JP2017195059A - Method of recovering output of electricity storage element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of recovering the output of an electricity storage element, capable of sufficiently recovering a temporary decrease in output caused due to repeated charge/discharge at a high rate.SOLUTION: A method of recovering the output of an electricity storage element includes a step of obtaining the relationship between the state of charge SOC of an electricity storage element that includes a negative electrode containing particulate amorphous carbon as an active material and the open circuit potential OCP of the negative electrode at each state of charge SOC and changing the state of charge of an electricity storage element so as to go through a state of charge in the case when the absolute value of a rate of change of an open circuit potential OCP to a charge of state SOC is at least 10[mV/SOC(%)].SELECTED DRAWING: None

Description

  The present invention relates to a method for recovering the output of a storage element.

  Conventionally, an electrode body composed of a negative electrode, a positive electrode, and a separator, and a storage element in which a non-aqueous electrolyte containing a lithium salt is housed in an exterior body are known. As this type of power storage element, an element including a negative electrode material formed of a porous carbon material capable of occluding and releasing lithium ions as a negative electrode active material is known (for example, Patent Document 1).

  In the battery described in Patent Document 1, the amount of mesopores derived from pores having a diameter of 20 mm or more and 500 mm or less calculated by the BJH method in the porous carbon material is Vm1 (cc / g), and the diameter calculated by the MP method is less than 20 mm. When the amount of micropores derived from the pores is Vm2 (cc / g), 21 ≦ Vm1 / Vm2 ≦ 100 and 0.20 <Vm1 ≦ 0.65, and further, The primary particle diameter is 1 to 20 μm.

  However, in the battery described in Patent Document 1, when charging and discharging are repeated at a high rate, the output may be temporarily reduced. Therefore, there is a demand for a method for sufficiently recovering the primary decrease in output caused by repeated charging and discharging at a high rate.

JP2013-080780A

  This embodiment makes it a subject to provide the recovery method of the output of an electrical storage element which can fully recover the primary fall of the output which generate | occur | produced by repeating charging / discharging at a high rate.

  The method for recovering the output of the electricity storage device according to the present embodiment includes a charge amount SOC of an electricity storage device having a negative electrode containing particulate amorphous carbon as an active material, and an open circuit potential OCP of the negative electrode at each charge amount SOC. Obtaining the relationship and changing the charge amount of the storage element so as to pass through the charge amount when the absolute value of the change rate of the open circuit potential OCP with respect to the charge amount SOC is at least 10 [mV / SOC (%)]. .

  In the output recovery method described above, the charge amount of the power storage element passes through the charge amount when the absolute value of the rate of change of the open circuit potential OCP with respect to the charge amount SOC is at least 10 [mV / SOC (%)]. To change. As a result, it is possible to recover a primary decrease in output (hereinafter, also simply referred to as transient deterioration) caused by repeated charging and discharging at a high rate. Specifically, the transient deterioration occurs due to variation in the charging depth in the thickness direction and the surface direction of the active material layer of the negative electrode when charging and discharging are repeated at a high rate. Even if the state where the charging depth varies is left unattended, the difference in the charging depth becomes the driving force, and the variation in the charging depth can be gradually recovered. On the other hand, the potential difference with respect to the difference in the charge amount is obtained by changing the charge amount of the electric storage element so as to pass through the charge amount when the absolute value of the change rate is at least 10 [mV / SOC (%)]. Is relatively large. As the potential difference with respect to the difference before and after the change in the charge amount of the power storage element increases, the driving force for equalizing the dispersed potential difference increases. That is, the driving force for making the variation in the charging depth uniform within the active material layer of the negative electrode becomes large. Therefore, the temporary deterioration can be sufficiently recovered.

  In the output recovery method described above, the charge amount of the power storage element may be changed while applying a load to the negative electrode. Thereby, since it can suppress that the particulate active materials of a negative electrode leave | separate, the driving force which equalizes the above potential differences can be caused more reliably. Thereby, transient deterioration can be more fully recovered.

  In the output recovery method described above, the charge amount of the storage element is set so as to pass through the charge amount when the absolute value of the change rate of the open circuit potential OCP with respect to the charge amount SOC is at least 10 [mV / SOC (%)] for one hour or more. The amount of charge may be changed. By changing the amount of charge as described above for at least one hour or more, transient deterioration can be more fully recovered.

  According to the present embodiment, it is possible to provide a method for recovering the output of a storage element that can sufficiently recover a primary decrease in output caused by repeated charge and discharge at a high rate.

FIG. 1 is a perspective view of a power storage element used in the output recovery method of this embodiment. FIG. 2 is a front view of the power storage element used in the output recovery method of the embodiment. 3 is a cross-sectional view taken along line III-III in FIG. 4 is a cross-sectional view taken along the line IV-IV in FIG. FIG. 5 is a perspective view of a state in which a part of the energy storage device used in the output recovery method of the embodiment is assembled, in which the liquid injection stopper, the electrode body, the current collector, and the external terminal are assembled to the lid plate. It is a perspective view of a state. FIG. 6 is a diagram for explaining the configuration of the electrode body of the storage element used in the output recovery method of the embodiment. FIG. 7 is a cross-sectional view of the superimposed positive electrode, negative electrode, and separator (cross section VII-VII in FIG. 6). FIG. 8 is an example of the SOC-OCP curve of the negative electrode. FIG. 9 is a flowchart showing the steps of the method for recovering the output of the storage element.

  Hereinafter, an embodiment of a method for recovering the output of a power storage device according to the present invention will be described. A power storage element used in such an output recovery method is shown in FIGS. Examples of power storage elements include secondary batteries and capacitors. Hereinafter, a chargeable / dischargeable secondary battery will be described as an example of a storage element. In addition, the name of each component (each component) of the secondary battery in this embodiment is in this embodiment, and may differ from the name of each component (each component) in the background art.

  In this embodiment, the electrical storage element 1 is a nonaqueous electrolyte secondary battery. More specifically, the electricity storage element 1 is a lithium ion secondary battery that utilizes electron movement that occurs in association with movement of lithium ions. This type of power storage element 1 supplies electric energy. The electric storage element 1 is used singly or in plural. Specifically, the storage element 1 is used as a single unit when the required output and the required voltage are small. On the other hand, when at least one of the required output and the required voltage is large, the power storage element 1 is combined with another power storage element 1 and used in the power storage device. In the power storage device, the power storage element 1 used in the power storage device supplies electric energy.

  As shown in FIGS. 1 to 7, the storage element 1 includes an electrode body 2 including a positive electrode 11 and a negative electrode 12, a case 3 that houses the electrode body 2, and an external terminal 7 that is disposed outside the case 3. And an external terminal 7 that is electrically connected to the electrode body 2. In addition to the electrode body 2, the case 3, and the external terminal 7, the power storage element 1 includes a current collector 5 that electrically connects the electrode body 2 and the external terminal 7.

  The electrode body 2 is formed by winding a laminated body 22 in which the positive electrode 11 and the negative electrode 12 are laminated with the separator 4 being insulated from each other.

  The positive electrode 11 includes a metal foil 111 (positive electrode base material) and an active material layer 112 that is superimposed on the surface of the metal foil 111 and contains an active material. The active material layer 112 overlaps on both sides of the metal foil 111. The thickness of the positive electrode 11 is usually 40 μm or more and 150 μm or less.

  The metal foil 111 has a strip shape. The metal foil 111 of the positive electrode 11 is, for example, an aluminum foil. The positive electrode 11 has an uncovered portion (a portion where the positive electrode active material layer is not formed) 115 of the positive electrode active material layer 112 at one edge portion in the width direction, which is the short direction of the band shape.

  The positive electrode active material layer 112 includes 85% by mass to 99% by mass of the active material, 4.5% by mass to 9% by mass of the conductive additive, and 3% by mass to 4.5% by mass of the binder. Note that the thickness of the positive electrode active material layer 112 is usually 10 μm or more and 50 μm or less.

  The active material of the positive electrode 11 is a compound that can occlude and release lithium ions. The average particle diameter D50 of the active material of the positive electrode 11 is usually 3 μm or more and 8 μm or less.

In the present embodiment, the active material of the positive electrode 11 is, for example, a lithium metal oxide. Specifically, the active material of the positive electrode, for _example, Li p _MeO t (Me represents one or more transition metal) complex oxide represented by _{(Li p Co s O 2,} Li p Ni q O _{2, Li p Mn r O 4} , Li p Ni q Co s Mn r O 2 , etc.), _{or, Li t Me u (XO v} ) w (Me represents one or more transition metals, X is e.g. P, Si, B, a polyanion compounds represented by the representative of the _{V) (Li t Fe u PO} 4, Li t Mn u PO 4, Li t Mn u SiO 4, Li t Co u PO 4 F , etc.).

Active material of the positive electrode 11 _is a lithium-metal composite oxide represented by the chemical composition of _{Li p Ni q Mn r Co s} O t ( provided that at 0 <p ≦ 1.3 are q + r + s = 1, 0 <q <1, 0 <r <1, 0 <s <1, and 1.7 ≦ t ≦ 2.3).

Additional such _{Li p Ni q Mn r Co s} O lithium-metal composite oxide represented by the chemical composition of the _t, for _{example, LiNi 1/3 Co 1/3 Mn 1/3 O} 2, LiNi 1/6 Co 1 _{/ 6} Mn _2/3 O ₂ , LiCoO ₂ and the like.

  Examples of the binder used for the positive electrode active material layer 112 include polyvinylidene fluoride (PVdF), a copolymer of ethylene and vinyl alcohol, polymethyl methacrylate, polyethylene oxide, polypropylene oxide, polyvinyl alcohol, polyacrylic acid, and polymethacrylic acid. Acid, styrene butadiene rubber (SBR). In the present embodiment, the binder is polyvinylidene fluoride.

  The conductive additive of the positive electrode active material layer 112 is a carbonaceous material containing 98% by mass or more of carbon. Examples of the carbonaceous material include ketjen black (registered trademark), acetylene black, and graphite. The positive electrode active material layer 112 has acetylene black as a conductive additive.

  The negative electrode 12 includes a metal foil 121 (negative electrode base material) and a negative electrode active material layer 122 formed on the metal foil 121. The negative electrode active material layers 122 are respectively stacked on both surfaces of the metal foil 121. The metal foil 121 has a strip shape. The negative metal foil 121 is, for example, a copper foil. The negative electrode 12 has an uncoated portion 125 of the negative electrode active material layer 122 (a portion where the negative electrode active material layer is not formed) at one end edge in the width direction, which is the short direction of the belt shape. In addition, the thickness of the negative electrode 12 is usually 40 μm or more and 150 μm or less.

  The negative electrode active material layer 122 includes a particulate active material and a binder. The negative electrode active material layer 122 is disposed so as to face the positive electrode 11 with the separator 4 interposed therebetween. The width of the negative electrode active material layer 122 is larger than the width of the positive electrode active material layer 112. The thickness of the negative electrode active material layer 122 is usually 10 μm or more and 50 μm or less.

  In the negative electrode active material layer 122, the ratio of the binder may be 5% by mass or more and 10% by mass or less with respect to the total mass of the negative electrode active material and the binder.

  The active material of the negative electrode 12 is amorphous carbon, specifically, non-graphitizable carbon (hard carbon). The average particle diameter D50 of the active material of the negative electrode 12 is usually 2 μm or more and 7 μm or less.

The weight per unit area (one layer) of the negative electrode active material layer 122 is usually 2.5 mg / cm ² or more and 5.0 mg / cm ² or less. The measurement of the basis weight is calculated from the mass of the negative electrode 12 and the mass after the negative electrode active material layer 122 is removed from the negative electrode 12.

  The binder used for the negative electrode active material layer 122 is the same as the binder used for the positive electrode active material layer 112. In the present embodiment, the binder is polyvinylidene fluoride.

  The negative electrode active material layer 122 may further include a conductive additive such as ketjen black (registered trademark), acetylene black, or graphite.

  In the electrode body 2, the positive electrode 11 and the negative electrode 12 configured as described above are wound while being insulated by the separator 4. That is, in the electrode body 2, the stacked body 22 of the positive electrode 11, the negative electrode 12, and the separator 4 is wound. The separator 4 is a member having insulating properties. The separator 4 is disposed between the positive electrode 11 and the negative electrode 12. Thereby, in the electrode body 2 (specifically, the laminated body 22), the positive electrode 11 and the negative electrode 12 are insulated from each other. The separator 4 holds the electrolytic solution in the case 3. Thereby, at the time of charging / discharging of the electrical storage element 1, lithium ion moves between the positive electrode 11 and the negative electrode 12 which are laminated | stacked alternately on both sides of the separator 4. FIG.

  The separator 4 has a strip shape. The separator 4 has a sheet-like porous separator base material. In this embodiment, the separator 4 has only a separator base material. The separator 4 is disposed between the positive electrode 11 and the negative electrode 12 in order to prevent a short circuit between the positive electrode 11 and the negative electrode 12.

  The separator substrate is configured to be porous by, for example, a woven fabric, a nonwoven fabric, or a porous film. Examples of the material for the separator substrate include polymer compounds, glass, and ceramics. Examples of the polymer compound include polyesters such as polyacrylonitrile (PAN), polyamide (PA), and polyethylene terephthalate (PET), polyolefins (PO) such as polypropylene (PP) and polyethylene (PE), and cellulose. .

With respect to the sum of the pore volume of the active material layer of the negative electrode 12 per unit area and the pore volume of the separator substrate per unit area, the coating amount of the negative electrode active material layer 121 per unit area (the negative electrode active material layer 121 The weight per unit area) is usually 1.5 g / cm ³ or more and 2.5 g / cm ³ or less.

  The width of the separator 4 (the dimension of the strip shape in the short direction) is slightly larger than the width of the negative electrode active material layer 122. The separator 4 is disposed between the positive electrode 11 and the negative electrode 12 that are stacked in a state of being displaced in the width direction so that the positive electrode active material layer 112 and the negative electrode active material layer 122 overlap. At this time, as shown in FIG. 6, the non-covered portion 115 of the positive electrode 11 and the non-covered portion 125 of the negative electrode 12 do not overlap. That is, the uncovered portion 115 of the positive electrode 11 protrudes in the width direction from the region where the positive electrode 11 and the negative electrode 12 overlap, and the non-covered portion 125 of the negative electrode 12 extends from the region where the positive electrode 11 and the negative electrode 12 overlap in the width direction ( It protrudes in a direction opposite to the protruding direction of the non-covering portion 115 of the positive electrode 11. The electrode body 2 is formed by winding the stacked positive electrode 11, negative electrode 12, and separator 4, that is, the stacked body 22. The portion where only the uncovered portion 115 of the positive electrode 11 or the uncovered portion 125 of the negative electrode 12 is stacked constitutes the uncoated stacked portion 26 in the electrode body 2.

  The uncoated laminated portion 26 is a portion that is electrically connected to the current collector 5 in the electrode body 2. The uncoated laminated portion 26 has two parts (divided uncoated laminated portions divided by sandwiching the hollow portion 27 (see FIG. 6) between the wound positive electrode 11, the negative electrode 12, and the separator 4 in the winding center direction. ) 261.

  The uncoated laminated portion 26 configured as described above is provided on each electrode of the electrode body 2. That is, the non-coated laminated portion 26 in which only the non-coated portion 115 of the positive electrode 11 is laminated constitutes the non-coated laminated portion of the positive electrode 11 in the electrode body 2 and the non-coated laminated layer in which only the non-coated portion 125 of the negative electrode 12 is laminated. The portion 26 constitutes an uncoated laminated portion of the negative electrode 12 in the electrode body 2.

  The case 3 includes a case main body 31 having an opening and a cover plate 32 that closes (closes) the opening of the case main body 31. The case 3 houses the electrolytic solution in the internal space together with the electrode body 2 and the current collector 5. Case 3 is formed of a metal having resistance to the electrolytic solution. The case 3 is made of an aluminum-based metal material such as aluminum or an aluminum alloy, for example. The case 3 may be formed of a metal material such as stainless steel and nickel, or a composite material obtained by bonding a resin such as nylon to aluminum.

The electrolytic solution is a non-aqueous electrolytic solution. The electrolytic solution is obtained by dissolving an electrolyte salt in an organic solvent. Examples of the organic solvent include cyclic carbonates such as propylene carbonate and ethylene carbonate, and chain carbonates such as dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. The electrolyte salt is LiClO ₄ , LiBF ₄ , LiPF ₆ or the like. The electrolytic solution is obtained by dissolving 0.5 to 1.5 mol / L of LiPF ₆ in a mixed solvent in which propylene carbonate, dimethyl carbonate, and ethyl methyl carbonate are mixed at a predetermined ratio.

The case 3 is formed by joining the peripheral edge of the opening of the case main body 31 and the peripheral edge of the rectangular lid plate 32 in an overlapping state. The case 3 has an internal space defined by the case main body 31 and the lid plate 32. In this embodiment, the opening peripheral part of the case main body 31 and the peripheral part of the cover plate 32 are joined by welding.
In the following, as shown in FIG. 1, the long side direction of the cover plate 32 is the X-axis direction, the short side direction of the cover plate 32 is the Y-axis direction, and the normal direction of the cover plate 32 is the Z-axis direction.

  The case body 31 has a rectangular tube shape (that is, a bottomed rectangular tube shape) in which one end in the opening direction (Z-axis direction) is closed. The lid plate 32 is a plate-like member that closes the opening of the case body 31.

  The cover plate 32 has a gas discharge valve 321 that can discharge the gas in the case 3 to the outside. The gas discharge valve 321 discharges gas from the inside of the case 3 to the outside when the internal pressure of the case 3 rises to a predetermined pressure. The gas discharge valve 321 is provided at the center of the lid plate 32 in the X-axis direction.

  The case 3 is provided with a liquid injection hole for injecting an electrolytic solution. The liquid injection hole communicates the inside and the outside of the case 3. The liquid injection hole is provided in the lid plate 32. The liquid injection hole is sealed (closed) by a liquid injection stopper 326. The liquid filling tap 326 is fixed to the case 3 (the cover plate 32 in the example of the present embodiment) by welding.

  The external terminal 7 is a part that is electrically connected to the external terminal 7 of another power storage element 1 or an external device. The external terminal 7 is formed of a conductive member. For example, the external terminal 7 is formed of a highly weldable metal material such as an aluminum-based metal material such as aluminum or aluminum alloy, or a copper-based metal material such as copper or copper alloy.

  The external terminal 7 has a surface 71 to which a bus bar or the like can be welded. The surface 71 is a flat surface. The external terminal 7 has a plate shape extending along the lid plate 32. Specifically, the external terminal 7 has a rectangular plate shape when viewed in the Z-axis direction.

  The current collector 5 is disposed in the case 3 and is directly or indirectly connected to the electrode body 2 so as to be energized. The current collector 5 is connected to the electrode body 2 via the clip member 50 so as to be energized. That is, the electrical storage element 1 includes a clip member 50 that connects the electrode body 2 and the current collector 5 so as to allow energization.

  The current collector 5 is formed of a conductive member. As shown in FIG. 3, the current collector 5 is disposed along the inner surface of the case 3. The current collector 5 is disposed on each of the positive electrode 11 and the negative electrode 12 of the power storage element 1. In the above-described power storage device 1, the case 3 is disposed in the uncoated laminated portion 26 of the positive electrode 11 and the uncoated laminated portion 26 of the negative electrode 12, respectively.

  The current collector 5 of the positive electrode 11 and the current collector 5 of the negative electrode 12 are formed of different materials. Specifically, the current collector 5 of the positive electrode 11 is formed of, for example, aluminum or an aluminum alloy, and the current collector 5 of the negative electrode 12 is formed of, for example, copper or a copper alloy.

  In the power storage device 1, the electrode body 2 (specifically, the electrode body 2 and the current collector 5) accommodated in the bag-like insulating cover 6 that insulates the electrode body 2 and the case 3 is contained in the case 3. Be contained.

  The output of the electricity storage device 1 may be temporarily reduced (hereinafter also referred to as transient deterioration) when charging / discharging is repeated at a high rate of 10 CA or more, for example. The transient deterioration occurs when the charging depth becomes non-uniform (the charging depth varies) in the thickness direction and the surface direction of the active material layer of the positive electrode or the negative electrode.

  Next, the manufacturing method of the electrical storage element 1 of the said embodiment is demonstrated.

  In the manufacturing method of the electrical storage element 1, the mixture containing an active material is apply | coated to metal foil (electrode base material), an active material layer is formed, and an electrode (the positive electrode 11 and the negative electrode 12) is produced. Next, the positive electrode 11, the separator 4, and the negative electrode 12 are overlapped to form the electrode body 2. Subsequently, the electrode body 2 is put in the case 3 and the electrolytic solution is put in the case 3 to assemble the power storage element 1.

  In producing the electrode (positive electrode 11), the positive electrode active material layer 112 is formed by applying a mixture containing an active material, a binder, and a solvent to both surfaces of the metal foil. The basis weight of the positive electrode active material layer 112 can be adjusted by adjusting the coating amount of the mixture. As a coating method for forming the positive electrode active material layer 112, a general method is employed. The applied positive electrode active material layer 112 is roll-pressed at a predetermined pressure. The density of the positive electrode active material layer 112 can be adjusted by adjusting the pressing pressure. The negative electrode is produced in the same manner.

  In the formation of the electrode body 2, the electrode body 2 is formed by winding a laminate 22 in which the separator 4 is sandwiched between the positive electrode 11 and the negative electrode 12. Specifically, the positive electrode 11, the separator 4, and the negative electrode 12 are overlapped so that the positive electrode active material layer 112 and the negative electrode active material layer 122 face each other through the separator 4, thereby forming the laminate 22. Subsequently, the stacked body 22 is wound to form the electrode body 2.

  In assembling the electricity storage element 1, the electrode body 2 is inserted into the case body 31 of the case 3, the opening of the case body 31 is closed with the cover plate 32, and the electrolytic solution is injected into the case 3. When closing the opening of the case main body 31 with the cover plate 32, the electrode body 2 is inserted into the case main body 31, the positive electrode 11 and the one external terminal 7 are electrically connected, and the negative electrode 12 and the other external terminal 7 are connected to each other. In the conductive state, the opening of the case body 31 is closed with the lid plate 32. When the electrolytic solution is injected into the case 3, the electrolytic solution is injected into the case 3 from the injection hole of the cover plate 32 of the case 3.

  Next, a method for recovering the output of the electricity storage device 1 according to the above embodiment (a method for charging and discharging the electricity storage device 1) will be described with reference to FIG.

  The output recovery method described above obtains the relationship between the charge amount SOC of the electricity storage element 1 having the negative electrode 12 containing particulate amorphous carbon as an active material and the open circuit potential OCP of the negative electrode at each charge amount SOC. Thus, the charge amount of the storage element is changed so as to pass through the charge amount when the absolute value of the change rate of the open circuit potential OCP with respect to the charge amount SOC is at least 10 [mV / SOC (%)] (step S1). ).

  Specifically, the output recovery method described above includes the charge amount SOC of the power storage element having the negative electrode 12 containing particulate non-graphitizable carbon as an active material, and the open circuit potential OCP of the negative electrode at each charge amount SOC. The relationship is obtained by the SOC-OCP curve, and the charge amount of the storage element is changed so as to pass through the charge amount when the absolute value of the slope of the SOC-OCP curve is at least 10 [mV / SOC (%)]. (Step S1).

  In step S1, the open circuit potential OCP of the negative electrode 12 with respect to the charge amount SOC of the power storage element 1 is obtained as follows, for example. First, the storage element (battery) is disassembled in an inert atmosphere in a completely discharged state. The Li reference electrode is inserted, and the OCP between the reference electrode and the negative electrode (OCP at SOC-0%) is measured. Next, the battery is charged up to a predetermined charge amount. After charging, the battery is paused for 10 minutes, and then the Li reference electrode is inserted, and the OCP between the reference electrode and the negative electrode (OCP at a predetermined SOC%) is measured. Then, the absolute value of the change rate of the open circuit potential OCP of the negative electrode 12 when the SOC is a predetermined percentage is obtained. In addition, when performing the above-described output recovery method for a storage element (battery) whose internal structure is unknown, prepare a plurality of storage elements (batteries) of the same design, and one of the storage elements (batteries) is The OCP can be measured at a predetermined SOC%.

Specifically, in step S1, when obtaining the SOC-OCP curve, the open circuit potential OCP of the negative electrode 12 with respect to the charge amount SOC of the storage element 1 can be obtained as follows. First, the specification of the discharge capacity A (Ah) of the electricity storage element (battery) is examined to know the discharge capacity A (Ah) of the electricity storage element (battery). Alternatively, a charge / discharge test is performed using a value obtained by dividing the upper and lower limit voltage of the battery pack or module by the number of cells (unit cell) in series, and the discharge capacity A (Ah) of the storage element (battery) is measured. The storage element (battery) is disassembled in an inert atmosphere in a state in which the storage element (battery) has been discharged to the discharge end voltage. The Li reference electrode is inserted, and the OCP between the reference electrode and the negative electrode (OCP at SOC-0%) is measured. Next, charging is performed for 1% when the already measured capacity A is 100%. After charging, the battery is paused for 10 minutes, and then the Li reference electrode is inserted, and the OCP between the reference electrode and the negative electrode (OCP at 1% SOC) is measured. Thereafter, the charge capacity is increased by 1%, charging and OCP measurement are repeated, and the OCP of the negative electrode is measured until it corresponds to SOC 100%. The absolute value of the rate of change of the open circuit potential OCP of the negative electrode 12 when the SOC is x% (SOC _x ) is obtained by the following equation. Specifically, the absolute value of the slope of the open circuit potential of the negative electrode 12 in the SOC-OCP curve is obtained by the following equation.
ΔOCP _x (mV / SOC [%]) = | OCP _{x + 1} −OCP _x |

  In step S <b> 1, the charge amount of the power storage element is changed so as to include SOC (%) in which the slope obtained as described above is 10 [mV / SOC (%)] or more. The slope determined as described above is usually 100 [mV / SOC (%)] or less. Such an inclination may be larger than 100 [mV / SOC (%)]. Such an inclination is preferably 40 [mV / SOC (%)] or less. The amount of change in the charge amount is normally 0% or more and 80% or less in SOC.

  In step S1, in order to change the charge amount of the power storage element 1, normally, the power storage element 1 is charged and / or discharged at a current value of 1CA to 10CA. For example, the storage element 1 is charged or discharged.

  In step S1, the charge amount of the power storage element may be changed while applying a load to the negative electrode 12 so that the negative electrode 12 (negative electrode active material layer 122) is compressed. Specifically, the charge amount of the power storage element may be changed while applying a load of 0.3 MPa to 1 MPa to the case 3. The load is applied to at least the negative electrode active material layer 112 in the thickness direction. The magnitude of the load is such that the porosity of the negative electrode active material layer 122 is at least reduced.

  In step S1, the storage element is charged so as to pass through the charge amount when the absolute value of the rate of change of the open circuit potential OCP with respect to the charge amount SOC is at least 10 [mV / SOC (%)] for one hour or more per time. The amount may vary. The above time may be one hour or more per day. The above time is usually 5 hours or less, preferably 3 hours or less per time (or per day).

  In step S1, the amount of charge of the storage element is usually changed by both charging and discharging. Specifically, both charging and discharging are performed at least once for the power storage element 1. Preferably, charging and discharging are alternately repeated.

  In the method for recovering the output of the electricity storage device 1 of the present embodiment as described above, when the absolute value of the change rate of the open circuit potential OCP with respect to the charge amount SOC is at least 10 [mV / SOC (%)], as described above. The charge amount of the electric storage element 1 is changed so as to pass through the charge amount of Specifically, in the SOC-OCP curve, the charge amount of the electricity storage element 1 is changed so as to pass through the charge amount when the absolute value of the slope is at least 10 [mV / SOC (%)]. . As a result, it is possible to recover a primary decrease in output (hereinafter, also simply referred to as transient deterioration) caused by repeated charging and discharging at a high rate. Specifically, the transient deterioration occurs due to variations in the charging depth in the thickness direction and the surface direction of the negative electrode active material layer 122 when charging and discharging are repeated at a high rate. Even if the state where the charging depth varies is left unattended, the difference in the charging depth becomes the driving force, and the variation in the charging depth can be gradually recovered. On the other hand, the potential difference with respect to the difference in the charge amount is obtained by changing the charge amount of the electric storage element 1 so as to pass through the charge amount when the absolute value of the slope is at least 10 [mV / SOC (%)]. Is relatively large. As the potential difference with respect to the difference between before and after the change in the charge amount of the storage element 1 increases, the driving force for equalizing the dispersed potential difference increases. That is, the driving force for making the variation in the charging depth uniform in the negative electrode active material layer 122 becomes large. Therefore, the temporary deterioration can be sufficiently recovered.

  In the method for recovering the output of the electricity storage device 1, the charge amount of the electricity storage device 1 may be changed while applying a load to the negative electrode 12. Thereby, since it can suppress that the particulate active materials of the negative electrode 12 leave | separate, the driving force which makes the above-mentioned potential difference uniform can be caused more reliably. Thereby, transient deterioration can be more fully recovered.

  In the above-described method for recovering the output of the electricity storage device 1, the charge amount when the absolute value of the rate of change of the open circuit potential OCP with respect to the charge amount SOC is at least 10 [mV / SOC (%)] is 1 hour or more per day. You may change the charge amount of the electrical storage element 1 so that it may pass. Since the above-described variation in the charging depth increases as time elapses, the transient deterioration can be more fully recovered by changing the charging amount as described above for at least one hour per day. it can.

  In the above-described method for recovering the output of the electricity storage device 1, the amount of charge of the electricity storage device is usually changed by both charging and discharging. That is, both charging and discharging are performed at least once for the power storage element 1. Preferably, charging and discharging are alternately repeated. Thereby, transient deterioration can be more fully recovered.

  Note that the method for recovering the output of the electricity storage device of the present invention is not limited to the above-described embodiment, and it is needless to say that various changes can be made without departing from the scope of the present invention. For example, the configuration of another embodiment can be added to the configuration of a certain embodiment, and a part of the configuration of a certain embodiment can be replaced with the configuration of another embodiment. Furthermore, a part of the configuration of an embodiment can be deleted.

  In the above embodiment, the positive electrode in which the active material layer containing the active material is in direct contact with the metal foil has been described in detail. However, in the present invention, the positive electrode has a conductive layer containing a binder and a conductive additive, and the metal foil A conductive layer may be disposed between the active material layer and the active material layer.

  In the above embodiment, the electrodes in which the active material layers are disposed on both sides of the metal foil of each electrode have been described. However, in the electricity storage device of the present invention, the positive electrode 11 or the negative electrode 12 has the active material layer on one side of the metal foil. It may be provided only on the side.

  In the said embodiment, although the electrical storage element 1 provided with the electrode body 2 by which the laminated body 22 was wound was demonstrated in detail, the electrical storage element of this invention may be provided with the laminated body 22 which is not wound. Specifically, the storage element may include an electrode body in which a positive electrode, a separator, a negative electrode, and a separator each formed in a rectangular shape are stacked a plurality of times in this order.

  In the above embodiment, the case where the power storage element 1 is used as a chargeable / dischargeable non-aqueous electrolyte secondary battery (for example, a lithium ion secondary battery) has been described. However, the type and size (capacity) of the power storage element 1 are arbitrary. is there. Moreover, although the lithium ion secondary battery was demonstrated as an example of the electrical storage element 1 in the said embodiment, it is not limited to this. For example, the present invention can be applied to various secondary batteries, and other power storage elements such as electric double layer capacitors.

  A nonaqueous electrolyte secondary battery (lithium ion secondary battery) was produced as shown below.

(Experimental example 1)
-Production of positive electrode N-methyl-2-pyrrolidone (NMP) as a solvent, conductive auxiliary agent (acetylene black), binder (PVdF), and active material (LiNi _1/3 Co _{1 / 3} Mn _1/3 O ₂ ) particles were mixed and kneaded to prepare a mixture for the positive electrode. The blending amounts of the conductive assistant, binder, and active material were 4.5% by mass, 4.5% by mass, and 91% by mass, respectively. The prepared positive electrode mixture was applied to both surfaces of an aluminum foil (15 μm thickness) so that the application amount (weight per unit area) after drying was 6.92 mg / cm ² . After drying, a roll press was performed. Thereafter, it was vacuum dried to remove moisture and the like. The thickness of the active material layer (for one layer) was 30 μm.

-Production of negative electrode As an active material, particulate amorphous carbon (non-graphitizable carbon) having an average particle diameter D50 of 4 μm was used. Moreover, PVdF was used as the binder. The negative electrode mixture was prepared by mixing and kneading NMP as a solvent, a binder, and an active material. The binder was blended so as to be 7% by mass, and the active material was blended so as to be 93% by mass. The prepared negative electrode mixture was applied to both surfaces of a copper foil (thickness: 10 μm) so that the coating amount (weight per unit area) after drying was 4.0 mg / cm ² . After drying, roll pressing was performed and vacuum drying was performed to remove moisture and the like. The thickness of the active material layer (for one layer) was 35 μm.

-Separator A polyethylene microporous film having a thickness of 22 μm was used as a separator substrate. The air permeability of the polyethylene microporous membrane was 100 seconds / 100 cc.

-Preparation of electrolyte solution As an electrolyte solution, what was prepared with the following method was used. As a non-aqueous solvent, propylene carbonate, dimethyl carbonate, and ethyl methyl carbonate were mixed in a volume of 1 part by volume, and LiPF ₆ was dissolved in this non-aqueous solvent so that the salt concentration was 1 mol / L. An electrolyte solution was prepared.

-Arrangement of electrode body in case A battery was manufactured by a general method using the positive electrode, the negative electrode, the electrolytic solution, the separator, and the case.
First, a sheet-like material in which a separator was disposed between the positive electrode and the negative electrode and laminated was wound. Next, the wound electrode body was placed in the case body of an aluminum square battery case as a case. Subsequently, the positive electrode and the negative electrode were electrically connected to the two external terminals, respectively. Further, a lid plate was attached to the case body. The above electrolytic solution was injected into the case from a liquid injection port formed on the cover plate of the case. Finally, the case was sealed by sealing the liquid injection port of the case.

Next, the SOC-OCP curve of the negative electrode in the battery manufactured as described above was obtained. In addition, a cycle test causing transient deterioration and an output inspection before and after the cycle test were performed. Then, discharging and charging (recovery test) for output recovery were performed.
(1) SOC-OCP curve [battery capacity check]
The battery capacity was confirmed in a constant temperature layer at 25 ° C. Details are as follows. Note that both charging and discharging were performed at 1 CA.
Charging: CCCV 4.1V.
Discharge: CC2.5V. Discharge in 4A discharge test (upper limit 4.1V, lower limit 2.5V).
The current capacity during discharge was defined as the battery capacity.
Each battery was charged / discharged at an environmental temperature of 25 ° C. under the conditions of an upper limit voltage of 4.2 V and a lower limit voltage of 2.4 V to obtain a discharge capacity, and the discharge was completed in 1 hour from the obtained discharge capacity. A current value, that is, 1C (A) was obtained.
[Measurement of OCP at each SOC]
Discharge: CC discharge was performed at 1C (A) determined above. The lower limit voltage was 2.5V.
SOC-OCP:
The battery is disassembled in an inert atmosphere, a Li reference electrode is inserted, and OCP between the reference electrode and the negative electrode (OCP when SOC is 0%) is obtained. Next, 1% of charging was performed when the previously obtained capacity A was 100%. After charging, the battery was stopped for 10 minutes, and then the Li reference electrode was inserted to determine the OCP between the reference electrode and the negative electrode (OCP at 1% SOC). Thereafter, charging and OCP measurement were repeated 1% at a time, and negative electrode OCP measurement values up to equivalent to SOC 100% were obtained. The absolute value of the change rate of the negative electrode open circuit potential when SOCx% was obtained by the following formula.
The slope of the absolute value of the negative open circuit potential is as follows.
ΔOCP _x (mV / SOC [%]) = | OCP _{x + 1} −OCP _x |
(2) Output inspection (at 25 ° C ± 3 ° C)
The current capacity discharged in the confirmation of the battery capacity was set to 1 C (A), and the SOC was adjusted to 50% SOC at 25 ° C., 0.5 C (A), and the charging time of 1 hour from the discharged state.
1C (A) is defined as Q1 (Ah) when the current capacity discharged in the immediately preceding 25 ° C. 4A discharge test (upper limit 4.1 V, lower limit 2.5 V) is Q1 (Ah). ) Means a current value to energize. Energization was performed after adjustment. The resistance value, output value, and output density were calculated according to the following formula.
Calculated by resistance D1: (difference between voltage at 10 seconds and voltage before energization) / current Output W1: (voltage before energization−lower limit voltage) / calculated by D1 * lower limit voltage Weight output density: W1 / battery weight Volume Output density: W1 / battery volume (3) Cycle test that causes output transient deterioration (implemented at 25 ° C ± 3 ° C)
A cycle including continuous discharge for 30 seconds and continuous charge for 30 seconds at a current of 10 C in an SOC of 50% was performed continuously for 1000 cycles.
In addition, when 1 hour passed after the end of the cycle, an output inspection was performed in the same manner as described above, and a resistance value D2 at 10 seconds after discharge was calculated. The transient (initial) deterioration rate was calculated by D2 / D1.
(4) Recovery test (at 25 ° C ± 3 ° C)
Within 1 hour after completion of the above cycle test (with the same time conditions for all batteries), discharge at 1 CA until the SOC reaches a predetermined slope [mV / SOC (%)] shown in Table 1 or more. Furthermore, the battery was charged at 0.5 CA to the use area (SOC about 50%). In addition, the holding time in Table 1 is the time held in the SOC when the inclination is equal to or greater than the predetermined inclination.
The recovery test was performed while applying a predetermined weight to the battery. Specifically, the load was applied to the long side surface of the battery (the surface perpendicular to the Y-axis direction in FIG. 1) so that a load was applied to the negative electrode active material layer of the electrode body inside the battery case. The batteries were arranged so that the long side surfaces of the batteries faced in the vertical direction, resin plates that were not deformed by the corresponding pressure were arranged above and below the batteries, and a constant load (0.3 MPa) was applied by an autograph.

(Experimental Examples 2 to 11)
The above recovery method was carried out in the same manner as in Experimental Example 1 except that the conditions were changed to those shown in Table 1.

<Evaluation of battery output recovery degree>
After the cycle test, an output test was performed in the same manner as described above, and the resistance value D3 was calculated. The post-recovery deterioration rate was calculated by D3 / D1. The deterioration rate of Experimental Example 1 was set to 100%.
The evaluation results are shown in Table 1. As can be seen from Table 1, by performing the method for recovering the output of the electricity storage device (the method for using the electricity storage device) of this embodiment, it was possible to sufficiently recover the transient deterioration of the battery. On the other hand, in the method of Experimental Example 2, the transient deterioration of the battery could not be sufficiently recovered.

1: Power storage element (non-aqueous electrolyte secondary battery),
2: Electrode body,
26: Uncoated laminated part,
3: Case, 31: Case body, 32: Cover plate,
4: Separator,
5: current collector, 50: clip member,
6: Insulation cover
7: External terminal, 71: Surface,
11: positive electrode,
111: Metal foil of positive electrode (positive electrode base material), 112: Positive electrode active material layer,
12: negative electrode,
121: Metal foil of negative electrode (negative electrode base material), 122: Negative electrode active material layer.

Claims (3)

  Obtaining the relationship between the charge amount SOC of a storage element having a negative electrode containing particulate amorphous carbon as an active material and the open circuit potential OCP of the negative electrode at each charge amount SOC, the open circuit potential OCP with respect to the charge amount SOC A method for recovering the output of the storage element, comprising: changing the charge amount of the storage element so as to pass through the charge amount when the absolute value of the rate of change of at least 10 [mV / SOC (%)] is passed.   The method for recovering the output of the electricity storage device according to claim 1, wherein a charge amount of the electricity storage device is changed while applying a load to the negative electrode.   The charge amount of the storage element is changed so as to pass through the charge amount when the absolute value of the change rate of the open circuit potential OCP with respect to the charge amount SOC is at least 10 [mV / SOC (%)] for one hour or more. A method for recovering the output of the electricity storage device according to 1 or 2.