JP6697687B2 - Non-aqueous electrolyte secondary battery - Google Patents

Description

  The present invention relates to a lithium ion secondary battery and other non-aqueous electrolyte secondary batteries.

A non-aqueous electrolyte secondary battery such as a lithium ion secondary battery is a battery that is preferable as a high output power source for driving a vehicle such as an electric vehicle or a hybrid vehicle because it is lightweight and has a high energy density.
This type of battery is typically a positive electrode in which a positive electrode mixture layer containing a positive electrode active material as a main component is formed on a positive electrode current collector made of aluminum foil or the like, and a negative electrode current collector made of copper foil or the like. The negative electrode, on which the negative electrode mixture layer containing the negative electrode active material as a main component is formed, is provided with a laminated or wound electrode body having a shape of being alternately laminated with a separator interposed therebetween. Then, for the purpose of further improving the battery performance, studies and improvements have been made on the configuration and form of members constituting such an electrode body, for example, the positive electrode mixture layer and the negative electrode mixture layer.
As an example thereof, in Patent Documents 1 and 2, in addition to a carbon material such as graphite, which is a negative electrode active material, particles made of inorganic compounds such as Al ₂ O ₃ , SiO ₂ , and ZrO ₂ that do not participate in the battery reaction are used. Disclosed is a negative electrode mixture layer for a lithium ion secondary battery, which is configured by adding the inorganic filler (filler). By adding such an inorganic filler to the negative electrode mixture layer, it is possible to increase the mechanical strength of the negative electrode mixture layer and improve the ion conductivity in the electrode to improve the internal resistance of the battery (for example, when using a high rate). The degree of increase in resistance) can be reduced.

JP, 10-255807, A JP, 2008-041465, A JP, 2016-131128, A JP, 2014-035939, A

  However, the present inventor has found that when an inorganic filler is added to the negative electrode mixture layer, the internal resistance of the battery can be reduced, but the input/output characteristics deteriorate (deteriorate). Therefore, the present invention was created to solve the above-mentioned problems relating to a non-aqueous electrolyte secondary battery provided with an electrode body having a negative electrode mixture layer containing an inorganic filler. It is an object of the present invention to provide a non-aqueous electrolyte secondary battery capable of suppressing the deterioration of the input/output characteristics while suppressing the increase in IV resistance). Moreover, it aims at providing the method of manufacturing such a non-aqueous electrolyte secondary battery.

  The present inventor has conducted various studies focusing on the properties of various members constituting a non-aqueous electrolyte secondary battery provided with an electrode body having a negative electrode mixture layer containing an inorganic filler. Then, inside the battery case, the wettability of the surface on the electrode body side of the insulating film arranged to prevent direct contact between the battery case and the electrode body (the non-aqueous electrolytic solution existing in the battery case It has been found that the deterioration of the input/output characteristics can be prevented by improving the wettability with respect to the above.

That is, as one mode for achieving the above object, the present invention provides a non-aqueous electrolyte secondary battery having the following configuration. That is, the non-aqueous electrolyte secondary battery disclosed herein is
An electrode body having a positive electrode having a positive electrode mixture layer containing a positive electrode active material on a positive electrode current collector, and a negative electrode having a negative electrode mixture layer containing a negative electrode active material on a negative electrode current collector,
Non-aqueous electrolyte,
A battery case containing the electrode body and the non-aqueous electrolyte therein,
An insulating film arranged between an inner wall of the battery case and the electrode body, the insulating film blocking direct contact between the battery case and the electrode body,
Equipped with. And, in the non-aqueous electrolyte secondary battery disclosed herein,
The negative electrode mixture layer contains an inorganic filler composed of an inorganic compound that does not participate in a battery reaction,
The insulating film has improved wettability with respect to the non-aqueous electrolyte on the surface facing the electrode body as compared with the surface facing the inner wall of the battery case.

In the non-aqueous electrolyte secondary battery having such a configuration, since the negative electrode mixture layer contains the inorganic filler, the internal resistance of the battery (for example, an increase in IV resistance when using a high rate) is reduced, and the negative electrode mixture does not include the inorganic filler. It can be reduced compared to the case where layers are adopted.
Furthermore, in the non-aqueous electrolyte secondary battery of this configuration, the surface of the insulating film (typically, an insulating film made of a synthetic resin such as polyolefin) facing the electrode body (hereinafter referred to as Wettability of the "surface" also to the non-aqueous electrolyte is higher (improved) than the surface of the side facing the inner wall of the battery case (hereinafter, also referred to as "outer surface" of the insulating film). It is characterized by
The present inventor has improved the wettability of the inner surface side of the insulating film to the non-aqueous electrolyte by subjecting the inner surface side of the insulating film to surface treatment such as corona discharge treatment, thereby improving the input/output characteristics. It was found that the decrease can be suppressed. That is, according to the non-aqueous electrolyte secondary battery of the present configuration, it is possible to reduce internal resistance of the battery (for example, increase in IV resistance when using a high rate) and also suppress deterioration in input/output characteristics.
In addition, although the secondary batteries provided with the insulating film are described in the above Patent Documents 3 to 4, they do not disclose the object or configuration of the present invention.

Therefore, the present invention provides, as another aspect, a method for producing the non-aqueous electrolyte secondary battery disclosed herein. That is, the manufacturing method disclosed here is
An electrode body having a positive electrode having a positive electrode mixture layer containing a positive electrode active material on a positive electrode current collector, and a negative electrode having a negative electrode mixture layer containing a negative electrode active material on a negative electrode current collector,
Non-aqueous electrolyte,
A battery case containing the electrode body and the non-aqueous electrolyte therein,
An insulating film arranged between an inner wall of the battery case and the electrode body, the insulating film blocking direct contact between the battery case and the electrode body,
A method of manufacturing a non-aqueous electrolyte secondary battery comprising:
Then, in the manufacturing method disclosed herein, the negative electrode mixture layer contains an inorganic filler made of an inorganic compound that does not participate in a battery reaction, and as the insulating film, a corona discharge is formed on the surface facing the electrode body. By using a surface treatment such as a treatment, an insulating film having improved wettability with respect to the non-aqueous electrolyte on the surface facing the electrode body as compared with the surface facing the battery case inner wall is used. It is characterized by doing.

It is an exploded perspective view which shows typically the structure of the nonaqueous electrolyte secondary battery (lithium ion secondary battery) which concerns on one Embodiment. It is a figure which shows typically the structure inside the case of the nonaqueous electrolyte secondary battery (lithium ion secondary battery) which concerns on one Embodiment. It is a figure which shows the winding type electrode body of the non-aqueous electrolyte secondary battery (lithium ion secondary battery) which concerns on one Embodiment.

Hereinafter, embodiments according to the present invention will be described with reference to the drawings. It is to be noted that matters other than matters particularly referred to in the present specification and matters necessary for carrying out the present invention (for example, a general configuration and manufacturing process of a battery that does not characterize the present invention) are in the relevant field. It can be understood as a matter of design by those skilled in the art based on the conventional technology. The present invention can be carried out based on the contents disclosed in this specification and the common general technical knowledge in the field. Further, in the following drawings, the same reference numerals are given to the members/sites that have the same effect. Further, the dimensional relationships (length, width, thickness, etc.) in each drawing do not reflect the actual dimensional relationships.
In the present specification, when the numerical range is described as A to B (A and B are arbitrary numerical values), it is the same as a general interpretation and means A or more and B or less. ..

In the present specification, the “non-aqueous electrolyte secondary battery” refers to a secondary battery including one non-aqueous (that is, organic solvent-based) electrolytic solution. Here, the "secondary battery" generally refers to an electricity storage device that can be repeatedly charged and discharged, and is a term that includes so-called storage batteries such as lithium ion secondary batteries and sodium ion secondary batteries, and electricity storage elements such as electric double layer capacitors. ..
The “lithium ion secondary battery” refers to a secondary battery in which lithium ions in the non-aqueous electrolyte carry charge transfer. Further, the "electrode body" refers to a structure that mainly forms a battery including a positive electrode, a negative electrode, and a porous insulating layer that can function as a separator between the positive and negative electrodes. The “positive electrode active material” or the “negative electrode active material” is capable of reversibly occluding and releasing a substance responsible for a battery reaction, specifically, a chemical species as a charge carrier (lithium ion in a lithium ion secondary battery). Refers to a compound.
Hereinafter, the present invention will be described in more detail with reference to a lithium-ion secondary battery, which is a typical example of a rectangular non-aqueous electrolyte secondary battery including a flat box-shaped (square) battery case. It should be noted that the present invention is not intended to be limited to those described in such embodiments.

  FIG. 1 is an exploded perspective view schematically showing the configuration of the lithium-ion secondary battery according to this embodiment. FIG. 2 is a diagram schematically showing the internal structure of the case of the lithium-ion secondary battery 100 according to this embodiment. As shown in FIGS. 1 and 2, the lithium-ion secondary battery 100 according to the present embodiment roughly includes an electrode body 80, a battery case 30, and an insulating film 10.

  As shown in FIGS. 2 and 3, the electrode body 80 according to the present embodiment is formed by laminating and winding a positive electrode (positive electrode sheet) 50, a negative electrode (negative electrode sheet) 60, and two separators 70 and 72. It is a flat wound electrode body 80. In the wound electrode body 80, the separator 70 is located on the outermost surface (the outermost surface and the exposed surface). The electrode body 80 is not limited to the wound type electrode body, and may be a laminated type electrode body.

  As shown in FIG. 3, the positive electrode sheet 50 has a long positive electrode current collector 52 (positive electrode core material). Further, the positive electrode sheet 50 has a positive electrode composite material layer non-forming portion (non-coated portion) 53 and a positive electrode composite material layer 54. The positive electrode composite material layer non-forming portion 53 is provided along the edge portion on one side in the width direction of the positive electrode current collector 52. In the present embodiment, the positive electrode mixture layer 54 is formed on both surfaces of the positive electrode current collector 52, but may be formed on only one surface of the positive electrode current collector 52.

  The positive electrode mixture layer 54 may typically have a form in which a positive electrode active material and a conductive material are bonded to each other by a binder (binding agent) and bonded to the positive electrode current collector 52. Such a positive electrode sheet 50 is typically, for example, a positive electrode paste (slurry or ink-like composition, which is a paste-like composition obtained by dispersing a positive electrode active material, a conductive material and a binder in an appropriate solvent). Is included on the surface of the positive electrode current collector 52 excluding the portion 53 where the positive electrode mixture layer is not formed, and is then dried to remove the solvent. As the positive electrode current collector 52, a conductive member made of a metal having good conductivity (eg, aluminum, nickel, titanium, stainless steel) can be preferably used. Here, aluminum foil is used as the positive electrode current collector 52.

As the positive electrode active material, a lithium transition metal composite oxide containing a lithium element and one or more transition metal elements can be preferably used, which is a material capable of inserting and extracting lithium ions. For example, a lithium manganese composite oxide having a spinel crystal structure (LiMn ₂ O ₄ ), a lithium manganese nickel composite oxide having a spinel structure in which a part of manganese is replaced with nickel (LiNi _x Mn _2-x O ₄ , where 0 <x <2), further Co other lithium-manganese-nickel-containing composite oxide having a spinel crystal structure containing a transition metal element _{(LiNi x Me y Mn 2-} x-y O 4, where Me is, Co, Ti, Fe , W, etc., and at least one transition metal element, such as 0<x+y<2). As another preferable example, a lithium-containing composite oxide having a so-called ternary layered crystal structure, such as a lithium nickel cobalt manganese composite oxide (for example, LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ), Alternatively, polyanion compounds (eg, LiFePO ₄ , LiMnPO ₄ ) and the like can be mentioned.

  The conductive material may be any material conventionally used in this type of lithium ion secondary battery, and examples thereof include carbon powder and carbon materials such as carbon fiber. As the carbon powder, various carbon powders such as carbon black and graphite powder can be used. Such conductive materials may be used alone or in combination of two or more kinds as appropriate.

As the binder, the same binder as that used for the positive electrode of a general lithium ion secondary battery can be appropriately adopted. Specifically, a polymer having a property capable of being uniformly dissolved or dispersed in the solvent forming the positive electrode paste can be used as the binder. A suitable example is polyvinylidene fluoride (PVDF).
As the solvent in which the material forming the positive electrode mixture layer 54 is dispersed, both an aqueous solvent and a non-aqueous solvent (organic solvent) can be used as long as they are suitable for the properties of the binder used. A suitable example is N-methyl-2-pyrrolidone.
Although not particularly limited, the content of the conductive material with respect to 100 parts by mass of the positive electrode active material may be, for example, 1 to 20 parts by mass (preferably 5 to 15 parts by mass). Further, the content of the binder with respect to 100 parts by mass of the positive electrode active material can be, for example, 0.5 to 10 parts by mass.

  As shown in FIG. 3, the negative electrode sheet 60 has a long negative electrode current collector 62 (negative electrode core material). Further, the negative electrode sheet 60 has a negative electrode composite material layer non-forming portion (non-coated portion) 63 and a negative electrode composite material layer 64. The negative electrode mixture layer non-formed portion 63 is provided along the edge portion of the negative electrode current collector 62 on one side in the width direction. In the present embodiment, the negative electrode mixture layer 64 is formed on both surfaces of the negative electrode current collector 62, but may be formed on only one surface of the negative electrode current collector 62.

  The negative electrode mixture layer 64 may typically have a form in which the negative electrode active materials are bonded to each other with a binder (binder) and are bonded to the negative electrode current collector 62. Such a negative electrode sheet 60 is, for example, a paste obtained by dispersing a negative electrode active material, a binder, and an inorganic filler described below in a suitable solvent (for example, water or N-methyl-2-pyrrolidone, preferably water). The composition can be prepared by supplying a negative electrode paste (including a slurry and an ink composition), which is a composition, to the surface of the negative electrode current collector 62 and then drying it to remove the solvent. As the negative electrode current collector 62, a conductive member made of a metal having good conductivity (eg, copper, nickel, titanium, stainless steel) can be preferably used. Here, a copper foil is used as the negative electrode current collector 62.

  The negative electrode active material is not particularly limited, and one kind of various materials known to be usable as the negative electrode active material of this kind of lithium ion secondary battery is used alone or in combination of two or more kinds (mixed). Alternatively, it can be used as a complex). Suitable examples include carbon-based materials such as graphite, non-graphitizable carbon (hard carbon), and easily graphitizable carbon (soft carbon). Of these, a graphite material, particularly a material in which amorphous carbon is arranged on at least a part of the surface, can be preferably used. In addition to such carbon-based materials, lithium transition metal composite oxides such as lithium titanium composite oxide and lithium transition metal composite nitride can also be used.

As the binder, the same binder as that used for the negative electrode of a general lithium ion secondary battery can be appropriately adopted. A preferred example is styrene butadiene rubber (SBR).
Although not particularly limited, the content of the binder with respect to 100 parts by mass of the negative electrode active material may be, for example, 0.5 to 10 parts by mass.

  Moreover, the negative electrode mixture layer 64 may include a thickener. As the thickener, the same binders as above may be used, and examples thereof include cellulose-based polymers such as methyl cellulose (MC), carboxymethyl cellulose (CMC), and cellulose acetate phthalate (CAP), polyvinyl alcohol ( Water-soluble or water-dispersible polymers such as PVA) may be employed.

The negative electrode mixture layer 64 disclosed herein is characterized by containing an inorganic filler. Here, the inorganic filler is composed of an inorganic compound that does not participate in the battery reaction (that is, does not function as an active material). Typical examples include inorganic oxide (ceramic) particles such as Al ₂ O ₃ , SiO ₂ , ZrO ₂ , and MgO. The size (particle diameter) of the inorganic filler is not particularly limited, but it is preferable to use an inorganic filler having an average particle diameter based on the laser diffraction method of about 10 μm or less (for example, 1 μm to 5 μm). By adding such an inorganic filler to the negative electrode mixture layer, the liquid retention property and ionic conductivity in the electrode body are improved, and a battery having low internal resistance can be realized. Also, the mechanical strength of the negative electrode mixture layer can be improved.
Although not particularly limited, the content of the inorganic filler with respect to 100 parts by mass of the negative electrode active material is appropriately about 0.1 to 20 parts by mass, and more preferably 1 to 10 parts by mass.

  The separators 70 and 72 are members that separate the positive electrode sheet 50 and the negative electrode sheet 60. The separators 70 and 72 are configured to have a non-aqueous electrolyte holding function and a shutdown function. As the separators 70 and 72, a porous film made of synthetic resin such as polyethylene (PE), polypropylene (PP), polyester, cellulose and polyamide can be used. Of these, a porous film made of a polyolefin resin such as PE or PP is preferable. The separators 70 and 72 may have a single layer structure composed of a single porous film, and two or more kinds of porous films having different materials and properties (for example, average thickness and porosity) are laminated. It may have a structure (for example, a three-layer structure in which a PP layer is laminated on both surfaces of a PE layer).

The wound electrode body 80 according to the present embodiment is manufactured by laminating the positive electrode sheet 50 and the negative electrode sheet 60 with the separators 70 and 72 interposed therebetween and winding them into a flat shape, as in the conventional one. can do.
As shown in FIG. 3, in the present embodiment, the width b1 of the negative electrode mixture layer 64 is slightly wider than the width a1 of the positive electrode mixture layer 54. Further, the widths c1 and c2 of the separators 70 and 72 are slightly wider than the width b1 of the negative electrode mixture layer 64 (c1&c2>b1>a1). The positive electrode sheet 50, the negative electrode sheet 60, and the separators 70 and 72 are laminated in the order of the positive electrode sheet 50, the separator 70, the negative electrode sheet 60, and the separator 72 in the same length direction. Further, the positive electrode composite material layer non-formed portion (non-coated portion) 53 of the positive electrode sheet 50 and the negative electrode composite material layer non-formed portion (non-coated portion) 63 of the negative electrode sheet 60 are arranged in the width direction of the separators 70 and 72. They are stacked so that they stick out on opposite sides. The stacked sheet materials are wound around a winding axis set in the width direction.

  The insulating film 10 that separates the electrode body 80 and the battery case 30 is disposed between the wound electrode body 80 and the battery case 30. The insulating film 10 prevents direct contact between the wound electrode body 80 and the battery case 30, and ensures electrical insulation between the electrode body 80 and the battery case 30. In the present embodiment, the insulating film 10 is formed in a bottomed bag shape with one end (the upper end side corresponding to the opening of the case body 32) opened so that the wound electrode body 80 is accommodated. There is. The shape of the insulating film 10 is not limited to a bag shape as long as it can insulate the electrode body 80 from the battery case 30, and may be, for example, a tubular film or a flat film.

The material of the insulating film 10 may be any material that can function as an insulating member, and for example, a resin material such as polyolefin (eg, polypropylene (PP), polyethylene (PE)) can be preferably used. ..
The thickness of the insulating film 10 is not particularly limited, but a relatively thin one is preferable from the viewpoint of the volumetric efficiency of the battery. Specifically, it is preferably 70 μm or less, more preferably 60 μm or less, and particularly preferably 55 μm or less. On the other hand, from the viewpoint of film strength, it is preferably 30 μm or more, more preferably 40 μm or more, and particularly preferably 45 μm or more.

  In the insulating film 10 disclosed herein, the wettability of the surface (inner surface) on the side facing the electrode body 80 with respect to the non-aqueous electrolyte is more than that on the surface (outer surface) on the side facing the inner wall of the battery case 30. high. The high wettability can be confirmed using various wettability evaluation methods. For example, the ratio of the contact angle of the droplet of the non-aqueous electrolyte on the inner surface of the surface-treated insulating film 10 to the contact angle of the droplet when the non-aqueous electrolyte is dropped on the outer surface of the insulating film 10 is 0. It may be 0.7 or less (more preferably 0.5 or less). Such a contact angle can be easily measured by using a general-purpose contact angle measuring device or the like based on, for example, the contact angle test method of JIS K2396.

  Examples of the surface treatment for enhancing (improving) the wettability include treatments such as corona discharge treatment, plasma treatment and ozone treatment. Of these, corona discharge treatment is preferable. Here, the surface treatment means a treatment in which a polar functional group such as a hydroxyl group or a carboxyl group is introduced into the surface of the insulating film 10. By introducing the polar functional group to the surface, the wettability with respect to the electrolytic solution can be improved. Since such a surface treatment method itself is a conventionally known method, further detailed description will be omitted.

As shown in FIG. 2, the battery case 30 has a so-called rectangular shape (typically, a rectangular parallelepiped shape) having a total of eight corners formed so that the internal space has a box shape corresponding to the electrode body 80. The battery case 30 of FIG. The battery case 30 includes a case body 32 and a lid 34. The case body 32 has a bottomed square tube shape, and is a flat box-shaped container having one side surface (upper end) opened. The lid 34 is a member that is attached to the opening (upper end) of the case body 32 and closes the opening. The case body 32 can accommodate the electrode body 80 and the insulating film 10 through the opening at the top thereof. The case body 32 includes a pair of wide surfaces 36 (FIG. 1) facing the flat surface of the wound electrode body 80 housed in the case, a pair of narrow surfaces 38 adjacent to the wide surface 36, and a bottom surface 39. It consists of The lid 34 is provided with a gas release valve 35 that is opened when the gas pressure inside the battery case becomes higher than a predetermined value. Next to the gas release valve 35, an injection port (not shown) for injecting a non-aqueous electrolyte solution when the battery is assembled is provided.
Although not particularly limited, examples of the material of the battery case 30 include metal materials such as aluminum, stainless steel, and nickel-plated steel, and resin materials such as polyphenylene sulfide resin and polyimide resin. Of these, metallic materials are preferable.

Next, a battery assembling process will be described. As shown schematically in FIG. 1, the above-prepared wound electrode body 80 is first housed in the bag-shaped insulating film 10, and the wound electrode body 80 and the insulating film 10 are separated from each other. It is housed in the case body 32. At this time, the positive electrode terminal 42 and the negative electrode terminal 44 are attached to the lid 34 of the battery case 30 (FIG. 2), and one ends 92 and 94 thereof are respectively wound electrode bodies housed in the battery case 30. The positive electrode composite material layer non-forming portion 53 and the negative electrode composite material layer non-forming portion 80 of 80 are joined by welding (ultrasonic welding, etc.).
The lid 34 and the case body 32 are hermetically sealed by laser welding along the joint 32a.

After sealing, a desired non-aqueous electrolytic solution is injected into the battery case 30. The non-aqueous electrolyte used may be the same as that used in the conventional battery of this type, and is not particularly limited.
For example, LiPF ₆ and LiBF ₄ are suitable examples of the lithium salt containing elemental fluorine. Further, as preferable examples of the non-aqueous solvent (that is, organic solvent), cyclic carbonate solvents such as ethylene carbonate (EC) and propylene carbonate (PC), chain carbonates such as dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC). Examples include system solvents and ester solvents such as ethyl propionate (EP). A non-aqueous electrolyte solution for a lithium ion secondary battery can be prepared by incorporating a lithium salt into these non-aqueous solvents at a concentration of about 0.1 to 5 mol/L.
For various purposes, additives such as a gas generating agent, a film forming agent, a dispersant, and a thickener may be added to the non-aqueous electrolyte solution. For example, fluorophosphate salts such as lithium difluorophosphate (LiPO ₂ F ₂ ), oxalate complexes such as lithium bisoxalate borate (LiBOB), vinylene carbonate and the like are suitable additives that contribute to improving the performance of the battery. .. Further, an overcharge preventing agent such as cyclohexylbenzene or biphenyl may be used.

  Next, an initial charging process is performed on the sealed battery assembly supplied with the non-aqueous electrolyte. Similar to a conventional lithium-ion secondary battery, an external power source is connected to the battery assembly between the positive electrode terminal and the negative electrode terminal for external connection, and the positive and negative electrode terminals are connected at room temperature (typically about 25° C.). Initial charging is performed until the voltage reaches a predetermined value. For example, in the initial charging, charging is performed with a constant current of about 0.1 C to 10 C from the start of charging until the voltage between terminals reaches a predetermined value, and then constant voltage is maintained until SOC (State of Charge) reaches about 60% to 100%. The charging can be performed by constant current constant voltage charging (CC-CV charging). After that, a usable lithium ion secondary battery 100 can be provided by performing an appropriate aging treatment.

  Hereinafter, some test examples relating to the present invention will be described, but the present invention is not intended to be limited to the specific examples.

<Test Example 1: Construction of test lithium-ion secondary battery>
Five types of test lithium ion secondary batteries of Examples 1 to 5 were constructed by the following materials and processes. The positive electrode was manufactured by the following procedure.
LiNi _1/3 Co _1/3 Mn _1/3 O ₂ (LNCM) as a positive electrode active material, acetylene black (AB) as a conductive material, and polyvinylidene fluoride (PVDF) as a binder were added to LNCM:AB : PVDF=91:6:3 by mass ratio was mixed with N-methylpyrrolidone (NMP) to prepare a positive electrode mixture layer forming composition (positive electrode paste). This paste was applied in a strip shape on both surfaces of a long aluminum foil (positive electrode current collector), dried, and pressed to produce a positive electrode.

The negative electrode was manufactured by the following procedure. Graphite (C) as a negative electrode active material, styrene-butadiene rubber (SBR) as a binder, and carboxymethyl cellulose (CMC) as a thickener were used in a mass ratio of C:SBR:CMC=98:1:1. Alumina (Al ₂ O ₃ ) particles, which are inorganic fillers, were added at a ratio of 5 parts by mass with respect to 100 parts by mass of graphite by mixing with ion-exchanged water to prepare a composition for forming a negative electrode mixture layer (negative electrode paste). Prepared. A negative electrode was prepared by applying the composition in a strip shape on both surfaces of a long copper foil (negative electrode current collector), drying and pressing.

The positive electrode and the negative electrode produced by the above method were superposed in the longitudinal direction with two separators having a three-layer structure in which porous polypropylene layers were formed on both surfaces of the porous polyethylene layer, and were wound in the longitudinal direction. A flat wound electrode body was produced by crushing and squeezing it later.
On the other hand, an insulating film formed into a bag shape corresponding to the shape of the flat wound electrode body was produced. Specifically, such a bag-shaped insulating film is subjected to corona discharge treatment on the inner surface (the surface facing the electrode body) in advance, and the outer surface (the surface facing the inner wall of the battery case). A bag made by cutting a sheet made of a thermoplastic resin (polyolefin) that has improved wettability into a predetermined shape, bending it into a predetermined shape, and fixing a part of the overlapping surfaces by heat fusion. Is. The average thickness was about 50 μm.
Then, the flat wound electrode body produced as described above was housed in the bag through the opening of the insulating film.

Next, the wound electrode body was housed together with an insulating film in a corresponding rectangular battery case (see FIGS. 1 and 2). Then, the lid and the case body were welded and joined (sealed), and the non-aqueous electrolyte was injected into the battery case to construct the lithium-ion secondary battery according to Example 1.
Here, as the non-aqueous electrolyte, a mixed solvent containing ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a volume ratio of EC:DMC:EMC=30:40:30, LiPF ₆ as a supporting salt was dissolved at a concentration of 1.1 mol/L and used.

Except that the corona discharge treatment is not performed (that is, the degree of wettability is the same as that of the thermoplastic resin sheet that is the raw material of the insulating film, and there is no difference between the outer surface and the inner surface). A lithium-ion secondary battery according to Example 2 was constructed by using the same material and process as in 1.
In addition, except that the corona discharge treatment was performed on the outer surface side (that is, the wettability of the insulating film was higher on the outer surface than on the inner surface), the same material and process as in Example 1 were used to obtain Example 3. Such a lithium ion secondary battery was constructed.
In addition, except that the corona discharge treatment was performed on both the inner surface side and the outer surface side (that is, the wettability of the insulating film was increased at the same level on the inner surface and the outer surface), the above Example 1 was performed. A lithium ion secondary battery according to Example 4 was constructed by using the same material and process as described above.
In addition, as a comparison target, the same material and process as in Example 2 (that is, the wettability of the insulating film is the same on the outer surface and the inner surface) except that the negative electrode mixture layer containing no inorganic filler is formed. ), the lithium ion secondary battery according to Example 5 was constructed.

<Test Example 2: Evaluation of input/output characteristics>
The following outputs were measured as an index for evaluating the input/output characteristics. Specifically, the output of the battery of each example was discharged at a constant output from a potential of SOC 60% to 2.5 V, and the output of each battery of each example was sequentially changed from 2 mW to 80 mW and discharged. It was Then, the output value for 5 seconds was calculated from the relationship between the output and the time. The results are shown in the relevant column of Table 1. Here, the output result of the battery according to Example 5 was set to 100%, and the output results of the batteries according to other Examples 1 to 4 were evaluated relatively in %.

<Test Example 3: Evaluation of resistance increase rate after high rate cycle test>
Next, the batteries according to each example were subjected to a charge/discharge cycle test in which high rate charge/discharge was repeated 1000 cycles under a temperature condition of 25° C., and a resistance increase rate (%) after the cycle test was calculated. Specifically, it is as follows.
First, each battery was charged with a constant current (CC) under a temperature condition of 25° C. until the SOC reached a state of 60%. Then, the measured voltage rise value (V) is divided by the corresponding current value to calculate the IV resistance (mΩ) (typically, a linear plot of current (I)-voltage (V)). The IV resistance (mΩ) was calculated from the slope of the approximate straight line), and the average value was used as the initial battery resistance.
Next, under a temperature condition of 25° C., constant current charge (CC charge) is performed for 240 seconds at a charge rate of 2.5 C, then paused for 120 seconds, and then constant current discharge for 20 seconds at a discharge rate of 30 C. (CC discharge) was performed, and then, charging/discharging in which 120 seconds of rest were performed was set as one cycle. The battery resistance (IV resistance) after the charge/discharge cycle test was measured by the same method as the above-mentioned initial battery resistance measurement for each battery after the end of the test in which this was repeated about 1000 cycles. And the following formula:
Resistance increase rate (%)=(IV resistance after cycle)÷(initial battery resistance)×100;
The resistance increase rate (%) was calculated from The results are shown in the relevant column of Table 1.

As shown in Table 1, in all of the batteries according to Examples 1 to 4 including the inorganic filler in the negative electrode mixture layer, the resistance increase rate after the high rate charge/discharge cycle test was such that the inorganic filler was contained in the negative electrode mixture layer. The value was lower than that of the battery according to Example 5 containing no. This means that by including an inorganic filler in the negative electrode mixture layer, the ionic conductivity in the electrode is improved, and as a result, the internal resistance of the battery (for example, the resistance during high-rate charge/discharge use as in this test example) is increased. Rise) can be reduced.
Furthermore, it was confirmed that in the battery according to Example 1 in which the wettability of the inner surface of the insulating film was improved, the output value was not decreased and the input/output characteristics were excellent. This indicates that the improved wettability makes it easier for the electrolytic solution once extruded from the electrode body during charge/discharge to return to the electrode body again.
On the contrary, in the batteries according to Examples 2 to 4, a decrease in output value (input/output characteristics) was observed. This is not particularly limited, but the following causes are considered. That is, in the batteries according to Examples 3 and 4 in which the wettability of the outer surface of the insulating film (the surface facing the battery case) is improved, the improved wettability makes it easier for the insulating film to stick to the inner wall surface of the battery case. It is considered that the gap between the electrode body and the insulating film becomes large and it becomes difficult for the electrolytic solution to return to the inside of the electrode body, so that the output value (input/output characteristic) decreases.

10 Insulating Film 30 Battery Case 32 Case Body 34 Lid 42 Positive Electrode Terminal 44 Negative Terminal 50 Positive Electrode 52 Positive Electrode Current Collector 54 Positive Electrode Mixture Layer 60 Negative Electrode 62 Negative Current Collector 64 Negative Electrode Mixture Layer 70, 72 Separator 80 Winding Electrode Body 100 Lithium-ion secondary battery

Claims (1)

An electrode body having a positive electrode having a positive electrode mixture layer containing a positive electrode active material on a positive electrode current collector, and a negative electrode having a negative electrode mixture layer containing a negative electrode active material on a negative electrode current collector,
Non-aqueous electrolyte,
A battery case containing the electrode body and the non-aqueous electrolyte therein,
An insulating film arranged between an inner wall of the battery case and the electrode body, the insulating film blocking direct contact between the battery case and the electrode body,
A non-aqueous electrolyte secondary battery comprising:
The negative electrode mixture layer contains an inorganic filler made of an inorganic compound that does not participate in a battery reaction,
The insulating film is characterized in that the wettability of the surface on the side facing the electrode body with respect to the non-aqueous electrolyte is improved as compared with the surface on the side facing the battery case inner wall. Water electrolyte secondary battery.

Images