Secondary battery and separator for secondary battery

Abstract

This secondary battery comprises: a positive electrode; a negative electrode; a separator disposed between the positive electrode and the negative electrode; a spacer disposed between the positive electrode or the negative electrode and the separator; and an electrolyte solution. The spacer contains a first resin and a second resin. The first resin has a degree of swelling with respect to the electrolyte solution of 1.1 times or more, and the second resin has a degree of swelling with respect to the electrolyte solution of less than 1.1 times. The abundance ratio of the first resin to the total of the first resin and the second resin is greater on the positive electrode side of the spacer than on the negative electrode side of the spacer.

Description

Secondary batteries and separators for secondary batteries Cross-reference of related applications

[0001] This disclosure claims priority rights to Japanese Patent Application No. 2025-030704, filed with the Japan Patent Office on 27 February 2025, and the entirety of the said patent application is incorporated herein by reference.

[0002] This disclosure relates to secondary batteries and separators for secondary batteries.

[0003] A secondary battery comprises an electrode group and a non-aqueous electrolyte. The electrode group includes a positive electrode, a negative electrode, and a separator placed between the positive and negative electrodes. Examples of secondary batteries include lithium-ion batteries and lithium secondary batteries (lithium metal secondary batteries).

[0004] To suppress volume changes in the electrode group during charging and discharging, it is conceivable to place a spacer between the positive or negative electrode and the separator.

[0005] Patent Document 1 proposes a metallic lithium secondary battery in which a negative electrode having lithium or a lithium alloy as the negative electrode active material and a positive electrode made of a rechargeable material are arranged opposite each other with a separator in between, characterized in that there is a buffer space between the negative electrode or the positive electrode and the separator for accommodating lithium deposited on the surface of the negative electrode.

[0006] Patent Document 2 describes a pattern coating slurry for pattern coating at least one side of a polyolefin porous substrate used as a substrate for a separator for an energy storage device, wherein the pattern coating slurry comprises a thermoplastic polymer and a dispersion medium or solvent, and the pattern coating slurry has a shear rate of 50,000 s. －１ A slurry for pattern coating has been proposed in which the maximum high-shear viscosity is 5 cps or more.

[0007] Japanese Patent Publication No. 10-012279 Japanese Patent Publication No. 2019-008882

[0008] In recent years, there has been a growing demand for improved initial and cycle characteristics of secondary batteries equipped with spacers.

[0009] One aspect of this disclosure relates to a secondary battery comprising a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, a spacer disposed between the positive electrode or the negative electrode and the separator, and an electrolyte, wherein the spacer comprises a first resin and a second resin, the first resin having a degree of swelling of 1.1 times or more relative to the electrolyte, the second resin having a degree of swelling of less than 1.1 times relative to the electrolyte, and the ratio of the first resin to the sum of the first resin and the second resin is greater on the positive electrode side of the spacer than on the negative electrode side of the spacer.

[0010] Another aspect of the present disclosure relates to a separator having a spacer, which is disposed between the positive and negative electrodes of a secondary battery, wherein the spacer is disposed on the main surface of the separator, and the spacer comprises a first resin and a second resin, wherein the first resin has a degree of swelling of 1.1 times or more relative to the electrolyte, and the second resin has a degree of swelling of less than 1.1 times relative to the electrolyte, and the ratio of the first resin to the sum of the first resin and the second resin is greater on the positive electrode side of the spacer than on the negative electrode side of the spacer.

[0011] According to this disclosure, the initial and cycle characteristics of secondary batteries can be improved. Novel features of the present invention are described in the appended claims, but the present invention, in conjunction with other objects and features of the present invention, will be better understood by the following detailed description in conjunction with the drawings, both in terms of structure and content.

[0012] This is a schematic longitudinal cross-sectional view showing an example of a secondary battery according to the embodiment of this disclosure. This is a schematic cross-sectional view showing a part of the secondary battery shown in Figure 1. This is a schematic top view showing an example of a spacer pattern. This is a schematic top view of the main part showing an example of a spacer. This is a schematic cross-sectional view showing an example of a spacer. This is a schematic cross-sectional view showing another example of a spacer. This is a schematic cross-sectional view showing yet another example of a spacer. This is a schematic top view showing yet another example of a spacer pattern.

[0013] Hereinafter, embodiments according to the present disclosure will be described by way of examples, but embodiments according to 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 according to the present disclosure can be implemented. In this specification, the description "from numerical value A to numerical value B" includes numerical value A and numerical value B, and can be read as "not less than numerical value A and not more than numerical value B". In the following description, when lower limits and upper limits are exemplified for numerical values of specific physical properties, conditions, etc., any combination of any of the exemplified lower limits and any of the exemplified upper limits can be freely used, as long as the lower limit does not exceed the upper limit. When a plurality of materials are exemplified, one type may be selected from them and used alone, or two or more types may be combined and used.

[0014] The present disclosure encompasses combinations of matters recited in two or more claims arbitrarily selected from the plurality of claims recited in the appended claims. In other words, as long as no technical contradiction arises, matters recited in two or more claims arbitrarily selected from the plurality of claims recited in the appended claims can be combined.

[0015] 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, a spacer disposed between the positive electrode or the negative electrode and the separator, and an electrolytic solution. The spacer includes a first resin and a second resin. The first resin has a degree of swelling with respect to the electrolytic solution of 1.1 times or more, and the second resin has a degree of swelling with respect to the electrolytic solution of less than 1.1 times. The abundance ratio of the first resin to the total of the first resin and the second resin is higher on the positive electrode side of the spacer than on the negative electrode side of the spacer (the abundance ratio of the second resin to the total of the first resin and the second resin is lower). The electrolytic solution included in the secondary battery may have the same composition as or a different composition from the electrolytic solution for the swelling test described later.

[0016] With the above configuration, initial characteristics (initial efficiency and initial discharge capacity) and cycle characteristics (capacity retention rate) can be improved.

[0017] On the positive electrode side of the spacer, the high abundance ratio of the first resin improves Li ion permeability. Accordingly, when Li ions move between the positive electrode and the negative electrode during (initial) charging, the Li ions easily permeate through the inside of the spacer. Therefore, the amount of Li ions that travel around the spacer to move from the positive electrode to the negative electrode during charging and discharging can be reduced, and the deterioration of initial characteristics caused by the decrease in (initial) charging capacity is suppressed.

[0018] On the negative electrode side of the spacer, the low abundance ratio of the first resin, that is, the high abundance ratio of the second resin, suppresses excessive swelling of the spacer caused by the electrolytic solution. The formation of a region having a high abundance ratio of the second resin suppresses excessive swelling of the spacer caused by the electrolytic solution, making it easy to maintain the shape of the spacer. Therefore, the deterioration of the spacer function (the function of suppressing volume change of the electrode group) is suppressed, and the deterioration of cycle characteristics is also suppressed. If the spacer function deteriorates, sufficient space cannot be formed by the spacer, the volume change of the electrode group during charging and discharging increases, and cycle characteristics may deteriorate due to occurrence of buckling of the electrode or the like.

[0019] In the case of a lithium secondary battery, since lithium metal is precipitated on the negative electrode during charging, the effect of improving initial characteristics provided by the above spacer can be remarkably obtained. Further, in the case of a lithium secondary battery, since the degree of expansion of the negative electrode caused by precipitation of lithium metal during charging is large, the effect of improving cycle characteristics provided by the above spacer can be remarkably obtained.

[0020] If the abundance ratio of the first resin is lower (the abundance ratio of the second resin is higher) on the positive electrode side of the spacer than on the negative electrode side of the spacer, Li ions travel around the spacer to move from the positive electrode to the negative electrode during (initial) charging, which reduces the (initial) charging capacity and deteriorates the initial characteristics.

[0021] If the abundance ratio of the first resin is high on both the negative electrode side and the positive electrode side of the spacer, the progress of swelling of the spacer caused by the electrolytic solution tends to reduce the stability of space formation by the spacer, which increases the volume change of the electrode group during charging and discharging and deteriorates the cycle characteristics.

[0022] If the proportion of the second resin is large on both the negative and positive sides of the spacer, during the (initial) charge, Li ions will move from the positive to the negative electrode by circling around the spacer, reducing the (initial) charge capacity and consequently degrading the initial performance.

[0023] As described above, in this disclosure, the proportion of the first resin is greater on the positive electrode side of the spacer than on the negative electrode side (the proportion of the second resin is smaller). The above proportion may be, for example, a volume ratio or a mass ratio. The proportion of the first resin may be increased stepwise (or continuously) from the negative electrode side to the positive electrode side of the spacer. In a cross-section parallel to the thickness direction of the spacer, the area ratio of the first resin may be greater on the positive electrode side than on the negative electrode side. In a cross-section parallel to the thickness direction of the spacer, the area ratio of the first resin may be increased stepwise (or continuously) from the negative electrode side to the positive electrode side of the spacer.

[0024] The spacer may have a region with a higher concentration of the first resin on the positive electrode side and a region with a higher concentration of the second resin on the negative electrode side. Each region may be a single region where the ratio of the first resin is approximately constant, or it may include two or more regions with different ratios of the first resin. In the region with a higher concentration of the first resin, the ratio of the first resin to the total of the first and second resins may be, for example, 50% by volume or more (or 70% by volume or more). In the region with a higher concentration of the second resin, the ratio of the first resin to the total of the first and second resins may be, for example, less than 50% by volume (or 30% by volume or less).

[0025] (First region, second region) The spacer may have a first region on the positive electrode side and a second region on the negative electrode side. In the first region, the proportion of the first resin to the sum of the first and second resins is greater than in the second region. In a cross section parallel to the thickness direction of the spacer, the area ratio X1 of the first resin to the sum of the first and second resins in the first region is greater than the area ratio X2 of the first resin to the sum of the first and second resins in the second region. It is preferable that the area ratio X1 of the first resin is 50% or more, and the area ratio X2 of the first resin is less than 50%. In other words, in a cross section parallel to the thickness direction of the spacer, it is preferable that the area ratio Y1 of the second resin to the sum of the first and second resins in the first region is 50% or less, and the area ratio Y2 of the second resin to the sum of the first and second resins in the second region is greater than 50%.

[0026] In a cross-section parallel to the thickness direction of the spacer, the ratio of the area ratio of the first resin to the sum of the first and second resins in the second region, X2 / X1, to the area ratio of the first resin to the sum of the first and second resins in the first region, X1, may be 0 or more and 1 / 2 or less, or 0 or more and 1 / 3 or less (or 1 / 4 or less).

[0027] The sum of the area ratio Y1 of the second resin to the total area of ​​the first resin and the second resin in the first region, and the above area ratio X1, is 100%. The sum of the area ratio Y2 of the second resin to the total area of ​​the first resin and the second resin in the second region, and the above area ratio X2, is 100%.

[0028] From the viewpoint of improving initial properties, the area ratio X1 of the first resin is preferably 50% or more, more preferably 70% or more (or 75% or more). The area ratio Y1 of the second resin is preferably 50% or less, more preferably 30% or less (or 25% or less).

[0029] Furthermore, the area ratio X1 of the first resin may be 100% or less, and the area ratio Y1 of the second resin may be 0% or more. From the viewpoint of improving cycle characteristics, the area ratio X1 of the first resin may be 90% or less, or 85% or less. All of the resin contained in the first region may be the first resin. That is, in the first region, the area ratio X1 of the first resin may be 100%, and the area ratio Y1 of the second resin may be 0%.

[0030] From the viewpoint of improving cycle characteristics, the area ratio X2 of the first resin is preferably less than 50%, and more preferably 30% or less (or 25% or less). The area ratio Y2 of the second resin is preferably greater than 50%, and more preferably 70% or more (or 75% or more).

[0031] Furthermore, the area ratio X2 of the first resin may be 0% or more, and the area ratio Y2 of the second resin may be 100% or less. The area ratio X2 of the first resin may be 10% or more, or 15% or more. In this case, the decrease in discharge capacity due to Li ions moving from the negative electrode to the positive electrode around the spacer during discharge is suppressed, and the discharge capacity is further improved. All of the resin included in the second region may be the second resin. That is, in the first region, the area ratio Y1 of the first resin may be 0%, and the area ratio Y2 of the second resin may be 100%.

[0032] From the viewpoint of improving initial characteristics, the area ratio S1 of the first region in a cross-section parallel to the thickness direction of the spacer is preferably 20% or more, and more preferably 50% or more. From the viewpoint of improving cycle characteristics, the area ratio S1 of the first region in a cross-section parallel to the thickness direction of the spacer may be 90% or less, 80% or less, or 60% or less. The sum of the area ratio S2 of the second region in a cross-section parallel to the thickness direction of the spacer and the area ratio S1 of the first region is 100%. The area ratio S1 (S2) of the first region (second region) in a cross-section parallel to the thickness direction of the spacer may be adjusted by the thickness of the first region (second region) in that cross-section.

[0033] The first region may be a single region where the abundance ratio of the first resin is approximately constant, or it may include two or more regions with different abundance ratios of the first resin. In a cross-section parallel to the thickness direction of the spacer, the first region may be a single region where the area ratio of the first resin is approximately constant, or it may include two or more regions with different area ratios of the first resin. In the first region, the abundance ratio (area ratio) of the first resin may be increased stepwise or continuously as it moves away from the second region.

[0034] The second region may be a single region where the abundance ratio of the second resin is approximately constant, or it may include two or more regions with different abundance ratios of the second resin. In a cross-section parallel to the thickness direction of the spacer, the second region may be a single region where the area ratio of the second resin is approximately constant, or it may include two or more regions with different area ratios of the second resin. In the second region, the abundance ratio (area ratio) of the second resin may be increased stepwise or continuously as it moves away from the first region.

[0035] The first region may have a first A region on the positive electrode side and a first B region on the second region side. In the first A region, the proportion of the first resin to the sum of the first and second resins is greater than in the first B region. In a cross-section parallel to the thickness direction of the spacer, the area ratio X1A of the first resin to the sum of the first and second resins in the first A region is greater than the area ratio X1B of the first resin to the sum of the first and second resins in the first B region.

[0036] In a cross-section parallel to the thickness direction of the spacer, the area ratio X1A of the first resin to the sum of the first and second resins in region 1A is preferably greater than 65%, and the area ratio X1B of the first resin to the sum of the first and second resins in region 1B is preferably 50% or more and 65% or less.

[0037] The area ratio X1A of the first resin in the first A region may be greater than 65% and 100% or less, or 75% or more and 100% or less. The area ratio S1A of the first A region in a cross section parallel to the thickness direction of the spacer may be 10% or more and 60% or less, or 20% or more and 60% or less (or 50% or less). In a cross section parallel to the thickness direction of the spacer, the area ratio of the first B region to the first A region may be, for example, 1 / 3 or more and 3 or less.

[0038] The second region may have a second A region on the first region side and a second B region on the negative electrode side. In the second A region, the proportion of the first resin to the sum of the first and second resins is greater than in the second B region. In a cross-section parallel to the thickness direction of the spacer, the area ratio X2A of the first resin to the sum of the first and second resins in the second A region is greater than the area ratio X2B of the first resin to the sum of the first and second resins in the second B region.

[0039] In a cross-section parallel to the thickness direction of the spacer, the area ratio X2A of the first resin to the sum of the first and second resins in region 2A is preferably 35% or more and less than 50%, and the area ratio X2B of the first resin to the sum of the first and second resins in region 2B is preferably less than 35%.

[0040] The area ratio X2B of the first resin in the second B region may be 0% or more and less than 35%, or 0% or more and 25% or less. The area ratio S2B of the second B region in a cross section parallel to the thickness direction of the spacer may be 10% or more and 60% or less, or 20% or more and 60% or less (or 50% or less). In a cross section parallel to the thickness direction of the spacer, the area ratio of the second B region to the second A region may be, for example, 1 / 3 or more and 3 or less.

[0041] (Measurement of resin swelling degree) The degree of swelling of the resin contained in the spacer relative to the electrolyte can be determined by the following swelling test.

[0042] First, the secondary battery is disassembled to remove the spacer, and the resin contained in the spacer is identified. The components of the resin contained in the spacer can be determined by analytical methods such as Fourier transform infrared spectroscopy (FT-IR) and pyrolysis gas chromatography-mass spectrometry (GC / MS).

[0043] The resin obtained above is prepared and dissolved in a predetermined solvent to obtain a resin solution. The resin solution is applied to a substrate (e.g., PET), and the coating is heated and dried at 100°C to obtain a resin film as a sample. The mass W1 and volume V1 of the sample are measured using a hydrometer.

[0044] Next, prepare an electrolyte solution (non-aqueous electrolyte) containing the following non-aqueous solvent and lithium salt for the swelling test.

[0045] (Electrolyte for swelling test) Non-aqueous solvent: Mixed solvent of ethylene carbonate (EC) and dimethyl carbonate (DMC) (EC:DMC = 3:7 volume ratio) Lithium salt: LiPF ６ (Concentration: 1 mol / L) and LiBF ２ (C ２ O ４ (Concentration: 0.1 mol / L)

[0046] Next, the sample is immersed in an electrolyte solution for swelling testing at an environment of 25±1℃ for 24 hours. After that, the sample is removed from 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.

[0047] Using the mass W1 and volume V1 of the sample before immersion and the mass W2 of the sample after immersion, as determined above, the degree of swelling can be calculated using the following formula. In the formula, the specific gravity of the electrolyte is the specific gravity of the electrolyte used for the swelling test described above. V2 is the volume of the sample after immersion.

[0048] Swelling degree (times) = V2 / V1 = (((W2-W1) / specific gravity of electrolyte) / V1) + 1

[0049] If the required swelling is 1.1 times or more, it is designated as the first resin; if the required swelling is less than 1.1 times, it is designated as the second resin.

[0050] The first and second regions can be determined as follows: Disassemble the battery and remove the spacer. Confirm the first and second resins contained in the spacer using the method described above. Take a cross-sectional image of the spacer parallel to its thickness using a scanning electron microscope (SEM). If the spacer contains filler, the resin and filler can be distinguished in the SEM image. Perform energy-dispersive X-ray spectroscopy (EDX) analysis (SEM-EDX analysis) using the SEM image to perform mapping analysis for specific elements contained in the resin and investigate the distribution state of the resin. For example, in the case of PVP resin, perform mapping analysis for nitrogen. Alternatively, the distribution state of either the first or second resin can be determined by SEM-EDX analysis, and the distribution state of the other resin can be determined based on the distribution state of one resin and the SEM image. Based on the above SEM images and mapping analysis results, it was confirmed that the proportion of the first resin is greater on the positive electrode side of the spacer than on the negative electrode side. The regions with a high concentration of the first resin (region 1) and regions with a high concentration of the second resin (region 2) were identified, and the area ratio of the first resin in each region was determined. The total cross-sectional area of ​​the first resin and the total cross-sectional area of ​​the second resin were determined from the cross-sectional images of the first region (region 2) obtained by SEM, and the area ratio X1 (area ratio X2) was calculated from these values.

[0051] (Spacer) The spacer may be placed between the positive electrode and the separator, or between the negative electrode and the separator. The spacer may also include a first spacer placed between the positive electrode and the separator, and a second spacer placed between the negative electrode and the separator. In this case, in the second spacer, the proportion of the first resin is greater on the positive electrode side (separator side) than on the negative electrode side. In the first spacer, the proportion of the first resin is greater than in the second spacer, and the proportion of the first resin is greater on the positive electrode side than on the negative electrode side (separator side).

[0052] The spacer comprises a first resin and a second resin. The components of the first resin (or second resin) may differ between the first and second regions, but it is preferable that the components of the first and second resins are the same in both regions. By increasing the proportion (area ratio) of the first resin in the first region compared to the second region, it is easier to improve the initial properties and cycle properties.

[0053] (First Resin) The first resin is a resin that swells easily, and its degree of swelling with respect to the electrolyte is 1.1 times or more. The degree of swelling of the first resin 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.

[0054] The first resin preferably contains cellulose resin. In this case, the compressive strength and heat resistance of the spacer are improved, which is advantageous in terms of improving the durability of the spacer against volume changes of the electrode group. The cellulose resin content in the first resin may be 50% by volume or more, 75% by volume or more, or 90% by volume or more. The first resin may consist only of cellulose resin.

[0055] Cellulose resin is a polymer with cellulose as its basic backbone. A cellulose resin is at least one selected from the group consisting of cellulose and cellulose derivatives. The cellulose resin contained in the spacer may be cellulose, a cellulose derivative, or a mixture of cellulose and a cellulose derivative. Examples of cellulose resins include cellulose in which a portion is substituted with a different substituent. Examples of cellulose derivatives include alkylcellulose, carboxymethylcellulose, nitrocellulose, and acetylcellulose. Examples of alkylcellulose include methylcellulose and ethylcellulose.

[0056] The cellulose resin preferably contains at least one selected from the group consisting of methylcellulose (swells twice), ethylcellulose (swells tenfold), and carboxymethylcellulose (swells 1.4 times).

[0057] Examples of the first resin include cellulose resin, as well as fluororesin, oxetane resin, and urethane resin. Examples of fluororesin include polyvinylidene fluoride (swelling degree 1.1 times). The first resin may be used alone or in combination of two or more types.

[0058] (Second Resin) The second resin is less prone to swelling than the first resin, and its degree of swelling in relation to the electrolyte is less than 1.1 times. The degree of swelling of the second resin may be, for example, 1.0 times or more and less than 1.1 times, or 1.0 times or more and 1.05 times or less.

[0059] From the viewpoint of improving the durability and cycle characteristics of the spacer, the second resin preferably contains at least one selected from the group consisting of polyvinylpyrrolidone resin, polyimide resin, and alkyd resin.

[0060] In particular, from the viewpoint of improving the dispersibility of the filler, it is more preferable that the second resin contains polyvinylpyrrolidone (PVP) resin. When forming a spacer by applying a coating solution containing the spacer components and a liquid medium, the PVP resin dissolves easily in the liquid medium and can be included in large quantities in the liquid medium.

[0061] The PVP resin (swelling degree 1.01 times) is at least one selected from the group consisting of polyvinylpyrrolidone and its derivatives. Polyvinylpyrrolidone is a polymer of N-vinyl-2-pyrrolidone.

[0062] Polyimide resins (swelling degree 1.001 times) are polymers that contain imide bonds in their repeating units. Examples of polyimide resins include aromatic polyimides that contain aromatic rings. Alkyd resins (swelling degree 1.01 times) are polyester resins produced by the condensation reaction of a polyhydric alcohol with a polybasic acid or its anhydride. Examples of second resins include acrylic resins. Examples of acrylic resins include polymethyl methacrylate. The second resin may be used alone or in combination of two or more types.

[0063] (Filler) The spacer may be composed of resin only, but may also contain resin and filler, or may be formed in a state in which resin and filler are mixed. Preferably, the composition of the filler is the same in the first region and the filler content is approximately the same. In the first region, the initial properties and cycle properties can be easily improved by increasing the proportion (area ratio) of the first resin compared to the second region. The composition of the filler may be different in the first region and the filler content may be different.

[0064] The resin content in the spacer may be 30% by volume or more, 40% by volume or more, or 50% by volume or more, and may be 90% by volume or less, 80% by volume or less, or 60% by volume or less. By setting the resin content in the spacer to 30% by volume or more, the formation of voids in the spacer layer can be suppressed, thereby suppressing the deposition of lithium in the voids in the spacer layer during charging and improving the capacity retention rate.

[0065] 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.

[0066] Fillers are used, for example, to improve the strength, thermal stability, and chemical stability of spacers. Typically, fillers are made of materials that do not swell easily in the electrolyte (for example, materials with a swelling degree of 1.02 times or less, or 1.01 times or less). The fillers contained in spacers are not particularly limited. The fillers may also be insulating fillers. For example, inorganic fillers (inorganic particles) are used. Examples of filler materials include oxides, nitrides, and carbides. Examples of oxides include aluminum oxide (alumina), magnesium oxide, titanium oxide, zirconium oxide, and silicon oxide. Examples of nitrides include silicon nitride, aluminum nitride, and titanium nitride. Examples of carbides include silicon carbide.

[0067] The shape of the filler (particles) may be spherical or other shapes. The average particle size of the filler is not particularly limited, but may be 0.1 μm or larger, 0.3 μm or larger, 0.4 μm or larger, or 0.5 μm or larger, and may be 10 μm or smaller, 5 μm or smaller, or 4 μm or smaller. The filler may also contain two or more types of fillers with different average particle sizes. The average particle size can be measured by the following method. First, the cross-section of the spacer is photographed with an electron microscope to obtain an image of the cross-section. Next, image processing such as binarization is performed on the image to identify the parts containing particles. Next, the diameter of a circle with the same area as the cross-sectional area of ​​each particle (equivalent circle diameter) is determined, and the arithmetic mean of the obtained equivalent circle diameters can be used as the average particle size. The arithmetic mean can be calculated, for example, from 20 particles. The average particle size of other particles contained in the electrode plate and separator can be determined by the same method.

[0068] The spacer may be formed on at least one component selected from the group consisting of a positive electrode, a negative electrode, and a separator. The spacer may be formed on the positive electrode, on the negative electrode, or on the separator. Depending on the configuration of the secondary battery, the spacer may be formed on only one side of the at least one component, or on both sides. When the spacer is formed on the positive electrode, the spacer may be formed on at least the main surface 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 the main surface of the negative electrode that faces the positive electrode.

[0069] From the viewpoint of ease of manufacturing the electrode group and ensuring good adhesion between the spacer and the component, it is preferable that the spacer is formed on the separator. That is, a separator having a spacer is preferred. In this case, the spacer is arranged on the main surface of the separator, and may be arranged on the main surface on the positive electrode side of the separator, or on the main surface on the negative electrode side of the separator.

[0070] The spacer creates a space in at least one region selected from the group consisting of the region between the positive electrode and the separator, and the region between the negative electrode and the separator. In a lithium secondary battery, the lithium metal deposited during charging is contained in this space, thereby suppressing volume changes in the electrode group. There are no particular limitations as long as the spacer can form this space. The spacer may include at least one selected from the group consisting of linear protrusions and dot-shaped protrusions.

[0071] The spacer may include linear protrusions arranged in a mesh-like pattern. The mesh-like pattern may be a pattern of combinations of polygons (triangles, quadrilaterals, hexagons, etc.). For example, the mesh-like pattern may be a honeycomb pattern. The spacer may include multiple linear protrusions arranged in a stripe pattern. The spacer may include multiple dot-shaped protrusions regularly arranged at regular intervals.

[0072] The width W of the linear protrusion may be, for example, 100 μm or more, 200 μm or more, or 2000 μm or less, or 1000 μm or less. The thickness T of the linear protrusion may be within the range of the average height Hs of the spacer described later.

[0073] The shape of the cross-section of the linear protrusion (the cross-section perpendicular to the direction in which the linear protrusion extends) is not particularly limited. The shape of the cross-section may be rectangular, trapezoidal, or semicircular.

[0074] In a member on which a spacer is formed, the ratio Rs of the spacer area to the total area of ​​the surface on which the spacer is formed may be 30% or less, 20% or less, 10% or less, or 5% or less. The ratio Rs may also be 1% or more, 3% or more, or 5% or more. When a spacer is formed on one side of a separator, the ratio of the spacer area to the total area of ​​that side may be within the range exemplified above for the ratio Rs. For example, when a spacer is formed on one side of a separator, the ratio of the spacer area to the total area of ​​that side may be 30% or less.

[0075] The average height Hs (thickness T) of the spacer may be 10 μm or more, or 20 μm or more, and may be 100 μm or less, 50 μm or less, 40 μm or less, or 30 μm or less. The height of the spacer may be approximately constant so that the spacing between the electrode plates formed by the spacer is approximately constant.

[0076] The average height Hs of a spacer can be measured by the following method. First, a cross-section of the member on which the spacer is formed (e.g., a separator) in the thickness direction is photographed with an electron microscope to obtain an image of the cross-section. Multiple images may be obtained as needed. Next, five arbitrary locations on the spacer are selected from the image, and the height of the spacer at those locations is measured. Then, the heights of the five measured locations are arithmetic mean, and the resulting average value is taken as the average height Hs.

[0077] There are no particular limitations on the method of forming the spacer, and it may be formed by the following method. First, a coating solution is prepared by mixing the spacer components with a liquid medium (dispersion medium). Next, the coating solution is applied to the member that will form the spacer (e.g., a separator), and then dried. In this way, a spacer can be formed. The liquid medium used to form the coating solution is not particularly limited. Examples of liquid media include organic solvents (such as N-methyl-2-pyrrolidone). The coating solution may be applied using a dispenser or by known printing methods such as gravure printing, inkjet printing, and screen printing. Drying may be carried out by known methods such as heating or natural drying.

[0078] For example, by preparing a coating liquid for forming a first region and a coating liquid for forming a second region, and applying them to predetermined locations on a member (e.g., a separator), a spacer having a first region and a second region can be formed.

[0079] (Separator) The separator may include a base layer, or it may consist only of the base layer. The base layer may be 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 base layer is not particularly limited, but it may be a polymer material. Examples of polymer materials include polyolefin resins, polyamide resins, and cellulose. Examples of polyolefin resins include polyethylene, polypropylene, and copolymers of ethylene and propylene. The base layer may contain additives as needed. Examples of additives include inorganic fillers. The base layer may be a sheet used as a separator in non-aqueous electrolyte secondary batteries (e.g., lithium secondary batteries).

[0080] The separator may include a base layer and a composite material layer formed on the base layer. When the temperature of the electrode group, which consists of a positive electrode, a negative electrode, and a separator, rises excessively, the base layer contracts, which makes it easier for the positive electrode and the negative electrode to short-circuit, thus causing the temperature of the electrode group to rise further. By laminating the composite material layer on the base layer, the contraction of the base layer when the temperature of the electrode group rises can be suppressed. As a result, further temperature increases of the electrode group can be suppressed.

[0081] When the separator comprises a base material 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 separator comprises a base material layer and a composite material layer, the spacer may be formed on the base material layer or on the composite material layer. When the spacer is formed on the composite material layer, the effect of suppressing thermal shrinkage of the base material layer is particularly high.

[0082] The composite material layer comprises a polymer and inorganic particles. The inorganic particles may include a first particle and / or a second particle. The first particle is a lithium-containing phosphate particle. The second particle is a particle other than the first particle. The composite material layer is a layer that allows lithium ions to pass through.

[0083] The phosphate that makes up the first particle is lithium phosphate (Li ３ PO４ ), dilithium hydrogen phosphate (Li ２ HPO ４ ), and lithium dihydrogen phosphate (LiH ２ PO ４ ), may be at least one selected from the group consisting of the above. Among these, lithium phosphate is preferred because it has a high effect of suppressing heat generation of the battery during an abnormal situation.

[0084] A preferred example of the second particles (inorganic particles) is particles composed of an insulating inorganic compound that does not melt or decompose during abnormal heat generation of the battery. The second particles may be inorganic particles generally used as inorganic fillers. Examples of materials for the second particles include aluminum oxide, boehmite, talc, titanium oxide, magnesium oxide, and silicon oxide.

[0085] For the polymer contained in the composite material layer, it is preferable to use a polymer having higher heat resistance than the main component of the base material layer of the separator. The polymer may contain at least one selected from the group consisting of aromatic polyamides, aromatic polyimides, and aromatic polyamideimides, and may be said at least one. These are known as polymers with high heat resistance. Aramid (fully aromatic polyamide) is preferred from the viewpoint of heat resistance.

[0086] The inorganic particles may include the first particles described above and second particles other than phosphates. In this case, the composite material layer may include a first layer containing the first particles and a second layer containing the second particles. According to this configuration, the effect of suppressing excessive temperature rise of the electrode group can be particularly enhanced. Note that the composite material layer may be composed of only the first layer or only the second layer.

[0087] The first and second layers may be laminated on the positive electrode side main surface of the base layer, on the negative electrode side main surface, or on different main surfaces. For example, the separator and spacer may have a laminated structure of base layer / first layer / second layer / spacer, base layer / second layer / first layer / spacer, first layer / second layer / base layer / spacer, or second layer / first layer / base layer / spacer. Alternatively, the first and second layers may be arranged on different main surfaces of the base layer. For example, the separator and spacer may have a laminated structure of first layer / base layer / second layer / spacer, or second layer / base layer / first layer / spacer.

[0088] The thickness of the separator is not particularly limited and may be 5 μm or more, 10 μm or more, 50 μm or less, or 40 μm or less. If the separator comprises a base material layer and a composite material layer, the base material layer may be 5 μm or more, 10 μm or more, 50 μm or less, or 40 μm or less.

[0089] If the separator comprises a base layer and a composite material layer, it may be manufactured by the following method. First, the base layer is prepared. A commercially available base layer may be used. Next, the composite material layer is formed on the base layer.

[0090] There are no particular limitations on the method for forming the composite material layer, and it may be formed by the following method. First, a coating solution is formed by mixing the components of the composite material layer with a liquid medium (dispersion medium). Next, the coating solution is applied to the substrate layer to form a coating film, and then the coating film is dried. In this way, the composite material layer can be formed. There are no particular limitations on the liquid medium used to form the coating solution. Examples of such liquid media include organic solvents (such as N-methyl-2-pyrrolidone).

[0091] 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 using a known method such as a bar coater. Drying may also be performed using known methods such as heating or natural drying.

[0092] (Secondary Batteries) Examples of secondary batteries include lithium secondary batteries (lithium metal secondary batteries) and lithium-ion batteries. For example, the negative electrode of a lithium secondary battery is an electrode in which lithium metal is deposited during charging and dissolves in a non-aqueous electrolyte during discharge. The negative electrode of a lithium-ion battery is an electrode in which lithium ions are absorbed into the negative electrode active material during charging and released from the negative electrode active material during discharge.

[0093] The following sections will provide specific examples of each component of the secondary battery. Note that the components described below are illustrative, and the components of the secondary battery in this embodiment are not limited to those described below. For components other than those characteristic of the secondary battery in this embodiment, known components may be used. The following section will primarily describe the case where the secondary battery is a lithium-ion battery. If the secondary battery is a battery other than a lithium-ion battery, the appropriate positive and negative electrodes for that battery should be used. Since the separator and spacer have been described above, a redundant explanation will be omitted.

[0094] The shape of a rechargeable battery is not particularly limited. Examples of rechargeable battery shapes include cylindrical, coin-shaped, prismatic, sheet-shaped, and flattened shapes.

[0095] The negative electrode is positioned opposite the positive electrode. The separator is positioned between the positive and negative electrodes. The positive electrode, negative electrode, and separator may be wound together such that the separator is positioned between the positive and negative electrodes. When forming a wound electrode group, a strip-shaped positive electrode, a strip-shaped negative electrode, and a strip-shaped separator are used. Alternatively, the positive electrode, negative electrode, and separator may be stacked. For example, a flat positive electrode, a flat negative electrode, and a flat separator may be stacked. In other words, the electrode group may be a wound electrode group or a stacked electrode group.

[0096] The following provides a detailed explanation of the positive electrode, negative electrode, and electrolyte of a secondary battery.

[0097] (Lithium secondary battery) (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 by charging. More specifically, lithium ions contained in the non-aqueous electrolyte accept electrons on the negative electrode current collector during charging, becoming lithium metal, and are 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 during discharge. The lithium ions contained in the non-aqueous electrolyte may originate from lithium salts added to the non-aqueous electrolyte, or they may be supplied from the positive electrode active material during charging, or both.

[0098] A conductive sheet can be used for the negative electrode current collector. If the electrode group is of the wound type, a strip-shaped conductive sheet is used. Examples of conductive sheets include conductive films and metal foils.

[0099] 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. Preferably, the conductive material is one that does not react with lithium. Preferably, the conductive material does not form any alloys or intermetallic compounds with lithium. Examples of such conductive materials include copper (Cu), nickel (Ni), iron (Fe), and alloys containing these metallic elements, or graphite with preferentially exposed basal surfaces. 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.

[0100] A negative electrode composite layer may be formed on the surface of the negative electrode current collector. The negative electrode composite 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 lithium secondary battery with a higher capacity than lithium-ion batteries, the thickness of the negative electrode composite layer is set to be sufficiently thin so that lithium metal can be deposited on the negative electrode.

[0101] The negative electrode may include a negative electrode current collector and a sheet-like lithium metal or lithium alloy placed on the negative electrode current collector. That is, the negative electrode current collector may have a pre-existing underlayer containing lithium metal (a layer of lithium metal or lithium alloy). The lithium alloy may contain elements other than lithium, such as aluminum, magnesium, indium, and zinc. By pre-existing this underlayer and allowing lithium metal to deposit on it during charging, dendrite-like deposition can be suppressed even more effectively. The thickness of the underlayer is not particularly limited, but may be, for example, in the range of 5 μm to 25 μm.

[0102] (Positive electrode) The positive electrode may include a positive electrode current collector and a positive electrode composite layer supported on the positive electrode current collector. The positive electrode composite layer contains a positive electrode active material. The positive electrode composite layer may also contain a positive electrode active material, a conductive material, and a binder. The positive electrode composite layer may be formed on only one side of the positive electrode current collector or on both sides. The positive electrode can be formed, for example, by applying a positive electrode composite slurry containing a positive electrode active material, a conductive material, and a binder to a positive electrode current collector, drying the coating, and then rolling it.

[0103] The positive electrode active material is a material that intercepts and releases lithium ions. Examples of positive electrode active materials 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 they have low manufacturing costs and a high average discharge voltage.

[0104] Examples of transition metal elements included in lithium-containing transition metal oxides include Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Y, Zr, and W. Lithium-containing transition metal oxides may contain one transition metal element or two or more. The transition metal element may be Co, Ni, and / or Mn. Lithium-containing transition metal oxides may optionally contain one or more main group elements. Examples of main group elements include Mg, Al, Ca, Zn, Ga, Ge, Sn, Sb, Pb, and Bi. The main group element may also be Al.

[0105] Conductive materials include, for example, carbon materials. Examples of carbon materials include carbon black, acetylene black, Ketjenblack, carbon nanotubes, and graphite.

[0106] Examples of binders include fluororesins, polyacrylonitrile, polyimide resins, acrylic resins, polyolefin resins, and rubbery polymers. Examples of fluororesins include polytetrafluoroethylene and polyvinylidene fluoride.

[0107] The positive electrode current collector can be any conductive sheet. Examples of conductive sheets include foil and film. The surface of the positive electrode current collector may also be coated with a carbon material.

[0108] Examples of materials for the positive electrode current collector (conductive sheet) include metallic materials containing Al, Ti, Fe, etc. The metallic material may be Al, Al alloy, Ti, Ti alloy, 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.

[0109] (Electrolyte) An electrolyte (non-aqueous electrolyte) includes, for example, a non-aqueous solvent and lithium ions and anions dissolved in the non-aqueous solvent. A non-aqueous electrolyte is prepared by dissolving a lithium salt in a non-aqueous solvent. Lithium ions and anions are generated when the lithium salt dissolves in the non-aqueous solvent.

[0110] The non-aqueous electrolyte may be in gel form. The gel-like non-aqueous electrolyte contains a lithium salt, a non-aqueous solvent, and a matrix polymer. As the matrix polymer, for example, a polymer material that absorbs the non-aqueous solvent and gels is used. Examples of polymer materials include fluororesins, acrylic resins, and polyether resins.

[0111] As the lithium salt or anion, known ones used in non-aqueous electrolytes for lithium secondary batteries can be used. Specifically, BF ４ － , ClO ４ － , PF ６ － CF３ SO ３ － CF ３ CO ２ － Examples include anions of imides and anions of oxalate complexes. An example of an imide anion is N(SO ２ CF ３ ) ２ － , N(C ｍ F ２ｍ＋１ SO ２ ) ｘ (C ｎ F ２ｎ＋１ SO ２ ) ｙ － Examples include (where m and n are independently 0 or an integer greater than or equal to 1, and x and y are independently 0, 1 or 2, satisfying x + y = 2). The anion of the oxalate complex may contain boron and / or phosphorus. Examples of anions of the oxalate complex include bisoxalate borate anion and difluorooxalate borate anion (BF ２ (C ２ O ４ ) － ), PF ４ (C ２ O ４ ) － , PF ２ (C ２ O ４ ) ２ － Examples include these. The non-aqueous electrolyte may contain these anions individually or in combination of two or more.

[0112] From the viewpoint of suppressing the dendritic deposition of lithium metal, it is preferable that the non-aqueous electrolyte contains anions of the oxalate complex. The interaction between the oxalate complex anions and lithium makes it easier for lithium metal to precipitate uniformly in fine particulate form. Therefore, localized deposition of lithium metal is more easily suppressed. The oxalate complex anions may be combined with other anions. Other anions include PF ６ － And / or imide anions.

[0113] The non-aqueous electrolyte contains LiBF as the solute (lithium salt). ２ (C ２ O ４ It may also contain (lithium difluorooxalatoborate).

[0114] Examples of non-aqueous solvents include esters, ethers, nitriles, amides, or halogen-substituted versions thereof. The non-aqueous electrolyte may contain one of these non-aqueous solvents or two or more of them. Examples of halogen-substituted versions include fluorides.

[0115] 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 linear 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 linear carboxylic acid esters include ethyl acetate, methyl propionate, and methyl fluoropropionate.

[0116] Examples of ethers include cyclic ethers and linear ethers. Examples of cyclic ethers include 1,3-dioxolane, 4-methyl-1,3-dioxolane, tetrahydrofuran, and 2-methyltetrahydrofuran. Examples of linear ethers include 1,2-dimethoxyethane, diethyl ether, ethyl vinyl ether, methylphenyl ether, benzyl ethyl ether, diphenyl ether, dibenzyl ether, 1,2-diethoxyethane, and diethylene glycol dimethyl ether.

[0117] The concentration of lithium salt in the non-aqueous electrolyte is, for example, 0.5 mol / L or more and 3.5 mol / L or less. The concentration of anions in the non-aqueous electrolyte may be 0.5 mol / L or more and 3.5 mol / L or less. Alternatively, the concentration of anions of the oxalate complex in the non-aqueous electrolyte may be 0.05 mol / L or more and 1 mol / L or less.

[0118] The non-aqueous electrolyte may contain additives. The additives may form a film on the negative electrode. The formation of a film derived from the additive on the negative electrode makes it easier to suppress dendrite formation. Examples of such additives include vinylene carbonate, FEC, vinyl ethyl carbonate (VEC), and the like.

[0119] (Lithium-ion battery) The negative electrode of a lithium-ion battery contains a negative electrode active material capable of intercalating and releasing lithium ions. The positive electrode and non-aqueous electrolyte of a lithium-ion battery can be those exemplified in lithium secondary batteries.

[0120] The negative electrode comprises, for example, a negative electrode current collector and a negative electrode composite layer supported on the negative electrode current collector. The negative electrode composite layer may be supported on one main surface of the negative electrode current collector or on both main surfaces of the negative electrode current collector. The negative electrode composite contains a negative electrode active material and may also contain other components (such as binders, conductive materials, and thickeners). Examples of negative electrode active materials include graphite and silicon-containing materials. Binders and conductive materials can be appropriately selected from those exemplified above. The negative electrode current collector can be appropriately selected from those exemplified above.

[0121] (Other) A secondary battery typically includes an casing that houses an electrode group and a non-aqueous electrolyte. The casing is not particularly limited, and known casings can be used.

[0122] Aside from using the spacers described above, the method for manufacturing a secondary battery is not particularly limited. The secondary battery may be manufactured by a method similar to that known. The secondary battery can be manufactured by enclosing an electrode group including a positive electrode, a negative electrode, and a separator, and a non-aqueous electrolyte in an outer casing.

[0123] In the following, an example of a secondary battery according to this embodiment will be specifically described with reference to the drawings. The components of the secondary battery example described below can be the components described above. Furthermore, the components of the example described below can be modified based on the above description. In addition, the matters described below may be applied to the above embodiment. Furthermore, in the secondary battery described below, components that are not essential to the secondary battery according to this disclosure may be omitted. Note that the scale of the components in the following figures has been changed to facilitate understanding.

[0124] (Embodiment 1) In Embodiment 1, a lithium secondary battery will be described as an example of a secondary battery. In this example, an example in which a spacer is formed on a separator will be described. Figure 1 is a schematic longitudinal cross-sectional view showing a secondary battery 10 according to Embodiment 1. Note that in Figure 1, the spacer and the space formed by the spacer are not shown.

[0125] The secondary battery (lithium secondary battery) 10 shown in Figure 1 includes a cylindrical battery case and a wound electrode group 14 and a non-aqueous electrolyte (not shown) housed within the battery case. The battery case includes a case body 15, which is a bottomed cylindrical metal container, and a sealing body 16 that seals the opening of the case body 15. A gasket 27 is placed between the case body 15 and the sealing body 16. The gasket 27 ensures that the battery case is airtight. Inside the case body 15, insulating plates 17 and 18 are placed at both ends of the electrode group 14 in the direction of the winding axis, respectively.

[0126] The case body 15 has a stepped portion 21 formed, for example, by partially pressing the side wall of the case body 15 from the outside. The stepped portion 21 may be formed in an annular shape on the side wall of the case body 15 along the circumferential direction of the case body 15. In this case, the sealing body 16 is supported on the opening side surface of the stepped portion 21.

[0127] 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. In the sealing body 16, these members are stacked in this order. Each of the above members constituting the sealing body 16 is, for example, disc-shaped or ring-shaped. The lower valve body 23 and the upper valve body 25 are connected to each other at their respective centers, with the insulating member 24 interposed between their respective peripheries. 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, each member except the insulating member 24 is electrically connected to one another.

[0128] The lower valve body 23 has a ventilation hole (not shown) formed therein. Therefore, if the internal pressure of the battery case rises due to abnormal heat generation or the like, the upper valve body 25 bulges towards the cap 26 and separates from the lower valve body 23. This disconnects the electrical connection between the lower valve body 23 and the upper valve body 25. If the internal pressure rises further, the upper valve body 25 ruptures, and gas is discharged through an opening (not shown) formed in the cap 26.

[0129] Figure 2 is an enlarged view of a part of the electrode group 14. Figure 2 includes the area near the positive electrode enclosed by region II in Figure 1 and the area near the negative electrode enclosed by region III in Figure 1. Figure 2 shows the height h of the spacer 53.

[0130] The electrode group 14 includes a positive electrode 11, a negative electrode 12, and a separator 50 having a spacer 53. The positive electrode 11, the negative electrode 12, and the separator 50 are all strip-shaped. The spacer 53 is formed on the separator 50. The electrode group 14 is formed by winding the positive electrode 11, the negative electrode 12, and the separator 50 so that the separator 50 is positioned between the positive electrode 11 and the negative electrode 12.

[0131] 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 Figure 2, the negative electrode 12 is shown as a negative electrode (negative electrode current collector) in a state where lithium metal has not been 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.

[0132] The separator 50 has a main surface 50a facing the positive electrode 11 and a main surface 50b facing the negative electrode 12. The separator 50 comprises a porous sheet 51 and a composite material layer 52 (heat-resistant layer). The composite material layer 52 is formed on the main surface of the porous sheet 51 that faces the positive electrode 11. The spacer 53 is formed on the main surface 50a facing the positive electrode 11. The spacer 53 is formed on the composite material layer 52 and is in contact with the positive electrode 11. The spacer 53 creates a space 14s between the positive electrode 11 and the negative electrode 12 (between the negative electrode 12 and the separator 50). Figure 2 shows the height h of the spacer 53. This height h is the thickness of the protrusions that make up the spacer 53.

[0133] In Figure 2, the spacer 53 is positioned on the main surface 50a on the positive electrode 11 side of the separator 50, but it may also be positioned on the main surface 50b on the negative electrode 12 side of the separator 50. The spacer 53 is formed on the composite material layer 52, but it may also be formed on the porous sheet 51. The composite material layer 52 of the separator 50 is positioned on the main surface on the positive electrode 11 side of the porous sheet 51, but it may also be positioned on the main surface on the negative electrode 12 side of the porous sheet 51.

[0134] In the secondary battery 10, lithium metal is deposited on the negative electrode 12 during charging. Since a space 14s exists between the positive electrode 11 and the negative electrode 12, the volume change of the electrode group 14 due to the deposition of lithium metal is reduced, and the cycle characteristics are improved.

[0135] Figure 3 shows an example of the planar shape (arrangement pattern) of the spacers. Figure 3 is a schematic top view showing an example of a separator with spacers, and is a view of the separator from above.

[0136] The spacer 53 shown in Figure 3 is composed of linear protrusions 53a. The linear protrusions 53a shown in Figure 3 are arranged in a mesh-like pattern. More specifically, the linear protrusions 53a are formed in a honeycomb pattern. The honeycomb pattern is a pattern in which multiple hexagons are arranged so that they share sides with each other. In the example shown in Figure 3, a space 14s is formed in the area where the linear protrusions 53a are not formed.

[0137] The linear protrusions 53a constituting the spacer 53 have a first region on the positive electrode side and a second region on the negative electrode side. In the first region, the proportion of the first resin to the sum of the first and second resins is greater than in the second region. In a cross-section parallel to the thickness direction of the spacer, the area ratio X1 of the first resin to the sum of the first and second resins in the first region is greater than the area ratio X2 of the first resin to the sum of the first and second resins in the second region. It is preferable that the area ratio X1 of the first resin is 50% or more, and the area ratio X2 of the first resin is less than 50%.

[0138] Figure 4 is a schematic top view of the main part of an example of a honeycomb-shaped spacer. Figure 5 is a cross-sectional view taken along line V-V in Figure 4, and is a cross-sectional view parallel to the thickness and width directions of the linear protrusions constituting the spacer. In Figure 4, W is the width of the linear protrusions. In Figure 5, T is the thickness of the linear protrusions. For convenience, in Figure 5, the separator 50, positive electrode 11 and negative electrode 12 are also shown together with the spacer 53 (linear protrusions 53a).

[0139] As shown in Figures 4 and 5, the linear protrusion 53a constituting the spacer 53 has a first region 63 on the positive electrode 11 side and a second region 73 on the negative electrode 12 side. In the first region 63, the ratio of the first resin to the total of the first and second resins is greater than in the second region 73.

[0140] As shown in Figure 5, in a cross-section parallel to the thickness and width directions of the linear protrusion 53a constituting the spacer 53, the area ratio X1 of the first resin to the sum of the first and second resins in the first region 63 is greater than the area ratio X2 of the first resin to the sum of the first and second resins in the second region 73. It is preferable that the area ratio X1 of the first resin is 50% or more, and the area ratio X2 of the first resin is less than 50%.

[0141] Within the second region 73, the proportion (area ratio) of the first resin may be continuously (stepwise) increased from the negative electrode 12 side toward the first region 63 side. Within the first region 63, the proportion (area ratio) of the first resin may be continuously (stepwise) increased from the second region 73 side toward the positive electrode 11 side.

[0142] The area ratio of the first region 63 (second region 73) to the cross-section of the linear protrusion 53a constituting the spacer 53, parallel to the thickness direction and width direction, may be adjusted, for example, by the thickness of the first region 63 (second region 73).

[0143] As shown in Figure 6, the spacer 53 has a first region 63 and a second region 73, and the first region 63 may have a first A region 63a on the positive electrode 11 side and a first B region 63b on the second region 73 side. In the first A region 63a, the proportion of the first resin to the sum of the first and second resins is greater than in the first B region 63b. In a cross section parallel to the thickness direction of the linear protrusion 53a constituting the spacer 53, the area ratio X1A of the first resin to the sum of the first and second resins in the first A region 63a is greater than the area ratio X1B of the first resin to the sum of the first and second resins in the first B region 63b.

[0144] In a cross-section parallel to the thickness direction of the linear protrusion 53a constituting the spacer 53, it is preferable that the area ratio of the first resin to the sum of the first resin and the second resin in the first A region 63a, X1A, is greater than 65%, and the area ratio of the first resin to the sum of the first resin and the second resin in the first B region 63b, X1B, is 50% or more and 65% or less.

[0145] As shown in Figure 7, the spacer 53 has a first region 63 and a second region 73, and the second region 73 may have a second A region 73a on the first region 63 side and a second B region 73b on the negative electrode 12 side. In the second A region 73a, the proportion of the first resin to the sum of the first and second resins is greater than in the second B region 73b. In a cross section parallel to the thickness direction of the linear protrusion 53a constituting the spacer 53, the area ratio X2A of the first resin to the sum of the first and second resins in the second A region 73a is greater than the area ratio X2B of the first resin to the sum of the first and second resins in the second B region 73b.

[0146] In a cross-section parallel to the thickness direction of the linear protrusion 53a constituting the spacer 53, it is preferable that the area ratio of the first resin to the sum of the first and second resins in the second A region 73a, X2A, is 35% or more and less than 50%, and the area ratio of the first resin to the sum of the first and second resins in the second B region 73b, X2B, is less than 35%.

[0147] As shown in Figure 8, the boundary between the first region 63 and the second region 73 may have a wavy (uneven) shape.

[0148] Figure 9 shows another example of the planar shape (arrangement pattern) of the spacer 53. Figure 9 is a schematic top view showing another example of a separator having a spacer, and is a view of the separator from above. The spacer 53 in Figure 9 is composed of a plurality of linear protrusions 53a arranged in a stripe pattern. In the example shown in Figure 9, a space 14s is formed in the area where the linear protrusions 53a are not formed.

[0149] Each of the multiple linear protrusions 53a constituting the spacer 53 in Figure 9 has a first region and a second region. In a cross-section parallel to the thickness direction and width direction of the linear protrusion 53a in Figure 9, the first region 63 and the second region 73 shown in Figures 5 to 8 may be formed.

[0150] (Note) The above description discloses 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, a spacer disposed between the positive electrode or the negative electrode and the separator, and an electrolyte, wherein the spacer comprises a first resin and a second resin, the first resin having a degree of swelling of 1.1 times or more relative to the electrolyte, the second resin having a degree of swelling of less than 1.1 times relative to the electrolyte, and the ratio of the first resin to the sum of the first resin and the second resin is greater on the positive electrode side of the spacer than on the negative electrode side of the spacer. (Technology 2) The secondary battery according to Technology 1, wherein the spacer has a first region on the positive electrode side and a second region on the negative electrode side, and in a cross section parallel to the thickness direction of the spacer, the area ratio X1 of the first resin to the sum of the first resin and the second resin in the first region is 50% or more, and the area ratio X2 of the first resin to the sum of the first resin and the second resin in the second region is less than 50%. (Technology 3) The secondary battery according to Technology 2, wherein the area ratio of the first region to the cross section parallel to the thickness direction of the spacer is 20% or more. (Technology 4) The secondary battery according to Technology 2, wherein the area ratio of the first region to the cross section parallel to the thickness direction of the spacer is 50% or more. (Technical 5) The secondary battery according to any one of Technical 2 to 4, wherein the first region comprises a first A region on the positive electrode side and a first B region on the second region side, and in a cross section parallel to the thickness direction of the spacer, the area ratio X1A of the first resin to the sum of the first resin and the second resin in the first A region is greater than 65%, and the area ratio X1B of the first resin to the sum of the first resin and the second resin in the first B region is 50% or more and 65% or less.(Technical 6) The secondary battery according to any one of Technical 2 to 5, wherein the second region comprises a second A region on the first region side and a second B region on the negative electrode side, and in a cross section parallel to the thickness direction of the spacer, the area ratio X2A of the first resin to the sum of the first and second resins in the second A region is 35% or more and less than 50%, and the area ratio X2B of the first resin to the sum of the first and second resins in the second B region is less than 35%. (Technical 7) The secondary battery according to any one of Technical 1 to 6, wherein the first resin includes a cellulose resin. (Technical 8) The secondary battery according to Technical 7, wherein the cellulose resin includes at least one selected from the group consisting of methylcellulose, ethylcellulose, and carboxymethylcellulose. (Technical 9) The secondary battery according to any one of Technical 1 to 8, wherein the second resin includes at least one selected from the group consisting of polyvinylpyrrolidone resin, polyimide resin, and alkyd resin. (Technology 10) A secondary battery according to any one of Technologies 1 to 9, wherein the negative electrode is an electrode in which lithium metal is deposited during charging and the lithium metal dissolves in the electrolyte during discharge. (Technology 11) A separator having a spacer, disposed between the positive electrode and the negative electrode of a secondary battery, wherein the spacer is disposed on the main surface of the separator, and the spacer comprises a first resin and a second resin, the first resin having a degree of swelling of 1.1 times or more relative to the electrolyte, the second resin having a degree of swelling of less than 1.1 times relative to the electrolyte, and the ratio of the first resin to the sum of the first resin and the second resin is greater on the positive electrode side of the spacer than on the negative electrode side of the spacer. (Technical 12) The separator according to Technical 11, wherein the spacer has a first region on the positive electrode side and a second region on the negative electrode side, and in a cross section parallel to the thickness direction of the spacer, the area ratio X1 of the first resin to the sum of the first resin and the second resin in the first region is 50% or more, and the area ratio X2 of the first resin to the sum of the first resin and the second resin in the second region is less than 50%.(Technical 13) The separator according to Technical 12, wherein the area ratio of the first region to the cross-section parallel to the thickness direction of the spacer is 20% or more. (Technical 14) The separator according to Technical 12, wherein the area ratio of the first region to the cross-section parallel to the thickness direction of the spacer is 50% or more. (Technical 15) The separator according to any one of Technical 12 to 14, wherein the first region comprises a first A region on the positive electrode side and a first B region on the second region side, and in a cross-section parallel to the thickness direction of the spacer, the area ratio X1A of the first resin to the sum of the first resin and the second resin in the first A region is greater than 65%, and the area ratio X1B of the first resin to the sum of the first resin and the second resin in the first B region is 50% or more and 65% or less. (Technical 16) The separator according to any one of Technical 12 to 15, wherein the second region comprises a second A region on the first region side and a second B region on the negative electrode side, and in a cross section parallel to the thickness direction of the spacer, the area ratio X2A of the first resin to the sum of the first resin and the second resin in the second A region is 35% or more and less than 50%, and the area ratio X2B of the first resin to the sum of the first resin and the second resin in the second B region is less than 35%. (Technical 17) The separator according to any one of Technical 11 to 16, wherein the first resin comprises a cellulose resin. (Technical 18) The separator according to Technical 17, wherein the cellulose resin comprises at least one selected from the group consisting of methylcellulose, ethylcellulose, and carboxymethylcellulose. (Technical 19) The separator according to any one of Technical 11 to 18, wherein the second resin comprises at least one selected from the group consisting of polyvinylpyrrolidone resin, polyimide resin, and alkyd resin.

[0151] [Examples] The secondary battery according to this embodiment will be described in detail below based on examples.

[0152] 《Secondary Batteries E1-E17, R1》 (Preparation of Positive Electrode) A rock salt-type lithium-containing transition metal oxide (NCA: positive electrode active material) containing Li, Ni, Co, and Al (with a molar ratio of Li to the total of Ni, Co, and Al being 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 mixture slurry. Next, the obtained positive electrode mixture slurry was applied to both sides of a strip-shaped Al foil (positive electrode current collector) and then dried. In this way, a laminate containing the positive electrode current collector and the positive electrode mixture formed on the positive electrode current collector was formed. Next, the laminate was rolled using rollers. Finally, the rolled laminate was cut to a predetermined size. In this way, a positive electrode was produced that included a positive electrode current collector and a positive electrode composite layer formed on both sides of the positive electrode current collector.

[0153] (Preparation of the negative electrode) As the negative electrode, a strip of copper foil (12 μm thick) with layers of rolled lithium metal (25 μm thick) on both sides was used.

[0154] (Separator Fabrication) First, a porous sheet (base layer) made of polyethylene, in the shape of a strip (average thickness 10 μm), was prepared. Next, a separator was obtained by forming a porous composite material layer (average thickness 2 μm) on one side of the porous membrane. The composite material layer was formed by forming a second layer and a first layer on the porous membrane in that order.

[0155] 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, the solution was allowed to return to room temperature, and 2200 g was taken. 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 amounts. The resulting solution was aged at approximately 20°C for 1 hour to obtain a polymerization solution. Next, 100 g of this polymerization solution was mixed with an N-methyl-2-pyrrolidone solution containing 5.8% by mass of calcium chloride to obtain a solution (coating solution) with a concentration of 2% by mass of paraphenylene terephthalamide (PPTA), an aromatic polyamide (aramid).

[0156] Next, the coating solution was applied to the substrate layer using a slot die method to form a coating film. Then, the substrate layer with the coating film was left for 1 hour in an atmosphere of 70% relative humidity at a temperature of 25°C to precipitate aromatic polyamide. Next, NMP and calcium chloride in the coating film were removed by washing with water. Finally, the coating film was dried at 60°C for 5 minutes to form a second layer.

[0157] The first layer was formed as follows: First, lithium phosphate (Li ３ PO ４ A mixture was obtained by mixing lithium phosphate particles and poly-N-vinylacetamide (PNVA) in a mass ratio of 100:8. The lithium phosphate particles used had a volume-based median diameter of 0.19 μm. Water (deionized water) was added to the obtained mixture and stirred to prepare a slurry (coating liquid) with a solid content concentration of 12% by mass. Next, the slurry was coated onto the second layer by microgravure coating to form a coating film. Next, the coating film was dried in a drying oven attached to the coating machine. In this way, the first layer was formed. In this way, the composite material layer was formed.

[0158] (Spacer preparation) A coating solution containing resin and 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 solution. Alumina particles (inorganic filler) were used as the filler.

[0159] Next, the coating liquid was applied to the composite material layer of the separator using a dispenser, and the coating film was vacuum-dried to form spacers (linear protrusions). The arrangement pattern of the spacers (coating liquid application pattern) was a honeycomb shape as shown in Figure 3.

[0160] In the above, a coating liquid for forming the first region and a coating liquid for forming the second region were prepared and applied to a separator to form a spacer (linear protrusion) having the first region and the second region. Specifically, a linear protrusion 53a having the first region 63 and the second region 73 as shown in Figures 4 and 5 was formed. The width W of the linear protrusion 53a was 250 μm, and the thickness T (height) of the linear protrusion 53a was 50 μm.

[0161] By appropriately adjusting the thickness of the first region and the second region, the area ratio S1 of the first region and the area ratio S2 of the second region were set to the values ​​shown in Table 1. By appropriately adjusting the mixing ratio of the first resin and the second resin contained in the coating liquid for forming the first region, the area ratio X1 of the first resin and the area ratio Y1 of the second resin in the first region were set to the values ​​shown in Table 1. By appropriately adjusting the mixing ratio of the first resin and the second resin contained in the coating liquid for forming the second region, the area ratio X2 of the first resin and the area ratio Y2 of the second resin in the second region were set to the values ​​shown in Table 1.

[0162] The first resin used was a cellulose resin (methylcellulose (swells twice), ethylcellulose (swells ten times), carboxymethylcellulose (CMC) (swells 1.4 times)), polyvinylidene fluoride (PVDF) resin (swells 1.1 times), oxetane resin (swells 1.11 times)), or a urethane resin (swells 1.2 times).

[0163] For the second resin, we used polyvinylpyrrolidone (PVP) resin (swelling degree 1.01 times), polyimide resin (swelling degree 1.001 times), alkyd resin (swelling degree 1.01 times), or polymethyl methacrylate (swelling degree 1.005 times).

[0164] (Preparation of non-aqueous electrolyte) Ethylene carbonate (EC) and dimethyl carbonate (DMC) were mixed in a volume ratio of EC:DMC = 30:70. LiPF was added to the resulting mixed solvent. ６ The concentration becomes 1 mol / L, and LiBF ２ (C ２ O ４ A non-aqueous electrolyte was prepared by dissolving these substances so that their concentration was 0.1 mol / L.

[0165] (Battery Fabrication) An aluminum positive electrode lead was attached to the positive electrode obtained above. A nickel negative electrode lead was attached to the negative electrode. A wound electrode group was obtained by spirally winding the positive and negative electrodes with a separator having a spacer in between. At this time, a separator was placed between the positive and negative electrodes, and a spacer was placed between the positive electrode and the separator.

[0166] An electrode group was housed in a bottomed cylindrical case body, and a non-aqueous electrolyte was injected. A sealing body was placed at the opening of the case body via a gasket, sealing the electrode group and non-aqueous electrolyte inside the battery case. In this way, a lithium secondary battery with the structure shown in Figure 1 was completed.

[0167] Battery R2 was manufactured in the same manner as Battery E1, except that methylcellulose was used as the resin throughout the entire spacer region.

[0168] Battery R3 was manufactured in the same manner as Battery E1, except that PVP resin was used as the resin throughout the entire spacer area.

[0169] Battery R4 was manufactured in the same manner as Battery E1, except that the same coating solution used for forming the second region in Battery E1 was used to create the spacer, thereby forming a spacer containing methylcellulose (20% area ratio) and PVP resin (80% area ratio) throughout the entire region.

[0170] [Evaluation] Charge and discharge tests were performed on each battery manufactured as described above. In the charge and discharge tests, the batteries were charged in a constant temperature chamber at 45°C under the following conditions, then left to rest for 20 minutes, and then discharged under the following conditions.

[0171] (Charging) Constant current charging was performed at a current of 2.15 mA per unit area (square centimeter) of the electrodes until the battery voltage reached 4.1 V. Then, constant voltage charging was performed at a voltage of 4.1 V until the current value per unit area of ​​the electrodes reached 0.54 mA.

[0172] (Discharge) A constant current discharge was performed at a current of 2.15 mA per unit area of ​​the electrodes until the battery voltage reached 3.75 V.

[0173] (Evaluation of Cycle Characteristics) The above charge-discharge process was repeated, and the discharge capacity C1 after the first cycle and the discharge capacity Cn after the nth cycle were measured. The ratio of Cn to C1 (percentage): Cn / C1 × 100 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. A capacity retention rate of 70% or higher at the 100th cycle was marked as "○", and a capacity retention rate below 70% by the 100th cycle was marked as "×".

[0174] (Evaluation of initial characteristics) The initial capacity and initial efficiency were also determined for each fabricated battery. The initial capacity is the discharge capacity in the first cycle. The initial efficiency is the ratio of the discharge capacity in the first cycle to the charge capacity in the first cycle.

[0175] The evaluation results are shown in Table 1. In Table 1, E1 to E17 are secondary batteries of the examples, and R1 to R4 are secondary batteries of the comparative examples. Note that the initial capacity in Table 1 is expressed as a relative value when the initial capacity of battery R4 is set to 100.

[0176]

[0177] Batteries E1 to E17 exhibited high initial efficiency, initial capacity, and capacity retention rates, resulting in excellent initial and cycle characteristics.

[0178] In battery R1, where the area ratio X1 of the first resin on the positive electrode side of the spacer is smaller than the area ratio X2 of the first resin on the negative electrode side of the spacer, Li ions moved from the positive electrode to the negative electrode by circling around the spacer during the first charging cycle, resulting in a decrease in the charging capacity during the first cycle and a decrease in the initial discharge capacity.

[0179] In battery R2, which uses only methylcellulose with a high degree of swelling, the volume change of the electrode group increased due to a decrease in the spacer function during charging and discharging, and the capacity retention rate dropped to less than 70% by the 100th cycle. In battery R3, which uses only PVP resin with a low degree of swelling, the initial efficiency and initial capacity decreased as Li ions moved between the positive and negative electrodes by circumventing the spacer during charging and discharging.

[0180] In battery R4, the area ratio of methylcellulose (PVP resin) was not changed between the negative and positive electrode sides of the spacer, and the area ratio of PVP resin was high throughout the entire spacer region, resulting in a decrease in initial efficiency and initial capacity.

[0181] 《Batteries E18-E21》 In the fabrication of the spacers, coating liquids for forming the first A region, the first B region, and the second region were prepared and applied to the separator to form a spacer (linear protrusion) having the first A region, the first B region, and the second region. Specifically, a linear protrusion 53a having the first A region 63a, the first B region 63b, and the second region 73 as shown in Figure 6 was formed.

[0182] By appropriately adjusting the thicknesses of the first A region, the first B region, and the second region, the area ratio S1A of the first A region, the area ratio S1B of the first B region, and the area ratio S2 of the second region were set to the values ​​shown in Table 2.

[0183] By appropriately adjusting the mixing ratio of the first resin and the second resin contained in the coating liquid for forming region 1A, the area ratio X1A of the first resin and the area ratio Y1A of the second resin in region 1A were set to the values ​​shown in Table 2. By appropriately adjusting the mixing ratio of the first resin and the second resin contained in the coating liquid for forming region 1B, the area ratio X1B of the first resin and the area ratio Y1B of the second resin in region 1B were set to the values ​​shown in Table 2. By appropriately adjusting the mixing ratio of the first resin and the second resin contained in the coating liquid for forming region 2, the area ratio X2 of the first resin and the area ratio Y2 of the second resin in region 2 were set to the values ​​shown in Table 2.

[0184] Methylcellulose was used as the first resin, and PVP resin was used as the second resin.

[0185] Except as described above, batteries E18 to E21 were manufactured and evaluated in the same manner as battery E1. The evaluation results are shown in Table 2.

[0186]

[0187] As shown in Table 2, batteries E18 to E21 exhibited high initial efficiency, initial capacity, and capacity retention rates, resulting in excellent initial and cycle characteristics.

[0188] In the fabrication of the spacer for the battery E22, a coating liquid for forming the first region, a coating liquid for forming the second A region, and a coating liquid for forming the second B region were prepared and applied to the separator to form a spacer (linear protrusion) having the first region, the second A region, and the second B region. Specifically, a linear protrusion 53a having the first region 63, the second A region 73a, and the second B region 73b shown in Figure 7 was formed.

[0189] By appropriately adjusting the thicknesses of the first region, the second A region, and the second B region, the area ratio S1 of the first region, the area ratio S2A of the second A region, and the area ratio S2B of the second B region were set to the values ​​shown in Table 3.

[0190] By appropriately adjusting the mixing ratio of the first resin and the second resin contained in the coating liquid for forming the first region, the area ratio X1 of the first resin and the area ratio Y1 of the second resin in the first region were set to the values ​​shown in Table 3. By appropriately adjusting the mixing ratio of the first resin and the second resin contained in the coating liquid for forming the second A region, the area ratio X2A of the first resin and the area ratio Y2A of the second resin in the second A region were set to the values ​​shown in Table 3. By appropriately adjusting the mixing ratio of the first resin and the second resin contained in the coating liquid for forming the second B region, the area ratio X2B of the first resin and the area ratio Y2B of the second resin in the second B region were set to the values ​​shown in Table 3.

[0191] Methylcellulose was used as the first resin, and PVP resin was used as the second resin.

[0192] Except as described above, battery E22 was fabricated and evaluated in the same manner as battery E1. The evaluation results are shown in Table 3.

[0193]

[0194] As shown in Table 3, battery E22 exhibited high initial efficiency, initial capacity, and capacity retention rate, resulting in excellent initial and cycle characteristics.

[0195] The secondary battery of this disclosure can be used in electronic devices such as mobile phones, smartphones, and tablet devices, electric vehicles including hybrid and plug-in hybrid vehicles, and home battery storage systems combined with solar cells.

[0196] Although the present invention has been described in relation to preferred embodiments at present, such disclosure should not be interpreted restrictively. Various modifications and alterations will undoubtedly become apparent to those skilled in the art in the field to which the invention pertains by reading the above disclosure. Accordingly, the appended claims should be interpreted as encompassing all modifications and alterations without departing from the true spirit and scope of the invention.

[0197] 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, 53: Spacer, 53a: Linear protrusion, 63: First region, 73: Second region

Claims

1. A secondary battery comprising a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, a spacer disposed between the positive electrode or the negative electrode and the separator, and an electrolyte, wherein the spacer comprises a first resin and a second resin, the first resin having a degree of swelling of 1.1 times or more relative to the electrolyte, the second resin having a degree of swelling of less than 1.1 times relative to the electrolyte, and the ratio of the first resin to the sum of the first resin and the second resin being greater on the positive electrode side of the spacer than on the negative electrode side of the spacer.

2. The secondary battery according to claim 1, wherein the spacer has a first region on the positive electrode side and a second region on the negative electrode side, and in a cross section parallel to the thickness direction of the spacer, the area ratio X1 of the first resin to the sum of the first resin and the second resin in the first region is 50% or more, and the area ratio X2 of the first resin to the sum of the first resin and the second resin in the second region is less than 50%.

3. The secondary battery according to claim 2, wherein the area ratio of the first region to the cross-section parallel to the thickness direction of the spacer is 20% or more.

4. The secondary battery according to claim 2, wherein the area ratio of the first region to the cross-section parallel to the thickness direction of the spacer is 50% or more.

5. The secondary battery according to claim 2, wherein the first region comprises a first A region on the positive electrode side and a first B region on the second region side, and in a cross section parallel to the thickness direction of the spacer, the area ratio X1A of the first resin to the sum of the first resin and the second resin in the first A region is greater than 65%, and the area ratio X1B of the first resin to the sum of the first resin and the second resin in the first B region is 50% or more and 65% or less.

6. The secondary battery according to claim 2, wherein the second region comprises a second A region on the first region side and a second B region on the negative electrode side, and in a cross section parallel to the thickness direction of the spacer, the area ratio X2A of the first resin to the sum of the first resin and the second resin in the second A region is 35% or more and less than 50%, and the area ratio X2B of the first resin to the sum of the first resin and the second resin in the second B region is less than 35%.

7. The secondary battery according to claim 1 or 2, wherein the first resin comprises a cellulose resin.

8. The secondary battery according to claim 7, wherein the cellulose resin comprises at least one selected from the group consisting of methylcellulose, ethylcellulose, and carboxymethylcellulose.

9. The secondary battery according to claim 1 or 2, wherein the second resin comprises at least one selected from the group consisting of polyvinylpyrrolidone resin, polyimide resin, and alkyd resin.

10. The secondary battery according to claim 1 or 2, wherein the negative electrode is an electrode in which lithium metal is deposited during charging and the lithium metal dissolves in the electrolyte during discharge.

11. A separator having a spacer, which is disposed between the positive electrode and the negative electrode of a secondary battery, wherein the spacer is disposed on the main surface of the separator, and the spacer comprises a first resin and a second resin, the first resin having a degree of swelling of 1.1 times or more relative to the electrolyte, the second resin having a degree of swelling of less than 1.1 times relative to the electrolyte, and the ratio of the first resin to the sum of the first resin and the second resin is greater on the positive electrode side of the spacer than on the negative electrode side of the spacer.

12. The separator according to claim 11, wherein the spacer has a first region on the positive electrode side and a second region on the negative electrode side, and in a cross section parallel to the thickness direction of the spacer, the area ratio X1 of the first resin to the sum of the first resin and the second resin in the first region is 50% or more, and the area ratio X2 of the first resin to the sum of the first resin and the second resin in the second region is less than 50%.

13. The separator according to claim 12, wherein the area ratio of the first region to the cross-section parallel to the thickness direction of the spacer is 20% or more.

14. The separator according to claim 12, wherein the area ratio of the first region to the cross-section parallel to the thickness direction of the spacer is 50% or more.

15. The separator according to claim 12, wherein the first region comprises a first A region on the positive electrode side and a first B region on the second region side, and in a cross section parallel to the thickness direction of the spacer, the area ratio X1A of the first resin to the sum of the first resin and the second resin in the first A region is greater than 65%, and the area ratio X1B of the first resin to the sum of the first resin and the second resin in the first B region is 50% or more and 65% or less.

16. The separator according to claim 12, wherein the second region comprises a second A region on the first region side and a second B region on the negative electrode side, and in a cross section parallel to the thickness direction of the spacer, the area ratio X2A of the first resin to the sum of the first resin and the second resin in the second A region is 35% or more and less than 50%, and the area ratio X2B of the first resin to the sum of the first resin and the second resin in the second B region is less than 35%.

17. The separator according to claim 11 or 12, wherein the first resin comprises a cellulose resin.

18. The separator according to claim 17, wherein the cellulose resin comprises at least one selected from the group consisting of methylcellulose, ethylcellulose, and carboxymethylcellulose.

19. The separator according to claim 11 or 12, wherein the second resin comprises at least one selected from the group consisting of polyvinylpyrrolidone resin, polyimide resin, and alkyd resin.

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