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 nonaqueous electrolyte. The separator (13) includes: a base material layer (13a) having a first main surface (13a1) disposed on the negative electrode side and a second main surface (13a2) disposed on the positive electrode side; and an adhesive layer (13b) formed on the second main surface (13a2) of the base material layer (13a). At least a portion of the adhesive layer (13b) is adhered to the positive electrode. The average value Tn ([mu] m) of the increase in thickness of one surface of the negative electrode due to charging in 90% of the charged state and the average thickness Ts ([mu] m) of the separator (13) satisfy the relationship 1.2 < Ts / Tn.

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 in the past regarding 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, wherein the separator is bonded to the positive electrode for at least one turn along the winding direction from the starting end of the winding 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] In non-aqueous electrolyte secondary batteries, the degradation of the positive electrode surface and the oxidative decomposition of the non-aqueous electrolyte at the positive electrode become problems. Furthermore, the large expansion of the electrode assembly during charging becomes a problem in non-aqueous electrolyte secondary batteries. These problems lead to a decrease in charge-discharge cycle characteristics. There is now a demand for improved charge-discharge cycle characteristics in 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 is a non-aqueous electrolyte secondary battery comprising:

[0011] The electrode assembly, comprising a positive electrode, a negative electrode, and a separator, is wound in such a manner that the separator is disposed between the positive electrode and the negative electrode; and

[0012] Non-aqueous electrolytes

[0013] The aforementioned separator comprises: a substrate layer having a first main surface disposed on the negative electrode side and a second main surface disposed on the positive electrode side; and an adhesive layer formed on the second main surface of the substrate layer.

[0014] At least a portion of the aforementioned adhesive layer is adhered to the aforementioned positive electrode.

[0015] When the charge is at 90%, the average value of the increase in thickness of one side of the negative electrode caused by charging, Tn (μm), satisfies the relationship 1.2 < Ts / Tn with respect to the average thickness of the separator, Ts (μm).

[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 of the present disclosure.

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

[0022] The following description illustrates embodiments of this disclosure by way of examples, but this disclosure is not limited to the examples described below. In the following description, specific numerical values ​​and / or materials are sometimes used as examples, 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 given for numerical values ​​relating to specific physical properties and / or conditions, any of the lower limits and any of the 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 and / 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.

[0023] (Non-aqueous electrolyte secondary battery)

[0024] Hereinafter, the non-aqueous electrolyte secondary battery of this embodiment will sometimes be referred to as "non-aqueous electrolyte secondary battery (B)" or "secondary battery (B)". The secondary battery (B) includes: an electrode assembly, a positive electrode, a negative electrode, and a separator wound together such that the separator is disposed between the positive and negative electrodes; and a non-aqueous electrolyte. The separator includes: a substrate layer having a first main surface disposed on the negative electrode side and a second main surface disposed on the positive electrode side; and an adhesive layer formed on the second main surface of the substrate layer. At least a portion of the adhesive layer is adhered to the positive electrode. At 90% state of charge (SOC), the average value Tn (μm) of the increase in thickness of one side of the negative electrode due to charging satisfies the relationship 1.2 < Ts / Tn with respect to the average thickness Ts (μm) of the separator.

[0025] 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.

[0026] 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% and / or 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 of this disclosure differs from a negative electrode where the migration of electrons during charging and discharging depends primarily on the absorption and release of lithium ions by a negative electrode active material (graphite, etc.). For example, the negative electrode of the lithium-ion secondary battery of this disclosure may not contain a negative electrode active material (graphite, etc.) for absorbing and releasing lithium ions.

[0027] 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 at the positive electrode are prone to occur. These also contribute to a decrease in cycle characteristics.

[0028] Based on their research, the inventors of this application have discovered that by using an adhesive layer to bond a separator of a specified thickness to the positive electrode, cycle characteristics can be significantly improved. This disclosure is based on this new insight. By bonding the positive electrode to the 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 satisfying the relationship 1.2 < Ts / Tn, the expansion of the electrode assembly during charging can be suppressed. It is believed that the significant improvement in cycle characteristics is not due to the simple addition of the above two effects, but rather to the synergistic effect of bonding the positive electrode to the separator using an adhesive layer and satisfying the relationship 1.2 < Ts / Tn.

[0029] (Separator)

[0030] As described above, the separator comprises a substrate layer and an adhesive layer, at least a portion of which is bonded to the positive electrode. There is no particular limitation on the method for bonding the adhesive layer of the separator to the positive electrode. For example, methods such as planar hot pressing or heated calendering can be used.

[0031] The substrate layer is not particularly limited. Separators 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 membranes, 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 can consist of multiple layers with different morphologies and / or compositions.

[0032] The adhesive layer is formed of a material capable of bonding with 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.

[0033] Vinylidene fluoride (VDF) polymers contain structural units derived from vinylidene fluoride. The VDF unit (a structural unit derived from vinylidene fluoride) accounts for 50 mol% to 100 mol% of all structural units in the vinylidene fluoride polymer. This percentage 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.

[0034] 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 can be 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, the battery resistance decreases, further improving cycle characteristics.

[0035] Vinylidene fluoride polymers can be copolymers of vinylidene fluoride and hexafluoropropylene (HFP). The proportion of HFP units (structural units derived from hexafluoropropylene) in all structural units of the vinylidene fluoride polymer can be in the range of 0 to 50 mol% (e.g., 0.5 to 25 mol%, and / or 2 to 10 mol%).

[0036] 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.

[0037] Inorganic particles can preferably be insulating, but conductive inorganic particles can also be used. Insulating inorganic particles can include 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.

[0038] 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.

[0039] 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.

[0040] 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 enhancing lithium-ion conductivity. As a result, the battery resistance decreases, leading to good cycle characteristics.

[0041] The thickness of the adhesive layer can be 0.1 μm or more, or 0.3 μm or more, or 5 μm or less, or 2 μm or less. It should be noted that the adhesive layer can be formed on both sides of the substrate layer. That is, the adhesive layer can be formed on both the first main surface and the second main surface. At least a portion of the second adhesive layer formed on the first main surface can be bonded to the negative electrode. Alternatively, the second adhesive layer formed on the first main surface may not be bonded to the negative electrode. By bonding the second adhesive layer to the negative electrode, dendritic deposition of lithium metal during charging can be suppressed. As a result, the expansion of the electrode assembly during charging can be particularly suppressed.

[0042] The average thickness Ts (μm) of the separator was obtained by arithmetically averaging the thicknesses at 15 points. The thickness of the separator could be measured according to JIS (Japanese Industrial Standard) K6250. Specifically, a test piece thickness gauge (SDA-12 type) manufactured by Polymer Gauge Co., Ltd., based on JIS K6250, was used to measure the thickness. The measurement was performed using a 5mm diameter probe under a pressure of 22kPa. The thickness was measured at 15 intersection points where five lines dividing the separator into six equal parts along its length and three lines dividing it into four equal parts along its width. The arithmetic mean of the 15 measured thicknesses was then taken as the average thickness Ts.

[0043] As described above, the ratio Ts / Tn, which is the average thickness Ts (μm) of the separator to the average value Tn (μm) of the increase in thickness of one side of the negative electrode due to charging, is greater than 1.2 (e.g., greater than 1.20). The ratio Ts / Tn can be 1.25 or higher, 1.30 or higher, or 1.50 or higher, and can be 5.0 or lower, 3.5 or lower, or 2.0 or lower. By making the ratio Ts / Tn greater than 1.2, the expansion of the electrode assembly during charging can be suppressed. By setting the ratio Ts / Tn to 3.0 or lower, the decrease in volumetric capacity density can be suppressed.

[0044] The average value Tn (μm) can be determined by the following method. First, prepare two batteries made under the same conditions. Then, set one battery to a state of discharge (SOC=0%) and the other battery 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 is discharged from a fully charged state to 100% of its rated capacity. It should also be noted that in this specification, the rated capacity of the battery refers to the 1-hour rate capacity.

[0045] 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. At positions p1, p2, and p3, the negative electrode is sandwiched between two sides of the separator and faces the positive electrode. The average value Tn of the increase in thickness on one side of the negative electrode due to charging is calculated using the following formula.

[0046] Tn = {(the sum of thicknesses T(90) at point 3) - (the sum of thicknesses T(0) at point 3)} / 6

[0047] The porosity of the substrate layer can be 40% or more, or 50% or more, or 90% or less, or 80% or less. The porosity of the substrate layer can be 40% or more and 90% or less (e.g., 50% or more and 80% or less). The porosity of the substrate layer can be determined by the following method: First, collect 4cm square samples at four points in the central portion of the spacer in the width direction. Next, use adhesive tape to peel off the adhesive layer of each sample, separating only the substrate layer. Next, measure the mass of each substrate layer, and measure the thickness of the substrate layer using the method described above (the method for measuring the thickness of the spacer). Next, calculate the apparent density of the substrate layer from the mass, area, and thickness of the substrate layer. 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.

[0048] Porosity (%) = 100 × {1 - (apparent density of substrate layer) / (true density of substrate layer)}

[0049] (Method for manufacturing the separator)

[0050] An example of the method (M) for manufacturing the separator used in this embodiment will be described. However, the separator for the secondary battery (B) can also be manufactured by methods other than the manufacturing method (M) described below. Regarding the separator, the above-mentioned matters can be applied to the manufacturing method (M), so repeated descriptions are omitted. The matters described in the manufacturing method (M) can be applied to the separator for the secondary battery (B).

[0051] In manufacturing method (M), the separator is manufactured by forming an adhesive layer on a substrate layer. The method for forming the adhesive layer is not particularly limited and can be any known method. In one example, an adhesive layer is formed by applying a coating liquid containing components of the adhesive layer onto the substrate layer and then allowing it to dry. The method of applying the coating liquid is not limited and can be any known method. For example, it can be applied using spraying, methods using rollers and / or dies (gravure coating, die coating, etc.), printing methods (screen printing, inkjet printing, etc.).

[0052] The solvent for the coating solution can be acetone, dimethylformamide, dimethylacetamide, N-methyl-2-pyrrolidone, dimethyl sulfoxide, tripropylene glycol, etc. In the case of forming a porous adhesive layer, a non-solvent-induced phase separation method (NIPS) can be used. In one example, a coating solution is first prepared by dissolving the resin in the aforementioned solvent (a good solvent), and then the coating solution is applied to a substrate layer to form a coating film. Next, before the coating film dries, the coating film can be made porous by immersing it in a poor solvent. Poor solvents can be 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 solvent, the porosity of the adhesive layer can be altered.

[0053] In the negative electrode of the secondary battery (B), lithium metal is deposited during charging and dissolves in the non-aqueous electrolyte during discharging. That is, the secondary battery (B) can be a lithium secondary battery.

[0054] 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 can be suppressed at the negative electrode during charging.

[0055] 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 with hydrogen and fluorine atoms. By using hydrofluoroethers, the reduction resistance of the non-aqueous electrolyte is improved, and the decomposition of the non-aqueous electrolyte at the negative electrode surface becomes less likely to occur. 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.

[0056] The fluorination rate of the hydrofluoroether 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 a hydrofluoroether is defined by the following formula.

[0057] Fluorination rate (%) = 100 × (number of fluorine atoms in hydrofluoroether) / (sum of the number of fluorine and hydrogen atoms in hydrofluoroether)

[0058] The hydrofluoroether used in the non-aqueous solvent 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.

[0059] The positive electrode of the secondary battery (B) may include a positive current collector and positive electrode binder layers formed on both sides of the positive current collector. The positive electrode binder layers 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, further enhancing cycle characteristics. In the secondary battery (B), the positive electrode binder layer may contain PVDF, and the adhesive layer of the 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.

[0060] (Manufacturing method of secondary battery (B))

[0061] The manufacturing method is not limited as long as a secondary battery (B) can be manufactured. An example manufacturing method includes steps (i), (ii), and (iii). The matters described for the secondary battery (B) can be applied to the following manufacturing methods, therefore repeated descriptions are omitted.

[0062] Process (i) is a process of forming a laminate of the separator and the positive electrode by bonding the separator to both sides of the positive electrode via an adhesive layer. The bonding of the 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 according to 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.

[0063] Step (ii) is a process of forming a wound electrode assembly by winding the aforementioned laminate and negative electrode. A separator is placed between the positive and negative electrodes. 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 by methods other than this manufacturing method.

[0064] (Examples of constituent elements)

[0065] 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. Commonly known constituent elements may also be used, in addition to the characteristic portions of this embodiment.

[0066] (The negative electrode of a lithium secondary battery)

[0067] In the case of a lithium-ion secondary battery (B), the negative electrode includes a negative current collector. In a lithium-ion secondary battery, lithium metal is deposited on the negative current collector during charging. The deposited lithium metal dissolves as lithium ions in the non-aqueous electrolyte during discharge.

[0068] 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 due to their high conductivity. Stainless steel is preferred because it is not easily cut.

[0069] The lithium-containing metal layer laminated on the substrate is a lithium metal layer or a lithium alloy layer. The lithium alloy layer contains trace amounts (less than 10 atomic percent) of elements other than lithium. Examples of elements other than lithium in lithium alloys include aluminum, magnesium, indium, and zinc. By forming a lithium-containing metal layer, the decrease in discharge capacity accompanying repeated charge and discharge can be suppressed. Furthermore, by forming a lithium-containing metal layer, the dendritic precipitation of lithium metal can be suppressed. There is no particular limitation on the method of forming the lithium-containing metal layer; known methods can be used. 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 lithium-containing metal layer is dense, which is quite different from the lithium metal deposited during charging (which is usually porous).

[0070] 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.

[0071] The thickness of the substrate sheet 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.

[0072] The negative electrode current collector (e.g., the substrate sheet) may contain austenitic stainless steel. In this case, it is possible to obtain a negative electrode current collector that exhibits suppressed embrittlement, moderate strength and flexibility, and excellent resistance to stress generated at the negative electrode. As a result, the fracture of the negative electrode current collector during charging and discharging and the associated reduction in cycle characteristics are suppressed.

[0073] 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 as {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.

[0074] The austenite content can be above 70%, above 90%, or even 100%.

[0075] The austenite ratio can be determined by the following method. First, prepare a sample of the negative 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-part) is, for example, 15 mm square.

[0076] The preferred XRD measurement conditions are shown below.

[0077] <Analytical Device>

[0078] Two-dimensional micro-area X-ray diffraction apparatus (RINT-RAPID II, manufactured by Rigaku Corporation, Japan)

[0079] <Analysis Conditions>

[0080] Tube ball: Co

[0081] Monochromaticization: using a monochromator (CoKα)

[0082] PLC output: 40kV-30mA

[0083] Detector: Imaging plate (two-dimensional)

[0084] (Reflection method)

[0085] Collimator: Φ300μm

[0086] ω angle: 25°~35° (2° / sec)

[0087] Φ angle: 360° rotation (1° / sec)

[0088] Measurement time (exposure): 30 minutes

[0089] 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 the software accompanying the analysis device. Through this analysis, the ratio (mass ratio) of the austenite phase to the sum 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.

[0090] 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, very low-carbon, or nitrogen-added stainless steels, or duplex stainless steels containing austenite.

[0091] 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.

[0092] The negative current collector may comprise a resin film and a transition metal layer laminated thereon. That is, the substrate may comprise a resin film and a transition metal layer laminated thereon. The negative current collector (e.g., the substrate) may be composed of a resin film and a transition metal layer. The resin film may comprise 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 also comprise a lithium-containing metal layer laminated on the substrate.

[0093] Resin films are lightweight, which facilitates the improvement of energy density in secondary batteries. They are also less prone to breakage during roller conveying 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. 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.

[0094] The main surface of the resin film can be smooth, roughened, or subjected to plasma treatment and / or corona treatment, etc. When the main surface of the resin film is smooth, the maximum height roughness Rz is less than 2.5 μm. When the main surface of the resin film is roughened, the maximum height roughness Rz exceeds 2.5 μm, and can be greater than 8 μm. The maximum height roughness Rz is measured according to JIS B 0601:2013. The main surface of the resin film refers to the surface other than the end faces of the resin film, specifically the two surfaces with the largest area. In this specification, "surface" generally refers to "main surface".

[0095] From the viewpoint of improving the energy density of secondary batteries, a thin resin film is preferred, provided that mechanical strength is ensured. An example of a preferred range for the thickness of the resin film is 1.5 μm or more and 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.

[0096] 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.

[0097] 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, after removing or wet-removing the active material from 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 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).

[0098] (FTIR-ATR method)

[0099] Measurement apparatus: Varian 670FTIR (manufactured by Varian)

[0100] Measurement mode: Attenuated total internal reflection

[0101] Light source: special ceramic

[0102] Detector: DLaTGS (deuterated L-alanine-doped triglycine sulfate)

[0103] Resolution: 4cm -1

[0104] Total number of times: 256

[0105] IRE: Ge

[0106] Angle of incidence: 60 degrees

[0107] Attachment: Attachment for Single-Reflection ATR (Seagull)

[0108] 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.

[0109] 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.

[0110] 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. In particular, thermosetting polyurethane resins, due to the use of polyisocyanates as raw materials, have a high probability of containing residual unreacted isocyanate groups. It is believed that the isocyanate groups are reduced at the negative electrode to generate a coating component for forming a stable coating at the negative electrode. Furthermore, thermosetting resins form a robust three-dimensional coating, thus exhibiting a significant 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 caused by antisymmetric stretching vibration, so its presence or absence can be confirmed based on the infrared absorption peak.

[0111] The surface resin layer may contain fillers. By adding fillers (such as silica and / or alumina) 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 can be those that 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.

[0112] 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 then 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.

[0113] The thickness of the surface resin layer is, for example, less than 5 μm, and in a preferred example, it is 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.

[0114] Most resin films are non-conductive. The transition metal layer imparts good conductivity to the negative electrode current collector. The transition metal layer simply needs to be a layer containing a transition metal and possessing electronic conductivity. Preferably, the transition metal layer contains a transition metal in a metallic state that has electronic conductivity based on free electrons.

[0115] From the viewpoint of easily 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.

[0116] Transition metals can cause resin film embrittlement. Embrittlement is particularly prevalent when the transition metal layer contains copper. As a novel insight, it has also been established that resin film embrittlement caused by transition metals (e.g., copper damage) due to lithium metal is significantly accelerated. Specifically, in lithium-ion secondary batteries where lithium metal is deposited at the negative electrode, significant degradation of the resin film due to the transition metal layer occurs. 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.

[0117] It should be noted that a nickel-chromium alloy layer could be considered as a metal layer to shield copper ions from transferring to the resin film. However, in lithium-ion batteries, the shielding effect based on a nickel-chromium alloy layer is completely unattainable. 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 by the transition metal ions. On the other hand, a surface resin layer containing nitrogen-containing resin can significantly suppress polymer breakage.

[0118] 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. It is possible that the transition metals are stabilized by nitrogen atoms, inhibiting the breaking of carbon-carbon bonds.

[0119] 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 electroplating / 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 by electroplating. 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.

[0120] The thickness of the transition metal layer can be, for example, 5 μm or less, or even 3 μm or less. A preferred range for the thickness of the transition metal layer is 0.05 μm to 1.5 μm, or even 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 current collector). Then, the thickness of the transition metal layer (average thickness) is calculated by arithmetically averaging the obtained measurements. The transition metal layer can also be composed of multiple layers of different metals.

[0121] The substrate resin layer is the main component of the negative electrode current collector, and is typically thicker than the surface resin layer and thicker than 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 / or 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 a large number of regularly arranged pores. The substrate resin layer can be insulating, conductive, or non-conductive. There are no particular limitations on the morphology and properties of the substrate resin layer.

[0122] 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-formaldehyde resins, unsaturated polyester resins, etc. The substrate resin layer may contain one type of resin alone or in combination of two or more types.

[0123] 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.

[0124] 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, ionomers, etc., are preferred.

[0125] The extrusion method for the substrate resin layer can be either T-die extrusion or blow extrusion, and can be unstretched, uniaxially stretched, successively biaxially stretched, or simultaneously biaxially stretched. 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.

[0126] To ensure adhesion to other layers (such as vapor-deposited films), the surface of the substrate resin layer can be subjected to corona treatment and / 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 to form irregularities on its surface.

[0127] (The negative electrode of a lithium-ion secondary battery)

[0128] 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) and / or a resin film, as exemplified by the substrate sheet of the negative electrode of a lithium secondary battery.

[0129] 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 3 μm or more, 5 μm or more, or less than 200 μm or less than 150 μm.

[0130] The negative electrode active material contained in the negative electrode composite layer can be a substance capable of reversibly absorbing 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 Si-containing materials alone. 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 conducting 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.

[0131] 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 for the binder, conductive material, and thickener used in the positive electrode binder layer.

[0132] (positive electrode)

[0133] 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 positive electrode is obtained by calendering the laminate consisting of the positive current collector and the coating film. It should be noted that the formed positive electrode is cut to a specified size as needed.

[0134] 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.

[0135] 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 due to their low manufacturing cost and high average discharge voltage.

[0136] 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.

[0137] Conductive materials can include carbon materials. Examples of carbon materials include carbon black (acetylene black, Ketjen black, etc.), carbon nanotubes, and graphite.

[0138] 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).

[0139] Thickeners can be cellulose derivatives, etc. Examples of cellulose derivatives include carboxymethyl cellulose (CMC) and its modified forms, methyl cellulose, etc. Examples of CMC modified forms also include salts of CMC. As salts, alkali metal salts (e.g., sodium salts), ammonium salts, etc., can be listed.

[0140] 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.

[0141] Examples of materials for the positive current collector (conductive sheet) include metallic materials containing Al, Ti, Fe, etc. The metallic material 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.

[0142] (Separator)

[0143] A separator is placed between the positive and negative electrodes. The separator described above can be used.

[0144] In the case where the secondary battery (B) is a lithium secondary battery, the secondary battery (B) may or may not include a spacer disposed between the negative electrode and the separator. The spacer may be formed on the main surface of the negative electrode side of the separator or on the negative electrode. Typically, a non-aqueous electrolyte secondary battery (B) does not include a spacer disposed between the positive electrode and the negative electrode (a spacer that is not a separator).

[0145] The spacers may comprise 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 spacers may comprise a plurality of linear portions configured in a stripe pattern.

[0146] (Non-aqueous electrolyte)

[0147] Non-aqueous electrolytes can be non-aqueous electrolytes with lithium-ion conductivity. Non-aqueous electrolytes can be liquid or gel-like. Liquid non-aqueous electrolytes are prepared by dissolving a lithium salt in a non-aqueous solvent. Dissolving the lithium salt in the non-aqueous solvent generates lithium ions and anions.

[0148] Gel-like non-aqueous electrolytes can contain lithium salts and matrix polymers, or lithium salts, non-aqueous solvents, and matrix polymers. Matrix polymers can be, for example, polymeric materials that gel by absorbing non-aqueous solvents. Examples of polymeric materials include fluoropolymers, acrylic resins, and polyether resins.

[0149] 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.

[0150] 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.

[0151] The concentration of lithium salt in non-aqueous electrolytes 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, non-aqueous electrolytes with excellent ionic conductivity and moderate viscosity can be obtained.

[0152] Non-aqueous electrolytes may contain additives (such as known additives). Examples of additives include 1,3-propane sulpholactone, methylbenzene sulfonate, cyclohexylbenzene, biphenyl, diphenyl ether, fluorobenzene, etc.

[0153] (outer body)

[0154] 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.

[0155] Hereinafter, an example of the secondary battery (B) of 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 to be 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) of this disclosure can be omitted.

[0156] (Implementation Method 1)

[0157] 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, an electrode assembly 14 housed within the battery casing, and a non-aqueous electrolyte (not shown). The electrode assembly 14 includes a positive electrode 11, a negative electrode 12, and a separator 13.

[0158] The battery casing includes a casing body 15, which is a 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.

[0159] 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.

[0160] 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 and separates 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.

[0161] 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.

[0162] A schematic cross-sectional view of an example of the separator 13 is shown in Figure 3 The separator 13 includes a substrate layer 13a and an adhesive layer 13b formed on the substrate layer 13a. The substrate layer 13a has a first main surface 13a1 and a second main surface 13a2. The first main surface 13a1 is disposed on the negative electrode 12 side, and the second main surface 13a2 is disposed on the positive electrode 11 side. That is, the first main surface 13a1 is opposite to the negative electrode 12, and the second main surface 13a2 is opposite to the positive electrode 11. The adhesive layer 13b is laminated on the second main surface 13a2. As described above, in the electrode assembly 14, at least a portion of the adhesive layer 13b is bonded to the positive electrode 11.

[0163] (Postscript)

[0164] The following technology is disclosed through the above description.

[0165] (Technology 1)

[0166] A non-aqueous electrolyte secondary battery, comprising:

[0167] The electrode assembly, comprising a positive electrode, a negative electrode, and a separator, is wound in such a manner that the separator is disposed between the positive electrode and the negative electrode; and

[0168] Non-aqueous electrolytes

[0169] The aforementioned separator comprises: a substrate layer having a first main surface disposed on the negative electrode side and a second main surface disposed on the positive electrode side; and an adhesive layer formed on the second main surface of the substrate layer.

[0170] At least a portion of the aforementioned adhesive layer is adhered to the aforementioned positive electrode.

[0171] When the charge is at 90%, the average value of the increase in thickness of one side of the negative electrode caused by charging, Tn (μm), satisfies the relationship 1.2 < Ts / Tn with respect to the average thickness of the separator, Ts (μm).

[0172] (Technology 2)

[0173] According to the non-aqueous electrolyte secondary battery of technology 1, the adhesive layer contains a vinylidene fluoride-based polymer synthesized by polymerizing a monomer containing vinylidene fluoride.

[0174] (Technology 3)

[0175] According to the non-aqueous electrolyte secondary battery of technology 1 or 2, the adhesive layer contains a copolymer synthesized by polymerizing monomers comprising vinylidene fluoride and hexafluoropropylene.

[0176] (Technology 4)

[0177] In the non-aqueous electrolyte secondary battery according to any one of techniques 1 to 3, the adhesive layer contains inorganic particles.

[0178] (Technology 5)

[0179] In the non-aqueous electrolyte secondary battery according to any one of techniques 1 to 4, the adhesive layer is porous.

[0180] (Technology 6)

[0181] According to any one of the techniques 1 to 5, in the non-aqueous electrolyte secondary battery, lithium metal is deposited in the negative electrode during charging and the lithium metal dissolves in the non-aqueous electrolyte during discharging.

[0182] (Technology 7)

[0183] The non-aqueous electrolyte secondary battery according to any one of techniques 1 to 6, wherein...

[0184] The aforementioned non-aqueous electrolytes contain non-aqueous solvents and lithium salts.

[0185] The above-mentioned non-aqueous solvents contain ethers.

[0186] The content of the above-mentioned ether in the above-mentioned non-aqueous solvent is 80% by mass or more.

[0187] (Technology 8)

[0188] The non-aqueous electrolyte secondary battery according to any one of techniques 1 to 7, wherein...

[0189] The aforementioned positive electrode includes a positive current collector and a positive electrode flux layer formed on both sides of the aforementioned positive current collector.

[0190] The above-mentioned positive electrode binder layer contains polyvinylidene fluoride.

[0191] (Technology 9)

[0192] According to any one of the techniques 1 to 8, in the non-aqueous electrolyte secondary battery, the porosity of the substrate layer is 40% or more and 90% or less.

[0193] (Technology 10)

[0194] The non-aqueous electrolyte secondary battery according to any one of techniques 1 to 9, wherein...

[0195] The aforementioned negative electrode includes a negative current collector.

[0196] The aforementioned negative electrode current collector contains austenitic stainless steel.

[0197] (Technology 11)

[0198] The non-aqueous electrolyte secondary battery according to any one of techniques 1 to 9, wherein...

[0199] The aforementioned negative electrode includes a negative current collector.

[0200] The aforementioned negative electrode current collector comprises a resin film and a transition metal layer laminated on the resin film.

[0201] The aforementioned resin film comprises a substrate resin layer and a surface resin layer formed on the substrate resin layer.

[0202] The above-mentioned surface resin layer contains nitrogen-containing resin.

[0203] (Technology 12)

[0204] According to the non-aqueous electrolyte secondary battery of technology 11, the nitrogen-containing resin contains nitrogen-hydrogen bonds.

[0205] (Technology 13)

[0206] According to the non-aqueous electrolyte secondary battery of technology 11 or 12, the nitrogen-containing resin may be 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.

[0207] (Technology 14)

[0208] According to any one of the techniques 11 to 13, 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.

[0209] Example

[0210] 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 were fabricated and evaluated.

[0211] (Battery A1)

[0212] Make battery A1 by following these steps.

[0213] (1) Production of the positive electrode

[0214] 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. An appropriate amount of N-methyl-2-pyrrolidone (NMP) was then added and 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.

[0215] 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. This creates a positive electrode comprising a positive current collector and positive electrode slurry layers formed on both sides of the positive current collector. Then, aluminum tabs are attached to the fabricated positive electrode.

[0216] (2) Fabrication of the negative electrode

[0217] A silicon-containing material and graphite were mixed at a mass ratio of 5:95 (Si material:graphite) to form 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. The negative electrode slurry was then coated onto the surface of a copper foil (negative electrode current collector, thickness: 10 μm) to form a laminate containing the copper foil and a coating film formed on the copper foil. The coating film was then dried and the laminate was calendered. This formed a negative electrode containing the copper foil and negative electrode slurry layers formed on both sides of the copper foil. The thickness of each of the two negative electrode slurry layers was set to approximately 75 μm.

[0218] (3) Preparation of non-aqueous electrolytes

[0219] 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 (a carbonate-based non-aqueous solvent) was used as the non-aqueous solvent.

[0220] (4) Preparation of the separator

[0221] As a separator, a separator consisting of a substrate layer and an adhesive layer formed only on one side (the second main side) of the substrate layer was prepared. The substrate layer was a microporous membrane of polyethylene. The adhesive layer was an adhesive layer made of polyvinylidene fluoride (PVDF) (thickness: approximately 1 μm). The average thickness Ts of the separator was measured using the method described above.

[0222] (5) Battery manufacturing

[0223] The spacers are overlapped on both sides of the positive electrode with the adhesive layer in contact with the positive electrode, and then heated and rolled to bond the adhesive layer to the positive electrode. In this way, a laminate with spacers stacked on both sides of the positive electrode is formed.

[0224] Next, in an inert gas atmosphere, the aforementioned laminate (positive electrode and separator) and negative electrode are wound together to create a wound electrode assembly. 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.

[0225] (Determination of the average value Tn)

[0226] 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 using the method described above at 90% charge.

[0227] (Charge-discharge cycle test)

[0228] 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.

[0229] (Charge)

[0230] 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 .

[0231] (Discharge)

[0232] At 10mA / cm 2 Perform constant current discharge until the voltage reaches 3V.

[0233] (Batteries A2~A11 and batteries C1~C3)

[0234] 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 changed as shown in Table 1. Otherwise, batteries A2 to A11 and batteries C1 to C3 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 varies depending on the thickness of the positive electrode adhesive layer. In the separators of batteries A2 to A11 and C1, an adhesive layer (VDF-HFP copolymer) is formed on the positive electrode side of the substrate layer, and the adhesive layer is bonded to the positive electrode. No adhesive layer is formed on the main surface of the negative electrode side of the substrate layer of the separator. The separators of batteries C2 and C3 do not have an adhesive layer and consist only of the substrate layer. In Table 1, 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 batteries A7, A9, and A11.

[0235] The negative electrode active material of batteries A2 and C1 is the same as that used in battery A1. Batteries A3-A11 and batteries C2-C3 are used to make lithium secondary batteries with lithium metal as the negative electrode active material. These negative electrodes are made by the following method.

[0236] (2') Fabrication of the negative electrode current collector (negative electrode) for lithium secondary batteries

[0237] A negative electrode current collector comprising copper foil and a lithium-containing metal layer is fabricated by pressing lithium alloy foil (thickness: 10 μm) onto both sides of a copper foil (thickness: 25 μm). Next, nickel tabs are attached to the negative electrode current collector. This creates the negative electrode for a lithium-ion secondary battery.

[0238] The negative electrode current collector of battery A10 uses austenitic stainless steel foil (SUS foil) instead of copper foil, and otherwise has the same structure as the negative electrode current collector of battery A3. The negative electrode current collector of battery A11 uses a specified laminate (a laminate having a resin film and a transition metal layer laminated on the resin film) instead of copper foil, and otherwise has the same structure as the negative electrode current collector of battery A3. The resin film is a polyethylene terephthalate (PET) film coated with polyurethane resin (nitrogen-containing resin). A copper layer is used for the transition metal layer. Specifically, copper is first attached to the resin film by sputtering, and then deposited by wet plating. The negative electrode current collectors of batteries A10 and A11, respectively, have a lithium-containing metal layer, just like the negative electrode current collector of battery A3.

[0239] Table 1 lists the non-aqueous solvents used in the non-aqueous electrolytes. In Table 1, "carbonate" indicates the use of dimethyl carbonate, and "ether" indicates the use of 1,2-dimethoxyethane. Each battery was evaluated in the same manner as battery A1. Additionally, the average thickness Ts of the separators used in the fabrication of each battery was measured.

[0240] Table 1 shows a portion of the manufacturing conditions and evaluation results for each battery. 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.

[0241] [Table 1]

[0242]

[0243] Batteries A1 to A11 are secondary batteries (B) of this disclosure. Batteries C1 to C3 are comparative examples. As shown in Table 1, batteries A1 to A11 exhibit better cycle characteristics compared to batteries C1 to C3. As shown in Table 1, the cycle characteristics are improved by including inorganic particles in the adhesive layer. Furthermore, the cycle characteristics are improved by including ether in the non-aqueous solvent. Additionally, the cycle characteristics are improved by using stainless steel foil and / or resin film as the substrate for the negative electrode current collector.

[0244] Industrial availability

[0245] This disclosure can be applied to non-aqueous electrolyte secondary batteries.

[0246] 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.

[0247] Explanation of reference numerals in the attached figures

[0248] 10: Non-aqueous electrolyte secondary battery

[0249] 11: Positive electrode

[0250] 12: Negative electrode

[0251] 13: Divider

[0252] 13a: Substrate layer

[0253] 13a1: 1st main surface

[0254] 13a2: Second Main Face

[0255] 13b: Adhesive layer

[0256] 14: Electrode assembly

Claims

1. A non-aqueous electrolyte secondary battery, comprising: The electrode assembly, comprising a positive electrode, a negative electrode, and a spacer, is wound such that the spacer is disposed between the positive electrode and the negative electrode; and Non-aqueous electrolytes The separator comprises: a substrate layer having a first main surface disposed on the negative electrode side and a second main surface disposed on the positive electrode side; and an adhesive layer formed on the second main surface of the substrate layer. At least a portion of the adhesive layer is adhered to the positive electrode. The average value of the increase in thickness of one side of the negative electrode caused by charging under 90% charging conditions, Tn (μm), satisfies the relationship 1.2 < Ts / Tn with respect to the average thickness Ts (μm) of the separator.

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

3. The non-aqueous electrolyte secondary battery according to claim 1, wherein, The adhesive layer contains a copolymer synthesized by polymerizing monomers comprising vinylidene fluoride and hexafluoropropylene.

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

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

6. 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 dissolves in the non-aqueous electrolyte during discharging.

7. 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 ether. The content of the ether in the non-aqueous solvent is 80% or more by mass.

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

9. The non-aqueous electrolyte secondary battery according to any one of claims 1 to 3, wherein, The porosity of the substrate layer is above 40% and below 90%.

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

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

12. The non-aqueous electrolyte secondary battery according to claim 11, wherein, The nitrogen-containing resin contains nitrogen-hydrogen bonds.

13. The non-aqueous electrolyte secondary battery according to claim 11, wherein, The nitrogen-containing resin may be 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.

14. The non-aqueous electrolyte secondary battery according to claim 11, 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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