Nonaqueous electrolyte secondary battery

Abstract

The disclosed nonaqueous electrolyte secondary battery comprises: an electrode group in which a positive electrode, a negative electrode, and a separator (13) are wound such that the separator (13) is disposed between the positive electrode and the negative electrode; and a non-aqueous electrolyte. The separator (13) includes a first separator (131) and a second separator (132) disposed between the first separator and the negative electrode. The first separator (131) includes a first base material layer (131a) having a first main surface (131a1) disposed on the positive electrode side and a second main surface (131a2) disposed on the negative electrode side, and a first adhesive layer (131b1) formed on the first main surface (131a1) of the first base material layer (131a). At least a portion of the first adhesive layer (131b1) is adhered to the positive electrode.

Description

Technical Field

[0001] This disclosure relates to non-aqueous electrolyte secondary batteries. Background Technology

[0002] Non-aqueous electrolyte secondary batteries are used for various applications as high-capacity secondary batteries. Various solutions have been proposed for non-aqueous electrolyte secondary batteries.

[0003] Claim 1 of Patent Document 1 (International Publication No. 2019 / 181286) describes "a non-aqueous electrolyte secondary battery, which is a cylindrical non-aqueous electrolyte secondary battery having a wound electrode body and a non-aqueous electrolyte, wherein the wound electrode body has a positive electrode having a positive electrode composite material layer disposed on both sides of a positive electrode core, a negative electrode having a negative electrode composite material layer disposed on both sides of a negative electrode core, and a separator between the positive electrode and the negative electrode, the separator being bonded to the positive electrode for at least one circumference along the winding direction from the winding start end of the positive electrode composite material layer."

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: International Publication No. 2019 / 181286 Summary of the Invention

[0007] The problem the invention aims to solve

[0008] The degradation of the positive electrode surface and the oxidative decomposition of the non-aqueous electrolyte in the positive electrode are problems in non-aqueous electrolyte secondary batteries. Furthermore, the large expansion of the electrode assembly during charging becomes a problem. These problems lead to a decrease in charge-discharge cycle characteristics. Currently, there is a demand for improved charge-discharge cycle characteristics of non-aqueous electrolyte secondary batteries. One of the objectives of this disclosure is to provide a non-aqueous electrolyte secondary battery with excellent charge-discharge cycle characteristics.

[0009] Solution for solving the problem

[0010] One aspect of this disclosure relates to a non-aqueous electrolyte secondary battery, comprising:

[0011] An electrode assembly consisting of a positive electrode, a negative electrode, and a separator wound together such that the separator is positioned between the positive and negative electrodes; and

[0012] Non-aqueous electrolytes

[0013] The separator includes a first separator and a second separator disposed between the first separator and the negative electrode.

[0014] The first separator includes a first substrate layer and a first adhesive layer. The first substrate layer has a first main surface disposed on the positive electrode side and a second main surface disposed on the negative electrode side. The first adhesive layer is formed on the first main surface of the first substrate layer.

[0015] At least a portion of the first adhesive layer is adhered to the positive electrode.

[0016] The effects of the invention

[0017] According to this disclosure, a non-aqueous electrolyte secondary battery with good charge-discharge cycle characteristics can be obtained.

[0018] The novel features of the invention are set forth in the claims, but the invention relates to both its structure and content, and will be better understood, together with other objects and features of the invention, by reference to the following detailed description of the accompanying drawings. Attached Figure Description

[0019] Figure 1 This is a schematic diagram illustrating the method for measuring the thickness of the negative electrode.

[0020] Figure 2 This is a cross-sectional view schematically illustrating an example of a non-aqueous electrolyte secondary battery related to this disclosure.

[0021] Figure 3 This is a cross-sectional view schematically representing an example of a separator.

[0022] Figure 4 This is a cross-sectional view schematically representing another example of a separator. Detailed Implementation

[0023] The following examples illustrate the embodiments covered by this disclosure, but this disclosure is not limited to the examples described below. In the following description, specific numerical values ​​and / or materials are sometimes cited, but other numerical values ​​and / or materials can be applied as long as the effects of this disclosure are achieved. In this specification, the description of "numerical value A to numerical value B" includes both numerical value A and numerical value B, and can be replaced with "numerical value A or higher and numerical value B or lower." In the following description, when lower and upper limits are cited for numerical values ​​relating to specific physical properties and / or conditions, any of the cited lower limits and any of the cited upper limits can be arbitrarily combined, as long as the lower limit does not exceed the upper limit. In the following description, when examples of constituent elements or methods are listed, unless specifically stated otherwise, only one of the listed examples can be used, or multiple of the listed examples can be used together.

[0024] (Non-aqueous electrolyte secondary battery)

[0025] Hereinafter, the non-aqueous electrolyte secondary battery according to this embodiment will sometimes be referred to as a "non-aqueous electrolyte secondary battery (B)" or "secondary battery (B)". The secondary battery (B) includes: an electrode assembly formed by winding a positive electrode, a negative electrode, and a separator such that the separator is disposed between the positive electrode and the negative electrode; and a non-aqueous electrolyte. The separator includes a first separator and a second separator disposed between the first separator and the negative electrode. The first separator includes a first substrate layer and a first adhesive layer. The first substrate layer has a first main surface disposed on the positive electrode side and a second main surface disposed on the negative electrode side. The first adhesive layer is formed on the first main surface of the first substrate layer. At least a portion of the first adhesive layer is adhered to the positive electrode.

[0026] Non-aqueous electrolyte secondary batteries can be either lithium-ion or lithium-ion batteries. In lithium-ion batteries, lithium metal is deposited at the negative electrode during charging and dissolves into the non-aqueous electrolyte during discharging. In lithium-ion batteries, a negative electrode active material capable of reversibly absorbing and releasing lithium ions is used.

[0027] In lithium-ion secondary batteries, for example, over 70% of the rated capacity is achieved through the deposition and dissolution of lithium metal. The migration of electrons in the negative electrode during charging and discharging depends primarily on the deposition and dissolution of lithium metal in the negative electrode. Specifically, 70-100% (e.g., 80-100%, 90-100%) of the electron migration (current in other views) in the negative electrode during charging and discharging depends on the deposition and dissolution of lithium metal. That is, the negative electrode of the lithium-ion secondary battery disclosed herein differs from a negative electrode where the migration of electrons during charging and discharging depends primarily on the absorption and release of lithium ions using a negative electrode active material (graphite, etc.). For example, the negative electrode of the lithium-ion secondary battery disclosed herein may not contain a negative electrode active material (graphite, etc.) for absorbing and releasing lithium ions.

[0028] In non-aqueous electrolyte secondary batteries, the negative electrode expands during charging. In conventional non-aqueous electrolyte secondary batteries, the large expansion of the electrode assembly caused by the expansion of the negative electrode during charging has been a problem. This is especially true in lithium-ion secondary batteries, where the large expansion of the negative electrode during charging leads to a large expansion of the electrode assembly. If the expansion of the electrode assembly (particularly the radial expansion) is large, it can easily lead to a decrease in the cycle performance of the non-aqueous electrolyte. As a result, the charge-discharge cycle characteristics (hereinafter sometimes simply referred to as "cycle characteristics") of the non-aqueous electrolyte secondary battery are reduced. Furthermore, in conventional non-aqueous electrolyte secondary batteries, degradation of the positive electrode surface and oxidative decomposition of the non-aqueous electrolyte in the positive electrode are prone to occur. These also contribute to a decrease in cycle characteristics.

[0029] Based on their research, the inventors of this application have discovered that by using first and second separators and bonding the first separator to the positive electrode via an adhesive layer, cycle characteristics can be significantly improved. This disclosure is based on this new insight. By bonding the positive electrode and the first separator with an adhesive layer, direct contact between the surface of the positive electrode and the non-aqueous electrolyte can be reduced. As a result, degradation of the positive electrode surface and oxidative decomposition reactions of the non-aqueous electrolyte can be suppressed. Furthermore, by using two separators, expansion of the electrode assembly during charging can be suppressed. It can be considered that the significant improvement in cycle characteristics is not obtained by simply adding the above two effects, but rather by the synergistic effect of using two separators and bonding the first separator to the positive electrode.

[0030] (Separator)

[0031] A first separator and a second separator are disposed overlappingly between the positive and negative electrodes. The first and second separators typically have the same shape. However, as long as they are disposed between the positive and negative electrodes, the shape of the first separator can differ from that of the second separator. The first and second separators may or may not be bonded together. By making the first and second separators unbonded, the stress within the electrode assembly caused by the expansion of the negative electrode can be mitigated, and damage to the components constituting the electrode assembly can be suppressed.

[0032] As described above, the first separator comprises a first substrate layer and a first adhesive layer, at least a portion of which is bonded to the positive electrode. There is no particular limitation on the method of bonding the adhesive layer of the separator to other components (negative electrode, positive electrode, other separators). For example, methods such as planar hot pressing or heated rolling can be used.

[0033] The first spacer may further include a second adhesive layer formed on a second main surface of the first substrate layer. At least a portion of the second adhesive layer may be bonded to the second spacer. Alternatively, the second adhesive layer may not be bonded to the second spacer.

[0034] The substrate layer is not particularly limited. A separator commonly used in non-aqueous electrolyte secondary batteries can be used as the substrate layer. The substrate layer can be a porous sheet with ion permeability and insulation. Examples of porous sheets include microporous films, woven fabrics, and nonwoven fabrics. The material of the substrate layer is not particularly limited; polymeric materials can be used. Examples of polymeric materials include olefin resins, polyamide resins, and cellulose. Examples of olefin resins include polyethylene, polypropylene, and copolymers of ethylene and propylene. The substrate layer may contain additives (inorganic fillers, etc.) as needed. The substrate layer may consist of multiple layers with different morphologies and / or compositions.

[0035] Hereinafter, all adhesive layers (first to fourth adhesive layers) will sometimes be referred to simply as "adhesive layers". The first adhesive layer is formed of a material capable of adhering to the positive electrode. The material of the adhesive layer is required to be stable within the secondary battery (B). The adhesive layer may contain a vinylidene fluoride-based polymer synthesized by polymerizing monomers containing vinylidene fluoride. The vinylidene fluoride-based polymer is preferred in terms of high adhesion to the positive electrode and high stability within the secondary battery (B). The content of the vinylidene fluoride-based polymer in the adhesive layer may be 3% by mass or more or 50% by mass or more, or 100% by mass or less or 80% by mass or less. The material of the adhesive layers other than the first adhesive layer (second adhesive layer, third adhesive layer, and fourth adhesive layer) may be the same as or different from the material of the first adhesive layer. The thickness of the adhesive layers other than the first adhesive layer (second adhesive layer, third adhesive layer, and fourth adhesive layer) may be the same as or different from the thickness of the first adhesive layer.

[0036] Vinylidene fluoride (VDF) polymers contain structural units derived from vinylidene fluoride. In all structural units of VDF polymers, the proportion of VDF units (structural units derived from vinylidene fluoride) is 50 mol% to 100 mol%. This proportion can be 75 mol% or more, or 90 mol% or more, or 99.5 mol% or less, or 95 mol% or less. Examples of monomers copolymerized with vinylidene fluoride include tetrafluoroethylene and hexafluoropropylene.

[0037] The vinylidene fluoride-based polymer can be polyvinylidene fluoride (PVDF). Alternatively, it can be a copolymer synthesized by polymerizing monomers containing vinylidene fluoride and hexafluoropropylene. That is, the adhesive layer can contain a copolymer synthesized by polymerizing monomers containing vinylidene fluoride and hexafluoropropylene. Hexafluoropropylene has a larger molecular structure than vinylidene fluoride, therefore the copolymer synthesized by polymerizing monomers containing vinylidene fluoride and hexafluoropropylene has a lower density than the vinylidene fluoride-based polymer. By using monomers containing hexafluoropropylene, polymer crystallization is suppressed, resulting in a flexible adhesive layer. Furthermore, the retention of non-aqueous electrolytes in the adhesive layer is improved, and lithium-ion conductivity is enhanced. As a result, battery resistance decreases, further improving cycle characteristics.

[0038] Vinylidene fluoride polymers can be copolymers of vinylidene fluoride and hexafluoropropylene (HFP). In all the structural units of vinylidene fluoride polymers, the proportion of HFP units (structural units derived from hexafluoropropylene) can be in the range of 0 to 50 mol% (e.g., 0.5 to 25 mol%, 2 to 10 mol%).

[0039] The adhesive layer can contain inorganic particles. By including inorganic particles in the adhesive layer, the strength and durability of the adhesive layer are improved.

[0040] Inorganic particles can preferably be insulating, but conductive inorganic particles can also be used. Inorganic particles can be insulating materials such as metal oxides, metal hydroxides, metal nitrides, metal carbides, and metal sulfides. Examples of materials for inorganic particles include alumina, magnesium oxide, titanium oxide, zirconium oxide, silicon oxide, zinc oxide, magnesium hydroxide, silicon nitride, aluminum nitride, titanium nitride, silicon carbide, aluminum hydroxide, lithium phosphate, lithium fluoride, carbon black (acetylene black, etc.), amorphous silica, and crystalline silica. Solid electrolyte particles such as LLZO (lithium lanthanum zirconium oxide) and LATP (lithium aluminum titanium phosphate) can also be used.

[0041] The average primary particle size of inorganic particles can be greater than or equal to 0.1 µm or 1.0 µm, or less than or equal to 5.0 µm or 3.0 µm. The average primary particle size is the median particle size (D0) that constitutes 50% of the total volume in the particle size distribution on a volume basis. 50 Median particle size (D) 50 The particle size distribution can be measured using a laser diffraction / scattering particle size distribution measuring device.

[0042] The content of inorganic particles in the adhesive layer can be above 10% by mass or above 20% by mass, or below 99% by mass or below 90% by mass.

[0043] The adhesive layer can be porous. By using a porous adhesive layer, the contact area between the adhesive layer and the non-aqueous electrolyte is increased, thereby further improving the retention of the non-aqueous electrolyte in the adhesive layer and improving lithium-ion conductivity. As a result, the battery resistance decreases, and good cycle characteristics are achieved.

[0044] The thickness of the adhesive layer can be greater than 0.1µm or greater than 0.3µm, or less than 5µm or less than 2µm. It should be noted that the adhesive layer can be formed on both sides of the first substrate layer. That is, the adhesive layer can be formed on both the first main surface and the second main surface of the first substrate layer. In this case, the separator includes a second adhesive layer formed on the second main surface of the first substrate layer.

[0045] The second spacer includes at least a substrate layer (second substrate layer). The second spacer may consist of only the second substrate layer. Alternatively, the second spacer may also include the second substrate layer and an adhesive layer formed on the second substrate layer.

[0046] The second substrate layer has a third main surface disposed on the negative electrode side and a fourth main surface disposed on the positive electrode side. That is, the fourth main surface is disposed on the first separator side. The second separator may include the second substrate layer and an adhesive layer (third adhesive layer) formed on the third main surface of the second substrate layer. At least a portion of the third adhesive layer of the second separator may be bonded to the negative electrode. Alternatively, the third adhesive layer may not be bonded to the negative electrode. By bonding the third adhesive layer to the negative electrode, dendritic precipitation of lithium metal can be suppressed, resulting in further improvement of cycle characteristics. The second separator may include the second substrate layer and an adhesive layer (fourth adhesive layer) formed on the fourth main surface of the second substrate layer.

[0047] When at least a portion of the third adhesive layer of the second separator is bonded to the negative electrode, the secondary battery (B) preferably further includes a third separator disposed between the first separator and the aforementioned second separator. The third separator includes a third substrate layer. Preferably, no adhesive layer is formed on the third substrate layer. For example, the third separator may be composed only of the substrate layer. When at least a portion of the first adhesive layer of the first separator is bonded to the positive electrode, and at least a portion of the third adhesive layer of the second separator is bonded to the negative electrode, a separator composed of the first separator and the second separator can be used, but by using a separator composed of the first, second, and third separators, an electrode assembly can be easily fabricated. In this case, firstly, a first laminate formed by bonding the negative electrode and the first separator, a second laminate formed by bonding the positive electrode and the second separator, and the third separator are stacked such that the third separator without an adhesive layer is disposed between the first separator and the second separator, and a portion of the third separator is wound up. Then, by winding the first laminate and the second laminate, a wound electrode assembly is formed. It should be noted that the average thickness Ts3 of the third separator can be greater than 5µm or greater than 10µm, or less than 30µm or less than 20µm.

[0048] The average thickness Ts1 of the first separator can be 5µm or more, or 10µm or more, or less than 30µm or less than 20µm. The average thickness Ts2 of the second separator can be 20µm or more, or 30µm or more, or less than 80µm or less than 60µm. The ratio Ts2 / Ts1 of the average thickness Ts2 to the average thickness Ts1 can be 1.1 or more, 1.3 or more, or 1.5 or more, or less than 3.0 or less than 2.0. By setting the ratio Ts2 / Ts1 to 1.5 or more, it is easy to absorb the expansion of the negative electrode with the second separator.

[0049] When the state of charge is 90%, the average value Tn (μm) of the increase in thickness caused by charging on one side of the negative electrode and the total thickness Ts (μm) of the average thickness of the first separator and the average thickness of the second separator can satisfy the relationship 1.2 < Ts / Tn. By satisfying the relationship 1.2 < Ts / Tn, it is possible to particularly suppress the expansion of the electrode group during charging. In addition, when a third separator is disposed between the first separator and the second separator, the above-mentioned thickness Ts (μm) is the total thickness of the average thickness Ts1 of the first separator, the average thickness Ts2 of the second separator, and the average thickness Ts3 of the third separator. In this case, the relationship 1.2 < Ts / Tn can also be satisfied.

[0050] The ratio Ts / Tn can be 1.07 or more, and can also be greater than 1.2 (for example, can be greater than 1.20). The ratio Ts / Tn can be 1.07 or more, 1.25 or more, or 1.50 or more, and can be 5.0 or less, 3.5 or less, or 2.0 or less. By making the ratio Ts / Tn greater than 1.2, it is possible to suppress the expansion of the electrode group during charging. By setting the ratio Ts / Tn to 3.0 or less, it is possible to suppress the decrease in the volume capacity density.

[0051] By making the thickness Ts greater than the thickness of a general separator, it is easy to satisfy the relationship 1.2 < Ts / Tn. The thickness Ts can be 20 μm or more or 30 μm or more, and can be 80 μm or less or 60 μm or less. The average thickness Ts1 (μm) of the first separator can be measured by the following method. It should be noted that the average thickness Ts2 (μm) of the second separator and the average thickness Ts3 (μm) of the third separator can also be measured by the same method.

[0052] The average thickness Ts1 (μm) of the first separator is obtained by arithmetically averaging the thicknesses at 15 locations. The thickness of the first separator can be measured by the method according to JIS (Japanese Industrial Standards) K6250. Specifically, a test piece thickness gauge (SDA-12 type) manufactured by Polymer Gauge Co., Ltd. according to JIS K6250 can be used to measure the thickness. The measurement is carried out using a probe with a diameter of 5 mm under a pressure of 22 kPa. The thickness measurement is carried out at 15 intersections of 5 lines that divide the first separator into 6 equal parts in the length direction and 3 lines that divide it into 4 equal parts in the width direction. Then, the arithmetic average of the measured thicknesses at 15 locations is used as the average thickness Ts1.

[0053] The average value Tn (µm) can be determined using the following method. First, prepare two batteries manufactured under identical conditions. Then, set one battery to a state of discharge (SOC = 0%) and the other to a state of charge (SOC = 90%). It should be noted that a state of charge (SOC) of 90% means that the battery is charged to 90% of its rated capacity. A state of charge (SOC) of 0% means that the battery has discharged 100% of its rated capacity from a fully charged state. It should also be noted that in this specification, the rated capacity of the battery refers to the 1-hour rate capacity.

[0054] Next, the negative electrode was removed from both the discharged and charged batteries. The thickness T(0) (µm) of the negative electrode in the discharged state and the thickness T(90) (µm) of the negative electrode in the charged state (SOC = 90%) were measured at three points on the negative electrode. Specifically, firstly, as... Figure 1 As shown, the portion 12a of the negative electrode 12, which is separated from the positive electrode by a separator, is divided into four equal regions 12a1, 12a2, 12a3, and 12a4 along the length of the negative electrode 12. In portion 12a, the negative electrode expands during charging. Next, positions p1, p2, and p3 are defined as the central positions in the width direction of the three boundaries between the four regions 12a1 to 12a4. Then, thicknesses T(0) and T(90) are measured at positions p1, p2, and p3. The two sides of the negative electrode at positions p1, p2, and p3 are separated from the positive electrode by the separator. The average value Tn of the thickness increase caused by charging on one side of the negative electrode is calculated using the following formula.

[0055] Tn = {(total thickness T(90) at 3 points) - (total thickness T(0) at 3 points)} / 6

[0056] As described above, the second separator includes at least a substrate layer (second substrate layer). The porosity V2 of the second substrate layer can be greater than the porosity V1 of the first substrate layer. In the case that the secondary battery (B) is a lithium secondary battery, it is preferable that the porosity V2 is greater than the porosity V1. By making the porosity V2 greater than the porosity V1, the expansion of the negative electrode can be easily absorbed by the second substrate layer.

[0057] The ratio of porosity V2 (%) to porosity V1 (%), V2 / V1, can be 1.1 or more, or 1.2 or more, or 2.0 or less, or 1.7 or less. Porosity V2 can be 60% or more, or 70% or less, or 90% or less, or 80% or less. By making porosity V2 60% or more, the expansion of the negative electrode can be easily absorbed by the second substrate layer. By making porosity V2 90% or less, the strength of the second substrate layer can be maintained.

[0058] The porosity of the substrate layer can be determined by the following method. First, collect 4 cm square samples at four points along the central portion of the spacer in the width direction. Next, peel off the adhesive layer of each sample using adhesive tape, separating only the substrate layer. Then, measure the mass of each substrate layer and determine its thickness using the method described above (the method for measuring the thickness of the spacer). Next, calculate the apparent density of the substrate layer from its mass, area, and thickness. The porosity of the substrate layer is calculated using the following formula. The true density of the substrate layer is determined based on the material of the substrate layer.

[0059] Porosity (%) = 100 × {1 - (apparent density of the substrate layer) / (true density of the substrate layer)}

[0060] In the secondary battery (B), at least one of the following conditions (1) to (3) can be satisfied. For example, conditions (1) and (2) can be satisfied, conditions (1) and (3) can be satisfied, and conditions (2) and (3) can be satisfied. Alternatively, all of conditions (1) to (3) can be satisfied.

[0061] (1) The ratio of porosity V2 (%) to porosity V1 (%) is greater than 1.2.

[0062] (2) The ratio of average thickness Ts2 to average thickness Ts1, Ts2 / Ts1, is greater than 1.5.

[0063] (3) The ratio Ts / Tn is greater than 1.2. The ratio Ts / Tn can also be within the range mentioned above.

[0064] (Method for making the separator)

[0065] An example of the manufacturing method (M) for the first separator used in this embodiment will be described. However, the first separator of the secondary battery (B) can also be manufactured by methods other than the manufacturing method (M) described below. The above-described matters concerning the first separator are applicable to the manufacturing method (M), therefore repeated descriptions are omitted. The matters described in the manufacturing method (M) can also be applied to the first separator of the secondary battery (B). It should be noted that when the second separator has an adhesive layer, the second separator can be manufactured by the same method as the manufacturing method (M).

[0066] Manufacturing method (M) involves forming a separator by creating an adhesive layer on a substrate layer. The method for forming the adhesive layer is not particularly limited and can be any known method. One example is forming the adhesive layer by applying a coating containing adhesive components to the substrate layer and then allowing it to dry. The method for applying the coating is not limited and can be any known method. For example, it can be applied using spraying, roller coating, stencil methods (gravure coating, die coating, etc.), or printing methods (screen printing, inkjet printing, etc.).

[0067] Solvents for the coating solution can include acetone, dimethylformamide, dimethylacetamide, N-methyl-2-pyrrolidone, dimethyl sulfoxide, tripropylene glycol, etc. When forming a porous adhesive layer, a solvent-inducible phase separation (NIPS) method can be used. One example method involves first preparing a coating solution by dissolving the resin in the aforementioned solvent (a good solvent), and then applying this coating solution to a substrate layer to form a coating film. Next, before the coating film dries, immersing it in a poor solvent can make the coating film porous. Poor solvents can include water, methanol, ethanol, isopropanol, or mixtures thereof. Furthermore, by mixing acetone, dimethylformamide, dimethylacetamide, N-methyl-2-pyrrolidone, dimethyl sulfoxide, tripropylene glycol, etc., into the aforementioned poor solvents, the porosity of the coating film can be altered.

[0068] The non-aqueous electrolyte can be a non-aqueous electrolyte containing a non-aqueous solvent and a lithium salt. The non-aqueous solvent may contain ether. The ether content in the non-aqueous solvent may be 80% by mass or more, or 90% by mass or more. The non-aqueous solvent may consist of only ether. By using a non-aqueous solvent containing ether, the cycle characteristics can be further improved. In particular, in the case where the secondary battery (B) is a lithium secondary battery, the dendritic precipitation of lithium metal in the negative electrode during charging can be suppressed.

[0069] The ether used in the non-aqueous solvent may be any ether described later. The ether may be a fluoroether containing a fluorine group (-F) or a hydrofluoroether. Hydrofluoroethers contain carbon atoms bonded to hydrogen and fluorine atoms. By using hydrofluoroethers, the reduction resistance of the non-aqueous electrolyte is improved, and decomposition of the non-aqueous electrolyte at the negative electrode surface is less likely. The content of hydrofluoroether in the non-aqueous solvent may be 80% by mass or more, or 90% by mass or more. The non-aqueous solvent may consist solely of hydrofluoroethers.

[0070] The fluorination rate of hydrofluoroethers is preferably 60% or more, more preferably 65% ​​or more. This fluorination rate can be 95% or less, 90% or less, or 80% or less. The fluorination rate of one hydrofluoroether is defined by the following formula.

[0071] Fluorination rate (%) = 100 × (number of fluorine atoms in the hydrofluoroether) / (total number of fluorine and hydrogen atoms in the hydrofluoroether)

[0072] The hydrofluoroether used in non-aqueous solvents may be at least one selected from the group consisting of 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

[0073] The positive electrode of the secondary battery (B) may include a positive current collector and a positive electrode binder layer formed on both sides of the positive current collector. The positive electrode binder layer may contain polyvinylidene fluoride (PVDF). PVDF functions as a highly stable binder in non-aqueous electrolyte secondary batteries. Therefore, by including PVDF in the positive electrode binder layer, the stability of the positive electrode can be improved, resulting in further improvement in cycle characteristics. In the secondary battery (B), the positive electrode binder layer may contain PVDF, and the first adhesive layer of the first separator may contain a PVDF-based polymer. According to this configuration, the adhesion between the positive electrode binder layer and the adhesive layer can be improved.

[0074] In the negative electrode of the secondary battery (B), lithium metal can be deposited during charging and dissolved in the non-aqueous electrolyte during discharging. That is, the secondary battery (B) can be a lithium secondary battery.

[0075] (Manufacturing method of secondary battery (B))

[0076] The manufacturing method is not limited as long as the secondary battery (B) can be manufactured. One example manufacturing method includes steps (i), (ii), and (iii). The matters described regarding the secondary battery (B) are applicable to the following manufacturing method, therefore repeated descriptions are omitted.

[0077] Step (i) is a step of forming a laminate of the first separator and the positive electrode by bonding the first separator to both sides of the positive electrode using a first adhesive layer. The bonding of the first separator and the positive electrode can be achieved by overlapping and hot-pressing the two together. The heating temperature during hot pressing can be selected appropriately based on the material of the adhesive layer. For example, if the adhesive layer contains a vinylidene fluoride-based polymer, the heating temperature during hot pressing can be in the range of 60~120°C.

[0078] Step (ii) is a process of forming a wound electrode assembly by winding the aforementioned laminated body (positive electrode and first separator), second separator, and negative electrode. The first separator and the second separator are disposed between the positive electrode and the negative electrode. At this time, the second separator is disposed between the first separator and the negative electrode. Step (iii) is a process of sealing the electrode assembly and non-aqueous electrolyte into an outer casing. The method of performing steps (ii) and (iii) is not limited, and known methods can be used. In this way, a secondary battery (B) is manufactured. However, the secondary battery (B) can also be manufactured using manufacturing methods other than this method.

[0079] (Examples of constituent elements)

[0080] The following provides specific examples of other constituent elements of the secondary battery (B). It should be noted that the constituent elements described below are illustrative, and the constituent elements of the secondary battery (B) in this embodiment are not limited to the examples shown below. Constituent elements other than the characteristic portions of this embodiment may also use known constituent elements.

[0081] (Negative electrode of a lithium secondary battery)

[0082] In the case of a lithium-ion secondary battery (B), the negative electrode includes a negative current collector. During charging, lithium metal is deposited on the negative current collector. The deposited lithium metal dissolves as lithium ions in the non-aqueous electrolyte during discharge.

[0083] The negative current collector may consist solely of a substrate sheet in which lithium is not a major component (content: 50% by mass or more). Alternatively, the negative current collector may also comprise a substrate sheet and lithium-containing metal layers laminated on both sides of the substrate sheet. The substrate sheet may be a conductive sheet such as a metal foil. Examples of materials for the metal foil include copper, copper alloys, and stainless steel. Copper and copper alloys are preferred for their high conductivity. Stainless steel is preferred for its ease of cutting.

[0084] The lithium-containing metal layer laminated on the substrate is a lithium metal layer or a lithium alloy layer. Elements other than lithium contained in the lithium alloy layer are present in trace amounts (less than 10 atomic percent). Examples of elements other than lithium contained in lithium alloys include aluminum, magnesium, indium, and zinc. By forming a lithium-containing metal layer, the decrease in discharge capacity associated with repeated charging and discharging can be suppressed. Furthermore, by forming a lithium-containing metal layer, the dendritic precipitation of lithium metal can be suppressed. The method for forming the lithium-containing metal layer is not particularly limited and can be formed using known methods. For example, a lithium-containing metal layer can be formed by pressing a lithium metal foil or a lithium alloy foil onto the substrate. The density of the lithium-containing metal layer distinguishes it from the lithium metal deposited during charging (which is typically porous).

[0085] The surface of a negative electrode current collector made of metal can be smooth. By using a negative electrode current collector with a smooth surface, lithium metal can be easily and uniformly deposited on the negative electrode current collector during charging. Surface smoothness of a negative electrode current collector made of metal refers to a maximum vertical roughness Rz of 20 µm or less. The maximum vertical roughness Rz of a negative electrode current collector made of metal can be 10 µm or less. The maximum vertical roughness Rz is measured according to JIS (Japanese Industrial Standard) B 0601:2013.

[0086] The thickness of the substrate can be greater than 3µm or greater than 5µm, or less than 20µm or less than 15µm. When the negative electrode current collector includes a lithium-containing metal layer, the thickness of the lithium-containing metal layer can be in the range of 5µm to 25µm.

[0087] The negative electrode current collector (e.g., the substrate sheet) may contain austenitic stainless steel. In this case, embrittlement of the negative electrode current collector is suppressed, and the negative electrode current collector has moderate strength and flexibility, resulting in a negative electrode current collector with excellent resistance to stress generated at the negative electrode. As a result, fracture of the negative electrode current collector during charging and discharging and the subsequent reduction in cycle characteristics are suppressed.

[0088] It should be noted that the "austenitic stainless steel" mentioned above refers to stainless steel with an austenite content of 50% or more. The austenite content refers to the proportion (by mass) of the austenite phase in stainless steel. When the contents of the austenite, ferrite, and martensite phases in stainless steel are set as O, F, and M, respectively, the austenite content is calculated by {O / (O+F+M)}×100. The austenite structure is a face-centered cubic (FCC) crystal structure, while the ferrite and martensite structures are body-centered cubic (BCC) crystal structures.

[0089] The austenite content can be above 70%, above 90%, or even 100%.

[0090] The austenite ratio can be determined using the following method. First, prepare a sample of the negative electrode current collector (stainless steel foil) (e.g., size: 25 mm square). Perform X-ray diffraction (XRD) on the sample using a two-dimensional detection function to obtain the XRD pattern (vertical axis: X-ray diffraction intensity, horizontal axis: diffraction angle 2θ). The size of the measurement area (micro-area) is, for example, 15 mm square.

[0091] The following shows the desired XRD measurement conditions.

[0092] <Analytical Device>

[0093] Two-dimensional micro-area X-ray diffraction apparatus (RINT-RAPID II, manufactured by Rigaku Corporation)

[0094] <Analysis Conditions>

[0095] X-ray tube: Co

[0096] Monochromaticization: using a monochromator (CoKα)

[0097] X-ray tube output: 40kV-30mA

[0098] Detector: Imaging panel (two-dimensional)

[0099] (Reflection method)

[0100] Collimator: Φ300µm

[0101] ω angle: 25°~35° (2° / sec)

[0102] Φ angle: 360° rotation (1° / sec)

[0103] Measurement time (exposure): 30 minutes

[0104] For the diffraction peaks observed in the obtained XRD pattern, a standard database was used for least-squares fitting, followed by quantitative analysis based on Rietveld analysis. The XRD pattern can have at least one diffraction peak corresponding to one of the austenite, ferrite, and martensite phases. This analysis can be performed using software attached to the analytical apparatus. Through this analysis, the proportion (mass ratio) of the austenite phase relative to the total of the austenite, ferrite, and martensite phases is determined as the austenite ratio. Several measurement regions were arbitrarily selected in the above sample, and the austenite ratio in each measurement region was calculated, and their average value was determined.

[0105] Austenitic stainless steels can contain elements other than Fe, such as C, Si, Mn, P, S, Ni, Cr, Mn, Mo, Cu, and N. These stainless steels can be low-carbon, ultra-low-carbon, or nitrogen-added stainless steels, or duplex stainless steels containing austenite.

[0106] Examples of austenitic stainless steels include SUS301, SUS302, SUS303, SUS304, SUS305, SUS309, SUS310, SUS312, SUS315, SUS316L, SUS317, SUS321, and SUS347. Among these, SUS304 and SUS316L are preferred.

[0107] The negative current collector may include a resin film and a transition metal layer laminated on the resin film. That is, the substrate may include a resin film and a transition metal layer laminated on the resin film. The negative current collector (e.g., the substrate) may be composed of a resin film and a transition metal layer. The resin film may include a substrate resin layer and a surface resin layer formed on the substrate resin layer. The surface resin layer is present on the surface of the resin film. The transition metal layer may be in contact with the resin film (e.g., the surface resin layer). As described above, the negative current collector may include a lithium-containing metal layer laminated on the substrate.

[0108] Resin films are lightweight, which facilitates the improvement of energy density in secondary batteries. They are also less prone to breakage during roller transport and are easy to handle. Furthermore, resin films are not easily embrittled even at low negative electrode potentials. Resin films are excellent current collector materials due to their high resistance to stress during electrode expansion and contraction and their resistance to breakage. In lithium-ion secondary batteries, lithium metal is deposited at the negative electrode during charging, leading to significant expansion of the negative electrode. This expansion is further amplified when lithium metal is deposited in a dendritic form, thus easily generating stress at the negative electrode.

[0109] The main surface of the resin membrane can be smooth, roughened, or treated with plasma, corona, etc. When the main surface of the resin membrane is smooth, the maximum vertical roughness Rz is less than 2.5 µm. When the main surface of the resin membrane is roughened, the maximum vertical roughness Rz can be greater than 2.5 µm and greater than 8 µm. The maximum vertical roughness Rz is measured according to JIS B 0601:2013. The main surface of the resin membrane refers to the surface other than the end faces, and consists of the two surfaces with the largest area. In this specification, "surface" usually refers to the "main surface".

[0110] From the perspective of improving the energy density of secondary batteries, a thin resin film is desirable as long as mechanical strength can be ensured. An example of a preferred range for resin film thickness is 1.5 µm to 30 µm or less. The thickness of the resin film can be determined by measuring the thickness at any 10 points on a cross-section of the resin film using a scanning electron microscope (SEM) and then arithmetically averaging them.

[0111] The surface resin layer of the resin film may contain nitrogen-containing resin. At least 90% by mass of the surface resin layer may be nitrogen-containing resin. The nitrogen-containing resin may be a polymer having nitrogen atoms in its main chain and / or side chains. The nitrogen atom content in the nitrogen-containing resin may be at least 3% by mass. The nitrogen atom content in the surface resin layer may be at least 2.5% by mass.

[0112] Nitrogen-containing resins can contain nitrogen-hydrogen bonds (bonds between nitrogen and hydrogen atoms). The characteristic infrared absorption peak of nitrogen-hydrogen bonds is located at 1655 cm⁻¹. -1 (1640~1670cm -1 Near 1530cm -1 (1515~1545cm -1 The presence or absence of nitrogen-hydrogen bonds can be determined based on peaks near the anode. Specifically, firstly, after removing or wet-processing the active material of the negative electrode, the transition metal layer is dissolved with an aqueous nitric acid solution, exposing the surface resin layer. Then, the presence or absence of nitrogen-hydrogen bonds can be determined by analyzing the exposed surface resin layer using infrared absorption spectroscopy. A specific example of the analysis is shown below. Alternatively, the presence or absence of nitrogen-hydrogen bonds can also be determined by chemical shifts in X-ray electron spectroscopy (XPS).

[0113] (FTIR-ATR method)

[0114] Measurement apparatus: Varian 670FTIR (manufactured by Varian)

[0115] Measurement mode: Attenuated total internal reflection

[0116] Light source: special ceramic

[0117] Detector: DLaTGS (deuterated L-alanine-doped triglycine sulfate)

[0118] Resolution: 4cm -1

[0119] Total number of times: 256

[0120] IRE: Ge

[0121] Angle of incidence: 60 degrees

[0122] Attachment: Attachment for 1-time reflection ATR (seagull)

[0123] Nitrogen-containing resins can be polymers having at least one group selected from the group consisting of urea bonds, melamine structures, triazine rings, amino groups, amide bonds, aromatic polyamide bonds, imide bonds, urethane bonds, carbodiimide bonds, urea diketone structures, isocyanurate rings, nitrile groups, and amide groups. Examples of such polymers include polyurethane resins, polyurea resins, melamine resins, polyamide resins, aramid resins, and polyimide resins. Among these, polyurethane resins are excellent as current collector materials due to their high flexibility, high resistance to stress during electrode expansion and contraction, and resistance to breakage.

[0124] Polyurethane resins can be synthesized by reacting polyols with polyisocyanates (especially diisocyanates) that have two or more functionalities. By arbitrarily selecting polyols and polyisocyanates, polyurethane resins with various physical properties can be synthesized.

[0125] Nitrogen-containing resins can be polymers having at least one group selected from the group consisting of aliphatic isocyanate groups, aromatic isocyanate groups, urea-formate groups, and biuret groups. Thermosetting polyurethane resins, in particular, use polyisocyanates as raw materials, thus having a high probability of residual unreacted isocyanate groups. It is believed that isocyanate groups are reduced at the negative electrode to generate coating components for forming a stable coating at the negative electrode. Furthermore, thermosetting resins form a robust three-dimensional coating, thus exhibiting a strong inhibitory effect on copper damage. UV-curable resins also have the same effect. Isocyanate groups at 2250 cm⁻¹... -1 (2270~2240cm -1 The vicinity of the infrared absorption peak is based on antisymmetric stretching vibration, so its presence or absence can be confirmed based on the infrared absorption peak.

[0126] The surface resin layer may contain fillers. By adding fillers (silica, alumina, etc.) to the surface resin layer, an uneven surface is created. This results in an anchoring effect, improving the adhesion between the surface resin layer and the substrate resin layer. The fillers used can roughen the surface of the surface resin layer and are less prone to degradation of battery characteristics due to side reactions with non-aqueous electrolytes. Fillers can be particles of resin, metal oxides, ceramics, metals, etc.

[0127] The surface resin layer can be a coating formed by applying a nitrogen-containing resin to the surface of a substrate resin layer. In this case, the nitrogen-containing resin can be a thermosetting resin or a UV-curable resin. The nitrogen-containing resin can be diluted with a solvent and applied to the surface of the substrate resin layer. The cured product of the curable resin can have a three-dimensional network of molecular chains.

[0128] The thickness of the surface resin layer is, for example, less than 5 µm, and preferably in the range of 0.05 µm to 1.5 µm. The thickness of the surface resin layer can be determined by measuring the thickness of any 10 points in a cross-section of a specified component (negative electrode or negative electrode current collector) using a scanning electron microscope (SEM) and then arithmetically averaging them.

[0129] Most resin films are non-conductive. The transition metal layer plays a crucial role in imparting good conductivity to the negative electrode current collector. The transition metal layer simply needs to contain a transition metal and possess electronic conductivity. Ideally, the transition metal layer should contain a transition metal in a metallic state with electronic conductivity based on free electrons.

[0130] For ease of ensuring corrosion resistance and conductivity, the transition metal layer preferably comprises copper, nickel, chromium, titanium, iron, silver, gold, tin, etc. The transition metal layer preferably comprises at least one material selected from the group consisting of copper, copper alloys, stainless steel, nickel, and nickel alloys. The transition metal layer particularly preferably comprises copper or copper alloys with excellent conductivity.

[0131] Transition metals can cause resin film embrittlement. This embrittlement is particularly pronounced when the transition metal layer contains copper. As a previously unreported insight, it has also been determined that lithium metal significantly accelerates resin film embrittlement caused by transition metals (e.g., copper damage). That is, in lithium secondary batteries where lithium metal is deposited at the negative electrode, significant degradation of the resin film due to the transition metal layer is possible. In contrast, by including at least the surface resin layer of the resin film in a nitrogen-containing resin, resin film embrittlement is significantly suppressed.

[0132] It should be noted that a nickel-chromium alloy layer is considered as the metal layer to shield the transfer of copper ions to the resin film. However, in lithium-ion batteries, the shielding effect of the nickel-chromium alloy layer is completely lost. This is presumably because, when easily ionized lithium metal comes into contact with transition metals such as copper, the ionization of the transition metal is accelerated, and the breakage of polymers is accelerated due to the transition metal ions. On the other hand, a surface resin layer containing nitrogen-containing resin can significantly suppress polymer breakage.

[0133] The breaking of carbon-carbon bonds has the greatest impact on the embrittlement of resin films. In the case of resin films containing nitrogen-containing resins, carbon-nitrogen bonds exist within the nitrogen-containing resin. It is believed that these carbon-nitrogen bonds are not easily affected by transition metals or their ions. There is a possibility that transition metals are stabilized by nitrogen atoms, thus suppressing the breaking of carbon-carbon bonds.

[0134] The transition metal layer can be formed by depositing it on the surface of the surface resin layer using liquid-phase or vapor-phase methods. Liquid-phase methods include electrodeposition techniques such as electrolytic plating / chemical plating. Vapor-phase methods include evaporation, sputtering, and atomic layer deposition (ALD). Alternatively, a base layer can be formed by sputtering, and the transition metal layer can be thickened on top using electrolytic plating. In other words, multiple methods can be used in combination. The transition metal layer can also be formed by lamination. However, the method for forming the transition metal layer is not particularly limited.

[0135] The thickness of the transition metal layer is, for example, less than 5 µm, or less than 3 µm. A preferred range for the thickness of the transition metal layer is 0.05 µm to 1.5 µm, and it can be 0.1 µm to 1.5 µm. An example of measuring the thickness of the transition metal layer is as follows: First, using a scanning electron microscope (SEM), the thickness of the transition metal layer is measured at any 10 points in a cross-section of a specified component (negative electrode or negative electrode current collector). Then, the thickness of the transition metal layer (average thickness) is calculated by arithmetic averaging the obtained measurements. The transition metal layer can consist of multiple layers composed of different metals.

[0136] The substrate resin layer is the main component of the negative electrode current collector, and is typically thicker than the surface resin layer and the transition metal layer. At least 51% by mass of the substrate resin layer is composed of resin or organic matter. To improve adhesion to the transition metal layer and lithium layer, the substrate resin layer may contain inorganic materials such as inorganic particles. The substrate resin layer can be a stretched film, a non-porous film, or a film with multiple regularly arranged pores. The substrate resin layer can be insulating, conductive, or non-conductive. There are no particular limitations on the morphology and physical properties of the substrate resin layer.

[0137] The substrate resin layer is formed, for example, by molding raw materials (general-purpose plastics, general-purpose engineering plastics, etc.) into sheets. Examples of raw materials include polyester resins, olefin resins, polyphenylene sulfide resins, acrylic resins, polycarbonate resins, polyetheretherketone resins, polysulfone resins, polyphenylene sulfone resins, polyethersulfone resins, polyamide resins, polyimide resins, polyetherimide resins, polybenzimidazole resins, liquid crystal polymer resins, polyacetal resins, polyvinyl chloride resins, polyarylate resins, silicone resins, nylon resins, polyvinylidene chloride resins, ethylene-vinyl alcohol copolymers, polyvinyl alcohol resins, polystyrene resins, epoxy resins, polyurethane resins, phenolic resins, melamine resins, urea resins, unsaturated polyester resins, etc. The resins contained in the substrate resin layer can be used alone or in combination of two or more.

[0138] The resin contained in the substrate resin layer is preferably a resin with aromatic rings, a resin without fluorine atoms, or an olefin resin. When the resin has aromatic rings (e.g., benzene rings) within its molecules, the affinity between the substrate resin layer and the lithium metal layer increases, and the adhesion between the two is improved.

[0139] As a polyester resin, aromatic polyesters are preferred, especially unstretched polyethylene terephthalate, biaxially stretched polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate. As an acrylic resin, polymethyl methacrylate (PMMA) can be used. As a polyimide resin, aromatic polyimide is preferred. As a polyamide resin, aromatic polyamide (aramid resin) is preferred. As an olefin resin, unstretched polypropylene, biaxially stretched polypropylene, low-density polyethylene, medium-density polyethylene, high-density polyethylene, linear low-density polyethylene, metallocene polyethylene, ethylene-vinyl acetate copolymer, ethylene-methyl acrylate copolymer, ethylene-ethyl acrylate copolymer, ethylene-methyl methacrylate copolymer, ethylene-acrylic acid copolymer, ethylene-methacrylic acid copolymer, and ionomers are preferred.

[0140] The extrusion method for the substrate resin layer can be either T-die extrusion or blow extrusion, and can involve non-stretching, uniaxial stretching, sequential biaxial stretching, or simultaneous biaxial stretching. The resin can be a homopolymer, a copolymer, or a terpolymer. The arrangement of the structural units constituting the resin is not limited; it can be a random copolymer or a block copolymer. Two or more substrate resin layers can also be combined. For example, two or more substrate resin layers can be stacked. The crystalline resin can be in a crystalline state, an amorphous state, or a mixture of both. Amorphous resin can be formed by methods such as rapid cooling. The substrate resin layer can be an alloy resin composed of multiple resins as described above.

[0141] To ensure adhesion to other layers (such as vapor-deposited films), the surface of the substrate resin layer can be subjected to corona treatment or plasma treatment. To improve adhesion to the surface resin layer by creating irregularities in the substrate resin layer, fillers (comprising ceramics, resins, metals, etc.) can be added to the substrate resin layer, forming irregularities on its surface.

[0142] (Negative electrode of a lithium-ion secondary battery)

[0143] In the case where the secondary battery (B) is a lithium-ion secondary battery, the negative electrode includes a negative current collector and negative electrode flux layers formed on both sides of the negative current collector. The negative current collector can be a conductive sheet (e.g., metal foil) or a resin film, as exemplified by the substrate sheet of the negative electrode of a lithium secondary battery.

[0144] The negative electrode mixture layer contains a negative electrode active material, such as a negative electrode active material and additives (binder, conductive material, thickener, etc.). The negative electrode can be formed by known methods. For example, firstly, a negative electrode mixture slurry containing a negative electrode active material and additives is prepared. Next, the negative electrode mixture slurry is coated onto a negative electrode current collector and dried to form a coating film. Then, the negative electrode is obtained by calendering the laminate consisting of the negative electrode current collector and the coating film. The formed negative electrode is cut to a specified size as needed. The thickness of the negative electrode mixture layer can be 3µm or more, or 5µm or more, or 200µm or less, or 150µm or less.

[0145] The negative electrode active material contained in the negative electrode composite layer can be a substance capable of reversibly absorbing, storing, and releasing lithium ions. Examples of such negative electrode active materials include carbonaceous materials and Si-containing materials. The negative electrode active material can contain Si-containing materials or be solely Si-containing materials. Examples of carbonaceous materials include graphite, easily graphitized carbon (soft carbon), and difficult-to-graphitize carbon (hard carbon). Examples of Si-containing materials include elemental Si, silicon alloys, silicon compounds (silicon oxides, etc.), and composite materials in which a silicon phase is dispersed within the lithium-ion conductive phase (matrix). The negative electrode can contain only one type of negative electrode active material or two or more types of negative electrode active materials.

[0146] There are no particular limitations on the additives contained in the negative electrode binder layer. The binder, conductive material, and thickener may each be the substances exemplified regarding the binder, conductive material, and thickener of the positive electrode binder layer.

[0147] (positive electrode)

[0148] The positive electrode comprises a positive current collector and a positive electrode additive layer disposed on the positive current collector. The positive electrode additive layer contains a positive electrode active material, such as a positive electrode active material and additives (conductive material, binder, thickener, etc.). The positive electrode additive layer is formed on both sides of the positive current collector. The positive electrode can be formed by known methods. For example, firstly, a positive electrode additive slurry containing a positive electrode active material and additives is prepared. Next, the positive electrode additive slurry is coated onto the positive current collector and dried, thereby forming a coating film. Then, the laminate consisting of the positive current collector and the coating film is calendered, thereby obtaining the positive electrode. It should be noted that the formed positive electrode is cut to a specified size as needed.

[0149] The thickness of the positive electrode compound layer can be greater than 50µm or greater than 100µm, or less than 300µm or less than 250µm.

[0150] The positive electrode active material can be a substance capable of reversibly absorbing and releasing lithium ions. Examples of positive electrode active materials include lithium-containing transition metal oxides, transition metal fluorides, polyanions, fluorinated polyanions, and transition metal sulfides. Lithium-containing transition metal oxides are preferred for their low manufacturing cost and high average discharge voltage.

[0151] Examples of transition metal elements contained 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 only one transition metal element or two or more. The transition metal element can be at least one element selected from the group consisting of Co, Ni, and Mn. Lithium-containing transition metal oxides may contain more than one typical element. Examples of typical elements include Mg, Al, Ca, Zn, Ga, Ge, Sn, Sb, Pb, Bi, and B.

[0152] Conductive materials can include carbon materials. Examples of carbon materials include carbon black (acetylene black, Ketjen black, etc.), carbon nanotubes, and graphite.

[0153] Examples of adhesives include fluoropolymers, polyacrylonitrile, polyimide resins, acrylic resins, polyolefin resins, and rubber-like polymers. Examples of fluoropolymers include polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF).

[0154] Thickeners can be cellulose derivatives, etc. Examples of cellulose derivatives include carboxymethyl cellulose (CMC) and its modified forms, methyl cellulose, etc. Examples of modified forms of CMC also include salts of CMC. As salts, alkali metal salts (e.g., sodium salts), ammonium salts, etc., can be mentioned.

[0155] A conductive sheet can be used as the positive current collector. Metal foil or similar materials can be used as the conductive sheet. Carbon material can be coated onto the surface of the positive current collector.

[0156] Examples of materials for the positive current collector (conductive sheet) include metallic materials containing Al, Ti, Fe, etc. The metallic materials can be Al, Al alloys, Ti, Ti alloys, Fe alloys (e.g., stainless steel), etc. The thickness of the positive current collector is not particularly limited and can range from 5 to 300 µm.

[0157] (Separator)

[0158] The separators described above can be used.

[0159] The secondary battery (B) may or may not include a spacer disposed between the negative electrode and the second separator. The spacer may be formed on the main surface of the negative electrode side of the second separator, or it may be formed on the negative electrode. Typically, the secondary battery (B) does not include a spacer (not a separator) disposed between the positive electrode and the negative electrode.

[0160] The spacer may include linear portions and / or dotted portions. The linear portions may also be mesh portions configured in a mesh-like (e.g., honeycomb) pattern. Alternatively, the spacer may also include multiple linear portions configured in a stripe pattern.

[0161] (Non-aqueous electrolyte)

[0162] Non-aqueous electrolytes can be non-aqueous electrolytes with lithium-ion conductivity. Non-aqueous electrolytes can be in liquid or gel form. Liquid non-aqueous electrolytes are prepared by dissolving a lithium salt in a non-aqueous solvent. Dissolving the lithium salt in a non-aqueous solvent generates lithium ions and anions.

[0163] Gel-like non-aqueous electrolytes can contain lithium salts and matrix polymers, or they can contain lithium salts, non-aqueous solvents, and matrix polymers. For example, a polymeric material that gels by absorbing a non-aqueous solvent can be used. Examples of polymeric materials include fluoropolymers, acrylic resins, and polyether resins.

[0164] As a non-aqueous solvent, known solvents can be used. Examples of non-aqueous solvents include cyclic carbonates, chain carbonates, cyclic carboxylic acid esters, chain carboxylic acid esters, chain ethers, fluorinated chain ethers, cyclic ethers, and fluorinated cyclic ethers. Examples of cyclic carbonates include propylene carbonate (PC), ethylene carbonate (EC), fluoroethylene carbonate (FEC), and vinylene carbonate (VC). Examples of chain carbonates include diethyl carbonate (DEC), methyl ethyl carbonate (EMC), and dimethyl carbonate (DMC). Examples of cyclic carboxylic acid esters include γ-butyrolactone (GBL) and γ-valerolactone (GVL). Examples of chain carboxylic acid esters include ethyl acetate, methyl propionate, and fluoromethyl propionate. Examples of cyclic ethers include 1,3-dioxolane, 4-methyl-1,3-dioxolane, tetrahydrofuran, and 2-methyltetrahydrofuran. Examples of chain ethers include 1,2-dimethoxyethane, diethyl ether, ethyl vinyl ether, methyl phenyl ether, benzyl ethyl ether, diphenyl ether, dibenzyl ether, 1,2-diethoxyethane, diethylene glycol dimethyl ether, etc. Non-aqueous solvents can be used alone or in combination of two or more.

[0165] Examples of lithium salts include lithium salts containing chloric acid (LiClO4, LiAlCl4, LiB). 10 Cl 10 Lithium salts include those containing fluorine acids (LiPF6, LiPF2O2, LiBF4, LiSbF6, LiAsF6, LiCF3SO3, LiCF3CO2, etc.), lithium salts containing fluorinated imides (LiN(FSO2)2, LiN(CF3SO2)2, LiN(CF3SO2)(FSO2), LiN(CF3SO2)(C4F9SO2), LiN(C2F5SO2)2, etc.), lithium halides (LiCl, LiBr, LiI, etc.), and lithium salts containing oxalate complexes (LiB(C2O4)2, LiBF2(C2O4), LiPF4(C2O4), LiPF2(C2O4)2, etc.). Lithium salts can be used alone or in combination of two or more.

[0166] The concentration of lithium salt in the non-aqueous electrolyte can be above 0.5 mol / L, above 1.0 mol / L, or above 1.5 mol / L, or below 3.5 mol / L, below 2.0 mol / L, or below 1.5 mol / L. By setting the concentration of lithium salt within the above ranges, a non-aqueous electrolyte with excellent ionic conductivity and moderate viscosity can be obtained.

[0167] Non-aqueous electrolytes may contain additives (such as known additives). Examples of additives include 1,3-propanesulfonyl lactone, methyl benzenesulfonate, cyclohexylbenzene, biphenyl, fluorobenzene, etc.

[0168] (outer body)

[0169] The outer casing houses the non-aqueous electrolyte and electrode assembly. There are no particular limitations on the outer casing; any known outer casing can be used. The outer casing may include a bottom cylindrical battery housing, a sealing body that seals the opening of the battery housing, and a gasket.

[0170] Hereinafter, an example of the secondary battery (B) according to this embodiment will be specifically described with reference to the accompanying drawings. The constituent elements of the non-aqueous electrolyte secondary battery described below can be applied using the constituent elements described above. Furthermore, the constituent elements of the example described below can be modified based on the above description. Additionally, the matters described below can also be applied to the above embodiment. Furthermore, in the non-aqueous electrolyte secondary battery described below, constituent elements not required for the secondary battery (B) disclosed herein can be omitted.

[0171] (Implementation Method 1)

[0172] Figure 2 This is a longitudinal cross-sectional view schematically illustrating an example of a non-aqueous electrolyte secondary battery according to Embodiment 1. Figure 2 The cylindrical non-aqueous electrolyte secondary battery 10 shown includes: a cylindrical battery casing, and an electrode assembly 14 and a non-aqueous electrolyte (not shown) housed within the battery casing. The electrode assembly 14 includes a positive electrode 11, a negative electrode 12, and a separator 13. The electrode assembly 14 is a wound type electrode assembly formed by winding the positive electrode 11, the negative electrode 12, and the separator 13. The separator 13 is disposed between the positive electrode 11 and the negative electrode 12.

[0173] The battery casing includes a casing body 15, which is a bottomed cylindrical metal container, and a sealing body 16 that seals the opening of the casing body 15. A gasket 27 is disposed between the casing body 15 and the sealing body 16. The gasket 27 ensures the airtightness of the battery casing. Inside the casing body 15, insulating plates 17 and 18 are respectively disposed at both ends of the electrode assembly 14 in the winding axis direction. The casing body 15 has a stepped portion 21.

[0174] The sealing body 16 includes a perforated metal plate 22, a lower valve body 23, an insulating member 24, an upper valve body 25, and a cover 26. The lower valve body 23 and the upper valve body 25 are connected at their respective central portions. The insulating member 24 is disposed between the peripheral portions of the lower valve body 23 and the upper valve body 25. The perforated metal plate 22 and the lower valve body 23 are connected at their respective peripheral portions. The upper valve body 25 and the cover 26 are connected at their respective peripheral portions. All components constituting the sealing body 16, except for the insulating member 24, are electrically connected.

[0175] A vent hole is formed on the lower valve body 23. Therefore, when the internal pressure of the battery casing rises due to abnormal heating, the upper valve body 25 expands towards the cover 26, separating from the lower valve body 23. As a result, the electrical connection between the lower valve body 23 and the upper valve body 25 is cut off. When the internal pressure rises further, the upper valve body 25 breaks, and gas is discharged from the opening formed in the cover 26.

[0176] The positive electrode 11 is electrically connected to the cover 26, which functions as the positive terminal, via the positive lead 19. The negative electrode 12 is electrically connected to the housing body 15, which functions as the negative terminal, via the negative lead 20.

[0177] Figure 3 This is a schematic cross-sectional view illustrating an example of the separator 13. The separator 13 includes a first separator 131 and a second separator 132 overlapping the first separator 131. The first separator 131 and the second separator 132 may or may not be bonded. The first separator 131 includes a first substrate layer 131a and a first adhesive layer 131b1. The first substrate layer 131a has a first main surface 131a1 disposed on the positive electrode 11 side and a second main surface 131a2 disposed on the negative electrode 12 side. The first adhesive layer 131b1 is formed on the first main surface 131a1 of the first substrate layer 131a. In the electrode assembly 14, at least a portion of the first adhesive layer 131b1 is bonded to the positive electrode 11.

[0178] Figure 4 This is a cross-sectional view schematically showing another example of the separator 13. Figure 4 The separator 13 has an adhesive layer in relation to the second separator 132. Figure 3 The separator 13 is different. Figure 4 The second separator 132 of the separator 13 includes a second substrate layer 132a and a third adhesive layer 132b3. The second substrate layer 132a has a third main surface 132a3 disposed on the negative electrode 12 side and a fourth main surface 132a4 disposed on the positive electrode 11 side. The third adhesive layer 132b3 is formed on the third main surface 132a3 of the second substrate layer 132a. In the electrode assembly 14, at least a portion of the third adhesive layer 132b3 can be bonded to the negative electrode 12.

[0179] (Postscript)

[0180] Based on the above description, the following technology is disclosed.

[0181] (Technology 1)

[0182] A non-aqueous electrolyte secondary battery, comprising:

[0183] An electrode assembly consisting of a positive electrode, a negative electrode, and a separator wound together such that the separator is positioned between the positive and negative electrodes; and

[0184] Non-aqueous electrolytes

[0185] The separator includes a first separator and a second separator disposed between the first separator and the negative electrode.

[0186] The first separator includes a first substrate layer and a first adhesive layer. The first substrate layer has a first main surface disposed on the positive electrode side and a second main surface disposed on the negative electrode side. The first adhesive layer is formed on the first main surface of the first substrate layer.

[0187] At least a portion of the first adhesive layer is adhered to the positive electrode.

[0188] (Technology 2)

[0189] According to the non-aqueous electrolyte secondary battery of technology 1, the first adhesive layer contains a vinylidene fluoride-based polymer synthesized by polymerizing a monomer containing vinylidene fluoride.

[0190] (Technology 3)

[0191] According to the non-aqueous electrolyte secondary battery of technique 1 or 2, the first adhesive layer contains a copolymer synthesized by polymerizing monomers comprising vinylidene fluoride and hexafluoropropylene.

[0192] (Technology 4)

[0193] According to any one of the techniques 1 to 3, in the non-aqueous electrolyte secondary battery, the first adhesive layer contains inorganic particles.

[0194] (Technology 5)

[0195] According to any one of the techniques 1 to 4, in the non-aqueous electrolyte secondary battery, the first adhesive layer is porous.

[0196] (Technology 6)

[0197] According to any one of techniques 1 to 5, in the non-aqueous electrolyte secondary battery, the second separator comprises a second substrate layer and an adhesive layer, the second substrate layer having a third main surface disposed on the negative electrode side and a fourth main surface disposed on the positive electrode side, and the adhesive layer being formed on the third main surface of the second substrate layer.

[0198] At least a portion of the adhesive layer of the second separator is adhered to the negative electrode.

[0199] (Technology 7)

[0200] The non-aqueous electrolyte secondary battery according to technology 6 further includes a third separator disposed between the first separator and the second separator.

[0201] The third separator includes a third base material layer,

[0202] and no adhesive layer is formed on the third base material layer.

[0203] (Technology 8)

[0204] For the non-aqueous electrolyte secondary battery according to any one of Technologies 1 to 6, wherein, at a state of charge of 90%, the average value Tn (μm) of the increase in thickness caused by charging on one side of the negative electrode and the total thickness Ts (μm) of the average thickness of the first separator and the average thickness of the second separator satisfy the relationship of 1.2 < Ts / Tn.

[0205] (Technology 9)

[0206] For the non-aqueous electrolyte secondary battery according to any one of Technologies 1 to 8, wherein the non-aqueous electrolyte contains a non-aqueous solvent and a lithium salt,

[0207] the non-aqueous solvent contains an ether,

[0208] and the content rate of the ether in the non-aqueous solvent is 80% by mass or more.

[0209] (Technology 10)

[0210] For the non-aqueous electrolyte secondary battery according to any one of Technologies 1 to 9, wherein the positive electrode includes a positive electrode current collector and positive electrode mixture layers formed on both sides of the positive electrode current collector,

[0211] and the positive electrode mixture layer contains polyvinylidene fluoride.

[0212] (Technology 11)

[0213] For the non-aqueous electrolyte secondary battery according to any one of Technologies 1 to 10, wherein, in the negative electrode, lithium metal is deposited during charging and the lithium metal dissolves in the non-aqueous electrolyte during discharging.

[0214] (Technology 12)

[0215] For the non-aqueous electrolyte secondary battery according to Technology 11, wherein the second separator includes a second base material layer,

[0216] and the porosity of the second base material layer is greater than the porosity of the first base material layer.

[0217] (Technology 13)

[0218] For the non-aqueous electrolyte secondary battery according to any one of Technologies 1 to 12, wherein the negative electrode includes a negative electrode current collector,

[0219] and the negative electrode current collector contains austenitic stainless steel.

[0220] (Technology 14)

[0221] In the non-aqueous electrolyte secondary battery according to any one of techniques 1 to 12, the negative electrode includes a negative current collector.

[0222] The negative electrode current collector comprises a resin film and a transition metal layer stacked on the resin film.

[0223] The resin film comprises a substrate resin layer and a surface resin layer formed on the substrate resin layer.

[0224] The surface resin layer contains nitrogen-containing resin.

[0225] (Technology 15)

[0226] According to the non-aqueous electrolyte secondary battery of technology 14, the nitrogen-containing resin contains nitrogen-hydrogen bonds.

[0227] (Technology 16)

[0228] According to the non-aqueous electrolyte secondary battery of technology 14 or 15, the nitrogen-containing resin is a polymer having at least one of the following groups: urea bond, melamine structure, triazine ring, amino group, amide bond, aromatic polyamide bond, imide bond, urethane bond, carbodiimide bond, urea diketone structure, isocyanurate ring, nitrile group, and amide group.

[0229] (Technology 17)

[0230] According to any one of art 14 to 16, the non-aqueous electrolyte secondary battery, wherein the nitrogen-containing resin is a polymer having at least one selected from the group consisting of aliphatic isocyanate group, aromatic isocyanate group, urea formate group and biuret group.

[0231] Example

[0232] The following examples provide a detailed description of the non-aqueous electrolyte secondary batteries involved in this disclosure. However, this disclosure is not limited to the following examples. In these examples, multiple non-aqueous electrolyte secondary batteries with different configurations are fabricated and evaluated.

[0233] (Battery A1)

[0234] Make battery A1 by following these steps.

[0235] (1) Production of the positive electrode

[0236] A lithium-containing transition metal oxide (positive electrode active material), acetylene black (AB, conductive material), and polyvinylidene fluoride (PVDF, binder) were mixed at a mass ratio of positive electrode active material:AB:PVDF = 95:2.5:2.5. Then, an appropriate amount of N-methyl-2-pyrrolidone (NMP) was added and the mixture was stirred to prepare the positive electrode slurry. The positive electrode active material used was a lithium-containing transition metal oxide containing Li, Ni, Co, and Al.

[0237] Next, the positive electrode slurry is coated onto both sides of the positive current collector (aluminum foil) and dried. The coating of the positive electrode slurry is then calendered using rollers. Finally, the resulting laminate of the positive current collector and the positive electrode slurry is cut to the specified electrode size. In this way, a positive electrode comprising a positive current collector and positive electrode slurry layers formed on both sides of the positive current collector is fabricated. Then, aluminum tabs are attached to the fabricated positive electrode.

[0238] (2) Fabrication of the negative electrode

[0239] A silicon-containing material and graphite were mixed at a mass ratio of 5:95 (Si material:graphite) to serve as the negative electrode active material. SiC was used as the silicon-containing material. A negative electrode slurry was prepared by mixing the negative electrode active material, sodium carboxymethyl cellulose (CMC-Na), styrene-butadiene rubber (SBR), and water. Next, the negative electrode slurry was coated onto the surface of a copper foil (negative electrode current collector, thickness: 10µm) to form a laminate containing the copper foil and a coating formed on the copper foil. The coating was then dried and the laminate was calendered. This process formed a negative electrode containing the copper foil and negative electrode slurry layers on both sides of the copper foil. The thickness of each of the two negative electrode slurry layers was set to approximately 75µm. Finally, nickel tabs were attached to the negative electrode current collector.

[0240] (3) Preparation of non-aqueous electrolytes

[0241] A non-aqueous electrolyte was prepared by dissolving LiPF6 at a concentration of 1 mol / L and LiBF2(C2O4) at a concentration of 0.1 mol / L in a non-aqueous solvent. Dimethyl carbonate (carbonate) was used as the non-aqueous solvent.

[0242] (4) Preparation of separators

[0243] As the first separator, a separator consisting of a first substrate layer and a first adhesive layer formed on one side (first main surface) of the first substrate layer is prepared. The first substrate layer is a microporous film of polyethylene. The adhesive layer is an adhesive layer made of polyvinylidene fluoride (PVDF) (thickness: approximately 1 µm). The second separator is a microporous film of polyethylene. The porosity of the substrate layer (second substrate layer) of the second separator is greater than the porosity of the substrate layer (first substrate layer) of the first separator. The average thickness Ts1 of the first separator and the average thickness Ts2 of the second separator are measured using the method described above, and the total thickness Ts is calculated.

[0244] (5) Battery manufacturing

[0245] The first separator is overlapped on both sides of the positive electrode with the first adhesive layer in contact with the positive electrode, and then heated and rolled to bond the first adhesive layer to the positive electrode. In this way, a laminate with the first separator stacked on both sides of the positive electrode is formed.

[0246] Next, in an inert gas atmosphere, the aforementioned laminate (positive electrode and first separator), second separator, and negative electrode are wound together to create a wound electrode assembly. At this time, the second separator is positioned between the first separator and the negative electrode. Then, the electrode assembly and the aforementioned non-aqueous electrolyte are housed in an outer casing, and the outer casing is sealed to create battery A1 (non-aqueous electrolyte secondary battery). The outer casing is a bag-shaped casing formed from a laminate containing an aluminum layer.

[0247] (Determination of average value Tn)

[0248] For battery A1, the average value Tn (µm) of the increase in thickness of one side of the negative electrode caused by charging was measured at 90% charge using the method described above.

[0249] (Charge-discharge cycle test)

[0250] For battery A1, a charge-discharge cycle test was conducted at 25°C. The charge and discharge were performed under the following conditions: a 20-minute rest period between charging and discharging. The charge-discharge cycle was repeated 100 times, and the discharge capacity after 100 cycles was measured.

[0251] (Charge)

[0252] At 10mA / cm 2 Perform constant current charging until the voltage reaches 4.1V, then perform constant voltage charging at 4.1V until the current reaches 1mA / cm. 2 .

[0253] (Discharge)

[0254] At 10mA / cm 2Perform constant current discharge until the voltage reaches 3V.

[0255] (Batteries A2~A9 and batteries C1~C5)

[0256] The average value Tn (µm), negative electrode active material, separator, non-aqueous solvent of non-aqueous electrolyte, and substrate of negative electrode current collector were modified as shown in Tables 1 and 2. Otherwise, batteries A2 to A9 and batteries C1 to C5 were manufactured using the same methods and conditions as battery A1. As mentioned above, the average value Tn (µm) is the average of the increase in thickness on one side of the negative electrode at 90% charge. The thickness of the adhesive layer included in the separator is the same as the thickness of the adhesive layer included in the separator of battery A1. The average value Tn is varied according to the thickness of the positive electrode binder layer.

[0257] In batteries A2-A9 and C1, the first separator has an adhesive layer (first adhesive layer) formed on the positive electrode side of the first substrate layer, which is bonded to the positive electrode. No adhesive layer is formed on the negative electrode side of the first substrate layer of the first separator. The second separator in batteries A5-A9 includes a second substrate layer and an adhesive layer (third adhesive layer) formed on the main surface (third main surface) of the negative electrode side of the second substrate layer. The third adhesive layer is bonded to the negative electrode. In the fabrication of batteries A5-A9, the second separator and the negative electrode are fabricated using the same method as that used for fabricating the laminate of the first separator and the positive electrode. Then, an electrode assembly is fabricated by winding them together.

[0258] The separator of battery C1 consists only of the first separator. The separators of batteries C2 to C5 do not have an adhesive layer and consist only of a substrate layer. In Table 2, P(VDF-HFP) refers to a copolymer of vinylidene fluoride (VDF) and hexafluoropropylene (HFP). Inorganic particles (Al2O3 particles) are added to the adhesive layer of battery A7.

[0259] In the fabrication of batteries A2 and C1-C3, a material composed of a Si-containing material and graphite mixed at a mass ratio of Si-containing material:graphite = 5:95 was used as the negative electrode active material. SiC was used as the Si-containing material. Batteries A3-A9 and batteries C4-C5 are lithium-ion secondary batteries with lithium metal as the negative electrode active material. These negative electrodes were fabricated using the following method.

[0260] (2') Fabrication of the negative electrode current collector (negative electrode) for lithium secondary batteries

[0261] A negative electrode current collector comprising copper foil and a lithium-containing metal layer is fabricated by pressing lithium alloy foil (thickness: 10µm) onto both sides of a copper foil (thickness: 25µm). Next, nickel tabs are attached to the negative electrode current collector. This produces the negative electrode for a lithium-ion secondary battery.

[0262] The negative electrode current collector of battery A8 is configured the same as that of battery A3, except that austenitic stainless steel foil (SUS foil) is used instead of copper foil. The negative electrode current collector of battery A9 is configured the same as that of battery A3, except that a specified laminate (a laminate having a resin film and a transition metal layer laminated on the resin film) is used instead of copper foil. As the resin film, a polyethylene terephthalate (PET) film coated with polyurethane resin (nitrogen-containing resin) is used. A copper layer is used as the transition metal layer. Specifically, copper is first deposited onto the resin film by sputtering, and then deposited by wet plating. The negative electrode current collectors of batteries A8 and A9 each have a lithium-containing metal layer, similar to those of battery A1.

[0263] Table 2 lists the non-aqueous solvents used in the non-aqueous electrolytes. In Table 2, "carbonate" indicates the use of dimethyl carbonate, and "ether" indicates the use of 1,2-dimethoxyethane (DME). Each battery was evaluated in the same manner as battery A1. Furthermore, for the separators used in the fabrication of each battery, the average thickness Ts1 and average thickness Ts2 were measured using the methods described above, and the total thickness Ts was calculated.

[0264] Part of the manufacturing conditions for each battery are shown in Tables 1 and 2, and the evaluation results for each battery are shown in Table 2. In Table 1, the discharge capacity of each battery at 100 cycles is expressed as a relative value when the discharge capacity of battery A1 at 100 cycles is set to 100.

[0265] [Table 1]

[0266]

[0267] [Table 2]

[0268]

[0269] Batteries A1 to A9 are non-aqueous electrolyte secondary batteries (B) disclosed herein. Batteries C1 to C5 are comparative examples. As shown in Table 2, batteries A1 to A9 exhibit better cycle characteristics compared to batteries C1 to C5. As shown in Tables 1 and 2, the cycle characteristics are improved by bonding the positive electrode to the first separator and the negative electrode to the second separator. Furthermore, the cycle characteristics are improved by the inclusion of inorganic particles in the adhesive layer. Additionally, the cycle characteristics are improved by the presence of ether in the non-aqueous solvent. Furthermore, the cycle characteristics are improved by using stainless steel foil and resin film as the substrate for the negative electrode current collector.

[0270] Industrial availability

[0271] This disclosure can be used in non-aqueous electrolyte secondary batteries.

[0272] The present invention has been described with reference to preferred embodiments, but such disclosure should not be interpreted as limiting. Various modifications and alterations will be apparent to those skilled in the art from the foregoing disclosure. Therefore, the appended claims should be construed as encompassing all modifications and alterations without departing from the true spirit and scope of the invention.

[0273] Explanation of reference numerals in the attached figures

[0274] 10: Non-aqueous electrolyte secondary battery

[0275] 11: Positive electrode

[0276] 12: Negative electrode

[0277] 13: Separator

[0278] 14: Electrode assembly

[0279] 131: First separator

[0280] 131a: First substrate layer

[0281] 131a1: First Main Face

[0282] 131a2: Second Main Face

[0283] 131b1: First adhesive layer

[0284] 132: Second separator

[0285] 132a: Second substrate layer

[0286] 132a3: Third Main Face

[0287] 132a4: Fourth Main Face

Claims

1. A non-aqueous electrolyte secondary battery, comprising: An electrode group formed by winding a positive electrode, a negative electrode, and a separator in such a manner that the separator is disposed between the positive electrode and the negative electrode; and A non-aqueous electrolyte, The separator includes a first separator and a second separator disposed between the first separator and the negative electrode, The first separator includes a first base material layer and a first adhesive layer. The first base material layer has a first main surface disposed on the positive electrode side and a second main surface disposed on the negative electrode side. The first adhesive layer is formed on the first main surface of the first base material layer, At least a part of the first adhesive layer is adhered to the positive electrode.

2. The non-aqueous electrolyte secondary battery according to claim 1, wherein, The first adhesive layer contains a polyvinylidene fluoride-based polymer synthesized by polymerizing a monomer containing polyvinylidene fluoride.

3. The non-aqueous electrolyte secondary battery according to claim 1, wherein, The first adhesive layer contains a copolymer synthesized by polymerizing a monomer containing polyvinylidene fluoride and hexafluoropropylene.

4. The non-aqueous electrolyte secondary battery according to any one of claims 1 to 3, wherein, The first adhesive layer contains inorganic particles.

5. The non-aqueous electrolyte secondary battery according to any one of claims 1 to 3, wherein, The first adhesive layer is porous.

6. The non-aqueous electrolyte secondary battery according to any one of claims 1 to 3, wherein, The second separator includes a second base material layer and an adhesive layer. The second base material layer has a third main surface disposed on the negative electrode side and a fourth main surface disposed on the positive electrode side. The adhesive layer is formed on the third main surface of the second base material layer, At least a part of the adhesive layer of the second separator is adhered to the negative electrode.

7. The non-aqueous electrolyte secondary battery according to claim 6, further comprising a third separator disposed between the first separator and the second separator, The third separator includes a third base material layer, No adhesive layer is formed on the third base material layer.

8. The non-aqueous electrolyte secondary battery according to any one of claims 1 to 3, wherein, At a 90% state of charge, the average value Tn (μm) of the increase in thickness caused by charging on one side of the negative electrode and the total thickness Ts (μm) of the average thickness of the first separator and the average thickness of the second separator satisfy the relationship of 1.2 < Ts / Tn.

9. The non-aqueous electrolyte secondary battery according to any one of claims 1 to 3, wherein, The non-aqueous electrolyte contains a non-aqueous solvent and a lithium salt, The non-aqueous solvent contains an ether, The content rate of the ether in the non-aqueous solvent is 80% by mass or more.

10. The non-aqueous electrolyte secondary battery according to any one of claims 1 to 3, wherein, The positive electrode includes a positive electrode current collector and positive electrode mixture layers formed on both sides of the positive electrode current collector, The positive electrode mixture layer contains polyvinylidene fluoride.

11. The non-aqueous electrolyte secondary battery according to any one of claims 1 to 3, wherein, In the negative electrode, lithium metal is deposited during charging and the lithium metal dissolves in the non-aqueous electrolyte during discharging.

12. The non-aqueous electrolyte secondary battery according to claim 11, wherein, The second separator includes a second base material layer, The porosity of the second base material layer is greater than the porosity of the first base material layer.

13. The non-aqueous electrolyte secondary battery according to any one of claims 1 to 3, wherein, The negative electrode includes a negative electrode current collector, The negative electrode current collector contains austenitic stainless steel.

14. The non-aqueous electrolyte secondary battery according to any one of claims 1 to 3, wherein, The negative electrode includes a negative electrode current collector, The negative electrode current collector includes a resin film and a transition metal layer laminated on the resin film, The resin film includes a base resin layer and a surface resin layer formed on the base resin layer, The surface resin layer contains a nitrogen-containing resin.

15. The non-aqueous electrolyte secondary battery according to claim 14, wherein, The nitrogen-containing resin contains a nitrogen-hydrogen bond.

16. The non-aqueous electrolyte secondary battery according to claim 14, wherein, The nitrogen-containing resin is a polymer having at least 1 kind selected from the group consisting of a urea bond, a melamine structure, a triazine ring, an amino group, an amide bond, an aromatic polyamide bond, an imide bond, a urethane bond, a carbodiimide bond, a uretdione structure, an isocyanuric acid ring, a nitrile group, and an amide group.

17. The non-aqueous electrolyte secondary battery according to claim 14, wherein, The nitrogen-containing resin is a polymer having at least one group selected from the group consisting of aliphatic isocyanate group, aromatic isocyanate group, urea formate group and biuret group.

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