JP2011090876A - Lithium secondary battery and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lithium secondary battery having superior battery characteristics (cycling performance or high rate performance) by improving a reduction resistance by forming a film on a negative electrode and at the same time preventing oxidative decomposition by forming a similar film on a positive electrode. <P>SOLUTION: The lithium secondary battery includes a non-aqueous electrolytic solution that contains at least one kind of additive agent that decomposes by oxidoreduction reaction on the positive electrode and/or negative electrode side along with charging and discharging of the battery and generates a film on the surface of an active material on the positive electrode and/or negative electrode side. A positive electrode active material layer and/or a negative electrode active material layer (440) include a self-sacrifice auxiliary substance (442). The self-sacrifice auxiliary substance reacts with the additive agent that decomposes by oxidoreduction reaction along with charging and discharging of the battery, and adjusts an amount of the film generated on the surface of the active material on the positive electrode and/or negative electrode side by the reaction. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a lithium secondary battery and a method for manufacturing the same. In detail, it is related with the electrode active material used for manufacture of this battery.

  In recent years, secondary batteries such as lithium secondary batteries and nickel metal hydride batteries have become increasingly important as power sources mounted on vehicles using electricity as a drive source, or power sources mounted on personal computers, portable terminals, and other electrical products. . In particular, a lithium secondary battery that is lightweight and obtains a high energy density is expected to be preferably used as a high-output power source for mounting on a vehicle (for example, an automobile, particularly a hybrid automobile or an electric automobile). This type of lithium secondary battery (typically a lithium ion battery) is roughly an electrode having an electrode active material capable of reversibly occluding and releasing a chemical species (lithium ion) serving as a charge carrier. Has a configuration in which a positive electrode and a negative electrode) and an electrolytic solution (typically a non-aqueous electrolytic solution) serving as a movement path of the charge carrier are accommodated in a battery case.

  When a carbon material such as carbon particles is used as the negative electrode active material of the lithium secondary battery, the negative electrode active material functions as a strong reducing agent in the state of charge of the battery, and becomes extremely easy to react with the electrolytic solution. For this reason, a coating (SEI: Solid Electrolite Interface) is generated on the surface of the negative electrode (typically, the negative electrode active material) by the decomposition reaction of the electrolytic solution by the first charge. By covering the negative electrode active material with such a film, the reductive decomposition reaction on the negative electrode is suppressed, and as a result, deterioration and overcharge that affect battery characteristics (for example, cycle characteristics or high rate characteristics) are suppressed, and the battery Durability performance is improved. However, when an excessive amount of film is formed, the conductive path (conductive path) is partially blocked, thereby increasing the internal resistance and reducing the charging efficiency. In addition, this decomposition reaction results in self-discharge of the battery, and the electric charge consumed by the battery becomes an irreversible capacity, so that the capacity may be reduced.

  As a conventional technique related to the generation of a coating intended to suppress the reductive decomposition reaction on the negative electrode of such a lithium secondary battery, a battery in which an additive is added to an electrolytic solution is known. Patent Document 1 discloses a lithium secondary battery in which a sustained-release capsule that continuously releases a desired amount of an additive necessary for an electrolyte or an electrode at a certain level is blended in the electrolyte and / or electrode material. ing. Further, Patent Document 2 can be cited as another conventional technique for controlling the film formation by adding such an additive to the electrolytic solution.

JP 2009-501419 A JP 2004-228010 A

  As described in Patent Documents 1 and 2, according to the technique of adding an additive to an electrolytic solution, it is possible to suppress the reductive decomposition reaction of the electrolytic solution on the negative electrode surface to some extent, but still a sufficient level Not a thing. In addition, since the stable potential region (potential window) is relatively narrow, the additive decomposes even at a high positive potential, and an oxidatively decomposed film is excessively generated on the surface of the positive electrode (typically the surface of the positive electrode active material). There is a risk of causing an undesirable surplus reaction such as generation of gas. That is, the additive added in anticipation of film formation at one electrode (for example, the negative electrode) may be decomposed at the other electrode (for example, the positive electrode) to excessively generate a film.

  Therefore, the present invention was created to solve the above-described problem relating to suppression of excess reaction in the electrode related to the lithium secondary battery, and the object is to produce a coating on the negative electrode to improve reduction resistance. Thus, it is to provide a lithium secondary battery having excellent battery characteristics (for example, cycle characteristics or high-rate characteristics) by generating a similar coating on the positive electrode side to prevent oxidative decomposition. Another object is to provide a vehicle including such a lithium secondary battery.

  In order to achieve the above object, according to the present invention, a positive electrode having a positive electrode active material layer, a negative electrode having a negative electrode active material layer, and a positive electrode side and / or a negative electrode side are decomposed by an oxidation-reduction reaction with charge / discharge of the battery, There is provided a lithium secondary battery comprising: a non-aqueous electrolyte solution containing at least one additive that forms a film on the surface of the active material on the positive electrode side and / or the negative electrode side. The lithium secondary battery according to the present invention includes a self-sacrificial auxiliary material in at least one of the positive electrode active material layer and the negative electrode active material layer, and the self-sacrificial auxiliary material is used for charging and discharging the battery. It is a substance that reacts with the additive that is decomposed by the accompanying oxidation-reduction reaction, and enables the adjustment of the amount of film produced on the surface of the active material on the positive electrode side and / or the negative electrode side by the reaction. Features.

In the present specification, the “lithium secondary battery” refers to a secondary battery that uses lithium ions as electrolyte ions and is charged and discharged by movement of lithium ions between the positive and negative electrodes. In general, a secondary battery referred to as a lithium ion battery is a typical example included in the lithium secondary battery in this specification.
In this specification, the term “positive electrode active material layer” or “negative electrode active material layer” refers to reversibly occlusion and release (typically insertion) of chemical species (ie, lithium ions) that serve as charge carriers in a secondary battery. And an electrode active material (positive electrode active material or negative electrode active material) that can be detached).

The lithium secondary battery provided by the present invention generates a film on the surface of the active material on the positive electrode side and / or the negative electrode side as the battery is charged / discharged (in order to recover the film in the damaged portion) The same shall apply hereinafter.) A non-aqueous electrolyte containing at least one additive is provided. In general, by adding an additive that improves battery performance in the non-aqueous electrolyte, all or part of the additive during the initial charge is oxidized / reduced with the positive electrode active material and / or the negative electrode active material. And a film is formed on the surface of the positive electrode and / or the negative electrode (typically, the positive electrode active material and / or the negative electrode active material). The coating thus produced suppresses the subsequent decomposition reaction of the electrolyte solution on the positive electrode and / or negative electrode, and contributes to the improvement of battery characteristics (cycle characteristics or high-rate characteristics) because deterioration and overcharge are suppressed. . However, if the thickness of the coating becomes too thick, the conductive path (conductive path) is partially blocked, which increases internal resistance and decreases charge / discharge efficiency. . In addition, since the potential window of such an electrolyte is relatively narrow, an additive added in anticipation of film formation at one electrode (for example, the positive electrode) is decomposed at the other electrode (for example, the negative electrode) and excessively coated. There was a possibility of generating.
Therefore, the present invention provides a self-sacrificial auxiliary material for at least one of the positive electrode active material layer and the negative electrode active material layer as a material that reacts with the additive that is decomposed by the oxidation-reduction reaction accompanying charging and discharging of the battery. By including it, it is possible to adjust the amount of coating produced on the surface of the active material on the positive electrode side and / or the negative electrode side. As described above, in the electrode including the self-sacrificial auxiliary substance, the decomposition reaction of the additive by oxidation-reduction is caused to react not only with the electrode active material but also with the self-sacrificial auxiliary substance. Therefore, it is possible to suppress a decrease in battery capacity due to the formation of an excessive film on the surface of the electrode active material as in the past. As a result, in the present invention, a suitable amount of a coating that does not become excessive is generated on the surface of the active material on the positive electrode and / or negative electrode side, and an increase in internal resistance is suppressed, and the battery characteristics are excellent as a high-output power supply for vehicles. A lithium secondary battery having (cycle characteristics or high rate characteristics) can be provided.

In a preferred embodiment of the lithium secondary battery provided by the present invention, the positive electrode side and / or negative electrode side active material capacity (A [mAh / cm ² ]) and the self-sacrificial auxiliary material capacity are provided. The positive electrode active material layer and / or the negative electrode active material layer are configured so that the capacity ratio (A: S) to (S [mAh / cm ² ]) satisfies 90:10 to 97: 3.
The active material layer configured so that the capacity ratio between the capacity of the positive electrode side and / or the negative electrode side active material and the capacity of the self-sacrificial auxiliary material is within the above range includes a self-sacrificial auxiliary material. A high capacity can be maintained even when charging and discharging are repeated under high output conditions without causing a decrease in electrical conductivity. For example, the capacity ratio (A: S) between the capacity of the active material on the positive electrode side or the negative electrode side (A [mAh / cm ² ]) and the capacity of the self-sacrificial auxiliary material (S [mAh / cm ² ]) The positive electrode active material layer or the negative electrode active material layer is configured to satisfy 90:10 to 97: 3.

In another preferable aspect of the lithium secondary battery disclosed herein, the self-sacrificial auxiliary material is present in a state of being attached to at least a part of the surface of the active material on the positive electrode side and / or the negative electrode side.
In another preferred embodiment, the self-sacrificial auxiliary material is present in a state where the surface of the active material on the positive electrode side and / or the negative electrode side is coated with a uniform layer thickness.
The self-sacrificial auxiliary material contained in at least one of the positive electrode active material layer and the negative electrode active material layer is at least on the surface of the active material on the positive electrode side and / or the negative electrode side by a solid phase method such as powder mixing. The surface of the active material on the positive electrode side and / or the negative electrode side can be made uniform by a vapor deposition method such as a chemical vapor deposition (CVD) method or a liquid phase method of dipping in a solvent and drying (baking). It can be present in the active material layer in a manner coated with a layer thickness. Thereby, in the electrode containing the self-sacrificial auxiliary material, a stable film is generated on the surface of the active material. As a result, it is possible to provide a lithium secondary battery having excellent battery characteristics (cycle characteristics or high-rate characteristics) as a vehicle-mounted high-output power supply in which an increase in internal resistance is suppressed.

In a further preferred aspect of the lithium secondary battery disclosed herein, the self-sacrificial auxiliary material is contained in at least the positive electrode active material layer, and the self-sacrificial auxiliary material contained in the positive electrode active material layer is a battery. A material that oxidizes and decomposes the additive in accordance with the discharge, and has a potential lower than that of the positive electrode active material (specifically, a potential with respect to a lithium reference electrode).
In a lithium secondary battery in which a self-sacrificial auxiliary material having a lower potential than the positive electrode active material is used, the oxidative decomposition reaction between the additive and the self-sacrificial auxiliary material occurs preferentially over the reaction with the positive electrode active material. As a result, most of the additive is decomposed by the self-sacrificial auxiliary material, thereby suppressing the formation of an excessive film on the surface of the positive electrode active material.

Preferably, the positive electrode active material layer includes a lithium transition metal composite oxide having a layered structure or a spinel structure as the positive electrode active material, and a lithium-containing phosphate having an olivine structure as the self-sacrificial auxiliary material. .
Layered lithium transition metal composite oxide (eg, LiNiO ₂ , LiNi _1/2 Co _1/2 O ₂ , LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ) or spinel structure lithium transition metal composite In the positive electrode active material layer, a lithium-containing phosphate (for example, LiFePO ₄ ) having a lower olivine structure than a positive electrode active material made of an oxide (eg, LiMn ₂ O ₄ ) is used as a self-sacrificial auxiliary material. In the lithium secondary battery including the oxidative decomposition reaction between the additive and the self-sacrificial auxiliary material, the oxidative decomposition reaction between the additive and the positive electrode active material is selectively given priority. Thereby, the decomposition reaction between the positive electrode active material and the additive can be further suppressed, and the formation of an excessive film on the surface of the positive electrode active material can be suppressed. As a result, it is possible to provide a lithium secondary battery having excellent battery characteristics (cycle characteristics or high rate characteristics) as a vehicle-mounted high-output power source, particularly good low temperature cycle characteristics under low temperature high rate conditions.

In another preferred embodiment, a nonaqueous electrolytic solution containing vinylene carbonate is used as the additive that is oxidatively decomposed by the self-sacrificial auxiliary material contained in the positive electrode active material layer.
Vinylene carbonate added to the non-aqueous electrolyte is known to produce a very thin and suitable film on the negative electrode side, but in some cases, it may be decomposed on the positive electrode side to produce an excessive amount of film. Therefore, in a lithium secondary battery in which a self-sacrificial auxiliary material is included in at least the positive electrode active material layer, the decomposition reaction between the positive electrode active material and vinylene carbonate can be further improved by using a non-aqueous electrolyte containing vinylene carbonate. Further suppression and excessive film formation can be suppressed.

In another preferred embodiment of the lithium secondary battery disclosed herein, the self-sacrificial auxiliary material is included in at least the negative electrode active material layer, and the self-sacrificial auxiliary material included in the negative electrode active material layer includes: It is a substance that reduces and decomposes the additive as the battery is charged, and is characterized in that the potential (specifically, the potential with respect to the lithium reference electrode) is higher than that of the negative electrode active material.
In a lithium secondary battery using a self-sacrificial auxiliary material having a higher potential than the negative electrode active material, the reductive decomposition reaction between the additive and the self-sacrificial auxiliary material occurs preferentially over the reaction with the negative electrode active material. As a result, most of the additive is decomposed by the self-sacrificial auxiliary material, and it is possible to suppress the formation of an excessive film on the surface of the negative electrode active material.

Preferably, the negative electrode active material includes a carbon material, and the self-sacrificial auxiliary material includes lithium titanate.
In a lithium secondary battery including, as a self-sacrificial auxiliary material, lithium titanate having a higher potential than a negative electrode active material made of a carbon material such as carbon particles in a negative electrode active material layer, the additive and the self-sacrificial auxiliary material The reductive decomposition reaction occurs with priority over the reductive decomposition reaction between the additive and the negative electrode active material. Thereby, the decomposition reaction between the negative electrode active material and the additive is suppressed, and the formation of an excessive film on the surface of the negative electrode active material can be suppressed. As a result, it is possible to provide a lithium secondary battery having excellent battery characteristics (cycle characteristics or high rate characteristics) as a vehicle-mounted high-output power source, particularly good low temperature cycle characteristics under low temperature high rate conditions.

In another preferred embodiment, a non-aqueous electrolyte containing LiPF ₂ (C ₂ O ₄ ) ₂ is used as the additive that is reduced and decomposed by the self-sacrificial auxiliary material contained in the negative electrode active material layer. Is done.
LiPF ₂ (C ₂ O ₄ ) ₂ (hereinafter sometimes simply referred to as “LPFO”) added to the non-aqueous electrolyte is known to produce a very thin and suitable film on the positive electrode side, In some cases, it may be decomposed on the negative electrode side to produce an excessive amount of coating. Therefore, in a lithium secondary battery in which the self-sacrificial auxiliary material is included in at least the negative electrode active material layer, the decomposition reaction between the self-sacrificial auxiliary material and LPFO is prevented by using a non-aqueous electrolyte containing LPFO. It progresses preferentially over the decomposition reaction of the active material and LPFO, and it is possible to suppress the formation of an excessive amount of film on the surface of the negative electrode active material.

  Moreover, according to this invention, the vehicle provided with the lithium secondary battery disclosed here is provided. The secondary battery provided by the present invention has a suppressed internal resistance, particularly suitable as a power source for a battery mounted on a vehicle and battery performance (cycle characteristics or high rate characteristics), particularly under low temperature and high rate conditions. It may exhibit good low temperature cycle characteristics. Therefore, the secondary battery disclosed herein can be suitably used as a power source for a motor (electric motor) mounted on a vehicle such as an automobile equipped with an electric motor such as a hybrid vehicle or an electric vehicle.

It is sectional drawing which shows typically the negative electrode (40A) of the lithium secondary battery which concerns on one Embodiment. It is sectional drawing which shows typically the negative electrode (40B) of the lithium secondary battery which concerns on one Embodiment. It is a perspective view which shows typically the external shape of the lithium secondary battery which concerns on one Embodiment. It is the IV-IV sectional view taken on the line in FIG. It is a perspective view which shows typically the state which winds and produces an electrode body. It is a side view showing typically a vehicle (automobile) provided with a lithium secondary battery concerning one embodiment. The charging / discharging curve of the lithium secondary battery using graphite (comparative example 1) as a negative electrode active material is shown. The charging / discharging curve of the lithium secondary battery using lithium titanate (comparative example 2) as a negative electrode active material is shown. The charging / discharging curve of the lithium secondary battery using the mixture (Example 1) of the graphite as a negative electrode active material and the lithium titanate as a self-sacrificial auxiliary material is shown. 2 is a graph for relatively comparing outputs of lithium secondary batteries of Examples 1 to 3 and Comparative Example 1. FIG. Shows the charge-discharge curves of a lithium secondary battery using a mixture of a positive electrode active material _{(LiNi 1/3 Co 1/3 Mn 1/3 O} 2) and a self-immolative auxiliary substances (LiFePO ₄₎ (Example 5) . It is the graph which compared the output of each lithium secondary battery of Examples 4-6 and Comparative Example 3 relatively.

  Hereinafter, preferred embodiments of the present invention will be described. Note that matters other than matters specifically mentioned in the present specification and necessary for the implementation of the present invention can be grasped as design matters of those skilled in the art based on the prior art in this field. The present invention can be carried out based on the contents disclosed in this specification and common technical knowledge in the field.

  The lithium secondary battery (typically a lithium ion battery) disclosed herein includes a positive electrode having a positive electrode active material layer, a negative electrode having a negative electrode active material layer, a positive electrode side as the battery is charged and discharged, as described above. And / or a non-aqueous electrolyte solution containing at least one additive that decomposes by an oxidation-reduction reaction on the negative electrode side and forms a film on the surface of the active material on the positive electrode side and / or the negative electrode side.

  The non-aqueous electrolyte provided in the lithium secondary battery disclosed herein includes at least a non-aqueous solvent and an additive that forms a film on the surface of the active material on the positive electrode side and / or the negative electrode side as constituent components. Is characterized by Here, in the lithium secondary battery, the negative electrode active material functions as a strong reducing agent in a charged state, and the electrolytic solution is reduced and decomposed at the first charge, and a film (SEI: Solid Electrolite Interface) is generated on the surface of the active material. . It is known that such a film serves as a physical barrier that prevents decomposition of the electrolytic solution, suppresses the reductive decomposition reaction on the negative electrode, and contributes to improvement of battery characteristics (for example, cycle characteristics or high rate characteristics). However, if an excessive amount of coating is generated, it is not preferable because it leads to a decrease in capacity and a decrease in charging efficiency. Therefore, the non-aqueous electrolyte disclosed herein contains an additive for controlling the formation of such a film.

Additives contained in the non-aqueous electrolyte include vinylene carbonate, methyl vinylene carbonate, ethyl vinylene carbonate, propyl ethylene carbonate, dimethyl vinylene carbonate, diethyl vinylene carbonate, dipropyl vinylene carbonate, vinyl ethylene carbonate, fluoroethylene carbonate, Carbonate compounds having an ethylenically unsaturated bond, such as trifluoropropylene carbonate, phenylethylene carbonate and erythritan carbonate, or lithium-containing alkali metal salt LiPF ₂ (C ₂ O ₄ ) ₂ (so-called LPFO), Li [( C ₂ O ₄ ) ₂ B], Li (C ₂ O ₄ ) BF _{2 and the} like. Particularly preferred is vinylene carbonate or LiPF ₂ (C ₂ O ₄ ) ₂ . In addition, these additives may be used individually by 1 type, and 2 or more types may be mixed and used for them.

  As the non-aqueous solvent, aprotic solvents such as carbonates, esters, ethers, nitriles, sulfones, and lactones can be used. For example, in addition to carbonates such as ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), 1,2-dimethoxyethane, 1,2- Diethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dioxane, 1,3-dioxolane, diethylene glycol dimethyl ether, ethylene glycol dimethyl ether, acetonitrile, propionitrile, nitromethane, N, N-dimethylformamide, dimethyl sulfoxide, sulfolane, γ-butyrolactone, etc. One kind or two or more kinds selected from non-aqueous solvents that are generally known as those that can be used for an electrolytic solution of a lithium secondary battery can be used.

The non-aqueous electrolyte typically further includes a lithium salt as a supporting electrolyte (supporting salt) as a constituent component. For example, LiPF ₆ , LiBF ₄ , LiN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ C ₂ F ₅ ) ₂ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiC (SO ₂ CF ₃ ) ₃ , LiClO _One or two or more selected from various lithium salts known to be capable of functioning as a supporting electrolyte in the electrolyte solution of a lithium secondary battery such as ₄ can be used. LiPF ₆ is particularly preferable. The concentration of the supporting electrolyte is not particularly limited, and can be the same as the nonaqueous electrolytic solution used in the conventional lithium secondary battery. Usually, a nonaqueous electrolytic solution containing a supporting electrolyte at a concentration of about 0.1 mol / L to 5 mol / L (for example, about 0.8 mol / L to 1.5 mol / L) is preferable.

Here, as an additive contained in the non-aqueous electrolyte, for example, when vinylene carbonate is used, it is known that the reductive decomposition reaction by the negative electrode active material is suppressed to some extent by the additive vinylene carbonate. However, since the potential window is relatively narrow, there is a risk of decomposition at a high positive potential. That is, there is a possibility of causing an undesirable surplus reaction such as excessive formation of a film on the surface of the positive electrode (typically, the surface of the positive electrode active material) due to oxidative decomposition or generation of gas.
Further, when LiPF ₂ (C ₂ O ₄ ) ₂ (that is, the above LPFO) is used as an additive contained in the non-aqueous electrolyte, the oxidative decomposition reaction by the positive electrode active material is suppressed to some extent by the additive LPFO. In addition, since the potential window is relatively narrow, there is a possibility that an excessive film is formed on the surface of the negative electrode (typically, the surface of the negative electrode active material) by reductive decomposition. That is, an additive added in the hope of forming a film on one electrode (eg, positive electrode) is decomposed on the other electrode (eg, negative electrode) to produce an excessive film, thereby producing a suitable amount of film. It was difficult to do.
However, in the lithium secondary battery disclosed herein, as a substance that reacts with the additive contained in the non-aqueous electrolyte, a self-sacrificial auxiliary material is provided on at least one of the positive electrode active material layer and the negative electrode active material layer. include. Such a self-sacrificial auxiliary substance is a substance that decomposes by an oxidation-reduction reaction with an additive contained in the non-aqueous electrolyte accompanying charging / discharging of the lithium secondary battery, and the positive electrode active material and / or the negative electrode by the reaction This makes it possible to adjust the amount of film produced on the surface of the active material. As described above, in the electrode including the self-sacrificial auxiliary substance, the decomposition reaction due to the oxidation / reduction of the additive causes not only the electrode active material but also the self-sacrificial auxiliary substance to react. Therefore, there is no possibility that an excessive film is generated on the surface of the electrode active material as in the conventional case, and the decrease in battery capacity can be suppressed.

  Hereinafter, a lithium secondary battery including a self-sacrificial auxiliary material in both the positive electrode active material layer and the negative electrode active material layer will be described, but the present invention is not intended to be limited to such an embodiment. That is, any of the lithium secondary battery including the self-sacrificial auxiliary material only on the positive electrode side or the lithium secondary battery including the self-sacrificial auxiliary material only on the negative electrode side can be a preferred embodiment of the present invention.

  First, each component of the negative electrode of the lithium secondary battery according to the present embodiment will be described. The negative electrode disclosed here has a configuration in which a negative electrode active material layer is formed on the surface of a negative electrode current collector. As the negative electrode current collector serving as the base material of the negative electrode, a conductive member made of a highly conductive metal is preferably used. For example, copper or an alloy containing copper as a main component can be used. The shape of the negative electrode current collector may vary depending on the shape of the lithium secondary battery and the like, and thus is not particularly limited, and may be various forms such as a rod shape, a plate shape, a sheet shape, a foil shape, and a mesh shape. A copper foil having a thickness of about 5 to 100 μm is suitably used as a negative electrode current collector of a lithium secondary battery used as a high-output power source for mounting on a vehicle.

  The negative electrode active material layer formed on the surface of the negative electrode current collector includes a negative electrode active material capable of inserting and extracting lithium ions serving as charge carriers and a self-sacrificial auxiliary material. The self-sacrificial auxiliary material contained in the negative electrode active material layer is a substance that decomposes by a reduction reaction with the additive contained in the non-aqueous electrolyte as the lithium secondary battery is charged. This makes it possible to adjust the amount of coating produced on the surface. Thus, by including the self-sacrificial auxiliary material in the negative electrode active material layer as a substance that reacts with the additive contained in the non-aqueous electrolyte, the additive is not only the negative electrode active material but also the self-sacrificial auxiliary material. Since it reacts with the substance and decomposes, it is possible to prevent an excessive amount of coating from being generated on the surface of the negative electrode active material.

  Moreover, as a negative electrode active material disclosed here, as long as the objective of this invention is realizable, 1 type, or 2 or more types of the substance conventionally used for a lithium secondary battery can be used without limitation. An example is carbon particles. A particulate carbon material (carbon particles) containing a graphite structure (layered structure) at least partially is preferably used. Any carbon material of a so-called graphitic material (graphite), a non-graphitizable carbonaceous material (hard carbon), a graphitizable carbonaceous material (soft carbon), or a combination of these materials is preferably used. obtain. Among these, graphite particles can be preferably used. Graphite particles (eg, graphite) are excellent in conductivity because they can suitably occlude lithium ions as charge carriers. Further, since the particle size is small and the surface area per unit volume is large, it can be a negative electrode active material suitable for high-rate pulse charge / discharge.

Further, as a self-sacrificial auxiliary material constituting the negative electrode active material layer, a substance that reduces and decomposes the additive as the battery is charged, and has a potential (specifically, relative to a lithium reference electrode) from the negative electrode active material. Those having noble potential can be preferably used. Examples include transition metal oxides or sulfides (for example, titanium-based oxides or sulfides). For example, lithium titanate, titanium oxide (TiO ₂ ), titanium sulfide, tungsten oxide, molybdenum oxide, cobalt oxide, iron sulfide, and the like are preferable. Particularly preferred is lithium titanate, and examples include Li _{4 + x} Ti ₅ O ₁₂ (0 ≦ x ≦ 3) and Li _{2 + x} Ti ₃ O ₇ (0 ≦ x ≦ 3).
By using a self-sacrificial auxiliary material having a higher potential than the negative electrode active material, the reductive decomposition reaction between the additive and the self-sacrificial auxiliary material occurs preferentially over the reaction between the additive and the negative electrode active material. As a result, most of the additive is decomposed by the self-sacrificial auxiliary material, and it is possible to suppress the formation of an excessive film on the surface of the negative electrode active material.

  In addition, the negative electrode active material layer can typically contain an optional component such as a binder as necessary in addition to the negative electrode active material and the self-sacrificial auxiliary material. As such a binder, the same binder as that used for the negative electrode of a general lithium secondary battery can be appropriately employed. It is preferable to select a polymer that is soluble or dispersible in the solvent used. For example, in the case of using an aqueous solvent, cellulose polymers such as carboxymethyl cellulose (CMC) and hydroxypropyl methyl cellulose (HPMC); polyvinyl alcohol (PVA); polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene Water-soluble or water-dispersible polymers such as fluorine resins such as polymers (FEP); vinyl acetate copolymers; rubbers such as styrene butadiene rubber (SBR) and acrylic acid-modified SBR resins (SBR latex); Can be adopted. When a non-aqueous solvent is used, a polymer such as polyvinylidene fluoride (PVDF) or polyvinylidene chloride (PVDC) can be preferably used. Such a binder may be used individually by 1 type, and may be used in combination of 2 or more type. In addition to the function as a binder, the polymer material exemplified above may be used for the purpose of exhibiting the function as a thickener or other additive of the above composition.

Next, a method for manufacturing the negative electrode of the lithium secondary battery will be described.
First, a negative electrode active material and a self-sacrificial auxiliary material are prepared, and a mixture of the negative electrode active material and the self-sacrificial auxiliary material is prepared. The negative electrode active material layer disclosed herein includes a negative electrode active material and a self-sacrificial auxiliary material. The negative electrode active material capacity (A [mAh / cm ² ]) and the self-sacrificial auxiliary material capacity (S [MAh / cm ² ]) and the volume ratio (A: S) preferably satisfies 90:10 to 97: 3 (preferably approximately 94: 6 to 96: 4). The negative electrode active material layer is formed so that the capacity ratio between the capacity of the negative electrode active material and the capacity of the self-sacrificial auxiliary material is within the above range, thereby reducing conductivity due to the inclusion of the self-sacrificial auxiliary material. Without it, a high capacity can be maintained even after repeated charging and discharging under high output conditions.

  Further, the negative electrode active material layer disclosed herein is not particularly limited as to the mode (arrangement) of the material in the layer as long as the negative electrode active material and the self-sacrificial auxiliary material are included. 2, for example, a state in which a self-sacrificial auxiliary material is attached to at least a part of the surface of the negative electrode active material (FIG. 1), or a self-sacrificial type with a uniform layer thickness on the surface of the negative electrode active material The negative electrode active material layer is preferably formed so as to have a state (FIG. 2) covered with the auxiliary material. Thereby, the reduction reaction in which the self-sacrificial auxiliary substance decomposes the additive contained in the non-aqueous electrolyte occurs preferentially over the decomposition reaction between the additive and the negative electrode active material. As a result, most of the additive is decomposed by the self-sacrificial auxiliary material, and a stable coating is formed on the surface of the negative electrode active material. As a result, it is possible to provide a lithium secondary battery having excellent battery characteristics (cycle characteristics or high-rate characteristics) as a vehicle-mounted high-output power supply in which an increase in internal resistance is suppressed.

  1 and 2 show a negative electrode 40 (40A, 40B) of a lithium secondary battery in which a negative electrode active material layer 44 (44A, 44B) is formed on the surface of a negative electrode current collector 42. FIG. In the negative electrode active material layer 44 (44A, 44B), the negative electrode active material layer is preferably formed so that the negative electrode active material 440 and the self-sacrificial auxiliary material 442 exist in a state as shown in FIG. For example, a mixture of the negative electrode active material and the self-sacrificial auxiliary material can be prepared in advance using the following method.

First, as shown in FIG. 1, a negative electrode active material layer 44 </ b> A having a state in which a self-sacrificial auxiliary material 442 is attached (for example, scattered in an island shape) to at least part of the surface of the negative electrode active material 440 is formed. As a method for preparing the above mixture, the prepared negative electrode active material and self-sacrificial auxiliary material are mixed or stirred in a solid phase. As a result, a mixture in which the self-sacrificial auxiliary material adheres to at least a part of the surface of the negative electrode active material (for example, is scattered in an island shape) is obtained. The working time of mixing or stirring is not limited, but the longer the time is, the more the mixture of the negative electrode active material and the self-sacrificial auxiliary material is such that more self-sacrificial auxiliary material adheres to the surface of the negative electrode active material. can get.
In addition, as shown in FIG. 2, preparation of the mixture for forming a negative electrode active material layer 44B having a state in which the surface of the negative electrode active material 440 is coated with a self-sacrificial auxiliary material 442 with a uniform layer thickness is provided. As a method, various known methods such as a liquid phase method (crystallization method) in which a negative electrode active material is immersed in a solvent containing a self-sacrificial auxiliary material and dried (fired), or a vapor deposition method (gas phase method) are used. The membrane techniques can be used alone or in appropriate combination. The concept of the vapor deposition method here includes various vapor deposition methods such as physical vapor deposition (PVD method, for example, sputtering method), chemical vapor deposition method (CVD method, for example, plasma CVD method), and reactive vapor deposition method.
Although not limited to such an embodiment, it is more preferable that the surface of the negative electrode active material be coated with a self-sacrificial auxiliary material with a uniform layer thickness (FIG. 2). Accordingly, when the mixture is prepared by using a liquid phase method or a gas phase method, a negative electrode active material layer in a suitable state that can realize the object of the present invention can be formed. .

  Next, the prepared mixture of the negative electrode active material and the self-sacrificial auxiliary material is mixed with the appropriate solvent (aqueous solvent or non-aqueous solvent) together with the binder or the like, and the paste or slurry negative electrode active material A layer forming composition (hereinafter referred to as “negative electrode active material layer forming paste”) is prepared. As for the blending ratio of each constituent material, for example, the ratio of the mixture of the negative electrode active material and the self-sacrificial auxiliary material in the negative electrode active material layer is preferably about 50 mass% or more, and about 85 to 99 mass%. (For example, 90 to 97% by mass) is more preferable. Further, the ratio of the binder in the negative electrode active material layer can be, for example, about 1 to 15% by mass, and is usually preferably about 3 to 10% by mass. The paste thus prepared is applied to the negative electrode current collector, the solvent is volatilized and dried, and then compressed (pressed). Thereby, the negative electrode of the lithium secondary battery which has the negative electrode active material layer formed using this paste on a negative electrode collector is obtained.

  As a solvent used for preparing the negative electrode active material layer forming paste, either an aqueous solvent or a non-aqueous solvent can be used. The aqueous solvent is typically water, but may be any water-based solvent as a whole, that is, water or a mixed solvent mainly composed of water can be preferably used. As the solvent other than water constituting the mixed solvent, one or more organic solvents (lower alcohol, lower ketone, etc.) that can be uniformly mixed with water can be appropriately selected and used. For example, it is preferable to use a solvent in which about 80% by mass or more (more preferably about 90% by mass or more, more preferably about 95% by mass or more) of the aqueous solvent is water. A particularly preferred example is a solvent consisting essentially of water. Further, preferred examples of the non-aqueous solvent include N-methyl-2-pyrrolidone (NMP), methyl ethyl ketone, toluene and the like.

  In addition, as a method of apply | coating the said paste to a negative electrode collector, the technique similar to a conventionally well-known method is employable suitably. For example, the paste can be suitably applied to the negative electrode current collector by using an appropriate application device such as a slit coater, a die coater, a gravure coater, or a comma coater. Moreover, when drying a solvent, it can dry favorably by using natural drying, a hot air, low-humidity air, a vacuum, infrared rays, far-infrared rays, and an electron beam individually or in combination. Furthermore, as a compression method, a conventionally known compression method such as a roll press method or a flat plate press method can be employed. In adjusting the thickness, the thickness may be measured with a film thickness measuring instrument, and the press pressure may be adjusted to compress a plurality of times until a desired thickness is obtained.

  Next, each component of the positive electrode of the lithium secondary battery disclosed here will be described. Such a positive electrode has a configuration in which a positive electrode active material layer is formed on the surface of a positive electrode current collector. As the positive electrode current collector that becomes the base material of the positive electrode, a conductive member made of a metal having good conductivity is preferably used. For example, aluminum or an alloy containing aluminum as a main component can be used. The shape of the positive electrode current collector is not particularly limited because it can be different depending on the shape of the lithium secondary battery and the like, similarly to the negative electrode current collector.

  The positive electrode active material layer formed on the surface of the positive electrode current collector includes a positive electrode active material capable of inserting and extracting lithium ions serving as charge carriers and a self-sacrificial auxiliary material. The self-sacrificial auxiliary material contained in the positive electrode active material layer is a substance that decomposes by an oxidation reaction with an additive contained in the non-aqueous electrolyte along with the discharge of the lithium secondary battery. This makes it possible to adjust the amount of coating produced on the surface. Thus, by including a self-sacrificial auxiliary material in the positive electrode active material layer as a substance that reacts with the additive contained in the non-aqueous electrolyte, the additive is not only a positive electrode active material but also a self-sacrificial auxiliary material. Since it reacts with the substance and decomposes, it is possible to prevent an excessive amount of film from being generated on the surface of the positive electrode active material.

Moreover, as a positive electrode active material disclosed here, as long as the objective of this invention is realizable, 1 type, or 2 or more types of the substance conventionally used for a lithium secondary battery can be used without limitation. As a typical positive electrode active material, a lithium transition metal composite oxide having a layered structure or a spinel structure containing lithium (Li) and at least one transition metal element can be given. For example, cobalt lithium composite oxide (LiCoO ₂ ), nickel lithium composite oxide (LiNiO ₂ ), manganese lithium composite oxide (LiMn ₂ O ₄ ), or nickel-cobalt-based LiNi _x Co _1-x O ₂ (0 <X <1), cobalt-manganese LiCo _x Mn _1-x O ₂ (0 <x <1), nickel-manganese LiNi _x Mn _1-x O ₂ (0 <x <1) and LiNi _x A so-called binary lithium transition metal composite oxide containing two kinds of transition metal elements as represented by Mn _2−x O ₄ (0 <x <2) may be used. Alternatively, a ternary lithium transition metal composite oxide (typically LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ) such as nickel / cobalt / manganese containing three kinds of transition metal elements may be used. The lithium transition metal composite oxide illustrated above has a potential in the range of about 3.5 to 5 V (specifically, the potential with respect to the lithium reference electrode).
Here, the lithium transition metal composite oxide includes at least lithium (Li) and at least one transition metal element nickel (Ni) cobalt (Co), an oxide having manganese (Mn) as a main constituent metal element, and at least The meaning also includes an oxide containing one kind of metal element (that is, a transition metal element other than the main constituent metal element and / or a typical metal element) as a fine constituent metal element in a proportion smaller than the molar ratio of each main constituent metal element. It is. Examples of such minute constituent metal elements include aluminum (Al), chromium (Cr), iron (Fe), vanadium (V), magnesium (Mg), titanium (Ti), zirconium (Zr), niobium (Nb), Selected from the group consisting of molybdenum (Mo), tungsten (W), copper (Cu), zinc (Zn), gallium (Ga), indium (In), tin (Sn), lanthanum (La) and cerium (Ce). Can be one or more.

  In addition, as such a lithium transition metal oxide, for example, a lithium transition metal oxide powder prepared and provided by a conventionally known method can be used as it is. For example, the oxide can be prepared by mixing several raw material compounds appropriately selected according to the atomic composition at a predetermined molar ratio and firing by an appropriate means. In addition, a granular lithium transition metal oxide powder substantially composed of secondary particles having a desired average particle size and / or particle size distribution by pulverizing, granulating and classifying the fired product by appropriate means Can be obtained.

Further, as a self-sacrificial auxiliary material capable of realizing the object of the present invention, a potential (specifically, a potential with respect to a lithium reference electrode) is higher than the potential (approximately 3.5 to 4.2 V) of the positive electrode active material listed above. Can be preferably used. For example, a lithium-containing phosphoric acid having an olivine structure represented by the general formula LiMPO ₄ (wherein M is at least one transition metal element selected from the group consisting of Co, Ni, Mn, and Fe) Salt. Preferable examples of the olivine type lithium-containing phosphate include lithium iron phosphate (LiFePO ₄ ), lithium manganese phosphate (LiMnPO ₄ ) and the like. The potential is approximately 3.2 to 3.8V (vs. lithium reference electrode potential).
By using a self-sacrificial auxiliary material having a lower potential than the positive electrode active material, the oxidative decomposition reaction between the additive and the self-sacrificial auxiliary material occurs preferentially over the reaction between the additive and the positive electrode active material. As a result, most of the additive is decomposed by the self-sacrificial auxiliary material, and it is possible to suppress the formation of an excessive film on the surface of the positive electrode active material.

The combination of the positive electrode active material and the self-sacrificial auxiliary material is not particularly limited, but some suitable combinations are exemplified. For example, a combination using a layered structure of LiNi _1/3 Co _1/3 Mn _1/3 O ₂ as a positive electrode active material and a olivine-structured LiFePO ₄ as a self-sacrificial auxiliary material may be mentioned. The combination of the positive electrode active material and the self-sacrificial auxiliary material constituting the positive electrode active material layer is not limited to such a combination. The lithium transition metal composite oxide having a layered structure may be used as a self-sacrificial auxiliary material as long as it satisfies the material. For example, one using LiMn ₂ O ₄ having a spinel structure with a high potential (approximately 4.2 V) as a positive electrode active material and using LiNiO ₂ having a layered structure having a lower potential as a self-sacrificial auxiliary material can be given.

  Further, the positive electrode active material layer typically contains, as necessary, optional components such as a conductive material and a binder in addition to the positive electrode active material and the self-sacrificial auxiliary material. obtain. As the conductive material, a conductive powder material such as carbon powder or carbon fiber is preferably used. As the carbon powder, various carbon blacks such as acetylene black, furnace black, ketjen black, and graphite powder are preferable. In addition, conductive fibers such as carbon fibers and metal fibers, metal powders such as copper and nickel, and organic conductive materials such as polyphenylene derivatives can be contained alone or as a mixture thereof. In addition, only 1 type may be used among these, or 2 or more types may be used together. In addition, as the binder, the same binder as that used for the positive electrode of a general lithium secondary battery can be adopted as appropriate, and functions as the binder listed in the above-described negative electrode components. Various polymer materials that can be used are preferably used.

Next, a method for manufacturing the positive electrode of the lithium secondary battery will be described.
First, a positive electrode active material and a self-sacrificial auxiliary material are prepared, and a mixture of the positive electrode active material and the self-sacrificial auxiliary material is prepared. That is, the positive electrode active material layer disclosed herein includes a positive electrode active material and a self-sacrificial auxiliary material. Similarly to the negative electrode, the positive electrode active material capacity (A [mAh / cm ² ]) and the above The capacity ratio (A: S) with the capacity of the self-sacrificial auxiliary substance (S [mAh / cm ² ]) satisfies 90:10 to 97: 3 (preferably approximately 94: 6 to 96: 4). Weigh each. Then, after weighing, a mixture of the positive electrode active material and the self-sacrificial auxiliary material is prepared. The positive electrode active material layer disclosed herein is a state in which a self-sacrificial auxiliary material is attached to at least a part of the surface of the positive electrode active material, or the surface of the positive electrode active material is coated with the self-sacrificial auxiliary material with a uniform layer thickness. It is preferable to be formed so as to have the above state. Therefore, a mixture of the positive electrode active material and the self-sacrificial auxiliary material is prepared using the same method as that for the negative electrode. In addition, as long as the positive electrode active material and the self-sacrificial auxiliary material are included, the aspect (arrangement) in the layer of the material is not particularly limited, but the self-sacrificial auxiliary material is at least on the surface of the positive electrode active material. When the above mixture is prepared so as to be partly attached (for example, scattered in an island shape) (see FIG. 1), a positive electrode active material layer in a suitable state capable of realizing the object of the present invention is formed. be able to.

  Next, the prepared mixture of the positive electrode active material and the self-sacrificial auxiliary material is mixed with the appropriate solvent (aqueous solvent or non-aqueous solvent) together with the conductive material, the binder, and the like to form a paste or slurry. A composition for forming a positive electrode active material layer (hereinafter referred to as “positive electrode active material layer forming paste”) is prepared. The blending ratio of each constituent material is, for example, about 50% by mass or more (typically 50 to 95% by mass) of the mixture of the positive electrode active material and the self-sacrificial auxiliary material in the positive electrode active material layer. It is preferably about 70 to 95% by mass (for example, 75 to 90% by mass). The proportion of the conductive material in the positive electrode active material layer can be, for example, about 2 to 20% by mass, and preferably about 2 to 15% by mass. Furthermore, in the composition using the binder, the proportion of the binder in the positive electrode active material layer can be, for example, about 1 to 10% by mass, and usually about 2 to 5% by mass. The paste prepared by mixing the constituent materials in this way is applied to the positive electrode current collector 32, and after the solvent is evaporated and dried, the paste is compressed (pressed). Thereby, the positive electrode of the lithium secondary battery in which the positive electrode active material layer is formed on the positive electrode current collector is obtained. In addition, the application | coating, drying, and the compression method can use a conventionally well-known means similarly to the manufacturing method of the above-mentioned positive electrode.

  Hereinafter, as one specific example of the lithium secondary battery according to the present invention, a square-shaped lithium secondary battery including a wound electrode body will be described. However, the present invention is not intended to be limited to such an example. Absent. Further, matters other than the matters specifically mentioned in the present specification and matters necessary for carrying out the present invention (for example, the configuration and manufacturing method of the electrode body, the configuration and manufacturing method of the separator, the lithium secondary battery, etc. General techniques related to battery construction, etc.) can be grasped as design matters of those skilled in the art based on conventional techniques in the field. In addition, in the following drawings, the same code | symbol is attached | subjected to the member and site | part which show | plays the same effect | action, and the overlapping description may be abbreviate | omitted or simplified. In addition, the dimensional relationships (length, width, thickness, etc.) in each drawing do not reflect actual dimensional relationships.

FIG. 3 is a perspective view schematically showing a rectangular lithium secondary battery according to one embodiment, and FIG. 4 is a sectional view taken along line IV-IV in FIG. FIG. 5 is a perspective view schematically showing a state in which the electrode body is wound and manufactured.
As shown in FIG. 3 and FIG. 4, the lithium secondary battery 100 according to the present embodiment includes a rectangular parallelepiped battery case 10 and a lid body 14 that closes the opening 12 of the case 10. A flat electrode body (wound electrode body 20) and an electrolyte can be accommodated in the battery case 10 through the opening 12. The lid 14 is provided with a positive terminal 38 and a negative terminal 48 for external connection, and a part of the terminals 38 and 48 protrudes to the surface side of the lid 14. Also, some of the external terminals 38 and 48 are connected to the internal positive terminal 37 or the internal negative terminal 47, respectively, inside the case.

  Next, the wound electrode body 20 according to the present embodiment will be described with reference to FIGS. 4 and 5. As shown in FIG. 4, the wound electrode body 20 includes a sheet-like positive electrode sheet 30 having a positive electrode active material layer 34 on the surface of a long positive electrode current collector 32, a long sheet-like separator 50, a long A sheet-like negative electrode sheet 40 having a negative electrode active material layer 44 on the surface of a long negative electrode current collector 42 is formed. As shown in FIG. 5, in the cross-sectional view in the winding axis direction R, the positive electrode sheet 30 and the negative electrode sheet 40 are laminated via two separators 50. 50, the negative electrode sheet 40, and the separator 50 are laminated in this order. The laminate is wound around a shaft core (not shown) in a cylindrical shape, and is formed into a flat shape by squashing the obtained wound electrode body 20 from the side surface direction.

Further, as shown in FIG. 5, the wound electrode body 20 according to the present embodiment has a positive electrode active material layer formed on the surface of the positive electrode current collector 32 at the center in the winding axis direction R. 34 and the negative electrode active material layer 44 formed on the surface of the negative electrode current collector 42 overlap each other to form a densely stacked portion. Further, in a cross-sectional view in the direction along the winding axis direction R, the exposed portion of the positive electrode current collector 32 (positive electrode active material layer) without forming the positive electrode active material layer 34 at one end in the direction R. The non-forming portion 36) is laminated in a state of protruding from the separator 50 and the negative electrode sheet 40 (or a dense laminated portion of the positive electrode active material layer 34 and the negative electrode active material layer 44). That is, a positive electrode current collector laminated portion 35 formed by laminating the positive electrode active material layer non-forming portion 36 in the positive electrode current collector 32 is formed at the end of the electrode body 20. Also, the other end of the electrode body 20 has the same configuration as that of the positive electrode sheet 30, and the negative electrode active material layer non-formation portion 46 in the negative electrode current collector 42 is laminated to form the negative electrode current collector lamination portion 45. ing.
Here, as the separator 50, a separator having a width larger than the width of the laminated portion of the positive electrode active material layer 34 and the negative electrode active material layer 44 and smaller than the width of the electrode body 20 is used, and the positive electrode current collector 32 and the negative electrode The current collectors 42 are disposed so as to be sandwiched between the stacked portions of the positive electrode active material layer 34 and the negative electrode active material layer 44 so as not to contact each other and cause an internal short circuit.

The separator 50 is a sheet interposed between the positive electrode sheet 30 and the negative electrode sheet 40, and is disposed so as to be in contact with the positive electrode active material layer 34 of the positive electrode sheet 30 and the negative electrode active material layer 44 of the negative electrode sheet 40. Then, short-circuit prevention due to the contact between the active material layers 34 and 44 in the positive electrode sheet 30 and the negative electrode sheet 40 and the conduction path between the electrodes by impregnating the electrolyte (non-aqueous electrolyte) in the pores of the separator 50. It plays a role of forming (conductive path).
As a constituent material of the separator 50, a porous sheet (microporous resin sheet) made of a resin can be preferably used. Particularly preferred are porous polyolefin resins such as polypropylene, polyethylene, and polystyrene.

  The lithium secondary battery according to the present embodiment can be constructed as follows. It has the positive electrode (typically positive electrode sheet 30) which has the positive electrode active material layer containing the produced positive electrode active material and the self-sacrificial auxiliary material, and the negative electrode active material layer containing the negative electrode active material and the self-sacrificial auxiliary material. The negative electrode (typically, the negative electrode sheet 40) is stacked and wound together with the two separators 50, and the obtained wound electrode body 20 is formed into a flat shape by being crushed from the side surface direction and dragged. The positive electrode active material layer non-formation portion 36 of the positive electrode current collector 32 is ultrasonically welded and the internal negative electrode terminal 47 is formed on the negative electrode current collector 42 and the negative electrode active material layer non-formation portion 46 is ultrasonically welded. It joins by welding etc. and it electrically connects with the positive electrode sheet 30 or the negative electrode sheet 40 of the winding electrode body 20 formed in the said flat shape. After the wound electrode body 20 obtained in this way is accommodated in the battery case 10, the lithium secondary battery 100 of this embodiment can be constructed by injecting a non-aqueous electrolyte and sealing the inlet. . In particular, the structure, size, material (for example, can be made of metal or laminate film) of the battery case 10, and the structure of the electrode body (for example, a wound structure or a laminated structure) having the positive and negative electrodes as main components, etc. There is no limit.

  As described above, the lithium secondary battery 100 constructed in this manner suppresses an increase in internal resistance and exhibits good battery characteristics (cycle characteristics or high rate characteristics) as a vehicle-mounted high-output power supply. obtain. Due to such characteristics, the lithium secondary battery 100 according to the present invention can be suitably used as a power source for a motor (electric motor) mounted on a vehicle such as an automobile. Therefore, as schematically shown in FIG. 6, a vehicle including such a lithium secondary battery 100 (which may be in the form of an assembled battery formed by connecting a plurality of lithium secondary batteries 100 in series) as a power source. (Typically automobiles, in particular automobiles equipped with electric motors such as hybrid cars, electric cars, fuel cell cars) 1 are provided.

  In the following test examples, a lithium secondary battery (test battery) disclosed herein was constructed and its performance was evaluated. However, it is not intended to limit the present invention to those shown in the specific examples.

[Construction of lithium secondary battery (1)]
A test lithium secondary battery including a self-sacrificial auxiliary material in the negative electrode active material layer was constructed as follows. First, a mixture of a negative electrode active material (graphite) and a self-sacrificial auxiliary material (lithium titanate) was prepared by a gas phase method (CVD method), a liquid phase method, and a solid phase method, respectively. The above mixtures were prepared so that the volume ratio of the negative electrode active material (graphite) and the self-sacrificial auxiliary material (lithium titanate) satisfied 95: 5.

<Preparation of mixture of negative electrode active material and self-sacrificial auxiliary material: gas phase method (Example 1)>
A mixture of the negative electrode active material and the self-sacrificial auxiliary material was prepared by a vapor phase method (CVD method). That is, graphite (average particle size 10 μm) was placed in the reaction vessel, and the pressure (10 ⁻⁷ Pa) and temperature (300 ° C.) in the reaction vessel were set. Tetraisopropoxy titanate (Ti [OCH (CH ₃ ) ₂ ] ₄ ) as a titanium raw material is heated and sublimated at 300 ° C., and lithium sulfate (Li ₂ SO ₄ ) as a lithium raw material is heated and sublimated at 600 ° C. to obtain a raw material gas And was introduced into the reaction vessel while flowing oxygen as a carrier gas. And the heat processing for 15 hours was performed and the mixture was prepared by growing lithium titanate on the surface of a graphite.

<Preparation of Mixture of Negative Electrode Active Material and Self-Sacrificial Auxiliary Material: Liquid Phase Method (Example 2)>
A mixture of the negative electrode active material and the self-sacrificial auxiliary material was prepared by a liquid phase method (crystallization method). That is, graphite (average particle size 10 μm) was added to an aqueous ammonium carbonate solution ((NH ₄ ) ₂ SO ₄ ) and stirred. Titanium chloride (TiCl ₄ ) was added thereto and stirred at a reaction temperature of 25 ° C. to prepare a titanic acid raw material liquid. After sufficiently mixing the raw material liquid, the mixture was heated to 60 ° C., and lithium hydroxide (LiOH) was added and mixed to prepare a mixture.

<Preparation of mixture of negative electrode active material and self-sacrificial auxiliary material: solid phase method (Example 3)>
A mixture of a negative electrode active material and a self-sacrificial auxiliary material was prepared by a solid phase method. That is, graphite (average particle diameter: 10 μm) and lithium titanate were charged into a stirring tank, and the mixture was prepared by stirring using a ball mill apparatus. The stirring conditions were as follows: ball filling rate: 30%, ball diameter: Φ10, revolution number: 300 rpm, stirring time: 3 hours.

  Next, the negative electrode of the lithium secondary battery was produced. That is, when forming the negative electrode active material layer in the negative electrode, a negative electrode active material layer forming paste was prepared. The paste is prepared by mixing the prepared mixture, a styrene butadiene block copolymer (SBR) as a binder, and carboxymethyl cellulose (CMC) with a mass% ratio of these materials of 98: 1: 1. Prepared by mixing with ion exchange water. In addition, the negative electrode active material layer formation paste which used only graphite (comparative example 1) or only lithium titanate (comparative example 2) as a negative electrode active material instead of the mixture as a negative electrode active material was prepared similarly.

Mixture of graphite and lithium titanate (Example 1: Gas phase method, Example 2: Liquid phase method, Example 3: Solid phase method), Graphite only (Comparative Example 1), Lithium titanate only (Comparative Example 2) ) To a copper foil (thickness 10 μm) as a negative electrode current collector so that the amount of the negative electrode active material coating per unit area is about 6.5 mg / cm ^2. It was applied to both sides and dried. After drying, the film was stretched into a sheet by a roller press to form a thickness of about 60 μm, and the negative electrode active material layer was slit so as to have a predetermined width, thereby preparing negative electrodes (negative electrode sheets).

Then, the positive electrode of the lithium secondary battery for a test was produced. That is, a positive electrode active material layer forming paste was prepared for forming the positive electrode active material layer in the positive electrode. The paste comprises LiNi _1/3 Co _1/3 Mn _1/3 O ₂ as a positive electrode active material, acetylene black (AB) as a conductive material, and carboxymethyl cellulose (CMC) in a mass% ratio of these materials. Was prepared by mixing with ion-exchanged water so that the ratio was 87: 10: 3.
Next, the positive electrode active material layer forming paste is applied to the positive electrode current collector so that the coverage of the positive electrode active material per unit area is about 12 mg / cm ² on the aluminum foil (thickness 15 μm) as the positive electrode current collector. It was applied to both sides and dried. After drying, the sheet was stretched into a sheet shape with a roller press to form a thickness of about 90 μm, and slit so that the positive electrode active material layer had a predetermined width to produce a positive electrode (positive electrode sheet).

Using the prepared positive electrode sheet and negative electrode sheet, a test lithium secondary battery (laminate cell) was constructed. That is, positive electrode sheets (dimensions (cm) approximately 4.8 × 4.8) and two negative electrode sheets (dimensions (cm) approximately 5.0 × 5.0) are alternately laminated, and between the two sheets. Two polypropylene / polyethylene / polypropylene three-layer film (PP / PE / PP film) separators were inserted to produce an electrode body. This electrode body was housed in a laminated battery container together with a non-aqueous electrolyte, and a test lithium secondary battery was constructed. As the non-aqueous electrolyte, a 1: 7 (volume ratio) mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC), 1 mol / L LiPF ₆ (LPFO) as a lithium salt, and an additive A solution in which 0.05 mol / L LiPF ₂ (C ₂ O ₄ ) ₂ was dissolved was used.

[Charge / discharge curve]
7 to 9 show the charge / discharge curves of the first cycle of the lithium secondary batteries constructed as described above. FIG. 7 shows a charge / discharge curve of graphite (Comparative Example 1), FIG. 8 shows a charge / discharge curve of lithium titanate (Comparative Example 2), and FIG. 9 shows a mixture of graphite and lithium titanate (Example 1: The gas-phase method charge / discharge curve is shown.
According to this, as shown in FIG. 8, the charge / discharge curve of lithium titanate (Comparative Example 2) is around 1.5 V (reference potential to lithium: hereinafter referred to as “vs Li / Li ⁺ ”). It is confirmed that lithium ions are occluded and released in the potential range and the additive (LPFO) in the non-aqueous electrolyte is decomposed. However, the charge / discharge curve of the mixture of graphite and lithium titanate (Example 1: vapor phase method) shows titanic acid in a potential range near 1.5 V (vs. Li / Li ⁺ ) as shown in FIG. It was confirmed that the additive (LPFO) was decomposed by lithium and a charge / discharge curve (FIG. 7) similar to that of graphite (Comparative Example 1) was drawn at a potential lower than that. Therefore, in a lithium secondary battery having a negative electrode active material layer containing a mixture of graphite as a negative electrode active material and lithium titanate as a self-sacrificial auxiliary material, an additive (non-aqueous electrolyte) containing lithium titanate ( It was revealed that a reaction for decomposing LPFO) occurred.

[Battery characteristics evaluation]
Next, as an index for evaluating the output characteristics of each lithium secondary battery constructed as described above, a cycle test by pulse charge / discharge was performed at a temperature condition of 0 ° C., and the output after the cycle was measured. That is, each battery was adjusted to a SOC 60% charge state by constant current constant voltage (CC-CV) charging under a temperature condition of 0 ° C. After that, under a temperature condition of 0 ° C., a pulse charge / discharge cycle of 10 seconds at 16 to 20 C was repeated 500 cycles. After the cycle, the output was measured using a current value at which the capacity retention rate of the battery was 99% or more. Moreover, the output of each battery was converted into the output ratio when the output measurement value of the lithium secondary battery using graphite (Comparative Example 1) as the negative electrode active material was 100. The result is shown in FIG.

FIG. 10 is a graph that relatively compares the outputs of the respective lithium secondary batteries. According to this, the output ratio of the lithium secondary battery constructed using a mixture of graphite and lithium titanate (Examples 1 to 3) is the same as that of the lithium secondary battery constructed using only graphite (Comparative Example 1). Both values were higher than the output ratio. Moreover, the output ratio of the graphite / lithium titanate mixture decreased in the order of Example 1: gas phase method, Example 2: liquid phase method, and Example 3: solid phase method.
From this, it was confirmed that when a mixture of graphite as the negative electrode active material and lithium titanate as the self-sacrificial auxiliary material was prepared, the output of the lithium secondary battery was improved.

[Construction of lithium secondary battery (2)]
Next, a test lithium secondary battery including a self-sacrificial auxiliary material in the positive electrode active material layer was constructed as follows. First, a mixture of a positive electrode active material (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ) and a self-sacrificial auxiliary material (LiFePO ₄ ) was prepared by a liquid phase method and a solid phase method, respectively. The above mixtures were prepared so that the volume ratio of the positive electrode active material (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ) and the self-sacrificial auxiliary material (LiFePO ₄ ) satisfied 95: 5. did.

<Preparation of Mixture of Positive Electrode Active Material and Self-Sacrificial Auxiliary Material: Liquid Phase Method (Example 4)>
A mixture of a positive electrode active material and a self-sacrificial auxiliary material was prepared by a liquid phase method. That is, after pulverizing and mixing iron oxalate dihydrate (FeC ₂ O ₄ .2H ₂ O), ammonium dihydrogen phosphate (NH ₄ H ₂ PO ₄ ), and lithium carbonate (Li ₂ CO ₃ ) Acetone was added to prepare a raw material solution. After sufficiently mixing the raw material liquid, LiNi _1/3 Co _1/3 Mn _1/3 O ₂ was added and further mixed, and heated and fired at 700 ° C. to prepare a mixture.

<Preparation of Mixture of Positive Electrode Active Material and Self-Sacrificial Auxiliary Material: Solid Phase Method (Examples 5 and 6)>
A mixture of a positive electrode active material and a self-sacrificial auxiliary material was prepared by a solid phase method. That is, LiNi _1/3 Co _1/3 Mn _1/3 O ₂ and LiFePO ₄ and LiFePO ₄ were put into a stirring tank and stirred using a ball mill apparatus to prepare a mixture. The stirring conditions were as follows: ball filling rate: 30%, ball diameter: Φ10, revolution number: 300 rpm, stirring time: 1.5 hours (Example 5), 3 hours (Example 6).

Next, the positive electrode of the lithium secondary battery was produced. That is, a positive electrode active material layer forming paste was prepared for forming the positive electrode active material layer in the positive electrode. The paste is prepared by mixing the prepared mixture, acetylene black (AB) as a conductive material, and carboxymethyl cellulose (CMC) with ion-exchanged water so that the mass% ratio of these materials is 87: 10: 3. Prepared by mixing. In addition, the positive electrode active material layer forming paste using only LiNi _1/3 Co _1/3 Mn _1/3 O ₂ (Comparative Example 3) as the positive electrode active material instead of the mixture is the same as the positive electrode active material. Prepared.

Mixture of LiNi _1/3 Co _1/3 Mn _1/3 O ₂ and LiFePO ₄ (Example 4: Liquid phase method, Example 5: Solid phase method, Example 6: Solid phase method), LiNi _1/3 A paste prepared using only Co _1/3 Mn _1/3 O ₂ (Comparative Example 3) was applied to an aluminum foil (thickness: 15 μm) as a positive electrode current collector with a coating amount of the positive electrode active material per unit area. It apply | coated to both surfaces of the positive electrode electrical power collector so that it might become about 12 mg / cm < ² >, and it was made to dry. After drying, the sheet was stretched into a sheet shape with a roller press to form a thickness of about 90 μm, and slit so that the positive electrode active material layer had a predetermined width to produce a positive electrode (positive electrode sheet).

Then, the negative electrode of the lithium secondary battery for a test was produced. That is, when forming the negative electrode active material layer in the negative electrode, a negative electrode active material layer forming paste was prepared. The paste comprises graphite as a negative electrode active material, styrene butadiene block copolymer (SBR) as a binder, and carboxymethyl cellulose (CMC) in a mass% ratio of these materials of 98: 1: 1. It was prepared by mixing with ion exchange water.
Next, the prepared paste is applied to both sides of the negative electrode current collector so that the coating amount of the negative electrode active material per unit area is about 6.5 mg / cm ² on the copper foil (thickness 10 μm) as the negative electrode current collector. And dried. After drying, the film was stretched into a sheet by a roller press to form a thickness of about 60 μm, and the negative electrode active material layer was slit so as to have a predetermined width, thereby preparing negative electrodes (negative electrode sheets).

Using the prepared positive electrode sheet and negative electrode sheet, a test lithium secondary battery (laminate cell) was constructed. However, as a non-aqueous electrolyte, a 1: 7 (volume ratio) mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC), 1 mol / L LiPF ₆ as a lithium salt, and 0. The lithium secondary battery was constructed in the same procedure as the above-described construction (1) of the lithium secondary battery except that the one in which 02 mol / L vinylene carbonate (VC) was dissolved was used.

[Charge / discharge curve]
FIG. 11 shows a charge / discharge curve for the first cycle of a lithium secondary battery constructed using a mixture of LiNi _1/3 Co _1/3 Mn _1/3 O ₂ and LiFePO ₄ (Example 5: solid phase method). Indicates.
As shown in FIG. 11, decomposition of the additive (VC) by LiFePO ₄ was confirmed in a potential region near 3.25 V (vs. Li / Li ⁺ ). Therefore, in a lithium secondary battery having a positive electrode active material layer including a mixture of LiNi _1/3 Co _1/3 Mn _1/3 O ₂ as a positive electrode active material and LiFePO ₄ as a self-sacrificial auxiliary material, LiFePO ₄ It was shown that the reaction which decomposes | disassembles the additive (VC) contained in nonaqueous electrolyte solution has arisen.

[Battery characteristics evaluation]
Next, as an index for evaluating the output characteristics of each lithium secondary battery constructed as described above, a cycle test by pulse charge / discharge was performed at a temperature condition of 0 ° C., and the output after the cycle was measured. The measurement was performed by the same means as the battery characteristic evaluation described above. However, the output of each battery was converted into the output ratio when the output measurement value of the lithium secondary battery using only LiNi _1/3 Co _1/3 Mn _1/3 O ₂ (Comparative Example 3) was 100. . The result is shown in FIG.

FIG. 12 is a graph that relatively compares the outputs of the respective lithium secondary batteries. According to this, the output ratio of the lithium secondary battery constructed using a mixture of LiNi _1/3 Co _1/3 Mn _1/3 O ₂ and LiFePO ₄ (Examples 4 to 6) is LiNi _1/3 Co _1/3 Mn _1/3 O ₂ alone (Comparative Example 3) showed a value higher than the output ratio of the lithium secondary battery constructed. Also, a mixture of LiNi _1/3 Co _1/3 Mn _1/3 O ₂ and LiFePO ₄ (Example 5: solid phase method), LiNi _1/3 Co _1/3 Mn _1/3 O ₂ and LiFePO ₄ The output ratio decreased in the order of the mixture (Example 6: solid phase method) and the mixture of LiNi _1/3 Co _1/3 Mn _1/3 O ₂ and LiFePO ₄ (Example 4: liquid phase method).
Therefore, when a mixture of LiNi _1/3 Co _1/3 Mn _1/3 O ₂ as the positive electrode active material and LiFePO ₄ as the self-sacrificial auxiliary material is prepared, the output of the lithium secondary battery is improved. It was confirmed.

  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. For example, the present invention is not limited to the above-described wound type battery, and can be applied to lithium secondary batteries having various shapes. Further, the size and other configurations of the battery can be appropriately changed depending on the application (typically for in-vehicle use).

  Since the lithium secondary battery according to the present invention exhibits excellent battery characteristics (cycle characteristics or high rate characteristics) as described above, particularly good low-temperature cycle characteristics under low-temperature pulse charge / discharge conditions, the lithium secondary battery is mounted on a vehicle such as an automobile. It can be suitably used as a power source for a motor (electric motor). Therefore, as schematically shown in FIG. 6, the present invention provides a vehicle 1 (typically an automobile, particularly a hybrid) provided with such a lithium secondary battery (typically, a battery pack formed by connecting a plurality of series batteries) 100 as a power source. Automobiles, electric vehicles, automobiles equipped with electric motors such as fuel cell vehicles).

DESCRIPTION OF SYMBOLS 1 Vehicle 10 Battery case 12 Opening part 14 Cover body 20 Winding electrode body 30 Positive electrode sheet 32 Positive electrode collector 34 Positive electrode active material layer 35 Positive electrode collector lamination | stacking part 36 Positive electrode active material layer non-formation part 37 Positive electrode current collection terminal 38 External positive electrode current collector terminal 40 Negative electrode sheet 42 Negative electrode current collector 44 Negative electrode active material layer 45 Negative electrode current collector laminated portion 46 Negative electrode active material layer non-formation portion 47 Negative electrode current collector terminal 48 External negative electrode current collector terminal 50 Separator 100 Lithium secondary Battery 440 Negative electrode active material 442 Self-sacrificial auxiliary material R Winding axis direction

Claims (11)

A positive electrode having a positive electrode active material layer;
A negative electrode having a negative electrode active material layer;
Non-aqueous electrolyte containing at least one additive that decomposes by oxidation-reduction reaction on the positive electrode side and / or negative electrode side with charge / discharge of the battery and forms a film on the surface of the active material on the positive electrode side and / or negative electrode side When,
A lithium secondary battery comprising:
A self-sacrificial auxiliary material is included in at least one of the positive electrode active material layer and the negative electrode active material layer;
The self-sacrificial auxiliary material is a material that reacts with the additive that is decomposed by a redox reaction associated with charging / discharging of the battery, and is caused on the surface of the active material on the positive electrode side and / or the negative electrode side by the reaction. A lithium secondary battery, characterized in that it enables adjustment of the amount of film produced. Capacity ratio (A: S) of the capacity of the active material on the positive electrode side and / or the negative electrode side (A [mAh / cm ² ]) and the capacity of the self-sacrificial auxiliary material (S [mAh / cm ² ]) The lithium secondary battery according to claim 1, wherein the positive electrode active material layer and / or the negative electrode active material layer are configured to satisfy 90:10 to 97: 3.   3. The lithium secondary battery according to claim 1, wherein the self-sacrificial auxiliary material is present in a state of being attached to at least a part of a surface of the active material on the positive electrode side and / or the negative electrode side.   3. The lithium secondary battery according to claim 1, wherein the self-sacrificial auxiliary material is present in a state where the surface of the active material on the positive electrode side and / or the negative electrode side is coated with a uniform layer thickness.   The self-sacrificial auxiliary material is included in at least the positive electrode active material layer, and the self-sacrificial auxiliary material included in the positive electrode active material layer is a material that oxidatively decomposes the additive as the battery discharges, The lithium secondary battery according to claim 1, wherein the potential is lower than that of the positive electrode active material.   6. The lithium according to claim 5, wherein the positive electrode active material layer includes a lithium transition metal composite oxide having a layered structure as the positive electrode active material and a lithium-containing phosphate having an olivine structure as the self-sacrificial auxiliary material. Secondary battery.   The lithium secondary battery according to claim 5 or 6, wherein a non-aqueous electrolyte containing vinylene carbonate is used as the additive that is oxidatively decomposed by a self-sacrificial auxiliary material contained in the positive electrode active material layer.   The self-sacrificial auxiliary material is included in at least the negative electrode active material layer, and the self-sacrificial auxiliary material included in the negative electrode active material layer is a substance that reduces and decomposes the additive as the battery is charged. The lithium secondary battery according to claim 1, wherein the lithium secondary battery has a higher potential than the negative electrode active material.   The lithium secondary battery according to claim 8, wherein the negative electrode active material layer includes a carbon material as the negative electrode active material and lithium titanate as the self-sacrificial auxiliary material. The non-aqueous electrolyte containing LiPF ₂ (C ₂ O ₄ ) ₂ is used as the additive that is reduced and decomposed by the self-sacrificial auxiliary material contained in the negative electrode active material layer. The lithium secondary battery as described. A vehicle comprising the lithium secondary battery according to claim 1.

Images