Secondary battery

Abstract

The secondary battery has a positive electrode, a negative electrode, and an electrolyte. The negative electrode includes a coating film covering a negative electrode active material layer, and the electrolyte includes a chain carboxylic acid ester. When the coating film is analyzed using an inductively coupled plasma emission spectrometry, the content of boron in the coating film is 10 μmol / m 2 or less, and the content of sulfur in the coating film is 20 μmol / m 2 or less. Hereinafter, the ratio of the content of sulfur to the content of boron is 1.0 or more and 3.0 or less. 2 or less, and the content of sulfur in the coating film is 20 μmol / m 2 or less. Hereinafter, the ratio of the content of sulfur to the content of boron is 1.0 or more and 3.0 or less.

Description

Technical Field

[0001] This technology relates to secondary batteries. Background Technology

[0002] With the widespread adoption of mobile phones and other electronic devices, secondary batteries are being developed as small, lightweight power sources capable of delivering high energy density. These secondary batteries contain a positive electrode, a negative electrode, and an electrolyte, and various studies have been conducted on their structure.

[0003] Specifically, to obtain excellent cycle characteristics, the analysis results of the surface of the negative electrode using X-ray photoelectron spectroscopy (XPS) specify a ratio of two peak intensities (e.g., see Patent Document 1). To obtain excellent shelf life, the analysis results of the surface of the negative electrode using XPS specify a ratio based on sulfur concentration (e.g., see Patent Document 2). To improve cycle characteristics, a coating containing sulfates or the like is provided on the negative electrode active material layer (e.g., see Patent Document 3). To suppress changes in battery characteristics over time during long-term storage, a compound containing boron-oxygen bonds is included in the electrolyte (e.g., see Patent Document 4).

[0004] To manufacture an electrode modified by heating or the like (a surface-modified electrode), an electrode surface modification coating agent containing a sulfate ester compound or the like is applied to the surface of the electrode (see, for example, Patent Document 5). To suppress the rise in resistance of the negative electrode, a coating containing boron and oxalate ions (a coating derived from an oxalate-borate type compound) is provided on the surface of the negative electrode (see, for example, Patent Document 6). To suppress the rise in resistance of the initial negative electrode active material layer while suppressing lithium deposition, the electrolyte contains lithium bis(oxalate-borate), and a coating containing a decomposition product of the lithium bis(oxalate-borate) is provided on the surface of the negative electrode active material particles (see, for example, Patent Document 7).

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: International Publication No. 2014 / 069460

[0008] Patent Document 2: International Publication No. 2005 / 029613

[0009] Patent Document 3: Japanese Patent Application Publication No. 2009-026691

[0010] Patent Document 4: Japanese Patent Application Publication No. 2008-027782

[0011] Patent Document 5: Japanese Patent Application Publication No. 2016-201244

[0012] Patent Document 6: Japanese Patent Application Publication No. 2014-011065

[0013] Patent Document 7: Japanese Patent Application Publication No. 2016-100051 Summary of the Invention

[0014] Various studies have been conducted to improve the performance of secondary batteries, but the expansion characteristics are still insufficient, so there is room for improvement.

[0015] This technology was developed in view of the above-mentioned problems, and its purpose is to provide a secondary battery that can achieve excellent expansion characteristics.

[0016] One embodiment of this technology provides a secondary battery comprising a positive electrode, a negative electrode, and an electrolyte. The negative electrode includes a coating covering an active material layer, and the electrolyte contains a chain-like carboxylic acid ester. When the coating is analyzed using inductively coupled plasma optical emission spectrometry, the boron content in the coating is found to be 10 μmol / m³. 2 Above and 30 μmol / m 2 The sulfur content in this coating is 20 μmol / m³. 2 Above and 70 μmol / m 2 The ratio of sulfur content to boron content is 1.0 or more and 3.0 or less.

[0017] Here, as mentioned above, the sulfur content and boron content in the coating were measured by analyzing the coating using inductively coupled plasma optical emission spectrometry (ICP-OES). Details of the analytical procedures for the coating using ICP-OES will be described later.

[0018] According to one embodiment of the present technology, the negative electrode includes a coating, the electrolyte contains a chain carboxylic acid ester, and the analysis results of the coating using inductively coupled plasma optical emission spectrometry satisfy the above three conditions, thus achieving excellent expansion characteristics.

[0019] It should be noted that the effects of this technology are not limited to those described herein, but can be any of the series of effects related to this technology described later. Attached Figure Description

[0020] Figure 1 This is a perspective view showing the structure of a secondary battery in one embodiment of the present technology.

[0021] Figure 2 It means Figure 1The diagram shows a cross-sectional view of the structure of the battery element.

[0022] Figure 3 This is a block diagram illustrating the structure of a secondary battery application example. Detailed Implementation

[0023] The following is a detailed description of one embodiment of the present technology with reference to the accompanying drawings. It should be noted that the description is presented in the following order.

[0024] 1. Secondary battery

[0025] 1-1. Structure

[0026] 1-2.Physical properties

[0027] 1-3. Actions

[0028] 1-4. Manufacturing Method

[0029] 1-5. Functions and Effects

[0030] 2. Variations

[0031] 3. Uses of secondary batteries

[0032] <1. Secondary Battery>

[0033] First, a secondary battery according to one embodiment of this technology will be described.

[0034] The secondary battery described herein is a secondary battery in which battery capacity is obtained by the intercalation and deintercalation of electrode reactants, and it includes a positive electrode, a negative electrode, and an electrolyte in liquid form. In this secondary battery, in order to prevent the electrode reactants from depositing on the surface of the negative electrode during charging, the charging capacity of the negative electrode is greater than the discharging capacity of the positive electrode. That is, the electrochemical capacity per unit area of ​​the negative electrode is set to be greater than the electrochemical capacity per unit area of ​​the positive electrode.

[0035] There are no particular restrictions on the types of substances used in the electrode reactions. Specifically, they are light metals such as alkali metals and alkaline earth metals. Alkali metals include lithium, sodium, and potassium, while alkaline earth metals include beryllium, magnesium, and calcium.

[0036] The following example uses lithium as the electrode reactant. A secondary battery that utilizes the insertion and extraction of lithium to obtain battery capacity is called a lithium-ion secondary battery. In this lithium-ion secondary battery, lithium is inserted and extracted in an ionic state.

[0037] <1-1. Structure>

[0038] Figure 1 The three-dimensional structure of the secondary battery is shown, and at the same time Figure 2 It shows Figure 1The cross-sectional structure of the battery element 20 is shown. Additionally, Figure 1 The outer packaging film 10 and the battery element 20 are shown in a state where they are separated from each other. Figure 2 Only a portion of battery element 20 is shown.

[0039] like Figure 1 as well as Figure 2 As shown, the secondary battery includes an outer packaging film 10, a battery element 20, a positive electrode lead 31 and a negative electrode lead 32, and sealing films 41 and 42. The secondary battery described here is a laminated film type secondary battery that uses a flexible (or soft) outer packaging film 10 as an outer packaging component for housing the battery element 20.

[0040] [Outer packaging film]

[0041] like Figure 1 As shown, the outer packaging film 10 is a flexible outer packaging component that houses the battery element 20, namely, the positive electrode 21, the negative electrode 22, and the electrolyte, as described later, and has a bag-like structure.

[0042] Here, the outer packaging film 10 is a film-shaped component that can be folded along the folding direction R. A recess 10U (so-called deep stretch portion) for accommodating the battery element 20 is provided on the outer packaging film 10.

[0043] The structure (material and number of layers, etc.) of the outer packaging film 10 is not particularly limited, so it can be a single-layer film or a multi-layer film.

[0044] Here, the outer packaging film 10 is a three-layer laminated film formed by sequentially stacking a welding layer, a metal layer, and a surface protective layer from the inside. The welding layer contains a polymer compound such as polypropylene. The metal layer contains a metal material such as aluminum. The surface protective layer contains a polymer compound such as nylon. When the outer packaging film 10 is folded, the outer peripheral portions of the opposing outer packaging films 10 (welding layers) are welded together.

[0045] [Sealing film]

[0046] like Figure 1 As shown, sealing films 41 and 42 are sealing components used to prevent external gases from entering the interior of the outer packaging film 10. Sealing film 41 is inserted between the outer packaging film 10 and the positive lead 31, while sealing film 42 is inserted between the outer packaging film 10 and the negative lead 32. Alternatively, one or both of sealing films 41 and 42 may be omitted.

[0047] Specifically, the sealing film 41 contains a polymer compound such as a polyolefin that has a sealing effect on the positive electrode lead 31, and the polyolefin is polypropylene or the like.

[0048] The structure of the sealing membrane 42 is the same as that of the sealing membrane 41, except that it provides a tight seal for the negative electrode lead 32. That is, the sealing membrane 42 contains a polymer compound such as polyolefin that provides a tight seal for the negative electrode lead 32.

[0049] [Battery Components]

[0050] like Figure 1 as well as Figure 2 As shown, the battery element 20 is a power generation element housed inside the outer packaging film 10, including a positive electrode 21, a negative electrode 22, a separator 23, and an electrolyte (not shown).

[0051] Here, the battery element 20 is a so-called wound electrode body. That is, in the battery element 20, the positive electrode 21 and the negative electrode 22 are stacked on top of each other with a separator 23 in between, and the positive electrode 21, the negative electrode 22 and the separator 23 are wound around a winding axis (an imaginary axis extending in the Y-axis direction). In other words, the positive electrode 21 and the negative electrode 22 are opposite to each other with a separator 23 in between.

[0052] The battery element 20 has a flat, three-dimensional shape; therefore, the shape of the cross-section (along the XZ plane) of the battery element 20 intersecting the winding axis is a flat shape defined by the major axis and the minor axis. The major axis is an imaginary axis that extends in the X-axis direction and has a length longer than the minor axis, while the minor axis is an imaginary axis that extends in the Z-axis direction that intersects the X-axis direction and has a length shorter than the major axis. Here, the cross-sectional shape of the battery element 20 is a flat, approximately elliptical shape.

[0053] (positive electrode)

[0054] like Figure 2 As shown, the positive electrode 21 includes a positive current collector 21A and a positive active material layer 21B.

[0055] The positive current collector 21A has one side with a positive active material layer 21B disposed thereon. The positive current collector 21A contains a conductive material such as a metal, which is aluminum, etc.

[0056] The positive electrode active material layer 21B comprises any one or more positive electrode active materials capable of lithium insertion and extraction, and is disposed on both sides of the positive electrode current collector 21A. Additionally, the positive electrode active material layer 21B may also include a positive electrode binder and a positive electrode conductive agent, and may be disposed on only one side of the positive electrode current collector 21A. The method for forming the positive electrode active material layer 21B is not particularly limited; specifically, it may be a coating method, etc.

[0057] The positive electrode active material contains lithium compounds. Lithium compounds are a general term for compounds containing lithium as a constituent element; more specifically, they are compounds containing lithium and one or more transition metal elements as constituent elements. This is because high energy density can be achieved. In addition, lithium compounds can also contain one or more other elements (excluding lithium and transition metal elements). The types of lithium compounds are not particularly limited; specifically, they include oxides, phosphoric acid compounds, silicate compounds, and borate compounds. Specific examples of oxides are LiNiO2, LiCoO2, and LiMn2O4, while specific examples of phosphoric acid compounds are LiFePO4 and LiMnPO4.

[0058] The positive electrode binder includes any one or more of synthetic rubber and polymer compounds. The synthetic rubber is styrene-butadiene rubber, etc., and the polymer compound is polyvinylidene fluoride, etc. The positive electrode conductive agent includes any one or more of conductive materials such as carbon materials, including graphite, carbon black, acetylene black, and Ketjen black, etc. Alternatively, the conductive material can also be a metallic material or a polymer compound, etc.

[0059] (negative electrode)

[0060] like Figure 2 As shown, the negative electrode 22 includes a coating 22C covering the negative electrode active material layer 22B. More specifically, the negative electrode 22 includes a negative electrode current collector 22A, a negative electrode active material layer 22B, and a coating 22C.

[0061] The negative current collector 22A has one side with a negative active material layer 22B disposed thereon. The negative current collector 22A contains a conductive material such as a metal, which is copper, etc.

[0062] The negative electrode active material layer 22B comprises one or more negative electrode active materials capable of lithium insertion and extraction, and is disposed on both sides of the negative electrode current collector 22A. Additionally, the negative electrode active material layer 22B may also comprise a negative electrode binder and a negative electrode conductive agent, and may be disposed on only one side of the negative electrode current collector 22A. The details regarding the negative electrode binder and negative electrode conductive agent are the same as those regarding the positive electrode binder and positive electrode conductive agent. The method for forming the negative electrode active material layer 22B is not particularly limited; specifically, it can be any one or more of the following: coating method, vapor phase method, liquid phase method, spraying method, and firing method (sintering method).

[0063] The negative electrode active material is one or both of carbon materials and metallic materials. This is because high energy density can be obtained. Carbon materials include easily graphitized carbon, difficult-to-graphitize carbon, and graphite (natural and artificial graphite). Metallic materials are a general term for materials containing one or more metallic elements and half-metallic elements that can form alloys with lithium as constituent elements. These metallic elements and half-metallic elements are one or both of silicon and tin. Metallic materials can be monomers, alloys, compounds, mixtures of two or more of them, or materials containing two or more of them. Specific examples of metallic materials are TiSi2 and SiO. x (0 < x ≤ 2, or 0.2 < x < 1.4), etc.

[0064] The coating 22C can cover the entire surface of the negative electrode active material layer 22B, or it can cover only a portion of the surface of the negative electrode active material layer 22B. In the latter case, multiple coatings 22C can cover the surface of the negative electrode active material layer 22B at multiple locations that are separated from each other. Figure 2 The diagram shows the situation where the coating 22C covers the entire surface of the negative electrode active material layer 22B.

[0065] As described later, in the manufacturing process of the secondary battery, the coating 22C is formed on the surface of the negative electrode active material layer 22B by impregnation treatment of the negative electrode active material layer 22B and stabilization treatment (charge and discharge treatment) of the assembled secondary battery. Thus, the coating 22C contains one or more of the following components: reactants and decomposition products of substances (boron-containing compounds) used in the impregnation treatment; and also contains one or more of the following components: reactants and decomposition products of substances (sulfur-containing compounds) in the electrolyte.

[0066] Boron-containing compounds are substances that serve as a source of boron; more specifically, they are compounds that contain boron as a constituent element. Sulfur-containing compounds are substances that serve as a source of sulfur; more specifically, they are compounds that contain sulfur as a constituent element. Therefore, the coating 22C formed using the above-described impregnation and stabilization treatments contains both boron and sulfur as constituent elements.

[0067] In this secondary battery, to improve expansion characteristics, the physical properties of the coating 22C meet specified physical property conditions. Details regarding the physical properties of the coating 22C will be described later.

[0068] (Septum)

[0069] like Figure 2As shown, the separator 23 is an insulating porous membrane located between the positive electrode 21 and the negative electrode 22, preventing contact (short circuit) between the positive electrode 21 and the negative electrode 22 while allowing lithium ions to pass through. The separator 23 contains a polymer compound such as polyethylene.

[0070] (electrolyte)

[0071] An electrolyte, comprising a solvent and an electrolyte salt, is impregnated in each of the positive electrode 21, the negative electrode 22, and the separator 23.

[0072] The solvent contains one or more chain carboxylic acid esters as non-aqueous solvents (organic solvents). This is because chain carboxylic acid esters have low viscosity, thus increasing the ionic conductivity (lithium-ion conductivity) of the electrolyte. This improves the high-rate (high charging current and high discharging current) charge-discharge characteristics, thus suppressing capacity reduction even when the secondary battery is charged and discharged at high rates. The type of chain carboxylic acid ester is not particularly limited; specifically, it includes methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, propyl propionate, isopropyl propionate, methyl butyrate, ethyl butyrate, and isoethyl butyrate, etc. The content of chain carboxylic acid esters in the solvent is not particularly limited and can be arbitrarily set. Electrolytes containing non-aqueous solvents (chain carboxylic acid esters) are called non-aqueous electrolytes.

[0073] The solvent may also contain one or more other non-aqueous solvents. The types of other non-aqueous solvents are not particularly limited, but specifically include carbonate compounds and lactone compounds, such as cyclic carbonates and chain carbonates.

[0074] It should be noted that the solvent may contain any one or more sulfur-containing compounds. This is because even if part of the coating 22C decomposes during charging and discharging, additional coating 22C can be easily formed during subsequent charging and discharging using the reaction of the sulfur-containing compounds. Thus, even with repeated charging and discharging, each of the physical property conditions 1 to 3 described below can be easily maintained.

[0075] As described above, sulfur-containing compounds are substances that serve as a source of sulfur (compounds containing sulfur as a constituent element). These sulfur-containing compounds can be cyclic or chain-like. Furthermore, sulfur-containing compounds can contain one or both of the following: carbon-carbon double bonds and carbon-carbon triple bonds, which are unsaturated carbon bonds.

[0076] There are no particular limitations on the types of sulfur-containing compounds; specifically, they include cyclic sulfonates, chain sulfonates, cyclic disulfonic anhydrides, and cyclic sulfonic acid carboxylic anhydrides. The content of sulfur-containing compounds in the electrolyte is also not particularly limited and can therefore be set arbitrarily.

[0077] Specific examples of cyclic sulfonates include propane sulfonate lactone (1,3-propane sulfonate lactone), propylene sulfonate lactone (1-propylene-1,3-sulfonate lactone), 4-methyl-1,3,2-dioxazothiophene-2,2-dioxide, and 1,3,2-dioxazothiophene-2,2-dioxide. Specific examples of chain sulfonates include propargyl methanesulfonate, propargyl ethanesulfonate, and 2-propyne benzenesulfonic acid. Cyclic disulfonic anhydrides include ethane disulfonic anhydride and propane disulfonic anhydride. Specific examples of cyclic sulfonic acid carboxylic anhydrides include sulfobenzoic anhydride, sulfopropionic anhydride, and sulfobutyric anhydride.

[0078] The electrolyte salt includes one or more light metal salts such as lithium salts. The content of the electrolyte salt in the electrolyte is not particularly limited and can therefore be set arbitrarily.

[0079] [Positive and negative leads]

[0080] like Figure 1 As shown, the positive lead 31 is the positive terminal connected to the battery element 20 (positive electrode 21) and extends from the inside of the outer packaging film 10 to the outside. The positive lead 31 contains a conductive material such as aluminum, and the shape of the positive lead 31 can be any one of a thin plate or a mesh.

[0081] like Figure 1 As shown, the negative electrode lead 32 is the negative terminal connected to the battery element 20 (negative electrode 22). Here, the negative electrode lead 32 is led out from the inside of the outer packaging film 10 to the outside in the same direction as the positive electrode 21. The negative electrode lead 32 contains a conductive material such as copper, and the details of the shape of the negative electrode lead 32 are the same as the details of the shape of the positive electrode lead 31.

[0082] <1-2.Physical Properties>

[0083] In this secondary battery, as described above, in order to improve the expansion characteristics, the physical properties of the coating 22C meet the specified physical property conditions.

[0084] [Physical Properties]

[0085] Specifically, when using inductively coupled plasma (ICP) luminescence spectrophotometry to analyze the coating 22C, the analytical results must simultaneously meet the three physical property conditions described below.

[0086] (Physical property condition 1)

[0087] The boron content (CB) in the 22C coating is 10 μmol / m. 2 ~30μmol / m 2That is, by using ICP emission spectrophotometry to analyze the coating 22C, the boron content CB contained in the coating 22C is measured, and the boron content CB is within the above-mentioned range.

[0088] The content CB can be adjusted to the desired value by changing conditions such as the type and content of boron-containing compounds in the impregnation solution and the impregnation time of the negative electrode active material layer 22B in the impregnation solution.

[0089] (Physical property condition 2)

[0090] The sulfur content (CS) in the 22C film is 20 μmol / m. 2 ~70μmol / m 2 That is, by using ICP emission spectrophotometry to analyze the coating 22C, the sulfur content CS contained in the coating 22C was measured, and the content CS was within the above-mentioned range.

[0091] The CS content can be adjusted to the desired value by changing conditions such as the type and content of sulfur-containing compounds in the electrolyte.

[0092] (Physical property condition 3)

[0093] The ratio of sulfur content (CS) to boron content (CB) (content ratio R) is 1.0 to 3.0. That is, the content ratio R (=content CS / content CB) calculated based on the above-mentioned contents of CB and CS is within the above-mentioned range.

[0094] As described above, by changing the contents of CB and CS respectively, the content ratio R can be adjusted to the desired value.

[0095] Simultaneously satisfying physical property conditions 1 to 3 significantly improves the electrochemical durability of the coating 22C. Consequently, on the surface of the negative electrode active material layer 22B, the decomposition reaction of the electrolyte is specifically suppressed, thus significantly inhibiting the generation of gas from the decomposition reaction of the electrolyte. The reasons for this will be explained in detail later.

[0096] [Analysis Steps]

[0097] The steps for determining the content of CB, CS, and content ratio R by using ICP luminescence spectrophotometry to analyze the coating 22C are as follows.

[0098] First, the secondary battery is discharged until the voltage reaches 3V. The discharge current is not particularly limited and can be set arbitrarily. Next, the negative electrode 22 is recovered by disassembling the discharged secondary battery. Next, the negative electrode 22 is cleaned using a cleaning solvent. The type of cleaning solvent is not particularly limited; specifically, organic solvents such as dimethyl carbonate are acceptable. Next, the negative electrode 22 is stamped into a disc shape (diameter = 19mm) to obtain the analytical sample.

[0099] Next, the sample (coated 22C) was analyzed using an ICP-ELISA spectrophotometer, and the boron content (μmol) and sulfur content (μmol) contained in the coated 22C were measured respectively. As this ICP-ELISA spectrophotometer, an ICP-ELISA spectrophotometer (sequential type) SPS3500 manufactured by HITACHI HI-TECH SCIENCE Co., Ltd. (formerly SII NANOTECHNOLOGY Co., Ltd.) can be used. Next, based on the sample area (m²... 2 The boron content CB (μmol / m) was calculated respectively. 2 ) and sulfur content CS (μmol / m 2 ).

[0100] Finally, based on the contents of CB and CS, the content ratio R (=content CS / content CB) was calculated. Thus, based on the analysis results of the coated 22C using ICP luminescence spectrophotometry, the contents of CB and CS were measured respectively, and the content ratio R was calculated.

[0101] <1-3. Actions>

[0102] When the secondary battery is charged, lithium is deintercalated from the positive electrode 21 in the battery element 20, and simultaneously intercalated into the negative electrode 22 via the electrolyte. Conversely, when the secondary battery is discharged, lithium is deintercalated from the negative electrode 22 in the battery element 20, and simultaneously intercalated into the positive electrode 21 via the electrolyte. During these charge and discharge cycles, lithium is intercalated and deintercalated in an ionic state.

[0103] <1-4. Manufacturing Method>

[0104] The secondary battery is manufactured using the steps described below. In this case, after assembling the secondary battery using a positive electrode 21, a negative electrode precursor, and an electrolyte, as described below, the secondary battery undergoes a stabilization treatment.

[0105] [The production of the positive electrode]

[0106] A positive electrode mixture is prepared by mixing positive electrode active material, positive electrode binder, and positive electrode conductive agent. This mixture is then added to an organic solvent to create a paste-like positive electrode slurry. Next, the positive electrode slurry is coated onto both sides of the positive electrode current collector 21A, thereby forming a positive electrode active material layer 21B. Afterward, the positive electrode active material layer 21B can be compressed and molded using a roller press or similar device. In this process, the positive electrode active material layer 21B can be heated, or the compression molding process can be repeated multiple times. Thus, the positive electrode active material layer 21B is formed on both sides of the positive electrode current collector 21A, thereby producing the positive electrode 21.

[0107] [Making the negative electrode]

[0108] The negative electrode active material layer 22B is formed using the same steps as those described for forming the positive electrode active material layer 21B. Specifically, a negative electrode mixture is prepared by mixing the negative electrode active material, negative electrode binder, and negative electrode conductive agent, and then a paste-like negative electrode mixture slurry is prepared by adding the negative electrode mixture to an organic solvent. Next, the negative electrode mixture slurry is coated onto both sides of the negative electrode current collector 22A, thereby forming the negative electrode active material layer 22B. After this, the negative electrode active material layer 22B can be compressed and molded.

[0109] Next, an impregnation solution is prepared by adding a boron-containing compound to an organic solvent or the like. This impregnation solution is used to form a coating 22C by impregnation treatment and contains any one or more boron-containing compounds. The type of organic solvent is not particularly limited; specifically, it is any one or more of the aforementioned carbonate compounds. The content of the boron-containing compound in the impregnation solution can be arbitrarily set according to conditions such as boron content CB.

[0110] There is no particular limitation on the types of boron-containing compounds; specifically, they include boron-containing lithium salts. Specific examples of boron-containing lithium salts include lithium tetrafluoroborate (LiBF4), lithium bis(oxalate)borate (lithium di(oxalate)borate), and lithium difluorooxalateborate (lithium difluoro(oxalate)borate), etc.

[0111] Next, the negative electrode current collector 22A (hereinafter referred to as "negative electrode active material layer 22B"), on which the negative electrode active material layer 22B is formed, is immersed in an immersion solution. The immersion time can be arbitrarily set according to conditions such as the boron content CB. Next, after the negative electrode active material layer 22B is removed from the immersion solution, the organic solvent is evaporated by drying the negative electrode active material layer 22B. As a result, a coating film of the immersion solution is formed on the surface of the negative electrode active material layer 22B, thereby producing a negative electrode precursor. This negative electrode precursor has the same structure as the negative electrode 22, except that the coating film of the immersion solution replaces the film 22C.

[0112] Finally, as described later, after assembling the secondary battery using the negative electrode precursor, a stabilization treatment (charge-discharge treatment) is performed on the secondary battery. This forms a coating 22C containing boron and sulfur as constituent elements on the surface of the negative electrode active material layer 22B. Thus, the negative electrode active material layer 22B and the coating 22C are formed on both sides of the negative electrode current collector 22A, thereby fabricating the negative electrode 22.

[0113] (Preparation of electrolyte)

[0114] After the electrolyte salt is added to the solvent, a sulfur-containing compound is added to the solvent. Thus, the electrolyte salt and the sulfur-containing compound are dispersed or dissolved in the solvent, thereby preparing the electrolyte. The content of the sulfur-containing compound in the impregnation solution can be arbitrarily set according to conditions such as sulfur content and CS.

[0115] (Assembly of a secondary battery)

[0116] First, the positive lead 31 is connected to the positive electrode 21 (positive current collector 21A) using a soldering method or the like, and the negative lead 32 is connected to the negative electrode 22 (negative current collector 22A) using a soldering method or the like.

[0117] Next, the positive electrode 21 and the negative electrode precursor are stacked together with the separator 23 in between, and then the positive electrode 21, the negative electrode precursor, and the separator 23 are wound together to form a wound body. This wound body has the same structure as the battery element 20, except that the negative electrode precursor replaces the negative electrode 22, and the positive electrode 21, the negative electrode precursor, and the separator 23 are not impregnated with electrolyte. Next, the wound body is pressed using a press or similar device to form a flat shape.

[0118] Next, after housing the wound body inside the recess 10U, the outer packaging film 10 is folded so that the outer packaging films 10 are facing each other. Next, using a heat fusion method or the like, the outer peripheral portions of two sides of the facing outer packaging films 10 (fusion layers) are fused together, thereby housing the wound body inside the bag-shaped outer packaging film 10.

[0119] Finally, after injecting the electrolyte into the pouch-shaped outer packaging film 10, the outer periphery of the remaining edge of the outer packaging film 10 (welded layer) is fused together using a heat fusion method or the like. In this case, a sealing film 41 is inserted between the outer packaging film 10 and the positive electrode lead 31, while a sealing film 42 is inserted between the outer packaging film 10 and the negative electrode lead 32. Thus, the electrolyte permeates into the wound body, thereby forming a battery element 20 as a wound electrode body. Simultaneously, the battery element 20 is sealed inside the pouch-shaped outer packaging film 10, thereby assembling a secondary battery.

[0120] (Stabilization of secondary batteries)

[0121] This allows the assembled secondary battery to be charged and discharged. Ambient temperature, number of charge / discharge cycles, and charging / discharging conditions can be set arbitrarily.

[0122] Thus, as described above, a coating 22C containing boron and sulfur as constituent elements is formed on the surface of the negative electrode active material layer 22B, thereby forming the negative electrode 22. In this case, since the surface of the negative electrode active material layer 22B is protected by the coating 22C, the secondary battery is electrochemically stable.

[0123] It should be noted that after the stabilization treatment of the secondary battery is completed, that is, after the negative electrode 22 is made (a coating 22C is formed on the surface of the negative electrode active material layer 22B), the sulfur-containing compound used to form the coating 22C may remain in the electrolyte or may not remain in the electrolyte.

[0124] Therefore, a secondary battery using outer packaging film 10, i.e., a laminated film type secondary battery, is completed.

[0125] <1-5. Functions and Effects>

[0126] According to this secondary battery, the negative electrode 22 includes a coating 22C, and the electrolyte contains a chain carboxylic acid ester. Furthermore, the analytical results of the coating 22C using ICP-based spectral analysis (the contents of the coating 22C as physical properties, CB, CS, and the content ratio R) simultaneously satisfy the aforementioned physical property conditions 1 to 3.

[0127] In this case, since the electrolyte contains chain-like carboxylic esters, the ionic conductivity of the electrolyte is improved as described above. Furthermore, since the properties of the coating 22C simultaneously satisfy property conditions 1 to 3, the electrochemical durability of the coating 22C is significantly improved. Therefore, even though the electrolyte contains chain-like carboxylic esters, the decomposition reaction of the electrolyte (chain-like carboxylic esters) on the surface of the negative electrode active material layer 22B can be specifically suppressed. Thus, in particular, even when using (charging and discharging) and storing the secondary battery in a high-temperature environment, the decomposition reaction of the electrolyte can be sufficiently suppressed, thereby effectively suppressing gas generation.

[0128] Therefore, even if the electrolyte contains chain carboxylic acid esters, it can effectively suppress the expansion of the secondary battery caused by gas generation, thus achieving excellent expansion characteristics.

[0129] Here, it can be assumed that the mechanism by which gas is significantly suppressed by the decomposition reaction of the electrolyte is as follows, since physical property conditions 1 to 3 are satisfied simultaneously.

[0130] When a coating 22C containing boron as a constituent element is formed on the surface of the negative electrode active material layer 22B, the decomposition reaction of the electrolyte on the surface of the negative electrode active material layer 22B can be suppressed even when the secondary battery is used and stored in a high-temperature environment, thus suppressing the generation of gas due to the decomposition reaction of the electrolyte. This coating 22C containing boron as a constituent element is formed on the surface of the negative electrode active material layer 22B by charging and discharging a secondary battery equipped with an electrolyte containing a boron compound.

[0131] However, when the electrolyte contains chain carboxylic esters, even if a coating 22C containing boron as a constituent element is formed on the surface of the negative electrode active material layer 22B, the decomposition reaction of the electrolyte (chain carboxylic ester) on the surface of the negative electrode active material layer 22B cannot be sufficiently suppressed, thus easily generating gas. This is because chain carboxylic esters, as solvents in the electrolyte, have the property of being more easily decomposed during charging and discharging than carbonate compounds and the like.

[0132] Therefore, as a method for manufacturing a secondary battery that is a comparative example of the secondary battery in this embodiment, it is considered to form a coating 22C containing boron and sulfur as constituent elements by charging and discharging a secondary battery having an electrolyte containing a boron compound and a sulfur compound.

[0133] In this case, when the coating 22C contains boron and sulfur as constituent elements, even if the electrolyte contains chain carboxylic esters, the decomposition reaction of the electrolyte (chain carboxylic esters) on the surface of the negative electrode active material layer 22B can be suppressed, thus making it difficult to generate gas. The reason for this is believed to be that during the formation of the coating 22C (charge-discharge treatment), the electrophilic boron-containing compound and the nucleophilic sulfur-containing compound are firmly bonded together, thereby improving the electrochemical durability of the coating 22C.

[0134] However, it is actually difficult to sufficiently improve the electrochemical durability of the coating 22C when forming a coating 22C containing boron and sulfur as constituent elements.

[0135] The reason for this is that when the electrolyte contains both boron-containing and sulfur-containing compounds, during charging and discharging, before forming a coating 22C containing boron derived from the boron-containing compound as a constituent element, a coating 22C containing sulfur derived from the sulfur-containing compound is preferentially formed. Therefore, the coating 22C can adequately contain sulfur as a constituent element, but not adequately contain boron as a constituent element.

[0136] Furthermore, this is because, when a coating 22C derived from boron-containing compounds is formed, the oxidative decomposition reaction of boron-containing compounds in the positive electrode 21 preferentially occurs compared to the reductive decomposition reaction of boron-containing compounds in the negative electrode 22. Consequently, the coating derived from boron-containing compounds readily forms on the surface of the positive electrode active material layer 21B, while the coating 22C derived from sulfur-containing compounds readily forms on the surface of the negative electrode active material layer 22B. Therefore, the coating 22C formed on the surface of the negative electrode active material layer 22B still cannot sufficiently contain boron as a constituent element.

[0137] Therefore, in the secondary battery manufactured by the manufacturing method of the comparative example, even if the electrolyte contains both boron-containing compounds and sulfur-containing compounds, it is actually difficult to form a coating 22C that appropriately contains both boron and sulfur as constituent elements in order to improve electrochemical durability, that is, a coating 22C that simultaneously satisfies physical property conditions 1 to 3.

[0138] In contrast, in the secondary battery manufacturing method of this embodiment, as described above, after immersing the negative electrode active material layer 22B in an impregnation solution containing a boron compound, a secondary battery having an electrolyte containing a sulfur compound is stabilized (charge-discharge treatment) to form a coating 22C.

[0139] In this case, by charging and discharging a secondary battery containing an electrolyte containing a sulfur compound while a sufficient amount of boron-containing compound is present on the surface of the negative electrode active material layer 22B after impregnation treatment, a coating 22C is formed on the surface of the negative electrode active material layer 22B. Thus, the coating 22C not only sufficiently contains sulfur as a constituent element but also sufficiently contains boron as a constituent element, thereby simultaneously satisfying physical property conditions 1 to 3.

[0140] Therefore, in the secondary battery manufactured by the manufacturing method of this embodiment, unlike the secondary battery manufactured by the manufacturing method of the comparative example described above, a coating 22C is formed that appropriately contains both boron and sulfur as constituent elements, that is, a coating 22C that simultaneously satisfies physical property conditions 1 to 3.

[0141] Based on the above description, in the secondary battery of this embodiment, by simultaneously satisfying physical property conditions 1 to 3, the electrochemical durability of the coating at 22C is sufficiently improved, thus significantly suppressing the generation of gas due to the decomposition reaction of the electrolyte (chain carboxylic ester). Therefore, even when the electrolyte contains chain carboxylic ester, the expansion of the secondary battery can be effectively suppressed, thereby improving the expansion characteristics. In this case, even when using and storing the secondary battery in a high-temperature environment, the expansion of the secondary battery can be sufficiently suppressed, thus effectively improving the expansion characteristics.

[0142] In particular, if the electrolyte contains sulfur-containing compounds, an additional coating 22C is formed when using a secondary battery (during charging and discharging). Therefore, even with repeated charging and discharging, it is easier to maintain physical property conditions 1 to 3, thus achieving higher performance. In this case, if the sulfur-containing compounds include cyclic sulfonates, it is even easier to maintain physical property conditions 1 to 3, thus achieving even higher performance.

[0143] Furthermore, if the secondary battery has a flexible outer packaging film 10, even if the outer packaging film 10 is easily deformed due to changes in internal pressure (gas is generated due to the decomposition reaction of the electrolyte (chain carboxylic acid ester), the expansion of the secondary battery can be effectively suppressed, thus achieving a higher performance.

[0144] In addition, if the secondary battery is a lithium-ion secondary battery, sufficient battery capacity can be stably obtained by utilizing the insertion and extraction of lithium, thus achieving higher performance.

[0145] <2. Variations>

[0146] Next, variations of the aforementioned secondary battery will be described. As explained below, the structure of the secondary battery can be appropriately modified. Furthermore, any two or more of the variations described below can be combined with each other.

[0147] [Variation Example 1]

[0148] A membrane 23 was used as a porous membrane. However, although not specifically illustrated here, a laminated membrane comprising layers of polymer compounds can be used instead of the porous membrane 23.

[0149] Specifically, the laminated separator includes a porous membrane with one and two faces and a polymer compound layer disposed on one or both faces of the porous membrane. This is because, due to the improved adhesion of the separator to each of the positive electrode 21 and the negative electrode 22, positional displacement of the battery element 20 (winding displacement of each of the positive electrode 21, negative electrode 22, and separator) is less likely to occur. Therefore, even if electrolyte decomposition reactions occur, the secondary battery is less likely to expand. The polymer compound layer contains polymers such as polyvinylidene fluoride (PVDF). This is because PVDF and similar compounds possess excellent physical strength and electrochemical stability.

[0150] It should be noted that one or both of the porous membrane and the polymer compound layer may contain any one or more types of insulating particles. This is because multiple insulating particles dissipate heat when the secondary battery heats up, thus improving the safety (heat resistance) of the secondary battery. Insulating particles include inorganic particles and resin particles. Specific examples of inorganic particles include particles of alumina, aluminum nitride, boehmite, silicon dioxide, titanium dioxide, magnesium oxide, and zirconium oxide. Specific examples of resin particles include particles of acrylic resin and styrene resin.

[0151] In the case of fabricating a layered membrane, a precursor solution containing a polymer compound and an organic solvent is prepared, and then the precursor solution is coated onto one or both sides of the porous membrane. In this case, multiple insulating particles can also be added to the precursor solution as needed.

[0152] With the use of this layered separator, lithium ions can also move between the positive electrode 21 and the negative electrode 22, thus achieving the same effect.

[0153] [Variation Example 2]

[0154] An electrolyte solution, which is a liquid electrolyte, was used. However, although not specifically illustrated here, an electrolyte layer, which is a gel electrolyte, can also be used instead of an electrolyte solution.

[0155] In the battery element 20 using an electrolyte layer, after the positive electrode 21 and the negative electrode 22 are stacked on top of each other with the separator 23 and the electrolyte layer in between, the positive electrode 21, the negative electrode 22, the separator 23 and the electrolyte layer are wound together. The electrolyte layer is located between the positive electrode 21 and the separator 23, and also between the negative electrode 22 and the separator 23.

[0156] Specifically, the electrolyte layer comprises an electrolyte and a polymer compound, and the electrolyte is held in place by the polymer compound within the electrolyte layer. This is to prevent leakage. The composition of the electrolyte is as described above. The polymer compound includes polyvinylidene fluoride, etc. In the case of forming the electrolyte layer, after preparing a precursor solution comprising an electrolyte, a polymer compound, and an organic solvent, the precursor solution is coated on one or both sides of each of the positive electrode 11 and the negative electrode 12.

[0157] When this electrolyte layer is used, lithium ions can also move between the positive electrode 21 and the negative electrode 22 via the electrolyte layer, thus achieving the same effect.

[0158] <3. Uses of Secondary Batteries>

[0159] Next, we will explain the uses (application examples) of the aforementioned secondary batteries.

[0160] There are no particular limitations on the uses of secondary batteries. Secondary batteries used as power sources are the main power source or auxiliary power source for electronic devices and electric vehicles. The main power source is the preferred power source, regardless of the availability of other power sources. The auxiliary power source is used to replace the main power source, or is switched from the main power source.

[0161] Specific examples of applications for rechargeable batteries are as follows: Electronic devices such as camcorders, digital still cameras, mobile phones, laptops, stereo headphones, portable radios, and portable information terminals. Storage devices such as backup power supplies and memory cards. Power tools such as electric drills and chainsaws. Battery packs integrated into electronic devices. Medical electronic devices such as pacemakers and hearing aids. Electric vehicles such as electric cars (including hybrid vehicles). Power storage systems such as household or industrial battery systems that pre-store power in preparation for emergencies. In these applications, one or multiple rechargeable batteries can be used.

[0162] Battery packs can use single cells or battery arrays. Electric vehicles are vehicles that operate (drive) using a secondary battery as a power source, and can also be hybrid vehicles that have a power source other than the secondary battery. In home power storage systems, electricity stored in a secondary battery that serves as a power storage source can be used to operate household electrical appliances, etc.

[0163] Here, we will specifically illustrate one application example of a secondary battery. The structure of the application example described below is only one example and can therefore be modified as appropriate.

[0164] Figure 3 The frame structure of the battery pack is shown. The battery pack described here is a battery pack (so-called a pouch) that uses a secondary battery and is installed in electronic devices such as smartphones.

[0165] like Figure 3 As shown, the battery pack includes a power supply 51 and a circuit board 52. The circuit board 52 is connected to the power supply 51 and includes a positive terminal 53, a negative terminal 54, and a temperature detection terminal 55.

[0166] The power supply 51 includes a secondary battery. In this secondary battery, the positive lead is connected to the positive terminal 53, and the negative lead is connected to the negative terminal 54. Since the power supply 51 can be connected to an external source via the positive terminal 53 and the negative terminal 54, it can be charged and discharged. The circuit board 52 includes a control unit 56, a switch 57, a thermistor element (PTC element) 58, and a temperature detection unit 59. Alternatively, the PTC element 58 may be omitted.

[0167] The control unit 56 includes a central processing unit (CPU) and memory, etc., and controls the operation of the battery pack as a whole. The control unit 56 detects and controls the usage status of the power supply 51 as needed.

[0168] It should be noted that when the voltage of the power supply 51 (secondary battery) reaches the overcharge detection voltage or the over-discharge detection voltage, the control unit 56 cuts off the switch 57, thereby preventing the charging current from flowing through the current path of the power supply 51. The overcharge detection voltage and the over-discharge detection voltage are not particularly limited. For example, the overcharge detection voltage is 4.2V ± 0.05V, and the over-discharge detection voltage is 2.4V ± 0.1V.

[0169] Switch 57 includes a charging control switch, a discharging control switch, a charging diode, and a discharging diode, etc., and switches the connection between power supply 51 and external devices according to the instructions of control unit 56. Switch 57 includes a field-effect transistor (MOSFET) using metal-oxide-semiconductor, and the charging and discharging current is detected based on the on-resistance of switch 57.

[0170] The temperature detection unit 59 includes temperature detection elements such as a thermistor, measures the temperature of the power supply 51 using the temperature detection terminal 55, and outputs the temperature measurement result to the control unit 56. The temperature measurement result measured by the temperature detection unit 59 is used for charging and discharging control by the control unit 56 when abnormal heating occurs, and for correction processing by the control unit 56 when calculating the remaining capacity.

[0171] Example

[0172] The embodiments of this technology are described below.

[0173] (Examples 1-11 and Comparative Examples 1-7)

[0174] As described below, the performance of the secondary battery was evaluated after it was manufactured.

[0175] [Manufacturing of secondary batteries]

[0176] A laminated film type secondary battery (lithium-ion secondary battery) was manufactured by following the steps described below.

[0177] (The production of the positive electrode)

[0178] First, a positive electrode mixture was prepared by mixing 95 parts by mass of positive electrode active material, 4 parts by mass of positive electrode binder (polyvinylidene fluoride), and 1 part by mass of positive electrode conductive agent (graphite). Next, the positive electrode mixture was added to an organic solvent (N-methyl-2-pyrrolidone), and the solvent was stirred to prepare a paste-like positive electrode mixture slurry. Next, the positive electrode mixture slurry was coated onto both sides of a positive electrode current collector 21A (a strip of aluminum foil with a thickness of 15 μm) using a coating apparatus, and then dried to form a positive electrode active material layer 21B. Finally, the positive electrode active material layer 21B was compressed and molded using a roller press. Thus, the positive electrode 21 was manufactured.

[0179] (Making the negative electrode)

[0180] First, a negative electrode mixture was prepared by mixing 90 parts by mass of the negative electrode active material (graphite) and 10 parts by mass of the negative electrode binder (polyvinylidene fluoride). Next, the negative electrode mixture was added to an organic solvent (N-methyl-2-pyrrolidone), and the solvent was stirred to prepare a paste-like negative electrode mixture slurry. Next, the negative electrode mixture slurry was coated onto both sides of the negative electrode current collector 22A (a strip of copper foil with a thickness of 15 μm) using a coating apparatus, and then dried to form a negative electrode active material layer 22B. Finally, the negative electrode active material layer 22B was compressed and molded using a roller press.

[0181] Next, the negative electrode current collector 22A, to which the negative electrode active material layer 22B is formed, is immersed in an impregnation solution (concentration = 1 mol / kg) containing a boron-containing compound (lithium tetrafluoroborate (LiBF4)). The impregnation time (hours) is shown in Tables 1 to 3. Next, the negative electrode current collector 22A to which the negative electrode active material layer 22B is formed is removed from the impregnation solution, thereby drying the impregnation solution coated on the surface of the negative electrode active material layer 22B. Thus, a coating film of the impregnation solution is formed on the surface of the negative electrode active material layer 22B, obtaining the negative electrode precursor.

[0182] Finally, as described later, after assembling the secondary battery using the negative electrode precursor, the secondary battery underwent a stabilization treatment (charge-discharge treatment). As a result, a coating 22C containing boron and sulfur as constituent elements was formed on the surface of the negative electrode active material layer 22B, thus forming the negative electrode 22.

[0183] (Preparation of electrolyte)

[0184] After adding the electrolyte salt (lithium hexafluorophosphate (LiPF6)) to the solvent, the solvent was stirred. Ethyl carbonate and propylene carbonate, as cyclic carbonates, and propyl propionate (PP), as a chain carboxylic acid ester, were used as solvents. In this case, the solvent mixing ratio (volume ratio) was ethylene carbonate:propylene carbonate:chain carboxylic acid ester = 10:20:70, and the electrolyte salt concentration relative to the solvent was 1 mol / kg.

[0185] Next, a sulfur-containing compound (as propanesulfonate lactone (PS)) was added to a solvent containing an electrolyte salt, and the solvent was stirred. In this case, the content of the sulfur-containing compound in the electrolyte was set to 1% by weight. Thus, an electrolyte containing a sulfur-containing compound was prepared.

[0186] (Assembly of a secondary battery)

[0187] First, the positive lead 31 (a strip of aluminum foil) is soldered to the positive electrode 21 (positive current collector 21A), and the negative lead 32 (a strip of copper foil) is soldered to the negative electrode precursor (negative current collector 22A).

[0188] Next, the positive electrode 21 and the negative electrode precursor are stacked together with a separator 23 (a microporous polyethylene film with a thickness of 25 μm) in between, and then the positive electrode 21, the negative electrode precursor, and the separator 23 are wound together to create a wound body. Next, the wound body is pressed using a press to form a flat shape.

[0189] Next, after folding the outer packaging film 10 with the wound body housed in the recessed portion 10U sandwiched between it, the outer peripheral portions of two sides of the outer packaging film 10 (welding layer) are heat-fused together, thereby housing the wound body inside the bag-shaped outer packaging film 10. As the outer packaging film 10, an aluminum laminate film is used, which consists of a welding layer (a polypropylene film with a thickness of 30 μm), a metal layer (an aluminum foil with a thickness of 40 μm), and a surface protective layer (a nylon film with a thickness of 25 μm) stacked sequentially from the inside.

[0190] Finally, after injecting the electrolyte into the pouch-shaped outer packaging film 10, the outer periphery of the remaining edge of the outer packaging film 10 (welded layer) is thermally fused together under reduced pressure. In this case, a sealing film 41 (a 5 μm thick polypropylene film) is inserted between the outer packaging film 10 and the positive electrode lead 31, and a sealing film 42 (a 5 μm thick polypropylene film) is inserted between the outer packaging film 10 and the negative electrode lead 32. Thus, the electrolyte permeates into the wound body, thereby forming a battery element 20 as a wound electrode body, and the battery element 20 is sealed inside the pouch-shaped outer packaging film 10, assembling a secondary battery.

[0191] (Stabilization of secondary batteries)

[0192] The assembled secondary battery was subjected to one charge-discharge cycle at room temperature (temperature = 25℃). During charging, a constant current of 0.1C was used until the voltage reached 4.2V, followed by constant voltage charging at 4.2V until the current reached 0.005C. During discharging, a constant current of 0.1C was used until the voltage reached 2.5V. 0.1C is the current value required to fully discharge the battery (theoretical capacity) in 10 hours, and 0.005C is the current value required to fully discharge the battery (theoretical capacity) in 200 hours.

[0193] Thus, as described above, a coating 22C is formed on the surface of the negative electrode active material layer 22B in the negative electrode precursor, thereby forming the negative electrode 22. Therefore, the state of the secondary battery is stabilized, thus completing the laminated film type secondary battery.

[0194] After completing the secondary battery, the negative electrode 22 was recovered by disassembling the secondary battery. The negative electrode 22 (coated 22C) was then analyzed using ICP-MS (Inductively Coupled Phosphorus) spectrophotometry to measure the content of CB and CS (μmol / m³). 2 The content ratio R was calculated, and the results shown in Tables 1 to 3 were obtained.

[0195] In the manufacturing process of secondary batteries, the contents of CB, CS and the content ratio R are adjusted by changing any one or more of the following: the content of boron-containing compounds in the impregnation solution, the impregnation time during the impregnation treatment, and the content of sulfur-containing compounds in the electrolyte.

[0196] It should be noted that, for comparison purposes, a secondary battery was fabricated using the same steps, except that the electrolyte contained both sulfur-containing and boron-containing compounds, instead of undergoing an impregnation treatment. In this case, the content of the boron-containing compound in the electrolyte was 1% by weight. As a result, during the stabilization treatment of the secondary battery (charge and discharge), a coating 22C containing boron and sulfur as constituent elements was formed on the surface of the negative electrode active material layer 22B. The contents of CB, CS, and the content ratio R at this time are shown in Table 1.

[0197] [Performance Evaluation]

[0198] The performance (expansion characteristics) of the secondary battery was evaluated, and the results are shown in Tables 1 to 3.

[0199] To examine the expansion characteristics, firstly, after charging the secondary battery at room temperature (temperature = 23°C), the thickness of the secondary battery (thickness before storage (mm)) was measured. The charging conditions were the same as those used during the stabilization treatment of the secondary battery described above. Next, the charged secondary battery was stored in a high-temperature environment (temperature = 60°C) for 720 hours, and the thickness of the secondary battery (thickness after storage (mm)) was measured. Finally, the expansion rate (%) was calculated as: [(thickness after storage - thickness before storage) / thickness before storage] × 100.

[0200] [Table 1]

[0201]

[0202] [Table 2]

[0203]

[0204] [Table 3]

[0205]

[0206] [Inspection]

[0207] As shown in Tables 1 to 3, the expansion characteristics vary significantly depending on the physical properties of the coating 22C (content of CB, CS, and content ratio R).

[0208] Specifically, in cases where an impregnation treatment using an impregnation solution was performed (Examples 1-11 and Comparative Examples 1, 2, 4-7), since a coating 22C containing both boron and sulfur as constituent elements was formed, the contents of CB and CS were measured respectively, and the content ratio R was calculated.

[0209] In this case, when the content of CB is simultaneously 10 μmol / m 2 ~30μmol / m 2 The CS content is 20 μmol / m 2 ~70μmol / m 2 When the content ratio R is 1.0 to 3.0 (physical property conditions 1 to 3) (Examples 1 to 11), the expansion rate is significantly reduced compared with cases where physical property conditions 1 to 3 are not met simultaneously (Comparative Examples 1, 2, 4 to 7).

[0210] It should be noted that, in the case of impregnation treatment without the use of impregnation solution (Comparative Example 3), a coating 22C containing both boron and sulfur as constituent elements was formed, but since physical property conditions 1 to 3 were not satisfied at the same time, the expansion rate increased.

[0211] [Summarize]

[0212] According to the results shown in Tables 1 to 3, when the negative electrode 22 contains a coating 22C, the electrolyte contains a chain carboxylic acid ester, and the physical property conditions 1 to 3 regarding the analytical results (content of CB, CS, and content ratio R) of the coating 22C obtained by ICP-based spectral analysis are simultaneously met, the expansion rate is significantly reduced. Therefore, excellent expansion characteristics are obtained in the secondary battery.

[0213] The above description, which presents the present technology through one implementation method and embodiment, does not limit the structure of the present technology to the structure described in one implementation method and embodiment, and various modifications are possible.

[0214] Specifically, although the battery structure of the secondary battery is described as a laminated film type, the battery structure is not particularly limited and can be other battery structures such as cylindrical, square, coin-shaped, and button-shaped.

[0215] Furthermore, although the case of a wound battery element structure has been described, the battery element structure is not particularly limited, so other element structures can be used, such as a stacked type where the electrodes (positive and negative electrodes) are stacked, and a repeatedly folded type where the electrodes (positive and negative electrodes) are folded into a Z-shape.

[0216] Furthermore, while the use of lithium as the electrode reactant has been described, it is not particularly limited. Specifically, as mentioned above, the electrode reactant can be other alkali metals such as sodium and potassium, or alkaline earth metals such as beryllium, magnesium, and calcium. Additionally, other light metals such as aluminum can also be used as the electrode reactant.

[0217] The effects described in this specification are merely illustrative, and therefore the effects of this technology are not limited to those described in this specification. Thus, other effects can also be obtained with this technology.

Claims

1. A secondary battery, The secondary battery comprises a positive electrode, a negative electrode, and an electrolyte solution, The negative electrode includes a coating film covering a negative electrode active material layer, The electrolyte solution contains a chain carboxylic acid ester, When the coating film is analyzed using an inductively coupled plasma emission spectrometry method, The content of boron in the coating is 10 μmol / m 2 above and 30 μmol / m 2 Hereinafter, The content of sulfur in the coating film is 20 μmol / m 2 above and 70 μmol / m 2 Hereinafter, The ratio of the content of the sulfur to the content of the boron is 1.0 or greater and 3.0 or less.

2. The secondary battery according to claim 1, wherein The electrolyte solution further contains a sulfur-containing compound.

3. The secondary battery according to claim 2, wherein The sulfur-containing compound contains at least one of a cyclic sulfonic acid ester, a chain sulfonic acid ester, a cyclic disulfonic anhydride, and a cyclic sulfonic acid carboxylic anhydride.

4. The secondary battery according to any one of claims 1 to 3, wherein The secondary battery further comprises a flexible outer packaging member that houses the positive electrode, the negative electrode, and the electrolyte solution.

5. The secondary battery according to any one of claims 1 to 4, wherein The secondary battery is a lithium ion secondary battery.

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