JP2008091259A - Method for manufacturing nonaqueous electrolyte secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery that is satisfactory in the cycle characteristics and reliability, by forming a satisfactory coating on a negative electrode at initial charging. <P>SOLUTION: In the nonaqueous electrolyte secondary battery comprising an electrode plate group containing a positive electrode plate that holds a positive electrode active material, a negative electrode plate that holds a negative electrode active material, and a separator; and a nonaqueous electrolyte containing 0.5-1.5 mol/l lithium salt containing lithium hexafluorophosphate (LiPF<SB>6</SB>) and a nonaqueous solvent, the initial charge of a charging current is carried out at a hour rate of 1.0 or lower, with respect to the rated capacity in an environment of -5 to 10°C, to form the satisfactory coating on a negative electrode surface. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for producing a non-aqueous electrolyte secondary battery, and particularly relates to a method that suitably improves the initial charge.

In recent years, non-aqueous electrolyte secondary batteries having a high energy density have been widely used as electronic devices such as AV devices and personal computers become cordless and portable. Moreover, as the capacity increases, there are concerns about the reliability and cycle characteristics of the battery. On the other hand, the solid electrolyte interface (SEI) is formed on the negative electrode surface by activating the positive electrode and the negative electrode and performing the initial charge in the finishing step of the nonaqueous electrolyte secondary battery. However, this SEI coating is highly directed to lithium ions and electrolytic solvents. As the diffusion of lithium ions increases, the amount of SEI formed on the negative electrode surface increases, so that the lithium ions present in the electrolysis are insufficient, and the cycle characteristics deteriorate rapidly. As a method for reducing the amount of SEI, a method of stabilizing the amount of SEI film by charging the initial charge in a cooling atmosphere (−20 ° C. to 20 ° C.) and charging at a low current of 1 C or less is proposed. (For example, refer to Patent Document 1.)
Japanese Patent Application Laid-Open No. 11-111267

However, in the method as disclosed in Patent Document 1, since the reactivity between the lithium salt and the electrolytic solution is not studied, for example, when LiBF ₄ is used at 1.0 M, the reactivity with the electrolytic solution on the negative electrode is reduced. As a result, a large amount of lithium fluoride (LiF) product can be formed on the surface of the negative electrode, so that the charge acceptability at low temperatures deteriorates, and the electrode plate expands by repeated charging and discharging and the electrode plate is cut. As a result, there was a problem that reliability was lowered. Further, when excessive charging at −20 ° C. is performed, lithium metal is deposited on the negative electrode surface and grows in a dendritic state by repeating charge and discharge. As a result, it breaks through the separator and causes an internal short circuit. There was a problem that cycle life characteristics deteriorated by causing deterioration of materials. In particular, this problem is remarkable when the lithium-containing composite oxide includes nickel, manganese, and cobalt, such as LiNi _x Mn _y Co _z O ₂ , in the positive electrode active material.

  An object of the present invention is to solve the conventional problems and to provide a method for manufacturing a non-aqueous electrolyte secondary battery excellent in cycle characteristics and reliability.

In order to solve the above-described conventional problems, the method for producing a non-aqueous electrolyte secondary battery of the present invention includes a positive electrode plate holding a positive electrode active material, a negative electrode plate holding a negative electrode active material, and a separator. And a non-aqueous electrolyte secondary battery comprising a non-aqueous electrolyte composed of a lithium salt 0.5 mol / l to 1.5 mol / l composed of lithium hexafluorophosphate (LiPF ₆ ) and a non-aqueous solvent, The charging current of the first charge in an environment of 5 ° C. to 10 ° C. is 1.0 It or less with respect to the rated capacity.

  The time rate with respect to the rated capacity is also called C rate, and 1 It is also called 1C. The charging current of 1C is a current that reaches the rated capacity in 1 hour, and the charging current of 2C is a current that reaches the rated capacity in 1/2 hour, that is, 0.5 hours.

According to the present invention, only LiPF ₆ is used as the type of lithium salt, and the reaction with the electrolyte on the negative electrode is suppressed and the LiF generated on the negative electrode surface by setting the temperature of the low-temperature charging to a more preferable range. Reduce things.

  Furthermore, when a non-aqueous electrolyte includes a cyclic carbonate having C═C as an additive, diffusion of lithium ions can be suppressed, and a decrease in lithium ions in the electrolyte can be prevented. A good film can be formed on top.

  Examples of the cyclic carbonate having C═C include vinylene carbonate (VC) and vinyl ethyl carbonate (VEC). VC is particularly preferable because it forms a good SEI film.

  In the present invention, the effect is more prominent when the positive electrode active material is a lithium-containing composite oxide containing nickel, manganese, and cobalt.

  ADVANTAGE OF THE INVENTION According to this invention, the reaction with the electrolyte solution on a negative electrode can be suppressed, and the product of LiF made on the negative electrode surface can be reduced. In addition, when VC or the like is used as an additive, a non-aqueous electrolyte secondary battery with improved cycle characteristics and excellent reliability is formed by forming a good coating on the negative electrode surface in order to prevent a decrease in lithium ions in the electrolyte. The manufacturing method of can be provided.

A preferred embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows a charge / discharge system used in the production method of the present invention. The gist of the present invention is to first charge a non-aqueous electrolyte secondary battery using a suitable non-aqueous electrolyte in a low temperature environment with a controlled current.
A non-charged non-aqueous electrolyte secondary battery 10 having a non-aqueous electrolyte composed of 0.5 mol / l to 1.5 mol / l of a lithium salt composed of lithium hexafluorophosphate and a non-aqueous solvent is set at an environmental temperature. It is installed in a constant temperature bath 11 that can be controlled to a constant level, and is connected by a charge / discharge controller 13 that takes in power from a commercial power source 12 and a connector 14, and is charged at a predetermined current value. A plurality of non-aqueous electrolyte secondary batteries 10 may be installed. Further, in order to suppress the heat generation of the non-aqueous electrolyte secondary battery 10 or to average the charging conditions between the plurality of non-aqueous electrolyte secondary batteries 10, a fan 15 is installed in the thermostat 10. It is also preferable to charge in a blown state by sending wind to the non-aqueous electrolyte secondary battery 10.

  Hereinafter, the present invention will be described in detail using Examples and Comparative Examples using the above-described charge / discharge system, but the present invention is not limited to these Examples, and the scope does not change the gist thereof. However, it can be implemented with appropriate modifications.

(Example 1)
FIG. 2 shows a cylindrical nonaqueous electrolyte secondary battery (outer diameter: 18 mm, height: 65 mm) used in this example. As is apparent from this figure, the electrode plate group 1 is configured by winding the belt-like positive electrode plate and the negative electrode plate a plurality of times in a spiral manner via a separator. An aluminum positive electrode lead 2 and a nickel negative electrode lead 3 are welded to the positive electrode plate and the negative electrode plate, respectively. An insulating ring made of polyethylene resin is attached to the upper and lower parts of the electrode plate group and accommodated in the battery case 4. The other end of the positive electrode lead 2 is spot welded to the sealing plate 5, and the other end of the negative electrode lead 3 is spot welded to the battery case. After injecting a predetermined amount of nonaqueous electrolyte, the battery is sealed to complete the battery.

First, preparation of the positive electrode will be described. LiNi _0.4 Mn _0.4 Co _0.2 O ₂ is used as the positive electrode active material, and 3 parts by weight of acetylene black is used as the conductive material, and 5 parts by weight of polyvinylidene fluoride is used as the binder. An N-methylpyrrolidinone solution was prepared and mixed by stirring to obtain a paste-like positive electrode mixture. Next, an aluminum foil having a thickness of 15 μm was used as a current collector, the paste-like positive electrode mixture was applied to both surfaces thereof, dried and then rolled with a rolling roller, and cut into predetermined dimensions to obtain a positive electrode plate.

Moreover, the negative electrode was produced as follows. First, flaky graphite pulverized and classified so as to have an average particle size of about 20 μm and a specific surface area of 3 m 2 / g and 3 parts by weight of styrene / butadiene rubber as a binder are mixed, and then carboxymethyl cellulose is added to the graphite. A carboxymethyl cellulose aqueous solution was added so as to be in weight percent, and the mixture was stirred and mixed to obtain a paste-like negative electrode mixture. A copper foil having a thickness of 12 μm was used as a current collector, a paste-like negative electrode mixture was applied to both surfaces thereof, dried and then rolled using a rolling roller, and cut into a predetermined size to obtain a negative electrode plate. As the non-aqueous electrolyte, a solution prepared by dissolving 1.0 mol / l LiPF ₆ in a solvent prepared by mixing ethylene carbonate and ethyl methyl carbonate at a volume ratio of 30:70 at 20 ° C. did.

For the uncharged battery assembled in this way, as Example 1, the following initial charging is performed.
First charge in an environment of 5 ° C, constant current charge for 1 hour at a charge current of 660 mA, then discharge to a specified end-of-discharge voltage with a discharge current of 1200 mA, then charge to the specified end-of-charge voltage A lithium secondary battery was produced.

Further, (Table 1) lithium salts such as shown in (LiBF ₄₎ was changed to 1.0M, the non-aqueous electrolyte of Comparative Example 1 that performs processing at the time of initial charging in the same manner as in Example 1 A secondary battery was prepared.

In Comparative Example 1, the use of 1.0M LiBF ₄ increased the reactivity with the electrolyte on the negative electrode, and a large amount of lithium fluoride (LiF) product was formed on the negative electrode surface. As a result, the charge acceptability at low temperatures deteriorates, and the electrode plate expands and the electrode plate breaks due to repeated charge and discharge.

In (Table 2), the non-aqueous electrolyte secondary batteries Comparative Examples 2-3 and Examples 2-5 in the same manner as in Example 1 except for changing the concentration of lithium hexafluorophosphate (LiPF ₆₎ Created.

In addition, FIG. 3 shows that each non-aqueous electrolyte secondary battery shown in (Table 1) is charged with a battery voltage of 4.2 V by CVCC charging to a maximum current of 1540 mA, charging with a current termination of 100 mA, and a discharge current of 2200 mA. , Shows a 45 ° C. cycle characteristic diagram when charging and discharging are repeated up to 500 cycles under the condition of performing a constant current discharge with a discharge end voltage of 3.0 V, the vertical axis is the battery capacity maintenance rate of the 500th cycle, and the horizontal axis is The concentration of LiPF ₆ is shown.

  As can be seen from FIG. 3, in Examples 1-5, the deterioration of the cycle life characteristics is small compared to Comparative Examples 2-3. In Comparative Example 3, since the electric conductivity of the organic electrolytic solution is small, the movement of lithium ions in the electrolytic solution is reduced. Therefore, it can be said that the concentration of 0.5 mol / l or more is necessary in the organic electrolyte. In Comparative Example 2, it is considered that as the viscosity increases, the electrical conductivity increases and the lithium ions also increase, so that the movement of lithium ions decreases, so that the cycle characteristics deteriorate rapidly. Therefore, in the organic electrolytic solution, the concentration needs to be 1.5 mol / l or less.

  In (Table 3), non-aqueous electrolyte secondary batteries were prepared for Examples 6 to 11 and Comparative Examples 4 to 7 in the same manner as Example 1 except that the temperature and charging current (mA) at the time of initial charge were changed. did.

  In addition, FIG. 4 shows that each non-aqueous electrolyte secondary battery shown in (Table 3) is charged with a battery voltage of 4.2 V by CVCC charging to a maximum current of 1540 mA, charging with a current termination of 100 mA, and a discharge current of 2200 mA. , Shows a 45 ° C. cycle characteristic diagram when charging and discharging are repeated up to 500 cycles under the condition of performing a constant current discharge with a discharge end voltage of 3.0 V, the vertical axis is the battery capacity maintenance rate of the 500th cycle, and the horizontal axis is It shows the environmental temperature during initial charging.

As can be seen from FIG. 4, in Examples 1, 6, 7, and 10, the deterioration of the cycle characteristics is small compared to Comparative Examples 4 to 5. When Comparative Example 4 was decomposed after the initial charge, a large amount of lithium metal was deposited on the negative electrode surface. From this, it is considered that the reaction is not uniformly caused by excessive charging in an environment of −20 ° C., and lithium metal is deposited. Moreover, it is thought that the cycle life characteristics deteriorated because it grew on the dendride by repeating charge and discharge, and it broke through the separator and caused an internal short circuit. In Comparative Example 5, by performing the initial charge, lithium ions in the electrolytic solution diffuse, and since the reaction with the solvent is high, the amount of products formed on the negative electrode surface increases, A good film cannot be formed. In addition, it is considered that the deterioration of the positive electrode / negative electrode active material occurred due to the decrease of lithium ions present in the electrolytic solution, and the cycle life characteristics rapidly deteriorated due to the influence thereof. In Examples 1, 6, 7, and 10, since the diffusion of lithium ions in the electrolytic solution decreases in the initial charge at a low temperature, the amount of products formed on the negative electrode surface decreases, and Can form a good film. In addition, by suppressing the diffusion of lithium ions in the electrolyte, it was possible to prevent the decrease of lithium ions in the electrolyte, thereby suppressing deterioration of the positive and negative electrode active materials and improving the cycle life characteristics. I think.

  In addition, FIG. 5 shows that each non-aqueous electrolyte secondary battery shown in (Table 3) is charged with a battery voltage of 4.2 V by CVCC charging to a maximum current of 1540 mA, charging with a current termination of 100 mA, and a discharge current of 2200 mA. , Shows a 45 ° C. cycle characteristic diagram when charging and discharging are repeated up to 500 cycles under the condition of performing a constant current discharge with a discharge end voltage of 3.0 V, the vertical axis is the battery capacity maintenance rate of the 500th cycle, and the horizontal axis is The charging current is shown.

  As can be seen from FIG. 5, in Examples 1 and 8 to 11, the deterioration of the cycle characteristics is smaller than that in Comparative Example 7. When Comparative Example 7 was decomposed after the initial charge, a large amount of lithium metal was deposited on the negative electrode surface. From this fact, it was considered that a large amount of lithium metal was deposited on the negative electrode surface because the charge current was excessively charged at 1.0 C or more and the reaction at the electrode plate proceeded non-uniformly. Moreover, it is thought that the cycle life characteristics deteriorated because it grew on the dendride by repeating charge and discharge, and it broke through the separator and caused an internal short circuit. In Examples 1 and 8 to 11, the battery reaction at the electrode plate was able to proceed uniformly by performing the initial charging current at a specified 1.0 C or less, and as a result, the cycle life characteristics were improved. It is thought that.

Next, addition of VC to Example 1 was examined.
Examples 12 to 14 in which the initial charge was performed in the same manner as in Example 1 except that the amount of VC added as shown in Table 4 was changed (% is% by weight relative to the nonaqueous electrolyte). A non-aqueous electrolyte secondary battery was prepared.

  In addition, FIG. 6 shows that each non-aqueous electrolyte secondary battery shown in (Table 4) is charged with a battery voltage of 4.2 V, CVCC charging to a maximum current of 1540 mA, charging with a current termination of 100 mA, and a discharge current of 2200 mA. The 45 ° C. cycle characteristic diagram when charging and discharging are repeated up to 600 cycles under the condition of constant current discharge with a discharge end voltage of 3.0 V, the vertical axis is the battery capacity maintenance rate at the 600th cycle, and the horizontal axis is The additive VC amount (%) is shown.

  As can be seen from FIG. 6, the batteries of Examples 12 to 14 all have less cycle deterioration than that of Example 1, so that the amount of product formed on the negative electrode surface can be increased by adding VC. It is considered that the cycle characteristics are improved because the number of the active materials is reduced and a better film can be formed on the negative electrode, and the deterioration of the active material during the cycle can be suppressed.

  Except for changing the positive electrode active material as shown in Table 5, non-aqueous electrolyte secondary batteries of Examples 15 to 16 that were charged for the first time in the same manner as Example 1 were prepared.

  Further, FIG. 7 shows that each non-aqueous electrolyte secondary battery shown in (Table 5) is charged at a battery voltage of 4.2 V by CVCC charging to a maximum current of 1540 mA, charging at a current end of 100 mA, and a discharge current of 2200 mA. , Shows a 45 ° C. cycle characteristic diagram when charging and discharging are repeated up to 500 cycles under the condition of performing a constant current discharge with a discharge end voltage of 3.0 V, the vertical axis is the battery capacity maintenance rate of the 500th cycle, and the horizontal axis is The type of positive electrode active material is shown.

As can be seen from FIG. 7, the cycle deterioration is small as compared with Examples 14 and 15. Although the mechanism is not clear from the results of intensive studies, lithium composite oxides containing nickel manganese cobalt each have a greater irreversible capacity during initial charge and a large change in voltage polarization compared to lithium cobaltate (LiCoO ₂ ). From this, it is considered that the cycle life characteristics were improved because the balance between the positive electrode and the negative electrode was improved.

Schematic diagram of the charge / discharge system used in the present invention Perspective view of the battery prepared in this example (partially cut away view) It shows the relationship between the concentration of the capacity retention ratio and LiPF ₆ in the 500th cycle of the battery in this embodiment The figure which shows the capacity | capacitance maintenance ratio of the 500th cycle of the battery in a present Example, and the relationship of the temperature at the time of initial charge. The figure which shows the relationship of the capacity maintenance rate of the 500th cycle of a battery and a charging current in a present Example. The battery capacity retention rate at the 600th cycle of the battery in this example, and the horizontal axis represents the amount of additive VC (%). The figure which shows the relationship between the capacity maintenance rate of the 500th cycle of the battery in a present Example, and the kind of positive electrode active material.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Electrode plate group 2 Positive electrode lead 3 Negative electrode lead 4 Battery case 5 Sealing plate 10 Nonaqueous electrolyte secondary battery 11 Constant temperature bath 12 Commercial power supply 13 Charge / discharge controller 14 Connector 15 Fan

Claims (4)

  A positive electrode plate holding a positive electrode active material, a negative electrode plate holding a negative electrode active material, and a separator, and a lithium salt consisting of lithium hexafluorophosphate 0.5 mol / l to 1.5 mol / l A non-aqueous electrolyte secondary battery comprising a non-aqueous electrolyte composed of an aqueous solvent is characterized in that the charge current of the first charge in an environment of -5 ° C. to 10 ° C. is 1.0 It or less in terms of the time rate with respect to the rated capacity. A method for producing a non-aqueous electrolyte secondary battery.   The method for producing a non-aqueous electrolyte secondary battery according to claim 1, wherein the non-aqueous electrolyte includes a cyclic carbonate having C═C.   The method for producing a nonaqueous electrolyte secondary battery according to claim 1, wherein the cyclic carbonate having C═C is vinylene carbonate. The method for producing a non-aqueous electrolyte secondary battery according to claim 1, wherein the positive electrode active material is a lithium-containing composite oxide containing nickel, manganese, and cobalt.

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