JP2017045621A - Capacity recovery method for lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a capacity recovery method for a lithium ion secondary battery which allows a battery capacity to be appropriately recovered.SOLUTION: A capacity recovery method provided by the present invention includes steps of: charging a lithium ion secondary battery at a current value of 5 C or more until SOC becomes 70% or higher, if a specific charging process which supplies a pulsed current of 20 C or more to the battery for 5 seconds or longer is performed for a predetermined number of times, within 10 minutes after the last specific charging process has been completed; and leaving the charged battery as it is in a dormant state for 10 hours or longer.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a capacity recovery method for a lithium ion secondary battery.

  In recent years, lithium ion secondary batteries, nickel metal hydride batteries, and other secondary batteries have become increasingly important as power sources for mounting on vehicles or as power sources for personal computers and portable terminals. In particular, a lithium ion secondary battery that is lightweight and obtains a high energy density is preferably used as a high-output power source mounted on a vehicle. In one typical configuration of this type of lithium ion secondary battery, charging and discharging are performed by lithium ions traveling between the positive electrode and the negative electrode. Patent document 1 is mentioned as a prior art regarding a lithium ion secondary battery.

JP 2011-151943 A

  By the way, some uses of a lithium ion secondary battery are assumed to be used in a mode in which charging / discharging (rapid charging / discharging) at a high rate is repeated. Lithium ion secondary battery used as a vehicle power source (for example, a lithium ion secondary battery mounted on a hybrid vehicle using a lithium ion battery and another power source having different operating principles such as an internal combustion engine as a power source) Battery) is a typical example of a lithium ion secondary battery in which such a use mode is assumed. However, according to the knowledge of the present inventor, in a lithium ion secondary battery that is repeatedly charged and discharged at a high rate, the lithium salt concentration of the non-aqueous electrolyte that has permeated the positive electrode and the negative electrode can be uneven (uneven) depending on the location. Thus, if there is a bias in the distribution of the non-aqueous electrolyte (lithium salt concentration), the battery capacity of the lithium ion secondary battery may decrease.

The capacity recovery method proposed here is a method for recovering the capacity of a lithium ion secondary battery including a positive electrode, a negative electrode, and a non-aqueous electrolyte. This capacity recovery method has the following process:
(1) A specific charging process for supplying a pulsed current of 20 C or more to the lithium ion secondary battery for 5 seconds or more is performed a predetermined number of times;
(2) A specific discharge process for extracting a pulsed current of 20 C or more from the lithium ion secondary battery for 5 seconds or more is performed a predetermined number of times;
If any one of the above is performed, the battery is charged at a current value of 5C or more until SOC reaches 70% or more within 10 minutes after the end of the last specific charge process or specific discharge process, and ,
It includes leaving the battery after charging for 10 hours or more in a resting state. According to this configuration, it is possible to properly recover the reduced battery capacity due to the uneven distribution of the non-aqueous electrolyte (typically, the lithium salt concentration), and to extend the life and reuse of the lithium ion secondary battery ( Recycling) can be realized.

It is a figure which shows typically the lithium ion secondary battery used for one Embodiment. It is a figure which shows typically the wound electrode body used for one Embodiment. It is a figure which shows the processing flow of the capacity | capacitance recovery method which concerns on one Embodiment. It is a figure which shows the processing flow of the capacity | capacitance recovery method which concerns on one Embodiment.

  Hereinafter, preferred embodiments of the present invention will be described. Note that matters other than matters specifically mentioned in the present specification and necessary for the implementation of the present invention can be grasped as design matters of those skilled in the art based on the prior art in this field. The present invention can be carried out based on the contents disclosed in this specification and common technical knowledge in the field. In the present specification, the “lithium ion secondary battery” refers to a secondary battery that uses lithium ions as electrolyte ions and is charged and discharged by movement of lithium ions between the positive and negative electrodes. “SOC” means a state of charge, and a charge state (that is, a full charge state) in which an upper limit voltage is obtained in an operating voltage range that can be reversibly charged and discharged is 100. %, And the state of charge when the lower limit voltage is obtained (that is, the state of being not charged) is 0%.

<First Embodiment>
Hereinafter, the capacity recovery method for a lithium ion secondary battery according to an embodiment of the present invention will be described in the order of the configuration of the target lithium ion secondary battery and the capacity recovery method.

<Lithium ion secondary battery>
A lithium ion secondary battery 100 (hereinafter, referred to as “battery” as appropriate) targeted by the capacity recovery method of the present embodiment is, for example, as shown in FIG. An electrode body (rolled electrode body) 80 in which the negative electrode sheet 20 is wound flatly through a long separator 40 can accommodate the wound electrode body 80 together with a non-aqueous electrolyte (not shown). It has a configuration accommodated in a case (flat box type) case 50.

  The case 50 includes a flat rectangular parallelepiped case main body 52 having an open upper end, and a lid 54 that closes the opening. As a material constituting the case 50, a metal material such as aluminum or steel is preferably used (in this embodiment, aluminum). On the upper surface of the case 50 (that is, the lid body 54), a positive electrode terminal 70 that is electrically connected to the positive electrode of the wound electrode body 80 and a negative electrode terminal 72 that is electrically connected to the negative electrode 20 of the electrode body 80 are provided. Yes. In the case 50, a flat wound electrode body 80 is accommodated together with a non-aqueous electrolyte (not shown).

  The wound electrode body 80 according to the present embodiment is the same as the wound electrode body of a normal lithium secondary battery, and as shown in FIG. ) Sheet structure.

The positive electrode sheet 10 has a structure in which a positive electrode active material layer 14 containing a positive electrode active material is held on both surfaces of a foil-like positive electrode current collector 12 in the form of a long sheet. However, the positive electrode active material layer 14 is not attached to one side edge (the left side edge portion in the drawing) along the edge in the width direction of the positive electrode sheet 10, and the positive electrode current collector 12 is exposed with a certain width. The positive electrode active material layer non-formed part 16 is formed. For the positive electrode current collector 12, an aluminum foil or other metal foil suitable for the positive electrode is preferably used. As the positive electrode active material, one kind or two or more kinds of substances that can be used as the positive electrode active material of the lithium ion secondary battery can be used. For example, an oxide (lithium transition metal oxide) containing lithium and a transition metal element as constituent metal elements such as LiNi _1/3 Mn _1/3 Co _1/3 O ₂ can be given.

  Similarly to the positive electrode sheet 10, the negative electrode sheet 20 has a structure in which a negative electrode active material layer 24 containing a negative electrode active material is held on both surfaces of a long sheet-like foil-shaped negative electrode current collector 22. However, the negative electrode active material layer 24 is not attached to one side edge (the right side edge portion in the drawing) along the widthwise edge of the negative electrode sheet 20, and the negative electrode current collector 22 is exposed with a certain width. The negative electrode active material layer non-forming part 26 is formed. For the negative electrode current collector 22, a copper foil or other metal foil suitable for the negative electrode is preferably used. As the negative electrode active material, one or two or more materials conventionally used in lithium ion secondary batteries can be used without any particular limitation. Preferable examples include carbon materials such as graphite carbon and amorphous carbon.

  As the separator 40 disposed between the positive and negative electrode sheets 10 and 20, various porous sheets similar to those of a general lithium secondary battery provided with a wound electrode body can be used. Preferable examples include porous resin sheets (films, nonwoven fabrics, etc.) made of polyolefin resins such as polyethylene (PE) and polypropylene (PP).

  In producing the wound electrode body 80, the positive electrode sheet 10 and the negative electrode sheet 20 are laminated via the separator 40. At this time, the positive electrode sheet 10 and the negative electrode sheet 20 are placed so that the positive electrode active material layer non-formation part of the positive electrode sheet 10 and the negative electrode active material layer non-formation part of the negative electrode sheet 20 protrude from both sides of the separator 40 in the width direction. Laminate slightly shifted in the width direction. The laminated body thus stacked is wound, and then the obtained wound body is crushed from the side surface direction and ablated, whereby a flat wound electrode body 80 can be produced.

  A wound core portion 82 (that is, the positive electrode active material layer 14 of the positive electrode sheet 10, the negative electrode active material layer 24 of the negative electrode sheet 20, and the separator 40) is densely laminated at the center portion in the winding axis direction of the wound electrode body 80. Part) is formed. Further, the electrode active material layer non-formed portions 16 and 26 of the positive electrode sheet 10 and the negative electrode sheet 20 protrude outward from the wound core portion 82 at both ends of the wound electrode body 80 in the winding axis direction. . A positive electrode lead terminal 74 and a negative electrode lead terminal 76 are provided on the protruding portion 16 (that is, the non-formed portion of the positive electrode active material layer 14) 16 and the protruding portion 26 (that is, the non-formed portion of the negative electrode active material layer 24) 26, respectively. Attached and electrically connected to the positive terminal 70 and the negative terminal 72 described above.

Then, the wound electrode body 80 is accommodated in the main body 52 from the upper end opening of the case main body 52, and an appropriate nonaqueous electrolytic solution is disposed (injected) in the case main body 52. Such a non-aqueous electrolyte typically has a composition in which a supporting salt is contained in a suitable non-aqueous solvent. As said non-aqueous solvent, ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), propylene carbonate (PC) etc. can be used, for example. Further, as the supporting salt, for _{example, LiPF 6, LiBF 4, LiAsF} 6, LiCF 3 can be preferably used a lithium salt of SO ₃ and the like.

  Thereafter, the opening is sealed by welding with the lid 54 or the like, and the assembly of the lithium ion secondary battery 100 according to the present embodiment is completed. The sealing process of the case 50 and the arrangement (injection) process of the nonaqueous electrolytic solution may be the same as the method used in the manufacture of the conventional lithium ion secondary battery, and do not characterize the present invention. In this way, the construction of the lithium ion secondary battery 100 according to this embodiment is completed.

  Here, according to the knowledge of the present inventor, in the lithium ion secondary battery provided with the wound electrode body 80, a high rate and a short time (pulsed) as expected in a lithium ion secondary battery for a vehicle power source. When the discharge or charging of the shape is repeated, the concentration (unevenness) in the lithium salt concentration of the non-aqueous electrolyte that has permeated the wound electrode body may vary. For example, when used in a high-rate pulse discharge at 20 C for 5 seconds, a part of the nonaqueous electrolyte or lithium salt moves from the axial center to both ends of the wound electrode body, or from both ends to the electrode body. By moving to the outside, an event may occur in which the lithium salt concentration in the central portion in the axial direction of the wound electrode body becomes lower than both end portions (the lithium salt concentration decreases compared to the initial state). In addition, when used at 20C for a high-rate pulse charge for 5 seconds, a part of the non-aqueous electrolyte or lithium salt moves from the outside of the wound electrode body to both ends in the winding axis direction, or from both ends to the center. By moving to the portion, an event may occur in which the lithium salt concentration in the central portion in the axial direction of the wound electrode body is higher than both ends (the lithium salt concentration is increased compared to the initial state). Thus, if there is a bias in the distribution of the non-aqueous electrolyte (lithium salt concentration), the positive electrode potential and the negative electrode potential tend to decrease in the portion where the lithium salt concentration is relatively high (and the potential difference between the positive and negative electrodes becomes uneven). All) capacity cannot be used up, and battery capacity (capacity that can be charged and discharged) may be reduced. Therefore, the capacity recovery method according to the present embodiment capable of recovering the reduced battery capacity can be particularly suitably applied to the lithium ion secondary battery having the above configuration.

<Capacity recovery method>
The capacity recovery method of a lithium ion secondary battery disclosed here is a capacity recovery method of a lithium ion secondary battery including a positive electrode, a negative electrode, and a non-aqueous electrolyte. FIG. 3 is a diagram showing a processing flow of the capacity recovery method according to the present embodiment. In the capacity recovery method, as shown in FIG. 3, when a specific charging process for supplying a pulsed current of 20 C or more to a lithium ion secondary battery for 5 seconds or more is performed a predetermined number of times (“YES” in step S10). In the case of “”, the battery is charged within 10 minutes after the end of the last specific charging process until the SOC reaches 70% or more at a current value of 5 C or more (step S20). Further, the method includes leaving the charged battery in a resting state for 10 hours or longer (step S30).

  The capacity recovery method is executed when a specific charging process for supplying a pulsed current of 20 C or more to the lithium ion secondary battery for 5 seconds or more is performed a predetermined number of times (step S10). Preferably, the capacity recovery process is performed when the specific charge process is performed 100 to 500 times (preferably 200 to 400 times, for example, 300 times) for the lithium ion secondary battery. Thus, the lithium salt concentration of the non-aqueous electrolyte that has permeated the wound electrode body is obtained by performing a specific charging process for supplying a pulsed current of 20 C or more for 5 seconds or more to the lithium ion secondary battery for a predetermined number of times. In some cases, unevenness (unevenness) may occur depending on the location. As a result, the positive electrode potential and the negative electrode potential tend to decrease in a portion where the lithium salt concentration is relatively high, and distribution may occur in the positive electrode potential and the negative electrode potential (as a result, the potential difference between the positive and negative electrodes becomes uneven). The distribution of the positive electrode potential and the negative electrode potential can be a factor that decreases the battery capacity.

  In the capacity recovery method of the lithium ion secondary battery disclosed herein, when the distribution of the lithium salt concentration is biased by the predetermined number of times of the specific charging process, the last specific charging process is completed within 10 minutes. In addition, the battery is charged until the SOC reaches 70% or more (for example, 70% to 90%, preferably 70% to 80%) at a current value of 5C or more (for example, 5C to 10C, preferably 5C to 8C) (step S20). ). Thus, by charging until the SOC reaches 70% or more at a high current value of 5C or more, a large amount of charging current flows in a portion where the lithium salt concentration is relatively high (that is, the battery reaction concentrates). As the positive electrode potential increases locally, the negative electrode potential of the portion decreases locally. By locally increasing the positive electrode potential of the portion, the non-uniform positive electrode potential caused by the distribution can be returned to flat (constant).

  According to the knowledge of the present inventor, when left for a long time (more than 10 minutes) after the end of the last specific charging process, the distribution of the lithium salt concentration is maintained while maintaining the distribution of the positive electrode potential and the negative electrode potential. Will be eliminated. For this reason, it was confirmed by test examples described later that the above-described effect of returning the positive electrode potential to a flat state could not be sufficiently obtained even if the above-described charging was performed after a long time had elapsed since the last specific charging process was completed. That is, it can be said that it is important to perform the charging within 10 minutes after the last specific charging process is completed.

  Further, in the capacity recovery method of the lithium ion secondary battery disclosed herein, in step S30, the battery after charging is in a resting state for 10 hours or longer (for example, 10 hours to 20 hours, preferably 10 hours to 15 hours). put. Thus, by leaving the battery after charging for 10 hours or more in a resting state, the negative electrode potential is relaxed so that the potential difference between the positive and negative electrodes becomes constant. That is, the distribution of the negative electrode potential is relaxed so as to approach the flat shape of the positive electrode potential, and the potential difference between the positive and negative electrodes becomes uniform.

  As a result, the reduced battery capacity (capacity that can be charged and discharged) due to the uneven distribution of lithium salt concentration in the non-aqueous electrolyte can be properly recovered, and the life and reuse of lithium ion secondary batteries ( Recycling) can be realized.

  In a preferred embodiment, after leaving in step S30, the battery is discharged at a current value of 0.5 C or less (for example, 0.1 C to 0.5 C, preferably 0.3 C to 0.5 C) until SOC reaches 0% ( Step S40). Then, the discharged battery is left in a resting state for 24 hours or longer (for example, 24 hours to 50 hours, preferably 24 hours to 30 hours) (step S50). Even after step S30 is left, the charge amount (lithium ion occlusion amount) in the negative electrode is uneven (uneven) depending on the location, so that a slight gradient may remain in the negative electrode potential. On the other hand, the battery after being left is completely discharged until the SOC becomes 0% at a low current value of 0.5 C or less (that is, lithium ions are completely released from the negative electrode), and further left in a rest state for 24 hours or more. Thus, it is possible to equalize the amount of charge in the negative electrode (and hence the gradient of the negative electrode potential). As a result, the negative electrode potential can be returned to flat (constant) more effectively. As a result, further capacity recovery can be realized.

Second Embodiment
FIG. 4 is a diagram illustrating a processing flow of the capacity recovery method according to the second embodiment. This embodiment is different from the above-described first embodiment in that the capacity recovery process is performed when the specific discharge process is performed a predetermined number of times. That is, in this capacity recovery method, as shown in FIG. 4, when a specific discharge process for extracting a pulsed current of 20 C or more from a lithium ion secondary battery for 5 seconds or more is performed a predetermined number of times (“YES” in step S110). In the case of (5), the battery is charged until the SOC reaches 70% or more at a current value of 5C or more within 10 minutes after the end of the last specific discharge process (step S120). Further, the method includes leaving the charged battery in a resting state for 10 hours or longer (step S130). Since details of each processing of Steps S120 and S130 are the same as Steps S20 and S30 of the above-mentioned first embodiment, the duplicated explanation is omitted.

  Preferably, the capacity recovery process is performed when the specific discharge process is performed 100 to 500 times on the lithium ion secondary battery. Thus, the lithium salt concentration of the non-aqueous electrolyte that has permeated into the wound electrode body is obtained by performing a specific discharge process for extracting a pulsed current of 20 C or more from the lithium ion secondary battery for 5 seconds or more in Step S110 a predetermined number of times. In some cases, unevenness (unevenness) may occur depending on the location. As a result, the positive electrode potential and the negative electrode potential tend to decrease in a portion where the lithium salt concentration is relatively high, and distribution may occur in the positive electrode potential and the negative electrode potential (as a result, the potential difference between the positive and negative electrodes becomes uneven). The distribution of the positive electrode potential and the negative electrode potential can be a factor that decreases the battery capacity.

  On the other hand, according to the present embodiment, in step S120, by charging the battery at a current value of 5C or more until SOC 70% or more within 10 minutes after the end of the last specific discharge process, The positive electrode potential that has become uneven due to the distribution can be returned to a flat (constant) state. In step S130, by leaving the charged battery in a resting state for 10 hours or more, the distribution of the negative electrode potential is relaxed, and the potential difference between the positive and negative electrodes can be made uniform. Thereby, the battery capacity reduced due to the uneven distribution of the lithium salt concentration can be properly recovered, and the life and reuse (recycling) of the lithium ion secondary battery can be realized.

  If necessary, after leaving step S130, the battery may be discharged at a current value of 0.5 C or less (for example, 0.1 C to 0.5 C) until SOC becomes 0% (step S140). Then, the discharged battery may be left in a resting state for 24 hours or longer (for example, 24 hours to 50 hours) (step S150). In this way, the negative electrode potential can be returned to flat (constant) more effectively, and further capacity recovery can be realized.

  In order to confirm the application effect of the present invention, the following tests were conducted.

<Cycle test>
Lithium ions having a configuration in which positive and negative electrode sheets each holding a positive electrode active material and a negative electrode active material are wound on a sheet-like positive electrode current collector and a negative electrode current collector through a separator sheet and housed in a case together with an electrolyte A secondary battery was constructed. After adjusting the lithium ion secondary battery to SOC 50%, a cycle test was performed in which a pulse current of 5 seconds was continuously input at 20 C in a temperature environment of 25 ° C. Then, the capacity deterioration rate = (1−B / A) × 100 was calculated from the battery capacity (initial capacity) A before the cycle test and the battery capacity B after the cycle test. As a result, the capacity deterioration rate was 12%.

Example 1
In this example, the battery after the cycle test was charged to SOC 70% at a current value of 5 C within 10 minutes after the cycle test was performed. Then, it was left to stand for 10 hours. Then, the capacity deterioration rate was calculated by measuring the battery capacity after being left standing. As a result, the capacity deterioration rate was 8%, and the capacity deterioration rate was improved by about 4% compared to immediately after the cycle test.

(Example 2)
In this example, the battery after the cycle test was charged to SOC 70% at a current value of 5 C within 10 minutes after the cycle test was performed. Then, it was left to stand for 10 hours. Next, the battery was discharged at a current value of 0.5 C until the SOC reached 0%. Then, it was left for 24 hours in a resting state. Then, the capacity deterioration rate was calculated by measuring the battery capacity after being left standing. As a result, the capacity deterioration rate was 2%, and the capacity deterioration rate was improved by about 10% compared to immediately after the cycle test.

(Comparative Example 1)
In this example, after the cycle test was performed, the battery after the cycle test was allowed to stand at room temperature for 10 hours. Then, the capacity deterioration rate was calculated by measuring the battery capacity after being left standing. As a result, the capacity deterioration rate was 11%, and almost no improvement in the capacity deterioration rate was observed compared to immediately after the cycle test.

(Comparative Example 2)
In this example, after the cycle test was performed, the battery after the cycle test was allowed to stand at room temperature for 10 hours. Thereafter, the battery was charged to a SOC of 70% at a current value of 5C. Then, it was left to stand for 10 hours. Next, the battery was discharged at a current value of 0.5 C until the SOC reached 0%. Then, it was left for 24 hours in a resting state. Then, the capacity deterioration rate was calculated by measuring the battery capacity after being left standing. As a result, the capacity deterioration rate was 11%, and almost no improvement in the capacity deterioration rate was observed compared to immediately after the cycle test.

Although the present invention has been described in detail above, these are merely examples, and the invention disclosed herein includes various modifications and changes of the above-described specific examples.
For example, the first embodiment and the second embodiment described above may be combined. That is, the above-described capacity recovery process may be performed when at least one of a predetermined number of specific charge processes and a predetermined number of specific discharge processes is performed. In this way, the reduced battery capacity can be recovered more efficiently.

DESCRIPTION OF SYMBOLS 10 Positive electrode sheet 20 Negative electrode sheet 80 Winding electrode body 100 Lithium ion secondary battery

Claims (1)

A capacity recovery method for a lithium ion secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte,
The following processing:
(1) A specific charging process for supplying a pulsed current of 20 C or more to the lithium ion secondary battery for 5 seconds or more is performed a predetermined number of times;
(2) A specific discharge process for extracting a pulsed current of 20 C or more from the lithium ion secondary battery for 5 seconds or more is performed a predetermined number of times;
If any one of the above is performed, the battery is charged at a current value of 5C or more until SOC reaches 70% or more within 10 minutes after the end of the last specific charge process or specific discharge process, and ,
A method for recovering the capacity of a lithium ion secondary battery, comprising leaving the battery after charging for 10 hours or more in a resting state.

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