JP2005191003A - Lithium secondary battery and method of manufacturing lithium secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lithium secondary battery having a long life and suppressed dispersion. <P>SOLUTION: An NaOH water solution is dropped in 100 ml of sulfuric acid water solution, and pH of blank water solution is measured with a potential of manganese sulfate water solution, the NaOH water solution is dropped in test water solution made by dissolving 1 g of lithium manganese nickel cobalt multiple oxide in sulfuric acid water solution and pH is measured with potential of the test water solution. The lithium manganese nickel cobalt multiple oxide, in which a slope of pH change corresponding to the drop quantity of NaOH water solution in the test water solution is larger than a slope of pH change corresponding to the drop quantity equal to that in the blank water solution, is used as positive electrode active substance. The manganese eluted from the lithium manganese nickel cobalt multiple oxide by transfer of electrons caused by charge and discharge has the small degree of effect as acid. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a lithium secondary battery and a method for manufacturing the lithium secondary battery, and more particularly to a lithium secondary battery using lithium manganese nickel cobalt complex oxide as a positive electrode active material and a method for manufacturing the lithium secondary battery.

  Lithium ion secondary batteries, which are representative of non-aqueous electrolyte secondary batteries, are mainly used as power sources for portable devices such as VTR cameras, notebook computers, and mobile phones, taking advantage of the high energy density. A typical cylindrical lithium ion secondary battery has a diameter of 18 mm and a height of 65 mm, which is called 18650 type, and is widely used as a small-sized consumer lithium ion secondary battery. The positive electrode active material of the 18650 type lithium ion secondary battery mainly uses lithium cobalt oxide, which is characterized by high capacity and long life. The battery capacity is approximately 1.3 Ah to 1.8 Ah, and the output is approximately 10 W. Degree.

  On the other hand, in the automobile industry, in order to deal with environmental problems, there are no exhaust gas, electric vehicles that use only batteries as power sources, and hybrid (electric) vehicles that use both internal combustion engine and batteries as power sources. Development has been accelerated, and part of it has been put to practical use. The batteries that serve as power sources for these electric vehicles are required to have characteristics of obtaining high output and high energy, which naturally influence acceleration performance, and lithium secondary batteries are attracting attention as batteries that meet these requirements. In addition, it is required to extend the life of the battery in order to cope with a long use period of the electric vehicle. The extension of the life here means satisfying not only the battery capacity but also the electric energy supply capability necessary for running the electric vehicle by reducing the deterioration rate of the output over a long period of time. If a long-life lithium secondary battery can be obtained, the spread of electric vehicles can be expected to accelerate. Therefore, realization of a long-life lithium secondary battery is strongly desired.

  Further, for the spread of electric vehicles, it is essential to reduce the cost of the battery. For example, in the case of a positive electrode active material, a complex oxide containing manganese that is abundant in resources has attracted particular attention. Improvements have been made with the aim of making it easier. For example, in order to suppress the deterioration of the discharge capacity in a long-term cycle, a technique for limiting the average ion valence of manganese of a lithium manganese complex oxide and using it as a positive electrode active material is disclosed (see Patent Document 1). In general, the quality of the produced positive electrode active material is controlled by an inspection method such as chemical composition analysis such as ICP (Inductively Coupled Plasma) emission analysis or structural analysis such as X-ray diffraction.

JP-A-10-172570

  However, in Patent Document 1 described above, the lithium manganese complex oxide is affected by the characteristics of manganese oxide or the like used as a raw material. Therefore, even if the same chemical composition and structure are used, the production lot of the active material is the same. There is a problem that quality control is difficult due to variations in capacity and output battery characteristics of the obtained lithium secondary battery. In addition, it is clear that differences in the production lots of lithium manganese nickel cobalt complex oxides also affect the life of lithium secondary batteries using lithium manganese nickel cobalt complex oxides, which are complex oxides containing manganese, as the active material. It is becoming. In the conventional inspection method described above, since the quantitative correspondence between the inspection results for each production lot of lithium manganese nickel cobalt complex oxide and the battery characteristics is not recognized, Variations in battery characteristics and a decrease in service life are found. For this reason, since the yield of battery manufacture is reduced, it is important to select an appropriate lithium manganese nickel cobalt complex oxide as an active material of the lithium secondary battery before battery manufacture.

  An object of the present invention is to provide a lithium secondary battery having a long life and suppressing variations, and a method for manufacturing the lithium secondary battery, in view of the above-mentioned cases.

  In order to solve the above-mentioned problem, a first aspect of the present invention is a lithium secondary battery using lithium manganese nickel cobalt double oxide as a positive electrode active material, wherein the lithium manganese nickel cobalt double oxide contains manganese. Mixing amount of the alkaline aqueous solution in a mixed aqueous solution obtained by mixing an alkaline aqueous solution capable of reacting with the lithium manganese nickel cobalt double oxide into a dissolved aqueous solution in which the lithium manganese nickel cobalt double oxide is dissolved in a predetermined amount of an acidic aqueous solution The control potential with respect to the same mixed amount in the control aqueous solution obtained by mixing the alkaline aqueous solution mixed with the alkaline aqueous solution mixed with the dissolved aqueous solution into the acidic aqueous solution containing manganese in the same amount as the predetermined amount. It is characterized by being larger than the ratio.

  In the first aspect, since manganese in an acidic aqueous solution containing manganese has a stable oxidation number, the control potential of a control aqueous solution obtained by mixing an alkaline aqueous solution with a predetermined amount of the acidic aqueous solution is equal to the mixed amount of the alkaline aqueous solution. After increasing with the increase, manganese having a stable oxidation number is oxidized by the mixed alkaline aqueous solution to act as an acid, and the acid-base reaction with the alkaline aqueous solution is equilibrated. In a dissolved aqueous solution in which lithium manganese nickel cobalt complex oxide is dissolved in a predetermined amount of an acidic aqueous solution containing manganese, lithium manganese nickel cobalt complex oxide does not elute manganese with a different oxidation number from manganese with a stable oxidation number. A leveling reaction takes place. The smaller the oxidation number of the eluted manganese, the smaller the size acting as an acid, so that the alkali action of the mixed aqueous alkali solution increases and the potential of the mixed aqueous solution increases beyond the control potential. For this reason, the ratio of the potential of the mixed aqueous solution to the mixed amount of the mixed alkaline aqueous solution is larger than the ratio of the control potential of the control aqueous solution to the same mixed amount. According to this aspect, the lithium manganese nickel cobalt complex oxide has a potential ratio with respect to the mixed amount of the alkaline aqueous solution in the mixed aqueous solution. Since it is larger than the ratio of the control potential to the same mixing amount in an aqueous solution, the size of the eluted manganese acting as an acid is small, so the effect on battery characteristics is reduced. Can be obtained.

  In this case, the acidic aqueous solution containing manganese may be a manganese sulfate aqueous solution. The potential and the control potential may be measured using a pH measurement electrode. Moreover, you may use sodium hydroxide aqueous solution for alkaline aqueous solution.

  A second aspect of the present invention is a method for manufacturing a lithium secondary battery using lithium manganese nickel cobalt complex oxide as a positive electrode active material, wherein the lithium manganese nickel cobalt complex oxide is added to a predetermined amount of an acidic aqueous solution containing manganese. The aqueous solution obtained by mixing a fixed amount of an aqueous alkaline solution capable of reacting with the lithium manganese nickel cobalt complex oxide in a dissolved aqueous solution in which a product is dissolved is sequentially measured, and the alkaline aqueous solution mixed in the dissolved aqueous solution and A reference mixture in which the potential is the same and the potential is the same as the reference potential measured in advance by mixing the alkaline aqueous solution with an acidic aqueous solution containing the same amount of manganese as the predetermined amount. The ratio of the control potential to the amount of the mixture that is the same as the amount of the mixture that exceeds the reference amount of mixture with respect to the amount of the mixture that exceeds the amount The lithium-manganese-nickel-cobalt composite oxide is characterized by selecting said as a positive electrode active material when Ri large. In this embodiment, the acidic aqueous solution containing manganese may be a manganese sulfate aqueous solution. Further, if the potential and the control potential are measured using the electrode for pH measurement, the potential and pH are correlated, so that the potential can be measured by pH. Moreover, you may use sodium hydroxide aqueous solution for alkaline aqueous solution.

  According to the present invention, the lithium manganese nickel cobalt complex oxide is obtained by mixing an alkaline aqueous solution having the same mixing amount as the alkaline aqueous solution mixed with the dissolving aqueous solution in which the ratio of the potential to the mixing amount of the alkaline aqueous solution in the mixed aqueous solution is Since it is larger than the ratio of the control potential to the same mixing amount in an aqueous solution, the size of the eluted manganese acting as an acid is small, so the effect on battery characteristics is reduced. The effect that it can be obtained can be obtained.

  Embodiments in which the present invention is applied to a cylindrical lithium ion secondary battery will be described below with reference to the drawings. In the present embodiment, the potential is evaluated by pH using a composite electrode for pH measurement, which is easy to obtain and operate for measuring the potential.

(Constitution)
As shown in FIG. 1, a cylindrical lithium ion secondary battery 20 according to the present embodiment includes a nickel-plated steel bottomed cylindrical battery container 7 and a polypropylene hollow cylindrical shaft core 1. A strip-shaped positive and negative electrode plate has an electrode plate group 6 wound in a spiral shape with a separator W5 interposed therebetween.

  On the upper side of the electrode plate group 6, an aluminum positive electrode current collecting ring 4 for collecting the electric potential from the positive electrode plate is disposed substantially on the extension line of the shaft core 1. The positive electrode current collecting ring 4 is fixed to the upper end portion of the shaft core 1. The edge part of the positive electrode lead piece 2 led out from the positive electrode plate is ultrasonically welded to the peripheral edge of the flange portion integrally protruding from the periphery of the positive electrode current collecting ring 4. A disc-shaped battery lid serving as a positive electrode external terminal is disposed above the positive electrode current collecting ring 4. The battery lid includes a lid case 12, a lid cap 13, a valve retainer 14 that keeps airtightness, and a cleavage valve 11 that cleaves when the internal pressure rises, and these are laminated to crimp the periphery of the lid case 12. Is assembled. One end of two positive electrode lead plates 9 formed by stacking a plurality of aluminum ribbons is fixed to the upper portion of the positive electrode current collecting ring 4, and another one is fixed to the lower surface of the lid case 12. One end of the book is welded. The other ends of the two positive electrode lead plates 9 are connected by welding.

  On the other hand, a copper negative electrode current collecting ring 5 for collecting the electric potential from the negative electrode plate is disposed below the electrode plate group 6. The outer peripheral surface of the lower end portion of the shaft core 1 is fixed to the inner peripheral surface of the negative electrode current collecting ring 5. The outer peripheral edge of the negative electrode current collecting ring 5 is welded with the end portion of the negative electrode lead piece 3 led out from the negative electrode plate. A copper negative electrode lead plate 8 for electrical conduction is welded to the lower portion of the negative electrode current collecting ring 5, and the negative electrode lead plate 8 is welded to the inner bottom portion of the battery container 7. In this example, the battery container 7 has an outer diameter of 40 mm and an inner diameter of 39 mm.

The battery lid is fixed by caulking to the upper part of the battery container 7 via an insulating and heat resistant EPDM resin gasket 10. For this reason, the inside of the lithium ion secondary battery 20 is sealed. In addition, a non-aqueous electrolyte (not shown) is injected into the battery container 7. The non-aqueous electrolyte is obtained by dissolving 1 mol / liter of lithium hexafluorophosphate (LiPF ₆ ) in a solvent in which ethylene carbonate, dimethyl carbonate, and diethyl carbonate are mixed at a volume ratio of 1: 1: 1. It is used. The lithium ion secondary battery 20 has a PTC (Positive Temperature Coefficient) element that operates electrically in response to an increase in battery temperature, or a positive or negative electrical lead in response to an increase in battery internal pressure. There is no current interrupting mechanism to be disconnected.

  The electrode plate group 6 is arranged around the shaft core 1 via a polyethylene separator W5 having a width of 90 mm and a thickness of 40 μm so that the positive electrode plate and the negative electrode plate are not in direct contact with each other. Has been wounded. The positive electrode lead piece 2 and the negative electrode lead piece 3 are respectively disposed on opposite end surfaces of the electrode plate group 6. Insulation coating is applied to the entire circumference of the collar surface of the electrode plate group 6 and the positive electrode current collecting ring 4. For the insulation coating, an adhesive tape in which a hexamethacrylate adhesive is applied to one side of a polyimide base material is used. The pressure-sensitive adhesive tape is wound one or more times from the peripheral surface of the collar portion to the outer peripheral surface of the electrode plate group 6. By adjusting the lengths of the positive electrode plate, the negative electrode plate, and the separator W5, the diameter of the electrode plate group 6 is set to 38 ± 0.1 mm.

  The negative electrode plate constituting the electrode plate group 6 has a rolled copper foil W3 having a thickness of 10 μm as a negative electrode current collector. A negative electrode mixture W4 containing amorphous carbon capable of occluding and releasing lithium ions as a negative electrode active material is coated on both surfaces of the rolled copper foil W3 substantially uniformly and uniformly. For example, 8 parts by mass of a binder (binder) polyvinylidene fluoride (hereinafter abbreviated as PVDF) is blended with 92 parts by mass of graphite powder in the negative electrode mixture W4. When the negative electrode mixture W4 is applied to the rolled copper foil W3, a dispersion solvent N-methyl-2-pyrrolidone (hereinafter abbreviated as NMP) is used. An uncoated portion of the negative electrode mixture W4 having a width of 30 mm is formed on the side edge on one side in the longitudinal direction of the rolled copper foil W3. The uncoated part is notched in a comb shape, and the negative electrode lead piece 3 is formed in the notch remaining part. The interval between the adjacent negative electrode lead pieces 3 is set to 50 mm, and the width of the negative electrode lead piece 3 is set to 5 mm. After drying, the negative electrode plate is pressed by a heatable roll press machine so as to have a negative electrode active material coating portion thickness of 70 μm that does not include the rolled steel foil W3, and is cut into a width of 86 mm.

  On the other hand, the positive electrode plate has an aluminum foil W1 having a thickness of 20 μm as a positive electrode current collector. On both surfaces of the aluminum foil W1, a positive electrode mixture W2 containing lithium manganese nickel cobalt complex oxide powder as a positive electrode active material is applied substantially uniformly and uniformly. In the positive electrode mixture W2, for example, 8 parts by mass of graphite powder as a main conductive material, 2 parts by mass of acetylene black as a secondary conductive material, and 5 parts by mass of PVDF as a binder with respect to 85 parts by mass of the positive electrode active material Is blended. When the positive electrode mixture W2 is applied to the aluminum foil W1, a dispersion solvent NMP is used. An uncoated portion of the positive electrode mixture W2 having a width of 30 mm is formed on the side edge on one side in the longitudinal direction of the aluminum foil W1, and the positive electrode lead piece 2 is formed. The interval between the adjacent positive electrode lead pieces 2 is set to 50 mm, and the width of the positive electrode lead piece 2 is set to 5 mm. After drying, the positive electrode plate is pressed in the same manner as the negative electrode plate and cut to a width of 82 mm so that the thickness of the positive electrode active material coated portion not including the aluminum foil W1 is 90 μm.

  As the positive active material lithium manganese nickel cobalt complex oxide, those selected by inspection with the following inspection system and inspection method are used.

(Lithium manganese nickel cobalt double oxide inspection system)
As shown in FIG. 2, an inspection system 50 for inspecting lithium manganese nickel cobalt double oxide includes an automatic titrator 40 for measuring pH from the potential of a test aqueous solution in which lithium manganese nickel cobalt double oxide is dissolved. A stirrer 38 for stirring the test aqueous solution by a magnetic rotational force and a bottomed cylindrical measurement cell 33 are provided.

  A test aqueous solution in which a predetermined amount of lithium manganese nickel cobalt complex oxide is dissolved in a predetermined amount of an aqueous manganese sulfate solution as an acidic aqueous solution containing manganese is injected into the measurement cell 33. The measurement cell 33 is placed on the stirrer 38. In the measurement cell 33, a substantially cylindrical rotor 37 in which a rod-like magnet is covered with a resin is disposed at the substantially central portion of the bottom. The rotor 37 can be rotated by a stirrer 38. The measurement cell 33 is fitted with a lid 41 at the top to prevent the liquid level of the test aqueous solution from coming into contact with the outside air. The lid 41 includes a composite electrode 31 that detects the potential of the test aqueous solution, a nitrogen gas introduction pipe 34 that introduces nitrogen gas that reduces the influence of dissolved carbon dioxide gas in the test aqueous solution, and lithium manganese nickel cobalt double oxidation into the test aqueous solution. A microburette 32 for dropping a predetermined amount of a sodium hydroxide (NaOH) aqueous solution capable of reacting with the product and a gas discharge pipe 35 for avoiding a pressure increase in the measurement cell 33 due to the introduction of nitrogen gas are inserted.

  The tip of the composite electrode 31 is immersed in the approximate center of the depth of the test aqueous solution. An automatic titration device 40 is connected to the composite electrode 31. The tip of the nitrogen gas inlet tube 34 is immersed in the upper part of the test aqueous solution. A nitrogen gas cylinder 36 into which nitrogen gas is press-fitted is connected to the nitrogen gas introduction pipe 34 through a valve V1 capable of adjusting pressure. The microburette 32 has a tip disposed above the liquid surface of the test aqueous solution. A titrant container 39 in which an aqueous NaOH solution is stored is connected to the microburette 32 via a valve V <b> 2 that can be opened and closed by an automatic titrator 40.

  The automatic titration apparatus 40 includes a microcomputer (not shown) that measures pH based on the potential of the test aqueous solution detected by the composite electrode 31 and a display device (not shown) that displays pH with respect to the amount of NaOH dropped. The microcomputer of the automatic titration apparatus 40 opens and closes the valve V2 to drop NaOH aqueous solution into the test aqueous solution from the tip of the microburet 32 by a certain amount.

(Inspection method)
As a blank test, the pH change was measured when an aqueous NaOH solution was dropped into an aqueous manganese sulfate solution (blank aqueous solution) that did not dissolve lithium manganese nickel cobalt complex oxide, and then manganese sulfate in which lithium manganese nickel cobalt complex oxide was dissolved. An inspection method for determining an appropriate lithium manganese nickel cobalt complex oxide by measuring pH when NaOH is dropped into an aqueous solution (test aqueous solution) will be described in order.

  In the blank test, 100 ml of a 1/1000 (mol / liter) manganese sulfate aqueous solution is injected into the measurement cell 33, the lid 41 is fitted, and the tip of the composite electrode 31 and the tip of the nitrogen gas introduction pipe 34 are made into the blank aqueous solution. Soak. When a power supply (not shown) is turned on to the automatic titrator 40, the microcomputer (not shown) of the automatic titrator 40 measures the pH based on the potential of the blank aqueous solution detected by the composite electrode 31 and displays it on a display device (not shown). . While the blank aqueous solution is stirred by rotating the rotor 37 with the stirrer 38, nitrogen gas is introduced into the blank aqueous solution from the nitrogen gas cylinder 36 through the nitrogen gas introduction pipe 34 (bubbling). Thereby, the dissolved carbon dioxide gas in the blank aqueous solution is excluded and discharged from the gas discharge pipe 35.

  While bubbling nitrogen gas, after the blank aqueous solution is stirred and equilibrated until the pH change of the blank aqueous solution displayed on a display device (not shown) is within ± 0.01 / min, titration is started in the automatic titrator 40 Let The microcomputer of the automatic titration apparatus 40 opens and closes the valve V2, and 0.5 mol / liter NaOH aqueous solution stored in the titrant container 39 from the tip of the microburette 32 to the blank aqueous solution at a rate of 0.01 ml / min. Let it drip. One minute after dropping, the pH of the blank aqueous solution is sequentially measured and displayed on a display device (not shown). The titration is terminated when the pH of the blank aqueous solution reaches 10.5. Thereby, the pH change of the blank aqueous solution with respect to the dripping amount of NaOH aqueous solution is measured.

  In the measurement of the test aqueous solution, as shown in FIG. 3, in dissolving the sample, 100 ml of a 1/1000 (mol / liter) manganese sulfate aqueous solution is injected into the measurement cell 33 and 1 g of lithium manganese nickel cobalt complex oxide is added. By rotating the rotor 37 with a stirrer 38, the manganese sulfate aqueous solution is stirred to dissolve the lithium manganese nickel cobalt complex oxide to obtain a test aqueous solution. After the lid 41 is fitted to the measurement cell 33, the pH of the test aqueous solution is measured by the automatic titrator 40 in the same manner as the blank test and displayed on a display device (not shown).

  In the equilibration, dissolved carbon dioxide in the aqueous test solution is eliminated by bubbling nitrogen gas while stirring the aqueous test solution. While bubbling nitrogen gas, the test aqueous solution is stirred and equilibrated until the pH change of the test aqueous solution is within ± 0.01 / min.

  In the titration, while the test aqueous solution is stirred, the titration is started by the automatic titrator 40 in the same manner as in the blank test, and the pH of the test aqueous solution is sequentially measured, and the titration is finished when the pH of the test aqueous solution reaches 10.5. Let Thereby, the pH change of the test aqueous solution with respect to the dropping amount of NaOH aqueous solution is measured.

  From the measurement result of the obtained pH change, the dripping amount that is substantially the same dripping amount as the dropping amount of the NaOH aqueous solution dropped into the test aqueous solution, and the pH of the aqueous test solution and the pH of the blank aqueous solution are substantially the same. Is the reference dripping amount. When the slope (ratio) of the pH of the test aqueous solution with respect to the drop amount exceeding the reference drop amount is greater than the slope of the pH of the blank aqueous solution with respect to the drop amount exceeding the reference drop amount, the lithium manganese nickel cobalt complex It is determined that the oxide is appropriate as the active material of the lithium secondary battery. Note that substantially the same or substantially the same may be substantially the same or substantially the same even if they do not completely match.

  Since manganese in the manganese sulfate aqueous solution is in a stable oxidation state having an oxidation number of +2, the pH of the blank aqueous solution rises with a relatively small drop amount of the NaOH aqueous solution and becomes alkaline. Thereafter, manganese having an oxidation number of +2 is oxidized in an alkaline aqueous solution to act as an acid, and the acid-base reaction with the aqueous NaOH solution is equilibrated, so that the pH of the blank aqueous solution becomes substantially constant. On the other hand, in the test aqueous solution, a disproportionation reaction occurs in which lithium manganese nickel cobalt complex oxide elutes manganese having an oxidation number greater than +2 in an acidic environment. Since the size acting as an acid differs depending on the oxidation number of the eluted manganese, the change in pH of the test aqueous solution with respect to the dropping amount of the NaOH aqueous solution varies depending on the oxidation number of the eluted manganese. The smaller the oxidation number of the eluted manganese is, the smaller the size that acts as an acid is. Therefore, when the dropping amount exceeds the reference dropping amount of the NaOH aqueous solution, the magnitude of the alkali action of the dropped NaOH aqueous solution becomes large, and The slope of the pH change becomes larger than the slope of the pH change of the blank aqueous solution with respect to the dripping amount substantially the same as this dripping amount.

  Since the oxidation number of the eluted manganese is larger than +2 at the dropping amount of the NaOH aqueous solution below the reference dropping amount, the pH increase of the test aqueous solution is smaller than the pH increase of the blank aqueous solution, and the oxidation number of the eluted manganese is small (to +2). The closer it is) the closer the pH of the aqueous test solution is to the pH of the blank aqueous solution. From this, it is theoretically possible to determine that lithium manganese nickel cobalt double oxide is suitable as an active material, with the drop amount below the reference drop amount being close to the pH increase of the test aqueous solution and the pH increase of the blank aqueous solution. . However, since manganese eluting from lithium manganese nickel cobalt complex oxide has an oxidation number greater than +2 and reduces the pH increase of the test aqueous solution, the appropriate range should be close to the pH increase of the test aqueous solution and the pH increase of the blank aqueous solution. It is difficult to determine the criteria for judging.

  In the lithium ion secondary battery 20 of this embodiment, the slope of the pH change of the test aqueous solution with respect to the drop amount exceeding the reference drop amount is substantially the same as the drop amount exceeding the reference drop amount. A lithium manganese nickel cobalt double oxide larger than the inclination is selected and used as the positive electrode active material. For this reason, since the manganese that elutes from the lithium manganese nickel cobalt complex oxide due to the disproportionation reaction similar to that in the acidic environment described above due to the transfer of electrons accompanying charge and discharge is small in size, it acts as an acid. The influence which it has on can be suppressed. In addition, by selecting and using lithium manganese nickel cobalt double oxide having substantially the same difference between the pH change of the test aqueous solution and the pH change of the blank aqueous solution, the production lot of the positive electrode active material differs. Even in the ion secondary battery 20, variations in battery characteristics can be suppressed. Therefore, the lithium ion secondary battery 20 of the present embodiment is a battery that has a long life and suppresses variations in battery characteristics.

  In the present embodiment, lithium manganese nickel cobalt complex oxide is shown as the positive electrode active material, but the mixing ratio of lithium, manganese, nickel, and cobalt is not particularly limited.

  Moreover, in this embodiment, although the comparatively large cylindrical lithium ion secondary battery 20 used for the power supply for electric vehicles was illustrated, this invention is not restrict | limited to the capacity | capacitance, size, shape, etc. of a battery. Absent. For example, the battery shape may be a rectangular shape or other polygonal shapes. In addition, the structure to which the present invention can be applied may be other than a battery having a structure in which a battery lid is sealed by caulking on the battery container described above. As an example of such a structure, a battery in which positive and negative external terminals penetrate the battery lid and the positive and negative external terminals are pressed against each other via an axis in the battery container can be cited. Further, the present invention can be applied to a lithium secondary battery in which the positive electrode and the negative electrode have a stacked structure instead of a wound structure.

  Furthermore, in the present embodiment, amorphous carbon is exemplified as the negative electrode active material, but the present invention is not limited to this. As the negative electrode active material that can be used other than the present embodiment, for example, natural graphite, artificial graphite materials, carbon materials such as coke, etc., also in the particle shape, scaly, spherical, fibrous, It is not particularly limited to a lump shape or the like.

Furthermore, in the present embodiment, the non-aqueous electrolyte was prepared by dissolving 1 mol / liter of LiPF ₆ in a mixed solvent in which ethylene carbonate, dimethyl carbonate, and diethyl carbonate were mixed at a volume ratio of 1: 1: 1. The present invention is not limited to this, and a nonaqueous electrolytic solution in which a general lithium salt is used as an electrolyte and this is dissolved in an organic solvent can be used. The lithium salt and organic solvent used are not particularly limited. For example, examples of the electrolyte include LiClO ₄ , LiAsF ₆ , LiBF ₄ , LiB (C ₆ H ₅ ) ₄ , CH ₃ SO ₃ Li, CF ₃ SO ₃ Li, and a mixture thereof. Examples of the organic solvent include propylene carbonate, ethylene carbonate, ethyl methyl carbonate, 1,2-dimethoxyethane, 1,2-diethoxyethane, γ-butyrolactone, tetrahydrofuran, 1,3-dioxolane, 4-methyl-1, Examples include 3-dioxolane, diethyl ether, sulfolane, methyl sulfolane, acetonitrile, propionitrile, and a mixed solvent of two or more of these. The mixing ratio is not limited.

  Furthermore, in this embodiment, the manganese sulfate aqueous solution is exemplified as the acidic aqueous solution containing manganese in the selection of the positive electrode active material, but the present invention is not limited to this, and manganese is in an stable oxidation state in the acidic aqueous solution. If it is. In addition to using the manganese sulfate aqueous solution, for example, a manganese nitrate aqueous solution, a manganese acetate aqueous solution, or the like may be used, or a mixture of two or more of these may be used.

  Moreover, the inspection system and inspection conditions for lithium manganese nickel cobalt double oxide shown in the present embodiment are examples, and within a range where the difference between lithium manganese nickel cobalt double oxide can be discriminated, the type and concentration of the alkaline aqueous solution are appropriately selected. Needless to say, the dropping rate of the alkaline aqueous solution at the time of titration, the upper limit value of pH at the end of the titration, the type of the electrode for pH measurement, and the like can be adjusted and changed. As a kind of alkaline aqueous solution which can be used except this embodiment, hydroxides, such as potassium hydroxide aqueous solution, can be mentioned, for example, You may mix and use several alkaline aqueous solution. The electrode is not particularly limited as long as the potential of the test aqueous solution or the blank aqueous solution can be measured in addition to the pH measurement.

  Furthermore, in this embodiment, although the method of dripping alkaline aqueous solution was illustrated while stirring test aqueous solution with a stirrer, this invention is not limited to this. What is necessary is just to be able to mix so that test aqueous solution may be equilibrated, for example, you may make it mix by vibration, such as an ultrasonic wave.

  Next, examples of the lithium ion secondary battery 20 manufactured according to the present embodiment will be described. In this example, four types of samples (lot A, lot B, lot C, lot D) having different production lots were prepared and inspected as lithium manganese nickel cobalt complex oxide. The life characteristics of the lithium ion secondary battery 20 produced using the lithium manganese nickel cobalt complex oxide of each production lot were evaluated. In addition, as the automatic titration apparatus 40, a commercially available automatic titration apparatus (manufactured by Toa Denpa Kogyo Co., Ltd., AUT-3000 type) was used.

  As shown in FIG. 4, in the range where the amount of NaOH aqueous solution dropped is small, the pH increase of the test aqueous solution in which the lithium manganese nickel cobalt complex oxide of each lot is dissolved is small with respect to the pH increase of the blank aqueous solution. Thus, it was found that lithium manganese nickel cobalt double oxide acts as a so-called “acid” in the test aqueous solution. This is presumably because lithium manganese nickel cobalt double oxide caused a disproportionation reaction in an aqueous manganese sulfate solution, and manganese larger than the oxidation number +2 was eluted, so that the size acting as an acid was increased.

  It was also found that there was a difference in pH change depending on the production lot. That is, in the range where the dropping amount of the NaOH aqueous solution is not more than the reference dropping amount, the lithium manganese nickel cobalt complex oxides of lots A and B are compared with the test aqueous solution in which the lithium manganese nickel cobalt complex oxides of lots C and D are dissolved. The dissolved test aqueous solution showed a pH change close to that of the blank aqueous solution. In the range exceeding the reference dripping amount, the pH of the test aqueous solution in which the lithium manganese nickel cobalt complex oxides of lots C and D are dissolved is substantially constant, whereas the lithium manganese nickel cobalt complex oxides of lots A and B are constant. The pH of the aqueous test solution in which was dissolved increased beyond the pH of the blank aqueous solution. From this, it can be judged that lots C and D and lots A and B have greatly different reactivity between manganese in the lithium manganese nickel cobalt complex oxide and NaOH aqueous solution. This is probably because the oxidation number of manganese eluted from the lithium manganese nickel cobalt complex oxide differs depending on the production lot, resulting in a difference in the acid-base reaction.

  About the produced four types of battery, the following tests were implemented and the lifetime characteristic was evaluated. Each battery was charged and then discharged, and the initial discharge capacity was measured in an atmosphere having an environmental temperature of 25 ± 2 ° C. The charging conditions were a 4.2 V constant voltage, a limiting current of 5 A, and a charging time of 2.5 hours. The discharge conditions were a 5 A constant current and a final voltage of 2.7 V.

  In addition, after charging under the above-mentioned charging conditions, charging / discharging under the same charging / discharging conditions was repeated 200 times in an atmosphere with an environmental temperature of 50 ± 2 ° C., and then the discharge capacity was measured in the same manner. The ratio of the discharge capacity at the cycle was calculated as a percentage, and the capacity maintenance rate at the 200th cycle was obtained. Table 1 below shows the measurement results of the capacity retention rate at the 200th cycle for lithium ion batteries using lithium manganese nickel cobalt complex oxides in each lot.

  As shown in Table 1, in the batteries using the lithium manganese nickel cobalt complex oxides of lots A and B, the capacity retention rate at the 200th cycle was high and the life reduction was small, whereas the lithium manganese of lots C and D In batteries using nickel-cobalt double oxide, it was found that the capacity retention rate was greatly reduced and the life was greatly reduced. Further, it was found that there is almost no difference in capacity maintenance rate between lot A and lot B.

  From the above evaluation results, the slope of the pH change of the test aqueous solution with respect to the drop amount exceeding the reference drop amount of the NaOH aqueous solution is larger than the slope of the pH change of the blank aqueous solution with respect to the drop amount substantially exceeding the reference drop amount. By using lithium manganese nickel cobalt composite oxide as an active material, a long-life lithium ion battery can be obtained, and a production lot with a similar slope of pH change at a drop amount exceeding the reference drop amount (see also FIG. 4) ) Was selected, it was found that a lithium ion battery with suppressed variation in capacity retention rate could be obtained.

  The present invention contributes to the manufacture and sale of lithium secondary batteries in order to provide a lithium secondary battery having a long life and suppressed variations, and a method for producing the lithium secondary battery, and thus has industrial applicability.

It is sectional drawing of the cylindrical lithium ion secondary battery of embodiment which can apply this invention. It is a block diagram which shows the outline of the test | inspection system used for selection of the positive electrode active material of a cylindrical lithium ion secondary battery. It is process drawing which shows the principal part of the inspection method used for selection of a positive electrode active material. It is a graph which shows the relationship between the dripping amount of NaOH aqueous solution, and pH when test | inspecting the lithium manganese nickel cobalt complex oxide from which the production lot used for the positive electrode active material of a cylindrical lithium ion secondary battery differs.

Explanation of symbols

W2 Positive electrode mixture layer 6 Electrode plate group 20 Cylindrical lithium ion secondary battery (lithium secondary battery)
31 Composite electrode 39 Sodium hydroxide aqueous solution (alkaline aqueous solution)
50 Inspection system

Claims (8)

  In a lithium secondary battery using lithium manganese nickel cobalt complex oxide as a positive electrode active material, the lithium manganese nickel cobalt complex oxide is obtained by dissolving the lithium manganese nickel cobalt complex oxide in a predetermined amount of an acidic aqueous solution containing manganese. In the mixed aqueous solution obtained by mixing the alkaline aqueous solution capable of reacting with the lithium manganese nickel cobalt complex oxide into the dissolved aqueous solution, the ratio of the potential with respect to the mixed amount of the alkaline aqueous solution is an acid containing manganese in the same amount as the predetermined amount. A lithium secondary battery, wherein a ratio of the control potential to the same mixture amount in a control aqueous solution obtained by mixing an aqueous solution with an alkaline aqueous solution having the same mixing amount as that of the alkaline aqueous solution mixed with the dissolved aqueous solution.   The lithium secondary battery according to claim 1, wherein the acidic aqueous solution containing manganese is a manganese sulfate aqueous solution.   The lithium secondary battery according to claim 1, wherein the potential and the control potential are measured using a pH measurement electrode.   The lithium secondary battery according to any one of claims 1 to 3, wherein the alkaline aqueous solution is a sodium hydroxide aqueous solution.   A method for producing a lithium secondary battery using lithium manganese nickel cobalt composite oxide as a positive electrode active material, wherein the lithium manganese nickel cobalt composite oxide is dissolved in a predetermined amount of an acidic aqueous solution containing manganese. The potential of a mixed aqueous solution obtained by mixing a certain amount of an alkaline aqueous solution capable of reacting with lithium manganese nickel cobalt complex oxide is sequentially measured, and the same mixed amount as the alkaline aqueous solution mixed in the dissolved aqueous solution, the potential being And a predetermined amount of the alkaline aqueous solution mixed with an acidic aqueous solution containing the same amount of manganese as the predetermined amount, and the potential of the potential with respect to a mixed amount exceeding a reference mixed amount in which the control potential measured in advance becomes the same potential. When the ratio is larger than the ratio of the control potential to the same mixing amount as the mixing amount exceeding the reference mixing amount, Manufacturing method characterized by selecting um manganese-nickel-cobalt complex oxide as the positive active material.   6. The production method according to claim 5, wherein the acidic aqueous solution containing manganese is an aqueous manganese sulfate solution.   The manufacturing method according to claim 5, wherein the potential and the control potential are measured using a pH measurement electrode.   The manufacturing method according to claim 5, wherein the aqueous alkali solution is an aqueous sodium hydroxide solution.

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