JP4736380B2 - Secondary battery and secondary battery aging treatment method - Google Patents

Description

  In the present invention, an electrode plate using a lithium composite oxide as a positive electrode active material is laminated via a separator, and the laminated electrode plate and separator are accommodated in a battery exterior and sealed and connected to the electrode plate. The present invention relates to a secondary battery in which an electrode terminal is led out from a battery exterior and an aging treatment method for the secondary battery.

  2. Description of the Related Art Conventionally, an aging process is known in which a secondary battery just manufactured is initially charged, gas generated at that time is removed, and then the secondary battery is left for about one week to one month (for example, a patent) Reference 1). This aging process is performed for the purpose of removing initial deterioration and stabilizing battery performance, but this also affects the life of the secondary battery.

Since secondary batteries are generally used repeatedly by charging / discharging, it is desirable to optimize the various conditions in the above aging process to further extend the life to withstand repeated charge / discharge cycles. It is rare.
WO 97/30487 pamphlet

An object of the present invention is to provide a secondary battery and a secondary battery aging treatment method capable of extending the service life.
To achieve the above object, according to the present invention, an electrode plate using LiMn ₂ O ₄ as a positive electrode active material and a carbon-based material as a negative electrode active material is laminated through a separator, and the laminated electrode An aging process for a secondary battery in which a plate and a separator are accommodated in a battery exterior and sealed, and an electrode terminal connected to the electrode plate is subjected to an aging process after manufacturing the secondary battery derived from the battery exterior. In this method, an electrode potential with respect to lithium is equal to or higher than an electrode potential at 60% SOC (State Of Charge) and equal to or lower than an electrode potential at 90% SOC, and the voltage of the secondary battery is 3.9 [V ] To 4.0 [V], and after the charging, the gas generated inside the secondary battery is discharged, and after the gas is discharged, it is left for one week to one month for aging. Process Aging process the following methods cell is provided.

In the present invention, with respect to a secondary battery using LiMn ₂ O ₄ as a positive electrode active material, the electrode potential relative to lithium is an electrode potential within a range corresponding to SOC 60% to 90%, and the voltage of the secondary battery. Is initially charged to be 3.9 [V] to 4.0 [V], and after the charging, the gas generated inside the secondary battery is discharged, and after the gas is discharged, 1 The aging treatment is performed after leaving for one week to one month . By initially charging with an electrode potential in such a range, the voltage of the initial charging is optimized to a voltage that appropriately proceeds with initial deterioration in the aging process, so that the life of the secondary battery can be extended. Is possible.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1A is a plan view showing the entirety of a thin secondary battery (hereinafter also simply referred to as “thin battery”) according to an embodiment of the present invention, and FIG. 1B is a BB in FIG. It is sectional drawing along a line. FIG. 1 shows one thin battery (unit battery), and an assembled battery having a desired voltage and capacity is formed by stacking a plurality of thin batteries 10.

  Referring to FIG. 1, the overall configuration of a thin battery 10 according to an embodiment of the present invention will be described. The thin battery 10 of this example is a lithium-based thin secondary battery, and includes three positive electrode plates 101 and 7. The sheet separator 102, the three negative electrode plates 103, the positive electrode terminal 104, the negative electrode plate 105, the upper battery outer casing 106, the lower battery outer casing 107, and an electrolyte (not shown) are included. The number of the positive electrode plate 101, the separator 102, and the negative electrode plate 103 is not limited at all, and may be one positive electrode plate 101, three separators 102, and one negative electrode plate 103, and if necessary. Thus, the number of the positive electrode plate 101, the negative electrode plate 103, and the separator 102 can be selected and configured.

  FIG. 2 specifically shows the inside of the thin battery 10 having three positive plates 101, seven separators 102, and three negative plates 103. As shown in the figure, the positive electrode plate 101 of the present embodiment is connected to the positive electrode current collector 104a connected to the positive electrode terminal 104 via the positive electrode lead 104c, and both main surfaces of the positive electrode current collector 104a. A positive electrode layer 104b formed. Similarly, the negative electrode plate 103 includes a negative electrode side current collector 105a connected to the negative electrode terminal 105 via a negative electrode lead 105c, and a negative electrode layer 105b formed on both main surfaces of the negative electrode side current collector 105a. Have. Further, a separator 102 is interposed between the positive electrode layer 104 b of the positive electrode plate 101 and the negative electrode layer 105 b of the negative electrode plate 103.

In this embodiment, LiMn ₂ O ₄ belonging to a lithium-containing composite oxide is used as a positive electrode active material, carbon black belonging to a carbon-based material is used as a conductive material, and polyvinylidene fluoride (PVDF) is used as a binder. A positive electrode active material and a conductive material are mixed, and a slurry is prepared by uniformly dispersing the mixed positive electrode active material and the conductive material in N-methyl-2-pyrrolidone (NMP) in which polyvinylidene fluoride is dissolved. The slurry is uniformly applied onto a 20 μm-thick aluminum metal foil serving as the positive electrode side current collector 104a, NMP is evaporated, and rolled with a roll press to produce the positive electrode layer 104b on the aluminum metal foil 104a. . The weight ratio of LiMn ₂ O ₄ to be mixed, carbon black, and polyvinylidene fluoride (PVDF) is 75 to 85:10 to 20: 5 to 10, preferably 85: 10: 5 to 75:20. : 5. After the positive electrode layer 104b is fabricated, the positive electrode plate 102 is obtained by cutting into a predetermined size (width 70 mm, length 120 mm, thickness 0.18 mm).

  In terms of output, the above-mentioned lithium composite oxide preferably has an average particle size r of 0.1 μm <r <1 μm, and more preferably 0.1 μm <r <0.5 μm. Here, the average particle size is a 50% cumulative particle size, and is a particle size when the volume integrated from 0 μm is 50% in the particle size distribution diagram. In this measurement, a microtrack particle size distribution analyzer is used to measure the number n of particles and the diameter d per particle by scattering of laser light. Of course, other particle size analyzers can be used.

  Further, the particle structure of the lithium composite oxide is preferably primary particles having properties close to single crystals or difficult crystals. At this time, secondary particles formed by aggregation of the primary particles may be included, but the content is preferably small. Specifically, the content of the secondary particles in the lithium composite oxide is 50%. The following is preferable. In terms of life, it is preferably a single crystal.

  In this embodiment, hard carbon belonging to a carbon-based material is used as the negative electrode active material, and polyvinylidene fluoride (PVDF) is used as the binder. Hard carbon and polyvinylidene fluoride (PVDF) are mixed at a weight ratio of 90:10 and dispersed in N-methyl-2-pyrrolidone (NMP) to produce a slurry. A negative electrode layer 105b is formed on a copper metal foil 105b having a thickness of 10 μm to be 105a. The produced negative electrode layer 105b is cut into a predetermined size (width 70 mm, length 120 mm, thickness 0.11 mm) to obtain the negative electrode plate 103.

  Examples of the negative electrode active material include materials that occlude and release lithium ions of the positive electrode active material, such as amorphous carbon including hard carbon, non-graphitizable carbon, graphitizable carbon, or graphite. I can do it.

  The separator 102 prevents the short-circuit between the positive electrode plate 101 and the negative electrode plate 103 described above, and may have a function of holding an electrolyte. The separator 102 is a microporous membrane made of polyolefin such as polyethylene (PE) or polypropylene (PP), for example, and when an overcurrent flows, the pores of the membrane are blocked by the heat generation, thereby blocking the current. Also have. The separator 102 of the present invention is not limited to a single-layer film such as polyolefin, but a three-layer structure in which a polypropylene layer is sandwiched between polyethylene layers, or a laminate of a polyolefin microporous film and an organic nonwoven fabric can also be used. . By forming the separator 102 in multiple layers, various functions such as an overcurrent prevention function, an electrolyte holding function, and a separator shape maintenance (stiffness improvement) function can be provided. Further, instead of the separator 102, a gel electrolyte or an intrinsic polymer electrolyte can be used.

  The positive electrode plates 101 and the negative electrode plates 103 are alternately stacked in such an order that the separators 102 are positioned between the positive electrode plates 101 and the negative electrode plates 103, and further, the separators are provided at the uppermost and lowermost parts. 102 are stacked one by one. In each of the two positive plates 101, the positive current collector 104a is connected to the positive terminal 104 made of metal foil via the positive lead 104c, while the two negative plates 103 are connected to the negative electrode side. A current collector 105a is connected to a negative electrode terminal 105 made of metal foil through a negative electrode lead 105c. The positive electrode terminal 104 and the negative electrode terminal 105 are not particularly limited as long as they are electrochemically stable metal materials. Examples of the positive electrode terminal 104 include aluminum and an aluminum alloy, and examples of the negative electrode terminal 105 include nickel and copper. Or stainless steel etc. can be mentioned. In addition, both the positive electrode side current collector 104a and the negative electrode side current collector 105a of this example are configured by extending the aluminum foil, nickel foil, or copper foil constituting the current collector of the positive electrode plate 101 and the negative electrode plate 103. However, the current collectors 104a and 105a can be formed of separate materials and parts.

  The positive electrode plate 101, the negative electrode plate 103, the separator 102, and the like are sealed by the upper battery casing 106 and the lower battery casing 107. The upper battery outer casing 106 and the lower battery outer casing 107 are made of, for example, a resin film such as polyethylene or polypropylene, or an inner surface of a metal foil such as aluminum laminated with a resin such as polyethylene or polypropylene. It is made of a flexible material such as a resin-metal thin film laminate material laminated with a polyester resin or the like.

The upper battery casing 106 and the lower battery casing 107 allow the positive electrode plate 101, the negative electrode plate 103, the separator 102, the positive electrode side current collector 104a, a part of the positive electrode terminal 104, the negative electrode side current collector 105a, and the negative electrode. A part of the terminal 105 is wrapped, and in a space formed by the battery casings 106 and 107, an organic liquid solvent is lithium perchlorate (LiClO ₄ ), lithium borofluoride (LiBF ₄ ), or lithium hexafluorophosphate (LiPF). ₆ ) After injecting a liquid electrolyte having a lithium salt as a solute, the outer peripheral edges of the upper battery outer casing 106 and the lower battery outer casing 107 are sealed by a technique such as heat sealing.

  Examples of the organic liquid solvent of the liquid electrolyte enclosed in the battery exterior include ester solvents such as propylene carbonate (PC), ethylene carbonate (EC), and dimethyl carbonate (DMC). It is not limited only to this, The organic liquid solvent which mixed and prepared ether solvents, such as (gamma) -butylactone ((gamma) -BL), dietoshietane (DEE), etc. can also be used for ester solvent.

  Note that the positive terminal 104 is led out from one end of the sealed battery casings 106 and 107, but a gap is generated at the joint between the upper battery casing 106 and the lower battery casing 107 by the thickness of the positive terminal 104. Therefore, in order to maintain the sealing performance in the thin battery 10, a seal film made of polyethylene or polypropylene is applied to a portion where the positive electrode terminal 104 and the battery exterior 106, 107 are in contact with each other by a technique such as heat fusion. It can also be interposed. Similarly, the negative electrode terminal 105 is led out from the other end portion of the sealed battery casings 106 and 107. Here, similarly to the positive electrode terminal 104 side, the negative electrode terminal 105 and the battery casing 106 are also connected. , 107 can also be interposed with a seal film. Note that, in any of the positive electrode terminal 104 and the negative electrode terminal 105, it is desirable from the viewpoint of heat-fusibility that the seal film is made of a resin of the same system as the resin constituting the battery casings 106 and 107.

FIG. 3 is a graph showing the relationship between the electrode potential of the positive electrode active material (LiMn ₂ O ₄ ) with respect to lithium and the DOD of the secondary battery in the embodiment of the present invention.

  The thin battery 10 produced as described above is usually subjected to an aging process in order to remove initial deterioration and stabilize battery performance. In this aging process, first charging is performed, and the gas generated at that time is discharged, and then left in that state for about one week to one month.

  In the present embodiment, during this aging treatment, the electrode potential with respect to lithium is not less than the electrode potential at 40% DOD (Depth Of Discharge) and not more than the electrode potential at 10% DOD, that is, Initial charging is performed so that the electrode potential is at or above the SOC (State Of Charge) 60% and below the electrode potential at the SOC 90%. In addition, the electrode potential with respect to lithium in the present invention is a potential in which a lithium metal is used as a negative electrode when a lithium composite oxide is used as a positive electrode, and means an electrode potential in an open circuit state.

  When the initial charge is performed so that the electrode potential with respect to lithium is less than the electrode potential at 40% DOD, as shown in FIG. 3, at the inflection point of the electrode potential existing in the vicinity of 40% to 50% DOD, the aging process is performed. Sufficient voltage cannot be applied, and initial deterioration does not proceed sufficiently in the aging process, and battery performance may not be stable.

  On the other hand, when the initial charge is performed so that the electrode potential with respect to lithium is larger than the electrode potential at the time of DOD 10%, as shown in the figure, the electrode potential rapidly rises below DOD 10%. At this time, a large voltage is applied, and the battery may be deteriorated during the aging process.

  Therefore, in the aging process, the initial charge is performed at an electrode potential within a range corresponding to the DOD of 10% to 40%, thereby optimizing the voltage of the initial charge so that the initial deterioration proceeds appropriately in the aging process. It becomes possible to extend the life of the battery 10.

  FIG. 4 is a graph showing the relationship between the open circuit voltage of the secondary battery and the DOD of the secondary battery in the embodiment of the present invention. When the above-described carbon-based material is used as the negative electrode active material, the voltage of the secondary battery 10 is set to 3.9 [V] to 4.0 [V] during the aging treatment as shown in FIG. By performing the initial charge at a voltage of, it is possible to ensure an electrode potential for lithium in the above range. In addition, the vertical axis | shaft of FIG. 3 shows the electrode potential [V] with respect to lithium, while the vertical axis | shaft of FIG. 4 shows the voltage [V] of a secondary battery.

  The embodiment described above is described for facilitating the understanding of the present invention, and is not described for limiting the present invention. Therefore, each element disclosed in the above embodiment is intended to include all design changes and equivalents belonging to the technical scope of the present invention.

  Hereinafter, the effects of the present invention were confirmed by examples and comparative examples that further embody the present invention. The following examples and comparative examples are for confirming the effects of the secondary batteries used in the above-described embodiments.

Example 1
A powder obtained by mixing carbon black (conductive agent) and polyvinylidene fluoride (PVDF) with LiMn ₂ O ₄ (positive electrode active material) is dispersed in N-methyl-2-pyrrolidone (NMP) to form a slurry, and the slurry is made of aluminum foil. After coating uniformly on both main surfaces of the (positive electrode side current collector) and drying, compression and cutting were performed to prepare a positive electrode plate.

  A powder obtained by mixing polyvinylidene fluoride (PVDF) with hard carbon (negative electrode active material) is dispersed in N-methyl-2-pyrrolidone (NMP) to form a slurry, and the slurry is used as both copper foil (negative electrode side current collector). After uniformly applying to the main surface and drying, compression and cutting were performed to prepare a negative electrode plate.

  The positive electrode plate and the negative electrode plate thus prepared were alternately laminated with a separator interposed therebetween to form an electrode laminate. The number of stacked electrode plates was set so as to ensure a predetermined battery capacity.

  Each positive current collector extending from the electrode laminate was welded to an aluminum positive terminal, and each negative current collector extending from the laminate was welded to a nickel negative terminal.

  Next, the electrode stack connected to the electrode terminals is accommodated between the two battery casings, and a part of the electrode terminals are led out from the outer peripheral edge while the two short sides and one long side of the battery casing are taken out. The total three sides of the battery were heat-sealed, a predetermined amount of electrolyte was injected from the opening, and the remaining one side was heat-sealed in a state where the space formed by the battery exterior was decompressed. A sample was created.

  For the battery exterior, a resin-metal thin film laminate in which the inner layer of aluminum foil was laminated with polyethylene and the outer layer was laminated with nylon was used.

As the electrolytic solution, a solution obtained by dissolving lithium hexafluorophosphate (LiPF ₆ ) as a supporting electrolyte in a mixed solvent of propylene carbonate (PC), ethylene carbonate (EC), and diethyl carbonate (DMC) was used.

The secondary battery of Example 1 manufactured in this way was initially charged at a voltage of 3.9 [V], the gas generated at that time was discharged, and then left for about two weeks to perform an aging treatment. It was. Table 1 shows the voltage values of the initial charging in Example 1.

  The battery life of the battery sample of Example 1 was evaluated by the following charge / discharge cycle test. In this charge / discharge cycle test, one cycle is a charge / discharge cycle composed of four steps of charge → charge stop → discharge → discharge stop under an environment of 45 ° C., and the discharge capacity [Ah] (= Discharge current [A] × discharge time [h]) was measured, and discharge capacity retention ratio [%] (= discharge capacity at each cycle / discharge capacity at the first cycle) was calculated. And it was evaluated that the battery life was longer as the discharge capacity maintenance rate after 1000 cycles was higher, and the battery life was shorter as the discharge capacity maintenance rate was lower.

  In the charging step of the charging / discharging cycle, charging was performed at a current value of 1CA (current value that discharges the entire capacity in 60 minutes), and the charging was terminated when the voltage value reached 4.2 [V]. In the discharging step of the charge / discharge cycle, discharging was performed at a current value of 1 CA, and discharging was terminated when the voltage value reached 2.5 [V]. Further, each pause step of the charge / discharge cycle was provided with a pause time of 10 minutes. The test results of the charge / discharge cycle test of Example 1 are shown in FIG.

Example 2
For the secondary battery of Example 2, a battery sample was produced under the same conditions as in Example 1 except that the initial charging was performed at a voltage of 3.95 [V] during the aging treatment. Table 1 shows the voltage values of the initial charging in Example 2. The battery life of the battery sample of Example 2 was evaluated by a charge / discharge cycle test under the same conditions as in Example 1. The test results of the charge / discharge cycle test of Example 2 are shown in FIG.

Example 3
For the secondary battery of Example 3, a battery sample was produced under the same conditions as in Example 1 except that the initial charging was performed at a voltage of 4.0 [V] during the aging treatment. Table 1 shows the voltage values of the initial charge in Example 3. The battery life of the battery sample of Example 3 was evaluated by a charge / discharge cycle test under the same conditions as in Example 1. The test results of the charge / discharge cycle test of Example 3 are shown in FIG.

Comparative Example 1
For the secondary battery of Comparative Example 1, a battery sample was produced under the same conditions as in Example 1 except that the initial charging was performed at a voltage of 3.85 [V] during the aging treatment. Table 1 shows the voltage values of the initial charge in Comparative Example 1. The battery life of the battery sample of Comparative Example 1 was evaluated by a charge / discharge cycle test under the same conditions as in Example 1. The test results of the charge / discharge cycle test of Comparative Example 1 are shown in FIG.

Comparative Example 2
For the secondary battery of Comparative Example 2, a battery sample was produced under the same conditions as in Example 1 except that the initial charging was performed at a voltage of 4.05 [V] during the aging treatment. Table 1 shows the voltage values of the initial charge in Comparative Example 2. The battery life of the battery sample of Comparative Example 2 was evaluated by a charge / discharge cycle test under the same conditions as in Example 1. The test results of the charge / discharge cycle test of Comparative Example 2 are shown in FIG.

Consideration From the results of the charge / discharge cycle test, it can be seen that the battery samples of Examples 1 to 3 that were initially charged at a voltage of 3.9 [V] to 4.0 [V] during the aging treatment have a long life. In particular, it can be seen that, among these, the battery sample of Example 3 that was initially charged at a voltage of 4.0 [V] has the longest life.

  In contrast, the battery sample of Comparative Example 1 that was initially charged at 3.85 [V] and the battery sample of Comparative Example 2 that was initially charged at 4.05 [V] had a short battery life. I understand. This is considered to be because when initial charge is performed at a voltage lower than 3.9 [V], initial deterioration is not sufficiently performed in the aging process, and deterioration proceeds during the charge / discharge cycle, and charge / discharge characteristics deteriorate. It is done. In addition, it is considered that when the initial charge is performed at a voltage higher than 4.0 [V], the battery deteriorates during the aging process, and the initial capacity decreases.

FIG. 1A is a plan view showing an entire thin secondary battery according to an embodiment of the present invention, and FIG. 1B is a cross-sectional view taken along line BB in FIG. . FIG. 2 is a cross-sectional view showing in detail the inside of the thin battery according to the embodiment of the present invention. FIG. 3 is a graph showing the relationship between the electrode potential with respect to lithium and the DOD of the secondary battery in the embodiment of the present invention. FIG. 4 is a graph showing the relationship between the open circuit voltage of the secondary battery and the DOD of the secondary battery in the embodiment of the present invention. FIG. 5 is a graph showing the relationship between the discharge capacity of the secondary battery and the number of charge / discharge cycles in the example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Thin battery 101 ... Positive electrode plate 102 ... Separator 103 ... Negative electrode plate 104a ... Positive electrode side collector 104b ... Positive electrode layer 104c ... Positive electrode lead 105a ... Negative electrode side collector 105b ... Negative electrode layer 105c ... Negative electrode lead 106 ... Upper battery exterior 107 ... lower battery exterior

Claims (2)

An electrode plate using LiMn ₂ O ₄ as a positive electrode active material and a carbon-based material as a negative electrode active material is laminated through a separator, and the laminated electrode plate and separator are accommodated in a battery exterior and sealed, An aging treatment method for a secondary battery in which an electrode terminal connected to the electrode plate is subjected to an aging treatment after the production of the secondary battery derived from the battery exterior,
The electrode potential with respect to lithium is equal to or higher than the electrode potential at 60% SOC (State Of Charge) and equal to or lower than the electrode potential at 90% SOC, and the voltage of the secondary battery is 3.9 [V] to 4.0. Charge to be [V],
After the charging, exhaust the gas generated inside the secondary battery,
A secondary battery aging treatment method of performing aging treatment by leaving the gas discharged for 1 week to 1 month.   The secondary battery aging treatment method according to claim 1, wherein the aging treatment is performed by charging the secondary battery so that a voltage thereof is substantially 4.0 [V].

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