JP7025715B2 - How to reuse non-aqueous electrolyte secondary battery - Google Patents

Description

The present invention relates to a method for reusing a non-aqueous electrolyte secondary battery.

Non-aqueous electrolyte secondary batteries such as lithium-ion secondary batteries are lightweight and can obtain high energy density, so they can be used as portable power sources for personal computers and mobile terminals, EVs (electric vehicles), HVs (hybrid vehicles), and PHVs. It is widely used as a power source for driving vehicles such as (plug-in hybrid vehicles). Since the performance of the non-aqueous electrolyte secondary battery may deteriorate in the process of charging and discharging, it is desirable to be able to recover the deteriorated battery performance. For example, in the method for regenerating a non-aqueous electrolytic solution secondary battery described in Patent Document 1, at least a part of the non-aqueous electrolytic solution secondary battery is opened, and then the film formed on the surface of the electrode plate is removed. The battery performance is restored by adding the film removing agent to the inside from the opening portion.

Japanese Unexamined Patent Publication No. 2012-109048

In a non-aqueous electrolyte secondary battery, while the non-aqueous electrolyte is stored at a high temperature or high voltage, the non-aqueous electrolyte is decomposed to generate bubbles, and the generated bubbles stay between the electrodes (that is, inside the electrode body). In some cases. When air bubbles are stagnant between the electrodes, current concentration occurs due to the influence of the variation in the distance between the electrodes or the variation in the reaction, and the ions in the non-aqueous electrolyte solution (for example, lithium ion) may be deposited on the negative electrode as a metal. There is. Precipitation of metal on the negative electrode may lead to deterioration of battery performance. Therefore, it is preferable to suppress the deterioration of the battery performance by removing the bubbles stagnant between the electrodes. Further, it is desirable that air bubbles can be removed from between the electrodes while the electrode body and the non-aqueous electrolytic solution are kept sealed in the battery case.

A typical object of the present invention is to appropriately remove air bubbles stagnant between electrodes while maintaining the state in which the electrode body and the non-aqueous electrolyte solution are sealed in the battery case, and suppress deterioration of battery performance. It is to provide a method of reusing a non-aqueous electrolyte secondary battery which is possible.

In order to realize such an object, one aspect of the method for reusing a non-aqueous electrolytic solution secondary battery disclosed herein is a positive electrode body, a negative electrode body, and a separator interposed between the positive electrode body and the negative electrode body. A method for reusing a non-aqueous electrolyte secondary battery comprising an electrode body having an electrode body, a non-aqueous electrolytic solution, and a battery case for accommodating the electrode body and the non-aqueous electrolytic solution inside, wherein the electrode is provided. By the cooling step of cooling the body and the non-aqueous electrolyte secondary battery in a state where the non-aqueous electrolyte is sealed inside the battery case to a temperature lower than the freezing point of the non-aqueous electrolyte, and the cooling step. The temperature of the non-aqueous electrolytic solution secondary battery cooled to a temperature lower than the freezing point is raised to a temperature equal to or higher than the freezing point, and bubbles existing in the non-aqueous electrolytic solution inside the electrode body are formed on the electrode. The temperature rise process to make it discharged to the outside of the body,
It is characterized by including.

According to the method for reusing a non-aqueous electrolytic solution secondary battery according to the present disclosure, the non-aqueous electrolytic solution is solidified by the cooling step to shrink the volume and is held by the separator and the electrode, so that bubbles are generated between the electrodes (for example,). , In the non-aqueous electrolytic solution existing in the electrode body), a path for discharging to the outside is generated. After that, the temperature of the non-aqueous electrolytic solution is raised by the temperature raising step, so that bubbles are discharged from between the electrodes to the outside. Therefore, the bubbles staying between the electrodes are removed while the electrode body and the non-aqueous electrolytic solution are kept sealed in the battery case. As a result, deterioration of battery performance is suppressed.

It is sectional drawing which shows typically the internal structure of the non-aqueous electrolytic solution secondary battery 1 of this embodiment. It is a schematic diagram which shows the structure of the electrode body (rolling electrode body) 20 of the non-aqueous electrolytic solution secondary battery 1 of this embodiment. It is sectional drawing which shows typically a part of the electrode body 20 in the state where the bubble 80 is stagnant. It is a graph which shows an example of the relationship between the temperature of a non-aqueous electrolyte secondary battery 1 and the DC resistance measured at each temperature. FIG. 3 is an explanatory diagram schematically illustrating a state in which the electrode body 20 shown in FIG. 3 is cooled to a temperature below the freezing point of the non-aqueous electrolytic solution 10.

Hereinafter, one of the typical embodiments in the present disclosure will be described in detail with reference to the drawings. Matters other than those specifically mentioned in the present specification and necessary for implementation can be grasped as design matters of those skilled in the art based on the prior art in the art. The present invention can be carried out based on the contents disclosed in the present specification and the common general technical knowledge in the art. In the following drawings, members / parts having the same function are described with the same reference numerals. Further, the dimensional relations (length, width, thickness, etc.) in each drawing do not reflect the actual dimensional relations.

As used herein, the term "battery" refers to a general storage device capable of extracting electrical energy, and is a concept including a primary battery and a secondary battery. "Secondary battery" refers to a general storage device that can be charged and discharged repeatedly, and includes so-called storage batteries (that is, chemical batteries) such as lithium ion secondary batteries, nickel hydrogen batteries, and nickel cadmium batteries, as well as electric double layer capacitors and the like. Includes capacitors (ie, physical batteries). Hereinafter, a method for reusing the non-aqueous electrolyte secondary battery according to the present disclosure will be described in detail by exemplifying a flat rectangular lithium ion secondary battery which is a kind of non-aqueous electrolyte secondary battery. However, the method for reusing the non-aqueous electrolyte secondary battery according to the present disclosure is not intended to be limited to those described in the following embodiments.

<Structure of non-aqueous electrolyte secondary battery>
The non-aqueous electrolyte secondary battery 1 shown in FIG. 1 is a sealed lithium-ion secondary battery including an electrode body 20, a non-aqueous electrolyte 10 (see FIGS. 3 and 5), and a battery case 30. The battery case 30 houses the electrode body 20 and the non-aqueous electrolytic solution 10 in a sealed state. The shape of the battery case 30 in this embodiment is a flat square shape. The battery case 30 includes a box-shaped main body 31 having an opening at one end, and a plate-shaped lid 32 that closes the opening of the main body. The battery case 30 (specifically, the lid 32 of the battery case 30) is provided with a positive electrode terminal 42 and a negative electrode terminal 44 for external connection, and a safety valve 36. The safety valve 36 opens when the internal pressure of the battery case 30 rises above a predetermined level, and releases the internal pressure. Further, the battery case 30 is provided with an injection port (not shown) for injecting the non-aqueous electrolytic solution 10 into the inside. As the material of the battery case 30, for example, a lightweight metal material having good thermal conductivity such as aluminum is used. However, it is also possible to change the configuration of the battery case. For example, a flexible laminate may be used as the battery case. Further, the shape of the battery case may be a shape other than a square shape (for example, a cylindrical shape).

As shown in FIG. 2, the electrode body 20 of the present embodiment includes a long positive electrode body (positive electrode sheet) 50, a long negative electrode body (negative electrode sheet) 60, and two long negative electrodes. A wound electrode body in which a separator (separator sheet) 70 is overlapped and wound in the longitudinal direction is adopted. Specifically, in the positive electrode body 50, the positive electrode active material layer 54 is formed along the longitudinal direction on one side or both sides (both sides in the present embodiment) of the long positive electrode current collector 52. In the negative electrode body 60, the negative electrode active material layer 64 is formed along the longitudinal direction on one side or both sides (both sides in the present embodiment) of the long negative electrode current collector 62. The positive electrode active material layer non-formed portion 52A (that is, the positive electrode active material layer 54) formed so as to protrude outward from both sides of the electrode body 20 in the winding axis direction (sheet width direction orthogonal to the longitudinal direction). The positive electrode current collector 52 is exposed without being formed) and the negative electrode active material layer non-formed portion 62A (that is, the portion where the negative electrode active material layer 64 is not formed and the negative electrode current collector 62 is exposed). , The positive electrode current collector plate 42A and the negative electrode current collector plate 44A are joined, respectively. The positive electrode terminal 42 (see FIG. 1) is electrically connected to the positive electrode current collector plate 42A, and the negative electrode terminal 44 (see FIG. 1) is electrically connected to the negative electrode current collector plate 44A. It is also possible to change the configuration of the electrode body. For example, a laminated electrode body may be used instead of the wound electrode body.

As the materials and members constituting the positive and negative electrodes of the electrode body 50, the same materials and members as those used in the conventional general non-aqueous electrolytic solution secondary battery can be used without limitation. For example, as the positive electrode current collector 52, those used as the positive electrode current collector of this type of non-aqueous electrolytic solution secondary battery can be used without particular limitation. Typically, a metal positive electrode current collector having good conductivity is preferred. For example, a metal material such as aluminum, nickel, titanium, or stainless steel can be adopted as the positive electrode current collector 52. In particular, aluminum (for example, aluminum foil) is preferable. Examples of the positive electrode active material of the positive electrode active material layer 54 include lithium composite metal oxides having a layered structure or a spinel structure (for example, LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , LiNiO ₂ , LiCoO ₂ , LiFeO). ₂ , LiMn ₂ O ₄ , LiNi _0.5 Mn _1.5 O ₄ , LiCrMnO ₄ , LiFePO ₄ , etc.). In the positive electrode active material layer 54, the positive electrode active material and a material (conductive material, binder, etc.) used as needed are dispersed in an appropriate solvent (for example, N-methyl-2-pyrrolidone: NMP) to form a paste (or It can be formed by preparing a composition (in the form of a slurry), applying an appropriate amount of the composition to the surface of the positive electrode current collector 52, and drying the composition.

As the negative electrode current collector 62, those used as the negative electrode current collector of this type of non-aqueous electrolytic solution secondary battery can be used without particular limitation. Typically, a metal negative electrode current collector having good conductivity is preferable, and for example, copper (for example, copper foil) or an alloy mainly composed of copper can be used. Examples of the negative electrode active material of the negative electrode active material layer 64 include a particle-like (or spherical or scaly) carbon material containing a graphite structure (layered structure) at least in part, and a lithium transition metal composite oxide (for example, Li ₄ ). Lithium-titanium composite oxides such as Ti ₅ O ₁₂ ), lithium transition metal composite nitrides and the like. In the negative electrode active material layer 64, a negative electrode active material and a material (binder or the like) used as needed are dispersed in an appropriate solvent (for example, ion-exchanged water) to prepare a paste-like (or slurry-like) composition. , An appropriate amount of the composition can be applied to the surface of the negative electrode current collector 62 and dried.

As the separator 70, a separator made of a conventionally known porous sheet can be used without particular limitation. For example, a porous sheet (film, non-woven fabric, etc.) made of a polyolefin resin such as polyethylene (PE) and polypropylene (PP) can be mentioned. The porous sheet may have a single-layer structure or a plurality of layers (for example, a three-layer structure in which PP layers are laminated on both sides of a PE layer). Further, the porous sheet may be configured to have a porous heat-resistant layer on one side or both sides. This heat-resistant layer can be, for example, a layer containing an inorganic filler and a binder (also referred to as a filler layer). As the inorganic filler, for example, alumina, boehmite, silica and the like can be preferably adopted.

The non-aqueous electrolytic solution 10 housed in the battery case 30 together with the electrode body 20 contains a supporting salt in an appropriate non-aqueous solvent, and a conventionally known non-aqueous electrolytic solution can be adopted without particular limitation. For example, as the non-aqueous solvent, ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC) and the like can be used. Further, as the supporting salt, for example, a lithium salt can be preferably used, and LiPF ₆ is adopted in this embodiment.

With reference to FIG. 3, the influence that the bubble 80 stagnant between the electrodes can have on the battery performance will be described. In the non-aqueous electrolytic solution secondary battery 1, the electrolytic solution 10 may be decomposed and bubbles 80 may be generated while the battery 1 is stored at a high temperature or a high voltage. For example, the electrode body 20 is affected by the shape of a jig (not shown) for restraining the electrode body 20 and the distortion of the members (positive electrode body 50, negative electrode body 60, and separator 70) constituting the electrode body 20. Bubbles 80 may stagnate in the non-aqueous electrolytic solution 10 inside (that is, between the electrodes). When the bubbles 80 are stagnant between the electrodes, current concentration occurs due to the influence of the variation in the distance between the electrodes or the variation in the reaction, and the lithium ion in the non-aqueous electrolytic solution may be deposited as a metal. Precipitation of metal may lead to deterioration of battery performance (for example, deterioration of overcharge resistance). In the method of reusing the non-aqueous electrolytic solution secondary battery exemplified below, the electrode body 20 and the non-aqueous electrolytic solution 10 stay between the electrodes while being sealed in the battery case 30 (see FIG. 1). Bubbles are removed.

<How to reuse non-aqueous electrolyte secondary battery>
A method of reusing the non-aqueous electrolyte secondary battery according to the present embodiment will be described. In the method for reusing the non-aqueous electrolytic solution secondary battery according to the present embodiment, the cooling step and the raising step are sequentially performed.

(Determination of cooling conditions)
In this embodiment, suitable cooling conditions are determined before the cooling step is carried out. That is, the cooling conditions of the non-aqueous electrolytic solution secondary battery 1 in the cooling step are acquired. Although the details will be described later, in the cooling step in the present embodiment, the non-aqueous electrolytic solution secondary battery 1 is cooled to a temperature below the freezing point of the non-aqueous electrolytic solution 10. Therefore, in the cooling condition determination step, the freezing point of the non-aqueous electrolytic solution 10 contained in the non-aqueous electrolytic solution secondary battery 1 is acquired as one of the cooling conditions.

When the freezing point of the non-aqueous electrolytic solution 10 is known in advance, the already known freezing point can be determined as the cooling condition without performing the cooling condition determination step. On the other hand, when the freezing point of the non-aqueous electrolytic solution 10 is unknown, for example, a method of acquiring the freezing point based on the temperature dependence of the DC resistance of the non-aqueous electrolytic solution secondary battery 1 can be adopted. In the present embodiment, each of the plurality (9) non-aqueous electrolyte secondary batteries 1 having the same composition is cooled to each target temperature set at 1 ° C. between −35 ° C. and −43 ° C. .. As a cooling method, a method of cooling the non-aqueous electrolyte secondary battery 1 from room temperature to a target temperature at a rate of 0.5 ° C./min using a constant temperature bath was adopted. For each non-aqueous electrolyte secondary battery 1, the DC resistance at the time when the temperature reached the target temperature and was held for 2 hours was measured.

FIG. 4 graphically shows the relationship between each target temperature and the measurement result of DC resistance. The degree of change in DC resistance differs before and after the non-aqueous electrolytic solution 10 solidifies. Therefore, as shown in FIG. 4, the temperature IP (−38 ° C. in the example of FIG. 4) at the change point of the slope of the DC resistance is used as the freezing point of the non-aqueous electrolytic solution 10 contained in the non-aqueous electrolytic solution secondary battery 1. To be acquired.

In determining the cooling conditions, conditions other than the freezing point (for example, the cooling rate and the holding time for holding the non-aqueous electrolyte secondary battery 1 at a set temperature below the freezing point) are determined in the cooling step and the temperature raising step. It may be appropriately set within a range in which the change in the DC resistance of the non-aqueous electrolyte secondary battery 1 before and after is less than the threshold value. As an example, in this embodiment, the cooling rate is set to 0.5 ° C./min and the holding time is set to 2 hours.

(Cooling process)
In the cooling step of the present embodiment, the non-aqueous electrolyte secondary battery 1 is heated to a temperature below the freezing point of the non-aqueous electrolyte 10 while the electrode body 20 and the non-aqueous electrolyte 10 are sealed inside the battery case 30. Is cooled. In this embodiment, the cooling conditions are as described above, and a constant temperature bath is used for cooling.

As schematically shown in FIG. 5, when the non-aqueous electrolytic solution secondary battery 1 is cooled to a temperature below the freezing point, the non-aqueous electrolytic solution 10 inside the electrode body 20 solidifies and the volume shrinks, resulting in a positive electrode. It is held by the body 50, the negative electrode body 60, and the separator 70. As a result, a path 10R is formed in which the bubbles 80 (see FIG. 3) stagnant between the electrodes are discharged to the outside between the electrodes.

(Heating process)
In the temperature raising step in the present embodiment, the non-aqueous electrolytic solution secondary battery 1 cooled by the cooling step is heated to a temperature equal to or higher than the freezing point (normal temperature in the present embodiment). As a result, the bubbles 80 stagnant between the electrodes (that is, in the non-aqueous electrolytic solution 10 between the positive electrode body 50 and the negative electrode body 60 in the electrode body 20) are discharged to the outside between the electrodes. Since the inside of the battery case 30 remains sealed, the bubbles 80 are not discharged to the outside of the battery case 30. However, since the state in which the bubbles 80 are stagnant between the electrodes may cause a deterioration in battery performance, the bubbles 80 may be discharged to the outside between the electrodes. Therefore, the cooling step and the raising temperature step can be performed in a state where the inside of the battery case 30 is sealed.

Further, the temperature rising rate in the temperature raising step of the present embodiment is 0.5 ° C./min or less. As a result, the deterioration of battery performance is further suppressed. The reason for this will be described later.

(Checking the internal resistance of the battery)
In the method for reusing a non-aqueous electrolytic solution secondary battery according to the present embodiment, preferably, the internal resistance of the test battery is confirmed after the completion of the temperature raising step. In the resistance confirmation step, it is confirmed that the change in the internal resistance of the non-aqueous electrolytic solution secondary battery 1 through the cooling step and the temperature raising step is less than the threshold value. The non-aqueous electrolytic solution secondary battery 1 in which the change in internal resistance is less than the threshold value is appropriately reused because the deterioration of battery performance is suppressed.

<Example>
The test results using Comparative Examples and Examples will be described with reference to Table 1. In this test, comparative examples and Examples 1 to 7 were compared. The configurations of the non-aqueous electrolyte secondary batteries (test cell: hereinafter simply referred to as “cell”) according to Comparative Examples and Examples 1 to 7 are the same, and the supporting salt of the non-aqueous electrolyte 10 is 1. A mixture of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethylmethyl carbonate (EMC) (EC: DMC: EMC = 3: 4: 3) was used as the 1M LiPF ₆ and the non-aqueous solvent. In addition, a bubble generation step was performed on each of the cells according to Comparative Examples and Examples 1 to 7. In the bubble generation step, after charging and discharging for 3 cycles at a rate of 3.0 V to 4.55 V and 1/10 C, the cells were stored at 4.55 V and 75 ° C. for 100 hours. One of the saved cells (SOC: 0%) was used as a comparative example.

In addition, the cooling step, the raising temperature step, and the reaction resistance increase rate were measured for each of the cells according to Examples 1 to 7. In the cooling step, each cell (SOC: 0%) after storage described above is placed in a constant temperature bath, cooled to the cooling temperature shown in Table 1 at a cooling rate of 0.5 ° C./min, and then the temperature is set to the cooling temperature. It was stored for 2 hours while being maintained. In the temperature raising step, each cell after the cooling step was heated to room temperature (25 ° C.) at the heating rate shown in Table 1. Next, the AC impedance of each cell (temperature: 25 ° C.) after the temperature rise step is measured with an AC impedance measuring device (Solatron 1260 manufactured by Solartron) at an applied voltage of 10 mV and a measurement frequency range of 0.01 to 1 MHz, and the temperature returns to room temperature. The reaction resistance increase rate of each cell was measured by dividing the subsequent reaction resistance value by the value of the comparative example.

Next, an overcharge determination was made for each of the cells according to Comparative Examples and Examples 1 to 7. In the overcharge determination, a current of 10 C was passed through each cell in a temperature environment of −10 ° C., and charging was performed from 4 V until the separator shut down. If the temperature rise of the battery case after shutdown was less than 10 ° C, it was judged as "◯", and if it was 10 ° C or higher, it was judged as "x".

As shown in Table 1, in Examples 1 to 4, the temperature rise rate in the temperature rise step is the same, and the cooling temperature in the cooling step is different. Comparing Comparative Examples and Examples 1 to 4, the cooling temperature in the cooling step is set to a temperature lower than the temperature IP at the change point of the slope of the DC resistance (that is, a temperature lower than the freezing point of the non-aqueous electrolytic solution 10). It can be seen that the overcharge resistance could be improved while the reaction resistance increase rate was set to 1.04% or less. It is considered that this is because the non-aqueous electrolytic solution 10 coagulates and shrinks in volume, and the bubbles 80 stagnant between the electrodes are removed to the outside between the electrodes.

Further, as shown in Table 1, in Examples 4 to 7, the cooling temperatures in the cooling step are all the same, and the heating rate in the raising step is different. Comparing Examples 4 to 7, it can be seen that the reaction resistance increase rate was increased and the overcharge resistance was not improved by increasing the temperature increase rate in the temperature increase step to more than 0.5 ° C./min. As a cause of this, it is considered that if the temperature rising rate is increased, bubbles may not be sufficiently removed from between the electrodes. Further, if the temperature rise temperature is increased, the concentration distribution of the supporting salt in the non-aqueous electrolyte 10 may vary, which may lead to an increase in resistance and precipitation of lithium metal. From the test results shown in Table 1, it can be said that the heating rate in the heating step is preferably 0.5 ° C./min or less.

The technique disclosed in the above embodiment is only an example. Therefore, it is possible to modify the techniques exemplified in the above embodiments. For example, the cooling conditions in the cooling step (for example, cooling temperature and cooling rate, etc.) and the raising conditions in the raising step (for example, raising rate, etc.) depend on the configuration and material of the non-aqueous electrolyte secondary battery. Can change. Therefore, the various conditions exemplified in the above embodiment may be changed depending on the configuration and material of the non-aqueous electrolyte secondary battery.

1 Non-aqueous electrolyte secondary battery 10 Non-aqueous electrolyte 20 Electrode body 30 Battery case 50 Positive electrode body 60 Negative electrode body 70 Separator

Claims (1)

A positive electrode body, a negative electrode body, and an electrode body having a separator interposed between the positive electrode body and the negative electrode body, and
With non-aqueous electrolyte
A battery case for accommodating the electrode body and the non-aqueous electrolytic solution inside,
It is a method of reusing a non-aqueous electrolyte secondary battery equipped with
A cooling step of cooling the non-aqueous electrolyte secondary battery in a state where the electrode body and the non-aqueous electrolyte are sealed inside the battery case to a temperature lower than the freezing point of the non-aqueous electrolyte.
The non-aqueous electrolytic solution secondary battery cooled to a temperature below the freezing point by the cooling step was heated to a temperature equal to or higher than the freezing point, and was present in the non-aqueous electrolytic solution inside the electrode body. A temperature raising step in which bubbles are discharged to the outside of the electrode body, and
A method for reusing a non-aqueous electrolyte secondary battery, which comprises.

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