive electrode active material is 0.01 or more, the thermal stability of the positive electrode active material at high temperatures is also improved. It also proved to be excellent in safety. From the above, the molar ratio of cobalt to aluminum in the positive electrode active material was such that aluminum was 0.01 or more and the amount of lithium carbonate added was 5% by weight.
It is understood that the following is desirable.

Table 7 (Example), Table 8 (Comparative Example 1), and Table 9 (Comparative Examples 2 and 3) show the results of overcharging in Examples and Comparative Examples. In the overcharge test, in the table, ○ indicates that there was no abnormality, and X indicates that there was liquid leakage or smoke. If there was no abnormality, the valve operated smoothly and there was no liquid leakage or smoke.

[0045]

[Table 7]

[0046]

[Table 8]

[0047]

[Table 9]

As can be seen from Tables 7, 8 and 9, when lithium carbonate was not added or the amount of addition was 0.5% by weight, the molar ratio of cobalt to aluminum in the positive electrode active material was 0.9:
It can be seen that all the batteries other than 0.1 led to liquid leakage or smoke. At 1.5% by weight or more, before the battery undergoes thermal runaway during overcharging, the safety valve is activated by the generation of CO2 gas due to the electrochemical decomposition reaction. Did not reach. From this result, it can be seen that it is desirable that the addition amount of lithium carbonate is 1% by weight or more.

As can be seen from the above results, when the lithium-cobalt composite oxide is used as the positive electrode active material, the molar ratio of aluminum is at least 0.01 and less than 0.1 in the molar ratio of cobalt to aluminum. The amount of lithium carbonate is 1% by weight or more and 5% by weight based on the amount of the positive electrode active material.
A battery having particularly excellent thermal stability and overcharge resistance can be obtained in the following cases.

In this embodiment, the case where the lithium cobalt composite oxide is used as the positive electrode active material has been described.
Similar effects can be obtained when other lithium composite oxides as described in the above embodiment are used. In this example, an example in which an electrolytic solution was used as an electrolyte was shown. However, a similar effect can be obtained in a case where a polymer electrolyte or a solid electrolyte is used as an electrolyte. Similar effects can be obtained with lithium batteries other than batteries.

[0051]

According to the present invention, it is possible to provide a battery excellent in the safety of the battery at high temperatures and the safety against overcharging.

[Brief description of the drawings]

FIG. 1 is a schematic structural view of a battery of an example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Battery main body 2 Electrode group 3 Positive electrode 4 Negative electrode 5 Separator 6 Battery case 7 Lid 8 Safety valve 9 Positive electrode terminal 10 Positive electrode current collecting lead

Claims (2)

[Claims] (1) The general formula is Li _x M _(1-y) Al _y O ₂ (provided that
0.05 ≦ x ≦ 1.10, 0.01 ≦ y <0.10, M
Is an element containing at least one or more elements selected from transition metals. A non-aqueous electrolyte battery comprising a positive electrode containing a lithium composite oxide represented by the formula (1) and lithium carbonate. 2. The non-aqueous electrolyte battery according to claim 1, wherein a ratio of the content of the lithium carbonate to the content of the lithium composite oxide is 1% by weight or more and 5% by weight or less.