Secondary battery and separator for secondary battery

Abstract

This secondary battery comprises: a positive electrode; a negative electrode; a separator that is disposed between the positive electrode and the negative electrode; and a nonaqueous electrolyte solution. At the negative electrode, a metal that is a negative electrode active material is deposited during charging, and the metal is dissolved in the nonaqueous electrolyte solution during discharging. The separator comprises a sheet-shaped base material and a spacer that is disposed on the main surface of the base material. The spacer contains a resin. The degree of swelling of the spacer with respect to the nonaqueous electrolyte solution is 1.1 times to 2 times inclusive.

Description

Secondary battery and separator for secondary battery

[0001] The present disclosure relates to a secondary battery and a separator for a secondary battery.

[0002] Lithium secondary batteries (lithium metal secondary batteries) are known as one type of non-aqueous electrolyte secondary battery. In lithium secondary batteries, lithium metal precipitates on the negative electrode during charging, and the lithium metal dissolves in the non-aqueous electrolyte during discharging. Various proposals have been made for lithium secondary batteries.

[0003] Patent Document 1 proposes "a metal lithium secondary battery in which a negative electrode using lithium or a lithium alloy as the negative electrode active material and a positive electrode made of a chargeable and dischargeable material are arranged opposite each other with a separator interposed therebetween, the metal lithium secondary battery being characterized in that a buffer space for accommodating lithium deposited on the surface of the negative electrode is provided between the negative electrode or the positive electrode and the separator."

[0004] Patent Document 2 proposes "a pattern coating slurry for pattern coating at least one surface of a polyolefin porous substrate used as a substrate for a separator for an electrical storage device, the pattern coating slurry containing a thermoplastic polymer and a dispersion medium or a solvent, and having a maximum high-shear viscosity of 5 cps or more at a shear rate of 50,000 s-1 or less."

[0005] JP 10-012279 A JP 2019-008882 A

[0006] There is a demand for improvements in the initial characteristics and cycle characteristics of secondary batteries equipped with spacers.

[0007] One aspect of the present disclosure relates to a secondary battery including a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte, wherein the negative electrode is an electrode from which a metal serving as a negative electrode active material precipitates during charging and from which the metal dissolves in the non-aqueous electrolyte during discharging, the separator including a sheet-like substrate and a spacer disposed on a main surface of the substrate, the spacer including a resin, and a degree of swelling of the spacer with respect to the non-aqueous electrolyte of 1.1 to 2 times.

[0008] Another aspect of the present disclosure relates to a separator for a secondary battery including a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte solution, the separator including a sheet-like substrate and a spacer disposed on a main surface of the substrate, the spacer including a resin, and a degree of swelling of the spacer with respect to the non-aqueous electrolyte solution of 1.1 times or more and 2 times or less.

[0009] According to the present disclosure, the initial characteristics and cycle characteristics of a secondary battery can be improved.

[0010] The novel features of the present invention are set forth in the appended claims, but the present invention, both in terms of structure and content, together with other objects and features of the present invention, will be better understood from the following detailed description taken in conjunction with the drawings.

[0011] Fig. 2 is a longitudinal sectional view schematically showing an example of a nonaqueous electrolyte secondary battery according to an embodiment of the present disclosure. Fig. 3 is a sectional view schematically showing a part of the lithium secondary battery shown in Fig. 1. Fig. 4 is a top view showing an example of a spacer pattern. Fig. 5 is a top view showing another example of a spacer pattern. Fig. 6 is a top view showing another example of a spacer pattern.

[0012] The following describes embodiments of the present disclosure using examples, but the embodiments of the present disclosure are not limited to the examples described below. In the following description, specific numerical values ​​and materials may be exemplified, but other numerical values ​​and other materials may be applied as long as the invention of the present disclosure can be implemented. In this specification, the term "numerical value A to numerical value B" includes numerical value A and numerical value B and can be read as "numerical value A or more and numerical value B or less." In the following description, when lower and upper limits are exemplified for numerical values ​​of specific physical properties or conditions, any of the exemplified lower limits and any of the exemplified upper limits can be arbitrarily combined as long as the lower limit is not equal to or greater than the upper limit. When multiple materials are exemplified, one of the materials may be selected and used alone, or two or more of the materials may be used in combination.

[0013] A secondary battery according to an embodiment of the present disclosure includes a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte. Hereinafter, the positive electrode, the negative electrode, and the separator are collectively referred to as an "electrode group." The negative electrode is an electrode in which a metal serving as a negative electrode active material precipitates during charging and dissolves into the non-aqueous electrolyte during discharge.

[0014] The metal (negative electrode active material) deposited during charging may be at least one selected from the group consisting of lithium and sodium. The metal deposited during charging may contain lithium. The metal deposited during charging may be lithium metal. The lithium metal may contain trace amounts of other metal elements.

[0015] Lithium secondary batteries, in which lithium metal is deposited on the negative electrode during charging, are also called lithium metal secondary batteries. In the negative electrode of a lithium secondary battery, lithium metal is deposited during charging and dissolves during discharging. The negative electrode has at least a negative electrode current collector, and lithium metal is deposited on the negative electrode current collector.

[0016] In a lithium secondary battery, for example, 70% or more of the rated capacity is realized by the deposition and dissolution of lithium metal. The movement of electrons at the negative electrode during charging and discharging is mainly due to the deposition and dissolution of lithium metal at the negative electrode. Specifically, 70 to 100% (e.g., 80 to 100% or 90 to 100%) of the movement of electrons (or current from another perspective) at the negative electrode during charging and discharging is due to the deposition and dissolution of lithium metal.

[0017] The separator includes a sheet-like substrate and a spacer disposed on a main surface of the substrate. The spacer includes a resin. The spacer has a swelling degree with respect to a non-aqueous electrolyte (an electrolyte solution for a swelling test described later) of 1.1 times or more and 2 times or less. The non-aqueous electrolyte solution contained in the secondary battery may have the same composition as or different from the electrolyte solution for a swelling test described later.

[0018] By disposing the spacer on the main surface of the substrate, a space is formed between the positive electrode and the negative electrode. By accommodating the metal deposited during charging in this space, volumetric change of the electrode group during charge and discharge is suppressed, and deterioration of cycle characteristics due to volumetric change of the electrode group (expansion of the negative electrode due to metal deposition) is suppressed. The spacer is disposed on the main surface of the substrate on the positive electrode side and / or the main surface of the substrate on the negative electrode side.

[0019] The inventors have conducted extensive research focusing on the swelling properties of the spacer and have newly discovered that when the swelling degree of the spacer with respect to the non-aqueous electrolyte solution is in the range of 1.1 times or more and 2 times or less, the initial characteristics (initial efficiency and initial capacity) and cycle characteristics (capacity retention rate) can be improved.

[0020] When the swelling degree of the spacer is 1.1 times or more, the metal ion permeability of the spacer is improved, and deterioration of initial characteristics due to metal ions moving around the spacer between the positive and negative electrodes during charge and discharge can be suppressed. When the swelling degree of the spacer is 2 times or less, dissolution of the spacer in the electrolyte can be suppressed, and deterioration of cycle characteristics due to deterioration of spacer function associated with such dissolution can be suppressed. The swelling degree of the spacer may be 1.2 times or more and 1.8 times or less.

[0021] The degree of swelling of the spacer in a nonaqueous electrolyte can be determined by the following swelling test. First, the secondary battery is disassembled to remove the spacer. The spacer is washed with an organic solvent (dimethoxyethane), and the solvent is then removed by drying to obtain a spacer sample. A coating liquid containing the resin (or resin and filler) that is the component of the spacer is prepared and applied to a substrate (e.g., made of PET). The coating film is then dried at 100°C to form a film on the substrate, which may be used as a spacer sample. The mass W1 and volume V1 of the sample are measured using a hydrometer.

[0022] Next, as a non-aqueous electrolyte solution for the swelling test, an electrolyte solution containing the following non-aqueous solvent and lithium salt is prepared.

[0023] (Electrolyte solution for swelling test) Non-aqueous solvent: mixed solvent of ethylene carbonate (EC) and dimethyl carbonate (DMC) (volume ratio of EC:DMC=3:7) Lithium salt: LiPF ６ (concentration: 1 mol / L) and LiBF ２ (C ２ O ４ ) (concentration: 0.1 mol / L)

[0024] Next, the sample is immersed in the electrolyte solution for the swelling test for 24 hours in an environment of 25±1° C. Thereafter, the sample is taken out of the solution, the electrolyte solution adhering to the surface of the sample is wiped off, and the mass W2 of the sample after immersion is weighed.

[0025] Using the mass W1 and volume V1 of the sample before immersion and the mass W2 of the sample after immersion, the swelling degree is calculated by the following formula: where the specific gravity of the electrolyte is the specific gravity of the electrolyte used in the swelling test, and V2 is the volume of the sample after immersion.

[0026] Swelling ratio (times) = V2 / V1 = (((W2-W1) / specific gravity of electrolyte) / V1) + 1

[0027] (Spacer) The resin contained in the spacer may include a first resin and a second resin. The spacer may be formed in a mixed state of the first resin and the second resin. The first resin is a resin that swells easily, and the swelling degree of the first resin in a non-aqueous electrolyte is 1.1 times or more. The second resin is a resin that swells less than the first resin, and the swelling degree of the second resin in a non-aqueous electrolyte is less than 1.1 times. The swelling degree of the spacer may be adjusted within the above-mentioned range by including the first resin and the second resin in a predetermined ratio. Even if the swelling degree of the first resin exceeds 2 times, the swelling degree of the spacer can be adjusted within the above-mentioned range by using the first resin and the second resin in a predetermined ratio. Furthermore, when the swelling degree of the first resin is 1.1 times or more and 2 times or less, the resin contained in the spacer may be composed only of the first resin. The spacer may be composed only of resin.

[0028] The components of the resin contained in the spacer can be determined by analytical methods such as Fourier transform infrared spectroscopy (FT-IR), pyrolysis gas chromatography mass spectrometry (GC / MS), etc. The resin determined by analysis is used to measure the swelling degree in the same manner as in the case of the swelling degree of the spacer described above, and if the swelling degree is 1.1 times or more, it is determined to be the first resin, and if the swelling degree is less than 1.1 times, it is determined to be the second resin.

[0029] The content of the first resin in the resin (the total of the first resin and the second resin) contained in the spacer may be 2% by volume or more and 50% by volume or less, or may be 10% by volume or more and 40% by volume or less. The content of the first resin can be determined by the analytical method exemplified above.

[0030] The swelling degree of the first resin may be 1.1 to 5 times, or 1.1 to 3 times, or 1.1 to 2 times. In this case, the content of the first resin may be within the above range (2 to 50% by volume or 10 to 40% by volume).

[0031] The swelling degree of the first resin may be 5 times or more and 11 times or less. In this case, the content of the first resin may be 1 volume % or more and less than 20 volume %, or 2 volume % or more and 15 volume % or less. The swelling degree of the second resin may be 1.0 times or more and 1.05 times or less.

[0032] (First Resin) The first resin preferably contains a cellulose compound. In this case, the compressive strength of the spacer is improved, which is advantageous in terms of improving the durability of the spacer against volume changes of the electrode group. The content of the cellulose compound in the first resin may be 80% by volume or more, or 90% by volume or more. The first resin may be composed solely of a cellulose compound. Depending on the type (swelling degree) of the cellulose compound, the resin contained in the spacer may be composed solely of a cellulose compound. The swelling degree of such a cellulose compound may be, for example, 1.1 times or more and 5 times or less, 1.1 times or more and 3 times or less, or 1.1 times or more and 2 times or less.

[0033] A cellulose compound is a polymer having cellulose as a basic skeleton. The cellulose compound is at least one selected from the group consisting of cellulose and cellulose derivatives. The cellulose compound contained in the spacer may be cellulose, a cellulose derivative, or a mixture of cellulose and a cellulose derivative. Examples of cellulose compounds include cellulose in which a portion is substituted with a substituent different from the portion. Examples of cellulose derivatives include alkyl cellulose, carboxymethyl cellulose, nitrocellulose, acetyl cellulose, etc. Examples of alkyl cellulose include methyl cellulose and ethyl cellulose.

[0034] The cellulose compound preferably contains at least one selected from the group consisting of methyl cellulose (swelling degree: 2 times), ethyl cellulose (swelling degree: 10 times), and carboxymethyl cellulose (swelling degree: 1.4 times).

[0035] Examples of the first resin include fluororesins in addition to cellulose compounds. Examples of fluororesins include polyvinylidene fluoride (swelling ratio: 1.1). The first resin may contain, in addition to the cellulose compound, other resins such as fluororesins, alkyl resins, and urethane resins. One type of first resin may be used alone, or two or more types may be used in combination.

[0036] (Second Resin) From the viewpoint of improving the dispersibility of the filler, the second resin preferably contains a polyvinylpyrrolidone compound. When forming a spacer by applying a coating liquid containing spacer components and a liquid medium, the polyvinylpyrrolidone compound is easily dissolved in the liquid medium and can be contained in a large amount in the liquid medium. The polyvinylpyrrolidone compound is at least one selected from the group consisting of polyvinylpyrrolidone (swelling degree 1.01 times) and its derivatives. Polyvinylpyrrolidone is a polymer of N-vinyl-2-pyrrolidone.

[0037] In addition to polyvinylpyrrolidone compounds, examples of the second resin include polyimide resins (swelling degree 1.001 times) and alkyd resins (swelling degree 1.01 times). Alkyd resins are polyester resins produced by a condensation reaction between a polyhydric alcohol and a polybasic acid or its anhydride. Polyimide resins are polymers containing imide bonds in the repeating unit. Examples of polyimide resins include aromatic polyimides containing aromatic rings. One type of second resin may be used alone, or two or more types may be used in combination.

[0038] The resin contained in the spacer may include, as a first resin, at least one resin selected from the group consisting of cellulose compounds and fluororesins, and as a second resin, at least one resin selected from the group consisting of polyvinylpyrrolidone compounds, polyimide resins, and alkyd resins. In this case, the content of the first resin in the total of the first and second resins may be 2% by volume or more and 50% by volume or less. In this case, the effects of the spacer can be stably obtained, and initial characteristics and cycle characteristics are likely to be improved.

[0039] (Others) The spacer may further include a filler. The spacer may be formed in a state where a resin and a filler are mixed. When the spacer further includes a filler, the swelling degree of the spacer is the swelling degree of the spacer including the resin and the filler. For example, the filler may be a material that does not easily swell in a non-aqueous electrolyte solution (for example, a swelling degree of 1.04 times or less or 1.02 times or less).

[0040] The resin content in the spacer may be 30% by volume or more, 40% by volume or more, or 50% by volume or more, or may be 90% by volume or less, 80% by volume or less, or 60% by volume or less. By making the resin content in the spacer 30% by volume or more, it is possible to prevent voids from being formed in the spacer layer, thereby preventing lithium from being deposited in the voids in the spacer layer during charging and improving the capacity retention rate.

[0041] The filler content in the spacer may be 10% by volume or more, 20% by volume or more, or 40% by volume or more, and may be 70% by volume or less, 60% by volume or less, or 50% by volume or less.

[0042] The filler contained in the spacer is not particularly limited. The filler may be an insulating filler. The filler may be an inorganic filler (inorganic particles), an organic filler (organic particles), or a mixture thereof. Examples of filler materials include oxides, nitrides, carbides, etc. Examples of oxides include aluminum oxide (alumina), magnesium oxide, titanium oxide, zirconium oxide, silicon oxide, etc. Examples of nitrides include silicon nitride, aluminum nitride, titanium nitride, etc. Examples of carbides include silicon carbide, etc.

[0043] The shape of the filler (particle) may be spherical or non-spherical. The average particle size of the filler is not particularly limited, but may be 0.1 μm or more, 0.3 μm or more, 0.4 μm or more, or 0.5 μm or more, and may be 10 μm or less, 5 μm or less, or 4 μm or less. The filler may also contain two or more fillers with different average particle sizes. The average particle size can be measured using the following method. First, a cross-section of the spacer is photographed using an electron microscope to obtain an image of the cross-section. Next, the image is subjected to image processing such as binarization to identify the particle portion. Next, the diameter of a circle having the same area as the cross-section of each particle (equivalent circle diameter) is calculated, and the arithmetic mean of the calculated equivalent circle diameters can be used as the average particle size. The arithmetic mean can be calculated from, for example, 20 particles. The average particle size of other particles contained in the electrode plate and separator can also be calculated using a similar method.

[0044] The spacer may be formed on at least one member selected from the group consisting of a positive electrode, a negative electrode, and a substrate. The spacer may be formed on the positive electrode, the negative electrode, or the substrate. From the viewpoint of adhesion, it is preferable that the spacer be formed on the substrate. In the electrode group, the spacer may be disposed on the main surface of the substrate (the main surface on the positive electrode side and / or the main surface on the negative electrode side).

[0045] Depending on the configuration of the secondary battery, the spacer may be formed on only one surface of the at least one member, or may be formed on both surfaces. When the spacer is formed on the positive electrode, the spacer may be formed on at least one of the two main surfaces of the positive electrode that faces the negative electrode. When the spacer is formed on the negative electrode, the spacer may be formed on at least one of the two main surfaces of the negative electrode that faces the positive electrode. When the spacer is formed on the substrate of the separator, the spacer may be formed on either the main surface of the substrate facing the positive electrode or the main surface of the substrate facing the negative electrode.

[0046] The spacer forms a space in at least one region selected from the group consisting of the region between the positive electrode and the substrate and the region between the negative electrode and the substrate. There are no particular limitations on the spacer as long as it can form the space. The spacer may include at least one type selected from the group consisting of linear convex portions and dot-shaped convex portions, or may be at least one type.

[0047] The spacer may include linear protrusions arranged in a mesh pattern. The mesh pattern may be a pattern combining polygons (triangles, squares, hexagons, etc.). For example, the mesh pattern may be a honeycomb pattern. The spacer may include a plurality of linear protrusions arranged in a stripe pattern. The spacer may include a plurality of dot-shaped protrusions regularly arranged at regular intervals.

[0048] The shape of the cross section of the linear protrusions (a cross section perpendicular to the direction in which the linear protrusions extend) is not particularly limited, and may be rectangular, trapezoidal, or semicircular.

[0049] In a member on which spacers are formed, the ratio Rs of the area of ​​the spacers to the area of ​​the surface on which the spacers are formed may be 30% or less, 20% or less, 10% or less, or 5% or less. The ratio Rs may be 1% or more, 3% or more, or 5% or more. When spacers are formed on one side of a substrate, the ratio of the area of ​​the spacers to the area of ​​that one side may be within the range exemplified for the ratio Rs above. For example, when spacers are formed on one side of a substrate, the ratio of the area of ​​the spacers to the area of ​​that one side may be 30% or less.

[0050] The average height Hs of the spacers may be 10 μm or more, or 20 μm or more, or may be 100 μm or less, 50 μm or less, 40 μm or less, or 30 μm or less. The height of the spacers may be approximately constant so that the gap between the electrodes formed by the spacers is approximately constant.

[0051] The average height Hs of the spacers can be measured by the following method. First, a cross section in the thickness direction of a member (e.g., a separator substrate) on which the spacers are formed is photographed using an electron microscope to obtain an image of the cross section. At this time, multiple images are obtained as necessary. Next, five arbitrary locations among the spacers are selected in the image, and the heights of the spacers at those locations are measured. Next, the heights measured at the five locations are arithmetically averaged, and the obtained average value is defined as the average height Hs.

[0052] The spacer may have a non-porous structure that is impermeable to ions of the metal (e.g., lithium ions) that are the negative electrode active material. Such a spacer can be realized by forming the spacer under conditions that prevent the spacer from becoming porous. The method for forming a spacer having a non-porous structure is not particularly limited, and known methods may be used. For example, a spacer having a non-porous structure may be formed by applying the spacer constituent material as an ink to the separator substrate. In this specification, "lithium ion impermeable" means that an amount of lithium ions that would affect the battery's characteristics or shape does not permeate, and includes cases where an amount of lithium ions that is considered to be substantially not permeating moves within the spacer.

[0053] (Method of Forming Spacers) The method of forming spacers is not particularly limited, and they may be formed by the following method. First, a coating liquid is prepared by mixing the spacer components with a liquid medium (dispersion medium). Next, the coating liquid is applied to the area where the spacers are to be formed and then dried. In this manner, the spacers can be formed. The liquid medium used to form the coating liquid is not particularly limited. Examples of the liquid medium include organic solvents (N-methyl-2-pyrrolidone, etc.). The coating liquid may be applied using a dispenser or by using known printing methods such as gravure printing, inkjet printing, and screen printing. Furthermore, drying may be performed by known methods such as drying by heating or natural drying. The swelling degree of the spacer can be adjusted by the resin (or the resin and filler).

[0054] (Separator Substrate) A sheet that can be used as a separator for a non-aqueous electrolyte secondary battery is used as the separator substrate. The substrate may be composed of only a substrate layer. Alternatively, the substrate may include a substrate layer and a composite material layer formed on the substrate layer. The composite material layer contains a polymer and inorganic particles. When the substrate includes a substrate layer and a composite material layer, the separator may be arranged so that the composite material layer faces the positive electrode, or so that the composite material layer faces the negative electrode. When the substrate includes a substrate layer and a composite material layer, a spacer may be formed on the substrate layer or on the composite material layer. By forming a spacer on the composite material layer, the effect of suppressing thermal shrinkage of the substrate layer is particularly enhanced.

[0055] If the temperature of an electrode assembly composed of a positive electrode, a negative electrode, and a separator rises excessively, the substrate layer will shrink, which will likely cause a short circuit between the positive electrode and the negative electrode, further increasing the temperature of the electrode assembly. By laminating a composite material layer on the substrate layer, it is possible to suppress the substrate layer from shrinking when the temperature of the electrode assembly rises. As a result, it is possible to suppress a further temperature rise in the electrode assembly.

[0056] The substrate layer is made of a porous sheet having ion permeability and insulating properties. Examples of porous sheets include porous membranes, woven fabrics, and nonwoven fabrics. The material of the substrate layer is not particularly limited, but may be a polymeric material. Examples of polymeric materials include polyolefin resins, polyamide resins, and cellulose. Examples of polyolefin resins include polyethylene, polypropylene, and copolymers of ethylene and propylene. The substrate layer may contain additives as needed. Examples of additives include inorganic fillers. The substrate layer may be made of a sheet used as a separator in a nonaqueous electrolyte secondary battery (e.g., a lithium secondary battery).

[0057] The composite layer includes a polymer and inorganic particles. The inorganic particles may include first particles and / or second particles. The first particles are particles of a lithium-containing phosphate. The second particles are particles other than the first particles. The composite layer is a layer that allows lithium ions to pass through.

[0058] The phosphate constituting the first particles is lithium phosphate (Li ３ P.O. ４ ), dilithium hydrogen phosphate (Li ２ HPO ４ ), and lithium dihydrogen phosphate (LiH ２ P.O. ４ Among these, lithium phosphate is preferred because it is highly effective in suppressing heat generation in the battery during abnormal conditions.

[0059] A preferred example of the second particles (inorganic particles) is a particle made of an insulating inorganic compound that does not melt or decompose when the battery generates abnormal heat. The second particles may be inorganic particles commonly used as inorganic fillers. Examples of materials for the second particles include aluminum oxide, boehmite, talc, titanium oxide, magnesium oxide, and silicon oxide.

[0060] The polymer contained in the composite material layer is preferably a polymer having higher heat resistance than the main component of the separator substrate layer. The polymer may include at least one selected from the group consisting of aromatic polyamide, aromatic polyimide, and aromatic polyamideimide, or may be at least one of these. These are known as polymers with high heat resistance. Aramid (wholly aromatic polyamide) is preferred from the viewpoint of heat resistance.

[0061] The inorganic particles may include the first particles and second particles other than phosphate. In this case, the composite material layer may include a first layer including the first particles and a second layer including the second particles. This configuration can particularly enhance the effect of suppressing excessive temperature rise in the electrode group. Note that the composite material layer may be composed of only the first layer or only the second layer.

[0062] The first layer and the second layer may be laminated on the main surface of the substrate layer that is the positive electrode side, the main surface that is the negative electrode side, or different main surfaces. For example, the substrate and the spacer may have a laminate structure of substrate layer / first layer / second layer / spacer, substrate layer / second layer / first layer / spacer, first layer / second layer / substrate layer / spacer, or second layer / first layer / substrate layer / spacer. Alternatively, the first layer and the second layer may be arranged on different main surfaces of the substrate layer. For example, the substrate and the spacer may have a laminate structure of first layer / substrate layer / second layer / spacer, or second layer / substrate layer / first layer / spacer.

[0063] The thickness of the substrate is not particularly limited and may be 5 μm or more, or 10 μm or more, and may be 50 μm or less, or 40 μm or less. When the substrate includes a substrate layer and a composite material layer, the thickness of the substrate layer may be 5 μm or more, or 10 μm or more, and may be 50 μm or less, or 40 μm or less.

[0064] When the separator substrate includes a substrate layer and a composite material layer, it may be produced by the following method. First, a substrate layer is prepared. A commercially available substrate layer may be used as the substrate layer. Next, a composite material layer is formed on the substrate layer.

[0065] There is no particular limitation on the method for forming the composite material layer, and it may be formed by the following method. First, a coating liquid is formed by mixing the components of the composite material layer with a liquid medium (dispersion medium). Next, the coating liquid is applied to the substrate layer to form a coating film, and the coating film is then dried. In this manner, the composite material layer can be formed. There is no particular limitation on the liquid medium used to form the coating liquid. Examples of the liquid medium include organic solvents (such as N-methyl-2-pyrrolidone).

[0066] There are no particular limitations on the steps in forming the composite material layer, and known methods can be applied. For example, the coating liquid may be applied by a known method such as a method using a bar coater. Furthermore, the drying may be performed by a known method such as drying by heating or natural drying.

[0067] Examples of each component of the secondary battery will be specifically described below. Note that the components described below are merely examples, and the components of the secondary battery of this embodiment are not limited to the following components. Known components may be used for components other than those characteristic of the secondary battery of this embodiment. Below, the case where the secondary battery is a lithium secondary battery will be mainly described. If the secondary battery is a battery other than a lithium secondary battery, a positive electrode and a negative electrode appropriate for that battery may be used. The separator (substrate and spacer) has been described above, so a duplicated description will be omitted.

[0068] The shape of the secondary battery is not particularly limited, and examples of the shape of the secondary battery include a cylindrical shape, a coin shape, a square shape, a sheet shape, and a flat shape.

[0069] The negative electrode is disposed opposite the positive electrode. The separator is disposed between the positive electrode and the negative electrode. The positive electrode, the negative electrode, and the separator may be wound together so that the separator is disposed between the positive electrode and the negative electrode. When forming a wound electrode assembly, a strip-shaped positive electrode, a strip-shaped negative electrode, and a strip-shaped separator are used. Alternatively, the positive electrode, the negative electrode, and the separator may be stacked. For example, a flat positive electrode, a flat negative electrode, and a flat separator may be stacked. That is, the electrode assembly may be a wound electrode assembly or a stacked electrode assembly.

[0070] (Negative Electrode) The negative electrode includes a negative electrode current collector. In a lithium secondary battery, lithium metal is deposited on the negative electrode current collector upon charging. More specifically, lithium ions contained in the non-aqueous electrolyte solution receive electrons on the negative electrode current collector upon charging, becoming lithium metal, which is then deposited on the negative electrode current collector. The lithium metal deposited on the negative electrode current collector dissolves as lithium ions in the non-aqueous electrolyte solution upon discharging. The lithium ions contained in the non-aqueous electrolyte solution may be derived from a lithium salt added to the non-aqueous electrolyte solution, may be supplied from the positive electrode active material upon charging, or may be both.

[0071] The negative electrode current collector may be a conductive sheet. When the electrode group is a wound type, a strip-shaped conductive sheet is used. Examples of the conductive sheet include a conductive film and a metal foil.

[0072] The material of the negative electrode current collector (conductive sheet) may be any conductive material other than lithium metal and lithium alloys. The conductive material may be a metal. The conductive material is preferably a material that does not react with lithium. The conductive material preferably does not form either an alloy or an intermetallic compound with lithium. Examples of such conductive materials include copper (Cu), nickel (Ni), iron (Fe), alloys containing these metal elements, or graphite with a preferentially exposed basal surface. Examples of alloys include copper alloys and stainless steel (SUS). In terms of high conductivity, the conductive material is preferably copper and / or a copper alloy. The thickness of the negative electrode current collector is not particularly limited and may be in the range of 5 to 300 μm.

[0073] A negative electrode mixture layer may be formed on the surface of the negative electrode current collector. The negative electrode mixture layer is formed, for example, by applying a paste containing a negative electrode active material such as graphite to at least a portion of the surface of the negative electrode current collector. However, from the viewpoint of achieving a high-capacity lithium secondary battery exceeding that of a lithium ion battery, the thickness of the negative electrode mixture layer is set to be sufficiently thin so that lithium metal can be precipitated on the negative electrode.

[0074] The negative electrode may include a negative electrode current collector and a sheet-like lithium metal or lithium alloy disposed on the negative electrode current collector. That is, the negative electrode current collector may be provided with a base layer (a layer of lithium metal or lithium alloy) containing lithium metal in advance. The lithium alloy may contain elements such as aluminum, magnesium, indium, and zinc in addition to lithium. By providing the base layer in advance and depositing lithium metal on it during charging, dendritic deposition can be more effectively suppressed. The thickness of the base layer is not particularly limited, but may be, for example, in the range of 5 μm to 25 μm.

[0075] (Positive Electrode) The positive electrode may include a positive electrode current collector and a positive electrode mixture layer supported on the positive electrode current collector. The positive electrode mixture layer includes a positive electrode active material. The positive electrode mixture layer may include a positive electrode active material, a conductive material, and a binder. The positive electrode mixture layer may be formed on only one side of the positive electrode current collector, or may be formed on both sides. The positive electrode can be formed, for example, by applying a positive electrode mixture slurry containing the positive electrode active material, a conductive material, and a binder to the positive electrode current collector, drying the coating, and then rolling it.

[0076] The positive electrode active material is a material that absorbs and releases lithium ions. Examples of the positive electrode active material include lithium-containing transition metal oxides, transition metal fluorides, polyanions, fluorinated polyanions, and transition metal sulfides. Among these, lithium-containing transition metal oxides are preferred because of their low production cost and high average discharge voltage.

[0077] Examples of transition metal elements contained in the lithium-containing transition metal oxide include Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Y, Zr, and W. The lithium-containing transition metal oxide may contain one or more transition metal elements. The transition metal element may be Co, Ni, and / or Mn. The lithium-containing transition metal oxide may contain one or more typical elements as needed. Examples of typical elements include Mg, Al, Ca, Zn, Ga, Ge, Sn, Sb, Pb, and Bi. The typical element may be Al, etc.

[0078] The conductive material is, for example, a carbon material, such as carbon black, acetylene black, ketjen black, carbon nanotubes, and graphite.

[0079] Examples of the binder include fluororesin, polyacrylonitrile, polyimide resin, acrylic resin, polyolefin resin, rubber polymer, etc. Examples of the fluororesin include polytetrafluoroethylene, polyvinylidene fluoride, etc.

[0080] The positive electrode current collector may be a conductive sheet. Examples of the conductive sheet include foil and film. The surface of the positive electrode current collector may be coated with a carbon material.

[0081] Examples of materials for the positive electrode current collector (conductive sheet) include metal materials containing Al, Ti, Fe, etc. The metal material may be Al, an Al alloy, Ti, a Ti alloy, an Fe alloy, etc. The Fe alloy may be stainless steel (SUS). The thickness of the positive electrode current collector is not particularly limited and may be in the range of 5 to 300 μm.

[0082] (Non-aqueous electrolyte) A non-aqueous electrolyte having lithium ion conductivity contains, for example, a non-aqueous solvent and lithium ions and anions dissolved in the non-aqueous solvent. The non-aqueous electrolyte is prepared by dissolving a lithium salt in the non-aqueous solvent. The dissolution of the lithium salt in the non-aqueous solvent generates lithium ions and anions.

[0083] The non-aqueous electrolyte may be in a gel form. The gel non-aqueous electrolyte contains a lithium salt, a non-aqueous solvent, and a matrix polymer. The matrix polymer may be, for example, a polymer material that absorbs the non-aqueous solvent and gels. Examples of the polymer material include fluororesin, acrylic resin, and polyether resin.

[0084] As the lithium salt or anion, any known material used in the non-aqueous electrolyte of a lithium secondary battery can be used. Specifically, BF ４ － , ClO ４ － , P.F. ６ － , C.F. ３ SO ３ － , C.F. ３ CO ２ － , anions of imides, anions of oxalate complexes, etc. Examples of the anions of imides include N(SO ２ CF ３ ) ２ － , N(C ｍ F ２ｍ＋１ SO ２ ) ｘ (C ｎ F ２ｎ＋１ SO ２ ) ｙ －(m and n are each independently an integer of 0 or 1 or more, and x and y are each independently 0, 1, or 2, satisfying the relationship x+y=2). The anion of the oxalate complex may contain boron and / or phosphorus. Examples of the anion of the oxalate complex include bisoxalate borate anion and difluorooxalate borate anion (BF ２ (C ２ O ４ ) － ), P.F. ４ (C ２ O ４ ) － , P.F. ２ (C ２ O ４ ) ２ － The non-aqueous electrolyte may contain one of these anions alone or two or more of them.

[0085] From the viewpoint of suppressing the deposition of lithium metal in a dendritic form, the nonaqueous electrolyte preferably contains an anion of an oxalate complex. The interaction between the anion of the oxalate complex and lithium facilitates the uniform deposition of lithium metal in the form of fine particles. This facilitates the suppression of local deposition of lithium metal. The anion of the oxalate complex may be combined with another anion. The other anion may be PF ６ － and / or an anion of an imide.

[0086] The non-aqueous electrolyte contains LiBF as a solute (lithium salt). ２ (C ２ O ４ ) (lithium difluorooxalatoborate).

[0087] Examples of non-aqueous solvents include esters, ethers, nitriles, amides, and halogen-substituted derivatives thereof. The non-aqueous electrolyte may contain one or more of these non-aqueous solvents. Examples of halogen-substituted derivatives include fluorides.

[0088] Examples of esters include carbonate esters and carboxylic acid esters. Examples of cyclic carbonate esters include ethylene carbonate, propylene carbonate, and fluoroethylene carbonate (FEC). Examples of chain carbonate esters include dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and diethyl carbonate. Examples of cyclic carboxylic acid esters include γ-butyrolactone and γ-valerolactone. Examples of chain carboxylic acid esters include ethyl acetate, methyl propionate, and methyl fluoropropionate.

[0089] Examples of the ether include cyclic ethers and chain ethers. Examples of the cyclic ethers include 1,3-dioxolane, 4-methyl-1,3-dioxolane, tetrahydrofuran, and 2-methyltetrahydrofuran. Examples of the chain ethers include 1,2-dimethoxyethane, diethyl ether, ethyl vinyl ether, methyl phenyl ether, benzyl ethyl ether, diphenyl ether, dibenzyl ether, 1,2-diethoxyethane, and diethylene glycol dimethyl ether.

[0090] The concentration of the lithium salt in the non-aqueous electrolyte may be, for example, 0.5 mol / L or more and 3.5 mol / L or less. The concentration of the anion in the non-aqueous electrolyte may be 0.5 mol / L or more and 3.5 mol / L or less. Furthermore, the concentration of the anion of the oxalate complex in the non-aqueous electrolyte may be 0.05 mol / L or more and 1 mol / L or less.

[0091] The non-aqueous electrolyte may contain an additive. The additive may form a coating on the negative electrode. The formation of a coating derived from the additive on the negative electrode makes it easier to suppress the formation of dendrites. Examples of such additives include vinylene carbonate, FEC, and vinyl ethyl carbonate (VEC).

[0092] (Others) A secondary battery usually includes an exterior body that houses an electrode group and a non-aqueous electrolyte. The exterior body is not particularly limited, and any known exterior body can be used.

[0093] The method for manufacturing the secondary battery is not particularly limited except for using the separator described above. The secondary battery may be manufactured by a manufacturing method similar to a known manufacturing method. The secondary battery can be manufactured by enclosing an electrode group including a positive electrode, a negative electrode, and a separator, and a nonaqueous electrolyte solution in an exterior case.

[0094] An example of a nonaqueous electrolyte secondary battery according to the present embodiment will be specifically described below with reference to the drawings. The components described above can be applied to the components of the example secondary battery described below. The components of the example described below can be modified based on the above description. The matters described below may also be applied to the above embodiment. In the secondary battery described below, components that are not essential for the secondary battery according to the present disclosure may be omitted. Note that the scale of the components has been changed in the following drawings to facilitate understanding.

[0095] (Embodiment 1) In Embodiment 1, an example of a lithium secondary battery will be described as an example of a nonaqueous electrolyte secondary battery. In this example, a case where a spacer is formed on a separator substrate will be described. Fig. 1 is a vertical cross-sectional view schematically showing a nonaqueous electrolyte secondary battery 10 according to Embodiment 1. Note that in Fig. 1, the spacer and the space formed by the spacer are not shown.

[0096] The cylindrical secondary battery (nonaqueous electrolyte secondary battery) 10 shown in FIG. 1 includes a cylindrical battery case and a wound electrode group 14 and a nonaqueous electrolyte (not shown) housed within the battery case. The battery case includes a case body 15, which is a cylindrical metal container with a bottom, and a sealing body 16 that seals the opening of the case body 15. A gasket 27 is disposed between the case body 15 and the sealing body 16. The gasket 27 ensures the airtightness of the battery case. Within the case body 15, insulating plates 17 and 18 are disposed at both ends of the electrode group 14 in the winding axis direction.

[0097] Case body 15 has a step 21 formed, for example, by pressing a portion of the side wall of case body 15 from the outside. Step 21 may be formed in an annular shape along the circumferential direction of case body 15 on the side wall of case body 15. In this case, sealing body 16 is supported by the surface of step 21 on the opening side.

[0098] The sealing body 16 includes a filter 22, a lower valve body 23, an insulating member 24, an upper valve body 25, and a cap 26. These members are stacked in this order in the sealing body 16. The above-mentioned members constituting the sealing body 16 are, for example, disk-shaped or ring-shaped. The lower valve body 23 and the upper valve body 25 are connected to each other at their respective centers, and an insulating member 24 is interposed between their respective peripheral edges. The filter 22 and the lower valve body 23 are connected to each other at their respective centers. The upper valve body 25 and the cap 26 are connected to each other at their respective centers. In other words, all members except the insulating member 24 are electrically connected to each other.

[0099] A vent hole (not shown) is formed in the lower valve body 23. Therefore, if the internal pressure of the battery case increases due to abnormal heat generation or the like, the upper valve body 25 bulges toward the cap 26 and separates from the lower valve body 23. This cuts off the electrical connection between the lower valve body 23 and the upper valve body 25. If the internal pressure increases further, the upper valve body 25 breaks, and gas is discharged from an opening (not shown) formed in the cap 26.

[0100] Fig. 2 is an enlarged view of a portion of the electrode group 14. Fig. 2 includes a portion near the positive electrode surrounded by region II in Fig. 1 and a portion near the negative electrode surrounded by region III in Fig. 1. Fig. 2 also shows the height h of the spacer 53.

[0101] The electrode group 14 includes a positive electrode 11, a negative electrode 12, and a separator (a substrate 50 having a spacer 53 disposed on a main surface thereof). The positive electrode 11, the negative electrode 12, and the substrate 50 are all strip-shaped. The spacer 53 is formed on the substrate 50. The electrode group 14 is formed by winding the positive electrode 11, the negative electrode 12, and the separator (a substrate 50 having a spacer 53 disposed on a main surface thereof) so that the separator is disposed between the positive electrode 11 and the negative electrode 12.

[0102] The positive electrode 11 includes a positive electrode current collector 11a and a positive electrode composite layer 11b. The positive electrode current collector 11a is electrically connected to a cap 26, which functions as a positive electrode terminal, via a positive electrode lead 19. In FIG. 2, the negative electrode 12 is shown as a negative electrode (negative electrode current collector) on which no lithium metal is deposited. The negative electrode 12 is electrically connected to a case body 15, which functions as a negative electrode terminal, via a negative electrode lead 20.

[0103] 2 , the spacer 53 is formed on the main surface of the substrate 50 on the negative electrode 12 side, but may be formed on the main surface of the substrate 50 on the positive electrode 11 side. The spacer 53 forms a space 14s between the positive electrode 11 and the negative electrode 12.

[0104] During charging of the secondary battery 10, lithium metal is deposited on the negative electrode 12. Because a space 14s exists between the positive electrode 11 and the negative electrode 12, the volume change of the electrode group 14 caused by the deposition of lithium metal is reduced, improving the cycle characteristics.

[0105] An example of the planar shape of the spacer 53 is shown in Fig. 3. The spacer 53 shown in Fig. 3 is composed of linear protrusions. The linear protrusions shown in Fig. 3 are arranged in a mesh pattern. More specifically, the linear protrusions are formed in a honeycomb pattern. The honeycomb pattern is a pattern in which a plurality of hexagons are arranged so as to share sides with each other.

[0106] Another example of the planar shape of the spacer 53 is shown in FIG. 4. The spacer 53 shown in FIG. 4 includes a plurality of linear protrusions that are spaced apart from one another. A gap P exists between the linear protrusions. Another example of the planar shape of the spacer 53 is shown in FIG. 5. The spacer 53 in FIG. 5 includes a plurality of linear protrusions arranged in a stripe pattern. In the examples shown in FIGS. 3 to 5, the areas where no linear protrusions are formed constitute the spaces 14s shown in FIG. 2.

[0107] (Additional Notes) The above embodiments disclose the following technologies. (Technology 1) A secondary battery comprising a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte, wherein the negative electrode is a negative electrode in which a metal serving as a negative electrode active material precipitates during charging and the metal dissolves in the non-aqueous electrolyte during discharging, the separator comprising a sheet-like substrate and a spacer disposed on a main surface of the substrate, the spacer comprising a resin, and a swelling degree of the spacer with respect to the non-aqueous electrolyte of 1.1 times or more and 2 times or less. (Technology 2) The secondary battery according to Technology 1, wherein the resin comprises a first resin and a second resin, and the swelling degree of the first resin with respect to the non-aqueous electrolyte is 1.1 times or more, and the swelling degree of the second resin with respect to the non-aqueous electrolyte is less than 1.1 times. (Technology 3) The secondary battery according to Technology 2, wherein a content of the first resin in the resin is 2% by volume or more and 50% by volume or less. (Technology 4) The secondary battery according to Technology 2 or 3, wherein the first resin contains a cellulose compound. (Technology 5) The secondary battery according to Technology 4, wherein the cellulose compound contains at least one selected from the group consisting of methyl cellulose, ethyl cellulose, and carboxymethyl cellulose. (Technology 6) The secondary battery according to any one of Technology 2 to 5, wherein the second resin contains a polyvinylpyrrolidone compound. (Technology 7) The secondary battery according to any one of Technology 1 to 6, wherein the spacer further contains a filler. (Technology 8) A separator for a secondary battery including a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte, the separator including a sheet-like substrate and a spacer disposed on a main surface of the substrate, the spacer including a resin, and a swelling degree of the spacer with respect to the non-aqueous electrolyte of 1.1 times or more and 2 times or less. (Technology 9) The separator for a secondary battery according to Technology 8, wherein the resin includes a first resin and a second resin, the swelling degree of the first resin with respect to the non-aqueous electrolyte of 1.1 times or more, and the swelling degree of the second resin with respect to the non-aqueous electrolyte of less than 1.1 times.(Technology 10) A secondary battery separator according to Technology 9, wherein the content of the first resin in the resin is 2% by volume or more and 50% by volume or less. (Technology 11) A secondary battery separator according to Technology 9 or 10, wherein the first resin is a cellulose compound. (Technology 12) A secondary battery separator according to Technology 11, wherein the cellulose compound includes at least one selected from the group consisting of methyl cellulose, ethyl cellulose, and carboxymethyl cellulose. (Technology 13) A secondary battery separator according to any one of Technology 9 to 12, wherein the second resin includes a polyvinylpyrrolidone compound. (Technology 14) A secondary battery according to any one of Technology 8 to 13, wherein the spacer further includes a filler.

[0108] [Examples] The secondary battery according to this embodiment will be specifically described below based on examples.

[0109] Secondary Batteries A1-A13, B1-B2 (Preparation of Positive Electrodes) A ​​rock-salt lithium-containing transition metal oxide (NCA: positive electrode active material) containing Li, Ni, Co, and Al (the molar ratio of Li to the total of Ni, Co, and Al was 1.0) and having a layered structure was prepared. This lithium-containing transition metal oxide (NCA), acetylene black (AB: conductive material), and polyvinylidene fluoride (PVdF: binder) were mixed in a mass ratio of NCA:AB:PVdF = 95:2.5:2.5, and an appropriate amount of N-methyl-2-pyrrolidone (NMP) was added and stirred to prepare a positive electrode composite slurry. Next, the resulting positive electrode composite slurry was applied to both sides of a strip-shaped Al foil (positive electrode current collector) and then dried. In this way, a laminate including a positive electrode current collector and a positive electrode composite formed on the positive electrode current collector was formed. Next, the laminate was rolled using a roller. Finally, the rolled laminate was cut to a predetermined size. In this way, a positive electrode including a positive electrode current collector and positive electrode composite layers formed on both sides of the positive electrode current collector was produced.

[0110] (Preparation of Negative Electrode) A negative electrode was prepared by providing rolled lithium metal layers (thickness: 25 μm) on both sides of a strip of copper foil (thickness: 12 μm).

[0111] (Preparation of Separator) (Preparation of Substrate) First, a strip-shaped porous membrane (average thickness 10 μm) made of polyethylene was prepared as a porous sheet (substrate layer). Next, a porous composite material layer (average thickness 2 μm) was formed on one side of the porous membrane to obtain a substrate. The composite material layer was formed by forming a second layer and a first layer in this order on the porous membrane.

[0112] The second layer was formed as follows. First, N-methyl-2-pyrrolidone (NMP) and calcium chloride were mixed in a mass ratio of 94.2:5.8. This mixture was heated to approximately 80°C to completely dissolve the calcium chloride. Then, this solution was returned to room temperature, and 2200 g of it was collected. 0.6 mol of paraphenylenediamine (PPD) was added and completely dissolved. While maintaining this solution at approximately 20°C, 0.6 mol of terephthalic acid dichloride (TPC) was added in small portions. The resulting solution was aged at approximately 20°C for 1 hour to obtain a polymerized solution. Next, 100 g of this polymerized solution was mixed with an N-methyl-2-pyrrolidone solution containing 5.8% by mass of calcium chloride to obtain a solution (coating liquid) containing 2% by mass of paraphenylene terephthalamide (PPTA), an aromatic polyamide (aramid).

[0113] The coating solution was then applied to a substrate layer using a slot die method to form a coating film. The substrate layer on which the coating film was formed was then left to stand for 1 hour in an atmosphere at a temperature of 25°C and a relative humidity of 70% to precipitate the aromatic polyamide. The NMP and calcium chloride in the coating film were then removed by rinsing with water. The coating film was then dried at 60°C for 5 minutes to form a second layer.

[0114] The first layer was formed as follows: First, lithium phosphate (Li ３ P.O. ４Particles of lithium phosphate (LiPO4) and poly(N-vinylacetamide) (PNVA) were mixed in a mass ratio of 100:8 to obtain a mixture. The lithium phosphate particles used had a volume-based median diameter of 0.19 μm. Water (ion-exchanged water) was added to the resulting mixture and stirred to prepare a slurry (coating liquid) with a solids concentration of 12 mass%. The slurry was then applied to the second layer by microgravure coating to form a coating film. The coating film was then dried in a drying oven attached to the coating machine. In this manner, the first layer was formed. In this manner, a composite material layer was formed.

[0115] (Fabrication of Spacers) A coating liquid containing a resin and a filler in a volume ratio of resin:filler=40:60 was prepared. N-methyl-2-pyrrolidone was used as the dispersion medium for the coating liquid. Alumina particles (inorganic filler) were used as the filler.

[0116] The resin contained in the spacer was a first resin and / or a second resin. Batteries A1 to A10 and B1 used the first resin and the second resin. Batteries A11 to A13 used only the first resin. Battery B2 used only the second resin. The compounds shown in Table 1 (methyl cellulose (swelling degree: 2 times), ethyl cellulose (swelling degree: 10 times), carboxymethyl cellulose (swelling degree: 1.4 times), and polyvinylidene fluoride (swelling degree: 1.1 times)) were used as the first resin. The compounds shown in Table 2 (polyvinylpyrrolidone (swelling degree: 1.01 times), polyimide resin (swelling degree: 1.001 times), or alkyd resin (swelling degree: 1.01 times)) were used as the second resin. The values ​​shown in the columns for each compound in Table 1 for the first and second resins represent the content (volume %) of each compound in the resin.

[0117] Next, the coating liquid was applied to the composite material layer using a dispenser so as to form the pattern (honeycomb shape) shown in Figure 3. Thereafter, the coating liquid applied to the composite material layer was dried under vacuum. In this manner, spacers arranged in the pattern shown in Figure 3 were formed. The swelling degrees of the spacers with respect to the non-aqueous electrolyte were the values ​​shown in Table 1. The swelling degrees were determined by the method described above.

[0118] (Preparation of non-aqueous electrolyte) Ethylene carbonate (EC) and dimethyl carbonate (DMC) were mixed in a volume ratio of EC:DMC=30:70. LiPF ６ The concentration of LiBF becomes 1 mol / L. ２ (C ２ O ４ ) were dissolved in the solution so that the concentration of the compound was 0.1 mol / L to prepare a non-aqueous electrolyte solution.

[0119] (Fabrication of Battery) An aluminum tab was attached to the positive electrode obtained above. A nickel tab was attached to the negative electrode. The positive electrode and the negative electrode were spirally wound with a separator in an inert gas atmosphere to prepare a wound electrode group. At this time, the separator was arranged so that the spacer was in contact with the negative electrode. That is, the separator was arranged so that the substrate was arranged on the positive electrode side and the spacer was arranged on the negative electrode side.

[0120] The electrode group was placed in a cylindrical case body with a bottom, and a non-aqueous electrolyte was poured into it. A sealing member was placed over the opening of the case body via a gasket, sealing the electrode group and the non-aqueous electrolyte inside the battery case. In this way, a lithium secondary battery was completed.

[0121] [Evaluation] A charge / discharge test was carried out on each of the batteries prepared as described above. In the charge / discharge test, the batteries were charged in a thermostatic chamber at 45°C under the following conditions, then rested for 20 minutes, and discharged under the following conditions.

[0122] (Charging) The battery was charged at a constant current of 2.15 mA per unit area (cm 2 ) of the electrode until the battery voltage reached 4.1 V, and then charged at a constant voltage of 4.1 V until the current value per unit area of ​​the electrode reached 0.54 mA.

[0123] (Discharge) Constant current discharge was carried out at a current of 2.15 mA per unit area of ​​the electrode until the battery voltage reached 3.75 V.

[0124] (Evaluation of cycle characteristics) The above charge / discharge cycle was repeated, and the discharge capacity C1 at the first cycle and the discharge capacity Cn at the nth cycle were measured. The ratio (percentage) of Cn to C1: 100 × Cn / C1 was calculated as the capacity retention rate. If the capacity retention rate fell below 70%, it was determined that an abnormality had occurred, and the test was stopped. If the capacity retention rate at 100 cycles was 70% or more, it was evaluated as "◯", and if the capacity retention rate fell below 70% by the 100th cycle, it was evaluated as "X".

[0125] (Evaluation of Initial Characteristics) The initial capacity and initial efficiency of each battery were determined. The initial capacity was the discharge capacity at the first cycle. The initial efficiency was the ratio of the discharge capacity at the first cycle to the charge capacity at the first cycle.

[0126] The evaluation results are shown in Table 1. In Table 1, A1 to A13 are secondary batteries of the examples, and B1 and B2 are secondary batteries of the comparative examples.

[0127]

[0128] Batteries A1 to A13 had high initial efficiency, initial capacity, and capacity retention, and exhibited excellent initial characteristics and cycle characteristics. Battery B2, which used only low-swelling polyimide resin, had low initial efficiency and initial capacity due to Li ions migrating between the positive and negative electrodes around the spacer during charge and discharge. Battery B1 contained a large amount of ethyl cellulose, which has a high swelling degree, and the spacer function deteriorated during charge and discharge, causing a large volume change in the electrode group, resulting in an abnormal stop at the 100th cycle.

[0129] The secondary battery of the present disclosure can be used in electronic devices such as mobile phones, smartphones, and tablet terminals, electric vehicles including hybrids and plug-in hybrids, and home storage batteries combined with solar cells.

[0130] While the present invention has been described in terms of presently preferred embodiments, such disclosure is not to be interpreted as limiting. Various changes and modifications will no doubt become apparent to those skilled in the art to which the present invention pertains upon reading the above disclosure. It is therefore intended that the appended claims be interpreted to cover all changes and modifications that do not depart from the true spirit and scope of the invention.

[0131] 10: Lithium secondary battery, 11: Positive electrode, 12: Negative electrode, 14: Electrode group, 14s: Space, 15: Case body, 16: Sealing body, 23: Lower valve body, 25: Upper valve body, 50: Separator substrate, 53: Spacer

Claims

1. A secondary battery comprising: a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte; wherein the negative electrode is an anode from which a metal serving as a negative electrode active material precipitates during charging and from which the metal dissolves in the non-aqueous electrolyte during discharging; the separator comprises a sheet-like substrate and a spacer disposed on a main surface of the substrate; the spacer comprises a resin; and the degree of swelling of the spacer with respect to the non-aqueous electrolyte is 1.1 times or more and 2 times or less.

2. The secondary battery according to claim 1, wherein the resin comprises a first resin and a second resin, the degree of swelling of the first resin with respect to the non-aqueous electrolyte solution is 1.1 times or more, and the degree of swelling of the second resin with respect to the non-aqueous electrolyte solution is less than 1.1 times.

3. The secondary battery according to claim 2, wherein the content of the first resin in the resin is 2% by volume or more and 50% by volume or less.

4. The secondary battery according to claim 2 or 3, wherein the first resin contains a cellulose compound.

5. The secondary battery according to claim 4, wherein the cellulose compound includes at least one selected from the group consisting of methyl cellulose, ethyl cellulose, and carboxymethyl cellulose.

6. The secondary battery according to claim 2 or 3, wherein the second resin contains a polyvinylpyrrolidone compound.

7. The secondary battery according to claim 1, wherein the spacer further includes a filler.

8. A separator for a secondary battery comprising a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte, the separator comprising: a sheet-like substrate; and a spacer disposed on a main surface of the substrate, the spacer including a resin, and a degree of swelling of the spacer with respect to the non-aqueous electrolyte of 1.1 times or more and 2 times or less.

9. The secondary battery separator according to claim 8, wherein the resin comprises a first resin and a second resin, the degree of swelling of the first resin with respect to the non-aqueous electrolyte is 1.1 times or more, and the degree of swelling of the second resin with respect to the non-aqueous electrolyte is less than 1.1 times.

10. The secondary battery separator according to claim 9, wherein the content of said first resin in said resin is 2% by volume or more and 50% by volume or less.

11. The secondary battery separator according to claim 9 or 10, wherein the first resin is a cellulose compound.

12. The secondary battery separator according to claim 11, wherein the cellulose compound includes at least one selected from the group consisting of methyl cellulose, ethyl cellulose, and carboxymethyl cellulose.

13. The secondary battery separator according to claim 9 or 10, wherein the second resin contains a polyvinylpyrrolidone compound.

14. The secondary battery separator according to claim 8, wherein the spacer further contains a filler.

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