JP2011210609A - Lithium secondary battery and method of manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium secondary battery in which lithium deactivated during initial charge can be replenished.SOLUTION: The lithium secondary battery includes positive and negative electrodes having active material which can store and emit lithium ions, and an electrolyte. The positive electrode includes: a lithium source as one or more compounds selected from a group of LiO, LiO, LiCO, LiOH, and LiH; and a lithium generation auxiliary agent as one or more compounds selected from a group of Pt, Au, MeO(Me is Mn, Fe, Co, Ni, V, or Cr, and X is a positive number corresponding to an oxidation number of Me).

Description

  The present invention relates to a lithium secondary battery which is an electricity storage device having high output and high energy density and excellent charge / discharge cycle characteristics, and a method for producing the same.

  With the rapid market expansion of portable electronic devices such as notebook PCs and mobile phones, there is an increasing demand for small, large-capacity secondary batteries with high energy density and excellent charge / discharge cycle characteristics. Yes. In order to meet this demand, a secondary battery using lithium ions as a charge carrier and utilizing an electrochemical reaction accompanying charge transfer by the charged particles has been developed.

By the way, after manufacturing a lithium battery, there exists a problem that the quantity which can be charged / discharged after that becomes smaller than the quantity of the initial charge which is the charge performed initially.
The main cause is thought to be that the activity of lithium is lost because the electrolyte solution decomposes on the surface of the negative electrode active material during initial charging to produce lithium compounds and the like.
Further, when an insertion type material such as C, Sn, Si, Cu ₆ Sn ₅ is adopted as the negative electrode material, it is not possible to take out all of the lithium taken into the negative electrode during the initial charging during the subsequent discharge. This is considered to be a cause of a decrease in charge / discharge capacity. That is, it is considered that a side reaction at the negative electrode proceeds during charging and lithium deactivation occurs at the negative electrode.
In order to replenish lithium decreased due to side reactions, a production method is disclosed in which at least one compound selected from Li ₂ CO ₃ , Li ₂ O and LiOH is contained in the positive electrode during initial charging (Patent Document 3).

Considering the presence of acid generated during initial charging as another factor, it reacts with acid generated by decomposition of electrolyte and other battery components in order to suppress degradation of battery performance caused by the acid generation. A basic substance selected from the group consisting of LiOH, Li ₂ O, LiAlO ₂ , Li ₂ SiO ₃ , Li ₂ CO ₃ , Na ₂ CO ₃ , and CaCO ₃ , which is a neutralizing substance, is contained in the positive electrode A lithium battery is disclosed (Patent Document 1).

  Moreover, the electrode active material for lithium secondary batteries which further contains an amphoteric compound, an alkali metal sulfide, or an oxide in the electrode active material is shown (patent document 2).

JP-T-2006-523368 (Claim 27, paragraphs 0085-0087, etc.) JP-T-2005-510017 (Claims, Abstract, etc.) JP 2004-172112 A (claim 24, paragraphs 0052, 0054, etc.)

  In view of the above circumstances, it is an object of the present invention to provide a lithium secondary battery capable of effectively replenishing deactivated lithium and a method for manufacturing the same.

The feature of the lithium secondary battery according to claim 1 for solving the above problem is a lithium secondary battery comprising a positive and negative electrode comprising an active material capable of occluding and releasing lithium ions, and an electrolyte solution,
The positive electrode is
A lithium source that is one or more compounds selected from the group consisting of Li ₂ O, Li ₂ O ₂ , Li ₂ CO ₃ , LiOH, and LiH;
Lithium formation aid which is one or more compounds selected from the group consisting of Pt, Au, MeO _X (Me is Mn, Fe, Co, Ni, V, or Cr; X is a positive number corresponding to the oxidation number of Me) Agent,
It is in having.

  In addition to the lithium source that generates lithium by its own decomposition, it contains lithium generation aids that can effectively decompose the lithium source, thereby supplementing the deactivated lithium with the addition of a minimum lithium source. can do.

  The feature of the lithium secondary battery according to claim 2 for solving the above-mentioned problem is that the Me is Mn, Fe, or Co. These compounds are excellent in that they are highly available and do not adversely affect the battery reaction.

  The feature of the lithium secondary battery according to claim 3 for solving the above-mentioned problem is that the content of the lithium source is an amount corresponding to or more than lithium deactivated during initial charging. Since the lithium secondary battery of the present invention can efficiently generate lithium from a lithium source due to the presence of a lithium generation aid, the amount of lithium source added can be reduced.

  The feature of the lithium secondary battery according to claim 4 for solving the above-mentioned problem is that the negative electrode active material comprises a carbon material, a metal material capable of forming an alloy with lithium, lithium titanium oxide, titanium oxide, and vanadium oxide. It is one or more compounds selected from the group. When these insertion type materials are employed as the negative electrode active material, the deactivation of lithium due to initial charging is remarkable, and therefore, the adoption of the embodiment of the present invention is very effective.

The feature of the method for producing a lithium secondary battery according to claim 5 for solving the above-mentioned problem is to produce a lithium secondary battery comprising a positive and negative electrode comprising an active material capable of occluding and releasing lithium ions, and an electrolyte. A method,
A lithium source that is one or more compounds selected from the group consisting of Li ₂ O, Li ₂ O ₂ , Li ₂ CO ₃ , LiOH, and LiH;
Lithium formation aid which is one or more compounds selected from the group consisting of Pt, Au, MeO _X (Me is Mn, Fe, Co, Ni, V, or Cr; X is a positive number corresponding to the oxidation number of Me) Agent,
In the presence of the positive electrode active material, and an initial charging step of performing initial charging of the positive and negative electrodes in the presence of the electrolytic solution.

  When a lithium battery is manufactured, initial charging may be performed. In this case, in addition to the lithium source, a lithium generation aid capable of effectively decomposing the lithium source is included, thereby reducing the minimum lithium source. Since lithium deactivated by the addition can be replenished, a lithium secondary battery having a high charge / discharge capacity can be manufactured.

  A feature of the method of manufacturing a lithium secondary battery according to claim 6 for solving the above-described problem is that the Me is Mn, Fe, or Co. These compounds are excellent in that they are highly available and do not adversely affect the battery reaction.

  The feature of the method for producing a lithium secondary battery according to claim 7 for solving the above-mentioned problem is that the content of the lithium source is an amount corresponding to or more than lithium deactivated during initial charging. Since the lithium secondary battery of the present invention can efficiently generate lithium from a lithium source due to the presence of a lithium generation aid, the amount of lithium source added can be reduced.

  The feature of the method for producing a lithium secondary battery according to claim 8 for solving the above problem is that the negative electrode active material is a carbon material, a metal material capable of forming an alloy with lithium, a titanium oxide, and a vanadium oxide. It is to be one or more selected compounds. When these insertion type materials are employed as the negative electrode active material, the deactivation of lithium due to initial charging is remarkable, and therefore, the adoption of the embodiment of the present invention is very effective.

It is a graph which shows the result of the test 1 (type of negative electrode active material) of an Example. It is a graph which shows the result of the test 1 (existence of a lithium source and a lithium production | generation auxiliary agent) of an Example. It is a graph which shows the result of the test 2 (content of lithium source) of an Example. It is a graph which shows the result of the test 3 (content of lithium production | generation adjuvant) of an Example. It is a graph which shows the result of the test 4 (initial charge voltage) of an Example. It is a graph which shows the result of the test 5 (removal of reaction gas) of an Example. It is a graph which shows the result of the test 6 (type of lithium production | generation adjuvant) of an Example. It is a graph which shows the result of the test 7 (type of lithium source) of an Example.

  The lithium secondary battery and the manufacturing method thereof according to the present invention will be described below in detail based on the embodiments.

(Lithium secondary battery)
The lithium secondary battery of this embodiment includes a positive and negative electrode including an active material capable of occluding and releasing lithium ions, an electrolytic solution, and other necessary members. The positive electrode has a lithium source and a lithium production assistant.

As the positive electrode active material, a lithium-containing transition metal oxide can be employed. The lithium-containing transition metal oxide is a material capable of removing and inserting Li ⁺ , and can be exemplified by a lithium-metal composite oxide having a layered structure or a spinel structure. Specifically, Li ₁ -Z NiO ₂ , Li ₁ -Z MnO ₂ , Li ₁ -Z Mn ₂ O ₄ , Li ₁ -Z CoO ₂ and other metal oxide materials, Li ₁ -Z βPO ₄ (β is And LiFePO ₄ which is Fe), and one or more of them can be included. Z in this illustration shows the number of 0-1. A material obtained by adding or substituting a transition metal such as Li, Mg, Al, or Co, Ti, Nb, or Cr may be used. Moreover, not only these lithium-metal composite oxides are used alone, but also a plurality of them can be mixed and used. In addition, a conductive polymer material, a material having a radical, or the like can be mixed.

The lithium source is one or more compounds selected from the group consisting of Li ₂ O, Li ₂ O ₂ , Li ₂ CO ₃ , LiOH, and LiH. The lithium source can be contained in the positive electrode in the form of particles. The lithium source is decomposed by charging the lithium secondary battery to supply lithium ions. It is conceivable that the lithium source generates a reaction gas after decomposition. For example, oxygen, carbon dioxide and the like are generated as a reaction gas.

As the lithium source content, the amount of lithium deactivated by the initial charge of the lithium secondary battery is obtained by preliminary experiments, theoretical calculations, etc., and the amount corresponding to that amount or the amount that can produce lithium more than that is adopted It is desirable to do. For example, it is desirable to mix 1 or more, further 1.2 or more on a mass basis with respect to the amount of lithium source required. The method for calculating the amount of the lithium source to be mixed is not particularly limited. Formula (1): (Amount of necessary lithium source: g) = {(Charge capacity of negative electrode single electrode: mAh−Discharge capacity of single electrode of negative electrode: mAh) )-(Positive electrode single electrode charge capacity: mAh-Positive electrode single electrode discharge capacity: mAh)} / (Theoretical discharge capacity per gram of lithium source: Lithium source is Li ₂ O. For example, 1794 mAh / g, which is uniquely determined by the type of lithium source). Note that, in the lithium secondary battery that has been initially charged, the lithium source is consumed up, and the lithium source may not exist.

Lithium ions are generated by decomposition of the lithium source. For example, a reaction of 2Li ₂ O → 4Li ⁺ + O ₂ ↑ + 4e ⁻ proceeds and lithium ions are supplied. O ₂ or the like produced by the decomposition of the lithium source takes a form such as a gas and is directly discharged out of the battery reaction system.

A lithium production aid is added so that the lithium source is efficiently decomposed. One or more compounds selected from the group consisting of Pt, Au, MeO _X (Me is Mn, Fe, Co, Ni, V, or Cr; X is a positive number corresponding to the oxidation number of Me). It is. Me is particularly preferably Mn, Fe, or Co. When a compound containing manganese, iron, nickel, and cobalt is employed as the positive electrode active material, the battery reaction proceeds with the charging, and a compound (oxide) similar to the lithium generation aid is generated. In the present invention, efficient lithium production from a lithium source is realized by including such a lithium production assistant before the initial charging. Although it does not specifically limit as the quantity which adds a lithium production | generation adjuvant, 1 mass% or more can be contained on the basis of the quantity of a positive electrode active material. Moreover, it is preferable to add a lithium production | generation adjuvant in a particulate form, and when adding in a particulate form, it is desirable that the particle size is smaller than a positive electrode active material and a lithium source. Further, it is desirable that the lithium production assistant is well mixed with the lithium source.

  The negative electrode active material includes one or more compounds selected from the group consisting of carbon materials such as graphite and amorphous carbon, metal materials capable of forming an alloy with lithium, lithium titanium oxide, titanium oxide, and vanadium oxide. Can be adopted. In these active materials, insertion / extraction of lithium (ion) proceeds as the battery reaction proceeds. Since a part of lithium inserted at the time of initial charging is deactivated without being desorbed, a decrease in charge / discharge capacity is compensated by newly supplying lithium from the lithium source contained in the present invention.

  When these positive electrode active materials and negative electrode active materials are used to form an electrode, it can be used in a state in which a composite material layer is formed on a current collector after forming a composite material together with other necessary members. Other necessary members include a conductive material and a binder.

  Examples of the conductive material include ketjen black, acetylene black, carbon black, graphite, carbon nanotube, and amorphous carbon. Moreover, conductive polymers (polyaniline, polypyrrole, polythiophene, polyacetylene, polyacene, etc.) whose aspect ratio is not limited can be exemplified.

  The binder is preferably formed of a polymer material, and is desirably a material that is chemically and physically stable in the atmosphere in the secondary battery. For example, a fluorine-based polymer material (polyvinylidene fluoride and the like) can be given.

  Such a composite material layer is formed on the surface of an appropriate current collector. An example of the current collector is a foil formed of an electrochemically stable metal. Examples of the method of forming the electrode mixture layer on the surface of the current collector include a method in which the material constituting the mixture layer is dispersed or dissolved in an appropriate dispersion medium and then applied to the surface of the current collector and dried. it can.

  Although it does not specifically limit as electrolyte solution, What melt | dissolved electrolyte in solvents, such as an organic solvent, the ionic liquid which is liquid itself, and what melt | dissolved electrolyte further with respect to the ionic liquid can be illustrated.

  As an organic solvent, the organic solvent normally used for the electrolyte solution of a lithium secondary battery can be illustrated. For example, carbonates, halogenated hydrocarbons, ethers, ketones, nitriles, lactones, oxolane compounds and the like can be used. In particular, propylene carbonate, ethylene carbonate, 1,2-dimethoxyethane, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, and the like, and mixed solvents thereof are suitable. Among these organic solvents mentioned in the examples, in particular, by using one or more non-aqueous solvents selected from the group consisting of carbonates and ethers, the solubility, dielectric constant and viscosity of the electrolyte are excellent, and the battery Charge / discharge efficiency is also high, which is preferable.

An ionic liquid will not be specifically limited if it is an ionic liquid normally used for the electrolyte solution of a lithium secondary battery. For example, examples of the cation component of the ionic liquid include N-methyl-N-propylpiperidinium and dimethylethylmethoxyammonium cation, and examples of the anion component include BF ⁴⁻ , N (SO ₂ CF ₃ ) ^2−. Etc.

The electrolyte is not particularly limited. For example, LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ , LiSbF ₆ , LiSCN, LiClO ₄ , LiAlCl ₄ , NaClO ₄ , BClO ₄ , NaI, and salt compounds such as derivatives thereof. Among these, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ , LiN (FSO ₂ ) ₂ , LiN (CF ₃ One or more selected from the group consisting of a derivative of SO ₂ ) (C ₄ F ₉ SO ₂ ), a derivative of LiCF ₃ SO _3, a derivative of LiN (CF ₃ SO ₂ ) _{2 and} a derivative of LiC (CF ₃ SO ₂ ) ₃ It is preferable to use a salt from the viewpoint of electrical characteristics.

  The lithium secondary battery can have other necessary members in addition to the positive and negative electrodes and the electrolytic solution. Examples of other necessary members include a separator and a case. The separator is interposed between the positive and negative electrodes and is a member that achieves both electrical insulation and ion conduction. When the electrolytic solution is liquid, the separator also plays a role of holding the liquid supporting electrolyte. Examples of the separator include a porous synthetic resin film, particularly a porous film of a polyolefin polymer (polyethylene or polypropylene). Furthermore, it is preferable that the separator adopts a form larger than the area of the positive electrode and the negative electrode for the purpose of ensuring insulation between the positive electrode and the negative electrode.

(Method for producing lithium secondary battery)
The manufacturing method of the lithium secondary battery of this embodiment is a method of manufacturing a lithium secondary battery including a positive and negative electrode including an active material capable of inserting and extracting lithium ions, and an electrolytic solution.

  The positive electrode and the negative electrode have a positive electrode and a negative electrode active material and other necessary members. As the positive electrode and the negative electrode active material, those described in the column of the lithium secondary battery can be applied almost as they are. As for the electrolytic solution, the one described above can be applied almost as it is. As other necessary members, a conductive material, a binder, a current collector and the like can be employed as they are as described in the section of the lithium secondary battery described above. In addition, other necessary members (separator, case, electrode terminal, etc.) for forming the lithium secondary battery can be used.

  The lithium secondary battery thus formed is activated by performing initial charging. When this initial charging is performed, the lithium source and the lithium generation aid described above are contained in the positive electrode. It is preferable that the lithium source and the lithium production assistant are contained in the positive electrode simultaneously with the formation of the positive electrode.

  The initial charging condition is not particularly limited. Charging can be performed until the potential difference between the positive and negative electrodes reaches an upper limit potential (for example, 4.1 V or more) that is appropriately determined depending on the type of the active material, the electrolytic solution, and the like. For charging, a general charging method such as constant current charging, constant voltage charging, or constant current-constant voltage charging can be employed. And even if it does not complete | finish an initial stage charge once, it can also add discharge operation and it can also repeat twice or more. When the initial charging is performed twice or more, a lithium source can be added into the positive electrode every charging operation. In order to remove the gas (derived from the lithium source) present in the battery after the initial charging, the inside and outside of the battery can be communicated, or the initial charging can be performed in a state before the battery is sealed. . When charging is performed before sealing, or when the inside and outside of the battery are connected after charging, it is desirable to perform in a low humidity atmosphere.

  Hereinafter, the nonaqueous electrolyte secondary battery of the present invention will be described in detail based on examples.

(Test 1: Examination of the type of negative electrode active material and examination of the presence or absence of a lithium source and a lithium generation aid)
The effect of including a lithium source and a lithium production assistant in the positive electrode for the test battery 1 using graphite (carbon material) as the negative electrode active material and the test battery 2 using Sn ₅ Cu ₆ (metal material). It was investigated.

-Manufacture of the test battery 1 The test battery 1 is a lithium secondary battery using a lithium nickel composite oxide represented by the composition formula LiNiO ₂ as a positive electrode active material and graphite as a negative electrode active material.

The positive electrode of the test battery 1 was manufactured as follows. First, 87 parts by mass of the above LiNiO ₂ , 1.6 parts by mass of Li ₂ O as a lithium source, 3 parts by mass of MnO ₂ as a lithium generation aid, and 10 parts by mass of carbon black as a conductive material Then, 3 parts by mass of polyvinylidene fluoride (PVdF) as a binder was mixed, and an appropriate amount of N-methyl-2-pyrrolidone was added and kneaded to obtain a paste-like positive electrode mixture. This positive electrode mixture was applied to both surfaces of a positive electrode current collector made of aluminum foil having a thickness of 15 μm, dried, and a sheet-like positive electrode was produced through a pressing process.

  The negative electrode is obtained by mixing 95 parts by mass of graphite and 5 parts by mass of PVdF as a binder, adding an appropriate amount of N-methyl-2-pyrrolidone and kneading to obtain a paste-like negative electrode mixture. It was. This negative electrode mixture was applied to both sides of a copper foil negative electrode current collector having a thickness of 10 μm, dried, and subjected to a pressing step to produce a sheet-like negative electrode.

The positive electrode and the negative electrode were each cut into predetermined sizes (positive electrode: 780 mm × 54 mm, negative electrode: 820 mm × 56 mm). The cut positive electrode and negative electrode were wound with a 25 μm thick polyethylene separator sandwiched therebetween to form a roll-shaped electrode body. A current collecting lead was attached to the electrode body, inserted into a 18650 type battery case, and then an electrolytic solution was injected into the battery case. As the electrolytic solution, a solution obtained by dissolving LiPF ₆ at a concentration of 1 mol / L in a mixed solvent in which ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed at a volume ratio of 3: 7 was used. Finally, the battery case was sealed to complete the lithium secondary battery (cylindrical type) of this example. Sealing was performed after the initial charge / discharge because there was a risk of reaction gas generation by the initial charge / discharge operation described below.
The amount of the lithium source to be added was determined by converting the amount of lithium to be deactivated from the value of the decrease in charge / discharge capacity after the initial charge in the lithium secondary battery to which the lithium source and the lithium generation aid were not added. In the following examples, the amount of lithium source added was calculated in the same manner.

-Manufacture of the test battery 2 The test battery 2 is a lithium secondary battery using a lithium nickel composite oxide represented by the composition formula LiNiO ₂ as a positive electrode active material and Sn ₅ Cu ₆ as a negative electrode active material.

The positive electrode of the test battery 2 was manufactured as follows. First, 87 parts by mass of the above LiNiO ₂ , 6.8 parts by mass of Li ₂ O as a lithium source, 3 parts by mass of MnO ₂ as a lithium generation aid, and 10 parts by mass of carbon black as a conductive material Then, 3 parts by mass of polyvinylidene fluoride (PVdF) as a binder was mixed, and an appropriate amount of N-methyl-2-pyrrolidone was added and kneaded to obtain a paste-like positive electrode mixture. This positive electrode mixture was applied to both surfaces of a positive electrode current collector made of aluminum foil having a thickness of 15 μm, dried, and a sheet-like positive electrode was produced through a pressing process.

The negative electrode was prepared by mixing 85 parts by mass of Sn ₅ Cu ₆ , 10 parts by mass of PVdF as a binder and 5 parts by mass of Ketjen black as a conductive material, and adding an appropriate amount of N-methyl-2-pyrrolidone. By adding and kneading, a paste-like negative electrode mixture was obtained. This negative electrode mixture was applied to both sides of a copper foil negative electrode current collector having a thickness of 10 μm, dried, and subjected to a pressing step to produce a sheet-like negative electrode.

  Using these positive and negative electrodes, a lithium secondary battery was produced in the same manner as in test battery 1.

-Manufacture of test batteries 3 and 4 Batteries having the same configuration as those of the test batteries 1 and 2 except that the positive electrode does not contain a lithium source and a lithium generation auxiliary agent are manufactured. Test batteries 3 (graphite) and 4 (Sn ₅ Cu ₆ ).

-Manufacture of test battery 1a A battery having the same configuration as that of the test battery 1 except that the positive electrode does not contain a lithium generation auxiliary agent was manufactured as a test battery 1a.

-Measurement of charging / discharging capacity CC-CV charge was performed on the conditions of 4.1V and 1 / 3C about each manufactured test battery. Constant voltage (CV) charging was performed for 2.5 hours (hereinafter, CV charging was performed for 2.5 hours unless otherwise specified). Thereafter, CC discharge was performed under the condition of 1C up to 3V. This set of charging and discharging was repeated twice, and then the reaction gas stored inside was removed. After removal of the reaction gas, the battery case was hermetically sealed (initial charge / discharge: hereinafter, initial charge / discharge was performed under these conditions unless otherwise specified).

  After completion of the initial charge / discharge, CC-CV charge was performed under conditions of 4.1V and 1C, and CC discharge was performed under conditions of 1C up to 3V. The capacity at the time of discharge was defined as the initial battery capacity.

The results are shown in FIG. 1A. As is clear from FIG. 1A, the initial battery capacity was increased by adding the lithium source and the lithium generation aid to the positive electrode as compared with the case where the lithium source and the lithium generation aid were not added. Both the test battery 1 using graphite as the negative electrode active material and the test battery 2 using Sn ₅ Cu ₆ as the negative electrode active material were found to increase the initial capacity of the battery. In addition, for any of the battery using graphite as the negative electrode active material and the battery using Sn ₅ Cu ₆ , a battery that contains a lithium source and does not contain a lithium production assistant (see test battery 10 in Test 3), lithium Batteries containing a production assistant and no lithium source (test battery 1a: battery initial capacity 288 mAh) are both batteries than test batteries 1 and 2, both containing a lithium source and a lithium production assistant. The initial capacity was small (FIG. 1B).

(Test 2: Mixing amount of lithium source (Li ₂ O))
0.75 (test battery 5), 1.0 (test battery 6), 1.2 (test battery 7), 1.45 (test) on the basis of the mass of the lithium source calculated by the above formula (1). The initial battery capacities of the batteries 8) and 1.8 (test battery 9) were measured. The test battery was manufactured in the same configuration as that of the test battery 2 except that the mixing amounts of Li ₂ O were mixed so as to correspond to each other. Thereafter, the initial battery capacity was measured in the same manner as in Test 1. The results are shown in FIG.

  As can be seen from FIG. 2, a high effect can be achieved if the ratio of the mixing amount of the lithium source is 1.0 or more based on the amount calculated by calculation, and a further sufficient effect is exhibited if the ratio is 1.2 or more. I understood that I could do it. When the amount exceeding 1.2 was added, it was estimated that the degree of increase was small compared to the case of 1.2, and the mixture ratio was almost saturated at 1.2. That is, it was speculated that an amount of lithium corresponding to the inactivated amount could be replenished by including a slight excess of the lithium source.

(Test 3: Mixing amount of lithium production assistant (MnO ₂ ))
The variation of the initial capacity of the battery when the amount of MnO ₂ as a lithium generation aid was changed was examined. Specifically, the mixed amount of MnO ₂ was changed to 0 part by mass (test battery 10), 1 part by mass (test battery 11), 3 parts by mass (test battery 12), and 5 parts by mass (test battery 13). The configuration was the same as test battery 2. In the test battery 2, the total amount of the active material, the binder, and the conductive material in the positive electrode is 100 parts by mass. The results are shown in FIG.

  As can be seen from FIG. 3, when the total amount of the active material, the binder and the conductive material is 100 parts by mass, the inclusion of 1 part by mass of the lithium generation aid can provide a sufficient initial battery capacity. It was revealed. It was found that the increase in the initial capacity of the battery was almost saturated even when the amount of the lithium generation aid was 3 parts by mass or more. Therefore, it was found that the content of the lithium generation assistant is preferably 1 part by mass or more when the total amount of the active material, the binder and the conductive material is 100 parts by mass. In other words, it was estimated that the lithium production assistant exerts a catalyst-like action, and that the addition of 1 part by mass or more exerts a sufficient action.

(Test 4: Initial charge / discharge conditions)
A test battery 14, which is a battery having the same configuration as the test battery 2 except that the amount of the lithium source was 8 parts by mass, was manufactured. The test battery 14 was subjected to CC-CV charging under conditions of a charging voltage (x) and 1 / 3C. Thereafter, CC discharge was performed under the condition of 1C up to 3V. This set of charging and discharging was repeated twice. Here, the initial battery capacity when initial charge / discharge was performed under three conditions of x = 4V, 4.1V, and 4.2V was examined. The results are shown in FIG.

  As is clear from FIG. 4, it was found that by setting the charging voltage (x) during initial charging / discharging to 4.1 V or higher, a high battery initial capacity is obtained. That is, it was estimated that necessary lithium was released from the lithium source by applying a voltage of 4.1V.

(Test 5: Presence or absence of reaction gas removal)
The initial capacity of the battery was evaluated after the initial charge / discharge performed in Test 1 except that the reaction gas was removed from the test battery 14 when the reaction gas was removed and when the reaction gas was not removed. . The results are shown in FIG.

  As is clear from FIG. 5, it was found that the initial battery capacity was increased by removing the reaction gas. That is, it has been estimated that by removing the reaction gas, the state of the components inside the battery becomes appropriate and a high initial battery capacity is exhibited.

(Test 6: Types of lithium production assistant)
A battery having the same configuration as that of the test battery 1 was produced except that the lithium production assistant was changed. Specifically, as a lithium production assistant, Fe ₂ O ₃ (test battery 15), Fe ₃ O ₄ (test battery 16), Co ₃ O ₄ (test battery 17), CoO (test battery 18), and Pt ( Test battery 19). The results are shown in FIG.

  As is clear from FIG. 6, it was found that sufficient effects for improving the initial capacity of the battery can be exhibited even though there is a slight difference in the effects of the respective lithium production assistants. Accordingly, it has been clarified that various compounds can be employed as the lithium generation aid.

(Test 7: Type of lithium source)
A battery having the same configuration as that of the test battery 1 was manufactured except that the lithium source was changed. Specifically, Li ₂ O ₂ (test battery 20: 2.4 parts by mass added) and Li ₂ CO ₃ (test battery 21: 3.9 parts by mass added) were used as the lithium source. Here, the addition amount was determined from the value calculated by the above-described equation (1). The results are shown in FIG.

  As is apparent from FIG. 7, it was found that sufficient effects that can improve the initial battery capacity can be exhibited for each lithium source, even if there is a slight difference in the effects. Therefore, it became clear that various compounds can be adopted as the lithium source.

Claims (8)

A lithium secondary battery comprising positive and negative electrodes comprising an active material capable of occluding and releasing lithium ions, and an electrolyte solution,
The positive electrode is
A lithium source that is one or more compounds selected from the group consisting of Li ₂ O, Li ₂ O ₂ , Li ₂ CO ₃ , LiOH, and LiH;
Lithium formation aid which is one or more compounds selected from the group consisting of Pt, Au, MeO _X (Me is Mn, Fe, Co, Ni, V, or Cr; X is a positive number corresponding to the oxidation number of Me) Agent,
A lithium secondary battery comprising:   The lithium secondary battery according to claim 1, wherein the Me is Mn, Fe, or Co.   3. The lithium secondary battery according to claim 1, wherein the content of the lithium source is an amount corresponding to or more than lithium deactivated during initial charging.   The negative electrode active material is one or more compounds selected from the group consisting of a carbon material, a metal material capable of forming an alloy with lithium, lithium titanium oxide, titanium oxide, and vanadium oxide. The lithium secondary battery according to claim 1. A method for producing a lithium secondary battery comprising a positive and negative electrode comprising an active material capable of occluding and releasing lithium ions, and an electrolyte solution,
A lithium source that is one or more compounds selected from the group consisting of Li ₂ O, Li ₂ O ₂ , Li ₂ CO ₃ , LiOH, and LiH;
Lithium formation aid which is one or more compounds selected from the group consisting of Pt, Au, MeO _X (Me is Mn, Fe, Co, Ni, V, or Cr; X is a positive number corresponding to the oxidation number of Me) Agent,
In the presence of the positive electrode active material, and an initial charging step in which the positive and negative electrodes are initially charged in the presence of the electrolytic solution.   The method for producing a lithium secondary battery according to claim 5, wherein the Me is Mn, Fe, or Co.   7. The method for producing a lithium secondary battery according to claim 5, wherein the content of the lithium source is an amount corresponding to or more than lithium deactivated during initial charging.   The negative electrode active material is one or more compounds selected from the group consisting of a carbon material, a metal material capable of forming an alloy with lithium, a titanium oxide, and a vanadium oxide. Manufacturing method for lithium secondary battery.