JP7356636B2 - Non-aqueous electrolyte secondary battery - Google Patents

Description

The present invention relates to a non-aqueous electrolyte secondary battery. Specifically, the present invention relates to a non-aqueous electrolyte secondary battery in which an electrode body and a non-aqueous electrolyte are housed in a battery case.

In recent years, non-aqueous electrolyte secondary batteries (hereinafter also referred to as "secondary batteries") such as lithium ion secondary batteries and nickel-metal hydride batteries have been widely used as power sources for various devices. Examples of uses of such secondary batteries include power sources for driving vehicles such as electric vehicles (EVs), hybrid vehicles (HVs), and plug-in hybrid vehicles (PHVs), and portable power sources for personal computers and mobile terminals. .

This type of secondary battery has, for example, a structure in which an electrode body and a nonaqueous electrolyte are housed in a battery case. The electrode body has a structure in which a positive electrode and a negative electrode are stacked with a separator interposed therebetween. Examples of the structure of this electrode body include a wound electrode body and a laminated electrode body. The wound electrode body is formed by winding a laminate in which a pair of positive electrode and negative electrode are stacked on top of each other with a separator interposed therebetween. On the other hand, a stacked electrode body is formed by sequentially stacking a plurality of positive electrodes and negative electrodes with a separator interposed therebetween.

When manufacturing a secondary battery having the above structure, a non-aqueous electrolyte is poured into the case after reducing the pressure inside the battery case housing the electrode body. Then, the battery case is kept open for a predetermined period of time to allow the non-aqueous electrolyte to penetrate into the inside of the electrode body (between the positive electrode and the negative electrode), and then the battery case is sealed. In such a manufacturing process, if the permeability of the non-aqueous electrolyte into the electrode body is low, an area of negative pressure will remain inside the electrode body, and the non-aqueous electrolyte will continue to permeate into the electrode body even after the case is sealed. , the internal space of the battery case (the space between the electrode body and the battery case) may become under negative pressure. In such a secondary battery, when the positive electrode and the negative electrode expand due to charging and discharging, it is difficult for the electrode body to expand outward, so that the gap between the positive electrode and the negative electrode tends to collapse. As a result, the non-aqueous electrolyte that has permeated between the positive electrode and the negative electrode may leak out of the electrode body, and the high rate characteristics may deteriorate.

Therefore, in recent years, there has been an increasing demand for technology that improves the permeability of non-aqueous electrolytes into electrode bodies. For example, Patent Document 1 proposes a technique in which tris phosphate and a nonionic surfactant are added to a nonaqueous electrolyte to increase the permeability of the nonaqueous electrolyte into the positive electrode.

Japanese Patent Application Publication No. 2015-201309

However, according to studies by the present inventors, it has been found that the technique described in Patent Document 1 has various disadvantages, and there remains room for improvement. Specifically, as in Patent Document 1, when a nonionic surfactant (for example, an ether surfactant) is added to a nonaqueous electrolyte, foaming (cavitation) occurs significantly when the liquid is injected into the battery case. There was a possibility that the non-aqueous electrolyte would overflow from the battery case during injection, significantly reducing productivity.

The present invention has been made in view of the above circumstances, and its purpose is to provide a technology that can improve the permeability of a non-aqueous electrolyte into the inside of an electrode body while suppressing the occurrence of cavitation during injection. It is to be.

In order to solve the above-mentioned problems, a non-aqueous electrolyte secondary battery disclosed herein is provided. In such a non-aqueous electrolyte secondary battery, an electrode body in which a sheet-shaped positive electrode and a sheet-shaped negative electrode are stacked with a separator interposed therebetween, and a non-aqueous electrolyte are housed in a battery case. In the nonaqueous electrolyte secondary battery disclosed herein, hexadecyltrimethylammonium bromide is dissolved in the nonaqueous electrolyte, and when the total amount of the nonaqueous electrolyte is 100 wt%, hexadecyl bromide The content of trimethylammonium is 0.1 wt% or more and less than 5 wt%.

As a result of various studies conducted by the present inventors, a non-aqueous electrolyte to which a cationic surfactant (cationic surfactant) is added is different from a non-aqueous electrolyte to which a non-ionic surfactant is added. In comparison, it was found that the degree of cavitation during injection was small. Among these cationic surfactants, hexadecyltrimethylammonium bromide (hereinafter also referred to as "CTAB") particularly suppresses cavitation during injection, and is suitable for use as a constituent material of the electrode body (i.e., It was found that the compatibility of the nonaqueous electrolyte with each of the separator, positive electrode, and negative electrode was significantly improved. The technology disclosed herein is based on such knowledge, and can improve the permeability of the non-aqueous electrolyte into the inside of the electrode body while suppressing the occurrence of cavitation. Note that even when CTAB is added to the non-aqueous electrolyte, if the amount added is too small, the permeability of the non-aqueous electrolyte may be insufficient. Furthermore, if the amount of CTAB added is too large, cavitation may occur during injection. From this viewpoint, in the technology disclosed herein, the content of CTAB is adjusted to 0.1 wt% or more and less than 5 wt% when the total amount of the nonaqueous electrolyte is 100 wt%.

FIG. 1 is a cross-sectional view schematically showing the internal configuration of a lithium ion secondary battery according to an embodiment. FIG. 1 is a perspective view schematically showing an electrode body of a lithium ion secondary battery according to an embodiment. It is a graph showing the results of permeability evaluation in test examples. Note that the vertical axis in FIG. 3 indicates the liquid level height (mm) of the non-aqueous electrolyte inside the battery case, and the horizontal axis indicates the elapsed time (sec) when the time when the injection is completed is 0 seconds.

Hereinafter, one embodiment of the non-aqueous electrolyte secondary battery disclosed herein will be described with reference to the drawings. Note that matters other than those specifically mentioned in this specification, which are necessary for implementing the technology disclosed herein, can be understood based on conventional technology in the relevant field. That is, the technology disclosed herein can be implemented based on the content explicitly disclosed in this specification and common technical knowledge in the field. Note that the following embodiments are not intended to limit the technology disclosed herein. Further, in the drawings shown in this specification, the same reference numerals are given to members and parts that have the same function. Further, the dimensional relationships (length, width, thickness, etc.) in each figure do not reflect actual dimensional relationships.

As used herein, the term "nonaqueous electrolyte secondary battery" refers to a general battery that uses a nonaqueous electrolyte as an electrolyte and can be repeatedly charged and discharged. A typical example of such a nonaqueous electrolyte secondary battery is a lithium ion secondary battery. This lithium ion secondary battery is a secondary battery that uses lithium (Li) ions as electrolyte ions (charge carriers) and charges and discharges by moving lithium ions between a positive electrode and a negative electrode. Furthermore, in this specification, the term "active material" refers to a material that reversibly absorbs and releases charge carriers.

1. Structure of Lithium Ion Secondary Battery FIG. 1 is a sectional view schematically showing the internal structure of a lithium ion secondary battery according to this embodiment. Moreover, FIG. 2 is a perspective view schematically showing the electrode body of the lithium ion secondary battery according to the present embodiment. Note that in each figure shown in this specification, the symbol X indicates the "width direction (of the lithium ion secondary battery)" and the symbol Z indicates the "height direction (of the lithium ion secondary battery)." However, these directions are determined for convenience of explanation, and are not intended to limit the installation mode when using the secondary battery disclosed herein.

(1) Overall Configuration As shown in FIG. 1, in a lithium ion secondary battery 100 according to the present embodiment, an electrode body 20 and a non-aqueous electrolyte 30 are housed in a battery case 10. Further, although a detailed description is omitted since the technology disclosed herein is not limited, this lithium ion secondary battery 100 includes a pair of electrode terminals 70 consisting of a positive electrode terminal 72 and a negative electrode terminal 74. . One end of these electrode terminals 70 is electrically connected to the electrode body 20 inside the battery case 10, and the other end is exposed to the outside of the battery case 10. This allows the electrode body 20 inside the battery case 10 to be electrically connected to external equipment (such as a motor or other secondary battery).

(2) Battery Case As described above, the battery case 10 is a container that houses the electrode body 20 and the non-aqueous electrolyte 30. The battery case 10 shown in FIG. 1 is a rectangular container with an internal space, and includes a box-shaped case body 12 with an open top, and a lid 14 that is a plate material that closes the top opening of the case body 12. ing. Further, the reference numeral 18 in FIG. 1 is a safety valve. By providing such a safety valve 18, the internal pressure of the battery case 10 can be released when the internal pressure rises above a predetermined level. Note that the battery case 10 is preferably made of a metal material that is lightweight and has good thermal conductivity (for example, aluminum, aluminum alloy, etc.).

Further, in this embodiment, a liquid injection port 16 is provided in the lid 14 of the battery case 10. As will be described in detail later, by attaching a liquid injection device to the liquid injection port 16 and injecting the non-aqueous electrolyte 30 after reducing the pressure inside the battery case 10, the non-aqueous electrolyte 30 penetrates into the inside of the electrode body 20. can be done. Then, the liquid injection port 16 is sealed after a sufficient amount of the non-aqueous electrolyte 30 has penetrated into the electrode body 20.

(3) Electrode Body As shown in FIG. 2, the electrode body 20 is formed by stacking a sheet-shaped positive electrode 40 and a sheet-shaped negative electrode 50 with a separator 60 in between. Specifically, the electrode body 20 in this embodiment is a wound electrode body formed by winding a laminate in which a long positive electrode 40 and a long negative electrode 50 are stacked on top of each other with a separator 60 in between. It is. A positive electrode active material layer 44 and a negative electrode active material layer 54, which will be described later, are laminated at the center of the wound electrode body 20 in the width direction A portion 20a is formed. Further, a positive electrode connection part 20b connected to the positive electrode terminal 72 is formed at one end of the wound electrode body 20 in the width direction X, and a negative electrode connection part 20b connected to the negative electrode terminal 74 is formed at the other end. A portion 20c is formed.

(a) Positive electrode Next, each member constituting the electrode body 20 will be explained. The positive electrode 40 includes an elongated positive electrode current collector foil 42 and a positive electrode active material layer 44 provided on the surface (for example, both surfaces) of the positive electrode current collector foil 42. The positive electrode active material layer 44 is not provided on one side edge of the positive electrode 40 in the width direction 46 are provided. When forming the wound electrode body 20, the positive electrode exposed portion 46 is rolled up so as to protrude from the negative electrode 50, which will be described later, to form the positive electrode connecting portion 20b. Note that as the materials constituting each of the positive electrode current collector foil 42 and the positive electrode active material layer 44, materials that can be used for conventionally known positive electrodes of lithium ion batteries can be used without particular restriction, and the technology disclosed herein can be used. The detailed explanation is omitted because it is not intended to limit.

(b) Negative Electrode On the other hand, the lithium ion secondary battery 100 according to the present embodiment uses a negative electrode 50 having substantially the same configuration as the positive electrode 40 described above. Specifically, the negative electrode 50 includes an elongated negative electrode current collector foil 52 and a negative electrode active material layer 54 provided on the surface (for example, both surfaces) of the negative electrode current collector foil 52. The negative electrode active material layer 54 is not provided on the other side edge of the negative electrode 50 in the width direction 56 are provided. When forming the wound electrode body 20, the negative electrode exposed portion 56 is rolled up in a state protruding from the positive electrode 40, thereby forming the negative electrode connecting portion 20c. Note that as the materials constituting each of the negative electrode current collector foil 52 and the negative electrode active material layer 54, materials that can be used for conventionally known negative electrodes of lithium ion batteries can be used without particular restrictions, and the technology disclosed herein is not limited. The detailed explanation will be omitted because it is not a real thing.

(c) Separator The separator 60 is an insulating member interposed between the positive electrode 40 and the negative electrode 50. The separator 60 has micropores through which charge carriers (lithium ions) can pass. A non-aqueous electrolyte 30, which will be described later, penetrates into the electrode body 20 and fills the micropores of the separator 60, thereby allowing charge carriers to move between the positive electrode 40 and the negative electrode 50. Note that for the separator 60 as well, materials that can be used in conventionally known lithium ion batteries can be used without particular restriction, and the technology disclosed herein is not limited, so a detailed explanation will be omitted.

(4) Non-aqueous electrolyte The non-aqueous electrolyte 30 is prepared by dissolving a supporting salt in a non-aqueous solvent. The non-aqueous electrolyte 30 is housed in the battery case 10 together with the electrode body 20 and permeates into the electrode body 20 . It should be noted that the non-aqueous electrolyte 30 does not necessarily have to all penetrate into the electrode body 20, and as shown in FIG. You can leave it there. By setting the injection amount of the non-aqueous electrolyte 30 so that this surplus electrolyte 32 is generated, when the non-aqueous electrolyte 30 in the electrode body 20 becomes insufficient during charging and discharging, the surplus electrolyte 32 can be poured into the electrode. It can be delivered into the body 20.

(a) Nonaqueous Solvent As the nonaqueous solvent contained in the nonaqueous electrolyte, any nonaqueous solvent that can be used in conventionally known lithium ion batteries can be used without particular limitation. Examples of such nonaqueous solvents include carbonate solvents, ether solvents, ester solvents, nitrile solvents, sulfone solvents, and lactone solvents. Suitable examples of these nonaqueous solvents include carbonate solvents such as ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), and ethylmethyl carbonate (EMC). Further, the non-aqueous solvent of the non-aqueous electrolyte 30 may be one using the above-mentioned materials alone or a mixture of two or more thereof. For example, from the viewpoint of suitably dissolving CTAB, which will be described later, a mixed solvent in which EC, DMC, and EMC are mixed at a predetermined ratio may be suitably used.

(b) Supporting salt As the supporting salt, any supporting salt that can be used in conventionally known lithium ion batteries can be used without particular limitation. Examples of such supporting salts include LiPF ₆ , LiBF ₄ , lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethane)sulfonimide (LiTFSI), and the like. Further, the molar concentration of the supporting salt contained in the non-aqueous electrolyte 30 is not particularly limited, and can be adjusted as appropriate depending on the configuration of other battery materials. The lower limit of the molar concentration of the supporting salt in the nonaqueous electrolyte 30 may be 0.5 mol/L or more, or 0.7 mol/L or more. On the other hand, the upper limit of the molar concentration of the supporting salt may be 5 mol/L or less, 2.5 mol/L or less, or 1.5 mol/L or less.

(c) Hexadecyltrimethylammonium bromide In the lithium ion secondary battery 100 according to the present embodiment, hexadecyltrimethylammonium bromide (CTAB) is dissolved in the nonaqueous electrolyte 30, and the nonaqueous It is characterized in that the content of CTAB is 0.1 wt% or more and less than 5 wt% when the total amount of the electrolytic solution 30 is 100 wt%. Thereby, cavitation when injecting the non-aqueous electrolyte 30 can be suitably suppressed, and the permeability of the non-aqueous electrolyte 30 into the inside of the electrode body 20 can be improved. This will be explained in detail below.

The above hexadecyltrimethylammonium bromide ((C ₁₆ H ₃₃ )N(CH ₃ ) ₃ Br) is a type of cationic surfactant. According to experiments and studies conducted by the present inventors, cationic surfactants have a higher degree of cavitation than conventional nonionic surfactants (nonionic surfactants) when nonaqueous electrolyte 30 is injected. is small, so there is little risk of non-aqueous electrolyte 30 overflowing from battery case 10. Among cationic surfactants, CTAB has the characteristics of causing less cavitation during injection and improving the compatibility of the non-aqueous electrolyte 30 with the constituent materials of the electrode body 20.

In the lithium ion secondary battery 100 according to the present embodiment, the content of CTAB is set to 0.1 wt% or more and less than 5 wt% when the total amount of the nonaqueous electrolyte 30 is 100 wt%. Specifically, even when CTAB is used, if the content is too low, it is difficult to sufficiently improve the permeability of the non-aqueous electrolyte 30 into the electrode body 20. Therefore, in this embodiment, the content of CTAB is set to 0.1 wt% or more. Moreover, from the viewpoint of exhibiting more suitable permeability, the content of CTAB is preferably 0.2 wt% or more, and more preferably 0.3 wt% or more. On the other hand, even when CTAB is used, if its content is too large, cavitation may occur during injection. From this viewpoint, in this embodiment, the upper limit of the content of CTAB is set to less than 5 wt%. In addition, from the viewpoint of reliably preventing the occurrence of cavitation, the upper limit of the content of CTAB is preferably 4 wt% or less, more preferably 3 wt% or less, even more preferably 2 wt% or less, and particularly preferably 1 wt% or less.

In addition to improving the permeability of the non-aqueous electrolyte 30 described above, CTAB can also exhibit various advantageous effects. Specifically, when the lithium ion secondary battery 100 according to the present embodiment is charged and discharged, CTAB is polymerized due to the electric charge added to the electrode body 20, and the non-aqueous electrolyte 30 in the electrode body 20 is gelled. do. This further suppresses outflow of the non-aqueous electrolyte 30 to the outside of the electrode body 20, and more preferably prevents deterioration of high rate characteristics. Furthermore, when the non-aqueous electrolyte 30 is gelled, it is also possible to prevent the electrode active material from falling off from the electrode current collector foil, deforming the electrode body 20, and the like. In addition, in a typical lithium ion secondary battery, a portion of the non-aqueous electrolyte may decompose during charging and discharging, and an SEI film may be formed on the surface of the negative electrode, thereby stabilizing the negative electrode. On the other hand, when the gelled non-aqueous electrolyte 30 is in contact with the surface of the negative electrode 50 as in the present embodiment, the formation of the SEI film is promoted, so that the negative electrode 50 is more preferably stabilized. can.

Note that the technology disclosed herein does not limit the addition of surfactants other than CTAB to the nonaqueous electrolyte. That is, the non-aqueous electrolyte may contain cationic surfactants and anionic surfactants other than CTAB, as long as they do not impede the effects of the technology disclosed herein (typically cavitation does not occur during injection). , may contain a nonionic surfactant. By adding a small amount of these surfactants to an extent that cavitation does not occur during injection, the permeability of the non-aqueous electrolyte into the electrode body can be further improved. As for the surfactants other than CTAB, detailed explanations will be omitted since conventionally known surfactants can be used without any particular restrictions.

2. Manufacturing of Lithium Ion Secondary Battery Next, a method for manufacturing the lithium ion secondary battery 100 according to the present embodiment will be described. The manufacturing method according to this embodiment includes an assembly manufacturing process, a liquid injection process, and a sealing process. Each step will be explained below.

(1) Assembly manufacturing process In the manufacturing method according to this embodiment, first, a battery assembly in which the electrode body 20 is housed in the battery case 10 is manufactured. Specifically, in this step, first, the positive electrode terminal 20b of the electrode body 20 and the positive electrode terminal 72 of the lid body 14 are connected, and the negative electrode terminal 20c and the negative electrode terminal 74 are connected. Thereby, the electrode body 20 and the lid body 14 are integrated. Note that conventionally known welding means such as ultrasonic welding can be used to connect the positive electrode terminal 72 and the positive electrode connection portion 20b (the negative electrode terminal 74 and the negative electrode connection portion 20c). Then, after housing the electrode body 20 in the internal cavity of the case body 12 and closing the top opening of the case body 12 with the lid body 14, the case body 12 and the lid body 14 are welded. As a result, a battery assembly is manufactured in which the materials except for the non-aqueous electrolyte 30 are housed in the battery case 10. Note that in this step, any conventionally known method can be used without particular restriction, and the procedure is not limited to the above-mentioned procedure.

(2) Liquid injection step Next, in this embodiment, the non-aqueous electrolyte 30 in which CTAB is dissolved is poured into the battery case 10. At this time, since CTAB is difficult to dissolve in the non-aqueous electrolyte 30, it is required to perform a dissolution process to sufficiently dissolve it in the non-aqueous electrolyte 30 before injection. To dissolve CTAB, it is preferable to use a conventionally known stirring device and stir and mix while adjusting the temperature of the non-aqueous electrolyte 30 as appropriate.

When injecting the non-aqueous electrolyte 30 into the battery case 10, first, a liquid injection device is attached to the liquid injection port 16 of the battery case 10 (lid 14), and the inside of the battery case 10 is suctioned to reduce the pressure. Perform depressurization treatment.

Next, in this step, the non-aqueous electrolyte 30 is injected into the battery case 10 from the liquid injection device attached to the liquid injection port 16, and then held for a predetermined period of time. As a result, the non-aqueous electrolyte 30 permeates into the reduced pressure of the electrode body 20 (ie, between the positive electrode 40 and the negative electrode 50). At this time, in this embodiment, since the permeability of the non-aqueous electrolyte 30 into the electrode body 20 is improved by CTAB, a sufficient amount of the non-aqueous electrolyte 30 permeates into the electrode body 20 and penetrates into the electrode. Negative pressure inside body 20 is appropriately relieved. Further, in the manufacturing method according to the present embodiment, since the nonaqueous electrolyte 30 in which less than 5 wt % of CTAB is dissolved is used, overflow of the nonaqueous electrolyte 30 due to cavitation during injection can be suitably prevented.

In addition, from the perspective of more appropriately preventing overflow of the non-aqueous electrolyte 30 due to cavitation, in this step, rather than injecting the entire amount of the non-aqueous electrolyte 30 to be injected at once, It is preferable to inject the electrolyte solution in multiple doses. Furthermore, when such split injection is performed, mainly the first injected non-aqueous electrolyte permeates into the electrode body 20 . For this reason, it is preferable to dissolve CTAB only in the non-aqueous electrolyte that is first injected. In this case, since it is not necessary to add a surfactant to the non-aqueous electrolyte during the second and subsequent injections where the liquid level after injection tends to be high, cavitation can be suppressed more suitably. In addition, in the lithium ion secondary battery 100 produced by such a procedure, the non-aqueous electrolyte 30 that has permeated into the electrode body 20 is more likely to be absorbed by the excess electrolyte present between the electrode body 20 and the battery case 10. The concentration of CTAB is higher than that of 32.

(3) Sealing process In this process, the liquid injection port 16 is sealed and the battery case 10 is hermetically sealed. As a result, a lithium ion secondary battery 100 (see FIG. 1) in which the electrode body 20 and the non-aqueous electrolyte 30 are housed in the battery case 10 is constructed. At this time, in the manufacturing method according to the present embodiment, the non-aqueous electrolyte 30 has sufficiently penetrated into the electrode body 20 in the liquid injection step, and the negative pressure inside the electrode body 20 has been eliminated, so that the battery After the case 10 is sealed, the non-aqueous electrolyte 30 can be prevented from penetrating into the electrode body 20 and the internal space of the battery case 10 can be prevented from becoming under negative pressure. Thereby, when the positive electrode 40 and the negative electrode 50 expand due to charging and discharging, the electrode body 20 can be expanded outward (toward the battery case 10 side). As a result, the gap between the positive electrode 40 and the negative electrode 50 is prevented from collapsing and the non-aqueous electrolyte 30 flows out of the electrode body 20, and deterioration of high rate characteristics due to a shortage of the non-aqueous electrolyte 30 can be suppressed.

3. Other Embodiments An embodiment of the technology disclosed herein has been described above. Note that the above-described embodiment shows an example to which the technology disclosed herein is applied, and does not limit the technology disclosed herein.

For example, in the embodiments described above, a wound electrode body is used as the electrode body. However, the electrode body may be one in which a positive electrode and a negative electrode are stacked on top of each other with a separator interposed therebetween, and is not limited to a wound electrode body. Another example of such an electrode body is a laminated electrode body in which a plurality of positive electrodes and negative electrodes are sequentially laminated with a separator interposed therebetween. However, when comparing a wound electrode body and a laminated electrode body, the wound electrode body is more difficult to penetrate the non-aqueous electrolyte, so that the effects of the technology disclosed herein can be exhibited more favorably.

Furthermore, in the above-described embodiments, a lithium ion secondary battery is used as the nonaqueous electrolyte secondary battery, but the technology disclosed herein is not limited to lithium ion secondary batteries, and is applicable to other nonaqueous electrolyte secondary batteries. It can also be applied to liquid secondary batteries (for example, nickel-metal hydride batteries).

[Test example]
Test examples related to the present invention will be explained below. Note that the contents of the test examples described below are not intended to limit the present invention.

1. Preparation of each sample In this test example, six types of lithium ion secondary batteries (samples 1 to 6) with different compositions of non-aqueous electrolytes were prepared. Each sample will be explained below.

(1) Sample 1
In the production of this sample, first, a sheet-like positive electrode was prepared, in which positive electrode active material layers were provided on both sides of a positive electrode current collector (aluminum foil). The positive electrode active material layer of this positive electrode includes a positive electrode active material, a conductive material, and a binder. In addition, lithium nickel cobalt manganese composite oxide (LiNi _0.33 Co _0.33 Mn _0.33 O ₂ ) was used as the positive electrode active material, acetylene black (AB) was used as the conductive material, and acetylene black (AB) was used as the binder. Polyvinylidene fluoride (PVdF) was used. On the other hand, the negative electrode used in this test example was a sheet-like negative electrode in which negative electrode active material layers were provided on both sides of a negative electrode current collector (copper foil). Note that the negative electrode active material layer contains a negative electrode active material (graphite), a binder (SBR: styrene-butadiene copolymer), and a thickener (CMC: carboxymethyl cellulose).

Next, a laminate in which a positive electrode and a negative electrode were laminated with a separator interposed therebetween was formed, and the laminate was wound to produce a wound electrode body. A battery assembly was constructed by housing this wound electrode body inside a transparent glass case. After reducing the pressure inside the case of this battery assembly, 41 g of non-aqueous electrolyte was injected so that the liquid level reached a height of 55 mm from the bottom of the case. Then, after holding the liquid injection port in an open state, the liquid injection port was sealed and the case was hermetically sealed, thereby constructing a lithium ion secondary battery (sample 1) for evaluation testing. The non-aqueous electrolyte used was a mixed solvent containing EC, DMC, and EMC at a volume ratio of 3:4:3 and a supporting salt (LiPF ₆ ) at a concentration of about 1 mol/L. .

Here, in Sample 1, hexadecyltrimethylammonium bromide (CTAB) was dissolved in the nonaqueous electrolyte having the composition described above. Note that the amount of CTAB added in Sample 1 was set to 0.3 wt% with respect to the total amount of nonaqueous electrolyte 100 wt%.

(2) Sample 2
In Sample 2, a test lithium ion secondary battery was constructed under the same conditions as Sample 1, except that the amount of CTAB added was changed to 0.1 wt% with respect to the total amount of nonaqueous electrolyte of 100 wt%.

(3) Sample 3
In Sample 3, a test lithium ion secondary battery was constructed under the same conditions as Sample 1, except that the amount of CTAB added was changed to 1 wt% with respect to the total amount of nonaqueous electrolyte of 100 wt%.

(4) Sample 4
In Sample 4, a test lithium ion secondary battery was constructed under the same conditions as Sample 1, except that the amount of CTAB added was changed to 5 wt% with respect to the total amount of non-aqueous electrolyte of 100 wt%.

(5) Sample 5
In sample 5, after CTAB was housed in the case together with the wound electrode body when constructing the battery assembly, a non-aqueous electrolyte containing no CTAB was injected into the case. The amount of CTAB accommodated at this time was set to 0.3 wt% with respect to the total amount of non-aqueous electrolyte of 100 wt%. Note that, as described above, a test lithium ion secondary battery was constructed under the same conditions as Sample 1, except that CTAB and a nonaqueous electrolyte were mixed in the battery case.

(6) Sample 6
In Sample 6, a test lithium ion secondary battery was constructed under the same conditions as Sample 1, except that a non-aqueous electrolyte containing no CTAB was used.

2. Evaluation of permeability of non-aqueous electrolyte In this test example, the permeability of non-aqueous electrolyte in each sample mentioned above was evaluated. Specifically, as described above, after the non-aqueous electrolyte was injected to a height of 55 mm, the test battery was visually observed until the liquid level of the non-aqueous electrolyte did not drop. FIG. 3 shows the change in liquid level height over time for each sample, and Table 1 shows the liquid level height 1000 seconds after injection.

As shown in Figure 3, in sample 6, the rate at which the liquid level decreases (i.e., the non-aqueous electrolyte permeates into the electrode body) decreases significantly from around 400 seconds after injection, and after 800 seconds The rate of penetration of the non-aqueous electrolyte into the electrode body further decreased after . As shown in Table 1, in this sample 6, the liquid level height 1000 seconds after injection was 31.8 mm. From this result, it is predicted that in sample 6, the nonaqueous electrolyte continues to slowly permeate into the electrode body even after the battery case is sealed, and the internal space of the battery case becomes negative pressure.

On the other hand, in Samples 1 to 3, the non-aqueous electrolyte continued to penetrate into the electrode body even after 400 seconds had passed since injection, and the liquid level height 1000 seconds after injection was significantly higher than in Sample 6. became low. From this, it was found that by dissolving CTAB in the non-aqueous electrolyte, the non-aqueous electrolyte becomes more compatible with the constituent materials of the electrode body, and the permeability of the non-aqueous electrolyte into the inside of the electrode body can be improved. Ta. In sample 4, cavitation occurred during injection, and the non-aqueous electrolyte overflowed from the injection port, making it impossible to evaluate permeability. From this, it was found that the amount of CTAB added to the non-aqueous electrolyte needs to be less than 5 wt%.

In addition, in sample 5, although the same amount of CTAB as in sample 1 was added, as with sample 6, almost no non-aqueous electrolyte penetrated into the electrode body over time, and after 1000 seconds The liquid level height after that was 31.8 mm. Then, when the inside of the case was checked after 3600 seconds, CTAB that was not dissolved in the non-aqueous electrolyte was present. From this, it was found that when adding CTAB to the non-aqueous electrolyte, it was necessary to dissolve CTAB in the non-aqueous electrolyte before injection.

Although the present invention has been described in detail above, the above description is merely an example. That is, the technology disclosed herein includes various modifications and changes of the above-described specific example.

10 Battery case 12 Case body 14 Lid 16 Liquid injection port 18 Safety valve 20 Wound electrode body 20a Core part 20b Positive electrode connection part 20c Negative electrode connection part 30 Non-aqueous electrolyte 32 Surplus electrolyte 40 Positive electrode 42 Positive electrode current collector foil 44 Positive electrode active Material layer 46 Positive electrode exposed portion 50 Negative electrode 52 Negative electrode current collector foil 54 Negative electrode active material layer 56 Negative electrode exposed portion 60 Separator 70 Electrode terminal 72 Positive electrode terminal 74 Negative electrode terminal 100 Lithium ion secondary battery

Claims (3)

A non-aqueous electrolyte secondary battery in which an electrode body in which a sheet-like positive electrode and a sheet-like negative electrode are stacked with a separator interposed therebetween, and a non-aqueous electrolyte are housed in a battery case,
The negative electrode includes a negative electrode active material layer containing graphite as a negative electrode active material,
Hexadecyltrimethylammonium bromide is dissolved in the non-aqueous electrolyte,
A nonaqueous electrolyte secondary battery, wherein the content of the hexadecyltrimethylammonium bromide is 0.1 wt% or more and less than 5 wt% when the total amount of the nonaqueous electrolyte is 100 wt%. The non-aqueous electrolyte secondary battery according to claim 1, wherein the positive electrode includes a positive electrode active material layer containing lithium nickel cobalt manganese composite oxide as a positive electrode active material. The nonaqueous electrolyte secondary battery according to claim 1 or 2, wherein the electrode body is a wound electrode body in which the positive electrode, the negative electrode, and the separator are wound.

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