JP2003242963A - Battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a battery which is improved in safety in the external destruction test or the like without sacrificing the battery performance. <P>SOLUTION: This is a battery which houses in a packaging body a flat lamination type battery element that laminates plural layers of a unit battery element comprising a flat-shape positive electrode made of a collector and an electrode material layer containing an active material, a flat-shape negative electrode made of a collector and an electrode material layer containing an active material, a separator, and an electrolyte. Out of the unit battery elements constituting the flat lamination type battery element, the thickness of the electrode material layer of at least one of the positive electrode and the negative electrode in the first unit battery element in which short-circuit of the positive electrode and negative electrode may happen firstly by an impact from the outside is made thinner than at least one of the thickness of the electrode material layer of the positive electrode and negative electrode in the unit battery elements other than the first unit battery element. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a battery, and more particularly to a battery having excellent battery characteristics and improved safety in heating, external breakdown and the like.

[0002]

2. Description of the Related Art A battery is usually a plate-shaped positive electrode composed of a current collector and an electrode material layer containing an active material, and a plate-shaped negative electrode composed of a current collector and an electrode material layer containing an active material. And a flat plate-shaped separator interposed between the positive electrode and the negative electrode, and is formed on the basis of a unit battery element formed by impregnating each of the positive electrode, the negative electrode and the separator with an electrolyte. A battery having a flat plate shape in which a flat plate laminated battery element formed by stacking the unit battery elements is housed in an exterior body is widely used as, for example, a lithium secondary battery. In particular, since the flat plate type lithium secondary battery using a laminate film as the outer package is lightweight, it is expected to be adopted in the future.

Batteries are required to have high performance battery characteristics such as large capacity and ability to drive devices for a long time.
In addition to this, since the application of the device in which the battery is used is wide-ranging, it is also possible to prevent the battery from igniting or exploding even if the device used is accidentally shocked and destroyed. is important. In order to ensure the safety of the battery against such an unexpected impact, for example, in a lithium secondary battery, as one of the external destruction tests, a nail penetration test, that is, a predetermined direction in the thickness direction of the flat plate type lithium secondary battery is used. Intruding a size nail to destroy the lithium secondary battery,
At that time, a test for observing phenomena such as temperature rise, smoke generation, and ignition, and thereby evaluating the safety when the lithium secondary battery is destroyed from the outside is conducted. Also, as another test of the external destructive test, an external impact test, that is, a drop,
A test is conducted to evaluate the safety of the lithium secondary battery by observing phenomena such as temperature rise, smoke emission, and ignition when the lithium secondary battery is impacted from the outside by a hammer or the like.

Heretofore, in the field of lithium secondary batteries, proposals such as devising the material of the electrolytic solution have been made as a method of enhancing the safety in the above tests.
However, there is a problem that the improvement of the safety by the above-mentioned proposal often causes the performance of the battery to be relatively lowered, and another method for enhancing the safety is demanded.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object thereof is to provide a battery with enhanced safety against external damage without impairing battery performance. is there.

[0006]

The present inventors have found that among the unit battery elements constituting the flat plate type battery element, the short-circuit current in the unit battery element in which the short circuit between the positive electrode and the negative electrode first occurs due to an external impact. By suppressing the heat generation due to the heat generation and the heat generation due to the self-decomposition reaction of the active material in the electrode material layer accompanied therewith, even when the battery is destroyed by an external impact,
The present invention has been completed by finding that the battery does not ignite or explode.

That is, the gist of the present invention is to provide a plate-shaped positive electrode composed of a current collector and an electrode material layer containing an active material, and a plate-shaped negative electrode composed of a current collector and an electrode material layer containing an active material. In a battery in which a flat-plate laminated battery element in which a plurality of unit battery elements having a separator and an electrolyte are laminated is housed in an outer package, a positive electrode and a negative electrode of the unit battery element constituting the flat-plate laminated battery element due to an external impact The thickness of the electrode material layer of at least one of the positive electrode and the negative electrode in the first unit battery element where a short circuit with the first occurs is the thickness of the electrode material layer of the positive electrode and the negative electrode in the unit battery element other than the first unit battery element. A battery characterized by being thinner than at least one of

In the present invention, among the unit battery elements constituting the flat plate type battery element, an impact from the outside causes
The thickness of the electrode material layer of at least one of the positive electrode and the negative electrode in the first unit battery element in which a short circuit between the positive electrode and the negative electrode first occurs is defined as the electrode material layer of the positive electrode and the negative electrode in the unit battery element other than the first unit battery element. When at least one of the positive electrode and the negative electrode of the first unit battery element is short-circuited, the heat generated by the short-circuit current flowing through the battery and the electrode material layer caused by the heat generation The heat generation due to the self-decomposition reaction of the active material contained in can be significantly reduced. As a result, the battery does not ignite or explode, and the safety of the battery is ensured.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION 1. In the present invention, a plate-shaped positive electrode comprising a current collector and an electrode material layer containing an active material, and an electrode containing a current collector and an active material are provided. A battery in which a flat plate-type negative electrode consisting of a material layer, a separator and a flat plate-type battery element having a plurality of unit battery elements having an electrolyte are housed in an outer package, among the unit battery elements constituting the flat-plate type battery element The thickness of the electrode material layer of at least one of the positive electrode and the negative electrode in the first unit battery element in which a short circuit between the positive electrode and the negative electrode first occurs due to an impact from the outside, and the positive electrode in the unit battery element other than the first unit battery element is And thinner than at least one of the film thicknesses of the electrode material layer of the negative electrode. With such a battery structure, even if the battery is destroyed from the outside, the battery will not ignite or explode, and the reason why it becomes a safe battery is that the mechanism of heat generation of the battery in the case of external destruction occurs. It will be described below together.

When a battery having a flat-plate laminated battery element in a charged state is destroyed from the outside and a short circuit occurs between the positive electrode and the negative electrode in one of the unit battery elements constituting this flat-plate laminated battery element, the battery is discharged. Short circuit current due to
Heat is generated due to this short-circuit current. Since the short-circuit current is a discharge that does not pass through a resistor, the amount of current becomes extremely large. Further, in the very early stage of the short circuit between the positive and negative electrodes, conduction occurs due to the short circuit only in a very limited portion, so that heat is locally generated. To more specifically explain this phenomenon, refer to FIG. FIG. 1 is a schematic cross-sectional view showing a state in which a nail has started to be pierced into a first unit battery element of flat plate stacked battery elements as one specific example in which a battery having flat plate stacked battery elements is destroyed from the outside. It is intended to be shown. Figure 1
FIG. 1A is a sectional view showing a state where a nail is stuck in a conventional flat plate type battery element, and FIG. 1B is a sectional view showing a state where a nail is stuck to a flat plate type battery element used in the present invention.

In FIG. 1A, when the battery 50 is destroyed by the nail 50 sticking into the flat plate type battery element 10, a short circuit occurs in the first unit cell element 8 located outside the battery.
It occurs between the positive electrode 100 and the negative electrode 300 of a. Then, the battery starts discharging due to this short circuit, and heat is generated due to a current flowing during this discharging (this current may be referred to as a short circuit current in this specification), which causes an electrode material layer containing an active material and thus a battery. The temperature will rise. Although this heat generation time is extremely short, the amount of current flowing due to a short circuit is large and the heat generation occurs locally, so the heat generation amount can sufficiently heat the minute volume of the short circuit part. It will be about.

On the other hand, the active material contained in the electrode material layer of the battery in the charged state is thermally unstable, and the self-decomposition reaction accompanied by heat generation proceeds at a temperature exceeding 200 ° C. in both the positive electrode and the negative electrode. To do. For example, when a lithium nickel composite oxide-based material is used as an active material used for the positive electrode (hereinafter, may be referred to as a positive electrode active material), these materials have a temperature of around 200 ° C. when measured by a differential scanning calorimeter (DSC). Very sharp peak (this is 200 ℃
It means that sudden heat generation occurs in the vicinity). Therefore, the heat generated by the self-decomposition reaction of the active material induced by the heat generated by the short-circuit current causes thermal runaway, and as a result, the battery ignites and explodes. That is, the battery capacity consumed by the current flowing by the discharge due to the short circuit is a very small part of the total battery capacity.
This means that even if a short circuit occurs, the active material remains in a sufficiently charged state, and if the heat generation due to the short circuit current exceeds a predetermined amount, the active material can self-decompose. The danger of the battery igniting or exploding due to external destruction is caused by the heat generated by the thermal decomposition reaction of the active material, causing thermal runaway.

The point to be noted here is that the heat generated by the current flowing due to the short circuit between the positive electrode and the negative electrode occurs in the portion where the resistance exists when the discharge circuit of the battery formed by the short circuit is taken into consideration. is there. Since the short-circuit discharge circuit is a closed circuit, the flowing current is constant. Therefore, I × V (I × I × R) that determines the heat generation W is proportional to the magnitude of the resistance. That is, even when the positive electrode and the negative electrode are short-circuited, if the resistance value R is small, the heat generation W can be suppressed to be small. This will be described with reference to FIG. 1A. When the tip of the nail 50 penetrates the electrode material layer 4a of the negative electrode in the first unit battery element 8a and reaches the negative electrode current collector 3, a short circuit due to breakdown is caused. A short circuit occurs between the positive electrode current collector 1 and the negative electrode current collector 3, but since the positive and negative electrode current collectors are generally highly conductive materials, the short circuit results in an extremely low resistance. And the heat generated from the battery in this state is
It occurs depending on the internal resistance of the battery. Here, since the internal resistance of the battery is distributed throughout the battery, heat is dispersed in the battery as a result. Therefore, since the temperature rise of the electrode material layer due to the heat generation based on the internal resistance is small, the self-decomposition of the active material does not occur, or even if it occurs, the calorific value is small, and the battery does not run into thermal runaway. . It should be noted that this is also clear from the fact that the battery does not run out of heat in the test in which the battery is externally short-circuited. From the above, in FIG. 1A, the tip of the nail 50 is in contact with the negative electrode current collector 3 of the first unit battery element 8a, and the first unit battery element 8
When the positive electrode current collector 1 and the negative electrode current collector 3 of a are in a short-circuited state, the battery does not run into thermal runaway.

On the other hand, even when the positive electrode and the negative electrode are short-circuited, when the resistance value R becomes large, the heat generation W also becomes large, so that the self-decomposition reaction of the active material is caused,
Eventually, the battery will run out of heat. That is, when the positive electrode and the negative electrode are short-circuited due to external breakdown, the danger is great before the mutual contact between the positive electrode current collector and the negative electrode current collector occurs, that is, in FIGS. ) Is a state in which a short circuit occurs through the electrode material layer (hereinafter, such a state may be referred to as a partial short circuit). When the degree of partial short circuit through the electrode material layer is small (in FIG. 1A, the tip of the nail 50 is the separator 5).
When the electrode material layer 4a of the negative electrode 300 of the first unit battery element 8a is reached), the short-circuit current is also small, so that heat generation is small and there is no problem. On the other hand, when the partial short circuit progresses considerably (in FIG. 1 (a), the tip of the nail 50 pierces the separator 5 and further proceeds downward), and the short circuit between the current collectors does not occur. (Fig. 1
In (a), heat generation due to a short-circuit current flowing in a state where the tip of the nail 50 does not reach the negative electrode current collector 3 becomes a serious problem. As for this short-circuit current, the nail 50 is the first unit battery element 8a.
Although it flows only for a very short time while passing through the negative electrode material layer 4a, the heat generation due to the short circuit current cannot be ignored.

To summarize the above, the local heat generation due to the short-circuit current is most likely to proceed in FIG.
The nail 50 penetrates the positive electrode 100 and the separator 5 of the first unit battery element 8a, and the negative electrode 300 of the first unit battery element 8a.
From the time of contact with the surface of the negative electrode 300 to the time at which the negative electrode current collector 3 of the negative electrode 300 is reached (hereinafter, this time may be referred to as a short circuit time). When the local heat generation due to the short-circuit current progresses, heat generation occurs due to the self-decomposition reaction of the active material, which increases the risk of thermal runaway of the battery. On the other hand, nail 50
When reaches the negative electrode current collector 3, the resistance decreases, and the heat generation due to the short-circuit current shifts to the heat generation to the entire battery due to the internal resistance, and the risk of thermal runaway of the battery at this point decreases.

As a result of earnest studies on the heat generation from the battery when the battery is destroyed by being shocked from the outside, the present inventor has found the above mechanism, and based on the above mechanism, a method for ensuring the safety of the battery is found. Also found. That is, according to the study by the present inventor, in order to prevent thermal runaway due to destruction of the battery from the outside, the local heat generation due to the partial short circuit should not cause the thermal decomposition reaction of the active material, or the thermal decomposition reaction should not occur. Even if it occurs, it is essential to suppress the degree of reaction.

The temperature at which thermal runaway starts is dependent on the type of active material and has a unique value, which cannot be changed or controlled. Since the current flowing due to the short circuit between the positive electrode and the negative electrode occurs inside the battery, it is necessary to suppress the flowing current value with a resistor. Therefore, it is necessary to increase the internal resistance of the battery, but this is not realistic because it significantly deteriorates the battery characteristics. In addition, the degree of short-circuiting when the battery is destroyed from the outside is different each time, and it is difficult to control the internal resistance to be high.

In view of the above situation, the present inventor has focused on the controllable factors such as the short-circuit time, the local heat generation range due to the short-circuit current, and the degree of temperature rise. That is, if the short-circuit time is short, the amount of heat generated by the short-circuit current decreases, and if the heat dissipation is good, the temperature rise is suppressed and even if the same amount of heat is generated, the temperature rises to the runaway start temperature due to the heat generated by the self-decomposition reaction of the active material. The inventors have found that it becomes difficult, and have completed the present invention.
That is, the film thickness of at least one of the positive electrode and the negative electrode of the positive electrode and the negative electrode in the first unit battery element of the flat plate type battery element in the present invention is the same as the positive electrode and the negative electrode in the unit battery elements other than the first unit battery element. The configuration in which the thickness of the electrode material layer is made thinner than at least one achieves such an effect efficiently and without lowering battery characteristics.

When the battery is destroyed by the impact from the outside, the first short circuit between the positive electrode and the negative electrode first occurs, and the first unit battery element is the portion which is first destroyed in the external breakdown as described above. This is a part that is prone to thermal runaway due to a partial short circuit. In the present invention, since the thickness of the electrode material layer of the first unit battery element is made thin, the time to stay in the partial short circuit (short circuit time) is shortened first and the amount of heat generated by the short circuit current is reduced. This will be described with reference to FIG. FIG. 1B is a schematic cross-sectional view showing a state in which a nail is stuck in the flat plate type battery element 10 which is an example used in the present invention. In the present invention, the first unit battery element 8a
Of the electrode material layer 2a of the positive electrode 100 and the negative electrode 3 in
00 is at least one of the thickness of the electrode material layer 2 of the positive electrode 100 and the thickness of the electrode material layer 4 of the negative electrode 300 in the unit cell elements 8 other than the first unit cell element 8a. Since the nail 50 is thinner, the time required for the nail 50 to reach the negative electrode current collector 3 from the positive electrode current collector 1 of the outermost first unit battery element 8a is shortened.

Secondly, in the present invention, since the thickness of the electrode material layer of the first unit battery element is thin, the heat generated by the short-circuit current and the self-decomposition reaction of the active material, if any, occur. The generated heat is easily dissipated to the current collector, which is a good conductor of heat, and the temperature rise is suppressed. Thirdly, in order for thermal runaway to occur, a chain of self-decomposition reaction of the active material is necessary, but in the present invention, since the thickness of the electrode material layer in the first unit battery element is thin, The three-dimensional spread is limited, and the chain is mainly a two-dimensional spread. With respect to the two-dimensional spread of this reaction chain, heat dissipation is promoted by the heat capacity of the current collector spreading in the two-dimensional direction, so that the self-decomposition reaction is easily extinguished. Due to these three reasons, thermal runaway of the battery due to external breakdown is effectively suppressed.

The present invention solves the problem only by partially changing the configuration of the unit cell element, and does not impair the chemical stability because no new material is incorporated into the cell. In other words, the present invention has an advantage that it is not necessary to consider the adverse effect on the battery characteristics due to the introduction of the new material. Further, since the unit that secures the safety of the battery is the unit battery element, not only is there an advantage that it contributes to the battery characteristics unless the battery is broken from the outside, for example, Japanese Patent Laid-Open No. 2001-68156. There is little concern about a short circuit or the like due to an unintended defect that may occur in a member formed by facing metal foils having sharp edges such as the short circuit formation and heat dissipation promotion unit as introduced in.

Furthermore, the present invention achieves its object by reducing the thickness of the electrode material layer of the first unit battery element, and the thickness of this electrode material layer can basically be set arbitrarily. Therefore, the thickness of the first unit battery element can be freely controlled. Therefore, in the present invention, it is sufficient to install the first unit battery element in the extra space between the outer package and the flat plate type battery element excluding the first unit battery element, and there is also an advantage that the extra space can be effectively used. .

The unit battery elements other than the first unit battery element are
It is an important factor that greatly affects battery performance, and the thickness of the electrode material layer of these unit battery elements is limited by the characteristics required for the battery and the materials used, especially the characteristics of the electrolyte, and it is difficult to change it arbitrarily. . In general, unless the electrode material layer has a certain thickness or less, the rate characteristic of the battery is deteriorated and the predetermined performance cannot be satisfied. This gives the following restrictions in a flat plate type battery element in which a plurality of unit cell elements are laminated. That is, for example, when the thickness of the space inside the outer package in which the unit battery element can be used is 1 mm, the most advantageous capacity is to use one unit battery element having a thickness of 1 mm. According to this, the thickness of the member that does not contribute to the capacity is minimized and the deposition density of the battery is maximized because there is one set of current collectors and one separator. However, it is difficult to use a battery having such a structure in a battery having high performance specifications that requires high cycle characteristics and rate characteristics. Actually, a flat plate type battery element is configured by stacking a plurality of unit battery elements having a thickness smaller than the thickness of the space inside the outer casing where the unit battery elements can be used. For example, in order to satisfy the rate characteristic, the unit cell element has a thickness of 0.1
If mm is the upper limit, in order to satisfy the space thickness of 1 mm, 10 unit battery elements having a thickness of 0.1 mm are laminated to form a flat plate laminated battery element. However, the size of the battery required varies depending on the specifications of the device that uses the battery as a power source. Therefore, the thickness of the space inside the exterior body in which the unit battery element can be used is not always the thickness that can be exactly satisfied by stacking an integral number of unit battery elements. For example, when a battery having a space thickness of 0.95 mm that can be used as a unit battery element is required, a unit battery element having a thickness of 0.1 mm is laminated in nine layers to form a battery. The space of 05 mm is wasted. According to the present invention, since the thickness of the electrode material layer of the first unit battery element can be arbitrarily reduced, it is possible to effectively use the wasted space. 2. Structure of Battery of the Present Invention The battery of the present invention has a flat plate-shaped positive electrode composed of a current collector and an electrode material layer containing an active material, and a flat plate-shaped positive electrode composed of a current collector and an electrode material layer containing an active material. In a battery in which a flat plate laminated battery element in which a plurality of unit battery elements having a negative electrode, a separator and an electrolyte are laminated is housed in an outer package, among the unit battery elements constituting the flat plate laminated battery element, a positive electrode is generated by an external impact. The film thickness of the electrode material layer of at least one of the positive electrode and the negative electrode in the first unit battery element in which a short circuit with the negative electrode first occurs is the film of the electrode material layer of the positive electrode and the negative electrode in the unit battery element other than the first unit battery element. Characterized by being thinner than at least one of the thicknesses.

When the battery receives an impact from the outside, the electrode structure of the first unit battery element in which a short circuit between the positive electrode and the negative electrode first occurs is changed to the electrode structure of the other unit battery elements constituting the flat plate type battery element. On the other hand, the reason why the safety of the battery in the case of external damage is improved by the above is as follows. As described in. The flat plate stack type battery element is formed by stacking unit battery elements. Therefore, the shape of the flat plate type battery element can be freely designed by appropriately changing the shape and size of each unit battery element to be stacked. Therefore, in the battery using the flat plate type battery element, there is an advantage that the shape of the battery can be made to match the power source space of the electronic device. In the present invention, in the battery using the flat plate type battery element, the film thickness of the electrode material layer of the first unit battery element in which the positive electrode and the negative electrode are first short-circuited by an external impact is made thin.

FIG. 6 is a cross-sectional view of a flat plate type battery element in which the unit cell elements have different sizes. As shown in FIG. 6, when the nail 50 stabs the flat plate stack type battery element 10 in the direction of the arrow 500 as a shock from the outside, the unit battery element in which the short circuit between the positive electrode and the negative electrode first occurs in FIG. It is the unit cell element that is stacked third from the bottom. In such a case, this unit battery element is the first unit battery element 8
a. Therefore, the electrode material layer of the third unit battery element 8a stacked third from the bottom may be thinned. That is, in the flat plate type battery element, the first unit battery element may be installed in a portion where the external impact is first concentrated.

By the way, the flat plate type battery element generally used at present has a substantially rectangular parallelepiped shape. However, when the flat plate type battery element has the above-mentioned substantially rectangular parallelepiped shape, an impact from the outside is first. The portion concentrated in the area is usually the uppermost surface or the lowermost surface of the flat plate type battery element. Therefore, when the flat plate type battery element has a substantially rectangular parallelepiped shape as shown in FIGS. 2 to 4, the first unit battery element is the uppermost one of the unit battery elements constituting the flat plate type battery element. It is preferable to locate it at the lowest position. That is, it is preferable that the first unit battery element is the uppermost and / or lowermost unit battery element in the thickness direction (stacking direction) of the flat plate type battery element.

Hereinafter, a specific example of the battery of the present invention will be described with reference to the accompanying drawings when the flat plate type battery element has a substantially rectangular parallelepiped shape. It should be noted that "the flat plate stacked battery element has a substantially rectangular parallelepiped shape" does not only mean that the flat plate stacked battery element needs to have a perfect rectangular parallelepiped shape, but the shape of the unit battery element is It is almost the same, and is meant to include the case where the flat plate type battery element in which these are stacked has a substantially rectangular parallelepiped shape. For example, in FIG. 3, since the electrode tabs 6 and 7 are present, the shape of the flat plate stack type battery element 10 is not strictly a rectangular parallelepiped. However, the flat plate battery element 10 of FIG.
Since it can be said that the flat plate type battery element 10 has a substantially rectangular parallelepiped shape, it is said that the flat plate stacked battery element 10 has a substantially rectangular parallelepiped shape.

FIG. 2 shows an example of a schematic diagram of a cross-sectional view of a battery when the flat plate type battery element has a substantially rectangular parallelepiped shape. Note that, in FIG. 2, each element is illustrated separately for convenience of view, unlike actual elements. Further, FIG. 2 shows only one lower side of the cross section of the battery in which the flat plate type battery element is housed in the exterior body, and the upper side is omitted. In FIG. 2, the first unit battery element 8a or the unit battery element 8 is
A plate-shaped positive electrode 100 having a structure in which a positive electrode current collector 1 is laminated with a positive electrode material layer 2 or 2a, and a flat plate negative electrode having a structure in which a negative electrode current collector 3 is laminated with a negative electrode material layer 4 or 4a. An electrolyte (not shown) is impregnated in each of 300 and the flat plate-shaped separator 5 provided between the positive electrode and the negative electrode. A plurality of the first unit battery elements 8a and the unit battery elements 8 are stacked to form a flat plate type battery element 10, which is housed in a case 40 to form a battery.

In the flat plate type battery element shown in FIG. 2, the thickness of the electrode material layer 2a of the positive electrode 100 of the first unit battery element 8a is the same as that of the positive electrode 100 of the unit battery element 8 other than the first unit battery element 8a. It is thinner than at least one of the film thicknesses of the electrode material layer 2. Similarly, the film thickness of the electrode material layer 4a in the negative electrode 300 of the first unit battery element 8a is at least one of the film thicknesses of the electrode material layers 4 in the negative electrodes 300 of the unit battery elements 8 other than the first unit battery element 8a. It is thinner than one.

In the case of the battery illustrated in FIG. 2, the positive electrode of the unit battery element is located on the lower side of the drawing, but the negative electrode may be located. Further, the first unit battery element having a thin electrode material layer is located on the lowermost side in FIG. 2, but it is also preferable to form it on the uppermost upper side which is not shown. The top surface and the bottom surface of the flat plate stack type battery element 10 may have the same pole or different polarities. further,
In FIG. 2, in the positive electrode 100 other than the positive electrode 100 located on the outermost side of the flat plate type battery element, the positive electrode material layer 2 is formed on both surfaces of the positive electrode current collector 1. Also, the negative electrode 300
Also, the negative electrode material layer 4 is formed on both surfaces of the negative electrode current collector 3. As described above, when the electrode having the electrode material layers formed on both surfaces of the current collector is used, the positive electrode 1 is formed from a position approximately half the thickness of the positive electrode current collector 1 located in the center of the positive electrode 100.
00 and the separator 5 are located in the center of the negative electrode 300, and the unit battery element 8 extends to a position approximately half the thickness of the negative electrode current collector 3.

Here, the thickness of the electrode material layer of at least one of the positive electrode and the negative electrode in the first unit battery element is the film of the electrode material layer of the positive electrode and the negative electrode of all the unit battery elements constituting the flat plate type battery element. It is preferable that the thickness is the thinnest. Specifically, the film thickness of the electrode material layer 2a of the positive electrode 100 of the first unit battery element 8a is such that the electrode material of the positive electrode 100 of the first unit battery element 8a and the unit battery element 8 constituting the flat plate stack type battery element 10. It is preferable that the thickness of the layer 2a and the electrode material layer 2 is the thinnest.
The film thickness of the electrode material layer 4a of the negative electrode 300 of a is the film thickness of the electrode material layer 4a and the electrode material layer 4 of the first unit battery element 8a and the negative electrode 300 of the unit battery element 8 which constitute the flat plate battery element 10. Of these, the thinnest is preferable. This is because the thicker the electrode material layer is, the larger the capacity of the battery is. Therefore, in the unit battery elements 8 other than the first unit battery element 8a that is present for the purpose of improving the safety assurance against external damage. It is preferable to increase the thickness of the electrode material layers 2 and 4 for the purpose of improving the capacity, while in the outermost first unit battery element 8a, the electrode material layers 2a and 2a are for the purpose of ensuring safety against external damage. This is because it is more effective to reduce the thickness of 4a.

In addition to the above, as preferred electrode configurations in the present invention, for example, the following three modes can be mentioned.
First, of the unit battery elements that constitute the flat plate type battery element, the film thickness of the electrode material layer of the electrode in the first unit battery element is the thinnest, and the electrode material layer of the electrodes in the other unit battery elements is the same. A mode in which the film thickness is constant can be mentioned.

Secondly, among the unit cell elements constituting the flat plate type cell element, the electrode material layers of the electrodes of the first unit cell element and the unit cell element adjacent thereto are made the thinnest, respectively. In the unit battery element, the film thickness of the electrode material layer of the electrode can be constant. Thirdly, among the unit battery elements constituting the flat plate type battery element, the electrode material layer of the electrode in the first unit battery element is made thinnest, and the electrode material layer of the electrode in the other unit battery elements is made the thinnest. The film thickness of is in the order of a unit battery element stacked adjacent to the first unit battery element, a unit battery element stacked further adjacent to this unit battery element (in FIG. 2, the first unit battery element). In the order from the battery element 8a to the unit battery elements stacked in the upper part of the drawing), the thickness of the electrode material layer may be gradually increased.

The above three aspects are merely examples of preferred aspects of the present invention. That is, in the present invention, the thickness of the electrode material layer of the electrode in the first unit battery element in which the short circuit between the positive electrode and the negative electrode first occurs due to an impact from the outside is a unit battery element other than the first unit battery element. It suffices that the thickness is smaller than at least one of the electrode material layers of the electrodes in (1), and an electrode configuration that satisfies this condition can be arbitrarily adopted.

The thickness of the electrode material layer of the positive electrode in the first unit cell element is usually 1 μm or more, preferably 5 μm or more,
It is more preferably 10 μm or more, usually 200 μm or less, preferably 100 μm or less, more preferably 50 μm or less, particularly preferably 30 μm or less. Within this range, the volume capacity of the battery can be improved by effectively using the internal space of the battery, and the safety can be improved by reducing the short circuit time and promoting heat dissipation. In particular, when the thickness of the electrode material layer of the positive electrode is 30 μm or less, the heat dissipation by the current collector becomes large, and the thermal runaway chain can be effectively suppressed.

The thickness of the electrode material layer of the positive electrode of the unit cell elements other than the first unit cell element is usually 10 μm or more, preferably 30 μm or more, more preferably 50 μm or more,
Usually 1000 μm or less, preferably 500 μm or less, more preferably 200 μm or less, particularly preferably 100 μm.
m or less. Within this range, the capacity can be increased while maintaining the rate characteristic.

The ratio of the thickness of the positive electrode material layer of the first unit battery element to the thickness of the positive electrode material layer of the unit battery element other than the first unit battery element is particularly limited as long as it is less than 1. However, it is usually 0.83 or less, preferably 0.71 or more, and more preferably 0.5 or less. By reducing the film thickness of the electrode material layer in the positive electrode of the first unit battery element, the short-circuit time of partial short-circuiting is shortened and heat dissipation is promoted. The ratio of the film thickness of the electrode material layer to the film thickness of the electrode material layer on the positive electrode of the unit cell element other than the first unit cell element contributes to improving the safety of the cell as a multiplier.

On the other hand, the thickness of the electrode material layer in the negative electrode of the first unit battery element is usually 1 μm or more, preferably 5 μm.
Or more, more preferably 10 μm or more, usually 200 μm or less, preferably 100 μm or less, more preferably 50 μm
m or less, particularly preferably 30 μm or less. Within this range, the volume capacity of the battery can be improved by effectively using the internal space of the battery, and the safety can be improved by reducing the short circuit time and promoting heat dissipation.

The thickness of the electrode material layer in the negative electrode of the unit cell elements other than the first unit cell element is usually 10 μm or more, preferably 30 μm or more, more preferably 50 μm.
As described above, usually 1000 μm or less, preferably 500 μm or less, more preferably 200 μm or less, and particularly preferably 1
It is not more than 00 μm. Within this range, the capacity can be increased while maintaining the rate characteristic.

The ratio of the thickness of the electrode material layer in the negative electrode of the first unit battery element to the thickness of the electrode material layer in the negative electrode of the unit battery element other than the first unit battery element is particularly limited as long as it is less than 1. However, it is usually 0.83 or less, preferably 0.71 or less, more preferably 0.5 or less.
Since the positive electrode material layer and the negative electrode material layer preferably maintain a constant ratio from the viewpoint of capacity balance, the film thickness of the electrode material layer in the positive electrode and the film thickness of the electrode material layer in the negative electrode of the first unit battery element are It is preferable to reduce the thickness of the electrode material layers of the positive and negative electrodes of the other unit battery elements to the same extent. 3. Material of Battery in Preferred Embodiment of Present Invention The battery of the present invention is preferably a lithium secondary battery. Lithium secondary batteries are widely used as a power source for consumer devices such as mobile phones, and are often subject to external shock such as dropping the device or stepping on it. Therefore, in the lithium secondary battery, increasing the safety of the battery against external damage is particularly heavy.

The detailed structures of the materials used for the lithium secondary battery and the elements thereof will be described below with reference to FIGS. FIG. 2 is an example of a schematic diagram of a cross-sectional view of a battery used in the present invention as described above. FIG. 3 is an explanatory view of a tab structure of the flat plate type battery element 10 in the battery used in the present invention, and FIG.
FIG. 5 is an explanatory view of a terminal structure of a flat plate type battery element stacked in a battery used in the present invention and housed in a flat case, and FIG. 5 is an explanatory view of an example of an external appearance of the battery used in the present invention.

In the lithium secondary battery, as the material of the current collector used for the unit cell elements 8 and 8a, a conductive foil made of a metal such as aluminum, nickel, copper or SUS can be used. The thickness of the current collector is usually 0.1 to 100 μm. In particular, aluminum is usually used for the positive electrode current collector 1, and copper is usually used for the negative electrode current collector 1.

The positive electrode material layers 2 and 2a and the negative electrode material layers 4 and 4a contain an active material and a normal binder, and if necessary, a conductive agent. Examples of the positive electrode active material include a composite oxide of one or more metals selected from the group of cobalt, nickel and manganese and lithium. These are usually used in a particle size of 1 to 30 μm.

In the present invention, the positive electrode active material is preferably a lithium cobalt composite oxide and / or a lithium nickel composite oxide. The lithium-cobalt composite oxide and / or the lithium-nickel composite oxide has a characteristic that the capacity is higher than that of the lithium-manganese composite oxide, but the thermal stability in a charged state is low. Therefore, the characteristic improvement due to the effect of the present invention is the largest. In particular, the lithium nickel composite oxide is low in thermal stability and is prone to thermal runaway, so that the complete effect is remarkable.

The lithium-cobalt composite oxide is a useful positive electrode active material having excellent rate characteristics because it has a flat discharge curve. Examples of the lithium-cobalt composite oxide include LiCoO ₂ having a layered structure. The lithium-cobalt composite oxide may be one in which some of the sites occupied by Co are replaced with an element other than Co. By substituting the Co site with another element, the cycle characteristics and rate characteristics of the battery may be improved. When substituting part of the site occupied by Co with an element other than Co, the substituting elements include Al, Ti, V, and C.
r, Mn, Fe, Li, Ni, Cu, Zn, Mg, G
a, Zr, Sn, Sb, Ge and the like, and preferably Al, Cr, Fe, Li, Ni, Mg, Ga, Zr, S.
n, Sb, Ge, more preferably Al, Mg, Zr, Sn
Is. The Co site may be substituted with two or more other elements.

When substituting the Co site with the substituting element, the proportion thereof is usually 0.03 mol% or more, preferably 0.05 mol% or more of the Co element, and usually 3% of the Co element.
It is 0 mol% or less, preferably 20 mol% or less. If the substitution ratio is too small, the stability of the crystal structure may not be sufficiently improved, and if it is too large, the capacity of the battery may decrease.

The lithium-cobalt composite oxide is usually represented by LiCoO ₂ as a basic composition before charging,
As described above, part of the Co site may be replaced with another element. In the above composition formula, a small amount of oxygen deficiency,
It may have indefiniteness, and a part of the oxygen site may be replaced with sulfur or a halogen element. Furthermore, in the above composition formula, the amount of lithium can be made excessive or insufficient.

The specific surface area of the lithium cobalt composite oxide is usually 0.01 m ² / g or more, preferably 0.1 m ² /
g or more, more preferably 0.4 m ² / g or more, and usually 10 m ² / g or less, preferably 5.0 m ² / g or less, more preferably 2.0 m ² / g or less. If the specific surface area is too small, the rate characteristics are deteriorated, and in some cases, the capacity is also decreased, and if it is too large, an undesired reaction with an electrolytic solution or the like is caused, and cycle characteristics may be deteriorated. The specific surface area is measured according to the BET method.

The average particle size of the lithium cobalt composite oxide is usually 0.1 μm or more, preferably 0.2 μm or more,
More preferably 0.3 μm or more, most preferably 0.
5 μm or more, usually 300 μm or less, preferably 1
The thickness is 00 μm or less, more preferably 50 μm or less, and most preferably 20 μm or less. If the average particle size is too small, the cycle deterioration of the battery may be large, or a safety problem may occur. If the average particle size is too large, the internal resistance of the battery may be large and the output may be difficult to output.

The lithium nickel composite oxide is a useful positive electrode active material because it has a large current capacity per unit weight and can increase the battery capacity. However,
The lithium-nickel composite oxide is more likely to undergo a self-decomposition reaction than the lithium-cobalt composite oxide, and thus is more prone to thermal runaway, and when external damage occurs, the battery is more likely to be exposed to a more dangerous state. Therefore, when the lithium nickel composite oxide is contained in the positive electrode active material, the effect of the present invention is remarkably exhibited. The lithium-nickel composite oxide is an oxide containing at least lithium and nickel. As the lithium nickel composite oxide, for example, a lithium nickel composite oxide such as LiNiO ₂ having a layered structure such as α-NaCrO ₂ structure is preferable. As a specific composition, for example, Li
Mention may be made of _{NiO 2, Li 2 NiO 2,} LiNi 2 O 4 or the like. In this case, the lithium nickel composite oxide is
A part of the site occupied by Ni may be replaced with an element other than Ni. By substituting a part of the Ni site with another element, the stability of the crystal structure can be improved, and a part of the Ni element during repeated charge and discharge is L
Since the capacity decrease caused by moving to the i-site is suppressed, the cycle characteristics are also improved. Furthermore, by substituting a part of the Ni site with an element other than Ni, DSC
(Differential Scanning Ca
Lorimetry: Differential scanning calorimetry) shifts the heat generation start temperature to the high temperature side, so the thermal runaway reaction of the lithium nickel composite oxide when the battery temperature rises is also suppressed, resulting in safety during external destruction and high temperature storage. It leads to improvement of sex.

When a part of the site occupied by Ni is replaced with an element other than Ni, the element (hereinafter referred to as a replacement element) is, for example, Al, Ti, V, Cr, Mn,
Fe, Co, Li, Cu, Zn, Mg, Ga, Zr and the like can be mentioned. Of course, the Ni site may be substituted with two or more kinds of other elements. Preferably Al, Cr, Fe, C
O, Li, Mg, Ga and Mn are mentioned, and more preferably Al and Co are mentioned. Part of Ni element is Co, A
Substitution with l enhances the effect of improving cycle characteristics and safety.

When substituting the Ni site with a substituting element, the ratio is usually 2.5 mol% or more, preferably 5 mol% or more of the Ni element, and usually 50 mol% of the Ni element.
It is preferably 30 mol% or less. If the replacement ratio is too small, the effect of improving cycle characteristics may not be sufficient, and if the replacement ratio is too large, the capacity of the battery may decrease.

A part of Li may be replaced with an element such as Al. The above composition may have a small amount of oxygen deficiency or nonstoichiometry. Further, part of the oxygen site may be replaced with sulfur or a halogen element.
The lithium nickel composite oxide is particularly preferably a compound represented by the following general formula (1), which is unsubstituted or whose Ni site is replaced with Co and Al.

[0054]

## EQU1 ## Liα Ni _X Co _Y Al _Z O ₂ (1)

In the general formula (1), α is a number that changes depending on the charging / discharging condition in the battery, and usually 0 ≦ α ≦ 1.1,
The number is preferably in the range of 0.2 ≦ α ≦ 1.1. Further, X is usually 0.5 ≦ X ≦ 1, preferably 0.7.
It is a number in the range of ≦ X ≦ 0.9. Y is usually 0 ≦ Y ≦
It is a number in the range of 0.5, preferably 0.1 ≦ Y ≦ 0.3. When it is more than this range, the capacity is lowered, while when it is less than this range, the effect becomes insufficient. Z is usually 0
≦ Z ≦ 0.1, preferably 0 ≦ Z ≦ 0.05. If it exceeds this range, the capacity will decrease,
If it is below this range, the effect becomes insufficient. Although the above X, Y, and Z satisfy the relationship of X + Y + Z = 1.0,
The value may deviate slightly from 1.0 (specifically, about ± 0.1) due to the presence of crystal (lattice) defects in the material. In the present invention, by substituting part of the Ni element with Co, the effect of improving the cycle characteristics and safety becomes large as described above, but by substituting part of the Ni element with Al, the cycle is improved. Further improvements in properties and safety are achieved.

The specific surface area of the lithium nickel composite oxide used in the present invention is usually 0.01 m ² / g or more, preferably 0.1 m ² / g or more, more preferably 0.5 m ² / g or more, and Usually 10 m ² / g or less, preferably 5 m ²
/ G or less, more preferably 2 m ² / g or less. If the specific surface area is too small, rate characteristics and capacity are deteriorated, and if it is too large, an undesired reaction with the electrolytic solution or the like is caused, and cycle characteristics may be deteriorated. The specific surface area is measured according to the BET method.

The average particle size of the lithium nickel composite oxide used in the present invention is usually 0.1 μm or more, preferably 0.2 μm or more, more preferably 0.3 μm or more, and most preferably 0.5 μm or more. 300 μm or less, preferably 100 μm or less, more preferably 50
It is not more than μm, most preferably not more than 20 μm. If the average particle size is too small, the cycle deterioration of the battery may be large, or a safety problem may occur. If the average particle size is too large, the internal resistance of the battery may be large and the output may be difficult to output.

In the present invention, a lithium cobalt composite oxide and a lithium nickel composite oxide may be mixed to form a positive electrode active material. By using both composite oxides, the advantages of both materials are utilized, the initial efficiency and energy density are high, the slope of the discharge curve is suppressed to a certain extent, and further, the well-balanced lithium having excellent low-temperature output characteristics is obtained. A secondary battery can be obtained.

The weight ratio of the lithium nickel composite oxide and the lithium cobalt composite oxide is not particularly limited, but the ratio of the lithium nickel composite oxide to the total weight of the lithium nickel composite oxide and the lithium cobalt composite oxide is usually 1 to 99% by weight, preferably 40 to 9
It is 0% by weight. With the above range, the advantages of both materials can be utilized.

On the other hand, in FIG. 2, the negative electrode material layer 4 or 4a
Examples of the negative electrode active material contained in are carbonaceous materials such as graphite and coke. These are usually used in a particle size of 1 to 30 μm. Examples of the binder include fluororesins such as polyvinyl fluoride, polyvinylidene fluoride and polytetrafluoroethylene, and CN group-containing polymers such as polyacrylonitrile and polyvinylidene cyanide. The amount of the binder used is usually 0.1 to 30 parts by weight with respect to 100 parts by weight of the active material, and the amount of the solvent used is usually 10 to 90% by weight as a concentration in the coating material.

Examples of the conductive agent include graphite such as natural graphite and artificial graphite, carbon black such as acetylene black, and carbon material such as amorphous carbon such as needle coke. The positive electrode 100 and the negative electrode 300 are kneaded with the above materials forming the electrode material layers 4 and 4a or the electrode material layers 2 and 2a using a mortar or the like, and then pressed onto the positive electrode current collector 1 or the negative electrode current collector 3. Can be formed. Alternatively, the electrode material layers 4, 4a or the electrode material layers 2, 2a can be formed by applying and drying a coating material in which the above materials are dissolved on the positive electrode current collector 1 or the negative electrode current collector 3. In this case, examples of the solvent used for the coating material include N-methylpyrrolidone and dimethylformamide.

In FIG. 2, the positive electrode 100, the negative electrode 300,
Examples of the electrolyte with which the separator 5 is impregnated include a highly fluid electrolyte solution and a non-fluid electrolyte. Here, the non-fluidic electrolyte usually contains an electrolytic solution. The electrolytic solution usually has a liquid property in which a lithium salt is used as a supporting electrolyte and is dissolved in a non-aqueous solvent.

Examples of the lithium salt (supporting electrolyte) constituting the electrolytic solution include LiPF ₆ and LiClO ₄ .
Examples of the non-aqueous solvent include carbonates such as ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate, and lactones such as gamma butyrolactone. Among these, it is preferable to use ethylene carbonate, propylene carbonate, and gamma butyrolactone. The concentration of the supporting electrolyte in the electrolytic solution is usually 0.5 to 2 mol / L.

In the present invention, the electrolyte is preferably a non-fluidic electrolyte. By using the non-fluidic electrolyte, it becomes possible to more effectively prevent the electrolyte from leaking to the outside of the case. In particular, in order to reduce the weight of the lithium secondary battery, when using a material having shape changeability as the case for accommodating the flat plate type battery element, the mechanical strength of the case tends to be insufficient, and The case may be torn by the impact of. When such a case breakage occurs, the electrolyte leaks to the outside of the case, but since the non-fluidic electrolyte has a solid or gel property, the leakage of the electrolyte is reduced. As a result, the safety of the lithium secondary battery is improved.

As the non-fluidic electrolyte, those having various properties such as a polymer solid electrolyte, a gel electrolyte and an inorganic solid electrolyte can be used. In the present invention, it is preferable to use a gel electrolyte. The gel electrolyte has a higher lithium ion conductivity than the solid electrolyte and thus has excellent battery characteristics. In addition, the gel electrolyte has a high stability against heating due to the gelled electrolyte.

The gel electrolyte usually contains a polymer obtained by polymerizing a polymerizable monomer by heat or light or a polymer meltable by heating and the above-mentioned electrolytic solution. The polymerizable monomer used for the preparation of the gel electrolyte (hereinafter, sometimes referred to as polymer electrolyte) is a monomer polymerizable by heat, ultraviolet rays, electron beams, etc., that is, for example,
Examples thereof include various monomers having functional groups such as acryloyl group, methacryloyl group, vinyl group, and allyl group. Examples of the polymer for heating and melting liquid include the above-mentioned fluororesin, C
In addition to N group-containing polymers, acrylic derivative-based polymers such as polymethacrylic acid, polyvinyl alcohol-based polymers such as polyvinyl acetate, and halogen-containing polymers such as polyvinyl chloride can be mentioned.

As a method of impregnating the non-fluidic electrolyte into the electrode and the separator, a method of dissolving a heat-dissolvable polymer in an electrolytic solution at a high temperature, impregnating this into the electrode and the separator, and then returning the temperature to room temperature can be mentioned. it can. Also,
When a polymerizable monomer is used, a solution containing a polymerizable monomer, a polymerization initiator, and an electrolytic solution is prepared, and the electrode and the separator are impregnated with this solution, and then the polymerizable monomer is polymerized by heat or light. The method of making it possible can be mentioned.

The separator 5 in FIG. 2 is a porous film provided between the positive electrode and the negative electrode, which separates the positive electrode from the negative electrode and impregnates with the electrolyte. Examples of the material of the separator include polyolefins such as polyethylene and polypropylene, polyolefins in which some or all of hydrogen atoms thereof are substituted with fluorine atoms, and polymers such as polyacrylonitrile and polyaramid. Preferred are polyolefins and fluorine-substituted polyolefins. Specific examples include polyethylene, polypropylene, polytetotrafluoroethylene, polyvinylidene fluoride and the like. Needless to say, it may be a copolymer containing monomer units of the above polymers or a mixture of polymers. The separator is uniaxially stretched or 2
It may be a stretched film formed by axial stretching, or may be a non-woven fabric. The thickness of the separator is usually 100 μm or less, preferably 50 μm or less, more preferably 30 μm or less, and most preferably 20 μm.
It is the following. If the film thickness is too large, the rate characteristics and the volume energy density of the battery tend to decrease. If it is too thin, it tends to be difficult to cut due to insufficient rigidity, and a short circuit is likely to occur. Therefore, the thickness is usually 5 μm or more, preferably 7 μm or more, more preferably 8 μm or more. The porosity of the separator is usually 45 to 90%, preferably 45 to 75%. If the porosity is too large, the mechanical strength will be insufficient, and if it is too small, the rate characteristics of the battery will tend to deteriorate.

In FIG. 2, as a material of an outer package (sometimes referred to as a case in the present specification) 40 for accommodating the flat plate type battery element, for example, as shown in FIG. An example of the flexible film is a flexible film such as a laminated film composed of the synthetic resin layers 42 arranged on both sides. In the case of a laminated film, a metal or metal oxide layer is usually used as the gas barrier layer. Here, aluminum or silicon is usually used as the metal. Among the synthetic resin layers, the outer layer synthetic resin located outside the lithium secondary battery is polyamide or polyester, and the inner layer synthetic resin located on the side encapsulating the flat plate laminated battery element is polyethylene or polypropylene. Is preferred. The laminated film has a good gas barrier property and can be made lighter and thinner, so that it is suitable for improving the energy density of the battery. Further, the above-mentioned laminated film tends to be inferior in strength against nail penetration and the like, as compared with a metal can that has been used most generally in the past. Therefore,
The effect of the present invention when a laminated film is used is particularly remarkable.

In the above description, a lithium secondary battery is given as a specific example of a battery using a case having a shape changeable property such as a laminated film. But,
It is needless to say that the shape-variable case is preferably used as an exterior body of not only the lithium secondary battery but also other types of batteries (for example, nickel-hydrogen battery) that can be used in the present invention. Since the shape-variable case has low rigidity and is easily broken by an external impact, the external battery is easily broken. Therefore, when the shape-variable case is used for the outer casing, the safety of the battery can be ensured by devising the electrode configuration of the flat plate type battery element.

In the battery of the present invention, for example, as shown in FIGS. 2 to 4, a flat plate type battery element 10 in which unit battery elements 8a, 8 are stacked in the thickness direction is housed in a case 40. Become. And, for example, it has an appearance as shown in FIG. 2 to 5, reference numerals 6 and 7 are electrode tabs formed by mutually assembling from a positive electrode and a negative electrode, and 20 and 30 are lead-out terminals joined to the electrode tabs for taking out an electric current to the outside of the case.

The flat plate type battery element is formed by stacking a plurality of unit battery elements, but preferably has a structure in which three or more unit battery elements are stacked. When three or more sets are laminated, the amount of heat generated in the nail penetration test or the like becomes large, so that the effect of the present invention becomes remarkable. The number of stacked unit battery elements is more preferably 6 layers or more, and most preferably 10 layers or more. From the viewpoint of increasing the battery capacity of the battery, the larger the number of laminated layers, the more preferable, but the number of laminated unit battery elements is actually 50 layers or less. 4. Uses of the Battery of the Present Invention There is no particular limitation on the electric equipment in which the battery of the present invention is used as a power source. Examples of the electric device include a laptop computer, a pen input computer, a mobile computer, an electronic book player, a mobile phone, a cordless phone handset, a pager, a handy terminal, a mobile fax, a mobile copy, a mobile printer, a headphone stereo, a video movie, a liquid crystal display. TV, handy cleaner, portable CD, mini disk, electric shaver,
Walkie-talkie, electronic organizer, calculator, memory card, portable tape recorder, radio, backup power supply, motor, lighting equipment, toys, game equipment, road conditioner, clock, strobe, camera, medical equipment (pacemaker, hearing aid, shoulder massager, etc.) Etc. can be mentioned.

[0073]

EXAMPLES The present invention will be described in more detail with reference to examples below, but the present invention is not limited to the examples unless it exceeds the gist. In the following examples, the following evaluations and tests were carried out. (1) Battery capacity: A battery charged by constant current charging to a voltage density of 4.2 V at a current density of 0.6 C and then to a current density of C / 25 at a voltage of 4.2 V. It is measured by discharging with a constant current up to 3.0 V at a current density of 2C. In addition, 1 C means a current value capable of discharging the rated capacity of the battery in 1 hour. (2) External breakdown test: A battery charged by constant-current charging to a voltage of 4.0 V at a constant current of C / 25 after constant-current charging to a voltage of 4.0 V at a current density of 0.6 C. A battery having a diameter of 2.5 mm is penetrated from the side where the first unit battery element is located in the thickness direction of the case to destroy the battery, and the behavior at that time is observed. Then, there was no change (only the nail penetrates), smoke and ignition were classified and evaluated. Example 1 First, each component was treated with a kneading machine for 2 hours in accordance with the composition of Tables 1 and 2 below to prepare a positive electrode material layer forming coating material and a negative electrode material layer forming coating material. did.
In addition, according to the composition of Table 3 below, each component was mixed and stirred and dissolved to prepare a coating material for forming an electrolyte.

[0074]

[Table 1]

[0075]

[Table 2]

[0076]

[Table 3]

An extrusion type die coater was used to apply a positive electrode coating material on a positive electrode current collector made of aluminum and having a thickness of 15 μm and then dried to collect a positive electrode material layer of a porous film. I attached it to one side of my body. Similarly, after applying a negative electrode coating material on a negative electrode current collector with a copper tab having a thickness of 10 μm by an extrusion type die coater, the negative electrode coating material is dried to form a porous electrode material layer of the negative electrode current collector. It was attached to one side of.

Then, by a roll press (calender), the positive electrode material layer and the negative electrode material layer are each subjected to a consolidation treatment, and then cut into a predetermined size to obtain a flat plate-shaped positive electrode αc and negative electrode αa. did. The film thickness of the positive electrode material layer thus obtained was 53.4 μm, and the film thickness of the negative electrode material layer was 62.5 μm. Separately, a positive electrode βc and a negative electrode βa were manufactured by changing only the thickness of the positive electrode material layer and the negative electrode material layer. Here, the thickness of the positive electrode material layer of the positive electrode βc is 26 μm, and the thickness of the negative electrode material layer of the negative electrode βa is 30 μm.
So that

The positive electrode αc and the negative electrode αa are coated with the above-mentioned electrolyte-forming coating material, and a polymer porous film (separator) impregnated with the separately prepared electrolyte-forming coating material is sandwiched between them to form a laminate. The electrolyte was non-fluidized by heating at 0 ° C for 10 minutes to form a gel electrolyte. Then, a flat unit battery element α having the positive electrode αc, the negative electrode αa, and the non-fluidic electrolyte layer was obtained.

The same operation was performed for the positive electrode βc and the negative electrode βa to produce a flat unit battery element β (first unit battery element) having an electrode material layer thinner than that of the unit battery element α. Twenty-two obtained unit battery elements α were alternately laminated in the order in which the negative electrode current collectors were the upper and lower outermost surfaces. The unit battery elements stacked in this way are sequentially referred to as “unit battery element α
-1 "," unit battery element α-2 "..." Unit battery element α
-21 "and" unit battery element α-22 ". Next, the unit battery element β was stacked under the unit battery element α-1, and the unit battery element β was stacked over the unit battery element α-22. Then, terminals for extracting current were connected to the positive electrode and the negative electrode, respectively, to produce a flat plate type battery element as shown in FIG.

Then, as shown in FIG. 4, the above flat plate type battery element was housed in a vacuum in a case in which a laminate film composed of an aluminum layer and synthetic resin layers arranged on both sides thereof was preform-molded. After sealing, a lithium secondary battery having an appearance as shown in FIG. 5 was produced.
Table 4 shows the evaluation and test results of the obtained lithium secondary battery.
Shown in.

Comparative Example 1 A lithium secondary battery was obtained in the same manner as in Example 1 except that the unit cell element β (first unit cell element) was omitted. Table 4 shows the evaluation and test results of the obtained lithium secondary battery. Example 2 In Example 1, the unit battery elements α were alternately stacked in the order in which the positive electrodes were the upper and lower outermost surfaces. Two sets of the unit battery element β were laminated on the lower surface of the unit battery element α-1. Further, two sets of the unit battery element β were laminated on the unit battery element α-22. That is, a lithium secondary battery in which the film thickness of the electrode material layers in the unit battery elements of the outermost two layers of the flat plate type battery element is smaller than the film thickness of the electrode material layers of the unit battery elements other than the outermost two layers A lithium secondary battery was obtained in the same manner as in Example 1 except that the lithium secondary battery was produced. Here, the unit battery elements β located at the upper and lower outermost sides of the flat plate type battery element are the first unit battery elements. Table 4 shows the evaluation and test results of the obtained lithium secondary battery.

[0083]

[Table 4]

From the results shown in Table 4, among the unit battery elements constituting the flat plate type battery element of the lithium secondary battery, the unit battery elements are located at least at the outermost position, and the positive electrode and the negative electrode of the unit battery element are first tested by the external breakdown test. By making the film thickness of the electrode material layer in the unit battery element where the short circuit occurs at a smaller thickness than the film thickness of the electrode material layer in the other unit battery elements, the safety of the battery against external destructive tests is significantly improved. I understand that

[0085]

According to the present invention, among the unit battery elements constituting the flat plate type battery element, an impact from the outside causes
The thickness of the electrode material layer of the electrode in the first unit battery element in which the short circuit between the positive electrode and the negative electrode first occurs is at least one of the thicknesses of the electrode material layers of the electrodes in the unit battery elements other than the first unit battery element. By making it thinner than the above, it is possible to significantly improve the safety of the battery when the battery is externally damaged without impairing the basic battery performance such as the battery capacity, rate characteristics and cycle characteristics. .

[Brief description of drawings]

FIG. 1 is a schematic explanatory diagram when a battery is destroyed from the outside by a nail piercing a flat plate type battery element.

FIG. 2 is a schematic explanatory view of a cross-sectional view of an example of the battery of the present invention.

FIG. 3 is an explanatory view of a tab structure of stacked flat plate type battery elements.

FIG. 4 is an explanatory view of a cross-sectional view of a terminal structure of flat plate type battery elements that are stacked and housed in a case.

FIG. 5 is a perspective view of an example of the appearance of a battery.

FIG. 6 is another schematic explanatory diagram when the battery is destroyed from the outside by the nail being stuck in the flat plate type battery element.

[Explanation of symbols]

1: Positive electrode current collector 2: Positive electrode material layer 2a: Electrode material layer of the positive electrode of the first unit battery element 3: Negative electrode current collector 4: Negative electrode material layer 4a: Electrode material layer of the negative electrode of the first unit battery element 5: Separator 6: Electrode tab 7: Electrode tab 8: Single cell element 8a: First unit battery element 10: Flat plate type battery element 20: Takeout terminal 30: Takeout terminal 40: Case 50: nail 100: Positive electrode 300: Negative electrode 500: Arrow

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) H01M 10/40 H01M 10/40 ZF term (reference) 5H011 AA13 CC10 5H029 AJ12 AK03 AL06 AL07 AM00 AM03 AM05 AM07 AM16 BJ04 HJ04 5H050 AA15 BA18 CA08 CB07 CB08 DA02 DA03 EA10 EA23 EA24 FA02 HA04 HA12

Claims (8)

[Claims] 1. A flat plate-shaped positive electrode composed of a current collector and an electrode material layer containing an active material, a flat plate-shaped negative electrode composed of a current collector and an electrode material layer containing an active material, a separator and an electrolyte. In a battery in which a flat plate laminated battery element in which a plurality of unit battery elements are laminated is housed in an outer package, a short circuit between a positive electrode and a negative electrode is first caused by an external impact among the unit battery elements constituting the flat plate laminated battery element. The film thickness of at least one of the electrode material layers of the positive electrode and the negative electrode in the first unit battery element that occurs is at least one of the film thicknesses of the electrode material layers of the positive electrode and the negative electrode in the unit battery element other than the first unit battery element. A battery characterized by being thin. 2. The flat plate type battery element has a substantially rectangular parallelepiped shape, and the first unit battery element is located at the top and / or the bottom of unit battery elements forming the flat plate type battery element. The battery according to claim 1. 3. The thickness of the electrode material layer of at least one of the positive electrode and the negative electrode in the first unit battery element is
The battery according to claim 1 or 2, which is the thinnest of the film thicknesses of the electrode material layers of the positive electrode and the negative electrode of all the unit battery elements constituting the flat plate stack type battery element. 4. The battery according to claim 1, wherein the film thickness of the electrode material layer of the positive electrode of the first unit battery element is 1 to 200 μm. 5. The battery according to claim 1, wherein the thickness of the electrode material layer of the negative electrode of the first unit battery element is 1 to 200 μm. 6. The battery is a lithium secondary battery.
6. The battery according to any one of 1 to 5. 7. The positive electrode material layer as a positive electrode active material,
The battery according to claim 1, further comprising a lithium cobalt composite oxide and / or a lithium nickel composite oxide. 8. The battery according to claim 1, wherein the outer casing for accommodating the battery is a case having variable shape.