JP3511906B2 - Lithium ion secondary battery - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lithium ion secondary battery and a method for manufacturing the same. In general, in a lithium ion secondary battery, a positive electrode material layer made of a lithium-containing double oxide and a negative electrode material layer made of a carbon material that occludes and releases lithium ions comprise a nonaqueous electrolyte layer. It is configured to be laminated through the intermediary. This lithium ion secondary battery is manufactured as follows. First,
Positive electrode material composed of lithium-containing double oxide, binder and N-
A positive electrode material slurry is prepared by kneading an organic solvent such as methyl-2-pyrrolidone (NMP). Then, after applying this positive electrode material slurry onto the positive electrode current collector, a positive electrode plate provided with a positive electrode material layer is produced through a drying step and pressing. Further, a negative electrode material slurry is prepared by kneading a negative electrode material made of a carbon material that absorbs and releases lithium ions, a binder, and an organic solvent made of NMP or the like. Then, after applying this negative electrode material slurry onto the negative electrode current collector, a negative electrode plate provided with a negative electrode material layer is produced through a drying step and pressing. Next, a positive electrode plate and a negative electrode plate are laminated via a separator to form an electrode plate group,
This electrode group is placed in a battery case. Then, the electrode group is impregnated with a non-aqueous electrolyte in which a lithium salt such as lithium hexafluorophosphate is dissolved in an organic solvent such as a carbonate ester to complete a battery. Lithium ion secondary batteries have a high energy density and low self-discharge, and thus are widely used as portable power supplies for miniaturized and lightweight electronic devices. However, in this lithium ion secondary battery,
When preparing the positive electrode material slurry and the negative electrode material slurry, there is a problem that dispersibility of the positive electrode material and the negative electrode material in an organic solvent is poor. Further, there is a problem that the wettability of the nonaqueous electrolyte with respect to the positive electrode material layer and the negative electrode material layer is poor. In particular, when manufacturing electrode plates,
When the electrode plate is compression-molded in the thickness direction by a roll press machine, the wettability is significantly reduced. Therefore, it has been proposed to add a cationic surfactant composed of oleic amide to at least one of the positive electrode material layer and the negative electrode material layer as disclosed in JP-A-9-306501 to improve the wettability. When oleic acid amide is added, oleic acid amide is eluted in the space inside the electrode plate and on the electrode surface, and the wettability of the entire electrode plate is increased. [0003] However, even if oleic amide is added to at least one of the positive electrode material layer and the negative electrode material layer, the wettability of the electrolytic solution inside the electrode plate is increased. Has a limitation, and the high-rate discharge characteristics and the number of life cycles of the battery cannot be significantly increased. In particular,
Since the positive electrode material slurry shows alkalinity, the dispersibility of the positive electrode material in an organic solvent could not be increased even if a cationic surfactant such as oleic acid amide was added. An object of the present invention is to provide a lithium ion secondary battery capable of sufficiently increasing the wettability of an electrolytic solution inside an electrode material layer and improving the high rate discharge characteristics and the number of life cycles of the battery, and a method of manufacturing the same. To provide. Another object of the present invention is to provide, in addition to the above objects,
An object of the present invention is to provide a method for manufacturing a lithium ion secondary battery capable of increasing the dispersibility of a positive electrode material in an organic solvent when preparing a positive electrode material slurry. According to the present invention, a positive electrode material layer mainly composed of a lithium-containing composite oxide and a negative electrode material layer mainly composed of a substance that occludes and releases lithium ions are used. A lithium ion secondary battery laminated with a water electrolyte layer interposed therebetween is an object of improvement. In the present invention, the cathode material layer,
At least one of the negative electrode material layer and the non-aqueous electrolyte layer contains an amphoteric surfactant. Here, the amphoteric surfactant is
A surfactant having both properties of an anionic surfactant and a cationic surfactant. The amphoteric surfactant can increase the wettability of the electrolytic solution inside the electrode plate as compared with a conventional cationic surfactant such as oleic acid amide. Therefore, the high-rate discharge characteristics and the number of life cycles of the lithium ion secondary battery can be increased as compared with the case where a cationic surfactant is used. The amphoteric surfactants include carboxylate type, sulfate type, sulfonate type and phosphate type. In particular, many carboxylate-type amphoteric surfactants are commercially available, and have an advantage that they can be easily synthesized as compared with others. As the carboxylate type amphoteric surfactant, an amine type in which the cation part is an amine salt or a betaine type in which the cation part is a quaternary ammonium salt can be used. [0008] As the lithium-containing double oxide used as the positive electrode material, an oxide containing lithium and a transition metal can be used. As transition metals, Ti, V, C
At least one selected from r, Mn, Fe, Co, Ni, Mo, W, and Cu can be employed. Further, as a substance used as a negative electrode material,
As the graphite, flaky natural graphite, mesophase pitch graphite, massive artificial graphite and the like can be used. Further, as the amorphous carbon material, mesocarbon microbeads, fired furfuryl alcohol resin, and the like can be used. As the non-aqueous electrolyte, one obtained by dissolving an electrolyte composed of a lithium salt in an organic solvent is used.
As the organic solvent, propylene carbonate, ethylene carbonate, 1,2-dimexethane, 1,2-diethoxyethane, 2-methyltetrahydrofuran, diethyl carbonate, γ-butyl lactone, tetrahydrofuran, diethyl ether, sulfolane, acetonitrile, and the like, Alternatively, a mixture of these can be used. As the lithium salt, LiCl
O ₄ , LiPF ₆ , LiBF ₄ , LiCl, LiBr,
CH ₃ SO ₃ Li, Li (CF ₃ SO ₂ ) ₂ N, Li
(C ₂ F ₅ SO ₂ ) ₂ N, LiAsF ₆ or the like can be used. When the carboxylate type amphoteric surfactant is contained in the positive electrode material layer, it is preferably contained in an amount of 0.01 to 0.2% by weight based on the lithium-containing double oxide of the positive electrode material layer. If the amount is less than 0.01% by weight, the wettability of the electrolyte solution into the inside of the positive electrode plate becomes insufficient, and the capacity cannot be increased. On the other hand, if it exceeds 0.2% by weight, there is a problem that the filling amount of the positive electrode material decreases and the capacity decreases. When the carboxylate type amphoteric surfactant is contained in the negative electrode material layer, it is preferably contained in an amount of 0.01 to 0.2% by weight based on the carbon material of the negative electrode material layer. 0.
When the content is less than 01% by weight, the wettability of the electrolyte solution inside the negative electrode plate becomes insufficient, and the capacity cannot be increased. Also,
If it exceeds 0.2% by weight, there is a problem that the filling amount of the positive electrode material decreases and the capacity decreases. When the carboxylate type amphoteric surfactant is contained in the nonaqueous electrolyte layer, it is preferably contained in an amount of 0.01 to 0.2% by weight based on the lithium salt of the nonaqueous electrolyte layer. If the content is less than 0.01% by weight, the wettability of the electrolytic solution inside the positive electrode plate and the negative electrode plate becomes insufficient, and the capacity cannot be increased. On the other hand, when the content exceeds 0.2% by weight, there is a problem that the lithium conductivity of the non-aqueous electrolyte layer decreases and the capacity decreases. To manufacture the lithium ion secondary battery of the present invention, first, a positive electrode material slurry containing a lithium-containing double oxide and an organic solvent is applied on a positive electrode current collector, followed by a drying step and a press working. To produce a positive electrode plate provided with a positive electrode agent layer. Further, after a negative electrode material slurry containing a carbon material that occludes and releases lithium ions and an organic solvent is applied on a negative electrode current collector, a negative electrode plate provided with a negative electrode material layer is produced through a drying step and pressing. Next, a positive electrode plate and a negative electrode plate are laminated via a separator to form an electrode plate group, and the electrode plate group is impregnated with a non-aqueous electrolyte to manufacture a lithium ion secondary battery. Then, an amphoteric surfactant is added to at least one of the positive electrode material slurry, the negative electrode material slurry and the non-aqueous electrolyte.
By manufacturing a lithium ion secondary battery in this way, it is possible to easily manufacture a lithium ion secondary battery capable of improving the wettability of the electrolytic solution inside the electrode plate. In particular, the cathode material slurry is
Since it exhibits alkalinity, the dispersibility of the cathode material in an organic solvent can be enhanced by adding an amphoteric surfactant to the cathode material slurry. Further, since the positive electrode material slurry contains the conductive powder, when the dispersibility is increased in this way, a conductive network of the conductive powder is uniformly formed in the positive electrode material layer. Therefore, the reaction in the positive electrode material layer becomes uniform, and the movement of ions becomes easy. As a result, the charge transfer resistance decreases,
The high rate discharge characteristics of the battery are improved. DESCRIPTION OF THE PREFERRED EMBODIMENTS (Test 1) FIG. 1 is an end view of each lithium ion secondary battery used in Test 1. As shown in this figure, this lithium ion secondary battery has a structure in which a wound electrode group 1 is housed in a battery can 2. The wound electrode plate group 1 has a structure in which the positive electrode plate 3 and the negative electrode plate 4 are wound so as to be stacked via an electrolyte layer (separator) 5. In this example, a lithium ion secondary battery was manufactured as follows. First, the positive electrode plate 3 was manufactured. First, a positive electrode material made of lithium cobalt oxide (Li _x CoO ₂ ) having an average particle diameter of 10 μm and an average particle diameter of 3 μm
m and a binder made of polyvinylidene fluoride and an amphoteric surfactant in the amounts shown in Table 1 (weight relative to lithium cobalt oxide of the positive electrode material), respectively.
A positive electrode slurry was prepared by dispersing in a solvent comprising methyl-2-pyrrolidone (NMP). Here, among the amphoteric surfactants shown in Table 1, Levon 2000 (liquid) and NSA
-2000 (liquid) is a betaine-type amphoteric surfactant manufactured by Sanyo Chemical Co., Ltd., and Levon 101-H (liquid) and Levon 105 (liquid) are isodazoline-type amphoteric surfactants manufactured by Sanyo Chemical Co., Ltd. is there. The basic structure of the betaine-type amphoteric surfactant is shown in the following chemical formula 1, and the following chemical formula 2
Shows the basic structure of an isodazoline-type amphoteric surfactant. ## STR1 ## Embedded image Next, a positive electrode slurry is applied to both surfaces of a positive electrode current collector 6 made of aluminum foil having a thickness of 20 μm to a uniform thickness,
The NMP was dried to remove NMP, and rolled by a roll press to form a positive electrode material layer 7 having a length of 480 mm and a width of 54 m.
m, and a positive electrode plate 3 having a thickness of 174 μm. Next, a negative electrode plate 4 was manufactured. First, a negative electrode material made of a graphite carbon material having an average particle diameter of 20 μm and a binder made of polyvinylidene fluoride were mixed with N-methyl-2-methyl-2-vinyl-2-nitride.
A negative electrode slurry was prepared by dispersing in a solvent comprising pyrrolidone (NMP). Next, the negative electrode slurry was applied to both surfaces of a negative electrode current collector 8 made of copper foil having a thickness of 10 μm to a uniform thickness, dried, NMP was removed, and rolled with a roll press to form a negative electrode material layer 9. The negative electrode plate 4 having a length of 500 mm, a width of 56 mm, and a thickness of 174 μm was formed. Next, the positive electrode plate 3 and the negative electrode plate 4 are
m-shaped separator 5 made of a polyethylene microporous membrane
And the electrode group 1 was formed. The strip-shaped separator 5 is constituted by a pair of separator portions.
Then, a pair of separator portions was arranged on both surfaces of the negative electrode plate 4 and wound so that the separators were arranged on the radially outer portion and the radially inner portion of the winding adjacent to the battery can 2.
Next, after disposing the electrode group 1 in the cylindrical battery can 2 made of Ni-plated iron, the nickel tab terminal 11 previously welded to the negative electrode current collector 8 is welded to the bottom 2 a of the battery can 2. did. Next, an organic electrolytic solution (non-aqueous electrolytic solution) in which a lithium salt composed of LiPF ₆ was dissolved at a concentration of 1 mol / l in a solvent in which propylene carbonate and dimethyl carbonate were mixed at a volume ratio of 1: 1 was placed in the battery can 2. 5 ml was injected. Next, the aluminum tab terminal 1 previously welded to the positive electrode current collector 6
0 was welded to the battery lid 12 equipped with a pressure switch. Then, the battery lid 12 is disposed on the upper portion of the battery can 2 via the gasket 13 made of insulating polypropylene, and then caulked to tightly seal the inside of the battery can 2 to form a cylindrical cylinder having a diameter of 18 mm and a height of 65 mm. Each uncharged lithium ion secondary battery was made. Next, each uncharged lithium ion secondary battery is
At 5 ° C, set voltage 4.2V, limited current 1400m
2.5 A at 1400 mA after charging for 2.5 hours at A
The discharge capacity of each battery at the time of discharging to the maximum was determined. Further, the charge and discharge described above were repeated, and the discharge capacity after 500 cycles was measured, and the ratio of this discharge capacity to the discharge capacity at the time of the first discharge (charge-discharge cycle characteristics) was calculated. Table 1 shows the results. Table 1 also shows, as a comparative example, the results of the case where the additive was not added (no addition) and the case where the oleic acid amide used conventionally was added. [Table 1] From Table 1, as compared with the case where no oleic acid amide was added and the case where no oleic acid amide was conventionally used, in the lithium ion secondary battery in which the amphoteric surfactant was contained in the cathode material layer in an amount of 0.01 to 0.2% by weight, It can be seen that the discharge capacity can be increased and the charge / discharge cycle characteristics can be improved. (Test 2) Next, instead of the positive electrode material slurry, the respective amounts (weight of the negative electrode material with respect to the carbon material) of the amphoteric surfactant shown in Table 2 were added to the negative electrode material slurry, and the others were used in Test 1. A battery similar to the battery was prepared, and the discharge capacity and charge / discharge cycle characteristics of each battery were determined under the same test conditions as in Test 1. Table 2 shows the results. Table 2 also shows, as a comparative example, the results of the case where no additive was added (no addition) and the case where the conventionally used oleic amide was added. [Table 2] From Table 2, as compared with those without addition and with oleic acid amide used conventionally, in the lithium ion secondary battery in which the amphoteric surfactant was contained in the negative electrode material layer at 0.01 to 0.2% by weight, It can be seen that the discharge capacity can be increased and the charge / discharge cycle characteristics can be improved. (Test 3) Next, instead of the positive electrode material slurry, an amphoteric surfactant in the amounts shown in Table 3 (weight relative to the lithium salt of the non-aqueous electrolyte) was added to the non-aqueous electrolyte, and the other components were used in Test 1. A battery similar to the battery that was used was prepared, and the discharge capacity and charge / discharge cycle characteristics of each battery were determined under the same test conditions as in Test 1. Table 3 shows the results. Table 3 also shows, as a comparative example, the case where no additive was added (no addition).
The results obtained by adding oleic acid amide, which has been conventionally used, are also shown. [Table 3] From Table 3, as compared with the case where no oleic acid amide was added and the case where no oleic acid amide was used conventionally, in the lithium ion secondary battery in which the amphoteric surfactant was contained in the negative electrode material layer in an amount of 0.01 to 0.2% by weight, It can be seen that the discharge capacity can be increased and the charge / discharge cycle characteristics can be improved. Tables 1 to 3 show that the addition of an amphoteric surfactant to the positive electrode material layer and the negative electrode material layer is particularly effective. In the above embodiment, the amphoteric surfactant was added to each of the positive electrode material layer, the negative electrode material layer and the non-aqueous electrolyte layer, but at least one of the positive electrode material layer, the negative electrode material layer and the non-aqueous electrolyte layer was added. It is only necessary to add an amphoteric surfactant to the positive electrode material layer and the negative electrode material layer, or to add the amphoteric surfactant to all of the positive electrode material layer, the negative electrode material layer and the non-aqueous electrolyte layer. is there. In the above embodiment, the wound electrode group and the cylindrical battery can were used. However, the electrode group and the polygonal prism (triangular prism, square prism) formed by simply laminating plate-shaped electrode plates were used. And the like, the same effect can be obtained in a battery using the battery can. In this embodiment, an amorphous carbon material is used as the negative electrode material. However, it goes without saying that graphite may be used as the negative electrode material. According to the present invention, since at least one of the positive electrode material layer, the negative electrode material layer and the non-aqueous electrolyte layer contains an amphoteric surfactant, the wettability of the electrolytic solution inside the electrode plate is improved. And the high-rate discharge characteristics and the number of life cycles of the lithium ion secondary battery can be increased. Particularly, since the positive electrode material slurry shows alkalinity, the dispersibility of the positive electrode material in an organic solvent can be enhanced by adding an amphoteric surfactant to the positive electrode material slurry. Further, since the positive electrode material slurry contains the conductive powder, when the dispersibility is increased in this way, a conductive network of the conductive powder is uniformly formed in the positive electrode material layer. Therefore, the reaction in the positive electrode material layer becomes uniform, and the movement of ions becomes easy. As a result, the charge transfer resistance is reduced, and the high rate discharge characteristics of the battery are improved.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an end view of a lithium ion secondary battery manufactured by a method according to an embodiment of the present invention. [Explanation of Symbols] 1 Winding electrode group 2 Battery can 3 Positive electrode plate 4 Negative electrode plate 5 Electrolyte layer (separator) 6 Positive current collector 7 Positive electrode material layer 8 Negative current collector 9 Negative electrode material layer

────────────────────────────────────────────────── ─── Continuation of front page (56) References JP-A-7-153467 (JP, A) JP-A-7-37578 (JP, A) JP-A-10-83837 (JP, A) JP-A 8- 213022 (JP, A) JP-A-7-29605 (JP, A) JP-A-10-92436 (JP, A) JP-A-10-12273 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01M 10/40 H01M 4/00-4/62

Claims (1)

(57) [Claims 1] A positive electrode material layer mainly composed of a lithium-containing double oxide and a negative electrode material layer mainly composed of a carbon material that occludes and releases lithium ions are composed of a lithium salt. In a lithium ion secondary battery laminated via a non-aqueous electrolyte layer containing 0.01% to 0.2% by weight of lithium based on the lithium salt.
A lithium ion secondary battery, wherein a borate type surfactant is contained in the nonaqueous electrolyte layer .