JP2020035566A - Reuse method of non-aqueous electrolyte secondary battery - Google Patents

Abstract

To provide a reuse method of a non-aqueous electrolyte secondary battery that appropriately removes air bubbles stagnating between electrodes and suppresses a decrease in a battery performance while maintaining the state in which an electrode body and a non-aqueous electrolyte are sealed in a battery case.SOLUTION: A reuse method of a non-aqueous electrolyte secondary battery according to the present invention includes a cooling step and a temperature rise step. In the cooling step, a non-aqueous electrolyte secondary battery in a state where an electrode body 20 and a non-aqueous electrolyte 10 are sealed inside a battery case is cooled to a temperature lower than a freezing point of the non-aqueous electrolyte 10. In the temperature rise step, the non-aqueous electrolyte secondary battery cooled in the cooling step is heated to a temperature equal to or higher than the freezing point, and air bubbles existing in the non-aqueous electrolyte inside the electrode body are discharged to the outside of the electrode body.SELECTED DRAWING: Figure 5

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 have high energy densities. Therefore, portable power sources such as personal computers and portable terminals, or EVs (electric vehicles), HVs (hybrid vehicles), and PHVs (Plug-in hybrid vehicles) are widely used as power sources for driving vehicles. Since the performance of the non-aqueous electrolyte secondary battery may decrease in the course of charging and discharging, it is desirable to be able to recover the reduced battery performance. For example, in the method for regenerating a non-aqueous electrolyte secondary battery described in Patent Document 1, after at least a part of the non-aqueous electrolyte secondary battery is opened, a film formed on the surface of the electrode plate is removed. The recovery of the battery performance is achieved by adding the film removing agent to the inside from the opening.

JP 2012-109048 A

  In a non-aqueous electrolyte secondary battery, while stored at high temperature or high voltage, the non-aqueous electrolyte is decomposed to generate bubbles, and the generated bubbles stagnate between the electrodes (that is, inside the electrode body). There are cases. If air bubbles stagnate between the electrodes, current concentration may occur due to variations in the distance between the electrodes or variations in the reaction, and ions (eg, lithium ions) in the non-aqueous electrolyte may precipitate as metals on the negative electrode. There is. Deposition of metal on the negative electrode may lead to a decrease in battery performance. Therefore, it is preferable to suppress the deterioration of the battery performance by removing the bubbles stagnating between the electrodes. In addition, it is desirable that bubbles can be removed from between the electrodes while maintaining the state in which the electrode body and the non-aqueous electrolyte are sealed in the battery case.

  A typical object of the present invention is to appropriately remove bubbles stagnating between electrodes while maintaining a state in which an electrode body and a non-aqueous electrolyte are sealed in a battery case, and to suppress a decrease in battery performance. It is an object of the present invention to provide a method for recycling a non-aqueous electrolyte secondary battery.

In order to achieve such an object, a method of recycling a nonaqueous electrolyte secondary battery according to one embodiment disclosed herein includes a positive electrode body, a negative electrode body, and a separator interposed between the positive electrode body and the negative electrode body. A non-aqueous electrolyte, a non-aqueous electrolyte, and a battery case containing the electrode body and the non-aqueous electrolyte therein, and a method for reusing a non-aqueous electrolyte secondary battery, comprising: A cooling step of cooling the non-aqueous electrolyte secondary battery in a state in which the body and the non-aqueous electrolyte are sealed inside the battery case, to a temperature lower than a freezing point of the non-aqueous electrolyte; and The non-aqueous electrolyte secondary battery cooled to a temperature lower than the freezing point is heated to a temperature equal to or higher than the freezing point, and the bubbles existing in the non-aqueous electrolyte inside the electrode body are reduced in the electrode. A temperature-raising step to be discharged to the outside of the body,
It is characterized by including.

  According to the method for reusing a nonaqueous electrolyte secondary battery according to the present disclosure, the nonaqueous electrolyte is solidified by the cooling step and contracts in volume, and is held by the separator and the electrodes, so that bubbles are generated between the electrodes (for example, In addition, a path is created for discharging from the non-aqueous electrolyte present in the electrode body to the outside. Thereafter, the temperature is raised in the non-aqueous electrolyte in the temperature raising step, so that air bubbles are discharged to the outside from between the electrodes. Therefore, the air bubbles that have stayed between the electrodes are removed while the state in which the electrode body and the non-aqueous electrolyte are sealed in the battery case is maintained. As a result, a decrease in battery performance is suppressed.

FIG. 1 is a cross-sectional view schematically illustrating an internal structure of a nonaqueous electrolyte secondary battery 1 of the present embodiment. FIG. 2 is a schematic diagram illustrating a configuration of an electrode body (rolled electrode body) 20 of the nonaqueous electrolyte secondary battery 1 of the present embodiment. It is sectional drawing which shows typically a part of electrode body 20 in the state in which the bubble 80 was stagnating. 4 is a graph showing an example of the relationship between the temperature of the nonaqueous electrolyte secondary battery 1 and the DC resistance measured at each temperature. FIG. 4 is an explanatory diagram schematically illustrating a state in which the electrode body 20 illustrated in FIG. 3 is cooled to a temperature lower than the freezing point of the nonaqueous electrolyte 10.

  Hereinafter, one of exemplary embodiments of 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 the implementation can be understood as design matters of those skilled in the art based on conventional techniques in the field. The present invention can be implemented based on the contents disclosed in this specification and common technical knowledge in the field. In the following drawings, members / parts having the same function are denoted by the same reference numerals. The dimensional relationships (length, width, thickness, etc.) in each drawing do not reflect actual dimensional relationships.

  In this specification, the term “battery” is a term generally indicating a power storage device capable of extracting electric energy, and is a concept including a primary battery and a secondary battery. “Secondary battery” refers to a general storage device that can be repeatedly charged and discharged, and includes a so-called storage battery (ie, a chemical battery) such as a lithium ion secondary battery, a nickel hydride battery, and a nickel cadmium battery, as well as an electric double layer capacitor. Includes capacitors (ie, physical batteries). Hereinafter, a method for reusing a nonaqueous electrolyte secondary battery according to the present disclosure will be described in detail by exemplifying a flat rectangular lithium ion secondary battery that is a kind of nonaqueous electrolyte secondary battery. However, the method for reusing the nonaqueous electrolyte secondary battery according to the present disclosure is not intended to be limited to the method described in the following embodiment.

<Configuration 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 accommodates the electrode body 20 and the non-aqueous electrolyte 10 in a sealed state. The shape of the battery case 30 in the present embodiment is a flat rectangular shape. The battery case 30 includes a box-shaped main body 31 having an opening at one end, and a plate-shaped lid 32 for closing 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. When the internal pressure of the battery case 30 rises above a predetermined level, the safety valve 36 is opened to release the internal pressure. The battery case 30 is provided with an inlet (not shown) for injecting the non-aqueous electrolyte 10 into the inside. As a material of the battery case 30, for example, a lightweight metal material having good heat conductivity such as aluminum is used. However, the configuration of the battery case can be changed. 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 positive electrodes (negative electrode sheets). A wound electrode body in which a separator (separator sheet) 70 is overlapped and wound in the longitudinal direction is employed. Specifically, in the positive electrode body 50, a positive electrode active material layer 54 is formed on one or both surfaces (both surfaces in the present embodiment) of the long positive electrode current collector 52 along the longitudinal direction. In the negative electrode body 60, a negative electrode active material layer 64 is formed on one surface or both surfaces (both surfaces in the present embodiment) of a long negative electrode current collector 62 along the longitudinal direction. The positive electrode active material layer-free portion 52A (that is, the positive electrode active material layer 54) is formed so as to protrude outward from both sides in the winding axis direction (the sheet width direction perpendicular to the longitudinal direction) of the electrode body 20. Are formed, and the negative electrode active material layer non-formed portion 62A (that is, the portion where the negative electrode current collector 62 is exposed without forming the negative electrode active material layer 64) is included in The positive current collector 42A and the negative current collector 44A are respectively joined. 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. The configuration of the electrode body can be changed. For example, a laminated electrode body may be used instead of the wound electrode body.

Materials and members constituting the positive and negative electrodes of the electrode body 50 may be the same as those used in conventional general nonaqueous electrolyte secondary batteries without any limitation. For example, as the positive electrode current collector 52, one used as a positive electrode current collector of this type of nonaqueous electrolyte secondary battery can be used without any particular limitation. Typically, a metal positive electrode current collector having good conductivity is preferable. For example, a metal material such as aluminum, nickel, titanium, and stainless steel can be used as the positive electrode current collector 52. Particularly, aluminum (for example, aluminum foil) is preferable. As the positive electrode active material of the positive electrode active material layer 54, for example, a lithium composite metal oxide having a layered structure or a spinel structure (eg, LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , LiNiO ₂ , LiCoO ₂ , LiFeO _{2) 2, LiMn 2 O 4, LiNi} 0.5 Mn 1.5 O 4, LiCrMnO 4, LiFePO 4 , etc.). The positive electrode active material layer 54 is obtained by dispersing a positive electrode active material and a material (conductive material, binder, or the like) used as needed in a suitable solvent (for example, N-methyl-2-pyrrolidone: NMP) and forming a paste (or A slurry-like composition is prepared, an appropriate amount of the composition is applied to the surface of the positive electrode current collector 52, and the composition is dried.

As the negative electrode current collector 62, one used as a negative electrode current collector of this type of nonaqueous electrolyte secondary battery can be used without any particular limitation. Typically, a metal negative electrode current collector having good conductivity is preferable. For example, copper (for example, copper foil) or an alloy mainly containing copper can be used. As the negative electrode active material of the negative electrode active material layer 64, for example, a particulate (or spherical or flaky) carbon material containing at least a part of a graphite structure (layer structure), a lithium transition metal composite oxide (for example, Li ₄ Lithium-titanium composite oxide such as Ti ₅ O ₁₂ ), and a lithium-transition metal composite nitride. The negative electrode active material layer 64 is prepared by dispersing a negative electrode active material and a material (such as a binder) used as needed in a suitable solvent (for example, ion-exchanged water) to prepare a paste-like (or slurry-like) composition. The composition can be formed by applying an appropriate amount of the composition to the surface of the negative electrode current collector 62 and drying.

  As the separator 70, a conventionally known separator made of a porous sheet can be used without particular limitation. For example, a porous sheet (film, nonwoven fabric, etc.) made of a polyolefin resin such as polyethylene (PE) and polypropylene (PP) can be used. Such a porous sheet may have a single-layer structure or a multi-layer structure of two or more layers (for example, a three-layer structure in which a PP layer is laminated on both sides of a PE layer). Further, the porous sheet may be provided with a porous heat-resistant layer on one or both sides thereof. The heat-resistant layer may 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 used.

The non-aqueous electrolyte 10 accommodated in the battery case 30 together with the electrode body 20 contains a supporting salt in a suitable non-aqueous solvent, and a conventionally known non-aqueous electrolyte can be employed without any particular limitation. For example, as a 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 suitably used, and LiPF ₆ is employed in the present embodiment.

  With reference to FIG. 3, an influence that air bubbles 80 stagnated between the electrodes may have on battery performance will be described. In the non-aqueous electrolyte secondary battery 1, the electrolyte 10 may be decomposed to generate bubbles 80 during storage at high temperature or high voltage. For example, the shape of the jig (not shown) that restrains the electrode body 20 and the distortion of the members (the positive electrode body 50, the negative electrode body 60, and the separator 70) that form the electrode body 20 are affected by the shape of the electrode body 20. Bubbles 80 may stagnate in the non-aqueous electrolyte 10 inside (i.e., between the electrodes). When the bubbles 80 stagnate between the electrodes, current concentration occurs due to the variation in the distance between the electrodes or the variation in the reaction, and lithium ions in the non-aqueous electrolyte may precipitate as metal. The deposition of metal may lead to a decrease in battery performance (for example, a decrease in overcharge resistance). In the following non-aqueous electrolyte secondary battery recycling method, the electrode body 20 and the non-aqueous electrolyte 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 batteries>
A method for reusing the nonaqueous electrolyte secondary battery according to the embodiment will be described. In the method for recycling a nonaqueous electrolyte secondary battery according to the present embodiment, a cooling step and a temperature increasing step are performed in order.

(Determining cooling conditions)
In the present embodiment, suitable cooling conditions are determined before performing the cooling step. That is, the cooling condition of the non-aqueous electrolyte secondary battery 1 in the cooling step is obtained. As will be described in detail later, in the cooling step in the present embodiment, the non-aqueous electrolyte secondary battery 1 is cooled to a temperature lower than the freezing point of the non-aqueous electrolyte 10. Therefore, in the cooling condition determination step, the freezing point of the nonaqueous electrolyte 10 included in the nonaqueous electrolyte secondary battery 1 is obtained as one of the cooling conditions.

  If the freezing point of the non-aqueous electrolyte 10 is known in advance, the already known freezing point can be determined as the cooling condition without performing the cooling condition determining step. On the other hand, when the freezing point of the nonaqueous electrolyte 10 is unknown, for example, a method of acquiring the freezing point based on the temperature dependency of the DC resistance of the nonaqueous electrolyte secondary battery 1 can be adopted. In the present embodiment, each of a plurality (nine) of nonaqueous electrolyte secondary batteries 1 having the same composition is cooled to a target temperature set every 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 thermostat 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 maintained for 2 hours was measured.

  FIG. 4 is a graph showing the relationship between each target temperature and the measurement result of the DC resistance. The degree of change in the DC resistance differs before and after the nonaqueous electrolyte 10 solidifies. Accordingly, as shown in FIG. 4, the temperature IP (−38 ° C. in the example of FIG. 4) at the changing point of the gradient of the DC resistance is determined as the freezing point of the nonaqueous electrolyte 10 included in the nonaqueous electrolyte secondary battery 1. Is obtained.

  In the determination of the cooling condition, conditions other than the freezing point (for example, the cooling rate and the holding time for holding the nonaqueous electrolyte secondary battery 1 at a set temperature lower than the freezing point) are determined in the cooling step and the temperature increasing step. What is necessary is just to set suitably within the range in which the change of the DC resistance of the nonaqueous electrolyte secondary battery 1 before and after is less than the threshold value. As an example, in the present 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 in the present embodiment, the non-aqueous electrolyte secondary battery 1 is kept at a temperature lower than the freezing point of the non-aqueous electrolyte 10 while the electrode body 20 and the non-aqueous electrolyte 10 are sealed in the battery case 30. Is cooled. In the present 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 electrolyte secondary battery 1 is cooled to a temperature lower than the freezing point, the non-aqueous electrolyte 10 inside the electrode body 20 solidifies and contracts in volume, and the positive electrode Body 50, negative electrode body 60, and separator 70. As a result, a path 10R for discharging the air bubbles 80 (see FIG. 3) stagnated between the electrodes to the outside between the electrodes is formed.

(Heating process)
In the temperature raising step in the present embodiment, the non-aqueous electrolyte secondary battery 1 cooled in 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 stagnated between the electrodes (that is, in the nonaqueous electrolyte 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 air bubbles 80 are not discharged to the outside of the battery case 30. However, the state in which the air bubbles 80 are stagnant between the electrodes may cause a decrease in the battery performance. Therefore, the air bubbles 80 may be discharged to the outside between the electrodes. Therefore, the cooling step and the temperature raising step can be performed in a state where the inside of the battery case 30 is sealed.

  In addition, the heating rate in the heating step of the present embodiment is 0.5 ° C./min or less. As a result, a decrease in battery performance is further suppressed. The reason will be described later.

(Confirmation of battery internal resistance)
In the method of reusing a nonaqueous electrolyte secondary battery according to the present embodiment, preferably, the internal resistance of the test battery is checked after the completion of the temperature raising step. In this resistance checking step, it is checked that the change in the internal resistance of the nonaqueous electrolyte secondary battery 1 that has gone through the cooling step and the temperature raising step is less than a threshold value. The non-aqueous electrolyte secondary battery 1 in which the change in the internal resistance is less than the threshold value is appropriately reused because the decrease in battery performance is suppressed.

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

  In addition, for each of the cells according to Examples 1 to 7, the cooling step, the heating step, and the measurement of the reaction resistance increase rate were performed. In the cooling step, each of the cells (SOC: 0%) after storage described above is placed in a constant temperature bath, cooled at a cooling rate of 0.5 ° C./min to the cooling temperature described in Table 1, and then cooled to the cooling temperature. Stored for 2 hours while maintaining. In the heating 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 raising step was measured by an AC impedance measuring device (Solartron 1260 manufactured by Solartron) at an applied voltage of 10 mV and a measurement frequency range of 0.01 to 1 MHz, and returned to room temperature. By dividing the value of the reaction resistance after the above by the value of the comparative example, the rate of increase in the reaction resistance of each cell was measured.

  Next, overcharge determination was performed on each of the cells according to the comparative example and the examples 1 to 7. In the overcharge determination, a current of 10 C was applied to each cell under a temperature environment of -10 ° C, and charging was performed from 4 V until the separator was shut down. When the temperature rise of the battery case after the shutdown was less than 10 ° C., it was judged as “○”, and when it was 10 ° C. or more, it was judged as “×”.

  As shown in Table 1, in Examples 1 to 4, the heating rates in the heating step are all the same, and the cooling temperatures in the cooling step are different. When the comparative example and Examples 1 to 4 are compared, the cooling temperature in the cooling step is set to a temperature lower than the temperature IP at the change point of the gradient of the DC resistance (that is, a temperature lower than the freezing point of the nonaqueous electrolyte 10). It can be seen that the overcharge resistance was improved while the reaction resistance increase rate was 1.04% or less. It is considered that this is because the nonaqueous electrolyte 10 solidified and contracted in volume, and the bubbles 80 stagnated between the electrodes were 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 rates in the heating step are different. Comparing Examples 4 to 7, it can be seen that the rate of increase in the reaction resistance was increased and the overcharge resistance was not improved by increasing the heating rate in the heating step to more than 0.5 ° C./min. One possible reason for this is that if the heating rate is increased, bubbles may not be sufficiently removed from between the electrodes. Also, when the temperature raising temperature is increased, the concentration distribution of the supporting salt in the non-aqueous electrolyte 10 may vary, which may cause an increase in the resistance and the deposition 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.

  Note that the technology disclosed in the above embodiment is only an example. Therefore, the technology exemplified in the above embodiment can be changed. For example, the cooling conditions (for example, cooling temperature and cooling rate, etc.) in the cooling step and the temperature raising conditions (for example, temperature rising rate, etc.) in the temperature raising step depend on the configuration and material of the nonaqueous electrolyte secondary battery. Can change. Therefore, the various conditions exemplified in the above embodiment may be changed according to 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 body 60 Negative 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,
A non-aqueous electrolyte,
A battery case containing the electrode body and the non-aqueous electrolyte therein;
A method for reusing a non-aqueous electrolyte secondary battery comprising:
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 below the freezing point of the non-aqueous electrolyte,
The non-aqueous electrolyte secondary battery cooled to a temperature lower than 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 electrolyte inside the electrode assembly. A temperature raising step of causing air bubbles to be discharged to the outside of the electrode body,
A method of reusing a non-aqueous electrolyte secondary battery, comprising:

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