JP2023173677A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

To provide a nonaqueous electrolyte secondary battery which can suppress the rise of a reaction force from an electrode body over a long period of time.SOLUTION: A battery 100 herein disclosed comprises: an electrode body 20 arranged by laminating a positive electrode and a negative electrode on each other to alternate in a laminating direction; an outer packaging body 10 for housing the electrode body 20; and a spacer 50 opposed to a face of the electrode body 20 in the laminating direction thereof. The negative electrode contains graphite and a silicon-based active substance. The silicon-based active substance is 3 mass% or more in terms of Si. The spacer 50 is no less than 2.5% of a thickness of the electrode body 20 in quantity of being squashed when it is compressed with a load of 1 MPa, and 0.1 MPa or more and 5 MPa or less in Young's modulus after 1000 cycles of charge and discharge.SELECTED DRAWING: Figure 3

Description

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

In general, a non-aqueous electrolyte secondary battery includes an electrode body in which a positive electrode containing a positive electrode active material and a negative electrode containing a negative electrode active material are stacked in the stacking direction in an insulated state, and an exterior body housing the electrode body. , is provided. When charging and discharging are performed in such a non-aqueous electrolyte secondary battery, the electrode body expands and contracts in the stacking direction, and the thickness of the exterior body in the stacking direction changes. If the thickness of the outer package changes in the stacking direction, the load applied to the electrode body changes, resulting in a decrease in battery characteristics (e.g. cycle characteristics), or uneven charging/discharging, which may lead to metal precipitation (e.g. Li precipitation) on the negative electrode. may occur. Prior art documents related to this include Patent Documents 1 to 3.

For example, Patent Document 1 discloses that by disposing a polymer foam between the side surface of the electrode body in the stacking direction and the inner surface of the exterior body, the polymer foam contracts in accordance with the expansion of the electrode body during charging and discharging. It is described that the load applied to the electrode body can be homogenized.

JP2017-76476A JP2016-522546A Japanese Patent Application Publication No. 2010-287466

The spacer facing the electrode body, for example, a polymer foam as disclosed in Patent Document 1, is susceptible to pressure fluctuations due to repeated charging and discharging and temperature changes in the usage environment (for example, from below freezing to 60 degrees Celsius). It is repeatedly subjected to reaction force from For this reason, according to studies conducted by the present inventors, depending on the type of spacer, etc., it may gradually harden due to repeated reaction force, and at a certain point it may no longer maintain a certain level of elasticity. As a result, the reaction force from the electrode body increases rapidly, and the load applied to the electrode body may not be able to be adjusted. In particular, this tendency was noticeable in batteries containing a silicon-based active material in the negative electrode because the electrode body expands and contracts significantly during charging and discharging.

The present invention has been made in view of the above circumstances, and its purpose is to provide a non-aqueous electrolyte secondary battery that includes silicon in the negative electrode and that can suppress the increase in reaction force from the electrode body over a long period of time. There is a particular thing.

According to the present invention, an electrode body in which a positive electrode including a positive electrode active material layer containing a positive electrode active material and a negative electrode including a negative electrode active material layer including a negative electrode active material are laminated in a stacking direction in an insulated state; A non-aqueous electrolyte secondary battery is provided that includes an exterior body that houses the body, and a spacer that faces a surface of the electrode body in the stacking direction. The negative electrode includes graphite and a silicon-based active material as the negative electrode active material, and when the total amount of the negative electrode active material is 100% by mass, the silicon-based active material accounts for 3% by mass or more in terms of Si. The spacer has a crushing amount of 2.5% or more of the thickness of the electrode body when compressed at 1 MPa, and after 1000 cycles of charging and discharging, stress is applied using an autograph, and the horizontal axis is the strain amount. , when creating a stress strain curve with the vertical axis as the stress per unit volume, the Young's modulus determined by the slope of the stress strain curve in the section from the beginning of collapse to the inflection point is 0.1 MPa or more and 5 MPa or less. be.

The spacer disclosed herein has compression characteristics such that the amount of collapse or Young's modulus satisfies a predetermined range. By using such a spacer, even if the negative electrode contains silicon in a predetermined proportion or more, the spacer can suitably absorb the reaction force from the electrode body over a long period of time. As a result, the increase in reaction force can be stably suppressed even after repeated charge/discharge cycles, and the swelling of the battery can be effectively suppressed.

In a preferred embodiment of the non-aqueous electrolyte secondary battery disclosed herein, the amount of collapse is 50% or more and 99% or less of the thickness of the spacer. When the amount of collapse is large in this way, the volume occupied by the spacer can be minimized. Therefore, a decrease in volumetric energy density can be suppressed.

In a preferred embodiment of the non-aqueous electrolyte secondary battery disclosed herein, stress is applied to the electrode body using an autograph to create a stress-strain curve in which the horizontal axis is the amount of strain and the vertical axis is the stress per unit volume. , the Young's modulus determined by the slope of the stress strain curve in the stress range of 0.5 MPa to 1 MPa is 30 MPa or more and 200 MPa or less. By satisfying the above range, the electrode body itself has a structure that is difficult to swell, and the effects of the technology disclosed herein can be stably exhibited at a high level.

In a preferred embodiment of the nonaqueous electrolyte secondary battery disclosed herein, the area of the surface of the spacer that faces the electrode body is greater than or equal to the area of the positive electrode active material layer. Thereby, the effects of the technology disclosed herein can be more stably exhibited.

In a preferred embodiment of the nonaqueous electrolyte secondary battery disclosed herein, the spacer is housed inside the exterior body and is in contact with the electrode body. Thereby, when the electrode body expands and the spacer collapses due to charging and discharging, the electrolyte is discharged from the spacer, and the electrolyte can be supplied to the electrode body in a timely manner.

In a preferred embodiment of the non-aqueous electrolyte secondary battery disclosed herein, the exterior body is made of a laminate film, the spacer is disposed outside the exterior body, and with respect to the exterior body and the spacer, The apparatus further includes a restraining member that applies restraint pressure from the stacking direction. By arranging the spacer outside the exterior body, the spacer is not exposed to the electrolyte, so that the effects of the technology disclosed herein can be stably exhibited.

In a preferred embodiment of the non-aqueous electrolyte secondary battery disclosed herein, the spacer is made of urethane foam or rubber sponge having open cells. Thereby, the effects of the technology disclosed herein can be exhibited at a high level.

FIG. 1 is a perspective view schematically showing a nonaqueous electrolyte secondary battery according to an embodiment. FIG. 2 is a schematic vertical cross-sectional view taken along line II-II in FIG. 1. FIG. FIG. 2 is a schematic vertical cross-sectional view taken along line III-III in FIG. 1. FIG. FIG. 2 is a schematic vertical cross-sectional view showing the arrangement of a laminate cell and a spacer according to an example. It is a graph showing the relationship between charge/discharge cycles and reaction force from an electrode body. It is a graph showing the relationship between the charge/discharge cycle and the amount of swelling of the electrode body. It is a graph showing the relationship between confining pressure and expansion speed. It is a graph showing the relationship between dimensions of cells and spacers and confining pressure. It is a graph showing the relationship between the Young's modulus of the spacer, the amount of swelling of the cell, and the reaction force after 1000 cycles.

Hereinafter, preferred embodiments of the technology disclosed herein will be described with reference to the drawings. Further, matters other than those specifically mentioned in this specification that are necessary for carrying out the present invention (for example, the general structure and manufacturing process of a battery that do not characterize the present invention) are well known in the field. This can be understood as a matter of design by a person skilled in the art based on the prior art. The present invention can be implemented based on the content disclosed in this specification and the common general knowledge in the field.

In this specification, "secondary battery" is a term that refers to all electricity storage devices that can be repeatedly charged and discharged, and includes so-called storage batteries (chemical batteries) such as lithium-ion secondary batteries and nickel-metal hydride batteries, and electric This concept includes capacitors (physical batteries) such as double layer capacitors. Further, in this specification, the notation "A to B" indicating a range includes the meanings of "A to B" as well as "preferably larger than A" and "preferably smaller than B."

<Nonaqueous electrolyte secondary battery 100>
FIG. 1 is a perspective view of a nonaqueous electrolyte secondary battery 100 (hereinafter sometimes simply referred to as "battery 100"). FIG. 2 is a schematic vertical cross-sectional view taken along line II-II in FIG. FIG. 3 is a schematic vertical cross-sectional view taken along line III--III in FIG. In the following description, the symbols L, R, F, Rr, U, and D in the drawings represent left, right, front, rear, top, and bottom, and the symbols X, Y, and Z in the drawings represent batteries. The long side direction of 100, the short side direction perpendicular to the long side direction, and the vertical direction are respectively expressed. The short side direction Y is an example of the stacking direction. However, these directions are merely for convenience of explanation, and do not limit the installation form of the battery 100 in any way.

As shown in FIG. 2, the battery 100 includes an exterior body 10, an electrode body 20, a positive terminal 30, a negative terminal 40, and a spacer 50 (see FIG. 3). Although not shown, the battery 100 further includes an electrolyte here. The battery 100 includes an electrode body 20, a spacer 50, and an electrolyte (not shown) housed inside the exterior body 10. Battery 100 is a lithium ion secondary battery here. The battery 100 is characterized by including the spacer 50 disclosed herein, and other configurations may be conventional.

The exterior body 10 is a housing that houses the electrode body 20, the spacer 50, and an electrolyte (not shown). As shown in FIG. 1, the exterior body 10 is formed in the shape of a flat rectangular parallelepiped (square) with a bottom. However, the shape of the exterior body 10 is not limited to a square shape, and may be any shape such as a cylinder or a bag shape. The material of the exterior body 10 may be the same as that conventionally used and is not particularly limited. The exterior body 10 is made of a metal material that is lightweight and has good thermal conductivity, such as aluminum, aluminum alloy, and stainless steel. The exterior body 10 may be a so-called laminate film, for example, an aluminum laminate film having a metal layer containing aluminum and a fusion layer containing resin.

As shown in FIG. 2, the exterior body 10 here includes a case body 12 having an opening 12h, and a lid (sealing plate) 14 that closes the opening 12h. As shown in FIG. 1, the case body 12 includes a flat bottom wall 12a, a pair of long side walls 12b extending from the bottom wall 12a and facing each other, and a pair of short side walls 12c extending from the bottom wall 12a and facing each other. It is equipped with. The bottom wall 12a has a substantially rectangular shape. The bottom wall 12a faces the opening 12h. The long side wall 12b and the short side wall 12c each have a flat surface. In plan view, the area of the long side wall 12b is larger than the area of the short side wall 12c. As shown in FIG. 3, the long side wall 12b faces a flat portion 20f of the electrode body 20 and a spacer 50, which will be described later.

The lid body 14 is attached to the case body 12 so as to close the opening 12h of the case body 12. The lid 14 faces the bottom wall 12a of the case body 12. The lid body 14 has a substantially rectangular shape here. The exterior body 10 is integrated by joining (for example, welding) the lid 14 to the periphery of the opening 12h of the case body 12. The exterior body 10 is hermetically sealed (sealed).

The electrode body 20 has a positive electrode and a negative electrode (not shown). The electrode body 20 is a laminated electrode in which a rectangular (typically rectangular) positive electrode and a rectangular (typically rectangular) negative electrode are stacked in the lamination direction Y with a separator in between. It is the body. However, the electrode body 20 may be, for example, a flat wound electrode body in which a band-shaped positive electrode and a band-shaped negative electrode are laminated with a band-shaped separator interposed therebetween and are wound around a winding axis.

As shown in FIG. 3, the electrode body 20 has a pair of flat portions 20f at both ends in the stacking direction Y. As shown in FIG. Here, one flat portion 20f (on the front side in FIG. 3) faces the long side wall 12b of the exterior body 10, and the other flat portion 20f (on the rear side in FIG. 3) faces the spacer 50. When the battery 100 is shipped, it is preferable that a gap exist between the flat portion 20f of the electrode body 20 and the long side wall 12b of the exterior body 10. Further, end faces of the electrode body 20 perpendicular to the stacking direction Y face the bottom wall 12a, the lid body 14, and the pair of short side walls 12c, respectively.

In this embodiment, the electrode body 20 preferably has a Young's modulus of 30 MPa to 200 MPa. By satisfying the above range, the electrode body 20 itself has a structure that is difficult to swell, and the effects of the technology disclosed herein can be stably exhibited at a high level. Note that in this specification, "Young's modulus of the electrode body 20" refers to a value determined as follows. That is, first, using an autograph, a constant stress is applied to the central part of the electrode body 20 in the stacking direction Y in an area smaller than the positive electrode (for example, 2 x 2 ^cm2, etc.), and the stress is maintained until there is almost no change in thickness. Read the amount of distortion. Next, the stress applied to the electrode body 20 is increased stepwise, and the measurement results are plotted with the horizontal axis representing the amount of strain and the vertical axis representing the stress per unit volume to create a stress strain curve. Then, in the obtained stress strain curve, the slope in the section where the stress is from 0.5 MPa to 1 MPa is defined as the Young's modulus of the electrode body 20. The stress strain curve of the electrode body 20 preferably has a slope of 10 MPa to 100 MPa in the stress range of 0.1 MPa to 0.5 MPa, and preferably has a slope of 50 MPa to 300 MPa in the stress range of 1 MPa to 2 MPa. is preferred.

As shown in FIG. 2, the positive electrode includes a positive electrode current collector 21 and a positive electrode active material layer (not shown) fixed on at least one surface of the positive electrode current collector 21. The positive electrode current collector 21 is made of a conductive metal such as aluminum, aluminum alloy, nickel, stainless steel, or the like. The packing density (average packing density) of the positive electrode active material layer is preferably 3.0 to 3.8 g/cm ³ . The positive electrode active material layer includes a positive electrode active material that can reversibly occlude and release charge carriers. Examples of the positive electrode active material include lithium transition metal composite oxide. The positive electrode active material layer may contain arbitrary components other than the positive electrode active material, such as a conductive material, a binder, and various additive components. As the conductive material, for example, a carbon material such as acetylene black (AB) can be used. As the binder, for example, polyvinylidene fluoride (PVdF) can be used.

As shown in FIG. 2, the negative electrode includes a negative electrode current collector 22 and a negative electrode active material layer (not shown) fixed on at least one surface of the negative electrode current collector 22. The negative electrode current collector is made of conductive metal such as copper, copper alloy, nickel, and stainless steel. The packing density (average packing density) of the negative electrode active material layer is typically smaller than that of the positive electrode active material layer, preferably 1.4 to 1.7 g/cm ³ , and 1.4 to 1.6 g/cm ³ . More preferred. This makes it easier to adjust the Young's modulus of the electrode body 20 within the above range.

The negative electrode active material layer includes a negative electrode active material that can reversibly occlude and release charge carriers. In this embodiment, the negative electrode active material essentially contains graphite and a silicon-based active material. In addition to graphite and silicon-based active materials, the negative electrode active material may further contain other negative electrode active materials, such as carbon materials other than graphite. Examples of silicon-based active materials include SiOx, Si--C composites, and materials in which nano-Si particles are dispersed within porous carbon particles. When the total amount of the negative electrode active material is 100% by mass, the proportion of the silicon-based active material is 3% by mass or more in terms of Si. The proportion of the silicon-based active material in the total amount of the negative electrode active material may be 3 to 20% by mass, or 5 to 10% by mass in terms of Si. Further, the proportion of the silicon-based active material is preferably 3% by mass or more in terms of Si, when the sum of the mass of the silicon-based active material and the mass of graphite is 100% by mass.

The negative electrode active material layer may contain arbitrary components other than the negative electrode active material, such as a binder and various additive components. As the binder, for example, a rubber binder such as styrene butadiene rubber (SBR), a cellulose binder such as carboxymethyl cellulose (CMC), an acrylic binder such as polyacrylic acid (PAA), etc. can be used. In the negative electrode active material layer, the proportion of the binder in the negative electrode active material layer is preferably 3% by mass or more. This makes it easier to adjust the Young's modulus of the electrode body 20 within the above range.

The separator is a member that is interposed between the positive electrode active material layer of the positive electrode and the negative electrode active material layer of the negative electrode in the stacking direction Y, and insulates them. As the separator, for example, a porous sheet made of a polyolefin resin such as polyethylene (PE) or polypropylene (PP) is suitable. The separator is preferably an adhesive separator having a base material made of a porous sheet made of resin and an adhesive layer provided on at least one surface of the base material part. The adhesive layer is a layer containing a sticky (or adhesive) resin material with a melting point of 100° C. or less. Examples of resin materials that can be included in the adhesive layer include fluororesins such as polyvinylidene fluoride (PVdF) and polytetrafluoroethylene (PTFE). It is preferable that the separator is bonded and integrated with the positive electrode and/or the negative electrode via an adhesive layer. This makes it easier to adjust the Young's modulus of the electrode body 20 within the above range. Note that "adhered" here means that the peel strength in a dry state is 1 N/m or more.

As shown in FIG. 2, a laminated portion in which a positive electrode active material layer and a negative electrode active material layer are laminated in an insulated state is formed in the central portion of the electrode body 20 in the long side direction X. On the other hand, at the left end portion of the electrode body 20 in the long side direction X, a portion of the positive electrode current collector 21 (positive electrode current collector exposed portion) protrudes from the laminated portion. A positive electrode lead member 23 is attached to the exposed portion of the positive electrode current collector. Further, at the right end portion of the electrode body 20 in the long side direction X, a portion of the negative electrode current collector 22 (negative electrode current collector exposed portion) protrudes from the laminated portion. A negative electrode lead member 24 is attached to the negative electrode current collector exposed portion.

The positive electrode terminal 30 and the negative electrode terminal 40 are arranged at both ends of the lid body 14 in the long side direction X, as shown in FIG. The positive electrode terminal 30 and the negative electrode terminal 40 protrude to the outside of the exterior body 10. Here, the positive electrode terminal 30 and the negative electrode terminal 40 each protrude from the same surface of the exterior body 10 (specifically, the lid body 14). However, the positive electrode terminal 30 and the negative electrode terminal 40 may each protrude from different surfaces of the exterior body 10. As shown in FIG. 2, the positive electrode terminal 30 is electrically connected to the positive electrode of the electrode body 20 via the positive electrode lead member 23 inside the exterior body 10. The negative electrode terminal 40 is electrically connected to the negative electrode of the electrode body 20 via the negative electrode lead member 24 inside the exterior body 10 .

The electrolyte may be the same as conventional ones and is not particularly limited. The electrolyte is, for example, a non-aqueous liquid electrolyte (non-aqueous electrolyte) containing a non-aqueous solvent and a supporting salt. The non-aqueous solvent includes carbonates such as ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate. The supporting salt is, for example, a fluorine-containing lithium salt such as lithium hexafluorophosphate (LiPF ₆ ). However, the electrolyte may be in a solid state (solid electrolyte) and may be integrated into the electrode body 20.

The spacer 50 is a member that faces the flat portion 20f (the surface in the stacking direction Y) of the electrode body 20 and absorbs the reaction force of the electrode body 20. The number of spacers 50 is one in FIG. 3. The number of spacers 50 is the same as the number of electrode bodies 20. The spacer 50 is arranged inside the exterior body 10. In the stacking direction Y, the spacer 50 is arranged between the electrode body 20 and the long side wall 12b of the exterior body 10. The spacer 50 is in contact with the flat portion 20f of the electrode body 20. However, in other embodiments, the number of spacers 50 may be different from the number of electrode bodies 20. Further, the spacers 50 may be two or more in number, and may be arranged to sandwich the electrode body 20 from both sides in the stacking direction Y, for example. Further, as shown in the embodiments and modifications described later, the spacer 50 may be arranged outside the exterior body 10.

The spacer 50 has a sheet shape. It is preferable that the area of the surface of the spacer 50 facing the electrode body 20 is greater than or equal to the area of the positive electrode active material layer. Thereby, the effects of the technology disclosed herein can be stably exhibited. The spacer 50 may be integrated with the electrode body 20 by being adhered to the electrode body 20, for example. The spacer 50 may be removably sandwiched, for example, between the electrode body 20 and the inner surface of the exterior body 10 or between two electrode bodies 20.

In this embodiment, the amount of collapse of the spacer 50 when compressed at 1 MPa is 2.5% or more of the thickness of the electrode body 20 (length in the stacking direction Y). In this specification, the term "amount of collapse" refers to the maximum amount of change in thickness when the spacer 50 is compressed using an autograph to apply a stress of 1 MPa from the stacking direction Y until the thickness change is almost eliminated. say. When a plurality of spacers 50 are used for one electrode body 20, the maximum amount of change in the total thickness of the plurality of spacers 50 is defined as the amount of collapse. The amount of collapse is preferably 3% or more of the thickness of the electrode body 20, more preferably 5% or more, more preferably 6% or more, and approximately 20% or less, for example 10% or less, and even 8%. It is preferable that it is below.

The amount of collapse is preferably 50% or more of the thickness of the spacer 50 (length in the stacking direction Y), and preferably 50 to 99%, for example. The amount of collapse is more preferably 60% or more of the thickness of the spacer 50, and even more preferably 70% or more. When the amount of collapse is large in this way, the volume occupied by the spacer 50 can be minimized. Therefore, it is possible to prevent the volumetric energy density of the battery 100 from decreasing due to the spacer 50 becoming larger.

Further, in this embodiment, the spacer 50 has a Young's modulus of 0.1 MPa to 5 MPa after 1000 cycles of charging and discharging. It is preferable that the spacer 50 maintains the above Young's modulus during 1 to 1000 cycles of charging and discharging. Note that in this specification, "Young's modulus of a spacer" refers to a value determined as follows. That is, first, using an autograph, a constant stress is applied to the spacer 50 from the stacking direction Y, and the stress is maintained until the thickness almost disappears, and the amount of strain at that time is read. Next, the stress applied to the spacer 50 is increased step by step, and the measurement results are plotted with the horizontal axis representing the amount of strain and the vertical axis representing the stress per unit volume to create a stress strain curve. Then, in the obtained stress-strain curve, the slope in the section from the beginning of collapse to the inflection point is defined as the Young's modulus of the spacer 50. The Young's modulus of the spacer 50 is preferably 0.15 MPa or more, and preferably 3 MPa or less, for example, 2 MPa or less.

As the spacer 50 having the above-mentioned collapse amount and Young's modulus, for example, a porous or crosslinked structure made of rubber sponge, urethane foam, expanded polystyrene, etc., or a fibrous structure such as glass wool, nonwoven fabric, etc. can be mentioned. More specifically, for example, urethane rubber, silicone rubber, ethylene proprene rubber (EPDM), nitrile rubber (NBR), styrene-butadiene rubber (SBR), butyl rubber, chloroprene rubber, acrylic rubber, fluororubber, ethylene-propylene rubber, etc. Among vinyl acetate rubber, epichlorohydrin rubber, etc., those having impact resilience that can withstand long-term use and are resistant to aging can be mentioned. Among these, structures such as foam are preferred from the viewpoint of ensuring the amount of collapse. From the viewpoint of ease of pore return, it is preferable that the structure such as a foam has open cells or through-pores rather than airtight closed cells. It is more preferable to have open cells in the surface direction). It is preferable that the spacer 50 has a porosity of 40% or more, and in particular, one that has elasticity, low viscosity, and small permanent deformation is preferable.

Although not particularly limited, in applications such as on-vehicle use, it is preferable that the Young's modulus satisfies the above range even after compression is repeated 1000 times or more in a wide range of environments from low to high temperatures. The spacer 50 preferably has a heat resistance temperature of 100° C. or higher, and more preferably has weather resistance and aging resistance of −30° C. or lower. Further, the spacer 50 is preferably flame retardant and has high heat insulation properties, and is more preferably made of a flame retardant material having a thermal conductivity of approximately 10 W/(m·K) or less at 300K. Moreover, when the spacer 50 is arranged inside the exterior body 10 as in this embodiment, it is preferable that the spacer 50 has a porous structure and has a function of retaining the electrolyte. Thereby, when the electrode body 20 expands and the spacer 50 collapses due to charging and discharging, the electrolyte is discharged from the spacer 50, and the electrolyte can be supplied to the electrode body 20 in a timely manner.

<Applications of battery 100>
Although the battery 100 can be used for various purposes, it can be suitably used, for example, as a power source (driving power source) for a motor mounted on a vehicle such as a passenger car or a truck. Although the type of vehicle is not particularly limited, examples thereof include a plug-in hybrid electric vehicle (PHEV), a hybrid electric vehicle (HEV), and a battery electric vehicle (BEV).

Some examples relating to the present invention will be described below, but the present invention is not intended to be limited to these examples.

[Test example: Consideration of spacer type]
<Example 1> First, a positive electrode including a positive electrode active material layer (packing density: 3.5 g/cm ³ ) containing a positive electrode active material and the like was produced. In addition, a negative electrode active material containing graphite (93% by mass of the total negative electrode active material) and a Si-C composite (7% by mass of the total negative electrode active material) as a negative electrode active material, and CMC, SBR, and PAA as binders. A negative electrode including a material layer (packing density: 1.6 g/cm ³ ) was produced. Next, these positive electrodes and negative electrodes were cut into a rectangular shape leaving an uncoated part, and were alternately laminated with separators interposed therebetween to produce an electrode body (thickness in the lamination direction was approximately 10 mm). Note that the separator used was one in which an adhesive layer containing PVdF was applied on both sides. Then, the electrode body was pressed at 1 to 4 MPa to adhere the positive electrode, separator, and negative electrode to each other and integrate them.

Next, a bag-shaped aluminum laminate film was prepared as a battery case. A large laminate film was used so that it would not be stretched even when the electrode body expanded, and an amount of electrolyte solution sufficient to immerse the electrode body was filled and sealed. As a result, a laminate cell (lithium ion secondary battery) was constructed.

Next, as a spacer, a highly durable polyether type urethane foam (thickness: 2 mm) having open cells was prepared. When the physical properties of this spacer were measured using the method described above, the (initial) Young's modulus was 1.2 MPa, the amount of collapse relative to the thickness of the spacer was 60%, and the amount of collapse relative to the thickness of the electrode body was 6.0 %Met.

Next, as shown in FIG. 4, two of the produced laminate cells are arranged in the stacking direction, one spacer is placed between the laminate cells so as to face the flat part of the electrode body, and two restraining plates ( sandwiched between SUS plates). Next, a load cell (not shown) was placed between one of the SUS plates and the laminate cell to measure stress (reaction force from the electrode body). Next, the bolts on the four sides of the SUS plate were lightly tightened by hand, and stress P was applied from the stacking direction to bring the laminate cell and spacer into close contact. Then, in an atmospheric environment at a temperature of 35°C, charging and discharging were repeated for 1000 cycles in a voltage range of 3 to 4.25V, and at the 1st cycle, 250th cycle, 500th cycle, and 1000th cycle, the laminate cell The reaction force and the amount of swelling (change in thickness) of the laminate cell were measured. Further, after the charge/discharge test was completed, the spacer was taken out, and the Young's modulus of the spacer after 1000 cycles of charge/discharge was measured.

<Example 2> A cell was constructed and evaluated in the same manner as in Example 1 above, except that an EPDM rubber sponge (thickness: 2 mm) having open cells was used as a spacer. The (initial) Young's modulus of this spacer was 0.5 MPa, the amount of collapse relative to the thickness of the spacer was 70%, and the amount of collapse relative to the thickness of the electrode body was 7.0%.

<Example 3> A cell was constructed and evaluated in the same manner as in Example 1 above, except that a silicone rubber sponge (thickness: 2 mm) having open cells was used as a spacer. The (initial) Young's modulus of this spacer was 0.1 MPa, the amount of collapse relative to the thickness of the spacer was 80%, and the amount of collapse relative to the thickness of the electrode body was 8.0%.

<Comparative Example 1> A cell was constructed and evaluated in the same manner as in Example 1 above, except that an EPDM rubber sponge (thickness: 2 mm) without air bubbles was used as a spacer.

<Comparative Example 2> A cell was constructed and evaluated in the same manner as in Example 1 above, except that no spacer was used (Young's modulus was 0 MPa) and only a laminate cell was used.

<Comparative Example 3> A cell was constructed and evaluated in the same manner as in Example 1, except that six laminate cells were arranged in the stacking direction and used for one rubber sponge as in Example 1. Note that the rubber sponge of Example 1 has a thickness of 2 mm and the amount of collapse relative to the thickness of the spacer is 60%, so the actual collapse is 1.2 mm (=2 mm x 0.6). In Comparative Example 3, six laminate cells are arranged, so the amount of collapse with respect to the total thickness of the electrode body (10 mm x 6) is 2% (=(1.2 mm/60 mm) x 100).

<Comparative Example 4> A cell was constructed and evaluated in the same manner as in Example 1 above, except that a hard polyurethane foam (thickness: 2 mm) with a high expansion rate was used as a spacer.

<Example 4> A cell was constructed and evaluated in the same manner as in Example 1 above, except that a natural rubber sponge (thickness: 2 mm) having closed cells was used as a spacer. The (initial) Young's modulus of this spacer was 0.4 MPa, the amount of collapse relative to the thickness of the spacer was 70%, and the amount of collapse relative to the thickness of the electrode body was 7.0%.

The results are summarized in Table 1. Note that the thickness of the aluminum laminate is approximately several tens of microns, which is extremely thin compared to the thickness of the electrode body in the stacking direction (about 20 mm in total for two). The reaction force is considered to be the reaction force of the electrode body. FIG. 5 shows the relationship between the charge/discharge cycle and the reaction force from the electrode body, and FIG. 6 shows the relationship between the charge/discharge cycle and the amount of swelling of the electrode body.

Confirming the results in Table 1, in Comparative Example 1 using a spacer with a small amount of collapse relative to the thickness of the electrode body and a large Young's modulus, as shown in FIG. The reaction force was large, and at the 250th cycle, the reaction force increased further. Furthermore, in Comparative Example 2 in which the spacer was omitted, Li precipitation occurred on the negative electrode and the separator, and as shown in FIG. 6, the laminate cell expanded abnormally and the battery capacity after 1000 cycles decreased significantly. Further, in Comparative Example 3 in which a spacer with a small amount of collapse relative to the thickness of the electrode body was used, as shown in FIG. 5, when the spacer was completely crushed at the 500th cycle, the reaction force from the electrode body rapidly increased. Furthermore, in Comparative Example 4 using a spacer with a small Young's modulus after 1000 cycles, as shown in FIG. 5, the reaction force from the electrode body increased as the number of cycles increased. The reason for this is thought to be that the spacer hardened due to heat generation of the electrode body during charging and discharging or repeated compression.

In contrast to these comparative examples, we used a spacer whose collapse amount when compressed at 1 MPa was 2.5% or more of the thickness of the electrode body, and whose Young's modulus after 1000 charge/discharge cycles was 0.1 MPa to 5 MPa. In Examples 1 to 4 used, as shown in FIG. 5, the reaction force from the electrode body can be suitably absorbed by the spacer during 1 to 1000 cycles of charging and discharging, and the increase in reaction force is stabilized. It was suppressed. As a result, as shown in FIG. 6, the swelling of the cell (electrode body) was effectively suppressed. Such results demonstrate the significance of the technology disclosed herein.

[Theoretical calculation: Simulation of spacer collapse amount]
Furthermore, the appropriate value for the amount of spacer collapse was investigated through theoretical calculations. Specifically, first, a plurality of laminate cells were produced using the same procedure as in the above test example. Note that the proportion of the Si—C composite in the negative electrode active material was 3.15% by mass based on the total negative electrode active material. Next, the laminated cell was restrained together with the spacer with a certain restraining force. At this time, the confining pressure was varied between 5 KPa and 3 MPa, and a plurality of combinations of laminate cells and spacers were prepared. Next, the amount of change in cell thickness (expansion/contraction) and stress fluctuation due to charging/discharging were measured in the same manner as in the above test example. Then, as shown in FIG. 7, the results were plotted with the horizontal axis representing the confining pressure and the vertical axis representing the expansion rate, and an approximate expression for the obtained curve was obtained.

Next, the compression characteristics of the spacer and cell were measured using an autograph, and the restraining force was increased and held for a certain period of time, and the displacement was plotted repeatedly, resulting in a load-displacement curve as shown in Figure 8 (a). (FS curve) was obtained. Next, as shown in FIG. 8(b), the FS curve of the spacer was inverted and plotted so that the starting point coincided with the FS curve of the cell. Then, a simulation was performed in which the following calculations (1) to (3) were performed for 1000 cycles.
(1) Based on the approximation formula of the curve in FIG. 7, calculate the amount of cell expansion for +1 cycle from the expansion speed.
(2) In (a) of FIG. 8, slide the FS curve of the cell by the amount of swelling in (1) (see (c) of FIG. 8).
(3) In FIG. 8, the intersection of the spacer with the FS curve is defined as the reaction force.

Using the results obtained above and the Young's modulus of the spacer separately measured using the same procedure as the test example above, graph the relationship between the Young's modulus of the spacer, the amount of cell swelling, and the reaction force after 1000 cycles, It is shown in FIG. As shown in FIG. 9, the simulation results revealed that it is necessary for the spacer to collapse by at least 2.5% under a stress of 1 MPa when the Young's modulus is in the range of 0.1 MPa to 5 MPa. In other words, it was found that in order to suppress the reaction force from the cell (electrode body) after 1000 cycles to 1 MPa or less, it is necessary to make the amount of spacer collapse 2.5% or more of the thickness of the electrode body. Ta.

As mentioned above, specific aspects of the technology disclosed herein include those described in the following sections.
Item 1: An electrode body in which a positive electrode including a positive electrode active material layer containing a positive electrode active material and a negative electrode including a negative electrode active material layer including a negative electrode active material are laminated in a stacking direction in an insulated state, and the electrode body and a spacer facing the surface of the electrode body in the stacking direction, and the negative electrode includes graphite and silicon-based active materials as the negative electrode active materials, and the total amount of the negative electrode active materials is When expressed as 100% by mass, the silicon-based active material is 3% by mass or more in terms of Si, and the spacer has a crushing amount of 2.5% of the thickness of the electrode body when compressed at 1 MPa. In addition, after 1000 cycles of charging and discharging, stress is applied using an autograph to create a stress-strain curve with the horizontal axis as strain amount and the vertical axis as stress per unit volume. A non-aqueous electrolyte secondary battery, wherein the Young's modulus determined by the slope in the section from the beginning of collapse to the inflection point is 0.1 MPa or more and 5 MPa or less.
Item 2: The nonaqueous electrolyte secondary battery according to Item 1, wherein the amount of collapse is 50% or more and 99% or less of the thickness of the spacer.
Item 3: When stress is applied to the electrode body using an autograph and a stress-strain curve is created with the horizontal axis representing the amount of strain and the vertical axis representing the stress per unit volume, the stress is between 0.5 MPa and 1 MPa. Item 2. The nonaqueous electrolyte secondary battery according to Item 1 or 2, wherein the Young's modulus determined by the slope of the stress strain curve in the section is 30 MPa or more and 200 MPa or less.
Item 4: The nonaqueous electrolyte secondary battery according to any one of Items 1 to 3, wherein the area of the surface of the spacer facing the electrode body is greater than or equal to the area of the positive electrode active material layer.
Item 5: The nonaqueous electrolyte secondary battery according to any one of Items 1 to 4, wherein the spacer is housed inside the exterior body and is in contact with the electrode body.
Item 6: The exterior body is made of a laminate film, and the spacer is disposed outside the exterior body, and further includes a restraining member that applies a restraining pressure to the exterior body and the spacer from the lamination direction. The non-aqueous electrolyte secondary battery according to any one of Items 1 to 4.
Item 7: The non-aqueous electrolyte secondary battery according to any one of Items 1 to 6, wherein the spacer is made of urethane foam or rubber sponge having open cells.

Although the embodiments of the present invention have been described above, the above embodiments are merely examples. The present invention can be implemented in various other forms. The present invention can be implemented based on the content disclosed in this specification and the common general knowledge in the field. The technology described in the claims includes various modifications and changes to the embodiments exemplified above.

For example, in the embodiment described above, the spacer 50 is housed inside the exterior body 10. However, it is not limited to this. As described in the above embodiments, when the exterior body 10 is made of a thin material such as a laminate film, the spacer 50 may be placed outside the exterior body 10. In that case, a restraint means may be further provided that applies restraint pressure to the exterior body 10 and the spacer 50 from the stacking direction Y. By arranging the spacer 50 outside the exterior body 10, the spacer 50 is not exposed to the electrolyte, and the effects of the technology disclosed herein can be stably exhibited over a long period of time. According to the studies of the present inventors, the effects of the technology disclosed herein can be exerted regardless of whether the spacer 50 is placed inside or outside the exterior body 10.

10 Exterior body 20 Electrode body 50 Spacer 100 Non-aqueous electrolyte secondary battery (battery)

Claims (7)

an electrode body in which a positive electrode including a positive electrode active material layer containing a positive electrode active material and a negative electrode including a negative electrode active material layer including a negative electrode active material are stacked in a stacking direction in an insulated state;
an exterior body that houses the electrode body;
a spacer facing the surface of the electrode body in the stacking direction;
A non-aqueous electrolyte secondary battery comprising:
The negative electrode is
The negative electrode active material includes graphite and a silicon-based active material,
When the total amount of the negative electrode active material is 100% by mass, the silicon-based active material is 3% by mass or more in terms of Si,
The spacer is
The amount of collapse when compressed at 1 MPa is 2.5% or more of the thickness of the electrode body, and after 1000 cycles of charging and discharging, stress is applied using an autograph, and the horizontal axis is the strain amount and the vertical axis is the amount of strain. When a stress strain curve is created with stress per unit volume, the Young's modulus determined by the slope in the section from the beginning of collapse to the inflection point of the stress strain curve is 0.1 MPa or more and 5 MPa or less,
Nonaqueous electrolyte secondary battery. The amount of collapse is 50% or more and 99% or less of the thickness of the spacer,
The non-aqueous electrolyte secondary battery according to claim 1. When stress is applied to the electrode body using an autograph and a stress-strain curve is created with the horizontal axis as strain amount and the vertical axis as stress per unit volume, the stress in the range of 0.5 MPa to 1 MPa is determined. Young's modulus determined by the slope of the stress strain curve is 30 MPa or more and 200 MPa or less,
The non-aqueous electrolyte secondary battery according to claim 1 or 2. the area of the surface of the spacer facing the electrode body is greater than or equal to the area of the positive electrode active material layer;
The non-aqueous electrolyte secondary battery according to claim 1 or 2. the spacer is housed inside the exterior body and is in contact with the electrode body;
The non-aqueous electrolyte secondary battery according to claim 1 or 2. The exterior body is made of a laminate film,
the spacer is arranged outside the exterior body,
further comprising restraint means for applying restraint pressure to the exterior body and the spacer from the stacking direction;
The non-aqueous electrolyte secondary battery according to claim 1 or 2. The spacer is made of urethane foam or rubber sponge having open cells.
The non-aqueous electrolyte secondary battery according to claim 1 or 2.

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