JP2010277790A - Lithium ion secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lithium ion secondary battery having an excellent load characteristic, even after initial charge. <P>SOLUTION: This lithium ion secondary battery 100 has structure of storing a positive electrode 10, a negative electrode 20 and a nonaqueous electrolyte in a battery case 50. The positive electrode 10 contains, as a positive active material, lithium manganese oxide of a manganese-containing solid solution with Li<SB>2</SB>MnO<SB>3</SB>formed into solid solution, expressed by General Formula Li<SB>x</SB>Mn<SB>(1-y)</SB>M<SB>y</SB>O<SB>z</SB>where M represents at least one of metal element other than Li and Mn, 1<x<2, 0≤y<1, and 1.5<z<3. At least one of reducing gas for reducing oxygen is arranged in an inside of the battery case 50. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a lithium ion secondary battery. Specifically, the present invention relates to a lithium ion secondary battery having a structure in which a positive electrode having a positive electrode active material and a non-aqueous electrolyte are accommodated in a battery case.

  In recent years, a lithium ion secondary battery that is lightweight and has a high energy density is expected to be preferably used as a high-output power supply for vehicles. Such a lithium ion secondary battery includes an electrode body configured with a separator interposed between a positive electrode and a negative electrode, and lithium ions (hereinafter referred to as Li ions) between the positive and negative electrodes. Charging / discharging is performed by movement.

This type of lithium ion secondary battery includes a positive electrode having a configuration in which a positive electrode active material capable of reversibly occluding and releasing Li ions is formed on a positive electrode current collector. Examples of positive electrode active materials used for such positive electrodes include lithium and transition metal elements such as lithium nickelate (LiNiO ₂ ), lithium cobaltate (LiCoO ₂ ), and lithium manganate (LiMnO ₂ ) as constituent metal elements. Examples thereof include positive electrode active materials mainly containing an oxide (lithium transition metal oxide) containing them (Patent Documents 1 and 2, etc.). Further, many solid solutions of these oxides have been studied. For example, a part of the Ni site of LiNiO ₂ such as LiNi _1/3 Co _1/3 Mn _1/3 O ₂ is also used for lithium manganate. solid solution and was replaced with Co and _{Mn, Li 1.2 Mn 0.5 Co 0.14} Ni 0.14 high manganese-containing solid solution in which a solid solution of LiNiO ₂ or LiCoO ₂ and _Li 2 MnO ₃ as O ₂ to the base Has been proposed.

International Publication No. 2003/044881 Pamphlet JP 2004-241390 A

Among the positive electrode active _material, Li 2 MnO ₃ a manganese-containing solid solution which is based _(Li 2 MnO ₃ and that a solid solution and other metal oxides) is represented by the general formula _{Li x [Mn (1-y} ) M _y ] O _z (wherein M represents one or more metal elements other than Mn and Li) and is expected as a positive electrode active material having a high energy density. However, the solid solution based on Li ₂ MnO ₃ has a problem that load characteristics (characteristic for maintaining a high capacity even during large current discharge) are greatly reduced by the initial charge / discharge treatment. The present invention has been made in view of the foregoing, the main object is a lithium ion secondary battery using the solid solution in which the Li ₂ MnO ₃ on the base as a positive electrode active material was subjected to initial charging and discharging process It is an object of the present invention to provide a lithium ion secondary battery with good load characteristics even later.

When the present inventors use a manganese-containing solid solution based on Li ₂ MnO ₃ as a positive electrode active material, the load characteristics (characteristics for maintaining a high capacity even during large current discharge) are greatly reduced by the initial charge / discharge treatment. the was considered part during initial charging to with the release of Li ions from solid solution (positive electrode active material) of oxygen (O ₂₎ is because eliminated. That is, when a part of oxygen is desorbed from the solid solution (positive electrode active material), the desorbed oxygen is dissolved in the electrolyte and moves to the negative electrode side, and Li is formed on the negative electrode (typically the surface of the negative electrode active material). Precipitates such as ₂ O are produced. Since the precipitate produced on the negative electrode inhibits the subsequent negative electrode charge / discharge reaction, it can be a factor of deteriorating the load characteristics of the battery.

  Based on such knowledge, the present inventor can prevent a decrease in load characteristics after initial charging by an approach of inactivating oxygen desorbed from the solid solution (positive electrode active material) by reaction with a reducing gas. The present invention was conceived.

That is, the lithium ion secondary battery provided by the present invention is a lithium ion secondary battery having a structure in which a positive electrode, a negative electrode, and a non-aqueous electrolyte are accommodated in a battery case. The positive electrode is a manganese-containing solid solution in which Li ₂ MnO ₃ is dissolved as a positive electrode active material, and has a general formula Li _x [Mn _(1-y) M _y ] O _z (M is at least one type other than Li and Mn). A lithium manganese oxide represented by 1 <x <2, 0 ≦ y <1, 1.5 <z <3). In the battery case, at least one reducing gas capable of reducing oxygen is disposed.

According to the configuration of the present invention, by arranging the oxygen reducible reducing gas in the battery case, to capture the oxygen generated from the time of initial charging the positive electrode active material (solid solution in which the Li ₂ MnO ₃ based) Can be inactivated. As a result, it is possible to avoid the formation of precipitates such as Li ₂ O on the negative electrode, and it is possible to obtain a lithium ion secondary battery with good load characteristics even after initial charging.

As the reducing gas, a gas having a function capable of quickly capturing oxygen generated from the positive electrode active material is preferable. Further, the reducing gas is preferably chemically inert with respect to a predetermined battery constituent material (active material for each positive and negative electrode, current collector for each positive and negative electrode, separator, non-aqueous electrolyte, etc.). . Further, the reducing gas is preferably one that changes oxygen generated from the positive electrode active material into a substance that is chemically inert with respect to the battery constituent material described above. In a preferred embodiment disclosed herein, CO gas is used as the reducing gas. When using the CO gas as the reducing gas, the oxygen generated from the positive electrode active material CO + 1 / 2O ₂ → the reaction of CO ₂ can be changed to an inert CO ₂ gas, effectively removing it the oxygen Can do.

  In a preferable aspect of the lithium ion secondary battery disclosed herein, at least a part of the reducing gas is disposed in a state of being dissolved in the nonaqueous electrolytic solution. Oxygen generated from the positive electrode active material dissolves in the non-aqueous electrolyte and moves to the negative electrode side. Therefore, by dissolving a part of the reducing gas in the non-aqueous electrolyte, oxygen dissolved in the non-aqueous electrolyte (dissolved oxygen generated from the positive electrode active material) can be reliably captured. Note that a part of the reducing gas may not be dissolved in the non-aqueous electrolyte, and the surplus gas may be disposed in the battery case with the gas remaining. When reducing gas dissolved in the non-aqueous electrolyte is consumed by reaction with oxygen generated from the positive electrode active material, surplus reducing gas (reducing gas arranged as a gas in the battery case) is generated. Newly dissolves in non-aqueous electrolyte. As a result, the reducing gas consumed by the reaction with oxygen can be replenished as needed, and oxygen dissolved in the non-aqueous electrolyte (dissolved oxygen generated from the positive electrode active material) can be reliably captured. The surplus reducing gas only needs to be disposed in direct contact with the non-aqueous electrolyte, for example, between the non-aqueous electrolyte and the battery case (typically in the battery case). It is good to arrange it in the space part).

  Since such a lithium ion secondary battery exhibits good battery performance as described above, it is suitable as a battery mounted on a vehicle such as an automobile. Therefore, according to the present invention, there is provided a vehicle including any of the lithium ion secondary batteries disclosed herein (which may be in the form of an assembled battery in which a plurality of batteries are connected). In particular, since good load characteristics can be obtained, a vehicle (for example, an automobile) including the lithium ion secondary battery as a power source (typically, a power source of a hybrid vehicle or an electric vehicle) is provided.

It is a schematic diagram which shows the structure of the lithium ion secondary battery which concerns on one Embodiment of this invention. It is a schematic diagram which shows the structure of the wound electrode body which concerns on one Embodiment of this invention. It is a side view which shows the vehicle provided with the lithium ion secondary battery which concerns on one Embodiment of this invention.

  Embodiments according to the present invention will be described below with reference to the drawings. In the following drawings, members / parts having the same action are described with the same reference numerals. Note that the dimensional relationship (length, width, thickness, etc.) in each drawing does not reflect the actual dimensional relationship. In addition, matters other than the matters specifically mentioned in the present specification and matters necessary for the implementation of the present invention (for example, the configuration and manufacturing method of separators and electrolytes, general construction relating to the construction of lithium ion secondary batteries and other batteries) Technical technology etc.) can be understood as a design matter of those skilled in the art based on the prior art in the field.

  Although not intended to be particularly limited, in the following, a flatly wound electrode body (winding electrode body) and a non-aqueous electrolyte are accommodated in a flat box-shaped (cuboid shape) battery case. The present invention will be described in detail by taking a lithium ion secondary battery as an example.

  A schematic configuration of a lithium ion secondary battery according to an embodiment of the present invention is shown in FIGS. The lithium ion secondary battery 100 includes an electrode body (a wound electrode body) in which a long positive electrode sheet 10 and a long negative electrode sheet 20 are wound flatly via a long separator 40. 80 has the structure accommodated in the battery case 50 of the shape (flat box shape) which can accommodate this winding electrode body 80 with the non-aqueous electrolyte solution which is not shown in figure.

  The battery case 50 includes a flat cuboid case main body 52 having an open upper end, and a lid 54 that closes the opening. As a material constituting the battery case 50, a metal material such as aluminum or steel is preferably used (in this embodiment, aluminum). Or the battery case 50 formed by shape | molding resin materials, such as a polyphenylene sulfide (PPS) resin and a polyimide resin, may be sufficient. On the upper surface of the battery case 50 (that is, the lid body 54), a positive electrode terminal 70 that is electrically connected to the positive electrode of the wound electrode body 80 and a negative electrode terminal 72 that is electrically connected to the negative electrode 20 of the electrode body 80 are provided. It has been. Inside the battery case 50, a flat wound electrode body 80 is accommodated together with a non-aqueous electrolyte (not shown).

  The constituent elements constituting the wound electrode body 80 may be the same as those of the wound electrode body of the conventional lithium ion secondary battery, and are not particularly limited. For example, the positive electrode sheet 10 may be formed by applying a positive electrode mixture layer 14 mainly composed of a positive electrode active material for a lithium ion battery on a long positive electrode current collector 12. For the positive electrode current collector 12, an aluminum foil or other metal foil suitable for the positive electrode is preferably used.

The positive electrode active material used in this embodiment is a manganese-containing solid solution in which Li ₂ MnO ₃ is dissolved, and is a lithium manganese oxide represented by the general formula Li _x [Mn _(1-y) M _y ] O _z It is. Here, M in the formula is composed of at least one metal element other than Li and Mn, for example, one or two selected from the group consisting of Co, Ni, Fe, Ti, Mo, W, Cr, Zr, and Sn. Contains more than seed elements. Further, the values of x, y, and z in the formula are in the range of 1 <x <2, 0 ≦ y <1, and 1.5 <z <3. Preferable examples thereof include a manganese-containing solid solution in which LiNiO ₂ and LiCoO ₂ are solid-solved based on Li ₂ MnO ₃ such as Li _1.2 Mn _0.5 Co _0.14 Ni _0.14 O ₂ . Lithium manganese oxide composed of a solid solution based on such Li ₂ MnO ₃ is expected as a positive electrode active material having a high energy density, while oxygen (O ₂ ) from the solid solution (positive electrode active material) at the time of initial charge. ) May be detached. In the lithium ion secondary battery 100 according to the present embodiment, an appropriate amount of reducing gas is disposed in the battery case 50 in order to inactivate oxygen desorbed from such a solid solution (positive electrode active material). . This will be described later.

  As such a lithium manganese oxide (typically in particulate form), for example, a lithium manganese transition metal oxide powder prepared by a conventionally known method can be used as it is.

  The positive electrode mixture layer 14 can contain one or two or more materials that can be used as a constituent component of the positive electrode mixture layer in a general lithium ion battery, if necessary. An example of such a material is a conductive material. As the conductive material, a carbon material such as carbon powder or carbon fiber is preferably used. Alternatively, conductive metal powder such as nickel powder may be used. In addition, examples of the material that can be used as a component of the positive electrode mixture layer include various polymer materials that can function as a binder for the above constituent materials.

  The negative electrode sheet 20 can be formed by applying a negative electrode mixture layer 24 mainly composed of a negative electrode active material for a lithium ion battery on a long negative electrode current collector 22. For the negative electrode current collector 22, a copper foil or other metal foil suitable for the negative electrode is preferably used. As the negative electrode active material, one or more of materials conventionally used in lithium ion batteries can be used without any particular limitation. Preferable examples include carbon-based materials such as graphite carbon and amorphous carbon, lithium-containing transition metal oxides and transition metal nitrides.

  Suitable separator sheets 40 used between the positive and negative electrode sheets 10 and 20 include those made of a porous polyolefin resin. For example, a porous separator sheet made of synthetic resin (for example, made of polyolefin such as polyethylene) having a thickness of about 5 to 30 μm (for example, 25 μm) can be suitably used.

The wound electrode body 80 having such a configuration is accommodated in the case main body 52, and an appropriate nonaqueous electrolytic solution is disposed (injected) into the case main body 52. As the non-aqueous electrolyte accommodated in the case main body 52 together with the wound electrode body 80, the same non-aqueous electrolyte used in conventional lithium ion batteries can be used without any particular limitation. Such a nonaqueous electrolytic solution typically has a composition in which a supporting salt is contained in a suitable nonaqueous solvent. Examples of the non-aqueous solvent include ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), propylene carbonate (PC), and the like. Further, as the supporting salt, for _{example, LiPF 6, LiBF 4, LiAsF} 6, LiCF 3 can be preferably used a lithium salt of SO ₃ and the like.

Here, at least one reducing gas capable of reducing oxygen is disposed inside the battery case 50. As the reducing gas, a gas having a function capable of quickly capturing oxygen generated from the positive electrode active material is preferable. The reducing gas is preferably chemically inert with respect to the above-described battery constituent materials (positive and negative active materials, positive and negative current collectors, separators, non-aqueous electrolytes, etc.). . Further, the reducing gas is preferably one that changes oxygen generated from the positive electrode active material into a substance that is chemically inert with respect to the battery constituent material described above. As the reducing gas, for example, CO gas, H ₂ gas, SO ₂ gas, H ₂ S gas, a mixed gas thereof or the like can be used. In a preferred embodiment disclosed herein, CO gas is used as the reducing gas. When CO gas is used as the reducing gas, oxygen generated from the positive electrode active material can be changed to inactive CO ₂ gas by the reaction of CO + 1 / 2O ₂ → CO ₂ , thereby effectively removing oxygen. Can do.

  In a preferred embodiment disclosed herein, at least a part of the reducing gas is disposed in a state of being dissolved in the non-aqueous electrolyte. Oxygen generated from the positive electrode active material dissolves in the non-aqueous electrolyte and moves to the negative electrode side. Therefore, by dissolving a part of the reducing gas in the non-aqueous electrolyte, oxygen dissolved in the non-aqueous electrolyte (dissolved oxygen generated from the positive electrode active material) can be reliably captured.

The dissolved amount (dissolved volume) of the reducing gas in the non-aqueous electrolyte solution may be appropriately adjusted so that oxygen generated from the positive electrode active material can be captured without shortage. For example, the amount of oxygen generated from the positive electrode active material during initial charging is measured by preliminary experiments, and the reducing gas is dissolved in the non-aqueous electrolyte so that oxygen corresponding to the amount generated can be captured without shortage. Adjust the amount appropriately.
In a preferred embodiment disclosed herein, the reducing gas dissolution amount (dissolution concentration) is 1 × 10 ⁻³ mol / ml or more, preferably 1 × 10 ⁻² mol / ml per unit volume of the non-aqueous electrolyte. That's it. If the amount is less than this range, oxygen generated from the positive electrode active material may not be sufficiently captured. The upper limit value of the dissolution amount is not particularly limited, but is typically a saturated dissolution amount of the reducing gas in the nonaqueous electrolytic solution, that is, the nonaqueous electrolytic solution is saturated with the reducing gas. It is preferable.
The method for dissolving the reducing gas in the nonaqueous electrolytic solution is not particularly limited. For example, a method of holding the non-aqueous electrolyte in a reducing gas atmosphere can be employed. In this case, an appropriate amount of reducing gas can be dissolved according to the solubility, temperature and pressure of the reducing gas. In this embodiment, after the wound electrode body 80 is accommodated in the battery case 50 and a nonaqueous electrolyte is injected into the case, reducing gas is allowed to flow into the battery case from the opening of the battery case 50 (for example, Store in a reducing gas atmosphere with the opening of the battery case 50 open.) The reducing gas that has flowed into the battery case 50 comes into contact with the nonaqueous electrolyte solution in the case 50 and dissolves therein. Then, reducing gas can be arrange | positioned in the battery case 50 by sealing the opening part of the battery case 50 airtightly. Or you may perform the bubbling process which blows the bubble of reducing gas in a non-aqueous electrolyte. Thereby, reducing gas can be dissolved more efficiently. The operation of dissolving the reducing gas in the non-aqueous electrolyte may be performed before or after the electrolyte is injected into the battery case.

  In a preferred embodiment disclosed herein, a part of the reducing gas is not dissolved in the non-aqueous electrolyte, and the surplus gas is disposed in the battery case 50 with the gas remaining. When reducing gas dissolved in the non-aqueous electrolyte is consumed by reaction with oxygen generated from the positive electrode active material, surplus reducing gas (reducing gas arranged as a gas in the battery case) is generated. Newly dissolves in non-aqueous electrolyte. As a result, the reducing gas consumed by the reaction with oxygen can be replenished as needed, and oxygen dissolved in the non-aqueous electrolyte (dissolved oxygen generated from the positive electrode active material) can be reliably captured. The surplus reducing gas only needs to be disposed in direct contact with the non-aqueous electrolyte, for example, between the non-aqueous electrolyte and the battery case 50. .

  The reducing gas flows into the battery case from the opening of the battery case 50, and after the reducing gas that has flowed in contact with the nonaqueous electrolyte in the case is dissolved, the opening of the battery case is hermetically sealed. By sealing, the construction (assembly) of the lithium ion secondary battery 100 according to the present embodiment is completed. In addition, the sealing process of the case main body 52 and the arrangement | positioning (injection) process of electrolyte solution can be performed similarly to the method currently performed by manufacture of the conventional lithium ion secondary battery.

Since the battery 100 immediately after assembly is in an uncharged state, the battery 100 is then conditioned (initial charge). When conditioning (initial charge) is performed, Li ions are released from the positive electrode active material (lithium manganese oxide) and taken into the negative electrode active material. At this time, part of oxygen (O ₂ ) is desorbed from the positive electrode active material with the release of Li ions. When a part of oxygen is desorbed from the positive electrode active material in this way, the desorbed oxygen is dissolved in the non-aqueous electrolyte and moves to the negative electrode side, and Li ₂ O is deposited on the negative electrode (negative electrode active material layer). There is a fear. Li ₂ O deposited on the negative electrode hinders the subsequent charge / discharge reaction of the negative electrode, which may cause a decrease in battery performance (battery load characteristics).

In contrast, in the present embodiment, a reducing gas capable of reducing oxygen (here, CO gas) is disposed in the battery case, so that oxygen generated from the positive electrode active material during initial charging is captured, and CO + 1 / It can be inactivated by a reaction of 2O ₂ → CO ₂ . As a result, it is possible to avoid the formation of precipitates such as Li ₂ O on the negative electrode, and it is possible to obtain a lithium ion secondary battery with good load characteristics even after initial charging. A lithium ion secondary battery having good battery performance (especially load characteristics) can be obtained even after initial charging. Note that the CO ₂ gas generated by the above reaction can be released out of the battery case by a subsequent degassing step.

<Example>
In order to confirm that the deterioration of battery performance (load characteristics) can be eliminated by introducing CO gas into the battery case, the following experiment was conducted as an example. The embodiment described above will be described in more detail based on examples.

  That is, a test lithium ion secondary battery in which CO gas was introduced into the battery case was produced, and the discharge specific capacity after the initial charge of the produced test lithium ion secondary battery was measured and evaluated. The test lithium ion secondary battery of the example was manufactured as follows.

As the positive electrode active material a lithium manganese oxide comprising a solid solution of _Li 2 MnO ₃ and LiNiO ₂ and LiCoO ₂ synthesized by heat treatment of lithium hydroxide and manganese carbonate and cobalt hydroxide and nickel hydroxide. Specifically, lithium hydroxide, manganese carbonate, cobalt hydroxide, and nickel hydroxide were weighed so as to have a predetermined molar ratio, mixed, and then fired at 800 ° C. for 10 hours in an oxygen stream. Lithium manganese oxide was synthesized. In this example, a lithium manganese oxide having a composition ratio represented by Li _1.2 Mn _0.5 Co _0.14 Ni _0.14 O ₂ was synthesized.

  Using the above lithium manganese oxide as a positive electrode active material, the lithium manganese oxide powder, carbon black (conductive material), and polyvinylidene fluoride (PVdF) are made to have a mass ratio of 85: 10: 5. Were mixed in N-methylpyrrolidone (NMP) to prepare a paste-like composition for a positive electrode mixture layer. The paste-like positive electrode mixture layer composition is applied in layers on both sides of a long sheet-like aluminum foil (positive electrode current collector) and dried, whereby the positive electrode mixture layer is formed on both sides of the positive electrode current collector. The provided positive electrode sheet was obtained. This positive electrode sheet was punched into a circular shape of a predetermined size to produce a positive electrode.

  Moreover, the negative electrode was produced as follows. Graphite powder (negative electrode active material), styrene butadiene rubber (SBR), and carboxymethyl cellulose (CMC) are dispersed in a suitable solvent so that the mass ratio of these materials is 98: 1: 1, and a paste-like negative electrode A composition for the composite material layer was prepared. This composition for paste-like negative electrode mixture layer was applied in layers on both sides of a long sheet-like copper foil (negative electrode current collector) and dried, and a negative electrode mixture layer was provided on both sides of the negative electrode current collector. A negative electrode sheet was obtained. This negative electrode sheet was punched into a circular shape of a predetermined size to produce a negative electrode.

The positive electrode sheet and the negative electrode sheet are disposed opposite to each other with a polypropylene porous separator interposed therebetween, and are incorporated into a stainless steel coin-type battery case together with a non-aqueous electrolyte, and have a diameter of 20 mm and a thickness of 3.2 mm (2032 type). Built a coin cell. This battery case includes an upper container (also serving as a positive electrode terminal) in contact with the positive electrode sheet and a lower container (also serving as a negative electrode terminal) in contact with the negative electrode sheet, and is insulative and airtight between both containers. It has a structure in which a gasket is interposed. As the non-aqueous electrolyte, a mixed solvent containing ethylene carbonate (EC) and dimethyl carbonate (DMC) at a volume ratio of 3: 7 and containing LiPF ₆ as a supporting salt at a concentration of about 1 mol / liter. Using. Then, a negative electrode sheet is placed on the lower container, an appropriate amount of electrolytic solution is dropped to overlap the separator, and an appropriate amount of electrolytic solution is dropped to overlap the positive electrode sheet, and then the upper container is not covered. The CO gas was sufficiently brought into contact with the non-aqueous electrolyte by storing in an atmosphere of 100% CO gas in a state (in a state where the battery case was opened) for 1 hour. Next, the battery case was hermetically sealed by covering the upper container in an atmosphere of 100% CO gas. In this way, a test battery in which CO gas was introduced into the battery case was constructed.

  As Comparative Example 1, the test battery of Comparative Example 1 was produced in the same manner as the production of the test battery of the above example, except that CO gas was not introduced into the battery case. A test battery was constructed in the same manner as in the example except that CO gas was not introduced into the battery case.

Further, as Comparative Example 2, a test battery of Comparative Example 2 was constructed using positive electrode active materials having different composition ratios of lithium manganese oxide. Specifically, a lithium manganese oxide having a composition ratio represented by LiMn _1/3 Co _1/3 Ni _1/3 O ₂ was synthesized, and a test battery was constructed using this as a positive electrode active material. A test battery was constructed in the same manner as in Example except that the composition ratio of lithium manganese oxide was changed.

  Further, as Comparative Example 3, the test battery of Comparative Example 3 was produced in the same manner as the production of the test battery of Comparative Example 2 except that no CO gas was introduced into the battery case. A test battery was constructed in the same manner as Comparative Example 2 except that no CO gas was introduced into the battery case.

  Appropriate conditioning (initial charge / discharge) treatment is performed on each of the test batteries of Examples and Comparative Examples 1 to 3 constructed as described above, and then the load characteristics (high capacity is maintained even during large current discharge). Characteristic). Here, the load characteristics were calculated from the discharge capacity when discharging was performed at 1C and the discharge capacity when discharging was performed at 20C. Specifically, the load characteristic (discharge capacity ratio) is obtained by [discharge capacity when discharged at 20 C / 1 discharge capacity when discharged at 1 C] × 100. As charging / discharging conditions, in Example and Comparative Example 1, after carrying out constant current charge to 4.8V at 1 / 3C, operation which performed constant current discharge to 2.5V at 1C was performed. Next, after performing constant current charging to 4.8 V at 1/3 C, an operation for discharging constant current to 2.5 V at 20 C was performed. Further, in Comparative Example 2 and Comparative Example 3, after performing constant current charging at 1/3 C to 4.3 V, an operation for discharging constant current to 2.5 V at 1 C was performed. Subsequently, after performing constant current charge to 4.3V at 1 / 3C, operation which performed constant current discharge to 2.5V at 20C was performed. Table 1 shows the measurement results of load characteristics (discharge capacity ratio).

First, comparing an example in which Li _1.2 Mn _0.5 Co _0.14 Ni _0.14 O ₂ was used as a positive electrode active material and Comparative Example 1, the example in which CO gas was introduced into the battery case was compared. The battery had a larger discharge capacity ratio and improved load characteristics compared to the battery of Comparative Example 1 in which no CO gas was introduced into the battery case. This is because, in the battery of Comparative Example 1, Li ₂ O and the like were deposited on the negative electrode due to oxygen generated from the positive electrode active material during initial charging, and the charge / discharge reaction of the negative electrode was inhibited. In the battery, the oxygen is reacted with the CO gas to change it into an inactive CO ₂ gas, thereby suppressing the generation of Li ₂ O and the like, thereby preventing the inhibition of the charge / discharge reaction of the negative electrode. From this, it was confirmed that a lithium ion secondary battery having good load characteristics even after the initial charge can be obtained by disposing CO gas in the battery case.

When Comparative Example 2 and Comparative Example 3 using LiMn _1/3 Co _1/3 Ni _1/3 O ₂ as the positive electrode active material were compared, the discharge capacity was irrespective of the presence or absence of CO gas in the battery case. The ratio was almost the same, and the load characteristics were almost unchanged. This is because in the positive electrode active material made of LiMn _1/3 Co _1/3 Ni _1/3 O _2, oxygen does not fall off from the positive electrode active material, and there is almost no problem that the load characteristics are deteriorated. From these results, the effect of improving the load characteristics by arranging the CO gas in the battery case is the lithium manganese oxide represented by the general formula Li _x [Mn _(1-y) M _y ] O _z. Thus, it was found to be particularly effective for lithium manganese oxide satisfying x> 1.

  As mentioned above, although this invention was demonstrated by suitable embodiment, such description is not a limitation matter and of course various modifications are possible.

  Since the lithium ion secondary battery according to the present invention can suppress a decrease in load characteristics as described above and exhibits better battery performance, it is particularly suitable as a power source for a motor (electric motor) mounted on a vehicle such as an automobile. Can be used for Therefore, as schematically shown in FIG. 3, the present invention provides a vehicle (typically an automobile, particularly a hybrid) provided with such a lithium ion secondary battery 100 (typically, a battery pack formed by connecting a plurality of series batteries) as a power source. An automobile equipped with an electric motor such as an automobile, an electric vehicle, and a fuel cell vehicle) 1 is provided.

DESCRIPTION OF SYMBOLS 10 Positive electrode sheet 12 Positive electrode collector 14 Positive electrode composite material layer 20 Negative electrode sheet 22 Negative electrode collector 24 Negative electrode composite material layer 40 Separator 50 Battery case 52 Case main body 54 Lid body 70 Positive electrode terminal 72 Negative electrode terminal 80 Winding electrode body 100 Lithium Ion secondary battery

Claims (4)

A lithium ion secondary battery having a structure in which a positive electrode, a negative electrode, and a nonaqueous electrolytic solution are housed in a battery case,
The positive electrode is a manganese-containing solid solution in which Li ₂ MnO ₃ is dissolved as a positive electrode active material, and has a general formula Li _x [Mn _(1-y) M _y ] O _z (M is at least one type other than Li and Mn) A lithium manganese oxide represented by 1 <x <2, 0 ≦ y <1, 1.5 <z <3),
The lithium ion secondary battery is characterized in that at least one reducing gas capable of reducing oxygen is disposed inside the battery case.   The lithium ion secondary battery according to claim 1, wherein at least a part of the reducing gas is disposed in a state of being dissolved in the non-aqueous electrolyte.   The lithium ion secondary battery according to claim 1, wherein the reducing gas is CO gas.   A vehicle comprising the battery according to any one of claims 1 to 3.

Images